Title:
METHOD AND APPARATUS FOR RAPID ACCESS FILM PROCESSING
United States Patent 3585917
Abstract:
An apparatus for the rapid production of graphic information on a radiation-sensitive heat-developable strip material by exposing to radiant energy a smoothly continuously advancing strip, developing the strip material by a small efficient heating unit contiguous with the apparatus, and moving the developed material past an image-viewing station. The heating unit consists of a chamber member with a fine porous wall over which the strip material is moved and a resistance heater. Air is moved through the chamber and through the wall against the strip material at a rate to aerodynamically support the strip material from the wall and to afford convective heating of the strip material to a developing temperature. The strip material is maintained at the developing temperature for a time sufficient to develop the strip material.
US Patent References:
Apparatus for developing light-sensitive material
Uhlich et al. - May 1932 - 1861329
Processing of photographic material
Townley et al. - November 1960 - 2961938
Apparatus for producing a picture
Limberger - December 1967 - 3359404
Photographing and developing apparatus
Pfaff - March 1968 - 3372617
SENSITIZED PAPER DEVELOPMENT DEVICE
Ishikawa et al. - May 1969 - 3442589
Apparatus for developing light-sensitive material
Uhlich et al. - May 1932 - 1861329
Processing of photographic material
Townley et al. - November 1960 - 2961938
Apparatus for producing a picture
Limberger - December 1967 - 3359404
Photographing and developing apparatus
Pfaff - March 1968 - 3372617
SENSITIZED PAPER DEVELOPMENT DEVICE
Ishikawa et al. - May 1969 - 3442589
Application Number:
04/713759
Publication Date:
06/22/1971
Filing Date:
03/18/1968
View Patent Images:
Export Citation:
Assignee:
Minnesota Mining and Manufacturing Company (Saint Paul, MN)
Primary Class:
Other Classes:
396/564, 396/445, 392/419, 392/360, 355/27, 392/417, 396/661, 219/216
International Classes:
G03B17/50; G03D13/00; G03G15/22; G03B17/48; G03G15/00; G03D7/00
Field of Search:
95/89,89G,94 219/216 355/27
US Patent References:
| 3060829 | Rapid film processor | October 1962 | Leighton et al. | |
| 3144334 | Method of developing photographic materials by means of gases or vapours and to apparus for carrying the method into effect | August 1964 | Lambert | |
| 3230858 | Photographic apparatus | January 1966 | Brown et al. | |
| 3440944 | PROCESS AND APPARATUS FOR THE DEVELOPMENT OF PHOTOCOPYING MATERIAL | April 1969 | Endermann et al. |
Primary Examiner:
Matthews, Samuel S.
Assistant Examiner:
Braun, Fred L.
Claims:
What I claim is
1. A method of directly converting modulated energy input to visible output comprising the steps of:
2. The method of claim 1 comprising the step of continuing the smooth continuous advancement of said strip material past a viewing station disposed along said path beyond the trailing edge of said porous surface to permit viewing of the visible image.
3. The method according to claim 1 comprising the steps of continuously drawing said energy-sensitive heat-developable strip material from a supply and smoothly and continuously winding the developed image-bearing strip material under tension to draw the strip material smoothly continuously past said energy input station and said porous surface.
4. An apparatus for the rapid production of visible graphic information from modulated energy input to an energy-sensitive heat-developable strip material comprising
5. An apparatus according to claim 4 wherein said porous metal strip has a semicylindrical outer surface of constant radius positioned along said path and has a predetermined length.
6. The apparatus according to claim 4 wherein said means for moving said gas includes blower means for moving gas at a rate of about 150 cu. ft./min,/sq. ft. of surface of said porous metal strip along said path to aerodynamically support said strip material.
7. The apparatus according to claim 4 comprising means for supporting a supply of a said strip material, means for advancing a said strip material from said supply at a continuous rate in advance of said energy input means, and
8. The apparatus according to claim 7 wherein image viewing means is disposed along said path adjacent the end of said porous metal strip between the said porous metal strip and said strip material takeup means for viewing the developed image imparted to a said strip material.
