US3496332A

US3496332A - Porous plate developer for thermally sensitive film

Info

Publication number: US3496332A
Application number: US704131A
Authority: US
Inventors: George G Lunde
Original assignee: Minnesota Mining and Manufacturing Co
Current assignee: 3M Co
Priority date: 1968-02-08
Filing date: 1968-02-08
Publication date: 1970-02-17
Anticipated expiration: 1987-02-17
Also published as: DE1905239A1; FR2001549A1; GB1261247A

Description

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POROUS PLATE DEVELOPER' FQR THERMALLY SENSITIVE FILM Filed Feb. 8, 1968 IN VENTOR. BY gen/e 5 6*. z 0N0! wz zwww United States Patent 3,496,332 POROUS PLATE DEVELOPER FOR THERMALLY SENSITIVE FILM George G. Lunde, White Bear Lake, Minn., assignor to Minnesota Mining and Manufacturing Company, St. Paul, Minn, a corporation of Delaware Filed Feb. 8, 1968, Ser. No. 704,131

Int. Cl. H051) 1/00 US. Cl. 219216 3 Claims ABSTRACT OF THE DISCLOSURE Apparatus for uniformly developing an image-exposed intermittently advancing continuous strip of radiationsensitive heat-developable film by drawing the film between porous plate diffusers of low pressure heated air includes means for retracting said plates upon stoppage of the film and for controllably delaying the forward motion of said film after returning the plates to operative position.

This invention relates to apparatus and method for use in the development of visible images in image-exposed radiation-sensitive heat-developable sheet or film strip materials.

A type of radiation-sensitive thermally developable strip material which is particularly useful for making a visible record of transient electronically produced latent images has a sensitive coating comprising a combination of photosensitive silver halide and light-stable organic silver salt in conjunction with a reducing agent, a described, for example in US. patent application Ser. No. 693,714. The sensitive coating is soft and subject to abrasion. Thermal development to a uniform end-point requires careful control of both time and temperature of heating and is particularly difficult to achieve in a system requiring frequent or occasional discontinuous movement of the exposed strip.

Thus, exposure of the advancing strip to contact with heated air in an oven results in over-development of that portion of the strip remaining within the oven during periods of stoppage. Contact with smooth heated metal platens or drums produces a similar problem. Attempts to cool the oven or to lift the strip from the metal surface during stoppage periods are ineffective due to the inherent heat capacity of the strip, the difiiculties in obtaining uniform full contact with heated surfaces, and other problems.

It has now been found possible to achieve fully uniform development of intermittently advancing exposed radiation-sensitive heat-developable strip materials of the type hereinbefore described by heating the strip with heated air applied smoothly over one or both of the strip surfaces from retractable porous diffuser elements. The process may be carried out in a manner now to be described in conjunction with the appended schematic drawing which illustrates in elevation and partly in section a presently preferred embodiment of apparatus applicable to the development of a normally smoothly continuously advancing narrow strip of sensitive film.

In using the apparatus, which is enclosed within suitable cabinets, not shown, a strip of sensitive film 10 from supply reel 11 is drawn through a first vacuum buffer station 12, past an exposure station 13, and through a second vacuum buffer station 14 before progressing to the developing unit indicated generally at 15. The film advances from the station 12, past the station 13, and to the station 14 in an intermittent manner, i.e. one frame at a time, under the force supplied by friction drive wheels 16 and 17 which are operated in synchronism. Exposure may be with a light-image supplied by suitable optical equipment, or by any other desired means. A presently preferred exposure source employs a modulated electron beam operating in a vacuum chamber through whlch the film is passed by means of suitable vacuum ports as indicated in the drawing. As an example, from two to six 16 mm. frames may be exposed per second, thus requiring a rate of advance of the film of about three to about ten cm./sec. The two vacuum buffer or storage stations provide for smooth flow of film from the supply reel and to the developing unit while maintaining uniform tension on the intervening segment of film.

The film is fed to the developing unit by pull drum 18 and passes around idler roll 19, between platens 20 and 21, between ducts 22 and 23, through a third vacuum buffer station 24, past a viewer station 25, and finally to windup reel 26. Uniform tension on the film is supplied by the vacuum buffer station, from which the film is mtermittently withdrawn by the windup reel 26, the action being controlled by opposing switch contacts 52, 53. Random inspection is permitted at the viewer station while the film is at rest.

The two platens 20, 21 are identical and, as illustrated for platen 20, comprise a back wall 27 and sides 28 forming a plenum chamber 29 which is closed with a porous face plate 30. A coil of resistance wire 31 is wound around a ceramic supporting rod 32 which is itself fastened within the chamber 29 on supporting frames 33. Electrical connection with the coil is established through contacts 34, 35. Air under low positive pressure enters the chamber 29 through one or more ports 36 in wall 27, is heated through the agency of the coil 31, and flows from the chamber through the porous plate 30 which is itself thereby heated and assures a uniform temperature in the issuing air. The temperature of the plate is sensed by a thermocouple 37 appropriately embedded in the plate 30 and is controlled to the desired level by regulation of the power input to the coil 31.

In an illustrative embodiment useful in developing the 16-II1II1. film referred to hereinbefore, the porous plate 30 is a fiat smooth-surfaced section of fine porous bronze filter plate measuring x 1% x 24 inches which passes approximately ten cubic feet of air per minute per square foot under the applied pressure differential of two inches of water and at a temperature of C. The coil 31 is made of No. 22 gage Nichrome wire and has a resistance of 35 ohms. Plate temperatures within the range of up to about 200 C. may easily be maintained with variations of less than one degree.

