Patent Publication Number: US-2002004994-A1

Title: Coating dryer system

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S)  
     [0001] This application is a continuing application of application Ser. No. 08/697,407, filed Aug. 23, 1996. 
    
    
     
       BACKGROUND OF TE INVENTION  
       [0002] The present invention relates to heating systems for drying wet coatings such as printing inks, paint, sealants, etc. applied to a substrate. In particular, the invention relates to a drying system in which a blower having an inlet directs a current of heated gas such as air towards a wet coating on a substrate to dry the coating and wherein the heated air is circulated back to the inlet of the blower once the air impinges the coating on the substrate. The present invention also relates to a drying system in which the substrate is supported about a thermally conductive roll having a plurality of energy emitters disposed within the conductive roll along a length of the conductive roll. The plurality of energy emitters are controlled to selectively emit energy along the length of the conductive roll. The dryer system preferably includes means for sensing temperatures of the roll along the length of the conductive roll, wherein the energy emitted by the energy emitters along the length of the roll varies based upon the sensed temperatures along the length of the roll.  
       [0003] Coatings, such as printing inks, are commonly applied to substrates such as paper, foil or polymers. Because the coatings often are applied in a liquid form to the substrate, the coats must be dried while on the substrate. Drying the liquid coatings is typically performed by either liquid vaporization or radiation-induced polymerization depending upon the characteristics of the coating applied to the substrate.  
       [0004] Water or solvent based coatings are typically dried using liquid vaporization. Dying the wet waterbased or solvent-based coatings on the substrate requires converting the base of the coating, either a water or a solvent, into a vapor and removing the vapor latent air from the area adjacent the substrate. For the base within the coatings to be converted to a vapor state, the coatings must absorb energy. The rate at which the state change occurs and hence the speed at which the coating is dried upon the substrate depends on the pressure and rate at which energy can be absorbed by the coating. Because it is generally impractical to increase drying speeds by decreasing pressure, increasing the drying speed requires increasing the rate at which energy is absorbed by the coating.  
       [0005] Liquid vaporization dryers typically use convection, radiation, conduction or a combination of the three to apply energy to the coating and the substrate to dry the coating on the substrate. With convection heating, a gas, such as relatively dry air, is heated to a desired temperature and blown onto the coating and the substrate. The amount of heat transferred to the substrate and coating is dependent upon both the velocity and the angle of the air being blown onto the substrate and the temperature difference between the air and the substrate. At a higher velocity and a more perpendicular angle of attack the air blown onto the substrate will transfer a greater amount of heat to the substrate. Moreover, the amount of heat transferred to the substrate will also increase as the temperature difference between the air and the substrate increases. However, once the substrate obtains a temperature equal to that of the temperature of the air, heat transfer terminates. In other words, the substrate will not get hotter than the air. Thus, the temperature of the air being heated can be limited to a level that is safe for the substrate.  
       [0006] Although controllable, convection heating is thermally inefficient. Because air, as well as nitrogen, have very low heat capacities, high volumes of air are required to transfer heat. Moreover, because the heated air blown onto the coating and substrate is typically allowed to escape once the heated air impinges upon the coating and the substrate, conventional drying systems employing convection heating typically use extremely large amounts of energy to continuously heat a large volume of outside ambient air to an elevated temperature in order to provide the high volumes of flow required for heat transfer. Because convection heating requires extremely large amounts of energy, drying costs are high.  
       [0007] Radiation heating occurs when two objects at different temperatures in sight are in view of one another. In contrast to convection heating, radiation heating transfers heat by electromagnetic waves. Radiation heating is typically performed by directing infrared rays at the coating and substrate. The infrared radiation is typically produced by enclosing electrical resistors within a tube of transparent quartz or translucent silica and bringing the electrical resistors to a red heat to emit a radiation of wavelengths from 10,000 to 30,000 angstrom units. The tubes typically extend along an entire width of the substrate.  
       [0008] The last method of applying energy to a coating and a substrate is through the use of conduction. Conductive heating of the coating and substrate is typically achieved by advancing a continuous substrate web about a thermally conductive roll or drum. Hot oil or steam is injected into the drum to heat the drum. As a result, the heated drum conducts heat to the substrate in contact with the drum. Because the drum must be configured so as to contain the hot oil or high pressure steam, the drum or roll is extremely complex and expensive to manufacture. In addition, because of the large mass of the drum required to accommodate the oil or high pressure steam, the dryer system employing the drum often requires a complex drive mechanism for rotating the heavy drums or rolls. This complex drive mechanism also increases the cost of the drying system. Moreover, because the oil or hot steam uniformly heats the thermally conductive drum across its entire length, the thermally conductive drum uniformly conducts energy or heat along the entire width of the substrate in contact with the drum regardless of varying drying requirements along the width of the substrate due to varying substrate and coating characteristics along the width of the substrate. As a result, portions of the substrate which do not contain wet coatings or which contain coatings that have already been dried unnecessarily receive excessive heat energy which is wasted. Conversely, other portions of the substrate containing large amounts of wet coatings may receive an insufficient amount of heat energy, resulting in extremely long drying times or offsetting of the wet coatings onto surfaces which come in contact with the wet coatings.  
       BRIEF SUMMARY OF THE INVENTION  
       [0009] The present invention is an improved dryer system for drying coatings applied to a substrate. In one preferred embodiment of the present invention, the dryer system includes a substrate support supporting the substrate, means for impinging the substrate with heated air, wherein the means for impinging has an inlet, and means for creating a partial vacuum adjacent the substrate to withdraw the heated air away from the substrate once the heated air has impinged the substrate. Preferably, the heated air withdrawn away from the substrate is circulated to the inlet once the heated air has impinged the substrate. In the preferred embodiment, the means for impinging preferably includes a pressure chamber adjacent the substrate, means for heating air within the pressure chamber and means for pressurizing air within the pressure chamber. The pressure chamber defies the inlet of the means for impinging and includes at least one outlet directed at the substrate. The means for circulating the heated air of the dryer system preferably includes a vacuum chamber in communication with the inlet of the means for impinging. The vacuum chamber has at least one inlet adjacent the substrate. Preferably, the pressure chamber includes a plurality of outlets and the vacuum chamber includes a plurality of inlets interspersed among and between the plurality of outlets. In the most preferred embodiment, the substrate support comprises a roll, wherein the means for impinging includes a plurality of outlets arcuately surrounding at least a portion of the roll and wherein the means for circulating includes a plurality of inlets arcuately surrounding at least a portion of the roll.  
       [0010] In another preferred embodiment of the dryer system, the dryer system includes a thermally conductive roll having a length and a peripheral surface for supporting the substrate. The dryer system also includes a plurality of energy emitters disposed within the conductive roll along the length of the conductive roll for emitting energy. The plurality of energy emitters are controlled to selectively emit energy along the length of the conductive roll. Preferably, the dryer system includes a plurality of temperature sensors along the length of the conductive roll. The energy emitted by the energy emitters along the length of the conductive roll is varied based upon sensed temperatures from the temperature sensors. In a most preferred embodiment of the dryer system, the energy emitters comprise band heaters.  
       [0011] In one preferred embodiment, the inventive dryer system is adapted for drying a coating applied to an advancing web. The dryer system includes a thermally conductive roll having an axial length and a circumferential outer surface for supporting the web. The housing extends about at least a portion of the roll, and the housing has an arcuate panel member radially spaced from the circumferential outer surface of the roll that extends along the length of the roll. The arcuate panel member has a plurality of alternating rows of coaxially extending inlet slots and recessed outlet troughs therein A blower and plenum chamber assembly is disposed in the housing between the inlet slots and the outlet troughs, and is in communication with the slots and troughs to substantially recirculate air that has been forced toward the cylindrical outer surface through the inlet slots and that has been drawn away from the cylindrical outer surface through the outlet troughs. An axially extending radiant energy heating element and a radiant energy reflective member are both removably mounted within selected outlet troughs, and the reflective member is aligned to reflect radiant energy emitted from its respective heating element toward the cylindrical outer surface.  
       [0012] In another preferred embodiment of the dryer system for drying a coating applied to an advancing web, the dryer system is convertible between a first dryer and a second dryer. In either event, the dryer system includes a thermally conductive roll having an axial length and a circumferential outer surface for supporting the web. A housing extends about at least a portion of the roll with the housing having an arcuate panel member radially spaced from the circumferential outer surface and extending along the length of the roll. The arcuate panel member has a plurality of alternating rows of coaxially extending inlet slots and recessed outlet troughs therein. A blower and plenum chamber assembly is disposed in the housing between the inlet slots and the outlet troughs, and is in communication with the slots and troughs to substantially recirculate air that has been forced toward the cylindrical outer surface through the inlet slots and that has been drawn away from the cylindrical outer surface through the outlet troughs. By exchanging components in the outlet trough, the dryer system is convertible between its first dryer configuration and its second dryer configuration. The first dryer has an axially extending radiant heating element and a radiant energy reflective member movably mounted within selected outlet troughs. The reflective member is aligned to reflect radiant energy emitted from its respective heating element toward the cylindrical outer surface, and has an aperture therein to permit the flow of air therethrough. The second dryer has a trough cover panel removably mounted over selected outlet troughs. Each cover panel has a plurality of openings therein to permit the flow of air therethrough and into the outlet trough, with the openings being selected and spaced to minimize the presence of an air flow gradient across each outlet trough. An air heater is provided for selectively preheating the air before it flows through the inlet slots.  
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0013] The present invention will be further explained with reference to the drawing figures listed below, wherein like structure is referred to by like numerals throughout the several views.  
     [0014]FIG. 1 is a side elevational view of a coating dryer system including a pair of convection units adjacent a substrate support.  
     [0015]FIG. 2 is a perspective view of a convection unit taken from a rear of the convection unit with portions exploded away.  
     [0016]FIG. 3 is a perspective view of a front side of the convection unit. IG.  4  is an enlarged sectional view of the substrate support.  
     [0017]FIG. 5 is an enlarged fragmentary cross-sectional view of the dryer system.  
     [0018]FIG. 6 is a schematic perspective view of an alternate embodiment of the dryer system.  
     [0019]FIG. 7 is a side elevational view of a second alternative embodiment of a coating dryer system of the present invention.  
