Photocurable mixture and material containing diazonium salt polycondensation product or organic azido compound photosensitizer and polyurethane binder grafted with vinyl alcohol and vinyl acetal units

A photocurable mixture is disclosed that contains a diazonium salt polycondensation product or an organic azido compound as the photosensitive compound and a high-molecular weight polymer as the binder, the polymer being a graft copolymer with a polyurethane as the graft backbone, onto which chains containing vinyl alcohol units are grafted. The mixture is suitable for use in the production of printing plates and photoresists, which can be developed with aqueous solutions. It yields printing plates having a good ink acceptance and long shelf life that produce large print runs.

BACKGROUND OF THE INVENTION 
The present invention relates to a photocurable mixture which comprises a 
diazonium salt polycondensation product or an organic azido compound as a 
photosensitive compound, and a polymeric binder, and which is especially 
suitable for the production of printing plates and photoresists. 
DE 20 24 244 (=U.S. Pat. No. 3,867,147) discloses photosensitive recording 
materials comprising cocondensation products of diazonium salts capable of 
condensation and other, non-photosensitive compounds, capable of 
condensation, if appropriate combined with polymeric binders, for 
producing printing plates. These photosensitive materials are 
distinguished by their high photosensitivity and long print runs. The 
number of prints obtained is particularly high if water-insoluble binders, 
for example, polyvinyl formal, are used, but such layers can only be 
properly processed by means of developers containing a considerable amount 
of volatile organic solvents. For ecological reasons it is desirable to 
develop printing plates of this type with purely aqueous solutions. In the 
most favorable cases, the mentioned printing plates can be developed with 
relatively aggressive acidic or alkaline purely aqueous solutions by 
suspending the non-image areas of the layer in the developer, in the form 
of flakes or relatively small particles. There is, however, the danger of 
uncontrolled redeposition of flaky matter in non-image areas of the plates 
whereby the plates are rendered unusable. DE 31 30 987 describes similar 
mixtures which contain styrene/maleic acid anhydride copolymers as the 
binders and which can be developed with purely aqueous alkaline solutions. 
The printing plates obtained using these mixtures, however, yield print 
runs which are inferior to those of printing plates containing binders 
which are insoluble in aqueous-alkaline solutions. 
DE 30 36 077 (=U.S. Pat. No. 4,387,151) discloses corresponding mixtures 
which contain binders comprising polymers with alkenylsulfonylurethane 
side groups. Layers prepared from these mixtures can also be developed by 
means of purely aqueous solutions. However, when the mixtures are 
processed to form lithographic printing plates, they yield light-cured 
coatings whose ink acceptance is unsatisfactory. 
DE 24 29 251 discloses a mixture comprising a photosensitive diazo compound 
and a binder, the binder being obtained by reacting a polymer containing 
hydroxyl groups or carboxyl groups with a crosslinking agent containing 
isocyanate groups, epoxide groups or acid anhydride groups. By the 
crosslinking reaction the solubility of the polymer is reduced. Where 
these mixtures give materials of high print runs, development cannot be 
performed without an addition of organic solvents. Products crosslinked to 
a lesser extent often contain unreacted crosslinking groups and hence have 
a limited shelf life. 
EP 152,819 discloses photosensitive mixtures comprised of diazonium salt 
polycondensation products and binders containing carboxyl groups, which 
are obtained by reacting hydroxyl group-containing polymers with acid 
anhydrides. Plates produced using these mixtures can be developed with 
aqueous-alkaline solutions, and the mixtures are suited for the production 
of lithographic printing forms giving high print runs. It is, however, 
desirable to achieve even better print runs. For this purpose, the 
publication proposes the addition of minor amounts of other polymers, for 
example, polyurethanes, in order to increase the abrasion resistance. 
However, this combination results in a poorer copying performance, such as 
undesired dot gain. Furthermore, the developing behavior and shelf life of 
the plates are impaired. Like other mixtures prepared with 
carboxyl-containing binders, these mixtures also suffer from the draw-back 
that upon being processed with developers based on tap water there is the 
risk of the formation of precipitates in the form of sparingly soluble 
calcium salts, which are deposited developing machines and cause 
disturbances. 
Mixtures of the above generic type, where polyurethanes are employed as 
polymeric binders, are known from U.S. Pat. No. 3,660,097 and DE 27 39 
774. It is a disadvantage of these mixtures that the binders are sparingly 
soluble in the solvents conventionally used for coatings and that the 
solutions have to be filtered several times to remove insoluble residues. 
The developability of these mixtures in aqueous-alkaline media is very 
limited and the print runs are inadequate for high-performance machines. 
A similar mixture is known from EP 30,001. The binder contained therein is 
a branched polyurethane. Using this mixture, relatively high print runs 
can be achieved, but there are still a number of drawbacks. For example, 
acidic aqueous developer solutions with an addition of organic solvents 
are preferably employed for achieving a scum-free, rapid development of 
the photocured layer. When used for automatic processing, these developers 
may cause corrosion problems at the light metal parts of the processing 
equipment. 
In DE 37 32 089 graft polymers are described, which comprise a polyurethane 
as the graft backbone and grafted-on vinyl ester units, which are at least 
partially saponified to give vinyl alcohol units. The polymers are 
suitable as binders for pigments; for preparing printing inks, 
thermoplastic adhesives and solvent-containing adhesives; as constituents 
of varnishes or coatings for fibers, films and metals, and for 
thermoplastic shaped articles. 
JP 246,047/87 describes photopolymerizable mixtures wherein graft polymers 
of polyurethanes and polyvinyl alcohol with mercapto groups are contained 
as binders. 
Graft polymers obtained from the graft polymers mentioned above by 
acetalizing with aldehydes, are described in German Patent Application P 
38 35 840.9. 
German Patent Application P 38 24 146.3 discloses photocurable elastomeric 
mixtures which contain a compound polymerizable by a free-radical process, 
a photoinitiator and, as the binder, a graft polymer according to DE 37 32 
089, which is soluble or dispersible in an aqueous solution. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a negative-working 
photosensitive mixture suitable for use in the production of printing 
plates, particularly lithographic printing plates which has all the 
advantages of the known compositions based on diazonium salt 
polycondensation products or azido compounds, can be developed by means of 
virtually solvent-free, neutral or alkaline aqueous solutions, without 
resulting in disturbing deposits when developer solutions containing tap 
water are employed and, at the same time, yields printing plates producing 
high print runs and having a good ink acceptance and long shelf life, 
properties which could up to now only be achieved with printing plates 
requiring the addition of relatively large amounts of organic solvents in 
the developing process. 
