Cleaning timing determination method and printing device

Abstract

Provided are: a cleaning timing determination method in which, in a printing device that prints an image by ejecting ink onto a recording medium coated with a pretreatment liquid, a preset determination image for determining the state of an application unit which applies the pretreatment liquid is printed, and a cleaning timing of the application unit is determined on the basis of the determination image; and a printing device.

Description

Method for Determining Cleaning Timing and Printing Apparatus

[0001] The present disclosure relates to a method for determining cleaning timing and a printing apparatus.

[0002] Printing apparatuses that eject ink onto a recording medium to form an image are known. Some printing apparatuses are configured such that a pretreatment liquid for aggregating ink and fixing the same onto the recording medium is applied onto the recording medium, and then ink is ejected onto the coating film of the pretreatment liquid to print an image. Such a printing apparatus is provided with a coating unit having an anilox roller for supplying the pretreatment liquid (which may be simply referred to as a treatment liquid) to the recording medium. The anilox roller is a roller having fine depressions (cells) engraved on the surface thereof. The anilox roller pumps a predetermined amount of the pretreatment liquid into the depressions and supplies the same onto the recording medium. Japanese Patent Application Laid-Open No. 2015-223720 discloses a treatment liquid coating apparatus including a squeeze roller such as an anilox roller and an application roller that applies the treatment liquid supplied from the squeeze roller onto a recording medium.

[0003] If the pretreatment liquid adheres to and solidifies on the surface of a member in the coating unit, such as an application roller or a pass roller, or if the pretreatment liquid clogs the cells on the surface of the anilox roller, coating unevenness may occur. Since the pretreatment liquid has a function of fixing ink, coating unevenness of the pretreatment liquid causes image defects such as bleeding.

[0004] In Japanese Patent Application Laid-Open No. 2015-223720, regarding cleaning of an application roller to which a treatment liquid that thickens when exposed to air adheres in a treatment liquid coating apparatus, it is proposed that the efficiency of the cleaning operation is improved by variably setting the period of the cleaning operation based on an estimated viscosity of the treatment liquid obtained by a predetermined calculation.

[0005] Japanese Patent Publication No. 2015-223720 uses the estimated viscosity of the processing liquid, which can improve the efficiency of cleaning work, but it is not sufficient to reliably guarantee the quality of printed materials. Generally, simple surface cleaning of the coating parts, especially the anilox rollers which are prone to clogging with pre-treatment liquid, is performed during the daily shutdown of the printing machine. However, since the surface cleaning performed during daily shutdown is simple, clogging of the pre-treatment liquid occurs with long-term use. Currently, if image bleeding is discovered during a test print of an actual printing job, the actual job is interrupted, the anilox roller is removed from the printing machine, and a surface cleaning operation is performed using a special solvent. Interrupting an actual job to perform cleaning work on the coating parts such as the anilox roller disrupts the printing work schedule.

[0006] In light of the above circumstances, this disclosure aims to provide a determination method for determining the timing of cleaning the coated area and a printing apparatus, in order to enable cleaning work to be carried out without disrupting the printing work schedule.

[0007] The cleaning timing determination method of this disclosure relates to a printing apparatus that prints an image by ejecting ink onto a recording medium coated with a pretreatment liquid, and involves printing a preset determination image for determining the state of the coated area to which the pretreatment liquid is applied, and determining the cleaning timing of the coated area based on the determination image.

[0008] The judgment image preferably includes a reference concentration region recorded at the maximum amount of ink that is aggregated by the pretreatment solution coated on the recording medium.

[0009] It is preferable to determine whether cleaning is necessary based on the presence or absence of seepage in the standard concentration range.

[0010] The judgment image preferably includes a high-density region recorded with an ink amount greater than the maximum ink amount.

[0011] It is preferable to determine the cleaning timing based on the presence or absence of seepage in the high-concentration area.

[0012] The high-concentration region includes multiple high-concentration regions with different concentrations, and it is preferable to estimate the time until cleaning based on the presence or absence of seepage in these multiple high-concentration regions.

[0013] The judgment image preferably includes a low-density region recorded with an ink amount less than the maximum ink amount.

[0014] It is preferable to determine whether immediate cleaning is necessary based on the presence or absence of seepage in the low-concentration area.

[0015] Preferably, the judgment image is composed of stripe images extending in a direction intersecting the transport direction of the recording medium.

[0016] If the judgment image includes multiple stripe images, it is preferable that non-printable areas are placed between the stripe images.

[0017] The coating section is equipped with an anilox roller having multiple depressions on its surface for drawing up the pretreatment liquid, and it is preferable to determine the cleaning timing of the anilox roller as the cleaning timing for the coating section.

[0018] The printing apparatus of this disclosure is a printing apparatus that prints an image on a recording medium while transporting the recording medium, and comprises a coating unit that coats the recording medium with a pretreatment liquid, an image forming unit that ejects ink toward the recording medium coated with the pretreatment liquid to print an image, an optical sensor that reads the image printed on the recording medium, and a processor, wherein the processor is configured to control the image forming unit to print a preset determination image for determining the state of the coating unit, to control the optical sensor to read the determination image, to obtain a reading result for the determination image from the optical sensor, to determine the cleaning timing of the coating unit based on the reading result, and to output information regarding the cleaning timing.

[0019] The optical sensor is preferably a line sensor that extends in the width direction of the recording medium.

[0020] Preferably, the line sensor is positioned downstream of the image forming unit in the direction of transport of the recording medium, and the judgment image is read while the recording medium is being transported.

