JP2009285845A - Printer and printing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To promptly raise the temperature of an ink in the whole circulation path after starting the circulation of the ink in the circulation path of a printer. <P>SOLUTION: The printer 1 includes the first ink tank 34 connected to a head 32 and the second ink tank 51 for storing the ink. The ink in the second ink tank 51 is fed to the first ink tank 34 by a pump 54, and the ink is returned to the second ink tank 51 from the first ink tank 34 through the head 32 by reducing the pressure of the inside of the second ink tank 51 with a main pressure reducing mechanism 55. Immediately after starting the circulation of the ink in the circulation path by the pump 54 and the main pressure reducing mechanism 55, the pressure inside the second ink tank 51 is made lower than the one at the normal operation by the main pressure reducing mechanism 55 while heating the ink. Thereby, the ink temperature in the whole circulation path can be promptly raised with assuring the certain ink flow even in the state of the ink temperature being low and the viscosity being high. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an inkjet printing apparatus and a printing method in the printing apparatus.

  2. Description of the Related Art Conventionally, an ink jet printing apparatus that performs printing on a print medium by scanning a print medium along a head on which a plurality of ejection openings for ejecting fine ink droplets is arranged has been used. Also known is a printing apparatus that performs printing while circulating ink between an ink tank that stores ink and a head. For example, the apparatus disclosed in Patent Document 1 is located below the print head and opened to the atmosphere. The ink is circulated by supplying ink from the lower container to the upper container located above the print head and opened to the atmosphere by a pump, and returning the ink from the upper container to the lower container through the print head. Is done.

  In a printing apparatus that circulates ink, even if bubbles are generated in the ink in the head (for example, in a piezo drive type head, bubbles may be generated in the ink due to vibration caused by high-speed piezo drive. The air bubbles can be returned to the ink tank together with the ink, and the air bubbles move to the ejection port of the head, and the ink is not temporarily ejected from the ejection port (so-called nozzle missing occurs). Is suppressed. In addition, the sedimentation of pigment, which is often seen when using white ink, can be improved by circulation of the ink.

In Patent Document 2, in the flow path plate that supplies ink from the ink tank to the head, a flow path plate heater that indirectly heats the ink is disposed around the ink flow path. A flow path heater that directly heats the ink is arranged, temperature control is performed only by the flow path plate heater during normal operation, and both heaters are driven when starting up after power-on, etc. A technique for shortening the start-up time until image recording is possible in the recording apparatus is disclosed.
JP-T-2002-533247 JP 2000-103081 A

  By the way, in a printing apparatus in which ink circulation is performed, printing may be performed in a state where the ink is heated to a predetermined set temperature and the viscosity of the ink is lower than that at room temperature. After stopping, when the printing apparatus is restarted and printing is performed, it is necessary to raise the circulating ink to a set temperature. However, immediately after the start of ink circulation, the viscosity of the ink is high, so that the ink flow rate in the circulation path is significantly lower than in normal operation, and it takes a long time to heat the ink in the entire circulation path. .

  The present invention has been made in view of the above problems, and an object of the present invention is to quickly increase the temperature of ink in the entire circulation path after the start of ink circulation in the circulation path of the printing apparatus.

  The invention according to claim 1 is an ink jet printing apparatus, wherein a plurality of discharge ports arranged in a predetermined arrangement direction are relative to the plurality of discharge ports in a direction crossing the arrangement direction. A head that discharges micro droplets of ink toward a printing medium that moves to the first position, a first ink tank that stores ink in the vicinity of the head and is connected to the head, stores ink, and a supply line And a second ink tank connected to the head via a recovery line, and a supply line. The ink in the second ink tank is supplied to the first ink tank. A pump for supplying to the tank; and the pressure in the second ink tank is reduced, thereby the second ink tank from the first ink tank via the head and the recovery line. A pressure reducing mechanism for returning ink from the first ink tank to the second ink tank through the flow path in a state where the flow path to be filled is filled with ink, the supply line from the second ink tank, the first Ink circulation in the circulation path is started by a heater provided at any position on the circulation path returning to the second ink tank via the ink tank, the head, and the recovery line, and the pump and the pressure reducing mechanism. Immediately after the heating, the controller includes a controller that heats the ink by the heater and lowers the pressure in the second ink tank to be lower than the normal circulation pressure that is a pressure during normal operation by the pressure reducing mechanism.

  Invention of Claim 2 is a printing apparatus of Claim 1, Comprising: The ink temperature measurement part which measures ink temperature in the position in any one of the said circulation path | route is further provided, and the said control part is the said control part. By controlling the pressure reducing mechanism based on the measured value of the ink temperature measuring unit, the pressure in the second ink tank is gradually increased to the normal circulation pressure as the ink temperature increases.

  The invention according to claim 3 is the printing apparatus according to claim 2, further comprising a flow rate adjusting unit provided in the recovery line for adjusting the flow rate of the ink, and immediately after starting the circulation of the ink, The flow rate adjuster widens the opening, which is an internal flow path, than during normal operation.

  According to a fourth aspect of the present invention, there is provided the printing apparatus according to the third aspect, wherein the pressure adjustment mechanism that adjusts the pressure in the first ink tank and the ink flow rate measurement that measures the ink flow rate in the recovery line. And the control unit controls the pressure adjustment mechanism based on the pressure in the second ink tank and the measured value of the ink flow rate measurement unit, thereby allowing the ink meniscus to be contained in the plurality of ejection ports. Keep the state formed.

  A fifth aspect of the present invention is the printing apparatus according to the second aspect, further comprising a pressure adjusting mechanism that adjusts a pressure in the first ink tank, wherein the control unit includes the ink temperature measuring unit. By controlling the pressure reducing mechanism and the pressure adjusting mechanism based on the measured values, the pressure in the second ink tank is reduced to the normal circulation pressure while maintaining a state in which an ink meniscus is formed in the plurality of ejection openings. Gradually increases.

  A sixth aspect of the present invention is the printing apparatus according to any one of the first to fifth aspects, wherein the heater is provided in the second ink tank.

