Method of refurbishing rotogravure cylinders, rotogravure cylinders and their use

Abstract

The rotogravure cylinder comprising a rotary gravure base and thereon a copper engraving layer is refurbished to contain a zinc layer between a gravure base and a layer package suitable for engraving and printing. This layer package for instance comprises a metallic support layer, a copper engraving layer and suitably a protection layer. Deposition of the zinc layer may be tuned for thickness variation, in combination with deposition of the layer package in a fixed thickness.

Claims

1. Method of refurbishing a rotogravure cylinder comprising a rotary gravure base and thereon a copper engraving layer, which method comprises the steps of: (i) providing the rotogravure cylinder to be refurbished; (ii) removing the copper engraving layer, therewith obtaining the exposed rotary gravure base; (iii) applying a zinc layer to the exposed rotary gravure base, wherein the zinc layer comprises zinc or a zinc alloy; and (iv) applying a layer package suitable for engraving and printing, comprising a metallic support layer that contains copper and a new copper engraving layer, wherein the metallic support layer is applied by at least partial melting of deposited copper particles.

2. The method as claimed in claim 1, wherein the exposed rotary gravure base is roughened prior to the application of the zinc layer.

3. The method as claimed in claim 2, wherein the roughening occurs in a single process step jointly with the removal of the copper engraving layer.

4. The method as claimed in claim 1, wherein the removal occurs by sandblasting.

5. The method as claimed in claim 1, wherein the zinc layer is deposited in multiple sublayers.

6. The method as claimed in claim 1, further comprising the step of engraving of the new copper engraving layer according to a desired pattern.

7. The method as claimed in claim 6, further comprising: protecting the engraved new copper engraving layer with a new protection layer.

8. The method as claimed in claim 1, wherein step (iii) comprises applying a zinc layer to achieve a cylinder having diameter which is around 300 m smaller than a final diameter.

9. The method as claimed in claim 1, wherein the step of applying the layer package comprises: depositing a metallic support layer to the zinc layer; and electroplating a new copper engraving layer on the metallic support layer thereby providing a refurbished rotogravure cylinder.

10. The method as claimed in claim 1, wherein the copper engraving layer is formed by deposition and subsequent thinning and polishing.

11. The method as claimed in claim 1, wherein the copper of the copper engraving layer is chosen from pure copper, copper with small additions of other materials and copper alloys.

12. The method as claimed in claim 1, wherein the zinc layer contains a zinc alloy with at least one of nickel, aluminum, copper and magnesium.

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

ILLUSTRATED DISCUSSION OF DETAILED EMBODIMENTS

(4) The FIGS. 1 and 2 are not drawn to scale and they are only intended for illustrative purposes. Equal reference numerals in different figures refer to identical or corresponding figures.

(5) 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 length of such cylinders is typically at least 1.0 meter, more preferably in the order of 1.5-2.5 meter.

(6) 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 aluminium top layer.

(7) The term aluminum in the present invention refers to pure aluminum, aluminum with small addition of other materials or aluminum alloys. Likewise, the term copper refers to pure copper, copper with small addition of other materials or copper alloys. Most suitably, however, in the process in accordance with a preferred embodiment of the invention, particles are sprayed that contain at least 99% copper, more preferably at least 99.5% copper or more. Likewise, the term zinc layer comprises a zinc layer and a zinc alloy.

(8) The term high velocity spraying relates to a spraying process wherein particles are sprayed with a velocity of at least 300 m/s, more preferably at least 500 m/s, at least 800 m/s or even at least 1,000 m/s. Preferably, use is made of a jet with a velocity above the said particle velocity. Generation of a supersonic jet is considered most advantageous. Herein, the jet velocity may be higher than 1,400 m/s.

(9) High velocity spraying may for instance be implemented with High-Velocity Air Fuel (HVAF) technology and guns as commercially available from UniqueCoat Technologies, LLC from Oilville, Va. 23129, USA.

(10) In a preferred embodiment, the present applying of a zinc layer to the exposed rotary gravure base comprises thermal wire spraying of the exposed rotary gravure base with zinc, or a zinc containing layer such as a zinc alloy, preferably comprising thermal wire spraying of multiple layers.

(11) In a preferred embodiment, the present applying of a zinc layer to the exposed rotary gravure base comprises applying a zinc layer to achieve a cylinder having a diameter, which is smaller than a final diameter according to a predefined difference. The difference is for instance in the range of 200-400 m, or between 250-350 m, such as 300 m. The relevance hereof is that the properties of the resulting cylinder, relevant for engraving and use, can be the same, even though the final diameter varies. A final diameter is defined as the desired diameter of the provided refurbished rotogravure cylinder.

(12) 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 copper support layer created by melting of copper particles is actually an alloy with some zinc of the underlying zinc layer. Such an alloy may well be created, particularly close to the interface with the zinc layer. The composition of the copper support layer further away from the zinc layer may thus be different from the composition near to said interface.

(13) In the preferred embodiment wherein the copper particles are sprayed onto the present zinc layer in a high velocity process, it is foreseen that the impact of the copper particles onto the zinc layer may result in deformation and fracture of the top layer of the zinc layer. Such deformation is deemed beneficial so as to obtain a larger interface area and/or some mechanical anchoring of the copper into the zinc.

