WO2023274728A1

WO2023274728A1 - High-security magnetic security element for valued papers

Info

Publication number: WO2023274728A1
Application number: PCT/EP2022/066352
Authority: WO
Inventors: Annalisa COLOMBO; Marco DURINI; Matteo GALLIGANI; Maurizio Lazzerini
Original assignee: Eptainks S.P.A.
Priority date: 2021-06-29
Filing date: 2022-06-15
Publication date: 2023-01-05

Abstract

A magnetic security element (1) for valued papers, particularly banknotes and identity documents, comprising a series of magnetizable magnetic units (2) which are aligned along a longitudinal axis (X) and mutually spaced; at least one of the magnetic units (2) comprises two portions (2a, 2b), a first portion (2a) and a second portion (2b), which are separated by a separation slit (3) which is oblique with respect to the longitudinal axis (X) and are positioned so that at least one axis (Y) that is perpendicular to the longitudinal axis (X) affects both the first portion (2a) and the second portion (2b); the first portion (2a) is composed of a first magnetic ink which has a first magnetic coercivity and the second portion (2b) is composed of a second magnetic ink which has a magnetic coercivity that is lower than the first magnetic coercivity.

Description

HIGH-SECURITY MAGNETIC SECURITY ELEMENT FOR VALUED PAPERS

The present invention relates to a security element for valued papers, particularly banknotes and identity documents (for example passports) and the like.

In greater detail, the security element according to the present invention is a magnetic element of the type known as security thread or stripe or patch containing a magnetic or in any case magnetically encodable coding that is useful, particularly but not exclusively, to be inserted in bill paper and in particular in the paper of banknotes, in order to certify the authenticity of said banknotes, or in passports or in any other document in order to certify its authenticity.

As is known, the first systems of magnetic coding for security threads were provided in the 1980s; in particular, reference is made to the magnetic code known as SISMA, disclosed in 1986 by EP0310707. The basic principle of this system consists in providing a sequence of right-angled parallelepipeds with a magnetic property, interleaved by empty spaces, the length of which is free but the thickness of which is different in at least one parallelepiped for each code. A simplified recognition method can be performed by classifying the bits in sequence by measuring the length of the bits with high thickness, of the bits with low thickness and of the empty spaces.

The coding system as described in EP0428779B1 was provided in 1989 by utilizing the basic principle of the SISMA System. This system is again based on the printing of right-angled parallelepipeds with free length, provided with identical and/or different thickness but printed with magnetic inks provided with different coercivity, interleaved by spaces with free lengths.

Another magnetic security element, based on a system known as IMT, is described in WO 90/08367. This solution consists in providing magnetic right-angled parallelepipeds and spaces having a fixed length (for example 2 mm) and thus creating codes by filling with magnetic material said fixed measurement (assigning it the binary value "1") or by not filling said fixed measurement (assigning it the binary value "0").

A further magnetic security element, based on a magnetic coding system known as "MAG3", again consists in printing in a superimposed manner two right-angled parallelepipeds with two inks the coercivity of which is different but with a surface, of one of the two parallelepipeds, that is smaller on at least two sides with respect to the underlying parallelepiped.

EP2156414 discloses a further magnetic security element in which the alternation of parallelepipeds provided with magnetic inks with different coercivity and spaces, arranged on a medium continuously in a longitudinal direction, creates a coding.

In summary, therefore, known magnetic security elements are usually based on the printing of regular right-angled parallelepipeds.

Mainly two types of reader are known for the reading/decoding of these magnetic security elements of the type of magnetic security threads present in banknotes and provided with the combination of inks with high and low coercivity:

- the first type provides for making the magnetic thread that is present in the banknote transit at right angles to a reading head (entry of the banknotes from the long side);

- the second type provides for making the magnetic thread that is present in the banknote transit obliquely with respect to the head (entry of the banknote from the short side) for a transverse detection, the heads being arranged with an inclination from 40 to 50° (generally 45°) with respect to the longitudinal axis of the security thread.

