Secure documents - methods and applications
The invention teaches a paper substrate having a laser treated area which has benefits for anti copy, copy deterrence and/or copy detection applications. The laser treatment may be in the form of a dense array of a plurality of microperforations which may or may not be visible to the naked eye or in form of fine graphics on the paper surface incorporated via partial ablations. The laser treated area serves as an authenticated field. In one aspect, the authentication field when copied on reprographic equipment reproduces as a field of dark separated dots. The authentication field optionally can take the form of various shapes including alphanumeric characters or other patterns. In an alternate aspect the laser treated area is an area of laser-formed partial ablations creating a synthetic watermark.
1 . A paper substrate having an authentication field area comprising an array of a plurality of laser-formed microperforations separated by a land area, the array of microperforations having diameter in the range 80-120 microns, the land area separating adjacent microperforations being at least 600 microns.
2 . The paper substrate according to claim 1 wherein the plurality of laser microperforations are not readily ascertainable by the unaided eye when viewed at an angle approximately perpendicular to the surface of the substrate using reflected light,
said microperforations being visible to the unaided eye when viewed at an angle approximately perpendicular to the surface of the substrate but using light transmitted through the substrate,
whereby when the surface is illuminated by a light source located at an angle relative to the surface of the substrate and viewed from a position at substantially the same angle relative to the surface as the light source, the microperforations appear not readily ascertainable and not contrasting with the surface.
3 . The paper substrate according to claim 1 wherein the plurality of laser microperforations are visible to the unaided eye as individual dots separated by land area.
4 . The paper substrate according to claim 1 wherein the paper substrate when copied on reprographic equipment reproduces as a field of separated dots.
5 . The paper substrate according to claim 1 including in addition a dark colored backing sheet laminated to a surface of the paper substrate, the dark colored backing sheet augmenting the contrast of the microperforations in the substrate.
6 . The paper substrate according to claim 2 wherein at least the area of the paper substrate that is microperforated includes in addition a latex material applied to the substrate to strengthen the paper.
7 . The paper substrate according to claim 2 wherein the authentication field is a square or rectangular area.
8 . The paper substrate according to claim 2 wherein the authentication field is in the shape of alphanumeric characters.
9 . The paper substrate according to claim 8 wherein the authentication field is a geometric or artistic shape.
10 . A paper substrate having a laser ablated field area comprising an array of a plurality of laser-formed partial ablations that do not completely pierce the paper, the array having a density rate of ablations of at least 600 ablations per square centimeter, the partial ablations are not readily ascertainable by the unaided eye when viewed at an angle approximately perpendicular to a surface of the substrate using reflected light, and not readily ascertainable when viewed at an angle approximately perpendicular to the surface of the substrate but using light transmitted through the substrate, whereby when the surface is illuminated by a light source located at an angle relative to the surface of the substrate and viewed from a position at substantially the same angle relative to the surface as the light source the laser ablations appear lighter than the substrate outside the laser ablated field area.
11 . A method of verifying a document comprising providing a paper substrate having an array of a plurality of laser formed microperforations separated by a land area, the array of microperforations having a diameter in the range of 80 to 120 microns, the land area separating adjacent microperforations being at least 600 microns, wherein the paper substrate when copied on reprographic equipment reproduces as a field of visible dots.
12 . The method according to claim 11 wherein the paper substrate includes in addition a dark colored backing sheet laminated to the surface of the paper substrate, wherein the dark colored backing sheet augments the contrast of the microperforations in the substrate so as to make the microperforations visible.
13 . A method for creating a synthetic watermark in a paper substrate which comprises providing a paper substrate, applying a laser to the substrate to form partial ablations in the substrate in an area array having a density of at least 600 ablations per square centimeter.
14 . The method of claim 13 further comprising verifying the synthetic watermark by illuminating the surface with a light source at an angle relative to the surface of the substrate and viewing the surface at substantially the same angle relative to the surface as the light source, the laser ablations appearing lighter than the substrate outside of the ablated area.