Dryer and drying method

Abstract

To enable drying of a printing medium under a condition corresponding to humidity in a drying furnace without providing a humidity sensor in the drying furnace.SOLUTION: Outside air humidity Im (outside air data) and submitted data Ds (print image information) are acquired. Then, a transfer speed command Cv output from a transfer speed command unit 586 (transfer unit) is controlled based on the humidity Im and the submitted data Ds. As a result, drying of the printing medium M under a condition according to the humidity in the drying furnace 6 can be carried out without providing a humidity sensor in the drying furnace 6.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to a technique for drying a print medium on which an image formed by ink has been printed. [Background technology]

[0002] Patent Document 1 discloses a drying device equipped with a heating unit that dries a print medium on which an image formed with ink is printed. The heating unit has a heating section that faces the print medium and heats the print medium, and a blower that blows air between the heating section and the print medium. Furthermore, a humidity detection section is provided that detects the humidity in the area between the heating unit and the print medium, and the blower, for example, is controlled based on the humidity detected by the humidity detection section. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2023-119172 Summary of the Invention [Problem to be solved by the invention]

[0004] To quickly dry the print media, it is necessary to dry the print media under conditions that correspond to the humidity inside the drying oven that the print media is dried in. However, when a humidity sensor is placed inside the drying oven, the temperature inside the drying oven cannot be raised high in order to prevent the humidity sensor from breaking down, making it difficult to quickly dry the print media.

[0005] The present invention has been made in consideration of the above-mentioned problems, and has as its object to make it possible to dry a print medium under conditions according to the humidity inside a drying oven without providing a humidity sensor inside the drying oven. [Means for solving the problem]

[0006] The drying device of the present invention comprises a drying furnace, a transport unit that transports a printing medium on which an image formed with ink is printed within the drying furnace, a hot air supply unit that takes in hot air generated by heating the outside air outside the drying furnace and supplies it into the drying furnace, a hot air temperature adjustment unit that adjusts the temperature of the hot air taken in by the hot air supply unit, a hot air guide unit that guides the hot air supplied into the drying furnace by the hot air supply unit to the printing medium transported by the transport unit, a hot air recovery unit that recovers the hot air discharged from the drying furnace to the hot air supply unit, and a control unit that controls at least one controlled object of the transport unit, the hot air temperature adjustment unit, and the hot air recovery unit, wherein the hot air supply unit supplies the hot air recovered by the hot air recovery unit into the drying furnace, and the control unit has an outside air data acquisition unit that acquires outside air data indicating at least the amount of water vapor contained in the outside air, and a print image information acquisition unit that acquires print image information related to an image printed on the print medium, and controls the controlled object based on the outside air data and the print image information.

[0007] The drying method of the present invention includes the steps of transporting a printing medium having an image formed by ink printed thereon through a drying oven by a conveying unit, taking in warm air generated by heating the outside air outside the drying oven using a warm air supply unit and supplying it into the drying oven, adjusting the temperature of the warm air taken in by the warm air supply unit using a warm air temperature adjustment unit, guiding the warm air supplied into the drying oven by the warm air supply unit to the printing medium being transported by the conveying unit using a warm air guide unit, recovering the warm air discharged from the drying oven to the warm air supply unit by a warm air recovery unit, and controlling at least one of the control objects of the conveying unit, the warm air temperature adjustment unit, and the hot air recovery unit using a control unit, wherein the warm air supply unit supplies the warm air recovered by the hot air recovery unit into the drying oven, and the control unit has an outside air data acquisition unit that acquires outside air data indicating at least the amount of water vapor contained in the outside air, and a print image information acquisition unit that acquires print image information related to the image printed on the printing medium, and controls the control object based on the outside air data and the print image information.

[0008] In the present invention (drying device and drying method) configured as described above, warm air generated by heating outside air is supplied into the drying oven by the warm air supply unit. The temperature of this warm air is adjusted by the warm air temperature adjustment unit. Furthermore, warm air recovered from the drying oven to the warm air supply unit by the warm air recovery unit is also supplied into the drying oven. In this drying oven, a print medium with an ink-printed image is transported by the conveying unit. The warm air supplied into the drying oven is then guided toward the print medium by the warm air guide unit, drying the print medium. In this configuration, the humidity inside the drying oven is significantly affected by the ink that forms the image on the print medium and the humidity of the outside air. Therefore, in the present invention, outside air data indicating at least the amount of water vapor contained in the outside air and print image information related to the image printed on the print medium are acquired. At least one of the control targets—the transport unit, the warm air temperature adjustment unit, and the warm air recovery unit—is then controlled based on the outside air data and the print image information. As a result, it is possible to dry the print medium under conditions appropriate for the humidity inside the drying oven without installing a humidity sensor inside the drying oven.

[0009] The control unit may also be configured to acquire an ink amount reflection value that reflects the amount of ink adhered to the print medium based on the print image information, and control the control target based on the outside air data and the ink amount reflection value. By performing control based on the ink amount reflection value in this way, it is possible to dry the print medium under conditions that correspond to the humidity inside the drying oven.

[0010] Various specific examples of the ink amount reflection value are possible. For example, the control unit may configure the drying device so that the control unit acquires a printing rate, which indicates the proportion of the area of ​​an image to which ink is attached, as the ink amount reflection value. Alternatively, the control unit may configure the drying device so that the control unit acquires the gradation values ​​of each of the multiple pixels that make up the image from the print image information and acquires the ink amount reflection value based on the result of binarizing the gradation values.

[0011] The control unit may be configured to control the drying device based on a combined value obtained by combining a drying time index value corresponding to the drying time of the ink adhered to the print medium and an ink amount reflection value, and on outside air data. By performing control based on this combined value of the drying time index value and the ink amount reflection value, it is possible to dry the print medium under conditions corresponding to the humidity inside the drying oven.

[0012] The control unit may be configured to calculate a composite value for each of multiple target regions included in the image and control the target based on the composite value of one of the target regions that satisfies a predetermined condition. With this configuration, even if there are localized areas that require a long drying time, it is possible to dry the print medium under conditions that correspond to the humidity inside the drying oven.

[0013] The control unit may be configured to reduce the speed at which the transport unit transports the print medium as the ink volume reflected by the ink volume reflection value increases. With this configuration, the print medium can be dried while being transported at a transport speed that corresponds to the humidity inside the drying oven.

[0014] The control unit may be configured to reduce the speed at which the transport unit transports the print medium as the drying time indicated by the drying time index value increases. In this configuration, the print medium can be dried while being transported at a transport speed that corresponds to the humidity inside the drying oven.

[0015] The control unit may be configured to adjust the temperature of the hot air by the hot air temperature adjustment unit so that the greater the amount of ink reflected by the ink amount reflection value, the higher the temperature of the hot air. With this configuration, it is possible to dry the print medium with hot air at a temperature that corresponds to the humidity inside the drying oven.

[0016] The control unit may be configured to adjust the temperature of the hot air by the hot air temperature adjustment unit so that the longer the drying time indicated by the drying time index value, the higher the temperature of the hot air. With this configuration, it is possible to dry the print medium with hot air at a temperature that corresponds to the humidity inside the drying oven.

[0017] The control unit may also be configured to control the hot air supply unit, and the control unit may be configured to increase the flow rate of hot air supplied into the drying oven as the ink amount reflected by the ink amount reflection value increases. With this configuration, it is possible to dry the print medium with hot air at a flow rate that corresponds to the humidity inside the drying oven.

[0018] The drying device may also be configured such that the control unit controls the hot air supply unit, and the control unit increases the flow rate of hot air supplied by the hot air supply unit into the drying oven as the drying time indicated by the drying time index value increases. With this configuration, it is possible to dry the print medium with hot air at a flow rate that corresponds to the humidity inside the drying oven.

[0019] The control unit may be configured to reduce the flow rate of hot air collected by the hot air collection unit to the hot air supply unit as the ink amount reflected by the ink amount reflection value increases. With this configuration, it is possible to dry the print medium while collecting hot air from the drying oven to the hot air supply unit in an amount that corresponds to the humidity inside the drying oven.

