Laser Marking Polypropylene Battery Covers

International Battery (IB) is a green technology company providing environmentally friendly, large format, rechargeable lithium-ion cells and batteries that are designed, developed, and manufactured in the USA. Their cell unit arrays can be found in a wide range of places including many stationary applications such as energy storage for neighborhoods or utilities and in mobile applications such as military projects or local transit systems.

The outer covers of their battery cells are made from fire retardant polypropylene (FR PP) and require both in-process and after-the-sale traceability information for each cell. However, traditional adhesive printed labels did not adhere well to the polypropylene surface and were prone to lifting or peeling. While searching for a better, more permanent method of identification, they contacted Synrad and discovered that CO₂ laser marking was the perfect solution for them. The laser mark is permanent and easily read, and it also eliminates the consumables inherent in other marking processes, like ink or paper labels, which further reinforces International Battery's green business philosophy.

A CO₂ laser mark on FR polypropylene provides no physical color change; however, the polypropylene does vaporize cleanly which creates deep engraved marks with good quality. These permanently engraved, clearly readable marks are perfect for applications that require traceability over the lifetime of the product. There is also enough mark contrast for readable 2D codes allowing International Battery to implement a more efficient and robust identification system.

For this product application, an FH Flyer marking head was set-up with a 48-2 (25 W) laser and controlled by our WinMark Pro laser marking software. The marking head was equipped with a 200 mm focal length lens that provides a 290 um (0.011”) spot size. The identification mark object consisted of a 3.8 mm (0.15”) high Simple Stroke text object with eight numeric characters. For this process, mark velocity was set to 203 millimeters per second (8 in/sec) and laser power was set to a duty cycle equivalent of 25 W. The resulting eight-character mark was completed in a cycle time of 480 milliseconds per part.

Laser Cutting PET at the 9.3 μm Wavelength

Polyethylene Terephthalate, better known as PET or PETE, is a naturally clear plastic that provides a good boundary against many common liquids and organic materials while minimizing the absorption of plastic residuals into the item being packaged. As a result, PET is widely used in the manufacturing of food packaging and beverage bottles as well as other packaged consumer items.

Cutting PET at the standard 10.6-µm CO₂ wavelength may result in some amount of out-gassing due to incomplete absorption, which sometimes stains the edges near the cut surface while thicker materials may exhibit more edge melting at the cut. The less common 9.3-µm CO₂ wavelength is better absorbed by PET, resulting in much less out-gassing and melting.

For this particular application, the requirement was to cut an oval hang hole in 0.45 mm (0.018”) thick PET packaging. Because the PET product package was so thin, a marking head was used with no assist gas. The application setup consisted of a 9.3 µm version of our Firestar ti60 laser and an FH Flyer marking head (equipped with a 125 mm HP focal length lens)—all controlled by our WinMark Pro laser marking software. This setup produced a focused spot size of 158 µm (0.018”) at the cut surface.

For the hang hole we created a 42 mm x 14.5 mm (1.65” x 0.57”) ellipse using WinMark’s Circle Tool. For this object, the Power property was set to a duty cycle equivalent of 60 W and the Velocity was set to 178 millimeters per second (7 in/sec). The resulting cycle time to cut each hole was 580 milliseconds.

The resulting cut edge has very little residue or vapor deposition from the cutting process compared to an identical 10.6 µm wavelength laser cutting setup using the same parameters. In this case no cut velocity differences were seen between the two wavelengths–the only difference was better cut quality due to the increased absorption at 9.3 µm.

For more information about SYNRAD's new line of 9.3 µm CO₂ lasers click here. We have also just released a line of 10.2 µm lasers. Click here for 10.2 µm model availability and specifications.

Q-Mark Fiber Laser Marking System

Occasionally, the Synrad Applications Lab receives a processing request where the CO₂ wavelength does not interact effectively because of specific absorption characteristics of the material under test. A shorter wavelength laser is often more effective for processing these materials, which include metals like bare aluminum, copper, and brass or plastics that require a distinct color change.

In partnership with our sister GSI Lasers company, Quantronix Lasers, we can now recommend the Q-Mark 20W Fiber Laser Marking System. The Q-Mark fiber laser is a 20 watt Yb (Ytterbium) laser with an output at 1062 nm (higher powers are available).

This Class 4 marking package includes the computer and laser control unit in a rack mount chassis, a monitor, the marking head (along with mounting bracket), a 15 foot fiber umbilical, and Q-Mark Design Commander software. For high-level automation, an optional I/O package is available. The marking head includes a visible diode pointer and supports a flat-field lens assembly with your choice of either 3.6”, 5.6”, or 11” square mark fields.

Quantronix’s Design Commander laser marking software has a full suite of drawing tools, supports TrueType fonts and popular 1D and 2D codes, includes import capability for both vector and raster files, and provides several hatch fill options. In addition, Design Commander features a visual Flow Control Editor that allows you to drag and drop I/O, database, formula, DLL, and flow control (conditional logic) elements to fully automate the marking process.

For more information, contact Synrad at 1.800.796.7231 and ask for Bill Stull or contact Quantronix at 1.800.289.7707 and ask for Siva Thangarajah.