JP5168031B2 - Liquid ejecting apparatus and image forming apparatus provided with the same - Google Patents

Description

  The present invention relates to a liquid ejection device and an image forming apparatus including the same.

  Liquid ejection devices using ink are often used in image forming apparatuses such as printers, copiers, and fax machines. Also known are liquid ejecting apparatuses that eject liquids other than ink, such as DNA samples, resists, pattern materials, and the like, or image forming apparatuses including these.

  A liquid ejection device for an on-demand type ink jet (IJ) recording device is provided with a diaphragm on a part of the wall of a liquid chamber filled with ink, and the diaphragm is displaced by a piezoelectric actuator or the like to change the volume in the liquid chamber. Widely known is a system that discharges ink by increasing the pressure, and a heating element that generates heat when energized in the liquid chamber and discharges ink by increasing the pressure in the liquid chamber by the air generated by the heat generated by the heating element. Yes. In recent years, many IJ printers are used for various purposes due to the low price of IJ printers, high image quality, and the spread of personal computers to general households.

  One of the major technical problems in the IJ printer is speeding up. Usually, the number of nozzles and the number of heads are increased, and a head tank (also referred to as a sub tank) is provided above the head to stably supply a large amount of printing so that ink is smoothly supplied to the head. Has been done. The head tank is often configured to be supplied with ink from an ink cartridge using a resin tube. However, it is difficult to always fill the volume of the head tank with 100% ink, and an air layer is formed in the upper part of the head tank. Is formed. The amount of air in the head tank tends to increase over time due to air permeation from the resin tube and the head tank wall surface and air mixed when the ink cartridge is detached. If the amount of air in the head tank is small, there is no problem. Becomes out of the allowable range, and ink oozes out from the head or does not discharge normally. In addition, when the air in the head tank is large, there is a problem that air is mixed with the ink in the head and the ink cannot be discharged.

  Therefore, techniques for keeping the pressure in the head tank at a constant negative pressure and preventing air from exceeding a predetermined amount have been studied. For example, Patent Document 1 discloses an invention in which an air discharge path is provided from a head tank (sub tank) to a head, a suction cap is brought into close contact with the nozzle surface of the head, and air is discharged together with ink.

  Patent Document 2 discloses an invention in which a check valve is provided in an upper portion of a head tank (sub tank), and an exhaust device is appropriately connected to the check valve portion to discharge air in the head tank.

In Patent Document 3, the exhaust tube connected to the air layer in the sub tank is configured to communicate with a liquid tank, one of which is open to the atmosphere in a two-chamber configuration, so that the negative pressure is stabilized, and the middle of the exhaust tube is branched. An invention is disclosed in which air in a sub-tank is discharged by a valve and a pump.
JP 2000-301732 A JP 11-320901 A JP 2002-240310 A

  However, liquid ejecting apparatuses used in a wide range of fields including printers are required to have a simple structure, hardly break down, and can be manufactured at low cost. In this respect, since the invention disclosed in Patent Document 1 is a system in which a thin tube as an air discharge path is provided in the head and sucked from the nozzle surface, there is a problem that suction cannot be performed when the thin tube is clogged. When an image is formed using a pigment ink, the ink tends to thicken, so air discharge is likely to be poor, and stable performance may not be obtained.

  Since the invention disclosed in Patent Document 2 does not allow leakage at the check valve, it is necessary to provide a check valve with high sealing reliability in the sub tank, and the structure is likely to be complicated and expensive.

  The invention disclosed in Patent Document 3 requires a highly reliable valve and pump device because the negative pressure in the sub-tank is destroyed when there is a leak from the valve and pump connected to the exhaust tube. It cannot be installed in a low-cost printer.

  In view of the above problems, an object of the present invention is to provide a liquid ejection device that can easily maintain the negative pressure in the head tank within an appropriate range with a simple configuration, and an image forming apparatus using the same. Is to provide.

The present invention includes a liquid discharge head that has a nozzle and discharges liquid from the nozzle, a head tank that contains the liquid, and a lower portion that communicates with the liquid discharge head, and supplies the liquid to the head tank. A liquid discharge device comprising a feeding means for feeding, an air discharge container for discharging the air in the head tank to the atmosphere through a stored sealing liquid, and one end of the air tank above the head tank And an air discharge pipe having the other end opened in the sealing liquid in the air discharge container.
In the present invention, the air discharge pipe has an expansion portion at a position higher than the liquid surface of the seal liquid, a contraction portion in the vicinity of the communication portion with the seal liquid, and a seal in the air discharge container. A check valve that prevents liquid from flowing into the head tank, a check valve that prevents seal liquid in the air discharge container from flowing into the head tank, or the air discharge pipe The one end of the liquid discharge device is disposed above the liquid level of the sealing liquid in the air discharge container.

According to the present invention, it is possible to provide a liquid ejection apparatus that can maintain the negative pressure in the head tank within an appropriate range with a simple configuration, facilitate air discharge, and stably supply liquid. In addition, according to the present invention, it is possible to provide a liquid ejection apparatus having a simple or reliable and simple backflow prevention means.

  In a preferred aspect of the present invention, the upper part of the air discharge container is open to the atmosphere.

  According to the present invention, it is possible to provide a liquid ejecting apparatus that easily discharges air from the head tank only by controlling a feeding unit that feeds liquid to the head tank.

  In a preferred aspect of the present invention, the upper part of the air discharge container is open to the atmosphere through a porous body.

  According to the present invention, it is possible to provide a liquid ejecting apparatus that can prevent the leakage, drying, evaporation, and dust mixing of the sealing liquid without impairing the air discharging function, maintain the quality, and supply a stable liquid. .

  In a preferred aspect of the present invention, the liquid ejection device is characterized in that the sealing liquid has a viscosity or density larger than that of the liquid.

  According to the present invention, it is possible to provide a liquid ejection device that can easily prevent the backflow of the sealing liquid in the air discharge container to the head tank and keep the quality of the liquid in the head tank stable.

  In a preferred aspect of the present invention, the sealing liquid is a non-volatile or low-volatile liquid.

  According to the present invention, it is possible to provide a liquid ejecting apparatus that can stably maintain a seal liquid for a long period of time and can maintain a stable operation of the head tank.

