WO2007042718A1

WO2007042718A1 - Method for producing a sheet material provided with at least one window

Info

Publication number: WO2007042718A1
Application number: PCT/FR2006/050998
Authority: WO
Inventors: Michel Camus; Pascal Barher
Original assignee: Arjowiggins Security
Priority date: 2005-10-06
Filing date: 2006-10-06
Publication date: 2007-04-19
Also published as: FR2891761B1; EP1931825A1; FR2891761A1

Abstract

The invention relates to a method for producing a sheet material (22), comprising at least one paper layer, by using a paper-making process consisting in spraying at least one jet of pressurised fluid (29), in particular a water jet, on a still wet layer in such a way that at least one window (25) is formed therein by material-removing processing.

Description

Method of manufacturing a sheet material having at least one window

The present invention relates to a method of manufacturing a sheet material comprising at least one window.

Patent GB 1 552 853 discloses a bank note comprising a paper layer in which a security thread is incorporated. The paper layer has windows on the side revealing the security thread. The windows can be made using a laser capable of removing material from the paper layer while leaving the security thread intact. The windows may, alternatively, be made mechanically, by cutting or abrasion. WO 2004/096482 discloses a machine for making a hole in a paper substrate using a laser beam. This machine further comprises means for evacuating the paper portions removed.

EP 0 229 645 describes a method of making secure paper comprising a security thread disposed between two layers of paper. According to one embodiment, one of the layers of paper may comprise holes. These holes can be formed by means of a jet of water or air directed towards the paper. This jet locally causes a displacement of the fibers which can lead to the formation of craters or holes in the paper web.

The application WO 2004/001130 describes a method for producing a paper substrate consisting in bringing, in contact with a paper forming web, a security thread, the fabric having reliefs making it possible to produce windows on the substrate through which an edge of the security thread is visible. This method is not suitable for incorporating into the paper substrate a safety wire having a relatively large width. EP 0 059 056 discloses a papermaking process that can be applied to security documents. A security thread is implanted continuously in the paper. This document teaches directing a jet of fluid on the surface of the paper in order to temporarily remove fibers covering the security element.

DE 3,431,577 discloses a method for making watermarks in paper. Water or air can be pulsed into the paper sheet to change its thickness. US patent application 2001/0004007 describes a method of processing a paper sheet comprising a step of cutting the peripheral strips by means of water jets.

Patent applications EP 0 860 298 and EP 0 625 431 also disclose a method for producing a security paper in which a security thread is incorporated within a first layer of paper according to the so-called "window thread" technique. described in the patent application EP 0 059 056. This paper layer has on one side a plurality of windows revealing the security thread. In the case where the security thread has a relatively large width, especially greater than 2 mm, defects may appear on the first paper layer during the formation thereof. This first layer is then assembled with a second layer of paper in order to mask the defect (s).

Incorporating a relatively large width security thread into a sheet material may require the separate formation of two layers of paper. US Pat. No. 6,428,051 discloses a security paper comprising a fibrous layer having a window covered by a foil, the window being made by punching ("punching" in English). The dimensions and / or shape of the window depend on the punching tool used, which requires changing the tool if it is desired to form windows of different sizes and / or shapes. The present invention aims at providing a new method of manufacturing a sheet material by paper means, the sheet material having at least one window in at least one layer of paper, for example two layers assembled.

The term "sheet material" may denote in the specification and claims a fibrous sheet based on cellulosic and / or synthetic fibers. A sheet material may for example have a relatively small thickness, especially less than or equal to 3 mm, for example equal to about 100 microns, and be at least partially or completely flexible. In an exemplary implementation of the invention, the sheet material can be packaged in a reel, especially before being cut to the desired format. The method according to one of the aspects of the invention may comprise the following step: projecting at least one jet of pressurized fluid, in particular a jet of water, onto the layer of still wet paper so as to form thereon, by removal of material, at least one window.

A layer of still wet paper may have, for example, a moisture content of greater than 5%, especially 10%, for example 20%.

Thanks to the invention, the cutting of one or more windows in the sheet material can be performed in a relatively easy manner.

In an exemplary embodiment of the invention, the formation of windows on the sheet material by means of a fluid jet is performed in line, for example on a paper machine used to form a layer of paper .

Preferably, the paper layer is formed in a wet portion of the paper machine.

