Photographic drying apparatus using air pressure to secure the film on the conveyor

Abstract: A film dryer (8) for a colour film processor (7) has a perforated belt conveyor (10) onto which film strip (17) to be dried is fed, emulsion side up, by feed rollers (18). The conveyor (10) carries the film strip (17) under the perforated bottom of a plenum chamber (13) and over an infra-red heater (16). A fan (14) draws air into the plenum chamber (13). That air emerges from the perforated bottom of the plenum chamber (13) as jets which are directed towards the conveyor (10) and which press the film strip (17) against the moving perforated material of the conveyor (10) so that it is transported by that material. Thus the film strip (17) is transported without its emulsion surface being physically contacted by mechanical handling means. The jets of air remove surface moisture from the film (17). The underside of the film (17) is heated by the infra-red heater (16) and a temperature gradient is established in the film (17), the temperature diminishing from the underside to the gelatin emulsion surface.

Description: This invention relates to film transport means for use in a film dryer. If film is pulled or pushed through a dryer, problems can arise because the emulsion surface of the film is touched by mechanical pulling or pushing means. Each one of US-A-4 693 016 and GB-A-2192447 discloses a dryer including film transport means comprising a conveyor for conveying film on a path, means operable to feed film strip onto the conveyor and means to direct jets of air towards the conveyor along the path whereby film strip laid on the conveyor is pressed against the conveyor by air that is so directed so that it is transported by movement of the conveyor and its surface is not damaged due to rubbing guide members while it is being so conveyed and dried. Hot air is used for the jets of air that are directed towards the conveyor both to retain the material being dried against the conveyor and to heat that material from the exposed gellatin surface. The top gellatin emulsion surface would "skin over" because it will be dried faster than the underlying layers. This skin acts as a barrier to the removal of water from the gellatin emulsion. If the interior of the gellatin emulsion is not dried out, moisture in it will make the surface sticky. According to this invention there is provided a film dryer as claimed by claim 1. Preferred features of the film dryer are claimed in sub-claims 2 to 6. The dryer may be incorporated in a film processor. Provision of the heating means, preferably an infrared heater, below the perforated conveyor enables film strip to be dried by being warmed from its back which is held in contact with the conveyor belt by the air jets. Hence a temperature gradient is established in the film decreasing from the back to the emulsion surface thus minimising the risk that the top gellatin emulsion surface will "skin over" by being dried faster than the underlying layers. As a result the film can be dried without being contacted by any rollers during the critical drying stage when gellatin becomes sticky. Surface drying is unlikely, the drying rate can be maximised and post drying problems are minimised. The invention enables separate strips of film to be dried individually. The film can be kept flat during drying by the action of the air jets directed onto it so that the risk of curling of the film is minimised. As cool, moist air is used the risk of generation of excessive static is minimised, and the film should emerge from the drying section in moisture equilibrium with the atmosphere in the room. One embodiment of this invention will be described now by way of example with reference to the accompanying drawings of which:- Figure 1 is a schematic illustration of film transport means in a dryer of a film processor, and Figure 2 is an end view of the apparatus shown in Figure 1. The drawings show a film processor 7 having a dryer 8 and film transport means 9 for transporting processed film strip through the dryer 8. The film processor may be as is described and illustrated in PCT International Patent Publication no. WO9O/08981 and in the co-pending application that designates the priority of British Patent Application no. 9215957.3 filed 27 July 1992. The film transport means 9 comprises an endless conveyor belt 10 formed of an open weave polyester material (see Figure 2) which runs on two spaced rollers 11 and 12, of which one is driven. A plenum chamber 13 extends above the upper run of the conveyor belt 10. The length of the plenum chamber 13 is substantially the same as the distance between the pair of rollers 11 and 12 and its width is at least the width of the conveyor belt 10. The bottom surface 13A of the plenum chamber 13 has a number of small holes 13B drilled in it, each communicating with the hollow interior of the plenum chamber 13 as can be seen in the broken away fragment of the plenum chamber 13 in Figure 1. A fan 14 is operable to draw room air through a filter 15 and to force the air into the plenum chamber 13 and cause it to emerge from the holes 13B as a number of air jets which flow across the narrow gap between the bottom of the plenum chamber 13 and the upper run of the conveyor belt 10. The jets are arranged in a preselected pattern at fairly closely spaced intervals over the whole of the surface of the upper run of the conveyor belt 10. A flat low temperature infra-red heater 16 is mounted between the upper and lower runs of the conveyor belt 10 so as to direct its heat output at the underside of the upper run of the conveyor belt 10. In operation the air of the air jets will pass through the interstices of the open mesh upper run of the conveyor belt 10 when they are played directly onto that conveyor belt 10. Strips 17 of film fed one at a time by conventional means 18 to the dryer 8 from a preceding processing station of the film processor 7, say a washing station, are directed to and laid on the upper run of the open mesh polyester conveyor belt 10. As the film strip 17 is advanced into the dryer 8 and onto the upper run of the conveyor belt 10, more and more of the air jets are directed onto it. They exert a pressure urging the film strip 17 onto the conveyor belt 10 and, as the film strip 17 advances, that pressure increases as the number of jets acting directly upon it increases. The arrangement of the jets is such that sufficient pressure is generated to hold the film strip 17 on the conveyor belt 10 so that it moves along a path through the dryer 8 with movement of the conveyor belt 10 and is pulled from the part of the processor apparatus 7 that introduced it into the dryer 8. The jets of air effectively remove surface moisture from the film 17. The underside of the film 17 is heated by the infra-red heater 16 and a temperature gradient is established in the film 17, the amount of heat diminishing from the underside to the gelatin emulsion surface. The use of a low temperature infra-red heater 16 enables heat radiation to be evenly admitted to the film 17 and thus avoids the need for mirrors and other devices to concentrate the heat onto the film 17. Triacetate film support, which is used for color negative film processed in conventional film processors, is strongly absorbing in the region 7 to 10 microns where the so-called perfect (black body) infra-red emitters reach peak emissions at temperatures of around 80°C. At this low temperature, danger to the film support is minimised and heat transfer efficiency is maximised. The air of the air jets directed onto film strip 17 on the conveyor belt 10 does several jobs. In addition to providing the extra downwards force that holds the film strip 17 on the belt 10 and enables the belt 10 to transport the film strip 17, it scrubs the surface of the film strip 17, removing moisture, whereby it promotes efficient mass transfer. It keeps the film strip 17 flat whilst it is being dried and it helps to ensure the film strip 17 is in moist equilibrium with the atmosphere in the room so that the risk of film curl after drying is minimised.