  In a preferred aspect of the present invention, the head tank includes an elastic member that is formed of a flexible film on at least a part of the surface and biases the flexible film in a direction that increases the volume of the head tank. The liquid ejecting apparatus.

  According to the present invention, it is possible to easily form a stable negative pressure in the head tank with the flexible film and the elastic member, and adjust the negative pressure of the head tank by controlling the feeding means for feeding the liquid to the head tank. And a liquid ejection device that can easily discharge air.

  In a preferred aspect of the present invention, the liquid ejecting apparatus is characterized in that the feeding means is connected to a buffer tank that can be opened to the atmosphere.

  According to the present invention, a stable negative pressure can be formed and maintained easily by a head difference using a buffer tank, and the head tank is controlled by controlling the feeding means for feeding liquid to the head tank and controlling the opening of the buffer tank to the atmosphere. It is possible to provide a liquid ejection device that can easily perform negative pressure adjustment and air discharge.

  In a preferred aspect of the present invention, the other end of the air discharge pipe opens at the bottom of the air discharge container and communicates with the sealing liquid.

  According to the present invention, since the opening of the air discharge pipe is provided at the bottom of the air discharge container, the air discharge pipe is opened in the sealing liquid, and the head tank provides a liquid discharge device that is surely cut off from the atmosphere by the sealing liquid. can do.

  In a preferred aspect of the present invention, the air discharge pipe is provided with a backflow prevention means for preventing the sealing liquid in the air discharge container from flowing into the head tank.

  According to the present invention, it is possible to provide a liquid ejection device that prevents the liquid sealing liquid in the air discharge container from flowing back to the head tank by the backflow preventing means and preventing the quality of the liquid in the head tank from deteriorating.

  In a preferred aspect of the present invention, the head tank includes a liquid level detecting unit that detects a liquid level of the liquid.

  According to the present invention, it is possible to provide a liquid ejecting apparatus that can maintain the liquid level of the head tank at an appropriate position and can easily control the negative pressure of the head tank and discharge the air.

  The present invention is an image forming apparatus including the liquid ejection device.

  According to the present invention, it is possible to provide an image forming apparatus provided with a liquid ejection device having the above characteristics.

  According to the present invention, it is possible to provide a liquid ejecting apparatus that can maintain the negative pressure in the head tank in an appropriate range with a simple configuration and that can be easily exhausted from the head tank, and an image forming apparatus using the liquid ejecting apparatus. .

(Embodiment 1)
An embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a schematic configuration diagram of an image forming apparatus of the present invention, which is equipped with a liquid ejection apparatus of the present invention. 1A is a front view, FIG. 1B is a side view of the image forming unit, and FIG. 1C is a plan view. This image forming apparatus is an example of an ink jet printer that uses ink as a liquid. This ink jet printer holds a carriage 120 slidably in a main scanning direction (guide rod longitudinal direction) with a guide rod 122 and a guide rail, which are horizontally mounted on left and right side plates 123L and 123R. The scanning can be performed in the longitudinal direction (main scanning direction) of the guide rod 122 by the scanning motor and the timing belt. The carriage 120 includes, for example, a recording head 1 that ejects ink droplets of each color of yellow (Y), cyan (c), magenta (M), and black (Bk), and a plurality of ink ejection ports in the main scanning direction. They are arranged in the crossing direction and mounted with the ink droplet ejection direction facing downward.

  Below the carriage 120, the paper 8 on which an image is formed is conveyed in a direction (sub-scanning direction) perpendicular to the main scanning direction. As shown in FIG. 1B, the paper 8 is sandwiched between the transport roller 125 and the pressing roller 126, transported to the printing unit, and sent to the paper guide unit 128. The scanning of the carriage 120 in the main scanning direction and the ink ejection from the recording head 1 are synchronized at an appropriate timing according to the image data, and an image for one band is formed on the paper 8. After image formation for one band is completed, a predetermined amount of paper is fed in the sub-scanning direction, and the same recording operation as described above is performed. These operations are repeated to form an image for one page. On the other hand, a head tank 101 in which an ink chamber for temporarily storing ink to be ejected is formed on the upper portion of the recording head 1 is integrally connected to the recording head 1. The term “integral” as used herein includes that the recording head 1 and the head tank 101 are connected by a tube, a pipe, and the like, both of which are mounted on the carriage 120 together.

  A liquid supply tube 16 is connected to the ink chamber and communicates with the ink cartridge 76. The configuration of the head tank 101 is shown in FIG. 2A is a front view (cross-sectional view) of the head tank 101, and FIG. 2B is a side view (cross-sectional view) of the head tank 101. In both figures, in order to facilitate understanding, the description of components is omitted as appropriate, or partially conceptualized. Inside the head tank 101, a filter 109 is provided in the vicinity of the connection portion with the recording head 1, and ink that has been filtered to remove foreign matters is supplied to the recording head 1.

  A flexible film member 107 formed in a convex shape is provided on one wall surface of the head tank 101, and is urged by a spring 108 in the direction of expanding the volume of the head tank 101. A filler 106 is provided in contact with the film member 107, and the deformation state of the film member 107 and the amount of ink in the head tank 101 can be detected by detecting the position of the filler 106 with a photo sensor or the like. .

  Above the head tank 101, an air amount detection sensor 103 for detecting the air amount in the head tank 101 by detecting the ink liquid level and a pressure sensor 104 for detecting the pressure in the head tank 101 are provided. In the head tank 101 shown in FIG. 2, the air amount detection sensor 103 is a liquid level gauge, and its measurement part is provided at a different position so that a plurality of liquid level states can be detected.

  The head tank 101 is provided with an ink supply port 110 and an exhaust port 111. The ink supply port 110 is connected to the liquid supply tube 16, and the exhaust port 111 is connected to an exhaust tube 112. The other end of the liquid supply tube 16 is connected to a cartridge holder 77 stationary on the main body, and communicates with the ink cartridge 76 via a conduit and a pump (not shown) in the cartridge holder 77. The other end of the exhaust tube 112 opens into a high-viscosity seal liquid 63 stored in an exhaust tank 60 serving as a main body stationary air discharge container.

