EP0813957B1 - Process and apparatus for intaglio printing using an erasable form - Google Patents

Description

The invention relates to a method and a device for gravure printing an erasable and reusable gravure form, starting from one Gravure blank with a minimum of the maximum to be transferred Basic grid of colors.

Gravure refers to a printing process using printing elements that face each other the mold surface are lowered. After the complete coloring of the Printing form, the surface is freed from the printing ink. This only remains in the recessed positions. As a printing form z. B. copper-plated steel cylinders Clamping cores pushed on hollow cylinders or in some cases on cylinders stretched copper sheets.

The type of coloring and the blank coating of the mold surface do not allow pure surface pressure. The whole drawing must be in lines, dots or Raster elements can be resolved. Because of the different depth and size of the individual printing elements, these more or less ink, the As a result, the imprint has different characters at the different image points Color strength.

Different working methods for the production of a gravure form are used today applied. In the case of the depth-variable processes, the etching principle consists in the slow diffusion of concentrated iron chloride solutions through a Pigment gelatin layer. The pigment copy on the copper plate consists of a hardened gelatin relief that corresponds to the tone gradations of the slides. The engraving processes are characterized by scanning the image and line by line Text with photocells and simultaneous engraving of the printing form with engraving heads. Particularly noteworthy is the introduction of recesses in the Copper layer of the printing form by means of a high-energy electron beam is directed in a vacuum onto the raw form and removes material there. The so engraved printing form can be provided with depth and area-variable grids.

Indentations can also be made using a high-energy laser beam , taking care that suitable measures are taken to ensure the coupling of the laser energy into the substrate, because copper for the most part uses a laser beam without special pretreatment reflected.

Furthermore, DE-OS 27 48 062 describes a method for producing a engraved printing form is known, in which only a gravure raw form is provided, by making the smooth surface even with depressions of the same depth and Size, then the engraved surface with a light-sensitive Mass is covered so that all the wells are filled. On it photographically exposed the raw form with the desired image so that the polymerize exposed areas, wash out the unexposed portions can and this results in an image differentiation.

In general it can be said that the following applies to all gravure printing processes: Printing form are lower than non-image areas. Forms especially in squeegee printing the grid network of uniformly high webs, the image areas and limit one Form the contact surface for the squeegee. There is a special set of for each print job Printing form cylinders (one printing form cylinder with a corresponding one for each printing ink) Number of printed pages) required. These cylinders are in depending on the print format the required cylinder circumference. When setting up the gravure or Rotary printing presses are the corresponding printing form cylinders to replace. Such a cylinder z. B. today weighs in a width of 200 cm about 800 kg. Since the methods described so far are only outside the Printing machine are feasible, this is a high mechanical effort required. In addition, each of these manufacturing processes involves steps such as Electroplating or coating, exposure and development, which exclude that the same printing form without extensive, in particular chemical treatment can be reused. In addition, usually takes place after the pictorial Etching or engraving, i.e. removal of material, chrome plating to increase the Service life.

If the printing form is to be stored for repeat orders, this is usually the To provide space for the entire cylinder. The printing form production is also especially if galvanic steps are necessary, very complex and therefore expensive. The resulting toxic sludge is also ecologically unsafe.

In contrast, DE 38 37 941 C 2 discloses a method for producing a Intaglio printing form, through which the images take place directly in the printing press can, in addition, the images of the rotogravure form deleted in the printing press and can be prepared for a new illustration. It will too a gravure blank with at least one to be transferred to the maximum Color amount of basic grid produced. Now in the printing press a nozzle of the pixel transfer unit or by image-correlated ironing a quantity of a thermoplastic which is inversely proportional to the image information Substance introduced into the well to increase the volume of the wells reduce. This means that in contrast to the imaging of a gravure blank, the other process applied image material. Can in the press then after the print job the thermoplastic substance by means of a Liquefied heat source and by means of a wiping and / or blowing or Suction device can be removed from the printing form cylinder.

