Method for manufacturing a security element having a lens grid image
A method includes using a lenticular image having a lens grid composed of a plurality of microlenses and a metallic motif layer arranged spaced apart from the lens grid; the refractive effect of the microlenses defines a focal plane and the metallic motif layer being arranged substantially in the focal plane; a line width is chosen for the demetalized sub-regions to be produced in the metallic motif layer; a marking laser source having a laser wavelength λ is selected such that the resolving power D(λ) of the microlenses of the lenticular image at the selected laser wavelength λ substantially corresponds to the line width of the demetalized sub-regions to be produced; and the metallic motif layer is impinged on through the microlenses with laser radiation of the marking laser source to produce demetalized sub-regions in the metallic motif layer.
1. A method for manufacturing a security element having a lenticular image for depicting one or more target images that are visible only from predetermined viewing directions and whose motifs are formed by visually perceptible, contrasting metallic and demetalized sub-regions of a motif layer, and in the method
a lenticular image having a lens grid composed of a plurality of microlenses and a metallic motif layer arranged spaced apart from the lens grid is provided,
a refractive effect of the microlenses defining a focal plane and the metallic motif layer being arranged substantially in said focal plane,
a line width is chosen for the demetalized sub-regions to be produced in the metallic motif layer,
a marking laser source having a laser wavelength λ is selected such that a resolving power D(λ) of the microlenses of the lenticular image at the selected laser wavelength λ substantially corresponds to the line width of the demetalized sub-regions to be produced, and
the metallic motif layer is impinged on through the microlenses with laser radiation of the selected marking laser source to produce demetalized sub-regions in the metallic motif layer.
2. The method according to claim 1 , wherein the lenticular image is adapted for depicting n≥2 target images, and for the demetalized sub-regions to be produced, a line width is chosen that is between 0.6*dML/n and 1.4*dML/n, where dML is a diameter of the microlenses.
3. The method according to claim 1 , wherein a lenticular image having a lens grid composed of a plurality of micro-cylindrical lenses is provided.
4. The method according to claim 1 , wherein a lenticular image is provided whose metallic motif layer is arranged at a distance from the focal plane that is less than 25% of a focal length of the microlenses.
5. The method according to claim 1 , wherein the resolving power D(λ) of the microlenses of the lenticular image is determined by a formula
D (λ)=2.44*λ* f/d ML,
where f is a focal length of the microlenses and dML is a diameter of the microlenses, and the marking laser source is adjusted in such a way that D(λ) differs from the line width of the demetalized sub-regions to be produced by less than 15%.
6. The method according to claim 1 , wherein, as the marking laser source, a Nd:YAG laser, a frequency-doubled Nd:YAG laser, a frequency-tripled Nd:YAG laser or an Er:glass laser is used.
7. The method according to claim 1 , wherein two or more different marking laser sources of different wavelengths are used.
8. The method according to claim 1 , wherein, for fine control, a laser power of the marking laser source is adjusted to adapt the line width of the produced demetalized sub-regions to the chosen line width.
9. The method according to claim 1 , wherein a lenticular image is provided whose lens grid comprises microlenses having a lens diameter between 5 μm and 20 μm and whose lens period is between 100% and 125% of the lens diameter.
10. The method according claim 1 , wherein a lenticular image is provided whose lens grid is embedded in an embedding layer whose refractive index differs from the refractive index of the microlenses by 0.2 or more.
11. The method according to claim 1 , wherein two different wavelengths are used.
12. The method according to claim 11 , wherein the lenticular image is adapted for depicting n≥2 target images, and for the demetalized sub-regions to be produced, a line width is chosen that is between 0.6*dML/n and 1.4*dML/n, where dML is a diameter of the microlenses.
13. The method according to claim 11 , wherein a lenticular image having a lens grid composed of a plurality of micro-cylindrical lenses is provided.
14. The method according to claim 11 , wherein the resolving power D(λ) of the microlenses of the lenticular image is determined by a formula
D (λ)=2.44*λ* f/d ML,
where f is a focal length of the microlenses and dML is a diameter of the microlenses, and the marking laser source is adjusted in such a way that D(λ) differs from the line width of the demetalized sub-regions to be produced by less than 15%.
15. The method according to claim 11 , wherein, as the marking laser source, a Nd:YAG laser, a frequency-doubled Nd:YAG laser, a frequency-tripled Nd:YAG laser or an Er:glass laser is used.
16. The method according to claim 11 , wherein two or more different marking laser sources of different wavelengths are used.
17. The method according to claim 11 , wherein, for fine control, a laser power of the marking laser source is adjusted to adapt the line width of the produced demetalized sub-regions to the chosen line width.
18. The method according to claim 11 , wherein a lenticular image is provided whose lens grid comprises microlenses having a lens diameter between 5 μm and 20 μm and whose lens period is between 100% and 125% of the lens diameter.
19. The method according claim 11 , wherein a lenticular image provided with the lens grid embedded in an embedding layer whose refractive index differs from the refractive index of the microlenses by 0.2 or more.
20. A method for manufacturing a security element having a lenticular image that depicts one or more target images that are visible only from predetermined viewing directions and whose motifs are formed by visually perceptible, contrasting metallic and demetalized sub-regions of a motif layer, the method comprising:
providing a lenticular image having a lens grid composed of a plurality of microlenses and a metallic motif layer arranged spaced apart from the lens grid, the lenticular image being provided such that a refractive effect of the microlenses defines a focal plane and the metallic motif layer is arranged substantially in said focal plane,
choosing a line width for the demetalized sub-regions to be produced in the metallic motif layer,
selecting a laser wavelength of a marking laser source such that a resolving power D(λ) of the microlenses of the lenticular image at the selected laser wavelength λ substantially corresponds to the line width of the demetalized sub-regions to be produced, and
impinging on the metallic motif layer through the microlenses with laser radiation of the marking laser source at the selected laser wavelength to produce demetalized sub-regions in the metallic motif layer.
21. A security element having a lenticular image that depicts one or more target images that are visible only from predetermined viewing directions and whose motifs are formed by visually perceptible, contrasting metallic and demetalized sub-regions of a motif layer, the security element comprising:
a lenticular image having a lens grid composed of a plurality of microlenses and a metallic motif layer arranged spaced apart from the lens grid, a refractive effect of the microlenses defining a focal plane and the metallic motif layer being arranged substantially in said focal plane,
wherein the demetalized sub-regions in the metallic motif layer have a line width,
wherein the demetalized sub-regions in the metallic motif layer are produced by the metallic motif layer being impinged on through the microlenses with laser radiation of a marking laser source having a selected laser wavelength λ, and
wherein the selected laser wavelength λ of the marking laser source is selected such that a resolving power D(λ) of the microlenses of the lenticular image at the selected laser wavelength λ substantially corresponds to the line width of the demetalized sub-regions.