EP1410924A1 - Method for producing a printing plate for intaglio printing, printing plate for intaglio printing and use of said plate - Google Patents

Abstract

The printing plate manufacturing method has indents, e.g. with a depth of between 15 and 35 microns, formed in the surface of the printing plate, which is provided with a hard wear-resistant layer applied before formation of the indents. The wear-resistant layer can be provided by a mixture of a plastics material and quartz sand grains, or by a metallic chrome layer applied via a vapor deposition process. An Independent claim for an intaglio printing plate is also included.

Description

The invention relates to a method for producing a Printing form for gravure printing, especially for Rotogravure, with the cell in the surface the printing form are formed, a printing form for the Rotogravure, especially for rotogravure, and the use of such a printing form in a Printing device.

Printing forms for gravure printing, also printing cylinders or Engraving cylinders are mainly used in engraving devices by means of a recording organ in the form a mechanical engraving device or by means of a Electron or laser beam or etching produced.

A template to be reproduced is provided with a scanning organ scanned point by point and line by line to obtain an image signal to gain what the tonal values of the scanned original represents. The image signal is made according to the requirements reproduction, for example after a predetermined gradation curve, corrected and a raster signal overlaid to generate the print screen. The through the superimposition of image signal and raster signal formed recording signal controls the recording element, which is in the axial direction on the rotating Printing cylinder moved along and a sequence of im Depressions or recesses arranged in the printing grid, Called well, in the outer surface of the printing cylinder engraved. Scanning the template that the previous one Principle follows, is usually done nowadays only with electronic scanning of the template. The image data supplied by the scanning are recorded on a Given computer, in which a program-based processing and processing is done. In many cases no more templates are scanned these days, because photographs are often already digital Data in front of and texts and graphics can be saved on the computer also generated in the form of digital data become. The computer then delivers the image signals based on which the cups either mechanically or by means of Direct laser engraving or a laser mask process formed in the outer surface of the printing cylinder were. The depths or volumes of the engraved cells determine the tonal values to be printed between "black" and "white" in the printing terminology too labeled "depth" and "light".

The engraved impression cylinder is used for the printing process then clamped in a rotogravure press.

Before printing, each cell takes one of its own Volume dependent amount of ink on the tonal value to be printed corresponds. When printing is done then the color transfer from the wells to the Media.

There is a gravure cylinder that is used in practice generally from a cylinder core made up of Steel, aluminum or more recently also from a plastic composite can exist and which also with a Base layer, for example made of copper, is provided. In this basic copper layer, or in another specially applied layer, the wells are engraved. Copper exhibits due to its physical and chemical Characteristics good engraving characteristics on which to support the generation of high-quality prints. The Thickness of the electroplated copper engraving surface is approx. 60 µm to 140 µm. In addition, the copper layer to be engraved polished so that the surface provided with a defined micro roughness is. Then use a diamond stylus electromechanically the information to be printed from picture and writing into the copper surface in the form of a fine cell grid introduced.

Disadvantageous when using copper as engraving material however, it is relatively low in hardness and abrasion resistance having. This would result in the printing process in the rotogravure printing machine due to the mechanical Stress on the copper layer by the squeegee wear occurs with increasing operating time, the reduces the print quality and the service life of the Printing cylinder and thus the number of copies limited. Around the wear resistance of the engraved copper layer improve and thus the service life of the printing cylinder increase, it is common in practice to print the to degrease engraved copper layer and then with a layer of a harder than copper Metal, for example made of chrome, to provide what, for example. can be done by a galvanizing process. Before the finished printing form is inserted into the printing press the surface of the applied layer polished.

After printing, the layer and the underlying, the engraved copper layer from the Printing form removed chemically, electrochemically or mechanically. As a result, the printing cylinder stands for a new one Cycle to produce another printing form Available.

It has also been used in gravure printing in the past Printing forms by means of chemical and / or electrolytic Etching produced, which led to good results Has. Here, the printing cylinder with a Mask layer covered, followed by a photographic Exposure of the mask over film templates and that Wash out the mask and etch the copper surface with z. B. iron chloride.

