Method for making an offset printing plate according to the silver salt diffusion transfer process

The present invention provides a method for making an offset printing plate according to the silver salt diffusion transfer process comprising the steps of: PA1 image-wise exposing an imaging element comprising in the order given on a hydrophilic surface of a support (i) an image receiving layer containing physical development nuclei and (ii) a photosensitive layer comprising one or more photosensitive silver halide emulsions said photosensitive layer being in water permeable relationship with said image receiving layer, PA1 applying an aqueous alkaline solution to the imaging element comprising at least 0.05 mole/l of ascorbic acid as the main developer, at least 0.010 mole/l of an auxiliary developer of the class of the 1-phenyl-3-pyrazolidones and an aminoalcohol in an amount from 0.1 ml to 10 ml as silver halide solvent to form a silver image in said image receiving layer, PA1 treating the imaging element to remove the layer(s) on top of the image receiving layer, thereby exposing the imaged surface of the support by uncovering said silver image formed in said image receiving layer, characterized in that said aqueous alkaline solution contains sodium ions but no potassium ions or sodium and potassium ions in which case the molar ratio of sodium ions to potassium ions in said aqueous alkaline solution is at least 3:1.

DESCRIPTION 
Benefit is claimed from Provisional application 60/014,899 filed Apr. 4, 
1996 under 35 usc 119. 
Field of the Invention 
The present invention relates to a method for making improved lithographic 
printing plates according to the silver salt diffusion transfer process. 
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-repellent 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. 
Two types of the mono-sheet DTR offset printing plate exist. According to a 
first type disclosed in e.g. U.S. Pat. No. 4,722,535 and GB-1,241,661 a 
support is provided in the order given with a silver halide emulsion layer 
and a layer containing physical development nuclei serving as the 
image-receiving layer. After information-wise exposure and development the 
imaged element is used as a printing plate without the removal of the 
emulsion layer. 
According to a second type of mono-sheet DTR offset printing plate a 
hydrophilic support, mostly anodized aluminum, is provided in the order 
given with a layer of physical development nuclei and a silver halide 
emulsion layer. After information-wise exposure and development the imaged 
element is treated to remove the emulsion layer so that a support carrying 
a silver image is left wich is used as a printing plate. Such type of 
lithographic printing plate is disclosed e.g. in U.S. Pat. No. 3,511,656. 
As for other printing plates it is required that the offset printing plates 
belonging to the second type of mono-sheet DTR offset printing plates have 
good printing properties: a high printing endurance, good ink acceptance 
in the printing areas and no ink acceptance in the non-printing areas (no 
toning). An appropriate sensitometry, particularly a high gradient of the 
printing plate is therefore required. 
Furthermore the processing of the exposed imaging element in order to 
obtain a printing plate comprises the step of developing said exposed 
imaging element using an alkaline processing liquid in the presence of 
developing agent(s) and silver halide solvent(s). Nowadays hydroquinone or 
a derivative thereof are used as developing agent. These compounds are 
from an ecological viewpoint not interesting. So the use of other more 
ecologically friendly developing agents is desirable. Ascorbic acid is 
such an ecologically friendly developer but the results when using 
ascorbic acid as the main developer in the processing of a lithographic 
printing plate precursor according to the silver salt diffusion were 
unsatisfactory. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a method for making a 
lithographic printing plate according to the DTR-process with an improved 
sensitometry, particularly a high gradient of the printing plate. 
It is a further object of the present invention to provide a method for 
making a lithographic printing plate according to the DTR-process 
comprising the use of a developing solution containing ascorbic acid as 
the main developer. 
Still further objects of the present invention will become clear from the 
description hereinafter. 
According to the present invention there is provided a method for making an 
offset printing plate according to the silver salt diffusion transfer 
process comprising the steps of: 
image-wise exposing an imaging element comprising in the order given on a 
hydrophilic surface of a support (i) an image receiving layer containing 
physical development nuclei and (ii) a photosensitive layer comprising one 
or more photosensitive silver halide emulsions said photosensitive layer 
being in water permeable relationship with said image receiving layer, 
applying an aqueous alkaline solution to the imaging element comprising at 
least 0.05 mole/l of ascorbic acid as the main developer, at least 0.010 
mole/l of an auxiliary developer of the class of the 
1-phenyl-3-pyrazolidones and an aminoalcohol in an amount from 0.1 ml to 
10 ml as silver halide solvent to form a silver image in said image 
receiving layer, 
treating the imaging element to remove the layer(s) on top of the image 
receiving layer, thereby exposing the imaged surface of the support by 
uncovering said silver image formed in said image receiving layer, 
characterized in that said aqueous alkaline solution contains sodium ions 
but no potassium ions or sodium and potassium ions in which case the molar 
ratio of sodium ions to potassium ions in said aqueous alkaline solution 
is at least 3:1. 
DETAILED DESCRIPTION OF THE INVENTION 
In order to provide a method for making a lithographic printing plate 
according to the DTR-process with an improved sensitometry, usually 
research is directed to improve the imaging element. Now it has been found 
by us that said improved sensitometry can be obtained by optimizing the 
developing solution. 
According to the invention the molar ratio of sodium ions to potassium ions 
in said aqueous alkaline solution is preferably at least 9:1, more 
preferably 95:5 and most preferably 98:2. The upper limit is an aqueous 
alkaline solution containing sodium ions but completely free of potassium 
ions. 
