JP7786565B2 - Degassing device and liquid ejection device - Google Patents

Description

The present invention relates to a degassing device for degassing a liquid and a liquid ejection device equipped with the degassing device.

In inkjet recording devices, the amount of dissolved gas in the ink can sometimes become large. In this case, air bubbles can form inside the inkjet head, which can cause poor ink ejection.

Therefore, technologies for reducing the amount of dissolved gas in ink have been studied. For example, Patent Document 1 describes a configuration including a pressure reduction chamber and a vacuum pump. The pressure reduction chamber contains a hollow fiber membrane connected to an ink flow path. The vacuum pump degasses the ink inside the hollow fiber membrane by reducing the pressure in the pressure reduction chamber.

Patent document 2 describes a second configuration in addition to the first configuration similar to that of patent document 1. In the second configuration, ultrasonic vibrations are used to release tiny air bubbles attached to pigments or metal particles contained in the ink.

Patent document 3 describes a third configuration that includes a defoaming chamber and a decompression chamber. In this third configuration, the decompression chamber decompresses the defoaming chamber to remove air from the liquid, and the wall between the defoaming chamber and the decompression chamber is gas-permeable.

JP 2015-147365 A Japanese Patent Application Laid-Open No. 2019-217712 JP 2010-46820 A

While hollow fiber membranes have high gas separation performance, they are characterized by low durability. Gas-permeable wall members have the advantage of being more durable and less expensive than hollow fiber membranes.

However, when water-based ink is used, the wall member is more permeable to water vapor generated by evaporation of water in the ink than the hollow fiber membrane. This can easily lead to problems such as high ink viscosity.

The object of the present invention is to provide a degassing device and a liquid ejection device that can suppress the loss of moisture in a liquid when the liquid is degassed using a gas-permeable membrane.

A degassing device according to one aspect of the present invention comprises a flow path through which a water-containing liquid flows, a pressure reduction chamber, a membrane, a pressure reduction pump, and a humidifier. The pressure reduction chamber is disposed in contact with the flow path. The membrane is provided at the boundary between the flow path and the pressure reduction chamber. Gas can permeate the membrane. The pressure reduction pump reduces the pressure in the pressure reduction chamber. The humidifier humidifies the pressure reduction chamber.

The humidifier may include a reservoir for storing water and a water supply pump. The water supply pump supplies water from the reservoir to the pressure reduction chamber.

The degassing device may include a water sensor and a control unit. The water sensor detects a predetermined amount of water in the decompression chamber. The control unit controls the water supply pump. The control unit operates the water supply pump when the water sensor does not detect the predetermined amount of water.

The control unit may be configured to operate the water supply pump while the pressure reducing pump is stopped.

The membrane may be silicone rubber.

In another aspect of the present invention, a liquid ejection device comprises the degassing device and a head that ejects liquid supplied from the flow path.

According to the present invention, when a liquid is degassed using a gas-permeable membrane, the loss of moisture in the liquid can be suppressed.

FIG. 1 is a front view schematically illustrating the internal configuration of a printer according to an embodiment of the present invention. FIG. 2 is a perspective view showing the arrangement of inkjet heads according to one embodiment of the present invention. FIG. 3 is a cross-sectional view of an inkjet head according to an embodiment of the present invention. FIG. 4 is a diagram schematically illustrating an ink supply path according to one embodiment of the present invention. FIG. 5 is a diagram schematically illustrating the configuration of a degassing device according to one embodiment of the present invention. FIG. 6 is a diagram schematically illustrating the configuration of a degassing device according to one embodiment of the present invention. FIG. 7 is a flow chart showing the control of the degassing device according to one embodiment of the present invention.

Below, we will explain a printer 1 according to one embodiment of the present invention with reference to the drawings. The printer 1 is an example of an inkjet recording device.

