Patent Publication Number: US-11390050-B2

Title: Sheet drying device and method, and box making machine

Description:
RELATED APPLICATIONS 
     The present application is a National Phase of International Application Number PCT/JP2017/046305 filed Dec. 25, 2017 and claims priority to Japanese Application Number 2017-024079 filed Feb. 13, 2017. 
     TECHNICAL FIELD 
     The present invention relates to sheet drying device and method of drying a sheet such as a printed corrugated fiberboard or a printed sheet, and a box making machine provided with the sheet drying device. 
     BACKGROUND ART 
     For example, a general box making machine makes a box body (a corrugated box) by processing a sheet material (for example, a corrugated fiberboard) and is composed of a sheet feeding section, a printing section, a slotter creaser section, a die-cut section, a folding section (a folder gluer), and a counter-ejector section. In this box making machine, after printing is performed on the corrugated fiberboard in the printing section, in the slotter creaser section, creasing lines are formed in the printed corrugated fiberboard and grooving processing or gluing margin strip processing is performed on the printed corrugated fiberboard, and then, in the die-cut section, punching processing is carried out. 
     At this time, if drying of ink applied to the surface of the corrugated fiberboard by the printing is insufficient, the ink is rubbed by a knife at the time of the punching processing in the die-cut section, and thus a printing failure occurs. Further, at this time, the ink or the like sticks to the knife of the die-cut section, and thus, at the time of the punching processing of the next corrugated fiberboard, there is a concern that the corrugated fiberboard may be stained with the ink. Therefore, it has been considered to provide a drying device downstream of the printing section in the box making machine to dry the ink applied to the corrugated fiberboard. As the drying device of the box making machine, for example, there is a drying device disclosed in PTL 1 below. 
     CITATION LIST 
     Patent Literature 
     [PTL 1] Japanese Unexamined Patent Application Publication No. 05-138771 
     SUMMARY OF INVENTION 
     Technical Problem 
     In the printing drying device of the box making machine disclosed in PTL 1 described above, when the corrugated fiberboard travels from a printing unit to a printing ink drying unit, a pattern on the corrugated fiberboard is detected by a pattern detection sensor, and only a printing ink drying unit corresponding thereto is operated, whereby energy saving is achieved. In this case, the ink is dried by supplying hot air only to an area where the pattern is detected. However, the printing section is generally made to be capable of performing multi-color printing, and the amount of heat required for drying differs between a single-color printed area and a multi-color printed area, and thus sufficient energy saving cannot be achieved only by turning on and off hot air supply. 
     The present invention is for solving the problem described above and has an object to provide sheet drying device and method, and a box making machine, in which energy saving and prolongation of the life of a heating lamp are achieved. 
     Solution to Problem 
     A sheet drying device according to the present invention for achieving the above object is a sheet drying device that dries water-based paint on a sheet that is conveyed, and includes a heating lamp that is disposed to face a printing surface of the sheet, a voltage adjusting unit that adjusts a voltage of electric power to be supplied to the heating lamp, a voltage setting unit that sets a working voltage of the heating lamp by setting a voltage that is lower than a rated voltage of the heating lamp by a predetermined value set in advance as a reference voltage and increasing or decreasing the reference voltage according to an application amount of the water-based paint on the sheet, and a control unit that changes a voltage of the heating lamp to the working voltage set by the voltage setting unit by using the voltage adjusting unit. 
     Therefore, the working voltage of the heating lamp is set by setting a voltage lower than the rated voltage of the heating lamp as a reference voltage and increasing or decreasing the reference voltage according to the application amount of the water-based paint on the sheet, and the set working voltage is applied to the heating lamp to light the heating lamp, whereby the water-based paint on the sheet is dried. For this reason, the water-based paint is dried with the minimum amount of energy, and thus energy saving of the heating lamp can be achieved while maintaining the drying performance of the water-based paint and prolongation of the life of the heating lamp can be achieved. 
     In the sheet drying device according to the present invention, the reference voltage is set to a voltage between 75% of the rated voltage of the heating lamp and 85% of the rated voltage of the heating lamp. 
     Therefore, since the reference voltage is set to a voltage between 75% of the rated voltage of the heating lamp and 85% of the rated voltage of the heating lamp, energy saving of the heating lamp can be achieved while maintaining the drying performance of the water-based paint and prolongation of the life of the heating lamp can be achieved. 
     In the sheet drying device according to the present invention, the water-based paint is water-based ink of at least one or more colors or water-based varnish, and the voltage setting unit sets the working voltage by increasing the reference voltage as an overlapping amount of the water-based paint increases. 
     Therefore, the working voltage is set by increasing the reference voltage as an overlapping amount of the water-based ink or the water-based varnish on the sheet increases, whereby even in an area where the water-based ink or the water-based varnish overlaps, sufficient drying performance can be secured. 
     In the sheet drying device according to the present invention, the voltage setting unit sets the working voltage by increasing or decreasing the reference voltage, based on print information. 
     Therefore, the working voltage is set by increasing or decreasing the reference voltage, based on print information, whereby the working voltage of the heating lamp according to a print pattern can be set, and drying unevenness can be suppressed. 
     In the sheet drying device according to the present invention, the voltage setting unit increases the working voltage as a conveying speed of the sheet as the print information increases. 
     Therefore, since the working voltage increases as the conveying speed of the sheet increases, insufficient drying due to an increase in the conveying speed of the sheet can be suppressed. 
     In the sheet drying device according to the present invention, a moisture sensor that measures the amount of moisture of the water-based paint on the sheet after drying is provided, and the voltage setting unit increases the working voltage when a measurement value of the moisture sensor is higher than a determination value set in advance. 
