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 coatings must be dried (or cured) 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.

Water or solvent based coatings are typically dried using liquid vaporization. Drying the wet water-based 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 laden 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 on the substrate depends upon the atmospheric pressure surrounding the substrate, the relative humidity and the rate at which energy can be absorbed by the coating. Because it is generally impractical to increase drying speeds by decreasing atmospheric pressure, increasing the drying speed requires increasing the rate at which energy is absorbed by the coating.

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 relative 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. The substrate is thereby prevented from burning or discoloring.

Although controllable, convection heating is thermally inefficient. Because air in general (and nitrogen specifically), has a very low heat capacity, 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.

Radiation heating occurs when two objects at different temperatures 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 produced by enclosing electrical resistors within a tube of transparent quartz or translucent silica, or exposing the electrical resistors, and bringing the electrical resistors to a red heat to emit radiation waves having wavelengths from 1.0 to 3.0 microns. The tubes typically extend along an entire width of the substrate. A common problem with the this method of heating is that a portion of the radiation is not directed at the substrate. The resistors direct radiation in all directions, which is emitted through the transparent tube. Reflectors have been used to attempt to direct all radiation towards the substrate, however, this method causes a portion of the radiation to impinge back on the resistors themselves, resulting in less energy reaching the substrate. Additionally, the resistors typically consume a large amount of power for the amount of radiation generated. Finally, the radiant heat applied to the substrate can easily be applied at levels which cause burning or discoloring of the substrate.

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. Internal to the drum, a heating agent (oil, steam or other heating devices) is placed in continuous contact with the internal surface of the drum. Using the drum to heat the substrate conductively has required a sealed heavy drum to contain the heating agent. Alternatively, heating agents have been mounted to the inner surface of the drum. Again, this has added to the heaviness of the drum. The heavier a drum is, the more energy and structure is required to rotate the drum.

Previous drying equipment has generally been large, heavy and consumed great amounts of energy in order to adequately dry the substrate. If too much heat is applied to the substrate, it can scorch the substrate. To rectify this problem, heat has been applied to the substrate riding on a conductive drum at a lower temperature over

a longer period of time. Thus, the equipment has been large in size to provide adequate drying time to the substrate so that quickerthroughput of the substrate can be achieved. Smaller equipment requires the throughput to be slowed to provide a longer dwell time of the substrate on the drum. When drying a thick substrate on previous drying equipment, the throughput must be slowed to allow use of a conductive drum to dry the coating on the outer portion of the substrate.

BRIEF SUMMARY OF THE INVENTION The present invention is a dryer system for drying the coating applied to a substrate. An exemplary embodiment of the invention includes a substrate support having a peripheral surface for supporting the substrate as it is advanced through the drying system.

The substrate is moved over the substrate support and is heated by heater lamps adjacent a substantial portion of the substrate support.

The heater lamps radiate energy onto the advancing substrate.

An alternative embodiment of the dryer system includes a preheating station located proximate the substrate upstream from the substrate support, preferably comprised of carbon emitter lamps. The carbon emitter lamps of the preheating station radiate energy onto the substrate before it moves over the substrate support. A substrate heater located adjacent the substrate support heats the substrate as it advances over the substrate support.

Another embodiment of the dryer system has a substrate support having a length and peripheral surface for supporting the substrate as it is moved over the substrate support. A heater plenum is disposed about a portion of the substrate support, with the inner surface of the plenum proximate to the peripheral surface of the substrate support. Reflectors are secured to the heater plenum forming a portion of the inner surface. Heater lamps are mounted to the heater plenum and each lamp is disposed between the peripheral surface and one of the reflectors. Each reflector directs substantially all the radiation emitted by its respective heater lamp onto the substrate support.

A final embodiment of the dryer system includes a rotatable substrate support having a length, an inner circumferential surface and an outer circumferential peripheral surface for supporting the substrate. A substrate heater located adjacent to a substantial arcuate portion of the substrate support heats the substrate as it advances over the substrate support. Energy emitters are fixedly supported relative to the rotatable substrate support. The energy emitters are disposed so as to direct radiant energy towards the inner circumferential surface of the substrate support and heat that arcuate portion of the substrate support not surrounded by the substrate heater.

BRIEF DESCRIPTION OF THE DRAWINGS 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.

FIG. 1 is a perspective view of the inventive coating dryer system.

FIG. 2 is a cross-sectional view of the coating dryer system of FIG. 1, taken along lines 2-2.

FIG. 3 is a cutaway view of a front side of the substrate support.

FIG. 4 is a side view of the substrate support.

FIG. 5 is an exploded perspective view of the energy emitters.

FIG. 6 is a schematic diagram of the convective heating system.

FIG. 7 is a perspective view of the side plenum.

FIG. 8 is a perspective view of the convection plenum.

FIG. 9 is an exploded perspective view of an air trough.

FIG. 10 is an enlarged sectional view of area 7 in FIG. 2.

FIG. 11 is a sectional view of a reflector.

FIG. 12 is a graph of a first comparison between radiation emitted by tungsten filament lamps and carbon emitter lamps.

FIG. 13 is a graph of a second comparison between radiation emitted by tungsten filament lamps and carbon emitter lamps.

FIG. 14 is an enlarged sectional view of area 7A in FIG. 2.

FIG. 15 is a perspective view of a top heater.

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.

Note that in the following detailed description of FIGs. 1- 15, specific examples of dryer components such as"positioning roll 20A" are referred to with a reference number that includes an appended letter, in this case the letter"A". On the other hand, when components are referred to generally, no letter is appended (e. g., positioning rolls 20) referring collectively to all of the positioning rolls which appear in the invention embodiment.

