Inkjet printer

Abstract

This inkjet printer comprises: an inkjet head including a nozzle for discharging ink to a recording surface of a recording medium; a drying unit for drying the ink on the recording medium to which the ink has been applied; and a superheated steam generation system including a water tank for pooling a liquid with a hardness of 30 mg / L or less and a heating unit that heats the liquid to generate superheated steam. The drying unit includes a steam chamber that stores the superheated steam generated in the superheated steam generation system, and applies the superheated steam stored in the steam chamber onto the recording medium to dry the ink.

Description

Inkjet printing apparatus

[0001] The present disclosure relates to an inkjet printing apparatus.

[0002] An inkjet printing apparatus that discharges a liquid such as ink to form an image is known. In an inkjet printing apparatus, generally, after forming an image on a recording medium, a drying process for drying the ink is performed. Hot air drying is mainly used for the drying process. However, hot air drying may cause uneven drying or deformation of the base material, and may affect the print quality.

[0003] On the other hand, International Publication No. 2017 / 138439 and Japanese Patent Application Laid-Open No. 2010-158861 propose a method of using superheated steam in the drying process. Superheated steam obtained by heating water to steam at 100° C. or higher can heat the recording medium by high sensible heat and condensation heat. Since the condensation location changes according to the temperature distribution of the recording medium, it leads to suppression of temperature unevenness. In addition, since the water generated by condensation humidifies the recording medium, deformation of the recording medium can be suppressed. Therefore, drying with superheated steam is useful for improving print quality.

[0004] However, superheated steam has a higher temperature than hot air, and the temperature of the entire apparatus tends to rise. For example, when the periphery of the head becomes high temperature, the moisture of the ink around the head nozzle evaporates, the ink dries, and clogging or the like occurs, and ejection failure is likely to occur. In order to suppress the drying of the ink, a method of increasing the humidity by discharging mist or steam around the head can be considered. However, even if ejection failure due to ink drying can be suppressed, scale is generated on the nozzle surface by minerals such as calcium and magnesium contained in the mist and steam, and problems such as ejection failure due to scale may occur. In addition, when the humidity is increased by mist or steam, scale may also occur on the image surface, and image defects may occur.

[0005] The present disclosure has been made in view of the above circumstances, and an object thereof is to provide an inkjet printing apparatus that suppresses deformation of a recording medium and suppresses ejection failure of an inkjet head.

[0006] The inkjet printing apparatus of this disclosure comprises an inkjet head equipped with nozzles for ejecting ink onto the recording surface of a recording medium, a drying unit for drying the ink on the recording medium to which the ink has been applied, and a superheated steam generation system including a reservoir for storing a liquid with a hardness of 30 mg / L or less, and a heating unit for heating the liquid to generate superheated steam. The drying unit comprises a steam chamber for containing the superheated steam generated in the superheated steam generation system, and dries the ink on the recording medium by applying the superheated steam contained in the steam chamber.

[0007] The liquid stored in the reservoir preferably has a calcium ion concentration of 20 mg / L or less and a magnesium ion concentration of 10 mg / L or less.

[0008] The inkjet head is equipped with a control unit that controls ink ejection, and it is preferable that the control unit controls the meniscus oscillation of the ink inside the nozzle when ink is not being ejected.

[0009] The inkjet head is preferably a circulating type head that circulates the ink.

[0010] It is preferable that the inkjet printing apparatus is equipped with a head humidification mechanism that introduces a misted liquid from a water reservoir, or vapor generated from the liquid, into the housing containing the inkjet head to humidify at least the ink ejection port of the inkjet head.

[0011] In an inkjet printing apparatus, an inkjet head and a drying unit are provided on a transport path that transports a recording medium, and it is preferable that the apparatus is equipped with an upstream region humidification mechanism that humidifies the region upstream of the inkjet head on the transport path with a mist of liquid from a water reservoir or with steam generated from the liquid.

[0012] Inkjet printing apparatus preferably includes a steam recovery mechanism that recovers superheated steam contained in the steam chamber and returns it to at least one of the steam chamber and the water reservoir.

[0013] As a steam recovery mechanism, it is preferable to have a recovery duct that flows the superheated steam along the outer wall surface of the steam chamber when recovering the superheated steam contained within the steam chamber.

[0014] Preferably, the inkjet printing apparatus is equipped with a water softening apparatus that produces a liquid with a hardness of 30 mg / L or less, and the water softening apparatus is equipped with a sensor that detects the hardness of the liquid and an input mechanism that introduces a solid material for water softening into the water softening apparatus when the hardness of the liquid detected by the sensor exceeds 30 mg / L.

[0015] In an inkjet printing apparatus, it is preferable that the film surface temperature of the recording medium to which superheated steam is applied is between 60°C and 200°C.

[0016] In an inkjet printing apparatus, it is preferable that the recording medium exposed to superheated steam has a higher surface temperature and a moisture content equal to or greater than that before exposure to superheated steam.

[0017] The drying unit preferably includes a hot air chamber for drying the recording medium with hot air upstream of the steam chamber.

[0018] The hot air chamber is positioned adjacent to the steam chamber, and it is preferable to heat the walls of the steam chamber by outputting hot air from the hot air chamber.

[0019] Inkjet printing apparatus preferably includes two or more steam chambers, and is configured such that the number of steam chambers to which superheated steam is supplied from the heating unit is selected according to the type of recording medium.

[0020] According to this disclosure, it is possible to provide an inkjet printing apparatus that suppresses deformation of the recording medium and suppresses ejection defects of the inkjet head.

[0021] This is a schematic diagram of an inkjet printing apparatus according to an embodiment. Figures 2A and 2B show specific configuration examples of the deposition chamber, respectively. This is a diagram of a deposition chamber equipped with a recovery duct. This is a diagram of a configuration for humidifying the inkjet head. Figures 5A and 5B show configurations for humidifying the inkjet head. This is a diagram of one embodiment of a method for heating the wall surface of the deposition chamber. This is a diagram of a configuration when multiple deposition chambers are provided.

