JPWO2018225333A1 - Ink jet head and ink jet recording apparatus - Google Patents

Abstract

It is an object of the present invention to provide an inkjet head having a nozzle circulation mechanism that can reliably discharge bubbles in the pressure chamber to a path for nozzle circulation. Pressure control means 105a, 105b for controlling the pressure difference between the generated ink and the ink discharged from the pressure chamber 23 to the discharge path 423, and the flow velocity of the ink flow in the pressure chamber 23 generated by the pressure control means 105a, 105b. (V1) is solved by being higher than the component (V2) of the rising speed of the bubble in the direction facing the ink flow when the bubble is present in the ink in the pressure chamber 23.

Description

  The present invention relates to an ink-jet head and an ink-jet recording apparatus, and more particularly, to an ink-jet head having a nozzle circulating mechanism, which is provided with an ink-jet head capable of reliably discharging bubbles in a pressure chamber to a nozzle circulating path, and the ink-jet head. The present invention relates to an inkjet recording apparatus.

  Various inkjet heads such as a shear mode (edge (end) shooter and side shooter) type and a bend mode type have been proposed as an inkjet head used in a general printer (inkjet recording apparatus).

  Among these various inkjet heads, an inkjet head having a nozzle circulation mechanism has been proposed (Patent Document 1). The nozzle circulation mechanism is a mechanism that discharges the ink injected into the pressure chamber (ink channel) from the vicinity of the nozzle that discharges the ink to the recording medium. The ink discharged from the vicinity of the nozzle can be returned to the ink tank. The purpose of providing the nozzle circulation mechanism is to remove bubbles in the pressure chamber, prevent sedimentation of particles in the ink, reduce the amount of ink waste at the initial introduction, and prevent decap.

JP-A-2006-107418

  However, in the ink jet head having the nozzle circulation mechanism as described above, if the speed at which bubbles in the pressure chamber rise in the ink in the pressure chamber is high, the bubbles cannot be reliably removed to the nozzle circulation path. There is a fear. The bubble that could not be removed may reach the nozzle by the flow of the ink in the pressure chamber when discharging from the nozzle next time, and may hinder good discharge. Further, if bubbles exist in the ink in the pressure chamber, when the pressure chamber is pressurized, the volume of the bubbles is reduced, so that the pressure of the ink may not be sufficiently increased and normal ejection may not be performed.

  In view of the above, the present invention provides an inkjet head having a nozzle circulation mechanism, which is capable of reliably discharging bubbles in a pressure chamber to a nozzle circulation path, and an inkjet recording apparatus having the inkjet head. Make it an issue.

  Other objects of the present invention will become apparent from the following description.

  The above object is achieved by the following inventions.

1.
At least one pressure chamber into which ink is injected;
Pressure generating means for causing pressure fluctuation of the pressure chamber,
A nozzle that communicates with the pressure chamber and serves as a flow path for ink ejected from the pressure chamber to the outside due to pressure fluctuations in the pressure chamber;
At least one discharge path communicating with the vicinity of the nozzle inward of the nozzle and discharging ink near the nozzle;
With
The flow velocity of the ink flow toward the discharge path of the ink inside the nozzle is a direction in which the rising speed of the bubble is opposed to the ink flow when bubbles are present in the ink inside the nozzle. Inkjet head faster than the component.
2.
By adjusting the ink discharge pressure, which is the pressure difference between the ink injected into the pressure chamber and the ink discharged from the pressure chamber to the discharge path, the flow of ink inside the nozzle toward the discharge path 2. The ink jet head according to the above 1, further comprising a pressure adjusting means for causing the pressure.
3.
The flow velocity V1 of the ink flow inside the nozzle is obtained as follows.
V1 = (P1-P2) / (8πηL / Φ) [m / s]
P1: Pressure at inlet of pressure chamber [Pa]
P2: Pressure at outlet of pressure chamber (室 P1> P2) [Pa]
η: ink viscosity [Pa · s]
L: Length of pressure chamber [m]
Φ: Equivalent channel sectional area [m ² ]
3. The ink jet head according to 1 or 2, wherein the rising speed V0 of bubbles existing in the ink inside the nozzle is determined as follows.
V0 = | (Ps−Pw) gD ² / 18η | [m / s]
Ps: air density (= 1.21) [kg / m ³ ]
Pw: ink density [kg / m ³ ]
g: Gravitational acceleration [m / s ² ]
D: bubble diameter (≦ diameter of nozzle 22) [m]
η: ink viscosity [Pa · s]
4.
When the inclination angle of the direction of the ink flow inward from the nozzle with respect to the vertically downward direction is θ, and the rising speed of the bubbles in the ink inside the nozzle is V0, the ink flow at the rising speed V0 4. The ink jet head according to the above 1, 2 or 3, wherein the component in the facing direction is V0 · cos θ.
5.
5. The ink jet printer according to 2, 3, or 4, wherein the pressure adjusting unit adjusts the ink discharge pressure in a range where a meniscus of the ink in the nozzle is maintained in accordance with a density of the ink inside the nozzle. head.
6.
Bubbles that may be present in the ink inside the nozzle are bubbles caught in the ink when the ink inside the nozzle is ejected from the nozzle, and the maximum diameter of the bubble is 6. The ink jet head according to any one of the above items 1 to 5, which has an inner diameter of a nozzle.
7.
7. The ink jet head according to any one of 1 to 6, wherein a flow rate of the ink in the discharge path is also faster than a component of a rising speed of the bubble in a direction facing the ink flow.
8.
8. The inkjet head according to any one of 1 to 7, wherein the discharge path has a shape in which a flow path resistance is inversely proportional to a flow path cross-sectional area.
9.
The inkjet head according to any one of 1 to 8,
An ink tank in which the ink transferred to the inkjet head is stored,
A transfer path for transferring the ink in the ink tank to a common ink chamber in which the pressure chamber is communicated in the inkjet head,
A collection path for collecting the ink transferred to the common ink chamber,
An ink jet recording apparatus wherein the ink discharged from the pressure chamber to the discharge path joins the ink recovered from the common ink chamber in the recovery path.

  According to the present invention, it is possible to provide an ink jet head having a nozzle circulation mechanism, in which bubbles in a pressure chamber can be reliably discharged to a nozzle circulation path, and an ink jet recording apparatus having the ink jet head. it can.

Schematic configuration diagram of an essential part showing an example of an ink jet recording apparatus according to the present invention. Flow path diagram showing ink flow paths in the ink jet recording apparatus according to the present invention Perspective view of a head chip and a nozzle plate of an inkjet head according to the present invention. Enlarged sectional view of the head chip shown in FIG. FIG. 3 is a plan view of the nozzle plate shown in FIG. FIG. 1 is an enlarged sectional view of an ink channel of the inkjet head shown in FIG. 1. FIG. 2 is an enlarged cross-sectional view of an ink channel in a state where the inkjet head shown in FIG. Equivalent circuit diagram showing the flow path resistance in the ink jet head shown in FIG. Longitudinal sectional view showing a main part of an ink jet head (side shooter type) according to the present invention. Longitudinal sectional view showing a main part of an inkjet head (MEMS type) according to the present invention.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[Inkjet recording device]
FIG. 1 is a schematic diagram showing a main part of an example of an ink jet recording apparatus 100 according to the present invention, in which an ink jet head 1 is shown in a partial cross section.