The paper layer is for example formed by dripping onto a forming fabric partially immersed in a suspension of fibers of a round shape. Alternatively, the paper layer may be formed by dripping onto a flat table forming web (also known as a Foudrinier Machine) or by injecting and draining fibrous material onto a web of a rotating cylinder.

When the sheet material has at least two layers of paper assembled, the fluid jet advantageously serves to form at least one window extending through the two layers of paper.

In an exemplary implementation of the invention, the method comprises the following steps: forming a first, respectively a second, of the two layers of paper on a first, respectively a second forming web partially immersed in a fiber suspension , assemble the two layers of paper. In a variant, the process comprises the following steps: forming a first of the two layers of paper by injection and dewatering fibrous material on a web of a rotating cylinder (also called "forming" in English), forming a second of the two layers of paper on a training cloth partially immersed in a suspension of fibers, assemble the two layers.

The two layers may have different grammages, one being for example greater than 50 g / m ² and the other less than this value.

Preferably, the jet of fluid is projected intermittently, two successive projections of the jet being separated by a stopping time.

By controlling the size and / or shape of the fluid jet and the duration of each projection, as well as the speed of travel of the paper layer (s) on the paper machine, it is possible to form on the sheet material windows having the desired size and / or shape, for example a succession of windows having different dimensions and / or shapes.

The invention thus allows great flexibility in the choice of dimensions and / or shapes of the windows, which is particularly advantageous, especially with respect to the case where the windows would be made using a punching tool that must be changed. according to the desired dimensions and / or shapes of the windows. The invention makes it possible, if desired, to make windows of relatively large dimensions.

In an exemplary implementation of the invention, between two jet stopping times, the jet is projected for a duration chosen so as to form a window having a length, measured in a direction of movement of the sheet material. on the paper machine, for example between 4 mm and 40 mm, in particular between 7 mm and

15 mm.

The stopping time between two successive projections may be chosen so that two successive windows are spaced apart by a distance of between 1 cm and 40 cm, in particular between 4 cm and 15 cm, for example being close to 8 cm. The jet may have a width, measured transversely to a direction of movement of the sheet material on the machine, between 4 mm and 40 mm, in particular between 5 mm and 20 mm, being for example close to 15 mm.

The jet may also have a width, measured transversely to a direction of movement of the sheet material on the machine, between 5 mm and 50 mm, in particular between 10 mm and 30 mm, being for example close to 20 mm.

Preferably, the fluid jet is a jet of water sprayed at a pressure of between 50 and 4000 bar, for example between 1000 and 2000 bar. Advantageously, the windows are formed on the sheet material immediately downstream of the wet portion of the paper machine, before passing over a dryer assembly of the paper machine. For example, the moisture content may be at least 50%, for example 60 to 70%, the moisture content being measured according to ISO 287: 1985.

Alternatively, the windows are formed on the sheet material at a dryer assembly of the paper machine, before the paper layer or layers are completely dried.

Advantageously, the paper machine comprises a system for recovering the material removed by the jet of fluid, this recovery system being able to be arranged to evacuate the material removed towards the wet part of the paper machine in order to be reused, which reduces material losses.

All material initially present at the window location can be removed and recovered. In an exemplary implementation of the invention, the paper machine comprises a cutting system comprising at least one jet nozzle of the fluid jet, the cutting system being advantageously arranged to prevent the formation of drops of liquid at the of the projection nozzle. The cutting system may comprise for example a system generating a vacuum at the nozzle to suck any drops that may form, which prevents them from falling on the paper layer.

The one or more nozzles of the cutting system may be arranged, if necessary, to be movable relative to a fixed portion of the paper machine when cutting the window into the sheet material. This displacement may for example be in a direction opposite or identical to the direction of travel of the paper layer on the paper machine. Such displacement may allow for a lower relative speed between the nozzle and the sheet material and may allow for a relatively high sheet material travel speed while having a relatively short operating time of the nozzle. In an exemplary implementation of the invention, the fluid jet may have in cross section a shape chosen from: a straight segment, a corner such as a right angle corner, a non-rectilinear curve such as a circular arc, an oval portion or an S, this list not being limiting.

The invention thus makes it possible to produce windows with a large variety of shapes. The cutting system may comprise for example at least two separate nozzles arranged to project two jets of fluid to form together a window in the sheet material.