The platens 20, 21 are supported on the frame by movably mounted support linkages 38-41 as shown and in position for movement toward and away from each other under the action of connecting links 42, 43, 44 and hydraulic cylinder 45, the platen faces remaining parallel to each other at all times. Support 40 and link 44 are each keyed to a common rotatably supported shaft 50. The application of pressure to the cylinder 45, through air entry port 46, forces the platens toward each other and into close proximity with the flat surfaces of the strip 10, which is then uniformly heated by the warm air flowing from the porous plates 30. Under conditions of constant rate of advance of the strip, and with proper adjustment of temperature and air flow, development of the exposed strip proceeds with complete uniformity.

If for any reason the movement of the strip 10' must be halted, as for example when data input is curtailed or a correction must be made, a three-way valve 47 simultaneously is actuated to permit the piston of the hydraulic cylinder 45 to return to closed position, under the pressure of the spring 51 thereby promptly separating the platens 20 and 21. In the example given, the platens are each removed to a distance of approximately inch (about 2 cm.) from the interposed strip of film.

The rapid retraction of the platens, combined with the low rate of flow of the heated air through the porous plates and the presence of an adequate volume of cooler air surrounding the area, results in a rapid cooling of the film strip to a temperature at which further development is effectively prevented. An examination of the strip at this point will show complete image development at the point of exit from between the platens, changing gradually to a condition of initial visible development at a point approximately midway between input and exit. If new the platens be brought into developing position and movement of the strip resumed, it will be found that a portion of the strip first issuing from the development area will be inadequately developed. To overcome this difficulty there is provided a time delay relay 48 in the film drive circuit. Closing of the starting switch 49 then promptly actuates the solenoid valve 47 to return the platens to the developing position closely adjacent the strip, but the operation of the pull drum 18 and the advancement of the strip is delayed by the relay 48 for a controllable period of time, usually about one second, sufficient to preheat the enclosed strip to a degree such that all parts of the strip will be evenly and uniformly developed.

Cool air is supplied to the interior of the cabinet and to the space surrounding the unit through opposing ducts 22, 23 and directly onto the strip of film as it issuesfrom beetween the platens 20, 21, thereby immediately terminating the development reaction as well as providing for rapid cooling of the strip upon separation of the platens in the manner described.

Where a single retractable heating platen is to be used, cooling may if desired be provided simultaneously at the reverse surface of the sheet from a similar porous plate supplied with cool air, and additional cooling platens may be positioned adjacent either or both surfaces of the sheet as it is removed from the heating area.

In place of smooth continuous advance through the developing station, the strip may be subjected to frameby-frame or other regular intermittent advance motion but at an over-all constant rate, for example by means of a Geneva drive as employed for cinematographic exposure and projection. During such regular intermittent advance the heating platens will remain in position closely adjacent the film; but any delay in the over-all constant rate of advance will call for prompt retractionof the platens. The same principle may be extended to the situation wherein only a single frame or segment or sheet of sensitive material is to be developed at a time, with prompt retraction of the heating platen or platens and cooling of the sheet on completion of development, followed by removal of the developed sheet and insertion of a next following sheet. Particularly in such instances the use of a single heating platen adjacent the sensitive surface, in conjunction with an opposing cooling platen adjacent the back surface of the sheet, is found desirable.

It will be understood that the apparatus suitable switches, vacuum and pressure pumps, means for regulating and controlling temperatures, pressures, speeds and other variables, means for connecting to suitwill include able power supply, and other auxiliary equipment, not shown for reasons of clarity and simplicity. It will further be understood that equivalent but specifically different components may be substituted for those here described and illustrated in obtaining substantially the same results in substantially the same way without departing from the spirit of the invention.

What is claimed is as follows:

1. Apparatus for uniformly heat-developing an extended-length strip of image-exposed radiation-sensitive heat-developable sheet material and comprising in combination, porous plate heating means for supplying heated air at low flow rates uniformly over at least one side of a segment of said strip, drive means for advancing said strip past said heating means at a constant rate just sufficient to permit full development of said strip, retraction means, responsive to the stopping of said drive means, for the prompt separation of said heating means from close proximity to said segment, cooling means for cooling said strip promptly after full development and for cooling said segment promptly after said separation, and delay means for briefly delaying the advancement of said strip after again bringing said heating means into close proximity with said segment.

2. Apparatus of claim 1 wherein said porous plate heating means includes means for supplying heated air over both sides of said Segment.

3. Method of uniformly developing an extended-length strip of image-exposed radiation-sensitive heat-developable sheet material comprising advancing said strip, during periods of movement thereof, at constant full-development rate through a zone of uniformly heated air obtained from porous plate heating means closely adjacent at least one side of a segment of said strip while continuously cooling said strip promptly after said full development, and, in the event of cessation of movement of the advancing strip, promptly retracting said heating means from closely adjacent said strip and simultaneously cooling said segment, and thereafter and prior to again initiating the advancing of said strip, returning said heating means to said closely adjacent position and delaying said advancing for a short time suflicient to bring said segment to its previous point in the heat-development cycle.

References Cited UNITED STATES PATENTS 1,517,434 12/1924 Kluever 219369 2,532,032 11/1950 Offen 341S5 X 2,668,701 2/1954 Dietrich 2633 3,084,489 4/1963 Seefiuth 156497 X 3,311,525 3/1967 Fanuzzi et al. 156497 3,382,789 5/1968 Barker 219--388 X JOSEPH V. TRUHE, Primary Examiner P. W. GOWDEY, Assistant Examiner US. Cl. X.R.