[0020] The control unit may be configured to reduce the flow rate of hot air collected by the hot air collection unit to the hot air supply unit as the drying time indicated by the drying time index value increases. With this configuration, it is possible to dry the print medium while collecting hot air from the drying oven to the hot air supply unit in an amount that corresponds to the humidity inside the drying oven. [Effects of the Invention]

[0021] As described above, according to the present invention, it is possible to dry the print medium under conditions that correspond to the humidity inside the drying oven, without providing a humidity sensor inside the drying oven. [Brief explanation of the drawings]

[0022] [Figure 1] 1 is a front view schematically illustrating an example of a printing system including a drying device according to the present invention. [Figure 2] FIG. 2 is a front view schematically showing a drying device provided in the printing system of FIG. 1. [Figure 3] 3 is a partially enlarged schematic view showing the blower dryers of the upper and lower conveying sections. FIG. [Figure 4] FIG. 4 is a partially enlarged schematic view of the air blow dryer in the middle conveying section. [Figure 5] FIG. 4 is a block diagram showing a hot air supply unit that supplies hot air to a drying furnace. [Figure 6] FIG. 2 is a block diagram showing an electrical configuration of the drying device. [Figure 7A] 6 is a flowchart showing a first example of a drying condition determination process executed by a control unit of the drying device. [Figure 7B] FIG. 7B is a diagram schematically illustrating an example of a calculation executed in the flowchart of FIG. 7A. [Figure 7C] FIG. 7B is a diagram schematically illustrating an example of a calculation executed in the flowchart of FIG. 7A. [Figure 7D] FIG. 7B is a diagram schematically showing an example of a table used for setting drying conditions in the flowchart of FIG. 7A. [Figure 7E] FIG. 7B is a diagram schematically showing an example of a table used for setting drying conditions in the flowchart of FIG. 7A. [Figure 8A] 10 is a flowchart showing a second example of the drying condition determination executed by the control unit of the drying device. [Figure 8B] FIG. 7B is a diagram schematically illustrating an example of a calculation executed in the flowchart of FIG. 7A. [Figure 8C] FIG. 7B is a diagram schematically illustrating an example of a calculation executed in the flowchart of FIG. 7A. [Figure 9] 10 is a flowchart showing a third example of the drying condition determination executed by the control unit of the drying device. DETAILED DESCRIPTION OF THE INVENTION

[0023] FIG. 1 is a front view schematically illustrating an example of a printing system equipped with a drying device according to the present invention. In FIG. 1 and the following figures, a horizontal direction X, a horizontal direction Y perpendicular to the horizontal direction X, and a vertical direction Z are indicated as appropriate. As shown in FIG. 1, the printing system 1 includes a coating device 2, a printing device 3, and a drying device 5 arranged in this order in the horizontal direction X (arrangement direction). In this printing system 1, a long strip of printing medium M is transported roll-to-roll from a supply roll 11 to a take-up roll 12. The printing device 3 inkjet prints an image on the printing medium M, which has been coated with a coating liquid by the coating device 2. The drying device 5 dries the printing medium M with the printed image. The printing medium M is made of a film such as OPP (oriented polypropylene) or PET (polyethylene terephthalate). However, the material of the printing medium M is not limited to film and may be paper or the like. The printing medium M is flexible. In the following description, the surface of the print medium M on which an image is printed will be referred to as the front surface M1, and the surface opposite the front surface M1 will be referred to as the back surface M2.

[0024] The coating device 2 has a pan 21 that stores a liquid primer (coating liquid), a gravure roller 22 that is partially immersed in the primer stored in the pan 21, and a conveying unit 23 that conveys the print medium M. The coating device 2 has a coating area where the gravure roller 22 contacts the print medium M conveyed by the conveying unit 23 from below, and the conveying unit 23 conveys the print medium M along the coating area while facing the surface M1 of the print medium M downward. Meanwhile, the gravure roller 22 supplies the primer to the coating area by rotating while holding the primer on its circumferential surface. In this way, the primer supplied by the gravure roller 22 is applied to the surface M1 of the print medium M in the coating area. Furthermore, in the coating area, the traveling direction of the print medium M and the rotation direction of the circumferential surface of the gravure roller 22 are opposite. In other words, the primer is applied to the print medium M using a so-called reverse kiss method. Then, the transport unit 23 transports the printing medium M from the coating device 2 to the printing device 3 while facing the surface M1 of the printing medium M coated with the primer upward.

[0025] The printing device 3 comprises a housing 31, a color printing unit 32 arranged within the housing 31, a white printing unit 33 arranged above the color printing unit 32 within the housing 31, and a transport unit 34 that transports the printing medium M using multiple rollers arranged within the housing 31.

[0026] The color printing unit 32 has multiple (six) ejection heads 321 arranged in the direction of travel of the printing medium M above the printing medium M transported by the transport unit 34. Each of the multiple ejection heads 321 has a nozzle facing from above toward the surface M1 of the printing medium M passing below it, and ejects different color inks from the nozzles using an inkjet method. Here, color ink refers to ink other than white, and includes inks such as cyan, magenta, yellow, and black. In this way, the multiple ejection heads 321 of the color printing unit 32 print a color image on the surface M1 of the printing medium M by ejecting color inks from above onto the surface M1 of the printing medium M passing below it.

[0027] The white printing unit 33 also has a single ejection head 331 arranged above the printing medium M transported by the transport unit 34. The ejection head 331 has nozzles facing from above toward the surface M1 of the printing medium M passing below it, and ejects white ink from the nozzles using an inkjet method. In this way, the ejection head 331 of the white printing unit 33 prints a white image on the surface M1 of the printing medium M by ejecting white ink from above onto the surface M1 of the printing medium M passing below it.

[0028] The printing medium M is carried from the coating device 2 into the housing 31 of the printing device 3 with the surface M1 facing upward. Meanwhile, the transport unit 34 turns the printing medium M carried into the housing 31 upside down twice before transporting the printing medium M to the color printing unit 32. This allows the ejection heads 321 of the color printing unit 32 to eject color inks onto the surface M1 of the printing medium M facing upward. Furthermore, the transport unit 34 turns the printing medium M with the color inks attached upside down twice before transporting the printing medium M to the white printing unit 33. This allows the ejection head 331 of the white printing unit 33 to eject white ink onto the surface M1 of the printing medium M facing upward. In this way, the printing medium M with the color inks and white ink attached to its surface M1 is transported from the printing device 3 to the drying device 5 by the transport unit 34.

[0029] 2 is a front view schematically illustrating the drying device provided in the printing system of FIG. 1. In the figure, one side X1 and the other side X2 of the horizontal direction X are shown, with the one side X1 and the other side X2 facing opposite each other. The drying device 5 dries the printing medium M while transporting the printing medium M in the horizontal direction X, folding it back and forth as appropriate. The drying device 5 includes a drying oven 6 disposed on one side X1 of the housing 31 of the printing device 3. The drying oven 6 is a rectangular parallelepiped housing extending in the horizontal direction X, and both side walls 6a, 6b of the drying oven 6 in the horizontal direction X are parallel to the vertical direction Z and perpendicular to the horizontal direction X, facing each other with a gap in between in the horizontal direction X.

[0030] Of the side walls 6a, 6b, an inlet 61 penetrates in the horizontal direction X through the side wall 6a on the other side X2 in the horizontal direction X (the side facing the printing device 3), and an outlet 66 penetrates in the horizontal direction X through the side wall 6b on one side X1 in the horizontal direction X (the opposite side of the printing device 3). The printing medium M discharged from the printing device 3 is carried into the drying furnace 6 through the inlet 61 and then discharged out of the drying furnace 6 through the outlet 66.

[0031] That is, the drying device 5 includes a transport unit 51 for transporting the printing medium M in the drying furnace 6, and the transport unit 51 transports the printing medium M from the inlet 61 to the outlet 66. The transport unit 51 has an upper transport unit 51u that transports the printing medium M from the other side X2 to the one side X1, a middle transport unit 51m that transports the printing medium M from the one side X1 to the other side X2, and a lower transport unit 51l that transports the printing medium M from the other side X2 to the one side X1. The middle transport unit 51m is located below the upper transport unit 51u, and the lower transport unit 51l is located below the middle transport unit 51m. Therefore, the printing medium M transported by the upper transport unit 51u, the printing medium M transported by the middle transport unit 51m, and the printing medium M transported by the lower transport unit 51l are aligned in the vertical direction Z, or in other words, overlap each other when viewed from the vertical direction Z. Specifically, the upper transport unit 51u transports the printing medium M at the same height as the entrance 61, and the printing medium M is transported in the horizontal direction X by the upper transport unit 51u with the front surface M1 facing upward and the back surface M2 facing downward. The middle transport unit 51m transports the printing medium M below the upper transport unit 51u, and the printing medium M is transported in the horizontal direction X by the middle transport unit 51m with the front surface M1 facing downward and the back surface M2 facing upward. The lower transport unit 51l transports the printing medium M below the middle transport unit 51m, and the printing medium M is transported in the horizontal direction X by the lower transport unit 51l with the front surface M1 facing upward and the back surface M2 facing downward.