The projected fluid jets may be identical, symmetrical to one another with respect to a plane or may have different dimensions and / or shapes. The windows formed on the sheet material preferably have a closed outline.

The window can be made at least partially, for example totally, in a region of the sheet material having a filigree clear zone, that is to say having regions of reduced thickness relative to the vellum zone of the sheet, for example a clear watermark, preferably a screened watermarked area (area which has a plurality of small regions of reduced thickness).

The presence of this clear watermarked zone may facilitate the formation of the window by reducing the amount of material to be removed with the fluid jet (s).

This can also lead to a sheet material that is more difficult to counterfeit.

The wet part of the paper machine may comprise one or more round shapes or, alternatively, at least one flat table.

The layers of paper may, where appropriate, be glued after the formation of the windows by the jet of fluid. In an exemplary implementation of the invention, the method comprises the following step:

- At least partially introduce a web structure within the sheet material.

The strip structure introduced at least partially into the sheet material may have a relatively large width, for example a width greater than 1.5 mm, especially greater than 2 mm, for example between 4 and 20 mm. When the sheet material comprises at least two layers of paper, the method may comprise the following step:

- bring the band structure between the two layers of paper during assembly thereof. Alternatively, the method may comprise the following step:

at least partially incorporating the strip structure into a layer of paper of the sheet material, during the formation of this paper layer, this layer may in particular comprise, on one side, at least one window leaving at least one least a portion of the band structure. The first layer of paper provided with windows can be assembled, if necessary, with another layer of paper in order to hide any defects appearing on the first layer of paper, as described in patent applications EP 0 860 298. and EP 0 625 431. The paper layer for masking defects preferably has a basis weight less than that of the first layer. At least one of the layers of paper may comprise a filigree clear zone, preferably a clear watermark, for example an intricate watermark.

The window can be made in this watermark, as mentioned previously.

The window may be surrounded, at least partially, with a watermarked area, this area may include light portions and / or dark portions of thicknesses equal to or greater than the vellum area of the paper.

The window may be formed on the sheet material away from the strip structure, the strip structure not being apparent through the windows formed by the jet of fluid. The watermark can also be formed away from the web structure.

The web structure may comprise a layer of transparent synthetic material, for example polyester, and, if desired, one or more coatings such as a magnetic coating. The band structure may include inscriptions and / or patterns. The structure may comprise an at least partially metallized layer or a metal layer.

In an exemplary implementation of the invention, the band structure comprises at least one authentication and / or identification element chosen from least one of the following elements: an element for highlighting a falsification, in particular visible and / or detectable by means of a specific detection device, an element with variable, interferential and / or diffractive optical effect, iridescent or liquid crystal, a magnetic or crystalline coating, magnetic fibers, magnetic resonance detectable tracers, X-ray detectable tracers, biomarkers, a varnish or an ink, luminescent, fluorescent or phosphorescent tracers, photochromic compounds , thermochromic, electroluminescent and / or piezochromic and / or that change color in contact with one or more predetermined products. The aforementioned watermark may be at least partially covered by a film or foil of synthetic material, for example polyester or polyethylene. The latter may have a thickness between 10 and 30 microns. The film or foil may in particular comprise on its underside a heat-sealable adhesive which is applied to the paper and security elements such as a hologram, in particular on its outer face. The sheet material may comprise at least one layer of paper comprising at least one window made during the formation of the paper layer.

Another subject of the invention, according to another of its aspects, is a paper machine comprising:

a wet part arranged to form at least one layer of paper; a cutting system arranged to project at least one jet of fluid under pressure, in particular a jet of water, onto the layer of paper still wet so as to form on this, by removal of material, at least one window. The moisture content of the still wet paper layer is for example between 60 and 70%.

Preferably, the wet part of the machine comprises at least one of the following elements:

a forming fabric at least partially immersed in a suspension of fibers,

a fabric of a rotating cylinder, also called "forming", and a device for injecting fibrous material onto this surface. The paper may be based on synthetic and / or natural fibers. Preferably, the machine comprises a system for recovering the material removed by the jet of fluid, this recovery system being advantageously arranged to evacuate the recovered material to the wet part in order to reuse it.

