FR3085974A1 - METHOD FOR MANUFACTURING SHEET MATERIAL, MACHINE, SHEET MATERIAL AND RELATED SAFETY DOCUMENT - Google Patents

Abstract

The present invention relates in particular to a method of manufacturing a material (6) consisting of fibers and shaped in a strip, by wet papermaking, this material (6) being multilayer and comprising a first layer (4) of fibers and at least a second layer (5) of fibers joined together, process in which each layer of fibers (4, 5) is formed individually by draining on a forming fabric (3) in a forming section ( 1), then conveyed in a strip to an assembly section (2) in which said layers (4, 5) are assembled to form the multilayer material (6), and then to a dehydration and drying section, characterized by the fact that one proceeds, using a pressurized fluid, between said forming (1) and assembly (2) sections, at least one longitudinal strip (R) of material fibrous in only one (4) of said layers (4, 5) so as to form a continuous longitudinal window there.

Description

FIELD OF THE INVENTION

The present invention relates to a process for manufacturing a material consisting of fibers and shaped into a strip.

It also relates to a machine for manufacturing such a material. Other aspects of the invention relate to a sheet material, that is to say cut from the strip, as well as to a security and / or valuable document which includes it.

TECHNOLOGICAL BACKGROUND OF THE INVENTION

In the field of security documents and more particularly banknotes, the support usually used is paper. It has many advantages, in particular that of being able to integrate a certain number of security elements such as, for example, a watermark or a security thread.

Another advantage is, among other things, to be able to be easily printed in intaglio, that is to say with reliefs easily detectable to the touch. These elements are easily recognized by the general public and provide a strong means of authentication.

In order to improve the physical resistance of the support, some national banks use a transparent polymer which is subsequently opacified in white and printed. In addition to being mechanically more resistant, it makes it possible to achieve effective security of the transparent window type making it possible to see through the said support, from one or the other of its opposite faces.

This construction of a ticket, or rather of a transparent ticket portion, opened up many possibilities in terms of structure and made it possible to bring in a new element that is easily recognizable by the general public.

There are of course techniques known as paper transparency, which make it possible to create less opaque zones in the mass of paper fibers. However, it is impossible to obtain a completely transparent area, unless you physically create an opening in the window type paper.

Banknotes with this type of window perforation are becoming more and more popular today. Of course, the resulting windows are closed with transparent security films, on the one hand, to offer physical resistance to handling in circulation and, on the other hand, to serve as a platform (i.e. a support ), so as to accommodate security elements which can be authenticated from either side.

Thus, in order to close the windows, it is necessary to seal a film, for example plastic, on the paper area immediately adjacent to the window. The corresponding implementation methods are known to those skilled in the art under the term lamination.

This lamination process differs from the widely used hot transfer process. Thus, in particular, in the lamination process, the film carrying the security elements is directly deposited on the support, as opposed to hot transfer in which the carrier film is rewound after the thin film containing the security elements has been transferred on the support.

This lamination process suffers from several drawbacks, however. Thus, the film has mechanical properties, water absorption and contraction / expansion different from that of the paper support, so that the film, especially when deposited in strip over the entire height of a ticket , tends to cause curling of cut paper (which means that the paper tends to curl locally). In English, we talk about a curl phenomenon.

These problems are all the more important when the film is deposited on reel-to-reel machines before cutting the paper to obtain individual sheets. The film could have been stretched when it was deposited on the support and tends to regain its initial shape at the time of cutting, thus causing undesired deformation of the paper.

A solution to this problem has been provided by the marked application of a plastic film on the back of the paper having on the front the laminated film, called, in terms of the counterfoil profession to counterbalance the “curl” effect mentioned above. before. This is notably described in document EP 2077190.

This technique responds to the problem of paper deformation but creates a problem of excess thickness on the paper reels at the level of the laminated film and the back-foil, due to the cumulative thickness at this location of the laminated film, of the paper and of the cross foil.

Document EP 2860040 describes a paper formed from two layers of paper joined together. In each layer is formed a bowl (that is to say a recess which opens only on one of the two faces of the layer), the two bowls being located opposite one another.

Thus, vacuum areas are created locally in which the thickness of the paper is reduced and advantage is taken of the presence of the bowls to accommodate the aforementioned foils and counter foils. Thus, the thickness of the final product is drastically reduced in this area.

