JP2010012637A - Image formation system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent air from being sucked into a head from a nozzle as ink is cooled and contracted at the time of non-heating control by simple configuration in an image formation system which ejects ink while heating. <P>SOLUTION: The image formation system comprises: a print head unit 100 which is equipped with print heads 1A-1F each having a means for controlling the heating of ink and a nozzle for ejecting ink; and a means for supplying ink to the print head unit 100. In the system, the print head unit 100 has an ink inlet 21 through which ink supplied from the ink supply means is made to flow and an ink discharge port 22, the ink inlet 21 is connected with the ink supply means through a first on/off valve V1, the ink discharge port 22 is opened to the atmosphere through a second on/off valve V2, and a means is provided for controlling the first on/off valve V1 and the second on/off valve V2 at least according to the control state of the heating control means. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image forming apparatus in which ink supplied to a print head is heated and ejected from a nozzle, and more specifically, air in the head due to cooling and contraction of ink and bubbles during non-heating control. The present invention relates to an image forming apparatus capable of preventing pull-in.

  A common flow path member (distributor) that supplies ink to each of a plurality of print heads in an image forming apparatus that records and forms various images by ejecting ink from nozzles provided in the print head And a print head unit is known in which a plurality of print heads and a common flow path member are connected in parallel through branch flow paths (Patent Document 1). In such an image forming apparatus, even if the number of print heads increases, ink can be supplied to all the print heads by simply connecting the ink tanks to the common flow path member with a single tube. Has advantages.

  Incidentally, the image forming apparatus may use high viscosity ink such as ultraviolet curable ink. Since high-viscosity ink cannot be stably ejected from the nozzle as it is, the ink is heated to a predetermined temperature by using a heating means such as a heater generally provided in the print head during image formation. A method is adopted in which the viscosity is lowered to a predetermined viscosity at which stable discharge is possible.

  However, when the main power supply of the image forming apparatus is turned off, the ink and bubbles previously heated by the heater are gradually cooled and contracted, and the inside of the print head becomes a negative pressure exceeding the allowable level, and the ink meniscus is generated. There is a problem that the nozzle is greatly drawn into the nozzle and breaks. In general, an image forming apparatus temporarily stores ink from an ink tank or the like in an intermediate tank, and supplies the ink to the print head through the intermediate tank, whereby a predetermined back pressure is applied to the print head by the intermediate tank. However, when the main power of the image forming apparatus is turned off, not only the heater but also the back pressure control by this intermediate tank is turned off, so no back pressure is applied to the print head. As a result, the ink meniscus is drawn into the nozzle due to the cooling and contraction of ink and bubbles.

  FIG. 8 shows the result of measuring the back pressure of the print head portion by a sensor provided in the middle of the branch flow path from the common flow path member to each print head. As shown in this figure, when both the heater and the back pressure control are turned off by turning off the main power supply of the image forming apparatus, the ink and bubbles in the print head are cooled and contracted to gradually reduce the pressure. The pressure changes to (-20 to -30 cmAq). Along with this, the ink meniscus of the nozzle tends to be drawn into the print head, but it becomes unbearable at some point and breaks, and external air enters from the nozzle. The inside of the print head once becomes positive pressure due to air entering, but gradually becomes negative pressure again due to cooling and contraction of ink and bubbles, etc., and such negative pressure is maintained until the ink temperature is in equilibrium with the outside air temperature. The positive pressure recovery operation is repeated. When the heater and the back pressure control are both turned on by turning on the main power supply, the pressure in the print head is recovered.

  When a large amount of air is drawn into the print head in this way, it cannot be easily discharged by normal pressure maintenance that forcibly discharges ink from the nozzle, and it takes time to recover and a large amount of air is required. There is a problem that ink is consumed wastefully.

  Patent Document 1 does not disclose solving the problem that air is drawn from the nozzle due to the phenomenon of drawing the ink meniscus into the nozzle accompanying the cooling and contraction of the ink and bubbles.

  On the other hand, in Patent Document 2, an air release valve is provided in the middle of the ink supply path from the sub tank to the print head, and the negative pressure generated in the ink supply path due to ink suction is eliminated by opening the air release valve. Techniques to do this are disclosed. Accordingly, it is conceivable that the negative pressure in the print head that is generated due to cooling or contraction of ink or bubbles is also eliminated by providing an air release valve in the middle of the ink supply path and opening it. .