[0032] The transport unit 51 also has a front-stage folding unit 52 that folds back the printing medium M from the upper transport unit 51u to the middle transport unit 51m. This front-stage folding unit 52 has two rollers 521, 522 arranged in the vertical direction Z on one side X1 of the drying furnace 6. Each of the rollers 521, 522 is arranged parallel to the horizontal direction Y and is supported by the drying furnace 6 around a rotation axis parallel to the horizontal direction Y. Of the rollers 521, 522, the upper roller 521 wraps around the back surface M2 of the printing medium M transported to the one side X1 by the upper transport unit 51u and folds back the printing medium M downward, and the lower roller 522 wraps around the back surface M2 of the printing medium M folded back downward by the roller 521 and folds back the printing medium M to the other side X2.

[0033] In this way, the front surface M1 and the back surface M2 of the printing medium M are inverted upside down by folding the printing medium M from one side X1 to the other side X2 by the front-stage folding unit 52. The printing medium M folded to the other side X2 by the front-stage folding unit 52 is transported to the other side X2 by the middle-stage transport unit 51m.

[0034] The transport unit 51 also has a rear-stage turning unit 54 that turns the printing medium M from the middle transport unit 51m to the lower transport unit 51l. This rear-stage turning unit 54 has two air turn bars 541, 542 arranged in the vertical direction Z on the other side X2 of the drying oven 6. The air turn bars 541, 542 are each arranged parallel to the horizontal direction Y and supported by the drying oven 6. Of the air turn bars 541, 542, the upper air turn bar 541 sprays air onto the surface M1 of the printing medium M transported from the middle transport unit 51m toward the other side X2. This causes the air turn bar 541 to bend the printing medium M downward while leaving a gap between it and the surface M1 of the printing medium M. Of the air turn bars 541, 542, the lower air turn bar 542 sprays air onto the surface M1 of the printing medium M transported downward from the air turn bar 541. As a result, the air turn bar 542 bends the printing medium M to one side X1 while leaving a gap between the air turn bar 542 and the surface M1 of the printing medium M.

[0035] In this way, the rear-stage folding unit 54 folds the printing medium M from the other side X2 to the one side X1, thereby inverting the front side M1 and the back side M2 ​​of the printing medium M upside down. The printing medium M folded back to the one side X1 by the rear-stage folding unit 54 is transported to the one side X1 by the lower-stage transport unit 51l.

[0036] The transport unit 51 also has a roller 561 that supports the printing medium M transported from the lower transport unit 51l to the one side X1. The roller 561 is arranged parallel to the horizontal direction Y on the one side X1 of the drying furnace 6, and is supported by the drying furnace 6 so as to be rotatable around an axis of rotation parallel to the horizontal direction Y. The roller 561 supports the printing medium M by rotating while contacting the back surface M2 of the printing medium M transported from the lower transport unit 51l to the one side X1.

[0037] The drying device 5 includes six air dryers 7a to 7f housed in the drying furnace 6. Of these, two air dryers 7a and 7b are provided in the upper conveying section 51u and arranged between the inlet 61 and the rollers 521. The air dryers 7a and 7b dry the printing medium M transported from the inlet 61 toward the rollers 521. The two air dryers 7c and 7d are provided in the middle conveying section 51m and arranged between the rollers 522 and the air turn bar 541. The air dryers 7c and 7d dry the printing medium M transported from the rollers 522 toward the air turn bar 541. The two air dryers 7e and 7f are provided in the lower conveying section 51l and arranged between the air turn bar 542 and the rollers 561. The air blowers 7e and 7f dry the print medium M that is transported from the air turn bar 542 toward the roller 561.

[0038] Fig. 3 is a partially enlarged schematic view of the blow dryers in the upper and lower conveying sections, and Fig. 4 is a partially enlarged schematic view of the blow dryer in the middle conveying section. Next, blow dryers 7a to 7f will be described with reference to Figs. 3 and 4.

[0039] The blower dryer 7a has an air blowing unit 71u arranged above the printing medium M being transported from the carry-in entrance 61 toward the rollers 521. The air blowing unit 71u has an air blowing chamber 72u extending in the horizontal direction X above the printing medium M. Both end surfaces of the air blowing chamber 72u in the horizontal direction X are planes perpendicular to the horizontal direction X and parallel to the vertical direction Z. Warm air generated by heating air outside the drying oven 6 is supplied to the air blowing chamber 72u. The lower surface of the air blowing chamber 72u is a nozzle arrangement plane 73u that faces from above the surface M1 (upper surface) of the printing medium M facing upward. This nozzle arrangement plane 73u is a plane parallel to the horizontal direction X and perpendicular to the vertical direction Z. Furthermore, the air blowing unit 71u has a plurality of nozzles 76u arranged at a predetermined pitch in the horizontal direction X on the nozzle arrangement plane 73u. In this way, the multiple nozzles 76u are lined up between the nozzle arrangement plane 73u and the surface M1 of the printing medium M, and face the surface M1 of the printing medium M. Each nozzle 76u is in communication with the air blowing chamber 72u, and warm air supplied to the air blowing chamber 72u is sprayed from the nozzles 76u onto the surface M1 of the printing medium M, drying the printing medium M. In this way, of the multiple air blowing dryers 7a to 7f, the air blowing dryer 7a dries the printing medium M that has been carried into the drying oven 6 first.

[0040] Furthermore, the blower dryer 7a has multiple rollers 74 (the same number as the nozzles 76u) arranged below the printing medium M transported from the carry-in entrance 61 toward the rollers 521. The multiple rollers 74 are arranged at a predetermined pitch in the direction of travel of the printing medium M (horizontal direction X), and the circumferential surface of each roller 74 contacts the back surface M2 (lower surface) of the printing medium M from below. Each roller 74 supports the printing medium M from below while rotating in response to the printing medium M around a rotation axis parallel to the horizontal direction Y. The rollers 74 also have fine spiral grooves that allow air to easily escape between the printing medium M and the circumferential surface of the rollers 74.

[0041] Incidentally, the nozzles 76u face from above the area between two adjacent rollers 74 in the horizontal direction X, and the rollers 74 face from below the area between two upper adjacent nozzles 76u in the horizontal direction X. That is, in the horizontal direction X, the nozzles 76u and the rollers 74 are alternately arranged at a pitch that is half the predetermined pitch, and are alternately arranged one by one in the horizontal direction X in a plan view from the vertical direction Z. In other words, the nozzles 76u and the rollers 74 are arranged in a staggered pattern.

[0042] 3, in the portion of the printing medium M facing the nozzle 76u, the printing medium M is pushed downward by the warm air from the nozzle 76u, causing the printing medium M to be biased downward from the upper end of the roller 74, and the portion of the printing medium M facing the roller 74 is supported by the roller 74. Therefore, the printing medium M is transported in the horizontal direction X from the other side X2 to the one side X1 while undulating between the upper end of the roller 74 and below the upper end.

[0043] The blower dryer 7b is disposed downstream of the blower dryer 7a in the traveling direction of the printing medium M transported from the carry-in entrance 61 toward the rollers 521. Similar to the blower dryer 7a, the blower dryer 7b has an air blowing unit 71u disposed above the printing medium M transported from the carry-in entrance 61 toward the rollers 521, and a plurality of rollers 74 disposed below the printing medium M. In the blower dryer 7b, the plurality of rollers 74 support the back surface M2 of the printing medium M from below, while the plurality of nozzles 76u of the air blowing unit 71u (the same number as the rollers 74) spray warm air from above onto the front surface M1 of the printing medium M, thereby drying the printing medium M.

[0044] The blower dryer 7c has air blowing units 71u and 71l arranged above and below the printing medium M being transported from the roller 522 toward the air turn bar 541. The upper air blowing unit 71u has an air blowing chamber 72u extending in the horizontal direction X above the printing medium M. Both end surfaces of the air blowing chamber 72u in the horizontal direction X are planes perpendicular to the horizontal direction X and parallel to the vertical direction Z. The above-mentioned warm air is supplied to the air blowing chamber 72u. The lower surface of the air blowing chamber 72u is a nozzle arrangement plane 73u that faces from above the back surface M2 (upper surface) of the printing medium M facing upward. This nozzle arrangement plane 73u is a plane parallel to the horizontal direction X and perpendicular to the vertical direction Z. Furthermore, the air blowing unit 71u has a plurality of nozzles 76u arranged at a predetermined pitch in the horizontal direction X on the nozzle arrangement plane 73u. In this way, the multiple nozzles 76u are lined up between the nozzle arrangement plane 73u and the back surface M2 of the printing medium M, and face the back surface M2 of the printing medium M. Each nozzle 76u is in communication with the air blowing chamber 72u, and the hot air supplied to the air blowing chamber 72u is sprayed from the nozzles 76u onto the back surface M2 of the printing medium M.

