EP1581397B2 - Sheet with an anticpopying, reduced opacity area - Google Patents

Abstract

The present invention relates to printable security paper that includes a region capable of receiving printed indicia on the front side and on the reverse side which are observable in reflected light and form an image observable in transmitted light, as security element protecting against two-sided copying, characterized in that such region is a screened region having an average overall opacity less than the opacity of the vellum part of the rest of the paper, said screened region being made up from alternations of vellum miniregions, having an approximately constant thickness equal to that of the vellum part of the rest of the paper, and of miniregions of reduced opacity because of their smaller thickness compared with the vellum miniregions. The invention also relates to the security document obtained with this paper.

Description

The invention relates to a security document protected against forward and backward copying as support for a security paper having an area of reduced opacity made of a frame able to receive patterns by printing in particular front and back observable in addition to light transmitted as a security feature against double-sided copying.

In order to fight counterfeiting of bank notes by double-sided photocopy or using a scanner and a printer, suitable patterns have been created in a given area, with patterns on the front and reasons on the back of the note so that that these motifs complement each other to form an image or final representation, for example a set of graphic lines or alphanumeric characters or an image of a character or an animal, etc. When one observes the banknote in reflected light, one sees only the pattern realized on the observed face whereas, when one observes the ticket in transmitted light, one sees all the reasons which thus complete the final representation. According to a variant, identical patterns are made in coincidence on the front and back so as to observe in transmitted light an image which is also identical to the superimposed patterns.

These patterns are realized by impressions of solid colors or by impressions of lines or lines or other forms.

The skilled person qualifies these impressions under their English term "see-through" and for the variant of "print-through".

Some bills are of a weight and opacity low enough to allow the observation of these reasons to the extent that the prints are flat and / or are not too thin.

It has been desired to apply these prints to security documents having a higher grammage and / or opacity. We then came up against a problem of observation of the representation in transvision. In the European patent application EP 0388090 to remedy this, it has been proposed to make these prints in an area of reduced opacity, this area being made concretely by a watermark obtained in a traditional manner that is to say using a filigranous canvas embossed with a paper machine round-shaped type or a embossed embossed roll of a flat-table machine.

The problem which then arose was to obtain a zone of reduced opacity homogeneous and of large surface in order to be able to make patterns of sufficiently large size, the process with the traditional watermark zones only obtaining homogeneous areas of small area.

It was then proposed in the patent application EP687324 to make an area of reduced thickness and opacity of an area of more than 0.4 cm 2 by providing a paper obtained in twin-jet of which a jet has a zone of reduced thickness or even zero. This last means is limited to bi-jet paper and the area is quite fragile. Security papers, especially banknotes, are subject to heavy traffic, therefore they must have a high resistance to traffic and therefore a high mechanical strength.

Furthermore, the means for reproducing the patterns, such as photocopiers and scanners, allow the color copying recto / verso and have resolution powers increasingly important, so we search for patterns more difficult to counterfeit.

Nevertheless the plaintiff has found that currently the prints made of solid areas are the most used but also that they are relatively easy to reproduce by photocopiers or color scanners front and back. For example, the current notes of the new Euro coin of the European Community present, in one of their angles, on both sides of the bill, solid impressions of the dominant color of the said note and which form the value of the note. when observed in transvision. These impressions are not made in an area of reduced opacity, the opacity of the ticket allowing their observation; the solids are rather coarse and could be quite easy to reproduce.

The current papers do not allow to have reasons of a fineness and / or complexity sufficient to effectively fight against their reproduction, the areas of reduced opacity proposed until now being of too high opacity to allow to observe lines of a great finesse and / or not enough extended to print patterns large enough and / or too fragile to withstand traffic.

The applicant therefore aims to propose a security document comprising as support a security paper to make and observe patterns more complex and / or finer.

The document WO 0043216 also shows the state of the art.

The object of the invention is therefore to provide a security document protected against duplicate reproduction by photocopy or by scanner having as support a paper for observing more complex duplex prints and / or finer than currently to be difficult to reproduce, the mechanical characteristics of the paper necessary for its use being sufficient and moreover the printing area of these patterns being of a fairly large area.

