Patent Publication Number: US-7581334-B2

Title: Drying apparatus

Description:
This Non-provisional application claims priority under 35 U.S.C. § 119(a) on Patent Application No(s). 2003-312433 filed in Japan on Sep. 4, 2003, the entire contents of which are hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a drying apparatus, particularly to the drying apparatus suitable for a drying process in a manufacturing line of a presensitized plate (hereinafter PS plate). 
     2. Background Arts 
     In a PS plate manufacturing line, an aluminum web is coated with a coating liquid and dried in a dryer booth. Then, a coated aluminum web is cut into a predetermined size to obtain a PS plate. 
     A drying apparatus for drying a coated surface of the aluminum web by blowing hot air thereto is well known (for example, cited in Japanese Patent Laid-Open Publication Number 2003-98685). The coating liquid used for the PS plate of such as conventional type or digital-corresponding type (called CTP) are different depending on the types of the PS plate, and a web temperature for drying the coated surface is varied widely in accordance with properties of the coating liquids. Accordingly, it requires a wide range of temperature (for example, about 50-200° C.) for drying air corresponding to all types of the PS plate. 
     In the drying apparatus for the PS plate cited in Japanese Patent Laid-Open Publication Number 2003-98685 above set forth, steam is supplied to a heat exchanger from a boiler for generating hot air. High pressure steam is required to gain hot air; for example, in order to generate hot air of 200° C., 2 Mpa (20 kg/cm 2 ) of high pressure steam is required. Meanwhile, in order to generate air of 50° C., it is required to reduce the steam or steam pressure. The steam is reduced by providing a plural of steam controlling valves in parallel with each other, while steam pressure is reduced by piping via a decompression control valve. However, it is hard to adjust the temperature of drying air for drying the PS plates, which requires that the temperature of drying air is controlled to be a predetermined temperature with high accuracy (±1° C. of error). 
     Equipments such as a high pressure boiler and a high pressure piping are necessary to supply the heat exchanger with steam such that the heat exchanger send hot air in a wide range of 50-200° C. into the dryer booth in the PS plate manufacturing line, and accuracy of the temperature of hot air needs to be maintained corresponding to the change of the amount of hot air. However, it results in rising of costs for equipments and maintenance. An oil heater and an electronic heater may be alternatively used to heat air for drying the aluminum web, or a heat roll and a coil may also be used to heat the aluminum web directly by induction heating. Nevertheless, the problem of raising costs for equipments and maintenance is still remained. 
     SUMMARY OF THE INVENTION 
     A main object of the present invention is to provide a drying apparatus having an ability to control the temperature of hot air with high accuracy. Other object of the present invention is to provide the drying apparatus that may reduce costs for equipments and maintenance. Furthermore, the other object of the present invention is to provide the drying apparatus fulfilling the conditions for drying coating liquid on a PS plate. 
     In order to achieve the above objects, a drying apparatus according to the present invention is provided with a gas burner indirect heat exchanger (hereinafter GHE), wherein a gas flow rate may be adjusted by controlling a turn down ratio of the burner furnace. The air heated in the GHE is supplied to a dryer booth by a blowing fan provided in a blowing duct. The hot air is blown at the surface of a web, coated with a coating liquid, to dry the coating liquid while the web is passing through the dryer booth. 
     The GHE contains a gas burner furnace and a heat exchanger in the housing thereof. Combustible gas in the gas burner furnace is supplied to the heat exchanger, then a part of the combustible gas is returned to the gas burner furnace. The air having entered the housing is heated while passing around the gas burner furnace and heated furthermore as passing through the heat exchanger. 
     In a preferred embodiment of the present invention, the drying apparatus is used in a PS plate manufacturing line for forming a photosensitive layer on an aluminum web. In the GHE, the turn down ratio of the burner furnace is controlled within a range of 1 (fully opened)- 1/20. The temperature of the hot air is controlled to be a predetermined temperature within a range of 50-200° C. with high accuracy (±1° C. of error). 
