Note: Descriptions are shown in the official language in which they were submitted.
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BACKGROUND OF THE INVEN~ION
1. Field of the Invention
The present invention relates to a method for making improved lithographic
aluminium offset printing plates according to the silver complex diffusion
transfer reversal process and to the photosensitive monosheet layer as-
semblage used for making such printing plates.
2. Description of the Prior art :
The principles of the silver complex diffusion transfer reversal process,
briefly called DTR-process herein, have been described in e.g. US-A
2,352,014.
A lithographic printing plate can be made according to the DTR-process. In
US-A 3,511,656 a method has been described for making a printing plate by
photo-exposing a material comprising in the given sequence a silver halide
emulsion layer, a silver-receptive stratum conta;ning nuclei for precipita-
tion of silver from diffusing water-soluble silver complexes, and a base
sheet e.g. an aluminium foil, and applying an aqueous alkaline solution of a
developing agent and silver halide solvent to the photo-exposed silver halide
emulsion layer, reducing the exposed silver halide, allowing the unre~4ced
silver halide or complexes formed thereof to diffuse from the unexposed areas
of the silver halide emulsion layer to the silver-receptive stratum to
produce from the unreduced silver halide or complexes formed thereof in
conjunction with the nuclei a visible silver image in the silver-receptive
stratum, said image being oleophilic ink-receptive, and removing the
photo-exposed silver halide emulsion layer from the surface of`the
silver-receptive stratum with warm water. Printing can be achieved by
wetting the imaged silver-receptive stratum with aqueous dampening liquid to
wet out the non-i~aged areas, coating the silver-receptive stratum with an
ink, which wets out the imaged areas, and pressing the inked surface onto
copy sheets for the transfer of the ink image thereto. It is possible also
to dispense with the silver-receptive stratum containing nuclei so that the
oleophilic ink-receptive image is formed directly on the base sheet e.g. an
aluminiu~ foil, the surface of which has been rendered hydrophilic previously
by brushing, silicating, anodi~ing, etching, or the like. By treatment with
a lacquer the oleophilicity of the silver image can be increased, if desired.
In US-A 4,772,535 a light-sensitive lithographic printing plate material
2 GVI735
has been described, which material comprises a support e.g. a metal support,
an optional subbing or antihalation layer or undercoat, a non-light-sensitive
silver halide emulsion layer, a light-sensitive silver halide emulsion layer,
and an image-receiving layer containing physical development nuclei. The
material is exposed image-wise through the image-receiving layer and
developed to form a diffusion transfer silver image in the image-receiving
layer (not in the metal support). The imaged element thus obtained is used
as such as a printing plate without separation of the now useless emulsion
layers from the layer that contains the printing image.
According to EP-A 0,278,766 a lithographic printing plate precursor has
been proposed, said precursor comprising a grained and anodized aluminium
foil coated with a sol containing nuclei in a gelatin binder and - according
to one embodiment - covered with a silver halide emulsion layer. Extensive
experimentation with a said printing plate precursor has shown unfortunately
that satisfactory printing results can only be obtained on the condition that
after development of said precursor, the residual emulsion layer is remoYed
by washing with hot water (50 C) and that the image plate is treated with a
finisher comprising large amounts (20 g/l) of trypsin. The use of hot water
has several disadvantages. The cost of hot water is high. Moreover, hot
water dissolves the proteinic binder, usually gelatin, of the emulsion layer7
thus causing decomposition of said layer so that a dirty black waste water
comprising silver particles and disso1ved silver salts is obtaineds which
upon cooling may clog filters and draining pipes. As for trypsin, this is a
proteolytic enzyme that should be present in the finisher to degrade or
decompose the proteinic binder that has adsorbed onto the silver grains
precipitating on the aluminium foil during image formation. Substantial
amounts of proteinic binder can indeed easily reach the silver grains owing
to the fact that a silver-receptive stratum comprising gelatin and a gelatin
silver halide emulsion layer have been coated directly on the aluminium foil~
After oleophilization of said silver image the adsorbed gelatin, which is
inherently hydrophilic, constitutes an undesired hydrophilic element in the
master image so that prints having an insatisfactory quality are obtained.
Moreover, said trypsin, which is essential to degrade the proteinic binder in
the silver image, is extraordinarily expensive and is ecologically harmful as
can be derived from i.a. Sigma Aldrich Library of Chemical Safety Data : MSD
Book, 2,35553A,B,C and from Registry of Toxic Effects of Chemical Substances,
YN507500.
In addition to the above disadvantages it has also been established that
the gelatin present in substantial amounts in the nuclei-containing layer and
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in the emulsion of the lithographic printing plate precursor layer has a
corrosive effect on the aluminium foil. The corrosive effect of gelatin on
aluminium has indeed been described by J.H. Penn and G.A.W. Murray in Br.
Ccrros. J., 1967, Vol.2, September, pages 193-4. Even though the corrosive
S influence of gelatin on the aluminium foil may be limited thanks to the
presenc of the anodization layer thereon, this protection is incomplete
owing tG random defects in the continuity of the anodization layer.
Furthermore, it is generally known that aluminium ions have a hardening
influence on gelatin (see e.g. the paragraph bridging pages 78 and 79 of ~The
Theory c,~ the Photographic Process~ 4th Ed.. edited by T.H. James).
Aluminium ions of the foil can indeed cause a hardening reaction in the
gelatin layers so that removal of the emulsion layer gradually becomes more
difficult.
Finallv, as 2 result of the corrosive effect of gelatin on aluminium and
the hardening reaction caused by aluminium in the gelatin layers, the
shelf-life of the lithographic printing plate precursor is limited
substantially.
According to US Serial No. 07/~52,94~ these disadvantages have been
circumvented for the major part by providing between the aluminium foil and
the si7ver halide emulsion layer a thin water-swellable intermediate layer
compris~ng for at least 70~ of its total weight at least one non-proteinic
hydrophilic film-forming polymer.
However, since on a microscopic scale the grained surface of an aluminium
foii is very rugged with deep valleys and steep peaks, it is practically
2~ impossi~le to completely cover this rugged aluminium surface with just a thin
water-s~ellable intermediate layer. It was, therefore, tried to fill up this
ruggedness by enhancing the thickness of the water-swellable intermediate
layer, but although a thicker intermediate layer offered a solution with
respect to creating a more efficient barrier between the aluminium surface
and the emulsion layer, it led to another disadvantage. During diffusion
transfer the silver salts migrating from the emulsion layer to tre aluminium
surface ~hrcugh the thick wa~er-swollen intermediate layer have to cover a
longer ciffusicn path so that lateral diffusion becomes more substantial. ~s
a consecience. the deposition of silver on the aluminium surface and the
3~ sharpn2~s of the transferred silver image are reduced.
SUMMARY OF THE INVENTIO~J
It is ~herefore an obJec~ of the present invention to provide an improved
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method for making lithographic aluminium printing plates according to the
DTR-process in a convenient and ecologically as well as econom;cally
acceptable way.
It is another object of the present invention to provide a photosensitive
monosheet layer assemblage for making a lithographic aluminium printing
plat:e, by which sharp high quality prints can be made according to the
DTR-process, said photosensitive monosheet layer assemblage having an
improved shelflife.
These and other objects are achieved by providing an improved method for
making lithographic aluminium offset printing plates according to the
DTR-process comprising the steps of :
(a) photo-exposing a photosensitive monosheet layer assemblage comprising:
- a hydrophilic grained and anodized aluminium foil,
- an intermediate layer comprising hydrophobic polymer beads prepared
by polymerization of at least one ethylenically unsaturated monomer
and having an average diameter not lower than 0.2 ~m, and
- at least one silver halide emulsion layer,
(b) applying an aqueous alkaline solution to the photo-exposed silver
halide emulsion layer in the presence of at least one developing agent
and at least one silver halide solvent to form a silver image and to
allow unreduced silver halide or complexes formed thereof to diffuse
image-wise from the developed silver halide emulsion layer to said
hydrophilic grained and anodized aluminium foil to produce thereon a
silver image, and
(c) separating said at least one emulsion layer and said intermediate
layer from the imaged hydrophilic grained and anodized aluminium foil.
In the above step (c) said separating can be accomplished e.g. by the steps
of :
- bringing said monosheet layer assemblage with its side showing said at
least one emulsion layer during the period of time starting with the
application of said aqueous alkaline solution and ending with said
,~ormation of a silver image on said hydrophilic grained and anodized
surface in contact with a receiving means, said at least one emulsion
'ayer and said intermediate layer being wet with said aqueous alkaline
solution having an adherence to said receiving means that is stronger
than that to the imaged hydrophilic grained and anodized aluminium
foil and
- peeling off said at least one emulsion layer and said intermediate
layer adhering to said receiving means from the imaged hydrophilic
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grained and anodized aluminium foil,
or by the steps of :
- removing said monosheet layer assemblage from the alkaline
solution-applying means after completion of said formation of a silver
image on said hydrophilic grained and anodized aluminium foil and
- detaching said at least one emulsion layer and said intermediate layer
from the imaged hydrophilic grained and anodized aluminium foil with
the aid of unheated water or unheated aqueous medium,
or by the steps of :
- removing said monosheet layer assemblage from the alkaline
solution-applying means after completion of said formation of a
silver image on said hydrophilic grained and anodized aluminium foil
and
- detaching said at least one emulsion layer and said intermediate
layer, while still being wet with alkaline solution or while being
wet with unheated water or an unheated aqueous medium applied
thereto subsequent to the removal of said monosheet layer assemblage
from said alkaline solution, from the imaged hydrophilic grained and
anodized aluminium foil with the aid of an air current directed onto
an edge of said monosheet layer assemblage.
The imaged hydrophilic grained and anodized aluminium foil can be used for
making prints as follows :
- treating said imaged aluminium foil by rubbing with a fixer to enhance
the water-receptivity of the non-image areas and to make the image areas
oleophilic ink-receptive,
- wetting said imaged aluminium foil with an aqueous dampening liquid to
wet out the non-imaged areas,
- coating said imaged aluminium foil with an ink that wets out the imaged
areas, and
- pressing the inked surface of the resulting lithographic aluminium
offset printing plate in an offset press onto a blanket that transfers
the ink onto copy sheets.
The present invention also provides a photosensitive monosheet layer
assemblage for making a lithographic aluminium printing plate according to
the DTR-process, said assemblage comprising in the given sequence a
hydrophilic grained and anodized aluminium foil and at least one silver
halide emulsion layer, wherein an intermediate layer comprising hydrophobic
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polymer beads prepared by polymerization of at least one ethylenically
unsaturated monomer and having an average diameter not lower than 0.2 ~m is
provided between said hydrophilic grained and anodized aluminium foil and
saicl at least one silver halide emulsion layer.
