Marking HDPE at the 9.3 μm CO₂ Wavelength

High-density polyethylene, also known by the abbreviation HDPE, is a strong and robust thermoplastic used in a large variety of applications. Some of the most common uses for HDPE are for blow-molded heavy-duty jugs, barrels, cartons, and bottles. These storage containers are used in industries ranging from the beverage industry for bottling milk to the automotive industry for storing various fuels.

When marking HDPE containers, the standard 10.6 μm CO₂ laser wavelength creates a very shallow surface mark with no color change. It has very low visibility from a distance and can only be seen at certain viewing angles where the light catches the slight surface depth. This type of mark is preferred when the packaging information must be unobtrusive.

On the other hand, the 9.3 μm CO₂ wavelength is better absorbed by the HDPE material. The material still doesn't change color, but the mark is much deeper and it catches the light easier making it visible from farther away and at more viewing angles. The 9.3 μm mark is better for marking expiration dates or packaging information that must be easily read by the user.

To compare HDPE's absorption behavior, two identical Flyer marking heads equipped with 125 mm focal length lenses were attached to 10.6 μm wavelength and 9.3 μm wavelength Firestar v30 lasers. The focused spot size of each setup was 180 μm (0.007"). Both Flyer heads were controlled by our WinMark Pro laser marking software configured using identical mark file parameters of 3.2 mm (0.125") high Arial TrueType® text marked at a scan speed (Velocity) of 203 millimeters per second (8 ips). The only difference was the duty cycle percentage (Power), which was individually set so each laser produced 18 W of output power. Each resulting mark took 1.47 seconds to complete.

When these identical marks were completed on a sheet of white HDPE, the side-by-side differences in visibility were obvious. The 10.6 μm mark was very faint and shallow whereas the 9.3 μm mark was significantly deeper and as a result was much more readable.

Cutting Decorative Cards

Thin materials like paper are often laser cut using a marking head. Because these materials are cut quickly and generate little debris or melting, there is no need to use a traditional cutting head and assist gas to cool the cut edge and blow debris away.

Laser cutting is an extremely flexible process because it is very easy to change designs and patterns unlike methods such as stencils and dies where it is very cumbersome to change designs quickly or produce small batches.

Laser cutting with a marking head lends itself well to customized cards and decorations where individual cards or small batches need to be personalized.

For this application, red-inked 80 lb text weight paper was used to create laser cut holiday cards. The card cutting equipment consisted of a Synrad 30 W laser along with a Flyer marking head, equipped with a 200 mm focal length lens, and Synrad's WinMark Pro software. This setup produced a focused spot size of 290 μm (0.011") on the paper. The artistic cut file was created as a vector graphic and imported into WinMark Pro. The imported object's Power value was set to a duty cycle equivalent of 30 W and the Velocity property was set to a speed of 267 millimeters per second (10.5 in/sec).

The resulting decorative card measures 127 mm × 50.9 mm (5.2" × 3.8"). The 80 lb text weight paper cuts cleanly and the intricate design exhibits very good edge quality. As seen in the accompanying video, the cutting process takes only 12.41 seconds to complete.

Evolution Series lasers being phased out

After twenty years of production, the evolution™ series will be phased out at the end of this year. The evolution series, consisting of 100, 125, 200, and 240 watt lasers, were developed in the early 1990's and are no longer cost effective to manufacture. These lasers use older technology components that are expensive and, in some cases, are being discontinued by suppliers. In addition, many critical electronic parts are not available in RoHS-compliant versions.

Our firestar line of 100, 200, and 400 watt lasers, first introduced in 2002, have proven themselves to be reliable, dependable replacements for evolution lasers with the advantages of being smaller, lighter, less expensive, and more energy efficient. For example, firestar ti100 and t100 lasers have rise/fall times that are twice as fast (75 µs) as the evolution 100. The ti100 offers integrated RF in a package measuring only 21.4" × 4.1" × 5.9" while the t100 is available in a fan-cooled version. Our f-series 100, 200, and 400 watt lasers all feature integrated RF, making them easy to integrate into flatbed cutters, robotic arms, or gantry-based systems. These firestar lasers also include built-in tickle pulse generation, color-coded status LEDs, and "industrial-strength" I/O.

While we will continue to service evolution lasers for several more years, production of new lasers will end in 2012. For those customers who wish to purchase additional evolution lasers for existing product lines or as spares, please place your order no later than September, 2012. Please contact your Regional Sales Manager or Synrad Distributor to place an evolution order or to discuss the specifics of replacing evolution with a new firestar series laser. See these links for further information, manuals, and outline & mounting drawings as an aid in comparing the evolution series with our firestar t-series, ti-series, and f-series lasers.