DETAILED DESCRIPTION FIG. 1 is a perspective view of a coating dryer system 10 for drying a coating applied to substrate 12 having a front surface 14 and a back surface 16. Arrows 17 on substrate 12 indicate the direction in which substrate 12, is moved within coating dryer system 10. The substrate 12 (typically paper) thereby forms a continuous web traveling through the dryer system 10. Ink is applied to the front surface of the substrate 12 at a point upstream from the dryer system 10. The dryer system 10 generally includes frame 18, positioning rolls 20, a substrate support 22, a blower unit (blower) 26 and a controller 31. The frame 18 is preferably made from aluminum and houses and encloses dryer system 10.

Positioning rolls 20 are rotatably coupled to the frame 18 in locations so as to engage back surface 16 of substrate 12 to guide

substrate 12 about substrate support 22. Positioning rolls 20 preferably support substrate 12 so as to wrap substrate 12 approximately 294 degrees about substrate support 22 for longer dwell times and atlow for a more compact dryer size. In addition, positioning rolls 20 guide and direct movement of substrate 12 through heater system 10.

As the substrate 12 advances along its processing path, the substrate 12 enters the dryer 10 and is engaged by positioning roll 20A as illustrated in FIG. 2. The substrate 12 is directed downwardly by the roll 20A until it engages positioning roll 20B. Positioning roll 20B directs the substrate 12 onto the substrate support 22, which engages back surface 16 of substrate 12 and disposes substrate 12 adjacent to heater plenum 36, where the main drying occurs. After traveling on the substrate support 22, the substrate 12 traverses from the substrate support 22 onto positioning roll 20C. The substrate 12 then travels on a substantially parallel path to its incoming path along positioning rolls 20D, 20E and 20F. At positioning roll 20F, the substrate 12 may continue onto positioning rolls 20G and 20H to exit the dryer system 10, or instead it may be fed onto positioning roll 201 (web path shown in phantom). If it is fed to positioning roll 201, the substrate 12 exits the dryer 10, is turned over using a turnbar (not shown) as is known in the art, and the back surface 16 of the substrate 12 is printed on. The substrate 12 can then be re-fed into the dryer 10 in the manner described above. Since the substrate has been turned over, the back surface 16 from the first pass through the dryer 10 becomes the front surface 14 on the second pass through the dryer 10. The substrate 12 then travels through the dryer system 10 on a parallel path to the one described above, but at a position axially displaced along the positioning rolls 20A-201 and the substrate support 22. Thus, printing on both sides of the substrate 12 can be dried with one dryer system 10.

Substrate support 22 preferably includes a roll 32, a shaft 33 and bearings 34. Roll 32 preferably comprises an elongate cylindrical drum having an outer peripheral surface 35 in contact with the

back surface 16 of the substrate 12. The roll 32 is preferably formed from a material having a high degree of thermal conductivity such as metal. In the preferred embodiment, the roll 32 is made from aluminum and has a thickness of about 1/2 of an inch. Preferably, the outer peripheral surface 35 on the roll 32 contacts the entire back surface 16 of the substrate 12. Heat is directed onto the substrate 12 via a heater plenum 36. Because the roll 32 is formed from a material having a high degree of thermal conductivity, the roll 32 conducts excess heat away from areas on the front surface 14 of the substrate 12 which are not covered by wet coating (e. g., inks). As a result, the areas of substrate 12 that are not covered by a wet coating do not burn from being over heated. At the same time, the roll 32 conducts the excess heat back into the portions of the substrate 12 that are covered by the wet coating so that the wet coating will dry in less time than when a non-conductive roll is used. Shaft 33 and bearings 34 rotatably support the roll 32 with respect to the frame 18 inside the heater plenum 36. The shaft 33 is hollow to allow electrical wires to be run to the interior of the roll 32.

Although supporting the substrate 12 inside the heater plenum 36 is preferably accomplished by the rotatably supported, thermally conductive roll 32, the 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, as known in the art.

The blower unit 26 is preferably positioned in the upper portion of the dryer 10. The placement of the blower 26 in this position makes the blower 26 accessible for maintenance, repair or change-out.

This is different from prior art blowers which were disposed more internally in the dryer. The blower 26 generally comprises a conventionally known blower. Air is directed from the blower 26, through a heater 37 to the heater plenum 36. Ducting 38 (shown in FIGs. 6 and 8) is used to direct the heated air to the heater plenum 36.

In the preferred embodiment, heated air is also directed to a pair of preheating plenums 39, a top preheating plenum 39A and a side preheating plenum 39B. The top preheating plenum 39A is preferably mounted adjacent to positioning roller 20A and the side preheating plenum 39B is preferably mounted adjacent to positioning roller 20B. Thus, as the substrate 12 is introduced to the dryer system 10 and passes onto positioning rolls 20A and 20B, the top and side preheating plenums 39A and 39B direct heated air at the substrate 12 to"preheat"the substrate 12. In a preferred embodiment, the preheating section of the dryer system 10 further includes a top pre- heater 41 A proximate to the substrate 12 along the path of the substrate 12 prior to positioning roll 20A. A side pre-heater41B can additionally be disposed proximate to the substrate 12 along the path of the substrate 12 between positioning rolls 20A and 20B. A person skilled in the art would realize that additional preheating plenums and heating means may be positioned along the path of the substrate 12 if additional preheating of the substrate 12 is desired.

