Diazo vesicular imaging films with nitrate salt

Vesicular imaging films have good speed and stable latent images when comprised of a diazonium compound, nitrate salt, and binder comprising gelatin or poly(vinyl alcohol). The film can even have highly stable final images when the binder comprises poly(vinyl alcohol).

BACKGROUND OF THE INVENTION 
The present invention relates to photosensitive imaging systems, and 
particularly diazonium vesicular imaging systems. 
Vesicular images are formed in a photosensitive film by small bubbles or 
vesicles of gas which are formed and trapped in the areas of the film 
exposed to light. Generally speaking, the film has a colloid or a resin 
coating, referred to as a vehicle, on a backing material and a 
light-sensitive agent, most commonly a diazo compound, dispersed 
throughout the coating. When the film is selectively exposed to imagewise 
distributed radiation, the light-sensitive agent is decomposed and 
releases molecules of a gas (nitrogen in the case of diazo compounds). The 
gas ordinarily may be dissolved in the coating and does not form vesicles 
immediately, but does so when the film is developed by heating, presumably 
because the vehicle is softened sufficiently on heating for the gas 
molecules to form bubbles in the vehicle and for the bubble to expand. The 
resulting vesicles make the vehicle opaque to transmission of light in the 
imagewise exposed areas. The vesicles also reflect and scatter light so 
that they appear white. 
Early vesicular materials employed gelatin as the vehicle. These suffered 
from the difficulties of slow speed, short-lived latent images, and rapid 
fading of the vesicular images. Later work revealed that this last problem 
was caused, in part, by the sensitivity of gelatin to water. Gelatin 
vehicles absorbed moisture from the atmosphere and became soft, thus 
collapsing the vesicles and destroying the image. 
It is now preferred to employ polymers or resins as the vehicle. Vehicles 
which are particularly preferred include those described in U.S. Pat. Nos. 
3,620,743 and 3,622,336. U.S. Pat. No. 3,620,743 discloses a vehicle made 
from a water-insoluble polymer selected from a group consisting of 
homopolymers of .alpha.-chloroacrylonitrile and copolymers of 
.alpha.-chloroacrylonitrile with a different vinyl monomer in which the 
mole fraction of the vinyl monomer in the copolymer is less than 0.50. 
U.S. Pat. No. 3,622,336 discloses a vehicle which is a copolymer of 
.alpha.-chloroacrylonitrile and .alpha.-methacrylonitrile. 
It would be desirable to use water-soluble vehicles in the manufacture of 
vesicular films as this would remove the cost of organic solvents and 
reduce the manufacturing costs and health risks involved in working with 
organic solvents. Previous attempts to use water soluble resins such as 
poly(vinyl alcohol) have sought to prevent penetration of moisture into 
the vehicle by the application of a water-impermeable topcoat. This 
construction somewhat reduced the moisture sensitivity of the film, but 
images would still shortly fade because of the collapse of vesicles under 
ambient humidity conditions. 
SUMMARY OF THE INVENTION 
Vesicular imaging films having high speed, latent image stability and which 
can also have final image stability comprise radiation sensitive diazonium 
material and a nitrate salt in a water-soluble vehicle comprising either 
gelatin or poly(vinyl alcohol). Oxidation products generated from the 
photoinitiated decomposition of the nitrate by the diazonium material 
crosslink the poly(vinyl alcohol) and render it less water soluble in the 
image areas where vesicles are formed. 
DETAILED DESCRIPTION OF THE INVENTION 
A vesicular imaging film is constructed of a transparent or translucent 
support base and a photosensitive layer of a water-soluble polymeric 
binder comprising at least 30% by weight of either gelatin or poly(vinyl 
alcohol), a photosensitive diazonium component, and a nitrate salt. A 
topcoat of a water vapor-resistant polymer is optionally used over the 
photosensitive layer. 
The water-soluble polymeric binder should preferably comprise at least 50% 
by weight of gelatin or poly(vinyl alcohol). Preferably the binder 
comprises at least 75% by weight of gelatin or poly(vinyl alcohol), more 
preferably 90% by weight gelatin or poly(vinyl alcohol) and most 
preferably 100% gelatin or poly(vinyl alcohol). The other binder 
components should blend well with the gelatin or poly(vinyl alcohol) and 
be water soluble to a degree themselves. The preferred material for the 
other binder component wound be vinyl ether/maleic acid copolymers such as 
Gantrez.RTM. resins. The binder system must be sufficiently water soluble 
to be applied from an aqueous (e.g., 90% water, 10% ethanol by volume) or 
solely water solvent system. 