These and other objects according to the invention are provided by a 
photocurable mixture, comprising a photosensitive compound selected from 
the group consisting of a diazonium salt polycondensation product and an 
organic azido compound; and a binder comprising a high-molecular weight 
polymer having vinyl alcohol units, wherein said polymer is a graft 
polymer comprising a polyurethane graft backbone onto which chains 
containing vinyl alcohol units are grafted. A photocurable recording 
material comprising a layer support and a photosensitive layer comprising 
this mixture is also provided. 
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 the 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 THE PREFERRED EMBODIMENTS 
In accordance with the present invention, a photocurable mixture is 
proposed, which contains a diazonium salt polycondensation product or an 
organic azido compound as the photosensitive compound, and a 
high-molecular polymer having vinyl alcohol units as the binder. 
The mixture of the invention is characterized in that the polymer is a 
graft polymer obtained from a polyurethane graft backbone, onto which 
chains containing vinyl alcohol units are grafted. 
In accordance with the present invention, a photocurable recording material 
is also proposed, comprising a layer support and a photosensitive layer 
comprising the photocurable mixture. 
The graft polymers contained in the mixture of the instant invention are 
described in DE 37 32 089 and in German Patent Application P 38 35 840.9. 
To prepare them, a carboxylic acid vinyl ester, and optionally another 
ethylenically-unsaturated compound copolymerizable therewith, is grafted 
onto a polyurethane graft backbone and completely or partially saponified. 
The polymers having vinyl alcohol units which are obtained in this way can 
be further reacted with aldehydes to give polyvinyl acetals. 
The proportion of the grafted-on components is in general about 10 to 95, 
preferably about 30 to 90, and in particular about 40 to 80 % by weight, 
based on the total graft polymer. 
The graft backbone consists of polyurethanes having at least two urethane 
groups in the molecule, the number of urethane groups per molecule being 
subject to no particular upper limit and in general having values higher 
than 2. 
The polyurethanes employed as graft backbone can be produced from diols and 
diisocyanates by conventional processes of polyurethane synthesis. In 
principle, all of the diols customarily used in polyurethane synthesis can 
be employed. Cycloaliphatic diols, such as cyclohexanediols, and in 
particular aliphatic diols having 2 to 12 carbon atoms are preferred. 
Polyetherdiols, for example polypropylene oxides, polybutylene oxides and 
copolymers of ethylene oxide, propylene oxide and butylene oxide, 
preferably the block copolymers thereof, are also preferred; polyethylene 
oxides with molecular weights of between 200 and 10,000, and more 
preferably of between 400 and 1,500 are particularly preferred. The 
polyetherdiols are advantageously employed in combination with 
low-molecular aliphatic diols, for example 1,4-butanediol, 
1,3-propanediol, ethylene glycol, diethylene glycol, 1,2-hexanediol, 
1,2-propanediol, pentanediol or cyclohexanediol. The molar ratio of 
polyetherdiol to low-molecular aliphatic diol is preferably from about 
1:0.1 to 1:0.7. 
Diisocyanate components which can be employed are aromatic diisocyanates. 
Aliphatic and/or cycloaliphatic diisocyanates are preferred. Preferred 
aliphatic diisocyanates are those having 2 to 12 carbon atoms in the 
aliphatic radical, for example, ethylene diisocyanate, propylene 
diisocyanate, tetramethylene diisocyanate and 2,2,4-trimethylhexamethylene 
diisocyanate. Preferred cycloaliphatic diisocyanates are, for example, 
1,4-diisocyanato-cyclohexane, dicyclohexylmethane-4,4'-diisocyanate and 
isophorone diisocyanate. Hexamethylene diisocyanate and isophorone 
diisocyanate are particularly preferred. 
The molar ratio of diol diisocyanate component is preferably between about 
1:0.99 and 1:0.5, in particular between about 1:0.98 and 1:0.7. The 
average molecular weights of the polyurethanes are preferably between 
about 200 and 100,000, in particular between about 1,000 and 50,000, and 
more particularly between about 3,000 and 25,000. 
Carboxylic acid vinyl esters having about 3 to 20 and preferably about 4 to 
14 carbon atoms are employed for grafting onto the polyurethane. Vinyl 
acetate and/or vinyl propionate, in particular vinyl acetate, are 
preferred mixtures of vinyl acetate and/or vinyl propionate and vinyl 
versatate are also preferred. In particular in the case of partial or 
complete saponification of the products following the graft 
polymerization, the co-use of vinyl propionate in addition to vinyl 
acetate during grafting is advantageous. Moreover, copolymerizable 
mixtures of carboxylic acid vinyl esters can be grafted, preferably 
mixtures of vinyl acetate and minor amounts of vinyl versatate. 
Grafting with different carboxylic acid vinyl esters in the form of block 
copolymers, optionally in combination with further 
ethylenically-unsaturated and copolymerizable monomers, can also be 
advantageous. Furthermore, the carboxylic acid vinyl esters can also be 
grafted together with other ethylenically-unsaturated and copolymerizable 
monomers, such as maleic acid, itaconic acid, mesaconic acid, crotonic 
acid, acrylic acid or the esters thereof. 
The graft polymers obtained can be converted by hydrolysis, alcoholysis or 
transesterification into partially or completely saponified products, the 
degree of hydrolysis being at least about 1 mol %, preferably about 45 to 
99 mol %, based on the mole number of saponifiable monomer units in the 
graft polymer. The production of graft polymers with a polyurethane graft 
backbone is described in DE 37 32 089. 
The saponified graft polymers can be acetalized in an acidic medium by 
means of known methods. 
Aliphatic aldehydes having 1 to 20 carbon atoms, which may be substituted, 
and aromatic aldehydes, which may also be substituted, are employed for 
acetalizing. Preference is given to aliphatic aldehydes having 1 to 5 
carbon atoms, such as n-butyraldehyde, isobutyraldehyde, propionaldehyde 
or formaldehyde. Substituted or unsubstituted benzaldehydes, such as 
benzaldehyde, p-chlorobenzaldehyde or p-methoxybenzaldehyde are also 
suited. It is also possible to employ combinations of several of these 
aldehydes. 
