U.S. patent number 3,793,022 [Application Number 05/276,979] was granted by the patent office on 1974-02-19 for diffusion transfer films with anti-reflection layers and processes.
This patent grant is currently assigned to Polaroid Corporation. Invention is credited to Stanley M. Bloom, Edwin H. Land, Howard G. Rogers.
United States Patent |
3,793,022 |
Land , et al. |
February 19, 1974 |
DIFFUSION TRANSFER FILMS WITH ANTI-REFLECTION LAYERS AND
PROCESSES
Abstract
Photographic images, particularly multicolor images, viewed
through a transparent support have an anti-reflection coating on
the outer surface of said support. The images may be formed by
multicolor diffusion transfer processes using dye developers or
other image dye-providing materials. In the preferred embodiments,
the photographic image is an integral negative-positive reflection
print. Where photoexposure is effected through a transparent
support, e.g., the transparent support through which the final
image is viewed, provision of an anti-reflection coating and
effecting photoexposure therethrough will permit more effective
recording of light passing through the camera lens. The transparent
support preferably has an index of refraction of at least 1.6.
Inventors: |
Land; Edwin H. (Cambridge,
MA), Bloom; Stanley M. (Waban, MA), Rogers; Howard G.
(Weston, MA) |
Assignee: |
Polaroid Corporation
(Cambridge, MA)
|
Family
ID: |
23058932 |
Appl.
No.: |
05/276,979 |
Filed: |
August 1, 1972 |
Current U.S.
Class: |
430/220; 359/582;
427/164; 430/212; 430/236; 430/523; 430/536; 359/588; 430/227;
430/510; 430/533 |
Current CPC
Class: |
G03C
8/52 (20130101) |
Current International
Class: |
G03C
8/00 (20060101); G03C 8/52 (20060101); G03c
007/00 (); G03c 005/54 (); G03c 001/76 (); G03c
001/48 (); G03c 001/40 (); G03c 001/84 (); G03c
001/78 () |
Field of
Search: |
;96/87R,3,29R,67,76R,77,84R |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Brown; J. Travis
Assistant Examiner: Schilling; Richard L.
Attorney, Agent or Firm: Mervis; Stanley H.
Claims
What is claimed is:
1. A photographic product for use in diffusion transfer processes
comprising a transparent support carrying on one side thereof an
image-receiving layer, the other side of said transparent support
carrying an anti-reflection coating.
2. A photographic product as defined in claim 1, including at least
one layer containing photosensitive silver halide carried on said
first side.
3. A photographic product as defined in claim 2, including an image
dye-providing material in a layer contiguous to said silver halide
containing layer.
4. A photographic product as defined in claim 1 wherein said
image-receiving layer includes a mordant for a dye.
5. A photographic product as defined in claim 1 wherein said
image-receiving layer is a silver receptive layer containing a
silver precipitant.
6. A photographic product as defined in claim 4 wherein said dye is
a dye developer.
7. A photographic product as defined in claim 1 wherein said
transparent support has an index of refraction of at least about
1.6.
8. A photographic product as defined in claim 7 wherein said
transparent support is a polyester.
9. A photographic product as defined in claim 8 wherein said
polyester is polyethylene terephthalate.
10. A photographic product as defined in claim 7 wherein said
transparent support is polystyrene.
11. A photographic product as defined in claim 1 wherein said
anti-reflection coating has an index of refraction at least 0.20
less than said transparent support.
12. A photographic product as defined in claim 1 wherein said
anti-reflection coating has an index of refraction of about 0.25 to
0.3 less than said transparent support.
13. A photographic product as defined in claim 7 wherein said
anti-reflection coating has an index of refraction at least 0.20
less than said transparent support.
14. A photographic product as defined in claim 13 wherein said
anti-reflection coating has an index of refraction at least 0.25 to
0.3 less than said transparent support.
15. A photographic product as defined in claim 7 wherein said
anti-reflection coating has an index of refraction of about 1.3 to
about 1.4.
16. A photographic product as defined in claim 1 wherein said
anti-reflection coating has an index of refraction of about 1.3 to
about 1.4.
17. A photographic product as defined in claim 1 wherein said
transparent support is cellulose acetate.
18. A photographic product as defined in claim 1 wherein said
anti-reflection coating comprises a fluorinated polymer.
19. A photographic product comprising a transparent support
carrying on one side thereof a layer containing a photosensitive
silver halide, said silver halide layer being exposable through
said transparent support, the other side of said transparent
support carrying an anti-reflection coating.
20. A photographic product as defined in claim 19, including an
image dye-providing material in a layer contiguous to said silver
halide containing layer.
21. A photographic product as defined in claim 20 wherein said
image dye-providing material is a dye developer.
22. A photographic product as defined in claim 20 wherein said
image dye-providing material is a compound which provides a
diffusible dye as a function of oxidation or color coupling.
23. A photographic product as defined in claim 19 including an
image-receiving layer, said layer of silver halide being positioned
between said support and said image-receiving layer.
24. A photographic product as defined in claim 19 wherein said
transparent support has an index of refraction of at least about
1.6.
25. A photographic product as defined in claim 24 wherein said
transparent support is a polyester.
26. A photographic product as defined in claim 25 wherein said
polyester is polyethylene terephthalate.
27. A photographic product as defined in claim 24 wherein said
transparent support is polystyrene.
28. A photographic product as defined in claim 19 wherein said
anti-reflection coating has an index of refraction at least 0.20
less than said transparent support.
29. A photographic product as defined in claim 19 wherein said
anti-reflection coating has an index of refraction of about 0.25 to
0.3 less than said transparent support.
30. A photographic product as defined in claim 24 wherein said
anti-reflection coating has an index of refraction at least 0.20
less than said transparent support.
31. A photographic product as defined in claim 30 wherein said
anti-reflection coating has an index of refraction at least 0.25 to
0.3 less than said transparent support.
32. A photographic product as defined in claim 24 wherein said
anti-reflection coating has an index of refraction of about 1.3 to
about 1.4.
33. A photographic product as defined in claim 19 wherein said
anti-reflection coating has an index of refraction of about 1.3 to
about 1.4.
34. A photographic product as defined in claim 19 wherein said
transparent support is cellulose acetate.
35. A photographic product as defined in claim 19 wherein said
anti-reflection coating comprises a fluorinated polymer.
36. A photographic film product comprising a first support and a
second support, at least one of said supports being transparent, a
plurality of layers including a photosensitive layer carried on one
of said supports, and a rupturable container releasably holding a
processing composition adapted, when distributed between a pair of
predetermined layers carried by said supports, to develop said
photosensitve layer and provide an image viewable through said
transparent support, the external surface of said transparent
support carrying an anti-reflection coating.
37. A photographic product as defined in claim 36, wherein both of
said supports are transparent and each said transparent support
carries an anti-reflection coating on the external surface
thereof.
38. A photographic product as defined in claim 36, including an
image-receiving layer and means adapted to provide a masking layer
between said photosensitive layer and said image-receiving layer to
mask the developed photosensitive layer when the image in said
image-receiving layer is viewed through said transparent
support.
39. A photographic product as defined in claim 38 wherein said
product includes a silver halide solvent and said image is a silver
transfer image.
40. A photographic product for forming a diffusion transfer image
in dye within a permanent laminate including at least one developed
silver halide layer, said photographic product comprising, in
combination, an image-receiving layer; at least one silver halide
emulsion, each said silver halide emulsion having associated
therewith an image dye-providing substance selected from the group
consisting of image dyes and image dye intermediates; means
providing a light-reflecting layer between said image-receiving
layer and said silver halide emulsion(s) to mask said silver halide
emulsion(s) after development thereof and to provide a white
background for viewing a dye image in said image-receiving layer; a
transparent support through which image-receiving layer may be
viewed; means providing a processing composition for developing
said silver halide emulsion(s) after photoexposure and for forming
a transfer image in at least one dye in said image-receiving layer;
said image in at least one dye in said image-receiving layer; said
product including an anti-reflection coating on the outer surface
of said transparent support.
