JP2011251427A - Liquid discharging head unit and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid discharging head unit capable of stably discharging liquid droplets from a head, and an image forming apparatus equipped with the liquid discharging head unit.SOLUTION: A recording head 1 includes the head 2 and a sub-tank 4, the sub-tank 4 is spatially partitioned by a bulkhead 202 into an ink storage part 22 and a supply flow passage 24. The recording head further includes a partitioning wall 205 disposed extending downward from a top face 22a toward the bulkhead 202 in the ink storage part 22 so that a position of a lower end 205a is lower than a position of an upper end 202a. A liquid storage tank discharging flow passage which is a flow passage of ink from a flow passage inlet formed in a clearance between the lower end 205a of the partitioning wall 205 and the bulkhead 202 through a flow passage 207 in front of the bulkhead, a communication passage 206, the supply flow passage 24, and to a supply flow passage outlet 24e of the supply flow passage 24 communicating with a common liquid chamber 13 has an inverted U shape.

Description

  The present invention relates to a liquid discharge head unit that discharges liquid as droplets from a nozzle and an image forming apparatus including the liquid discharge head unit.

  As an image forming apparatus such as a printer, a facsimile machine, a copying machine, a plotter, and a complex machine of these, for example, an inkjet is used as an image forming apparatus of a liquid discharge recording method using a recording head having a head unit that discharges liquid ink as droplets. Recording devices are known. This liquid discharge recording type image forming apparatus means that ink droplets are transported from a recording head (not limited to paper, including OHP, and can be attached to ink droplets and other liquids). Yes, it is also ejected to a recording medium or a recording medium, recording paper, recording paper, etc.) to form an image (recording, printing, printing, and printing are also used synonymously). It is. As an image forming apparatus of such a liquid discharge recording method, a serial type image forming apparatus that forms an image by ejecting ink droplets while the recording head moves in the main scanning direction, or ink droplets without moving the recording head. There is a line-type image forming apparatus using a line-type head that forms an image by discharging ink.

  In the present application, the “image forming apparatus” of the liquid discharge recording method is an apparatus that forms an image by discharging liquid onto a medium such as paper, thread, fiber, fabric, leather, metal, plastic, glass, wood, ceramics, or the like. In addition, “image formation” means not only giving an image having a meaning such as a character or a figure to a medium but also giving an image having no meaning such as a pattern to the medium (simply It also means that a droplet is landed on a medium). “Ink” is not limited to ink, but is used as a general term for all liquids capable of image formation, such as recording liquid, fixing processing liquid, and liquid. DNA samples, resists, pattern materials, resins and the like are also included. In addition, the “image” is not limited to a planar one, but includes an image given to a three-dimensionally formed image, and an image formed by three-dimensionally modeling a solid itself.

  As an ink jet recording apparatus used as such an image forming apparatus, an ink jet recording apparatus in which a sub tank is disposed above a head portion of a recording head and a main tank is disposed on the apparatus main body side is known. In an ink jet recording apparatus provided with a sub tank, a system is known in which ink is replenished and supplied from a main tank to a sub tank of a recording head, and ink is supplied from the sub tank to the head portion.

  As a conventional sub-tank configuration, an ink storage unit that stores ink supplied from the main tank and ink supplied from the ink storage unit to the head unit pass through a partition wall that extends upward from the bottom of the internal space. There is one that is spatially partitioned into a supply channel (for example, Patent Document 1). In such a sub tank, the upper end of the partition wall is lower than the ceiling portion of the internal space of the sub tank, and the ink storage portion and the supply flow path are formed by a communication path formed by a gap between the upper end of the partition wall and the ceiling portion of the internal space of the sub tank. It is the structure which communicates. Then, when ink is supplied from the main tank while the sub tank is empty, the ink is first filled in the ink container, and when the ink reaches a position higher than the upper end of the partition wall, the ink passes through the communication path and is supplied. It flows into the flow path. The supply channel has a supply channel outlet communicating with the channel in the head portion at the bottom, and the ink flowing into the supply channel passes through the supply channel and passes from the supply channel outlet to the channel in the head unit. It flows. With such a configuration, by setting the inflow speed from the main tank to the sub tank to be higher than the outflow speed of the ink from the supply flow path outlet, even after the outflow of ink from the sub tank to the head portion has started. The amount of ink in the sub tank increases. Thereafter, the space inside the supply flow path and the upper end of the partition wall is also filled with ink, and the ink filling into the sub tank is completed.

As described above, in the sub tank provided with the partition wall, the ink storage portion partitioned by the partition wall is filled with a certain amount of ink and then the ink that has passed above the partition wall is supplied to the head portion. Until the ink is completely filled, there is no or almost no outflow of ink.
On the other hand, in the configuration in which the outlet is provided at the bottom of the internal space of the sub tank without providing the partition wall, when ink is supplied with the sub tank being empty, the ink flows out from the outlet at the bottom from the beginning of supply. It becomes. In this state, by making the inflow speed of ink into the sub tank faster than the outflow speed from the outlet, although the ink filling into the sub tank is completed, it takes time to fill the ink. The amount of ink discharged toward the part also increases. In an apparatus that does not have a configuration that circulates ink so that the ink supplied to the head unit returns to the main tank or the sub tank, the ink supplied to the head unit during the filling operation is changed to ink or air supplied later. Extruded and discarded. For this reason, if the amount of ink discharged from the sub-tank before the ink filling into the sub-tank is large, the ink consumption will increase.
On the other hand, in the sub tank provided with the partition wall, the ink does not flow out or almost does not flow until it is filled up to the height of the upper end of the partition wall, so that the time until the sub tank is filled with ink can be shortened. . In addition, in an apparatus that does not have a configuration for circulating ink, ink consumption can be suppressed.

However, in a recording head having a sub tank with a partition wall, ink containing bubbles may be supplied to the head portion. This is considered to be due to the following reason.
That is, as described above, when the sub tank is filled with ink from an empty state and the ink in the ink storage unit reaches a position higher than the upper end of the partition wall, the ink flows through the communication path and into the supply flow path. At this time, the ink passing through the communication path moves in the horizontal direction, but air exists above the ink moving in the horizontal direction. The presence of air along the ink movement direction causes the air in contact with the ink to move in the horizontal direction as the ink moves. Thereafter, when the ink that has passed through the communication path falls into the supply flow path, air also drops together with the ink, the ink and air are mixed, and ink containing bubbles is supplied into the supply flow path, from the supply flow path outlet. Supplied to the head part.
The ink in the ink container is not limited to the case where the ink is filled from the empty state in the sub tank, and the ink in the ink container is filled even when the ink in the ink container is replenished from a state lower than the upper end of the partition. A similar phenomenon can occur by reaching a position higher than the upper end of the tube and passing through the communication path.

The head unit includes a nozzle hole and a liquid chamber that contains ink to be ejected in communication with the outside through the nozzle hole, and ejects ink droplets from the nozzle hole by temporarily pressurizing the liquid chamber. When ink containing bubbles is supplied to such a head portion and bubbles enter the liquid chamber, the amount of ink discharged when a predetermined amount of pressure is applied varies, and ink droplets are discharged from the head portion. It becomes unstable.
Such a problem is not limited to the ink ejection head unit in which the liquid ejected is ink, as in the recording head, but may be similarly caused if the liquid ejection head unit ejects liquid.

  The present invention has been made in view of the above problems, and a purpose thereof is a liquid discharge head unit that can stably discharge liquid droplets from a head portion, and image formation including the liquid discharge head unit. Is to provide a device.

In order to achieve the above object, a first aspect of the present invention is directed to a head unit including a plurality of nozzles that discharge liquid as droplets, and a common liquid chamber through which the liquid supplied to the plurality of nozzles passes, and the head A liquid storage tank for storing the liquid to be supplied to the section, and the internal space of the liquid storage tank stores the liquid to be supplied to the head section by a partition wall arranged so as to extend upward from the bottom. And a supply passage through which the liquid supplied from the liquid storage portion to the common liquid chamber passes, and the upper end of the partition wall is from the ceiling portion of the internal space of the liquid storage tank A liquid discharge head unit configured such that the liquid storage portion and the supply flow path communicate with each other through a communication path formed by a gap between the upper end of the partition wall and the ceiling portion of the internal space of the liquid storage tank. The above-mentioned separation in the liquid container A partition wall that extends downward from the near ceiling and has a lower end positioned lower than the upper end of the partition wall, and a gap between the lower end of the partition wall and the partition wall is provided. A flow path inlet is formed by a gap between the partition wall and the partition wall, and a flow path before the partition wall is formed as a flow path of liquid flowing from the liquid storage portion toward the communication path. The liquid storage tank discharge flow path, which is the flow path of the liquid from the flow path, the communication path, and the supply flow path to the supply flow path outlet communicating with the common liquid chamber of the supply flow path, is inverted U It has a character shape.
According to a second aspect of the present invention, in the liquid discharge head unit according to the first aspect, from the inlet of the channel to the outlet of the supply channel via the channel in front of the partition wall, the communication channel, and the supply channel. The liquid flow path is characterized in that the cross-sectional area of the flow path continuously decreases from the upstream side toward the downstream side.
According to a third aspect of the present invention, there is provided an image forming apparatus that includes an ink discharge head unit that discharges ink droplets from the head portion, and forms an image by attaching the ink droplets discharged from the head portion to a recording medium. The liquid discharge head unit according to claim 1 or 2 is used as the ink discharge head unit.

