Patent Publication Number: US-6655040-B2

Title: Combination ultraviolet curing and infrared drying system

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     None. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to infrared drying units and more particularly relates to an infrared drying system having an incorporated ultraviolet curing unit. 
     In the art of printing and coating, liquid substances are applied to sheets and webs of material such as paper, film, and foil. These substances, when manufactured appropriately and solidified, are used to impart various surface properties to the material. Such surface properties include defined patterns of color, through a process of printing, scuff resistance, through a process of clear coating, or stickiness, through a process of applying an adhesive coating. These liquid substances are designed specifically for solidification by one of several methods. 
     One of the most commonly used methods of solidification is evaporation of the liquid portion of the substance through exposure to a combination of air movement and electrically generated infrared energy. When using air movement and infrared energy, the liquid substance used must be an evaporative coating. The machines used to evaporate such coatings are referred to as infrared dryers (IR dryers). Another method of solidification is polymerization of the liquid substance through exposure to specific wavelengths of electrically generated ultraviolet light. Such liquid substances are called ultraviolet coatings, and the machines used to polymerize such coatings are referred to as ultraviolet curing units (UV curing units). 
     In general, users of printing and coating machinery have found that evaporative coatings and ultraviolet coatings, and their associated methods of solidification, each have advantages and disadvantages. For example, evaporative coatings are generally less expensive than ultraviolet coatings, but the UV curing units used to solidify ultraviolet coatings generally require less space than the IR dryers used to dry evaporative coatings. These and other considerations dictate whether the user, when printing or coating a particular product, should apply evaporative coatings or ultraviolet coatings. 
     It is not possible to use IR dryers and UV curing units interchangeably. Because the solidification of ultraviolet coatings requires specific wavelengths of ultraviolet energy, infrared energy cannot be used for solidification of ultraviolet coatings due to infrared energy occupying an entirely different portion of the electromagnetic spectrum. Furthermore, although ultra-violet light sources currently in use generally produce significant amounts of infrared energy in addition to ultraviolet energy, the economics of shorter bulb life and higher power consumption have dictated that a separate infrared source should be used when drying evaporative coatings. Therefore, users of printing and coating equipment who want to have the most flexibility in printing or coating find it necessary to purchase and install both IR drying and UV curing equipment. 
     Modern drying and curing equipment frequently uses applied power densities in the range of 40 to 100 watts per square inch or higher. At such power densities, efficient and safe operation requires that the equipment be equipped with cooling systems. Electric IR dryers are commonly equipped with moving air cooling systems or water cooling systems to cool the heat emitting elements, electrical connections, and element supports. With either air or water cooling methods, it has been found that the addition of air directed against the substrate and coating enhances the drying by transferring liquid vapor from the substrate and coating to the air. Rather than permit the heated air used for cooling and vapor removal to blow into an area where machine operators are performing their work tasks, an air exhaust system is typically incorporated into the IR drying equipment to remove the heat and vapor laden air and convey it to a controlled destination. 
     Similar to IR dyers, UV curing equipment is commonly equipped with air or water cooling systems to carry away a portion of the large quantity of heat created by the operation of the ultraviolet energy source used in these systems. When air is used for cooling, the resulting heated air is generally exhausted from the ultraviolet equipment and conveyed to a controlled destination in such a way that it does not contact and heat the substrate unnecessarily. This is additionally beneficial because it prevents the heated air from contacting the UV lamp. As is commonly known by experienced ultraviolet equipment designers, potentially hazardous levels of ozone are formed in quantities proportional to the amount of cooling air which contacts the lamp. 
     Though it is possible to combine a UV curing unit with an IR dryer, challenges arise which have thus far prevented a successful combination system. In particular, designing a cooling system for use in such a combination system has proven particularly difficult. As a result, IR drying equipment and UV curing equipment are commonly designed and built as separate units, each having its own set of cooling systems. To allow for printing a variety of applications, a facility must have both an IR dryer and a UV curing unit. Requiring both such systems increases costs and occupies more floor space. 
     Thus, there is a need in the art for an IR drying system capable of incorporating UV curing equipment without compromising the performance of either the IR drying unit or the UV curing unit. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention is a combination UV curing and IR drying system. The combination system comprises both an IR dryer module and a UV curing unit. To allow both the IR dryer module and the UV curing unit to operate at the same time, a cooling system is used to cool the modules. The cooling system comprises an air supply for supplying air to the UV curing unit and IR dryer module. The air passes through the UV curing unit and IR dryer module, cooling the units as necessary. Once the air exits the UV curing unit and IR dryer module, the now warm air is exhausted from the system using an air exhaust system. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a typical infrared heater module suitable for use with the present invention. 