     The blowing duct has a length of more than 10 m, and is preferably provided with a stirrer to achieve uniformity of temperature distribution of the hot air in the blowing duct. 
     According to the present invention, hot air having a wide range of temperature (50-200° C., for example) may be generated with high accuracy of controlling the temperature. Additionally, using the GHE may reduce the costs for equipments and maintenance, as neither a high pressure boiler nor a high pressure piping, which are conventionally used, are necessary. Therefore, the costs for manufacturing the PS plate may be reduced by applying the drying apparatus of the present invention into the PS plate manufacturing line. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       One with ordinary skill in the art would easily understand the above-described objects and advantages of the present invention when the following detailed description is read with reference to the drawings attached hereto. 
         FIG. 1  is a schematic view of a PS plate manufacturing line; 
         FIG. 2  is a schematic view illustrating a composition of a drying apparatus of the present invention; and 
         FIG. 3  is a schematically perspective view illustrating a composition of a GHE. 
     
    
    
     PREFERRED EMBODIMENTS OF THE INVENTION 
     In  FIG. 1  showing a manufacturing line of a presensitized plate (PS plate) wherein a drying apparatus of the present invention is applied, an aluminum web  10 , whose surface is treated by a surface treating device (not shown), is transported to a coating device  12  by a plural of rollers  11 . The surface of the aluminum web  10  is coated with a coating liquid by the coating device  12  to form a coated layer. Then, the aluminum web  10  is transported sequentially to a dryer booth by the rollers  11  with following a conveying path for the aluminum web  10 . A plural of dryer booths are provided in the drying apparatus: a first dryer booth  13 A, a second dryer booth  13 B, a third dryer booth  13 C, and a fourth dryer and cooler booth  13 D. 
     Each of the first dryer booth  13 A, the second dryer booth  13 B, the third dryer booth  13 C, and the fourth dryer and cooler booth  13 D is provided with a first dryer  14 A, a second dryer  14 B, a third dryer  14 C, and a fourth dryer and cooler  14 D respectively. Each of the first dryer  14 A, the second dryer  14 B, the third dryer  14 C, and the fourth dryer and cooler  14 D sends hot air respectively to the first dryer booth  13 A, the second dryer booth  13 B, the third dryer booth  13 C, and the fourth dryer and cooler booth  13 D so as to dry the coated layer formed on the aluminum web  10 . Next, the aluminum web  10  is transported by the rollers  11  to the next process, wherein another coated layer is formed on the aluminum web  10 , then dried and cooled. After that, the aluminum web  10  is cut by a slitter (not shown) into PS plates having a predetermined size. Alternatively, a cooler may be provided in addition to the fourth dryer and cooler  14 D to cool the aluminum web  10 . 
     The PS plate is manufactured by forming a coating layer on a rectangular and thin aluminum support. The coating layer is a photosensitive layer for a photosensitive PS plate and a heat-sensitive layer for a heat-sensitive PS plate. An overcoat layer and a mat layer may also be formed, if necessary. Plate-making processes such as exposing, developing and gum coating are executed for the coated layer, and then the PS plate is set in a printer to be coated with ink and prints characters and images on a paper. Though the composition of the PS plate is not limited specifically in the present embodiment, the PS plate for a laser printing of a heat mode system or a photon mode system, for example, are capable of direct plate making from digital data. 
       FIG. 2  shows the first dryer  14 A, the second dryer  14 B, the third dryer  14 C, and the fourth dryer and cooler  14 D. Since the first dryer  14 A, the second dryer  14 B, and the third dryer  14 C have approximately the same composition, the second dryer  14 B is used as an example to explain. The second dryer  14 B is composed of a heat pipe  30 , which functions as a heat exchanger, a plural of manual dampers  31 , a plural of automatic dampers  32 , a Pitot tube  33  for measuring flowing velocity of fluid, a Gas burning Heat Exchanger (GHE)  34 , a blowing fan  35  as a blowing means, an exhaust fan  36 , a filter  37  to trap dust, a temperature sensor  38 , a blowing duct  40 , an exhaust duct  41 , a first circulating duct  42 , and a second circulating duct  43 . 