First, the overall configuration of the printer 1 will be described. In the following description, the front side of the paper in Figure 1 will be the front side (front side) of the printer 1. Furthermore, the left and right directions will be described based on the direction when viewing the printer 1 from the front. In each figure, U, Lo, L, R, Fr, and Rr represent top, bottom, left, right, front, and rear, respectively.

The printer 1 has a rectangular parallelepiped main body housing 3 (see Figure 1). A paper feed cassette 4 and a paper feed roller 5 are provided in the lower part of the main body housing 3.

The paper feed cassette 4 contains individual sheets S, such as plain paper and coated paper. The paper feed roller 5 feeds the sheets S from the paper feed cassette 4 to the right.

Above the paper feed cassette 4, there is a transport unit 7 that adsorbs the sheet S and transports it in the Y direction. Above the transport unit 7, there is an image-forming unit 6 that ejects ink to form an image.

A paper discharge roller 8 and a paper discharge tray 9 are provided in the upper right corner of the main housing 3. Inside the main housing 3, a transport path 10 is provided that runs from the paper feed roller 5 through the gap between the transport unit 7 and the imaging unit 6 to the paper discharge roller 8.

The discharge roller 8 discharges the sheet S with the image formed thereon from the conveying path 10. The discharged sheet S is then stacked on the discharge tray 9.

The transport path 10 is mainly composed of plate-like members that face each other with a gap between them to allow the sheet S to pass through. Transport rollers 17 that grip and transport the sheet S are provided at multiple locations in the transport direction Y on the transport path 10. Registration rollers 18 are provided upstream of the imaging unit 6 in the transport direction Y.

The conveying unit 7 comprises an endless conveying belt 21, a support plate 23, and a suction unit 24. The conveying belt 21 has a number of ventilation holes (not shown) and is wrapped around a driving roller 25 and a driven roller 22.

The support plate 23 has numerous ventilation holes. The upper surface of the support plate 23 is in contact with the inner surface of the conveyor belt 21. The suction unit 24 sucks air through the ventilation holes in the support plate 23 and the ventilation holes in the conveyor belt 21, thereby adsorbing the sheet S to the conveyor belt 21.

The drive roller 25 is driven counterclockwise by a drive unit (not shown) that includes a motor and a reduction gear. This causes the conveyor belt 21 to rotate counterclockwise, and the sheet S adsorbed to the conveyor belt 21 is conveyed in the Y direction.

The imaging unit 6 includes head units 11Y, 11Bk, 11C, and 11M, which eject yellow, black, cyan, and magenta ink, respectively. Head units 11Y, 11Bk, 11C, and 11M are connected to ink containers 20Y, 20Bk, 20C, and 20M, which are filled with yellow, black, cyan, and magenta ink, respectively.

In the following description, head unit 11 is a general term for head units 11Y, 11Bk, 11C, and 11M. Also, ink container 20 is a general term for ink containers 20Y, 20Bk, 20C, and 20M.

The head unit 11 includes one or more inkjet heads 12. For example, the head unit 11 includes three inkjet heads 12 arranged in a staggered pattern (see Figure 2). The inkjet head 12 includes a housing 12H and a nozzle plate 12P (see Figure 3). The housing 12H is a rectangular parallelepiped with its longitudinal direction extending in the front-to-rear direction. The nozzle plate 12P is located at the bottom of the housing 12H.

The nozzle plate 12P has a large number of nozzles 12N arranged in the front-to-rear direction. Each nozzle 12N includes a branch flow path 12B and an ejection port 12A. The branch flow path 12B branches off from a flow path 31 that connects to the sub-tank 64. The ejection port 12A is provided in the nozzle surface 12F.

The vibration plate 12V forms part of the inner wall of the branch flow path 12B. Each vibration plate 12V is provided with a pressure element 12Z. The housing 12H is provided with a driver 50 and a control circuit 40. The driver 50 drives the pressure element 12Z. The control circuit 40 controls the driver 50.