Light sensitive diazonium materials such as polymers, oligomers and salts 
are well known in the art. These salts comprise a light sensitive aromatic 
nucleus with an external diazonium group and an anion associated therewith 
(e.g., Light-Sensitive System, Kosar, pp. 202-214, John Wiley and Sons, 
Inc. 1965, N.Y.; and Photographic Chemistry, Vol. II, P. Glafkides, pp. 
709-725, Fountain Press, London). They may be generally represented by the 
formula: 
EQU ArN.ident.N.sup.+ X.sup.- 
wherein Ar is an aromatic nucleus, and X.sup.- is an anion. 
Any anion may be used on the diazonium salt. Anions as diverse as zinc 
chloride, tri-isopropyl naphthalene sulfonate, fluoroborate (i.e., 
BF.sub.4.sup.-), and bis(perfluoroalkylsulfonyl)methides may be used. The 
change in anions may affect the speed of the imaging layer, but not its 
function. Preferably the anion is selected to increase the water 
solubility or compatibility of the compound. Any light sensitive aromatic 
diazonium nucleus, as known in the art, may also be used in the practice 
of the present invention. These nuclei are well known in the art and 
include, for example, p-anilinobenzene; 1-diazo-2,4-diethoxy-4-morpholino 
benzene; 1-diazo-4-benzoyl amino-2,5-diethoxy benzene; 
4-diazo-2,5-dibutoxy phenyl morpholino; 4-diazo-1-dimethyl aniline; 
1-diazo-N,N-dimethyl aniline; 3-methyl-4-pyrrollidone benzene; 
1-diazo-4-N-methyl-N-hydroxyethyl aniline; etc. Light sensitive oligomeric 
diazonium resins as known in the art (e.g., U.S. Pat. No. 2,714,066) are 
useful and are specifically included within the definition of diazonium 
salts as they are merely condensation products of the salts (with 
aldehydes such as formaldehyde) and retain their light sensitive and 
active properties. Diazo oxides are also equally useful in the present 
invention and are included in the term diazonium materials. 
The nitrate salt component is believed to be desired in a form that is 
capable of generating an oxidizing component (e.g., HNO.sub.3, NO, 
NO.sub.2 or N.sub.2 O.sub.4) in combination with the diazonium salt when 
light struck and heated for development of the vesicles. The oxidizing 
component should thus be generable after being irradiated in the presence 
of a diazonium material sensitive to the incident radiation and heated to 
a temperature between 160.degree. and 250.degree. C. for one minute. No 
nitrate salts have as yet been tested which do not accomplish this, but 
nitric acid alone will not work well in this manner as it is already an 
active oxidizing agent. 
The nitrate salt component of the present invention is preferably in a form 
within the imaging layer so that HNO.sub.3, NO, NO.sub.2 or N.sub.2 
O.sub.4 will be provided within the layer when it is heated to a 
temperature no greater than 200.degree. C. for 60 seconds and preferably 
no greater than 160.degree. C. for 60 or most preferably 30 seconds. This 
may be accomplished with many different types of salts, both organic and 
inorganic, and in variously different types of constructions. 
The most convenient way of providing such thermal oxidant-providing nitrate 
salts is to provide a hydrated nitrate salt such as aluminum nitrate 
nonahydrate (Al(No.sub.3).sub.2,9H.sub.2 O). This salt, when heated in a 
binder, will generate HNO.sub.3, NO, NO.sub.2 and/or N.sub.2 O.sub.4 in 
various amounts. The binder should not be at such a high pH that the 
liberated nitric acid would be immediately neutralized as this would 
adversely affect the oxidizing capability of the system. It is not 
essential that a completely acidic or neutral pH environment be provided, 
but pH levels above 8.5 may in many cases completely prevent oxidation. It 
is, therefore, desired that the nitrate salt containing layer have a pH 
less than 7.5, preferably equal to or less than 7.0, and more preferably 
equal to or less than 6.5. 
In addition to hydrated nitrate salts, non-hydrated salts in layers having 
a pH less than 7.5, and preferably in an acidic environment are also 
capable of providing HNO.sub.3, NO, NO.sub.2 and/or N.sub.2 O.sub.4 in 
sufficient quantities to provide the oxidizing capability necessary for 
practice of the present invention. Ammonium nitrate, for example, does not 
enable good oxidation in the present invention in a layer having a pH of 
8.0 or higher, but when a moderate strength organic acid such as phthalic 
acid is added to lower the pH to below 7.0, a quite acceptable imaging 
system is provided. 