In an exemplary implementation of the invention, the cutting system is disposed between the wet portion and a dryer assembly of the paper machine.

Alternatively, the cutting system is disposed at a dryer assembly.

The invention further relates, in another of its aspects, to a sheet material comprising: at least one layer of paper, in particular two layers of paper assembled,

- in particular at least one web structure introduced at least partially within the sheet material, and having a width less than that of the sheet material, - at least one window passing through the sheet material and arranged, if necessary, remotely of the band structure.

The strip structure may have a width greater than 2 mm, in particular between 4 and 20 mm.

In an exemplary embodiment of the invention, the window formed on the sheet material by means of the fluid jet has on its inner contour portions of paper fibers extending in the window, which gives an impression that the window was formed by a cut not perfectly clear.

The pressure of the fluid jet can thus be chosen so that the window is cut relatively cleanly while giving this window the aforementioned appearance. In an exemplary implementation of the invention, the sheet material comprises an applied film or foil, for example glued, on one of its faces so as to cover the window.

The material may comprise a plurality of windows spaced two by two from a distance of between 1 cm and 40 cm, in particular between 4 cm and 15 cm, for example being close to 8 cm.

The windows may, if necessary, have an area of between 10 mm ² and 1600 mm ² , in particular between 30 mm ² and 300 mm ² . The invention further relates, in another aspect, to a security document and / or value incorporating a sheet material as defined above.

The security and / or value document may be one of the following: a bank note, an identity document, a passport slip or cover, a visa, a coupon, a document of value other than a bank note, for example a check or a credit card, a protection and / or authentication label, a traceability label.

at least one filigree clear zone in at least one of the layers of paper, in particular a clear watermark, for example a screened watermark,

at least one window extending at least partially in the filigree clear zone.

The window can be completely surrounded by the light area.

The window may be present only in the paper layer having the watermark or alternatively in the two layers of paper.

The sheet material may comprise a web structure introduced at least partially within the sheet material, for example away from the window and the filigree clear area.

The invention will be better understood on reading the following detailed description of nonlimiting examples of implementation of the invention and on examining the appended drawing, in which: FIG. schematically and partially, a paper machine according to the invention,

FIGS. 2 and 3 are enlarged diagrammatic and partial views of a wet part of the machine of FIG. 1,

FIG. 4 represents, schematically and partially, a cutting system of the paper machine of FIG. 1, - Figures 5 and 6 show schematically and partially in cross section, sheet materials according to two examples of implementation of the invention,

FIG. 7 schematically and partially shows the sheet material of FIG. 6, seen from above,

FIG. 8 is a graph illustrating the variations in the time of the pressure of the water jet,

FIG. 9 is a diagrammatic and partial representation of a wet part of a paper machine according to another embodiment of the invention, FIG. 10 is a diagrammatic and partial representation of a sheet material conforming to a example of the invention,

FIG. 11 is an enlarged, schematic and partial view of a window of a sheet material according to an example of the invention,

FIGS. 12 to 14 show, schematically and partially, various examples of jet nozzle design of the fluid jet as well as examples of windows obtained using these nozzles, and

- Figure 15 shows, in top view, a security document according to another example of implementation of the invention.

In the drawing, for the sake of clarity, the relative proportions of the various elements represented have not always been respected, the views being schematic.

FIG. 1 shows a paper machine 10 comprising a wet part 9 comprising first and second 2 paper-forming portions, a circuit of a gripper strip 3, in particular made of felt, a set of dryer 4 and a assembly press-binder 5 (or set sizepress). In the example shown, the paper machine 10 is round.

Alternatively, the paper machine may be of the flat table type. Each forming portion of the paper 1, 2 comprises a tank 11 containing a suspension 12 of fibers, for example cellulose fibers and / or cotton linters and / or synthetic and / or artificial fibers, in which is partially immersed a rotating roll 13 defining a surface 14 in contact with which a layer of paper is continuously formed. As illustrated in FIGS. 2 and 3, the paper layer 15 formed by dripping onto the first portion 1 is conveyed by means of the gripper belt 3 to the second portion 2, the assembly of the first paper layer 15 with a second paper layer 16 formed on the portion 2 is made for example by passing these layers of paper 15 and 16 between the rotating fabric cylinder 13 of the wet part 2 and a rotating cylinder 18.

