Drying equipment

Abstract

To provide a drying device capable of automatically adjusting a recycle rate so that a solvent concentration falls within a predetermined range and capable of obtaining uniform print quality. [Solution] The present invention relates to a drying device 1 that dries ink. The drying device 1 includes a drying chamber 2, a solvent concentration detection unit 3, multiple ducts 10, multiple dampers 20, and a control unit 5. The multiple ducts 10 include an air supply duct 11, an exhaust duct 12, and an exhaust recirculation duct 13. The multiple dampers 20 include a fresh air volume adjustment damper 26, an exhaust volume adjustment damper 27, and a recirculation volume adjustment damper 28. The control unit 5 adjusts the opening degree of each of the fresh air volume adjustment damper 26, the exhaust volume adjustment damper 27, and the recirculation volume adjustment damper 28 in stages until the solvent concentration detected by the solvent concentration detection unit 3 falls within a preset range.

Description

[Technical Field]

[0001] The present invention relates to a drying device. [Background technology]

[0002] Conventionally, drying devices that dry ink coated on a continuously transported long web have been known for use in printing devices such as gravure printing. Patent Document 1 below also proposes a drying device that recirculates a portion of the exhaust air discharged from a drying chamber back into the drying chamber. Such drying devices have the advantage of being able to effectively utilize the thermal energy remaining in the exhaust air, thereby reducing running costs such as utility expenses.

[0003] In the drying device of Patent Document 1, the opening of a return flow rate adjusting damper or the like is controlled according to the area ratio of the printed pattern, and the recycle rate (the ratio of the amount of air returned from the exhaust return duct to the amount of air supplied to the drying chamber) is adjusted. On the other hand, in this drying device, an operator determines the area ratio of the printed pattern and then inputs it into the device. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-237548 Summary of the Invention [Problem to be solved by the invention]

[0005] The drying device of Patent Document 1 has the problem that the operator has to input the area ratio, which is cumbersome, and there has been a demand for automation. Furthermore, simply automatically controlling the return flow rate adjustment damper according to the solvent concentration in order to maintain a constant solvent concentration in the air exhausted from the drying chamber can disrupt the balance between the air supply and exhaust in the drying chamber, resulting in uneven print quality (particularly the quality of ink drying).

[0006] The present invention was devised in consideration of the above-described circumstances, and its main object is to provide a drying device that can automatically adjust the recycle rate so that the solvent concentration falls within a predetermined range, and that can obtain uniform print quality. [Means for solving the problem]

[0007] The present invention relates to a drying device for drying ink coated on the surface of a continuously transported long web, the drying device including: a drying chamber through which the web passes and into which drying air is supplied and discharged; a solvent concentration detection unit for detecting the solvent concentration of the air discharged from the drying chamber; a plurality of ducts serving as air passages; a plurality of dampers disposed inside the ducts and for adjusting the amount of air passing through; and a control unit for controlling the plurality of dampers, the plurality of ducts including an air supply duct communicating with the drying chamber to supply air to the drying chamber, an exhaust duct communicating with the drying chamber to exhaust air from the drying chamber, and an exhaust recirculation duct communicating with the exhaust duct and the air supply duct; and the plurality of dampers are arranged between the air supply duct and the air supply duct. a fresh air volume adjustment damper that is arranged in the air supply duct upstream of the communication portion between the exhaust duct and the exhaust recirculation duct and adjusts the volume of fresh air supplied to the drying chamber side; an exhaust volume adjustment damper that is arranged in the exhaust duct downstream of the communication portion between the exhaust duct and the exhaust recirculation duct and adjusts the volume of air discharged to the outside; and a recirculation volume adjustment damper that is arranged in the exhaust recirculation duct and adjusts the volume of air recirculated from the exhaust duct side to the air supply duct side, and the control unit adjusts the opening degrees of the fresh air volume adjustment damper, the exhaust volume adjustment damper, and the recirculation volume adjustment damper in a stepwise manner until the solvent concentration detected by the solvent concentration detection unit falls within a predetermined range.