  However, the negative pressure state in the print head caused by ink suction is canceled almost instantaneously by the opening operation of the air release valve and returns to the normal pressure, but occurs with the cooling and contraction of ink and bubbles. The negative pressure condition in the print head continues until the ink temperature is in equilibrium with the ambient temperature, which causes the air release valve to continue to open. Therefore, since this air release valve is on the ink supply path from the sub tank to the print head, a large amount of air is drawn into the ink supply path until the negative pressure is eliminated, and then the ink supply is started. There is a problem that a large amount of air drawn into the ink supply path is supplied to the print head as it is.

  Patent Document 3 discloses a technique for solving a problem caused by cooling or contraction of ink, bubbles, or the like by applying a predetermined pressure in the ink flow path of the print head in conjunction with stopping energization of the heater. Has been.

  However, since the shrinkage amount of ink and bubbles changes depending on the degree of cooling, if the pressure is not adjusted in accordance with this change, there is a risk of air drawing from the nozzle or ink outflow from the nozzle, and the pressure state is strictly Therefore, there is a problem that a high-level control means is required for the control.

Moreover, once the heater is deenergized, it takes a certain waiting time for the heater to rise to a predetermined temperature, and during that time the printing operation is stagnant. Therefore, as long as the main power of the image forming apparatus is on, the energization is continued. It is preferable to keep it. Therefore, when the main power supply of the image forming apparatus is turned off and the energization to the heater is stopped, a configuration in which a predetermined pressure is applied to the ink flow path of the print head as in Patent Document 3 is a pressure application. It is necessary to provide a power supply of a different system from the image forming apparatus, and there is a problem that the structure becomes complicated and the cost is increased.
JP-A-63-254048 JP-A 64-87354 JP-A-8-281935

  Accordingly, the present invention provides an image forming apparatus in which ink supplied to a print head is heated and ejected from a nozzle, with a simple configuration, from a nozzle caused by cooling or contraction of ink or bubbles during non-heating control. It is an object to prevent air from being drawn into the head.

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

  The above problems are solved by the following inventions.

  According to a first aspect of the present invention, there is provided a print head unit having a print head having a heating control means for controlling the heating of ink and a nozzle for discharging ink, and an ink supply for supplying ink to the print head unit. The print head unit has an ink inlet for allowing ink supplied from the ink supply means to flow in, and an ink outlet for discharging ink. The ink supply port is connected to the ink supply means via a first on-off valve, and the ink discharge port is opened to the atmosphere via a second on-off valve, and at least according to the control state of the heating control means. An image forming apparatus comprising valve control means for controlling one on-off valve and the second on-off valve.

  According to a second aspect of the present invention, the valve control means controls the first on-off valve to be closed and the second on-off valve to be opened when the ink is not heated by the heating control means. The image forming apparatus according to claim 1.

  3. The image forming apparatus according to claim 1, wherein the second on-off valve is an electromagnetic valve that operates to open the flow path when power is not supplied. It is.

  According to a fourth aspect of the present invention, the ink supply means includes an intermediate tank that is controlled so as to apply a predetermined back pressure to the print head by storing a predetermined amount of ink, The ink inlet of the print head unit is connected via the first on-off valve, and back pressure control for the print head by the intermediate tank is performed during non-heating control of the ink by the heating control means. 4. The image forming apparatus according to claim 1, wherein the image forming apparatus is not performed.

  According to a fifth aspect of the present invention, the print head unit is constituted by one or a plurality of the print heads, stores ink supplied from the ink supply means, and stores one or a plurality of the print heads. A common flow path member for commonly supplying the ink via a branch flow path connected to a side surface or a lower surface, and the ink inlet and the ink discharge port are provided in the common flow path member. The valve control means opens the first on-off valve and the second on-off valve for a predetermined time when ink is supplied by the ink supply means prior to ink discharge from the print head. The image forming apparatus according to claim 1, wherein ink containing bubbles in a common flow path is discharged from the ink discharge port.

  According to a sixth aspect of the present invention, the ink inlet and the ink outlet are provided on a lower surface of the common flow path member, and an upper end opening is disposed close to a ceiling surface inside the common flow path member. And an ink discharge channel is formed for discharging the air in the common channel from the upper end opening toward the ink discharge port together with the ink and discharging the ink from the ink discharge port. The image forming apparatus according to claim 5.