     The heat pipe  30  is provided adjacent to an intake of the blowing duct  40  and an outlet of the exhaust duct  41 . The heat pipe  30  heats the air enters the blowing duct  40  by transmitting the heat from the air discharged from the exhaust duct  41 . Since the heat pipe  30  reuses the heat of discharged air to heat the air enters the blowing duct  40 , it may improve energy efficiency. 
     The blowing duct  40  is provided with the manual damper  31  and the automatic damper  32  on the downstream side of the heat pipe  30 . The manual damper  31  is operated by an operator to adjust flow amount in the blowing duct  40 . The Pitot tube  33  is provided on the downstream side of the automatic damper  32  to measure flowing velocity of the air in the blowing duct  40 . The automatic damper  32  is electrically connected to the Pitot tube  33  and controlled based on the flow velocity measured by the Pitot tube  33 . 
     The GHE  34  is provided on the downstream side of the Pitot tube  33 , and the blowing fan  35  is provided on the downstream side of the GHE  34 . As stated later, the GHE  34  heats air by a gas burner furnace and send hot air. The hot air is guided to further downstream side by the blowing fan  35 . 
     The manual damper  31 , the automatic damper  32 , and the Pitot tube  33  are provided on the downstream side of the blowing fan  35  and operate in the same way as them on the upstream side of the GHE  34  to control the flow velocity of the air heated in the GHE  34 . The filter  37  is provided on the downstream side of them, and the hot air, from which dust is removed by the filter  37 , is sent into the second dryer booth  13 B via the outlet of the blowing duct  40 . 
     The temperature sensor  38  is provided between the filter  37  and the second dryer booth  13 B and electrically connected to the GHE  34  to send the GHE  34  the measured value of the temperature gained by the temperature sensor  38 . Based on the measured value of the temperature, the GHE  34  controls the gas burner furnace to adjust the temperature of the heated air. 
     The heated air sent into the second dryer booth  13 B is discharged via the exhaust duct  41 . The manual damper  31 , the automatic damper  32 , and the Pitot tube  33  are provided to the exhaust duct  41  and operate in the same way as them disposed at the blowing duct  40  to control the flowing velocity of the air in the exhaust duct  41 . The exhaust fan  36  is provided on the downstream side of them to suck the air from the second dryer booth  13 B into the exhaust duct  41 . 
     The first circulating duct  42  connecting the blowing duct  40  and the exhaust duct  41  is provided between the downstream side of the blowing fan  35  and the upstream side of the exhaust fan  36 . The manual damper  31 , the automatic damper  32 , and the Pitot tube  33  are provided on the first circulating duct  42  and operate in the same way as them provided on the blowing duct  40  to control the flow velocity of the air in the first circulating duct  42 . The air flowing from the exhaust duct  41  to the first circulating duct  42  enters the blowing duct  40  and is sent to the second dryer booth  13 B again via the manual damper  31 , the automatic damper  32 , the Pitot tube  33 , and the filter  37 . 
     The second circulating duct  43  connecting the blowing duct  40  and the exhaust duct  43  is provided between the downstream side of the exhaust fan  36  and the upstream side of the GHE  34 . The manual damper  31 , the automatic damper  32 , and the Pitot tube  33  are provided on the second circulating duct  43  and operate in the same way as them provided on the first circulating duct  42  to control the flow velocity of the air in the second circulating duct  43 . The air flowing from the exhaust duct  41  to the second circulating duct  43  enters the blowing duct  40  again and is mixed with the air flowing from the intake of the blowing duct  40 . 
