Decorating thermoplastics with laser marking has taken longer to gain acceptance than was expected a decade ago. Nonetheless, laser technology has been winning converts at the expense of ink marking technologies such as pad printing and inkjet printing in certain markets.
So-called “non-aesthetic” applications are estimated to account for some 90% of Kunststoff Lasermarkieren today. Such markings, typically made with a sealed CO2 gas laser, include part numbers, date of manufacture, and expiration dates. Often the marks are dark letters and numbers on transparent or light-color backgrounds or off-white marks on dark backgrounds.
“Aesthetic” laser marking is the 10% of the market that has lots of potential for growth in replacing ink-based technologies. These are typically white markings on darker engineering resins, made with solid-state Nd:YAG lasers that are easily programmable and allow for very crisp marks in unlimited shapes.
Examples of successful commercial applications include ABS keyboards for business machines; HDPE, PP, PET, and PVC rigid containers and closures; nylon and PBT automotive and non-automotive electrical connectors; and underhood components such as fuse boxes and gas caps. Still others include TPE ear tags for swine and cattle, appliance parts like HDPE on/off knobs on washer/dryer units, and PVC plumbing parts such as elbows and fittings.
Emerging applications include light-switch covers, cosmetics packaging, toys, and auto-interior buttons and knobs on doors and instrument panels. The latter has become an important market focus in the last couple of years.
Technical advances in computer-programmable laser equipment over the last decade have been followed by development of more laser-markable grades of resins as well as custom colorant and additive packages for use with a variety of plastics from polyolefins and ABS to PVC, polyesters, PC, nylons, acetal, and TPEs.
Today’s laser-markable plastics offer high contrast and, in many cases, a contrasting color rather than just black or white. Even degrees of shading are now possible. These more varied color effects are one of the concurrent trends that are bringing renewed interest in decorating plastics with lasers, according to marketing manager Patrick Schlather of Rofin-Baasel, Inc., a leading supplier of plastics laser-marking equipment.
Product traceability has become a major driving force behind this technology, notes Rick Stevenson, sales manager at Control Microsystems, another laser supplier. Product identity data and operating instructions that last throughout the product’s life, often in more than one language, are ever more common requirements. Information on production history and specifications are particularly crucial for parts that have the highest liability in case they fail, such as electrical/electronic switch bodies.
Laser marking also satisfies the growing need to imprint greater amounts of data on ever-smaller plastic parts. For example, two-dimensional barcodes have been developed that have 10-times the data density of conventional barcodes. Marking these 2D codes requires more accurate and higher-resolution marking than had been adequate for previous barcodes. According to Schlather, laser marking meets these requirements with spot sizes and position repeatability in the range of 0.001 in.—performance that is difficult to match with pad or inkjet printers.
Marking equipment basics
While there is a wide array of laser sources available for decorating plastics, the sealed CO2 gas laser is by far the most widely used, followed by lamp-pumped, solid-state Nd:YAG lasers, and the more recent diode-pumped Nd:YAG configuration.
Most of these laser-marking systems use high-speed, beam-steered galvonometer marking technology. The steering system sweeps the laser beam using two computer-controlled mirrors, or galvonometers, that move the beam in x and y directions. Explains Robin Barbero, marketing director of Preco Industries, “When the programmed laser path is completed, a new part indexes into position, and the cycle repeats. Since the marking pattern exists entirely in software, no tooling or masks are needed.”
Software that allows marking of plastics with on-the-fly beam steering is also offered by several laser equipment suppliers. This is basically the same technique but applied to production situations with continuous motion such as conveyors or web converting, explains Barbero. “The advantage of such a system is that it can be easily retrofitted into existing production lines to maximize throughput. Encoder feedback is provided to the computer which makes appropriate adjustments to track the moving target in real time.”
Adds Schlather from Rofin-Baasel, “Current systems use straightforward graphics-creation software that can be easily programmed to mark unique data on each and every part on the fly.”
In recent years, programming, calibration, and troubleshooting of laser markers have become much easier, and marking speeds have increased greatly. Says Barbero, “Today’s software allows marking of more than 400 characters per second, compared with 40 type-size, single-stroke characters/sec 10 years ago.”
Most laser software has the capability for mark serialization, multiple types of barcode, and text of any type—including company logos. Using Windows-based “Help” functions, laser-marker suppliers have embedded service and calibration techniques along with troubleshooting software.
Another advance has been the development of systems that that can mark two parts simultaneously using one laser source. With the addition of another deflection head and a programmable beam splitter, a single laser can simultaneously mark two parts with the same information. Schlather points out this kind of system can also be used to mark a larger area without moving the part or tray of parts.