The present invention relates to an imaging element for making a lithographic
printing plate according to the silver salt diffusion transfer process and more
in particular to an imaging material that will yield printing plates having improved
lithographic printing properties such as an improved ink acceptance.
2. Background of the invention.
The principles of the silver complex diffusion transfer reversal process,
hereinafter called DTR-process, have been described e.g. in US-P 2,352,014 and in
the book "Photographic Silver Halide Diffusion Processes" by André Rott and Edith
Weyde - The Focal Press - London and New York, (1972).
In the DTR-process non-developed silver halide of an information-wise
exposed photographic silver halide emulsion layer material is transformed with a
so-called silver halide solvent into soluble silver complex compounds which are
allowed to diffuse into an image-receiving element and are reduced therein with
a developing agent, generally in the presence of physical development nuclei, to
form a silver image having reversed image density values ("DTR-image") with respect
to the black silver image obtained in the exposed areas of the photographic material.
A DTR-image bearing material can be used as a planographic printing
plate wherein the DTR-silver image areas form the water-repellant ink-receptive
areas on a water-receptive ink-repellant background. For example, typical lithographic
printing plates are disclosed e.g. EP-A-423399 and EP-A-410500.
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.
As for other printing plates it is required that the printing plates
obtained according to the DTR-process have a high printing endurance, good ink acceptance
in the printing areas and no ink acceptance in the non-printing areas (no staining).
It is furthermore desirable, especially for low printing runs, that the number of
copies that have to be disposed of because of poor ink acceptance in the printing
areas and/or ink acceptance in the non-printing areas during start-up of the printing
process is limited.
In the preparation of these plates the exposure and developing step
of the imaging element is in most cases followed by a neutralization step. This
step is very important for the number of copies that have to be disposed of because
of poor ink acceptance in the printing areas during start-up of the printing process.
When the pH of the neutralization liquid is to high (i.e. higher than 8) the resulting
printing plate has a (very) bad ink acceptance. It is thus very important that the
neutralization liquid is refreshed in time in order to keep the pH of the neutralization
liquid low enough.
This is especially important for printing plates made in a camera
platemaker. This is an integrated apparatus wherein the exposure and the processing
of the photosensitive material is executed in one apparatus and control of the neutralization
liquid will require the stop of the total process of plate making. Furthermore,
in many cases plates made in such a camera platemaker are used for printing a few
days after their preparation while still new plates are made in said camera platemaker.
If then is discovered that the ink acceptance of a plate is bad due to an exhausted
neutralization liquid, the plates made in the mean time will also have a bad ink
acceptance, requiring for all these plates an extra treatment with a starter to
get a printing plate with a good ink acceptance. This is an ecological uninteresting,
time consuming and thus costly processus, that is even not possible for plates with
In JP-A-06-301216 a method for detecting the degree of exhaustion
of a treating solution for a lithographic plate by incorporating an acid/base indicator
in the solution is described. This solution has however serious drawbacks in that
visual inspection of said liquid requires stopping of the camera platemaker and
thus loss of production capacity and is in many instances practically impossible
due to discoloration of the neutralization solution and the presence of sludge therein.
3. Summary of the invention.
It is an object of the present invention to provide an imaging element
for detecting the degree of exhaustion of a neutralization liquid used in the preparation
of a lithographic plate from a photosensitive material according to the DTR-process.
It is a further object of the present invention to provide a method
for making a lithographic printing plate according to the DTR-process having good
printing properties i.e. good ink acceptance in the printing areas, no ink acceptance
in the non-printing areas and a low number of copies that have to be disposed of
because of poor ink acceptance in the printing areas and/or ink acceptance in the
non-printing areas during start-up of the printing process.