In the present invention, the lower end of the partition wall is lower than the upper end of the partition wall. For this reason, when the liquid is supplied from the outside into the liquid storage portion and the liquid reaches a position higher than the lower end of the partition wall, the flow path inlet of the flow path in front of the partition formed by the gap between the partition wall and the partition wall is cross-sectioned by the liquid. The whole is satisfied. Thereafter, the liquid is further supplied into the liquid storage portion to raise the liquid surface in the channel before the partition, and the liquid surface is an inverted U-shape formed by the channel before the partition, the communication channel, and the supply channel. In the liquid storage tank discharge flow path.
The liquid storage tank discharge flow path from the flow path inlet to the liquid surface is filled with liquid without any gaps, and surface tension acts on the liquid surface. The action to maintain works.
By this action, when the liquid surface is in the communication path, the liquid and the gas tend to exist in the lateral direction with the liquid surface as a boundary. When the liquid surface is in the supply channel, the gas flows with the liquid surface as the boundary. It is going to be in a state where liquid exists above. However, in the state where the liquid is in the lateral direction or upward with respect to the gas, the liquid drips in the flow path due to the weight of the liquid and tries to flow into the gas side by breaking the liquid surface substantially matching the flow path cross section. Work. For this reason, if the speed at which the liquid surface travels in the liquid storage tank discharge flow path is slow, the liquid hangs down in the flow path due to its own weight and the liquid surface cannot be maintained, and the liquid flows into the gas side by flowing into the gas side. May mix. On the other hand, the liquid surface can be maintained even in the communication path and the supply flow path by advancing the liquid surface at a speed faster than the speed at which the liquid hangs down in the flow path due to its own weight.

The traveling speed of the liquid surface is obtained by dividing the flow rate of the liquid passing through the flow path inlet by the cross-sectional area of the flow path. Since the flow rate of liquid passing through the flow channel inlet increases as the supply amount per unit time to the liquid storage unit increases, the liquid supply tank discharge flow path increases as the supply amount per unit time to the liquid storage unit increases. It acts to maintain the liquid surface. In addition, the smaller the cross-sectional area of the flow path, the more the liquid surface traveling in the liquid storage tank discharge flow path is maintained.
Further, the liquid surface in the liquid storage tank discharge flow path is maintained so that the liquid is less likely to drip in the flow path due to its own weight. For this reason, as the characteristics of the liquid, wettability and viscosity with respect to the surface of the liquid storage tank discharge flow path are high, and the liquid surface in the liquid storage tank discharge flow path is more easily maintained as the specific gravity is small.
Therefore, the supply amount per unit time to the liquid storage unit and the cross-sectional area of the flow path are set so that the liquid surface in the liquid storage tank discharge flow path is maintained according to the characteristics of the liquid.

  In this way, in the liquid storage tank discharge flow path configuration in which the liquid surface traveling through the liquid storage tank discharge flow path is maintained, after the entire cross section of the flow path inlet is filled with liquid, The gas is pushed by the liquid level and discharged into the head portion. For this reason, it is possible to prevent the generation of a liquid containing bubbles generated by mixing the gas and the liquid, and it is possible to prevent the liquid containing bubbles from being supplied to the head unit. It is possible to prevent variations in the discharge amount of droplets from the head due to the above.

  According to the present invention, since it is possible to prevent variation in the discharge amount of the droplets from the head unit, there is an excellent effect that it is possible to stably discharge droplets from the head unit.

FIG. 2 is a schematic explanatory diagram of a recording head of Example 1. 1 is a schematic configuration diagram of an inkjet printer. 2 is an explanatory diagram of an ink conveyance system including a recording head according to Embodiment 1. FIG. FIG. 3 is a horizontal sectional view of the recording head of Example 1. 6 is a flowchart of an ink filling operation. The flowchart of bubble discharge | emission operation | movement. FIG. 3 is an enlarged explanatory view around the communication path of the recording head according to the first exemplary embodiment. FIG. 6 is a schematic explanatory diagram of a recording head of Example 2. FIG. 6 is a horizontal sectional view of the recording head of Example 2, (a) is a sectional view of an AA section, and (b) is a sectional view of a BB section. FIG. 4 is a side sectional view of the recording head of Example 2, (a) is a sectional view of a CC section, and (b) is a sectional view of a DD section. FIG. 10 is a schematic explanatory diagram of a recording head according to a modified example. 3 is a schematic explanatory diagram of a recording head of Comparative Example 1. FIG. FIG. 4 is an enlarged explanatory view around the communication path of the recording head of Comparative Example 1; FIG. 6 is a schematic explanatory diagram of a recording head of Comparative Example 2. The horizontal sectional view of the recording head of the comparative example 2, (a) is a sectional view of the AA section, (b) is the sectional view of the BB section. FIG. 6 is a side cross-sectional view taken along the line CC of the recording head of Comparative Example 2.

Hereinafter, an ink jet printer (hereinafter, printer 100) will be described as an embodiment of an image forming apparatus to which the present invention is applied.
FIG. 2 is a schematic configuration diagram of the printer 100.
In the printer 100, a recording head 1, which is an ink ejection head unit that ejects ink from nozzle holes, is mounted on a carriage 103. The carriage 103 is slidably supported by a main guide rod 104 laid horizontally between the left side plate 100A and the right side plate 100B and a sub guide member (not shown).

In addition, the printer 100 includes a main scanning motor 106 and a timing belt 105 that moves endlessly when the main scanning motor 106 is driven. The printer 100 drives the main scanning motor 106 and moves the timing belt 105 endlessly. 103 is moved in the main scanning direction. On the other hand, the recording paper 107 as a recording medium is conveyed by a conveying roller 109 in a direction orthogonal to the moving direction of the recording head 1 (a direction orthogonal to the paper surface in FIG. 2), and a position facing the nozzle surface 11 a of the recording head 1. It is the structure which passes. On the recording paper 107, ink droplets ejected from the recording head 1 in accordance with the image are attached at a position facing the nozzle surface 11a, and an image is formed on the surface thereof.
Ink is supplied to the recording head 1 by a flexible ink supply pipe 51 connected to the recording head 1 from the main tank 5 via the ink supply pump 52. Further, an ink discharge pipe 53 is connected to the recording head 1, and ink that has not been discharged or discharged from the nozzle hole is discharged to the waste liquid tank 6 through the flexible ink discharge pipe 53.

Further, a cap member 111 is disposed outside the recording area in the main scanning direction (left and right direction in FIG. 2) in the printer 100 (a position outside the area through which the recording paper 107 can pass). The cap member 111 is made of an elastic body (preferably silicon rubber or the like) that caps the nozzle surface 11 a having the plurality of nozzle holes 11.
When the printer 100 is not forming an image, the position in the main scanning direction of the carriage 103 on which the recording head 1 is mounted is above the cap member 111 outside the recording area, as shown in FIG. Then, the cap member 111 is moved upward from the state shown in FIG. 2 by a cap moving mechanism (not shown) to cap the nozzle surface 11a.
Further, an ink absorbing sheet 112 is provided in the cap member 111 for facilitating suction during ink suction, moistening the atmosphere in the cap, and the like.

The cap member 111 has two tubes, an air release tube 113 and a waste liquid tube 114 connected to the bottom surface. The atmosphere release tube 113 communicates with the atmosphere via the atmosphere release valve 115, and the waste liquid tube 114 is connected to the waste liquid suction pump 116.
With the cap member 111 capping the nozzle surface 11a and closing the air release valve 115, the waste liquid suction pump 116 is driven to generate a negative pressure in the cap member 111, whereby ink is ejected from the nozzles of the recording head 1. Suction. Thereafter, by opening the air release valve 115, the ink accumulated in the space 117 in the cap member 111 can be discharged to the waste liquid tank 6.
Further, the cap member 111 prevents the nozzles of the recording head 1 from being dried by holding the air release valve 115 in a closed state in contact with the nozzle surface 11a.

