US3589262A

US3589262A - Photographic processing apparatus

Info

Publication number: US3589262A
Application number: US738954A
Authority: US
Inventors: Richard J Chen
Original assignee: Polaroid Corp
Current assignee: Polaroid Corp
Priority date: 1968-06-21
Filing date: 1968-06-21
Publication date: 1971-06-29
Anticipated expiration: 1988-06-29
Also published as: CH518574A; NL6909469A; DE1931306B2; GB1225908A; FR2011440A1; NL164677C; DE1931306A1; NL164677B; SE356611B; BE735005A; AT301335B

Abstract

An apparatus in which a viscous photographic, processing liquid is distributed in a thin layer between an exposed photosensitive element and another element by moving the elements in superposition through a convergent passage between a pair of juxtaposed pressure-applying members. The viscosity of the liquid varies inversely with temperature. The speed of movement of the elements is constant while the pressure-applying members are biased toward one another with a force that is varied in inverse relation to the ambient temperature to insure uniform liquid distribution despite temperature changes.

Description

, United States Patent [72] Inventor Richard J. Chen Winchester, Mass! [21 Appl No, 738,954

[22] Filed June 21, 1968 [45] Patented June 29, 1971 [73] Assignee Polaroid Corporation Cambridge, Mas.

[54] PHOTOGRAPHIC PROCESSING APPARATUS 8 Claims, 4 Drawing Figs.

[52] 0.8. CI 95/89, 95/ l 3 [5| Int. Cl 603d 9/02 [50] Field ofSearch 95/89, l3, 14

[56] References Cited UNITED STATES PATENTS 3,108,525 10/1963 Eburnetal.

3,264,963 8/1966 Finelli 95/13 3.441437 6/1969 Tiffany 95/13 3,457,846 7/l969 Little 95/13 Primary Examiner-Samuel S. Matthews Assistant Examiner-Fred L. Braun AttorneysBrown and Mikulka and Robert E. Corb ABSTRACT: An apparatus in which a viscous photographic, processing liquid is distributed in a thin layer between an exposed photosensitive element and another element by moving the elements in superposition through a convergent passage between a pair of juxtaposed pressure-applying members. The viscosity of the liquid varies inversely with temperature. The speed of movement of the elements is constant while the pressure-applying members are biased toward one another with a force that is varied in inverse relation to the ambient temperature to insure uniform liquid distribution despite temperature changes.

PATENTEUJUM29|97| 3589.262

SHEET 2 OF 2 IOG FIG.4

INVENTOR. c'cland ffiim ammm ATTORNEYS PHOTOGRAPHIC PROCESSING APPARATUS ln photographic apparatus for exposing and processing photographic sheet material, and particularly in portable, handheld, self-developing cameras, an exposed photosensitive element is treated in an externally dry process, preferably to produce a positive photographic print formed by diffusion transfer, by distributing a viscous thixotropie liquid in a thin layer between the photosensitive element and another element. The processing liquid may be provided initially in a rupturable pod or container coupled to one of the elements and is distributed between the elements by moving them in superposition together with the rupturable container through a convergent passage between a pair of juxtaposed pressure-applying members. f

For optimum results, measured for example in terms of image quality and uniformity, as well as reliability and re peatability, and particularly when the quantity of processing liquid available is limited to approximately the minimum amount of liquid required, the layer of processing liquid distributed between the elements in contact with the photosensitive element should be of uniform, predetermined thickness. When the liquid is distributed by moving the elements through a convergent passage between a pair of pressure-applying members that are free to move apart from one another and are resiliently biased toward one another,'the thickness of the layer of liquid is dependent upon a number of factors, including the pressure exerted by the pressure-applying members, the viscosity of the processing liquid, and the speed of movement of the elements through the passage between the pressure-applying members. The nature and composition of the processing liquid are such that the viscosity of the liquid varies with changes in temperature and since the thickness of the layer of the processing liquid is, in large part, dependent upon the viscosity of the liquid, a problem arises in apparatus such as self-developing cameras which can be carried and employed both indoors and out and are likely to be employed under a wide range of temperature conditions.