  The invention according to claim 7 is a printing method in an ink jet printing apparatus, wherein the plurality of printing apparatuses are arranged in a direction intersecting the arrangement direction from a plurality of ejection openings arranged in a predetermined arrangement direction. A head that ejects fine ink droplets toward a print medium that moves relative to the ejection port, a first ink tank that stores ink near the head and is connected to the head, A second ink tank that stores ink and is connected to the first ink tank via a supply line and connected to the head via a recovery line; and the second ink tank provided in the supply line. A pump for supplying the ink in the first ink tank and a pressure in the second ink tank to reduce the pressure in the head and the recovery line from the first ink tank. A pressure reducing mechanism for returning ink from the first ink tank to the second ink tank through the flow path in a state where the flow path to the second ink tank via the ink is filled with ink; A heater provided at any position on the circulation path from the ink tank to the second ink tank via the supply line, the first ink tank, the head, and the recovery line, and the printing method A) starting the circulation of ink in the circulation path by driving the pump and the pressure reducing mechanism, and b) immediately after the step a), heating the ink by the heater and the pressure reducing mechanism by the pressure reducing mechanism. A step in which the pressure in the second ink tank is made lower than the normal circulation pressure, which is the pressure during normal operation, and c) the ink temperature in the circulation path is set After a more degrees, and a step of performing printing by ejecting ink toward the second ink tank to the print medium from said head while said normal circulation pressure.

  According to the present invention, the temperature of ink in the entire circulation path of the printing apparatus can be quickly raised, and printing can be started in a short time after the start of ink circulation in the circulation path.

  In the invention of claim 3, the ink flow rate can be increased and the temperature of the ink in the entire circulation path can be raised in a shorter time. In the inventions of claims 4 and 5, ink from the ejection port can be increased. In addition to preventing leakage, it is possible to prevent air from being sucked into the head from the ejection port and causing problems in ink ejection during normal operation. In the invention of claim 6, the heater can be easily placed in the circulation path. Can be provided.

  FIG. 1 is a perspective view showing an appearance of the printing apparatus 1. The printing apparatus 1 performs color printing by an inkjet method on a sheet-like substrate 9 having liquid repellency such as a film.

  The printing apparatus 1 in FIG. 1 includes a main body 11 and a control unit 4, and the main body 11 moves a sheet-like base material 9 in the Y direction (hereinafter also referred to as “scanning direction”) in FIG. In addition, a discharge unit 3 that discharges fine droplets of ink toward the base material 9 that is moving by the transport unit 27 is provided. In the transport unit 27, a plurality of rollers 271 that are each long in the X direction in FIG. 1 are arranged in the Y direction, and a roll-shaped substrate 9 (supply roll) is placed on the (+ Y) side of the plurality of rollers 271. A supply unit 272 for holding is provided, and a winding unit 273 for holding the roll-shaped base material 9 (winding roll) is provided on the (−Y) side of the plurality of rollers 271. In the following description, the term “base material 9” refers to a part in the middle of conveyance (that is, part of the base material 9 on the plurality of rollers 271).

  One roller 271a of the transport unit 27 is provided with an encoder 29 that detects the moving speed of the base material 9 in the scanning direction, and the control unit 4 controls the rotation of the motor of the winding unit 273 based on the output of the encoder 29. As a result, the substrate 9 moves in the (−Y) direction at a constant speed. Actually, by applying a load (tension) in the direction opposite to the moving direction (that is, (+ Y) direction) to the base material 9 by the motor of the supply unit 272, the bases on the plurality of rollers 271 are set. The material 9 moves smoothly without undulations.

  The discharge unit 3 is disposed above the plurality of rollers 271 (on the (+ Z) side in FIG. 1), and the discharge unit 3 is fixed to the frame 25 provided on the base 20 so as to straddle the plurality of rollers 271. . A light source 39 for emitting ultraviolet rays is provided on the frame 25, and a plurality of optical fibers (actually, the plurality of optical fibers are bundled. In FIG. The light from the light source 39 is introduced into the inside of the discharge section 3 through the above.

  FIG. 2 is a bottom view of the discharge unit 3. As shown in FIG. 2, the ejection unit 3 includes a plurality (four in FIG. 2) of head units 33 that eject inks of different colors, and the plurality of head units 33 are arranged in the Y direction. It is fixed to the main body 30 of the discharge part 3. The most (+ Y) side head unit 33 in FIG. 2 ejects K (black) color ink, and the (−Y) side head unit 33 of the K head unit 33 is C (cyan) color ink. The (−Y) side head unit 33 of the C head unit 33 discharges M (magenta) color ink, and the (−Y) side head unit 33 has Y (yellow) color ink. Ink is ejected. Each color ink contains an ultraviolet curing agent and has ultraviolet curing properties. The ejection unit 3 may further be provided with head units for other colors such as light cyan, light magenta, and white.

  In each head unit 33, for example, a plurality of piezo drive type heads 32 are arranged in a staggered manner in the X direction in FIG. 2 (the direction perpendicular to the Y direction and the Z direction, hereinafter referred to as the “width direction”). In addition, a plurality of ejection ports (shown by dots 321 only for some of the heads 32) are arranged in the width direction on the lower surface (the surface on the (−Z) side) of each head 32. As a result, in the entire head unit 33, a large number of discharge ports 321 are arranged at a constant pitch in the width direction, which is the arrangement direction, and are arranged in a row in the width direction at each position in the scanning direction on the substrate 9. A plurality of dots can be formed. Actually, the plurality of ejection ports 321 of each head unit 33 are provided over the entire printing region on the base material 9 in the width direction (here, over the entire width of the base material 9 in the width direction). Thus, the printing of the image on the base material 9 is completed only once the base material 9 passes under the discharge unit 3 (so-called one-pass printing).

  Further, in the ejection unit 3 of FIG. 2, a light irradiation unit 38 connected to the light source 39 is provided on the (−Y) side of the plurality of head units 33. In the light irradiation unit 38, a plurality of optical fibers are arranged along the X direction, and the light irradiation unit 38 irradiates the linear region extending in the X direction on the substrate 9 with ultraviolet rays.

  In the printing apparatus 1, each head unit 33 is connected to the ink circulation mechanism 5 (see FIG. 3 to be described later), and the ink circulation mechanism 5 supplies ink to the head unit 33 and collects ink from the head unit 33. Is done. In the following description, attention is paid to the head unit 33 and the ink circulation mechanism 5 of one of a plurality of colors, but the other colors have the same configuration.