Top pre-heater 41A and side pre-heater 41 B are preferably carbon emitter lamps. Carbon emitter lamps cool down very quickly (in approximately 1-2 seconds). Pre-heaters 41 A and 41 B preferably operate when the throughput of the dryer system is at 150 feet per minute. When the dryer system stops, it shuts down immediately and takes approximately 3 seconds for substrate 12 to stop moving through the system. Substrate 12 will stop proximate top pre- heater 41A and side pre-heater 41 B. Pre-heaters must cool down rapidly to avoid igniting substrate 12 once it is stalled through the dryer system. Carbon emitters cool down in approximately 1-2 seconds and will shut off before substrate 12 stops moving. Those skilled in the art will recognized pre-heaters 41A and 41 B may utilize alternate heating and cooling down means without departing from the spirit and scope of the invention.

After the substrate 12 travels over the substrate support 22, it is run behind the incoming substrate 12 (with respect to the top and side pre-heaters 41 A and 41 B and top and side preheating plenums 39A and 39B). Thus, the substrate 12 is subjected to a lesser amount of heat from the"preheating"elements as it is withdrawn from the dryer 10. Disposing the withdrawn substrate 12 behind the incoming substrate 12 allows a final drying to occur while limiting the potential for scorching the substrate 12. The effect of placing the top and side pre- heaters 41A and 41 B and the top and side preheating plenums 39 in this fashion provides additional drying time to the substrate 12, allowing the dryer system 10 to have a smaller footprint while still allowing the same throughput as previously known drying systems 10.

In the preferred embodiment, the main drying of the substrate is accomplished by the heater plenum 36. The heater plenum 36 includes an arcuate surface 40 extending substantially along the length of roll 32 and configured so as to arcuately surround the peripheral surface 35 of the roll 32, in close proximity with substrate 12.

The heater plenum 36 applies energy in the form of heated air (or other gas) and radiant energy to the substrate 12. The blower 26 and heater plenum 36 supply the heated air to the heater plenum 36. The heater plenum 36 impinges the substrate 12 with heated dry air to dry the coating applied to substrate 12, moving water vapor away from the substrate 12. Heater lamps 84 (or preferably carbon emitter lamps) are disposed in the heater plenums 36 to provide radiant energy to the substrate (as discussed with respect to FiGs. 9 and 12). The radiant energy heats the substrate so that the water in the wet coatings evaporates, forming water vapor. The heated dry air also acts to dry the coating but more importantly the heated air moves water vapor away from the substrate 12, allowing evaporation to continue. The heater plenum 36 is disposed so as to arcuately surround greater than 270 degrees, and preferably greater than 280 degrees, and more preferably greaterthan 290 degrees, and most preferably about 294 degrees of roll

32. The heater pienum 36 thereby surrounds a greater portion of the roll than previously known plenums. By increasing the portion of the roll surrounded by heater plenum 36, more energy is applied to substrate 12 for a greater period of time allowing the inventive dryer system 10 to be more compact and practical than previously known dryer systems.

A person skilled in the art would realize that other convection system configurations (i. e., placement of the blower, recycling of heated air) may be used in the inventive dryer 10. Alternate methods are described in U. S. Patent No. 5,901,462, which is incorporated in its entirety by reference herein.

Heater 37 reaches temperatures of approximately 1200 ° F (649°C) to effectively transfer heat to the air passing from the blower 26 through the ducting 38. Heater 37 preferably comprises a duct heater as is known in the art. An example of the duct heater is Part No.

066473 supplied by Osram Sylvania Inc. (Danvers, MA USA). Although heater 37 is illustrated as a type of duct heater, the air may be heated by any one of a variety well known conventional heating mechanisms and structures fortransferring heat and energy to air. In addition, the air may also be heated by multiple heating units positioned throughout the convection system. In the preferred embodiment, the heater 37 is disposed directly at the exhaust of blower 26, allowing easy access for maintenance of the heater 37.

Temperature sensor 42A is supported by the frame 18 adjacent to the roll 32. Temperature sensor 42A senses the temperature of roll 32 and substrate 12. Additional temperature sensors 42A (not shown in FIG. 2) may be positioned longitudinally along roll 32, as known by persons skilled in the art. In an alternate embodiment of the invention, the temperature sensor 42A may be positioned to sense the temperature of substrate 12 on roll 32. Sensor 42A is typically optical pyrometers positioned where the substrate 12 leaves the surface 35 of the substrate support 22. An additional resistive temperature sensor 42B is typically positioned in the heater 37. The temperature

sensors 42A and 42B provide feedback to the controller 31. A person skilled in the art would realize that additional temperature sensors 42 may be positioned throughout the dryer 10 to provide additional operating parameter information to the controller 31 for drying system operation.

Operation parameters of the dryer system 10 include air temperature, air pressure, substrate 12 temperature and/or roll 32 temperature. Some substrates can endure temperatures approaching approximately 350° F. However, at such temperatures the fibers become brittle and pre-printed thermal-set inks melt. Therefore, the preferable substrate 12 temperature is approximately 240° F. The upper temperature limit for air temperature blown through the heater plenum 36 and preheating plenums 39A and 39B by the blower 26 is preferably approximately 240° F. However, the nominal temperature setting is preferably approximately 180 ° F. Airtemperatures maintained at these levels avoids stressing the substrate when the web is stopped within the drying system.

