Method and apparatus for manufacturing gravure cylinders

Description

BACKGROUND OF INVENTION

[0001] The invention relates to a method for manufacturing gravure cylinders and to a corresponding gravure cylinder making equipment, in particular to a manufacturing line having several workstations for engraving, plating, finishing etc. In a further aspect, the invention relates to the gravure cylinders themselves.

[0002] Gravure cylinders are used in the gravure printing process. This process makes use of rotating, ink-carrying gravure cylinders on the surface of which the print information has been previously impressed or mechanically punched by engraving machines.

[0003] A gravure cylinder is commonly manufactured in a complex production line comprising a plurality of stations, with a particular process being performed at each station. In the conventional process of manufacturing gravure cylinders, the initial or preceding engraving step is followed by various plating and finishing steps.

[0004] The established technique for producing gravure cylinders comprises attaching a copper layer to a steel roll, either through electroplating or by attaching a copper sheet. A negative of the image to be printed is then engraved on the surface of the copper. In order to provide a reasonable lifetime for the cylinder, the engraved image is then coated with a hard chromium plating layer in an electroplating operation.

[0005] The engraving step is the process step where the highest expenses in terms of time and costs reside. The subsequent steps are less time-consuming, but harder to control and susceptible to mistakes that tend to impair the finish quality of the previously engraved cylinder. In the chromium plating process, up to half of the cylinders may develop faults in the surface which would affect the quality of the final printed image. In such cases, it is necessary to remove the chromium layer and inevitably the engraved image. The engraving and plating must then be repeated and consequently such a process is costly and inefficient.

SUMMARY OF INVENTION

[0006] The present invention provides a method of manufacturing a gravure cylinder comprising the steps of:

providing a relatively soft surface of a metal cylinder,

plating a relatively hard coating on said relatively soft surface to form a plated metal cylinder, and

engraving a desired print pattern on said plated metal cylinder.

[0007] In the method of the invention, the hard coating is thus deposited on the surface of the cylinder prior to the engraving step. If such a sequence of events were to be performed using the known techniques, the hard coating would not be able to withstand the engraving operation and would flake off.

[0008] Preferably, the hard coating is a nickel/boron coating which may be deposited in an electroless coating manner. Ideally, the hard coating has a columnar, or nodular structure, which allows the coating layer to withstand the engraving operation while the underlying relatively soft surface is deformed.

[0009] A further beneficial aspect of using a nickel/boron coating is that such a coating may be harder and more wear-resistant than the conventional chrome coating, extending the life time of the gravure cylinder, perhaps by a factor of two. Printing a desired circulation of an illustrated publication would thus require only two identical gravure cylinders where the conventional art may require the production of four identical gravure cylinders.

[0010] Due to the ductility of the hard and wear-resistant nickel/boron coating, the mechanical forming or shaping may be performed later, i.e. after the hard plating has been achieved. In particular, the mechanical punches of the engraving process are impressed onto the relatively hard surface without harming or destroying or impairing the wear-resistant and well-bonded coating.

[0011] Where a copper sheet provides the underlying relatively soft surface, even the bending stress that occurs when a copper sheet is wrapped onto the steel roll would not impair the quality of the coating so that the hard coating might even be applied to the flat copper sheet before it is wrapped onto the steel roll.

[0012] In a further aspect of the invention, there is provided a method of manufacturing a gravure cylinder comprising the steps of:

wrapping a copper foil onto a cylinder surface of a steel roll,

plating the copper foil with a hard coating,

and engraving the wrapped or unwrapped, plated or unplated copper foil,

   wherein the step of plating the copper foil is a process of nickel/boron coating comprising the steps of

• providing a nickel/boron plating bath having a pH of about 10 to about 14;
• immersing the copper foil to be coated into the bath; and
• electrolessly depositing said nickel/boron coating on the copper foil.

[0013] In a further aspect, the invention provides a manufacturing line for manufacturing a gravure cylinder comprising a plurality of workstations for

providing a relatively soft surface of a metal cylinder,

plating a relatively hard coating on said relatively soft surface to form a plated metal cylinder, and

engraving a desired print pattern on said plated metal cylinder respectively.

