METHOD AND APPARATUS FOR CHANGING THE TEMPERATURE OF A MOVING CONTINUOUS WEB

Abstract: A method and apparatus for changing the temperature of a moving continuous web (12). The apparatus includes a chamber (26) within which are mounted spaced parallel rollers (10) for contacting one side of the web and a housing (18) interposed between adjacent rollers and having an upper perforated surface (22) which is in close proximity to and along the entire width of the side of the web contacting the rollers. A suction device (30) in fluid communication with the chamber (26) establishes a pressure differential on opposite sides of the web (12) to deflect the web section extending between adjacent rollers (10) to provide a predetermined angle of contact of the web with the rollers. Said suction device (30) is in fluid communication with the elongated housing (18) and causes fluid to be withdrawn from the housing. The fluid has a temperature different from that of the web and flows substantially longitudinally of the web and in proximity to the entire width of the web section which extends between the rollers.

Description: METHOD AND APPARATUS FOR CHANGING ' THE TEMPERATURE OF A MOVING CONTINUOUS WEB Thig invention relates to a method and apparatus for changing the temperature of a moving continuous web, and in particular to a method and apparatus for uniformly heating or cooling a moving continuous support coated with a photograpnic emul¬ sion. In the coating of a photographic support, a ' gelatin emulsion is applied to the support and cooled until the emulsion gels. The emulsion is free to flow for an appreciable time before it gels, and, during this free-flow period, movement of the support tends to cause the emulsion to gel non-uniformly. It is essential that as much uniformity as possible be maintained in the treatment of the emulsion coating on the support during the free-flow period. It is known in the cooling of supports coated with photographic emulsions to employ a suction device in cooperation with closely-spaced chill rollers. The suction device produces a downward air flow to assist in producing a predetermined angle of contact of the web with the chill rollers. Toe rollers may be idler rollers turned by the movement of the support thereon. A disadvantage of this type of suction device is that the support does not change temperature uniformly across its width. This results in a higher temperature at its center portion and a lower temperature at the edge portions. This non-uniformity is believed to result from air flowing under the support from edge to center, which results in greater cooling effect on the edge portion of the support than on tne center portion. This creates a temperature gradient across the support, resulting in undesirable variations in the photographic coating widthwise across the support. U.S. Patent 3,738,018 discloses an example of such a suction device. This disclosure describes guiding a moving support through a dryer by closely spaced pairs- of guide rollers in engagement with one surface of the support. An arcuately pointed suction device disposed closely adjacent and between peripheries of adjacent rollers maintains the support in a predetermined angle o ' f contact of the support with the rollers. The drying effect results from contact with the heated rollers and hot air in the dryer. However, any portion of air flow passing parallel to the support must be drawn by the suction device around and under the edges of the moving support.. There a-re no means for guiding the air flow " to the center of the support. Such a device is not capable of solving the edge-to-center temperature gradient problem which is the problem to which our invention is directed. U.S. Patent 3,065,098 teaches cooling a continuous moving support by conveying it on a supporting cushion of air flowing from perforations in a plurality of hollow stationary tubes. Air is S n drawn downwardly into the space between adjacent tubes by a suction device which establishes a different pressure on the two sides of the support, causing it to move in an undulated path. The cooling effect is produced solely by transfer of heat from the support to the air cushion, and thus is somewhat limited in effectiveness. In addition, tnis device is not capable of providing a uniform coating because unstable air flow is created between the tube and the moving support causing the support to vibrate, resulting in disruption of the emulsion coating. The present invention has as its object to provide improvement in unformity of heat transfer to or from a moving web, permitting more rapid and uniform setting of a coating on the web. This object is achieved by causing a fluid, such as air, having a temperature different from that of the web to flow in contact with and substantially longitudinally of the web and along its entire width. The advantage of such an arrangement is that it greatly reduces the temperature gradient across the web which occurred heretofore. Thus the invention reduces variations in the characteristics of a coating across the width of the web, and results in greatly improved uniformity particularly with respect to photographic coatings. The invention provides an additional advantage when used in photographic coating. Since contact with the rollers is important for heat transfer, the length of support "chilled" during the period of time the rollers require to reach an -equilibrium temperature following machine startup must be discarded due to non-uniform beat transfer. This constitutes waste to the manufacturer. Because the area of contact of- the support with the rollers is important for heat transfer, increasing such contact, together with the addition of a flow of fluid produced between adjacent rollers, will increase heat transfer and thereby reduce the time required for the rollers to achieve temperature equilibrium. Tne invention provides a method for changing the temperature of a moving, continuous