Process for producing negative copies by means of a material based on 1,2-quinone diazides with 4-ester or amide substitution

A process for producing negative relief copies is disclosed in which a light-sensitive material, consisting essentially of (1) a binder which is insoluble in water and soluble in aqueous-alkaline solutions and (2) a light-sensitive ester or amide of a 1,2-benzoquinone-2-diazide-4-sulfonic acid, a 1,2-benzoquinone-2-diazide-4-carboxylic acid, a 1,2-naphthoquinone-2-diazide-4-sulfonic acid, or a 1,2-naphthoquinone-2-diazide-4-carboxylic acid, is imagewise exposed, thereafter heated and, after cooling, exposed again without an original, and subsequently developed by means of an aqueous-alkaline developer. The disclosed process permits the production of negative copies with the aid of a material which yields positive copies when it is processed in a conventional manner.

BACKGROUND OF THE INVENTION 
The present invention relates to a reversal process for producing negative 
copies by means of a normally positive-working light-sensitive material 
based on 1,2-quinone diazides. 
It is known that positive-working reproduction materials based on 
1,2-naphthoquinone diazides can be negatively processed by a particular 
sequence of treatment steps. In U.S. Pat. No. 3,264,104, a reversal 
process of this kind is described in which the light-sensitive layer, 
which preferably contains thermoplastic polymers, is imagewise exposed, is 
treated with an alkaline solution or with water (if appropriate, at an 
elevated temperature) without washing off the exposed areas in the 
process, is then exposed again without an original, and finally is 
developed in a conventional manner, such that the originally imagewise 
exposed areas remain on the support and the other areas are washed off. 
This process has the disadvantages that a comparatively large number of 
treatment steps are required; that the first treatment with alkali must 
invariably be carried out with particular care, in order to detach as 
little as possible of the exposed layer, which is soluble in aqueous 
alkali; and that it is necesary to add polymers which are sparingly 
soluble in alkali and which limit the applicability of the material to 
other uses. 
European Patent Application No. 0,024,916 discloses a similar reversal 
process for the production of resist layers, in which a photosensitive 
material based on 1,2-quinone diazides is heated after imagewise exposure, 
then exposed again without an original and developed with an aqueous 
alkaline solution to form a negative. The light-sensitive layer of the 
disclosed material contains particular photochromic compounds which react 
with the products of the photoreaction undergone by the quinone diazide 
with heating of the material, and are stated to effect curing of the 
layer. In this material, photochromic substances must be present, the 
photoreaction of which produces a discoloration which is inconvenient in 
some applications. 
British Patent Application No. 2,082,339 describes a light-sensitive 
composition comprising an o-quinone diazide and at least one resol, for 
use in the manufacture of a lithographic printing plate which is suitable 
for both positive and negative processing. This reversal process covers 
the same sequence of steps as the process disclosed by the aforementioned 
European patent application. The reversal action is based on the fact that 
the photodecomposition products of the o-quinone diazide form an insoluble 
reaction product with the resol, under the action of heat. A reaction of 
this kind does not occur if novolaks are used. The printing plates so 
produced have the disadvantage of a relatively poor shelf-life, due to the 
self-curing character of resols. 
In German Offenlegungsschriften Nos. 2,855,723 and 2,529,954 resist layers 
comprising 1,2-quinone diazides are described, which layers are used for a 
reversal process and contain, in addition, 
N-acyl-N'-methylol-ethylenediamines or hydroxyethylimidazoles to effect 
thermal curing of the layer. A similar material comprising secondary or 
tertiary amines is described in U.S. Pat. No. 4,196,003. 
Additives of the kind mentioned above, however, generally have an adverse 
influence on the shelf-life of the copying layers and on specific 
properties relating to copying technique, such as, for example, 
sensitivity to light and image contrast after exposure. 
SUMMARY OF THE INVENTION 
It is, therefore, an object of the present invention to provide a reversal 
process for producing negative copies by means of a normally 
positive-working light-sensitive material based on 1,2-quinone diazides, 
which process does not have the above-indicated disadvantages and which 
does not require the use of additives in the copying layer in order to 
make possible thermal curing of the exposed layer areas. 