For example, a piezoelectric element, an electrostatic element (electrostatic actuator), or a heating element () used in a thermal inkjet method may be used as the pressure element 12Z.

The printer 1 is equipped with an ink supply path 60 (see Figure 4). In Figure 4, an ink supply path 60 corresponding to one color of ink is shown. However, in this embodiment, four colors of ink are used, so four similar ink supply paths 60 are provided.

The printer 1 comprises a container mounting section 61, an ink supply pump 63, and a sub-tank 64. The container mounting section 61 is the part where the ink container 20 is mounted. The ink supply pump 63 draws ink from the ink container 20. The sub-tank 64 stores the ink pumped out from the ink supply pump 63.

The control unit 2 (see Figure 1) includes a calculation unit and a memory unit. The calculation unit is, for example, a CPU (Central Processing Unit). The memory unit includes a storage medium such as ROM (Read Only Memory), RAM (Random Access Memory), or EEPROM (Electrically Erasable Programmable Read Only Memory).

The calculation unit performs various processes by reading and executing the control program stored in the memory unit. Note that the control unit 2 may also be realized by an integrated circuit that does not use software.

A display/operation unit 19 is provided on the top of the main body housing 3 (see Figure 1). The display/operation unit 19 includes a display panel, a touch panel, and a keypad. The touch panel is provided on top of the display surface of the display panel. The keypad is located adjacent to the display panel.

The control unit 2 displays screens showing the printer 1's operation menu, status, etc. on the display panel. Furthermore, the control unit 2 controls each part of the printer 1 in response to operations detected on the touch panel or keypad.

The basic image formation operation of the printer 1 is as follows: When an image formation job is input to the printer 1 from the display/operation unit 19 or an external computer, the paper feed roller 5 feeds the sheet S from the paper feed cassette 4 into the transport path 10. Furthermore, the registration roller 18, whose rotation has been stopped, corrects any skew in the sheet S.

The registration roller 18 sends the sheet S to the transport unit 7 at a predetermined timing. As a result, the transport unit 7 transports the sheet S in the Y direction while adsorbing it to the transport belt 21.

The control unit 2 supplies raster-format image data to the control circuit 40 in synchronization with the transport of the sheet S, and the driver 50 supplies an ejection signal corresponding to the gradation data to the pressure element 12Z. This causes ink to be ejected from the nozzle 12N, forming an image on the sheet S. The paper ejection roller 8 ejects the sheet S with the image formed onto the paper ejection tray 9.

Next, the configuration of the degassing device 30 will be described. Figures 5 and 6 are diagrams that schematically show the configuration of the degassing device 30. Figure 5 shows the II-II cross section of Figure 6, and Figure 6 shows the I-I cross section of Figure 5.

The degassing device 30 comprises a flow path 31, a pressure reduction chamber 34, a gas-liquid permeable membrane 35, a pressure reduction pump 36, and a humidifying device 41. Ink flows through the flow path 31. Ink is an example of a liquid that contains water.

The decompression chamber 34 is arranged adjacent to the flow path 31. The gas-liquid permeable membrane 35 is provided at the boundary between the flow path 31 and the decompression chamber 34. The gas-liquid permeable membrane 35 is an example of a membrane that is permeable to gas.

The vacuum pump 36 reduces the pressure in the vacuum chamber 34. The humidifier 41 humidifies the vacuum chamber 34.

The ink according to this embodiment is a water-based ink (aqueous ink). For example, the ink contains water, pigment or dye, glycerin, and organic solvent.

[Flow path (ink chamber)]
A section of the flow path 31 between the ink supply pump 63 and the subtank 64 is the ink chamber 33. The cross section of the ink chamber 33 perpendicular to the ink supply direction F is larger than the cross sections of the ink chamber 33 on the upstream and downstream sides in the ink supply direction F in the flow path 31. The ink chamber 33 constitutes a part of the flow path 31.