  According to a seventh aspect of the present invention, a concave portion is formed on the ceiling surface in the common flow channel member at a position facing the upper end opening of the ink discharge flow channel, and the concave portion is formed of the ink discharge flow channel. The image forming apparatus according to claim 6, wherein the image forming apparatus is formed in a size so as to cover the upper end opening.

  According to an eighth aspect of the present invention, the ink inlet and the ink outlet are spaced apart from each other on one end side and the other end side in the length direction of the common channel member, 8. The image forming apparatus according to claim 5, wherein the ceiling surface is inclined so as to become higher from a position facing the ink inlet to a position facing the upper end opening of the ink discharge channel. Device.

  The invention according to claim 9 is characterized in that the ink supply port of the print head is disposed below the connection position of the branch flow path in the common flow path member. An image forming apparatus as described above.

  According to a tenth aspect of the present invention, the print head unit is connected to an ink inflow pipe and an ink discharge pipe provided in an image forming apparatus body with respect to the ink inlet and the ink outlet of the common flow path member. The image forming apparatus according to claim 5, wherein the image forming apparatus is attached by being detachably fitted.

  According to the present invention, in the image forming apparatus in which the ink supplied to the print head is heated and ejected from the nozzle, the air from the nozzle to the head due to the cooling or contraction of the ink or bubbles during the non-heating control. Can be prevented.

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

  FIG. 1 is a schematic configuration diagram showing an example of an image forming apparatus according to the present invention. The image forming apparatus includes a print head unit 100 having a plurality of print heads 1A to 1F and a common flow path member 2 that supplies ink in common to the print heads 1A to 1F. Each of the print heads 1A to 1F has a heater (not shown) built therein, and the energization is controlled by a heating control means (not shown), so that a high-viscosity ink such as ultraviolet curable ink sent from the common flow path member 2 is used. The ink can be heated and lowered to a viscosity that enables stable ejection from the nozzle.

  An ink inflow tube 200 is connected to the ink inlet 21 of the common flow path member 2. The ink inflow pipe 200 is connected to the intermediate tank 300 via an on-off valve V1 (first on-off valve) made of an electromagnetic valve, and can supply ink in the intermediate tank 300 to the common flow path member 2.

  The intermediate tank 300 is connected to the common flow path member 2 by the ink inflow pipe 200, and applies a predetermined back pressure to the print head unit 1 by the liquid level of the ink stored inside. SH1 is a liquid level reference position sensor, and SH2 is a liquid level upper limit sensor. The inside of the intermediate tank 300 is connected to an air release pipe 301 that is opened and closed by an on-off valve V3 made of an electromagnetic valve. Further, the back pressure in the intermediate tank 300 is detected by the back pressure air pressure sensor SP1 by opening the on-off valve V4 made of an electromagnetic valve. When the image forming apparatus is in operation, a predetermined back pressure is applied to the print head unit 1 by the ink level in the intermediate tank 300 by opening the on-off valve V3 connected to the atmosphere opening pipe 301.

  An ink cartridge 500 is connected to the intermediate tank 300 via an ink supply pipe 400, and the ink in the ink cartridge 500 can be supplied into the intermediate tank 300 by a predetermined amount by a supply pump 600. Here, two ink cartridges 501 and 502 are shown, and are connected to the ink supply pipe 400 by branch supply pipes 401 and 402, respectively. The branch supply pipes 401 and 402 are provided with open / close valves V5 and V6, respectively, which are electromagnetic valves, so that ink supply paths from the ink cartridges 501 and 502 can be selectively opened and closed. The ink supply pipe 400 is provided with a filter 403 so as to remove dust and the like in the ink. SP2 is an ink non-detection sensor for detecting the absence of ink from the ink cartridge 500.

  On the other hand, an ink discharge pipe 700 is connected to the ink discharge port 22 of the common flow path member 2. The ink discharge pipe 700 can be opened and closed by an on-off valve V2 (second on-off valve) made of an electromagnetic valve, and its discharge end 701 is open to the atmosphere.

