Method for preparing physical development nuclei for use in silver salt diffusion transfer processing

According to the present invention, a method is provided for preparing physical development nuclei for use in silver salt diffusion transfer processing, said physical development nuclei comprising a heavy metal sulphide, said method comprising the steps of: precipitating said heavy metal sulphide by bringing a water soluble heavy metal compound in reactive association with a water soluble sulphide in an aqueous liquid and said precipitation being carried out in the presence of a hydrophilic polymer so as to disperse said heavy metal sulphide, said hydrophilic polymer comprising a heterocyclic group, characterized in that said heterocyclic group is present in a recurring unit of said hydrophilic polymer, said recurring unit being comprised in said polymer in an amount between 0.1 mol % and 5 mol %.

Benefit from provisional application 60/097,873, filed Dec. 5, 1995, is 
claimed. 
DESCRIPTION 
1. Field of the Invention 
The present invention relates to a method for preparing physical 
development nuclei comprising a heavy metal sulphide for use in silver 
salt diffusion transfer processing. In particular the present invention 
relates to the preparation of physical development nuclei that can be used 
in preparing an imaging element from which a lithographic printing plate 
can be prepared according to the silver salt diffusion transfer process. 
2. Background of the Invention 
The principles of the silver complex diffusion transfer reversal process, 
hereinafter called DTR process, have been described e.g. in U.S. Pat. No. 
2,352,014 and in the book "Photographic Silver Halide Diffusion Processes" 
by Andre Rott and Edith Weyde, The Focal Press, London and New York, 
(1972). 
In the DTR process non developed silver halide of an information wise 
exposed photographic silver halide emulsion layer material is transformed 
with a so called silver halide solvent into soluble silver complex 
compounds which are allowed to diffuse into an image receiving element and 
are reduced therein with a developing agent, generally in the presence of 
physical development nuclei, to form a silver image having reversed image 
density values ("DTR image") with respect to the black silver image 
obtained in the exposed areas of the photographic material. 
A DTR image bearing material can be used as a planographic printing plate 
wherein the DTR silver image areas form the water repellant ink receptive 
areas on a water receptive ink repellent background. The DTR image can be 
formed in the image receiving layer of a sheet or web material which is a 
separate element with respect to the photographic silver halide emulsion 
material (a so called two sheet DTR element) or in the image receiving 
layer of a so called single support element, also called mono sheet 
element, which contains at least one photographic silver halide emulsion 
layer integral with an image receiving layer in waterpermeable 
relationship therewith. It is the latter mono sheet version which is 
preferred for the preparation of offset printing plates by the DTR method. 
For example the United Kingdom Patent Specification 1,241,661 discloses a 
method for the production of a planographic printing plate consisting of a 
sheet material comprising an outer hydrophilic colloid layer on the 
surface of which there is concentrated a silver image stemming from an 
underlying exposed silver halide emulsion layer by the silver complex 
diffusion transfer reversal process. The silver image formed on the 
surface is suitable for printing images in a lithographic printing process 
using a dampening liquid. 
Commercial lithographic printing plate precursors of the latter type 
typically contain on a flexible support, e.g. polyester or paper in the 
order given a base layer serving as an anti-halation layer, a silver 
halide emulsion layer and a surface layer containing physical development 
nuclei in which the silver image is formed. 
Alternatively, a lithographic printing plate according to the silver salt 
diffusion transfer processing may be obtained by providing in the order 
given on a hydrophilic support such as e.g. an aluminum support (see e.g. 
EP-A-410500), a receiving layer containing physical development nuclei and 
a silver halide emulsion. Subsequent to exposure and development the plate 
is rinsed with water or an aqueous liquid to remove the silver halide 
emulsion layer and other optional layers on top of the receiving layer so 
as to expose the silver image formed in the receiving layer. 
The above lithographic printing plate precursors, also called imaging 
elements may be camera exposed or they can be exposed by means of a scan 
exposure e.g. a laser or L.E.D. exposure. The latter offers the advantage 
that the preparation of the printing plate is simplified in that a 
paste-up to be used for the exposure of the imaging element can be 
completely prepared on a computer. This paste-up prepared on the computer 
is then transferred to an image setter equipped with e.g. laser that takes 
care of the exposure of the imaging element. 
Lithographic printing plates obtained according to the silver salt 
diffusion transfer process and in particular those having a flexible 
support are generally limited in printing endurance as compared to the 
aluminium based printing plates that use a diazo composition or 
photopolymer composition as the photosensitive coating for making the 
printing plate. Nevertheless, lithographic printing plates based on a 
flexible support offer the advantage that they are less expensive than 
printing plates based on an aluminum support. DTR-plates having an 
aluminum support offer an advantage of high sensitivity over a large 
spectral range. 
Accordingly, there is a continuing need for improving the printing 
endurance of silver salt diffusion transfer plates. A possible improvement 
in printing endurance should preferably not increase the number of copies 
that have to be disposed of at start-up of the printing process as a 
result of e.g. bad ink acceptance or ink acceptance at the non image 
areas. 
EP-A-546598 suggests the use of physical development nuclei having an 
average diameter less than 6 nm and wherein the relative number of nuclei 
having a diameter of more than 4.5 nm is less than 15% of the total number 
of nuclei in the image receiving layer, to reduce the ink acceptance in 
the non-printing areas. 