Further objects of the present invention will become clear from the
According to the present invention there is provided an imaging element
comprising on one side of a support a photosensitive layer comprising a silver halide
emulsion and an image receiving layer containing physical development nuclei in
water permeable relationship with said emulsion layer and on the other side of the
support at least one backing layer comprising gelatin and a dye and/or a dye precursor
characterized in that said dye or dye precursor is such that said backing layer
after treatment of said imaging element in an alkaline solution with a pH of 10.9
for 20 s at a temperature of 30°C the backing layer has a reflection spectrum when
treated for 20 s at 20°C in a neutralizing solution with a pH of 7.5 that is visually
different from the reflection spectrum when treated for 20 s at 20°C in a neutralizing
solution with a pH of 8.5.
According to the present invention there is provided a method for
making a lithographic printing plate according to the silver salt diffusion transfer
process comprising the steps of:
image-wise exposing an imaging element as described above;
developing said imaging element in the presence of developing agent(s) and silver
halide solvent(s) using an alkaline processing solution and
treating the thus obtained developed imaging element using a neutralizing solution
having a pH at 20 °C between 5 and 8.
4. Detailed description of the invention.
It has been found that with an imaging element as described above
a very easy method for detecting the degree of exhaustion of a neutralization liquid
used in the preparation of a lithographic plate from a photosensitive material according
to the DTR-process is provided. Indeed there is a visual difference in reflection
spectrum between a plate obtained by neutralizing an exposed and developed imaging
element in a neutralization liquid having a pH of at most 7.5 (a still effective
neutralizer) and a plate obtained by neutralizing an exposed and developed imaging
element in a neutralization liquid having a pH of at least 8.5 (an exhausted neutralizer).
One can even perfectly visualize a system wherein the last compartment
of such a camera platemaker comprises a reflection densitometer which measures the
reflection spectrum of a processed plate and gives a signal as soon as the processed
plate's reflection spectrum is not longer in accordance with the prescribed reflection
spectrum obtained by processing in a neutralization liquid with a pH of 7.5.
A visual difference in reflection spectra means a displacement over
at least 20 nm in the wavelenght of the minimum or maximum of said spectra or an
increase or decrease with at least 10%, more preferably with at least 20% of the
absorption coefficient at the wavelenght of the maximum or minimum of said spectra
in the range between 400 and 700 nm.
Said alkaline solution is preferably a solution in water of 10.6 g/l
sodium carbonate, 8.4 g/l sodium hydrogen carbonate and 60 ml/l 2-aminoethyl-aminoethanol.
Said solution may further comprise other ingredients which may be present in an
activating solution as described hereinafter. Said solution should comprise no dye
or dye precursor.
Said neutralizing solution with at 20°C a pH of 7.5 contains 10 g/l
of triethanolamine, 40 g/l of NaH2PO4.H2O and sodium
hydroxide to obtain the desired pH. The neutralizing solution with at 20°C a pH
of 8.5 contains 10 g/l of triethanolamine, 40 g/l of NaH2PO4.H2O
and sodium hydroxide to obtain the desired pH.
The amount of dye or dye precursor in said backing layer is i.a. dependant
on the structure of said dye or dye precursor but is preferably between 5 and 1000
mg/m2, more preferably between 10 and 500 mg/m2, most preferably
between 15 and 300 mg/m2.
Dyes suitable for use in accordance with the present invention belong
to a class selected from the group consisting of e.g. oxazines, monomethin pyrazolone-oxonoles
and p-amino-triphenyl methanes. An example of such dyes is a dye corresponding to
the following formula.
The imaging element in connection with the present invention essentially comprises
on one side of a support a photosensitive layer comprising a silver halide emulsion
and an image receiving layer containing physical development nuclei in water permeable
relationship with said emulsion layer and on the other side of the support at least
one backing layer comprising gelatin and a dye or a dye precursor
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 complexed silver ions.
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. cellulose nitrate
film, cellulose acetate film, poly(vinyl acetal) film, polystyrene film, poly(ethylene
terephthalate) film, polycarbonate film, polyvinylchloride 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.
