ES2691231T3 - Watermark formation element - Google Patents

Abstract

A watermark forming element (20) for forming at least one watermark on a paper, said watermark forming element (20) having an integrated body comprising a watermark forming surface (21 ), having one or more watermarking zones, and a drainage surface (25), said watermarking element (20) having a plurality of drainage channels extending from surface openings front openings on the watermarking surface (21) to the drainage surface (25), characterized in that each front surface opening on the watermarking surface has a rounded rim (26).

Description

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DESCRIPTION

Watermark formation element

The present invention relates to a watermark forming element for forming watermarks on paper, a cylinder mold cover comprising such a watermark forming element, a method of manufacturing a water cover. cylinder mold of this type, a papermaking method using a cylinder mold cover of this type and paper manufactured in this way.

The use of watermarks is quite common in many security documents. High security multitonal watermarks are usually created using a cylinder mold process and are commonly known as cylinder mold watermarks. Cylinder mold watermarks are formed by varying the density of the paper fibers, so that in some areas the fibers are denser, and in others less dense, than that of the base paper layer that surrounds and separates the denser and less dense areas. When viewed with transmitted light, the less dense areas are lighter and the denser areas darker than the base paper and contrasts can be seen very clearly. Different types of watermarks have different advantages. A cylinder mold watermark, normally formed in a embossed cylinder mold cover, is often a pictorial image, such as a portrait, and can be very detailed and complex, which significantly reduces the risk of forgery .

In the manufacture of paper with a cylinder mold, the paper is formed in a mold cylinder covered with partially submerged wire cloth, which rotates in a bowl containing a pulp comprising a diluted suspension of paper fibers. As the mold cylinder rotates, water passes through the wire net by depositing fibers on the surface of the cylinder. When the metal fabric of the cylinder mold cover is embossed, the fibers are deposited with a greater or lesser thickness on the raised and sunken elements, respectively, of the embossing to form a three-dimensional watermark on the paper finish.

The variation of paper thickness in the final watermark is the result of the movement of fibers from the raised areas of the embossed mesh to the sunken areas of the embossed mesh as water passes through the fabric metallic The movement of fibers and, therefore, the tonal variation in the watermark, is governed by the drainage speed and depends on the profile of the embossing. This allows excellent control in the gradation of the watermark pattern, producing a subtle tonal range that is exclusive to the embossed cylinder mold watermark process.

Traditional embossed cylinder mold watermarks have to be made within the constraints imposed by the physical properties of the wire mesh. Embossing the metal fabric of the cylinder mold cover reduces its strength and increases the risk of damaging the mold cover and the paper during the papermaking process. This is especially the case if there is a sharp transition from a deep embossing area to a significantly elevated area. In addition, within a complex pictorial watermark it is difficult to juxtapose a very light tone next to a very dark tone due to the tensions that this would cause in the mold cover itself during embossing. The limit of the "verticality" of a side wall within an embossing is approximately 70% to avoid these problems. However, the more vertical the side wall is, the sharper the image will be, since there is a greater contrast between a light and a dark area. One way to avoid these problems is to use a cut in the stamping die

in relief, which provides the space for deformation of the wire netting. However, it is often very difficult

adjust the image of the watermark to provide such cuts.

The image resolution of the watermark is also limited by the roughness of the fabric mesh

metallic In addition, the metallic fabric overlaps with a mark on the paper as a result of being a woven structure. This can also detract from the resolution and clarity of the watermark image.

Some of these limitations can be reduced by using a thinner wire, but this leads to a reduction in the durability of the mold cover since the thinner wires wear out more quickly.

It is also very difficult to produce areas of clear watermarks that show a significant surface area using the embossed cylinder mold technique.

An alternative process for generating tonal zones of uniform light (and providing improved watermark security) is the electrotyping process. In the electrotyping process, a thin piece of metal, generally in the form of an image or letter, is applied to the metal fabric of the cylinder mold cover, usually by sewing or welding. Electrotyping creates a significant decrease in drainage and fiber deposition and, therefore, forms a clear watermark on the paper. An electrotypic watermark produced in this manner may be clearer than the lighter areas of an embossed cylinder mold watermark. The electrotyping process is well known in papermaking and has been described, for example, in US-B-1901049 and US-B-2009185.

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Therefore, an electrotypic watermark is an area of paper that has only a uniform decrease in paper thickness. Usually, the area is quite small and the change in paper thickness (fiber density) is very different in order to create very clear areas. The electrotyping process is limited because if the electrotype is too large this can produce a hole in the paper. The usual width of the electrotype is between 0.2 and 1.2 mm and the thickness is between 500 and 700 pm, to avoid these problems.

The two types of watermarks mentioned above have security advantages (anti-counterfeiting) and have been the backbone of paper safety for hundreds of years. However, both can be compromised and, as with all security devices, it is necessary to improve them. One approach is to provide increasingly complex and technically demanding designs.

Such complex designs may require the combination of embossed and electrotypic embossed cylinder mold watermarks, or areas of watermarks, in the same design. For example, electrotypes have been used to produce very clear enhancement points within a watermark of embossed cylinder mold. An example of this is an animal head shaped watermark, in which the bright eyes of the lion are electrotypic watermarks. In transmission, the eyes will appear significantly brighter than the parts of the watermark produced by embossing and, therefore, will provide a level of contrast that normally cannot be achieved only with a watermark embossed.

A problem with the integration of an electrotypic watermark into an embossed embossed cylinder mold watermark is found in the difficulty of attaching the electrotype to the undulating embossed area of the cylinder mold wire mesh. The specific area to which the electrotype is attached must be flat, which of course is problematic within an undulating structure. However, the process for placing an electrotype within the embossed area of the wire netting is very difficult. Normally a reinforced platform, or other form of support, is required, while the electrotype is welded to the metal fabric, to avoid deformation of the metal fabric and, therefore, embossing. Any deformation can make the watermark design compromised. However, it often happens that it is difficult to provide adequate support due to the nature of embossing.

The addition of an electrotype to an embossed cylinder mold cover is also a time-consuming process. This increases the time to produce the cylinder mold cover for production, and the cost thereof. The process for producing cylinder mold covers for embossed cylinder mold watermarks is already long. Once the illustration has been created, this should become a program that operates a milling machine to produce embossing dies. Embossing dies are then used to emboss the wire mesh.

As an alternative to the use of electrotypes for the production of enhancement points in a cylinder mold watermark, it is possible to close the mesh openings in certain areas to prevent drainage. However, this does not create the sharpness of contrast that is possible with electrotypes.

In general, a cylinder mold machine is used to make one or more paper bands. Subsequently, the band is divided into intermediate sheets of paper and then divided into smaller sheets to make documents. The length of the cylinder mold cover, on which the paper is formed, is determined by the number of bands produced, where the width of each band corresponds to the width of an intermediate sheet. Usually, the length will be such as to produce three bands. The circumference of the cylinder mold cover is equivalent to the length of a number of intermediate sheets. As a non-limiting example, there may be three bands and six intermediate sheets, whereby the surface area of the cylinder mold cover would correspond to the surface area of 18 (3 x 6) intermediate sheets. Since each intermediate sheet is subsequently divided into a plurality of smaller security documents, the number of watermarks produced on each intermediate sheet must be such as to produce the necessary watermarks on each of the finished documents. Therefore, a usual mold cover could have embossed prints / electrotypes for approximately 700 documents.

However, it may be convenient for each of the bands to have different watermarks. This allows production in a single manufacturing run of, for example, all pages for a passport that have different watermarks on each page. The requirement of different watermarks in different bands adds complications to the manufacture of the cylinder mold cover, due to the difficulty of placing them in a robotic manner. This also significantly increases the cost, due to the cost of manufacturing individual dies or electrotypes for each variant.