The decoding of both types occurs by making the magnetic security thread that is present in the documents (banknotes) transit under a magnetic permanent magnet with high coercive power (approximately 10,000 Oe) which orients in saturation all the magnetic areas (printed with magnetic ink) univocally (N/S - N/S, etc.) so that a first inductive reading head detects the extent, position and dimensions of all the magnetic areas and of the associated interspaces; a second magnet, with a coercive power of approximately 1000/2000 Oe, rotates through 90° the magnetic flux of the areas printed with ink with low coercive power so that a second inductive head can detect only the areas printed with ink with high coercive power. The detection performed by the first head is termed first channel, while the detection performed by the second head is termed second channel.

This system comprising two heads and two magnets is termed dual channel sensor.

Although the magnetic security elements of the known type that have been mentioned are numerous and useful, the need continues to be felt to improve the security of these elements and in particular to obtain magnetic coding that is more difficult to forge.

Counterfeitings of magnetic codes on security threads are currently performed, for example, by cutting right-angled parallelepipeds from magnetic tapes used for other purposes. In this case the detected bits have, at both entry and exit, a leading edge that is parallel to the gap of the inductive head used to detect the code when they are read at right angles to the sequence of bits, or have the same angle, at both entry and exit, when they are read with inductive heads the gap of which is inclined.

The aim of the present invention is to improve the background art described above by providing a magnetic security element for valued papers that is capable of ensuring a higher security level.

Within this aim, an object of the present invention is to provide a magnetic security element for valued papers that allows to obtain coding that is more difficult to forge.

Another object of the invention is to provide a magnetic security element for valued papers that is easy to provide and economically competitive if compared with the background art.

A further object of the invention is to provide an alternative to the background art.

This aim, the objects mentioned and others which will become better apparent hereinafter are achieved by a magnetic security element for valued papers according to claim 1.

This aim and these and other objects are also achieved by a method for providing a magnetic security element according to claim 12.

Further characteristics and advantages will become better apparent from the description of some preferred but not exclusive embodiments of a magnetic security element for valued papers, illustrated by way of non limiting example with the aid of the accompanying drawings, wherein:

Figure 1A is a schematic plan view of a first possible embodiment of a magnetic security element contained in a valued paper;

Figure IB is a plan view of the security element of Figure 1A in isolation;

Figure 1C is a perspective view of the security element of Figure 1A in isolation;

Figure 2 is a view of the outcome of a reading of the magnetic security element of Figures 1A-1C performed with a head that is perpendicular to the longitudinal axis of the security element;

Figure 3 is a view of the outcome of a reading of the magnetic security element of Figures 1A-1C performed with a head inclined at 45° with respect to the longitudinal axis of the security element;

Figure 4A is a schematic plan view of a second possible embodiment of a magnetic security element contained in a valued paper;

Figure 4B is a plan view of the security element of Figure 4 A in isolation;

Figure 4C is a perspective view of the security element of Figure 4A alone, in which only the first portions of the magnetic units have been isolated;

Figure 4D is a perspective view of the security element of Figure 4A alone, in which only the second portions of the magnetic units have been isolated; Figure 5 is a view of the outcome of a reading of the magnetic security element of Figure 4 A, performed with a head that is perpendicular to the longitudinal axis of the security element;

Figure 6 is a view of the outcome of a reading of the magnetic security element of Figure 4A performed with a head that is inclined at 45° with respect to the longitudinal axis of the security element;

Figure 7 is a schematic plan view of a third possible embodiment of a security element and also shows the outcome of a reading performed with a head that is perpendicular to the longitudinal axis of said security element;

Figures 8, 9 and 10 are each a schematic plan view of a further possible embodiment of a security element according to the invention.

With reference to the figures, the magnetic security element, generally designated by the reference numeral 1 for all the embodiments, is of the type of a magnetic security thread for valued papers, particularly banknotes and identity documents (for example passports), i.e., it is adapted to be inserted therein in order to allow their authenticity control.