The photographic silver halide emulsions can be prepared from soluble
silver salts and soluble halides according to different methods as described e.g.
by P. Glafkides in "Chimie et Physique Photographique", Paul Montel, Paris (1967),
by G.F. Duffin in "Photographic Emulsion Chemistry", The Focal Press, London (1966),
and by V.L. Zelikman et al. in "Making and Coating Photographic Emulsion", The Focal
Press, London (1966).
According to the present invention the emulsion or emulsions preferably
consist principally or totally of silver chloride while a fraction of silver bromide
may be present ranging from 1 mole % to 40 mole %. When the fraction of silver bromide
is 5% or more, the emulsions preferably belong to the core/shell type well known
to those skilled in the art in the sense that substantially all the bromide is concentrated
in the core. This core contains preferably 10 to 40 % of the total silver halide
precipitated, while the shell consists preferably of 60 to 90 % of the total silver
The average size of the silver halide grains may range from 0.10 to
0.70 µm , preferably from 0.25 to 0.45 µm.
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 10-8 to 10-3 mole per mole of AgNO3,
preferably between 0.5*10-7 and 10-5 mole per mole of AgNO3.
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-A-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).
Apart from negative-working silver halide emulsions that are preferred
for their high photosensitivity, use can be made also of direct-positive silver
halide emulsions that produce a positive silver image in the emulsion layer(s) and
a negative image on the image-receiving layer.
Suitable direct positive silver halide emulsions for use in accordance
with the present invention are silver halide emulsions that have been previously
fogged or that mainly form an internal latent image.
Internal latent image-type silver halide emulsions that can be used
in accordance with the present invention have been described in e.g. US-A 2,592,250,
3,206,313, 3,271,157, 3,447,927, 3,511,662, 3,737,313, 3,761,276, GB-A 1,027,146,
and JP Patent Publication No. 34,213/77. However, the silver halide emulsions used
in the present invention are not limited to the silver halide emulsions described
in these documents.
The other type of direct positive type silver halide emulsions for
use in accordance with the present invention, which is of the previously fogged
type, may be prepared by overall exposing a silver halide emulsion to light and/or
by chemically fogging a silver halide emulsion. Chemical fog specks may be formed
by various methods for chemical sensitization.
Chemical fogging may be carried out by reduction or by a compound
which is more electropositive than silver e.g. gold salts, platinum salts, iridium
salts, or a combination of both. Reduction fogging 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 or mixtures thereof.
When fogging 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 fogging chemical
fogging 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
The emulsions of the DTR element can be spectrally sensitized according
to the spectral emission of the exposure source for which the DTR element is designed.
Suitable sensitizing dyes for the visible spectral region include
methine dyes such as those described by F.M. Hamer in "The Cyanine Dyes and Related
Compounds", 1964, John Wiley & Sons. Dyes that can be used for this purpose
include cyanine dyes, merocyanine dyes, complex cyanine dyes, complex merocyanine
dyes, homopolar cyanine dyes, hemicyanine dyes, styryl dyes and hemioxonol dyes.
Particularly valuable dyes are those belonging to the cyanine dyes, merocyanine
dyes, complex merocyanine dyes.
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
sensizing 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. US-P 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
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 stabilizers. Suitable
stabilizers are azaindenes, preferably tetra- or penta-azaindenes, especially those
substituted with hydroxy or amino groups. Compounds of this kind have been described
by BIRR in Z. Wiss. Photogr. Photophys. Photochem. 47, 2-27 (1952). Other suitable
stabilizers are i.a. heterocyclic mercapto compounds e.g. phenylmercaptotetrazole,
quaternary benzothiazole derivatives, and benzotriazole. Preferred compounds are
mercapto substituted pyrimidine derivatives as disclosed in US-P 3,692,527.
The silver halide emulsions may contain pH controlling ingredients.
