U.S. patent number 3,904,412 [Application Number 05/402,883] was granted by the patent office on 1975-09-09 for method for the preparation of planographic printing plates from silver images.
This patent grant is currently assigned to Agfa-Gevaert N.V.. Invention is credited to Robert Joseph Pollet, Francis Jeanne Sels, Frans Philomena Serrien, Bernard Hippoliet Tavernier.
United States Patent |
3,904,412 |
Serrien , et al. |
September 9, 1975 |
Method for the preparation of planographic printing plates from
silver images
Abstract
A method for the preparation of a planographic printing plate
wherein a sheet material comprising an outer hardenable hydrophilic
colloid layer on the surface of which is concentrated a silver
image which has been formed at that surface from complexed silver
halide by silver complex diffusion transfer process, is treated
with an aqueous lithographic fixer having a pH-value in the range
from about 4.5 to about 7.2 and containing : 1. an iron(III)
ammonium salt of an aliphatic dicarboxylic acid which at least
superficially oxidizes said silver image 2. a precipitating agent
for silver ions, and 3. an organic nitrogen-containing compound,
which reacts with said oxidized silver at the surface of the silver
image to render said image hydrophobic and contains a structural
part corresponding to the following tautomeric structure :
##EQU1##
Inventors: |
Serrien; Frans Philomena
(Wilrijk, BE), Tavernier; Bernard Hippoliet (Edegem,
BE), Pollet; Robert Joseph (Vremde, BE),
Sels; Francis Jeanne (Kontich, BE) |
Assignee: |
Agfa-Gevaert N.V. (Mortsel,
BE)
|
Family
ID: |
10438626 |
Appl.
No.: |
05/402,883 |
Filed: |
October 3, 1973 |
Foreign Application Priority Data
|
|
|
|
|
Oct 4, 1972 [GB] |
|
|
45792/72 |
|
Current U.S.
Class: |
430/204; 430/302;
101/466; 430/460 |
Current CPC
Class: |
C07D
233/42 (20130101); C07D 513/04 (20130101); C07D
235/28 (20130101); G03F 7/066 (20130101) |
Current International
Class: |
C07D
235/00 (20060101); C07D 235/28 (20060101); C07D
233/42 (20060101); C07D 513/04 (20060101); C07D
513/00 (20060101); C07D 233/00 (20060101); G03F
7/06 (20060101); G03C 005/54 (); G03F 007/02 ();
B41M 005/00 (); B41N 003/00 () |
Field of
Search: |
;96/29L,33,6B,6F
;101/466 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Torchin; Norman G.
Assistant Examiner: Schilling; Richard L.
Attorney, Agent or Firm: Daniel; William J.
Claims
We claim:
1. A method for preparing a planographic printing plate wherein a
sheet material comprising an outer hardenable hydrophilic colloid
layer on the surface of which is concentrated a silver image which
has been formed at that surface from complexed silver halide by
silver complex diffusion transfer process is contacted with an
aqueous lithographic fixer having a pH-value in the range from
about 4.5 to about 6.2 and containing:
1. an iron(III) ammonium salt of an aliphatic dicarboxylic acid
which at least superficially oxidizes said silver imgage,
2. a compound yielding iodide ions for precipitating said silver
ions, and
3. an organic heterocyclic nitrogen compound having in a 5- or
6-membered ring a thione group corresponding to the following
tautomeric structure: ##EQU19## for rendering said superficial
oxidized silver image hydrophobic.
2. A method according to claim 1, wherein said lithographic fixer
contains as said iron(III) salt from 20 to 120 g of iron(III)
ammonium malonate per litre.
3. A method according to claim 1 wherein said heterocyclic nitrogen
compound includes a sulphonic acid group in free acid or salt
form.
4. A method according to claim 1, wherein said heterocyclic
compound has the following structural formula: ##EQU20##
5. A method according to claim 1, wherein the said lithographic
fixer contains from 0.5 to 15 g of said organic thiol or thione
compound per litre.
6. An aqueous lithographic fixer having a pH generally in the range
of about pH 4.5-6.2 containing:
1. an iron(III) ammonium salt of an aliphatic dicarboxylic
acid,
2. a compound yielding iodide ions for precipitating said silver
ions, and
3. an organic heterocyclic nitrogen compound having in a 5- or
6-membered ring a thione group corresponding to the following
tautomeric structure: ##EQU21##
7. An aqueous lithographic fixer according to claim 6 wherein said
heterocyclic nitrogen compound includes a sulfonic acid group in
free acid or salt form.
8. An aqueous lithographic fixer according to claim 6, wherein the
heterocyclic nitrogen compound corresponds to the following
structural formula: ##EQU22##
9. An aqueous lithographic fixer according to claim 6, wherein said
fixer contains a water-miscible solvent that improves the
dissolving of the mercapto or thione compound in the fixer.
10. A lithographic fixer according to claim 6 of the following
composition: iron(III) salt in the form of iron(III) ammonium
malonate 20 g to 120 g SN .angle..angle. NaO.sub.3 S--CNH 0.5 g to
15 g .vertline..vertline. ----N----C=S n-octylamine 10 g to 75 ml
potassium iodide 5 g to 40 g organic solvent(s) n-propanol 0 ml to
200 ml ethylene glycol monoacetate 0 ml to 150 ml water to make 1 l
pH adjusted to 6-6.2 by means of malonic acid and ammonium
hydroxide.
