EP2088003B1

EP2088003B1 - Colour switching

Info

Publication number: EP2088003B1
Application number: EP08101159A
Authority: EP
Inventors: Monique Golaire; Maryke Degryse; Nathalie Paquot; Paul Van Braeckel; Beni Haeyaert
Original assignee: National Bank of Belgium
Current assignee: National Bank of Belgium
Priority date: 2008-01-31
Filing date: 2008-01-31
Publication date: 2011-03-02
Anticipated expiration: 2028-01-31
Also published as: DE602008005253D1; ES2359536T3; EP2088003A1; PL2088003T3; ATE500069T1

Abstract

The invention relates to a method for printing one or more security items (10) on a substrate of which at least a part is made of a transparent material, wherein the method comprises the steps of - printing a first pattern of indicia (1) in at least two colours (Y, M, C) on one side of the said transparent material, this first pattern of indicia (1) being provided such that a partitive mixing of colours occurs between the colours (Y, M, C) of these indicia of the first pattern (1); - printing a second pattern of indicia (2) on the opposite side of the said transparent material, such that particular indicia of the first pattern (1) are at least partially overlapped by the indicia of the second pattern (2); - the overlapping indicia of the second pattern (2) having a filtering or masking function with relation to the overlapped indicia of the first pattern (1) such that, because of the parallax effect due to the thickness of the substrate, the partitive colour mixing of the indicia of the first pattern (1) changes with a changing angle of view resulting in a change of the overall colour of the indicia. The invention furthermore relates to a security item (10) printed on a security document according to such a method.

Description

The present invention relates to a method for printing one or more security items on a substrate of which at least a part is made of a transparent material, and in particular to a method for printing one or more security items on security documents, on a part of a security document or on a substrate that can be transferred to a security document. Security documents are in particular: banknotes, postage stamps, identity cards, passports, checks, certificates, certificates of authenticity, ... The present invention relates also to a printed security item manufactured according to such a method.
Printing security items, so called security printing is an application or combination of printing technologies such as offset, intaglio, silkscreen and letterpress. Security printing encompasses the printing of banknotes, postage stamps, stamps, stock certificates, identity cards, passports, checks, deeds, plane tickets, diploma's and other documents needing a protection against counterfeiting.
Security papers, such as banknotes circulate in a world where the threat of the counterfeiter is ever present. With the development of new printing processes and the introduction of new technologies, more methods of reproduction are available to the counterfeiter than ever before. It is therefore essential that security documents, such as banknotes should be practically forgery proof. This is achieved not only by the way in which the printing technologies and their combinations are used, but also through the nature of the substrate and the ink, and the use of special additional elements such as security threads, holograms, and so on.
Banknotes are generally printed on a substrate made of 100 % cotton and are further protected by a watermark, a security thread, fluorescent fibres of different colours and length, optical variable inks or other visual or machine detectable characteristics.
Document WO 97/47478 A discloses a method for printing one or more security items on a substrate of which at least a part is made of a transparent material. The substrate may be a paper sheet having a plastics material as the transparent viewing region. Said method results in a "see-through" feature wherein complementary images are provided on each side of the sheet precisely registered relative to one another such that when the sheet is held up to the light, the image on the back will fit exactly onto spaces within the image on the front, optionally with an even unprinted margin around the perimeter. For example, each image could comprise a series of coloured segments, segments on one side of the sheet fitting within the spaces between the segments on the other.
A disadvantage of banknotes made of cotton is their restricted lifespan. Banknotes in a synthetic material do not have this drawback, as they can last about four times as long as the conventional cotton notes. The plastic note technology uses a polymer plastic substrate instead of paper. Compared to paper, plastic banknotes are stronger and non-porous.
However, plastic banknotes have the disadvantage that a number of safety features such as real multitone watermarks, windowed security threads which are successfully used in paper notes, can not be used or are less effective when used in plastic notes.
Therefore it is an object of the present invention to provide a new method for printing one or more security items on a substrate, in particular, a method for printing one or more security items on a banknote, with which the above mentioned drawbacks are overcome and which results in a security item with a much higher security level against counterfeiting than the known methods.
The above mentioned object is achieved by providing a method for printing one or more security items on a substrate of which at least a part is made of a transparent material, as defined in claim 1.
The expression "indicia" as used in this text refers to any pattern consisting of lines, dots, etc. which may be applied in visible form on a document or which can be visualised under specific light circumstances, for example use of an invisible fluorescent ink which becomes visible under black light, etc.
As this invention is meant to be printed on a transparent substrate, it is clear that beyond the traditional printing technique all possible techniques to transfer images to the transparent substrate or to generate an image on such a substrate can be used, such as inkjet printing, thermal transfer printing, sublimation printing, etc.
This invention enables the printer of security documents to improve the security level of security documents, through an optimal use of the technical possibilities of existing banknote presses and/or other high tech machinery.
In an advantageous method according to the invention, the thickness of the substrate is of the same order of magnitude as the width of the indicia constituting the first and second pattern.
In a more advantageous method according to the invention, the thickness of the substrate and the width of the indicia of the first and second pattern are situated between 5 and 1200 µm.
The indicia preferably consist of lines and/or dots, more preferably being a line pattern.
In a favourable method according to the invention, the first and second pattern are printed in register.
This seriously hampers the counterfeiting, because the slightest shift of the images with respect to one another results in a situation wherein another colour pattern of the indicia is obtained than originally is intended.
In an advantageous method according to the invention, the overlapping indicia of the second pattern having a masking function with relation to the overlapped indicia of the first pattern are printed in an opaque ink or in a transparent ink printed in a high density such that, at least part of the first pattern is not visible because it is masked by the second pattern.
In a preferred method according to the invention, the overlapping indicia of the second pattern having a filtering function with relation to the overlapped indicia of the first pattern are printed in a transparent ink such that when the observer looks at the security item (10), at least part of the first pattern (1) has an altered colour because it is filtered by the second pattern.
It is a further object of the present invention to provide a new security item printed on a security document consisting of a substrate of which at least a part is made of a transparent material, in particular, a security item that is printed on a banknote, with which the above mentioned drawbacks are overcome and which results in a security item with a much higher security level against counterfeiting than the known security items.
This further object of the invention is solved by providing a security item printed on a security document consisting of a substrate of which at least a part is made of a transparent material, as defined in claim 9.
In a preferred embodiment of a security item according to the invention, the transparent material is a transparent synthetic material.
The transparent material preferably has a thickness of between 5 and 1200 µm.
In an advantageous embodiment of a security item according to the invention, the security item is printed by a method according to the invention as described above.
Additional features and advantages of the invention will be further explained on the basis of non-restricting exemplifying embodiments represented in the attached drawings and in the following detailed description. In this description reference is made to the following drawings wherein

