# Patent

## Title
Liquid ejection head and recording apparatus having the same

## Abstract

A liquid ejection head includes: an ejection port; a supply section and a discharge section; a main flow channel; a supply flow channel; a filter; and a sub flow channel, one end of which is connected to a first connection position near the supply section, and the other end of which is connected to a second connection position near the discharge section, wherein the main flow channel and the sub flow channel are formed such that, in supplying the liquid from the supply section to the main flow channel at a predetermined flow rate, the higher the predetermined flow rate is, the more the ratio of a flow rate in the main flow channel from the first connection position to the second connection position to a flow rate in the sub flow channel increases.

## Background
CROSS REFERENCE TO RELATED APPLICATION
The present application claims priority from Japanese Patent Application No. 2010-154949, which was filed on Jul. 7, 2010, the disclosure of which is herein incorporated by reference in its entirety.
TECHNICAL FIELD
The present invention relates to a liquid ejection head having ejection ports ejecting a liquid, and a recording apparatus having the liquid ejection head.
BACKGROUND
A recording head disclosed in Patent Document 1 has an ink flow channel. The ink flow channel includes a flow channel which supplies ink to ejection ports ejecting ink and a flow channel which discharges ink from the flow channel outside the recording head. In the related art, a technique is known in which a filter is provided in a flow channel of the head to filter a liquid, such as ink. When the above-described filter is provided in the flow channel of the head, the head is configured as described in Patent Document 2 so as to remove bubbles remaining in the filter. A liquid flows from the supply side of the flow channel provided in the head to the discharge side, such that bubbles remaining in the filter are removed.

    [Patent Document 1] JP-A-2007-203641
    [Patent Document 2] JP-A-2004-351664


SUMMARY
In order to adjust the flow rate of the liquid flowing toward the ejection ports, a sub flow channel is provided separately from a main flow channel, in which the liquid is directed from the supply side of the flow channel to the discharge side, such that the liquid bypasses the supply side and the discharge side of the main flow channel. This is because, if the flow rate of the liquid toward the ejection ports is high, a meniscus formed in the ejection ports may be broken, and the liquid may be unnecessarily ejected from the ejection ports.
In this configuration, if the viscosity of the liquid decreases due to variations in the environmental conditions outside the head, or the like, a high flow rate is required to sweep out bubbles in the main flow channel. Meanwhile, if the flow rate of the liquid which is supplied to the head increases, the flow rate of the liquid in the main flow channel increases, and the flow rate in the sub flow channel also increases. For this reason, the flow rate in the main flow channel insufficiently increases, such that the ability to sweep out bubbles from the filter may be insufficiently exhibited.
An object of the invention is to provide a liquid ejection head which easily secures the ability to sweep out bubbles from a filter in accordance with variations in the environmental conditions, and a recording apparatus having the liquid ejection head.
According to an aspect of the invention, there is provided a liquid ejection head comprising: an ejection port for ejecting a liquid; a supply section and a discharge section for the liquid; a main flow channel which connects the supply section and the discharge section; a supply flow channel which branches off from the main flow channel and supplies the liquid to the ejection port; a filter which is disposed in the vicinity of a branch position in which the supply flow channel is branched from the main flow channel; and a sub flow channel, one end of which is connected to a first connection position closer to the supply section rather than the branch position in the main flow channel, and the other end of which is connected to a second connection position closer to the discharge section rather than the branch position in the main flow channel, wherein the main flow channel and the sub flow channel are formed such that, in supplying the liquid from the supply section to the main flow channel at a predetermined flow rate, the higher the predetermined flow rate is, the more the ratio of a flow rate in the main flow channel from the first connection position to the second connection position to a flow rate in the sub flow channel increases.
According to another aspect of the invention, there is provided a recording apparatus comprising: the liquid ejection head described above; a liquid supply unit which supplies a liquid from the supply section to the main flow channel; a return flow channel which returns the liquid from the discharge section to the liquid supply unit; and a valve which switches a state where the liquid flows through the return flow channel and a state where the liquid does not flow through the return flow channel.
With the liquid ejection head and the recording apparatus according to the aspects of the invention, the main flow channel and the sub flow channel are formed such that, when the flow rate of the liquid which is supplied from the supply section to the head increases, the ratio of the flow rate in the main flow channel to the flow rate in the sub flow channel increases. For this reason, if the flow rate of the liquid which is supplied from the supply section to the head increases, the liquid easily flows into the main flow channel rather than the sub flow channel. Therefore, when the flow rate of the entire liquid which is supplied to the head increases because the viscosity of the liquid decreases, or the like, it is easy to secure the ability to sweep out bubbles remaining in the filters.



BRIEF DESCRIPTION OF THE DRAWINGS
Illustrative aspects of the invention will be described in detail with reference to the following figures wherein:
FIG. 1 is a schematic side view showing the internal structure of an ink jet printer according to an embodiment of the invention;
FIG. 2 is a perspective view of an ink jet head of FIG. 1;
FIG. 3A is an exploded perspective view of a filter unit in the head of FIG. 1, and FIG. 3B is a plan view of a unit main body of the filter unit;
FIG. 4A is an exploded perspective view of a reservoir unit in the head of FIG. 1, and FIG. 4B is a plan view of a reservoir formed in the reservoir unit;
FIG. 5 is a sectional view of the filter unit and the reservoir unit taken along the line V-V of FIG. 3B;
FIG. 6 is a plan view of a flow channel unit in the head of FIG. 1;
FIG. 7 is a schematic view showing an ink flow channel which is formed over the head and an ink supply unit supplying ink to the head;
FIGS. 8A and 8B are graphs showing the measurement results of the flow rates of ink which branches into a main flow channel and a sub flow channel formed in the head; and
FIG. 9 is a plan view showing modifications of an ink flow channel formed in the head.



DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS OF THE PRESENT INVENTION
Hereinafter, a preferred embodiment of the invention will be described with reference to the drawings.
First, the overall configuration of an ink jet printer according to an embodiment of the invention will be described with reference to FIG. 1. As shown in FIG. 1, ahead 1 (recording head) is a line head which is elongated in one direction (a direction perpendicular to the paper of FIG. 1), and is incorporated into an ink jet printer 500 with the longitudinal direction thereof as a main scanning direction. The printer 500 is a line-type color ink jet printer.
The printer 500 has a rectangular parallelepiped housing 501a. A sheet discharge section 531 is provided above the top panel of the housing 501a. The internal space of the housing 501a can be divided into spaces A, B, and C in order from above. In the space A, conveying of a sheet P and image formation on the sheet P are performed. In the space B, an operation relating to sheet feed is carried out. In the space C, main tanks 58 as an ink supply source are accommodated.
In the space A are provided four heads 1, ink supply units 50 which supply ink to the heads 1, a conveying unit 521 which conveys the sheet P, guide portions which guide the sheet P, and the like. At the upper part of the space A, a controller 501 (supply control means) is arranged to control the operations of the respective sections of the printer 500 to manage the overall operation of the printer 500.
Each head 1 substantially has a rectangular parallelepiped shape which is elongated in the main scanning direction. The four heads 1 are arranged in parallel at a predetermined pitch in the sub scanning direction and supported by the housing 501a through a head frame 503. Ink droplets of magenta, cyan, yellow, and black are respectively ejected from the lower surfaces 4a (ejection surfaces) of the four heads 1 onto the sheet P. The ink supply units 50 supply ink from the main tanks 58 to the heads 1. A temperature sensor 1a is fixed to each of the heads 1, and the detection result of the temperature sensor 1a is sent to the controller 501. The specific configuration of the heads 1 and the ink supply units 50 will be described below in detail.
The conveying unit 521 has two belt rollers 506 and 507, an endless conveying belt 508 which is wound around both rollers 506 and 507, a nip roller 504 and a separating plate 505 which are arranged outward of the conveying belt 508, a platen 519 which is arranged inward of the conveying belt 508, and the like. The belt roller 507 is a driving roller and rotates with driving of a conveying motor (not shown) in the clockwise direction of FIG. 1 under the control of the controller 501. With the rotation of the belt roller 507, the conveying belt 508 travels in a direction indicated by an arrow of FIG. 1. The belt roller 506 is a driven roller and rotates in the clockwise direction of FIG. 1 with the traveling of the conveying belt 508. The nip roller 504 is arranged to face the belt roller 506 and presses the sheet P fed from an upstream-side guide portion (described below) against an outer circumferential surface 508a of the conveying belt 508. On the outer circumferential surface 508a, a weak adhesive silicon layer is formed. The separating plate 505 is arranged to face the belt roller 507, separates the sheet P from the outer circumferential surface 508a, and guides the sheet P to a downstream-side guide portion (described below). The platen 519 is arranged to face the four heads 1 and supports the upper loop of the conveying belt 508 from the inner circumferential surface side of the belt. Thus, a predetermined gap suitable for image formation is formed between the outer circumferential surface 508a and the ejection surfaces 4a of the heads 1.
The guide portions are arranged on both sides of the conveying unit 521 so as to sandwich the conveying unit 521 therebetween. The upstream-side guide portion has two guides 527a and 527b, and a pair of feed rollers 526. This guide portion connects a sheet feed unit 501b (described below) and the conveying unit 521. The downstream-side guide portion has two guides 529a and 529b, and two pairs of feed rollers 582. This guide portion connects the conveying unit 521 and the sheet discharge section 531.
In the space B, the sheet feed unit 501b is arranged. The sheet feed unit 501b has a sheet feed tray 523 and a sheet feed roller 525, and the sheet feed tray 523 is provided detachably with respect to the housing 501a. The sheet feed tray 523 is a box which is opened upward and stores a plurality of sheets P. The sheet feed roller 525 sends the uppermost sheet P in the sheet feed tray 523 under the control of the controller 501 and feeds the sheet to the upstream-side guide portion.
As described above, in the spaces A and B, a sheet conveying path is formed from the sheet feed unit 501b to the sheet discharge section 531 through the conveying unit 521. The controller 501 sends the sheet P from the sheet feed roller 523 on the basis of a recording command. The sheet P is sent to the conveying unit 521 through the upstream-side guide portion. When the sheet P passes through directly below the ejection surfaces 4a of the heads 1 in the sub scanning direction, ink droplets are sequentially ejected from the heads 1, and a desired color image is formed on the sheet P. Thereafter, the sheet P is separated from the outer circumferential surface 508a by the separating plate 505 and discharged to the upper sheet discharge section 531 through the downstream-side guide portion.
The sub scanning direction is the direction parallel to the conveying direction of the sheet P by the conveying unit 521, and the main scanning direction is the direction perpendicular to the sub scanning direction along the horizontal plane.
In the space C, a tank unit 501c is provided detachably with respect to the housing 501a. The tank unit 501c has a tray 535 and four main tanks 58. The four main tanks 58 correspond to the four heads 1 one-to-one, and are arranged in parallel in the sub scanning direction in the tray 535.
Hereinafter, the heads 1 will be described with reference to FIGS. 2 to 6. As shown in FIG. 2, each head 1 substantially has a rectangular parallelepiped shape which is elongated in the main scanning direction. The head 1 includes a laminate in which a filter unit 2, a reservoir unit 3, and a flow channel unit 4 are laminated in order from above. In the upper surface of the filter unit 2, joints 2a to 2c are formed to protrude upward. Ink is exchanged between the ink supply unit 50 (described below) and the head 1 through the joints 2a to 2c. Multiple ejection ports 4y are formed in the lower surface of the flow channel unit 4, and ink is ejected from the ejection ports 4y when forming an image. Inside the laminate, ink flow channels communicate the joints 2a to 2c and the ejection ports 4y. Flexible printed boards 6 are drawn out between the reservoir unit 3 and the flow channel unit 4. The flexible printed boards 6 are connected to actuator units 5 (described below), and supply a driving command from the controller 501 to the actuator units 5.
The filter unit 2 has a unit main body 20 made of a resin material, and performs filtering of ink and adjustment of flow channel resistance. As shown in FIG. 3A, the filter unit 2 is configured such that a filter 2f is arranged therein, and a flow channel resistance adjustment section (linear flow channel 26) is formed. The unit main body 20 has the joints 2a to 2c, and an upper filter chamber 24a, a lower filter chamber 24b, a communicating flow channel 25, and a linear flow channel 26 which constitute ink flow channels communicating with the joints 2a to 2c. 
As shown in FIG. 3B, the joints 2a and 2b are arranged in one end portion of the unit main body 20 in the main scanning direction, and the joint 2c is arranged in the opposing end position. The upper filter chamber 24a is substantially arranged at the center position of the unit main body 20 in the sub scanning direction near the joint 2a. The upper filter chamber 24a is a concave portion which is opened in the upper surface of the unit main body 20, and schematically has a hexagonal planar shape which is elongated with respect to the main scanning direction. Both ends of the upper filter chamber 24a in the main scanning direction are formed to be tapered outward in the main scanning direction. A flexible thin flat plate 2i is attached around the upper filter chamber 24a from above. The flat plate 2i seals the entire opening of the upper filter chamber 24a in plan view, and constitutes the upper wall of the upper filter chamber 24a (see FIG. 5).
