EP2826915A1 - Dewatering fabric and method for producing the same - Google Patents

Abstract

The invention relates to a dewatering screen for the production of paper with multi-level watermark, with a support screen, which has a multi-level relief in the form of the watermark to be generated in partial areas. The invention further relates to a method for producing such a dewatering screen. According to the invention, the multi-level relief is formed by a perforated watermark insert produced by means of 3D printing or a method belonging to rapid prototyping.

Description

The invention relates to a dewatering screen for the production of paper with multi-level watermark, with a carrier screen, which has a multi-level relief in the form of the watermark to be generated in partial areas. The invention further relates to a method for producing such a dewatering screen.

For banknotes and security papers, the real watermark is an important security element to protect against unauthorized reproduction. The quality of the presentation in terms of detail of the image and the variety of presentation options represents an important prerequisite for the future acceptance of the security feature.

Today, paper with a genuine watermark is either produced on round-screen paper machines or on long-screen paper machines with dandy cutter. The watermark motif is located on the sieve of the round cylinder or, in the case of the fourdrinier, on the sieve of the egg cutter. One speaks of a watermark round screen or of a watermark Egoutteur.

On the watermark screen, the relief of the desired watermark is placed several times on the circumference and in the transverse direction ( Fig. 1 ), so that the paper produced with this dewatering screen has a corresponding multiplicity of watermarks in its entire production length.

The watermark is also already positioned in the finished paper so that it is in the further processing of the paper, for example, a security document or a banknote, at the designated Place in the final product ( Fig. 2 ).

In papermaking, pulp accumulates continuously on the moving dewatering screen. The watermark is created by the fibers attach differently to the watermark motif, which is in relief on the screen. At the deep places, more fibers are deposited than at the higher places. The fiber mass of the paper, which is increased at the lower points, appears darker in the view than the fiber-poor points of the higher relief points.

During the dewatering process, the paper pulp is solidified so far that it can be removed as a moist paper web from the dewatering screen. In the continuous process of the paper machine, the web is further dewatered in the press, dried and smoothed at the end of the machine and rolled up as dry paper.

Depending on the quality of the watermark in terms of its light-dark form, a distinction is made between the two-level watermark with a strong light-dark effect and multi-level (shaded) watermarks with smooth transitions between light and dark. The shaded (multilevel) watermark is the most advanced form of true watermark and is used primarily in pictorial representations. Due to the light or dark gradations pictorial representations with high "depth effect" can be generated. The term "multi-level" or "shaded" is to be understood in contrast to two-stage light-dark watermark and includes all watermarks with more than two brightness levels and includes in particular watermarks with continuous light-dark transitions.

Shaded (multi-level) watermarks are nowadays mainly produced on slow-speed round screening machines, whereas two-level watermarks are preferably produced on long-screen machines with dandy cutter. However, if the watermark relief on the dandy screen is correspondingly fine, it is also possible to produce simple shaded (multilevel) watermarks in the paper.

Typically, metal wires or metal moldings are soldered onto the dewatering screen (watermark round screen or watermark dicer) to seal the screen structure at these locations to obtain sharply demarcated two-level watermarks. Are these metal moldings without perforation for drainage, one speaks of electric types. The application of perforated metal moldings is also used today to create two-step watermarks with dark pixel dots on a light background (Pixel Watermark / Trademark).

The multilevel watermark screen, on the other hand, today is primarily produced by embossing a three-dimensional relief in the screen surface by means of an embossing stamp or embossing plate. The sieve material used are metallic sieves made of bronze, stainless steel, copper or other copper alloys.

The embossing tool consists of an elaborate metal mold with a negative and a positive relief. The drainage screen is placed between these two metallic plates. By firmly pressing the molds are transferred into the sieve.

The embossing process can only image and depict fine structures of an image to a limited extent in the watermark relief. This limitation results from the minimum possible embossing radii of the relatively thick screen. Thus, the resolution of the image representation in the watermark are also limited. In addition, the drainage resistance in the embossed area can not be specifically influenced, apart from the costly and limited influence of soldering on perforated moldings.

Another known possibility to produce a multilevel watermark screen is in the published patent application DE 10 2006 058 513 A1 described. In this case, the screen embossing is replaced by an injection-molded perforated insert. The injection-molded perforated relief can either be fastened on the drainage sieve or be arranged in a suitably cut-out region of the drainage sieve and be connected to it only in the edge region.

In this method, although clearly finer structures can be depicted in contrast to the embossing technique, the tool production for injection molds, the complex introduction into the sieve and the processing to produce the necessary for the drainage perforation are to be seen as disadvantages of this method.

Description of the invention

Based on the prior art, the present invention seeks to provide a dewatering screen of the type mentioned, which avoids the disadvantages of the prior art. In particular, the dewatering screen should allow the production of paper with multi-level watermark high detail accuracy with less tooling and high speed.

Dewatering screens with watermark relief produced in this manner should also be able to be used directly on the dewatering screen of long-screen paper machines (ie without dandy cutter), on oblique screen paper machines and short formers, in addition to the known applications on the dandy line of fourdrinier machines.

This object is achieved by the dewatering screen having the features of the independent claims. Several variants of the method for producing dewatering screens according to the invention, a watermark insert which is produced by means of 3D printing or a method belonging to rapid prototyping and a method for producing a paper with multistage watermark are specified and are subject matter of the subclaims.

A significant advantage over the prior art is that neither an embossing tool nor an injection mold for producing the watermark relief are required.

