Note: Descriptions are shown in the official language in which they were submitted.
2228
1046865
PROCESS FOR THE PREPARATION OF P~INTING FORMS
This invention relates to the preparation of printing forms or
metallic etchings from electrophotographic or electrographic reproduc~
tion material composed of a support with a photoconductive or high-
ohmic layer thereon, by charging and image-wise exposure of the
material, or by image-wise charging of the material, followed by de-
velopment of the electrostatic image with a finely divided toner, fix-
lng, removal of the layer in the image-free areas by means of a decoat-
ing solution, and, optionally, etching of the bared areas of the support.
Processes for the preparation of printing forms by electrophoto-
- graphic means are known. In German Patent No. 974,162, for example,
a process is described for the preparation of lithographic printing
plates from coated papers, in which the surface of an electroconduc-
tive, moisture~resistant paper foil is coated with a layer composed of
a photoconductor substance suspended in a dielectric, film-forming
carrier substance, the layer ls electrostatically charged, image-wlse
exposed, and then developed with a powder which accepts greasy ink.
Subsequently, the non-printing areas of the printlng plate are rendered
hydrophilic. For this purpose, the powder is either fixed to the photo-
conductlve layer in such a manner, by heat action, that it substantially
fuses through the photoconductive layer, or it is forced into the photo-
conductive layer, or the powder image is provided with a thin film of
a material serving as a solvent for the powder image or for the photo-
conductive layer in order to provide satisfactory adhesion. The sol-
vent is then removed by heating. Subsequently, the non-image areas
are converted into a hydrophilic material by an impregnation step which
should not affect the fixed powder image. If the photoconductive layer
is coated on top of a hydrophilic layer, or if the photoconductive layer
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1046865 K-2228
is composed of a substance which is easily removed, the photoconduc-
tive coating may also be removed from the non-image areas.
A process of this type can be used only for paper printing plates
which are known to yield only short runs, and lithographic copies of
poor quality. Moreover, the powder image must be anchored by heat
fixation, pressure or solvents must be applied, and further heat is
possibly required, so that the process is also less advantageous as
regards expendlture in time and equipment.
It is also known from German Auslegeschrift No. 1,117,391, -
I0 to use photoconductive organic compounds in the layers of electro-
photographic reproduction materials from which printing forms are ~;
produced. The materials have a support which is suitable for printing
purposes. The photoconductive layer is composed of a mono-molecular
photoconductor and hlgh molecular welght alkali-soluble substances.
The material is charged and exposed in the conventional manner and
developed with a colored resin powder. The resin powder ls fixed by
heating the materlal to a temperature between 100 and 250C, and
the layer is then treated with an alkaline solutlon, so that the non-
lmage areas are d-ssolved away and a planographic printing plate - -
results. Although foils of metal, paper, or plastlc materials are
suggested for this process, a dimenslonally accurate reproductlon ls
not guaranteed, because a thermal fixlng process always lnvolves the
risk of a dimensional alteration. Moreover, the expenditure on equip-
ment necessary for performing the thermal flxing process always lm-
pedes the automation of a process for the preparation of printing plates.
Thus, it is the object of the present invention to provide a
process for the preparation of printing forms which may be performed
at a relatively low temperature, preferably at room temperature, and
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1046865
does not require an additional fixing step. Accordingly the invention pro-
vides in a process for the preparation of printing forms or metallic etchings
from electrographic or electrophotographic reproduction materials composed
of a support with a high-ohmic resin layer or a layer containing an organic
photoconductive material in a resin binder thereon by image-wise charging
or by charging and image-wise exposure, development of the electrostatic
image with a finely divided toner, fixing, and removal of the layer in the
image-free areas by means of a decoating solution, the improvement which
comprises developing and fixing the electrostatic image on said layer by
treating it with a developer composed of a high-ohmic liquid phase and a fine-
ly divided solid phase therein which solid phase is at least one high mole-
cular weight product selected from the group consisting of the high-vacuum
bitumen, wax and resin type, which renders the image areas hydrophobic at
; room temperature, and simultaneously effects development and resistance to
the decoating solution.
As an optional step, the re val of the layer in the image-free
areas by means of the decoating solution may be followed by etching of the
bared surface of the support.
The composition of the developer material to be used depends also
upon the composition of the decoating solution employed for removing the
copying layer from the non-image areas.