(14) The subsequent melting and furthermore the thinning step are highly suitable in combination therewith, so as to ensure appropriate dimensions and particularly appropriate roundness when seen in cross-sectional view perpendicular to an axial direction of the cylindrical base.

(15) Preferably, a high velocity spraying process is used for the present spraying of copper particles. Use may be made of a gun as available from UniqueCoat Technologies, LLC, as sold as M3. The copper particles, with an average diameter of less than 50 m, preferably in the range of 40-45 m, were sprayed with a jet velocity of 1,200-1,400 m/s, resulting in a particle velocity of 900-1000 m/s. During the spraying process, the cylinder was rotated. Impact of the substantially pure copper particles onto the cylinder resulted in deformations in the cylinder, and in heating up of the particles, to the extent of at least partial melting. This melting resulted in formation of a single support 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 support layer. For the jet spraying, the same gun as mentioned above was used, but this is not considered essential.

(16) Alternatively, the present metallic support layer, preferably a copper support layer, is applied in a process comprising a preplating step and a subsequent plating step. Suitably, the preplating step is carried out in an alkaline bath, whereas the plating step is carried out in an acid bath. In one specific implementation, the preplating step comprises plating a copper layer of for instance 5 to 10 m to the zinc layer by using an alkaline copper or nickel copper solution, suitably having a pH within the range of 8 to 10.

(17) Preferably, during the present preplating, the cylinder is revolving with a speed of 100-150 rpm, the current density preferably ranges between 1 and 2 amps/dm.sup.2 and/or the plating time is preferably approximately 30 minutes at a temperature up to 55 C., more preferably from 40 C.-55 C.

(18) In a further specific implementation, the plating step comprises electroplating the cylinder by using a solution comprising copper sulfate and sulfuric acid to apply a copper layer of 100 to 300 m thick. The solution suitably has a temperature within the range of 30 to 40 C. A typical concentration is 190-230 gr CuSO.sub.45H.sub.2O per liter of solution.

(19) Preferably, the solution also comprises a hardness additive to provide a copper support layer having a hardness up to 220 to 230 HV. It is advantageous when during the electroplating the cylinder is revolved with a speed of 100 to 150 rpm. Preferably, the electroplating current density is within the range of 20 to 40 amps/dm.sup.2 and electroplating time is 50 to 150 minutes.

(20) In one embodiment, the resulting metallic support layer had a thickness of approximately 125 m. This layer was thereafter thinned and polished, by means of a sawing process. Use was made of a diamond saw, as known for the sawing of copper or copper-containing elements. A lubricant was sprayed while sawing so as to prevent too much heating of the metallic support layer. Moreover, herewith a polishing was achieved as well. The sawing resulted in removal of about 50 m thickness of copper. The copper support layer was therewith ready. It is however not excluded that additional layers are deposited.

(21) In an alternative embodiment, the deposited metallic support layer had a thickness of 40-80 microns, for instance about 50 microns. This layer was thereafter thinned, for instance with 40-60%. Use was made herein of grinding with a conventional grinding machine with grinding and polishing stones.

(22) In a subsequent step, a copper engraving layer with a high hardness, suitably in the range of 200-240 HV, was deposited. The layer was deposited in a thickness of 60-200 m, for instance 150 m. In one embodiment, a layer thickness was chosen that was substantially corresponding to the layer thickness of the copper support. However, thicker layers are not excluded. The deposition process for such an engraving layer is known per se and involves electroplating. Use was made in one embodiment of a solution of copper sulfate (200-230 gr CuSO.sub.45H.sub.2O) and sulfuric acid (60-65 gr H.sub.2SO.sub.4 per liter of solution) and a catalyst for hardness. The catalyst does not have any particular properties and can be found easily in the market. During the plating, the cylinder is revolved with a speed of about 100 rpm. The current density during electroplating in this phase ranges from 20 to 25 amps/dm.sup.2 for about 80-100 min and with a solution temperature maintained at about 30 C. Further details in relation to this process are known from various patents, such as U.S. Pat. No. 4,334,966, U.S. Pat. Nos. 4,781,801, 5,417,841 and 7,153,408, which are herein included by reference.

(23) Thereafter, the present refurbished rotogravure cylinder was preferably polished to achieve desired surface roughness (usually R.sub.z is between 0.03 m and 0.07 m). A protection layer and engraving may thereafter be applied, as known to the skilled person.

(24) In an alternative embodiment, which was tested particularly in combination with a ground and thin copper support layer as discussed above, the copper engraving layer was formed by deposition and subsequent thinning and polishing. Here again, a thinning to approximately half of the deposited thickness turned out suitable in practice. However, it is not excluded that the thinning removes merely 20-40% of the deposited thickness.

(25) In summary, the rotogravure cylinder of the invention comprises a rotary gravure base and thereon a copper engraving layer is refurbished to contain a zinc layer between a gravure base and a layer package suitable for engraving and printing. This layer package for instance comprises a metallic support layer, a copper engraving layer and suitably a protection layer. Deposition of the zinc layer may be tuned for thickness variation, in combination with deposition of the layer package in a fixed thickness.