Security document with reversibly photochromic printing inks
First Claim
1. A security document comprising a substrate having an ink pattern on a surface thereof, said ink comprising binder and particles of at least one photodyestuff consisting of a solid solution or dispersion of photochromic compound and polymeric protecting composition, wherein said polymeric protecting composition is a light-transparent thermoplastic having a melting point between 50°
- and 150°
C., a barrier for any ink component which is capable of irreversibly interfering with the photochromic reaction sites on said photochromic compound, inert to the photochromic compound, and which is further a barrier for oxygen.
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Accused Products
Abstract
Photochromic printing inks are disclosed which are in particular used for the printing of security documents. Prints are normally nearly colorless and become colored when energy irradiated, such as by ultraviolet light. This photocoloration is reversible. The printing inks contain photochromic compounds which are protected against other ink components. Methods are described to prepare the inks, to print security documents, and to detect counterfeiting.
78 Citations
26 Claims
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1. A security document comprising a substrate having an ink pattern on a surface thereof, said ink comprising binder and particles of at least one photodyestuff consisting of a solid solution or dispersion of photochromic compound and polymeric protecting composition, wherein said polymeric protecting composition is a light-transparent thermoplastic having a melting point between 50°
- and 150°
C., a barrier for any ink component which is capable of irreversibly interfering with the photochromic reaction sites on said photochromic compound, inert to the photochromic compound, and which is further a barrier for oxygen. - View Dependent Claims (2, 3, 4, 5, 6, 7)
- and 150°
- 8. A security document comprising a substrate having an ink pattern on a surface thereof, said ink comprising a solid solution or dispersion of photochromic compound and a binder, wherein said binder has an acid number below 10 and is free from carboxyl groups and their salts and from other functional groups which are capable of interfering irreversibly with the photochromic compound, said binder being further capable of forming a light transparent thermoplastic film after chemical hardening which contains said photochromic compound as solid solution or dispersion and further acts as barrier for oxygen and for ink components which are capable of interfering with the photochromic reaction sites of said photochromic compound.
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15. A method for the printing of security documents, comprising the following steps:
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A) selecting a photochromic composition comprising (1) a thermoplastic binder, (2) a liquid phase, (3) and at least one photochromic compound, said binder being free from carboxyl groups and their salts and from other functional groups which are capable of interfering irreversibly with the photochromic compound, said binder being further capable of forming a light transparent film after chemical hardening which contains said photochromic compound as solid solution or dispersion and further acts as barrier for oxygen and for ink components which are capable of interfering with the photochromic reaction sites of said photochromic compound, (B) selecting a non-photochromic printing ink, (C) printing with these inks simultaneously or in the course of the same printing procedure a flat substrate accepting the inks of steps (A) and (B) according to the predetermined patterns, (D) drying the print obtained in step (C), (E) collecting a printing security document showing photochromic lines or patterns and non-photochromic lines and patterns. - View Dependent Claims (16, 17, 18, 19, 20, 21, 23, 24, 25, 26)
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22. The method of claim 41 comprising mixing the printing inks of step (A) and (B) and collecting in step (E) a printed security document showing photochromic lines or patterns where the printed color reversibly changes by photochromism to another color.
Specification