; It is achieved by the present invention that the additional
fixing step, i.e. the heating or burning-in of the material within a sub-
stantially constant, controllable temperature range, can be completely omitted,
providing a process for the preparation of printing ~orms which can be easily
and economically applied to any type of appropriate support.
If metallized plastic films are used, for example, decoating and
etching away of the metal layer in the non-image areas produces
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~046865
transparent images whose image areas are distinguished by a very high
optical density. Moreover, the images produced on the film bases are
true to scale. Altogether, the inventive process provides a consider-
able saving in time and apparatus, which is of decisive importance with
aviewto the automation of the entire process.
By the process of the present invention, printing forms for
planographic prlnting, gravure printing, letterpress printing, and
screen printing, as well as printed circuits, may be produced by
electrophotographic or electrographic methods.
The electrophotographic printing form used as the starting ma-
terial for the process of the invention is known in principle. The use
of photoconductive organic substances in electrophotographic layers
and the conversion of these layers into printing forms is known, for - ~-
example from the publications mentioned above for defining the pres- ~-
ent state of the art~ Photoconductors containing one or more dialkyl
amlno groups may be used with particular advantage for the present
lnvention. Particular mention is made of heterocyclic compounds,
such as the oxadiazole derivatives Icnown from German Patent No.
1, 058, 836, especially the 2, 5-bis- (4'-diethylaminophenyl)-oxadiazole-
1,3,4. Other suitable photoconductors are, for example, triphenyl-
amine derivatives, highly condensed aromatic compounds, such as
anthracene, benzo-condensed heterocyclic compounds, pyrazoline
derivatives, and imidazole derivatives. The triazole and oxazole
derivatives disclosed in German Patents Nos . 1, 060, 260, and
1,120,875, also may be used. Further, vinyl-aromatic polymers,
such as polyvinyl anthracene, polyacenaphthylene, and polyvinyl
carbazole, and the copolymers of these compounds, are also suitable,
provided they are capable of a differentiation in solubility character-
istics, if necessary in combination with a resin binder. Other suitable
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1046865
compounds are the polycondensates of aromatic amines and aldehydes
described in German Auslegeschrift No. 1,197,325.
In addition to the compounds just mentioned, which prepon-
derantly are of p-conductive nature, n-conductive compounds also
may be used. These so-called electron acceptors are known, e.g.,
from German Patent No. 1,`127,218.
As regards film-forming characteristics and adhesion, both
natural and synthetic resins are suitable as resin binders. In addition
to their film-forming and electrical characteristics and their adhesion
to the support, the solubility characteristics of the resins are of
particular importance. Resin binders which are soluble in aqueous
or alcoholic solvent systems, to which, if desired, an acid or an
alkaline substance may be added, are particularly suitable for practi-
cal purposes. For physiological and safety reasons, readily flamm-
able aromatic or aliphatic solvents are ruled out. Therefore, the
preferred resin binders are high molecular weight substances contain-
ing groups which render them alkali-soluble, such as acid anhydride
groups, carboxyl groups, phenol groups, sulfonic acid groups, sulfon-
amide groups, or sulfonimide groups. Resin binders having high acid
numbers are preferred because they are particularly readily soluble in
alkaline-aqueous-alcoholic solvent systems. Copolymers containing
anhydride groups may be used with particular advantage because, due
to the absence of free acid groups, the conductivity of the electro-
photographic layer in the dark is low, in spite of its good solubility
in alkaline solutions.
Copolymers of styrene and maleic anhydride, such as those
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known by the name of " Lytron" (products of Monsanto Chemical Com-
pany, St. Louis, Mo., USA), andphenolresins, suchasthoseknown
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1046865 K-22 2 8
by the name of "Alnovol'r~ (products of Chemische Werke Albert,
Wiesbaden-Biebrich, Germany) have proved to be particularly suit-
able.
Further, the copying layer of the electrophotographic printing
form used as the starting material may contain ~cnown sensitizers .
Only small quantities of sensitizer are added to the copying layer,
i.e. about 0.001% to about 1%, calculated on the weight of the photo-
conductor component. Suitable sensitizers, most of them dyestuffs,
are known, for example, from Belgian Patent No. 558,078.
If electrographic layers are used, the same resin binders as
described in connection with the electrophotographic layers may be
employed. The layers must meet the same requirements as the photo-
conductive layers, except that the photoconductor component is
omitted.
