Coding on Ink Coated Card Stock Packaging
The CO2 laser wavelength is very well suited to ablating many common inks used on card stock packaging for consumer items because the CO2 wavelength typically bleaches out the ink, leaving behind a crisp white mark. This type of mark is achieved at very quick velocities even at low laser power and is perfect for marking ID information or expiration dates.
In these types of applications, laser marking has several advantages over traditional ink and adhesive labels. Unlike adhesive labels, lasers create a permanent mark that cannot be removed and compared to inkjet printers, a laser marking produces a higher quality mark while eliminating consumables and maintenance issues.
This particular application demonstrated the laser’s ability to mark expiration dates at high speed on varnished, ink coated card stock. The setup consisted of a Synrad 48-1 (10 W) laser and an FH Flyer marking head equipped with a 125 mm focal length lens and controlled by Synrad’s WinMark Pro laser marking software. The lens choice provided a focused spot size of 180 mm (0.007”) on the inked card stock. The mark file contained two lines of 3.8 mm (0.15”) high “Little” stroke text with the Power property set to a duty cycle equivalent of 10 W and the mark Velocity property set to 1778 mm/sec (70 in/sec).
The resulting high-contrast mark was completed in a cycle time of 60 milliseconds. The laser mark bleaches the ink coating providing a crisp white mark which has excellent contrast with the ink color. In a tracking application, these packages could be marked at a rate of approximately 16 cartons per second.
This expiration date code was marked on 12-point coated card stock using 10 W of laser power at a velocity of 1778 mm/sec (70 in/sec) in 60 milliseconds.