  FIG. 3 is a diagram showing the configuration of the head unit 33 and the ink circulation mechanism 5. Although three heads 32 are illustrated in FIG. 3, the actual head unit 33 is provided with a number of heads 32 as shown in FIG.

  As shown in FIG. 3, the head unit 33 includes a first ink tank 34 that stores ink near the top of the plurality of heads 32, and an ink introduction that introduces ink from the first ink tank 34 to the plurality of heads 32. A plurality of ink introduction pipes 351 which are parts, a manifold body 36 which is provided in a two-stage structure with the first ink tank 34 above the plurality of heads 32 and has an internal space into which ink from the plurality of heads 32 flows, In addition, the plurality of heads 32 and the manifold main body 36 are connected to each other, and a plurality of ink lead-out tubes 352 that are ink lead-out portions that lead the ink in the plurality of heads 32 to the manifold main body 36 are provided. One head 32 is provided with a temperature sensor 322 which is an ink temperature measuring unit, and the ink temperature in the head 32 is measured.

  The ink circulation mechanism 5 includes a second ink tank 51 that stores ink. The second ink tank 51 is connected to the first ink tank 34 of the head unit 33 via a supply line 52, and also includes a recovery line 53, and The head unit 33 is connected to the plurality of heads 32 via the manifold main body 36 and the plurality of ink outlet pipes 352. The supply line 52 is provided with a pump 54 and a filter 521, and the ink in the second ink tank 51 is supplied to the first ink tank 34 by the pump 54 while removing unnecessary substances in the ink by the filter 521. Ink is stored in the ink tank 34. The cross-sectional area on the horizontal surface of the internal space of the second ink tank 51 is substantially constant in the vertical direction (the same applies to the first ink tank 34), and the cross-sectional area is larger than that of the first ink tank 34.

A main decompression mechanism 55 having a pump, a pressure adjustment valve, a pressure gauge, and the like is connected to the second ink tank 51. During normal operation of the printing apparatus 1, the main decompression mechanism 55 causes (in the second ink tank 51 to Gas) is set to a pressure (hereinafter referred to as “normal circulation pressure”) that is lower than atmospheric pressure by several hundred millibars (mbar) (for example, 500 mbar (ie, 5 × 10 ⁴ Pascals (Pa))). A flow path (hereinafter referred to as “recovery flow”) from one ink tank 34 to a second ink tank 51 via a plurality of ink introduction pipes 351, a plurality of heads 32, a plurality of ink outlet pipes 352, a manifold main body 36 and a recovery line 53. The ink is returned from the first ink tank 34 to the second ink tank 51 through the recovery flow path in a state where the “path” is filled with ink.

  The recovery line 53 is provided with an ink flow rate measuring unit 532 that measures the ink flow rate, and a flow rate adjusting valve 531 that is a flow rate adjusting unit that adjusts the ink flow rate. The flow rate of ink from the first ink tank 34 to the second ink tank 51 is limited according to the area of a certain opening (hereinafter referred to as “flow path opening”). In the normal operation in the present embodiment, since the area of the flow path opening in the flow rate adjustment valve 531 is not changed, the flow rate of ink from the first ink tank 34 to the second ink tank 51 is the pressure in the second ink tank 51. (Accurately, it depends mainly on the pressure difference between the first ink tank 34 and the second ink tank 51). In the ink circulation mechanism 5, since the pressure in the second ink tank 51 is controlled to be substantially constant by the main decompression mechanism 55, the ink flow rate in the head 32 becomes substantially constant over time.

  Each of the first ink tank 34 and the second ink tank 51 is provided with ink level sensors 341 and 511 for detecting the position of the ink surface (that is, the ink level). In each of the first ink tank 34 and the second ink tank 51, a replenishment stop level that is an upper limit centered on a predetermined set liquid level (shown by broken lines with reference numerals L1 and L2 in FIG. 3), and The replenishment start level that is the lower limit is set. In the first ink tank 34, when the ink level is below the replenishment start level, ink is replenished (supplied) from the second ink tank 51 by the pump 54. In the second ink tank 51, the ink level is increased. When the position falls below the replenishment start level, ink is replenished from a main ink tank (not shown).

  The second ink tank 51 is provided with a heater 512 and a temperature sensor 513, and the ink is heated to a predetermined set temperature (for example, 45 ° C.) higher than the normal temperature so that the viscosity of the ink is lower than the viscosity at the normal temperature. . Actually, the head 32 is provided with a driver circuit, and the ink whose temperature is adjusted passes through the head 32, whereby the driver circuit is also cooled. Thereby, in the printing apparatus 1, the manufacturing cost of a printing apparatus is reduced compared with the case where a separate cooling mechanism is provided.

  The first ink tank 34 includes a pump, a pressure adjustment valve, a pressure gauge, and the like, and an auxiliary pressure adjustment mechanism 37 that can adjust the pressure in the first ink tank 34 is connected to the first ink tank 34 for normal operation. Sometimes, the auxiliary pressure adjusting mechanism 37 causes the pressure in the first ink tank 34 to be lower than the atmospheric pressure by several mbar (hereinafter referred to as “normal auxiliary pressure”) (that is, the first ink tank 34 is slightly negative). Pressure). In the printing apparatus 1, in the state where the pressure in the first ink tank 34 is reduced as described above, the ink pressure at the plurality of ejection ports of each head 32 becomes negative, and the ink meniscus is formed in the ejection ports and discharged. Ink leakage from the outlet is prevented. The ink pressure at the ejection port when the ink meniscus is formed in the ejection port is also referred to as the meniscus pressure.

  As described above, in the ink circulation mechanism 5 of FIG. 3, the ink in the second ink tank 51 is supplied to the first ink tank 34 of the head unit 33 through the supply line 52 by driving the pump 54. Ink is returned from the first ink tank 34 to the second ink tank 51 via the recovery line 53 by making the pressure in the second ink tank 51 negative. As a result, the second ink tank 51 circulates ink in a circulation path that returns to the second ink tank 51 via the supply line 52, the first ink tank 34, the head 32, and the recovery line 53, while Using the negative pressure in the ink tank 51, the ink is efficiently degassed in the second ink tank 51, and the ink is discharged such as defective discharge that occurs when bubbles are present in the ink in the head 32. Problems are prevented from occurring.

  Next, the operation of the printing apparatus 1 immediately after starting the ink circulation in the circulation path when the printing apparatus is restarted and printing is performed after the entire driving is stopped will be described. FIG. 4 is a diagram illustrating a flow of operations related to printing in the printing apparatus 1.

