OPTICAL EFFECT LAYERS SHOWING A VIEWING ANGLE DEPENDENT OPTICAL EFFECT, PROCESSES AND DEVICES FOR THEIR PRODUCTION, ITEMS CARRYING AN OPTICAL EFFECT LAYER, AND USES THEREOF

• US 20150352883A1
• Filed: 12/20/2013
• Published: 12/10/2015
• Est. Priority Date: 01/09/2013
• Status: Active Grant

• Current Assignee: Sicpa Holding SA
• Original Assignee: Sicpa Holding SA
• Inventors: SCHMID, Mathieu, DEGOTT, Pierre, LOGINOV, Evgeny, DESPLAND, Claude Alain
• Granted Patent: US 9,849,713 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: B05D 3/20 by magnetic fields
• CPC Class Codes: B05D 3/207 post-treatment by magnetic fields
• CPC Class Codes: B41M 3/148 Transitory images, i.e. images only visible from certain viewing angles
• CPC Class Codes: B42D 2033/16 Magnetic or magnetisable material
• CPC Class Codes: B42D 2033/20 Coloured material; Pigments or inks
• CPC Class Codes: B42D 2035/20 Optical effects
• CPC Class Codes: B42D 25/29 Securities; Bank notes
• CPC Class Codes: B42D 25/30 Identification or security features, e.g. for preventing forgery
• CPC Class Codes: B42D 25/369 Magnetised or magnetisable materials
• CPC Class Codes: H01F 41/16 the magnetic material being applied in the form of particles, e.g. by serigraphy , to form thick magnetic films or precursors therefor H01F41/18 -H01F41/24 take precedence
• CPC Class Codes: H01F 7/0273 Magnetic circuits with PM for magnetic field generation
• CPC Class Codes: H01F 7/0278 for generating uniform fields, focusing, deflecting electrically charged particles for magnetic separation by Lorentz force B03C1/023; specially adapted for NMR applications G01R33/383
• CPC Class Codes: Y10T 428/24273 including aperture

Abstract

The invention relates to the field of the protection of security documents such as for example banknotes and identity documents against counterfeit and illegal reproduction. In particular, the invention relates to optical effect layers (OEL) showing a viewing-angle dependent optical effect, devices and processes for producing said OEL and items carrying said OEL, as well as uses of said optical effect layers as an anti-counterfeit means on documents. The OEL comprises a plurality of non-spherical magnetic or magnetizable particles, which are dispersed in a coating composition comprising a binder material, the OEL comprising two or more loop-shaped areas, being nested around a common central area that is surrounded by the innermost loop-shaped area, wherein, in each of the loop-shaped areas, at least a part of the plurality of non-spherical magnetic or magnetizable particles are oriented such that, in a cross-section perpendicular to the OEL layer and extending from the centre of the central area to the outer boundary of the outermost loop-shaped area, the longest axis of the particles in each of the cross-sectional areas of the looped-shaped areas follow a tangent of either a negatively curved or a positively curved part of hypothetical ellipses or circles.

Claims

1. An optical effect layer (OEL) comprising a plurality of non-spherical magnetic or magnetizable particles, wherein at least a part of the plurality of non-spherical magnetic or magnetizable particles is constituted by non-spherical optically variable magnetic or magnetizable pigments, and wherein the non-spherical magnetic or magnetizable particles are dispersed in a coating composition comprising a binder material,

the OEL comprising two or more loop-shaped areas, being nested around a common central area that is surrounded by the innermost loop-shaped area,

wherein, in each of the loop-shaped areas, at least a part of the plurality of non-spherical magnetic or magnetizable particles are oriented such that, in a cross-section perpendicular to the OEL layer and extending from the centre of the central area to the outer boundary of the outermost loop-shaped area, the longest axis of the particles in each of the cross-sectional areas of the looped-shaped areas follow a tangent of either a negatively curved or a positively curved part of hypothetical ellipses or circles.

2. The optical effect layer (OEL) according to claim 1, wherein the OEL further comprises an external area outside the outermost loop-shaped area, the external area surrounding the outermost loop-shaped area comprises a plurality of non-spherical magnetic or magnetizable particles, wherein at least a part of the plurality of non-spherical magnetic or magnetizable particles within the external area are oriented such that their longest axis is substantially perpendicular to the plane of the OEL or randomly oriented.