     Therefore, when the amount of moisture of the water-based paint on the sheet after drying is higher than the determination value, the working voltage is increased, whereby even if variation in drying of the water-based paint occurs, the working voltage is increased early to increase the heating amount, and therefore, stable drying performance can be maintained. 
     In the sheet drying device according to the present invention, the heating lamp includes a plurality of lamp bodies that extend in a transfer direction of the sheet and are disposed at predetermined intervals in a direction crossing the transfer direction of the sheet, and the voltage setting unit sets the working voltage for each of the plurality of lamp bodies according to the application amount of the water-based paint on the sheet. 
     Therefore, the working voltage is set for each of the plurality of lamp bodies according to the application amount of the water-based paint on the sheet, whereby even if the ink application amount changes in the width direction of the sheet, stable drying performance can be maintained. 
     Further, a sheet drying method according to the present invention is a sheet drying method of drying water-based paint on a sheet that is conveyed, by using a heating lamp that is disposed to face the water-based paint on the sheet, and includes a step of setting a voltage that is lower than a rated voltage of the heating lamp by a predetermined value set in advance as a reference voltage, and a step of setting a working voltage of the heating lamp by increasing or decreasing the reference voltage according to an application amount of the water-based paint on the sheet. 
     Therefore, energy saving of the heating lamp can be achieved while maintaining the drying performance of the water-based paint, and prolongation of the life of the heating lamp can be achieved. 
     Further, a sheet drying method according to the present invention is a sheet drying method of drying water-based paint on a sheet that is conveyed, by using a heating lamp that is disposed to face the water-based paint on the sheet, and includes a step of setting a rated voltage of the heating lamp according to a maximum application amount of the water-based paint on the sheet, and a step of adjusting the rated voltage according to the application amount in a range between the rated voltage and a voltage of 75% of the rated voltage when the application amount of the water-based paint on the sheet decreases below the maximum application amount. 
     Therefore, energy saving of the heating lamp can be achieved while maintaining the drying performance of the water-based paint, and prolongation of the life of the heating lamp can be achieved. 
     Further, a box making machine according to the present invention includes a sheet feeding section that supplies a corrugated fiberboard, a printing section that performs printing on the corrugated fiberboard, the sheet drying device that dries water-based paint on the printed corrugated fiberboard, a slotter creaser section that performs creasing line processing and grooving processing on the dried corrugated fiberboard, a folding section that makes a flat corrugated box by folding the corrugated fiberboard along creasing lines, and a counter-ejector section that discharges the flat corrugated boxes every predetermined number after stacking the flat corrugated boxes while counting the flat corrugated boxes. 
     Therefore, printing is performed on the corrugated fiberboard from the sheet feeding section in the printing section, the water-based paint on the corrugated fiberboard is dried in the sheet drying device, creasing line processing and grooving processing are performed in the slotter creaser section, punching processing is performed on the corrugated fiberboard by a rotary die-cutter, and in the folding section, folding is performed and the end portions are joined to each other, so that a box body is formed, and the box bodies are stacked while being counted in the counter-ejector section. At this time, in the sheet drying device, the water-based paint on the sheet is dried by setting a voltage lower than the rated voltage of the heating lamp as a reference voltage, setting the working voltage of the heating lamp by increasing or decreasing the reference voltage according to the application amount of the water-based paint on the sheet, and applying the set working voltage to the heating lamp to light the heating lamp. For this reason, energy saving of the heating lamp can be achieved while maintaining the drying performance of the water-based paint, and prolongation of the life of the heating lamp can be achieved. 
     Advantageous Effects of Invention 
     According to the sheet drying device and method, and the box making machine according to the present invention, since the working voltage of the heating lamp is set by setting a voltage lower than the rated voltage of the heating lamp as a reference voltage and increasing or decreasing the reference voltage according to the application amount of the water-based paint on the sheet, energy saving of the heating lamp can be achieved while maintaining the drying performance of the water-based paint and prolongation of the life of the heating lamp can be achieved. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic configuration diagram showing a box making machine of the present embodiment. 
         FIG. 2  is a block configuration diagram showing a sheet drying device of the present embodiment. 
         FIG. 3  is a schematic diagram showing a relationship between an ink application state and a heating state of a heating lamp. 
         FIG. 4  is a graph showing a lamp wavelength required for drying of ink and varnish. 
         FIG. 5  is a graph showing a change in lamp wavelength due to a decrease in lamp radiation intensity. 
         FIG. 6  is a graph showing drying performance, lamp energy saving magnification, and lamp life magnification with respect to a lamp voltage. 
         FIG. 7  is a graph showing a required lamp voltage with respect to a water film thickness. 
         FIG. 8  is a table showing the comparison of the operational effects of a conventional sheet drying device and the sheet drying device of the present embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, a preferred embodiment of sheet drying device and method and a box making machine according to the present invention will be described in detail with reference to the accompanying drawings. The present invention is not limited by this embodiment, and in a case where there are a plurality of embodiments, the present invention also includes configurations made by combining the respective embodiments. 
     This embodiment will be described by applying the sheet drying device and method according to the present invention to a box making machine.  FIG. 1  is a schematic configuration diagram showing a box making machine of this embodiment. 
     In this embodiment, as shown in  FIG. 1 , a box making machine  10  is for making a corrugated box (a box body) B by processing a corrugated fiberboard (a sheet) S. The box making machine  10  is configured to include a sheet feeding section  11 , a printing section  21 , a slotter creaser section  31 , a die-cut section  41 , a speed-increasing section  51 , a folding section  61 , and a counter-ejector section  71 , which are disposed linearly in a transfer direction D in which the corrugated fiberboard S and the corrugated box B are conveyed. 