[0008] In the drying apparatus of the present invention, it is preferable that the adjustment dampers, which include the fresh air volume adjustment damper, the exhaust volume adjustment damper, and the reflux volume adjustment damper, are each adjusted by the control unit to one of a first opening degree, a second opening degree, a third opening degree, and a fourth opening degree, which are preset, and that the control unit selects one of the following settings depending on the solvent concentration: a first setting in which each of the adjustment dampers is set to the first opening degree, a second setting in which each of the adjustment dampers is set to the second opening degree, a third setting in which each of the adjustment dampers is set to the third opening degree, and a fourth setting in which each of the adjustment dampers is set to the fourth opening degree.

[0009] In the drying device of the present invention, it is desirable that the recycle rate, which is the ratio of the amount of air recirculated from the exhaust gas recirculation duct side to the amount of air supplied to the drying chamber, has a relationship of the first setting < the second setting < the third setting < the fourth setting, and that the control unit sets the recycle rate to the first setting at the start of operation, and when the solvent concentration falls below the range, changes the setting to the second setting, the third setting, and the fourth setting in that order.

[0010] In the drying device of the present invention, it is preferable that the control unit changes the setting of the recycle rate to a smaller value when the solvent concentration exceeds the range during normal operation.

[0011] In the drying apparatus of the present invention, it is preferable that the control unit, after confirming that the solvent concentration has deviated from the range for a certain period of time, adjusts the opening degrees of the fresh air volume adjustment damper, the exhaust volume adjustment damper, and the reflux volume adjustment damper in a stepwise manner.

[0012] In the drying device of the present invention, it is desirable that the control unit issues an alarm when the solvent concentration exceeds a first threshold value set higher than the range, and stops operation of the device when the solvent concentration exceeds a second threshold value set higher than the first threshold value. [Effects of the Invention]

[0013] By adopting the above-described features, the drying device of the present invention can automatically adjust the recycle rate so that the solvent concentration falls within a predetermined range, and can also obtain uniform print quality. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a perspective view schematically illustrating the appearance of a drying device according to an embodiment of the present invention. [Figure 2] 1 is a schematic configuration diagram of a drying device according to an embodiment of the present invention; [Figure 3] FIG. 4 is a graph showing the change over time in solvent concentration C and recycle rate Re when the drying device of the present embodiment is operated. [Figure 4] FIG. 4 is a graph showing the time changes of the solvent concentration C and the recycle rate Re in a control mode different from that in FIG. 3. [Figure 5] 4 is a flowchart showing a control method for the drying device according to the present embodiment. [Figure 6] 6 is a flowchart of a print preparation process in FIG. 5. [Figure 7] FIG. 10 is a schematic configuration diagram of a drying device according to another embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0015] An embodiment of the present invention will be described below with reference to the drawings. The drawings are intended to illustrate the features of the present invention, but may include exaggerated representations and representations that differ from the dimensional ratios of the actual structure to facilitate understanding of the present invention. Furthermore, identical or common elements are designated by the same reference numerals throughout the embodiments, and redundant explanations will be omitted. Furthermore, well-known configurations may be appropriately adopted for configurations not described in this specification.

[0016] FIG. 1 is a perspective view schematically illustrating the exterior of a drying apparatus 1 according to this embodiment. FIG. 1 also illustrates a state in which an air supply duct 11, an exhaust duct 12, and the like (described later) are arranged in a ceiling 7 of a factory, and a drying chamber 2 communicating with these ducts is arranged. FIG. 2 is a schematic diagram illustrating the configuration of the drying apparatus 1 according to this embodiment. As shown in FIGS. 1 and 2, the drying apparatus 1 according to this embodiment is used in a printing apparatus for performing gravure printing or the like to dry ink applied to the surface of a continuously conveyed long web (not shown). The web is configured as a film made of, for example, a plastic material, but the web of the present invention is not limited to such a material.