In the example under consideration, the first paper layer 15 has a density of about 25 g / m ² and the second paper layer 16 has a density of about 65 g / m ² . A strip structure 20 is introduced between the paper layers 15 and 16, during the assembly thereof.

In an example not shown in the figures, the strip structure 20 is introduced into one of the paper layers 15 and 16 during the formation of this layer. The latter may have windows revealing on one side the web structure 20. These windows can be made for example using reliefs present on the rotary web cylinder 13, as described for example in patent applications. EP 0 860 298 and EP 0 625 431.

The web structure 20 has a width smaller than that of the paper layers 15 and 16, being in particular between 2 mm and 20 mm, and may comprise for example a polyester film and, where appropriate, a metallized layer.

The strip structure 20 may have rectilinear and parallel longitudinal edges.

The band structure 20 may comprise, if desired, at least one authentication and / or identification element chosen from one of the following elements: a highlighting element of a falsification, in particular visible and / or or detectable by means of a specific detection device, an element with variable optical effect, interferential and / or diffractive, iridescent or liquid crystal, a magnetic or crystalline coating, magnetic fibers, tracers detectable by magnetic resonance, detectable tracers by X-ray fluorescence, biomarkers, a varnish or an ink, luminescent, fluorescent or phosphorescent tracers, photochromic, thermochromic, electroluminescent and / or piezochromic compounds and / or which change color in contact with one or more predetermined products. The paper layers 15 and 16 with the web structure incorporated therebetween form a sheet material 22 which is transported by means of the gripper belt 3 to the dryer assembly 10.

The gripper 3 is separated from the sheet material 22 at a location A of the paper machine 10, upstream of the dryer assembly 4, the paper layers 15 and 16 being still wet and having a moisture content of example greater than 10%, especially 20%.

In order to form windows 25 on the sheet material 22, as illustrated in FIGS. 5 and 6, a cutting system 27 is disposed between the location A and the dryer assembly 4, this cutting system 27 being arranged to projecting a jet of water pulsed at a pressure for example between 1000 and 2000 bar, to form the windows 25, by removal of material, on the moving sheet material 22.

As illustrated in FIG. 4, the cutting system 27 comprises a nozzle 28 projecting the jet of water 29, the cutting system being able to be arranged to prevent the formation of drops of liquid at the nozzle 28.

The paper machine 10 further comprises, below the cutting system 27, a recovery system 30 arranged to evacuate the material removed by the jet of water 29 to the wet part 9, as illustrated in particular in Figures 1 and 4 .

The recovery system 30 may for example be arranged to create a vacuum to suck up the removed material.

This makes it possible to recycle the recovered material by reinjecting it into the fiber suspensions 12.

In the example shown, the water jet 29 has a width /, measured transversely to a direction F of displacement of the sheet material 22 on the paper machine 10, this width / being for example between 5 mm and 5 cm , especially between 5 mm and 3 cm, being for example close to 15 mm.

By controlling the width / water jet 29, it is possible to form windows 25 with the desired width.

The jet of water 29 is sprayed intermittently, two successive projections of the jet 29 being separated by a stopping time At ₁ , as illustrated in the graph of FIG. 8. This time At ₁ can be chosen so that two successive windows 25 are spaced apart by a distance of between 1 cm and 40 cm, in particular between 4 cm and 15 cm, for example being close to 8 cm.

This downtime At ₁ corresponds for example to a duration of between 7 ms and 310 ms, in particular between 30 ms and 150 ms.

The jet 29 can be projected for a duration At ₂ chosen so as to form a window 25 having a length, measured in the direction F, of between 4 mm and 40 mm, in particular between 7 mm and 15 mm. This duration At ₂ can be for example between 3 ms and 30 ms, in particular between 6 ms and 12 ms. The windows 25 obtained have a rectangular shape, with a surface included in particular between 20 mm ² and 1600 mm ² , in particular between 40 mm ² and 200 mm ² .

The windows 25 are in particular made at a distance from the strip structure 20 and the longitudinal edges 32 of the sheet material 22.

After the formation of the windows 25, the sheet material 22 is fed into the dryer assembly 4.

The latter comprises a plurality of rotary cylinders 33 in contact with which the sheet material 22 is displaced.