     The sheet feeding section  11  is for feeding the corrugated fiberboards S one by one to send them to the printing section  21  at a constant speed. The sheet feeding section  11  includes a table  12 , a front stop  13 , a feed roller  14 , a suction device  15 , and a feed roll  16 . The table  12  allows a large number of corrugated fiberboards S to be stacked and placed thereon and is supported so as to be movable up and down. The front stop  13  can position the front end positions of the corrugated fiberboards S stacked on the table  12 , and a gap through which one corrugated fiberboard S can pass is secured between a lower end portion of the front stop  13  and the table  12 . A plurality of feed rollers  14  are disposed corresponding to the table  12  in the transfer direction D of the corrugated fiberboard S and can send forward the corrugated fiberboard S at the lowermost position among the stacked corrugated fiberboards S when the table  12  has been moved down. The suction device  15  sucks the stacked corrugated fiberboards S downward, that is, toward the table  12  side or the feed roller  14  side. The feed roll  16  can supply the corrugated fiberboard S sent by the feed roller  14  to the printing section  21 . 
     The printing section  21  is for performing multi-color printing (in this embodiment, four-color printing) on the surface of the corrugated fiberboard S. In the printing section  21 , four printing units  21 A,  21 B,  21 C, and  21 D and one varnish application unit  21 E are disposed in series, printing is performed on the surface of the corrugated fiberboard S by using four ink colors, and varnish can be applied thereon. The printing units  21 A,  21 B,  21 C, and  21 D and the varnish application unit  21 E are configured in substantially the same manner, and each of the units has a printing cylinder  22 , an ink supply roll (an anilox roll)  23 , an ink chamber  24 , and an impression roll  25 . The printing cylinder  22  has a printing plate  26  mounted on an outer peripheral portion thereof and is rotatably provided. In the case of the varnish application unit  21 E, the printing cylinder  22  is a coater cylinder, and the ink supply roll (the anilox roll)  23  is a roller with a coater. The ink supply roll  23  is disposed in contact with the printing plate  26  in the vicinity of the printing cylinder  22  and is rotatably provided. The ink chamber  24  stores water-based ink (or water-based varnish) as water-based paint and is provided in the vicinity of the ink supply roll  23 . The impression roll  25  nips the corrugated fiberboard S between itself and the printing cylinder  22  to convey the corrugated fiberboard S while applying a predetermined printing pressure thereto, and is rotatably provided to face the lower side of the printing cylinder  22 . 
     Further, a drying unit (a sheet drying device)  21 F is disposed further on the downstream side than the varnish application unit  21 E of the printing section  21 . Although will be described later, the drying unit  21 F is for drying the water-based ink or the water-based varnish on the corrugated fiberboard S which is conveyed, by using a heating lamp and air. 
     The slotter creaser section  31  is for carrying out creasing line processing, cutting processing, grooving processing, and gluing margin strip processing on the corrugated fiberboard S by using a slotter device. The slotter creaser section  31  has a first creasing line roll  32 , a second creasing line roll  33 , a first slotter head  34 , a second slotter head  35 , and a slitter head  36 . The first creasing line roll  32  and the second creasing line roll  33  are for carrying out the creasing line processing on the back surface (lower surface) of the corrugated fiberboard S. The first slotter head  34  and the second slotter head  35  are for performing the grooving processing at a predetermined position in the corrugated fiberboard S and also performing the gluing margin strip processing. The slitter head  36  is provided adjacent to the second slotter head  35  and cuts end portions in a width direction of the corrugated fiberboard S. 
     The die-cut section  41  is for carrying out punching processing of a hand hole or the like on the corrugated fiberboard S. The die-cut section  41  has a pair of upper and lower feed rolls  42 , an anvil cylinder  43 , and a knife cylinder  44 . The feed rolls  42  nip the corrugated fiberboard S from above and below to convey it and is rotatably provided. The anvil cylinder  43  and the knife cylinder  44  are each formed in a circular shape and can be synchronously rotated by a drive device (not shown). The anvil cylinder  43  has an anvil formed on an outer peripheral portion thereof, while the knife cylinder  44  has a head and a die formed at predetermined positions on an outer peripheral portion thereof. 
     The speed-increasing section  51  is for increasing the speed of the cut corrugated fiberboard S to secure a predetermined conveyance interval between the corrugated fiberboards S which are conveyed. The speed-increasing section  51  has a pair of upper and lower conveyance belts  52  and  53 . The conveyance belts  52  and  53  nips the corrugated fiberboard S from above and below to convey it and can be synchronously rotated by a drive device (not shown). The conveying speed of the corrugated fiberboard S in the speed-increasing section  51  is set to a speed higher than the conveying speed of the corrugated fiberboard S to the die-cut section  41 . 
     The folding section  61  is for folding the corrugated fiberboard S while moving it in the transfer direction D and joining both end portions in the width direction to form a flat corrugated box B. The folding section  61  has an upper conveyance belt  62 , lower conveyance belts  63  and  64 , and a sheet folding device (a folder gluer)  65 . The upper conveyance belt  62  and the lower conveyance belts  63  and  64  nip the corrugated fiberboard S and the corrugated box B from above and below to convey them. Although will be described later, the sheet folding device  65  is for folding the respective end portions in the width direction of the corrugated fiberboard S while bending them downward. 
     Further, the folding section  61  is provided with a gluing device  66 . The gluing device  66  has a glue gun and can perform glue application at a predetermined position on the corrugated fiberboard S by discharging a glue at a predetermined timing. 
