JP7753780B2 - Inkjet printing device - Google Patents

Description

This disclosure relates to an inkjet printing device.

Inkjet printing devices are known that form images on a recording medium by ejecting ink droplets from the nozzles of an inkjet head.

In recent years, pigment-based inks have been developed for use in this type of inkjet printing device. While pigment-based inks are expected to have excellent water resistance and light resistance, they are known to cause pigment aggregation and sedimentation. To solve this problem, various dispersants have been developed to maintain stable pigment dispersion over long periods of time. A wide range of dispersants are used in pigment inks, from relatively low-molecular-weight dispersants such as surfactants to high-molecular-weight dispersants such as styrene-acrylic resins. All dispersants have a hydrophobic portion that adsorbs to the pigment and a hydrophilic portion that disperses in water, allowing hydrophobic organic pigments to disperse in water, and the carbon chains are long enough to exert a steric effect sufficient to maintain a stable dispersion.

In addition, recent trends in pigment ink development have seen an increase in the pigment concentration in the ink, a reduction in the amount of high-boiling-point solvent in the ink, and an increase in the proportion of water, all with the aim of reducing ink costs and improving image quality. However, this has raised concerns about a decrease in the dispersion stability of the dispersion stabilizer in the ink and an increase in the ink's drying properties (i.e., ink viscosity), making it necessary to master the use of ink on inkjet printing devices.

WO 2009/157139

Inkjet printing devices that use such pigment inks have an ink circulation system between the inkjet head and the ink tank to prevent the ink from drying out. Ink is then supplied to the inkjet head from this circulation system so that the back pressure at the nozzles is maintained at a predetermined pressure.

As a result of extensive research by the inventors of this application, they have found that in such an ink circulation system, the ink continually passes through filters for degassing the ink, filters for removing foreign matter, and filters inside the head, and that the shear force applied to the dispersant in the ink as it passes through the filters causes it to peel off from the pigment in the ink or to split within the ink, destroying the stable dispersion state of the pigment and causing the pigment to aggregate at a rapid rate.

Figure 1 is a diagram that shows the process by which pigment aggregation occurs. When this type of pigment aggregation occurs, not only does it render the ink itself unusable, but it also clogs the filter inside the head, ultimately shortening the head life of the inkjet head (for example, resulting in ejection problems).

In such ink circulation systems, simply reducing the ink flow rate and the frequency with which the ink is circulated can suppress the rate at which the pigment in the ink aggregates, but this does not solve the underlying problem, as it leads to another problem: the settling of the pigment in the ink (i.e., the sedimentation of pigment particles). Furthermore, the settling of the pigment in the ink leads to a decrease in the pigment concentration in the ink, which is a factor in degrading image quality during printing.

Patent Document 1 proposes an inkjet printing device in which an ink supply channel is attached to an ink supply tank, allowing ink to circulate without passing through the inkjet head. Even when ink is not being supplied to the inkjet head, the inkjet printing device in Patent Document 1 performs an ink circulation operation in which ink is drawn up from the ink tank through one end of the ink supply channel, flows into the ink supply channel, and then returned to the ink tank through the other end of the ink supply channel, thereby preventing pigment sedimentation in the ink supply channel or ink tank.

The ink circulation system described in Patent Document 1 is an effective measure for preventing the pigment in the ink from settling, but even with this ink circulation system, the pigment ink is continuously subjected to shear forces as it passes through the filter, which can cause pigment aggregation due to circulation.

This disclosure was made in consideration of the above-mentioned problems, and aims to provide an inkjet printing device that can suppress both pigment sedimentation and pigment aggregation in ink.

The present disclosure mainly solves the above-mentioned problems by:
an inkjet head that ejects ink;
an ink tank for storing the ink;
a circulation flow path that circulates the ink between the ink tank and the inkjet head;
a bypass flow path connected to the circulation flow path so as to bypass a position where a first in-passage filter in a main flow path of the circulation flow path and/or a head filter of the inkjet head are disposed;
a control device that controls a flow pattern of the ink in the main flow path and the bypass flow path by controlling a flow path switching valve disposed in the main flow path and/or the bypass flow path;
Equipped with
When printing is performed under a first printing condition, the control device causes the ink to flow through the main flow path without causing the ink to flow through the bypass flow path, and when printing is performed under a second printing condition that has a lower coverage rate of the printing target than the first printing condition or when not printing, causes the ink to flow through both the bypass flow path and the main flow path.
An inkjet printing device.

In other respects,
an inkjet head that ejects ink;
an ink tank for storing the ink;
a circulation flow path that circulates the ink between the ink tank and the inkjet head;
a bypass flow path connected to the circulation flow path so as to bypass a position where a first in-passage filter is disposed in the main flow path of the circulation flow path, and which is used simultaneously with the main flow path when the operating state of the printing device is in a predetermined state;
a control device that controls a flow pattern of the ink in the main flow path and the bypass flow path by controlling a flow path switching valve disposed in the main flow path and/or the bypass flow path;
An inkjet printing apparatus comprising:

In other respects,
an inkjet head that ejects ink;
an ink tank for storing the ink;
a circulation flow path that circulates the ink between the ink tank and the inkjet head;
a bypass flow path connected to the circulation flow path so as to bypass a position where the inkjet head is disposed in the main flow path of the circulation flow path, and which is used simultaneously with the main flow path when the operating state of the printing apparatus is in a predetermined state;
a control device that controls a flow pattern of the ink in the main flow path and the bypass flow path by controlling a flow path switching valve disposed in the main flow path and/or the bypass flow path;
An inkjet printing apparatus comprising:

The inkjet printing device disclosed herein can suppress both pigment sedimentation and pigment aggregation in the ink.

Schematic diagram showing the process of pigment aggregation FIG. 1 is a diagram showing a schematic configuration of an inkjet printing apparatus according to an embodiment of the present invention. FIG. 1 is a schematic diagram illustrating the configuration of a head unit according to an embodiment of the present invention. FIG. 1 is a block diagram showing the main functional configuration of an inkjet printing apparatus according to an embodiment of the present invention. An example of the configuration of an ink circulation system according to an embodiment of the present invention FIG. 10 is a diagram showing an example of a data table that defines the usage conditions of bypass channels (first bypass channel, second bypass channel, and third bypass channel) in the ink circulation system according to an embodiment of the present invention. FIG. 7 is a diagram showing the ink circulation state in the first circulation mode shown in FIG. 6 . FIG. 7 is a diagram showing the ink circulation state in the second circulation mode shown in FIG. 6 . FIG. 7 is a diagram showing the ink circulation state in the third circulation mode shown in FIG. 6 . FIG. 7 is a diagram showing the ink circulation state in the fourth circulation mode shown in FIG. 6 . FIG. 7 is a diagram showing an example of an ink circulation mode change operation executed by a control unit according to an embodiment of the present invention, with reference to the data table of FIG. 6; FIG. 1 is a diagram showing a comparison of the shear force acting on ink when the ink is circulated once in the circulation flow path via a bypass flow path and the shear force acting on ink when the ink is circulated once in the circulation flow path without passing through the bypass flow path in an ink circulation system according to an embodiment of the present invention. Diagram showing the configuration of the ink circulation system prepared for the verification experiment FIG. 10 shows the results of the first verification experiment. FIG. 10 shows the results of the second verification experiment.