U.S. Pat. No. 4,160,670 discloses specific hydrophilic copolymers for 
improving the ink repellant properties of the background areas. Amongst 
the numerous mentioned copolymers there are mentioned copolymers of 
acrylamide and a comonomer that has affinity for the physical development 
nuclei such as e.g. pyridine and imidazole. 
DE-A 2.165.358 discloses the use of high molecular weight compounds in the 
image receiving layer among which are copolymers of acrylamid and 
N-vinylimidazole. 
U.S. Pat. No. 5,236,802 discloses that the presence of polyacrylamide or a 
copolymer of acrylamide in the physical development nuclei layer or an 
adjacent layer improves the ink reception of the image areas and further 
improves the ink repellant properties of the background areas. 
U.S. Pat. No. 2,698,237 discloses a DTR-image receiving material comprising 
an image receiving layer having metal sulfide nuclei precipitated in an 
aqueous siliciumdioxide dispersion. Said nuclei are teached to show a high 
activity. Furthermore the presence of hydrophilic organic polymers binders 
in the layer containing physical development nuclei of a mono-sheet DTR 
material suitable for preparing a lithographic plate has been disclosed in 
e.g. U.S. Pat. Nos. 3,728,114; 4,160,670; 4,606,985; 4,510,228; 4,743,525; 
4,879,193; 5,153,097; 5,108,871 and 5,041,354. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to improve the lithographic 
performance of DTR-based lithographic printing plates in particular such 
properties as ink-acceptance of the printing areas, ink-repellance of the 
background (reducing staining and toning) and the printing endurance. 
Further objects of the present invention will become clear from the 
description hereinafter. 
It has been found that the objects of the present invention can be met by 
preparing physical development nuclei comprising heavy metal sulphide and 
that are comprised in a receiving layer of an imaging element from which a 
lithographic printing plate can be prepared according to silver salt 
diffusion transfer processing, the physical development nuclei being 
prepared according to a method comprising the steps of: 
precipitating said heavy metal sulphide by bringing a water soluble heavy 
metal compound in reactive association with a water soluble sulphide in an 
aqueous liquid and 
said precipitation being carried out in the presence of a hydrophilic 
polymer so as to disperse said heavy metal sulphide, said hydrophilic 
polymer comprising a heterocyclic group characterized in that said 
heterocyclic group is present in a recurring unit of said hydrophilic 
polymer, said recurring unit being comprised in said polymer in an amount 
between 0.1 mole % and 5 mole %. 
The present invention further provides a use of physical development nuclei 
prepared as set out above in preparing an imaging element from which a 
lithographic printing plate according to the silver salt diffusion 
transfer processing can be made. 
The present invention further provides a method for making a lithographic 
printing plate according to the silver salt diffusion transfer process 
comprising image-wise exposing an imaging element comprising on a support 
a silver halide emulsion layer and a receiving layer comprising physical 
development nuclei prepared according to a method as defined above and 
developing a thus obtained image-wise exposed imaging element in the 
presence of a silver halide solvent and a developing agent.

DETAILED DESCRIPTION OF THE INVENTION 
In accordance with the method of the present invention for preparing 
physical development nuclei comprising a heavy metal sulphide, a water 
soluble heavy metal compound and a water soluble sulphide are brought in 
reactive association in an aqueous liquid. Suitable heavy metals for use 
in connection with the present invention are for example Pd, Ag, Ni, Co 
etc.. or combinations thereof. Particularly preferred is Pd. A suitable 
water soluble Pd compound is e.g. (NH.sub.4).sub.2 PdCl.sub.4. As water 
soluble sulphide, sodium and/or potassium sulphide are conveniently used. 
According to the present invention the water soluble heavy metal compound 
and water soluble sulphide are reacted with each other to precipitate a 
corresponding heavy metal sulphide in the presence of a hydrophilic 
polymer comprising a heterocyclic group. The hydrophilic polymer thereby 
acts as a dispersing agent for the heavy metal sulphide. 
The heterocyclic group is present in a recurring unit of the hydrophilic 
polymer and the recurring unit being comprised in the hydrophilic polymer 
in an amount between 0.1 mol % and 5 mol % and preferably between 0.5 mol 
% and 1.5 mol %. The optimal amount is dependent on the particular 
structure of the hydrophilic polymer. 
Suitable hydrophilic polymers for use in connection with the present 
invention are copolymers of a first monomer having a water solubilising 
group such as e.g. an amide, a carboxylic acid, a hydroxy group, a 
sulphonic acid group, a phosphonic acid group etc.. and a second monomer 
having a heterocyclic group. In addition to these two monomers, a 
hydrophilic polymer in accordance with this invention may contain further 
additional monomers. 
Specific examples of heterocyclic groups comprised in the second monomer 
are e.g. imidazoles, imidazolines, pyrazole, thiazolidine, thiazolidone, 
thiazolone, indazole, pyridine, triazine, benztriazole, tetrazole, etc. 
According to a particularly preferred embodiment in connection with the 
present invention, the hydrophilic polymer is a copolymer of 
(meth)acrylamide and one or more vinyl monomer having a heterocyclic 
group. Such vinyl monomers are e.g. vinyl imidazole, vinyl pyridine, vinyl 
piperidine, vinyl imidazoline, vinyl quinoline etc. Additional vinyl 
monomers may be present in such copolymers. Examples of such additional 
vinyl monomers are vinyl monomers such as vinyl acetate, vinyl butyral, 
vinyl chloride, vinylidene chloride, vinyl (meth)acrylic acid esters, 
styrene and derivatives, vinyl ethers, etc. The copolymers may be random 
copolymers, alternating copolymers or block-copolymers. 