Beside the inorganic types of salts generally described above, organic 
salts in non-alkaline environments are also quite useful in the practice 
of the present invention. In particular, nitrated quaternary ammonium 
salts such as guanadinium nitrate work quite well in acid environments, 
but will not provide any useful image at alkaline pH levels of 8.0 or 
higher. 
It is believed that the alkaline environment causes any oxidizing agent 
(e.g., HNO.sub.3, NO, NO.sub.2 and/or N.sub.2 O.sub.4) which is liberated 
from the nitrate salt to be preferentially reacted with hydroxy ions or 
other neutralizing moities so as to prevent oxidation of the dyes. For 
this reason it is preferred to have the environment of the nitrate salt at 
a pH no greater than 7.0 and more preferably less than 6.5. 
Preferred salts are the hydrated metal salts such as nickel nitrate 
hexahydrate, magnesium nitrate hexahydrate, aluminum nitrate nonahydrate, 
ferric nitrate nonahydrate, cupric nitrate trihydrate, zinc nitrate 
hexahydrate, cadmium nitrate tetrahydrate, bismuth nitrate pentahydrate, 
thorium nitrate tetrahydrate, cobalt nitrate hexahydrate, gadolinium or 
lanthanum nitrate nonahydrate, mixtures of these hydrated nitrates and the 
like. Non-hydrated or organic nitrates may be admixed therewith. 
Organic nitrates are also quite useful in the practice of the present 
invention. These nitrates are usually in the form of quaternary nitrogen 
containing compounds such as guanadinium nitrate, pyridinium nitrate, and 
the like. Ammonium nitrate may also be used. Nitrated dyes will also be 
useful, but again, they must be used in an environment which will not 
neutralize any liberated HNO.sub.3, NO, NO.sub.2 and/or N.sub.2 O.sub.4. 
Acids and acidic materials are preferably present in the photosensitive 
layer along with the diazonium materials, not only to provide an acidic 
environment, but also to stabilize the diazonium materials. Organic acids 
are preferred, but inorganic acids are also useful, although generally in 
smaller concentrations. Organic acids having carboxylic acids are 
generally preferred, and aromatic carboxylic acids such as phthalic acid, 
isophthalic acid and the like are particularly desirable. 
The proportions of the ingredients have been found to be critical in the 
practice of the present invention. The use of proportions outside of the 
following range has been found to produce very poor images, with either 
high D.sub.min or low D.sub.max. Considering only the proportions of the 
required three components, the following range of weight concentrations 
must be used in order to provide good quality images. The binder must 
comprise 70-95% by weight of the layer, the diazo material must comprise 
from 0.08 to 3.5 percent by weight, and the nitrate must comprise from 4.5 
to 25% by weight of the layer. Preferably, the binder comprises 75 to 90%, 
the diazo comprises from 0.1 to 3%, and the nitrate comprises from 6 to 
20% by weight of the layer. Most preferably the binder comprises from 80 
to 90%, the diazo comprises from 0.25 to 2.5%, and the nitrate comprises 
from 8 to 15% by weight of the photosensitive layer. The improvement 
obtained by restricting the compositions to the narrow most preferred 
range are significant, even over other compositions within the broad 
range. 
Other additives may also be present in the photosensitive layer or on the 
composite article. For example, priming layers may be on the translucent 
or transparent support, and coating aids, lubricants, antistatic agents, 
antioxidants and the like may be present in the photosensitive layer 
and/or the optional moisture resistant top layer. It is generally not 
desirable to use dyes or pigments in the photosensitive layer as this 
tends to increase the background density (D.sub.min) on projection of the 
image. Even though dark or black images on a colored background can thus 
be projected, it is preferred that there be insufficient dye in the 
photosensitive layer to provide a transmission optical density of 0.3. It 
is more preferred that there be substantially no dye in the photosensitive 
layer. By substantially no dye in the layer, it is meant that there is a 
transmission optical density of less than 0.10 in the photosensitive 
layer. 
These and other aspects of the invention will be shown in the following 
non-limiting examples.

EXAMPLE 1 
This Example shows the effect of nitrate salt addition on the formation of 
a vesicular image in a poly(vinyl alcohol) binder. 
