WO2010089020A1

WO2010089020A1 - Method for producing anilox rolls

Info

Publication number: WO2010089020A1
Application number: PCT/EP2010/000172
Authority: WO
Inventors: Heribert Wille; Roland Winter; Andreas Tillmann; Günter Fuchs
Original assignee: Heidelberger Druckmaschinen Ag
Priority date: 2009-02-03
Filing date: 2010-01-14
Publication date: 2010-08-12
Also published as: EP2393661A1; CN102307730A; EP2393661B1; DE102010004632A1; CN102307730B

Abstract

The invention relates to anilox rolls for anilox color decks, engraved by a short-pulse laser, wherein the cross-sectional shape of the engraved cells or hachures is machined out by a plurality of pulses of the repeatedly operating laser. The pulse energy and mean power of the laser are selected or set so that at least 0.5 cm3 of material/hour is ablated. The surface of the roll is subsequently smoothed or cleaned by a mechanical finishing step.

Description

Process for producing anilox rolls

The invention relates to a process for the production of anilox rollers, in particular z. For example, those that are used under the name "anilox rollers" in so-called short inking units of offset printing machines to take in conjunction with a doctor blade or a chambered doctor blade paint from a paint reservoir and to promote more rollers in the direction of the printing plate. However, anilox rolls are also used in coating plants to meter the amount of paint to be applied and, in addition to offset printing, are also used in other printing processes, such as flexographic printing or in the corresponding machines, for example The etching process has been structured by etching or mechanically engraved by a stylus penetrating into the soft copper skin on a steel roll body, and recently engraved with laser tools as described, for example, in the article "Universal Anilox Rolls for the Printing Press" the magazine "Flexo and Gravure Printing", Issue 2, 2004.

Today, the anilox rollers intended for use in anilox inking units are usually provided on the surface with a hard ceramic layer for the purpose of longer service life. In the laser engraving of such rolls, however, problems occur. Often, after a relatively short lifetime, streaks appear in the print image due to the fact that ceramic particles detach from the anilox roller, jam against the cutting edge of the doctor blade and then generate grooves on the roller surface. The reason for this lies in the manufacturing process of laser engraving. Because there were previously used thermal YAG laser or CO ₂ laser whose laser pulses partially evaporate material from the wells produced by them, but partly also drive out in the molten state, in which case the material on both sides of the generated depression as a "mountain" precipitates on the surface.

Since now also to be engraved wells or Haschuren with rotating roller in the circumferential direction (ie in the cross-sectional profile) are driven out with a single relatively long-lasting, high-energy laser pulse at once and, as long as it concerns elongated wells or Haschuren, this in the longitudinal direction repeatedly juxtaposed recesses were created, namely whenever the roller has rotated further by about one revolution, resulting in this production process along the Haschuren running individual scales of molten ceramic material. These also do not adhere well to each other or on the roll surface and are therefore easily by the doctor blade in

Printing operation broken out, which then creates the grooves in the roll surface, which can lead to the pre-formed stripes in the printed image. To solve this problem, it has already been proposed to heat the surface of the ceramic roller after laser engraving again with a laser to just below the melting temperature, thereby closing cracks and pores and compacting the surface, as described in EP 1 967 381 A2 is described. Although this can extend the life of the anilox rollers, but it also prolongs the manufacturing process, because by this additional step of over-melting or Zusinterns the surface is once again required considerable additional time. Overall, engraving by this method takes about 10 to 12 hours for an anilox roll having a diameter of 180 millimeters and a length of 560 millimeters.

Furthermore, it has been proposed to solve the problem described to adjust the pulse shape of the laser used so that after an intense first laser pulse immediately followed by a second less intense pulse, then smoothed by the wells generated by the first laser pulse and the remaining therebetween ridges and cured should be. This process known under the name "Ultramelf technology" is described, for example, in the journal "Deutscher Drucker" No. 44 of Nov. 29, 2001. Even with this process, the service life of the laser-engraved anilox rollers can be improved, but still not drifting into adequate orders of magnitude For example, a service life of up to 50 million revolutions is required before the anilox roller is replaced and refurbished.

It has also been proposed that in addition to the engraved by a CO ₂ laser wells then material in a variety of

Sand grinding passes with a finer diamond abrasive to the desired surface roughness (EP 0 396 114 B1). After each second grinding pass was Measure the roughness and scoop volume of the roller to ensure that the grinding process does not "overrun" the desired optimum, which is a complex process that is difficult to reproduce and takes a long time to complete.

It is therefore the object of the present invention to provide a production process for the laser engraving of anilox rolls with a ceramic surface, with which it is possible to achieve long service lives for the rolls, without thereby drastically increasing the production process itself.

This object is achieved with the measures specified in the characterizing part of claim 1.

According to the invention, the recesses in the laser engraving are produced by a repetitively operated short-pulse laser, wherein in each case a plurality of laser pulses are used to work out the depression in the cross-sectional profile.