In the preferred embodiment, a plurality of energy emitters 44 are disposed proximate to an inner circumferential surface 46 of the roll 32. Because energy emitters 44 are located within the substrate support 22, the energy emitters 44 are shielded from the hot air and radiated energy emitted by the heater plenum 36. The energy emitters 44 are disposed proximate to an"open area"48, which is the arcuate portion of the roll 32 that is not covered by the heater plenum 36 (preferably about seventy degrees). The open area 48 is positioned so that the substrate 12 can be fed onto the substrate support 22 and exits from the substrate support 22 (generally between points 48A and 48B on the roll 32). The energy emitters 44 are attached to and supported by the shaft 33. The shaft 33 is fixed to the frame 18, and does not rotate. The roll 32 is mounted on the bearings 34 relative to the frame 18, which allow the roll 32 to rotate about the fixed shaft 33.

The emitters 44 are attached to the fixed shaft 33 so as to be disposed proximate to the open area 48 along the inner circumferential surface 46. Thus, the emitters 44 are always directed towards the portion of the roll 32 which is not being impinged by the heated gas from the plenum 36. Because the roll 32 is thermally conductive, the energy emitted by energy emitters 44 is conducted through the roll 32 to the outer peripheral surface 35 thereof, and then to the back surface 16 of the substrate 12. Preferably, the energy emitters 44 are not directly exposed to any hot air which could potentially degrade or age the energy emitters 44 (depending upon the type of energy emitters utilized). Additionally, in one embodiment of the invention, ambient cool air is directed by the blower (before entering the heater 37) through the shaft 33 to the emitters 44. Thus, cooling air is directed at the emitters 44 to prolong their useful life and prevent premature aging. Placing the emitters 44 inside the roll 32 in this fashion has the advantage of maintaining the roll outer surface 35 at the desired temperature. In other words, the outer surface 35 of the roll 32 maintains its temperature despite the fact that the plenum 36 does not surround the roll 32 completely. If the emitters 44 are not used, the open area 48 of the roll 32 can cool due to a lack of energy supplied to the roll by the heater plenum 36 and the heater lamps 84 (discussed with respect to FIGs. 9-12). Particularly at high operation speeds substrate 12 requires more heat from roll 32 and generates more heating load from energy emitters 44. The energy emitters 44 provide heat to the roll 32, preventing the cooling of the roll 32 during operation.

Ink on the substrate typically will not dry fast enough if the temperature of the roll 32 is less than approximately 130° F. A substrate that is difficult to dry requires a roll 32 temperature of at least approximately 215° F. Without the extra heat energy supplied by the emitters 44, the roll 32 could not be maintained at these temperatures when operated at high speeds. The use of the emitters 44 remedies this problem and

eliminates the need for a larger roll 32 to provide additional drying time, as was required previously.

Additionally, the use of the emitters 44 allows for quicker and more reliable start up of the dryer 10. The open area 48 portion of the roll 32 does not receive heat during start up and preparation of the dryer 10 since it (open portion 48) is not exposed to the heater plenum 36. To prepare the dryer system 10 for use, heated air is blown through the heater plenum 36 and the emitters 44 are energized before the substrate 12 is fed into the dryer system 10. The emitters 44 are placed behind the open area 48 of the roll 32, warming the inner surface 46 from 48A to 48B. The heat is conducted by the roll 32 to the outer surface 35, allowing the roll 32 to warm more evenly. Without the emitters 44 the portion of the roll 32 surrounded by the heater plenum 36 would warm more quickly than the open area 48. Since the temperature sensors 42 are typically placed proximate to the open area 48 (on the outer surface 35), by the time the sensed surface is warmed to the desired temperature (due to conduction from the surrounded portion of the roll 32), the portion of the roll surrounded by the heater plenum 36 would become overheated, possibly blistering the substrate 12 when drying commenced. The use of the emitters 44 prevents this uneven warming of the roll 32.

The emitters 44 are typically cycled by the controller 31 to maintain the roll 32 at a constant temperature. Once the roll 32 is evenly warmed up and reaches its target temperature, energy emitters 44 are cycled off. At high operation speeds, roll 32 begins to cool because heater lamps 84 are not putting out enough heat. Heater lamps 84 increase total powerto maintain a constant temperature about roll 32. Once heater lamps 84 reach greater than 75% of their rated power, controller 31 cycles energy emitters 44 on. Emitters 44 begin heating open area 48 and returning roll 32 to a constant temperature.

Emitters 44 have a short life span, thus on and off cycling is cost effective and results in fewer part replacements.

Controller 31 is typically a conventional control unit (i. e., a programable logic controller) that includes both power controls and process controls. Controller 31 is preferably mounted to the frame 18 and is electrically coupled to the temperature sensors 42, energy emitters 44, heater lamps 84 (discussed with respect to F ! Gs. 9-12), heater 37 and blower 26. The controller 31 uses the feedback provided by the temperature sensors 42 to control the heater lamps 84 in order 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.

As shown in F ! Gs. 3 and 4, the preferred embodiment of roll 32 is an elongate cylindrically shaped hollow drum having an exterior wall 60, a pair of opposing end plates 62,64, and interior divider walls 65A and 65B. The inner circumferential surface 46 and outer surface 35 are disposed on either side of the wall 60. Outer peripheral surface 35 is in contact with and supports substrate 12. Because the wall 60, including surfaces 35 and 46, is formed from a highly thermally conductive material, such as aluminum, heat is thermally conducted through the wall 60 and absorbed by the substrate 12 (or vice versa, to thermally remove or distribute heat energy from parts of the substrate 12). The end plates 62 and 64 are fixably coupled to wall 60 at opposite ends of roll 32. The wall 60 and side plates 62 and 64 form a substantially enclosed interior which contains the energy emitters 44.

