Printing apparatus and printing method

Abstract

The invention provides a printing apparatus and a printing method capable of improving dryness, suppressing deformation of a base material, and suppressing poor discharge. The printing apparatus includes: a print head that forms an image by discharging a water-based ink onto a substrate; a substrate moisture reducing member that reduces moisture of the substrate prior to image formation by the print head; and an absolute humidity adjusting member that adjusts the absolute humidity around the nozzle surface of the print head.

Description

Technical Field

[0001] The present invention relates to a printing device and a printing method, and in particular to an inkjet printing technology. Background Art

[0002] Patent Document 1 describes a discharge device including: a cooling unit for cooling a recording medium; a humidifying unit for humidifying the recording medium whose temperature has been lowered by the cooling unit; and a discharge unit for discharging liquid droplets onto the recording medium humidified by the humidifying unit.

[0003] Patent document 2 describes an inkjet recording device, which is characterized in that, in an inkjet recording device that prints by ejecting ink droplets from a print head and causing them to adhere to a printed material, a pre-processing device consisting of a halogen lamp arranged opposite to the printed material directly in front of the print head and a post-processing device consisting of a halogen lamp arranged opposite to the printed material at the rear of the print head are provided, and the peak value of the radiation intensity of the halogen lamp assembled in the pre-processing device is set to a wavelength longer than the peak value of the radiation intensity of the halogen lamp assembled in the post-processing device.

[0004] Previous technical literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Laid-Open No. 2017-35870

[0007] Patent Document 2: Japanese Patent Application Laid-Open No. 2000-203007 Summary of the Invention

[0008] Technical issues to be solved by the invention

[0009] [Topic 1: Drying Topic]

[0010] The drying system of a printing press must be able to fully dry both the maximum amount of water expected to be contained in the substrate and the ejected liquid used to form the image. If the image surface of the substrate is not sufficiently dried and the image surface contacts the transport roller, the image surface is transferred to the transport roller, resulting in white spots, a defect commonly known as "white spots."

[0011] The water content of the substrate is significantly greater than the amount of ink discharged onto the substrate. To achieve robust drying performance, this amount of water must be carefully considered. Consequently, conventional techniques have employed a large drying device after the ink is discharged onto the substrate. This, however, results in increased device size and costs.

[0012] In perfecting printing presses, the drying system is typically designed to have the same drying capacity for both the front and back sides to ensure mass production compatibility. However, since the moisture content of the back side substrate decreases before printing due to drying after front side printing, if the drying system after front side printing and back side printing have equivalent performance, the capacity of the back side drying system after back side printing is often redundant.

[0013] [Topic 2: Substrate deformation]

[0014] Printing presses sometimes experience deformation of the substrate due to image formation, a common issue due to its direct impact on the quality and transportability of printed materials. When the substrate is paper, image formation can cause the surface of the paper to undulate, commonly known as "wrinkling." This phenomenon is particularly noticeable on thin paper. This occurs when the ink applied to the paper penetrates the pulp layer within the paper, partially wetting the pulp and causing shrinkage in both the image and non-image areas. In other words, to prevent wrinkling, the moisture content of the printed material must be kept to an appropriate level across all surfaces.

[0015] Conventional techniques for suppressing wrinkles include applying roll-to-roll tension during or before and after drying after image formation, or stretching the paper using suction. These mechanical measures require the addition of additional wrinkle suppression units, increasing costs. In particular, in the case of a double-sided printing press, wrinkle suppression units must be installed before and after drying both the front and back sides.

[0016] [Topic 3: Discharge problems]

[0017] As a countermeasure to issues 1 and 2, the substrate is sometimes dried before image formation (see Patent Document 2). However, this can lead to the following problem: as the dried substrate passes directly under the nozzle surface of the printhead, the humidity of the ambient air surrounding the head decreases, drying the nozzle surface. This drying of the nozzle surface thickens the ink within the nozzle, impairing the printhead's ejection performance, and sometimes causing image defects such as streaks on the printed product.

[0018] With regard to this problem of poor ejection, the inventors of the present invention have found through experiments that in a double-sided printing machine that forms an image on the front side and then forms an image on the back side, the image formed on the back side is less likely to have streaks than the image formed on the front side (see Figure 3 The reason for this is that the substrate's moisture content increases as an image is formed on the surface, resulting in a higher humidity around the print head where the image is formed on the surface than around the print head where the image is formed on the back. Therefore, measures must be taken to address the issue of poor ejection before the image is formed on the surface.

[0019] In addition, the "surface" and "back" of the substrate mentioned here refer to the order of image formation, that is, the first side on which the image is formed first is set as the "surface", and the second side on which the image is formed after the image is formed on the first side is set as the "back", and do not refer to the surface and back in the use of the printed material itself.

[0020] Regarding issues 1 to 3 above, the ejection device described in Patent Document 1 cools the recording medium before image formation and then humidifies the recording medium to suppress ejection defects. However, cooling the recording medium is only intended to suppress ejection defects and does not serve as a countermeasure for white spots or wrinkles.

[0021] Furthermore, in order to cope with the variation in moisture content and temperature of the original substrate before image formation, it is necessary to deal with it before the surface image is formed. However, in the patent document 1, Figure 6 In the double-sided printing structure described in , the cooling section of the recording medium is located between a first image forming device for forming an image on the surface and a second image forming device for forming an image on the back, and there is no countermeasure in this regard (paragraph 0103 of patent document 1).

[0022] The inkjet recording device described in Patent Document 2 dries the paper before image formation, aiming to improve drying performance of printed materials and suppress paper deformation. However, Patent Document 2 does not implement measures to dry the ink ejection surface, which addresses Problem 3, potentially leading to ejection defects. Furthermore, Patent Document 2 does not describe duplex printing.

[0023] Patent Documents 1 and 2 are not all solutions to Problems 1 to 3.

[0024] The present invention has been made in view of such circumstances, and an object of the present invention is to provide a printing apparatus and a printing method capable of improving drying performance, suppressing deformation of a substrate, and suppressing ejection defects.

[0025] Means for solving technical problems

[0026] A printing device according to a first embodiment of the present invention comprises: a print head that ejects water-based ink onto a substrate to form an image; a substrate moisture reducing member that reduces the moisture of the substrate before image formation by the print head; and an absolute humidity adjusting member that adjusts the absolute humidity around the nozzle surface of the print head.

[0027] According to the first embodiment, by reducing the moisture content of the substrate before image formation, the substrate is dried more efficiently after image formation, thereby suppressing deformation of the substrate. Furthermore, by adjusting the absolute humidity around the nozzle face of the print head, it is possible to suppress the occurrence of defective printhead discharge. The nozzle face area includes the space between the nozzle face and the substrate.

[0028] The printing device involved in the second embodiment can be configured as follows in the printing device involved in the first embodiment: the substrate moisture reducing component includes a first drying device for heating the substrate before image formation, and the absolute humidity adjusting component adjusts the absolute humidity around the nozzle surface by changing the drying capacity of the first drying device according to the properties of the substrate.

[0029] The properties of the substrate may be, for example, the basis weight, material, or size of the substrate, or a combination thereof. By adjusting the moisture content of the substrate delivered to the position facing the nozzle face of the print head, the absolute humidity around the nozzle face can be adjusted.

[0030] For example, the relationship between the properties of the substrate, the drying conditions in the first drying device, and the printing quality is experimentally investigated, and based on the experimental results, the drying capacity is changed to suit the properties of the substrate.

[0031] The printing apparatus according to the third aspect may be configured to change the drying capacity by changing at least one of the substrate conveyance speed and the temperature of the first drying device in accordance with properties of the substrate in the second aspect.

[0032] The printing apparatus according to the fourth aspect may be configured such that, in the printing apparatus according to the second or third aspect, the heat applied to the substrate is changed by changing the substrate conveyance path in the first drying device according to properties of the substrate.

[0033] A printing apparatus according to a fifth aspect may be the printing apparatus according to any one of the second to fourth aspects, wherein the properties of the substrate include a basis weight of the substrate.

[0034] A printing apparatus according to a sixth aspect may be the printing apparatus according to any one of the first to fifth aspects, further comprising a static eliminating device disposed between the substrate moisture reducing member and the print head for eliminating static electricity from the substrate.

[0035] A printing apparatus according to a seventh aspect may be the printing apparatus according to any one of the first to sixth aspects, wherein the substrate moisture reducing member heats the substrate before image formation to bring the substrate into a decelerated drying state.

[0036] A printing apparatus according to an eighth aspect may be a printing apparatus according to any one of the first to seventh aspects, wherein the absolute humidity adjustment member includes a humidification source for humidifying the periphery of the nozzle surface.