41. A photographic film as defined in claim 40 wherein each said
image dye-providing substance is a dye.
42. A photographic film as defined in claim 41 wherein each said
dye is a dye developer.
43. A photographic film as defined in claim 40 wherein each said
image dye-providing substance is an intermediate for an image
dye.
44. A photographic product as defined in claim 40 wherein said
silver halide emulsion(s) are adapted to be exposed through said
transparent support.
45. A photographic product as defined in claim 40 including a
second transparent support, said silver halide emulsion(s) being
adapted to be exposed through said second transparent support.
46. A photographic product as defined in claim 45 wherein said
second transparent support also carries an anti-reflection coating
on the outer surface thereof.
47. A photographic product as defined in claim 40 wherein said
means providing a light-reflecting layer comprise a white pigment
dispersed in said processing composition, and said processing
composition is contained in a rupturable container positioned to
distribute said processing composition containing said pigment
between said image-receiving layer and said silver halide
emulsion(s).
48. A photographic product as defined in claim 40 comprising a
temporary laminate including said layers confined between two
dimensionally stable supports, at least one of said supports being
transparent, the bond between a predetermined pair of layers being
weaker than the bond between other pairs of layers, and including a
rupturable container releasably holding said processing
composition, said rupturable container being so positioned as to
distribute said processing composition between said predetermined
layers, said processing composition being adapted to provide said
permanent laminate following distribution and drying.
49. A photographic product as defined in claim 40 wherein said
transparent support has an index of refraction of at least about
1.6.
50. A photographic product as defined in claim 49 wherein said
transparent support is a polyester.
51. A photographic product as defined in claim 50 wherein said
polyester is polyethylene terephthalate.
52. A photographic product as defined in claim 49 wherein said
transparent support is polystyrene.
53. A photographic product as defined in claim 40 wherein said
anti-reflection coating has an index of refraction at least 0.20
less than said transparent support.
54. A photographic product as defined in claim 40 wherein said
anti-reflection coating has an index of refraction of about 0.25 to
0.3 less than said transparent support.
55. A photographic product as defined in claim 49 wherein said
anti-reflection coating has an index of refraction at least 0.20
less than said transparent support.
56. A photographic product as defined in claim 55 wherein said
anti-reflection coating has an index of refraction at least 0.25 to
0.3 less than said transparent support.
57. A photographic product as defined in claim 49 wherein said
anti-reflection coating has an index of refraction of about 1.3 to
about 1.4.
58. A photographic product as defined in claim 40 wherein said
anti-reflection coating has an index of refraction of about 1.3 to
about 1.4.
59. A photographic product as defined in claim 40 wherein said
transparent support is cellulose acetate.
60. A photographic product as defined in claim 40 wherein said
anti-reflection coating comprises a fluorinated polymer.
61. A photographic product comprising a first support; a
red-sensitive silver halide emulsion; a green-sensitive silver
halide emulsion; and a blue-sensitive silver halide emulsion; said
silver halide emulsions having associated therewith, respectively,
a cyan dye developer, a magenta dye developer and a yellow dye
developer; an image-receiving layer for receiving image dyes
transferred thereto by diffusion as a function of exposure and
development of said silver halide emulsion layers, a second support
which is transparent and through which said image-receiving layer
may be viewed; a rupturable container releasably holding a
processing composition adapted, upon distribution between
predetermined layers of said film to develop said silver halide
emulsions and to effect the formation of a transfer image in dye in
said image-receiving layer, said processing composition also being
adapted to provide a permanent laminate including said developed
silver halide emulsions and said image-receiving layer; and means
providing a light-reflecting layer between said image-receiving
layer and said silver halide emulsions effective to provide a white
background for viewing said transfer image and for masking said
developed silver halide emulsions; said product including an
anti-reflection coating on the outer surface of said transparent
support.
62. A photographic product as defined in claim 61 wherein said
means for providing a light-reflecting layer comprises a white
pigment dispersed in said processing composition.
63. A photographic product as defined in claim 61 wherein said
first support is opaque.
64. A photographic product as defined in claim 61 wherein said
transparent support has an index of refraction of at least about
1.6.
65. A photographic product as defined in claim 64 wherein said
transparent support is a polyester.
66. A photographic product as defined in claim 65 wherein said
polyester is polyethylene terephthalate.
67. A photographic product as defined in claim 64 wherein said
transparent support is polystyrene.
68. A photographic product as defined in claim 61 wherein said
anti-reflection coating has an index of refraction at least 0.20
less than said transparent support.
69. A photographic product as defined in claim 61 wherein said
anti-reflection coating has an index of refraction of about 0.25 to
0.3 less than said transparent support.
70. A photographic product as defined in claim 64 wherein said
anti-reflection coating has an index of refraction at least 0.20
less than said transparent support.
71. A photographic product as defined in claim 70 wherein said
anti-reflection coating has an index of refraction at least 0.25 to
0.3 less than said transparent support.
72. A photographic product as defined in claim 64 wherein said
anti-reflection coating has an index of refraction of about 1.3 to
about 1.4.
73. A photographic product as defined in claim 61 wherein said
anti-reflection coating has an index of refraction of about 1.3 to
about 1.4.
74. A photographic product as defined in claim 61 wherein said
transparent support is cellulose acetate.
75. A photographic product as defined in claim 61 wherein said
anti-reflection coating comprises a fluorinated polymer.
76. A photographic product as defined in claim 61 wherein said
anti-reflection coating comprises an inorganic material.
77. A photographic product as defined in claim 61 wherein said
transparent support and said image-receiving layer comprise a
separate element adapted to be brought into superposed relationship
with said silver halide emulsions.
78. A photographic product as defined in claim 61 wherein said
layers are held in fixed relationship between said supports prior
to and during exposure.
79. A photographic product as defined in claim 78 wherein said
fixed relationship is provided by binder means along at least two
parallel sides of said product.
80. A photographic product as defined in claim 78 wherein said
product is a laminate of said layers between said first and said
second supports, the bond between a pair of predetermined layers
being weaker than the bonds between the other layers, said
rupturable container being so positioned as to release said
processing composition for distribution between said pair of
layers.
81. A photographic product as defined in claim 61 wherein said
silver halide emulsions are present as separate planar layers.
82. A photographic product as defined in claim 61 wherein said
silver halide emulsions are present in the form of minute elements
arranged in side-by-side relationship in a photosensitive screen
pattern.
83. A photographic product as defined in claim 81 wherein said
blue-sensitive silver halide emulsion layer is between said
image-receiving layer and said other silver halide emulsion
layers.
84. A photographic product as defined in claim 81 wherein said
blue-sensitive silver halide emulsion layer is between said first
support and said other silver halide emultion layers, and said
first support is transparent.
85. A photographic product as defined in claim 84 wherein said
transparent first support carries an anti-reflection coating on the
outer surface thereof.
86. A method of forming a diffusion transfer dye image by
developing an exposed silver halide emulsion, forming an imagewise
distribution of a diffusible dye image-providing substance as a
function of said development, and transferring at least a portion
of said imagewise distribution of diffusible dye image-providing
substance to an image-receiving layer in superposed relationship
with said silver halide emulsion to provide said dye image, said
image-receiving layer and said silver halide emulsion forming a
permanent laminate including a light-reflecting layer positioned
between said image-receiving layer and said silver halide emulsion,
the step of said exposure of said silver halide emulsion being
effected through a transparent support having an anti-reflection
coating on the outer surface thereof.
87. A method as defined in claim 86 wherein said diffusion transfer
dye image is viewed through said transparent support and said
anti-reflection coating.
88. The method as defined in claim 86 wherein said diffusible dye
image-providing substance is a dye developer.
89. The method as defined in claim 86 wherein a red-sensitive
silver halide emulsion, a green-sensitive silver halide emulsion
and a blue-sensitive silver halide emulsion are present, said
silver halide emulsions having associated therewith, respectively,
a cyan dye developer, a magenta dye developer, and a yellow dye
developer, and said dye image is a multicolor image.