  As shown in FIG. 2, a wiper blade 119, which is a wiper member for wiping the nozzle surface 11a, is disposed on the left side of the cap member 111 in the drawing. The wiper blade 119 can be moved in the vertical direction by a wiper moving mechanism (not shown). When the image formation by the printer 100 is completed, the wiper blade 119 moves to a height at which the wiper blade 119 comes into contact with the nozzle surface 11a, and performs main scanning from a position facing the area where the recording paper 107 can pass to a position facing the cap member 111. It contacts the nozzle surface 11a of the recording head 1 that moves in the direction. In this way, by moving the recording head 1 in the main scanning direction with the wiper blade 119 being in contact, ink and dust adhering to the nozzle surface 11a are wiped off by the wiper blade 119, and a meniscus is generated on the nozzle surface 11a. And can be cleaned.

[Example 1]
Next, a first embodiment (hereinafter, referred to as Embodiment 1) of a recording head 1 which is a liquid discharge head unit having the features of the present invention will be described with reference to the drawings. FIG. 1 is a schematic explanatory diagram of the recording head 1 of the first embodiment, and FIG. 3 is an explanatory diagram of an ink conveyance system including the recording head 1 of the first embodiment.
4 is a horizontal sectional view of the recording head 1 shown in FIG. 4A is a cross-sectional view taken along the line AA in FIG. 1, and FIG. 4B is a cross-sectional view taken along the line BB in FIG.
As shown in FIGS. 1 and 3, the recording head 1 includes a head unit 2 that ejects liquid droplets, and a sub tank 4 that is a liquid storage tank that stores ink to be supplied to the head unit 2.

The head unit 2 includes a plurality of nozzle holes 11 that discharge droplets, and a liquid chamber 12 that communicates with the outside through the nozzle holes 11 and that is a liquid discharge storage unit that stores liquid discharged from the nozzle holes 11. The head unit 2 also supplies a common liquid chamber 13 that supplies ink to each liquid chamber 12, an ink supply port 14 that is a supply port for supplying ink to the common liquid chamber 13, and ink from the common liquid chamber 13. An ink discharge port 15 that is a discharge port for discharging is provided.
Pressure changing means (not shown) is arranged in the liquid chamber 12, and ink droplets are ejected from the nozzle holes 11 by instantaneously pressurizing the liquid chamber 12 while the liquid chamber 12 is filled with ink. Discharge. When the pressurization is released after the ink droplets are discharged, the pressure in the liquid chamber 12 where the ink in the interior has run out decreases and the ink in the common liquid chamber 13 is supplied into the liquid chamber 12.
In the present embodiment, the pressure changing means is configured to temporarily increase the pressure in the liquid chamber 12 by providing a vibrating member, but the pressure changing means is not limited to this.

The sub tank 4 includes an ink storage unit 22 that stores ink to be supplied to the head unit 2 in the tank case 21, and a supply flow path 24 that supplies ink from the ink storage unit 22 to the ink supply port 14 of the head unit 2. . Further, the sub tank 4 includes a discharge channel 25 that discharges ink discharged from the ink discharge port 15 of the head unit 2 to the outside. Further, the ink container 22 and the discharge channel 25 are communicated with the top surface central part 22b which is the highest part of the central part of the shape in which the top surface 22a of the ink container 22 is inclined to the central part. A tank upper communication passage 26 is provided. The fluid resistance of the tank upper communication path 26 is formed larger than the fluid resistance from the ink supply port 14 to the ink discharge port 15 of the head unit 2.
Further, the tank case 21 of the sub-tank 4 is provided with a supply flow path 24 that is partitioned by a partition wall 202 extending (rises) from the bottom surface of the ink storage portion 22 and through which the ink from the ink storage portion 22 toward the ink supply port 14 passes. It has been. The upper end 202 a of the partition wall 202 is lower than the ceiling (the top surface 22 a and the upper end of the supply flow path 24) of the internal space (the ink storage unit 22 and the supply flow path 24) of the sub tank 4. In addition, the ink containing portion 22 and the supply flow path 24 communicate with each other through a communication path 206 formed by a gap between the upper end 202 a of the partition wall 202 and the ceiling portion of the internal space of the sub tank 4.

As shown in FIG. 4, the tank case 21 of the sub-tank 4 is a member having an opening on the near side in the near rear direction in FIG. 1, and a film member 23 as a flexible elastically deformable member is formed in the opening. It is pasted. When ink vibration that causes a pressure fluctuation in the internal space of the sub tank 4 occurs, the film member 23 is elastically deformed to absorb the pressure fluctuation. In the sub-tank 4, each of the ink storage portion 22 and the supply flow path 24 partitioned by the partition wall 202 is configured by the film member 23 on the front wall surface in FIG. In each of the paths 24, a damper effect that absorbs pressure fluctuation due to ink vibration can be obtained.
Further, the tank case 21 is provided with a sub tank supply port 27 above the ink containing portion 22.
The recording head 1 shown in FIG. 1 is mounted on the carriage 103 of the printer 100 described with reference to FIG. 2 and is configured to move relative to the apparatus main body of the printer 100 by the movement of the carriage 103.

On the other hand, on the apparatus main body side of the printer 100, a main tank 5 that is an ink cartridge that contains ink to be supplied and supplied to the sub tank 4 and can be replaced by being attached to and detached from the apparatus main body is disposed. Further, a waste liquid tank 6 that stores ink discharged from the sub tank 4 is disposed on the apparatus main body side of the printer 100.
By driving the ink supply pump 52, the liquid is fed from the main tank 5 to the sub tank 4 through the ink supply pipe 51. An ink discharge valve 54 that is an on-off valve is interposed in the ink discharge pipe 53 that connects the sub tank 4 and the waste liquid tank 6.

The main tank 5 is provided with an air release pipe 55 to prevent the ink in the main tank 5 from being exposed to the outside air for a long time and drying or solidifying. The flow path of the atmosphere opening pipe 55 has an elongated tubular shape, and the humidity in the pipe changes along its length, so that it is possible to prevent the ink in the main tank 5 from coming into direct contact with the outside air. The ink is prevented from drying, thickening or coagulating.
In the ink transport system shown in FIG. 3, the ink stored in the sub tank 4 passes from the ink supply port 14 at one end of the head unit 2 through the supply channel 24 to one end of the common liquid chamber 13 (the right end in FIG. 1). ). Of the inks supplied to the common liquid chamber 13, the ink supplied to the liquid chamber 12 is ejected from the nozzle holes 11. On the other hand, the ink that has not been supplied to the liquid chamber 12 and has reached the other end portion (the left end portion in FIG. 1) of the common liquid chamber 13 passes through the ink discharge port 15 and is discharged from the discharge flow path 25 of the sub tank 4 to the ink discharge pipe 53. To the waste liquid tank 6. In this ink transport system, the ink flowing from the sub tank 4 to the waste liquid tank 6 can be stopped by closing the ink discharge valve 54 provided in the ink discharge pipe 53.

Next, the operation of filling the recording head 1 of Example 1 with ink will be described with reference to FIG. FIG. 5 is a flowchart showing the flow of the ink filling operation.
First, the ink discharge valve 54 is opened (S11), and the ink supply pump 52 is driven (S12), whereby liquid is fed from the main tank 5 to the sub tank 4 through the ink supply pipe 51. The ink flows from the sub tank supply port 27 of the sub tank 4 to the ink storage unit 22, and a part of the ink is sent to the head unit 2.
On the other hand, the air in the ink storage unit 22 in the sub tank 4 increases the height of the ink in the ink storage unit 22 due to the supply of the ink, so that the upper part of the tank that communicates the ink storage unit 22 and the discharge channel 25. It is discharged to the discharge channel 25 through the communication path 26. In this manner, ink filling into the ink storage unit 22 is started.

As the ink is supplied, the height of the ink in the ink containing portion 22 is increased and the ink is filled up to the top surface central portion 22b, which is the highest portion of the top surface 22a of the ink containing portion 22, and then passes through the tank upper communication passage 26. And reaches the discharge channel 25.
Further, the ink sent from the ink containing part 22 to the head part 2 is sent to the common liquid chamber 13 through the ink supply port 14. Part of the ink that has flowed into the common liquid chamber 13 is discharged from each nozzle hole 11. Further, the ink in the common liquid chamber 13 flows to the discharge flow path 25 through the ink discharge port 15 and merges with the ink flowing out from the tank upper communication path 26.
The ink that has reached the upper end of the discharge flow path 25 is further sent to the ink discharge pipe 53 and sent to the waste liquid tank 6.

