Laser marking in plastics extrusion: potential savings in continuous production

For sewage pipes alone, this means a processed weight of more than seven million tons of PVC. And the trend is rising. Almost all products are provided with markings during the process. In times of digitalization and increasing demands for sustainable production methods, hot stamping processes and solvent-based ink printing are an anachronism.

We explain the potential savings that laser technology offers for marking plastics in general and PVC in particular.

What type of laser is used?

When marking extrusion products with lasers, a distinction is primarily made between two types of beam sources and their basic wavelengths: As a rough guide,_{CO2 Lasers} can be used for engravings in organic materials and fiber lasers for color change markings on plastics and metals. Whereby the boundary is not sharp. While the CO2 Laser emits at 10.6 µm in the infrared range, melting and partially vaporizing plastics, the fiber laser with a wavelength of 1.06 µm in the near-infrared(NIR) range produces thermal effects such as foaming or carbonization with color change as a result.

While many plastics from the PP, PA and ABS families already react with color change on their own, the addition of appropriate additives can enhance, influence and secure these effects. PP-homo and PETG plastics can generally only be laser-marked in the NIR with additives of sufficient quality. However, PVC has a special position here: it also reacts to_{CO2 radiation} with high-contrast color changes.

The most obvious difference between laser marking and conventional marking methods is the potential savings due to the elimination of consumables and the associated hidden costs for material planning, procurement, storage and personnel.

Furthermore, the downtimes for maintenance and cleaning with the associated service costs, which are common with mechanical or application technologies, are eliminated. Both the deflection unit and the laser source are designed for several 10,000 operating hours. Accordingly, the maintenance effort for laser marking devices is limited to the occasional cleaning of the focusing lens or the protective glass - an operation that only takes seconds if accessibility is good.

As an extraction system with corresponding filter technology is usually used, filter changes still have to be included in the calculation for the sake of fairness. Due to the small volume of material vaporized per marking, the change intervals are long, usually in the weekly or monthly range.

In addition to reducing production costs, laser marking has other advantages for customers due to its properties. It is permanent, abrasion-resistant and resistant to solvents within the limits of the resistance of the plastic itself. This is the most outstanding property that enhances the end product and thus reliably guarantees traceability from placing on the market to recycling as well as protection against counterfeiting. It also offers the option of adding very precise length dimensions to products for the processing trade. The high graphic resolution of the laser systems also enables complex logos to be transferred to the product in high quality.

The laser marking - whether by color change or engraving - is not applied to the extrusion profile but into it. No pre- or post-treatment of the marking surface is required. Laser marking is therefore a single-stage process that is statistically less prone to errors than multi-stage processes with pre- and post-processing. The use of lasers also offers the advantage that no additives are required and therefore do not have to be moved. Laser markers are also insensitive to electrostatic charging of the extrusion profiles. Distorted markings due to electric fields are therefore impossible.

This raises the question as to why laser markers are not much more common in the world's production plants. In addition to the higher purchase costs compared to ink jets, this is probably mainly due to a lack of information on the subject of laser safety.

Laser safety: not rocket science

Industrial laser technology has been established for almost 60 years now. During this time, extensive expertise has been acquired by both the system manufacturers and the relevant testing bodies, and clear guidelines and standards have been established according to which installations are approved. Essentially, these are DIN EN ISO 13849-1 for the general functional safety of machines, which already applies during product development, and DIN EN 60825-1 and -4, which relate to safety in connection with laser technology.

As an episode, the area around the laser process should be enclosed to prevent possible scattered radiation outside the process chamber. It is not necessary to enclose the entire device, but only the working area, with appropriate design of the material supply and removal, in order to meet the requirements of laser class 1.

In addition to the housing solution, established manufacturers also offer the appropriate extraction system with filter technology from a single source.

Is the laser technology suitable for my process?

Before purchasing a marking solution, an appropriate sample is always produced. If the samples meet the customer's requirements in terms of surface quality, contrast, readability and marking speed, the installation situation is verified. Solutions for permanent installation in a production line are possible as well as mobile concepts for different applications of a coder.

If the application changes, be it a product change or a modified graphic, the user is not tied to a specific number of lines and can determine the optimum parameterization fast and usually purely via entries in the operating software, thus increasing flexibility on the line.

Conclusion: A flexible, reliable and virtually maintenance-free production tool

Although industrial laser technology has now been around for almost 60 years, there are still reservations in the industry. Those who embrace the technology are provided with a flexible, reliable and virtually maintenance-free production tool. The main advantages of laser marking are permanent product markings with maximum flexibility in terms of design, a high degree of forgery-proofing and all this while reducing material logistics and costs. This means that sustainability can not only be practiced in the product creation process, but also implemented in the recycling process and increase the company's own competitiveness.

Author: Christian Dini, laser expert at REA Elektronik GmbH