JP2008137199A - Inkjet printer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inkjet printer which can easily adjust a viscosity. <P>SOLUTION: The inkjet printer includes a print head 1, an ink liquid feeding part 4 which supplies the ink liquid to the print head 1, an ink liquid recovering part 3 which returns the ink liquid to the ink liquid feeding part 4, a viscosity detecting means 2 which detects the viscosity of the ink liquid, and a viscosity adjusting means 6 which adjusts the viscosity of the ink liquid to a predetermined value. In the inkjet printer, the ink liquid recovering part 3 branches a channel of the ink liquid by a branching part to a channel 13 large in channel resistance and a channel 14 small in channel resistance. A valve 15 is set at the branching part 16, which switches so that the ink liquid flows to one of the channels. A control part 9 is incorporated which switches the valve to flow the ink liquid to the channel 13 small in channel resistance when the viscosity of the ink liquid detected by the viscosity detecting means 2 decreases below the predetermined value. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an ink jet printer, and more particularly to viscosity adjustment of an ink liquid used in a continuous ink jet printer.

  A conventional inkjet printer ejects ink liquid supplied from an ink liquid supply unit from a nozzle, deflects ink particles used for printing out of the ejected ink particles, and prints a predetermined image. Ink particles that are not used are captured by the gutter, the ink liquid captured by the gutter is returned to the ink liquid supply unit, and is used again for printing.

  In order to perform appropriate printing with such an ink jet printer, it is necessary to keep the viscosity of the ink liquid constant.

  Therefore, in Patent Document 1 below, a heater is installed in the print head, and the ink liquid is always heated to keep the viscosity constant, and when the viscosity is too low, the heating is stopped and the ink is stopped. A technique for increasing the viscosity is disclosed.

JP 07-137294 A

  Although the viscosity control method described in Patent Document 1 can control the viscosity, it is necessary to provide a heater for heating the nozzles and a sensor for detecting the temperature of the ink liquid in the print head. A control unit for controlling the temperature is also required. Therefore, there is a problem that the structure of the print head becomes complicated and the print head itself becomes large.

  The present invention has been made in view of the above-described conventional problems, and an object of the present invention is to provide an ink jet printer capable of easily adjusting the viscosity.

  In order to achieve the above object, an ink jet printer according to the present invention prints a predetermined image by deflecting ink particles used for printing out of ink particles ejected from a nozzle, and ink particles that are not used for printing. Print head captured by gutter, ink liquid supply unit for supplying ink liquid to the print head, ink liquid recovery unit for returning ink liquid captured by the gutter of the print head to the ink liquid supply unit, and ink liquid supply unit An ink jet comprising: viscosity detecting means for detecting the viscosity of the ink liquid in the ink; and viscosity adjusting means for adjusting the viscosity of the ink liquid in the ink liquid supply section to a predetermined value according to the viscosity of the ink liquid detected by the viscosity detecting means In the printer, the ink liquid recovery unit includes a flow path and a flow path having a large flow resistance by a branching portion of the ink liquid flow path. When a branching valve is provided at the branching part to switch to one of these channels, and the viscosity of the ink liquid detected by the viscosity detecting means falls below a predetermined value. In addition, a control unit is provided that switches the valve so that the ink liquid flows through the channel having a small channel resistance.

  In addition, a predetermined image is printed by deflecting ink particles used for printing out of the ink particles ejected from the nozzle, and the ink particles that are not used for printing are captured by a gutter, and the print head is supplied to the print head An ink tank for storing the ink liquid, an ink liquid supply part for supplying the ink liquid from the ink tank to the print head, an ink liquid recovery part for returning the ink liquid captured by the gutter of the print head to the ink liquid supply part, Viscosity detecting means for detecting the viscosity of the ink liquid in the ink liquid supply section, and viscosity adjusting means for adjusting the viscosity of the ink liquid in the ink liquid supply section to a predetermined value according to the viscosity of the ink liquid detected by the viscosity detection means In the ink jet printer comprising: A branch section is provided for branching into a gas phase communication flow path that communicates with the liquid phase communication flow path that communicates with the ink liquid in the ink tank, and a valve that switches the ink liquid to flow in one of the flow paths. And a control unit that switches a valve so that the ink liquid flows through the liquid-phase communication channel when the viscosity of the ink liquid detected by the viscosity detecting means falls below a predetermined value.