The polymerisation degree (number average) of the polymers used in 
accordance with the present invention is preferably between 20 and 1000. 
The average polymerisation degree in accordance with the present invention 
is determined using GPC wherein a solution of 0.05 mol/1 of sodium 
chloride in water is used as the eluent, a TSK column 3000 PW and 
polyethylene glycol as a standard were used. A too low polymerisation 
degree will result in dissolution of the polymers from the plate during 
processing whereas a too large polymerisation degree may present coating 
difficulties. 
The hydrophilic polymer is preferably present or added during the 
precipitation of the heavy metal sulphide in amount between 0.2% by weight 
and 2% by weight, more preferably between 0.3% by weight and 1% by weight. 
Additional hydrophilic polymer may be added subsequent to completion of 
the precipitation. The total amount of hydrophilic polymer is preferably 
present from the start of the precipitation although it is also possible 
to add hydrophilic polymer gradually during precipitation or at discrete 
intervals during precipitation. 
According to a preparation method in connection with the present invention, 
there can be used a single jet, double jet or multiple jet technique for 
adding the reactants to each other. According to a single jet method, 
either the water soluble sulphide is added to the water soluble heavy 
metal compound or vice versa. In that case, the hydrophilic polymer is 
preferably present in the solution of the reactant to which the other one 
is added. Alternatively, the hydrophilic polymer can be added together 
with one of the reactants to the other. Furthermore, part of the total 
amount of hydrophilic polymer used during preparation can be present in 
the solution of the reactant to which the other is added and part can be 
added with the other reactant. 
According to a highly preferred embodiment, the physical development nuclei 
are prepared by the double jet technique wherein both reactants (water 
soluble sulphide and water soluble heavy metal compound) are added to a 
third solution. This third solution preferably contains the hydrophilic 
polymer. It is also possible to add at least part or even all of the 
hydrophilic polymer via one or both of the solutions containing the 
reactants. 
According to a third embodiment for the precipitation of the heavy metal 
sulphide, one may use 3 jets for adding the various ingredients together. 
Thus, one may add the two reactants and the hydrophilic polymer via 
separate jets. 
In accordance with any of the above double or multi jet techniques, it is 
also possible to add part of one of the reactants (e.g. the water soluble 
sulphide) to the solution to which the reactants are added via the jets. 
Furthermore, the speed of addition of one or more of the reactants may be 
varied, kept constant or increased during the course of precipitation. In 
particular, it may be desirable to add part of the hydrophilic polymer at 
an initial stage and then at one or more discrete intervals during 
advanced stages (e.g. at the end) of the precipitation. 
With respect to obtaining optimal lithographic performance, it is further 
desirable to prepare heavy metal sulphides with an excessive amount of 
sulphide relative to its stoichiometric proportion in the heavy metal 
sulphide that is precipitated. Thus, for example it is preferred in 
precipitating palladium sulphide, which contains the sulphide ion in a 1:1 
stoichiometric amount, to add at least 2 moles of sulphide for one mole of 
palladium. 
During precipitation, there may be present various other ingredients and in 
particular there may be present other hydrophilic polymers not within the 
scope of the present invention such as e.g. polyvinyl alcohol and/or 
poly(meth)acrylic acid. 
Alternatively or additionally, hydrophilic polymers that are not in 
accordance with the present invention may be added after completion of the 
precipitation. In particular, poly(meth)acrylic acid or 
poly(meth)acrylamide. It is furthermore possible, to add an additional 
amount of hydrophilic polymer in accordance with the present invention 
subsequent to precipitation of the physical development nuclei. 
Further, an inorganic colloidal substance can be added during precipitation 
but preferably after precipitation of the physical development nuclei. 
Suitable inorganic colloidal substances are e.g. colloidal silica or 
colloidal clays. 
Clays are essentially hydrous aluminum silicates, wherein alkali metals or 
alkaline-earth metals are present as principal constituents. Also in some 
clay minerals magnesium or iron or both replace the aluminum wholly or in 
part. The ultimate chemical constituents of the clay minerals vary not 
only in amounts, but also in the way in which they are combined or are 
present in various clay minerals. Natural clays are well known, but it is 
also possible to prepare synthetic clays in the laboratory, allowing more 
degrees of freedom that can lead to reproducible tailor made clay products 
for use in different applications. 
From the natural clays smectite clays, including laponites, hectorites and 
bentonites are well-known and can be used with the present invention. For 
the smectite clays some substitutions in both octahedral and tetrahedral 
layers of the crystal lattice may occur, resulting in a small number of 
interlayer cations. Smectite clays form a group of "swelling" clays which 
take up water and organic liquids between the composite layers and which 
have marked cation exchange capacities. From these smectite clays, 
synthetic chemically pure clays have been produced. They are particularly 
suitable for use in the present invention. 
The clays used in accordance with the invention are preferably smectic 
clays, more preferably synthetic smectic clays, most preferably synthetic 
laponites. Preferred synthetic laponite clays for the purposes of this 
invention are e.g. LAPONITE RD, LAPONITE RDS and LAPONITE JS, trade mark 
products of LAPORTE INDUSTRIES Limited, London. 
Synthetic clays and process for the production thereof have been described 
in EP-Patent 161 411 B1. 