The basis of the invention is to convert a previously created on the computer three-dimensional CAD drawing, which is a solid model, by means of 3D printing or belonging to rapid prototyping method in a watermark insert. This "printed" 3D watermark relief replaces the embossed relief or other process used today.

In preferred embodiments of the invention, a solid model is created that allows watermark inserts including the drainage perforation and defined contact surfaces to be made with the wire.

In the following, the term 3D printing is generally used because this is the most commonly used generic term for rapid prototyping. In the process, CAD data is converted directly into a workpiece (here watermark insert), without manual detours or expensive forms. The object is built up layer by layer from informal or form neutral material. The basic idea behind this tool-less production is to generatively build an object from individual layers. Layer by layer, the shapeless material is solidified. The individual layers are connected with each other and gradually form the finished object. As a material, inter alia, plastics, synthetic resins, metals or ceramics can be used.

• selektive Lasersysteme, bei denen Kunststoff- oder Metallpulver schichtweise zu einem Element aufgebaut wird,
• Stereolithografie, bei der ein flüssiger Kunststoff schichtweise zum Modell aufgebaut wird,
• Multijet Printing, bei dem ein Polymer (Photopolymer) in Form extrem feiner Teilchen schichtweise aufgetragen wird und mit Licht (z.B. UV) nachgehärtet wird.

Typical rapid prototyping / 3-D printing processes are, for example

• selective laser systems in which plastic or metal powder is built up in layers to form an element,
• Stereolithography, in which a liquid plastic is built up layer by layer to the model,
• Multijet printing, in which a polymer (photopolymer) in the form of extremely fine particles is applied in layers and cured with light (eg UV).

In those process variants in which the watermark relief including the required dewatering perforation is produced, stereolithographic rapid prototyping methods have been found to be particularly suitable. These methods use liquid plastics (photopolymer) for the layered construction of the watermark relief. With this method, the required fine drainage structures can be formed. Furthermore, the light-curing plastics (UV light, or laser light) with respect to their material properties to the requirements of Trägeriebmaterials and the conditions of use in paper production in terms of stiffness, wear resistance and the non-positive connection to the support beam customizable.

Here are two methods of stereolithography, which are particularly addressed here. In the first case, the Reliefeinsatzerzeugung done in a bath, which is filled with the base monomers of the photosensitive (photosensitive) plastic. The relief is built in the bath layer by layer either on the support or independent of the support. In the second method belonging to stereolithography, the relief insert is produced analogously from a photopolymer. The material is applied layer by layer via a printhead (similar to an inkjet printer). In addition, a light source ensures exposure and thus curing of the polymers. This system often works with a wax as a support material, which is liquefied by heating. Both materials are applied simultaneously in layers.

According to a first aspect of the invention, in a dewatering screen of the type mentioned above, the multi-level relief is formed by means of 3D printing / rapid prototyping. The use according to the invention of 3D printing or of a method belonging to rapid prototyping permits the production of multi-level watermark inserts with extremely detailed relief images and without additional embossing or casting molds. With a correspondingly high print resolution, the drainage perforation of the watermark insert can also be produced in the same operation.

In a preferred variant of the invention, the watermark insert with the relief structure including the required perforation in one Operation made (printed).

There are now several ways to integrate the watermark relief thus formed into the dewatering screen.

In a variant of the invention, the watermark relief is printed directly on the dewatering screen ( Fig. 5a to Fig. 5d ). The plastic or metal sieve must be designed or prepared in such a way that a firm connection between the printed material and the sieve surface occurs. Roughening or the use of adhesion primer are mentioned here by way of example. But it is also possible to choose the nature of the materials to be joined (sieve and watermark insert) so that the pressure enters into a firm connection with the sieve without additional aids.

In an alternative, likewise advantageous variant of the invention, the watermark insert is produced independently of the screen and, in a further working step, welded to the carrier screen, fused, glued, positively connected or connected by means of mechanical connection (eg grid connection) ( Fig. 4a to 4d ).

In both variants, the watermark insert can be arranged in a cut-out region of the carrier screen and connected to it only in the edge region. It may be advantageous to scan the screen surface in the vicinity of the cut-out screen and / or the cut contour and to take this into account in the production of the insert in the 3D CAD models.

For all mentioned application variants, the watermark insert be introduced lowered compared to the general screening level. This can be done, for example, by embossing the screen ( Fig.4b, 4d . 5b, 5d and 6c ) can be achieved. It is also possible to print the watermark insert with the sieve cut out without a deeper sieve edge so that the maximum height of the watermark relief essentially corresponds to the sieve level ( Figure 6b ).

The pressure edge 12 can also be designed in the transition between sieve and watermark insert according to different criteria with respect to wear, drainage perforation ( Fig. 5a, 5b, 5c . 6c ). If the sieve is also cut out in the area of the depression so that only one lower edge remains in the sieve, the watermark insert is only connected to it ( Fig. 5d . 6c ). The circumference of the printing edge 12, whether with low material thickness ( Fig. 6b ) or filling the recessed edge area of the cut-out screen ( Fig. 4d . 5d ), depending on the operating conditions of the watermark screen are possible options.

Furthermore, the watermark insert preferably has a plurality of perforations (pores, bores, channels) or a material structure-related porosity, which ensure drainage during sheet formation. The open area may also be different in different areas of the relief and is typically between 10% and 90% open area, preferably 15% and 75%, more preferably between 25% and 40%.