Preferably the emulsion layer is coated at a pH value near the isoelectric point
of the gelatin to improve the stability characteristics of the coated layer. Other
ingredients such as antifogging agents, development accelerators, wetting agents,
and hardening agents for gelatin may be present. The silver halide emulsion layer
may comprise light-screening dyes that absorb scattering light and thus promote
the image sharpness. Suitable light-absorbing dyes are described in i.a. US-P 4,092,168,
US-P 4,311,787 and DE-P 2,453,217.
More details about the composition, preparation and coating of silver
halide emulsions can be found in e.g. Product Licensing Index, Vol. 92, December
1971, publication 9232, p. 107-109.
The layer containing physical development nuclei can be free of hydrophilic
binder but preferably comprises amounts upto 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 heavy metal 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.
Between the support and the silver halide emulsion layer there is
preferably provided a base layer that preferably contains an anti-halation substance
such as e.g. light-absorbing dyes absorbing the light used for image-wise exposure
of the imaging element. As alternative finely divided carbon black can be used as
an anti-halation substance. On the other hand, in order to gain sensitivity, light
reflecting pigments, e.g. titaniumdioxide can be present in the base layer. Further
this layer can contain hardening agents, matting agents, e.g. silica particles,
and wetting agents. Suitable matting agents preferably have an average diameter
of 2-10 µm and more preferably between 2 µm and 5 µm. The matting agents are generally
used in a total amount in the imaging element of 0.1 g/m2 to 2.5 g/m2.
At least part of these matting agents and/or light reflection pigments may also
be present in the silver halide emulsion layer and/or in the cover layer. As a further
alternative the light reflecting pigments may be present in a separate layer provided
between the antihalation layer and the photosensitive silver halide emulsion layer.
Like the emulsion layer the base layer is coated preferably at a pH value near the
isoelectric point of the gelatin in the base layer.
In an imaging element 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. When the backing layer consists
of a double layer packet, the layer comprising gelatin and a dye and/or a dye precursor
may be any of the two layers but is preferably the outerlying layer of said packet.
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. Like the 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.
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,
triacrylformal 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 US 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 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.
Suitable additives for improving the dimensional stability of the
photographic element are e.g. dispersions of a water-soluble or hardly soluble synthetic
polymer e.g. polymers of alkyl (meth)acrylates, alkoxy(meth)acrylates, glycidyl
(meth)acrylates, (meth)acrylamides, vinyl esters, acrylonitriles, olefins, and styrenes,
or copolymers of the above with acrylic acids, methacrylic acids, Alpha-Beta-unsaturated
dicarboxylic acids, hydroxyalkyl (meth)acrylates, sulphoalkyl (meth)acrylates, and
styrene sulphonic acids.
The above described DTR mono-sheet imaging element in connection with
the present invention is exposed in an apparatus according to its particular application,
e.g. a conventional process camera containing a conventional light source or a high
intensity short time exposure such as e.g. a laser containing device. Subsequently
the imaged element is developed with an alkaline processing liquid in the presence
of developing agent(s) and silver halide solvent(s).
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 14 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 e.g. a benzotriazole which is known to
improve the printing endurance, calcium-sequestering compounds, anti-sludge agents,
development accelerators and hardeners including latent hardeners.
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. US-P-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 as disclosed in e.g. EP-A 554,585.
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
The development step is 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 8. The pH of a fresh neutralizing solution lies preferably between
5 and 7. The neutralization liquid preferably contains a buffer e.g. a phosphate
buffer, a citrate buffer, an amine or a 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. Generally these compounds
contain a mercapto group or thiolate group and one or more hydrophobic substituents,
e.g. those described in US-P-3,776,728 and US-P-4,563,410. Preferred hydrophobizing
agents are 2-mercapto-l,3,4-thiadiazoles as described in DE-A 1,228,927 and in US-P
4,563,410, 2-mercapto-5-alkyl-1,3,4-oxadiazoles, 3-mercapto-5-alkyl-l,2,4-triazoles
and long chain (at least 5 carbon atoms) alkyl substituted mercaptotetrazoles. Particularly
preferred compounds are 2-mercapto-5-n-heptyl-1,3,4-oxadiazole and 3-mercapto-4-acetamido-5-n-heptylalkyl-1,2,4-diazoles
A lithographic printing plate is thus obtained.