  In the printing apparatus 1 of FIG. 3, the main power supply of the printing apparatus is turned on to reduce the pressure in the second ink tank 51 by the main pressure reducing mechanism 55 and supply of ink to the first ink tank 34 by the pump 54 ( In practice, this is intermittently performed according to the position of the ink level in the first ink tank 34.) and the circulation of the ink in the circulation path is started (step S11). Heating of ink by the heater 512 is started in the ink tank 51 (step S12). Subsequently, in order to start printing in a short time, an initial operation of ink circulation is performed (step S13).

  FIG. 5 is a diagram showing the flow of the initial operation of ink circulation, and shows the processing performed in step S13 of FIG. When the ink circulation is started, in the printing apparatus 1, the ink temperature is measured by the temperature sensor 322 of the head 32 (step S21). The measured value of the ink temperature is input to the control unit 4 (see FIG. 1), and when the measured value is lower than the set temperature (step S22), the main decompression mechanism 55 is controlled based on the measured value (step S23). ).

  FIG. 6 is a diagram showing the relationship between the target pressure of the second ink tank 51 and the ink temperature. The vertical axis of FIG. 6 shows the target pressure of the second ink tank 51, and the horizontal axis shows the ink temperature in the head 32. . In the control unit 4, the relationship between the target pressure of the second ink tank 51 and the ink temperature shown in FIG. 6 is prepared in advance. For example, when the measured value of the ink temperature is θ, the relationship shown in FIG. A target pressure P corresponding to the ink temperature θ is specified. Then, the main pressure reducing mechanism 55 is controlled so that the inside of the second ink tank 51 becomes the target pressure P.

In this case, the relationship between the target pressure and the ink temperature of the second ink tank 51 shown in FIG. 6, the target pressure in a range in which the ink temperature is the set temperature theta _S or is constant in the normal circulation pressure P _S cage, ink temperature target pressure also becomes lower as lower than the set temperature theta _S (i.e., a negative pressure is large.). In fact, the relationship shown in FIG. 6 is a lower limit pressure P _L is also determined which is the lower limit of the target pressure, in the range equal to or less than a temperature theta _L with the ink temperature, target pressure and constant at the lower limit pressure P _L Is done. In the printer 1, for changing the pressure even slightly in the head 32 by a change in pressure in the second ink tank 51, the lower limit pressure P _L with respect to the second ink tank 51, the first ink tank 34 is typically an auxiliary pressure In this state, the pressure is determined in advance as the limit pressure at which the ink meniscus is formed at the ejection port of the head 32. Incidentally, during the period until the set temperature theta _S from the temperature theta _L in FIG. 6, the target pressure of the second ink tank 51 is not necessarily changes linearly with respect to the ink temperature.

In the printing apparatus 1, while the ink temperature in the head 32 is measured, the operation of controlling the main decompression mechanism 55 based on the measured value of the ink temperature is repeated (steps S21 to S23). As a result, as indicated by a broken line denoted by reference numeral 711 in FIG. 7, the ink temperature in the head 32 increases with the passage of time from the ink circulation start time T1, and reaches the set temperature θ _S at time T2. . Further, as shown by a solid line denoted by a reference numeral 712 in FIG. 7, in the period in which the ink temperature is equal to or less than theta _L is constant at a pressure lower limit pressure P _L in the second ink tank 51, the ink temperature theta _L so that the pressure in the second ink tank 51 is gradually increased to the normal circulation pressure P _S in accordance with increase of the ink temperature (and over time) is higher becomes period than.

When the controller 4 confirms that the ink temperature in the head 32 has become equal to or higher than the set temperature θ _S (steps S21 and S22), the initial operation of ink circulation is terminated, and then the substrate 9 is scanned. Printing is performed by controlling the ejection of ink from the plurality of head units 33 to the substrate 9 while moving in the direction (FIG. 4: step S14). Actually, during the normal operation after the completion of the initial operation of the ink circulation, the heater 512 is controlled while measuring the ink temperature in the head 32 so that the ink temperature is maintained at the set temperature θ _S , and the main decompression mechanism 55 The inside of the second ink tank 51 is kept constant at the normal circulation pressure.

  When the entire printing apparatus 1 is stopped after the printing operation in the printing apparatus 1 is completed, the heating of the ink by the heater 512 is stopped (step S15), and the main decompression mechanism 55 and the pump 54 are stopped. Thus, ink circulation in the circulation path is stopped (step S16).

  As described above, in the printing apparatus 1, immediately after the ink circulation in the circulation path is started by the pump 54 and the main pressure reducing mechanism 55, the second ink tank 51 is heated by the main pressure reducing mechanism 55 while the ink is heated by the heater 512. The internal pressure is made lower than the normal circulation pressure, which is the pressure during normal operation. This ensures a certain amount of ink flow even in a state where the temperature of the ink is low and the viscosity is high, so that the temperature of the ink in the entire circulation path can be quickly raised, and after the start of ink circulation in the circulation path, Printing can be started in a short time. In the printing apparatus 1, the pressure in the second ink tank 51 can be changed smoothly by gradually increasing the pressure in the second ink tank 51 to the normal circulation pressure as the ink temperature increases.

  Next, another example of the initial operation of ink circulation will be described. FIG. 8 is a diagram showing a part of the flow of the initial operation of ink circulation according to another example, and shows processing performed between step S23 and step S21 of FIG.

  In this operation example, when ink circulation in the circulation path is started and it is confirmed that the ink temperature in the head 32 is lower than the set temperature (FIG. 5: Steps S21 and S22), as in the above operation example, The main pressure reducing mechanism 55 is controlled based on the measured value of the ink temperature (step S23), and the auxiliary pressure adjusting mechanism 37 is also controlled (FIG. 8: step S23a).

Here, in this operation example, the area of the flow path opening in the flow rate adjusting valve 531 in FIG. 3 is constant, and in this case, the first ink tank 34 passes through the head 32 to the second ink tank 51. The resistance of the flow path leading from the first ink tank 34 to the head 32 via the ink introduction pipe 351 in the recovery flow path leading to the R _in , and the second resistance via the ink discharge pipe 352, the manifold body 36 and the recovery line 53 to the second. Assuming that the resistance of the flow path to the ink tank 51 is R _out , the pressure in the first ink tank 34 is U, the pressure of the ink in the head 32 is V, and the pressure in the second ink tank 51 is W, (U− The ratio between V) and (V−W) becomes equal to the ratio between R _in and R _out (that is, ((U−V) :( V−W) = R _in : R _out )), and the head 32 Ink pressure V Is represented as ((U · R _out + W · R _in ) / (R _in + R _out )).

