Field of the Invention

Provided are nozzles for conveying heated air. The nozzles can be used to provide heat to a substrate in a continuous web oven or dryer.

In a continuous manufacturing process, it is sometimes necessary to perform drying operations on solvent-based or water-based coatings. Web dryers are devices that facilitate these drying operations, and are typically incorporated in a process line for web coating applications. Impingement dryers use streams of hot air to convectively heat and dry moving films, coatings, and other bulk materials.

Summary

There are instances where a new product manufacture requires additional dryer zones for higher speed or finer controlled gradient within a zone. Some products can also demand a high degree of temperature control within a zone. Meeting these requirements using conventional web dryers can impact commercialization speed. For example, the addition of new oven zones can involve great time and effort and require a significant capital outlay. Such modifications also add length and/or complexity to the process line and can significantly increase building footprint. The cost of goods sold also increases when there are significant modifications to the existing equipment.

Provided is a heated air nozzle that disposes finned tube electrical heaters within an air flow nozzle normally used within impingement dryers, and potentially other web ovens and dryers. The addition of heating elements within a nozzle make it possible to save space and reduce capital costs by creating new temperature zones within an existing oven or dryer. This is possible because a web dryer system with the provided nozzles enables a highly customizable temperature profile to be achieved along both down-web and, potentially, cross-web directions.

In a first aspect, a nozzle for a web dryer system is provided. The nozzle comprises: an elongated housing having a cavity therein; an inlet and an outlet coupled to the elongated housing, wherein the inlet has a configuration to couple with a source of gas within the web dryer system, each of the inlet and the outlet being in fluid communication with the cavity, and at least the cavity and the outlet each extend along the length of the elongated housing; and a heating element disposed within the cavity to heat a gas passing from the inlet to the outlet. In a second aspect, a web dryer system is provided comprising: an elongated enclosure having opposing top and bottom surfaces; and a plurality of the nozzles described above, each of the plurality of nozzle independently being coupled to either the top or bottom surface to heat and/or dry a continuous web passing through the elongated enclosure.

In a third aspect, a method of using a nozzle is provided, the nozzle having an elongated housing with a cavity therein, an inlet and an outlet coupled to the elongated housing, each of the inlet and the outlet being in fluid communication with the cavity, and a heating element disposed within the cavity. The method comprises: coupling the inlet to a source of heated gas within a web dryer system; directing the heated gas into the cavity through the inlet; using the heating element to apply supplemental heat to the heated gas; and discharging the heated gas through the outlet.

Brief Description of the Drawings

FIG. 1 is a schematic of web dryer system incorporating a nozzle according to a first embodiment;

FIG. 2 is a top view of the nozzle of FIG. 1;

FIG. 3 is a front/rear cross-sectional view of the nozzle of FIGS. 1-2, looking at its interior components;

FIG. 4 is a side view of the nozzle of FIGS. 1-3, looking at its short dimension;

FIG. 5 is a side cross-sectional view of the nozzle of FIGS. 1-4, showing its interior components;

FIG. 6 is a top view of a heater air nozzle according to a second embodiment, shown with the feed duct removed;

FIG. 7 is a bottom view of the nozzle of FIG. 6;

FIG. 8 is a front/rear cross-sectional view of the nozzle of FIGS. 6-7, looking at its interior components;

FIG. 9 is a side view of the nozzle of FIGS. 6-8, looking at its short dimension;

FIG. 10 is a side cross-sectional view of the nozzle of FIGS. 6-9, showing its interior components; and

FIG. 11 is a side cross-sectional view of a nozzle according to a heated air nozzle according to a third embodiment, showing a path of air flow within the nozzle.

Repeated use of reference characters in the specification and drawings is intended to represent the same or analogous features or elements of the disclosure. 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 the disclosure. The figures may not be drawn to scale.

DEFINITIONS

“Ambient temperature” means at a temperature of 21 degrees Celsius.

“Areal porosity” refers to the total amount of the surface area represented by voids as a percentage of total surface area when viewed perpendicular to the surface.

Detailed Description

As used herein, the terms “preferred” and “preferably” refer to embodiments described herein that can afford certain benefits, under certain circumstances. However, other embodiments may also be preferred, under the same or other circumstances. Furthermore, the recitation of one or more preferred embodiments does not imply that other embodiments are not useful and is not intended to exclude other embodiments from the scope of the invention.

As used herein and in the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a” or “the” component may include one or more of the components and equivalents thereof known to those skilled in the art. Further, the term “and/or” means one or all of the listed elements or a combination of any two or more of the listed elements.