In the example shown in Figures 5 and 6, the cross section of the ink chamber 33 is rectangular, but the cross section of the ink chamber 33 may have any shape. The ink supply pump 63 is, for example, a diaphragm pump. The ink supply pump 63 operates in accordance with a control signal output by the control unit 2.

[Gas-liquid permeable membrane]
An opening is formed in a part of the ink chamber 33. In the example shown in Figures 5 and 6, the opening is formed in the bottom of the ink chamber 33. The opening is covered with a gas/liquid permeable membrane 35.

The gas-liquid permeable membrane 35 is, for example, silicone rubber with a thickness of approximately 0.1 mm. Alternatively, a membrane such as polyethylene or polypropylene may be used as the gas-liquid permeable membrane 35.

[Decompression chamber]
The decompression chamber 34 is in contact with the ink chamber 33 via a gas/liquid permeable membrane 35. An opening having the same dimensions as the opening of the ink chamber 33 is formed in a part of the decompression chamber 34 (the ceiling portion in this example). In the example shown in Figures 5 and 6, the opening is formed in the ceiling portion of the decompression chamber 34.

The opening of the ink chamber 33 and the opening of the decompression chamber 34 are joined together via a gas-liquid permeable membrane 35. In other words, the gas-liquid permeable membrane 35 is located at the boundary between the ink chamber 33 and the decompression chamber 34, which are part of the flow path 31.

[Decompression pump, valve]
A decompression pump 36 is connected to the decompression chamber 34. The decompression pump 36 is, for example, a diaphragm pump. The decompression pump 36 operates in accordance with a control signal output by the control unit 2.

A valve 37 is provided between the pressure reduction pump 36 and the pressure reduction chamber 34. The valve 37 is, for example, a solenoid valve. The valve 37 opens and closes in accordance with a control signal output by the control unit 2.

[humidifier]
The humidifying device 41 includes a reservoir 42 for storing water and a water supply pump 43. The water supply pump 43 supplies water from the reservoir 42 to the decompression chamber 34. The reservoir 42 is a tank.

The water supply pump 43 is, for example, a tube pump. The water supply pump 43 operates in accordance with a control signal output by the control unit 2.

[Water sensor]
The water sensor 51 is provided at the bottom of the decompression chamber 34 and is connected to the control unit 2 .

The water sensor 51 comprises, for example, a pair of horizontally opposing electrodes located at a predetermined height from the bottom of the decompression chamber 34. When the water level supplied to the decompression chamber 34 reaches the position of the pair of electrodes, an electric current flows between the pair of electrodes via the water.

When a current flows between the pair of electrodes, the water sensor 51 outputs a detection signal to the control unit 2 indicating that water has been detected. In other words, the water sensor 51 detects a predetermined amount of water in the decompression chamber 34.

[Barometric pressure sensor]
The air pressure sensor 52 is provided at the top of the decompression chamber 34 and is connected to the control unit 2. The air pressure sensor 52 measures the air pressure inside the decompression chamber 34 and outputs air pressure data indicating the measured air pressure value to the control unit 2.

Next, the operation of the degassing device 30 will be described. Figure 7 is a flow chart showing the control content of the degassing device 30. When the printer 1 is turned on, the control unit 2 controls the degassing device 30 according to the flow chart shown in Figure 6.

First, the control unit 2 opens the valve 37 (step S01). Next, the control unit 2 determines whether the water sensor 51 has detected a predetermined amount of water (step S02).

If the control unit 2 determines that the water sensor 51 has detected a predetermined amount of water, it proceeds to processing step S06 described below (YES in step S02).

On the other hand, if the control unit 2 determines that the water sensor 51 has not detected the specified amount of water, it operates the water supply pump 43 (NO in step S02, step S03).

After the water supply pump 43 is activated, the control unit 2 determines whether the water sensor 51 has detected a predetermined amount of water (step S04). If the control unit 2 determines that the water sensor 51 has not detected a predetermined amount of water, it repeats the determination in step S04 (NO in step S04).

