Laser Additives for Plastics Marking Using Fiber Lasers
by Scott Sabreen
The Sabreen Group, Inc.
Near Infrared (NIR) laser marking of clear and opaque polymer products: a) white and black marking contrast on the same part (including grayscale shades) and b) opaque white contrast.
Near-infrared laser additives improve the degree of contrast, which can be further intensified by changing the laser setup parameters. Polymers possess inherent characteristics to yield “dark-colored” or “light-colored” marking contrast. Some colorant compounds containing low amounts of titanium dioxide (TiO2), and carbon black also may absorb laser light, and in some instances, improve the marking contrast. Each polymer grade, even within the same polymeric family, can produce different results. Additive formulations cannot be toxic or adversely affect the products’ appearance or physical or functional properties.
Compared to ink printing processes (pad/screen printing and inkjet), laser additives are cost-saving and can demonstrate 20 percent and faster marking speeds vs. non-optimized materials. Laser additives are supplied in pellet granulate and powder form. Granulate products can be blended directly with the polymer resin, while powder forms are converted to masterbatch. Most are easily dispersed in polymers. Based upon the additive and polymer, the loading concentration level by weight (in the final part) ranges between 0.01 and 4.0 percent.
Both granulate and powder form can be blended into precompounded color material or color concentrate. The selection of which additive to incorporate depends upon the polymer composition, substrate color, desired marking contrast color and end-use certification requirements. For extrusion, injection molding and thermoforming operations, precolor compounded materials vs. color concentrate yields better uniformity. Hand mixing should be avoided. Mold flow and gate type/location are important factors. Homogeneous distribution/dispersion of laser additives throughout each part is critical to achieve optimal marking performance.
Some additives contain mixtures of antimony-doped tin oxide and antimony trioxide that can impart a grayish tint to the natural (uncolored) substrate opacity. Other additives can contain aluminum particles, mixed metal oxides and proprietary compounds. Color adjustments are made using pigments and dyes to achieve the final colormatch appearance. Commercially supplied, specific additives (also used for laser welding) have received FDA approval for food contact and food packaging use under conditions A-H of 21 CFR 178.3297 Colorants for Polymers. For the European Union, there are similar compliance statements. Certification conditions are specific for polymer type, loading level threshold and direct or indirect contact. Further qualification of FDA-approved additives blended into a final part can achieve biocompatibility of medical devices.