In order to maximize the difference between the light and dark areas of a watermark formed by the profiled surface of the embossed prints, it is desirable to control the drainage in both the elevated and sunken areas of the embossing. This is currently achieved in elevated areas by reducing the drainage speed (i.e., the rate at which water passes through the wire net during the forming process), usually by placing an impermeable element, such as a metal plate or a plastic element, below the innermost layer of the metal fabric. The fabric structure of the wire net follows

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allowing water to drain laterally through it, although at a reduced speed. However, the radial drain is blocked by the impermeable element.

In sunken areas, control is achieved by increasing the general drainage rate, for example, by applying a vacuum to the cylinder mold, or by starting the drainage process below the level of the material, for example using a mold curtain. Another method is to increase the stamping depth of the forming surface. However, this makes the mold cover more vulnerable to damage and can cause difficulties in releasing partially formed paper on the felt (formex) that transports the paper from the wet end of the papermaking machine to the section Press

None of these solutions is very effective. The restriction of wire drainage is limited by the side drain resulting from the three-dimensional structure of the wire net. The application of vacuum and mold curtain affect the elevated and sunken areas simultaneously, which makes them coarse tools for selective drainage control.

Documents US-A-2010/0175843 and US-A-2013/0092337 propose an alternative method to produce multitonal watermarks. In this method, instead of embossing the cylinder mold cover, a perforated watermark "insert" joins the cylinder mold cover, which provides a multi-level relief. The insert can be injection molded to provide profiled surface perforations. Alternatively, the insert is embedded or hot stamped.

Document US-A-2013/0255896 also proposes an alternative method for producing multitonal watermarks. In this method, a "part" is attached to the cylinder mold cover, part that has a profiled surface and conical perforations extending from the profiled surface to an opposite drainage surface. The part is manufactured by a laser sintering method, such as SLM or SLS.

Document DE 102006058513 A1 discloses a watermark forming element according to the preamble of the present claim 1.

However, it is not always necessary to improve the watermarking process. An object is to improve the quality of watermarks and, in particular, to improve the ability to create the effects currently produced by embossed and electrotypic embossed cylinder mold watermarks, so that complex multitonal designs or images can be created with dark and very light areas strongly contrasted adjacent to each other.

Another object is to provide a process for the production of cylinder mold covers that allows each watermark or some watermark to be individually modified.

Another object is to improve the process for the production of cylinder mold covers by reducing the time elapsed from the production of the illustration to the realization of the mold cover.

A further object is to reduce the production cost of the cylinder mold covers by simplifying the manufacturing process, while maintaining the ability to produce complex multitonal designs or images with dark and very light areas strongly contrasted adjacent to each other from the resulting cylinder mold cover.

A further object is to reduce the cost of production of cylinder mold covers using a process that allows cheaper materials to be used and material waste to be reduced.

The invention therefore provides a watermarking element for forming at least one watermark on a paper, said watermarking element having an integrated body comprising a watermarking surface. , which has one or more watermarking areas, and a drainage surface, said watermarking element having a plurality of drainage channels extending from front surface openings on the surface forming watermarks to the drainage surface, each opening of the front surface on the watermarking surface having a rounded edge.

Preferably, the flange has a radius of curvature that is in the range of 0.05 mm to 0.25 mm and more preferably in the range of 0.1 mm to 0.15 mm.

The watermarking element is preferably formed from a plurality of layers, each layer being provided with drainage openings, the drainage openings in each layer superimposing at least partially with the drainage openings in any of the layers adjacent to form said drainage channels.

Each layer can be formed from a plurality of sub-layers.

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The layers and / or sub-layers are preferably fused together to form the integrated body.

Preferably, the watermark forming element is formed by 3D printing.

The watermark forming element may be formed from a polymeric material or a plurality of different polymer materials or from a metallic material or a plurality of different metallic materials.

In a preferred embodiment, the minimum cross-sectional area of the front surface opening and any section of the drainage channels is 0.01 mm2

The shape of the drain openings in different layers may be different.

Preferably, any one of the layers may have drainage openings, not all of its areas and / or cross-sectional shapes being the same.

Preferably, the total cross-sectional area of the front surface openings is in the range of 1% to 40% of the total surface area of the watermark forming element, preferably 15% to 30% and more preferably of the 15% to 25%.

The layers can be flat or non-flat.

Preferably, the watermark formation surface is contoured in the one or more watermark formation zones to provide a tonal variation in the paper formed therein.

The shape, size, spacing and / or distribution of the drainage surface openings varies within the one or more areas of watermark formation to provide a tonal variation in the paper formed therein.

The invention further provides a cylinder mold cover for manufacturing a paper having at least one watermark, comprising at least one foraminous layer and at least one watermark forming element attached thereto.

The watermarking element may be located in a recess formed in the at least one foraminous layer or in a cut portion formed in the at least one foraminous layer.

Alternatively, the watermarking element is located in a recess formed in the at least one foraminous layer and a cut portion formed in another foraminous layer.

The invention further provides a method for manufacturing the cylinder mold cover where the one or more watermark forming elements are formed by a 3D printing process.

Preferably, the one or more watermarking elements are formed and subsequently joined to the at least one foraminous layer.

Alternatively, the one or more watermarking elements are formed directly on the at least one foraminous layer.

The invention further provides a method of making watermarked paper comprising the step of depositing fibers on the cylinder mold cover.

The invention further provides paper formed by this method.

The invention further provides a secure document made from this paper comprising a banknote, a passport, a certificate, a ticket or the like.

Next, only by way of example, the watermark forming elements and the elements thereof, the cylinder mold covers and the manufacturing methods of the cylinder mold covers, the forming elements will be described. of watermarks and paper, with reference to the attached drawings, in which:

Fig. 1 is a cross section of a section of a wire mesh used to form a cylinder mold cover;

Figures 2a and 2b are plan views of different watermarking elements;

Figure 3a is a cross-sectional side elevation view of the watermark forming element

from figure 2a on the MI-MI line;

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Figures 3b to 3d are side elevational views in cross section of the watermark forming element of Figure 2b;

Figure 4 is a plan view of a front surface opening in the watermark forming surface of the watermark forming element of Figure 2;

Figures 5a and 5b are elevational views in cross section through an adjacent pair of two members of

different apertures defining the front surface opening of Figure 4 on the V-V line;

Figures 6a to 6e illustrate the construction of an alternative watermarking element;

Figures 7a to 7d illustrate the construction of an additional alternative watermark formation element;

Figures 8 to 17 are side elevational views in cross section of other forming elements of

additional alternative watermarks attached to the metal fabric of a cylinder mold cover;

Figure 18 is a plan view of a single watermark forming element;

Figure 19 is a tiled sheet section formed by the watermark forming elements of the

figure 18;

Figure 20 is a single watermarking element used to produce multiple documents that have identical watermarks;

Figures 21 to 24 and 26 to 28 are parts of different watermark formation surfaces of different watermark formation elements;

Figure 25 is an additional alternative watermark formation element; Y

Figures 29 to 32 are perspective views showing how adjacent sheets of the watermark forming elements can be joined together.

It should be noted that, although the following description refers specifically to the manufacture of paper, this should be interpreted as a reference to paper manufactured from any fibrous substrate, or manufactured from natural and / or synthetic fibers.

Watermarked paper is usually formed in a partially submerged cylinder mold cover, at the wet end of a papermaking machine, as it rotates in a bowl containing a paper pulp. In general, the paper pulp comprises an aqueous suspension of paper fibers, which may be natural fibers, synthetic fibers or a combination of both. As the cylinder mold rotates, the liquid passes through the metal cloth 10 by depositing the fibers on the surface cloth 11.