The photosensitive monosheet layer assemblage according to the present
invention can be made by coating a hydrophilic grained and anodized surface
of an aluminium foil with an intermediate layer comprising hydrophobic
polymer beads prepared by polymerization of at least one ethylenically
unsaturated monomer and having an average diameter not lower than 0.2 ~m, and
coating said intermediate layer with at least one silver halide emulsion
layer.
According to another embodiment the said photosensitive monosheet layer
assemblage can be prepared by the steps of -
- coating a temporary base with at least one silver halide emulsion layer,
- coating said at least one silver halide emulsion layer with an
inter~ediate layer comprising hydrophobic polymer beads prepared by
polymerization of at least one ethylenically unsaturated monomer and
having an average diameter not lower than 0.2 ~m, and
- pressing the thus formed photosensitive layer packet with its side
carrying said intermediate layer against the hydrophilic grained and
anodized surface of an aluminium foil, which has been wet with an
aqueous moistening liquid, the said temporary base being removed before
or after said photo-exposure.
The invention thus also provides a photosensitive layer packet intended for
25 making 2 lithographic aluminium printing plate according to the DTR-process,
wherein said photosensitive layer packet comprises a temporary base
temporarily carrying a separable layer sandwich comprising in the given
sequence at least one silver halide emulsion layer and an intermediate layer
comprising hydrophobic polymer beads prepared by polymerization of at least
one ethylenically unsaturated monomer and having an average diameter not
lower than 0.2 ~m, said layer sandwich being transferable onto a wet separate
hydrophilic grained and anodized aluminium foil when pressed thereon. The
temporary base can be peeled off before or after photo-exposure of the silver
halide e~ulsion layer(s).
DETAILED DESCRIPTION OF THE INVENTION
The method of the invention for making prints according to the DTR-process
by means of an improved lithographic aluminium offset printing plate
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comprises the consecutive steps of :
(1) ~aking a photosensitive monosheet layer assemblage e.g. by the steps
of :
- coating the hydrophilic grained and anodized surface of an aluminium
foil, preferably after having applied thereto a silver-receptive
stratum containing development nuclei for precipitation of silver
from diffusing water-soluble silver complexes, with an intermediate
layer comprising hydrophobic polymer beads having an average
diameter not lower than 0.2 ~m and having been prepared by
polymerization of at least one ethylenically unsaturated monomer
e.g. chosen from the group consisting of alkyl methacrylates e.g.
methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl
methacrylate and the higher methacrylates such as stearyl
methacrylate, substituted alkyl methacrylates e.g. hydroxyethyl
methacrylate, alkyl acrylates, substituted alkyl acrylates, styrene,
substituted styrene e.g. chlorostyrene, vinyltoluene ans substituted
vinyltoluene e.g. vinylbenzyl chloride and the homologues thereof,
butadiene, substituted butadiene e.g. chlorobutadiene, 2-
methylbutadiene, isobutylene, and substituted isobutylene, and
vinylpyridine e.g. 2- and 4-vinyl-pyridine, said intermediate layer
preferably comprising an antihalation dye or pig~ent, and
- coating said intermediate layer with at least one silver halide
emulsion layer, at least one silver halide emulsion layer being
photosensitive and optionally comprising a light-screening dye,
or by the steps of :
- coating a temporary base, preferably a cellulose triacetate or
polyethylene terephtalate film base, with at least one silver halide
emulsion layer, at least one silver halide emulsion layer being
photosensitive and optionally comprising a light-screening dye,
- coating said at least one silver halide emulsion layer with an
intermediate layer comprising hydrophobic polymer beads having an
average diameter not lower than 0.2 y~ and having been prepared by
polymerization of at least one ethylenically unsaturated monomer,
said intermediate layer optionally comprising an antihalation dye or
pigment,
- pressing the thus formed photosensitive layer packet with its side
carrying said intermediate layer against the hydrophilic grained and
anodized surface of an aluminium foil, which has been wet with an
aqueous moistening liquid that may comprise additives,
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8 GV1735
- removing said te~porary base to leave a photosensitive monosheet
layer assemblage supported by said aluminium foil and optionally
drying said photosensitive monosheet layer assemblage supported by
said aluminium foil,
(2) - photo-exposing the thus formed photosensitive monosheet layer
assemblage,
(3) - applying an aqueous alkaline solution to the photo-exposed silver
halide emulsion layer in the presence of at least one developing
agent and at least one silver halide solvent to form a silver image
and to allow unreduced silver halide or complexes formed thereof to
diffuse image-wise from the developed silver halide emulsion layer
to said hydrophilic grained and anodized surface to produce thereon
a silver image preferably under the catalytic influence of
development nuclei,
(4) - separating said at least one emulsion layer and said intermediate
layer from the imaged hydrophilic grained and anodized surface, said
separating being accomplished e.g. by the steps of :
- bringing said monosheet layer assemblage with its side showing
said at least one emulsion layer during the period of time that
starts with the application of said aqueous alkaline solution and
ends with said formation of a silver image on said hydrophilic
grained and anodized surface in contact with a receiving means,
said at least one emulsion layer and said intermediate layer
being wet with said aqueous alkaline solution having an adherence
to said receiving means that is stronger than that to the imaged
hydrophilic grained and anodized surface and
- peeling off said at least one emulsion layer and said
intermediate layer adhering to said receiving means from the
imaged hydrophilic grained and anodized surface,
or by the steps of :
- removing said monosheet layer assemblage from the alkaline
solution-applying means e.g. a bath or a roller system such as a
lick roller, after completion of said formation of a silver image
on said hydrophilic grained and anodized surface and
- detaching said at least one emulsion layer and said intermediate
layer from the imaged hydrophilic grained and anodized surface
with the aid of unheated water or unheated aqueous medium, said
detaching being performed e.g. :
- according to a preferred mode, by rinsing with a spray or jet
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of unheated water or unheated aqueous medium directed onto said
at least one emulsion layer and said intermediate layer, or
- by agitating or shaking a tray comprising said monosheet layer
assemblage immersed in unheated water or unheated aqueous
medium, or agitating said monosheet layer assemblage while
being immersed in unheated water or unheated aqueous medium,
- according to another preferred mode, by pressing said monosheet
layer assemblage with its side showing said at least one
emulsion layer, while being moistened with unheated water or
unheated aqueous medium, against a receiving sheet such as a
polyethylene-coated paper sheet and peeling off said receiYing
sheet together with said at least one emulsion layer and said
intermediate layer, which remain strongly adhering to said
receiving sheet, from said imaged aluminium foil,
lS the mechanical effect obtained by said rinsing or agitating or
pressing against a receiving sheet and peeling off, being
sufficient to eliminate said at least one emulsion layer and said
intermediate layer from the imaged hydrophilic grained and
anodized surface,
or by the preferential steps of :
- removing the monosheet layer assemblage from the alkaline
solution-applying means e.g. a bath or a roller system such as a
lick roller, after completion of said formation of a silver image
on said hydrophilic grained and anodized surface and
- detaching said at least one emulsion layer and said intermediate
layer, while still being wet with alkaline solution or while
being wet with unheated water or an unheated aqueous medium
applied thereto subsequent to the removal of said monosheet layer
assemblage from said alkaline solution, from the imaged
hydrophilic grained and anodized aluminium foil with the aid of
an air current directed onto an edge of said monosheet layer
assemblage,
the mechanical effect obtained by said air current being sufficient to
climinate said at least one emulsion layer and said intermediate layer
from the imaged hydrophilic grained and anodized surface,
(5) -;reating said imaged surface by rub~ing it with a fixer to enhance
the water-receptivity of the non-image areas and to make the image
areas oleophilic ink-receptive,
(6~ -~etting said imaged surface with an aqueous dampening liquid to wet
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out the non-imaged areas,
(7) -coating said imaged surface with an ink that wets out the imaged
areas, and
(8) -pressing the inked surface of said resulting lithographic aluminium
offset printing plate in an offset press onto a blanket that transfers
the ink onto copy sheets.
An above-described embodiment of the method of the invention comprises the
following consecutive steps :
- making a photosensitive monosheet layer assemblage by coating a
temporary base successively with at least one silver halide emulsion
layer and a said intermediate layer,
- next pressing the thus formed photosensitive layer packet against an
aluminium foil, which has been wet with an aqueous moistening liquid,
to transfer said intermediate layer and said emulsion layer onto said
wet foil,
- removing said temporary base to leave a photosensitive monosheet layer
assemblage supported by said aluminium foil,
- photo-exposing the thus formed photosensitive monosheet layer
assemblage.
It has, however, been found that this sequence of steps may be altered in
the sense that said temporary base is not removed before the photo-exposure
step. Thus, according to this interesting variant said photosensitive layer
packet is pressed against a wet aluminium foil to transfer said intermediate
layer and said emulsion layer onto said wet foil, the aluminium side of the
resulting sandwich is dried slightly, and the photo-exposure of the sandwich
is then performed through said temporary base, which for this embodiment
obviously is a transparent film base. It is further possible to expose the
photosensitive silver halide emulsion layer(s) on the temporary base, then to
press the packet against the wet aluminium foil, and finally to remove the
temporary base. Thanks to the presence of the temporary base the silver
halide e~ulsion layer~s) find themselves protected from mechanical
deformation, especially in wet condition.
The irvention also provides a photosensitive monosheet layer assemblage for
making a lithographic aluminium print;ng plate for use according to the
DTR-process, said assemblage comprising in the given sequence :
- a hydrophilic grained and anodized aluminium foil, the anodization
layer of which may be coloured with an antihalation dye or pigment,
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- optionally a silver-receptive stratum containing development nuclei for
precipitation of silver from diffusing water-soluble silver complexes,
~hich stratum may comprise an antihalation dye or pigment,
- at least one silver halide emulsion layer, at least part of the silver
halide emulsion being photosensitive and optionally comprising a
light-screening dye,
wherein an intermediate layer is provided between on the one hand said
silver-receptive stratum or in the absence of said silver-receptive stratum
said hydrophilic grained and anodized surface and on the other hand said at
least one silver halide emulsion layer, said intermediate layer comprising
hydrophobic polymer beads having an average diameter not lower than 0.2 ~m
and having been prepared by polymerization of at least one ethylenically
unsaturated monomer, said intermediate layer optionally comprising an
antihalation dye or pigment and optionally comprising a matting or spacing
agent. Preferably, said intermediate layer in dry condition comprises said
hydrophobic polymer beads in an amount of up to 80% of its total weight.
