EP1432868A1

EP1432868A1 - Papermaking mould for producing two-stage watermarks and a method for producing the same

Info

Publication number: EP1432868A1
Application number: EP02777101A
Authority: EP
Inventors: Wittich Kaule; Karlheinz Mayer; Bernd Stumbeck; Wolfgang Wensauer; Günther WILD; Thomas Gerhardt; Andreas Aigner
Original assignee: Giesecke and Devrient GmbH
Current assignee: Giesecke and Devrient Currency Technology GmbH
Priority date: 2001-09-17
Filing date: 2002-09-13
Publication date: 2004-06-30
Also published as: PL200780B1; KR100965039B1; PL367995A1; US8524039B2; WO2003025281A1; UA76200C2; RU2004111790A; KR20040054686A; DE10145782A1; US20040249754A1; RU2300596C2; CN1266335C; HUP0401448A2; HU228322B1; CN1555443A

Abstract

The invention relates to a papermaking mould (20), which is used to produce two-stage watermarks (1). To produce said mould, partial sections of the papermaking mould (20) are completely sealed by a viscous sealing paste (10), which is subsequently actively or passively cured. The agglomeration of paper during the paper production is impeded in the sections of the paper mould (20) that have been sealed in this manner, so that these areas of the finished paper appear lighter in transmitted light. A mask (30) is used to accurately position the sealing paste (10) on the partial sections of the papermaking mould (20) and/or to cure the sealing paste (10) only in predetermined partial sections, whereby in the latter case, the areas of the sealing paste (10) that have not been cured are washed away.

Description

Paper screen for the production of two-stage watermarks and process for its production

The invention relates primarily to a method for producing a paper screen for paper production with watermarks, in particular for the production of securities, such as banknotes, checks, ID cards and other security papers. The invention further relates to a mask for use in the aforementioned method, a paper sieve which can be produced by means of the nerf and a security paper produced by means of such a paper sieve.

The paper production takes place in a continuous way on so-called

Circular screening machines or Fourdrinier machines, where paper mass is deposited on a moving paper screen and solidified to such an extent that it can be removed from the paper screen as a moist paper web for further processing such as drying etc.

In the manufacture of paper with watermarks, a distinction is made between two-stage watermarks with a strong chiaroscuro effect and multi-tier watermarks with many smooth transitions between light and dark. To create two-stage watermarks, metal wires or molded metal parts (so-called electrotypes) are soldered onto the paper screen structure in order to completely close the paper screen at these points. As a result, the paper accumulation in these areas of the paper screen is hindered and thin spots are formed in the

Paper that appears very bright when viewed in transmitted light. However, when producing multi-level watermarks, no holes in the paper screen are closed. Instead, a three-dimensional relief is embossed into the paper screen, so that the paper thickness of the finished paper varies according to the relief and allows soft transitions between light and dark areas to be seen in transmitted light. In contrast to two-stage watermarks, multi-stage watermarks can only be created on circular screening machines, since the screens of circular screening machines are rigid. On Fourdrinier machines, on the other hand, the so-called Fourdrinier machines, the paper sieve is designed as an encircling belt and an embossed relief for producing multi-level watermarks would be destroyed by the repeated deflection. However, paper production on rotary screening machines is time and cost intensive, which is why embossed, multi-level watermarks are only used in the production of security-relevant papers, such as banknotes or other securities.

However, the generation of two-stage watermarks, although at first glance more versatile, is problematic in several ways. For example, soldering the metal wires or electrotypes onto the paper sieve requires extensive manual work by highly specialized specialists and is therefore time-consuming and expensive. Furthermore, the firmly soldered parts are mechanically stressed on Fourdrinier machines and often detach from the sieve, which has a negative impact on production safety and product quality, since the loose parts can get stuck in the sieve and destroy the paper.

Similar problems also occur with rotary screen machines, especially when the two-stage watermark is combined with an embossed multi-stage watermark, for example to emphasize certain details, lettering, crests or the like through special brightness in a multi-stage watermark.