A cylinder mold cover of the usual prior art is formed from a multilayer wire mesh 10, as shown in Figure 1. In general, the layers are manufactured from wire mesh or other foraminous surface. The outermost layer (when the metal fabric 10 is wrapped around the cylinder mold) is known as the surface fabric 11 and the next layer is a backing layer, referred to herein as the first backing layer 12. The surface fabric 11 and the first backing layer 12 are the layers that are normally provided with the embossed prints 13 that form the watermarks. Behind these layers 11,12 there is normally a second backing layer 14, which usually has clipped areas 15 that adapt to the areas that protrude into the embossed prints 13. The innermost layer (when the wire net 10 is wrapped around the cylinder mold) is normally a third backing layer 16 that is not embossed or cut, which provides general support and resistance to the overlapping layers 11, 12, 14. Usually, the surface fabric 11 has the smaller mesh openings, the third backing layer (the innermost one) having 16 the largest mesh openings.

To form electrotypic watermarks, electrotypes 17 can be attached to surface fabric 11 by a suitable method, such as hard or soft welding.

For some types of embossments 13, support elements 18 can be inserted between the most rear embossed embossed layer, in this example the first backing layer 12, and the next adjacent layer, in this example the third backing layer 16 The support elements 18 are usually manufactured from stainless steel with holes drilled therein to provide drainage. These support elements 18 do not provide a drainage restriction as do the electrotypes 17, but are provided to help prevent distortion of embossed prints 13 when the mold cover is subjected to pressure during the papermaking process.

As an alternative to the use of embossments 13 and / or electrotypes 17 of the prior art, watermarks can be formed using the watermark forming elements 20. At least one watermark forming element 20 it is preferably attached to the metal fabric 10 of the cylinder mold cover. It should be noted that the metallic fabric 10 may have a construction similar to that of Figure 1, in terms of the number of layers 11, 12, 14, 16, or it may have a different number of layers. The watermarking element 20 has a watermarking surface 21. At least a part of the watermarking surface 21 can have a contoured profile, such as the surface of a embossed brand of water 13, which provides one or more watermark formation sections 52. The fibers are deposited with a greater or lesser thickness in the raised and sunken elements of the watermark formation section (s) 52 to form a three-dimensional watermark on the finished paper. The watermarking surface 21 may also have non-contoured sections (non-marking sections of watermarks).

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water) in which paper is produced that has no watermarks. However, the deposition of fibers to form watermarks can be controlled by additional and / or alternative means, for example, by varying the rate of drainage of the liquid from the paper pulp through the watermarking element. These means are described below.

The watermarking element 20 has an integrated body (i.e., one that does not comprise discernible separate layers) by a plurality of drainage channels 22 extending from the front surface openings 23 on the marking surface. of water 21 to drain surface openings 24 into an opposite drain surface 25 (see Figures 3a to 3d). The drainage channels 22 are not only located in the watermark formation sections 52, but also in the non-watermark sections. The drainage channels 22 allow the liquid from the paper pulp to drain through the watermark forming element 20 to allow the fibers to settle on the watermark formation surface 21. The cross-sectional area of each drainage channel 22 preferably increases as it extends from the watermarking surface 21 to the drainage surface 25 to stimulate the flow of liquid (as shown in Figures 6a to 6e). Preferably, the minimum cross-sectional area of the front surface openings 23 and any section of the drainage channels 22 is 0.01 mm2. However, the cross-sectional area of one or more drainage channels 22 may remain constant as it extends from the watermarking surface 21 to the drainage surface 25, or it may decrease.

Preferably, each of the front surface openings 23 has a curved flange 26 extending from the watermarking surface 21 to an inner wall 29 of the drainage channel 22. The radius of curvature (r) of the flange 26 it is selected to reduce fiber retention as the liquid drains through the watermark forming element 20 and to aid in cleaning the watermark formation element 20. Preferably, the flange 26 has a radius of curvature (r) (see Figures 5a and 5b) in the range of 0.05 to 0.25 mm, and more preferably in the range of 0.1 to 0.15 mm.

The continuous flow of liquid through the drainage channels 22 is important, as blockages can lead to imperfections in the watermark. The size, number, cross-sectional shape and / or profile of the drainage channels 22 are preferably selected to provide controlled drainage rates in different areas to form the desired watermark (s). Therefore, the watermark forming element (s) 20 and the cylinder mold cover provide a forming surface with a variable porosity, such that areas with less porosity produce areas of reduced weight (i.e., lighter areas with a lower fiber density) in the paper, and areas with a higher porosity allow areas of higher weight to be produced (i.e. darker areas with a higher fiber density).

From Figures 3a to 3d it can be seen that some of the drainage channels 22 may be longer than others as a result of a variable profile of the watermarking surface 21. The longer drainage channels 20 provide more resistance to liquid flow than shorter drainage channels 20 and, therefore, produce lighter areas on paper than those produced by shorter drainage channels 20. Therefore, variations in paper density can controlled not only by variations in the profile of the surface of watermark formation 21, but also (as an alternative or additionally) by the speed of the flow of liquid through the drainage channels 22.

Between the front surface openings 23, the watermarking surface 21 comprises solid areas 27. These solid areas 27 also allow the control of fiber deposition on the watermarking surface 21. These solid areas 27 can be regular and small or can be used, varying their size and position, to create the equivalent of electrotypic watermarks, that is, significantly brighter / lighter areas. The deposition of fibers in each solid area 27 is a function of the width of the solid area 27 (i.e., the distance between the adjacent front surface openings 23) and the height of the solid area 27 in relation to adjacent portions of the surface for forming watermarks 21. In order to produce a watermark, the preferred maximum width of a solid area 27 is approximately 2 mm; otherwise, the fibers cannot save the solid area 21, which would result in a hole in the paper. However, if it is desirable to create a hole in the paper, the solid areas 27 may be larger.

Solid areas 27 may be rounded (as shown in Figure 5a) or flat (as shown in Figure 5b). When the watermarking surface 21 has a variable profile, which has peaks (where fibers are less densely deposited) and depressions (where fibers are more densely deposited), solid areas 27 can be located within the peaks or Depressions, having different effects. Therefore, a peak would only produce a clear area, and a high solid area 27 located within the peak would produce an even lighter area. A depression would only produce a dark area, and a high solid area 27 located within the depression would produce a very bright high light directly adjacent to, or completely surrounded by, a dark area.

The solid areas 27 of the watermark forming element 20 may form a regular pattern, for example, the mesh-like pattern, as shown in Figures 2a and 2b. They can also form more areas

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large, for example, the areas marked with reference number 28 in Figure 2b. These larger solid areas 28 can be formed in several different ways, some examples of which are shown in Figures 3b-3d. In the example illustrated in Figure 3b, the largest solid areas 28 extend along, and block, a series of drainage channels 22. In the examples illustrated in Figures 3c and 3d, the largest solid areas 28 they extend from the watermarking surface 21 to the drainage surface 25. In the examples illustrated in Figures 3b and 3c, one of the largest solid areas 28 has a variable profile, in this case a stepped profile, while the other has a flat surface.

The larger solid areas 28 between the drain surface openings 24 preferably have a cross-sectional area at least three times larger than that of the drain surface openings 24.

The front surface openings 24 define a shape, and the shape defined by the front surface openings 24 may be different from a set of front surface openings 24 to another. The shape can be a geometric shape, such as a rectangle. Alternatively, the shape may be a circle, a hexagon or another geometric shape. As an additional alternative, they can define a non-geometric shape. The shape defined by the front surface openings 24 may be regular or irregular.

The shape defined by the front surface openings 24 may be the shape of at least one alphanumeric, a pictorial image or a symbol. In the example illustrated in Figure 22, the front surface openings 24 themselves have the shape of an apple. In Figures 23 and 24, the front surface openings 24 are in text form, in this example the letters TNW. Preferably, the watermark forming element 20 has front surface openings 24 defining at least two different shapes. In these examples, the front surface openings 24 define the shapes positively. However, as an alternative, they can define the shapes negatively, so that the solid areas 27 between the front surface openings 24 have the shapes mentioned above. As mentioned above, some of the drainage surface openings 24 may define the shapes negatively and some may define them positively.