The degree of acetalization of the graft polyvinyl acetals used as binders 
in accordance with this invention is preferably selected such that the 
content of non-acetalized polyvinyl alcohol units in the graft polyvinyl 
acetals is greater than about 15 mol %, in particular about 18 to 60 mol 
%, and most preferably about 20 to 45 mol %, each time relative to the 
molar amount of vinyl alcohol units contained in the saponified graft 
polymers used, it being possible for up to about 55 mol %, relative to the 
original amount, to be present as vinyl ester units. The hydroxyl number 
of the ready-for-use binder should be in the range of about 100 to 800. 
The acetalization can be performed employing two different methods. In 
accordance with the first, the graft polymer is dissolved or dispersed in 
an alcohol or in a water/alcohol mixture, mixed with a catalytic amount of 
an organic or inorganic acid and an aldehyde or aldehyde mixture, and 
heated. The resulting polymer solution, which where appropriate also 
contains an anti-oxidant, can either be used directly for preparing the 
mixtures according to this invention, or alternatively, the polymer can be 
precipitated and purified by dropwise adding the solution to a 
non-solvent. 
In accordance with the second process, the graft polymer is dissolved in 
water and mixed with an aldehyde or aldehyde mixture. Subsequently, an 
aqueous solution of an inorganic or strong organic acid--if appropriate 
with the addition of a surfactant and an antioxidant--is added dropwise at 
a low temperature. Thereby, the acetalized graft polymer is precipitated. 
The reaction is completed at an increased temperature of about 20.degree. 
to 60.degree. C. The isolated polymer is purified by washing with water or 
re-precipitation. 
To prepare the graft polyvinyl acetals in an aqueous medium, known methods 
are employed to produce about 1 to 50% strength, preferably about 5 to 20% 
strength, aqueous solutions of the graft polyvinyl alcohols, preferably at 
elevated temperatures. The acid catalyst is added, the solutions are then 
cooled to temperatures of less than about 25.degree. C., and the 
acetalization reaction is finally performed by metering in the aldehyde 
with agitating, preferably within a time of 3 to 300 minutes. As is known, 
the aldehyde conversion is incomplete in most cases, and therefore an 
excess of aldehyde, preferably of about 10 to 20 mole percent, is usually 
added. 
In a preferred process variant, the aqueous solution is allowed to stand 
for at least about 30 minutes at temperatures of about 0.degree. to 
5.degree. C. prior to the start of the reaction, whereupon the graft 
polyvinyl acetal formed is generally separated off after a short time, as 
a pulverulent substance. To complete the reaction, the reaction mixture is 
slowly heated to room temperature, and where appropriate it is 
post-reacted at elevated temperatures, for example at about 25.degree. to 
70.degree. C., during about one to three hours. The added amount of acid 
catalyst depends, inter alia, on the degree of acetalization to be 
achieved and may preferably be up to about 1.1 mole, relative to the molar 
content of vinyl alcohol units. 
The resulting graft polyvinyl acetal is isolated by suction, washed with 
weakly alkaline water (pH 9 to 12) and dried. Acetalization products that 
do not precipitate from the aqueous reaction solution can be isolated by 
the addition of precipitating agents, purified and dried. 
The acetalization can also be performed in organic solvents. Suitable 
solvents include water-miscible solvents, in particular water-soluble 
alcohols, such as ethanol and/or methanol, to which water may be added. 
Preferred acid catalysts are organic sulfonic acids, for example, toluene 
sulfonic acids, and also mineral acids, for example sulfuric acid, 
phosphoric acid, hydrochloric acid or nitric acid. Among these, preference 
is given to phosphoric acid and hydrochloric acid. 
For performing the preparation in organic solvents, the acid catalyst, the 
aldehyde and the graft polyvinyl alcohol are dispersed or dissolved in the 
solvent, and the mixture is refluxed. It may also be expedient to add the 
aldehyde in the course of the reaction. The graft polyvinyl alcohols which 
are insoluble in the organic solvents gradually dissolve as a consequence 
of the acetalization in progress. 
When the acetalization reaction is completed, the reaction product is 
precipitated by adding non-polar solvents, for example, aliphatic 
hydrocarbons, or by pouring the reaction solution into ice-cold water or 
an ice-cold water/alcohol mixture, isolated by suction, washed with weakly 
alkaline water (pH 9 to 12), and dried. 
The preparation of the graft polyvinyl acetals is also described in German 
Patent Application P 38 35 840.9. 
In combination with diazonium salt polycondensation products or azido 
derivatives, the polymers obtained in this way result in layers which can 
be developed easily and without scumming. Depending on their individual 
composition, the layers can be developed with aqueous solutions of 
inorganic salts and/or surfactants or with aqueous-alkaline solutions. The 
layers are distinguished by a high abrasion resistance, good ink 
acceptance and adequate shelf lives and can therefore be used for numerous 
applications, in particular for producing planographic printing plates, 
screen printing stencils and photoresists. 
Suitable diazonium salt polycondensation products are condensation products 
of condensible aromatic diazonium salts, for example, of 
diphenylamine-4-diazonium salts, with aldehydes, preferably with 
formaldehyde. It is particularly advantageous to use cocondensation 
products containing, in addition to the diazonium salt units A-N.sub.2 X, 
other, non-photosensitive units B which are derived from condensible 
compounds, particularly from aromatic amines, phenols, phenol ethers, 
aromatic thioethers, aromatic hydrocarbons, aromatic heterocyclic 
compounds and organic acid amines. These condensation products are 
described in DE 20 24 244. Generally, all diazonium salt polycondensation 
products described in DE 27 39 774 are suitable. 
The diazonium salt units A-N.sub.2 X are preferably derived from compounds 
corresponding to the formula 
EQU (R.sup.1 -R.sup.2 -).sub.p R.sup.3 -N.sub.2, 
in which 
X is the anion of the diazonium compound, 
p is an integer from 1 to 3, 
R.sup.1 is an aromatic radical which is capable, in at least one position, 
of condensation with an active carbonyl compound, 
R.sup.3 is an arylene group, preferably a phenylene group which may be 
substituted, 
R.sup.2 is a single bond or one of the groups: 
EQU --(CH.sub.2).sub.q --NR.sup.4 --, 
EQU --O--(CH.sub.2).sub.r --NR.sup.4 --, 
EQU --S--(CH.sub.2).sub.r --NR.sup.4 --, 
EQU --S--CH.sub.2 CO--Nr.sup.4 --, 
EQU --O--R.sup.5 --O--, 
EQU --O--, 
EQU --S--, or 
EQU --CO--NR.sup.4 --, 
where 
q is a number from 0 to 5, 
r is a number from 2 to 5, 
R.sup.4 is a hydrogen atom, an alkyl group having from 1 to 5 carbon atoms, 
an aralkyl group having from 7 to 12 carbon atoms or an aryl group having 
from 6 to 12 carbon atoms, and 
R.sup.5 is an arylene group having from 6 to 12 carbon atoms. 
