Inkjet printing device

Abstract

To provide an ink jet printer which can suppress the breakage of a meniscus of ink formed on a nozzle of an ink jet head when stopping an ink circulation operation in a circulation channel of ink.SOLUTION: An ink jet printer comprises: a first opening / closing valve 114 which is arranged in a path of supplying ink to an ink jet head 240 from an ink tank 111 in a circulation channel 110 of ink; and a second opening / closing valve 115 which is arranged in a path of returning the ink to the ink tank 111 from the ink jet head 240 of the circulation channel 110. Control means 40 closes the first opening / closing valve 114 first when stopping a circulation operation of ink in the circulation channel 110, closes the second opening / closing valve 115 after the elapse of first stand-by time after closing the first opening / closing valve 114, and stops the operations of circulation flow generation means 112, 117, 118 after the elapse of second stand-by time after closing the second opening / closing valve 115.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present disclosure relates to inkjet printing devices. [Background technology]

[0002] 2. Description of the Related Art Inkjet printing devices are known that form images on a recording medium by ejecting ink droplets from nozzles in an inkjet head.

[0003] The nozzles of an inkjet head are open to the atmosphere, and an ink meniscus is formed at the tip of the nozzle. Generally, the ink on the meniscus surface is exposed to air. If this condition continues for a long time, the viscosity of the ink inside the nozzle increases, and it eventually becomes impossible to eject the ink. In particular, if the meniscus is destroyed by the nozzle coming into contact with a recording medium, air from the atmosphere will enter the nozzle, further worsening the situation. On the other hand, when pigment ink or dispersible ink is used, if the ink is left in the flow path, the color particles in the ink will settle, clogging the flow path with color particles and causing uneven density in the ink.

[0004] To prevent this situation from occurring, recent inkjet printing devices have an ink circulation flow path between the inkjet head and the ink tank, and ink is supplied to the inkjet head from this circulation flow path so that the back pressure of the nozzles becomes a predetermined negative pressure (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-030425 Summary of the Invention [Problem to be solved by the invention]

[0006] In general, in this type of inkjet printing device, the ink circulation operation in the ink circulation flow path is continuously continued even when printing is not being performed. However, in recent years, there has been a demand for this type of inkjet printing device to be able to stop the ink circulation operation depending on the situation, from the perspective of energy conservation and safety measures when an operator is not present.

[0007] However, when the ink circulation in the ink circulation flow path is stopped, there is a risk that the ink meniscus formed in the nozzle may be destroyed due to a drop in the nozzle back pressure in the inkjet head, etc. (This will be described later with reference to FIG. 8). Once the ink meniscus formed in the nozzle is destroyed, ink leaks from the nozzle. In addition, this may cause the ink in the inkjet head to thicken and air to get mixed into the inkjet head. This may require a very complicated procedure, such as replacing all the ink in the ink circulation flow path, when the ink circulation in the ink circulation flow path is restarted.

[0008] The present disclosure has been made in consideration of the above-mentioned problems, and aims to provide an inkjet printing device that can prevent the ink meniscus formed in the nozzle of the inkjet head from being destroyed when the ink circulation operation in the ink circulation flow path is stopped. [Means for solving the problem]

[0009] The present disclosure mainly solves the above-mentioned problems by: an inkjet head that ejects ink droplets from nozzles; an ink tank for storing ink; a circulation flow path that communicates the ink tank with the inkjet head and constitutes a flow path through which the ink circulates; a circulation flow generating means for generating a circulation flow of the ink in the circulation flow path; a first on-off valve disposed in a path of the circulation flow path that supplies the ink from the ink tank to the inkjet head; a second on-off valve disposed in a path of the circulation flow path that returns the ink from the inkjet head to the ink tank; a control means for controlling the operation of each of the first on-off valve, the second on-off valve, and the circulation flow generating means; Equipped with when stopping the circulation operation of the ink in the circulation flow path, the control means first closes the first on-off valve, closes the second on-off valve after a first waiting time has elapsed since the first on-off valve was closed, and stops the operation of the circulation flow generating means after a second waiting time has elapsed since the second on-off valve was closed. An inkjet printing device. [Effects of the Invention]

[0010] According to the inkjet printing device of the present disclosure, it is possible to prevent the ink meniscus formed in the nozzle of the inkjet head from being destroyed when the ink circulation operation in the ink circulation flow path is stopped. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a diagram showing a schematic configuration of an inkjet printing apparatus according to an embodiment of the present invention. [Figure 2] FIG. 1 is a schematic diagram illustrating the configuration of a head unit according to an embodiment of the present invention. [Figure 3] FIG. 1 is a block diagram showing the main functional configuration of an inkjet printing apparatus according to an embodiment of the present invention. [Figure 4] FIG. 1 is a diagram showing the configuration of an ink circulation system according to an embodiment of the present invention. [Figure 5] FIG. 10 is a diagram showing an example of an operation flow when stopping the ink circulation operation in the ink circulation system according to one embodiment of the present invention. [Figure 6] FIG. 10 is a diagram showing the behavior of nozzle back pressure when the ink circulation operation is stopped in the ink circulation system according to one embodiment of the present invention. [Figure 7] FIG. 1 is a diagram showing the configuration of an ink circulation system according to a comparative example. [Figure 8] FIG. 10 is a diagram showing the behavior of nozzle back pressure when the ink circulation operation is stopped in the ink circulation system according to the comparative example. [Figure 9] FIG. 10 is a diagram showing an example of an operation flow when restarting the ink circulation operation in the ink circulation system according to one embodiment of the present invention. [Figure 10] FIG. 10 is a diagram showing the behavior of nozzle back pressure when the ink circulation operation is resumed in the ink circulation system according to one embodiment of the present invention. [Figure 11] FIG. 10 is a diagram showing the configuration of an ink circulation system according to a modified example. [Figure 12] FIG. 10 is a diagram showing the behavior of nozzle back pressure when the ink circulation operation is stopped in the ink circulation system according to the modified example. [Figure 13] FIG. 10 is a diagram showing the behavior of nozzle back pressure when the ink circulation operation is resumed in the ink circulation system according to the modified example. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, preferred embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. In this specification and drawings, components having substantially the same functions are designated by the same reference numerals, and redundant description will be omitted.

