DE102021004848A1 - Cylinder mold for a cylinder mold paper machine and manufacturing method - Google Patents

Abstract

The invention relates to a cylinder mold (10) for a cylinder mold paper machine for the production of security paper with watermarks, with a plastic screen cylinder (12) with a plate-like cylinder jacket made of a laser-absorbing plastic material, the cylinder jacket being at least partially penetrated by the action of laser radiation (18 ) a plurality of watermark reliefs (24) and a plurality of drainage perforations (26) are incorporated. The invention also relates to a method for producing a cylinder mold for a cylinder mold paper machine.

Description

The invention relates to a cylinder mold for a cylinder mold paper machine for producing security paper with watermarks, and associated production methods.

When paper is made on cylinder mold machines, a cylinder mold with a production screen jacket rotates in a trough with fiber suspension and scoops paper. A negative pressure is generated inside the cylindrical mold cylinder, which leads to a lowering of the liquid level there. The fiber suspension runs against the cylinder jacket from the outside and stock fibers are continuously deposited on the production screen. The accumulated paper pulp is solidified to such an extent that it can be pulled off the production screen as a moist paper web for further processing.

Cylindrical molds for the production of papers with watermarks require complex production. Screen manufacture is both time consuming and costly. Typical watermark screens consist of multiple screen layers of metal, such as copper, or a metal alloy, such as brass or bronze. The metallic screen material, especially copper, is a limited raw material that leads to high environmental pollution during mining and production.

Visually attractive, high-resolution watermarks can only be produced in relatively small areas with the cylinder screens, since the watermark inserts required for the watermark production either have to be produced separately and then inserted into openings in the screen or have to be produced directly in a recess in the metal screen.

The cylinder screens are also heavy and therefore not easy to transport. The screen material is ductile and is deformed by the high mechanical loads during paper production, which also changes the shape of the watermark over time. The service life of a watermark cylinder mold is therefore limited.

A further difficulty is that the embossing dies used for the production of the screen wear out after repeated use and have to be remanufactured. In addition, two embossing dies, a matrix and a patrix, are always required for screen embossing. For the position in the paper web, several, typically three to five different pairs of embossing dies have to be manufactured because of the distortion during paper production.

Finally, in the case of watermark screens, the individual elements of the various watermark reliefs are always arranged in blocks in the composition due to the production process. Embossing on bronze screens also depends on the design. For example, relief embossing with repetitive bar patterns cannot be produced because the screen fabric would draw in too much and distortions would occur in the screen.

Proceeding from this, the invention is based on the object of specifying a cylinder mold of the type mentioned at the outset, which avoids the disadvantages of the prior art. In particular, a cylinder mold is to be specified that can be produced easily and inexpensively and at the same time allows great freedom in the design of the watermark reliefs. In addition to a cylinder mold itself, advantageous manufacturing processes for such a cylinder mold should also be specified.

This object is solved by the features of the independent claims. Developments of the invention are the subject matter of the dependent claims.

The invention provides a cylinder mold for a cylinder mold paper machine for the production of watermarked security paper. The cylinder screen comprises a plastic screen cylinder with a plate-like cylinder jacket made of a laser-absorbing plastic material, a plurality of watermark reliefs and a plurality of drainage perforations being introduced into the cylinder jacket at least partially by the action of laser radiation.

Unlike conventional screens, the plastic screen cylinder is not formed from a fabric of interwoven thread systems, but advantageously has a substantially homogeneous, net-free structure, which is referred to as "plate-like" in the context of this description.

The plate-like cylinder shell is advantageously formed from a rigid plastic material or from a flexible plastic material, which is preferably doped with laser-absorbing dyes or pigments in order to ensure high absorption of the laser radiation acting on it. Carbon black, for example, can be used as the laser-absorbing material for this purpose; the use of ammonium octamolybdate has also proven itself, particularly when using a CO ₂ laser.

For the rigid plastic material, in particular, there are polyurethanes, polyester resins, fibers impregnated with resins, phenolic resins, phenolic resins, epoxy resins, urea resin, melamine resin, carbon fiber reinforced plastics, glass fiber reinforced plastics, polycarbonate, polyamide, polyamideimide, polyethylene, polypropylene, polycarbonate, polyvinylchloride, polyvinylurethane, polyethyleneterephthalate, polyetheretherketone, polyethersulfone, polyetherimide or combinations of these materials.