In accomplishing the foregoing object, there has been provided, in 
accordance with one aspect of the present invention, a process for 
producing negative relief copies, comprising the steps of imagewise 
exposing a light-sensitive material through an original, said material 
comprising a light-sensitive layer which comprises a binder that is 
insoluble in water and soluble in aqueous-alkaline solutions and a 
1,2-quinone diazide comprising at least one of an ester and an amide of 
one selected from the group consisting of 
1,2-benzoquinone-2-diazide-4-sulfonic acid, a 
1,2-benzoquinone-2-diazide-4-carboxylic acid, a 
1,2-naphthoquinone-2-diazide-4-sulfonic acid, and a 
1,2-naphthoquinone-2-diazide-4-carboxylic acid, thereafter heating the 
material; then, after cooling, exposing the material again without the 
original; and thereafter developing the material with an aqueous-alkaline 
developer. 
Other objects, features, and advantages of the present invention will 
become apparent from the following detailed description. It should be 
understood, however, that the detailed description and specific examples, 
while indicating preferred embodiments of the invention, are given by way 
of illustration only, since various changes and modifications within the 
spirit and scope of the invention will become apparent to those skilled in 
the art from this detailed description. 
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
The process of the present invention is characterized in that the material 
comprises, as a light-sensitive compound, as ester or an amide of a 
1,2-benzoquinone-2-diazide-4-sulfonic acid, of a 
1,2-benzoquinone-2-diazide-4-carboxylic acid, of a 
1,2-naphthoquinone-2-diazide-4-sulfonic acid, or of a 
1,2-naphthoquinone-2-diazide-4-carboxylic acid. 
Unexpectedly, it has been found that the naphthoquinone-(1,2)-diazide-(2)-4 
derivatives are much more suitable for use as sensitizers in the reversal 
process described in greater detail below than are the corresponding 
naphthoquinone-(1,2)-diazide-(2)-5 derivatives. More specifically, it has 
been found, according to the invention, that the exposed layer areas of 
the light-sensitive material are cured at an elevated temperature, even 
without additives, and are thus rendered insoluble in the developer, when 
o-quinonediazide-4-sulfonic acid esters are used as sensitizers in the 
copying layer, rather than, for example, o-quinonediazide-5 derivatives. 
This thermal curing can only be achieved if the copying layers are admixed 
with special additives which effect a solidification of the irradiated 
layer areas. 
A copying layer, for example, which comprises a 
naphthoquinone-(1,2)-diazide-(2)-4-sulfonic acid ester and a 
cresol-formaldehyde novolak as a binder, and which is heated to 
140.degree. C. after irradiation with ultraviolet radiation, is already 
cured after 1 minute and is insoluble in the developer. In contrast, an 
irradiated copying layer, in which the corresponding 
naphthoquinone-(1,2)-diazide-(2)-5-sulfonic acid ester is used under 
conditions which are otherwise identical, is not cured at 140.degree. C. 
and, thus, remains soluble in the developer. Only after the latter 
irradiated copying layer is heated for 3 minutes does a slight curing of 
the layer occur, but this slight curing does not produce any resistance to 
the developer. If the heating time at 140.degree. C. is extended, for 
example, to 4 or 5 minutes, the unexposed constituents of the layer begin 
to decompose and are rendered sparingly soluble or insoluble in the 
developer. Consequently, it is impossible thereafter to obtain a 
differentiation between a positive an a negative copy. 
It is only possible to effect reversal development with material based on a 
naphthoquinone-(1,2)-diazide-(2)-5-sulfonic acid ester by including 
therewith specific additives, such as a resol, a secondary or tertiary 
amine, or some other compound. In contrast, the process of the present 
invention has the advantage that o-quinonediazide-4-sulfonic acid 
derivatives or o-quinonediazide-4-carboxylic acid derivatives used as 
sensitizers in the copying layer do not require such additives. 
Consequently, particular drawbacks in copying technique which are 
occasioned by these additives do not arise. 
Sensitizers which are suitable for use according to the present invention 
comprise any 1,2-quinonediazide-4-sulfonic acid ester, 
1,2-quinonediazide-4-sulfonic acid ester, 1,2-quinonediazide-4-sulfonic 
acid amide, 1,2-quinonediazide-4-carboxylic acid ester, or 
1,2-quinonediazide-4-carboxylic acid amide that is rendered soluble in 
aqueous-alkaline solutions after irradiation with actinic light. Included 
are the reaction products of 1,2-benzoquinonediazide-4-sulfonic acid or 
1,2-benzoquinonediazide-4-sulfonic acid chloride, or of 
1,2-naphthoquinonediazide-4-sulfonic acid or 
1,2-naphthoquinonediazide-4-sulfonic acid chloride, with 
phenol-aldehyde/acetone condensation products or with polymers of 
p-hydroxystyrene, p-aminostyrene, or copolymers of these last two 
compounds. 