  The inkjet recording apparatus 100 records an image by ejecting ink from the inkjet head 1 to form dots on a recording medium 109 transported in a fixed direction (sub-scanning direction) by a transport unit 108. In a so-called one-pass type ink jet recording apparatus, the ink jet head 1 is fixedly arranged, and discharges ink from the nozzles 22 toward the recording medium 109 while the recording medium 109 is being conveyed to record an image. Further, in a so-called scan type ink jet recording apparatus, the ink jet head 1 is mounted on a carriage mechanism 107, and is reciprocated in the main scanning direction by the carriage mechanism 107 so that the ink jets from the nozzles 22 toward the recording medium 109. Is ejected to record an image. The transport unit 108 and the carriage mechanism 107 are drive-controlled by the control unit 104.

  Although only one ink jet head 1 is shown in FIG. 1, the ink jet recording apparatus 100 generally includes, for example, inks for respective color inks such as yellow (Y), magenta (M), cyan (C), and black (K). A plurality of inkjet heads 1 are mounted. In the ink jet recording apparatus 100 according to the present embodiment, an ink tank 101 for storing ink and a common ink chamber 41 of the ink jet head 1 are communicated by an ink transfer pipe 102 serving as a transfer path and an ink return pipe 103 serving as a recovery path. Have been.

  The ink jet head 1 is arranged so that the ink tank 101 and the common ink chamber 41 have a height difference. The inkjet head 1 is arranged such that the ink tank 101 is located at a position higher than the common ink chamber 41. Due to this height difference, the ink in the ink tank 101 has a higher potential energy than the ink in the common ink chamber 41, and therefore flows to the common ink chamber 41 via the ink transfer pipe 102.

  A transfer pump 105a that is driven and controlled by the control unit 104 of the inkjet recording apparatus 100 is provided in the middle of the ink transfer tube 102. When the transfer pump 105a is driven, the ink in the ink tank 101 is transferred to the inkjet head 1 via the ink transfer pipe 102.

  Further, a transfer side sub-tank 111a is provided in the middle of the ink transfer tube 102. The transfer-side sub-tank 111a is configured as a buffer space in which the ink transferred to the inkjet head 1 is temporarily stored. Through the transfer side sub-tank 111a, the pressure of the ink in the ink transfer tube 102 can be adjusted by the transfer pressure adjusting pump 110a constituting the pressure adjusting means. The transfer pressure control pump 110a is controlled by the control unit 104a in the inkjet head 1.

  A return pump 105b that is driven and controlled by the control unit 104 is provided in the middle of the ink return tube 103. When the return pump 105b is driven, the ink in the inkjet head 1 is returned to the ink tank 101 via the ink return pipe 103.

  Further, in the middle of the ink return pipe 103, a return side sub-tank 111b is provided. The return-side sub-tank 111b is configured as a buffer space in which the ink returned from the inkjet head 1 is temporarily stored. The pressure of the ink in the ink return pipe 103 can be adjusted via the return side sub-tank 111b by the return pressure adjusting pump 110b constituting the pressure adjusting means. The return pressure control pump 110b is controlled by the control unit 104a in the inkjet head 1.

  The pressure adjusting means is not limited to the one configured by the transfer pressure adjusting pump 110a and the return pressure adjusting pump 110b, and may be configured by any of these.

  The ink tank 101 is not particularly limited, but is preferably partitioned into an ink transfer chamber 101b and an ink return chamber 101c by a partition plate 101a that does not reach the bottom of the tank. In this case, one end of the ink transfer pipe 102 is arranged in the ink transfer chamber 101b, and one end of the ink return pipe 103 is arranged in the ink return chamber 101c. The partition plate 101a is provided to sufficiently deaerate the ink so that bubbles contained in the ink returned to the ink return chamber 101c do not flow into the ink transfer tube 102 again. Since the bubbles themselves have high buoyancy, the bubbles are suppressed from flowing under the partition plate 101a and flowing into the ink transfer chamber 101b. Such a mode is a preferable mode when the ink is circulated.

[Inkjet head]
Next, the configuration of the inkjet head 1 according to the present invention shown in FIG. 1 will be described.

  The present invention can be applied to various inkjet heads such as a shear mode (edge (end) shooter, side shooter) type, a bend mode type, and a so-called MEMS type. That is, the inkjet head according to the present invention can be configured as these various inkjet heads, and is not limited to the inkjet head of the type described in the embodiments described below.

  The inkjet head 1 shown in the present embodiment is configured as a shear mode head (end shooter type). In this embodiment, the inkjet head 1 is installed with the ink ejection surface 1S directed vertically downward. However, the use state of the inkjet head 1 of the present invention is not limited to the state where the ink ejection surface 1S is directed vertically downward, and may be used in an inclined state. In this specification, “upper” and “lower” mean “vertical upper” and “vertical lower”, and correspond to upper and lower sides in the side view of the use state shown in FIG. 1.

  As shown in FIG. 1, the ink jet head 1 includes an ink manifold 4 forming a common ink chamber 41, a wiring board 3 bonded to the ink manifold 4, and a head chip 2 bonded to the lower surface of the wiring board 3. And a nozzle plate 21 adhered to the lower surface of the head chip 2.

  The ink manifold 4 is formed of a synthetic resin material or the like into a horizontally long box shape having an opening 4a on the lower surface. The opening 4a of the ink manifold 4 is closed by the wiring board 3 bonded to the lower surface. The internal space of the ink manifold 4 serves as a common ink chamber 41 for storing the ink transferred from the ink tank 101. The wiring substrate 3 is, for example, a glass substrate. The wiring board 3 has a wiring pattern (not shown) connected to a power supply circuit (not shown) via an FPC board.

  FIG. 2 is a flow chart showing the flow path of the ink in the inkjet head 1. Note that FIG. 2 is a flow chart showing an ink discharge path, and does not represent an actual height difference. In FIG. 2, the nozzle plate 21 is not shown.

  As shown in FIGS. 1 and 2, the common ink chamber 41 is provided with an ink supply pipe 5 a serving as a flow path for supplying ink into the common ink chamber 41. The ink supply pipe 5 a is communicated with the common ink chamber 41 on the side (upper side) far from the wiring board 3. A connection portion 7a is provided on the upper end side of the ink supply pipe 5a. The connection part 7a is detachably connected to the connection part 106a on the side of the inkjet recording apparatus 100. The connection part 106 a on the side of the ink jet recording apparatus 100 communicates with the ink transfer pipe 102. Thus, the inkjet head 1 can transfer ink from the ink tank 101 and supply ink to the common ink chamber 41.