It is therefore used here for the production of anilox rolls on known short-pulse laser. These lasers deliver light pulses of very short duration in the range of a few hundred nanoseconds or less and generate very high energy densities in a small focus range, as a result of which the material to be removed in the

Basically, it evaporates or evaporates and does not or only to a very small extent precipitates on the webs on which the doctor blade slides.

As it turns out, the leached material adheres to the ridges of an anilox roll in a manner such that these remaining rests can be removed by a short, inexpensive finishing operation such as honing, lapping or polishing, or by a non-burst cleaning operation , Manual overpolishing or wiping off residues from the roller engraved in the manner described with the short pulse laser is already sufficient to produce a very smooth and stable surface on which the doctor blade slides. Although the use of ultrashort laser pulses in the femtosecond range for the microstructuring of materials is known per se and z. In Physical Sheets 55 (1999, No. 6 on page 41 in the article by Nolte, Momma, Chichkov and Welling). However, the production of anilox rolls for the inking units of printing presses is not mentioned there as an application field and the problems occurring in the production of such anilox rolls and their removal are also not described. Femtosecond lasers are also currently unable to quench the amounts of material needed with anilox rolls at a processing time of a few hours, which is acceptable for engraving. Because the energy densities and amounts of energy that are needed for it, can be at present possible

Pulse repetition rates do not concentrate in the laser pulses. The lasers used according to the invention, preferably fiber lasers or disk lasers, deliver laser pulses in the range between 20 picoseconds and 200 nanoseconds and average laser powers in the range between 10 watts to several 100 watts. It is important that the used short-pulse laser provides sufficient energy density to optimally use the built-in light energy for ablation of the material to be processed. In addition, the incoming material on the average power must be large enough to ablate, for example, in the case of anilox rolls having a ceramics surface with a pick-up volume of typically 3 cm ^{3 is} at least 0.5 cm ³ ceramic material per hour. Because otherwise the processing time for the laser engraving of a roller would be unacceptably long or the simultaneous use of multiple lasers, the plant technical effort will be too large.

A suitable for the processing of anilox rollers short pulse laser generates z. B. laser beam pulses at a wavelength of 1065nm with a pulse duration, which is expediently below 200 nanoseconds, preferably between 100 and 150 nanoseconds. Below a pulse duration of 200 nanoseconds, it has been found that thermal contributions to material ablation generated in ceramic material are low enough and do not produce any melting of greater extent at the edges of the wells to be engraved. With a pulse peak power of 2 to 6 kilowatts can be at

Anilox inking in anilox inking customary Well depths readily reach, wherein for working out the cross-sectional profile in each case a plurality of laser pulses be placed one behind the other, typically 5 to 100 laser pulses depending on the width and depth of the wells or Haschuren. Wells with relatively smooth clean flanks can be produced with this number of pulses and, incidentally, the cross-sectional flank shape of the wells or hafors can be influenced in such a way that, compared to the other methods mentioned at the beginning, one is responsible for the ink release / acceptance behavior of the wells good geometry yields. Optionally, the anilox roller is then engraved in several passes, so that the cross-sectional shape is worked out in several superimposed layers by the laser pulses. The pulse repetition rate of the laser is several 100,000 kHz. In this way, an anilox roller for a 35/50 cm printing unit can be engraved within a few hours at speeds between 100 and 1,000 rpm. It is useful if the laser engraving is followed by a finishing step and / or a cleaning step, for. B. in the same clamping of the roller as in the previous laser engraving itself, wherein the finishing step or cleaning step, however, can also be done manually, for example, by polishing or wiping the lasered rollers z. B. with a cleaning agent, either still in the set or after it was taken out of the clamping. Also, cleaning the roll in an ultrasonic bath may be sufficient, and in some cases, such a finishing step may be completely eliminated.

Further advantages of the invention will become apparent from the following description of an embodiment.

Example 1: a) Was provided with a bearing journal steel roller ST52 with a cylinder length L of 560 mm and a diameter D of 180 mm of the cylinder jacket. This turned into shape roll body was then provided in a plasma spraying on the cylinder jacket with a chromium oxide layer with a thickness of 0.275 mm.

b) Subsequently, the cylinder surface was cylindrically shaped with the aid of a ceramic-bonded diamond grinding wheel with a tolerance of 0.01 mm ground. Finally, the cylinder surface was smoothed in three passes in a honing machine at 200 rpm, and a feed rate of 200 mm / min, with a contact pressure of 2.5 bar. Here, a honing stone with a grain size of 2000 was used. The thus treated cylinder surface then had a roughness of Rz = 1, 9 microns.

Thereafter, the thus treated roll body was placed in a laser processing plant. This system contains a repetitively operated ytterbium fiber laser with a pulse duration of 130 ns at a repetition rate of 500 kHz. The average power of the laser was 150 W, it delivered a pulse peak power of

2.5 kW. He was set to these values in order to engrave on the cylinder surface hafors with a mean depth of 20 microns and a mean width of 90 microns with a web width of 20 microns approximately over a length of 520 millimeters.

