US3834040A

US3834040A - Dryer for photographic film

Info

Publication number: US3834040A
Application number: US00352847A
Authority: US
Inventors: H Russell; J Lin
Original assignee: Logetronics Inc
Current assignee: AFP ACQUISITION Corp; LOG ETRONICS Inc
Priority date: 1973-04-19
Filing date: 1973-04-19
Publication date: 1974-09-10
Anticipated expiration: 1991-09-10
Also published as: GB1409699A; NL7405076A; CA1017560A; CH577666A5; JPS5335724B2; JPS503339A

Abstract

A dryer for photosensitive material using both convection and conduction is disclosed having a bank of rollers aligned in coplanar axes on each side of the material path. The rollers are roughened to provide a plurality of surfaces for removing surface moisture from the material being dried. A plenum is arranged on each side of said material path to define a plurality of slots that direct heated and pressurized air against the rollers in a tangential plane to heat and dry the leading circumference of each of the rollers just before it contacts the material. The dryer also contains a plurality of floating finger guides immediately adjacent said rollers for removing any material being transported which may attempt to adhere to the rollers.

Description

United States Patent [191 Russell et al.

[111 3,834,040 [451 Sept. 10, 1974 DRYER FOR PHOTOGRAPHIC FILM Inventors: Harold D. Russell, Clinton, N.Y.;

James G. Lin, Springfield, Va.

Assignee: LogEtronics lnc., Springfield, Va. Filed: Apr. 19, 1973 Appl. No.: 352,847

US. Cl 34/160, 34/155, 34/120 Int. Cl. F26b 13/00 Field of Search 34/151, 155, 160, 162,

References Cited UNITED STATES PATENTS 11/1926 Read 34/120 5/1954 Fischer 159/11 R 10/1968 Shepherd 34/155 3/1969 Knibiehly 34/160 5/1971 Martino 34/218 3/1973 Crowell 34/156 Primary Examiner-Carroll B. Dority, Jr. Assistant Examiner-Larry I. Schwartz Attorney, Agent, or Firm-Elliott I. Pollock 5 7] ABSTRACT A dryer for photosensitive material using both convection and conduction is disclosed having a bank of rollers aligned in coplanar axes on each side of the material path. The rollers are roughened to provide a plurality of surfaces for removing surface moisture from the material being dried. A plenum is arranged on each side of said material path to define a plurality of slots that direct heated and pressurized air against the rollers in a tangential plane to heat and dry the leading circumference of each of the rollers just before it contacts the material. The dryer also contains a plurality of floating finger guides immediately adjacent said rollers for removing any material being transported which may attempt to adhere to the rollers.

7 Claims, 4 Drawing Figures Pmmwww 3.884.040

' SHEET 1 OF 2 FIG. I

PATENIEDSEP 1 (H974 Q sum 2 or 2 BACKGROUND OF THE INVENTION The present invention is concerned with improvements in the dryer section of a Graphic Arts film processing apparatus. In recent years, it has become commonplace to machine process graphic arts film to ensure consistency in the development process. With the advent of hardened emulsions, high temperature processing, and high energy developers, the wet" processing of silver halide photographic film has reached a relative plateau where the rate of processing is fast becoming dryer limited, particularly for wide film processing. In fact, the drying portion of the film processing cycle is now the largest portion of the dry-to-dry time in many processors. The drying of large sheets of graphic arts film is particularly difficult, since the film is extremely susceptible to scratching or other damage during the drying cycle, even with hardened emulsions.

Although the efficiency of the prior art dryers has been enhanced by improved heat exchangers, high velocity impingement jets or slots, and air bearings on which the film floats as it moves through the drier, the drying step is still the limiting factor in the rapid processing of graphic arts film. Graphic arts photographic film consists of a very thin (0.003 to 0.006 inches thick) synthetic-base material which absorbs practically no liquid, and coatings which may be on one or both surfaces of the base, which absorb a relatively large amount of water. The maximum hygroscopic moisture content of a gelatin emulsion at a room temperature of 25C is equal to 50 percent, but the maximum fluid content when saturated is in the order of 1,500 percent. The drying of this type of photographic film thus involves not only the thermodynamics principles of heat transfer, but also those of mass transfer. Fundamentally, the problem falls in the general category of a solid substance more or less saturated with a liquid component, and a gaseous environment in which the liquid phase will be transferred under proper conditions. As soon as the wet film surface comes into contact with the drying air, evaporation commences, and the concentration of water on the surface diminishes. This causes a difference in fluid concentration between the wet interior of the film and its surface, which has been partially dried by evaporation. This difference affects the rate at which fluid diffuses from the interior of the emulsion to the surface and constitutes an effect which will continue until the emulsion is in equilibrium with dry air.