[0013] [Overall configuration of inkjet printing device] Hereinafter, the configuration of an inkjet printing apparatus 1 according to one embodiment of the present invention will be described with reference to FIGS.

[0014] FIG. 1 is a diagram showing a schematic configuration of an inkjet printing apparatus 1 according to this embodiment.

[0015] The inkjet printing apparatus 1 includes a paper feed unit 10, an image forming unit 20, a paper discharge unit 30, and a control unit 40.

[0016] Under the control of the control unit 40, the inkjet printing device 1 transports the recording medium P stored in the paper feed unit 10 to the image forming unit 20, which then ejects ink onto the recording medium P to record an image, and transports the recording medium P with the recorded image to the paper discharge unit 30. In more detail, the inkjet printing device 1 records a color image on the recording medium P by outputting four colors, yellow (Y), magenta (M), cyan (C), and black (K), overlapping each color on the recording medium P at a predetermined number of recording gradations.

[0017] As the recording medium P, in addition to paper such as plain paper or coated paper, various media such as fabric or sheet-like resin, on whose surface the ink that has landed can be fixed, can be used.

[0018] The paper feed unit 10 has a paper feed tray 11 that stores the recording medium P, and a medium supply unit 12 that transports and supplies the recording medium P from the paper feed tray 11 to the image forming unit 20. The medium supply unit 12 has a ring-shaped belt supported on the inside by two rollers, and transports the recording medium P from the paper feed tray 11 to the image forming unit 20 by rotating the rollers with the recording medium P placed on this belt.

[0019] The image forming section 20 includes a conveying section 21, a delivery unit 22, a heating section 23, a head unit 24, an irradiation section 25, and a delivery section 26.

[0020] The conveying section 21 holds the recording medium P placed on the conveying surface of a cylindrical conveying drum 211, and the conveying drum 211 rotates around a rotation axis (cylindrical axis) extending in the width direction of the recording medium P and moves in a circular motion, thereby conveying the recording medium P on the conveying drum 211 in the conveying direction along the conveying surface.

[0021] The conveying drum 211 has claws and an air intake section (not shown) for holding the recording medium P on its conveying surface. The recording medium P is held on the conveying surface by having its edges pressed down by the claws and being drawn to the conveying surface by the air intake section.

[0022] The transfer unit 22 is provided at a position between the medium supply section 12 of the paper feed section 10 and the conveying section 21, and holds and picks up one end of the recording medium P conveyed from the medium supply section 12 with a swing arm section 221, and hands it over to the conveying section 21 via a transfer drum 222.

[0023] The heating unit 23 is provided between the position where the delivery drum 222 is disposed and the position where the head unit 24 is disposed, and heats the recording medium P conveyed by the conveying unit 21 so that the temperature of the recording medium P falls within a predetermined range. The heating unit 23 has, for example, an infrared heater or the like, and energizes the infrared heater based on a control signal supplied from the control unit 40 to cause the infrared heater to generate heat.

[0024] The head unit 24 records an image by ejecting ink onto the recording medium P from nozzle openings provided on the ink ejection surface facing the transport surface of the transport drum 211 at appropriate timing according to the rotation of the transport drum 211 on which the recording medium P is held.

[0025] The head unit 24 has a plurality of inkjet heads 240, which are arranged such that the ink (droplets) ejection surface and the transport surface of each inkjet head 240 are spaced apart by a predetermined distance.

[0026] In the inkjet printing device 1 of this embodiment, four head units 24, each corresponding to one of the four colors of ink, Y, M, C, and K, are arranged at predetermined intervals in the order of Y, M, C, and K from the upstream side in the transport direction of the recording medium P. In other words, each head unit 24 is configured to be capable of ejecting a plurality of different types of ink.

[0027] In the inkjet printing device 1 of this embodiment, the head unit 24 is used in a fixed position when recording an image, and records an image using a single pass method by sequentially ejecting ink at predetermined intervals (transport direction intervals) at different positions in the transport direction as the recording medium P is transported.

[0028] 2 is a schematic diagram showing the configuration of the head unit 24 according to this embodiment. In FIG. 2, the surface of the head unit 24 that faces the outer peripheral surface of the transport drum 211 is shown.

[0029] Here, the head unit 24 includes four inkjet heads 240 attached to a mounting member 244. Each of the inkjet heads 240 includes a plurality of image-forming elements, each of which has a pressure chamber (not shown) that stores ink, a piezoelectric element (not shown) provided on the wall of the pressure chamber, and a nozzle 243. When a drive signal that causes the piezoelectric element to deform is input, the image-forming element deforms the pressure chamber due to the deformation of the piezoelectric element, changing the pressure inside the pressure chamber, and ejecting ink from the nozzle 243 that communicates with the pressure chamber.

[0030] The four inkjet heads 240 are arranged in a staggered pattern so that the arrangement range of the nozzle rows in the X direction (which indicates the direction perpendicular to the transport direction; the same applies below) is continuous without any gaps. The arrangement range in the X direction of the nozzles 243 included in the head unit 24 covers the X-direction width of the area on the recording medium P transported by the transport drum 211 where an image is formed, and the head unit 24 is used while fixed to the rotation axis of the transport drum 211 when forming an image. In other words, the head unit 24 forms a line head that can eject ink across the image formable width in the X direction on the recording medium P.

[0031] The inkjet head 240 is equipped with an ink heating unit (not shown) that heats the ink stored in the inkjet head 240, and ejects the heated ink in a sol state. When this sol ink is ejected onto the recording medium P, the ink droplets land on the recording medium P, and then the ink quickly turns into a gel state and solidifies on the recording medium P due to natural cooling.

[0032] The irradiation unit 25 is disposed across the width of the transport unit 21, and irradiates the recording medium P placed on the transport unit 21 with electromagnetic waves (for example, ultraviolet light with a wavelength of 395 nm) to cure and fix the ink ejected onto the recording medium P. The irradiation unit 25 is disposed opposite the transport surface between the position where the head unit 24 is disposed and the position where the delivery drum 261 of the delivery unit 26 is disposed in the transport direction.

