FR3090992A1 - Device configured to orient particles sensitive to the magnetic field, machine and apparatus equipped therewith - Google Patents

Abstract

The present invention relates in particular to a device (1) configured to orient particles sensitive to the magnetic field, these particles being contained in a printing material affixed to a support (4), device which comprises an array R of magnets, characterized in that said magnets consist of electromagnets (2) arranged side by side in a vertical position, the upper ends (22) of these electromagnets (2) extending either substantially in the same plane (P) , or offset, so as to generate a curved surface. Figure for the abstract: Fig. 1

Description

Description

Title of the invention: Device configured to orient particles sensitive to the magnetic field, machine and apparatus equipped therewith

Technical area

The present invention relates to a device for orienting particles contained in a printing material affixed to a support, as well as to a machine for printing supports for fiduciary use and to a device for verifying the authenticity of printed tickets fitted with them.

Prior art

Inks with remarkable optical effects are widely used in the field of fiduciary printing for the production of anti-counterfeiting security elements. More particularly, there are some whose visual effects are obtained by the use of magnetic fields. The pigments contained in these inks are then in the form of thin multilayer plates which have the following characteristics:

- A core made of a ferromagnetic material (based on iron, cobalt or nickel) which, thanks to the planar shape of the wafer, allows it to orient itself under the action of a magnetic field due to the shape anisotropy;

- A reflective layer (often metallic) with which the wafer takes on a brilliant luster when the positions of the lighting and of the observer meet certain specific geometrical conditions, and a much darker shade in the opposite case;

- A possible layer of transparent dielectric material whose thickness adjustment makes it possible to modulate the color of the pigment;

- In connection with the previous characteristic, an absorbent layer allowing the shade to be more precisely modulated.

[0007] Such pigments are described in detail, in particular in the documents of the family of document US 2002/0160194.

The use of these inks is based on a printing system allowing, when the ink is applied but not yet crosslinked (that is to say not yet dry), to orient the pigments platelets by a magnetic field to achieve unique patterns and optical effects in reflection, before freezing the ink.

The magnetic field is generally produced by one or more magnets, arranged so as to create the desired pattern and encapsulated in a box which is just inserted into the printing cylinders. This is notably described in US2011 / 0168088.

The best known pattern is that called "rolling bar" (or "rolling bar" in English). It is a pattern in the form of a light bar, which gives the impression of "rolling" up and down when you tilt the support towards you.

To produce it, we use a flat magnet with magnetic orientation parallel to the support and perpendicular to the direction of the desired bar, located at a distance of a few millimeters below the support, and whose horizontal dimensions slightly exceed those of the treated area. Many variations of this rolling bar are proposed, in particular in document CA2871381, where the insertion of a two-dimensional network (checkerboard) of small magnets between the main rolling bar magnet and the printed support makes it possible to generate aesthetic patterns and varied.

In document WO2017148789 is described a technique which makes it possible to produce a closed line, circular or of more complex shape, which seems to enlarge or shrink when the support is inclined.

It is also possible to produce less abstract inscriptions, such as a drawing or text, using plasto-magnets engraved on a few hundred microns deep, with a resolution of the order of a millimeter. Reference can be made to document EP1493590 on this subject.

Despite their diversity, none of these systems mentioned above can be reconfigured at will, instantly and easily.

Indeed, to change the reason for the inscription to be made, we must disassemble the magnetic boxes of the support on which they are mounted and set up other boxes which have other geometries (ie provisions) of magnets inside, or other engravings on their surface.

In other words, the orientation system is fixed and it is not possible to modify the optical effect from one sheet to another or between different portions of strip during printing, if we wish. This means that each note on each sheet or portion of strip receives the same magnetic orientation and therefore the same pattern. It is not possible to modify the visual effect produced without a prolonged stoppage of production.

The present invention aims precisely to overcome these drawbacks. In other words, it aims to propose a device which makes it possible to reconfigure the magnetic effect at will, that is to say when it is desired and thus, to provide a specific magnetic orientation to each sheet or portion of strip, even on each ticket if necessary and thus obtain a kind of personalization of the magnetic effect.

Statement of the invention

Thus, the present invention relates to a device configured to orient particles sensitive to the magnetic field, these particles being contained in a printing material affixed to a support, device which comprises a network of magnets, characterized by the fact that said magnets consist of electromagnets arranged side by side in a vertical position, the upper ends of these electromagnets extending either substantially in the same plane, or in an offset manner, so as to generate a curved surface.