The diameter of the perforation on the design side usually ranges from 0.15 mm to 1.3 mm, preferably from 0.2 mm to 0.5 mm, particularly preferably from 0.2 to 0.4 mm.

Preferably, the perforation openings taper towards the uppermost design surface of the watermark insert.

In the case of the perforations produced during printing, they can be designed in any shape, for. B. circular, star-shaped, oval, slit-shaped, etc. The perforation can be designed for this purpose in the Z-direction such that it extends from a circular opening in the design surface, for example, cone-shaped to a polygon at the bottom ( Fig. 7a and b). This results, for example, a honeycomb bearing surface with defined webs on the side facing the sieve of the watermark insert. The webs formed between the individual through holes are best suited as a connecting surface to the support.

The targeted design of the conical enlargement, which is only possible in 3-D printing / rapid prototyping, allows the pressure loss in the perforation openings to be influenced in a targeted manner. This is a prerequisite for the application on the closed screen surface, d. H. without cut out sieve surface. The manufacturing cost of the screen compared to the design with cut-out support screen is again lower.

The dimensions of the perforations can also be chosen so large (0.7 mm to 1.2 mm) that they are visually recognizable in the finished paper as dark marks, preferably marking points. In this case, it is advisable to arrange the perforations and thus the resulting markings in the form of characters, patterns or a coding.

If the perforation does not occur during the printing process, it will be retrofitted introduced in a separate operation using laser beam, drill, plasma cutting, water jet cutting, etc. The watermark relief may already be connected to the screen or the operation is performed outside in a position independent of the screen.

The perforations are preferably generated by means of a laser beam, in particular by means of an infrared laser, such as a CO ₂ laser. Preferably, the watermark insert is acted upon by its side facing away from the design surface back with laser radiation, so that there are tapered perforations to the design surface of the watermark insert.

Especially in those variants in which the perforation already occurs during printing, but also in the variant where the watermark insert is perforated in a separate operation, the transition from watermark insert to carrier screen in the finished paper can be laminated by the design of the drainage perforation. In the finished paper, the lamination is in the shape of the desired light-dark transition.

The invention also includes the process variants described below in accordance with claims 14, 15, 16, 17 and 18 for producing a dewatering screen for papermaking with multi-level watermarks.

1. a) ein Trägersieb bereitgestellt wird, und
2. b) der Wasserzeicheneinsatz mit einem mehrstufigen Relief in Form des zu erzeugenden Wasserzeichens einschließlich der erforderlichen Entwässerungsperforierung mittels 3D-Druck oder eines zum Rapid Prototyping gehörenden Verfahren schichtweise aus formlosem oder formneutralem Material direkt auf dem Trägersieb hergestellt (gedruckt) und mit diesem im selben Arbeitsgang verbunden wird. Optional kann das Trägersieb im Bereich des Wasserzeicheneinsatzes vertieft sein und/oder ausgeschnitten, wodurch der Einsatz nur am Rand mit diesem verbunden ist.

The method solution according to claim 14 is characterized in that

1. a) a carrier screen is provided, and
2. b) the watermark insert with a multi-level relief in the form of generating watermark including the required drainage perforation by means of 3D printing or belonging to rapid prototyping process layer by layer of informal or shape-neutral material directly on the support wire (printed) and connected to this in the same operation. Optionally, the support screen can be recessed in the region of the watermark insert and / or cut, whereby the insert is connected only at the edge with this.

1. a) ein Trägersieb bereitgestellt wird,
2. b) der Wasserzeicheneinsatz mit einem mehrstufigen Relief in Form des zu erzeugenden Wasserzeichens ohne der erforderlichen Entwässerungsperforierung mittels 3D-Druck oder eines zum Rapid Prototyping gehörenden Verfahren direkt auf dem Trägersieb erzeugt (gedruckt) und verbunden wird, und
3. c) die Perforierung des Wasserzeicheneinsatz vorzugsweise mittels Laserstrahl am Sieb erzeugt wird. Optional kann das Trägersieb im Bereich des Wasserzeicheneinsatzes vertieft sein und /oder ausgeschnitten, wodurch der Einsatz nur am Rand mit diesem verbunden ist.

The method solution according to claim 15 is characterized in that

1. a) a carrier screen is provided,
2. b) the watermark insert with a multi-level relief in the form of the watermark to be generated without the required drainage perforation by means of 3D printing or rapid prototyping associated method directly on the support screen is generated (printed) and connected, and
3. c) the perforation of the watermark insert is preferably produced by means of a laser beam on the screen. Optionally, the support screen can be recessed in the region of the watermark insert and / or cut, whereby the insert is connected only at the edge with this.

1. a) ein Trägersieb bereitgestellt wird,
2. b) ein separater Wasserzeicheneinsatz mit einem mehrstufigen Relief in Form des zu erzeugenden Wasserzeichens einschließlich der erforderlichen Entwässerungsperforierung mittels 3D-Drucker oder eines zum Rapid Prototyping gehörenden Verfahren hergestellt wird, und
3. c) der Wasserzeicheneinsatz mit dem Trägersieb verschweißt, verschmolzen, verklebt, formschlüssig oder mittels mechanischer Verbindung (z.B. Rasterverbindung) verbunden wird.

The method solution according to claim 16 is characterized in that

1. a) a carrier screen is provided,
2. b) a separate watermark insert having a multi-level relief in the form of the watermark to be generated, including the required dewatering perforation by means of a 3D printer or a rapid prototyping method, is manufactured, and
3. c) the watermark insert welded to the support screen, fused, glued, positive or by mechanical connection (eg Grid connection) is connected.

