EP0197374B1 - Printing roller and a method of manufacturing the surface of a printing roller - Google Patents

Abstract

A printing press roller (10) is surface-treated by applying one or more adhesion-promoting, corrosion-resistant or wear-resistant layers (21, 24) by the plasma-spraying process to the running surface of the roller (10). To improve the adhesion properties of the layers (21, 24) on the base material (20) of the roller, and the paper-running properties, the layers (21, 24) are fused onto the whole surface and preferably finely distributed recesses (32) are fused into each outermost layer (24). <IMAGE>

Description

The invention relates to a printing unit of an offset printing machine with a plate cylinder provided with printing ink, a blanket cylinder running in contact with the plate cylinder and a printing cylinder running in contact with the blanket cylinder, which on its roller base material with a lower, plasma-sprayed, corrosion-resistant layer and a Upper, plasma-sprayed, abrasion-resistant layer is provided, with sheets or sheets of paper to be printed running between the blanket cylinder and the printing cylinder, such that the side of the paper to be printed runs past the blanket cylinder.

The invention further relates to a method for producing a printing cylinder for a printing unit of the aforementioned type.

A printing unit and a method of the type mentioned above are known from DE-U-71 32 746.

In the known printing unit or the known method, one provides to counteract the chemical and mechanical loads on the printing unit cylinders which are involved in offset printing by applying a wear-resistant and corrosion-resistant layer to the printing unit cylinders. For this purpose, the known method provides for an intermediate layer of nickel aluminide to be applied to the base material of the roller and a layer of armor made of aluminum oxide with titanium oxide in a plasma spraying process.

As is known, each printing unit of an offset printing machine has a so-called inking unit for printing on sheets or webs, i.e. a plurality of rollers rolling on each other, which serve to distribute a color supplied from a container evenly over the running surface of the rollers. The color is then applied to a so-called plate cylinder, i.e. transfer the cylinder carrying the printing form, for example a film or a metal plate.

The writing to be printed or the image to be printed are formed in that the non-image areas are water-absorbing and ink-repellent, while the image areas are water-repellent and ink-absorbing. A so-called dampening system is used to moisten these areas.

The plate cylinder in turn rolls on the so-called blanket cylinder, i.e. a cylinder covered with a rubber blanket, which prints the image transferred from the plate cylinder onto the paper by means of indirect printing. The paper is pressed against the blanket cylinder by the so-called impression cylinder.

It has now been found that such arrangements occasionally cause problems because printed sheets flutter into the printing zone and are not easily detached from the printing cylinder even after printing. In order to counter this problem, it is also known to provide mesh-like mats in the area of the printing cylinder, with which a kind of air cushion is formed between the printing sheets and the printing cylinder.

However, these mesh-like mats are subject to high wear and very cumbersome to use.

Similar problems occur with other press configurations.

From GB-A-2 049 102 an ink distribution roller of an inking unit of a printing press is known, in which a corrosion-resistant layer made of stainless steel, nickel, titanium or aluminum-titanium is first applied to a metallic base body, and a ceramic layer is applied thereon in the plasma spraying process e.g. consists of aluminum oxide, titanium oxide, chromium oxide and the like. In the outer surface of the ceramic layer, depressions are made by means of a scanned laser beam which do not overlap one another. The surface of the ink distribution roller designed in this way has the purpose of making the distribution of the ink on the surface more uniform and thus making the use of doctor blades and the like unnecessary or at least less critical. This is to be achieved in that the printing ink penetrates into the depressions and, since the depressions are evenly distributed over the surface, is also uniformly distributed over the surface.

From GB-A-2 022 016 a printing press cylinder of a general type is known, in which a base material, e.g. Cast iron, steel is first a layer of nickel and / or chrome and then a metal oxide layer is applied. The metal oxide layer has an irregular surface, in which plastic particles, in particular PTFE particles, are additionally embedded. The irregular surface should form an air space between the cylinder surface and a printed sheet, which enables a flutter-free entry into the printing zone.

From DE-A-30 23 246 a single or multi-layer jacket for sheet-guiding cylinders in printing machines is known. The jacket has a single layer of high adhesive strength applied directly to the base body and an outer layer which is particularly corrosion-resistant and abrasion-resistant.