  The common ink chamber 41 is provided with an ink collection pipe 5b which is a flow path for collecting ink from inside the common ink chamber 41. The ink collection tube 5 b is communicated with the common ink chamber 41 on the side (upper side) far from the wiring board 3. A connection portion 7b is provided on the upper end side of the ink recovery tube 5b. The connecting portion 7b is detachably connected to the connecting portion 106b of the inkjet recording apparatus 100. The connection section 106 b on the side of the inkjet recording apparatus 100 communicates with the ink return pipe 103. Thus, the inkjet head 1 can collect the ink from the common ink chamber 41 and return the ink to the ink tank 101.

  In the ink jet head 1, a flow path from the ink supply pipe 5a to a buffer space 6 described later in the middle of the ink recovery pipe 5b is a main flow path F1.

  It is preferable that the ink supply pipe 5a and the ink recovery pipe 5b are arranged apart from each other at both ends in the longitudinal direction of the common ink chamber 41. The ink supply pipe 5a in the present embodiment is disposed at the left end in FIG. 1 on the upper surface side of the ink manifold 4, and the ink recovery pipe 5b is located on the right side in FIG. 1 on the upper surface side of the ink manifold 4. It is located at the end. Thus, the ink supplied from the ink supply pipe 5a to the common ink chamber 41 can be caused to flow over the whole of the common ink chamber 41 toward the ink recovery pipe 5b. Therefore, it is difficult to form a portion where the ink stays in the common ink chamber 41, and it is possible to more efficiently eliminate bubbles in the ink.

FIG. 3 is a perspective view of the head chip 2 of the inkjet head 1 according to the present invention.
FIG. 4 is an enlarged sectional view of the head chip 2 of the inkjet head 1 shown in FIG.

  As shown in FIGS. 3 and 4, a plurality of ink channels (pressure chambers) 23 and a plurality of dummy channels (pseudo pressure chambers) 25 are formed in the head chip 2. Each of the ink channels 23 and each of the dummy channels 25 are through holes formed from the upper surface to the lower surface of the head chip 2. The upper end of each ink channel 23 communicates with a common ink chamber 41 via an injection hole 31a opened in the wiring board 3. Each ink channel 23 is filled with ink from the injection hole 31a by the potential energy of the ink in the ink tank 101 and the pressure adjusted by the transfer pressure adjusting pump 110a due to the transfer pump 105a. The lower end of each ink channel 23 communicates outward (downward) through the nozzle 22. In the inkjet head 1, the inside of the nozzle 22 is inside the ink channel 23. When a communication path exists between the ink channel 23 and the nozzle 22, the inside of the nozzle 22 is inside the communication path. Each dummy channel 25 has an upper end closed by the wiring board 3 and a lower end closed by the nozzle plate 21 to form a sealed air chamber. Each ink channel 23 and each dummy channel 25 are arranged in one direction (the direction of arrow X in FIGS. 3 and 4) to form a channel row.

  Note that the number of channel columns (the number of columns) is two in FIGS. 3 and 4, but is not limited thereto, and may be three or more. By increasing the number of channel arrays (the number of arrays) and scanning in a direction orthogonal to the channel array direction (X direction), the pitch between dots formed on the recording medium can be reduced without reducing the pitch between the ink channels 23. Can be narrowed.

  As shown in FIG. 4, both walls of each ink channel 23 (partitions between the ink channel 23 and the dummy channel 25) are constituted by a pair of piezoelectric elements (drive walls) 24, 24 serving as pressure generating means. ing. The piezoelectric elements 24, 24 undergo shear deformation when a voltage is applied from a power supply circuit (not shown) via the FPC board and the wiring pattern of the wiring board 3. Due to the shear deformation of the piezoelectric elements 24, 24 forming both walls of the ink channel 23, a pressure change (a pressure reduction due to expansion or a pressure increase due to contraction) of the ink channel 23 occurs. Due to the pressure fluctuation (pressure reduction or pressure increase) of the ink channel 23, pressure is applied to the ink inside the nozzle 22, that is, the ink in the ink channel 23, and this ink is ejected through the nozzle 22.

  Two (one pair) of the piezoelectric elements 24 are provided for each ink channel 23, and form two walls of each ink channel 23. There is a gap between the piezoelectric elements 24, 24 forming the wall of one ink channel 23 and the piezoelectric elements 24, 24 forming the wall of the adjacent ink channel 23, and this gap is a dummy channel 25. is there. Therefore, each ink channel 23 can be independently driven (pressure reduction or pressure increase).

  The dummy channels 25 are located on both sides at least with the ink channel 23 interposed therebetween, and change in volume in accordance with the change in volume of the adjacent ink channel 23. In this embodiment, the ink channels 23 and the dummy channels 25 are alternately arranged one by one, so that the dummy channels 25 are located on both sides of each ink channel 23.

  In addition, the inkjet head 1 may be configured so that the adjacent ink channels 23 share a single drive wall 24 without providing the dummy channel 25. In this case, since each ink channel 23 cannot be driven (expanded or contracted) independently, so-called three-cycle driving is performed.

  The number of the ink channels 23 formed in the head chip 2 is not particularly limited. In the head chip 2 according to the present embodiment, a plurality of ink channels 23 are arranged in a plurality of rows along the X direction in FIGS. Further, regardless of the specific configuration of the pressure generating means for applying the ejection pressure to the ink in the ink channel 23, various known configurations can be adopted.

  Then, an introduction path 425 may be formed in the head chip 2. The introduction path 425 is provided at one end of a channel row formed by each ink channel 23 and each dummy channel 25 and outside the channel row. The introduction path 425 is a through hole formed from the upper surface to the lower surface of the head chip 2, and has a cross-sectional opening area larger than that of one ink channel 23. The upper end of the introduction path 425 communicates with the common ink chamber 41 through an introduction hole 31c formed in the wiring board 3, and the transfer pressure caused by the potential energy of the ink in the ink tank 101 and the transfer pump 105a. The ink is introduced from the introduction hole 31c by the pressure adjusted by the adjustment pump 110a.

  FIG. 5 is a plan view of the nozzle plate 21 of the inkjet head 1 shown in FIG.

  As shown in FIGS. 3 to 5, a plurality of nozzles 22 corresponding to each ink channel 23 are formed in a flat nozzle plate 21 bonded to the lower surface of the head chip 2. The nozzle 22 is a through hole that communicates the ink channel 23 to the outside (downward). The ink in each ink channel 23 is given a discharge pressure by the action of the piezoelectric element 24, and is discharged toward the external (lower) recording medium through the nozzle 22. That is, the nozzles 22 serve as flow paths for ink ejected from the inside of each ink channel 23 to the outside (downward). The lower surface of the nozzle plate 21 becomes the ink ejection surface 1S.