For example, during normal operation, the difference between the pressure U in the first ink tank 34 and the atmospheric pressure is 0 bar, and the difference between the pressure W in the second ink tank 51 and the atmospheric pressure is (−0.3) bar. (Ie, the pressure W is 0.3 bar lower than the atmospheric pressure), and the ratio of R _in to R _out is 1: 9, the atmospheric pressure of the ink pressure V in the head 32 is The difference is (−0.03) bar, and an ink meniscus is formed in the ejection port in this state. To be precise, the pressure U in the first ink tank 34 is several mbar lower than the atmospheric pressure.

  Therefore, in the printing apparatus 1, when the target pressure in the second ink tank 51 is set to a value at which the difference from the atmospheric pressure is (−0.6) bar in the process of step S23 of FIG. In the process of step S23a in FIG. 8, a value at which the difference from the atmospheric pressure is (+0.033) bar is specified as the target pressure of the first ink tank 34, and the inside of the first ink tank 34 becomes the target pressure. The auxiliary pressure adjusting mechanism 37 is controlled. As a result, the difference between the ink pressure in the head 32 and the atmospheric pressure becomes (−0.03) bar as in the normal operation, and an ink meniscus is formed in the ejection port. At this time, as described above, since the target pressure of the second ink tank 51 is determined based on the measured value of the ink temperature, the first pressure determined based on the pressure (target pressure) in the second ink tank 51 is determined. The target pressure in one ink tank 34 is also specified substantially based on the measured value of the ink temperature. The difference between the ink pressure V in the head 32 and the atmospheric pressure is larger than (−0.03) bar (close to 0) depending on the design of the head.

  When the pressure in the first ink tank 34 is adjusted by the auxiliary pressure adjustment mechanism 37 (or in parallel with the adjustment operation), the process returns to step S21 in FIG. 5 and the ink temperature in the head 32 is measured. Then, when it is confirmed that the measured value of the ink temperature is lower than the set temperature (step S22), the target pressure of the second ink tank 51 and the target pressure of the first ink tank 34 are specified based on the measured value, The main pressure reducing mechanism 55 and the auxiliary pressure adjusting mechanism 37 are controlled (step S23, FIG. 8: step S23a).

  In the printing apparatus 1, the operation of controlling the main pressure reducing mechanism 55 and the auxiliary pressure adjusting mechanism 37 based on the measured value of the temperature sensor 322 is repeated while measuring the ink temperature in the head 32 (FIG. 5: Steps S21 to S23, FIG. 8: Step S23a), the pressure of the ink in the head 32 is set to a pressure during the normal operation, and the second ink is increased as the ink temperature increases while maintaining the state where the ink meniscus is formed in the plurality of ejection openings of the head 32. The pressure in the ink tank 51 is gradually increased to the normal circulation pressure. When the control unit 4 confirms that the ink temperature in the head 32 has become equal to or higher than the set temperature (FIG. 5: Steps S21 and S22), the initial operation of ink circulation ends. After the completion of the initial operation of ink circulation, the inside of the second ink tank 51 is maintained at the normal circulation pressure, and the inside of the first ink tank 34 is also maintained at the normal auxiliary pressure.

  FIG. 9 is a diagram showing the ink pressure distribution in the recovery flow path from the first ink tank 34 to the second ink tank 51 via the head 32 and the recovery line 53. The vertical axis in FIG. 9 indicates the ink pressure, and the horizontal axis indicates the distance from the first ink tank 34 in the recovery flow path.

  In FIG. 9, the pressure distribution during normal operation of the printing apparatus 1 is indicated by a broken line denoted by reference numeral 721, and the normal auxiliary pressure is displayed in the first ink tank 34 (position where the distance in FIG. 9 is 0) during normal operation. In the second ink tank 51 (the position of the distance B in FIG. 9), the normal circulation pressure W0 is set. In the recovery flow path, as the distance from the first ink tank 34 increases (as a general rule), The pressure drops. At this time, at the head 32 (position A in FIG. 9), the pressure V0 is slightly lower than the atmospheric pressure so that an ink meniscus is formed in the ejection port. Actually, the ink pressure does not decrease linearly with respect to the distance from the first ink tank 34, but a line 721 in FIG. 9 shows a simplified ink pressure distribution (a line 722 described later). , 723).

  Here, in the initial operation of the ink circulation, when the inside of the second ink tank 51 is set to the pressure W1 lower than the normal circulation pressure W0 while keeping the inside of the first ink tank 34 at the normal auxiliary pressure U0, in FIG. As indicated by a one-dot chain line denoted by reference numeral 722, the pressure of the ink in the head 32 becomes a pressure V1 lower than the pressure V0 during normal operation.

On the other hand, in this operation example, when the main pressure reducing mechanism 55 and the auxiliary pressure adjusting mechanism 37 are controlled based on the measured value of the temperature sensor 322, the inside of the second ink tank 51 is set to the pressure W1, As indicated by a solid line denoted by reference numeral 723 in FIG. 9, the pressure in the first ink tank 34 is higher than the normal auxiliary pressure U0 so that the pressure of the ink in the head 32 becomes equal to the pressure V0 in the normal operation. Adjusted to U1. Thereby, in the initial operation of the ink circulation, the state in which the ink meniscus is formed in the plurality of ejection openings is reliably maintained. As a result, ink leakage from the ejection port is prevented, and air is sucked into the head 32 from the ejection port, and it is reliably prevented that a problem (for example, nozzle missing) occurs in ink ejection during normal operation. be able to. In this operation example, the pressure in the second ink tank 51 may be lower than the above-described lower limit pressure P _L (see FIGS. 6 and 7). By adjusting the pressure in the first ink tank 34 in accordance with the (target pressure), it is possible to maintain a state where an ink meniscus is formed in the ejection port.