The pictorial material application, however, poses problems for the position accuracy the illustration. It is not readily possible to find material on the webs is placed completely in the wells. The complete one However, it is necessary to bring in all of the transferred material desirably contributes to reducing the volume of the depressions.

Therefore, is already in the document published on September 11, 1996 EP-A-0 730 953 has proposed the recesses of the basic grid of the Gravure blank evenly by means of a liquefiable substance through a Fill the application device, then imagewise material through a pixel transfer device ablate from the wells that so figuratively to color screened gravure form by means of a coloring system and then in Gravure printing, the gravure blank after printing can be regenerated and the wells are filled evenly again can.

It is used as a liquefiable substance for filling the basic grid for example a thermoplastic, i.e. thermoplastics (plastomers), such as polyolefins, vinyl polymers, polyamides, polyesters, polyacetates, Polycarbonates, partly also polyurethanes and ionomers, or hotmelt (wax), Lacquer or a cross-linkable polymer melt or solution used.

Using a laser, preferably an NdYAG or NDYLF laser, the filled rotogravure plate burned free of image.

Using a chambered doctor blade, inking is carried out with aqueous printing ink and preferably printed in indirect gravure on a substrate.

After the required edition has been printed, the rotogravure plate is printed using a Regeneration device, preferably in the form of an ultrasonic cleaning system, cleaned of paint residues and the liquefiable substance from the wells of the Basic grid removed so that the cycle filling, image-like ablation, coloring, Printing and regeneration can begin again.

The image deletion (regeneration) can also be done by a complete cleaning of the Basic shape with the help of a pressurized water jet Pressure washer are made possible. An arrangement is used for this, such as it has already been disclosed, for example, by EP 0 570 879 A3. Such Arrangement consists of a double-walled chamber that faces the gravure form open and by means of seals over the mold to the environment is sealed off. The inner cell contains nozzles through which the water flows with high Pressure is sprayed onto the surface of the gravure form. From the encased outer chamber area is suctioned off, so that in particular from the already cleaned area the liquid is drawn off and the gravure form after the Treatment is clean and dry.

The pressure washer can work on at least two different levels, a level with low fluid pressure and / or temperature in Mainly used to remove the remaining colors and the other levels with a correspondingly higher liquid pressure and / or temperature, sometimes up to complete removal of the filler.

The above statements all relate to the implementation of the Measures described within a gravure printing press, of course however, that the measures described naturally also outside of one Printing machine are feasible.

It should be noted that, as a rule, such a rotary printing process solvent-based printing ink (also include water-based printing inks certain amounts of solvent) is transferred to the substrate and then the solvent in a drying section of the printing press the substrate and from the part lying on it or partially penetrating layer of paint must be driven out. Here is the high one Space requirement for the dryer and the high energy consumption for drying Disadvantage. The release of solvents also pollutes the environment. Both water-based printing inks also escape when the ink film dries nor the amines used for the saponification or the ammonia in the Ambient air. These released compounds are not only unpleasant to smell but also harmful to health.

Furthermore, especially when using a pressure washer Regeneration of the basic form at least three different process media, namely the extinguishing fluid (water), the printing ink (usually solvent-based Ink) and the filler (liquefiable substance) involved in the process, see above that there is a certain risk of process media mixing during production consists.

DE-A-2 100 031 describes a process for the production of gravure forms a latent engraving plate that has a regular pattern of fixed bars and contains a liquid mixture between the webs that can be removed to to leave a regular pattern of open cells between the bars, this mixture being curable by actinic radiation and a solid product results.

A further development of the printing inks is directed towards those with UV-curable ones Binder systems based on the well-known principle of UV curing Make use.

DE 43 07 766 C1 describes a process for producing a UV-curing agent Flexographic printing ink and its use in flexographic printing machines.

The UV printing inks also contain coloring substances and additives Photoinitiators that also polymerize when exposed to UV radiation trigger contained binder component. Such UV systems can, such as is also described in DE 43 07 766 C1, according to a radical or polymerize using a cationic mechanism. Solvents or water are in UV inks not included. Technical, health or environmentally relevant Disadvantages and problems caused by solvents or water in printing inks do not occur with UV printing inks.

