Resin blends for improved vesicular systems

A vesicular photographic material comprising a polymeric matrix containing a sensitizer which liberates gas when exposed to light, and a process for manufacture of said material. The polymeric matrix comprises a blend of polymethacrylonitrile homopolymer with another resin selected from the group consisting of vinyl polymers and copolymers; epoxy polymers; and copolymers with polyurethane segments. Improved photometrics, particularly film speed, are realized.

BACKGROND OF THE INVENTION 
The present invention is directed to the photographic arts, and more 
particularly to that field of photography concerned with vesicular 
photographic materials. Most specifically, the instant invention provides 
a vesicular photographic material comprising a sensitizer suspended in a 
resin blend of polymethacrylonitrile and at least one other polymeric 
material applied to a suitable base, as well as a method for its 
manufacture. 
As is well known in the arts, a photographic material for the preparation 
of vesicular images generally comprises a thermoplastic resin vehicle in 
which is dispersed a photosensitive compound (a "sensitizer") which is 
capable of decomposing to yield a gas when exposed to radiation of 
appropriate ("actinic") wave lengths. This mixture is usually coated on a 
suitable support, which can be transparent or opaque, so as to form a 
photographic material as conventionally defined in the art. Upon imagewise 
exposure to actinic radiation, e.g. through a superimposed transparency 
which is desired to be copied, the photosensitive compound dispersed 
within the vehicle is decomposed in the pattern of the imagewise exposure. 
Development is accomplished by heating the material to at least the glass 
transition temperature of the thermoplastic resin vehicle, whereby it is 
softened sufficiently to allow the photolytically generated gas 
constrained therein to distend the softened vehicle with the resultant 
formation of bubbles or vesicles therein. These vesicles are trapped when 
the material is cooled. They are arranged in a pattern corresponding to 
the original design copied, and they serve to reflect and refract light, 
thereby giving rise to a visible image under suitable viewing conditions, 
similar in appearance to that obtainable by better known photographic 
processes, e.g., the silver halide process and the like. 
Early inventions concerning vesicular photographic materials, for example, 
as disclosed in British Pat. spec. No. 402,737, were directed to the use 
of naturally derived gelatin as the thermoplastic resin vehicle. It 
subsequently proved impossible, however, to base a practical commercial 
embodiment on gelatin because of its moisture sensitivity and its 
inadequate mechanical durability, among other disadvantages for many 
commercial applications. 
In light of the above limitations, the thrust in the art was directed to 
vesicular materials employing a hydrophobic polymer as the thermoplastic 
vehicle. The lack of mechanical integrity inherent in a hydrophylic 
gelatin medium was first successfully overcome by the system disclosed by 
James et al in U.S. Pat. No. 3,032,414, which teaches the use of certain 
classes of synthetic, water insoluble, non-hydroscopic, non-water swelling 
thermoplastic polymers as the thermoplastic resin vehicle. Vesicular 
photographic materials prepared in accord with that method, as well as the 
many subsequent improvements which followed the original teachings of 
James et al, are characterized by excellent physical and mechanical 
properties. 
In light of the James et al teachings, subsequent efforts in the art have 
been directed toward improving the photographic sensitivity of the 
material by selection of other thermoplastic polymers for the hydrophobic 
resin vehicle. In particular, Parker et al in U.S. Pat. No. 3,161,511 
disclose the use of polymethacrylonitrile as the resin vehicle for 
vesicular photographic materials. This polymer has proven extremely unique 
in the art, particularly by providing vesicular materials of relatively 
high photographic sensitivity. Its practical use for many applications, 
however, is hampered by several undesirable phyical properties. For one, 
it shows a tendency to craze or crack, and second, it adheres only with 
difficulty to the more commonly used photographic substrates. Subsequent 
to the teachings of Parker et al, improvements in the art have been 
directed to combining the high speed characteristics of 
polymethacrylonitrile with other resinous materials which do not exhibit 
the aforementioned physical limitations of polymethacrylonitrile. 