Further advantageous polycondensation products are obtained by condensing 
an optionally-substituted diphenylamine diazonium salt first with an 
aromatic compound R'--O--CH.sub.2 --B and then with an aromatic compound 
R'--O--CH.sub.2 --B--CH.sub.2 --O--R', R' denoting a hydrogen atom, an 
alkyl radical or an aliphatic acyl radical, and B denoting the radical of 
any one of the condensible compounds listed above. These condensation 
products are described in detail in EP 126,875. 
Low- or high-molecular weight azido derivatives are also suitable for use 
as photosensitive compounds for certain applications, preference being 
given to low-molecule weight azido compounds having at least two azido 
groups per molecule. Examples of suitable compounds include 
4,4'-diazidostilbenes, 4,4'-diazidobenzophenones, 
4,4'-diazidobenzalacetophenones, 4,4'-diazidobenzalacetones and 
4,4'-diazidobenzalcyclohexanones. Where appropriate, the photospeed of 
azido compounds of this type can be increased by adding suitable 
sensitizers, for example 1,2-benzanthraquinone. It is also possible to use 
polyfunctional azides whose absorption is shifted as a result of 
conjugation with double bonds in the molecule, so that no additional 
sensitization is required upon exposure. Further suitable azido compounds 
are described in GB 790,131, DE 950,618 and U.S. Pat. No. 2,848,328. 
The mixtures according to the present invention generally comprise from 
about 5 to 90, preferably from about 10 to 70, percent by weight of 
photosensitive compound, and from about 90 to 10, preferably from about 75 
to 20, percent by weight of graft polymer. 
To stabilize the photosensitive mixture, it is advantageous to add a 
compound having an acidic character. Compounds which can be used include 
mineral acids and strong organic acids, with phosphoric acid, sulfuric 
acid, perchloric acid, boric acid or p-toluene sulfonic acid being 
preferred. Phosphoric acid is a particularly suitable acid. 
Plasticizers, adhesion promoters and contrast-enhancing agents can also be 
added to the mixtures. 
The types and quantities of such additions depend upon the field of 
application for which the photosensitive mixture is intended. In 
principle, care must be taken that the added substances do not absorb an 
excessive portion of the actinic light which is required for 
cross-linking, because this would result in a reduction of the practical 
sensitivity to light. 
In addition, the photosensitive mixtures can contain dyes and/or pigments 
which may serve to enhance the contrast upon exposure and also to harden 
the layer. Suitable dyes are, for example, specified in U.S. Pat. No. 
3,218,167 and U.S. Pat. No. 3,884,693. Particularly suitable are, for 
example, Victoria Pure Blue FGA, Victoria Pure Blue BO (C.I. 42,595), 
Malachite Green, Victoria Blue B (C.I. 44,045), Renol Blue B2G-H (C.I. 
74,160), Crystal Violet, Fatty Red 5B (C.I. 26,125), Neozapon Blue FLE 
(C.I. Solvent Blue 70), Brilliant Blue Salt Acetate, Samarone Navy-Blue, 
Orasol Blue GN, Zapon Fast Fire-Red B (C.I. 13,900:1) or Rhodamine 6 GDN 
(C.I. 45,160). To enhance the image contrast after exposure, Metanil 
Yellow (C.I 13,065), Methyl Orange (C.I. 13,025) or phenylazodiphenylamine 
can be used. 
For particular purposes it can be favorable to admix the photosensitive 
mixtures of the invention with further polymers in quantities of up to 
about 50 percent by weight, preferably up to about 20 percent by weight, 
relative to the above-described polymeric binders. 
Within the scope of the present invention, the following weight proportions 
of the most important components of the photosensitive mixture are 
preferred, which are, in each case, based on the content of non-volatile 
constituents, i.e., the constituents of the solid photosensitive layer 
obtained after evaporation of the solvent: 
______________________________________ 
Binder: 20 to 90% 
photosensitive compound: 
10 to 70% 
acid: 0 to 10% 
dye or pigment: 0 to 12% 
dye which changes its 0 to 5%. 
color upon exposure: 
______________________________________ 
The support material is coated from appropriate organic solvents or solvent 
mixtures, generally by flow-coating, spraying or dipping. The coating 
method depends on the desired layer thickness, the dried layers usually 
having thicknesses between about 0.5 and 200 .mu.m. 
Suitable supports are, for example, magnesium, zinc, copper, mechanically, 
chemically and electrochemically grained aluminum, anodically oxidized 
aluminum, steel, and also polyester film or cellulose acetate film, Perlon 
gauze, etc., the surface of which may have been subjected to a 
pretreatment. The support material may function as the final support or as 
a temporary support material from which the photosensitive layer is 
transferred by lamination to the workpiece to be processed. 
The recording material which is prepared using the photosensitive mixtures 
of the invention serves, on the one hand, to produce images on suitable 
supports or receptor sheets and, on the other hand to produce reliefs 
which are used as printing plates, screens, resists, and the like. 
In addition, it is also possible to use the photosensitive mixtures for the 
formulation of UV-hardenable printing inks or for the preparation of 
lacquers which are hardenable by ultraviolet radiation and may be used for 
the protection of surfaces. 
Primarily, the compositions are used for the production of lithographic 
printing plates, in which aluminum is the preferred support material. It 
is particularly preferred to pretreat the aluminum used for this purpose 
in the usual manner, for example, by a mechanical, chemical or 
electrochemical graining process which is optionally followed by an anodic 
oxidation. A further treatment of this support material, for example, with 
polyvinyl phosphonic acid, alkali metal silicate, phosphate, 
hexafluorozirconate, chromate, borate, polyacrylamide and cellulose 
derivatives is advantageous. 