Thus, the invention provides a magnetic system for orienting magnetizable inks which is versatile. In other words and as will be seen later in the description which follows, it makes it possible to locally produce a magnetic field and, by combining the fields produced by the different nuclei, to generate a pattern in ink by the only control of the polarity of the currents which supply the coils of the electromagnets.

The visual effect produced by this system is therefore not set in stone as is the case in the prior art, where the arrangement of the magnets in the housings fixes the pattern and forces the housing to be changed if the 'we want to change the pattern.

The present invention allows the same device to be used to produce as many patterns as the resolution of the two-dimensional network (matrix) allows, by a simple adjustment of the currents introduced into the system, which can be done by means of '' a suitable interface.

According to other non-limiting and advantageous characteristics of the invention:

- said electromagnets have a tubular shape;

- Each of said electromagnets is supplied individually with electricity and the device comprises means for controlling on demand the flow / non-flow of current in each electromagnet;

- said electromagnets include a soft ferromagnetic core made of a ferromagnetic material with high magnetic permeability and high saturation induction;

- Said electromagnets are secured to a base;

- Said base is made of ferromagnetic material.

- Said base comprises a set of individual cavities in which are positioned the lower ends of said electromagnets;

- Said base has grooves and / or perforations for the passage of the supply wires of said electromagnets;

Another aspect of the invention relates to a machine for printing media for fiduciary use, characterized in that it comprises at least one device conforming to one of the preceding characteristics.

Advantageously, said at least one device is positioned, considering the direction of movement of the supports through the machine, downstream or in the immediate vicinity of a printing station with a printing material containing particles configured for orienting themselves in the direction of the magnetic field lines before total crosslinking of said printing material containing them.

Finally, the invention relates to an apparatus for verifying the authenticity of tickets printed with a material comprising particles configured to orient themselves in the direction of the magnetic field lines, characterized in that it comprises at least one device conforming to one of the preceding characteristics.

Brief description of the drawings

Other features and advantages of the invention will appear on reading the detailed description which follows. It will be made with reference to the accompanying drawings in which:

[Fig.l] is a simplified side view of a device according to the invention, it being understood that only the ferromagnetic cores, their support are shown here, as well as the schematic representation of a sheet coated with ink ;

[Fig-2] is a perspective view of the device of the previous figure;

[Fig.3] is a perspective view of the base visible in the previous figures, highlighting methods of assembly and extraction of the supply wires of the ferromagnetic cores;

[Fig-4] is a diagram of the pixelation of the desired pattern;

[Fig.5] is a top view of the device of Figures 1 and 2 showing the horizontal spatial extent of the printing medium relative to the matrix of wound ferromagnetic cores;

[Fig.6] is a view similar to Figure 4 showing the necessary distribution of the currents injected into the cores to obtain the desired pattern;

[Fig-7] is a view of a computer simulation of the visual result obtained for the representation of the letter M;

[Fig.8] is a view of a computer simulation of a visual result at a first angle obtained using the device according to the invention for the representation of the letter "K" combined with a rolling bar magnet according to the state of the art;

[Fig.9] is a view similar to Figure 8, shown from a second different angle, to highlight the effect of movement;

[Fig.10] is a view similar to Figure 8, shown from a third different angle, to highlight the effect of movement;

[Fig.l 1] is a view similar to Figure 8, shown from a fourth different angle, to highlight the effect of movement.

Description of the embodiments

An example of device 1 according to the present invention is visible in Figures 1 and 2 attached. In the embodiment presented here, we are dealing with a qua5 drillage, that is to say a two-dimensional network R of one hundred (10 by 10) electromagnets 2, otherwise called wound cores. This makes it possible to constitute 100 magnetic pixels, each pixel being able to be controlled by Γ through an electric current flowing through the coil of the corresponding electromagnet 2.

In the above figures, the network R takes the form of a regular grid, in other words a square tiling of the plane. However, this distribution of the wound cores is by no means limiting and it is conceivable that the network takes the form of any tiling of the plane. There are three regular tiling of the plane: square, triangular and hexagonal, as well as a large number of tiling combining several types of regular polygons.

Similarly, one can make use of a greater or lesser number of electromagnets 2. Of course, with an equal network area R, the greater the number of electromagnets 2, the finer the aforementioned pixels.

The electromagnets 2 here have a cylindrical shape. Again, even if this form is advantageous, it is not compulsory and one can envisage other embodiments (elongated parallelepipeds, prisms, cubes, biconical diabolo with circular or square base, etc.).

The electromagnets 2 are advantageously fixed to a base 3, preferably made of ferromagnetic material such as martensitic steel, which allows, in addition to mechanical support, to close one of the sides of magnetic flux loops generated by the wound cores. This increases the intensity of the magnetic field produced at the free end of the wound cores.