  A predetermined image is printed by deflecting ink particles used for printing out of the ink particles ejected from the nozzles, and a print head that captures ink particles that are not used for printing by a gutter, and is supplied to the print head. An ink tank that stores the ink liquid, an ink liquid supply unit that supplies the ink liquid from the ink tank to the print head, an ink liquid recovery unit that returns the ink liquid captured by the gutter of the print head to the ink liquid supply unit, Viscosity detecting means for detecting the viscosity of the ink liquid in the ink liquid supply section; and viscosity adjusting means for adjusting the viscosity of the ink liquid in the ink liquid supply section to a predetermined value in accordance with the viscosity of the ink liquid detected by the viscosity detection means; In the ink jet printer having the above, the ink liquid recovery unit has a flow path resistance for the flow path through which the ink liquid flows. A branch portion branches into a large gas phase communication channel that communicates with the gas phase of the ink tank and a liquid phase communication channel that has a small channel resistance and communicates with the ink liquid in the ink tank. A valve for switching the flow of the ink liquid to one of the flow paths is provided, and when the viscosity of the ink liquid detected by the viscosity detection means falls below a predetermined value, the liquid phase communication flow path A control unit that switches valves so that ink liquid flows is provided.

  According to the ink jet printer according to the present invention, when the viscosity of the ink liquid detected by the viscosity detecting unit is lower than a predetermined value, the valve is switched so that the ink liquid flows through the flow path having a small flow path resistance. When passing through a channel having a small channel resistance, volatilization of the solvent is promoted, the viscosity of the ink liquid can be quickly increased, and the viscosity of the ink liquid can be quickly returned to a predetermined value.

  In addition, when the valve is switched so that the ink liquid flows into the liquid phase communication channel communicating with the ink liquid in the ink tank when the viscosity of the ink liquid detected by the viscosity detecting means is lower than a predetermined value, Since the ink liquid is released into the liquid phase of the ink tank, the ink liquid in the ink tank is agitated to promote the volatilization of the solvent of the ink liquid, and the viscosity of the ink liquid can be quickly increased. The viscosity can be quickly returned to the predetermined value.

  Then, when the viscosity of the ink liquid detected by the viscosity detecting means falls below a predetermined value, the valve is set so that the ink liquid flows through the liquid phase communication flow path having a small flow path resistance and communicating with the ink liquid in the ink tank. When switching, the effect of reducing the flow path resistance and the effect of discharging the ink liquid into the ink liquid in the ink tank are synergistic, and the solvent can be volatilized more quickly. The viscosity can be adjusted to the predetermined value more quickly.

  The best embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a schematic configuration diagram of an ink jet printer according to the present embodiment. In FIG. 1, the ink jet printer includes a print head 1, an ink liquid supply unit 4, an ink liquid recovery unit 3, a viscosity detection unit 2, a viscosity adjustment unit 6, and a solvent tank 40.

  The print head 1 includes a nozzle 52 having a diameter of 50 μm to 60 μm that ejects ink liquid, and a gutter 53 that captures ink particles that are not used for printing among the ink particles ejected from the nozzle 52.

  The ink liquid supply unit 4 includes an ink tank 10 that stores ink liquid to be supplied to the print head 1, a replenishment ink tank 30 that stores ink liquid that is replenished when the ink liquid in the ink tank 10 is insufficient, and ink. A pipe 65 that connects between the tank 10 and the print head 1, and a pump 61, a filter 62, a regulator 63, and a pressure sensor 64 are provided in the pipe 65.

  The ink tank 10 stores an ink liquid whose viscosity is adjusted by mixing the ink liquid supplied from the ink tank 30 and the solvent supplied from the solvent tank 40. The ink tank 10 includes a liquid level sensor 11 that detects the level of the stored ink liquid. In the following description, for convenience of explanation, the “ink tank 10” is referred to as a “main tank” 10. However, since the “main tank 10” is a tank for storing ink liquid, it functions as an ink tank. The technical scope is not limited.

  The ink tank 30 temporarily stores the ink liquid captured by the gutter 53 of the print head 1 and sent by the pump 72, and stores the ink liquid replenished by the operator when the ink liquid flowing through the ink jet printer is insufficient. . The stored ink liquid is supplied to the main tank 10 when the ink liquid in the main tank 10 is insufficient.

  The regulator 63 adjusts the ink liquid supplied to the print head 1 to a predetermined pressure.

