The present invention provides a photographic material with a pH at 25.degree. C. of at most 7, containing on a support at least one layer, comprising a prefogged direct-positive silver halide emulsion spectrally sensitized with one or more electron-accepting sensitizing dyes in a total amount of at least 0.15 mmole/mole silver halide, the silver halide crystals of said prefogged direct-positive silver halide emulsion containing silver chloride for at least 60 mole %, silver bromide in a range from 0.5 mole % to 39.98 mole % and silver iodide in a range from 0.02 mole % to 2 mole %, characterized in that said silver halide cristals contain silver iodide for at least 0.20 mmole/mole AgX in the outer 10% by weight of said cristals and said layer contains a gelatin species containing Ca.sup.2+ in an amount ranging from 0.2% to 1% by weight.

FIELD OF THE INVENTION 
The present invention relates to a direct positive type silver halide 
photographic material with high sensitivity. The present invention further 
relates to a method for obtaining images with said photographic material 
and to a method for obtaining a lithographic printing plate with said 
photographic material. 
BACKGROUND OF THE INVENTION 
With recent rapid progress of information transmitting systems, silver 
halide photographic materials have been increasingly required to have high 
sensitivity. This high sensitivity is a necessity as well in the field of 
negative working as of positive working silver halide photographic 
materials. A negative working photographic material is one giving a 
negative image while a positive working photographic material is one 
giving a positive image. The term negative image means that image reversal 
occurred while the term positive image indicates that no image reversal 
took place. 
So, for a photographic material to be suitable for use in graphical 
applications it is required that the material is of high speed to the 
applied illumination, it being a classical analogous one or a so-called 
high intensity-short time exposure (flash exposure or scanning exposure) 
and yields images of high contrast and high resolving power. 
Photographic materials for graphic applications include photographic films 
and papers used after processing as interoriginals in a process for 
preparing a lithographic printing plate and silver salt diffusion transfer 
based (hereinafter called DTR-) lithographic printing plates disclosed in 
e.g. U.S. Pat. No. 4,501,811 and U.S. Pat. No. 4,784,933. With the latter 
materials a lithographic printing plate can be obtained without the need 
of a photographic interoriginal. 
In most cases it is required that said interoriginals have a negative image 
because most printing plates are negative working. Time and cost are then 
saved when said interoriginals are prepared by phototypesetting when using 
a positive working silver halide photographic material e.g. a photographic 
material comprising a positive working (hereinafter called 
direct-positive) silver halide emulsion. 
In the conventional DTR-process i.e. a DTR-process wherein a photographic 
material comprising a negative working (hereinafter called negative) 
silver halide emulsion is used a positive image is formed in the receiving 
layer. 
At the exposed areas of the silver halide emulsion layer the silver halide 
is developed (chemical development) and thus cannot be dissolved anymore 
to diffuse to the receiving layer. 
At the unexposed areas of the silver halide emulsion layer the silver 
halide is converted into a soluble silver complex salt and is transferred 
to the receiving layer, where it forms a silver image usually in the 
presence of physical development nuclei. 
If a negative image of the original is to be formed in the receiving layer 
a photographic material comprising a direct-positive silver halide 
emulsion should be used. The formation of negative images from the 
original are interesting where positive DTR-images are desired from 
negatives or vice versa. 
It is further known to make lithographic printing plates by the 
DTR-process. 
Here too printing plates made by the conventional DTR-process are of the 
positive type and a photographic material comprising a direct-positive 
silver halide emulsion is required in the DTR-process to obtain a positive 
printing plate starting from negative originals. 
Furthermore the conventional positive type DTR-process for direct plate 
making by lasers and scanners e.g. computer to plate applications which 
are widely employed, have the disadvantage of requiring a long exposure 
time since the non-image areas of the negative silver halide emulsion 
layer should be exposed in order to obtain in the image receiving layer 
image areas that are printing. Thus for computer to plate applications it 
is also desirable to have a DTR-material comprising a direct-positive 
silver halide emulsion. 
For the formation of a direct-positive image in the silver halide emulsion 
layer two main types of direct positive silver halide emulsions are known. 
One type is a silver halide emulsion that has been prefogged. Such types of 
emulsion are commonly known as Herschel reversal emulsions and are 
described in e.g. U.S. Pat. No. 3,367,778. U.S. Pat. No. 3,733,199 
discloses the use of such a type of emulsion for use in a diffusion 
transfer process. U.S. Pat. No. 4,149,889, U.S. Pat. No. 4,175,965 and 
JP-Pi 01-96648 describe the use of Herschel reversal emulsions for the 
production of a negative type lithographic printing plate. 
The second type of direct positive emulsions are inner latent image type 
silver halide emulsions that have not been previously prefogged. Such a 
type of direct positive emulsions is disclosed in e.g. EP-A365.926. U.S. 
Pat. No. 4,309,499 discloses its use in a DTR imaging element. 
This last type of direct positive emulsion shows normally a higher speed 
than the first type but can not be developed in the classical way. While 
with the first type of direct positive type emulsions a positive image in 
the emulsion layer is obtained by effecting a normal surface development, 
the second type of direct positive type emulsions requires a supplementary 
fogging treatment subsequent to the image-wise exposure before or while 
applying a normal surface development. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a photographic material 
comprising a layer containing a direct-positive silver halide emulsion, 
having a high sensitivity, developable in a classical surface developer 
without a supplementary treatment and that can yield images of good 
quality, especially of high contrast. 
