Title: Apparatus and method for thermally processing an imaging material employing a preheat chamber
Abstract: A preheat chamber for conditioning an imaging material having a conditioning threshold temperature and a developing threshold temperature. The preheat chamber includes a chamber housing and a heating system. The heating system is configured to heat imaging material to a desired conditioning temperature above the conditioning threshold temperature and below the developing threshold temperature as the imaging material is moved through the chamber housing.
Patent Number: 6,979,802 Issued on 12/27/2005 to Struble, et al.
| Inventors:
|
Struble; Kent R. (Woodbury, MN);
Preszler; Duane A. (River Falls, WI)
|
| Assignee:
|
Eastman Kodak Company (Rochester, NY)
|
| Appl. No.:
|
815027 |
| Filed:
|
March 31, 2004 |
| Current U.S. Class: |
219/388; 399/328; 432/60 |
| Intern'l Class: |
F27D 011/00 |
| Field of Search: |
219/216,469-471
399/328-332,335-338
432/60,228
118/60
|
References Cited [Referenced By]
U.S. Patent Documents
Primary Examiner: Campbell; Thor S.
Attorney, Agent or Firm: Parulski; Susan L.
Claims
1. A preheat chamber for conditioning an exposed imaging material having a conditioning
threshold temperature and a development temperature higher than said conditioning
threshold temperature, the preheat chamber comprising:
a chamber housing having an entrance and an exit;
a transport system for moving exposed imaging material through said chamber housing
between said entrance and said exit;
a heating system configured to heat the exposed imaging material to a desired
conditioning temperature above the conditioning threshold temperature and below
the development temperature as the imaging material is moved through the chamber housing;
wherein the imaging material includes an aqueous-based emulsion of heat sensitive
materials in an aqueous-based solvent, wherein the desired conditioning temperature
causes moisture to be released from the aqueous-based emulsion and wherein the
preheat chamber maintains the imaging material at the desired conditioning temperature
for a required time period to cause substantially all moisture to be released from
the aqueous-based emulsion before it is developed; and
an evacuation system for removing from said chamber housing substantially all
water vapor and other byproducts released from the aqueous based emulsion.
2. The preheat chamber of claim 1, wherein the desired conditioning temperature
is within a conditioning temperature range.
3. The preheat chamber of claim 2, wherein the desired conditioning temperature
ranges from 110 degrees centigrade to 130 degrees centigrade.
4. The preheat chamber of claim 2, wherein an upper temperature level of the
temperature range at a margin below the development temperature to ensure that
development does not occur, and a lower temperature level at a margin above the
conditioning threshold temperature.
5. The preheat chamber of claim 1, wherein the desired conditioning temperature
is substantially equal to 110 degrees centigrade.
6. The preheat chamber of claim 1, wherein said transport system is configured
to move the imaging material through the chamber housing along a transport path
proximate to the heating system.
7. The preheat chamber of claim 6, wherein the transport system receives the
imaging material at an ambient temperature at the entrance and, after moving the
imaging material through the preheat chamber along the transport path, provides
the imaging material at the exit substantially at the conditioning temperature
and with substantially all of the moisture released from the emulsion.
8. The preheat chamber of claim 7, wherein the transport system moves the imaging
material through the preheat chamber at a rate such that the imaging material is
maintained at the desired conditioning temperature for the required time period.
9. The preheat chamber of claim 1, wherein the imaging material is coated on
a first and a second major surface with the emulsion, and wherein the heating system
is configured to heat the first and second major surfaces to a temperature substantially
equal to the desired conditioning temperature.
10. The preheat chamber of claim of claim 9, wherein the heating system includes
a plurality of zones, wherein a temperature of each zone is individually controllable.
11. A thermal processor for thermally developing an image in an imaging material
having a conditioning threshold temperature and a developing threshold temperature
higher than said conditioning threshold temperature, the thermal processor comprising:
a preheat chamber configured to receive the imaging material at an ambient temperature
and to heat the imaging material to a desired conditioning temperature at least
equal to the conditioning threshold temperature but less than the development threshold
temperature; and
a dwell chamber thermally isolated from said preheat chamber configured to receive
the imaging material at the conditioning temperature and to heat the imaging material
to a desired developing temperature at least equal to the developing threshold temperature.
12. The thermal processor of claim 11, wherein an incremental difference between
the desired conditioning temperature and the desired developing temperature does
not exceed a predetermined amount.
13. The thermal processor claim 12, wherein the predetermined amount is 40 degrees centigrade.
14. The thermal processor of claim 11, wherein the dwell chamber is configured
to maintain the imaging material at the desired developing temperature for a time
period resulting in substantially optimal development of the image.
