Compositions: coating or plastic – Materials or ingredients – Pigment – filler – or aggregate compositions – e.g. – stone,...
Patent
1995-04-21
1996-11-12
Bell, Mark L.
Compositions: coating or plastic
Materials or ingredients
Pigment, filler, or aggregate compositions, e.g., stone,...
106415, 101491, C04B 1420
Patent
active
055735843
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to the use of specific interference pigments combined with scattering color pigments which are complementary in color to the reflection color of the interference pigments, for preparing valuable documents that are forgeryproof, in particular difficult or impossible to photocopy.
The forgeryproofing of valuable documents such as paper money, postage stamps, checks, tax stamps, check cards, rail or air tickets, credit cards, telephone cards, lottery tickets, share certificates, gift tokens, passes or identity cards is becoming more and more important in view of the introduction of evermore powerful color copiers and the attendant scope for forgery.
Forgeryproofness has in the past been pursued in various ways. For instance, the originals were marked using magnetic pigments or fluorescent dyes. However, these markings have the disadvantage that their presence is not immediately recognizable visually; they can only be detected using appropriate, more or less complex reading apparatus. The same is true of marking with IR or UV dyes or pigments.
Greater interest therefore pertains to marks which are sufficiently reliably identifiable with the unaided, naked eye and make it easy to distinguish the original from the copy. In practice this kind of mark took the form of water marks--silvery bright metal strips which show up black in the copy owing to the total reflection of the light--or holograms. However, the disadvantage of these marks is that they are easy to imitate or, in the case of holograms, costly and prone to damage. The most recent addition to the ways of marking authenticity is the use of simple interference pigments. However, applied atop a light-colored background, interference pigments are virtually invisible and the marking is consequently easily overlooked.
Interference pigments in the conventional sense (described for example in US-A-3 087 827) are platelet-like luster pigments consisting predominantly of a mica substrate coated with a layer of highly refractive material, eg. rutile, zirconium dioxide or tin dioxide, in a certain thickness (in general >50 nm) to form thin platelet colors. Interference pigments have to be applied in an oriented state. However, the intensity of the color of interference color pigments is low compared with that of scattering color pigments. They have an angle-dependent reflection maximum. Interference pigments of this type have for many years been used in cosmetics and plastics.
US-A-3 087 827 describes interference pigments coated with a highly absorbing carbon layer, but these pigments have never been used for documents.
EP-A-353 544 describes interference pigments which have a metal coating as being suitable for security printing; however, these pigments are not used in combination with specific color pigments.
There have also been disclosed multi-layer pigments which exhibit a distinct angle-dependent color change and are prepared by pulverizing thin film security devices--thin multi-layer films detached from the substrate; cf. US-A-4 434 010, US-A-5 059 245. The optical principle of such pigments is that of the transmission filter. The sequence of layers making up such pigments typically includes a dielectric layer of low refractive index, eg. silicon dioxide, a semitransparent reflecting metal layer, eg. titanium, aluminum or chromium, a dielectric layer of low refractive index, eg. silicon dioxide, a highly reflecting opaque metal layer, eg. aluminum or titanium, a dielectric layer of low refractive index, eg. silicon dioxide, a semitransparent reflecting metal layer, eg. aluminum, chromium or titanium, and a dielectric layer of low refractive index, eg. silicon dioxide.
Pigments of this type have the disadvantage that they are costly and not stable to alkali and, what is more, usually do not have the desired acid fastness.
It is an object of the present invention to provide suitable pigments or pigment combinations for the forgeryproof marking of valuable documents, so that in particular photocopying these documents with power
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Ostertag Werner
Schmidt Helmut
BASF - Aktiengesellschaft
Bell Mark L.
Hertzog Scott L.
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