Description
The present invention relates to a method for the preparation of
planographic printing plates by converting silver images into
hydrophobic ink-receptive images and to liquid compositions for
improving the ink-receptivity of the silver images.
It is known to produce planographic printing plates of improved
quality by the use of a sheet material comprising an outer
hydrophilic colloid layer, on the surface of which there is
concentrated a silver image that has been formed on this surface
from complexed silver halide by a silver complex diffusion transfer
process.
According to the method for the preparation of planographic
printing plates described in the United Kingdom Patent
Specification 1,241,661 the thus prepared silver image is rendered
hydrophobic with an aqueous liquid, called "lithographic fixer",
which liquid has a pH-value between 7 and 12 and contains (1)
hexacyanoferrate(III) ions, by means of which said silver image is
at least superficially oxidized, and (2) an organic compound that
is at least in part dissolved in said liquid and which reacts with
said oxidized silver to render said image hydrophobic.
Although the lithographic fixer described in the above-mentioned
Patent Specification has particularly favourable hydrophobizing
properties some disadvantages are associated therewith. For example
the cyanoferrate(III) ion under the defined condition of a
relatively high pH is not inert with respect to the
mercapto-compounds, which are the preferred compounds for the
purpose cited under the above item (2). Indeed, as a consequence of
the presence of the mercapto compound some of the
hexacyanoferrate(III) ions become reduced and the thus formed
cyanoferrate(II) ions form a blue precipitate with the excess
cyanoferrate(III) ions. Further, also during the preparation of the
printing plate by the oxidation of the silver image
hexacyanoferrate(II) ions are formed, causing the formation of a
blue precipitate and as a result thereof a more or less pronounced
staining of the image background.
A further disadvantage associated with the use of a lithographic
fixer containing hexacyanoferrate(III) ions resides in the fact
that these ions have to be kept carefully out of contact of acids,
for acids set free the highly toxic hydrogen cyanide.
With reference to the relatively high pH (11-12) of the
lithographic fixer special precautionary measures have to be taken
for the operating personnel and only highly alkali-resistant
machine parts can be used.
It is an object of the present invention to provide a lithographic
fixer of improved stability and presenting a good ink-receptivity
to silver images.
It has been found that said object can be attained by means of an
aqueous lithographic fixer having a pH-value in the range of about
4.5 to about 7.2 and containing:
1. an iron(III) ammonium salt of an aliphatic dicarboxylic acid as
oxidizing agent for the silver image,
2. a precipitating agent for silver ions and
3. an organic nitrogen-containing compound having a thiol group or
in its tautomeric structure a thione group as represented in the
following tautomeric structural parts: ##EQU2## capable of reacting
with silver ions present at the surface of a silver image and
hydrophobizing the silver image.
In order to avoid that during the oxidation of the silver image
with the organic iron(III) ammonium salt, silver ions are accepted
by the fixer solution and removed from the silver image portions so
that they are lost for the hydrophobizing process, a compound is
present in the fixer solution that keeps the silver ions formed at
the place where they have been formed. For this purpose use is made
of a substance that precipitates silver ions in the form of a
poorly water-soluble silver salt.
A preferred precipitating agent is therefor a substance yielding
iodide ions e.g. potassium iodide, forming the very poorly soluble
silver iodide.
A preferred lithographic fixer combination of the present invention
contains in admixture with the above-cited compounds (1) to (3) an
aliphatic amino compound comprising at least 4 unbranched carbon
atoms, preference being given to n-octylamine. The pH of the fixer
is kept within the above-cited range and preferably at 6 to 6.2 by
means of the dicarboxylic acid used for preparing the iron(III)
ammonium salt thus preventing the precipitation of Fe(OH).sub.3. A
suitable amount of aliphatic amino compound is in the range of 10
to 75 ml per litre.
A preferred iron(III) salt for use according to the present
invention is iron(III) ammonium malonate. A preferred lithographic
fixer contains from 20 to 120 g of iron(III) ions present in the
form of iron(III)ammonium malonate.
Other suitable iron(III) ammonium salts are derived from the
aliphatic dicarboxylic acids: oxalic acid, maleic acid and fumaric
acid.
Preferred thione compounds correspond to the following structural
formulae:
1. Compound 1 is prepared as described in DT-OS 1,946,263 ##EQU3##
2. Compound 2 is prepared as described in BE-P 523,115 ##EQU4## 3.
Compound 3 is prepared as described in BE-P 719,338 ##EQU5## and
comprise a sulphonic acid salt group for improving the
water-solubility of the tiol or thione compound.
The thione compound No. 4 which is the most preferred one can be
prepared according to the following reaction scheme: ##EQU6##
Preparation of compound 4
98 g of 2-hydrazino-6-sulfobenzothiazole are dissolved in 1.5 l of
pyridine and 450 ml of water. 24 ml of carbon disulphide are added
thereto and the resulting solution is refluxed for 12 h.