42.0 grams of a poly(vinyl alcohol) polymer (Elvanol 71-30) as solution of 
10% solids with 5% ethanol and 85% by weight water was combined with 0.2 
grams of the diazonium salt, 1-diazo-3-methyl-4-pyrrolidinobenzene zinc 
chloride. One half of this composition was removed (Sample A) and the 
remaining half was combined with 2 grams of zinc nitrate. Two strips of 
polyester were coated at a thickness of 4 mils wet thickness and dried for 
seven minutes at 70.degree. C. Each sample was then exposed for 1.3 
minutes through a 0-4 continuous density wedge to a ultraviolet radiation 
source (mercury halide lamp). The samples were then heat developed at 
102.degree. C. for seven seconds. The results were as follows: 
______________________________________ 
D.sub.max 
D.sub.min 
______________________________________ 
Sample A 0.23 0.06 
Sample B 2.03 0.06 
______________________________________ 
A second strip of Sample A was exposed as before and imaged at 138.degree. 
C. to evaluate the effects of development temperature on the system. A 
D.sub.max of only 0.24 and a D.sub.min of 0.06 were obtained. The dramatic 
gain in optical density from the nitrate salt can be readily noted. 
EXAMPLE 2 
A comparison between a vesicular film containing nitrate according to the 
present invention and a commercial vesicular film is made in this Example. 
A solution was made of the ingredients: 
4 g Cerric Magnesium Nitrate (Ce.sub.2 Mg(NO.sub.3).sub.12.24H.sub.2 O) 
1 g Aluminum Nitrate (Al(NO.sub.3).sub.3.9H.sub.2 O) 
0.01 g Phenidone A 
0.04 g Diazo salt of Example 1 
The above solution was dissolved in 2 g distilled H.sub.2 O then the 
following polymer solutions were added: 
10 g Elvanol 85-80 solution (10 g PVA, 5 g ethanol, 85 g H.sub.2 O) 
10 g Elvanol 71-30 solution (10 g PVA, 5 g ethanol, 85 g H.sub.2 O) 
The resulting solution was coated at 4 mils over a polyester base and dried 
for 12 minutes at 70.degree. C. A sample was then imaged through a 0-4 
wedge on a 3M Model 261 ultraviolet imaging apparatus for 77.1 seconds and 
subsequently developed at 102.degree. C. for 7 seconds. 3M Brand VMCB 
vesicular film (a diazonium salt in a poly-.alpha.-chloroacrylonitrile 
polymer) was imaged in the same way and developed at 126.degree. C. for 4 
seconds. The results are as follows: 
______________________________________ 
Speed Pt. 
D.sub.min 
D.sub.max at D = .6 Contrast 
______________________________________ 
Type VMCB .14 1.77 3.34 2.76 
PVA + Nitrate 
.05 1.59 1.33 0.73 
______________________________________ 
The sample containing the PVA+Nitrate demonstrates a speed increase of 2 
orders of magnitude over the standard vesicular film and a lower 
D.sub.min. 
EXAMPLE 3 
Latent image retention of the films of the present invention are examined 
in this Example. A solution was prepared as follows: 
2 g Cerric Magnesium Nitrate were mixed with 0.04 g of the diazonium salt 
of Example 1 and then mixed with 20 grams of the resin combination used in 
Example 2. 
The solution was coated at 4 mils on a polyester film and dried for 12 
minutes at 70.degree. C. The film was then overcoated with the following 
solution at 3 mils and dried for 10 minutes at 70.degree. C. 
30 g Saran F310 (polyvinylidene chloride) Resin 
5 g tetrahydrofuran 
3.4 g Syloid R-972 (hydrophobic silica particles) 
61.6 g MEK 
The Saran functions as a moisture barrier. Two samples were exposed as in 
Example 2. One was immediately developed at 250.degree. F. for 4 seconds. 
The other was held at room temperature for 24 hours in the dark and then 
developed in the same manner. Results are as shown: 
______________________________________ 
Speed Pt. 
D.sub.min 
D.sub.max at D = .6 Contrast 
______________________________________ 
Original .05 1.82 2.87 1.33 
24 hour .05 1.70 2.87 1.31 
______________________________________ 
The comparison demonstrates good latent image retention. 
