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Close-up of the surface structure of black marking

Black marking – permanent, deep-black and corrosion-resistant markings

Black marking is a procedure in laser processing which causes extremely dark, high-contrast markings on a surface without material ablation. Extremely short laser pulses cause structures on the surface at the nanometer level. The microstructured surface ensures that light scattering is reduced, and creates a marking with constant depth and a consistent black colour. When the laser pulses used for this marking are ultrashort, the colour changes also remain corrosion-resistant within certain parameter ranges. The reason for this is that the use of ultrashort pulse lasers means that the heat-affected zone is extremely small, meaning that enough free chrome remains on the surface that a self-healing oxide film can form.

An overview of your advantages

Black marking with the TruMicro Series 2000
Viewing angle consistency

One advantage of black marking is the "viewing angle consistency". The very high, even contrast from all viewing angles is the result of periodic nanostructures which reflect the light in a very scattered manner, as well as absorb it. This represents a quality attribute, especially in the watch and automotive industry, where many visible parts are used.

Black marking on a valve
Deep-black colouration

Processing with a laser causes a noticeable colour change on the metal – right through to a deep, dark-black colour. Black marking also creates a strong contrast and a very matte appearance, without reflections. This noticeably increases the manual and automatic legibility of even the smallest of pixels

Black marking on a medical valve using TRUMPF products
Filigree markings

Black markings using ultrashort pulse lasers are ideal for very small and delicate markings or small area DMC's (Data Matrix Codes) as well as UDI (Unique Device Identification) codes. When using ultrashort pulse lasers, pulse durations are around ten thousand times shorter and are more energized than with other marking lasers. Markings can also be applied at very small spot sizes, making the process ideal for filigree markings.

Corrosion test of a black marking application using TRUMPF products
Corrosion resistance

Corrosion-resistance markings are required in many industries. According to the EU Medical Devices Directive, implants or surgical instruments must be be assigned a traceable UDI code (Unique Device Identification), for example. Shorter exposure times mean virtually no chromium atoms diffuse into the lower layers thereby maintaining a surface's chemical integrity. Black marking enables all kinds of corrosion-resistant markings which remain legible even after numerous cleaning and passivation cycles.

Medical instrument with UDI code, black marking with TRUMPF lasers
UDI-compliant marking

The EU's Medical Device Directive and FDA regulations (Food and Drug Administration) in the USA require permanently legible labelling of medical devices with a traceable UDI code (Unique Device Identification). The properties of black marking using ultrashort pulses make it ideal in meeting all the requirements of UDI-compliant marking. The corrosion resistance, viewing-angle stability and deep black colour of the UDI codes make them permanently legible even in the smallest dimensions.

Curious about the advantages that black marking could bring to your marking task?

Our experts would be pleased to advise you.

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White paper: corrosion-resistant black marking

Read our white paper on black marking and its applications in medical technology. Click here for the white paper!

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Process description

Black marking process outline - how black marking works

  1. Surface structure: Ultrashort pulse lasers with a pulse duration in the range of pico or femtoseconds provide the basis for corrosion-resistant black marking. It becomes possible to process materials with virtually no thermal or mechanical impact. This is because the laser pulse, and therefore the duration of the energy input, is so short that temperature transport to neighboring atoms does not even occur. This prevents thermal stress cracks which can occur in conventional annealing when the parameters are not considered. This is why it is referred to as "cold processing". The laser structures the material at the nanometer level.
  2. Oxide film: In addition to surface structuring, a chromium oxide film plays the second central role in corrosion-resistant black marking. The low exposure to heat in comparison to annealing with short-pulse lasers allows for a sufficient amount of chrome to remain on the surface, which promotes the self-healing process of the passive film. This creates more corrosion-resistant films with chromite (Fe2+Cr2O4) and magnetite (Fe3O4), as well as films consisting of a mixed phase: FeFe2-xCrxO4 (iron-chrome-spinel).
  3. Passivation: Marking is followed by the cleaning of the medical products. The legibility and durability of laser marking can be affected by prolonged exposure times, aggressive cleaning agents or high temperatures. This is why a targeted passivation procedure is often opted for when it comes to refinishing. In this process, an acid bath consisting of saltpetre or citric acid removes highly reactive elements (e.g. free iron ions) from the surface, and supports the clean, fast formation of a new chrome oxide film for even better corrosion resistance. At the same time, the surface is also cleaned and sulphid es removed during this process.

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Applications examples for black marking

Black marking on a medical valve using TRUMPF products

Valve for cerebral pressure equalisation

Permanently easy-to-read markings are vitally important to uniquely identify and trace implants. The shunt shown is used to treat hydrocephalus ("water on the brain") and it guides the excess fluid in the brain from the ventricles under the skin to the abdomen.

Kidney dishes

Kidney dishes made of precious metals are provided with a uniquely traceable, corrosion-resistant UDI code (Unique Device Identification) through black marking.

Flexible catheter structure

The TruMicro Mark 1020's exceptionally high peak pulse power means that implants can be marked with jet-black, corrosion-resistant UDI codes.

Black marking with TruMicro Mark

In this video, you can see how the  TruMicro Mark uses black marking to apply a jet-black, traceable and corrosion-resistant UDI code (Unique Device Identification) to the component.  

White paper

We have compiled a selection of white papers on topics that may be of interest to you

PDF - 585 KB
Corrosion-resistant black marking
Want to find out more about black marking? The white paper will give you deeper insights into the process and its applications in medical technology. Simply complete the form below.
PDF - 374 KB
Reprocessing of laser-marked medical products
According to MDR and FDA regulations, labels on medical devices must be clear and legible throughout the life cycle. This study presents results on the reprocessing of laser-marked medical steel 1.4301. Find out more in this white paper.

Curious about the advantages that black marking could bring to your marking task?

Our experts would be pleased to advise you.

Contact

You may also find these topics interesting

Miethke's success story

Marking brain implants to a high level of quality – Miethke, a family-run company based in Potsdam, Germany, does just this. The company produces neurosurgical implants to treat hydrocephalus ("fluid in the brain") using TRUMPF marking lasers. Read the customer report to find out how motivating it is for the employees to work towards improving the quality of life of patients every day.
Medical instrument with UDI code, black marking with TRUMPF lasers
UDI-compliant marking

In accordance with EU and US standards, medical products must be labelled with a uniquely traceable UDI code (UDI = Unique Device Identification). TRUMPF can offer you the perfect complete package comprised of marking laser and software for this.
TruMicro Mark 1020
TruMicro Mark

If you're looking for a marking unit for laser markings with ultrashort pulses, the TRUMPF TruMicro Mark 2000 provides an all-round turnkey solution.
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