The disadvantages were the low process reliability and the not enough good representation of halftones for Pictures. The etching process has also been modified by for the mask layer on the one hand a so-called photoresist and on the other hand, a so-called thermoresist was chosen. In both Cases were masked by a laser beam exposed (one also says illustrated). In the case of The laser beam creates a photoresist Conversion of the irradiated areas of the resist layer, being before etching to produce the finished mask another development step is necessary. In the case of The laser beam generates the thermal resist Mask in one step by passing the laser through thermal processing removes the mask layer there, where a cell should be created by etching. Both procedures are complex, in the sense that they are relatively many Show process steps. You are therefore in practice susceptible to quality problems. Beyond they also the fundamental disadvantage of all Etching process, namely the halftones for pictures are poorly represented.

It is also known to produce the wells on a printing cylinder the one used in material processing To use electron beam engraving, the because of the high energy of the electron beam and the enormous precision in terms of beam deflection and Beam geometry had shown very good results. The Cups are placed in the copper layer with a High power density electron beam at high speed shot. Because of the great effort and the high investment costs for an electron beam engraving machine was the electron beam engraving in the So far, this has not been the practice for engraving copper cylinders used for gravure printing, but only in the steel industry for surface engraving of so-called texture rollers for sheet metal manufacturing, with which textures in the sheets be rolled.

Attempts have also been made to use lasers for gravure engraving insert to the printing cylinder with an outer copper layer to engrave with a laser. Because copper but is a very good reflector for laser radiation, are very great achievements and especially very high ones Power densities of the lasers to be used are required, to melt the copper. To solve this problem solve, it was suggested the copper layer that the Engraving contains to be replaced by a zinc layer. The Cups are placed in a laser beam Zinc coating shot. Zinc laser engraving requires less overall beam power than copper. There is a major disadvantage of these methods in that the galvanic application of zinc to a Gravure cylinders less so in industrial practice can be performed reliably than if the Engraving containing layer is copper.

As with the engraving in copper, the zinc layer must also after the imaging (laser engraving) with a wear-resistant layer, for example made of chrome to be sufficient in the printing press To achieve service life. The problem is that the application of chromium to zinc is also less reliable works as chrome plating on copper, so the combination of a zinc with a chrome plating is complicated. Therefore, there is a need for more Introduce procedural steps. In addition to the difficult Handling zinc makes disposal especially in combination with chrome is another problem.

It is therefore an object of the present invention To create procedures in the manner mentioned above with the printing forms can be produced and made available deliver consistently good printing results using the printing form is easy to manufacture and the cost price such printing forms should be kept lower than the production costs on previous conventional Printing forms produced in this way, the printing forms in Printing devices without changing the printing devices should be able to be used as they have been for conventional manufactured and assembled printing forms used become.

The object is achieved according to the method according to the invention in that the surface with a wear-resistant Layer is provided.

Copper has a Vickers hardness in the range from 40 kp / mm ² (soft) to in the range from 110 kp / mm ² (hard). Chrome has a Vickers hardness in the range from 120 kp / mm ² (soft) to 670 kp / mm ² (hard) - information from "Stoffhütte", 4th edition, 1978, p. 1102, 1103. For the wear-resistant layer according to According to the invention, basically all materials that have a greater Vickers hardness than copper, that is to say greater than 110 kp / mm ^2, are advantageously possible for the formation of this layer.

The actual engraving layer is copper on the Printing form, which is regularly designed as a so-called printing cylinder is. So far, the copper layer is, as at the beginning described to the service life of the printing form during increase their intended use, Chrome applied. So there were two shifts so far to apply to the printing form, for which two separate galvanic baths must be provided and therefore two separate galvanic coating processes must be carried out.

According to the invention, there is basically only one layer the printing form to apply what the manufacturing process the printing form as a whole in terms of time and in relation to the Manufacturing costs significantly reduced. In addition, certain wear-resistant layers not necessarily galvanic be applied, which also has the advantage that after the end of the intended period of use the printing form the wear-resistant layer often with simpler measures from the printing form can be removed again as before.

