FR2630555A1 - METHOD AND DEVICE FOR CREATING A LATENT IMAGE ON A LIGHT-SENSITIVE COATING OF AN OFFSET PRINTING PLATE - Google Patents

Abstract

The present invention relates to a device for creating a latent image on a light-sensitive coating of an offset printing plate by means of a beam of rays emitted by a light source and modulated by means of a photomask. characterized by: - a first unit 1 of liquid crystal layer; a brush 2 controlled by a computer oriented on a first face of this first unit of liquid crystal layer, sending pulses in correlation with the image; - a mirror 10 which sends the light emitted by the light source 4 onto a second face of the first unit of liquid crystal layer opposite the first face; and - a lens system 9 creating an image of the second face of the first unit 1 of liquid crystal layer on the offset printing plate 7.

Description

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  dissolved by means of a developer.

  According to another method, the original image is projected or reflected on a scale that can be selected on the printing plate starting from a new film, possibly a microfilm, which can be traced by a computer ( See: Druckindustrie (St. Gallen) 1987, 6

October, page 116).

  In any case, we therefore use a film that must be executed in the form of a photomask before

  manufacture of the printing plate from the artwork.

  The production of films already requires a long process, which moreover imposes binding conditions of dust-free workrooms. There is also the expensive editing of individual films on a

mounting sheet.

  The object of the invention is therefore to propose a method and a device allowing a simplified process and

  shortcut for the manufacture of a photomask.

  This object is achieved by a method for creating a latent image on a light-sensitive coating of an offset printing plate by means of a beam of rays emitted by a light source and modulated by means of a photomask, which is distinguished by the fact that a photoelectric relay matrix is used as a photomask and that the photoelectric relay matrix is controlled by signals which correlate with the image and by means of devices intended for use of this process which are distinguished on the one hand by a first liquid crystal layer unit, a computer-controlled brush oriented on a first face of this

263055S

  the first liquid crystal layer unit, sending pulses in correlation with the image, a mirror, which sends the light emitted from the light source to a second face of the first liquid crystal layer unit opposite to the first face and a lens system creating an image of the second face of the first liquid crystal layer unit on the offset printing plate, and secondly a second liquid crystal layer unit having an electrode array, the an array of electrodes that can be occupied by electrical signals, which correlates with the image, a beam beam guide such as this reaches a first face of the second liquid crystal layer unit and a radiation system. lenses for forming an image of a portion of the penetrating ray beam

  in the liquid crystal layer unit.

  Non-film production means for printing plates adapted to offset printing are certainly already described in the literature (see "Der Druckspiegel", notebook 8/81, pages 662 and following, and notebook 9/81 pages 744 to 748 and "Philips technische Rundschau" No. 1977/78, pages 214-224), but they require printing plates specially adapted for this purpose. With such a method the layout of a complete page of a print can be directly projected on a semiconductor layer of a printing plate. For this purpose the semiconductor layer is charged in the dark, and exposed to form the image by the projection of the artwork and discharged in this way and is then coated with toner. The exposure of such a printing plate by means of a computer guided light beam or laser pulse is described in "Der Polygraph", notebook 9/82, pages 675 to 682. This process uses the high sensitivity of the light conductivity of the semiconductor layer, so that it implements high light sources in the long wavelength range which are hardly suitable for the printing slab coatings that are produced according to the "positive or negative methods" mentioned in the introduction. Exposure variants with light or laser beams are described in

  "Angewandte Chemie", notebook 2/80, pages 95 & 106.

  Finally, German Offenlegungsschrift No. 32 48 178 discloses a method for coating, for imaging purposes, a printing plate for offset printing, in which color-receiving surface elements are transferred under the effect of heat and pressure and form the image on a hydrophilic surface of a

printing plate.

  Writing on a hydrophilic surface of a printing plate by means of oleophilic surface elements of a thermostained strip can be performed by thermal writing head or laser beam (LogEscan process) (see "Angewandte Chemie"). ", 92 (1980) pages 95 to 106, Vollmann: Neue Technologien zur filmlosen

Herstellung von Druckformen).

  The method according to the invention not only simplifies and shortens the photomask manufacturing process, but it has, compared to the known "no-film" exposure method of an offset printing plate, the advantage of the invention. can also be used for the "film-free" exposure of printing plates whose coatings are adapted to the "positive" or "negative" processes mentioned in

1 introduction.