The imaging element for use in the present invention for making an offset 
printing plate comprises in the order given on a hydrophilic surface of a 
support (i) a layer of physical development nuclei as image receiving 
layer and (ii) a photosensitive layer comprising one or more silver halide 
emulsions being in water permeable relationship with said image receiving 
layer. 
Layers being in waterpermeable contact with each other are layers that are 
contiguous to each other or only separated from each other by (a) 
waterpermeable layer(s). The nature of a waterpermeable layer is such that 
it does not substantially inhibit or restrain the diffusion of water or of 
compounds contained in an aqueous solution e.g. developing agents or the 
complexed silver. 
The imaging element is preferably prepared by coating the different layers 
on a hydrophilic surface of a support. Alternatively the different layers 
may be laminated to said image receiving layer from a temporary base 
holding the layers in reverse order as disclosed in U.S. Pat. No. 
5,068,165. 
Said hydrophilic surface of a support can be a hardened hydrophilic layer, 
containing a hydrophilic binder and a hardening agent coated on a flexible 
support. 
Such hydrophilic binders are disclosed in e.g. EP-A 450,199, which therefor 
is incorporated herein by reference. Preferred hardened hydrophilic layers 
comprise partially modified dextrans or pullulan hardened with an aldehyde 
as disclosed in e.g. EP-A 514,990 which therefor is incorporated herein by 
reference. More preferred hydrophilic layers are layers of polyvinyl 
alcohol hardened with a tetraalkyl orthosilicate and preferably containing 
SiO.sub.2 and/or TiO.sub.2 wherein the weight ratio between said 
polyvinylalcohol and said tetraalkyl orthosilicate is between 0.5 and 5 as 
disclosed in e.g. GB-P 1,419,512, FR-P 2,300,354, U.S. Pat. No. 3,971,660, 
U.S. Pat. No. 4,284,705, EP-A 405,016 and EP-A 450,199 which therefor are 
incorporated herein by reference. 
Flexible supports may be opaque or transparent, e.g. a paper support or 
resin support. When a paper support is used preference is given to one 
coated at one or both sides with an Alpha-olefin polymer. It is also 
possible to use an organic resin support e.g. poly(ethylene terephthalate) 
film or poly-Alpha-olefin films. The thickness of such organic resin film 
is preferably comprised between 0.07 and 0.35 mm. These organic resin 
supports are preferably coated with a hydrophilic adhesion layer which can 
contain water insoluble particles such as silica or titanium dioxide. 
Metal supports e.g. aluminum may also be used. 
Said hydrophilic surface of a support may be a hydrophilic metallic support 
e.g. an aluminum foil. 
The aluminum support of the imaging element for use in accordance with the 
present invention can be made of pure aluminum or of an aluminum alloy, 
the aluminum content of which is at least 95%. The thickness of the 
support usually ranges from about 0.13 to about 0.50 mm. 
The preparation of aluminum or aluminum alloy foils for lithographic offset 
printing comprises the following steps graining, anodizing, and optionally 
sealing of the foil. 
Graining and anodization of the foil are necessary to obtain a lithographic 
printing plate that allows the production of high-quality prints in 
accordance with the present invention. Sealing is not necessary but may 
still improve the printing results. Preferably the aluminum foil has a 
roughness with a CLA value between 0.2 and 1.5 .mu.m, an anodization layer 
with a thickness between 0.4 and 2.0 .mu.m and is sealed with an aqueous 
bicarbonate solution. 
According to the present invention the roughening of the aluminum foil can 
be performed according to the methods well known in the prior art. The 
surface of the aluminum substrate can be roughened either by mechanical, 
chemical or electrochemical graining or by a combination of these to 
obtain a satisfactory adhesiveness of a silver halide emulsion layer to 
the aluminum support and to provide a good water retention property to the 
areas that will form the non-printing areas on the plate surface. 
The electrochemical graining process is preferred because it can form a 
uniform surface roughness having a large average surface area with a very 
fine and even grain which is commonly desired when used for lithographic 
printing plates. 
Electrochemical graining can be conducted in a hydrochloric and/or nitric 
acid containing electrolyte solution using an alternating or direct 
current. Other aqueous solutions that can be used in the electrochemical 
graining are e.g. acids like H.sub.2 SO.sub.4, H.sub.3 PO.sub.4, that if 
desired, contain additionally one or more corrosion inhibitors such as 
Al(NO.sub.3).sub.3, AlCl3, boric acid, chromic acid, sulphates, chlorides, 
nitrates, monoamines, diamines, aldehydes, phosphates, H.sub.2 0.sub.2, 
etc. . . . 
Electrochemical graining in connection with the present invention can be 
performed using single-phase and three-phase alternating current. The 
voltage applied to the aluminum plate is preferably 10-35 V. A current 
density of 3-150 Amp/dm.sup.2 is employed for 5-240 seconds. The 
temperature of the electrolytic graining solution may vary from 
5.degree.-50.degree. C. Electrochemical graining is carried out preferably 
with an alternating current from 10 Hz to 300 Hz. 
The roughening is preferably preceded by a degreasing treatment mainly for 
removing greasy substances from the surface of the aluminum foil. 