[0017] As shown in FIG. 2, the drying device 1 of this embodiment includes a drying chamber 2, a solvent concentration detection unit 3, multiple ducts 10, multiple dampers 20, and a control unit 5 that controls the multiple dampers 20. The web passes through the drying chamber 2, and air is supplied and exhausted to dry the ink coated on the web. The ink used here is a solvent in which solid components are dissolved. After the ink is coated on the web, the solvent volatilizes, causing the solid components to adhere to the surface of the web. Therefore, the air exhausted from the drying chamber 2 contains solvent.

[0018] The solvent concentration detection unit 3 detects the solvent concentration of the air discharged from the drying chamber 2. In addition to toluene, substances constituting the solvent may include ethyl acetate, propyl acetate, propanol, IPA, PGME, etc., but the solvent concentration detection unit 3 of this embodiment detects the combined solvent concentration of these substances. The LEL concentration is used as an indicator of the detected concentration. LEL stands for Lower Explosive Limit. The LEL concentration refers to a concentration expressed as a ratio to the LEL. For example, the LEL of toluene is 1.2 vol%, and stating that "the LEL concentration of toluene in a certain air is 50%" means that "the concentration of toluene in the air is 0.6 vol%." In this embodiment, the LEL of the solvent of the ink used is determined in advance through various tests, and the solvent concentration detection unit 3 can detect the LEL concentration of the solvent in the air discharged from the drying chamber 2.

[0019] A well-known sensor is appropriately employed for the solvent concentration detection unit 3. In this embodiment, a catalytic combustion type sensor is employed as the solvent concentration detection unit 3. This type of sensor is inexpensive compared to other types, which helps reduce the cost of the device. However, the solvent concentration detection unit 3 is not limited to this type of sensor, and various types of sensors, such as an infrared type sensor or an optical interference type sensor, can also be employed. Note that these sensors are used after being appropriately calibrated according to the main component of the solvent to be detected.

[0020] The multiple ducts 10 are cylindrical bodies that can serve as air passages, and are schematically shown by solid lines in FIG. 2. The multiple ducts 10 include an air supply duct 11, an exhaust duct 12, and an exhaust recirculation duct 13. One end 11a of the air supply duct 11 is disposed in a location where fresh air can be drawn in, and the other end 11b is connected to the drying chamber 2. This allows the air supply duct 11 to supply air to the drying chamber 2. The air supply duct 11 of this embodiment is provided with a heater 31 that heats air, and an air supply fan 32 that pressurizes and delivers the heated air. Well-known configurations may be used for these as appropriate.

[0021] The exhaust duct 12 has one end 12a connected to the drying chamber 2 and the other end 12b located outside the drying chamber 2 so that air can be discharged therefrom. The exhaust duct 12 of this embodiment has two ends 12a, which connect to two sections of the drying chamber 2 (for example, the upstream and downstream sides of the continuously transported web). That is, the exhaust duct 12 of this embodiment includes a first duct section 16 connected to the drying chamber 2 and a second duct section 17 connected to the drying chamber 2 at a location different from the first duct section 16. The first duct section 16 and the second duct section 17 merge midway. The first duct section 16 and the second duct section 17 are each provided with a separate damper 22. However, the present invention is not limited to this configuration.

[0022] The exhaust recirculation duct 13 communicates with the exhaust duct 12 and the air supply duct 11, and can guide a portion of the air passing through the exhaust duct 12 to the air supply duct 11. The exhaust recirculation duct 13 communicates with the air supply duct 11, for example, upstream of the air supply fan 32 and the heater 31. The exhaust recirculation duct 13 also communicates with the exhaust duct 12 downstream of the first duct portion 16 and the second duct portion 17 of the exhaust duct 12.

[0023] A plurality of dampers 20 are disposed inside various types of ducts 10 for use. The dampers 20 include fixed dampers 21 for suppressing air pressure loss and adjustment dampers 25 for adjusting the amount of air passing through the duct 10. The fixed dampers 21 are disposed, for example, upstream of the adjustment dampers 25, and in this embodiment, well-known fixed dampers are used as appropriate. The adjustment dampers 25 can select any opening degree between 0% (fully closed state) and 100% (fully open state) of the duct 10. Note that even in the fully closed state, slight air movement may occur depending on the pressure difference between the two regions on either side of the adjustment damper 25.