Further, after the operation of the ink supply pump 52 is started, whether or not the ink has passed through the ink discharge valve 54 is continuously monitored by a sensor (not shown) (S13). When the inside of the sub tank 4 and the head part 2 are filled with ink, the ink passing through the ink discharge port 15 and the tank upper communication path 26 merge in the discharge flow path 25, and the ink is sent to the ink discharge pipe 53. Is done. Thereafter, when the ink passes through the ink discharge valve 54, it is detected by the above-described sensor (not shown) ("Y" in S13).
When it is detected that the ink has passed through the ink discharge valve 54, the ink discharge valve 54 is closed (S14). Thereafter, the operating force of the ink supply pump 52 is adjusted (S15), and the pressure in the internal space of the sub tank 4 and the head unit 2 is adjusted, whereby the ink is discharged from the nozzle holes 11 of the head unit 2 to the outside. Bubbles in the hole 11 and the liquid chamber 12 are discharged (S16).

Thereafter, the operation of the ink supply pump 52 is stopped, the ink flow by the pump is stopped, and the ink supply pump 52 is opened so that the ink can pass through the position where the pump is disposed (S17). As a result, a negative pressure is generated in the nozzle hole 11 due to a water head difference between the opening of the ink supply pipe 51 on the main tank 5 side and the nozzle hole 11 of the head portion 2. By this negative pressure, it is possible to hold the ink so that it does not drip from the nozzle hole 11.
After the ink supply pump 52 is opened, the nozzle surface 11a is wiped by the wiper blade 119 shown in FIG. 2 (S18), the ink dripping on the nozzle surface 11a is wiped off, and the meniscus of the nozzle hole 11 is formed, and recording is performed. The ink filling to the head 1 is completed.
In this way, the head unit 2 can be filled with ink, and ink can be supplied from the main tank 5 to the head unit 2 through the sub tank 4 so that ink can be ejected.

  Note that an ink detection sensor that detects the presence or absence of ink is used as the sensor (not shown). Before the ink is filled, the ink discharge pipe 53 is empty. Therefore, before the ink passes through the ink discharge valve 54, the ink detection sensor continues to detect the absence of ink. When the ink passes through the ink discharge valve 54, the ink is present at the position of the ink detection sensor. Therefore, the ink detection sensor detects the presence of ink, and the ink is discharged based on the detection result. The passage through the valve 54 can be detected.

Next, a bubble discharge operation for discharging bubbles mixed in the ink transport system will be described with reference to FIG. FIG. 6 is a flowchart showing the flow of the bubble discharging operation.
When the main tank 5 is replaced to replenish the ink consumed by printing or when air enters the nozzle hole 11 or the like for some reason, bubbles are generated in the ink flow paths and the ink containing portions 22. May be mixed. When bubbles are mixed in, there is a possibility that the ejection of droplets from the nozzle hole 11 may be hindered. Therefore, a bubble discharging operation for eliminating this is performed.

  First, the ink supply pump 52 is operated (S21), the liquid is supplied from the main tank 5 to the sub tank 4, and the ink discharge valve 54 (S22) is immediately opened. If the ink discharge valve 54 is opened while the ink supply pump 52 is opened, the ink in the sub tank may flow backward. On the other hand, the ink backflow can be prevented by opening the ink discharge valve 54 in a state where the ink supply pump 52 is operated and pressurized.

By operating the ink supply pump 52 and opening the ink discharge valve 54, the ink flows from the sub tank supply port 27 into the ink containing portion 22. If air bubbles are mixed in the ink supply pipe 51, the air bubbles flow into the ink storage unit 22 and accumulate on the ink storage unit 22. Further, the inside of the ink containing portion 22 is pressurized by the ink feeding, and the bubbles accumulated in the upper portion of the ink containing portion 22 are discharged from the tank upper communication passage 26 to the discharge passage 25.
Ink is also sent from the ink containing portion 22 to the head portion 2, and when bubbles are mixed in the common liquid chamber 13, the bubbles are discharged to the discharge flow path 25.
The ink merged in the discharge flow path 25 is further sent to the ink discharge pipe 53 and sent to the waste liquid tank 6, so that bubbles discharged from the tank upper communication path 26 to the discharge flow path 25 and the common liquid chamber 13 are discharged. The bubbles discharged to the flow path 25 are sent to the waste liquid tank 6 together with the ink.
Further, after opening the ink discharge valve 54, it is continuously monitored whether or not all bubbles have passed through the ink discharge valve 54 by a sensor (not shown) (S23). After a certain amount of time has elapsed after opening the ink discharge valve 54, all ink detection sensors (not shown) arranged in the vicinity of the ink discharge valve 54 detect the state in which ink is continuously detected. It is possible to detect the passage of bubbles. This is because when the bubbles pass the detection position by the ink detection sensor, a state where there is no ink is detected, and it can be determined that all the bubbles have passed by continuing to detect the state where there is ink.

When it is detected that all the air bubbles mixed in the ink storage unit 22 and each flow path are conveyed to the downstream part of the ink discharge valve 54 (“Y” in S23), the ink discharge valve 54 is closed (S24). Thereafter, the operating force of the ink supply pump 52 is adjusted (S25), and the pressure in the internal space of the sub tank 4 and the head portion 2 is adjusted, whereby ink is discharged from the nozzle holes 11 of the head portion 2 to the outside. Bubbles in the hole 11 and the liquid chamber 12 are discharged (S26).
Thereafter, the operation of the ink supply pump 52 is stopped, the ink flow by the pump is stopped, and the ink supply pump 52 is opened so that the ink can pass through the position where the pump is disposed (S27). As a result, a negative pressure is generated in the nozzle hole 11 due to a water head difference between the opening of the ink supply pipe 51 on the main tank 5 side and the nozzle hole 11 of the head portion 2. By this negative pressure, it is possible to hold the ink so that it does not drip from the nozzle hole 11.

After the ink supply pump 52 is opened, the nozzle surface 11a is wiped by the wiper blade 119 shown in FIG. 2 (S28), the ink dripping on the nozzle surface 11a is wiped off, and the meniscus of the nozzle hole 11 is formed, and recording is performed. The ink filling to the head 1 is completed.
In this way, it is possible to discharge all of the air bubbles mixed in the ink container 22 and each flow path, and it is possible to recover the ink droplet ejection performance.

  In addition, two detection electrodes 29 (a and b) for detecting that the amount of ink in the ink containing portion 22 has become a predetermined amount or less are mounted on the upper part of the sub tank 4. The detection electrode 29 is connected to a control unit (not shown) that inputs a detection signal, and constitutes a liquid amount detection sensor. The conduction state between the two detection electrodes 29 changes between a state where both of the two detection electrodes 29 are immersed in ink and a state where at least one of the two detection electrodes 29 is not immersed in ink. When the control unit detects the change in the conduction state, it can be detected that the ink has become a predetermined amount or less.

  By using this liquid amount detection sensor, it is possible to detect a state in which bubbles are accumulated in the ink containing portion 22. Further, when the ink is filled, it is possible to detect the state in which the ink is filled from the empty state of the ink containing portion 22, and when the bubbles are discharged, the bubbles are discharged from the state where the bubbles are accumulated in the ink containing portion 22. It will be possible to recognize this reliably.

  Further, during the ink filling operation described with reference to FIG. 5, after the operation of the ink supply pump 52 is started (S12), it is continuously monitored whether or not the ink has passed through the ink discharge valve 54 by a sensor (not shown) ( S13) Control was performed. On the other hand, it is more preferable to start monitoring whether the ink has passed through the ink discharge valve 54 after detecting the state in which the ink container 22 is filled with the ink by the detection electrode 29. In this case, it is only necessary to perform control for monitoring the passage of the ink in a short time from when the ink in the ink containing portion 22 is filled to when the ink passes through the ink discharge valve 54, thereby increasing the reliability of the ink filling property. Because it can.

  In the bubble discharge operation described with reference to FIG. 6, after the ink discharge valve 54 is opened (S22), it is monitored by a sensor (not shown) whether all the bubbles have passed through the ink discharge valve 54 or not. Continue (S23) The control was performed. On the other hand, it is more preferable to start monitoring whether or not all the bubbles have passed through the ink discharge valve 54 after detecting the state in which the ink container 22 is filled with ink by the detection electrode 29. This is achieved by performing control for monitoring the passage of bubbles in a short time from when the bubbles in the ink containing portion 22 are discharged until the bubbles remaining in the flow path pass through the ink discharge valve 54. This is because the reliability of the recovery performance of the ink ejection function can be increased.

