EP2151324B1 - Method for producing a rotative printing plate for insertion in a roller rotation printing method - Google Patents

Description

The invention relates to a method for erasing and re-imaging a rotary printing form for use in a web-fed rotary printing process with the method steps of claim 1.

Rotogravure, in contrast to other printing processes such as flat, screen, digital or screen printing, is suitable for the production of predominantly high-stock products. Characteristic of rotogravure printing is that the individual dots of the printed image lie deepened in the surface of the plate cylinder. They are referred to as cups and result from the print image transfer by means of engraving or etching. During the printing process, depending on their volume, they take up the appropriate amount of printing ink and apply it punctiform to the substrate.

When printing magazines and catalogs (illustration gravure printing) is made more aggravating that the time between file entry and completion of the printing form and ultimately the delivery of the printed product plays a crucial role. The paper web speed is very high at> 15 m / s and the quantities of ink transferred at web widths of up to 4.32 m are very large. To dry them fast enough, solvent-based paint is used.

In practice, different methods for producing these wells and different materials, in which the wells are introduced, are used.

As a basic state of the art gravure printing is known for many years, which consist of a steel cylinder with a copper base coat. On top of this copper base coat, another copper layer is electroplated as an engraving copper layer, which has a layer thickness of approximately 0.5 mm. This engraved copper layer is surface-treated and then engraved to impress in it a print or typeface in the form of wells.

To improve the wear resistance, the already engraved engraved copper layer is additionally provided with a hard chrome plating, to which galvanic application methods are used.

Such "classic" metal coated rotary printing plates may be reused after printing by removing the thin copper coating to the surface of the steel cylinder.

A disadvantage of these classic metal-coated rotary printing plates is in particular that on the one hand a large number of process steps with high time and cost and on the other environmentally polluting galvanic coating steps are required.

As a further prior art, processes for the production of erasable and reusable intaglio printing plates are already known, which are represented in the patent literature as follows:
For example, describes WO 02/40272 A1 a method for the production of screening cups in preferably rotationally symmetrical basic body by means of time-modulated, in particular pulsed laser radiation. An ablation support layer is applied over the upper layer area provided for the information embossing, through which sieve cups are introduced by means of laser radiation into the upper layer areas by material ablation. Subsequently, this erosion assist layer is removed with the aim of obtaining burr-free screen wells.

An in EP 1568490 A1 described, high-resolution direct laser process of chrome or copper cylinders achieved in comparison to conventional electromechanical or laser engraving significantly higher cell resolutions and thus finer contours in the printed image. However, a disadvantage is the significantly extended engraving time at not reduced manufacturing costs of the cylinder.

Out DE 10 2005 052 156 A1 For example, a method and apparatus for gravure printing by means of a erasable and reusable gravure printing form are known. The gravure printing forms shown there are formed as a solid cylinder, as a tubular or thin-walled sleeve on which a basic grid is engraved analogously to a conventional gravure mold in copper. To increase the durability is on the engraved with the basic layer first a layer of chromium and then a hard coating such. As diamond-like carbon, titanium nitride or tungsten carbide applied.

In addition, anilox rollers are described which carry thermally sprayed ceramic coatings, in which a gravure gravure grid is engraved by means of laser.

From this document it is known that to increase the abrasion resistance of the filler hard powder with, a particle size of less than 1 micron, is to be added.

The imaging is carried out by thermal ablation by means of a pixel transfer device by imagewise removing filler material from the depressions.

After the printing process, the known gravure form passes through an erasing process in which the filler material and residual ink from the printing process are completely or partially removed by means of laser. Subsequently, the basic grid of the gravure mold can be refilled again, whereby it is prepared for the imaging with a new print job.

Out DE 10 2005 052 157 A1 For example, an apparatus and method for imaging a erasable and reusable gravure printing form is known, using a plurality of laser beams that may be derived from one or more lasers.

Out EP 1 410 924 A1 a manufacturing method for a gravure printing is known in which only a wear-resistant layer is applied according to the desired application to the cylindrical printing plate. This wear-resistant layer forms the engraving surface of the printing form and may consist of a hard material, composite material or metal. Different coating methods are mentioned. Cups for receiving the ink are formed by mechanical engraving, laser engraving or etching. For reuse, it is intended to remove the imaged wear-resistant layer chemically, electrochemically or mechanically after the printing process.

Out DE 101 26 264 A1 are known a gravure cylinder, a method for producing a gravure cylinder and method for recycling a gravure cylinder, wherein a gravure cylinder is described in detail, wherein on a provided with an auxiliary layer steel cylinder, a ceramic coating is applied by means of a plasma spraying. To "erase" the gravure cylinder after the printing process, a recycling treatment is provided in which the imaged cylinder is abraded. This creates a used reusable cylinder blank.