It is noted that the term “comprises”, and variations thereof do not have a limiting meaning where these terms appear in the accompanying description. Moreover, “a,” “an,” “the,” “at least one,” and “one or more” are used interchangeably herein. Relative terms such as left, right, forward, rearward, top, bottom, side, upper, lower, horizontal, vertical, and the like may be used herein and, if so, are from the perspective observed in the particular drawing. These terms are used only to simplify the description, however, and not to limit the scope of the invention in any way.

Reference throughout this specification to “one embodiment,” “certain embodiments,” “one or more embodiments” or “an embodiment” means that a particular feature, structure, material, or characteristic described relating to the embodiment is included in at least one embodiment of the invention. Thus, the appearances of the phrases such as “in one or more embodiments,” “in certain embodiments,” “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily referring to the same embodiment of the invention. Where applicable, trade designations are set out in all uppercase letters.

FIG. 1 illustrates the interior of a web dryer system 100. The web dryer system 100 includes an enclosure 102 having opposed top and bottom surfaces 104, 106. The enclosure 102 has an elongated shape, with openings in the front and back such that a continuous web 101 can be conveyed horizontally through the enclosure 102. The continuous web 101 need not be particularly restricted and can be, for example, a coating or fdm. Such films can be self-supporting or disposed on a backing or removable release liner. It is to be understood that while removal of volatiles from the continuous web 101 is a primary application, the web dryer system 100 could also be useful in facilitating a chemical reaction, such as a curing reaction.

Disposed within the enclosure 102 and coupled to the top and bottom surfaces 104, 106 are a series of ten nozzles 110, five directed upward and five directed downward. The nozzles 110 face each other, optionally in a staggered configuration as shown, and each emits a stream of a heated gas, typically heated air, toward the continuous web 101 passing through the enclosure 102. In this example, the web 101 floats over the facing surfaces of the nozzles 110 in a sinusoidal, or wavelike, pattern as shown as induced by the positive pressure exerted against the web by impingement of the heated gas. Clearance between the web 101 and the nozzles 110 are typically in the range of 0.5 to 1 centimeter. Bending the web 101 as shown can be advantageous because it helps impart a shape stiffness to resist buckling of the web 101.

FIGS. 2-5 show features of an exemplary nozzle 110 from FIG. 1 in greater detail. As shown in FIGS. 2 and 3, the nozzle 110 is comprised of an elongated housing 112 having a longitudinal axis 114 with an orientation perpendicular (or transverse) to the travel direction of the continuous web as it is conveyed through the enclosure 102 of the web dryer system 100. A cavity resides within the housing 112 and extends along its length. The cavity communicates with outlets 116, 118, allowing egress of heated gas from within the cavity. As depicted, the outlets 116, 118 assume the shape of narrow slits extending along the length of the nozzle 110, although other sizes and shapes are possible.

As further shown, a pair of electrical ports 131, 133 provide access points where electrical wires can enter and exit the housing 112. A third port 135 can provide outside communication with an internally located thermocouple or thermistor to measure the temperature of the gas within the housing 112. Through ports 131, 133, 135, the nozzle 110 can communicate with a computerized controller that can be used to monitor and control temperature profiles within the web dryer.

FIG. 3 shows the interior components of the nozzle 110 in a front view. Shown is a heating element 126 disposed within the cavity. The heating element 126 extends across the length of the interior of the housing 112 and is coupled to side walls 122, 124 at each end. The heating element 126 has a configuration to heat a gas within the cavity as it passes from inlet 144 (visible in FIG. 5) to the outlets 116, 118. Optionally, the heating element 126 is a finned tube heater as shown. The finned tube heater, as depicted, includes a shaft 128 and a helical fin 130 that is wound around the shaft 128. The shaft 128 contains an electrically-resistive material that generates heat when a sufficiently high electrical current flows through it. The configuration of the fin 130 is not particularly limited, and the fin 130 can assume other forms, including that of a ribbon or other shapes protruding from the shaft 128. The heating element 126 can be suspended within the cavity, as shown, to enable circulation of the gas around the heating element 126.

Optionally and as shown, the heating element 126 has an orientation that is parallel to that of the outlets 116, 118. As an alternative, the heating element 126 can have an orientation perpendicular to that of the outlets 116, 118 and wired to lugs on electrical port 131 for connection to an electrical cable. In another configuration, power to the heating element 126 could be provided by electrical cables that simply pass through the port 131 uninterrupted. Other heating elements are also possible, and could be implemented according to an ordinary level of skill in the art.

