Processes for producing optical effects layers

1. A process for producing an optical effect layer (OEL) on a substrate comprising a photomask, said OEL comprising a motif made of at least two areas, preferably at least two adjacent areas, made of a single hardened layer, said process comprising the steps of:

a) applying on the substrate comprising the photomask a radiation curable coating composition comprising one or more photoinitiators and a plurality of magnetic or magnetizable pigment particles so as to form a coating layer, said coating layer being in a first state and said coating layer at least partially facing the photomask;

b)

b1) hardening one or more first substrate areas carrying the coating layer through the substrate, said hardening being performed by irradiation with a UV-Vis irradiation source to a second state so as to fix or freeze the magnetic or magnetizable pigment particles in their positions and orientations; and

c)

c1) exposing at least one or more second substrate areas carrying the coating layer which are in the first state due to the presence of the photomask of the substrate to a magnetic field of a magnetic-field-generating device thereby orienting the plurality of magnetic or magnetizable pigment particles so as to follow any magnetic or magnetizable pigment particles orientation pattern except a random orientation; and

c2) simultaneously, partially simultaneously or subsequently hardening by irradiation with a UV-Vis irradiation source at least the one or more second substrate areas carrying the coating layer to the second state so as to fix or freeze the magnetic or magnetizable pigment particles in their adopted positions and orientations,

wherein the photomask has an optical density D M equal to or higher than 1.0.

2. The process according to claim 1 , wherein said the step b) comprises the steps of :

b0) exposing one or more first substrate areas carrying the coating layer to a magnetic field of a first magnetic-field-generating device, thereby orienting the plurality of magnetic or magnetizable pigment particles so as to follow a magnetic or magnetizable pigment particles orientation pattern being any magnetic or magnetizable pigment particles orientation pattern except a random orientation, and

b1) simultaneously or partially simultaneously or subsequently hardening through the substrate the coating layer, said hardening being performed by irradiation with a UV-Vis irradiation source to a second state so as to fix or freeze the magnetic or magnetizable pigment particles in their adopted positions and orientations,

wherein the orientation pattern of step b0) is different from the orientation pattern of step c1).

3. The process according to claim 2 , wherein said first magnetic-field generating device is located on a side of the substrate carrying the coating layer.

4. The process according to claim 3 , wherein said first magnetic-field generating device orients the plurality of magnetic or magnetizable pigment particles so as to follow a concave curvature when viewed from the side carrying the coating layer.

5. The process according to claim 2 , wherein step b1) is carried out partially simultaneously or simultaneously with step b0).

6. The process according to claim 1 , wherein the step c1) is carried out with a second magnetic-field-generating device thereby orienting the plurality of magnetic or magnetizable pigment particles so as to follow a convex curvature when viewed from a side carrying the coating layer.

7. The process according to claim 2 , wherein the magnetic or magnetizable pigment particles are non-spherical magnetic or magnetizable pigment particles.

8. The process according to claim 7 , wherein the magnetic or magnetizable pigment particles are prolate or oblate ellipsoid-shaped, platelet-shaped or needle-shaped particles or a mixture of two or more thereof.

9. The process according to claim 7 , wherein the magnetic or magnetizable pigment particles are platelet-shaped particles.

10. The process according to claim 1 , wherein at least a part of the plurality of the magnetic or magnetizable pigment particles is constituted by magnetic thin-film interference pigments, magnetic cholesteric liquid crystal pigments, interference coated pigments including one or more magnetic materials and mixtures thereof.

11. The process according to claim 1 , wherein the photomask is a printed UV-absorbing photomask made of a UV-absorbing photomask composition comprising a binder and one or more UV-absorbing materials.

12. The process according to claim 11 , wherein the one or more UV absorbing materials are selected from the group consisting of dyes, organic pigments, inorganic pigments, optically variable pigments, fillers, UV-absorbers, mineral oxides nanoparticles and mixtures thereof.

13. The process according to claim 1 , wherein the step c2) of hardening by irradiation with a UV-Vis irradiation source at least the one or more second substrate areas carrying the coating is carried out simultaneously or partially simultaneously with the step c1) of exposing at least one or more second substrate areas to the magnetic field of the magnetic-field-generating device.

14. The process according to claim 1 , wherein the photomask has an optical density D M equal to or higher than 1.1.

15. The process according to claim 1 , wherein the photomask has an optical density D M equal to or higher than 1.2.

16. An optical effect layer (OEL) prepared by the process recited in claim 1 .

17. A security document comprising one or more optical effect layers (OEL) as recited in claim 16 .

18. An optical effect layer (OEL), wherein the OEL is disposed on a substrate comprising a photomask, said OEL comprising a motif made of at least two areas made of a single hardened layer, the OEL comprising a radiation cured coating composition comprising a plurality of magnetic or magnetizable pigment particles fixed or frozen in the coating composition by radiation curing so as to form a coating layer, said coating layer at least partly overlapping with the photomask to provide a masked area and an unmasked area thereof;

wherein the magnetic or magnetizable pigment particles of the masked area of the coating layer are oriented so as to follow any magnetic or magnetizable pigment particles orientation pattern except a random orientation; and

wherein the magnetic or magnetizable pigment particles of the unmasked area of the coating layer follow a random pattern or are oriented so as to follow a different orientation pattern than that of the magnetic or magnetizable pigment particles of the masked area to provide visually distinct optical impressions as determinable by the human eye.