Laser Marking and engraving on polyolefin plastics, such as polypropylene and polyethylene, is difficult due to their polymeric properties, and there are different types ranging from homopolymer and copolymer polypropylenes including HDPE, LDPE, LLDPE and others that intrinsically mark differently. When developing a product to be laser marked, engineers should consider which grade is best in terms of performance and markability. MOPA Ytterbium fiber lasers are ideal for marking polyolefin plastics because of their capability to produce short pulse widths to create scratch resistant dark and light-colored marking contrast. Long pulse widths more than 100ns can cause excessive burning.
Recent advancements in colorant technology, such as laser-specific carbon blacks and titanium dioxides, as well as foaming agents, provide superior contrast quality, line edge detail, and the fastest speed, including “on-the-fly” marking. These attributes make them ideal for laser marking wire and cable insulation in automotive, construction, medical, packaging, piping, and other applications.
Optimal laser marking. Laser marking on polypropylene and polyethylene plastics normally require laser-sensitive additives incorporated into optimized colorant compounds, color concentrates or precompounded. Flame retardants are commonly used in wire/cable and insulator products which affect colormatch and compound formulations. Additives such as antimony-doped tin oxide and antimony trioxide 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.
When properly blended, laser marking additives, compounds, and colorants have no adverse impact on polymer properties, meet requirements such as UL, NEMA, FDA, RoHS and Yellow Card, and do not require recertification. The chemical components of laser optimized formulations are influenced by a number of factors, including polymer type and color, marking contrast color, surface reaction mechanism type, and laser wavelength. Two types of surface reactions when laser marking polyolefins are Carbonization “charring” and Chemical change “foaming”.
Inline “on-the-fly” laser marking on polyolefin products provide state-of-the-art manufacturing advantages. Marking speeds for wine corks and undercap promotions on linerless beverage closures are capable of 2,000 pieces per minute for alphanumeric text and graphics. Equally impressive results are achieved on extruded medical and wire/cable products.
Laser Markability of Polyolefins
Polyolefins have different surface reaction mechanism temperatures than other polymers, necessitating the use of specialized formulations. Even polyolefins from the same family, such as polyethylene and polypropylene, laser mark differently. This is one reason why High-density polyethylene is generally the easiest to mark. Polyethylene plastics are generally easier to mark than polypropylenes.
Polyolefin is a class of polymers formed from olefins. This versatile group of materials includes well-known polymers like polyethylene (PE) and polypropylene (PP), which are widely used in a variety of industries due to their outstanding chemical and physical properties. The four most popular varieties of polyolefins are low-density polyethylene, linear low-density polyethylene, high-density polyethylene, and polypropylene.
Not All Plastics and Lasers Produce Identical Marks!
The quality of laser components, optics, scan-heads, and versatile software is critical. Industrial lasers are superior to cheap wholesale (resellers) hobbyist-type lasers. Cheap lasers have serious problems with erratic marking quality, as well as low-cost optics and electronics, resulting in variations in beam quality and inconsistent marking.
Some laser equipment resellers and manufacturers’ websites use internet buzz terms about polyolefins to gain “clicks” and high rankings – they are not experts in polymers, colorants and the chemical interaction pathways with various laser wavelengths which are critical for achieving optimized laser marking quality. Robust and cost-effective laser solutions integrate polymer material science with the optimal laser source (wavelength).
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