The upper filter chamber 24a communicates with the joint 2a through a communicating flow channel 21 (discharge flow channel) formed in the unit main body 20. At one end of the upper filter chamber 24a near the joint 2a in the main scanning direction, a communicating hole 21a which is a communicating portion with the communicating flow channel 21 is formed. The communicating hole 21a passes through the unit main body 20 vertically. The communicating flow channel 21 is a concave portion (see FIG. 5) which is opened in the lower surface of the unit main body 20. A flexible thin flat plate 2e is attached around the communicating flow channel 21 from below. The flat plate 2e seals the entire opening of the communicating flow channel 21 in plan view, and constitutes the lower wall of the communicating flow channel 21.
The low filter chamber 24b is a concave portion (see FIG. 5) which is opened in the bottom surface of the upper filter chamber 24a, and schematically has a planar shape which is substantially similar to the upper filter chamber 24a. When viewed in plan view, the lower filter chamber 24b is slightly smaller than the upper filter chamber 24a. The lower filter chamber 24b is separated from the communicating hole 21a in the main scanning direction. A filter 2f is attached to the communicating portion of the upper filter chamber 24a and the lower filter chamber 24b. The filter 2f covers the entire lower filter chamber 24b in plan view, and constitutes a partition wall of the upper filter chamber 24a and the lower filter chamber 24b. The filter 2f transmits ink from the upper filter chamber 24a to the lower filter chamber 24b, and filters a foreign substance in the ink at that time.
As shown in FIG. 3B, the communicating flow channel 25 is a flow channel which is constituted by the concave portion opened in the upper surface of the unit main body 20, and extends in the sub scanning direction from the end portion opposite to the communicating hole 21a in the upper filter chamber 24a. The communicating flow channel 25 is bent toward the joint 2b near the end portion of the unit main body 20 in the sub scanning direction and then extends in the main scanning direction therefrom to communicate with a communicating flow channel 22 through a communicating hole 22a at the distal end in the extension direction. The communicating hole 22a passes through the unit main body 20 vertically. The communicating flow channel 25 is covered with the flat plate 2i from above, and the upper wall of the communicating flow channel 25 is constituted by the flat plate 2i. The communicating flow channel 22 is a concave portion which is opened in the lower surface of the unit main body 20. This opening is covered with the flat plate 2e from below, and the lower wall of the communicating flow channel 22 is constituted by the flat plate 2e. The communicating flow channel 22 communicates with the joint 2b. 
The linear flow channel 26 is constituted by a concave portion which is opened in the upper surface of the unit main body 20 (FIGS. 3B and 5), and has a linear portion 26a which extends linearly in the main scanning direction and a plurality of expanded portions 26b which are expanded on both sides in the sub scanning direction. The linear portion 26a is arranged in the central portion of the unit main body 20 in the sub scanning direction, and is formed to have a certain width. The expanded portions 26b provided in the linear portion 26a all have a rectangular planar shape of the same form and of the same size, and are arranged at regular intervals in the main scanning direction. The expanded portions 26b have a rectangular shape in plan view. A flexible thin flat plate 2g is attached around the expanded portions 26b from above. The flat plate 2g covers the entire linear flow channel 26 including the linear portion 26a and all the expanded portions 26b in plan view, and constitutes the upper wall of the linear flow channel 26.
The linear flow channel 26 communicates with an end portion of the lower filter chamber 24b on the linear flow channel 26 side through a communicating flow channel 23 in an end portion on the lower filter chamber 24b (see FIG. 5). The communicating flow channel 23 is a concave portion which is opened in the lower surface of the main body unit 20, communicates with the lower filter chamber 24b through a communicating hole 23a at one end, and communicates with the linear flow channel 26 through a communicating hole 23b at the other end. The communicating hole 23a passes through the bottom wall of the lower filter chamber 24b, and the communicating hole 23b passes through the unit main body 20 vertically. The communicating flow channel 23 is sealed with the flat plate 2e from below, and the lower wall of the communicating flow channel 23 is constituted by the flat plate 2e. In the end portion of the linear flow channel 26 on the lower filter chamber 24b, a dropping flow channel 27 is connected at a position J1 (first connection position) slightly separated from the communicating hole 23b toward the opposing end portion. The dropping flow channel 27 is opened downward in the lower surface of the unit main body 20, and communicates with a through hole 31a of the reservoir unit 3 in the opening.
The end portion of the linear flow channel 26 on the joint 2c communicates with the joint 2c through a communicating flow channel 29 (see FIG. 5). The communicating flow channel 29 is a concave portion which is opened in the lower surface of the unit main body 20, and communicates with the linear flow channel 26 through a communicating hole 29a. The communicating hole 29a passes through the unit main body 20 vertically. A flexible thin flat plate 2h is attached around the communicating flow channel 29 from below. The flat plate 2h constitutes the lower wall of the communicating flow channel 29. In the end portion of the linear flow channel 26 on the joint 2c, a dropping flow channel 28 is connected at a position J2 (second connection position) slightly separated from the communicating hole 29a toward the opposing end portion. The dropping flow channel 28 is opened downward in the lower surface of the unit main body 20, and communicates with a through hole 31b of the reservoir unit 3 in the opening.
As shown in FIG. 4A, the reservoir unit 3 is a laminate in which flat plate members 31 to 33 having a rectangular planar shape elongated in the main scanning direction, and a plurality of flat plate members 34x and 34y smaller than the flat plate members 31 to 33 are laminated. Through holes are formed in the flat plate members 31 to 33, 34x, and 34y, and the through holes communicate with each other to form an ink flow channel.
Through holes 31a and 31b are formed in both end portions of the flat plate member 31 in the main scanning direction. All the through holes 31a and 31b are arranged at the center of the flat plate member 31 in the sub scanning direction. In the flat plate member 32, through holes 32a and 32b are formed at the positions facing the through holes 31a and 31b. A reservoir 32c is formed in the main scanning direction between the through hole 32a and the through hole 32b. The reservoir 32c forms a storage space which stores ink in the reservoir unit 3. The reservoir 32c is formed such that a portion other than end portions 32x and 32y substantially has a certain width over the entire width of the flat plate member 32 with respect to the sub scanning direction. As shown in FIG. 4B, the end portions 32x and 32y are formed to have a tapered shape in which the width gradually decreases toward the through holes 32a and 32b. The reservoir 32c faces a solid region of the flat plate member 31 where no through hole is formed, and the corresponding region of the flat plate member 31 constitutes the upper wall of the reservoir 32c. 
