By: Heidi Piili
Laser cutting of paper materials
1 Introduction
It is known that CO2 laser beam is suitable for cutting of paper materials. Laser technology has been applied to paper cutting since 1970’s. Mainly the application of laser technology are in paper slitting applications, even though paper materials can be laser cut with high cutting speeds and with good quality (see figure 1). [1, 2, 3]
a) b)
Figure 1. Example of laser cut paper material products: (a) laser cut DVD package and (b) laser cut double-CD-package. [5]
The combination of laser an paper has been studied over 30 years, but still implementation of laser technology in the paper industry has remained limited. This situation changed in 1990´s: laser equipments were cheaper, improved lasers were developed and the laser technology became more reliable. [3, 4, 5]
2 Basic principle
When a laser beam with high energy intensity hits paper, material is heated and it decomposes chemically. Degradation products are evaporated or removed from cut kerf by cutting gas jet. A cut kerf is formed, when cutting head is removed in relation to work piece. [6, 7, 8] Figure 2 shows the basic mechanism of laser cutting of paper materials.
Figure 2. Basic mechanism of laser cutting of paper materials. [9]
3 Cutting mechanism
Cutting mechanism in laser cutting of paper materials is vaporisation cutting. This mechanism means a cutting method where laser beam heats up the material top surface to evaporation temperature or to temperature where chemical degradation happens. [8, 10] Usually inert cutting gas (like nitrogen) is used to prevent combustion of vaporised material. [6, 8]
4 Cutting processes in paper making
In paper/board making process there are several needs for cutting, like
– edge trimming of web ,
– cross-machine direction cutting of web,
– slitting of web to customer width,
– sheeting of web,
– cutting of package blanks etc.
Paper/board making and converting industry needs high-capacity machines. Conventionally cutting of fibre material is done by mechanical blades or die-cutting. In 80´s water jet became as a competitive cutting method. [5]
In laser cutting studies of paper materials carried out in Lappeenranta Laser Processing Centre (LLPC) it has been found that a magazine paper can be cut with laser beam at speed of 4400 m/min. This speed totally fulfils the requirements of papermaking process. [11]
Laser cutting technology can be combined with digital printers. Conventionally paper materials have been printed with rotogravure or offset method. When these printing methods are used, batch sizes usually are large and each change in print image needs a special modification to print tool. Advantage of digital printing is that even very small batch sizes can be printed easily and change in print image is only question about programming. Laser cutting could provide also as on-line cutter further flexibility to whole printing process. A change in cutting pattern is only question of programming and no new cutting tool is needed. [12]
Generally it can be said that laser cutting in cutting of paper materials is recommended in following circumstances [5]:
– wherever production size is small or constantly below 1000 pieces.
– always with digital printing.
– when high accuracy with complex geometries is needed.
– when flexible production and fast delivery is needed.
– when tailor-made products are needed.
5 Advantages and disadvantages of laser cutting
When paper/board is cut with conventional mechanical blades there are several problems, which make the cutting quality bad or even destroy it. A big problem in mechanical cutting of fibre material is dust which consists of piece of fibres and pigment particles ripped out of paper by cutting blades. This dust causes for example runnability problems in printing houses. Also in many cases coarse cut edge which contains out-sticking fibre endings causes many problems. For example in liquid packaging industry such a problem is not wanted because liquid absorption properties of cut edge are very important (see figure 3). [6, 8, 13]
a) b)
Figure 3. Scanning electron microscopy (SEM) images of (a) laser cut edge and (b) mechanically cut edge. [13]
Technically, laser cutting of paper/board is possible and the cut kerf quality is very good. Also the amount of dust released during laser cutting is much lower than with mechanical or water jet cutting. The most important advantage of laser technology is its flexibility where batch sizes of one piece to ten thousand pieces can be accomplished. [13]
6 References:
[1] Anon., Cutting it fine, Paper, vol. 217, 1992 no. 5, p. 38.
[2] Anon., Laser – soveltuuko puuntyöstöön?, Paperi ja Puu, vol. 68, 1986, no. 10, pp. 694-696.
[3] Malmberg, H., Characterisation of laser cutting of consumer boards, Master of Science Thesis, Lappeenranta University of Technology, 2003, 181 p.
[4] Schable, R., Changing slitting methods, Paper, film & foil converter, vol. 67, 1993, 9, pp. 82-83.
[5] Malmberg, H., Immonen, M.; Kujanpää, V., Laser cutting of paper, Proceedings of Challenges´06 Symposium, 8.-10.11.2006, Bratislava, Slovakia, 32 p.
[6] Federle, H., Keller, S., Papierschneiden mit Laser (Teil 1), Papier+Kunststoff+Verarbeiter, vol. 27, 1992, no. 7, pp. 32-39.
[7] Rickli, M., Alternative Schneidtechniken für Papier, Diploma Papier, Lausanne, 1982.
[8] Malmberg, H., Kujanpää V., Paperimateriaalien laserleikkaus on tulevaisuutta, Pakkaus, No. 11/2006, Finland, 3 p.
[9] Piili, H., Characterisation of interaction phenomena of laser beam and paper materials in cutting, Licentiate Thesis, Lappeenranta University of Technology, 2009, 258 p.
[10] Malmberg, H., Kujanpää V., Paperimateriaalien laserleikkaus, Vol. 88, Paperi ja Puu, No. 8/2006, Finland, pp. 452-454.
[11] Hovikorpi, J., Malmberg, H., Laakso, P., Kujanpää, V., Miikki, N., Kurittu, M., Laser cutting of paper, Proceedings of the 23rd International Congress on Applications of Lasers and Electro-Optics ICALEO 2004, October 4-7, 2004, San Francisco, USA, 11 p.
[12] Boyle, E., Lasers are on the cutting edge, digitally speaking, Paper, film & foil converter, 1999, no. 4, pp. 14-15.
[13] Malmberg, H., Leino, K., Kujanpää, V., Laser Cutting of Paper and Board (ILACPaper), Research Report 68, Department of Mechanical Engineering, Lappeenranta University of Technology, Finland, 2006, 344 p.
Author:
Mrs. Heidi Piili (previously Malmberg), M.Sc., Lic.Tech., has more than 7 years experience of laser processing of different materials at Laser Processing Research Group (LUT Laser) of Lappeenranta University of Technology (LUT). Her specialty field is laser processing of non-metallic materials. At the moment she is working as project manager in a project of laser processing of microscale process devices for chemical industry. She is a Doctoral student and will graduate within next couple of years.
The above brief overview was extracted from its original abstract and paper presented at The International Congress on Applications of Lasers & Electro-Optics (ICALEO) in Orlando, FL. To order a copy of the complete proceedings from this conference click here