EXAMPLES 4-9 
Various nitrates are shown as substitutions for the nitrates used in 
Example 2. Solutions were prepared of the following materials: 
______________________________________ 
Diazo of 
Example 1 Resin Solutions 
Grams of 
Ex. Nitrate (grams) as in Ex. 2 
Nitrate 
______________________________________ 
4. Zn(NO.sub.3).sub.2.6H.sub.2 O 
.2 g 20 g 2 g 
5. NH.sub.4 NO.sub.3 
" " 1.08 g 
6. Co(NO.sub.3).sub.2.6H.sub.2 O 
" " 1.96 g 
7. Cd(NO.sub.3).sub.2.4H.sub.2 O 
" " 2.07 g 
8. Cu(NO.sub.3).sub.2.3H.sub.2 O 
" " 1.62 g 
9. Ni(NO.sub.3).sub.2.6H.sub.2 O 
" " 1.95 g 
______________________________________ 
The solutions were each coated at a wet thickness of 4 mils over a 
polyester substrate and dried for 6 minutes at 70.degree. C. A second 
coating containing the following was prepared: 
30 g Saran F310 (polyvinylidene Chloride) 
5 g tetrahydrofuran 
65 g methyl ethyl ketone 
The second coating was applied over the first coatings at a thickness of 3 
mils (wet) and dried for 6 minutes at 70.degree. C. The samples were 
exposed to a 0-4 wedge as before and developed for 10 seconds at 
138.degree. C. The results are shown in the following table. 
______________________________________ 
Example D.sub.min 
D.sub.max 
______________________________________ 
4 .11 1.88 
5 .15 1.92 
6 .17 2.00 
7 .12 1.70 
8 .14 0.52 
9 .13 1.69 
______________________________________ 
EXAMPLE 10 
The moisture resistance of the developed image when practicing the present 
invention is shown in this Example. A solution was prepared of the 
following ingredients: 
1.5 g Zinc Nitrate 
0.6 g Aluminum Nitrate 
0.08 g Diazonium salt (4-diazo-2,5-diethoxyphenylmorpholine borofluoride) 
10 g Elvanol 85-80 Solution 
10 g Elvanol 71-30 Solution 
The solution was coated at 4 mils over a polyester substrate and dried for 
10 minutes at 70.degree. C. An overcoat of Saran F310 as in Examples 4-9 
was applied. Eight samples were imaged to a microfilm master for 9 seconds 
on the 3M Model 261. They were then developed in succession at increasing 
temperatures for 10 seconds. 
______________________________________ 
Development Temp. D.sub.min 
D.sub.max 
______________________________________ 
220.degree. F. .08 .95 
230 .08 1.11 
240 .08 1.48 
250 .08 1.89 
260 .09 2.00 
270 .08 2.07 
280 .09 2.08 
290 .09 2.09 
______________________________________ 
The developed samples were placed in an 80.degree. F./80% RH room for 72 
hours. The images in samples developed through 270.degree. F. had 
disappeared. The samples developed at 280.degree. and 290.degree. F. had 
the following readings: 
______________________________________ 
Development Temp. D.sub.min 
D.sub.max 
______________________________________ 
280.degree. F. .08 .96 
290 .08 1.96 
______________________________________ 
A combination of nitrate and increased development temperature has a 
stabilizing effect on the resistance of the vesicles to collapse by 
moisture. 
EXAMPLE 11 
Comparison of various poly(vinyl alcohol) resins of varying viscosity and 
percent hydrolysis is shown. The comparison was made with Dupont's Elvanol 
series where grade destinations are made with 2 numbers. The number 
preceeding the hyphen is assigned by degree of hydrolysis and those 
following refer to viscosity. 
Each solution was prepared according to the following formula: 
2 g Zinc Nitrate 
0.2 g Diazo salt of Example 1 
20 g Resin Solution (10% Resin, 5% Ethanol, 85% H.sub.2 O) 
They were each coated and overcoated as in Example 6. They were exposed as 
in Example 6 and developed for 10 seconds at 280.degree. F. 
______________________________________ 
Latent Image 
80/80 Room 72 hours 
Resin D.sub.min 
D.sub.max 
D.sub.min 
D.sub.max 
D.sub.min 
D.sub.max 
______________________________________ 
71-30 .13 1.98 .12 1.06 .49 1.01 
75-15 .11 1.87 .11 1.28 .29 .89 
85-50 .11 1.71 .11 .11 .12 .35 
85-60 .10 1.81 .11 1.55 .15 .95 
85-80 .11 1.51 .02 .09 .09 .16 
85-82 .11 1.83 .11 1.66 .16 1.04 
90-50 .10 1.85 .11 1.31 .16 1.21 
HV .12 1.75 .11 1.48 .14 1.44 
______________________________________ 
All samples gave good initial images. The data shows that some resins 
retain the latent image while others are more resistant to collapse of the 
vesicles by H.sub.2 O. The effect of increasing the percent hydrolysis or 
viscosity is not well defined. 