The invention will now be illustrated by the following example without
however the intention to limit the invention thereto. All parts are by weight unless
EXAMPLEPreparation of the silver halide emulsion coating solution.
A silver chloroiodide emulsion composed of 99.7 mole% of chloride
and 0.3 mole% of iodide was prepared by the double jet precipitation method. The
average silver halide grain size was 0.38 µm (diameter of a sphere with equivalent
volume) and contained Rhodium ions as internal dopant. The emulsion was orthochromatically
sensitized and stabilized by a 1-phenyl-5-mercapto-tetrazole.
A base layer coating solution was prepared having the following composition:
The emulsion coating solution and base layer coating solution were
simultaneously coated by means of the slide-hopper coating technique to a polyethylene
terephthalate support provided with a pack of two backing layers such that the base
layer coating was coated directly to the side of the support opposite to the side
containing said backing layers. The emulsion layer was coated such that the silver
halide coverage expressed as AgNO3 was 1.5g/m2 and the gelatin
content was 1.5g/m2. The emulsion layer further contained 0.15g/m2
of 1-phenyl-4,4'-dimethyl-3-pyrazolidone and 0.25g/m2 of hydroquinone.
The base layer was coated such that the amount of gelatin in the coated layer was
The layer nearest to the support of the backing layer pack contained
0.3 g/m2 of gelatin and 0.5 g/m2 of the antistatic agent co(tetraallyloxyethane
/ methacrylate / acrylic acid-K-salt) polymer. The second backing layer contained
4 g/m2 of gelatin, 0.15 g/m2 of a matting agent consisting
of transparent spherical polymeric beads of 3 micron average diameter according
to EP-A 80225, 0.05 g/m2 of hardening agent triacrylformal, 0.030 g/m2
of dye 1 and 0.021 g/m2 of wetting agent F15C7-COONH4.
The thus obtained element was dried and subjected to a temperature
of 40°C for 5 days and then the emulsion layer was overcoated with a layer containing
PdS as physical development nuclei, hydroquinone at 0.4g/m2 and formaldehyde
The thus obtained element was dried and again subjected to a temperature
of 40°C for 5 days.
Two imaging elements I were each image-wise exposed, processed with
the above described activator for 20 s at 30 °C and subsequently neutralized for
20 s at 20°C with one of the neutralization solutions K or L and dried.
The obtained plates were visually clearly different, the first plate
has an absorption at 460 nm = 0.35, while the second plate has an absorption at
460 nm = 0.40.
The printing plates thus prepared were mounted on the same offset
printing machine ( A B Dick 9860) and were used for printing under identical conditions.
The above mentioned dampening solution was used at a 5 % concentration in an aqueous
solution containing 15% isopropanol as fountain solution. The ink used was A B Dick
1020. A compressible rubber blanket was used.
The plates were evaluated for the number of copies that had to be
disposed of at the start of the printing process because of poor quality, mainly
non-ink acceptance in the printing areas. It was found that the number of useless
copies in case the neutralizing solution K was used, was 15 whereas in case the
neutralizing solution L was used the ink acceptance in the printing area was more
than 50 before a good copy was obtained.