From the generic EP 584 857 A2 is a gravure cylinder consisting of a steel cylinder with a the engraving image bearing coating known. To increase the service life of the coating consists of polyamide, the service life can be increased by the addition of pigments in the sub-micron range.

In general, it must be stated with regard to the aforementioned sources in the prior art that the polymer materials, thermoplastics, resins, waxes, etc. proposed there do not meet the essential requirements of a rotary gravure printing process. In particular, they are not sufficiently resistant to toluene and not sufficiently resistant to wear. With regard to the quality of the laser engraving, it should be noted that the focus of the gravitational laser beam leads to flow phenomena of the material in the well and thus to contour sharpening.

JP 2000-015770 A teaches the erasing and re-imaging of gravure cylinders by ablation, reapplication and laser engraving of a plastic layer, wherein the cylindrical body does not have a preformed cell pattern.

DE 31 09 096 A1 teaches a gravure mold with a closed plastic surface, wherein as plastic, for example, epoxy resins and as filler material of the plastic is used carbon black.

DE 196 31 469 C1 teaches the partial erasure of erasable printing forms for gravure printing processes, the erasable gravure printing form having a closed surface. The deletion is done partially so that it is area by area.

DE-A1-101 15 434 describes prepolymer and anilox filler for depth-variable laser ablation.

Based on this prior art, the present invention seeks to provide a method for erasing and re-imaging a rotary printing form or a gravure cylinder or a gravure printing form, in which a cell structure can be deleted very quickly.

This object is achieved by the features of method claim 1. Advantageous developments of the invention will become apparent from the dependent claims.

It is regarded as the core of the invention that a composite material curing by polymerization after the coating process comprising at least one organic binder with nano- and / or microparticles contained therein is applied as the coating material.

This makes it possible to apply a radiation-curable composite material in a single technology sequence on the cylinder surface of the mold body, which can be cured there, the image information-bearing cell structure can be generated by laser engraving and after the printing process, the cell structure is leveled by a re-coating process with said composite and thus available for re-imaging.

It has been found that the combination of an acrylate-based matrix and nanoparticles contained therein significantly improves the laser engravability of the surface formed. In the case of known non-metallic coating materials, laser engraving regularly presents considerable difficulties; the incident laser beam leads to thermally induced flow processes in the vicinity of the beam, so that the laser beam can not form sufficiently sharp cell structures. The resulting in the prior art cups are usually surrounded by a crater rim, which leads to a significant deterioration of the image quality of the printed product. The formulated in claim 1 combination of micro- or nanoparticles embedded in a composite material, such as a polymer matrix, for. As a polyacrylate avoids such negative flow phenomena. The wells formed with laser beams are significantly contour sharper than in the prior art and thus suitable to ensure a much better, print result. In addition, the material is sufficiently hard, tensile and compressive strength, elongation at break, modulus of elasticity and wear resistance are suitable to withstand the high mechanical stresses associated with a high speed web-fed rotary printing process. Also the heat resistance is sufficient for such loads. In thermal terms, the claimed composite layer advantageously has a low coefficient of expansion, which has an advantageous effect on its bonding to the substrate. In addition, the radiation-curable micro- or nanoparticles have an advantageous effect in terms of abrasion resistance of the composite material.

The optical and thermal absorption, dissipation and / or emission properties of such a layer can be advantageously influenced by the embedding of micro- or nanoparticles, i. H. The above-mentioned flow processes and smearing effects, which usually occur during laser engraving of other plastic layers, are so greatly reduced that the lasered cell structure is made much sharper than is possible with other known plastic coatings. In addition, it is basically possible to tune the UV absorption of the hardened layer to the wavelength of the engraving laser in order to further refine the engraving result with an optimized energy absorption.

However, the composite layers mentioned are not only advantageous with regard to cup formation by means of a laser, they also have other advantages with respect to deletion of the cup structure. The layers are easy to recoat, d. H. a deletion process can be performed without having to completely detach a composite layer from its backing. Existing structures can be erased by "over-lasers" and the surface re-coated in the required layer thickness with composite material.

Also, in a manner not according to the invention, the composite filling the cells of the structuring can be exposed by laser radiation and then completely refilled. This will "delete" the structure and provide it for refining after refilling. Both the "over-lasing" of existing structures, as well as the exposure and subsequent refilling can only on sections of the molding Thus, it is possible to delete a printing cylinder only partially or to provide new image information.