Several techniques for forming these bowls are mentioned, namely the preparation of a specific canvas for the main layer and the secondary layer, thus creating strips of paper of smaller thicknesses, but also localized calendering and localized shrinkage. of material in the secondary layer.

It appears from this document that the local reduction of the thickness of each layer requires additional specific means and that, when the two layers are assembled, it is necessary to position them correctly with respect to each other, at the risk of having bowls that are not exactly on the register.

An additional state of the art in this area is made up of the following documents:

WO 2007/042718 describes a method of manufacturing a sheet material comprising at least one window. This window extends transversely to the direction of movement of the sheet material on the manufacturing machine (running direction). When the material is formed from two assembled layers of paper, the window is formed through the assembly of the two layers by spraying a pressurized fluid. This fluid extends in the form of a brush whose width corresponds to the longitudinal extent of the window to be formed.

Although the formation of the window takes place while the material is still wet, it is indicated in this document that the pressure of the fluid pressure is between 50 and 4000 bar, for example between 1000 and 2000 bar.

It is easy to understand that this range of values is high and requires a significant amount of energy.

DE 3431577 relates to the formation of watermarks in the thickness of a paper during manufacture, which makes use of a partial removal of material using jets of water, air or by laser radiation.

US 2001/0004007 is concerned with cutting the irregular edges of a sheet material during manufacture.

It is the same for document US 2003/01196531 in which use is made of water jet cutting. This action is performed after the sheet material has passed between drying rollers.

Starting from this prior art, it is clear that there remains a need for a technique for manufacturing a material consisting of fibers and shaped in a strip, in which at least one depression is formed which is as simple as possible. to realize, very energy efficient and which requires, for its establishment, only a minimal modification of the existing paper making machines.

SUMMARY OF THE INVENTION

Thus, according to a first aspect, the present invention relates to a process for manufacturing a material made of fibers and shaped as a strip, by the wet papermaking process, this material being multilayer and comprising a first layer of fibers and at least one second layer of fibers joined together, process in which each layer of fibers is formed individually by draining on a forming fabric in a forming section, then conveyed in a strip to an assembling section in which said layers layers are assembled to form the multilayer material, and then to a dehydration and drying section, characterized in that the removal is carried out, using a pressurized fluid, between said forming sections and assembling, at least one longitudinal ribbon of fibrous material in only one of said layers so as to form a continuous longitudinal window therein.

Thus, advantage is taken, within the machine, of an area where there is space available for placing a source of fluid under pressure therein. In addition, the moisture content of the strip being very high in this area, a relatively low pressure of fluid is necessary to clear the window, resulting in significant energy savings.

Of course, for the sake of simplification, the rest of the online process is not described here, but the strip undergoes other processing steps (sizing or “sizing” in English, additional drying, calendering, etc.) before to be wound on itself in a reel.

According to other non-limiting and advantageous characteristics of this process:

- said pressurized fluid is water or air;

- the fluid pressure is less than 10 bar, preferably between 5 and 9 bar;

- The water content of said fiber layers, when carrying out said removal, is greater than 70%;

- Said forming section comprises means of draining through a canvas of a round shape or of a flat table partially bathed in an aqueous suspension of fibers, or by injection and draining of fibrous material on a canvas of a rotary cylinder;

- Use is made, for each longitudinal strip, of two jets of pressurized fluid, which are positioned so as to delimit the opposite edges of said longitudinal window;

- Said jets are oriented convergently, that is to say they are oriented towards the center of said longitudinal strip to be removed, so as to form with the plane in which said strip is contained, an angle x ° less than 90 °, preferably included between 45 ° and 90 °;

- Orienting said jets in the direction of movement of said strip material, from said forming section to said assembly section, preferably at an angle y ° less than 90 °, preferably between 45 ° and 90 °;

- use is made of jets having point or quasi-point impact zones;

- We proceed to the removal of said longitudinal strip from below said layer;

- Air is blown onto said layer, from above it, in an area exactly marked with that in which said pressurized fluid operates, this in order to facilitate the removal of the longitudinal ribbon of fibrous material.

Furthermore, the present invention provides a paper making machine, sheet material and a security and / or valuable document.