On the other hand, if the control unit 2 determines that the water sensor 51 has detected a predetermined amount of water, it stops the water supply pump 43 (YES in step S04, step S05).

Next, the control unit 2 activates the decompression pump 36 (step S06). Furthermore, the control unit 2 determines whether the air pressure in the decompression chamber 34 measured by the air pressure sensor 52 has dropped to a predetermined value (step S07). The predetermined value of air pressure is, for example, 0.6 kPa.

If the control unit 2 determines that the air pressure has not dropped to the specified value, it repeats the judgment of step S07 (NO in step S07).

On the other hand, if the control unit 2 determines that the air pressure has dropped to a predetermined value, it closes the valve 37 and stops the decompression pump 36 (YES in step S07, step S08). When the valve 37 is closed, the air pressure in the decompression chamber 34 is maintained at a predetermined value.

Next, the control unit 2 determines whether a print job has started (step S09). If the control unit 2 determines that a print job has not started, it repeats the determination of step S09 (NO in step S09).

On the other hand, if the control unit 2 determines that a print job has started, it opens the valve 37 and activates the decompression pump 36 (NO in step S09, step S10). In other words, the decompression chamber 34 is decompressed in parallel with the execution of the print job.

Next, the control unit 2 determines whether the print job has ended (step S11). If the control unit 2 determines that the print job has not ended, it repeats the determination of step S11 (NO in step S11).

On the other hand, if the control unit 2 determines that the print job has ended, it stops the pressure reduction pump 36 and repeats the processing from step S02 onwards (YES in step S11, step S12).

As described above, the degassing device 30 comprises a flow path 31, a pressure reduction chamber 34 adjacent to the flow path 31, a gas-liquid permeable membrane 35, a pressure reduction pump 36, and a humidifier 41. Ink, an example of a liquid containing water, flows through the flow path 31. The gas-liquid permeable membrane 35 is provided at the boundary between the flow path 31 and the pressure reduction chamber 34. The gas-liquid permeable membrane 35 is an example of a membrane that is permeable to gas. The pressure reduction pump 36 reduces the pressure in the pressure reduction chamber 34. The humidifier 41 humidifies the pressure reduction chamber 34.

The gas-liquid permeable membrane 35 has a mesh-like molecular structure. Therefore, microscopically, the ink chamber 33 and the decompression chamber 34 are connected via the gaps between the molecules in the gas-liquid permeable membrane 35.

The gaps between the molecules are large enough for gas molecules to pass through. Therefore, liquid and water vapor coexist near the surface of the gas-liquid permeable membrane 35 on the ink chamber 33 side. In conventional devices, when the pressure in the decompression chamber 34 is reduced, the amount of water vapor in the decompression chamber 34 also decreases, causing the water in the ink to vaporize and be sucked into the decompression chamber 34.

In contrast, in this embodiment, the decompression chamber 34 is humidified, thereby suppressing a decrease in the amount of water vapor within the decompression chamber 34. This prevents the moisture in the ink from evaporating and being sucked into the decompression chamber 34. According to this embodiment, when degassing a liquid using a gas-permeable membrane, the decrease in moisture within the liquid can be suppressed.

Furthermore, according to the degassing device 30 of this embodiment, the humidifying device 41 includes a storage section 42 for storing water, and a water supply pump 43. The water supply pump 43 supplies water from the storage section 42 to the decompression chamber 34. With this configuration, the decompression chamber 34 is humidified by water vapor that is naturally generated from the water. Therefore, humidification of the decompression chamber 34 can be achieved at low cost.

The degassing device 30 according to this embodiment is equipped with a water sensor 51 that detects a predetermined amount of water in the decompression chamber 34, and a control unit 2 that controls the water supply pump 43. The control unit 2 activates the water supply pump 43 when the water sensor 51 does not detect the predetermined amount of water. This configuration prevents the humidifying device 41 from becoming unable to humidify.