[0045] The lower blower unit 71l has an air-blowing chamber 72l extending in the horizontal direction X below the printing medium M. Both end surfaces of the air-blowing chamber 72l in the horizontal direction X are planes perpendicular to the horizontal direction X and perpendicular to the vertical direction Z. The above-mentioned warm air is supplied to the air-blowing chamber 72l. The upper surface of the air-blowing chamber 72l is a nozzle arrangement plane 73l that faces from below the surface M1 (lower surface) of the printing medium M, which faces downward. This nozzle arrangement plane 73l is a plane that is parallel to the horizontal direction X and perpendicular to the vertical direction Z. Furthermore, the air-blowing unit 71l has a plurality of nozzles 76l arranged at a predetermined pitch in the horizontal direction X on this nozzle arrangement plane 73l. In this way, the plurality of nozzles 76l are lined up between the nozzle arrangement plane 73l and the surface M1 of the printing medium M, and face the surface M1 of the printing medium M. Each nozzle 76l is in communication with the air blowing chamber 72l, and the hot air supplied to the air blowing chamber 72l is sprayed onto the surface M1 of the printing medium M from the nozzles 76l.

[0046] In this way, the air blowing units 71u and 71l sandwich the printing medium M. In other words, the printing medium M transported by the middle transport section 51m passes between the air blowing units 71u and 71l. In this way, the air blowing dryer 7c dries the printing medium M by spraying hot air from the air blowing units 71u and 71l on both the upper and lower sides toward the printing medium M transported by the middle transport section 51m.

[0047] The upper nozzle 76u faces from above the area between two adjacent lower nozzles 76l in the horizontal direction X, and the lower nozzle 76l faces from below the area between two adjacent upper nozzles 76u in the horizontal direction X. That is, in the horizontal direction X, the upper nozzles 76u and the lower nozzles 76l are alternately arranged at a pitch that is half the predetermined pitch, and are alternately arranged one by one in the horizontal direction X in a plan view from the vertical direction Z. In other words, the nozzles 76u, 76l are arranged in a staggered pattern. This staggered arrangement of the nozzles 76u, 76l is achieved by shifting the positions of the blower chambers 72u, 72l relative to each other in the horizontal direction X.

[0048] 4, in the portion of the printing medium M facing the upper nozzle 76u, the warm air from the nozzle 76u pushes the printing medium M downward, causing it to deviate downward from the transport center line L, and in the portion of the printing medium M facing the lower nozzle 76l, the warm air from the nozzle 76l pushes the printing medium M upward, causing it to deviate upward from the transport center line L. Here, the transport center line L is a horizontal imaginary straight line that is equidistant from the nozzle 76u and the nozzle 76l in the vertical direction Z. Therefore, the printing medium M is transported in the horizontal direction X from one side X1 to the other side X2 while undulating between above and below the transport center line L.

[0049] The blower dryer 7d is disposed downstream of the blower dryer 7c in the traveling direction of the printing medium M transported from the roller 522 toward the air turn bar 541. Similar to the blower dryer 7c, the blower dryer 7d has blower units 71u and 71l that sandwich the printing medium M in the vertical direction Z. In the blower dryer 7d, the blower unit 71u sprays hot air from above onto the back surface M2 of the printing medium M, and the blower unit 71l sprays hot air from below onto the front surface M1 of the printing medium M, thereby drying the printing medium M.

[0050] Similar to the air blower 7a, the air blower 7e has an air blowing unit 71u arranged above the print medium M and multiple rollers 74 that contact the print medium M from below. However, the air blower 7e is arranged relative to the print medium M being transported from the air turn bar 542 to the roller 561. Therefore, multiple nozzles 76u provided in the air blowing unit 71u of the air blower 7e face the print medium M from above as it moves from the air turn bar 542 to the roller 561. Furthermore, the multiple rollers 74 of the air blower 7e contact the print medium M from below as it moves from the air turn bar 542 to the roller 561. In this way, the air blower 7e has multiple nozzles 76u arranged at equal intervals in the horizontal direction X above the print medium M, and multiple rollers 74 (the same number as the nozzles 76u) arranged at equal intervals in the horizontal direction X below the print medium M. 2 and 3, the nozzles 76u and rollers 74 are arranged in a staggered pattern in the horizontal direction X. In this way, in the blower dryer 7e, the multiple rollers 74 support the back surface M2 of the printing medium M from below, while the multiple nozzles 76u spray warm air onto the front surface M1 of the printing medium M from above, thereby drying the printing medium M.

[0051] The blower dryer 7f is disposed downstream of the blower dryer 7e in the traveling direction of the printing medium M transported from the air turn bar 542 toward the roller 561. Similar to the blower dryer 7e, the blower dryer 7f has a plurality of nozzles 76u that face the printing medium M from above and a plurality of rollers 74 that contact the printing medium M from below, the nozzles 76u and rollers 74 being arranged in a staggered pattern in the horizontal direction X. In this way, in the blower dryer 7f, the plurality of rollers 74 support the back surface M2 of the printing medium M from below, while the plurality of nozzles 76u spray warm air from above onto the front surface M1 of the printing medium M, thereby drying the printing medium M.

[0052] Incidentally, the nozzles 76u, 76l described above extend parallel to the horizontal direction Y. In the horizontal direction Y, the width of each nozzle 76u, 76l is wider than the width of the print medium M, and the print medium M is transported so that both ends of the print medium M are located between both ends of the nozzles 76u, 76l. Similarly, each roller 74 extends parallel to the horizontal direction Y. In the horizontal direction Y, the width of each roller 74 is wider than the width of the print medium M, and the print medium M is transported so that both ends of the print medium M are located between both ends of the roller 74.

[0053] The drying device 5 also includes exhaust units 8a and 8b arranged within the drying furnace 6, and each of the exhaust units 8a and 8b exhausts the air within the drying furnace 6 to the outside. The exhaust unit 8a is arranged at the end of the other side X2 of the drying furnace 6, and is located between the blower dryers 7a, 7d, and 7e and the side wall 6a. The exhaust unit 8b is arranged at the end of the one side X1 of the drying furnace 6, and is located between the blower dryers 7b, 7c, and 7f and the side wall 6b. These exhaust units 8a and 8b have a common configuration. The exhaust units 8a and 8b each have four exhaust chambers 81 to 84 arranged in the vertical direction Z. Exhaust chamber 81 is located above the printing medium M transported by upper transport unit 51u, exhaust chamber 82 is located between the printing medium M transported by upper transport unit 51u and the printing medium M transported by middle transport unit 51m, exhaust chamber 83 is located between the printing medium M transported by middle transport unit 51m and the printing medium M transported by lower transport unit 51l, and exhaust chamber 84 is located below the printing medium M transported by lower transport unit 51l. Each of exhaust chambers 81 to 84 exhausts air sucked from the inside of drying furnace 6 to the outside of drying furnace 6.

[0054] FIG. 5 is a block diagram showing a hot air supply unit that supplies hot air to the drying oven. In the figure, the blower dryers 7a to 7f are referred to without distinction as the blower dryer 7, and the exhaust units 8a and 8b are referred to without distinction as the exhaust unit 8. The drying device 5 has the hot air supply unit 9 shown in FIG. 5, which supplies hot air generated by the hot air generator 4 provided separately from the drying device 5 to each blower dryer 7 in the drying oven 6. Each blower dryer 7 then sprays the hot air supplied from the hot air supply unit 9 onto the printing medium M as described above.

[0055] The hot air generator 4 has a heater 41, an outside air introduction pipe 42 that introduces outside air into the heater 41, and a hot air output pipe 43 that outputs the hot air generated by the heater 41 heating the outside air to the hot air supply unit 9. One end of the outside air introduction pipe 42 is an inlet end 421 that opens to outside air at room temperature, and the other end of the outside air introduction pipe 42 is an outlet end 422 connected to the heater 41. One end of the hot air output pipe 43 is an inlet end 431 that is connected to the heater 41, and the other end of the hot air output pipe 43 is an outlet end 432 that outputs hot air.