Above all, the adhesion of the electrotypes in the relief-like embossed areas is critical. In addition, the exact positioning of the Electrotypes difficult in the relief-like areas of the paper screen. It is correspondingly problematic to reattach detached parts in exactly the same position.

Proceeding from this, the present invention is based on the object of proposing a paper screen and a method for producing a paper screen for paper production with a watermark, in which the means responsible for the formation of the watermark can be produced with little effort and with precise positioning even in embossed screen areas and even withstand heavy loads.

This object is achieved according to the invention by a paper screen and a method for producing the same with the features of the independent claims. A specially designed mask is also proposed for use in this method. Advantageous refinements and developments of the invention are specified in the claims dependent thereon.

The invention is based on the consideration that it is not necessary to generate elevations on the paper screen by means of wires or electrotypes in order to close off areas of the paper screen underneath. Rather, it is sufficient if the screen is closed in some way in precisely these areas, namely according to the invention by means of a sealing compound which is partially applied to the paper screen and completely closes the screen at these points. The purpose achieved with conventional electrotypes to hinder the paper accumulation in these areas and to produce very bright spots in the paper in this way is achieved to the same extent by the measure according to the invention. The sealing compound applied to the paper sieve forms a firm connection with the paper sieve, the sealing compound preferably completely enclosing the sieve fabric. The composite mass therefore does not separate easily from the paper sieve, so that the above-mentioned disadvantages of the soldered electrotypes are avoided. Fabrics can be used as sealing compound that can be applied to the sieve in a tough state and can be firmly attached to the sieve after additional treatment or independent hardening. For example, tough adhesives, such as systems based on epoxy resins, or solder paste can be used, which only bond firmly to the mesh of the screen after heating. Radiation-curing adhesives, such as UV-curable adhesive compounds, can also be used.

The invention can be used both on Fourdrinier machines and on rotary sieve machines. In the case of circular screening machines, the choice of material for the sealing compound is relatively uncritical due to the lower mechanical load, and brittle materials can also be used. When used in Fourdrinier machines, higher demands must be placed on the elasticity of the sealing compound, so that the closed paper sieve areas do not break open due to the repeated deflection. For example, materials such as rubber or other elastomers can be used in this case.

The invention is also not limited to the production of two-stage watermarks. By appropriately rasterizing the sealing compound, multi-level watermarks can also be created. If one assigns a certain area coverage of the sealing compound to the different gray tones of image information, more or less paper compound is deposited in the individual areas. Numerous possibilities of applying the sealing compound locally can be imagined. The application can be accomplished, for example, by screen printing, pad printing, spraying technology or knife application. According to a special embodiment of the method according to the invention, a mask controls the order in each case. The mask can be used for partial application of the sealing compound or for partial hardening of sealing compound applied over a large area.

According to a first embodiment, the mask is placed over the paper screen and then the sealing compound is applied to the mask. The mask has cutouts with the contour of the partial area to be closed, so that the sealing compound can only flow into the screen fabric in this partial area and close it.

According to a second embodiment, the sealing compound is first applied to the paper screen over a large area and then the same mask is placed over it as in the first exemplary embodiment. The sealing compound is then hardened in the cutouts in the mask, so that the paper screen is only permanently sealed in these areas. A suitable material for an activatable sealing compound is, for example, UN radiation-curing adhesive. In a subsequent step uncured compound is washed out of the paper screen.

In a third embodiment, as in the second embodiment, the sealing compound is first applied to the paper screen over a large area and then covered with a mask, which in this case has the shape of the partial area of the paper screen to be closed. The areas of the paper screen that are not covered by the mask are freed of the non-sealing compound, for example by the non-sealing compound is blown off or hosed. The remaining closing compound then hardens actively or passively.