The invention further provides a photosensitive layer packet and a separate
hydrophilic grained and anodized aluminium foil, together intended for use in
transferring a transferable layer sandwich of said photosensitive layer
packet by sepàration from a temporary base onto said separate hydrophilic
grained and anodized aluminium foil in wet condition to form a photosensitive
monosheet layer assemblage therewith for making a lithographic aluminium
printing plate for use according to the DTR-process. Said photosensitive
layer packet comprises a temporary base temporarily carrying a said separable
layer sandwich comprising in the given sequence at least one silver halide
emulsion layer, at least part of the silver halide emulsion being
photosensitive and optionally comprising a light-screening dye,
and an intermediate layer comprising hydrophobic polymer beads prepared by
polymerization of at least one ethylenically unsaturated monomer and having
an average diameter not lower than 0.2 ~m, said intermediate layer optionally
comprising an antihalation dye or pigment and optionally comprising a matting
or spacing agent, and said layer sandwich being transferable onto said wet
separate aluminium foil when pressed thereon. Preferably, said intermediate
layer in dry condition comprises said hydrophobic polymer beads in an amount
of up tc 80% of its total weight.
As referred to hereinbefore the removal of the temporary base can be
delayed until the photo-exposed material ;s to be treated with the aqueous
alkaline solution.
It has been established that thanks to the presence of the thin layer
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comprising hydrophobic polymer beads prepared by polymerization of at least
one ethylenically unsaturated monomer and having an average diameter not
lower than 0.2 ~m as an intermediate layer between on the one hand said
silver-receptive stratum or in the absence of said silver-receptive stratum
said hydrophilic grained and anodized surface and on the other hand said at
least one silver halide emulsion layer, an efficient barrier is formed
against the mutual above-mentioned adverse effects that a proteinic binder,
usually gelatin, and aluminium exert on each other when in contact with one
another. By eliminating or reducing these adverse effects in this way the
shelf-life of the photosensitive monosheet layer assemblage is increased
considerably. It is self-evident that when the above-defined photosensitive
layer packet and separate aluminium foil are used, the contact between the
proteinlc binder and aluminium is excluded during storage of the separate
materials so that the above-mentioned adverse effects cannot occur. Thanks
1~ to the elimination or reduction of these adverse effects the printing platesmade according to any of the embodiments of the method of the present
invention yield prints having a high quality. Moreover, no ecologically
harmful substances such as enzymes e.g. trypsin have to be incorporated into
the finisher liquids such as e.g. the fixer, which are needed to prepare the
printina plate. furthermore, the process is convenient and economically
interesting in that no hot water is needed. Since the rinsing water or
aqueous medium may be in unheated condition, it does not dissolve the
proteinic binder of the developed emulsion layer. In fact the emulsion layer
detaches in the form of swollen flakes that can easily be filtered from the
rinsing water or aqueous medium. No clogging of filters and draining pipes
can be occasioned. After filtration the rinsing water or aqueous medium is
clear and non-pollutant and comprises substantially no silver particles nor
silver salts so that it may be discharged in the sewage. By the term
"unheat~d" as used herein in connection with the rinsing water or aqueous
medium is meant that no external heating means are applied for heating said
water or aqueous medium. However, it is self-evident that the invention also
encompasces the use of warm water.
Due tc the thinness of the intermediate layer lateral diffusion therein of
the migrating silver salts during diffusion transfer is neglegible so that
sharp transfer images are obtained on the aluminium surface. As a result,
sharp high quality prints can be made with the aluminium printing plates.
The ~chanical effect either obtained by said rinsing with a spray or jet
directea onto said at least one emulsion layer and said intermediate layer or
- obtained by said agitation or shaking or obtained by said pressure against
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said receiving sheet must be sufficient to detach these layers from said
imaged hydrophilic grained and anodized surface.
Ihe hydrophobic polymer beads for use in the intermediate layer of the
present invention are prepared by polymerization of at least one ethylenical-
ly unsaturated monomer. Preferred polymer beads are e.g. polymethyl metha-
crylate beads, polystyrene beads, ethyl acrylate/stearyl methacrylate copoly-
mer beads, methacrylic acid/methyl methacrylate/stearyl methacrylate copoly-
mer beads, and beads prepared as described in US-A 4,614,708 and 4,861,818.
The average size of the hydrophobic polymer beads for use in accordance
with the invention is, of course, determined by the nature of said at least
one ethylenically unsaturated monomer, but can also be controlled by
adjustment of other reaction parameters as described in the above-mentioned
US-A 4,614,708 and 4,861,818.
The preparation of hydrophobic polymer beads for use in accordance with the
invention is illustrated by the following preparation example.
Preparation example : polymethyl methacrylate beads
At room temperature 271.73 9 of a 20% by weight solution of
co(styrene/maleic acid monosodium salt (pH = 7) and 3752.2 g of demineralized
water are mixed in a 10 l cylindrical double-walled reaction vessel. The
solution is stirred by means of a rotor having a length of 15.5 cm and a
width of 4 cm set at a speed of 100 rpm.
The reaction vessel is equipped with a reflux condenser and a nitrogen
inlet reaching below the liquid level and is sealed. Hot water (65 C) is fed
through the double wall of the reaction vessel so that after 1 h the
temperature of the solution reaches 65 C.
A continuous inlet of nitrogen keeps the solution free from oxygen.
An am~unt of 10.86 9 of potassium persulphate is then added at once to the
solution. Heating of the solution to 65 C and stirring are continued.
After this preliminary reaction step the stirring speed is maintained at
100 rpm. Next, 21.74 9 of ARKOPAL N60 commercially available from Hoechst,
2137.48 ~l of methanol, and 1086.95 g of methyl methacrylate (not distilled
prelimirarily) are added in the given sequenve under nitrogen atmosphere
At thls very moment the following parameters should be met :
- 1.G g of potassium persulphate is present per 100 9 of methyl methacrylate
- 2.0 9 of ARKOPAL N60 is present per 100 9 of methyl methacrylate
- the ratio by volume of methanol/water is 35/65
- the concentration of monomer at the start of the reaction is 1.50 mol of
14 ~ `J '' GV1735
methyl methacrylate per litre
- the stirring speed is 100 rpm.
The temperature of the water-bath is continuously kept at 65 C. The
pol~erization reaction is very slightly exothermic so that the temperature
in t:he reaction vessel rises to a maximum of 65.5 C. At this moment a weak
flow of cold tap water is pumped in addition to the hot water (65 C) into the
double wall, the flow of cold water being adjusted automatically with the aid
of a contact thermometer, a relay, and an automatic water valve in such a way
that as soon as the temperature in the reaction vessel drops to 65 C the flow
of cold water is interrupted immediately.
At the start of the polymerization reaction the solution has a clear
aspect, but after some 30 min the solution becomes turbid and then slowly and
gradually turns into a milky white dispersion.
Eventually, after a total polymerization period of 18 h the supply of hot
water and of nitrogen is stopped. The bead dispersion obtained is cooled by
means of cold tap water to about 30 C with continuous stirring and then
filtered through a nylon cloth having a mesh width of 60 x 60 ~m. Filtering
is easy, a maximum of 2.0 g of polymer in amorphous state remaining on the
cloth
Yield : 6795 9 of dispersion having 16.5 g of dry residue per 100 g of
dispersion (pH = 5.6). The polymethyl methacrylate beads obtained have an
average diameter of 1 ~m.
The presence of antihalation dyes or pigments in the intermediate layer
offers the supplemental advantage that said layer loosens more easily from
the imaged aluminium foil. To further improve the loosening of the
intermediate layer, said layer may also comprise matting agents or spacing
agents e.g. finely divided silica particles. In case the photosensitive
layer assemblage consisting of a temporary base, photosensitive silver halide
emulsion layer(s), and an intermediate layer is to be exposed in a vacuum
contact exposure unit such matting or spacing agents also promote an
effective vacuum suction.
According to a special embodiment of the present invention the intermediate
layer may in addition to the hydrophobic polymer beads prepared by
polymerization of at least one ethylenically unsaturated monomer also
comprise an aqueous dispersion of alkali-soluble hydrophobic polymer
particles, all particles having an average particle size not lower than 0.2
~m. The amount of said aqueous dispersion of hydrophobic polymer particles
present in said intermediate layer may be up to 10 % by weight calculated on
'3~ ? ``~ ~
GV1735
the total weight of said layer. The use of such alkali-soluble hydrophobic
polymer particles in addition to the hydrophobic polymer beads of the present
inventio~ in the intermediate layer offers the advantage that during
processing of the photo-exposed emulsion layer(s) in an aqueous alkaline
solution at least part of said alkali-soluble hydrophobic polymer particles
are dissolved so that cavities or holes are formed in the intermediate layer,
through which the diffusion transfer of migrating silver salts to the
aluminium surface is facilitated. As a result, a high density buildup of
transferred silver is accomplished.
Non-proteinic hydrophilic film-forming polymers may be present in the
intermediate layer in an amount of e.g. up to 20% by weight of the total
weight of said layer. Suitable non-proteinic hydrophilic film-forming
polymers are e.g. polyvinyl alcohol, polyvinyl pyrrolidone, polyethylene
oxide, partly hydrolyzed polyvinyl acetate, sulphonated polystyrene,
hydroxyethyl cellulose, carboxymethyl cellulose, cellulose acetate hydrogen
phthalate, dextran, dextrins or derivatives thereof, starch, gum arabic, and
alginic acid derivatives such as salts or esters thereof. It is also
possible to use mixtures of two or more different non-proteinic hydrophilic
film-forming polymers.
According to the preferred way of separating said at least one emulsion
layer and said intermediàte layer from the imaged aluminium foil by means of
an airstream, the process of the present invention is even more convenient
and economically interesting in that the blown off layers detach as a
cohesive mass that in contrast with the other separation methods of the
present invention does not need any further separation or filtration from
water or aqueous medium. The loosened cohesive mass dries rapidly and
recovery of silver therefrom is easy and complete.