This paper making machine, which comprises a forming section with at least two stations for forming a strip of wet paper within which are formed, individually, at least two layers of fibers, an assembly section in which said layers are assembled to form the multilayer material, as well as a dehydration and drying section, is characterized in that it comprises, between said forming section and assembly section, removal means, at the using a pressurized fluid, at least one longitudinal ribbon of fibrous material in only one of said layers so as to form a continuous longitudinal window therein.

This individual sheet paper material, which comprises a first layer of paper and at least a second layer of paper joined together, said first layer being a surface layer, characterized in that said first layer of paper comprises at least one longitudinal window whose opposite edges are convergent, while the at least one second layer has no window opposite that of said first layer and is of constant thickness.

The security and / or value document is remarkable in that it consists, at least in part, of a material according to the preceding characteristic.

BRIEF DESCRIPTION OF THE DRAWINGS

Other characteristics and advantages of the invention will appear on reading the following description of a preferred embodiment of the invention. This description is made with reference to the accompanying drawings in which:

- Figure 1 is a schematic and partial view of a paper making machine according to the present invention;

- Figure 2 is a cross section of a layer of fibers formed within the machine of Figure 1 and means which allow to remove from this layer a longitudinal ribbon of fibers;

- Figure 3 is a partial cross-sectional view of the layer of Figure 2, this diagram being intended to show how the material of the longitudinal strip is removed;

- Figure 4 is a partial cross-sectional view of the layer of Figure 3 and air blowing means;

- Figure 5 is a cross-sectional view of the layer of the preceding figures after making a window;

- Finally, Figure 6 is a partial cross-sectional view of two layers of fibers assembled together.

DETAILED DESCRIPTION OF THE INVENTION

As indicated above, the present invention relates to a process for manufacturing a material made up of fibers and shaped into a strip.

By the expression, shaped as a band, it is meant that the material is manufactured continuously so as to constitute a single band of a few hundred to a few thousand meters in length. Of course, in the end, this strip will be cut into a series of individual sheets.

This process is implemented in a machine for manufacturing such a material which will be described below as a paper machine.

In general, the figures accompanying this text are for illustrative purposes only. This means that dimensions, including thicknesses, spacings and angles are exaggerated for the sake of simplicity and readability and do not accurately reflect reality.

This paper machine M is partially and symbolically shown in Figure 1. Only the sections of this machine are visible which are of interest in relation to the subject of the invention. This is particularly a training section 1 and an assembly section 2.

However, such a machine advantageously comprises a dryer assembly and a sizing press assembly not shown here. In the end, the material produced within this machine is intended to be wound on itself.

In a manner known per se, the training section 1 comprises two substantially identical training stations 10 and 11. Thus, station 10 comprises a tank 100 containing a suspension of fibers S which can be cellulose fibers, more particularly cotton fibers, synthetic fibers, natural fibers reconstituted with or without additional chemical grafting or any mixture of at least two of these different fibers.

In this tank is partially submerged a rotary cylinder 101 in canvas which defines, when it is rotated counterclockwise by arrow f, a peripheral surface in contact with which a layer 4 of fibers.

Similarly, the second training station 11 comprises a tank 110 in which is contained a suspension S identical or different in composition from the first mentioned above and where a cylinder 111 is bathed similar to the cylinder 101 and with the same direction of rotation f . This second station makes it possible to form a second layer 5 of fibers. These fibers are of the same nature or of a different nature to that of layer 4.

Of course, the speed of rotation of the cylinders 101 and 111 is one of the parameters which determines the thickness of the layers 4 and 5.

In an embodiment not shown, the two aforementioned cylinders bathe in one and the same tank.

Relative to the direction of advance of the layers 4 and 5 thus created, qualified as machine direction S _M , the station 10 is located upstream with respect to the station 11.

When layers 4 and 5 are formed, they are pressed and guided in the machine direction against a fabric 3 of a mat which is designed to have good retention of the fine fibers and fillers contained in the fiber layer but which remain sufficiently permeable to let air and water through.

Voluntarily, in FIG. 1, the fabric 3 is shown slightly apart from the layer 4, but only in order to clearly distinguish it from this layer.

It is for example a woven fabric of polyester and polyamide having a permeability of the order of 350 CFM (Cubic Feet per square feets of sample per Minute). Such a fabric is qualified as an SSB (Sheet Support Binder) fabric which qualifies a multi-layer fabric whose connecting threads are part of the structure, which makes it possible to bind the paper side to the machine side while serving as a support for the strip in constitution courts.