The advantage of using masks is that they can be easily designed and machine-made on the computer. With the help of the data generated on the computer, the masks can e.g. by milling, laser cutting or milling or also by etching according to a previously created film template. In addition, the application of the sealing compound can be automated, so that the production of a paper screen for generating watermarks by means of the present

Invention can be significantly rationalized. Since the positioning of the masks is simple and precise, the invention also has an effect on the quality of the paper screen and the paper produced with it. The quality can also be reproduced at any time if a new identical paper screen is produced.

The invention can be used particularly advantageously if a particularly bright watermark area (a so-called “highlight watermark”) is to be generated within a multi-level watermark. In this case, these areas are within the embossed screen, preferably in the apex area of the relief with the sealing compound A mask can be used which has a surface structure adapted to the embossed relief of the paper screen, so that the mask, when placed on the paper screen, snaps into the embossed relief of the paper screen. The positioning of the sealing compound relative to the multi-level watermark is exactly defined and 100% repeatable. For further stabilization, fiber-reinforcing fillers are preferably added to the sealing compound, such as, for example, glass or carbon fibers in the case of sealing compound based on adhesive, or fine copper threads in the case of sealing compound consisting of solder paste.

The invention is explained below by way of example with reference to the accompanying drawings. In it show:

Figure 1 is a banknote with two-stage watermark 1 and multi-stage watermark 2.

Fig. 2 shows schematically a cross section through a paper wire after

Applying sealing compound using a mask;

3 schematically shows a cross section through a paper screen after

Applying sealing compound in a relief-like embossed area of the paper screen using a mask;

4 schematically shows a cross section through a paper screen during the active, partial hardening of sealing compound applied over a large area using a mask; and

Fig. 5 schematically shows a cross section through a paper screen after the large-area application of sealing compound and before

Remove excess sealant using a mask. 1 shows a banknote which has a plurality of two-stage watermarks 1 in the form of the denomination "100" and a multi-stage watermark 2 in the form of a portrait. Individual two-stage watermarks 1 partially or completely cover the multi-stage watermark 2. Because of the multi-stage watermark the paper for such a banknote is produced on a circular sieving machine with a paper sieve embossed in relief to produce the portrait 2.

A method according to the invention is described below with reference to FIG. 2, how a paper sieve 20 is to be produced according to a first embodiment in order to be able to produce a pure two-stage watermark with the paper sieve. Accordingly, a mask 30 is placed over the paper sieve 20, which has cutouts 31 which define those partial areas 11 of the paper sieve 20 in which the paper sieve 20 is to be closed with sealing compound 10. On the mask 30, sealing compound 10 is applied, which only penetrates through the mask 30 into the paper screen 20 in the recesses 31 and completely closes the tissue of the paper screen 20. This state of the method according to the invention is shown in FIG. 2.

In a next step, the mask 30 is removed and the sealing compound either cures passively or the curing process is activated, depending on the sealing compound material, for example by temperature control or UV radiation. Alternatively, the sealing compound 10 can first be cured or allowed to harden and only then can the mask 30 be removed, as a result of which the contour of the two-stage watermark is given a particularly precise and sharp delimitation! It must be taken into account that the size relationships in FIG. 2 do not correspond to reality. The thickness of the mask 30 is shown oversized compared to the thickness of the paper screen 20.

After the sealing compound has bonded to the structure of the paper screen 20 and has completely closed it in these areas, the screen is partially impermeable to water, as a result of which the paper accumulation at these points is hindered during the paper production. These areas appear in the paper produced with such a paper screen in transmitted light as very bright areas compared to the surrounding paper material.