Polyether block amides in particular come into consideration as flexible plastic materials; the use of PET (polyethylene terephthalate) is also possible.

In an advantageous embodiment, the cylinder mold comprises a rigid, independent plastic screen cylinder. The cylinder jacket has a sufficient thickness to ensure the required stability of such a stand-alone screen cylinder, for example a thickness between 30 mm and 200 mm.

According to another, also advantageous embodiment, it is provided that the cylinder mold comprises a thin plastic screen cylinder, which is arranged over one or more perforated support cylinders, which are advantageously provided with a coarse perforation. In this way, time and energy can be saved during production, since the coarsely perforated support cylinders can be used several times and the perforations in the thin plastic screen cylinder are easier to make than in a thicker stand-alone plastic screen cylinder. The cylinder jacket of the thin plastic screen cylinder advantageously has a thickness between 0.25 mm and 3 mm, the cylinder jacket of the support cylinder advantageously has a thickness between 20 mm and 200 mm.

In an advantageous embodiment, it is provided that the plastic screen cylinder contains two or more different watermark reliefs, at least partially produced by the action of laser radiation, which are selected from the group consisting of high-resolution watermark reliefs, two-stage watermark reliefs, filigree watermark reliefs, large-area watermark reliefs, pixel watermark embossing, corner enhancing watermark embossing, edge enhancing watermark embossing and support watermark embossing.

According to a preferred embodiment, the drainage perforations are arranged in the majority of the plastic screen cylinder in the form of a first grid, and the plastic screen cylinder also contains hidden watermark areas that are formed by areas of the plastic screen cylinder in which the drainage perforations in the form of a second , different grid are arranged.

Predominant part of the plastic screen cylinder means a surface area of more than 50%, in particular more than 75%, advantageously more than 90%, or even more than 95%. The first and second grid can differ in the grid geometry, for example rectangular, square, hexagonal or parallelogram-shaped grid and/or in the grid width, ie the spacing of the drainage perforations in the grid. Different diameters of the perforations are also possible, but the perforations are expediently not so large that they are darkly visible in the paper. It goes without saying that more than two areas with different grids can also be provided.

The different grids make the accumulation of paper somewhat easier, more difficult or possibly only modified, so that the paper structure and/or the paper thickness and thus ultimately the appearance of the paper produced differs depending on the local grid of the drainage perforations. The influence on the paper structure is subtle and usually only detectable by machine. The areas in which the drainage perforations are present in the form of the second, different grid therefore produce a hidden watermark in the paper which, because of its complex production, represents a level 3 security element with high protection against counterfeiting.

• - ein Kunststoff-Siebzylinder mit einem plattenartigen Zylindermantel aus einem laserabsorbierenden Kunststoffmaterial bereitgestellt wird, und
• - in den Zylindermantel zumindest teilweise durch die Einwirkung von Laserstrahlung eine Mehrzahl von Wasserzeichenreliefs und eine Mehrzahl von Entwässerungsperforationen eingebracht werden.

The invention also includes a method for manufacturing a cylinder mold for a cylinder mold paper machine, in which

• - a plastic screen cylinder with a plate-like cylinder jacket made of a laser-absorbing plastic material is provided, and
• - A plurality of watermark reliefs and a plurality of drainage perforations are introduced into the cylinder jacket at least partially by the action of laser radiation.

A laser source in the mid-infrared with a wavelength between 5 μm and 20 μm, such as a CO ₂ laser, is advantageously used as the laser source. The laser impingement can take place in one stage, in multiple stages, or in multiple stages. In the case of a multi-stage or multi-stage laser treatment, the perforation to be produced is first drilled and, after a certain waiting time, further drilled. The pause(s) allows the material to cool down, which is gentler on the material.

In an advantageous method, it is provided that the lasering of the plastic screen cylinder from the inside to the outside, with the laser source preferably being adjusted in such a way that the beam shape produces conical dewatering perforations with a smaller diameter on the outside of the screen cylinder. Such a design of the dewatering perforations promotes dewatering in papermaking and prevents clogging of the perforations.