  An ink tray 800 is disposed at a position facing the nozzle surface of each of the print heads 1A to 1F, and accepts ink droplets that are forcibly ejected from the nozzles of the print heads 1A to 1F by, for example, a maintenance operation. The liquid is discharged to the waste liquid tank 900 through the discharge channel 801. The ink discharged from the common flow path member 2 is also sent into the waste liquid tank 900 via the ink discharge pipe 700.

  The on-off valves V1 to V6 are all controlled to be opened and closed by valve control means (not shown).

  In such an image forming apparatus, when the print heads 1 </ b> A to 1 </ b> F are filled with ink, the ink supplied from the ink cartridge 500 by driving the supply pump 600 is supplied from the ink inflow pipe 200 via the intermediate tank 300. 2 and supplied from the common flow path member 2 to the print heads 1A to 1F. At this time, the on-off valve V1 of the ink discharge pipe 700 is opened together with the opening of the on-off valve V1 of the ink inflow pipe 200.

  Ink supplied from the intermediate tank 300 is stored in the print heads 1A to 1F from the common flow path member 2, and excess ink is sent to the waste liquid tank 900 through the ink discharge pipe 700. At this time, air that has entered the common flow path member 2 is discharged, and bubbles are prevented from entering the print heads 1A to 1F. When the print heads 1A to 1F are filled with ink in this way, the on-off valve V2 of the ink discharge pipe 700 is closed.

  The heaters in the print heads 1A to 1F are energized and controlled by the heating control means to heat the ink to a predetermined temperature. The image forming apparatus executes printing with the ink heated to the predetermined temperature. During printing, a predetermined amount of ink is supplied to the intermediate tank 300 by the supply pump 600 and stored, so that a predetermined back pressure is applied to each of the print heads 1A to 1F.

  Here, when the main power supply is turned off, for example, when the operation of the image forming apparatus is stopped, the heating control unit is in a non-controlled state, the power supply to the heaters in the print heads 1A to 1F is cut off, and the ink is not heated. At the same time, the on-off valve V1 of the ink inflow pipe 200 is closed, and the on-off valve V3 connected to the atmosphere release pipe 301 is also closed, whereby the back pressure control by the ink level in the intermediate tank 300 is stopped. . For this reason, the print heads 1A to 1F are almost sealed, and when the ink or bubbles in the heated state starts to cool, they gradually contract. Conventionally, the ink meniscus is brought into the nozzle along with the contraction. A phenomenon of pulling in occurred.

  Therefore, in the present invention, the valve control means controls the on-off valve V1 and the on-off valve V2 according to at least the control state of the heating control means. That is, when the main power supply of the image forming apparatus is turned off and the heater is turned off, the valve control unit opens the on-off valve V2 of the ink discharge pipe 700 in conjunction with this. At this time, the on-off valves V1, V3, V5, V6 are closed, and the on-off valve V4 is open.

  When the on-off valve V2 of the ink discharge pipe 700 is opened, back pressure fluctuations due to cooling and contraction of ink and bubbles generated in the print heads 1A to 1F are caused, and the ink in the ink discharge pipe 700 is interfaced with the atmosphere. Relax by moving the position.

  FIG. 2 is a graph showing the result of measuring the back pressure after the main power supply of the image forming apparatus is turned off. The back pressure was measured by a sensor provided in the middle of the flow path between one print head and the common flow path member 2. As a result, when the main power supply is turned off and the heater is turned off, the ink and air bubbles in the print head are cooled and contracted, resulting in a slight negative pressure. However, the ink is discharged when the main power supply is turned off. Since the opening / closing valve V2 of the pipe 700 is opened and the interface position of the ink in the ink discharge pipe 700 is moved to alleviate the back pressure fluctuation in the print head, the transition to the negative pressure state is extremely gradual. Only a very small change of about 2 cmAq is required. Thereby, it is suppressed that air is drawn from the nozzles of the print heads 1A to 1F, and the problem that the meniscus in the nozzles breaks does not occur.

  The inside of the ink discharge pipe 700 is closed when the ink is supplied to the extent that it overflows from the discharge end 701 of the ink discharge pipe 700 when the common flow path member 2 is filled with ink. It is in a full state. Further, the discharge end 701 of the ink discharge pipe 700 is below the position of the nozzle surface of each of the print heads 1A to 1F in order to keep the pressure on the nozzle surface when the on-off valve V2 is opened at an appropriate value of negative pressure. positioned. For this reason, there is no possibility that air enters the common flow path member 2 from the ink discharge pipe 700.