While the method described with reference to FIG. 2 is suitable both for the production of a paper screen for a longitudinal screening machine and for a circular screening machine, the same method is described below with reference to FIG. 3 specifically for use in a circular screening machine, in which subregions 11 a relief-like embossed paper screen 20 can be provided with sealing compound. As can be seen in FIG. 3, the surface of the mask 30 adjoining the paper screen 20 has a surface structure 32 which, in the manner of a negative relief, affects the relief-like structure of the paper screen 20 and at the same time also the curvature thereof the use of the paper screen 20 in a rotary screen machine is conditioned, is adapted. Otherwise, the procedure for closing the partial areas 11 with sealing compound 10 does not differ from the method described with reference to FIG. 2. That is, the mask 30 is placed on the paper screen 20 in such a way that its surface structure 32 snaps into the relief-like structure of the paper screen 20. Subsequently, the sealing compound 10 is applied to the mask 30, so that the sealing compound 10 through the cutouts in the mask 30 into the Paper screen penetrates and thus only surrounds the screen fabric in the partial areas 11 of the paper screen 20. The excess closure material is then removed from the mask 30 (state in FIG. 3) and the mask 30 is removed from the paper screen 20. Finally, the sealing compound 10 is cured or, if necessary, the curing compound 10 is first cured and then the mask 30 is removed.

A second embodiment of the method according to the invention is described below with reference to FIG. Accordingly, in a first method step, the sealing compound 10 is applied to the paper screen 20 over a large area, so that it completely flows around the screen fabric and closes it. In this context, “large area” means an area that is larger than the partial areas 11 of the paper screen 20 that are ultimately to be permanently closed with sealing compound, which areas will be responsible for the later creation of a watermark during paper manufacture.

After the paper sieve 20 is impregnated with the sealing compound 10, the same mask 30, which is also used in connection with the exemplary embodiment according to FIG. 2, is placed over it, and the hardening of the sealing compound 10 in the partial areas 11, which is caused by the recesses 31 of the mask 30 are defined, is activated in the exemplary embodiment shown by means of UN radiation sources 40. After the sealing compound 10 has hardened in the partial regions 11, the mask 30 is removed and the non-hardened regions of the sealing compound 10 are washed out, so that they are permeable again. As a result, a paper screen 20 is obtained with the same configuration as can be obtained with the method described with reference to FIG. 2.

According to a third embodiment of the method according to the invention, which is described below with reference to FIG. 5, the closure mass 10, as already described with reference to FIG. 4, applied to the paper screen 20 over a large area and a mask 30 placed thereon, the outer contour 33 of which corresponds to the shape of the partial area 11 to be closed. The areas of the sealing compound 10 which are not covered by the mask 30 are removed, for example blown out through the paper screen 20, and the portion of the sealing compound 10 remaining in the partial areas 11 is then hardened. Alternatively, hardening can first take place in the partial areas 11, for example by using a heated mask 30 and a thermosetting sealing compound 10, and the remaining, uncured part of the sealing compound 10 is subsequently removed, for example washed out.

Particularly suitable as a sealing compound are substances which can be applied to the paper screen 20 in the tough state and which, after their active or passive curing, firmly bond to the paper screen. Tough adhesives are suitable, such as systems based on epoxy resin, but also solder paste, such as is used in SMD technology, for example, and which only bonds firmly to the mesh of the paper screen after it has been heated. Sealing compounds based on a UV-curable adhesive are also suitable. This applies primarily to the method described with reference to FIG. 4.

In order to increase the stability and bond strength of the sealing compound, it can be mixed with fillers, for example with glass or carbon fibers in the case of adhesives and with fine copper threads in the case of solder paste.

The application of the sealing compound 10 to the paper sieve 20 can be done by screen printing, pad printing, spraying, knife coating and other common methods Methods take place, the location-specific application preferably being controlled by the mask 30.

The mask 30 can be designed on a computer and can be produced automatically by means of CAD / CAM technology by milling, laser cutting or laser milling. Etching mask 30 from a film template is also practical.

Claims

Patent claims

1. A method for producing a paper screen (20) for paper production with watermark (1), which comprises the following steps:

Providing a paper screen (20),

Applying a sealing compound (10) to the paper sieve (20) in such a way that a partial area (11) of the paper sieve (20) is closed by the sealing compound (10) in the form of the watermark (1) to be produced later during paper manufacture.