  The ink liquid recovery unit 3 is provided to return the ink liquid captured by the gutter 53 of the print head 1 to the ink tank 30. FIG. 2 is a partial configuration diagram of the ink liquid recovery unit 3 and its peripheral components. As shown in the figure, the ink liquid recovery unit 3 includes a pump 72 provided in a pipe 66 connecting the gutter 53 and the ink tank 30, and the viscosity increasing means 5.

  The viscosity increasing means 5 includes a flow path 13 having a high flow resistance, a flow path 14 having a low flow resistance, a valve 15, and a control unit 9. The flow path 13 having a large flow resistance is constituted by a pipe 17 having a small diameter (for example, a diameter of 0.5 mm to 1 mm), and the flow path 14 having a small flow resistance is constituted by a pipe 18 having a large diameter (for example, a diameter of 3 mm to 4 mm). Is done. The flow path 13 having a high flow resistance and the flow path 14 having a low flow resistance are formed by being branched by a branching portion 16 provided in a pipe 66 constituting the flow path of the ink liquid. The valve 15 is a three-way valve that is provided in the branch portion 16 and switches to flow the ink liquid through one of the flow paths 13 and 14.

  The control unit 9 includes a CPU (Central Processing Unit) 92, a memory 93, and valve control means 91. The memory 93 periodically stores viscosity measurement data that is detected by the viscosity detection means 2 and input to the control unit 9, and a predetermined value that is an appropriate viscosity value of the ink liquid input in advance. The valve control means 91 switches the valve 15 so that the ink liquid flows through the flow path 14 having a small flow path resistance when the viscosity of the ink liquid detected by the viscosity detection means 2 falls below a predetermined value.

  The viscosity detection means 2 is provided above the main tank 10 and detects the viscosity of the ink liquid in the main tank 10. The viscosity detection means 2 includes a Zaan cup tank 20 that stores ink liquid supplied from the main tank 10 via the valve unit 8. A through hole 23 is formed in the lower part of the Zaan cup tank 20, and a capillary tube 22 is connected to the through hole 23, and the ink liquid in the Zaan cup tank 20 is dropped to the main tank 10. Further, the Zahn cup tank 20 is provided with a liquid level sensor 21 for detecting the liquid level of the ink liquid at two upper and lower points.

  The viscosity adjusting means 6 is constituted by a valve portion 8. The valve unit 8 forms a flow path for connecting the ink tank 30 or the solvent tank 40 and the main tank 10, and also forms a flow path for supplying the ink liquid in the main tank 10 to the viscosity detecting means 2. The valve unit 8 includes valves 80 to 83, pipes 85 to 91, and a pump 84. Among these, the valve 83 is a three-way valve for switching whether the ink liquid from the pipe 91 is allowed to flow to the pipe 88 side or the pipe 89 side.

  The solvent tank 40 stores a highly volatile solvent such as methyl ethyl ketone, ethyl acetate, ethanol, and methanol. The replenishment ink tank 30, the solvent tank 40, and the main tank 10 are all connected to the opening 95 and open to the atmosphere.

  Next, the operation will be described. The ink liquid stored in the main tank 10 of the ink liquid supply unit 4 is sent to the print head 1 through the filter 62, the regulator 63, and the pressure sensor 64 by the pump 61, and becomes ink particles having a diameter of about 100 μm from the nozzle 52 every second. About 70,000 are injected. Since a continuous ink jet printer uses a fast-drying ink liquid, the ink liquid is always ejected from the nozzle 52 so that the ink liquid does not solidify.

  Of the ink particles, the ink particles used for printing are deflected to print a predetermined image on a printing surface (not shown). Ink particles that are not used for printing are captured by the gutter 53 and sent to the ink tank 30 for replenishment by the pump 72 of the ink liquid recovery unit 3.

  The ink liquid that has flowed into the replenishing ink tank 30 is returned to the main tank 10 through the valve unit 8 and is used again for printing. Since the ink liquid gradually decreases with the operation of the ink jet printer, the ink tank 30 for replenishment is filled with unused ink liquid by the operator. Similarly, since the solvent gradually decreases, the solvent tank 40 is replenished by the operator.

