EP2835269A1

EP2835269A1 - A precursor plate for the manufacture of an intaglio printing plate, a method of manufacturing the precursor plate and use of the precursor plate

Info

Publication number: EP2835269A1
Application number: EP20130179785
Authority: EP
Inventors: Marco Viticoli; Giorgio Maria Paesano; Fabrizio Pitacco; Gerardo Coletta
Original assignee: European Central Bank
Current assignee: European Central Bank
Priority date: 2013-08-08
Filing date: 2013-08-08
Publication date: 2015-02-11

Abstract

A precursor plate, a method of manufacturing the precursor plate and the advantageous use of said precursor plate is provided. The precursor plate comprises an engraved surface, which is covered by a coating. The coating is formed by physical vapour deposition of a coating material.

Description

FIELD OF THE INVENTION

The invention relates to a precursor plate for the manufacture of an intaglio printing plate. Furthermore, the invention relates to a method of manufacturing the precursor plate and to the use of this precursor plate.

BACKGROUND

Intaglio printing plates are frequently used for the production of banknotes and like printed securities. For manufacture of intaglio printing plates, a polymer plate or a polymer layer, which is supported by a base plate, is engraved. For example, a polyimide material containing dispensed carbon black material can be engraved by a laser engraving technique. The polymer plate is subsequently used as a precursor material for the manufacture of the intaglio printing plate. The polyimide material is usually silvered and used as the master die for the production of the so called (nickel) alto plate. This is performed by processing the engraved polymer plate in an electroforming process, in which the silvered polymer plates are put in a nickel galvanic bath. Once the electroforming process is ended, the polymeric precursor material and the nickel alto plate are separated. The alto plate is therefore a mirror image basically showing the relief of the engraved precursor plate. The surface quality of the nickel alto plate is significantly affected by the quality of the silvered polymeric plate.
However, the silvering the polymer precursor plate is carried out by the electroforming chemical process, which consists in the use of chemical solutions containing silver salts and reducing agents. The dissolved silver irons are reduced at the surface of the polymeric plate forming the silver layer. This chemical process, however, requires the use of various hazardous substances, mainly formaldehyde and ammonia solution. The chemical solutions are typically applied on the polymeric surface by a spray technique or by using an oscillating tube. The repeatability of this process is relatively low, since the main operations are carried out manually. This implies that in some cases the process of chemical deposition should be repeated as the result of the presence of defects on the silver layer. In the very worst case, a new polymer plate should be engraved and coated.