Materials for plasma-sprayed layers are known from a brochure "Surface Metallurgy Bernex Spray Layers" from Bernex GmbH, D-4018 Langenfeld (DE), with print date "1984", which act as self-flowing alloys and can be applied by means of plasma or in a fusion bond. Chromium-nickel-cobalt-boron, chromium-nickel-silicon-boron and chromium-nickel-silicon-molybdenum-boron compounds are specified as materials for this.

From DE-B-23 43 283 an application of the plasma spraying of oxide-ceramic layers and adhesive layers on printing rollers and printing plates is known, according to which certain layers to prevent the electrolytic Stress corrosion of printing rollers and printing plates are to be used. Thereafter, oxide-ceramic layers made of Al ₂ 0 ₃ and 1-50% Ti0 ₂ and heat-resistant adhesive layers made of Ni, Mo, Ni-Al or Cr-Ni alloys are to be used.

From DD-A-0 154 081 a method for producing surface layers for dampening rollers is known. Thereafter, a rough surface layer is to be applied to the base body of a dampening roller of an offset printing machine by means of powder coating in a plasma spraying process using powders of the metals chromium, nickel, tungsten, cobalt, their oxides and carbides, which is then treated with a fleece, so that the The tips of the supporting points are broken and rounded and the valleys are cleaned.

From DE-A-28 13707 it is known to modify metal surfaces by means of laser treatment by changing the structure of the treated layer.

From GB-A-2 100 621 it is known to melt ceramic layers by means of laser radiation and to allow the partially melted ceramic layer to solidify again.

Finally, DE-Z VDI reports 522 "Blechbearbitung'84" also describe that high-power lasers in the multi-kilowatt range make it possible to use a local, low-warpage surface treatment of metallic materials for hardening, alloying or coating highly stressed tools.

The invention is based on the object of further developing a printing unit or a method of the type mentioned in such a way that the paper guide when entering and leaving the printing zone without problems, in particular without fluttering and without excessive detaching forces in the paper web or in the printed sheet.

According to the printing unit mentioned in the introduction, this object is achieved in that the corrosion-resistant layer is melted over the entire surface and in that finely distributed depressions are melted into the surface of the abrasion-resistant layer.

According to the above-mentioned method, this object is achieved in accordance with the invention in that a corrosion-resistant layer is applied in a plasma spray process to the roller base material of the printing cylinder, that the corrosion-resistant layer is melted over the entire surface by means of a laser, that an upper, abrasion-resistant layer on the corrosion-resistant layer Plasma spray process is applied, and that finely divided depressions are melted into the surface of the abrasion-resistant layer by means of a laser.

The task is completely solved in this way, because the melted-in finely distributed depressions automatically form an effective air cushion between the paper and the cylinder in question, which causes the paper to flutter as it enters the printing zone and excessive release forces when it exits the printing zone certainly diminished. The particular advantage of the invention lies in the fact that, while maintaining the print, even the finest grid or grid forms, an air space is created between the cylinder jacket and the printed sheet, which ensures easy detachment of the printed sheet after printing and a flutter-free entry of the printed sheet into the printing zone, in particular for printing cylinders in sheetfed offset, in perfecting or reverse printing.

In a practical experiment of the invention, it was possible, for example, to process up to 10,000 sheets of velvet offset paper per hour on a conventional sheet-fed offset printing machine, which corresponds approximately to a doubling of the processing speed compared to the prior art.

In the context of the present invention, a first, adhesion-promoting and corrosion-resistant layer preferably consists of Cr, Ni, Al, CrNi, AINi, CrAI or the like. It preferably has a thickness of 15 to 100 μm.

A further, abrasion-resistant layer is preferably designed according to the invention either as a ceramic layer consisting of aluminum oxide, titanium oxide, chromium oxide, aluminum oxide + chromium oxide, aluminum oxide + titanium oxide, chromium oxide + titanium oxide, chromium carbide, chromium carbide + cobalt, tungsten carbide, tungsten carbide cobalt, calcium zirconate or the like it is a metal layer made of molybdenum, cobalt or the like.

The abrasion-resistant layer preferably has a thickness of 60 to 300 μm, preferably 200 μm.

These materials and dimensions have proven particularly useful in practical trials.