It is another object of the present invention to provide a method for 
obtaining said photographic material. 
It is further object of the present invention to provide a method for 
obtaining an image with said photographic material. 
It is a still further object of the present invention to provide a method 
for obtaining with said photographic material an imaging element having a 
high sensitivity that can be used for obtaining a lithographic printing 
plate of high contrast according to the silver salt diffusion transfer 
process in a classical silver salt diffusion transfer processing. 
It is an even further object of the present invention to provide a method 
for obtaining a lithographic printing plate of high contrast and good 
printing properties according to the silver salt diffusion transfer 
process by using said imaging element. 
Further objects of the present invention will become clear from the 
description hereinafter. 
According to the present invention there is provided a photographic 
material with a pH at 25.degree. C. of at most 7, containing on a support 
at least one layer, comprising a prefogged direct-positive silver halide 
emulsion spectrally sensitized with one or more electron-accepting 
sensitizing dyes in a total amount of at least 0.15 mmole/mole silver 
halide, the silver halide crystals of said prefogged direct-positive 
silver halide emulsion containing silver chloride for at least 60 mole %, 
silver bromide in a range from 0.50 mole % to 39.98 mole % and silver 
iodide in a range from 0.020 mole % to 2.0 mole %, characterized in that 
said silver halide cristals contain silver iodide for at least 0.20 
mmole/mole AgX in the outer 10% by weight of said cristals and said layer 
contains a gelatin species containing Ca.sup.2+ in an amount ranging from 
0.20% to 1% by weight. 
According to the present invention there is also provided a method for 
obtaining the above mentioned photographic material by 
--preparing a prefogged direct-positive silver halide emulsion comprising 
the steps of (i) formation of a silver halide emulsion by precipitation in 
an aqueous medium of silver halide crystals containing silver chloride for 
at least 60 mole %, silver bromide in a range from 0.50 mole % to 39.98 
mole % and silver iodide in a range from 0.020 mole % to 2.0 mole %, (ii) 
desalination of said silver halide emulsion, (iii) prefogging of said 
silver halide emulsion, (iv) adding one or more electron-accepting 
sensitizing dyes to said prefogged silver halide emulsion in a total 
amount of at least 0.15 mmole/mole silver halide and (v) adjusting the pH 
of said spectrally sensitized prefogged silver halide emulsion so as to 
obtain a photographic material with a pH at 25.degree. C. of at most 7 and 
--coating on a support at least said spectrally sensitized prefogged silver 
halide emulsion layer, characterized in that one of more water soluble 
iodide salts are added to the emulsion of said silver halide cristals in a 
stage after the addition of at least 90% of the silver salt in a total 
amount from 0.20 mmole/mole AgX to 0.020 mole/mole AgX and a gelatin 
species containing Ca.sup.2+ in an amount ranging from 0.20 % to 1% by 
weight is added to said aqueous medium before adding said one or more 
electron-accepting sensitizing dyes to said prefogged silver halide 
emulsion. 
According to the present invention there is also provided a method for 
obtaining an image with the above defined photographic material by 
exposing said photographic material followed by development. 
According to the present invention there is also provided a method for 
obtaining an imaging element by coating on a support at least one silver 
halide emulsion layer as defined above and an image receiving layer 
containing physical development nuclei in water permeable relationship 
with said silver halide emulsion layer. 
According to the present invention there is also provided a method for 
obtaining a lithographic printing plate according to the silver salt 
diffusion transfer process comprising image-wise exposing an imaging 
element as described above and developing said imaging element using an 
alkaline processing liquid in the presence of developing agent(s) and a 
silver halide solvent.

DETAILED DESCRIPTION OF THE PRESENT INVENTION 
After extensive research it has been found that a silver halide 
photographic material with a specified value of pH, containing on a 
support at least one layer comprising a spectrally sensitized prefogged 
direct-positive silver halide emulsion wherein the silver halide crystals 
contain silver chloride for at least 60 mole %, silver bromide in a range 
from 0.50 mole % to 39.98 mole % and silver iodide in a range from 0.020 
mole % to 2.0 mole % when said silver halide cristals contain silver 
iodide for at least 0.20 mmole/mole AgX in the outer 10% by weight of said 
cristals and said layer contain a gelatin species containing Ca.sup.2+ in 
an amount ranging from 0.2% to 1% by weight has a high sensitivity. Said 
photographic material yields images of good quality, especially of high 
contrast. Furthermore, a lithographic printing plate with good printing 
properties can be obtained according to the silver salt diffusion transfer 
process by image-wise-exposing an imaging element containing such a silver 
halide emulsion. 
The silver halide cristals of said prefogged direct-positive silver halide 
emulsion contain silver iodide from 0.20 mmole/mole AgX to 20 mmole/mole 
AgX, preferably from 0.50 mmole/mole AgX to 10 mmole/mole AgX, more 
preferably from 1.0 mmole/mole AgX to 5.0 mmole/mole AgX in the outer 10% 
by weight, preferably in the outer 5% by weight, most preferably in the 
outer 2% by weight of said cristals. 