The hafs are said to extend over the cylinder surface at a line of 90 L / cm in a variety of steep spirals. However, since the engraving process takes place with rapid rotation of the workpiece in the circumferential direction, the pulsing of the laser was very synchronized with the speed of the roller. The speed was set from 150 W to 750 rpm in consideration of the maximum pulse repetition frequency of 500 kHz and the average power of the laser, in order to achieve the required width and depth of the hurdles. In each case, 6 pulses resulted over the cross section of the Haschur, with which the cross-sectional shape was machined out of the material, before the pulses in the region of the web between the Haschuren each short interrupted, d. H. there 2 laser pulses were suppressed.

The advance of the laser unit along the cylinder axis was 5 μm per revolution of the roll, i. H. at the set speed of 750 rpm, the engraving process over the cylinder length L of 560 millimeters took about 2.4 hours.

During this time, approximately 1.5 cm were removed in the area of 0.3 m ² to be engraved. Subsequently, the roller was with the same settings engraved again in a second pass, to get to the desired average depth of Haschuren of 20 microns. In total, this resulted in a material removal of 3 cm ³ for a total processing time of 4.8 hours for engraving.

d) The thus structured anilox roll was then subjected to a second finishing step. Here, the engraved surface was in two overflows with a 4000 grain honing stone with a lower contact pressure of about 1 bar at a speed of 200 rev / min, at a feed rate of 600 mm / min. smoothed.

The roller thus treated could then be installed in the printing unit of a sheet-fed offset printing machine type SM52 and provide there as anilox anilox roll their service. The entire machining process, from the ceramic coating to the final finishing process, took 5.5 hours

Hours.

Example 2:

Here, in comparison to the manufacturing process according to Example 1, the production step b) was changed as follows: The honing was carried out with a 4000 grade honing stone in four overflows with a contact pressure of 1.5 bar. The thus treated cylinder surface then had a roughness of Rz = 1.5 microns.

During the subsequent laser engraving, the roller speed was reduced to 250 rpm, and the axial feed rate was increased to 7.5 μm / rev at otherwise identical settings for the laser. Already with a simple sweeping of the roll surface, sufficiently clean hides with an average depth of about 20 μm were obtained, so that a further engraving could be dispensed with.

After the laser engraving (step c)), the structured anilox roll was not honed again but polished manually for about 10 minutes. The thus obtained anilox roll had comparable good properties to those of Example 1.

Claims

claims

1. A process for the production of anilox rolls (for printing presses) by means of laser engraving, wherein in rolls, which may have a ceramic surface, by material removal by means of laser radiation depressions such. B. Wells or Haschuren are introduced, characterized by the following process steps:

the depressions are produced by a repetitively operated short-pulse laser, wherein in each case a plurality of laser pulses are used in order to work out a depression in the cross-sectional profile,

- The short pulse laser is selected or adjusted so that it ablates at least 500 mm ³ material per hour from the roll surface.

2. The method of claim 1, wherein the roll surface is then smoothed and / or cleaned by a mechanical finishing step.

3. The method of claim 2, wherein the finishing step and / or cleaning step takes place in the same clamping of the roller as in the preceding step of the laser engraving.

4. The method of claim 2, wherein the finishing step and / or cleaning step is manual.

5. The method of claim 2, wherein the cleaning step is carried out in an ultrasonic bath.

6. The method of claim 1, wherein the laser used for the engraving is a fiber laser.

7. The method of claim 1, wherein the laser used for the engraving generates radiation pulses having a pulse duration in the range below 200 ns.

8. The method of claim 1, wherein the laser used for the engraving provides a peak pulse power of at least 2 kW and an average power of at least 80 watts.

The method of claim 1, wherein the pulse repetition rate is between 100 and 1000 kHz, preferably at or near 500 kHz.

10. The method of claim 1, wherein the number of laser pulses for working out the Querschnittsprofϊls the wells between 5 and 100, preferably between 10 and 50, is located.

11. The method according to any one of claims 1 to 10, for processing a roll with a metallic core and a ceramic jacket.

12. The method of claim 11, wherein the ceramic layer is chromium dioxide, which is applied to a metallic roller body, preferably vapor-deposited, sputtered on or applied by a plasma spraying process.

13. The method of claim 11, wherein before the laser engraving of the roller on the shell of a metallic roller body, a ceramic layer is applied and the ceramic surface is ground round.

14. The method of claim 13, wherein the roller receives a cylindrical shape with a tolerance of <0.01 mm by the grinding process.

15. The method of claim 14, wherein the ground surface is laser finished prior to laser engraving by a first finishing step so that the mean roughness of the surface R _z <2 microns.

16. The method according to any one of claims 1 to 14, wherein the rolls are ground with ceramic surface before the step of the laser engraving in the form and then engraved without a further finishing step.

17. The method according to any one of claims 1 to 16, wherein the roll surface is repeatedly scanned when engraving by the laser radiation for working out the shape or depth of the cross-sectional profile.

18. The method of claim 2, wherein the finishing step is one or more of the following methods: honing, lapping, polishing.