The melting of the layers has the essential advantage over the classic pure plasma spraying process without subsequent melting that a significantly increased adhesion of the layers is achieved because in the plasma spraying process, layers applied without further post-treatment only adhere through pure adhesion, so that there is in principle the risk of peeling off of the sprayed layer. The melting of the depressions by means of the laser has the essential advantage that the position and dimensions of the depressions can be selected and adjusted almost arbitrarily, in particular if one uses a CO _z laser which can be easily modulated in intensity. A particularly good effect is achieved in this context by simultaneously melting the outermost layer by means of the laser and melting the depressions in one operation.

In a practical embodiment of the method according to the invention, this is achieved by rotating the printing cylinder about its longitudinal axis at a constant, slow speed in order to melt the depressions and at the same time moving the laser parallel to the longitudinal axis by a slow feed, while a laser beam is directed onto the surface of the printing cylinder and the intensity of the laser beam is modulated.

In this way, the point of incidence of the laser beam on the surface of the printing cylinder describes a spiral line with a very small pitch, which can be set so small that the entire surface of the printing cylinder is subjected to a laser treatment. If the intensity of the laser beam is modulated at the same time, the pulse duty factor of the modulation in connection with the speed of the printing cylinder and the feed speed of the laser can be used to apply almost any grid of depressions. The shape of the depressions can be determined by suitably adjusting the modulation, in particular by either switching the laser beam back and forth suddenly between minimum and maximum intensity or modulating it with smooth transitions. The dynamics of the intensity of the laser beam between maximum and minimum power can also be used to form certain forms of depressions.

In a particularly preferred exemplary embodiment of this method, the laser beam is modulated approximately three times per millimeter in length of the line which it describes on the surface of the printing cylinder.

It has already been mentioned that different shapes of the depressions can be achieved. In variants of the invention, the depressions are melted in such a way that they have a sinusoidal or a triangular cross-sectional image in a direction perpendicular to the surface of the layer.

It has also been mentioned that different types of screens, i.e. a different area distribution of the depressions can be achieved by appropriately setting the process parameters.

In a variant of the invention, the depressions are melted in such a way that their upper openings lie against one another at least approximately in a square-dense grid. An even denser packing of the depressions on the surface can, however, also be achieved in that they abut one another in a hexagonally dense grid.

It is particularly preferred in these embodiments if the openings of the depressions overlap one another in at least one coordinate direction. In this way it is ensured that the entire surface of the printing cylinder is subjected to a laser treatment because the zones of subsequent melting of depressions merge into one another.

In a preferred embodiment of the invention, the depressions are melted to a depth of approximately 0.05 to 0.5 mm and to a diameter of approximately 0.1 to 0.5 mm.

It goes without saying that the features described above and those still explained below can be used not only in the respectively specified combination, but also in other combinations or on their own, without thereby departing from the scope of the present invention.

• Fig. 1 Prinzipdarstellung einer üblichen Bogenoffsetmaschine zur Erläuterung der Erfindung.
• Fig. 2a bis 4b ein Ausführungsbeispiel eines erfindungsgemäßen Verfahrens, mit einer Prinzipdarstellung aufeinanderfolgender Verfahrensschritte sowie eine Prinzipdarstellung des jeweils erzielten Schichtaufbaus;
• Fig. 5a und 5b Darstellungen ähnlich Fig. 3b, jedoch in weiter vergrößertem Maßstab;
• Fig. 6 bis 9 Prinzipdarstellungen zur Erläuterung erfindungsgemäß erzielbarer Vertiefungsraster;
• Fig. 1 zeigt eine an sich bekannte Offset-Druckmaschine, wie sie zum Bedrucken von Bögen oder Bahnen verwendet werden kann.

Embodiments of the invention are shown in the drawing and are explained in more detail in the following description. Show it:

• Fig. 1 schematic diagram of a conventional sheetfed offset machine to explain the invention.
• 2a to 4b show an exemplary embodiment of a method according to the invention, with a basic illustration of successive method steps and a basic illustration of the layer structure achieved in each case;
• 5a and 5b representations similar to FIG. 3b, but on a further enlarged scale;
• 6 to 9 are schematic diagrams for explaining deepening grids achievable according to the invention;
• Fig. 1 shows a known offset printing machine, as it can be used for printing on sheets or webs.