  The nozzle plate 21 is preferably formed of a silicon material, a polyimide resin material or another organic material, stainless steel, nickel or another metal material. In terms of price (being cheap), stainless steel and polyimide resin materials are excellent, stainless steel and polyimide resin materials are excellent in ease of processing, and silicon materials are excellent in processing accuracy, In terms of stability, a polyimide resin material is excellent. Although the silicon material is a hard material, if the area around the ink channel 23 is made thin, crosstalk to the adjacent ink channel 23 due to driving of the piezoelectric elements 24 can be prevented.

  FIG. 6 is an enlarged sectional view of an ink channel of the inkjet head shown in FIG.

  As shown in FIG. 6, in the vicinity of each injection hole 31a in the common ink chamber 41, the pressure wave in the ink channel 23 propagates through the ink in the common ink chamber 41 to the other ink channels 23. An air damper 46 for preventing crosstalk may be provided.

  As shown in FIG. 6, the inkjet head 1 has a nozzle circulation mechanism for discharging the ink injected into the ink channel 23 from the vicinity of the nozzle 22. The ink discharged from the vicinity of the nozzle 22 can be returned to the ink tank 101. As shown in FIGS. 3 to 6, each ink channel 23 is connected to two individual ink discharge paths 26 a, 26 a. The individual ink discharge passages 26 a communicate with the ink channel 23 at both ends in the longitudinal direction of the cross section of the ink channel 23. Since the vicinity of both ends of the ink channel 23 is a place where air bubbles often remain, it is preferable to provide the individual ink discharge passages 26a at both ends in the longitudinal direction of the cross section of the ink channel 23. The individual ink discharge passages 26 a may communicate with the ink channel 23 at any position of the ink channel 23. Further, the number of the individual ink discharge passages 26a for one ink channel 23 may be increased or decreased.

  In the present embodiment, the individual ink discharge paths 26a, 26a are configured by closing the flow path forming groove 28 formed on the upper surface of the nozzle plate 21 with the vicinity of the nozzle 22 as a start end by the lower surface of the head chip 2. Have been.

  As described above, the individual ink discharge passages 26a, 26a are constituted by the flow path forming grooves 28 formed on the upper surface of the nozzle plate 21 and the lower surface of the head chip 2, and are provided below the ink channel 23, so that the ink An ink flow path can be formed over the entire channel 23 in the depth direction, and air bubbles remaining near the end of the ink channel 23 can be satisfactorily removed. In this case, since the individual ink discharge passages 26a, 26a can be formed by processing only the nozzle plate 21, the production is easy.

  When the introduction path 425 is provided, two introduction grooves 425a and 425a are connected to the introduction path 425 as shown in FIG. The introduction grooves 425a and 425a communicate with the introduction path 425 on both sides of the introduction path 425. The introduction grooves 425a and 425a may communicate with the introduction path 425 at any position of the introduction path 425. Further, the number of the introduction grooves 425a and 425a for one introduction path 425 may be increased or decreased.

  In the present embodiment, the introduction grooves 425a and 425a are formed on the upper surface of the nozzle plate 21 with the vicinity of the introduction passage 425 as a start end, and are closed by the lower surface of the head chip 2 to form a flow path.

  As described above, since the introduction grooves 425a and 425a are formed on the upper surface of the nozzle plate 21 and the lower surface of the head chip 2 forms the flow path, the flow path can be formed by processing only the nozzle plate 21. Easy to make.

  As shown in FIGS. 3 to 6, a common ink discharge path 421 is formed on the lower surface of the head chip 2. The common ink discharge path 421 is configured by abutting a groove formed on the lower surface of the head chip 2 with a groove 422 formed on the upper surface of the nozzle plate 21. By forming the common ink discharge path 421 by the grooves formed on both the lower surface portion of the head chip 2 and the upper surface portion of the nozzle plate 21 in this manner, the cross-sectional opening area of the common ink discharge path 421 is increased, and the flow path resistance is increased. Can be reduced, and a sufficient ink flow rate can be secured. Since the thickness (height) of the head chip 2 is greater than the thickness of the nozzle plate 21, the groove on the lower surface of the head chip 2 that forms the common ink discharge path 421 can have a sufficient depth.

  The common ink discharge path 421 is composed of a plurality of flow paths formed in the direction of the channel row (X direction). The individual ink discharge paths 26a, 26a communicating with the respective ink channels 23 join by communicating with the common ink discharge path 421. Due to the pressure difference between each ink channel 23 and the common ink discharge path 421, ink flows from each ink channel 23 to the common ink discharge path 421. When the introduction path 425 is provided, the introduction grooves 425a and 425a communicate with the common ink discharge path 421. Due to the pressure difference between the introduction path 425 and the common ink discharge path 421, ink flows from the introduction path 425 to the common ink discharge path 421. Then, these flows merge to generate an ink flow in the common ink discharge path 421.

  In order to set the common ink discharge path 421 to a desired flow path resistance, the number of flow paths constituting the common ink discharge path 421 and the structure thereof can be appropriately changed. The number of flow paths constituting the common ink discharge path 421 can be appropriately increased or decreased according to the setting of the flow path resistance. When a sufficient ink flow rate can be ensured only by the groove on the lower surface of the head chip 2, the groove on the lower surface of the head chip 2 is not provided with the groove 422 on the upper surface of the nozzle plate 21. The common ink discharge path 421 may be configured by closing the lid with the upper surface. This is because the groove on the lower surface of the head chip 2 can have a sufficient depth. When a sufficient ink flow rate can be secured only by the grooves 422 on the upper surface of the nozzle plate 21, the grooves 422 on the upper surface of the nozzle plate 21 are not provided on the lower surface of the head chip 2. The common ink discharge path 421 may be configured by closing the cover with the lower surface of the common ink discharge path.

  As shown in FIGS. 2 to 5, the other end of the common ink discharge path 421 communicates with a lower end of a discharge channel 424 formed in the head chip 2. The discharge channel 424 is provided at the other end of the channel row formed by each ink channel 23 and each dummy channel 25 and outside the channel row. When the introduction path 425 is provided, the cross-sectional opening area of the discharge channel 424 is set to about 1.5 to 2 times the cross-sectional opening area of the introduction path 425. Since the ink flow rate in the discharge channel 424 is larger than the ink flow rate in the introduction path 425 by the amount of ink that has passed through each ink channel 23, the ink flow rate in the discharge channel 424 crosses the discharge channel 424 so as not to increase the flow path resistance. The surface opening area is increased.