15. The thermal processor of claim 11, wherein the dwell chamber is thermally
isolated from the preheat chamber.
16. The thermal processor of claim 11, wherein the preheat chamber further comprises:
a heating system configured to heat the imaging material to the desired conditioning
temperature; and
a transport system configured to move the imaging material through the preheat chamber.
17. The thermal processor of claim 16, wherein the dwell chamber further comprises:
a heating system configured to heat the imaging material from the desired conditioning
temperature to the desired developing temperature; and
a transport system configured to move the imaging material through the preheat chamber.
18. The thermal processor of claim 17, wherein the imaging material is coated
with an aqueous-based emulsion having a moisture level, wherein preheat chamber
heating system heats said imaging material to a temperature at least equal to the
conditioning threshold temperature causes moisture to be released from the emulsion,
and wherein said dwell chamber heating system heats said imaging material to a
temperature at least equal to the development threshold temperature causes the
image to develop.
19. The thermal processor of claim 18, wherein the preheat chamber is configured
to maintain the imaging material at the conditioning temperature for a time period
necessary to cause substantially all of the moisture to be released from the emulsion
and including an evacuation system for removing substantially all of the released
moisture vapor from said preheat chamber.
20. The thermal processor of claim 19, wherein the preheat chamber transport
system moves the imaging material through the preheat chamber at a rate such that
imaging material is maintained at the desired conditioning temperature for the
time period necessary to cause substantially all of the moisture to be released
from the emulsion.
21. The thermal processor of claim 20, wherein the dwell chamber transport system
moves that imaging material through the dwell chamber at a rate substantially equal
to the rate at which the preheat chamber transport system moves the imaging material
through the preheat chamber.
22. A preheat chamber for preconditioning a thermally processable exposed imaging
material for development, the exposed imaging material having a first and a second
major surface and coated on at least one of the major surfaces with a moisture-sensitive
aqueous-based emulsion, the preheat chamber comprising:
a heating system configured to heat the thermally processable exposed imaging
material to a desired temperature within a temperature range high enough to cause
substantially all moisture to be released from the aqueous-based emulsion but below
a development temperature of the imaging material;
an evacuation system configured to couple to an external vacuum system to remove
the released moisture from the preheat chamber; and
a transport system that moves the imaging material through the preheat chamber
along a transport path.
23. The preheat chamber of claim 22, wherein the desired temperature is within
a temperature range.
24. The preheat chamber of claim 22, wherein the desired temperature is substantially
equal to 110 degrees centigrade.
25. The preheat chamber of claim 22, wherein the heating system comprises:
a first heating member positioned along the transport path so as to be proximate
to the first major surface of the imaging material; and
a second heating member positioned along the transport path so as to be proximate
to the second major surface of the imaging material.
26. The preheat chamber of claim 25, wherein the first and second heating members
each comprise a plurality of individually controllable zones that can each be heated
to a different temperature level.
27. The preheat chamber of claim 26, wherein each zone has a corresponding sensing
device to monitor the temperature level of the zone.
28. The preheat chamber of claim 25, wherein the first and second heating members
each comprise:
a heat plate having a first major surface proximate to the imaging material and
a second major surface; and
a blanket heater bonded to the second major surface.
29. The preheat chamber of claim 28, wherein the heat plate is aluminum.
30. The preheat chamber of claim 22, wherein the conveyance system comprises:
a first plurality of rotatable members positioned along the transport path so
as to contact the first major surface of the imaging material; and
a second plurality of rotatable member positioned along the transport path so
as to contact the second major surface of the imaging material.
31. The preheat chamber of claim 30, wherein at least one of the first plurality
of rotatable members is driven in a first direction and at least one of the second
plurality of rotatable members is driven in direction opposite the first direction
such that contact with the imaging material moves the imaging material along the
transport path.
32. The preheat chamber of claim 30, wherein each of the rotatable members comprises
a roller having a cylindrical shaft covered with a support material.
33. The preheat chamber of claim 32, wherein the cylindrical shafts are aluminum.
34. The preheat chamber of claim 22, further comprising:
an enclosure encompassing the heating system and the conveyance system, wherein
the enclosure and heating system form an oven enclosing the conveyance system,
wherein the enclosure has an entrance to the oven and an exit from the oven, and
wherein the conveyance system moves the imaging material through the oven along
the transport path from the oven entrance to the oven exit.
