LISSAGE D'UNE PELLICULE DE POLYTETRAFLUOROETHYLENE RUGUEUSE PAR EXPOSITION AUX RAYONS LASER

SMOOTHING ROUGHENED POLYTETRAFLUOROETHYLENE FILM BY EXPOSING TO LASER RADIATION

Abrégé anglais

Abstract of the Disclosure
This invention relates to an improvement in the process for the
manufacture of a planographic printing form by imagewise exposure to
radiation of a roughened polytetrafluoroethylene film,
the improvement comprising exposing the film to laser light until
the film surface is smooth.

Revendications

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. In the process for the production of a planographic printing form
by imagewise exposure to radiation of a roughened polytetrafluoroethylene
film,
the improvement wherein said exposure to radiation comprises
exposing the film to laser light until the film surface is smooth.
2. A process according to claim 1 in which the laser light has a
wavelength in the range of about 300 to 600 nm.
3. A process according to claim 2 in which the laser is an argon
laser.
4. A process accord to claim 1 wherein said roughened film is
obtained by treatment with a solution of sodium in liquid ammonia.

Description

~ 108~3363 K-2395
PROCESS FOR THE PRODUCTION OF PLANOGRAPHIC PRINTING ~ -
FORMS BY MEANS OF LASER BEAMS
.
The present invention relates to a process for the production of
planographic printing forms in which a roughened polytetrafluoroethyLene
film is imagewise expased to a laser beam and ink repellent non-image
areas are thereby produced.
In the photomechanical production of planographic prLnting forms
a copying material usually provided with a light-sensitive layer is
imagewise exposed to light and then developed with a suitable developer
solution, whereby oleophilic image areas and hydrophilic non-image
areas are obtained. The oleophilic image areas of the layer usually re-
main after development, whereas the non-image areas are usually dissolv-
ed during development, leaving the carrier surface bared.
For development, organic solvents or alkaline or acidic aqueous -
solutions are generally used, depending upon the nature of the layer. In
working with these solutions, certain safety measures, for example dis-
tillation or neutralization, must be observed. It would be desirable,
therefore, to eliminate such developer solutions.
It is known that polytetrafluoroethylene films having a smooth
surface repel all printing ink ~greasy ink and water-based ink) and that
polytetrafluoroethylene films having a roughened surface are ink recep-
tive.
The films are usually roughened in solutions of sodium in liquid
ammonia or by means of a corona discharge. Further methods are de-
scribed in the journal "Kunststoff-Rundschau" (1964), Volume 10, pages
574 ff.
It is also known to use polytetrafluoroethylene films as printing
form carriers for lithographic printing. U. S. Patent No. 3,368,483,

- ~ K-2395
` 1088363
discloses the production of a lithographic two-color printing form in-
cluding the following steps:
1. roughenlng of polytetrafluoroethylene,
2. sensitizing with the ald of a water-soluble diazo
compound,
3. first exposure under a (negative) original for the
first (water-based) printing ink and devetopment, and
4. second exposure under a (positive) original, whereby
the roughened surface is to be changed back into its
original smooth condition in the areas struck by light.
The result is a printlng form comprising three areas that have -
different affinities towards printing ink and thus allowing,among other
thlngs, to obtaln a two-color print with greasy and water-based printing
ink from one printing form.
A considerable disadvantage of this process is the low light-
sensitivity to UV llght of the roughened polytetrafluoroethytene surface. -~It has been found that exposure to conventlonal UV light sources must
be sustained for many hours in order to change the roughened, ink re-
ceptive material back into its original ink repellent state.
A simSlar process is disclosed in DL Patent No. 103,977, in
which polyvinyl chloride surfaces or polyamide surfaces are Imagewise
exposed to high-energy radiation. Thus their wetting propertles relative
to liquids are changed. There is no information as to the nature of the
high-energy radiation and the llquid used for measuring the contact
angle. It Ss not evident whether or not the treatment described in the
above-mentioned patent leads at all to a differentiation sufficient for
practical use in planographic printing.