[0037] A printing apparatus according to a ninth aspect may be configured such that, in the printing apparatus according to the eighth aspect, the absolute humidity adjusting member changes the amount of humidification according to properties of the substrate.

[0038] The printing device involved in the tenth embodiment may be configured as follows in the printing device involved in the eighth or ninth embodiment: the absolute humidity adjustment component includes a processor that monitors the absolute humidity around the nozzle surface and adjusts the humidification amount of the humidification source if the absolute humidity is below a threshold.

[0039] The printing apparatus according to the eleventh aspect may be configured such that, in the printing apparatus according to the tenth aspect, a measuring device is provided for measuring the absolute humidity around the nozzle surface, and the processor adjusts the humidification amount based on information obtained from the measuring device.

[0040] The measuring device can be a thermometer or hygrometer for measuring temperature and relative humidity, or a hygrometer for measuring absolute humidity.

[0041] The printing apparatus according to the twelfth aspect may be configured such that, in the printing apparatus according to the eleventh aspect, the processor calculates the absolute humidity based on the measured values ​​of the temperature and relative humidity obtained from the measuring device.

[0042] The printing device involved in the 13th embodiment may be a printing device involved in any one of the 8th to 12th embodiments, and may have the following structure: the humidification source includes a hose connected to the humidifier, and a plurality of holes are formed on the hose at specific intervals, and humidified air is supplied to the periphery of the nozzle surface through the hose.

[0043] A printing apparatus according to a fourteenth aspect is the printing apparatus according to any one of the eighth to twelfth aspects, wherein the humidification source may be an ultrasonic humidifier.

[0044] A printing apparatus according to a fifteenth aspect may be configured such that, in the printing apparatus according to any one of the eighth to twelfth aspects, the humidification source includes a conduit connected to the humidifier, and the humidified air is supplied to the vicinity of the nozzle surface through the conduit.

[0045] The printing device involved in the 16th mode can be a printing device involved in any one of the 1st to 15th modes, and can have the following structure: the absolute humidity adjustment component includes: an exhaust component that discharges dry air from the inside of the printing device; and an air intake component that draws moist external air into the machine, and the absolute humidity around the nozzle surface is adjusted by adjusting the exhaust volume based on the exhaust component.

[0046] A printing apparatus according to a seventeenth aspect may be configured such that, in the printing apparatus according to the sixteenth aspect, the absolute humidity adjustment means includes a processor that adjusts the exhaust volume according to properties of the substrate.

[0047] The printing apparatus according to the eighteenth aspect may be configured such that, in the printing apparatus according to any one of the first to seventeenth aspects, a second drying device is provided for drying the substrate to which the aqueous ink has been applied by the print head.

[0048] The printing apparatus according to the nineteenth aspect may be configured such that, in the printing apparatus according to any one of the first to eighteenth aspects, the second printing head is provided, which forms an image on a second side of the substrate, the opposite side of the first side, after the first printing head forms an image on the first side of the substrate, and the substrate moisture reducing member is provided only before the image is formed on the first side, between before the image is formed on the first side and before the image is formed on the second side. In the case of a double-sided printing apparatus, the substrate moisture reducing member may not be provided before the image is formed on the second side.

[0049] The printing apparatus according to the 20th aspect may be configured such that, in the printing apparatus according to the 19th aspect, only the first print head is provided with an absolute humidity adjustment member. In the case of a double-sided printing apparatus, the absolute humidity around the nozzle surface of the second print head need not be adjusted.

[0050] The printing method involved in the 21st embodiment of the present invention is a printing method for forming an image by ejecting water-based ink from a print head onto a substrate, and the printing method includes: a process of reducing the moisture of the substrate before the image is formed based on the print head; and a process of adjusting the absolute humidity around the nozzle surface of the print head.

[0051] The printing method according to the 21st aspect can be configured to include the same specific aspects as the printing apparatus according to any one of the 2nd to 20th aspects. The printing method of the present invention can be understood as a method for producing a printed material (a printed material manufacturing method).

[0052] Effects of the Invention

[0053] According to the present invention, in a printing device that ejects water-based ink from a print head onto a substrate to form an image, it is possible to improve drying performance, suppress deformation of the substrate, and suppress ejection defects. According to the present invention, it is possible to produce high-quality printed materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Figure 1 It is a diagram showing the overall configuration of a printing device according to an embodiment.

[0055] Figure 2 This is a structural diagram schematically showing the structures of the preliminary drying unit and the surface printing main drying unit.

[0056] Figure 3This is a graph showing data from an experiment investigating the relationship between the basis weight of the substrate, the drying conditions in the pre-drying unit, the number of streaks, white spots, and wrinkles generated in printed materials.

[0057] Figure 4 This is a graph showing the relationship between the absolute humidity around the nozzle surface of the print head and the number of streaks.

[0058] Figure 5 This is a graph showing the experimental results of investigating the number of streaks, white spots, and wrinkles when the combination of the basis weight of the substrate and the pre-drying conditions was changed.

[0059] Figure 6 This is a graph showing an example of setting the pre-drying conditions relative to the basis weight of the substrate.

[0060] Figure 7 This is a graph showing the experimental results of investigating the number of streaks, white spots, and wrinkles when the combination of the basis weight of the substrate S and the pre-drying path was changed.

[0061] Figure 8 This is a graph showing an example of setting a pre-drying path relative to the basis weight of a substrate.

[0062] Figure 9 This is an explanatory diagram showing a first embodiment of a humidification source.

[0063] Figure 10 yes Figure 9 Illustration of the hose used as a humidification source.

[0064] Figure 11 This is an explanatory diagram showing another installation example of the humidification source.

[0065] Figure 12 This is an explanatory diagram showing a second embodiment of a humidification source.

[0066] Figure 13 It is an explanatory diagram showing an example of a humidifier.

[0067] Figure 14 This is an explanatory diagram showing a third embodiment of a humidification source.

[0068] Figure 15 This is a structural diagram schematically showing an example of an air intake structure and an exhaust structure applicable to the printing apparatus according to the embodiment.

[0069] Figure 16 This is a functional block diagram showing a first example of the electrical configuration of a printing device according to the embodiment.

[0070] Figure 17 This is a functional block diagram showing a second example of the electrical configuration of the printing device according to the embodiment.

[0071] Figure 18 This is a functional block diagram showing a third example of the electrical configuration of the printing device according to the embodiment.

[0072] Figure 19 This is a block diagram showing an example of the hardware configuration of an information processing device that functions as a control device for a printing device according to an embodiment. DETAILED DESCRIPTION

[0073] Hereinafter, the traveling direction of the substrate S is referred to as the transport direction, and the direction perpendicular to the transport direction and parallel to the recording surface of the substrate S is referred to as the width direction.

[0074] Example of a Printing Device Structure

[0075] [Overall structure]

[0076] Figure 1 This is an overall structural diagram of a printing device 10 according to an embodiment. The printing device 10 is a duplex printing system that conveys a long recording medium, a substrate S, in a roll-to-roll process and forms an image by applying aqueous ink to the substrate S using single-pass inkjet printing. The substrate S is, for example, paper. The paper can be any general printing paper primarily composed of cellulose, such as premium paper, coated paper, or coated paper used for general offset printing, or dedicated inkjet paper.

[0077] The printing apparatus 10 includes a paper feeding unit 12 , a preliminary drying unit 14 , a front printing main drying unit 16 , a reversing unit 18 , a back printing main drying unit 20 , and a paper discharge unit 22 .

[0078] The paper feeding unit 12 includes a delivery roller (not shown) that rolls the substrate S before image formation. The paper feeding unit 12 rotates the delivery roller by a motor (not shown) to feed the substrate S before image formation. The substrate S fed from the delivery roller is conveyed to the pre-drying unit 14 .

[0079] The pre-drying unit 14 is a drying section that performs a process to reduce the moisture content of the substrate S before image formation (substrate moisture reduction process). The pre-drying unit 14 includes a mechanism for conveying the substrate S and a heating device for heating the substrate S. The pre-drying unit 14 heats the substrate S by the heating device while conveying the substrate S, thereby pre-drying the substrate S before image formation. As a heating method for the pre-drying process of the substrate S, at least any one of heat conduction, convection, radiation, and dielectric heating can be applied. The pre-drying unit 14 adjusts the moisture content of the substrate S entering the surface printing main drying unit 16. The substrate S discharged from the pre-drying unit 14 is conveyed to the surface printing main drying unit 16.

[0080] The surface printing main drying unit 16 includes a conveying mechanism for conveying the substrate S; a print head for discharging aqueous ink onto the substrate S; and a drying device for drying the aqueous ink applied to the substrate S. The print head applies aqueous ink to the recording surface of the substrate S to form an image. The drying device of the surface printing main drying unit 16 dries the aqueous ink applied to the substrate S while conveying the substrate S with the image formed on it. The process of drying the aqueous ink applied to the substrate S from the print head is called "main drying." Main drying can also be referred to as "main drying."