9. An apparatus according to claim 4 wherein said means for heating a said strip material comprises
10. An apparatus according to claim 9 wherein said second porous metal strip and said first-mentioned porous metal strip have arcuate outer surfaces of constant radius disposed along said path, said strips each having a leading and trailing edge along said path of movement, and wherein said trailing edge of said second porous metal strip and the leading edge of said first-mentioned porous metal strip are disposed in spaced relation sufficient to position said energy input means therebetween.
11. An apparatus according to claim 10 wherein said energy input means is disposed on a said path opposite said arcuate surfaces of said porous metal strips.
1. A method of directly converting modulated energy input to visible output comprising the steps of:
2. The method of claim 1 comprising the step of continuing the smooth continuous advancement of said strip material past a viewing station disposed along said path beyond the trailing edge of said porous surface to permit viewing of the visible image.
3. The method according to claim 1 comprising the steps of continuously drawing said energy-sensitive heat-developable strip material from a supply and smoothly and continuously winding the developed image-bearing strip material under tension to draw the strip material smoothly continuously past said energy input station and said porous surface.
4. An apparatus for the rapid production of visible graphic information from modulated energy input to an energy-sensitive heat-developable strip material comprising
5. An apparatus according to claim 4 wherein said porous metal strip has a semicylindrical outer surface of constant radius positioned along said path and has a predetermined length.
6. The apparatus according to claim 4 wherein said means for moving said gas includes blower means for moving gas at a rate of about 150 cu. ft./min,/sq. ft. of surface of said porous metal strip along said path to aerodynamically support said strip material.
7. The apparatus according to claim 4 comprising means for supporting a supply of a said strip material, means for advancing a said strip material from said supply at a continuous rate in advance of said energy input means, and
8. The apparatus according to claim 7 wherein image viewing means is disposed along said path adjacent the end of said porous metal strip between the said porous metal strip and said strip material takeup means for viewing the developed image imparted to a said strip material.
9. An apparatus according to claim 4 wherein said means for heating a said strip material comprises
10. An apparatus according to claim 9 wherein said second porous metal strip and said first-mentioned porous metal strip have arcuate outer surfaces of constant radius disposed along said path, said strips each having a leading and trailing edge along said path of movement, and wherein said trailing edge of said second porous metal strip and the leading edge of said first-mentioned porous metal strip are disposed in spaced relation sufficient to position said energy input means therebetween.
11. An apparatus according to claim 10 wherein said energy input means is disposed on a said path opposite said arcuate surfaces of said porous metal strips.
Description:
BACKGROUND OF THE INVENTION
This invention relates to an apparatus and method for rapidly obtaining a visible image on an energy-sensitive heat-developable strip material and in one aspect relates to an apparatus and method for the rapid access of visible graphic information from a source of picture signal, digital or analog information.
Prior known devices have been built to obtain and preserve in visible graphic form, information generated by various types of energy in the least possible amount of time. Known examples of such devices are disclosed in U.S. Letters Pat. Nos. 2,446,668; 2,961,938; 3,115,079; and 3,319,549. In the first three mentioned patents the devices disclosed require a considerable amount of time to effect the exposure, chemical development and advancement of the strip material between the stations to permit the first viewing of the information. The last-mentioned patent discloses a device where exposure, development and projection take place at one station, however, with this device a heated developing liquid and/or vapor combination is disposed in the path of the exposing and projecting light and the need for and use of special liquids or vapors, besides restricting image quality, is an expensive nuisance. In another embodiment a heated transparent block is utilized for development which practically cannot achieve uniform development of heat developed materials. These devices have attempted to solve the problem but where time is of the essence it is of course important to eliminate seconds or fractions thereof between exposure and readout. Examples of situations where this is important include aircraft aerial reconnaissance, radar photography and information transmission. In each instance it is important to obtain the visible information in permanent form as rapidly as possible.
The present invention provides an apparatus and method for reducing the time presently required to produce in visible permanent form information received as picture signal, digital or analog signal information.