  The ink discharge pipe 700 is configured so that the ink in the ink discharge pipe 700 and the atmosphere correspond to back pressure fluctuations caused by cooling and contraction of ink and bubbles generated in the print heads 1A to 1F after the main power is turned off. Depending on the internal volume of each print head 1A to 1F, the internal volume of the common flow path member 2, the ink characteristics, etc., so that the interface position does not move to the ink discharge port 22 of the common flow path member 2. It is preferable to appropriately set the tube length and the tube diameter.

  The on-off valve V2 provided in the ink discharge pipe 700 is preferably an electromagnetic valve that operates to open the flow path when power is not supplied. This is because there is no need to add a special configuration, and the on-off valve V2 can be opened simply and inexpensively in conjunction with the main power supply OFF. Moreover, even if the power supply to the device is unexpectedly stopped due to some trouble such as a power supply trouble, the on-off valve V2 is opened, and a meniscus break or air generated by cooling or contraction of ink or air bubbles, etc. Pull-in can be prevented.

  Next, a specific configuration of the print head unit 100 preferable in the present invention will be described.

  FIG. 3 is a perspective view of the print head unit 100. The same reference numerals as those in FIG. 1 denote the same components.

  In the print head unit 100, a plurality of print heads 1 </ b> A to 1 </ b> F are fixed to a single plate-like head fixing member 3. Each of the print heads 1 </ b> A to 1 </ b> F ejects ink downward from the nozzles arranged in a large number on the nozzle surface located on the lower surface in the drawing, and is arranged in a staggered manner with respect to the head fixing member 3. ing. As a result, the print head unit 100 constitutes a line head that performs wide-width image recording in the width direction from the print head 1A to the print head 1F in one pass.

  One common flow path member 2 for supplying ink in common to the plurality of print heads 1 </ b> A to 1 </ b> F is also fixed to the head fixing member 3. The common flow path member 2 has a horizontally long box shape having a length substantially equal to the length in the width direction from the print head 1A to the print head 1F. A support plate 3b rising substantially vertically is attached to the attachment surface 3a of each print head 1A to 1F in the head fixing member 3, and the common flow path member 2 is attached to the head fixing member 3 by the support plate 3b. It is supported at a predetermined distance above 3a.

  One end of six branch pipes 4A to 4F for supplying ink inside the common flow path member 2 to each of the print heads 1A to 1F is connected to the common flow path member 2. The connecting portions of the branch pipes 4 </ b> A to 4 </ b> F are located below the side surface 2 a of the common flow path member 2, but may be connected to the lower surface 2 b of the common flow path member 2.

  The other ends of the branch pipes 4A to 4F are directed downward from the common flow path member 2, and are supplied with ink from the print heads 1A to 1F disposed below the position of the connection portion at one end of each branch pipe 4A to 4F. It is connected to the mouths 11A to 11F. In FIG. 3, only the ink supply port 11B of the print head 1B, the ink supply port 11D of the print head 1D, and the ink supply port 11F of the print head 1F are shown.

  4 is a cross-sectional view showing the internal structure of the common flow path member 2. FIG. 5 (a) is a cross-sectional view taken along the line aa in FIG. 4, and FIG. 5 (b) is a cross-sectional view taken along the line bb in FIG. FIG.

  Inside the common flow path member 2, a common flow path 23 for storing ink is formed in the length direction (left and right direction in FIG. 4). The ink inflow port 21 of the common flow path member 2 opens to one end in the length direction of the lower surface 2b, and the ink discharge port 22 opens to the other end of the lower surface 2b. 21a and 22a are packing, and 24A-24F is a connection part with branch pipe 4A-4F.

  The ink inlet 21 and the ink outlet 22 are formed so that the ink inlet pipe 200 and the ink outlet pipe 700 provided in the printer main body can be inserted and removed, respectively.

  A flow path wall 25 is formed around the ink discharge port 22 inside the common flow path member 2 and rises straight upward from the ink discharge port 22 toward the ceiling wall 23a of the common flow path 23. It is arranged close to the ceiling wall 23a so as to leave a slight gap with the wall 23a. As a result, an ink discharge channel 26 is formed in which ink flows downward from the upper end opening 26 a formed at the upper end of the channel wall 25 to the ink discharge port 22 and discharged to the outside.

