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EP-4157552-B1 - MAGNETIC ASSEMBLIES AND METHODS FOR PRODUCING OPTICAL EFFECT LAYERS COMPRISING ORIENTED PLATELET-SHAPED MAGNETIC OR MAGNETIZABLE PIGMENT PARTICLES

EP4157552B1EP 4157552 B1EP4157552 B1EP 4157552B1EP-4157552-B1

Inventors

  • LOGINOV, Evgeny
  • BAUDRAZ, Christophe
  • DESPLAND, CLAUDE-ALAIN

Dates

Publication Date
20260506
Application Date
20210521

Claims (14)

  1. A magnetic assembly (x00) for producing an optical effect layer (OEL) on a substrate (x20), said magnetic assembly (x00) being configured for receiving the substrate (x20) in an orientation substantially parallel to a first plane and above the first plane, and further comprising: a) at least a first set (S1) and a second set (S2), each of the first and second sets (S1, S2) comprising: i. one first bar dipole magnet (x31) having a first thickness (L1), a first length (L4) and a first width (L5), and having its magnetic axis oriented to be substantially parallel to the first plane, ii. two second bar dipole magnets (x32 a and x32 b ) having a second thickness (L2), a second length (L6) and a second width (L7), the two second bar dipole magnets (x32 a , x32 b ) having their upmost surfaces flush with each other, and having their magnetic axes oriented to be substantially perpendicular to the first plane, the first plane being located above the upmost surface of the two second bar dipole magnets (x32 a and x32 b ) the first bar dipole magnet (x31) of the first set (S1) having a magnetic direction opposite to the magnetic direction of the first bar dipole magnet (x31) of the second set (S2), the first bar dipole magnets (x31) of the first and second sets (S1, S2) being spaced apart by a first distance (d1), the first bar dipole magnet (x31) of the first set (S1) having substantially the same first length (L4) and first width (L5) as the first bar dipole magnet (x31) of the second set (S2), and the two second bar dipole magnets (x32 a and x32 b ) of the first set (S1) having substantially the same second lengths (L6) and second widths (L7) as the two second bar dipole magnets (x32 a and x32 b ) of the second set (S2), the first bar dipole magnet (x31) and the second bar dipole magnets (x32 a and x32 b ) of each of the first and second sets (S1, S2) being aligned to form a column, in that the first bar dipole magnet (x31) of the first and second sets (S1, S2) is respectively placed between and spaced apart from the second bar dipole magnets (x32 a and x32 b ) by a second distance (d2), the first width (L5) and the second length (L6) being substantially the same, the North pole of one second bar dipole magnet (x32 a and x32 b ) of each of the first and second sets (S1, S2) pointing towards the first plane as the North Pole of the first bar dipole magnet (x31) pointing towards said one, and the South pole of the other of the second bar dipole magnet (x32 a and x32 b ) of each of the first and second sets (S1, S2) pointing towards the first plane and the South Pole of the first bar dipole magnet (x31) pointing towards said other, and further comprising: b) a first pair (P1) of third bar dipole magnets (x33 a and x33 b ) having a third thickness (L3), a third length (L8) and a third width (L9) and having their magnetic axes oriented to be substantially parallel to the first plane, the second width (L7) of the two second bar dipole magnets (x32 a and x32 b ) of the first and second sets (S1, S2) having substantially the same value as the third width (L9) of the third bar dipole magnets (x33 a and x33 b ), each of the third bar dipole magnets (x33 a and x33 b ) being aligned with one second bar dipole magnet (x32 a and x32 b ) of the first set (S1) and one second bar dipole magnet (x32 a and x32 b ) of the second set (S2) so as to form two lines, the third bar dipole magnets (x33 a and x33 b ) being placed between and spaced apart from the respective second bar dipole magnets (x32 a and x32 b ) by a third distance (d3), the North poles of the third bar dipole magnets (x33a and x33 b ) respectively pointing towards one of the second bar dipole magnets (x32 a and x32 b ) and the North Poles of said ones of the second bar dipole magnets (x32 a and x32 b ) pointing towards the first plane or the South poles of the third bar dipole magnets (x33 a and x33 b ) respectively pointing towards one of the second bar dipole magnets (x32 a and x32 b ) and the South Poles of said ones of the second bar dipole magnets (x32 a and x32 b ) pointing towards the first plane, wherein the first bar dipole magnets (x31) of the first and second sets (S1, S2), the second bar dipole magnets (x32 a and x32 b ) of the first and second sets (S1, S2), and the third bar dipole magnets (x33 a and x33 b ) are at least partially embedded in a non-magnetic supporting matrix.