The present invention has the advantage of minimizing the time necessary to expose and produce a visible image on a strip material with a small easily operated and position-insensitive device.
The present invention also has the advantage of reduced cost, for the apparatus, reduced setup time, and reduction of inventory materials necessary to operate the apparatus.
The method of the present invention comprises the exposure of a strip material having an energy-sensitive heat-developable layer on a suitable backing while smoothly continuously advancing the strip material past an energy output station, continuing the advancement past a contiguous porous surface from which heated gas is continuously emitted against said strip material at a rate and temperature and for a distance just sufficient to cause development of a visible image, and a viewing station including means for illuminating or projecting said visible image. The preheating of the strip material prior to exposure further improves this method and with some radiation-sensitive materials exposure speed rating is increased by preheating.
DESCRIPTION OF THE DRAWING
The method may be carried out in a manner to be described in conjunction with the appended schematic drawing which illustrates in elevation and partly in section a presently preferred embodiment of an apparatus made in accordance with the present invention.
DESCRIPTION OF THE INVENTION
In using apparatus shown, which would be enclosed within suitable frames or housings (not shown) a strip 10 of energy-sensitive heat-developable strip material is advanced from a supply reel 11 by a spring biased pressure roller 12 and motor 13 driven capstan 14 at a smoothly continuous rate along a path past an exposing and developing unit, generally designated 16, and a viewing station 17 to a takeup reel 18. The takeup reel 18 is suitably driven by a motor 19 to maintain a constant tension on the strip 10 between the takeup reel and the capstan 14.
The exposing and developing unit 16 comprises a first strip preheating member 21, an exposure station 22, and a second strip heating and developing member 23. The first strip heating member comprising an air chamber 24 formed by top wall 26, a sidewall 27, spaced parallel end walls, and an arcuate porous metal wall 28 having an arcuate outer surface disposed along the path of the strip and representing one-fourth of a fine porous bronze hollow cylinder; a heating element 29 disposed within the chamber adjacent to the inner surface of wall 28; and an inlet 31 for introduction into the chamber of a gas under a given pressure. The first strip heating member serves to preheat the strip to a first temperature below the developing temperature of the strip. The gas introduced into the chamber may be air pumped from a blower 32 through a conduit 33 at a rate and pressure to aerodynamically support the strip on the surface of wall 28. The heating element 29 may comprise a ceramic supporting rod around which is wound a coil of resistance wire to dissipate electrical energy sufficient to warm the air to the desired temperature. The temperature of the heated air may be measured by a thermocouple embedded in the wall 28. The gas pumped into the chamber will pass over the heating element and through wall 28 to aerodynamically support the strip in close spaced proximity to the surface to provide a very uniform and high heat exchange rate between the wall and the strip.
The exposure station 22 can be positioned on either side of the path of the strip at or contiguous to the trailing edge of the arcuate wall 28 and comprises means for generating and directing radiant energy at the surface of the now heated strip 10 to record information on the strip in the form of a latent image. This source of energy to expose the strip and impart thereto a latent image of graphic information may be a high light output projector, a modulated transversely scanning laser beam, or an optically focused light image produced on the face of a cathode-ray tube. The operation of the energy source is regulated to produce precise exposure of the energy-senstive strip, e.g., the laser would receive picture signals and the beam placement is controlled by oscillating mirrors or other means controlled by synchronizing signals, and blanking signals to impart the latent image on the moving strip.
The second strip heating member 23 is disposed along the path of the advancing strip contiguous to the exposure station and is constructed similar to the heating member 21, in that it comprises a chamber 34 formed by a top wall, sidewall, spaced parallel end walls and an arcuate porous wall 38, a heating element 39 and a gas inlet 41. In this member 23 the heating element is supplied with sufficient electrical energy to heat the gas passing through the porous walls to or above the developing temperature of the strip and the wall has a length proportioned to the rate of advancement of the strip such that the strip is quickly brought to development temperature and held at that temperature to cause development of a visible image.