  Ink supply and air discharge from the head tank 101 will be described with reference to FIG. FIG. 3 illustrates an ink filling process in the head tank 101 in the liquid ejection apparatus of the present invention. FIG. 3A is a diagram before the head tank 101 is filled with ink. FIG. 3B is a diagram illustrating a state in which the head tank 101 is filled with ink. FIG. 3C is a diagram illustrating a state in which the head tank 101 has been filled with ink. When the pump 78 is driven in a state where no ink is contained in either the head tank 101 or the recording head 1 as shown in FIG. 3A, the ink in the ink cartridge 76 is filtered by the filter 75, and the liquid supply tube 16, The ink flows into the head tank 101 via the ink supply port 110. At this time, the air originally in the head tank 101 is discharged from the exhaust tube 112 via the exhaust port 111.

  In the initial stage of ink filling, air is also pushed out from the nozzles of the recording head 1. However, if the filter 109 in the head tank 101 gets wet with ink, the filter 109 is fine and has a large meniscus holding force, so that it is difficult for air to pass through. Most of the air in the head tank 101 is exhausted through the exhaust tube 112. Since the other end of the exhaust tube 112 is immersed in the high-viscosity seal liquid stored in the exhaust tank 60, the air pushed out by the pressure of the pump 78 is once released into the seal liquid, and the exhaust tank 60 is discharged to the outside from the exhaust part 62 at the top.

  When the liquid level of the ink in the head tank 101 rises and the state shown in FIG. 3C is reached after the state shown in FIG. 3B, the air amount detection sensor 103 detects the ink level. The pump 78 is stopped. In the present embodiment, a liquid level sensor composed of an electrode pair is employed as the air amount detection sensor 103. This detects the resistance value between the electrode pair, and detects the ink liquid level because the volume low efficiency differs between air and ink. In the present embodiment, air amount detection sensors 103a and 103b are provided at two different depths as shown in FIG. Accordingly, first, the ink liquid level rises to the position shown in FIG. 3B, and the interelectrode resistance of the air amount detection sensor 103a provided at a deep position decreases to detect the liquid level. If the pump 78 is stopped at this point, a relatively large air layer can be formed in the head tank. However, in this embodiment, the pump is not stopped at the position of the air amount detection sensor 103a. As shown in FIG. 3C, the ink level is raised and the pump 78 is stopped when the ink level comes into contact with the air amount detection sensor 103b. In this state, an ink layer and an air layer are formed in the head tank 101, but the ink liquid level is formed at a position below the exhaust port 111.

  Next, as shown in FIG. 3C, the nozzle surface of the recording head 1 is sealed with a cap 83, and air in the cap is sucked by a pump 84 connected to the cap. As a result, the ink in the head tank 101 is filled in the recording head 1, and the internal volume of the head tank 101 is reduced by the amount of ink in the head tank 101 discharged to the outside by suction, so that the film member 107 becomes a tank. Deforms inward. At this time, since the spring 108 presses the film member 107 to try to return it to the original state, a negative pressure is formed in the head tank 101. In this embodiment, since the pressure in the head tank 101 can be detected by the pressure sensor 104, cap suction can be controlled so as to be a desired pressure (for example, −20 mmaq). Even if the pressure sensor 104 is not provided, if the relationship between the negative pressure and another control parameter such as the ink suction amount and the pump driving time can be grasped in advance, another control parameter can be used instead of directly detecting the negative pressure. It is also possible to create a negative pressure by suction.

  At the time of ink suction by the pump 84, a pressure that causes air to flow backward from the exhaust tube 112 to the head tank 101 is formed in the head tank, but in order to cause air to flow backward from the exhaust tube 112, a seal in the exhaust tank 60 is used. The condition is that the liquid 63 is sucked up by the exhaust tube 112. Therefore, if the exhaust tube 112 is made thin enough not to impair the function of discharging air, the ink in the head tank 101 can be discharged without sucking the seal liquid 63. In order to prevent backflow from the exhaust tube 112 when sucking ink from the nozzles of the recording head 1, it is also effective to increase the viscosity and specific gravity of the high-viscosity liquid as a method other than narrowing the exhaust tube 112. It is. Alternatively, a part of the exhaust tube 112 may be made sufficiently higher than the liquid level of the seal liquid 63 in the exhaust tank 60 to increase the water head difference for the backflow of the seal liquid 63.

  In an ink jet printer, resin materials are often used for piping members and tank members that supply ink. In particular, in the case where the head tank 101 is mounted on the carriage 120 as in the present embodiment and ink is supplied from the ink cartridge 76 stationary on the main body using the liquid supply tube 16, the resin tube or the resin film is made of a thin material. It is common to do. In that case, water and air are transferred back and forth between the ink and the outside air through a thin-walled resin tube or resin film. As a result, as shown in FIG. The ink liquid level may change from the position of the air amount detection sensor 103b to the position of the air amount detection sensor 103a as shown in FIG. A certain change in the ink liquid level does not impair the function of the printer. However, if the ink liquid level drops too much and the air layer becomes too large, the change in the air layer volume in the head tank 101 with respect to the temperature change becomes large. The negative pressure cannot be maintained, or air is mixed into the recording head 1 to cause ink ejection failure.

  In the present embodiment, in addition to the air amount detection sensor 103b that detects that the liquid level has reached a predetermined value when ink is charged into the head tank 101, an air amount detection sensor that detects a liquid level at a position lower than that. Since the position 103a is provided, the position is set to a water level when there is a maximum amount of air allowed in the head tank 101, and when the water level falls below the air amount detection sensor 103a, the air in the head tank 101 is set. It is sufficient to perform control for discharging the gas. Specifically, when the resistance between the electrode pairs of the air amount detection sensor 103a increases, the pump 78 is driven and ink is sent from the ink cartridge 76, whereby the air is exhausted from the head tank 101 through the exhaust tube 112.

  The exhaust tube 112 is a thin tube, and air flows smoothly with little resistance, and is discharged into the highly viscous seal liquid in the exhaust tank 60. During exhaust, the pressure in the head tank 101 is positive, but the flow path in the recording head 1 is fine, so the fluid resistance between the filter 109 and the flow path is high, and the amount of ink that oozes out from the nozzles of the recording head 1 There are few. Further, if the nozzle surface of the recording head 1 is sealed with the suction cap 83 during the exhaust, the amount of ink oozing out from the nozzle can be further reduced. When the air in the head tank 101 is discharged and the ink level rises to the position of the air amount detection sensor 103b, the pump 78 is stopped. Thereafter, if the negative pressure is adjusted by sucking the cap as in the above-described initial filling, the ink is filled to the normal liquid level in the head tank 101 and an appropriate negative pressure state is obtained, as shown in FIG. Then, it is possible to form an image by ejecting ink from the recording head 1.