  The control signals of the photoelectric relay matrix can be obtained by scanning a print artwork. It is also possible to use as an "image print" an image generated in a computer itself. In this way, by means of the method according to the invention, it is possible, for example, to complete the image to be created of the printing plate of a physically available artwork by means of additional "printing types" generated in a computer. . The use according to the invention of a photoelectric relay matrix as a photomask makes it possible in particular to avoid a chemical film development process which always requires a certain reaction time, which is therefore saved. Similarly, the drying of a developed film is eliminated, and the generally necessary mounting of

  individual films on an assembly sheet.

  The photoelectric relay matrix furthermore represents an extremely manageable photomask

flexible and always reusable.

  The control of the matrix & photoelectric relay by signals, which correlate with the image, can

  be done using a computer.

  The invention will now be described in more detail with reference to the drawing which represents: FIG. 1 a diagrammatic representation of a device according to the invention employing a photomask in the form of a reflection mask, FIG. 2 a schematic representation of a device according to the invention employing a photomask in

form of transmission mask.

  The method according to the invention essentially consists in forming, by means of the signals, on the light-sensitive coating of an offset printing plate, chosen light points of a corresponding display.

To the picture.

  In the variants described below of the process according to the invention, it is used that the liquid crystal layers modify their optical behavior.

controllable way.

  In the use of this fact according to the invention it is thus provided according to the first variant according to FIG. 1 to realize the photoelectric relay matrix of a first type of liquid crystal coating, to direct it on one side of a first liquid crystal layer unit 1 constituted in this way by means of the correlation pulse image of a computer-guided brush 2 and to use the opposite face of the liquid crystal coating unit 1 as a reflection mask for the light beam 3, which is emitted by a light source 4. It is possible to use here as a light source 4 for example a mercury vapor lamp doped with metal halide. As

  brush 2 can be used a cathode ray or laser.

  In FIG. 1 a brush 2 is indicated in a position

arbitrary, instantaneous.

  A detailed description of the units to be omitted can be omitted

  layer? used in the context of the invention and their control since the corresponding indications are available in technical documents (see for example: "SPSE-The Society for

  Imaging Science and Technology "1987, pp. 108-115).

  Details regarding the use of brushes can be found in "Journal of Applied Physics", American Institute of Physics, Bd. 57 (4) of 15.2. 1985 pages

1356 and following.

  For the first variant of the method according to the invention it is essential to use a first type of liquid crystal layers, where, by local application of a brush to a first face, locally reflective and non-reflective zones are produced for

  the light coming on the opposite side.

  In a second variant, the photoelectric relay matrix is made in a second type of liquid crystal layer, an electrode matrix is created on a second unit 1 'of

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  Liquid crystal formed in this way, electrical signals 5, correlated with the image, are applied to the electrode array and the second liquid crystal layer unit 1 'serves as a transmission mask for the light beam 3 (FIG. .2). It is essential here for this second variant, unlike the first variant mentioned above, to employ a second type of liquid crystal layer in which, as a result of the local application of electrical signals, zones of the crystal layer are formed. locally transparent liquids to

  light and not transparent to light.

  The local application of electrical signals 5 is shown in FIG. 2 schematically by the arrow

indicating the signals.

  In the two mentioned processes, a respective display of the desired image in the form of light spots is produced on the respective unit 1, 1 'of liquid crystal layer, and this display forms an image on the light-sensitive coating 6 of the plate.

offset printing 7.

  For this imaging a lens system is provided in a complementary structure. This lens system has, according to a development of the invention, a projection lens 9 movable in the direction of the projection 8 and in the opposite direction. In this way, it is possible to project on the coating 6 an image of

the dimension display to choose from.

  A device for carrying out the method according to the invention employing the first mentioned type of liquid crystal layer is schematically shown in FIG. 1. With this device the light beam 3 emitted by the light source 4 and brought into convergence With the aid of a lens 11 comes, by means of a mirror 10, striking a face opposite to the beam 2 of

  the first unit 1 of liquid crystal layer.

  In order to obtain a luminous efficiency as large as possible from the light beam 3, the mirror 10 is a beam splitter and is arranged in such a way that the light of the beam 3 reflects on the unit 1 of the liquid crystal layer. striking substantially perpendicularly the unit 1 of layer of

liquid crystal.

