Objective
1. Laser-induced colouring on a dark background
By selective bleaching of colourants, and by foaming of the polymer, both multicolouring and white on a dark background were obtained. It also became clear that high-intensity irradiation and short pulse lengths are favourable for high bleaching efficiencies. This can be achieved using either the laser energy or the wavelength as a parameter. Note that a laser with tunable wavelength gives the broadest range of possibilities. One always has to optimise the mixture of additives to the desired background colour and to demand range of colours originating from the laser action.
2. Laser-induced colouring on a light background
Two routes were investigated:
First, thermally induced mobility of colourless chemicals which can get several colours after recombination were synthesised. The feasibility of this system was proven, and resulted in a patent application. A drawback is that these chemicals do not survive the temperature of the plastic moulding-process. After further development, such a system can only be used for lacquers.
Second, photo-induced (UV) colour-forming chemicals were synthesised. Their feasibility was proven both in lacquers (PMMA) and plastics (ABS) for a few colours. The colours were induced using UV Excimer lasers. A problem with these UV-sensitive additives is their UV light-stability. This particular needs more research.
3. Laser System
A prototype laser system for laser-induced colouring was developed. The system is a diode-pumping YAG laser with a second harmonic generation crystal, so the wavelength is green visible light. The laser pulses are relatively short, and have rather high energy, yielding, in principle, high quality decorations and a short processing time. The resonator design of the laser system has to be optimised to achieve a better pulse-to-pulse stability, which directly influences the quality of the decoration.
4. Conclusions
The plastics and lacquers showing the effects described can be developed on customer demand, because the mechanism is understood, and the behaviour of a wide range of pigments and additives is known.
Fields of science
Topic(s)
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5600 MD EINDHOVEN
Netherlands