35. The preheat chamber of claim 34, wherein the evacuation system includes at
least one exhaust port extending through the enclosure and configured to couple
to the external vacuum system such that the external vacuum system draws air from
the oven through the at least one exhaust port to thereby exhaust air and substantially
all of the released moisture from the oven via the at least one exhaust port.
36. The preheat chamber of claim 35 wherein the evacuation system further includes
an air flow path through the heating system such that the external vacuum system
draws external air through the heating system and into the oven, such that the
external air is heated to a temperature substantially equal to a temperature of
the oven before entering the oven.
37. A method of thermally processing an exposed imaging material having a conditioning
threshold temperature and a development threshold temperature higher than said
conditioning threshold temperature, the method comprising:
first heating the exposed imaging material to a conditioning temperature at least
equal to the conditioning threshold temperature but less than the development threshold
temperature; and
maintaining the imaging material at the conditioning temperature for a time period.
38. The method of claim 37, further comprising:
second heating the exposed imaging material from the conditioning temperature
to a developing temperature at least equal to the development threshold temperature
wherein said second heating is thermally isolated from said first heating; and
maintaining the imaging material at the developing temperature for a time period
to develop the image in said exposed imaging material.
39. A thermal processor for thermally developing an image in an exposed imaging
material having a conditioning temperature range and a developing temperature range
higher than said conditioning temperature range, the thermal processor comprising:
means for heating the exposed imaging material from a given ambient temperature
to a desired conditioning temperature that is at least within the conditioning
temperature range but less than a temperature within the developing temperature
range so as not to develop said image in said exposed imaging material.
40. The thermal processor of claim 39, wherein the imaging material includes
a moisture-sensitive aqueous-based emulsion including heat sensitive materials
in an aqueous-based solvent, and wherein the desired conditioning temperature range
causes moisture to be released from the emulsion, the thermal processor further comprising:
means for maintaining the imaging material at the desired conditioning temperature
for a time period necessary to cause substantially all moisture to be released
from the emulsion; and
means for evacuating said moisture from the environment around said imaging material.
41. The thermal processor of claim 40, further comprising:
means for heating the imaging material from the desired conditioning temperature
to a desired developing temperature, wherein the desired developing temperature
is within the developing temperature range.
42. The thermal processor of claim 41, further comprising:
means for maintaining the imaging material at the desired developing temperature
for a time period resulting in substantially optimal thermal development of the image.
43. A method of developing a gelatin based photothermographic imaging material comprising:
providing an exposed photothermographic imaging material including a base material
coated on each side with an aqueous based emulsion of heat sensitive materials
including developers in an aqueous based solvent;
heating said exposed photothermographic imaging material in an enclosed preheat
chamber to a temperature within a conditioning temperature range, but below a development
temperature range to release fluid, consisting primarily of water, in the form
of vapor from the emulsion for a period so that substantially all of the fluid
including water is released from the emulsion; and
evacuating said vapor from said preheat chamber.
44. The method of claim 43 including developing said exposed photothermographic
imaging material in a dwell chamber thermally isolated from said preheat chamber
at a development temperature within a development temperature range that is higher
than said conditioning temperature range for a development period that will provide
substantially optimal development of the exposed image in said imaging material.
Description
FIELD OF THE INVENTION
The present invention relates generally to an apparatus and method for processing
an imaging material, and more specifically to an apparatus and method for thermally
developing an imaging material employing a preheat chamber.
BACKGROUND OF THE INVENTION
Light sensitive photothermographic or heat sensitive film typically includes
a thin polymer or paper base coated, generally on one side, with an emulsion of
dry silver or other heat sensitive material. Such photothermographic film is normally
processed or developed at a temperature generally in the vicinity of 120 degrees
centigrade. To produce a high quality image, controlling heat transfer to the photothermographic
film during the development process is critical. If heat transfer is not uniform
during development, visual artifacts such as non-uniform density and streaking
may occur. If heat is transferred too quickly, the base of some types of photothermographic
film can expand too rapidly, resulting in expansion wrinkles that can cause visual
artifacts in a developed image.
Several processing machines have been developed in efforts to achieve optimal
heat transfer to the photothermographic film during processing. One employs a heated
drum with multiple rollers around the exterior of the drum's circumference to press
the film against the drum. This technique is typically best suited for film having
an emulsion coating on only one side, as more heat is generally transferred to
the side of the film facing the drum as compared to the side opposite the drum.
Another machine slides the photothermographic film over flat heated surfaces in
a horizontal path or over plates arranged in a circular path. Still another machine
is a flat-path processor having rollers above and below the film to transport the
film through the processor.