Preferred embodiments of the present disclosure will be described in detail below with reference to the accompanying drawings. Note that in this specification and drawings, components having substantially the same functions will be designated by the same reference numerals, and redundant explanations will be omitted.

[Overall configuration of inkjet printing device]
The configuration of an inkjet printing apparatus (hereinafter also referred to as "printing apparatus") 1 according to one embodiment of the present invention will be described below with reference to FIGS.

Figure 2 is a diagram showing the general configuration of an inkjet printing device 1 according to one embodiment of the present invention.

The printing device 1 includes a paper feed unit 10, an image forming unit 20, a paper discharge unit 30, and a control unit 40.

Under the control of the control unit 40, the 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 printing device 1 records a color image on the recording medium P by overlaying and outputting four colors, yellow (Y), magenta (M), cyan (C), and black (K), onto the recording medium P at a predetermined number of recording gradations.

The recording medium P can be any medium capable of fixing ink that lands on its surface, such as plain paper, coated paper, fabric, or sheet-like resin.

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

The image forming unit 20 has a conveying unit 21, a transfer unit 22, a heating unit 23, a head unit 24, an irradiation unit 25, and a delivery unit 27.

The transport unit 21 holds the recording medium P placed on the transport surface of the cylindrical transport drum 211, and the transport drum 211 rotates and moves around a rotation axis (cylindrical axis) extending in the width direction of the recording medium P, thereby transporting the recording medium P on the transport drum 211 in the transport direction along the transport surface.

The transport drum 211 is equipped with claws and an air intake (not shown) for holding the recording medium P on its transport surface. The recording medium P is held on the transport surface by having its edges pressed down by the claws and being drawn to the transport surface by the air intake.

The transfer unit 22 is located between the media supply unit 12 and the transport unit 21 of the paper feed unit 10, and uses the swing arm unit 221 to hold and pick up one end of the recording medium P transported from the media supply unit 12, and then transfers it to the transport unit 21 via the transfer drum 222.

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 transported by the transport unit 21 so that the temperature of the recording medium P falls within a predetermined temperature range. The heating unit 23 has, for example, an infrared heater, and energizes the infrared heater based on a control signal supplied from the control unit 40 to cause the infrared heater to generate heat.

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.

The head unit 24 has multiple inkjet heads, which are arranged so that the ink (droplet) ejection surface and transport surface of each inkjet head are separated by a predetermined distance.

In the printing device 1 of this embodiment, four head units 24, each corresponding to one of the four ink colors Y, M, C, and K, are arranged at a predetermined interval 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 multiple different types of ink.

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.

Figure 3 is a schematic diagram showing the configuration of the head unit 24. This shows the surface of the head unit 24 that faces the outer peripheral surface of the transport drum 211.

Here, the head unit 24 comprises three inkjet heads 240 attached to a mounting member 244. Each inkjet head 240 is provided with a plurality of image-forming elements (recording 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 within the pressure chamber, and ejecting ink from the nozzle 243 that communicates with the pressure chamber.

The three inkjet heads 240 are arranged in a staggered pattern so that the nozzle row's arrangement range in the X direction is continuous without 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 has a line head that can eject ink across the image formation width in the X direction on the recording medium P.

The inkjet head 240 is equipped with an ink heating unit (not shown) that heats the ink stored within 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.

The irradiation unit 25 is positioned across the width of the transport unit 21 and irradiates the recording medium P placed on the transport unit 21 with electromagnetic waves (e.g., ultraviolet light with a wavelength of 395 nm) to harden and fix the ink ejected onto the recording medium P. The irradiation unit 25 is positioned opposite the transport surface in the transport direction, between the position of the head unit 24 and the position of the transfer drum 271 of the delivery unit 27.

The delivery unit 27 has a belt loop 272 with a circular belt supported on the inside by two rollers, and a cylindrical transfer drum 271 that transfers the recording medium P from the conveyance unit 21 to the belt loop 272. The recording medium P transferred from the conveyance unit 21 onto the belt loop 272 by the transfer drum 271 is then transported by the belt loop 272 and sent to the paper discharge unit 30.

The paper discharge unit 30 has a plate-shaped paper discharge tray 31 on which the recording medium P sent from the image forming unit 20 by the delivery unit 27 is placed.

Figure 4 is a block diagram showing the main functional configuration of the printing device 1. The printing device 1 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 100.

The control unit 40 has a CPU 41 (Central Processing Unit), RAM 42 (Random Access Memory), ROM 43 (Read Only Memory), and a storage unit 44, and controls the overall operation of the printing device 1.

The head unit drive unit 50 supplies drive signals corresponding to the image data to the recording elements of the head unit 24 at appropriate timing under the control of the control unit 40, causing the nozzles of the head unit 24 to eject an amount of ink corresponding to the pixel values of the image data.

Based on a control signal supplied from the control unit 40, the transport drive unit 60 supplies a drive signal to a transport drum motor provided on the transport drum 211, causing the transport drum 211 to rotate at a predetermined speed and timing. Based on a control signal supplied from the control unit 40, the transport drive unit 60 also supplies drive signals to motors for operating the medium supply unit 12, the transfer unit 22, and the delivery unit 27, causing the recording medium P to be supplied to and discharged from the transport unit 21.

The image processing unit 70 performs predetermined image processing on the image data input from the input/output interface 80 and stores the resulting image data in the storage unit 44. This image processing includes correction processing to correct the image data, as well as color conversion processing, gradation correction processing, and pseudo-halftoning processing.

The input/output interface 80 is connected to the input/output interface of an external device (e.g., 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 may be configured, for example, as one of various serial interfaces, various parallel interfaces, or a combination of these.

The ink supply unit 90 supplies ink stored in the ink tank 101 (see Figure 5) 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 control signals from the control unit 40.

[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 includes a circulation flow path 110 (see FIG. 5 ) that circulates ink between an ink tank 101 and an inkjet head 240.

Figure 5 is a diagram showing an example of the configuration of an ink circulation system 100 according to this embodiment. Note that the ink circulation system 100 shown in Figure 5 is provided for each color of ink.