Next, the characteristic part of the recording head 1 of Example 1 is demonstrated.
As illustrated in FIG. 1, the recording head 1 according to the first exemplary embodiment includes a partition wall 205 disposed so as to extend downward from the top surface 22 a near the partition wall 202 in the ink storage unit 22. The position of the lower end 205 a of the partition wall 205 is lower than the position of the upper end 202 a of the partition wall 202. As a result, the gap between the lower end 205a of the partition wall 205 and the partition wall 202 serves as a flow path inlet, and the partition wall serves as a flow path for ink flowing from the ink containing portion 22 toward the communication path 206 by the gap between the partition wall 205 and the partition wall 202. A front flow path 207 is formed. A flow path 207 in front of the partition wall is a flow path from the flow path inlet to the upstream end portion of the communication path 206 through the gap between the partition wall 205 and the partition wall 202. The supply channel 24 is a channel from the downstream end of the communication channel 206 to the supply channel outlet 24e.

Here, the problem of the conventional liquid discharge head unit will be described.
The configuration described in Patent Document 1 includes a plate-like partition that partitions the space in the sub-tank into an entrance-side space and an exit-side space. And a slit having an increased fluid resistance between the inner wall of the sub-tank. Then, the ink from the main tank is supplied to the entrance side space, and the head portion is made from an outlet provided at the bottom of the exit side space.
With such a configuration, even if the liquid level of the ink in the entry side space does not reach a position higher than the upper end of the partition wall, the ink in the entry side space can move to the exit side space through the slit. . Since the slit has high fluid resistance and it is difficult for ink to pass through, when ink is supplied from the main tank to the sub tank, ink is supplied from the main tank to the input side space, and the ink level in the input side space rises. Even so, the ink level in the exit space does not immediately follow. That is, it takes time until the liquid level of the ink in the exit side space becomes the same level as the liquid level of the ink in the entrance side space.

In the configuration of this Patent Document 1, in order to suck the gas in the sub tank, a negative pressure is applied to the head portion by the suction device, and the negative pressure is applied to the outlet side space. At this time, even if the ink remaining in the exit space together with the gas in the exit space is sucked by suction, the ink in the entrance space moves to the exit space by providing the partition having the slits as described above. Therefore, it is possible to prevent the ink supplied from the main tank into the entry side space of the sub tank from immediately moving to the exit side space. In this way, by suppressing the movement of ink from the entry side space to the exit side space, the amount of ink sucked into the suction device together with the gas in the suction operation for removing the gas in the sub tank can be suppressed, and ink consumption Can be suppressed.
However, even if the ink is difficult to move by the slit, it moves to the exit space. For this reason, the ink is discharged until the ink in the entry side space is filled up to the height of the upper end of the partition wall, and it takes time to fill the ink, and the ink supplied to the head unit is discarded. This leads to an increase in ink consumption.

Without providing such a slit, the ink container is filled with ink, and when the ink level is lower than the upper end of the partition wall, it does not flow into the supply channel, and when the ink reaches a position higher than the upper end of the partition wall, The configuration of Comparative Example 1 flowing into the supply flow path is shown in FIG.
FIG. 12 is a schematic explanatory diagram of the recording head 1 of the first comparative example.

Similar to the recording head 1 of the first embodiment, the recording head 1 of Comparative Example 1 is partitioned into the tank case 21 of the sub-tank 4 by a partition wall 202 that extends (rises) from the bottom surface of the ink storage unit 22. A supply channel 24 through which ink from 22 toward the ink supply port 14 passes is provided. Further, the upper end 202 a of the partition wall 202 is lower than the ceiling (the top surface 22 a and the upper end of the supply flow path 24) of the internal space (the ink storage part 22 and the supply flow path 24) of the sub tank 4. In addition, the ink containing portion 22 and the supply flow path 24 communicate with each other through a communication path 206 formed by a gap between the upper end 202 a of the partition wall 202 and the ceiling portion of the internal space of the sub tank 4.
The recording head 1 of Comparative Example 1 is different from the recording head 1 of Example 1 in that the partition wall 205 is not provided and the shape of the flow path near the communication path 206.

  Similar to the recording head 1 of the first embodiment, the sub tank 4 of the recording head 1 of the first comparative example includes a partition wall 202, and the ink from the ink storage unit 22 toward the supply flow path 24 always passes through the communication path 206. It has become. For this reason, there is no outflow of ink to the head unit 2 until the ink in the ink container 22 is filled to the height of the upper end 202a of the partition wall 202. For this reason, compared with the structure described in the above-mentioned Patent Document 1, it is possible to shorten the time until filling, and furthermore, the structure that discards the ink supplied to the head unit can suppress the ink consumption. it can.

However, in the recording head 1 of Comparative Example 1, ink containing bubbles may be supplied to the head unit 2. This cause will be described with reference to FIG.
13 is an enlarged explanatory view of the periphery of the communication path 206 in a state where the ink in the ink containing portion 22 is filled up to the height of the upper end 202a of the partition wall 202 in the recording head 1 of Comparative Example 1. FIG.
When the sub tank 4 is filled with the ink I from the empty state and the ink I in the ink container 22 reaches a position higher than the upper end 202a of the partition wall 202, the ink I passes through the communication path 206 as shown in FIG. Flow into the supply channel 24. At this time, the ink I passing through the communication path 206 moves in the horizontal direction as indicated by an arrow F in FIG. 13, but air is present in the region indicated by G in the figure above the ink I moving in the horizontal direction. Exists. As shown in FIG. 13, the presence of air along the direction of movement of ink I causes the air that contacts ink I to move in the horizontal direction as indicated by arrow F ′ in FIG. Moving. Thereafter, when the ink I that has passed through the communication path 206 falls into the supply flow path 24, the air also drops along with the ink I, and the ink I and the air are mixed and the ink I including the bubbles G 1 enters the supply flow path 24. Supplied and supplied from the supply channel outlet 24e to the head unit 2.
When the ink I containing the bubble G1 is supplied to the head unit 2 and the bubble G1 enters the liquid chamber 12, the discharge amount of the ink I when a predetermined amount of pressurization is performed varies, Ink droplet ejection becomes unstable.

  For such a problem, the recording head 1 according to the first exemplary embodiment includes a partition wall 205 that is disposed so as to extend downward from the top surface 22 a near the partition wall 202 in the ink storage unit 22. FIG. 7 is an enlarged view of the periphery of the communication path 206, showing a state in which the ink I filled in the ink containing portion 22 has started to pass through the communication path 206 in the recording head 1 of the first embodiment.

  As shown in FIG. 7, the lower end 205 a of the partition wall 205 is at a lower position than the upper end 202 a of the partition wall 202. For this reason, when the ink I is supplied from the main tank 5 into the ink containing portion 22 and the ink I reaches a position higher than the lower end 205a of the partition wall 205, the partition wall 205 and the partition wall 202 are formed in front of the partition wall. The entire inlet section 207a of the channel 207 is filled with the ink I. Thereafter, the ink I is further supplied into the ink container 22 to raise the liquid surface If of the ink I in the flow path 207 before the partition, and the liquid surface If is supplied to the flow path 207, the communication path 206, and the supply path 206. It proceeds in the inverted U-shaped liquid storage tank discharge channel formed by the channel 24.

The liquid storage tank discharge flow path from the flow path inlet 207a to the liquid surface If is filled with ink I without a gap, and surface tension acts on the liquid surface If, so that the liquid surface If substantially matches the cross section of the flow path. The action which tries to maintain the surface to work works.
In the recording head 1 according to the first embodiment, after the entire cross section of the flow path inlet 207a is filled with the liquid, the air in the front flow path 207, the communication path 206, and the supply flow path 24 is pushed by the liquid surface. Then, the liquid is discharged to the common liquid chamber 13 in the head unit 2. That is, in the flow path 207 before the partition wall, the communication path 206, and the supply flow path 24, the liquid surface If is divided into a region where air is present and a region where ink I is present. For this reason, it is possible to prevent the generation of the ink I including the bubbles G1 generated by mixing the air and the ink I. As a result, it is possible to prevent the ink I containing the bubbles G1 from being supplied to the common liquid chamber 13, and therefore, the ejection amount of ink droplets from the head unit 2 varies due to the bubbles G1 in the ink I. Can be prevented.