The three classic methods of introducing heat to a material to be dried are conduction, convection, and radiation. Generally speaking, the art of machine drying of photographic film has concentrated on convection or conduction, with relatively little emphasis on machines which combine both conduction and convection.

PRIOR ART The prior art discloses various types of dryers for photosensitive material. These dryers include all-roller machines in which film is passed through a bank of rollers and the surface of the film is dried with high velocity impingement air from jets or slots. The prior art also includes dryers which use air jets to transport the material through the dryer. These jets simultaneously effect the support and drying of the film. The prior art also discloses drum-type conduction dryers wherein paperbased photographic material is placed in intimate contact with a heated drum to effect drying of the material. Many of the older dryers also used an absorbent surface to dry the photographic material.

SUMMARY OF THE INVENTION In accordance with the present invention, an improved drying section is provided for use in connection with the automatic processing of graphic arts film and other photosensitive materials. The dryer uses both conduction and convection to heat the material being dried and remove the moisture. The dryer uses a roller transport section to convey the material, and air blasts to heat and dry the rollers which, in turn, act as heat conductors to dry the material through conduction. In addition, the air jets are so positioned as to provide impingement jets which strike the surface of the material and break up the inhibiting boundary layer of air which otherwise prevents the efficient transfer of moisture from the emulsion to the surrounding atmosphere. The roughness of the roller surfaces is used to provide a plurality of surfaces or pockets for removing surface moisture from the photosensitive material and convey it away from the material. This surface moisture is then evaporated as the rollers rotate.

It is an object of the present invention to provide a dryer housing having a material inlet and outlet which contains a plurality of spaced rollers mounted for rotation on first and second coplanar axes within the housing. The rollers define, between said first and second coplanar axes, a material transport path from inlet to outlet. The rollers are also positioned relative to said path to enable the outermost surface of said rollers to slightly overlap said path on both sides thereof to effect the positive transport of the material through the dryer. Plenums are mounted on either side of the combined roller assembly and transport path to define therebetween a drying zone. This plenum means also defines a plurality of air inlets and air outlets for the drying zone. Conventional means are used for heating and pressurizing the drying air that is delivered to the plenum for use in the drying zone. The plenum itself defines a plurality of air inlet slots mounted behind the rollers to direct the heated and pressurized air against the rollers in a tangential plane. The plane of air intersects the rollers along their leading circumference to dry and heat the circumference immediately before it contacts the material. In addition, the dryer includes a pluality of laterally spaced floating finger guides which are mounted immediately adjacent the trailing circumference of the rollers. These fingers are adapted to be pivoted into the surface of any roller in the event that the leading edge of a sheet of photographic film adheres to that roller surface.

BRIEF DESCRIPTION OF THE DRAWINGS portion FIG. 4 is an isometric view of the film dryer housing illustrating the housing in its open position.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 illustrates diagrammatically and in cross section a dryer constructed in accordance with the present invention. The dryer is contained within a housing having a material inlet 11 and a material outlet 12. The dryer comprises a first roller rack 8 and a second roller rack 9. Roller rack 9 is designed to pivot around pin 160 as illustrated in FIG. 4. As it pivots about pin 160, it carries the outer portion of housing 10 with it. Pin 160 is mounted within slot 170 for easy removal of the roller rack 9 in the event cleaning or servicing becomes necessary. Likewise, roller rack 8 is secured by means of pin 190 within slot 180 so that it may be removed for cleaning and servicing.