90. A method as defined in claim 86 wherein said exposure is
effected in a camera having an image reversing optical system
utilizing mirror optics.
91. A method of forming a photographic image comprising
photoexposing a silver halide emulsion and thereafter developing
said exposed silver halide emulsion, the step of said photoexposure
being effected through a transparent support having an
anti-reflection coating on the outer surface thereof.
92. A method as defined in claim 91 wherein said exposure is
effected in a camera having an image reversing optical system
utilizing mirror optics.
93. A method of forming a diffusion transfer image by developing an
exposed silver halide emulsion, forming an imagewise distribution
of a diffusible image-providing substance as a function of said
development, and transferring at least a portion of said imagewise
distribution of diffusible image-providing substance to an
image-receiving layer in superposed relationship with said silver
halide emulsion to provide said diffusion transfer image, said
exposure of said silver halide emulsion being effected through a
transparent support having an anti-reflection coating on the outer
surface thereof.
94. A method as defined in claim 93 wherein said transparent
support carries said image-receiving layer.
95. A method as defined in claim 93 wherein said transparent
support carries said silver halide emulsion.
Description
This invention is concerned with photography and, more
particularly, with the formation of images in color or
black-and-white by diffusion transfer processing.
A number of photographic processes have been proposed wherein the
resulting photograph comprises the developed silver halide
emulsion(s) retained as part of a permanent laminate, with the
desired image being viewed through a transparent support. Of
particular significance are those processes where the image is in
color and is formed by a diffusion transfer process. If the image
is to be viewed as a reflection print, the image-carrying layer is
separated from the developed silver halide emulsion(s) in said
laminate by a light-reflecting layer, preferably a layer containing
titanium dioxide. Illustrative of patents describing such products
and processes are U.S. Pat. No. 2,983,606 issued Mar. 9, 1961 to
Howard G. Rogers, U.S. Pat. Nos. 3,415,644, 3,415,645 and 3,415,646
issued Dec. 10, 1968 to Edwin H. Land, U.S. Pat. Nos. 3,594,164 and
3,594,165 issued July 20, 1971 to Howard G. Rogers, and U.S. Pat.
No. 3,647,347 issued Mar. 7, 1972 to Edwin H. Land.
Referring more specifically to the aforementioned U.S. pat. No.
3,415,644, said patent discloses photographic products and
processes employing dye developers wherein a photosensitive element
and an image-receiving layer are maintained in fixed relationship
prior to photoexposure and this fixed relationship is maintained
after processing and image formation to provide a laminate
including the processed silver halide emulsions and the
image-receiving layer. Photoexposure is made through a transparent
(support) element and application of a processing composition
provides a layer of light-reflecting material to provide a white
background for viewing the image and to mask the developed silver
halide emulsions. The desired color transfer image is viewed
through said transparent support against said white background.
While such processes provide very useful and good quality images,
it has been found that the full potential quality of the image is
not obtained because the transparent support through which the
image is viewed in fact reflects "white" light to the viewer's
eyes. Furthermore, this property of reflecting some of the light
incident on the surface of of the transparent support adversely
affects the ability of the film to record a subject when
photoexposure is effected through such a transparent support.
It is, threfore, a primary object of this invention to provide
novel photographic products and processes which provide high
quality color or black-and-white images as part of a permanent
laminate, said laminate exhibiting substantially less surface
reflection of incident light.
It is a further object of this invention to provide diffusion
transfer images, particularly multicolor transfer images, which are
viewed through a transparent element the outer surface of which
carries an anti-reflection coating.
Yet another object of this invention is to provide diffusion
transfer films which are exposed through a transparent support, the
outer surface of which carries an anti-reflection coating.
Other objects of this invention will in part be obvious and will in
part appear hereinafter.
The invention accordingly comprises the product possessing the
features, properties and relation of components and 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 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 of the invention taken in conjunction with the
accompanying drawings wherein:
FIGS. 1 and 2 are diagrammatic, enlarged cross-sectional views of
two embodiments of film units embodying the present invention,
illustrating the arrangement of layers during the three illustrated
stages of a monochrome diffusion transfer process, i.e., exposure,
processing and final image; and
FIG. 3 is a diagrammatic, enlarged cross-sectional view of another
film unit embodying the present invention.
As noted above, this invention is particularly concerned with color
diffusion transfer processes wherein the layer containing the
diffusion transfer image, i.e., the image-receiving layer, is not
separated from the developed photosensitive layers after processing
but both components are retained together as part of a permanent
laminate. Film units particularly adapted to provide such diffusion
transfer images have frequently been referred to as "integral
negative-positive" film units. The resulting image may be referred
to as an "integral negative-positive reflection print" and as so
used this expression is intended to refer to a reflection print
wherein the developed photo-sensitive layers have not been
separated from the image layer, i.e., the layer containing the
transfer dye image. A light-reflecting layer between the developed
photosensitive layer(s) and the image layer provides a white
background for the dye image and masks the developed photosensitive
layer(s). These layers are part of a permanent laminate which
usually includes dimensionally stable outer or support layers, the
transfer dye image being viewable through one of said supports.
This invention is particularly concerned with improving the
aesthetic qualities of such integral negative-positive reflection
prints.
The present invention is applicable to a wide variety of diffusion
transfer processes. The arrangement and order of the individual
layers of the film used in such processes may vary in many ways as
is known in the art, provided the final photograph is a laminate
wherein the desired image is viewed through a transparent support,
e.g., an integral negative-positive reflection print as described
above. For convenience, however, the more specific descriptions of
the invention hereinafter set forth may be by use of dye developer
diffusion transfer color processes and of integral
negative-positive film units of the type contemplated in the
previously mentioned patents, particularly U.S. Pat. Nos. 3,415,644
and 3,594,164. It will be readily apparent from such descriptions
that other image-forming reagents may be used, e.g., color
couplers, coupling dyes or dyes (couplers) which release a dye or
dye intermediate as a result of coupling or oxidation.
When such integral negative-positive reflection prints are viewed
under ordinary lighting conditions, a small but significant amount
of light is reflected from the external surface of the transparent
support. The effect of this reflection of incident light is to
limit the clarity with which the image may be seen except when the
viewer's eyes are "just right," i.e., good viewing may be highly
directional, in that the print may have to be "tilted" with respect
to the viewer's line of vision to avoid obscuring image detail.
This problem becomes more acute when several persons try to view
the same image, as those not directly in front of the print will
experience substantial glare, with the amount of glare increasing
as the angle of view becomes more oblique. In addition, the
color(s) of a color image may appear less saturated.
If photoexposure is effected through such a transparent support,
reflection of light from the surface of the transparent support
will, in effect, reduce the exposure index or "speed" of the film.
This result follows from the fact that some of the light which has
passed through the camera lens will be reflected before it can
reach the photosensitive layer(s) and the thus reflected light will
not participate in the recording of the photographed subject
matter. Furthermore, such reflected light has a tendency to
"bounce" within the camera, and may cause flare and reduced
contrast and resolution in the final image.
It has now been found that such undesirable reflection from the
transparent support may be substantially reduced, if not completely
eliminated, by modifying the external surface of such transparent
supports so as to provide a controlled change in the index of
refraction to which incident light is subjected as it passes from
air into the transparent support. This objective may be most
readily achieved by providing an anti-reflection coating on the
external surface of the transparent support.