The printing press has a printing cylinder 1, a blanket cylinder 2 and a plate cylinder 3. An inking unit is 4 and a dampening unit is 5. Transport cylinders 6 and 6 'are also provided.

The inking unit 4 evenly distributes a certain printing ink onto the surface of the plate cylinder 3 which bears the printing ink. At the same time, the dampening unit 5 with a similar distribution ensures adequate moistening of the surface areas of the plate cylinder 3 provided for this purpose.

The plate cylinder 3 runs on the blanket cylinder 2 and transfers the image to be printed or the font to be printed on its elastic surface. The blanket cylinder 2 in turn rolls on the sheet or web that is passed between the blanket cylinder 2 and the impression cylinder 1. For this purpose, for example, a paper sheet along direction 7 first reaches the area of the transport cylinder 6 and is guided from there between the blanket cylinder 2 and the printing cylinder 1. After circulation around the printing cylinder 1, the paper sheet is then conveyed out of the area of the printing unit again by means of a further transport cylinder 6 'in the direction of the arrow 8.

If, in one example of the invention, the surface of the printing cylinder 1 is now provided with depressions, as will be explained below, this has the effect that the paper sheet runs in flutter-free along the arrow 7 between the blanket cylinder 2 and the printing cylinder 1 and also without Solves problems again from the printing cylinder 1 in order to be delivered to the second transport cylinder 6 '.

2a to 4b show, in a simplified representation, different steps of the method according to the invention, the same elements being provided with the same reference numerals. 2a to 4a show in principle a device for performing the inventions method according to the invention, while FIGS. 2b, 3b and 4b represent the layer structure achieved in each case in a greatly enlarged representation. 2, the pressure cylinder 1 is clamped in a device (not shown) in such a way that it can be rotated about its longitudinal axis 11 in the direction of the arrow 12 at a very slow speed.

In addition to the printing cylinder 1, there is a radial spray gun 13, which can be slowly adjusted in the direction of an arrow 14 parallel to the longitudinal axis 11 of the printing cylinder 1 by means of a feed, also not shown.

It goes without saying that the movement process thus explained between the pressure cylinder 1 and the plasma spray gun 13 can also be implemented in different kinematic reversals in a different way without going outside the scope of the present invention.

2a, a spiral line on the surface of the printing cylinder 1 is indicated in FIG. 2a. A first material 16, which emerges from the plasma spray gun 13, is distributed along this line 15 when the pressure cylinder 1 and the plasma spray gun 13 move in the manner described. It is easy to see that the slope of the spiral line 15 can be adjusted as desired by adjusting the speed of the pressure cylinder 1 and the feed speed of the plasma spray gun 13, as well as the speed at which the plasma spray gun 13 along the line 15 moves.

2b shows that a first layer 21 can be applied to a roller base material 20 of the printing cylinder 1 in the manner described above.

The first layer 21 is an adhesion-promoting and corrosion-resistant layer. The first material 16, from which the first layer 21 is made, can be a material that is suitable for this purpose and can be applied in a plasma spraying process, for example Cr, Ni, Al, CrNi, AiNi, CrAI or the like.

According to the invention, a second layer 24 is next applied to the adhesion-promoting and corrosion-resistant first layer 21, as shown in FIG. 3b.

For this purpose, as indicated in FIG. 3a, a further process step is carried out which corresponds to the process step according to FIG. 1a, but with the difference that instead of the first material 16, a second material 23 is sprayed by the plasma spray gun 13. With 12a, 14a and 15a it is indicated that the process parameters in the second process step according to FIG. 3a can differ from those of the first step according to FIG. 2a if this appears advisable due to the specially used second material 23.

The resulting layer structure is shown in Fig. 3b, where you can see that there is now a second layer 24 on the first layer 21. An abrasion-resistant material is used as the second material 23 from which the second layer 24 is made. On the one hand, this can be a ceramic layer which consists of aluminum oxide or titanium oxide or chromium oxide or aluminum oxide + chromium oxide, aluminum oxide + titanium oxide, chromium oxide + titanium oxide, chromium carbide, chromium carbide + cobalt, tungsten carbide, tungsten carbide cobalt, calcium zirconate or the like. However, a metal layer made of molybdenum, cobalt or the like can also be used as an abrasion-resistant layer.