Optionally, the support screen can be recessed in the region of the watermark insert and / or cut, whereby the insert is connected only at the edge with this.

1. a) ein Trägersieb bereitgestellt wird,
2. b) ein separater Wasserzeicheneinsatz mit einem mehrstufigen Relief in Form des zu erzeugenden Wasserzeichens ohne der erforderlichen Entwässerungsperforierung mittels 3D-Drucker oder eines zum Rapid Prototyping gehörenden Verfahren hergestellt wird,
3. c) die Perforierung des Wasserzeicheneinsatz vorzugsweise mittels Laserstrahl in einem eigenen Arbeitsgang erzeugt wird, und
4. d) der Wasserzeicheneinsatz nachträglich mit dem Trägersieb verschweißt, verschmolzen, verklebt, formschlüssig oder mittels mechanischer Verbindung (z.B. Rasterverbindung) verbunden wird. Optional kann das Trägersieb im Bereich des Wasserzeicheneinsatzes vertieft sein und/ oder ausgeschnitten, wodurch der Einsatz nur am Rand mit diesem verbunden ist.

The method solution according to claim 17 is characterized in that

1. a) a carrier screen is provided,
2. b) a separate watermark insert having a multi-level relief in the form of the watermark to be produced is produced without the required dewatering perforation by means of a 3D printer or a method belonging to rapid prototyping,
3. c) the perforation of the watermark insert is preferably generated by means of a laser beam in a separate operation, and
4. d) the watermark insert is subsequently welded to the carrier screen, fused, glued, positively connected or by means of a mechanical connection (eg grid connection). Optionally, the support screen can be recessed in the region of the watermark insert and / or cut, whereby the insert is connected only at the edge with this.

• a) ein Trägersieb bereitgestellt wird,
• b) ein separater Wasserzeicheneinsatz mit einem mehrstufigen Relief in Form des zu erzeugenden Wasserzeichens ohne der erforderlichen Entwässerungsperforierung mittels 3D-Druck oder eines zum Rapid Prototyping gehörenden Verfahren hergestellt wird,
• d) der Wasserzeicheneinsatz mit dem Trägersieb verschweißt, verschmolzen, verklebt, formschlüssig oder mittels mechanischer Verbindung (z.B. Rasterverbindung) verbunden wird und
• c) die Perforierung des Wasserzeicheneinsatzes vorzugsweise mittels Laserstrahl in einem eigenen Arbeitsgang an dem im Sieb fixierten Wasserzeicheneinsatz erzeugt wird. Optional kann das Trägersieb im Bereich des Wasserzeicheneinsatzes vertieft sein und oder ausgeschnitten, wodurch der Einsatz nur am Rand mit diesem verbunden ist.

The method solution according to claim 18 is characterized in that

• a) a carrier screen is provided,
• b) a separate watermark insert having a multi-level relief in the form of the watermark to be produced is produced without the required drainage perforation by means of 3D printing or a method belonging to rapid prototyping,
• d) the watermark insert welded to the support screen, fused, glued, positive or by mechanical connection (eg Grid connection) is connected and
• c) the perforation of the watermark insert is preferably generated by means of a laser beam in a separate operation on the fixed in the screen watermark insert. Optionally, the support screen can be recessed in the region of the watermark insert and or cut, whereby the insert is connected only at the edge with this.

The invention further includes a watermark insert for a dewatering screen of the type described, wherein the watermark insert is a 3D printed / rapid prototyped perforated insert having a multi-level relief in the form of the watermark to be formed.

embodiment

The invention will be explained in more detail below with reference to several embodiments.

Fig. 1

ein Rundsiebzylinder mit aufgezogenem Entwässerungssieb, welches als Trägersieb für die Wasserzeicheneinsätze dient,

Fig. 2

eine schematische Darstellung einer Banknote mit einem mehrstufigen Wasserzeichen hoher Detailschärfe,

Fig. 3

in a und b einen in einem Trägersieb fixierten Wasserzeicheneinsatz. In a als Aufsicht und in b den Querschnitt des mit dem Siebgewebe eines Trägersiebs im Randbereich des ausgeschnittenen Siebes verbundenen, perforierten Wasserzeicheneinsatzes (Perforation nicht dargestellt).

Fig. 4

in a bis d vier mögliche Varianten, um einen Wasserzeicheneinsatz mit einem mehrstufigen Relief in Form des zu erzeugenden Wasserzeichens mittels 3D-Druck oder eines zum Rapid Prototyping gehörenden Verfahren unabhängig vom Trägersieb herzustellen und nachträglich mit dem Sieb zu verbinden (Perforation nicht dargestellt), in (a) auf das geschlossene Trägersieb, in (b) auf ein Trägersieb mit Vertiefung, in (c) auf ein Trägersieb mit ausgeschnittenem Sieb in Form des Wasserzeicheneinsatzes, in (c) auf ein Trägersieb mit ausgeschnittenem Sieb in Form des Wasserzeicheneinsatzes, in (d) auf ein Trägersieb mit Vertiefung und mit ausgeschnittenem Sieb in Form des Wasserzeicheneinsatzes,

