EP0545468A1

EP0545468A1 - Metal plate for manufacturing a gravure printing sleeve, method for the manufacture thereof, as well as a roller provided with a pattern

Info

Publication number: EP0545468A1
Application number: EP92203621A
Authority: EP
Inventors: Wilhelmus Aloysius Pruyn
Original assignee: Stork Screens BV
Current assignee: Stork Screens BV
Priority date: 1991-11-25
Filing date: 1992-11-23
Publication date: 1993-06-09
Also published as: JPH05221171A; NL9101971A

Abstract

A description is given of a metal plate which is suitable, in particular, for the manufacture of an gravure printing sleeve. Said metal plate comprises a mechanically engravable metal layer on which there is at least one mechanically engravable a harder top layer, which top layer is wear-resistant, has a material stretch of 0.1-5%, and has a Vickers hardness of 400-1050. The mechanically engravable metal layer has a material stretch of less than 3% and a Vickers hardness of approximately 80-350. The top layer can be chosen from the metals or metal alloys which can be electrolessly or electrolytically deposited, or it may be composed of ceramic material. Expediently, the top layer can be hardened so that, after engraving, the metal plate has an engraved top layer having a still higher Vickers hardness. A method for manufacturing the present composite metal plate comprises applying, moreover, at least one top layer having a hardness which is greater than the hardness of the engravable metal layer and a thickness of not more than 10 µm to the mechanically engravable metal layer. Further, a process for mechanically engraving a pattern into an engravable metal basic layer is described.

Description

The invention relates to a metal plate which is suitable, in particular, for the manufacture of a gravure printing sleeve comprising a mechanically engravable metal layer.
It is known that, in the engraving of metal layers which have been applied to a support, such as a supporting roller, in order to obtain pattern configuration which can be used, for example, in the gravure printing sector of the graphics industry, a problem may arise in relation to the pattern definition as a consequence of the types of metal from which the layer to be engraved has been formed and the properties thereof:

In the case of soft types of metal, the machining edges due to the scribing of the engraving tool (for example, a hard metal chisel or a diamond) are ragged and fuzzy, as a result of which the machined/unmachined junctions are "diffuse" and the image quality is poor.
Although a good pattern definition is obtained in the case of hard types of metal, the engraving tool has a particularly short useful service life as a result of wear.