The energy emitters 44 radiate heat (energy) to the inner circumferential surface 46. This surface 46 conducts the heat through the wall 60 to the outer surface 35. As best shown by FtGs. 3,4 and 5, the energy emitters 44 preferably include a plurality of distinct energy emitters 44A-44X disposed within roll 32 along the length of roll 32.

Energy emitters 44A-44X preferably are positioned side-by-side so as to extend along a substantial portion of the length of roll 32.

The energy emitters 44A-44X are preferably broken into two groups, 44A-44L and 44M-44X, and placed on opposite sides of the

interior divider walls 65A and 65B. The interior divider walls 65A and 65B divide the roll 32 into two distinct halves. A first half 32A is defined between end plate 64 and interior divider wall 65A. A second half 32B is defined between end plate 62 and interior divider wall 65B. The two halves of the roll 32A and 32B are able to rotate freely with respect to each other, allowing the substrate 12 to be dried on the first half 32A.

The substrate 12 can then be directed out of the dryer system 10, turned over and redirected through the dryer system 10 (as described with respect to FIG. 2) and dried on the second half 32B of the roll 32.

Thus, a first emitter group 44A-44L is disposed in the first half 32A of the roll 32 and a second emitter group 44M-44X is disposed in the second half 32B of the roll 32. Each energy emitter group 44A-44L and 44M-44X is controllable so as to selectively emit energy along the length of conductor roll 32. As a result, the amount of heat conducted through wall 60 to the surface 35 of each half 32A and 32B may be selectively varied according to the desired operation characteristics of the dryer system 10. Alternatively, one side of a large piece of substrate 12 may be dried by extending it across the length of the entire drum 32 (first and second half 32A and 32B), or one half of the roll can be used to dry the substrate 12, and the elements applying heat to the non-used half can be turned off to conserve energy. First half 32A and second half 32B each has a separate temperature sensor 42A to independently control the temperature on its half of roll 32.

The emitters 44 are secured to the shaft 33. The emitters 44 extend annularly about a portion of the shaft 33, directing energy at the open area 48 of the roll 32. Typically, twenty-four emitters will be used in the inventive dryer system 10. The result is that twelve emitters are disposed in each half 32A and 32B of the roll 32. Preferably, each group of twelve emitters (44A-44L and 44M-44X) are controlled separately by the controller 31, allowing more precise control of the heating of the roll 32. A person skilled in the art would realize that

individual emitters (44A-44L) may be controlled by the controller 31 to obtain more precise heating of the roll 32.

In the preferred embodiment, the energy emitters 44 preferably are of the tungsten filament lamp type, as manufactured by various companies including Ushio (Cypress, CA USA), Osram Sylvania (Danvers, MA USA), Philips (Somerset, NJ USA) and General Electric (Glen Allen, VA USA). The emitters 44 are attached to the shaft 33 by clamps 67. Since the emitters 44 attach to the shaft 33, they do not add extra weight to the roll 32. As a result, the roll 32 can act as an idler roll, freely rotating with the movement of the substrate 12. Thus, the substrate 12 itself provides the motive force to drive the rotation of the roll 32. A complex drive mechanism is not needed, although a person skilled in the art would realize a drive mechanism may be used.

Eliminating the need for a drive mechanism further decreases the weight, size and complexity of the dryer. The energy emitters 44 receive powerthrough electrical wires disposed through the shaft 33. As shown in FIG. 3, the shaft 33 includes lead wires 66 which supply power to the energy emitters 44. Since the energy emitters 44 are fixed to the shaft 33, an expensive slip ring system is not required to deliver power to the energy emitters 44. Energy emitters 44 are fixed to shaft 33 with a spring loaded friction fit. Emitters 44 require no disassembly to access and replace. Thus, the configuration of the roll 32 and energy emitters 44 allows the manufacture, construction cost and maintenance of the dryer system 10 to be simpler and less expensive.

Although the energy emitters 44 are preferably the tungsten filament type, the energy emitters 44 may alternatively comprise any one of a variety of well known energy emitters known in the art. One example is resistive energy emitters, which may be conductive energy emitters or radiant energy emitters. Examples of radiant energy emitters include tubular quartz infra-red lamps, quartz tube heaters, metal rod sheet heaters and ultraviolet heaters which emit

radiation having a variety of different wave lengths and radiant energy levels.

FIG. 6 is a block diagram illustrating the convection heating system of the dryer 10. The blower 26 draws air through a blower intake 26A, and expels pressurized air through a blower exhaust 26B. The air is directed to the heater 37 which is typically attached directly to the blower exhaust 26B. The heater has first and second manifold outlets 68A and 68B, and first and second periphery outlets 69A and 69B. The total volume of heated air is exhausted through the outlets 68A, 68B, 69A and 69B in accordance with the size of each outlet 68A, 68B, 69A and 69B. Typically, the periphery outlets 69A and 69B are smaller and direct air to the top pre-heat plenum 39A and the side pre-heat plenum 39B, respectively. The manifold outlets 68A and 68B are preferably larger than the periphery outlets 69A and 69B, and direct heated airto the heater plenum 36. The air is conducted from the heater 37 to the heater plenum 36, and the pre-heat plenums 39A and 39B, via flexible ducting 38A-38D.