figure 1a is a representation of a star that is provided with a line pattern that is printed in three colours being yellow, cyan and magenta on one side of a transparent substrate;
figure 1b is a representation of detail A as shown in figure 1a;
figure 2 is a representation of a line pattern that is printed on the opposite side of the transparent substrate and that is intended to overlap the line pattern as shown in figure 1a;
figure 3a is a representation of what is viewed when an observer looks perpendicularly to the security item;
figure 3b is a representation of detail S as shown in figure 3a;
figure 4a is a representation of what is viewed when the visual angle with which the observer looks at the security item changes by tilting the security item in one direction around an imaginary axis that is parallel to the lines of the line patterns as shown in figures 1a and 2;
figure 4b is a representation of detail T as shown in figure 4a;
figure 5a is a representation of what is viewed when the visual angle with which the observer looks at the security item changes by tilting the security item in opposite direction around an imaginary axis that is parallel to the lines of the line patterns as shown in figures 1a and 2;
figure 5b is a representation of detail U as shown in figure 5a;
figure 6a is a representation of what is viewed when the security item is reproduced by a counterfeiter by copying the security item;
figure 6b is a representation of detail X as shown in figure 6a;
figure 7a is a representation of what is viewed when the security item is reproduced by a counterfeiter when the lines of the different line patterns at each side of the transparent substrate are not printed in perfect register;
figure 7b is a representation of detail Z as shown in figure 7a.