[0014] In a still further aspect, the present invention provides a manufacturing line for manufacturing a gravure cylinder from a copper foil comprising workstations for performing at least the steps of:

wrapping the copper foil onto a cylinder surface of a steel roll,

plating the wrapped or unwrapped copper foil with a hard coating,

and engraving the wrapped or unwrapped, plated or unplated copper foil,

   wherein the workstation for plating the copper foil comprises

• a bath for nickel/boron plating having a pH of about 10 to about 14;
• an arrangement for immersing the copper foil to be coated into the bath; and
• a chemical solution for electrolessly depositing said nickel/boron coating on the copper foil.

[0015] In a yet further aspect, the invention also provides a gravure cylinder comprising a metal-covered cylinder, and an engraved nickel/boron coating on said metal-covered cylinder.

DETAILED DESCRIPTION OF THE INVENTION

[0016] The following provides a description of the preferred method for depositing a hard coating on a relatively soft surface which may then be subsequently engraved to provide the desired patterned surface.

[0017] In a conventional manner, a relatively soft layer is applied to a steel roll. Ideally, this relatively soft layer is a layer of copper. A copper foil may be wrapped onto the steel roll or the steel roll may be copper plated in a known manner. This first step (that may be performed in a stand-alone workstation separate from the throughput of the manufacturing line) allows for the mechanical deformation that is linked with the engraving process.

[0018] A relatively hard nickel/boron coating is then applied to the copper layer using an electroless plateing technique. The nickel/boron coating may be applied as described in U.S. patent 4,833,041. A further suitable technique is described in U.S. patent 6,066,406.

[0019] The electroless nickel/boron coating can have particles dispersed in the coating by codepositing the particles with nickel boron coating. US Application Serial Number     filed on September 11, 2000 by Ed McComas, titled "Coating Compositions containing Nickel and Boron and Particles" provides a methodology for co-depositing particles. Hard particles such as boron carbide particles can be dispersed throughout the deposit. This coating does not require heat treatment and as plated will outperform the conventional hard chrome cylinder due to its hardness and wear resistance.

[0020] The thickness of the hard layer of the new gravure cylinder is preferably in the range 2 - 52 µm (micrometer), more preferable in the range 6 - 15 µm (micrometer), and typically 11 - 13 µm (micrometer).
The nickel/boron coating is accomplished by a process comprising the steps of providing a nickel/boron bath having a pH of about 10 to about 14, immersing the soft (copper) surface to be coated into the bath using a hoist arrangement, and electrolessly depositing said nickel/boron coating on the soft (copper) surface. Such a plating method and of the employed bath stations are known under the tradename CEMKOTE. Any conventional electroless nickel/boron coating bath can be used. Electroplating of the hard nickel/boron coating may be used instead of the preferred electroless coating.

[0021] Following deposition of the hard coating, the gravure cylinder is engraved to apply the desired print pattern. A conventional engraving machine may be employed using known techniques.

[0022] Nickel/boron coatings applied using the methods of U.S. patent 4,833,041 or U.S. patent 6,066,406 typically have a columnar, nodular microstructure. This microstructure enables an engraving operation to be carried out after deposition. In the engraving operation, columns of the hard coating are pushed into the soft copper layer by the action of a stylus found in conventional engraving machines.

[0023] The coating has a very dense, high nickel concentration that deposits uniformly over the coated surface. The surface image is determined by non-directional humps having a roughness of about 10 µm (micrometer). Two advantageous effects of the new gravure cylinder are (1) the inferior or printing parts of the gravure cylinder carry the ink better than previously known and (2) the superior or non-printing parts of the gravure cylinder, when stripped by the doctor blade during the printing process in the known manner, are better lubricated and cooled by the ink that is stripped from the humps.

[0024] Because of the superior properties of the nickel/boron coating compared with hard chromium, it is beneficial to replace the chromium layer of the known processes with a nickel/boron layer. As indicated above, it is preferable that the hard coating is deposited before engraving. However, the hard nickel/boron coating may be applied to an already engraved copper surface.

[0025] Although preferred embodiments have been described in detail herein, it will be apparent to the expert in the relevant art that various modifications and substitutions and the like can be made.

Claims

1. A method of manufacturing a gravure cylinder comprising the steps of

providing a relatively soft surface of a metal cylinder,

plating a relatively hard coating on said relatively soft surface to form a plated metal cylinder, and

engraving a desired print pattern on said plated metal cylinder.

