EP1994224B1 - Fibrous material sheet comprising a window and method for making same - Google Patents

Description

The present invention relates to a sheet of fibrous material comprising a window and a method of producing this sheet.

BACKGROUND OF THE INVENTION

When it is desired to make a window in a sheet of fibrous material, it is known first of all to produce the sheet of fibrous material and then to cut the fibrous material in a contour of the window to be made, for example by laser cutting and then gluing a segment of film having dimensions greater than the window and whose edges are applied on the periphery of the window on one side of the sheet of fibrous material. This method is not very satisfactory when the window is intended to provide a means of authentication of a document, for example a bank note, because it is relatively easy for a fraudster even poorly equipped to achieve in a sheet of paper a cutout having the same outline as the window of the authentic ticket and to apply a segment of film as on the authentic ticket.

It is also known from the document EP 860 298 to make a window using a transparent tape whose rectilinear longitudinal edges are trapped in the fibrous material during the production of the sheet of fibrous material. However, it is known that during the interlocking of a non-porous ribbon in a fibrous material, the fibers can only cover the edges of the ribbon on a small width, of the order of 2 mm, which does not constitute a sufficient imbrication. to fix a ribbon along the entire length of its edges. To to increase the width in which the ribbon edges are embedded in the fibrous material, it is also known to make perforations along the edges of the ribbon as is also recalled in the aforementioned document. This arrangement allows to interleave the ribbon edge to a width that can reach 4 mm but this is still insufficient to ensure satisfactory resistance of the fixing of the ribbon along its edge.

In order to attempt to solve this problem, it is provided in the aforementioned document to form on at least part of the ribbon a layer of complementary fibrous material which bridges the leaf portions extending on either side of the ribbon. transparent ribbon. However, this complementary layer is applied on one side of the transparent ribbon so that even if it is made with perforations, there is a risk of delamination of the complementary layer and therefore of deterioration of the sheet along one of the ribbon edges. In practice, it is therefore not possible to use this technique to make a large window in a sheet of fibrous material.

Moreover, it is known from the document W02004 / 050990 making windows in a sheet of paper from a transparent film ribbon having a variable width, the wide portions having only their edge covered with fibrous material while the narrow portions of the ribbon are completely covered with fibrous material to realize an anchoring of the ribbon in the sheet of fibrous material.

• former une première partie de couche de matière fibreuse au moyen d'un bain de fibres dans lequel est immergée une forme poreuse à laquelle sont associés des masques en relief non poreux,

• appliquer sur les masques des segments de film transparent ayant des dimensions supérieures à celles des masques, les segments de film étant reliés les uns aux autres par des tronçons de ruban qui sont en une seule pièce avec les segments de film et qui ont une largeur permettant un dépôt direct de fibres sur les tronçons de ruban, et
• assurer la formation d'une deuxième partie de couche fibreuse jusqu'à ce que les tronçons de ruban soient emprisonnés dans la couche fibreuse.

According to this document, it is intended to incorporate the ribbon in the fibrous material by implementing a method comprising the steps of:

• forming a first portion of fibrous material layer by means of a fiber bath in which is immersed a porous shape with which are associated non-porous relief masks,

• applying to the masks transparent film segments having dimensions greater than those of the masks, the film segments being connected to each other by ribbon sections which are in one piece with the film segments and which have a width allowing a direct deposit of fibers on the sections of ribbon, and
• forming a second fibrous layer portion until the ribbon sections are trapped in the fibrous layer.

However, it has proven difficult in practice to match the film segments with the relief masks of the porous form.

It was further envisaged in the document US 6,036,230 making windows in a sheet of fibrous material by incorporating into the fibrous material film segments whose edges are embedded in the fibrous material. It is known, however, that the overlap width of the edges of a film segment is a function of the porosity of the film, for example for a fully sealed segment the edges are covered over a width of about 2 mm while with a segment of micro-perforated film, we can achieve a recovery of about 4 mm. In either case the anchoring is insufficient to ensure a long-term maintenance of a large window in the sheet of fibrous material.