In an advantageous variant of the method, a rough form of the watermark relief is first produced with a mechanical milling machine, and this is then supplemented by a detailed fine structure by the action of the laser radiation. In principle, however, it is also possible that a rough form of the watermark relief is first produced by the action of the laser radiation and this is then supplemented with a detailed fine structure using a mechanical milling machine. In an advantageous embodiment, the entire watermark relief is generated only by the action of the laser radiation.

A single laser source or a plurality of laser sources can be used simultaneously for laser impingement, and a multi-head laser can also be used advantageously. When using mechanical milling machines, a single milling machine or several milling machines or a multi-head milling machine can be used. The laser sources and, if necessary, the milling cutters can be moved to process the cylinder surface; alternatively or additionally, the cylinder to be processed can also be moved. The milling and the laser impingement can take place simultaneously or sequentially. Hot air can be used to advantage for deburring milled elements.

The drainage perforations can be drilled mechanically into the cylinder jacket, but the drainage perforations are advantageously also produced by the action of the laser radiation. This can take place in the same step as the processing of the watermark reliefs and in particular using the same laser source or sources. Alternatively, different laser sources can also be used for processing the watermark reliefs and drilling the drainage perforations.

• - eine formbare Masse bahnförmig ausgewalzt wird,
• - in die ausgewalzte Bahn Grobformen der Wasserzeichenreliefs eingeprägt werden,
• - die geprägte Bahn zu einem fest-elastischen Band verfestigt wird,
• - das fest-elastische Band mit Laserstrahlung beaufschlagt wird, um die Grobformen der Wasserzeichenreliefs mit einer detailreichen Feinstruktur zu den vollständigen Wasserzeichenreliefs zu ergänzen,
• - in das fest-elastischen Band eine Mehrzahl von Entwässerungsperforationen eingebracht wird, und
• - das bearbeitete Band zu einem Zylindermantel des Rundsiebs geformt wird.

In another, likewise advantageous method according to the invention for producing a cylinder mold for a cylinder mold paper machine, it is provided that

• - a malleable mass is rolled out in web form,
• - Rough forms of the watermark relief are embossed into the rolled web,
• - the embossed web is consolidated into a firm-elastic band,
• - the firm-elastic band is exposed to laser radiation in order to supplement the rough forms of the watermark relief with a detailed fine structure to form the complete watermark relief,
• - a plurality of drainage perforations are made in the rigid-elastic band, and
• - The processed strip is formed into a cylinder jacket of the cylinder mold.

This procedure significantly simplifies and speeds up the screen manufacturing process. In addition, if a favorable choice of material is made for the malleable mass, only low raw material costs are incurred. The moldable mass can advantageously consist of granules made of plastic and metal, the grain size of which is specifically adjusted for good sintering properties. Residual materials from paper production can be added to the mass as porosity agents to reduce costs.

The drainage perforations can be drilled mechanically into the rigid-elastic band, but they are advantageously also produced by the action of the laser radiation. Here, too, the same or different laser sources can be used for processing the watermark reliefs and drilling the drainage perforations.

• Die Wasserzeichensiebe können schneller und kostengünstiger als herkömmliche Metallsiebe hergestellt werden. Die Wasserzeichensiebe weisen aufgrund ihres geringeren Gewichts eine längere Standzeit auf und erlauben eine leichtere Handhabung. Die Wasserzeichensiebe können auch mit resourcenschonenden Materialien hergestellt werden und ein Recycling nicht mehr benötigter Kunststoff-Rundsiebe ist einfach möglich.

In addition to the advantages mentioned elsewhere, the cylinder molds described and the manufacturing processes described have the following advantages in particular:

• The watermark screens can be made faster and cheaper than traditional metal screens. Due to their lower weight, the watermark screens have a longer service life and are easier to handle. The watermark screens can also be made with resource-saving materials and plastic cylinder screens that are no longer required can be easily recycled.

The number and size of the surface areas with watermark reliefs on the cylinder mold is not limited, so that the banknote and security papers produced can in particular have a number of high-resolution watermarks and/or large-area high-resolution watermarks. The watermark reliefs can also be arranged across multiples and, for example, record two, four or more multiple banknotes on the security paper. The watermark screens can can have several different watermark types for different functions, and support watermark reliefs are also possible to a large extent.