Proceeding from this, the object of the present invention is a method and to provide a device for gravure printing, whereby on the one hand evaporating solvents or harmful compounds Avoid using an erasable and reusable gravure form and on the other hand the generic process concept is simplified.

This object is achieved by the method steps of claim 1 and Device for performing the method according to claim 8 solved.

Characterized in that the wells of the basic grid already in the filling process Gravure blank can be filled using a UV printing ink, this in the Wells is hardened, then in the imaging process by thermal ablation hardened UV printing ink is removed, then the Image grid is colored again with liquid UV printing ink and after Printing process for retrofitting the gravure form under a deletion process Use of UV printing ink is only a process medium Process involved that all functions, namely the extinguishing fluid, the printing ink and of the filler, apart from the fact that evaporating solvents or harmful connections no longer occur, a Process media mixing excluded and at the same time increased Process reliability achieved.

The direct result of this advantage is that the overall process is simplified and thus fewer subsystems for a device for carrying out the method required are. Thus, in the present invention, the generic extinguishing, filling and chamber doctor blade systems required can be realized by an aggregate.

By using liquid UV printing inks in the invention Process concept there are further special advantages.

The property of the color that it does not dry has a beneficial effect especially for indirect gravure and for automatic processes over a longer period Period.

The high color strength, in turn, is favorable for laser power requirements and not lastly, the dryers can advantageously be built comparatively very small be, whereby a compact design of the device is possible.

Fig. 1

den prinzipiellen Ablauf der erfindungsgemäßen Verfahrensschritte,

Fig. 2

den prinzipiellen Aufbau einer Vorrichtung zur Durchführung des erfindungsgemäßen Verfahrens in einem Tiefdruckwerk,

Fig. 3

eine Druckvariante mittels des erfindungsgemäßen Verfahrens.

A preferred exemplary embodiment or variants of the invention are explained below with reference to the drawing. It shows a highly schematic:

Fig. 1

the basic sequence of the method steps according to the invention,

Fig. 2

the basic structure of a device for carrying out the method according to the invention in a gravure printing unit,

Fig. 3

a print variant using the inventive method.

As shown in Fig. 1, the inventive method can by four Describe process steps:

Filling a gravure blank 1 with filler (A).

The depressions of the basic grid of the gravure blank 1 become even by means of a UV printing ink by an application device 2 in the form of a Chamber doctor blade filled and a UV dryer 3, which is directly above the raw form 1 positioned, activated. The printing ink supplied by the doctor blade 2 becomes thereby hardened in the recesses. The low shrinkage that occurs in the The color is solidified by turning it several times during the filling process compensated, that is, through successive filling can be any exact filling be generated. In practice, 1 to 20, preferably 3 to 8 turns the rotogravure blank 1 optimal filling per filling process.

Imaging of the filled gravure blank 4 by thermal ablation of the Filler (B).

The ink supply of the filling process (A) is interrupted, the doctor blade 2 is switched off and the imaging process started. The imaging takes place by means of a pixel transmission device 5 using a laser by thermal ablation. A YAG laser is preferably used, which due to its emitted wavelength of 1.064 µm is very well absorbed by the pigment black of the black UV printing ink. Alternatively, IR diode lasers with a comparable effect can be used. When using this type of laser, the printing ink "black" is therefore preferably used as the filler. When using lasers whose absorption behavior is determined less by the pigment type of the printing ink and more by the binder of the printing ink, colored printing inks can also be used for filling. For example, the emitted light of the CO ₂ laser with a wavelength of approximately 10.6 µm is preferably absorbed by many organic binders.