More recent attempts in the art have been directed to the development of 
copolymeric systems incorporating various monomeric materials which are 
compatible with and copolymerisable with methacrylonitrile, for example, 
as disclosed in U.S. Pat. No. 3,622,336. While such vesicular materials 
exhibit improved physical properties in comparison to the 
methacrylonitrile homopolymer, the resulting copolymeric materials do not 
demonstrate the highly efficient gas utilization of the methacrylonitrile 
homopolymer. Another distinct problem with some of these copolymeric 
systems is their relative incompatibility with methacrylonitrile 
homopolymer. This art recognized incompatibility of methacrylonitrile 
homopolymer and mixtures with other resins known to be useful in the 
preparation of vesicular films as discussed at length in U.S. Pat. No. 
3,661,589 to Notley. However, it has been found that interfacial prints 
prepared in accord with the Notley disclosure exhibit an objectionably 
high optical haze level, suggested by Notley as being due to the 
moderating influence of domains of a second resinous phase and do not 
approach the sensitivity levels of films prepared from pure 
methacrylonitrile homopolymer. These and other problems are overcome by 
the present invention which provides a vesicular photographic material 
whose vehicle is a methacrylonitrile homopolymer homogeneously blended 
with other resins to form a single phase. A number of these other resins, 
prior to the present invention, have been thought to be incompatible with 
polymers of methacrylonitrile. 
SUMMARY OF THE INVENTION 
The present invention comprises both a light-sensitive vesicular material 
and a process for its manufacture having a homogeneously blended polymeric 
matrix wherein a light-sensitive compound is dispersed. The matrix 
comprises a blend of polymethacrylonitrile homopolymer with another resin 
selected from the group consisting of vinyl polymers and copolymers; epoxy 
polymers; and copolymers with polyurethane segments. Vinyl polymers and 
copolymers are further defined as being selected from a group consisting 
of (a) polymers of vinyl chloride; polymers of vinylidene chloride; and 
their respective copolymers; (b) polymers of acrylonitrile; polymers of 
substituted acrylonitrile; and their respective copolymers; (c) polymers 
of styrene; polymers of substituted styrene; and their respective 
copolymers; and (d) polymers of vinyl alcohol derivatives and copolymers 
thereof. Polymeric blends of polymethacrylonitrile with a copolymer of 
vinylidene chloride and acrylonitrile are especially preferred. Also 
preferred are blends of polymethacrylonitrile and a copolymer of 
.alpha.-chloroacrylonitrile and methacrylonitrile. 
Among the advantages and features of the present invention is the fact 
that, contrary to the assumption of the prior art, compatible mixtures 
incorporating the methacrylonitrile homopolymer as a modifier to the 
second polymeric resin can be achieved with common solvents. In this 
respect, compatibility is defined as the ability of the blend to form a 
clear, as distinguished from a hazy, film when a film is formed by 
evaporation of the solvent or mixture of solvents, from a solution of the 
film. 
These compatible mixes form vesicular photographic materials having a 
single phase polymeric vehicle which possess photographic responses which 
are comparable to those found in pure polymethacrylonitrile film, even in 
embodiments in which the polymethacrylonitrile is present to an extent of 
less than 50%. Further, the blended photographic vehicles of the present 
invention exhibit the excellent craze resistant and adhesion 
characteristics of the preferred second polymers. Due presumably to the 
degree of homogeneity and lack of phase separation within the blended 
resinous vehicle, images resulting from the practice of the present 
invention show improved resolution of pictorial detail and a low level of 
background haze, as well as improved film speed and other enhanced 
photometrics. These and other features and advantages of the present 
invention will be evident from the following detailed description. 
DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The present invention provides both a light-sensitive vesicular material 
and a process for its manufacture wherein the polymeric matrix of the 
material comprises a blend of polymethacrylonitrile homopolymer with 
another resin selected from the group consisting of vinyl polymers and 
copolymers; epoxy polymers; and copolymers with polyurethane segments. 
Within the polymeric vehicle is dispersed a photosensitive compound 
capable of decomposing to yield a gas upon exposure to actinic radiation. 
Pursuant to the process of the present invention, vesicular images are 
formed in the polymeric matrix by exposing the vesicular material to light 
to decompose the photosensitive compound which thereby forms a gas, 
followed by heating of the material to develop a vesicular image therein 
consisting of minute bubbles or vesicles. 