According to the method of the invention, security documents, such as banknotes, credit cards, drivers' licenses, etc. printed on a substrate of which at least a part is made of a transparent material, for example a synthetic material such as polypropylene or polyester, can be provided with a new security item via known banknote presses. Another possibility is transferring a transparent substrate, comprising a security item according to the invention, to a document.
According to this invention, a first pattern of indicia is printed on one side of said transparent material, wherein this pattern of indicia is provided in such a way that a partitive mixing of colours occurs between the colours of these indicia, partitive mixing of colours being defined as the mixing of small colour patches that are placed next to one another. On the opposite side of the transparent substrate, a second pattern of indicia is printed in such a way that particular indicia of the first pattern are at least partially overlapped by the indicia of the second pattern. The overlapped indicia of the second pattern can therewith have a filtering or a masking function with relation to the overlapped indicia of the first pattern such that, because of the parallax effect due to the thickness of the substrate, the partitive colour mixing of the indicia of the first pattern changes with a changing angle of view.
It is furthermore possible to provide at least part of the side of the substrate where the second indicia are situated with a reflective layer, for instance a white layer printed in an opaque ink, over the second indicia (such that the second indicia are situated between this reflective layer and the substrate).
The thickness of the substrate is preferably of the same order of magnitude as the width of the indicia constituting first and second pattern. The thickness of the substrate and the width of the indicia are preferably situated in between 5 and 1200 µm. The thickness of the substrate therewith depends from the type of security document and also from the design of the security document ("graphism").
The indicia of the first and second pattern preferably consist of lines and dots, more preferably being a line pattern.
In order to hamper the counterfeit, the indicia of the first and second pattern are preferably printed in perfect register.
When the overlapping indicia of the second pattern have a masking function with relation to the overlapped indicia of the first pattern, then these overlapping indicia are preferably printed in an opaque ink or in an ink that is darker coloured than the ink in which the indicia of the first pattern are printed, the best result being obtained when the second pattern of indicia is printed in a black colour. When the overlapping indicia of the second pattern however have a filtering function with relation to the overlapped indicia of the first pattern, then these overlapping indicia are preferably printed in a transparent ink not having a masking effect.
In an exemplary security item (10) printed by a method according to the invention, on one side of a transparent substrate having a thickness of 150 µm, a star (1) (as can be seen in figure 1a) is printed on one side of the transparent substrate, wherein this star (1) is provided with a line pattern that is printed in three colours being yellow (Y), cyan (C) and magenta (M) (as can be seen in figure 1b). The width of the lines of the line pattern is such that a partitive mixing of the colours yellow (Y), cyan (C) and magenta (M) is obtained, as can be seen in figure 1a, for instance 150 µm for the cyan (C) and the magenta (M) coloured lines, and 300 µm for the yellow (Y) coloured line. On the other side of the transparent substrate, a line pattern (2) consisting of black opaque lines (B) having a width of 300 µm is printed in register with the line pattern of the star (1), the black lines (B) thus having a masking function with relation to the lines (Y, C, M) of the line pattern of the star (1). This black line pattern (2) is printed such that, when an observer looks perpendicularly at the side onto which this black line pattern (2) is printed, only the yellow lines (Y) are visible, as can be seen in figures 3a and 3b, thus masking the cyan and magenta coloured lines (C, M).
When now the visual angle with which the observer looks at the security item (10) changes by tilting the security item in one direction (here clockwise) around an imaginary axis that is parallel to the lines of the line patterns (1, 2) as shown in figures 1a and 2, because of the parallax effect due to the thickness of the substrate, half of the yellow lines (Y) and the cyan coloured lines (C) becomes visible, as can be seen in figure 4b, giving a partitive colour mixing into the colour green (G)(see figure 4a).
When the visual angle with which the observer looks at the security item (10) changes by tilting the security item in opposite direction (here counterclockwise) around an imaginary axis that is parallel to the lines of the line patterns (1, 2) as shown in figures 1a and 2, because of the parallax effect due to the thickness of the substrate, half of the yellow lines (Y) and the magenta coloured lines (M) becomes visible, as can be seen in figure 5b, giving a partitive colour mixing into red (R) (see figure 5a).
When this security item (10) is reproduced by a counterfeiter by simply copying the security item (10), then the magenta and cyan coloured lines (M, C) get lost because they are masked by the black line pattern (2). Then, only the yellow and black lines (Y, B) are visible as a whole, resulting in a counterfeited security item (11) as can be seen in figures 6a and 6b. The counterfeiter then has to reproduce himself the magenta and cyan coloured lines (M, C), and adding these by the yellow lines that have to be separated from the black lines (B) in order to become the colour pattern of the star (1). When the counterfeiter succeeds to also reproduce the black masking lines (B), then he has to apply the coloured and black lines (Y, M, C and B), with the same accuracy as the original, on the correct side of the transparent substrate. When he doesn't succeed to do this, or in other words the line patterns (1,2) are not printed in perfect register, when the observer looks perpendicularly at the reproduced security item (11), then not only a star (1) in a yellow colour (Y) with black lines (B) occur, but also a line pattern in another colour or other colours occur, this depending on the displacement of the black lines (B) with relation to the coloured lines (Y, C, M). When for instance the yellow lines are masked, then the cyan and magenta coloured lines (C, M) become visible, as can be seen in figure 7a, and, due to the partitive mixing, a star (1) in a blue colour (BL) occurs (as can be seen in figures 7a and 7b).