[0024] The dampers 20 (particularly, the adjustment dampers 25) include a fresh air volume adjustment damper 26, an exhaust volume adjustment damper 27, and a return volume adjustment damper 28. The fresh air volume adjustment damper 26 is disposed in the air supply duct 11 upstream of the communication between the air supply duct 11 and the exhaust recirculation duct 13. The fresh air volume adjustment damper 26 can adjust the volume of fresh air supplied to the drying chamber 2. The exhaust volume adjustment damper 27 is disposed in the exhaust duct 12 downstream of the communication between the exhaust duct 12 and the exhaust recirculation duct 13. The exhaust volume adjustment damper 27 can adjust the volume of air discharged to the outside. The return volume adjustment damper 28 is disposed in the exhaust recirculation duct 13. The return volume adjustment damper 28 can adjust the volume of air recirculated from the exhaust duct 12 to the air supply duct 11.

[0025] In FIG. 2, the direction of travel of air passing through the inside of the duct 10 is indicated by arrows A1 to A5. As shown in FIG. 2, in this embodiment, fresh air entering from the end 11a of the air supply duct 11 passes through the air supply duct 11 (see arrow A1), and then passes through the heater 31 and the air supply fan 32, and is supplied to the drying chamber 2. This promotes drying of the ink on the web in the drying chamber 2. In addition, air exhausted from the drying chamber 2 passes through the exhaust duct 12 (see arrows A2, A3, and A4) and is exhausted to the outside. A portion of the air passing through the exhaust duct 12 passes through the exhaust recirculation duct 13 (see arrow A5) and is returned to the air supply duct 11. This makes it possible to effectively utilize the thermal energy remaining in the exhaust air, thereby reducing utility costs, etc.

[0026] A higher recycle rate, which is the ratio of the amount of air recirculated from the exhaust recirculation duct 13 to the amount of air supplied to the drying chamber 2, can improve the effect of reducing utility costs, etc. However, as the recycle rate increases, the solvent concentration in the air discharged from the drying chamber 2 increases. For this reason, the drying device 1 is required to increase the recycle rate while keeping the solvent concentration within an appropriate range.

[0027] The control unit 5 of this embodiment adjusts the opening degrees of the fresh air volume adjustment damper 26, the exhaust volume adjustment damper 27, and the reflux volume adjustment damper 28 in stages until the solvent concentration detected by the solvent concentration detection unit 3 falls within a preset range. In FIG. 2, the electrical connection between the control unit 5 and the adjustment dampers 25 is indicated by two-dot chain lines. Here, the phrase "adjusting the opening degrees of each in stages" refers to selecting and adjusting each of the three adjustment dampers 25 from among a plurality of opening degrees preset in stages. The control unit 5 of this embodiment can adjust the opening degrees of the adjustment dampers 25 via the electro-pneumatic converter 9, but this is not limited to this.

[0028] As a result, the drying device 1 of this embodiment can automatically adjust the recycle rate so that the solvent concentration falls within a predetermined range. Also, because the opening degrees of the fresh air volume adjustment damper 26, the exhaust volume adjustment damper 27, and the return volume adjustment damper 28 are adjusted in stages, the balance between the air supply and exhaust (hereinafter referred to as "air supply / exhaust balance") in the drying chamber 2 is less likely to be disrupted, and uniform print quality can be obtained.

[0029] A more detailed configuration of this embodiment will be described below. In this embodiment, the three adjustment dampers 25 are each adjusted by the control unit 5 to one of the preset first, second, third, and fourth opening degrees depending on the recycling rate to be achieved. In a more preferable embodiment, the three adjustment dampers 25 can also be adjusted to a fifth opening degree. Table 1 below shows an example of the first to fifth opening degrees for the three adjustment dampers 25.

