Advantages of laser marking
Stainless steel is the steel that is resistant to weak corrosive media such as air, steam, water and chemically etching media such as acids, alkalis and salts, also known as stainless acid-resistant steel. Because of its weldability, heat resistance, corrosion resistance and other characteristics, stainless steel is used in a wide range of applications, which is most suitable for hospitals or other areas with special requirements for hygiene, such as: food processing, catering, brewing, chemical industry, etc. Because stainless steel is easy to clean with water and chemical reagents, it is not easy to breed bacteria.
In practice, there is also a strong demand for information marking of stainless steel surfaces, especially in black. Traditional painting and silk-screening methods can strip paint and film after a long period of time; thermal transfer marking will discolour after a period of time; chemical etching and steel marking will not achieve the black effect and other problems exist. Laser marking is non-contact processing, no damage to the processing material, with non-toxic, high environmental protection, marking content flexible, permanent marking and other characteristics, especially has an inherent advantage in the medical device industry.
Picosecond laser: Corrosion resistance of laser black markings
In the medical device industry, corrosion resistance is an important indicator. The general method of testing corrosion resistance is to place the laser engraved metal into a certain concentration of salt spray for a certain period of time and then remove it to observe the laser engraved area in a magnified manner. After the corrosion resistance test, there may be problems with the mark coming off or the laser marking area rusting. However, through the selection of the laser and the adjustment of the process parameters, the best effect of corrosion resistance of the laser black mark can be achieved.
Commonly appearing as a silvery white, stainless steel coloured by laser marking retains its original good properties, making it more versatile. The principle of black marking of the picosecond laser: a nanostructure is generated that does not reflect light, creating a visual black effect.
Marking with picosecond laser pulses leaves a sufficient amount of chromium (around 20 atomic layers) on the surface to replace the oxide film with chromium, thus maintaining corrosion resistance, for example in the form of chromite or chromium-iron spinel. The black markings therefore show no corrosion-induced damage and remain clearly visible even after many, long corrosion tests; secondly, the markings form fine, periodically homogeneous corrugated structures after completion, which can be observed using a scanning electron microscope as minimised nanostructures that directly reflect and scatter light through the "light trap effect". These nanostructures are minimised and reflect and scatter light directly through the "light trap effect", resulting in a matt black colour.
【Picosecond laser marking sample】
Since the introduction of the UDI (Unique Device Identification) standard in the USA and the European Union, the medical industry is facing increased demands in terms of the traceability of its products. For surgical stainless steel materials in the medical industry, this means creating legible and corrosion-resistant marks that are preferably black in colour and that maintain their high quality level in subsequent clinical routines even after multiple cleaning and disinfection cycles.
Black markings using picosecond pulsed lasers are ideally suited to the production of matte black, corrosion-resistant markings that will remain stable and clear for a long time in clinical use.
The picosecond laser is marked in black on the medical surgical forceps and on the ablation needle as shown below.
In the application scenario of stainless steel black marking with high requirements and large process demand, laser process has gradually replaced the traditional marking process, in order to obtain better quality assurance, under a variety of conditions tested, the use of picosecond pulse laser for stainless steel surface black marking is currently the better choice in the market, UDI marking is already a more mature application, but in the future with increasing demand, it is believed that laser technology with its special performance and high efficiency will have a wider range of development applications in the medical industry.