     [0020]FIG. 8 is a perspective view of convection components of the inventive dryer system, as viewed from the rear, top and one side thereof, with portions exploded away.  
     [0021]FIG. 9 is a perspective view of the second alternative embodiment in a maintainance position, adjacent a web travel path, as viewed from the front, top and one side thereof  
     [0022]FIG. 10 is a generated planar view of an arcuate panel member of the convection components of the second alternative embodiment.  
     [0023]FIG. 11 is a sectional view as taken along lines  11 - 11  in FIG. 9.  
     [0024]FIG. 12 is an enlarged view of the circular portion labeled “FIG. 12” in FIG. 11.  
     [0025]FIG. 13 is an enlarged sectional view of one of the trough outlets in the arcuate panel member of a third alternative embodiment of the coating dryer system of the present invention.  
     [0026]FIG. 14 is a perspective view of a trough cover plate used to define a portion of the arcuate panel member of the third alternative embodiment.  
     [0027]FIG. 15 is a generated planar view of the arcuate panel member of the third alternative embodiment. 
    
    
     [0028] While the above-identified drawing figures set forth preferred embodiments of the invention, other embodiments are also contemplated, as noted in the discussion. In all cases, this disclosure presents the present invention by way of representation and not limitation It should be understood that numerous other modifications and embodiments can be devised by those skilled in the art which fall within the scope and spirit of the principles of this invention. It should be specifically noted that the figures have not been drawn to scale, as it has been necessary to enlarge certain portions for clarity.  
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
     [0029]FIG. 1 is a side elevational view of a coating dryer system  10  for drying a coati applied to substrate  12  having a front surface  14  and back surface  16 . Arrow heads  17  on substrate  12  indicate the direction in which substrate  12 , preferably a continuous web, is moved within coating dryer system  10 . System  10  generally includes enclosure  18 , positioning rolls  20 , substrate support  22 , energy emitters  24 , slip ring assembly  25 , convection units  26 ,  28 , temperature sensors  30  and controller  31 . Enclosure  18  is preferably made from stainless steel and houses and encloses dryer system  10 .  
     [0030] Positioning rolls  20  are rotatably coupled to enclosure  18  in locations so as to engage back surface  16  of substrate  12  to stretch and position substrate  12  about substrate support  22 . Positioning rolls  20  preferably support substrate  12  so as to wrap substrate  12  greater than approximately  290  degrees about substrate support  22  for longer dwell times and more compact dryer size. In addition, positioning rolls  20  guide and direct movement of substrate  12  through heater system  10 .  
     [0031] Substrate support  22  engages back surface  16  of substrate  12  and supports substrate  12  between and adjacent to convection units  26 ,  28 . Substrate support  22  preferably includes roll  32 , axle  33  and bearings  34 . Roll  32  preferably comprises an elongate cylindrical drum or roll having an outer peripheral surface  35  in contact with back surface  16  of substrate  12 . Roll  32  is preferably formed from a material having a high degree of thermal conductivity such as metal. In the preferred embodiment, roll  32  is made from aluminum and has a thickness of about {fraction (3/8)} of a inch. Preferably, surface  35  of roll  32  contacts the entire back surface  16  of substrate  12 . Because roll  32  is formed from a material having a high degree of thermal conductivity, roll  32  conducts excess heat away from areas on the front surface  14  of substrate  12  which do not carry wet coating such as inks. As a result, the areas of substrate  12  that do not contain a wet coating do not burn from being over heated by heater  36 . At the same time, because roll  32  is also in contact with areas on the front surface  14  of substrate  12  containing wet coatings such as inks, roll  32  conducts the excess heat back into the portions of substrate  12  containing wet coatings so that the coatings dry in less time. Axle  33  and bearings  34  rotatably support roll  32  with respect to enclosure  18  between convection units  26  and  28 . Although substrate support  22  preferably comprises a thermally conductive roll rotatably supported between convection units  26  and  28 , substrate support  22  may alternatively comprise any one of a variety of stationary or movable supporting structures having different configurations and made of different materials for supporting substrate  12  adjacent to convection units  26  and  28 .  
     [0032] Energy emitters  24  are positioned within roll  32  and are configured and oriented so as to emit energy towards surface  35  for drying coatings applied to substrate  12 . Slip ring assembly  25  transmits power to energy emitters  24  while energy emitters  24  rotate about axle  33  within roll  32 . Slip ring assembly  25  preferably comprises a conventional slip ring assembly as supplied by Litton Poly-Scientific, Slip Ring Products, 1213 North Main Street, Blacksburg, Va. 24060.  
     [0033] In the preferred embodiment illustrated, emitters  24  are supported along the inner circumferential surface of roll  32 . Because roll  32  is thermally conductive, the energy emitted by energy emitters  24  is conducted through roll  32  to back surface  16  of substrate  12 . This energy is absorbed by substrate  12  to dry the coatings applied to substrate  12 . Because energy emitters  24  are located within substrate support  22 , energy emitters  24  are shielded from hot air emitted by convection units  26  and  28 . As a result, energy emitters  24  are not directly exposed to the hot air which could otherwise damage energy emitters  24  depending upon the type of energy emitters utilized.  
     [0034] Convection units  26  and  28  are substantially identical to one another and are positioned adjacent substrate  12  opposite roll  32  of substrate support  22 . In the preferred embodiment illustrated, convection units  26  and  28  each include an arcuate surface  38  extending substantially along the length of roll  32  and configured so as to arcuately surround substrate  12  and roll  32  in close proximity with substrate  12 . Together, convection units  26  and  28  arcuately surround approximately  290  degrees of roll  32 . As a result, energy emitters  24  and convection units  26 ,  28  apply energy to substrate  12  for a greater period of time, allowing dryer system  10  to be more compact.  
     [0035] Convection units  26  and  28  apply energy in the form of a heated gas to substrate  12 . In particular, each convection unit  26 ,  28  impinges substrate  12  with heated dry air to dry the coating applied to substrate  12 . After the heated dry air has impinged upon substrate  12 , each convection unit  26 ,  28  recycles the heated air by repressurizing the air and reheating the air, if necessary, to the preselected desired temperature before once again impinging substrate  12  with the recycled heated air. To recycle the heated air once the heated air impinges upon substrate  12 , each convection unit  26 ,  28  circulates the heated air to an inlet of the means for impinging substrate  12  with heated air. Although dryer system is shown as including two convection units  26 ,  28  arcuately surrounding and positioned adjacent to substrate support  22  and substrate  12 , dryer system  10  may alternatively include a single convection unit or greater than two convection units adjacent to substrate support  22 .  
     [0036] Temperature sensors  30  are supported by enclosure  18  adjacent to and in contact with roll  32 . Temperature sensors  30  sense the temperature of substrate support  22 , and, in particular, roll  32 . Alternatively, sensors  30  may be positioned to sense temperatures of substrate  12 .  
     [0037] Controller  31  comprises a conventional control unit that includes both power controls and process controls. Controller  31  is preferably mounted to enclosure  18  and is electrically coupled to temperature sensors  30 , energy emitters  24  and convection units  26  and  28 . Controller  31  uses the sensed temperatures of roll  32  sensed by temperature sensors  30  to control energy emitters  24  and convection units  26 ,  28  to vary the energy applied to substrate  12 . As a result, dryer system  10  provides closed-loop feed back control of the energy applied to substrate  12 .  
     [0038]FIG. 2 is a perspective view of a preferred convection unit  26  taken from a rear of convection unit  26 , with portions exploded away for illustration purposes. As best shown by FIG. 2, the exemplary embodiment of convection unit  26  generally includes pressure chamber  42 , vacuum chamber  44 , blower  48 , heater  50 , temperature sensors  51  and seals  52 ,  54 . Pressure chamber  42  is an elongate fluid or air flow passage through which pressurized air flows until impinging substrate  12  (shown in FIG. 1). Pressure chamber  42  includes inlet  56 , blower housing  58 , duct  60  and plenum  62 . Inlet  56  of pressure chamber  42  is generally the location in which pressurized air enters pressure chamber  42 . In the preferred embodiment illustrated, inlet  56  comprises an outlet of blower  48 . Alternatively, inlet  56  may comprise any fluid passage in communication between pressure chamber  42  and whatever conventionally known means or mechanisms are used for pressurizing air within pressure chamber  42 .  
     [0039] Blower housing  58  is a generally rectangular shaped enclosure defining blower cavity  64  and forming flange  65 . Flange  65  extends along an outer periphery of blower housing  58  and fixedly mounts against seal  52  to seal blower cavity  64  about duct  60 . As a result, blower cavity  64  completely encloses and surrounds the outlet of blower  48  to channel and direct pressurized air from blower  48  through duct  60 .  
     [0040] Duct  60  is a conduit extending between blower cavity  64  and an interior of plenum  62 . Duct  60  provides an air tight passageway for pressurized air to flow from blower cavity  64  past vacuum chamber  44  into plenum  62 .  
     [0041] Plenum  62  is a generally sealed compartment formed from a plurality of walls including sidewalls  66 , rear wall  67 , interface wall  68  and top walls  69   a ,  69   b . The compartment forming plenum  62  is configured for containing the pressurized air and directing the pressurized air at substrate  12  along substrate support  22  (shown in FIG. 1). In particular, interface wall  68  extends opposite rear wall  67  and preferably defines the arcuate surface  38  adjacent to roll  32  (shown in FIG. 1). Rear wall  67  defines an inlet  70  while interface wall  68  defines a plurality of outlets  72 . Inlet  70  is an opening extending through rear wall  67  sized for mating with duct  60  for permitting pressurized air from duct  60  to enter into plenum  62 . Outlets  72  are apertures along arcuate surface  38  that extend through interface wall  68  to communicate with an interior of plenum  62 . Outlets  72  are preferably located and oriented so as to permit pressurized air within plenum  62  to escape through outlets  72  and to impinge upon substrate  12  before being recycled or recirculate by vacuum chamber  44 .  