The principles of physics by which anti-reflection coatings
function are well known and may be used to special advantage in the
present invention. Thus, it is well known that application of a
single layer transparent coating will reduce surface reflection
from a transparent layer (support) if the refractive index of said
coating is less than that of the transparent layer to which it is
applied and the coating is of appropriate optical thickness. In the
photographic products with which this invention is concerned, the
anti-reflection coating will normally be in optical contact with
air. Under these circumstances, and because the index of refraction
of air is 1, the applicable principles of physics give the
following rule: if the index of refraction of the coating material
(anti-reflection layer) is exactly equal to the square root of the
index of refraction of the substrate (transparent support), then
all surface reflection of light will be eliminated for that
wavelength at which the product of the refractive index times
thickness is equal to one-quarter of the wavelength. At other
wavelengths the destructive interference between light reflected
from the top and bottom surfaces of the anti-reflection coating is
not complete but a substantial reduction in overall reflectivity is
obtained. By selecting the optical thickness of the anti-reflection
coating to be one-quarter of a wavelength for approximately the
midpoint of the visible light wavelength range (i.e., one-quarter
of 5,500 Angstroms or about 1,400 Angstroms), the reduction in
reflectivity is optimized. The term "optical thickness" as used
herein refers to the product of the physical thickness of the
coating times the refractive index of the coating material.
The anti-reflection coating should be optically clear and provide
an essentially uniform layer. In certain embodiments of this
invention, the anti-reflection coating is also effective as an
anti-abrasion coating. While the above discussion of the applicable
principles of physics has concerned itself with a single layer
anti-reflection coating, it is also within the scope of this
invention to employ an anti-reflection coating comprising several
layers, the index of refraction of each layer being selected in
accordance with well known principles. In the latter situation, the
reduced effectiveness of a single layer in eliminating reflections
as the wavelength gets further from the midpoint of the visible
light range may be compensated for by appropriate selection of a
different wavelength as to which the optical thickness of a second
layer should be related. The anti-reflection coating may be organic
or inorganic in nature, and many suitable materials are known.
Illustrative examples of useful anti-reflection coatings and their
method of application will be described hereinafter.
Transparent supports used in integral negative-positive reflection
prints include polyesters, polystyrene, cellulose acetate and
similar art known polymeric film base materials. Polyester and
polystyrene films have higher refractive indices than cellulose
acetate, and the resultant greater incidence of surface reflected
light as compared with cellulose acetate would normally be
considered to be a disadvantage of using such materials in integral
negative-positive reflection prints. (Indeed, the greater surface
reflection resulting in greater glare, and the resultant need for
more directional viewing, exhibited by polyester films as compared
with cellulose acetate is well known from the commonly used
protective transparent covers for notebook pages.) These higher
indices of refraction are turned into an advantage by the present
invention, for the high index of refraction makes it much more
possible to provide anti-reflection coatings which practically
eliminate all reflectivity, whereas reflectivity can only be
reduced when using cellulose acetate.
Particularly useful transparent supports are films of polyethylene
terephthalate, such as those commercially available under the
trademarks "Mylar" (E.I.DuPont de Nemours & Co.) and "Estar"
(Eastman Kodak Co.) Such polyester films have an index of
refraction on the order of about 1.66. A number of materials
suitable for anti-reflection coatings, e.g. fluorinated polymers,
have indices of refraction of about 1.33, which is quite close to
the 1.29 ideal index of refraction, i.e., the geometric mean of the
indices of refraction of the polyethylene phthalate and the
surrounding air, or, because the index of refraction of air is 1,
the square root of the 1.66 index of refraction of polyethylene
terephthalate. Furthermore, the fact that the difference of about
0.3 in the indices of refraction between air and the
anti-reflection coating is close to the approximate 0.3 difference
in the indices of refraction of the anti-reflection coating and the
polyethylene terephthalate support means that maximum benefit will
be obtained from the anti-reflection coating; the amplitude of the
light entering the anti-reflection coating will more closely match
the amplitude of the light reflected back from the interface of the
polyethylene phthalate and the anti-reflection coating, and more
effectively cancel out the thus reflected light.
Reference is now made to the accompanying drawings wherein a
plurality of embodiments of this invention are illustrated and
wherein like numbers, appearing in the various figures, refer to
like components. For ease of understanding, these emboidments
illustrate the formation of a monochrome image using a single dye
developer. The illustrated embodiments include appropriate means of
opacification to permit the processing of the film unit outside of
a dark chamber, i.e., the film unit is intended to be removed from
the camera prior to image completion and while the film is still
photosensitive. Opacifying systems are described in the previously
noted patents and per se form no part of the present invention
which is equally applicable to film units intended to be processed
within a dark chamber.
A particularly useful opacifying system for film units of the type
shown in FIGS. 1 and 3 utilizes a color dischargeable reagent,
preferably a pH-sensitive optical filter agent or dye, sometimes
referred to as an indicator dye, as is described in detail in the
aforementioned U.S. Pat. No. 3,647,437. In film units of the type
shown in FIG. 2, photoexposure is effected from the side opposite
the side from which the image is viewed. An opaque layer to protect
the exposed silver halide from further exposure may be provided by
including a light-absorbing opacifying agent, e.g., carbon black,
in the processing composition which is distributed between the
photosensitive layer(s) and a transparent support or spreader
sheet. In such film units, it may be desirable to include a
preformed opaque layer, e.g., a dispersion of carbon black in a
polymer permeable to the processing composition, between a
preformed light-reflecting layer and the silver halide emulsion(s).
Such opacifying systems are shown and described in the
aforementioned U.S. Pat. Nos. 3,594,164 and 3,594,165.
Referring to FIG. 1, Stages A, B, and C show in diagrammatic
cross-section, respectively, imaging, processing, and the finished
print in one embodiment of this invention. In Stage A, there is
shown a photosensitive element 30 in superposed relationship with
an image-receiving element 32, with a rupturable container 16
(holding an opaque processing composition 17) so positioned as to
discharge its contents between said elements upon suitable
application of pressure, as by passing through a pair of pressure
applying rolls or other pressure means (not shown). Photosensitive
element 30 comprises an opaque support 10 carrying a layer 12 of a
dye developer over which has been coated a silver halide emulsion
layer 14. The image-receiving element 32 comprises a transparent
support 24 carrying, in turn, a polymeric acid layer 22, a spacer
layer 20 and an image-receiving layer 18. An anti-reflection
coating 26 is present on the outer surface of the transparent
support 24. Photoexposure of the silver halide emulsion layer is
effected through the anti-reflection coating 26 and the transparent
support 24 and the layers carried thereon, i.e., the polymeric acid
layer 22, the spacer layer 20 and the image-receiving layer 18
which layers are also transparent, the film unit being so
positioned within the camera that light admitted through the camera
exposure or lens systems is incident upon the outer surface of the
anti-reflection coating 26. After exposure the film unit is
advanced between suitable pressure-applying members, rupturing the
container 16, thereby releasing and distributing a layer 17a of the
opaque processing composition between the photosensitive element 30
and the image-receiving element 32. The opaque processing
composition contains a film-forming polymer, a white pigment and
has an initial pH at which one or more optical filter agents
contained therein are colored; the optical filter agent (agents) is
(are) selected to exhibit light absorption over at least a portion
of the wavelength range of light actinic to the silver halide
emulsion. As a result, ambient or environmental light within that
wavelength range incident upon transparent support 24 and
transmitted through said transparent support and the transparent
layers carried thereon in the direction of the photoexposed silver
halide emulsion 14a is absorbed thereby avoiding further exposure
of the photoexposed and developing silver halide emulsion 14a. In
exposed and developed areas, the dye developer is oxidized as a
function of the silver halide development and immobilized.
Unoxidized dye developer associated with undeveloped and partially
developed areas remains mobile and is transferred imagewise to the
image-receiving layer 18 to provide the desired positive image
therein. Permeation of the alkaline processing composition through
the image-receiving layer 18 and the spacer layer 20 to the
polymeric acid layer 22 is so controlled that the process pH is
maintained at a high enough level to effect the requisite
development and image transfer and to retain the optical filter
agent (agents) in colored form, after which pH reduction effected
as a result of alkali permeation into the polymeric acid layer 22
is effective to reduce the pH to a level which "discharges" the
optical filter agent, i.e., changes it to a colorless form.