After passing through the dryer assembly 4, the sheet material 22 is fed into the press-and-roll assembly 5 (or "size press") arranged to glue the two paper layers 15 and 16 and finish drying of these layers 15 and 16.

The cutting system 27 may be placed at another location of the paper machine 10, provided that at this location the paper layers 15 and 16 are still wet. The cutting system 27 may for example be arranged within the dryer assembly 4.

The sheet material 22 can receive an applied film or foil 35, for example glued, on one of its faces, so as to cover at least partially or completely at least one previously made window 25, as illustrated in FIG. The sheet material 22 can be cut into the desired format, as illustrated in FIG. 7, to form, for example, a security and / or valuable document such as a banknote or an identity document, and to receive a or more impressions. The film or foil 35 may comprise at least one authentication and / or identification element chosen in particular from at least one of the following elements: an element for evidencing a forgery, in particular visible and / or detectable at with the aid of a specific detection device, an element with an optical effect that is variable, interferential and / or diffractive iridescent or liquid crystal, a magnetic or crystalline coating, magnetic fibers, tracers detectable by magnetic resonance, tracers detectable by X-ray fluorescence, biomarkers, a varnish or an ink, luminescent, fluorescent or phosphorescent tracers, photochromic, thermochromic, electroluminescent and / or piezochromic compounds and / or which change color in contact with one or more predetermined products.

The film or foil 35 can be observed by transparency, through the window 25, for authentication and / or identification of the document.

Of course, the invention is not limited to the implementation examples which have just been described. For example, several cutting systems 27 may be provided at different locations of the paper machine 10 to form, for example, windows of different dimensions.

The sheet material 22 may comprise, where appropriate, a number of layers of paper greater than two, for example three or four layers of paper. As illustrated in FIG. 10, the sheet material 39 may be devoid of strip structure and be made for example with a single layer of paper.

This sheet material 39 comprises for example two windows 25 of rectangular shape.

The pressure at which the water jet 29 is projected can be chosen so that the window formed has an inner contour 37 along which portions of papermaking fibers 38 appear from the cut by the jet of water 29.

As illustrated in FIG. 11, the presence of these fiber portions 38 gives the window 25 a different appearance than a window formed on a plastic substrate.

FIGS. 12 to 14 show different examples of water jet shapes. In the example illustrated in FIG. 12, the water jet 29 has, in cross-section, a curvilinear shape substantially in an oval portion making it possible to form on the sheet material a window 25 having two parallel curvilinear edges 40.

In the example illustrated in FIG. 13, the window 25 is made using two water jets 29 projected by two separate nozzles. The water jets 29 are substantially symmetrical to one another with respect to a plane and each have an oval portion shape.

In the example illustrated in FIG. 14, the window 25 with a flag shape is made using a jet of water 29 having a substantially S-shaped shape. FIG. of a paper machine according to another example of implementation of the invention.

This wet part 42 differs from the wet part 9 previously described in that the paper forming portion 1 is replaced by a set 43 comprising a device 44 for injecting fibrous material onto a fabric of a rotating cylinder 45 still called "train".

The first paper layer 15 thus formed passes between the cylinder 45 and an additional cylinder 46.

This paper layer 15 is assembled with the second paper layer 16 formed on the forming portion 2. The weight of the layer 15, for example 25 g / m, is lower than that of the layer 16, which is for example 65 g / m.

FIG. 15 shows a sheet material comprising two superimposed layers of paper between which is arranged a web structure 20 such as a security thread, for example. The sheet material includes a screened watermark 50.

By "screened watermark" is meant a watermark in the sense of the application EP 1 122 360, comprising a set of small light regions 51 arranged in the manner of a halftone image.

The distribution of these light regions within the watermark may be non-uniform. These light regions have a surface mass strictly lower than that of vellum. Light regions with low optical density contrast with the higher density paper around them, and only a finite number of optical densities are found.

The presence of light regions in the paper, with variable distributions according to the locations of the pattern produced, can provide a macroscopic visual effect that reproduces the shadows of a classical watermark.

Preferably, the light regions all have the same surface mass, which results in the same optical density for all the light regions, with the irregularities of the paper. In this case, there are only two optical densities, namely that of the light regions and that of the paper.

The term "raster image" must be given a broad meaning that covers all types of frames or pseudo-frames, the shape and arrangement of the light regions and those of the "dark" regions not being limited to one particular shape and arrangement but may be arbitrary. A window 25 is made through the watermark 50.