Preferably, the iodide is built-in into the silver halide cristals by 
adding one or more water soluble iodide salts to the emulsion of said 
silver halide cristals in the formation stage after the addition of at 
least 90% of the silver salt and before the onset of the prefogging, more 
preferably after the addition of 95% of the silver salt and before the end 
of the desalting of the emulsion, most preferably after the completion of 
the addition of the silver salt and the beginning of the desalting of the 
emulsion. 
Said water soluble iodide salts are added to the emulsion of the silver 
halide cristal in the formation stage in a total amount from 0.20 
mmole/mole AgX to 20 mmole/mole AgX, preferably in a total amount from 
0.50 mmole/mole AgX to 10 mmole/mole AgX, more preferably in a total 
amount from 1.0 mmole/mole AgX to 5.0 mmole/mole AgX. 
Water soluble iodide salts are preferably also added to the emulsion of the 
silver halide cristals in a latter stage after the addition of the 
electron-accepting sensitizing dye(s), preferably as the next step in the 
preparation of the coating layer. It is preferred to wait at least 5 
minutes, more preferred at least 10 minutes after the addition of said 
electron-accepting sensitizing dye(s) before adding this latter portion of 
the water soluble iodide salt(s). 
Said water soluble iodide salts are added to the emulsion of the silver 
halide cristal in the latter stage in a total amount from 0.10 mmole/mole 
AgX to 4 mmole/mole AgX, preferably in a total amount from 0.20 mmole/mole 
AgX to 2.5 mmole/mole AgX, more preferably in a total amount from 0.30 
mmole/mole AgX to 1.5 mmole/mole AgX. 
The water soluble iodide salt(s) can be added to the emulsion of the silver 
halide cristals in the formation stage and/or in the latter stage as 
solids but are preferably added as aqueous solutions. Preferably sodium 
and potassium iodide are used. Although a mixture of these salts can be 
used, the use of a sole iodide salt is preferred. Most preferred is the 
use of potassium iodide in an aqueous solution. 
The layer of the photographic material comprising a prefogged 
direct-positive silver halide emulsion also contains a gelatin species 
containing Ca.sup.2+ in an amount ranging from 0.20% to 1.0% by weight, 
preferably in an amount ranging from 0.35% to 1.0% by weight, more 
preferably in an amount ranging from 0.35% to 0.7% by weight, most 
preferably an above mentioned gelatin species whereof a 10% by weight 
aqueous solution at 36.degree. C. and pH 6 has a viscosity from 10 mPas to 
17 mPas at a shearing rate of 1000 s.sup.-1. 
Said gelatin species is added to the aqueous medium preferably before or 
during the prefogging of the silver halide emulsion, more preferably after 
the precipitation of the silver halide cristals and before the prefogging. 
Preferably said gelatin species is added to the silver halide emulsion in 
an amount ranging from 10 g/mole AgX to 200 g/mole AgX, more preferably in 
an amount ranging from 30 g/mole AgX to 150 g/mole AgX, most preferably in 
an amount ranging from 60 g/mole AgX to 100 g/mole AgX. 
Preferably said silver halide emulsion layer of the photographic material 
also comprises a Ca.sup.2 +-free gelatin species in an amount ranging from 
10 g/mole AgX to 200 g/mole AgX, more preferably in an amount ranging from 
50 g/mole AgX to 150 g/mole AgX. 
The pAg at 25.degree. C. of the photographic material comprising the 
spectrally sensitized prefogged direct-positive silver halide emulsion 
layer is at least 6.8, more preferably from 7 to 8, most preferably from 
7.2 to 7.8. 
The pH at 25.degree. C. of the photographic material comprising the 
spectrally sensitized prefogged direct-positive silver halide emulsion 
layer is at most 7, more preferably at most 6, most preferably from 5.5 to 
4.3. 
The desired pAg and pH of the photographic material are preferably obtained 
by bringing the prefogged silver halide emulsion layer to said required pH 
and pAg. 
The required pH of said emulsion layer is obtained by adding pH-regulating 
compound (acids, bases or buffers) to said emulsion layer. 
The desired pAg is preferably obtained by adding water soluble bromide 
salt(s) to the prefogged direct-positive silver halide emulsion after the 
addition of said one or more electron-accepting sensitizing dyes to said 
prefogged silver halide emulsion and the optional latter addition of water 
soluble iodide salt(s), more preferably just before or after the pH of 
said prefogged direct-positive silver halide emulsion is adjusted, one of 
these two steps being usually the last one before said prefogged 
direct-positive silver halide emulsion is coated. Preferably sodium and 
potassium bromide are used. Although a mixture of these salts can be used, 
the use of a sole bromide salt is preferred. Most preferred is the use of 
potassium bromide in an aqueous solution. 
The desired pAg and/or pH of the photographic material can also be obtained 
by coating an additional layer in water permeable relationship with said 
prefogged silver halide emulsion layer, containing halides preferably 
bromides, and/or pH-regulating compounds in such an amount that the 
required pAg and/or pH of the photographic material is obtained. 
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 pH and pAg are determined on the surface of the emulsion layer 
containing side of a coated and dried material. 
The pH of said material is measured with a pH-meter--691 from Metrohm and a 
combined glass-electrode from Metrohm art. 6.0217.000. The electrode is 
firstly activated by dipping it for 12 hours in a 3 molar KCl solution. 
Afterwards, the electrode is thoroughly rinsed with demineralized water 
and dried. The electrode is then ready for use. 