Any of the known materials suitable for this purpose, e.g.
alumlnum, zinc, magnesium, chromium, or copper plates, may be used
as the support of the electrophotographic or electrographic printing
plate employed as the starting material, and their surfaces may be
pre-treated, if desired. Cellulose products, such as cellulose hy-
drate, cellulose acetate, or cellulose butyrate films, or paper that
has been superficially hydrophilized and made electrically conductive,
as well as plastic films and compound materials composed of paper
or plastic film and metal layers, also may be used. Supports com-
posed of layers of different metals are also suitable.
For the preparation of metallic etchings, metallized plastic
materials in the form of films or plates are used as supports, the metal
layer being applied by vapor deposition, lamination, or by chemical
or galvanic metal deposition.
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K-222 8
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Developers which are suitable for the present invention are
hydrophobic substances which are not easily wetted by the decoating
solution, for example, high molecular weight natural or synthetic
waxes and resins. The developer substances must, as far as possible,
dlstinguish in their solubility characteristics from the copying layer.
They must not easily dissolve in the decoating solutions used for re-
moving the copying layer in the non-image areas. Further, they must
have a good adhesion to the reproduction layer and provlde a good
coverage for the image areas. Compounds of the group of bitumen,
waxes, and resins have proved to be particularly suitable, for example,
synthetic ester waxes with saponification values between 130 and 150
and drop points between about 75 and 90 C, hard paraffin with a soft-
enlng range between about 50 and 70C, carnauba wax, colophony,
or shellac. High~vacuum bitumen with a softening range between
about 130 and 150 C has proved to be particularly suitable.
The aforementioned substances may be used either in a dry de-
velopment process, or they may be applied as developer dlspersions,
in a liquid developing process. A liquid developing process is preferr-
ed, uslng a developer composed of a high-ohmic liquid phase with a
~20 finely-divided solid phase dispersed therein. Liquid development has
proved to be particularly advantageous because the developing process
ls clean and free from dust and the copies produced are distinguished
by a very good photographic dissolution.
The liquid developer is composed of a dispersion medium, the
developer component, and additives which assist the dispersion of the
components and influence the electrical charge of the developer.
The preparation and use of suitable additives is described in
German Auslegeschrift No . 1, 047, 616 .
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1046865
Suitable dispersion media are those liquids which do not dis-
solve the solid phases at room temperature. A number of halogenated
hydrocarbons have proved to be advantageous, but, above all, liquid
aliphatic hydrocarbons, for example an isoparaffin with a boiling range
between 185 and 210C. The polarity of the charge of the dispersed
phase depends upon the properties of the dispersed substance itself
as well as upon the selected dispersion medium.
Wax-based developer dispersions are advantageously prepared
by dlssolving the developer substance in the hot dispersion medium
and then chilling the solution to room temperature, an excellently
sultable flnely-divided wax dispersion belng the result.
The developer may be applled in known manner. In the case
of a liquld developer, the developer may be applied by immersion or
by roller application, the latter method being preferred for an automatic
process .
After development of the latent electrostatic Image, the devel-
oper substance adheres to the copying layer in the form of the image,
Appllcatlon of the decoating solution follows.
The decoating solution is distributed over the layer, e.g., by
wiping with a cotton pad. Alternatively, the plates may be immersed
ln the decoating solution. As a preferred method, the decoating solu-
tion ls sprayed upon the layer. Suitably constructed apparatuses also
may be used for decoating, e.g., application roll systems. In this
manner, the differentiation between hydrophilic and oleophllic areas
necessary for offset printing is produced, the image areas represent-
ing the oleophilic areas of the printing plate.
The composition of suitable decoating solutions is known, for
example, from German Patent No. 1,117,391. Decoating solutions
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1046865
which have proved to be particularly suitable for the inventive process
are mixtures of alcohols containing sodium metasilicate or ethanol-
amine as the alkaline component. A 5% by weight aqueous solution of
phosphoric acid has proved to be suitable as an acid decoating
solution .
After treatment with the decoating solution, the printing form
is advantageously rinsed with water; if desired, its hydrophobic
properties may be further increased by wiping with dilute phosphoric
acid solution, After inking with greasy ink, printing may be performed -
ln known manner in a planographic printing machine (offset printing).
Alternatlvely, printing forms for letterpress, or, if desired,
for gravure prlnting may be produced by the subsequent dissolution
of the bared supporting material.