Continued advancement of the strip 10 moves the strip with the developed image past the viewing station 17. The viewing station 17 may illuminate the strip for viewing or produce and project a light image of the visible image by either light transmitted through the strip, if translucent, or by projecting an illuminated image if the strip is opaque. The illustrated viewing station 17 is in the form of a projector for use with translucent or transparent film and comprises an enclosed light source 42 and a condensing lens 43 on one side of the strip path and a projection lens assembly 44 on the opposite side to project the light image onto a viewing screen 45.
A type of radiation-sensitive thermally developable strip useful in practicing the present invention has a sensitive coating comprising a combination of photosensitive silver halide and light-stable organic silver salt in conjunction with a reducing agent, made generally in accordance with the disclosure in U.S. application Ser. No. 693,714, now U.S. Pat. No. 3,457,075. The sensitive coating is soft and subject to abrasion. Thermal development to a uniform end point requires careful control of the rate of heating, temperature and time at the developing temperature.
In an illustrative example, a strip as above described of 35-millimeter width having a transparent backing is drawn from a supply thereof wound on a reel. The strip heating members 21 and 23 have fine porous bronze walls 28 and 38, each representing one-fourth of a cylinder cut axially and diametrically, giving each wall an arcuate outer configuration of continuous radius and an area of about 51/4 square inches. The trailing edge of wall 28 is spaced from the leading edge of wall 38. Air is forced from the blower 32 into the chambers 24 and 34 at a pressure of about 5 p.s.i. guage and a flow rate through the walls 28 and 38 is between 3 and 5 cubic feet per minute (resulting in about 150 cu. ft./min./sq. ft.). The wall 28 is heated to below 240° F. and wall 38 is heated between 320° F. and 370° F., and maintained preferably at 340° F. The strip material is advanced by the capstan 14 at 1 inch per second and the strip is exposed at the exposure station 22 with light having an intensity of 1,000 to 10,000 foot candles to impart a latent image onto the heated strip. The strip reaches development temperature and is held at that temperature for approximately 1 second during advancement across the wall 38 to develop the visible image. The heating member 23 operates at a rate to rapidly heat the strip to developing temperature and its length is sufficient to maintain the moving strips at its developing temperature to complete development.
In some instances it is desirable to cool the strip immediately after the strip moves out of the developer member to prevent further or uneven development. Methods of cooling the strip include moving cool air through a porous metal plate past which the strip is advanced, directing cool air through jets at the strip or moving the strip about a cooled metal roller.
The strip material, generally of the type disclosed in U.S. application Ser. No. 693,714 can be treated to a temperature close to the development temperature for short periods without affecting the quality of the resulting image. The strip after exposure, as above-mentioned, must then be heated to a temperature at which development will occur and must be held at this temperature for a predetermined length of time. To obtain the developed image as rapidly as possible it is important to bring the strip to development temperature as rapidly as possible. Development time is thus shortened when the strip is preheated so the time required to obtain development temperature is decreased. Also a very efficient heating device is important. These results are obtained by the present invention. The results obtained by the apparatus of the present invention can also be described by the following relation: h(T p -T f )=cρtdT f /dθ
where:
h is a unit area heat transfer coefficient, in
Engineering Units, B.t.u./hr. sq. ft. °F.
T p is the processor temperature, °F.
T f is the strip temperature, °F.
c is the strip heat capacitance, B.t.u./1b. °F.
t is the strip thickness, ft.
ρis the strip mass density, 1bs./cu. ft.
dT f /dθ is the time rate of strip temperature change.
This equation represents the balance between the heat energy in the strip and the heat energy added by convective heating, neglecting heat generation within the strip, and thus applies universally to all strips which are at uniform temperature across the thickness and which are being heated by a uniform temperature processor. When the physical properties, ρ and c, of the web do not change appreciably with temperature and when the physical method of heating can be represented by a unit area heat transfer coefficient, h, which is constant over the film surface area and constant with temperature, the above equation can be rearranged and integrated to yield:
Where T fo is the strip temperature at the entrance to the processor, θ=0. This equation describes the decrease of the initial difference in temperature between the strip and processor as the strip passes through the processor.