The circulation flow path 110 of the ink circulation system 100 has main flow paths (hereinafter also referred to as main flow paths 110a and 110b) that form an ink supply flow path 110a that supplies ink from the ink tank 101 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 101. Note that the main flow paths 110a and 110b are flow paths that are always in use.

In other words, the ink circulation system 100 supplies ink to the pressure chambers of each image forming element in the inkjet head 240 via the ink supply channel 110a. Of the ink supplied to the pressure chambers of each image forming element in the inkjet head 240, any ink that is not ejected from the nozzles 243 of the inkjet head 240 is recovered into the ink tank 101 via the ink recovery channel 110b. The ink supply channel 110a is connected to the ink inlet of the inkjet head 240, and the ink recovery channel 110b is connected to the ink outlet of the inkjet head 240.

The inkjet head 240 is provided with a head filter 240a in a flow path formed within the inkjet head 240, and further downstream, a pressure chamber and nozzle 243 connected to the flow path are provided. In other words, ink supplied to the inkjet head 240 is ejected from the nozzle 243 via the head filter 240a. The head filter 240a is a filter for removing foreign matter from the ink supplied to the inkjet head 240, and is made, for example, of a nonwoven fabric with a porous structure.

Note that although Figure 5 shows three inkjet heads 240, in this embodiment, all three inkjet heads 240 have the same configuration, and when no distinction is made between these three inkjet heads 240, only one of the inkjet heads 240 will be described.

A bypass flow path 111 is connected to the circulation flow path 110 so as to bypass the position of the first in-passage filter 140 or the head filter 240a of the inkjet head 240 in the main flow paths 110a, 110b. The ink circulation system 100 according to this embodiment is provided with the following bypass flow paths 111: a first bypass flow path 111a that bypasses the first in-passage filter 140, a second bypass flow path 111b that bypasses the head filter 240a, and a third bypass flow path 111c that bypasses the first in-passage filter 140 and the head filter 240a. The configuration of the bypass flow path 111 will be described in detail below.

The ink supply flow path 110a, the ink recovery flow path 110b, and the bypass flow path 111 are configured, for example, by piping formed from hoses or pipes.

The ink circulation system 100 includes an ink tank 101, a supply pump 121, a recovery pump 122, a supply damper 102, a recovery damper 103, a degassing module 130, a first passage filter 140, a second passage filter 141, and first, second, and third flow path switching valves 150a to 150c.

Here, the supply-side pump 121, degassing module 130, supply damper 102, and first passage filter 140 are arranged in this order in the ink supply flow path 110a, from the ink tank 101 side toward the inkjet head 240 side. Furthermore, the recovery damper 103 and recovery-side pump 122 are arranged in this order in the ink recovery flow path 110b, from the inkjet head 240 side toward the ink tank 101 side.

The ink tank 101 is a container for storing ink. The ink stored in the ink tank 101 is supplied to the inkjet head 240 via the ink supply flow path 110a. At this time, the ink stored in the ink tank 101 is supplied to the inkjet head 240 via the supply side pump 121, degassing module 130, supply damper 102, and first passage filter 140, in that order. Meanwhile, 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 101 via the ink recovery flow path 110b. At this time, the ink that is not ejected from the inkjet head 240 is returned to the ink tank 101 via the recovery damper 103 and the recovery side pump 122.

In addition, a removable ink pack (not shown) is attached to the ink tank 101, for example, via a connecting pipe, and ink is supplied from the ink pack at appropriate times.

The supply-side pump 121 sends ink from the ink tank 101 to the inkjet head 240 via the ink supply flow path 110a. The ink sent from the supply-side pump 121 is supplied to the inkjet head 240 via the degassing module 130, filter 140, and supply damper 102. The supply-side pump 121 is disposed, for example, between the degassing module 130 and the ink tank 101 in the ink supply flow path 110a. The supply-side pump 121 is controlled by a control signal from the control unit 40.

The recovery pump 122 recovers ink from inside the inkjet head 240 via the ink recovery flow path 110b and sends it to the ink tank 101. The ink recovered from the inkjet head 240 by the operation of the recovery pump 122 is returned to the ink tank 101 via the recovery damper 103. The recovery pump 122 is disposed, for example, between the recovery damper 103 and the ink tank 101 in the ink recovery flow path 110b. The recovery pump 122 is controlled by a control signal from the control unit 40.

When the supply pump 121 and the recovery pump 122 are driven, ink is pumped out of the ink tank 101, passes through the supply damper 102, the inkjet head 240, and the recovery damper 103, and a circulating flow is generated in which ink returns to the ink tank 101.

The supply damper 102 and recovery damper 103 are damper mechanisms arranged to maintain the pressure inside the pressure chamber of the inkjet head 240 (i.e., the back pressure of the nozzle 243) within an appropriate pressure range. The supply damper 102 is arranged, for example, between the supply-side pump 121 and the inkjet head 240 in the ink supply flow path 110a, and absorbs pressure fluctuations in the supply pressure of the ink supplied to the inkjet head 240. The recovery damper 103 is arranged, for example, between the inkjet head 240 and the recovery-side pump 122 in the ink recovery flow path 110b, and absorbs pressure fluctuations in the suction pressure of the ink recovered from the inkjet head 240.

The supply damper 102 and recovery damper 103 are configured, for example, to include a housing and a flexible damper membrane (e.g., a rubber member) that covers the opening surface of the housing. The damper membrane bends outward or inward in response to ink pressure fluctuations, changing the volume of the damper chamber formed inside the housing and absorbing the pressure fluctuations.

In the printing device 1 according to this embodiment, the back pressure of the nozzle 243 is adjusted by the differential pressure between the ink pressure in the supply damper 102 and the ink pressure in the recovery damper 103. That is, by controlling the ink pressure in the supply damper 102 and the ink pressure in the recovery damper 103, the flow rate (i.e., flow velocity) of ink circulating through the circulation flow path 110 is adjusted, and the flow rate of ink flowing from the ink tank 101 to the nozzle 243 (i.e., the amount of ink ejected from the nozzle 243) is adjusted. This adjustment process is performed by, for example, the control unit 40.

The degassing module 130 is a filter that removes air (gas) contained in the ink. The degassing module 130 uses a structure that selectively sucks air from the ink into the vacuum region by bringing the ink into contact with the vacuum region via a degassing membrane, for example.

The first intra-passage filter 140 removes foreign matter such as dust and dirt that gets mixed in with the ink flowing through the circulation flow path 110. The first intra-passage filter 140 is disposed, for example, between the supply damper 102 and the inkjet head 240 in the ink supply flow path 110a. The first intra-passage filter 140 is made, for example, of a nonwoven fabric with a porous structure.