[0022] 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.

[0023] 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.

[0024] Figure 1 is a schematic diagram of an inkjet printing apparatus 1 according to one embodiment. The inkjet printing apparatus 1 is an inkjet-type color digital printing apparatus that forms a desired image on the recording surface of a recording medium P, which is a sheet of paper. The inkjet printing apparatus 1 is capable of single-sided printing, which forms an image on only one side of the recording medium P, and double-sided printing, which forms an image on both sides of the recording medium P. In this example, the recording medium P is paper.

[0025] The inkjet printing apparatus 1 comprises a transport mechanism 10, a paper feeder 20, a pre-processing unit 30, an image forming unit 40, a drying unit 50, a cooling unit 60, an accumulation unit 70, and a superheated steam generation system 100. Although not shown in Figure 1, the inkjet printing apparatus 1 also includes a processor to control each of its components.

[0026] The transport mechanism 10 has a transport path 12 for transporting the recording medium P. In Figure 1, the direction in which the recording medium P is transported is indicated by a dashed arrow. The recording medium P is transported along the transport path 12 to various units, where each unit performs its respective processing.

[0027] The transport path 12 includes a main transport path 13, a supply path 14 for supplying the recording medium P to the main transport path 13, an discharge path 15 for discharging paper from the main transport path 13, and a return transport path 16 that branches off from the main transport path 13 and the discharge path 15. The return transport path 16 constitutes a path that returns the recording medium P, which has passed through the main transport path 13, back to the main transport path 13 for double-sided printing.

[0028] The supply path 14 supplies the recording medium P from the paper feed device 20 to the main transport path 13. One end of the supply path 14 is located on the paper feed device 20 side, and the other end is connected to the main transport path 13. The recording medium P is supplied from the paper feed device 20 to one end of the supply path 14, transported along the supply path 14, and supplied to the main transport path 13 from the other end of the supply path 14.

[0029] The discharge channel 15 transports the recording medium P from the main transport channel 13 to the accumulating device 70. One end of the discharge channel 15 is connected to the main transport channel 13, and the other end is connected to the accumulating device 70. The recording medium P is discharged from the main transport channel 13 to one end of the discharge channel 15, transported along the discharge channel 15, and discharged from the other end of the discharge channel 15 to the accumulating device 70.

[0030] The return transport path 16 has its starting end connected to the end of the main transport path 13, and its end is connected to the starting end of the main transport path 13, forming a circumferential circuit together with the main transport path 13. The return transport path 16 returns the recording medium P, which has passed through the main transport path 13 and had an image formed on its first recording surface by the image forming unit 40, back to the image forming unit 40, enabling image formation on the second recording surface.

[0031] The return transport path 16 is equipped with a switchback section 17 that reverses the direction of travel of the recording medium P. The switchback section 17 temporarily pulls the recording medium P out of the return transport path 16 and reverses the direction of travel of the recording medium P. That is, the leading end of the recording medium P in the direction of travel when it was being transported along the return transport path 16 before being pulled into the switchback section 17 becomes the trailing end in the direction of travel after it is returned to the return transport path 16 from the switchback section 17. By passing through this switchback section 17, the front and back sides of the recording medium P that is supplied again from the return transport path 16 to the main transport path 13 are reversed.

[0032] The conveying mechanism 10 includes a plurality of conveying members (not shown) along the conveying path 12. Examples of the plurality of conveying members include a conveying drum, a belt conveyor, a pair of conveying rollers, a chain gripper, and a conveying guide. The conveying mechanism 10 also includes a drive unit, such as a motor (not shown) and a motor drive circuit (not shown), which serve as a power source. The recording medium P is conveyed along the conveying path 12 by these elements constituting the conveying mechanism 10.

[0033] The paper feeder 20 is equipped with a paper feed tray on which a stack of numerous recording media P is placed. The type of paper used as the recording media P is not particularly limited, but for example, cellulose-based printing paper such as fine paper, coated paper, and art paper can be used.

[0034] The paper feeder 20 takes out the stack of recording media P set inside it one by one from the top and supplies them to the supply path 14 of the transport path 12.

[0035] The pre-treatment unit 30 applies a pre-treatment liquid to the recording surface of the recording medium P before ink is applied. Here, the pre-treatment liquid is a liquid called a "pre-coat," "pre-conditioner," "undercoat liquid," or "treatment agent," and is a liquid that has the function of coagulating, insolubilizing, or thickening the colorant components in the ink.

[0036] The image forming unit 40 includes inkjet heads 42K, 42C, 42M, and 42Y. Inkjet head 42K is a recording head equipped with a nozzle 43K for ejecting droplets of black ink. Inkjet head 42C is a recording head equipped with a nozzle 43C for ejecting droplets of cyan ink. Inkjet head 42M is a recording head equipped with a nozzle 43M for ejecting droplets of magenta ink. Inkjet head 42Y is a recording head equipped with a nozzle 43Y for ejecting droplets of yellow ink. Each of the inkjet heads 42C, 42M, 42Y, and 42K is supplied with ink from an ink tank (not shown), which is an ink source for the corresponding color, via a piping route (not shown). For example, water-based ink is used as the ink for drawing. Water-based ink refers to ink in which colorants such as pigments and dyes are dissolved or dispersed in water and / or a water-soluble solvent. In the following, when it is not necessary to distinguish between inkjet heads 42K, 42C, 42M, and 42Y, they will simply be referred to as inkjet head 42. Similarly, when it is not necessary to distinguish between nozzles 43K, 43C, 43M, and 43Y, they will simply be referred to as nozzle 43.