The material enters the dryer after exiting from the wash tank of a photographic processor generally designated as 20. As it exits from the processor it passes between a pair of

squeegee rollers

21, 21a, 22 and 22a. The squeegee rollers utilize two small diameter stainless

steel pressure rollers

21 and 22 arranged above a pair of rubber covered stainless steel rollers 21a and 22a. The excess water removed from the material by means of the squeegee rollers is collected by means of catch tray 23 and conveyed to a drain by means of conduit 24. The material is directed into the dryer transport path by means of guides 33 and 34. The material then follows a slightly serpentine path (exaggerated in FIG. 1) through the transport to the exit 12. At the exit point 12, the material is directed laterally outwards by means of guides 35. The guides 35 constitute a plurality of laterally spaced plates more fully illustrated in FIG. 4

Roller rack 9 contains a plurality of elongate rollers l3-20 which are mounted for rotation in a coplanar axis within the housing 10. Roller rack 8 contains a second set of rollers 25-32 which are also arranged for rotation along a second coplanar axis within housing 10. The two banks of rollers define between them a material transport path from the inlet to the outlet. Each of the rollers is positioned relative to the material transport path to provide that the outermost surface of the rollers (a, 16a) slightly overlaps the path on both sides thereof to effect a positive transport of the material through the dryer. The serpentine nature of the path illustrated in FIG. 1 is exaggerated to illustrate the interaction of the rollers 13-20 and rollers 25-32.

The housing 10 also includes a pair of supply ducts 95 and 96 (see FIG. 4) which supply heated air under pressure to the

plenums

36 and 37 through a plurality of openings 55-57 for plenum 36 and 58-60 for plenum 37. These openings 55-60 serve to equalize the pressure distributed to the plenums and aid in the even distribution of the air to the air inlets 38-54. The

plenums

36 and 37 also define a plurality of outlet openings 59-62 which allow the removal of air from the drying zone either for recirculation or for discharge to the atmosphere at a remote point. The drying zone is defined by the inner side walls of the

plenums

36 and 37 fully encompasses the rollers 13-20 and 25-32.

The air supplied to the plenums is heated and pressurized in a conventional manner. In the preferred embodiment a pair of heaters and a blower are contained within the processor, or may be located in the supply ducts at and 96 (see FIG. 4). They provide dry, warm air, preferably having a temperature of approximately to the air inlets 55-60 defined in the side walls of

plenums

36 and 37. As an alternate to the heaters, appropriate inlet dehumidifiers may be provided for supplying dry air at room temperature.

The air inlets 38-54 illustrated in FIG. 1 are also shown in the partial cross section of FIG. 4 by the numerals 40-42 and 40a-42a. These air inlets are defined as a plurality of elongated slots spaced the length of the rollers 13-20 and 25-32. These air inlet slots are mounted behind the rollers to direct the heated and pressurized air against the rollers in a tangential plane, with the plane intersecting the rollers along the leading circumference of the rollers. The heated air dries and heats the roller circumference just before it contacts the film. The path of the heated and pressurized air is illustrated in FIG. 2. FIG. 2 is an enlarged diagrammatical cross sectional view of a portion of the air inlet openings and rollers shown in FIG. 1. The air inlets 38-40 provide a planar jet of air which strikes the rollers 13-15 in a tangential plane at l3a-l5a. Rollers 13-15 are rotating counter clockwise, and numerals 13a-15a indicate the leading circumferential portions of the rollers just before they contact the film A.

A portion of roller 13 is illustrated in FIG. 3. In this figure, the roughened surface of the roller is exaggerated as indicated by the multiplicity of surfaces shown at 13b. This roughened surface defines a multiplicity of small pockets which collect moisture from the surface of the film and carry it away from the material as the roller rotates. The water actually transferred to the roller from the surface is then evaporated by the jets of air. The rollers in the preferred embodiment of the invention were constructed of a paper-based phenolic laminate having a slightly roughened surface. The roughened surface results from machining of the rollers to obtain a No. 16 grind surface finish.

