Laser Marking of Plastics in Medical Technology
A great number of medical applications, many of which require direct part marking for device identification purposes, are made of plastics. Since lasers can create durable and high-quality marks, laser technology is the proven method for plastic marking.
Medical technology uses plastics for hygienic disposable consumables as well as for implants, high-tech wearables or reusable instruments. Other application examples include syringes and cannulas, respiratory masks, hearing aids or insulin pumps.
Due to its low cost and high versatility plastic is considered enormously efficient. Its material properties are widely demanded for medical applications such as transparency, flexibility, low weight and robustness against strain.
In any case, biocompatibility is crucial for plastic medical devices so as not to jeopardize patient health. This also applies to a laser marked plastic part: a possible change in the material surface must not lead to an emission of harmful substances.
Traceability ensures patient safety
Traceability is, besides biocompatibility, another premise for patient safety, mainly in the event of product defects and recalls. But part identification is also crucial for streamlining manufacturing processes throughout the entire production chain. Reliable tracking codes on a product surface must therefore be abrasion resistant and long-term human and machine readable.
This applies in particular if a medical device is used multiple times and reprocessed after each use. Direct marking is then required by law and regulated by FDA and MDR regulations. In the medical industry this is referred to as unique device identification (UDI).
The requirements for UDI code marking can be met for almost any plastic with the help of suitable laser technology. In addition, plastic products are sometimes also marked “only” for decoration or to increase counterfeit protection.
Methods of plastic marking: from foaming to material removal
Depending on the properties of the plastics, CO₂, UV, fiber and other solid-state lasers are applicable for marking plastics. Any laser’s thermal energy acts locally and with high precision, so that a sharply defined, high-contrast and thus easily legible marking can be achieved.
Another advantage of laser marking is its high abrasion resistance: since the marking is usually created within the material substance, the plastic surface remains smooth and rather even. This not only has advantages for the durability of the marks, but also for product hygiene.
Plastics absorb light best in the ultraviolet range (UV laser) and in the far infrared range (CO₂ laser). However, plastics can be “laser-optimized” by using special additives in the raw material mix. The used additives, fillers and pigments help to improve the absorption behavior of the plastic.
This leads to optimal marking results when using certain lasers. Additives may facilitate or even enable the employment of the versatile fiber lasers (with a wavelength of 1,064 nm) or visible green laser light (532 nm)
The thermal changes in the material brought about by the laser produce different marking effects: while color changes to light or dark hardly affect the surface structure, melting or evaporation results in structural changes or engraving effects.
A lighter coloring usually results on dark plastics, whereas on lighter substrates the created marks appear dark. But also sometimes – as with transparent materials – the laser creates a light marking. The four marking processes to mention when marking plastic are carbonizing, foaming, layer removal including day-night design, and engraving.