A Tamper-evident Ink


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Toshiki Hayashi


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Ink on checks used for payment contains a reactive substance that thwarts chemical tampering. This is known as isochromatic pair ink, and contains two or more ink types that appear isochromatic despite their different dye/pigment compositions thanks to careful selection of colorants in precise amounts. They appear identical until tampered, at which point they change color due to dye dissolving. In the work reported here, an isochromatic polymerizable dye and a non-polymerizable dye were used to address issues associated with isochromatic pair ink, such as the high level of expertise required for its manufacture and deterioration of isochromatic property due to dye decomposition. The two dyes were synthesized. The print matter produced with a pair ink made using them showed good isochromatic and tamper-evident properties. The polymerizable dye dissolved less than nonpolymerizble dye did thanks to stability stemming from copolymerization with the UV varnish using its polymerizable unit, while non-polymerizble dye did not have such stability.

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