  As described above, the sealing liquid 63 in the present invention is preferably non-volatile or low-volatile in addition to having a higher viscosity and specific gravity than ink. The exhaust tank 60 is not suitable for a highly volatile liquid because the upper exhaust part 62 is always in communication with the atmosphere. Note that the non-volatile or low volatility has the same meaning, and the degree that the sealing liquid evaporates and decreases in the normal use state of the liquid discharge apparatus, and does not hinder the use of the liquid discharge apparatus. It means that it is below the vapor pressure. From such a point, as the sealing liquid 63, a solvent such as ethylene glycol or glycerin that is generally used as a wetting agent for oils or inks is suitable. It is also possible to use a liquid in which a large amount of such a solvent is contained in the ink and the composition ratio is changed from that of a normal ink. In this way, it is also preferable to use the sealing liquid 63 that is unlikely to interfere with the printing of the ink jet printer even if it is mixed in the ink.

  In order to further reduce the evaporation of the sealing liquid 63, it is effective to narrow the opening of the sealing liquid storage part 61 of the exhaust tank 60 as shown in FIG. Moreover, the sealing liquid 63 does not need to be one type of liquid, and can be configured using a plurality of types of liquids that are not compatible. For example, there are a liquid A and a liquid B that do not melt together, and the liquid A has a characteristic that the specific gravity is heavy and the viscosity is high, and the liquid B has a characteristic that is low in specific gravity and low in volatility. Since liquid A and liquid B are stored in a two-layer state, the liquid A can be allowed to be volatile, the liquid B can be allowed to have a low viscosity, and the range of usable liquids is widened. be able to.

(Embodiment 2)
With reference to FIGS. 4 and 5, another embodiment of the liquid ejection apparatus applicable to the image forming apparatus of the present invention will be described. The head tank 80 of the liquid ejection apparatus shown in FIG. 4 is reduced in size and weight by removing the pressure sensor 104, the spring 108, and the filler 106 from the head tank 101 of the liquid ejection apparatus shown in FIGS. It is a thing. The ink cartridge 81 is provided with an air opening 79 at the top. In the head tank 101 shown in FIG. 2, a part of the wall surface is formed by the film member 107 to have a variable volume structure, and the spring 108 is urged to expand the volume to obtain a negative pressure. In the present embodiment, as shown in FIG. 4, the ink cartridge 81 released to the atmosphere and the head tank 80 are connected by the liquid supply tube 16, and the water head difference h between the liquid surface in the ink cartridge 81 and the nozzle surface of the recording head 1. I try to get negative pressure.

  The air layer above the head tank 80 communicates with the exhaust tank 60 via the exhaust tube 112, and the exhaust tank 60 of the present embodiment has a tube connection portion 66 provided on the bottom surface portion and the top surface portion of the liquid storage portion 61. A pipe line 67 is provided. Further, the conduit 67 is provided with a contraction portion 64 having a reduced cross section in the vicinity of the connection portion with the liquid storage portion 61. Further, in the vicinity of the tube connection part 66 of the pipe line 67, an extension part 65 having a pipe line cross section is provided at a position higher than the liquid level of the sealing liquid 63 in the liquid storage part 61. The liquid reservoir 61 holds and holds a high-viscosity sealing liquid 63 such as glycerin, leaving the air layer 82 at the top. In addition, a pump 88 is connected to the upper part of the liquid reservoir 61 so as to communicate with the air layer 82 and be evacuated.

  FIG. 5A is an explanatory diagram showing the ink supply operation to the liquid ejection device shown in FIG. 4, FIG. 4A is before ink supply to the head tank 80, and FIG. 4B is after ink supply. Represents the state. In the state of FIG. 4A, the sealing liquid 63 is also contained in the pipe line 67 of the exhaust tank 60. From this state, the cap 83 is brought into close contact with the nozzle surface, the space between the nozzle surface and the cap 83 is sealed, and the pump 88 is driven to exhaust the air layer 82 of the exhaust tank 60 to a negative pressure. Then, the sealing liquid 63 in the pipe 67 is sucked toward the liquid storage unit 61 and gradually rises the liquid level of the sealing liquid 63 in the liquid storage unit 61. When the liquid level in the pipe 67 of the seal liquid 63 passes through the contraction part 64 and reaches the connection part with the bottom surface of the liquid storage part 61, the air drawn by the seal liquid 63 becomes bubbles, Evacuated and exhausted to the outside through the air layer 82 and the pump 88. In this state, the rise in the liquid level of the seal liquid 63 in the liquid storage unit 61 is stopped, and only the air in the head tank 80 is exhausted. When the pump 88 is continuously driven, the air in the head tank 80 is sucked into the seal liquid 63 through the exhaust tube 112 and exhausted from the pump 88.

  When the air in the head tank 80 is exhausted, the ink in the ink cartridge 81 is sucked into the head tank 80, and the air amount detection sensor 103b causes the ink liquid in the head tank 80 to be liquid as shown in FIG. When the surface is detected, the pump 88 is stopped. At this time, the lower part of the filter 109 in the head tank 80 is not filled with ink. Therefore, the pump 84 is driven to suck ink from the nozzle side of the recording head 1. Thereafter, the cap 83 is moved, the nozzle surface is wiped with a wiper (not shown), wiping is performed, a meniscus is formed on the nozzle, and the recording head 1 is ready for image formation.

  When discharging the cap or sucking the cap as a nozzle recovery operation, the inside of the head tank 80 becomes negative pressure, and a force that flows backward toward the head tank 80 acts on the seal liquid 63 in the exhaust tank 60. Since the fluid resistance at which ink is supplied from the ink cartridge 81 to the head tank 80 is sufficiently smaller than the resistance at which the seal liquid 63 passes through the contraction portion 64, the seal liquid 63 does not flow backward and is shown in FIG. The state of the sealing liquid 63 shown is maintained. When the viscosity of the seal liquid 63 is small or when the amount of suction from the cap 83 is large, an expansion portion 65 is provided to function as a buffer for preventing the backflow of the seal liquid 63 to the head tank 80 during cap suction. Can do. In the present embodiment, since the air layer of the head tank 80 is liquid-sealed using the sealing liquid 63, sealing performance is not required when the pump 88 is not driven, so that the pump 88 is simple and inexpensive. Can do. Further, with only one pump 88, a stable negative pressure can be formed on the recording head 1 due to the water head difference between the head tank 80 and the ink cartridge 81, and air can be discharged. Can be realized.