     The counter-ejector section  71  is for stacking the corrugated boxes B while counting them, and then sorting them into a predetermined number of batches, and discharging them. The counter-ejector section  71  has a hopper device  72 . The hopper device  72  has a liftable elevator  73  on which the corrugated boxes B are stacked, and the elevator  73  is provided with a front stopper and a corner guard. A discharge conveyor  74  is provided below the hopper device  72 . 
     Here, an operation of making the corrugated box B from the corrugated fiberboard S in the box making machine  10  of this embodiment described above will be described. The box making machine  10  of this embodiment is for making the corrugated box B by performing printing, creasing line processing, grooving processing, gluing margin strip processing, and punching processing on the corrugated fiberboard S and then folding it. 
     The corrugated fiberboard S is formed by pasting a corrugated medium between a bottom liner and a top liner. In a previous process of the box making machine  10 , two folding lines are formed in the corrugated fiberboard S. The folding lines are for folding flaps when assembling the corrugated box B made in the box making machine  10  later. The corrugated fiberboards S are stacked on the table  12  of the sheet feeding section  11 , as shown in  FIG. 1 . 
     In the sheet feeding section  11 , the large number of corrugated fiberboards S stacked on the table  12  are first positioned by the front stop  13 , and then the table  12  is moved down, whereby the corrugated fiberboard S at the lowermost position is sent out by the plurality of feed rollers  14 . Then, the corrugated fiberboard S is supplied to the printing section  21  at a predetermined constant speed by the pair of feed rolls  16 . 
     In the printing section  21 , in each of the printing units  21 A,  21 B,  21 C, and  21 D, ink is supplied from the ink chamber  24  to the surface of the ink supply roll  23 , and if the printing cylinder  22  and the ink supply roll  23  rotate, the ink on the surface of the ink supply roll  23  is transferred to the printing plate  26 . Then, if the corrugated fiberboard S is conveyed between the printing cylinder  22  and the impression roll  25 , the corrugated fiberboard S is nipped by the printing plate  26  and the impression roll  25 , and printing pressure is applied to the corrugated fiberboard S, so that printing is carried out on the surface thereof. Further, in the varnish application unit  21 E, varnish is likewise applied to the surface of the corrugated fiberboard S. Then, in the drying unit  21 F, incandescent light is irradiated from a heating lamp to the water-based ink or the water-based varnish on the corrugated fiberboard S which is conveyed, and air is blown to reduce the moisture of the water-based ink or the water-based varnish, whereby the water-based ink or the water-based varnish is dried. The printed and dried corrugated fiberboard S is conveyed to the slotter creaser section  31  by the feed roll. 
     In the slotter creaser section  31 , first, when the corrugated fiberboard S passes through the first creasing line roll  32 , a creasing line is formed on the back surface (top liner) side of the corrugated fiberboard S. Further, when the corrugated fiberboard S passes through the second creasing line roll  33 , a creasing line is formed on the back surface (top liner) side of the corrugated fiberboard S. 
     Next, when the corrugated fiberboard S on which the creasing lines are formed passes through the first and second slotter heads  34  and  35 , grooves are formed at the positions of the creasing lines. At this time, an end portion is cut at the position of each of the creasing lines, so that a gluing margin strip is formed. Further, when the corrugated fiberboard S passes through the slitter head  36 , an end portion is cut at a cutting position. For this reason, the corrugated fiberboard S is composed of four sheet pieces with the creasing lines (grooves) as boundaries. 
     In the die-cut section  41 , when the corrugated fiberboard S passes between the anvil cylinder  43  and the knife cylinder  44 , a hand hole or the like is formed. However, the punching processing of the hand hole or the like is appropriately performed according to the type of the corrugated fiberboard S, and when the hand hole or the like is unnecessary, a knife mounting base (a punching blade) for carrying out the punching processing is removed from the knife cylinder  44 , and the corrugated fiberboard S passes between the anvil cylinder  43  and the knife cylinder  44  which rotate. Then, the corrugated fiberboard S with the hand hole or the like formed therein is conveyed to the speed-increasing section  51 . 
     In the speed-increasing section  51 , the corrugated fiberboard S is conveyed while being nipped by the upper and lower conveyance belts  52  and  53 . At this time, the corrugated fiberboard S is conveyed at a conveying speed increased from the conveying speed of the die-cut section  41 , whereby a predetermined conveyance interval is formed between the corrugated fiberboards S. Thereafter, the corrugated fiberboard S is conveyed to the folding section  61 . The speed-increasing section  51  may not be provided. In this case, the corrugated fiberboard S is conveyed from the die-cut section  41  to the folding section  61 . 
     In the folding section  61 , the corrugated fiberboard S is folded downward by the sheet folding device  65  with the creasing line as a base point, after the glue is applied to the gluing margin strip by the gluing device  66 , while the corrugated fiberboard S is moved in the transfer direction D by the upper conveyance belt  62  and the lower conveyance belts  63  and  64 . If the folding progresses to nearly 180 degrees, a folding force becomes stronger, and thus the gluing margin strip and the end portion of the corrugated fiberboard S are pressed against each other and brought into close contact with each other, and both end portions of the corrugated fiberboard S are joined to each other to form the corrugated box B. Then, the corrugated box B is conveyed to the counter-ejector section  71 . 
     In the counter-ejector section  71 , the corrugated box B is sent to the hopper device  72 , and a leading end portion in the transfer direction D of the corrugated box B comes into contact with the front stopper and is stacked on the elevator  73  in a state of being trimmed by the corner guard. Then, if a predetermined number of corrugated boxes B are stacked on the elevator  73 , the elevator  73  is moved down, and a predetermined number of corrugated boxes B are discharged as one batch by the discharge conveyor  74  and sent to a post-process of the box making machine  10 . 