The recording materials obtained from the mixtures are processed in the 
conventional manner, by exposing imagewise and washing-out the unexposed 
areas of the layer with a suitable developer. 
The recording material is exposed under an original, as is known in the 
art, using light sources which emit light with the highest possible 
spectral fraction in the near ultraviolet region. The material can also be 
exposed by laser irradiation. Suitable lasers for irradiation are 
shorter-wave lasers of adequate performance, for example, Ar lasers, 
krypton ion lasers, helium/cadmium lasers, emitting in the region between 
about 300 and 600 nm and, for some layers, even CO2 lasers, which emit at 
about 10.6 .mu.m, or YAG lasers emitting at about 1.06 .mu.m. 
As the developer solutions, water or neutral or alkaline aqueous solutions 
are used, which have a pH value in the range from about 6 to 14, 
preferably from about 7.5 to 12, and which contain buffer salts, for 
example, water-soluble alkali metal phosphates, alkali metal silicates, 
alkali metal borates, alkali metal carbonates, alkali metal acetates or 
alkali metal benzoates. Additional constituents used are wetting agents, 
preferably anionic wetting agents and, if appropriate, water-soluble 
polymers. The solution can also contain minor amounts, for example, up to 
about 5 percent by weight, preferably not more than about 2 percent by 
weight, of water-miscible organic solvents. Solvents that are difficultly 
volatile are preferred, for example, araliphatic alcohols, the vapor 
pressure of which is of no consequence in the handling of the developer. 
Development can be performed in the conventional manner by dipping, 
spraying, brushing or wiping-over with a pad. If desired, the developed 
material can be treated with a gumming solution. 
The photosensitive recording materials of this invention are distinguished 
by good reproduction properties and an adequate shelf life. They can be 
easily developed without scum, using developer solutions which from an 
ecological point of view are virtually neutral. 
The large print runs and the good ink acceptance obtained with printing 
forms prepared using the material of the present invention are 
particularly advantageous. The printing stencils are also highly resistant 
to alkaline developers and other processing solutions. 
The preparation of the polyvinyl acetals used in the Examples is described 
below. 
a) PREATION OF POLYURETHANE GRAFT BACKBONES 
In each case, the diol component and the catalyst were first introduced 
into a reaction vessel equipped with a stirrer and supplied with a 
nitrogen atmosphere, and the mixture was heated to a reaction temperature 
of between 65.degree. C. and 100.degree. C. Then the diisocyanate 
component was metered in, with care being taken to ensure that the 
temperature of the reaction mixture did not exceed 120.degree. C., and 
preferably did not exceed 100.degree. C. After the complete addition of 
the diisocyanate component, the mixture was post-heated to a temperature 
between 80.degree. C. and 100.degree. C. for a period of up to two hours 
in order to complete the reaction. The completion of the conversion, and 
thus the end of the reaction, were determined by an analysis of the 
diisocyanate consumption with the aid of known methods (p.e., 
IR-spectroscopy, titration). 
The detailed composition of the reaction mixtures used in the Examples and 
the calculated mean molecular weights (M.sub.calc) of the resulting 
polyurethanes (PU) are compiled in Table 1 below. The molecular weights 
result from the molar ratio diol component/diisocyanate, assuming a 
complete conversion of the NCO groups. 
TABLE 1 
______________________________________ 
Diol Molar ratio 
Poly- component Reaction diol com- 
urethane 
PEG/PU temperature ponent/ 
(PU) (molar ratio) 
(.degree.C.) 
diisocyanate 
-- M.sub.calc 
______________________________________ 
A 7:3 80 1:0.9 6,470 
B 7:3 72 1:0.9 6,470 
C 3:2 78 1:0.97 18,300 
D 7:3 75 1:0.97 19,900 
E 7:3 78 1:0.95 13,200 
______________________________________ 
PEG = Polyethylene glycol, molecular weight 600 
Bu = 1,4butanediol 
All products were prepared using isophorone diisocyanate as the 
diisocyanate component. In each case, 1,4-dimethylpiperazine was used as 
the catalyst in an amount of 0.48 mol %, relative to the diisocyanate. 
b) PREATION OF THE GRAFT POLYMERS 
In each case, the polyurethane graft backbone was melted in a reaction 
vessel in a nitrogen atmosphere or was dissolved, respectively, by adding 
small amounts of methanol, and heated to a temperature between 60.degree. 
C. and 100.degree. C. The monomers to be grafted on, which had optionally 
been dissolved in a solvent, e.g., methanol, including the free-radical 
initiator dissolved in the monomer, were then slowly metered to the 
polyurethane graft backbone, such that homopolymer formation was largely 
suppressed. 
The maximum temperature of the reaction mixture should be 120.degree. C., 
more preferably 100.degree. C. 
When the post-reaction was completed, excess monomer remainders were 
removed by azeotropic distillation with methanol. The compositions of the 
individual reaction mixtures and the reaction parameters are compiled in 
Table 2 below. 
TABLE 2 
__________________________________________________________________________ 
VAc 
Cr Start 
Metering 
Post- 
Grafted-on 
calc. 
Graft g/g 
g/g temp. 
time react. 
monom. 
J.sub.o 
molecular 
polymer 
PU PU PU .degree.C. 
min min wt % ml/g 
weight 
__________________________________________________________________________ 
AV A 4 0 75 420 45 79.8 21.9 
31,300 
BV B 2.32 
0 73 420 45 69.3 18.3 
21,000 
CV C 3.16 
0 75 300 45 74.7 26.3 
72,500 
DV D 3.16 
0 75 420 45 74.5 28.7 
78,000 
EVCr E 3.13 
0.027 
75 300 45 75.1 30.5 
53,000 
EVCr' 
E 3.03 
0.126 
75 300 45 75.3 31.5 
53,000 
__________________________________________________________________________ 
VAc = Vinyl acetate 
Jo = intrinsic viscosity 
Cr = Crotonic acid 
All products were prepared employing 0.2 mol % of dibenzoyl peroxide 
(relative to the monomer used in each case). The intrinsic viscosities 
were determined at 25 C in tetrahydrofuran, using an Ostwald Viscosimeter, 
with the measured concentrations being selected such that a Hagenbach 
correction was not necessary. The grafted-on amount of monomer, in % by 
weight, is related to the weight of the total polymer. 
c) SAPONIFICATION OF THE GRAFT POLYMERS 
The graft polymers of Table 2 were transesterified or saponified within two 
hours at room temperature. For this purpose, the products were dissolved 
in methanol to give 50 % strength solutions and mixed with methanolic soda 
lye (10% strength). Depending on the added amount of alkali and the degree 
of grafting of the graft polymer, polymeric hydrolysis products having 
different degrees of hydrolysis were obtained. Partial saponifications 
were performed with the co-use of water. The resulting gels were 
granulated using conventional mills, the granules were washed with 
methanol (where appropriate with an addition of acetic acid to neutralize 
the soda lye) and dried. The process parameters and results are compiled 
in Table 3 below. 