2. The method according to claim 1, characterized in that the sealing compound is applied in the form of a grid.

3. The method according to claim 1 or 2, characterized in that the sealing compound (10) is hardened so that a permanent connection between the sealing compound (10) and the paper screen (20) is produced.

4. The method according to at least one of claims 1 to 3, characterized in that a mask (30) is used in the step of applying the sealing compound (10) or in the step of curing the sealing compound (10).

5. The method according to claim 4, characterized in that the mask (30) has a recess (31) with a contour corresponding to the shape of the partial area (11) to be closed and the sealing compound (10) through the recess (31) of the mask ( 30) is applied to the paper screen (20).

6. The method according to claim 4, characterized in that the sealing compound (10) is applied over a large area and the mask (30) either for the subsequent removal of sealing compound (10) lying outside the partial area (11) or for the targeted hardening of the in the partial area (11) lying sealing compound (10) is used.

7. The method according to claim 6, characterized in that the mask (30), which has a contour (33) corresponding to the shape of the partial area (11) to be closed, is arranged above the sealing compound (10) applied over a large area and that of the mask ( 30) uncovered area of the sealing compound (10) is removed.

8. The method according to any one of claims 1 to 7, characterized in that an adhesive based on epoxy resin is selected as the sealing compound (10).

9. The method according to any one of claims 1 to 7, characterized in that a thermally curable solder paste is selected as the sealing compound.

10. The method according to any one of claims 1 to 7, characterized in that a UV-curing adhesive is selected as the sealing compound (10).

11. The method according to claim 6, characterized in that the mask (30), which has a recess (31) with a contour corresponding to the shape of the partial area (11) to be closed, is arranged over the large-area sealing compound (10) that Hardening of the sealing compound (10) through the recess (31) of the mask (30) is activated, and uncured sealing compound (10) is subsequently removed.

12. The method at least according to one of claims 1 to 11, characterized in that the paper screen (20) has an embossed relief for producing a multi-level watermark (2), and a mask (30) is selected which follows the embossed relief Has a surface structure (32) adapted to the type of a negative relief, and the mask (30) with its surface structure (32) is applied in a snap-in manner to the embossed relief of the paper screen (20).

13. The method according to any one of claims 1 to 11, characterized in that the paper screen (20) has an embossed relief for producing a multi-level watermark (2), and that certain areas of the relief, preferably the apex areas, are provided with the sealing compound.

14. The method according to at least one of claims 1 to 13, characterized in that the paper screen (20) is a paper screen for a rotary screen machine.

15. The method according to any one of claims 1 to 14, characterized in that the sealing compound (10) contains fiber-reinforcing fillers.

16. Mask for use in the method according to claim 12, comprising a surface structure (32), which is adapted in the manner of a negative relief to a relief embossed in a paper screen (20) to produce a multi-stage watermark (2).

17. System for carrying out the method according to claim 12, consisting of a mask (30) according to claim 16 and a paper sieve (20) with a to the surface structure (32) of the mask (30) adapted for production a multi-level watermark (2) embossed into the paper screen (20).

18. Paper screen (20) for paper production with watermark, which has a partial area (11) closed by a sealing compound (10).

19. Paper screen according to claim 18, characterized in that the paper screen (20) is formed by a screen fabric which is enclosed in the partial area (11) by the sealing compound (10).

20. Paper sieve according to claim 18 or 19, characterized in that the sealing compound (10) is a hardened plastic.

21. Paper screen according to at least one of claims 18 to 20, characterized in that it is a paper screen (20) for a rotary screen machine.

22. Paper screen according to claim 21, characterized in that the partial area (11) closed by the sealing compound (10) lies at least partially in an embossed relief surface of the paper screen (20).

23. A method for producing a security, characterized in that the paper is deposited on a paper sieve according to one of claims 18 to 22.