  Note that the introduction path 425 may be formed of a through hole having the same structure as the plurality of ink channels 23. That is, a plurality of through-holes having the same structure as the ink channel 23 outside the print area are formed at one end of the head chip 2, and only the individual ink discharge path 26 a is provided without the nozzle 22 below these. The plurality of through holes function as an introduction path. In this case, it is preferable to make the total of the cross-sectional areas of the plurality of through holes equal to the cross-sectional area of the introduction path 425 described above. With this configuration, the introduction path can be created in a process that follows the process of creating each ink channel 23 with the same process content as the ink channel 23, and the creation is easy.

  As shown in FIGS. 1, 2, and 4, an ink discharge chamber 412 is provided in the ink manifold 4 above the discharge channel 424. The ink discharge chamber 412 is provided adjacent to the common ink chamber 41 in the ink manifold 4, as shown in FIGS. The ink discharge chamber 412 is separated from the common ink chamber 41 by a partition wall 45. The partition wall 45 can be formed integrally with the ink manifold 4.

  In this manner, a part of the ink (ink not ejected from the nozzle 22) that has flowed into the ink channel 23 from the injection hole 31a passes through the individual ink discharge paths 26a, 26a, and through the common ink discharge path 421 to the discharge channel 424. Then, the ink reaches the ink discharge chamber 412 through the discharge hole 31b formed in the wiring board 3.

  The ink flowing from the introduction hole 31c into the introduction path 425 reaches the discharge channel 424 through the introduction grooves 425a and 425a and the common ink discharge path 421, and reaches the ink discharge chamber 412 through the discharge hole 31b.

  In the inkjet head 1, it is preferable that the introduction path 425 is located upstream of each ink channel 23 in the ink flow in the common ink discharge path 421. When the introduction path 425 is located on the upstream side of the ink flow in the common ink discharge path 421 with respect to each ink channel 23, the ink flow rate at one end side (uppermost stream portion) of the common ink discharge path 421 can be increased. It is possible to more reliably remove bubbles in the common ink discharge path 421 and in each ink channel 23 and prevent sedimentation of ink particles.

  In addition, in the ink jet head 1, the flow velocity in the common ink discharge path 421 is increased by the flow from the introduction path 425 to the common ink discharge path 421 as compared with the case where the introduction path 425 is not provided. Therefore, the ink in the common ink discharge path 421 has a sufficient flow velocity, the ink can be discharged well from the nozzles 22, and the air bubbles in the common ink discharge path 421 and each ink channel 23 are removed. Prevention of sedimentation of the internal particles can be reliably performed.

  Further, as described above, when the cross-sectional opening area of the introduction path 425 is larger than the cross-sectional opening area of one ink channel 23, the common ink chamber 41 passes through the introduction path 425 to the common ink discharge path 421. Is smaller than the flow path resistance of the flow path from the common ink chamber 41 to the common ink discharge path 421 via one ink channel 23. Therefore, the flow rate of the flow path from the introduction path 425 to the common ink discharge path 421 can be made larger than the flow rate of the flow path from one ink channel 23 to the common ink discharge path 421. Therefore, it is possible to more reliably increase the ink flow rate at one end side (uppermost stream portion) of the common ink discharge path 421, to remove bubbles in the common ink discharge path 421 and in each ink channel 23, and to settle particles in the ink. Prevention and the like can be performed more reliably.

  In the ink jet head 1, since a flow path is formed from the inside of the introduction path 425 and the inside of each ink channel 23 to the ink discharge chamber 412 via the common ink discharge path 421, the total of these flow path resistances is taken into consideration. The conditions such as the height difference between the ink tank 101 and the common ink chamber 41 and the pressure applied by the transfer pump 105a and the return pump 105b are determined so that meniscus breaks from the nozzles 22 do not occur under these conditions. The sum of the flow path resistances of the individual ink discharge paths 26a, 26a is determined by the height difference between the ink tank 101 and the common ink chamber 41, the transfer pump 105a, and the return pump 105b so that meniscus break from the nozzle 22 does not occur. Is defined in consideration of conditions such as pressure given by The opening areas and lengths of the individual ink discharge paths 26a, 26a can be appropriately set as long as the total flow path resistance does not deviate from a predetermined value.

  In this embodiment, the inflow of the ink into the introduction path 425 is performed from the common ink chamber 41 as in the case of the injection into each ink channel 23. This embodiment can be realized simply by forming the ink channels 23 and the introduction paths 425 in parallel with the head chip 2, so that the production is easy.

  As shown in FIGS. 1 and 2, the ink discharge chamber 412 is connected to an ink discharge pipe 5c serving as a flow path for discharging ink from the ink discharge chamber 412 via a discharge path connecting portion 5d. I have. The discharge path connecting portion 5d is located above the discharge channel 424 and is provided outside the channel row at the other end of the channel row formed by the ink channels 23 and the dummy channels 25. . The upper end side of the ink discharge pipe 5c joins the ink recovery pipe 5b. The ink recovery pipe 5b and the ink discharge pipe 5c are joined by being connected to the junction box 61.

  The junction box 61 is integrally formed of a synthetic resin material or a metal material, and has a buffer space 6 formed therein. On the outer surface of the junction box 61, first to third openings 48a, 48b, 48c reaching the buffer space 6 are formed. The flow path from the first opening 48a to the third opening 48c via the buffer space 6 is interposed in the middle of the ink recovery tube 5b. In the mounting state, the ink recovery pipe 5b is divided into an upstream side and a downstream side in the middle, the upstream side is connected to the first opening 48a, and the downstream side is connected to the third opening 48c. Then, the ink discharge pipe 5c is connected to the second opening 48b.

  As described above, in the ink jet head 1 according to the present embodiment, since the ink collection pipe 5b and the ink discharge pipe 5c are merged by the merging box 61, the connection portion with the piping or the like on the ink jet recording apparatus 100 requires the ink supply. Only two places, the pipe 5a (connection part 7a) and the ink recovery pipe 5b (connection part 7b), are required. Therefore, the number of connection portions with the piping and the like on the side of the ink jet recording apparatus 100 does not increase compared to a general ink jet head, and the connection work does not become complicated. In other words, the inkjet head 1 of the present embodiment can be replaced and installed by connecting only the two connecting portions 7a and 7b without changing the design of the existing device.

  In the ink-jet head 1, the buffer space 6 from the introduction path 425 and the individual ink discharge paths 26a, 26a passes through the common ink discharge path 421, the discharge channel 424, the discharge hole 31b, the ink discharge chamber 412, and the ink discharge pipe 5c. The flow path that reaches is the discharge path 423. The discharge path 423 is a flow path that communicates with the introduction path 425 and the ink channel 23, discharges the ink in the introduction path 425 and the ink channel 23, and joins the ink recovery pipe 5b in the buffer space 6. However, as long as the discharge path 423 discharges ink from the individual ink discharge paths 26a, 26a near the nozzle 22, the subsequent path does not need to be limited at all. Then, the sub flow path F2 extends from the introduction hole 31c and the respective injection holes 31a to the discharge path 423 (see FIG. 2).