[0021] The processor is preferably configured to perform the following in a series of steps: printing a judgment image, reading the judgment image, determining the cleaning timing, and outputting information regarding the cleaning timing.

[0022] The processor is preferably configured to execute the sequence within the device downtime sequence.

[0023] The coating section preferably includes an anilox roller having multiple depressions on its surface for drawing up the pretreatment liquid.

[0024] According to the determination method and printing apparatus for determining cleaning timing described herein, cleaning work can be carried out in a manner that does not disrupt the printing work schedule.

[0025] This is a schematic diagram of an inkjet printing apparatus according to an embodiment. This is an explanatory diagram of an anilox roller. This is a block diagram showing the electrical configuration of the inkjet printing apparatus. This is a diagram showing an example of an image for judgment. This is a diagram for explaining bleeding.

[0026] Hereinafter, an inkjet printing apparatus according to an embodiment of this disclosure will be described with reference to the drawings. In each figure, the same components are denoted by the same reference numerals.

[0027] In this disclosure, numerical ranges indicated using "~" mean a range that includes the numerical values ​​before and after "~" as the minimum and maximum values, respectively. In this disclosure, unless otherwise specified, "upstream side" means the upstream side in the transport direction of the recording medium, and unless otherwise specified, "downstream side" means the downstream side in the transport direction of the recording medium.

[0028] Figure 1 is a schematic diagram of an inkjet printing apparatus 1 according to one embodiment of the printing apparatus of the present disclosure. The inkjet printing apparatus 1 of this embodiment transports a long, non-permeable substrate 5 and forms a printed image including a color image on the printing surface of the substrate 5. The substrate 5 is not limited to a long one, but may also be a single-fed one. Here, the substrate 5 is an example of a recording medium of the present disclosure.

[0029] The substrate 5 is a non-permeable medium, such as a transparent film substrate used in flexible packaging. Examples of film substrates include PET (Polyethylene Terephthalate), OPP (Oriented Poly Propylene), and NY (Nylon). The inkjet printing apparatus 1 produces reverse-printed materials on the substrate, where the printed object is visible from the non-printed side, which is the side opposite the printed surface.

[0030] Furthermore, "non-permeable" means that it is non-permeable to water-based inks, as described later. Flexible packaging refers to packaging made of a material that deforms according to the shape of the article being packaged. Transparent means that the transmittance of visible light is 30% or more and 100% or less, preferably 70% or more and 100% or less.

[0031] The inkjet printing apparatus 1 includes a transport device 10, a coating unit 20, a first printing unit 30, a second printing unit 40, an optical sensor 50, and a processor 100 (see Figure 3).

[0032] The conveying device 10 conveys the base material 5 along the conveying path from the unwinding roll 12 to the winding roll 14 in a roll-to-roll manner. The conveying device 10 includes a plurality of pass rollers (not shown). The pass rollers rotate in contact with the base material 5, thereby conveying the base material 5 in the conveying direction. The base material 5 may be conveyed under tension. The speed at which the base material 5 moves in the conveying direction (conveying speed) is, for example, 50 m / min.

[0033] The coating section 20, the first printing section 30, and the second printing section 40 are arranged in order from the upstream side along the transport path of the substrate 5. The substrate 5, unwound from the unwinding roll 12, is transported sequentially to the coating section 20, the first printing section 30, and the second printing section 40, and then wound onto the winding roll 14.

[0034] The coating unit 20 coats one surface of the substrate 5 with a pretreatment liquid. It includes an anilox roller 22, a rubber plate 24, and an impression cylinder 26. The anilox roller 22, rubber plate 24, and impression cylinder 26 are all cylindrical in shape and are arranged so that their axial direction is in the width direction of the substrate 5. The anilox roller 22, rubber plate 24, and impression cylinder 26 rotate around their axes. The rubber plate 24 and the impression cylinder 26 are positioned opposite each other, and the substrate 5 is conveyed between them. The anilox roller 22 draws up a predetermined amount of pretreatment liquid from a doctor chamber (not shown) and supplies the pretreatment liquid to the rubber plate 34. The rubber plate 24 coats the surface of the substrate 5 with the pretreatment liquid supplied from the anilox roller 22.

[0035] As previously described, the anilox roller 22 is used to supply the pretreatment solution to the surface of the substrate 5. As shown in Figure 2, the anilox roller 22 has a plurality of fine depressions (cells) 23 (see enlarged view in Figure 2) on its cylindrical surface 22A. In this example, the cells 23 are arranged in a honeycomb pattern. The volume of the cells 23 of the anilox roller 22 is determined according to the amount of pretreatment solution supplied to the surface of the substrate 5.

[0036] The first printing unit 30 includes a first image forming unit 31 and a first drying unit 38. The first image forming unit 31 is equipped with inkjet heads 32K, 32C, 32M, and 32Y. Inkjet head 32K ejects black ink, inkjet head 32C ejects cyan ink, inkjet head 32M ejects magenta ink, and inkjet head 32Y ejects yellow color ink. Each color ink is an aqueous ink obtained by dissolving or dispersing dyes and pigments in water and a water-soluble solvent. Each of the inkjet heads 32K, 32C, 32M, and 32Y is supplied with the corresponding color ink from an ink tank (not shown) via a piping route (not shown).

[0037] The inkjet heads 32K, 32C, 32M, and 32Y are arranged at regular intervals along the transport path of the substrate 5. Each of the inkjet heads 32K, 32C, 32M, and 32Y is a line-type recording head capable of forming an image on the substrate 5 transported by the transport device 10 in a single scan. Each of the inkjet heads 32K, 32C, 32M, and 32Y may be configured by connecting multiple head modules in the width direction (X direction) of the substrate 5, intersecting (for example, orthogonal to) the transport direction (Y direction) of the substrate 5.

