Making Security Paper

from Warner, Richard D. and Richard M. Adams II, Introduction to Security Printing. (Pittsburge: PIA/GATF Press, 2005).

Security printing papers must be a suitable substrate for the many security devices that will be embedded in or printed on them.

Rag pulp is used to produce currency paper. It’s made from cotton fiber, and produces the highest level of quality (higher-quality than wood pulp, for instance). “Cotton fibers are long and contribute to the durability of the paper.”

The fibers are processed (mechanically or chemically), and then mixed with water so they can be beaten or refined.

Refining softens and frays the fibers, giving them more surface area and causing them to hydrate or take up water, which improves adhesion and paper strength.”

During refining, paper characteristics are manipulated with various additives.

Sizing, usually rosin or synthetic polymer, makes paper more resistant to water, which is important for paper for offset lithographic printing. Fillers, such as calcium carbonate or titanium dioxide, improve paper smoothness, opacity, and brightness. The mixture of fibers, water, and additives is known as furnish.”

After refining, the paper has to be formed.

 “Paper for security printing is manufactured using a unique combination of wide-angle and narrow-angle refiners. Refining reduces fiber length to a predetermined level, resulting in a strong and durable paper bond and clear watermark clarity. Security paper is manufactured using a cylinder mold paper machine. In a cylinder mold, a wire cloth or mold sleeve is held around a cylinder that rotates in a vat of paper fibers and water (furnish). A vacuum inside the cylinder draws furnish through the wire mold, leaving a layer of fibers on the outside. As the cylinder rotates, the newly formed paper layer is squeezed by a couch roll to remove surplus water. The paper layer is peeled away from the mold cover and then transferred into the press section where it is dried and further processed.”

Security paper has to be “UV-dull” – unlike most commercial papers, which are artificially brightened.

“Brightening agents absorb ultraviolet radiation and reradiate visible light in the blue region of the spectrum, making commercial paper look brighter and more neutral in color. UV-dull paper improves security by allowing the use of fluorescent inks as a security feature, the appearance of which would be altered by brightened paper, and by not fluorescing under UV light as would counterfeits produced on ordinary, brightened commercial paper.”

Security fibers and threads are security features incorporated during the manufacture of the paper (as opposed to printed onto the paper)

Threads are normally distributed randomly throughout the paper, although it is possible to apply them in bands. Fibers are made to a controlled thickness, cut to a specific length, made to a specific color, and distributed with a specified frequency throughout the paper. Security threads can be of visibly different color or nearly invisible under normal lighting but fluorescent when illuminated with UV. Fibers can be of a single color or banded with different colors. They can also be machine-readable or encodable. Virtually all security threads are made by applying various coatings to polyester film that is slit into ribbons between .5 and 1.5-mm wide and incorporated into the paper at the time of manufacture.

When putting together a security product it is important to ensure that each of the component parts work well together and are not mutually exclusive of each other. For example, the designer must ensure that the chemical sensitizing in the paper does not interfere with the adhesive system or vice versa, or that they do not interfere with the printing techniques. The product components must be totally compatible with each other.”

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