Various homopolymers of methacrylonitrile may be used. However, it is 
preferable to use lower molecular weight polymers because they are 
compatible with the other polymers over a wider range of proportions. Thus 
it is preferred that the molecular weight of the methacrylonitrile is less 
than about 500,000. By gel permeation chromatography, particularly useful 
polymers have a weight average size of 1440 to 2450. 
Vinyl polymers and copolymers thereof are especially preferred for use as 
the second component of the blends of the instant invention, particularly 
vinylidene chloride-acrylonitrile copolymers, especially those vinylidene 
chloride-acrylonitrile copolymers having between about 60 to about 90% by 
weight vinylidene chloride present, the balance consisting of 
acrylonitrile and other constituents normally present in a commercial 
preparation. These polymers are preferred for use in the instant invention 
because they are not only readily available and hence offer economic 
advantage but additionally exhibit physical properties whereby the 
distinct advantages of the present invention are maximized, especially 
with regard to an improvement in speed achieved by those vesicular 
materials in comparison with polymethacrylonitrile homopolymer vesicular 
material. As brought out above, the latter polymers are blended with 
polymethacrylonitrile in the present system and which is preferably 
present within about 10 to 40% by weight. 
Another particularly preferred embodiment of the instant invention is a 
vesicular material comprising from about 50 to about 70% by weight 
methacrylonitrile and the balance, excluding normal impurities and 
additives, of a copolymer of from about 30 to about 50% by weight 
chloroacrylonitrile and the balance methacrylonitrile. It has been found 
that these polymeric materials also produce an enhanced vesicular medium 
prepared by way of the present invention. 
As brought out above, vinyl polymers and copolymers thereof are especially 
preferred resins for use as the polymeric matrix of the present vesicular 
photographic films. Among the vinyl polymers and their copolymers are the 
polymers of vinyl chloride and vinylidene chloride and their respective 
copolymers, e.g., vinylidene chloride-acrylonitrile copolymers; poly vinyl 
chlorides; vinyl chloride-vinylidene chloride copolymers; vinyl 
chloride-vinyl acetate copolymer; vinyl chloride-vinyl alcohol copolymers; 
vinylidene chloride-methylacrylonitrile copolymers; and vinylidene 
chloride-methyl methacrylate copolymers. 
By vinyl polymers and their copolymers is also meant polymers of 
acrylonitrile and substituted acrylonitriles, such as methylacrylonitrile 
and .alpha.-chloroacrylonitrile and their respective copolymers, exemplary 
of which are acrylonitrilemethyl acrylate copolymers; poly 
.alpha.-chloroacrylonitrile; 
methylacrylonitrile-.alpha.-chloroacrylonitrile copolymers; 
acrylonitrile-ethylacrylate copolymers; methylacrylonitrile-itaconic acid 
copolymers; methylacrylonitrile-diallyl maleate; and 
methylacrylonitrile-methacrylic acid. 
The vinyl polymers and their copolymers also include polymers of styrene 
and substituted styrene such as .alpha.-methylstyrene and vinyl toluene 
and their respective copolymers, e.g., styrene-acrylonitrile copolymers; 
styrene-maleic anhydride copolymers; styrene-butadiene-acrylonitrile 
terpolymer; and styrene-methacrylonitrile copolymers. 
Also included as vinyl polymers and copolymers are the polymers of vinyl 
alcohol derivatives, such as vinyl ethers, vinyl esters, and vinyl acetals 
and their respective copolymers, for example, poly(methyl vinyl 
ether-maleic anhydride) copolymers; poly(vinyl formals); poly(vinyl 
butyrals); and vinyl alcoholvinyl acetate copolymers. 