TABLE 3 
______________________________________ 
mole % 
Graft Graft of NaOH mole % of 
Degree of 
polyvinyl 
polyvinyl 
per H.sub.2 O per 
hydrolysis 
alcohol 
acetate ester unit 
ester unit 
in % M.sub.calc 
______________________________________ 
F AV 1.92 0 98.2 22,000 
G BV 5.00 0 98.9 14,000 
H CV 1.92 0 98.0 47,000 
I DV 1.97 0 98.4 44,000 
K CV 0.56 12.53 60.0 56,600 
L CV 0.50 11.13 56.5 57,600 
M EVCr 1.59 0 92.7* 40,000 
N EVCr' 2.00 0 94.5* 36,000 
______________________________________ 
*found by determination of the acid present following saponification; the 
crotonic acid present in the polymer is also measured. 
d) PREATION OF THE GRAFT POLYVINYL ACETALS 
The graft polymers listed in Table 3 were dissolved in about eight times 
their amount of distilled water. The corresponding amount of aldehyde and 
a small amount of 2,6-di-tert.-butyl-4-methylphenol were added at room 
temperature. A solution comprising a small amount of sodium octyl sulfate, 
1/3 of the weight amount of the aldehyde of concentrated hydrochloric acid 
and water was dropwise added to this solution, with agitating. The mixture 
was stirred for one hour at room temperature, then heated to 40.degree. 
C., and stirring was continued for another two hours. Thereafter 
concentrated hydrochloric acid (the same weight amount as the aldehyde) 
was added and stirring was continued at 40.degree. C. for a further two 
hours. When the mixture had cooled down to room temperature the aqueous 
phase was decanted from the precipitated polymer, the polymer was 
dissolved in ethanol and precipitated by pouring it into an excess amount 
of water. The polymer was dried in a vacuum drier at 40.degree. C. until 
its weight remained constant. 
TABLE 4 
______________________________________ 
Graft Graft 
polyvinyl acetal 
polyvinyl alcohol 
Aldehyde OH number 
______________________________________ 
O F Bu 370 
P G Bu 290 
Q H Pr 336 
R K Bu 124 
S H Ac + Bu 1) 144 
T H Bz + Pr 2) 328 
U H Bz 393 
V H Bu 201 
W M Pr 401 
X N Bu 351 
______________________________________ 
Bu = nbutyraldehyde 
Ac = acetaldehyde 
Bz = benzaldehyde 
Pr = propionaldehyde 
1) Molar ratio 4.6:1 
2) Molar ratio 1:1 
Preferred embodiments of the invention are described in the Examples which 
follow. In most cases, amounts are indicated in parts by weight (pbw). 
Unless otherwise specified, percentages and proportions are given in 
weight units. 
EXAMPLE 1 
A coating solution comprised of 
______________________________________ 
2.600 pbw of polymer I, 
2.600 pbw of a diazonium salt poly- 
condensation product prepared from 
1 mole of 3-methoxy-diphenylamine- 
4-diazonium sulfate and 1 mole of 
4,4'-bis-methoxy-methy1- 
diphenylether, isolated as methane 
sulfonate, 
0.117 pbw of phosphoric acid (85% strength) 
and 
0.340 pbw of Basonyl Red 540 (C.I. 45,170), 
in 
160.000 pbw of distilled water 
______________________________________ 
is applied to a 0.3 mm thick aluminum foil which has been electrochemically 
grained in nitric acid, anodically-oxidized in sulfuric acid and 
post-treated with a 0.1% strength aqueous solution of polyvinyl phosphoic 
acid. Application is performed such that a dry layer weight of 0.52 
g/m.sup.2 results. 
The photosensitive layer obtained in this way is exposed for 36 seconds 
through a standard test original by means of a 5 kW metal halide lamp. The 
exposed layer exhibits a clear contrast between the exposed and unexposed 
areas and is developed by spraying with a jet of water, whereby the 
non-exposed layer portions are completely removed within a short time. The 
plate is subsequently dried. The copy reproduces even the finest elements 
of the original. 
EXAMPLE 2 
A coating solution comprised of 
______________________________________ 
2.500 pbw of polymer O, 
2.860 pbw of a diazonium salt poly- 
condensation product prepared from 
1 mole of 3-methoxy-diphenylamine- 
4-diazonium sulfate and 1 mole of 
4,4'-bis-methoxy-methy1- 
diphenylether, isolated as 
mesitylene sulfonate, 
0.100 pbw of phosphoric acid (85% strength) 
and 
0.028 pbw of phenylazodiphenylamine and 
0.130 pbw of Victoria Pure Blue FGA 
(C.I. Basic Blue 81), in 
22.900 pbw of tetrahydrofuran and 
118.000 pbw of 2-methoxyethanol 
______________________________________ 
is applied to an aluminum foil pretreated as described in Example 1, such 
that the dried layer has a weight of 1.0 g/m.sup.2. The layer is exposed 
for 30 seconds as described in Example 1. Development is performed with a 
developer solution having the following composition: 
______________________________________ 
5.0 pbw of sodium octyl sulfate, 
1.0 pbw of sodium metasilicate .times. 5 H.sub.2 O, and 
94.0 pbw of distilled water. 
______________________________________ 
The non-exposed layer areas are removed within a short time without 
remainders being left behind. The plate is then rinsed with water and 
dried. Even the finest image elements of the original are reproduced on 
the copy. More than 200,000 prints can be run in a sheet-fad offset press 
with the printing plate produced in this way. 