Furthermore, according to the degassing device 30 of this embodiment, the control unit 2 operates the water supply pump 43 while the vacuum pump 36 is stopped. With this configuration, the vacuum chamber 34 returns to atmospheric pressure when the vacuum pump 36 is stopped. Therefore, a decrease in the moisture content of the liquid is prevented when water is being supplied to the vacuum chamber 34.

Furthermore, according to the degassing device 30 of this embodiment, the gas-liquid permeable membrane 35 is made of silicone rubber. Silicone rubber is low-cost. However, the use of silicone rubber can easily lead to the inconvenience of moisture in the ink evaporating and being sucked into the decompression chamber 34. However, according to this embodiment, the humidifying device 41 suppresses the loss of moisture in the ink, thereby avoiding the above inconvenience and reducing the cost of the gas-liquid permeable membrane 35.

The above embodiment may be modified as follows:

In the above embodiment, an example was shown in which the opening of the ink chamber 33 and the opening of the decompression chamber 34 are joined via a gas-liquid permeable membrane 35. However, in a modified example, a portion of the flow path 31 may be formed by a tubular gas-liquid permeable membrane 35, and the decompression chamber 34 may be configured to surround the section formed by the gas-liquid permeable membrane 35. This configuration also achieves the same effects as the above embodiment.

In the above embodiment, an example is shown in which the present invention is applied to a degassing device 30 that uses a gas-liquid permeable membrane 35. However, in a modified example, the present invention may also be applied to a degassing device that uses a hollow fiber membrane instead of the gas-liquid permeable membrane 35. This is because even when a hollow fiber membrane is used, the phenomenon of moisture in the ink being sucked into the decompression chamber can occur.

In the above embodiment, the degassing device 30 is provided in the flow path 31 between the ink supply pump 63 and the subtank 64. However, in a modified example, the degassing device 30 may be provided at any location in the flow path 31 leading from the ink container 20 to the inkjet head 12.

In the above embodiment, an example of applying the present invention to an inkjet recording device is shown. However, the present invention may also be applied to a liquid ejection device that ejects liquids other than ink, including water.

For example, the heating unit may heat various liquids. For example, the objects to be heated by the heating unit may include a treatment liquid for performing a surface treatment on the sheet S, a liquid containing dispersed conductors used to form electrical circuits, a light-emitting material used in the manufacture of organic electroluminescence (EL) panels, dyes for textile printing, or liquefied resin or ceramics used to form three-dimensional objects using a 3D printer. In this case, the present invention may be applied to the heating unit.

Claims (5)

a liquid chamber that is part of a flow path through which a liquid containing water flows ;
a decompression chamber in contact with the liquid chamber ;
a gas-permeable membrane provided at a boundary between the liquid chamber and the decompression chamber;
a decompression pump connected to the decompression chamber and decompressing the decompression chamber;
a humidifying device for humidifying the decompression chamber;
a storage section for storing water;
a water supply pump that supplies water from the reservoir to the decompression chamber ,
A degassing device in which the cross section of the liquid chamber perpendicular to the direction of passage of the liquid is formed larger than both the cross section of the inlet portion of the liquid into the liquid chamber in the flow path and the cross section of the outlet portion of the liquid from the liquid chamber . a water sensor for detecting a predetermined amount of water in the decompression chamber;
a control unit that controls the water supply pump,
The degassing device according to claim 1 , wherein the control unit activates the water supply pump when the water sensor does not detect the predetermined amount of water. The degassing device according to claim 2 , wherein the control unit operates the water supply pump while the pressure reducing pump is stopped. 4. The degassing device according to claim 1 , wherein the membrane is made of silicone rubber. a head that ejects a liquid containing water supplied through a flow path through which the liquid flows;
A liquid ejection device comprising : the degassing device according to claim 1 , which is disposed in the flow path .