The processors in each of these machines heats the photothermographic film to
a processing temperature and maintains the film at the processing temperature for
a set time for optimal development. One processor includes a preheat zone that
rapidly heats the film to the development temperature to initiate the development
process, and a dwell zone that keeps the film at the development temperature for
the set time to complete development.
While such processors are effective at developing photothermographic films
prepared using polymeric binders coated from organic solvents, they are not as
well-suited for processing newly emerging gelatin-based photothermographic films.
These films are coated from aqueous-based solvents, contain heat sensitive materials
such as developers, and require a higher development temperature. The moisture
content of these aqueous-based emulsions can affect the heat transfer characteristics
of the film and, consequently, the quality of images produced during processing.
The moisture level of these emulsions is also susceptible to changes depending
on the temperature and humidity of the environment in which they are stored and
used. Consequently, the moisture level of the emulsion can vary between films.
This can result in film-to-film variations in image quality after processing.
It is evident that there is a need for a photothermographic film processor capable
of uniformly developing gelatin-based photothermographic film without introducing
visual artifacts as described above.
SUMMARY OF THE INVENTION
In one embodiment, the present invention provides a preheat chamber for conditioning
an imaging material having a conditioning threshold temperature and a developing
threshold temperature. The preheat chamber includes a chamber housing and a heating
system, the heating system is configured to heat the imaging material to a desired
conditioning temperature above the conditioning threshold temperature and below
the developing threshold temperature as the imaging material is moved through the
chamber housing.
In one embodiment, the present invention provides a thermal processor for thermally
developing an image in an imaging material having a conditioning threshold temperature
and a developing threshold temperature. The thermal processor includes a preheat
chamber and a dwell chamber. The preheat chamber is configured to receive the imaging
material at an ambient temperature and to heat the imaging material to a desired
conditioning temperature at least equal to the conditioning threshold temperature
but less than the development threshold temperature. The dwell chamber is configured
to receive the imaging material at the conditioning temperature and to heat the
imaging material to a desired developing temperature at least equal to the developing
threshold temperature.
In one embodiment, the imaging material includes an aqueous-based emulsion including
heat sensitive materials and having a moisture level, wherein a temperature level
at least equal to the conditioning threshold temperature causes moisture to be
released from the aqueous-based emulsion, and a temperature level at least equal
to the development temperature causes the image to develop. In one embodiment,
the preheat chamber is configured to maintain the imaging material at the conditioning
temperature for a time period necessary to cause substantially all of the moisture
to be released from the emulsion.
By removing substantially all of the moisture from the aqueous-based emulsion
of the imaging material prior to development, the present invention minimizes the
potential of post-development visual artifacts due to excessive moisture levels
and minimizes the potential for variations in image quality from film-to-film.
Also, heating the imaging material to a desired conditioning temperature prior
to heating the imaging material to a desired developing temperature reduces the
potential of visual artifacts related to expansion of a base material of the imaging material.
BRIEF DESCRIPTION OF THE DRAWINGS
Embodiments of the invention are better understood with reference to
the following drawings. The elements of the drawings are not necessarily to scale
relative to each other. Like reference numerals designate corresponding similar parts.
FIG. 1 is a block diagram illustrating one exemplary embodiment of a thermal
processor according to the present invention.
FIG. 2 is a block diagram illustrating one exemplary embodiment of a thermal
processor according to the present invention.
FIG. 3 is a graph illustrating temperature and moisture levels of a suitable
gelatin-based photothermographic film during processing by the thermal processor
of FIG. 2.
DETAILED DESCRIPTION OF THE INVENTION
The invention has been described in detail with particular reference to certain
preferred embodiments thereof, but it will be understood that variations and modifications
can be effected within the spirit and scope of the invention.
FIG. 1 is a block diagram illustrating generally one embodiment of a thermal
processor
30 in accordance with the present invention for developing an
image in an imaging material
32 having a conditioning threshold temperature
and a development threshold temperature.
An example of a thermally processable imaging material suitable for development
by thermal processor
30 is the gelatin- or aqueous-based photothermographic
imaging film disclosed in pending U.S. patent application Ser. No. 10/715,199,
filed on Nov. 17, 2003, commonly assigned, and incorporated herein by reference.
One type of gelatin-based photothermographic imaging material suitable for development
by thermal processor
30 comprises a base material coated on each side with
an aqueous-based emulsion of heat sensitive materials, including developers, in
an aqueous-based solvent. When heated to a temperature at or above a conditioning
threshold temperature, fluid, consisting primarily of water, is released in vaporous
form from the emulsion, leaving the heat sensitive materials on the imaging material.
