Method of manufacturing rotogravure cylinders

Abstract

The present invention describes a method for manufacturing rotogravure cylinders with a cylinder base made of aluminum and a single metallic layer on the cylinder surface. The method comprises the construction of the cylinder base, the deposition of the metallic layer on the cylinder surface, the thinning of the cylinder to achieve the required dimensions, the polishing of the cylinder surface and finally the etching of the cylinder with the desired printing pattern. The metallic layer can be any copper alloy that will produce a surface with a Vickers hardness of about 400 HV. The metallic layer is deposited onto the cylinder base using any thermal spraying method. The cylinder surface is then thinned and polished by using any conventional method. Finally, the cylinder is etched to provide a superb cylinder for the printing industry.

Claims

1. A rotogravure cylinder comprising a cylindrical base and an engraving layer comprising a copper alloy with a surface having a Vickers Hardness in the range of 300-600 HV, wherein the surface of the engraving layer constitutes a printing surface and is free of any subsequent protection layer.

2. The rotogravure cylinder as claimed in claim 1, wherein the engraving layer is present directly on the cylindrical base.

3. The rotogravure cylinder as claimed in claim 1, wherein the cylindrical base at least substantially comprises aluminum.

4. The rotogravure cylinder as claimed in claim 1, wherein the copper alloy is a brass comprising copper and zinc.

5. The rotogravure cylinder as claimed in claim 4, wherein the cooper alloy comprises 40-70 wt % copper and 30-50 wt % of zinc as a secondary alloying element.

6. The rotogravure cylinder as claimed in claim 1, wherein the Vickers Hardness is in the range of 400-500HV.

7. The rotogravure cylinder as claimed in claim 1, wherein the engraving layer has a surface roughness R.sub.z between 0.3 and 0.60 μm.

8. Use of the rotogravure cylinder as claimed in claim 1 for printing by transfer of ink from the rotogravure cylinder to a substrate.

9. Use as claimed in claim 8, wherein the printing constitutes the printing of packaging materials.

10. The rotogravure cylinder as claimed in claim 1, wherein the engraving layer is deposited by means of a high velocity thermal spraying method.

11. The rotogravure cylinder as claimed in claim 1, wherein the copper alloy comprises an element chosen from the group consisting of zinc, tin, aluminum and nickel as a secondary alloying element.

12. The rotogravure cylinder as claimed in claim 11, wherein the copper alloy comprises 40-70 wt % copper and 30-50 wt % of the secondary alloying element.

13. Method of manufacturing rotogravure cylinders comprising the steps of: providing a cylindrical base; depositing of a copper alloy for definition of an engraving layer by means of high-velocity thermal spraying, which engraving layer has at its surface a Vickers Hardness of 300-600 HV; and engraving the engraving layer, wherein the surface of the engraving layer serves as the printing surface and is free of any subsequent protection layer.

14. The method as claimed in claim 13 wherein the high-velocity spraying process is applied in velocity of at least 300 m/s.

15. The method as claimed in claim 13, further comprising the step of thinning the engraving layer.

16. The method as claimed in claim 13, further comprising the step of polishing the preferably thinned engraving layer.

17. The method as claimed in claim 13, wherein laser engraving is used in the engraving step.

18. The method as claimed in claim 13, wherein the engraving layer is provided with a final thickness in the range of 250-400 μm.

19. Rotogravure cylinder obtainable with the method as claimed in claim 13.

20. The method as claimed in claim 13, wherein the high-velocity spraying process is applied with a particle speed of at least 500 m/s.

Description

BRIEF INTRODUCTION OF THE FIGURES

(1) These and other aspects of the invention will be further elucidated with respect to the following figures, wherein:

(2) FIG. 1 shows a diagrammatical bird's eye view of a rotogravure cylinder;

(3) FIG. 2 shows a diagrammatical cross-sectional view of the rotogravure cylinder;

(4) FIG. 3 shows a diagrammatical bird's eye view of the proposed rotogravure cylinder, and

(5) FIG. 4 shows a diagrammatical cross-sectional view of the proposed rotogravure cylinder.

(6) FIGS. 1, 2, 3 and 4 are not drawn to scale and they are only intended for illustrative purposes. Equal reference numerals in different figures refer to identical parts of the cylinder.

ILLUSTRATED DISCUSSION OF DETAILED EMBODIMENTS

(7) The term ‘rotogravure cylinders” relates herein to rotogravure cylinders and/or any gravure cylinders used in the printing industry, particularly for the printing of packaging materials. The proposed invention is not limited in any way by the dimensional characteristics of the cylinder.

(8) The term ‘cylindrical base’ as used in the context of the present invention does not require the base to be a block-like material. Rather the base may be hollow. Alternatively, the base may comprise several layers, such as a steel core and an aluminum top layer. The term aluminum in the present invention refers to pure aluminum, aluminum with small addition of other materials or aluminum alloys.