The activated electrode is dipped into demineralized water of 25.degree. C. 
and then placed on the surface of the material, stored for at least one 
day at 25.degree. C. and stirred slightly a few times. The electrode is 
then kept still for 15 seconds and the pH is registered. The electrode is 
then carefully rinsed again with demineralized water and dried. 
The working temperature is fed into the pH-meter. 
This measurement is repeated for 10 times on different places of the 
photographic material. The number average of the last 5 measurements is 
taken as the pH value of the photographic material. 
The pAg of said material is measured with a pH-meter--691 from Metrohm and 
as electrodes a Ag.sub.2 S Solids State electrode from Orion art. 941.600 
and a Double Junction reference electrode Ag/AgCl with a potential of 243 
mV from Orion, art. 900.200. 
The Ag.sub.2 S Solids State electrode is polished for use. The inner 
junction of the Double Junction reference electrode is filled with a 
saturated AgCl solution and the outer junction is filled with a 10% by 
weight KNO.sub.3. 
The surface of the material, stored for at least one day at 25.degree. C. 
is wetted with two separate drops of demineralized water of 25.degree. C., 
the two electrodes were each dipped into a single drop and stirred therein 
slightly a few times. The electrodes are then kept still for 60 seconds 
and the potential E" is measured in mV. The electrode is then carefully 
rinsed with demineralized water and dried. 
This measurement is repeated for 10 times consecutively on different places 
of the photographic material. The number average of the last 5 
measurements is taken as the potential E'value of the photographic 
material. 
The pAg is then calculated by using the following formula: 
##EQU1## 
wherein E=E'+243 mV 
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). 
According to the present invention the silver halide crystals of said 
prefogged direct-positive silver halide emulsion contain silver chloride 
for at least 60 mole %, silver bromide in a range from 0.5 mole % to 39.98 
mole % and silver iodide in a range from 0.02 mole % to 2 mole %. 
Preferably the amount of silver bromide is kept below 5 mole %, more 
preferably below 2 mole % and is homogeneously distributed throughout the 
silver halide crystals. Although there may be iodide added during the 
precipitation of silver halide grains before the above mentioned two 
stages of iodide addition, preferably most and more preferably all of the 
iodide is added during said two stages. 
The silver halide crystals can be doped with Rh.sup.3+, Ir.sup.4+, etc. 
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 silver halide emulsion is desalted by one of the well known techniques 
e.g. by floculating said silver halide emulsion, washing it with water or 
an aqueous solution and redispersing it, by ultrafiltration, by dialysis, 
etc. Preferably, the desalination of the silver halide emulsion is carried 
out before the prefogging of the silver halide emulsion, but can also be 
carried out afterwards. 
The prefogging of the silver halide emulsions for use in accordance with 
the present invention may be effected by overall exposing a silver halide 
emulsion to light and/or by chemically prefogging a silver halide 
emulsion. Chemical fog specks are preferred and may be obtained by various 
methods. 
Chemical prefogging may be carried out by reduction or by a compound which 
is more electropositive than silver e.g. gold salts, platinum salts, 
iridium salts etc., or a combination of both. Reduction prefogging of the 
silver halide grains may occur by high pH and/or low pAg silver halide 
precipitation or digestion conditions e.g. as described by Wood J. Phot. 
Sci. 1 (1953), 163 or by treatment with reducing agents e.g. tin(II) salts 
which include tin(II)chloride, tin complexes and tin chelates of 
(poly)amino(poly)carboxylic acid type as described in British Patent 
1,209,050, formaldehyde, hydrazine, hydroxylamine, sulphur compounds e.g. 
thiourea dioxide, phosphonium salts e.g. tetra (hydroxymethyl)-phosphonium 
chloride, polyamines e.g. diethylenetriamine, bis (p-aminoethyl) sulphide 
and its water-soluble salts, hydrazine derivatives, alkali arsenite, amine 
borane etc. or mixtures thereof. 
When prefogging of the silver halide grains occurs by means of a reducing 
agent e.g. thiourea dioxide and a compound of a metal more electropositive 
than silver especially a gold compound, the reducing agent is preferably 
used initially and the gold compound subsequently. However, the reverse 
order can be used or both compounds can be used simultaneously. 
In addition to the above described methods of chemically prefogging 
chemical prefogging can be attained by using said fogging agents in 
combination with a sulphur-containing sensitizer, e.g. sodium thiosulphate 
or a thiocyanic acid compound e.g. potassium thiocyanate. 
A preferred way for prefogging a silver halide emulsion suitable for use in 
accordance with the present invention is the addition of potassium 
chloroaurate in an amount from 0.5 mg/mole AgX to 2.5 mg/mole AgX to said 
emulsion at a pH from 6 to 8, at a pAg from 5 to 7, both measured at 
50.degree. C., and at a temperature from 50.degree. C. to 55.degree. C. 
during 4 to 8 hours. 
Prefogged direct positive silver halide emulsions preferably comprise 
exterior electron traps. Prefogged direct-positive silver halide emulsions 
with exterior electron-traps are emulsions having adsorbed to the surface 
of the prefogged silver halide grains a compound accepting electrons e.g. 
electron-accepting dyes which may provide spectral sensitization or not or 
desensitizing compounds as described in e.g. the British Patent 
Specification 723,019. 