A perspective view of the pre-heat plenums 39 utilizing slots 41 C for air outlets is illustrated in FIG. 7 (representative of the top and side pre-heat plenums 39A and 39B). The pre-heat plenums 39A and 39B are used to preheat the substrate 12 as it enters the dryer system 10 (as discussed previously with respect to FIG. 2). To prevent inefficient heat loss by the pre-heat plenums 39A and 39B, as well as providing for operator safety by preventing exposure to the high temperatures, the pre-heat plenums 39A and 39B are preferably insulated. One example of such insulation is the Techlite brand insulation manufactured by Accessible Products Company, although a person skilled in the art would realize that other styles of insulation may alternatively be used. Additionally, a person skilled in the art would realize that the pre-heat plenums 39A and 39B may utilize alternate heating means (such as heaters disposed inside the ducting or internal

to the pre-heat plenums 39A and 39B) without departing from the spirit and scope of the invention.

A perspective view of the heater plenum 36 is illustrated in FIG. 8. The preferred embodiment of the heater plenum 36 generally includes manifolds 70A and 70B and a plurality of air troughs 72. Air inlets 74A and 74B are typically the location in which pressurized air enters the manifolds 70A and 70B. Inlets 74A and 74B may comprise any passage in communication between the heater plenum 36 and whatever conventionally known means or mechanisms are used for pressurizing air within the heater plenum 36 (preferably the blower 26, as shown in FIG. 2).

Manifolds 70A and 70B are disposed so as to form the arcuate surface 40. The manifolds 70A and 70B are disposed side by side along the width of the roll. The air troughs 72 are sealably connected to the manifolds 70A and 70B so as to be disposed between the manifolds 70A and 70B and the roll 32. The air troughs 72 run longitudinally along the roll 32, and surround the roll 32 coaxially. The sealed connection between the manifolds 70A and 70B and the air troughs 72 only allows the pressurized air to pass from the manifolds 70A and 70B into the air troughs 72.

Preferably, blower 26 pressurizes air within the heater plenum 36 (as was described with respect to FIG. 6). Overall, the blower 26 drives the current or flow of air to the substrate 12 inside the heater plenum 36 by pressurizing air within the manifold sections 70A and 70B of the heater plenum 36. Once within the manifold sections 70A and 70B, the pressurized air escapes into an air trough 72 to impinge upon substrate 12, assisting in drying the coatings upon the substrate 12. After impinging upon the substrate 12 (shown in FIG. 1), the air dissipates out the end of the roll 32. The plenum 28 has twenty- four air troughs 72 which are slightly angled with respect to one another to provide the arcuate surface 40 with its arcuate cross-sectional shape.

Uniform air flow is provided along the length of each trough 72 and

among the air troughs 72 to provide uniform air flow to the substrate 12 (shown in FIG. 1). The air flow impinging on the substrate 12 is preferably configured to optimize heat and mass transfer with convection flow.

FIG. 9 is an exploded perspective view of one of the air troughs 72. Each air trough 72 includes a plurality of outlets 80, a reflector 82, a heater lamp 84, and an inlet aperture 86. Longitudinal side walls 89A and 89B extend the length of the trough 72 and are disposed adjacent to other troughs 72 (forming the arcuate surface 40 as in FIG. 8). The heater lamp 84 is shaped to be readily received and removable from within the reflector 82. Each reflector 82 abuts against the lower legs 88 of the longitudinal walls 89A and 89B. Suitable fasteners (e. g., sheet metal screws, not shown) are used to secure the reflector 82 to the lower legs 88. Each reflector 82 is secured to the lower legs 88, and defines a seal thereto along its edges and ends.

Outlets 80 extend through lower legs 88 on the trough 72, proximate to the longitudinal side walls 89A and 89B of the trough 72. The outlets 80 are preferably uniformly dispersed along the length of each air trough 72 and among the air troughs 72. The particular size and distribution of outlets 80 in each trough 72 which makes up the arcuate surface 40 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, incorporated herein by reference.

As set forth in optimizing equations from the referenced heat transfer book, the size of each outlet 80 as well as the number of outlets 80 is dependent upon the distance between arcuate surface 40 and substrate 12 supported by substrate support 22 (shown in FIG. 1).

The optimal spacial arrangement of outlets 80 (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 80 :

the size of outlets 80, outlet-to-outlet spacing and the distance between arcuate surface 40 and substrate 12. The configuration is also dependent upon the static pressure created by blower 26.

Each of the outlets 80 is preferably slotted. The slots have a length of approximately 10 1/4 inches. Although outlets 80 are preferably slotted, outlets 80 may alternatively have a variety of different shapes including circles. Furthermore, outlets 80 may also comprise circular or slotted nozzles for directing heated air or other heated gas at the substrate. In the preferred embodiment of the air trough 72, heated air flows through each outlet 80 so as to strike the substrate with a velocity of between approximately 2,000 to 3,500 feet per minute. As can be appreciated, the maximum velocity of air flow is constrained by the particular substrate and the particular coating applied to the substrate 12.

The reflector 82 is sealably disposed between the lower legs 88 so that the portion of the lower legs 88 which includes the outlets 80 together with the reflector 82, form a lower surface 90 of the air trough 72, as shown in FIG. 10. The reflector 82 has a generally concave cross sectional shape into which the heater lamp 84 is mounted. The reflector cross-sectional shape is designed to direct substantially all radiation emitted from the heater lamp 84 (arrows 102) onto the substrate 12. The radiation is directed either directly or by reflection onto the substrate 12. The reflector 82 has a polished reflective finish applied to its lower surface 90 to reflect the radiation emitted by the heater lamp 84, as is known in the art. The unique design causes substantially all the energy of heater lamp 84 to impinge upon substrate 12, creating an increase in dryer energy efficiency over prior art designs.