The magnetic security element 1, in a manner similar to magnetic security threads of the known type, can be coded magnetically, i.e., can be magnetized so as to produce a magnetic code that can be detected by means of a magnetic sensor. The magnetic security element 1 comprises therefore a series of magnetizable magnetic units 2, 2’, 2” which are aligned along a longitudinal axis X and mutually spaced, i.e., the magnetic units 2, 2’, 2” are mutually separated by spaces which are empty or in any case magnetically neutral (i.e., spaces in which no magnetic ink is present). In practice, each magnetic unit 2, 2’, 2” forms one bit, i.e., it represents one bit of the magnetic code that is detected; i.e., one bit can be associated with each magnetic unit 2, 2’, 2”.

The magnetic units 2, 2’, 2” are therefore to be understood as functional groups, each of which is adapted to represent one bit, and not as monolithic elements, each magnetic unit 2, 2’, 2” being optionally formed by two or more separate and adjacent elements (which will be referenced hereinafter as portions

According to the invention, in fact, at least one of the magnetic units 2, 2’, 2” comprises two portions 2a, 2b, a first portion 2a and a second portion 2b, which are separated by a separation slit 3.

As is evident from the figures, this separation slit 3 is oblique with respect to said longitudinal axis X, i.e., it is neither parallel nor perpendicular thereto, affecting the longitudinal axis X and forming with it an angle other than 90°, and preferably an angle comprised between 30° and 60° (even more preferably comprised between 40° and 50°).

The first portion 2a and the second portion 2b are arranged so that the longitudinal axis X affects both the first portion 2a and the second portion 2b and so that at least one axis Y, Y’, Y” (shown for example in Figures IB, 4B, 8, 9 and 10) that is perpendicular to said longitudinal axis X also affects both said first portion 2a and said second portion 2b.

In this manner, by reading the magnetic code produced by the magnetic element 1 both in a longitudinal direction (along the longitudinal axis X) and transversely (at right angles to the longitudinal axis X) there is always at least one region in which the first portion 2a and the second portion 2b are superimposed transversely with respect to the reading axis.

In the magnetic unit 2 of the preferred embodiments, the separation slit 3 is linear and is extended along an oblique straight line J with respect to the longitudinal axis X (as shown for example in Figures IB and 4B).

Preferably, the separation slit 3, i.e., the oblique straight line J along which said slit is extended, forms with the longitudinal axis X an angle comprised between 30° and 60°, preferably between 40° and 50°.

In the preferred embodiments, the separation slit 3 has a width comprised between 0.10 and 0.40 mm, preferably between 0.2 and 0.3 mm.

In the illustrated embodiments, each one of the magnetic units 2, 2’, 2” that form the series comprises a respective first portion 2a and a respective second portion 2b, i.e., preferably all the magnetic units 2 that compose the code are formed by the two portions 2a, 2b separated by the separation slit 3 as described above. However, other embodiments (not shown) are also possible in which in the series of magnetic units 2, 2’, 2” there are also magnetic units provided in a known manner (for example formed by parallelograms of magnetic ink).

According to the invention, the first portion 2a is composed of a first magnetic ink which has a first magnetic coercivity and the second portion 2b is composed of a second magnetic ink which has a lower magnetic coercivity than said first magnetic coercivity.

The provision of magnetic inks with different coercivity is known. For example, the first and second magnetic inks can comprise a different percentage of magnetic pigment (for example iron oxide).

Preferably, the first magnetic coercivity (of the ink of the first portion 2a) is comprised between 2,500 and 5,000 Oe and the second magnetic coercivity (of the ink of the second portion 2b) is comprised between 100 and 2,300 Oe.

In the preferred embodiments, the first portion 2a and the second portion 2b (and optionally also the additional portions 2c, 2d that will be described hereinafter) of the magnetic units 2, 2’, 2” have, in plan view, one of the following shapes:

- triangle, and preferably a right-angled triangle, such as for example the portions 2a, 2b of Figures 1A-1C;

- rhomboid (i.e., non-right-angled parallelogram), such as for example the portions 2a, 2b of the first magnetic unit of the security element 1 of Figure 11;

- circular segment or semicircle, such as for example the portions 2a, 2b of Figures 4A-4D;

- trapezoid, such as for example the second portion 2b of the third magnetic unit 2 of the security element 1 of Figure 9.