Esters which may be used include the known reaction products of the acids, 
or of the halides thereof, with phenols, in particular with polyhydric 
phenols, such as 2,3,4-trihydroxybenzophenone, 2,4-dihydroxy-benzophenone, 
4-decanoyl-resorcinol, 4-(2-phenyl-prop-2-yl) phenol, gallic acid 
octylester, and 4,4-bis-(4-hydroxyphenyl)-valeric acid butylester. The 
amides may be derived in a known manner from aromatic or longer-chain 
aliphatic amines. 
The amount of o-quinonediazide compounds generally ranges from 3 to 50% by 
weight, preferably from 7 to 35% by weight, based on the weight of the 
nonvolatile constituents of the copying layer. 
In addition to the above-indicated 4-substituted o-quinonediazides, this 
total amount may also include relatively small quantities of conventional 
1,2-naphthoquinone-diazide-5-sulfonic acid derivatives, preferably 
1,2-naphthoquiononediazide-5-sulfonic acid esters. Generally, the quantity 
of 5-sulfonic acid derivatives should not exceed 50%, and preferably 
should not exceed about 20%, of the amount of 4-substituted quinone 
diazides. 
The light-sensitive compositions further contain a polymeric, 
water-insoluble resinous binder which is soluble in the solvents used for 
the composition according to the present invention and is also soluble, or 
at least swellable, in aqueous alkaline solutions. 
The novolak condensation resins, widely used in many positive copying 
materials based on naphthoquinone diazides, have also proved useful as 
binders in the process according to the present invention. These novolaks 
can also be modified, in a known manner, by reacting part of their hydroxy 
groups, for example, with chloroacetic acid, isocyanates, epoxides or 
carboxylic acid anhydrides. Additional preferred binders which are soluble 
or swellable in alkali include polyhydroxyphenyl resins which are prepared 
by condensing phenols with aldehydes or ketones; copolymers of styrene and 
maleic anhydride; polyvinylphenols; and copolymers of acrylic acid or 
methacrylic acid, in particular with acrylic or methacrylic acid esters. 
The type and quantity of the alkali-soluble resin may vary depending on the 
intended purpose; preferably, the proportion of alkali-soluble resins in 
the total solids is between 90 and 30% by weight, particularly preferably 
between 85 and 55% by weight. Moreover, numerous other resins can also be 
used; preferably these include epoxy resins and vinyl polymers, such as 
polyvinyl acetates, polyacrylates, polyvinyl acetals, polyvinyl ethers, 
polyvinylpyrrolidones and copolymers of the monomers on which these are 
based, as well as hydrogenated or partially hydrogenated colophony 
derivatives. 
The most advantageous proportion of these resins depends on technical 
requirements and the effect on the development conditions, and is, in 
general, not more than 50% by weight, preferably from about 2 to 35% by 
weight, of the alkali-soluble resin. To meet special requirements, such as 
flexibility, adhesion, gloss and coloration, the light-sensitive 
composition can additionally contain substances such as polyglycols; 
cellulose derivatives, such as ethylcellulose; surfactants, dyes, 
adhesion-promoters and finely-divided pigments; and also ultraviolet 
absorbers, if required. 
For color change after exposure, the light-sensitive composition can also 
be admixed with small amounts of radiation-sensitive components which 
preferably form or split-off strong acids upon exposure and produce a 
color change in a subsequent reaction with a suitable dye. 
Radiation-sensitive components of that kind include, for example, 
1,2-naphthoquinone-diazide-4-sulfonic acid chloride, 
halogenomethyl-s-triazines which have chromophoric substituents, and 
diazonium compounds in the form of their salts with complex acids, such as 
tetrafluoroboric acid or hexafluorophosphoric acid. 
For coating a suitable support, the compositions are in general dissolved 
in a solvent. The selection of the solvents should be matched to the 
coating process to be used, the desired layer thickness and the drying 
conditions. Suitable solvents for the composition according to the present 
invention are ketones, such as methyl ethyl ketone; chlorinated 
hydrocarbons, such as trichloroethylene and 1,1,1-trichloroethane; 
alcohols, such as n-propanol; ethers such as tetrahydrofuran; 
alcohol-ethers, such as ethylene glycol monoethyl ether; and esters, such 
as butyl acetate. It is also possible to use mixtures which, for special 
purposes, can also contain solvents, such as acetonitrile, dioxane or 
dimethylformamide. In principle, all those solvents which do not 
irreversibly react with the layer components can be used. Particularly 
preferred solvents comprise the partial ethers of glycols, especially 
ethylene glycol monomethyl ether. 