(Embodiment 3)
With reference to FIGS. 6 and 7, another liquid ejecting apparatus applicable to the printer will be described. The head tank 80 of the liquid ejection apparatus shown in FIG. 6 has the same configuration as the liquid ejection apparatus of the embodiment shown in FIG. 4, but the buffer tank 70 is connected to the head tank 80 via the liquid supply tube 16. Has been. The buffer tank 70 is provided with an air release valve 51 and an ink liquid level detection sensor 74 for managing the liquid level of the ink. The ink filtered by the filter 75 is supplied into the buffer tank 70 from the ink cartridge 76 by the pump 78. The

  The air release valve 51 is a normally open valve, and the water head between the liquid surface in the buffer tank 70 and the nozzle surface of the recording head 1 is the same as the liquid discharge device of the embodiment shown in FIG. A stable negative pressure is formed by the difference. An exhaust tube 112 is connected to the upper portion of the head tank 70. An exhaust tank 60 is connected to the other end of the exhaust tube 112. The exhaust tank 60 is substantially the same as the configuration shown in FIG. 4, but does not include the pump 88 that sucks the air in the air layer 82, and only the exhaust unit 62 made of a porous body 62 a is simplified. . A check valve 85 is provided in the middle of the exhaust tube 112. As shown in FIG. 7, the check valve 85 of the present embodiment has an umbrella valve 86 inside, and the umbrella valve 86 has a communication hole 87 with respect to the flow of the arrow E shown in FIG. The flow is blocked and stopped, and the flow of the arrow F shown in FIG. 7B has a function of allowing the fluid to flow by opening the communication hole 87 by deforming the umbrella valve 86.

  In the present embodiment, for example, air can easily flow through the exhaust tube 112 when ink is filled into the head tank 80 or when air is discharged from the head tank 80. In addition, when the ink is filled in the recording head 1 or the recovery operation is performed when the recording head 1 has an ejection failure, the nozzle face of the recording head 1 is sealed with a cap and the ink is sucked. Since the back flow of the tube 112 is closed, ink can be efficiently supplied to the recording head 1. Since the other end of the exhaust tube 112 is liquid-sealed with the sealing liquid 63 of the exhaust tank 60, the check valve 85 can be simplified. In this embodiment, since the check valve 85 is provided, for example, even when more nozzles are provided in the recording head 1 and ink suction from the nozzles has to be performed more strongly, the air from the exhaust tube 112 is used. And the back flow of the sealing liquid 63 can be prevented.

(Embodiment 4)
An image forming apparatus according to an embodiment of the present invention will be described with reference to FIGS. FIG. 8 shows four different colors (black, cyan, magenta, yellow) of the head array unit 100 (100K, 100C, 100M, 100Y) as a liquid discharge head having a length corresponding to the maximum paper width to be conveyed. Each of the four line printers is shown. The four head array units 100 are fixed to the head frame 36, and can be moved up and down simultaneously by four heads by a head lifting mechanism (not shown).

  As in the head array unit shown in FIG. 9, the head array unit 100 has a plurality of short recording heads 1 (six heads 1a to 1f in FIG. 9) arranged in a staggered manner on a head fixing member 20 as a head tank. It is formed by positioning and fixing. Each recording head 1 is a thermal liquid ejection head as shown in FIG. 10 as in the previous embodiment.

  As shown in FIG. 10, the recording head 1 is a thermal type that obtains a discharge pressure by ink film boiling by driving the heating element 4, and the ink to the discharge energy action part (heating element part) in the liquid chamber 6. This is a side shooter type configuration in which the flow direction of the nozzle 5 and the central axis of the opening of the nozzle 5 are perpendicular to each other. As the recording head 1, there are various methods such as a method in which a diaphragm is deformed using a piezoelectric element or a diaphragm is deformed by an electrostatic force to obtain a discharge pressure, and any method is applied to the present invention. However, while the thermal head method has the advantage of easily increasing the nozzle density, it is easy to generate air in the head in principle, and the problem of air discharge is larger than other methods. Is big. Among other thermal head methods, there is an edge shooter method in which the discharge direction is different, but in this edge shooter method, there is a problem of so-called cavitation phenomenon in which the heating element 4 is gradually destroyed by the impact when air disappears. There is. In the side shooter system, air grows, and when the air reaches the nozzle 5, the air is communicated with the atmosphere, so that the air does not contract due to a temperature drop. Therefore, there is an advantage that the life of the recording head is long. Further, there is a structural advantage that the energy from the heating element 4 can be more efficiently converted into the kinetic energy of ink droplet formation and flight, and the meniscus can be quickly restored by supplying ink. Therefore, the side shooter system is adopted in this apparatus.

  A cross-sectional view of the head array unit 100 shown in FIG. 9 in the virtual plane A is shown in FIG. FIG. 11 is a cross-sectional view of the section A of FIG. 9 as viewed from the exhaust port 12 side. A liquid supply path 21 for supplying ink as liquid to the recording head 1 through the liquid supply port 22 is provided inside the head fixing member 20. Is formed. An air amount detection sensor 103 that detects the amount of air in the liquid supply passage 21 is provided above the liquid supply passage 21. The air amount detection sensor 103 in FIG. 11 is an electrode pair, and the tips thereof are provided at different positions so that a plurality of liquid surface states can be detected. FIG. 12A shows a cross-sectional view of the head array unit 100 in the HH cross section of FIG. 11, and FIG. 12B shows a cross-sectional view of the head array unit 100 in the GG cross section. As shown in FIG. 12, the liquid supply path 21 communicates with all the recording heads 1, and is provided with a liquid supply port 13 at one end and an exhaust port 12 at the other end so that ink can be supplied to the outside. It is a form supplied from. The liquid supply port 13 is provided in the vicinity of the bottom surface of the liquid supply path 21, and the exhaust port 12 is provided in the vicinity of the top surface of the liquid supply path 21.