Preferably the physical development nuclei comprising heavy metal sulphide 
in connection with the present invention are prepared such that they have 
an average diameter less than 6 nm and the number of nuclei having a 
diameter larger than 4.5 nm is less than 15% of the total number of 
nuclei. Although the size of the nuclei above is expressed by a diameter 
this does not imply that the nuclei are necessarily spherical. By diameter 
is meant the diameter of a sphere having an equivalent volume so that the 
size of nuclei of a variety of shapes can be characterized by the same 
parameter. 
According to a highly preferred embodiment in connection with the present 
invention, the imaging element comprises on a support in the order given a 
silver halide emulsion layer and a receiving layer comprising physical 
development nuclei prepared in accordance with the present invention as 
described above. 
The photographic silver halide emulsions can be prepared from soluble 
silver salts and soluble halides according to different methods as 
described e.g. by P. Glafkides in "Chimie et Physique Photographique", 
Paul Montel, Paris (1967), by G. F. Duffin in "Photographic Emulsion 
Chemistry", The Focal Press, London (1966), and by V. L. Zelikman et al in 
"Making and Coating Photographic Emulsion", The Focal Press, London 
(1966). 
The photographic silver halide emulsions used according to the present 
invention can be prepared by mixing the halide and silver solutions in 
partially or fully controlled conditions of temperature, concentrations, 
sequence of addition, and rates of addition. The silver halide can be 
precipitated according to the single jet method or the double jet method. 
The silver halide particles of the photographic emulsions used according to 
the present invention may have a regular crystalline form such as a cubic 
or octahedral form or they may have a transition form. They may also have 
an irregular crystalline form such as a spherical form or a tabular form, 
or may otherwise have a composite crystal form comprising a mixture of 
said regular and irregular crystalline forms. 
According to the present invention the emulsion or emulsions preferably 
consist principally of silver chloride preferably at least 70 mol %, more 
preferably at least 80 mol % and most preferred at least 95 mol % of 
silver chloride. The remaining, if any, of the silver halide may be silver 
bromide and optionally an amount of silver iodide of up to 3 mol %, 
preferably up to 1.5mol %. According to a particularly preferred 
embodiment in connection with the present invention, a silver chloroiodide 
emulsion is used having up to 2 mol % of silver iodide. A silver 
chloroiodide emulsion may conveniently prepared by first precipitating 
silver nitrate together with a water soluble chloride, e.g. sodium 
chloride and then at the end of precipitation, typically during the last 
10% thereof, co-precipitating a water soluble iodide e.g. potassium 
iodide, so that silver halide grains having silver iodide in its shell are 
obtained. 
The average size of the silver halide grains may range from 0.10 to 0.70 
.mu.m, preferably from 0.25 to 0.45 .mu.m. 
The size distribution of the silver halide particles of the photographic 
emulsions to be used according to the present invention can be 
homodisperse or heterodisperse. A homodisperse size distribution is 
obtained when 95% of the grains have a size that does not deviate more 
than 30% from the average grain size. 
Preferably during the precipitation stage Iridium and/or Rhodium containing 
compounds or a mixture of both are added. The concentration of these added 
compounds ranges from 10.sup.-8 to 10.sup.-3 mole per mole of AgNO.sub.3, 
preferably between 10.sup.-7 and 10.sup.-6 mole per mole of AgNO.sub.3. 
This results in the building in in the silver halide crystal lattice of 
minor amounts of Iridium and/or Rhodium, so called Iridium and/or Rhodium 
dopants. As known to those skilled in the art numerous scientific and 
patent publications disclose the addition of Iridium or Rhodium containing 
compounds or compounds containing other elements of Group VIII of the 
Periodic System during emulsion preparation. 
The emulsions can be chemically sensitized e.g. by adding sulphur 
containing compounds during the chemical ripening stage e.g. allyl 
isothiocyanate, allyl thiourea, and sodium thiosulphate. Also reducing 
agents e.g. the tin compounds described in BE P 493,464 and 568,687, and 
polyamines such as diethylene triamine or derivatives of aminomethane 
sulphonic acid can be used as chemical sensitizers. Other suitable 
chemical sensitizers are noble metals and noble metal compounds such as 
gold, platinum, palladium, iridium, ruthenium and rhodium. This method of 
chemical sensitization has been described in the article of R. KOSLOWSKY, 
Z. Wiss. Photogr. Photophys. Photochem. 46, 65 72 (1951). 
The emulsions of the DTR element can be spectrally sensitized according to 
the spectral emission of the exposure source for which the DTR element is 
designed. 
Suitable sensitizing dyes for the visible spectral region include methine 
dyes such as those described by F. M. Hamer in "The Cyanine Dyes and 
Related Compounds", 1964, John Wiley & Sons. Dyes that can be used for 
this purpose include cyanine dyes, merocyanine dyes, complex cyanine dyes, 
complex merocyanine dyes, homopolar cyanine dyes, hemicyanine dyes, styryl 
dyes and hemioxonol dyes. Particularly valuable dyes are those belonging 
to the cyanine dyes, merocyanine dyes, complex merocyanine dyes. 