When subsequently heated to a temperature at or above a development threshold temperature,
the heat sensitive materials react to form an image on the imaging material.
Thermal processor
30 includes a preheat chamber
34 and a dwell
chamber
36 that is thermally isolated from preheat chamber
34. Preheat
chamber
34 includes a housing
38, having an entrance
40 and
an exit
42, enclosing a transport system
44 and a heating system
46. Dwell chamber
36 includes a housing
48, having an entrance
50 and an exit
52, enclosing a transport system
54 and a heating
system
56.
Preheat chamber
34 receives imaging material
32 at an ambient
temperature and with the emulsion having an arbitrary moisture level at entrance
40. Transport system
44 moves imaging material
32 through
preheat chamber
34 along a transport path
58 from entrance
40
to exit
42. As imaging material
32 moves through preheat chamber
34, heating system
46 heats imaging material
32 to a desired
conditioning temperature at least equal to the imaging material's preconditioning
threshold temperature but less than the development threshold temperature.
In one embodiment, the desired conditioning temperature is within a conditioning
temperature range. The low end of the range is at a margin above the conditioning
threshold temperature, and the high end of the range is a margin below the development
threshold temperature to ensure that desired conditioning temperature is high enough
to cause the water/moisture to be released from the emulsion but low enough to
prevent the heat sensitive developing compounds from reacting and developing the
image. In one embodiment, the conditioning temperature is within a range from 110
to 130 degrees centigrade (° C.), with a desired conditioning temperature
of 120° C.
As the temperature of imaging material
32 exceeds the conditioning threshold
temperature and reaches the desired conditioning temperature, water begins to be
released from the aqueous-based emulsion in the form of water vapor. Preheat chamber
34 maintains the imaging material at the conditioning temperature for a
conditioning period at least long enough for substantially all of the water/moisture
to be released from the emulsion. In one embodiment, the conditioning period is
within a time range. In a preferred embodiment, preheat chamber
34 maintains
imaging material
32 at a conditioning temperature of 120° C. for a
conditioning period of 5 seconds.
In one embodiment, transport system
44 moves imaging material
32
through preheat chamber
34 at a rate such that imaging material
32
is maintained at the desired conditioning temperature for the conditioning period.
In this embodiment, transport system
44 receives imaging material
32
at the ambient temperature at entrance
40, moves imaging material
32
along transport path
58, and provides imaging material
32 at exit
42 at substantially the conditioning temperature and with substantially
all of the water/moisture released from the emulsion. In one embodiment, transport
system
44 moves imaging material
32 through preheat chamber
34
at a rate within a range of 0.4-to-0.5 inches per second. It is noted, however,
that the rate at which transport system
44 moves imaging material
32
is dependent on the conditioning period and a length of preheat chamber
34.
Dwell chamber
36 receives imaging material
32 from preheat chamber
34 at entrance
50, with imaging material
32 at a temperature
substantially equal to the conditioning temperature and with substantially all
of the water/moisture released from the emulsion. Transport system
54 moves
imaging material
32 through dwell chamber
36 along transport path
58 in proximity to heating system
56 from entrance
50 to exit
52.
As imaging material
32 through dwell chamber
36, heating system
56 heats imaging material
32 from the preconditioning temperature
to a development temperature at least equal to the development threshold temperature.
In one embodiment, the development temperature is within a development temperature
range. In one embodiment, the development temperature range is from 135° C.
to 165° C., and in a preferred embodiment the development temperature is 150° C.
Dwell chamber
36 maintains imaging material
32 at the development
temperature for a development period that will provide substantially optimal development
of the image in imaging material
32. In one embodiment, the development
period is within a time range. In one embodiment, the development period ranges
from 18 to 25 seconds. In a preferred embodiment, dwell chamber
36 maintains
imaging material
32 at a development temperature of 150° C. for a development
period of 20 seconds.
In one embodiment, transport system
54 moves imaging material
32
through dwell chamber
36 at a rate such that imaging material
32
is maintained at the desired conditioning temperature for conditioning period.
In this embodiment, transport system
44 receives imaging material
32
at the ambient temperature at entrance
40, moves imaging material
32
along transport path
58, and provides imaging material
32 at exit
42 at substantially the conditioning temperature and with substantially
all of the water/moisture released from the emulsion.