Therefore the aluminum foil may be subjected to a degreasing treatment with 
a surfactant and/or an aqueous alkaline solution. 
Preferably roughening is followed by a chemical etching step using an 
aqueous solution containing an acid. The chemical etching is preferably 
carried out at a temperature of at least 30.degree. C. more preferably at 
least 40.degree. C. and most preferably at least 50.degree. C. 
Suitable acids for use in the aqueous etch solution are preferably 
inorganic acids and most preferably strong acids. The total amount of acid 
in the aqueous etch solution is preferably at least 150 g/l. The duration 
of chemical etching is preferably between 3 s and 5 min. 
After roughening and optional chemical etching the aluminum foil is 
anodized which may be carried out as follows. 
An electric current is passed through the grained aluminum foil immersed as 
an anode in a solution containing sulphuric acid, phosphoric acid, oxalic 
acid, chromic acid or organic acids such as sulphamic, benzosulphonic 
acid, etc. or mixtures thereof. An electrolyte concentration from 1 to 70% 
by weight can be used within a temperature range from 0.degree.-70.degree. 
C. The anodic current density may vary from 1-50 A/dm.sup.2 and a voltage 
within the range 1-100 V to obtain an anodized film weight of 1-8 
g/m.sup.2 Al.sub.2 O.sub.3.H.sub.2 O. The anodized aluminum foil may 
subsequently be rinsed with demineralised water within a temperature range 
of 10.degree.-80.degree. C. 
After the anodizing step sealing may be applied to the anodic surface. 
Sealing of the pores of the aluminum oxide layer formed by anodization is 
a technique known to those skilled in the art of aluminum anodization. 
This technique has been described in e.g. the "Belgisch-Nederlands 
tijdschrift voor Oppervlaktetechnieken van materialen", 24ste 
jaargang/januari 1980, under the title "Sealing-kwaliteit en 
sealing-controle van geanodiseerd Aluminum". Different types of sealing of 
the porous anodized aluminum surface exist. 
Preferably, said sealing is performed by treating a grained and anodized 
aluminum support with an aqueous solution containing a bicarbonate as 
disclosed in EP-A 567178, which therefor is incorporated herein by 
reference. 
Preferably each of the above described steps is separated by a rinsing step 
to avoid contamination of the liquid used in a particular step with that 
of the preceding step. 
To promote the image sharpness and, as a consequence thereof, the sharpness 
of the final printed copy, the anodization layer may be coloured in the 
mass with an antihalation dye or pigment e.g. as described in 
JA-Pu-58-14,797. 
Subsequent to the preparation of the hydrophilic layer of a support as 
described above, said hydrophilic layer may be immediately coated with a 
solution containing the physical development nuclei or may be coated with 
said solution at a later stage. 
The image receiving layer containing physical development nuclei may be 
free of hydrophilic binder but preferably comprises amounts upto e. g. 80% 
by weight of the total weight of said layer of a hydrophilic colloid e.g. 
polyvinyl alcohol to improve the hydrophilicity of the surface. 
Preferred development nuclei for use in accordance with the present 
invention are sulphides of heavy metals e.g. sulphides of antimony, 
bismuth, cadmium, cobalt, lead, nickel, palladium, platinum, silver, and 
zinc. Especially suitable development nuclei in connection with the 
present invention are palladium sulphide nuclei. Other suitable 
development nuclei are salts such as e.g. selenides, polyselenides, 
polysulphides, mercaptans, and tin (II) halides. Heavy metals, preferably 
silver, gold, platinum, palladium, and mercury can be used in colloidal 
form. 
The photosensitive layer used according to the present invention may be any 
layer comprising a hydrophilic colloid binder and at least one silver 
halide emulsion, at least one of the silver halide emulsions being 
photosensitive. 
The photographic silver halide emulsion(s) used in accordance with the 
present invention 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). 
For use according to the present invention the silver halide emulsion or 
emulsions preferably consist principally of silver chloride while a 
fraction of silver bromide may be present ranging from 0.1 mole % to 40 
mole % and a fraction of silver iodide ranging from 0.01 mole % to 2 mole 
%. More preferably a silver halide emulsion containing at least 90 mole% 
of silver chloride is used. Most preferably a silver halide emulsion 
containing at least 99 mole% of silver chloride and free of silver bromide 
is used. 
The sum of the silver halide in said one or more silver halide emulsions 
(expressed as AgNO.sub.3) is preferably not more than 2 g AgNO.sub.3 
/m.sup.2.sub.1 more preferably not more than 1.75 g AgNO.sub.3 /m.sup.2. 
The minimum amount of the the sum of the silver halide in said one or more 
silver halide emulsions (expressed as AgNO.sub.3) is not so critical but 
is preferably at least 0.9 g AgNO.sub.3 m.sup.2, more preferably at least 
1.1 g AgNO.sub.3 /m.sup.2. 
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. 
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.-3 mole per mole of AgNO.sub.3. 
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 silver halide 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 hemibxonol dyes. Particularly valuable dyes are those belonging 
to the cyanine dyes, merocyanine dyes, complex merocyanine dyes. 
In the case of a conventional light source, e.g. tungsten light, a green 
sensitizing dye is needed. In case of exposure by an argon ion laser a 
blue sensitizing dye is incorporated. In case of exposure by a red light 
emitting source, e.g. a LED or a HeNe laser a red sensitizing dye is used. 