The value of the ratio on the left side of the equation varies from 1.00 to zero as shown in the graph on the following page. As an example of the application of this analysis to the design of heat exchangers used to process heat developable strip material the following values for the thickness, density and heat capacitance are selected corresponding to a polyester-backed film.
t=0.0035 inches
ρ=86.4 1bs./cu. ft.
c=0.36 B.t.u./1b. °F.
The effect of the variation in the heat transfer coefficient h is displayed in the various curves on the graph below. Heat transfer coefficients on the order of 10 can be obtained by blowing heated air along the surface of the film. Values in the range of 50 can be obtained by heating one side of the film with air forced through an array of slots or circular jets. If both sides are heated with slots or circular jets. a value of 100 can be obtained.
A value of 100 or more is also obtained by forcing air through porous metal surfaces at one surface of the strip at a rate of airflow sufficient to provide an aerodynamic support for the film and permitting conduction heat transfer, e.g., 3--5 cu. ft./min./sq. ft. If a gas having a thermal conductivity higher than air is forced through porous surfaces at this low rate, e.g., helium, heat transfer coefficients on the order of 1000 can be obtained. In the practice of the ##SPC1## present invention, heat transfer coefficients on the order of 1000 are predicted when the air is forced at a high rate per sq. ft. of area through the porous metal plate to cause direct heat transfer from the hot gas to the film without having a significant temperature reduction in the gas doing the heating as it strikes the film, i.e., convective heat transfer.
As previously stated, when a specific rate of film advancement is chosen, the length of the preheating member and processor to heat the film to a desired temperature can be determined to obtain the desired temperature. The length of the processor to maintain the strip at the development temperature for the set time interval while the development reaction is taking place is determined by the speed of the film.
As another example, if the two heating members are combined into one element having a temperature of about 340° F. the exposure can take place after the film begins to move past the heating member, but it must occur before the film reaches a temperature at which development begins. Thus, using as an example a development temperature of 340° F. and a film which enters at 75° F., and which film may be heated as high as 240° F. during exposure without affecting the image quality, the value of the temperature ratio using the integrated formula above at this point is:
(340-240)/(340-75)=0.377
Placing this value on the graph shows how much exposure time can be allowed for various methods of heating the film. For example, if the processor is capable of heat transfer coefficients on the order of 1000, less than 0.03 second can be allowed for exposure within the heating member, or with the film moving at 1 inch per second the exposure station may be positioned along the first 300ths inch of the developing or heating member. For a heating member with a heat transfer coefficient of 100 the film may be exposed for 0.3 second without affecting finished image quality.
It can therefore be seen that by heating the strip prior to exposure (which with some materials, made generally in accordance with the disclosure in application Ser. No. 693,714, increases the exposure speed of the strip) and using the heat exchanger design as described herein, very rapid access of uniformly developed visible information can be obtained.
The processor and preheating unit of the present invention permit the coated-sensitive surface of the strip material to be disposed adjacent the external surfaces of the walls 28 and 38 because of the gas support which maintains the coating spaced from the surfaces. Since this coating is the portion of the strip material 10 which must receive the heat treatment to produce the development the amount of heat required to afford development is not as high as that required to bring the entire mass of the strip material to the required temperature. Thus, development time can be reduced also by positioning the strip material in this manner. The position of the energy input station relative to the path of the strip material would then be determined by the type of backing used with the strip material.
This invention relates to an apparatus and method for rapidly obtaining a visible image on an energy-sensitive heat-developable strip material and in one aspect relates to an apparatus and method for the rapid access of visible graphic information from a source of picture signal, digital or analog information.