According to this preferred way of separating, the emulsion layer and
intermediate layer, while both still being wet with said aqueous alkaline
solution or while being moistened with unheated water or an unheated aqueous
medium applied thereto subsequent to the removal of said monosheet layer
assemblage from said alkaline solution, are detached from the imaged
aluminium foil by means of an airstream e.g. a jet of compressed air,
preferably an airstream blown from a slot orifice e.g~ an air knife or air
doctor, said airstream being directed ~nto the lengthwise or breadthwise edge
of said monosheet layer assemblage. The device capable of generating the
airstream used for separating the emulsion layer and intermediate layer from
the imaged aluminium foil e.g. an air knife can be incorporated as a separate
station in the processing apparatus. In that case the latter processing
~3~ "
16 GV1735
apparatus includes a station for applying aqueous alkaline solution to the
photo-exposed emulsion layer and allowing unreduced silver halide or
co~lplexes formed thereof to diffuse to the aluminium foil and a said station
for separating by means of an airstream. As mentioned before unheated water
or an unheated aqueous medium may be applied optionally to the monosheet
layer assemblage after removal thereof from said alkaline solution and prior
to said detaching by means of an airstream. It is self-evident that the
invention also encompasses the use of hot water.
According to the variant using said receiving sheet, the receiving sheet
together with said at least one emulsion layer and said intermediate layer,
which remain strongly adhering to said receiving sheet, are peeled off from
said imaged aluminium foil.
~he restricted softening and swelling in alkaline activating or developing
solutions is due to ions such as e.g. sulphite and thiosulphate ions, which
are present conventionally therein. This restricted swelling is comparable
to that observed for emulsion gel layers. The typical changes in the degree
of swell of an emulsion gel layer as it passes through the development in an
alkaline solution causing a limited swell and subsequently through the
rinsing with a water bath causing high swell have been shown in figure 15.17
on page 453 of "The Theory of the Photographic Process" 4th edition, edited
by T.H. James, Macmillan Publishing Co., Inc. New York.
The aqueous moistening liquid used to wet said alumin;um foil so that the
transferable layers can be transferred thereto may consist of water or may be
an aqueous solution comprising additives such as i.a. surface-active agents,
a water-miscible alcohol e.g. ethanol, and hardeners including latent
hardeners.
On the one hand the nature of the hydrophobic polymer beads prepared by
polymerization of at least one ethylenically unsaturated monomer and having
an average diameter not lower than 0.2 ~m is chosen such that when a layer
thereof - even a layer thereof comprising up to 20% by weight of any non-
proteinic hydrophilic film-forming polymer - is immersed in said aqueous
alkaline solution, whether it is an activating solution or a developing
solution, softening and swelling of said layer is practically inexistent so
that it remains adhering to the aluminium foil. On the other hand the nature
of the hydrophobic polymer beads and of any non-proteinic hydrophilic
film-forming polymer used in admixture therewith is chosen such that when :
- either a spray or jet of water or of an aqueous non-alkaline medium is
directed onto said at least one emulsion layer and said intermediate
layer ,
17 ;` ~ ` `J " GV1735
- or a tray comprising said monosheet layer assemblage i~mersed in
unheated water or unheated aqueous medium is agitated or shaken, or said
monosheet layer assemblage is agitated while being immersed in unheated
water or unheated aqueous medium,
S - or said monosheet layer assemblage is pressed with its side showing said
at least one emulsion layer, while being moistened with unheated water
or unheated aqueous medium, against a receiving sheet such as e.g. a
subbed cellulose triacetate film sheet,
the intermediate layer is caused to detach from the aluminium foil and carry
along the swollen emulsion layer(s).
For use according to the preferred method of separating the emulsion
layer(s) and intermediate layer from the aluminium foil by means of an
airstream, the non-proteinic hydrophilic film-forming polymer or mixture of
non-proteinic hydrophilic polymers optionally present in said intermediate
lS layer is such that when said intermediate layer is immersed in said aqueous
alkaline solution, whether it is an activating solution or a developing
solution, or is immersed, after having been removed from said aqueous
alkaline solution, in unheated water or in an unheated aqueous medium,
softening and swelling of said polymer(s) is poor and is restricted
substantially to an extent that the layer containing said polymer(s) together
with said hydrophobic polymer beads remains adhering to the aluminium foil.
On the other hand the nature of the non-proteinic hydrophilic film-forming
polymer or mixture of non-proteinic hydrophilic polymers is such that when an
airstream is directed onto an edge of said monosheet layer assemblage, said
layers both still being wet with absorbed aqueous alkaline solution or with
subsequently applied unheated water or unheated aqueous medium, the
intermediate layer detaches readily from said alum;n;um foil while carrying
along the swollen emulsion layer(s).
The thickness of the intermediate layer may vary between wide limits.
However. the coating weight of the composition for making the intermediate
layer is preferably not lower than 0.1 g/m2, since otherwise an inadequate
or insufTicient barrier against the above-mentioned adverse effects may be
created. On the other hand the coating weight of the composition for making
the int~rmediate layer preferably must not be higher than S.O g/m2, since
3~ owing to an increased thickness of the layer the diffusion path of the
migrating silver complexes would be extended such that the chances of lateral
diffusion of these migrating s;lver complexes would increase. Lateral
diffusion may, of course, lead to insufficient sharpness of the silver image
formed on the alumin;um foil. Preferably, the composit;on for making the
18 ` '~``` GV1735
intermediate layer is thus coated at a ratio of from about 0.1 to about 5
g/m2.
The intermediate layer may incorporate at least one dye or pigment for
antihalation purposes. The usual dyes and pigments can be chosen depending
upon the desired absorption spectrum of the resulting layer relative to the
spectral sensitivity of the silver halide emulsion layer(s).
The hydrophobic polymer beads of the intermediate layer can be loaded with
a hydrophobic dye for antihalation purposes according to the so-called
technique of loading latices with a hydrophobic substance as described in
i.a. DE-A 2,541,274 and 2,541,230.
According to a preferred embodiment of the present invention the
hydrophobic polymer beads of the intermediate layer can be loaded with a dye
for antihalation purposes according to the method described in the EP Patent
Application ........ , filed on even date herewith and entitled "Method of
making aqueous loaded latex compositions".
The intermediate layer may in addition to dyes or pigments and matting
agents or spacing agents comprise further ingredients such as i.a. developing
agents, other development ingredients, base precursors, silver halide
solvents, and anticorrosive agents.
The aluminium foil of the photosensitive monosheet layer assemblage of the
present invention can be made of pure aluminium or of an aluminium alloy, the
aluminiu~ content of which is at least 95%. A useful alloy is e.g. one
comprising 99.55% by weight of Al, 0.29% of Fe, 0.10% of Si, 0.004% of Cu,
0.002% of Mn, 0.02% of Ti, and 0.03% of Zn. The thickness of the foil
usually ranges from about 0.13 to about 0.50 mm.
The preparation of aluminium or aluminium alloy foils for lithographic
offset printing comprises the following steps : graining, anod;zing, and
optionally sealing of the foil.
Graining and anodization of the foil are necessary to obtain a lithographic
printing plate that allows to produce high-quality prints in accordance with
the present invention. Sealing is not necessary but may still improve the
printing results.
Graining of the aluminium surface can be carried out mechanically or
electrolytically in any known way. The roughness produced by the graining is
measured as a centre line average value expressed in ~m and preferably varies
from about 0.2 to about 1.5 ~m.
The anodization of the aluminium foil can be performed in electrolytes such
as e.g. ch'romic acid, oxalic acid, sodium carbonate, sodium hydroxide, and
mixtures thereof. Preferably, the anodization of the aluminium is performed
19 GV1735
in dilute aqueous sulphuric acid medium until the desired thickness of the
anodization layer is reached. The aluminium foil may be anodized on both
sides. The thickness of the anodization layer is most accurately measured by
making a micrographic cut but can be determined likewise by dissolving the
anodized layer and weighing the plate before dissolution treatment and
subsequent thereto. Good results are obtained with an anodization layer
thickness of about 0.4 to about 2.00 ~m. To promote the image sharpness and,
as a consequence thereof, the sharpness of the final printed copy, the
anodization layer may be coloured in the mass with an antihalation dye or
pigment e.g. as described in ~A-A 58-14797. The dye or pigment or a
combination of dyes or pigments used for such colouring in the mass are
chosen such that they prevent or reduce halation in silver halide emulsions
having any desired photosensitivity range comprised between 300 and 900 nm.
After the anodizing step the anodic surface may be sealed. Sealing of the
pores of the aluminium oxide layer formed by anodization is a technique known
to those skilled in the art of aluminium 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 Aluminium".
Different types of sealing of the porous anodized aluminium surface exist.
An advantageous sealing method is the hydration-sealing method, according to
which the pores are closed or partially closed through water-acceptance so
that hydrated needle-like aluminium oxide crystals (bohmite) are formed. The
anodic surface of the aluminium foil can thus be rinsed with water at
70-100 C or with steam. The hot sealing water may comprise additives such as
nickel salts to improve the sealing effect. The sealing can also be
perfor~ed by treatment of the anodic surface with an aqueous solution
comprising phosphate ions or silicates. Thanks to the sealing treatment the
anodic layer is rendered substantially non-porous so that longer press runs
can be ~ade with the printing plate obtained. As a result of the sealing the
occurrence of fog in the non-printing areas of the printing plate is avoided
substantlally.
The graining, anodizing, and sealing of the aluminium foil can be performed
as descr,bed in e.g. US-A 3,861,917 and in the documents referred to therein.
To prc~ote the image sharpness and, as a consequence thereof, the sharpness
of the final printed copy, the grained, anodized, and optionally sealed
aluminiu~ foil can be provided with a very thin antihalation coating of a dye
or pigme~t. As already mentioned before, the usual dyes and pigments can be
chosen such that they prevent or reduce halation in the silver halide
r~ 'J Ji
GV1735
emulsions used, which have any desired photosensitivity range comprised
bet~een 300 and 900 nm.
According to one embodiment the aluminium foil constitutes the sole
receptor material for the silver image in that the aluminium itself takes
part actively in the formation of the silver image by electrochemically
reducing the transferred silver complexes. The use of such an aluminium foil
as sole receptor material has been described in i.a. EP-A 0059008.
According to a frequently used alternative embodiment the grained,
anodized, and optionally sealed aluminium foil can be provided with a
silver-receptive stratum comprising development nuclei that initiate the
physical development of the transferred silver complexes to form a silver
image therein. Suitable development nuclei are sulphides of heavy metals
e.g. sulphides of antimony, bismuth, cadmium, cobalt, lead, nickel,
palladium, platinum, silver, and zinc. Especially suitable development
nuclei are NiS.Ag2S nuclei as described in US-A 4,563,410. Other suitable
development nuclei are salts such as e.g. selenides, polyselenides,
polysulphides, mercaptans, and tin (Il) halides. Heavy metals or salts
thereof and fogged silver halide are suitable as well. The complex salts of
lead and zinc sulphides are active both alone and when mixed with
thioacetamide, dithiobiuret, and dithiooxamide. Heavy metals, preferably
silver, gold, platinum, palladium, and mercury can be used in colloidal form.