The Applicant has found that the objects of the invention are achieved by proposing a security document comprising as support a security paper which has a reduced overall opacity zone and which is a halftone zone composed of alternations of small areas of reduced opacity by reduction of thickness and small areas of vellum which, by their density in number (their number per unit area), maintain a mechanical strength of said halftone area sufficient to maintain characteristics specific to the normal use of paper .

The invention thus proposes a security document protected against the recto-verso reproduction by prints present on the front and back, these prints forming patterns observable in reflected light and said patterns being arranged so as to compose a final representation observable in light. transmitted, document which is characterized by the fact that it comprises as support, a paper with a halftone area, said halftone area having a mean overall opacity less than the opacity of the vellum part of the rest of the paper and being composed of alternations vine minizons having a thickness substantially constant and equal to that of the vellum part of the rest of the paper and minizones of reduced opacity due to their reduced thickness compared to the vellum minizones, and that the impressions are present on the front and back of said halftone zone. The mechanical strength of said halftone area is sufficient to maintain characteristics specific to the normal use of the paper.

The invention advantageously makes it possible to provide a security document comprising as support a paper with at least one area of reduced opacity but the total area of which can be large, the size will be chosen according to the size of the final document and the reasons that we want to achieve. The total area of said screened area may be for example 1 cm2 but may be larger or smaller. The smallest dimension of said zone may be relatively large if necessary, in particular it is at least 0.5 cm. It is possible to easily make an area with a smaller dimension of 1 to 5 cm for example.

Said halftone zone has any shape, in particular circular, rectangular, square, star-shaped.

In one particular case, the raster zone and / or the raster itself of said zone may represent a particular design, such as a personalized design forming a letter or a set of letters possibly characteristics of the issuer of the security document according to the invention or a drawing that corresponds to that of the final representation, resulting from the patterns that printed on front and back.

Said halftone area is printable recto / verso including offset printing and intaglio printing.

Said halftone zone is preferably made by a method of watermarking by weft as described in the patent application EP1122360 .

This watermarking papermaking process uses a cloth used during the wet-paper-making phase, provided with a set of masks which creates, in an area of the paper lying to the right of the masks at the time of forming the paper , a set of minizones of reduced thickness, thus of reduced opacity, formed in the thickness of the paper, the zones between these minizones forming vine minizons.

The masks that are present on the canvas limit the accumulation of constituents, cellulosic fibers, cotton fibers, synthetic fibers such as polyolefin fibers or polyester fibers, mineral fibers, possibly fillers, the aqueous suspension to make the paper, they form minizones of reduced thickness.

The vellum minizones, formed between the minizones of reduced thickness resulting from the masks of the network, have a thickness substantially equal to that of a vellum part of the rest of the paper, that is to say outside the raster zone and other elements of security or impressions.

In a first embodiment of the invention, the subject fabric constitutes the paper forming fabric.

In a second embodiment, the fabric in question serves to lift the formed sheet.

In a third embodiment, the fabric in question is attached to a wet press that works the sheet still wet after lifting.

In a fourth embodiment, the fabric in question is attached to a filigree roller.

In a fifth embodiment of the invention, the subject fabric is attached to a graining element located outside the forming zone of the sheet.

The web may, for example, be on a round-shaped paper machine or on a flat-table paper machine.

In each of the embodiments described above, the set of masks may be on the inner face of the fabric, in its thickness or on the outer face of the fabric, several canvases may be associated.

Preferably, the network of masks is on one side of the fabric rather than in its thickness.

Of course, any combination of the embodiments described above is also possible.

We will now describe different achievements of the set of masks.

In a first embodiment, the set of masks is constituted by a monobloc grid, resulting from a plate of small thickness, in which were made openings, for example circular, and arranged in a regular or irregular network according to the visual effects sought. The parts of the grid remaining between the openings constitute the masks of the network.

The density in number (number per unit area) of the openings and their size are determined by those skilled in the art as a function of the basis weight of the paper, its composition and the desired opacity variation between said screen area and the vellum part. the rest of the paper and the desired visual effect. The experiment shows that the couple density of openings and size of the openings is a determining factor for the overall opacity of said halftone area.

