Preparation of specialized paper.

APPLICATION: Made with transition metals or cellulose derivatives as additives along with fluorescent dye, security papers show identifiable fluorescent spots under ultraviolet light.

Specialty papers have long served to prevent or discourage counterfeiting and the forgery of banknotes and other security documents. The successful use of many security papers, foils, and films depends on the technology of chemical fastening systems.

In this work, the researchers produced paper for special applications using transition metals, cellulose derivatives, and fillers in the presence of fluorescent dye. Sheets from bleached wood pulp were prepared after fluorescein sodium was added, together with solutions of transition metals as well as methyl cellulose, cellulose sulfate, starch, and kaolin. The papers produced were identified with a UV light or by alkaline or acidic solutions.

The appearance of the papers changed under the UV light when the fluorescein sodium was used at pH 4.0. For the transition metals, complex cations formed as the transition metal ions become chemically bonded to the dye as a part of the paper manufacturing process, and slightly yellow fluorescent spots showed as a result of the ground state configuration of the transition metals.

When methyl cellulose, cellulose sulfate, kaolin, and starch were added as filler, a fluorescent yellow-green color was observed. Apparently, this color arises from the disruption of the fiber network resulting from the filler particles being included with the fluorescent dye. The fluorescent color that appears under the UV light is affected by the negative charge on the sulfate group for cellulose sulfate or, for methyl cellulose, by the lone pair of electrons on the methoxyl group. The performance of the cellulose derivatives depends on the nature of the substituted groups--electron-donating groups in methyl cellulose and electron-withdrawing groups in cellulose sulfate. View this paper online at http://www.tappi.org/index.asp?pid=29098

Waleed K. El-Zawawy, Maha M. Ibrahim, and Magda G. El-Meligy are with the Cellulose and Paper Dept., National Research Center, El-Tahrir St., Dokki, Cairo, Egypt. Email Ibrahim at [e-mail].