Subsequently, it is cooled to room temperature. The reaction
mixture is poured out in 2 litres of water and acidified with
concentrated hydrochloric acid. The precipitate formed is sucked
off and added to 250 ml of water and 125 ml of 5 N sodium
hydroxide, so that the precipitate is dissolved again. The
resulting solution is concentrated by evaporation. The residue is
added again to 1 litre of water and the solution obtained is
acidified again with concentrated hydrochloric acid. The
precipitate is sucked off, washed until neutral, and dried in vacuo
at 110.degree.C. Yield: 57 g.
Other suitable thione-thiol compounds for use according to the
present invention belong to the class of imidazoline-2-thiones and
imidazolidine-2-thiones and are e.g. ##EQU7##
Preparation of compound 5
105 g of carbon disulphide are added dropwise to a solution of 69.3
g of N-allylethylenediamine in 1200 ml of ethanol at a temperature
of 50.degree.C. A white precipitate forms. Subsequently, the
mixture is refluxed for 20 h. During the reaction hydrogen sulphide
is formed and a complete solution is obtained. The solution is
concentrated by evaporation to a volume of 400 ml and then cooled
down. The precipitate is sucked off and dried. Melting point:
90.degree.C. Yield: 46 g. ##EQU8##
Preparation of compound 6
20.6 g of .alpha.-amino-isobutyric acid are suspended in 100 ml of
ethanol. 12 g of potassium hydroxide in 12 ml of water are added
thereto, whereupon 20 g of allylisothiocyanate dissolved in 100 ml
of ethanol are added also. The reaction mixture is refluxed for 2
hours and then concentrated by evaporation. The residue is boiled
up with 900 ml of 2N hydrochloric acid, filtered while hot, and
cooled. The crystals are sucked off and recrystallized from a
mixture of methanol and water over animal chorcoal. Melting point:
77.degree.C. Yield: 13 g. ##EQU9##
Preparation of compound 7
160 g of 85% purity potassium hydroxide, 66 g of carbon disulphide,
770 ml of ethanol, and 115 ml of water are added to 149 g of
N-methyl-o-phenylenediamine-dihydrochloride. The reaction mixture
is stirred and refluxed for 3 hours while hydrogen sulphide
escapes. Subsequently, the mixture is cooled down. The precipitate
formed in the reaction mixture is dissolved again by the addition
of 750 ml of water. The solution is boiled with animal charcoal,
filtered and admixed at 70.degree.C with 64 ml of acetic acid and
120 ml of water. The reaction mixture is cooled down and the
resulting precipitate is sucked off and recrystallized from
ethanol. Melting point: 195.degree.C. Yield: 45 g. ##EQU10##
Preparation of compound 8
91 g of thiosemicarbazide and 158 g of caprylic acid methyl ester
are added to 23 g of sodium in 1 l of anhydrous methanol. The
reaction mixture is refluxed for 16 h and concentrated by
evaporation. The residue is dissolved in 200 ml of water by heating
and cooled afterwards. The solid product is sucked off and the
filtrate is acidified with 70 ml of acetic acid. During the cooling
crystallization occurs. The crystals are sucked off, recrystallized
from 40% ethanol and washed with dichloroethane. Melting point:
190.degree.C. Yield: 92 g. ##EQU11## Preparation of compound 9 is
described in FR-P Application 2,001,068. ##EQU12## Compound 10 is
prepared as described in J.Gen.Chem. USSR 33; 3250 (1963).
##EQU13##
Preparation of compound 11
50 ml of 40% formol are added dropwise to a mixture of 25.3 g of
thiourea and 43 g of octylamine in 200 ml of water with stirring
and cooling. 150 ml of ethanol are added as well and the stirring
is continued for 16 h. Subsequently, the reaction mixture is
concentrated completely by evaporation, so that a white amorphous
product is formed, which is recrystallized from ethanol and benzene
respectively. Melting point: 159.degree.C. Yield: 30 g. ##EQU14##
Compound 12 is prepared as described in Can.J.Chem. 32, 59 (1954).
##EQU15##
Preparation of compound 13
45.6 g of carbon disulphide are added dropwise to a solution of 50
g of N-propylethylenediamine in 275 ml of methylglycol at a
temperature of 40.degree.C. A white precipitate forms.
Subsequently, the mixture is heated for 1 hour at 90.degree.C, so
that hydrogen sulphide is formed. The methylglycol is then
evaporated partially in vacuo and 500 ml of water are added to the
residue. After having been cooled the precipitate is sucked off and
recrystallized from a mixture of benzene and hexane. Melting point:
90.degree.C. Yield: 54 g. ##EQU16## Preparation of compound 14 see
DOS 1,931,056. ##EQU17##
These compounds and the compounds 1 to 3 are prepared according to
techniques known to those skilled in the art.
A relatively high amount of thione or thiol compounds can be
incorporated in the aqueous fixer when it contains water-miscible
solvents e.g. n-propanol or ethylene glycol monoacetate.
A suitable amount of organic thiol or thione compound is in the
range of 0.5 to 15 g per litre.