A surfacing film 55 covers the watermark 50 and the window 25.

This film 55 may extend over the underlying paper layer on either side of the watermark.

The film 55 reinforces the area of the sheet material having the watermark.

The watermark can extend from one edge to the other of the material, as illustrated, or not reach the edges.

In one example, the watermark 50 is made of a fibrous layer 80 μm thick and a basis weight of 60 g / m ² . The film 55, 40 μm thick, is made of polyester and has on its outer surface a hologram.

The expression "having one" shall be understood as being synonymous with "having at least one", unless the opposite is specified.

Claims

A method of making a sheet material (22) by paper means, the sheet material having at least one layer of paper, the method comprising the step of: projecting at least one fluid jet (29) under pressure , especially a jet of water, on the layer of paper still wet so as to form thereon, by removal of material, at least one window (25).

2. Method according to the preceding claim, characterized in that the formation of one or more windows on the sheet material with the aid of the fluid jet is performed in line, on a paper machine (10) used to form the paper layer.

3. Method according to one of the preceding claims, characterized in that the paper layer is formed by dewatering on a forming web partially immersed in a suspension of fibers of a round shape.

4. Method according to one of claims 1 and 2, characterized in that the paper layer is formed by dripping on a forming web of a flat table.

5. Method according to one of claims 1 and 2, characterized in that the paper layer is formed by injection and dewatering fibrous material on a web of a rotating cylinder.

6. Method according to any one of the preceding claims, characterized in that the sheet material comprises at least two layers of paper (15, 16) assembled and in that the jet of fluid (29) serves to form at least one window extending across the two layers of paper.

7. Method according to the preceding claim, characterized in that it comprises the following steps: forming a first, respectively a second, said two layers of paper on a first, respectively a second forming web partially immersed in a suspension of fibers, assemble the two layers of paper (15, 16).

8. Method according to claim 6, characterized in that it comprises the following steps: forming a first of said two paper layers by injection and dewatering fibrous material on a web of a rotating cylinder (45), forming a second of the two layers of paper on a forming fabric (13) partially immersed in a suspension of fibers, - assemble the two layers.

9. Method according to any one of the preceding claims, characterized in that the jet of fluid is sprayed intermittently, two successive projections of the jet being separated by a stopping time (At ₁ ).

10. Method according to the preceding claim, characterized in that, between two stopping times, the jet is projected for a period (At ₂ ) chosen so as to form a window having a length, measured in a direction (F) moving the sheet material (22) on the paper machine (10) between 4 mm and 40 mm, especially between 7 mm and 15 mm.

11. Method according to one of claims 9 and 10, characterized in that the stopping time (At ₁ ) between two successive projections of the jet (29) is chosen so that two successive windows (25) are spaced apart by a distance of between 1 cm and 40 cm, in particular between 4 cm and 15 cm, for example being close to 8 cm.

12. Method according to any one of the preceding claims, characterized in that the jet (29) has a width (I), measured transversely to a direction (F) of displacement of the sheet material on the paper machine, included between 5 mm and 50 mm, in particular between 10 mm and 30 mm, being for example close to 20 mm.

13. Method according to any one of the preceding claims, characterized in that the jet of fluid is a jet of water sprayed at a pressure between 50 and 4000 bar, in particular between 1000 and 2000 bar.

Method according to one of the preceding claims, characterized in that the windows (25) are formed on the sheet material immediately downstream of the wet part of the paper machine, before passing over a drying unit ( 4) of the paper machine (10), the moisture content being for example at least 50%, for example from 60% to 70%.

Method according to one of claims 1 to 13, characterized in that the windows (25) are formed on the sheet material (22) at a dryer assembly (4) of the paper machine before the paper layer or layers are completely dried.

16. A method according to any one of the preceding claims, characterized in that the paper machine (10) comprises a system for recovering (30) the material removed by the jet of fluid, this recovery system being advantageously arranged to evacuate the removed material to the wet end of the paper machine.

17. Method according to any one of the preceding claims, characterized in that the paper machine comprises a cutting system (27) comprising a jet nozzle (28) of the fluid jet (29), the nozzle possibly being arranged to be movable relative to a fixed portion of the paper machine when cutting the window into the sheet material.

