NCJ Number
186086
Journal
International Journal of Forensic Document Examiners Volume: 5 Dated: December/January 1999 Pages: 249-254
Date Published
1999
Length
6 pages
Annotation
This paper describes how traditional ceramic fabrication techniques are being used to provide some unusual products that require abnormal properties; knowledge of the properties of both the solid targets and the transferred patches has been attained by using a number of microscopic methods.
Abstract
The Bank of Canada operates two high-capacity vacuum roll coaters capable of depositing up to four different coatings simultaneously, two by sputtering and two by electron beam evaporation, at web speed between 2 and 20 microns per minute. The product is an optically variable interference filter material on release-coated plastic film. Patches of this material are then transferred onto Canadian higher denomination banknotes as an anti-counterfeiting measure. The original interference filter material production required the evaporation of silica (SiO2) and zirconia (ZrO2) from solid targets. The former material sublimes under vacuum and is a good thermal insulator. On the other hand, there was no solid zirconia available which could be used, so custom-designed blocks had to be developed. The crux of the problem was how to contain the severe thermal stress to which the heated block would be subjected. The approach followed was to produce porous, lightly-sintered blocks with minimal strength but able to arrest the propagation of cracks as quickly as possible. Fabrication was by standard methods. 17 figures and 5 references