An object of the invention is to provide photographic apparatus and methods of the type described in which the speed of movement of a film assemblage between the pressure-applying members is maintained substantially constant and the compressive force exerted on the film assemblage by the pressure-applying members is varied in inverse relation to the ambient temperature to compensate for temperature-related changes in the viscosity of the processing liquid and thereby provide for distribution of the processing liquid in a layer of predetermined thickness despite changes in ambient temperature and the viscosity of the liquid.

Other objects of the invention will in part be obvious and will in part appear hereinafter.

The invention accordingly comprises the process involving the several steps and the relation and order of one or more of such steps with respect to each of the others, the apparatus possessing the construction, combination of elements and arrangement of parts which are exemplified in the following detailed disclosure, and the scope of the application of which will be indicated in the claims.

For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawing wherein:

FIG. 1 is a somewhat schematic, sectional view of a camera embodying the invention showing a film assemblage and illustrating the process of the invention:

FIG. 2 is a perspective view showing components of the camera of HO. 1;

FIGS. 3 and 4 are elevational views of components of the camera illustrating other embodiments thereof.

The photographic apparatus and process of the invention find particular utility in the treatment of photographic film assemblages of the type including all of the materials required to produce a finished photographic print, preferably in full color,

and including a photosensitive image-recording element adapted to be exposed to produce an image; a second, or image-receiving element adapted to be superposed with the photosensitive element, at least during processing to aid in the distribution of a viscous processing liquid in contact with the exposed photosensitive element and preferably to support the visible image formed by diffusion transfer; and a rupturable container of viscous processing liquid adapted, when distributed in contact with the exposed photosensitive element, to produce a positive image by a process in which image-forming substances are transferred by diffusion from an exposed photosensitive stratum to an image-receptive stratum. Film assemblages of this type may take a number of different forms including, for example, separate photosensitive and second sheets adapted to produce a single print or a plurality of prints; or individual film units each including a pair of layers ofsheets coupled with or secured to one another in face-to-face relation and adapted to be exposed and processed to produce a single print. The processing liquid may be supplied in a rupturable container coupled with one or both elements and adapted to be moved together with the superposed elements through a passage between a pair of juxtaposed pressure-applying members; or the liquid may be supplied from a source not associated with the superposed elements and dispensed between the elements for subsequent spreading in a thin layer during movement of the elements between the pressure-applying members.

The camera and process embodying the present invention are specially adapted for the treatment of photographic film units of the type shown and described, for example, in the copending US. Pat. application of Edwin H. Land, Ser. No. 622,287, filed Mar. 10, 1967, now Pat. No. 3,51 1,855. A typical film unit of this type includes all of the materials and reagents required to produce a full color, photographic print by a process such as disclosed in US. Pat. No. 2,903,606, issued May 9, I961, in the name of Howard G. Rogers. This patent discloses a photosensitive element including a silver halide emulsion and a dye developer, that is, a dye which is a silver halide developing agent; a second or image-receiving element, including an image-receptive layer of a dyable material; and a processing liquid in which the dye developer is soluble and reactive. The photosensitive and image-receiving elements are superposed with the emulsion and image-receptive layers in face-to-face relation and the processing liquid is distributed in a uniform layer of predetermined thickness between and in contact therewith for permeation into the photosensitive layer to initiate development of exposed silver halide. The dye developer is immobilized or precipitated in exposed areas as a consequence of development, while in unexposed areas or partially exposed areas of the emulsion, the dye developer remains unreacted and diffusible, thereby providing an imagewise distribution of unoxidized dye developer which transfers, at least in part, by diffusion to the image-receptive layer without altering the imagewise distribution of the developer, to form a reversed or positive color image of the developed latent image in the emulsion. Multicolor transfer images are obtained utilizing dye developers, for example, by employing an integral multilayer photosensitive element such as illustrated in H6. of the 2,983,606 patent, including at least two selectively sensitized overlying photosensitive strata on a single support. A typical photosensitive element of this type comprises a support carrying a red sensitive silver halide emulsion stratum, a green sensitive halide emulsion stratum and a blue sensitive halide emulsion stratum, each emulsion having associated therewith, respectively, a cyan dye developer, a magenta dye developer and a yellow dye developer, Each set of silver halide emulsions and associated dye developer strata may be separated from other sets by interlayers formed, for example, of gelatin or polyvinyl alcohol. ln the example given, the dye developers are selected for their ability to provide colors useful in producing a full color image by a subtractive process and may be incorporated in the respective silver halide emulsion with which they are associated or in a separate layer behind the respective silver hathere is illustrated film units of the foregoing type, the