Print (C)

The gravure printing plate 6, which is screened in terms of image, is inked by means of a inking system 7 in the form of a chamber doctor blade with UV printing ink, so that printing can be carried out on the printing material 8.
Indirect gravure, which permits an expanded range of substrates, is preferably used as the printing method. An intermediate carrier has a positive effect with regard to color management and color gradient when using UV printing ink. In principle, direct gravure printing is of course also possible with this method.

Deletion of gravure form 6 (D)

In the method according to the invention, the gravure form 6 is deleted in primarily by refilling the ablated image areas. Still can different variants serve to carry out.

The simplest case is with the printing ink "black" (or when using a laser-sensitive binder material even with "color printing ink") Describe as follows: The deletion process (D) is identical to that Filling process (A), that is, after the printing process (C) after setting the usually performed again at a significantly lower speed Filling process (A) activated the UV dryer 3. The liquid color that the Images were recorded, hardened, so that the gravure blank 1 again is evenly filled with a hardened UV printing ink. This variant is the number of cylinder revolutions for the filling process (A) is preferably identical with that for the deletion process (D).

When using "black" as filler and "color printing ink" as printing ink a cleaning process must preferably be carried out before the extinguishing by neither filling Preceding gravure form 6.

A printing plate cleaning is not necessary to ensure a good combination of old and to achieve a new filling (same type of binder results in a good bond), but not to increase the sensitivity of the filler at the contact points change. In the presence of colored pigments, the absorber density (Pigment black) reduced. The result is a sensitivity reduction that increases Color density errors in the proof of the subsequent order can result.

The cleaning process can be designed very simply: after the doctor blade 7 with colored printing ink and a large part of that in the wells remaining printing ink through the printing process over the substrate (paper) 8 was removed, the chamber doctor blade 2 for the filler (identical to the Chamber squeegee 7 for coloring the image areas). After a few Revolutions of the gravure form 6 under the activated filler chamber doctor blade 2, however, when the UV dryer 3 is turned off, the residual ink is from Wells of rotogravure plate 6 rinsed. Contamination of the filler in the Chamber squeegee 2 with colored printing ink is in the alcohol range and is therefore irrelevant.

The stability of the re-filling is the same as the previous filling comparable. Nevertheless, the accumulation of foreign substances in the filler is due of impurities (from the room air and in the printing process e.g. from paper dust) not be ruled out. This fact can be countered by following a definable number of changeovers complete removal of the Filler from the depressions of the gravure blank 1 using "laser erasing" (the means that the laser ablates the filler completely from the wells of the Gravure blank 1 and writes full-tone image).

2 shows a printing unit 10 for indirect gravure printing with a Ink transfer cylinder 12 and an impression cylinder 13, being between the latter the printing material 14 is carried out. At a gravure cylinder 11 is in Direction of rotation one for the complete filling of a basic grid of a raw form suitable application device 2 emitting UV printing ink in the form of a Chamber squeegee employed. A pixel transmission device 5 for imagewise Ablation in the form of a laser, in particular in the form of a high-power laser, the Part of an exposure unit traversing the gravure blank, but also can be a semiconductor laser arrangement of several semiconductor lasers is on the Surface of the gravure cylinder 11 positioned. On the application facility 2 for the filler opposite side of the gravure cylinder 11 is a UV printing ink emitting inking system 7 also in the form of a chambered doctor blade arranged. The doctor blade 2 for the filler and the doctor blade 7 for the Coloring is preferably of identical construction and can be set and switched off on the circumference of the gravure cylinder 11 positioned. Furthermore, at least one is anyway Printing dryer width spanning, swinging on and off UV dryer 3 am Gravure cylinder 11 is provided. By clever positioning, in the present Fall in the direction of rotation of the gravure cylinder 11 after the inking system 7, one Swiveling UV dryer is suitable for the filling process and for the printing process Sufficient UV dryer.

In special cases, the application device 2 and the coloring system 7 can also be used instead two identical chamber doctor blades just as a common unit in the form of one Chamber doctor blade be performed so that the filling and inking process with a single chamber doctor blade is feasible.

