To achieve a specific result when laser marking plastic parts, you need to understand how the laser acts on plastics based on their respective characteristics and the laser source. Whether you are considering acquiring a laser solution, changing technology, or implementing laser marking in a production process, this guide provides the advanced technical detail you need to make informed decisions.

The Advantages of Laser Marking on Plastics

Among the many technologies available for part identification in industrial sectors, laser marking has several key advantages:

The 4 Factors Influencing the Marking Result

1. The Polymer to Be Marked and Its Composition

The content and composition of the thermoplastic is the first criterion to consider. It influences the interactions between the material and the laser, as well as the final rendering of the marking. There are thousands of types of thermoplastics, and even within a given family, the composition varies greatly depending on the manufacturer or the intended use. Added to this are plastics filled with recycled or organic materials, which are increasingly present on the market. The possibilities for laser marking plastic are therefore almost endless -- but this also means it is essential to have a good understanding of the composition of the polymer you wish to mark before choosing a laser solution.

2. The Wavelength of the Laser

While it is tempting to consider laser power as the most important criterion, it is in fact the wavelength that takes precedence. The wavelength influences the power of the laser, the level of absorption by the thermoplastic, and the interaction of the laser with the thermoplastic (how it modifies or does not modify the physico-chemical properties of the material). When absorbed by the material, the laser can cause thermal excitation, which may lead to melting, sublimation, or ablation. It also influences the depth of penetration of the laser into the plastic. For optimal interaction with matter, experts recommend using a laser with a wavelength between 355 and 532 nanometers.

Common laser wavelengths include: UV laser at 355 nm, green laser at 532 nm, Nd laser/Yb fiber laser/MOPA laser at 1064 nm, and CO2 laser at 10,600 nm. The higher the wavelength, the hotter the point of contact of the laser on the plastic.

3. The Laser Pulse Frequency

A laser set to a high frequency (between 70 and 200 kHz) emits many closely spaced pulses. Those set to a low frequency (between 2 and 70 kHz) produce fewer, more spaced-out pulses. Low frequency lasers (around 30 kHz) can cause thermal shocks that damage plastic parts. In practice, it is better to opt for a high frequency laser to avoid material damage.

4. The Laser Wave Amplitude

Wave amplitude is the time distance between the laser's maximum energy emission and its resting position. It is closely linked to the notions of energy and time. When comparing a hybrid or DPSS (Diode-pumped Solid-state) laser and a fiber laser in the same operation, both may transmit the same amount of energy to the polymer. But the fiber laser, with its lower amplitude, applies it less intensely over a longer period of time, presenting a risk of thermal heating of the plastic part. It is generally better to mark thermoplastics with a laser having a higher wave amplitude over a short period of time, to avoid damaging the material.

5 Most Common Interactions Between Laser and Thermoplastics

Tests conducted by the French plastics union Polyvia and Gravotech on various polymers revealed five distinct types of interaction:

1. Gas Bubbles or Foaming

Following irradiation by the laser, gas bubbles form in the marked area under the effect of heat. When cooling, these bubbles become trapped in the upper layer of the material, resulting in a whitish swelling. This reaction produces a kind of discoloration and is therefore particularly visible on dark thermoplastics. Foaming can be coupled with carbonization, producing a grey or black swelling.

2. Surface Colouring

The material absorbs the energy provided by the laser radiation. The resulting thermal reactions lead to an increase in the molecular density of the marked area. This area then visibly swells, creating a colour change on the surface that can be useful for creating visual contrasts.

3. Body Colouring

Here, the laser changes the chemical composition of the material's constituents. More precisely, it modifies the pigments of the thermoplastic, which generally contain metal ions. The laser induces a modification of the crystalline structure of these ions, as well as the degree of hydration of the crystal. These pigments then become more intense and the material undergoes colouring within its body -- not just on the surface. This reaction also preserves the shape of the surface with no bumpy deformation.

4. Carbonization

This reaction occurs when the area facing the laser is continuously irradiated. The macromolecules of the material are carbonized, producing a black tint. Foaming can occur in conjunction with this interaction, resulting in carbonized foam.

5. Sublimation

The laser causes the material to sublimate by thermal effect, creating a depression (cavity) in the irradiated area. This cavity is revealed by the reflection of ambient light. Sublimation is the closest equivalent to engraving and is used particularly for multi-layer plastic components or automotive laminates.

Laser Technologies Compared for Plastic Marking

The Green DPSS Laser (532 nm)

The green DPSS laser provides excellent results for marking plastic. Thanks to its 532 nm wavelength, it ensures optimal absorption by polymers, especially transparent or clear plastics. Of the polymers tested, 30% showed satisfactory results, 45% showed excellent quality markings, and only 15% did not react. With a power of 5 W and a peak power of 95 W, this laser operates cold, reducing thermal stress on materials -- making it particularly suited for the identification of sensitive materials. Its short pulse duration (7 to 50 ns) and small beam spot size ensure superior marking accuracy and resolution.

The Fiber Laser (1064 nm)

Operating at 1064 nm, fiber laser technology is powerful and marks metals particularly well. It can also be used on most plastics, with decent results, though results vary greatly depending on the polymer used. The marking contrast is optimal for approximately 42% of polymers, and 16% show excellent results. Available powers include 20, 30, or 50 W with peak powers of 10 kW and pulse frequencies from 2 to 200 kHz.

The Hybrid DPSS Laser (1064 nm)

Hybrid DPSS lasers share the 1064 nm wavelength with fiber lasers but are far more precise thanks to their shorter laser pulse duration. They deliver better marking results on polymers: among 60% of polymers offering acceptable contrast, 30% offer an excellent marking result. With powers of 10 or 20 W and peak powers of up to 150 kW, these lasers address industrial constraints such as traceability challenges effectively.

The CO2 Laser (10,600 nm)

Operating at 10,600 nm, the CO2 laser causes ablation or sublimation of the marked area on most polymers, typically resulting in a low-contrast marking where a cavity allows the marking to be seen by light reflection. It is therefore more often used for engraving organic parts (wood, glass, leather, ceramics). However, transparent plastics are an exception -- the CO2 laser is very useful for engraving this type of material, where the marking stands out well.

Summary: Interactions by Thermoplastic Family

Different thermoplastic families react differently to each laser technology. Key examples include:

These results are based on internal tests by Gravotech. Not all colours are represented, and some laser technologies may cause different reactions. To ensure the best rendering for your specific plastic markings, contact our team to arrange sampling and testing phases.

Why Choose Gravotech for Plastic Marking

The in-depth study conducted by experts from Gravotech and Polyvia has enabled a comprehensive panel of tests to facilitate the choice of laser and its configuration, depending on the type of thermoplastic and the desired rendering. By turning to Gravotech, you benefit from:

Conclusion

Laser marking on thermoplastics is a complex field where the polymer composition, laser wavelength, pulse frequency, and wave amplitude all interact to produce the final result. Understanding these four factors and the five types of laser-plastic interactions will help you select the right laser technology and settings for your specific application. Whether you choose a green DPSS, fiber, hybrid DPSS, or CO2 laser depends on the polymers you work with, the contrast required, and your production environment.