web wherein the web is transported with one side in contact with a pair of spaced, parallel rollers and a pressure differential is established between opposite sides of the web, thereby causing the section of web which extends between said rollers to deflect to provide a predetermined angle of contact of the web with the rollers, said method being characterized in that a fluid which has a temperature different from that of the web is caused to flow substantially longitudinally along and in contact with the lower pressure side of said section substantially across the entire width thereof. In a preferred embodiment, a hollow housing is positioned between adjacent rollers with one surface adjacent to the web and extending the entire width of the web. The housing has one or more fluid discharge openings in ttie surface adjacent to the web and at least one fluid inlet opening. A fluid pressure condition is established on the side of the web contacting the rollers to cause fluid to be drawn into the housing through the fluid inlet opening(s) . This fluid pressure also causes fluid to be drawn from the bousing through the fluid discharge opening(s) to establish a flow of fluid in a direction substantially longitudinally of the web, in the space between the web and bousing surface, to cause uniform widtbwise beat transfer. In another embodiment, a fan is used to provide fluid, such as air, to the inlet opening of the housing to enhance control of the flow of air in ta space between the web and the housing surface. In a further embodiment of the invention, fluid from the bousing is also directed against adjacent rollers, thereby further heating or cooling the rollers. Figure 1 is a perspective with a portion broken away, of a preferred embodiment of the apparatus for beating or cooling a moving continuous web; Figure 2 is a segmental top plan view of a por¬ tion of the apparatus of Figure 1; Figure 3 is a schematic side sectional view of the apparatus of Figure 1 with a portion broken away. Figure 4 is a segmental schematic side section¬ al view of another embodiment of the apparatus of this invention with a portion broken away; Figure 5 is a graph showing the variation of web temperature widtbwise across the web with no air flow from the elongated bousing of the apparatus; and Figure 6 is a graph showing the variation of web temperature widtbwise across the web under the influence of an air flow from the elongated housing the apparatus. Referring to Figures 1-3, there is illustrated an apparatus in accordance with this invention for uniformly heating or cooling a web 12 across its width. The apparatus comprises a plurality of spaced support members such as parallel rollers 10 disposed * in a horizontal plane for supporting the web 12. The web 12 is conveyed lengthwise across rollers 10 by suitable means such as a drive roller 14 coupled to a drive means 16. Fluid (such as air) flow means comprising an elongated bousing 18 is positioned between adjacent rollers 10. Each bousing 18 has a rectangular cross-section and a length approximately the same as that of the rollers and sufficient to cover the entire width of the web. The housing 18 further has one or more discharge openings 20 in. an upper surface 22 adjacent to the web. For web chilling applications, the discharge openings 20 are preferably arranged in a plurality of rows. These discharge openings are countersunk (not shown) on the inside of the housing to prevent whistling upon passage of air through the openings. Alternatively, the discharge openings 20 may comprise one or more elongated openings extending along the length of the housing. Also, the housing 18 may have a cross-section other than rectangular, such as triangular, for example, provided the upper surface 22 faces the web along a length of the web. The upper surface 22 of housing 18 also has an air inlet opening 24 located laterally outside the edges of the web. The inlet opening 24 may be located at any other suitable exposed area of the bousing which is not covered by the web, such as the end of the housing. Alternatively housing 18 can also be pressurized by having air inlet opening 24 connected to fan 37 capable of supplying 1 to 1.025 atmospheres of air (absolute pressure) preferably 1.007 to 1.01 atmospheres of air (absolute pressure). The , rollers 10 and housings 18 are closely spaced with a small gap or space between each housing and its adjacent rollers. The gap or space is illustrated in the drawing in exaggerated form, being enlarged in relation to the size of the rollers 10 and housings 18 for purposes of clarity. The housings 18 and rollers 10 are mounted in the open upper portion of a chamber 26 (Figs. 1 and 2), rigidly mounted by any suitable means, not shown, within a room 34. The upper surface 22 of each housing is spaced a predetermined amount below a horizontal plane extending through the tops of rollers 10 adjacent the housing. Although only three rollers are illustrated for exemplary purposes in Figs. 2 and 3, it should be understood that any number of rollers and housings may be employed in the practice of this invention. The chamber 26 forms a part of the means for establishing a pressure differential at opposite sides of web 12. The chamber 26 comprises two end walls 21, and two side walls 23, only a portion being shown in Figs. 1-3, and supports the ends of rollers 10 and housings 18. The support is accomplished by having stub shafts 13, 15 at the ends of the rollers 10 and housings 18, respectively, rest within complementary notches 17, 19, respectively, in the side walls 23. Chamber 26 has a lower wall 25 and upper wall projections 27 defining the aforementioned open upper portion opposite lower wall 25. The open portion of chamber 26 is / ^BϋΛ- effectively closed off by rollers 10 and housings 18 spanning side walls 23, and by web 12 as it is conveyed in contact with the* roller ' s. The web width is less- than the distance beween air inlet openings 