Further, in this configuration, until the liquid surface If reaches the supply flow path outlet 24e of the supply flow path 24, only the air is supplied to the common liquid chamber 13 in the head portion 2, and the liquid surface If is supplied to the supply flow path 24e. After reaching the outlet 24e, only the ink I is supplied. For this reason, the air supplied first is discharged from the head unit 2, and the common liquid chamber 13 is filled with the ink I supplied later, whereby the common liquid chamber 13 of the head unit 2 is filled with ink. I can be satisfied.
As described above, in the recording head 1 according to the first embodiment, it is possible to prevent variation in the discharge amount from the head unit 2, and thus it is possible to stably discharge ink droplets from the head unit 2.

  Further, in the recording head 1 of the comparative example 1, the ink I in the ink containing portion 22 passes through the communication path 206 and starts to flow into the supply flow path 24, and then above the ink I in the ink containing portion 22. The existing air can move toward the communication path 206. For this reason, when ink I containing air bubbles G1 is generated by entraining the air present in the region G when the ink I passes through the communication path 206, only the ink I is transferred from the ink containing portion 22 to the communication path 206. Instead, the air above it is also supplied. Therefore, the recording head 1 of the comparative example 1 is configured such that air that causes the bubbles G1 can be supplied toward the communication path 206 until the inside of the ink containing portion 22 is filled with the ink I.

On the other hand, in the recording head 1 according to the first embodiment, when the entire cross section of the flow path inlet 207a is filled with the ink I in the ink containing portion 22, the ink flows toward the communication path 206 that exists on the left side of the partition wall 205 in FIG. Can no longer move. For this reason, after the ink I in the ink containing portion 22 reaches the height of the lower end 205a of the partition wall 205, the air moving toward the communication path 206 is only the air in the flow path 207 in front of the partition wall, and the bubble G1 It is possible to prevent the air that causes the air from being continuously supplied toward the communication path 206.
For this reason, the liquid surface If separating the area where the air exists and the area where the ink I exists in the flow path 207, the communication path 206, and the supply flow path 24 before the partition wall cannot be maintained for some reason, and the air and the ink I Even if they are mixed, the amount of bubbles G1 contained in the ink I can be minimized.

Further, as shown in FIG. 4B, in the recording head 1 of Example 1, the channel cross section of the channel 207 in front of the partition has a square shape, which is the channel cross section of the supply channel 24. It has the same shape as In the recording head 1 according to the first embodiment, the horizontal cross section of the front channel 207 and the supply channel 24 has a length in the width direction (left and right direction in FIGS. 1 and 4) of 3 [mm] and a depth direction. The length in the front-rear direction in FIG. 1 and the vertical direction in FIG. 4 is set to 9 [mm]. Further, the length of the communication path 206 in the height direction is set to 3 [mm], and the length in the depth direction is set to 9 [mm]. That is, the area of the cross section of the liquid storage tank discharge flow path is set to be constant.
As a result, the liquid storage tank discharge flow path that is the flow path of the ink I from the flow path inlet 207a to the supply flow path outlet 24e via the flow path 207, the communication path 206, and the supply flow path 24 is provided. The channel cross-sectional area is formed so as not to increase rapidly. If there is a portion where the cross-sectional area of the flow path suddenly widens, the ink I which is a liquid diffuses when passing through the portion, and there is a possibility that it will be mixed with air and contain bubbles G1. On the other hand, it is possible to prevent the bubbles G1 from being contained in the ink I by forming the flow path cross-sectional area so as not to increase rapidly.
In the printer 100 including the recording head 1 according to the first embodiment, the supply amount of ink per unit time from the main tank 5 to the sub tank 4 during the ink filling operation and the bubble discharging operation is 2 [ml / s]. Degree.

As shown in FIGS. 1 and 7, in the recording head 1 of Example 1, the ink I from the flow path inlet 207a to the supply flow path 24 via the flow path 207 and the communication path 206 in front of the partition wall. The channel has an inverted U shape with no corners.
The ink I that has passed through the flow path inlet 207 a moves upward in the flow path 207 before the partition wall, moves in the horizontal direction in the communication path 206, and moves down in the supply flow path 24. In such a configuration, if the flow path has a corner at a position where the direction of the flow path changes in a perpendicular direction, the cross-sectional area of the flow path suddenly increases at that portion, and the ink that is liquid when passing through the corner There is a possibility that I diffuses and mixes with air to include the bubbles G1. On the other hand, like the recording head 1 of the first embodiment, the flow path from the flow path inlet 207a to the supply flow path 24 is formed in a reverse U-shape without a corner, so that a flow path like a corner is formed. It is possible to prevent the bubble G1 from being contained in the ink I without the cross-sectional area becoming suddenly wide.

[Example 2]
Next, a second embodiment (hereinafter referred to as a second embodiment) of the recording head 1 which is a liquid discharge head unit having the features of the present invention will be described with reference to the drawings.
FIG. 8 is a schematic explanatory diagram of the recording head 1 of the second embodiment, and FIG. 9 is a horizontal sectional view of the recording head 1 shown in FIG. 9A is a cross-sectional view taken along the line AA in FIG. 8, and FIG. 9B is a cross-sectional view taken along the line BB in FIG. 10 is a side sectional view of the recording head 1 shown in FIGS. 8 and 9, and FIG. 10A is a sectional view taken along the line CC in FIGS. 8 and 9. (B) is sectional drawing of the DD cross section in FIG.8 and FIG.9.
FIG. 8 is a front sectional view of the HH section in FIGS. 9 and 10. 9 and 10 are cross-sectional views taken along the line E-E above the ink storage portion 22 (second ink storage portion 22e in the second embodiment) with respect to the front cross-sectional view of the first embodiment shown in FIG. Since the subtank supply port 27 and the tank upper communication path 26 are different in that they are not provided, the illustration is omitted.

  In the recording head 1 according to the second embodiment, among the internal space of the sub tank 4, the ink storage portion 22 is spatially partitioned into three parts: a first ink storage portion 22 d, a second ink storage portion 22 e, and an ink reservoir chamber 204. This is different from the recording head 1 of the first embodiment. Other configurations are common, and members having the same reference numerals have similar functions. The operation flow of the ink filling operation described with reference to FIG. 5 and the bubble discharging operation described with reference to FIG. 6 are the same as those in the first embodiment.

Hereinafter, differences of the recording head 1 of the second embodiment from the recording head 1 of the first embodiment will be described.
As shown in FIGS. 8 to 10, in the recording head 1 according to the second embodiment, the ink storage portion 22 is spatially divided into three parts: a first ink storage portion 22 d, a second ink storage portion 22 e, and an ink reservoir chamber 204. It is partitioned. In the second embodiment, the flow path 207 in front of the partition is a space above the ink reservoir chamber 204.
The first ink container 22d and the second ink container 22e are partitioned by the ink filter 20, and the first ink container 22d and the ink reservoir chamber 204 are partitioned by the shielding wall 208.
A sub tank supply port 27 into which ink supplied from the main tank 5 flows is provided on the top surface 22a of the first ink storage portion 22d. For this reason, the ink supplied into the ink containing portion 22 does not pass through the ink filter 20 from the first ink containing portion 22d as indicated by an arrow J in FIG. It is the structure which cannot flow into. The ink filter 20 is for filtering foreign matter contained in the ink.

As shown in the BB cross section, in the upper part of the sub tank 4, the second ink containing portion 22e and the ink reservoir chamber 204 (channel 207 near the partition wall) are spatially separated by a partition wall 205 as shown in FIG. However, the part below the lower end 205a of the partition wall 205 communicates as shown in FIG.
The communication between the ink reservoir chamber 204 and the second ink storage portion 22e extends to the lower end of the partition wall 205 in the height direction and is lower than the upper end 202a of the partition wall 202.
The ink that has passed through the ink filter 20 from the first ink containing portion 22d and has flowed into the second ink containing portion 22e is filled into the space formed by the second ink containing portion 22e and the ink reservoir chamber 204. For this reason, the ink accumulates at the same height in the second ink containing portion 22e and the ink reservoir chamber 204.

In the second ink containing portion 22e and the ink reservoir chamber 204, the ink is accumulated from the lower side and is accumulated at the same height until it reaches the lower end 205a of the partition wall 205. When the ink reaches the lower end 205 a of the partition wall 205, the entire flow path section of the flow path 207 in front of the partition wall is filled with ink in the ink reservoir chamber 204.
By continuing to supply ink to the first ink storage portion 22d, ink continues to be supplied to the second ink storage portion 22e, so that the liquid surface in the channel 207 in front of the partition wall rises. Thereafter, as in the first embodiment, the air in the channel 207, the communication channel 206, and the supply channel 24 is pushed by the liquid surface and discharged to the common liquid chamber 13 in the head unit 2. As a result, it is possible to prevent ink containing bubbles from being supplied to the head unit 2, and thus it is possible to prevent variations in the ejection amount of ink droplets from the head unit 2 due to bubbles in the ink.

