Article:

 Laser cutting of paper (Challenges´06)

Author:

 Malmberg, H.; Immonen, M.; Kujanpää, V.

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ABSTRACT In 1990´s laser technology increased it volume in papermaking industry. Lasers in paper industry are mainly used for perforating and scoring applications. Anyhow, use of laser technology in paper- and board making is small-case, mainly because of shortage of basic research. Especially, use of laser edge trimmers is minimal. Water jet cutting is widely used for this purpose. Disadvantage of water jet cutting is blocking of jet nozzle, swelling of cut edge etc. Laser cutting could be an alternative choice for water jet cutting in edge trimming process. Advantages of laser technology are flexibility, high speed and contact-free processing. This study introduces basic characteristics of laser cutting of paper. Also economical aspect of laser edge trimming is discussed. All laser cutting trials were performed within national project in Finland. A 2.7 kW CO2-laser equipment Trumpf TLF2700 HQ with high quality beam was used for the experiments. Also focal lengths of 63.5 mm, 127 mm and 190.5 mm were used. The cutting experiments contained the cutting tests of how different cutting parameters, like laser power and focal position, affected the cutting speed and cut edge quality. Paper could be laser cut with distinguished quality. Cut kerf was totally cut through (no fibre bonding could be seen) and no burning or carbonisation occured. It was noticed that cutting speed was linearly dependent on laser power. It was found that with coated materials, unlike with uncoated materials, in certain parameter points linear behaviour turned to non-linear behaviour. This was due to pigment type and amount of coating and it could be avoided by using longer focal length. In addition, it was also found that fastest cutting speeds and narrowest kerfs were obtained with optimal focal positions.