Absorption of the water from the applied layer 17a of the
processing composition results in a solidified film composed of the
film-forming polymer and the white pigment dispersed therein, thus
providing the reflecting layer 17b which also serves to laminate
together the photosensitive element 30 and the image-receiving
element 32 to provide the final laminate (Stage C). The positive
transfer image in dye developer present in the image-receiving
layer 18a is viewed through the transparent support 24 and the
intermediate transparent layers against the reflecting layer 17b
which provides an essentially white background for the dye image
and also effectively masks from view the developed silver halide
emulsion 14b and dye developer immobilized therein or remaining in
the dye developer layer 12.
The optical filter agent is retained within the final film unit
laminate and is preferably colorless in its final form, i.e.,
exhibiting no visible absorption to degrade the transfer image or
the white background therefor provided by the reflecting layer 17b.
The optical filter agent may be retained in the reflecting layer
under these conditions, and it may contain a suitable "anchor" or
"ballast" group to prevent its diffusion into adjacent layers.
Alternatively, if the optical filter agent is initially diffusible,
it may be selectively immobilized on the silver halide emulsion
side of the reflecting layer 17b, e.g., by a mordant coated on the
surface of the silver halide emulsion layer 14; in this embodiment
the optical filter in its final state may be colorless or colored
so long as any color exhibited by it is effectively masked by the
reflecting layer 17b.
The reflecting layer provided in the embodiment of this invention
shown in FIG. 1 is formed by solidification of a stratum of
pigmented processing composition distributed after exposure. It is
also within the scope of this invention to provide a preformed
pigmented layer, e.g., coated over the image-receiving layer 18,
and to effect photoexposure therethrough, in accordance with the
teachings of U.S. Pat. No. 3,615,421 issued Oct. 26, 1971 to Edwin
H. Land.
In the embodiment illustrated in FIG. 1, photo-exposure is effected
through the image-receiving element. While this is a particularly
useful and preferred embodiment, it will be understood that the
image-receiving element may be initially positioned out of the
exposure path as illustrated in FIG. 3 and superposed upon the
photosensitive element after photoexposure, in which event the
processing and final image stages would be the same as in FIG.
1.
In the embodiment illustrated in FIG. 1, photo-exposure and viewing
of the final image both are effected through the transparent
support 24. Accordingly, the advantages of the anti-reflection
coating 26 are obtained twice, i.e., first, by minimizing failure
of the film unit to record light passed by the camera lens and
second, by minimizing glare during viewing.
It will be noted in the embodiment illustrated in FIG. 1 that the
image-viewing layer 18 is temporarily bonded to the silver halide
emulsion layer 14 prior to exposure. The rupturable container or
pod 16 is so positioned that upon its rupture the processing
composition 17 will delaminate the film unit and distribute itself
between the image-receiving layer 18 and the silver halide emulsion
layer 14. The distributed layer of processing composition 17a upon
solidification forms a layer 17b which bonds the elements together
to form the desired permanent laminate. Procedures for forming such
prelaminated film units, i.e., film units in which the several
elements are temporarily laminated together prior to exposure, are
described, for example, in u.S. Pat. No 3,625,281 issued to Albert
J. Bachelder and Frederick J. Bindar and in U.S. Pat. No. 3,652,282
to Edwin H. Land, both issued Mar. 28, 1972. A particularly useful
and preferred prelamination utilizes a water-soluble polyethylene
glycol as described and claimed in the copending application of
Edwin H. Land, Ser. No. 247,023 filed Apr. 24, 1972.
The use of such temporarily laminated film units maximizes the
beneficial effects obtained in the photoexposure stage from having
the exposure effected through the anti-reflection coating 26, since
the prelamination eliminates any other layer-to-air interface which
could also reflect light and thus reduce the amount of light
recorded by the photosensitive layer(s).
It will be recognized that the transfer image formed following
exposure and processing of film units of the type illustrated in
FIG. 1 will be geometrically reversed image of the subject.
Accordingly, to provide geometrically nonreversed transfer images,
exposure of such film units should be accomplished through an image
reversing optical system, such as in a camera possessing an image
reversing optical system utilizing mirror optics, e.g., as
described in U.S. Pat. No. 3,447,437 issued June 3, 1969 to Douglas
B. Tiffany.
If desired, the photosensitive element 30 may utilize a transparent
support instead of the opaque support 10 shown in FIG. 1. In this
alternative embodiment, the film unit should be processed in a dark
chamber or an opaque layer, e.g., pressure-sensitive, should be
superposed over said transparent support to avoid further exposure
through the back of the film unit during processing outside of the
camera.
FIG. 2 illustrates another film structure adapted to provide an
integral negative-positive reflection print and wherein
photoexposure and viewing are effected from opposite sides. In this
embodiment, a photosensitive element 34 comprises a transparent
support 24 carrying a layer 22 of a polymeric acid, a spacer 20, an
image-receiving layer 18, a light-reflecting layer 60 (e.g., of
titanium dixoide), an opaque layer 62 (e.g., of carbon black), a
dye developer layer 12, and a silver halide emulsion layer 14.
After photoexposure, a processing composition 17 is applied by
rupturing a pod 16 and distributing the processing composition
between a cover or spreader sheet 64 and silver halide emulsion
layer 14. The cover sheet 64 may be transparent as illustrated in
FIG. 2 and described in detail in the above noted U.S. Pat. No.
3,594,165, in which event photoexposure may be effected through it
while it is held in place, e.g., by a binder tape around the edges
of the film unit or by temporary lamination prior to photoexposure,
as discussed above. In this embodiment, an anti-reflection coating
26 is provided on the outer or exposure surface of the transparent
cover sheet 64. (Alternatively, cover sheet 64 may be opaque in
which event it is positioned out of the exposure path prior to
photoexposure, as described in detail in the above noted U.S. Pat.
No. 3,594,164.) The opaque processing composition 17 contains
suitable opacifying agents, e.g., carbon black, titanium dioxide,
etc. The light-reflecting layer 60 preferably includes a white
pigment, such as titanium dioxide, to provide a white background
against which the transfer image may be viewed. The opaque layer
62, e.g., a layer of carbon black in gelatin, provides the
requisite light protection while assuring an aesthically pleasing
white background for the final image.
Processing of film units of the types described above is initiated
by distributing the processing composition between predetermined
layers of the film unit. In exposed and developed areas, the dye
developer will be immobilized as a function of development. In
unexposed and undeveloped areas, the dye developer is unreacted and
diffusible, and this provides an imagewise distribution of
unoxidized dye developer, diffusible in the processing composition,
as a function of the point-to-point degree of exposure of the
silver halide layer. The desired transfer image is obtained by the
diffusion transfer to the image-receiving layer of at least part of
this imagewise distribution of unoxidized dye developer. In the
illustrated embodiments, the pH of the photographic system is
controlled and reduced by the neutralization of alkali after a
predetermined interval, in accordance with the teachings of the
above noted U.S. Pat. No. 3,615,644, to reduce the alkalinity to a
pH at which the unoxidized dye developer is substantially insoluble
and non-diffusible. As will be readily recognized, the details of
such processes form no part of the present invention but are well
known; the previously noted U.S. patents may be referred to for
more specific discussion of such processes.
The film units illustrated in FIGS. 1, 2, and 3 have, for
convenience, been shown as monochrome films. Multicolor images may
be obtained by providing the requisite number of differentially
exposable silver halide emulsions, and said silver halide emulsions
are most commonly provided as individual layers coated in
superposed relationship. Film units intended to provide multicolor
images comprise two or more selectively sensitized silver halide
layers each having associated therewith an appropriate image
dye-providing material providing an image dye having spectral
absorption characteristics substantially complementary to the light
by which the associated silver halide is exposed. The most commonly
employed negative components for forming multicolor images are of
the "tripack" structure and contain blue-, green-, and
red-sensitive silver halide layers each having associated therewith
in the same or in a contiguous layer a yellow, a magenta and a cyan
image dye-providing material respectively. Interlayers or spacer
layers may, if desired, be provided between the respective silver
halide layers and associated image dye-providing materials or
between other layers. Integral multicolor photosensitive elements
of this general type are disclosed in U.S. Pat. No. 3,345,163
issued Oct. 3, 1967 to Edwin H. Land and Howard G. Rogers as well
as in the previously noted U.S. Patents.