[0038] The inkjet heads 32K, 32C, 32M, and 32Y are positioned so that their nozzle surfaces face the transport path of the substrate 5. Each nozzle surface of the inkjet heads 32K, 32C, 32M, and 32Y has multiple nozzles arranged in a two-dimensional pattern, which are the ink ejection ports.

[0039] Based on the image data of the color plate, ink droplets are ejected from at least one of the inkjet heads 32K, 32C, 32M, and 32Y toward the printing surface of the substrate 5 being transported by the transport device 10. When the ejected droplets adhere to the printing surface of the substrate 5, a color image is formed on the printing surface of the substrate 5.

[0040] Although this example shows a configuration using four color inks, the ink colors and number of colors are not limited to this embodiment. For example, additional inkjet heads may be added to eject light-colored inks such as light magenta and light cyan, special color inks such as green, orange, and violet, clear ink, or metallic ink. Furthermore, the arrangement order of the inkjet heads for each color is not limited.

[0041] The substrate 5 on which a color image has been formed by the first image forming unit 31 is transported to the first drying unit 38.

[0042] The first drying unit 38 is a device for drying the color ink on the printed surface of the substrate 5. The first drying unit 38 includes, for example, a plurality of hot air heaters (not shown).

[0043] Each warm air heater is arranged to be capable of blowing warm air onto the printed surface of the substrate 5. Each warm air heater blows warm air from the air outlet toward the printed surface of the substrate to heat the substrate 5 and dry the color ink adhering to the printed surface. Drying refers to, for example, a state in which the ink on the printed surface of the substrate 5 does not offset onto the non-printed surface when the substrate 5 is wound up.

[0044] The second printing unit 40 includes a second image forming unit 41 and a second drying unit 48. The second image forming unit 41 includes inkjet heads 42WA and 42WB. Both of the inkjet heads 42WA and 42WB use white (W) water-based ink. White ink is supplied to each of the inkjet heads 42WA and 42WB from an unillustrated ink tank via an unillustrated piping path. The configuration of the inkjet heads 42WA and 42WB is the same as that of the inkjet heads 32K, 32C, 32M, and 32Y.

[0045] A white image is formed by discharging white ink from the inkjet heads 42WA and 42WB. Note that the white image is formed overlapping the color image formed by the first printing unit 30. The substrate 5 on which the white image is formed by the second image forming unit 41 is conveyed to the second drying unit 48.

[0046] The second drying unit 48 is a device that dries the white ink on the printed surface of the substrate 5. The second drying unit 48 has the same configuration as the first drying unit 38.

[0047] The optical sensor 50 is an image reading unit and is arranged downstream of the second printing unit 40. It is a means that reads an image recorded on a substrate 5 by the first image forming unit 31 and the second image forming unit 41, and converts the image into electronic image data (read image data). The optical sensor 50 is a scanner, and for example, a CCD line sensor can be used. The optical sensor 50 of the present example is a line sensor arranged such that its longitudinal direction matches the width direction of the substrate 5, that is, extends in the width direction. The optical sensor 50 is installed in the middle of a conveyance path, and reads images recorded by the first image forming unit 31 and the second image forming unit 41 during conveyance before the images are wound by a winding roller. Specifically, the optical sensor 50 is arranged downstream of the two image forming units 31, 41 in the conveyance direction of the substrate 5. The optical sensor 50 reads an image from the conveyed substrate 5. The optical sensor 50 can read various test charts, and as one of the test charts, reads a determination image for determining the state of the coating unit 20. The optical sensor 50 also outputs read results to the processor 100 described later.

[0048] In the inkjet printing apparatus 1 having the above configuration, a pretreatment liquid is first applied by the coating unit 20 to the substrate 5 unwound from an unwinding roll 12. Thereafter, the substrate 5 is conveyed to the first printing unit 30, a color image is printed in the first image forming unit 31, and the color ink is dried in the first drying unit 38. Further, the substrate 5 is conveyed to the second printing unit 40, a white image is printed in the second image forming unit 41, the white ink is dried in the second drying unit 48, and the substrate 5 is wound by the winding roll 14. Note that image reading by the optical sensor 50 is performed during the period from when the image leaves the second printing unit 40 to when it is wound by the winding roll 14.

[0049] Figure 3 is a block diagram showing an electrical configuration of the inkjet printing apparatus 1. As shown in Figure 3, the inkjet printing apparatus 1 includes, in addition to the processor 100 serving as a control device, a storage device 102, a communication unit 104, an input device 106, and a display device 108.

[0050] The processor 100 comprehensively controls each part of the inkjet printing apparatus 1. In this embodiment, each process is executed on any computer. Alternatively, any computer may execute these processes using a processor as hardware, a program as software, or a combination thereof. In that case, the processor is configured to work in cooperation with the program to execute the various processes in this embodiment, and can function as each part (Unit) or each means (Means) in this embodiment. Furthermore, the execution order of the processes by the processor is not limited to the order described and may be changed as appropriate. Any computer may be a general-purpose computer, a computer for a specific application, a workstation, or any other system capable of executing each process.

