Polyethylene terephthalate (PET) is a clean synthetic plastic that is insoluble in most common liquids and does not dissolve plastic residues into the liquid. For this reason, polyester resin is widely used in the manufacture of beverage bottles, such as soft drinks and bottled water. The most common marking applications in the beverage industry are date codes and batch numbers. The large number of bottles requires extremely fast marking speeds to ensure throughput, yet the markings must also be clear and readable at a glance. The standard 10.6um wavelength CO laser produces a translucent effect with clear melt boundaries. This logo is easy to read when close by, but becomes less visible at a distance. On the other hand, using a 9.3um wavelength, we found that the PET material absorbed this wavelength much better, producing a high contrast logo with good visibility at all distances.
The 9.3 um (upper) wavelength laser produces a more visible logo than the 10.6 um (lower) when viewed with the naked eye. When we compare the two logos together, the difference becomes obvious: the 9.3 um wavelength logo appears to "boil" the surface, which seems to expand the entire logo and give it a white frosted effect, whereas the 10.6 um one just melts the surface, revealing a slimmer, semi-transparent effect. Depending on the application, faster marking speeds can be used at 9.3 um, as the logo does not fade as quickly at this speed. Materials such as Kapton and Polimide have a high absorption of light at 9.3 um and materials such as polypropylene, polyethylene and polystyrene have the same absorption at both wavelengths, so that the marking of these materials is not lost when marking in the same production line. The picture clearly shows the surface boundaries of the melt at different wavelengths, the 9.3 um marking has a frosted effect while the 10.6 um has a translucent effect.