EXAMPLE 12 
A 2.sup.4 design was run. The resin solution consisted of 10 g Elvanol 
85-60, 5 g Ethanol and 85 g H.sub.2 O. Zinc Nitrate was used as the 
nitrate source. The diazonium salt of Example 1 was used. The second trip 
was the Saran F310 solution described earlier. The design was run to 
examine the concentration effects on the image. The levels used were as 
follows: 
______________________________________ 
-1 0 +1 
______________________________________ 
A. Nitrate (grams) 
2.0 3.0 4.0 
B. Diazonium Salt (grams) 
.1 .2 .3 
C. Resin Solution (grams) 
15 20 25 
D. 2nd Coat Orifice in mils 
2 3 4 
______________________________________ 
Each design point was run once. The center point was replicated 4 times. 
The samples were exposed to a 0-4 wedge for 77.1 seconds on the 3M Model 
261 and developed for 10 seconds at 138.degree. C. Results were as follows 
for 24 hour ambient conditions and 72 hours at 80.degree. F. and 80% 
relative humidity storage: 
______________________________________ 
Trial Latent Image 24 hours 
80/80 Room 72 hours 
No. D.sub.min 
D.sub.max 
D.sub.min 
D.sub.max 
D.sub.min 
D.sub.max 
______________________________________ 
1 .11 1.84 .22 1.06 .21 1.29 
2 .12 1.76 .24 .89 .27 .65 
3 .26 2.36 1.23 1.86 1.14 2.07 
4 .99 1.73 .93 1.27 .32 .62 
5 .10 .63 .00 .00 .12 .12 
6 .11 1.84 .30 1.00 .17 1.10 
7 .16 1.98 .31 1.87 .31 1.15 
8 .12 2.18 .16 1.55 1.23 1.51 
9 .11 1.87 .12 1.41 .20 1.30 
10 .53 1.43 .14 .39 .21 .46 
11 .24 2.37 1.03 1.71 1.22 2.13 
12 1.09 1.97 .68 1.16 .38 .69 
13 .11 1.04 .11 .65 .00 .13 
14 .11 1.78 .11 1.47 .14 .85 
15 .14 1.90 .25 1.96 .29 .99 
16 .17 2.29 .68 1.73 1.32 1.81 
17 .11 2.07 .12 1.58 .84 1.54 
18 .11 2.08 .63 1.33 .94 1.59 
19 .11 2.09 .12 1.51 .78 1.60 
20 .12 2.08 .67 1.21 .86 1.44 
______________________________________ 
EXAMPLES 13-25 
The criticality of the gelatin and poly(vinyl alcohol) as the binder in the 
vesicular imaging system of the present invention is investigated. 
Standard formulations were prepared of: 
2.0 g resin binder 
0.02 moles of nitrate 
2.8.times.10.sup.-4 moles of diazonium salt 
diluted to 25 g with solvent 
which were coated at 4 mils (1.02.times.10.sup.-4 m) wet thickness and 
dried at 95.degree. C. The following resins and solvents were used: 
13. Acrylic resin (Carboset 525)--20% in methylethyl ketone 
14. Acrylic resin (Carboset 525)--20% methanol 
15. Polyvinyl butyral (Butvar B72A)--15% methanol 
16. Polyvinyl butyral (Butvar B73)--20% methanol 
17. Acrylic resin (Acryloid B-66)--20% in methylethyl ketone 
18. Polyester (Vitel 222)--20% in methylethyl ketone 
19. Polyvinylidenechloride (Saran F-310)--20% in methylethyl ketone 
20. Epoxy (Epon 1007)--20% in methylethyl ketone 
21. Poly(vinyl chloride/vinyl acetate)--20% in methylethyl ketone 
22. Poly-alpha-chloroacrylonitrile--20% in methylethyl ketone 
23. Inert gelatin--20% is distilled water 
24. 95% phthalated gelatin--20% in distilled water 
25. polyvinyl alcohol (Uvanol 85-60)--10% in 85% distilled water and 5% 
ethanol 
Both aluminum nitrate and zinc nitrate were used with the diazonium salt of 
Example 1. After exposure and development, only Examples 23-25 gave good 
quality images with D.sub.max of over 1.00. Example 22 provided the only 
readable image from amongst the other examples with a D.sub.max /D.sub.min 
of 0.83/0.55 which is not considered satisfactory. The ratios for Examples 
23-25, respectively were 1.63/0.04, 1.54/0.8 and 1.69/0.6. The criticility 
of the binder can be seen from this data.