thickness of the materials being exaggerated for purposes of clarity of illustration. Each film unit, designated 10, comprises a photosensitive or image-recording sheet 12; a second or image-receiving sheet 14; and a rupturable container 16 holding a quantity of processing liquid 18. Sheets l2 and 14 are preferably, although not necessarily, rectangular and coextensive with one another and are arranged in superposed, face-toface contact with at least the lateral edges of each sheet aligned with the lateral edges of the other. The two sheets are retained in superposedrelation by a binding element 20 in the form of a rectangular sheet at least wider than either of the photosensitive and image-receiving sheets and secured thereto at the margins thereof. Binding element 20 is in the general form of a rectangular frame having a large rectangular opening 22 defining the extent of the exposed area of the film unit,

surrounded by lateral edge portions and end portions 24 and 26. The lateral edge portions and end portion 24 of binding element 20 are adhered, respectively to the lateral and trailing end margins of second sheet 14 and are secured around the edges of the sheets and adhered respectively to the lateral and trailing end margins of photosensitive sheet 12, thereby effecposure of the photosensitive sheet and viewing'of the image formed between the sheets, the photosensitive sheet is opaque and a white pigment is provided in the processing liquid to provide a white background for the transfer image.

Container 16 is of the type shown and described in U.S. Pat No. 2,543,] 81 and is formed by folding a rectangular blank of fluid and air impervious sheet material medially and sealing the marginal sections of the blank to one another to form a cavity for containing processing liquid 18. The seal between marginal longitudinal sections 28 of the container is weaker than the end seals so that upon application of a predetermined compressive force to the walls of the container in the region of the liquid filled cavity, there will be generated within the liquid, hydraulic pressure sufi'tcient to separate longitudinal marginal sections 28 throughout the major portion of their length to form a discharge mouth through which liquid 18 is discharged. Container 16 is attached to sheets 12 and 14 at the leading edges of the sheets, preferably with the longitudinal edge of the container butted against the edges of the sheets with the discharge passage of the container aligned with the facing surfaces of the sheets.

End portion 26 of binding element 20 is secured to the leading marginal edge of sheet 14 and one marginal section 28 of the container, and a binding strip 32 is adhered to the leading marginal edge portion of sheet 12 and the other marginal section 28 of the container to secure the container to the sheets. Binding strip 32 also cooperates with end portion 26 to provide a conduit for channeling liquid 18 from the container between the sheets at the leading ends thereof.

The embodiment of the film unit illustrated and described 7 herein is adapted to-be exposed and processed to produce a 'multicolor dye transfer image located between transparent second sheet 14 supporting a dyeable polymeric layer and an opaque layer located between the transfer image and the photosensitive medium. This opaque layer comprises the liquid contents 18 of container 16 which are provided in suffirequisite thickness and extent thereby making it unnecessary to provide means for collecting and retaining excess processing liquid and also providing for minimization of the size of the container and hence the overall size,'complexity and cost of the film unit. The processing liquid contained in container 16 comprises an aqueous alkaline solution having a pH at which the dye developers are soluble and diffusable and contains an opacifyi ng agent in a quantity sufficient to mask the dye developers retained in the image-recording layer (laminate) subsequent to processing; and a film-forming viscosity increasing agent or agents to facilitate rupture of the container and distribution of the liquid processing composition and assist in maintaining the layer of processing composition as a structurally stable layer tending to bind the sheets to one another.