'` ~0~38363 K-2395
In German Offenlegungsschrift No. 1,960,959, a process for the
production of printing plates is described in which a relief pattern is
engraved in the surface of a polymer, e.g. a tetrafluoroethylene polymer, ~ ~
by means of laser radiation. This process also requires relatively high ~ -
energies, i.e. Iong exposure tlmes, since relief depths of about 0.2 to
0.8 mm are produced (see Table I, page 14).
It is the object of the present invention to provide a process for
the production of planographic printing plates by exposure to light of
light-insensitive or of iow light-sensitivity material, which process
works with considerably shorter exposure times.
The invention is a process for the production of planographic
printing forms by imagewise irradiation of a roughened polytetrafluoro-
ethylene film.
In the process, the film is exposed to laser light until the film
surface is smooth.
The invention achieves a reduction of the exposure time from
several hours to a few minutes, through the use of U~J light.
The process according to the invention provides a new and ex-
ceptionally simple method of producing planographic printing forms. The
recording material used ln the process is relatively insensitive to day-
light and artificial light as well as to aging. It has a practically un-
Iimited storage life. The only process step is the imagewise exposure
of the material to laser beams.
The exposed plate is placed into an offset printing machine with-
out further treatment, and greasy printing ink and fountain solution are
applied in the usual manner. In the case of an optimum differentiation
between image areas and non-image areas, and if printing ink adjusted
accordingly is used, no fountain solution is required in the offset
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`~ 1088363 K-2395
printing machine, i.e. printing may be carried out according to the dry
offset process with printing ink based on oil.
Lasers suitable for the purposes of the invention are efficient
lasers which emit radiation having shorter wavelengths, for example Ar-
lasers, krypton-ion lasers and the like, that emit radiation of wave-
lengths between 300 and 600 nm. A 3 to 30 watts argon laser having an
amperage of between 15 and 35 amperes and linear deflection speeds of
more than 10 cm/sec are preferred.
By focusing the làser beam by means of an optical system, foci
are produced on the surface to be irradiated that have a diameter of less `~
than 50,4m.
It is suitable to control the laser beam with the aid of a prede-
termined linear movement and/or screen movement. The process and
apparatus for controlling the laser beam by means of computers as well
as focusing, modulation or deflection of the beam are described, for
example, in German Offenlegungsschriften Nos. 2,318,133, pages 3
ff; 2,344,233, pages 8 ff, and in U. S. Patents Nos. 3,7S1,587; -
3,745,586; 3,747,117; 3,475,760; 3,506,779, and 3,664,737.
A particular advantage of the process according to the invention
is that the carrier whlch has been imagewise exposed to radiation may
be placed into an offset printing machine either immediately or after
storage for any time desired, and printing may be begun immediately.
The need for development or decoating of the image-free areas of the
- carrier, as is necessary for the known customer-coated and presensi-
tized offset printing plates and which often must be carried out in bulky
and exper.sive developing machines, is completely eliminated. This
advantage considerably supports the efforts made to speed up and
rationalize offset printing.
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~1088363 K-2 3 9 5
The invention wiLl be further illustrated by reference to the
following specific example:
Example
In order to roughen it, a polytetrafluoroethylene film is dipped
for 60 seconds into a 3 per cent by weight solution of sodium in liquid
ammonia and is then cleaned, rinsed and dried. The roughening causes
the surface tension to increase from 18 dynes/cm to more than 60
dynes/cm, and the surface becomes a dark brown color. For the manu~
facture of the printing form, imagewise exposure to radiation is carried
out with the aid of an argon/krypton laser having a total capacity of 13
watts and a current intensity o~ 32 amperes, the deflection speed
amounting to more than 100 mm/sec.
By focusing the beam by means of an optical system, a focus -
having a diameter of about 7~m is produced in the case of a power den-
sity of about 7.5 megawatts/cm2.
The areas exposed to radiation have a light color. The printlng
film is put into an offset printing machine without further treatment and
printing is begun, the non-exposed areas accepting greasy printing ink.
More than 40,000 prints are obtained.
It will be obvious to those skilled in the art that many modifi-
cations may be made within the scope of the present invention without
departing from the spirit thereof, and the invention includes all such
modifications.
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