In the flat plate member 33, as shown in FIG. 4A, dropping flow channels 33a and 33b are formed at the positions facing the through holes 32a and 32b. In the end portion of the flat plate member 33 in the sub scanning direction, a plurality of dropping flow channels 33c are formed such that every two dripping flow channels are adjacent to each other. The dropping flow channels 33c are flow channels which are arranged at the positions facing the reservoir 32c to lead ink stored in the reservoir 32c downward. The dropping flow channels 33c are arranged such that four pairs near one end of the flat plate member 33 and four pairs near the other end are arranged differently from each other in the main scanning direction. The dropping flow channels 33c are arranged in a zigzag manner as a whole. A solid region of the flat plate member 33 where no dropping flow channels 33a to 33c are formed faces the reservoir 32c to constitute the lower wall of the reservoir 32c. 
The flat plate members 34x and 34y face near the edge of the flat plate member 33. In the flat plate member 34x, dropping flow channels 34a are formed to face the dropping flow channels 33a and 33b. The flat plate members 34x and 34y are arranged at the positions away from the actuator units 5 (described below) in plan view. The flat plate members 34x and 34y also serve a spacer which forms the installation space of the actuator unit 5 and the flexible printed boards 6 between the reservoir unit 3 and the flow channel unit 4.
As shown in FIG. 6, the flow channel unit 4 is configured such that eight actuator units 5 having a trapezoidal shape are arranged on an upper surface 4b in two columns in a zigzag manner. The flexible printed boards 6 are attached to the upper surfaces of the actuator units 5 to supply a driving signal from the controller 501 (see FIG. 2). In the upper surface 4b, openings 4x are formed to be away from the arrangement regions of the actuator units 5, and are covered with filters 72. The filters 72 are fixed to be sandwiched between the lower surface of the reservoir unit 3 and the upper surface 4b of the flow channel unit 4, and communicate the through holes 34a and 34b with the openings 4x. The filters 72 are plate-shaped members arranged with a mesh-shaped material, and filter ink flowing from the reservoir unit 3 into the flow channel unit 4.
The region corresponding to the actuator units 5 in the lower surface 4a (see FIG. 5) of the flow channel unit 4 is an ejection region where multiple ejection ports 4y are opened. Inside the flow channel unit 4 are formed of a common ink flow channel (manifold flow channel 41 and sub manifold flow channel 41a) which communicates with the openings 4x, and individual flow channels which extend from the exit of the sub manifold flow channel 41a to the ejection ports 4y. As shown in FIGS. 4A and 4B, the sub manifold flow channel 41a branches off the manifold flow channel 41 and extends in the longitudinal direction of the head.
With the above-described configuration, in this embodiment, as schematically shown in FIG. 7, a main flow channel M, supply flow channels Y, and a sub flow channel S are formed. The main flow channel M is a flow channel which connects the joint 2b (supply section) to the joint 2c (discharge section) through the reservoir 32c. The supply flow channels Y are flow channels which branch off the reservoir 32c and reach the ejection ports 4y. The sub flow channel S is a flow channel which mainly bypasses between both ends of the reservoir 32c. Specifically, the main flow channel M is connected between the joint 2b and the joint 2c through the communicating flow channels 22 and 25, the upper filter chamber 24a, the filter 2f, the lower filter chamber 24b, the communicating flow channel 23, the linear flow channel 26, the dropping flow channel 27, the through holes 31a and 32a, the reservoir 32c, the through holes 31b and 32b, the dropping flow channel 28, and the linear flow channel 26. The supply flow channels Y branch off the main flow channel M in the branch portions of the dropping flow channels 33a, 33b, and 33c from the reservoir 32c, and are directed toward the flow channel unit 4 through the filters 72 arranged therearound to supply ink to the ejection ports 4y. The sub flow channel S branches off the main flow channel M at the connection position J1 between the linear flow channel 26 and the dropping flow channel 27, is directed toward the connection position J2 to the dropping flow channel 28 along the linear flow channel 26, and is joined with the main flow channel M.
In this way, the sub flow channel S branches off the main flow channel M at the connection position J1 on the joint 2b side with respect to the branch positions of the supply flow channels Y from the main flow channel M, and is joined again with the main flow channel M at the connection position J2 on the joint 2c. That is, the sub flow channel S serves as a bypass flow channel which bypasses a partial flow channel from the connection position J1 to the connection position J2 in the main flow channel M.
Next, the ink supply unit 50 (liquid supply means) which supply ink to the heads 1 will be described with reference to FIG. 7. The ink supply unit 50 has a sub tank 54 and a pump 56, and supplies ink from the main tank 58 to the head 1 (filter unit 2). The sub tank 54 stores ink therein and opens bubbles in the ink to the air through an air opening hole 54a. The sub tank 54 is connected to the joints 2a and 2c through an elastic tube 51 and an elastic tube 53 (return flow channel), and is also connected to the main tank 58 through an elastic tube 57. The end portions of the elastic tubes 51, 53, and 57 are arranged below the liquid level S of the liquid stored in the sub tank 54. The pump 56 is provided such that the suction side thereof is connected to the sub tank 54 through an elastic tube 55, and the discharge side thereof is connected to the joint 2b through an elastic tube 52. The pump 56 is controlled by the controller 501, sucks ink in the sub tank 54 through the elastic tube 55, and supplies the sucked ink to the filter unit 2 through the elastic tube 52 and the joint 2b. The pressure which is applied to ink by the pump 56 is controlled by the controller 501. Thus, the flow rate of ink flowing into the head 1 is adjusted.
In the elastic tubes 51, 53, and 57, opening/closing valves 61, 62, and 63 are provided to switch an open state where ink flows through the tubes and a closed state where ink does not flow through the tubes. When the opening/closing valve 61 or 62 is in the open state, a circulation path is formed such that ink flows into the filter unit 2 through the sub tank 54 and the pump 56, and ink flows out of the filter unit 2 to the sub tank 54 through the opening/closing valve 61 or 62 in the open state. With this pump driving, ink in which a foreign substance, such as bubbles or dust, is mixed can be discharged from the filter unit 2 to the sub tank 54. When the pump 56 operates in a state where the opening/closing valve 63 is in the open state, ink is supplied from the main tank 58 to the sub tank 54. The states of the opening/closing valves 61 to 63 are switched under the control of the controller 501.
Next, the flow of ink at the time of recording and purging in the ink jet head 1 will be described with reference to FIG. 7. When recording, the controller 501 puts the opening/closing valves 61 and 63 in the open state and puts the opening/closing valve 62 in the closed state. Thus, with consumption of ink when ink is ejected from the head 1, the flow of ink from the main tank 58 to the filter unit 2 through the sub tank 54 is spontaneously generated. Ink from the sub tank 54 flows into the upper filter chamber 24a through the elastic tube 51 and the joint 2a. Ink from the upper filter chamber 24a flows into the reservoir 32c along the main flow channel M, and ink branches off the main flow channel M to the supply flow channels Y and are supplied to the ejection ports 4y. Ink passes through two filters of the filters 2f and 72 until ink reaches the ejection ports 4y, such that a foreign substance in the ink is reliably filtered.