Dissolution may be performed in known one-bite or multi-
stage etching machines used for this purpose. If a multi-metal
material is used as the support, etching is performed by conventional
photoengraving methods. The printing plates obtained by the present
process are capable of very long runs.
By the process of the present invention, printing forms and
printed circuits may be produced; further, it may be used ln the
X-ray and microfilm field.
The lnvention will be further illustrated by reference to the
following specific examples:
ExamPle 1
A solution containing 10 g of 2-vinyl-4-(2'-chlorophenyl)-5-
(4"-diethyl-aminophenyl)-oxazole, 10 g of a styrene/malèic anhy-
dride copolymer with a softening point of 210C, and 20 mg of
"Rhodamine FB" in a mixture of 235 ml of glycol monomethyl ether
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1046865 K- 2 2 2 8
and 65 ml of butyl acetate is applied to an about lOOp thick, superfici-
ally roughened aluminum foil. After evaporation of the solvent, the
resulting- photoconductor layer is charged by means of a corona to be
negative potential of about 400 volts and exposed under a negative
transparency in a re-enlargement apparatus.
At stop 8 and using a 100 watt incandescent lamp as the light
source, the exposure time is 30 seconds for an enlargement scale of
1: 5. The latent image is developed with a toner liquid prepared by
finely dispersing 1 g of a synthetic ester wax having a saponification
value of 130 - 150 and a drop point between 81 and 86 C in a solu-
tion of 2 g of a pentaerythritol resin ester as a dispersing agent
(e.g. "Pentalyn H" ~), a product of Hercules Powder Company, i-
Wilmington, Delaware, USA) in 20 ml of isoparaffin and diluting the
resulting dispersion with 1,000 ml of an isoparaffin having a boiling
range between 185 and 210C. 0.5 g of soya lecithin is added to
the developer liquid as a charge control agent.
The developed plate is converted into a printing form by
immersing it for 1 minute in a solution of 35 g of sodium metasilicate
hydrate in a mixture of 140 ml of glycerol, 550 ml of ethylene glycol,
and 140 ml of ethanol, and then rinsing it with a water ~et while
brushing gently. A positive printing form is thus obtained from the
negative microfilm original.
Exam~le 2
The procedure described in Example 1 is repeated, except that
the synthetic ester wax used in Example 1 as the developer substance
is replaced by a phenol resin. The developer is prepared by finely
dispersing, in a ball mill, 1 g of a phenol-formaldehyde resin with a
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10468{j5 K-22 2 8
melting point of 75 - 83 C in a solution of 1.5 g of a pentaerythritol
resin ester in 70 ml of an isoparaffin, diluting the resuLting dispersion
with 1,000 ml of an isoparaffin with a boiling range of 185 - 210C,
and adding 0.2 g of soya lecithin as a charge control agent.
Example 3
A solution of 15 g of a condensation product of N-ethylaniline
and formaldehyde, 0.41 g of dibromo-succinic acid, and 0.15 g of
"Rhodamine FB" in a mixture of 40 ml of toluene, 20 ml of trichloro-
ethylene, and 25 ml of methanol is coated upon a mechanically rough-
ened aluminum foil. After evaporation of the solvents, a photoconduc-
tor layer is obtalned which is charged in the dark, to a negative
potential of 350 volts, by means of a coron~. The charged foil is then
exposed for approximately 2 minutes in a camera and developed with a
toner liquid which protects the image areas from the effect of the de-
coating solution by rendering them hydrophobic. The toner liquid is
prepared by finely dispersing 1 g of a hard paraffin with a softening
range between 50 and 62 C in a solution of 2 g of a pentaerythritol
resin ester in 20 ml of an isoparaffin and diluting the resulting disper-
slon wlth 1,000 ml of an isoparaffin having a boiling range between
185 and 210C. The developed plate is then bathed for about 2
mlnutes in 5% by weight aqueous phosphoric acid solution, and the
dissolved photoconductor substance present in the image-free areas
is rinsed off with water.