[0056] The outside air that flows into the outside air introduction pipe 42 from the inlet end 421 flows out from the outlet end 422 to the heater 41. The heater 41 generates hot air by heating the outside air that flows in from the outside air introduction pipe 42 with gas or electricity. The heater 41 heats the outside air so that the temperature detected by a temperature sensor (thermocouple) that detects the temperature of the hot air becomes the temperature indicated by the hot air temperature command Ct. The temperature sensor is disposed outside the drying oven 6 and detects the temperature of the hot air before it flows into the drying oven 6, for example, between a blower 912 (described later) and the drying oven 6. In this way, the hot air generated by the heater 41 flows out from the heater 41 to the hot air output pipe 43 via the inlet end 431. The hot air that flows into the hot air output pipe 43 flows out from the outlet end 432 to the hot air supply unit 9.

[0057] The hot air supply unit 9 has a hot air supply section 91 that supplies the hot air flowing in from the hot air generating device 4 to the blower dryer 7 in the drying furnace 6, a hot air exhaust section 93 that exhausts the hot air exhausted from the exhaust section 8 to the outside of the drying furnace 6, and a hot air recovery section 95 that recovers a portion of the hot air exhausted from the drying furnace 6 to the hot air exhaust section 93 and returns it to the hot air supply section 91.

[0058] The hot air supply unit 91 has a motor damper 911 attached to the outlet end 432 of the hot air output pipe 43, and a hot air supply pipe 92 connecting the motor damper 911 to the blower dryer 7. One end of the hot air supply pipe 92 is an inlet end 921 connected to the motor damper 911. That is, the motor damper 911 is provided between the outlet end 432 of the hot air output pipe 43 and the inlet end 921 of the hot air supply pipe 92. Therefore, the hot air flowing out from the outlet end 432 of the hot air output pipe 43 passes through the motor damper 911 and then flows into the inlet end 921 of the hot air supply pipe 92. The other end of the hot air supply pipe 92 is an outlet end 922 connected to the blower dryer 7.

[0059] Furthermore, the hot air supply unit 91 has a blower 912 attached to the hot air supply pipe 92 between the inlet end 921 and the outlet end 922. The blower 912 drives hot air in the hot air supply pipe 92 to generate an airflow that flows from the inlet end 921 along the hot air supply pipe 92 toward the outlet end 922. As a result, the hot air that flows into the hot air supply pipe 92 from the heater 41 via the motor damper 911 is supplied to the blower dryer 7 by the airflow generated by the blower 912. As a result, the hot air supplied to the blower dryers 7a, 7b, 7e, and 7f is sprayed from the nozzle 76u of the blower chamber 72u, and the hot air supplied to the blower dryers 7c and 7d is sprayed from the nozzles 76u and 76l of the blower chambers 72u and 72l.

[0060] The hot air exhaust section 93 has a hot air exhaust pipe 94 connected to the exhaust section 8. One end of the hot air exhaust pipe 94 is an inlet end 941 connected to the exhaust section 8, and the other end of the hot air exhaust pipe 94 is an outlet end 942 that opens to the outside air. The hot air exhaust section 93 also has a motor damper 931 attached to the hot air exhaust pipe 94 between the inlet end 941 and the outlet end 942. Therefore, hot air that flows into the hot air exhaust pipe 94 from the exhaust chambers 81, 82, 83, and 84 of the exhaust section 8 via the inlet end 941 passes through the motor damper 931 and is then exhausted to the outside air from the outlet end 942 of the hot air exhaust pipe 94.

[0061] The hot air collection section 95 has a hot air recovery pipe 96 that connects the hot air exhaust pipe 94 and the hot air supply pipe 92. One end of the hot air recovery pipe 96 is an inlet end 961 that is connected to the hot air exhaust pipe 94, and the other end of the hot air recovery pipe 96 is an outlet end 962 that is connected to the hot air supply pipe 92. The inlet end 961 is connected to the hot air exhaust pipe 94 between the inlet end 941 and the motor damper 931. The outlet end 962 is connected to the hot air supply pipe 92 between the inlet end 921 and the blower 912. The hot air collection section 95 also has a motor damper 951 attached to the hot air collection pipe 96 between the inlet end 961 and the outlet end 962. Therefore, hot air that flows from the hot air exhaust pipe 94 into the hot air collection pipe 96 via the inlet end 961 passes through the motor damper 951 and is then collected into the hot air supply pipe 92 from the outlet end 962 of the hot air collection pipe 96. The hot air thus collected in the hot air supply pipe 92 is supplied to the blower dryer 7 by the blower 912.

[0062] FIG. 6 is a block diagram showing the electrical configuration of the drying apparatus. As shown in FIG. 6, the warm air supply unit 9 of the drying apparatus 5 has a thermo-hygrometer 99. The thermo-hygrometer 99 is arranged outside the drying oven 6 and detects the temperature It and humidity Im (relative humidity) of the outside air. Note that no hygrometer is arranged inside the drying oven 6. The drying apparatus 5 also has a UI (User Interface) 57. The UI 57 has input devices such as a mouse and a keyboard and an output device such as a display, and accepts user operations via the input devices and outputs information to the user via the output devices. Note that it is not necessary to configure the input device and output device as separate entities; they may be configured integrally using a touch panel display or the like.

[0063] The drying device 5 also includes a control unit 58. The control unit 58 is a processor that executes calculations necessary for controlling the drying device 5. The control unit 58 includes a temperature and humidity acquisition unit 581, motor damper control units 582, 583, and 584, a blower control unit 585, a conveying speed command unit 586, a hot air temperature command unit 587, an image data acquisition unit 588, a UI control unit 589, and a drying condition setting unit 59.

[0064] The temperature and humidity acquisition unit 581 acquires the temperature It and humidity Im of the outside air detected by the thermo-hygrometer 99. The temperature It and humidity Im acquired by the thermo-hygrometer 99 are transmitted to the drying condition setting unit 59.

[0065] The motor damper control unit 582 adjusts the flow rate of hot air flowing from the hot air generator 4 into the hot air supply pipe 92 by controlling the opening degree of the motor damper 911. The motor damper control unit 583 adjusts the flow rate of hot air exhausted from the exhaust unit 8 to the outside air through the hot air exhaust pipe 94 by controlling the opening degree of the motor damper 931. The motor damper control unit 584 adjusts the flow rate of hot air recovered from the hot air exhaust pipe 94 to the hot air supply pipe 92 through the hot air recovery pipe 96 by controlling the opening degree of the motor damper 951. The blower control unit 585 adjusts the flow rate of hot air supplied to the blower dryer 7 through the hot air supply pipe 92 by controlling the rotation speed of the blower 912.

[0066] The transport speed command unit 586 determines the transport speed of the printing medium M in the drying oven 6 and transmits a transport speed command Cv indicating transport of the printing medium M at that transport speed to the transport motor 13. The transport motor 13 is a motor that transports the printing medium M, and is, for example, a winding motor that rotates the winding roll 12. Upon receiving the transport speed command Cv, the transport motor 13 transports the printing medium M at the transport speed indicated by the transport speed command Cv.

[0067] The hot air temperature command unit 587 determines the temperature of the hot air to be supplied to the blower dryer 7, and transmits a hot air temperature command Ct instructing the heater 41 to generate hot air at that temperature. Upon receiving the hot air temperature command Ct, the heater 41 generates hot air at the temperature indicated by the hot air temperature command Ct.

[0068] The image data acquisition unit 588 acquires submission data indicating an image to be printed on the printing medium M by the printing device 3. The submission data is, for example, data in a portable document format (PDF). However, the format of the submission data is not limited to PDF. In other words, the image data acquisition unit 588 can acquire submission data in various commonly used formats. For example, the image data acquisition unit 588 acquires submission data by receiving, from the printing device 3, submission data that has been input to the printing device 3. Alternatively, the image data acquisition unit 588 acquires submission data that the user has input via the UI 57. The submission data acquired by the image data acquisition unit 588 is sent to the drying condition setting unit 59.

[0069] The UI control unit 589 acquires data input by the user via the UI 57. The UI control unit 589 also outputs various information to the user by displaying it on a display or the like.

[0070] The drying condition setting unit 59 sets the drying conditions for drying the print medium M in the drying oven 6. The drying condition setting unit 59 sets the drying conditions based on the outside air humidity Im detected by the thermo-hygrometer 99 and the submitted manuscript data. Next, the setting of the drying conditions will be described.