[0030] [Table 1]

[0031] As shown in Table 1, the first opening degree of the fresh air volume control damper 26 is 55%. The first opening degree of the exhaust volume control damper 27 is 70%. The first opening degree of the return volume control damper 28 is 0%. These opening degree values ​​indicate the ratio when the fully closed state of the corresponding duct is 0% and the fully open state is 100%. Also, as mentioned above, even if the first opening degree is the same, the actual opening degree varies depending on the damper. Also, the "recycle rate" in Table 1 means the guideline recycle rate that can be expected to be achieved when the three control dampers 25 are adjusted to each opening degree.

[0032] The control unit 5 selects one of the first to fifth settings shown in the top row of Table 1 according to the detected solvent concentration. As shown in Table 1, the first setting is a setting in which each of the three adjustment dampers 25 is set to the first opening degree shown in Table 1. The second setting is a setting in which each of the three adjustment dampers 25 is set to the second opening degree shown in Table 1. The same applies to the third to fifth settings.

[0033] For example, in the first setting, the first opening degree of each of the three adjustment dampers 25 is set so that uniform print quality can be continuously obtained without disrupting the supply / discharge balance when the device is operated with a recycle rate of approximately 0%. Similarly, in the second setting, the second opening degree of each of the three adjustment dampers 25 is set so that uniform print quality can be continuously obtained without disrupting the supply / discharge balance when the device is operated with a recycle rate of approximately 20%. The same applies to the third to fifth settings. Note that the specific opening degrees of each adjustment damper 25 can be determined appropriately based on, for example, prior testing. Therefore, the numerical values ​​of each opening degree shown in Table 1 are merely examples.

[0034] The control aspects of the drying device 1 of this embodiment will be described below using graphs. FIG. 3 shows graphs illustrating the changes over time in the solvent concentration C and the recycle rate Re when the drying device 1 is operated. In FIG. 3, the horizontal axis represents time t, and the vertical axis represents the magnitude of the solvent concentration C or the recycle rate Re. The left vertical axis has a numerical value (%) indicating the magnitude of the solvent concentration C. The solvent concentration here refers to the aforementioned LEL concentration. The right vertical axis has a numerical value (%) indicating the magnitude of the recycle rate Re. Graph Ga (shown by a solid line) shows the change in the recycle rate Re. Graph Gb (shown by a two-dot chain line) shows the change in the solvent concentration C.

[0035] In Figure 3, region Z1 is a state in which the web is not being transported and the drying device is on standby (hereinafter referred to as the "standby state"). Region Z2 is a state in which the device has started and is increasing the web transport speed (hereinafter referred to as the "speed-up state"). Region Z3 is a state in which the web transport speed is constant (hereinafter referred to as the "constant speed state").

[0036] 3, in the standby state (area Z1), the recycle rate Re is kept high in order to reduce utility costs. Therefore, the control unit 5 sets the opening of the adjustment damper 25 to the fourth setting described above, for example. Furthermore, when the speed-up state (area Z2) is entered, the solvent concentration in the drying chamber 2 may rise suddenly. To prevent this, the control unit 5 sets the opening of each adjustment damper 25 to the first setting described above in order to set the recycle rate Re to 0.

[0037] Then, when the constant speed state (region Z3) is entered, the control unit 5 adjusts the setting in stages so that the solvent concentration C falls within a preset range. Note that, by law, equipment for drying ink such as that in this embodiment is required to ensure that the LEL concentration of the solvent does not exceed 30%. Therefore, in this embodiment, the solvent concentration C (LEL concentration) is set to a range of 15% to 25%. In FIG. 3, the area where dots are applied corresponds to this range.

[0038] In the initial constant speed state, the device is operated at the first setting (recycle rate = 0%). In this state, if the solvent concentration C remains below the range for a certain period of time (see Gb1), the control unit 5 changes the opening of each adjustment damper 25 from the first setting to the second setting (recycle rate = 20%) (see Ga1 and Ga2). Accordingly, the solvent concentration C also increases and approaches the range.

[0039] If the solvent concentration C remains below the range for a certain period of time (see Gb2) even after changing the settings as described above, the control unit 5 changes the opening of each adjustment damper 25 from the second setting to the third setting (recycle rate = 40%) (see Ga3 and Ga4). Accordingly, the solvent concentration C increases further and approaches the range described above.