Another suitable class of resins for use as the vehicle of the present 
vesicular films are epoxy resins. By epoxy resin is meant any polymeric 
material formed by the polymerization of a monomer having an oxirane ring 
with a monomer having a di-hydroxyl structure. Epoxy resins are generally 
marketed in the form of various combinations of these basic monomers, that 
is, polymers thereof, and in an uncured state. Exemplary of various 
uncured epoxy reins, or monomers, that can be employed as the vehicle in 
the present invention are: diglycidyl isophthalate; diglycidyl phthalate; 
o-glycidyl phenyl glycidyl ether; diglycidyl ether of resorcinol; 
triglycidyl ether of phloroglucinol; triglycidyl ether of methyl 
phloroglucinol; 2,6-phenylglycidyl ether; triglycidyl p-aminophenol; 
diglycidyl ether of bisphenol-A; diglycidyl ether of 
bisphenol-hexafluoroacetone; diglycidyl phenyl ether; diglycidyl ether of 
tetrachlorobisphenol-A; triglycidyl ether of trihydroxybiphenyl; 
tetraglycidyl ether of bisresorcinol-F; tetraglycidoxy tetraphenylethane; 
polyglycidyl ether of phenol-formaldehyde novolac; diglycidyl ether of 
butanediol; triglycidyl ether of glycerol; diglycidyl ether of 
dioxanediol; vinylcyclohexene dioxide; dicycloaliphatic diether diepoxy, 
and the like. 
Another suitable class of polymers for use as a vehicle in the present 
invention are copolymers with polyurethane segments. Such compounds are 
generally defined as those polymers having a segmented or block structure 
comprising segments containing regular repeating groups linked to 
polymeric segments of another type. Copolymers with polyurethane segments 
are generally obtained by reacting a diisocyanate, e.g., 2,4-tolylene 
diisocyanate; 4,4-diphenylmethane diisocyanate; 1,2-ethane diisocyanate; 
and the like, with a combination of hydroxyl containing polymer and low 
molecular weight diol, e.g., ethylene glycol; trimethylene glycol; 
diethylene glycol; and the like. Thus, suitable copolymer systems may 
contain any of the before mentioned polymers, preferably, however, 
methacrylonitrile and copolymers thereof, linked together by polyurethane 
segments as formed in the conventional manner well known in the art. 
In accordance with one aspect of the present invention, it has been found 
that the physical properties of the blends and their adhesion to a 
polyester film base can be improved by blending them with a compatible 
polyester in amount up to about 20%, or a small quantity of an acrylic 
rubber.

EXAMPLES 1-10 
In the following examples, film samples were made by first preparing the 
blended polymeric coating composition as shown in the table below by 
preferably simultaneously dissolving both the polymethacrylonitrile 
homopolymer and the respective second polymer in a solution of the 
solvents shown. However, the polymeric materials can be separately 
dissolved in the solvents shown and thereafter blended by combining the 
separate solutions. The sensitizer was then preferably dissolved in the 
solvent shown and the sensitizer solution thereafter added to the blended 
polymeric solution, with the exception of Example 3 wherein the sensitizer 
salt was added to the blended polymeric solution as a solid. 
The resulting coating composition was then coated onto a 
polyethyleneterephthalate film base with sufficient solution to produce a 
dry thickness of approximately 0.4 mil in the various examples. The 
samples were then dried, that is, the solvents contained therein were 
evaporated, by milding heating at 150.degree. F. for about 5 minutes and 
then cured at 240.degree. F. for about 10 minutes. The films also may be 
treated by the process of U.S. Pat. No. 3,149,971. 
The following table wherein all parts are by weight is a tabulation of the 
various materials employed in making the respective samples pursuant to 
the above procedure. 
__________________________________________________________________________ 
Parts of 
Polymeth- Parts of 
acrylo- 
Other Other 
Resin Sensitizer 
Ex. No. 