Fig. 5

in a bis d vier mögliche Varianten, um einen Wasserzeicheneinsatz mit einem mehrstufigen Relief in Form des zu erzeugenden Wasserzeichens, mittels 3D-Drucker oder eines zum Rapid Prototyping gehörenden Verfahren direkt auf das Sieb zu "Drucken" (Perforation nicht dargestellt), in (a) auf das geschlossene Trägersieb, in (b) auf ein Trägersieb mit Vertiefung, in (c) auf ein Trägersieb mit ausgeschnittenem Sieb in Form des Wasserzeicheneinsatzes, in (d) auf ein Trägersieb mit Vertiefung und mit ausgeschnittenem Sieb in Form des Wasserzeicheneinsatzes,

Fig. 6

in a bis c im Querschnitt: drei auf einem Trägersieb fixierte Wasserzeicheneinsätze einschließlich der Perforierung (nicht maßstäblich). In a ein auf dem Sieb, deutlich erhaben gegenüber dem Siebniveau, aufgebrachten Einsatz, in b ein Wasserzeicheneinsatz bei dem der Wasserzeicheneinsatz gegenüber dem Ausführungsbeispiel Fig. 6 a in einem ausgeschnittenen Bereich des Siebes angebracht ist und der Einsatz deutlich gegenüber dem Siebniveau abgesenkt ist, in Fig. 6c ein in einer Siebvertiefung ohne ausgeschnittenem Sieb aufgebrachter Wasserzeicheneinsatz, bei dem das Relief gegenüber dem allgemeinem Siebniveau abgesenkt ist.

Fig. 7

in a einen Querschnitt und b eine Aufsicht eines Wasserzeicheneinsatzes mit spezieller wabenförmiger Perforierung,

Fig. 8

einen Querschnitt einer Variante eines im Entwässerungssieb eingebrachten Wasserzeichensatzes,

Fig. 9

einen Ausschnitt aus einem Volumenmodell,

Fig. 10

einen Ausschnitt eines typischen Siebes.

Show it:

Fig. 1

a round cylinder with attached drainage sieve, which serves as a carrier screen for the watermark inserts,

Fig. 2

a schematic representation of a banknote with a multilevel watermark of high detail,

Fig. 3

in a and b a fixed in a support wire watermark insert. In a as a plan view and in b the cross-section of the perforated watermark insert connected to the screen fabric of a carrier screen in the edge region of the cut-out screen (Perforation not shown).

Fig. 4

in a to d four possible variants to produce a watermark insert with a multi-level relief in the form of the watermark to be generated by 3D printing or belonging to rapid prototyping method regardless of the support and subsequently connected to the screen (perforation not shown), in (a) on the closed carrier screen, in (b) on a carrier screen with recess, in (c) on a carrier screen with cut-out screen in the form of the watermark insert, in (c) on a carrier screen with cut-out screen in the form of the watermark insert, in ( d) on a carrier screen with recess and with cut-out screen in the form of the watermark insert,

Fig. 5

in a to d four possible variants, to a watermark insert with a multi-level relief in the form of the watermark to be generated by means of 3D printer or rapid prototyping process directly on the screen to "print" (perforation not shown), in (a (b) on a carrier screen with recess, in (c) on a carrier screen with cut-out screen in the form of the watermark insert, in (d) on a carrier screen with recess and with cut-out screen in the form of the watermark insert,

Fig. 6

in a to c in cross-section: three watermark inserts fixed on a support screen including the perforation (not to scale). In a a on the sieve, clearly sublime opposite the sieve level, applied insert, in b a watermark insert in which the watermark insert over the embodiment Fig. 6 a is mounted in a cut out area of the screen and the insert is lowered significantly above the screen level, in Fig. 6c a watermark insert applied in a sieve recess without a cut-out sieve, in which the relief is lowered relative to the general sieve level.

Fig. 7

a is a cross section and b is a plan view of a watermark insert with a special honeycomb perforation,

Fig. 8

a cross section of a variant of an introduced in Entwässungssieb watermark set,

Fig. 9

a section of a solid model,

Fig. 10

a section of a typical sieve.

The invention will be explained below using the example of a banknote. Fig. 2 shows a representation of a banknote 15, the multi-level watermark 16 high detail sharpness in the form of an in Fig. 2 contains only suggested portraits. The production of banknotes with such detail-sharp multilevel watermarks is carried out according to the invention using one of the dewatering screens described below with watermark inserts generated on the 3D printer. Fig. 1 shows how the Entwässungssieb (support wire) 11 is mounted, for example, on a cylinder mold 10 through which the dehydration takes place and the initialized paper web is formed with the watermark.

The watermark motif is located as a watermark insert 13 on the screen of the cylinder. On the watermark screen, the relief of the desired watermark is placed multiple times on the circumference and in the transverse direction, thus, the paper produced with this dewatering screen has a corresponding plurality of watermarks in its entire production length.

The watermark is also already positioned in the finished paper in such a way that it is located at the designated place in the end product during the further processing of the paper, for example to a security document or a banknote ( Fig. 2 ).

In a first, with respect to the Fig. 4a to d described variant of the invention, separate watermark inserts are first produced by means of 3D printing or a process belonging to rapid prototyping. These are, as already described in the process variants according to claims 16, 17 and 18, welded to the support wire, fused, glued, positively connected or by mechanical connection (eg grid connection).

The resulting watermark insert 13, which in Fig. 3a in supervision and in Fig. 3b is shown in cross-section, shows a very detailed illustration of the predefined as 3-D volume model CAD image motif.