[0033] The delivery section 26 has a belt loop 262 having a circular belt supported on the inside by two rollers, and a cylindrical transfer drum 261 that transfers the recording medium P from the conveying section 21 to the belt loop 262, and the recording medium P transferred from the conveying section 21 onto the belt loop 262 by the transfer drum 261 is transported by the belt loop 262 and sent to the paper discharge section 30.

[0034] The paper discharge unit 30 has a plate-shaped paper discharge tray 31 on which the recording medium P sent out from the image forming unit 20 by the delivery unit 26 is placed.

[0035] 3 is a block diagram showing the main functional configuration of the inkjet printing apparatus 1 according to this embodiment. The inkjet printing apparatus 1 according to this embodiment includes a control unit 40, a head unit drive unit 50, a transport drive unit 60, an image processing unit 70, an input / output interface 80, and an ink supply unit 90.

[0036] The control unit 40 has a central processing unit (CPU) 41, a random access memory (RAM) 42, a read only memory (ROM) 43, and a storage unit 44, and controls the overall operation of the printing device 1.

[0037] The head unit driving section 50 supplies a driving signal corresponding to the image data to the recording elements of the head unit 24 at an appropriate timing based on the control of the control section 40, thereby causing the nozzles of the head unit 24 to eject an amount of ink corresponding to the pixel values ​​of the image data.

[0038] The transport drive unit 60 supplies a drive signal to a transport drum motor provided on the transport drum 211 based on a control signal supplied from the control unit 40, thereby rotating the transport drum 211 at a predetermined speed and timing. In addition, the transport drive unit 60 supplies a drive signal to motors for operating the medium supply unit 12, the delivery unit 22, and the delivery unit 26 based on a control signal supplied from the control unit 40, thereby supplying the recording medium P to the transport unit 21 and discharging it from the transport unit 21.

[0039] The image processing unit 70 performs predetermined image processing on the image data input from the input / output interface 80, and stores the obtained image data in the storage unit 44. This image processing includes correction processing for correcting the image data, as well as color conversion processing, gradation correction processing, pseudo-halftoning processing, and the like.

[0040] The input / output interface 80 is connected to an input / output interface of an external device (for example, a personal computer) and mediates the transmission and reception of data between the control unit 40 and the external device. The input / output interface 80 is configured, for example, by any one of various serial interfaces, various parallel interfaces, or a combination of these.

[0041] The ink supply unit 90 supplies ink stored in an ink tank 111 (see FIG. 4) to each of the multiple inkjet heads 240 provided in the head unit 24. The ink supply unit 90 adjusts the amount of ink supplied to each of the multiple inkjet heads 240 in accordance with a control signal from the control unit 40.

[0042] [Configuration of ink supply unit 90] The configuration of the ink supply unit 90 according to this embodiment will be described below. The ink supply unit 90 according to this embodiment includes an ink circulation system 100 that is configured by a circulation flow path 110 that circulates ink between an ink tank 111 and an inkjet head 240.

[0043] 4 is a diagram showing the configuration of the ink circulation system 100 according to this embodiment. The ink circulation system 100 shown in FIG.

[0044] The ink circulation system 100 includes a circulation flow path 110, an ink tank 111, a liquid supply pump 112, a damper 113, a first on-off valve 114, a second on-off valve 115, an air conduit 116, a pressure adjustment valve 117, an air pump 118, and a liquid level sensor 119.

[0045] The circulation flow path 110 is a flow path through which ink circulates, communicating between the ink tank 111 and the inkjet head 240, and includes an ink supply flow path 110a that supplies ink from the ink tank 111 to the inkjet head 240, and an ink recovery flow path 110b that recovers ink from the inkjet head 240 and returns the ink to the ink tank 111. The circulation flow path 110 is configured by piping formed from, for example, hoses or pipes.

[0046] In the circulation flow path 110, ink is supplied through an ink supply flow path 110a to the pressure chambers of the image forming elements in the inkjet head 240. Of the ink supplied to the pressure chambers of the image forming elements in the inkjet head 240, the ink that is not ejected from the nozzles 243 of the inkjet head 240 is collected into the ink tank 111 through an ink collection flow path 110b.

[0047] One end of the ink supply flow path 110a is connected to the ink inlet of the inkjet head 240, and the other end is connected to the ink storage area of ​​the ink tank 111 (i.e., the lower part of the ink tank 111). Also, one end of the ink recovery flow path 110b is connected to the ink outlet of the inkjet head 240, and the other end is connected to the air buffer area 111a of the ink tank 111 (i.e., the air layer above the ink liquid surface in the ink tank 111).

[0048] For the sake of convenience, FIG. 4 shows only one inkjet head 240, but as described above, one head unit 24 is provided with a plurality of inkjet heads 240 (four in this case).

[0049] The ink tank 111 is a container for storing ink. The ink stored in the ink tank 111 is supplied to the inkjet head 240 via an ink supply flow path 110a. At this time, the ink stored in the ink tank 111 is supplied to the inkjet head 240 via a liquid feed pump 112 and a damper 113 in this order. On the other hand, of the ink supplied to the inkjet head 240, the ink that is not ejected from the inkjet head 240 is recovered into the ink tank 111 via an ink recovery flow path 110b.

[0050] The ink tank 111 is arranged in a sealed state and stores ink with a predetermined amount of air buffer area 111a remaining inside the ink tank 111. The air buffer area 111a is arranged in a state where it is suctioned by an air pump 118 so that a negative pressure higher than the negative pressure of the nozzle back pressure of the inkjet head 240 is maintained. More specifically, an air conduit 116 is connected to the air buffer area 111a of the ink tank 111, and the pressure of this air buffer area 111a is regulated by a pressure adjustment valve 117 and an air pump 118 arranged in the air conduit 116.

[0051] The liquid feed pump 112 feeds ink from the ink tank 111 to the inkjet head 240 via the ink supply flow path 110a. The ink fed from the liquid feed pump 112 is supplied to the inkjet head 240 via a damper 113. The liquid feed pump 112 is controlled by a control signal from the control unit 40.