[0071] Figure 7A is a flowchart showing a first example of determining drying conditions performed by the control unit of the drying device, Figures 7B and 7C are diagrams showing an example of a calculation performed in the flowchart of Figure 7A, and Figures 7D and 7E are diagrams showing an example of a table used to set drying conditions in the flowchart of Figure 7A.

[0072] In step S101, image data acquisition unit 588 acquires submitted data Ds (FIG. 7B). In step S102, drying condition setting unit 59 separates submitted data Ds acquired by image data acquisition unit 588 into image data Dc, Dm, Dy, Dk, and Dw for each color of C (cyan), M (magenta), Y (yellow), K (black), and W (white) (FIG. 7B).

[0073] In step S103, drying condition setting unit 59 calculates a printing rate (%) that indicates the proportion of the area to which ink is applied in the image represented by each of image data Dc, Dm, Dy, Dk, and Dw. In this way, the printing rates (0%, 94%, 95%, 0%, and 100%) for each of the K, C, M, Y, and W images are calculated, as shown in the "Printing Rate (%)" column in FIG. 7C.

[0074] In step S104, the drying condition setting unit 59 calculates drying time correlation values ​​(0, 89.3, 76, 0, and 100) for each of the colors K, C, M, Y, and W by multiplying the printing rate by the drying time ratio. Here, the drying time ratio can be calculated, for example, as the ratio of the time required for a unit amount of ink of each of the colors K, C, M, Y, and W to the time required for a unit amount of ink of W to dry (0.85, 0.95, 0.8, 0.9, and 1). The drying time ratios for each color are input to the UI control unit 589, for example, by the user operating the UI 57, and are stored in advance in the drying condition setting unit 59. The drying time correlation value is a value that correlates with the time required for ink adhering to the printing medium M to dry (ink drying time) to form an image; the longer the ink drying time, the larger the drying time correlation value. In step S105, the drying condition setting unit 59 calculates the sum (265.3) of the drying time correlation values ​​for each color, i.e., the total value.

[0075] In step S106, the drying condition setting unit 59 sets the reference drying conditions based on the sum of the drying time correlation values. In this example, the drying condition setting unit 59 sets the reference transport speed (reference drying conditions) for the printing medium M based on the table of FIG. 7D. Here, the table of FIG. 7D shows the correspondence relationship between the sum of the drying time correlation values ​​and the reference transport speed for the printing medium M. In particular, this table shows the relationship between the sum of the drying time correlation values ​​and the transport speed (reference transport speed) for the printing medium M when the humidity detected by the thermo-hygrometer 99 is the reference humidity (for example, 50%). Based on this table, the drying condition setting unit 59 sets the reference transport speed for the printing medium M lower as the sum of the drying time correlation values ​​increases, in other words, as the ink drying time increases.

[0076] In step S107, the drying condition setting unit 59 sets the drying conditions (conveying speed) based on the reference drying conditions (reference conveying speed) and the humidity Im detected by the thermo-hygrometer 99. That is, the drying condition setting unit 59 sets the conveying speed of the printing medium M by adjusting the reference conveying speed according to the difference between the reference humidity and the humidity Im. Specifically, the higher the humidity Im detected by the thermo-hygrometer 99, the lower the conveying speed of the printing medium M set by the drying condition setting unit 59. Such setting of the conveying speed can be performed, for example, as follows. That is, the drying condition setting unit 59 stores the table of FIG. 7E, which assigns a coefficient that decreases as the difference between the reference humidity and the actual humidity decreases. Then, the drying condition setting unit 59 sets the conveying speed of the printing medium M to the conveying speed obtained by multiplying the reference conveying speed by the coefficient indicated in the table for the humidity Im detected by the thermo-hygrometer 99. Once the drying condition setting unit 59 has set the transport speed of the printing medium M in this manner, the transport speed command unit 586 sends a transport speed command Cv indicating the set transport speed to the transport motor 13. As a result, the printing medium M is transported at the set transport speed.

[0077] In the embodiment described above, hot air generated by heating outside air is supplied into the drying oven 6 by the hot air supply unit 91. The temperature of this hot air is adjusted by the hot air temperature command unit 587 (hot air temperature adjustment unit). Hot air collected from the drying oven 6 to the hot air supply unit 91 by the hot air collection unit 95 is also supplied into the drying oven 6. Inside the drying oven 6, the print medium M, on which an image formed with ink is printed, is transported by the transport unit 51. In particular, the print medium M is transported at a transport speed indicated by a transport speed command Cv output by the transport speed command unit 586. The hot air supplied into the drying oven 6 is then guided toward the print medium M by the blower dryer 7 (hot air guide unit), thereby drying the print medium M. In this configuration, the humidity inside the drying oven 6 is significantly affected by the ink that adheres to the print medium M to form an image and the humidity of the outside air. Therefore, in this embodiment, the outside air humidity Im (outside air data) and input data Ds (print image information) are acquired. The conveying speed command Cv output by the conveying speed command unit 586 (conveying unit) is controlled based on the humidity Im and the input data Ds. As a result, it is possible to dry the print medium M under conditions according to the humidity inside the drying oven 6 without providing a humidity sensor inside the drying oven 6.

[0078] Furthermore, the control unit 58 acquires the printing rate (ink amount reflection value) that reflects the amount of ink adhered to the printing medium M based on the submitted data Ds, and controls the transport speed of the printing medium M based on the humidity Im and the printing rate. By performing control based on the printing rate in this way, it becomes possible to dry the printing medium M under conditions (transport speed of the printing medium M) that correspond to the humidity inside the drying oven 6.

[0079] The control unit 58 also controls the transport speed of the print medium M based on the humidity Im and a drying time correlation value (composite value) that combines the printing rate and a drying time ratio (drying time index value) that corresponds to the drying time of the ink adhered to the print medium M. By performing control based on the drying time correlation value that combines the drying time ratio and the printing rate in this way, it becomes possible to dry the print medium M under conditions that correspond to the humidity inside the drying oven 6.

[0080] Furthermore, the greater the amount of ink reflected by the printing rate (i.e., the higher the printing rate), the lower the conveying speed of the printing medium M. With this configuration, it is possible to dry the printing medium M while conveying the printing medium M at a conveying speed that corresponds to the humidity inside the drying oven 6.

[0081] Furthermore, the longer the drying time indicated by the drying time ratio, the lower the conveying speed of the print medium M. With this configuration, it is possible to dry the print medium M while conveying the print medium M at a conveying speed that corresponds to the humidity inside the drying oven 6.

[0082] FIG. 8A is a flowchart showing a second example of the drying condition determination executed by the control unit of the drying device, and FIGS. 8B and 8C are diagrams schematically showing an example of the calculation executed in the flowchart of FIG. 7A.

[0083] In step S201, the image data acquisition unit 588 acquires gradation data Dg. As shown in FIG. 8B, the gradation data Dg indicates the gradation value of the image to be printed on the printing medium M in multiple stages (for example, 16 stages) for each pixel. This gradation data Dg is acquired for each color of C (cyan), M (magenta), Y (yellow), K (black), and W (white). The image data acquisition unit 588 acquires the gradation data Dg, for example, by receiving the gradation data Dg from the printing device 3. Alternatively, the image data acquisition unit 588 acquires the gradation data Dg input by the user via the UI 57.

[0084] In step S202, the drying condition setting unit 59 performs halftoning on the gradation data Dg acquired by the image data acquisition unit 588. This halftoning is performed using, for example, a threshold matrix. The threshold matrix indicates a threshold value for binarizing the gradation value for each pixel. The drying condition setting unit 59 compares the gradation value of the gradation data Dg with the threshold value of the threshold matrix and performs a calculation for each pixel to binarize the gradation value, thereby obtaining binary data Db. As shown in FIG. 8C, the binary data Db indicates the presence or absence of ink ejection for each pixel. Such binary data Db is obtained for each color of K, C, M, Y, and W.

[0085] In step S203, the drying condition setting unit 59 calculates the ink ejection rate based on the binary data Db. That is, the ejection rate is calculated as the ratio of the number of pixels having ink ejection to the total number of pixels that make up the image. This ejection rate is calculated for each of the colors K, C, M, Y, and W.

[0086] In step S204, drying condition setting unit 59 calculates a drying time correlation value for each of the colors K, C, M, Y, and W by multiplying the discharge rate by the drying time ratio. In step S205, drying condition setting unit 59 calculates the sum of the drying time correlation values ​​for each of the colors K, C, M, Y, and W. The calculations in steps S204 and S205 correspond to the calculation shown in FIG. 7C using the discharge rate instead of the printing rate.