Prior known devices have been built to obtain and preserve in visible graphic form, information generated by various types of energy in the least possible amount of time. Known examples of such devices are disclosed in U.S. Letters Pat. Nos. 2,446,668; 2,961,938; 3,115,079; and 3,319,549. In the first three mentioned patents the devices disclosed require a considerable amount of time to effect the exposure, chemical development and advancement of the strip material between the stations to permit the first viewing of the information. The last-mentioned patent discloses a device where exposure, development and projection take place at one station, however, with this device a heated developing liquid and/or vapor combination is disposed in the path of the exposing and projecting light and the need for and use of special liquids or vapors, besides restricting image quality, is an expensive nuisance. In another embodiment a heated transparent block is utilized for development which practically cannot achieve uniform development of heat developed materials. These devices have attempted to solve the problem but where time is of the essence it is of course important to eliminate seconds or fractions thereof between exposure and readout. Examples of situations where this is important include aircraft aerial reconnaissance, radar photography and information transmission. In each instance it is important to obtain the visible information in permanent form as rapidly as possible.
The present invention provides an apparatus and method for reducing the time presently required to produce in visible permanent form information received as picture signal, digital or analog signal information.
The present invention has the advantage of minimizing the time necessary to expose and produce a visible image on a strip material with a small easily operated and position-insensitive device.
The present invention also has the advantage of reduced cost, for the apparatus, reduced setup time, and reduction of inventory materials necessary to operate the apparatus.
The method of the present invention comprises the exposure of a strip material having an energy-sensitive heat-developable layer on a suitable backing while smoothly continuously advancing the strip material past an energy output station, continuing the advancement past a contiguous porous surface from which heated gas is continuously emitted against said strip material at a rate and temperature and for a distance just sufficient to cause development of a visible image, and a viewing station including means for illuminating or projecting said visible image. The preheating of the strip material prior to exposure further improves this method and with some radiation-sensitive materials exposure speed rating is increased by preheating.
DESCRIPTION OF THE DRAWING
The method may be carried out in a manner to be described in conjunction with the appended schematic drawing which illustrates in elevation and partly in section a presently preferred embodiment of an apparatus made in accordance with the present invention.
DESCRIPTION OF THE INVENTION
In using apparatus shown, which would be enclosed within suitable frames or housings (not shown) a strip 10 of energy-sensitive heat-developable strip material is advanced from a supply reel 11 by a spring biased pressure roller 12 and motor 13 driven capstan 14 at a smoothly continuous rate along a path past an exposing and developing unit, generally designated 16, and a viewing station 17 to a takeup reel 18. The takeup reel 18 is suitably driven by a motor 19 to maintain a constant tension on the strip 10 between the takeup reel and the capstan 14.
The exposing and developing unit 16 comprises a first strip preheating member 21, an exposure station 22, and a second strip heating and developing member 23. The first strip heating member comprising an air chamber 24 formed by top wall 26, a sidewall 27, spaced parallel end walls, and an arcuate porous metal wall 28 having an arcuate outer surface disposed along the path of the strip and representing one-fourth of a fine porous bronze hollow cylinder; a heating element 29 disposed within the chamber adjacent to the inner surface of wall 28; and an inlet 31 for introduction into the chamber of a gas under a given pressure. The first strip heating member serves to preheat the strip to a first temperature below the developing temperature of the strip. The gas introduced into the chamber may be air pumped from a blower 32 through a conduit 33 at a rate and pressure to aerodynamically support the strip on the surface of wall 28. The heating element 29 may comprise a ceramic supporting rod around which is wound a coil of resistance wire to dissipate electrical energy sufficient to warm the air to the desired temperature. The temperature of the heated air may be measured by a thermocouple embedded in the wall 28. The gas pumped into the chamber will pass over the heating element and through wall 28 to aerodynamically support the strip in close spaced proximity to the surface to provide a very uniform and high heat exchange rate between the wall and the strip.
The exposure station 22 can be positioned on either side of the path of the strip at or contiguous to the trailing edge of the arcuate wall 28 and comprises means for generating and directing radiant energy at the surface of the now heated strip 10 to record information on the strip in the form of a latent image. This source of energy to expose the strip and impart thereto a latent image of graphic information may be a high light output projector, a modulated transversely scanning laser beam, or an optically focused light image produced on the face of a cathode-ray tube. The operation of the energy source is regulated to produce precise exposure of the energy-senstive strip, e.g., the laser would receive picture signals and the beam placement is controlled by oscillating mirrors or other means controlled by synchronizing signals, and blanking signals to impart the latent image on the moving strip.