[0052] The damper 113 is a damper mechanism provided to maintain the pressure in the pressure chamber (i.e., the back pressure of the nozzle 243) of the inkjet head 240 within an appropriate pressure range. The damper 113 is disposed between the liquid feed pump 112 and the inkjet head 240 in the ink supply flow path 110a, and absorbs pressure fluctuations in the supply pressure of the ink supplied from the liquid feed pump 112 to the inkjet head 240.

[0053] The air pump 118 applies negative pressure to the air buffer region 111a of the ink tank 111 by sucking air from the air buffer region 111a of the ink tank 111 through the air conduit 116. The pressure adjustment valve 117 is disposed between the air pump 118 and the ink tank 111 in the air conduit 116, and adjusts the suction force that the air pump 118 applies to the ink tank 111 to a suction force that corresponds to its own opening, thereby adjusting the pressure (negative pressure) within the air buffer region 111a. That is, in the ink circulation system 100, the air pump 118 and the pressure adjustment valve 117 function as an air pressure control unit that controls the pressure in the air buffer region 111a in the ink tank 111.

[0054] In the circulation flow path 110 according to this embodiment, the liquid feed pump 112, the air pump 118, and the pressure adjustment valve 117 are operated under the control of the control unit 40, thereby generating a circulation flow in which ink is sent out from the supply port of the ink tank 111, passes through the damper 113, and the inkjet head 240, and returns to the recovery port of the ink tank 111. Note that the back pressure of the nozzle 243 of the inkjet head 240 is adjusted under the control of the control unit 40 by the differential pressure between the pressure (positive pressure) of the ink ejected by the liquid feed pump 112 and the pressure (negative pressure) in the air buffer region 111a caused by the suction of air by the air pump 118 and the pressure adjustment valve 117.

[0055] The liquid pump 112, the air pump 118 and the pressure adjusting valve 117 correspond to the "circulation flow generating means" of the present invention.

[0056] The first on-off valve 114 is disposed in the ink supply flow path 110a of the circulation flow path 110, and switches the open / close state of the ink supply flow path 110a. The first on-off valve 114 is configured, for example, by a solenoid on-off valve, and opens and closes under the control of the control unit 40. Typically, the first on-off valve 114 is in an open state while ink is circulating in the circulation flow path 110 (i.e., in a normal state), and is switched to a closed state when the circulation of ink in the circulation flow path 110 is to be stopped.

[0057] The second on-off valve 115 is disposed in the ink recovery channel 110b of the circulation channel 110, and switches the open / close state of the ink recovery channel 110b. The second on-off valve 115 is configured, for example, by a solenoid on-off valve, and opens and closes under the control of the control unit 40. Typically, the second on-off valve 115 is in an open state while ink is circulating in the circulation channel 110 (i.e., in a normal state), and is switched to a closed state when the circulation of ink in the circulation channel 110 is to be stopped.

[0058] The liquid level sensor 119 is a sensor for detecting the remaining amount of ink in the ink tank 111. The liquid level sensor 119 is composed of, for example, an LED and a photosensor, and detects whether the ink level in the ink tank 111 is equal to or higher than a reference level based on the amount of light emitted from the LED received by the photosensor. The liquid level sensor 119 sends a detection signal related to the ink level in the ink tank 111 to the control unit 40.

[0059] A removable ink pack 120 is attached to the ink tank 111, and new ink is supplied from the ink pack 120 to the ink tank 111 at appropriate times. Specifically, the ink tank 111 and the ink pack 120 are connected via an ink introduction flow path 125 (e.g., a connecting pipe). The ink introduction flow path 125 is provided with an ink introduction on-off valve 124 that switches the open / close state of the ink introduction flow path 125, a degassing module 123 that removes air (gas) contained in the ink, a filter 122 that removes foreign matter such as dust and dirt that has become mixed in the ink, and a liquid feed pump 121 that sucks out ink from the ink pack 120 and pressure-feeds the ink to the ink tank 111. When the ink introduction on-off valve 124 is open, the liquid feed pump 121 is driven to flow the ink in the ink introduction flow path 125, and is sent to the ink tank 111 via the degassing module 123 and the filter 122.

[0060] The supply of ink from the ink pack 120 to the ink tank 111 is carried out under the control of the control unit 40. For example, when the control unit 40 acquires a detection signal from the liquid level sensor 119 and detects that the ink level in the ink tank 111 has fallen below a reference level, it switches the ink introduction opening / closing valve 124 from a closed state to an open state and drives the liquid feed pump 121 to supply new ink from the ink pack 120 to the ink tank 111.

[0061] Next, an operational flow when stopping the ink circulation operation in the ink circulation system 100 according to this embodiment will be described.

[0062] 5 is a diagram showing an example of an operation flow when stopping the ink circulation operation in the ink circulation system 100 according to this embodiment. Note that this operation is executed by the control unit 40, for example, when a command to stop the ink circulation operation is input by the user.

[0063] In step S1, when a command to stop the ink circulation operation or the like is input from the user, the control unit 40 first closes the first on-off valve 114.

[0064] In step S2, the control unit 40 waits for the first waiting time ΔTd1 to elapse after closing the first on-off valve 114 in step S1.

[0065] In step S3, the control unit 40 closes the second on-off valve 115 after the first waiting time ΔTd1 has elapsed in step S2.

[0066] In step S4, the control unit 40 waits for the second waiting time ΔTd2 to elapse after closing the second on-off valve 115 in step S3.

[0067] In step S5, after the second waiting time ΔTd2 has elapsed in step S4, the control unit 40 stops the operation of the circulating flow generating means (the liquid feed pump 112, the air pump 118, and the pressure regulating valve 117).

[0068] Through the above-described processing, the control unit 40 stops the ink circulation operation in the ink circulation system 100.

[0069] Figure 6 is a diagram showing the behavior of the nozzle back pressure (meaning the back pressure of the nozzle 243 of the inkjet head 240; the same applies below) when the ink circulation operation is stopped according to the operation of Figure 5 in the ink circulation system 100 of this embodiment.