     [0042] Vacuum chamber  44  is an elongate fluid or air flow passage extending from substrate  12  adjacent roll  32  of substrate support  22  (shown in FIG. 1) to blower  48 . Vacuum chamber  44  includes inlets  80 , channels  82  and outlet  84 . Inlets  80  are preferably interspersed among and between outlets  72  of pressure chamber  42  across the entire surface  38  adjacent substrate  12  and substrate support  22  for uniform withdrawal of air across the surface of the substrate. Inlets  80  extend along surface  38  between surface  38  and channels  82 . Channels  82  preferably comprise elongate troughs extending along surface  38  and recessed from inlets  80  to provide communication between vacuum chamber  44  and inlets  80 . Outlet  84  of vacuum chamber  44  communicates between vacuum chamber  44  and an inlet of blower  48 . As a result, blower  48  withdraws air from vacuum chamber  44  through outlet  84  to create the partial vacuum which draws heated air away from substrate  12  and substrate support  22  through inlets  80  once the heated air has impinged upon substrate  12 .  
     [0043] In the preferred embodiment illustrated, vacuum chamber  44  includes side walls  86  and rear wall  87 . Side walls  86  are spaced from side walls  66  of plenum  62  while rear wall  87  is spaced from rear wall  67  of plenum  62  to define the fluid or air flow passage comprising vacuum chamber  44 . As a result of this preferred construction in which vacuum chamber  44  partially encloses plenum  62 , side walls  66  and rear wall  67  of plenum  62  form a boundary of both plenum  62  and vacuum chamber  44  by serving as outer walls of plenum  62  and inner walls of vacuum chamber  44 . Consequently, convection unit  26  is more compact and less expensive to manufacture.  
     [0044] As further shown by FIG. 2, rear wall  87  of vacuum chamber  44  supports seals  52  and  54  and defines outlet  84  and opening  90 . Seal  52  is fixedly secured to an outer surface of rear wall  87  so as to encircle duct  60  and outlet  84  in alignment with flange  65  of blower housing  58 . Seal  52  preferably comprises a foam gasket which is compressed between flange  65  and rear wall  87  to seal between blower housing  58  and duct  60 .  
     [0045] Seal  54  is fixedly coupled to an exterior surface of rear wall  87  about outlet  84  of vacuum chamber  44 . Seal  54  is also positioned so as to encircle an inlet of blower  48 . Seal  54  seals between outlet  84  of vacuum chamber  44  and the inlet of blower  48 . Seal  54  preferably comprises a foam gasket.  
     [0046] Opening  90  extends through wall  87  and is sized for receiving duct  60 . Duct  60  extends between opening  90  within rear wall  87  and opening  70  within rear wall  67  of plenum  62 . Duct  60  is preferably sealed to both rear walls  67  and  87  by welding. Alternatively, duct  60  may be sealed adjacent to both rear wall  67  and  87  by gaskets or other conventional sealing mechanisms so as to separate the vacuum created between rear walls  67  and  87  of vacuum chamber  44  and the high pressure air flowing through duct  60 .  
     [0047] Blower  48  pressures air within pressure chamber  42  and creates the partial vacuum within vacuum chamber  44 . Blower  48  generally comprises a conventionally known blower having an inlet  92  and an outlet  94 . Blower  48  is preferably mounted within and partially through blower housing  58  so as to align inlet  92  with outlet  84  of vacuum chamber  44  surrounded by seal  54 . As a result, blower  48  draws air from vacuum chamber  44  through outlet  84  of vacuum chamber  44  and through inlet  92  to create the partial vacuum within vacuum chamber  44 . Blower  48  expels air through outlet  94  to pressure the air within pressure chamber  42 . Outlet  94  of blower  48  also serves as the inlet  56  of pressure chamber  42 .  
     [0048] Overall, blower  48  drives the current or flow of air by pressuring air within pressure chamber  42  and by withdrawing air from vacuum chamber  44 . As indicated by arrows  96   a , air is discharged from blower  48  out opening  94  into blower cavity  64  to pressurize air within blower cavity  64 . The pressurized air flows from blower cavity  64  through duct  60  into plenum  62  as indicated by arrows  96   b . Once within plenum  62 , the pressurized air escapes through outlets  72  to impinge upon substrate  12  to assist in drying coatings upon substrate  12  as indicated by arrows  96   c . Once the air has impinged upon substrate  12  (shown in FIG. 1), the vacuum pressure within vacuum chamber  44  draws the heated air into vacuum chamber  44  from substrate  12  through inlets  80 . As indicated by arrows  96   d , the vacuum pressure created at inlet  92  of blower  48  continues to draw the air through channels  82  and between side walls  66  and  86  and rear walls  67  and  87  until the heated air reaches outlet  84 . Finally, as indicated by arrows  96   e , the vacuum pressure created at inlet  92  of blower  48  sucks the air through outlet  84  of vacuum chamber  44  into inlet  92  of blower  48  where the air is once again recirculate.  
     [0049] Heater  50  heats recirculating air within convection unit  26 . As shown by FIG. 2, heater  50  preferably heats air within pressure chamber  42  just prior to the air entering plenum  62 . Preferably, heater  50  is positioned and supported within duct  60  so that the air flowing through duct  60  (as indicated by arrows  96   b ) flows through and across heaters  50  to elevate the temperature of the air flowing through duct  60 . Heater  50  reaches temperatures of approximately 1200° F. (649° C.) to effectively transfer heat to the air passing through duct  60 . Heater  50 , preferably comprises a fin heater such as those supplied by Watlow of St. Louis, Mo. under the trademark FINBAR. Although heater  50  is illustrated as consuming fin heaters mounted within duct  60  of convection unit  26 , heater  50  may comprise any one of a variety well known conventional heating mechanisms and structures for transferring heat and energy to air. Furthermore, heater  50  may alternatively be located so as to transfer heat to air within either pressure chamber  42  or vacuum chamber  44 . In addition, heater  50  may also alternatively comprise multiple heating units positioned throughout convection unit  26 . For example, heater  50  may alternatively include a fin heater positioned within duct  60  and a rod heater, such as those supplied by Watlow of St. Louis, Mo. under the trademark WATTROD, mounted within plenum  62 .  
     [0050] Temperature sensors  51  preferably comprise thermocouples mounted within duct  60  between heater  50  and plenum  62 . Temperature sensors  51  sense temperature of the air entering plenum  62 . The temperatures sensed by temperature sensors  51  are used by controller  31  (shown in FIG. 1) to regulate heater  50 . In particular, the amount of heat transferred to air flowing through duct  60  may be regulated by adjusting the temperature of heater  50  or by adjusting blower  48  to adjust the pressure of the air contained within pressure chamber  42  and flowing through duct  60 . As can be appreciated, temperature sensors  51  may alternatively be located in a large variety of alternative locations within convection unit  26 , including within plenum  62 .  
     [0051]FIG. 3 is a perspective view taken from a front side of convection unit  26  illustrating surface  38 , outlets  72  and inlets  80  in greater detail. As best shown by FIG. 3, arcuate surface  38  of wall has nine facets  98  which are slightly angled with respect to one another to provide arcuate surface  38  with its arcuate cross-sectional shape. Each facet  98  includes a plurality of outlets  72  along its length. Outlets  72  are preferably uniformly dispersed along the length of each facet  98  and among the facets  98  to establish an inlet array  100  that provides uniform air flow to substrate  12  (shown in FIG. 1). Inlet array  100  is preferably configured to optimize heat and mass transfer with convection flow. The particular size and distribution of outlets  72  along surface  38  is based upon optimum heat and mass transfer studies and calculations found in Holger Martin, “Heat and Mass Transfer Between Impinging Gas Jets and Solid Surfaces,” Advances in Heat Transfer Journal, Vol. 13, 1977, pp. 1-60 (herein incorporated by reference). In particular, assuming a turbulent air flow having a Reynolds value of greater than or equal to approximately 2,000, the size of outlets  72  is based upon the equation:  
       S= 1/5 H    
     [0052] where S is a diameter of the orifice constituting outlet  72  and H is the distance between outlet  72  and the surface of the substrate. Assuming an optimal orifice size, the spacing between outlets  72  is generally based upon the equation:  
       L= 7/5 H    
     [0053] where L is the spacing between the outlets  72  and H is the distance between outlet  72  and the substrate surface. As set forth in the optimizing equations, the size of each outlets  72  as well as the number of outlets  72  is dependent upon the distance between surface  38  and substrate  12  supported by substrate support  22  (shown in FIG. 1). The optimal spacial arrangement of outlet  72  (i.e. the combination of geometric variables that yields the highest average transfer coefficient for a given blower rating per unit area of transfer surface) is dependent upon three geometric variables for uniformly spaced arrays of outlets  72 : the size of outlets  72 , outlet-to-outlet spacing and the distance between surface  38  and substrate  12 . The configuration of inlet array  100  is also dependent upon the static pressure created by blower  48 .  
     [0054] In the preferred embodiment illustrated, surface  38  is approximately 450 square inches in surface area and is uniformly spaced from surface  35  of roll  32  (shown in FIG. 1) by approximately one inch. Blower  48  preferably creates approximately four inches water static pressure within plenum  62 . Due to minimal losses of air from convection unit  26 , blower  48  also creates approximately the same amount of vacuum within vacuum chamber  44 . Surface  38  includes approximately  378  outlets  72  which are dispersed in a generally hexagonal array pattern across surface  38  at a ratio of about 1.20 outlets 72 per square inch. Each of outlets  72  is preferably a circular orifice having a diameter of about 0.25 inches. To lower the velocity of the heated air exiting outlets  72 , the diameter of outlet  72  was increased from the calculated optimum of 0.2 inches to the preferred diameter of approximately 0.25 inches. As a result of the enlarged diameter of outlets  72 , the spacing between outlets  72  (0.5 inches) is less than the optimal spacing (1.4 inches) to ensure adequate surface area for inlets  80 . Although outlets  72  are preferably circular in shape, outlets  72  may alternatively have a variety of different shapes including slots. Furthermore, outlets  72  may also comprise circular or slotted nozzles for directing heated air or other heated gas at the substrate. In the preferred embodiment of convection unit  26 , heated air flows through each outlet  72  so as to strike the substrate with a velocity of approximately 25 miles per hour (36 feet per second). The air flowing through outlet  72  preferably has a maximum velocity of 30 miles per hour to prevent unintended movement of the coating across the surface of substrate  12 . As can be appreciated, the maximum velocity of air flow is dependent upon the particular substrate and the particular coating applied to the substrate.  