The second intra-passage filter 141, like the first intra-passage filter 140, is a filter that removes foreign matter such as dust and dirt that gets mixed in with the ink flowing through the circulation flow path 110. The second intra-passage filter 141 is disposed in the first bypass flow path 111a. As will be described in more detail below, the first bypass flow path 111a is a flow path used when the printing coverage rate is medium (e.g., 5% to 20%). Therefore, the second intra-passage filter 141 is not required to have the same high foreign matter removal function (i.e., foreign matter capture rate) as the first intra-passage filter 140, but rather is required to apply a small shear force to the ink.

From this perspective, the second passage filter 141 is preferably a filter with a larger filter pore size or effective filtration area than the first passage filter 140. This reduces the shear force applied to the ink as it passes through the filter, even when the ink circulation flow rate is increased. Furthermore, the second passage filter 141 is preferably, for example, a depth filter, which generally has filter characteristics that result in a larger effective filtration area than a screen filter.

The first, second, and third flow path switching valves 150a-150c are valves that switch whether or not ink flowing through the circulation flow path 110 is allowed to flow through the circulation flow path 110 via the bypass flow path 111.

Specifically, the first flow path switching valve 150a is disposed in the first bypass flow path 111a. When open, it allows ink to flow through the first bypass flow path 111a, and when closed, it prohibits ink from flowing through the first bypass flow path 111a. The second flow path switching valve 150b is disposed in the second bypass flow path 111b. When open, it allows ink to flow through the second bypass flow path 111b, and when closed, it prohibits ink from flowing through the second bypass flow path 111b. The third flow path switching valve 150a is disposed in the third bypass flow path 111c. When open, it allows ink to flow through the third bypass flow path 111a, and when closed, it prohibits ink from flowing through the third bypass flow path 111c.

The first, second, and third flow path switching valves 150a-150c can be independently switched between an open state and a closed state under the control of the control unit 40.

It is preferable that the valves used for the first, second, and third flow path switching valves 150a-150c are valves with adjustable opening. This makes it possible to adjust the ratio of the ink flow rate through the main flow paths 110a, 110b and the bypass flow path 111 by adjusting the opening of the valves when ink is flowing through both the main flow paths 110a, 110b and the bypass flow path 111.

The following provides a detailed description of the configuration of the bypass flow path 111 in the ink circulation system 100 according to this embodiment, as well as details of ink circulation control using this bypass flow path 111.

Figure 6 shows an example of a data table that defines the usage conditions of the bypass flow paths 111 (first bypass flow path 111a, second bypass flow path 111b, and third bypass flow path 111c) in the ink circulation system 100 according to this embodiment.

Figures 7 to 10 are diagrams showing the ink circulation patterns in the first circulation mode (Figure 7), second circulation mode (Figure 8), third circulation mode (Figure 9), and fourth circulation mode (Figure 10) shown in Figure 6, respectively.

When the ink ejection volume from the inkjet head 240 is low or when printing is not in progress, the bypass flow path 111 is used in conjunction with the main flow paths 110a and 110b as a flow path for ink, as shown in Figures 8 to 10, to reduce the shear force applied to the ink.

In the ink circulation system 100 for water-based ink, it is necessary to circulate the ink whether printing or not, in order to prevent the ink from drying out, stabilize the dispersant in the ink, and prevent the pigment in the ink from settling. In particular, in order to prevent the pigment in the ink from settling, a certain amount of ink needs to be circulated (described below with reference to Figure 15).

However, if the ink is continuously circulated, the shear forces acting on the ink as it passes through the filter can cause the dispersant in the ink to peel off from the pigment or break up within the ink, resulting in aggregation of the pigment. The amount of pigment aggregation in the ink is typically proportional to the magnitude of the shear forces acting on the dispersant as it passes through the filter.

From this perspective, in the ink circulation system 100 according to this embodiment, when the amount of ink ejected from the inkjet head 240 is relatively small or when printing is not in progress, ink is passed through both the main flow paths 110a and 110b and the bypass flow path 111. When circulating through the bypass flow path 111, the ink bypasses the location of at least one filter in the main flow paths 110a and 110b (here, the first in-path filter 140 and/or the head filter 240a), reducing the shear force applied to the ink. Furthermore, by passing ink through both the main flow paths 110a and 110b and the bypass flow path 111, it is possible to ensure a certain amount of ink is circulated throughout the entire circulation flow path 110. With this configuration, the ink circulation system 100 according to this embodiment suppresses pigment aggregation in the ink while also suppressing pigment sedimentation in the ink.

Specifically, the ink circulation system 100 according to this embodiment includes three bypass flow paths 111: a first bypass flow path 111a, a second bypass flow path 111b, and a third bypass flow path 111c.

The first bypass flow path 111a branches off from the main flow paths 110a, 110b at a position immediately upstream of the first filter 140 (e.g., the position of the ink inlet of the first filter 140) so as to bypass the location of the first filter 140, and merges with the main flow paths 110a, 110b at a position immediately downstream of the first filter 140 (e.g., the position of the ink outlet of the first filter 140). The first bypass flow path 111a is used in conjunction with the main flow paths 110a, 110b, for example, when the inkjet head 240 is discharging at a medium output (e.g., when the coverage rate of the printing target is 5% or more and less than 20%) (see Figure 8).

As described above, the second intra-passage filter 141 is disposed in the first bypass flow path 111a. During printing, pigment aggregates are the main foreign matter generated, and the amount of such foreign matter increases in proportion to the amount of ink ejected. The second intra-passage filter 141 is disposed due to the need to remove such foreign matter generated during printing. However, when the amount of ink ejected is not large, the foreign matter removal function (i.e., the foreign matter capture rate) of the first intra-passage filter 140 is not required, and therefore the second intra-passage filter 141 is a filter with a larger filter pore size or effective filtration area than the first intra-passage filter 140.

Incidentally, because the second intra-passage filter 141 uses a filter with a relatively large filter pore diameter or effective filtration area, the shear force that the ink experiences when passing through the second intra-passage filter 141 is smaller than the shear force that the ink experiences when passing through the first intra-passage filter 140. In other words, the shear force that the ink experiences when circulating through the circulation flow path 110 via the first bypass flow path 111a is smaller than the shear force that the ink experiences when circulating through the circulation flow path 110 via only the main flow paths 110a and 110b. Therefore, when the ejection volume from the inkjet head 240 is medium, the combined use of the first bypass flow path 111a and the main flow paths 110a and 110b reduces the integrated value of the shear force acting on the ink over time.

