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Method for Manufacturing Security Elements and Holograms by Direct Embossing of Printing Inks Containing Aluminum Particles

IP.com Disclosure Number: IPCOM000237715D
Publication Date: 2014-Jul-04

Publishing Venue

The IP.com Prior Art Database

Abstract

Described is a one step process for manufacturing a metallized microstructure. The process has been significantly simplified as compared to prior art processes without sacrificing the optical properties, such as high contrast, strong viewing angle dependency and high throughput. One step process means only one embossing and one curing step. The coating is a UV curable composition which contains additionally aluminum particles. The instant process allows printing microstructures on a substrate, in particular on a transparent or translucent substrate, embossing and metallizing of the surface relief in one process step using a conventional printing system such as flexography, rotogravure, offset printing, silkscreen printing, digital printing, and ink jet printing.

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Method for Manufacturing Security Elements and Holograms by Direct

       Embossing of Printing Inks Containing Aluminum Particles ___________________________________________________________________

Description

This publication relates to a method for forming a surface relief microstructure, especially an optically variable image (an optically variable device) on a substrate, in particular on a transparent or translucent substrate. Typically such microstructures contain holograms, Fresnel lens, gratings or tower structures.

There have been many attempts in the past to improve the manufacture of security elements by forming optically variable images (optically variable devices, OVD) on a substrate.

In WO2005051675 a method for forming a holographic diffraction grating on a substrate is described comprising the steps of: a) applying a curable composition to at least a portion of the substrate; b) contacting at least a portion of the curable composition with diffraction grating forming means; c) curing the curable composition and d) depositing a metallic ink on at least a portion of the cured composition.

There exists a need for efficient systems and methods for printing microstructures (surface relief structures) on a substrate, in particular on a transparent or translucent substrate that fully incorporates surface relief technologies into mainstream printing applications such as secure documents, flexible and rigid packaging, labels, and printed forms.

It has now been found, that the process can be significantly simplified without sacrificing the optical properties, such as high contrast, strong viewing angle dependency and high throughput by using a one step process, which means only one embossing and one curing step. The coating is a UV curable composition which contains additionally the aluminum particles. The instant process allows printing microstructures on a substrate, in particular on a transparent or translucent substrate embossing and metallizing of the surface relief in one process step using a conventional printing system such as flexography, rotogravure, offset printing, silkscreen printing, digital printing, and ink jet printing.

The term coating is used in this context as synonym for ink, laqcuer or varnish.


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[2]

The process is typically carried out on an apparatus for forming a surface relief microstructure on a substrate, which is coated with a curable composition (varnish, ink) on at least part of its frontside comprising a printing press and surface relief microstructure forming means, wherein the microstructure forming means comprise


a) surface relief microstructure forming means, especially a shim which carries the microstructure to be casted into the curable composition, and


b) a lamp having emission peak(s) in the UV-A range and preferably near VIS range for curing the curable composition when the coated substrate is pressed against the shim.

In one embodiment the apparatus may be an off-line or s...