When the front surface openings 24 define alphanumeric, the character width (when a front surface opening 24 acts) is preferably not thinner than 0.3 mm in width and the space between the characters (the solid areas 27 between the openings front surface 24) is preferably not less than 0.3 mm. The minimum and maximum size of the characters used for the front surface openings 24 can also be determined by the font style. It should also be noted that, although a minimum front surface opening size 24 / stem width of 0.3 mm may be intended, during the manufacturing process, these dimensions may vary depending on the model structure, material and tolerance of the machine used to make the watermark formation element.

The watermark forming element 20 may have a set of front surface openings 23 defining a shape, and another set of front surface openings 23 defining a different shape. The first set may be located within the second set.

In these examples, when the shape of the drain surface openings 24 defines a specific shape or set of shapes, the watermark forming surface 21 in the watermark forming section 52 need not be contoured, although it may be

In addition to selecting a specific shape of the front surface openings 24, the watermark forming element 20 may have a specific shape. For example, as shown in Figure 25, the watermark forming element 20 has the shape of an apple. The shape of the front surface openings 24, the shape of the watermark forming element 20 and / or the watermark formed can also be selected to be equal, or related in context to each other. Therefore, in the example of Figure 25, the drain surface openings 24 and the watermark forming element 20 are apple-shaped, while the watermark is a portrait of Sir Isaac Newton. Other related forms in the context could include an emblem or geographic contour of a country and the letters that indicate its currency; the nature of a currency and the numbers that indicate its value; the geographical outline of a country and the images of its flag, for example, Ghana and the star, Sri Lanka and the lion with a sword, Pakistan and the crescent moon; portraits and quotes or identification symbols, for example, Churchill and the phrase "Fight against them on the beaches", Lincoln and a fragment of the speech of Gettysburg, Washington or Franklin and the declaration of independence, Jane Austen and a bird feather. The shape of the watermark forming element 20 may be a symbol, a pictorial image, an alphanumeric or a geometric or non-geometric shape. In this example, a first section of watermark formation 52a forms a pictorial watermark that has light and dark tones, in the form of a head. The watermark forming element 20 may have a limit provided by the larger solid areas 28. These may provide a suitable means for anchoring the watermark forming element 20 to the surface fabric 11. A second section is provided. of watermark formation 52b that forms a type of watermark electrotype in the form of an apple that has light tones.

When a watermark forming element with said shape 20 is attached to the surface fabric 11 of a cylinder mold cover, the paper manufactured finished thereon may have two "wire markings"

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different. When a substrate band is formed using a cylinder mold cover, the mesh profile of the surface fabric 11 produces what is known as a "wire mark" throughout the band. In general, when the warp wires (in the machine direction) and the weft wires (in the transverse direction) intersect, a knuckle is formed that is slightly raised with respect to the warp and weft wires. The knuckles cause a very small variation in the density of the substrate fibers that are deposited on the surface of the mold cover. The printing of the surface fabric 11 also causes a barely noticeable undulation of the surface of the finished substrate and a regular pattern throughout the substrate that is practically indistinguishable to the naked eye. When a watermarking element 20 joins the surface fabric 11, the finished paper will have a wire mark formed by the mesh of the surface fabric 11 and another formed by any regular pattern formed by the front surface openings 23 and solid areas 27 of the watermark forming element 20.

As mentioned briefly above, the drainage rate can be controlled by a number of different means (alone or in combination) and this can be used to provide a tonal variation within the watermark (s). The size and / or shape of the drainage surface openings can be varied in a given horizontal plane, which is parallel to the drainage surface 25, to achieve this. Some examples of watermark forming elements 20 used to form a portrait shaped watermark are illustrated in Figures 28a and 28b. The watermarking surface 21 in each of these examples does not have to be contoured (although it can also be contoured) since the size of the drainage surface openings 24 varies to provide tonal variation. In these examples, the drain surface openings 24 have the same circular shape, although the shape may vary. Therefore, the size of the solid areas 27 between the drainage surface openings 24 also varies.

The drainage surface openings 24 can positively define a shape (such as the circle in Figures 28a and 28b) or they can define a shape negatively (so that the solid areas 27 between them have that shape positively). Alternatively, the watermark forming section 52 may have drainage surface openings 24, some of which positively define a shape and some of which negatively define the same shape.

In the example illustrated in Figure 28, the drain surface openings 24 have a circular shape. However, a tonal variation can be achieved by varying the shape and / or size of the symbols, pictorial images or alphanumeric shapes. For example, in the case of drainage surface openings 28 having the shape of a letter, then the areas of the watermarking element 20 that form the darkest areas in the final halftone image in the mark of water would have a rod width greater than that of the drainage surface openings 24 that form the lightest part of the halftone image.

The separation between the front surface openings 24 in a given horizontal plane, which is parallel to the drain surface 25, can also be varied to provide a tonal variation. Again, this may avoid the need to contour the watermarking surface 21 (although it could also do so). Thus, in the finished paper, the areas formed by the areas of the watermarking element 20 in which the front surface openings with less spacing between each other 24 are located are darker than the areas formed by the areas in which the front surface openings 24 are further spaced apart. In the example illustrated in Figure 25, there is a central band X in which the front surface openings 24 are closer together than those on both sides of the band X.

Said watermarking elements 20 can be used to provide a continuous variation in the watermark tone of a section (preferably an end or an edge) thereof, which has the lightest tone, to an opposite section. (preferably the other end or the opposite edge), which has the darkest tone. This can be achieved using any of the above-mentioned methods of tone transmission, such as varying the height / depth of at least one watermark forming section 52 of the watermark forming surface 21 or varying the openings or a combination of both. An example of this feature is illustrated in Figure 26. In this example, the watermark formation section 52 is configured to produce at least one watermark on the finished paper that is a continuous spiral and has a continuous tonal graduation from one end of the spiral, which is the darkest zone, to the other end, which is the lightest zone. The clear end of the spiral is produced by the larger solid areas 28 that rise in relation to the "normal" level (ie, the sections without watermark of the watermarking surface 21), gradually reducing the height at a continuous speed until the normal level of the watermarking surface 21 is reached, that is, the level of the sections that do not form watermarks. This is marked as point A in Figure 26. At this point, the watermarking surface 21 begins to fall below the normal level, forming a channel 60 that increases in depth at a continuous speed. The deepest end of the channel (that is, at the other end of the spiral) produces the darkest part of the spiral.

Said or said watermarks that have a continuous tonal variation preferably have the shape of a continuous line or band that can be straight, curved and can change direction, for example, a single straight line, an arc, a spiral , a zigzag or similar and that obviously have opposite ends. A watermark

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of this type it can provide a convenient method to check forgeries, since it comprises all multitones from light to dark within a single watermark in a continuous graduation.

In one example, the preferred weight of finished paper in the darkest area of the watermark is at least 140% of the weight of areas without watermarks. Therefore, in a preferred example, for a 100 gsm base paper, this would be approximately 140 gsm, and for a 90 gsm base paper it would be approximately 126 gsm. However, these areas could have an even heavier weight, preferably at least 160%, or more preferably at least 180%, of the weight in areas without watermarks. In the clearest area of the watermark, the weight is preferably not more than 50% of the weight in areas without watermarks, more preferably not more than 40% and more preferably not more than 25%. Therefore, in a preferred example for a 90 gsm base paper, the grammage in the lighter area is 20 gsm.

Therefore, for a 90 gsm paper the weight can vary from about 20 gsm to about 200 gsm.