  The ceiling wall 23a of the common flow path 23 gradually increases from a position facing the ink inlet 21 (right end in FIG. 4) to a position facing the upper end opening 26a of the ink discharge flow path 26 (left end in FIG. 4). It is inclined. For this reason, air (bubbles) that flows into the common flow path 23 and reaches the ceiling wall 23a is likely to naturally gather on the upper end opening 26a side of the ink discharge flow path 26 along the inclination. The inclination angle of the ceiling wall 23a is not particularly limited, but may be in the range of, for example, 1 to 6 ° with respect to the horizontal plane.

  Further, the surface of the ceiling wall 23a is preferably a smooth surface for smooth movement of air (bubbles), and more preferably has excellent affinity with ink. For this purpose, it is preferable to enhance the affinity with ink by surface-treating the ceiling wall 23a, or to form the common flow path member 2 using a material excellent in affinity with ink.

  A concave portion 27 is formed in the ceiling wall 23a at a position facing the upper end opening 26a of the ink discharge channel 26, so that the ceiling height is partially higher than the others. The size of the opening of the recess 27 is slightly larger than the outer diameter of the flow path wall 25 forming the ink discharge flow path 26, and is formed so as to cover the upper end opening 26 a including the flow path wall 25. Has been. The upper end opening 26 a of the ink discharge channel 26 is disposed in the recess 27 so as to be almost the same height as the ceiling wall 23 a around the recess 27 or slightly protruded into the recess 27. As a result, the discharge flow channel inlet 28 with a slight gap is opened downward so as to surround the outer periphery of the flow channel wall 25 between the upper peripheral edge of the flow channel wall 25 and the lower peripheral edge of the recess 27. Is formed. Reference numeral 23 b is a ceiling wall located in the recess 27 in the ceiling wall 23 a in the common flow path 23.

  The print head unit 100 is detachably mounted at a predetermined position in the ink jet printer so that the lower surface 2b of the common flow path member 2 is substantially horizontal. In one printer body, the ink inflow pipe 200 and the ink discharge pipe 700 have a distance corresponding to the separation distance between the ink inlet 21 and the ink outlet 22 of the common flow path member 2, and the tip is upward. It is arranged to become. Accordingly, the print head unit 100 is inserted into the ink inlet 21 and the ink outlet 22 formed in the common flow path member 2, and the ink inlet pipe 200 and the ink outlet pipe 700 are inserted and fitted into the printer main body. Installed. As a result, the connection for inflow and discharge of ink between the printer main body and the common flow path member 2 of the print head unit 100 can be completed. Since both the ink inlet 21 and the ink outlet 22 are opened on the lower surface 2b of the common flow path member 2, the ink inlet pipe 200 and the ink outlet pipe 700 can be obtained simply by moving the print head unit 100 downward. Can be fitted at a time, and the connection work can be performed very easily.

  Further, when removing the print head unit 100 from the printer main body, the print head unit 100 is simply moved so as to be pulled upward from the printer main body. The connection for inflow and discharge of the ink can be released at once, and the operation is similarly simple.

  After the print head unit 100 is mounted on the printer body, the ink is caused to flow into the common flow path member 2 via the ink inflow pipe 200 by operating the supply pump 600 shown in FIG. At this time, by opening the on-off valve V2 provided in the ink discharge pipe 700, the air in the common flow path 23 of the ink inflow pipe 200 and the common flow path member 2 is shared with the inflow of ink. The ink is discharged from the ink discharge pipe 700 through the ink discharge flow path 26 in the flow path member 2. The ink supply ports 11A to 11F of the print heads 1A to 1F to which the other ends of the branch pipes 4A to 4F are connected are arranged below the connection positions of the branch pipes 4A to 4F in the common flow path member 2. Therefore, even if air (bubbles) is mixed from the print heads 1A to 1F, the branch pipes 4A to 4F can be raised to flow into the common flow path 23 and discharged from the ink discharge flow path 26. .

  FIG. 6 shows an enlarged view of the common flow path member 2 in the vicinity of the ink discharge flow path 26, and the discharge of air (bubbles) in the common flow path member 2 will be further described using this.