Here, FIG. 14 shows a configuration of the second comparative example that includes the ink filter 20 as in the second embodiment and does not include the partition wall 205 and the ink reservoir chamber 204 that are included in the recording head 1 of the second embodiment.
14 is a schematic explanatory view of the recording head 1 of Comparative Example 2, and FIG. 15 is a horizontal sectional view of the recording head 1 shown in FIG. 15A is a cross-sectional view taken along the line AA in FIG. 14, and FIG. 15B is a cross-sectional view taken along the line BB in FIG. 14. FIG. 16 is a side sectional view of the recording head 1 shown in FIGS. 14 and 15, and is a sectional view taken along the line CC in FIGS. 14 and 15.
FIG. 14 is a front sectional view of the HH section in FIGS. 15 and 16. 15 and FIG. 16 is a cross-sectional view taken along the line E-E above the ink container 22 (second ink container 22e in Example 2) with respect to the front cross-sectional view of Comparative Example 1 shown in FIG. Since the subtank supply port 27 and the tank upper communication path 26 are different in that they are not provided, the illustration is omitted.

Since the recording head 1 of Comparative Example 2 does not include the ink reservoir chamber 204, the shielding wall 208 and the partition wall 202 are integrated.
In the recording head 1 of Comparative Example 2, the ink that has passed through the ink filter 20 from the first ink container 22d flows into the second ink container 22e and accumulates from below in the second ink container 22e. When the ink in the second ink containing portion 22e reaches a position higher than the upper end 202a of the partition wall 202, the ink flows through the communication path 206 and flows into the supply flow path 24 as in the first comparative example described with reference to FIG. To do. For this reason, as in Comparative Example 1, ink and air are mixed and ink containing bubbles is supplied into the supply channel 24 and supplied from the supply channel outlet 24 e to the head unit 2.

  Further, as shown in FIG. 16, the communication passage 206, which is a flow path of ink from the second ink containing portion 22e toward the supply flow path 24, has a narrow flow path cross-sectional area. When the ink that has passed through the communication path 206 having such a narrow channel cross-sectional area flows into the supply channel 24, the channel cross-sectional area rapidly increases, so that the ink diffuses and bubbles are more easily contained.

On the other hand, in the recording head 1 of Example 2, the cross-sectional shape of the ink flow path from the lower end (flow path inlet 207a) of the flow path 207 before the partition wall to the communication path 206 is a square shape and the same shape as the supply flow path 24. It has become. As a result, ink is collected in the ink reservoir chamber 204, and the ink is filled in the entire flow path section of the flow path 207 near the partition wall at the flow path inlet 207a, and the supply flow path 24 and the ink supply port 14 are maintained in this state. Thus, the ink is filled without bubbles.
With such a configuration, the cross-sectional area of the flow path does not increase rapidly, bubbles that are generated by ink diffusion can be suppressed, and bubbles can be prevented from remaining in the flow path.

  In the recording head 1 according to the second embodiment, the ink that has passed through the ink filter 20 is collected in the second ink container 22e and the ink reservoir chamber 204, and then flows into the channel 207 near the partition wall. Since the ink filter 20 has a certain amount of fluid resistance, fluctuations in the liquid level due to the momentum when ink is supplied from the sub tank supply port 27 into the first ink storage portion 22d are difficult to propagate. For this reason, the liquid surface of the ink flowing into the flow path 207 before the partition wall can be made a stable surface, and the air in the flow path 207, the communication path 206 and the supply flow path 24 before the partition wall can be more reliably Can be extruded.

  In the recording head 1 of Example 2, the cross-sectional shapes of the flow path 207, the communication path 206, and the supply flow path 24 in front of the partition are the same. An example of specific numerical values of these channel cross sections is a rectangle of 3 [mm] × 9 [mm]. The ink storage unit 22 of the recording head 1 according to the second embodiment has a horizontal plane of 58 [mm] × 9 [mm] and a height of 19 [mm]. Furthermore, the distance from the bottom surface of the ink containing portion 22 to the upper end 202a of the partition wall 202 is 16 [mm], and the distance to the lower end 205a of the partition wall 205 is 13 [mm]. In the printer 100 including the recording head 1 according to the second embodiment, the supply amount of ink per unit time from the main tank 5 to the sub tank 4 during the ink filling operation and the bubble discharging operation is 2 [ml / s]. Degree.

[Modification]
Next, modified examples applicable to the recording heads 1 of the first and second embodiments will be described.
FIG. 11 is a schematic explanatory diagram of a recording head 1 according to a modification.
In the recording head 1 of the modified example, the supply channel 24 connected to the ink supply port 14 of the head unit 2 has a continuous channel cross-sectional area from the upper end where the ink flows over the partition wall 202 to the supply channel outlet 24e. It is gradually becoming smaller. With such a configuration, the flow velocity of the ink flowing in the supply flow path 24 increases from the upper end 202a side of the partition wall 202 toward the supply flow path outlet 24e.
The higher the flow rate, the better the bubbles are discharged.However, if the flow path cross-sectional area is the same, the higher the flow speed, the more ink is discarded. If secured, the amount of ink discarded can be reduced.
In the recording head 1 of the modified example, since the flow velocity can be obtained even at a low pressure, it is possible to efficiently fill the ink and discharge the bubbles in the flow path of the sub tank 4 with a small amount of discarded ink. Become.

In the printer 100 of the above-described embodiment, the ink transport system is configured to transport the ink discharged from the discharge flow path 25 of the recording head 1 to the waste liquid tank 6, but is not limited thereto. The printer 100 including the recording head 1 having the characteristic part of the present invention described in the first and second embodiments has a configuration in which the ink transport system transports the ink discharged from the discharge flow path 25 to the main tank 5. There may be.
In the above-described embodiments, the present invention has been described with reference to an example in which the present invention is applied to an image forming apparatus having a printer configuration. However, the present invention is not limited to this, and as described above, for example, image forming such as a printer / fax / copier multifunction machine The present invention can be applied to an apparatus, and can also be applied to an image forming apparatus using a liquid other than the narrowly defined ink or a fixing processing liquid.

As described above, the recording head 1 that is the liquid discharge head unit of the present embodiment includes a plurality of nozzle holes 11 that discharge ink, which is liquid, as ink droplets, and a common liquid chamber 13 through which the ink supplied to the plurality of nozzle holes 11 passes. And a sub tank 4 that is a liquid storage tank that stores ink to be supplied to the head unit 2. The internal space of the sub tank 4 is divided into an ink storage portion 22 which is a liquid storage portion for storing ink to be supplied to the head portion 2, and an ink storage portion 22 by a partition wall 202 arranged so as to extend upward from the bottom thereof. Is partitioned spatially into a supply flow path 24 through which the ink supplied to the common liquid chamber 13 passes. The upper end 202 a of the partition wall 202 is lower than the top surface 22 a that is the ceiling portion of the internal space of the sub tank 4 and the upper end of the supply flow path 24. In addition, the ink containing portion 22 and the supply flow path 24 communicate with each other through a communication path 206 formed by a gap between the upper end 202 a of the partition wall 202 and the ceiling portion of the internal space of the sub tank 4. The recording head 1 extends downward from the top surface 22a near the partition wall 202 in the ink containing portion 22, and the lower end 205a of the recording head 1 is positioned lower than the position of the upper end 202a of the partition wall 202. A partition wall 205 is provided. With such a configuration, the gap between the lower end 205a of the partition wall 205 and the partition wall 202 serves as the flow path inlet 207a, and the flow of ink flowing from the ink containing portion 22 toward the communication path 206 by the gap between the partition wall 205 and the partition wall 202 is achieved. A flow path 207 in front of the partition wall is formed. The flow of ink from the flow path inlet 207a to the supply flow path outlet 24e communicating with the common liquid chamber 13 of the supply flow path 24 via the flow path 207, the communication path 206, and the supply flow path 24 in front of the partition wall. The liquid storage tank discharge channel, which is a channel, has an inverted U shape.
Since the lower end 205a of the partition wall 205 is located at a position lower than the upper end 202a of the partition wall 202, ink is supplied from the main tank 5 into the ink storage unit 22, and the ink reaches a position higher than the lower end 205a of the partition wall 205. The flow path inlet 207a of the front flow path 207 formed by the gap between the partition wall 205 and the partition wall 202 is filled with the entire cross section with ink. Thereafter, the liquid surface in the flow path 207 in front of the partition rises by further supplying ink into the ink container 22. Thereafter, the ink is further supplied into the ink containing portion 22, so that the surface of the liquid is discharged into the inverted U-shaped liquid containing tank formed by the front channel 207, the communication channel 206, and the supply channel 24. Proceed along the road.
The liquid storage tank discharge flow path from the flow path inlet 207a to the liquid surface is filled with ink without a gap, and surface tension acts on the liquid surface of the ink, so that the liquid surface substantially matches the cross section of the flow path. The action to maintain the surface works.
Due to this action, when the liquid surface of the ink is in the communication path 206, the liquid and the gas tend to exist in the lateral direction from the liquid surface, and when the liquid surface is in the supply flow path 24, the liquid surface is At the boundary, a liquid is present above the gas. However, in a state where the ink is laterally or upwardly with respect to the air, the ink hangs down in the flow path due to the weight of the ink, and the liquid surface that substantially matches the cross section of the flow path is broken to flow into the air side. Work. For this reason, if the speed at which the liquid surface travels in the liquid storage tank discharge flow path is slow, the ink hangs down in the flow path due to its own weight, and the liquid surface cannot be maintained, and the ink flows into the air side by flowing into the air side. May mix. On the other hand, the liquid surface can be maintained in the communication path 206 and the supply flow path 24 by advancing the liquid surface at a speed faster than the speed at which the ink hangs down in the flow path due to its own weight. For this reason, the larger the amount of ink supplied per unit time from the main tank 5 to the ink container 22, the smaller the cross-sectional area of the flow path, the easier it is to maintain the liquid surface.