According to Sheppard et al. J. Phys. Chem, 50 (1946), 210; desensitizers 
are dyestuffs whose cathodic polarographic half-wave potential, measured 
against the calomel electrode, is more positive than -1.0 V. It is well 
kown to characterize these electron-accepting or desensitizing compounds 
by means of their polarographic half-wave potential. Electron acceptors 
suitable for use in the direct-positive silver halide emulsions of the 
present invention have an anodic polarographic half-wave potential and a 
cathodic half-wave potential that when added together give a positive sum. 
Methods of determining these polarographic half-wave potentials have been 
described, e.g., in the U.S. Pat. No. 3,501,310 and U.S. Pat. No. 
3,531,290. 
Prefogged direct positive silver halide emulsions for use in accordance 
with the present invention comprise one or more electron-accepting 
spectral sensitizers as exterior electron trap in a total amount of at 
least 0.15 mmole/mole AgX, preferably in a total amount of at least 0.30 
mmole/mole AgX, more preferably in a total amount from 0.50 mmole/mole AgX 
to 2.50 mmole/mole AgX, most preferably in a total amount from 0.85 
mmole/mole AgX to 1.80 mmole/mole AgX. 
The silver halide emulsion is spectrally sensitized according to the 
spectral emission of the exposure source for which the photographic 
element is designed. 
Suitable electron-accepting 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. 
In the case of a conventional light source, e.g. tungsten light, a green 
electron-accepting sensitizing dye is needed. In case of exposure by an 
argon ion laser a blue electron-accepting sensitizing dye is incorporated. 
In case of exposure by a red light emitting source, e.g. a LED or a HeNe 
laser a red electron-accepting sensitizing dye is used. 
Other dyes, which per se do not have any spectral sensitization activity, 
or certain other compounds, which do not substantially absorb visible 
radiation, can have a supersensitization effect when they are incorporated 
together with said spectral electron-accepting sensitizing agents into the 
emulsion. Suitable supersensitizers are i.a. heterocyclic mercapto 
compounds containing at least one electronegative substituent as described 
e.g. in U.S. Pat. No. 3,457,078, aromatic organic acid/formaldehyde 
condensation products as described e.g. in U.S. Pat. No. 3,743,510, 
cadmium salts, and azaindene compounds. Preferred supersensitizers are 
pyridinium and chinolium derivatives and nitrogen-containing heterocyclic 
ring-substituted aminostilbene compounds as described e.g. in U.S. Pat. 
No. 2,933,390 and U.S. Pat. No. 3,635,721. 
Said supersensitizers are preferably used in a total amount of at least 
0.20 mmole/mole AgX, more preferably in a total amount from 0.65 
mmole/mole AgX to 3.20 mmole/mole AgX, most preferably in a total amount 
from 1.10 mmole/mole AgX to 2.40 mmole/mole AgX. 
Said compounds capable of acting as exterior electron traps and said 
supersensitizers are preferably added to the silver halide emulsion after 
the end of the prefogging, more preferably as the next step. When not only 
electron-accepting spectral sensitizers are used but also other 
desensitizing dyes or compounds or supersensitizers, said 
electron-accepting spectral sensitizers are preferably added after the 
other above mentioned compounds, but they can also be added before or 
between the addition of said above mentioned compounds. 
The direct positive silver halide emulsions may contain emulsion 
stabilizers. Suitable direct positive silver halide 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 direct positive silver halide emulsion stabilizers 
are i.a. heterocyclic mercapto compounds, quaternary benzothiazole 
derivatives, and other heterocyclic nitrogen-containing compounds. 
Examples of such compounds have been disclosed in e.g. EP-A 496127. Other 
suitable direct positive silver halide emulsion stabilizers are e.g. 
benzenethiosulphonic acid, benzenethiosulphinic acid, benzenethiosulphonic 
acid amide. Said stabilizers can be added to the silver halide emulsion 
prior to, during, or after the prefogging thereof and mixtures of two or 
more of these compounds can be used. 
The direct positive silver halide emulsion may contain other ingredients 
such as development accelerators, preferably polyalkyleneoxide derivatives 
having a molecular weight of at least 400 such as those described in e.g. 
U.S. Pat. Nos. 3,038,805, 4,038,075 and 4,292,400, wetting agents and 
hardening agents for gelatin may be present. The direct positive 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, DE-P 2,453,217. 
More details about the composition, preparation and coating of direct 
positive silver halide emulsions can be found in e.g. Product Licensing 
Index, Vol. 92, December 1971, publication 9232, p. 107-109. 
The photographic material of the present invention may contain additional 
hydrophilic layers, in water permeable relationship with the 
photosensitive direct positive silver halide emulsion layer. 
For example it is especially advantageous to include a base-layer between 
the support and the photosensitive direct positive silver halide emulsion 
layer. In a preferred embodiment of the present invention said base-layer 
serves as an antihalation layer. This layer can therefore contain the same 
light-absorbing dyes as described above for the direct positive silver 
halide emulsion layer; as alternative finely divided carbon black can be 
used for the same antihalation purposes as described in U.S. Pat. No. 