This has the result that it is always necessary to strive for a compromise in which the metals to be machined have properties such that, on the one hand, they provide a reasonable pattern definition as a result of the mechanical machining but, on the other hand, they must not have such a high hardness that the service life of the tool used is unacceptably short. A short tool service life is not only expensive but it can also result in a poor reproducibility of the pattern produced.
A metal plate of the type mentioned at the outset has now been found which eliminates these drawbacks.
The metal plate according to the invention is characterised by the fact that at least one mechanically engravable harder top layer is present on the mechanically engravable metal layer. Preferably, said top layer is wear-resistant, the degree of wear resistance being chosen to suit the utilisation situation.
Obviously, the adhesion of the top layer to the mechanically engravable metal layer has to be good. Both layers must not separate from one another during the mechanical machining.
Preferably, of the mechanically engravable system of layers present, the top layer has a material stretch of 0.1-5%, expediently approximately 2.5%. If the material stretch is higher, the material is too soft, as a result of which a sharp pattern cannot be obtained or is difficult to obtain. If the stretch is lower, the material is too hard or too brittle and, although a good pattern definition can be obtained, this is at the expense of excessive chisel wear. It is assumed that the structure of the engraved layer must be from finely crystalline to amorphous. Expediently, the layer according to the invention has a Vickers hardness of approximately 400-1050, preferably 450-500, at the surface, while the thickness of the top layer is not more than 15 µm, preferably approximately 2 µm. The presence of such a top layer does not appear to affect the application of a pattern having a high accuracy and reproducibility, and the acceptable service life of the engraving tool. The upper limit of the thickness of the top layer is critical insofar as, if said limit is exceeded, the hardness of the material will acquire an adverse effect on the tool and shorten the service life thereof, while the engraving quality will be adversely effected.
The thickness and other characteristics of the top layer must be such that during the mechanically engraving process at least through the whole thickness of said top layer can be engraved. The top layer is thus also subjected to the mechanically engraving and is not a (protective) layer applied afterwards.
In order to obtain a reproducible machining of the surface, the top layer preferably has a uniform thickness.
An optimum reproducibility of the image quality is obtained, in particular, if the top layer is composed of an electrolessly deposited layer of a metal or the alloy. Examples of such a metal or alloy are phosphor nickel, boron/nickel, tin/nickel, nickel and nickel/cobalt, the layers being hard or being thermally hardenable, as is known in the case of phosphor nickel. A number of types of ceramic, such as titanium nitride, boron nitride and chromium carbides, can also be used.
Obviously, other materials and combinations of materials such as, for example, chromium can also be used provided the abovementioned requirements for hardness and structure are satisfied.
The top layer may, however, also be obtained by electrolytic deposition but ion implantation techniques can also be used in principle to produce the desired engravable system of layers.
In this connection, in addition to ion implantation, various modern techniques may be mentioned which are based on high-energy radiation, including the alloying of one or more layers which have been applied with the aid of laser radiation. Furthermore, depending on the type desired, CVD/PVD and plasma jet techniques may also be employed.
Attention is drawn to the fact that the mechanically engravable metallic layer may be composed of a relatively soft material, for example a metal layer having a Vickers hardness of approximately 80 to 350 and a low stretch. Examples thereof are soft nickel, copper, aluminium, iron, various alloys, zinc, etc.
The engravable metal layer may, however, also be composed at least partly of a polymer which must, obviously, have the properties of hardness and stretch specified above, and in order to be able to apply the harder top layer, it must also be metallisable.
The invention also relates to a composite for producing a metal structure, suitable for use in printing systems, composed of a support and a metal plate comprising a mechanically engravable metal layer, which is characterised by the fact that the metal plate is a metal plate in accordance with the invention. The finished roller can be manufactured simply by clamping the present structure onto a support in the form of a roller.
The engraving in the relatively soft metal layer, already being provided with a thin top layer yields a pattern definition such as that obtained with fine-grained types of metal, such as hard copper. In relation to the life of the engraving tool, in this case a chisel or diamond, however, no reduction in the service life is observed with the composite of layers according to the invention. The image quality obtained in therefore particularly good.
It is pointed out that a layer of soft nickel, hard copper, aluminium, zinc, iron and various alloys can be chosen for the relatively soft engravable metal layer having a low stretch. The hardness of said layer is usually 80 to 350 in Vickers units. Although no limitations apply to the structure, it will be clear that a finely crystalline structure gives a better result than a coarsely crystalline one. This statement applies both to the support (the base metal layer) and to the top layer or top layers. The material stretch of the mechanically engravable metal layer is preferably less than 3%.
Incidentally, it is not necessary for the support to be provided with a separate metal plate if both are produced from the same metal or the same alloy. A solid support, for example a solid roller, will obviously also be satisfactory in that case. The thickness of the mechanically engravable metal layer must, however, be such that the underlying support roller is not affected by the engraving. An engravable metal layer thickness of approximately 50µm will therefore usually be sufficient, although deviating thicknesses of, for example, 100 µm or 25 µm are also possible without difficulty, obviously depending on the pattern to be transferred or the desired engraving depth.
It is pointed out that, within the scope of the invention, engraving is understood as meaning mechanical machining based on cutting machining with the associated mechanical deformation using a forming tool such as a scriber, chisel, diamond etc.
The invention also relates to a method for the manufacture of an composite metal plate, in particular suitable for use in printing systems, in which at least one mechanically engravable metal layer is applied to a support, said method being characterised by the fact that there is furthermore applied to the mechanically engravable metal layer at least one mechanically engravable top layer having a hardness which is greater than the hardness of the engravable metal layer. The adhesion of the top layer to the mechanically engravable metal layer must obviously be good; said layers must not separate from one another during the mechanical machining. Preferably, a wear-resistant top layer is applied.
The Vickers hardness of the wear-resistant top layer is preferably approximately 450-750, expediently 500-680, but in particular approximately 650.
The thickness of the top layer is, in particular, not more than 10 µm, preferably approximately 2 µm.
Attention is drawn to the fact that, if the thickness of the top layer is greater than 15 µm, depending on the type of top layer, there may be present a structure which has preferred fracture lines as a consequence of dislocations which may be present in the crystal structure, which structure adversely affects the achievement of a good image quality. In addition, such a thickness is too great to be able to apply the finer details during the mechanical machining and the effect of excessive chisel wear still occurs.
According to a particularly expedient embodiment, the top layer is applied by electroless deposition of a metal or metal alloy. Such a process promotes the achievement of a uniform thickness distribution of the top layer, as a result of which an excellent reproducibility of the image quality is achieved. In addition to electroless depositions of phosphor nickel, boron/nickel, tin/nickel, titanium nitride, boron nitride and other similar layers may also be used, each type of top layer having its own ideal layer thickness for the maximum effect within the scope of the invention. The adherence of the top layer to the engravable metal layer must obviously be good. If both layers separate from one another during the application of a pattern, it will be impossible to achieve a good image definition in accordance with the inventive idea.
The mechanically engravable metal layer may, for example, be composed of nickel or aluminium. Insofar as they can be metallised in the production of a printing sleeve and thermally and mechanically stable, the use of special plastics is also not excluded. Usually, said layer is applied to a support, but is obviously also possible for a solid metal plate or roller to be used. The thickness of the mechanically engravable metal layer is chosen to suit the pattern to be transferred and the desired pattern depth. Usually, this thickness will be approximately 50 µm; a thickness of the mechanically engravable layer of, for example, 25 µm or 100 µm may, however, be more expedient in certain application forms.
The top layer will preferably be composed of an electroless hardenable nickel or nickel alloy layer or thin chromium layer. The Vickers hardness thereof is approximately 450-550, but it can be increased to approximately 1100 by applying a conventional heat treatment. Increase in the hardness can also be brought about on the basis of particle bombardment or treatment with high-energy laser-based and/or magnetron-based radiation.
Attention is drawn to the fact that the mechanically engravable metal layer advantageously has a Vickers hardness of approximately 80-350. Since an accurately defined pattern has to be applied in the metal plate according to the invention, a metal layer with finely crystalline structure will give a better result than a metal layer with a coarse structure. It has furthermore been found that excellent results are achieved if the specification of the layer exhibits a combination of a relatively low hardness with a low stretch value. If an electrolytically deposited layer is involved, the requirements to be imposed on the bath are high dispersing power (even layer thickness), a finely crystalline deposition quality, thermal resistance, the correct Vickers hardness with respect to the base layer and low stretch value (NiCo, NiP, NiSn etc.), and possibly hardenability in additional process steps.
The invention also relates to a roller provided with a pattern achieved by mechanical engraving, which is suitable, in particular, for use in printing systems, comprising a support roller and a metal plate, which is characterised in that the metal plate is a plate in accordance with the invention.
Finally, the invention also relates to a process for mechanically engraving a pattern into an engravable metal basic layer, wherein before said engraving at least one thinner, engravable, harder top layer is applied, and the composite of layers is thereafter engraved to within the metal basic layer to obtain a pattern. The top layer is preferably wear-resistant. Expediently said layer has a material stretch of from 0.1-5%, preferably approximately 2.5%. The Vickers hardness of the top layer is from about 400-1050, preferably 450-500, whereas its thickness is preferably not more than 10 µm, expediently approximately 2 µm, the thickness preferably being uniform. Expediently the top layer is hardenable after being provided on the metal basic layer.
Other claims and many of the attendant advantages will be more readily appreciated as the same becomes better understood by reference to the following detailed description.