A preferred lithographic fixer according to the present invention
is composed as follows: iron(III) salt 20 g to 120 g SN
.angle..angle. Na--O.sub.3 S--CNH .vertline..vertline. ----N----C=S
0.5 15 g n-octylamine 10 75 ml potassium iodide 5 40 g organic
solvent(s) n-propanol 0 ml 200 ml ethylene glycol monoacetate 0 ml
150 ml water to make 1 l pH adjusted to 6-6.2 by means of malonic
acid and ammonium hydroxide.
The iron(III) salt is present in the form of iron(III) ammonium
malonate.
Optimum results were obtained by using a fixer solution prepared by
the following procedure: into 780 ml of an iron(III)ammonium
malonate solution containing 10.4% by weight of iron(III)ions 39 ml
of n-octylamine were dissolved whilst stirring. Subsequently after
adding 115 ml of n-propanol and 20 ml of ethylene glycol
monoacetate, 39 ml of a 10% by weight solution of the thione
compound No. 4 in highly concentrated aqueous ammonium hydroxide
were added. The pH was adjusted to 5.0 by means of additional
aqueous ammonium hydroxide whereupon 23 g of potassium iodide were
dissolved in the obtained composition. Additional aqueous ammonium
hydroxide was added so as to reach a total liquid volume of 1 litre
and a pH of 6.1. The iron(III)ammonium malonate solution was
prepared by dissolving 570 ml of iron(III)chloride in water in an
amount sufficient to obtain a volume of 3 l. To the obtained
solution 480 ml of ammonium hydroxide were added. The obtained
precipitate was stirred for 2 h at room temperature and separated
by suction whereafter it was freed from chloride ions by washing
with water. Then the precipitate was redispersed in 3 l of water
whereupon 750 ml of malonic acid dissolved in 1500 ml of water were
added. Stirring was continued for 1 h. The precipitate dissolved
gradually in about 24 h.
The green solution obtained was filtered and further diluted with
water up to a final volume of 7 l. The concentration of iron(III)
ions was 104 g per litre.
The preparation of a planographic printing plate by using a fixer
according to the present invention may be effected with a sheet
material comprising a silver image obtained by any of the silver
complex diffusion transfer processes hereinafter described by way
of example.
A first type of silver complex diffusion transfer process utilizes
a light-sensitive material and a separate image-receiving material
constituting the said sheet material and containing on an outer
surface thereof substance(s) for promoting the deposition of silver
in the said silver complex diffusion transfer process.
In an embodiment of such a process the light-sensitive material
comprises a water-permeable hydrophilic colloid layer on top of the
said silver halide emulsion layer. Such a feature is described in
the United Kingdom Patent Specifications 869,190 - 998,955 and
998,956. Alternatively a special type of image-receiving material
can be used as described in United Kingdom Patent Specifications
1,013,344 and 1,054,252. In such materials there may be
incorporated in the image-receiving material and/or light-sensitive
materials substances that are essential or useful for carrying out
the diffusion transfer image formation, e.g. developing agents,
preservatives for these developing agents, complexing agents,
stabilizers, alkaline substances, black-toning agents, hardeners
and softening agents, so that the aqueous processing liquid need
only be an aqueous solution of alkaline substances, or merely
water, the latter technique being described in United Kingdom
Patent Specification 1,013,343. The incorporation of developing
agents and preservatives thereof into the light-sensitive and/or
image-receiving material for diffusion transfer processes is
described in United Kingdom Patent Specifications 1,093,177 -
1,000,115 - 1,012,476 - 1,042,477 - 1,054,253 and 1,057,273.
Embodiments in which hardening agents and more particularly latent
hardening agents are incorporated into the light-sensitive and/or
image-receiving material for such processes are described in United
Kingdom Patent specification 962,483 and German Patent
Specification 1,203,604.
A second type of silver complex diffusion transfer process utilizes
a single material. Such a single material comprises a silver halide
emulsion layer and may comprise a hardenable hydrophilic colloid
layer, either beneath or above such silver halide layer. Substances
for bringing about the appearance of the diffusion transfer image
(development nuclei) from the diffusing complexed silver halide may
be present at an outer surface of the material or at an interface
of the said layer(s). In the latter arrangement the silver image
obtained by diffusion transfer is obtained on top of hardenable
hydrophilic colloid layer and preferably is hydrophobized
thereon.
According to a special embodiment the colloid layer with the silver
image obtained by diffusion transfer is transferred to another
sheet material, which may then be converted to a planographic
printing plate for instance as described in the United Kingdom
Patent Specification 1,001,558.
The development nuclei may be supplied in a liquid medium to the
hardenable hydrophilic colloid layer on top of the light-sensitive
silver halide emulsion layer. The development nuclei depositing at
the outer surface of the said layer make that the diffusion
transfer silver deposition thus occurs at this outer surface. The
silver image areas are converted into ink-receptive printing areas
to form a planographic printing plate with the lithographic fixer
of the present invention.
If desired, the development nuclei may be applied to the surface of
the light-sensitive recording material in the alkaline processing
liquid for carrying out the diffusion transfer image formation or
from a separate liquid composition containing such nuclei which
constitutes a step after the exposure of the light-sensitive
material and before wetting with the alkaline processing liquid for
forming the diffusion transfer image.