  The discharge path 423 may be provided both outside the channel row at one end of the channel row and outside the channel row at the other end of the channel row. In this case, the discharge channel 424 and the ink discharge chamber 412 are provided in both of the channel arrays, and the ink discharge pipe 5c is connected to each of them. These ink discharge tubes 5c are respectively joined to the ink recovery tubes 5b. In this case, when the introduction path 425 is provided, it is desirable to provide the introduction path 425 at the center position of the channel row.

  Since the discharge path 423 is configured as a flow path that passes through all of the individual ink discharge paths 26a, 26a corresponding to the respective ink channels 23, the flow resistance of the entire discharge path 423 is increased as the density of the ink channels 23 increases. Is getting bigger. Therefore, even if the ink discharge pipe 5c joins the ink recovery pipe 5b, the flow rate of the main flow path F1 from the ink supply pipe 5a to the ink recovery pipe 5b is large, and the sub flow path F2 from each injection hole 31a to the discharge path 423 is large. It is conceivable that they do not merge smoothly due to the small flow rate. In the ink jet head 1, the main flow path F1 and the sub flow path F2 are merged (the ink discharge pipe 5c and the ink recovery pipe 5b are merged) in the buffer space 6, and the flow rate adjusting member 8 is used. Thereby, even if the flow rates of the main flow path F1 and the sub flow path F2 are different, they can be smoothly merged.

  The flow rate adjusting member 8 is a cylindrical member disposed inside the ink recovery pipe 5b, and narrows the flow path diameter of the ink recovery pipe 5b. The flow rate adjusting member 8 gives the main flow path F1 a pressure loss corresponding to a difference in flow resistance between the main flow path F1 and the sub flow path F2. In the ink jet head 1, by balancing the flow path resistance of the main flow path F1 and the flow path resistance of the sub flow path F2 by the flow rate adjusting member 8, the ink pressure p0 in the ink supply pipe 5a can be easily adjusted. It is possible to flow ink evenly through both the main flow path F1 and the sub flow path F2.

  According to the above-described ink jet head 1 and the ink jet recording apparatus 100 including the same, by merely supplying ink from the ink supply pipe 5a, the residual bubbles in the common ink chamber 41 are transferred to the ink recovery pipe 5b via the main flow path F1. As well as the bubbles near the ink channel 23 drawn from the nozzle 22, the bubbles can be quickly discharged from the ink discharge tube 5c via the sub flow path F2. Therefore, it is possible to efficiently remove the residual air bubbles in the entire ink manifold 4 (in the common ink chamber 41 and in the vicinity of the ink channel 23). In addition, even when using ink containing particles, pigments, and the like that easily settle, the settling of particles, pigments, and the like in the individual ink discharge paths 26a, 26a and the common ink discharge path 421 during image recording is effectively suppressed. As a result, the density deviation of the ink can be suppressed.

(Bubble discharging operation)
The ink jet head 1 performs a bubble discharging operation in the ink channel 23 while discharging ink to the recording medium and also when discharging is not performed. Bubbles in the ink in the ink channel 23 include those that are caught in from the nozzle 22 after the ink is ejected from the nozzle 22, those that are mixed in the ink that is injected from the injection hole 31a, and those that are in the ink channel 23. This is what occurred in the ink when the pressure of the ink suddenly dropped.

  As shown in FIG. 6, the bubble discharging operation is performed by pressure adjusting means (transfer pressure adjusting pump 110a and return pressure adjusting pump 110b), as shown in FIG. This is performed by adjusting an ink discharge pressure ΔP, which is a pressure difference from the pressure P2 of the ink discharged from the nozzle 23 to the individual ink discharge path 26a. The pressure P1 of the ink injected into the ink channel 23 is larger than the pressure P2 of the ink discharged from the ink channel 23, and the ink discharge pressure ΔP is determined by the flow of the ink in the ink channel 23 toward the individual ink discharge path 26a. Cause.

  Let V1 be the flow velocity of the ink flow due to the ink discharge pressure ΔP. When the bubble B exists in the ink in the ink channel 23, the rising direction of the bubble B is vertically upward. The flow velocity V1 of the ink flow in the ink channel 23 is faster than the component V2 of the rising velocity V0 of the bubble B in the direction facing the ink flow. When the ink jet head 1 is not tilted (when the ink flow direction and the ink discharge direction are vertically downward), the component V2 of the rising speed V0 of the bubble B in the direction opposite to the ink flow becomes the rising speed V0. Equal (V2 = V0).

  In the ink jet head 1, since the flow velocity V1 of the ink flow is faster than the velocity component V2 of the bubble B, the bubble B can be prevented from remaining in the ink channel 23. As the flow velocity V1 of the ink flow becomes faster with respect to the velocity component V2 of the bubble B, the bubble B can be removed from the ink channel 23 more quickly. However, the pressure adjusting means adjusts the ink discharge pressure ΔP within a range where the meniscus of the ink in the nozzle 22 is maintained. It is preferable that the pressure adjusting unit adjusts the ink discharge pressure ΔP so that the ratio between the flow velocity V1 of the ink flow and the velocity component V2 of the bubble B becomes a predetermined ratio set in advance.

  In the ink-jet head 1, even when the bubble B is present in the ink in the ink channel 23, such as when the bubble B is entrained from the nozzle 22 after the ink is ejected from the nozzle 22, it can be performed within an extremely short time. The bubbles B can be discharged from the ink channel 23 to the individual ink discharge path 26a. Therefore, the ink jet head 1 can quickly recover from a discharge failure caused by the bubble B, and can reduce the number of prints damaged by the discharge failure and having to be discarded.

  FIG. 7 is an enlarged sectional view of the ink channel in a state where the inkjet head shown in FIG. 1 is inclined.

  As shown in FIG. 7A, when the inkjet head 1 is inclined and the inclination angle of the ink flowing direction in the ink channel 23 with respect to the vertically downward direction is θ, as shown in FIG. The component V2 of the rising speed V0 of B in the direction opposite to the ink flow is V0 · cos θ.

  In the ink jet head 1, even when the ink jet head 1 is used at an angle, the bubbles B can be quickly removed. This ink jet head 1 can exhibit the same air bubble elimination ability even in the inclined state as in the state without the inclination.

  FIG. 8 is an equivalent circuit diagram showing the flow path resistance in the inkjet head shown in FIG.