One characteristic of gelatin-based photothermographic imaging material is that
the moisture level, or the amount of water, in the aqueous-based emulsion can change
depending on the film's local operating environment, with humidity being the primary
factor. Essentially, the aqueous-based emulsion is somewhat sponge-like and can
absorb water from the surrounding air. Because humidity varies from location to
location and can vary over time at a given location, the moisture level of the
emulsion can vary from film to film at the time of development. Furthermore, since
the amount of water in the aqueous-based emulsion affects the film's heat transfer
characteristics (i.e., the more water the more heat that must be transferred to
heat the film to a desired temperature), the varying moisture levels can potentially
result in undesirable variations in image quality from film-to-film. For example,
excessive moisture levels can result in streaking or variations in development
density of developed images.
By substantially removing all of the moisture from the aqueous-based emulsion
of imaging material
32 at preheat chamber
34 prior to providing imaging
material
32 to dwell chamber
36 for development, thermal processor
30 minimizes the potential of visual artifacts due to excessive moisture
levels and minimizes the potential for variations in image quality from film to
film. Furthermore, by heating imaging material
32 to the conditioning temperature
prior to its entering dwell chamber
36, dwell chamber
36 needs to
raise the temperature of imaging material
32 to the developing temperature
from the conditioning temperature rather than the ambient temperature, thereby
reducing visual artifacts caused by expansion of the base material.
When rollers and heat plates are spaced along a horizontal transport path, a
thermal processor can be referred to as a flatbed-type processor. (For example,
as further described below with reference to FIG. 2, thermal processor
30
according to the present invention can be referred to as a flatbed-type processor
wherein rollers
70,
72 and heat plates
78 of preheat chamber
34, and rollers
96,
98 and heat plates
104 are spaced
adjacent to and along horizontal transport path
58.) Another type of thermal
processor can be referred to as a drum-type processor which, as the name implies,
employs a heated drum around which a photothermographic film is at least partially
wrapped and heated during a developing process. An additional and unexpected benefit
provided by thermal processor
30 in the development of gelatin-based photothermographic
imaging film is an improvement in the film's "Dmin Gain" relative to such film
developed using a drum-type thermal processor. Dmin Gain is a test to determine
how well a film ages. More specifically, Dmin is a minimum density of an image
after development as generally known to one skilled in the art.
FIG. 2 is a cross-sectional view illustrating one exemplary embodiment of thermal
processor
30 according to the present invention, including preheat chamber
34 and dwell chamber
36. Transport system
44 includes a plurality
of upper rollers
70 and a plurality of lower rollers
72. Heating
system
46 includes an upper heating member
74 and a lower heating
member
76, with each heating member including a heat plate
78 and
a corresponding heat blanket
80.
Rollers
70 and
72 can include support shafts
82 having
cylindrical sleeves of support material
84 surrounding the external surface
of shafts
72. Support shafts
72 are rotatably mounted to opposite
sides of enclosure
38 in a spaced relationship along transport path
58
between entrance
40 and exit
42, such that support material
74
contacts imaging material
32.
One or more of the rollers
70,
72 can be driven in order to drive
imaging material
32 through preheat chamber
34 adjacent to the heating
plates of heating members
74,
76 along transport path
58.
In one preferred embodiment, all of the rollers
70,
72 are driven
so that the surface of each roller is heated uniformly when no imaging material
is contacting rollers
70,
72. In one embodiment, rollers
70,
72 are driven at a rotational speed such that imaging material
32
is maintained at a desired conditioning temperature for a desired conditioning
period before exiting preheat chamber
34 at exit
42.
As illustrated, upper roller
70 can be positioned relative to lower rollers
72 to cause imaging material
32 to be bent or curved in an undulating
fashion when transported between rollers
70,
72. Creating these curvatures
can be accomplished, as shown, by horizontally offsetting upper rollers
70
from lower rollers
72 and vertically positioning them such that the upper
rollers
70 and lower rollers
72 overlap a horizontal transport path
58. Curving imaging material
32 in this fashion increases a column
stiffness of imaging material
32 and enables imaging material
32
to be transported through and heated to a conditioning temperature within preheat
chamber
34 without a need for nip rollers or other pressure transporting
means. Consequently, thermally-induced wrinkles of imaging material
32 associated
with "nipping" or pressure can be minimized.
Upper rollers
70 can be sufficiently spaced apart, as can lower rollers
72, so that imaging material
32 can expand with minimal constraint
in the direction generally perpendicular to transport path
58. This minimizes
the potential for formation of significant wrinkles across imaging material, generally
perpendicular to the direction of transport path
58. Furthermore, the minimization
of these wrinkles can be accomplished without requiring that imaging material
32
be under tension when transported through preheat chamber
34. This is particularly
important when developing imaging material
32 of relatively short lengths.