     [0055] Inlets  80  generally comprise openings uniformly spaced along surface  38  in communication with channels  82  behind surface  38  (shown in FIG. 2). Inlets  80  communicate between surface  38  and vacuum chamber  44  so that the partial vacuum created by blower  48  in vacuum chamber  44  draws heated air into vacuum chamber  44  through inlets  80  once the heated air has initially impinged upon the substrate. As shown by FIG. 3, inlets  80  extend along surface  38  between facets  98 . Inlets  80  are preferably sized as large as possible while maintaining the structural integrity of arcuate wall  68  and while also providing an adequate number of appropriately sized outlets  72  along surface  38 . Because inlets  80  are preferably sized as large as possible, inlets  80  permit the vacuum created by blower  48  within vacuum chamber  44  to withdraw a larger volume of heated air from along the substrate into vacuum chamber  44  to minimize losses of heated air from convection unit  26 . At the same time, by forming inlets  80  as large as possible, the suction through inlets  80  is reduced to insure that the heated pressurized air passing through outlets  72  impinges upon the substrate before being withdrawn into vacuum chamber  44  through inlets  80 .  
     [0056] In the preferred embodiment illustrated, surface  38  includes eighty inlets across the 450 square inch surface  38 . Each inlet  80  is a one by one square inch opening or orifice. As a result, surface  38  has approximately 80 square inches of vacuum inlets. Surface  38  also has approximately 18.55 square inches of pressurized outlets  72 . The ratio of inlet area to outlet area across surface  38  (i.e., the ratio of pressure to vacuum orifice area) is approximately 0.23. In other words, for every square inch opening in communication between substrate  12  and pressure chamber  42 , surface  38  has approximately 4.34 square inches of openings communicating between substrate  12  and vacuum chamber  44 . It has been discovered that this ratio of pressure chamber outlet opening to vacuum chamber inlet opening enables convection unit  26  to sufficiently impinge substrate  12  with heated air while adequately withdrawing heated air from substrate  12  to minimize the loss of heated air from convection unit  26  and to also improve drying efficiency by mining air pressure stagnation along substrate  12 .  
     [0057]FIG. 4 is a sectional view of roll  32  and energy emitters  24  with temperature sensors  30 . As best shown by FIG. 4, roll  32  is an elongate cylindrically shaped hollow drum having an exterior wall  110  and a pair of opposing end plates  112 ,  114 . Wall  110  has an exterior surface  35  and an interior surface  118  opposite surface  35 . Surface  35  is in contact with and supports substrate  12  (shown in FIG. 1). Because wall  110 , including surfaces  118  and  34 , is formed from a highly thermally conductive material such as aluminum, heat is thermally conducted through wall  110  and absorbed by substrate  12  (shown in FIG. 1).  
     [0058] End plates  112 ,  114  are fixedly coupled to wall  110  at opposite ends of roll  32 . Wall  110  and side plates  112 ,  114  form a substantially enclosed interior which contains energy emitters  24 .  
     [0059] Energy emitters  24  emit energy or heat to surface  118 . Surface  118  conducts the heat through wall  110  to the substrate supported by surface  35 . As best shown by FIG. 4, energy emitters  24  preferably include a plurality of distinct energy emitters  24   a - 24   i  disposed within roll  32  along the length of roll  32 . Energy emitters  24   a - 24   i  preferably extend along the entire inner circumferential surface of roll  32  and are positioned side-by-side so as to extend along a substantial portion of the length of roll  32 . Each energy emitter has a diameter comprised for sufficient encirculating the entire inner diameter of drum  32 . As shown by FIG. 4, each energy emitter  24   a - 24   i  generally comprises an annular thin band having an outer surface  120  placed in direct physical contact with surface  118  of roll  32  by adjustment of expansion mechanisms  122 . Expansion mechanisms  122  enable the diameter of each band heater to be adjusted to securely position surface  120  against surface  118  of roll  32 . Each energy emitter  24   a - 24   i  preferably has a width of approximately two inches.  
     [0060] Each energy emitter  24   a - 24   i  is selectively controllable so as to selectively emit energy along the length of conductor roll  32 . As a result, the amount of energy or heat conducted through wall  110  to the substrate supported by surface  35  may be selectively varied depending upon the character of the substrate and the coating applied to the substrate. For example, if the substrate upon which the coating is being dried has a reduced width relative to the length of roll  32 , one or more of energy emitters  24   a - 24   i  may be selectively controlled so as to emit a lower amount of heat or no heat at all to save energy and to maintain better control over the drying of the coating upon the substrate. If selected portions of the substrate along the width of the substrate have varying types or amounts of coatings applied thereon which require different amounts of heat for adequate drying, energy emitters  24   a - 24   i  may be selectively controlled to accommodate each substrate portion&#39;s specific coating drying requirements. As a result, energy emitters  24   a - 24   i  effectively dry coatings upon the substrate with less energy and with greater control of the heat applied to the substrate to provide for optimum drying times without damage such as burning or discolorization of the substrate.  
     [0061] In the preferred embodiment illustrated, energy emitters  24   a - 24   i  preferably comprise band heaters as are conventionally used for heating the inside diameter of large diameter blown film dies. Because energy emitters  24   a - 24   i  preferably comprise band heaters, the overall mass of roll  32  is low. As a result, roll  32  acts as an idler roll that rotates with movement of the substrate about roll  32  without a complex drive mechanism. Consequently, the manufacture, construction and cost of dryer system  10  is simpler and less expensive. The preferred band heaters are supplied by Watlow of St. Louis, Mo.  
     [0062] Although energy emitters  24   a - 24   i  are illustrated as being band heaters, energy emitters  24  may alternatively comprise any one of a variety of well known energy emitters such as resistive energy emitters, conductive energy emitters and radiant energy emitters. Examples of radiant energy emitters include tubular quartz infra-red lamps, quarts tube heaters, metal rod sheet heaters and ultraviolet heaters which emit radiation having a variety of different wave lengths and radiant energy levels. For example, energy emitters  24  may alternatively comprise a plurality of radiation emitting lamps aligned end to end along the length of roll  32  and positioned side by side around the entire inner surface of roll  32 . As with the band heaters, selective control of the end-to-end radiation emitting lamps could be used to provide selected controlled heating of wall  110  and the substrate in contact with wall  110  along the length of roll  32 .  
     [0063] Energy emitters  24   a - 24   i  receive power through slip ring assembly  25 . As shown in FIG. 4, slip ring assembly  25  includes lead wire  119  which supplies power to energy emitters  24   c ,  24   f  and  24   i . Slip ring assembly  25  also includes additional lead wires (not shown) for similarly supplying power to energy emitters  24   a ,  24   b ,  24   d ,  24   e ,  24   g ,  24   h  As further shown by FIG. 4, temperature sensors  30  include a plurality of individual temperature sensors  30   a - 30   i  corresponding to energy emitters  24   a - 24   i . Temperature sensors  30   a - 30   i  preferably comprise conventionally known thermocouples supported adjacent to surface  35  of roll  32  so as to glide upon surface  35 . Temperature sensors  30   a - 30   i  sense the temperature of roll  32  at surface  35  along the length of roll  32 . Controller  31  (shown in FIG. 1) uses the temperature sensed by sensors  30   a - 30   i  to control energy emitters  24   a - 24   i . As a result, sensors  30   a - 30   i  provide feed back for closed looped temperature control of energy emitters  24   a - 24   i  to precisely control the temperature of surface  35  along the entire length of roll  32 . The su temperature of surface  35  may be constant or selectively varied along the length of roll  32  based upon varying drying needs across the width of the substrate.  
     [0064]FIG. 5 is an enlarged fragmentary cross-sectional view of dryer system  10 . As best shown by FIG. 5, dryer system  10  includes an outer shell  130  that encloses convection units  26  and  28  and defines a dead air space  191  between convection units  26 ,  28  and shell  130  for insulating convection units  26 ,  28 .  
     [0065] As further shown by FIG. 5, back surface  16  of substrate  12  is positioned in close physical contact with surface  35  of roll  32  between roll  32  and convection units  26  and  28 . Energy emitter  24   a  (as well as the remaining energy emitters  24   b - 24   i  shown in FIG. 4) are positioned in close physical contact with surface  118  of drum  32  opposite substrate  12 . Energy emitters  24  emit energy in the form of heat towards surface  35 . This heat is conducted across the highly thermally conductive material forming wall  110  of roll  32  to back surface  16  of substrate  12 . Substrate  12  absorbs this heat to convert the base of the coating applied to substrate  12 , either a water or a solvent, into a vapor. At the same time, because surface  35  is highly thermally conductive, roll  32  conducts excessive heat away from areas on surface  14  of substrate  12  which do not carry wet coatings such as inks. As a result, the areas of substrate  12  not containing wet coatings do not burn from being over heated. At the same time, because roll  32  is also in contact with areas on the front surface  14  of substrate  12  containing wet coatings such as inks, roll  32  conducts the excessive heat back into these areas to decrease drying time and the amount of energy need to dry the coatings upon substrate  12 .  
     [0066] To precisely control the surface temperature of surface  35 , temperature sensors  30  glide over surface  35  to sense the temperature of surface  35  just prior to substrate  12  being wrapped about roll  32 . As a result, energy emitters  24  may be precisely controlled based upon sensing temperatures from temperature sensors  30  to precisely control the surface temperature of surface  35  and the heat applied to substrate  12  by energy emitters  24  and roll  32 .  