Purging is processing for forcibly discharging ink outside the head 1 to remove a foreign substance, such as bubbles, in the head 1. The purging processing of this embodiment includes (1) circulative purging in which ink is circulated on the upstream side from the filter 2f, (2) inter-filter purging in which ink is circulated so as to pass through a flow channel between the filters 2f and 72, and (3) nozzle purging in which ink is discharged from the ejection ports 4y. 
At the time of (1) circulative purging, the controller 501 puts the opening/closing valve 61 in the open state, puts the opening/closing valves 62 and 63 in the closed state, and operates the pump 56. Thus, ink in the sub tank 54 flows from the joint 2b into the upper filter chamber 24a. In the upper filter chamber 24a, ink flows into the communicating flow channel 21 along the upper surface of the filter 2f. Accordingly, a foreign substance, such as bubbles, remaining in the upstream-side surface of the filter 2f is removed, and clogging of the filter 2f is avoided. Ink directed toward the communicating flow channel 21 is discharged from the joint 2a to the outside and returns to the sub tank 54 through the elastic tube 51. That is, the joint 2a also serves as a discharge section (another discharge section in the invention) which discharges ink from the filter unit 2 to the outside at the time of circulative purging. The flow channel resistance of the flow channel which returns from the upper filter chamber 24a to the sub tank 54 through the joint 2a is smaller than the flow channel resistance of the flow channel which is directed from the upper filter chamber 24a to the ejection ports 4y beyond the filter 2f. For this reason, during circulative purging, even when the joint 2b communicates with the ejection ports 4y, there is little possibility that ink will leak from the ejection ports 4y. 
At the time of (2) inter-filter purging, the controller 501 puts the opening/closing valve 62 in the open state, puts the opening/closing valves 61 and 63 in the closed state, and operates the pump 56. Thus, ink in the sub tank 54 flows from the joint 2b into the upper filter chamber 24a. In turn, ink is directed toward the joint 2c through the reservoir 32c along the main flow channel M, and is also directed toward the joint 2c along the sub flow channel S which branches off the main flow channel M. Ink discharged from the joint 2c returns to the sub tank 54 through the elastic tube 53. Thus, a foreign substance, such as bubbles, in the flow channel between the filter 2f and the filter 72 is discharged outside the head 1.
The flow channel resistance of the flow channel which returns to the sub tank 54 through the joint 2c along the main flow channel M and the sub flow channel S with the connection position J1 of the linear flow channel 26 and the dropping flow channel 27 as a starting point is smaller than the flow channel resistance of the flow channel which is directed toward the ejection ports 4y along the main flow channel M and the supply flow channels Y with the connection point J1 as a starting point. For this reason, during inter-filter purging, even when the joint 2b communicates with the ejection ports 4y, there is little possibility that ink will leak from the ejection ports 4y. 
In particular, in this embodiment, in the flow channel from the lower filter chamber 24b to the joint 2c, the flow channel along the main flow channel M and the sub flow channel S which bypasses the main flow channel M are provided. This contributes to decrease the flow channel resistance of the flow channel from the lower filter chamber 24b to the joint 2c. Meanwhile, if ink excessively easily flows into the sub flow channel S, it is not possible to secure the flow rate in the main flow channel M, thereby making it impossible to sufficiently remove a foreign substance in the main flow channel M. For this reason, the sub flow channel S is configured to have the flow channel resistance such that, even when the flow channel resistance of the whole of the main flow channel M and the sub flow channel S is lowered, the flow rate in the main flow channel M can be sufficiently secured. For example, the flow channel resistance of the sub flow channel S is adjusted so as to substantially become equal to the flow channel resistance from the connection position J1 to the connection position J2 in the main flow channel M.
At the time of (3) nozzle purging, the controller 501 puts all the opening/closing valves 61 to 63 in the closed state, and operates the pump 56. Thus, ink in the sub tank 54 flows from the joint 2b into the upper filter chamber 24a. In turn, similarly to the flow of ink at the time of recording, ink reaches the ejection ports 4y and is ejected from the ejection ports 4y. Therefore, an increase in the viscosity of ink near the ejection ports 4y in the flow channel unit 4 or clogging of the ejection ports 4y is avoided.
If the temperature of ink changes due to variations in the external environment, the viscosity of ink also varies. If the ink temperature rises and the viscosity of ink decreases, pressure loss due to the viscous property of ink in the main flow channel M or the sub flow channel S is reduced. For this reason, the possibility that ink will leak from the ejection ports 4y during circulative purging or inter-filter purging is reduced. On the other hand, if viscosity decreases, the resistance against a foreign substance, such as bubbles, decreases, and the ability to sweep out a foreign substance in the ink flow channel is lowered. Accordingly, when removing a foreign substance through purging, it is necessary to change the flow rate of ink in accordance with the external environment so as to adjust the ability to discharge a foreign substance. For example, if it is determined that the temperature of the head 1 rises on the basis of the detection result of the temperature sensor 1a, the controller 501 of this embodiment increases the applied pressure to ink in the pump 56 and increases the flow rate of ink which is supplied to the head 1. A temperature sensor may be configured to directly detect the temperature of ink in the head 1.
However, as in this embodiment, if the sub flow channel S which bypasses the main flow channel M is formed, even when the flow rate of all the ink increases, the flow rate necessary for discharging a foreign substance in the main flow channel M may not be secured because the flow rate of ink flowing in the sub flow channel S as well as the main flow channel M increases.
Accordingly, the sub flow channel S of this embodiment is configured such that, as the flow rate of all the ink flowing in the main flow channel M and the sub flow channel S increases, the ratio of the flow rate of the sub flow channel S to the flow rate of the partial flow channel from the connection position J1 to the connection position J2 in the main flow channel M decreases. At this time, the amount of distribution of ink to the partial flow channel increases.
Specifically, as shown in FIG. 3B, a plurality of expanded portions 26b are formed in the linear flow channel 26 which constitutes the sub flow channel S. The expanded portions 26b are portions which are expanded from the linear portion 26a in the sub scanning direction, and in which a cross-section perpendicular to the extension direction (that is, ink flow direction) of the linear flow channel 26 rapidly changes. In detail, as shown in FIG. 3B, an ink inflow portion 26x (first change portion) of each of the expanded portions 26b is rapidly expanded along the ink flow direction with respect to the sub scanning direction, and the cross-sectional area thereof substantially discontinuously changes. An ink outflow portion 26y (first change portion) of each of the expanded portions 26 rapidly contracts along the ink flow direction with respect to the sub scanning direction, and the cross-sectional area thereof substantially discontinuously changes in the inflow direction. Thus, when ink passes through the ink inflow portion 26x and the ink outflow portion 26y, the flow velocity of ink changes, and pressure loss due to a change in velocity occurs. If pressure loss due to a change in velocity when ink passes through the ink inflow portion 26x is ΔP1, a loss coefficient is ζ1, the density of ink is ρ, and the flow velocity before and after passing is u1 and u2, ΔP1 is expressed as follows. Since the ink inflow portion 26x is a portion which is rapidly expanded with respect to the sub scanning direction, ζ1=1.