[0081] The detailed structure of the pre-drying unit 14 and the surface printing main drying unit 16 will be described later. Figure 2 The substrate S discharged from the surface printing main drying unit 16 is conveyed to the reversing unit 18 .

[0082] The reversing unit 18 includes a reversing lever (not shown). The reversing lever is a reversing mechanism that reverses the front and back sides of the substrate S. The substrate S with its front and back sides reversed by the reversing unit 18 is conveyed to the backside printing and drying unit 20 .

[0083] The backside printing main drying unit 20 is constructed similarly to the frontside printing main drying unit 16. While conveying the substrate S, the backside printing main drying unit 20 applies water-based ink to the backside of the substrate S using a print head to form an image. Furthermore, the backside printing main drying unit 20 conveys the substrate S, on which the image has been formed by the print head, while performing main drying in a drying device. The substrate S discharged from the backside printing main drying unit 20 is conveyed to the paper discharge unit 22.

[0084] The paper discharge unit 22 includes a take-up roller (not shown) connected to a motor (not shown). The paper discharge unit 22 rotates the take-up roller by the motor to take up the substrate S with the image formed thereon.

[0085] The printing device 10 according to this embodiment pre-dries the substrate S before image formation, thereby substantially reducing the moisture present in the substrate S introduced into the printing device 10. When the substrate S is sufficiently dehydrated, the drying process shifts from a constant-rate drying process to a decelerated drying process, slowing the change in moisture content. Therefore, by applying sufficient heat to the substrate S, the moisture content of the substrate S can be maintained constant with a certain degree of accuracy. The adjustment device for adjusting the moisture content and temperature of the substrate S may be constructed using a heating device for the substrate S, or may be a combination of a heating device and a cooling device. The pre-drying unit 14 functions as an adjustment device for adjusting the moisture content and temperature of the substrate S.

[0086] The heating device can be a warm air heating member, a contact heating member, a radiant heating member, a dielectric heating member, or a suitable combination thereof. Examples of the contact heating member include a heated roller (heating roller) or a hot plate. Examples of the radiant heating member include an infrared (IR) heater.

[0087] [Configuration Example of Pre-drying Unit 14 and Surface Printing Main Drying Unit 16]

[0088] Figure 2 This is a structural diagram schematically showing a structural example of the pre-drying unit 14 and the surface printing main drying unit 16. The heating device 30 suitable for the pre-drying unit 14 is composed of a combination of a warm air unit 32 and a hot roller 34. The warm air unit 32 and the hot roller 34 can each change the temperature setting. In addition, the path (conveying path) of the substrate S in the pre-drying unit 14 can also be changed, and the number of warm air units 32 and hot rollers 34 set can be changed according to the path. In this way, the heating intensity in the pre-drying unit 14, that is, the drying intensity, can be changed. The drying intensity in pre-drying can also be referred to as the drying capacity of the pre-drying unit 14.

[0089] exist Figure 2 , an example of a heating device 30 including 12 heat rollers 34 and 5 warm air units 32 is shown. Figure 2 In the figure, the heat roller 34 is illustrated by being filled in grey, and the transfer roller 36 is represented by being hollow (not filled).

[0090] The pre-drying unit 14 determines the number of turns of the path using the plurality of heat rollers 34 and the number of installed warm air units 32 according to the properties of the substrate S.

[0091] The preliminary drying unit 14 includes a cooling roller 38 as a cooling device for adjusting the temperature of the substrate S after preliminary drying by the heating device 30. In place of the cooling roller 38, a conveying roller without a cooling mechanism may be used.

[0092] The pre-drying unit 14 is an example of the “substrate moisture reducing member” and the “first drying device” in the present invention.

[0093] The surface printing and drying unit 16 includes a plurality of conveying rollers 40 , printing heads 42K, 42C, 42M, and 42Y, a radiation heating section 44 , and a drying cylinder 46 .

[0094] A plurality of conveyor rollers 40 are arranged along the conveyance path of the substrate S in the surface print main drying unit 16. The substrate S fed into the surface print main drying unit 16 is supported and conveyed by the conveyor rollers 40. One or more of the plurality of conveyor rollers 40 can function as tension rollers for applying tension to the substrate S. A tension detector for detecting the tension of the substrate S can be arranged along the conveyance path of the substrate S.

[0095] The print heads 42K, 42C, 42M, and 42Y are inkjet heads that eject water-based inks in black (K), cyan (C), magenta (M), and yellow (Y), respectively. The print heads 42K, 42C, 42M, and 42Y are positioned opposite the recording surface of the transported substrate S. In the case of front-side printing with the main drying unit 16, the recording surface of the substrate S refers to the front surface of the substrate S. In the case of back-side printing with the main drying unit 20, the recording surface of the substrate S refers to the back surface of the substrate S.

[0096] An image is formed by applying aqueous ink to the recording surface of substrate S using print heads 42K, 42C, 42M, and 42Y. The print heads 42K, 42C, 42M, and 42Y are line heads capable of forming an image on the conveyed substrate S with a single scan. Each of the line heads 42K, 42C, 42M, and 42Y has a nozzle surface with a plurality of nozzles serving as outlets for discharging aqueous ink arranged two-dimensionally across a length corresponding to the full width of the substrate S in a direction perpendicular to the conveyance direction of the substrate S. The nozzle surface is arranged so as to face the recording surface of the substrate S. The print heads 42K, 42C, 42Y, and 42Y are arranged at regular intervals along the conveyance path of the substrate S.

[0097] Here, the structure using four colors of ink, namely cyan, magenta, yellow and black, is illustrated. However, the combination of ink colors and the number of colors is not limited to this embodiment. Light ink, dark ink, white ink, transparent ink, and other special color inks can be added as needed. Print heads corresponding to the ink colors can be provided. In addition, the arrangement order of the print heads of each ink color is not limited to Figure 2 Example shown.

[0098] The print heads 42K, 42C, 42M, and 42Y can each be configured by connecting a plurality of head modules in the width direction of the substrate S. The print heads 42K, 42C, 42M, and 42Y are each supplied with aqueous ink from an ink tank (not shown) via a piping path (not shown).

[0099] Water-based inks are inks made by dissolving or dispersing colorants such as dyes and pigments in water or a water-soluble solvent. Here, water-based pigment inks are used as water-based inks. Water-based inks may also contain wax.

[0100] The print heads 42K, 42C, 42M, and 42Y are housed and unitized in a head case 43. The head case 43 including the print heads 42K, 42C, 42M, and 42Y corresponds to a printing unit that performs image formation on a substrate S.

[0101] The substrate S on which the images are formed by the print heads 42K, 42C, 42Y, and 42Y is guided by the plurality of conveying rollers 40 and conveyed from a position facing the head box 43 to a position facing the radiation heating unit 44 .

[0102] The radiation heating unit 44 includes an infrared heater that emits infrared rays toward the surface of the substrate S to heat the substrate S. The radiation heating unit 44 may include a fan heater that supplies warm air to the surface of the substrate S.

[0103] The substrate S is guided by the conveying rollers 40 and conveyed from a position facing the radiation heating unit 44 to the drying drum 46 .

[0104] The drying cylinder 46 is made of cylindrical SUS (Steel Use Stainless Steel). The substrate S is wound around the outer peripheral surface of the drying cylinder 46 .

[0105] The outer peripheral surface of the drying cylinder 46 is heated by a heater (not shown) provided inside. The drying cylinder 46 heats the substrate S by bringing the substrate S into contact with the outer peripheral surface. In addition, a plurality of warm air heaters (not shown) may be arranged around the drying cylinder 46, or a structure may be provided in which warm air is blown from these warm air heaters toward the substrate S wound on the drying cylinder 46. The drying cylinder 46 is driven to rotate around a rotating shaft by a motor (not shown). The drying cylinder 46 rotates around a rotating shaft by holding the surface on the side opposite to the recording surface of the substrate S, i.e., the opposite surface, on the outer peripheral surface, thereby heating the substrate S from the opposite surface while conveying it. In the case of the surface printing formal drying unit 16, the opposite surface of the substrate S is the back surface of the substrate S, and in the case of the back printing formal drying unit 20, the opposite surface of the substrate S is the surface of the substrate S. The radiation heating portion 44 and the drying cylinder 46 are an example of the "second drying device" in the present invention.