     FIG. 2 is a perspective view of a typical ultraviolet curing module suitable for use with the present invention. 
     FIG. 3 is a schematic view of an air flow system for use in a combination UV curing and IR drying system. 
     FIG. 4 is a schematic view of an alternate air flow system for use in a combination UV curing and IR drying system. 
     FIG. 5 is a schematic view of an yet another embodiment of a combination UV curing and IR drying system. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 is a perspective view of an infrared dryer  10 . The IR dryer  10  comprises a supply air inlet  12  for supplying cooling air to the dryer  10 . The dryer  10  also comprises a main housing  14  as well as several infrared bulbs  16  located on the bottom of the dryer  10 . A reflector  18  surrounds the infrared bulbs  16  and serves to reflect infrared energy from the bulbs  16  away from the IR dryer and toward the item to be dried, which is typically located a small distance below the dryer  10 . Visible at the bulbs  16  are several air outlets  20 . The air outlets  20  are located near the bulbs  16  and allow the air from the supply inlet  12  to exit the housing  14  near the bulbs  16 . As the air exits past the bulbs  16 , it cools the bulbs  16 . 
     Once the cool supply air enters the dryer  10  through the supply air inlet  12 , it is distributed inside the housing  14  such that the volume and velocity of the air leaving the IR dryer  10  through each of the multiple air outlets  20  is nearly the same. Due to the internal construction of the IR dryer  10 , the presence of the highly effective reflector  18 , and the location of the air outlets  20 , the cool air supplied via the air inlet  12  also cools the reflector and lamp power connections located inside the IR dryer housing  14 . 
     During this cooling process, energy is transferred from the hot surfaces to the air causing the air temperature to increase. Air temperature increases on the order of 100 degrees Fahrenheit have been measured on infrared heaters, depending on the heater configuration and the power of the radiant energy source. This warmed air can be used to assist in drying the product being dried by directing the warmed air toward the product being dried as the air exits the air outlets  20 . 
     FIG. 2 is a perspective view of an ultraviolet curing unit  30  with the curing unit  30  in an inverted positioned so that its features are more visible. The UV curing unit  30  comprises a housing  32  with an inner recess  34  covered with a reflective material  36 . The inner recess  34  is configured to receive a UV energy source, such as a bulb  35 . The reflective material  36  serves to reflect the UV rays emitted by the UV bulb  35  toward the material being cured. 
     Also shown on the UV curing unit  30  are shutters  38  which can be actuated by a cylinder  40 . Shutters  38  are used in web fed operations in instances when the movement of the web past the curing module  30  must be stopped. When the web is stationary, the shutters  38  can be closed using the cylinder  40  so that the shutters  38  shield the web located directly below the UV curing module  30  from the UV and IR energy emitted by the module  30 , preventing the web from potential damage from overexposure to the UV energy and overheating from the IR energy. 
     Finally, the UV curing unit  30  is also equipped with a supply air inlet  42 . Similar to the IR dryer, the UV curing unit must be cooled to ensure proper operation. The supply air inlet  42  is provided on the housing  32  opposite the shutters  38 . Cool air is supplied to the housing  32  via the supply air inlet  42 . The cool air is forced through the housing  32  and through the inner recess  34  past the UV bulb  35 . A variety of methods of supplying cooling air to the may be used with the UV curing unit  30 , including for instance an axial flow fan. As the air passes through the housing  32 , it cools the components in the housing  32 . Similarly, as the air moves past the UV bulb  35 , it cools the UV bulb  35  and allows for the most efficient operation of the UV curing unit. 
     Though there have been attempts at combining into a single system both an IR dryer and a UV curing unit, such as those shown in FIGS. 1 and 2, problems occur with respect to the need to cool the components of each unit. In one design combining an IR dryer and a UV curing unit, the air used to cool the IR dryer and the UV curing unit is exhausted through the UV curing unit. However, removing the air used to cool the IR dryer by passing it through the UV curing unit presents two practical problems. First, the scrubbing action of the supply cooling air impinges on the coated substrate and when drawn past the ultraviolet bulb, can transfer dust and vapor from the substrate or coating to the bulb. When dust or vapor contact the bulb, the bulb&#39;s life is shortened and the ultraviolet energy output of the bulb is adversely affected. Second, the IR dryer and UV curing unit cannot be operated simultaneously because cooling air passing through the IR dryer will be heated such that it is no longer able to provide sufficient cooling capacity for the ultraviolet bulb and housing. The heated air likewise shortens the UV bulb life and may cause structural failure of the UV module housing. 