FIG. 11 shows a sectional view of reflector 82 and the unique design necessary to cause substantially all the energy of heater lamp 84 to be absorbed by substrate 12. To achieve the reflection of substantially all the radiation emitted onto substrate 12, reflector 82 has wail angles (D1-D5) and wall lengths (L1-L5) as defined in the following table. These wall angles and wall lengths are required to achieve near total reflection of the radiation emitted. All values are approximations.

D1 33 degrees D2 34 degrees D3 47 degrees D4 65 degrees D5 1 degree L1.56 inches L2.59 inches L3.58 inches L4.57 inches L5 2. 75 I Fixing the refiector 82 between the lower legs 88 creates an internal cavity 92 in the trough 72. Pressurized heated air passes from the manifold 70A through the inlet aperture 86 into the internal cavity 92, as shown by arrows 94. In operation, the lower legs 88 are disposed proximate to the substrate 12. Substrate 12 absorbs heat from the heated air emitted from the trough 72. As indicated by arrows 96, outlets 80 direct the heated high pressure air within air troughs 72 towards front surface 14 of substrate 12. Furthermore, the pressurized heated air passing through inlet aperture 86 and directed out of outlet 80 has a temperature less than the temperature of reflector 82. The pressurized heated air cools reflector 82 as it passes through internal cavity 92 and prevents reflector 82 from melting.

As discussed above, outlets 80 are preferably sized and numbered so that the volume of air delivered is enough to adequately heat the substrate 12. The heated air delivers heat to the coatings on the front surface 14 of 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 surface 14 of substrate 12, the velocity and momentum of the air decreases substantially. The air then dissipates out the sides of the dryer 10 and along roll 32. The lower atmospheric pressure outside the dryer 10 bleeds off the heated air once the heated air has impinged upon the coating being dried. As can be appreciated, the desired velocity of air flow is constrained by the particular substrate 12 and particular coating applied to the substrate. An air flow velocity that is too high will disrupt the coating.

Each heater lamp 84 provides radiant energy to the substrate 12 as the substrate 12 passes by the heater lamp (by direct and reflected radiant energy). The rapid movement of air past the heater lamp 84 caused by the spinning of the roll 32, as well as the pressurize airfrom the trough 72, also serves to cool the heater lamp 84 and its supportive fittings.

Preferably, heater lamps 84 generate radiant energy with a desired peak radiation power wavelength between approximately 2. 0 microns and approximately 3.6 microns, and most preferably between approximately 2.0 microns and approximately 3.0 microns. Creating the desired peak radiation power wavelength within the desired range requires controlling the filament temperature of heater lamps 84.

Operating heater lamps 84 with a peak radiation power wavelength within the desired range minimizes the required power to run the lamps.

However, increasing the surface area of heater lamp 84 increases the power requirements of the lamp, thereby maximizing the surface area of heater lamp 84 while limiting the amount of power dissipated is required. Accordingly, it is desired to radiate energy within the desired range while minimizing the power required to do so. Preferably, the heater lamp is a carbon infrared emitter lamp such as is the type manufactured by Heraeus Amersil, Inc., Noblelight Division (Duluth, GA USA). Carbon emitter lamps generate radiant energy with a peak radiation power wavelength of approximately 2.0 microns.

The carbon emitter lamp 84 provides an increase in efficiency over prior art dryers. As shown by the graph in FIG. 12, the power of a 1000 W (Watt) carbon emitter lamp at rated voltage is indicated by line C, while the power of a 1000 W tungsten filament lamp at rated voltage is indicated by line T. The horizontal axis of the graph in FIG. 12 measures radiation wavelengths in microns. The vertical axis measures the power of the radiant energy in W. The carbon emitter lamp 84 emits a higher level of the desirable radiation wavelengths of between 2.3 and 3.6 microns than the tungsten filament lamps used in prior art heater designs. Radiation having wavelengths of between 2.3 and 3.6 microns is desirable since absorption of paper and ink peaks in this range, allowing for quick heating of the substrate 12. While the carbon emitter lamp 84 emits a higher level of desirable wavelength radiation, it also emits a lower level of undesirable wavelength radiation in the 0.5 to 1.5 micron range. Radiation having 0.5-1.5 micron wavelength can adversely affect the drying process by discoloring or blistering substrate 12 because pre-printed ink exhibits color sensitivity.

At the same power levels (1000 W), the tungsten filament lamps used in previous dryer systems produces radiant energy in the 0.5-1.5 micron range having a total power of approximately 448 W. By comparison at 1000 W, the carbon emitter lamp 84 produces radiant energy in the 0.5-1.5 micron range having a total power of approximately 113 W. The carbon emitter lamp 84 thereby produces much less radiant energy that will discolor the substrate 12 in the undesirable wavelength range. The first area"A"on the graph (between the boundary lines C and T in FIG. 12) illustrates the additional energy emitted by the tungsten filament lamp at the undesirable 0.5-1.5 mean range versus the inventive carbon emitter lamp 84.

On the other hand, the carbon emitter lamp produces radiant energy having a wavelength within the 2.3-3.6 micron range at a total power of approximately 334 W, while the prior tungsten filament lamps provided a total power of approximately 184 W in the 2.3-3.6

micron range. The second area"B"on the graph (between the boundary lines C and T in FIG. 12) illustrates the additional energy emitted by the carbon emitter lamp 84 at the desirable 2.3-3.6 micron range versus the prior tungsten filament lamps. FIG. 12 illustrates that when operating the carbon emitter lamp 84 at the same voltage as the tungsten filament lamp, the carbon emitter lamp 84 generates greater amount of energy in the desirable wavelength range and less energy in the undesirable wavelength range.