In case of exposure by a semiconductor laser special spectral sensitizing 
dyes suited for the near infra-red are required. Suitable infra-red 
sensitizing dyes are disclosed in i.a. U.S. Pat. Nos. 2,095,854, 
2,095,856, 2,955,939, 3,482,978, 3,552,974, 3,573,921, 3,582,344, 
3,623,881 and 3,695,888. 
A preferred blue sensitizing dye, green sensitizing dye, red sensitizing 
dye and infra-red sensitizing dye in connection with the present invention 
are described in EP-A 554,585. 
To enhance the sensitivity in the red or near infra-red region use can be 
made of so-called supersensitizers in combination with red or infra-red 
sensitizing dyes. Suitable supersensitizers are described in Research 
Disclosure Vol 289, May 1988, item 28952. The spectral sensitizers can be 
added to the photographic emulsions in the form of an aqueous solution, a 
solution in an organic solvent or in the form of a dispersion. 
The silver halide emulsions may contain the usual emulsion stabilizers. 
Suitable emulsion 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 emulsion 
stabilizers are i.a. heterocyclic mercapto compounds. 
The silver halide emulsion 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.. Preferably the silver halide emulsion layer contains at least one 
gelatin species whereof a 10% by weight aqueous solution at 36 .degree.C. 
and pH 6 has a viscosity lower than 20 mPas at a shearing rate of 1000 
s.sup.-1 combined with a gelatin of a higher viscosity. The weight ratio 
of said low viscosity gelatin versus the gelatin of a higher viscosity is 
preferably &gt;0.5. 
Preferably the gelatin layer(s) is(are) substantially unhardened. 
Substantially unhardened means that when such gelatin layer is coated on a 
subbed polyethylene terephtalate film base at a dry thickness of 1.2 
g/m.sup.2, dried for 3 days at 57.degree. C. .degree.and 35% R.H. and 
dipped in water of 30.degree. C., said gelatin layer is dissolved for more 
than 95% by weight within 5 minutes. 
The silver halide emulsions may contain pH controlling ingredients. 
Preferably at least one gelatin containing layer is coated at a pH value 
not below the iso-electric point of the gelatin to avoid interactions 
between said gelatin containing coated layer and the hereafter mentioned 
intermediate layer. More preferably the gelatin layer contiguous to said 
intermediate layer is coated at a pH value not below the iso-electric 
point of the gelatin. Most preferably all the gelatin containing layers 
are coated at a pH value not below the iso-electric point of their 
gelatin. 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 suitable for use in accordance with the present invention 
can be found in e.g. Product Licensing Index, Vol. 92, December 1971, 
publication 9232, p. 107-109. 
According to the invention said imaging element preferably comprises on top 
of the photosensitive layer and in water permeable relationship therewith 
an uppermost composition (antistress composition) comprising unhardened 
gelatin in an amount ranging from 0.60 to 1.75 g/m.sup.2, more preferably 
in an amount ranging from 0.80 to 1.25 g/m.sup.2. 
Preferably at least 50%, more preferably at least 75%, most preferably at 
least 90% by weight of said unhardened gelatin belongs to one or more 
gelatin species whereof a 10% by weight aqueous solution at 40.degree. C. 
and pH 6 has a viscosity lower than 20 mPas, more preferably lower than 15 
mPas at a shearing rate of 1000 s.sup.-1. 
The antistress composition can comprise more than one species of unhardened 
gelatin whereof a 10% by weight aqueous solution at 40.degree. C. and pH 6 
has a viscosity lower than 20 mPas at a shearing rate of 1000 s .sup.-1, 
but it is preferred for practical reasons that said composition comprises 
only one such gelatin. When a mixture of unhardened gelatins is used, a 
10% by weight aqueous solution of said mixture of unhardened gelatins has 
at 40.degree. C. and pH 6 preferably a viscosity lower than 20 mPas at a 
shearing rate of 1000 s.sup.-1. 
The antistress composition may contain small particles e.g. matting agents 
with a mean diameter between 0.2 and 10 .mu.m in order to improve the 
diffusion of processing solutions through said antistress composition. 
The antistress composition can comprise more than one layer, but for 
practical reasons it is preferred that said composition consists of one 
layer. 
Preferably, the imaging element also comprises an intermediate layer 
between the image receiving layer on the hydrophilic surface of a support 
and the photosensitive layer(packet) to facilate the removal of said 
layer(packet) thereby uncovering the silver image formed in the image 
receiving layer by processing the imaging element. 
In one embodiment, the intermediate layer is a water-swellable intermediate 
layer coated at a ratio of 0.01 to 2.0 g/m2 and comprising at least one 
non-proteinic hydrophilic film-forming polymer e.g. polyvinyl alcohol and 
optionally comprising an antihalation dye or pigment as disclosed in 
EP-A-410500. 
In another embodiment, the intermediate layer is a layer comprising 
hydrophobic polymer beads having an average diameter not lower than 0.2 
.mu.m and having been prepared by polymerization of at least one 
ethylenically unsaturated monomer. Preferably, said intermediate layer in 
dry condition comprises said hydrophobic polymer beads in an amount of up 
to 80% of its total weight. Further details are disclosed in EP-A-483415. 