The silver halide emulsions may contain the usual stabilizers e.g. 
homopolar or salt like compounds of mercury with aromatic or heterocyclic 
rings such as mercaptotriazoles, simple mercury salts, sulphonium mercury 
double salts and other mercury compounds. Other suitable stabilizers are 
azaindenes, preferably tetra or penta azaindenes, especially those 
substituted with hydroxy or amino groups. Compounds of this kind have been 
described by BIRR in Z. Wiss. Photogr. Photophys. Photochem. 47, 2 27 
(1952). Other suitable stabilizers are i.a. heterocyclic mercapto 
compounds e.g. heterocyclic mercapto compounds substituted with a bulky 
substituent such as e.g. an alkyl group having at least 5 carbon atoms or 
aryl group having at least 8 carbon atoms, e.g. a 
1-n-heptyl-5-mercaptotetrazole or 3-mercapto-5-n-heptyl-oxadiazole, 
phenylmercaptotetrazole, quaternary benzothiazole derivatives, and 
benzotriazole. Preferred compounds are mercapto substituted pyrimidine 
derivatives as disclosed in U.S. Pat. No. 3,692,527. 
The silver halide emulsions may contain pH controlling ingredients. 
Preferably the emulsion layer is coated at a pH value below the 
isoelectric point of the gelatin to improve the stability characteristics 
of the coated layer. Other ingredients such as antifogging agents, 
development accelerators, wetting agents, and hardening agents for gelatin 
may be present. The silver halide emulsion layer may comprise light 
screening dyes that absorb scattering light and thus promote the image 
sharpness. Suitable light absorbing dyes are described in i.a. U.S. Pat. 
No. 4,092,168, U.S. Pat. No. 4,311,787 and DE P 2,453,217. 
More details about the composition, preparation and coating of silver 
halide emulsions can be found in e.g. Product Licensing index, Vol. 92, 
December 1971, publication 9232, p. 107 109. 
Between the support and the silver halide emulsion layer there is 
preferably provided a base layer that preferably contains an anti-halation 
substance such as e.g. light absorbing dyes absorbing the light used for 
image-wise exposure of the imaging element. As alternative finely divided 
carbon black can be used as an anti-halation substance. On the other hand, 
in order to gain sensitivity, light reflecting pigments, e.g. 
titaniumdioxide can be present in the base layer. Further this layer can 
contain hardening agents, matting agents, e.g. silica particles, and 
wetting agents. Suitable matting agents preferably have a number average 
diameter of 2-10 .mu.m and more preferably between 2 .mu.m and 5 .mu.m. 
The matting agents are generally used in a total amount in the imaging 
element of 0.1 g/m.sup.2 to 2.5 g/m.sup.2. At least part of these matting 
agents and/or light reflection pigments may also be present in the silver 
halide emulsion layer the most part, preferably at least 80% by weight 
however preferably being present in said base-layer although all of the 
matting agent can be included in the silver halide emulsion layer, the 
base layer then being substantially free of matting agent. In case all 
matting agent is provided in the silver halide emulsion layer(s), it is 
preferred to add a non-water swellable latex in the base-layer. Example of 
a non-water swellable latex are copolymer of styrene and butadiene, 
polyethylacrylate, polymethylmethacrylate, copolymers of acrylates, 
copolymers of methacrylates etc. As a further alternative the light 
reflecting pigments may be present in a separate layer provided between 
the antihalation layer and the photosensitive silver halide emulsion 
layer. Like the emulsion layer the base layer is coated preferably at a pH 
value below the isoelectric point of the gelatin in the base layer. 
In a preferred embodiment in connection with the present invention a 
backing layer is provided at the non light sensitive side of the support. 
This layer which can serve as anti-curl layer can contain i.a. matting 
agents e.g. silica particles, lubricants, antistatic agents, light 
absorbing dyes, opacifying agents, e.g. titanium oxide and the usual 
ingredients like hardeners and wetting agents. The backing layer can 
consist of one single layer or a multiple layer pack e.g. a double layer 
pack. 
The hydrophilic layers usually contain gelatin as hydrophilic colloid 
binder. Mixtures of different gelatins with different viscosities can be 
used to adjust the theological properties of the layer. But instead of or 
together with gelatin, use can be made of one or more other natural and/or 
synthetic hydrophilic colloids, e.g. albumin, casein, zein, polyvinyl 
alcohol, alginic acids or salts thereof, cellulose derivatives such as 
carboxymethyl cellulose, modified gelatin, e.g. phthaloyl gelatin etc. 
The hydrophilic layers of the photographic element, especially when the 
binder used is gelatin, can be hardened with appropriate hardening agents 
such as those of the epoxide type, those of the ethylenimine type, those 
of the vinylsulfone type e.g. 1,3-vinylsulphonyl-2-propanol, chromium 
salts e.g. chromium acetate and chromium alum, aldehydes e.g. 
formaldehyde, glyoxal, and glutaraldehyde, N-methylol compounds e.g. 
dimethylolurea and methyloldimethylhydantoin, dioxan derivatives e.g. 
2,3-dihydroxy dioxan, active vinyl compounds e.g. 
1,3,5-triacryloyl-hexahydro-s-triazine, active halogen compounds e.g. 
2,4-dichloro-6-hydroxy-s-triazine, and mucohalogenic acids e.g. 
mucochloric acid and mucophenoxychloric acid. These hardeners can be used 
alone or in combination. The binders can also be hardened with fast 
reacting hardeners such as carbamoylpyridinium salts of the type, 
described in U.S. Pat. No. 4,063,952. 
The imaging element used according to the present invention may further 
comprise various kinds of surface active agents in the photographic 
emulsion layer or in at least one other hydrophilic colloid layer. 