24 so tba.t the openings are uncovered and in fluid communication with room 34 to provide air at atmospheric pressure. Alternatively air inlet openings 24 can be connected to fan 37 in wbicb case the web may extend beyond openings 24. The chamber 26 is connected by a conduit 28 to a suction device 30, such as an exhaust fan, to re¬ duce the fluid or air pressure in chamber 26 ' below the air pressure maintained within room 34. Since the pressure within room 34 is preferably atmos- pheric pressure, the reduced air pressure within chamber 26 is preferably subatmospberic. Naturally, if a fan is connected to air inlet opening 24, the pressure within chamber 26 need not be subatmospberic. The reduced, preferably subatmos- pneric, air pressure produced in chamber 26 has several functions. Firstly, it causes the web sec¬ tions ex.tending between adjacent rollers 10 to be deflected by the higher preferably atmospheric pres¬ sure above the web to produce a predetermined angle of contact of the web with the rollers. The exact angle of contact is influenced, for example, by parameters such as the fluid pressure differential above and below the web and by the tension of the web supplied by the drive means 14, 16. By proper selection of the parameters, the amount of deflec¬ tion of the web sections is controlled so that the web sections do not rub or engage the upper surface 22 of housing 18. Secondly, the pressure differen¬ tial between the air pressure in room 34 and the re- duced air pressure established in chamber 26 also causes air to enter into a cavity 32 within housing 18 through air inlet openings 24 and to be drawn tnrough air discbarge openings 20 to produce a heat- ing or cooling air flow (depending upon the tempera¬ ture of the web and air) . The beating or cooling air flow from air discbarge openings 20 passes through the space between the lower surface of web 12 and the upper surface 22 of bousing 18 substantially longitudinally of the web along and in proximity to the entire width of the side of the web section contacting the rollers. By virtue of the air flow moving along and in contact with the lower surface of web 12, good overall web heating or cooling effect is obtained. Furthermore, the heating or cooling air flow reaches the center portion of the web, as well as tπe edges of tne web, thus improving the widthwise temperature uniformity of the web. Although the portions of the gaps between roll¬ ers 10 and housings 18 and upper wall projections 27, and oetween the roller ends and side walls 23 are uncovered between the web edges and side walls 23 (Fig. 2) resulting in some air leakage through them into chamber 26, the area of such uncovered gap portions is negligible in relation to the entire system and does not unduly affect the operation of the apparatus. Tfte room 34 within which the apparatus of this invention is preferably enclosed is maintained at a predetermined temperature by any suitable means. The preferably solid metallic rollers 10 attain the predetermined room temperature within a short period of time, and act as beat or cold sinks for heating or cooling the web. The amount of beating or cool¬ ing of -the web by the rollers 10 is dependent, for example, _upon the temperature of the rollers, the nature of the web, and the angle of web wrap or con¬ tact with the rollers. The variables or parameters such as the area and configuration of the air discharge openings 20, the distance or gap between each roller 10 and its adjacent housings 18, the differential between pressures acting on opposite sides of the web, web tension, nature of the web, type of web coating, if any, etc., are selected and balanced to provide the desired web beating or cooling air flow for each web heating or cooling application. Figure 4 shows another embodiment of the inven¬ tion. In this embodiment, housing 18 has fluid discharge openings 36, such as slots, in its side surfaces adjacent to rollers 10. .These fluid discbarge openings 36 are in addition to air discharge openings 20 facing web 12. Fluid is withdrawn not only through openings 20, but also through fluid discbarge openings 36 by the reduced pressure within chamber 26 and directed against adjacent rollers 10, for assisting in beating or cooling the rollers. Figures 5 and 6 are plots of web temperature in degrees Celsius over the width of the web from each side of the web centerline for a web chilling application utilizing apparatus of the type illustrated in Figs. 1-3. The web temperatures for both tests were monitored by the same temperature sensing means under the same operating conditions such as type and temperature of the emulsion coating, web tension, room temperature, pressures, etc. F-igure 5 illustrates test results wherein air discharge openings 20 were closed off so that no air flow came into contact with the moving web. For the Figure 6 tests, the air discharge openings 20 were open and a web cooling air flow according, to our invention was produced. Figure 5 illustrates the considerable temperature gradient which exists be- tween the highest value at the web centerline and lowest value at the web edges when no air flow en¬ gages the web from air discharge openings ' 20. Figure 5 also illustrates that the temperature rapidly falls from a high centerline value to lower readings at the edge, clearly illustrating a temperature gradient across the entire width of the web. A temperature gradient produces non-uniformities in coating characteristics that are particularly troublesome when the web is coated with a photographic emulsion. Figure 6 illustrates a substantial "smoothing out" of this widtbwise temperature gradient due to the use of the cooling air flow provided by the elongated housings 18 between rollers 12 as described above. In the case of webs coated with photographic emulsion, a reduced temperature gradient decreases non-uniform drying and non-uniform photographic sensitometric effects across the width of the web.

