High value documents

Details High value documents High value documents

1995-01-23

1997-10-21

Fridie, Jr., Willmon

Printed matter

Having revealable concealed information, fraud preventer or...

Having watermark

283 72, 283 91, 283109, B42D 1500

Patent

active

056788630

DESCRIPTION:

BRIEF SUMMARY
The present invention relates to a means of identification or a document of value comprising a paper or polymer region, in particular, bank notes, passports, identification cards or any other document of sufficient value to make it liable to be copied or counterfeited.
The increasing popularity of colour photocopiers and other imaging systems and the improving technical quality of colour photocopies has lead to an increase in the counterfeiting of bank notes, passports and identification cards, etc. There is, therefore, a need to add additional security features to the identification or document of value or to enhance the perceptions and resistance to simulation of existing features. Steps have already been taken to introduce optically variable features into such documentation which cannot be reproduced by a photocopier. There is thus a demand to introduce features which are discernable by the naked eye but "invisible" to, or viewed differently, by a photocopier. Since a photocopying process typically involves reflecting high energy light off an original document containing the image to be copied, one solution would be to incorporate one or more features into the document which have a different perception in reflected and transmitted light, an example being watermarks and enhancements thereof.
It is known that certain liquid crystal materials exhibit a difference in colour when viewed in transmission and reflection as well as an angularly dependent coloured reflection.
Liquid crystal materials have been incorporated into documents, identification cards and other security elements with a view to creating distinctive optical characteristics. EP-A-0435029 is concerned with a data carrier, such as an identification card, which comprises a liquid crystal polymer layer or film in the data carrier. The liquid crystal polymer is in solid form at room temperature and is typically within a laminate structure. The intention is that the liquid crystal layer, which is applied to a black background, will demonstrate a high degree of colour purity in the reflected spectrum for all viewing angles. Automatic testing for verification of authenticity is described using the wavelength and polarisation properties of the reflected light in a single combined measurement. This has the disadvantage of being optically complex using a single absolute reflective measurement requiring a uniform liquid crystal area on a black background. AU-488,652 is also concerned with preventing counterfeit copies by introducing a distinctive optically-variable feature into a security element. This patent discloses the use of a liquid crystal "ink" laminated between two layers of plastic sheet. The liquid crystal is coated on a black background so that only the reflected wavelengths of light are seen as a colour. The patent is primarily concerned with the cholesteric class of liquid crystals which have the characteristic of changing colour with variation in temperature.
Cholesteric liquid crystals have certain unique properties in the chiral nematic phase. It is the chiral nematic phase which produces an angularly dependent coloured reflection and a difference in colour when viewed in either transmission or reflection. Cholesteric liquid crystals form a helical structure which reflects circularly polarised light over a narrow band of wavelengths. The wavelength is a function of the pitch of the helical structure which is formed by alignment within the liquid crystal material. An example of such a structure is depicted in FIG. 1 with the cholesteric helical axis in the direction of the arrow X. The reflection wavelength can be tuned by appropriate choice of chemical composition of the liquid crystal. The materials can be chosen to be temperature sensitive or insensitive. Both handednesses of circularly polarised light can be reflected by choice of the correct materials and thus high reflectivities at specific wavelengths can be achieved with double layers of liquid crystals. The wavelength of reflected light is also dependent on the angle of incidenc

REFERENCES:
patent: 4472627 (1984-09-01), Weinberger
patent: 4514085 (1985-04-01), Kaye
Patent Abstracts of Japan, vol. 015, No. 318 (M-1146) 14 Aug. 1991 + JP-A-31 18198.
Patent Abstracts of Japan,vol. 016, No. 396 (P-1407) 21 Aug. 1992 + JP-A-41 30412.

Affiliated with

Also associated with

Rating

High value documents does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with High value documents, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and High value documents will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-1001187