[0037] The inkjet head 42 can be a thermal head, a continuous head, a piezo head, an electrostatic attraction head, or a Microjet head. However, it is preferable that a control unit (not shown) that drives the inkjet head 42 controls the meniscus oscillation of the ink in the nozzles 43 when ink is not being ejected. Specifically, examples of types capable of meniscus oscillation include piezo heads. The ink meniscus can be oscillated by applying a voltage that does not cause ink to be ejected by the piezo head. Meniscus oscillation is preferably performed even in the Cap (high humidity chamber) where the inkjet head 42 is stored during non-printing periods. Furthermore, meniscus oscillation is applied, for example, while the inkjet head 42 is moving to the printing position, or during the period between the recording medium P being printed and the next recording medium P being transported. It may also be selectively applied to nozzles 43 that are not ejecting ink, even during printing. The meniscus oscillation in each sequence may be varied by selecting different waveforms for each sequence to change the fine oscillation. Because piezo heads allow for control over ink droplet size, they are also effective for image correction and other applications.

[0038] Furthermore, it is preferable that the inkjet head 42 is a circulating head that recovers and circulates ink that is not ejected from the nozzles 43 during ink ejection. A circulating head includes, for example, a circulation channel that circulates ink from each of the multiple nozzles 43 to an internal channel. Since a circulating head suppresses ink adhesion, it is highly effective in suppressing ink drying. Regarding circulating heads and meniscus oscillation, for example, descriptions in Japanese Patent Application Publication No. 2024-93608 can be referred to, and conventionally known technologies can be applied.

[0039] Furthermore, since the inkjet head 42 itself may become hot due to the ejection drive during printing, it is preferable to provide a cooling unit for cooling the inkjet head 42. Examples of cooling methods by the cooling unit include air cooling, contact heating, and liquid cooling.

[0040] In the image forming unit 40, ink droplets are ejected from the nozzle 43 toward the recording medium P which is being transported opposite the inkjet head 42. The ejected droplets adhere to the recording medium P, thereby forming an image on the recording medium P.

[0041] The drying unit 50 dries the ink applied to the recording medium P. The drying unit 50 comprises a hot air chamber 52 and a steam chamber 54. The hot air chamber 52 is located upstream of the steam chamber 54. The hot air chamber 52 is equipped with a hot air blower (not shown). In the hot air chamber 52, hot air output from the hot air blower is blown onto the recording medium P to dry the ink. Superheated steam S generated by the superheated steam generation system 100 is supplied to the steam chamber 54. The steam chamber 54 contains the superheated steam S and applies the superheated steam S to the recording medium P to dry the ink. The superheated steam generation system 100 will be described later.

[0042] Specific configuration examples of the steam chamber 54 are shown in Figures 2A and 2B. The steam chamber 54A shown in Figure 2A is configured so that the recording medium P can pass through the steam chamber 54A. The steam chamber 54A includes an inlet 55 into which the recording medium P is brought and an outlet 56 from which the recording medium P is discharged. Superheated steam S is supplied to the steam chamber 54A from the superheated steam generation system 100. After passing through the image forming unit 40, the recording medium P is transported into the steam chamber 54A from the inlet 55, exposed to the superheated steam S filling the steam chamber 54A, and then discharged from the outlet 56.

[0043] A fan (not shown) or the like is provided in the steam chamber 54A, and the superheated steam S is stirred in the steam chamber 54A. A part of the superheated steam is exhausted to the outside of the steam chamber 54A through the exhaust duct 57. An exhaust port connected to the exhaust duct 57 is provided with a shielding plate that can be opened and closed, and the opening and closing may be controlled by a sequence. Specifically, when starting up or drying the inkjet printing apparatus 1, the shielding plate is closed to fill the superheated steam S in the steam chamber 54A, and when shutting down, the shielding plate is opened to exhaust the superheated steam S. The opening and closing of the shielding plate does not have to be a complete opening and closing. For example, depending on the type of the recording medium, the exhaust amount may be adjusted by opening it partially. The startup of the inkjet printing apparatus 1 refers to the printing standby time from when the power is turned on until the printing process starts. Note that the shutdown refers to the time from when the printing process ends until the power is turned off.

[0044] The steam chamber 54B shown in FIG. 2B includes an injection port 58 for the superheated steam S. The steam chamber 54B is arranged such that the injection port 58 faces the conveyance path 12. The superheated steam S is supplied to the steam chamber 54A from the superheated steam generation system 100. After the recording medium P passes through the image forming unit 40, it is conveyed facing the surface of the steam chamber 54B provided with the injection port 58. The superheated steam S filled in the steam chamber 54B is injected from the injection port 58 toward the recording medium P.

[0045] Note that it is preferable that the superheated steam S injected from the steam chamber 54B is recovered through a recovery duct, a part of which is returned into the chamber and a part of which is exhausted to the outside air. For example, as shown in FIG. 3, it is preferable that the recovery duct 59 is arranged along the outer wall surface of the steam chamber 54B and is configured to flow and recover the superheated steam S injected from the steam chamber 54B along the outer wall surface.

[0046] The cooling unit 60 cools the recording medium P heated and dried in the drying unit 50. As an example, the cooling unit 60 includes a blower (not shown) that blows normal-temperature air or air cooled below normal temperature. The blower is arranged to face the recording surface (i.e., the ink film surface) of the recording medium P. The blower can change the blowing temperature and output. As a cooling means provided in the cooling unit 60, instead of a blower that cools the recording medium P in a non-contact manner, or together with it, a contact cooling mechanism that contacts the surface opposite to the recording surface and cools the recording medium P may be provided.

[0047] The stacking device 70 stacks the recording medium P on which an image has been formed. The stacking device 70 receives the recording medium P discharged from the discharge path 15 of the conveyance path 12 and stacks it on a stacking tray (not shown).

[0048] This inkjet printing apparatus 1 can perform single-sided printing and double-sided printing, and is configured to be selectively switched between a single-sided printing mode and a double-sided printing mode. Depending on either mode, the conveyance path is switched, and the recording medium P is conveyed along a conveyance path suitable for each mode.