The second bypass flow path 111b branches off from the main flow paths 110a, 110b at a position immediately upstream of the inkjet head 240 (e.g., the position of the ink inlet of the inkjet head 240) so as to bypass the position of the head filter 240a of the inkjet head 240, and merges with the main flow paths 110a, 110b at a position immediately downstream of the inkjet head 240 (e.g., the position of the ink outlet of the inkjet head 240). The second bypass flow path 111b is used in conjunction with the main flow paths 110a, 110b when the ejection volume from the inkjet head 240 is small (e.g., when the coverage rate of the printing target is less than 5%) or during short non-printing periods (e.g., when the line is down for less than 30 minutes) (see Figure 9).

The third bypass flow path 111c branches off from the main flow paths 110a, 110b immediately upstream of the first filter 140 (e.g., the ink inlet of the first filter 140) so as to bypass the first filter 140 and the head filter 240a of the inkjet head 240, and merges with the main flow paths 110a, 110b immediately downstream of the inkjet head 240 (e.g., the ink outlet of the inkjet head 240). The third bypass flow path 111c is used in conjunction with the main flow paths 110a, 110b during long periods of non-printing (e.g., when the line is down for 30 minutes or more) (see Figure 10).

When the inkjet head 240 is discharging a large amount of ink (for example, when the coverage rate of the printing target is 20% or more), only the main flow paths 110a and 110b are used, and the first bypass flow path 111a, the second bypass flow path 111b, and the third bypass flow path 111c are all closed.

Figure 12 is a diagram comparing the shear force acting on the ink when it is circulated once in the circulation flow path 110 via the bypass flow path 111 with the shear force acting on the ink when it is circulated once in the circulation flow path 110 without passing through the bypass flow path 111.

If the average hole diameter of the filter is h [mm] and the flow velocity of the ink circulating in the ink circulation channel 110 is v [mm/s], the shear force T applied to the dispersant as it passes through the filter can generally be expressed by the following formula (1): where k is a constant. The flow velocity v is the value obtained by dividing the circulation flow rate by the effective filtration area of the filter.
T=k×v/h...(1)

In Figure 12, the shear force applied to the dispersant as it passes through each filter is calculated, and the shear force acting on the ink when it is circulated once through the circulation channel 110 is calculated as the sum of these values.

As shown in FIG. 12, in this embodiment, if the shear force acting on the ink when it is circulated once in the circulation flow path 110 without passing through the bypass flow path 111 (i.e., when it is circulated once in the circulation flow path 110 using only the main flow path 110) is set to "1", the shear force acting on the ink when it is circulated once in the circulation flow path 110 via the first bypass flow path 111a is "0.74", the shear force acting on the ink when it is circulated once in the circulation flow path 110 via the second bypass flow path 111b is "0.53", and the shear force acting on the ink when it is circulated once in the circulation flow path 110 via the third bypass flow path 111c is "0.27".

That is, the shear force acting on the ink during ink circulation decreases in the order of the first bypass flow path 111a, the second bypass flow path 111b, and the third bypass flow path 111c (i.e., shear force when flowing through the first bypass flow path 111a > shear force when flowing through the second bypass flow path 111b > shear force when flowing through the third bypass flow path 111c). This is due to the positions at which the first bypass flow path 111a, the second bypass flow path 111b, and the third bypass flow path 111c bypass each other.

When designing the bypass flow path 111, if the shear force acting on the ink when it is circulated once in the circulation flow path 110 without passing through the bypass flow path 111 is set to "1," it is preferable that the shear force acting on the ink when it is circulated once in the circulation flow path 110 via the bypass flow path 111 be set to "0.1 to 0.9."

The conditions for selecting the first bypass flow path 111a, the second bypass flow path 111b, and the third bypass flow path 111c shown in Figure 6 are set mainly taking into consideration the need to ensure a sufficient amount of ink is supplied to the inkjet head 240, the need to remove foreign matter from the ink as it circulates, and the magnitude of the shear force acting on the ink as it circulates.

Specifically, when a certain amount of ink needs to be ejected from the inkjet head 240, the ink circulation system 100 needs to supply a certain amount of ink to the inkjet head 240 so that ink shortages do not occur in the inkjet head 240. Furthermore, because foreign matter such as pigment aggregates is likely to be generated during printing, it is necessary to circulate the ink in the circulation flow path 110 while removing foreign matter from the ink using some kind of in-path filter.

In other words, when the inkjet head 240 is discharging a large amount of ink (for example, when the coverage rate of the printing target is 20% or more), the bypass flow path 111 is not used to circulate ink within the circulation flow path 110, and only the main flow paths 110a and 110b are used (first circulation mode shown in Figure 6) in order to ensure a sufficient ink supply to the inkjet head 240 and sufficient removal of foreign matter that has formed in the ink. In other words, at this time, the first, second, and third flow path switching valves 150a-150c are all set to a closed state to prevent ink from flowing through the bypass flow path 111.

Furthermore, when the inkjet head 240 is ejecting at a medium output (for example, when the coverage rate of the printing target is 5% or more but less than 20%), it is necessary to ensure a sufficient ink supply to the inkjet head 240, but the ability to remove foreign matter generated in the ink can be reduced to some extent without causing any problems. Therefore, in this case, the first bypass flow path 111a, which circulates ink bypassing the first in-passage filter 140 but without bypassing the inkjet head 240, is used in conjunction with the main flow paths 110a and 110b (second circulation mode shown in Figure 6).

In this case, foreign matter generated in the ink is removed by the first in-passage filter 140 when passing through the main flow path 110a, and is removed by the second in-passage filter 141 when passing through the first bypass flow path 111a, which has a lower foreign matter capturing capacity than the first in-passage filter 140 but exerts a smaller shear force on the ink.

Furthermore, when the ejection volume from the inkjet head 240 is small (for example, when the coverage rate of the printing target is less than 5%), a small amount of ink is sufficient to supply to the inkjet head 240, so for example, the second bypass flow path 111b, which bypasses the inkjet head 240, is used in combination with the main flow paths 110a and 110b (third circulation mode shown in Figure 6).

On the other hand, when printing operations are stopped, there is no need to supply ink to the inkjet head 240. Therefore, when printing operations are stopped, the bypass flow path 111, which is used in conjunction with the main flow paths 110a and 110b, may be a flow path that bypasses the inkjet head 240 (head filter 240a).

However, immediately after printing has stopped (for example, immediately after a user issues a command to stop printing), foreign matter such as pigment aggregates generated during printing may be present in the ink. Therefore, immediately after printing has stopped (for example, within 30 minutes after printing has stopped), the second bypass flow path 111b, which circulates ink via the first in-path filter 140, is used in conjunction with the main flow paths 110a and 110b (third circulation mode shown in Figure 6).

