Laser perforation for computer paper

In today\u27s computer paper printing, cross and edge perforations are done only by mechanical perforators. The mechanical perforation process works fine since the width of the bridges and the length of the holes to be perforated remain large. Concerned with improvements in quality, printers have introduced microperforations. The holes and bridges of the perforation pattern are so small that after the user has torn off the sheet of computer paper along the perforation pattern, the edges of the document are very smooth and clean. Unfortunately, microperforations are reaching the limits of what can be achieved by the mechanical perforators. Because of the physical contact between the perforating tool and the paper, the perforation pattern is damaged. The tensile strength of the microperforation pattern decreases significantly and the paper often jams in the computer printers. Mechanical perforator dies wear and may even break.Therefore, holes are incompletely perforated or missing, so that the document is likely to be damaged when it is torn off along the perforation pattern by the user. Incomplete or missing perforations increases the tensile strength of the perforation pattern. Therefore, the printer can increase the quality of a perforation pattern by reducing its variability in tensile strength. This thesis studies the perforation of computer paper by laser beam. It is demonstrated through a microscopic study that laser perforations are free of all the defects which are inherent to the mechanical perforation process. It has been found that laser perforated holes remain open while mechanically perforated holes close back just after being perforated. The tests which have been carried out show that using a laser instead of a mechanical perforator to do microperforations reduces the variability in the tensile strength from 0.694 kilograms to 0.0751 kilograms. This improvement is significant. However, using a laser instead of a mechanical perforator to do large-size perforations reduces the variability in tensile strength only from 0.0421 kilograms to 0.0338 kilograms. This improvement is not significant. A mathematical model expressing the relationship between the tensile strength of a perforation pattern, the width of the bridges, and the number of bridges per inch has been established. The correlation found between the model and the experimental values is high (r = 0.98). This mathematical model is a simple method which allows the printer to adjust the tensile strength of a laser perforation pattern to the desired value. This model requires only simple calculations, and the knowledge of one basic characteristic - the tensile strength of the paper. As a conclusion, the laser beam is a very valuable tool which can achieve very high quality microperforations on computer paper. However, it seems not worth using a laser to do large-size perforations on computer paper since the decrease in tensile strength variability over the mechanical perforation process is not significant. The fact that laser perforated holes remain wide open could improve high speed folding and piling in the press deliveries by allowing the air trapped between the sheets of computer paper to escape through the perforated holes. This property has also already found an interesting application for cigarette filter paper