Claims

Method for printing one or more security items (10) on a substrate of which at least a part is made of a transparent material, characterised in that the method comprises the steps of
- printing a first pattern of indicia (1) in at least two colours (Y, M, C) on one side of the said transparent material, this first pattern of indicia (1) being provided such that a partitive mixing of colours occurs between two neighbouring colours (Y, M, C) of these indicia of the first pattern (1) ;

- printing a second pattern of indicia (2) on the opposite side of the said transparent material, such that particular indicia of the first pattern (1) are at least partially overlapped by the indicia of the second pattern (2) ;

- the overlapping indicia of the second pattern (2) having a filtering or masking function with relation to the overlapped indicia of the first pattern (1) such that, because of the parallax effect due to the thickness of the substrate, the partitive colour mixing of the indicia of the first pattern (1) changes with a changing angle of view resulting in a change of the overall colour of the security item (10).
Method according to claim 2, characterised in that the thickness of the substrate is of the same order of magnitude as the width of the indicia constituting the first and second pattern (1, 2).
Method according to claim 2, characterised in that the thickness of the substrate and the width of the indicia of the first and second pattern (1, 2) are situated between 5 and 1200 µm.
Method according to any one of claims 1 to 3, characterised in that the indicia of the first and second pattern (1, 2) consist of lines and/or dots.
Method according to claim 4, characterised in that the first and second pattern (1, 2) are a line pattern.
Method according to any one of claims 1 to 5, characterised in that the first and second pattern (1, 2) are printed in register.
Method according to any one of claims 1 to 6, characterised in that the overlapping indicia of the second pattern (2) having a masking function with relation to the overlapped indicia of the first pattern (1) are printed in an opaque ink or a transparent ink printed in a high density such that when the observer looks at the security item (10), at least part of the first pattern (1) is not visible because it is masked by the second pattern (2).
Method according to any one of claims 1 to 7, characterised in that the overlapping indicia of the second pattern (2) having a filtering function with relation to the overlapped indicia of the first pattern (1) are printed in a transparent ink such that when the observer looks at the security item (10), at least part of the first pattern (1) has an altered colour because it is filtered by the second pattern.
Security item printed on a security document consisting of a substrate of which at least a part is made of a transparent material provided with one or more security items, characterised in that the security item consists of
- a first pattern (1) of indicia in at least two colours (Y, M, C) that is printed on one side of the said transparent material, this first pattern (1) of indicia being such that a partitive mixing of colours occurs between two neighbouring colours of these indicia of the first pattern (1) ;

- a second pattern (2) of indicia that is printed on the opposite side of the said transparent material, such that particular indicia of the first pattern (1) are at least partially overlapped by the indicia of the second pattern (2) ;

- the overlapping indicia of the second pattern (2) having a filtering or masking function with relation to the overlapped indicia of the first pattern (1) such that, because of the parallax effect due to the thickness of the substrate, the partitive colour mixing of the indicia of the first pattern (1) changes with a changing angle of view resulting in a change of the overall colour of the security item.
Security item according to claim 9, characterised in that the transparent material is a transparent synthetic material.
Security item according to claim 9 or 10, characterised in that the transparent material has a thickness of between 5 and 1200 µm.
Security item according to any one of claims 9 to 11, characterised in that the security item is printed by a method according to any one of claims 1 to 8.