[0106] The substrate S heated by the drying cylinder 46 is guided by the conveying roller 40 and discharged from the drying cylinder 46 to the outside of the surface printing formal drying unit 16. In addition, among the rollers arranged at the downstream side of the drying cylinder 46 on the conveying path of the substrate S, when the image forming area (ink imparting area) of the recording surface of the substrate S subjected to the drying process by the drying cylinder 46 is away from the drying cylinder 46, the first contact roller 48 that first contacts is preferably a cooling roller. The cooling roller has a cooling structure for cooling the substrate S subjected to the drying process. The cooling structure of the cooling roller is suitable for a water cooling method in which water adjusted to a specified temperature range is circulated as a refrigerant.

[0107] [Overview of Operation of Printing Device 10]

[0108] The substrate S supplied from the paper supply unit 12 is conveyed to the pre-drying unit 14 and pre-dried. The pre-drying unit 14 heats the substrate S to a state of decelerated drying. The pre-dried substrate S is conveyed to the surface printing main drying unit 16.

[0109] In the surface printing and drying unit 16, the substrate S is guided by the conveyor roller 40 and transported to a position opposite the print heads 42K, 42C, 42Y, and 42Y. The print heads 42K, 42C, 42Y, and 42Y eject droplets of aqueous ink onto the surface of the substrate S. The ejected droplets adhere to the surface of the substrate S, forming an image on the surface of the substrate S. The surface of the substrate S is an example of the "first surface" in the present invention. The print heads 42K, 42C, 42Y, and 42Y in the surface printing and drying unit 16 are an example of the "first print head" in the present invention.

[0110] Next, the substrate S is conveyed to a position facing the radiation heating unit 44. The radiation heating unit 44 heats the substrate S using an infrared heater, thereby accelerating the drying of the aqueous ink applied to the surface of the substrate S.

[0111] The substrate S is then guided by the conveying rollers 40 and conveyed from a position opposite the radiant heating unit 44 to the drying drum 46. The substrate S is wound around the outer peripheral surface of the drying drum 46. The drying drum 46 rotates with its outer peripheral surface in contact with the back surface of the substrate S, thereby conveying the substrate S while heating it from the back. This promotes the drying of the aqueous ink applied to the surface of the substrate S.

[0112] The substrate S after the aqueous ink applied to the surface is dried is discharged to the outside of the surface printing main drying unit 16 .

[0113] The substrate S discharged from the front printing main drying unit 16 is conveyed to the reversing unit 18 and reversed on the front and back sides by a turning rod. The substrate S with its front and back sides reversed is conveyed to the back printing main drying unit 20.

[0114] In the backside printing main drying unit 20, the substrate S is guided by the conveyor roller 40 and transported to a position opposite the print heads 42K, 42C, 42Y, and 42Y. The print heads 42K, 42C, 42Y, and 42Y eject droplets of aqueous ink toward the backside of the substrate S. The ejected droplets adhere to the backside of the substrate S, forming an image on the backside of the substrate S. The backside of the substrate S is an example of the "second side" in the present invention. The print heads 42K, 42C, 42Y, and 42Y in the backside printing main drying unit 20 are an example of the "second print head" in the present invention.

[0115] Next, the substrate S is conveyed to a position facing the radiation heating unit 44. The radiation heating unit 44 heats the substrate S with an infrared heater, thereby accelerating the drying of the aqueous ink applied to the back surface of the substrate S.

[0116] The substrate S is then guided by the conveying roller 40 and conveyed from a position opposite the radiant heating unit 44 to the drying drum 46. The substrate S is wound around the outer peripheral surface of the drying drum 46. The drying drum 46 rotates with its outer peripheral surface in contact with the surface of the substrate S, thereby conveying the substrate S while heating the substrate S from the surface. This promotes the drying of the aqueous ink applied to the back surface of the substrate S.

[0117] The substrate S after the aqueous ink applied to the back surface is dried is discharged outside the back surface printing main drying unit 20. The substrate S discharged from the back surface printing main drying unit 20 is conveyed to the paper discharge unit 22 and wound onto a winding roller.

[0118] As described above, the printing apparatus 10 conveys a substrate S in the order of the paper feed unit 12, the pre-drying unit 14, the front-printing main drying unit 16, the reversing unit 18, the back-printing main drying unit 20, and the paper discharge unit 22, and performs the respective processes on the substrate S, thereby producing a printed article. The printing method executed by the printing apparatus 10 is understood to be a method for producing a printed article.

[0119] Necessity of adjusting absolute humidity around the nozzle surface

[0120] In the printing device 10 involved in this embodiment, before the image is formed by the printing heads 42K, 42C, 42M, and 42Y, pre-drying of the substrate S and adjustment of the absolute humidity around the nozzle surface are introduced, thereby achieving all the purposes of improving drying performance, suppressing substrate deformation, and suppressing ejection defects.

[0121] From the perspective of improving drying performance and suppressing substrate deformation, reducing the moisture content of substrate S (pre-drying) before image formation is effective. By reducing the moisture content within substrate S, the thermal conductivity of substrate S is improved, thereby enhancing drying performance. Furthermore, by reducing the moisture content of the pulp layer of substrate S, localized wetness can be avoided even after image formation. During reverse printing, since the moisture content of substrate S is reduced by drying after front printing, pre-drying only needs to be performed before front printing. Compared to an apparatus configuration in which the same drying device is provided before front and back printing, this reduces the number of drying devices and reduces costs.

[0122] While this pre-drying before image formation is highly effective, it also poses a risk of poor ejection from the print heads 42K, 42C, 42M, and 42Y. As a countermeasure, the printing device 10 is equipped with a mechanism for adjusting the absolute humidity around the nozzles. In a duplex printing press, the area around the nozzle face of the back-side printing print head is susceptible to moisture due to the influence of the image surface of the substrate S, on which an image is formed. Therefore, the mechanism for adjusting the absolute humidity can be incorporated only into the printing unit for front-side printing.

[0123] Example of the relationship between pre-drying and absolute humidity and printing results

[0124] As described above, the printing apparatus 10 incorporates the pre-drying unit 14 to improve drying properties such as white spots. However, pre-drying the substrate S can also cause a drawback problem, which can occur due to thickening of the ink within the nozzles of the print heads 42K, 42C, 42M, and 42Y. Therefore, in addition to pre-drying the substrate S, it is preferable to specify conditions around the nozzle surface to implement countermeasures against poor ejection.

[0125] Figure 3 This data chart shows experimental results investigating the relationship between the basis weight of substrate S, various drying conditions in the pre-drying unit 14, the number of streaks, the occurrence of white spots, and the occurrence of wrinkles in printed materials. The experiments were conducted by varying the pre-drying conditions, including the warm air temperature, heater temperature, and the conveyance speed of substrate S. The warm air temperature refers to the temperature of the warm air unit 32. The heater temperature refers to the temperature of the heat roller 34.

[0126] In this experiment, the radiant heating temperature for the main drying (main drying) of each of the front-printing main drying unit 16 and the back-printing main drying unit 20 was 80°C, the drying drum 46 and the warm air temperature were both 140°C, and the ambient humidity was 55%. The substrates S used in the experiment were thin paper (OK Topkote, manufactured by Oji Paper Co., Ltd., "Topkote" is a registered trademark) with a basis weight of 104 gsm (grams per square meter) and thick paper (von Ivory, manufactured by Oji Paper Co., Ltd., "von Ivory" is a registered trademark) with a basis weight of 210 gsm. Evaluations were conducted on each of these different substrates S. The ink droplet volume ejected from the nozzle was 3.15 pL (picoliters), and no pretreatment liquid was applied to the substrate S before ink application.

[0127] In the printing device 10 of this embodiment, ink is ejected onto a substrate S in the order of K, C, M, and Y to form an image. The absolute humidity value is the average of three measurements taken along the width of the nozzle surface of the most upstream print head 42K (near the K head). Since ink is ejected onto the substrate S, the humidity is higher downstream of the head than upstream of the head. Therefore, it is generally sufficient to specify the absolute humidity upstream of the head located most upstream among the multiple print heads 42K, 42C, 42M, and 42Y.

[0128] exist Figure 3 The figure shows the relationship between the absolute humidity around the nozzle surface under various drying conditions obtained experimentally and the number of streaks, white spots, and wrinkles generated on printed materials due to poor ejection. Figure 3 The occurrence of white spots and wrinkles was evaluated by the following four-stage sensory evaluation.

[0129] AA: Very good

[0130] A: Good

[0131] B: Yes

[0132] C: No

[0133] AA, A, and B are considered acceptable, and D is considered unacceptable. Figure 5 and Figure 7 .

[0134] from Figure 3The experimental results shown here show that the absolute humidity changes depending on the pre-drying intensity and the basis weight of the substrate S, and the degree of white spots and streaks also changes. A higher pre-drying intensity and a lower basis weight of the substrate S make the substrate S easier to dry, which helps suppress white spots and wrinkles. However, the absolute humidity around the nozzle surface decreases, making streaks more likely to occur.

