Security devices based on liquid crystals doped with a colour dye

• Autorzy: Carrasco-Vela C. , Quintana X. , Otón E. , Geday M. A. , Otón J. M.
• Języki publikacji: EN

Abstrakty

EN

Liquid crystal properties make them useful for the development of security devices in applications of authentication and detection of fakes. Induced orientation of liquid crystal molecules and birefringence are the two main properties used in security devices. Employing liquid crystal and dichroic colorants, we have developed devices that show, with the aid of a polarizer, multiple images on each side of the device. Rubbed polyimide is used as alignment layer on each substrate of the LC cell. By rubbing the polyimide in different directions in each substrate it is possible to create any kind of symbols, drawings or motifs with a greyscale; the more complex the created device is, the more difficult is to fake it. To identify the motifs it is necessary to use polarized light. Depending on whether the polarizer is located in front of the LC cell or behind it, different motifs from one or the other substrate are shown. The effect arises from the dopant colour dye added to the liquid crystal, the induced orientation and the twist structure. In practice, a grazing reflection on a dielectric surface is polarized enough to see the effect. Any LC flat panel display can obviously be used as backlight as well.

Słowa kluczowe

EN

liquid crystal; security device; dichroic dye; absorption; polarized light; latent image

• Wydawca: Stowarzyszenie Elektryków Polskich ; Polska Akademia Nauk ; Wojskowa Akademia Techniczna im. Jarosława Dąbrowskiego
• Czasopismo: Opto-Electronics Review
• Rocznik: 2011
• Tom: Vol. 19, No. 4
• Strony: 495--500
• Opis fizyczny: Bibliogr. 11 poz.

Twórcy

autor

Carrasco-Vela C.

autor

Quintana X.

autor

Otón E.

autor

Geday M. A.

autor

Otón J. M.

• ETSI Telecomunicación, Universidad Politécnica de Madrid, Ciudad Universitaria s/n, 28-040 Madrid, Spain,

Bibliografia

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• [7] R. Yamaguchi, R. Mizutori, T. Kawamura, and S. Sato, “Polarized latent image forming in liquid crystal devices using polymer surface photo-modification technique”, Proc. SPIE 5618, 166-173 (2004).
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• [10] R. Yamaguchi and S. Sato, “Double-faced optical writing in guest-host mode liquid crystal cell using crosslinkable polymer alignment film”, J. Photopolym. Sci. Technol. 21, 203-206 (2008).
• [11] X. Quintana, J. M. Otón, M. A. Geday, and C. Carrasco-Vela, “Procedimiento y dispositivo de seguridad documental porgeneración de imágenes múltiples”, Patent No: P200931088 (2009). (in Spanish).