SUMMARY

It is an object of the invention to provide an enhanced precursor plate for the manufacture of an intaglio printing plate. Furthermore, it is an object of the invention to provide a more reliable method of manufacturing the precursor plate. It is still another object of the invention to provide an advantageous use of this precursor plate.
In one aspect of the invention, a precursor plate for the manufacture of an intaglio printing plate is provided. The precursor plate comprises an engraved surface, which is covered by a coating. The coating is formed by physical vapour deposition (PVD) of a coating material.
Advantageously, the invention provides an alternative process for coating of a precursor plate, based on physical vapour deposition. This thin film technique operating under vacuum is able to overcome the drawbacks of the traditional chemical processes. The PVD process does not require the use of any hazardous chemicals and it can ensure both, a higher repeatability of the process and a better quality of the coating layer. This advantageously results in a (nickel) alto plate having an enhanced surface quality.
In an advantageous embodiment of the invention, the coating material comprises Silver (Ag), Gold (Au), Aluminium (Al), Palladium (Pd), Titanium (Ti), Chrome (Cr) and / or any other conductive material. In particular, the coating comprises any other electrically conductive metal. Further in particular, the coating material comprises a composition or an alloy of at least two of the named materials. In other advantageous embodiment of the invention, the coating material comprises nitrides and / or carbonitrides of any of the named materials and / or alloys.
In another embodiment of the invention, the coating is a multilayer. The mentioned materials, alloys and / or compositions can form at least the main component of the coating. This applies to a single layer and to a multilayer coating. When the coating is a multilayer, at least some of the individual layers can comprise the mentioned materials, alloys and / or compositions, wherein in particular, subsequent or directly adjacent layers can have different compositions. This advantageously applies to all embodiments of the invention. Furthermore, other alloying elements can be added to the coating to achieve the desired properties of the material, in particular a desired hardness, wear resistance, etc.
The coating is a thin layer having a thickness, which can be between 100 nm and 1000 nm. Advantageously, the coating of the precursor plate is performed by sputter deposition of the coating material. In particular, magneton sputtering is applied. For the manufacture of a high-quality coating, a working atmosphere during sputter deposition having a pressure, which is substantially equal to 0,1 Pa and 1 Pa (0,7*10^-2 mbar to 7*10^-1 mbar) turned out to be advantageous. In particular, this applies to a silver coating.
According to an advantageous embodiment of the invention, the precursor plate is made of a polymer material. In particular, the polymer material is a polyimide material, for example Kapton. Although Kapton is a polymer, it keeps stable in a wide range of temperatures and can therefore resist the thermal load during coating. Furthermore, Kapton exhibits low degassing properties under vacuum.
In still another embodiment of the invention, the polymer material comprises laser light absorbing particles or additives, which are dispensed in the polymer material. In particular, the particles or additives can be manufactured from carbon black material. The particles or additives enhance the absorption of laser light in the polymer material and therefore support the laser engraving process. This renderers the precursor plate particularly suitable for laser engraving of its surface. This entails that the engraved surface of the precursor plate can be advantageously a laser engraved surface.
According to another advantageous embodiment of the invention, at least the engraved surface of the precursor plate is pre-treated prior to deposition of the coating. This pre-treatment can include a step of surface cleaning and an activation step. In particular, the precursor plate can be first manually cleaned using isooctane or petrol. Residual dust can be removed using a water jet. Subsequently, oil skimming with calcium carbonate and vinegar can be performed. The surface of the precursor plate is then cleaned using deionized and ultra-deionized water. Finally, the precursor plate is dried in a forced air circulation oven. Subsequent to these steps of cleaning and surface activation, the precursor plate is transferred into the deposition chamber of the PVD unit. The deposition chamber is evacuated using a suitable vacuum system until the residual pressure in the deposition chamber is lower than 10^-2 Pa (10^-4 mbar).
In another advantageous aspect of the invention, a method of manufacturing a precursor plate for the manufacture of an intaglio printing plate is provided. A coating is deposited on an engraved surface of the precursor plate by physical vapour deposition (PVD) of a coating material.
The coating material can comprise Silver (Ag), Gold (Au), Aluminium (Al), Palladium (Pd), Titanium (Ti), Chrome (Cr) and / or any other conductive material. In particular, the coating comprises any other electrically conductive metal. Further in particular, the coating material comprises a composition or an alloy of at least two of the named materials. In other advantageous embodiment of the invention, the coating material comprises nitrides and / or carbonitrides of any of the named materials and / or alloys. According to an embodiment of the invention, the method comprises the step of depositing anyone of the mentioned materials. In particular, a coating is deposited, which comprises anyone of the mentioned materials as the main component. A thin film having a thickness, which is between 100 nm and 1000 nm, can be deposited. This can be a single layer or a multilayer.
The coating is advantageously deposited by sputter deposition, in particular by magneton sputter deposition. This can be performed in a working atmosphere having a pressure, which is substantially between 0,7 Pa and 1 Pa (0,7*10^-2 mbar to 7*10^-1 mbar). Other deposition technologies can be suitable, for example cathiodic arc deposition.
Furthermore, the method can include the step of depositing the coating on a precursor plate, which is manufactured from a polymer material. The polymer material can be a polyimide material, in particular Kapton.
To assist sublimation of the polymer material during laser engraving of the precursor plate, the polymer material can comprise laser light absorbing particles or additives, which can be dispensed in the polymer material. Carbon black can be applied for manufacturing the light absorbing particles or additives.
The method of manufacturing the precursor plate can further include a pre-treatment of at least the engraved surface of the precursor plate. This pre-treatment is performed prior to deposition of the coating material, in particular prior to transfer of the precursor plate into the deposition chamber. This step of pre-treating can comprise the steps of cleaning and activating at least the engraved surface of the precursor plate.
Same or similar advantages, which have been already mentioned with respect to the precursor plate, apply in the same or similar way to the method of manufacturing the precursor plate and should be therefore not repeated.
In still another advantageous aspect of the invention, an advantageous use of the precursor plate according to aspects of the invention is provided. The precursor plate can be used for the manufacture of a (nickel) alto plate, which is further designated for manufacturing an intaglio printing plate for the production of banknotes or other printed securities.
The enhanced quality of the coating of the precursor plate advantageously results in a (nickel) alto plate having a superb surface quality. This renders the alto plate particularly suitable for manufacturing of high precision intaglio printing plates being necessary for the production of banknotes and other printed securities.