The diameter of the core + coil assemblies of the electromagnets 2 generates a size which conditions the resolution of the patterns which can be produced from the system. This diameter will be chosen according to the following compromise: the larger it is, the coarser the patterns, but the better the magnetic alignment of the inks, because larger windings can generate a more intense field.

As shown in the accompanying figures, the upper face 31 of the base 3 has as many small cavities 30 as there are electromagnets 2. And the lower ends of the latter are partially engaged in these cavities.

The electromagnets 2 are arranged next to each other in a vertical position. They all have the same dimensions, so that their upper ends 22 all extend in the same plane P parallel to the upper face of the base 3. Thus, the magnetic field generated by the device is of comparable intensity over its entire surface . In a variant not shown here, it is conceivable that the electromagnets 2 have a radius of curvature both individually and collectively to match the shape of the support 4 if the latter is curved. In other words, the upper ends are progressively offset and can be cut at a bevel, so as to generate together a curved (curved) surface.

The ferromagnetic cores 20 of the electromagnets 2 are advantageously made of a ferromagnetic alloy with high induction, such as martensitic steel (saturation at 1.9 T), or, for better performance, an alloy of iron and cobalt (saturation at 2.3 T for a cobalt content close to 30%).

By the expression better performance is meant the fact that the magnetic field generated is more intense for the same current intensity in the supply windings. The diameter of the wires 5 used for this purpose is chosen to allow all the coils to be placed side by side.

The winding operation itself is advantageously carried out beforehand. Thus, small clip-type rings 50 can allow lateral retention of the coiled copper wire and ensure that a sufficient height of free core is retained by which the latter can be positioned in the base 3.

Grooves 6 and / or perforations 7 are preferably provided in the base 3 to allow the wires 5 to feed the windings to pass. In FIG. 3, only two electromagnets 2 and their associated supply wires 5 have been shown in order to facilitate their consultation.

These wires are of course assembled and connected so as to allow control of the supply of each electromagnet.

In Figures 1 and 5 is shown, above the device 1 according to the invention, just part of a support 4 such as a sheet or a support strip which is coated with a pigment or an ink containing magnetizable particles. We have deliberately limited ourselves to representing the fraction of the support 4 which is usefully affected by the device 1.

One way to configure the currents to obtain a given pattern is shown in Figure 4. In this case, in this example, the MO pattern in question is the representation of the letter M.

First, this MO pattern is cut into pixels according to the resolution allowed by the device used (10x10 pixels in the case shown here). Two zones are thus defined: the interior INT of the pattern MO, and the exterior EXT of the pattern.

It is then possible to make the contour of the area thus delimited appear in brightness by assigning a certain current value to the pixels of the interior area INT, and the value opposite to the pixels of the exterior area. This is the situation represented in FIG. 6. The absolute value of this current must be maximized so as to obtain the highest possible magnetic field, without causing excessive heating of the coils of the electromagnets.

A magneto static calculation shows that one can obtain a magnetic field of 20-30 mT with 50 A.tours per magnetic core, which can be achieved by a winding of turns traversed by a current of 1 A. This must allow to generate patterns with a resolution of about 1.5 mm.

In the case where a magnetizable pigment would be able to react quickly enough to a weaker magnetic field (10 mT, even 5 mT), it would be possible to improve the resolution up to 1 mm or even less, using smaller and closer spools.

An electronic control interface, not shown, makes it possible to distribute the currents in each electromagnet 2 that the support 3 has for the latter.

The visual result obtained by digital simulation is shown in Figure 7, taking into account the magnetic alignment capabilities of a commercial ink.

To make the best use of the magnetic field generated by the device, the printing medium 4 on which the ink is spread must be located as close as possible to the upper end 22 of the electromagnets 2, because the intensity of the field magnetic decreases rapidly depending on the distance between the support 4 and said upper end.

Even if this has not been shown in the accompanying figures, the device according to the invention may include a cover which extends just above the upper end of the electromagnets 2, so that no contact direct exists between the support 4 and the electromagnets 2.

We can however dispense with such a cover. In such a case, it may however be useful to fill the interstices between the ends of the nuclei to provide a flat area and not bristling with peaks. For example, the clips 50 may have a square shape and thus provide paving of the space under the printing medium.

The device 1 according to the invention can be used in the same way as a known type of magnetic orientation housing. The ink is applied to the support 4 to be printed and the latter is placed directly above the device 1, as shown in FIGS. 1, 2 and 5. Thus, the reflective magnetic plates contained in the pigment are oriented so as to generate the desired pattern. Then, the ink is crosslinked, if possible while it is still under the influence of the magnetic field, so as to permanently freeze the pattern.