In still another embodiment, the intermediate layer is a layer comprising 
particles of a water insoluble inorganic compound having a number average 
size not lower than 0.1 .mu.m. Preferably, said intermediate layer 
comprises said water insoluble inorganic compound in an amount of at least 
0.1 g/im.sup.2. Further details are disclosed in EP-A-94203779.7 
In still another embodiment, the intermediate layer is a layer comprising 
particles of an alkali insoluble non-polymeric organic compound having a 
melting point of at least 50.degree. C., said particles having a number 
average size between 0.1 .mu.m and 10 .mu.m. Preferably, said intermediate 
layer comprises said alkali insoluble non-polymeric organic compound in an 
amount of at least 0.1 g/m.sup.2. Further details are disclosed in 
EP-A-95201713.5 
In still another embodiment, the intermediate layer is a layer comprising 
particles of an alkali insoluble polymeric organic compound obtainable by 
polycondensation, said particles having a number average size between 0.02 
.mu.m and 10 .mu.m. Preferably, said intermediate layer comprises said 
alkali insoluble polymeric organic compound obtainable by polycondensation 
in an amount of at least 0.1 g/m.sup.2. Further details are disclosed in 
EP-A-95203052.6. 
A supplemental intermediate layer, which may be present between said silver 
halide emulsion containing layer and said intermediate layer may 
incorporate one or more ingredients such as i.a. antihalation dyes or 
pigment, developing agents, silver halide solvents, base precursors, and 
anticorrosion substances. 
When the imaging element is prepared by laminating a layer packet 
comprising a photosensitive layer onto the image receiving layer the 
intermediate layer(s) are provided on the photosensitive layer(s), the 
intermediate layer being the upper layer. 
According to the present invention the imaging element can be 
information-wise exposed in an apparatus according to its particular 
application. A wide choice of cameras for exposing the photosensitive 
silver halide emulsion exists on the market. Horizontal, vertical and 
darkroom type cameras and contact-exposure apparatus are available to suit 
any particular class of reprographic work. The imaging element in 
accordance with the present invention can also be exposed with the aid of 
i.a. laser recorders and cathode rays tubes. 
The development and diffusion transfer of the information-wise exposed 
imaging element in order to form a silver image in said photosensitive 
layer and to allow unreduced silver halide or complexes formed thereof to 
diffuse image-wise from the photosensitive layer to said image receiving 
layer to produce therein a silver image, are effected with the aid of an 
aqueous alkaline solution comprising at least 0.05 mole/l of ascorbic acid 
as the main developer, at least 0.010 mole/l of an auxiliary developer of 
the class of the 1-phenyl-3-pyrazolidones and an aminoalcohol in an amount 
from 0.1 ml to 10 ml as silver halide solvent. 
The developing agent(s) and/or the silver halide solvent(s) can be 
partially incorporated in the imaging element itself e.g. in at least one 
silver halide emulsion layer and/or in a water-swellable layer and/or in a 
supplemental hydrophilic colloid layer in water-permeable relationship 
with the silver halide emulsion layer(s). However preferably the total 
amount of all the developing agents and silver halide solvent(s) are 
present in the aqueous alkaline solution. 
According to the invention said developing solution comprises as the main 
developer ascorbic acid in a concentration of at least 0.05 mole/l, 
preferably in a concentration of at least 0.10 mole/l, more preferably in 
a concentration of at least 0.15 mole/l. 
According to the invention said developing solution comprises at least 
0.010 mole/l, preferably at least 0.020 mole/l, most preferably at least 
0.030 mole/l of an auxiliary developer of the class of the 
1-phenyl-3-pyrazolidones (also called phenidones). The upper limit is not 
so important but is preferably not higher than 0.10 mole/l. 
Said auxiliary developer of the class of the 1-phenyl-3-pyrazolidones are 
e.g. 1-phenyl-3-pyrazolidone, 1-phenyl-4-monomethyl-3-pyrazolidone, 
1-phenyl-4,4-dimethyl-3-pyrazolidone and 1-phenyl-3-pyrazolidones of which 
the aqueous solubility is increased by a hydrophilic substituent such as 
e.g. hydroxy, amino, carboxylic acid group, sulphonic acid group etc.. 
Examples of 1-phenyl-3-pyrazolidones subsituted with one or more 
hydrophilic groups are e.g. 
1-phenyl-4-methyl-4-hydroxymethyl-3-pyrazolidone, 
1-phenyl-4,4',-dihydroxymethyl-3-pyrazolidone, 
1-(4-carboxyphenyl)-4,4-dimethyl-3-pyrazolidone etc.. 
Preferably said alkaline developing solution contains a mono- or 
polysaccharide such as cyclodextrine as a preservative for ascorbic acid. 
Alkanolamines that are suitable for use in connection with the present 
invention may be of the tertiary, secundary or primary type. Examples of 
alkanolamines that may be used in connection with the present invention 
correspond to the following formula: 
##STR1## 
wherein X and X' independently represent hydrogen, a hydroxyl group or an 
amino group, 1 and m represent 0 or integers of 1 or more and n represents 
an integer of 1 or more. Preferably used alkanolamines are e.g. 
diethanolamine, N-methylethanolamine, triethanolamine, 
N-ethyldiethanolamine, diisopropanolamine, N,N-dimethylethanolamine, 
N,N-ethyl-2,2'-iminodiethanol etc. or mixtures thereof. 