As in Fig. 3 and in the following figures, however, the cross section of the detailed relief is shown only schematically by a curved line.

In Fig. 4a the watermark insert is connected to a sieve. In FIG. 4b The insert is placed in a sieve recess. Fig. 4c and 4d show corresponding variants with cut-out strainer.

In further, with reference to the Fig. 5a to d In the variants of the invention described, the watermark inserts are produced directly on the screen by means of 3D printing or a method belonging to rapid prototyping and connected thereto. The procedure for producing the watermark inserts is already described in the above-mentioned further variants of the method.

In Fig. 5a the watermark insert is "printed" on a flat screen. In Fig. 5b the insert is printed in a screen recess. Fig. 5c and 5d show corresponding variants with cut-out strainer.

In all variants, it is advantageous to scan the screen surface, the indentation in the screen or the vicinity of the cut screen and / or the cutting contour, and to consider these in the 3D CAD models during manufacture of the insert. In this way, a watermark insert can be made to fit the sieve cut or screen recess or it is possible to adapt the webs of the perforation of the screen structure.

The 3D printing / rapid prototyping allows the production of extremely detailed relief representations in the watermark inserts 13. Although always only the design surface 14 is shown with a shape in the figures, of course, with appropriate design of the CAD model, the back 15 a shape accordingly have a scanned surface, so that, for example, a watermark insert with the surface structure of the support screen or a use of certain material thickness arises

The pictures of the perforated watermark inserts in Fig. 3 . Fig. 4 and Fig. 5 are shown without perforation.

The perforation holes of the watermark inserts required for dewatering in papermaking arise, as already described in claim 14, 15, 16, 17 and 18, either when printing the watermark insert or these are subsequently introduced in a separate operation on the screen or outside the screen ,

The generation of the perforation of the watermark inserts in the "print" is possible only in conjunction with correspondingly high-resolution 3D printing, since the diameter of the perforation on the design surface about 0.1 mm to 0.7 mm, preferably 0.2 mm to 0.7 mm. The diameter as well as the hole spacing can vary within a relief. Due to the resulting different free surface shading in the watermark is specifically influenced.

The in cross section ( Fig. 6a, 6b, 6c ) drainage perforations 20 are, for example, designed such that their diameters taper from the screen support surface (underside) to the design surface. In this way it is ensured that the drainage resistance, which results from sieve and watermark insert, is not unduly increased. In this way, a sufficient drainage performance even when applying the insert on a sieve surface, as in the example Fig. 6a and Fig. 6c represented, guaranteed. It is also conceivable to provide the screen in partial areas with openings.

The perforation can also, as in Fig. 7a and b be designed such that the perforation openings in the design surface, for example, are round and widen conically to a polygon. The webs 30 formed between the individual through holes are best suited as a contact surface to the screen. This applies both in the case of the watermark insert printed on the screen, as well as for the insert welded to the screen, fused, glued, positively connected or by means of a mechanical connection (eg grid connection). The production of such complex through holes is possible only in 3-D printing.

It is also possible to adjust the screen structure by laser perforation in advance of the perforation structure of the insert.

In the case of subsequently produced perforations, this is done by water jet or laser. The dewatering perforations are advantageously drilled with a laser beam, for example the beam of a CO ₂ laser. The focus diameter of the laser corresponds to the desired maximum perforation diameter and is for example 500 microns. The laser irradiation is preferably carried out from the back of the watermark insert 13, so that due to the energy distribution or the heat of the laser beam to the front side surface 14 of the insert tapered perforations 20 arise, as in Fig. 6 (b) shown. The design options of the through holes are compared to the 3-D pressure, however, very limited.

In specific embodiments, in areas with a high local material thickness, the perforation can be dispensed with, at least in part, so that in these areas, in principle, only little or no dehydration takes place, and only very few or no paper fibers are deposited. In these areas, a two-level watermark or a hole is thus created in the paper. The non-perforated areas with high Material thickness act like electric types in this case. With such an application, detailed watermarks can be combined with two-level watermarks.

In the embodiment of Fig. 6a to c the diameter of the perforations on the back 15 of the watermark insert is between 0.2 mm and 1.8 mm. The diameter at the design surface 14 is dependent on the local material thickness of the insert for laser drilled perforations because of the tapering of the perforations. As in Fig. 3 (b) As can be seen, the perforation diameter d at the design surface 14 in regions of greater material thickness 17 is smaller than in regions of low material thickness 18. For example, the perforation diameters of laser drilled passage perforations on the design surface 14 are between 150 .mu.m with high material thickness and 350 .mu.m with low material thickness. In the case of "printed" perforation openings, the diameter corresponds to the design specification and is variable within wide ranges.

The perforations 20 tapering towards the design surface offer two advantages over straight perforations: On the one hand, they create a freewheel in the direction of flow of the fiber suspension in papermaking and thus effectively prevent a permanent clogging of the drainage perforations.

On the other hand, the areas of high material thickness 17 serve to produce thin areas in the paper. Since the smaller perforation diameters in these areas inhibit drainage more than in the low gauge areas 18, thinning in the areas is further assisted by the tapered perforations.

The distance of the perforations depends on the desired dewatering effect and is for example about 500 microns.

The perforation diameter can also be chosen so large that they are recognizable after paper production in paper in addition to the watermark as a dark marker points. The hole diameter for producing dark marking points is preferably at least 300 μm.