Of course, rather than occupying a single predetermined area of the printing support 4, the device according to the invention can encompass the entire surface of the support 4 and in particular its entire width (or width), so that it is possible to activate only certain areas, preferably non-adjacent and different from one sheet or portion of strip to the next. In addition, the MO pattern that is configured can also be different from one sheet to the next or from one strip portion to another. For example, each sheet or portion of strip can receive unique information of the serial number type which is incremented at each machine revolution. This mode of use further accentuates the modular nature and the flexibility of use of the invention.

The device according to the invention can be superimposed with a more conventional device such as for example that which allows to configure a rolling bar or a ring, obtained with a large magnet (comparable to those of the entire network R) placed a few millimeters below the printing medium 4. The overall movement effect, which cannot be reconfigured, can thus be dynamically personalized by superimposing a pattern applied by the device of the invention. The dimensions of the magnets, their nature and their position can be chosen so as to ensure a good balance between the two contributions.

An example is presented in Figures 8 to 11 which relate to the effect obtained, in the form of a simulation, by the superposition of a classic effect (rolling bar) on a MO pattern (here the letter K ) made using the device according to the invention. The printed support is represented from different angles to highlight the effect of movement.

The magnetic field delivered by the electromagnets 2 being quite weak, one way to enhance the sharpness of the result is to pre-align the reflective magnetic plates by means of a more intense and uniform magnetic field on the surface concerned. This magnetic field must be delivered by a system separate from the device 1 and before the latter. Thus a magnetic field parallel to the support 4 places the particles in a "bright" configuration, while a magnetic field perpendicular to the support places the particles in a "dark" configuration. Depending on the reason, either of these possibilities can be chosen.

Of course, one or more devices according to the invention can be used within a printing machine for fiduciary media, whether it is sheet-by-sheet or continuous printing on a bandaged. In these cases, it is (they are) positioned ^), considering the direction of movement of the support through the machine, downstream of a printing station or in the immediate vicinity and so as to be able to freeze the ink by crosslinking (for example ultraviolet) while the latter is still subject to the magnetic field generated by the device (s).

We will use inks which may or may not have a color change depending on the angle of incidence of the light.

The device presented here can also be used to perform interactive authentication on a security device containing active inks such as those described in document US2005181160, that is to say whose pigments have a degree of freedom their giving reactivity to a magnetic field even after the ink is frozen.

Claims (1)

Claims [Claim 1] Device (1) configured to orient particles sensitive to the magnetic field, these particles being contained in a printing material affixed to a support (4), device which comprises an array R of magnets, characterized in that said magnets consist in electromagnets (2) arranged side by side in a vertical position, the upper ends (22) of these electromagnets (2) extending either substantially in the same plane (P), or in an offset manner, so to generate a curved surface. [Claim 2] Device according to claim 1, characterized in that said electromagnets (2) have a tubular shape. [Claim 3] Device according to claim 1 or 2, characterized in that each of said electromagnets (2) is supplied with electricity individually and that it comprises means for controlling on demand the circulation / non-circulation of current in each electromagnet (2). [Claim 4] Device according to one of Claims 1 to 3, characterized in that the said electromagnets (2) comprise a soft ferromagnetic core (20) made of a ferromagnetic material with high magnetic permeability and with induction at high saturation. [Claim 5] Device according to one of the preceding claims, characterized in that the said electromagnets (2) are integral with a base (3). [Claim 6] Device according to claim 5, characterized in that said base (3) is made of ferromagnetic material. [Claim 7] Device according to claim 5 or 6, characterized in that said base (3) comprises a set of individual cavities (30) in which the lower ends of said electromagnets (2) are positioned. [Claim 8] Device according to one of Claims 5 to 7, characterized in that the said base (3) has grooves (6) and / or perforations (7) for the passage of the wires (5) supplying the said electromagnets (2). [Claim 9] Printing machine for fiduciary media, characterized in that it comprises at least one device (1) according to one of the preceding claims. [Claim 10] Machine according to claim 9, characterized in that said at least one device (1) is positioned, considering the direction of movement of the supports through the machine, downstream or in the immediate vicinity of a printing station with a printing material containing particles configured to orient themselves in the direction of the magnetic field lines. [Claim 11] Apparatus for verifying the authenticity of tickets printed with a material comprising particles configured to orient themselves in the direction of the magnetic field lines, characterized in that it comprises at least one device (1) conforming to one of claims 1 to 8.