Subsequent to exposure, film unit 10 is processed by moving the film unit with the container foremost relative to and between a pair of juxtaposed pressurc-applying members into and through a convergent passage between the members for applying compressive pressure, first to the container to eject the liquid contents of the container between photosensitive and image-receiving sheets 12 and 14, and then spread processing liquid 18 in a uniform, thin layer between the sheets over an area at least coextensive with opening 22 in binding element 20. As previously noted, the processing liquid includes an agent for increasing the viscosity of the liquid so as to promote the opening of the discharge passage of the container throughout substantially its entire length and facilitate the discharge of the liquid from the container and spreading of the liquid between the sheets. For this purpose, the liquid should be quite viscous and contain the film-forming agent in a quantity sufficient to impart a viscosity in'excess of 1,000 centipoises at a temperature of 20 C. and preferably of the order of 1,000 to 200,000 centipoises at said temperature. The processing liquid is preferably thixotropic, thereby facilitating complete rupture of the bond between sections 28 of the container comprising the discharge passage and subsequent spreading of the liquid between the sheets.

A liquid processing composition suitable for incorporation in container 16 for use in combination with sheet materials of the type described to produce a full color transfer image is dis.- closed in the following example:

Water cc. Potassium Hydroxide l 1.2 grams Hydroxyethyl cellulose 3.4 grams (high viscosity) [commercially available from Hercules Powder Co.,

- Wilmington, Del., under the trade name Natrasol 250] N-benzyl-ot-picolinium l.5 grams bromide Bensotriazole 1.0 grams Titanium dioxide 40.0 grams The viscosity of an aqueous liquid processing composition of the foregoing type varies inversely with temperature, increasing as the temperature is lowered and decreasing as the temperature is raised.

A pair of film units 10 are illustrated as comprising part of a film assemblage or pack adapted to be employed in a handheld camera. The film assemblage or pack includes a box or container 36 adapted to hold a plurality of film units 10 arranged in stacked relation and includes a forward wall 38 provided with an exposure aperture 40 substantially coextensive with opening 22 in binding element 20 and a spring and pressure plate assembly 42 for supporting the film units against the forward wall with the forwardmost film unit located in position for exposure in alignment with aperture 40. Box 36 includes an end wall 44 provided with a narrow slot 46 permitting the movement of the film units one at a time from the box through the slot.

A camera of the type adapted to employ the film assemblage for exposing and processing the film units thereof is illustratcd in FIG. 1 as comprising a housing 48 including a rear section 50 for holding and enclosing container 36, and an intermediate wall 51 having an exposure aperture 52 for locating the foreward wall 38 of container 36 in a position at which the forwardmost film unit is located in proper position for exposure. The camera includes a forward section 54 for support ing a conventional lens and shutter assembly 56, mirror 57 arranged in a plane at 45 to the film plane and lens axis for reversing the image formed by the lens on the film.

The preferred means for spreading the processing liquid between the sheets of a film unit comprise a pair of juxtaposed, pressure-applying members in the form of

cylindrical rolls

48 and 60, cooperating to define a convergent passage or throat through which the sheets are moved in superposition with container 16 foremost, to dispense the liquid contents of the container between the leading end portions of the sheets and then distribute the liquid from the leading end of the sheets toward the trailing end thereof. As shown in FIG. 2, roll 60 is mounted in a substantially fixed position for rotation about its axis and roll 58 is mounted for rotation about an axis located in the same plane as the axis of roll 60 and for'movement toward and away from roll 60. Means are provided for biasing roll 58 toward roll 60 and in the form shown comprise elongated cantilever springs 62, each mounted at one end of the camera housing and engaged at its other end with a shaft (or the journal therefor) on one end of roll 58. Means, to be described more fully hereinafter, are provided for engaging each spring 62 intermediate its ends for biasing the free end of each spring in the direction of roll 60.