[0051] A processor may consist of one or more hardware components, and the type of hardware is not limited. For example, a processor may consist of programmable logic devices such as a CPU (Central Processing Unit), MPU (Micro Processing Unit), FPGA (Field Programmable Gate Array), dedicated circuits for executing specific processes such as an ASIC (Application Specific Integrated Circuit), a GPU (Graphic Processing Unit), or an NPU (Neural Processing Unit). Furthermore, the hardware components may be a combination of different types of hardware. When multiple hardware components are configured to execute one or more processes of a processor, these components may reside in physically separate devices or in the same device. Furthermore, in any embodiment, the order of the processes performed by the processor is not limited to the order described above and may be changed as appropriate. The hardware components are composed of electrical circuits (circuits) and the like, which are combinations of circuit elements such as semiconductor elements.

[0052] Furthermore, the program may be firmware or software such as microcode. Alternatively, the program may be, for example, a group of program modules, each function of which may be implemented by a processor configured to perform its respective function. The program may be program code or multiple code segments stored on one or more non-temporary computer-readable media (e.g., storage media or other storage). The program may be divided and stored on multiple non-temporary computer-readable media located on physically separate devices. Program code or code segments may represent any combination of procedures, functions, subprograms, routines, subroutines, modules, software packages, classes, or instructions, data structures, or program statements. Program code or code segments may be connected to other code segments or hardware circuits by sending and receiving information, data, arguments, parameters, or memory contents.

[0053] The storage device 102 is a non-temporary storage medium and a tangible, computer-readable medium. The storage device 102 includes a main memory and an auxiliary storage device. The storage device 102 may be, for example, a semiconductor memory, a hard disk drive (HDD), or a solid state drive (SSD), or a combination of these. Part or all of the storage area of ​​the storage device 102 may be included in the processor 100.

[0054] The storage device 102 stores various parameters used in the inkjet printing device 1, as well as programs used in each part of the inkjet printing device 1. The storage device 102 also functions as a temporary storage unit for various data, including image data.

[0055] Various parameters stored in the storage device 102 are read via the processor 100 and set in each part of the device. Various programs stored in the storage device 102 are read by the processor 100 and executed in each part of the device.

[0056] The communication unit 104 is equipped with the necessary communication interface. The inkjet printer 1 is connected to the host computer 110 via the communication unit 104 and can send and receive data with the host computer 110. The term "connection" here includes wired connection, wireless connection, or a combination thereof. The communication unit 104 may be equipped with a buffer memory to speed up communication processing. The communication unit 104 also functions as an image input interface unit for acquiring image data representing the image to be printed. Image data acquired from the host computer 110 via the communication unit 104 is stored in the storage device 102.

[0057] The input device 106 is comprised of, for example, operation buttons, a keyboard, a mouse, a touch panel, a multi-touch screen, other pointing devices, or a voice input device, or an appropriate combination thereof. The input device 106 accepts various inputs from the operator.

[0058] The display device 108 is composed of, for example, a liquid crystal display, an organic electro-luminescence (OEL) display, a projector, or an appropriate combination thereof.

[0059] The information input via the input device 106 is sent to the processor 100. The processor 100 causes various parts to execute various processes according to the information input from the input device 106.

[0060] The display device 108 can display various information such as various device settings or abnormal information in response to commands from the processor 100. The user (operator) can set various parameters and input and edit various information using the input device 106 while viewing the contents displayed on the display device 108.

[0061] The processor 100 functions as a cleaning timing determination unit that determines the cleaning timing of the coated section 20. The processor 100 controls the first image forming unit 31 and the second image forming unit 41 to print a preset determination image 122 for determining the state of the coated section 20. The processor 100 controls the optical sensor 50 to read the determination image 122 and obtains the reading result for the determination image 122 from the optical sensor 50. Based on the reading result, the processor 100 determines the cleaning timing of the coated section 20 and outputs information regarding the cleaning timing.

[0062] The printing of the judgment image 122 is carried out in the same procedure as normal printing. That is, a pretreatment liquid is applied to the substrate 5, which is transported by the transport device 10, in the coating unit 20, and then the judgment image 122 is printed on the substrate 5, which is transported to the printing unit, by printing a color image in the first printing unit 30 and a white image in the second printing unit 40. The optical sensor 50 reads the judgment image 122 from the substrate 5, which is discharged from the second printing unit 40 and transported toward the winding roller.

[0063] Here, the judgment image 122 will be described. An example of the judgment image 122 is shown in Figure 4. One example of the judgment image 122 includes a stripe image extending in a direction intersecting the transport direction of the substrate 5. As an example, the judgment image 122 includes five stripe images S0 to S4. The five stripe images S0 to S4 are formed from multiple different density regions D0 to D4. Each density region D0 to D4 is printed as a stripe image extending in a direction intersecting the transport direction. Here, density refers to optical density. Of the density regions D0 to D4, density region D0 has the lowest density, and the density gradually increases from density region D0 to density region D4, with density region D4 having the highest density. Preferably, the stripe images S0 to S4 are formed in the width direction of the substrate 5 over the print width (the maximum width that can be printed by the inkjet printing device 1). The transport direction width of each stripe image S0 to S4 is not particularly limited as long as it is a width that can be confirmed if bleeding occurs. The transport direction width of each of the stripe images S0 to S4 is preferably about 1 mm or less, and as an example, it is about 0.5 mm. As shown in Figure 3, in the judgment image 122, a non-printed area 123 is provided between adjacent stripe images. The density area D1 is a reference density area (hereinafter referred to as the reference density area D1) recorded at the maximum amount of ink that is aggregated by the pretreatment liquid coated on the substrate 5.

[0064] Density regions D2 to D4 are high-density regions recorded with an ink volume greater than the maximum ink volume (hereinafter referred to as the first high-density region D2, the second high-density region D3, and the third high-density region D4). Here, the first high-density region D2, the second high-density region D3, and the third high-density region D4 have different densities.