The production methods described allow watermark reliefs to be produced with smooth transitions between different reliefs, in particular between different types of watermark reliefs. For example, a two-level "electrotype" watermark relief can smoothly fade into a high-resolution multi-level watermark relief.

The production of the watermark reliefs and the drainage perforations described allows both the creation of novel, visually striking, small and large-area customer designs, as well as the creation of subtly hidden, formation-like and production-specific area watermarks.

The cylinder molds produced according to the invention are very resistant to pressure and are therefore well protected against damage when used in a paper machine. By varying the perforation, the paper thickness can be influenced and process-related irregularities in the paper thickness can also be compensated for. The cylinder molds could also advantageously be cambered, which means that the diameter of the cylinder mold can be adjusted across the width to the deflection of the dandy roll and couch.

The laser impingement is usually controlled with the help of digital data, so that the cylinder screens have a significantly higher reproducibility than can be achieved with embossing stamps that wear out for metal screen embossing. Shrinkage and elongation over the entire screen surface can also be easily calculated.

Further exemplary embodiments and advantages of the invention are explained below with reference to the figures, which are not shown to scale and proportions in order to improve clarity.

• 1 schematisch die Fertigung eines erfindungsgemäßen Rundsiebs durch Bearbeitung eines Kunststoff-Siebzylinders mit einer mechanischen CAD-Fräse und einer Laserquelle,
• 2 in 2(a) und 2(b) einen Ausschnitt des Siebzylinders der 1 in zwei Bearbeitungsschritten im Querschnitt,
• 3 eine mit einem erfindungsgemäßen Rundsieb erzeugte Banknote, in die verschiedene Wasserzeichentypen unterschiedlicher Funktion eingebracht sind,
• 4 einen Querschnitt eines Siebzylinders nach einem Ausführungsbeispiel der Erfindung zur Erläuterung des Zustandekommens und des Erscheinungsbilds eines Krypto-Wasserzeichens, und
• 5 eine weitere vorteilhafte Vorgehensweise bei der Fertigung eines erfindungsgemäßen Rundsiebs.

Show it:

• 1 schematically the production of a cylinder mold according to the invention by processing a plastic screen cylinder with a mechanical CAD milling machine and a laser source,
• 2 in 2(a) and 2 B) a section of the screen cylinder 1 in two processing steps in cross section,
• 3 a banknote produced with a cylinder mold according to the invention, in which different types of watermarks with different functions have been introduced,
• 4 a cross section of a screen cylinder according to an embodiment of the invention to explain the formation and the appearance of a crypto watermark, and
• 5 another advantageous procedure in the manufacture of a cylinder mold according to the invention.

The invention will now be explained in more detail using the example of cylinder molds for a cylinder mold paper machine for the production of banknotes. 1 shows schematically the production of a cylinder mold 10 according to the invention by machining a plastic screen cylinder 12 with a mechanical CAD milling machine 14 and a laser source 16. 2 shows in 2(a) and 2 B) a section of the screen cylinder 12 in two processing steps in cross section.

Referring first to 1 A rigid plastic screen cylinder 12 is provided, the plate-like cylinder jacket of which is formed from polyurethane, for example, which is doped with laser-absorbing dyes or pigments in order to ensure high absorption of the laser radiation 18 . As explained in more detail above, the cylinder casing of the screen cylinder 12, unlike conventional screens, is not formed from a fabric made up of interwoven thread systems, but has a homogeneous, net-free structure.

In the exemplary embodiment, rough molds 20 of the desired watermark reliefs are first milled into the cylinder jacket using the CAD milling machine 14 in this plate-shaped plastic screen cylinder 12 . 2(a) 12 schematically shows the relief 30 of the screen cylinder 12 in cross section after the milling step. The relief 30 contains indentations 32 and raised areas 34 in the cylinder jacket, which form the milled rough shapes 20 of the watermark reliefs, as well as unprocessed, flat vellum areas 36.

After the milling step, the cylinder jacket is exposed to laser radiation 18 from the laser source 16, for example a CO ₂ laser. Due to the doping with the dyes or pigments, the plastic material of the cylinder jacket has a high absorptivity for the laser radiation 18 and is partially removed and perforated by it. The laser ablation supplements the rough forms 20 with a detailed fine structure 22 and thereby produces the desired watermark reliefs 24, as in the enlarged inset 38 of FIG 2 B) implied. on the other hand a large number of micro-channels 26 are drilled in the cylinder jacket by laser perforation in the same work step, which serve to dewater the paper during paper manufacture. 2 B) shows schematically the relief 30 of the screen cylinder 12 after the laser treatment with the microchannels 26 and the finished watermark reliefs 24.