These dark spots can serve as an additional security feature and / or as a recognition feature for the manufacturing process used. The perforations and thus the marking points can also be arranged in a predetermined pattern. For example, the perforations that result in dark spots in the paper may be arranged in a pattern that can be seen, for example, as a score within the pictorial representation.

Coming back to the in Fig. 4 and Fig. 5 possible manufacturing variants of the watermark screen with "printed" watermark insert, almost any screen suitable for paper production (single or multi-layer) as a support screen for a "printed" watermark insert is conceivable. According to the invention, the screen fabric may be a metal fabric, in particular a bronze fabric, a metal-plastic mixed fabric, in particular a bronze-plastic mixed fabric or a pure plastic fabric.

If a bronze sieve is used as the carrier screen 11, then the watermark insert 13 is permeable to perforations by means of a laser beam only at those points at which a perforation of the insert 13 coincides with an open position in the screen 11, since the bronze screen itself is separated from the screen CO ₂ laser is not perforated, another advantage to "print" the perforation.

In order to reduce the wear of the watermark insert 13 in papermaking, the watermark height h, which in the embodiment of FIGS Fig. 6a about 1.0 mm. As in Fig. 6b or 6c shown, the watermark insert 13 can be lowered so far that its maximum height h just corresponds to the screen level. In addition to a reduced wear of the watermark inserts, this reduction leads to watermarks, which at a consistently high contrast to the design of the Fig. 3b or Fig. 6a have a slightly darker visual appearance.

In Fig. 8 a further variant is shown to introduce a watermark insert (13) in a dewatering screen. The support screen is integrated in this case in a Entwässerungssiebverbund. This consists of the fine-mesh sieve (11), a cut-out intermediate sieve (31) and a support sieve (32). The fine strainer is also cut out and provided with a deep embossing in the edge area. As a result, the upper edge of the watermark insert when installed is approximately level with the sieve. The watermark insert also has a circumferential raster connection (33) on the underside. This can be carried out in one or more stages and optionally also be supported by gluing.

In order to ensure the positional accuracy and positional stability of the watermark insert, the insert may have nubs (34) at the bottom which correspond to the screening of the support screen structure and thus engage in the screen interstices of the support screen. These nubs have the same perforation holes with the same perforation structure like the watermark insert. Thus, a sufficient drainage performance is guaranteed in the nubs. The watermark insert can be welded to the support screen via the knobs, fused, glued, positively connected or connected by means of a mechanical connection (eg grid connection). These pimples also prevent a shifting of the watermark insert.

Based on FIGS. 9 and 10 a preferred embodiment of the invention will be described. It creates a solid model that makes it possible to make watermark inserts, including the drainage perforation and defined contact surfaces with the wire.

By default, the starting point for making a watermark insert is a solid model constructed in CAD. The image of the watermark to be generated is generated as a "grayscale model" with fine light-dark shades. The gray levels are then translated into height nodes for the volume model and determine the thickness of the solid model at the appropriate locations. This procedure corresponds to the current procedure for the production of embossing dies or injection molds.

According to the invention, the volume model still fulfills the following two requirements. The perforations required for drainage are part of the solid model and are included in the CAD. Furthermore, the surface on which the watermark insert is applied or printed, part of the solid model, ie, the volume model represents the screen surface as a negative image of the screen at the bottom in the area of contact surface between the screen and watermark insert.

In the CAD model, these three prerequisites are linked by functions. These can also be designed as "variant programs".

Fig. 9 shows a small section 90 (width b = 2.5mm, length 1 = 2.5mm) of a solid model to a watermark insert. For the sake of simplicity, the complex surface 91 is represented by a corrugated surface. In the case shown, the thickness C of the volume element is limited by a flat surface on the underside and said corrugated surface on the upper side.

This illustration also shows the perforation. These are tapered through-pores 92, which taper to the surface of the watermark insert. The mean cone diameters are of the order of about 0.3 mm to 0.5 mm. Depending on where the tips of the cones are cut by the corrugated surface contour, resulting in larger or smaller through holes. In the illustrated volume model, all cones are the same in terms of height and base diameter. Variants with polygonal cones or with cones of different heights or different base areas are possible. This results in the possibility of varying the open area at the top of the watermark insert in the entirety or locally.

Fig. 10 shows a section 11 of a typical sieve (width B = 5mm, length L = 7.5 mm) with its surface structure. To print directly on such a surface, it is advantageous to consider the illustrated surface in the solid model at the interface between watermark insert and screen in the CAD model. This applies both to a full-surface applied watermark relief as well as in the event that the relief is placed in a cut-out area of the screen. in the In the latter case, the sieve surface will only find itself in the area of the overlap between sieve and insert. In the cut-out area of the screen, the underside of the watermark insert can be a flat surface or even have the screen structure or another design.

In the prior art, watermark inserts are produced by injection molding and subsequently perforated by means of laser. The perforation is not a constructional element in terms of its shape. The resulting passage perforations essentially depend on the power of the laser used and can therefore be influenced only to a limited extent in terms of their shape. Likewise, the introduction of the watermark element in the Sieboberfläche takes place without consideration of the Sieboberfläche. The anchoring of the watermark insert is done arbitrarily by the flow of the liquefied material in the screen structure. According to the invention, these disadvantages are avoided.