[0049] In the single-sided printing mode, the recording medium P is conveyed along a path passing through the supply path 14, the main conveyance path 13, and the discharge path 15. Specifically, the recording medium P fed from the paper feeding device 20 to the supply path 14 is conveyed to the main conveyance path 13, and in the main conveyance path 13, a preprocessing step by the preprocessing unit 30, an image forming step by the image forming unit 40, a drying step by the drying unit 50, and a cooling step by the cooling unit 60 are sequentially executed. Thereafter, the recording medium P with an image printed on the first recording surface is conveyed to the discharge path 15 and discharged to the stacking device 70.

[0050] In double-sided printing mode, the recording medium P is transported along a path that sequentially passes through the supply path 14, the main transport path 13, the return transport path 16, the main transport path 13, and the discharge path 15. Specifically, the recording medium P fed from the paper feeder 20 to the supply path 14 is transported to the main transport path 13, where a pre-processing step, image formation step, drying step, and cooling step are sequentially performed on the first recording surface of the recording medium P. After that, the recording medium P is transported from the main transport path 13 to the return transport path 16, and via the switchback section 17, it is inverted to the front and rear ends, and the inverted recording medium P is transported along the return transport path 16. The recording medium P is returned to the main transport path 13 via the return transport path 16. When the recording medium P is returned to the main transport path 13, its front and back sides are inverted so that the second recording surface of the recording medium P becomes the image forming surface. In the main transport path 13, a pre-processing step, image formation step, drying step, and cooling step are sequentially performed on the second recording surface. Then, the recording medium P, on which images are printed on both sides, is transported from the main transport path 13 to the discharge path 15 and discharged to the accumulating device 70.

[0051] The processor that controls each part includes a CPU (Central Processing Unit). The processor functions as a processing unit and / or control unit that performs various processes by executing program instructions stored in a memory device. The processor comprehensively controls the transport mechanism 10, paper feed device 20, preprocessing unit 30, image forming unit 40, drying unit 50, cooling unit 60, integrator 70, and superheated steam generation system 100. The processor also functions as a control unit (not shown) that drives the inkjet head 42.

[0052] A storage device is a non-temporary storage medium and a tangible, computer-readable medium. A storage device includes primary memory and secondary storage. The storage device may be, for example, semiconductor memory, a hard disk drive (HDD), or a solid state drive (SSD), or a combination thereof. Part or all of the storage area of ​​the storage device may be included in the processor.

[0053] The memory device 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 memory device also functions as a temporary storage unit for various data, including image data.

[0054] Various parameters stored in the memory device are read via the processor and set in each part of the device. Various programs stored in the memory device are read via the processor and executed in each part of the device.

[0055] In terms of hardware structure, various types of processors can be used, as shown below. These types of processors include CPUs, which are general-purpose processors that execute software (programs) and function as various processing units, as well as PLDs (Programmable Logic Devices) such as FPGAs (Field-Programmable Gate Arrays) whose circuit configuration can be changed after manufacturing, and dedicated electrical circuits, which are processors with circuit configurations specifically designed to perform particular processing, such as ASICs (Application Specific Integrated Circuits).

[0056] Furthermore, the above processing may be executed on one of these various processors, or on a combination of two or more processors of the same or different types (for example, multiple FPGAs, and a combination of a CPU and an FPGA). Alternatively, multiple processing units may be configured on a single processor. An example of configuring multiple processing units on a single processor is the use of a processor that realizes the functions of the entire system, including multiple processing units, on a single IC (Integrated Circuit) chip, such as a System on a Chip (SOC).

[0057] Furthermore, more specifically, these processors can utilize electrical circuits (Circuitry) that combine circuit elements such as semiconductor devices as their hardware structure.

[0058] Next, returning to Figure 1, the superheated steam generation system 100 of the inkjet printing apparatus 1 will be described. The superheated steam generation system 100 includes a water softener 102, a water storage tank 104, and a heating unit 105. The heating unit 105 includes a boiler 106 and a superheated steam generator 108. In the figure, the double arrow lines schematically represent pipelines a1 to a5, b1 to b4, and c1 to c3 through which water, steam, or mist flows, and the direction of the arrow indicates the direction of flow.

[0059] The water softener 102 is connected to the water pipe and takes in tap water via pipe a1. The water softener 102 performs a water softening treatment to soften the tap water to a hardness of 30 mg / L or less. Although it varies by region, typical Japanese tap water has a calcium ion concentration of 20 mg / L or less, a magnesium ion concentration of 10 mg / L or less, and a hardness of about 60 mg / L. By softening the tap water, it is possible to produce softened water with a hardness of 30 mg / L or less, a calcium ion concentration of 20 mg / L or less, and a magnesium ion concentration of 10 mg / L or less.

[0060] The water softener 102 is equipped with ion exchange resin for water softening, and sodium chloride is added periodically. In this example, a sensor 102a is provided to detect the hardness of the softened water, and an adding mechanism 102b is provided to add sodium chloride as a solid for water softening treatment to the water softener 102 when the hardness detected by the sensor 102a exceeds 30 mg / L. The user may periodically measure the hardness of the softened water and add the solid for water softening treatment as needed. However, by providing the sensor 102a and automatically adding the solid by the adding mechanism 102b as needed, usability can be improved. In addition, although the sensor 102a is provided in this example, the system may be configured to add the solid for water softening treatment at predetermined intervals without the sensor 102a.

[0061] The water storage tank 104 stores softened water supplied from the water softener 102 via the pipeline a2. That is, the water storage tank 104 stores liquid (in this case, water) with a hardness of 30 mg / L or less. Preferably, the water storage tank 104 stores liquid with a hardness of 30 mg / L or less, a calcium ion concentration of 20 mg / L or less, and a magnesium ion concentration of 10 mg / L or less.

[0062] The heating unit 105 generates superheated steam by superheating soft water supplied from the water storage unit 104. In the heating unit 105, soft water is supplied from the water storage unit via pipe a3 to the boiler 106, where it is superheated to generate saturated steam. The saturated steam generated in the heating unit 105 is sent to the superheated steam generator 108 via pipe a4, where it is further heated. As a result, superheated steam is generated in the superheated steam generator 108.