     Here, the drying unit  21 F will be described in detail.  FIG. 2  is a block configuration diagram showing the sheet drying device of this embodiment, and  FIG. 3  is a schematic diagram showing the relationship between an ink application state and a heating state of the heating lamp. 
     In this embodiment, as shown in  FIG. 2 , a sheet drying device  100  includes the drying unit  21 F described above and a controlling device  101 . The drying unit  21 F is disposed to face a printing surface of the corrugated fiberboard S which is conveyed, and is composed of a heating lamp  111  and an air supply device  112 . The controlling device  101  controls the drying unit  21 F and is provided with a voltage adjusting unit  122  and a voltage setting unit  121 . 
     The heating lamp  111  is composed of a plurality of lamp bodies  113  which extend along the transfer direction D of the corrugated fiberboard S and are disposed at predetermined intervals in a direction orthogonal to (crossing) the transfer direction D to forms a rod shape, as shown in  FIG. 3 . The heating lamp  111  is, for example, an incandescent lamp, and an infrared irradiation lamp such as a halogen lamp, a carbon heater, or a ceramic heater, a krypton light bulb, a general light bulb, or the like is used. The plurality of lamp bodies  113  are disposed in parallel to the transfer direction D of the corrugated fiberboard S. However, the lamp bodies  113  may be disposed to be inclined at a predetermined angle (for example, an angle in a range of 5 to 10 degrees). The air supply device  112  is configured with a plurality of air injection ports (not shown) each provided between the plurality of lamp bodies  113 . 
     For this reason, as shown in  FIG. 2 , in the drying unit  21 F, heat generation light is irradiated from each of the lamp bodies  113  of the heating lamp  111  to the water-based ink or the water-based varnish on the corrugated fiberboard S which is conveyed, and air is injected from each of the air injection ports of the air supply device  112 . Then, the water-based ink or the water-based varnish on the corrugated fiberboard S receive incandescent light or air, so that the moisture evaporates, and thus the water-based ink or the water-based varnish is dried. 
     In the heating lamp  111  (the lamp body  113 ) of the drying unit  21 F, a rated voltage and a rated current are set. The rated voltage and the rated current are set according to the maximum film thickness (maximum application amount) of the ink and the varnish which are applied to the corrugated fiberboard S. When the amount of moisture (water content) of the ink or the varnish which is used is set to a predetermined value, an applied part where the ink by each of the printing units  21 A,  21 B,  21 C, and  21 D and the varnish by the varnish application unit  21 E overlap each other forms the maximum film thickness of the ink and varnish. When the corrugated fiberboard S travels at a predetermined conveying speed, the heating lamp  111  (the lamp body  113 ) capable of reducing the moisture of the ink and varnish of the maximum film thickness to a predetermined moisture amount is applied. 
     The voltage adjusting unit  122  is for adjusting the voltage of electric power which is supplied to the heating lamp  111 . The voltage setting unit  121  is for setting a working voltage of the heating lamp  111  by setting a voltage that is lower than the rated voltage of the heating lamp  111  by a predetermined value set in advance as a reference voltage and increasing or decreasing the reference voltage according to the film thickness (the application amount) of the water-based paint (ink or varnish) on the corrugated fiberboard S. The controlling device (control unit)  101  changes the voltage of the heating lamp  111  to the working voltage set by the voltage setting unit  121  by using the voltage adjusting unit  122 . Here, the application amount of the water-based paint is described as the film thickness of the water-based paint. However, the application amount of the water-based paint is an application amount per unit area and is a meaning substantially equivalent to the film thickness of the water-based paint. 
     In this case, the reference voltage is a voltage between 75% of the rated voltage of the heating lamp  111  and 85% of the rated voltage of the heating lamp  111 , and 80% of the rated voltage of the heating lamp  111  is optimum. 
     Further, the voltage setting unit  121  sets the working voltage by increasing or decreasing the reference voltage, based on print information. Here, the print information is pattern information to be printed and is an overlapping state of each ink and varnish in the width direction of the corrugated fiberboard S. The voltage setting unit  121  sets the working voltage by increasing the reference voltage as the overlapping amount of each ink and the water-based varnish on the corrugated fiberboard S increases. 
     Further, the print information is the conveying speed of the corrugated fiberboard S, and the voltage setting unit  121  increases the working voltage as the conveying speed of the corrugated fiberboard S increases. Further, the controlling device  101  receives sheet information, ink information, and varnish information. The voltage setting unit  121  increases the working voltage as the material of the corrugated fiberboard S is hard to be dried (low in water absorbency), based on the sheet information, and increases the working voltage as the amount of moisture of the corrugated fiberboard S is higher, based on the ink information and the varnish information. 
     A temperature sensor  131  which measures the atmosphere temperature of the drying unit  21 F, a humidity sensor  132  which measures the atmosphere humidity of the drying unit  21 F, and a temperature sensor  133  which measures the temperature of the corrugated fiberboard S are provided, and each measurement result is input to the controlling device  101 . The voltage setting unit  121  increases the working voltage as the atmosphere temperature is lower, increases the working voltage as the atmosphere humidity is higher, and increases the working voltage as the temperature of the corrugated fiberboard S is lower. 
     Further, a moisture sensor  134  which measures the amount of moisture of the ink and varnish on the corrugated fiberboard S after drying is provided further on the downstream side than the drying unit  21 F and further on the upstream side than the slotter creaser section  31 , and the measurement result is input to the controlling device  101 . The voltage setting unit  121  increases the working voltage when the measurement value of the moisture sensor, that is, the amount of moisture of the ink and varnish on the corrugated fiberboard S after drying is higher than a determination value set in advance. 