  The viscosity detection means 2 periodically detects the viscosity of the ink liquid in the ink liquid supply unit 4 by a capillary type viscosity measurement method (for example, every 5 minutes). At that time, the valve 82 is opened, and the three-way valve 83 is set to the pipe 88 side. As a result, the ink liquid in the main tank 10 is sent to the Zahn cup tank 20 through the pipe 87, the valve 82, the pipe 90, the pump 84, the pipe 91, the three-way valve 83, and the pipe 88. When the upper sensor of the liquid level sensors 21 in the Zaan cup tank 20 detects the liquid level, the valve 82 is closed and the three-way valve 83 is switched to stop the supply of ink liquid.

  The ink liquid stored in the Zaan cup tank 20 gradually falls to the main tank 10 through the capillary tube 22, but the ink liquid dropping speed becomes slower as the viscosity of the ink liquid is higher. Therefore, after the upper sensor of the liquid level sensor 21 detects the liquid level of the ink liquid, the viscosity is detected by measuring the time until the lower sensor detects the liquid level.

  When the liquid level sensor 11 detects that the liquid level in the main tank 10 has decreased, either the ink liquid or the solvent is replenished according to the viscosity of the ink liquid detected by the viscosity detection means 2.

  When the viscosity of the ink liquid is higher than a predetermined value that is a preset appropriate viscosity value, that is, the difference between the liquid level detection times of the upper and lower sensors of the liquid level sensor 21 of the viscosity detecting means 2 is, for example, a predetermined value of 30 seconds. When longer than the value, a solvent having a viscosity lower than that of the ink liquid is replenished in order to reduce the viscosity of the ink liquid. At that time, the valve 81 is opened, the three-way valve 83 is set to the pipe 89 side, and the main tank 10 passes from the solvent tank 40 through the pipe 86, valve 81, pipe 90, pump 84, pipe 91, three-way valve 83, pipe 89. Supply the solvent.

  On the other hand, when the viscosity of the ink liquid is lower than the preset appropriate viscosity value, that is, the difference between the liquid level detection times of the upper and lower sensors of the liquid level sensor 21 of the viscosity detecting means 2 is, for example, a predetermined value of 30 seconds. If it is shorter than the value, the ink liquid is replenished from the ink tank 30 for replenishment. In that case, the valve 80 is opened, the three-way valve 83 is set to the pipe 89 side, and the replenishment ink tank 30 is passed through the pipe 85, the valve 80, the pipe 90, the pump 84, the pipe 91, the three-way valve 83, and the pipe 89. Ink liquid is supplied to the main tank 10.

  As described above, when the viscosity of the ink liquid becomes higher than a predetermined value, the viscosity of the ink liquid can be easily lowered by replenishing a solvent having a viscosity lower than that of the ink liquid. However, when the viscosity of the ink liquid becomes lower than a predetermined value, the viscosity of the ink liquid in the replenishing ink tank 30 and the viscosity of the main tank 10 are substantially equal, so that the viscosity can hardly be increased.

  Here, the viscosity of the ink liquid is increased because when the ink particles are captured in the gutter 53, air is sucked together with the ink particles, and the air and the ink liquid are mixed to volatilize the solvent in the ink liquid. This is because the volatilized solvent is released from the opening 95 into the atmosphere. In addition, since the replenishing ink tank 30, the solvent tank 40, and the main tank 10 are all connected to the opening 95 and opened to the atmosphere, the volatilized solvent is gradually released into the atmosphere. Further, when the ink liquid is ejected from the nozzle 52, the solvent is volatilized and the viscosity of the ink liquid is similarly increased. In addition, the ambient temperature when using the ink jet printer tends to be lower than in the daytime in the early morning or evening, and the viscosity of the ink liquid tends to increase. When the viscosity of the ink liquid increases due to these reasons, the viscosity of the ink liquid can be easily reduced by replenishing the solvent as described above.

  On the other hand, the viscosity of the ink liquid decreases when the ambient temperature suddenly rises when using an inkjet printer, for example, when the temperature suddenly rises due to the weather of the day, or when the heating operation is performed. At the beginning. When the viscosity of the ink liquid decreases due to the increase in the ambient temperature in this way, the valve 15 is switched so that the ink liquid flows through the flow path 13 having a small flow path resistance, and the volatilization of the solvent is promoted to increase the viscosity of the ink liquid. To raise.

  That is, the CPU 92 of the control unit 9 reads the latest viscosity measurement data stored in the memory 93 and a predetermined value, and compares them. When the measured viscosity data is shorter than the predetermined value, that is, when the viscosity is lower than the predetermined value, the valve control unit 91 causes the ink liquid to flow to the pipe 18 side, which is the flow path 14 having a small flow resistance. The valve 15 is switched.