[0070] In Figure 6, P nozzle is the nozzle back pressure of the inkjet head 240, P in is the pressure at the ink inlet of the inkjet head 240, P out is the pressure at the ink outlet of the inkjet head 240, P 弁上流represents the pressure in the ink supply flow path 110a upstream of the first on-off valve 114 (same below). Also, T1 represents the timing when the first on-off valve 114 is closed, T2 represents the timing when the second on-off valve 115 is closed, and T3 represents the timing when the circulating flow generating means (liquid feed pump 112, air pump 118, pressure adjustment valve 117) is stopped (same below).

[0071] First, when the first on-off valve 114 is closed (timing T1 in FIG. 6), the ink flow between the liquid feed pump 112 and the inkjet head 240 in the ink supply flow path 110a is blocked (i.e., the pressurization from the liquid feed pump 112 is not transmitted to the flow path downstream of the first on-off valve 114), and the pressure in the flow path downstream of the first on-off valve 114 in the circulation flow path 110 (i.e., the nozzle back pressure P nozzle , and the pressure P at the ink outlet of the inkjet head 240 out ) is the pressure in the air buffer area 111a of the ink tank 111 (>P nozzle ) In other words, the ink present in the pressure chamber of the inkjet head 240 is sucked into the negative pressure of the air buffer region 111a of the ink tank 111, and the negative pressure at time T1 changes to a state in which an even greater negative pressure is applied over time.

[0072] The nozzle back pressure P of the inkjet head 240 at each time point from when the first on-off valve 114 is closed to when the second on-off valve 115 is closed is nozzle is the pressure P at the ink inlet of the inkjet head 240 in and the pressure P at the ink outlet of the inkjet head 240 out The pressure is approximately halfway between the above.

[0073] Next, when the second on-off valve 115 is closed (timing T2 in FIG. 6) after the first waiting time ΔTd1 has elapsed since the first on-off valve 114 was closed, the ink flow between the inkjet head 240 and the ink tank 111 in the ink recovery flow path 110b is blocked (i.e., the negative pressure from the air buffer region 111a of the ink tank 111 is not transmitted to the flow path downstream of the second on-off valve 115 in the circulation flow path 110), and the pressure chamber of the inkjet head 240 is sealed by the ink present in the pressure chamber at time T2 when the second on-off valve 115 is closed. Then, the nozzle back pressure P nozzle After the time T2 when the second on-off valve 115 is closed, the negative pressure becomes substantially steady at the magnitude of the negative pressure at the time T2 when the second on-off valve 115 is closed.

[0074] Next, when the circulation flow generating means (the liquid pump 112, the air pump 118, and the pressure adjustment valve 117) is stopped after the second waiting time ΔTd2 has elapsed since the second opening / closing valve 115 was closed (timing T3 in FIG. 6), the pressure in the air buffer area 111a of the ink tank 111 becomes atmospheric pressure, and the pressure P 弁上流 and the pressure (not shown) downstream of the second on-off valve 115 approaches atmospheric pressure over time. However, at this time, the pressure chamber of the inkjet head 240 is sealed with ink by the first on-off valve 114 and the second on-off valve 115, so there is no ink flowing out from the pressure chamber to the ink inlet and ink outlet. Therefore, the nozzle back pressure P nozzle The negative pressure is maintained at the magnitude of the negative pressure at time T2 when the second on-off valve 115 is closed.

[0075] In the operation flow of the ink circulation system 100 according to this embodiment, the first waiting time ΔTd1 from when the first on-off valve 114 is closed until when the second on-off valve 115 is closed is determined based on the nozzle back pressure P nozzle Therefore, the length of the first waiting time ΔTd1 is an important design factor.

[0076] This is because the nozzle back pressure P nozzle This is because the negative pressure at time T1 changes to a larger negative pressure as time passes. nozzle However, when the circulation of ink in the ink circulation channel 110 is stopped, it affects the ease with which the ink meniscus formed in the nozzle of the inkjet head 240 breaks. nozzle That is, the length of the first waiting time ΔTd1 is determined based on the nozzle back pressure P nozzle It is preferable that the first waiting time ΔTd1 is set to be equal to or greater than −30 mmAq and less than −50 mmAq. The length of the first waiting time ΔTd1 in this case is, for example, several msec to several tens of msec.

[0077] More specifically, the length of the first waiting time ΔTd1 is determined by the nozzle back pressure P nozzle Therefore, the nozzle back pressure P of the inkjet head 240 when the first on-off valve 114 is closed must be set based on the rate of change of the nozzle is -30 mmAq or more and less than -50 mmAq, the length of the first waiting time ΔTd1 is preferably changed based on the number of inkjet heads 240 installed in the circulation flow path 110. This is because the output of the circulation flow generating means during the ink circulation operation (here, the output of the liquid feed pump 112 and the output of the air pump 118) is usually set to a larger value as the number of inkjet heads 240 installed in the circulation flow path 110 increases, and the nozzle back pressure P of the inkjet head 240 during the period from when the first on-off valve 114 is closed to when the second on-off valve 115 is closed decreases as the number of inkjet heads 240 installed in the circulation flow path 110 increases. nozzleThat is, the length of the first waiting time ΔTd1 is preferably set to a shorter value as the number of inkjet heads 240 present in the circulation flow path 110 increases.

[0078] Furthermore, it is preferable that the length of the first waiting time ΔTd1 is further changed based on the difference in elevation between the ink tank 111 and the inkjet head 240. This is because, when the ink tank 111 is located vertically above the inkjet head 240, the output of the circulating flow generating means during the ink circulation operation (here, the output of the liquid feed pump 112 and the output of the air pump 118) is normally set to a larger value as the difference in elevation between the ink tank 111 and the inkjet head 240 becomes smaller, and the nozzle back pressure P of the inkjet head 240 during the period from when the first on-off valve 114 is closed to when the second on-off valve 115 is closed becomes smaller as the difference in elevation between the ink tank 111 and the inkjet head 240 becomes smaller. nozzle That is, it is preferable that the length of the first waiting time ΔTd1 is set to a shorter value as the difference in elevation between the ink tank 111 and the inkjet head 240 becomes smaller.