The advantage of the solution according to the invention, however, is in that a wear-resistant layer depending the desired goal especially with regard to the desired application of such a printing form can be selected, i.e. the hardness of the wear-resistant Layer with regard to the available for this standing material which is the wear-resistant layer forms, can be selected or adapted. This selection can also from the point of view of later removal the wear-resistant layer from the printing form, after the printing form after the intended Period of use removed from the printing form and the associated disposal criteria.

According to an extremely advantageous embodiment the invention, the method is designed such that the wear-resistant layer on the printing form before training the well is formed. This can be achieved be that the wear-resistant layer is the real one Engraving surface or layer of Printing form forms. This can advantageously be achieved will be that after completing the training of the wells, i.e. after completion of the engraving or illustration of the Printing form directly into the wear-resistant layer without further time-consuming preparatory steps. the quasi-finished printing form into the printing device Execution of the printing process can be introduced. Only the removal of material residues that arise in the course of the engraving or illustration, or that Deburring and, if necessary, a subsequent grinding, polishing or cleaning process may be required. This proposed advantageous further modification of the solution becomes the manufacturing process of the printing form in terms of time and also in relation to the expenditure involved Significantly reduced costs.

It should be emphasized that this may require post-treatment steps in principle already during the actual Engraving can be carried out with the intended Selection of the material of the wear-resistant Layer may not be necessary at all.

The wear-resistant layer can advantageously be a be a so-called hard material layer, for example such a layer, as used for surface coating of metal-cutting Tools such as drills, milling heads and turning tools are used to increase their service life. in principle everyone in the prior art is suitable for this Known hard material used for purposes, for example boron carbide and its derivatives in order to only use this material here, for example. to call.

The wear-resistant layer can also advantageously be formed by a composite material the example of a mixture of plastic and therein contained particulate elements. The particulate Elements can preferably be quartz sand his.

According to another advantageous embodiment of the method the wear-resistant layer can also be made from a metallic layer are formed, the metallic Layer formed on the one hand from elemental metal and on the other hand also from metal alloys, the choice of whether the layer is now made of a metallic Material, a hard material or a composite material trained in the sense of the above is, depending on the desired with the printing form or properties to be guaranteed in relation also on the type of printing with the printing form, the to achieve the desired service life, the later required Removal of the wear-resistant layer and the type performing the engraving of the printing form or the wear-resistant one Layer of the printing form can be selected.

The wear-resistant layers can go through regularly the coating methods known per se, such as preferably CVD or PVD (Chemical Vapor Deposition, physical vapor deposition) be using these techniques on a larger scale are technically proven and manageable.

Hard material layers and metallic layers can be in this way, using these known methods, with high precision in terms of coating uniformity and the desired thickness of the coating on one Apply the surface, here the printing form.

It is advantageous for certain purposes, for example in connection with the application of metallic layers, to apply them galvanically to the printing form, whereby but also metallic layers ultimately by means of The aforementioned PVD or CVD method can also be applied are.

The composite materials mentioned can be, for example, by means of a spraying process on the surface of the printing form Apply to form the wear-resistant layer and are then thermal and / or through Irradiation hardened by electrons.

The thickness of the layer can preferably be chosen in this way be what ultimately all types of layer composition and the application of the layers applies that the wells at least partially in the wear-resistant Layer are formed. This is to be understood that the wear-resistant layer on a previously conventional layer applied to the printing form, For example, made of metal such as copper or zinc, or on one non-metallic layer is applied and only the area close to the surface due to the wear-resistant Layer is formed and the well in the area of Well bottom in the under the wear-resistant layer lying layer are formed, but it is also possible to under the thickness of the wear-resistant layer No separate layer under the wear-resistant Layer, preferably the well to be completely formed in the wear-resistant layer.

Because the depth of the formed in the surface of a printing form Well, with a few exceptions, regular advantageously in the range between 15 to 35 microns lies, the wear-resistant layer is accordingly advantageous in the range between 20 to 50 µm thick be trained, using the known CVD and PVD process Layer thicknesses in the range of up to 10 µm are easy to manufacture and beyond down to the range of 15 µm, i.e. that also by means of of these known PVD or CVD coating processes such wear-resistant layers on printing forms can be produced in which the wells are even complete be trained without the underlying Layers, if any, are touched by the cells become.

Even with the wear-resistant proposed according to the invention The wells formed therein can layer basically in any suitable known manner be trained, for example, by a wide variety of them known methods, for example by means of a mechanical Engraving means or an engraving by means of laser light. These different engraving processes too depending on the wear-resistant layer forming material can be selected.

A mechanical engraving means is, for example, an engraving stylus from a suitably shaped diamond.

An engraving process using laser light can advantageously be chosen such that by means of the laser light the cells are formed directly, i.e. high-energy laser light forms the well in the wear-resistant layer in relation to its three-dimensional Shape (length, width, depth) directly from.

But it is also possible, which in turn depends on the material forming the wear-resistant layer, the type of material, the treatability for training the well, the desired service life of the invention trained printing form and later removability the wear-resistant layer can happen also advantageously form the cells by etching, previously before performing the etching process Photoresist or a thermoresist to form the etching mask is formed on the wear-resistant layer. These well-known etching engraving techniques, as they do previously with copper impression cylinders, in which the cells have been trained, have been and are being used, can in principle also be related here according to the invention with the etching of the wear-resistant layer be applied. This also applies to another advantageous development of the invention, namely the etching mask itself is exposed by means of laser light.

Finally, it is advantageous to do the process in this way to train that the surface of the wear-resistant Layer rough with a predetermined degree of roughness is formed to predetermined a frictional resistance Size between the surface of the wear-resistant Layer and the surface of it during the Corresponding material to be printed to ensure.

This degree of roughness preferably corresponds to one So-called. Micro roughness, which is preferably by polishing and / or grinding the surface becomes.

To solve the above problem, a printing form for rotogravure, especially for rotogravure, in which cups are formed on the surface of the printing form are wear-resistant on the surface Layer on in which the wells are related to their depth are at least partially formed.

The advantage of such a printing form, for which the above Advantages in the process for their production also apply, lies in the fact that compared to the in Printing forms known from the prior art are the inventive forms Printing form be designed to be very simplified can. The printing form can, except for the formation of the Well, i.e. up to their illustration, completely finished and be stored until the Printing form for the imaging is needed. Would they be Engraving surfaces of the printing form, as with conventional manufactured printing forms, consisting of zinc or copper, storage would not be possible because of zinc and copper surfaces undergo aging which is the following Imaging and a subsequent chrome plating would not allow without further manufacturing steps.

The printing form listed above can preferably according to the method according to one or more of the method steps, as described in detail above have been manufactured. But it is also possible fundamentally different manufacturing process steps to use the printing form according to the invention.

After imaging the previously described invention Printing form or after the production of the Printing form according to the inventive method can Printing form in a printing device, in particular in a Rotary printing machine, be inserted to the to be printed Print the material as intended.

The invention will be enlarged again in the following Described in detail.

Starting point for the process of making a Printing form for gravure printing, especially for rotogravure printing, is essentially cylindrical trained printing form, which regularly consists of a steel core consists, but basically also of other materials, For example, plastic. On this Steel core, a base copper layer can be formed, using known application techniques on the steel core is applied. But there are also other metallic ones Base layers can be applied to the steel core, e.g. a basic zinc layer. On this metallic base layer a wear-resistant layer is then applied. The wear-resistant layer can have a thickness have that a subsequent illustration of the Printing form, i.e. the training of the wells in which Layer takes place without the underlying metallic Base layer is acted upon by the cells or the cells in this underlying base layer penetration.

However, it should be noted that under no wear layer is formed in the wear-resistant layer must become. Rather, it is also possible that wear-resistant layer directly on the core element of the Printing form, whether made of steel or other materials, train.

After the wear-resistant layer has been applied the printing form is illustrated in a manner known per se, which, depending on the choice, by means of different Engraving techniques can be done.

The illustrated printing form, i.e. with the wear-resistant layer of the engravings Surface treatment by polishing and / or grinding subjected. Polishing and / or grinding can be done in this way take place that a predetermined roughness or microroughness the surface is reached. The polishing and / or grinding is used to remove unwanted ones Residues of the wear-resistant layer that during the engraving process or the imaging. This also removes burrs. A separate one Cleaning process after polishing and / or grinding can join. These editing steps can also during engraving or imaging done in one step. Depending on the Material of the wear-resistant layer results in certain materials no need at all, after imaging, a grinding, polishing or cleaning step perform.

Even under the condition that a grinding, polishing or Cleaning process should be required this is much less effort than the corresponding one Steps as in classic engraving layers made of copper or zinc before printing through complex Chrome plating and subsequent polishing necessary were.

After these manufacturing steps, the printing form is fundamentally qualified for the intended use in a printing device or rotary printing press to be used and the printing process as intended of material to be printed, which means known printing processes takes place.

To the printing form again after the intended printing To be able to use the the imaging contained wear-resistant layer of removed the printing form, so that the printing form, in particular the printing cylinder, for a new manufacturing cycle the printing form is available, which in principle can be done multiple times. The removal of the wear-resistant Layer can be by chemical, electrochemical or mechanical way, depending on the type of wear-resistant Layer.

Claims (27)

Method for producing a printing form for gravure printing, in particular for rotogravure printing, in which wells are formed in the surface of the printing form, characterized in that the surface is provided with a wear-resistant layer. Method according to Claim 1, characterized in that the wear-resistant layer is formed on the printing form before the cells are formed. Method according to one or both of claims 1 or 2, characterized in that the wear-resistant layer is a hard material layer. Method according to one or both of claims 1 or 2, characterized in that the wear-resistant layer is a layer made of a composite material. A method according to claim 4, characterized in that the composite material consists of a mixture of a plastic and particulate elements. A method according to claim 5, characterized in that the particulate elements are formed from quartz sand. Method according to one or both of claims 1 or 2, characterized in that the wear-resistant layer is a metallic layer. Method according to claim 7, characterized in that the metallic layer consists of chromium. Method according to one or more of claims 1, 2, 3, 7 and 8, characterized in that the layer is formed on the printing form by means of a PVD or CVD method. A method according to claim 7, characterized in that the metallic layer is galvanically formed on the printing form. Method according to one or more of claims 1 to 10, characterized in that the thickness of the layer is selected such that the cells are at least partially formed in the layer. Method according to one or more of claims 1 to 10, characterized in that the cells are completely formed in the layer. Method according to one or more of claims 1 to 12, characterized in that the wear-resistant layer is between 20 and 50 µm thick. Method according to one or more of claims 1 to 13, characterized in that the depth of the wells formed in the surface of the printing form is in the range between 15 to 35 µm. Method according to one or more of claims 2 to 13, characterized in that the cells are formed by engraving in the wear-resistant layer. A method according to claim 15, characterized in that the engraving is carried out by means of a mechanical engraving means. A method according to claim 16, characterized in that the engraving is carried out by means of laser light. Method according to claim 17, characterized in that the cells are formed directly by means of laser light. Method according to one or more of claims 2 to 16, characterized in that the cells are formed in the wear-resistant layer by etching. A method according to claim 19, characterized in that before the etching process is carried out, a photoresist or a thermoresist for forming an etching mask is applied to the wear-resistant layer. A method according to claim 19, characterized in that the etching mask is imaged by means of laser light. Method according to one or more of claims 1 to 21, characterized in that the surface of the wear-resistant layer is made rough with a predetermined degree of roughness. A method according to claim 22, characterized in that the degree of roughness corresponds to that of the microroughness. Method according to one or both of claims 22 or 23, characterized in that the roughness is formed by polishing and / or grinding the surface. Printing form for gravure printing, in particular for rotogravure printing, in which wells are formed on the surface of the printing form, characterized in that the surface has a wear-resistant layer in which the wells are at least partially formed with respect to their depth. Printing form according to claim 25, produced according to the Method according to one or more of claims 1 to 23rd Use of a printing form according to claim 25 in one Printing device for rotogravure printing.