  In this embodiment, since a thermal head is mounted, the material of the head fixing member 20 is preferably a material having good thermal conductivity. For example, when formed of a material having a high thermal conductivity such as metal, the heat generated from the recording head 1 can be effectively taken away to prevent heat storage of the recording head 1. As a material having a high thermal conductivity, a resin filled with a thermal conductive filler such as silica, alumina, boron nitride, magnesia, aluminum nitride, or silicon nitride is also suitable. When a resin material is used, it can be formed integrally with each port, liquid supply path, etc., and productivity is improved. Also, a foam metal such as SUS (for example, one having a preliminary diameter of 600 μm and a porosity of about 95%) has a large contact area with the temperature control liquid, and is therefore suitable as a material used for the temperature control fluid channel. Further, it is also effective to form a portion of the head fixing member 20 that fixes the recording head 1 with a high heat transmission material such as a metal, and to form the liquid supply path 21 with an inexpensive resin molded product and laminate them together. is there.

  An ink supply form to the head array unit 100 will be described with reference to FIG. In FIG. 13, a buffer tank 70 has a function of supplying ink to the head array unit 100 and receiving air and discharging it to the outside, and has an ink chamber having an air release port 73 connected to the air release valve 51 at the top. 71 is provided. A liquid level detection sensor 74 is provided above the ink chamber 71. The liquid level detection sensor 74 has the same structure as the air amount detection sensor 103 of the above-described embodiment, and is configured to detect two liquid levels having different heights. The liquid level detection sensor 74 is not limited to the electrode pair system of the present embodiment, and other systems such as a liquid level detection method using a float member and an optical liquid level detection method may be used.

  An ink cartridge 76 is connected to the ink chamber 71, and the ink filtered by the filter 75 can be replenished to the ink chamber 71 of the buffer tank 70 by the pump 78. An ink port is provided on the bottom surface of the ink chamber 71 and is connected to the liquid supply port 13 of the head fixing member 20 of the head array unit 100. The amount of ink in the ink chamber 71 is managed by the liquid level detection sensor 74 so that the head difference h between the ink liquid level and the head array unit 100 becomes a constant value (approximately 10 to 150 mm). On the other hand, an exhaust tube 112 is connected to the exhaust port 12 of the head fixing member 20, and the other end is connected to a tube connection portion 66 of an exhaust tank 60 as an air discharge container. Inside the exhaust tank 60, a liquid storage part 61 in which the seal liquid 63 is stored is provided, and a bottom part of the liquid storage part 61 and a tube connection part 66 are formed by a pipe 67 formed integrally with the exhaust tank 60. It has a connected structure. The conduit 67 is provided with a contraction portion 64 in the vicinity of the connection portion with the liquid storage portion 61. Further, an expansion portion 65 is provided in the vicinity of the tube connection portion 66 of the pipe line 67 at a position higher than the liquid surface of the high-viscosity liquid 63 in the liquid storage portion 61.

  The upper part of the liquid storage part 61 is an exhaust part made of a porous material such as a highly foamed resin, a porous resin film, a foamed metal, a metal mesh, or a porous ceramic, and air can freely enter and exit. .

  Here, a method of filling the exhaust tank 60 with the high viscosity liquid 63 will be described with reference to FIG. First, as shown in FIG. 14A, the tube connecting portion 66 is sealed with a sealing member 68. As a sealing method, various methods such as a method of sticking an elastic member such as rubber or a method of sticking an adhesive tape can be used. Next, the sealing liquid 63 is poured into the liquid reservoir 61 from the opening 62 at the top of the liquid reservoir 61 (see FIG. 14B). At this time, since the tube connection portion 66 is sealed, the high viscosity liquid 63 does not flow into the contraction portion 64 of the pipe line 67 provided at the bottom of the tank. Next, as shown in FIG. 14 (c), the opening 62 at the top of the liquid reservoir 61 is covered with a porous body 62a, and a sealing member 69 is provided thereon to cover the top of the porous body 62a. Seal. As the sealing member 69, an adhesive tape is suitable. Finally, the sealing member 68 is removed as shown in FIG. The sealing member 69 needs to be removed later, but is preferably removed immediately before the printer is operated.

  Next, ink supply and air discharge of the printer of this embodiment will be described with reference to FIG. FIG. 15A shows a state in which neither the buffer tank 70 nor the head array unit 100 contains ink. When the sealing member 69 is removed from the exhaust tank 60, the atmosphere release valve 51 connected to the buffer tank 70 is opened and the pump 78 is driven, the ink in the ink cartridge 76 is filtered by the filter 75, and the buffer tank 70. Flow into. The ink level in the buffer tank 70 rises, and the liquid level detection sensor 74b stops the pump 78 in the state of FIG. 15B in which the liquid level is detected. Next, when the atmosphere release valve 51 is closed, the exhaust valve 52 is opened, and the pump 78 is driven again, the ink is supplied to the head array unit 100 through the liquid supply tube 16. At this time, the air in the liquid flow path 21 in the head array unit 100 is pushed out to the exhaust tube 112 and is discharged from the exhaust unit 62 through the high viscosity liquid 63 in the exhaust tank 60. When the air amount detection sensor 103b in the liquid flow path 21 detects the liquid level, the exhaust valve 52 is closed. In this state, the inside of the liquid flow path 21 becomes a positive pressure by the action of the pump 78, and the ink in the liquid flow path 21 is forcibly filled in each recording head 1. After performing this filling state for a predetermined time, the pump 78 is stopped. After that, if the air release valve 51 and the exhaust valve 52 are opened and the nozzle surface is wiped to form a meniscus on the nozzle, a water head difference indicated by h in FIG. 13 is obtained, and the head array unit 100 can eject ink. .