The cavity within the housing 112 is divided into a heating zone 134 and a plenum 136, where the heating zone 134 is in communication with the inlet 144 and the plenum 136 is in communication with the outlets 116, 118. The heating zone 134 and plenum 136 communicate with each other through a perforated wall 137 that separates the chambers from each other. As illustrated, the perforated wall 137 extends along the length of the housing 112 and is also affixed to the side walls 122, 124. In a preferred embodiment, the perforated wall 137 is affixed to all four walls of the housing 112 such that air directly heated by the heating element 126 must pass through the perforated wall 137 in order to exit through the outlets 116, 118.

FIGS. 4 and 5 show a view of the nozzle 110 along a direction parallel to longitudinal axis 114, revealing the relative shapes of the heating zone 134 and the plenum 136. Optionally and as shown, a pair of baffles 142, 142 collectively having a “U”-shaped configuration direct to divert gas entering the nozzle 110 through the inlet 144 towards the heating elements 126, 126. A second set of baffles 146, 146 extends in a downward direction into the plenum 136 from the top inner surface of the housing 112. These baffles can serve to direct gas flow toward the heating elements 126, 126 and also spread out the flow pattern and achieve greater pressure uniformity along the outlet 116, 118.

As shown, the perforated wall 137 has perforations 140 disposed only over a portion of the perforated wall 137. This has the effect of directing the gas along a somewhat tortuous path to get from the inlet 144 to the outlets 116, 118. FIG. 5 in particular shows, with solid black lines, exemplary paths followed by a gas entering and exiting the nozzle 110. This air flow ensures that air is continually flowing across the heating elements 126, 126, reducing the risk of them burning out due to excessive heat. There is also a performance benefit from this configuration, as it enables good mixing of the gas within the housing 112 for a more uniform gas temperature.

Since each nozzle in an array of nozzles can be individually controlled, it is possible to make precise adjustments to down-web temperature profiles within a web dryer system. Advantageously, it is also possible for the provided nozzle 110 to control the temperature profde along the cross-web direction. For example, the heating elements 126 can be sub-divided into two or more inline heating elements that are individually controllable such that the gas impinging on the web is characterized by multiple temperature zones.

FIGS . 6-10 illustrate an example of an alternative nozzle 210 that proj ects air in a downward direction and could be suitable, for example, for mounting to the top surface 104 of the enclosure 102 in FIG. 1. Like the previously described nozzle 110, the nozzle 210 includes an elongated housing 212 having an inlet 244 and an outlet 216 comprised of multiple perforations as shown.

As shown in FIGS. 8-10, the cavity within the elongated housing 212 is subdivided into a heating zone 236 and a first and second plenums 234, 235. The inlet 244 communicates directly with the first plenum 234, the first plenum 234 in turn directly communicates with the second plenum 235, the second plenum 235 in turn directly communicates with the heating zone 236, and the heating zone 236 in turn directly communicates with the outlet 216.

The first and second plenums 234, 235 are separated from each other by a first perforated wall 240, while the second plenum 235 and the heating zone 236 are separated from each other by a second perforated wall 241. With an orderly progression in which the plenums 234, 235 and heating zone 236 are accessed, the gas flow within the nozzle 210 can be distributed more evenly along the cross-web direction and then progressively homogenized by the first and second perforated walls 240, 241.

Preferably, the porosities of the perforated walls 240, 241 progressively decrease from the inlet 244 to the outlet 216. The first perforated wall 240 can have an areal porosity of from 40 percent to 60 percent, from 45 percent to 55 percent, from 48 percent to 52 percent, or in some embodiments, less than, equal to, or greater than 40 percent, 42, 45, 48, 50, 52, 55, 57, or 60 percent. The second perforated wall 241 can have an areal porosity of from 10 percent to 30 percent, from 15 percent to 25 percent, from 18 percent to 22 percent, or in some embodiments, less than, equal to, or greater than 10 percent, 11, 12, 15, 18, 20, 22, 25, 27, or 30 percent.

Preferably, the first perforated wall 240 has an areal porosity significantly greater than that of the second perforated wall 241. On a relative scale, the areal porosity of the first perforated wall 240 can exceed that of the second perforated wall 241 by 50 percent, 60, 70, 80, 90, 100, 110, 120, 150, 200, 250, or even 300 percent, relative to the areal porosity of the second perforated wall 241.