ΔP1=ζ1*ρ*(u1−u2)2/2  (Expression 1-1)

If pressure loss due to a change in velocity when ink passing through the ink outflow portion 26y is ΔP1′, a loss coefficient is ζ1′, and the flow velocity before and after passing is u1′ and u2′, ΔP1′ is expressed as follows. Since the ink outflow portion 26y is a portion which rapidly contracts with respect to the sub scanning direction, ζ1′=1.

ΔP1′=ζ1′*ρ*(u1′−u2′)2/2  (Expression 1-2)

A plurality of expanded portions 26b having the above-described flow channel characteristic are formed in the sub flow channel S. Pressure loss includes pressure loss due to a change in velocity and pressure loss due to viscosity. Thus, the entire pressure loss ΔP1ALL in the sub flow channel S is expressed as follows. Σ means that pressure loss is summed for all the expanded portions 26b, and Δp1 represents pressure loss due to viscosity.

ΔP1ALL=Σ(ΔP1+ΔP1′)+Δp1  (Expression 1-3)

In the main flow channel M, the flow channel shape changes at both end portions 32x and 32y of the reservoir 32c, and this is one of the main factors for a change in velocity in the main flow channel M. In the end portion 32x, the cross-section perpendicular to the extension direction of the reservoir 32c is gradually expanded with respect to the inflow direction (main scanning direction) of ink flowing in the extension direction of the reservoir 32c. In the end portion 32y, the cross-section perpendicular to the extension direction of the reservoir 32c is gradually reduced with respect to the outflow direction (main scanning direction) of ink flowing in the extension direction of the reservoir 32c. If pressure loss due to a change in velocity when ink passes through the end portion 32x is ΔP2, a loss coefficient is ζ2, and the flow velocity before and after passing is v1 and v2, ΔP2 is expressed as follows. The end portion 32x is a portion (second change portion) which is gradually expanded with respect to the sub scanning direction, and in which the cross-sectional area continuously changes in the ink flow direction. For this reason, 0<ζ2<1.