More preferred aminoalcohols according to the invention are primary 
aminoalcohols such as ethanolamine, 4-aminobutanol, 3-aminopropanol, most 
preferred 2-aminoethyl-aminoethanol. 
Said aminoalcohols are preferably used in an amount between 0.3 and 5 ml/l 
aqueous alkaline solution, more preferably in an amount between 0.5and 3 
ml/l aqueous alkaline solution. 
Optionally a further silver halide solvent in the aqueous alkaline solution 
is used in an amount between 0.05% by weight and 5% by weight and more 
preferably between 0.5% by weight and 2% by weight. Further silver halide 
solvents that can be used in connection with the present invention are 
e.g. amines, 2-mercaptobenzoic acid, cyclic imide compounds such as e.g. 
uracil, 5,5-dialkylhydantoins, alkyl sulphones, thiocyanates and 
oxazolidones. 
Still other optional further silver halide solvents for use in connection 
with the present invention are thioethers. Preferably used thioethers 
correspond to the following general formula: 
EQU Z--(R.sup.1 --S).sub.t --R.sup.2 --S--R.sup.3 --Y 
wherein Z and Y each independently represents hydrogen, an alkyl group, an 
amino group, an ammonium group, a hydroxyl, a sulpho group, a carboxyl, an 
aminocarbonyl or an aminosulphonyl, R.sup.1, R.sup.2 and R.sup.3 each 
independently represents an alkylene that may be substituted and 
optionally contain an oxygen bridge and t represents an integer from 0 to 
10. Examples of thioether compounds corresponding to the above formula are 
disclosed in e.g. US-P-4.960.683 and EP-A 554,585. 
Still further suitable silver halide solvents are 
1,2,4-triazolium-3-thiolates, preferably 1,2,4-triazolium-3-thiolates 
substituted with at least one substituent selected from the group 
consisting of a C.sub.1 -C.sub.8 alkyl group that contains at least 3 
fluorine atoms, a C.sub.4 -C.sub.1 o hydrocarbon group and a 4-amino group 
substituted with a C.sub.1 -C.sub.8 alkyl group that contains at least 3 
fluorine atoms and/or a C.sub.4 -C.sub.1 hydrocarbon group. 
Combinations of different silver halide solvents can be used and it is also 
possible to incorporate at least one further silver halide solvent into a 
suitable layer of the imaging element and to add at least one other 
further silver halide solvent to the developing solution. 
The aqueous alkaline solution in accordance with the present invention may 
further comprise sulphite e.g. sodium sulphite in an amount ranging from 
40 g to 180 g per liter, preferably from 60 to 160 g per liter in 
combination with another silver halide solvent. 
The quantitative ranges given for the developing agents, silver halide 
solvents, and sulphite apply to the amount of these compounds present as 
solutes in the aqueous alkaline solution during the DTR-processing, 
whether these compounds make part of the aqueous alkaline solution or were 
dissolved from the layers containing them upon application thereto of the 
aqueous alkaline solution. 
The aqueous alkaline solution suitable for use according to the present 
invention preferably comprises aluminum ions in an amount of at least 0.3 
g/l, more preferably in an amount of at least 0.6 g/l in order to prevent 
sticking of the emulsion layer to the transporting rollers when the 
emulsion is swollen with the aqueous alkaline solution. 
The alkaline processing liquid preferably has a pH between 9 and 14 and 
more preferably between 10 and 13, but depends on the type of silver 
halide emulsion material to be developed, intended development time, and 
processing temperature. 
The processing conditions such as temperature and time may vary within 
broad ranges provided the mechanical strength of the materials to be 
processed is not adversely influenced and no decomposition takes place. 
The pH of the alkaline processing liquid may be established by an organic 
or inorganic alkaline substance or a combination thereof. Suitable 
inorganic alkaline substances are e.g. hydroxides of sodium and potassium, 
alkali metal salts of phosphoric acid and/or silicic acid e.g. trisodium 
phosphate, orthosilicates, metasilicates, hydrodisilicates of sodium or 
potassium, and sodium carbonate etc.. Suitable organic alkaline substances 
are e.g. alkanolamines. In the latter case the alkanolamines will provide 
or help providing the pH and serve as a silver halide complexing agent. 
The aqueous alkaline solution may further comprise hydrophobizing agents 
for improving the hydrophobicity of the silver image obtained in the image 
receiving layer. Generally these compounds contain a mercapto group or 
thiolate group and one or more hydrophobic substituents. Particularly 
preferred hydrophobizing agents are mercapto-1,3,4-thiadiazoles as 
described in DE-A 1,228,927 and in U.S. Pat. No. 4,563,410, 
2-mercapto-5-alkyl-oxa-3,4-diazoles, 3-mercapto-5-alkyl-1,2,4-triazoles 
and long chain (at least 5 carbon atoms) alkyl substituted 
mercaptotetrazoles. The hydrophobizing agents can be used alone or in 
combination with each other. 
These hydrophobizing compounds can be added to the aqueous alkaline 
solution in an amount of preferably 0.1 to 3 g per litre and preferably in 
admixture with 1-phenyl-5-mercaptotetrazole, the latter compound may be 
used in amounts of e.g. 50 mg to 1.2 g per litre of solution, which may 
contain a minor amount of ethanol to improve the dissolution of said 
compounds. 