[0135] That is, we know that Figure 3 Among the conditions shown in Experiments 1 to 7, the high pre-drying intensity conditions (Experiments 1 to 3) were effective in reducing white spots and wrinkles, but streaks occurred due to poor discharge. In contrast, the low pre-drying intensity conditions (Experiment 4) resulted in acceptable levels for all indicators, including streaks, white spots, and wrinkles, due to the increased absolute humidity around the nozzle surface. However, compared to Experiments 1 and 2, the wrinkle performance in Experiment 4 declined from AA to A, indicating room for improvement.

[0136] In short, as a measure to counteract streaks, it is important to adjust the absolute humidity around the nozzle surface.

[0137] Figure 4 This is a graph showing the relationship between the absolute humidity around the nozzle surface and the number of streaks. Figure 4 As shown, it is found that streaks are more likely to occur on the surface and less likely to occur on the back surface. Furthermore, when the absolute humidity is lower than 8.665, the number of streaks increases rapidly.

[0138] Therefore, in order to suppress streaks, it is effective to adjust the absolute humidity around the nozzle surfaces of the print heads 42K, 42C, 42M, and 42Y that form the surface image.

[0139] Absolute humidity adjustment method

[0140] The printing device 10 according to this embodiment addresses the three issues of white spots, wrinkles, and streaks by pre-drying the substrate S and adjusting the absolute humidity around the nozzle face of the print head 42K before image formation. A specific example of the absolute humidity adjustment method is given below.

[0141] [Method 1: Adjustment of pre-drying intensity]

[0142] As mentioned above, according to Figure 3The experimental results shown show that by varying the pre-drying intensity according to the basis weight of the substrate S, the substrate moisture content changes, thereby adjusting the absolute humidity. For example, with thin paper (basis weight 104 gsm), streaks occurred under the conditions of Experiments 1 to 3. However, by lowering the pre-drying warm air temperature and heater temperature to 80°C, as in Experiment 4, streaks were suppressed. In other words, simply setting the pre-drying intensity according to the basis weight of the substrate S resulted in the absolute humidity around the nozzle surface being adjusted within an appropriate range.

[0143] In the printing apparatus 10 according to this embodiment, appropriate absolute humidity is achieved by changing the hot air temperature of the hot air unit 32 in the pre-drying unit 14 , the temperature of the heat roller 34 , and the conveyance speed of the substrate S to appropriate values ​​according to the basis weight of the substrate S.

[0144] Figure 5 This graph shows data from experiments conducted to investigate the number of streaks, white spots, and wrinkles when varying the combination of substrate S basis weight and pre-drying conditions. The printing device 10 used in this experiment had five pre-drying stages in the pre-drying unit 14, 12 heat rollers 34, and five warm air units 32. Figure 5 The “heater” here refers to the hot roller 34 .

[0145] according to Figure 5 The experimental results shown in FIG. 1 and FIG. 2 show that if the appropriate pre-drying conditions (pre-drying strength) corresponding to the basis weight are extracted, the following can be obtained: Figure 6 The table shown. Figure 6 : is a graph showing an example of setting the pre-drying conditions relative to the basis weight of the substrate S. Figure 6 As shown, it is assumed that the greater the basis weight of the substrate S, the higher the pre-drying strength.

[0146] The printing device 10 can be configured as follows: Figure 6 The table shown in FIG. 1 shows how the drying conditions in the pre-drying unit 14 are changed according to the basis weight of the substrate S used. Thus, the pre-drying drying conditions corresponding to the basis weight of the substrate S can be applied using values ​​such as temperature determined through prior experiments. Alternatively, the pre-drying drying conditions can be freely adjusted by the user according to specific conditions.

[0147] like Figure 5 and Figure 6 As described above, the method is not limited to storing the relationship between the basis weight of the substrate and the set value of the pre-drying intensity as a table based on experiments and changing the pre-drying intensity according to the basis weight. The heat applied to the substrate S can also be adjusted by changing the conveyance path (path) of the substrate S in the pre-drying unit 14. By adopting a structure that can flexibly change the path in addition to changing the drying temperature, drying conditions that meet the user's usage conditions can be applied.

[0148] Figure 7 This is a graph showing the experimental results of investigating the number of streaks, white spots, and wrinkles when the combination of the basis weight of the substrate S and the pre-drying path is changed. The pre-drying path is the substrate conveying path of the pre-drying unit 14. Figure 2 The paths can be changed by adjusting the number of warm air units 32 and the number of heat rollers 34 shown. Figure 7 The "number of heaters" in the figure refers to the number of heat rollers 34. In this experiment, the heater temperature was 150°C, the warm air temperature was 160°C, and the conveying speed was 40 mpm (miles per minute).

[0149] according to Figure 7 The experimental results shown in FIG. 4 show that if the appropriate pre-drying path corresponding to the basis weight is extracted, the following can be obtained: Figure 8 The table shown. Figure 8 : is a graph showing an example of setting the pre-drying path relative to the basis weight of the substrate S. Figure 7 According to the table shown, an appropriate pre-drying path in the pre-drying unit 14 is selected according to the basis weight of the substrate S used.

[0150] The configuration in which the drying intensity of the preliminary drying and / or the preliminary drying path are changed according to the basis weight of the substrate S is an example of the “absolute humidity adjusting means” in the present invention.

[0151] [Method 2: Introduction of a humidifier]

[0152] In principle, increasing the absolute humidity of the ambient air around the nozzle surface can suppress streaks. Therefore, a humidification source that supplies humidified air to the nozzle surface can be introduced. The humidification source is preferably located between the pre-drying unit 14 and the head box 43, but a function that allows for flexible adjustment of the humidification source's position is also possible.

[0153] Specific examples of the form and installation position of the humidification source include Form Example 1 to Form Example 3 shown below.

[0154] [Example 1]

[0155] Figure 9 and Figure 10 This is an explanatory diagram showing Example 1 of a humidification source configuration. The printing device 10 may include a hose 50 serving as a humidification source upstream of the head box. The hose 50 may have, for example, an outer diameter of 8 mm and an inner diameter of 5 mm. It is positioned parallel to the print head 42K along the width of the print head 42K, facing the substrate S. For example, the hose 50 may have multiple holes with diameters of 0.2 mm to 0.3 mm spaced at 8 mm intervals along the length of the hose 50. This 8 mm interval is an example of a "specific interval" in the present invention.

[0156] A humidifier 54 is provided outside the printing device 10, and the humidifier 54 is connected to the hose 50 via a pipe (not shown) (see FIG. Figure 10 The humidified air sent from the humidifier 54 is sent to the periphery of the print head 42K through the hose 50. The humidified air discharged from the plurality of holes of the hose 50 humidifies the periphery of the print head 42K.

[0157] exist Figure 9 , an example is shown in which the hose 50 is fixed to the wall frame 43A on the upstream side of the header box 43 via the support member 52 , but the hose 50 may be arranged inside the header box 43 .

[0158] And, it can also replace Figure 9 The structure shown, or in addition to Figure 9 In addition to the structure shown, Figure 11 As shown, a hose 50 of a humidification source is provided between the plurality of print heads 42K, 42C, 42M, and 42Y. The number and arrangement position of the hose 50 are not limited to Figure 9 and Figure 11 For example, the hose 50 may be arranged only between the two print heads 42K and the print head 42C on the upstream side in the head box 43 , or the hose 50 may be arranged only on the upstream side of the print head 42K in the head box 43 .

[0159] [Example 2]

[0160] Figure 12 and Figure 13 This is an explanatory diagram showing Example 2 of the humidification source method. Figure 12 As shown, the printing apparatus 10 may include a humidifier 60 as a humidification source upstream of the head box 43. The humidifier 60 is fixed to the wall frame 43A on the upstream side of the head box 43 via a support member 62. Figure 13 Left figure F13A is a front view of humidifier 60, and right figure F13B is a side view of humidifier 60. Humidifier 60 is an ultrasonic humidifier with dimensions of, for example, 70 mm x 70 mm x 140 mm. Humidifier 60 includes a tank 64 for generating humidified air and a nozzle 65 as an outlet for discharging the humidified air. The humidification direction (the direction in which the humidified air is discharged) can be changed by changing the orientation of nozzle 65.

[0161] [Example 3]

[0162] Figure 14 This is an explanatory diagram showing Example 3 of the humidification source. Figure 14As shown, the printing device 10 may include a duct 70 serving as a humidification source upstream of the head box 43. The outer diameter of the duct 70 is, for example, 100 mm. A humidifier (not shown) is provided outside the printing device 10 and is connected to the duct 70 via piping (not shown). Humidified air from the humidifier is supplied to the periphery of the head through the duct 70. The periphery of the head is humidified by the humidified air flowing out of the opening of the duct 70.