2. A method according to claim 1, wherein the relatively soft surface is provided by a copper foil wrapped onto a cylinder surface of a steel roll.

3. A method according to claim 1, wherein the relatively soft surface is provided by a copper-plated steel roll.

4. A method according to claim 1, wherein the relatively hard coating is a nickel/boron coating.

5. A method according to claim 4, wherein the nickel/boron coating is accomplished by a process comprising the steps of:

providing a nickel/boron plating bath having a pH of about 10 to about 14;

immersing the copper foil to be coated into the bath; and

electrolessly depositing said nickel/boron coating on the copper foil.

6. A method according to claim 4, wherein the nickel/boron coating is accomplished by a process of nickel/boron electroplating.

7. A method of manufacturing a gravure cylinder comprising the steps, performed in any order, of:

wrapping a copper foil onto a cylinder surface of a steel roll,

plating the copper foil with a hard coating, and

engraving the wrapped or unwrapped, plated or unplated copper foil,

wherein the step of plating the copper foil is a process of nickel/boron coating comprising the steps of

- providing a nickel/boron plating bath having a pH of about 10 to about 14;

- immersing the copper foil to be coated into the bath; and

- electrolessly depositing said nickel/boron coating on the copper foil.

8. A method of manufacturing a gravure cylinder comprising a copper-plated steel roll comprising the steps of:

plating a copper surface with a hard coating,

and engraving the plated or unplated copper surface,

wherein the step of plating the copper surface is a process of nickel/boron coating comprising the steps of

- providing a nickel/boron plating bath having a pH of about 10 to about 14;

- immersing the copper surface to be coated into the bath; and

- electrolessly depositing said nickel/boron coating on the copper surface.

9. A manufacturing line for manufacturing a gravure cylinder comprising workstations for

(i) providing a relatively soft surface of a metal cylinder,

(ii) plating a relatively hard coating on said relatively soft surface to form a plated metal cylinder, and

(iii) engraving a desired print pattern on said plated metal cylinder.

10. A manufacturing line according to claim 9, wherein the work station for providing the relatively soft surface wraps a copper foil onto a cylinder surface of a steel roll.

11. A manufacturing line according to claim 9, wherein the workstation for providing the relatively soft surface plates copper onto a steel roll.

12. A manufacturing line according to claim 9, wherein the relatively hard coating is provided in work stations for nickel/boron coating.

13. A manufacturing line according to claim 12, wherein the nickel/boron coating workstations comprise

- a bath for nickel/boron plating having a pH of about 10 to about 14;

- an arrangement for immersing the copper foil to be coated into the bath; and

- a chemical solution for electrolessly depositing said nickel/boron coating on the copper foil.

14. A manufacturing line according to claim 12, wherein the workstations for nickel/boron coating perform a process of nickel/boron electroplating.

15. A manufacturing line for manufacturing a gravure cylinder comprising workstations for performing the steps of

wrapping the copper foil onto a cylinder surface of a steel roll,

plating the wrapped or unwrapped copper foil with a hard coating,

and engraving the wrapped or unwrapped, plated or unplated copper foil respectively

wherein the workstation for plating the copper foil comprises

- a bath for nickel/boron plating having a pH of about 10 to about 14;

- an arrangement for immersing the copper foil to be coated into the bath; and

- a chemical solution for electrolessly depositing said nickel/boron coating on the copper foil.

16. A manufacturing line for manufacturing a gravure cylinder comprising a copper-plated steel roll comprising workstations for performing the steps of

plating the copper surface with a hard coating, and

engraving the plated or unplated copper surface,

wherein the workstation for plating the copper surface comprises

- a bath for nickel/boron plating having a pH of about 10 to about 14;

- an arrangement for immersing the copper surface to be coated into the bath; and

- a chemical solution for electrolessly depositing said nickel/boron coating on the copper surface.

17. A gravure cylinder comprising a metal-covered cylinder, and an engraved nickel/boron coating on said metal-covered cylinder.

18. An article having a nickel boron hard coating made by a nickel/boron plating on a layer wherein the interfacial surface of the layer is altered or deformed.

19. An article according to claim 18 wherein the surface of the layer is altered or deformed after the coating is deposited.

20. An article according to claim 18 wherein the surface of the layer is altered or deformed before the coating is deposited.