18. Method according to the preceding claim, characterized in that the cutting system (27) is arranged to prevent the formation of drops of liquid at the projection nozzle.

19. Method according to any one of the preceding claims, characterized in that the fluid jet has in cross section a shape chosen from: a straight line segment, a corner such as a right angle corner, a non-rectilinear curve such as a circular arc, an oval portion or an S.

20. A method according to any one of claims 17 to 19, characterized in that the cutting system comprises at least two separate nozzles arranged to project two jets of fluid to form together a window in the sheet material.

21. Method according to any one of the preceding claims, characterized in that each window (25) has a closed contour.

The method of any of the preceding claims, comprising the step of: at least partially introducing a web structure (20) into the sheet material.

23. The method according to the preceding claim, the sheet material comprising at least two layers of paper, the method comprising the following step: bringing the strip structure (20) between the two layers of paper (15, 16) at the same time. assembly thereof.

24. The method of claim 22, comprising the step of: at least partially incorporating the band structure into a layer of paper of the sheet material, during the formation of this layer of paper, the latter may in particular have, on one side, at least one window leaving at least a portion of the strip structure free.

25. Method according to any one of claims 22 to 24, characterized in that the window is formed on the sheet material, away from the strip structure (20).

26. Method according to any one of claims 22 to 25, characterized in that the strip structure (20) has a width greater than 2 mm, in particular between 4 and 20 mm.

27. Method according to any one of the preceding claims, characterized in that the sheet material comprises at least one layer of paper comprising at least one window made during the formation of the paper layer.

28. Method according to any one of the preceding claims, the window being made in a clear watermarked zone.

29. The method of claim 28, said clear area being a halftone watermarked area.

Paper machine comprising: - a wet part arranged to form at least one layer of paper, a cutting system (27) arranged to project at least one jet of fluid under pressure, in particular a jet of water, on the layer; paper still wet so as to form thereon, by removal of material, at least one window (25).

31. Machine according to the preceding claim, characterized in that the wet part comprises at least one of the following elements: a forming fabric (13) at least partially immersed in a suspension of fibers, a fabric of a cylinder ( 45) and an injection device (44) of fibrous material on this surface.

32. Machine according to one of claims 30 and 31, characterized in that it comprises a recovery system (30) of material removed by the jet of fluid, this recovery system being advantageously arranged to evacuate the recovered material to the wet part of the paper machine.

33. Machine according to any one of claims 30 to 32, comprising a dryer assembly (4), characterized in that the cutting system (27) is arranged between the wet part and the dryer assembly (4) .

34. Machine according to any one of claims 30 to 32, characterized in that it comprises a dryer assembly and in that the cutting system is disposed at the entire dryer.

Sheet material (22) comprising: - at least one layer of paper, in particular two layers of paper (15;

16) assembled, at least one web structure (20) at least partially introduced within the sheet material, and having a width smaller than that of the sheet material, at least one window (25) passing through the sheet material and arranged remote from the strip structure, the window being made by removing material by spraying at least one jet of fluid (29) under pressure, in particular a water jet, on a layer of still wet paper.

36. Material according to claim 35, comprising a filigree clear zone (50) and the window being made through said filigree clear zone.

37. Material according to one of claims 35 or 36, characterized in that the window is at least partly surrounded by a filigree zone, in particular filigree halftone.

38. Material according to any one of claims 35 to 37, characterized in that the strip structure has a width greater than 2 mm, in particular between 4 and 20 mm.

39. Material according to one of claims 35 to 38, characterized in that it comprises a film or foil (35) applied on one of its faces so as to cover the window (25).

40. Material according to any one of the preceding claims 35 to 39, characterized in that the film or foil covers at least partially the filigree zone.

41. Material according to any one of claims 36 to 40, characterized in that it comprises a plurality of windows spaced two by two from a distance between 1 cm and 40 cm, in particular between 4 cm and 15 cm, being for example close to 8 cm.

42. Material according to any one of claims 36 to 40, characterized in that the windows each have an area of between 10 mm ² and 1600 mm ² , in particular between 30 mm ² and 300 mm ² .

43. Safety and / or value document incorporating a sheet material according to any one of claims 36 to 42.

44. Safety and / or value document incorporating a sheet material obtained with the method according to any one of claims 1 to 30.