nitrile 
Resin Resin 
Solvents*** Solvents*** 
Sensitizer** 
__________________________________________________________________________ 
1 10 vinylidene chloride- 
90 200-methylethyl ketone 
60-acetonitrile 
10 - 2,5-diethoxy- 
acrylonitrile (75/25)* 
100-tetrahydrofuran p-morpholino- 
copolymer 40-1,4 dioxane benzene diazoni- 
20-acetonitrile tetrafluorobora 
40-acetone 
2 20 vinylidene chloride- 
80 100-methylethyl ketone 
50-acetonitrile 
SAME AS EX. NO. 1 
acrylonitrile (80/20)* 
100-tetrahydrofuran 
copolymer 
3 20 vinylidene chloride- 
80 300-methylethyl-ketone 
NONE SAME AS EX. NO. 1 
acrylonitrile (75/25)* 
100-acetonitrile 
copolymer 
4 30 vinylidene chloride- 
80 160-methylethyl ketone 
50-acetonitrile 
SAME AS EX. NO. 1 
acrylonitrile (75/25)* 
100-tetrahydrofuran 
copolymer 40-1,4 dioxane 
30-acetonitrile 
40-acetone 
5 40 vinylidene chloride- 
60 90-methylethyl ketone 
40-methylethyl 
SAME AS EX. NO. 1 
acrylonitrile (75/25)* 
150-tetrahydrofuran 
ketone 
copolymer 80-1,3 dioxolane 
45-methanol 
60-acetonitrile 
6 50 vinylidene chloride- 
50 80-methylethyl ketone 
40-acetonitrile 
SAME AS EX. NO. 1 
acrylonitrile (75/25)* 
80-tetrahydrofuran 
copolymer 20-1,4 dioxane 
40-acetonitrile 
40-acetone 
__________________________________________________________________________ 
*Designates proportions of vinylidene chloride and acrylonitrile 
respectively 
***Numbers give parts by weight of solvent and sensitizer 
Parts of 
Polymeth- Parts of 
acrylo- 
Other Other 
Resin Sensitizer 
Ex. No. 
nitrile 
Resin Resin 
Solvents*** Solvents*** 
Sensitizer*** 
__________________________________________________________________________ 
7 30 .alpha.-chloroacrylonitrile- 
70 250-acetonitrile 
50-acetonitrile 
SAME AS EX. NO. 1 
methacrylonitrile (40/60)** 
50-acetone 
copolymer 25-methylethyl ketone 
8 40 .alpha.-chloroacrylonitrile- 
60 200-acetonitrile 
50-acetonitrile 
SAME AS EX. NO. 1 
methacrylonitrile (40/60)** 
50-acetone 
copolymer 25-methylethyl ketone 
9 50 .alpha.-chloroacrylonitrile- 
50 150-acetonitrile 
50-acetonitrile 
SAME AS EX. NO. 1 
methacrylonitrile (40/60)** 
50-acetone 
copolymer 25-methylethyl ketone 
10 60 .alpha.-chloroacrylonitrile- 
40 120-acetonitrile 
48-acetonitrile 
SAME AS EX. NO. 1 
methacrylonitrile (40/60)** 
48-acetone 24-methanol 
copolymer 48-methylethyl ketone 
11 23 acrylonitrile-methacrylo- 
77 246-acetonitrile 
19-acetonitrile 
SAME AS EX. NO. 1 
nitrile (60/40)** copolymer 19-methanol 
12 50 acrylonitrile-methacrylo- 
50 225-acetonitrile 
100-acetonitrile 
SAME AS EX. NO. 1 
nitrile (60/40)** copolymer 25-methanol 
13 43 hydroxy ethyl methacrylate- 
57 129-acetonitrile 
43-acetonitrile 
14.3 of above 
methacrylonitrile (4/96)**- sensitizer 
polyurethane (70/30)** 
copolymer 
14 51.7 hydroxy ethyl methacrylate 
29.0 168-acetonitrile 
29-acetonitrile 
12.9 of above 
methacrylonitrile (4/96)**- sensitizer 
polyurethane (70/30)** 
copolymer 
poly alpha-chloroacryloni- 
19.3 
trile 
__________________________________________________________________________ 
**Designates proportions of monomers in order listed 
***Numbers listed give parts by weight of solvents and sensitizers 
EXAMPLE 15 
20 parts of polymethacrylonitrile was blended with 80 parts of poly (methyl 
vinyl ether-maleic anhydride copolymer) (Gantrez AN-119-trademark GAF) in 
a solution of 460 parts 1,3-dioxolane. To this solution was added the 
sensitizer solution comprising 10 parts sensitizer of example 1 above 
dissolved in 20 parts acetonitrile and 20 parts methanol. A similar 
enhanced vesicular film was realized. 