  When the measured viscosity data is equal to or higher than the predetermined value, that is, when the difference between the liquid level detection times of the upper and lower sensors of the liquid level sensor 21 is equal to or longer than the predetermined value, In the valve control means 91, the valve 15 is switched so that the ink liquid flows to the pipe 17 side which is the flow path 13 having a large flow path resistance.

  As described above, when the viscosity of the ink liquid detected by the viscosity detecting means 2 falls below a predetermined value, the valve 15 is switched so that the ink liquid flows through the flow path 14 having a small flow path resistance, and the solvent in the ink liquid is volatilized. As a result, the viscosity of the ink liquid in the ink liquid supply section 4 is increased, so that the volatilization of the solvent in the ink liquid is greatly promoted when passing through the flow path 14, and the viscosity of the ink liquid in the ink liquid supply section 4 is rapidly increased. Can be raised.

  Further, since the viscosity of the ink liquid is adjusted as in the technique disclosed in Patent Document 1, the viscosity can be easily adjusted without providing the print head 1 with a heater, a sensor, a control unit, or the like. There is no need to unnecessarily complicate the structure.

  Further, the pipe 17 which is the flow path 13 having a large flow resistance of the ink liquid recovery unit 3 is already provided in the conventional ink jet printer for the purpose of collecting the volatilized solvent. It is only necessary to newly provide a pipe 15 having a large diameter and a control unit 9, and no major remodeling of the apparatus is required, and the cost can be kept low.

  On the other hand, when the measured viscosity data is higher than a predetermined value, that is, when the difference between the liquid level detection times of the upper and lower sensors of the liquid level sensor 21 is shorter than the predetermined value, the valve control means 91 determines the flow path resistance. Switching the valve 15 so that the ink liquid flows to the pipe 17 side that is the large flow path 13 minimizes the volatilization amount of the solvent in the ink liquid and reduces the amount of the solvent released from the opening 95 into the atmosphere. This is to reduce the consumption of the solvent, to reduce the burden on the environment, and to reduce the cost by suppressing the consumption of the solvent.

  In the above embodiment, the flow path 13 having a large flow resistance is a pipe 17 having a small diameter, and the flow path 14 having a small flow resistance is a pipe 18 having a large diameter. However, the flow path having a large flow path resistance may be a flow path having a large flow path resistance by providing irregularities on the inner wall of the pipe.

  Moreover, although the viscosity raising means 5 was provided in the piping 66, it is not limited to this, You may provide in the piping which comprises another flow path. The viscosity detecting means 2 uses a capillary type viscosity measuring method, but is not limited to this, and a viscosity measuring method such as a rotary type, a falling ball type, a vibration type, or an ultrasonic type may be used.

  Further, the viscosity increasing means 5 has branched the ink liquid flow path into the flow path 13 having a high flow resistance and the flow path 14 having a low flow resistance by the branching section 16, but the present invention is not limited to this. As shown, the ink liquid flow path is branched by a branching portion into a gas phase communication flow path 13a communicating with the gas phase of the ink tank 30a and a liquid phase communication flow path 14a communicating with the ink liquid of the ink tank. Alternatively, the gas-phase communication channel 13a may be a channel having a large channel resistance by using a pipe having a small diameter, and the liquid-phase communication channel 14a may be a channel having a large diameter. It is good also as a channel with small resistance. The gas phase communication flow path 13a is constituted by a pipe 17a, and the liquid phase communication flow path 14a is constituted by a pipe 18a.

  In this case, the CPU 92a of the control unit 9a reads the latest viscosity measurement data measured by the viscosity detection means and stored in the memory 93, and a predetermined value set in advance, and compares them. When the measured viscosity data is lower than the predetermined value, the valve 15a is switched in the valve control unit 91a so that the ink liquid flows to the pipe 18a side.

  As a result, the ink liquid passes through the pipe 18a constituting the liquid phase communication channel 14a and is discharged into the liquid phase of the ink tank 30a, and the ink liquid in the ink tank 30a is stirred. Thereby, since the volatilization of the solvent of the ink liquid is promoted, the viscosity of the ink liquid can be easily increased in a short time. Therefore, the viscosity of the ink liquid can be adjusted to a predetermined value.