EXAMPLE 3 
A coating solution comprised of 
______________________________________ 
3.40 pbw of polymer P, 
1.10 pbw of the diazonium salt 
polycondensation product described 
in Example 2, 
0.050 pbw of phosphoric acid (85% strength), 
0.11 pbw of Metanil Yellow (C.I. 13,065) 
and 
0.15 pbw of Victoria Blue B (C.I. 44,045), 
in 
160.00 pbw of 2-methoxyethanol 
______________________________________ 
is applied in an aluminum foil pretreated as described in Example 1, such 
that the dried layer has a weight of 0.9 g/m.sup.2. The layer is exposed 
for 30 seconds as described in Example 2. Development is performed with a 
developer solution having the following composition: 
______________________________________ 
5.0 pbw of sodium octyl sulfate, 
1.5 pbw of sodium metasilicate .times. 5 H.sub.2 O, 
1.5 pbw of trisodium phosphate .times. x 12 H.sub.2 O, and 
92.0 pbw of distilled water. 
______________________________________ 
The non-exposed layer areas are instantaneously removed. Even the finest 
image elements of the original are reproduced on the copy. More than 
250,000 prints can be run in a sheet-fad press machine with the printing 
plate produced in this way. 
EXAMPLE 4 
A coating solution comprised of 
______________________________________ 
3.60 pbw of polymer L, 
1.80 pbw of the diazonium salt polycondensation 
product described in Example 2, 
0.20 pbw of phosphoric acid (85% strength), 
0.10 pbw of Crystal Violet (C.I. 42,555) and 
0.06 pbw of phenylazodiphenylamine, in 
150.00 pbw of 2-methoxyethanol, 
______________________________________ 
is applied to an aluminum foil pretreated as in Example 1, in a way such 
that a dry layer weight of 1.2 g/m.sup.2 is obtained. 
After an exposure time of 15 seconds the layer is developed by wiping it 
with a plush dabber, using a developer solution having the following 
composition: 
______________________________________ 
5.0 pbw of sodium octyl sulfate, 
1.0 pbw of sodium metasilicate .times. 5 H.sub.2 O, 
1.0 pbw of trisodium phosphate .times. 12 H.sub.2 O, 
0.5 pbw of disodium hydrogen phosphate .times. 1 H.sub.2 O, 
and 
92.0 pbw of water. 
______________________________________ 
The non-exposed layer areas are completely removed. Subsequently, the plate 
is rinsed with water and dried. 
On the copy, a solid step 4 is obtained of a silver film continuous-tone 
step wedge having a density range of 0.15 to 1.50 with increments of 0.15. 
The plate thus produced gives 220,000 prints in a sheet-fed offset press. 
EXAMPLE 5 
A coating solution comprised of 
______________________________________ 
2.500 pbw of polymer R, 
2.500 pbw of the diazonium salt 
polycondensation product 
described in Example 2, 
0.118 pbw of phosphoric acid (85% strength), 
0.045 pbw of phenylazodiphenylamine and 
0.100 pbw of Crystal Violet, in 
160.000 pbw of 2-methoxymethanol 
______________________________________ 
is applied to the aluminum support described in Example 1, such that a dry 
layer weight of 1.0 g/m.sup.2 is obtained. The plate obtained following 
exposure and development as described in Example 2 gives several thousands 
of quality prints. 
EXAMPLE 6 
A coating solution comprised of 
______________________________________ 
1.300 pbw of polymer Q, 
1.300 pbw of the diazonium salt polycondensation 
poduct described in Example 2, 
0.059 pbw of phosphoric acid (85% strength), 
0.023 pbw of phenylazodiphenylamine and 
0.340 pbw of Renol Blue B2G-H (C.I. 74,160), in 
90.000 pbw of 2-methoxyethanol 
______________________________________ 
is applied to the support material described in Example 1, such that a dry 
layer weight of 1.1 g/m.sup.2 is obtained. After exposure and development 
as described in Example 2, a copy of the original is obtained where step 4 
of the continuous-tone step wedge (cf. Example 4) is solid. The printing 
plate gives 240,000 prints on a sheet-fed offset press. 
EXAMPLE 7 
Instead of the polymer Q, the binder S is employed for preparing a coating 
solution as in Example 6. 
This coating solution is applied onto an aluminum foil pretreated as in 
Example 1, and dried. The dry layer weight is about 1 g/m.sup.2. 
The photosensitive layer is exposed through a negative original for 30 
seconds, using the lamp described in Example 1, and is then developed with 
the developer specified in Example 3. 
The layer is rubbed with a plush dabber, and after a few seconds, the 
non-image areas of the copying layer dissolve away, and the plate is 
thereafter rinsed with water and dried. The copy has the same quality as 
the copy of Example 3. In a sheet-fed offset press, the plate gives 
210,000 good prints. 
EXAMPLE 8 
A coating solution is prepared as described in Example 6, with the 
exception that polymer T is employed. Processing is the same as in Example 
6. A high-resolution copy results after imagewise exposure (30 seconds) 
and development. When clamped in a sheet-fed offset press, the printing 
form obtained gives more than 200,000 high-quality prints. 
EXAMPLE 9 
A coating solution is prepared as described in Example 2, with the 
exception that polymer U is employed, and is applied to aluminum foil 
pretreated as described above such that a dry layer weight of 0.95 
g/m.sup.2 is obtained. 
The layer is exposed for 30 seconds as described in Example 1. Development 
is performed with a developer solution of the following composition: 
______________________________________ 
5.0 pbw of sodium octyl sulfate, 
1.5 pbw of sodium metasilicate .times. 5 H.sub.2 O, 
1.0 pbw of trisodium phosphate .times. 12 H.sub.2 O, 
1.0 pbw of phenoxyethanol, and 
91.5 pbw of water. 
______________________________________ 
The non-image areas of the layer are readily dissolved away after wiping 
the plate with a plush pad for just a few seconds; the plate is then 
rinsed with water and dried. The resulting copy of the original exhibits a 
high resolution. 
EXAMPLE 10 
The shelf life of the layer described in Example 6 is tested. For this 
purpose, plates are prepared using the photosensitive mixture described in 
Example 6 and are stored at 100.degree. C. in a drying oven for 1 to 4 
hours. Subsequently, the plates are imagewise exposed and developed with 
the developer solution of Example 2. To render visible any layer residues 
(toning) remaining in the non-image areas, the dried plates are dyed with 
a protective ink. The plates stored in the oven for 1 and 2 hours can be 
developed satisfactorily. They do not exhibit any extension of the 
continuous-tone step wedge. After a storage time of 3 hours, the 
continuous-tone step wedge is extended by half a step. Development is 
insignificantly retarded. The plate stored for 4 hours exhibits an 
increase of 1.5 step. Development is slightly retarded. These results show 
that the mixtures according to this invention have a relatively good 
resistance to storage in the heat. 