OBJECT OF THE INVENTION

An object of the invention is to provide a sheet of fibrous material having a large transparent window.

SUMMARY OF THE INVENTION

In order to achieve this object, the invention proposes a sheet of fibrous material having a window formed by a film segment having an edge forming a closed contour trapped in the fibrous material all along the closed contour in wherein the film segment has a serrated edge.

Thus, the film segment is firmly held in the fibrous material irrespective of the direction of the forces to which it is subjected. In addition, the fibrous material surrounding the film segment has a structure with a high resistance to forces, so that the film segment is weakly solicited during handling of the fibrous sheet.

According to an advantageous version of the invention, the serrated edge comprises sections of ribbon extending from a central part of the film segment in one piece with it, the ribbon sections having a width. less than the central portion of the film segment and being totally trapped in the fibrous material at least along the edge of the film segment. Thus, the ribbon sections constitute anchor lines of the film segment so that the attachment of the film segment is enhanced.

• immerger partiellement dans un bain de fibres une forme poreuse comportant des masques en relief,
• déposer successivement sur les masques en relief des segments de film ayant un bord formant un contour fermé dentelé ayant des dimensions supérieures à celles des masques en relief,
• assurer la formation d'une couche fibreuse jusqu'à ce que les bords dentelés des segments de film soient emprisonnés dans la couche fibreuse.

According to another aspect of the invention, this relates to a process for producing a sheet of fibrous material comprising windows, this method comprising the steps of:

• partially immersing in a fiber bath a porous shape with raised masks,
• depositing successively on the masks in relief segments of film having an edge forming a serrated closed contour having dimensions greater than those of the relief masks,
• forming a fibrous layer until the serrated edges of the film segments are trapped in the fibrous layer.

According to another embodiment of the method according to the invention, it comprises the steps of forming two jets of fibrous material each having openings and joining the jets by trapping the edges of film segments having a serrated closed contour having dimensions larger than the openings.

BRIEF DESCRIPTION OF THE DRAWINGS

• la figure 1 est une vue en coupe schématique illustrant un premier mode de mise en oeuvre du procédé selon l'invention,
• la figure 2 est une vue en perspective partielle d'un mode de réalisation du masque d'un premier mode de réalisation du segment de film,
• la figure 3 est une vue en coupe selon la ligne III-III de la figure 2, après réalisation de la feuille de matière fibreuse,
• la figure 4 est une vue en coupe analogue à celle de la figure 3 d'une variante de réalisation,
• la figure 5 est une vue de face d'un deuxième mode de réalisation de segment de film.
• la figure 6 est une vue de face d'un troisième mode de réalisation de segment de film.
• la figure 7 est une vue en coupe analogue à celle de la figure 1 illustrant un second mode de mise en oeuvre du procédé selon l'invention.

Other features and advantages of the invention will emerge on reading the following description of various embodiments of the method according to the invention, leading to different variants of the embodiment of the sheet according to the invention, with reference to FIGS. attached, including:

• the figure 1 is a schematic sectional view illustrating a first embodiment of the method according to the invention,
• the figure 2 is a partial perspective view of an embodiment of the mask of a first embodiment of the film segment,
• the figure 3 is a sectional view along line III-III of the figure 2 after making the sheet of fibrous material,
• the figure 4 is a sectional view similar to that of the figure 3 an alternative embodiment,
• the figure 5 is a front view of a second film segment embodiment.
• the figure 6 is a front view of a third film segment embodiment.
• the figure 7 is a sectional view similar to that of the figure 1 illustrating a second embodiment of the method according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

With reference to Figures 1 and 2 the process according to the invention uses, in a manner known per se, a porous form 1 partially immersed in a fiber bath 2 and driven in rotation while maintaining the liquid level inside the form 1 at a level lower than that bath 2.

The porous form 1 comprises relief masks 13 having a closed contour, here a star shape. In the embodiment illustrated, the masks 13 are made in a manner known per se by stamping the web of the porous form 1.