Ein bilderzeugendes Element, das auf einer Seite eines Trägers eine strahlungsempfindliche
Silberhalogenid-Emulsionsschicht und eine physikalische Entwicklungskeime enthaltende
Bildempfangsschicht in wasserdurchlässiger Beziehung zur Emulsionsschicht und auf
der anderen Trägerseite wenigstens eine Rückschicht mit Gelatine und einem Farbstoff
und/oder einem Farbstoffvorläufer enthält, dadurch gekennzeichnet, daß der
Farbstoff oder Farbstoffvorläufer derartig ist, daß nach einer 20sekündigen
Verarbeitung des bilderzeugenden Elements in einer alkalischen Lösung mit einem
pH von 10,9 bei einer Temperatur von 30°C die Rückschicht nach einer 20sekündigen
Verarbeitung in einer Neutralisierlösung mit einem pH von 7,5 bei einer Temperatur
von 20°C ein Reflexionsspektrum aufweist, das sich in der Wellenlänge der Mindest-
und Höchstwert der Reflexionsspektren im Wellenlängenbereich zwischen 400 und 700
nm um wenigstens 20 nm vom Reflexionsspektrum unterscheidet, das nach einer 20sekündigen
Verarbeitung in einer Neutralisierlösung mit einem pH von 8,5 bei einer Temperatur
von 20'C erhalten ist
Bilderzeugendes Element nach Anspruch 1, dadurch gekennzeichnet, daß der
Farbstoff aus der Gruppe bestehend aus Oxazinen, Monomethinpyrazolonoxonolen und
p-Aminotriphenylmethanen ausgewählt wird.
Bilderzeugendes Element nach Anspruch 2, dadurch gekennzeichnet, daß der
Farbstoff ein Farbstoff der folgenden Formel ist :
Bilderzeugendes Element nach irgendeinem der Ansprüche 1 bis 3, dadurch gekennzeichnet,
daß der Farbstoff in einer Menge zwischen 5 und 1.000 mg/m2 in
der Rückschicht enthalten ist.
Bilderzeugendes Element nach irgendeinem der Ansprüche 1 bis 4, dadurch gekennzeichnet,
daß der Farbstoff in einer Menge zwischen 15 und 300 mg/m2 in der
Rückschicht enthalten ist.
Bilderzeugendes Element nach irgendeinem der Ansprüche 1 bis 5, dadurch gekennzeichnet,
daß der visuelle Unterschied in den Reflexionsspektren eine Steigung oder
Abnahme um wenigstens 10% des Absorptionskoeffizienten bei der Wellenlänge der Mindest-
und Höchstwerte der Reflexionsspektren im Bereich zwischen 400 und 700 nm ist.
Ein Verfahren zur Herstellung einer lithografischen Druckplatte nach dem Silbersalz-Diffusionsübertragungsverfahren,
das folgende Stufen umfaßt :
die bildmäßige Belichtung eines nach irgendeinem der Ansprüche 1 bis 7
definierten bilderzeugenden Elements,
die Entwicklung des bilderzeugenden Elements mittels einer alkalischen Verarbeitungslösung
in Gegenwart einer oder mehrerer Entwicklersubstanzen und eines oder mehrerer Silberhalogenid-Lösungsmittel,
die Verarbeitung des so erhaltenen entwickelten bilderzeugenden Elements mit
einer Neutralisierlösung mit einem pH bei 25'C zwischen 5 und 8.
Verfahren nach Anspruch 7, dadurch gekennzeichnet, daß der pH einer frischen
Neutralisierlösung zwischen 5 und 7 liegt.
An imaging element comprising on one side of a support a photosensitive layer
comprising a silver halide emulsion and an image receiving layer containing physical
development nuclei in water permeable relationship with said emulsion layer and
on the other side of the support at least one backing layer comprising gelatin and
a dye and/or a dye precursor characterized in that said dye or dye precursor is
such that after treatment of said imaging element in an alkaline solution with a
pH of 10.9 for 20 s at a temperature of 30°C the backing layer has a reflection
spectrum when treated for 20 s at 20°C in a neutralizing solution with a pH of 7.5
that is displaced over at least 20 nm in the wavelenght of the minimum or maximum
of said spectra in the range between 400 and 700 nm from the reflection spectrum
when treated for 20 s at 20°C in a neutralizing solution with a pH of 8.5.
An imaging element according to claim 1 wherein said dye belongs to a class
selected from the group consisting of oxazines, monomethin pyrazolone-oxonoles and
An imaging element according to claim 2 wherein said dye is a dye corresponding
to the following formula.