One technique to measure the weight is as follows. An x-ray is generated by exposing a sample sheet to a beta-ray source (C-14) and recording the radiation transmitted through the sheet on an X-ray film. The developed film is scanned with a flatbed scanner, and the gray levels of the image are transformed into actual grammage values through a calibration scale obtained from a sample of known grammage.

The watermarking element 20 can also be configured to produce a continuously graduated watermark of this type located next to another watermark, which provides another convenient anti-counterfeiting check. The continuously graduated watermark provides a reference graph, as its darker end matches the darker areas of the adjacent watermark, and the lighter end matches its lighter zones. The continuously graduated watermark also has the color of the base paper in the middle.

The watermark forming element 20 can also be configured to produce a continuously graduated watermark of this type that is mixed with another watermark. In the example shown in Figure 27, in an area of the watermark forming element 20, a first watermark forming section 52a produces corner reinforcement watermarks of the type known from EP-A -1468142, which has darker tones formed by channels 60 that have a constant depth. A second watermark formation section 52b is formed adjacent to the first watermark formation section 52a, which is configured to provide a continuous tonal graduation from the end of the channels 60 to a pictorial watermark in a third Watermark formation section 52c.

The watermark forming element 20 can also be configured to produce a continuously graduated watermark of this type that has text or patterns within the continuous band or line. These may be darker and / or lighter areas.

The watermark forming element 20 can be formed from a plurality of separate layers, especially if it is formed using a 3D printing process as described below. However, in the finished watermarking element 20, these layers can be fused entirely together and be indistinguishable as separate layers. The layers are formed with openings, which combine to form the drainage channels 22. The openings in the upper layer or layers, which form the watermarking surface 21, preferably have a smaller cross-sectional area than those of the lower layer or layers, which form the drainage surface 25. However, as an alternative, they may have a larger cross-sectional area or the same cross-sectional area.

In one example, as shown in Figures 6a to 6e, there are pluralities of first layers 30, second layers 31, third layers 32 and fourth layers 33. Each of the first layers 30 is provided with openings of one size, which they form the front surface openings 23. Each of the second layers 31 is provided with openings 34 having a larger cross-sectional area than the front surface openings 23. Each of the third layers 31 is provided with openings 35 that have a larger cross-sectional area than the openings 34 in the second layers 31. Each of the fourth layers 31 is provided with openings that have a larger cross-sectional area than the openings 35 and that form the openings of drainage surface 24.

Although the illustrated example shows four of each of the four layers 30, 31, 32, 33, the number of layers that form the watermark forming element 20 is not limited and the number of identical layers may also vary.

The openings 23, 34, 35, 24 in the different layers may have the same cross-sectional shape with respect to each other, although with different cross-sectional areas, or the shape may vary from layer to layer.

The cross-sectional area of the openings 23, 34, 35, 24 in any layer can also be varied,

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providing the larger openings 23, 34, 35, 24 an increase in drainage and deposition of fibers over the smaller openings 23, 34, 35, 24.

The total cross-sectional area of the front surface openings 23 is preferably between 1% and 40% of the total surface area of the watermark forming element 20, more preferably between 5% and 30 %, and more preferably even between 15% and 25%.

Layers 30, 31, 32, 33 illustrated in Figures 6a-6d and 7a-7d are shown flat. However, the layers may not be flat, for example, be curved in one or more directions.

The drainage speed through the watermark forming elements 20 can also be controlled by the open area and the average open diameter of the openings of the metallic fabric 10 (or other foraminous surface), which provides the structure of support. The average diameter of the openings is preferably between 0.02 and 0.4 mm and, more preferably, between 0.05 and 0.1 mm. The metallic fabric 10 (or other foraminous surface) is preferably produced by a method that is not restricted by the rate of gradient change of the watermarking surface 21. This allows for improved resolution and contrast.

The drainage speed through the watermark forming elements 20 can also be controlled by spraying, coating or otherwise covering the watermark formation surface 21 with a material that changes the hydrophobic property of the material of the that the watermark formation element 20 is manufactured. Hydrophobia can be controlled by printing the watermark formation element 20 with two or more different materials with different hydrophilic or hydrophobic natures, possibly very variable, having different surface energies / contact angles. For example, if the wax support material (hydrophobic, non-moisturizing) is not completely removed from the 3D printed element, then the water is not easily drained through some drainage channels 22. This is because the angle of Water drop contact is too large and the water drop that forms will not pass through the drainage channels 22. As a result, the fiber is not deposited in that area to the same extent as the more hydrophilic areas and Produces an enhancement point. Therefore, if two construction polymers are used to form different areas of the watermark forming element 20, one more hydrophobic than the other, although the size of the drainage channel 22 may be uniform throughout the area, where it is used a hydrophobic material, then less fiber will be deposited and, therefore, the image density can be modulated.

Similarly, it may be possible to adjust the drainage in some areas by coating, painting, printing or spraying the desired area with a hydrophilic resin to stimulate drainage through wetting, or a hydrophobic material to inhibit drainage.

The structure of the watermark forming elements 20 can also be designed to allow (lateral) drainage to the sides of the liquid below the watermark formation surface 21, an example of which is shown in Figures 7a to 7d. The first layer 30, which forms a substantial portion of the watermarking surface 21, has a mesh-like construction with square front surface openings 23. The second underlying layer 31 is provided with openings 34 in the form of channels that extend through one edge of layer 31 to an opposite edge. The third layer 32, which in this embodiment forms the drain surface 25, is also provided with openings 35 in the form of channels extending through one edge of the layer 31 to the other in a direction similar to that of the second layer 31. The channels of the third layer have a width greater than that of the second layer 31. This structure produces a watermarking element 20 having a cross section as shown in Figure 7a. Therefore, in addition to the drainage channels 22 that extend through the watermarking element 20 from the watermarking surface 21 to the drainage surface 25, one or more drainage channels are provided additional that extend laterally within the watermark forming element 20 below the watermark formation surface. These laterally extending drainage channels can extend from one side of the watermark forming element 20 to the other, as shown in Figures 7a-7d. Alternatively, they can simply extend from one point on the perimeter of the watermark forming element 20 to another point. These drainage channels can be straight, angled, curved or in any other suitable way, and can extend in the machine direction or in the transverse direction. The lateral drainage channels can be in a single plane (or layer 30-33) or can be staggered through two or more layers 30-33.

Although the watermarking element illustrated in Figures 7a-7d is described as having only first, second and third layers 30, 31, 32, the same can be applied when each of the layers 30, 31, 32 is formed from the plurality of layers described above. Furthermore, although the illustrated example shows three layers 30, 31, 32, the number of layers that form the watermark forming element 20 is not restricted. In addition, layers other than those shown may have laterally extending openings 35.

Therefore, the watermark forming elements 20 described above can combine the advantages of contour formed watermarks (cylinder mold watermarks stamped on

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relief) and watermarks formed with restricted drainage (electrotypic watermarks) to obtain a greater contrast between the light and dark areas of a watermark and very light areas. They also alleviate a series of design restrictions that arise from cylinder and electrotypic mold watermarks, in particular:

- unlike the usual electrotypical method, the watermark forming elements 20 can be used to form any part of the watermark;

- The watermark forming elements 20 are not limited to specific dimensions in order to obtain good clarity and contrast compared to the background, such as traditional electrotypes. The use of such watermarking elements 20 allows a wider range to be used with greater flexibility in order to achieve a wider range of artistic effects. In particular, the image contrast of the electrotype can be reduced by reducing the thickness if such an effect is desirable from an aesthetic point of view. Such subtleties can also contribute to improving security by increasing the complexity of the tonality of the image;

- When the finished document requires a combination of cylinder and electrotypic mold watermarks, the location of the electrotypes in relation to embossed prints has always been restricted due to manufacturing problems and the problems described above. These no longer apply, since a single watermark element 20 can be used to provide equivalent watermarks. This does not apply to the watermark forming elements 20 of the present invention, since it is possible to create deeper areas within the profile of the watermark formation surface 21 and provide solid areas within the deeper areas. , as well as in the highest areas;

- In a traditional process that has electrotypes, there are some manufacturing and therefore design restrictions on the number of electrotypes per mold cover and its location. This is because they usually join using a robotic arm, which is a time-consuming process.