On the other hand, after a certain amount of time has passed since printing stopped (for example, 30 minutes or more after printing stopped), the amount of foreign matter in the ink also decreases. Therefore, the third bypass flow path 111c, which bypasses both the first in-passage filter 140 and the inkjet head 240 and minimizes the shear force acting on the ink, is used in conjunction with the main flow paths 110a and 110b (fourth circulation mode shown in Figure 6).

In addition, when the ink flow rate circulated through the circulation flow path 110 in the first circulation mode is set to "1," the ink circulation system 100 is controlled so that the ink flow rate circulated through the circulation flow path 110 in the second, third, and fourth circulation modes is, for example, "0.8 to 1.2," and more preferably, approximately "1." Such flow rate control is performed, for example, by the control unit 40 controlling the output of the supply pump 121 and the recovery pump 122.

Figure 11 shows an example of an ink circulation mode change operation performed by the control unit 40 according to this embodiment, with reference to the data table in Figure 6.

The processing of the flowchart in FIG. 11 is executed repeatedly by the control unit 40 at predetermined intervals (e.g., 100 msec) while the printing device 1 is operating (e.g., when the power is on). That is, the control unit 40 appropriately changes the ink circulation state of the circulation flow path 110 in sequence, in accordance with the processing of the flowchart in FIG. 11, based on, for example, the operating state of the printing device 1.

First, the control unit 40 determines whether a print command has been issued to the printing device 1 (step S1). During printing, a print flag is set in the RAM of the control unit 40, for example, and whether a print command has been issued is determined based on the print flag.

If a print command is issued to the printing device 1 (S1: YES), the control unit 40 performs a conditional branch to execute one of steps S3, S4, or S5 based on the coverage rate of the print target at that time.

That is, when the coverage rate of the printing target is 20% or more, the control unit 40 sets the first, second, and third flow path switching valves 150a-150c to a closed state so that ink circulates in the circulation flow path 110 only via the main flow paths 110a and 110b (i.e., first circulation mode) (step S3).

Furthermore, when the coverage rate of the printing target is equal to or greater than 5% and less than 20%, the control unit 40 sets the second and third flow path switching valves 150b, 150c to a closed state and the first flow path switching valve 150a to an open state so that ink circulates in the circulation flow path 110 via both the main flow path 110a and the first bypass flow path 111a (i.e., second circulation mode) (step S4).

Furthermore, if the coverage rate of the printing target is less than 5%, the control unit 40 sets the first and third flow path switching valves 150a and 150c to a closed state and the second flow path switching valve 150b to an open state so that ink circulates in the circulation flow path 110 via both the main flow path 110a and the second bypass flow path 111b (i.e., third circulation mode) (step S5).

On the other hand, if there is no print execution command to the printing device 1 (S1: NO), the control unit 40 proceeds to step S2 and determines whether the printing stop time is less than 30 minutes (step S2). If the printing stop time is less than 30 minutes (S2: YES), the control unit 40 executes step S6, and if the printing stop time is 30 minutes or more (S2: NO), the control unit 40 executes step S7.

That is, if the printing stop time is less than 30 minutes (S2: YES), the control unit 40 sets the first and third flow path switching valves 150a and 150c to a closed state and the second flow path switching valve 150b to an open state so that ink circulates in the circulation flow path 110 via both the main flow path 110a and the second bypass flow path 111b (i.e., third circulation mode) (step S6).

On the other hand, if the printing stop time is 30 minutes or more (S2: NO), the control unit 40 sets the first and second flow path switching valves 150a, 150b to a closed state and the third flow path switching valve 150c to an open state so that ink circulates in the circulation flow path 110 via both the main flow path 110a and the third bypass flow path 111c (i.e., fourth circulation mode) (step S7).

In steps S3 to S7, the control unit 40 controls the supply-side pump 121 and the recovery-side pump 122 so that the flow rate of ink circulated through the circulation flow path 110 is approximately the same in each circulation mode. The control unit 40 sets the target pressure of the supply-side damper 102 and the target pressure of the recovery-side damper 103 so that the back pressure of the nozzle 243 of the inkjet head 240 is within a predetermined range according to the ink ejection conditions from the nozzle 243, and the flow rate of ink circulated through the circulation flow path 110 is a predetermined amount. The control unit 40 then controls the output of the supply-side pump 121 and the recovery-side pump 122 through feedback control, for example, by referencing the sensor values of pressure sensors (not shown) arranged in the ink supply path 110a and the ink recovery path 110b.

In the ink circulation system 100 according to this embodiment, this control changes the ink circulation pattern according to the operating status of the printing device 1.

[Verification experiment]
13, 14, and 15, the results of an experiment to verify the aggregation and sedimentation states of pigments in ink according to the ink circulation mode in the ink circulation system 100 according to this embodiment are shown.

Figure 13 shows the configuration of an ink circulation system 100A prepared for the verification experiment. The ink circulation system 100A differs from the configuration of the ink circulation system 100 shown in Figure 5 only in that a fourth flow path switching valve 150d, a fifth flow path switching valve 150e, and a sixth flow path switching valve 150f are provided in the main flow paths 110a and 110b so that a portion of the main flow paths 110a and 110b can be closed.

Figure 14 shows the results of the first verification experiment. In the first verification experiment, the main flow paths 110a and 110b, the first bypass flow path 111a, the second bypass flow path 111b, and the third bypass flow path 111c were used individually to detect changes in the pigment concentration in the ink after circulating the ink in the circulation flow path 110.

In conditions 1 to 4 in FIG. 14, the ink was circulated under the following conditions.
Condition 1: Ink was passed through only the main flow paths 110a and 110b.
(150a: closed, 150b: closed, 150c: closed, 150d: open, 150e: open, 150f: open)
Condition 2: Ink was circulated through the first bypass flow path 111a.
(150a: open, 150b: closed, 150c: closed, 150d: open, 150e: closed, 150f: open)
Condition 3: Ink was circulated through the second bypass flow path 111b.
(150a: closed, 150b: open, 150c: closed, 150d: open, 150e: open, 150f: closed)
Condition 4: Ink was circulated through the third bypass flow path 111c.
(150a: closed, 150b: closed, 150c: open, 150d: closed, 150e: closed, 150f: closed)

Under conditions 1 to 4, ink was passed through the circulation flow path 110 at the same flow rate (360 cc/min in this case) for the same period of time (6 hours in this case). In Figure 14, the ink flow rate through each flow path is indicated by "100" and "0," with the ink flow rate of 360 cc/min being "100."

The shear forces acting on the ink under each of conditions 1 to 4 are shown in Figure 14. In addition, in this verification experiment, a relatively large flow rate of ink was circulated to prevent the pigment in the ink from settling.