ΔP2=ζ2*ρ*(v1−v2)2/2  (Expression 2-1)

If pressure loss due to a change in velocity when ink passes through the end portion 32y is ΔP2′, a loss coefficient is ζ2′, and the flow velocity before and after passing is v1′ and v2′, ΔP2′ is expressed as follows. The end portion 32y is a portion (second change portion) which is gradually reduced with respect to the sub scanning direction, and in which the cross-sectional area continuously changes in the ink flow direction. For this reason, 0<ζ2′<1.

ΔP2′=ζ2′*ρ*(v1′−v2′)2/2  (Expression 2-2)

Thus, the entire pressure loss ΔP2ALL in the reservoir 32c is expressed as follows. Δp2 represents pressure loss due to viscosity.

ΔP2ALL=ΔP2+ΔP2′+Δp2  (Expression 2-3)

As shown in (Expression 1-1), (Expression 1-2), (Expression 2-1), and (Expression 2-2), while pressure loss ΔP, ΔP1′, ΔP2, and ΔP2′ due to a change in velocity is proportional to the square of the change in velocity, pressure loss Δp1 and Δp2 due to viscosity depends on the first order of the flow velocity (for example, in the case of a laminar flow in a pipe line with a uniform cross-section, pressure loss Δp1 and Δp2 due to viscosity is proportional to the average flow velocity of ink which cuts across one cross-section of the pipe line). Thus, if the flow rate of ink increases and the flow velocity increases, in (Expression 1-3) and (Expression 2-3), the influence of pressure loss ΔP1, ΔP1′, ΔP2, and ΔP2′ due to a change in velocity relatively increases compared to pressure loss Δp1 and Δp2 due to viscosity. As described above, the loss coefficients ζ1 and ζ1′ are greater than the loss coefficients ζ2 and ζ2′. For this reason, pressure loss ΔP1 and ΔP1′ due to a change in velocity in the sub flow channel S undergoes a large degree of change when the flow rate of ink increases compared to pressure loss ΔP2 and ΔP2′ due to a change in velocity in the main flow channel M. That is, in the sub flow channel S, pressure loss when the flow rate of ink increases easily increases compared to the main flow channel M. For this reason, as the flow rate of all the ink increases, the ratio of the flow rate of the sub flow channel S to the flow rate of the main flow channel M decreases.
FIG. 8A shows the measurement results of the flow rate [ml/s] of ink branching into the main flow channel M at the connection position J1 and the flow rate [ml/s] of ink branching into the sub flow channel S at the connection position J1 with respect to a pressure [kPa] applied to ink by the pump 56 when inter-filter purging is performed in an example according to the head 1 of this embodiment. FIG. 8A also shows the ratio of the ink flow rates. The measurement results show that, if the flow rate of ink flowing into the head 1 increases, the ratio of the flow rate branching into the sub flow channel S to the flow rate branching into the main flow channel M decreases. This result is because, as described above, ζ1, ζ1′>ζ2, ζ2′, such that the degree of increase in pressure loss due to a change in velocity in the sub flow channel S when the flow rate increases is larger than the degree of increase in pressure loss due to a change in velocity in the main flow channel M.
FIG. 8B shows the measurement results of the flow rate [ml/s] of ink branching into the main flow channel M at the connection position J1 and the flow rate [ml/s] of ink branching into the sub flow channel S at the connection position J1 when the temperature condition changes and the flow rate of ink flowing into the head 1 also changes in the example of FIG. 8A. FIG. 8B also shows the ratio of the ink flow rates. FIG. 8B shows that, if the flow rate of ink flowing into the head 1 increases simultaneously with a temperature rise, the ratio of ink branching into the main flow channel M to ink branching into the sub flow channel S increases as might be expected. If the temperature rises, viscosity decreases, such that the influence of pressure loss due to a change in velocity further increases with respect to pressure loss due to viscosity. For example, at the time of inter-nozzle purging, the controller 501 of this embodiment controls the pump 56 to increase the flow rate of ink flowing into the head 1 as shown in FIG. 8B with a temperature rise of the head 1.
According to this embodiment described above, when increasing the flow rate of all the ink, the ratio of the flow rate of the main flow channel M to the flow rate of the sub flow channel S increases. For this reason, if the flow rate of ink flowing from the pump 56 into the head 1 increases, the ratio of ink branching into the main flow channel M to ink branching into the sub flow channel S increases. Accordingly, for example, when the ability to sweep out a foreign substance, which is reduced because the viscosity of ink decreases, is restored by increasing the flow rate of ink, the ratio of ink branching into the main flow channel M with an increase in the flow rate of ink increases, making it easy to secure the ability to sweep out a foreign substance.
When there is no flow channel resistance adjustment function of the sub flow channel S, it is also necessary to increase the flow rate of the sub flow rate S so as to increase the flow rate of the main flow channel M. For this reason, an excessive pressure is applied from the pump to ink. Accordingly, for example, at the time of inter-filter purging, ink leaks from the ejection ports 4y. However, in this embodiment, since the sub flow channel S has the flow channel resistance adjustment function, even when an excessive pressure is not applied from the pump to ink, it is possible to increase the flow rate of the main flow channel M. For this reason, a foreign substance is appropriately discharged, and no wasteful ink consumption occurs.
In increasing the flow rate of all the ink, a plurality of expanded portions 26b are provided in the sub flow channel S to form a flow channel such that the ratio of the flow rate of the main flow channel M to the flow rate of the sub flow channel S increases. The expanded portions 26b are portions in which pressure loss easily increases with a change in the cross-sectional area of the flow channel when the flow rate increases. Specifically, a configuration is made such that the loss coefficient ζ1 of each of the expanded portions 26b becomes greater than the loss coefficient ζ2 of each of the end portions 32x and 32y of the main flow channel M. For this reason, when the entire flow rate increases, the flow rate of the main flow channel M easily increases compared to the flow rate of the sub flow channel S.
MODIFICATIONS
Although the preferred embodiment of the invention has been described, the invention is not limited to the above-described embodiment, and various modifications may be made without departing from the scope described in the means for solving the problem.
For example, FIG. 9 shows linear flow channels 261 and 262 and a bent flow channel 263 according to modifications, instead of the linear flow channel 26 of the above-described embodiment. The linear flow channel 261 has a linear portion 261a, and expanded portions 261b which are expanded from the linear portion 261a in the sub scanning direction. Unlike the expanded portions 26b, the expanded portions 261b do not have a rectangular planar shape, and are formed such that the inflow portion and the outflow portion thereof are tapered. Preferably, the loss coefficient of each of the expanded portions 261b is greater than the loss coefficient in each of the end portions 32x and 32y of the reservoir 32c such that pressure loss increases. The linear flow channel 262 has a linear portion 262a and expanded portions 262b. Unlike the linear portion 26a, the width of the linear portion 262a in the sub scanning direction changes. The bent flow channel 263 is formed to have a plurality of bends 263a and is configured such that pressure loss increases due to the bends 263a. The bent flow channel 263 may be appropriately combined with the linear flow channels 261 and 262.
The ink supply unit 50 may have a configuration other than the above-described embodiment insofar as ink can be introduced from the joint 2b and ink can be discharged from the joint 2a or 2c. For example, a configuration may be made such that ink discharged from the joint 2b or 2c directly flows into the joint 2a without passing through the sub tank 54.
Although in the above-described embodiment, the sub tank 54 and the head 1 constitute a circulative flow channel through the pump 56, at least one of the elastic tube 51 and the elastic tube 53 as the return flow channel from the head 1 to the sub tank 54 may be connected to a portion (for example, a waste liquid tank) other than the sub tank 54. At this time, while part of ink sent by the pump is discarded, the exhaust amount may be small due to the flow channel resistance adjustment function of the sub flow channel S.
Although in the above-described embodiment, the flow channel width in each of the main flow channel M and the sub flow channel S is linearly changed, the flow channel width may change in a different form. For example, the change portion of the flow channel width may change in a curve form.
The above-described embodiment is an example where the invention is applied to an ink jet head which ejects ink from nozzles, and the invention is not limited to the ink jet head. For example, the invention may be applied to a liquid ejection head which ejects conductive paste to form a minute wire pattern on a substrate, ejects an organic luminescent material to a substrate to form a high-definition display, or ejects optical resin to a substrate to form a minute electronic device, such as an optical waveguide.

