Marking 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 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.

Improving Cut Quality in Polycarbonate Film Using the 9.3 µm Wavelength

Polycarbonate usually discolors and chars when cut at the typical 10.6 µm CO₂ wavelength due to chemical degradation of the plastic because of thermal input into the material. However, this discoloring and charring can be minimized or eliminated when processing very thin films that can be cut quickly in combination with a CO₂ laser wavelength that has the best absorption into that particular material.

For this particular application, the request was to cut a clear 250 mm (0.01”) thick polycarbonate film as cleanly as possible. The percentage of laser power transmission was measured through this particular film for several CO₂ laser wavelengths that Synrad manufactures: the standard 10.6 µm wavelength as well as the 9.3 µm wavelength, which can be better for processing some types of plastic such as PET. Measurements show that the 10.6 µm wavelength has a 7% transmission of power through the film while the 9.3 µm wavelength only had 1% transmission. This indicates there would be better absorption and penetration depth when a 9.3 µm wavelength laser is used.

To test this, a side-by-side comparison of the cut edges was done at each wavelength. Since the material was so thin, a scan head system was used with no assist gas. The Synrad test setup consisted of  two Firestar v30 lasers: one at 10.6 µm and one at 9.3 µm in combination with FH Flyer marking heads (equipped with 125 mm HP focal length lenses)—all controlled by our WinMark Pro laser marking software. This setup produced a focused spot size of 180 mm (0.007”) at the cut surface.

Using the 10.6 µm wavelength laser, the polycarbonate film was cut at a rate of 50 millimeters per second (1.97 ips) when 11 W of laser power was applied. However, at a wavelength of 9.3 µm, only 8 W of power was required to achieve the same cut velocity of 50 mm/s (1.97 ips) due to the better absorption of power. At 11 W of power, the velocity increased to 70 mm/s (2.76 ips). In addition, to the velocity increase (or power decrease), there is also a significant improvement to the cut edge at 9.3 µm —the yellow thermal effects of the cut edge seen at 10.6 µm were eliminated and the burr on the cut edge was also significantly reduced.

Synrad Laser Models

ynrad lasers are released in multiple configurations - OEM, keyswitch or both. All Synrad lasers are released as OEM models and most are also offered in keyswitch versions. To designate model configurations, each laser is assigned a laser model code that is imprinted on the laser. That code includes the laser's functional category (OEM or keyswitch), cooling method and laser version. The sample laser model guide below displays how to translate the code for a Firestar ti60. To learn more about laser codes and laser model availability, visit our Laser Model Information page.