EXAMPLE 16 
In this example, 50 parts of polymethacrylonitrile was blended with 50 
parts of poly .alpha.-chloroacrylonitrile in a solution of 460 parts 
acetonitrile. The sensitizer was added in the form of solution comprising 
10 parts of the sensitizer employed in example 1 above first dissolved in 
40 parts acetonitrile. Similar results were obtained. 
EXAMPLE 17 
20 parts of polymethacrylonitrile in this example was blended with 80 parts 
of styrene-maleic anhydride copolymer (SMA-4000 A-trademark Sinclair) in 
440 parts of acetonitrile as the solvent. The sensitizer of example 1 
above is added by dissolving 10 parts thereof and 40 parts of acetonitrile 
and this solution is added to the blended resin solution. A vesicular film 
with similar enhanced photometric properties is realized. 
EXAMPLE 18 
The coating composition in this example was made by blending together 50 
parts polymethacrylonitrile and 50 parts of a diglycidyl ether of 
bisphenol A type epoxy resin, epoxy equivalent weight 4000-6000, Durran's 
m.p. 155.degree.-165.degree. C., made by reaction of epichlorohydrin with 
bisphenol-A, identified as Epon 1010 (trademark-Shell) dissolved in 117 
parts methyl ethyl ketone and 75 parts 1,3 dioxolane. To this is added a 
solution comprising 50 parts methyl ethyl ketone in which 10 parts of the 
sensitizer as employed in examples 1-10 above is dissolved. 
The resulting coating composition is then coated onto a 
polyethyleneterephthalate film base with sufficient solution to produce a 
dry thickness of 0.5 mil. The sample is then dried and cured as described 
in the above examples. Accordingly, similar advantages of a film thus 
produced are realized. 
EXAMPLE 19 
Following the procedure of example 7 above, when a resin blend of 30 parts 
of polymethacrylonitrile and 70 parts of 
.alpha.-chloroacrylonitrile-methacrylonitrile (20/80) copolymer is 
employed, also employing the same sensitizer and solvents, similar results 
are obtained. 
EXAMPLE 20 
Following the procedure of example 8 above, when a resin blend of 40 parts 
of polymethacrylonitrile and 60 parts of 
.alpha.-chloroacrylonitrile-methacrylonitrile (60/40) copolymer is 
employed, also employing the same sensitizer and solvents, similar results 
are obtained. 
EXAMPLE 21 
Following the procedure of example 9 above, when a resin blend of 50 parts 
of polymethacrylonitrile and 50 parts of 
.alpha.-chloroacrylonitrile-methacrylonitrile (80/20) copolymer is 
employed, also employing the same sensitizer and solvents, similar results 
are obtained. 
EXAMPLE 22 
Following the procedure of the above examples, 40 parts of 
polymethacrylonitrile is blended with 60 parts of isobutyl 
acrylate-methacrylonitrile (50/50) in acetonitrile as a common solvent. To 
this solution is added a sensitizer solution comprising 50 parts 
acetonitrile and 10 parts paradimethylaminobenzene diazonium chloride 
(zinc chloride double salt). Similar beneficial results are obtained. 
EXAMPLE 23 
In this example 50 parts of polymethacrylonitrile is blended in acetone 
with 50 parts hexafluoroisopropylacrylatemethacrylonitrile (70/30). 10 
parts of the sensitizer employed in example 22 above is then dissolved in 
acetonitrile and is then added to the blended resin solution. A film of 
enhanced photometric properties is also realized. 
Similar substitution of the various polymeric materials listed above and 
blended with methylacrylonitrile following the procedures of the above 
working examples, also yields films of superior photometric properties. 
Among the advantages and features of the present invention is the 
realization of increased film speed. For example, in comparison of the 
present blended Saran/polymethacrylonitrile films with that of 
polymethacrylonitrile film, a film speed increase of 2/3 rds. of a stop is 
realized as shown in the table below. Similar improvements are realized 
for the other blended films of the present invention. 
______________________________________ 
Saran/polymeth- 
Term Polymethacrylonitrile 
acrylonitrile 
______________________________________ 
Dmax 2.50 2.64 
Dmin 0.17 0.20 
Sn 0.6 speed 
above background 
1.76 1.94 
______________________________________ 
The above data was obtained from projection f/4.5 densitometry. 