The second strip heating member 23 is disposed along the path of the advancing strip contiguous to the exposure station and is constructed similar to the heating member 21, in that it comprises a chamber 34 formed by a top wall, sidewall, spaced parallel end walls and an arcuate porous wall 38, a heating element 39 and a gas inlet 41. In this member 23 the heating element is supplied with sufficient electrical energy to heat the gas passing through the porous walls to or above the developing temperature of the strip and the wall has a length proportioned to the rate of advancement of the strip such that the strip is quickly brought to development temperature and held at that temperature to cause development of a visible image.
Continued advancement of the strip 10 moves the strip with the developed image past the viewing station 17. The viewing station 17 may illuminate the strip for viewing or produce and project a light image of the visible image by either light transmitted through the strip, if translucent, or by projecting an illuminated image if the strip is opaque. The illustrated viewing station 17 is in the form of a projector for use with translucent or transparent film and comprises an enclosed light source 42 and a condensing lens 43 on one side of the strip path and a projection lens assembly 44 on the opposite side to project the light image onto a viewing screen 45.
A type of radiation-sensitive thermally developable strip useful in practicing the present invention has a sensitive coating comprising a combination of photosensitive silver halide and light-stable organic silver salt in conjunction with a reducing agent, made generally in accordance with the disclosure in U.S. application Ser. No. 693,714, now U.S. Pat. No. 3,457,075. The sensitive coating is soft and subject to abrasion. Thermal development to a uniform end point requires careful control of the rate of heating, temperature and time at the developing temperature.
In an illustrative example, a strip as above described of 35-millimeter width having a transparent backing is drawn from a supply thereof wound on a reel. The strip heating members 21 and 23 have fine porous bronze walls 28 and 38, each representing one-fourth of a cylinder cut axially and diametrically, giving each wall an arcuate outer configuration of continuous radius and an area of about 51/4 square inches. The trailing edge of wall 28 is spaced from the leading edge of wall 38. Air is forced from the blower 32 into the chambers 24 and 34 at a pressure of about 5 p.s.i. guage and a flow rate through the walls 28 and 38 is between 3 and 5 cubic feet per minute (resulting in about 150 cu. ft./min./sq. ft.). The wall 28 is heated to below 240° F. and wall 38 is heated between 320° F. and 370° F., and maintained preferably at 340° F. The strip material is advanced by the capstan 14 at 1 inch per second and the strip is exposed at the exposure station 22 with light having an intensity of 1,000 to 10,000 foot candles to impart a latent image onto the heated strip. The strip reaches development temperature and is held at that temperature for approximately 1 second during advancement across the wall 38 to develop the visible image. The heating member 23 operates at a rate to rapidly heat the strip to developing temperature and its length is sufficient to maintain the moving strips at its developing temperature to complete development.
In some instances it is desirable to cool the strip immediately after the strip moves out of the developer member to prevent further or uneven development. Methods of cooling the strip include moving cool air through a porous metal plate past which the strip is advanced, directing cool air through jets at the strip or moving the strip about a cooled metal roller.
The strip material, generally of the type disclosed in U.S. application Ser. No. 693,714 can be treated to a temperature close to the development temperature for short periods without affecting the quality of the resulting image. The strip after exposure, as above-mentioned, must then be heated to a temperature at which development will occur and must be held at this temperature for a predetermined length of time. To obtain the developed image as rapidly as possible it is important to bring the strip to development temperature as rapidly as possible. Development time is thus shortened when the strip is preheated so the time required to obtain development temperature is decreased. Also a very efficient heating device is important. These results are obtained by the present invention. The results obtained by the apparatus of the present invention can also be described by the following relation: h(T p -T f )=cρtdT f /dθ
where:
h is a unit area heat transfer coefficient, in
Engineering Units, B.t.u./hr. sq. ft. °F.
T p is the processor temperature, °F.
T f is the strip temperature, °F.
c is the strip heat capacitance, B.t.u./1b. °F.
t is the strip thickness, ft.