An imaging element according to any of claims 1 to 3 wherein in said backing
layer said dye is present in an amount between 5 and 1000 mg/m2.
An imaging element according to any of claims 1 to 4 wherein in said backing
layer said dye is present in an amount between 15 and 300 mg/m2.
An imaging element according to any of claims 1 to 5 wherein said visual difference
in reflection spectra is an increase or decrease with at least 10% of the absorption
coefficient at the wavelenght of the maximum or minimum of said spectra in the range
between 400 and 700 nm.
A method for making a lithographic printing plate according to the silver salt
diffusion transfer process comprising the steps of:
image-wise exposing an imaging element according to any of claims 1 to 7;
developing said imaging element in the presence of developing agent(s) and silver
halide solvent(s) using an alkaline processing solution and
treating the thus obtained developed imaging element using a neutralizing solution
having a pH at 25 °C between 5 and 8.
A method according to claim 7 wherein the pH of a fresh neutralization solution
lies between 5 and 7.
Elément de formation d'image comprenant, sur un côté d'un support, une couche
photosensible comprenant une émulsion à l'halogénure d'argent et une couche de réception
d'image contenant des germes de développement physique en relation de perméabilité
à l'eau avec ladite couche d'émulsion et, sur l'autre côté du support, au moins
une couche dorsale comprenant de la gélatine et un colorant et/ou un précurseur
de colorant, caractérisé en ce que ledit colorant ou ledit précurseur de colorant
est tel qu'après traitement dudit élément de formation d'image dans une solution
alcaline avec un pH de 10,9 pendant 20 secondes à une température de 30°C, la couche
dorsale possède un spectre de réflexion, lorsqu'on la traite pendant 20 secondes
à 20°C dans une solution de neutralisation avec un pH de 7,5, qui se déplace sur
au moins 20 nm dans la longueur d'onde du minimum ou du maximum desdits spectre
dans le domaine entre 400 et 700 nm par rapport au spectres de réflexion que l'on
obtient lorsqu'on la traite pendant 20 secondes à 20°C dans une solution de neutralisation
avec un pH de 8,5.
Elément de formation d'image selon la revendication 1, dans lequel ledit colorant
appartient à une classe choisie parmi le groupe constitué par des oxazines, par
des pyrazolone-oxonoles de monométhine et par des p-amino-triphénylméthanes.
Elément de formation d'image selon la revendication 2, dans lequel ledit colorant
est un colorant répondant à la formule ci-après:
Elément de formation d'image selon l'une quelconque des revendications 1 à 3,
dans lequel, dans ladite couche dorsale, ledit colorant est présent en une quantité
entre 5 et 1000 mg/m2.
Elément de formation d'image selon l'une quelconque des revendications 1 à 4,
dans lequel, dans ladite couche dorsale, ledit colorant est présent en une quantité
entre 15 et 300 mg/m2.
Elément de formation d'image selon l'une quelconque des revendications 1 à 5,
dans lequel, ladite différence visuelle dans les spectres de réflexion est une augmentation
ou une diminution d'au moins 10% du coefficient d'absorption à la longueur d'onde
du maximum ou du minimum desdits spectres dans le domaine entre 400 et 700 nm.
Procédé de fabrication d'un cliché d'impression lithographique conformément
au procédé de transfert de sel d'argent par diffusion, comprenant les étapes consistant
exposer en forme d'image un élément de formation d'image selon l'une quelconque
des revendications 1 à 6;
développer ledit élément de formation d'image en présence d'un ou de plusieurs
agents développateurs et d'un ou de plusieurs solvants pour l'halogénure d'argent
en utilisant une solution de traitement alcaline, et
traiter l'élément de formation d'image développé ainsi obtenu en utilisant une
solution de neutralisation possédant un pH à 25°C entre 5 et 8.
Procédé selon la revendication 7, dans lequel le pH d'une solution fraîche de
neutralisation se situe entre 5 et 7.