A number of modifications to the structures described in connection
with the figures will readily suggest themselves to one skilled in
the art. Thus, for example, the multicolor multilayer negative may
be replaced by a screen-type negative as illustrated in U.S. Pat.
No. 2,968,554 issued Jan. 17, 1961 to Edwin H. Land and in the
aforementioned U.S. Pat. No. 2,983,606 particularly with respect to
FIG. 9 thereof.
The image dye-providing materials which may be employed in such
processes generally may be characterized as either (1) initially
soluble or diffusible in the processing composition but are
selectively rendered non-diffusible in an imagewise pattern as a
function of development; or (2) initially insoluble or
non-diffusible in the processing composition but which are
selectively rendered diffusible or provide a diffusible product in
an imagewise pattern as a function of development. These materials
may be complete dyes or dye intermediates, e.g., color couplers.
The requisite differential in mobility or solubility may, for
example, be obtained by a chemical action such as a redox reaction
or a coupling reaction.
As examples of initially soluble or diffusible materials and their
application in color diffusion transfer, mention may be made of
those disclosed, for example, in U.S. Pat. Nos. 2,774,668;
2,968,554; 2,983,606; 2,087,817; 3,185,567; 3,230,082; 3,345,163;
and 3,443,943. As examples of initially non-diffusible materials
and their use in color transfer systems, mention may be made of the
materials and systems disclosed in U.S. Pat. Nos. 3,185,567;
3,443,939; 3,443,940; 3,227,550; and 3,227,552. Both types of image
dye-providing substances and film units useful therewith also are
discussed in the aforementioned U.S. Pat. No. 3,647,437 to which
reference may be made.
It will be understood that dye transfer images which are neutral or
black-and-white instead of monochrome or multicolor may be obtained
by use of a single dye or a mixture of dyes of the appropriate
colors in proper proportions, the transfer of which may be
controlled by a single layer of silver halide, in accordance with
known techniques. It is also to be understood that "direct
positive" silver halide emulsions may also be used, depending upon
the particular image dye-providing substances employed and whether
a positive or negative color transfer image is desired.
It will also be understood that the present invention may be
utilized with films wherein the final image is in silver, and
photoexposure and/or viewing is effected through a transparent
support which may be provided with an anti-reflection coating in
accordance with the teachings of this disclosure. Indeed, the
transfer of silver may be utilized to provide a silver image or to
provide a dye image by silver dye bleach processing.
In the preferred embodiments, the layers comprising the individual
film units are secured in fixed relationship prior to, during, and
after photoexposure and processing to provide the desired integral
negative-positive image. Film units of this type are well known in
the art and are illustrated, for example, in the above cited U.S.
Pat. Nos. 3,415,644; 3,467,437; and 3,594,165, as well as in other
patents. In general, a binding member is provided extending around,
for example, the edges of the composite structure and securing the
elements thereof in fixed relationship. The binding member may
comprise a pressure-sensitive tape securing and/or maintaining the
layers of the structure together at its respective edges. If the
edge tapes are also opaque, edge leakage of actinic radiation
incident on the film unit will be prevented. The edge tapes also
will act to prevent leakage of the processing composition from the
laminate during and after processing. The rupturable pod is so
positioned as to discharge its contents between predetermined
layers; e.g., between the image-receiving layer 18 and the silver
halide emulsion layer 14 of FIG. 1; these layers may be temporarily
bonded to each other with a bond strength less than that exhibited
by the interface between the opposed surfaces of the remaining
layers, as described above. The binding member may also serve to
provide a white mask or border for the final image. The manufacture
of such film units or packets is well described in the above-noted
and other patents and need not be set forth in any detail here.
Rupturable container 16 may be of the type shown and described in
any of U.S. Pat. Nos. 2,543,181; 2,634,886; 3,653,732; 2,723,051;
3,056,492; 3,056,491; 3,152,515; and the like. In general, such
containers will comprise a rectangular blank of fluid- and
air-impervious sheet material folded longitudinally upon itself to
form two walls which are sealed to one another along their
longitudinal and end margins to form a cavity in which processing
composition 17 is retained. The longitudinal marginal seal is made
weaker than the end seals so as to become unsealed in response to
the hydraulic pressure generated within the fluid contents 17 of
the container by the application of compressive pressure to the
walls of the container, e.g., by passing the film unit between
opposed pressure applying rollers.
The rupturable container 16 is so positioned as to effect
unidirectional discharge of the processing composition 17 between
predetermined layers, e.g., the image-receiving layer 18 and the
silver halide layer 14 next adjacent thereto, upon application of
compressive force to the rupturable container 16. Thus, the
rupturable container 16, as illustrated in FIG. 1, is fixedly
positioned and extends transverse a leading edge of the
prelaminated film unit with its longitudinal marginal seal directed
toward the interface between the image-receiving layer 18 and the
silver halide emulsion layer 14. The rupturable container 16 is
fixedly secured to this laminate by a tape extending over a portion
of one wall of the container, in combination with a separate
retaining member or tape extending over a portion of the laminate's
surface generally equal in area to about that covered by said
tape.
A preferred opacification system to be contained in the processing
composition 17 to effect processing outside of a camera is that
described in the above-mentioned U.S. Pat. No. 3,647,437, and
comprises a dispersion of an inorganic light-reflecting pigment
which also contains at least one light-absorbing agent, i.e.,
optical filter agent, at a pH above the pKa of the optical filter
agent in a concentration effective when the processing composition
is applied, to provide a layer exhibiting optical transmission
density > than about 6.0 density units with respect to incident
radiation actinic to the photosensitive silver halide and optical
reflection density < than about 1.0 density units with respect
to incident visible radiation.
In lieu of having the light-reflecting pigment in the processing
composition, the light-reflecting pigment used to mask the
photosensitive strata and to provide the background for viewing the
color transfer image formed in the receiving layer may be present
initially in whole or in part as a preformed layer in the film
unit. As an example of such a preformed layer, mention may be made
of that disclosed in U.S. Pat. No. 3,615,421 issued Oct. 26, 1971
and in U.S. Pat. No. 3,620,724 issued Nov. 16, 1971, both in the
name of Edwin H. Land. The reflecting agent may be generated in
situ as is disclosed in U.S. Pat. Nos. 3,647,434 and 3,647,435,
both issued Mar. 7, 1972 to Edwin H. Land.
The dye developers (or other image dye-providing substances) are
preferably selected for their ability to provide colors that are
useful in carrying out subtractive color photography, that is, the
previously mentioned cyan, magenta and yellow. They may be
incorporated in the respective silver halide emulsion or, in the
preferred embodiment, in a separate layer behind the respective
silver halide emulsion. Thus a dye developer may, for example, be
in a coating or layer behind the respective silver halide emulsion
and such a layer of dye developer may be applied by use of a
coating solution containing the respective dye developer
distributed, in a concentration calculated to give the desired
coverage of dye developer per unit area, in a film-forming natural,
or synthetic, polymer, for example, gelatin, polyvinyl alcohol, and
the like, adapted to be permeated by the processing
composition.
Dye developers, as noted above, are compounds which contain the
chromophoric system of a dye and also a silver halide developing
function. By "a silver halide developing function" is meant a
grouping adapted to develop exposed silver halide. A preferred
silver halide development function is a hydroquinonyl group. Other
suitable developing functions include ortho-dihydroxyphenyl and
ortho- and para-amino substituted hydroxyphenyl groups. In general,
the development function includes a benzenoid developing function,
that is, an aromatic developing group which forms quinonoid or
quinone substances when oxidized.
The image-receiving layer may comprise one of the materials known
in the art, such as polyvinyl alcohol, gelatin, etc. It may contain
agents adapted to mordant or otherwise fix the transferred images
dye(s). Preferred materials comprise polyvinyl alcohol or gelatin
containing a dye mordant such as poly-4-vinylpyridine, as disclosed
in U.S. Pat. No. 3,148,061, issued Sept. 8, 1964 to Howard C.