(9) The coating material refers to any material which can be applied to the surface of the cylinder base to produce a surface suitable for engraving and to withstand the wear of the printing process. Different coating materials will produce a cylinder surface with different hardness. The preferred Vickers hardness of the cylinder surface is in the order of 400-500 HV. In the current invention a number of materials have been used with success, e.g. copper alloys such as copper and zinc, copper and tin, copper and aluminum, copper and nickel, etc.

(10) The term ‘at least partial melting’ refers to a process wherein at least the surface of individual particles is melted so as to create a homogeneous layer. It is not excluded that inner cores of the said particles remain in solid form. It is moreover not excluded that the circumferential layer created by melting of brass particles is actually an alloy with some aluminium of the underlying cylindrical base. Such an alloy may well be created, particularly close to the interface with the cylindrical base. The composition of the circumferential layer further away from the cylindrical base may thus be different from the composition near to said interface.

Example 1

(11) A gravure cylinder with a conventional steel base was produced to the desired dimensions. The steel cylinder was provided with a coating layer, for instance based on electroplated copper. Brass particles, with an average diameter of less than 50 μm, preferably in the range of 40-45 μm, were sprayed with a thermal spraying method. The brass in use was for instance common brass or high brass, containing 35-40 wt % zinc. During the spraying process, the cylinder was rotated. Impact of the brass particles onto the cylinder resulted in in heating up of the particles, to the extent of at least partial melting. This melting resulted in formation of a single layer extending circumferential around the base. Compressive stress developed in the course of cooling down. This cooling down was achieved by waiting in one embodiment; in an alternative embodiment, jetted air was sprayed onto the cylinder with the circumferential layer.

(12) The engraving layer was deposited in a thickness of approximately 400 μm. This layer was thereafter thinned and polished, by means of a fine grinding process. Use was made of a diamond saw, as known for the sawing of copper or copper-containing elements. The sawing resulted in removal of about 100 μm thickness of brass. A lubricant was sprayed while sawing so as to prevent too much heating of the brass layer. Moreover, herewith a polishing was achieved as well. Use was made herein of grinding with a conventional grinding machine with grinding and polishing stones. The resulting surface roughness R.sub.z was 0.4 μm.

(13) The intermediate product was therewith ready. In a subsequent step, this intermediate product was engraved in accordance with a desired and predefined pattern. Use was made herein of laser engraving.

Example 2

(14) A second gravure cylinder as shown in FIGS. 3 and 4 was produced on the basis of a cylinder with an aluminum base 1. This aluminum base 1 was produced from an aluminum tube to the desired dimensions. The brass particles of the type used in Example 1 were sprayed onto the aluminum base directly by means of high-velocity thermal spraying, in which the particle speed was generally above 300 m/s, typically in the order of 700-1,200 m/s. The thickness of the deposited engraving layer 5 was again set to 400 μm, which was subsequently thinned and polished.

Example 3

(15) The rotogravure cylinder manufactured in accordance with Example 1 was tested. Use was made of Vickers Hardness testing. This testing, standardized per se under ASTM E92 and ISO6507 was measured with the ultrasonic contact impedance (UCI) measurement, standardized under ASTM A 1038, using a diamond pyramid with a 136° roof angle. Measurement equipment for testing the Vickers Hardness on a surface with UCI measurement is commercially available from various suppliers. The Vickers Hardness is tested at room temperature, i.e. 20-25° C. The resulting Vickers Hardness was 430 HV.

(16) Although the above description is the recommended methodology for the manufacturing of a light weight gravure cylinder with a base made of aluminum and a circumferential single layer engraved appropriately, it is apparent that appropriate deviations or alterations or modifications can be implemented without significant deviations from the present invention.

(17) In summary, the invention relates to a gravure cylinder comprising an base, preferably of aluminium, onto which is deposited an engraving layer comprising a copper alloy. The copper alloy suitably comprising 40-70 wt % copper and 30-50 wt % of a secondary element. This secondary element is most suitably zinc, so as to form brass. An alternative is tin, to form bronze. The engraving layer is deposited by means of thermal spraying of particles, for instance with a diameter of 40-50 μm. The thermal spraying is most preferably a high-velocity thermal spraying process, in which the jet velocity is in the order of 1,000-1,500 m/s, such as 1,200-1,400 m/s. The engraving layer is most suitably provided in a thickness of 250-400 μm after optional thinning so as to harmonize the diameter of the cylinder. Suitably, the engraving layer is provided with a surface roughness R.sub.z in the range of 0.3-0.6 μm, preferably 0.4-0.5 μm. The Vickers Hardness of the layer is suitably in the range of 300-600 HV, more preferably in the range of 400-500 HV. With the use of an engraving layer of such copper alloy, suitably brass as obtainable in a (high-velocity) thermal spraying process, no subsequent coating, such as the conventional chrome coating, is needed anymore. Moreover, any intermediate electroplating layers may be left out. The resulting engraving layer is most suitably engraved by means of laser engraving.