[0040] Furthermore, even if the settings are changed as described above, if the solvent concentration C remains below the range for a certain period of time (see Gb3), the control unit 5 changes the opening of each adjustment damper 25 from the third setting to the fourth setting (recycle rate = 60%) described above (see Ga5). As a result, the solvent concentration C increases further, and falls within the range (see Gb4). In this embodiment, since the solvent concentration C falls within the range at the fourth setting, the device continues to operate in this state, and the fifth setting is not used. For example, if the solvent concentration C needs to be maintained higher, the fifth setting may be used.

[0041] As described above, in this embodiment, the expected recycle rates for the first to fifth settings have the following relationship: first setting < second setting < third setting < fourth setting < fifth setting. The control unit 5 sets the first setting when the device starts operating, and changes the setting to the second setting, the third setting, and the fourth setting in that order if the solvent concentration C falls below the range. Although not shown in FIG. 3, during normal operation, if the solvent concentration C exceeds the range, the control unit 5 changes the setting to a lower recycle rate so that the solvent concentration C falls within the range.

[0042] In this way, the drying device 1 of this embodiment can automatically adjust the recycle rate so that the solvent concentration C falls within a predetermined range. Furthermore, as described above, each adjustment damper 25 is adjusted in stages, so that the supply and discharge balance within the drying chamber 2 is appropriately maintained, and uniform print quality can be obtained.

[0043] In a preferred embodiment, the control unit 5 of this embodiment changes the setting step by step. In other words, control such as suddenly changing from the first setting to the fifth setting is not performed. This makes it possible to reliably maintain the supply / discharge balance. From a similar perspective, when changing the opening of each adjustment damper 25, the control unit 5 gradually changes the opening over, for example, 5 to 15 seconds (see Ga1 and Ga3 in FIG. 3).

[0044] Furthermore, after changing the setting by one step, the control unit 5 detects the solvent concentration C for a certain period of time (for example, 5 to 15 seconds) and then determines whether to change the setting further. That is, after confirming that the solvent concentration C has been outside the range for a certain period of time, the control unit 5 adjusts the opening degree of each adjustment damper 25 in a stepwise manner. This gradually changes the recycle rate, making it possible to prevent a sudden change in the solvent concentration C.

[0045] FIG. 4 is a graph similar to FIG. 3, but shows a different control mode from the one described above. As shown in FIG. 4, in this control, the LEL concentration is narrowly set to 20% to 25% for the range (the dotted area). In this control mode, the solvent concentration C (graph Gb) is below the range at the fourth setting (see Ga6 and Ga7 in FIG. 4), and exceeds the range at the fifth setting (see Ga8 and Ga9 in FIG. 4). As a result, the control unit 5 repeatedly alternates between the fourth setting and the fifth setting (this state is hereinafter referred to as the "hunting state").

[0046] To avoid this hunting state, it is desirable to set the range of the solvent concentration C to a fairly wide range, approximately 10 to 15 points in terms of LEL concentration (%). From another perspective, for example, the number of stages of the opening setting for each adjustment damper 25 may be increased. In the example of FIG. 4, a hunting state occurs between the fourth setting and the fifth setting. For this reason, for example, it is conceivable to provide a separate setting for the opening of each adjustment damper 25, which is between a fourth opening corresponding to the fourth setting and a fifth opening corresponding to the fifth setting. This allows the opening of the adjustment damper 25 to be set more precisely, making it possible to avoid the hunting state.

[0047] The drying apparatus 1 may experience a sudden increase in solvent concentration, particularly at the start of operation. To prepare for this, the control unit 5 of this embodiment issues an alarm when the solvent concentration exceeds a first threshold value set higher than the above-mentioned range. Furthermore, the control unit 5 stops operation of the apparatus when the solvent concentration exceeds a second threshold value set higher than the first threshold value. This further improves the safety of the apparatus. The first and second threshold values ​​are determined appropriately depending on the manner in which the apparatus is used. As an example, in this embodiment, the first threshold value is set to an LEL concentration of 40%, and the second threshold value is set to an LEL concentration of 50%.