Haas.
In the various color diffusion transfer systems which have
previously been described, and which employ an aqueous alkaline
processing fluid, it is well known to employ an acid-reacting
reagent in a layer of the film unit to lower the environmental pH
following substantial dye transfer in order to increase the image
stability and/or to adjust the pH from the first pH at which the
image dyes are diffusible to a second (lower) pH at which they are
not. For example, the previously mentioned U.S. Pat. No. 3,415,644
discloses systems wherein the desired pH reduction may be effected
by providing a polymeric acid layer adjacent the dyeable stratum.
These polymeric acids may be polymers which contain acid groups,
e.g., carboxylic acid and sulfonic acid groups, which are capable
of forming salts with alkali metals or with organic bases; or
potentially acid-yielding groups such as anhydrides or lactones.
Preferably the acid polymer contains free carboxyl groups.
Alternatively, the acid-reflecting reagent may be in a layer
adjacent to the silver halide most distant from the image-receiving
layer, as disclosed in U.S. Pat. No. 3,573,043 issued Mar. 30, 1971
to Edwin H. Land. Another system for providing an acid-reacting
reagent is disclosed in U.S. Pat. No. 3,576,625 issued Apr. 27,
1971 to Edwin H. Land.
An inert interlayer or spacer layer may be and is preferably
disposed between the polymeric acid layer and the dyeable stratum
in order to control or "time" the pH reduction so that it is not
premature and interferes with the development process. Suitable
spacer or "timing" layers for this purpose are described with
particularity in U.S. Pat. Nos. 3,362,819; 3,419,389; 3,421,893;
3,455,686; and 3,575,701.
While the acid layer and associated spacer layer are preferably
contained in the positive component employed in systems wherein the
dyeable stratum and photosensitive strata are contained on separate
supports, e.g., between the support for the receiving element and
the dyeable stratum; or associated with the dyeable stratum in
those integral film units, e.g., on the side of the dyeable stratum
opposed from the negative components, they may, if desired, be
associated with the photosensitive strata, as is disclosed, for
example, in U.S. Pat. Nos. 3,362,821 and 3,573,043. In film units
such as those described in the aforementioned U.S. Pat. Nos.
3,594,164 and 3,594,165, they also may be contained on the spreader
sheet employed to facilitate application of the processing
fluid.
As is now well known and illustrated, for example, in the
previously cited patents, the liquid processing composition
referred to for effecting multicolor diffusion transfer processes
comprises at least an aqueous solution of an alkaline material, for
example sodium hydroxide, potassium hydroxide, and the like, and
preferably possessing a pH in excess of 12, and most preferably
includes a viscosity-increasing compound constituting a
film-forming material of the type which, when the composition is
spread and dried, forms a relatively firm and relatively stable
film. The preferred film-forming materials disclosed comprise high
molecular weight polymers such as polymeric, water-soluble ethers
which are inert to an alkaline solution such as, for example, a
hydroxyethyl cellulose or sodium carboxymethyl cellulose.
Additionally, film-forming materials or thickening agents whose
ability to increase viscosity is substantially unaffected if left
in solution for a long period of time are so disclosed to be
capable of utilization. As stated, the film-forming material is
preferably contained in the processing composition in such suitable
quantities as to impart to the composition a viscosity in excess of
100 cps, at a temperature of approximately 24.degree. C. and
preferably in the order of 100,000 cps. to 200,000 cps. at that
temperature.
In particularly useful embodiments of this invention, the
transparent support contains a small quantity of a pigment, e.g.,
carbon black, to prevent fog formation due to light-piping by
internal reflection within the transparent support of actinic light
incident upon an edge thereof; such elements are described and
claimed in the copending application of Edwin H. Land Ser. No.
194,407 filed Nov. 1, 1971. Similarly, fog from such light-piping
may be avoided by incorporating an alkali-dischargeable dye in a
suitable layer, e.g., the image-receiving layer, in accordance with
the disclosure of the copending application of Howard G. Rogers,
Ser. No. 194,406 filed Nov. 1, 1971.
The above discussion of anti-reflection coatings has been in terms
of coatings a quarter wavelength thick. It should be understood
that coatings having a thickness equal to an odd multiple of a
quarter wavelength also will provide anti-reflection properties,
but the minimum thickness of one-quarter wavelength is preferred.
Generally speaking, the anti-reflection coating will have an
optical thickness in the range of from about 0.08 to about 0.2
micron and more preferably from about 0.12 to about 0.15 micron, or
a preferred physical thickness of about 0.09 to about 0.11
micron.
In the above discussion and in the drawings, the anti-reflection
properties have been imparted by a separate coating. The invention
is not limited to the use of separate coatings, but contemplates
the conversion of a thin surface portion of the transparent support
itself to a material having a desired lower index of refraction.
One such technique is to fluorinate the "outer" surface of a
polyethylene terephthalate film base to a depth of a quarter wave,
the resulting stratum of fluorinated polyester exhibiting a lower
index of refraction. Since the fluorinated surface stratum is
integral with the film base, problems of adhesion, such as may be
present with separate coatings, are reduced if not eliminated.
Accordingly, it will be understood that reference herein to an
"anti-reflection coating" or "anti-reflection layer" are intended
to include separately applied coatings or layers as well as strata
obtained by treatment of a transparent element to provide a surface
stratum having the requisite lower index of refraction.
Many materials suitable for use as anti-reflection coatings are
known in the art, and such materials may be used in the practice of
the present invention. It is only necessary that such materials be
compatible with and exhibit sufficient adhesion to the transparent
support to withstand the anticipated handling of the film unit, and
this may be determined by routine testings. While it is generally
desirable to provide the anti-reflection coating as part of the
transparent support prior to applying the photographically used
layers and subsequent assembly of the film unit, it is within the
scope of this invention to apply the anti-reflection coating at any
stage of the manufacture process that is best suited for the
particular materials and components, including applying the
anti-reflection coating after final assembly of the individual film
unit.
As discussed above, the anti-reflection coating or stratum should
comprise a material having an index of refraction less than that of
the transparent support. The optimum index of refraction to be
exhibited by the anti-reflection coating may be readily calculated
by the principles of physics previously discussed, but it is not
essential that such optimum value be used in order to obtain very
beneficial results. In the preferred embodiments of this invention,
the transparent support is formed of a polymer having a high index
of refraction, e.g., of about 1.6 or higher. The anti-reflection
coating preferably has an index of refraction at least 0.20 less
than, and more preferably at least 0.35 to 0.3 less than, the index
of refraction of the transparent support. Since the preferred
transparent supports will have an index of refraction of about 1.6
or higher, the preferred anti-reflection coatings will exhibit an
index of refraction of about 1.3 to 1.4.
As noted above, particularly useful materials for anti-reflection
coatings are fluorinated polymers. Examples of such fluorinated
polymers include perfluorinated polyolefins having an index of
refraction of about 1.35 to about 1.45, e.g.,
polytetrafluoethylene, such disclosed in U.S. Pat. No. 3,617,354.
As pointed out in said patent, such anti-reflection coatings may be
applied by coating from a solvent, by vacuum deposition of the
polymer, by polymerization in place of the corresponding monomer,
etc.
Other fluorinated polymers which provide anti-reflection coatings
include poly-(1,1-dihydropentadecafluorooctyl acrylate) with an
index of refraction of about 1.38; poly -
(1,1-dihydropentadecafluro-octyl methacrylate) with an index of
refraction of about 1.38; and ##SPC1##
wherein R is perfluoro-cyclohexyl (-C.sub.6 F.sub.11).
Inorganic materials such as vacuum deposisited magnesium fluoride
(index of refraction about 1.38) may also be used. Various
silicates [index of refraction about 1.41]) may also be used and
may be particularly useful for the relative hardness of the
resulting anti-reflection coating.