The silver-receptive stratum may incorporate at least one antihalation dye
or pigment to promote the image sharpness. Again, the usual dyes and
pigments can be chosen depending upon the desired absorption spectrum of the
silver-receptive stratum relative to the spectral sensitivity of the silver
halide emulsion layer(s) used.
The silver halide emulsion layer can be any photosensitive silver halide
emulsion comprising a hydrophilic colloid binder. The photosensitive silver
~ halide used in the present invention may comprise silver chloride, silverbromide. silver bromoiodide, silver chlorobromoiodide and the like, or
mixtures thereof. To obtain a sufficiently high rate of dissolution of the
silver halide and a satisfactory gradation necessary for graphic purposes a
silver halide emulsion mainly comprising silver chloride is often used. This
silver chloride emulsion may comprise minor amounts of silver bromide and/or
silver iodide.
The silver halide emulsions may be coarse- or fine-grained and can be
prepared by any of the well known procedures e.g. single jet emulsions,
double jet emulsions such as Lippmann emulsions, ammoniacal emulsions,
thiocyanate- or thioether-ripened emulsions such as those described in US-A
21 GV1735
2,222,264, 3,320,069, and 3,271,157. Surface image emulsions may be used or
internal image emulsions may be used such as those described in US-A
2,592,250, 3,206,313, and 3,447,927. If desired, mixtures of surface and
internal image emulsions may be used as described in US-A 2,996,382. The
silver halide particles of the photographic emulsions may have a regular
crystalline form such as a cubic or octahedral form or they may have a
transition form. Regular-grain emulsions are described in e.g. J. Photogr.
Sci., Vol. 12, No. 5, Sept./Oct. 1964, pp. 242-251. The silver halide grains
may also have an almost spherical form or they may have a tabular form
(so-called T-grains), or may have composite crystal forms comprising a
mixture of regular and irregular crystalline forms. The silver halide grains
may have a multilayered structure having a core and shell of different halide
composition. Besides having a differently composed core and shell the silver
halide grains may comprise also different halide compositions and metal
dopants inbetween.
Two or more types of silver halide emulsions that have been prepared
differently can be mixed for forming a photographic emulsion for use in a
photographic material treated with a processing liquid according to the
present invention.
The average size of the silver halide grains may range from 0.2 to 1.2 ~m,
and the size distribution can be homodisperse or heterodisperse. A
homodisperse size distribution is obtained when 95% of the grains have a size
that does not deviate more than 30 % from the average grain size.
In addition to silver halide the emulsions may also comprise organic silver
salts such as e.g. silver benzotriazolate and silver behenate.
The silver halide crystals can be doped with Rh3+, Ir4+, Cd2+, Zn2+, Pb2+.
The photographic emulsions can be prepared from soluble silver salts and
soluble halides according to different methods as described e.g. by P.
Glafkides in "Chimie et Physique Photographique", Paul Montel, Paris (1967),
by G.F. Duffin in "Photographic Emulsion Chemistry", The Focal Press, London
(1966), and by V.L. Zelikman et al in "Making and Coating Photographic
Emulsion~, The Focal Press, London (1966).
The emulsion can be desalted in the usual ways e.g. by dialysis, by
flocculation and re-dispersing, or by ultrafiltration.
Besides the silver halide another essential component of a photosensitive
emulsion layer is the binder. The binder is a hydrophilic colloid, usually a
protein, preferably gelatin. Gelatin can, however, be replaced in part or
integrally by synthetic, semi-synthetic, or natural polymers. Synthetic
substitutes for gelatin are e.g. polyvinyl alcohol, poly-N-vinyl pyrrolidone,
~ d~
22 ~V1735
polyvinyl imidazole,, poly~inyl pyrazole, polyacrylamide, polyacrylic acid,
and derivatives thereof, in particular copolymers thereof. Natural
substitutes for gelatin are e.g. other proteins such as zein, albumin and
casein, cellulose, saccharides, starch, and alginates. In general, the
semi-synthetic substitutes for gelatin are modified natural products e.g.
gelatin derivatives obtained by conversion of gelatin with alkylating or
acylating agents or by grafting of polymerizable monomers on gelatin, and
cellulose derivatives such as hydroxyalkyl cellulose, carboxymethyl
cellulose, phthaloyl cellulose, and cellulose sulphates.
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 aluminium foil.
For instance, direct-positive emulsions of the type described in US-A
3,062,651 may be employed. In direct-positive emulsions a non-hardening
fogging agent such as stannous chloride and formamidine sulphinic acid can be
used.
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
aminoethane-sulphonic acid can be used as chemical sensitizers. Other
suitable chemical sensitizers are noble metals and noble metal compounds such
as gold, platinum, palladium, iridium, ruthenium and rhodium. This method of
chemical sensitization has been described in the article of R. Koslowsky, Z.
Wiss. Photogr. Photophys. Photochem. 46, 65-72 (1951).
The emulsions can also be sensitized with polyalkylene oxide derivatives,
e.g. with polyethylene oxide having a molecular weight of 1000 to 20,000, or
with condensation products of alkylene oxides and aliphatic alcohols,
glycols. cyclic dehydration products of hexitols, alkyl-substituted phenols,
aliphatic carboxylic acids, aliphatic amines, aliphatic diamines and amides.
The condensation products have a molecular weight of at least 700, preferably
of more than 1250. It is also possible to combine these sensitizers with
each other as described in BE-A 537,278 and GB-A 727,982.
The spectral photosensitiYity of the silver halide can be adjusted by
proper sensitization to any desired spectral range comprised between 300 and
900 nm ~y means of the usual mono- or polymethine dyes such as acidic or
basic cyanines, hemicyanines, oxonols, hemioxone~s, styryl dyes or others,
} ~
23 GV1735
also tri- or polynuclear methine dyes e.g. rhodacyanines or neocyanines.
Such spectral sensitizers have been described by e.g. F.M. Hamer in "The
Cyanine Dyes and Related Compounds" (1964) Interscience Publishers, John
Willey & Sons, New York. The spectral photosensitivity of the silver halide
can also be adjusted for exposure by laser light e.g. helium-neon laser
light7 argon laser light, and solid state laser light. Dyes that can be used
for adjusting the photosensitivity to laser light have been described in i.a.
JA-A 62284344, 62284345, 62141561, 62103649, 62139555, 62105147, 62105148,
62075638, 62062353, 62062354, 62062355, 62157027, 62157028, 62113148,
61203445, 62003250, 60061752, 55070834, 51115821, 51115822, 51106422,
51106423, 51106425, DE-A 3,826,700; US-A 4,501,811, 4,725,532, 4,784,933;
GB^A 1~467,638; and EP-A 100,654 and in documents cited therein.
The silver halide can also be sensiti,ed with a dye or a mixture of dyes
providing a spectral sensitivity mainly in the range of 400 to 500 nm and not
extending the sensitivity substantially beyond 500 nm so that the sensitivity
at 530 nm is at least 102 lower than that at 500 nm and that the resulting
photosensitive monosheet layer assemblage can be handled in yellow safe-light
conditions prior to the photo-exposure, said conditions corresponding to the
light transmitted by a cut-off filter having at 500 nm a density of at least
2 5, at 530 nm a density not higher than 2.0, at 540 nm a density not higher
than 1.0, at 550 nm a density not higher than 0.4, at 560 nm a density not
higher than O.Z, and beyond 580 nm a density not higher than 0.1. Suitable
dyes that can be used for that purpose have been described in e.g. US-A
4,686,170. Image-wise exposure of silver halide emulsions sensitized in this
way can be performed by means of lasers emitting below 500 nm e.g. an argon
laser e~itting at 488 nm. A particular advantage in the case of image-wise
exposure of direct-positive silver halide emulsions sensitized with such dyes
and used for the production of printing plates according to the DTR-process
in general is that an economical and quick exposure by laser under yellow
safeligLI conditions is possible, since only the areas of the direct-positive
silver ~alide emulsions that correspond with the finally obtained printing
areas o~ the printing plate have to be exposed and not the background areas.
~he s lver halide emulsions may contain the usual stabilizers e.g.
homopol-~ or salt-like compounds of mercury with aromatic or heterocyclic
rings s ch as mercaptotriazoles, simple mercury salts, sulphonium mercury
double salts and other mercury compounds. Other suitable stabilizers are
azainde-es, preferably tetra- or penta-azaindenes, especially those
substit~ted with hydroxy or amino groups. Compounds of this kind have been
described by Birr in Z. Wiss. Photogr. Photophys. Photochem. 47, 2-27 (1952).
~ t~
~4 GV1735
Other suitable stabilizers are i.a. heterocyclic mercapto compounds e.g.
phenylmercaptotetrazole, quaternary benzothia~ole derivatives, and
benzotriazole.
The silver halide emulsions may comprise other ingredients e.g. antifogging
agenl;s, developers and/or development accelerators, wetting agents, and
hardeners. Optionally, the silver halide emulsions may comprise matting
agen1s or spacing agents e.g. finely divided silica particles and polymer
beads as described US-A 4,614,708, to promote an effective vacuum suction of
the photosensitive material in vacuum contact exposure units.
Whereas according to known methods in the art it is indeed customary to
substantially harden the silver halide emulsions, the binder of which usually
is gelatin, to prevent an undesired transfer of gelatin to the aluminium
foil, hardening is not necessary according to the present invention. The
transfer of gelatin to the aluminium foil indeed gives rise to the above
describe~ disadvantages. The intermediate layer actually prevents the binder
of the silver halide emulsion or emulsions from being transferred to the
aluminiun foil or substantially reduces such transfer. The hardening degree
of the silver halide emulsion layer can thus be adjusted at wish.
The silver halide emulsion may comprise light-screening dyes that absorb
~0 scatterir,g light and thus promote the image sharpness and, as a consequence
thereof, the sharpness of the f;nal printed copy.
Light-~bsorbing dyes that can be ùsed as light~screening dyes have been
described in i.a. ~S-A 4,092,168, US-A 4,311,787, DE-A 2,453,217, and GB-A
7,907,44~. Alternatively, light-absorbing dyes can be incorporated into a
thin supplemental intermediate layer provided between said at least one
silver hzlide emulsion layer and said intermediate layer. Again, the
light-screening dyes or light-absorbing dyes can be chosen depending upon the
desired -bsorption spectrum of the layer comprising them.
More c-tails about the composition, preparation and coating of silver
halide e~ulsions can be found in e.g. Product Licensing Index, Vol. 92,
December i971, publication 9232, p. 107-lO9.