Segments of film 14 separated from each other and having dimensions greater than the dimensions of the masks 13 are brought by a support band 41 to be deposited on a mask 13 while it is still outside the bath. Note in this regard that if the mask 13 is porous, the film segment 14 can be kept pressed onto the mask 13 by a slight depression maintained within the form 1. If on the contrary the masks 13 are sealed, for example by means of a varnish applied to the surface of the mask, the experiment shows that the film segments 14 are maintained applied to the masks 13 by surface tension forces resulting from the slight film of liquid remaining on the masks 13 during of the rotation of the form 1, even when the masks 13 are outside the bath. The film segment 4 can also be held in place by an adhesive having a low tack or by a water-soluble adhesive.

The film segments have a closed contour edge which according to the invention is a serrated edge. In the first embodiment illustrated by the figure 2 , the serrated edge comprises sections of ribbon 42 in the shape of an S extending from the central portion 43 of oval shape in one piece with it. In the illustrated embodiment, the ribbon sections 42 further include perforations 44 of sufficient size that fibers can engage the perforations 44 and entangle with fibers above and below them. sections of ribbon 42.

During the rotation of the form 1, the fibers are deposited on the porous part of the shape 1 surrounding the masks 13, firstly below the overflowing edge of the film segments 14 and then above them to form a layer 10 trapping ribbon sections 42 and the edge of central portion 43.

At the outlet of the bath 2, the sheet of fibrous material obtained is taken up by a conveyor belt 44 which drives it to a finishing station. The sheet of fibrous material has windows defined by openings 16 on the side of the masks 13 and openings 17 on the side opposite to the masks 13. In the embodiment of FIG. figure 1 , the central portion 43 of the film segments 14 slightly overhang the masks 13, so that the openings 16 and 17 have the same dimension and are centered relative to each other. During a visual inspection of the sheet, the windows appear in the same star shape both in reflection and transparency, regardless of the side of the sheet being examined.

In the embodiment of Figures 3 and 4 , the central portion 43 of the film segments 14 overflows very much of the star contour of the masks 13, for example of the order of 5 mm. During the formation of the layer of fibrous material, the fibers slip under the edges of the film segments to come into contact with the edge of the masks 13 but cover the edge of the central portion of the film segments 14 only across the width usual 2 mm, while the ribbon sections are completely covered by the fibers. In the sheet of fibrous material finally obtained as illustrated by the Figures 3 and 4 , the windows 15 made are delimited on the side of the masks 13 by openings 16, 116 in the form of a star and the side opposite the masks 13 by openings 17, 117 of oval shape and of dimensions greater than the openings 16. If the film segments 14 are centered on the masks 13, the sectional view illustrated by the figure 3 shows that on the side of the opening 17 the window 15 will appear oval in reflection and star-shaped centered on an oval frame in transparency, while on the side of the opening 16, the window will appear in the form of a star both in reflection only in transparency. If, on the other hand, the film segments 14 are applied offset from the masks 13, on the side of the opening 117, the window will appear in the form of a star offset from the oval frame of the opening 116 as illustrated. over there figure 4 .

The figure 5 illustrates an embodiment of the invention according to which the sheet of fibrous material is produced according to a bijet technique, that is to say that a first jet 29 is produced on a first form 30 and a second jet 31 is made on a second form (not shown) and is brought by a conveyor belt 32 above the first jet to be fused with it while the two jets are still in the wet state. In the implementation mode illustrated by the figure 5 , the form 30 includes masks 33 similar to the masks 13 of the figure 1 . At the time of its separation from the porous form 30, the jet 29 therefore comprises openings 34 having the size of the masks 33. In this embodiment, the second jet 31 is formed in exactly the same way as the first jet 29 and therefore has openings 35 having dimensions identical to the openings 34.