In the inkjet head 1, the flow path resistance R in the ink channel 23 and the flow path resistance R 'in the discharge path 423 are connected in series as shown in the equivalent circuit of FIG. . The flow path resistance R in the ink channel 23 can be obtained as follows according to Hagen-Poiseuille's law.
R = 8πηL / (SΦ)
= 8πηL / (abΦ)
= 8πηL / (ab (d / 2) ² π)
= 8ηL / (ab {a ² b ² / (a + b) ² })
= 8ηL (a + b) ² / (a ³ b ³ ) [Pa · s / m ³ ]
η: ink viscosity [Pa · s] (= [Ns / m ² ] = [kg / ms])
L: Length of ink channel [m]
a, b: Length of each side of flow channel cross section [m]
S: Channel cross-sectional area (= ab) [m ² ]
d: equivalent diameter (= 4ab / 2 (a + b)) [m]
Φ: equivalent flow path cross-sectional area (= (d / 2) ² π) [m ² ]

The amount (discharge flow rate) Q1 of the ink discharged from the ink channel 23 to the discharge path 423 can be obtained as follows.
Q1 = ΔP / (8πηL / (SΦ))
= (P1-P2) / (8πηL / (SΦ)) [m ³ / s]
ΔP: difference (= P1−P2) between the pressure P1 at the inlet (injection hole 31a) of the ink channel 23 and the pressure P2 (∵P1> P2) at the outlet (individual ink discharge passage 26a) [Pa]

The velocity (flow velocity) V1 of the ink flow in the ink channel 23 can be obtained as follows.
V1 = Q1 / S
= ΔP / (8πηL / Φ) [m / s]

The rising speed V0 of the bubble B in the ink channel 23 can be obtained by the Stokes equation as follows.
V0 = | (Ps−Pw) gD ² / 18η | [m / s]
し な い If you don't set the absolute value, it will be minus.
Ps: air density (= 1.21) [kg / m ³ ]
Pw: ink density [kg / m ³ ]
g: Gravitational acceleration [m / s ² ]
D: bubble diameter (≦ diameter of nozzle 22) [m]

When the inclination angle of the inkjet head 1 is θ, the component V2 facing the ink flow at the rising speed V0 of the bubble B can be obtained as follows.
V2 = V0 · cos θ [m / s]

  When the inkjet head 1 is used with an inclination, the pressure adjusting means preferably changes the ink discharge pressure ΔP according to the inclination angle θ of the inkjet head 1. The pressure adjusting means changes the ink discharge pressure ΔP in accordance with the inclination angle θ, so that the ratio between the flow velocity V1 of the ink flow and the velocity component V2 of the bubble B is set to a predetermined value regardless of the inclination angle θ. It is preferable to set the ratio.

  As described above, the rising speed V0 of the bubble B in the ink channel 23 differs depending on the ink density Pw. Therefore, the pressure adjusting means changes the ink discharge pressure ΔP in accordance with the ink density Pw in the ink channel 23, and adjusts the ratio between the flow velocity V1 of the ink flow and the velocity component V2 of the bubble B to a predetermined ratio. Is preferable. The ink density Pw is a substantially constant value as long as the ink conforms to the specifications of the inkjet head 1, and may be set in advance according to the type of ink to be used.

  Further, since the ink density Pw changes according to the temperature inside the ink jet head 1, the pressure adjusting means changes the ink discharge pressure ΔP according to the temperature inside the ink jet head 1 so that the ink flow velocity V1 and the bubble B It is preferable that the ratio with the speed component V2 be a predetermined ratio set in advance. Since the correlation between the ink density Pw and the temperature is known in advance for each ink specification, the correlation between the ink discharge pressure ΔP and the temperature can be set in advance. Information on the temperature in the inkjet head 1 can be obtained from a temperature sensor provided in the inkjet head 1.

  As described above, the inkjet head 1 can be configured as an inkjet head of various specifications in which the density Pw of the ink used is different.

  By the way, since the bubble B which can exist in the ink in the ink channel 23 is caught in the ink when the ink is ejected from the nozzle 22 and penetrates into the ink channel 23, the maximum diameter of the bubble B is 22 approximately equal to the inner diameter. Then, the rising speed V0 of the bubble B in the ink channel 23 increases as the bubble diameter D increases. Therefore, in the inkjet head 1, it is preferable that the ink discharge pressure ΔP is set and adjusted so that the bubble B having the bubble diameter D equal to the inner diameter of the nozzle 22 can be discharged. By adjusting the ink discharge pressure ΔP in this manner, all the bubbles B in the ink channel 23 can be quickly eliminated.

  Further, in the ink jet head 1, it is preferable that the flow velocity of the ink in the discharge path 423 is also higher than the component V2 of the rising velocity V0 of the bubble B in the direction opposite to the ink flow.

  Since the flow velocity of the ink in the discharge path 423 is higher than the velocity component V2 of the bubble B, the bubble B discharged from the ink channel 23 can be quickly moved away from the ink channel 23, and high bubble elimination ability can be realized. Can be.

  In order to increase the flow rate of the ink in the discharge path 423, it is preferable that the discharge path 423 remove as much as possible a shape that causes a pressure loss from the inside of the flow path and that the flow path resistance has a shape that is inversely proportional to the cross-sectional area of the flow path. . As described above, since the flow path resistance R in the ink channel 23 is connected in series with the flow path resistance R 'of the discharge path 423, the flow path resistance R' of the discharge path 423 is reduced. If it is set low, the flow velocity of the ink flow in the ink channel 23 can be efficiently increased by adjusting the ink discharge pressure ΔP.

  The ink pressure at each location in the ink jet head 1 can be measured by a manometer at a point where a T-shaped branch is provided in the ink flow path and the branch is made.

  In the ink jet recording apparatus 100 of the embodiment described above, ink is circulated between the ink jet head 1 and the ink tank 101, but the present invention is not limited to this. Although not shown, the ink that has flowed out of the ink recovery pipe 5b and the ink discharge pipe 5c may be discharged to a waste ink tank without returning to the ink tank 101.

[Other Embodiments of Inkjet Head]
FIG. 9 is a longitudinal sectional view showing a main part of an ink jet head (side shooter type) according to the present invention.
FIG. 10 is a longitudinal sectional view showing a main part of an inkjet head (MEMS type) according to the present invention.

  As described above, the present invention is not limited to the shear mode type ink jet head 1, but includes various types such as a side shooter type ink jet head 10 shown in FIG. 9 and a so-called MEMS type ink jet head 11 shown in FIG. Can be applied to the inkjet head. Note that the parts having the same reference numerals as those in FIG. 1 are the parts having the same configuration.

  In the side shooter type ink jet head 10, as shown in FIG. 9, the direction of ink flow in the ink channel 23 is substantially perpendicular to the direction of ink ejection from the nozzles 22. When the ink ejection direction is vertically downward, the direction of ink flow in the ink channel 23 is horizontal.

  In the ink jet head 10 as well, the bubble B is prevented from remaining in the ink channel 23 by setting the flow velocity V1 of the ink flow in the ink channel 23 sufficiently higher than the rising velocity V0 of the bubble B. be able to.

  In the ink jet head 10, the component V2 of the rising speed V0 of the bubble B in the direction facing the ink flow is V0 · cos 90 ° = 0. Accordingly, the flow velocity V1 of the ink flow is always higher than the velocity component V2 = 0 of the bubble B, but the bubble B moves upward in the ink channel 23 unless it is higher than the rising velocity V0. There is a fear.

