Document security method and system

A system for securing a substrate such as paper against facsimile transmission and photocopying, comprising:

• a) a substrate having a background color on one surface thereof;
• b) a covering on at least one selected area of the one surface with Chemical A.sub.1 comprising one of a first pair of a colorless color developer and a colorless color former dye, wherein the color developer and color former dye react when mixed to produce a first spectral response which is different from the background color and consists of one of the following:
• 1) a reflection spectral response A with a minimum of about 5% at lower visible wavelengths, rising to about 10% at a wavelength of about 580 nanometers, and then rising to a maximum of about 20% at about 700 nanometers;
• 2) a reflection spectral response B with a minimum of about 4% at lower visible wavelengths, rising to about 6% at a wavelength of about 580 nanometers, and then rising to a maximum of about 12% at about 700 nanometers;
• 3) a reflection spectral response C with a maximum of about 20% at lower visible wavelengths, falling to about 10% at a wavelength of about 480 nanometers, and falling to a minimum of about 8% at higher wavelengths;
• or 4) a reflection spectral response D with a maximum of about 12% at lower visible wavelengths, falling to about 6% at about 480 nanometers, and falling to a minimum of about 5% at higher wavelengths;
• and
• c) means for printing information in the at least one selected area having a substantially black color which is different from the color of said first spectral response over the wavelengths for the human eye but the same color over the wavelengths of a photocopier and facsimile machine;
• d) means for later applying Chemical B.sub.1 comprising the other of the first pair of the colorless color developer and the colorless color former dye to at least a portion of the at least one selected area to change the background color to said first spectral response when required, whereby information printed in the at least one portion will be readable by a human but be indistinguishable from the background by a photocopier and facsimile machine.

A security substrate, comprising:

• a) one surface having a background color;
• and
• b) a covering on at least one selected area of the surface comprising one of a fist pair of a colorless color developer and a colorless color former dye, wherein the color developer and color former dye react when mixed to produce a first spectral response which is different from the background color and consists of one of the following:
• 1) a reflection spectral response A with a minimum of about 5% at lower visible wavelengths, rising to about 10% at a wavelength of about 580 nanometers, and then rising to a maximum of about 20% at about 700 nanometers;
• or 2) a reflection spectral response C with a maximum of about 20% at lower visible wavelengths, falling to about 10% at a wavelength of about 480 nanometers, and falling to a minimum of about 8% at higher wavelengths, and comprising one of a second pair of a colorless color developer and a colorless color former dye, wherein the second pair react when mixed to produce a second spectral response which is different from the background color and consists of one of the following:
• 1) a reflection spectral response B with a minimum of about 4% at lower visible wavelengths, rising to about 6% at a wavelength of about 580 nanometers, and then rising to a maximum of about 12% at about 700 nanometers;
• or 2) a reflection spectral response D with a maximum of about 12% at lower visible wavelengths, falling to about 6% at about 480 nanometers, and falling to a minimum of about 5% at higher wavelengths and wherein the covering effects a spatially modulated reflection spectral characteristic in said at least one selected area, whereby the printing of information in said at least one selected area having a substantially black color which is different from the color of the spectral responses A, B, C and D will be readable by a human but is indistinguishable by photocopiers and facsimile machines over the wavelengths thereof.