2,327,828. On the other hand, in order to gain-sensitivity, light 
reflecting pigments, e.g. titaniumdioxide can be present. Further this 
layer can contain hardening agents, matting agents, e.g. silica particles, 
and wetting agents. At least part of these matting agents and/or light 
reflection pigments may also be present in the direct positive silver 
halide emulsion layer the most part however preferably being present in 
said base-layer. As a further alternative the light reflecting pigments 
may be present in a separate layer provided between the antihalation layer 
and the photosensitive direct positive silver halide emulsion 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 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 rheological properties of the layer. As explained 
before, the direct positive silver halide emulsion containing layer 
preferably has a mixture of at least two gelatin species. Unlike the 
direct positive silver halide emulsion layer the other hydrophilic layers 
are coated preferably at a pH value near the isoelectric point of the 
gelatin. 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 vinylsulfone type e.g. 
methylenebis(sulfonylethylene), aldehydes e.g. formaldehyde, glyoxal, and 
glutaraldehyde, N-methylol compounds e.g. dimethylolurea and 
methyloldimethylhydantoin, 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. 
Preferably used hardening agents are of the aldehyde type. The hardening 
agents can be used in wide concentration range but are preferably used in 
an amount of 4% to 7% of the hydrophilic colloid. Different amounts of 
hardener can be used in the different layers of the imaging element or the 
hardening of one layer may be adjusted by the diffusion of a hardener from 
another layer. 
The imaging-element used according to the present invention may further 
comprise various kinds of surface-active agents in the photographic direct 
positive silver halide emulsion layer or in at least one other hydrophilic 
colloid layer. Examples of suitable surface-active agents are described in 
e.g. EP 545452. Preferably compounds containing perfluorinated alkyl 
groups are used. 
The photographic material 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. 
Supports suitable for use in accordance with the present invention 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, e.g. a polyethylene layer which optionally 
contains an anti-halation dye or pigment. It is also possible to use an 
organic resin support e.g. poly(ethylene terephthalate) film or 
poly-Alpha-olefin films such as polyethylene or polypropylene film. 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 in accordance with the present invention. 
According to a preferred method of the present invention the above 
described photographic material element is information-wise exposed in an 
analogous or a digital way and is subsequently developed in an alkaline 
processing liquid in the presence of developing agents, yielding a 
positive image. 
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-pyrazolidinone-type developing agent and/or 
p-monomethylaminophenol. Particularly useful auxiliary developing agents 
are of the phenidone type e.g. 1-phenyl-3-pyrazolidinone, 
1-phenyl-4-monomethyl-3-pyrazolidinone, and 
1-phenyl-4,4-dimethyl-3-pyrazolidinone. However other developing agents 
can be used. Said developing agents may be contained in an alkaline 
processing liquid but are preferably contained in one or more layers of 
the photographic element. In the latter case the alkaline processing 
liquid merely serves as an alkaline activating liquid. 
The pH of said alkaline liquid is preferably between 9 and 14, more 
preferably between 10 and 13 and may be established by an organic and/or 
inorganic alkali agent. Examples of suitable alkali agents are e.g. sodium 
hydroxide, carbonates, phosphates, alkanolamines or mixtures thereof. 
The alkaline processing liquid preferably also contains a preserving agent 
having antioxidation activity, e.g. sulphite ions. Further may be present 
a thickening agent, fog inhibiting agents, calcium-sequestering compounds, 
anti-sludge agents, development accelerators and hardeners including 
latent hardeners. 
The above described development step is preferably followed by a washing 
step, a fixing step and another washing or stabilizing step. The first 
washing step may be omitted. 
The above described photographic material, obtained according to the 
present invention may yield an image according to the silver salt 
diffusion transfer process. 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 the book "Photographic 
Direct positive 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. 
Suitable silver complexing agents also called silver halide solvents for 
use in accordance with the present invention are e.g. thiosulphate or 
thiocyanate in an amount ranging from 5 g to 20 g per liter. Other 
interesting silver halide complexing agents are e.g. sulphite, amines, 
2-mercaptobenzoic acid, cyclic imide compounds such as e.g. uracil, 
5,5-dialkylhydantoins, alkyl sulfones and oxazolidones. 
Further silver halide solvents for use in connection with the present 
invention are alkanolamines. Said alkanolamines may be present in the 
alkaline processing liquid in a concentration preferably between 0.1% and 
5% by weight. However part or all of the alkanolamine can be present in 
one or more layers of the imaging element. 
Still other preferred further silver halide solvents for use in connection 
with the present invention are thioethers, preferably di- or 
poly-thioethers as disclosed in e.g. U.S. Pat. No. 4.960.683 and EP-A 
554,585. 
Still further suitable silver halide solvents are meso-ionic compounds, 
preferably 1,2,4-triazolium-3-thiolates. 
Combinations of different silver halide solvents can be used and it is also 
possible to incorporate at least one silver halide solvent into a suitable 
layer of the imaging element and to add at least one other silver halide 
solvent to the developing or activating solution. Preferably they are 
comprised in the alkaline processing liquid. 
Preferred physical 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 physical development nuclei in 
connection with the present invention are palladium sulphide nuclei. Other 
suitable physical 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. 
According to a preferred embodiment of the present invention a method is 
provided for obtaining an imaging element that can be used for obtaining a 
negative lithographic printing plate according to the DTR-method. Said 
imaging element is obtained by coating on a support in the order given at 
least one direct positive silver halide emulsion layer in accordance with 
the present invention and an image receiving layer containing physical 
development nuclei in water permeable relationship with said direct 
positive silver halide emulsion layer. Preferably the imaging element also 
comprises a base layer between the support and the direct positive silver 
halide emulsion layer as described above. A further intermediate layer 
between the direct positive silver halide emulsion layer and the layer 
containing physical development nuclei is also preferred. 