  2. The magnetic assembly (x00) according to claim 1, wherein the first thickness (L1) of the first bar dipole magnets (x31) of the first and second sets (S1, S2) is preferably equal to or smaller than the second thickness (L2) of the second bar dipole magnets (x32 a and x32 b ) of the first and second sets (S1, S2); preferably wherein the ratio of the second thickness (L2) of the second bar dipole magnets (x32 a and x32 b ) of the first and second sets (S1, S2) over the first thickness (L1) of the first bar dipole magnets (x31) of the first and second sets (S1, S2) (L2/L1) is equal to or smaller than 3 and greater than or equal to 1 (i.e. 1 ≤ L2/L1 ≤ 3); the first thickness (L1) of the first bar dipole magnets (x31) of the first and second sets (S1, S2) is preferably equal to or smaller than the third thickness (L3) of the third bar dipole magnets (x33 a and x33 b ) of the first pair (P1); preferably wherein the ratio of the third thickness (L3) of the third bar dipole magnets (x33 a and x33 b ) of the first pair (P1) over the first thickness (L1) of the first bar dipole magnets (x31) of the first and second sets (S1, S2) (L3/L1) is equal to or smaller than 3 and greater than or equal to 1 (1 ≤ L3/L1 ≤ 3); wherein the second distance (d2) between the first bar dipole magnet (x31) and the second bar dipole magnets (x32 a and x32 b ) is larger than or equal to 0 and smaller than or equal to ½ of the first thickness (L1) of the first bar dipole magnets (x31) (0 ≤ d2 ≤ ½ L1); and wherein the third distance (d3) between the third bar dipole magnets (x33 a and x33 b ) of the first pair (P1) and the second bar dipole magnets (x32 a and x32 b ) of the first and second sets (S1, S2) is larger than or equal to 0 and smaller than or equal to ½ of the first thickness (L1) of the first bar dipole magnets (x31) (0 ≤ d3 ≤ ½L1).
  3. The magnetic assembly (x00) according to claim 1 or 2, wherein the upmost surface of the second bar dipole magnets (x32 a and x32 b ) are flush with the upmost surfaces of the third bar dipole magnets (x33 a and x33 b ).
  4. The magnetic assembly (x00) according to any one of claims 1 to 3, wherein the first distance (d1) between the first bar dipole magnets (x31) of the first and second sets (S1, S2) is greater than or equal to 15% of the first length (L4) and smaller than or equal to 150% of the first length (L4) (i.e. 0.15*L4≤d1≤1.5*L4), preferably greater than or equal to 25% of the first length (L4) and smaller than or equal to 120% of the first length (L4) (i.e. 0.25*L4≤d1≤1.2*L4), even more preferably greater than or equal to 25% of the first length (L4) and smaller than or equal to 80% of the first length (L4) (i.e. 0.25*L4≤d1≤0.8*L4).
  5. The magnetic assembly (x00) according to any one of claims 1 to 4, further comprising one or more combinations comprising: i) a (2+i)th set (S (2+i) ) (i = 1, 2, etc.) comprising: one further first bar dipole magnet (x31) having the first thickness (L1), the first length (L4) and the first width (L5), and having its magnetic axis oriented to be substantially parallel to the first plane, and two further second bar dipole magnets (x32 a and x32 b ) having the second thickness (L2), the second length (L6) and the second width (L7), the two second bar dipole magnets (x32 a , x32 b ) having their upmost surfaces flush with each other, and having their magnetic axes oriented to be substantially perpendicular to the first plane, the first bar dipole magnet (x31) of the (2+i)th set (S 2+i ) having a magnetic direction opposite to the magnetic direction of the first bar dipole magnet (x31) of the (2+i-1)th set (S2+i-1) the first bar dipole magnets (x31) of the (2+i)th and (2+i-1)th sets (S 2+i , S 2+i-1 ) being spaced apart by the first distance (d1), the first bar dipole magnet (x31) of the (2+i)th set (S 2+i ) having substantially the same length (L5) and width (L4) as the first bar dipole magnet (x31) of the (2+i-1)th set (S 2+i-1 ), and the two second bar dipole magnets (x32 a , x32 b ) of the (2+i)th set (S (2+i) ) having substantially the same lengths (L6) and widths (L7) as the two second bar dipole magnets (x32 a , x32 b ) of the (2+i-1)th set (S 2+i-1 ), the first bar dipole magnet (x31) and the second bar dipole magnets (x32 a , x32 b ) being aligned to form a column, in that the first bar dipole magnet (x31) of the (2+i)th set (S 2+i ) is placed between and spaced apart from the second bar dipole magnets (x32 a , x32 b ) by the second distance (d2), the first and second lengths (L4 and L6) being substantially the same, the North pole of one of the second bar dipole magnets (x32 a , x32 b ) of the (2+i)th set (S 2+i ) pointing towards the first plane and the North Pole of the first bar dipole magnet (x31) pointing towards that second bar dipole magnet, and ii) a (1+i)th pair (P i+1 ) of third bar dipole magnets (x33 a and x33 b ) having the third thickness (L3), the third length (L9) and the third width (L8) and having their magnetic axes oriented to be substantially parallel to the magnetic axes of the third bar dipole magnets (x33 a and x33 b ) of the (1+i-1)th pair (P 1+i-1 ), each of the third bar dipole magnets (x33 a and x33 b ) being aligned with one second bar dipole magnet (x32 a and x32 b ) of the (2+i)th set (S 2+i ) and one second bar dipole magnet (x32 a and x32 b ) of the (2+i-1)th set (S 2+i-1 ) so as to form two lines, the third bar dipole magnets (x33 a and x33 b ) being placed between and spaced apart from the respective second bar dipole magnets (x32 a and x32 b ) by the third distance (d3), the North poles of the third bar dipole magnets (x33 a and x33 b ) respectively pointing towards one of the second bar dipole magnets (x32 a and x32 b ) of the (2+i)th and (2+i-1)th sets (S 2+i , S 2+i-1 ) and the North Poles of said ones of the second bar dipole magnets (x32 a and x32 b ) pointing towards the first plane or the South poles of the third bar dipole magnets (x33 a and x33 b ) respectively pointing towards one of the second bar dipole magnets (x32 a and x32 b ) of the (2+i)th and (2+i-1)th sets (S 2+i , S 2+i-1 ) and the South Poles of said ones of the second bar dipole magnets (x32 a and x32 b ) pointing towards the first plane, wherein the first bar dipole magnets (x31) of the (2+i)th set (S 2+i ), the second bar dipole magnets (x32 a and x32 b ) of the (2+i)th set (S (2+i) ), and the third bar dipole magnets (x33 a and x33 b ) of the (1+i)th pair (P 1+i ) are at least partially embedded in the non-magnetic supporting matrix.
  6. A printing apparatus comprising the magnetic assembly (x00) according to any one of claims 1 to 5 being mounted in the vicinity of a transferring device preferably selected from the group consisting of chains, belts, cylinders and combinations thereof.
  7. A method for producing an optical effect layer (OEL) on a substrate (x20) comprising the steps of: i) applying on a substrate (x20) surface a radiation curable coating composition comprising platelet-shaped magnetic or magnetisable pigment particles, wherein an X-axis and a Y-axis define a plane of predominant extension of the particles, said radiation curable coating composition being in a first, liquid state so as to form a coating layer (x10); ii) exposing the coating layer (x10) to a magnetic field of the magnetic assembly (x00) recited in any one of claims 1 to 5 so as to bi-axially orient at least a part of the platelet-shaped magnetic or magnetisable pigment particles; iii) at least partially curing the radiation curable coating composition of step ii) to a second, solid state so as to fix the platelet-shaped magnetic or magnetisable pigment particles in their adopted positions and orientations.
  8. The method according to claim 7, further comprising a further step of exposing the coating layer (x10) to a magnetic field of a magnetic-field-generating device so as to re-orient at least a part of the platelet-shaped magnetic or magnetisable particles, said further step being carried out subsequently to step ii).
  9. The method according to claim 8, wherein a step of selectively at least partially curing one or more first areas of the coating layer (x10) of the radiation curable coating composition of step ii) is carried out so as to fix at least a part of the platelet-shaped magnetic or magnetisable particles in their adopted positions and orientations, such that one or more second areas of the coating layer (x10) remain unexposed to irradiation, said step being carried out prior to, partially simultaneously with or subsequently to the step of claim 9 of further exposing the coating layer (x10) to the magnetic field of the magnetic-field-generating device.
  10. The method according to claim 7, wherein the coating layer (x10) is exposed, in a single step, to the interaction of magnetic fields of the magnetic assembly (x00) recited in any one of claims 1 to 7 and a magnetic-field-generating device comprising one or more hard magnetic magnets, the magnetic-field-generating device being mounted on a rotating magnetic cylinder (x60) or being a moveable magnetic-field-generating device.
  11. The method according to claim 7, wherein the coating layer (x10) is exposed, in a single step, to the interaction of the magnetic fields of the magnetic assembly (x00) recited in any one of claims 1 to 6 and one or more soft magnetic plates carrying one or more indicia in the form of voids and/or indentations and/or protrusions, said one or more soft magnetic plates being placed on a rotating magnetic cylinder (x60) or being placed on a moveable device below the substrate (x20).
  12. The method according to any one of claims 7 to 11, wherein a distance (h) between the upmost surface of the first bar dipole magnets (x31) and the substrate is greater than 0 and smaller than or equal to about 20 mm, preferably smaller than or equal to about 10 mm and greater than about 2 mm.
  13. The method according to any one of claims 7 to 12, wherein step iii) is carried out by UV-Vis light radiation curing.
  14. The method according to any one or claims 7 to 13, wherein at least a part of the platelet-shaped magnetic or magnetisable particles is constituted by platelet-shaped optically variable magnetic or magnetisable pigment particles, preferably selected from the group consisting of magnetic thin-film interference pigments, magnetic cholesteric liquid crystal pigments and mixtures thereof.