As is evident from the illustrated examples, the first portion 2a and the second portion 2b of a same magnetic unit 2 can have the same shape and the same dimensions or the same shape and different dimensions or also different shapes. The same applies for any additional portions 2c, 2d, depending on the coding that one wishes to obtain.

Likewise, in a same magnetic security element 1 it is possible to comprise magnetic units 2, 2’, 2” which all have the same shapes and/or the same dimensions (as in the example of Figures 1A-1C) or magnetic units 2 that are different in terms of shape and/or size and/or number of the portions 2a, 2b, 2c of which they are composed (as in the examples of Figures 8-10).

For example, in some embodiments, including the one of Figure 1A, in at least one magnetic unit 2, the first portion 2a and the second portion 2b have a triangular shape in plan view and are aligned so as to form substantially a right-angle quadrangle that is sectioned by the separation slit 3.

In other embodiments, including the one of Figure 4 A, in at least one of the magnetic units 2 the first portion 2a and the second portion 2b have a semicircular plan shape and are aligned so as to form substantially a circle that is sectioned by the separation slit 3.

Optionally, one or more of the magnetic units 2’, 2”, 2’” comprises, in addition to the first portion 2a and the second portion 2b, also a third portion 2c that is adjacent to one between said first portion 2a and said second portion 2b.

This third portion 2c is composed of one between said first magnetic ink and the second magnetic ink and is separated from the first portion 2a or second portion 2b to which it is adjacent by a secondary separation slit 4.

Such secondary slit 4 also has a width preferably comprised between 0.10 and 0.40 mm (even more preferably between 0.2 and 0.3 mm) and is not necessarily oblique with respect to the longitudinal axis X (for example, in the first magnetic unit of Figure 8 it is perpendicular thereto, while in the third magnetic unit 2” of Figure 10 it is oblique).

In some embodiments, such as the one of Figure 10, in at least one magnetic unit 2”, in addition to the third portion 2c, there are one or more further additional portions 2d which are separated from the third portion 2c (or from the adjacent portion) by a respective additional slit 4’ for which what has been already mentioned for the secondary slit 4 applies.

Such portions 2a, 2b, 2c of the magnetic unit 2 have a thickness comprised between 1 and 50 microns and preferably comprised between 3 and 15 microns.

Optionally, the first portion 2a and the second portion 2b of a same magnetic unit 2 have different thickness, so as to further vary the magnetic signal that can be detected by a sensor 80.

In the preferred embodiments, the magnetic units 2, 2’, 2” (and therefore the portions 2a, 2b, 2c that compose them) are supported by a medium 5 made of plastic material (for example polyester) which has preferably the shape of a stripe or thread, the magnetic ink that forms said magnetic units 2, 2’, 2” being in practice printed on the medium 5.

Conveniently, the thickness of the medium 5 is comprised between 8 and 50 microns (preferably between 10 and 20 microns).

Preferably, a hiding layer (preferably made of aluminum) adapted to render the magnetic units 2 invisible is deposited between the medium 5 and the magnetic units 2, 2’, 2” and can optionally have empty regions suitable to form graphic effects or transparent regions.

Optionally, a protective ink layer is deposited between the hiding layer and the magnetic units 2 which optionally also can have empty regions adapted to form graphic effects or transparent regions.

Preferably, the magnetic units 2 are covered, on the opposite side with respect to the medium 5, by a layer of magnetically neutral ink which is adapted to visually cover the magnetic units 2.

Optionally, a plastic layer (constituted for example by an element that is similar or identical to the medium 5) is present over the magnetically neutral ink or instead of it, so that the magnetic units 2 are included between the medium 5 and the plastic layer.

Optionally, the medium 5 and/or the plastic layer can be provided with additional graphic elements, such as for example layers of materials that are fluorescent, birefringent, color- shifting, provided by means of liquid crystals, or holographic, etc.