[0163] [Adjustment of humidification amount]

[0164] In each of the first to third embodiments, the humidification amount can be further adjusted. As a method for controlling the humidification amount, for example, the following method is available.

[0165] <Control method example 1>

[0166] The printing device 10 can adjust the humidification amount according to the basis weight of the substrate S. "Adjustment of the humidification amount" also includes adjustment without humidification (no humidification). The humidification amount set according to the substrate weight uses a value obtained in advance through experiments.

[0167] <Control method example 2>

[0168] The printing device 10 may be configured to include a measuring device (not shown) for measuring the temperature and humidity around the head, and to constantly monitor (supervise) the absolute humidity calculated based on the temperature and relative humidity values ​​obtained from the measuring device, and to adjust the humidification amount if the absolute humidity falls below a certain threshold. For example, Figure 5 As described above, the threshold value in this case can be determined based on the absolute humidity value at which the number of streaks has begun to increase rapidly, as determined experimentally. In addition, the printing device 10 may also include a measuring device capable of measuring the absolute humidity around the head.

[0169] The structure that uses a humidification source to adjust the absolute humidity is an example of the "absolute humidity adjustment means" in the present invention. Furthermore, as mentioned above, the reason for the improved drying performance due to pre-drying is that the heat transfer of the substrate S is improved due to the reduction of moisture within the substrate S. Therefore, even if moisture from the air humidified by the ambient gas adheres to the surface of the substrate S, the moisture content within the substrate S will not be restored, thus precluding the original benefit of improved drying performance. In other words, the combination of pre-drying before image formation and adjustment of the absolute humidity around the nozzle surface can achieve the desired effect of improving the heat transfer of the substrate S while simultaneously suppressing nozzle surface humidity that would otherwise cause poor discharge.

[0170] [Method 3: Adjustment of exhaust volume]

[0171] The absolute humidity around the nozzle surface can be adjusted by adjusting the exhaust volume of dry air in the printing apparatus 10 and drawing moist external air into the apparatus. In this case, the exhaust air can be reused by drying with warm air, etc., from the perspective of cost reduction.

[0172] Figure 15 This is a schematic diagram schematically illustrating an example of an air intake and exhaust structure applicable to the printing apparatus 10. The pre-drying unit 14 is provided with an air intake path 80 and an exhaust path 90. The air intake path 80 is connected to the warm air units 32 and supplies external air to each warm air unit 32. The exhaust path 90 has exhaust holes near the downstream side of each warm air unit 32, and draws air from the machine through the exhaust holes and exhausts it to the outside.

[0173] The surface printing main drying unit 16 is provided with air intake paths 82 and 84 and exhaust paths 92 and 94. The air intake path 82 supplies moistened outside air to the vicinity of the downstream side of the radiant heating section 44. The exhaust path 92 draws air into the machine from the vicinity of the upstream side of the radiant heating section 44 and exhausts it to the outside.

[0174] Furthermore, the air inlet passage 84 supplies moist external air to the drying cylinder 46. The exhaust passage 94 draws in the air in the machine from the drying cylinder 46 and discharges it to the outside of the machine. An unillustrated blower is connected to the exhaust passages 92 and 94. The air intake volume is adjusted by adjusting the exhaust volume. The air inlet passages 82 and 84 are an example of an "air intake component" in the present invention, and the exhaust passages 92 and 94 and the unillustrated blower are an example of an "exhaust component" in the present invention. By Figure 15 The structure for adjusting the absolute humidity by using the air intake structure and the exhaust structure shown is an example of the "absolute humidity adjusting means" in the present invention.

[0175] The above-mentioned methods 1 to 3 regarding the adjustment of absolute humidity can be combined as appropriate.

[0176] [Regarding the Necessity of Measures for Surface Printing in Double-Sided Printing Equipment]

[0177] according to Figure 3 The experimental results shown show that white spots and streaks are less likely to occur on the back side of substrate S. This is believed to be because during backside printing, the surface is dried, significantly reducing the moisture content within substrate S, thereby improving heat transfer. The absence of streaks is also believed to be due to the fact that the absolute humidity of the ambient air is less likely to decrease due to the wet surface image being transported. This eliminates the need for a pre-drying unit or absolute humidity adjustment device between front and backside printing, contributing to device miniaturization and cost reduction.

[0178] 〔Other additional structures〕

[0179] To prevent misting caused by static electricity during pre-drying of the substrate S, the substrate S may be de-staticized. Specifically, for example, an ionizer or de-staticizing brush may be disposed on the substrate conveying path between the pre-drying unit 14 and the head box 43 .

[0180] Example 1 of the electrical configuration of the printing device 10

[0181] Figure 16 This is a functional block diagram showing Example 1 of the electrical configuration of the printing device 10. The printing device 10 includes a centralized control unit 150, a transport control unit 152, a pre-drying control unit 154, a printing control unit 156, and a main drying control unit 158. Furthermore, the printing device 10 includes various sensors 160. Sensors 160 may include measuring devices such as thermohygrometers or absolute humidity meters for measuring the absolute humidity around the nozzle surface of the print head 42K.

[0182] The centralized control unit 150 performs centralized control of the printing device 10. The centralized control unit 150 includes a processor 150A and a memory 150B. The processor 150A may be, for example, a CPU (Central Processing Unit). The processor 150A executes commands stored in the memory 150B.

[0183] Memory 150B stores commands for processor 150A to execute. Memory 150B includes RAM (Random Access Memory) and ROM (Read Only Memory). Processor 150A uses RAM as a work area, executes software using various programs and parameters stored in memory 150B, and performs various processes for controlling printing device 10. Based on information obtained from sensor 160, central control unit 150 sends command signals to various control units, controlling the operation of each unit through these control units.

[0184] The transport control unit 152 controls the transport mechanism 170 for the substrate S. The transport mechanism 170 includes the paper feed unit 12, the reversing unit 18, and the paper discharge unit 22. The transport control unit 152 controls the motor of the paper feed unit 12, the turning lever of the reversing unit 18, and the motor of the paper discharge unit 22 to impart a predetermined transport tension to the substrate S and transport the substrate S at a predetermined transport speed. Furthermore, the transport control unit 152 controls the rotational drive of the drying cylinders 46 of the front printing main drying unit 16 and the back printing main drying unit 20.

[0185] The pre-drying control section 154 controls the warm air unit 32 and the heat roller 34 of the pre-drying unit 14 to pre-dry the substrate S.

[0186] The printing control unit 156 controls the print heads 42 of the front surface printing main drying unit 16 and the back surface printing main drying unit 20 so that an image is formed on the substrate S. Figure 16 The print head 42 is shown generally as Figure 2 The print control unit 156 includes a plurality of print heads 42K, 42C, 42M, and 42Y. The print control unit 156 includes an image processing unit that generates a halftone image of the print image from print data, and a correction processing unit that performs various correction processes. The print control unit 156 includes a drive voltage generating unit that generates a drive voltage to be supplied to the print head 42 based on dot placement information and dot size information based on the halftone image, and a drive voltage supply circuit that supplies the drive voltage.

[0187] The main drying control unit 158 ​​controls the radiation heating unit 44 and the drying drum 46 of each of the front printing main drying unit 16 and the back printing main drying unit 20 to dry the aqueous ink applied to the substrate S (main drying).

[0188] Example 2 of the electrical configuration of the printing device 10

[0189] Figure 17 1 is a functional block diagram showing a second example of the electrical configuration of the printing device 10. Figure 17 The structure shown is Figure 16 The differences are explained. Figure 17 In, with Figure 16 Components having the same configuration are denoted by the same reference numerals, and redundant descriptions are omitted.

[0190] Figure 17 The printing device 10 shown in FIG. 1 includes a humidifier 180 and a humidification control unit 184. The humidifier 180 may be a humidifier Figure 10 The humidifier 54 described in Figure 12 The humidifier 60 described in Figure 14 The humidifier is connected to the conduit 70 described in the above. The humidification control unit 184 controls the humidifier 60 to adjust the humidification amount. The centralized control unit 150 and the humidification control unit 184 control the humidification amount according to the basis weight of the substrate S. In addition, the centralized control unit 150 and the humidification control unit 184 can control the humidification amount according to the absolute humidity information obtained from the sensor 160. Other structures can be the same as Figure 16 same.

[0191] Example 3 of the electrical configuration of the printing device 10

[0192] Figure 18 1 is a functional block diagram showing a third example of the electrical configuration of the printing device 10. Figure 18 The structure shown is Figure 16 The differences are explained. Figure 18 In, with Figure 16Components having the same configuration are denoted by the same reference numerals, and redundant descriptions are omitted.