EXAMPLE 1

In this example, the starting point was a standard gravure printing sleeve having a thickness of approximately 300 µm. The Vickers hardness was approximately 450, while the material stretch was 7%. The surface of said sleeve was subjected to a heat treatment with laser radiation, as a result of which the surface layer having a thickness of 50-150 µm acquired a Vickers hardness of 200-350 and a material stretch of < 3%.
A layer of phosphor nickel having a thickness of approximately 2 µm was deposited on the gravure printing sleeve thus obtained by an electroless coating method. Said top layer had a Vickers hardness of 450-500.
The metal composite thus obtained was subjected to a mechanical engraving machining using a chisel.
Thermal treatment of the composite thus produced yielded a hardening of the top layer to a Vickers hardness of 900-1000.
The pattern configuration produced did not have the known disadvantages, in the case of which the machining edges of the scribing are ragged and fuzzy, resulting in poor image definition. In addition, an examination of the chisel used showed that there was no wear image at all which could eventually limit the life thereof.
Attention is drawn to the fact that the image definition achieved was at least the same as that which is achieved by means of conventional engraving situations.

EXAMPLE II

Manufacture of a gravure printing sleeve.
A copper layer having a thickness of 500 µm is applied to a hard-nickel roller (Vickers hardness 450).
A layer of electroless nickel having a thickness of 2 µm is applied to said copper layer.
The Vickers hardness of the electroless nickel layer was 550.
A desired pattern was then engraved in said roller with the aid of a helioklischograph. By subjecting the engraved roller thus produced to a heat treatment (15 min, approximately 800°C), the Vickers hardness of the electroless nickel top layer was increased to 1050. The wear resistance of the finished roller is therefore increased appreciably.