  The gas phase communication flow path 13a is a flow path having a large flow resistance by using a pipe having a small diameter, and the liquid phase communication flow path 14a is a flow path having a small flow resistance by using a pipe having a large diameter. In this case, when the viscosity of the ink liquid detected by the viscosity detecting means falls below a predetermined value, the ink liquid is caused to flow through the liquid phase communication flow path having a small flow resistance and communicating with the ink liquid in the ink tank. Since the valves are switched, the effects of both become synergistic, the solvent can be volatilized more rapidly, and the viscosity can be adjusted to a predetermined value more quickly.

1 is a schematic configuration diagram of an inkjet printer according to an embodiment of the present invention. It is a partial block diagram of the said inkjet printer. It is a partial block diagram of the inkjet printer concerning other embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Print head 2 Viscosity detection means 3 Ink liquid collection | recovery part 4 Ink liquid supply part 6 Viscosity adjustment means 9, 9a Control part 10 Ink tank (main tank)
13 Flow path 13a with high flow resistance Gas phase communication flow path 14 Flow path with low flow resistance 14a Liquid phase communication flow path 15 and 15a Valves 16 and 16a Branch part 30 Ink tank 52 Nozzle 53 Gutter

Claims (3)

Prints a predetermined image by deflecting ink particles used for printing out of the ink particles ejected from the nozzle, and captures ink particles not used for printing with a gutter, and supplies ink liquid to the print head An ink liquid supply section, an ink liquid recovery section for returning the ink liquid captured by the gutter of the print head to the ink liquid supply section, a viscosity detection means for detecting the viscosity of the ink liquid in the ink liquid supply section, and a viscosity detection means In the ink jet printer comprising the viscosity adjusting means for adjusting the viscosity of the ink liquid in the ink liquid supply unit to a predetermined value according to the viscosity of the ink liquid detected by the ink liquid, the ink liquid recovery unit has a flow path for the ink liquid. The branch part branches into a channel having a high channel resistance and a channel having a low channel resistance, and the ink liquid flows into one of these channels. And a control unit that switches the valve so that the ink liquid flows through the flow path having a small flow path resistance when the viscosity of the ink liquid detected by the viscosity detection unit drops below a predetermined value. An ink jet printer comprising: A print head that deflects ink particles used for printing out of ink particles ejected from a nozzle to print a predetermined image, and captures ink particles that are not used for printing with a gutter, and ink supplied to the print head An ink tank having an ink tank for storing the liquid, an ink liquid supply section for supplying the ink liquid from the ink tank to the print head, an ink liquid recovery section for returning the ink liquid captured by the gutter of the print head to the ink liquid supply section, and an ink Viscosity detection means for detecting the viscosity of the ink liquid in the liquid supply section, and viscosity adjustment means for adjusting the viscosity of the ink liquid in the ink liquid supply section to a predetermined value according to the viscosity of the ink liquid detected by the viscosity detection means. In the ink jet printer provided, the ink liquid recovery unit has a flow path of the ink liquid in a gas phase in the ink tank. A valve branches to branch to a gas phase communication channel that communicates with a liquid phase communication channel that communicates with the ink liquid in the ink tank, and to switch the ink liquid to flow through one of these channels. An ink jet printer comprising: a control unit that is provided in the unit and switches a valve so that the ink liquid flows into the liquid phase communication flow path when the viscosity of the ink liquid detected by the viscosity detecting unit falls below a predetermined value. . A print head that deflects ink particles used for printing out of the ink particles ejected from the nozzle to print a predetermined image, and captures ink particles that are not used for printing with a gutter, and an ink liquid supplied to the print head An ink tank that stores the ink liquid from the ink tank to the print head, an ink liquid recovery section that returns the ink liquid captured by the print head gutter to the ink liquid supply section, and an ink liquid. Viscosity detection means for detecting the viscosity of the ink liquid in the supply section, and viscosity adjustment means for adjusting the viscosity of the ink liquid in the ink liquid supply section to a predetermined value according to the viscosity of the ink liquid detected by the viscosity detection means. In the ink jet printer, the ink liquid recovery unit has a flow path for the ink liquid having a large flow path resistance and The gas phase communication channel communicating with the gas phase of the tank and the liquid phase communication channel having a small channel resistance and communicating with the ink liquid of the ink tank are branched by the branch portion, A valve for switching the flow of the ink liquid to one of the flow paths is provided, and when the viscosity of the ink liquid detected by the viscosity detecting means falls below a predetermined value, the ink liquid is supplied to the liquid phase communication flow path. An ink jet printer comprising a control unit that switches a valve to flow.

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