Laser-sensitive powder pigments and plastic granules
The laser demonstrates its great advantages particularly with the marking of plastics, since plastic components frequently do not have a flat surface, and during their operating life they are exposed to a variety of environmental influences. Also the texture of the surface can be a challenge for marking plastics – not so for the laser.
Today, the marking of plastics is often employed on technical components that need to guarantee a good traceability. Automotive applications, for example, where resistance to oil and heat plays a major role, or in the chemical industry, where packaging is to be individually and permanently marked, are increasingly relying on this clean and economical method of marking.
The laser marks without contact
Contact-free laser marking offers several advantages. Any type of surface structure can be marked. Neither the surface roughness nor the surface geometry plays a role, and even markings through laser-transparent plastics are feasible. There are no material pretreatments and no adhesion problems because there are no boundary surfaces and the material itself shows the color change (Fig.1).
Light is not consumed
Using laser additives in the polymer can produce a color change in the material. This means for the user that there are no consumables on site. No solvents, no inks, no warehousing, no empty consumables. In general, this means fewer downtimes because light is not consumed.
From laser-transparent plastic to laser marking
Most plastics are transparent to laser light; therefore they cannot be marked economically without a laser additive. Through the addition of laser additives, the laser light can be absorbed and thus trigger the color change in the plastic. Merck offers both pigment powders and pigment granules for laser marking. Our laser granules are in principle a plastic-based concentrate. They have the advantage of being dust-free, offer excellent performance in terms of contrast, edge sharpness and speed, and regardless of the plastic used, produce dark markings (Fig.2).
Polymer, laser and additive are strategically coordinated
Iriotec® 8000 pigment powders from Merck absorb the laser light energy and induce a color change through the interaction with the polymer. The core of each pigment particle is a mica platelet coated with a thin layer of a laser absorber.
Pigment powders of the Iriotec® 8000 Series incorporate easily into plastic formulations. Because of their high temperature stability and low use concentrations, they are especially well suited for technical and transparent plastics. They allow high-contrast, clear-cut markings; they increase marking speeds and are thus able to compete with inkjet technology. Since polycarbonate carbonates very easily, even small amounts of laser additive, here Iriotec® 8825, are sufficient to significantly increase the edge sharpness and marking speed. The color influence through the additive is hard to see; the transparency of the polycarbonate is retained (Fig.3)
The laser pigments in powder form support the reaction of the polymer. As you can see in the blue polyamide sample, varying the laser parameters can control the color change. Polyamide tends to react to light. By adding the pigment powder type laser additive, the marking result can be controlled through the laser parameters. Dark markings are also possible, which allow the depiction of black and white images (Fig.4). Depending on the composition of the polymer and the laser parameter settings, the result is a
dark mark – the surrounding polymer is carbonized
light mark – the surrounding polymer is foamed
Merck laser granules react independently of the base material
Besides a laser absorber, laser granules such as Iriotec® 8208 also contain a color former, causing them to react independently of the surrounding polymer. The marking is always dark, regardless of whether the additive is used in polymers such as polyethylene (PE), polypropylene (PP) or thermoplastic polyurethane (TPU), which tend to carbonize, or in polymers such as polyoxymethylene (POM), and polymethylmethacrylate (PMMA), which tend to foam and thus inherently create a light mark. When using laser pigment powders, POM cannot be marked dark. By adding laser-sensitive granules, a polymer-matrix-independent marking becomes possible (Fig.5).
Fillers, colorants, et cetera
The amount of laser-reactive polymer decreases with the use of glass fibers or other fillers in the polymer. In addition, the laser beam is scattered. This has an influence on the contrast with dark markings on light components as well as on the line width in light markings on black materials. Polyamide with 30% glass fiber can be marked light with a high contrast. The line width is slightly wider than with a non-filled material. Compared to an unfilled polyamide, the glass fibers have no influence on the marking speed and contrast (Fig.6).
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Further information about material influence, additives and fillers is also available at
www.merck-laserforum.de and www.merckgroup.com.