Coding on PP Coated Paperboard at 10.2 µm 

Various types of polymer-coated paperboard are used throughout the packaging industry. These coatings, which can have clear, matte, satin, or gloss finishes, enhance the paperboard substrate by adding strength, durability, printability, and moisture-resistance.

For this application, the customer request was to laser mark date codes on paperboard (also know as chipboard) packaging that featured a multicolored inked surface coated with a glossy Polypropylene (PP)  layer. PP is often laminated to paperboard packaging for extra durability and water-proofing capabilities which are especially helpful for industries such as pharmaceuticals. 

PP is in the thermoplastic family, meaning it typically exhibits some melting but does not chemically degrade when exposed to a CO2 beam. PP also responds very differently to various wavelengths in the CO2 band like the 10.6 µm (standard), 10.2 µm, and 9.3 µm wavelengths available in our line of ti-Series lasers. However at 10.2 µm, PP is highly absorptive which, in this application, means the energy is absorbed at the top surface of the paperboard with minimized melting.

To demonstrate the importance of selecting the right wavelength, we set up a 10.6 µm ti100 laser with an FH Flyer marking head equipped with a 200 mm focusing lens that provides a 290 µm focused spot. At a power level of 30 W and a speed of 1270 mm per second (50 in/sec), the mark appears as shown in the upper photograph. Under magnification, the PP shows signs of melting due to some absorption of the 10.6 µm energy.

Compare this to the result shown in the lower photo where the only change in the setup was to install a ti100 laser operating at a wavelength of 10.2 µm. Here, the magnified view shows how well the 10.2 µm energy was absorbed at the PP layer to the inked surface below. Although slightly raised, the PP layer was not melted or damaged and the integrity of the package coating was maintained. 

 

10.6 Mark

PP coated paperboard marked at 10.6 µm. Note the slight melting due to partial absorption of the 10.6 µm wavelength

 

10.2 Mark

PP coated paperboard marked at 10.2 µm. Increased absorption at the PP layer from 10.2 µm produces a higher quality mark while maintaining package integrity.

 


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