Thus the photosensitive material is dried in a number of ways. As the material enters the dryer, it carries on its surface a thin film of liquid, and the emulsion is saturated with liquid. This film of moisture is removed mechanically by transfer to the absorptive surfaces of the first few rollers. Second the rollers heat the material by conduction. Third, the rotation of rollers 13-15 carries the tangential blast of air over the upper portion of the rollers at 13a 15a, and causes it to impinge on the material just before the material encounters each successive roller. This generates a turbulent action resulting in vigorous agitation of the air immediately adjacent the surface of the material. In effect this action destroys the boundary layer which would normally accompany the material as it passes through the dryer. This boundary layer comprises a relatively stagnant air film which quickly becomes saturated with moisture and offers considerable resistance to heat and mass transfer. This thickness of the boundary layer is a function of transport velocity. Thus it is desirable to minimize the boundary layer effect by introducing jets of air perpendicular to the normal plane of the boundary layer. The rollers themselves also aid in the destruction of the boundary layer by scrubbing the material as each roller contacts the material along its transport path.

Evaporation of moisture from the graphic arts film is accompanied by a large absorption of heat, which is obtained from the drying air by convection and from the rollers by conduction. The convection occurs through the boundary layer and is proportional to the temperature differential between the film emulsion and the adjacent airf As long as the film surface remains sufficiently moist, the evaporation will take place at a constant temperature. As the drying proceeds, however, the surface becomes drier and the rate of evaporation decreases, as does the rate of heat consumption, but the rate of heat input remains unchanged. The surplus heat is then absorbed by the film raising the temperature of the surface and causing it to harden.

The foregoing illustrates two separate stages of drying. The first period includes a constant rate drying period which is of relatively short duration. The second is a falling rate drying period which is governed by molecular diffusion. During the first period, constant rate drying can be achieved by use of high velocity air which generates a turbulent action resulting in vigorous agitation and a thinning of the boundary layer.

During the second rate of drying, a different set of parameters are in effect. As the surface concentration of water drops below saturation, the evaporative rate decreases. This lowers heat consumption, but the rate of input remains unchanged, therefore heating the film. At a given point, the film reaches an equilibrium with the drying air and evaporation ceases. Any excessive increase in relative heat will cause the surface of the emulsion to shrink, and be placed under high stress by the moisture trapped underneath. What is needed at this point is a method of increasing the drying temperature within the film itself, while minimizing the drying effect on the surface of the film. By heating the rollers, and using a conduction transfer, it is possible to convey heat directly into the film without excessively drying the surface of the film. Thus the conductive method of drying assumes more and more importance as the drying of the film progresses.

As the film changes from its constant rate drying period to its falling rate drying period, it undergoes a tacky state which has caused considerable difficulty in the design of machine dryers. During the tacky state the film may adhere to the surface of the rollers. The present invention utilizes a novel means for preventing the adhesion of the film to the rollers as it passes through the dryer. As illustrated in FIG. 2, a plurality of floating finger guides 60-62 are used immediately adjacent each of the rollers to prevent the film from adhering to the rollers. The floating finger guides are laterally spaced along the entire length of each roller at approximately two-inch intervals. The lateral spacing is more fully illustrated in FIG. 4. Each of the floating finger guides is formed from a thin sheet of plastic material.

In normal operation, as illustrated in FIG. 2 by the floating finger guide 60, the upper edge 60a of the guide is biased to lightly engage the surface of the roller 25. This is accomplished by having the center of gravity of the finger on the opposite side of the pivot point from edge 60a. The floating guides help to reduce material costs in manufacture by enabling the use of transport rollers which are not absolutely straight.

The guide 61, as illustrated in FIG. 2 is pivoted about a central point 63 and is carried by an elongate channel 64 having a plurality of slots indicated by 65 in FIG. 2. The slots serve to maintain the finger guide 61 in its lateral position, and let it pivot in the direction of the arrow B illustrated in FIG. 2. The floating finger guide defines, on its leading edge, a sharpened portion 66 which engages the film A in the event the film adheres to roller 26. The configuration shown in FIG. 2 has been used for the purposes of illustration. In this illustration the film A has adhered to the roller 26 and has started to follow the roller as it rotates clockwise about its axis. As the leading edge 67 of the film A strikes the floating finger guide 61, the guide is rotated as indicated by the arrow B which brings the upper leading edge 66 of the guide into firm contact with roller 26. Since the point of contact is over center of the pivot point 63, any further pressure against the leading edge 66 will cause additional pressure against the roller 26. The floating finger guide is self energizing in this respect.