3. The optical effect layer (OEL) according to claim 1, wherein the central area surrounded by the innermost loop-shaped area comprises a plurality of non-spherical magnetic or magnetizable particles, wherein a part of the plurality of non-spherical magnetic or magnetizable particles within the central area are oriented such that their longest axis is substantially parallel to the plane of the OEL, forming the optical effect of a protrusion.

4. The optical effect layer (OEL) according to claim 3, wherein the outer peripheral shape of the protrusion is similar to the shape of the innermost loop-shaped area.

5. The optical effect layer (OEL) according to claim 3, wherein the loop-shaped areas each have the form of a ring, and the protrusion has the shape of a solid circle or half-sphere.

7. The optical effect layer (OEL) according to claim 1, wherein the optically variable magnetic or magnetizable pigments are selected from the group consisting of magnetic thin-film interference pigments, magnetic cholesteric liquid crystal pigments and mixtures thereof.

8. The optical effect layer (OEL) according to claim 3, wherein the plurality of non-spherical magnetic or magnetizable particles within the loop-shaped areas and/or within the central area surrounded by the loop-shaped areas are oriented such as to provide the optical effect of (a) three-dimensional object(s) extending from the surface of the OEL.

21. An optical effect layer coated substrate (OEC) comprising one or more optical effect layers according to claim 1 on a substrate.

22. A security document, preferably a banknote or an identity document, comprising an optical effect layer recited in claim 1.

23. Use of the optical effect layer recited in claim 1 for the protection of a security document against counterfeiting or fraud or for a decorative application.

6. (canceled)

9. A magnetic field-generating device comprising a plurality of elements selected from magnets and pole pieces and comprising at least one magnet, the plurality of elements being either (i) located below a supporting surface or a space configured to receive a substrate acting as supporting surface or (ii) forming a supporting surface, and being configured such as to be capable of providing a magnetic field wherein magnetic field lines run substantially parallel to said supporting surface or space in two or more areas above said supporting surface or space, and wherein

i) the two or more areas form nested loop-shaped areas surrounding a central area;

and/or

ii) the plurality of elements comprise a plurality of magnets, and the magnets are arranged rotatable around an axis of rotation such that the areas with field lines running substantially parallel to the supporting surface or space combine upon rotation around the axis of rotation, thereby forming, upon rotation around the axis of rotation, a plurality of nested loop-shaped areas surrounding one central area.

10. The magnetic field-generating device according to claim 9, option ii), wherein the magnets are arranged such that in an area, which is above said supporting surface or space and which is centered on the axis of rotation, a magnetic field with field lines running substantially parallel to the plane of magnets is generated.

11. The magnetic field-generating device according to claim 9, option i), wherein the two or more areas of parallel field lines, which form the nested loop-shaped areas surrounding a central area, are caused by an arrangement of a plurality of elements selected from magnets and pole pieces, at least one of said elements having a loop-shaped form corresponding to the loop-shaped area with parallel field lines above the supporting surface or space.

12. The magnetic field-generating device according to claim 11, wherein the arrangement of a plurality of elements selected from magnets and pole pieces comprises at least one loop-shaped magnet having its magnetic axis substantially perpendicular to said supporting surface or space, which arrangement preferably further contains a pole piece having a loop-shaped form, the loop-shaped magnet and the looped shaped pole piece surrounding a central area in a nested manner.

13. The magnetic-field-generating device according to claim 12, wherein the central area comprises a bar dipole magnet having its magnetic axis substantially perpendicular to said supporting surface or space or a central pole piece, and wherein the pole piece and that magnet are arranged in alternating manner starting from the central area.

14. The magnetic field-generating device according to claim 9, option ii), wherein the plurality of magnets are arranged symmetrically around the axis of rotation and have their magnetic axis substantially parallel or substantially perpendicular to the supporting surface or space.