  When ink flows into the common flow path 23 and the water level of the ink gradually rises, the internal air (bubbles) X is pushed to the discharge flow path inlet 28 by the inclination of the ceiling wall 23a and the inflow pressure of the ink. Air (bubbles) X that have reached the vicinity of the discharge channel inlet 28 are caused to flow into the ink due to the inclination of the ceiling wall 23a and the narrow clearance-like discharge channel inlet 28 opening downward. The ink flows into the recess 27 by the pressure, and further moves downward along with the ink from the ink discharge channel 26 while being pushed by the ink, and is discharged to the outside of the common channel member 2 through the ink discharge pipe 700. The discharged ink is collected in the waste liquid tank 900.

  In order to improve the discharge action of the air (bubbles) X, the relationship between the discharge channel inlet 28 and the recess 27 is such that the opening width of the discharge channel inlet 28 is D1, the bottom of the recess 27 and the ink discharge channel. When the distance from the upper end opening 26a of 26 is D2, it is preferable that D1 = D2, and 1.0 to 2.5 mm is appropriate for specific numerical values.

  Thereby, the common flow path 23 in the common flow path member 2 is filled only with ink without air (bubbles). In order to discharge the air (bubbles) in the common flow path member 2, only the ink inflow pressure generated by the operation of the supply pump 600 that is normally provided to supply ink to the common flow path member 2 is used. Therefore, it is not necessary to provide a special driving device for discharging air (bubbles) such as a suction means for sucking ink from the nozzles.

  Also, air (bubbles) that naturally rises in the common flow path 23 and collects at one location near the upper end opening 26a of the ink discharge flow path 26 is discharged downward from the position by the ink discharge flow path 26. Ink can be discharged by the shortest path, and ink consumed for discharging air (bubbles) can be minimized, so that waste of ink can be suppressed.

  After the air (bubbles) in the common flow path 23 is discharged in this way, the on-off valve V2 of the ink discharge pipe 700 is closed, and the supply pump 600 is operated to supply ink from the ink inflow pipe 200 to the common flow path member 2. Ink flows into the branch pipes 4A to 4F, and the air in the branch pipes 4A to 4F is discharged from the nozzles of the print heads 1A to 1F. As a result, all air in the flow path from the common flow path member 2 to each of the print heads 1A to 1F is discharged, and ink can be stably ejected from each of the print heads 1A to 1F.

  In addition, as described above, when the on / off valve V2 of the ink discharge pipe 700 is opened after the main power supply of the image forming apparatus is turned off, the ink discharge that moves with the cooling or contraction of ink, bubbles, etc. should be avoided. Even if air enters the common flow path member 2 when the interface position between the ink and the atmosphere in the tube 700 enters the common flow path 23 from the ink discharge port 22, the air that has entered the ink discharges the ink. It can be retained in the flow path 26 or in the vicinity of the recess 27. This air can be quickly discharged from the ink discharge channel 26 to the ink discharge pipe 700 when ink is supplied by driving the supply pump 600 at the next operation.

  FIG. 7 schematically shows another aspect of the image forming apparatus in which the print head unit 100 is mounted at a predetermined position of the printer main body. For simplicity of explanation, only the common flow path member 2 is shown in the print head unit 100.

  In this image forming apparatus, the waste ink in the waste liquid tank 900 is returned to the ink tank 503 between the waste liquid tank 900 for collecting the ink discharged from the common flow path member 2 and the ink tank 503 for storing the ink. A circulation pipe 901 for connecting is connected. A circulation pump 902 and a filter 903 are provided in the middle of the circulation pipe 901, and the circulation pipe 901, the circulation pump 902, and the filter 903 constitute a circulation unit.

  Thereby, the waste ink once collected in the waste liquid tank 900 from the common flow path member 2 can be supplied again to the common flow path member 2 via the ink tank 503. Since bubbles are removed from the waste ink collected in the waste liquid tank 900, ink without bubbles is returned to the ink tank 503.