Substances for promoting the silver deposition from the diffusing
complexed silver halide are sulphides of heavy metals such as the
sulphides of antimony, bismuth, cadmium, cobalt, lead, nickel,
silver and zinc. Other suitable salts are the selenides,
polysulphides, polyselenides, mercaptans and tin(II) halides. Heavy
metals or their salts and fogged silver halides are suitable too.
The complexed 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 may be used in their colloidal form. The
support of the photographic material comprising the silver halide
emulsion layer may be any conventional flexible support sheet e.g.
a paper sheet or a transparent hydrophobic film support, such as a
support of cellulose triacetate or of a polyester e.g. polyethylene
terephthalate.
The image sharpness of the silver pattern and, as a consequence
thereof, the sharpness of the final result of printing can be
improved by applying antihalation dyes or pigments. These dyes or
pigments may be present in the silver halide emulsion layer or in
the support, but preferably are incorporated into a layer situated
between the silver halide emulsion layer and the support. If a
transparent support is used, the antihalation dyes or pigments, may
be applied to the rear side of the material or on top of the
emulsion layer dependent on the manner in which the exposure is
carried out, viz. at the front side or through the support.
Preferably a red or black antihalation dye or pigment is used. Any
silver halide emulsion of the negative or direct-positive type may
be used depending on the nature of the original to be reproduced.
Preferably emulsions of the negative type are used, having a
somewhat high sensitivity suitable for use in a camera. As a matter
of fact, although the exposure of the silver halide emulsion layer
may be carried out according to any usual technique e.g. by
contact, by back reflection, by transmission or episcopically.
Usually an episcopic exposure in a camera is carried out,
particularly when the development nuclei are provided on top of the
silver halide emulsion layer as detailedly described hereinafter.
The silver halide emulsion layer generally comprises an amount of
silver halide equivalent to from 0.5 g.sq. metre to 1.5 g sq. metre
of silver nitrate and preferably amounting only to the equivalent
of about 1 g sq. metre of silver nitrate. This means a considerable
economy of silver halide with respect to the silver halide content
of emulsion layers commonly used in the production of diffusion
transfer copies. If necessary a suitable subbing layer is provided
for strongly adhering the hydrophilic colloid layer(s) to the
support sheet. The data in this paragraph also apply to any
embodiment for the production of silver pattern substantially at
the surface of a hydrophilic colloid layer according to the silver
complex diffusion transfer process described hereinafter.
The sheet materials suited for use with the fixer solution of the
invention are generally of simple composition, and may comprise a
suitable support such as transparent hydrophobic film support or a
paper sheet, either in direct contact or indirectly, e.g., by means
of a suitable subbing layer, with a hydrophilic colloid outer layer
having at its surface a pattern of finely divided silver particles.
A silver halide emulsion layer may be present between the colloid
outer layer and the support and also antihalation dyes or pigments
are provided. The silver pattern obtained by the complex diffusion
transfer process may be intensified by chemical or physio-chemical
after-treatment for intensifying the silver pattern in or at the
surface of the outer colloid layer.
According to a preferred embodiment, a photographic material is
used which comprises successively a support layer (preferably a
paper support), an antihalation layer, a silver halide emulsion
layer and development nuclei on top thereof.
In order to obtain a diffusion transfer silver deposition that will
be sufficiently dense, the said photographic material has to be
kept for a period of time, e.g. for about 10 seconds, in the dark
after it has been wetted with the alkaline processing liquid for
carrying out the diffusion transfer image formation. The
application of the lithographic fixer composition may take place
during the period the multi-layer material is kept in the dark.
However, this application of lithographic fixer may also occur
thereafter.
For the production of the diffusion transfer silver image a
photographic material comprising development nuclei on top of the
silver halide emulsion layer may be provided in roll-form. After
image-wise exposure, e.g. an episcopic exposure in a camera or an
exposure through a transparent original in contact with the
photographic material, the latter may be guided automatically
through a usual processing unit containing the alkaline processing
liquid and comprising guiding and driving means as generally known
in the art.
For the preparation of the hydrophilic colloid outer layer any
hardenable hydrophilic colloid is suitable. Although gelatin is
favoured, other hardenable hydrophilic colloids such as polyvinyl,
alcohol, casein, carboxymethylcellulose and sodium alginate can be
used too, the nature of the hardener used being dependent on the
type of hydrophilic colloid to be hardened. If gelatin is used for
forming the hydrophilic colloid outer layer, it may be submitted to
a treatment as described in the United Kingdom Patent Specification
883,843 in order to improve the printing characteristics of the
planographic printing plate.
Hardening of the hydrophilic colloid layer may occur before, during
or after the treatment with the lithographic fixer composition and
must occur at least to such an extent that no substantial amount of
colloid is transferred on printing either to the rollers for
applying water and ink to the printing plate or to the material to
be printed. In other words hardening (i.e. insolubilizing in water
and strengthening against mechanical damage) must occur at least to
such an extent that the material obtained can be used as
planographic printing plate.