Due to the permanent presence of two UV printing inks in the printing unit ("black" and "color printing ink") is the rapid automatic changeover from color printing to b / w - printing or vice versa possible. For example, according to FIG skilful printing material management a conversion of a four-color printing machine to four Single color printing machines possible.

A ceramic anilox roller with a high gravure blank is preferred Line number used. Ceramic material shows better wetting behavior as chrome. The high number of lines improves the color transfer qualitatively and quantitatively.

The lamps available on the market with mercury vapor tubes come as UV dryers in question. Ozone-reduced or ozone-free lamp types are preferred used.

UV printing inks are characterized by a high reaction speed at the Solidification from. Solidification in the ms range is state of the art. In the Solidification creates a highly cross-linked and therefore poorly soluble and infusible substance. In principle, any UV-curable, solvent-free liquid paint can be used. The are particularly suitable for this cathionically crosslinking color types.

Claims (13)

1. Process for gravure printing by means of an erasable and re-usable gravure forme (4), starting from a blank gravure forme (1) having a basic screen designed at least for the maximum amount of ink to be transferred, in which, to produce the printing forme, the depressions in the basic screen of the blank gravure forme (1) are uniformly filled in a filling procedure (A) by a UV printing ink by means of an applicator (2), the uniformly applied UV printing ink is hardened by means of a dryer (3) which can be positioned over the blank gravure forme, then hardened UV printing ink from the depressions is removed in a subsequent imaging procedure (B) by thermal ablation by means of a pixel transfer device (5), the image-conformally screened gravure printing forme (4) is inked with UV printing ink by means of an inking system (7), and then a printing process (C) is carried out, and the gravure forme passes through an erasure procedure (D) for re-working.
2. Process according to claim 1, characterised in that the erasure process (D) is carried out using UV printing ink.
3. Process according to claim 1, characterised in that the printing process (C) is carried out in indirect gravure.
4. Process according to claims 1 to 3, characterised in that the erasure procedure (D) includes the steps of uniformly filling the gravure forme (4) with UV ink, and solidifying the applied liquid UV printing ink by means of a UV dryer (3).
5. Process according to claims 1 to 3, characterised in that the erasure procedure (D) includes a cleaning process of the gravure printing forme (4) by way of rinsing out the residual liquid ink from the printing forme screen by liquid UV printing ink by means of the applicator (2) provided for the filling, and then the uniform filling of the gravure forme (4) with UV ink, and the solidification of the applied liquid UV printing ink is carried out by means of a UV dryer.
6. Process according to one of the preceding claims, characterised in that after a pre-determinable number of re-working procedures a complete re-production of the basic screen of the blank gravure forme (1) is carried out by complete removal of the filling in the depressions.
7. Process according to one of the preceding claims, characterised in that at least cationically or radically hardening UV printing inks are used for the filling procedure (A) and erasure procedure (D).
8. Device for gravure printing for carrying out the process according to claim 1, characterised in that an applicator (2) suitable for completely filling the basic screen, and delivering UV printing ink, at least one UV dryer (3) which can be pivoted on and off and which engages over the printing forme width, a pixel transfer device (5) for the image-conformal ablation of the surface of the gravure forme (4) and an inking system delivering UV printing ink can be positioned in the circumferential direction on a rotating gravure forme (1) having a basic screen designed at least for the maximum amount of ink to be transferred.
9. Device according to claim 8, characterised in that a ceramic screen roller with a high number of lines is provided for the blank gravure forme.
10. Device according to claim 8, characterised in that a chambered doctor blade of similar construction is respectively provided for the applicator (2) and the inking system (7).
11. Device according to claim 10, characterised in that the applicator (2) and the inking system (7) is constructed as a common unit in the form of a single chambered doctor blade.
12. Device according to claim 8, characterised in that a traversing exposure unit in the form of a laser, in particular in the form of a high-power laser, is used for the pixel transfer device (5).
13. Device according to claim 12, characterised in that a semi-conductor laser arrangement comprising several semi-conductor lasers is provided for the laser (5).

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