Food and pet food are accurate indicators of changing lifestyles in the developed world. Convenience but also environmental aspects such as biodegradability and avoidance of excess packaging are high on the agenda.
Key challenges include intelligent protection during shipping and storage, management of ripening, and ease of preparation and handling. In a highly competitive market, all these features must be combined with cost-effectiveness and attractive brand presentation.
Laser technology offers novel solutions to some of these issues. Tiny perforations, invisible to the naked eye, enhance the properties of stand-up pouches, plastic bags, and lidded trays for pet food, convenience food, fruit and vegetables, and medical products.
Laser perforations can enhance shelf life, make packaging easier to open, and improve ease of preparation for foods. Mondi Consumer Flexibles has all the necessary know-how and specialised equipment for such applications.
LASER PERFORATION: HOW IT’S DONE
A perforation pattern is generated either via special polygon mirrors (for high-volume production) or via fixed optics with synchronous pulse triggering. Up to 16 lines can be placed in parallel on a single web. In a given line, up to 50 holes/cm can be made, to allow ventilation and ease of tearing.
Typical hole sizes in films without an aluminium layer range from 60 to 400 μm. Aluminium-coated films require greater laser power and thermal input. In polymer film perforating, laser technology competes with needle technologies and flame perforating. Its advantage over those technologies is that the holes are smaller and also crack-proof thanks to the micro-melted edge.
Almost all packaging films are multi-layer structures, i.e. several films on top of each other, each having a thickness of several micrometers. Each layer has a different function: PET is used as carrier web, PE for sealing and tear-proof qualities, PP for vapour impermeability, aluminium for general light hermetic sealing, and paper for stiffness.
Most of the polymer materials used in the packaging industry, e.g. PET, PS or OPA, absorb a laser beam very efficiently at the typical wavelength of 10.6 micrometres. The result is local heating, resulting in complete ablation of the polymer layer in the small scribing area.
Aluminium layers act as perfect mirrors for all wavelengths of a CO2 laser at low laser power, i.e. they neither absorb nor transmit the beam. The desired scribing structures can be achieved on most packaging materials provided the wavelength is right and the scribing is applied from the correct side.
Under the microscope, materials like PE and PET are inhomogeneous: depending on the manufacturing process, films of the same material and thickness may have different qualities. Just as with multi-coloured imprints, a reliable high-quality laser process must take this into account, and it is for precisely this level of quality that Mondi Consumer Flexibles has built a reputation.