Marking PET recyclable containers

PET (Polyethylene Terephthalate) is a plastic material commonly used in the beverage industry, especially for plastic bottles and cups, but also in other industries such as textiles. Although it will be banned for single-use applications from 2021, today it is still a widely used material, and it will continue to be used for reusable products since it becomes more and more recyclable. Its main application is transparent plastic, which is achieved through rapid cooling in the manufacturing process. This transparent and recyclable plastic has a very special feature regarding its coding that must be taken into account when selecting the best marking techniques.

Up till now, the most popular way to code best before dates onto PET containers has been by CIJ (Continuous Inkjet Printers), but there are many downsides of using this technology.

Laser marking systems were considered to be a more expensive marking solution, however lasers have evolved where total cost of ownership of a laser solution is now considerably cheaper than CIJ options More and more manufacturers are now choosing to switch from old CIJ printers to lasers to mark legally required consumer information onto their PET products, but also to add value by marking consumer messages, competition codes and even advertising.

When coding transparent PET with a laser, the choice of wavelength to be used is vital for an optimum result. There are several different wavelength of laser available:

When we use the most common wavelength, 10.6 μm, or its close variant of 10.2 μm, the reaction of the laser on the PET results in engraving, which generates a transparent mark and weakens the material. However, when we use a 9.3 μm wavelength, the reaction between the material and the radiation is one of foaming, in which a white foam is generated that provides greater contrast and greater protection for the container. 

This difference in reaction is clearly advantageous both in maintaining the integrity of the package, avoiding any risk of carbonated drinks exploding from internal pressure, and in coding the package, where we have a much more visible brand to the customer. Whether the aim is to code an expiry date, or an advertising logo, as in the example above, coding with the SPA CP 30 laser makes it possible to add value, meet legal requirements and have a permanent mark with no waste, mess and in a simple and effective way. 

Laser marking of PET is a fast, cost effective method of part marking, whilst offering reliability, security (no ink to be rubbed off) and lower running costs, with reduced environmental issues from waste and harsh chemicals.