In such a configuration, after the entire cross section of the flow path inlet 207a is filled with the liquid, the air in the front flow path 207, the communication path 206, and the supply flow path 24 is pushed by the liquid surface, and the inside of the head unit 2 Is discharged. That is, in the flow path 207 in front of the partition wall, the communication path 206, and the supply flow path 24, the liquid surface is divided into a region where air is present and a region where ink is present. For this reason, it is possible to prevent the generation of the ink containing bubbles generated by mixing the air and the ink, and it is possible to prevent the ink including the bubbles from being supplied to the head unit 2. It is possible to prevent variation in the discharge amount of droplets from the head unit 2 due to bubbles. As a result, when the ink is initially filled, ink can be filled without bubbles remaining in the ink storage portion 22 and each flow path in the sub tank 4, the ink consumption is suppressed, and the head portion 2 can be stably supplied. Ink can be supplied.
In this configuration, only air is supplied to the flow path in the head unit 2 until the liquid surface reaches the supply flow path outlet 24e, and only ink is supplied after the liquid surface reaches the supply flow path outlet 24e. Is supplied. For this reason, the air supplied first is discharged from the head unit 2, and the flow path in the head unit 2 is filled with ink supplied later, so that the inside of the flow path in the head unit 2 is filled. Can be filled with ink.
Therefore, in the recording head 1 of the present embodiment, it is possible to prevent variations in the discharge amount from the head unit 2, and thus it is possible to stably discharge droplets from the head unit 2.

  In addition, the recording head 1 according to the second embodiment includes the ink reservoir chamber 204 in which ink is stored before the ink reaches the flow path inlet 207a. At the time of ink filling, when the ink flows into the supply flow path 24 from the ink storage portion 22 of the sub tank 4, the ink is once stored in the ink reservoir chamber 204, and after the ink gradually accumulates from below, the supply flow path is passed over the partition wall 202. Ink flows into 24. For this reason, since there is no sudden change in the cross-sectional area of the flow path, the ink flows without stagnation and bubbles are less likely to be generated. If a large amount of bubbles remain in the sub tank 4, the pressure (negative pressure) in the sub tank 4 cannot be maintained within a certain range. On the other hand, since the recording head 1 of the present embodiment can maintain the negative pressure by preventing the bubbles from remaining in the sub tank 4 and can prevent the bubbles from flowing into the head unit 2. Reliability as an ink tank can be improved.

  In the recording head 1 of this embodiment, the ink flow path from the flow path inlet 207a to the supply flow path 24 via the flow path 207 and the communication path 206 in front of the partition wall has an inverted U shape. Yes. If there is a corner in this flow path, the cross-sectional area of the flow path suddenly widens at that portion, and ink may diffuse when passing through the corner and may be mixed with air and contain bubbles. As in the present embodiment, the liquid storage tank discharge flow path has an inverted U shape with no corners, so that the cross-sectional area of the channel having the corners does not suddenly increase, and the ink is contained in the ink. It is possible to prevent bubbles from being contained. In addition, the inverted U-shape prevents the ink from being supplied to the head unit 2 until the upper end 202a of the partition wall 202 at the center of the U-shape is overcome, and also maintains the state where the ink has filled the flow path cross section. However, since it flows all at once, it is possible to reduce the amount of ink that flows to the head unit 2 and is discarded before the ink filling is completed.

  Further, as shown in FIG. 11, the ink flow path from the flow path inlet 207a to the supply flow path 24 via the flow path 207 and the communication path 206 of the recording head 1 of the present embodiment is as shown in FIG. The channel cross-sectional area may continuously decrease from the upstream side toward the downstream side. In the configuration shown in FIG. 11, the flow path cross-sectional area is gradually reduced. As a result, the flow velocity of the ink flowing in the supply channel 24 increases from the upper end 202a of the partition wall 202 toward the supply channel outlet 24e. Thereby, since the flow rate can be obtained even at a low pressure, it is possible to efficiently fill the ink and discharge the bubbles in the flow path of the sub tank 4 with a small amount of the discarded ink.

  In addition, the printer 100 according to the present embodiment includes an ink discharge head unit that discharges ink droplets from the head unit 2, and the ink droplets discharged from the head unit 2 are attached to the recording paper 107 that is a recording medium, thereby generating an image. An image forming apparatus to be formed. By using the recording head 1 of Example 1 or Example 2 as the ink ejection head unit of such a printer 100, stable droplet ejection from the head unit 2 can be performed, and thus reliability is improved. Image quality can be maintained.

DESCRIPTION OF SYMBOLS 1 Recording head 2 Head part 4 Sub tank 5 Main tank 6 Waste liquid tank 11 Nozzle hole 12 Liquid chamber 13 Common liquid chamber 14 Ink supply port 15 Ink discharge port 20 Ink filter 21 Tank case 22 Ink storage part 22a Top surface 22d First ink storage Section 22e Second ink storage section 23 Film member 24 Supply flow path 24e Supply flow path outlet 25 Discharge flow path 51 Ink supply pipe 52 Ink supply pump 53 Ink discharge pipe 54 Ink discharge valve 55 Atmospheric release pipe 100 Printer 202 Bulkhead 204 Ink reservoir Chamber 205 Partition wall 206 Communication path 207 Bulkhead flow path 208 Shielding wall

JP 2004-188740 A

Claims (3)

A head unit including a plurality of nozzles that discharge liquid as droplets, and a common liquid chamber through which the liquid supplied to the plurality of nozzles passes;
A liquid storage tank for storing a liquid to be supplied to the head portion;
The internal space of the liquid storage tank includes a liquid storage portion for storing the liquid to be supplied to the head portion, and a liquid storage portion from the liquid storage portion to the common liquid chamber by a partition wall arranged so as to extend upward from the bottom thereof. It is spatially partitioned from the supply flow path through which the liquid to be supplied passes,
The upper end of the partition wall is lower than the ceiling part of the internal space of the liquid storage tank, and the liquid storage part and the liquid are formed in a communication path formed by a gap between the upper end of the partition wall and the ceiling part of the internal space of the liquid storage tank. In the liquid discharge head unit configured to communicate with the supply flow path,
A partition wall that extends downward from the ceiling portion near the partition in the liquid storage portion and is arranged so that the position of the lower end is lower than the position of the upper end of the partition,
A gap between the lower end of the partition wall and the partition wall serves as a flow path inlet, and a flow path in front of the partition wall serving as a flow path of liquid flowing from the liquid storage portion toward the communication path is formed by the gap between the partition wall and the partition wall. Formed,
A liquid flow path from the flow path inlet to the supply flow path outlet communicating with the common liquid chamber of the supply flow path via the flow path in front of the partition, the communication path, and the supply flow path. A liquid discharge head unit, wherein the liquid storage tank discharge channel has an inverted U shape. In the liquid discharge head unit according to claim 1 or 2,
The liquid discharge head unit, wherein the liquid storage tank discharge channel has a shape in which a channel cross-sectional area continuously decreases from the upstream side toward the downstream side. An ink discharge head unit that discharges ink droplets from the head unit is provided.
In an image forming apparatus for forming an image by causing ink droplets ejected from the head portion to adhere to a recording medium,
An image forming apparatus using the liquid discharge head unit according to claim 1 or 2 as the ink discharge head unit.

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