The said hardening mostly occurs before the treatment with
lithographic fixer. In that case the said hardening may be effected
by addition of the generally known hardening agents for gelatin and
similar colloids, such as formaldehyde, glyoxal, mucochloric acid
and chrome alum, to the coating composition of the outer layer, at
the surface of which the silver pattern will be produced, and/or to
the coating composition of another layer, with which the said outer
layer is in water-permeable relationship whereby hardening of the
said outer layer takes place by diffusion of hardener from said
other layer to said outer layer. When, as hereinbefore described a
coating composition comprising development nuclei, possibly
together with a minor amount of a hydrophilic colloid to keep the
development nuclei in dispersion but insufficient to form a
continuous binder layer with the nuclei enclosed is applied on top
of the said outer layer, the hardeners can also be incorporated
into said coating composition. Hardening of the hydrophilic colloid
binder of the outer layer may also occur during the production of
the silver pattern. The said hardening may be effected by
incorporating a latent hardeners in one or more layers of the sheet
material, whereby a hardener is released at the stage of the
application of an alkaline processing liquid for carrying out the
complex silver diffusion transfer process. These latent hardeners
are active only in a well defined pH-range, mostly the pH-range of
the usual developing liquids. Finally, hardening of the outer
hydrophilic colloid layer can also occur after the production of
the silver pattern namely by treatment with a hardening liquid.
This liquid may be an aqueous hardening composition applied before
the treatment with the lithographic fixer, the fixer composition
itself, or an aqueous hardening composition applied after the
treatment with the said fixer. At least one compound for improving
the hydrophilic properties of the non-printing areas may be applied
during the preparation of the printing plate.
Thus the presence of certain hydrophilic colloid binders e.g.
carboxymethylcellulose, gum arabic, sodium alginate,
propyleneglycol ester of alginic acid, hydroxyethyl starch,
dextrine, hydroxyethylcellulose, polyvinylpyrrolidone, polystyrene
sulphonic acid and polyvinyl alcohol in the outer hydrophilic
colloid layer carrying at its surface the pattern of silver
particles often improves the hydrophilic, ink-reppelent properties
of the non-printing areas of the printing plate finally obtained.
Also hygroscopic substances e.g. sorbitol, glycerol,
tri(hydroxyethyl)ether of glycerol and turkey red oil, and certain
wetting agents, may be present.
The hydrophilic colloid layer also may advantageously comprise a
pigment particles homogeneously dispersed therein to prevent the
so-called "scumming" (i.e. ink-acceptance that arises in the
non-printing areas of the printing plate after a certain number of
copies has been printed). The usual inorganic pigments e.g. barium
sulphate, titanium dioxide, china clay and silica applied from a
colloidal solution, have proved to be particularly suitable for
this purpose. The pigment particles are generally homogeneously
applied in such an amount that about 5-20 g sq.cm of the
hydrophilic colloid outer layer are present. A similar
anti-scumming effect may also be obtained by adding at least one
member selected from colloidal silica, an inorganic acid e.g.
o-phosphoric acid, a hygroscopic substance hereinbefore described
and a suitable wetting agent to the fountain solution used during
the printing process. Suitable wetting agents include:
H.sub.3 C--(CH.sub.2).sub.16 --COO--(CH.sub.2 CH.sub.2 --O).sub.5
--H
sodium dodecylsulphate
sodium tetradecylsulphate
R--ch.sub.2 --so.sub.3 na wherein R represents an alkyl group
comprising from 14 to 18 carbon atoms ##EQU18##
The lithographic fixer of the present invention is very stable to
airial oxidation and to temperature fluctuations and it is suited
for the production of planographic printing plates having
non-staining image background parts.
At the moment the treatment with the aqueous lithographic fixer
starts the outer colloid layer showing the silver pattern may be in
a dry or wet condition. A superficial oxidation of the silver
pattern suffices, although complete oxidation is advantageous.
Generally the treatment with the lithographic fixer does not last
long, mostly not longer than about 20 seconds and can be
accelerated by increasing the concentration of the components in
the said fixer. The plate may be stored for a long time before
being fixed and even thereafter it may be stored for a long time
before being used in the printing process. Preferably, however, the
lithographic fixing step is carried out just before printing.
The lithographic fixer as well as the development or activating
liquid for the production of the diffusion transfer image can be
applied in different ways, e.g. by spraying, by rubbing with a
roller, or by dipping the material to be treated in the liquid
composition. The lithographic fixing step of the printing plate may
proceed automatically by conducting the plate through a device
having a narrow channel filled with the fixer composition and
conveying the printing plate at the end of the channel between two
squeezing rollers removing the excess of liquid.
The production of a silver image on top of the outer hydrophilic
colloid layer and the treatment with the fixed may occur in a
compact processing unit comprising both the processing
stations.