[0065] The density region D0 is a low-density region recorded with an ink amount less than the maximum ink amount (hereinafter referred to as the low-density region D0).

[0066] In this example, if the ink amount in the standard density area D1 is set to 100%, the first high-density area D2 is set to 110%, the second high-density area D3 to 115%, the third high-density area D4 to 120%, and the low-density area D0 to 90% of the ink amount.

[0067] The pretreatment liquid applied to the substrate 5 by the coating unit 20 is a solution for agglomerating and fixing the ink. Since this pretreatment liquid reacts with the ink to agglomerate it, the amount of ink that can be agglomerated is determined by the type and amount of pretreatment liquid applied. The maximum amount of ink that can be agglomerated by the pretreatment liquid applied to the substrate 5 is uniquely determined by the type and amount of pretreatment liquid applied. Since a dedicated pretreatment liquid is used in the printing device and the application amount is set in advance, the maximum amount of ink that can be agglomerated by the pretreatment liquid can be determined from the printing device. Hereinafter, "the maximum amount of ink that can be agglomerated by the pretreatment liquid" will simply be referred to as "maximum ink amount". Note that "maximum ink amount" is set relative to the total amount of ink ejected from all inkjet heads equipped in the inkjet printing device.

[0068] Furthermore, if an amount of ink greater than the maximum amount of ink in the pretreatment solution is ejected, the ink cannot be coagulated and fixed by the pretreatment solution, causing it to move from its position on the ejected substrate 5, resulting in bleeding. In inkjet printing devices equipped with multiple inkjet heads, bleeding occurs when the total amount of ink ejected from all inkjet heads exceeds the maximum ink amount.

[0069] Here, "bleeding" refers to the phenomenon where ink does not coagulate with the pretreatment solution and spreads instead of settling completely in its intended recording position. Figure 5 is an image illustrating bleeding. When ink is ejected toward a recording medium (in this case, substrate 5) being transported in one direction (transport direction A) to record an image, the ink that does not coagulate with the pretreatment solution spreads upstream of the recording medium in the transport direction, causing bleeding. In Figure 5, bleeding can be observed upstream of the gray area G, the white area W, and the black area B at the boundary. The area enclosed by the dashed line in the enlarged view of the black area B and white area W in Figure 5 is what is shown as "bleeding." The presence or absence of bleeding can be determined visually. It is also possible to determine the presence or absence of bleeding through image processing.

[0070] The inkjet printing apparatus 1 of this embodiment is equipped with six inkjet heads: inkjet heads 32K, 32C, 32M, and 32Y provided in the first image forming unit 31, and inkjet heads 42WA and 42WB provided in the second image forming unit 41. In this case, if the total amount of ink ejected from the six inkjet heads 32K, 32C, 32M, 32Y, 42WA, and 42WB exceeds the maximum ink amount, bleeding will occur. Therefore, the amount of ink ejected by each inkjet head 32K, 32C, 32M, 32Y, 42WA, and 42WB is set so that the total amount of ink ejected from all inkjet heads 32K, 32C, 32M, 32Y, 42WA, and 42WB does not exceed the maximum ink amount.

[0071] However, if the amount of pretreatment liquid to be applied is less than the set value, the maximum ink volume will be less than the initially set value. As previously described, the volume of the cells 23 of the anilox roller 22 is formed according to the amount of pretreatment liquid to be applied, which is set in advance. On the other hand, as shown in Figure 2, the anilox roller 22 has fine cells 23, so the pretreatment liquid tends to clog it. Therefore, proper cleaning and maintenance are necessary. The coating section 20 is equipped with a cleaning mechanism (not shown) for cleaning the anilox roller 22 and the rubber plate 24. Cleaning by the cleaning mechanism is performed, for example, during the startup sequence or shutdown sequence of the inkjet printing device 1. Cleaning by the cleaning mechanism is a simple cleaning, for example, wiping off the pretreatment liquid adhering to the surface with a wiping material, and is performed without removing the anilox roller 22 and the rubber plate 24, and does not use special solvents. Even if cleaning is performed by the internal cleaning mechanism, prolonged use can cause dirt to accumulate in areas that cannot be cleaned by the cleaning mechanism, or cleaning solution to accumulate and harden in the cells 23 of the anilox roller 22. If dirt accumulates in the coating section 20, the amount of pretreatment solution coated onto the substrate may fall below the set value, leading to bleeding during printing.

[0072] To suppress bleeding caused by contamination of the coated section 20, it is necessary to remove the anilox roller 22 (or rubber plate 24) from the printing device and perform surface cleaning using a special solvent. The special solvent is a solvent that can dissolve solidified pretreatment liquid, such as an isopropyl alcohol solution. In the cleaning timing determination method of this embodiment, the timing of cleaning performed outside the printing device using the special solvent after removing the anilox roller (or rubber plate 24) from the printing device is determined. Hereinafter, "cleaning" means cleaning the component for coating the coated section 20 with the pretreatment liquid after removing it from the printing device and using the special solvent. In this embodiment, since clogging of the cells 23 of the anilox roller 22 is the main cause of reduced pretreatment liquid application, the cleaning timing can also be said to be the cleaning timing of the anilox roller 22.

[0073] Next, the process of determining whether cleaning is necessary and the timing of cleaning based on the judgment image 122 will be described. The processor 100 detects from the image data of the judgment image 122 acquired from the optical sensor 50 whether blurring has occurred in each density region D0 to D4. Specifically, the processor 100 detects, using known image processing, whether blurring as shown in Figure 5 above has occurred on the upstream side in the transport direction of each density region D0 to D4. Then, the processor 100 determines whether cleaning is necessary and the timing of cleaning according to the state in which blurring has occurred (states 1 to 5 in the table below).