Claims: A film dryer including film transport means comprising a conveyor (10) for conveying film along a path, means (18) operable to feed film strip (17) onto the conveyor (10), and means (13 and 14) operable to direct jets of air towards the conveyor (10) along the path whereby film strip (17) laid on the conveyor (10) is pressed against the conveyor (10) by air that is directed so that the film strip is transported by movement of the conveyor (10), said film strip feeding means (18) being arranged so as to lay film strip (17) on the conveyor (10) emulsion side up, the conveyor (10) being perforated, characterised in that heating means (16) are provided below a portion of the perforated conveyor (18) on which the film strip (17) is laid so that the film strip (17) is warmed from its back which is held in contact with the perforated conveyor (10) by the air jets whereby a temperature gradient is established in the film strip (17) decreasing from the back to the emulsion surface and said means (13 and 14) operable to direct air jets towards the conveyor (10) are operable to so direct jets of cool air which scrub the emulsion surface of the film strip (17), removing surface moisture, whereby to promote efficient mass transfer. A film dryer according to claim 1, wherein the means (13 and 14) operable to direct jets of air comprise a fan (14) and a plenum chamber (13) with holes (13B) formed in a wall (13A) which faces the conveyor (10), the fan (14) being operable to blow the air through the holes (13B) and towards the conveyor (10). A film dryer according to claim 1 or claim 2, wherein the conveyor (10) comprises a perforated belt which is formed of an open weave material. A film dryer according to any one of claims 1 to 3, wherein the heating means (16) comprise an infrared heater. A film dryer according to claim 4, wherein the infrared heater is a low temperature infrared heater which is arranged so that heat radiation from it is directed towards the film and is evenly admitted to the film. A film processor (7) having a dryer according to any one of claims 1 to 5.

Inventors: PUMMELL LESLIE JAMES HORACE, PUMMELL,LESLIE JAMES HORACE
Applicants: EASTMAN KODAK CO, KODAK LTD, EASTMAN KODAK COMPANY, KODAK LIMITED
Application year: 1993
Main classification: G03D15
IPC codes: G03C11, B65H20, G03D3, G03D15, F26B13, B65H5