[0063] Boiler 106 has, for example, a heat transfer area of ​​5 m². ２ The following heater is provided: Softened water is supplied from the reservoir 104 to the boiler 106, and within the boiler 106, under a pressure of 1.0 MPa or less, the heat transfer area is 5 m². ２ Saturated steam is generated by heating with the following heaters. To minimize power consumption, the pressure inside boiler 106 is kept below 0.3 MPa, and the heat transfer area of ​​the heaters is 1.01 m². ２ The following is more preferable:

[0064] The superheated steam generator 108 is equipped with a burner, electric heater, or electromagnetic induction heating device to further heat the saturated steam. In the superheated steam generator 108, for example, superheated steam in the range of 100°C to 500°C is generated at a steam flow rate in the range of 5 kg / h to 50 kg / h. To avoid over-specification, it is desirable to configure it to generate superheated steam at a flow rate of 35 kg / h or less and a temperature of 350°C or less. The steam temperature and steam flow rate may be changed depending on the type of recording medium P.

[0065] The superheated steam generated in the heating unit 105 is sent to the steam chamber 54 via the pipeline a5 and is applied to the recording medium P as it passes through the steam chamber 54 to dry the ink.

[0066] As described above, the inkjet printing apparatus 1 includes a water reservoir 104 for storing liquid with a hardness of 30 mg / L or less, and a superheated steam generation system 100 including a heating unit 105 that heats the liquid to generate superheated steam. The drying unit 50 includes a steam chamber 54 that contains the superheated steam generated in the superheated steam generation system 100, and dries the ink by applying the superheated steam contained in the steam chamber 54 to the recording medium P. With this configuration, since the ink is dried by applying superheated steam to the recording medium P, the recording medium P can be heated by high sensible heat and condensation heat. As the condensation location changes according to the temperature distribution of the recording medium P, temperature unevenness is suppressed. In addition, since the liquid generated by condensation humidifies the recording medium P, deformation of the recording medium P can be suppressed compared to drying methods that do not use superheated steam, such as hot air drying. Suppression of deformation of the recording medium P leads to improved print quality. Furthermore, since a liquid with a hardness of 30 mg / L is used for the superheated steam, the formation of scale on the nozzle surface due to minerals such as calcium and magnesium can be suppressed, thereby preventing discharge problems caused by scale. If the calcium ion concentration in the liquid used for the superheated steam is 20 mg / L or less and the magnesium ion concentration is 10 mg / L or less, the formation of scale can be suppressed even more effectively.

[0067] In the inkjet printing apparatus 1, the superheated steam generation system 100 includes a water softener 102. However, if a sufficient amount of liquid is contained in the water storage container 104, the water softener 102 is not required. Furthermore, even if the water softener 102 is included, it is preferable that it be located outside the housing that contains the other components of the inkjet printing apparatus 1.

[0068] Furthermore, this inkjet printing apparatus 1 is equipped with a recovery mechanism 110 that recovers at least a portion of the superheated steam contained in the steam chamber 54 from a pipeline b1 connected to an exhaust duct 57 or a recovery duct 59 (described later), and reuses or exhausts it. The recovery mechanism 110 consists of pipelines b1 to b4 and a pump (not shown). The recovery mechanism 110 recovers at least a portion of the superheated steam contained in the steam chamber 54 and returns it to at least one of the steam chamber 54 and the water storage 104. In this example, a portion of the recovered superheated steam is returned to pipeline a5 via pipelines b1 and b2 and then to the steam chamber 54. A portion of the recovered superheated steam is returned to the water storage 104 via pipelines b1 and b2 and further via pipeline b4. A portion of the recovered superheated steam is drained to the outside via pipeline b3, which is a drainage channel, via pipelines b1 and b2.

[0069] By providing a superheated steam recovery mechanism 110, the steam can be reused, and excessive humidification inside the inkjet printing apparatus 1 can be suppressed.

[0070] Furthermore, the inkjet printing apparatus 1 includes a head humidification mechanism 120 and an upstream region humidification mechanism 130 that utilize at least a part of the superheated steam generation system 100.

[0071] The head humidification mechanism 120 introduces misted liquid from the water reservoir 104, or vapor generated from the liquid, into the housing 41 that houses the inkjet head 42, thereby humidifying at least the ink ejection port of the inkjet head 42. Here, the ejection port refers to the tip of the nozzle 43 that holds the ink just before ejection. The head humidification mechanism 120 includes pipelines c1 and c2, a pump (not shown), and a mist generating unit, etc. Mist m is introduced into the housing 41 of the image forming unit 40 from pipeline c1 connected to the water reservoir 104 through pipeline c2, humidifying the inside of the housing 41 and thereby humidifying the ejection port of the inkjet head 42. Alternatively, a heater may be provided instead of the mist generating unit to introduce water vapor into the housing 41 for humidification.

[0072] As shown in Figure 4, for example, the outlet of the conduit C2 may be placed upstream of the transport path 12 inside the housing 41 to introduce the mist m into the housing 41. The outer diameter of the tip of the conduit C2 placed inside the housing 41 is, for example, 100 mm.

[0073] Alternatively, as shown in Figure 5A, a tube 122 that sprays mist between the inkjet heads 42 may be placed to humidify the area near the ejection port of the inkjet heads 42. In this case, the tube 122 is connected to, for example, a pipeline c2. Figure 5B is an illustrative diagram of the tube 122. The tube 122 is positioned to extend in the depth direction of the paper in Figure 5A and sprays mist from multiple locations along its length. The tube 122 is connected to a pipeline c2, and liquid from the water reservoir 104 is supplied to the tube 122 via pipelines c1 and c2. The tube 122 has, for example, an outer diameter of 8 mm and an inner diameter of 5 mm, and holes with a diameter of 0.2 mm to 0.3 mm are formed at 8 mm pitch intervals.

