The selection of an IR Absorber for use in inks depends on several Factors:
- Wavelength of the detector – If the detector is set to read at say 990 nm, then you need a substance with good absorbance at 990nm.
- Solubility of the Absorber in the ink vehicle. The aminium IR absorbing dyes have relatively good solubility in most ink vehicles.
- Color of the credit card or package. Most of the aminium dyes are either green or brown in color. If the credit card or package has even a faintly green or brown area, the IR ink can be hidden underneath it.
The concentration of IR Absorber in the ink, depends on several factors:
- The thickness of the ink film. Infrared absorption is inversely related to the path length of the light beam. Therefore, the thinner the ink film, the higher the concentration of absorber is needed.
- The level of light transmission required. If it is required that 90% of the light at 990 nm must be blocked, this will require much less absorber than if 99% of the light at 990 nm must be blocked.
- The solubility of the absorber in the ink vehicle. If the absorber has limited solubility in the ink vehicle, and the ink film is very thin, and the light transmission requirement is very high, it will be a challenge to obtain a successful formulation.
The successful development of a security application requires a systems approach and cooperation between the ink formulator, the manufacturer of the detector, and the designer of the credit card (or other application).