[0048] The control method for the drying device 1 of this embodiment will be described below with reference to the flowchart shown in FIG. 5. As shown in FIG. 5, in this control method, first, a print preparation step Sa is performed. FIG. 6 shows a detailed flowchart of the print preparation step Sa. As shown in FIG. 6, in the print preparation step Sa, the air intake fan 32 (shown in FIG. 2) is turned off and each adjustment damper 25 (shown in FIG. 2) is set to 0% (see step Sa1). Then, the air intake fan 32 is turned on and each adjustment damper 25 is set to a high recycle rate (for example, the fourth or fifth setting) (see step Sa2). Note that the web remains stationary at this stage. The device is operated in this state for approximately 10 to 20 seconds. Note that step Sa2 corresponds to area Z1 in the graph of FIG. 3.

[0049] Thereafter, printing begins, the impression cylinder is lowered, and the web conveying speed is increased (see step Sa3). Also, each adjustment damper 25 is set to a low recycle rate (for example, the first setting) (see step Sa4). Note that steps Sa3 and Sa4 correspond to region Z2 in the graph of FIG. 3. After that, once the web conveying speed stabilizes (see step Sa5), it enters region Z3 in the graph of FIG. 3, and automatic control begins (see step Sb1 in FIG. 5).

[0050] As shown in FIG. 5, in step Sb1, if the solvent concentration C detected by the solvent concentration detector 3 is equal to or less than 40% LEL (C≦40%), the process proceeds to normal control (step Sc1, described below). Otherwise, an alarm is issued (step Sb2). Subsequently, a low recycle rate setting (e.g., the first setting) is selected, and the solvent concentration C is detected again (see step Sb3). If the solvent concentration C is equal to or less than 40%, the alarm is reset (see step Sb4), and the process returns to normal processing. On the other hand, if the solvent concentration C exceeds 40% in step Sb3, a determination is made as to whether the solvent concentration C exceeds 50% (see step Sb5). If it exceeds 50%, operation is stopped (see step Sb6), and the process restarts from the print preparation step Sa (particularly step Sa2). In these steps, a solvent concentration of 40% corresponds to the first threshold, and a solvent concentration of 50% corresponds to the second threshold.

[0051] In step Sb1, if the solvent concentration C is equal to or less than 40% LEL concentration (C≦40%), it is determined in step Sc1 whether the solvent concentration C is within a preset range. As shown in FIG. 3, in this embodiment, the solvent concentration C is controlled to be within the LEL concentration range of 15% to 25%. Therefore, as shown in FIG. 5, it is determined in step Sc1 whether "15%≦C≦25%."

[0052] In step Sc1, if the solvent concentration C is not within the range, it is further determined whether the solvent concentration C is below the lower limit of the range (C<15%) or above the upper limit of the range (C>25%) (see step Sc2). If the solvent concentration C is below the lower limit (C<15%), there is room for increasing the recycle rate, so the settings of the adjustment dampers 25 are changed to increase the recycle rate (see step Sc3). Conversely, if the solvent concentration C is above the upper limit (C>25%), it is necessary to decrease the recycle rate. Therefore, the settings of the adjustment dampers 25 are changed to decrease the recycle rate (see step Sc4). In step Sc1, as described above, the solvent concentration C is determined after a certain period of time has elapsed.

[0053] After step Sc3 or step Sc4 is performed, the process returns to step Sc1 and similar control is performed. If the solvent concentration is stable and printing is to continue, the above-mentioned control is performed in a loop (see step Sc5). If printing is to end, a printing end step Sd is performed and printing ends. In the printing end step Sd, well-known steps are performed, such as fully opening each adjustment damper 25 to perform a purge operation, then fully closing each adjustment damper 25 and turning off the air supply fan 32.