     [0067] At the same time that substrate  12  is absorbing heat conducted through roll  32  from energy emitters  24 , substrate  12  is also absorbing heat from convection units  26  and  28 . As indicated by arrows  126 , outlets  72  direct the heated high pressure air within plenum  62  towards front surface  14  of substrate  12 . As discussed above, outlets  72  are preferably sized and numbered so as to direct the heated high pressure air towards substrate  12  with a sufficient velocity and momentum so as to impinge upon front surface  14  of substrate  12  despite the relatively smaller vacuum or suction from inlets  80  of vacuum chamber  44 . The heated air striking front surface  14  of substrate  12  delivers heat to the coatings upon substrate  12  to assist in the conversion of the water or solvent in the coating into a vapor to dry the coating upon the substrate  12 . Once the heated air has impinged upon front surface  14  of substrate  12 , the velocity and momentum of the air decreases substantially. At this point, the vacuum created by blower  48  within vacuum chamber  44  (shown in FIG. 2) draws the heated air through inlets  80  into channels  82  where the heated air is recirculated back to blower  48  for repressurization and reheating. As a result, once the heated air impinges upon substrate  12 , the heated air is recycled by being recirculated back to blower  48  (shown in FIG. 2). As a result, a substantial portion of the heated air is returned to blower  48  for recirculation. Because a substantial portion of the heated air is not permitted to escape from dryer system  10  after impinging upon substrate  12 , dryer system  10  does not need to heat as large of a volume of air and is therefore more energy efficient. Moreover, the suction created by blower  48  and vacuum chamber  44  also enables the heated air flowing through outlets  72  to effectively dry the coatings upon substrate  12  with less energy and in less time. Typical convection dryers simply rely upon atmospheric pressure to bleed off heated air once the heated air has impinged upon the coating being dried. It has been discovered that once the heated air strikes the coating and the substrate, the air forms a layer or cushion of air over the coating and substrate to create a mild back pressure. Consequently, this cushion or layer of air interferes with and inhibits higher velocity air from subsequently reaching and impinging upon the coating and substrate. The vacuum created through openings  80  of vacuum chamber  44  withdraws the heated air once the heated air strikes or impinges upon the coating and substrate to minimize or prevent the formation of the stagnant cushion of air over the coating and substrate. The vacuum created through inlets  80  of vacuum chamber  44  also removes vapor saturated air from adjacent the substrate and coating so that air having a lower relative humidity may strike the coating to further absorb released vapors.  
     [0068] To maintain a low relative humidity of the air within plenum  62  (preferably between about one to five percent relative humidity), an extremely small amount of the circulating air, preferably approximately forty cubic feet per minute, is permitted to escape through natural openings within dryer system  10 . These natural openings occur between the outer walls of each convection unit  26 ,  28  which are preferably pop riveted together. Alternatively, a conventional exhaust system may be used for removing vapor saturated air to control the relative humidity of the air circulating within dryer system  10 . Because dryer system  10  recirculates most of the heated air rather than permitting a large volume of the heated air to escape to the outside environment, the user does not need to remove a large volume of air conditioned air from the building to operate the system. As a result, dryer system  10  conserves energy.  
     [0069] Overall, dryer system  10  effectively dries coatings applied to a surface of the substrate at a lower cost with less energy and in a smaller amount of time. Because energy emitters  24  may be controlled to selectively emit energy along the length of roll  32 , the amount of heat delivered along the length of roll  32  may be varied based upon varying drying requirements of the substrate and coating. Temperature sensors  30  further enable precise control of the surface temperature along the length of roll  32  to control the amount of heat delivered to substrate  12 . As a result, the amount of heat applied to substrate  12  from energy emitters  24  may be controlled to effectively dry the coating upon substrate with the least amount of energy in the shortest amount of time. Because a vacuum created by blower  48  (shown in FIG. 2) within vacuum chamber  44  withdraws heated air from the substrate once the heated air impinges upon the substrate, dryer system  10  achieves more effective air circulation adjacent to the substrate and coatings to more effectively dry the coatings upon the substrate. In addition, because the heated air is recirculated, rather than being released to the environment, system  10  requires less energy for heating air to an elevated temperature and also saves on cooling costs for the outside environment.  
     [0070] In addition to drying coatings with less energy, dryer system  10  is more compact, simpler to manufacture and less expensive than typical drying systems. Due to the arrangement of pressure chamber  42  and vacuum chamber  44 , dryer system  10  is compact and requires less space. Due to its simple construction and lightweight components, such as the band heaters comprising energy emitters  24 , dryer system  10  is lightweight and easy to manufacture. Because energy emitters  24  preferably comprise band heaters, roll  32  and heaters  24  have an extremely low mass. As a result, roll  32  does not require a complex drive mechanism which increases both the cost of manufacture and the cost of operation. In sum, dryer system  10  provides a cost effective apparatus for drying wet coatings applied to the surface of the substrate.  
     [0071]FIG. 6 is a schematic perspective view of dryer system  210 , an alternate embodiment of dryer system  10 . Dryer system  210  additionally further includes printers  213  and  215  and a substrate turn bar  217 . Dryer system  210  is substantially similar to dryer system  10  illustrated in FIGS.  1 - 5  except that dryer system  210  is alternatively configured for drying coatings applied to both surfaces, sure  14  and surface  16 , of substrate  12 . In particular, dryer system  210  includes a substrate support  22  including two rolls, rolls  232   a  and  232   b . Rolls  232   a  and  232   b  are each substantially identical to roll  32  of dryer system  10 . Rolls  232   a  and  232   b  each freely rotate about an axis  241  of a single axle  223 . As with roll  32  (shown in FIGS.  1 - 5 ), rolls  232   a  and  232   b  each contain energy emitters  24  which emit energy that is conducted through rolls  232   a  and  232   b  to dry the coating on substrate  12 . Because energy emitters preferably comprise band heaters, rolls  232   a  and  232   b  do not require complex space consuming drive mechanisms. Consequently, rolls  232   a  and  232   b  may be positioned end-to-end in relatively close proximity to one another. As a result, rolls  232   a  and  232   b  may be compactly positioned between convection units  26  and  28  for drying both sides of a substrate with a single drying unit. Temperature sensors  30  sense the temperatures of rolls  232   a  and  232   b  which is used by controller  31  to individually regulate energy emitters  24  within each roll  232   a  and  232   b . Also with dryer system  10 , dryer system  210  includes mirroring convection units  26  and  28  that arcuately surround a majority of rolls  232   a  and  232   b  to direct heated pressurized air with a selected velocity at the substrate  12  supported by rolls  232   a  and  232   b  to further deliver heat to the coatings. Once the heated air impinges upon substrate  12 , the heated air is withdrawn and recirculate as described above.  
     [0072] In operation, printer  213  applies a coating to surface  14  of substrate  12 . Substrate  12  is then advanced into a first end of convection unit  26  about roll  232   a  while heat is applied to the coating to dry the coating upon surface  14  of substrate  12 , as indicated by arrow  245 . Once the coating is dried upon surface  14  of substrate  12 , substrate  12  is withdrawn from roll  232   a  as indicated by arrow  247 . Once substrate  12  is withdrawn from roll  232   a , substrate turn bar  217  preferably flips or overturns substrate  12  and printer  215  applies a second coating to surface  16  of substrate  12 . As indicated by arrows  249 , substrate  12  is then advanced about roll  232   b  with surface  14  in contact with roll  232   b  while the second coating applied to surface  16  is dried. Once the second coating has dried upon surface  16  of substrate  12 , substrate  12  is withdrawn from between convection units  26  and  28  and is advanced about positioning rolls  20  as indicated by arrows  251  until substrate  12  reaches a second opposite side for further processing of substrate  12 . Dryer system  210  provides for fast and efficient drying of a coating applied to both surfaces of a substrate with a single compact dryer unit.  
     [0073]FIG. 7 is a side elevational view of another alternative coating dryer system  310  for drying a coating applied to a substrate  12  having a front surface  14  and back surface  16 . Arrowheads  317  on substrate  12  indicate the direction in which substrate  12 , preferably a continuous web, is moving within coating dryer system  310 . The system  310  is supported relative to a frame structure (not shown) which may or may not be enclosed. The frame structure also preferably supports positioning rolls  320 , substrate support  322 , convection housing  327  and controller  331 . Controller  331  comprises a conventional control unit that includes both power controls and process controls. Controller  331  may be mounted on the frame structure adjacent the dryer system  310 , or it may be mounted at a remote control panel for the substrate conveying stream process controls.  
     [0074] Positioning rolls  320  are rotatably coupled to the frame structure in locations so as to engage back surface  16  of substrate  12  to stretch and position substrate  12  about substrate support  322 . Positioning rolls  320  preferably support substrate  12  so as to wrap substrate  12  greater than approximately 290° about substrate support  322  for longer dwell times and more compact dryer size. In addition, positioning rolls  320  guide and direct movement of substrate  12  through heater system  310 .  
     [0075] Substrate support  322  engages back surface  16  of substrate  12  and supports substrate  12  within the convention housing  327 . Substrate support  322  preferably includes roll  332 , axle  333  and bearings  334 . Roll  332  preferably comprises an elongate cylindrical drum or roll having a cylindrical outer surface  335  in contact with back surface  16  of substrate  12 . Roll  332  is preferably formed from a material having a high degree of thermal conductivity such as metal. In the preferred embodiment, roll  332  is made from aluminum and has a thickness of about {fraction (3/8)} of an inch. Preferably, surface  335  of roll  332  contacts the entire back surface  16  of substrate  12 . Because roll  332  is formed from a material having a high degree of thermal conductivity, roll  332  conducts excess heat away from areas on the front surface  14  of substrate  12  which do not carry wet coatings such as inks. As a result, the areas of substrate  12  that do not contain a wet coating do not burn from being overheated during the drying process. At the same time, because roll  332  is also in contact with areas on the front surface  14  of substrate  12  containing wet coatings such as inks, roll  332  conducts the excess heat back into portions of substrate  12  containing wet coati so that the coating dry in less time. Axle  333  and bearings  334  rotatably support roll  332  with respect to the frame structure and in alignment with the convection housing  327 . Although substrate support  322  preferably comprises a thermally conductive roll rotatably supported and aligned relative to convection housing  327 , substrate support  322  may alternatively comprise any one of a variety of stationary or movable supporting structures having different configurations and made of different materials for supporting substrate  12  adjacent to the convection housing  327 .  
     [0076] The convection housing  327  is further illustrated in FIGS. 8 and 9. The convection housing  327  extends about the roll  332  of substrate support  322 . In the preferred embodiment illustrated, the convection housing  327  includes an arcuate panel member  337  extending substantially along the length of the roll  332  and configured so as to arcuately surround substrate  12  and roll  332  in close proximity with substrate  12 . The arcuate panel member  337  extends approximately 290° about the cylindrical outer sure  335  of roll  332  for the application of drying energy to substrate  12  thereon in as large an arc as possible (and for the largest possible dwell time of the substrate  12  within the coating dryer system  310 , thereby allowing the coating dryer system  310  to be more compact).  
