Vacuum roll coated security thin film interference products with overt and/or covert patterned layers

Abstract

A security thread for embedding in or on a sheet such as a document, currency or packaging is disclosed, wherein the thread has a thin film interference structure deposited thereon. The structure may be a Fabry-Perot structure in the form of a single filter, or may be plural filters, spaced side-by-side. The thread appears to have separated interference filters deposited thereon. Preferably the thread is first roll coated with oil using an oil-ablation technique to remove deposited material in situ in the coating process. A magnetic layer may be deposited within, behind or in front of the thin film interference structure.

Description

CROSS-REFERENCE TO RELATED APPLICATION [0001] The present application claims the benefit of previously filed, co-pending U.S. Application Ser. No. 60 / 487,527, filed Jul. 14, 2003, by Phillips et al, entitled: “IMAGED OPTICAL FOILS,” the disclosure of which is incorporated herein.BACKGROUND OF THE INVENTION [0002] The use of security threads for protecting banknotes, credit cards and other valuable documents is well known. A security thread is a strip of material placed on the surface of a banknote document or sheet such as banknote; alternatively a security thread may be serpentined or woven into the banknote paper (a window type effect) to confer additional security (authenticity) to the bank note. Typical dimensions of a hot stamp thread are a width of 1-5 mm, a thickness of 3-4 μm; windowed polyester terephthalate (PET) based threads have a thickness of about 0.5 mil or 12.5 microns. By way of example, one of the earliest forms of security threads consisted of reflective foil tra...

AI Technical Summary

Benefits of technology

[0030] Such threads as described in accordance with this invention cannot be accurately reproduced by way of being photocopied, photographed, or printed since these technologies do not possess optically variable effects. Furthermore, in the case of optically variable foil, the optics of copiers prevents even the face color at normal incidence from being imaged; since just a black image results as the reflective surface of the optically variable thread causes the light to miss the entrance optics of the copier. In addition, the intricate design of the text, having a resolution down to 60 microns, would prevent any counterfeiter from using scissors to simulate this security device.

Problems solved by technology

However, these aforementioned threads either take too much time to make and or have other associated problems; for example, it is found that laser etching takes too long to be cost effective, etching by use of chemicals requires multiple steps and is not considered to be environmentally-friendly; holograms can be readily copied, and in many instances the features of the threads are not readily seen by eye by the average person and machines are required to read them.

A major impediment to providing several thin film layers, was residual oil remaining on the images and on non-patterned areas of the web.

This residual oil was detrimental to further thin film coating since left over oil would cause “ghosting”; a process whereby the inhibiting oil is transferred to the back side of plastic film when roll coating, which in turn causes inhibiting oil to be transferred further down the web on the front side.

Left over inhibiting oil also causes adhesion failures to subsequent thin film layers.

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