     On the further downstream side of the exhaust fan  36 , two pairs of the manual dampers  31  and the automatic dampers  32  are provided to control the flow velocity of the air in the exhaust duct  41 . When the air passing through the automatic damper  32  is discharged outside the second dryer  14 B via the heat pipe  30 , the heat pipe  30  transmits heat of the discharged air to the air flowing into the blowing duct  40 . The variable amount of drying air is maintained within a range of 40-360 m 3 /min by controlling the rotary velocity of both of the blowing fan  35  and the exhaust fan  36  and the opening degrees of both of the manual damper  31  and the automatic damper  32 . 
     As shown in  FIG. 3 , the GHE  34  compactly contains a gas burner furnace and a heat exchanger in a housing thereof to enhance heat exchange efficiency. The GHE  34  is composed of a housing  49 , a gas burner furnace  50 , a blowing duct  51 , a heat exchanger  52 , a circulating fan  53 , and a duct  54 . Liquefied natural gas (LNG) and compressed air are supplied to the gas burner furnace  50  that burns LNG as fuel. 
     An intake duct  40   a  and an outlet duct  40   b  are respectively connected to the rear side of the housing  49  and to the front side of the housing  49 . The intake duct  40   a  and the outlet duct  40   b  compose a part of the blowing duct  40  shown in  FIG. 2 . The gas burner furnace  50 , the blowing duct  51 , the heat exchanger  52 , and the circulating fan  53  are contained in the housing  49 . 
     The combustible gas, wherein LNG and compressed air are mixed together, is supplied to the gas burner furnace  50  via a pipe  50   a  to be burnt in the gas burner furnace  50 . Then, the combustible gas is transferred to the heat exchanger  52  via the blowing duct  51 . After passing the heat exchanger  52 , the combustible gas is returned by the circulating fan  53  to the gas burner furnace  50  via the duct  54  to be burnt again. An exhaust hole  54   a  is formed on the duct  54 , such that a part of the combustible gas is discharged outside the housing  49  via the exhaust hole  54   a  and a chimney (not shown). 
     In the housing  49 , air enters the intake duct  40   a  is heated while passing around the gas burner furnace  50  and through the heat exchanger  52 . The heated air is sucked by the blowing fan  35  through the outlet duct  40   b.    
     A control valve may control calorific value of the gas burner furnace  50  by changing the flow amount of the combustible gas (mixed gas of LNG and air). A turn down ratio of the control valve is adjusted within a range of 1 (fully opened)- 1/20. Alternatively, the control valve turns down either the compressed air or LNG, and the other one is turned down in proportion. Note that LNG and the compressed air are mixed together before being supplied to the gas burner furnace  50  or, alternatively, LNG and the compressed air are supplied separately to the gas burner furnace  50  to be mixed together in the gas burner furnace  50 . 
     In the burner furnace  50 , as stated above, the turn down ratio is selected within a range of 1 (fully opened)- 1/20, and the calorific value per unit time is controlled within a range of 6,300-15,750 kcal/h. Thereby, the temperature of the hot air may be controlled to be a predetermined temperature within a range of 50-200° C. with high accuracy (±1° C. of error), with 40-360CMM of the variable amount of drying air. 
     In order to ensure safety of the gas burner furnace  50 , combustion safety devices such as a safety control relay, a prepurge, a pilot burner, a main burner, an after-purge, an interlock, an emergency cut off valve, an ultra vision, a pressure switch, an air pressure switch, a rotary switch, an interlock with the burner, and a vent valve are controlled in the GHE  34 . 
     A surface temperature of the heat exchanger  52  in the GHE  34  is controlled to be under 400° C., wherein combustible gas of any concentration does not catch fire. In addition, the heat exchanger  52  is constituted to have negative pressure inside thereof such that the combustible gas does not leak into the housing  49  in case the heat exchanger  52  cracks. Furthermore, an inspection window (not shown) is provided such that cracks may be inspected visually. 