Film segments 36 separated from one another and having dimensions greater than the dimensions of the masks 33 are brought by a support strip 37 to be deposited on the first jet 29 immediately upstream of its junction with the second jet 31. During the junction. jets, the film segments 36 are then clamped between the jets and the edge of the film segments 36 is thus trapped over the entire closed contour of the film segments 36. The film segments 36 may have a structure similar to the film segments 14 described with respect to the first embodiment of the method according to the invention.

The Figures 6 and 7 illustrate two other nonlimiting examples of film segments that can be used for the implementation of the invention. The figure 6 illustrates a segment of film whose edge has a serrated contour according to triangular teeth 39 while the figure 7 illustrates a segment of film having a serrated contour according to crenelated teeth 40. It should be noted in this connection that when the width of the teeth is small, for example less than 2 mm, it is possible to produce high teeth similar to the sections of ribbon of the figure 2 which then appear as spokes around the central portion of the film segment and provide particularly strong anchoring of the film segment in the fibrous mass.

In the case of large teeth, it is also possible to perforate the serrated edge so that it is possible to make a significant shift between the openings of the two jets vis-à-vis. By using different color jets and different aperture shapes in both jets, it is possible to obtain visual effects that are particularly difficult to reproduce.

Of course, the invention is not limited to the embodiments described and variations can be made without departing from the scope of the invention as defined by the claims.

In particular, although the invention has been described by mentioning only the entrapment of the edges of the film segments and ribbon portions in the fibrous mass, this imprisonment can be associated with a bonding by providing for a coating of the edges or the all of the surface of the film segments as well as the sections of tape with an activatable adhesive during the drying operations of the sheet of fibrous material.

It is also possible to use in a manner known per se the window thus produced to obtain particular visual effects, whether these are optical and / or chromatic. For this purpose the film segments can be transparent, semi-transparent or opaque depending on the desired effect.

Although the masks have been mainly illustrated as embossed areas of the porous form, masks reported on the porous form can also be used. It is also possible to deposit on the masks anti-adherent or hydrophobic substances avoiding any deposit of fiber on the masks.

Although the ribbon sections have been illustrated completely embedded in the mass of fibrous material, they may be flush with the sheet surface at a sufficient distance from the edge of the film segments so that near the edge of the film segments the ribbon sections are totally trapped in the fibrous material.

The film segments and sections of ribbon can also be used in a manner known per se to support authentication data produced by metallization, printing, etc.

Claims (10)

1. Sheet of fibrous material comprising a window formed by a segment (14; 36) of film having an edge forming a closed contour trapped in the fibrous material all along the closed contour, characterized in that the edge of the film segment (14; 36) is serrated (42; 39; 40).
2. Sheet of fibrous material according to claim 1, characterized in that the serrated edge comprises triangular teeth (39).
3. Sheet of fibrous material according to claim 1, characterized in that the serrated edge comprises crenellated teeth (40).
4. Sheet of fibrous material according to claim 1, characterized in that the serrated edge comprises short strips (42).
5. Sheet of fibrous material according to claim 1, characterized in that the fibrous material extends along offset contours (116, 117) on two opposite sides vertically aligned with the film segment (14).
6. Sheet of fibrous material according to claim 5, characterized in that the film segment is transparent or semi-transparent.
7. Sheet of fibrous material according to claim 1, characterized in that the fibrous material extends along contours (16, 17; 116, 117) having different shapes on opposite sides vertically aligned with the film segment (14).
8. Sheet of fibrous material according to claim 7, characterized in that the film segment is transparent or semi-transparent.
9. Method of making a sheet of fibrous material including windows, characterized in that it includes steps of partially immersing in a bath (2) of fibres a porous former (1) including masks (13) in relief, depositing successively on these masks segments (14) of film having an edge forming a serrated closed contour having dimensions greater than those of the masks in relief, and forming a fibrous layer (10) until the serrated edges of the film segments are trapped in the fibrous layer.
10. Method of making a sheet of fibrous material including windows, characterized in that it includes the steps of forming two jets (29, 31) of fibrous material each including openings (34, 35) and joining the jets by trapping edges of film segments (36; 6) having a serrated closed contour having dimensions larger than the openings.

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