     The present invention solves both of these problems by combining both an IR dryer and a UV curing unit into a single system with a unique cooling system. FIG. 3 is a schematic view of a combination UV curing and IR dryer system  50  according to the present invention. The combination system  50  comprises an enclosure  52  containing two infrared heater modules  54 , one air-cooled ultraviolet curing module  56 , and a pathway  58  allowing a printed or coated substrate  60  to pass through the enclosure  52 . The IR heater and UV curing modules  54 ,  56  are mounted in close proximity to the coated side of the moving substrate  60  so that the substrate  60  can obtain either the required drying or curing. The substrate  60  may either be in the form of a supported or unsupported web or in the form of supported, discrete sheets. 
     An air supply  62 , such as a blower, is connected either remotely or directly to the enclosure  52 . The air supply  62  conveys cooling air into the enclosure  52  and to the IR heater modules  54  and the UV curing module  56 . Once supplied to the modules  54 ,  56 , the air may circulate through each module  54 ,  56  to cool any internal components as necessary. As the air exits the IR dryer modules  54 , it cools the IR bulbs. Similarly, as the air exits the UV curing unit  56 , it cools the UV bulb. After exiting the modules,  54 ,  56 , the now warmed air flows through the enclosure  52  as indicated generally by arrows  68 . The warmed air  68  may further be directed toward the printed material  60  as the substrate  60  passes through the enclosure to speed the drying of the material  60 . The warm air in the enclosure  52  is removed using an exhaust system, such as an air exhaust system  64 . 
     As can be seen, clean air is supplied to all modules  54 ,  56  by the air supply blower  62  along an air supply path  66 . Preferably, the air supply path  66  supplies an appropriate amount of air to each module  54 ,  56  as required for proper operation of the module. By supplying air to the modules  54 ,  56 , the modules are pressurized with clean air so that no contamination from the substrate  60  reaches the bulbs of either module  54 ,  56  and in particular the bulbs are kept clean and free of life shortening contaminants. The amount of air supplied to each module  54 ,  56  may vary depending on the desired performance of each module. It may be possible to design a controllable air supply to vary the amount of cooling air supplied to the modules  54 ,  56 . 
     The ability to control the amount of air supplied to the IR dryer module  54  may be used to increase an amount of air supplied to the dryer module  54  so that in addition to cooling the module  54 , the air can be directed toward the substrate  60 . Directing the air toward the substrate  60  may be advantageous because the warmed air can assist in removing water vapor in and near the IR coating on the substrate  60  allowing the substrate  60  to dry faster. The air flow to the UV curing module  56  may similarly be controlled to ensure the proper amount of air is supplied to the UV curing module  56 , which typically comprises only the amount of air necessary for cooling the UV module  56  and none extra directed toward the substrate  60  to be cured. 
     It will be apparent to those skilled in the art that there are many options for the air supply source, including an air supply blower attached to the housing or an air supply blower remotely located but capable of supplying the required air through a series of duct work. Further, it may be possible to draw air through the air supply system using only the air exhaust blower  64 . 
     The infrared heater and ultraviolet curing modules  54 ,  56  are spaced apart from one another by a distance sufficient to permit the cooling air which exits the drying and curing modules  54 ,  56  to be drawn into the unoccupied portions of the enclosure  52  and thence be conveyed to an air exhaust blower  64 . During the cooling process, energy is transferred from the hot surfaces to the air such that the air temperature will increase. 
     A particular benefit of the combination ultraviolet and infrared drying system is that the IR dryer module  54  and UV curing unit  56  can be used simultaneously. This is particularly advantageous because UV coating liquid is highly viscous, and when applied to a substrate  60 , may coat the substrate  60  unevenly and have a slightly bumpy appearance. The application of heat to the UV coating reduces the viscosity of the coating, removing the bumpy appearance of the coating on the substrate and making it easier to evenly apply the UV coating liquid to the substrate. In addition, when ultraviolet coatings with reduced viscosity are cured, they attain a smoother surface and provide increased gloss on the finished product, frequently considered a desirable attribute. 
     When operating the IR dryer module  54  during UV curing, it is not necessary to operate the IR dryer  54  at full capacity. Rather, the IR dryer module  54  may be operated at a lower energy, sufficient to have the desired effect on the UV coating. 
     Though only two IR heater modules  54  and a single UV curing module  56  are shown, the invention is not so limited and may contain more of either type of module. For instance, IR dryers having as many as eight IR dryer modules are not uncommon. The configuration and location of the IR dryers and UV curing modules  54 ,  56  is not important. However, it is desirable to arrange the modules  54 ,  56  so that when performing a UV cure, that the modules  54 ,  56  are configured to allow the substrate having the UV coating to be exposed to the IR dryer  54  first, thus reducing the viscosity of the UV coating before the substrate is exposed to the UV curing module  56  for curing. 