In the event the film adheres as illustrated with roller 26, the leading edge of the film will be stopped by floating finger guide 61. Since the circumference of the roller will continue to advance, the area of the film immediately behind the leading edge (illustrated by the dotted line D) will begin to buckle and pull away from roller 26. The effect of the finger guide is to cause buckling in the same area affected by adhesion. As the film buckles away, as illustrated at B, its leading edge 67 will slide down the fingers frontal surface 66. The frontal surface 66 is angled to divert the film back into the film path defined between

rollers

14, 26, and 15. Thus the floating finger guides serve as intermediate guides between the rollers in addition to preventing the adhesion of film.

The air flow through a typical input slot is particularly illustrated around roller 25 in FIG. 2. As the entering heated air strikes the leading circumferential portion 25a of roller 25, it is carried up, around and over roller 25 by rotation of the roller, to engage film A directly. A portion of the air following the roller circumference indicated at 25b, and that portion of the air striking the roller directly at 25c, serve to heat the surface of the roller over almost a third of its circumference. That portion of the plane of air which is diverted downwardly as illustrated at 25d is in a counter flow relationship to the rotation of roller 25 and serves to remove any moisture trapped in the surface pockets of the roller. Thus, the loation of the slots serves three functions. First, it heats the roller to effect a conductive transfer of heat from the roller to the film. Second, it strikes the film at approximately a angle to minimize the boundary layer which would inhibit convective drying of the film. Third, it serves to evaporate moisture collected on the surface of the roller as a result of its blotting action.

The dryer is illustrated isometrically in FIG. 4. In this view, a wide sheet of film A is advancing through the dryer, and has been cut away to show the various features of the dryer. Means and 96 are provided for heating and pressurizing the air supplied to the

plenums

36 and 37. The roller racks 8 and 9 are carried within the

main frame members

70 and 71. These frame members also provide means for locking the pivotable frame 71 to urge the two

roller sections

8 and 9 into engagement with one another. As was discussed'previously, the second roller section 9 is pivotably mounted to the frame by means of pin 16. When the dryer is opened, the roller rack 9, the plenum 36, and the outer cover 73 open the dryer along a vertical axis between the roller assemblies. This allows the operator of the processing machine to quickly remove any film which may become jammed during its transit through the drying section, and to gain access to the drying system for maintenance purposes.

FIG. 4 also illustrates the longitudinally extending channels 64 which supports the plurality of laterally spaced floating guide fingers 61 immediately below the rollers, as illustrated at roller 26.

The drive means for rotating the rollers is taken from a common shaft of the processor 20. Rotation of the common shaft (not shown) is translated by a worm gear to the main roller rack drive gears illustrated as 81 and 82 in FIG. 1. Each of the rollers 13-20 and 25-32 contains a spur gear on one end thereof. These spur gears are interconnected by a plurality of idler gears 83-88. The idler gears which serve to drive the rollers in roller rack 8 are illustrated at 89-92 in FIG. 4. This enables the rollers of each roller rack to turn in a common direction to advance the film through the dryer section.

While we have thus described a preferred embodiment of the present invention, other variations will be suggested to those skilled in the art. It must therefore be understood that the foregoing description is meant to be illustrative only, and not limitative of the present invention; and all such variations and modifications as are in accord with the principles described above fall within the scope of the appended claims.

We claim:

1. A dryer for photographic film comprising:

a. a dryer housing having a film inlet and film outlet defined therein,

b. a plurality of spaced rollers mounted for rotation within first and second coplanar axes within said housing, said rollers defining between said first and second coplanar axes a film transport path from said inlet to said outlet, said rollers being positively driven to effect the positive transport of said film through said dryer,

0. plenum means mounted on either side of said film transport path, said plenum means defining a drying zone on either side of said film transport path, said plenum means also defining a plurality of air inlets and air outlets for said drying zone,

d. a plurality of vertically oriented laterally spaced fingers each formed from a thin sheet of material and mounted immediately adjacent at least one of said rollers, each of said fingers defining a single point of contact with said roller, said fingers being pivotably mounted and lightly biased toward said roller in normal operation to engage the roller in the event a leading edge of a sheet of photographic film adheres to said roller.

2. A dryer for photographic film as claimed in claim 1 wherein said fingers are pivoted about a pivot point, said fingers defining on one side of said pivot point a photographic film engaging edge, and on the other side of said pivot point the center of gravity for said fingers.