  Next, still another example of the initial operation of ink circulation will be described. FIG. 10 is a diagram showing a part of the flow of the initial operation of ink circulation according to still another example, and shows processing performed between step S23 and step S21 of FIG. In addition, the process enclosed with the broken-line rectangle which attach | subjects code | symbol S29 in FIG. 10 is a process performed by the below-mentioned operation example.

  In this operation example, after the start of ink circulation in the circulation path, it is confirmed that the measured value of the ink temperature in the temperature sensor 322 in FIG. When controlled (FIG. 5: Steps S21 to S23), the ink flow rate measurement unit 532 measures the ink flow rate, and the measured value of the ink flow rate is input to the control unit 4 (see FIG. 1) (FIG. 10: Step S24). ). Actually, as shown in FIG. 11, immediately after the ink circulation start time T1, the ink temperature is low because the ink temperature is low, and the ink flow rate is low.

Here, the lower limit F _L and an upper limit F _U ink flow in the control unit 4 is set in advance, immediately after the circulation start time T1 of the ink, that measured value of the ink flow rate is less than the lower limit value F _L Is confirmed (step S25), and the flow path opening of the flow rate adjusting valve 531 is expanded by a predetermined amount (that is, the opening degree is increased) than the area during the normal operation described above (step S26). As a result, the ink flow rate in the recovery flow path from the first ink tank 34 to the second ink tank 51 via the head 32 is increased. The pressure in the first ink tank 34 is normally held at an auxiliary pressure.

Subsequently, returning to step S21 in FIG. 5, the ink temperature in the head 32 is measured. When it is confirmed that the measured value of the ink temperature is lower than the set temperature and the main pressure reducing mechanism 55 is controlled (steps S22 and S23), the ink flow rate measurement unit 532 measures the ink flow rate (FIG. 10: step S24). ). Then, if the measured value of the ink flow rate is less than the lower limit value F _L is (step S25), and the flow path opening of the flow control valve 531 is expanded further by a predetermined amount (step S26), the flow returns to step S21 in FIG. 5 . The measurement values of the ink flow rate is greater than the lower limit value F _L, and is smaller than the upper limit value F _U (step S25, S27), the size of the flow path opening of the flow control valve 531 is not changed Return to step S21 in FIG.

In this way, the control of the main pressure reducing mechanism 55 based on the measured value of the ink temperature and the control of the flow rate adjusting valve 531 based on the measured value of the ink flow rate are repeatedly performed (FIG. 5: Steps S21 to S23, FIG. 10: Steps S24 to S27). When a certain amount of time elapses from the ink circulation start time T1, the temperature of the ink increases and the negative pressure in the second ink tank 51 also decreases. However, as shown in FIG. it may become the upper limit F _U or more. Thus, if the measured value of the ink flow rate is equal to or more than the upper limit value F _U is confirmed (step S24, S25, S27), the flow path opening of the flow control valve 531 is narrowed by a predetermined amount (step S28). Thus, the ink flow rate is reduced in the recovery flow path, the ink flow is prevented from becoming significantly more than the upper limit value F _U.

Here, the upper limit value F _U ink flow, the supply amount of the ink from the second ink tank 51 by the pump 54 to the first ink tank 34 (i.e., flow) are a maximum value of, in this operation example the It is possible to prevent the ink flow rate from the first ink tank 34 to the second ink tank 51 from being significantly larger than the amount of ink supplied from the second ink tank 51 to the first ink tank 34. Is prevented from excessively decreasing (the ink amount in the second ink tank 51 is excessively increased).

On the other hand, when the ink flow rate from the first ink tank 34 to the second ink tank 51 is excessively small, in the first ink tank 34, the pump 54 is set so that the position of the ink liquid level is near the set liquid level L1. Therefore, the amount of ink heated in the second ink tank 51 is supplied to the head 32, and the ink temperature in the head 32 is set by the influence of heat radiation in the supply line 52 and the first ink tank 34. It converges at a temperature lower than the temperature. Therefore, the lower limit value F _L of the ink flow rate is determined as minimum ink flow rate capable of maintaining the ink temperature inside the head 32 at a set temperature, so that the ink flow rate is greater than the lower limit value F _L In addition, by controlling the flow rate adjusting valve 531, the ink temperature in the head 32 can be raised to the set temperature. The upper limit F _U ink flow is, for example, 110% of the ink flow rate during normal operation (provided that the above lower than the upper limit value F _U.), 90 lower limit F _L is the ink flow rate during normal operation % and is (however, the above higher than the lower limit value F _L.), may be narrowed allowable range of the ink flow rate in the initial operation of the ink circulation (i.e., the ink flow rate may be stable.).

  In the printing apparatus 1, when it is confirmed that the ink temperature in the head 32 has become equal to or higher than the set temperature (FIG. 5: Steps S21 and S22), the initial operation of ink circulation ends. After completion of the initial operation of ink circulation, the flow path opening of the flow rate adjusting valve 531 is returned to the area during normal operation, and the inside of the second ink tank 51 is set to the normal circulation pressure.

  Here, immediately after starting the circulation of the ink in the circulation path, it may be possible to increase only the area of the flow path opening of the flow rate adjustment valve 531 while maintaining the inside of the second ink tank 51 at the normal circulation pressure. Actually, even if only the area of the flow path opening of the flow rate adjusting valve 531 is increased while the temperature of the ink is low and the viscosity is high, the flow rate of the ink cannot be increased so much.

  On the other hand, in this operation example, immediately after the ink circulation is started, the main decompression mechanism 55 reduces the pressure in the second ink tank 51 to be lower than the normal circulation pressure, and the flow path adjustment valve 531 has a flow path opening. It is wider than during normal operation. As a result, when only the area of the flow path opening of the flow rate adjustment valve 531 is increased while maintaining the inside of the second ink tank 51 at the normal circulation pressure, and the pressure in the second ink tank 51 is made higher than the normal circulation pressure. Compared with the case where the size of the flow path opening of the flow rate adjusting valve 531 is not changed while being lowered (that is, in the case of the above operation example described with reference to FIG. 5 only), the ink flow rate is increased and the entire circulation path is increased. It becomes possible to raise the temperature of the ink in a shorter time. Further, in the present operation example, the pressure in the second ink tank 51 is approximated to the normal circulation pressure (that is, the control range of the negative pressure is set as compared with the case of the operation example described with reference to FIG. 5 only). It is also possible to ensure an ink flow rate equal to or higher than that (narrowly).