As a result, the pigment concentration was 4.2% under condition 1, 4.7% under condition 2, 4.8% under condition 3, and 4.9% under condition 4. These results show that there is almost no decrease in the pigment concentration in the ink under conditions 2 to 4, but that there is a significant decrease in the pigment concentration in the ink under condition 1.

The reason why the pigment concentration in the ink dropped significantly under condition 1 is thought to be because when ink is circulated in the circulation channel 110 using only the main channels 110a and 110b, which exert a relatively large shear force on the ink, the pigment aggregates and is trapped in the filters (here, the first in-channel filter 140, head filter 240a, and degassing module 130). In contrast, the reason why almost no drop in the pigment concentration in the ink was observed under conditions 2 to 4 is thought to be because, since the first bypass channel 111a, second bypass channel 111b, and third bypass channel 111c bypass the first in-channel filter 140 or head filter 240a, the shear force acting on the ink is smaller than that in the main channels 110a and 110b, and therefore no pigment aggregation occurs.

Figure 15 shows the results of the second verification experiment. In the second verification experiment, the main flow paths 110a and 110b and the bypass flow path 111 were used in combination to detect changes in the pigment concentration in the ink after circulating the ink.

In Comparative Examples 1 to 3 and Examples 1 to 3 shown in FIG. 15, the ink was circulated under the following conditions.
Comparative Example 1: Ink was passed through only the main flow paths 110a and 110b at a large flow rate.
(150a: closed, 150b: closed, 150c: closed, 150d: open, 150e: open, 150f: open)
Comparative Example 2: Ink was allowed to flow only through the main flow paths 110a and 110b at a certain flow rate.
(150a: closed, 150b: closed, 150c: closed, 150d: open, 150e: open, 150f: open)
Comparative Example 3: Ink was passed through only the main flow paths 110a and 110b at a small flow rate.
(150a: closed, 150b: closed, 150c: closed, 150d: open, 150e: open, 150f: open)
Example 1: Ink was circulated using both the main flow paths 110a and 110b and the first bypass flow path 111a.
(150a: open, 150b: closed, 150c: closed, 150d: open, 150e: open, 150f: open)
Example 2: Ink was circulated using both the main flow paths 110a and 110b and the second bypass flow path 111b.
(150a: closed, 150b: open, 150c: closed, 150d: open, 150e: open, 150f: open)
Example 3: Ink was circulated using both the main flow paths 110a and 110b and the third bypass flow path 111c.
(150a: closed, 150b: closed, 150c: open, 150d: open, 150e: open, 150f: open)

In Figure 15, the ink flow rate through each flow path is indicated by "1," "0.8," "0.5," "0.2," and "0," with an ink flow rate of 360 cc/min being "1." In Comparative Examples 1 to 3 and Examples 1 to 3, the ink was allowed to flow through the circulation flow path 110 for the same amount of time (6 hours in this case). The shear force acting on the ink in Comparative Examples 1 to 3 and Examples 1 to 3 was calculated from the values shown in Figure 12.

As a result, the pigment concentration was 4.2% in Comparative Example 1, 4.5% in Comparative Example 2, 4.6% in Comparative Example 3, 4.7% in Example 1, 4.8% in Example 2, and 4.9% in Example 3. These results show that while there is a significant decrease in the pigment concentration in the ink in Comparative Examples 1 to 3, there is almost no decrease in the pigment concentration in the ink in Examples 1 to 3.

In Comparative Example 1, similar to the verification results shown in Figure 14, when ink was circulated in the circulation flow path 110 using only the main flow paths 110a and 110b, which exert a relatively large shear force on the ink, the pigment aggregated and was trapped in the first in-passage filter 140, which is thought to have resulted in a decrease in pigment concentration. On the other hand, in Comparative Examples 2 and 3, the flow rate of the ink circulated in the circulation flow path 110 was reduced compared to Comparative Example 1, which suppressed pigment aggregation and resulted in a smaller decrease in the pigment concentration in the ink than in Comparative Example 1.

However, in Comparative Examples 2 and 3, the flow rate of the ink circulating in the circulation flow path 110 was reduced, which resulted in the pigment settling, and it is believed that this resulted in a decrease in the pigment concentration in the ink.

In contrast, the reason why almost no decrease in the pigment concentration in the ink was observed in Examples 1 to 3 is thought to be because the shear force acting on the ink in the first bypass flow path 111a, second bypass flow path 111b, and third bypass flow path 111c was smaller than that in the main flow paths 110a and 110b, and therefore no aggregation of the pigment in the ink occurred.

Furthermore, in Examples 1 to 3, ink is passed through the first bypass flow path 111a, the second bypass flow path 111b, and the third bypass flow path 111c in combination with the main flow paths 110a and 110b, and the flow rate of the ink circulating in the circulation flow path 110 is not reduced. Therefore, no settling of the pigment in the ink occurs, and as a result, it is believed that no reduction in the pigment concentration in the ink occurs.

[effect]
As described above, the inkjet printing apparatus 1 according to this embodiment has the following features:
an inkjet head 240 that ejects ink;
an ink tank 101 for storing ink;
a circulation flow path 110 for circulating ink between the ink tank 101 and the inkjet head 240;
a bypass flow path 111 connected to the circulation flow path 110 so as to bypass the position where the first in-path filter 140 and/or the head filter 240a of the inkjet head 240 are disposed in the main flow paths 110a and 110b of the circulation flow path 110;
a control device (40) that controls the ink flow patterns in the main channels (110a, 110b) and the bypass channel (111) by controlling a channel switching valve (150) disposed in the main channels (110a, 110b) and/or the bypass channel (111);
Equipped with
When printing is performed under first printing conditions, the control device 40 causes ink to flow through the main flow paths 110a and 110b without causing it to flow through the bypass flow path 111, and when printing is performed under second printing conditions which have a lower coverage rate of the printing object than the first printing conditions or when not printing, causes ink to flow through both the bypass flow path 111 and the main flow paths 110a and 110b.