The use of the watermark forming elements 20, as opposed to embossing the metallic fabric 10 of the cylinder mold cover or joining electrotypes thereto, provides the ability to produce multitonal designs or images complexes that can be created with dark and very light areas strongly contrasted adjacent to each other. However, it represents a series of additional manufacturing challenges.

The durability of the resulting cylinder mold cover is extremely important, as it undergoes significant stresses. The tensions may be due to a couch roller, a dandy roller or felt (formex) depending on the configuration of the paper machine. In a machine that uses a couch roller, for example, the couch roller rotates in contact with the cylinder mold and is used to transfer the partially formed paper web from the cylinder mold cover to the felt (formex) that carries the web from the wet end of the papermaking machine to the press section. Therefore, there is a significant pressure formed between the cylinder mold and the couch roller. This means that, when there is an element that protrudes from the surface of the metallic fabric 10, there will be an additional tension that is constantly repeated on the metallic fabric 10.

The watermark forming elements 20 may also be provided with impact absorption properties, which allow the watermark formation element 20 and, therefore, the cylinder mold cover, to withstand the pressure of the roller. couch. This can be achieved by manufacturing all, or part, of the watermark forming element 20 from an elastic material, such as rubber.

Alternatively, the watermark forming element 20 may comprise a support layer 40, as an additional layer to those described above, on the back of the watermark forming element 20 either behind or forming the surface of drain 25. For example, with reference to the embodiments described above, the support layer 40 may be located at the back of the fourth layer (s) 33 in Figures 6a-6e or the third layer 32 in Figures 7a-7d.

Alternatively, the support layer 40 may be one or more of the layers 30, 31, 32, 33 of these embodiments described above.

The support layer 40 can be manufactured from an elastic material. In the embodiment shown in Figure 8, the support layer 40 is an additional layer located at the back of the watermark forming element 20. The support layer 40 can be attached to the watermark forming element 20 by any suitable medium, for example, UV cured resin.

The support layer 40 can be made from a material having a tensile modulus different from the main body of the watermark forming element 20. The preferred minimum and maximum values for the tensile modulus of a conventional material used for the main body of the watermark forming element 20 and for a polymer material similar to the shock absorbing rubber, for the support layer 40,

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They are offered below with the most preferred values shown in parentheses.

 Conventional material Polymer (similar to rubber) impact absorption

 Property

 Min Max Min Max

 Traction Module (Mpa)

 110 (500) 12000 (5000) 0.5 (2) 100 (50)

The following standard test methods can be used to measure the tensile modulus:

- ASTM D638: this is for non-elastomeric materials and, therefore, would apply to conventional materials in the table above;

- ASTM D412: this is for elastomers such as rubber-like materials and is applied to the shock absorption materials in the table.

Alternatively, the support layer 40 may have a structure that is elastic. In the embodiment shown in Figure 9, the support layer 40 is located at the rear of the watermark forming element 20. The support layer 40 is formed from a series of springs (which can be crossbows, volutes, coils, zigzags or other types of spring configurations).

Alternatively, the support layer 40 may have a honeycomb or tessellated structure.

It is important that the support layer 40 has a shape and / or configuration that does not interfere with the drainage flow through the drain surface 25 of the watermark forming element 20 or the fabric backing layer (s) metal 10. Therefore, in any of these embodiments, the support layer 40 must have openings that ensure that the support layer 40 does not interfere with the drainage requirements identified above and / or that form part of the drainage channels 22

In a further alternative construction (see Figure 10), the watermark forming element 20 comprises an annular elastic support layer 40 extending around the circumference of the watermark forming element 20.

The method used to locate and / or join one or more of the watermarking elements mentioned above 20 to the wire mesh 10 is also an important factor in ensuring the durability of the cylinder mold cover. The following description refers to the location / attachment of a single watermarking element 20 to the metal fabric 10. In the embodiment illustrated in Figures 8, 9 and 11, the metal fabric 10 is formed from a surface fabric 11, a first backing layer 12, a second backing layer 14 and, only in the case of Figure 10, a third backing layer 16. The surface fabric 11 and the first backing layer 12 each have thereof, a cropped area 15a, 15b, respectively. The trimmed area 15a on the surface fabric 11 is smaller than that of the first backing layer 12 and is substantially the same size, or slightly larger, than an upper section 41 of the watermark forming element 20. This allows that the upper section 41 passes through the clipped area 15a. The support layer 40 of the watermark forming element 20 and / or a lower section 42 of the watermark forming element 20 has at least one cross-sectional dimension that is larger than that of the trimmed area 15a in the fabric surface 11, but is equal to or slightly smaller than the trimmed area 15b in the first backing layer 12. This allows the watermark forming element 20 to be anchored between the layers of the metal fabric 10. The rear surface of the watermarking element 20 (either the drain surface 25 or the support layer 40) is located against, and supported by, the second backing layer 14.

Alternatively, a watermarking element 20 can be located, at least partially, in a recess 43 in the surface fabric 11 of the cylinder mold cover as shown in Figure 12. The recess 43 is preferably formed , embossing surface fabric 11 (and possibly also the first underlying backing layer 12). The recess 43 is preferably shallow (for example, between 0.5 mm and 2 mm deep). The recess 43 is preferably arranged so that the watermark forming element 20 is pushed upward against a location corner. The watermarking element 20 is thus protected by the surrounding walls of the recess 43.

Figure 13 shows an alternative arrangement in which the surface fabric 11 is provided with a trimmed area 15 (similar to the clipped area 15 illustrated in Figures 8 and 9) through which a watermarking element 20 protrudes. The first backing layer 12 is provided with a recess 43 in which a watermarking element 20 can be located, at least partially.

These are not the only suitable constructions. In other variations, some or all of the layers of the metallic fabric 10 may be provided with clipped areas 15 and / or recesses 43.

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One or more watermark forming elements 20 can also be attached to one or more layers of the metal fabric 10. Suitable methods for attaching a metal watermark formation element 20 to the metal fabric 10 are the resistance or the laser welding and soft welding. The plastic welding can be used to join polymeric watermark forming elements 20. Alternatively, the watermark forming element (s) 20 can be sewn, for example, with a thin wire, onto the metal fabric 10. The or The watermark forming elements 20 can also adhere to the metal fabric 10, for example, with a UV cured resin or other suitable adhesive.

One or more fasteners 45 may be used to join one or more watermark forming elements 20 to one or more layers of the metal fabric 10. Such fasteners may be threaded metal inserts, weldable metal inserts, plastic or metal components with flanges, staples, components with flexible legs, etc. The fasteners 45 are preferably porous or hollow (for example, tubular).

Figure 14 illustrates a suitable type of fixation 45. This comprises a rod 46, which can be a wire or plastic filament or an elastic thread, which passes through one or more layers of the metal fabric 10 and a channel drainage 22 of the watermark forming element 20. One end of the rod 46 has a foot 47 integrally formed therein or attached thereto. The foot 47 may have at least one dimension greater than that of the opening of the wire mesh in the backmost backing layer to which the fastener 45 is attached, in the first backing layer illustrated by way of example 12. The opposite end of the rod 46 is screwed through the drain channel 22 and a head 48 is attached thereto or formed therein. The size of the head 48 is larger than the size of the front surface opening 23 of the drain channel 22 to ensure that the watermark forming element 20 remains firmly in position. One or more fasteners 45 may be used per watermarking element 20.