BRIEF DESCRIPTION OF DRAWINGS

Further aspects, characteristics and features of the invention ensue from the following description of preferred embodiments of the invention with reference to the accompanying drawings, wherein

FIG. 1 is a simplified cross-section of a precursor plate for the manufacture of a (nickel) alto plate for intaglio printing,
FIG. 2 is a simplified cross-section of a coated precursor plate for the manufacture of a (nickel) alto plate for intaglio printing, according to an embodiment of the invention and
FIG.3 is a simplified flow-chart illustrating a method of manufacturing a precursor plate for intaglio printing, according to another embodiment of the invention.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

FIG. 1 is a simplified cross-section of a precursor plate 2. The precursor plate 2 comprises various engravings 4, which reside in an engraved surface 6 thereof. In particular, the engravings 4 are manufactured by laser engraving of the precursor plate 2. However, the surface 6 can alternatively be engraved chemically, by means of a rotating chisel or by other suitable engraving tools. By way of an example only, the engravings 4 in the precursor plate 2 according to the embodiment in FIG. 1 are manufactured by laser engraving.
To assist laser engraving and to ensure optimal absorption of the laser light and sublimation of the processed polymer material of the precursor plate 2, laser light absorbing particles or additives are dispensed in the precursor plate 2. Optimal engraving quality can be achieved when the absorber is manufactured using a carbon black material.
A particularly convenient polymer material to be used within the context of the embodiments is a polyimide material. For example a Kapton material can be applied.
Prior to transfer of the precursor plate 2 into the deposition chamber of a PVD unit, at least the engraved surface 6 of the precursor plate 2 can undergo a pre-treatment. This pre-treatment can include surface cleaning and surface activation. In particular, the surface cleaning and activation, which is preferably performed outside the PVD unit, comprises the following stages:

manual cleaning of the surface using isooctane or petrol,
removal of residual dust by water jet,
oil skimming with calcium carbonate and vinegar,
cleaning by deionized and ultra-deionizer water,
drying in a forced air circulation oven.

After cleaning and surface activation, the precursor plate 2 is mounted on a suitable sample holder and directly transferred into the deposition chamber of the PVD unit. For example, the PVD unit is a sputter unit, in particular a magneton sputter unit. However, other suitable PVD units, for example a cathodic arc unit, can be used.
The deposition or coating process starts by evacuating the deposition chamber until a residual pressure of less than 10^-2 Pa (10^-4 mbar) is reached. The deposition process is performed using for example the process parameters, which are summarized in table 1 below. These process parameters are optimized for deposition of a silver coating on a Kapton precursor plate 2 using a magneton sputter unit.
However, other materials, for example: Gold (Au), Aluminium (Al), Palladium (Pd), Titanium (Ti), Chrome (Cr) and / or any other conductive material, in particular any other electrically conductive metal can be suitable. Furthermore, a composition or an alloy of at least two of the mentioned materials can be applied. The coating material can also comprise nitrides and / or carbonitrides of any of the named materials and / or alloys.
The mentioned materials, alloys or compositions can form at least the main component of the coating. This advantageously applies to all the mentioned materials. The composition and the ratio of the components can be adjusted to the particular requirements of the coating, in particular with respect to its hardness, in particular its surface hardness.
Deposition of the coating is furthermore not limited to magneton sputtering. Other PVD-techniques can be applied. For example, the coating can be deposited using cathodic arc deposition.
By way of an example only, continued reference is made to a magneton sputtering of a silver coating on a Kapton precursor plate. The process parameters are summarized in the table 1 below. Table 1:

Process Step BIAS [V] MS Power [W] Pressure [Pa] Ar [sccm] Time [min]

Coating 0-100 1000-5000 0,1-1 1 100-1000 5-15
During the deposition of silver on the engraved surface 6 of the precursor plate 2, the bias voltage (BIAS) between the sputter target, i. e. a silver target, and the substrate, which is the precursor plate 2, is set to 0 V. It can be, however set to any value, which is between 0 V and 100 V. The magneton sputter current (MS Power) is adjusted to at least approximately 3000 W. Other suitable values are between 1000 W and 5000 W. The residual pressure of the working atmosphere is at least approximately 0,7 Pa (0,7*10^-2 mbar) using argon (Ar) as a sputter gas. Further suitable pressures of the working atmosphere are between 0,1 Pa and 1 Pa. The deposition run takes at least approximately between 5 minutes and 15 minutes, until a desired thickness of the coating is achieved. The engraved surface 6 of the Kapton precursor plate 2 is now homogenously covered by a silver coating 8.
In FIG. 2, there is a simplified cross-section of the coated precursor plate 2 having a coating 8, which resides on the engraved surface 6.
It is to be appreciated, that the dimensions in FIG. 1 and 2, in particular the thickness of the precursor plate 2, the depth of the engravings 4 and the thickness of the coating 8 are not necessarily down to scale.
An in-depth analysis of the surface of the coating 8 revealed that the silver coating does neither include macroscopic defects nor variations in surface colour. The latter indicates that a film having a very homogenous thickness was deposited. Similar experiments, which have been performed for the other materials and compositions, which are mentioned within the context of this specification, revealed similar results.
In addition to this, surface roughness measurements have been performed on both, the uncoated substrate, a coated substrate. By way of an example, reference is made to a surface having a silver coating, which was deposited using a traditional electroforming process and on samples of precursor plates 2 having a silver coating according to embodiments of the invention. The results of the surface roughness measurements are summarized in the following table 2: Table 2:

Sample Thickness (nm) Ra (µm) Rz (µm) Rq (µm)

Kapton - 0,07 0,9 0,09

Chemical Ag 800 0,12 1,2 0,16

PVD Ag 200 0,07 0,7 0,09

500 0,06 0,5 0,07
In the first line of table 2 (Kapton), various values of surface roughness of the uncoated Kapton precursor plate 2 are summarized. The second line below (Chemical Ag) refers to a sample of a precursor plate 2, which was coated with 800 nm of silver in a traditional electroforming process. The last and second last line of table 2 comprises surface roughness values of precursor plates 2 according to two embodiments of the invention. The first sample in the second last line is coated with 200 nm of silver in a magneton sputter process. The second sample in the last line comprises a silver coating 8 having a thickness of 500 nm.
In table 2, the values in the column denoted Ra refer to an arithmetic average roughness. In the column Rz, the values of the average depth of roughness are given. In the last column named Rq, values of the cubic average roughness are summarized. These three different values characterize the surface roughness of the bare substrate, a traditional coating or a coating of a precursor plate 2 according to embodiments of the invention. As it is apparent from the above table 2, the surface roughness of both samples, which are coated with PVD silver, is lower when compared to the surface roughness of a traditional silver layer. This verifies the superb quality of the silver coating 8, which was deposited in the PVD process.
Because the surface roughness of the silver coated precursor plate 2 is very low, a high quality nickel alto plate can be manufactured. For the manufacture of the nickel alto plate, the PVD silvered precursor plate 2 can be subsequently transferred into a nickel bath, wherein the nickel alto plate is manufactured using the conventional electroforming parameters.
FIG. 3 illustrates and summarizes the method of manufacturing a precursor plate 2 by application of physical vapour deposition (PVD). Firstly, the engraved precursor plate 2 is cleaned and activated (step S1). It is subsequently transferred to the vacuum chamber of the PVD unit (step S2). The coating 8 is deposited on the engraved surface 6 by the PV-deposition technology, in particular by magneton sputtering (step S3). Further in particular, the process parameters, which are summarized in table 1, can be applied. When the deposition run is finished, the coated precursor plate 2 is transferred from the vacuum chamber of the PVD unit (step S4). For the manufacture of a nickel alto plate, the coated precursor plate 2 can be subsequently used in an electroforming process.The process, which is illustrated in FIG. 3, advantageously applies to all materials, alloys, compounds and compositions, which are mentioned within the context of this specification.
Although the invention has been described hereinabove with reference to specific embodiments, it is not limited to these embodiments and no doubt further alternatives will occur to the skilled person that lie within the scope of the invention as claimed.