[0074] Table 1 shows an example of how to determine whether cleaning is necessary or when cleaning should be done based on the presence or absence of smudging in each area.

[0075]

[0076] State 5, where bleeding occurs in the low-density area D0, is an abnormal condition in which bleeding occurs with a smaller amount of ink than the standard density. In this case, the processor 100 determines that cleaning is required and that cleaning should be done immediately. State 5 means that the amount of pretreatment solution applied is significantly less than the set value. Since the amount of pretreatment solution applied is less than the set value, it is presumed that contamination has occurred on the coated area 20. In this case, the processor 100 displays a message on the display device 108 prompting immediate cleaning. For example, it displays a message such as, "Please clean the anilox roller. Printing will not be possible due to printing defects and internal contamination."

[0077] In state 4, where there is no bleeding in the low-density area D0 but there is bleeding in the standard-density area D1, the processor 100 determines that immediate cleaning is not necessary but cleaning is due soon. Since the amount of ink in the standard-density area D1 is set to be the same as the maximum ink amount, bleeding should not occur under normal conditions. Therefore, it is suspected that the amount of pre-treatment solution is slightly less than the initial setting example. Normally, the maximum total amount of ink ejected during printing by all inkjet heads 32K, 32C, 32M, 32Y, 42WA, and 42WB installed in the inkjet printer 1 is often set slightly lower than the maximum ink amount, so immediate cleaning is not necessary. However, since the amount of pre-treatment solution is less than the set value, it is presumed that dirt is starting to accumulate on the coated area 20. In this case, the processor 100 displays a message prompting cleaning on the display device 108. For example, it displays the message, "Please clean the anilox roller. Printing defects may occur with dark images." The operator who receives the message may perform the cleaning immediately, or, if an actual job is in progress, may perform the cleaning after the series of prints have been completed, or may perform the cleaning when the inkjet printer 1 is shut down.

[0078] If there is no bleeding in the low-concentration region D0 and the standard concentration region D1, it is determined that the condition is normal and cleaning is unnecessary. In other words, conditions 1 to 3, in which bleeding occurs for the first time in any of the high-concentration regions D2 to D4, can all be considered normal. Here, "normal" means that the amount of pretreatment solution applied is approximately the set value.

[0079] In addition, under normal conditions where there is no bleeding in the low-concentration region D0 and the standard concentration region D1, the cleaning timing is estimated based on the presence or absence of bleeding in the high-concentration regions D2 to D4. Here, the time until the cleaning timing is estimated based on the presence or absence of bleeding in the first high-concentration region D2 to the third high-concentration region D4, where the concentration increases in stages.

[0080] State 3, in which there is no bleeding in the low-density area D0 and the standard-density area D1, but there is bleeding in the first high-density area D2, indicates that bleeding is occurring with an ink amount slightly greater than the maximum ink amount (110% in this case). In state 3, the processor 100 determines that the cleaning timing is in the near future. In this case, the processor 100 displays a message on the display device 108 prompting the user to perform cleaning in the near future. For example, it displays a message such as, "Please clean the anilox roller after shutdown."

[0081] In state 2, where there is no bleeding in the low-concentration region D0, the reference concentration region D1, and the first high-concentration region D2, but there is bleeding in the second high-concentration region D3, the processor 100 determines that the cleaning timing will come later than in state 3 (for example, about a week later). In this case, the processor 100 displays a cleaning guideline on the display device 108. For example, it displays a message such as, "The anilox roller will need to be cleaned in about a week."

[0082] If the condition is 3 or 2, you should research in advance how often cleaning will be necessary.

[0083] If there is no bleeding in the low-concentration area D0, the reference concentration area D1, the first high-concentration area D2, and the second high-concentration area D3, but there is bleeding in the third high-concentration area D4, the processor 100 determines that the cleaning timing is still some time away. In this case, the processor 100 may display a message on the display device 108 indicating that cleaning is not necessary, but it does not have to display a message regarding cleaning.

[0084] The operator can clean the anilox roller 22 or pre-set a cleaning plan according to the message displayed on the cleaning timing display device 108.

[0085] The processor 100 performs the following in a series of steps: printing the judgment image 122, reading the judgment image 122, determining the cleaning timing, and outputting information regarding the cleaning timing. In particular, it is preferable that this series of steps is performed within the shutdown sequence of the inkjet printer 1.

[0086] As described above, the cleaning timing determination method of this embodiment involves printing a preset determination image 122 for determining the state of the coating section 20 that applies the pretreatment liquid to a printing device that prints an image by ejecting ink onto a recording medium coated with a pretreatment liquid, and determining the cleaning timing of the coating section 20 based on the determination image 122. Conventionally, the blurring of the image was checked during a test print of the actual job, and if blurring occurred, the actual job was canceled and cleaning was performed. In contrast, with the cleaning timing determination method of this embodiment, instead of checking for blurring of the image during a test print of the actual job, a preset determination image 122 is printed to determine whether cleaning of the coating section 20 is necessary, thereby preventing disruptions to the printing work plan, such as interrupting the actual job to perform cleaning work.

[0087] In this embodiment, an example has been described in which the inkjet printing apparatus 1 is equipped with a processor 100, and the processor 100 is configured to print a determination image, read the image, and determine the cleaning timing. However, the cleaning timing determination method of this disclosure is not limited to this embodiment, and an operator may visually inspect the determination image 122 printed by the inkjet printing apparatus 1 to determine whether or not there is bleeding and to determine the cleaning timing.