ρis the strip mass density, 1bs./cu. ft.
dT f /dθ is the time rate of strip temperature change.
This equation represents the balance between the heat energy in the strip and the heat energy added by convective heating, neglecting heat generation within the strip, and thus applies universally to all strips which are at uniform temperature across the thickness and which are being heated by a uniform temperature processor. When the physical properties, ρ and c, of the web do not change appreciably with temperature and when the physical method of heating can be represented by a unit area heat transfer coefficient, h, which is constant over the film surface area and constant with temperature, the above equation can be rearranged and integrated to yield:
Where T fo is the strip temperature at the entrance to the processor, θ=0. This equation describes the decrease of the initial difference in temperature between the strip and processor as the strip passes through the processor.
The value of the ratio on the left side of the equation varies from 1.00 to zero as shown in the graph on the following page. As an example of the application of this analysis to the design of heat exchangers used to process heat developable strip material the following values for the thickness, density and heat capacitance are selected corresponding to a polyester-backed film.
t=0.0035 inches
ρ=86.4 1bs./cu. ft.
c=0.36 B.t.u./1b. °F.
The effect of the variation in the heat transfer coefficient h is displayed in the various curves on the graph below. Heat transfer coefficients on the order of 10 can be obtained by blowing heated air along the surface of the film. Values in the range of 50 can be obtained by heating one side of the film with air forced through an array of slots or circular jets. If both sides are heated with slots or circular jets. a value of 100 can be obtained.
A value of 100 or more is also obtained by forcing air through porous metal surfaces at one surface of the strip at a rate of airflow sufficient to provide an aerodynamic support for the film and permitting conduction heat transfer, e.g., 3--5 cu. ft./min./sq. ft. If a gas having a thermal conductivity higher than air is forced through porous surfaces at this low rate, e.g., helium, heat transfer coefficients on the order of 1000 can be obtained. In the practice of the ##SPC1## present invention, heat transfer coefficients on the order of 1000 are predicted when the air is forced at a high rate per sq. ft. of area through the porous metal plate to cause direct heat transfer from the hot gas to the film without having a significant temperature reduction in the gas doing the heating as it strikes the film, i.e., convective heat transfer.
As previously stated, when a specific rate of film advancement is chosen, the length of the preheating member and processor to heat the film to a desired temperature can be determined to obtain the desired temperature. The length of the processor to maintain the strip at the development temperature for the set time interval while the development reaction is taking place is determined by the speed of the film.
As another example, if the two heating members are combined into one element having a temperature of about 340° F. the exposure can take place after the film begins to move past the heating member, but it must occur before the film reaches a temperature at which development begins. Thus, using as an example a development temperature of 340° F. and a film which enters at 75° F., and which film may be heated as high as 240° F. during exposure without affecting the image quality, the value of the temperature ratio using the integrated formula above at this point is:
(340-240)/(340-75)=0.377
Placing this value on the graph shows how much exposure time can be allowed for various methods of heating the film. For example, if the processor is capable of heat transfer coefficients on the order of 1000, less than 0.03 second can be allowed for exposure within the heating member, or with the film moving at 1 inch per second the exposure station may be positioned along the first 300ths inch of the developing or heating member. For a heating member with a heat transfer coefficient of 100 the film may be exposed for 0.3 second without affecting finished image quality.
It can therefore be seen that by heating the strip prior to exposure (which with some materials, made generally in accordance with the disclosure in application Ser. No. 693,714, increases the exposure speed of the strip) and using the heat exchanger design as described herein, very rapid access of uniformly developed visible information can be obtained.
The processor and preheating unit of the present invention permit the coated-sensitive surface of the strip material to be disposed adjacent the external surfaces of the walls 28 and 38 because of the gas support which maintains the coating spaced from the surfaces. Since this coating is the portion of the strip material 10 which must receive the heat treatment to produce the development the amount of heat required to afford development is not as high as that required to bring the entire mass of the strip material to the required temperature. Thus, development time can be reduced also by positioning the strip material in this manner. The position of the energy input station relative to the path of the strip material would then be determined by the type of backing used with the strip material.