In most cases, the supports used for layer thickness of less than about 10 
.mu.m are metals. The following may be used for offset printing plates: 
mill-finished, mechanically or electrochemically roughened aluminum which, 
if desired, has been anodically oxidized and which additionally can also 
have been chemically pretreated, for example, with polyvinylphosphonic 
acid, silicates, phosphates, hexafluorozironates, or with hydrolyzed 
tetraethyl orthosilicate. 
Coating of the support material is carried out in a known manner by 
spin-coating, by spraying, by dipping, by roller-coating, by means of slot 
dies, by blade-spreading or by means of a coater application. Light 
sources customary in industry are used for exposure. Irradiation with 
electrons or with a laser is another possiblity for producing an image. 
The aqueous-alkaline solutions which are used for developing have a 
graduated alkalinity, that is to say, they have a pH which is preferably 
in the range between 10 and 14, and they can also contain minor amounts of 
organic solvents or surfactants. 
After imagewise irradiation or exposure, the material is heated without any 
further intermediate treatment. Heating can be effected by irradiation, 
convection, contact with heated surfaces, for example, with rollers, or by 
immersion in a heated bath comprising an inert liquid, for example, water. 
The temperature can range between 80.degree. and 160.degree. C., 
preferably between 110.degree. and 140.degree. C. These temperatures are 
tolerated by the compositions of the present invention without any 
considerable change in the properties of the unexposed areas. The duration 
of heating can vary widely, depending on the method chosen for the 
application of heat. If a heat-transferring medium is used, the heating 
time generally ranges between 30 seconds and 30 minutes, preferably 
between 1 minute and 4 minutes. 
Following heating and cooling, the light-sensitive layer is subjected to an 
overall exposure, whereby the layer areas which are still sensitive to 
light are completely converted into their photodecomposition products. For 
the second exposure, the light source employed in the imagewise exposure 
can advantageously be used again. 
The second exposure is followed by developing with conventional developers, 
whereby the layer areas which were not struck by light in the original 
imagewise exposure are washed off. Suitable developers preferably comprise 
aqueous solutions of alkaline substances, for example, of alkali-metal 
phosphates, silicates, carbonates or hydroxides, which can additionally 
contain surfactants or relatively small amounts of organic solvents. In 
particular cases, suitable developers also comprise organic solvents or 
mixtures of organic solvents with water. The material can be developed 
either immediately after heating and cooling, or after a time interval of, 
for example, several hours, without any attack occurring in the hardened 
layer areas. This indicates that the exposed layer areas are irreversibly 
cured by heating. 
The process according to the invention has the advantage that it is not 
necessary to use special additives which can cause solidifiction of the 
exposed layer areas at an elevated temperature and moreover, that neither 
additional treatment steps in which liquids are used nor a particular 
composition of the light-sensitive material are required. For the only 
additional treatment step, i.e., heating, existing drying apparatus can 
easily be used in most cases. The second exposure without an original is 
most simply performed with the aid of the light source used for imagewise 
exposing the material. 
The process also makes it possible to control resolution by varying the 
exposure times. 
The process of the present invention can, for example, be applied in the 
production of printing forms for letterpress printing, gravure printing 
and planographic printing; in the production of photoresist stencils for 
the subtractive and additive preparation of printed circuit boards; in the 
production of nickel screen-printing cylinders prepared by an 
electroplating process; and in the production of masks in 
microelectronics, according to the lift-off technique. 
In the examples which follow, preferred embodiments of the process 
according to the present invention are described. Percentages and 
quantitative ratios are to be understood as units of weight, unles 
otherwise indicated.