EXAMPLE 11 
A coating solution comprised of 
______________________________________ 
1.10 pbw of polymer V, 
1.10 pbw of 4,4'-diazido-stilbene-2,2'-disulfonic 
acid sodium salt, 
0.15 pbw of Rhodamine 6 GDN extra (C.I. 45,160), 
and 
0.05 pbw of Michler's ketone, in 
15.00 pbw of tetrahydrofuran, 
10.00 pbw of water and 
50.00 pbw of 2-methoxyethanol 
______________________________________ 
is applied to the support described in Example 1. such that a dry layer 
weight of 0.8 g/mz is obtained The copying layer is exposed for 35 seconds 
through a negative original and then developed with pure water, whereby 
the non-image areas are removed within a short time. 
EXAMPLES 12 TO 18 
The Examples which follow are intended to illustrate that the 
photosensitive layers according to this invention can be more readily 
developed with aqueous developers than layers containing customary, 
commercially-available polyvinyl acetals, and that at the same time the 
copying and printing behavior of the plates according to this invention is 
as good as or superior to that of the plates employed in the Comparative 
Examples (C). For this purpose, six coating solutions are prepared which 
only differ in the polymer employed: 
______________________________________ 
3.60 pbw of the respective polymer, 
1.80 pbw of the diazonium salt polycondensation 
product of Example 2, 
0.20 pbw of phosphoric acid (85% strength), 
0.10 pbw of Crystal Violet (C.I 42,555) and 
0.06 pbw of phenylazodiphenylamine, in 
150.00 pbw of 2-methoxyethanol. 
______________________________________ 
The polymers employed in the individual Examples, their OH numbers as well 
as the developability, resolution, ink acceptance and print run of the 
individual photosensitive layers are specified in Table 5 below. All 
layers have a dry weight of 1.0 g/m.sup.2. They are applied to supports 
comprising aluminum which has been electrolytically grained in nitric 
acid, anodically oxidized and post-treated with polyvinyl phosphoric acid. 
TABLE 5 
__________________________________________________________________________ 
Example 
12 13 14 15(C) 
(16(C) 
17(C) 
18(C) 
__________________________________________________________________________ 
Polymer 
0 L Q But But But For 
Molecular 
30,400 
57,600 
62,300 
85,000 
85,000 
85,000 
30,000 
weight 
OH-number 
370 
347 
336 
300 
220 
160 
85 
Developer 
(a) + + + - - - - 
(b) + + + - - - - 
(c) + (+) (+) (+) - - + 
(d) + + + - - - - 
(e) (+) (+) (+) + + (+) (+) 
Ink good good good good good good good 
acceptance 
Print run 
200,000 
220,000 
240,000 
120,000 
120,000 
120,000 
220,000 
__________________________________________________________________________ 
But = commercially available polyvinyl butyrals 
For = commercially available polyvinyl formal 
+ = developer well suited 
- = developer not suited, since no layer differentiation 
(+) = developer not very well suited, since poor layer differentiation o 
attack on exposed layer areas 
______________________________________ 
Composition of the developers: 
(a) Developer of Example 2 
(b) 0.2 pbw of sodium metasilicate .times. 9 H.sub.2 O, 
4.0 pbw of disodium hydrogen phosphate .times. 
12 H.sub.2 O, 
3.5 pbw of trisodium phosphate .times. 12 H.sub.2 O, 
1.5 pbw of potassium tetraborate .times. 4 H.sub.2 O, 
2.0 pbw of potassium oxalate .times. 1 H.sub.2 O, 
88.8 pbw of water 
(c) 1.0 pbw of sodium tetraborate .times. 4 H.sub.2 O, 
2.0 pbw of sodium octylsulfate, 
15.0 pbw of sodium salicylate, 
2.5 pbw of sodium benzoate, 
5.0 pbw of trisodium citrate .times. 2 H.sub.2 O, 
1.0 pbw of phenoxyethanol, 
73.5 pbw of water 
(d) 1.0 pbw of NaOH, 
4.0 pbw of pelargonic acid, 
12.0 pbw of ethylene oxide/propylene oxide 
copolymer, 
4 pbw of sodium tetrapolyphosphate, 
79 pbw of water 
(e) 0.5 pbw of ethylene carbonate, 
15.0 pbw of 2-hydroxyethylacetate, 
10.0 pbw of glycerol, 
1.0 pbw of sodium benzoate, 
0.5 pbw of benzoid acid 
50.0 pbw of propylene glycol monomethyl 
ether, 
23.0 pbw of water. 
______________________________________ 
These Examples show that the photosensitive mixtures according to this 
invention can be easily developed with aqueous solutions, whereas this is 
not the case with the mixtures used in the Comparative Examples. The 
latter can only be processed with solvent-containing developers. 
EXAMPLE 19 
A coating solution is prepared from 
______________________________________ 
1.1 pbw of polymer I 
1.1 pbw of 4,4'-diazidostilbene-2,2'-disulfonic 
acid disodium salt, 
0.15 pbw of Basonyl Red 540 and 
0.05 pbw of Michler's ketone, in 
50.00 pbw of methanol and 
50.00 pbw of water 
______________________________________ 
and applied onto an aluminum support grained by means of a wire brush, in a 
way such that a dry layer weight of 0.9 g/m.sup.2 is obtained. The layer 
is exposed for 35 seconds and developed by spraying with pure water. 
EXAMPLE 20 
A coating solution is prepared as described in Example 2, with the 
exception that the polymer W is employed as the binder, and is spin-coated 
onto the support material described in Example 1. The dried layer has a 
weight of 0.96 g/m.sup.2. The photosensitive layer is exposed for 30 
seconds through a standard negative original, and thereafter the unexposed 
areas are instantly removed with the developer solution of Example 3. The 
resulting printing plate is distinguished by excellent resolution and ink 
acceptance. 
EXAMPLE 21 
A coating solution is prepared as described in Example 1, with the 
exception that the polymer X is employed as the binder, and is spin-coated 
onto the support material described in Example 1. The dried layer has a 
weight of 1.1 g/m.sup.2. The exposed layer is immediately developed by 
spraying with pure water. A high-resolution printing plate is obtained.