[0087] In step S206, the drying condition setting unit 59 sets the reference drying conditions based on the sum of the drying time correlation values. In step S207, the drying condition setting unit 59 sets the drying conditions (conveying speed) based on the reference drying conditions (reference conveying speed) and the humidity Im detected by the thermo-hygrometer 99. Steps S206 and S207 can be executed, for example, by using a table, similar to steps S106 and S107 above. Then, the conveying speed command unit 586 sends a conveying speed command Cv indicating the conveying speed to the conveying motor 13. As a result, the printing medium M is conveyed at the conveying speed.

[0088] In the embodiment described above, hot air generated by heating outside air is supplied into the drying oven 6 by the hot air supply unit 91. The temperature of this hot air is adjusted by the hot air temperature command unit 587 (hot air temperature adjustment unit). Hot air collected from the drying oven 6 to the hot air supply unit 91 by the hot air collection unit 95 is also supplied into the drying oven 6. Inside the drying oven 6, the print medium M on which an image formed with ink is printed is transported by the transport unit 51. In particular, the print medium M is transported at a transport speed indicated by a transport speed command Cv output by the transport speed command unit 586. The hot air supplied into the drying oven 6 is then guided toward the print medium M by the blower dryer 7 (hot air guide unit), thereby drying the print medium M. In this configuration, the humidity inside the drying oven 6 is significantly affected by the ink that adheres to the print medium M to form an image and the humidity of the outside air. Therefore, in this embodiment, the outside air humidity Im (outside air data) and gradation data Dg (print image information) are acquired. The conveying speed command Cv output by the conveying speed command unit 586 (conveying unit) is controlled based on the humidity Im and the gradation data Dg. As a result, it is possible to dry the print medium M under conditions according to the humidity inside the drying oven 6 without providing a humidity sensor inside the drying oven 6.

[0089] Furthermore, the control unit 58 acquires the ejection rate (ink amount reflection value) that reflects the amount of ink adhered to the printing medium M based on the gradation data Dg, and controls the transport speed of the printing medium M based on the humidity Im and the ejection rate. By performing control based on the ejection rate in this manner, it becomes possible to dry the printing medium M under conditions (transport speed of the printing medium M) that correspond to the humidity inside the drying oven 6.

[0090] The control unit 58 also controls the transport speed of the printing medium M based on the humidity Im and a drying time correlation value (composite value) that combines the drying time ratio (drying time index value) corresponding to the drying time of the ink adhered to the printing medium M and the ejection rate (ink amount reflection value). By performing control based on the composite value of the drying time ratio and the ejection rate in this way, it becomes possible to dry the printing medium M under conditions (transport speed of the printing medium M) that correspond to the humidity inside the drying oven 6.

[0091] Furthermore, the greater the amount of ink reflected by the ejection rate (i.e., the higher the ejection rate), the lower the transport speed of the print medium M. With this configuration, it is possible to dry the print medium M while transporting it at a transport speed that corresponds to the humidity inside the drying oven 6.

[0092] Furthermore, the longer the drying time indicated by the drying time ratio, the lower the conveying speed of the print medium M. With this configuration, it is possible to dry the print medium M while conveying the print medium M at a conveying speed that corresponds to the humidity inside the drying oven 6.

[0093] Fig. 9 is a flowchart showing a third example of the drying condition determination executed by the control unit of the drying device. In the example of Fig. 9, an image to be printed on the print medium M is divided into Ix target areas, and a drying time correlation value is calculated for each target area.

[0094] The drying condition setting unit 59 resets the count value I for identifying the target area to zero (step S301) and increments the count value I by 1 (step S302). Then, the drying condition setting unit 59 calculates the sum of the drying time correlation values ​​of the colors K, C, M, Y, and W for the target area indicated by the count value I (step S303). The method for calculating the sum of the drying time correlation values ​​is the same as in the first or second example. Then, step S303 is executed until the count value I matches the value Ix.

[0095] When the sum of the drying time correlation values ​​for each of the Ix target regions is calculated and the Ix total values ​​are obtained ("YES" in step S304), the drying condition setting unit 59 obtains the maximum value of the Ix total values ​​(step S305). In step S306, the drying condition (the conveying speed of the print medium M) is set from the maximum total value. Specifically, a reference conveying speed is calculated from the maximum total value using a table similar to that in FIG. 7D, and the conveying speed is calculated from the reference conveying speed using a table similar to that in FIG. 7E.

[0096] In this way, the control unit 58 calculates the drying time correlation value for each of the multiple target areas included in the image printed on the print medium M. The control unit 58 then controls the conveying speed of the print medium M based on (the total value of) the drying time correlation value of one target area among the multiple target areas that satisfies the condition (predetermined condition) that the total value of the drying time correlation values ​​of each color is the largest. With this configuration, even if there are localized areas that require a long time to dry, it is possible to dry the print medium M under conditions (the conveying speed of the print medium M) that correspond to the humidity inside the drying oven 6.

[0097] As described above, in this embodiment, the drying oven 6 corresponds to an example of the "drying oven" of the present invention, the printing medium M corresponds to an example of the "printing medium" of the present invention, the conveying unit 51 and the conveying speed command unit 586 correspond to an example of the "conveying unit" of the present invention, the hot air supply unit 91 corresponds to an example of the "hot air supply unit" of the present invention, the hot air temperature command unit 587 corresponds to an example of the "hot air temperature adjustment unit" of the present invention, the blower dryer 7 corresponds to an example of the "hot air guide unit" of the present invention, the hot air collection unit 95 corresponds to an example of the "hot air collection unit" of the present invention, the control unit 58 corresponds to an example of the "control unit" of the present invention, the humidity Im corresponds to an example of the "outside air data" of the present invention, the thermo-hygrometer 99 corresponds to an example of the "outside air data acquisition unit" of the present invention, the submission data Ds or the gradation data Dg corresponds to an example of the "printing image information" of the present invention, the image data acquisition unit 588 corresponds to an example of the "printing image information acquisition unit" of the present invention, and the drying device 5 corresponds to an example of the "drying device" of the present invention.

[0098] The present invention is not limited to the above-described embodiment, and various modifications other than those described above are possible without departing from the spirit of the present invention. For example, the drying conditions set in steps S107, S207, or S306 are not limited to the transport speed of the printing medium M described above.

[0099] For example, the hot air temperature indicated by the hot air temperature command Ct output by the hot air temperature command unit 587 may be set as the drying condition. In this example, the drying condition setting unit 59 sets the hot air temperature indicated by the hot air temperature command Ct higher as the total value of the drying time correlation values ​​increases, in other words, as the ink drying time increases. Furthermore, the drying condition setting unit 59 sets the hot air temperature indicated by the hot air temperature command Ct higher as the humidity Im increases.

[0100] That is, the control unit 58 increases the temperature of the hot air indicated by the hot air temperature command Ct as the amount of ink indicated by the printing rate or ejection rate increases. This makes it possible to dry the print medium M with hot air at a temperature that corresponds to the humidity inside the drying oven 6.

[0101] Furthermore, the longer the drying time indicated by the drying time ratio, the higher the temperature of the hot air indicated by the hot air temperature command Ct, by the control unit 58. With this configuration, it is possible to dry the print medium M with hot air at a temperature according to the humidity inside the drying oven 6.

[0102] Alternatively, the rotation speed of the blower 912 controlled by the blower control unit 585, in other words, the flow rate of hot air supplied by the hot air supply unit 91 into the drying oven 6, may be set as the drying condition. In this example, the drying condition setting unit 59 sets a higher flow rate of hot air supplied by the hot air supply unit 91 into the drying oven 6 as the total value of the drying time correlation values ​​increases, in other words, as the ink drying time increases. Furthermore, the drying condition setting unit 59 sets a higher flow rate of hot air supplied by the hot air supply unit 91 into the drying oven 6 as the humidity Im increases.

[0103] That is, the greater the amount of ink indicated by the printing rate or ejection rate, the greater the flow rate of hot air supplied by the hot air supply unit 91 into the drying oven 6. With this configuration, it is possible to dry the print medium M with hot air at a flow rate that corresponds to the humidity inside the drying oven 6.

[0104] Furthermore, the longer the drying time indicated by the drying time ratio, the greater the flow rate of the hot air supplied by the hot air supply unit 91 into the drying oven 6. With this configuration, it is possible to dry the print medium M with hot air at a flow rate that corresponds to the humidity inside the drying oven 6.