[0088] In the inkjet printing apparatus 1 of this embodiment, the processor 100 controls the image forming units 31 and 41 to print a preset determination image 122 for determining the state of the coated section 20, controls the optical sensor 50 to read the determination image 122, obtains the reading result for the determination image 122 from the optical sensor 50, determines the cleaning timing of the coated section 20 based on the reading result, and outputs information regarding the cleaning timing. Since the operator does not need to perform the cleaning timing determination process, the operator's workload is reduced. Also, since the determination process can be performed inline, time loss can be suppressed. Furthermore, although the determination image 122 shown in Figure 4 is shown as a dedicated grayscale chart, for example, a single stripe image may be embedded in a part of the actual printed material. For example, one stripe image of a different density may be printed on each page (or equivalent to one page), and five different stripe images may be printed on five pages. In this way, it is preferable to perform the cleaning timing determination process in parallel with the actual job.

[0089] If the judgment image 122 includes a reference density region D1 recorded with the maximum ink amount, the necessity of cleaning can be determined by the presence or absence of bleeding in the reference density region D1. If there is no bleeding in the reference density region D1, it is in a normal state and cleaning is not necessary. If there is bleeding, it is clear that cleaning is necessary.

[0090] If the judgment image 122 includes high-density areas D2 to D4 recorded with an ink amount greater than the maximum ink amount, the cleaning timing can be determined by the presence or absence of bleeding in the high-density areas D2 to D4. If there is no bleeding in the standard density area D1, but there is bleeding in the high-density areas D2 to D4, an estimate of the cleaning timing can be obtained. In particular, as in this embodiment, if there are multiple high-density areas D2 to D4 with different densities, it is possible to estimate the period until the cleaning timing. In this embodiment, a configuration with three high-density areas D2 to D4 has been described, but the number of high-density areas may be one, two, or even four or more. If the period until the cleaning timing can be estimated, cleaning can be carried out systematically, and planned job management becomes easier.

[0091] If the judgment image 122 includes a low-density area D0 recorded with less ink than the maximum ink amount, the need for immediate cleaning can be determined by the presence or absence of bleeding in the low-density area D0. If bleeding is present in the low-density area D0, it indicates an abnormal condition where the pretreatment solution is insufficient to meet the set value. By immediately stopping printing and taking appropriate measures such as cleaning, contamination of the device and the occurrence of printing defects can be suppressed. The low-density area may also include multiple areas with different densities.

[0092] If the judgment image 122 consists of stripe images S0 to S4 that extend in a direction intersecting the transport direction of the recording medium (in this case, the substrate 5), then it is possible to detect even if a blockage occurs in a part of the longitudinal direction of the cylindrical anilox roller 22.

[0093] When the judgment image 122 includes multiple stripe images S0 to S4, as in this embodiment, it is preferable to place non-printed areas 123 between adjacent stripe images S0 to S4. This is because it makes it easier to observe the blurring in each density area D0 to D4.

[0094] When the coating unit 20 is equipped with an anilox roller 22, determining the cleaning timing as described above allows for the appropriate removal of blockages in the anilox roller 22, thereby suppressing image defects.

[0095] The inkjet printing apparatus 1 of the above embodiment comprises a first printing unit 30 and a second printing unit 40, and prints a color image and a white image superimposed on a substrate 5 for flexible packaging. This disclosure is not limited to this embodiment of the printing apparatus. A printing apparatus may also have only one printing unit for color images. Furthermore, the printing apparatus is not limited to a roll-to-roll printing method on a long substrate 5 for flexible packaging, but may also be a sheet-fed printing apparatus.

[0096] The embodiments of the Disclosure described above can be modified, added to, or deleted as appropriate without departing from the spirit of the Disclosure. The present invention is not limited to the embodiments described above, and many modifications are possible within the technical concept of the present invention by those with ordinary skill in the equivalent related art.

