In 1990’s laser technology increased its volume in papermaking industry. Advantages of laser technology in these branches are flexibility, high speed, contact-free processing and possibilities of multifunctional applications. Anyhow, use of laser technology in papermaking has a minor role, mainly because of shortage of basic research results.
Previous laser cutting trials performed within a national project in Finland had shown that uncoated paper and board can be laser cut with high speeds and good cutting edge quality (bright kerf, no carbonisation). The materials used in this study were talc, calcium carbonate and clay coated commercial LWC (light weight coated), CWF (coated wood free) paper grades and SC (supercalandered) papers. Also uncoated LWC paper was included. The cutting experiments contained tests of effect of different laser parameters like power, focal point position and focal length on the cutting speed and the cut edge quality.
Tested papers all were suitable for laser cutting. Behaviour of cutting speed in relation to laser power was linear. Increase of mineral pigment coating increased laser power needed to cut mineral coated papers.
Some of these cutting tests of coated papers showed also nonlinear behaviour. This occurred when CWF papers were cut with laser beam and laser power values were above 1100 W and a short focal length (63.5 mm) were used. Also cutting kerf widths were broadened. This behaviour was related to blue flame which occurs during cutting. This blue flame was concluded to consist of ionized CaCO3 pigment particles, which formed a cloud that blocked the laser beam entrance to workpiece. However, tested CWF-papers can be cut successfully with focal lengths 127 mm and 190.5 mm. With 127 mm focal length optics CWF papers could be even laser cut faster than with 63.5 mm focal length optics.