15. The magnetic-field-generating device according to claim 9, which is selected from the group consisting of the following:

a) a magnetic-field-generating device, wherein a loop-shaped axially magnetized dipole magnet is provided such that the North-South axis is perpendicular to the supporting surface or space, wherein the loop-shaped magnet surrounds a central area, and the device further comprises a pole piece that is provided below the loop-shaped axially magnetized dipole magnet with respect to the supporting surface or the space and that closes one side of the loop formed by the loop-shaped magnet, and wherein the pole piece forms one or more projections extending into the space surrounded by the loop-shaped magnet and being spaced apart therefrom, wherein

a1) the pole piece forms one projection that extends into the central area surrounded by the loop-shaped magnet, wherein the projection is laterally spaced apart from the loop-shaped magnet and fills a part of the central area;

a2) the pole piece forms one loop-shaped projection and surrounds a central bar dipole magnet having the same North-South direction as the loop-shaped magnet, the projection and the bar dipole magnet being spaced apart from each other, or

a3) the pole piece forms two or more spaced-apart projections, either all of these or all but one of these are loop-shaped, and, depending on the number of projections, one or more additional axially magnetized loop shaped magnets having the same North South direction as the first axially magnetized loop-shaped magnet is/are provided in the space formed between the spaced-apart loop-shaped projections, the additional magnets being spaced apart from the loop-shaped projections, and wherein the central area surrounded by the loop-shaped projections and the loop-shaped magnets is partly filled with either a central bar dipole magnet having the same North-South direction as the surrounding loop-shaped magnets or with a central projection of the pole piece, such that, as viewed from the supporting surface or the space, an alternating arrangement of spaced-apart loop-shaped pole piece projections and loop-shaped axially magnetized dipole magnets is formed, surrounding one central area, wherein the central area is filled either with a bar dipole magnet or a central projection as set out above;

b) a magnetic-field-generating device, comprising two or more bar dipole magnets and two or more pole pieces, wherein

the device comprises an equal number of pole pieces and bar dipole magnets, wherein the bar dipole magnets have their North-South axis substantially perpendicular to the supporting surface or space, have the same North-South direction and are provided in different distances from the supporting surface or space, preferably along one line extending perpendicular from the supporting surface or space, and spaced apart from each other; and

the pole pieces being provided in the space between the bar dipole magnets and in contact therewith, wherein the pole pieces form one or more projections which, in loop-shaped form, surrounds a central area in which the bar dipole magnet located next to the supporting surface or space is located;

c) a magnetic-field-generating device, comprising one bar dipole magnet located below the supporting surface or space and having its North-South direction perpendicular to said supporting surface or space,

one or more loop-shaped pole pieces arranged above the magnet and below the supporting surface or space, which, for a plurality of loop-shaped pole pieces, are arranged spaced apart and coplanar nested, the one or more pole pieces laterally surrounding a central area under which the magnet is located,

the device further comprising a first plate-like pole piece having about the same size and about the same outer peripheral shape as the outermost loop-shaped pole piece, the plate-like pole piece being arranged below the magnet such that its outer peripheral shape is superimposed with the periphery of outermost of the loop-shaped pole pieces in direction from the supporting surface or space, and which is in contact with one of the poles of the magnet; and

a central pole piece in contact with the respectively other pole of the magnet, the central pole piece having the outer peripheral shape of a loop, partly filling the central area and being laterally and spaced apart from and surrounded by the one or more loop-shaped pole pieces;

d) a magnetic-field-generating device according to item c) above, wherein a second plate like pole piece having the outer peripheral shape of a loop is provided at a position above and in contact with one pole of the magnet and below and in contact with the one or more loop-shaped pole pieces and below and in contact with the central pole piece, so that the central pole piece is no longer in direct contact with the pole of the magnet, the second plate-like pole piece being of about the same size and shape as the first plate-like pole piece;

e) a magnetic-field-generating device, wherein two or more bar dipole magnets are arranged below the supporting surface or space and such as to be rotatable around an axis of rotation that is perpendicular to the supporting surface or space, the two or more bar dipole magnets being spaced apart from the axis of rotation and from each other and provided symmetrically on opposite sides of the axis of rotation, the device optionally further comprising one bar dipole magnet that is arranged below the supporting surface or space and on the axis of rotation, wherein either

