JP5784660B2 - Inkjet device - Google Patents

Description

  Embodiments described herein relate generally to an ink jet apparatus including an ink jet head in which a drive electrode is provided in a flow path for circulating ink, and ink is ejected from an ink ejection port by applying an electric field to the drive electrode.

  Conventionally, an ink jet head in which an ink nozzle is provided at the tip of an ink flow path and ink droplets are ejected from the nozzle to form an image. dry. That is, nozzle clogging or ink ejection failure due to the accumulation of thickened ink in the nozzle may occur. For this reason, there are various dry prevention methods. As a typical method, when the ink jet reaches a non-printing region, there is a method of covering the nozzle with a nozzle cap to block the outside air. In addition, there is a method in which ink in a nozzle is sucked by a suction means provided outside after a nozzle cap having an ink absorption pad provided therein (see, for example, Patent Document 1).

  Further, as a method for preventing nozzle clogging and ink ejection failure, an idle driving operation in which the ink meniscus of each nozzle is finely oscillated by the pressure generating means is performed during the carriage movement period prior to the printing operation. Is disclosed (for example, see Patent Document 2).

Japanese Patent Publication No. 63-15911 JP 2005-96272 A

  However, the method of simply covering the nozzle cap of the nozzle of the ink jet head cannot prevent the nozzle from being dried unless the airtightness of the nozzle cap is sufficiently maintained, and is insufficient as a method for preventing nozzle drying. . The method of sucking the ink in the nozzle toward the outside by the sucking means needs to suck the ink solidified by drying in the nozzle vigorously, and there is a problem that the amount of ink consumption increases.

  As described above, in the ink jet head, when the printing pause time becomes long, the nozzle clogging occurs due to the increase in the ink viscosity at the nozzle. In addition, there has been a problem that even if no clogging occurs, the ink droplets are not ejected normally due to the length of the printing pause time, and the image quality deteriorates.

  In order to solve this problem, there is known a method of discharging the ink with thickened nozzles by performing preliminary ejection unrelated to printing. However, in this method, excessive ink is consumed by preliminary ejection. There is a problem.

  In addition, in the method of reducing the ink thickening of the nozzles by performing idle driving that slightly vibrates the meniscus, the thickened ink is not discharged to the outside, so depending on the state transition in which the head is used, It is not possible to remove the clogging. This idle driving process is performed only in the acceleration / deceleration region during the period in which the inkjet head is moved from the home position to the printing position, and the idle driving process according to the printing state is not performed. There was also a problem that it could not be made longer.

An inkjet apparatus according to an embodiment of the present invention is an inkjet apparatus including an inkjet head having a plurality of flow paths for circulating ink, and provided with nozzles corresponding to each of the plurality of flow paths. The ink circulation system includes an ink circulation system that communicates with the ink jet head and constitutes an ink circulation system. The ink circulation system is configured to be capable of adjusting the pressure of the nozzle, and the nozzle pressure is reduced from an appropriate pressure to a pressure at which the meniscus moves backward. Then, the ink in the nozzle flows out downstream of the ink circulation system through the plurality of flow paths corresponding to the nozzle and circulating the ink .

1 is a configuration diagram of an inkjet apparatus according to an embodiment of the present invention. It is a figure explaining the judgment function of the pressure judgment means used for one Embodiment of this invention. It is a figure explaining the state from which the thickened ink etc. in a nozzle are discharged | emitted by one Embodiment of this invention.

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

  FIG. 1 shows a configuration of an ink jet apparatus including an ink head jet 1 according to an embodiment of the present invention. Although the detailed illustration of the inkjet head 1 is omitted, the inkjet head 1 has a configuration as described in Japanese Unexamined Patent Application Publication No. 2009-20275, and includes a plurality of channels for circulating ink. Thin film drive electrodes are respectively provided on the inner surface, and ink discharge ports (hereinafter referred to as nozzles) corresponding to a plurality of flow paths are provided on the lower surface portion in the figure. Ink droplets are ejected from the nozzles by applying an electric field to the drive electrodes.

  The ink-jet head 1 is connected to the upstream ink tank 3 via a conduit member 4 and is also connected to the downstream ink tank 5 via a conduit member 6. The downstream ink tank 5 is connected to the suction side of the liquid feed pump 13 via a pipe line member 20, and the discharge side of the liquid feed pump 13 is upstream via a pipe line member 18, a filter 17 and a pipe line member 16 in this order. It is connected to the side ink tank 3. These mutually connected ink circulation facilities communicate with the above-described flow path of the inkjet head 1, and constitute an ink circulation system 2 together with this flow path.

  A liquid feed pump 23 is provided between the pipe member 20 constituting the ink circulation system 2 and the supply ink tank 14. The liquid feed pump 23 supplies the ink in the supply ink tank 14 to the ink circulation system 2 by forward rotation, returns the ink from the ink circulation system 2 to the supply ink tank 14 by reverse rotation, and the negative pressure value of the ink circulation system 2. Function to enhance. Accordingly, the pump 23 also functions as a negative pressure adjusting unit that adjusts the negative pressure value of the ink circulation system 2.