As an interesting variant the silver halide emulsion may consist of a first
photosensitive direct-positive or negative silver halide emulsion in which a
normal l-lent image is formed upon image-wise exposure and a second low-speed
silver h lide emulsion whose speed is so low that no or almost no latent
image is formed therein. When the low-speed silver halide emulsion and the
photosencitive silver halide emulsion are coated to form different layers,
the res~ ting emulsion layers are arranged in such a way that the low-speed
emulsion is remotest from the aluminium foil. It is also possible to coat
25 GYl735
one single layer comprising a mixture of said photosensitive silver halide
emulsion and said low-speed silver halide emulsion.
Thanks to the combination of photosensitive and low-speed emulsions a
higher amount of silver can migrate to form the silver image on the aluminium
foil. As a result, an enhanced contrast and a high resistance against
mechanical wear are obtained. It has indeed been established that upon
application of an aqueous alkaline solution to the image-wise exposed
photosensitive silver halide emulsion in the presence of a developing agent
and a silver halide solvent a silver image is formed therein and that the
unreduced silver halide or complexes formed thereof diffuse from the non-
silver image areas to said hydrophilic grained and anodized aluminium foil
and that additionally silver halide or complexes formed thereof diffuse from
the low-speed emulsion through the non-silver image areas of the
photosensitive silver halide emulsion also to the aluminium foil, the silver
lS image areas of the photosensitive emulsion forming a barrier for silver
halide or complexes of the low-speed emulsion that would also tend to migrate
towards the alumin;um foil. As a result, the silver halide or complexes
thereof diffusing from both the photosensitive emulsion and the low-speed
emulsion together build up said strengthened high-contrast silver halide on
the a1uminium foil.
The low-speed silver halide emulsion is a silver chloride-containing
emulsion, the speed of which is so low, that no visible image is formed
therein under the conditions of exposure and development of the
photosensitive silver halide emulsion layer. Inasmuch as the sensitivity of
the silver chloride-containing emulsion must be low, no second ripening or
after-ripening thereof is needed. The low-speed silver chloride-containing
emulsion, which is rinsed to be free of excess salts, preferably is a
fine-grain silver chloride-containing emulsion having a particle size in the
range of 50 to 500 nm.
The low-speed emulsion may be a pure silver chloride emu)sion or an
emulsion of mixed silver halides comprising silver chloride e.g. a silver
chlorobromide or chlorobromoiodide emulsion. However, the low-speed emulsion
preferably is a silver chloride emulsion for the greater part.
In case a mixture of low-speed emulsion and of imaging emulsion is coated
to form one single layer, the amount of low-speed emulsion may vary within
wide limits. Favourable results c~n be obtained when the ratio of low-speed
silver chloride-containing emulsion to image-forming emulsion, expressed in
parts by weight of silver nitrate, ranges from 10:1 to 1:1. The amount of
low-speed emulsion to be added depends i.a. on its own nature, on the type of
: ' - .
26 GV1735
image-forming emulsion used, and on the effect desired. It can be determined
easily by routineers in the art by making a few comparative tests.
When separate layers of low-speed emulsion and of imaging emulsion are
used, the ratio expressed in parts by weight of silver nitrate of said
different layers, also ranges from 10:1 to 1:1.
An optional supplemental intermediate layer, which may be present between
said at least one silver halide emulsion layer and said intermediate layer
comprising the hydrophobic polymer beads according to the present invention,
may incorporate one or more ingredients such as i.a. antihalation dyes or
pigment. developing agents, silver halide solvents, base precursors, and
anticorrosion substances.
With respect to the above-mentioned embodiment of the present invention,
according to which a temporary base is coated first with at least one silver
halide emulsion layer and next with said intermediate layer comprising
hydrophobic polymer beads, and according to which the resulting
photosensitive layer packet comprising said intermediate layer and said at
least one silver halide emulsion layer is transferred onto the wet
hydrophilic grained and ar,odized surface of an aluminium foil, the following
particulars can be given.
The adherence of said at least one silver halide emulsion layer to said
temporary base should be such that an easy stripping off from the temporary
base is possible after pressing said photosensitive layer packet against said
wet hydrophilic grained and anodized aluminium foil. Therefore, a relatively
hydropho~ic temporary base is used, which preferably is flexible and is made
of i.a. cellulose triacetate, polystyrene, polyester e.g. polyethylene
terephthalate, and copoly(vinyl acetate/vinyl chloride). Preferably, the
temporary base is an unsubbed cellulose triacetate or polyethylene
terephthalate fil~ base. The thickness of the cellulose triacetate or
polyethylene terephthalate film base may vary between wide limits, but
preferably is approximately 100 ~m.
The said at least one silver halide emulsion layer can be composed in such
a way th2t its adherence to the temporary base in wet state is less than that
in dry s;ate. Optionally, hygroscopic substances e.g. water-soluble organic
hygroscc~ic compounds such as glycerol, or wetting and/or plasticizing agents
can be cdded to said at least one silver halide emulsion layer to adjust its
adherence.
Other temporary bases having a repelling power for wet gelatin coatings are
e.g. a paper base coated with a polyethylene layer, a paper base impregnated
with wax. a paper base coated with a layer of cellulose nitrate, a paper base
C~
27 GV1735
coated with a layer of insolubjljzed polyvinyl alcohol, and a layer of
alginic acid insolubilized with an alkaline earth metal salt. Temporary
bases comprising a paper support should be removed before the photo-exposure,
whereas transparent film bases may remain during the photo-exposure and are
in that case removed afterwards.
The transfer of the transferable layers onto the aluminiu~ foil can be
carried out in an apparatus, in which the aluminium foil is moistened and the
wet aluminium foil and the photosensitive layer packet are pressed together
between rollers. An apparatus particularly suitable for use in transferring
transferable layers from the temporary base to the wet aluminium foil has
been described in US-A 4,701,401. Suitable apparatus for that purpose are
the AGFAPROOF ~R unit and the AGFAPROOF TR S unit, both marketed by
AGFA-GE~AERT, Belgium.
A wide choice of cameras for exposing the photosensitive silver halide
emulsion exists on the market. Horizontal, vertical and darkroom type
cameras and contact-exposure apparatus are available to suit any particular
class of reprographic work. The photosensitive silver halide emulsion(s)
used in the layer assemblages according to the present invention can also be
exposed with the aid of i.a. laser recorders and cathode rays tubes.
The development and diffusion transfer are effected with the aid of an
aqueous alkaline solut1on in the presence of at least one developing agent
and at least one silver halide solvent. The developing agent(s) and/or the
silver halide solvent(s) can be incorporated in the aqueous alkaline solution
and/or in said at least one silver halide emulsion layer and/or in said
intermediate layer and/or in a supplemental hydrophilic colloid layer in
water-permeable relationship with said at least one silver halide emulsion
layer. The latter supplemental hydrophilic colloid layer can be coated on
top of said at least one silver halide emulsion layer remotest from said
aluminium foil e.g. it can be provided between said temporary base and said
at leas; one silver halide emulsion layer.
The silver halide solvent can also be incorporated at least in part in the
silver-receptive stratum coated on the aluminium foil. When the aqueous
alkaline solution does not comprise the developing agent(s), it is merely an
activating liquid that is capable of dissolving the developing agent(s)
contain~d in one of the layers.
The conventional developing agents for DTR-processing are a
hydroquinone-type compound in combination with a secondary developing agent
of the class of l-phenyl-3-pyrazolidinone compounds and p-N-methyl-
minophenol. Particularly useful l-phenyl-3-pyrazolidinone developing agents
,
28 GV1735
are l-phenyl-3-pyrazolidinone, 1-phenyl-4-methyl-3-pyrazolidinone, l-phenyl-
4-ethyl-5-methyl-3-pyrazolidinone, and 1-phenyl-4,4-dimethyl-3-
pyrazolidinone.
The hydroquinone-type compound is e.g. hydroquinone, methyl-hydroquinone,
or chlorohydroquinone.
The silver halide solvent, which acts as a complexing agent for silver
halide, preferably is a water-soluble thiosulphate or thiocyanate e.g.
sodium, potassium, or ammonium thiosulphate and sodium, potassium, or
ammonium thiocyanate.
Other suitable silver halide solvents are i.a. sulphites, amines, and such
alkanolamines like e.g. ethanolamine, diethanolamine, triethanolamine,
diisopropanolamine, 2-methyl-aminoethanol, 2-ethyl-aminoethanol,
2-dimethylaminoethanol, 2-diethyl-aminoethanol, 2-methyl-2-amino-1-propanol,
I-diethylamino-2-propanol, 3-diethylamino-1-propanol, isopropylaminoethanol,
3-amino-1-propanol, 2-methyl-2-amino-1,3-propanediol, benzyldiethanolamine,
and 2-(hydroxymethyl)-2-amino-1,3-propanediol.
Further suitable silver halide solvents are those disclosed in "The Theory
of the Photographic Process" 4th Ed., edited by T.H.James, pages 474-475.
Further interesting silver halide solvents have been described in i.a. US-A
2,857,276 and 4,297,430. Among these are cyclic imide compounds such as e.g.
uracil and 5,5-dialkylhydantoins. Other suitable silver halide solvents are
the alkyl sulfones.
Combinations of different silver halide solvents can be used and it is even
possible to incorporate at least one silver halide solvent into a suitable
layer and add at least one other silver halide solvent to the developing
solution.
The following quantitative ranges given for the developing agents, silver
halide solvents, and sulphite apply to the amount of these compounds present
as solutes in the aqueous alkaline solution during the D~R-processing,
whether these compounds make part of the aqueous alkaline solution, which in
that particular case actually is an aqueous alkaline developing solution, or
were dissolved from the layers containing them upon application thereto of
the aqueous alkaline solution, in which case it is an activating solution.
A suitable quantitative combination of hydroquinone and at least one
secondary developing agent of the class of 1-phenyl-3-pyrazolidinones and
p-N-methyl-aminophenol comprises hydroquinone in an amount not lower than
0.078 mole per litre of aqueous alkaline solution and the secondary
developing agent(s) in an amount not lower than 0.0080 mole per litre, the
molar ratio of hydroquinone to said secondary developing agent(s) not being
'`` ~ '`j jl1 `~ `,
29 GV1735
lower than 9.7. Preferred amounts of hydroquinone are in the range of 0.05
mole to 0.25 mole per litre and preferred amounts of secondary developing
agent(s) in the range of 1.8 x 10~3 to 2.0 x 10-2 mole per litre.
lhe aqueous alkaline solution may comprise sulphite e.g. sodium sulphite in
an amount ranging from 40 g to 180 9 per litre, preferably from 60 to 160 9
per litre, and thiosulphate and/or thiocyanate in an amount ranging from 5 g
to 20 9 per litre.