Preferably, one will choose a network of masks with the largest possible number of openings and these openings being of small dimensions. Indeed, according to the numerous tests made by the Applicant, it seems that such a network makes it possible to obtain a paper with a halftone area having a global opacity reduced at best for producing and observing anti-copying motifs of a large size. finesse. The opacity measurements that follow were made according to ISO 2471 on an ELREPHO 2000 spectral photometer.

By way of particular example, circular openings with a diameter of 0.8 mm in a circular metal plate 1, 5 cm in diameter and present at a density of 55 per cm 2 led to the production of a screened area in cellulosic paper having a difference in opacities of 9.4 points between the average overall opacity of said area and the opacity of a vellum part of the rest of the paper.

According to another particular example, circular openings with a diameter of 0.39 mm in a circular metal plate 1.5 cm in diameter and present at a density of 115 per cm 2 led to the obtaining of a screened area in a cellulosic paper having a difference in opacities of 21 points between the overall average opacity of said area and the opacity of a vellum part of the rest of the paper.

However, care should be taken to maintain good mechanical strength in the screened area. At the end of these numerous tests, the Applicant estimates that a difference in opacity between 5 and 12 points, preferably between 6 and 10, between the overall mean opacity of said zone and the opacity of a vellum part of the remaining paper, allows to maintain a suitable mechanical strength to be able to withstand the various constraints related to traffic, including bank notes, the opacity has been measured according to ISO 2471.

In a second embodiment, the set of masks is constituted by a juxtaposition of small parts fixed individually to the fabric.

In a particular embodiment, the masks are at least partly in accordance with a particular pattern for customizing the sheet of paper, creating in the thickness thereof paper minizones repeating the pattern masks. For example, each pattern may form a letter or a set of letters possibly characteristic of the issuer of the security document according to the invention.

A grid can be easily made by photogravure from an image, the openings of this grid will correspond to the vellum minizones of the screened area of the paper.

A grid may be made of a network of elementary masks, the elementary masks being interconnected by narrow bridges.

The network can also be made in one-piece form, for example by cutting or etching a thin plate of metal or plastic. It can also be made from photosensitive compounds such as photocurable polymers, for example deposited on the fabric, the parts forming the openings being protected from radiation and removed by dissolution with a solvent. The network is preferably constituted by a flat metal grid fixed on the outer face of the fabric, that is to say the face which is in contact with the suspension of the fibrous paper composition.

During the paper forming phase, each elementary mask limits the accumulation of the constituents of the composition, in particular fibers suspended in the fabric and creates a minizone of reduced thickness, hence of reduced opacity, in the area. of paper lying at the right of this elementary mask.

Bridges create link portions that also form minizones of reduced thickness on the sheet.

When the elementary masks and the connection points are made in one-piece form, there is no such portion of reduced thickness which is isolated from the others.

The network of masks can still be made in the thickness of the fabric by sealing the pores of the latter locally. In particular, photosensitive compounds may be used according to the method described above.

The network of masks is replaced, in an alternative embodiment, by a plate having openings, this grid being obtained from a computer generated screen image.

Thanks to the halftone area of reduced opacity it is possible to make a double-sided identification of the impressions made therein and to obtain complex and / or fine patterns which will be easily observable in transvision.

Preferably, said prints comprise thin lines made on the front and back in said halftone area to form patterns observable in reflected light, said patterns being superimposed or being arranged to compose a final representation observable in transmitted light, such embodiments of prints have been described in the French patent application filed on July 19, 2002 under the filing number FR 02/09221 .

More particularly, at least a portion of said lines on the front and back have a width less than or equal to 110 μm, preferably less than or equal to 100 μm.

Preferably, the final representation observable in transmitted light has a relief and volume effect (3D effect) obtained by the variations in density and intensity of the lines.

One way to make the lines may be to print the lines such that two adjacent lines of the image are always one on one side and the next on the other side.

More generally, another way may be to print, by means of algorithms, series of lines on one side and their complementary to the other. The sets of front and back lines can be determined by mathematical means, encryption, etc.

The image to be observed in transvision can be an image as such but also a part of a larger image or portrait and in particular already existing on the document.