Example 4
A solution containing 10 g of 2,5-bis-(4'-diethylaminophenyl)-
1,3,4-oxadiazole, 10 g of a styrene/maleic anhydride copolymer with
a softening point of 210C, and 20 mg of "Rhodamine FB" in 300 ml
of glycol monomethyl ether is applied to an about lOOp thick polyester
,
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104S865
foil carrying a vacuum-deposited aluminum layer. The coated foil is
charged to a negative potential of about 400 volts by means of a corona
and is then exposed for 3 seconds, in contact with a transparent film
original, to the light of a 100 watt incandescent lamp from a dis-tance
of 65 cm. The exposed foil is developed with a developer liquid pre-
pared by dissolving or dispersing 1.5 g of a high-vacuum bitumen with
a softening range from 130 to 140C ("Bitumen D 130-140 HVB", a
product of Shell AG, Hamburg, Germany) and 6.5 g of a pentaerythritol
resin ester in 1,000 ml of an isoparaffin with a boiling range between
185 and 210C. In the areas not covered by the bitumen developer, - -
the photoconductor layer is removed with a sodium metasilicate solu-
tion as described in Example 1. In order to dissolve the about 1~
thick alumlnum layer in the image-free areas, the foil is bathed in 2N
caustlc soda solution. A positive transparency of the original is thus
produced which has a very good covering power.
ExamPle 5
Equally good resùlts are obtained by using a chemically
nickel-plated polvester film instead of the foil with the vacuum-
deposited aluminum layer. In order to remove the nickel layer after
the production of the image, a commercial nickel etching solution is
used .
Example 6
The photoconductive material described in Example 1 and com-
posed of an alumlnum foil with a photoconductor layer thereon is used.
The foil is charged in the dark to a negative potential of 400 volts by
means of a corona and is then exposed for approximately 20 seconds
in a camera. The latent charge image thus produced on the foil is then
developed in a dispersion of 1 g of colophony in a solution of 2 g of a
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pentaerythritol resin ester in 1,000 ml of an isoparaffin with a boiling
range between 185 and 210C to which 0.2 g of zirconyl linoleate is
added as a charge control agent.
The developed plate is converted into a printing form as de-
scribed in Example 1.
Example 7
An alumlnum foil coated with a photoconductor layer as de-
scribed ln Example 1 ls charged to a negative potential of 400 volts
by means of a corona and exposed in contact with a positive trans-
parency (transparent original). The exposure time is 3 seconds, using
a 100 watt incandescent lamp at a dlstance of 65 cm. The latent
charge image thus produced is developed with a developer liquid pre-
pared by finely dispersing 0.3 g of a bleached, white, wax-free
shellac powder with a melting point of 63 C in a solution of 0 . 4 g of
a pentaerythrltol resin ester ln 1, 000 ml of an isoparaffin with a boil-
ing range of 185 - 210C. 3 ml of a 6% by weight solution of zlrconyl
linoleate are added to the developer liquid as a charge control agent.
The developed plate is converted into a printing form inthe
manner described in Example 1, by removal of the image-free areas
with a sodium metasilicate solution.
Example 8
The method described in Example 7 is repeated, except that the
developer liquid used for developing the latent charge image is re-
placed by a dry developer. For this purpose, 6 g of a bleached,
white, wax-free shellac powder with a melting point of 63 C are
mixed with 100 g of iron powder having a grain size between 75 and
150~. The mixture is applied to the plate in the manner normally used
ln electrophotographic processes, i.e. by means of a magnetic brush.
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1046865
After development of the latent charge image, the plate is immersed
in a decoating solution, as described in Example 1, and thus con-
verted into a printing form.
Example 9
A solution of 6 9 of a styrene/maleic anhydride copolymer
with a softenlng point of 210C in a mixture of 74 ml of glycol mono-
methyl ether and 20 ml of butyl acetate is mechanically applied to a
superficially roughened aluminum foil having a thickness of 100 ~
After evaporation of the solvent, the coated foil is charged by means
of a corona, using an image-wise blanked-out aluminum foil as a -
stencil. The charged image areas have a negative potential of 300
volts. The charge image thus produced is then developed with a
toner liquld prepared by dispersing 0 . 5 g of carnauba wax in a solution
of l g of a pentaerythrltol resin ester in lO ml of an isoparaffin and
diluting the resulting dlsperslon with a solution of 0 . 3 g of zirconyl-
2-ethylhexoate in 1, 000 ml of an isoparaffln wlth a boiling range bet-
'~ ween 189 and 210C. The toner-covered foil is converted into a print- ing form as described in Example 1.
It wlll be obvious to those skllled in the art that many modi-
fications may be made within the scope of the present invention without
departing from the spirit thereof, and the invention includes all such
mod~f~cat~ons .
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