     [0077] The convection housing  327  applies energy in the form of a heated gas to substrate  12  by impinging substrate  12  with heated dry air to dry the coating applied to substrate  12 . After the heated dry air has impinged upon substrate  12 , the convection housing  327  recycles the heated air by re-pressurizing the air and reheating the air, if necessary, to the preselected desired temperature before once again impinging substrate  12  with the recycled heated air. To recycle the heated air once the heated air impinges upon substrate  12 , the convection housing  327  circulates the heated air to an inlet of the means for impinging substrate  12  with heated air. Although the dryer system  310  is shown with the convection housing formed as a single unit arcuately surrounding and positioned adjacent to substrate support  322  and substrate  12 , the dryer system  310  may alternatively include two or more convection units adjacent to substrate support  322 .  
     [0078]FIG. 8 is a perspective view of the convection housing  327 , with some portions removed and a back portion exploded away for illustrative purposes. More specifically, an outer shell  339  of the convection housing  327  is shown in FIG. 7, along with an insulation layer  340  positioned between the outer shell  339  and an inner shell  341  of the convection housing  327 . In FIG. 8, the outer shell  339  and insulation layer  340  are removed for clarity of illustration.  
     [0079] As best shown by FIG. 8, the exemplary embodiment of convection housing  327  generally includes pressure chamber  342 , vacuum chamber  344 , blower  348 , one or more temperature sensors  351  and seals  352  and  354 . Pressure chamber  342  is an elongate fluid or air flow passage through which pressurized air flows until impinging surface  12  (shown in FIG. 7). Pressure chamber  342  includes inlet  356 , blower housing  358 , duct  360  and plenum  362 . Inlet  356  of pressure chamber  342  is generally the location in which pressuried air enters pressure chamber  342 . In the preferred embodiment illustrated, inlet  356  comprises an outlet of blower  348 . Alternatively, inlet  356  may comprise any fluid passage in communication between pressure chamber  342  and whatever conventionally known means or mechanisms are used for pressurizing air within pressure chamber  342 .  
     [0080] Blower housing  358  is a generally rectangular shaped enclosure defining blower cavity  364  and forming flange  365 . Flange  365  extends along an outer periphery of blower housing  358  and fixedly mounts against seal  352  to seal blower cavity  364  about duct  360 . As a result, blower cavity  364  completely encloses and surrounds the outlet of blower  348  to channel and direct pressurized air from blower  348  through duct  360 .  
     [0081] Duct  360  is a conduit extending between blower cavity  364  and an interior of plenum  362 . Duct  360  provides an airtight passageway for pressurized air to flow from blower cavity  364  past vacuum chamber  344  into plenum  362 .  
     [0082] Plenum  362  is a generally sealed compartment formed from a plurality of walls including side walls  366 , rear wall  367 , arcuate panel member  337 , top wall  369 , front walls  371   a ,  371   b ,  371   c  and  371   d  and bottom wall  373 . The compartment forming plenum  362  is configured for containing the pressurized air and directing the pressurized air at substrate  12  and along roll  332  (shown in FIG. 1). In particular, arcuate panel member  337  defines an arcuate surface adjacent to and spaced from roll  332  (as shown in FIG. 1). Rear wall  367  defines an inlet  370 , and arcuate panel member  337  defines a plurality of inlet slots  372 . Inlet  370  is an opening extending through rear wall  367  sized for mating with duct  360  for permitting pressurized air from duct  360  to enter into plenum  362 . Inlet slots  372  are apertures extending coaxially (relative to the axis of the roll  332 ) through the arcuate panel member  337  to communicate with an interior of plenum  362 . Inlet slots  372  are preferably located and oriented so as to permit pressurized air within plenum  362  to escape through inlet slots  372  and to impinge upon substrate  12  before being recycled or recirculate by vacuum chamber  344 .  
     [0083] Vacuum chamber  344  is an elongate fluid or air flow passage extending from substrate  12  adjacent roll  332  (shown in FIG. 7) to blower  348 . Vacuum chamber  344  includes inlets  380 , outlet troughs  382  and outlet  384 . Inlets  380  are preferably interspersed among and between inlet slots  372  of pressure chamber  342  across the entire arcuate panel member  337  adjacent substrate  12  and roll  332  for uniform withdrawal of air across the surface of the substrate  12 . Inlets  380  extend along the arcuate panel member  337  between its arcuate surface and the outlet troughs  382  therebelow. Each outlet trough  382  preferably comprises an elongated recess or trough extending laterally along the arcuate surface of arcuate panel member  337  and recessed radially outwardly from inlets  380  to provide fluid communication between vacuum chamber  344  and inlets  380 . Outlet  384  of vacuum chamber  344  communicates between vacuum chamber  344  and an inlet of blower  348 . As a result, blower  348  withdraws air from vacuum chamber  344  through outlet  384  to create the partial vacuum which draws heated air away from substrate  12  and roll  332  through inlets  380 , once the heated air has impinged upon substrate  12 .  
     [0084] In the preferred embodiment illustrated, vacuum chamber  344  includes side walls  386 , rear wall  387 , top wall  388  and bottom wall  389 . Side walls  386  are spaced from side walls  366  of plenum  362  while rear wall  387  is spaced from rear wall  367  of plenum  362  to define the fluid or air flow passage comprising vacuum chamber  344 . A front wall  391  also serves to define a portion of the fluid or air flow passage comprising vacuum chamber  344  (and also in part defines front wall sections  371   a ,  371   b ,  371   c , and  371   d  of the plenum  362 ). As a result of this preferred construction in which vacuum chamber  344  partially encloses plenum  362 , side walls  366  and rear wall  367  of plenum  362  form a boundary of both plenum  362  and vacuum chamber  344  by serving as outer walls of plenum  362  and inner walls of vacuum chamber  344 . Consequently, convection housing  327  is more compact and less expensive to manufacture.  
     [0085] As further shown by FIG. 8, rear wall  387  of vacuum chamber  344  supports seals  352  and  354  and defines outlet  384  and opening  390 . Seal  352  is fixedly secured to an outer surface of rear wall  387  so as to encircle duct  360  and outlet  384  in alignment with flange  365  of blower housing  358 . Seal  352  preferably comprises a foam gasket which is compressed between flange  365  and rear wall  387  to seal between blower housing  358  and duct  360 .  
     [0086] Seal  354  is fixedly coupled to an exterior surface of rear wall  387  about outlet  384  of vacuum chamber  344 . Seal  354  is also positioned so as to encircle an inlet of blower  348 . Seal  354  (preferably a foam gasket) seals between outlet  384  of vacuum chamber  344  and the inlet of blower  348 .  
     [0087] Opening  390  extends through wall  387  and is sized for receiving duct  360 . Duct  360  extends between opening  390  within rear wall  387  and opening  370  within rear wall  367  of plenum  362 . Duct  360  is preferably sealed to both rear walls  367  and  387  by welding. Alternatively, duct  360  may be sealed adjacent to both rear walls  367  and  387  by gaskets or other conventional sealing mechanisms so as to separate the vacuum created between rear walls  367  and  387  of vacuum chamber  344  and the high pressure air flowing through duct  360 .  
     [0088] Blower  348  pressurizes air within pressure chamber  342  and creates the partial vacuum within vacuum chamber  344 . Blower  348  generally comprises a conventionally known blower having an inlet  392  and an outlet  394 . Blower  348  is preferably mounted within and partially through blower housing  358  so as to align inlet  392  with outlet  384  of vacuum chamber  344  surrounded by seal  354 . As a result, blower  348  draws air from vacuum chamber  344  through outlet  384  of vacuum chamber  344  and through inlet  392  to create the partial vacuum within vacuum chamber  344 . Blower  348  expels air through outlet  394  to pressurize the air within pressure chamber  342 . Outlet  394  of blower  348  also serves as the inlet  356  of pressure chamber  342 .  
     [0089] Overall, blower  348  drives the current or flow of air by pressurizing air within pressure chamber  342  and by withdrawing air from vacuum chamber  344 . As indicated by arrows  396   a , air is discharged from blower  348  out opening  394  into blower cavity  364  to pressurize air within the blower cavity  364 . The pressurized air flows from blower cavity  364  through duct  360  into plenum  362  as indicated by arrows  396   b . Once within plenum  362 , the pressurized air escapes through inlet slots  372  to impinge upon substrate  12  to assist in drying coatings upon substrate  12  as indicated by arrows  396   c . Once the air has impinged upon substrate  12  (shown in FIG. 7), the vacuum pressure within vacuum chamber  344  draws the air into vacuum chamber  344  from substrate  12  through inlets  380 . As indicated by arrows  396   d , the vacuum pressure created at inlet  392  of blower  348  continues to draw the air through outlet troughs  382  and between side walls  366  and  386  and rearwall  367  and  387  until the air reaches outlet  384 . Finally, as indicated by arrows  396   e , the vacuum pressure created at inlet  392  of blower  348  sucks the air through outlet  384  of vacuum chamber  344  into inlet  392  of blower  348  where the air is once again recirculate. Blower  348  is driven by motor  397  which is coupled thereto by drive belt  398  and associated pulleys therefor (or other suitable drive means). The activation and operation of motor  397  (and hence blower  348 ) is controlled by controller  331 .  
     [0090] In FIG. 9, an exemplary frame structure  399  for the coating dryer system  310  is illustrated. Roll  332  and positioning rolls  320  are rotatably supported on frame structure  399 . Convection housing  327  is preferably supported upon sliding rail structure  400  which, in turn, is mounted on frame structure  399 . As seen, the convection housing  327  has been slid axially or laterally out of the frame structure  399  along sliding rail structure  400  to permit access to arcuate panel member  337  thereof. Movement of the convection housing  327  in direction of arrow  401  repositions the convection housing  327  in position surrounding and along the roll  332  for drying of coatings on a web traversed thereby.  
     [0091]FIG. 10 is a flat, generated view of the arcuate panel member  337 , and is provided to more fully illustrate the surface of the arcuate panel member  337  facing the substrate  12  and roll  332 . The side-by-side arrangement of inlet slots  372  and outlet troughs  382  is more clearly shown in this representation. The inlet slots are aligned in parallel rows which extend coaxial with the axis of the roll  332  and perpendicular to the path of travel of the substrate  12 . Preferably, a plurality of slots comprise each lateral roll of slots  372 . The outlet troughs  382  also extend coaxially with the roll  332  axis and laterally across the travel path of the substrate  12 , with each outlet trough  382  disposed between adjacent rows of inlet slots  372 . In FIG. 10, each outlet trough  382  is covered by a lamp assembly  402  which includes the heating lamp bulb  403 , reflective member  404  and trough cover  405 .  