The outlet 216 of the nozzle 210 need not be particularly limited in size or shape, and can be comprised of a single opening or a plurality of openings. In the depicted embodiment, the outlet 216 is comprised of a two-dimensional array of circular openings (visible in FIG. 7) disposed on the bottom surface. In a preferred embodiment, the outlet 216 is characterized by an areal porosity of from 0.5 percent to 5 percent, from 1 percent to 4 percent, from 1.5 percent to 3.5 percent, or in some embodiments, less than, equal to, or greater than 0.5 percent, 0.7, 1, 1.2, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, or 5 percent, relative to the overall area of the bottom surface of the nozzle 210.

As further shown in FIGS. 8-10, the nozzle 210 includes a plurality ofheating elements 232. Here, five heating elements 232 are suspended parallel to each other within the heating zone 236, each having its ends fixtured to the side walls of the housing 212. The heating elements 232 are aligned within a common plane, wherein in the predominant direction of air flow in approximately perpendicular to the common plane. This co-planar arrangement is advantageous because it helps the air flow passing each heating element 232 to be as closely matched as possible, resulting in a more uniform heating of the air and more uniform heat output provided by the nozzle 210.

A series of baffles 242 are disposed in the interposing spaces between the heating elements 232 to concentrate gas flow through the heating elements 232 for greater heating efficiency. The location and orientation of the baffles 242 described above afford another technical benefit, which to help match air flow volume passing by the heating elements 232 as closely as possible.

FIG. 11 shows a further variant of the nozzles 110, 210 in which combines aspects previously described. Like previous embodiments, nozzle 310 has a housing 312 divided into several sections that communicate with each other — a heating zone 335, and first and second plenums 334, 336. While the operation of this nozzle 310 is similar to that of the nozzle 210 in that gas flow begins at an inlet 344, progressively passes through first plenum 334, heating zone 335, second plenum 336, and finally outlet 316, the gas is discharged not through an array of multiple perforations or openings but a singular elongated slit or opening.

Like in FIG. 5, the solid lines in FIG. 11 show the predominant direction of air flow within the nozzle 310. Internal structures, such as the perforated walls 340, 341 and baffles 342, 342 cooperate in guiding air flow within the housing 312 for the purposes previously described.

Optionally and as shown, the nozzle 310 is an airfoil-style nozzle that can be positioned on the uncoated side of the web to facilitate both transport and heat transfer. With these nozzles, air emitted from the outlet 316 along a direction almost parallel to the web, supporting the web while avoiding disturbance of any coating disposed thereon. Here, the nozzle 310 includes an angularly- displaced surface 350 extending outwardly from the housing 312 along a generally complementary direction relative to the direction of web travel to allow the nozzle 310 to enhance the web flotation stability and heat transfer uniformity across the web.

Remaining features, options and advantages of the nozzles 210, 310, where illustrated and not explicitly described, are generally analogous to those already described with respect to nozzle 110 and shall not be repeated here.

Further described herein are methods of using the aforementioned nozzles, such as nozzles 110, 210, and 310 to dry a continuous web. These methods can be useful in any of a number of manufacturing or converting processes that requires removal of a volatile composition from a moving web. Generally, a heated gas is directed into the cavity through the inlet, the heating element used to apply supplemental heat to the heated gas, and the heated gas discharged through the outlet toward a major surface of the continuous web as it is conveyed across the outlet of one or more nozzles.

In general, the gas may or may not be pre-heated before it enters a given nozzle. If preheated, incoming temperatures may range from 21°C to 200°C, 30°C to 175°C, 40°C to 150°C, or in some embodiments, less than, equal to, or greater than 21°C, 22, 23, 24, 25, 26, 27, 28, 29, 30, 32, 35, 37, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 110, 120, 130, 140, or 150°C. While the provided nozzles can be advantageously deployed to make temperature adjustments to a gas that has been pre-heated, feeding air at ambient temperatures may be appropriate in applications with lower drying temperatures or where precise control of drying conditions is less critical.

The pressure of the gas as measured at the nozzle inlet is preferably consistent, but can vary over a wide range. Advantageously, the provided nozzles do not require use of compressed gas; positive air pressure generated by inline fans can be sufficient. Typical ranges of air pressure provided by the web dryer system can range from 62 pascals to 4000 pascals. In some embodiments, air pressures provided to the nozzle can be less than, equal to, or greater than 60 pascals, 65, 70, 75, 80, 85, 90, 95, 100, 110, 120, 125, 150, 175, 200, 250, 300, 400, 500, 600, 700, 800, 900, 1000, 1200, 1500, 2000, 2500, 3000, 3500, or 4000 pascals.

