Laser marking of plastics

Laser marking of plastic, or plastic engraving, is a process during which components are labelled or marked with the aid of a laser. The polymer that the plastic parts are made of dictates the methods used and also the energy input needed to laser the plastic. The result of the laser marking depends, to a significant extent, on the type of plastic, additives such as colorants and the type of laser. Laser marking is a non-contact optical process in which the plastic has to absorb the laser beam. This behaviour is also used in the laser welding of plastics, during which one welding partner absorbs the laser beam and the other welding partner is transparent for the laser beam.

Many plastics and thermoplastics can be laser marked. Should a plastic’s properties mean that it cannot be laser marked, it can usually be modified with a suitable additive or masterbatch for plastic laser marking. Additives such as colour pigments can also influence the capacity for laser marking.

Advantages of laser marking

Laser marking is becoming more and more frequent in industrial applications as they are seen as particularly reliable and provide numerous advantages. Laser marking is extremely robust and also forgery-proof. Its application can also be of a high quality. Further advantages of plastic laser marking (versus conventional marking technologies) are:

• Permanent marking, as it is waterproof, wear- and heat-resistant, lightfast and resistant to chemicals
• Maximum flexibility in the marking design – also suitable for locations that are hard to access
• Non-contact process
• and therefore no wear and tear of tools and no costs for consumables such as chemicals, inks etc.
• The material remains free from pressure, tensions and fixings, so that consistently uniform results can be guaranteed
• Unimpaired surface (colour change)
• Simple handling, no pre or post-treatment required

Types of lasers

During the laser marking through laser beam exposure, the plastics undergo optical surface changes. A variety of laser media are used here, and these differ in how the laser is generated. A distinction is drawn between gas, dye and solid-state lasers. During the lasering of plastic the result is influenced not only by the type of laser but also by the wavelength used. For most laser marking applications, solid-state lasers such as Nd:YAG, fibre lasers and CO2 lasers are the ideal beam sources.

At Ensinger, successful trials have been performed with the Nd:YAG solid-state laser. Nd:YAG stands for neodymium-doped yttrium aluminium garnet laser. It uses a neodymium-doped YAG crystal as an active medium.  This laser is also used very frequently in practice. The best results were obtained at a wavelength of 1064nm – this is also the one that is most frequently used.

Fields of applications

Laser marking is increasingly replacing conventional printing methods. Particularly in the labelling of plastics, laser marking has developed into an established method. Above all, it has become more important in the context of quality assurance and traceability. The plastics are frequently given bar codes, articles or batch numbers for unique identification. Countless applications across all industries benefit from this. These include:

• Casing components made from plastic
• Electronic components
• Circuit boards for car parts
• Tools and tool handles

Not all high-performance plastics are intrinsically capable of being laser marked. For example, POM (acetal) and polyamide PA without modification do not usually display any colour change upon marking with a NdYAG laser. Ensinger therefore offers a selected portfolio of plastic stock shapes which are very suitable for laser marking. These include TECAFORM AH LM white, TECASON P MT and TECAPEEK natural. Lasering POM, in particular, is often a challenge, which is why TECAFORM AH LM white has been modified with a laser additive.