     [0092] While alternating inlet slots  372  and outlets  380 /lamp assemblies  402  can be arranged for use on a single substrate travel path, FIG. 10 illustrates an arcuate panel member  337  which is sized for a pair of side-by-side rolls  332  (for a dryer system such as that shown in FIG. 6). Thus, along each side of the arcuate panel member  337 , the lamp assemblies  402  are positioned in alternate troughs, with a trough cover  405  in place over the other outlet troughs  382  on that side of the arcuate panel member  337 . The trough covers  405  serve to mask portions of the outlet troughs  382  and prevent airflow therethrough. Thus, air being recirculate must travel past the lamp bulbs  403  in order to enter the inlets  380  in the reflective members  404  and get into the outlet troughs  382 . This arrangement is reversed on the other side of the arcuate panel member so that the lamp assemblies  402  are aligned in a laterally staggered pattern across the surface of the arcuate panel member  337 . Preferably, the heating laments of the heating lamp bulbs  403  do not overlap adjacent the lateral center of the arcuate panel member  337  in order to minimize energy spillover from one web path to the other web path (thereby maintaining the discrete heating functions for each of the separate side-by-side rolls in a duplex coating dryer system of the type shown in FIG. 6). The lamp assemblies  402  and related air flows for each of the separate side-by-side rolls are separately controlled in operation by controller  331 . While a side-by-side arrangement is illustrated, it is contemplated that a number of alternative configurations will work to achieve the desired end, and it is not intended that the invention be limited by way of mere illustration.  
     [0093] As perhaps best shown in FIG. 11, the arcuate panel member  38  is actually comprised of a plurality of laterally extending planar facets  440  which are angled with respect to one another to define an arcuate surface about the roll  332 . Each facet  440  includes a plurality of the inlet slots  372  which are preferably uniformly dispersed along the length of each facet  440  and among the facets  440  to establish an inlet array that provides uniform air flow to substrate  12  (shown in FIG. 7). As discussed herein with respect to other embodiments, the inlet array is preferably configured to optimize heat and mass transfer with convection flow.  
     [0094] In the preferred embodiment illustrated in FIG. 10, arcuate panel member  337  is approximately 450 square inches in surface area and is uniformly spaced from surface  335  of roll  332  (shown in FIG. 7) by approximately one inch. Blower  348  preferably creates approximately 4 inches of water static pressure within plenum  362 . Due to minimal losses of air from convection housing  327 , blower  348  also creates approximately one inch of vacuum within vacuum chamber  344 . Arcuate panel member  337  includes 20 rows of laser cut inlet slots  372 , with each row having approximately 22 inches of slot length, and each slot being approximately 0.025 inches thick. In the preferred embodiment of convection housing  327 , air flows out of each inlet slot at a velocity of approximately 7000 feet per minute. As can be appreciated, the desired velocity of air flow is dependent upon the particular substrate and particular coating applied to the substrate.  
     [0095] As used in FIGS. 11 and 12, inlets  380  are formed as openings in the reflective member  404 . Preferably, these openings are slots extending laterally across the path of the substrate  12  in communication with the outlet troughs  382  behind arcuate surface panel  337 . Inlets  380  communicate between arcuate panel member  337  and vacuum chamber  344  so that the partial vacuum created by blower  348  in vacuum chamber  344  draws air into vacuum chamber  344  through inlets  380  once the air has initially impinged upon the substrate  12 .  
     [0096] Inlets  380  are preferably sized as large as possible while maintaining the structural integrity of the reflective member  404  and while also providing an adequate number of appropriately sized inlets  380  therethrough. Because inlets  380  are preferably sized as large as possible, inlets  380  permit the vacuum created by blower  348  within vacuum chamber  344  to draw a larger volume of air from along the substrate  12  into vacuum chamber  344  to minimize losses of air from the convection housing  327 . Forming the inlets  380  as large as possible also aids in minimizing back pressure. As best seen in FIG. 12, inlets  380  are preferably formed as slots with punched tabs or louvers  406  associated therewith. The reflective member  404  is preferably formed from an aluminum sheet which is highly polished on its reflective side  407  so that radiation emitted from the heating lamp bulb  403  is directed toward the substrate  12  and wet coating  408 .  
     [0097] In the preferred embodiment illustrated, each inlet  380  is 0.10 inches wide and 0.50 inches long, and there are 960 inlets  380  across the surface of the arcuate panel member  337 . As a result, the arcuate panel member  337  has approximately 48 square inches of vacuum inlets. The arcuate panel member also has approximately 6.6 square inches of pressurized inlet slots  372 . The ratio of inlet area to outlet area across the arcuate panel member  337  (i.e., the ratio of pressure to vacuum orifice area) is approximately 0.14:1. In other words, for every square inch opening in communication between substrate  12  and pressure chamber  342 , the arcuate panel member  337  has approximately 7.3 square inches of openings communicating between substrate  12  and vacuum chamber  344 . This ratio of pressure chamber outlet opening to vacuum chamber inlet opening enables convection housing  327  to sufficiently impinge substrate  12  with air while adequately withdrawing air from substrate  12  to minimize the loss of air from convection housing  327  and to also improve drying efficiency by minimizing air pressure stagnation along substrate  12 .  
     [0098] In one preferred embodiment, the lamp assemblies  402  are the sole means for heating the air being channeled through the convection housing  327 . The heating lamp bulb  403  provides radiant heat energy to the substrate  12  as it passes thereby (by direct and reflected radiant energy), and also heats the air as it moves past the lamp bulb  403  and into the outlet trough  382  for recirculation by blower  348 . The rapid movement of air past the heating lamp bulb  403  also serves to cool the lamp bulb  403  and its supportive fittings. Preferably, the lamp bulb is a Model No. 150072 Phillips HeLeN infrared halogen lamp, 1000 watts, T3 lamp, rated at 240 volts (having an overall length of approximately 13 inches, a lighted length of about 10 inches and a diameter of about {fraction (3/8)} inches), available from Phillips Lighting.  
     [0099] The lamp assemblies  402  are shaped to be readily received and removable within the outlet troughs  382 . As best seen in FIG. 12, side walls  410  of each reflective member  404  at least partially abut against side walls  412  of its respective outlet trough. Each reflective member  404  has side flanges or a plurality of side tabs  414  which are adapted to extend along the surface of the arcuate panel member  337  adjacent the opening of its respective outlet trough  382 . Suitable fasteners  416  (e.g., sheet metal screws) are used to secure the tabs  414  of the reflective member  404  to the arcuate panel member  337 , as seen in FIG. 12. Each trough cover  405  is likewise removably secured in place over its respective outlet trough  382 . This arrangement provides for easy assembly and defines a modularity for the components for the coating dryer system  310 , allowing its ready conversion to alternative dryer configurations, as disclosed herein. Each reflective member  404  and trough cover  405  is secured to the arcuate panel member  337  and defines a seal thereto along its edges and ends so that the passage of air into the outlet trough  382  must take place through the inlets  380 .  
     [0100] The coati dryer system  310  thus provides radiant and convection heating means for the substrate  12  and coatings  408  thereon. While not illustrated in this embodiment, other additional heating means may be provided for drying the coatings  408  on the substrate  12 , including further heaters in the air stream or energy emitters within the roll  32 , such as those energy emitters  24  shown on the roll  32  in FIGS. 4 and 5.  
     [0101] In a preferred embodiment, the surface  335  of roll  332  has a coating  420  thereon to assist in dissipation of vapors from the substrate  12  (see FIG. 12). Preferably, coating  420  is a thin, thermally conductive and roughened coating on the cylindrical outer surface  335  of roll  332 . In one embodiment, coating  420  is formed as a two-part coating, with a first layer of tungsten carbide particles, and a second layer of silicone-based release coating material which provides a good grip on the substrate, with a somewhat roughened texture so that water vapors can migrate away from the substrate. Such coatings are available from Plasma Coatings, Inc., Bloomington, Minn., and the preferred coating is more specifically identified as a PC-914 coating In one embodiment, coating  420  is relatively dark (i.e., black or some other dark color) to more fully absorb infrared energy emitted from the heating lamp bulbs  403  and reflected onto the roll  332  by the reflective member  404 .  
     [0102] The operation of the lamp assemblies  402  and other possible heating assemblies are controlled by the controller  331 . One or more temperature sensors are provided to sense the temperature of the surface  335  of the roll  332 . One such sensor  409  is illustrated in FIG. 11 as an optical sensor, although contact temperature sensors (such as sensors  30  shown in FIGS. 4 and 5) may suffice. Inputs are provided to the controller relative to the substrate  12  and its desired coatings  408 , and operational inputs are provided from temperature sensors  351  and  409  so that the desired air temperature and dwell time for the substrate within the convection housing  327  is achieved. Preferably, temperature sensor  351  is a thermocouple mounted within plenum  362 , and more preferably, temperature sensor  351  is mounted within pressure chamber  342  and adjacent the inlet slots  372  to ascertain the heated air temperature just prior to its impingement on substrate  12 . The preferred air temperature will vary depending upon the application, but temperature ranges (as measured in pressure chamber  342 ) of 150-225° F. are contemplated. Additional temperature sensors  351  located within the air stream in convection housing  327  may also be desired, such as within outlet troughs  382  or adjacent blower  348 , for example. The temperature sensed by temperature sensors  351  are used by controller  331  to regulate the energy emitted by the heating lamp bulbs  403 . As a result, the dryer system  310  thus provides closed loop feedback control of the energy applied to substrate  12 .  
     [0103]FIG. 11 is an enlarged fragmentary cross-sectional view of coating dryer system  310 . As best shown in FIG. 11, dryer system  310  includes an outer shell  339  that encloses convection unit  327  and defines a space between an inner shell  341  thereof for reception of insulating material  340 , such as Melamine polymeric foam sheeting available from Accessible Products Co., Tempe, Ariz.  