e1) the device comprises, on either side of the axis of rotation, one or more bar dipole magnets all having their North-South axis substantially perpendicular to the supporting surface or space and substantially parallel to the axis of rotation, the North-South direction of all magnets being identical with respect to the supporting surface or space, and the magnets being spaced apart from each other,

the device optionally comprising one bar dipole magnet that is arranged below the supporting surface or space and on the axis of rotation, the North-South axis thereof being substantially perpendicular to the supporting surface or space and substantially parallel to the axis of rotation, and the North-South direction of which is either identical to the North South direction of the magnets that are arranged rotatable around the axis and spaced apart therefrom or opposite thereto;

e2) no optional bar dipole magnet on the axis of rotation is present and the device comprises, on either side of the axis of rotation, two or more bar dipole magnets arranged spaced apart from each other and from the axis of rotation, the North-South axis of the magnets being substantially perpendicular to the supporting surface or space and substantially parallel to the axis of rotation, and wherein the magnets provided on either side of the axis have alternating North-South directions, and the innermost magnets with regard to the axis of rotation either have the same or opposite North-South directions;

e3) no optional bar dipole magnet on the axis of rotation is present and the device comprises, on either side of the axis of rotation, two or more bar dipole magnets arranged spaced apart from each other and from the axis of rotation, the North-South axis of the magnets being substantially perpendicular to the supporting surface or space and substantially parallel to the axis of rotation, and wherein the magnets provided on either side of the axis have the same North-South direction and the magnets provided on different sides of the axis of rotation have opposite North-South directions;

e4) the device comprises, on either side of the axis of rotation, one or more bar dipole magnets that are arranged spaced apart from the axis of rotation and, if more than one magnet is present on one side, spaced apart from each other,

the North-South axis of the magnets being substantially parallel to the supporting surface or space and substantially radial to the axis of rotation, and

the North-South directions of the magnets being arranged such that the North-South directions of all magnets point essentially in the same direction, wherein further either

e4-1) no optional magnet is provided on the axis of rotation and at least two magnets are provided on either side of the axis of rotation;

or

e4-2) an optional magnet is provided on the axis of rotation, the magnets on either side being arranged spaced apart therefrom, the magnet on the axis of rotation being a bar dipole magnet having its North-South axis substantially parallel to the supporting surface and its North-South direction pointing in the same direction as the other magnets provided on either side of the axis or rotation;

e5) the device comprises no optional magnet provided on the axis of rotation and comprises, on either side of the axis of rotation, two or more bar dipole magnets that are arranged spaced apart from the axis of rotation and spaced apart from each other, the North-South axis of the magnets being substantially parallel to the supporting surface or space and substantially radial to the axis of rotation, wherein the North-South directions of all magnets are symmetrical with respect to the axis of rotation (i.e. all pointing towards or away from the axis of rotation);

e6) the device comprises no optional magnet provided on the axis of rotation and comprises, on either side of the axis of rotation, one or more pairs of bar dipole magnets that are arranged spaced apart from the axis of rotation and spaced apart from each other, the North-South axis of all magnets being substantially parallel to the supporting surface or space and substantially radial to the axis of rotation, and each pair of magnets being formed by two magnets with opposite North-South directions pointing towards each other or away from each other, respectively, and wherein the innermost magnets of the innermost pairs of magnets on either side have either

e6-1) symmetric North South directions with respect to the axis of rotation, both pointing either away or towards the axis of rotation;

or

e6-2) asymmetric North-South direction with respect to the axis of rotation, one pointing away and one towards the axis of rotation;

or

e7) the device either

e7-1) comprises the optional bar dipole magnet on the axis of rotation and one or more magnets on either side of the axis of rotation, the North-South axis of all magnets being substantially parallel to the supporting surface and the North-South axis of the magnets on either side of the axis of rotation is essentially radial to the axis of rotation;

or

e7-2) the device does not comprise the optional bar dipole magnet on the axis of rotation and comprises two or more magnets on either side of the axis of rotation that are arranged spaced apart from the axis of rotation, the North-South axis of all magnets being substantially parallel to the supporting surface or space and substantially radial to the axis of rotation,

