Virtually every trigger or pump sprayer on the market today uses a dip tube to transfer the container contents up to, and out of the nozzle. Dip tubes are manufactured by extruding molten plastic through a die, cooling the tubing, and then trimming to length using mechanical cutters or lasers. The application presented here is unique because a requirement exists to mark a ten-character code along the length of the tube during the assembly process.

The marking setup consists of a Synrad CO₂ laser, an FH Series marking head, and WinMark Pro laser marking software. To focus the beam on the dip tube, a 200 mm lens was installed to provide a 290-micron (0.011”) spot with a 5-mm (0.196”) depth of focus. We created the mark file using one of WinMark Pro’s twelve built-in stroke fonts (Simple) arranged vertically along the length of the tubing. The text, consisting of 0.1486” high by 0.052” wide characters, was marked using 20 watts of power at a velocity of 20 inches per second. Cycle time to mark the ten-character string was 0.16 seconds. In a tracking or continuous motion application, this text string could be marked at line speeds approaching 1620 inches per minute.

Notice that the marked polyethylene tubing exhibits a slight contrast. This is because the CO₂ beam “boils” the surface of the polyethylene, changing the material’s density and volume enough to generate a raised, slightly contrasting mark.

Polyethylene is one of a few plastics to exhibit a raised, contrasting mark caused by an interaction between the CO₂ beam and the material surface.