EXAMPLE 1 
An electrolytically roughened and anodically oxidized aluminum sheet was 
coated with a solution comprising 
3.00 parts by weight of the esterifiction product obtained from 1 mole of 
4-(2-phenyl-prop-2-yl)-phenol and 1 mole of 
naphthoquinone-(1,2)-diazide-(2)-4-sulfonic acid chloride, 
0.10 parts by weight of naphthoquinone-(1,2)-diazide-(2)-4-sulfonic acid 
chloride, 
6.00 parts by weight of a cresol-formaldehyde novolak having a softening 
range from 105.degree. to 120.degree. C., as measured according to the 
capillary method DIN 53,181, and 
0.07 part by weight of crystal violet, in 
50.00 parts by weight of ethylene glycol monomethyl ether and 
50.00 parts by weight of tetrahydrofuran. 
The anodically oxidized aluminum support had been treated with an aqueous 
solution of polyvinylphosphonic acid, as described in German Pat. No. 
1,621,478, before it was coated with the light-sensitive copying layer. 
The presensitized material prepared in this manner, in which the 
light-sensitive layer had a weight of about 2.0 g/m.sup.2, was imagewise 
exposed under a transport positive original and thereafter developed with 
a 2% strength aqueous solution of sodium metasilicate.9H.sub.2 O. In the 
developing procedure, those portions of the copying layer which had been 
struck by light were removed and the unexposed image areas remained on the 
support, such that a printing stencil corresponding to the original was 
obtained. The printing stencil was inked with a greasy ink to produce a 
positive printing form which was ready for printing. 
Another sample of the same presensitized material was processed to give a 
negative printing plate. For this purpose, the sample was exposed under a 
negative original, then heated for 1 minute at 140.degree. C. and exposed 
again without an original for the same period of time as used in the 
imagewise exposure. Upon developing in the same developer and for the same 
period of time as used above, a reversed image of the original was 
obtained. 
If the sensitizer indicated in Example 1 was replaced by the corresponding 
ester of naphthoquinone-(1,2)-diazide-(2)-5-sulfonic acid and the 
above-described reversal process repeated under identical test conditions, 
reversal developing of the positive-working light-sensitive material 
proved to be impossible. In the presence of the above-specified 
naphthoquinone-(1,2)-diazide-(2)-4-sulfonic acid ester, the exposed layer 
areas became insoluble in the developer after heating for 1 minute at 
140.degree. C., whereas the exposed layer areas comprising the 
naphthoquinone-(1,2)-diazide-(2)-5-sulfonic acid ester were still soluble 
in the developer, even after heating for 3 minutes at 140.degree. C. 
Consequently, differentiation between a positive and a negative copy was 
impossible. If the heating time and/or the temperature were further 
increased in the latter case, the unexposed layer areas began to decompose 
so that differentiation was impossible. 
EXAMPLE 2 
An electrochemically roughened and anodically oxidized alumium sheet which 
had been treated with an aqueous solution of 0.1% by weight of 
polyvinylphosphonic acid, was coated with a solution comprising 
4.00 parts by weight of the naphthoquinone-diazide sulfonic acid ester used 
in Example 1, 
5.00 parts by weight of a poly-p-vinylphenol having a mean molecular weight 
of 10,000, 
0.10 part by weight of naphthoquinone-(1,2)-diazide-(2)-4-sulfonic acid 
chloride, and 
0.07 part by weight of crystal violet, in 
50.00 parts by weight of ethylene glycol monomethyl ether and 
50.00 parts by weight of tetrahydrofuran. 
The presensitized material prepared in this manner was imagewise exposed 
under a transparent positive original and then was developed with a 0.5% 
strength solution of sodium metasilicate to produce a positive printing 
stencil corresponding to the original. 
Another sample of the same material was processed to give a negative 
printing plate. For this purpose, the sample was exposed under a negative 
original, then was heated for 1 minute at 140.degree. C. and exposed again 
without an original for the same period of time as used in the imagewise 
exposure. Upon developing in the same developer and for the same period of 
time as used above, a reversed image of the original was obtained. 
EXAMPLE 3 
An aluminum sheet which had been treated as indicated in Example 1 was 
coated with a solution comprising 
2.00 parts by weight of the esterification product obtained from 1 mole of 
4-(2-ethylhexanoyl)-resorcinol and 2 moles of 
naphthoquinone-(1,2)-diazide-(2)-4-sulfonic acid chloride, 
5.00 parts by weight of the cresol-formaldehyde novolak specified in 
Example 1, 
0.10 part by weight of 
2-(4-ethoxy-paphth-1-yl)-4,6-bistrichloromethyl-s-triazine, and 
0.07 part by weight of crystal violet, in 
50.00 parts by weight of ethylene glycol monomethyl ether and 
50.00 parts by weight of tetrahydrofuran. 