Suitable surface active agents include non ionic agents such as saponins, 
alkylene oxides e.g. polyethylene glycol, polyethylene 
glycol/polypropylene glycol condensation products, polyethylene glycol 
alkyl ethers or polyethylene glycol alkylaryl ethers, polyethylene glycol 
esters, polyethylene glycol sorbitan esters, polyalkylene glycol 
alkylamines or alkylamides, silicone polyethylene oxide adducts, glycidol 
derivatives, fatty acid esters of polyhydric alcohols and alkyl esters of 
saccharides; anionic agents comprising an acid group such as a carboxy, 
sulpho, phospho, sulphuric or phosphoric ester group; ampholytic agents 
such as aminoacids, aminoalkyl sulphonic acids, aminoalkyl sulphates or 
phosphates, alkyl betaines, and amine N oxides; and cationic agents such 
as alkylamine salts, aliphatic, aromatic, or heterocyclic quaternary 
ammonium salts, aliphatic or heterocyclic ring containing phosphonium or 
sulphonium salts. Preferably compounds containing perfluorinated alkyl 
groups are used. Such surface active agents can be used for various 
purposes e.g. as coating aids, as compounds preventing electric charges, 
as compounds improving slidability, as compounds facilitating dispersive 
emulsification and as compounds preventing or reducing adhesion. 
The imaging element of the present invention may further comprise various 
other additives such as e.g. compounds improving the dimensional stability 
of the photographic element, UV absorbers, spacing agents and 
plasticizers. 
Suitable additives for improving the dimensional stability of the 
photographic element are e.g. dispersions of a water soluble or hardly 
soluble synthetic polymer e.g. polymers of alkyl (meth)acrylates, 
alkoxy(meth)acrylates, glycidyl (meth)acrylates, (meth)acrylamides, vinyl 
esters, acrylonitriles, olefins, and styrenes, or copolymers of the above 
with acrylic acids, methacrylic acids, Alpha Beta unsaturated dicarboxylic 
acids, hydroxyalkyl (meth)acrylates, sulphoalkyl (meth)acrylates, and 
styrene sulphonic acids. 
Suitable supports of the imaging element in connection with the present 
invention can be either opaque or transparent, the latter offering the 
advantage of exposure through the support so that exposure may be carried 
out in camera's without reversing mirrors. Specific examples of supports 
are polyethylene coated paper, polypropylene coated paper, opaque or 
transparent polyester film in particular polyethylene terephthalate. 
Aluminum supports or other hydrophilic supports may also be used as set 
out in the introduction. In that case, the receiving layer will be located 
between the support and the silver halide emulsion layer. 
According to a preferred embodiment in connection with the present 
invention, a polyester film support is used having a thickness between 0.1 
mm and 0.35 mm and having a Young-modulus (E-modulus) of at least 4300 
N/mm.sup.2 and more preferably at least 4500 N/mm.sup.2. The Young-modulus 
also called E-modulus in connection with the present invention can be 
measured according to method A of the ANSI-D882-91 standard. 
A polyester film support is preferably coated with a layer improving the 
adhesion of the hydrophilic layers. 
A particularly suitable adhesion improving layer, comprises a copolymer 
containing water-soluble monomers and water-insoluble monomers in a molar 
ratio between 1:99 and 20:80. Preferably the water soluble monomer is a 
monomer having one or more carboxylic acid groups. An example of an 
especially preferred copolymer for use in said adhesion improving layer is 
a polymer containing 1% to 10% by weight, more preferably 1% to 5% by 
weight of itaconic acid. Suitable polymers containing itaconic acid are 
e.g. copolymers of itaconic acid and vinylidene chloride, copolymers of 
itaconic acid, vinylidene chloride and vinylacetate, copolymers of 
itaconic acid, vinylidene chloride and methyl (meth) acrylate, copolymers 
of itaconic acid and vinyl chloride, copolymers of itaconic acid, vinyl 
chloride, vinylidene chloride and methyl(meth)acrylate etc. A copolymer of 
itaconic acid, vinylidene chloride and optionally methyl(meth)acrylate 
wherein the amount of itaconic acid is between 1% and 5%, the amount of 
vinylidene chloride is between 70% and 95% and the amount of 
methyl(meth)acrylate is between 0% and 15%. The adhesion improving layer 
is preferably free of gelatin. 
On top of this adhesion improving layer there may be provided a further 
intermediate layer containing microparticles having an average diameter of 
less than 50 nm preferably colloidal silica and gelatin preferably in a 
weight ratio of 1:2 and 2:1. 
According to a preferred method of the present invention an imaging element 
comprising on a support in the order given a silver halide emulsion layer 
and a receiving layer comprising physical development nuclei prepared in 
accordance with the present invention is image-wise exposed and 
subsequently developed according to the DTR-process. The DTR mono sheet 
imaging element in connection with the present invention may be exposed in 
an apparatus according to its particular application, e.g. a conventional 
process camera containing a conventional light source or a high intensity 
short time exposure such as e.g. a laser containing device. 
The alkaline processing liquid used for developing the imaging element 
preferably contains at least part of the silver halide solvent(s). 