A matting agent is preferably included in said base layer and optionally in 
small amounts i.e. from 1 to 20% by weight in the direct positive silver 
halide emulsion layer. When the matting agent is included in the direct 
positive silver halide emulsion layer it is preferable added to the direct 
positive silver halide emulsion after spectral sensitization of the direct 
positive silver halide emulsion to avoid adsorption of the sensitizer to 
the matting agent. Suitable matting agents for use in accordance with the 
present embodiment are water insoluble inorganic or organic particles 
having an average diameter between 1 .mu.m and 10 .mu.m most preferably 
between 4 .mu.m and 8 .mu.m. A preferred matting agent is silica. 
The layer containing physical development nuclei is preferably free of 
hydrophilic binder but may comprise small amounts up to 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. 
Preferably used supports in connection with the present embodiment are 
paper supports or resin supports e.g. polyester film supports. 
To obtain a negative lithographic printing plate the above described 
DTR-imaging element is information-wise exposed and is subsequently 
developed with an alkaline processing liquid in the presence of developing 
agent(s) and silver halide solvent(s). Said development step is preferably 
followed by a neutralization of the surface of the imaged element by 
guiding the element through a neutralization liquid having a pH between 4 
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 bactericides, e.g. phenol, thymol or 
5-bromo-5-nitro-1,3-dioxan as described in EP-150,517, wetting agents e.g. 
saponins or pluronics etc. 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. Finally the 
neutralization solution can contain wetting agents, preferably compounds 
containing perfluorinated alkyl groups. 
To improve the differentiation between the hydrophobic silver image and the 
hydrophilic background the alkaline processing liquid and/or 
neutralization liquid preferably contain one or more hydrophobizing 
agents, e.g. those described in U.S. Pat. No. 3,776,728, and U.S. Pat. No. 
4,563,410. 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. Particularly preferred compounds are 
5-n-heptyl-2-mercapto-1,3,4,-oxadiazol and 
3-mercapto-4-acetamido-5-n-heptyl-1,2,4-triazole. 
According to an alternative embodiment of the present invention another 
method is provided for obtaining an imaging element that can be used for 
obtaining a lithographic printing plate according to the DTR-method by 
coating 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 a photosensitive direct positive silver 
halide emulsion in accordance with the present invention, said 
photosensitive layer being in water permeable relationship with said image 
receiving layer. To obtain a lithographic plate by means of the 
DTR-process said imaging element may be imaged using an information-wise 
exposure as described above followed by a development step in the presence 
of development agent(s) and silver halide solvent(s) so that a silver 
image is formed in the physical development nuclei layer. Subsequently the 
imaging element is treated to remove the layer(s) on top of the image 
receiving layer, preferably by rinsing the imaging element with water, 
thereby exposing the imaged surface of the support by uncovering said 
silver image formed in said image receiving layer. Finally the hydrophobic 
character of the silver image is preferably improved using a finishing 
liquid comprising hydrophobizing agents as described above. 
The hydrophilic surface of a support can be a hardened hydrophilic layer, 
containing a hydrophilic synthetic homopolymer or copolymer and being 
hardened with a hydrolyzed tetraalkyl orthosilicate crosslinking agent 
coated on a flexible hydrophobic base. 
More preferably an aluminum support is used as a hydrophilic base. 
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 post-treating of the foil. 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 post-treated 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 HCl, HNO.sub.3, H.sub.2 SO.sub.2, H.sub.3 
PO.sub.4, that if desired, contain additionally one or more corrosion 
inhibitors such as Al(NO.sub.3).sub.3, AlCl.sub.3, boric acid, chromic 
acid, sulfates, chlorides, nitrates, monoamines, diamines, aldehydes, 
phosphates, H.sub.2 O.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 toughening is preferably preceded by a degreasing treatment mainly for 
removing ferry 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 toughening 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 150g/l. The duration 
of chemical etching is preferably between 3 s and 5 min. 
After toughening 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 sulfuric acid, phosphoric acid, oxalic 
acid, chromic acid or organic acids such as sulfamic, benzosulfonic 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 a posttreatment such as 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. 
A preferred posttreatment 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 facilate the removal of the direct positive silver halide emulsion layer 
and to improve its photographic stability it is advantageous to provide a 
hydrophilic layer between the aluminum support and the direct positive 
silver halide emulsion layer. Preferably used hydrophilic layers for this 
purpose are layers comprising a hydrophilic non-proteinic film-forming 
polymer e.g. polyvinyl alcohol, polymer beads e.g. poly(meth)acrylate 
beads or mixtures thereof. Such type of layers are disclosed in 
EP-A-483415 and EP-A-410500. 
The present invention is illustrated by the following example without 
limiting it thereto. All parts are by weight unless otherwise specified. 
EXAMPLE I (COMATIVE EXAMPLE) 
Preparation of prefogged direct-positive silver halide emulsions I-IV. 
A gelatin silver halide emulsion of grain size 0.26 .mu. (98.7 mol % of 
chloride and 1.3 mol % of bromide) was prepared by double jet 
precipitation. 