Within this relatively traditional architecture of a paper machine M, there is between the two stations 10 and 11 a gap which, according to the invention, is used to proceed, at this level, that is to say between the sections formation 1 and assembly 2, with the removal using a pressurized fluid, of at least one longitudinal ribbon R of fibrous material in the single layer 4 formed within the station 10. Of course, the term “longitudinal strip” is understood to mean a strip which extends in the direction of the strip being formed, in this case in the machine direction.

Thus, in the embodiment shown in the figures, preferably pressurized water is used and for this purpose pairs of nozzles 7 are used which direct jets of fluid so as to have point impact zones or quasi-punctual on the layer of fibers 4. This is in particular shown in FIG. 2 where the jets J allow very fine cuts D to be made within the layer 4.

In this interval I, the water content of the layers of fibers 4 and 5 is greater than 50% and advantageously greater than 70, even 80%. Therefore, the fluid pressure which it is necessary to use to carry out the removal of the ribbon R is relatively low and advantageously between 7 and 9 bar, due to the poor mechanical strength of the layer of fibers to this stage. This is in no way comparable to the high pressures used in the prior art, pressures which can be of the order of 1000 bar, or even higher.

As also visible in FIG. 2, the jets J are oriented in a convergent manner, namely that they are oriented towards the center of the longitudinal strip R to be removed, so as to form with the plane in which the layer 4 is contained an angle x ° acute between 45 and 90 ° and this in order to carry out a frank cut without bead on the edges of the layer 4 intended to be added to the layer 5.

The fact of using jets J with point or quasi-point impact zones, which jets are inclined at the above-mentioned angle x °, has many advantages. Among these, we note in particular the fact that a punctual jet requires less water pressure than a nozzle which would provide a jet in the form of a large and flat brush.

In addition, as shown in FIG. 3, the relative inclination of the jets J will cause the fibers of layer 4 struck by the jets to be released towards the center of the window or fall by gravity as shown by the arrows g of the figure 3.

Thus, a layer 4 is finally obtained, in which we have just made cuts, the longitudinal edges 40 of which are in theory of the shape indicated in FIG. 3.

In order to complete the removal of the longitudinal ribbon R, air is blown on the layer 4 from above it, and in an area exactly marked with that where the jets J operate, this in order to facilitate the removal of the ribbon R of fibrous material. This is represented in FIG. 4 in which the source of compressed air is referenced 8, while the air brush projected against the layer 4 bears the reference P.

In FIG. 1, it is noted that the means 7 for projecting pressurized fluid and the means 8 for projecting pressurized air direct jets which are inclined in the longitudinal direction at angles y °, respectively z °.

The inclination at the angle y ° allows a cut to be made in the fiber layer in the direction of advance (machine direction s _M ) of the paper strip, which makes it possible to make a clean cut. This angle can of course be adjusted according to the operating speed of the paper machine.

The angle z ° (oriented opposite to the angle y ° but without the absolute values of these angles being necessarily equal) and the distance of the air nozzles 8 from the fabric 3 can be adjusted to have a perfect detachment of the paper tape cut by the water jets. In addition, these air nozzles must be positioned according to a careful identification with respect to the zone in which the water nozzles act. If they are badly positioned, they will take off the edges of the layer 4 which must remain on the fabric 3 to join the second layer 5, thus generating defects on the final assembly. The width of the brush of pressurized air must be at most equal to the width of the ribbon R of cut paper. In an optimized setting, it can be narrower for more flexibility of positioning.

Indeed, if the angle x ° is well adjusted, the edges of the ribbon R of cut paper will tend to come off on their own. Thanks to the blowing in the center of the paper tape, it will peel off from the canvas 3.

These nozzles 8 are positioned so that the ribbon R of paper falls back into a vat of pulp and is then recycled.

As indicated above, the window F which is formed in the layer 4 has longitudinal edges 40 which are generally inclined. This is of particular importance in the assembly 6 of the layers which is formed in the end. Thus, if the angle x ° of the air nozzles is too high, that is to say too close to 90 °, then the cut is too sharp and practically perpendicular to the edges of the layer 4 of fibers remaining on the carpet and is then visible on the final paper. Indeed, the border delimiting window F is then clear with a marked difference in thickness generating a visible black line. In addition, with such an angle that is too large, slopes form to the left and to the right of the cut ribbon R on layer 4, so that they are also visible on the final sheet.