Preferably the silver halide solvent is used in an amount between 0.01% by 
weight and 10% by weight and more preferably between 0.05% by weight and 
8% by weight. Suitable silver halide solvents for use in connection with 
the present invention are e.g. 2-mercaptobenzoic acid, cyclic imides, 
oxazolidones, thiocyanates and thiosulfates. Further suitable silver 
halide solvents for use in connection with the present invention are 
described in EP-A 554584. It should be noted that the effects of the 
present invention are particularly noticed when as silver halide solvents 
a combination of an alkanol amine and a meso-ionic thiolate compound, 
preferably a meso-ionic triazolium thiolate, is used. 
According to the present invention the alkaline processing liquid 
preferably also contains hydrophobizing agents for improving the 
hydrophobicity of the silver image obtained in the image receiving surface 
layer. The hydrophobizing agents used in connection with the present 
invention are compounds that are capable of reacting with silver or silver 
ions and that are hydrophobic i.e. insoluble in water or only slightly 
soluble in water. Generally these compounds contain a mercapto group or 
thiolate group and one or more hydrophobic substituents e.g. an alkyl 
group containing at least 3 carbon atoms. Examples of hydrophobizing 
agents for use in accordance with the present invention are e.g. those 
described in U.S. Pat. No. 3,776,728, U.S. Pat. No. 4,563,410 and EP-A 
554584. 
The alkaline processing liquid may also contain the developing agent(s) 
used in accordance with the present invention. In this case the alkaline 
processing liquid is called a developer. On the other hand some or all of 
the developing agent(s) may be present in one or more layers of the 
imaging element. When all of the developing agents are contained in the 
imaging element the alkaline processing liquid is called an activator or 
activating liquid. 
Silver halide developing agents for use in accordance with the present 
invention are preferably of the p-dihydroxybenzene type, e.g. 
hydroquinone, methylhydroquinone or chlorohydroquinone, preferably in 
combination with an auxiliary developing agent being a 
1-phenyl-3-pyrazolidone type developing agent and/or 
p-monomethylaminophenol. Particularly useful auxiliary developing agents 
are of the phenidone type e.g. 1-phenyl-3-pyrazolidone, 
1-phenyl-4-monomethyl-3-pyrazolidone, and 
1-phenyl-4,4-dimethyl-3-pyrazolidone. However other developing agents can 
be used. 
The alkaline processing liquid preferably also contains a preserving agent 
having antioxidation activity, e.g. sulphite ions provided e.g. by sodium 
or potassium sulphite. For example, the aqueous alkaline solution 
comprises sodium sulphite in an amount ranging from 0.15 to 1.0 mol/l. 
Further may be present a thickening agent, e.g. hydroxyethylcellulose and 
carboxymethylcellulose, fog inhibiting agents, e.g. potassium bromide, 
potassium iodide and a benzotriazole which is known to improve the 
printing endurance, calcium sequestering compounds, anti sludge agents, 
and hardeners including latent hardeners. 
Development acceleration can be accomplished with the aid of various 
compounds to the alkaline processing liquid and/or one or more layers of 
the photographic element, preferably polyalkylene derivatives having a 
molecular weight of at least 400 such as those described in e.g. U.S. Pat. 
No. 3,038,805, U.S. Pat. No. 4,038,075, U.S. Pat. No. 4,292,400, U.S. Pat. 
No. 4,975,354. 
Subsequent to the development in an alkaline processing liquid the surface 
of the printing plate is preferably neutralized using a neutralization 
liquid. 
A neutralization liquid generally has a pH between 5 and 7. The 
neutralization liquid preferably contains a buffer e.g. a phosphate 
buffer, a citrate buffer or mixture thereof. The neutralization solution 
can further contain bactericids, e.g. phenol, thymol, turpinal or 
5-bromo-5-nitro-1,3-dioxan as described in EP 0,150,517. The liquid can 
also contain substances which influence the hydrophobic/hydrophilic 
balance of the printing plate obtained after processing of the DTR 
element, e.g. silica. Further the neutralization solution can contain 
wetting agents, preferably compounds containing perfluorinated alkyl 
groups. 
The invention will now be illustrated by the following examples without 
however the intention to limit the invention thereto. All parts are by 
weight unless otherwise specified. 
EXAMPLE 
Preparation of the Silver Halide Emulsion Coating Solution 
A silver chlorobromide emulsion composed of 98.2 mol % of chloride and 1.8 
mol % of bromide was prepared by the double jet precipitation method. The 
average silver halide grain size was 0.38 .mu.m (diameter of a sphere with 
equivalent average volume) and contained Rhodium ions as internal dopant. 
The emulsion was orthochromatically sensitized and stabilized by a 
1-phenyl-5-mercapto-tetrazole. 
Preparation of the Imaging Elements 
Six polyethylene terephthalate film support having a thickness of 175 .mu.m 
and being provided with a adhesion improving layer were each coated with a 
layer containing gelatin in an amount of 0.4 g/m.sup.2 and colloidal 
silica having an average particle diameter of 7 nm in an amount of 0.4 
g/m.sup.2. The adhesion improving layer contained a copolymer of itaconic 
acid (2%), vinylidene chloride (88%) and methylmethacrylate (10%). 
A silver halide emulsion prepared as described above was coated to each of 
these coated polyethylene terephthalate film supports together with an 
anti-halation layer (underlying the silver halide emulsion layer) such 
that the amount of gelatin in the anti-halation layer was 2.7 g/m.sup.2 
and 1.34 g/m.sup.2 for the silver halide emulsion layer. The amount of 
silver halide expressed as AgNO.sub.3 was 1.25 g/m.sup.2 and the emulsion 
layer further contained developing agents and 120 mg/m.sup.2 of 
formaldehyde as a hardener. The anti-halation layer further contained a 
silica matting agent having an average particle size (weight average 
diameter) of 3.4 .mu.m and carbon black as anti-halation means. The thus 
obtained elements were kept at 57.degree. C. at a relative humidity of 34% 
for 1 day. 