35 Minutes after the end of the precipitation the emulsion is flocculated 
and washed with demineralized water. The washed gelatino silver halogenide 
emulsion was peptised with low viscosity (14 mPas) Ca.sup.2 +-free gelatin 
and was subsequently fogged by addition of potassium chloroaurate (1.2 mg 
per mole of silver halide) at pH 7 and pAg 6, at a temperature of 
52.degree. C. for 5 hours. To the emulsion was added at 40.degree. C. 
under continuously stirring the desensitizing dye chinolinium, 
1-methyl-5-ethoxy-2- 3-nitrophenyl! ethenyl methylsulfaat (4.6 mg/g 
AgNO.sub.3) and 20 minutes later the electron accepting spectral 
sensitizer A (5.6 mg/g AgNO.sub.3). So, gelatin prefogged direct-positive 
silver halide emulsion I was obtained. 
Gelatin prefogged direct positive silver halide emulsion II was prepared as 
emulsion I except that it was peptised with low viscosity (14 mPas) 
Ca.sup.2 +-containing (0.45-0.55%) gelatin 
Gelatin prefogged direct-positive silver halide emulsion III was prepared 
as emulsion I wherein however KI (2.50 mg/g AgNO.sub.3) was added to the 
emulsion 20 minutes after the end of the precipitation. 
Gelatin prefogged direct-positive silver halide emulsion IV was prepared as 
emulsion III except that it was peptised with low viscosity (14 mPas) 
Ca.sup.2 +-containing (0.45-0.55%) gelatin 
##STR1## 
Preparation of the imaging elements 1 to 4. 
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.sup.2 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 the prefogged direct-positive silver halide emulsion I to IV were 
coated on the intermediate layer after adjusting at 40.degree. C. the pH 
at 5 with sulfuric acid and adding 0.060 mole potassium bromide per mole 
silver halide, with the silver halide being provided in an amount 
corresponding to 2.40 g of silver nitrate per m.sup.2 and the gelatin 
content of the emulsion layer being 1.58 g/m.sup.2, consisting of 0.7 
g/m.sup.2 of a Ca.sup.2 +-free gelatin with a viscosity of 21 mPa.s and 
the remainder of the Ca.sup.2 +-containing gelatin with a viscosity of 14 
mPa.s 
The imaging elements were exposed for 5 s through a internegative on an 
Opticopy imposer (registered trade name of OPTICOPY INC, Kansas, U.S.A., 
equipped with a green light source contact screen and immersed for 10 s at 
24.degree. C. in a freshly made developing solution having the following 
ingredients: 
______________________________________ 
carboxymethylcellulose 4 g 
sodium hydroxide 22.5 g 
anhydrous sodium sulphite 120 g 
hydroquinone 20 g 
1-phenyl-3-pyrazolidinone 6 g 
potassium bromide 0.75 g 
anhydrous sodium thiosulphate 
8 g 
ethylene diamine tetraacetic acid tetrasodium salt 
2 g 
demineralized water to make 
1000 ml 
pH (24.degree. C.) = 13 
______________________________________ 
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. 
Next, the imaged surface of the aluminum foil was guided for 15 s through 
the finisher having a temperature of 40.degree. C. to enhance the 
water-receptivity of the non-image areas and to make the image areas 
oleophilic ink-receptive. In this way, four printing plates were prepared. 
The finisher had the following composition: 
______________________________________ 
AKYPO-OP-80 (trade mark for a surfactant sold by 
250 mg 
Chemische Fabrik Chem-Y, Gmbh, Germany) 
NaH.sub.2 PO.sub.4.2H.sub.2 O 
20.0 g 
potassium nitrate 12.5 g 
citric acid 20.0 g 
2-mercapto-5-n.heptyl- 0.5 
oxa-3.4-diazole 
sodium hydroxide 5.5 g 
HO (CH.sub.2 CH.sub.2 O).sub.33 H 
75 g 
water to make 1000 ml 
pH (20.degree. C.) = 6 
______________________________________ 
The sensitometric properties of the developed imaging elements were 
characterized by the reflection density in the image areas (D.sub.max) and 
non-image areas (D.sub.min) and by the yield of silver deposited in the 
printing areas of the plate. The results are given in the following table 
1. 
TABLE 1 
______________________________________ 
Sample nr Emulsion nr 
D.sub.min 
D.sub.max 
Ag/m.sup.2 
______________________________________ 
1 I 0.26 0.26 0 mg 
2 II 0.26 0.26 0 mg 
3 III 0.26 0.26 0 mg 
4 IV 0.30 1.01 1.09 mg 
______________________________________ 
The developed imaging element 4 was used as printing plate. The printing 
plate was mounted on an offset printing machine (HEIDELBERG GTO-46). A 
mixture of AQUA TAME 7035E at a 3% concentration and AQUA AYDE 7022A at a 
4% concentration, both marketed by Anchor/Lithemko Inc., Florida, U.S.A. 
was used in an aqueous solution containing 10 % isopropanol as dampening 
solution and K+E 123 W, marketed by Kast+Ehinger, A.G., as ink. Up to 
65.000 good copies were printed from said plate. 
Evaluation: 
From these results it is seen that the photographic silver halide material 
4, comprising the prefogged direct-positive silver halide emulsion IV 
(material according to the invention) has a much higher sensitivity than 
the photographic materials 1 to 3, comprising the prefogged 
direct-positive silver halide emulsions I to III (the photographic 
materials 1 to 3 being comparative materials). Furthermore, it is seen 
that said photographic materials can be used for preparing lithographic 
printing plates with good printing properties.