Description

FIELD OF THE INVENTION The present invention relates to the field of magnetic assemblies and methods for producing optical effect layers (OELs) comprising magnetically oriented platelet-shaped magnetic or magnetizable pigment particles. In particular, the present invention provides magnetic assemblies and methods for magnetically orienting platelet-shaped magnetic or magnetizable pigment particles in coating layers so as to produce OELs and the use of said OELs as anti-counterfeit means on security documents or security articles as well as decorative purposes. BACKGROUND OF THE INVENTION It is known in the art to use inks, compositions, coatings or layers containing oriented magnetic or magnetizable pigment particles, particularly also optically variable magnetic or magnetizable pigment particles, for the production of security elements, e.g. in the field of security documents. Coatings or layers comprising oriented magnetic or magnetizable pigment particles are disclosed for example in US 2,570,856; US 3,676,273; US 3,791,864; US 5,630,877 and US 5,364,689. Coatings or layers comprising oriented magnetic color-shifting pigment particles, resulting in particularly appealing optical effects, useful for the protection of security documents, have been disclosed in WO 2002/090002 A2 and WO 2005/002866 A1. Security features, e.g. for security documents, can generally be classified into "covert" security features on the one hand, and "overt" security features on the other hand. The protection provided by covert security features relies on the principle that such features are difficult to detect, typically requiring specialized equipment and knowledge for detection, whereas "overt" security features rely on the concept of being easily detectable with the unaided human senses, e.g. such features may be visible and/or detectable via the tactile sense while still being difficult to produce and/or to copy. However, the effectiveness of overt security features depends to a great extent on their easy recognition as a security feature. Magnetic or magnetizable pigment particles in printing inks or coatings allow for the production of magnetically induced images, designs and/or patterns through the application of a correspondingly structured magnetic field, inducing a local orientation of the magnetic or magnetizable pigment particles in the not yet hardened (i.e. wet) coating, followed by the hardening of the coating. The result is a fixed and stable magnetically induced image, design or pattern. Materials and technologies for the orientation of magnetic or magnetizable pigment particles in coating compositions have been disclosed for example in US 2,418,479; US 2,570,856; US 3,791,864, DE 2006848-A, US 3,676,273, US 5,364,689, US 6,103,361, EP 0 406 667 B1; US 2002/0160194; US 2004/0009308; EP 0 710 508 A1; WO 2002/09002 A2; WO 2003/000801 A2; WO 2005/002866 A1; WO 2006/061301 A1. In such a way, magnetically induced patterns which are highly resistant to counterfeit can be produced. The security element in question can only be produced by having access to both, the magnetic or magnetizable pigment particles or the corresponding ink, and the particular technology employed to print said ink and to orient said pigment in the printed ink. The methods and devices described hereabove use magnetic assemblies to mono-axially orient platelet-shaped magnetic pigment particles. Mono-axial orientation of magnetic pigment particles result in neighboring particles having their main axis parallel to each other and to the magnetic field, while their minor axis in the plane of the pigment particles is not, or much less constrained by the applied magnetic field. With the aim of producing coatings or layers comprising bi-axially oriented magnetic or magnetizable pigment particles, methods for generating time-dependent, direction-variable magnetic fields have been developed, thus allowing the bi-axial orientation of magnetic or magnetizable pigment particles. WO 2015/086257 A1 discloses a method for producing an optical effect layer (OEL) on a substrate, said process comprising two magnetic orientation steps, said steps consisting of i) exposing a coating composition comprising platelet-shaped magnetic or magnetisable pigment particles to a dynamic, i.e. direction changing, magnetic field of a first magnetic-field-generating device so as to bi-axially orient at least a part of the platelet-shaped magnetic or magnetisable pigment particles and ii) exposing the coating composition to a static magnetic field of a second magnetic-field-generating device, thereby mono-axially re-orienting at least a part of the platelet-shaped magnetic or magnetisable pigment particles according to a design transferred by said second magnetic-field-generating device. EP 2 157 141 A1 discloses magnetic-field-generating devices comprising a linear arrangement of at least three magnets that are positioned in a staggered fashion or in zigzag formation, each of said