     There are a variety of IR dryers, similar to that shown in FIG. 1, which are suitable for use with the present invention. Any type of IR dryer having an air supply system is suitable. In particular, any IR dryer in which an air supply source draws in ambient air and pressurizes the housing to distribute the cooling air past a light reflector and the radiant energy source is suitable. Similarly, any number of UV curing units similar to that illustrated in FIG. 2 may be suitable for use with the present invention. 
     In addition to air cooled UV curing units, the present invention may include UV curing units which are water cooled. FIG. 4 shows a second embodiment of the present invention in which the UV curing unit is not air cooled, but rather is water cooled. 
     FIG. 4 is a schematic view of an alternate air flow system for use in a combination UV curing and IR drying system  70 . The combination system  70  shown in FIG. 4 comprises an enclosure  72  containing two infrared heater modules  74 , one ultraviolet curing module  76 , and a pathway  78  allowing a printed or coated substrate  80  to pass through the enclosure  72 , either as a supported or unsupported web, or as supported, discrete sheets. An air supply blower  82 , either remotely or directly connected to the enclosure  72  conveys cooling air into the enclosure  72  and to the infrared heater modules  74 . The infrared heater modules  74  and the ultraviolet curing module  76  are mounted in close proximity to the coated side of the moving substrate  80  so as to allow the substrate  80  to obtain the required drying or curing. In addition, the infrared heater modules  74  and ultraviolet curing module  76  are spaced apart from one another by a distance sufficient to permit the cooling air which exits the modules  74 ,  76  to be drawn into the unoccupied portions of the enclosure  72  and thence be conveyed to an air exhaust blower  84 . 
     The cooling system of the embodiment illustrated in FIG. 4 differs slightly from that shown in FIG.  3 . As can be seen from FIG. 4, the air supply blower  82  conveys cooling air to only the IR dryer modules  74  along an air supply path  86 . The cooling air supplied to the IR dryer modules  74  serves to cool the modules  74  as it moves through the modules  74 . The path of the now warm air is indicated generally by arrows  88 . The warm air is exhausted from the enclosure  72  using the exhaust blower  84 . Rather than being air cooled, the UV curing module  76  is configured with a separate cooling system, such as a water cooling system. 
     Once again, the main benefit of this embodiment of the combination system  70  is that it allows both the IR dryer modules  74  to be used at the same time as the UV curing module  76 . This is particularly advantageous in UV cures, where the IR dryer  74  can be operated at a lower energy to warm the UV coating liquid to reduce its viscosity, and thus improve the finished appearance of the substrate, before the substrate is UV cured. 
     FIG. 5 is a schematic view of yet another embodiment of the present invention. Shown in FIG. 5 is a combination ultraviolet curing and infrared drying system  90 . The combination system  90  comprises a web enclosure  92  located proximate the web  94 . Above the web  94  are two IR heater modules  96  and one UV curing module  98 . The modules  96 ,  98  are cooled by an air supply  100 , which provides air to each module  96 ,  98  through ducts  102 . The warmed air is removed from the system by an air exhaust  104 . The air exhaust  104  allows warm air to exit the combination system  90  at exhaust ducts  106 . 
     The configuration of the system  90  illustrated in FIG. 5 differs in that the web enclosure  92  does not surround the modules  96 ,  98 . Rather, the system  90  is designed so that while the heated air exiting the modules  96 ,  98  after cooling is not contained in an enclosure with the modules  96 ,  98 , the heated air none-the-less can be directed to the exhaust  104 . For instance, the web enclosure  92  may be in the form of reflectors on the back of the modules  96 ,  98  or reflectors positioned on the unexposed side of the web  94  which contain the heated air and direct it to the exhaust ducts  106 . Alternatively, the web enclosure  92  may be in the form of an enclosure surrounding the web  94  while the modules  96 ,  98  and air ducts  102  remain unenclosed. In such a system  90 , the modules  96 ,  98  are positioned in close proximity to the web  92  so that the heated air exits the modules  96 ,  98  and flows toward the web  92 . The warm air can be contained in the enclosure  92  surrounding the web  94  so that the air flow from the modules is directed past the web  94  to a common exhaust  104  located on the enclosure  92 . 
     Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention. For instance, there are many ways of arranging the drying and curing modules in conjunction with air control baffles and duct work such that the air can be properly distributed to and collected from the modules and the working surfaces.