It is not uncommon for drying speed to be a rate limiting step in a manufacturing process. Drying speed can be increased by simply adding extra drying zones. A primary benefit of the provided nozzles and associated web dryer systems is the ability to create differentiated drying zones operating at different temperatures and conditions within the same web dryer system. Since these nozzles are modular and individually controllable, these enhancements can be realized from the outset or retrofitted to an existing web dryer. If an existing system is retrofitted, the provided nozzles allow these additional drying zones with customized temperature gradations to be created without enlarging the existing footprint of the web dryer system.

An added benefit is the potential to improve the quality of product made using the web dryer system, since the nozzle can be used to obtain enhanced levels of control in temperature profile that were not previously possible using conventional air nozzles. As previously mentioned, it is also possible to configure the heating elements such that the temperature profiles within the nozzle are non-uniform along the transverse direction. Advantageously, this can be used to mitigate specific problems encountered in web drying such as shrinkage at the edges of the film during heat stabilization. EXAMPLES

Objects and advantages of this disclosure are further illustrated by the following nonlimiting examples, but the particular materials and amounts thereof recited in these examples, as well as other conditions and details, should not be construed to unduly limit this disclosure. Unless otherwise noted, all parts, percentages, ratios, etc. in the Examples and the rest of the specification are by weight.

The individually heated air flotation nozzles for this test were of the two-slot pressure pad type with about 2.5 inches (6.4 cm) between the slots, and were fabricated by Global Technologies LLC (Hortonville, WI). The slots were each 0.070 - 0.080 inch (1.8 -2.0 mm) in width. These nozzles were modified to include the heating elements. 12 of these nozzles were fabricated for experimental use. The heaters employed in these test nozzles were single end finned tube heaters (obtained under the trade designation “FINTUBE SFTI-475” from Chromalox Inc., Pittsburgh, PA). The nozzles were designed to be used in an existing laboratory scale air flotation web oven system built in 1985 by International Thermal Systems (Milwaukee, WI). The balance of the nozzles in the oven were of the “air bar” type (obtained under the trade designation “IX HI-FLOAT” from Durr Megtec, De Pere, WI). The experimental oven was configured to have two 8 feet (2.4 m) long heating zones and one 8 feet (2.4 m) long cooling zone which used ambient air. The nozzles were placed in a staggered pattern with 10 inches (25.4 cm) between nozzle centers on the same side of the web. 6 of the nozzles, 3 above the web and 3 below the web, were placed at the downstream end of each of the heating zones, thus creating a four-temperature -zone web process. The heated air flotation nozzles were divided into four temperature control groups, one set of three nozzles above and below the web in each of the two zones. Each set of three nozzles had its own air temperature controller.

The experiment consisted of heating a conventional general grade tenter-process biaxially oriented PET film. The PET film was 2 mils (51 microns) thick. The film was passed through the oven at 16 feet/min (4.9 m/min), so that the dwell time in the heated portion of the oven was 1 minute. The web tension was 0.2 pli (pounds per linear inch) (0.35 N/cm). The air temperature in the upstream portion of the first zone was 150°F (66°C). The air temperature in the downstream portion of the first zone was 205 °F (96°C). The air temperature in the upstream portion of the second zone was 275°F (135°C). The air temperature in the downstream portion of the second zone was 350°F (177°C).

No rake lines (corrugation) were observed in the processed web. Based upon previous experiments in the field of heat stabilization of PET film, it was known that the measured shrinkage of the film in the machine direction at 302°F (150°C) after 15 minutes in an oven would be less than 0.1% when no rake lines are observed. Prior to the experiment described above, the oven had been run as follows: There were no heated air nozzles as described above, so there were only two temperature zones in the oven. The first zone was set around 200°F (93°C) and the second zone was set at 350°F (177°C). At the same line speed and same web tension as in the experiment above, there were noticeable rake lines in the film.

All cited references, patents, and patent applications in the above application for letters patent are herein incorporated by reference in their entirety in a consistent manner. In the event of inconsistencies or contradictions between portions of the incorporated references and this application, the information in the preceding description shall control. The preceding description, given in order to enable one of ordinary skill in the art to practice the claimed disclosure, is not to be construed as limiting the scope of the disclosure, which is defined by the claims and all equivalents thereto.