As previously noted, the thickness of the layer of processing liquid distributed between the elements ofa film unit is a function of the compressive pressure exerted on the film unit by the pressure-applying members, the viscosity of the processing liquid and the speed of movement of the film assemblage through the convergent passage between the pressure-applying members. In a handheld camera such as disclosed, it may be impossible to maintain the camera and film at a constant temperature so that one of the factors, i.e., liquid viscosity, controlling the liquid spread thickness will constitute an independent variable, while another factor, i.e., speed of movement of the film unit between the pressure-applying members, remains substantially constant so that control over the thickness of the layer of processing liquid distributed within a film unit can be achieved by controlling the third variable, namely, the compressive pressure exerted on the film unit by the pressure-applying members.

In the form of camera shown, the film unit is moved between the pressure-applying rolls to spread the processing liquid by advancing the leading end of the film unit, i.e., the container, into the bite of the rolls and driving the rolls in frictional engagement with the film unit. The means for driving the rolls comprise an electric motor 64, a source of energy for the motor such as a battery or batteries 66, and a transmission in the form of gear train, including

gears

68, 70, 72, 74 and 76 for driving roll 60. A gear 78 may be coupled with roll 58 and meshed with gear 76 on roll 60 for driving roll 58. The motor and the batteries for powering the motor are designed to provide for advancement of a film unit between the rolls at a substantially constant predetermined speed throughout the range of temperatures over which the camera is likely to be employed. The housing includes an opening 80 through which film units may be advanced by

rolls

58 and 60 and means (not shown) are provided for moving each film unit, following exposure thereof, from exposure position within container 36 through slot 46 into the bite ofrolls 58 and 60.

It has been found that the thickness of the layer of processing liquid spread within a film unit varies in inverse relation to the compressive pressure exerted on the film unit by the pressure-applying members so that this thickness can be increased by reducing the compressive pressure and, conversely, decreased by increasing the compressive pressure. The thickness of the layer of liquid also varies directly with the viscosity of the processing liquid and hence inversely as the temperature of-the processing liquid. Accordingly, constant liquid spread thickness can be obtained by varying the compressive pressure inversely as to temperature; that is, by applying increased compressive pressure at lower temperatures to compensate for the increased viscosity of the liquid and applying reduced compressive pressure at higher temperatures to compensate for the reduced viscosity ofthe liquid.

In accordance with the invention, the camera includes means for automatically sensing the ambient temperature and responding by varying the compressive pressure exerted by

rolls

58 and 60 on the film unit in inverse relation to the temperature so as to maintain constant a relationship between I liquid viscosity and compressive pressure that will insure spreading of the processing liquid in a layer of predetermined depth even though the temperature and viscosity may vary. Such means may take the form shown, for example, in FIG. 2 and include temperature-responsive means for automatically varying the effective length of each of cantilever springs 62 and thereby alter the bias exerted on rod 58 by the cantilever springs. In the form shown, these temperature-responsive means comprise a pair of elongated bars 82, each pivotally mounted at one end

adjacent rolls

58 and 60 and engaged at its other end 84 with a medial portion of a spring 62 for imparting a bias to the spring. A fixed support member 86 is provided for engaging spring 82 adjacent end 84 and supporting end 84 against spring 62. Bars 82 are formed of a material such as zinc-copper and zinc-cadmium alloys, having a relatively high coefficient of thermal expansion so that the length of each bar will vary with temperature, thereby altering the position of end 84 located in engagement with spring 62. The effective length of each spring 62 and hence, the force exerted by the spring, is a function of the length of the spring between end 84 of bar 82 and roll 58, so that by virtue of the construction shown, an increase in temperature will result in an increase in length of bars 82 and effective lengths of springs 62, thereby reducing the bias exerted by the springs on roll 58.