The presensitized material prepared in this manner was imagewise exposed 
under a transparent positive original and then developed with a 1% 
strength solution of sodium metasilicate to produce a positive printing 
stencil corresponding to the original. 
Another sample of the same material was processed to give a negative 
printing plate. For this purpose, the sample was exposed under a negative 
original, then was heated for 1 minute at 140.degree. C. and exposed again 
without an original for the same period of time as used in the imagewise 
exposure. Upon developing in the same developer and for the same period of 
time as used above, a reversed image of the original was obtained. 
EXAMPLE 4 
An electrochemically roughened and anodically oxidized aluminum sheet was 
coated with a solution comprising: 
3.00 parts by weight of the naphthoquinonediazide-sulfonic acid ester used 
in Example 1, 
6.00 parts by weight of the condensation product obtained from 
2-methyl-resorcinol and acetone, having a mean molecular weight of 2,000, 
0.20 part by weight of naphthoquinone-(1,2)-diazide-(2)-4-sulfonic acid 
chloride, and 
0.08 part by weight of crystal violet, in 
50.00 parts by weight of ethylene glycol monomethyl ether and 
50.00 parts by weight of tetrahydrofuran. 
The presensitized material prepared in this manner was imagewise exposed 
under a transparent positive original and then developed with a 6% 
strength solution of sodium metasilicate to produce a positive printing 
stencil corresponding to the original. 
Another sample of the same material was processed to give a negative 
printing plate. For this purpose, the sample was exposed under a negative 
original, then was heated for 3 minutes at 140.degree. C. and exposed 
again without an original for the same period of time as used in the 
imagewise exposure. Upon developing in the same developer and for the same 
period of time as used above, a reversed image of the original was 
obtained. 
EXAMPLE 5 
An aluminum sheet which had been treated as indicated in Example 1 was 
coated with a solution comprising 
1.00 part by weight of the esterification product obtained from 1 mole of 
4-hexadecanoylresorcinol and 2 moles of 
naphthoquinone-(1,2)-diazide-(2)-4-sulfonic acid chloride, 
5.00 parts by weight of the cresol-formaldehyde novolak specified in 
Example 1, 
0.10 part by weight of 
2-(4-ethoxy-naphth-1-yl)-4,6-bistrichloromethyl-s-triazine, and 
0.07 part by weight of crystal violet, in 
50.00 parts by weight of ethylene glycol monomethyl ether and 
50.00 parts by weight of tetrahydrofuran. 
The presensitized material prepared in this manner was imagewise exposed 
under a transparent positive original and then developed with a 3% 
strength solution of sodium metasilicate to produce a positive printing 
stencil corresponding to the original. 
Another sample of the same material was processed to give a negative 
printing plate. For this purpose, the sample was exposed under a negative 
original, then was heated for 90 seconds at 140.degree. C. and exposed 
again without an original for the same period of time as used in the 
imagewise exposure. Upon developing in the same developer and for the same 
period of time as used above, a reversed image of the original was 
obtained. 
EXAMPLE 6 
An electrolytically roughened and anodically oxidized aluminum sheet was 
coated with a solution comprising 
1.00 part by weight of the esterification product obtained from 1 mole of 
2,3,4-trihydroxybenzophenone and 3 moles of 
naphthoquionone-(1,2)-diazide-(2)-4-sulfonic acid chloride, 
0.10 part by weight of naphthoquinone-(1,2)-diazide-(2)-4-sulfonic acid 
chloride, 
6.00 parts by weight of the novolak used in Example 1, and 
0.07 part by weight of crystal violet, in 
50.00 parts by weight of ethylene glycol monomethyl ether and 
50.00 parts by weight of tetrahydrofuran 
The anodically oxidized aluminum support had been treated with an aqueous 
solution of polyvinylphosphonic acid, as described in German Pat. No. 
1,621,478, before the light sensitive copying layer was applied. 
The presensitized material prepared in this manner was imagewise exposed 
under a transparent positive original and then developed with a 2% 
strength solution of sodium metasilicate to produce a positive printing 
stencil corresponding to the original. 
Another sample of the same material was processed to give a negative 
printing plate. For this purpose, the sample was exposed under a negative 
original, then was heated for 2 minutes at 140.degree. C. and exposed 
again without an original for the same period of time as used in the 
imagewise exposure. Upon developing in the same developer and for the same 
period of time as used above, a reversed image of the original was 
obtained.