     Next, operations of the second dryer  14 B having composition stated above is explained. The air having entered the intake of the blowing duct  40  is transferred through the blowing duct  40  by the blowing fan  35 , while the flowing velocity of the air is controlled by the manual dampers  31  and the automatic dampers  32 . The air in the blowing duct  40  is heated by the GHE  34  and transferred. The temperature of the hot air is controlled to be a predetermined temperature within a range of 50-200° C. with high accuracy (±1° C. of error). In addition, the blowing duct  40  between the GHE  34  and the second dryer booth  13 B has a length of more than 10 m so as to achieve uniformity of temperature distribution of the hot air, blown by the blowing fan  35 , in the blowing duct  40 . Alternatively, a stirrer may be provided on the downstream side of the blowing fan  35  such that the temperature distribution of the hot air in the blowing duct  40  is more uniformed. 
     Additionally, energy efficiency is improved, since the hot air sent from the blowing duct  40  to the second dryer booth  13 B is guided to the blowing duct  40  again by the first circulating duct  42  and the second circulating duct  43 , the hot air in the exhaust duct  41  is reused. 
     Note that, in order to ensure safety, the air circulated by the first circulating duct  42  and the second circulating duct  43  for circulating dry air is limited to have less than 25% of organic solvent gas concentration, which is a lower limit of gas explosion. In the first dryer booth  13 A for example, the organic solvent gas concentration is higher than ones in other dryer booths, as the aluminum web shortly after coated with coating liquid is transported into the first dryer booth  13 A. Therefore, the GHE  34  heats not circulated air but instead fresh air taken from outside of the drying apparatus and transports the heated air into the first dryer booth  13 A. 
     Since the first dryer  14 A and the third dryer  14 C have approximately the same compositions as the second dryer  14 B, whose composition and the operation are explained above, the same devices in the first dryer  14 A and the third dryer  14 C as the devices in the second dryer  14 B are given corresponding numerals, and explanations for them are omitted. As for the operations of the first dryer  14 A and the third dryer  14 C, both of them operate in the same way as the second dryer  14 B. 
     Next, a composition of the fourth dryer and cooler  14 D is explained. The fourth dryer and cooler  14 D has the composition of the second dryer  14 B from which the first circulating duct  42 , the heat pipe  30 , and parts of a plural of the manual dampers  31  and the automatic dampers  32  are omitted. The same devices in the fourth dryer and cooler  14 D as the devices in the first dryer  14 A, the second dryer  14 B, and the third dryer  14 C are given corresponding numerals, and explanations for them are omitted. In the fourth dryer and cooler  14 D, a heat exchanger  44  is provided on the downstream side of the GHE  34 . 
     In order to dry the aluminum web  10  by blowing cooled air into the fourth dryer and cooler booth  13 D, the GHE  34  is stopped operating and cooling water is circulated in a cooling coil in the heat exchanger  44 . Thereby, the air having entered from outside of the fourth dryer and cooler  14 D is cooled by the heat exchanger  44  and transferred to the fourth dryer and cooler booth  13 D. 
     In order to dry the aluminum web  10  by blowing hot air into the fourth dryer and cooler booth  13 D, the GHE  34  is operated and the heat exchanger  44  is stopped operating. Thereby, the air having entered from outside of the fourth dryer and cooler  14 D is heated by the GHE  34  and transferred to the fourth dryer and cooler booth  13 D. The fourth dryer and cooler  14 D may transfer alternatively hot air or cooled air to the fourth dryer and cooler booth  13 D according to requirements. 
     Though the drying apparatus of the present invention is used in the PS plate manufacturing line in the above embodiment, the present invention is not limited in the above embodiment but may also be applied in a drying processes of continuous flexible webs such as baryta paper for printing paper and base materials for a photo film, a recording tape, a video tape, or a floppy (R) disk, for example. 
     Although the present invention has been described with respect to the preferred embodiments, the present invention is not to be limited to the above embodiments but, on the contrary, various modifications will be possible to those skilled in the art without departing from the scope of claims appended hereto.