  Next, a case where the pressure in the first ink tank 34 is also adjusted by the auxiliary pressure adjusting mechanism 37 in the initial operation of ink circulation in FIG. 10 will be described. In the following operation, a process surrounded by a broken-line rectangle denoted by S29 in FIG. 10 is also performed.

In this operation example, by changing the area of the flow path opening in the flow rate adjusting valve 531, the resistance R _{in of the} flow path from the first ink tank 34 to the head 32 via the ink introduction pipe 351 in the recovery flow path. And the resistance R _{out of the} flow path from the head 32 to the second ink tank 51 through the ink outlet pipe 352, the manifold main body 36, and the recovery line 53 varies.

  Therefore, in the printing apparatus 1, as a pre-preparation before the initial operation of ink circulation, the pressure in the first ink tank 34 is kept constant while the difference between the second ink tank 51 and the atmospheric pressure is, for example, ( -0.1), (-0.2), (-0.3), (-0.4), and (-0.5) bar, when the pressure (negative pressure) is set, the ink flow rate The pressure of the ink at the ejection port of the head 32 is measured when each is 100, 200, 300, 400 and 500 milliliters per minute (ml / min). As a result, a relational expression indicating the relationship among the pressure in the second ink tank 51, the ink flow rate, the pressure in the first ink tank 34, and the pressure of the ink at the ejection port is obtained.

  Actually, when the initial operation of ink circulation is performed, the ink temperature in the head 32 is measured in step S21 of FIG. 5, and it is confirmed that the measured value is lower than the set temperature, and the main decompression mechanism 55 is controlled. Then (steps S22 and S23), the ink flow rate measurement unit 532 measures the ink flow rate (FIG. 10: step S24), and the flow rate adjustment valve 531 is controlled (including the case where the size of the flow path opening is not changed). (Steps S25 to S28). Then, in the above relational expression, the pressure in the second ink tank 51 (may be the target pressure of the second ink tank 51), the measured value of the ink flow rate, and the pressure of the ink at the ejection port during normal operation ( The target pressure is substituted to obtain the target pressure of the first ink tank 34, and the auxiliary pressure adjusting mechanism 37 is controlled so that the inside of the first ink tank 34 becomes the target pressure (step S29).

  In the printing apparatus 1, the process returns to step S21 in FIG. 5 and the above processing is repeated (steps S22 and S23, FIG. 10: steps S24 to S29), and it is confirmed that the ink temperature in the head 32 is equal to or higher than the set temperature. (FIG. 5: Steps S21 and S22), the initial operation of ink circulation ends. After the completion of the initial operation of ink circulation, the flow path opening of the flow rate adjustment valve 531 is returned to the area during normal operation, and the inside of the first ink tank 34 and the second ink tank 51 are respectively the normal auxiliary pressure and the normal circulation pressure. It is said.

  In the printing apparatus 1, a table showing the relationship among the pressure in the second ink tank 51, the ink flow rate, the pressure in the first ink tank 34, and the ink pressure at the ejection port is prepared, and the initial operation of ink circulation is prepared. Sometimes, the target pressure of the first ink tank 34 is obtained by referring to the table using the pressure in the second ink tank 51, the measured value of the ink flow rate, and the pressure of the ink at the ejection port during normal operation. May be.

  As described above, in the printing apparatus 1, in the initial operation of the ink circulation, the auxiliary pressure adjusting mechanism 37 is controlled based on the measured values of the pressure in the second ink tank 51 and the ink flow rate that fluctuate. It is possible to approximate the ink pressure at the plurality of 32 ejection openings to the pressure during normal operation. Thereby, the second ink tank 51 passes through the supply line 52, the first ink tank 34, the head 32, and the recovery line 53 while reliably maintaining the state in which the ink meniscus is formed in the plurality of ejection openings. 2 The temperature of the ink in the entire circulation path returning to the ink tank 51 can be quickly raised, and high-precision printing that prevents the occurrence of nozzle chipping and the like after the start of ink circulation in the circulation path is achieved in a short time. To get started.

  Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications are possible.

  In the printing apparatus 1 of FIG. 3, a heater can be attached at an arbitrary position in the circulation path such as the first ink tank 34. However, in order to easily attach the heater to the circulation path, it is preferable that the heater 512 is provided in the second ink tank 51 which is a larger member than other components.

  In the above embodiment, the main pressure reducing mechanism 55 (and the auxiliary pressure adjusting mechanism 37) are controlled based on the measurement value of the temperature sensor 322 provided in the head 32, but the temperature sensor 513 provided in the second ink tank 51 is controlled. It is also possible to control the pressure in the second ink tank 51 based on the measured value. Further, a temperature sensor may be provided in the first ink tank 34, the supply line 52, and the like, and the measured value may be used for controlling the main pressure reducing mechanism 55. As described above, in the printing apparatus 1, by providing the temperature sensor at any position (that is, any position) in the circulation path, the main pressure reducing mechanism 55 can be controlled based on the measured value of the ink temperature.

  In the printing apparatus 1, immediately after the ink circulation in the circulation path is started, if the pressure in the second ink tank 51 is made lower than the normal circulation pressure by the main pressure reducing mechanism 55 while heating the ink by the heater 512. For example, the main pressure reducing mechanism 55 can be controlled based on the measured value of the ink flow rate in the ink flow rate measurement unit 532.

  In the printing apparatus 1 of FIG. 3, one head unit 33 is connected to the ink circulation mechanism 5, but a plurality of head units 33 having the same structure may be connected to the ink circulation mechanism 5. In this case, preferably, the side of the supply line 52 opposite to the second ink tank 51 is branched into a plurality of branch supply lines and connected to the first ink tanks 34 of the plurality of head units 33, respectively. The side opposite to the tank 51 is branched into a plurality of branch recovery lines and connected to the manifold bodies 36 of the plurality of head units 33, and the pressure adjustment pipes from one auxiliary pressure adjustment mechanism 37 are branched to form the plurality of head units 33. Connected to the first ink tank 34. Then, in the same manner as in the above operation example, by controlling the main pressure reducing mechanism 55 (and the auxiliary pressure adjusting mechanism 37 and the flow rate adjusting valve 531), printing is started in a short time after the start of ink circulation in the circulation path. It becomes possible to start.