Therefore, in the preferred embodiments the magnetic security element 1 has the shape of a thread or stripe, with a total thickness of no more than 55 microns (although embodiments are possible in which the thickness is equal to or lower than 150 microns), suitable to be integrated in the valued paper (for example included within the thickness of the bill paper of a banknote).

The present invention also relates to a method for providing a magnetic security element 1 as described previously, which in its essential features comprises the steps of: a) providing a preferably plastic (for example polyester) medium 5, preferably having a thickness comprised between 8 and 50 microns (even more preferably between 10 and 20 microns) and having the shape of a stripe or thread; b) printing with magnetic ink on the medium 5 a series of magnetic units 2, which are aligned along a longitudinal axis X and are mutually spaced.

According to the invention, in step b), at least one of the magnetic units 2 is provided by printing two portions 2a, 2b, a first portion 2a and a second portion 2b, which are separated by a separation slit 3 that is oblique with respect to the longitudinal axis X and are arranged so that at least one axis Y that is perpendicular to said longitudinal axis X affects both said first portion 2a and said second portion 2b.

The first portion 2a is printed with a first magnetic ink that has a first magnetic coercivity and the second portion 2b is printed with a second magnetic ink that has a lower magnetic coercivity than the first magnetic coercivity.

Preferably, the magnetic units 2 are printed so as to have one or more of the other characteristics described previously with reference to the magnetic security element 1.

Optionally, one or more of the following steps are performed prior to step b):

- depositing, over the medium 5, a hiding layer (preferably made of aluminum) which is adapted to render the magnetic units 2 invisible and which optionally can have empty regions adapted to form graphic effects or transparent regions;

- depositing, over the hiding layer (or instead of it), a layer of protective ink, which optionally also can have empty regions adapted to form graphic effects or transparent regions.

Optionally, one or more of the following steps are performed after step b):

- covering the magnetic units 2, on the opposite face with respect to the medium 5, with a layer of magnetically neutral ink, adapted to visually cover the magnetic units 2;

- fixing, over the magnetically neutral ink or instead of it, a plastic layer (for example similar or identical to the medium 5) so that the magnetic units 2 are included between the medium 5 and the plastic layer.

Obviously, the medium 5 and/or the plastic layer can have the previously described optional characteristics. The operation of the magnetic security element 1 is clear and evident from what has been described. During use, the magnetic code produced by the security element 1 can be read by means of a dual channel sensor (of the known type described previously and comprising: a first permanent magnet 88 with high coercive power for the magnetization in saturation of all the portions of the magnetic units; a first inductive sensor 81 for detecting the first channel Cl; a second inductive sensor 82 for detecting the second channel C2; and a second magnet 83 which rotates through 90° the magnetic flux of the areas printed with ink with low coercive power and is interposed between the first sensor 81 and the second sensor 82, in a manner similar to what occurs in the background art.

The particularities that the invention has during use are rendered even more evident by the figures.

Figure 1A shows a valued paper 99 containing a security element 1 which has a magnetic coding provided by three magnetic units 2 (therefore three bits) all composed of two separate triangular portions 2a, 2b (right- angled triangles).

Figure 2 shows, for the magnetic element of Figure 1A, the signals on the two channels Cl, C2 that are detected, after a magnetization in saturation, by a dual channel sensor 80 arranged at right angles to the longitudinal axis X (as in the sensors used to flip through banknotes with insertion from the longer side); it should be noted that:

- in the signals of the first channel Cl, the amplitude of the positive peak and the amplitude of the negative peak are substantially identical for each magnetic element 2 (for each bit) since the leading and trailing edge are identical, independently of the ink used;

- in the signals of the second channel C2, instead, there is a substantial difference between the positive peak and the negative peak of each individual bit, since the first triangular portion 2a has an extremely different impact surface between the beginning and the end of each individual magnetic unit 2, thus generating a difference in amplitude, between the positive peak and the negative peak, that can vary from 5% to 60% depending on the difference of the leading edge with respect to the trailing edge (how much magnetic area affects the reading sensor 82); - the signal of the second portion 2b is instead canceled in the second channel C2.