By way of illustration, an integral negative-positive multicolor
reflection print was prepared in accordance with the procedure
described in Example 2 of the copending application of Edwin H.
Land, Stanley M. Bloom, and Howard G. Rogers, Ser. No. 246,669
filed Apr. 24, 1972 The general format of the integral
negative-positive reflection print was similar to that shown in
FIG. 1 of the above-mentioned U.S. Pat. No. 3,415,644. The
transparent support through which photoexposure was effected and
through which the multicolor transfer image was viewed was a
transparent polyethylene terephthalate film base containing a small
quantity of carbon black to prevent light-piping by internal
reflection, as described and claimed in the above-mentioned
application of Edwin H. Land, Ser. No. 194,407 filed Nov. 1, 1971.
A coating solution was prepared by dissolving 0.8 g. of poly -
(1,1-dihydropentadecafluorooctyl methacrylate) and 2.0 cc. of
methyl cellosolve in 40 cc. of 1.4 - di- (trifluoromethyl)-
benzene. The print was placed on a rotating turntable and a small
quantity of the above coating solution was centrally placed on the
outer surface of the polyethylene terephthalate film base. The
continual rotation of the print on the turntable was effective to
cause the coating solution to spread substantially uniformly over
the outer surface of the polyethylene terephthalate film base.
(This coating technique is sometimes referred to as "spin coating,"
and is particularly suited for applying substantially uniform
coatings using extremely small quantities of coating solution. The
thickness of the coating may be controlled by the viscosity of the
coating solution and the speed of the turntable.) The resulting
layer of fluorinated polymer was an effective anti-reflection
coating and adhered well to the polyethylene terephthalate unless
roughly handled. The sharply reduced surface reflection, while not
complete, greatly increased the angle through which the print could
be viewed without disturbing glare as compared with a print which
did not have such an anti-reflection coating. The difference in
viewing ease and image quality was almost what one would have
expected if one were not viewing through a sheet of polyethylene
terephthalate. In addition, it was observed that the
anti-reflection coating was effective to reduce the minimum
reflection densities of the print as measured on an integral
densitometer, and this result was confirmed on a second print
prepared and coated in the same manner:
Reflection Density ______________________________________ Red Green
Blue Print No. 1: Before Coating 0.17 0.17 0.19 After Coating 0.13
0.14 0.17 Print No. 2: Before Coating 0.18 0.20 0.20 After Coating
0.15 0.17 0.18
A third test print was processed in the same manner, but without
first being photoexposed, to give a "black spread," i.e., an
integral negative positive reflection print which appeared to be
uniformly black and obtained by maximum overall transfer of all
three dye developers. The outer surface of the polyethylene
terephthalate transparent support of this "black spread" was spin
coated with poly- (1,1-dihydropentadecafluoro-octyl methacrylate in
the manner just described to provide an anti-reflection coating.
The reflection densities of this print, before and after coating,
as measured on an integral densitometer were:
Reflection Density ______________________________________ Red Green
Blue Print No. 3: Before Coating 2.18 2.27 2.14 After Coating 2.31
2.41 2.21
It will therefore be seen that application of an anti-reflection
coating has increased the visual maximum density and decreased the
visual minimum density.
Other solvents found useful in coating such fluorinated polymers
include Freon TF, trifluorobenzene and hexafluoro paraxylene. In
general, it has been found useful to use coating solutions
containing about 2 percent by weight of the polymer. It will be
recognized by those skilled in the art that the solvent of choice
for a particular polymer, and the concentration of the polymer in
the coating solution, may be readily determined by routine
experimentation. Obviously the solvent should be one which will not
adversely affect, mechanically or optically, the transparent
support upon which it is coated.
The transparent support advantageously has a moisture permeability
rate adapted to accelerate "drying" of the layers forming the
integral negative-positive reflection prints of the preferred
embodiments. Reference may be made to U.S. Pat. No. 3,573,044
issued Mar. 30, 1971 to Edwin H. Land for a detailed description of
dimensionally stable, transparent supports, e.g., microporous
polyesters, having suitable permeability rates, and said
description is hereby incorporated herein for convenience. It will
be understood that selection of an anti-reflection coating should
not adversely affect the desired moisture transmission rate of the
transparent support(s).
While the image dye-providing material is generally carried on the
same support as the photosensitive silver halide, it will be
understood that this initial location is not essential, as in
forming monochromes the image dye-providing material may initially
be contained in the processing composition or in a layer of the
image-receiving element as is taught, for example, in the use of
dye developers in the previously mentioned U.S. Pat. No.
2,983,606.
The provision of an anti-reflection coating provides a number of
advantages. In the absence of the anti-reflection coating provided
in accordance with this invention, the optimum angle for viewing an
image through the transparent support is very specific and limited,
if the viewer is to avoid to the maximum possible extent seeing
specular reflection from the surface of the transparent support of
light from the illumination source. The anti-reflection coating has
been found to substantially reduce or prevent such specular
reflection, thus greatly improving viewing. The resulting images
exhibit, as shown above, increased color saturation and density and
"cleaner" whites, i.e., reduced minimum densities. The avoidance of
light loss during photoexposure is useful also in films wherein
exposure is effected through a transparent support but the final
image is separated and not viewed through a transparent support.
The reduction in surface reflection (glare) simplifies copying
integral negative-positive reflection prints of the type with which
this invention is primarily concerned and aids in obtaining truer
copy prints; light polarizers are customarily used to eliminate
surface glare during copying. The anti-reflection coating may also
provide anti-abrasion protection and, depending upon the polymer or
other material used, desirable anti-friction properties to
facilitate transport during manufacture and/or processing.
It is recognized that anti-reflection coatings have been used on
photographic prints previously, e.g., U.S. Pat. No. 3,617,354
referred to above proposes to apply a layer of a polymerized
perfluorinated olefin over the image-bearing photographic emulsion
layer of a photographic print. The "photographic emulsion layer"
referred to is customarily gelatin, and that patent acknowledges
that only limited reduction of surface reflection is possible
because such perfluorinated polyolefins do not have indices of
refraction low enough to equal the ideal low index of about 1.23
required in view of gelatin's typical index of about 1.5. In
contrast, the preferred and most useful embodiments of the present
invention apply the anti-reflection coating to a polymeric layer
having a much higher index of refraction; the seeming disadvantage
of such high indices of refraction as about 1.66 for a polyester
transparent layer thus becomes a distinct advantage as the
resulting "ideal" index of refraction for an anti-reflection
coating becomes more practical to provide. For this reason, an
anti-reflection coating of a given "low" index of refraction will
provide a greater reduction in glare and surface reflection from a
high index polyester than from a lower index polymer such as
cellulose acetate. (It will be understood, however, that the
present invention expressly includes the use of cellulose acetate
as well as polyester and other high index transparent films.)
Furthermore, the teachings of the prior art as illustrated by said
U.S. Pat. No. 3,617,354 require that the anti-reflection coating be
applied after the final image is formed, to avoid interference with
processing solutions or chemicals, e.g., by virtue of
impermeability or low permeability to aqueous solutions as would be
true of perfluorinated polyolefin coatings. Other efforts to
provide anti-reflection coatings by aftertreatment have resulted in
coatings which reduce glare but also reduce density by virtue of a
coating which is not optically continuous and/or not optically
clear.
Where the expression "positive image" has been used, this
expression should not be interpreted in a restrictive sense since
it is used primarily for purposes of illustration, in that it
defines the image produced on the image-carrying layer as being
reversed, in the positive-negative sense, with respect to the image
in the photosensitive emulsion layers. As an example of an
alternative meaning for "positive image," assume that the
photosensitive element is exposed to actinic light through a
negative transparency. In this case, the latent image in the
photosensitive emulsion layers will be a positive and the dye image
produced on the image-carrying layer will be a negative. The
expression "positive image" is intended to cover such an image
produced on the image-carrying layer.
Since certain changes may be made in the above product and process
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.
* * * * *