The pH of the aqueous alkaline solution preferably is at least 12, but
depends on the type of silver halide emulsion material to be developed,
intended development time, and processing temperature.
The processing conditions such as temperature and time may vary within
broad ranges provided the mechanical strength of the materials to be
processed is not adversely influenced and no decomposition takes place.
The aqueous alkaline solution may comprise such alkali-providing substances
like hydroxides of sodium and potassium, alkali metal salts of phosphoric
acid and/or silicic acid e.g. trisodium phosphate, orthosilicates,
metasilicates, hydrodisilicates of sodium or potassium, and sodium carbonate.
The alkali-providing substances can be substituted in part or wholly by
alkanolæmines.
The aqueous alkaline solution may comprise at least one alkanolamine to
improve its life-time and performance for the DTR-process. Suitable
alkanolamines are i.a. N,N,N-triethanolamine, 2-amino-2-hydroxymethyl-
propan-1,3-diol, N-methyl-diethanolamine, N-ethyl-diethanolamine,
diisopropanolamine, N,N-diethanolamine, 3,3'-amino-dipropanol, 2-amino-
2-methyl-propan-1,3-diol, N-propyl-diethanolamine, N-butyl-diethanolamine,
N,N-dimcthyl-ethanolamine, N,N-diethyl-ethanolamine,
N,N-diethyl-isopropanolamine, l-amino-propan-2-ol, N-ethanolamine,
N-methyl-ethanolamine, N-ethyl-ethanolamine, 3-amino-propanol, 4-amino-
butanol. and 5-amino-pentan-1-ol.
According to a preferred embodiment described in Research Disclosure 27939
(July lC87) pages 450-451 the aqeuous alkaline solution comprises at least
one tertiary alkanolamine having a pKa value higher than 8.5. More
preferably, the solution comprises two or more tertiary alkanolamines having
a pKa v~lue higher than 9Ø
The aqueous alkaline solution may further comprise silver-image
hydrophobiz;ng compounds e.g. heterocyclic mercapto compounds. The addition
of heterocyclic mercapto compounds more particularly a mercapto-1,3,4-
thiadiazole to a developing liquid for the purpose of hydrophobizing the
silver i~age formed according to the DTR-process on an aluminium foil has
h ~
30 GV1735
been described already in DE-A 1,228,927. Other suitable
mercapto-thiadiazoles that can be added to the aqueous alkaline solution have
been disclosed in US-A 4,5~3,410. Another suitable hydrophobizing compound
is 2-mercapto-5-heptyl- oxa-3,4-diazole.
These hydrophobizing compounds can be added to the aqueous alkaline
solution in an amount of preferably 0.1 to 3 9 per litre and preferably in
admixture with l-phenyl-5-mercaptotetrazole, the latter compound being used
in amounts of e.g. 50 mg to 1.2 9 per litre of solution, which may contain a
minor amount of ethanol to improve the dissolution of said compounds.
The aqueous alkaline solution may comprise other ingredients such as e.g.
oxidation preservatives, a compound releasing bromide ions,
calcium-sequestering compounds, anti-sludge agents, and hardeners including
latent hardeners.
Regeneration of the aqueous alkaline solution according to known methods
is, of course, possible, whether the solution incorporates developing
agent(s) and/or silver halide solvent(s) or not.
The de~elopment may be stopped - though this is often not necessary - with
a so-called stabilization liquid, which actually is an acidic stop-bath
having a pH preferably in the range of 5 to 6.
Buffered stop bath compositions comprising a mixture of sodium dihydrogen
orthophosphate and disodium hydrogen orthophosphate 1nd having a pH in said
range are preferred.
The development and diffusion transfer can be initiated in different ways
e.g. by rubbing with a roller, by wiping with an absorbent means e.g. with a
plug of cotton or sponge, or by dipping the material to be treated in the
liquid composition. Preferably, they proceed in an automatically operated
apparatus such as the CR 430, CR 740, or CR 1100-Processors marketed by
AGFA-GEVAERT, Belgium. They are normally carried out at a temperature in the
range of 18 C to 30 C.
After formation of the silver image on the aluminium foil the excess of
alkaline solution still present on the foil is eliminated, preferably by
guiding the foil through a pair of squeezing rollers.
According to a preferred embodiment of uncovering the imaged aluminium foil
the intermediate layer and the emulsion layer(s) wet with alkaline solution
or moistened with unheated water or unheated aqueous medium applied
subsequent to the removal from said alkaline solution are separated from the
imaged aluminium foil by an airstream directed on an edge of said monosheet
layer assemblage.
According to another embodiment of uncovering the imaged aluminium foil the
31 GV1735
developed monosheet layer assemblage is rinsed with unheated water or an
unheated aqueous medium so that the intermediate layer and the emulsion
layler~s) are removed from the imaged aluminium foil.
According to another embodiment of uncovering the imaged aluminium foil the
S intermediate layer and the emulsion layer(s) can be removed also by slightly
agitating the developed monosheet layer assemblage while being dipped in
unheated water or unheated aqueous medium or by slightly agitating a tray
comprising unheated water or unheated aqueous medium in which said developed
monosheet layer assemblage has been immersed. According to a convenient
method of rinsing away said layers, the developed monosheet layer assemblage
is held under a spray or jet of unheated water or unheated aqueous medium.
The mechanical pressure of a water jet or spray directed onto these layers
suffices to detach them from the aluminium foil. The unheated aqueous medium
used to detach the intermediate layer and the emulsion layer(s) by rinsing
may comprise ingredients such as i.a. weak acidifying agents, wetting agents,
and hardeners including latent hardeners.
According to a further embodiment of uncovering the imaged aluminium foil
the monosheet ~layer assemblage is pressed with its side showing the emulsion
layer(s) while being moistened with unheated water or with unheated aqueous
medium against a receiving sheet such as e.g. a paper or film base coated
with a hardened gelatin layer comprising a matting agent or against a porous
web as described in Research Disclosure 23017 (June 1983) pages 223-4 and
said imaged aluminium foil is peeled off from the emulsion layer(s) and the
intermediate layer, which are supported by the receiving sheet and strongly
adhere thereto. According to an alternative embodiment the emulsion layer(s)
and the intermediate layer can also be removed by scraping off or by wiping
off e.g. with a sponge.
According to an alternative method of separating said at least one silver
halide emulsion layer and said intermediate layer from the imaged hydrophilic
grained and anodized surface, the monosheet layer assemblage is placed with
its side showing said at least one silver halide emulsion layer during the
period of time that starts with the application of said aqueous alkaline
solution and ends with said formation of a silver image on said hydrophilic
grained and anodized surface in contact with a receiving means, said at least
one silver halide emulsion layer and said intermediate layer after said
formation of a silver image while still being wet with said aqueous alkaline
solution. having an adherence to said receiving means that is stronger than
that to the imaged hydrophilic grained and anodized surface. Next, said at
least one s;lver halide emulsion layer and said intermediate layer adhering
32 GV1735
to and supported by said receiving means are peeled off from the imaged
hydrophilic grained and anodized surface. According to this method the
emulsion layer(s) and intermediate layer are separated from the imaged
hydrophilic grained and anodized surface after the silver image has been
for~led thereon and while they are still wet with said aqueous alkaline
solution. For carrying out this process the photo-exposed monosheet layer
assemblage and a receiving means e.g. a paper or film base coated with a
hardened gelatin layer comprising a matting agent can be introduced in a
processing device through different inlet openings and after completion of
the development and of the image transfer pressed together in the nip of two
rollers. When the contacting monosheet layer assemblage and the receiving
means leave the nip between the two rollers, a suitable and appropriately
mounted separating blade can separate the imaged aluminium foil from the
receiving means, to which said intermediate layer and said emulsion layer(s)
remain adhering. As a consequence the thus obtained bared aluminium foil
carrying the transferred silver image does not need any further rinsing,
although rinsing with water is possible, of course, if desired.
It is common practice in the art to subject the imaged surface of the
aluminium foil to a chemical treatment that increases the hydrophilicity of
the non-silver image parts and the oleophilicity of the silver image.
This chemical after-treatment is preferably carried out with a lithographic
composition often called fixer, which comprises at least one compound
enhancing the ink-receptivity and/or lacquer-receptivity of the silver image,
and also comprises at least one compound that improves the ink-repelling
characteristics of the aluminium. In US-A 4,563,410 an interesting method
for hydrophobizing the silver image has been described.
Suitêble ingredients for the fixer are e.g. organic compounds containing a
mercapto group such as dodecylmercaptans, benzothiazole-2-thiol,
1,3,4-thiadiazole-2-thiol, 1-phenyl-1-H-tetrazole-5-thiol, triazinethiols
e.g. 1-octyl-1,2,4,5-tetrahydro-S-triazine-5-thiol, and compounds containing
a thioacid or a thioamide group. Additives improving the oleophilic
ink-repellency of the bar~ anodized aluminium foil areas are e.g.
carbohydrates such as acid polysaccharides like gum arabic,
carboxy~thylcellulose, sodium alginate, propylene glycol ester of alginic
acid, hrdroxyethyl starch, dextrin, hydroxyethylcellulose, polyvinyl
pyrrolidone, polystyrene sulphonic acid, and polyvinyl alcohol. Optionally,
hygroscopic substances e.g. sorbitol, glycerol, tri(hydroxyethyl)ester of
glycerol, and turkey red oil may be added. Furthermore, phosphoric acid and
cationic surface-active compounds such as hexadecyl trimethyl ammonium
33 GV1735
bromide can also be added to the fixer. A suitable fixer is e.g. a
composition comprising a solution of
1-octyl-1,2,4,5-tetrahydro-S-triazine-5-thiol in acetone or a suspension
thereof in a solution of gum arabic. ~ther suitable fixers have been
described in i.a. US-A 4,062,682 and US-A 4,563,410.
At: the moment the treatment with the fixer is started the surface carrying
the silver pattern may be in dry or wet state. In general, the treatment
with the fixer does not take long, usually not longer than about 30 seconds
and it may be carried out immediately after the processing and uncovering
steps.
~he fixer can be applied in different ways such as by rubbing with a
roller~ by wiping with an absorbent means e.g. with a plug of cotton or
sponge, or by dipping the material to be treated in the fixer. The
image-hydrophobizing step of the printing plate may also proceed
automatically by conducting the printing plate through a device having a
narrow channel filled with the fixer and conveying the printing plate at the
end of the channel between two squeezing rollers removing the excess of
liquid. Suitable devices for automatic treatment with a fixer are the CRF 45
and CRF 85 fixing units, both marketed by AGFA-GEVAERT, Belgium.