Claims (29)

Entwässerungssieb for the production of paper with multi-level watermark, with a support screen, which has a multi-level relief in the form of the watermark to be generated in a sub-area, characterized in that the multi-level relief produced by a means of 3D printing or belonging to the rapid prototyping method , perforated watermark insert is formed. Entwässerungssieb according to claim 1, characterized in that the watermark insert welded to the support wire, fused, glued, positively connected or by mechanical connection (eg grid connection) is connected. Entwässerungssieb according to claim 1 or 2, characterized in that the watermark insert is printed directly on the support screen. Entwässerungssieb according to at least one of claims 1 to 3, characterized in that the watermark insert is located in a Siebvertiefung. Drainage screen according to at least one of claims 1 to 4, characterized in that the watermark insert is arranged in a cut-out region of the carrier screen and is connected thereto only in the edge region. Entwässerungssieb according to claim 4 or 5, characterized in that the maximum height of the watermark insert substantially corresponds to the screen level. Drainage screen according to at least one of claims 1 to 6, characterized in that the dewatering screen made of plastic, metal or combinations of both materials as a carrier screen for the watermark insert. Entwässerungssieb according to at least one of claims 1 to 7, characterized in that the watermark insert is made of any material suitable for the 3D printing or rapid prototyping method suitable material. Entwässerungssieb according to at least one of claims 1 to 8, characterized in that the watermark insert perforations having a diameter between 0.10 mm to 2.0 mm. Entwässerungssieb according to claim 9, characterized in that the perforations have different diameters in different areas of the watermark insert. Entwässerungssieb according to claim 9 or 10, characterized in that the watermark insert has an open area between 10% and 90%. Entwässerungssieb according to claim 10 or 11, characterized in that the perforations taper towards the overhead design surface of the watermark insert. Drainage screen according to claim 12, characterized in that the perforation openings extend from a round opening in the design surface to a polygon at the bottom. A method for producing a multistage watermark dewatering screen for papermaking according to claim 1, characterized in that a) a carrier screen is provided and b) the watermark insert with a multi-level relief in the form of the watermark to be generated including the required Entwässerungsperforierung by 3D printing or belonging to rapid prototyping process layers of informal or form neutral material directly on the support wire produced (printed) and connected to this in the same operation becomes. A method for producing a multistage watermark dewatering screen for papermaking according to claim 1, characterized in that a) a carrier screen is provided, b) the watermark insert with a multi-level relief in the form of the watermark to be generated without the required drainage perforation by means of 3D printer or belonging to rapid prototyping method directly on the support wire is generated (printed) and connected and c) the perforation of the watermark insert is preferably produced by means of a laser beam on the screen. A method for producing a multistage watermark dewatering screen for papermaking according to claim 1, characterized in that a) a carrier screen is provided, b) a separate watermark insert with a multi - level relief in the form of the watermark to be generated, including the required dewatering perforation is produced by means of 3D printing or a process belonging to rapid prototyping, and c) the watermark insert is welded to the carrier screen, fused, glued, positively connected or by means of mechanical connection (eg grid connection) is connected. A method for producing a multistage watermark dewatering screen for papermaking according to claim 1, characterized in that a) a carrier screen is provided, b) a separate watermark insert with a multi-level relief in the form of the watermark to be produced is produced without the required dewatering perforation by means of a 3D printer or a method belonging to rapid prototyping, c) the perforation of the watermark insert is preferably generated by means of a laser beam in a separate operation and d) the watermark insert is subsequently welded to the carrier screen, fused, glued, positively connected or by means of a mechanical connection (eg grid connection). A method for producing a multistage watermark dewatering screen for papermaking according to claim 1, characterized in that a) a carrier screen is provided, b) a separate watermark insert having a multi-level relief in the form of the watermark to be produced is produced without the required dewatering perforation by means of a 3D printer or a method belonging to rapid prototyping, c) the watermark insert is welded to the carrier screen, fused, glued, positively or by means of mechanical connection (eg grid connection) is connected and d) the perforation of the watermark insert is preferably generated by means of a laser beam in a separate operation on the insert fixed in the screen. Method according to one of claims 14, 15, 16, 17 or 18, characterized in that the watermark insert is applied to a carrier screen in such a way that the maximum height of the watermark insert is significantly above the screen level. A method according to claim 19, characterized in that the watermark insert is applied to a support screen in a recess corresponding approximately to the watermark size in the screen such that the maximum height of the watermark insert is either below, at or above the screen level. Method according to one of claims 14, 15, 16, 17 or 18, characterized in that the watermark insert is arranged in a cut-out region of the carrier screen and is connected to it only in the edge region. Method according to one of claims 14, 15, 16, 17 or 18, characterized in that the dewatering screen consists of plastic, metal or combinations of both materials as a carrier screen for the watermark insert. A method according to any one of claims 14, 15, 16, 17 or 18, characterized in that the watermark insert is from each one for 3D printing or a material suitable for rapid prototyping. A method according to claim 17 or 18, characterized in that the perforations are generated by means of a laser beam, preferably by means of an infrared laser. Method according to one of claims 14, 15, 16, 17 or 18, characterized in that the watermark insert is provided with a plurality of perforations having a perforation diameter of 0.1 mm to 2.0 mm. A method according to claim 25, characterized in that the perforations to the uppermost design surface of the watermark insert are made to taper. A method according to claim 14 and 26 or 16 and 26, characterized in that the perforation openings extend from a round opening in the design surface to a polygon at the bottom. Method according to at least one of claims 14 to 27, characterized in that the perforation of the watermark insert is produced during the production of the 3D relief. Method according to at least one of claims 14 to 27, characterized in that the perforation of the watermark insert is produced in a separate operation.

Images