[0193] Figure 18 The printing device 10 shown in FIG. 1 includes an exhaust blower 190 and an exhaust control unit 194. The blower 190 includes Figure 15 The exhaust control unit 194 controls the blower 190 to adjust the exhaust volume. Other structures can be Figure 16 same.

[0194] In addition, Figure 18 In the structure shown, it is also possible to further include Figure 17 The structures of the humidifier 180 and the humidification control unit 184 described in .

[0195] 《Hardware Configuration Example of Control Device》

[0196] Figure 19 This is a block diagram showing an example of the hardware configuration of an information processing device 200 that functions as a control device for printing device 10. Information processing device 200 is constructed by a combination of computer hardware and software. The computer can be a server, personal computer, workstation, tablet terminal, etc., regardless of its physical form. Information processing device 200 includes a processor 202, a computer-readable medium 204, a communication interface 206, an input / output interface 208, and a bus 210.

[0197] The processor 202 includes a CPU. The processor 202 may include a GPU (Graphics Processing Unit). The processor 202 is connected to the computer readable medium 204, the communication interface 206, and the input / output interface 208 via a bus 210.

[0198] Computer-readable medium 204 includes a memory 216 as a primary storage device and a storage device 218 as a secondary storage device. Storage device 218 may be, for example, a hard disk drive (HDD) or a solid-state drive (SSD), or a combination thereof. Furthermore, computer-readable medium 204 may include ROM. A portion of the storage area of ​​computer-readable medium 204 may be included in processor 202.

[0199] Processor 202 and memory 216 act as Figure 16 The processor 150A and memory 150B described in the above description function.

[0200] The computer-readable medium 204 stores programs and data that implement the control functions of the printing device 10. The term "program" encompasses program modules. Various programs are stored in the computer-readable medium 204, including a conveyance control program 252, a pre-drying control program 254, a printing control program 256, a main drying control program 258, a humidification control program 260, and an exhaust control program 262. Furthermore, the computer-readable medium 204 stores data such as a pre-drying path table 270, a pre-drying condition table 272, a humidification amount adjustment table 274, and an exhaust amount adjustment table 276.

[0201] The transport control program 252 includes the following: Figure 16 The pre-drying control program 254 is a program including commands for realizing the functions of the pre-drying control unit 154. The printing control program 256 and the main drying control program 258 are programs including commands for realizing the functions of the printing control unit 156 and the main drying control unit 158, respectively. The humidification control program 260 is a program including commands for realizing the functions of the pre-drying control unit 154. Figure 17 The exhaust control program 262 is a program that includes instructions for implementing the functions of the humidification control unit 184 shown in FIG. Figure 18 The pre-drying path table 270 is, for example, a program for instructing the functions of the exhaust control unit 194. Figure 8 The table shown defines the pre-drying path set according to the basis weight of the substrate S. When the basis weight of the substrate S used is changed, for example, the processor 202 displays the information in the pre-drying path table 270 on the display device 214 as needed, thereby prompting the user to change to a pre-drying path suitable for the basis weight of the substrate S.

[0202] The pre-drying condition table 272 is, for example, Figure 6 The table shown defines pre-drying conditions (pre-drying intensity) set according to the basis weight of the substrate S. The pre-drying control program 254 sets the pre-drying intensity based on the basis weight of the substrate S according to the pre-drying condition table 272. The pre-drying path table 270 and the pre-drying condition table 272 may also be combined.

[0203] The humidification amount adjustment table 274 defines the humidification amount to be set according to the basis weight of the substrate S. The humidification amount adjustment table 274 can be created based on experiments. The humidification control program 260 adjusts the humidification amount according to the basis weight of the substrate S based on the humidification amount adjustment table 274 .

[0204] The exhaust volume adjustment table 276 defines the exhaust volume set according to the basis weight of the substrate S. The exhaust volume adjustment table 276 can be created based on experiments. The exhaust control program 262 adjusts the exhaust volume according to the basis weight of the substrate S based on the exhaust volume adjustment table 276.

[0205] In addition, Figure 19 In FIG. 1 , an example of an information processing device 200 having a humidification control function and an exhaust control function is shown, but a method without a humidification control function and an exhaust control function may also be used (see FIG. 1 ). Figure 16 ), and, as Figure 17 or Figure 18 As shown in the example, only one of the humidification control function and the exhaust control function may be provided. Required programs and data are stored in the computer-readable medium 204 according to the functions implemented in the printing device 10 .

[0206] The processor 202 implements various control and processing functions by executing commands of a program stored in the computer-readable medium 204. A portion of the processing functions of the information processing device 200 can be implemented using an integrated circuit such as a DSP (Digital Signal Processor) or an FPGA (Field Programmable Gate Array).

[0207] And, although in Figure 19 Although not shown, a display control program is stored in the computer-readable medium 204. The display control program is a program including commands that realize functions of generating a display signal required for display output of the display device 214 and performing display control of the display device 214.

[0208] Communication interface 206 communicates with external devices via wired or wireless communication, exchanging information with the external devices. Information processing device 200 is connected to a communication line (not shown) via communication interface 206. The communication line can be a local area network or a wide area network.

[0209] The information processing device 200 is connected to an input device 212 and a display device 214 via an input / output interface 208. The input device 212 is configured, for example, by a keyboard, a mouse, a multi-touch panel, another pointing device, or a voice input device, or a suitable combination thereof. The display device 214 is configured, for example, by a liquid crystal display, an organic electroluminescence (OEL) display, or a projector, or a suitable combination thereof.

[0210] Alternatively, the input device 212 and the display device 214 may be integrally formed like a touch panel. The input device 212 and the display device 214 may be included in the information processing device 200 or may be integrally formed with the information processing device 200, the input device 212, and the display device 214.

[0211] Furthermore, the processing functions of the information processing device 200 are not limited to those implemented by a single computer, and the processing may be implemented by distributing the functions among a plurality of computers.

[0212] <About the program that runs the computer>

[0213] A program that causes a computer to implement part or all of the processing functions in the information processing device 200 can be recorded on an optical disc, a magnetic disk, a semiconductor memory, or other tangible non-transitory information storage medium, i.e., a computer-readable medium, and provided via the information storage medium.

[0214] Furthermore, instead of providing the program by storing it in such a non-transitory computer-readable medium, the program signal can also be provided as a download service using telecommunication lines such as the Internet.

[0215] A part or all of the processing functions in the information processing device 200 can be realized by cloud computing, and can also be provided as a SaaS (Software as a Service) service.

[0216] <About the hardware structure of each processing unit>

[0217] Figures 16 to 18 The hardware structure of the processing units that perform various processes, such as the centralized control unit 150, conveying control unit 152, pre-drying control unit 154, printing control unit 156, main drying control unit 158, humidification control unit 184 and exhaust control unit 194 shown, is, for example, the various processors shown below.

[0218] Various processors include general-purpose processors (CPUs) that execute programs and function as various processing units, processors specifically used for image processing (GPUs), FPGAs (Programmable Logic Devices: PLDs) and other processors whose circuit structures can be changed after manufacturing, and ASICs (Application Specific Integrated Circuits), which are dedicated circuits with circuit structures specifically designed to perform specific processing.

[0219] One processing unit may be composed of one of these various processors, or may be composed of two or more processors of the same type or different types. For example, one processing unit may be composed of multiple FPGAs or a combination of a CPU and an FPGA or a combination of a CPU and a GPU. Furthermore, multiple processing units may be composed of one processor. As an example of multiple processing units being composed of one processor, there is first a method in which a processor is composed of a combination of one or more CPUs and software, as represented by computers such as clients and servers, and the processor functions as multiple processing units. Second, there is a method in which a processor is used that implements the functions of the entire system including multiple processing units using one IC (Integrated Circuit) chip, as represented by a System On Chip (SoC). In this way, various processing units are composed of one or more of the above-mentioned various processors in terms of hardware structure.

[0220] Furthermore, more specifically, the hardware structure of these various processors is a circuit (circuitry) formed by combining circuit elements such as semiconductor elements.

[0221] Effects of this embodiment

[0222] According to this embodiment, it is possible to suppress poor drying and deformation of the substrate S after image formation, thereby suppressing poor ejection by the print head 42. This reduces image defects such as streaks, enabling the production of high-quality printed materials. Furthermore, in a duplex printing device 10, the pre-drying unit 14 is only provided before image formation on the front surface, and the absolute humidity around the nozzle surface of the print head 42 is adjusted only for front-side printing. The same configuration is not used for back-side printing, thereby reducing unnecessary (excessive) equipment costs.