[0074] Generating superheated steam requires a high-power heat source as the heating unit 105, and because the steam itself is very hot, the temperature of the entire device rises. When the temperature rises inside the device and the inkjet head 42 becomes hot, the ink inside the nozzle 43 dries out easily. Ink drying can cause clogging and lead to image defects such as streaks. By humidifying the ejection port of the inkjet head 42, ink drying can be suppressed and clogging can be prevented. Furthermore, if the inkjet head 42 is capable of meniscus oscillation, the effect of suppressing ink drying can be further enhanced, and the effect of suppressing clogging can also be improved. In addition, if the inkjet head 42 is a circulating head, ink drying can be suppressed even more effectively because the ink is circulating.

[0075] The upstream region humidification mechanism 130 humidifies the region upstream of the image forming unit 40 on the transport path 12 (i.e., upstream of the inkjet head 42) with mist from the liquid in the water reservoir 104, or with steam generated from the liquid. The upstream region humidification mechanism 130 includes pipes c1 and c3, a pump (not shown), and a mist generating unit. In this example, as shown in Figure 1, the upstream region humidification mechanism 130 introduces mist into the paper feed device 20 via pipe c3 from pipe c1 connected to the water reservoir 104, thereby humidifying the inside of the paper feed device 20. Note that the upstream region humidification mechanism 130 is not limited to a configuration that introduces mist into the paper feed device 20; it is sufficient to humidify the region on the transport path 12 upstream of the image forming unit 40. Therefore, for example, it may humidify the transport path from the paper feed device 20 to the preprocessing unit 30. Humidifying the region upstream of the image forming unit 40 can improve the transportability of the recording medium P. In particular, if the recording medium P is made of a material such as paper that generates static electricity when dry, humidifying it can suppress static electricity, thereby improving transportability. Furthermore, it can suppress deformation of the recording medium P due to drying.

[0076] In this inkjet printing apparatus 1, the drying unit 50 is equipped with either a steam chamber 54 or a hot air chamber 52. The hot air chamber 52 is not required. However, by providing the hot air chamber 52, the recording medium P can be dried with hot air to remove moisture from the ink, and then superheated steam drying can be performed to raise the film surface temperature in a short time, thereby shortening the drying process. In addition, ink fixing and paper humidification can be performed during the superheated steam drying after hot air drying.

[0077] Furthermore, in this embodiment, the drying unit 50 is equipped with one hot air chamber 52 and one steam chamber 54, but it is also possible to have multiple hot air chambers 52 and multiple steam chambers 54, arranged alternately. If multiple hot air chambers 52 and multiple steam chambers 54 are equipped and arranged alternately, rapid heating can be suppressed by performing hot air and superheated steam drying alternately at low intensity.

[0078] Furthermore, in this embodiment, a cooling unit 60 is provided downstream of the drying unit 50, and the process is carried out in the order of hot air drying → superheated steam drying → cooling, but cooling and drying may be mixed. For example, it may be configured to be carried out in the order of hot air drying → superheated steam drying → ambient temperature air cooling → superheated steam drying. By inserting a cooling process once during the drying process, the film surface temperature temporarily drops below 100°C, and when superheated steam heating is performed next, the steam condenses again, making humidification possible.

[0079] In the drying process using superheated steam, it is preferable to heat the film surface temperature of the recording medium P to 60°C or higher and 200°C or lower. Furthermore, it is preferable that the surface temperature of the recording medium P after exposure to superheated steam is higher and the moisture content is the same or higher than before exposure to superheated steam. That is, when comparing the film surface temperature and moisture content of the recording medium P immediately before being transported to the steam chamber 54 (i.e., immediately before superheated steam drying) with the film surface temperature and moisture content immediately after being discharged from the steam chamber 54 (i.e., immediately after superheated drying), it is preferable that the film surface temperature after superheated steam drying is higher and the moisture content is the same or higher than before superheated steam drying. If it is overheated, moisture adhering to the film surface may volatilize, so the superheated steam drying time is preferably in the range of 0.1 seconds to 5 seconds, and more preferably 1 second or less. The superheated steam drying time refers to the time the recording medium P is exposed to superheated steam.

[0080] By heating the film surface temperature of the recording medium P to between 60°C and 200°C using superheated steam, the drying and fixing of the ink can be efficiently promoted. Furthermore, by making the film surface temperature of the recording medium P after superheated steam drying higher than the film surface temperature before superheated steam drying, the drying and fixing of the ink can be further promoted. In addition, by making the moisture content of the recording medium P after superheated steam drying equal to or greater than that before superheated steam drying, deformation of the recording medium P can be suppressed.

[0081] In the steam chamber 54, it is preferable to keep the walls of the steam chamber 54 at a high temperature to prevent condensation of superheated steam S and to improve thermal efficiency. The temperature of the walls is preferably 100°C or higher. As shown in Figure 3, the temperature of the walls can also be kept high by arranging the recovery duct 59 along the outer wall surface of the steam chamber 54B. In addition, heaters may be provided on the walls of the steam chamber 54 to maintain a high temperature of 100°C or higher.

[0082] The superheated steam S recovered by the exhaust duct 57 or the recovery duct 59 is returned to the water storage 104 or the steam chamber 54, or treated as wastewater. The steam recovered by the exhaust duct 57 or the recovery duct 59 contains not only superheated steam S, but also moisture in the ink or recording medium P. Therefore, when returning the steam to the water storage 104 or the steam chamber 54, it is preferable to provide a mechanism to remove the ink.

[0083] As described above, it is preferable to keep the wall temperature high in the steam chamber 54 to prevent condensation, but a recovery mechanism may be provided to return some of the liquid generated by condensation back to the water storage 104 for reuse. For example, condensed water can be recovered from a hose connected to the steam chamber 54, exhaust duct 57, or recovery duct 59. A pan for temporarily storing condensed water may be provided separately from the water storage 104. In that case, the condensed water should be configured to be recovered periodically through a pump or the like. Note that when the inkjet printing device 1 is shut down, the condensed water may be drained by a pump instead of the water storage 104. The wastewater capacity of the drainage pump is preferably in the range of 1 L / h to 100 L / h.

