EP0368177B1 - Process and device for the production of intaglio printing plates - Google Patents

Description

8. The invention relates to a method and a device for producing an intaglio printing plate according to the preamble of claims 1 and 8, respectively.

In conventional gravure cylinders, the surface formed from depressions (wells) and the webs remaining between them is produced by mechanical, electromechanical, electrothermal or chemical material removal - partly with the interposition of photo-optical and chemical auxiliary processes; see e.g. GB-A-2 198 085. Since the cells have different sizes, depths or a different distance from one another for receiving different amounts of color, the method is very complex in terms of controlling the required tools or in terms of the numerous operations. The form cylinders, which weigh up to several tons in large machines, have to be removed from the printing press to produce a new printing form (= negative image), illustrated in voluminous apparatus and then reinserted into the printing press. For all of these reasons, the gravure printing process that delivers high-quality products in terms of printing technology has so far only been used for very long runs for economic reasons.

The invention has for its object to develop a method and an apparatus for producing a gravure printing plate, by means of which the same can be produced extremely economically.

This object is solved by the characterizing features of claims 1 and 8, respectively. The gravure printing plate can be imaged directly in the printing press using the method and the device according to the invention. Forme cylinder transport devices are therefore completely eliminated. The Gravure printing plate produced according to the invention can be easily deleted in the printing press and prepared for a new image.

Advantageous configurations can be found in the subclaims.

Fig. 1

einen schematischen Ausschnitt einer Tiefdruckmaschine mit einer unmittelbar an einen Tiefdruckformzylinder angestellten Bildpunkt- Übertragungseinheit,

Fig. 2

einen schematischen Ausschnitt einer Tiefdruckmaschine mit einer Substanzübertragung mittels eines Transferbandes,

Fig. 3 bis 6

in vergrößerter Darstellung vier verschiedene Stadien bei einer mittels Transferbandes erfolgenden Bebilderung einer Tiefdruckform,

Fig. 7 a bis c

eine Variante mit einer Ausbildung des Transferbandes als austauschbare Cassette,

Fig. 8

eine Variante mit einer Anordnung des Transferbandes, der Bildpunkt- Übertragungseinheit und der Bildabgabeeinheit in einem Umrüstroboter,

Fig. 9

einen schematischen Ausschnitt einer Tiefdruckmaschine mit einer Druckbild- Löscheinrichtung.

Several exemplary embodiments of the invention are explained below with reference to the drawings. It shows

Fig. 1

1 shows a schematic section of an intaglio printing machine with an image transfer unit directly attached to an intaglio printing cylinder,

Fig. 2

1 shows a schematic section of an intaglio printing machine with a substance transfer by means of a transfer belt,

3 to 6

in an enlarged view four different stages in an imaging of a rotogravure form using transfer ribbon,

7 a to c

a variant with the transfer belt being designed as an exchangeable cassette,

Fig. 8

a variant with an arrangement of the transfer belt, the pixel transmission unit and the image delivery unit in a conversion robot,

Fig. 9

a schematic section of an intaglio printing machine with a print image eraser.

In Fig. 1, 1 is a printing form cylinder of a rotogravure rotary printing machine. A pixel transfer unit 2 can be set on the latter, which in this case has a guide bar 3 arranged parallel to a surface line of the printing form cylinder and a print head 4 which can be moved along the latter. The print head 4 is provided with at least one nozzle, through which a solid substance that can be liquefied under the influence of heat is sprayed out under pressure. The timing and quantity of the spraying out is controlled analogously to the inkjet principle of an inkjet printer by a control unit 5, which reads, via a signal line 6, digitally coded data corresponding to a printed image from an image memory (not shown). The substance is transferred point by line line by line, and if several nozzles offset in the circumferential direction of the printing form cylinder 1 are used, several lines can be written in parallel. The depth of information - which corresponds to the range of variation with regard to the amount of substance transferred - is preferably 1 byte per pixel, ie 256 possible color gradations.

The surface of the printing form cylinder 1 is provided as a gravure blank with a basic cell grid (see FIG. 3) which is formed from small cells 7 and webs 8 arranged between them. The depth of the wells 7 is selected so that they can accommodate at least the maximum amount of paint to be transferred.

If an amount of the liquefied substance, which is inversely proportional to the image information, is injected into one of the wells 7 from a nozzle of the pixel transmission unit 2, it hardens very quickly in contact with the cold surface of the printing form cylinder and forms a well depth at the bottom of the well 7 reducing layer 9 (see Fig. 5). In the case of a coloring process following this imaging process, each well 7 only fills with an amount of ink which corresponds to the volume of the well in the case of the rotogravure raw form minus the volume of the layer 9 (see FIG. 6). The inking takes place in a known manner by means of a height-adjustable ink box 10, in which a part of the printing form cylinder 1 is immersed in the raised state. Excess ink is scraped off by a squeegee 11 which can be adjusted to the printing form cylinder 1 and is supported on the webs 8, and is conveyed back into the ink fountain 10. The printed image is transferred from the cells to a printing material web 12 in accordance with their color filling transferred, which is guided around a printing cylinder 13 and is pressed by this to the printing form cylinder 1.