wherein in both instances the North-South directions of the magnets arranged on one side of the axis of rotation are asymmetric to the North-South directions of the magnets arranged on the other side of the axis of rotation with respect to the axis of rotation (i.e. pointing towards the axis of rotation on one side and away from the axis of rotation on the other side), such that the North-South directions are in line from the outermost magnet on one side to the outermost magnet on the other side, the magnet on the axis of rotation in case e7-1 being aligned in this line;

e8) the device comprises, on either side of the axis of rotation two or more bar dipole magnets all having their North-South axis substantially perpendicular to the supporting surface or space and substantially parallel to the axis of rotation, and optionally a bar dipole magnet arranged on the axis of rotation and also having its North-South axis substantially perpendicular to the supporting surface or space and substantially parallel to the axis of rotation;

the North-South direction of adjacent magnets being opposite with respect to the supporting surface or space, and the magnets being spaced apart from each other;

or

e9) the device comprises, on either side of the axis of rotation two or more bar dipole magnets all having their North-South axis substantially parallel to the supporting surface or space and substantially radial to the axis of rotation, and optionally a bar dipole magnet arranged on the axis of rotation and also having its North-South axis substantially parallel to the supporting surface or space and substantially perpendicular to the axis of rotation;

the North-South directions of adjacent magnets pointing in opposite directions, and the magnets being spaced apart from each other;

f) a magnetic-field-generating device, wherein two or more loop-shaped dipole magnets are provided such that their North-South axis are perpendicular to the supporting surface or space, the two or more loop-shaped magnets being arranged nested, spaced apart and surrounding one central area, the magnets being axially magnetized, and adjacent loop-shaped magnets have opposite North-South directions pointing either to or away from the supporting surface or space,

the device further comprising a bar dipole magnet provided in the central area surrounded by the loop-shaped magnets, the bar dipole magnet having its North South axis substantially perpendicular to the supporting surface and parallel to the North-South axis of the loop-shaped magnets, the North-South direction of the bar dipole magnet being opposite to the North-South direction of the innermost loop-shaped magnet, the device optionally further comprising a pole piece on the side opposite to the supporting surface or space and in contact with the central bar dipole magnet and the loop-shaped magnets;

g) a magnetic-field-generating device, comprising a permanent magnetic plate that is magnetized perpendicular to the plane of the plate and having projections and impressions, the projections and impressions being arranged to form nested loop-shaped projections and impressions surrounding a central area, the projections and impressions forming opposite magnetic poles; and

h) a magnetic-field-generating device which comprises a plurality of bar dipole magnets provided around an axis of rotation, the magnets on either side of the axis of rotation being two or more bar dipole magnets all having their North-South axis either substantially parallel or perpendicular to the supporting surface or space, and optionally a bar dipole magnet arranged on the axis of rotation and also having its North-South axis substantially parallel or perpendicular to the supporting surface;

respectively, the North-South directions of adjacent magnets pointing in the same or in opposite directions, and the magnets being spaced apart from each other or in direct contact with each other, the magnets optionally being provided on a ground plate.

16. A printing assembly comprising the magnetic-field-generating devices recited in claim 9, which optionally is a rotating printing assembly.

17. Use of the magnetic-field-generating devices recited in claim 9 for producing the OEL.

18. A process for producing an optical effect layer (OEL) comprising the steps of:

a) applying on a supporting surface or a substrate surface a coating composition comprising a binder material and a plurality of non-spherical magnetic or magnetizable particles, wherein at least a part of the plurality of non-spherical magnetic or magnetizable particles is constituted by non-spherical optically variable magnetic or magnetizable pigments, said coating composition being in a first (fluid) state,

b) exposing the coating composition in a first state to the magnetic field of a magnetic-field-generating device, preferably one as defined in any of claims 9-15, thereby orienting at least a part of the non-spherical magnetic or magnetizable particles in a plurality of a nested loop-shaped areas surrounding one central area such that the longest axis of the particles in each of the cross-sectional areas of the looped-shaped areas follow a tangent of either a negatively curved or a positively curved part of hypothetical ellipses or circles; and

c) hardening the coating composition to a second state so as to fix the magnetic or magnetizable non-spherical particles in their adopted positions and orientations.

19. The process according to claim 18, wherein the hardening step c) is done by UV-Vis light radiation curing.

20. An optical effect layer, which is obtainable by the process of claim 18.