[0084] In this embodiment, as shown in Figure 6, the drying unit 50 has a configuration in which a steam chamber 54 and a hot air chamber 52 are arranged adjacent to each other within the housing 51. In such a case, when starting up the inkjet printing apparatus 1, it is preferable to raise the wall temperature of the steam chamber 54 by warming the hot air chamber 52 by outputting hot air from the hot air chamber 52 and warming the inside of the housing 51 by blowing hot air ha from the outlet 53 before starting to supply superheated steam to the steam chamber 54. This suppresses condensation that is likely to occur when superheated steam is introduced into the steam chamber 54 during startup. Note that the steam chamber 54 and the hot air chamber 52 may be arranged with their walls in contact, or, as shown in Figure 6, the chambers may be arranged with a gap between them.

[0085] Alternatively, the outlet 53 of the hot air chamber 52 may be provided on the side facing the steam chamber 54, so that the hot air is blown directly into the steam chamber 54 to raise the wall temperature of the steam chamber 54.

[0086] Furthermore, it is preferable that the steam chamber 54 be made of a material with high thermal conductivity, such as metal. In cases where a hot air chamber 52 is provided in addition to the steam chamber 54, as in this example, it is preferable that the hot air chamber 52 and the steam chamber 54 have the same shape. Making multiple chambers the same shape improves suitability for mass production.

[0087] In this example, the drying unit 50 is equipped with only one steam chamber 54, but it may be equipped with two or more steam chambers 54. Figure 7 schematically shows the piping of superheated steam from the superheated steam generator 108 when it is equipped with three steam chambers 54-1, 54-2, and 54-3.

[0088] When multiple steam chambers 54 are provided, it is preferable to configure the system so that the number of steam chambers to which superheated steam is supplied can be selected. Specifically, as shown in Figure 7, three pipelines a51, a52, and a53 are provided, branching off from pipeline a5 connected to the superheated steam generator 108. The three pipelines a51, a52, and a53 are connected to steam chambers 54-1, 54-2, and 54-3, respectively. In addition, pipelines a51, a52, and a53 are provided with valves V1, V2, and V3, respectively. With this configuration, the number of steam chambers to which superheated steam is supplied can be adjusted by selectively opening and closing valves V1, V2, and V3, and the amount of superheated steam applied to the recording medium P for drying can be adjusted. By adjusting the number of steam chambers to which superheated steam is supplied according to the type of recording medium P, the drying process can be carried out efficiently.

[0089] In this embodiment, paper was used as an example of the recording medium P, but the recording medium P is not limited to paper; it may also be an impermeable substrate, flexible packaging, or corrugated cardboard. In this specification, the term "type of recording medium P" refers to both a broad type of material such as paper, an impermeable substrate, flexible packaging, or corrugated cardboard, and a more specific type within that broad category, such as fine paper or coated paper.

[0090] Furthermore, although the inkjet printing apparatus 1 of this embodiment is equipped with a pre-processing unit 30, pre-processing may not be necessary depending on the type of ink or the type of recording medium P, and the apparatus may be configured without the pre-processing unit 30.

[0091] The inkjet printing apparatus 1 of this embodiment is a sheet-fed and double-sided printing apparatus, but the inkjet printing apparatus of this disclosure may be a single-sided printing apparatus that does not have a return transport path 16. Furthermore, the inkjet printing apparatus of this disclosure is not limited to a sheet-fed type, but may be a continuous paper printing apparatus using a roll-to-roll method.

[0092] The following further notes are disclosed regarding the above embodiments. <Note 1> An inkjet printing apparatus comprising: an inkjet head equipped with nozzles for ejecting ink onto the recording surface of a recording medium; a drying unit for drying the ink on the recording medium to which the ink has been applied; a superheated steam generation system including a reservoir for storing a liquid with a hardness of 30 mg / L or less, and a heating unit for heating the liquid to generate superheated steam, wherein the drying unit comprises a steam chamber for containing the superheated steam generated in the superheated steam generation system, and the ink is dried by applying the superheated steam contained in the steam chamber to the recording medium. <Note 2> The inkjet printing apparatus according to Note 1, wherein the liquid has a calcium ion concentration of 20 mg / L or less and a magnesium ion concentration of 10 mg / L or less. <Note 3> The inkjet printing apparatus according to Note 1 or Note 2, wherein the inkjet head is equipped with a control unit for controlling the ejection of ink, and the control unit controls the meniscus oscillation of the ink in the nozzle when not ejecting ink. <Note 4> The inkjet printing apparatus according to any one of Notes 1 to 3, wherein the inkjet head is a circulating head that circulates ink. <Note 5> The inkjet printing apparatus according to any one of Notes 1 to 3, further comprising a head humidification mechanism that introduces misted liquid from a water reservoir, or vapor generated from the liquid, into the housing in which the inkjet head is housed, to humidify at least the ink discharge port of the inkjet head. <Note 6> The inkjet printing apparatus according to any one of Notes 1 to 5, wherein the inkjet head and the drying unit are provided on a transport path that transports a recording medium, and the upstream region of the transport path upstream of the inkjet head is humidified with misted liquid from a water reservoir, or vapor generated from the liquid. <Note 7> The inkjet printing apparatus according to any one of Notes 1 to 6, further comprising a steam recovery mechanism that recovers superheated steam housed in a steam chamber and returns it to at least one of the steam chamber and the water reservoir. <Note 8> The inkjet printing apparatus described in Note 7, which has a recovery duct that flows the superheated steam along the outer wall surface of the steam chamber when recovering the superheated steam contained in the steam chamber.<Note 9> An inkjet printing apparatus according to any one of Notes 1 to 8, comprising a water softening treatment device that produces a liquid with a hardness of 30 mg / L or less, wherein the water softening treatment device comprises a sensor for detecting the hardness of the liquid and an input mechanism for introducing solid material for water softening into the water softening treatment device when the hardness of the liquid detected by the sensor exceeds 30 mg / L. <Note 10> An inkjet printing apparatus according to any one of Notes 1 to 9, wherein the film surface temperature of the recording medium to which superheated steam is applied is 60°C or more and 200°C or less. <Note 11> An inkjet printing apparatus according to any one of Notes 1 to 10, wherein the recording medium to which superheated steam is applied has a higher surface temperature and the same or greater moisture content compared to before the superheated steam was applied. <Note 12> An inkjet printing apparatus according to any one of Notes 1 to 11, wherein the drying unit comprises a hot air chamber for hot air drying of the recording medium upstream of the steam chamber. <Note 13> The inkjet printing apparatus according to Note 12, wherein the hot air chamber is located adjacent to the steam chamber, and the walls of the steam chamber are heated by outputting hot air from the hot air chamber. <Note 14> The inkjet printing apparatus according to any one of Notes 1 to 13, wherein the apparatus is equipped with two or more steam chambers, and the number of steam chambers to which superheated steam is supplied from the heating unit is selected according to the type of recording medium.

