Printing diffraction gratings on paper and board

Abstract

A method and an apparatus for forming a surface relief microstructure, especially an optically variable image on a paper substrate are provided, the method comprising the steps of: A) applying a curable composition to at least a portion of the frontside of the paper substrate; B) contacting at least a portion of the curable composition with surface relief microstructure, especially optically variable image forming means; C) curing the composition by using at least one UV lamp (1, 2, 3) which is arranged on the backside of the paper substrate; D) optionally depositing a layer of a transparent high refractive index material and/or a metallic layer on at least a portion of the cured composition, wherein the lamp (1, 2, 3) having emission peak(s) in the UV-A and near VIS range and the curable composition comprises at least a photoinitiator which absorbs in the UV-A region and preferably in the near VIS range. A paper product obtainable uses the method and an apparatus for forming a surface relief microstructure on a paper substrate. Surface relief microstructures, such as holograms may be replicated rapidly and with accuracy on a paper substrate by using the method and the apparatus.

Dependencies are inferred from the claim text.