In a further exemplary embodiment shown in FIG. 2, the imaging of the printing form cylinder 1 takes place in an indirect manner. For this purpose, a transfer belt 15 is arranged between a pixel transfer unit 14 and the printing form cylinder 1. The pixel transfer unit 14 is composed of a guide bar 16 arranged transversely to the transfer belt 15, a thermal print head 17 which can be moved along the latter and is equipped with at least one heatable element, and a transfer film 18 arranged between the latter and the transfer belt 15. The transfer film 18 is on its side Transfer belt 15 facing underside coated with a solid, meltable substance when exposed to heat. It is wound up on a drum 19 and is transported synchronously to it after each line by which the transfer belt 15 is moved, the part of the transfer film used being wound onto a drum 20.

A different amount of the substance is melted and deposited on the transfer belt 15 by the heating element (s) of the thermal print head 17 in accordance with digitally coded image information read out by a control unit 21 from an image memory (not shown). The substance is transferred point by line line by line, it being possible for several lines to be written in parallel when using a plurality of elements offset in the circumferential direction of the transfer belt 15.

The information depth - which corresponds to the range of variation with regard to the amount of substance transferred - is preferably 1 byte per pixel, i.e. 256 possible color gradations. It is achieved by varying the intensity of the heating and the contact pressure of the heating elements.

The transfer belt 15 is brought over a plurality of deflecting rollers 22 to the printing form cylinder 1 so that it is on part of it Circumferential. In this part, an image delivery device 23 is arranged which, by the action of energy on the back of the transfer belt 15, causes the substance parts to melt again and transfer them to the printing form cylinder 1. The image delivery unit 23 is preferably formed by a heatable roller 24, which can be adjusted to the back of the transfer belt 15 with adjustable pressure. The transfer of the substance from the transfer ribbon 15 to the printing form cylinder 1 takes place line by line or even flat and is therefore considerably faster than the selective transfer by the thermal print head to the transfer ribbon. The decoupling of the slower writing of the transfer belt 15 from the much faster delivery of the substance stored there to the printing form cylinder 1 brings considerable time advantages in production: after completion of a printing form, the transfer belt 15 can be switched off from the printing form cylinder 1 during production and already with a substance application for that next required print image can be provided. With the appropriate length of the transfer belt, all the print images required for a shift or daily production can also be stored there in advance and thus temporarily stored.

3 to 6, part of the surface of the printing form cylinder 1 is shown enlarged in several phases of the printing form production. As shown in FIG. 3, the transfer belt 15 is made up of two layers: a backing layer 25 which is very tensile in the longitudinal direction and is dimensionally stable and a non-stick layer 26 which is firmly connected thereto and which preferably consists of polytetrafluoroethylene (PTFE). On the latter, the substance parts 27 a, 27 b, 27 c, 27 d ... released by the pixel transfer unit 14 from the transfer film 18 are deposited. In Fig. 4, the transfer belt 15 is pressed with its substance parts 27 a, ..., 27 d ... underside of the roller 24 against the surface of the printing form cylinder 1, melted by the action of energy on the back of the transfer belt 15 and in the Cell base grid pressed in, where they harden quickly in contact with the cold surfaces (Fig. 5).

Possibly. Remnants of substance protruding beyond the wells can be scraped off in an intermediate step (not shown) by means of a hot squeegee pulled over the webs 8 with a slight contact pressure. During the subsequent inking (see FIG. 6) of the now finished gravure printing form by means of ink fountain 10 and doctor blade 11, each well absorbs only such an amount of ink 35 as the cooled substance 9 has left of the original well volume.

There are various possibilities for the design of the transfer belt 15: It can be arranged in an exchangeable cassette 28 (see FIG. 7), which is imaged by a pixel transfer unit 14 arranged far away from the printing form cylinder 1 and is then turned on the printing form cylinder 1, whereby the substance parts 27 adhering to their surface are transferred to the cassette by an image dispensing unit 23 which is integrated in the cassette or which can be adjusted thereon.

The transfer belt 15 can also be designed with the pixel transfer unit 14 and the image transfer unit 23 in the form of a conversion robot 29 (see FIG. 8), which can be moved along the printing machine on a rail system 30 and with its end carrying the image delivery device 23 alternately to different ones Printing form cylinder 1 is adjustable. In this case, the transfer belt 15 is guided over a plurality of deflection rollers 31, which are mounted on individually pivotable levers, as a result of which the retooling robot 29 is highly mobile.