It is to be understood that the various physical characteristics of the 
polymeric materials employed in the present blended vesicular film system 
can be varied as desired by the addition of modifiers. Moreover, various 
materials can be added for the preservation of the sensitizer compound 
employed, e.g., various acids as taught in the art. Moreover, other 
materials, such as dyes and other compounds, can be added to improve the 
photometrics of a particular film without departing from the true scope 
and spirit of the present invention. 
Where a support is employed on which the present vesicular photographic 
material is overcoated, the support can be any suitable material which is 
compatible with the medium, e.g. glass, polymeric materials, paper and the 
like. By compatibility with the photographic medium, it is meant that the 
support must be free from materials which will not degradate the emulsion 
overlay, e.g. due to the bleeding of constituents, such as plasticizers, 
from the polymeric support upon contact with the coating which may contain 
solvents that would initiate such phenomena. Of course, where the 
particular physical and/or chemical properties of a support are critical 
for a given application, this problem may be resolved by treating the 
support with an intermediate layer or coating which forms a suitable 
barrier. For photographic applications, a polyethylene terephthalate base 
material is preferred since it has excellent chemical and physical 
stability under standard processing conditions and it has excellent 
dimensional stability. As is well known in the art, where a transparent 
support is employed a vesicular image recorded thereon in the conventional 
manner produces a corresponding image having the opposite photographic 
sign. However, the use of an opaque support, e.g. a black support, will 
produce a photographic image having the same photographic sign. 
The vehicle and the sensitizer may be combined by any suitable method. 
However, it is preferred that they each be dissolved in a solvent and the 
resultant solutions combined. In this embodiment it is only necessary that 
the respective solutions be mutually miscible. For the most part, solvents 
such as alcohols, ketones, nitriles, esters, ethers and halogenated 
solvents may be used. Particularly useful are methyl, ethyl and isopropyl 
alcohols, alkyl acetates, acetone, methyl ethyl ketone, dioxane and 
acetonitrile. However, any inert solvent which meets the above miscibility 
requirement may be used. 
After the film is thus prepared, there are at least three different methods 
of processing it. In one form, the film is exposed to image forming light, 
e.g., by being placed in contact with a transparency and exposed to light 
passing through the transparency, then the film is heated to 
160.degree.-500.degree. F., for 1/1000 to 3 seconds. This will produce an 
image of the opposite photographic sign from the transparency. Thus, if 
the transparency is negative, a positive vesicular photograph will result. 
A second processing system which can be used is that described in U.S. Pat. 
No. 2,911,299. In it, the film is exposed to image forming light and gas 
released by the sensitizer is allowed to diffuse from the vehicle at a 
temperature too low for development to take place. Then the film is 
exposed overall to uniform light which actuates non-decomposed sensitizer, 
and it is heated to cause development at 160.degree.-500.degree. F. for 
1/1000 to 3 seconds either during or shortly after the second exposure, 
but before the gas has substantially diffused from the film. This results 
in image formation in areas not originally struck by light and an image of 
the same photographic sign as the transparency. Thus, a negative 
transparency results in the formation of a negative vesicular photograph 
which might be called a reversal image or a direct image. 
The third processing system is that decribed in U.S. Pat. No. 3,457,071. In 
that system, the film is exposed to image forming light of relatively low 
intensity for at least about 0.5 second and preferably for at least about 
2.0 seconds. That is, the light is of low enough intensity that the film 
does not receive a normal exposure in less than 0.5 second and preferably 
2.0 seconds. Then the film receives an overall exposure of light intensity 
which is sufficient to expose the film in less than 0.2 second and 
preferably less than 0.01 second. Overexposure or longer exposure can be 
tolerated, but there must be sufficient light to properly expose the film 
during the indicated time. This procedure avoids a separate diffusion step 
as used in the method of U.S. Pat. No. 2,911,299. In some cases, no 
heating is required to cause development, and the image appears 
spontaneously. However, in other cases, some heating may be used to 
advantage, as more fully described in U.S. Pat. No. 3,457,071.