The aqueous alkaline solution may comprise other ingredients such as e.g. 
oxidation preservatives, calcium-sequestering compounds, anti-sludge 
agents, and hardeners including latent hardeners. 
Regeneration of the aqueous alkaline solution according to known methods 
is, of course, possible, whether the solution incorporates developing 
agent(s) or not. 
The development may be stopped--though this is often not necessary--with a 
so-called stabilization liquid, which actually is an acidic stop-bath 
having a pH preferably in the range from 5 to 7. 
Bufferred stop bath compositions comprising a mixture of sodium dihydrogen 
orthophosphate and disodium hydrogen orthophosphate and having a pH in 
said range are preferred. 
The development and diffusion transfer can be initiated in different ways 
e.g. by rubbing with a roller, by wiping with an absorbent means e.g. with 
a plug of cotton or sponge, or by dipping the material to be treated in 
the liquid composition. Preferably, they proceed in an automatically 
operated apparatus. They are normally carried out at a temperature in the 
range of 18.degree. C. to 30.degree. C. and in a time from 5 s to 5 min. 
After formation of the silver image on the hydrophilic surface of a support 
an excess of aqueous alkaline solution still present on the base may be 
eliminated, preferably by guiding the foil through a pair of squeezing 
rollers. 
The silver image thus obtained in the layer of physical development nuclei 
is subsequently uncovered by treating the imaging element to remove all 
the layers above the layer containing physical development nuclei, thereby 
exposing the imaged surface of the hydrophilic support. 
According to a particularly preferred embodiment of the present invention 
the silver image in the layer of physical development nuclei is uncovered 
by washing off all the layers above the layer containing physical 
development nuclei with rinsing water. 
The temperature of the rinsing water may be varied widely but is preferably 
between 30 .degree.C. and 50 .degree.C., more preferably between 
35.degree. C. and 45.degree. C. 
The imaged surface of the hydrophilic surface of a support can be subjected 
to a chemical treatment that increases the hydrophilicity of the 
non-silver image parts and the oleophilicity of the silver image. 
This chemical after-treatment is preferably carried out with a lithographic 
composition often called finisher comprising at least one compound 
enhancing the ink-receptivity and/or lacquer-receptivity of the silver 
image and at least one compound that improves the ink-repelling 
characteristics of the hydrophilic surface. 
Suitable ingredients for the finisher are e.g. organic compounds containing 
a mercapto group such as the hydrophobizing compounds referred to 
hereinbefore for the alkaline solution. Preferred compounds correspond to 
one of the following formulas: 
##STR2## 
wherein R.sup.5 represents hydrogen or an acyl group, R.sup.4 represents 
alkyl, aryl or aralkyl. Most preferably used compounds are compounds 
according to one of the above formulas wherein R.sup.4 represents an alkyl 
containing 3 to 16 C-atoms. Said (a) hydrophobizing agent(s) is(are) 
comprised in the finisher preferably in a total concentration between 0.1 
g/l and 10 g/l, more preferably in a total concentration between 0.3 g/l 
and 3 g/l. 
Additives improving the oleophilic ink-repellency of the hydrophilic 
surface areas are e.g. carbohydrates such as acid polysaccharides like gum 
arabic, carboxymethylcellulose, sodium alginate, propylene glycol ester of 
alginic acid, hydroxyethyl starch, dextrin, hydroxyethylcellulose, 
polyvinyl pyrrolidone, polystyrene sulphonic acid, polyglycols being the 
reaction products of ethyleneoxide and/or propyleneoxide with water or an 
alcohol and polyvinyl alcohol. Optionally, hygroscopic substances e.g. 
sorbitol, glycerol, tri(hydroxyethyl)ester of glycerol, and turkish red 
oil may be added. 
Furthermore (a) surface-active compound(s) is (are) preferably also added 
to the finisher. The concentration thereof may vary within broad ranges 
provided the finisher shows no excessive degree of foaming when plates are 
finished. Preferred surface-active compound are anionic or non-ionic 
surface-active compound. 
A suitable finisher as disclosed in U.S. Pat. no. 4.563.410 is a 
composition comprising a solution of a mercaptotriazole in a solution of 
polyethylene oxide with a molecular weight of 4,000. Further suitable 
finishers have been described in i.a. U.S. Pat. No. 4.062.682 and EP 
681219. 
At the time the treatment with the finisher is started the surface carrying 
the silver pattern may be in dry or wet state. In general, the treatment 
with the finisher does not take long, usually not longer than about 30 
seconds and it may be carried out immediately after the processing and 
uncovering steps, preferably at a temperature of the finisher in the range 
from 30.degree. C. to 60.degree. C. 
The finisher can be applied in different ways such as by rubbing with a 
roller, by wiping with an absorbent means e.g. with a plug of cotton or 
sponge, or by dipping the material to be treated in the finisher. The 
image-hydrophobizing step of the printing plate may also proceed 
automatically by conducting the printing plate through a device having a 
narrow channel filled with the finisher and conveying the printing plate 
at the end of the channel between two squeezing rollers removing the 
excess of liquid. 
As soon as the hydrophilic surface of a support carrying the silver image 
has been treated with the finisher, it is ready to be used as a printing 
plate.