[0079] On the other hand, the length of the second waiting time ΔTd2 is determined by the nozzle back pressure P nozzle Therefore, the length of the second waiting time ΔTd2 may be short, for example, within several msec after the closing of the second on-off valve 115 is completed. Conversely, if the length of the second waiting time ΔTd2 is set to an excessively long time, the pressure P upstream of the first on-off valve 114 may decrease as time passes after the first on-off valve 114 is closed. 弁上流 If the second waiting time ΔTd2 becomes excessively large, the first on-off valve 114 may be damaged. Therefore, the length of the second waiting time ΔTd2 is preferably less than several seconds.

[0080] Next, the nozzle back pressure P of the inkjet head 240 in the ink circulation system 100 according to this embodiment nozzleThe behavior of the nozzle back pressure P nozzle Compare with the behavior of

[0081] Fig. 7 is a diagram showing the configuration of an ink circulation system 100Z according to a comparative example, and Fig. 8 is a diagram showing the behavior of nozzle back pressure when the ink circulation operation is stopped in the ink circulation system 100Z according to the comparative example.

[0082] The ink circulation system 100Z of the comparative example differs from the ink circulation system 100 of the above embodiment in that it does not have a first on-off valve 114 or a second on-off valve 115 in the circulation flow path 110.

[0083] In the ink circulation system 100Z according to the comparative example, the first on-off valve 114 and the second on-off valve 115 are not provided, so when the ink circulation operation is stopped (i.e., the liquid feed pump 112 is stopped and the air pump 118 is stopped) and the air buffer area 111a in the ink tank 111 becomes atmospheric pressure, ink flows are immediately generated on both sides of the ink supply flow path 110a and the ink recovery flow path 110b from the pressure chamber of the inkjet head 240, which is in a negative pressure state. Then, the nozzle back pressure P nozzle will rapidly approach atmospheric pressure.

[0084] That is, in the ink circulation system 100Z according to the comparative example, after the ink circulation operation is stopped, the nozzle back pressure P nozzle As a result, in the ink circulation system 100Z according to the comparative example, the meniscus of the ink formed in the nozzle of the inkjet head 240 becomes very susceptible to destruction.

[0085] Next, an operation performed when restarting the ink circulation operation in the ink circulation system 100 according to this embodiment will be described.

[0086] 9 is a diagram showing an example of an operation flow when restarting the ink circulation operation in the ink circulation system 100 according to this embodiment. Note that this operation is executed by the control unit 40, for example, when a command to restart the ink circulation operation is input by the user.

[0087] In step S11, the control unit 40 first restarts the operation of the circulation flow generating means (liquid feed pump 112, air pump 118, and pressure adjustment valve 117).

[0088] In step S12, the control unit 40 waits for a third waiting time ΔTd3 to elapse after restarting the operation of the circulating flow generating means (liquid feed pump 112, air pump 118, and pressure adjustment valve 117) in step S11. The length of the third waiting time ΔTd3 may be a short time, for example, within several msec after restarting the operation of the circulating flow generating means.

[0089] In step S13, after the third waiting time ΔTd3 has elapsed in step S12, the control unit 40 switches the second on-off valve 115 from the closed state to the open state.

[0090] In step S14, the control unit 40 waits for a fourth waiting time ΔTd4 to elapse after switching the second on-off valve 115 from the closed state to the open state in step S13. The length of the fourth waiting time ΔTd4 may be short, for example, within several msec after switching the second on-off valve 115 from the closed state to the open state.

[0091] In step S15, the control unit 40 opens the first on-off valve 114 after the fourth waiting time ΔTd4 has elapsed in step S14.

[0092] Through the above process, the control unit 40 restarts the ink circulation operation in the ink circulation system 100. When restarting the ink circulation operation, the nozzle back pressure P nozzleIf the pressure is reduced, the ink meniscus formed in the nozzle 243 of the inkjet head 240 will be destroyed, but by operating each part in the above order, it is possible to prevent this from happening.

[0093] Fig. 10 is a diagram showing the behavior of the nozzle back pressure when the ink circulation operation is resumed in the ink circulation system 100 according to this embodiment according to the operation of Fig. 9. In Fig. 10, T4 represents the timing when the operation of the circulation flow generating means (liquid feed pump 112, air pump 118, and pressure adjustment valve 117) is resumed, T5 represents the timing when the second on-off valve 115 is opened, and T6 represents the timing when the first on-off valve 114 is opened.

[0094] First, when the operation of the circulation flow generating means (liquid supply pump 112, air pump 118, pressure adjustment valve 117) is resumed (timing T4 in FIG. 10), the first on-off valve 114 is still in a closed state at this time, so the pressure P 弁上流 The positive pressure in the ink tank 110 gradually increases over time due to the influence of the ink delivery pressure (positive pressure) determined by the output of the liquid delivery pump 112. Similarly, because the second on-off valve 115 is still closed, the negative pressure in the circulation flow path 110 downstream of the second on-off valve 115 gradually increases over time due to the influence of the pressure (negative pressure) in the air buffer region 111a of the ink tank 111 (not shown).

[0095] Next, when the second on-off valve 115 is opened after a third waiting time ΔTd3 has elapsed since the operation of the circulating flow generating means was restarted (timing T5 in FIG. 10), the negative pressure from the air buffer region 111a of the ink tank 111 is transmitted to the pressure chamber of the inkjet head 240, and the nozzle back pressure P nozzle (and the pressure P at the ink outlet of the inkjet head 240 out) indicates a behavior in which the pressure approaches the pressure in the air buffer region 111a of the ink tank 111. That is, the ink present in the pressure chamber of the inkjet head 240 is sucked into the negative pressure in the air buffer region 111a of the ink tank 111, and the negative pressure at time T5 changes to a state in which an even greater negative pressure is applied over time.