     Specifically, as shown in  FIGS. 2 and 3 , when three ink application areas A 1 , A 2 , and A 3  exist on the printing surface of the corrugated fiberboard S and one varnish application area A 4  exists over the entire area, film thicknesses t 1 , t 2 , and t 3  of the three ink application areas A 1 , A 2 , and A 3  and a film thickness t 4  of the one varnish application area A 4  are set in the width direction of the corrugated fiberboard S. At this time, the voltage setting unit  121  sets the working voltage for each of the plurality of lamp bodies  113  according to the film thicknesses of the ink and the varnish on the corrugated fiberboard S. 
     On the printing surface of the corrugated fiberboard S, the film thickness t 4  of the varnish, in which there is no ink application area A 1 , A 2 , or A 3  and there is only the varnish application area A 4 , is an area with the thinnest film thickness, and the area is set to a working voltage V 0 . Further, the area of the varnish film thickness t 1 +t 4 , in which there are the ink application area A 1  and the varnish application area A 4 , is set to a working voltage V 1 , the area of the varnish film thickness t 1 +t 2 +t 4 , in which there are the ink application areas A 1  and A 2  and the varnish application area A 4 , is set to a working voltage V 2 , and the area of the varnish film thickness t 1 +t 2 +t 3 +t 4 , in which there are the ink application areas A 1 , A 2 , and A 3  and the varnish application area A 4 , is set to a working voltage V 3 . Here, the working voltage V 0  is set as the reference voltage, and the magnitude relationship between the working voltages V 0 , V 1 , V 2 , and V 3  is a relationship of V 0 &lt;V 1 &lt;V 2 &lt;V 3 . 
     In the corrugated fiberboard S, each end portion in the width direction is not easily heated, and therefore, it is desirable to increase a working voltage at each end portion in the width direction with respect to the working voltage (reference voltage) V 0 . Further, the temperature of the printing section  21  itself is low at the time of the beginning of printing, and therefore, it is desirable to increase the working voltage at the time of the beginning of printing. 
     Here, the reason why it is preferable to set the working voltage for each of the lamp bodies  113  according to the film thicknesses of the ink and the varnish on the corrugated fiberboard S will be described.  FIG. 4  is a graph showing a lamp wavelength required for the drying of the ink and the varnish, and  FIG. 5  is a graph showing a change in lamp wavelength due to a decrease in lamp radiation intensity. 
     As shown in  FIG. 4 , for example, a halogen lamp as the heating lamp  111  has a peak at 1.1 μm (A). Lamp protection glass transmits almost 100%, and therefore, intensity does not decrease here. The intrinsic absorption wavelength of water is mainly 3 μm (B), and the intensity which is absorbed by water is determined by (A)×(B). 
     On the other hand,  FIG. 5  shows the relationship between the lamp wavelength, the lamp radiation intensity, and an absorption rate of water in consideration of only the lamp radiation intensity and the inhalation rate of water except for the transmittance (%) of the lamp protection glass, because in the halogen lamp as the heating lamp  111 , the lamp wavelength is almost constant in a range of 0 μm to 4.0 μm. In  FIG. 5 , a solid line and a dotted line indicate the lamp radiation intensity, and a dot-and-dash line indicates the absorption rate of water. When the voltage of the heating lamp  111  (the lamp body  113 ) is set to a rated voltage (100%), the lamp wavelength at which the lamp radiation intensity becomes the maximum and the lamp wavelength at which the absorption rate of water becomes the maximum deviate from each other. Then, if the voltage of the heating lamp  111  is lowered to 80% of the rated voltage, although the lamp radiation intensity decreases, the lamp wavelength at which the lamp radiation intensity becomes the maximum shifts to the increase side, and the peak wavelength of the lamp comes close to the absorption rate of water. This is based on the Planck&#39;s law and is a formula relating to the spectral radiance of an electromagnetic wave which is radiated (emitted) from a black body in physics, or the wavelength distribution of energy density. As a result, even if the working voltage of the heating lamp  111  is lowered to 80% of the rated voltage, the lamp wavelength at which the lamp radiation intensity becomes the maximum comes close to the lamp wavelength at which the absorption rate of water becomes the maximum, and therefore, it can be seen that a large decrease in drying performance is suppressed. 
       FIG. 6  is a graph showing drying performance, lamp energy saving magnification, and lamp life magnification with respect to a lamp voltage. In  FIG. 6 , a dot-and-dash line indicates the drying performance (water film thickness) with respect to the lamp voltage, a two-dot chain line indicates the lamp energy saving magnification, and a solid line indicates the lamp life magnification. The operating condition in this case is to travel the corrugated fiberboard S at a conveying speed of 400 BPM and carry out four-color printing processing and varnish application processing. 
     As shown in  FIG. 6 , the drying performance indicated by the dot-and-dash line tends to decrease according to a decrease in lamp voltage. However, the limit value of the water film thickness remaining in the ink or the varnish is, for example, 4 μm, and the lamp voltage is secured as a voltage of 70% or more of the rated voltage. The lamp energy saving magnification indicated by the two-dot chain line tends to be improved according to a decrease in lamp voltage. However, if the lamp voltage becomes equal to or less than 70% of the rated voltage, the lamp does not function as a lamp for drying. Then, the lamp life magnification indicated by the solid line tends to be improved according to a decrease in lamp voltage. However, the lamp voltage decreases with 80% of the rated voltage as the peak. From this experimental results, it can be seen that, if only the lamp life magnification is taken into account, it is preferable to set the working voltage of the heating lamp  111  to 80% of the rated voltage. 