After the application of the lithographic fixer the sheet material
is ready for inking and use as a printing plate. Treatment of the
material with a lacquer composition for strengthening the printing
parts is not necessary. Nevertheless, in some cases the hydropobic
character of the ink-receptive parts and their mechanical strength
may be improved by applying a lacquer thereon. Suitable lacquer
compositions are solutions of oils, waxes and resins in organic
solvents. Suitable organic solvents are cyclohexanone, acetone,
butanol, monomethyl ether of ethylene glycol, monoethyl ether of
diethylene glycol, tetrahydrothiophene-1,1-dioxide, diacetone
alcohol, dioxane, 1,2-dichloroethane, ethyl acetate,
trichloroethylene, butyl butyrate, diethanolamine and
dimethylformamide. Mixtures of such organic solutions with an
aqueous phase or dispersions of such organic solutions in an
aqueous phase are also suitable. In that case the aqueous phase may
contain thickeners or other compounds for improving the hydrophilic
character of the non-printing areas of the lithographic printing
plate as described above. Suitable lacquers are described in the
United Kingdom Patent Specifications 967,598 - 968,706 - 1,004,342
- 1,071,163 and 1,071,164. Resins that have proved to be especially
suitable for improving the ink-receptive character of the printing
areas and strengthening them are phenol-formaldehyde resins e.g.
phenol-formaldehyde resins, a-cresol formaldehyde resins, and
p-tert.-butylphenol formaldehyde resins, alkyd resins e.g. rosin
maleic acid esters, epoxy resins, condensation products of a
poly(aryl ethylene oxide) with an acid anhydride, an amine or
another suitable compound and epoxidized polyesters.
The resin, wax or oil is usually used in a concentration of from
about 100 to about 500 g per litre of liquid lacquer composition.
The liquid lacquer composition may be applied after the aqueous
composition containing the oxidizing agent has been applied and
while the printing plate is still wet. When an emulsion lacquer is
used the plate needs not necessarily be wet at the stage the
lacquer is applied. The lacquer may be applied by dipping,
spraying, spreading or by means of a material soaked therewith. The
lacquer is rubbed e.g. with a plug of wadding. The hydrophobic
solid substances settle on the image areas and improve the
hydrophobic ink-receptive character thereof. At the same time the
mechanical strength of the printing areas is improved. The
adherence of the lacquer to the printing areas may further be
improved by heating the plate.
Instead of being applied by means of a separate after-treatment of
the printing plate, the liquid lacquer composition may also be
incorporated with the aqueous composition containing the iron(III)
ammonium salt of an aliphatic dicarboxylic acid and the organic
compounds for converting the silver image in a hydrophobic
ink-receptive pattern. The ratio of the organic phase that contains
the hydrophobic solid substances to the aqueous phase is generally
between 1:1 and 1:10.
The printing plate has to be wet at the stage the greasy printing
ink is applied. This is generally known in the art and it is usual
to apply an aqueous liquid before applying the printing ink. This
may occur by means of a wet sponge or by means of the fountain
arrangements (damping system) of the printing machine.
The following examples illustrate the use of the lithographic fixer
according to the present invention. All percentages are by weight
unless otherwise stated.
EXAMPLE 1
To a paper support of weight 135 g per sq.m a high sensitive,
negative silver chlorobromide gelatin emulsion layer, hardened by
means of formaldehyde, was applied so that an amount of silver
halide equivalent to 1 g of silver nitrate was present per sq.m.
After drying of the silver halide gelatin emulsion layer, the
latter was overcoated with the following composition to provide a
coating of 20 g per sq.m:
water 890 ml 12.5 % aqueous solution of saponin 10 ml aqueous
dispersion of colloidal nickel sul- phide comprising per 100 ccs
0.2 g of nickel sulphide and 10 g of gelatin as protective colloid
100 ml
The material obtained was exposed to an original and treated for 30
sec. in the following processing composition:
sodium hydroxide 10 g anhydrous sodium sulphite 75 g potassium
bromide 1 g hydroquinone 16 g 1-phenyl-3-pyrazolidinone 1 g water
up to 1000 ml anhydrous sodium thiosulphate 10 g
The material was then rubbed for some 20 seconds with a plug of
wadding saturated with the following lithographic fixer
composition:
iron(III)salt 74 g n-octylamine 39 ml n-propanol 115 ml ethylene
glycol monoacetate 20 ml SN .angle..angle. NaO.sub.3 S--CNH
.vertline..vertline. ----N----C=S 4 g potassium iodide 23 g aqueous
solution of ammonium hydroxide to reach a final volume of 1 litre
of composition having a pH of 6.00
The iron(III) salt is present in the form of iron(III) ammonium
malonate.
The material thus obtained was a positive planographic printing
plate with very good printing characteristics and with which more
than 1000 copies of high quality could be printed. Applying a
lithographic lacquer in order to strengthen the printing parts was
not necessary and could be omitted. The fountain solution used on
printing could be water or liquid having the following
composition:
water 90 ml glycerol 10 ml colloidal silica 1 ml phosphoric acid 2
ml
EXAMPLE 2
To a paper support of weight 250 g per sq.m a high-sensitive
negative silver chlorobromide gelatin emulsion layer, hardened by
means of formaldehyde and comprising hydroquinone and
1-phenyl-3-pyrazolidinone, was applied so that per sq.m were
present: an amount of silver halide equivalent to 1 g of silver
nitrate, 0.5 g of hydroquinone and 0.25 g of
1-phenyl-3-pyrazolidinone.
The light-sensitive material obtained was image-wise exposed and
then dipped for 10 sec. in the following processing liquid:
water 1000 ml sodium phosphate-12-water 75 g anhydrous sodium
sulphite 40 g potassium bromide 0.5 g anhydrous sodium thiosulphate
10 g aqueous dispersion of colloidal nickel sulphide of example 1
20 ml
In this way a positive diffusion transfer silver image was produced
at the surface of the silver halide emulsion layer.