  In the MEMS type ink jet head 11, as shown in FIG. 10, a piezoelectric element 24 is disposed on a substrate 3, and an ink channel 23 is formed on a lower surface side of the substrate 3. The piezoelectric element 24 is arranged on the upper surface (ceiling surface) of the ink channel 23, and when driven, changes the volume of the ink channel 23 to cause a pressure change. On the lower surface (bottom surface) of the ink channel 23, a communication path 23a to the nozzle 22 is formed. The nozzle 22 communicates with the ink channel 23 via the communication passage 23a, and communicates the ink channel 23 to the outside (downward). The lower surface of the inkjet head 11 becomes the ink ejection surface 1S. The ink in each ink channel 23 is applied with an ejection pressure by the action of the piezoelectric element 24 and is ejected (downward) toward the external recording medium through the nozzle 22.

  The ink channel 23 communicates with the common ink chamber 41 via the injection hole 31a. The ink in the common ink chamber 41 is injected into the ink channel 23 via the injection hole 31a.

  An individual ink discharge path 26a communicates with a communication path 23a from the ink channel 23 to the nozzle 22. The individual ink discharge path 26a communicates with the common ink discharge path 421.

  The ink that has reached the common ink discharge path 421 reaches an ink discharge chamber (not shown), as in the above-described embodiment, and joins the ink recovery pipe via the ink discharge pipe.

  In the ink jet head 11 as well, the flow velocity V1 of the ink flowing from the inside of the ink channel 23 toward the individual ink discharge path 26a is increased by the rising velocity V0 of the bubble B inside the nozzle 22 (in the communication path 23a or in the ink channel 23). Is faster than the component V2 in the direction opposite to the ink flow, it is possible to prevent the bubbles B from entering and remaining in the communication path 23a and the ink channel 23.

  In the above description, by using the pressure adjusting means, the flow velocity of the ink flow toward the ink discharge path inward of the nozzle is reduced when bubbles are present in the ink inward of the nozzle. Although the mode in which the rising speed of the bubble is higher than the component in the direction opposite to the ink flow has been described, the present invention is not limited to this. For example, you may use the piezoelectric element 24 which is a pressure generation means.

1: Inkjet head (end shooter type)
10: inkjet head (side shooter type)
11: Inkjet head (MEMS type)
2: Head chip 21: Nozzle plate 22: Nozzle 23: Ink channel 23a: Communication path 24: Piezoelectric element 25: Dummy channel 26a: Individual ink discharge path 28: Flow path forming groove 3: Wiring board 31a: Injection hole 31b: Discharge Hole 31c: introduction hole 4: ink manifold 41: common ink chamber 412: ink discharge chamber 421: common ink discharge path 422: groove 423: discharge path 424: discharge channel 425: introduction path 425a: introduction groove 45: partition wall 46: air Damper 5a: Ink supply pipe 5b: Ink recovery pipe 5c: Ink discharge pipe 5d: Discharge path connection part 6: Buffer space part 61: Merging box 7a: Connection part 7b: Connection part 8: Flow control member F1: Main flow path F2: Sub flow path 100: inkjet recording apparatus 101: ink tank 102: ink transfer tube 103: a Return pipe 104: Control unit 104a: Control unit 105a: Transfer pump 105b: Return pump 107: Carriage mechanism 108: Transport means 109: Recording medium 110a: Transfer pressure control pump 110b: Return pressure control pump 111a: Transfer-side subtank 111b: Return sub tank

Claims (9)

At least one pressure chamber into which ink is injected;
Pressure generating means for causing pressure fluctuation of the pressure chamber,
A nozzle that communicates with the pressure chamber and serves as a flow path for ink ejected from the pressure chamber to the outside due to pressure fluctuations in the pressure chamber;
At least one discharge path communicating with the vicinity of the nozzle inward of the nozzle and discharging ink near the nozzle;
With
The flow velocity of the ink flow toward the discharge path of the ink inside the nozzle is a direction in which the rising speed of the bubble is opposed to the ink flow when bubbles are present in the ink inside the nozzle. Inkjet head faster than the component.   By adjusting the ink discharge pressure, which is the pressure difference between the ink injected into the pressure chamber and the ink discharged from the pressure chamber to the discharge path, the flow of ink inside the nozzle toward the discharge path 2. The ink jet head according to claim 1, further comprising a pressure adjusting means for generating the pressure. The flow velocity V1 of the ink flow inside the nozzle is obtained as follows.
V1 = (P1-P2) / (8πηL / Φ) [m / s]
P1: Pressure at inlet of pressure chamber [Pa]
P2: Pressure at outlet of pressure chamber (室 P1> P2) [Pa]
η: ink viscosity [Pa · s]
L: Length of pressure chamber [m]
Φ: Equivalent channel sectional area [m ² ]
The ink jet head according to claim 1, wherein a rising speed V0 of bubbles existing in the ink inside the nozzle is determined as follows.
V0 = | (Ps−Pw) gD ² / 18η | [m / s]
Ps: air density (= 1.21) [kg / m ³ ]
Pw: ink density [kg / m ³ ]
g: Gravitational acceleration [m / s ² ]
D: bubble diameter (≦ diameter of nozzle 22) [m]
η: ink viscosity [Pa · s]   When the inclination angle of the direction of the ink flow inward from the nozzle with respect to the vertically downward direction is θ, and the rising speed of the bubbles in the ink inside the nozzle is V0, the ink flow at the rising speed V0 4. The ink jet head according to claim 1, wherein the component in the facing direction is V0 · cos θ.   5. The ink discharge pressure according to claim 2, wherein the pressure adjustment unit adjusts the ink discharge pressure according to a density of the ink inside the nozzle within a range in which a meniscus of the ink in the nozzle is maintained. Ink jet head.   Bubbles that may be present in the ink inside the nozzle are bubbles caught in the ink when the ink inside the nozzle is ejected from the nozzle, and the maximum diameter of the bubble is The ink jet head according to any one of claims 1 to 5, wherein the ink jet head is equal to an inner diameter of the nozzle.   The ink jet head according to claim 1, wherein a flow velocity of the ink in the discharge path is also faster than a component of a rising velocity of the bubble in a direction facing the ink flow.   The ink jet head according to claim 1, wherein the discharge path has a shape in which a flow path resistance is inversely proportional to a cross-sectional area of the flow path. An inkjet head according to any one of claims 1 to 8,
An ink tank in which the ink transferred to the inkjet head is stored,
A transfer path for transferring the ink in the ink tank to a common ink chamber in which the pressure chamber is communicated in the inkjet head,
A collection path for collecting the ink transferred to the common ink chamber,
An ink jet recording apparatus wherein the ink discharged from the pressure chamber to the discharge path joins the ink recovered from the common ink chamber in the recovery path.

Images