       FIG. 7  is a graph showing a required lamp voltage with respect to a water film thickness. As shown in  FIG. 7 , when the conveying speed of the corrugated fiberboard S is a minimum conveying speed V min  and the water film thickness becomes a maximum film thickness t max  by carrying out varnish application in four-color printing, the working voltage of the heating lamp  111  is set to 90% of the rated voltage, and the working voltage of the heating lamp  111  is lowered to the side of 80% of the rated voltage as the water film thickness shifts to a minimum film thickness t min . When the working voltage of the heating lamp  111  is 80% of the rated voltage, the water film thickness becomes equal to or less than a limit film thickness t g  (for example, 4 μm) of the remaining water film thickness. Further, when the conveying speed of the corrugated fiberboard S is a maximum conveying speed V max  and the water film thickness becomes the maximum film thickness t max  by carrying out varnish application in four-color printing, the working voltage of the heating lamp  111  is set to 100% of the rated voltage, and the working voltage of the heating lamp  111  is lowered to the side of 90% of the rated voltage as the water film thickness shifts to the minimum film thickness t min . When the working voltage of the heating lamp  111  is 90% of the rated voltage, the water film thickness becomes equal to or less than the limit film thickness t g  (for example, 4 μm) of the remaining water film thickness. The working voltage of the heating lamp  111  is changed according to the conveying speed of the corrugated fiberboard S. 
       FIG. 8  is a table showing the comparison of the operational effects of the conventional sheet drying device and the sheet drying device of this embodiment. 
     As shown in  FIG. 8 , as in the conventional sheet drying device, if the working voltage of the heating lamp  111  is set to 100% of the rated voltage and an operation of drying the ink or the varnish is carried out, electric power density becomes 70 kW/m 2 , a color temperature becomes 2500 k (Kelvin), a main wavelength becomes 1.1 μm, a moisture absorption rate becomes 13.3%, and moisture heat input becomes 9.3 kW/m 2 , and the lamp life magnification at this time is set to be 1 time. Then, as in this embodiment, if the working voltage of the heating lamp  111  is set to 80% of the rated voltage and an operation of drying the ink or the varnish is carried out, the electric power density becomes 50 kW/m 2 , the color temperature becomes 2250 k (Kelvin), the main wavelength becomes 1.3 μm, the moisture absorption rate becomes 16.4%, and the moisture heat input becomes 8.2 kW/m 2 , and the lamp life magnification at this time is quadrupled. Here, the electric power decreases to 50 kW/m 2 ÷70 kW/m 2 =71%. However, a decrease in heat input to water is suppressed to 8.2 kW/m 2 ÷9.3 kW/m 2 =88%, and the lamp life magnification can be quadrupled. 
     In this manner, the sheet drying device of this embodiment includes the heating lamp  111  which is disposed to face the printing surface of the corrugated fiberboard S, the voltage adjusting unit  122  which adjusts the voltage of electric power which is supplied to the heating lamp  111 , the voltage setting unit  121  which sets the working voltage of the heating lamp  111  by setting a voltage which is lower than the rated voltage of the heating lamp  111  by a predetermined value set in advance as a reference voltage and increasing or decreasing the reference voltage according to the film thickness (application amount) of the water-based paint on the corrugated fiberboard S, and the controlling device  101  which changes the voltage of the heating lamp  111  to the working voltage set by the voltage setting unit  121  by using the voltage adjusting unit  122 . 
     Therefore, the working voltage of the heating lamp  111  is set by setting a voltage lower than the rated voltage of the heating lamp  111  as a reference voltage and increasing or decreasing the reference voltage according to the film thickness of the water-based paint on the corrugated fiberboard S, and the set working voltage is applied to the heating lamp  111  to light the heating lamp  111 , whereby the water-based paint on the corrugated fiberboard S is dried. For this reason, the water-based paint is dried with the minimum amount of energy, and thus energy saving of the heating lamp  111  can be achieved while maintaining the drying performance of the water-based paint and prolongation of the life of the heating lamp  111  can be achieved. 
     In the sheet drying device of this embodiment, the reference voltage is set to a voltage between 75% of the rated voltage of the heating lamp  111  and 85% of the rated voltage of the heating lamp  111 . Therefore, energy saving of the heating lamp  111  can be achieved while maintaining the drying performance of the water-based paint and prolongation of the life of the heating lamp  111  can be achieved. 
     In the sheet drying device of this embodiment, the water-based paint is water-based ink of different colors and water-based varnish, and the voltage setting unit  121  sets the working voltage by increasing the reference voltage as an overlapping amount of the water-based ink and the water-based varnish on the corrugated fiberboard S increases. Therefore, even in an area where the water-based ink and the water-based varnish overlap each other, sufficient drying performance can be secured. Further, even in a case where the water-based varnish is not applied, sufficient drying performance can be secured even in an area where different types of water-based ink overlap each other or an area where the film thickness of ink of a single color is thick. 
     In the sheet drying device of this embodiment, the voltage setting unit  121  sets the working voltage by increasing or decreasing the reference voltage, based on print information. Therefore, the working voltage of the heating lamp  111  according to a print pattern can be set, and drying unevenness can be suppressed. 
     In the sheet drying device of this embodiment, the voltage setting unit  121  increases the working voltage as the conveying speed of the corrugated fiberboard S as the print information increases. Therefore, insufficient drying due to an increase in the conveying speed of the corrugated fiberboard S can be suppressed. 
     In the sheet drying device of this embodiment, a moisture sensor  134  which measures the amount of moisture of the water-based paint on the corrugated fiberboard S after drying is provided, and the voltage setting unit  121  increases the working voltage when the measurement value of the moisture sensor  134  is higher than a determination value set in advance. Therefore, even if variation in drying of the water-based paint occurs, the working voltage can be increased early to increase the heating amount, and therefore, stable drying performance can be maintained. 