     [0104] As further shown by FIG. 11, back surface  16  of substrate  12  is positioned in close physical contact with surface  335  of roll  332  between roll  332  and convection housing  327 . Heat energy emitted by the lamp assemblies  402  is absorbed by substrate  12 , as well as roll  332 . Substrate  12  absorbs this heat to convert the base of the coating  408  applied to substrate  12 , either a water or a solvent, into a vapor. At the same time, because surface  335  is highly thermally conductive, roll  332  conducts excessive heat away from areas on surface  14  of substrate  12  which do not carry wet coatings such as inks. As a result, the areas of substrate  12  not containing wet coatings do not burn or blister from being overheated. At the same time, because roll  332  is also in contact with areas on the front surface  14  of substrate  12  containing wet coatings such as inks, roll  332  conducts the excessive heat back into those areas to decrease drying time and the amount of energy needed to dry the coatings  408  upon substrate  12 .  
     [0105] To precisely monitor and control the surface temperature of surface  335 , one or more temperature sensors  409  sense the temperature of surface  335  just prior to substrate  12  being wrapped about roll  332 . As a result, the heat energy output from lamp assemblies  402  may be precisely controlled based upon sensing temperatures from temperature sensors  409  in order to precisely control the surface temperature of surface  335  and the heat applied thereto and to substrate  12  by lamp assemblies  402 .  
     [0106] At the same time that substrate  12  is absorbing heat conducted through roll  332 , substrate  12  is also absorbing radiant heat from lamp assemblies  402  and heat by means of convection from the heated air passing thereover from convection housing  327 . As indicated by arrows  396   c , inlet slots  372  direct the heated high pressure air within plenum  362  toward front surface  14  of substrate  12 . As discussed above, inlet slots  372  are preferably sized, shaped and numbered so as to direct the heated high pressure air toward substrate  12  with a sufficient velocity and momentum so as to impinge upon front surface  14  of substrate  12  despite the relatively smaller vacuum or suction from inlets  380  of vacuum chamber  344 . The heated air striking front surface  14  of substrate  12  delivers heat to the coatings  408  upon substrate  12  to assist in the conversion of the water or solvent in the coating  408  into a vapor to dry the coating  408  upon the substrate  12 . Once the heated air has impinged upon front surface  14  of substrate  12 , the velocity and momentum of the air decreases substantially. At this point, the vacuum created by blower  348  within vacuum chamber  344  (shown in FIG. 8) draws the heated air through inlets  380  in the reflective member  404  and into the outlet troughs  382 , where the heated air is recirculate back to blower  348  for repressurization and reheating. As a result, once the heated air impinges upon substrate  12 , the heated air is recycled by being recirculate back to blower  348  (shown in FIG. 8). Thus, a substantial portion of the heated air is returned to blower  348  for recirculation. Because a substantial portion of the heated air is not permitted to escape from coating dryer system  310  after impinging upon substrate  12 , dryer system  310  does not need to heat as large a volume of air and is therefore more energy efficient. Moreover, the suction created by blower  348  in vacuum chamber  344  also enables the heated air flowing through inlet slots  372  to effectively dry the coatings  408  upon substrate  12  with less energy and in less time. Lamp assemblies  402  may be controlled to selectively emit energy along the roll  332 , and the amount of heat delivered may be varied based upon varying drying requirements of the substrate and coating. Temperature sensors  409  further enable precise control of the surface temperature along the roll  332  to control the amount of heat delivered to substrate  12 . As a result, the amount of heat applied to substrate  12  may be controlled to effectively dry the coating upon substrate  12  with the least amount of energy and in the shortest amount of time. Because the vacuum created by blower  348  (shown in FIG. 8) within vacuum chamber  344  withdraws heated air from the substrate  12  once the heated air impinges upon the substrate  12 , coating dryer system  310  achieves more effective air circulation adjacent to the substrate  12  and coatings thereon to more effectively dry the coatings upon the substrate  12 . In addition, because the heated air is recirculate rather than being released to the environment, dryer system  310  requires less energy for heating air to an elevated temperature and also saves on cooling costs for the outside environment.  
     [0107] In addition to drying coatings with less energy, coating dryer system  310  is more compact, simpler to manufacture and less expensive than typical drying systems. Due to the arrangement of pressure chamber  342  and vacuum chamber  344 , dryer system  310  is compact and requires less space. Due to its simple construction and lightweight components, dryer system  310  is lightweight and easy to manufacture. In sum, dryer system  310  provides a cost-effective apparatus for drying wet coatings applied to the surface of a substrate.  
     [0108] Typical convection dryers simply rely upon atmospheric pressure to bleed off heated air once the heated air has impinged upon the coating being dried. It has been discovered that once the heated air strikes the coating and substrate, the air forms a layer or cushion of air over the coating and substrate to create a mild back pressure. Consequently, this cushion or layer of air interferes with and inhibits higher velocity air from subsequently reaching and impinging upon the coating and substrate. The vacuum created through inlets  380  of vacuum chamber  344  withdraws the heated air once the heat air strikes or impinges upon the coating and substrate to minimize or prevent the formation of the stagant cushion of air over the coating and substrate. The vacuum created through inlets  380  of vacuum chamber  344  also removes vapor-saturated air from adjacent the substrate and coating so that air having a lower relative humidity may strike the coating to further absorb released vapors.  
     [0109] To maintain a low relative humidity of the air within plenum  362  (preferably less than 15% relative humidity), an extremely small amount of circulating air, preferably approximately 40 cubic feet per minute, is permitted to escape through natural openings within dryer system  310 . These natural openings occur between the walls of convection housing  327 , which are preferably pop riveted together. Alternatively, a conventional exhaust system may be used for removing vapor-saturated air to control the relative humidity of the air circulating within coating dryer system  310 . Because dryer system  310  recirculates most of the heated air rather than permitting a large volume of the heated air to escape to the outside environment, the user does not need to remove a large volume of conditioned air from the building to operate the system. As a result, coating dryer system  310  conserves energy.  
     [0110] Overall coating dryer system  310  effectively dries coatings applied to a surface of the substrate at a lower cost with less energy and in a smaller amount of time. Lamp assemblies  402  may be controlled selectively to emit energy along the roll  332 , and the amount of heat delivered may be varied based upon varying drying requirements of the substrate and coating. Temperature sensors  409  further enable precise control of the surface temperature along the roll  352 , to control the amount of heat delivered to substrate  12 . As a result, the amount of heat applied to substrate  12  may be controlled to effectively dry the coating upon substrate  12  with the least amount of energy and in the shortest amount of time. Because the vacuum created by blower  348  (shown in FIG. 8) within vacuum chamber  344  withdraws heated air from the substrate  12  once the heated air impinges upon the substrate  12 , coating drying system  310  achieves more effective air circulation adjacent to the substrate  12  and coatings thereon to more effectively dry the coatings upon the substrate  12 . In addition, because the heated air is recirculate, rather than being released to the environment, dryer system  310  requires less energy for heating air to an elevated temperature also saves on cooling costs for the outside environment.  
     [0111] In addition to drying coatings with less energy, coating dryer system  310  is more compact, simpler to manufacture and less expensive than typical drying systems. Due to the arrangement of pressure chamber  342  and vacuum chamber  344 , dryer system  310  is compact and requires less space. Due to its simple construction and lightweight components, dryer system  310  is lightweight and easy to manufacture. In sum, dryer system  310  provides a cost-effective apparatus for drying wet coatings applied to the surface of a substrate.  
     [0112] An alternative embodiment for attaining convection heat and diverting the air flow related thereto is illustrated in FIGS.  13 - 15 . In this embodiment, lamp assemblies  402  are eliminated and radiant heat is not used to dry the coatings  408  on the substrate  12 . Instead, all heat for drying is provided by means of convection from heated air (and incidental conduction from roll  332 ). Instead of alternating arrays of lamp assemblies  402  and trough covers  405 , trough cover panel  425  is fitted over each of the outlet troughs  382 , as illustrated in FIGS. 13 and 15. Each trough cover panel  425  is sized to cover an entire outlet trough  382 , and has side flanges or tabs  426  which, in cooperation with fasteners  416 , allow secure of the trough cover panel  425  to the arcuate panel member  337 . Each trough cover panel  425  is removable by means of fasteners  416 , but once in place, it is sealed to its respective outlet trough  382  about the edges of its sides and ends.  
     [0113] As shown in FIGS. 14 and 15, each trough cover panel  425  has a plurality of apertures  428  therethrough. The apertures  428  are shaped, spaced apart and sized to achieve a relatively uniform flow of heated air into the outlet troughs  382 . For instance, as illustrated in FIGS. 14 and 15, a larger aperture  428   a  is positioned adjacent the center portion of each trough cover panel  425  with a pair of smaller apertures  428   b  adjacent thereto. A further pair of yet again smaller apertures  428   c  are spaced from the apertures  428   b . The relative size, shape and spacing of the apertures  428  is intended to minimize the presence of an air flow gradient laterally across each outlet trough (i.e., create uniform air flow into the outlet trough across its entire lateral dimension). Preferably, the apertures  428  define 48 square inches of outlet, as compared to the 6.6 square inches of air inlet defined by the inlet slots  372  (for an outlet to inlet ratio of approximately 1:0.14.  
     [0114] In this embodiment, the preferred means for heating the air is by the use of a plurality of rod heaters  430  disposed within convection housing  327 . Preferably, a rod heater  330  is provided within the pressure chamber  342  adjacent and just behind each row of inlet slots  372 . The rod heaters  430  thus heat the air immediately before it impinges the substrate  12  and coatings  408  thereon. The rod heaters emit radiant energy to heat the air passing thereby, and also serve to heat the sides  412  of the outlet troughs  382 , in order to heat the recirculating air passing through outlet troughs  382  and back toward blower  348 . In a preferred embodiment of the invention illustrated in FIGS.  13 - 15 , the rod heaters are WATTROD brand rod heaters, available from Watlow of St. Louis, Mo. Rod heaters  340  are controlled by controller  331  which, dependent upon a desired air temperature and feedback from temperature sensors  351  and  409 , controls the amount of energy emitted by rod heaters  430 .  
     [0115] This simple modification (exchanging trough cover panels  425  for lamp assemblies  402 , or vice versa) results in a modular form of dryer system  310  which can be relatively readily adapted for alternative constructions and drying applications. The features of the various embodiments disclosed herein can also be combined to achieve a desired dryer system. Thus, the use of energy emitters within the roll  322  of the embodiment of FIGS.  13 - 15  is contemplated, as well as using the latter embodiment for duplex drying, such as illustrated in FIG. 6, as well as other compatible feature combinations.  
     [0116] 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.