[0096] Next, when the first on-off valve 114 is opened after a fourth waiting time ΔTd4 has elapsed since the second on-off valve 115 was opened (timing T6 in FIG. 10), the ink flow in the ink supply flow path 110a is brought into a flowing state, and the pressure P in is the pressure P upstream of the first on-off valve 114 弁上流 (positive pressure) over time. nozzle (and the pressure P at the ink outlet of the inkjet head 240 out ) is the pressure P at the ink inlet of the inkjet head 240 in It changes to the positive side due to the rise in

[0097] In this way, the nozzle back pressure P nozzle Ultimately, the ink reaches a steady state at a predetermined negative pressure level due to the balance between the ink delivery pressure determined by the output of the liquid delivery pump 112 and the ink suction pressure determined by the output of the air pump 118 and the pressure adjustment valve 117.

[0098] [effect] As described above, the inkjet printing apparatus 1 according to this embodiment has the following features: an inkjet head that ejects ink droplets from nozzles; an ink tank for storing ink; a circulation flow path that communicates the ink tank with the inkjet head and constitutes a flow path through which the ink circulates; a circulation flow generating means for generating a circulation flow of the ink in the circulation flow path; a first on-off valve disposed in a path of the circulation flow path that supplies the ink from the ink tank to the inkjet head; a second on-off valve disposed in a path of the circulation flow path that returns the ink from the inkjet head to the ink tank; a control means for controlling the operation of each of the first on-off valve, the second on-off valve, and the circulation flow generating means; Equipped with When the control means stops the circulation operation of the ink in the circulation flow path, it first closes the first on-off valve, closes the second on-off valve after a first waiting time has elapsed since closing the first on-off valve, and stops the operation of the circulation flow generating means after a second waiting time has elapsed since closing the second on-off valve.

[0099] Therefore, according to the inkjet printing device 1 of this embodiment, when the circulation of ink in the ink circulation channel 110 is stopped, the pressure chamber of the inkjet head 240 can be sealed with ink, and the nozzle back pressure of the inkjet head 240 can be maintained at a predetermined negative pressure. This makes it possible to maintain the ink meniscus formed in the nozzle even when the circulation of ink in the ink circulation channel 110 is stopped.

[0100] (Variation) FIG. 11 is a diagram showing the configuration of an ink circulation system 100 according to a modified example.

[0101] In the inkjet printing device 1 according to the above embodiment, the circulation flow generating means (liquid supply pump 112, air pump 118, pressure adjustment valve 117) that generates a circulation flow of ink in the circulation flow path 110 is configured to include the liquid supply pump 112 that pressure-feeds the ink in the ink tank 111 toward the inkjet head 240, and the air pump 118 and pressure adjustment valve 117 that control the pressure in the air buffer region in the ink tank 111.

[0102] The inkjet printing device 1 of this modified example has, in the circulation flow path 110, a supply-side ink tank 111X arranged to supply ink to the inkjet head 240, and a recovery-side ink tank 111Y arranged to recover ink from the inkjet head 240, and in addition has a first air pressure control unit that controls the pressure in the air buffer area 111Xa in the supply-side ink tank 111, and a second air pressure control unit that controls the pressure in the air buffer area 111Ya in the recovery-side ink tank 111.

[0103] In the inkjet printing apparatus 1 according to this modification, the first air pressure control unit is made up of an air pump 118 and a pressure adjustment valve 117X disposed in an air conduit 116X connected to an air buffer region 111Xa in the supply-side ink tank 111X, and the second air pressure control unit is made up of an air pump 118 and a pressure adjustment valve 117Y disposed in an air conduit 116Y connected to an air buffer region 111Ya in the recovery-side ink tank 111Y. Here, the first air pressure control unit and the second air pressure control unit share the air pump 118, and the suction pressure of the first air pressure control unit (i.e., the negative pressure in the air buffer region 111Xa) and the suction pressure of the second air pressure control unit (i.e., the negative pressure in the air buffer region 111Ya) are adjusted to generate a predetermined pressure difference by controlling the pressure adjustment valves 117X and 117Y.

[0104] In the inkjet printing apparatus 1 according to this modification, the difference in pressure between the air buffer region 111Xa in the supply ink tank 111X and the air buffer region 111Ya in the recovery ink tank 111Y generates a circulating flow of ink in the circulation channel 110. That is, in the inkjet printing apparatus 1 according to this modification, the first air pressure control unit (air pump 118 and pressure adjustment valve 117X) and the second air pressure control unit (air pump 118 and pressure adjustment valve 117Y) are operated under the control of the control unit 40, thereby generating a circulating flow in which ink is sent out from the supply ink tank 111X, passes through the inkjet head 240, and returns to the recovery ink tank 111Y.

[0105] In the circulation flow path 110 according to this modification, the supply ink tank 111X and the recovery ink tank 111Y are connected by an ink feed flow path 110c, and ink recovered in the recovery ink tank 111Y is sent to the supply ink tank 111X via the ink feed flow path 110c. A liquid feed pump 112c is disposed in the ink feed flow path 110c, and liquid is sent from the recovery ink tank 111Y to the supply ink tank 111X by driving the liquid feed pump 112c.

[0106] Liquid level sensors 119X and 119Y are provided respectively in the supply-side ink tank 111 and the recovery-side ink tank 111. Using the detection signals of the liquid level sensors 119X and 119Y, the control unit 40 determines the timing and amount of ink to be sent from the recovery-side ink tank 111Y to the supply-side ink tank 111X, and the timing and amount of ink to be sent from the ink pack 120 to the supply-side ink tank 111X.

[0107] For example, when the control unit 40 detects, based on a detection signal from the liquid level sensor 119Y, that the amount of ink stored in the recovery side ink tank 111Y is equal to or greater than a reference value, the control unit 40 drives the liquid feed pump 112c to feed ink from the recovery side ink tank 111Y to the supply side ink tank 111X. Also, when the control unit 40 detects, based on a detection signal from the liquid level sensor 119X, that the amount of ink stored in the supply side ink tank 111X is less than a reference value, the control unit 40 drives the liquid feed pump 112c to feed ink from the ink pack 120 to the supply side ink tank 111X.

[0108] In the ink circulation system 100 according to this modified example, the operational flow when stopping the ink circulation operation and the operational flow when restarting the ink circulation operation are the same as the respective operational flows in the ink circulation system 100 according to the above embodiment (see Figures 5 and 9).