Another embodiment of temperature-responsive means for biasing

rolls

58 and 60 toward one another with a force inversely proportional to the ambient temperature, is illustrated in FIG. 3. These means comprise a pair of first elongated springs 88, each pivotally mounted at one end on a fixed stud 90 and engaged at its other end with roll 58, and a pair of second springs 92, each pivotally mounted intermediate its ends on a stud 90 and including a tab 94 on one end engaged with a medial portion of spring 88. Each spring 92 is biased in a counterclockwise direction viewing H6. 3, and cooperates with a spring 88 to effectively act as a single spring biases about stud 90 in a counterclockwise direction. The force exerted by the rolls is varied by altering the deflection of the spring 92, specifically, by changing the position of end section 96 of the spring. Means for changing the position of end section 96 in response to changes in temperature comprise an elongated bar 98 formed of a material having a high thermal coefficient of expansion, mounted in fixed position at one end near the rolls and extending toward end section 96 of spring 92. Bar 98 includes a wedge-shaped end section 100 slidably engaged between end section 96 and a fixed backing member 102 for cooperating with the end section of spring 96 to pivot or deflect the spring in response to temperature induced changes in the length of bar 98. Thus, when the temperature is lowered, bar 98 will shrink thereby, deflecting end section 96 of spring 92 away from fixed backing member 102, increasing the force exerted on roll 58 by

springs

88 and 92. The reverse occurs when the ambient temperature rises so that bar 98 increases in length and the deflection of spring 92 is reduced.

Another embodiment of the temperature-responsive means for varying the pressure exerted by the pressure-applying rolls is illustrated in FIG. 4. In this embodiment, a pair of U-shaped springs 104 formed of a bimetallic material, i.e., a laminate of two materials having different thermal coefficients of expansion, are provided for biasing roll 58 toward roll 60. One arm of each spring 104 is fixedly engaged within the camera housing and the other arm is coupled with one end of roll 58 by an L- s ha'pe'dlllever 106 pivotally mounted intermediate it s ends, engaged at one end with roll 58 and engaged atits other end, with the free armof spring 104. Thearms of'spring [04 are biased apart from one another'so as to pivot arm' 106' in a counterclockwise direction and the two materials comprising each bimetallic spring are selected such that the arms of the spring willtend to move apart from one another as the tem- .perature is reduced, thereby applying an additional force tending to urge roll 58 toward roll 60. This is achieved by forming thebimetallic spring of two elements with the outer- 1 element having a higher thermal coefficient of expansion than the inner clement, as'is well known in the art.

Although the invention has been illustrated in connection with a pair of pressure-applying members in the form of rolls,

with thefilm being moved between the rolls by rotation thereof, other'forms of pressure-applying members and other means for moving-thefilm through a passage between the pressure-applying members are known in the art and are considered to fall within the scope of the invention. Such other formsof pressure-applyingmembers "include, for example nonrotatable members','in"which case, other means such as are 7 well known'in the art are provided for pushing and/or pulling the filmbetween the pressure-applying members. lt should be apparent also that othertemperature-responsive means may control spring tension and deflection may be formed of a material having a very low temperature thermal coefficient of expansion relative to the springs and camera housing and it is in this" manner .that relative" movement of two elements in response to temperature change, is achieved.

It should be noted and appreciated that the novel apparatus and process of the invention enable the performance, over a wide range of temperature conditions, of a photographic process, particularly a diffusion transfer process, in which a viscous processing liquid characterized by a viscosity inversely proportional .to temperature is distributed in a thin layer between a pair of 'sheetlike elements by advancing the elements in superposition through a convergent passage between a pair of pressure-applying members; By virtue of the present invention, it is possible to achieve uniform liquid distribution of a predetermined thickness automatically and with relatively "simple apparatus which lends itself to incorporation in compact, lightweight, portable cameras; and toemploy film structures including a minimum of excess processing liquid which as a result, do not require c'omplexQexpensive and/or bulky components for collectingexcess processing liquid. The certainty with which uniform liquid distribution of predetermined thickness is obtained provides for consistent, reliable and high-quality results not obtainable with systems wherein the liquid spread thickness is subject to variations resulting from changes in temperature.

Since certain changes may be made in the above process and apparatus without departing from the scope of the invention herein involved, it is'intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

' wherein said temperature-responsive means for varying the efspring means.