It is further understood that adhesion-promoting and corrosion-resistant layers on the one hand and abrasion-resistant layers on the other hand can also be provided several times in succession.

Points 26 indicate that the first two process steps can be followed by further process steps of a similar type, so that overall a structure with more than two layers 21, 24 is formed on the roller base material 20.

4a shows a further method step in a schematic representation, in which, instead of the plasma spray gun 13, a laser 30 is guided parallel to the longitudinal axis 11 of the printing cylinder 1 by means of a suitable feed. The parameters 12b, 14b and 15b corresponding to the previous method steps can be set appropriately again. This is particularly recommended in view of the fact that the slope of the spiral line 15b is set much smaller than was the case for the lines 15 and 15a, because the point of incidence of the laser beam 31 of the laser 30 is significantly smaller than the spray zone, which is associated with the plasma spray gun 13 is swept over the surface of the printing cylinder 1.

Two things can now be effected by means of the laser beam 31 of the laser 30:

On the one hand, the laser 30 can be guided in continuous wave mode along the line 15b in such a way that the entire applied layer 21 or 24 or 21 is melted together with 24 over the entire surface onto the surface of the printing cylinder 1. The process steps according to FIGS. 2, 3 and 4 can be carried out in almost any order by melting the layers 21, 24 either individually or together or in each case over the entire surface in groups.

Another possibility, which is significant in the present context, results from modulating the laser beam 31, which means a temporal variation of the intensity. The laser beam 31 can either be switched on and off, i.e. be clocked, but you can also regulate the intensity with soft transitions between a maximum and a minimum intensity value.

In any case, this results in a structure as shown in Fig. 4b. Specifically distributed recesses 32 are introduced into the at least partially melted layer 24 by modulating the laser beam 31, the position and shape of which depends on the set process parameters.

5a and 5b show two examples. The depressions 32 according to FIG. 5a have a sinusoidal shape in the vertical cross section, while the depressions 32a according to FIG. 5b have a more triangular shape.

In a preferred embodiment of the invention, the depth T of the depressions 32 is approximately 0.05 to 0.5 mm, preferably 0.35 mm and the diameter D is approximately 0.1 to 0.5 mm, preferably 0.11 mm. However, this is not a restrictive statement, but rather the diameters D and the depths T of the depressions 32 can be varied within wide limits.

6 to 9 show various areal distributions of the depressions 32 on the surface of the printing cylinder 1.

6 shows an areal distribution with the densest square packing as an example, in which the grid dimensions x and y are the same size in the two coordinate directions and correspond to the upper diameter D of the depressions 32.

7 shows, likewise as an example, a hexagonally closest surface packing of the depressions 32.

In Fig. 8 it is indicated that the depressions 32 can at least partially overlap at least in the direction of the one coordinate, the grid dimension of two partially overlapping depressions 32 being designated by z. From this, the grid dimensions of the two surface coordinates are calculated as az or bz, where a and b are selectable factors and a can have a value of 1.414, for example, while b can have a value of 0.767, in which case the depressions 32 relative to one another are less than 45 ° are aligned. The resulting overlaps of the depressions 32 are designated 35.

Finally, FIG. 9 shows yet another variant in which the depressions 32 overlap in both coordinate directions, so that overlaps 35 and 36 arise in both coordinate directions.

The areal arrangements according to FIGS. 6 to 9, as already mentioned, can be achieved by suitably setting the process parameters. If, for example, the modulation of the laser beam 31 is set to three pulsations per millimeter along the line 15b of FIG. 4a, approximately 800 to 900 depressions 32 per square centimeter are obtained.

Claims (14)

1. A printing mechanism of an offset printing machine comprising a plate cylinder (3) provided with printing colour, a rubber blanket cylinder (2) running in abutment to the plate cylinder (3), and a printing cylinder (1) running in abutment to the rubber blanket cylinder (2), the printing cylinder (1) being provided with a lower, plasma-sprayed, corrosion-resistant layer (21) as well as with an upper, plasma-sprayed, anti-abrasive layer (24) on its roller base material (20), wherein paper sheets or webs to be printed run between the rubber blanket cylinder (2) and the printing cylinder (1) such that the side of the paper upon which printing is intended runs past the rubber blanket cylinder (2), characterized in that the corrosion-resistant layer (21) is molten on in a flat area and that highly dispersed dimples (32) are molten into the surface of the anti-abrasive layer (24).