More particularly, the prints are strokes in black and / or according to gradations of gray and / or in color and / or changing in appearance depending on the angle of observation or under the action of an excitation source such as radiation, especially fluorescent, thermochromic or photochromic, and / or have electromagnetic properties including electroconductive, magnetic or magnetic resonance.

The document may also include solid color prints.

More particularly the invention relates to a bank note obtained with a security document as described above.

Of course the security document may include other security elements, including a security thread, boards, iridescent prints, watermark, etc.

Exemplary embodiments of such a security document will now be described.

According to a first example, in the screened area of a paper obtained as described above, the portrait of a man wearing a beard, limited to the central part of the face, namely the mouth, the nose and a part of the beard.

Such an image consists of lines; a set of lines is printed on the front and the complementary set on the back to form the portrait that is observable in transvision.

The image consists of more or less large and more or less dense lines, some of the lines having a width of 100 microns. The effect of relief and volume is obtained by the variations of density and intensity of the lines.

These lines are printed using a printing machine used to print banknotes and valuable documents. These machines can print both sides of a paper perfectly located relative to each other, what a photocopier or a printer (after scanning) office can do with limited precision.

The double-sided printing of the portrait gives an image observable in transvision, clear and quality.

If a counterfeiter tries to photocopy this image on both sides, he will not be able to locate both sides of the photocopy accurately and then the image will no longer appear clearly, there will be clusters of lines, the image will no longer be visible by transvision.

The man in the street can easily and immediately see that the document or ticket has been forged.

According to a second example, a fine grid is produced by printing in the screen area a paper obtained as described above, a grid on one side of the zone and the same grid on the back. The double-sided printing, being pinpointed with extreme precision on the machines dedicated to the printing of banknotes and security documents, the front and back grids being superimposed, the image of a single grid appears when observed in transvision and also in reflected light.

If a counterfeiter reproduces these grids by means of a copier or a printer (after scanning), there will be a shift of a bar or part of the bars and then the resulting grid of the superposition of the two front grids and back will become a cluster or even a black square although in observation in reflected light we would see a grid on the front or on the back.

The man in the street can easily and immediately see that the document or ticket has been forged.

Claims (10)

1. Security document protected against reproduction on the front/on the back by printing on the front and on the back, this printing forming patterns, which may be observed in reflected light, and these patterns being arranged so as to form a final picture, which may be observed in transmitted light, characterised by the fact that it has a paper with a screened area as support, this screened area having an average global opacity less than the opacity of the wove part of the rest of the paper and being formed with alternating wove mini areas with a more or less constant thickness equal to that of the wove part of the rest of the paper and mini areas of reduced opacity because of their reduced thickness in relation to the wove mini areas and there is printing on the front and on the back of this screened area.
2. Security document according to claim 1, characterised by the fact that the smallest dimension of this screened area is at least 0.5 cm.
3. Security document according to one of the previous claims, characterised by the fact that the difference in opacity between the average global opacity of this screened area and the opacity of a wove part of the rest of the paper is between 5 and 12 points, preferably between 6 and 10, the opacity being measured according to the ISO 2471 standard.
4. Security document according to one of the previous claims, characterised by the fact that the printing comprises fine lines on the front and on the back of this screened area.
5. Security document according to claim 4, characterised by the fact that at least part of the lines on the front and on the back have a width less than or equal to 110 µm, preferably less than or equal to 100 µm.
6. Security document according to one of claims 4 to 5, characterised by the fact that the lines are of variable density and intensity so that the final picture, which may be observed in transmitted light, has a relief and volume effect.
7. Document according to one of the previous claims, characterised by the fact that the printing, particularly the lines, is in black and/or various shades of grey and/or in colour and/or changes in appearance according to the angle of observation or the action of a source of excitation, such as radiation, particularly fluorescent, thermochrone or photochrome radiation and/or has electromagnetic properties, particularly electroconductive, magnetic or magnetic resonance properties.
8. Document according to one of the previous claims, characterised by the fact that the screened area and/or the screen of this area forms a special design, particularly a personalised design or a design corresponding to that of the final picture, resulting from the patterns which are printed on the front and on the back.
9. Document according to one of the previous claims, characterised by the fact that it is resistant to high circulation.
10. Bank note obtained with a security document according to one of the previous claims.