[0093] The disclosure of Japanese Patent Application No. 2024-167875, filed on 26 September 2024, 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. An inkjet printing apparatus comprising: an inkjet head equipped with a nozzle for ejecting ink onto the recording surface of a recording medium; a drying unit for drying the ink on the recording medium to which the ink has been applied; a superheated steam generation system including a reservoir for storing a liquid with a hardness of 30 mg / L or less, and a heating unit for heating the liquid to generate superheated steam, wherein the drying unit comprises a steam chamber for containing the superheated steam generated in the superheated steam generation system, and the ink is dried by applying the superheated steam contained in the steam chamber to the recording medium.

2. The inkjet printing apparatus according to claim 1, wherein the liquid has a calcium ion concentration of 20 mg / L or less and a magnesium ion concentration of 10 mg / L or less.

3. The inkjet printing apparatus according to claim 1, wherein the inkjet head includes a control unit for controlling the ejection of the ink, and the control unit controls the meniscus oscillation of the ink in the nozzle when the ink is not being ejected.

4. The inkjet printing apparatus according to claim 2, wherein the inkjet head includes a control unit for controlling the ejection of the ink, and the control unit controls the meniscus oscillation of the ink in the nozzle when the ink is not being ejected.

5. The inkjet printing apparatus according to any one of claims 1 to 4, wherein the inkjet head is a circulating head that circulates the ink.

6. An inkjet printing apparatus according to any one of claims 1 to 4, comprising a head humidification mechanism that introduces a misted form of the liquid in the water reservoir, or vapor generated from the liquid, into a housing that houses the inkjet head, to humidify at least the ink discharge port of the inkjet head.

7. The inkjet printing apparatus according to claim 5, further comprising a head humidification mechanism that introduces a misted form of the liquid in the water reservoir, or vapor generated from the liquid, into a housing containing the inkjet head to humidify at least the ink discharge port of the inkjet head.

8. The inkjet printing apparatus according to any one of claims 1 to 4, wherein the inkjet head and the drying unit are provided on a transport path for transporting the recording medium, and the apparatus is equipped with an upstream region humidification mechanism that humidifies the region upstream of the inkjet head on the transport path with a mist of the liquid in the water reservoir or with steam generated from the liquid.

9. The inkjet printing apparatus according to claim 5, wherein the inkjet head and the drying unit are provided on a transport path for transporting the recording medium, and the apparatus includes an upstream region humidification mechanism that humidifies the region upstream of the inkjet head on the transport path with a mist of the liquid in the water reservoir or with steam generated from the liquid.

10. The inkjet printing apparatus according to claim 6, wherein the inkjet head and the drying unit are provided on a transport path for transporting the recording medium, and the apparatus includes an upstream region humidification mechanism that humidifies the region upstream of the inkjet head on the transport path with a mist of the liquid in the water reservoir or with steam generated from the liquid.

11. An inkjet printing apparatus according to any one of claims 1 to 4, further comprising a steam recovery mechanism for recovering the superheated steam contained in the steam chamber and returning it to at least one of the steam chamber and the water reservoir.

12. The inkjet printing apparatus according to claim 5, further comprising a steam recovery mechanism for recovering the superheated steam contained in the steam chamber and returning it to at least one of the steam chamber and the water reservoir.

13. The inkjet printing apparatus according to claim 11, further comprising a recovery duct for flowing the superheated steam along the outer wall surface of the steam chamber when recovering the superheated steam contained in the steam chamber.

14. The inkjet printing apparatus according to claim 12, further comprising a recovery duct for flowing the superheated steam along the outer wall surface of the steam chamber when recovering the superheated steam contained in the steam chamber.

15. An inkjet printing apparatus according to any one of claims 1 to 4, comprising a water softening apparatus that produces the liquid with a hardness of 30 mg / L or less, wherein the water softening apparatus comprises a sensor for detecting the hardness of the liquid and an input mechanism for introducing a solid material for water softening into the water softening apparatus when the hardness of the liquid detected by the sensor exceeds 30 mg / L.

16. The inkjet printing apparatus according to any one of claims 1 to 4, wherein the film surface temperature of the recording medium to which the superheated steam is applied is 60°C or more and 200°C or less.

17. The inkjet printing apparatus according to any one of claims 1 to 4, wherein the recording medium to which the superheated steam has been applied has a higher surface temperature and a moisture content equal to or greater than that of the recording medium before the superheated steam was applied.

18. The inkjet printing apparatus according to any one of claims 1 to 4, wherein the drying unit is provided with a hot air chamber for hot air drying of the recording medium upstream of the steam chamber.

19. The inkjet printing apparatus according to claim 18, wherein the hot air chamber is arranged adjacent to the steam chamber, and the wall surface of the steam chamber is heated by outputting hot air from the hot air chamber.

20. An inkjet printing apparatus according to any one of claims 1 to 4, comprising two or more steam chambers, wherein the number of steam chambers to which the superheated steam is supplied from the heating unit is selected according to the type of recording medium.

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