[0223] Modification 1

[0224] In the above embodiment, a printing device 10 using a page-width full-line head is described, but the scope of application of the present invention is not limited to this. The technology of the present invention can also be applied to inkjet printing devices such as serial nozzles that move a short-sized print head while forming an image through multiple nozzle scans.

[0225] Modification 2

[0226] exist Figure 1 The printing device 10 for printing images on both sides of the substrate S is shown as an example, but it is also possible not to have Figure 1 The embodiment of the reverse unit 18 and the back printing main drying unit 20 shown may be a single-sided printing apparatus for printing an image on a single side of the substrate S.

[0227] Modification 3

[0228] In the above embodiment, the absolute humidity is adjusted based on the basis weight of the substrate S. However, the present invention is not limited to the basis weight. For example, the absolute humidity can be adjusted based on the properties of the substrate S used, in combination with other properties such as the material and / or size of the substrate S. Furthermore, the brand of the substrate S can be used as a property of the substrate S.

[0229] About Base Materials

[0230] The material and shape of the substrate S are not particularly limited as long as it can be applied with water-based ink to form an image. For example, permeable media such as paper, cloth, and wood can be used. The term "substrate" can be understood as a general term for various terms such as recording media, paper, recording paper, printing paper, printing media, printing media, printed media, image forming media, image forming media, image receiving media, and ejected media used to form an image.

[0231] exist Figure 1 In the above description, an example of using continuous paper as the substrate S is described. However, the substrate is not limited to continuous paper, and a single sheet substrate such as cut-sheet paper may also be used.

[0232] 《About the conveying mechanism of the substrate》

[0233] In the above embodiment, a roll-to-roll printing apparatus 10 is exemplified, but the conveying mechanism for conveying the substrate can adopt various methods such as roller conveying, belt conveying, clamping conveying, chain conveying, or tray conveying, and these methods can also be appropriately combined.

[0234] 《About the ejection method of the print head》

[0235] The ejector of printhead 42 is composed of a nozzle that ejects ink, a pressure chamber connected to the nozzle, and an ejection energy generating element that imparts ejection energy to the liquid within the pressure chamber. Regarding the method of ejecting droplets from the ejector nozzle, the component that generates ejection energy is not limited to a piezoelectric element; various ejection energy generating elements such as heating elements or electrostatic actuators can be used. For example, a method can be used that utilizes the pressure of film boiling caused by the heating of the liquid by the heating element to eject droplets. Depending on the ejection method of printhead 42, a corresponding ejection energy generating element is provided on the flow path structure.

[0236] About Terminology

[0237] The term "printing device" includes concepts such as printing press, printing system, image forming device, printer, printing device, image recording device, image output device, or drawing device.

[0238] The term "printing" includes concepts such as image formation, image recording, printing, drawing and printing.

[0239] The term "image" is to be interpreted as a broad term that also includes color images, black and white images, monochrome images, gradient images, and uniform density (solid) images. The term "image" is not limited to photographic images, but is used as a comprehensive term that includes patterns, characters, symbols, lines, mosaic patterns, patterns filled with color distinctions, various other patterns, or appropriate combinations thereof.

[0240] Combinations of Implementation Methods and Modifications

[0241] The configurations described in the above-mentioned embodiments or the matters described in the modified examples can be used in appropriate combination, and some of the matters can be replaced.

[0242] "other"

[0243] The present invention is not limited to the above-described embodiment, and various modifications are possible without departing from the spirit of the technical concept of the present invention.

[0244] Explanation of symbols

[0245] 10-Printing device, 12-Paper supply unit, 14-Pre-drying unit, 16-Surface printing main drying unit, 18-Reversing unit, 20-Back printing main drying unit, 22-Paper discharge unit, 30-Heating device, 32-Warm air unit, 34-Hot roller, 36-Transport roller, 38-Cooling roller, 40-Transport roller, 42-Print head, 42K, 42C, 42M, 42Y-Print heads, 43-Head box, 43A-Wall frame Rack, 44-radiant heating unit, 46-drying cylinder, 48-first contact roller, 50-hose, 52-support component, 54-humidifier, 60-humidifier, 62-support component, 64-tank, 65-nozzle, 70-duct, 80, 82, 84-intake air path, 90, 92, 94-exhaust air path, 150-centralized control unit, 150A-processor, 150B-memory, 152-transport control unit, 154-pre-drying Control unit, 156-printing control unit, 158-formal drying control unit, 160-sensor, 170-conveying mechanism, 180-humidifier, 184-humidification control unit, 190-blower, 194-exhaust control unit, 200-information processing device, 202-processor, 204-computer-readable medium, 206-communication interface, 208-input and output interface, 210-bus, 212-input device, 214-display device, 216-memory, 218-storage device, 252-conveying control program, 254-pre-drying control program, 256-printing control program, 258-formal drying control program, 260-humidification control program, 262-exhaust control program, 270-pre-drying path table, 272-pre-drying condition table, 274-humidification amount adjustment table, 276-exhaust amount adjustment table, F13A-left figure, F13B-right figure, S-substrate.

Claims

1. A printing device comprising: The print head ejects water-based ink onto the substrate to form an image; a substrate moisture reducing member for reducing moisture from the substrate before image formation by the print head; and The absolute humidity adjustment member adjusts the absolute humidity around the nozzle surface of the print head.

2. The printing device according to claim 1, wherein The substrate moisture reducing means includes a first drying device for heating the substrate before the image is formed. The absolute humidity adjusting member adjusts the absolute humidity around the nozzle surface by changing the drying capacity of the first drying device according to the properties of the substrate.

3. The printing device according to claim 2, wherein The drying capacity is changed by changing at least one of a conveyance speed of the substrate in the first drying device and a temperature of the first drying device according to properties of the substrate.

4. The printing device according to claim 2, wherein The amount of heat applied to the substrate is changed by changing the conveyance path of the substrate in the first drying device according to the properties of the substrate.

5. The printing device according to claim 2, wherein The properties of the substrate include the basis weight of the substrate.

6. The printing device according to claim 1, comprising: The static elimination device is disposed between the substrate moisture reducing member and the printing head and performs static elimination on the substrate.

7. The printing device according to claim 1, wherein The substrate moisture reducing member heats the substrate before the image formation to bring the substrate into a decelerated drying state.

8. The printing device according to claim 1, wherein The absolute humidity adjustment member includes a humidification source for humidifying the periphery of the nozzle surface.

9. The printing device according to claim 8, wherein The absolute humidity adjusting member changes the amount of humidity change according to properties of the substrate.

10. The printing device according to claim 8, wherein The absolute humidity adjustment unit includes a processor configured to monitor the absolute humidity around the nozzle surface and adjust the humidification amount of the humidification source if the absolute humidity is equal to or lower than a threshold value.

11. The printing device according to claim 10, comprising: A measuring device for measuring the absolute humidity around the nozzle surface, The processor adjusts the humidification amount according to information obtained from the measurer.

12. The printing device according to claim 11, wherein The processor calculates absolute humidity based on the temperature and relative humidity measurements obtained from the measurer.

13. The printing device according to claim 8, wherein The humidification source includes a hose connected to the humidifier, A plurality of holes are formed on the hose at specific intervals. The humidified air is supplied to the periphery of the nozzle surface through the hose.

14. The printing device according to claim 8, wherein The humidification source is an ultrasonic humidifier.

15. The printing device according to claim 8, wherein The humidification source includes a conduit connected to the humidifier, The humidified air is supplied to the periphery of the nozzle surface through the duct.

16. The printing device according to claim 1, wherein The absolute humidity adjustment component comprises: an exhaust member for exhausting dry air from the interior of the printing device; and an air intake member for sucking moist external air into the machine. The absolute humidity around the nozzle surface is adjusted by adjusting the exhaust volume by the exhaust member.

17. The printing device according to claim 16, wherein The absolute humidity adjusting member includes a processor for adjusting the exhaust volume according to properties of the substrate.

18. The printing device according to claim 1, comprising: The second drying device dries the substrate to which the aqueous ink has been applied by the print head.

19. The printing device according to any one of claims 1 to 18, comprising: The second printing head forms an image on the second surface of the substrate, which is the opposite surface of the first surface, after the first printing head, which is the printing head, forms an image on the first surface of the substrate. Of the steps before image formation on the first surface and before image formation on the second surface, the substrate moisture reducing member is provided only before image formation on the first surface.

20. The printing device according to claim 19, wherein Of the first print head and the second print head, the absolute humidity adjusting member is provided only on the first print head.

21. A printing method for forming an image by ejecting water-based ink from a printing head onto a substrate, the printing method comprising: a step of reducing the moisture content of the substrate before image formation by the print head; and A step of adjusting the absolute humidity around the nozzle surface of the print head.

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