3. A dryer for photographic film as claimed in claim 1 wherein said plenum means defines a plurality of air inlet slots mounted behind said rollers to direct air which has been heated and pressurized against said rollers in a tangential plane, said plane intersecting said rollers along the leading circumference of the rollers to dry and heat the circumference just before it contacts said film.

4. A dryer for photographic film as claimed in claim 2 wherein said rollers are positioned relative to said film to provide that the outermost surface of said rollers slightly overlaps said path on both sides of said path to effect a positive transport of said film through said dryer.

5. A dryer for photographic film as claimed in claim 1 wherein said housing is vertical and formed of two halves, the rollers lying within said first coplanar axis being mounted in one half and the rollers lying within said second coplanar axis being mounted in said second half, said first and second halves being pivotably joined together to provide that said dryer may be opened along a vertical axis between said rollers.

6. A dryer for photographic film as claimed in claim 1 wherein the surface of each roller is slightly roughened to provide a plurality of surfaces for removing moisture from the surface of a sheet of photographic film.

7. A dryer for photographic film comprising:

a. a dryer housing having a film inlet and a film outlet defined therein,

c. plenum means mounted on either side of said film transport path, said plenum means defining a drying zone on either side of said film transport path, said plenum means also defining a plurality of air inlet slots and air outlets for said drying zone,

d. a plurality of vertically oriented fingers mounted immediately adjacent at least three of said rollers, each of said fingers being pivotably mounted on a pivot point and defining on one side of said pivot point the center of gravity for said finger, said fingers being lightly biased into engagement with said roller by gravitational force whereby said fingers will engage said film in the event a leading edge of a sheet of film adheres to said roller,

e. said fingers being formed from a thin sheet of material and defining a photographic film engaging edge on one side of said pivot point, said edge also defining a single point of contact with said roller, each of said fingers also defining an upwardly extending notch which extends above the center of gravity of said finger,

f. said pivot point further defining a longitudinal and upwardly extending flange member, said flange defining a plurality of slots for receiving said vertically aligned fingers.

Claims

1. hA dryer for photographic film comprising: a. a dryer housing having a film inlet and film outlet defined therein, b. a plurality of spaced rollers mounted for rotation within first and second coplanar axes within said housing, said rollers defining between said first and second coplanar axes a film transport path from said inlet to said outlet, said rollers being positively driven to effect the positive transport of said film through said dryer, c. plenum means mounted on either side of said film transport path, said plenum means defining a drying zone on either side of said film transport path, said plenum means also defining a plurality of air inlets and air outlets for said drying zone, d. a plurality of vertically oriented laterally spaced fingers each formed from a thin sheet of material and mounted immediately adjacent at least one of said rollers, each of said fingers defining a single point of contact with said roller, said fingers being pivotably mounted and lightly biased toward said roller in normal operation to engage the roller in the event a leading edge of a sheet of photographic film adheres to said roller.

7. A dryer for photographic film comprising: a. a dryer housing having a film inlet and a film outlet defined therein, b. a plurality of spaced rollers mounted for rotation within first and second coplanar axes within said housing, said rollers defining between said first and second coplanar axes a film transport path from said inlet to said outlet, said rollers being positively driven to effect the positive transport of said film through said dryer, c. plenum means mounted on either side of said film transport path, said plenum means defining a drying zone on either side of said film transport path, said plenum means also defining a plurality of air inlet slots and air outlets for said drying zone, d. a plurality of vertically oriented fingers mounted immediately adjacent at least three of said rollers, each of said fingers being pivotably mounted on a pivot point and defining on one side of said pivot point the center of gravity for said finger, said fingers being lightly biased into engagement with said roller by gravitational force whereby said fingers will engage said film in the event a leading edge of a sheet of film adheres to said roller, e. said fingers being formed from a thin sheet of material and defining a photographic film engaging edge on one side of said pivot point, said edge also defining a single point of contact with said roller, each of said fingers also defining an upwardly extending notch which extends above the center of gravity of said finger, f. said pivot point further defining a longitudinal and upwardly extending flange member, said flange defining a plurality of slots for receiving said vertically aligned fingers.