The material was then rubbed for some 15 seconds with a plug of
wadding saturated with the lithographic fixer described in Example
1, wherein, however, thione compound 4 had been replaced by a same
amount of mercapto compound 1. The printing plate thus prepared
could be used for printing in the same manner as described in
Example 1 and about the same good results were obtained.
EXAMPLE 3
To a paper support of weight 135 g per sq.m; a high-sensitive
silver chlorobromide gelatin emulsion layer comprising hydroquinone
and 1-phenyl-3-pyrazolidinone was applied so that per sq.m are
present, an amount of silver halide equivalent to 1 g of silver
nitrate, 1 g of hydroquinone and 0.5 g of
1-phenyl-3-pyrazolidinone.
After drying the silver halide gelatin emulsion layer the latter
was overcoated in a proportion of 100 g per sq.m with the following
composition:
water 926 ml gelatin 10 g 12.5 % aqueous solution of saponin 8 ml
20 % aqueous solution of formaldehyde 56 ml
Then the following liquid is applied in a proportion of 22 g per
sq.m:
water 890 ml 12.5 % aqueous solution of saponin 10 ml aqueous
dispersion of colloidal nickel sulphide of Example 1 100 ml
The light-sensitive material obtained was exposed image-wise and
then guided through an automatic two-bath processing device, the
baths of which had the following compositions respectively:
I. (activating liquid)
water 1000 ml sodium phosphate-12-water 75 g anhydrous sodium
sulphite 40 g potassium bromide 0.5 g anhydrous sodium thiosulphate
10 g
Ii. the lithographic fixer described in Example 1, with the
modification that thione compound 4 had been replaced by a same
amount of the thiol compound 15 listed herein.
The material obtained after this treatment was readly for use as
planographic printing plate with positive image values compared to
the original. More than 1000 copies could be printed therewith. The
fountain solution might be mere water or the specific fountain
composition of Example 1.
EXAMPLE 4
To a strong paper support of weight 135 g per sq.m a thin gray
antihalation was applied by pouring a dispersion of 3 g of lamp
black in 1 litre of a 4% aqueous solution of gelatin at a rate of 1
litre per 40 sq.m.
To this antihalation layer a high-sensitive silver chlorobromide
gelatin emulsion layer comprising hydroquinone and
1-phenyl-3-pyrazolidinone was applied in such a way that per sq.m.
were present: an amount of silver halide equivalent to 1 g of
silver nitrate, 1 g of hydroquinone and 0.5 g of
1-phenyl-3-pyrazolidinone.
After drying, the silver halide gelatin emulsion layer was
overcoated at a rate of 100 g per sq.m with the following
composition:
water 926 ml gelatin 10 g 12.5% aqueous solution of saponin 8 ml 20
% aqueous solution of formaldehyde 56 ml
Then the following liquid was applied at a rate of 22 g per
sq.m:
water 890 ml 12.5 % aqueous solution of saponin 10 ml aqueous
dispersion of colloidal nickel sulphide comprising per 100 ml of
0.2 g of nickel sulphide and 10 g of gelatin 100 ml
The light-sensitive multilayer thus obtained was image-wise exposed
to an original.
This exposure might be an episcopic exposure in a camera or an
exposure through an intermediate original having a sufficiently
transparent background and being pressed with its rearside against
the nuclei side of the multilayer material.
The multilayer material can be used in roller form and after the
image-wise exposure be cut off as desired.
After the image-wise exposure the multilayer material was guided
through a processing unit containing the following alkaline
liquid:
water 1000 ml sodium phosphate-12-water 75 g anhydrous sodium
sulphite 40 g potassium bromide 0.5 g anhydrous sodium thiosulphate
10 g
Thereafter the multilayer material was kept for some 10 seconds in
the dark in order to permit an intense diffusion transfer silver
deposition to take place. A sharp bronzed legible diffusion
transfer image became visible on a gray background.
The plate was then moistened (e.g. by means of a plug of wadding)
for some 20 seconds with the following lithographic fixer
composition:
iron(III) salt 60 g n-octylamine 42 g n-propanol 100 ml ethylene
glycol monoacetate 100 ml SN .angle..angle. NaO.sub.3 S--CNH 6 g
.vertline..vertline. ----N----C=S potassium iodide 30 g aqueous
ammonium hydroxide solution of to reach a final volume of 1 litre
of composition having a pH of 6.1.
The iron(III) salt is present in the form of iron(III) ammonium
malonate.
The said fixer composition was very stable to aerial oxidation and
to temperature fluctuations. With 1 litre thereof about 100
printing plates (21 cm .times. 29.7 cm size) could be prepared.
The preparation of the printing plate proceeded automatically in a
compact processing unit comprising the successive treating stations
and wherein the plate was transported automatically from one unit
to the other.
The printing plate thus obtained was ready for use as a
planographic printing plate with positive image values based on the
original. It was mounted on an offset apparatus and after having
been wetted with water or other fountain solution (e.g. a liquid
composed of 90 ml of water, 10 ml of glycerol, 2 ml of colloidal
silica and 2 ml of phosphoric acid), the fatty printing ink was
applied and printing started. More than 1000 copies were printed
with the plate thus prepared.
* * * * *