Figure 15 illustrates the use of another suitable form of fixation 45. This has a flexible rod 46, which can be a plastic wire or filament or an elastic thread. The rod 46 passes through one or more layers 11, 12, 14, 16 of the metal fabric 10, up a drainage channel 22, through the watermarking surface 21, down an adjacent drainage channel 22, and back through one or more layers 11, 12, 14, 16 of the wire mesh 10. The feet 47 are formed in, or joined to, each end of the rod 46, with the feet 47 at least a dimension larger than that of the wire mesh opening in the backmost backing layer to which the fastener 45 is attached.

Figure 16 illustrates the use of yet another suitable form of fixation 45. This comprises a tubular or porous barbed spike extending from the drain surface 25 of the watermark forming element 20 through one or more layers of the metal fabric 10. In the illustrated embodiment, the watermark forming element 20 is located in the cut out areas 15a, 15b in the surface fabric 11 and the first backing layer 12, so that the spike is pushed through of the wire mesh openings in the second and third backing layers 14, 16. The spike has a central drain passage 50 and its distal end is provided with one or more spikes 49 that engage in the wire of the layer of rearmost backrest through which the spike passes; In the illustrated embodiment, this is the third backing layer 16.

Figure 17 illustrates the use of another suitable fixation plus 45. This is in the form of a wire that extends from the drain surface 25 of the watermark forming element 20 through one or more layers of the wire net 10 In the illustrated embodiment, the watermark forming element 20 is located in the trimmed areas 15a, 15b in the surface fabric 11 and the first backing layer 12, and the wire is screwed through an opening of mesh of wire in the second backing layer 14. The end of the wire bends over itself to form a hook 51.

The above-mentioned fasteners 45 can be adhered or welded additionally to the wire mesh 10 to ensure that they are firmly attached.

In order to allow the attachment of the watermarking element 20 to the metallic fabric 10 by means of fasteners, it may be necessary that one or more of the layers forming the metallic fabric 10 be provided with additional or larger holes to receive the fixings 45.

The watermarking elements mentioned above 20 can be produced by 3D printing or other suitable manufacturing process, such as injection molding, laser ablation, vacuum formation, machining, etc.

3D printing, also known as rapid prototyping or additive manufacturing, is a relatively new technology, which uses a digital model, usually created by some type of computer-aided design (CAD) package or a 3D scanner, to create a three-dimensional object . The 3D printer reads the data from the CAD drawing and places successive layers of material to build a physical object from a series of cross sections. There are a large number of different 3D printing processes, including (but not limited to) stereolithography (SLA), selective laser sintering (SLS), selective laser fusion (SLM), fabrication of laminated objects (LOM), modeling by molten deposition (FDM), solid earth curing (SGC), direct metal laser sintering

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(DMLS), electron beam fusion (EBM) and inkjet printing techniques.

The 3D printing methods can be used to make the watermark forming elements 20 from a variety of materials. Examples include one or more polymeric materials, one or more metals or a combination of metals and polymers, for example, with a metal incorporated in a polymeric matrix. The material or materials selected for the watermark forming elements 20 need to be durable enough to withstand the pressure created between the cylinder mold and the couch roller and the continuous percussion thereof. The selection of the material or materials will also depend on the 3D printing process used.

Below are some examples of suitable polymeric materials, although this list is not exhaustive:

for fabrication by molten deposition (FDM):

- acrylonitrile butadiene styrene (ABS)

- polyphenylsulfone (PPS, PPSU or PPSF)

- polylactic acid (PLA)

- polyamide (PA)

- polycarbonate (PC)

- mixtures of materials, for example PC-ABS for selective laser sintering (SLS):

- Nylon, in particular PA12

- PA12 with fiberglass

for inkjet or photojet processes (UV curing resins):

- acrylic

- Simulated ABS

- simulated polypropylene (PP)

- qualities similar to rubber

- dental qualities

- biocompatible qualities.

Below are some examples of suitable metals, although this list is not exhaustive: for selective laser sintering (SLS) or selective laser melting (SLM) of metal powders:

- titanium, pure and alloys.

- steels, including stainless steels

- nickel-chromium alloys

- pure aluminum and alloys

- chrome-cobalt alloys

- Copper and copper alloys.

Advantageously, the watermark forming elements 20 comprising more than one different material can be formed using a single device, such as a 3D printer, since some commercial 3D printers, for example, the Stratasys Objet 350 Connex model, can Print multiple materials. This allows both multi-colored products and composite structures, for example, rigid and rubber-like polymers combined, to be produced in a single process.

A significant advantage of using a 3D printing process to form the watermark forming element (s) 20 is that the time required to manufacture a cylinder mold cover and, therefore, the cost, is significantly reduced in compared to the traditional process, since the illustration is used directly to form the watermark forming elements 20. It is no longer necessary to produce embossing dies, which then must be used to emboss the cover of cylinder mold The use of a computer-controlled process to form each individual watermark formation element 20 makes it possible to customize each individual watermark, for example, for passport pages or serial numbers of unique bills.

An additional advantage of 3D printing is that it makes it considerably easier to adapt to shrinkage. The paper band contracts as it goes through the various stages of the papermaking process. The degree of contraction at the edge of the paper web is greater than in the center and may vary according to the specific machine, the humidity, the type of processing speed of the material used. For

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To obtain a uniform finished document width, the actual width of the document in the cylinder mold cover during manufacturing has to vary to compensate for shrinkage. The design of any watermark should also allow contraction. The use of 3D printing means that the watermark forming elements 20 can be easily adjusted, depending on where they are located in the width of the cylinder mold cover.

Another advantage of 3D printing is that many of the methods described above can be used to form the watermark forming elements 20 directly on the metal fabric 10 of the cylinder mold cover without the need for additional fixations 45.

Alternatively, one or more watermark forming elements 20 may be formed on a wire mesh section that subsequently joins the metal fabric 10, for example, the surface fabric 11, of the mold mold cover. cylinder with suitable fixings 45.

3D pens are also available, such as 3Doodler (TM) or Lixpen (TM). These can be used to attach the watermark formation elements 20 to the metal fabric 10 by drawing loops from a 3D printed watermark formation element 20 around the wires of the surface fabric 11 and back to the element of watermark formation 20. Such 3D pens can also be used with the watermark formation elements 20 that have been manufactured by a method other than 3D printing.

As another alternative, the watermark forming elements 20 can be attached to a perforated lining or sleeve, which fits over a traditional wire mesh 10.

Another advantage of 3D printing is that it provides flexibility. For example, the resulting mold cover may have attached to it a series of discrete watermark forming elements 20 at regular intervals, each watermark forming element 20 being designed to produce a single watermark. The watermark forming elements 20 may all be designed to produce the same watermark, or different watermarks.

As described above, a series of bands can be produced simultaneously in a cylinder mold paper making machine. The bands are cut to form a series of smaller intermediate sheets, and the intermediate sheets are cut to form a series of smaller documents (usually after printing). Each watermarking element 20 may be the same size as a single document (see Figure 18) and be designed to produce all the watermarks (and holes or openings) required for a single document. This may include several different watermarks 52a, 52b, 52c, 52d. These watermarks 52a, 52b, 52c, 52d may be, among others, pictorial watermarks, corner reinforcement watermarks, safety wire tracks and / or alphanumeric electrotype-style watermarks. Sufficient identical watermark formation elements 20 can be attached to the wire mesh 10 adjacent to each other (to form a tiled sheet section as shown in Figure 19) to produce an intermediate sheet that, when cut, will form a series of identical smaller documents, all with the same combination of watermarks 52a, 52b, 52c, 52d. This can be repeated around the circumference of the mold cover, so that at least one of the paper bands can be divided to form identical intermediate sheets and then identical documents.