  The conveyance of the recording paper of the printer of this embodiment will be described with reference to FIG. A recording sheet on which an image is recorded with ink is conveyed immediately below the head array unit 100. The recording sheets are stacked and held on the sheet feeding tray 38, and are fed one by one by a separation sheet feeding mechanism (not shown), conveyed by the sheet conveying belt 30, and discharged onto the sheet discharge tray 39 after recording is completed. The paper conveying belt 30 is stretched by a belt conveying roller 31 and a tension roller 32. The surface layer is a high resistance layer made of a resin material, and the back layer is a medium resistance layer 2 in which a resin material is subjected to resistance control by carbon. Layer structure. The paper conveying belt 30 is in contact with a charging roller 33 in which an intermediate resistance layer is formed on the outer layer of the metal roller and a thin high resistance layer is formed on the outermost layer. By applying a high voltage to the charging roller 33, Discharge occurs in the air gap near the nip between the paper transport belt 30 and the charging roller 33, and charges are deposited on the paper transport belt. When the voltage applied to the charging roller 33 is a positive and negative AC voltage, positive and negative charges are alternately attached in a stripe pattern on the paper transport belt. When the recording paper is supplied to the paper transport belt 30 thus charged, the recording paper is attracted to the paper transport belt 30 by electrostatic force. Since printing can be performed with the recording paper firmly held on the paper conveyance belt 30, stable printing quality can be obtained even when printing is performed while conveying the paper at high speed. In this embodiment, the sheet is conveyed using an electrostatic adsorption belt. However, a high-speed and satisfactory image can be formed even by a system in which a recording sheet is adsorbed to the belt by air adsorption.

  Since ink consumed by printing is naturally supplied from the buffer tank 70, the liquid level in the buffer tank 70 is lowered as printing progresses. When it is detected that the liquid level has fallen below the tip of the liquid level detection sensor 74a, the pump 78 is driven while the air release valve 51 is open, and the buffer tank 70 is replenished with ink. By doing so, the water head difference h can always be maintained within a predetermined range, and stable image formation can be performed. In addition, when the print duty is large and the ink supply is insufficient only by the pumping action by the ink ejection from the recording head 1, the air release valve 51 and the exhaust valve 52 are closed and the pump 78 is finely driven to support the ink supply. You can also do it.

  During image formation, the pressure that acts to supply ink from the liquid supply tube 16 due to the pumping action that accompanies the drive of the recording head 1 also acts on the exhaust tube 112 side, and works in the direction that causes air to flow backward. However, since the tip of the exhaust path is liquid-sealed by the sealing liquid 63, the sealing liquid 63 needs to flow toward the liquid supply tube 112 in order for air to flow backward. In the exhaust tank 60, a contraction portion 64 is formed, and the viscosity of the sealing liquid 63 that is liquid-sealed is high, so that the fluid resistance when the sealing liquid 63 flows backward from the exhaust tank 60 is supplied by ink through the liquid supply tube 16. Since the fluid resistance is much larger than the fluid resistance at the time, the high-viscosity liquid 63 does not flow backward.

  A recovery method in the case where desired image quality cannot be obtained due to head clogging or the like will be described. When head clogging, ink ejection bending, or the like occurs, the head array unit 100 is restored. The head array unit 100 is moved upward from the state shown in FIG. 8, and the maintenance unit 35 is moved in the horizontal direction (moved rightward in the drawing from the state shown in FIG. 8) to be arranged directly below the head array unit 100. Then, the head array unit 100 is slightly lowered so as to be in close contact with the cap 40 of the maintenance unit 35 as shown in FIGS. In this state, the air release valve 51 and the exhaust valve 52 are closed and the pump 78 is driven to feed a certain amount of ink into the head array unit 100. Since the air release valve 51 and the exhaust valve 52 are closed, the ink is discharged from the nozzles 5 of the head array unit 100. Together with the discharged ink, air and foreign matters that cause clogging of the head are removed. After stopping the pump 78, the head array unit 100 is raised to a level at which the head array unit 100 is not in contact with the cap, and the maintenance unit 35 is moved in the horizontal direction (from the state shown in FIG. 17 to the right in the drawing). As shown, the nozzle surface of the head array unit 100 is wiped by the wiper blade 41. After a meniscus is formed in the nozzle 5 by wiping, the air release valve 51 and the exhaust valve 52 are opened, and the head array unit 100 is maintained in a negative pressure state corresponding to the water head difference h. Since the ink discharged from the head array unit 100 is accumulated in the cap 40, the ink is sucked with a pump and discharged to the waste liquid tank 44. If the ink in the cap is filtered using a filter, the sucked ink can be reused by returning it to the buffer tank 70 instead of the waste liquid tank 44. Thereafter, the recording operation is performed in the state shown in FIG. 8 by raising and lowering the head array unit 100 and the horizontal movement of the maintaining unit 35, or waits until a recording instruction is given in the state shown in FIG. By this recovery operation, clogging is eliminated and the head array unit 100 can be maintained in a good state.

  The air discharge from the liquid supply path 21 of the head array unit 100 will be described. In an apparatus for forming an image by ejecting ink, air is gradually introduced into the ink supply path over time due to air permeation of members constituting the liquid supply path, moisture permeability, or air mixing into the path when the cartridge is attached or detached. Accumulates. In the case of this embodiment, air accumulates in the liquid supply path 21 of the head array unit 100. If the amount of accumulated air exceeds a certain amount, it becomes necessary to exhaust air because it causes problems due to temperature changes and poor ink ejection due to air mixing into the recording head 1 as described above. In the case of the present embodiment, the air discharge operation is performed when it is detected that the liquid level is lower than the tip of the air amount detection sensor 103a in the liquid supply path 21 shown in FIG. Specifically, the air release valve 51 of the buffer tank 70 is closed and the pump 78 is driven. Thereby, the air in the liquid supply path 21 is pushed out to the exhaust tube 112 by the ink supplied from the ink cartridge 76, and the air is discharged from the exhaust tank 60. When the air amount detection sensor 103b detects the liquid level in the liquid supply path 21, the pump 78 is stopped and the atmosphere release valve 51 is opened. As a result, the amount of air in the liquid supply passage 21 is returned to an appropriate amount, and stable image formation can be performed.