Claims

A precursor plate for the manufacture of an intaglio printing plate, the precursor plate comprising an engraved surface, which is covered by a coating, wherein the coating is formed by physical vapour deposition (PVD) of a coating material.
The precursor plate according to claim 1, wherein the coating material comprises Silver (Ag), Gold (Au), Aluminium (Al), Palladium (Pd), Titanium (Ti), Chrome (Cr) and / or any other conductive material, in particular any other electrically conductive metal, at least as the main component, wherein in particular the coating material comprises a composition or an alloy of at least two of the named materials, at least as the main component, an wherein further in particular, the coating material comprises nitrides and / or carbonitrides of any of the named materials and / or alloys, at least as the main component.
The precursor plate according to claim 1 or 2, wherein the coating is a multilayer, in particular the multilayer comprises a plurality of layers, wherein at least some of the layers of the multilayer are manufactured from different materials.
The precursor plate according to anyone of the preceding claims, wherein the coating is a thin film having a thickness, which is between 100 nm and 1000 nm.
The precursor plate according to anyone of the preceding claims, wherein the coating is formed by sputter deposition of the coating material, in particular the coating is formed by magneton sputter deposition in a working atmosphere having a pressure, which is substantially between 0,1 Pa and 1 Pa or the coating is formed by cathodic arc deposition of the coating material.
The precursor plate according to anyone of the preceding claims, wherein the precursor plate is made of a polymer material, in particular the polymer material is a polyimide material, further in particular the polyimide material is a Kapton material, wherein in particular the polymer material comprises laser-light absorbing particles or additives, which are dispensed in the polymer material, further in particular the laser-light absorbing particles or additives are manufactured from carbon black material.
A method of manufacturing a precursor plate for the manufacture of an intaglio printing plate, the method comprising the step of depositing a coating on an engraved surface of the precursor plate by physical vapour deposition (PVD) of a coating material.
The method according to claim 7, wherein the coating material comprises Silver (Ag), Gold (Au), Aluminium (Al), Palladium (Pd), Titanium (Ti), Chrome (Cr) and / or any other conductive material, in particular any other electrically conductive metal, at least as the main component, wherein in particular the coating material comprises a composition or an alloy of at least two of the named materials, at least as the main component, an wherein further in particular, the coating material comprises nitrides and / or carbonitrides of any of the named materials and / or alloys, at least as the main component.
The method according to claim 7 or 8, wherein the step of depositing the coating comprises depositing a multilayer, in particular the step of depositing the multilayer comprises depositing a plurality of layers using different materials.
The method according to anyone of claims 7 to 9, wherein a thin film having a thickness, which is between 100 nm and 1000 nm, is deposited and forms the coating.
The method according to anyone of claims 7 to 10, wherein the coating is deposited by sputter deposition of the coating material, in particular the coating is deposited by magneton sputter deposition in a working atmosphere having a pressure, which is substantially between 0,1 Pa and 1 Pa or the coating is deposited by cathodic arc deposition of the coating material.
The method according to anyone of claims 7 to 11, wherein the coating is deposited on a precursor plate, which is manufactured from a polymer material, in particular the polymer is a polyimide material, further in particular the polyimide material is a Kapton material, wherein in particular the polymer material comprises laser-light absorbing particles or additives, which are dispensed in the polymer material.
The method according to anyone of claims 7 to 12, further comprising the step of pre-treating at least the engraved surface of the precursor plate, prior to deposition of the coating material, wherein in particular the step of pre-treating comprises the steps of cleaning and activating at least the engraved surface of the precursor plate.
Use of the precursor plate according to anyone of claims 1 to 7 for the manufacture of a (nickel) alto plate for manufacturing an intaglio printing plate for the production of banknotes or other printed securities.