The use of the watermarking elements mentioned above 20 in papermaking is especially advantageous when each is designed to produce multiple watermarks 52a, 52b, 52c, 52d. During the papermaking process, the paper contracts at an uneven speed through the web. Therefore, in order to ensure that the watermarks 52a, 52b, 52c, 52d in the finished document are correctly positioned, the position of the watermarking surface elements 21 that produce the watermarks Individual 52a, 52b, 52c, 52d may vary depending on where in the band the watermark is formed. The use of 3D printing simplifies this process.

Figure 21 provides a clear illustration of a section of a watermark forming surface 21 of a watermark forming element 20, part of which has a contoured profile. In this example, a watermark (in the form of a bird of which a section of the bird's wing is shown) has elevated and sunken elements. This produces a watermark similar to that of a prior art cylinder mold watermark. Another watermark is formed from solid areas 21 in the form of the numbers "0", which rise above the rest of the watermarking surface 21. This produces a watermark similar to that of an electrotypic watermark of the prior art.

It is also possible to use different sets of watermark forming elements 20 to form different sheets or bands, which means that more than one type of document can be produced simultaneously in a single cylinder mold.

Alternatively, instead of making a series of individual identical watermark formation elements 20 in the form of tiles to allow an intermediate sheet to be produced, a single element of

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formation of watermarks 20, which is designed to produce all required watermarks 52a, 52b, 52c, 52d for multiple documents (see Figure 20). In addition, the watermark forming element 20 can be used to provide cutter / puncher guide marks 52e, which are used to aid in the precise cutting of the bands / sheets. Margins can also be included between the areas that will form an individual document, which can be used as fixation points. Fixing points are required to join the different sets of watermark forming elements 20 used to form different bands together or in the cylinder mold cover. These will be cut when the paper is divided into the individual intermediate sheets and then into the documents.

As an additional alternative, the entire surface fabric 11 of a cylinder mold cover may be a watermark forming element 20 formed by 3D printing. In addition, the backing layers 12, 14 can also be printed in 3D.

When the watermark forming element (s) 20 replaces the metal fabric 10 (cylinder mold cover), a sleeve is formed that fits over the cylinder mold itself. The sleeve may comprise a single sheet or a plurality of smaller sheets joined together. Some suitable methods to join the sheets together are the following:

Figure 29: A hinge joint can be used to join the individual sheets end to end to allow forward and backward movement of the sheets;

Figure 30: A spike joint can be used to attach the main body of the watermark forming element 20 to the surface fabric 11; the drain surface 25 may have spikes that fit into the wire of the surface fabric 11;

Figure 31: A clip lock gasket can be used to join two adjacent leaf ends by fitting them from end to end, allowing tight sealing of the sheets in the joint;

Figure 32: A bushing joint, which is similar to a ball joint, can be used in which one end

square of a sheet fits into a square slot and locks in place;

Figure 33: A lap joint can be used in which two sheets are joined end to end; The joint fixation is completed by adding a clip to fix the two sheets together to prevent a sheet from coming out.

In a traditional process that uses an embossed cylinder mold, the presence of many embossed prints can make it difficult to hold the mold cover firm while embossing the wire mesh 10. The use of marking elements of water 20 overcomes this disadvantage since they are formed separately.

Advantageously, the watermark forming elements 20 are produced in order not to have the knuckles associated with the woven wire mesh of the surface fabric. This eliminates brand image interference from

water by the image of wire knuckles that inevitably occurs on paper.

Other manufacturing problems may arise when a watermark is combined with another safety feature, such as traditionally formed corner reinforcement watermarks as described in EP-A-1468142 or security threads. In these cases, the order or stages in the fabrication of the wire netting is important. For example, it may be necessary to perform any of the embossing required for these other safety features before any of the clipped areas 15 (for example, by laser cutting) is formed to prevent distortion of the mesh. of wire that can affect the watermark forming elements 20. Next, the watermark formation elements 20 can be inserted into the recesses 43 or through the trimmed areas 15 as required.

Watermarked paper produced in this way is suitable for many applications, including paper used in banknotes, passports, certificates, tickets, and many more applications. It is especially convenient for producing passport paper, which has a complex design and requires different watermarks on each page.

Claims (23)

5 10 fifteen twenty 25 30 35 40 Four. Five fifty 55 60 65 1. A watermark forming element (20) to form at least one watermark on a paper, said watermark formation element (20) having an integrated body comprising a watermark forming surface (21), which has one or more watermarking areas, and a drainage surface (25), said watermarking element (20) having a plurality of drainage channels extending from openings front surface on the watermark formation surface (21) to the drain surface (25), characterized in that each front surface opening on the watermark formation surface has a rounded flange (26). 2. A watermark forming element according to claim 1, wherein the flange has a radius of curvature that is in the range of 0.05 mm to 0.25 mm, and preferably in the range of 0.1 mm to 0.15 mm. 3. A watermark forming element according to any one of the preceding claims, said watermark forming element being formed from a plurality of layers (30, 31, 32, 33), each layer being provided of drain openings, the drain openings in each layer overlapping at least partially with the drain openings in any of the adjacent layers to form said drain channels. 4. A watermark forming element according to claim 3, wherein each layer is formed from a plurality of sub-layers. 5. A watermark forming element according to claim 3 or claim 4, wherein the layers and / or sub-layers are fused together to form the integrated body. 6. A watermark forming element according to any one of the preceding claims, wherein the watermark formation element is formed by 3D printing. 7. A watermark forming element according to any one of the preceding claims, wherein the watermark formation element is formed from a polymeric material or a plurality of different polymeric materials. 8. A watermark forming element according to any one of the preceding claims, wherein the watermark formation element is formed from a metallic material or a plurality of different metallic materials. 9. A watermark forming element according to any one of the preceding claims, wherein the minimum cross-sectional area of the front surface opening and any section of the drainage channels is 0.01 mm2 . 10. A watermark forming element according to any one of claims 3 to 9, wherein the shape of the drain openings in different layers is different. 11. A watermark forming element according to any one of claims 3 to 10, wherein any one of the layers may have drainage openings, not all of its areas and / or cross-sectional shapes being the same . 12. A watermarking element according to any one of the preceding claims, wherein the total cross-sectional area of the front surface openings is in the range of 1% to 40% of the surface area Total watermark formation element, preferably 15% to 30% and more preferably 15% to 25%. 13. A watermark forming element according to any one of claims 3 to 12, wherein the layers are flat, or the layers are not flat. 14. A watermark forming element according to any one of the preceding claims, wherein the watermark formation surface is contoured in the one or more watermark formation zones to provide a tonal variation in the paper formed in them. 15. A watermark forming element according to any one of the preceding claims, wherein the shape, size, spacing and / or distribution of the drainage surface openings within one or more more watermark formation zones to provide a tonal variation in the paper formed therein. 16. A cylinder mold cover for making a paper that has at least one watermark, comprising 5 10 fifteen twenty 25 at least one foraminous layer and at least one watermarking element according to any one of the preceding claims attached thereto. 17. A cylinder mold cover according to claim 16, wherein the watermark forming element is located in a recess formed in the at least one foraminous layer. 18. A cylinder mold cover according to claim 16, wherein the watermark forming element is located in a cut portion formed in the at least one foraminous layer. 19. A cylinder mold cover according to claim 17 or claim 18, wherein the watermark forming element is located in a recess formed in the at least one foraminous layer and a cut portion formed in another foraminous layer 20. A method of manufacturing the cylinder mold cover according to any one of claims 16 to 19, wherein the one or more watermark forming elements are formed by a 3D printing process. 21. A method of manufacturing the cylinder mold cover according to claim 20, wherein the one or more watermarking elements are formed and subsequently attached to the at least one foraminous layer. 22. A method of manufacturing the cylinder mold cover according to claim 20, wherein the one or more watermark forming elements are formed directly in the at least one foraminous layer. 23. A method of making watermarked paper, comprising the step of depositing fibers on the cylinder mold cover of any one of claims 16 to 19.