What I claimed is:

l. Photographic processingapparatus for treating an exposed photosensitive element by distributing a liquid processing agent having a viscosity which varies with temperature, as a thin layer in contact with said photosensitive element, said apparatus comprising, in combination:

a pair of pressure-applying members providing a passage between said members through which a photosensitive element and a second element are movable in superposition to distribute a viscous processing agent in a thin layer between said elements; l 1 t advancement meansfor moving said elementsat substantially constant speed in superposition through said passage between said members; and temperature-responsive biasing means for urging said pressure-applying memberstoward one another with a force. that'is an inverse function of the ambient temperature. 2. Photographic processing apparatus as defined in claim 1 wherein said biasing means include spring means and temperature-responsive means for varying the effective length of said spring means.

3. Photographic processing apparatus as defined in claim 2 fective length of said spring means include an element mounted at one section on a portion of said apparatus in ffixed position relative to said spring means, and including another section engaged with said spring means and at least an inter,-

1 mediate section formed of a material having a thermal coefficient of expansion substantiallydifferent from said spring means and portions of means.

4. Photographic apparatus as defined in claim 3 wherein. said element has a relatively high thennal coefficient of expansion.

5. Photographic processing apparatus as definedin claim 1 wherein said biasing means include spring means and temperature-responsive means for varying the deflection of said 6.'Photographic processing apparatus as defined in claim 5 wherein,said temperature-responsive means for varying the deflection of said spring means include an element mounted at one section on a portion of said apparatus in fixed position with respectto said spring means, and including another sec-.

tion engaged with said spring means and at least an intermediate section formed of a material having a thermal coefficient of expansion substantially different from said spring means and portions of said apparatus mounting said spring means.

7. Photographic processing apparatus as defined in claim wherein said element has a relatively high thermal coefficient of expansion. i

8. Photographic processing apparatus as defined in claim 1 wherein said biasing means include spring means formed of a bimetallic material, which changes its configuration in responseto changes in temperature.

said apparatus mounting said spring

Claims

1. Photographic processing apparatus for treating an exposed photosensitive element by distributing a liquid processing agent having a viscosity which varies with temperature, as a thin layer in contact with said photosensitive element, said apparatus comprising, in combination: a pair of pressure-applying members providing a passage between said members through which a photosensitive element and a second element are movable in superposition to distribute a viscous processing agent in a thin layer between said elements; advancement means for moving said elements at substantially constant speed in superposition through said passage between said members; and temperature-responsive biasing means for urging said pressureapplying members toward one another with a force that is an inverse function of the ambient temperature.

2. Photographic processing apparatus as defined in claim 1 wherein said biasing means include spring means and temperature-responsive means for varying the effective length of said spring means.

3. Photographic processing apparatus as defined in claim 2 wherein said temperature-responsive means for varying the effective length of said spring means include an element mounted at one section on a portion of said apparatus in fixed position relative to said spring means, and including another section engaged with said spring means and at least an intermediate section formed of a material having a thermal coefficient of expansion substantially different from said spring means and portions of said apparatus mounting said spring means.

4. Photographic apparatus as defined in claim 3 wherein said element has a relatively high thermal coefficient of expansion.

5. Photographic processing apparatus as defined in claim 1 wherein said biasing means include spring means and temperature-responsive means for varying the deflection of said spring means.

6. Photographic processing apparatus as defined in claim 5 wherein said temperature-responsive means for varying the deflection of said spring means include an element mounted at one section on a portion of said apparatus in fixed position with respect to said spring means, and including another section engaged with said spring means and at least an intermediate section formed of a material having a thermal coefficient of expansion substantially different from said spring means and portions of said apparatus mounting said spring means.

7. Photographic processing apparatus as defined in claim 6 wherein said element has a relatively high thermal coefficient of expansion.

8. Photographic processing apparatus as defined in claim 1 wherein said biasing means include spring means formed of a bimetallic material which changes its configuration in response to changes in temperature.