FIG. 1 is a schematic configuration diagram of an image forming apparatus (inkjet printer) according to the present invention; (a) is a front view, (b) is a side view, and (c) is a plan view. Structural diagram of the head tank; (a) is a transverse sectional view, and (b) is a longitudinal sectional view. Schematic diagram of an embodiment of a liquid ejection apparatus of the present invention; (a) before ink supply, (b) during ink supply, (c) represents an ink supply completion state. Schematic of other embodiment of the liquid ejection apparatus of the present invention FIG. 4 is an explanatory diagram of an ink supply operation to the liquid ejection apparatus; (a) shows before ink supply, and (b) shows that ink is being supplied. Schematic of other embodiment of the liquid ejection apparatus of the present invention Check valve operation explanatory diagram Configuration diagram of a line printer which is an image forming apparatus of the present invention Perspective view of the head array unit Cross section of recording head A side sectional view of the head array unit shown in FIG. FIG. 9 is a longitudinal sectional view of the head array unit shown in FIG. 9; (a) is a vertical sectional view, and (b) is a horizontal sectional view. Schematic of the liquid ejection apparatus of the present invention including the head array unit shown in FIG. Explanatory drawing of filling method of high viscosity liquid into exhaust tank FIG. 13 is an explanatory diagram of ink supply in the liquid ejection apparatus shown in FIG. 13; (a) shows a state before ink supply, and (b) shows a state in the middle of ink supply. Explanatory drawing of the recovery operation of the head array unit shown in FIG. Illustration of recording head capping Illustration of recording head wiping

Explanation of symbols

1: Recording head (liquid ejection head)
4: Heating element 5: Nozzle 6: Liquid chamber 8: Paper 12: Exhaust port 13: Liquid supply port 16: Liquid supply tube 20: Head fixing member 21: Liquid supply path 22: Liquid supply port 30: Paper transport belt 31: Belt transport roller 32: Tension roller 33: Charging roller 35: Maintenance unit 38: Paper feed tray 39: Paper discharge tray 40: Cap 41: Wiper blade 44: Waste liquid tank 51: Air release valve 52: Exhaust valve 60: Exhaust tank ( Air discharge container)
61: Sealing liquid storage part 62: Exhaust part 62a: Porous body 63: Sealing liquid 64: Contraction part 65: Expansion part 66: Tube connection part 67: Pipe line 68: Sealing member 69: Sealing member 70: Buffer tank 71: Ink chamber 73: Atmospheric opening 74, 74a, 74b: Liquid level detection sensor 75: Filter 76: Ink cartridge 77: Cartridge holder 78: Pump 79: Atmospheric opening 80: Head tank 81: Ink cartridge 82: Air layer 83: Cap 84: Pump 85: Check valve 86: Umbrella valve 87: Communication hole 88: Pump 100, 100K, 100C, 100M, 100Y: Head array unit 101: Head tank 103, 103a, 103b: Air amount detection sensor 104 : Pressure sensor 106: Filler 107: Film member 1 08: Spring 109: Filter 110: Ink supply port 111: Exhaust port 112: Exhaust tube 120: Carriage 122: Guide rod 123: Side plate 125: Conveying roller 126: Pressing roller 128: Paper guide part

Claims (14)

A liquid discharge head having a nozzle and discharging liquid from the nozzle;
A head tank containing the liquid and having a lower portion communicating with the liquid discharge head;
A liquid ejecting apparatus comprising a feeding means for feeding the liquid to the head tank,
An air discharge container for discharging the air in the head tank to the atmosphere through a stored seal liquid;
One end opened to the air layer above the head tank, the other end opened to the seal liquid in the air discharge container, and an air discharge pipe having an extended portion at a position higher than the liquid level of the seal liquid ;
A liquid ejection apparatus comprising: A liquid discharge head having a nozzle and discharging liquid from the nozzle;
A head tank containing the liquid and having a lower portion communicating with the liquid discharge head;
A liquid ejecting apparatus comprising a feeding means for feeding the liquid to the head tank,
An air discharge container for discharging the air in the head tank to the atmosphere through a stored seal liquid;
One end opened to the air layer above the head tank, the other end opened to the seal liquid in the air discharge container, and an air discharge pipe having a contraction part in the vicinity of the communicating part with the seal liquid ;
A liquid ejection apparatus comprising: A liquid discharge head having a nozzle and discharging liquid from the nozzle;
A head tank containing the liquid and having a lower portion communicating with the liquid discharge head;
A liquid ejecting apparatus comprising a feeding means for feeding the liquid to the head tank,
An air discharge container for discharging the air in the head tank to the atmosphere through a stored seal liquid;
One end opens to the air layer above the head tank, the other end opens to the sealing liquid in the air discharge container, and a check that prevents the sealing liquid in the air discharge container from flowing into the head tank An air exhaust pipe with a valve ;
A liquid ejection apparatus comprising: A liquid discharge head having a nozzle and discharging liquid from the nozzle;
A head tank containing the liquid and having a lower portion communicating with the liquid discharge head;
A liquid ejecting apparatus comprising a feeding means for feeding the liquid to the head tank,
An air discharge container for discharging the air in the head tank to the atmosphere through a stored seal liquid;
One end is open to the air layer above the head tank, and the other end is provided with an air discharge pipe that opens into the sealing liquid in the air discharge container,
The liquid discharge apparatus according to claim 1, wherein the one end of the air discharge pipe is disposed above a liquid surface of the sealing liquid in the air discharge container . The liquid discharge apparatus according to claim 1, wherein an upper portion of the air discharge container is open to the atmosphere. 6. The liquid ejection device according to claim 1, wherein an upper portion of the air discharge container is opened to the atmosphere via a porous body. The sealing liquid is a liquid ejecting apparatus according to any one of claims 1 to 6, wherein the viscosity or density is greater than the liquid. The sealing liquid is a liquid ejecting apparatus according to any one of claims 1 to 7, characterized in that a non-volatile or low-volatility liquids. The head tank is provided with an elastic member that is formed of a flexible film at least a part of the surface and urges the flexible film in a direction of increasing the volume of the head tank. Item 9. The liquid ejection device according to any one of Items 1 to 8 . It said feeding means is a liquid ejecting apparatus according to any one of claims 1 to 9, characterized in that connected to the air open freely buffer tank. The other end of the air discharge pipe, the liquid ejecting apparatus according to any one of claims 1 to 10, characterized in that in communication with the sealing liquid opens into the bottom of the air discharge vessel. The liquid discharge according to any one of claims 1 to 11 , wherein the air discharge pipe includes a backflow prevention means for preventing the sealing liquid in the air discharge container from flowing into the head tank. apparatus.   The liquid ejection apparatus according to claim 1, wherein the head tank includes a liquid level detection unit that detects a liquid level of the liquid.   An image forming apparatus comprising the liquid ejection device according to claim 1.

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