Physical development nuclei (PdS) were prepared according to a double jet 
precipitation wherein a soluble palladium salt (A) and a sodium sulphide 
solution (B) were added at a constant rate during 4 minutes to a third 
solution (C) containing sodium sulphide while stirring at 400 rpm. 
Subsequent to precipitation, the obtained precipitated nuclei were 
dialysed to a conductivity of 0.5 mS. 
The above procedure was applied using different solutions A, B and C to 
vary the precipitation conditions of the physical development nuclei. The 
following solutions were prepared: 
______________________________________ 
A-solutions: 
(NH.sub.4).sub.2 PdCl.sub.4 
PVA PAA PAI-1 PAI-2 water 
No (g) (ml) (ml) (ml) (ml) (ml) 
______________________________________ 
1 2.17 25 475 
2 2.17 25 475 
3 2.17 375 125 
4 2.17 375 125 
5 2.17 375 125 
______________________________________ 
PVA = 1% solution of polyvinyl alcohol in water 
PAA = 1% solution of polyacrylamide in water 
PAI1 = 1% solution of a copolymer of acrylamide (99 mol %) and 
vinylimidazole (1 mol %) 
PAI2 = 1% solution of a copolymer of acrylamide (98 mol %) and 
vinylimidazole (2 mol %) 
______________________________________ 
B-solutions: 
Na.sub.2 S 
PVA PAA PAI-1 PAI-2 water 
No (g) (ml) (ml) (ml) (ml) (ml) 
______________________________________ 
1 2 25 475 
2 2 25 475 
3 2 375 125 
4 2 375 125 
5 2 375 125 
______________________________________ 
______________________________________ 
C-solutions: 
Na.sub.2 S 
PVA PAA PAI-1 PAI-2 water 
No (g) (ml) (ml) (ml) (ml) (ml) 
______________________________________ 
1 3.2 40 760 
2 3.2 40 760 
3 3.2 600 200 
4 3.2 600 200 
5 3.2 600 200 
______________________________________ 
Five precipitations were carried out according to the procedure set out 
above using solutions Ai, Bi and Ci (wherein i corresponds to a solution 
number in the above tables). As a result five coating solutions for 
coating the physical development nuclei were obtained. These solutions 
were numbered 1 to 5 corresponding to the number of the A-C solutions from 
which they are obtained. A further coating solution was obtained by adding 
to coating solution 2 an amount of PAA corresponding to 0.7% (coating 
solution 2b). 
To each of these coating solutions was added formaldehyde and hydroquinone 
so that the amounts thereof in the final image receiving layer were 30 
mg/m.sup.2 and 0.4 g/m.sup.2 respectively. 
The obtained coating solutions were used to prepare 6 imaging elements by 
coating the solutions to 6 elements prepared as described above. 
Subsequently, the imaging elements were kept for 1 day at 57.degree. C. at 
a relative humidity of 34%. 
The following alkaline processing solution was prepared: 
______________________________________ 
sodium hydroxide (g) 
30 
methylhydroquinone (g) 
2 
sodium sulphite anh. (g) 
35 
amino-ethylaminoethanol (ml) 
45 
compound A (see below) (g) 
0.8 
EDTA.4Na (g) 1 
3-mercapto-5-n.heptyl- 
0.35 
oxadiazole (g) 
water to make 1 liter 
______________________________________ 
EDTA.4Na=sodium salt of ethylenediamine tetra-acetic acid 
##STR1## 
The following neutralization solution was prepared: 
______________________________________ 
citric acid 10 g 
sodium citrate 35 g 
sodium sulphite anh. 5 g 
phenol 50 mg 
water to make 1 l 
______________________________________ 
The following dampening liquid was prepared: 
______________________________________ 
water 880 ml 
citric acid 6 g 
boric acid 8.4 g 
sodium sulphate anh. 25 g 
ethyleneglycol 100 g 
colloidal silica 28 g 
______________________________________ 
The above described imaging elements were image-wise exposed and processed 
at 30.degree. C. with the above described alkaline processing solution, 
subsequently neutralized at 25.degree. C. with the neutralization solution 
described above and dried. 
The printing plates thus prepared were mounted on an offset printing 
machine (two color GTO printing machine). During the printing run the 
described dampening solution was used. The printing properties were 
evaluated in terms of ink-acceptance of the printing areas and unwanted 
ink-acceptance of the non-printing areas (toning) during start-up as 
follows: 
ink-acceptance=number of copies needed to obtain a stable density of the 
printing parts: 
1: &lt;10 copies needed 
2: 10-15 copies needed 
3: &gt;15 copies needed 
toning=number of copies needed to obtain a clear print with no ink 
acceptance in the non-printing areas: 
1: 100-150 copies 
2: 151-250 copies 
3: 251-300 copies 
4: &gt;300 copies 
The results obtained are as follows: 
______________________________________ 
Number of coating solution of 
the physical development nuclei 
Ink-acceptance 
toning 
______________________________________ 
1 2 2 
2 2 4 
2b 2 2 
3 2 3 
4 1 1 
5 1 2 
______________________________________