The manufacture of the cylinder mold can be modified in various ways, as already explained in more detail above. For example, several milling machines 14 and/or several laser sources 16 can be used simultaneously for the production of a plastic screen cylinder 12 . It is also possible to dispense with pre-machining by means of a milling machine and to produce the entire watermark relief 24 only by applying a laser.

With the procedure described, not only multi-stage, high-resolution watermark reliefs 24, but also watermark reliefs with practically any relief course 30 can be generated. Two-stage watermark reliefs with a large difference in height can also be provided, which lead to watermarks with a high-contrast appearance during paper production. Such watermark reliefs are particularly well suited for generating character strings and in particular value numbers, such as the denomination of a bank note in the watermark. Based on the conventional generation of such watermarks using metallic electrotypes, these two-stage watermarks are also referred to as electrotype watermarks in the present description, even if they are not generated using conventional electrotypes but by lasered watermark reliefs. Lasering also has advantages in the case of two-level watermark reliefs or watermark reliefs with only a few height levels, since sharp transitions and steep flanks can be produced by laser ablation. Smooth transitions between different types of reliefs, for example between a two-stage electrotype-like watermark relief and a high-resolution, multi-stage watermark relief, can also be produced without further ado.

A further advantage of the procedure described is that the cylinder molds 10 produced can be equipped with watermark structures 24 in practically any large area, since the limitations of conventional production methods described above do not apply.

The cylinder mold can also have a large number of different watermark reliefs with different properties and functions. For illustration shows 3 a banknote 40, as can be produced with the aid of a cylinder mold 10 according to the invention. In the paper substrate 42 of the banknote 40, different types of watermarks with different functions are introduced at the same time. Specifically, the banknote contains 40 watermarks for human authentication, namely a multi-tonal portrait watermark 44, a highlight electrotype watermark 46, a motif electrotype watermark 48 and an electrotype watermark with negative text 50. There are also watermarks for automatic authentication , namely a bar watermark 52, watermarks for substrate stabilization, namely the paper-reinforcing corner watermarks 54 and edge watermarks 56, and a watermark for better integration of security threads, namely the window bar watermark 58.

In addition, the bank note 40 has a hidden crypto watermark 60 in the vellum area, which cannot be produced with conventional drainage screens. The formation and appearance of the crypto watermark 60 in papermaking are based on the cross section of the screen cylinder 12 of the 4 explained in more detail.

The relief 30 of the screen cylinder 12 contains, like that in 2 described relief several watermark reliefs 24, as well as intermediate, flat vellum areas 62, 64. In these vellum areas 62, 64, just like in the watermark areas, microchannels 26, 26' for paper drainage are formed by the laser impact. The microchannels are arranged in a regular grid, for example a square grid.

While the microchannels 26 in the vellum areas 62, the watermark areas 24 and part of the vellum area 64 are arranged in the form of a first grid, the microchannels 26' are arranged in a partial area 66 of the vellum area 64 in the form of a second, different grid, for example a square grid larger grid width than in the first grid.

The different grid arrangement of the microchannels 26' leads to a small change in the paper accumulation in the partial area 66 during paper production, so that the paper structure and thus also the appearance of the paper in the partial area 66 differs subtly from the structure and appearance of the surrounding paper material. The change is not visible to the naked eye, but can be reliably detected by machine. The sub-area 66 therefore represents a watermark area which is a crypto watermark in the bank note 40 during paper production Chen 60 forms, which represents a level 3 security feature that a potential counterfeiter can hardly replicate due to its complex production.

5 illustrates a further advantageous procedure in the manufacture of a cylinder mold according to the invention. In this procedure, the screen jacket 70 is formed from a malleable mass 72, which is rolled out in the form of a web (left part of the figure 5 ) and into which the rough shapes 20 of the desired watermark reliefs are then embossed using an embossing device 80 (middle part of the figure 5 ). The embossed web is then consolidated, for example dried, cured or sintered, in a consolidation area 82 to form a solid-elastic band 74 .