[0105] Alternatively, the opening degree of the motor damper 951 controlled by the motor damper control unit 584, in other words, the flow rate of hot air recovered from the hot air exhaust pipe 94 to the hot air supply pipe 92 via the hot air recovery pipe 96, may be set as the drying condition. In this example, the drying condition setting unit 59 sets a smaller flow rate of hot air recovered from the hot air exhaust pipe 94 to the hot air supply pipe 92 via the hot air recovery pipe 96 as the total value of the drying time correlation values ​​increases. Furthermore, the drying condition setting unit 59 sets a smaller flow rate of hot air recovered from the hot air exhaust pipe 94 to the hot air supply pipe 92 via the hot air recovery pipe 96 as the humidity Im increases.

[0106] That is, the greater the amount of ink indicated by the printing rate or ejection rate, the smaller the flow rate of the hot air collected into the hot air supply pipe 92 via the hot air collection pipe 96. With this configuration, it is possible to dry the print medium M while collecting the amount of hot air corresponding to the humidity inside the drying oven 6 from the drying oven 6 into the hot air supply unit 91.

[0107] Furthermore, the longer the drying time indicated by the drying time ratio, the smaller the flow rate of the hot air collected in the hot air supply pipe 92 via the hot air collection pipe 96. With this configuration, it is possible to dry the printing medium M while collecting the amount of hot air corresponding to the humidity inside the drying oven 6 from the drying oven 6 into the hot air supply unit 91.

[0108] Also, various changes can be made to other objects to be controlled by the control unit 58. For example, the printing rate or the ejection rate may be used as the drying time correlation value without using the drying time ratio.

[0109] As described above, a plurality of (eight in total) air-blowing chambers 72u, 72l are provided in the drying furnace 6 of the drying device 5. Therefore, the hot air supply pipe 92 may have a manifold branching into a plurality of outlet ends 922, and the plurality of outlet ends 922 may be configured to be connected to the plurality of air-blowing chambers 72u, 72l, respectively.

[0110] Furthermore, the specific configuration for supplying hot air to the blower dryers 7a to 7e is not limited to the example using a manifold. That is, the hot air generator 4 and the hot air supply unit 91 may be provided for each of the plurality of blower dryers 7a to 7e.

[0111] As described above, a plurality of exhaust chambers 81, 82, 83, and 84 (eight in total) are provided in the drying furnace 6 of the drying device 5. Therefore, the hot air exhaust pipe 94 may have a manifold branching into a plurality of inlet ends 941, and the plurality of inlet ends 941 may be configured to be connected to the plurality of exhaust chambers 81, 82, 83, and 84, respectively.

[0112] Furthermore, the specific configuration for exhausting hot air from the exhaust chambers 81, 82, 83, and 84 is not limited to the example using a manifold. That is, the hot air exhaust unit 93 may be provided for each of the exhaust chambers 81, 82, 83, and 84.

[0113] Moreover, instead of the thermo-hygrometer 99, a hygrometer that acquires only the humidity Im out of the temperature It and the humidity Im may be provided.

[0114] The arrangement of the rollers 74 in the drying furnace 6 can be changed as appropriate. For example, in the lower conveying section 51l, a blower unit 71l may be arranged instead of the rollers 74.

[0115] Furthermore, the number of ink colors constituting the image printed on the printing medium M is not limited to the above example. In other words, an image made up of ink of a single color or any number of colors can be printed on the printing medium M. [Industrial Applicability]

[0116] The present invention is applicable to all techniques for drying print media on which an image formed with ink has been printed. [Explanation of symbols]

[0117] 5...Drying device 51...Transport unit 58...Control unit 586...Transport speed command unit 587...Hot air temperature command unit 588...Image data acquisition unit 6…Drying oven 7...Air dryer 91...Hot air supply unit 95...Hot air recovery section 99…Thermohygrometer Dg...Gradation data Ds...Submission data Im…Humidity M…Print media

Claims

1. A drying oven, a conveying unit that conveys a print medium on which an image formed by ink is printed within the drying oven; a warm air supply unit that takes in warm air generated by heating outside air that is air outside the drying oven and supplies the warm air into the drying oven; a hot air temperature adjusting unit that adjusts the temperature of the hot air taken in by the hot air supply unit; a hot air guide unit that guides the hot air supplied into the drying oven by the hot air supply unit to the print medium being transported by the transport unit; a hot air recovery unit that recovers the hot air discharged from the drying oven to the hot air supply unit; a control unit that controls at least one of the control targets of the conveying unit, the hot air temperature adjusting unit, and the hot air collecting unit; Equipped with The hot air supply unit supplies the hot air collected by the hot air collection unit into the drying furnace, The control unit includes an outside air data acquisition unit that acquires outside air data indicating at least the amount of water vapor contained in the outside air, and a print image information acquisition unit that acquires print image information regarding the image printed on the printing medium, and the drying device controls the controlled object based on the outside air data and the print image information.

2. The drying device according to claim 1, wherein the control unit acquires an ink amount reflection value that reflects the amount of ink adhered to the printing medium based on the print image information, and controls the controlled object based on the outside air data and the ink amount reflection value.

3. The drying device according to claim 2 , wherein the control unit acquires a printing rate indicating a proportion of an area of ​​the image to which ink is attached as the ink amount reflection value.

4. The drying device according to claim 2 , wherein the control unit acquires the gradation values ​​of each of a plurality of pixels that make up the image from print image information, and acquires the ink amount reflection value based on the result of binarizing the gradation values.

5. A drying device described in any one of claims 2 to 4, wherein the control unit controls the controlled object based on a combined value obtained by combining a drying time index value corresponding to the drying time of the ink adhered to the printing medium and the ink amount reflection value, and the outside air data.

6. The drying device according to claim 5, wherein the control unit calculates the composite value for each of a plurality of target areas included in the image, and controls the control object based on the composite value of one target area among the plurality of target areas that satisfies a predetermined condition.

7. The drying device according to claim 2 , wherein the control unit reduces the speed at which the transport unit transports the print medium as the ink amount reflected by the ink amount reflection value increases.

8. The drying device according to claim 5 , wherein the control unit reduces the speed at which the transport unit transports the print medium as the drying time indicated by the drying time index value becomes longer.

9. The drying device according to claim 2 , wherein the control unit increases the temperature of the hot air adjusted by the hot air temperature adjustment unit as the amount of ink reflected by the ink amount reflection value increases.

10. The drying device according to claim 5 , wherein the control unit increases the temperature of the hot air adjusted by the hot air temperature adjusting unit as the drying time indicated by the drying time index value increases.

11. The control unit controls the hot air supply unit, The drying device according to claim 2 , wherein the control unit increases the flow rate of the hot air supplied into the drying oven by the hot air supply unit as the amount of ink reflected by the ink amount reflection value increases.

12. The control unit controls the hot air supply unit, The drying device according to claim 5 , wherein the control unit increases the flow rate of the hot air supplied by the hot air supply unit into the drying oven as the drying time indicated by the drying time index value becomes longer.

13. The drying device according to claim 2 , wherein the control unit reduces the flow rate of the hot air collected by the hot air collection unit to the hot air supply unit as the amount of ink reflected by the ink amount reflection value increases.

14. The drying device according to claim 5 , wherein the control unit reduces the flow rate of the hot air recovered by the hot air recovery unit to the hot air supply unit as the drying time indicated by the drying time index value becomes longer.

15. a step of conveying the print medium, on which the image formed by ink is printed, through a drying oven by a conveying unit; a step of taking in warm air generated by heating outside air, which is air outside the drying oven, using a warm air supply unit and supplying the warm air into the drying oven; A step of adjusting the temperature of the hot air taken in by the hot air supply unit by a hot air temperature adjustment unit; a step of guiding the hot air supplied into the drying oven by the hot air supply unit to the print medium being transported by the transport unit by a hot air guide unit; A step of recovering the hot air discharged from the drying furnace to the hot air supply unit by a hot air recovery unit; a step of controlling at least one of the control targets of the conveying unit, the hot air temperature adjusting unit, and the hot air collecting unit by a control unit; Equipped with The hot air supply unit supplies the hot air collected by the hot air collection unit into the drying furnace, The control unit has an outside air data acquisition unit that acquires outside air data indicating at least the amount of water vapor contained in the outside air, and a print image information acquisition unit that acquires print image information regarding an image printed on the printing medium, and a drying method that controls the controlled object based on the outside air data and the print image information.

Images