In another aspect, the inkjet printing apparatus 1 according to the present embodiment includes:
an inkjet head 240 that ejects ink;
an ink tank 101 for storing ink;
a circulation flow path 110 for circulating ink between the ink tank 101 and the inkjet head 240;
a bypass flow path 111 connected to the circulation flow path 110 so as to bypass the position of the first in-path filter 140 in the main flow paths 110a and 110b of the circulation flow path 110, and used simultaneously with the main flow paths 110a and 110b when the operating state of the printing apparatus is in a predetermined state;
a control device (40) that controls the ink flow patterns in the main channels (110a, 110b) and the bypass channel (111) by controlling a channel switching valve (150) disposed in the main channels (110a, 110b) and/or the bypass channel (111);
It is equipped with:

In another aspect, the inkjet printing apparatus 1 according to the present embodiment includes:
an inkjet head 240 that ejects ink;
an ink tank 101 for storing ink;
a circulation flow path 110 for circulating ink between the ink tank 101 and the inkjet head 240;
a bypass flow path 111 connected to the circulation flow path 110 so as to bypass the position of the head filter 240a of the inkjet head 240 in the main flow paths 110a and 110b of the circulation flow path 110, and which is used simultaneously with the main flow paths 110a and 110b when the operating state of the printing apparatus is in a predetermined state;
a control device (40) that controls the ink flow patterns in the main channels (110a, 110b) and the bypass channel (111) by controlling a channel switching valve (150) disposed in the main channels (110a, 110b) and/or the bypass channel (111);
It is equipped with:

As such, with the inkjet printing device 1 according to this embodiment, under circumstances where ejection of large volumes of ink is not required (i.e., when printing with a low coverage rate or when not printing), it is possible to pass ink through both the main flow paths 110a and 110b and the bypass flow path 111. This makes it possible to suppress the shear force acting on the ink (i.e., the dispersant) as the ink circulates, thereby preventing the pigment from agglomerating in the ink. Furthermore, this allows a sufficient flow rate of ink to circulate within the circulation flow path 110 at all times, thereby preventing the pigment in the ink from settling.

Specific examples of the present invention have been described in detail above, but these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and variations of the specific examples exemplified above.

The inkjet printing device disclosed herein can suppress pigment sedimentation in the ink while also suppressing the occurrence of pigment aggregation.

REFERENCE SIGNS LIST 1 Inkjet printing device 10 Paper feed section 20 Image forming section 30 Paper discharge section 40 Control section 50 Head unit driving section 60 Conveyance driving section 70 Image processing section 80 Input/output interface 90 Ink supply section 100 Ink circulation system 101 Ink tank 102 Supply damper 103 Recovery damper 110 Circulation flow path 110a Ink supply flow path (main flow path)
110b Ink recovery flow path (main flow path)
111a First bypass flow path 111b Second bypass flow path 111c Third bypass flow path 121 Supply side pump 122 Recovery side pump 130 Degassing module 140 First passage filter 141 Second passage filter 150a First passage switching valve 150b Second passage switching valve 150c Third passage switching valve 240 Inkjet head 240a Head filter 243 Nozzle P Recording medium

Claims (12)

an inkjet head that ejects ink;
an ink tank for storing the ink;
a circulation flow path that circulates the ink between the ink tank and the inkjet head;
a bypass flow path connected to the circulation flow path so as to bypass a position where a first in-passage filter in a main flow path of the circulation flow path and/or a head filter of the inkjet head are disposed;
a control device that controls a flow pattern of the ink in the main flow path and the bypass flow path by controlling a flow path switching valve disposed in the main flow path and/or the bypass flow path;
Equipped with
When printing is performed under a first printing condition, the control device causes the ink to flow through the main flow path without causing the ink to flow through the bypass flow path, and when printing is performed under a second printing condition that has a lower coverage rate of the printing target than the first printing condition or when not printing, causes the ink to flow through both the bypass flow path and the main flow path.
Inkjet printing device. The flow path switching valve is a valve whose opening degree can be adjusted,
The flow rate ratio of the ink flowing through the main flow path and the ink flowing through the bypass flow path can be adjusted by adjusting the opening degree of the flow path switching valve.
The inkjet printing apparatus of claim 1 . When the shear force acting on the ink when the ink is circulated once in the circulation flow path without passing through the bypass flow path is set to 1,
a shear force acting on the ink when the ink is circulated once in the circulation flow path via the bypass flow path is 0.1 to 0.9;
3. The inkjet printing apparatus according to claim 1 or 2. the bypass flow path includes a first bypass flow path that branches off from the main flow path at a position immediately upstream of the first intra-passage filter and merges with the main flow path at a position immediately downstream of the first intra-passage filter,
a second intra-passage filter having a larger filter pore size or an effective filtration area than the first intra-passage filter is disposed in the first bypass flow path;
The inkjet printing apparatus according to any one of claims 1 to 3. the bypass flow path includes a second bypass flow path that branches off from the main flow path at a position immediately upstream of the inkjet head and merges with the main flow path at a position immediately downstream of the inkjet head.
The inkjet printing apparatus according to any one of claims 1 to 4. the bypass flow path includes a third bypass flow path that branches off from the main flow path at a position immediately upstream of the first intra-passage filter and merges with the main flow path at a position immediately downstream of the inkjet head.
The inkjet printing apparatus according to any one of claims 1 to 5. The bypass flow path is
a first bypass flow path that branches off from the main flow path at a position immediately upstream of the first intra-passage filter and merges with the main flow path at a position immediately downstream of the first intra-passage filter;
a second bypass flow path that branches off from the main flow path at a position immediately upstream of the inkjet head and merges with the main flow path at a position immediately downstream of the inkjet head; and
a third bypass flow path that branches off from the main flow path at a position immediately upstream of the first intra-passage filter and joins the main flow path at a position immediately downstream of the inkjet head;
The inkjet printing apparatus according to any one of claims 1 to 6. the order of magnitude of shear force acting on the ink when it flows through the bypass flow path is the third bypass flow path < the second bypass flow path < the first bypass flow path;
8. The inkjet printing apparatus of claim 7 . the control device determines the type of the bypass flow path through which the ink is circulated based on the coverage rate of the second printing condition.
9. The inkjet printing apparatus according to claim 7 or 8 . the control device, when not printing, determines the type of the bypass flow path through which the ink is circulated based on the duration of the non-printing state.
9. The inkjet printing apparatus according to claim 7 or 8 . When printing is performed under the first printing condition, if the flow rate of the ink circulated through the circulation flow path is set to 1,
When printing is performed under the second printing condition or when not printing, the flow rate of the ink circulated through the circulation flow path is 0.8 to 1.2.
The inkjet printing apparatus according to any one of claims 1 to 10 . an inkjet head that ejects ink;
an ink tank for storing the ink;
a circulation flow path that circulates the ink between the ink tank and the inkjet head;
a bypass flow path connected to the circulation flow path so as to bypass a position where a first in-passage filter is disposed in the main flow path of the circulation flow path, and which is used simultaneously with the main flow path when the operating state of the printing device is in a predetermined state;
a control device that controls a flow pattern of the ink in the main flow path and the bypass flow path by controlling a flow path switching valve disposed in the main flow path and/or the bypass flow path;
An inkjet printing apparatus comprising: