EP0384146B1 - Positive original template for galvanoplastic shape of metallic foils - Google Patents

Abstract

A metal foil made by electroforming from a master pattern with the interposition of a negative form, and serving as packing for sheet guiding cylinders and/or drums of rotary printing machines, including a substantially planar member having one flat face and an opposite face with a textured surface structure corresponding to an upper side of the master pattern, the upper side of the master patten having been roughened by a jet treatment and coated with a levelling galvano-layer in order to eliminate undercuts, the master pattern per se, and method of manufacture.

Description

The invention relates to a positive master mold for the galvanoplastic molding of metal foils as an elevator for sheet-guiding cylinders and / or drums of rotary printing presses, the one surface of the master mold being smooth and the opposite surface being structured.

Known metal foils of this type according to DE-AS 26 05 330 preferably consist of solid: nickel and have a surface structure which essentially corresponds to the glass bead cloth which is likewise known for the same purposes. This results from the fact that the galvanoplastic molding of the metal foils takes place from a negative mold, which in turn is molded from a positive master mold, which consists of a carrier foil with an applied rubber layer, in which glass balls protruding partially from the surface are embedded. An advantage of these metal foils is the fact that the surface structure is largely reproducible. This is important for speedy use in printing operations, for example for the control-free exchange of a damaged metal foil for a new one. A disadvantage of these metal foils, however, is that there is no optimal surface topography with regard to various work requirements.

The same disadvantages occur in another previously known solution according to EP-A-0 017 776, in which the sheet-guiding film, as an elevator for impression cylinders of rotary printing presses for perfecting, is made smooth on one surface and statistically uniform on the opposite surface Distributed, equally high spherical caps is provided and in which the film is formed by a support layer and a cover layer, the support layer made of nickel or plastic with a high Young's modulus, e.g. As polyamide or PVC, there is a thin chrome layer which compensates for their micro-roughness and is applied as a top layer on the spherical cap side. The compensation of only the micro roughness does not change the intended, very uniform spherical cap topography of the surface.

With regard to a compromise to be reached on the roughness, DE-PS 12 58 873 proposes surface structures of a impression cylinder or an aluminum foil to be assigned to it, which is designed as a chrome surface with a roughness (RMS) between 2 and 7.5 »m. This should optimally meet two boundary conditions in the compromise, namely that the roughness on the one hand is sufficiently large to achieve a certain (repelled) ink repellency effect, for example to prevent the freshly printed sheet from smearing on the reverse side during back printing, on the other hand however, the roughness should also be as small as possible in order to ensure the optimum load share for the contact surface of the arch. On the one hand, this compromise, as has been found, is not optimally achieved. On the other hand, this solution has the disadvantage that it is not reproducible with regard to the surface structure. Even if one reproduces the roughness dimensioning (viewed on average over the entire film) with a reasonable tolerance, the overall surface structure of each film differs very significantly from the other film or each cylinder surface from the next cylinder surface. The reproducible blasting treatment of such thin aluminum foils is also problematic, as is their stability in use. All previously known products with a blasted surface are therefore unique.

Furthermore, a metallic sheet guiding film is known from DE 28 20 549 A1, which consists of at least two layers. The carrier film is roughened by means of blasting treatment. This process is followed by one or two galvanoplastic finishing processes, namely either two nickel layers of different hardness or a chrome layer. Experience has shown that the roughness increases in these finishing processes insofar as existing undercuts are reinforced. The metallic sheet guiding foils produced in this way are unique. Due to the existing undercuts in the structured surface, these unique specimens cannot be reproduced by electroplating and can therefore not be used as the original form.

Finally, DE 35 37 483 C1 describes a galvanoplastic process for producing a large number of plate-shaped microstructure bodies made of metal. These are exclusively straight bodies, so that undercuts that could stand in the way of reproducibility do not occur.

The object of the present invention is to design a generic original in such a way that, with optimal adaptation of the surface structure to the functional conditions of the metal foil which can be produced therewith, for lubrication-free guiding of sheets, the reproducibility thereof is always identical.

This is achieved according to the invention in that the structured surface of the original form is roughened by blasting and is coated with a leveling galvanic layer made of bright nickel to eliminate undercuts.

As a result of this configuration, a metal foil can be produced as an elevator for sheet-guiding cylinders and / or drums of rotary printing presses, the surface structure of which basically represents the duplicate of a surface produced by beam roughening (and subsequently freed from undercuts), and on the one hand it is clearly reproducible at all times, and on the other hand it is optimal Brings anti-smear conditions. In this regard, it has been found that the structure of a beam-roughened and appropriately leveled surface offers the most favorable compromise, both directly (as a positive profile) and with its negative profile, in particular with regard to the load ratio, washability of the metal foil and the prevention of smearing. All together brings optimal conditions of use. The essence of the invention is the realization that this optimization can be achieved if the roughness elevations of the surface of the original mold produced by blasting are leveled and thereby freed from any undercuts, so that the finished metal foil can have no depressions that form Extend depth or no increases with an overhang. The blasting treatment for roughening the top of the master mold can be carried out by known blowing or blasting processes, e.g. B. by shot peening. The surface produced in this regard can additionally be provided with a chrome layer, also for stabilizing and extending the service life. Such a chrome layer, applied to a radiation-generated and then galvanically leveled surface topography, improves the surface compensation even further because, for. B. because of the lack of undercuts there are no electrolytically preferred edges and / or tips. The metal foil corresponding to the original form can also be used as a covering for the printing cylinder of a rotary printing press. The crests are ideally suited increase the coefficient of friction of the cylinder surface, so that the paper tensile forces for the grippers can be made smaller; pulling the sheet out of the grippers is still prevented. The formation of the crests (pointed or flat, high or low load share) can be adapted to the respective application (e.g. first transfer cylinder, third transfer cylinder, pressure cylinder or delivery drum). Despite the relatively thin structure, the design is very durable. The surface in contact with the arch is also easy to clean. The flattened flanks of the ridges avoid nests for paint accumulation or residues of any cleaning agent. The respective blasting process for roughening the top of the master mold enables a far-reaching adaptation to the later intended use of the metal foil to be achieved than was previously possible with the metal foils which had previously been electroplated in spherical cap structure. Because of the optimal load-bearing components that such a topography entails, such a metal foil is also ideally suited for making a very fine adjustment to different paper thicknesses on a cylinder by placing the foil underneath. As was found, because of the special conditions with regard to the bearing portion of the surface, wing shape, material, distribution of the bearing portions, height difference and their distribution, shape of the crests and valleys, in particular their flanks, a solution arises which is both technically smooth and micro-smoothed and evenly distributed spherical caps is superior to the jet-roughened (plus chrome-plated) cylinder surfaces (with undercut nests). The dimensioning of the shiny nickel mass to be applied gives a good opportunity to influence the above factors.

The object of the invention is shown in outline on the accompanying drawing in two exemplary embodiments.

In Fig. 1, 1 denotes a section of the top of the master form as a partial cross-sectional view. Overall, this archetype can have the shape of a cylinder, which is preferably made of aluminum. It has the top 0, which is surface-structured, the surface structure by blasting, z. B. shot peening is achieved so that the elevations 2 with the undercuts 2 'and the recesses 3 are formed. This structured surface is then electroplated with a chrome layer 4. As can be seen, the chromium layer 4 changes the topography of the surface at the points 4 ', that is to say in front of exposed points of the elevations 2, but more so that the undercuts enlarge. It is an essential element of the invention to have recognized that such undercuts are the reason why the blasted surface appears in many ways less favorable than e.g. B. a spherical cap topography. If the undercuts are removed, it has been found that the blasted surface is superior to all other surface structures. This chrome layer 4 is then covered with a bright nickel layer 5. This completely flattens the surface and in particular the flanks of the chrome layer-covered elevations / depressions, so that no undercuts / undercuts occur anymore, be it the undercuts from the blasting treatment or those from the galvanic application of the chrome layer 4. This is done by the leveling electroplating layer 5 (bright nickel layer ) The generated top of the original mold 1 is now used for the galvanoplastic molding of the metal foil 7 according to FIG. 2. Its material preferably consists of nickel. Your side coming into contact with the arch has the negative profile of the structural profile produced by blasting, but this without any overhangs on the flanks 8 of its elevations 9 it not only optimizes the printing function, but also improves cleaning technology and avoids nests for long-term corrosion. This metal foil 7 can be directly the metal foil according to the invention or the negative form N for producing a metal foil 7 ', shown in FIG. 3. Both the metal foil 7 and 7' are always material-homogeneous duplicates of the corresponding original mold surface, whereby for the positive version according to FIG. 7 ', it is very important that the differently high contact surfaces (mountain peaks) are provided relatively widely and can be influenced with regard to their position and formation, the factors of material homogeneity and the lack of any undercuts on these jointly contribute to optimizing the use.

As can be seen from FIG. 4, the metal foil 7 can still be coated with a thin chrome layer 10 after the galvanic molding, which not only optimizes the stability but also the lubrication-preventing behavior. The same applies, as shown in FIG. 5, to the metal foil 7 ', in which the positive profile of the original form is therefore equipped with this thin chrome layer 10'.

Each time there is a roughness structure in which the surface structure including the flanks of the roughness elevations generated by blasting is leveled. The roughness is 30 - 60 Rz; The load-bearing component TP is in the individual depths: TP at a depth of 10.0 »m = 15% TP at a depth of 20.0 »m = 50% TP at a depth of 30.0 »m = 84%

The thickness of the chrome layer 4 is preferably 40-50 »m, that of the bright nickel layer 10-15» m. The thickness of the chrome layer 10 or 10 'is 10 »m.

Claims (4)

1. Positive die for the galvanoplastic moulding of metal foils (7) as a packing for sheet-conveying cylinders and/or drums of rotary printing machines, the one surface of the die being of smooth design and the opposite surface being of structured design, characterized in that the structured surface of the die (1) is roughened by blasting and is coated by a levelling electrodeposition layer (5) of bright nickel to eliminate undercuts (2').
2. Positive die according to Claim 1, characterized in that the surface of the positive die (1) intended for the galvanoplastic moulding is roughened using a blasting method, and the roughened surface is coated with a chromium layer (4) and an electrodeposition layer (5) which levels the undercuts.
3. Positive die according to Claim 2, characterized in that the roughness achieved by blasting is between 30 and 50 Rz and, after application of the chromium layer (4) and the layer (5) of bright nickel, the bearing proportions rise from about 15% at a depth of 10 »m to 85% at a depth of 30 »m.
4. Use of the positive die to produce metal foils according to one or more of Claims 1 to 3, characterized in that the structured surface, corresponding to the die, of the metal foil (7) consisting of nickel is coated with a thin chromium layer (10) after moulding.

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