  A device for implementing the method according to the invention employing the second mentioned type of liquid crystal layer is schematically shown in FIG. 2. The light beam 3 is here guided so that it passes on its way to the offset printing plate 7 the second unit 1 'of liquid crystal layer depending on the application

  local to the latter electrical signals 5.

  The process according to the invention, as mentioned, can be used for the exposure of common offset plates, for example having a diazo emulsion or silver halide coating. Simply for this purpose to create the light beam 3 with a light source 4 rich in energy to create the necessary light output here on the

  corresponding offset printing plate.

  However, the method according to the invention can also be used for exposing semiconductor coatings of electrically charged offset printing plates. It suffices simply to employ a light beam 3, which has the necessary lighting power, which correspondingly is lower on the offset printing plate concerned. This relatively lower lighting power can also be obtained by means of a device according to the invention equipped for the exposure of current offset printing plates, by introducing a filter - not shown.

  in the drawing - in the light beam.

Claims (11)

  A method for creating a latent image on a light-sensitive coating of an offset printing plate by means of a ray beam emitted from a light source and modulated by means of a photomask, characterized in that what is used as photomask a photoelectric relay matrix (1, 1 ') and in that the photoelectric relay matrix is controlled by   signals that correlate with the image.   2. Method according to claim 1, characterized in that the photoelectric relay matrix consists of a first liquid crystal layer unit (1) on one side of which impulses are sent, in correlation with the image, d a brush (2) controlled by a computer, and the opposite side of which is used as   reflection mask for the beam of radius (3).   3. Method according to claim 1, characterized in that the photoelectric relay matrix is constituted by a second liquid crystal unit (1 ') comprising an array of electrodes, in that the matrix of electrodes is occupied by signals electrodes (5) which correlate with the image and that the second liquid crystal layer unit (1 ') is employed as a transmission mask for the radiation beam (3).   4. Method according to one of claims 1 & 3,   characterized in that the beam of radius (3) is guided by a lens system (9). -   5. Method according to claim 4, characterized in that a lens system (9) is used, with which the image created on the offset printing plate (7) can vary in size.   6. Device according to one of claims 1 to 5,   characterized in that the beam of radius (3) is created with a source of energy-rich light such that with the radiation beam (3) on the offset printing plate (7) an intensity of lighting which would be sufficient to expose a current offset printing plate, for example comprising a diazo emulsion or silver halide coating, with a photomask applied over the coating in the form of a usual film. of silver halide so that a latent image of the silver halide film is produced on the coating.   7. Method according to one of claims 1 to 5,   characterized in that a beam of rays (3) is used with which the illumination power is obtained on the offset printing plate (7) which is sufficient to discharge by exposure to the light beam (3) a semi- print plate driver   electrically charged offset in the dark.   8. Method according to one of claims 1 to 5,   characterized in that obtained on the offset printing plate by introducing a filter in a beam of radius (3) a lighting power adapted to a discharge of a charged semiconductor coating   electrically from the offset printing plate.   9. Device for creating a latent image on a light-sensitive coating of an offset printing plate by means of a beam of rays emitted by a light source and modulated by means of a photomask characterized by a first unit (1) of liquid crystal layer; - a computer-controlled brush (2) oriented on a first face of this first layer unit; 263055S   it liquid crystals, sending impulses in correlation with the image; a mirror (10) which sends the light emitted by the light source (4) to a second face of the first liquid crystal layer unit opposite to the first face and - a lens system (9) creating an image of the second face of the first layer unit (1)   liquid crystals on the offset printing plate (7).   10. Device according to claim 9, characterized in that the mirror (10) is a beam splitter and the light of the beam of beams (3) reflected by the mirror (10) on the first unit (1) layer   liquid crystal reaches substantially perpendicular   stretching on the first crystal layer unit liquids (1).   Apparatus for creating a latent image on a light-sensitive coating of an offset printing plate by means of a ray beam emitted from a light source and modulated by means of a photomask, characterized by a second liquid crystal layer unit (1 ') comprising an array of electrodes, the array of electrodes being able to be occupied by electrical signals (5), which correlate with the image,   a guide of the beam of beams (3) such as this   it arrives on a first face of the second liquid crystal layer unit (1 ') and - a lens system (9) to form an image of a part of the beam bundle (3) penetrating into   The unit (1) of liquid crystal layer.