[0097] The following additional notes are disclosed regarding the above embodiments. <Note 1> A method for determining cleaning timing in a printing apparatus that prints an image by ejecting ink onto a recording medium coated with a pretreatment liquid, wherein a predetermined determination image is printed for determining the state of the coated area to which the pretreatment liquid is applied, and the cleaning timing of the coated area is determined based on the determination image. <Note 2> The cleaning timing determination method according to Note 1, wherein the determination image includes a reference density region recorded with the maximum amount of ink that is aggregated by the pretreatment liquid applied to the recording medium. <Note 3> The cleaning timing determination method according to Note 2, wherein the necessity of cleaning is determined by the presence or absence of bleeding in the reference density region. <Note 4> The cleaning timing determination method according to any one of Notes 1 to 3, wherein the determination image includes a high density region recorded with an amount of ink greater than the maximum amount of ink. <Note 5> The cleaning timing determination method according to Note 4, wherein the cleaning timing is determined by the presence or absence of bleeding in the high density region. <Note 6> The cleaning timing determination method according to Note 4 or 5, wherein the high-density area includes multiple high-density areas with different densities, and the period until cleaning timing is estimated based on the presence or absence of bleeding in the multiple high-density areas. <Note 7> The cleaning timing determination method according to any one of Notes 1 to 6, wherein the determination image includes a low-density area recorded with an ink amount less than the maximum ink amount. <Note 8> The determination method according to Note 7, which determines whether immediate cleaning is necessary based on the presence or absence of bleeding in the low-density area. <Note 9> The cleaning timing determination method according to any one of Notes 1 to 8, wherein the determination image consists of stripe images extending in a direction intersecting the transport direction of the recording medium. <Note 10> The cleaning timing determination method according to Note 9, wherein the determination image includes multiple stripe images, and non-printed areas are arranged between the stripe images. <Note 11> The coating section is equipped with an anilox roller having multiple depressions on its surface for drawing up pretreatment liquid, and the cleaning timing of the coating section is determined by determining the cleaning timing of the anilox roller, as described in any one of Notes 1 to 10.<Note 12> A printing apparatus for printing an image on a recording medium while transporting the recording medium, comprising: a coating unit for coating the recording medium with a pretreatment liquid; an image forming unit for printing an image by ejecting ink toward the recording medium coated with the pretreatment liquid; an optical sensor for reading the image printed on the recording medium; and a processor, wherein the processor controls the image forming unit to print a preset determination image for determining the state of the coating unit, controls the optical sensor to read the determination image, obtains a reading result for the determination image from the optical sensor, determines the cleaning timing of the coating unit based on the reading result, and outputs information regarding the cleaning timing. <Note 13> The printing apparatus according to Note 12, wherein the optical sensor is a line sensor arranged extending in the width direction of the recording medium. <Note 14> The printing apparatus according to Note 13, wherein the line sensor is arranged downstream of the image forming unit in the transport direction of the recording medium and reads the determination image while the recording medium is being transported. <Note 15> The printing apparatus according to any one of Notes 12 to 14, wherein the processor performs the following in a series of steps: printing a judgment image, reading the judgment image, determining the cleaning timing, and outputting information regarding the cleaning timing. <Note 16> The printing apparatus according to Note 15, wherein the processor performs the sequence within the device shutdown sequence. <Note 17> The printing apparatus according to any one of Notes 12 to 16, wherein the coating section is equipped with an anilox roller having a plurality of depressions on its surface for drawing up the pretreatment liquid.

[0098] The disclosure of Japanese Patent Application No. 2025-052703, filed on 26 March 2025, is incorporated herein by reference in its entirety. All documents, patent applications, and technical standards described herein are incorporated herein by reference to the same extent as if each individual document, patent application, and technical standard were specifically and individually noted to be incorporated by reference.

Claims

1. A method for determining cleaning timing in a printing apparatus that prints an image by ejecting ink onto a recording medium coated with a pretreatment liquid, wherein the apparatus prints a preset determination image for determining the state of the coated area to which the pretreatment liquid is applied, and determines the cleaning timing of the coated area based on the determination image.

2. The method for determining the cleaning timing according to claim 1, wherein the determination image includes a reference concentration region recorded at the maximum amount of ink aggregated by the pretreatment liquid coated on the recording medium.

3. A method for determining the timing of cleaning according to claim 2, wherein the necessity of cleaning is determined based on the presence or absence of seepage in the reference concentration range.

4. The method for determining the cleaning timing according to claim 2 or 3, wherein the determination image includes a high-density region recorded with an ink amount greater than the maximum ink amount.

5. The method for determining the cleaning timing according to claim 4, wherein the cleaning timing is determined by the presence or absence of seepage in the high-concentration region.

6. The cleaning timing determination method according to claim 4, wherein the high-concentration region includes a plurality of high-concentration regions with different concentrations, and the period until the cleaning timing is estimated based on the presence or absence of seepage in the plurality of high-concentration regions.

7. The method for determining the cleaning timing according to claim 2 or 3, wherein the determination image includes a low-density region recorded with an ink amount less than the maximum ink amount.

8. The method for determining the timing of cleaning according to claim 7, wherein the necessity of immediate cleaning is determined based on the presence or absence of seepage in the low-concentration region.

9. The method for determining the cleaning timing according to any one of claims 1 to 3, wherein the determination image is composed of stripe images extending in a direction intersecting the transport direction of the recording medium.

10. The method for determining the cleaning timing according to claim 9, wherein the determination image includes a plurality of the stripe images, and non-printed areas are arranged between the stripe images.

11. The method for determining the cleaning timing according to claim 1 or 2, wherein the coating portion is provided with an anilox roller having a plurality of depressions on its surface for drawing up the pretreatment liquid, and the cleaning timing of the anilox roller is determined as the cleaning timing of the coating portion.

12. A printing apparatus for transporting a recording medium and printing an image on the recording medium, comprising: a coating unit for coating the recording medium with a pretreatment liquid; an image forming unit for printing an image by ejecting ink toward the recording medium coated with the pretreatment liquid; an optical sensor for reading the image printed on the recording medium; and a processor, wherein the processor controls the image forming unit to print a preset determination image for determining the state of the coating unit; controls the optical sensor to read the determination image, obtains a reading result for the determination image from the optical sensor; determines the cleaning timing of the coating unit based on the reading result; and outputs information regarding the cleaning timing.

13. The printing apparatus according to claim 12, wherein the optical sensor is a line sensor that extends in the width direction of the recording medium.

14. The printing apparatus according to claim 13, wherein the line sensor is positioned downstream of the image forming unit in the transport direction of the recording medium, and reads the determination image while the recording medium is being transported.

15. The printing apparatus according to claim 12, wherein the processor performs the following in a series of steps: printing the determination image, reading the determination image, determining the cleaning timing, and outputting information regarding the cleaning timing.

16. The printing apparatus according to claim 15, wherein the processor executes the sequence within the device shutdown sequence.

17. The printing apparatus according to any one of claims 12 to 16, wherein the coating section comprises an anilox roller having a plurality of depressions on its surface for drawing up the pretreatment liquid.

Images