  A pressure gauge 8 is attached to the upstream ink tank 3 via a pipe line member 7 to monitor the pressure A in the upstream ink tank 3. Further, a pressure gauge 10 is also attached to the downstream ink tank 5 via a conduit member 9 to monitor the pressure B in the downstream ink tank 5. The upstream pressure gauge 8 and the downstream pressure gauge 10 are connected to a calculator 11, and the pressure data A and B monitored by the pressure gauges 8 and 10 are transmitted to the calculator 11. Then, arithmetic processing is executed. The computing unit 11 obtains the pressure Y of the nozzle portion of the inkjet head 1 by an arithmetic expression described later. Therefore, the computing unit 11 functions as a computing means for obtaining the pressure Y of the nozzle portion based on the pressure detected from the ink circulation system 2 and using a preset computing equation.

  The calculator 11 is connected to the comparator 12, and the data Y calculated by the calculator 11 is transmitted to the comparator 12. The comparator 12 functions as a pressure determination unit that determines whether the value Y obtained by the calculator 11 is positive or negative with respect to a preset reference value. The determination result of the comparator 12 is output as a forward / reverse rotation command for the pump 13.

  Here, the reference value is an appropriate pressure when ink is not ejected (hereinafter also referred to as an appropriate nozzle pressure). On the other hand, the value Y obtained by the calculation means 11 is the current pressure of the nozzle portion obtained based on the pressure detected from the ink circulation system 2.

  The present embodiment is characterized in that the reference value can be changed to the negative pressure side.

  FIG. 2 shows a block diagram of the comparator 12. The data Y processed by the computing unit 11 has two comparison units as shown in FIG. 2, and is compared with appropriate nozzle pressures Pn + Δ and Pn−Δ. When the data Y is positive with respect to the appropriate nozzle pressure Pn + Δ, the comparator 12 issues an instruction to reverse the liquid feed pump 13 and performs the ink reduction operation. That is, while the data Y is positive with respect to the appropriate nozzle pressure Pn + Δ, the liquid feeding pump 13 is reversely rotated to perform the ink decreasing operation and operate to increase the negative pressure with respect to the nozzle. When the data Y becomes the same as the appropriate nozzle pressure Pn (data Y = Pn), the liquid feed pump 13 is stopped and the ink reduction operation is stopped.

  On the other hand, when the data Y is negative with respect to the appropriate nozzle pressure Pn-Δ, the comparator 12 issues an instruction to rotate the liquid feed pump 13 in the forward direction and performs an ink supply operation. That is, while the data Y is more negative than the appropriate nozzle pressure Pn−Δ (meaning that ink is dripped from the nozzles), the liquid supply pump 13 is rotated forward to perform the ink supply operation. When the data Y becomes the same as the proper nozzle pressure Pn (data Y = Pn), the liquid feed pump 13 is stopped and the ink supply operation is stopped.

  In the block diagram of the comparator 12 in FIG. 2, Δ (hysteresis) is added when the liquid feed pump 13 is rotated forward and backward. This is true when the liquid feed pump 13 is rotated forward. The liquid feed pump 13 is driven with the reference value (Pn−Δ) so as to return to the state before the rotation, and when the liquid feed pump 13 is reversed, the reference value is returned so as to return to the state before the reverse rotation. The liquid feed pump 13 is driven by (Pn + Δ).

Here, in the configuration of FIG. 1, when the normal inkjet head 1 does not discharge, the appropriate nozzle pressure Pn is set such that the upstream line resistance with respect to the inkjet head 1 is RU, the downstream line resistance is RL, and the flow path resistance ratio is RU: RL = 1: If set to r, P1 (energy per unit volume of the upstream pressure source -) and P2 (energy per unit volume of the downstream pressure source -) relationship with the, P1 · r / ( 1 + r) + P2 / (1 + r) = Pn (appropriate nozzle pressure≈−1 kPa). In the embodiment of FIG. 1, the liquid level heights of the upstream ink tank 3 and the downstream ink tank 4 are adjusted to the height of the nozzle surface (the lower surface in the drawing of the inkjet head), so P1 and P2 are the respective ink tanks. Is equal to the air pressure A and B. Even if the ambient temperature or the type of ink changes and the flow path resistance changes, the nozzle vicinity pressure does not change.

Therefore, the arithmetic expression in the arithmetic means 11 is determined as follows.

  Based on the actual pressures A and B in the ink circulation system 2, the pressure of the ink nozzle portion is obtained as data Y by the above arithmetic expression. Then, it is compared with the reference value Pn by the comparator 12 to determine whether the pressure is positive or negative with respect to the reference value. Hereinafter, the reference value Pn will be described.

