Browse Prior Art Database

Anti-Copy Paper

IP.com Disclosure Number: IPCOM000047179D
Original Publication Date: 1983-Oct-01
Included in the Prior Art Database: 2005-Feb-07
Document File: 2 page(s) / 28K

Publishing Venue

IBM

Related People

Bealle, FJ: AUTHOR [+2]

Abstract

By providing copy paper with the characteristics of a mirror, i.e., with the capability of reflecting the illuminating light emitted by a xerographic photocopier, data, etc., carried by that paper cannot be copied, but can be read easily under oblique illumination. The transparent plastic material, illustrated schematically in the figure, enjoys the desired characteristics by virtue of replicated grooves formed in the undersurface, such grooves having the reflector geometry specified in the drawing. To maintain readability, there should be at least 200 grooves per inch such that the dimension "1" in the figure should approximate 0.005" or less. For convenience, two layers of the material may be used to sandwich a white or black core layer.

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Anti-Copy Paper

By providing copy paper with the characteristics of a mirror, i.e., with the capability of reflecting the illuminating light emitted by a xerographic photocopier, data, etc., carried by that paper cannot be copied, but can be read easily under oblique illumination. The transparent plastic material, illustrated schematically in the figure, enjoys the desired characteristics by virtue of replicated grooves formed in the undersurface, such grooves having the reflector geometry specified in the drawing. To maintain readability, there should be at least 200 grooves per inch such that the dimension "1" in the figure should approximate 0.005" or less. For convenience, two layers of the material may be used to sandwich a white or black core layer. This provides writing surfaces on both sides of the composite sheet and greater sheet strength. The total thickness of the three elements of the sheet approximates the thickness of typical bond sheets. Returning to the geometry illustrated in the figure, the index of refraction of the plastic sheet is N, where N is chosen so that the critical angle r is less than 45 degrees. This is achieved when sin 45 degrees is greater than NAIR/N, where NAIR is approximately equal to 1.0 (i.e., N is greater than the square root of 2). If r is less than 45 degrees, vertical illumination as produced in a xerographic photocopier is totally reflected, as shown in the figure. However, when the document is illuminated at non-verti...