On the contrary, with an angle that is too small, the nozzles generating the jets J are too close to the paper and the congestion caused is significant with less flexibility for moving them.

A paper material is generated using the process of the invention which comprises a first perforated layer 4 as well as a second layer 5 of constant thickness. Usually, the window produced is not detectable with the naked eye but by vision systems, generally installed at the end of the paper machine. The area where the window is present is therefore checked online and, if drift occurs, the parameters for adjusting the water and air nozzles can be adjusted during production.

For purely indicative purposes, it is possible to remove according to the present invention, a ribbon 20 millimeters wide and a thickness of 12 micrometers.

Nozzles 7 and 8 can be easily adjusted if they are mounted on a graduated rail.

According to the invention, it is therefore possible to remove a ribbon of fibers at a stage when the layer of fibers has very little mechanical resistance and this without impacting the visual quality of the border zones for removing the ribbon.

Claims (14)

1. Method for manufacturing a material (6) consisting of fibers and shaped as a strip, by the wet papermaking process, this material (6) being multilayer and comprising a first layer (4) of fibers and at least a second layer (5 ) of fibers joined together, process in which each layer of fibers (4, 5) is formed individually by draining on a forming fabric (3) in a forming section (1), then routed in strip to an assembly section (2) in which said layers (4, 5) are assembled to form the multilayer material (6), and then to a dehydration and drying section, characterized in that one proceeds when removing, using a pressurized fluid, between said forming (1) and joining (2) sections, at least one longitudinal strip (R) of fibrous material in one ( 4) only said layers (4, 5) so as to form therein a continuous longitudinal window (F) . 2. Method according to claim 1, characterized in that said pressurized fluid is water or air. 3. Method according to one of claims 1 or 2, characterized in that the fluid pressure is less than 10 bar, preferably between 5 and 9 bar. 4. Method according to claim 1 to 3, characterized in that the water content of said layers (4, 5) of fibers, when carrying out said removal, is greater than 70%. 5. Method according to one of claims 1 to 4, characterized in that said forming section (1) comprises means for draining through a canvas of a round shape or a flat table partially bathed in a aqueous suspension (S) of fibers, or by injection and draining of fibrous material on a rotary cylinder fabric. 6. Method according to one of claims 1 to 5, characterized in that use is made, for each longitudinal strip, of two jets (J) of pressurized fluid, which are positioned so as to delimit the opposite edges (40) of said longitudinal window (F). 7. Method according to claim 6, characterized in that said jets (J) are oriented in a convergent manner, namely that they are oriented towards the center of said longitudinal strip (R) to be removed, so as to form with the plane in which said strip is contained an angle x ° less than 90 °, preferably between 45 ° and 90 °. 8. Method according to one of claims 6 or 7, characterized in that one directs said jets (J) in the direction of movement of said strip material, from said forming section (1) towards said section assembly (2), preferably at an angle y ° less than 90 °, preferably between 45 ° and 90 °. 9. Method according to one of claims 6 to 8, characterized in that use is made of jets (J) having point or quasipunctual impact zones. 10. Method according to one of claims 1 to 9, characterized in that one proceeds to the removal of said longitudinal strip from below said layer (4). 11. Method according to claim 10, characterized in that air is blown onto said layer (4), from above it, in an area exactly marked with that where the pressurized fluid operates in order to facilitate the removal of the longitudinal ribbon of fibrous material. 12. A paper-making machine (M), which comprises a training section (1) with at least two training stations (10, 11) of a strip of wet paper in which are formed, individually, the at least two layers (4, 5) of fibers, an assembly section (2) in which said layers are assembled to form a multilayer material (6), as well as a dehydration and drying section, characterized in that comprises, between said forming section (1) and assembly section (2), means of removal (7), using a pressurized fluid, of at least one longitudinal ribbon (R) of fibrous material in only one (4) of said layers so as to form a continuous longitudinal window (F) therein. 13. Individual sheet paper material, which comprises a first layer (4) of paper and at least a second layer (5) of paper joined together, said first layer (4) being a surface layer, characterized in that said first layer (4) of paper comprises at least one longitudinal window (F) whose opposite edges (40) are convergent, while the at least one second layer (5) is devoid of window facing that of said first layer (4) and is of constant thickness. 14. Security and / or valuable document made up, at least in part, of a material according to claim 13.