In principle, it is also possible to coat the composite material with a non-metallic barrier layer after imaging, which has a greater hardness and / or a greater solvent resistance than the coating material itself. Advantageously, it has been found that the durability of the barrier layer on the surface of the composite layer is improved by the microparticles and nanoparticles. The barrier layer comprises silazane or SiOx compounds. The provision of carbon and / or nitrogen atoms in the barrier layer has also proved to be advantageous.

Claim 4 deals with the curing of the composite layer. In order to increase the adhesion of the composite layer on the cylinder jacket surface of the mold base body, the cylinder jacket surface can be provided in a conventional manner with a basic structure. But it is also possible to apply the composite material on a ballard skin. Such a ballard skin, together with the composite layer applied to it, can be detached from the base cylinder without negatively affecting the structure of the base cylinder. A ballard skin is produced by electroplating on so-called ground copper an approximately 0.1 mm thick copper skin, which can be provided with a surface structure. After the print run, the ballard skin can be removed from the printing cylinder. Alternatively to Ballardhaut can also be a non-metallic intermediate layer, for. B. a primer fulfill the detachment function.

Advantageously, the layer thickness of the composite layer can be between 15 and 150 μm.

The laser engraving, ie the embossing of wells by means of laser radiation, can be carried out particularly well with pulsed lasers. The depth and shape of the wells in the composite layer can be adjusted by the number of pulses per spot and the energy deposited by the laser beam. Because the Composite layer compared to other plastic coatings has far more favorable, optical and thermal absorption properties, can be engraved by laser entry arbitrary cup shapes, such as square, triangular, round. Also different depth profiles on a basic shaped body can be generated, for. B. in step shape, in the form of a Gaussian curve or wedge-shaped. The Bebilderungsablauf the layer can be done either locally individually or by a raster method. In the usual way, the laser beams can be directed via scanners or multiple axis systems onto the composite layer to be imaged.

The cup shape can advantageously take place via beam shaping of the laser beam. Such beam shaping can be realized by diaphragms, masks and / or other optical elements.

Such a laser-registered structuring can be erased by laser ablation and the composite layer, which is then thinned in the ablated areas, re-coated, whereby coating material can be saved. The refilling of the partially removed wells leads to a closed composite surface layer. The time saving achievable in this case represents a significant advantage of the method according to the invention.

It is not according to the invention but also possible to completely remove or detach a composite surface layer provided with an imaging from the cylinder jacket surface of the molded body by exposure to radiation or mechanically and to perform a substantially complete recoating of the cylinder jacket surface of the molded base body by a composite material.

Before being imaged by laser engraving, an applied composite layer can be smoothed mechanically or also by laser action, which leads to a further improvement of the printing result.

Described is now a gravure form, which can be produced by the method of the claims. The imageable surface formed by a composite layer has, as a first component, the following compounds: acrylates of radically UV-curing systems, cycloaliphatic epoxides, aliphatic epoxides and compounds of cationically UV-curing systems. Such compounds for the composite layer lead to particularly advantageous laser engraving results with highly definable cup shape. The composite layer comprises several multifunctional radiation curing crosslinkable monomers, oligomers or polymers which may comprise orthogonal functional groups. The particles of the nanocomposite layer are micro- or nanoscale metal or semimetal oxides or oxides of transition metals or mixed oxides in powder form or organometallic particles. Compounds of Al ₂ O ₃ , SiO ₂ , ZrO ₂ , TiO _{2 have} proved to be particularly advantageous for the nanocomposite layer.

The compounds of the composite layer may be provided with an organophilic envelope.

The layer thickness of the composite layer can be between one nanometer as the theoretical lower limit and one millimeter. The hardness of the composite layer should be greater than 200 N / mm ² (Marten hardness). The cup structure of the composite layer should be chosen so that the depth of the wells is less than the thickness of the composite layer. In order to erase an imaged composite layer, the composite layer may carry a quenching layer that completely overlaps the wells.

Fig. 1:

einen schematischen Schnitt durch eine mit einer Ballardhaut versehene rotative Druckform zum Einsatz in einem Rollenrotationsdruckverfahren;

Fig. 2:

einen schematischen Detailschnitt gemäß I in Fig. 1;

Fig. 3:

eine schematische Schnittdarstellung einer alternativen rotativen Druckform;

Fig. 4:

einen schematischen Detailschnitt gemäß III. in Fig.3.

The connection is explained in more detail with reference to an advantageous embodiment in the drawing figures. These show:

Fig. 1:

a schematic section through a provided with a ballard skin rotary printing form for use in a web-fed rotary printing process;

Fig. 2:

a schematic detail section according to I in Fig. 1 ;

3:

a schematic sectional view of an alternative rotary printing plate;

4:

a schematic detail section according to III. in Figure 3 ,

In the Fig. 1 illustrated rotary printing plate 1 consists essentially of a cylindrical mold base body with structuring 2 and a non-metallic coating material, which can be applied to the surface, that is, the cylinder surface 4 of the mold body 2. The coating material is according to Fig. 2 from a composite material 3 and thus forms a composite layer 33. The composite material 3 comprises an acrylate-based matrix 5 and substantially uniformly distributed nanoparticles 6, which - as in Fig. 2 shown schematically - can have different shapes and sizes.