1 is a schematic configuration diagram showing an example of an image forming apparatus according to the present invention. Graph showing change in back pressure of print head portion after main power OFF of image forming apparatus A perspective view showing an example of a print head unit Sectional view showing internal structure of common channel member (A) is the sectional view on the aa line of FIG. 4, (b) is the sectional view on the bb line of FIG. Sectional drawing which expands and shows the state of the ink discharge flow path vicinity in a common flow path member Schematic diagram showing another aspect of the image forming apparatus Graph showing change in back pressure of print head portion after main power OFF of conventional image forming apparatus

Explanation of symbols

DESCRIPTION OF SYMBOLS 100: Print head unit 1A-1F: Print head 11A-11F: Ink supply port 2: Common flow path member 2a: Side surface 2b: Bottom surface 21: Ink inlet 21a: Packing 22: Ink discharge port 22a: Packing 23: Common flow Roads 23a and 23b: Ceiling walls 24A to 24F: Connection portion 25: Flow path wall 26 :: Ink discharge flow path 26a: Upper end opening 27: Recess 28: Discharge flow path inlet 3: Head fixing member 3a: Mounting surface 3b: Support Plates 4A to 4F: Branch pipe 200: Ink inflow pipe 300: Intermediate tank 301: Atmospheric release pipe 400: Ink supply pipe 401, 402: Branch supply pipe 500, 501, 502: Ink cartridge 503: Ink tank 600: Supply pump 700 : Ink discharge pipe 701: discharge end 800: ink tray 801: discharge flow path 90 0: Waste liquid tank 901: Circulation piping 902: Circulation pump 903: Filter V1 to V6: Open / close valve

Claims (10)

In an image forming apparatus, comprising: a print head unit including a print head having a heating control means for controlling heating of ink and a nozzle for discharging ink; and an ink supply means for supplying ink to the print head unit. ,
The print head unit has an ink inlet for allowing ink supplied from the ink supply means to flow in, and an ink outlet for discharging ink, and the ink inlet is connected to the ink via a first on-off valve. The ink discharge port is open to the atmosphere via a second on-off valve while being connected to the supply means.
An image forming apparatus comprising: valve control means for controlling the first on-off valve and the second on-off valve according to at least a control state of the heating control means.   2. The valve control unit according to claim 1, wherein the first on-off valve is closed and the second on-off valve is opened when the ink is not heated by the heating control unit. Image forming apparatus.   3. The image forming apparatus according to claim 1, wherein the second on-off valve is an electromagnetic valve that operates to open the flow path when power is not supplied. 4. The ink supply means has an intermediate tank that is controlled to apply a predetermined back pressure to the print head by storing a predetermined amount of ink, and the ink flow of the intermediate tank and the print head unit. An inlet is connected via the first on-off valve;
4. The image forming apparatus according to claim 1, wherein back pressure control for the print head by the intermediate tank is not performed during non-heating control of the ink by the heating control unit. The print head unit is constituted by one or a plurality of print heads, stores ink supplied from the ink supply means, and is connected to a side surface or a lower surface with respect to the one or a plurality of print heads. Having a common flow path member for commonly supplying the ink via the branch flow path;
The ink inlet and the ink outlet are provided in the common flow path member,
The valve control means opens the first on-off valve and the second on-off valve for a predetermined time when ink is supplied by the ink supply means prior to ink ejection from the print head, thereby the common flow path. The image forming apparatus according to claim 1, wherein ink containing bubbles therein is discharged from the ink discharge port. The ink inlet and the ink outlet are provided on the lower surface of the common flow path member,
Inside the common flow path member, an upper end opening is disposed close to the ceiling surface, and air in the common flow path flows downward along with the ink from the upper end opening toward the ink discharge opening. 6. The image forming apparatus according to claim 5, wherein an ink discharge channel for discharging the ink is formed. A concave portion is formed on the ceiling surface in the common flow path member at a position facing the upper end opening of the ink discharge flow path.
The image forming apparatus according to claim 6, wherein the concave portion is formed to have a size so as to cover the upper end opening of the ink discharge channel. The ink inlet and the ink outlet are arranged separately on one end side and the other end side in the length direction of the common flow path member,
6. The ceiling surface in the common flow path member is inclined so as to become higher from a position facing the ink inlet to a position facing an upper end opening of the ink discharge flow path. 6. The image forming apparatus according to 6 or 7.   The image forming apparatus according to claim 5, wherein an ink supply port of the print head is disposed below a connection position of the branch flow path in the common flow path member.   The print head unit is detachably fitted to an ink inflow pipe and an ink discharge pipe provided in the image forming apparatus main body with respect to the ink inlet and the ink outlet of the common flow path member. The image forming apparatus according to claim 5, wherein the image forming apparatus is attached.

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