  In the printing apparatus 1 shown in FIG. 1 (so-called roll-to-roll printing apparatus), the substrate 9 is moved in the scanning direction intersecting the arrangement direction of the plurality of discharge ports by the transport unit 27 that moves the substrate 9 in the scanning direction. Although it moves at a constant speed with respect to the ejection unit 3, the printing apparatus 1 may be provided with a mechanism for moving the ejection unit 3 in the scanning direction during printing. Further, like the printing apparatus 1a (sheet-fed printing apparatus) shown in FIG. 12, the stage 21 holding the rectangular base material 9 and the stage 21 are moved in the scanning direction (Y direction in FIG. 12). A stage moving mechanism 22 may be provided. As described above, the scanning mechanism for moving the base material 9 in the scanning direction relative to the discharge unit 3 can be realized in various configurations. 12, the position of the stage 21 relative to the base 20 can be detected by a position detection module 23 provided on the base 20.

  In addition to the sheet-like substrate 9, the printing medium in the printing apparatuses 1 and 1a may be a plate-like member made of plastic, printing paper, or the like.

1 is a perspective view illustrating an appearance of a printing apparatus. It is a bottom view of a discharge part. It is a figure which shows the structure of an ink circulation mechanism. It is a figure which shows the flow of the operation | movement which concerns on printing in a printing apparatus. It is a figure which shows the flow of the initial operation | movement of an ink circulation. It is a figure which shows the relationship between the target pressure of a 2nd ink tank, and ink temperature. It is a figure which shows the change of the ink temperature and the pressure in a 2nd ink tank. It is a figure which shows a part of flow of the other example of the initial operation | movement of an ink circulation. It is a figure which shows the pressure distribution of the ink in a collection | recovery flow path. It is a figure which shows a part of flow of the further another example of the initial operation | movement of an ink circulation. It is a figure which shows the change of an ink flow rate. It is a figure which shows the other example of a printing apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,1a Printing apparatus 4 Control part 9 Base material 32 Head 34 1st ink tank 37 Auxiliary pressure adjustment mechanism 51 2nd ink tank 52 Supply line 53 Recovery line 54 Pump 55 Main pressure reduction mechanism 321 Discharge port 322 Temperature sensor 512 Heater 531 Flow rate Adjustment valve 532 Ink flow measurement unit S11 to S14 Steps

Claims (7)

An inkjet printing apparatus,
A head that ejects micro droplets of ink from a plurality of ejection openings arranged in a predetermined arrangement direction toward a print medium that moves relative to the plurality of ejection openings in a direction intersecting the arrangement direction; ,
A first ink tank for storing ink in the vicinity of the head and connected to the head;
A second ink tank for storing ink, connected to the first ink tank via a supply line, and connected to the head via a recovery line;
A pump provided in the supply line and configured to supply ink in the second ink tank to the first ink tank;
By reducing the pressure in the second ink tank, the flow path from the first ink tank to the second ink tank via the head and the recovery line is filled with ink through the flow path. A pressure reducing mechanism for returning ink from the first ink tank to the second ink tank;
A heater provided at any position in the circulation path from the second ink tank to the second ink tank via the supply line, the first ink tank, the head, and the recovery line;
Immediately after starting the circulation of ink in the circulation path by the pump and the pressure reducing mechanism, the pressure in the second ink tank is the normal operating pressure by the pressure reducing mechanism while the ink is heated by the heater. A control unit for lowering the pressure,
A printing apparatus comprising: The printing apparatus according to claim 1,
An ink temperature measuring unit for measuring the ink temperature at any position of the circulation path;
The control unit controls the pressure reducing mechanism based on the measurement value of the ink temperature measurement unit to gradually increase the pressure in the second ink tank to the normal circulation pressure as the ink temperature increases. Characteristic printing device. The printing apparatus according to claim 2,
Further provided with a flow rate adjusting unit provided in the recovery line for adjusting the flow rate of the ink;
Immediately after starting the circulation of ink, the flow rate adjusting unit widens an opening, which is an internal flow path, than in a normal operation. The printing apparatus according to claim 3,
A pressure adjusting mechanism for adjusting the pressure in the first ink tank;
An ink flow rate measuring unit for measuring the ink flow rate in the recovery line;
Further comprising
The control unit controls the pressure adjustment mechanism based on the pressure in the second ink tank and the measurement value of the ink flow rate measurement unit, so that a state where ink meniscuses are formed in the plurality of ejection ports. A printing device characterized by keeping. The printing apparatus according to claim 2,
A pressure adjusting mechanism for adjusting the pressure in the first ink tank;
The control unit controls the pressure reduction mechanism and the pressure adjustment mechanism based on the measurement value of the ink temperature measurement unit, thereby maintaining the state where ink meniscus is formed in the plurality of ejection ports. A printing apparatus characterized by gradually increasing the pressure in the ink tank to the normal circulation pressure. The printing apparatus according to any one of claims 1 to 5,
The printing apparatus, wherein the heater is provided in the second ink tank. A printing method in an inkjet printing apparatus,
The printing device is
A head that ejects micro droplets of ink from a plurality of ejection openings arranged in a predetermined arrangement direction toward a print medium that moves relative to the plurality of ejection openings in a direction intersecting the arrangement direction; ,
A first ink tank for storing ink in the vicinity of the head and connected to the head;
A second ink tank for storing ink, connected to the first ink tank via a supply line, and connected to the head via a recovery line;
A pump provided in the supply line and configured to supply ink in the second ink tank to the first ink tank;
By reducing the pressure in the second ink tank, the flow path from the first ink tank to the second ink tank via the head and the recovery line is filled with ink through the flow path. A pressure reducing mechanism for returning ink from the first ink tank to the second ink tank;
A heater provided at any position in the circulation path from the second ink tank to the second ink tank via the supply line, the first ink tank, the head, and the recovery line;
With
The printing method is:
a) starting circulation of ink in the circulation path by driving the pump and the pressure reducing mechanism;
b) Immediately after the step a), while the ink is heated by the heater, the pressure in the second ink tank is made lower than the normal circulation pressure that is a pressure during normal operation by the pressure reducing mechanism;
c) a step of performing printing by ejecting ink from the head toward the print medium while maintaining the normal circulation pressure in the second ink tank after the ink temperature in the circulation path becomes equal to or higher than a set temperature;
A printing method comprising:

Images