Are you a company that has already purchased a laser machine and would like advice on how to get started with plastic marking? Or perhaps you are still wondering which laser technology to choose for engraving your plastic parts? To successfully mark plastic parts, you need to know the characteristics of your material, the laser sources to choose from, and the expected rendering. This guide gives you all the information you need to get started.
The Chemical Composition of Thermoplastics and Its Impact on Laser Marking
Before getting started with laser marking, you need to know the material you are marking. There are three main families of plastics:
- Thermoplastics (e.g. LDPE, HDPE, PVC, PP): No chemical change in plastic structure. Malleable with high deformability. The most widely used plastics.
- Thermosetting plastics (e.g. Bakelite, Epoxy, PU): Chemical change to be expected. Cannot change shape once transformed.
- Elastomers (e.g. Rubber, IR, CR, NBR): Elastic with high deformability.
Thermoplastic polymers are the most widely used plastics. They owe their popularity to their chemical stability -- even when subjected to heat -- and their malleability. Produced on a large scale since the 1970s, they are widely used in the automotive industry and many other sectors.
The 8 Sub-Families of Thermoplastics
There are 8 sub-families of thermoplastics, each with distinctly different properties:
- Polyolefin (PP, PE): Food storage, stretch film, automotive parts
- Polystyrenics (ABS): Automotive parts, household appliances, medical equipment
- Polyvinyl (PVC): Piping, coatings (floor, pool), doors and windows
- Polyester (PET, PETP, PBT): Bottles, textile fibres, automotive and electronic components
- Polyoxymethylene (POM, POM-C): Automotive electronic components, industrial components (gears, bearings)
- Polyacrylic (PMMA): Glazing, display panels, screens, packaging
- Polyamides (PA): Textile fibres, automotive components, industrial components
- Polycarbonate (HDPE, PS, PC): Food packaging, pipes and ducts, medical components, automotive parts
Composition Variations Within Sub-Families
The composition of plastics within each sub-family is not fixed. The ratios of components used to produce a thermoplastic vary according to the manufacturer and the final properties desired. For example, ABS (a material composed of acrylonitrile, butadiene, and styrene) is more rigid and solid when its formulation contains a high percentage of styrene, but more flexible and impact-resistant when rich in butadiene. This multiplicity of combinations broadens the range of materials available and means that laser marking results can vary even within the same plastic family.
The same principle applies to "new plastics" such as recycled plastics or those composed in part of organic materials. Their production processes differ from standard thermoplastics, as does their composition and reaction to laser marking. If your plastic of choice is not suitable for laser marking, it can generally be modified to make it suitable with a suitable additive or masterbatch.
Types of Laser Sources for Plastic Marking
The French plastics industry association Polyvia and Gravotech teams worked together to carry out a series of laser marking tests on polymers. Here are the results for each laser type:
Green DPSS Laser
This is the ideal solution for plastic marking. Results were excellent for 45% of polymers tested (only 15% of plastics failed to react). Their shorter wavelength allows a better absorption rate by certain light-coloured or transparent plastics. Their thermal stress is lower than CO2 lasers, meaning they can engrave heat-sensitive plastics without risk of deformation or thermal damage. Their smaller beam spot size enables greater precision and marking resolution. However, the green DPSS laser involves a larger investment compared to other sources.
Fiber Laser
Fiber technology is powerful and marks metals particularly well. You can also use it on most plastics with decent results, though results vary greatly depending on the polymer. Only 42% of polymers are marked with contrast.
DPSS Hybrid Laser
These lasers are far more precise than fiber technology and feature a shorter laser pulse duration. They deliver better marking results on polymers: while 30% of the polymers tested did not react, 30% showed excellent results.
CO2 Laser
CO2 lasers can also mark plastic, but without contrast. They are therefore more often used for engraving organic parts (wood, glass, leather, ceramics). Transparent plastics are an exception -- the CO2 laser is very useful for engraving this type of material, where the marking stands out well.
How Laser Marking Works on Plastics
The effect of lasers on plastic differs according to the laser source used and the properties of the material. There are 5 ways in which plastics react to laser marking:
1. Gas Bubbles or Foaming
The laser vaporizes volatile components in the plastic. Bubbles or small cavities appear on the surface. The marking appears brighter on dark plastics.
2. Surface Colourization
The laser's heat interacts with pigments or additives present on the surface of the polymer. It causes a colour change on the thermoplastic, which can be useful for creating visual contrasts or coloured marks.
3. Body Colourization
Similar to surface colourization, but the chemical structure of the material itself is modified by the heat of the laser. The colour change takes place within the body of the material, not just on the surface. This reaction produces contrasting markings while preserving the shape of the surface -- no bumpy deformation.
4. Carbonization
This occurs when the laser temperature is particularly high. The plastic decomposes thermally, and the result is the appearance of carbonized residues. Carbonization produces black or dark marks on the plastic.
5. Sublimation
Another possible reaction of plastic to a high-temperature laser beam. The marked area is sublimated: the laser scratches the surface, creating a depression. This marking method is used in particular for multi-layer plastic components or automotive laminates.
Types of Plastic Marking Possible with Laser Technology
The laser can be used for all types of marking, including those requiring a high level of detail. For example, you can produce:
- Alphanumeric characters: Serial numbers, part numbers, date codes
- Logos and drawings: Brand marks, certification symbols, technical drawings
- Codes: 1D barcodes, 2D DataMatrix codes, QR codes, flashcodes
What is important is that your choice of laser source and the way you use it are aligned with the plastic you are going to mark. Testing is essential -- with the virtually infinite thermoplastic compositions, various laser source options, and different machine settings, laser marking of plastics is subject to many variables. You can rely on Gravotech experts via SOFRAY EMS to accompany you through the testing phases.
The Advantages of Laser Marking on Plastics
Laser marking on plastic offers 4 major advantages:
- Durability: Laser marking is permanent and as durable as the polymer itself. It is resistant to oils, aggressive products (to a certain extent), and aging.
- Reliability: Laser marking requires no tools or products other than the laser itself -- no use of chemicals, inks, or labels.
- Non-contact marking: The laser marks plastic without touching it, resulting in no tool wear, less debris and dust, and the ability to mark surfaces impossible to engrave with other technologies, such as very small electronic components or delicate medical equipment.
- Respect for the material: The laser rarely alters the plastic part outside the marking zone, unlike mechanical engraving which hollows it out by removing material with a milling cutter.
Conclusion
Getting started with laser marking on plastics requires understanding your material, choosing the right laser source, and performing adequate testing. The composition of your thermoplastic, the laser wavelength, and the desired marking type all influence the final result. With the right guidance from experienced professionals, laser marking can become a highly efficient, permanent, and cost-effective identification solution for your plastic parts.