[0054] FIG. 7 shows a schematic diagram illustrating another embodiment of the drying apparatus 1 of the present invention. As shown in FIG. 7, this embodiment does not include the heater 31 shown in FIG. 2. In this embodiment, high-temperature air (hereinafter referred to as hot air) is supplied from the hot air generating furnace 35, and fresh air is also supplied from a separate route. The hot air and fresh air are mixed by the temperature control damper 23 in the mixing duct 18, thereby controlling the air temperature. Note that the hot air generating furnace 35 has a lower limit for the amount of heat it can control, and the amount of heat cannot be reduced below that limit. For this reason, this embodiment is provided with a bypass damper 24 for directly discharging the hot air from the hot air generating furnace 35, thereby controlling the temperature of the air supplied to the drying chamber 2.

[0055] Although a particularly preferred embodiment of the present invention has been described in detail above, the present invention is not limited to the illustrated embodiment and can be modified and implemented in various ways. [Industrial Applicability]

[0056] As described above, the present invention is useful as a drying device. [Explanation of symbols]

[0057] 2 Drying room 3 Solvent concentration detector 5. Control section 10 Duct 11 Air supply duct 12 Exhaust duct 13 Exhaust return duct 20 Damper 26 New air volume control damper 27 Exhaust volume control damper 28 Damper for adjusting reflux amount

Claims

1. A drying device that dries ink coated on a surface of a continuously transported long web, comprising: a drying chamber through which the web passes and into which the drying air is supplied and exhausted; a solvent concentration detection unit that detects the solvent concentration of the air discharged from the drying chamber; Multiple ducts that serve as air passages; a plurality of dampers disposed inside the duct and adjusting the amount of air passing through; a control unit that controls the plurality of dampers, The plurality of ducts are an air supply duct communicating with the drying chamber to supply air to the drying chamber; an exhaust duct communicating with the drying chamber and discharging air from the drying chamber; an exhaust gas recirculation duct communicating with the exhaust gas duct and the air supply duct; The plurality of dampers include: a fresh air volume adjusting damper that is disposed in the air supply duct upstream of a communication portion between the air supply duct and the exhaust gas recirculation duct and that adjusts the volume of fresh air supplied to the drying chamber; an exhaust amount adjustment damper that is disposed in the exhaust duct downstream of a communication portion between the exhaust duct and the exhaust recirculation duct and that adjusts the amount of air discharged to the outside; a return flow rate adjusting damper that is disposed in the exhaust gas return duct and adjusts the amount of air returned from the exhaust gas duct side to the air supply duct side, the control unit adjusts the opening degrees of the fresh air amount adjustment damper, the exhaust amount adjustment damper, and the reflux amount adjustment damper in a stepwise manner until the solvent concentration detected by the solvent concentration detection unit falls within a preset range; each of the adjustment dampers consisting of the fresh air volume adjustment damper, the exhaust volume adjustment damper, and the recirculation volume adjustment damper is adjusted by the control unit to any one of a first opening degree, a second opening degree, a third opening degree, and a fourth opening degree that are preset; The control unit, depending on the solvent concentration, a first setting for setting each of the adjustment dampers to the first opening degree; a second setting for setting each of the adjustment dampers to the second opening degree; a third setting for each of the adjustment dampers to the third opening degree; and a fourth setting in which each of the adjustment dampers is set to the fourth opening degree; a recycle rate, which is a ratio of an amount of air recirculated from the exhaust gas recirculation duct side to an amount of air supplied to the drying chamber, has a relationship of the first setting < the second setting < the third setting < the fourth setting; the control unit sets the setting to the first setting at the start of operation, and when the solvent concentration falls below the range, changes the setting to the second setting, the third setting, and the fourth setting in this order; drying equipment.

2. A drying device as described in Claim 1, wherein the control unit changes the setting to a smaller recycling rate when the solvent concentration exceeds the range during normal operation.

3. A drying device as described in claim 1 or 2, wherein the control unit, after confirming that the solvent concentration has deviated from the range for a certain period of time, gradually adjusts the opening degree of each of the fresh air volume adjustment damper, the exhaust volume adjustment damper, and the return volume adjustment damper.

4. The control unit issuing an alarm when the solvent concentration exceeds a first threshold value set higher than the range; The drying device according to claim 1 or 2, wherein operation of the device is stopped when the solvent concentration exceeds a second threshold value that is set higher than the first threshold value.

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