Heating system
46 includes an upper heating member
74 and a
lower heating member
76. Heating members
74,
76 each include
a heat plate
78 and, as illustrated, can be heated with a corresponding
heat blanket
80. In one embodiment, heat plates
78 can be aluminum.
Heat plates
78 associated with heating members
74,
76 can
be configured with multiple zones with the temperature of each zone individually
controlled, for example, by a controller (not shown) and a temperature sensor
86
corresponding to each zone, such as a resistance temperature device or a thermocouple.
Likewise, heat blankets
80 can be configured with multiple zones,
with each zone corresponding to one of the heat plate zones and providing a temperature
based on temperature sensor
86 of the corresponding heat plate zone. Additionally,
the zones of heat blankets
80 can be configured with varying watt densities,
such that one heat blanket zone may be capable of delivering more thermal energy
to its corresponding heat plate zone relative to another heat blanket zone. Since
different heat plate zones, depending upon their location within preheat chamber
34, may transfer more thermal energy to imaging material
32 than
other heat plate zones, zonal control of heat blankets
80 is beneficial
in maintaining imaging material
32 at an even temperature.
In one embodiment, as illustrated, heat plates
78 are shaped to partially
wrap around a portion of the circumference of rollers
70,
72 such
that rollers
70,
72. By partially nesting rollers
70,
72
within heat plates
78 in this fashion, heating members
74 and
76
can more effectively maintain the temperature of the outer surfaces of rollers
70,
72, resulting in their providing a more uniform heat transfer
to imaging material
32.
By positioning heating members
74,
76 proximate to each side of
transport path
58, each side of imaging material
32 is heated as
it passes through preheat chamber
34. Furthermore, by providing zoned control
of heat members
74,
76, the temperature across the surfaces of heat
plates
78 can be more uniformly controlled and heat may be more evenly transferred
to imaging material as it passes through preheat chamber
34. For example,
if imaging material
32 has a width less than that of heat plates
78,
the middle portions of heat plates
78 will transfer more heat to the imaging
material and, thus, lose heat faster than the edge portions. In this instance,
heat blankets
80 can be controlled so as to provide more heat to those zones
corresponding to the central portions of heat plates
78.
As a result, water from the aqueous-based emulsion of imaging material
32
will be more evenly out-gassed from the surfaces of imaging material
32,
thereby reducing the potential for visual artifacts in the developed image due
to uneven moisture levels in the emulsion. Also, by transporting imaging material
32 through preheat chamber
34 on upper rollers
70 and lower
rollers
72 proximate to, but without contacting heat plates
78, each
side of imaging material
32 is able to freely outgas water vapor from the
aqueous-based emulsion.
In one embodiment, as illustrated, preheat chamber
34 includes an evacuation
system that includes exhaust ports
88 and
90 that are configured
to couple to an external vacuum system
91. External vacuum system
91
is configured to draw air from preheat chamber
34 to thereby exhaust air
and substantially all water vapor and other byproducts released from the aqueous-based
emulsion of imaging material
32 from preheat chamber
34. In one embodiment,
the exhaust air is filtered after removal from preheat chamber
34. In one
embodiment, the evacuation system is configured such that external vacuum system
91 draws external air into preheat chamber
34 via entrance
40
and exit
42. Entrance
40 and exit
42 can be flow restricted
or sealed, and the evacuation system configured to include passages or channels
through heat plates
78 through which external vacuum system
91 draws
external air so that the external air is heated prior to entering preheat chamber
34 to thereby better maintain the temperature of imaging material
32
at a desired conditioning temperature.
In one embodiment, as illustrated, thermal processor
30 includes a transition
section
92 positioned between preheat chamber
34 and dwell chamber
36. Transition section
92 includes a guide channel
94 configured
to guide imaging material
32 from exit
42 of preheat chamber
34
to entrance
50 of dwell chamber
36. In one embodiment, exit
42
of preheat chamber
34 and entrance
50 to dwell chamber
36
include seals to substantially maintain thermal isolation between preheat chamber
34 and dwell chamber
36.
As illustrated, dwell chamber
36 can be configured in a fashion similar
to preheat chamber
34, with transport system
54 including a plurality
of upper rollers
96 and a plurality of lower rollers
98. Likewise,
heating system
56 includes an upper heating member
100 and a lower
heating member
102, with each heating member including a heat plate
104
and a corresponding heating blanket
106. In one embodiment, dwell chamber
36 can be similar to the dwell chamber disclosed in U.S. Pat. No. 5,869,806,
which is herein incorporated by reference.