Subsequently, the coarse forms 20 are supplemented with a more detailed fine structure in the rigid-elastic band 74 by laser ablation with the laser radiation 18 of a laser source 16, thereby producing the finished watermark reliefs 24, and in the same work step microchannels 26 are drilled into the band 74 by laser perforation (right image part of 5 ). The finished band is then formed into the cylinder jacket of a cylinder mold.

Reference List

10

cylinder sieve

12

plastic screen cylinder

14

CAD milling machine

16

laser source

18

laser radiation

20

rough forms

22

fine structure

24

watermark relief

26, 26'

microchannels

30

relief

32

indentations

34

superscript

36

flat vellum areas

38

inset

40

bank note

42

paper substrate

44

multitonal portrait watermark

46

Highlight electrotype watermark

48

Motif electrotype watermark

50

Electrotype watermark with negative text

52

bar watermark

54

paper stiffening corner watermark

56

paper stiffening edge watermarks

58

Gable Watermark

60

Crypto Watermark

62, 64

vellum areas

66

watermark area

70

screen jacket

72

malleable mass

74

firm-elastic band

80

embossing device

82

solidification area

Claims (13)

Cylinder mold for a cylinder mold paper machine for producing security paper with watermarks, with a plastic screen cylinder with a plate-like cylinder jacket made of a laser-absorbing plastic material, a plurality of watermark reliefs and a plurality of drainage perforations being introduced into the cylinder jacket at least partially by the action of laser radiation. round sieve after claim 1 , characterized in that the plate-like cylinder jacket is formed from a rigid or from a flexible plastic material, which is advantageously doped with laser-absorbing dyes or pigments. round sieve after claim 1 or 2 , characterized in that the cylinder mold comprises a rigid, self-contained plastic screen cylinder. round sieve after claim 1 or 2 , characterized in that the cylinder mold comprises a thin plastic screen cylinder placed over one or more perforated support cylinders. Cylinder screen according to at least one of Claims 1 until 4 , characterized in that the plastic screen cylinder contains two or more different watermark reliefs, at least partially produced by the action of laser radiation, which are selected from the group consisting of high-resolution watermark reliefs, two stepped watermark relief, delicate watermark relief, large area watermark relief, pixel watermark relief, corner-enhancing watermark relief, edge-enhancing watermark relief and support watermark relief. Cylinder screen according to at least one of Claims 1 until 5 , characterized in that the drainage perforations are arranged in the majority of the plastic screen cylinder in the form of a first grid and that the plastic screen cylinder also contains hidden watermark areas, which are formed by areas of the plastic screen cylinder in which the drainage perforations in the form of a second, different grid are arranged, in particular in the form of a grid with different grid width. Method for producing a cylinder mold for a cylinder mold paper machine, in which - a plastic screen cylinder with a plate-like cylinder jacket made of a laser-absorbing plastic material is provided, and - A plurality of watermark reliefs and a plurality of drainage perforations are introduced into the cylinder jacket at least partially by the action of laser radiation. procedure after claim 7 , characterized in that the plastic screen cylinder is lasered from the inside to the outside, the laser source preferably being adjusted in such a way that the beam shape produces conical dewatering perforations with a smaller diameter on the outside of the screen cylinder. procedure after claim 7 or 8th , characterized in that a rough form of the watermark relief is produced with a mechanical milling machine, and the rough form is then supplemented by the action of the laser radiation by a detailed fine structure. procedure after claim 7 or 8th , characterized in that the entire watermark reliefs are generated by the action of the laser radiation. Method according to at least one of Claims 7 until 10 , characterized in that the dewatering perforations are produced by the action of the laser radiation. Method for producing a cylinder mold for a cylinder mold paper machine, in which - a malleable mass is rolled out in web form, - Rough forms of the watermark relief are embossed into the rolled web, - the embossed web is consolidated into a firm-elastic band, - the firm-elastic band is exposed to laser radiation in order to supplement the rough forms of the watermark relief with a detailed fine structure to form the complete watermark relief, - a plurality of drainage perforations are made in the rigid-elastic band, and - The processed strip is formed into a cylinder jacket of the cylinder mold. procedure after claim 12 , characterized in that the dewatering perforations are produced by the action of the laser radiation.

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