Other combinations of the individual elements shown in the various exemplary embodiments are also conceivable: Thus, the imaging of the transfer belt 15 (as a cassette or also as a retrofitting robot) can also be carried out by a pixel transfer unit 2 of the first exemplary embodiment, which works on the principle of an inkjet printer. Various variants are also conceivable for the image delivery device 23. For example, the substance parts deposited on the transfer belt 15 can be heated up Various types are carried out, such as a separate heating device 32 upstream of the roller 24 (see FIG. 2). The substance transfer can be magnetically or electrostatically supported if the substance is appropriately doped (see magnet 33 in FIG. 7 c).

For example, a thermoplastic or a wax can be used as the substance for the imaging.

The gravure printing plate produced by the method according to the invention and with a device according to the invention can be restored very quickly for a further imaging process after a printing process has ended. For this purpose, after washing off the ink residues according to FIG. 9, an extinguishing device 34 is placed on the printing form cylinder 1, which liquefies the thermoplastic substance by means of a heat source and removes it from the printing form cylinder 1 by means of a wiping and / or blowing or suction device. In order to remove the molten substance, non-woven fabric tapes can also be used, which absorb the liquefied substance into the interstices of the fibers via capillary forces.

The printing form cylinder 1 is preferably made of a ceramic material. Due to the high wear resistance and high heat resistance, such a printing form cylinder has a long service life even with frequently changing print images. At the same time, wear on a doctor blade sliding on ceramic webs is reduced.

Claims (14)

1. Process for the production of an intaglio forme which, during inking before the printing process, picks up different amounts of ink (35) in cells of different size and/or depth, characterised by the following process steps:

   a) production of an intaglio blank forme (1) having a basic cell matrix designed at least for the maximum amount of ink to be transferred,

   b) introduction of a solid substance (27), liquefiable by the effect of energy in an image point transfer unit (2, 14) in an amount in reverse proportion to the amount of ink to be transferred, into each of the cells (7).
2. Process according to claim 1, characterised in that the substance is applied to a transfer foil (18) and is delivered by the thermotransfer process to the intaglio blank forme.
3. Process according to claim 1, characterised in that the substance is sprayed in a melt-spraying process by a device (4) similar to an ink-jet printer.
4. Process according to one of the preceding claims, characterised in that the substance is deposited first of all on a transfer belt (15) in accordance with an amount in reverse proportion to the ink intensity of the individual image points, from which belt it is transferred to the intaglio forme by a further application of energy.
5. Process according to claim 4, characterised in that the transfer speed during transfer of the substance from the transfer belt (15) to the intaglio forme is greater than during transfer of the substance to the transfer belt (15).
6. Process according to one of the preceding claims, characterised in that, as a further process step, after the substance has been applied to the intaglio forme it is wiped off with a heatable doctor blade.
7. Process according to one of the preceding claims, characterised in that the image point transfer unit (2, 14) is guided in a guide strip (3, 16) and, line by line, addressing each cell (7) individually with an information depth of one byte, transfers the substance (27) indirectly via the transfer belt (15) or directly to the intaglio blank forme (1).
8. Device for the production of an intaglio forme which, during inking before the printing process, picks up different amounts of ink (35) in cells (7) of different size and/or depth, characterised by an image point transfer unit (2, 14) which is connected by means of signal lines (6) to an electronic image memory, and is provided with one or several elements which can be acted on by energy in accordance with the image information, which elements release portions of a substance (27) from a transfer foil (18) passing by the unit and coated with a meltable substance according to the duration and/or intensity of the energy effect for a negative imaging of an intaglio forme (1) and, by an intaglio blank forme (1) which, in the non-imaged state, has a uniform matrix of cells (7) following a specific function in size, depth and/or spacing, which forms the actual intaglio forme variously filled by the hardening parts of the substance (27) introduced in the liquid or pasty state.
9. Device according to claim 8, characterised in that the image point transfer unit (14) with a transfer belt (15) pivotable at several joints and an image-delivery unit (23) is disposed in a change-over robot (29) which can be moved along a printing machine and can be set against various intaglio forme cylinders (1) with its end carrying the image delivery unit (23).
10. Device according to claim 8, characterised in that the portions of the substance (27) released from the image point transfer unit are deposited on a transfer belt (15) which is arranged in an exchangeable cassette (28).
11. Device according to claim 10, characterised in that the cassette (28) can be coupled to an image delivery unit (23).
12. Device according to claim 10, characterised in that an image delivery unit is integrated into the cassette (28) which can respectively be coupled to an energy source when the cassette (28) is applied to an intaglio blank forme (1) to be imaged.
13. Device according to one of the preceding claims, characterised in that the intaglio blank forme is constructed as a seamless intaglio forme cylinder with a ceramic surface.
14. Process for erasing an intaglio forme produced according to claim 1, characterised in that after cleaning residual ink an internal or external heating of the intaglio blank forme (1) leads to liquefaction or sublimation of the substance and this is removed by an erasing device (34) constructed as a wiping and/or blowing-out or suction device.

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