As soon as the aluminium foil carrying the silver image has been treated
with the fixer, it is ready to be inked and used as a printing plate so that
a treatment thereof with a lacquer composition for strengthening the printing
areas is not necessary. The printing plate has to be wet at the stage the
greasy printing ink is applied. This is a generally known fact in the art
and it is usual to apply an aqueous liquid before the printing ink is
applied. This can be done by means of a wet sponge or by means of the
fountain arrangements (dampening system) of the printing machine.
For the production of long-run printing plates requiring more than 100,000
prints 2 second after-treatment consisting in applying a lacquer onto the
silver mage areas may be advisable. For this purpose, lacquers based on
phenol- or cresol-formaldehyde alkyd resins and/or epoxyresins are commonly
used.
Anoth-r useful resin for such a lacquer is a mixture of homopolymers and
copolym~rs of styrene, ortho-, meta-, or para-vinyltoluene and indene units.
Cyclohexanone can be used as solvent and linseed oil as plasticizer.
Examples of suitable lacquer compositions have been described in i.a. GB-A
968,706 and 1,071~163 and in CA-A 686,284.
A lithographic composition in which the fixer and lacquer are combined to
one composition has been described in e.g. GB-A 969,072.
34 GV1735
The following examples illustrate the present invention.
EXAI~PLE 1
Three identical photosensitive monosheet layer assemblages were made as
follows-
An aluminium foil having a thickness of 0.20 mm was grained, anodized, and
sealed according to the method described in Example 1 of US-A 3,861,917. The
centre line average value obtained by the graining was 0.5 ~m. The
anodization layer having a weight of 2.7 9 per m2 was coated with a
silver-receptive stratum from a silver sol in water comprising no binder,
prepared according to the Carey Lea method, the resulting stratum having a
weight in dried condition of 4 mg of silver per m2.
The silver-receptive stratum was covered with a substantially unhardened
photosensitive negative-working cadmium-free gelatin silver chlorobromoiodide
emulsion layer (97.98 / 2 / 0.02 mol%), the silver halide being coated in an
amount corresponding to 2.40 9 of silver nitrate per m2 and the gelatin
content of the resulting photosensitive emulsion layer being 1.58 g/m2.
The resulting 3 identical photosensitive monosheet layer assemblages are
called rComparison A", "Comparison B", and "Comparison C" respectively
hereinafter.
A photosensitive monosheet layer assemblage called "Invention" was then
made in the same way as described for Comparison A, B, and C, with the only
difference that an intermediate layer comprising hydrophobic polymer beads
was provided between the silver-receptive stratum and the photosensitive
emulsion layer. The intermediate layer was coated on the dry
silver-receptive stratum from a composition comprising 50 ml of a 20%
dispersion of polymethyl methacrylate beads in a mixture of equal volumes of
water and ethanol, which beads have been prepared as described in Preparation
example 1 hereinbefore and have an average diameter of 1.0 ~m, 2.5 9 of
Helioechtpapierrot BL (trade mark for a dye sold by BAYER AG, D-5090
Leverkusen, West-Germany3, 2.5 9 of saponine, 1.25 9 of sodium
oleylmethyltauride, and 300 ml of demineralized water in such a way that the
resulting dried layer comprised 0.5 9 of polymethyl methacrylate beads per
m2.
The 4 photosensitive monosheet layer assemblages were exposed identically
through a contact screen in a process-camera and immersed for 8 s at 25 C in
a freshly made developing solution having the following ingredients in a CR
430 processor marketed by AGFA-GEVAERT, Belgium :
GY1735
carboxymethylcellulose 18 9
sodium hydroxide 22.5 9
anhydrous sodium sulphite 120 9
hydroquinone 20 9
1-phenyl-3-pyrazolidinone 3 g
potassium bromide 0.75 9
anhydrous sodium thiosulphate 7.5 9
ethylene diamine tetraacetic acid tetrasodium salt 2 9
demineralized water to make 1000 ml
pH (25 C) = 13
The initiated diffusion transfer was allowed to continue for 30 s to form a
silver image on the aluminium foil.
To remave the developed silver halide emulsion layer and the intermediate
layer (Invention) from the imaged aluminium foil, each of the 4 developed
monosheet layer assemblages was rinsed for 30 s with a water jet. In case
the emulsion layer did not detach with unheated water the test was repeated
with a fresh identical layer assemblage and the temperature of the rinsing
water was enhanced. The temperature used for each of the 4 monosheet layer0 assemblages is specified in Table 1 hereinafter.
Next, the imaged surface of the aluminium foil was rubbed with one of the
fixers A or 8 as specified in Table 1 hereinafter to enhance the
water-receptivity of the non-image areas and to make the image areas
oleophilic ink-receptive. Fixer A had the following composition :
10% aqueous n-hexadecyl trimethyl ammonium chloride 25 ml
20% aqueous solution of polystyrene sulphonic acid 100 ml
potassium nitrate 12.5 g
citric acid 20.0 9
1-phenyl-5-mercaptotetrazole 2.0 9
sodium hydroxide 5 5 g
water to make 1000 ml
pH (20 C) = 4
The composition of Fixer B was identical to that of Fixer A with the only5 difference that Fixer B additionally comprised 20 9 of trypsin per litre.
Each of the printing plates obtained was placed on an Heidelberg offset
printing press, type GT0, marketed by HEIDELBERGER DRUCKMAS~HINEN AG, D-6900
Heidelberg, West-Germany.
Each printing plate was inked with a commercially available KAST + EHINGER
h) ~
36 GV1735
123W ink and then used for printing copy sheets of paper.
The lithographic quality of each 25th print was evaluated as for its
lithographic quality~ The results of this evaluation are given in the
following Table 1. Four levels of appreciation of the lithographic quality
were attributable. The term "perfect" was used when the image printed on the
paper was an exact reproduction of the silver image on the printing plate,
had a perfect density, and showed no deficiencies such as pin-holes. The
term "good" could be used when the image was an almost exact reproduction of
the silver image on the printing plate, had an acceptable density, and showed
only few deficiencies. The term "bad" was used when the printed image was a
recognizable reproduction, but had an unpleasantly weak density, and showed
many deficiencies. The term "very bad" was used when the printed image was
unrecognizable and useless.
TABLE 1
Temperature of Fixer Lithographic
rinsing water quality
Comparison A 20 C A very bad
Comparison B 50 C A bad
Comparison C 50 C B (trypsin) perfect
Invention 20 C A perfect
With the "Invention" printing plate a run of 100tO00 prints on paper was
carried out. The quality of the last print was still perfect. No abnormal
wear or decline in image sharpness was visible.
EXAMPLE 2
A series of photosensitive monosheet layer assemblages comprising an
intermediate layer comprising hydrophobic polymethyl methacrylate beads
prepared as described in Preparation example 1 hereinbefore and having an
average diameter of 1.0 ~m were made as described in Example 1, the only
differenliation between the photosensitive monosheet layer assemblages being
that the weight of polymethyl methacrylate beads present per m2 of dried
intermediate layer was different as indicated in Table 2 hereinafter.
The intermediate layer was covered with a photosensitive silver
chlorobromoiodide emulsion layer as described in Example 1.
The procedure of exposure, DTR-development, treatment with fixer A, and
37 GV1735
printing described in Example 1 was repeated for each of the layer
assemblages.
The lithographic quality of each 25th print was evaluated as described in
Example 1. The coating weight of the intermediate layer and the results of
this evaluation are given in Table 2. Furthermore, the sharpness of the
silver image on the imaged aluminium foil and of each 25th print obtained
therefrom is measured with the aid of the FOGRA Precision Measuring Strip PMS
I as described in Fogra Praxis Report No 34 published by Deutsche
Forschungsgesellschaft fur Druck- und Reproduktionstechnik, P.O. 800469, 8000
Munich 80 - W.Ger~any.
Table 2 also compares the yield of silver (expressed in silver nitrate).
By yield of silver is meant the percent ratio by weight of transferred silver
present on the aluminium foil versus the silver of the transferable silver
ucomplexes present in the emulsion layer. In the column entitled "wash-off"
an appreciation is given for the removability of the intermediate layer and
the silver halide emulsion layer with a jet of unheated water.
TABLE 2
Coating weight Sharpness Yield of wash-off Lithographic
of beads (g/m2) Printing platesilver quality
0.0 6 ~m 55% very bad very bad
0.2 ~-8 ~m 59% good good
0.5 8 ~m 51% good perfect
1.0 8 ~m 50% perfect perfect
EXAMPLE 3
A photosensitive monosheet layer assemblage was made as follows.
An aluminium foil coated with a silver-receptive stratum, both as described
in Example 1, was covered in the given sequence at the side of the stratum
with an lntermediate layer and an emulsion layer as described in Example 1.
The intermediate layer was coated on the dry silver-recept;ve stratum from a
composition comprising 50 ml of a 20 % dispersion of polymethyl methacrylate
beads in a mixture of equal volumes of water and ethanol, which beads have
been prepared as described in Preparation example 1 hereinbefore and have an
average diameter of 1.0 ~m, 50 ml of a 5% aqueous solution of polyvinyl
alcohol having a molecular ~eight of 10,000 and comprising 95 mol% of vinyl
3 '' ~ ' f
38 G~1735
alcohol units and 5 mol% of vinyl acetate units, 2.5 g of Helioechtpapierrot
BL (trade mark for a dye sold by BAYER AG, D-5090 Leverkusen, West-Germany),
2.5 9 of saponine, 1.25 9 of sodium oleylmethyltauride, and 300 ml of
demineralized water in such a way that the resulting dried layer comprised
S 0.5 9 of polymethyl methacrylate beads and 0.125 9 of polyvinyl alcohol per m2.
The procedure of exposure and DTR-development described in Example 1 was
repeated. The developed silver halide emulsion layer and the intermediate
layer while still being wet with aqueous alkaline developing solution were
removed from the imaged aluminium foil with an airstream as described in
Example 1. Next, the imaged surface of the aluminium foil was rinsed with
water and rubbed with fixer A described in Example 1. Printing with the
printing plate obtained was then carrried out as described in Example 1 and
the lithographic quality of the 25th print was evaluated also as described in
Example 1. The results are listed in Table 3.
TAeLE 3
average diameter Yield of wash-off Lithographic
of beads silver quality
1.0 51% very good perfect