As shown in FIG. 13, when a 1000 W carbon emitter lamp is energized at its rated voltage (indicated by line C1), it has a stable filament temperature of approximately 1473 K (degrees Kelvin).

Operating at the same filament temperature of a carbon emitter lamp (1473 K), a 1000 W tungsten filament lamp must be energized at reduced voltage (indicated by line T,), with an actual wattage of 118 W.

Operating at 1000 W the stable filament temperature would be approximately 2500 K. The horizontal axis of the graph in FIG. 13 measures radiation wavelengths in microns, while the vertical axis measures power of the radiant energy in Watts.

FIG. 13 illustrates that the temperature of the dryer can be reduced while generating a high drying efficiency. Reducing the overall temperature of the dryer provides a safer system to operate, requires less insulation and reduces the risk of scorching the substrate 12. The increase in performance is due to the carbon emitter lamp 84 emitting a higher level of the desirable radiation wavelengths in the 2.3-3.6 micron range, than the tungsten filament lamps operating at the same temperature. Although, a prior art tungsten filament lamp requires less voltage to operate at the same temperature, it produces radiant energy in the 2.3-3.6 micron range having a total power of approximately 39 W.

By comparison, the carbon emitter lamp 84 produces radiant energy in the 2.3-3.6 micron range having a total power of approximately 334 W.

When at the same filament temperature as the tungsten lamp, the carbon emitter lamp 84 produces a much greater amount of a desirable

wavelength radiation, allowing the substrate 12 to dry more quickly and paper and ink absorption to peak.

Comparing the information in FIG. 12 to FIG. 13, the use of the carbon emitter lamp 84 generates a greater amount of desirable wavelength radiation than prior art tungsten filament lamps, even if less power is used to operate the tungsten filament lamp. The use of the prior tungsten filament lamp at the same voltage as the carbon emitter lamp 84 generates a greater filament temperature. The carbon emitter lamp 84 generates approximately 1473 K (line C), compared to the approximately 2500 K (line T) generated by the tungsten filament lamp.

The use of a carbon emitter lamp 84 thereby reduces the risk of discoloration or blistering substrate 12.

Although a carbon emitter lamp 84 is the preferred lamp for heating substrate 12, an alternative source is a nickel chromium heater. Nickel chromium heaters have the same general characteristics as carbon emitter lamps, but are less expensive. Nickel chromium heaters have a slightly longer desirable peak radiation power wavelength of approximately 2.5 microns. However, carbon emitter lamps cool down quicker than other heater lamps, including nickel chromium heaters, without igniting substrate 12 when substrate 12 is stationary or comes to a stop.

A spacer cover 100 is mounted between each air trough 72 containing the lamp 84 and reflector 82 (compare FtGs. 10 and 14).

The spacer cover 100 is secured to the lower legs 88 between two air troughs 72 and 72'defining a seal along first and second edges 105 and 106 of the spacer cover 100 and the longitudinal walls 89B and 89A of the adjacent air troughs 72 and 72'. Typically, the spacers 100 and troughs 72 and 72'are alternated both longitudinally and transversely about the arcuate surface 40.

The top heater41A (illustrated in FIG. 15) and side heater 41B (the details of which are identical to top heater 41A) preferably utilize a plurality of reflectors 82 with carbon emitter lamps 84 (described

with respect to the heater plenum 36) to preheat the substrate 12 before it reaches the heater plenum 36. The reflectors 82 and lamps 84 alternate with spacers 100 in the manner described above. The result is a flat panel surface containing alternating reflectors and spacers. In the preferred embodiment, the pre-heaters 41A and 41 B do not supply pressurized air, but merely radiant heat energy. Instead, the top and side plenums 39A and 39B provide heated air to the substrate 12 prior to the substrate 12 contacting the roll 32 (best shown in FIG. 2). A person skilled in the art would realize that in an alternate embodiment, heated air may be blown through the top and side pre-heaters 41A and 41 B at the substrate 12, using air troughs in a similar manner as was described with respect to the heater plenum 36.

The coating dryer system 10 of the present invention thus provides radiant, conductive and convective heating and drying means for the substrate 12 and coatings thereon. To do so, a compact designed pre-heating section as well as a drying roll 32 are utilized.

Carbon lamps provide heat to the substrate 12, as well as to the roll.

Internal to the roll 32, energy emitters 44 provide additional heat, and a convective system provides hot air to remove vapor from substrate 12 and lower vapor pressure at the surface of substrate 12. While not illustrated in this embodiment, other additional heating means may be provided for drying the coatings on the substrate 12, including additional heaters in the air stream or energy emitters within the roll 32.

In a preferred embodiment, the outer surface 35 of roll 32 has a coating (not shown) to assist in radiant heat absorption.

Preferably, the coating is a thin, thermally conductive smooth coating on the outer surface 35 of roll 32. In one embodiment, the coating is relatively dark (i. e., black or some other dark color) to more fully absorb infrared energy emitted from the carbon emitter lamps 84 directly or reflected onto the roll 32 by the reflector 82. A coating applied to the inner surface (not shown) of roll 32 assists in radiant heat absorption as

well, by more fully absorbing the radiant energy emitted from energy emitters 44.

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.