## Claims

1. A liquid ejection head comprising:
an ejection port for ejecting a liquid;
a supply section and a discharge section for the liquid;
a main flow channel which connects the supply section and the discharge section;
a supply flow channel which branches off from the main flow channel and supplies the liquid to the ejection port;
a filter which is disposed in the vicinity of a branch position in which the supply flow channel is branched from the main flow channel; and
a sub flow channel, one end of which is connected to a first connection position closer to the supply section rather than the branch position in the main flow channel, and the other end of which is connected to a second connection position closer to the discharge section rather than the branch position in the main flow channel,
wherein
the main flow channel and the sub flow channel are formed such that, in supplying the liquid from the supply section to the main flow channel at a predetermined flow rate, the higher the predetermined flow rate is, the more the ratio of a flow rate in the main flow channel from the first connection position to the second connection position to a flow rate in the sub flow channel increases.

2. The liquid ejection head according to claim 1,
wherein
the sub flow channel has a first change portion in which an area of a cross-section perpendicular to an extension direction of the sub flow channel changes along the extension direction of the sub flow channel.

3. The liquid ejection head according to claim 2,
wherein
the main flow channel has a second change portion between the first connection portion and the second connection portion in which an area of a cross-section perpendicular to an extension direction of the main flow channel changes along the extension direction of the main flow channel, and
the first and second change portions are formed such that ζ1 expressed by Expression 1 becomes greater than ζ2 expressed by Expression 2:


ΔP1=ζ1*ρ*(u1−u2)2/2  (Expression 1)



ΔP2=ζ2*ρ*(v1−v2)2/2  (Expression 2)


In Expressions 1 and 2, ΔP1, u1, and u2 respectively denote pressure loss in the first change portion, the flow velocity of the liquid flowing into the first change portion, and the flow velocity of the liquid flowing out of the first change portion, ΔP2, v1, and v2 respectively denote pressure loss in the second change portion, the flow velocity of the liquid flowing into the second change portion, and the flow velocity of the liquid flowing out of the second change portion, and ρ denotes the density of the liquid.

4. The liquid ejection head according to claim 3,
wherein, in a change portion of the first change portion, the area of the cross-section substantially discontinuously changes along the extension direction of the sub flow channel, and in a change portion of the second change portion, the area of the cross-section continuously changes along the extension direction of the main flow channel.

5. The liquid ejection head according to claim 2,
wherein a plurality of the first change portions are formed in the sub flow channel.

6. The liquid ejection head according to claim 1, further comprising:
another discharge section different from the discharge section;
another filter, different from the filter, which is arranged at a position closer to the supply section rather than the first connection position in the main flow channel; and
a discharge flow channel which branches off a position closer to the supply section rather than the another filter in the main flow channel and communicates with the another discharge section.

7. A recording apparatus comprising:
the liquid ejection head according to claim 1;
a liquid supply unit which supplies a liquid from the supply section to the main flow channel;
a return flow channel which returns the liquid from the discharge section to the liquid supply unit; and
a valve which switches a state where the liquid flows through the return flow channel and a state where the liquid does not flow through the return flow channel.