     In the sheet drying device of this embodiment, as the heating lamp  111 , the plurality of lamp bodies  113  which extend in the transfer direction D of the corrugated fiberboard S and are disposed at predetermined intervals in a direction crossing the transfer direction D of the corrugated fiberboard S are provided, and the voltage setting unit  121  sets the working voltage for each of the plurality of lamp bodies  113  according to the film thickness of the water-based paint on the corrugated fiberboard S. Therefore, even if the ink film thickness changes in the width direction of the corrugated fiberboard S, stable drying performance can be maintained. 
     Further, the sheet drying method of this embodiment includes a step of setting a voltage which is lower than the rated voltage of the heating lamp  111  by a predetermined value set in advance as a reference voltage, and a step of setting the working voltage of the heating lamp  111  by increasing or decreasing the reference voltage according to the film thickness (application amount) of the water-based paint on the corrugated fiberboard S. Therefore, energy saving of the heating lamp  111  can be achieved while maintaining the drying performance of the water-based paint and prolongation of the life of the heating lamp  111  can be achieved. 
     The sheet drying method according to the present invention is not limited to this method. For example, the sheet drying method may include a step of setting the rated voltage of the heating lamp  111  according to the maximum film thickness of the water-based paint on the corrugated fiberboard S, and a step of adjusting the rated voltage according to the film thickness (application amount) of the water-based paint in a range between the rated voltage and a voltage of 75% of the rated voltage when the film thickness of the water-based paint on the corrugated fiberboard S decreases below the maximum film thickness. Even in this case, energy saving of the heating lamp  111  can be achieved while maintaining the drying performance of the water-based paint, and prolongation of the life of the heating lamp  111  can be achieved. 
     Further, the box making machine of this embodiment includes the sheet feeding section  11 , the printing section  21 , the drying unit  21 F, the slotter creaser section  31 , the die-cut section  41 , the speed-increasing section  51 , the folding section  61 , and the counter-ejector section  71 . Therefore, printing is performed on the corrugated fiberboard S from the sheet feeding section  11  in the printing section  21 , creasing line processing and grooving processing are performed in the slotter creaser section  31 , and in the folding section  61 , folding is performed and the end portions are joined to each other, so that the corrugated box B is formed, and the corrugated boxes B are stacked while being counted in the counter-ejector section  71 . At this time, in the drying unit  21 F, the water-based paint on the corrugated fiberboard S is dried by setting a voltage lower than the rated voltage of the heating lamp  111  as a reference voltage, setting the working voltage of the heating lamp  111  by increasing or decreasing the reference voltage according to the film thickness of the water-based paint on the corrugated fiberboard S, and applying the set working voltage to the heating lamp  111  to light the heating lamp  111 . For this reason, energy saving of the heating lamp  111  can be achieved while maintaining the drying performance of the water-based paint, and prolongation of the life of the heating lamp  111  can be achieved. 
     In the embodiment described above, the voltage setting unit  121  sets the working voltage for each of the plurality of lamp bodies  113  disposed at predetermined intervals in the width direction according to the film thickness of the water-based paint on the corrugated fiberboard S. However, the plurality of lamp bodies  113  may be disposed at predetermined intervals in the transfer direction, and the voltage setting unit  121  may set the working voltage for each of the lamp bodies  113  in the transfer direction according to the film thickness of the water-based paint on the corrugated fiberboard S. 
     In the embodiment described above, the voltage of the electric power which is supplied to the heating lamp  111  is adjusted according to the film thickness of the water-based paint. However, instead of the heating lamp, a hot air fan may be provided and a heat source or the power source voltage of the hot air fan may be adjusted. Further, instead of the heating lamp, the amount of current of an infrared LED lamp may be controlled according to the film thickness (the application amount). 
     Further, in the embodiment described above, the working voltage of the heating lamp is set by increasing or decreasing the reference voltage according to the film thickness (application amount) of the water-based paint on the sheet. However, the working voltage of the heating lamp may be set by increasing or decreasing the reference voltage according to the number of rotations of a roller with a coater. 
     Further, in the embodiment described above, the box making machine  10  is composed of the sheet feeding section  11 , the printing section  21 , the slotter creaser section  31 , the die-cut section  41 , the speed-increasing section  51 , the folding section  61 , and the counter-ejector section  71 . However, there is no limitation to this configuration. The box making machine  10  may be composed of only the sheet feeding section  11 , the printing section  21 , and the folding section  61 . 
     Further, in the embodiment described above, the sheet drying device according to the present invention has been described as being applied to the box making machine  10 . However, the sheet drying device may be applied to a web offset press for newspaper, a commercial web offset press, an offset sheet-fed press, and the like. 
     REFERENCE SIGNS LIST 
       11 : sheet feeding section 
       21 : printing section 
       21 A,  21 B,  21 C,  21 D: printing unit 
       21 E: varnish application unit 
       21 F: drying unit 
       31 : slotter creaser section 
       41 : die-cut section 
       42 : feed roll 
       43 : anvil cylinder 
       44 : knife cylinder 
       51 : speed-increasing section 
       61 : folding section 
       65 : sheet folding device 
       71 : counter-ejector section 
       100 : sheet drying device 
       101 : controlling device 
       111 : heating lamp 
       112 : air supply device 
       113 : lamp body 
       121 : voltage setting unit 
       122 : voltage adjusting unit 
     D: transfer direction 
     S: corrugated fiberboard 
     B: corrugated box