Figure 3 shows the outcome of a detection performed by means of a dual channel sensor 80 arranged with an angle of 45° with respect to the longitudinal axis X (as is normal for flipping through banknotes from the shorter side). In this case also, the signals detected in the first channel Cl have substantially identical positive peaks and negative peaks for each magnetic unit 2 (bit); the signals detected in the second channel C2 instead have a different amplitude, which is indeed due to the larger magnetic surface that appears in front of the second reading head; the hypotenuse of the right-angled triangles formed by the first portion 2a is in fact longer than the other sides and furthermore appears with a substantially immediate flux variation (due to the presence/absence of magnetic area). It should be noted that said hypotenuse, and therefore also the separation sits 3, are appropriately positioned parallel to the sensor (which is inclined at 45° with respect to the longitudinal axis X).

Figure 5 shows the signals detected, for a security element 1 in which the first portion 2a and the second portion 2b of all the magnetic units 2 are shaped like a semicircle with different diameters, by means of a dual channel sensor 80 arranged at right angles to the longitudinal axis X. In the signals of the first channel Cl, the positive peaks and the negative peaks are substantially identical but with the difference that the amplitude of the signals depends on the diameter of the semicircular portions 2a, 2b. The signals of the second channel C2 instead have a different amplitude between the positive peaks and the negative peaks of each individual bit; this difference is generated by the quantity of magnetic area that affects the sensor 82.

Figure 6 shows a detection performed again on the element of Figure 5, with the dual channel sensor 80 inclined at 45° with respect to the longitudinal axis X. On the first channel Cl it is possible to note that the positive peaks and the negative peaks have substantially the same amplitude/intensity and reflect the diameter of the surfaces of the first and second portions 2a, 2b (the larger the diameter, the greater the amplitude). The differences between the positive peak and the negative peak related to the first portion 2a are highlighted on the second channel; these differences depend, as mentioned previously, on how much magnetic area appears simultaneously under the magnetic sensor 82. It should be noted that the separation slits 3 are conveniently arranged parallel to the sensor 80 (inclined at 45° with respect to the longitudinal axis X).

It is therefore evident that in the magnetic security element 1 according to the invention the detected signals, magnetized in saturation, depend on the thickness of the magnetic ink that constitutes the magnetic units 2, on the quantity of magnetic material that is present in the ink, but most of all on the number, shape and dimensions of the separate portions 2a, 2b, 2c that form the magnetic units 2 and appear below the reading sensor 80.

It is therefore possible to create more complex magnetic coding which cannot be reproduced with rectangular magnetic units.

In practice it has been found that the magnetic security element for valued papers, according to the present invention, achieves the intended aim and objects, since it is capable of ensuring a higher security level, since the coding that can be obtained is a strong barrier against the forging of said security element.

Another advantage of the security element according to the invention resides in that it allows coding which is more complex or in any case more difficult to forge. A further advantage of the security element according to the invention resides in that it is easy to provide and economically competitive if compared with the background art.

Furthermore, the present invention provides a valid alternative to the background art.

The magnetic security element for valued papers thus conceived is susceptible of numerous modifications and variations, all of which are within the scope of the accompanying claims.

All the details may furthermore be replaced with other technically equivalent elements.

In practice, the materials used, as well as the contingent shapes and dimensions, may be any according to the requirements and the state of the art.

The disclosures in Italian Patent Application No. 102021000016985 from which this application claims priority are incorporated herein by reference.

Where technical features mentioned in any claim are followed by reference signs, those reference signs have been included for the sole purpose of increasing the intelligibility of the claims and accordingly such reference signs do not have any limiting effect on the interpretation of each element identified by way of example by such reference signs.