Claims: CLAIMS 1. A method for changing the temperature of a moving, * continuous web wherein the web is transported with one side in contact with a pair of spaced, parallel rollers and a pressure differential is established between opposite sides of the web, thereby causing the section of web which- extends ' between said rollers to deflect to provide a predetermined angle of contact of the web with the rollers, said method being characterized in that a fluid which has a temperature different from that of the web is caused to flow substantially longitudinally along and in contact with the lower pressure side of said section substantially across entire width thereof. 2. A method as claimed in Claim 1 characterized by maintaining the rollers at a temperature different than that of the moving web to transfer heat between the web and the rollers. 3. A method as claimed in Claim 1 or 2 char¬ acterized by maintaining pressure on the other side of the web at least equal to atmospheric pressure, and the pressure on the side contacting the rollers at less than atmospheric pressure. 4. A method as claimed in Claim 1, 2 or 3 characterized by transporting tbe web with one side of the web in contact with a plurality of spaced parallel rollers and in close proximity to an elon¬ gated bousing extending across tbe entire width of the web for producing a flow of fluid between adja¬ cent rollers. 5. A method as claimed in Claim 1, 2, 3 or 4 characterized by producing a flow of fluid from air discharge openings in said elongated bousing in close proximity to the entire width of one side of tbe web * section. 6. A method as claimed in any of Claims 1 to 5 characterized by supplying a flow of fluid to said elongated housing which is greater than atmospheric pressure. 7. A method as claimed in any of Claims 1 to 6 characterized by producing a flow of fluid from air discbarge openings in said elongated housing to direct air flow against adjacent rollers. 8. An apparatus for changing the temperature of a continuous moving web, said apparatus having; at least two spaced parallel rollers (10) for supporting one side of the moving web (12) ; suction means (30) for establishing a pressure differential between opposite sides of tbe web (12) to (a) deflect a web section ex- • tending between said rollers (10) to provide a predetermined angle of contact of tbe web with the rollers and (b) produce flow of a fluid having a temperature different than that of the web; characterized in that fluid flow means (18) is positione ' d between adjacent rollers for guiding the fluid flow in a direction substantially longitudinal¬ ly of the web along and in proximity to tne en¬ tire width of tbe ^ide of the web section in contact with said rollers. 9. An apparatus as claimed in Claim 8 char¬ acterized in that a plurality of spaced rollers (10) are used to support one side of tbe moving web (12) baving said fluid flow means (18) between adjacent rollers. 10.. An apparatus as claimed in Claim 8 or 9 characterized in that said fluid flow means com- prises an elongated housing (18) having a surface (22) which is parallel and in close proximity to the web section in contact with said rollers and having at least one discbarge opening (20) in said surface. ^ 11. An apparatus as claimed in Claim 8, 9 or 10 characterized in that said elongated bousing (18) has an air inlet 24 to supply fluid to said housing wnereby fluid is drawn into the bousing and expelled through discharge openings (20) for establishing fluid flow to the space between tbe web section and surface (22). 12. An apparatus as claimed in Claim 11 char¬ acterized in that pressure fan (37) provides a flow of fluid to said elongated bousing (18) which is greater than atomspheric pressure. 13. An apparatus as claimed in any of Claims 8 to 11 characterized in that suction device 30 estab¬ lishes a subatmospberic pressure on tbe one side of tbe web which causes air at atmospheric pressure to be drawn into tbe cavity 32 through air inlet opening 24 and out of cavity 32 through air discharge openings (20) . 14. An apparatus as claimed in Claim 13 char¬ acterized in that suction device 30 and/or pressure fan 37 establish a temperature to tbe rollers (10) different than that of tbe web (10) to thereby change tbe temperature of the web as it contacts tbe rollers. 15. An apparatus as claimed in Claim 14 cbar- acteriaed in that fluid is expelled from bousing 18 through ^ discharge opening 36 and directed against adjacent rollers (10).

Inventors: BARBEE EUGENE H
Applicants: EASTMAN KODAK CO
Application year: 1980
Main classification: F26B3
IPC codes: F26B3, F26B13, G03C1, G03D15