Claims

Metal plate, which is suitable, in particular, for the manufacture of a gravure printing sleeve, comprising a mechanically engravable metal layer, characterized in that at least one mechanically engravable harder top layer is present on the mechanically engravable metal layer.
Metal plate according to claim 1, characterized in that the top layer is wear-resistant.
Metal plate according to claim 1 or 2, characterized in that the top layer has a material stretch of 0.1-5%, preferably about 2.5%.
Metal plate according to claims 1 to 3, characterized in that the top layer has a Vickers hardness of about 400-1050, preferably 450-500.
Metal plate according to one or more of the claims 1 to 4, characterized in that the top layer has a thickness of not more than 15 µm, preferably approximately 2 µm, the thickness preferably being uniform.
Metal plate according to one or more of the claims 1 to 6, characterized in that the top layer consists of an electrolessly or electrolytically deposited layer of a metal or alloy, or a ceramic material, selected from the group consisting of titanium nitride, boron nitride and chromium carbides.
Metal plate according to claim 6, characterized in that the electrolessly deposited metal or alloy is selected from the group consisting of phosphor nickel, boron/nickel, tin/nickel, nickel and nickel/cobalt.
Metal plate according to one or more of the claims 1 to 7, characterized in that the mechanically engravable metal layer has a Vickers hardness of about 80-350, and a material stretch less than 3%.
Metal plate according to one or more of the claims 1 to 8, characterized in that the top layer is hardenable.
Metal plate according to one or more of the claims 1 to 9, characterized in that the engravable metal layer consists at least partially of a plastic material.
Composite for the manufacture of a metal construction, suitable for use in printing systems, consisting of a support and a metal plate, comprising a mechanically engravable metal layer, characterized in that the metal plate is a metal plate according to one or more of the claims 1 to 10.
A method for the manufacture of a composite metal plate, in particular suitable for use in printing systems, at least one mechanically engravable metal layer being applied to a support, characterized in that at least one mechanically engravable top layer having a hardness greater than the hardness of the engravable metal layer is furthermore applied to the mechanically engravable metal layer.
A method according to claim 12, characterized in that the top layer has a Vickers hardness of about 400-1050, preferably 450-500.
A method according to claim 12 or 13, characterized in that the top layer has a material stretch of 0.1-5%, preferably approximately 2.5%.
A method according to one or more of the claims 12 to 14, characterized in that the top layer is wear-resistant.
A method according to one or more of the claims 12 to 15, characterized in that the top layer is applied in a thickness of not more than 10 µm, preferably approximately 2 µm.
A method according to one or more of the claims 12 to 16, characterized in that the top layer is formed by electroless or electrolytic deposition of a metal or a metal alloy.
A method according to claim 17, characterized in that the electrolessly deposited metal or metal alloy is selected from the group consisting of phosphor nickel, boron nickel, tin nickel, nickel cobalt and nickel.
A method according to one or more of the claims 12 to 16, characterized in that a top layer consisting of a ceramic material is applied, the ceramic material being selected from the group consisting of titanium nitride, boron nitride and chromium carbides.
A process according to one or more of the claims 12 to 18, characterized in that the composite metal plate is subjected to an additional treatment to increase the hardness of the top layer.
A roller, provided with a pattern obtained by mechanical engraving, especially suitable for use in printing systems, comprising a support roller and a metal plate, characterized in that the metal plate is a plate described in one or more of the claims 1 to 10 or obtained according to one or more of the claims 12 to 20.
A process for mechanically engraving a pattern into an engravable metal basic layer, characterized in that before said engraving at least one thinner, engravable, harder top layer is applied, and the composite of layers is thereafter engraved to within the metal basic layer.
A process according to claim 22, characterized in that said top layer is wear-resistant.
A process according to claim 22 or 23, characterized in that said top layer has a material stretch of 0.1-5%, preferably approximately 2.5%.
A process according to one or more of the claims 22 to 24, characterized in that said top layer has a Vickers hardness of about 400-1050, preferably 450-500.
A process according to one or more of the claims 22 to 25, characterized in that said top layer has a thickness of not more than 10 µm, preferably approximately 2 µm.
A process according to one or more of the claims 22 to 26, characterized in that said top layer is hardenable.