[0109] Fig. 12 is a diagram showing the behavior of nozzle back pressure when the ink circulation operation is stopped according to the operation of Fig. 5 in the ink circulation system 100 according to the modified example. Fig. 13 is a diagram showing the behavior of nozzle back pressure when the ink circulation operation is resumed according to the operation of Fig. 9 in the ink circulation system 100 according to the modified example.

[0110] The behavior of the nozzle back pressure when the ink circulation operation is stopped and restarted in the ink circulation system 100 according to this modified example is also substantially the same as the behavior of the nozzle back pressure according to the above embodiment (see FIGS. 6 and 10).

[0111] However, in the ink circulation system 100 according to this modification, the circulation flow generating means is configured by a first air pressure control unit that controls the pressure in the air buffer area 111Xa in the supply ink tank 111X, and a second air pressure control unit that controls the pressure in the air buffer area 111Ya in the recovery ink tank 111Y. Therefore, the behavior of the pressure in each unit shown in FIG. 12 is the pressure P 弁上流 13. Similarly, the behavior of the pressure at each part shown in FIG. 13 differs from the behavior in FIG. 6 only in the behavior of the pressure P 弁上流 Only the behavior of is different from that of Figure 10.

[0112] Specifically, in the ink circulation system 100 according to this modification, the suction pressure of the first air pressure control unit and the suction pressure of the second air pressure control unit are adjusted during the first waiting time ΔTd1 and the second waiting time ΔTd2. At this time, the pressure P 弁上流 In other words, in the ink circulation system 100 according to this modification, the pressure P 弁上流 Therefore, the situation where the temperature rises abnormally and the first on-off valve 114 is damaged can be prevented.

[0113] As described above, in the ink circulation system 100 according to this modified example, when the ink circulation operation in the ink circulation flow path 110 is stopped, the pressure chamber of the inkjet head 240 is sealed with ink, and the nozzle back pressure of the inkjet head 240 can be maintained at a predetermined negative pressure.

[0114] Although specific examples of the present invention have been described above in detail, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and alterations of the specific examples exemplified above. [Industrial Applicability]

[0115] According to the inkjet printing device of the present disclosure, it is possible to prevent the ink meniscus formed in the nozzle of the inkjet head from being destroyed when the ink circulation operation in the ink circulation flow path is stopped. [Explanation of symbols]

[0116] 1. Inkjet printing device 10 Paper feed section 20 Image forming unit 240 Inkjet head 243 Nozzle 30 Paper output section 40 Control unit (control means) 50 Head unit drive unit 60 Conveyor drive unit 70 Image processing section 80 Input / Output Interface 90 Ink supply unit 100 Ink Circulation System 110, 110a, 110b, 110c circulation flow path 111, 111X, 111Y Ink Tank 111a, 111Xa, 111Ya Air buffer area 112, 112c, 121 Liquid transfer pump 113 Damper 114 First shut-off valve 115 Second shut-off valve 116, 116X, 116Y Air ducts 117, 117X, 117Y Pressure Regulating Valve 118 Air Pump 119, 119X, 119Y Liquid Level Sensor 120 ink packs 122 filters 123 Degassing Module 124 Ink introduction opening / closing valve 125 Ink introduction channel P Recording medium

Claims

1. an inkjet head that ejects ink droplets from nozzles; an ink tank for storing ink; a circulation flow path that communicates the ink tank with the inkjet head and constitutes a flow path through which the ink circulates; a circulation flow generating means for generating a circulation flow of the ink in the circulation flow path; a first on-off valve disposed in a path of the circulation flow path that supplies the ink from the ink tank to the inkjet head; a second on-off valve disposed in a path of the circulation flow path that returns the ink from the inkjet head to the ink tank; a control means for controlling the operation of each of the first on-off valve, the second on-off valve, and the circulation flow generating means; Equipped with when stopping the circulation of the ink in the circulation flow path, the control means first closes the first on-off valve, closes the second on-off valve after a first waiting time has elapsed since the first on-off valve was closed, and stops the operation of the circulation flow generating means after a second waiting time has elapsed since the second on-off valve was closed; The length of the first waiting time is set to the time from when the first on-off valve is closed until the back pressure of the nozzle becomes equal to or greater than −30 mmAq and less than −50 mmAq. Inkjet printing device.

2. the circulating flow generating means is composed of a liquid feed pump that pressure-feeds the ink in the ink tank to the inkjet head, and an air pressure control unit that controls the pressure in an air buffer region in the ink tank. The inkjet printing apparatus of claim 1 .

3. the ink tank includes a supply-side ink tank arranged to supply the ink to the inkjet head, and a recovery-side ink tank arranged to recover the ink from the inkjet head; the circulation flow generating means is composed of a first air pressure control unit that controls the pressure in an air buffer region in the supply-side ink tank, and a second air pressure control unit that controls the pressure in an air buffer region in the recovery-side ink tank.

3. The inkjet printing apparatus according to claim 1 or 2.

4. an inkjet head that ejects ink droplets from nozzles; an ink tank for storing ink; a circulation flow path that communicates the ink tank with the inkjet head and constitutes a flow path through which the ink circulates; a circulation flow generating means for generating a circulation flow of the ink in the circulation flow path; a first on-off valve disposed in a path of the circulation flow path that supplies the ink from the ink tank to the inkjet head; a second on-off valve disposed in a path of the circulation flow path that returns the ink from the inkjet head to the ink tank; a control means for controlling the operation of each of the first on-off valve, the second on-off valve, and the circulation flow generating means; Equipped with when stopping the circulation of the ink in the circulation flow path, the control means first closes the first on-off valve, closes the second on-off valve after a first waiting time has elapsed since the first on-off valve was closed, and stops the operation of the circulation flow generating means after a second waiting time has elapsed since the second on-off valve was closed; When restarting the circulating operation of the ink in the circulation flow path after the circulating operation of the ink has been stopped, the control means first starts the operation of the circulating flow generating means, opens the first on-off valve after a third waiting time has elapsed since the operation of the circulating flow generating means has started, and opens the second on-off valve after a fourth waiting time has elapsed since the first on-off valve has been opened. Inkjet printing device.

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