One or more of the rollers
96,
98 can be driven so as to move imaging
material
32 through dwell chamber
36 along transport path
58
adjacent to heating members
100,
102. In one embodiment, rollers
100,
102 are driven at a rotational speed such that imaging material
32 is heated from the conditioning temperature to the developing temperature
and held at the developing temperature for a desired developing period as it is
transported through dwell chamber
36 from entrance
50 to exit
52.
In one preferred embodiment, the rotational speed of rollers
96,
98
of dwell chamber
36 substantially match the rotational speed of rollers
70,
72 of preheat chamber
34.
Heating members
100,
102 can be zoned in a fashion similar
to that of heating members
74,
76 of preheat chamber
34, with
the temperature of each zone being individually controlled based on a temperature
sensor
108 corresponding to each zone. By zoning heating members
100,
102, heat can be more uniformly transferred to imaging material
32.
For instance, zones adjacent to entrance
50 lose heat to imaging material
32 more quickly than zones adjacent to exit
52. Therefore, those
zones adjacent to entrance
50 can be controlled so as to provide more heat
than those zones adjacent to exit
52.
In one embodiment, as illustrated, dwell chamber
36 includes an evacuation
system that includes exhaust ports
110 and
112 that are configured
to couple to external vacuum system
91. External vacuum system is configured
to draw air from dwell chamber
36 through exhaust ports
110 and
112
in order to exhaust gaseous byproducts released by imaging material
32 during
development. In one embodiment, the exhaust air is filtered after removal from
preheat chamber
34. In one embodiment, the evacuation system is configured
such that the external vacuum system
91 draws external air into dwell chamber
36 via entrance
50 and exit
52. Entrance
50 and exit
52 can be flow restricted or sealed, and the evacuation system configured
to include passages or channels through heat plates
104 through which external
vacuum system
91 draws external air is so that the external air is heated
prior to entering dwell chamber
36 to thereby better maintain the temperature
of imaging material
32 at a desired conditioning temperature.
In one embodiment, thermal processor
30 includes a receiver section
114.
Receiver section
114 includes a pair of nip rollers
116 configured
to receive imaging material
32 at an ambient temperature and to feed imaging
material to transport system
44 of preheat chamber
34 via entrance
40.
FIG. 3 is a graph
120 illustrating the temperature and moisture levels
of gelatin-based imaging material
32 as it travels through thermal processor
30 as illustrated by FIG. 2. Temperature and moisture levels are illustrated
along the y-axis, as indicated respectively at
122a and
122b,
and a distance traveled through thermal processor
30 is illustrated along
the x-axis as indicated at
124. Graph
120 includes zones representative
of the sections/chambers of thermal processor
30, with a zone
126
representative of receiver section
114, a zone
128 representative
of preheat chamber
34, a zone
130 representative of transition section
92, and a zone
132 representative of dwell chamber
36. Waveforms
134 and
136 respectively represent the temperature and moisture level
of imaging material
32.
As imaging material
32 enters receiver section
114, it is at an
ambient temperature level as indicated at
138. After entering preheat chamber
34, the temperature of imaging material begins to rise, as indicated at
140, until the temperature of the imaging material reaches the desired conditioning
temperature, as indicated at
142. The temperature of imaging material
32
is maintained at the desired conditioning temperature by preheat chamber
34
until it enters transition section
92, where the temperature may drop slightly
as indicated at
144. After entering dwell chamber
36, the temperature
of imaging material
32 rises, as indicated at
146, until the temperature
reaches the desired developing temperature, as indicated at
148. Dwell chamber
36 maintains the temperature of imaging material
32 at the desired
developing temperature until imaging material exits the dwell chamber
36,
as indicated at
150.
As illustrated by waveform
136, imaging material
32 has an arbitrary
moisture level as it enters and travels through receiver section
114, as
indicated at
152. As imaging material
32 enters preheat chamber
34
and the its temperature begins to rise, its moisture level begins to drop, as indicated
at
154. As the temperature of imaging material
32 rises to the desired
conditioning temperature at
142, the removal of moisture from the aqueous-based
emulsion accelerates, as indicated at
156, until the moisture level drops
to substantially zero, as indicated at
158. The moisture level remains at
near-zero levels as it travels through transition section
92 and dwell chamber
36, as indicated at
160.
Although specific embodiments have been illustrated and described herein,
it will be appreciated by those of ordinary skill in the art that a variety of
alternate and/or equivalent implementations may be substituted for the specific
embodiments shown and described without departing from the scope of the present
invention. This application is intended to cover any adaptations or variations
of the specific embodiments discussed herein. Therefore, it is intended that this
invention be limited only by the claims and the equivalents thereof.
*