When the ink jet printing apparatus (not shown) equipped with the ink jet head 1 is not used for a long time or when the printing pause time is long, the reference value (appropriate nozzle pressure Pn) of the comparator 12 is set to the negative pressure side. To change. That is, the reference value when the normal inkjet head 1 does not discharge is set to Pn = −1 kPa as described above. This is matched to the pressure at which the meniscus retracts as shown in FIG. For example, the proper nozzle pressure Pn is set to −4 kPa as a reference value for the comparator 12. With this setting, the data Y maintains a positive pressure state with respect to the reference value until it reaches −4 kPa. During this time, the liquid feed pump 23 continues to reverse and performs the ink reduction operation. The ink is pulled downstream by this ink reduction operation, and at that time, the air bubbles and the thickened ink existing in the nozzle hole are caused to flow as shown in FIGS. The liquid is sent to the downstream ink tank 5 by the flow.

  3A to 3E are diagrams illustrating the behavior of the meniscus in the nozzle holes of the inkjet head 1 when the negative pressure is increased by the ink reduction operation described above. The meniscus shown in FIG. 3A starts to retreat as shown in FIG. 3B, and then retreats as shown in FIGS. 3C and 3D. At that time, bubbles and thickened ink existing in the nozzle holes are made to flow, and are sent from the nozzle holes to the downstream ink tank 5 by the flow of ink circulation as shown in FIG. 3E. Since the thickened ink is diluted in the downstream ink tank 5 or trapped by the filter 17, it does not return to the inkjet head 1 again. Thereafter, the pressure is returned to the normal appropriate negative pressure (-1 kPa) to enable printing.

  By adopting such a configuration, bubbles existing in the nozzle holes, thickened ink, and fixed ink can be flowed and removed from the nozzle holes. As a result, the inside of the nozzle hole is always wet with fresh ink, and the ink jet head 1 can be obtained in which the nozzle hole is not clogged with the thickened ink, no ejection, distortion in the ejection direction, or the like does not occur.

  As described above, when the ink jet printing apparatus equipped with the ink jet head is not used for a long period of time or when the print standby state is long, the negative pressure value is controlled, and the negative pressure larger than the normal negative pressure value (-1 kPa) ( -4 kPa), the ink meniscus in the nozzle hole can be moved, and thereby the thickened ink fixed in the nozzle hole can be surely fluidized and discharged downstream by ink circulation. Accordingly, the inside of the nozzle hole is always wet with ink, and the nozzle hole is not clogged or non-ejected by the thickened ink, and the ejection direction is not distorted.

    The determination that the ink jet printing apparatus is not used for a long time or that the print standby state is long is, for example, measuring the time when ink is not discharged from the discharge port by a timer or the like, and the time when this ink is not discharged is a predetermined value. By exceeding this, the reference value of the pressure determination means may be changed to the negative pressure side.

  Although several embodiments of the present invention have been described, these embodiments have been presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

DESCRIPTION OF SYMBOLS 1 ... Inkjet head 2 ... Ink circulation system 3 ... Upstream ink tank 4, 6, 13, 16, 17, 18, 20 ... Ink circulation equipment 5 ... Downstream ink tank 8, 10 ... Pressure gauge 11 ... Calculation means 12 ... Pressure judgment means 23 ... Negative pressure adjustment means (pump)

Claims (5)

An inkjet apparatus including an inkjet head having a plurality of flow paths for circulating ink, and provided with nozzles corresponding to each of the plurality of flow paths,
Having ink circulation equipment composing an ink circulation system in communication with the inkjet head;
The ink circulation system is configured to be capable of adjusting the pressure of the nozzle,
Inkjet that reduces the nozzle pressure from an appropriate pressure to a pressure at which the meniscus retreats, and causes the ink in the nozzle to flow downstream of the ink circulation system through the plurality of flow paths that circulate ink corresponding to the nozzle. apparatus.   The ink circulation system includes an upstream ink tank, a first conduit member, a plurality of flow paths of the inkjet head, a second conduit member, a downstream ink tank, and a first liquid feed pump. An ink jet apparatus according to claim 1, comprising: a filter.   The inkjet apparatus according to claim 2, further comprising a second liquid feed pump that supplies ink to the ink circulation system and returns the ink from the ink circulation system.   The inkjet apparatus according to claim 3, wherein the nozzle pressure is reduced by operating the second liquid feeding pump in a direction to reduce ink in the ink circulation system. A first pressure gauge for detecting an internal pressure of the upstream ink tank;
A second pressure gauge for detecting the internal pressure of the downstream ink tank;
A calculator for calculating the nozzle pressure of the inkjet head from the pressure detected by the first and second pressure gauges;
When the calculation result of the calculator is smaller than Pn−Δ, the second liquid feeding pump is driven in a direction to supply ink to the ink circulation system,
When the calculation result of the calculator is larger than Pn + Δ, the second liquid feeding pump is driven to return ink from the ink circulation system, and
The inkjet apparatus according to claim 4, wherein the value of Pn can be set to an appropriate nozzle pressure and a pressure at which the meniscus moves backward.

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