On the surface 7 of the composite material 3, a non-metallic barrier layer 8 is applied, which has a greater hardness than the composite material 3. In order to introduce a cup structure 9 in the coating material 3 for the purpose of imaging, a laser engraving method is used. The cell structure 9 can be seen in drawing figure 2. Overall, it should be noted with respect to the drawing figures that, of course, the sizes of the particles 6, the thickness of the illustrated layers 33, 8, 21, overall the size ratios of the cylindrical shaped body 2 with the layer thicknesses and particle sizes do not correspond to reality. For reasons of illustrative clarity, the layer thicknesses and particle sizes are widely coated and not shown to scale relative to each other.

As can furthermore be seen in FIG. 2, the surface 4 of the molded basic body 2 can be provided with a basic structure 20 on which a ballard skin 21 is applied, which ultimately carries the composite layer 33. In this regard, it should be noted that the application of a ballard skin 21 prior to application of the composite layer 33 is merely an option intended to facilitate the complete detachment of a coating from the mold base body 2.

In addition, the ballast skin 21 applied to the mold base body 2 may be provided with a structuring.

In the drawing figures 3 and 4, an alternative embodiment is shown. Here, the composite layer 33 is arranged without ballard skin directly on the mold base body 2. In order to increase the adhesion between the cylinder jacket surface 4 and the composite layer 33, the cylinder jacket surface 4 is provided with a z. B. web-like basic structure 20, which increases the contact area.

The cell structure 9 can have different shapes, depths and / or dimensions.

It is also clear from the introduction to the introduction that the composite layer 33 can be formed from a coating material 3 which can comprise a very wide variety of chemical compositions. The compositions can be selected by the person skilled in the art within the stated ranges in such a way that a scratch-resistant, abrasion-resistant and solvent-resistant coating is formed, which, as far as the core idea of the invention is concerned, ensures virtually residue-free laser engravability.

Claims (10)

1. Method for erasing and image re-setting an impression cylinder for the production of intaglio-printed illustrations between two printing operations which lead to different printed products, having the following method steps:

   - applying a non-metallic coating material onto the cylinder-sleeve face of a cylindrical basic moulding (2) of the impression cylinder, wherein a composite material (3) which can be cured by polymerization after the coating operation and comprises at least one organic binder with nanoparticles and/or microparticles (6) having a binder-compatible organophilic wrapping, which surrounds the particles (6), contained therein is applied as the coating material, in order to produce a compact surface of the composite material (3) ;

   - curing the applied coating material in order to form a composite layer (33) and

   - image re-setting by introducing a cup structure (9) into the coating material;

   - wherein, for erasing the impression cylinder which has already been used, a composite layer (3) which has already been image-set is partially removed from its subsurface without being completely detached;

   - the application to the required layer thickness takes place as an after-coating by dip coating, doctor application or roller application, using the prepolymer composite material (3), and

   - the image re-setting of the composite layer (33) is carried out by means of laser radiation prior to the subsequent printing operation.
2. Method according to Claim 1, characterized in that a non-metallic barrier layer (8) is applied onto the surface (7) of the composite material (3) after introduction of the cup structure (9).
3. Method according to Claim 2, characterized in that the hardened composite material (3) forms a composite layer (33), and the barrier layer (8) has a greater hardness and/or a greater resistance to solvents than the composite layer (33).
4. Method according to one of the preceding claims, characterized in that the applied composite material (3) is cured by VUV, UV, electron or gamma radiation and/or a plasma.
5. Method according to Claim 4, characterized in that the curing of the composite material (3) is thermally facilitated.
6. Method according to one of the preceding claims, characterized in that the composite material (3) is structured and/or removed by the laser radiation.
7. Method according to one of the preceding claims, characterized in that the cylinder-sleeve face (4) of the basic moulding (2) is provided with a basic structure (20).
8. Method according to one of the preceding claims, characterized in that the erasing and/or image re-setting takes place only on part-portions of the composite layer (33).
9. Method according to one of the preceding claims, characterized in that the composite layer (33), which has been applied to the cylinder-sleeve face (4), is mechanically smoothed prior to image re-setting.
10. Method according to one of the preceding claims, characterized in that beam shaping of the laser radiation takes place for setting defined cup shapes.

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