Claims

1. A magnetic security element (1) for valued papers (99), particularly banknotes and identity documents, comprising a series of magnetizable magnetic units (2) which are aligned along a longitudinal axis (X) and mutually spaced, characterized in that at least one of said magnetic units (2) comprises two portions (2a, 2b), a first portion (2a) and a second portion (2b), which are separated by a separation slit (3) which is oblique with respect to said longitudinal axis (X) and are positioned so that at least one axis (Y) that is perpendicular to said longitudinal axis (X) affects both said first portion (2a) and said second portion (2b), wherein said first portion (2a) is composed of a first magnetic ink which has a first magnetic coercivity and said second portion (2b) is composed of a second magnetic ink which has a magnetic coercivity that is lower than said first magnetic coercivity.

2. The security element (1) according to claim 1, wherein each one of said magnetic units (2) comprises a respective first portion (2a) and a respective second portion (2b).

3. The security element (1) according to claim 1, wherein said separation slit (3) is linear, extending along an oblique straight line (J) with respect to the longitudinal axis (X).

4. The security element (1) according to one or more of the preceding claims, wherein said separation slit (3) forms, with said longitudinal axis (X), an angle comprised between 30° and 60°, preferably between 40° and 50°.

5. The security element (1) according to one or more of the preceding claims, wherein said first magnetic coercivity is comprised between 2500 Oe and said second magnetic coercivity is comprised between 100 and 2300 Oe.

6. The security element (1) according to one or more of the preceding claims, wherein said separation slit (3) has a width comprised between 0.10 and 0.40 mm, preferably between 0.2 and 0.3 mm.

7. The security element (1) according to one or more of the preceding claims, wherein said first portion (2a) and said second portion (2b) have a shape in plan view chosen from the shapes of:

- triangle,

- rhomboid,

- circular segment,

- semicircle,

- trapezoid.

8. The security element (1) according to one or more of the preceding claims, wherein in at least one of said magnetic units (2) said first portion (2a) and said second portion (2b): have a triangular shape in plan view and are aligned so as to form substantially a right-angled quadrangle which is sectioned by said separation slit (3), or have the shape, in plan view, of a semicircle and are aligned so as to form substantially a circle that is sectioned by said separation slit (3).

9. The security element (1) according to one or more of the preceding claims, wherein at least one magnetic unit (2', 2") also comprises a third portion (2c) which is adjacent to one between said first portion (2a) and said second portion (2b) and is separated from it by a secondary separation slit (4), said third portion (2c) being composed of one between said first magnetic ink and said second magnetic ink.

10. The security element (1) according to one or more of the preceding claims, wherein said portions (2a, 2b, 2c) of the magnetic unit (2, 2', 2") have a thickness comprised between 3 and 15 microns.

11. The security element (1) according to one or more of the preceding claims, wherein said first portion (2a) and said second portion (2b) of a same magnetic unit (2, 2', 2") have different thickness.

12. A method for providing a magnetic security element (1) for valued papers (99), particularly banknotes and identity documents, comprising the steps of: a) providing a medium (5); b) printing with magnetic ink on said medium (5) a series of magnetic units (2) which are aligned along a longitudinal axis (X) and are mutually spaced; characterized in that in said step b) at least one of said magnetic units (2) is provided by printing two portions (2a, 2b), a first portion (2a) and a second portion (2b), which are separated by a separation slit (3) which is oblique with respect to said longitudinal axis (X) and are arranged so that at least one axis (Y) that is perpendicular to said longitudinal axis (X) affects both said first portion (2a) and said second portion (2b); said first portion (2a) being printed with a first magnetic ink that has a first magnetic coercivity, and said second portion (2b) being printed with a second magnetic ink that has a magnetic coercivity that is lower than said first magnetic coercivity.

13. The method according to claim 12, wherein prior to step b) one or more of the following steps are performed:

- depositing over the medium (5) a hiding layer adapted to render the magnetic units (2) invisible;

- depositing over the hiding layer, or instead of it, a layer of protective ink.

14. The method according to claim 12 or 13, wherein after step b) one or more of the following steps are performed:

- covering the magnetic units (2), on the opposite face with respect to the medium (5), with a layer of magnetically neutral ink adapted to visually cover the magnetic units (2);

- fixing, over the magnetically neutral ink or instead of it, a plastic layer so that the magnetic units (2) are included between the medium (5) and the plastic layer.