2. The mechanism of claim 1, characterized in that the adhesion-imparting and corrosion-resistant layer (21) consists of Cr, Ni, Al, CrNi, AINi or CrAl.

3. The mechanism of claim 2, characterized in that the adhesion-imparting and corrosion-resistant layer (21) has a thickness of between 15 and 100 pm.

4. The mechanism of any of claims 1 through 3, characterized in that the anti-abrasive layer (24) i8 a ceramic layer from aluminium oxide, titanium oxide, chromium oxide, aluminium oxide + chromium oxide, aluminium oxide + titanium oxide, chromium oxide + titanium oxide, chromium carbide, chromium carbide + cobalt, tungsten carbide, tungsten carbide cobalt, cal.- cium circonate, or a metal layer from moiyb- denum or cobalt.

5. The mechanism of claim 4, characterized in that the anti-abrasive layer (24) has a thickness of between 60 and 300 pm, preferably of 200 µm.

6. A method of manufacturing a printing rolleir for a printing mechanism of an offset printing machine comprising a plate cylinder (3) provided with printing colour, a rubber blanket cylinder (2) running in abutment to the plate cylinder (3) and a printing cylinder (1) running in abutment to the rubber blanket cylinder (2), wherein paper sheets or webs to be printed run between the rubber blanket cylinder (2) and the printing cylinder (1), such that the side of the paper on which printing is intended runs past the rubber blanket cylinder (2), characterized in that a corrosion-resistant layer (21) is applied on the roller base material (20) of the printing cylinder (1) using the plasma-spray method, that the corrosion-resistant layer (21) is molten on in a flat area by means of a laser, that an upper, anti-abrasive layer (24) is applied on the corrosion-resistant layer (21) by means of the plasma-spray method and that highly dispersed dimples (32, 32a) are molten into the surface of the anti-abrasive layer (24) by means of a laser.

7. The method of claim 6, characterized in that after the application of the corrosion-resistant layer (21) the printing cylinder (1) for melting on this layer (21) in a flat area is constantly and with low revolutional speed rotated about its longitudinal axis and, simultaneously, the laser (30) is displaced by means of a slow feeding mechanism in a direction parallel to the longitudinal axis (11), while a laser beam (31) is directed on the surface of the printing cylinder (1) and that, subsequently, the anti-abrasive layer (24) is applied onto the corrosion-resistant layer (21) and that the printing cylinder, for melting in the dimples (32, 32a) into the anti-abrasive layer (24) is rotated about its longitudinal axis (21) with constant, slow revolutional speed and, simultaneously, laser (30) is displaced by means of a slow feed-in mechanism in a direction parallel to the longitudinal axis (11), while the laser beam (31) is directed onto the surface of the printing cylinder (1) and modulated in its intensity.

8. The method of claim 7, characterized in that the laser beam (31) is modulated approximately three times per millimeter of length of a line (15b) which it imparts on the surface of the printing cylinder (1).

9. The method of any of claims 6 through 8, characterized in that the dimples (32) are molten in such that they have a sinusoidal cross-sectional appearance in a direction perpendicular to the surface of the layer (24).

10. The method of any of claims 6 through 8, characterized in that the dimples (32a) are molten in such that they have a triangular cross-sectional appearance in a direction perpendicular to the surface of the layer (24).

11. The method of any of claims 6 through 10, characterized in that the dimples (32) are molten in such that their upper openings approximately lie on a square, tight raster screen (x, y).

12. The method of any of claims 6 through 10, characterized in that the dimples (32) are molten in such that their upper openings approximately lie on a hexagonal tight raster screen.

13. The method of claim 11 or 12, characterized in that the openings overlap (35, 36) in at least one coordinate direction.

14. The method of any of claims 6 through 13, characterized in that dimples (32, 32a) are molten in with a depth (T) of about between 0,05 and 0,5 mm and having an upper diameter (D) of about between 0,1 and 0,5 mm.

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