EXAMPLE 
A 0,30 mm thick aluminum foil (AA 1050) was degreased by immersing the foil 
in an aqueous solution containing 10 % phosphoric acid and subsequently 
etched in an aqueous solution containing 2 g/l of sodium hydroxide. The 
foil was then electrochemically grained using an alternating current in an 
aqueous solution containing 4 g/l of hydrochloric acid and 4 g/l of 
hydroboric acid at a temperature of 35.degree. C. to form a surface 
topography with an average center-line roughness Ra of 0,6 .mu.m. The 
aluminum plate was then desmutted with an aqueous solution containing 30% 
of sulfuric acid at 60.degree. C. for 120 seconds. The foil was 
subsequently subjected to anodic oxidation in a 20% sulfuric acid aqueous 
solution to form an anodic oxidation film of 3.0 g/m of Al.sub.2 
O.sub.3.H.sub.2 O, treated with an aqueous solution containing 20 g/l of 
NaHCO.sub.3 at 45.degree. C. for 30 sec and then rinsed with demineralised 
water and dried. 
The imaging element was obtained by coating the grained, anodized and 
sealed aluminum support with a silver-receptive stratum containing 1.1 
mg/m.sup.2 PdS as physical development nuclei. 
An intermediate layer was then provided on the dry silver-receptive stratum 
from an aqueous composition in such a way that the resulting dried layer 
had a weight of 0.5 g of polymethyl methacrylate beads per m.sup.2, said 
composition comprising: 
______________________________________ 
a 20% dispersion of polymethyl methacrylate beads 
50 ml 
in a mixture of equal volumes of water and ethanol 
having an average diameter of 1.0 .mu.m 
Helioechtpapierrot BL (trade mark for a dye sold by 
2.5 g 
BAYER AG, D-5090 Leverkusen, West-Germany) 
saponine 2.5 g 
sodium oleylmethyltauride 1.25 g 
demineralized water 300 ml 
(pH-value : 5.6) 
______________________________________ 
Finally a substantially unhardened photosensitive negative-working 
cadmium-free gelatin silver chloroiodide emulsion layer (99.8/0.2 mol%) 
containing 1 mmole/mole AgX of 4-hydroxy-6-methyl-1,3,3a, 7-tetraazaindene 
was coated on the intermediate layer, the silver halide being provided in 
an amount corresponding to 1.80 g of silver nitrate per m.sup.2 and the 
gelatin content of the emulsion layer being 1.14 g/m.sup.2, consisting of 
0.50 g/m.sup.2 of a gelatin with a viscosity of 21 mPa.s and the remainder 
of a gelatin with a viscosity of 14 mPa.s 
Three samples of the imaging element were exposed through a contact screen 
in a process-camera and respectively immersed for 10 s at 24.degree. C. in 
one of the freshly made developing solutions 1 to 3 having the following 
ingredients: 
______________________________________ 
Developer 1 
carboxymethylcellulose 4 g 
sodium hydroxide 22.5 g 
anhydrous sodium sulphite 120 g 
ascorbic acid 35.2 g 
1-phenyl-3-pyrazolidinone 6 g 
aminoethyl-aminoethanol 1 ml 
ethylene diamine tetraacetate acid tetrasodium salt 
2 g 
aluminum sulphate. 18 aq 8.4 g 
demineralized water to make 
1000 ml 
pH (24.degree. C.) = 13 
______________________________________ 
Developer 2 is identical with developer 1 except that half of the amount of 
sodium hydroxide was replaced by 15.75 g of potassium hydroxyde and that 
half the amount of sodium sulphite was replaced by 72 gram of potassium 
sulphite. Developer 3 is identical with developer 1 except that the total 
amount of sodium hydroxide was replaced by 31.5 g of potassium hydroxide 
and that the total amount of sodium sulphite was replaced by 144 g of 
potassium sulphite. 
The initiated diffusion transfer was allowed to continue for 30 s to form a 
silver image in the image receiving layer. 
To remove the developed silver halide emulsion layer and the intermediate 
layer from the aluminum foil the developed monosheet DTR material was 
rinsed for 6 s with a water jet at 40.degree. C. The results are given in 
table 1. 
TABLE 1 
______________________________________ 
Developer Dmin.sup.a) 
Grad 1.sup.b) 
Grad 2.sup.c) 
Grad 3.sup.d) 
______________________________________ 
1 0.278 2.65 1.14 3.81 
2 0.391 2.23 1.00 1.74 
3 0.568 1.23 0.89 0.95 
______________________________________ 
.sup.a) Dmin: minimum density 
.sup.b) Grad 1: The gradient of the sensitometric curve of the printing 
plate between the points 25% above the minimum density and 25% below the 
maximum density. 
.sup.c) Grad 2: The gradient of the sensitometric curve of the printing 
plate between Dmin + 0.10 and Dmin + 0.25 
.sup.d) Grad 3: The gradient of the sensitometric curve of the printing 
plate between 25% and 10% below the maximum density. 
Evaluation: 
From these results it is seen that by using a developer comprising sodium 
ions but no potassium ions (developer 1) a printing plate is obtained with 
a lower Dmin and higher gradients than by using a developer having a molar 
ratio of sodium ions to potassium ions of 1 (developer 2) or than by using 
a developer comprising potassium ions but no sodium ions (developer 3).