Laser welding plastics for medical applications

The innovation in laser welding technology

The innovation in laser welding technology makes it possible to join two optically clear plastic parts for the first time. Previously, laser welding required one clear or “transmissive” plastic part and one dark or “absorptive” plastic part so the laser energy could pass through the clear plastic and be absorbed by the dark part.

The new process “clear-on-clear” 

The new process, called “clear-on-clear,” is particularly timely, as patient-point-of-care, in vitro diagnostic test kits, which require optically clear test cartridges, are being used for rapid detection of COVID-19 antigens and antibodies. The new technology also opens up new design possibilities by allowing the use of a wide range of polymers for medical devices, drug delivery systems, and other in vitro testing products.

The new process has an ultrasonic deposition technology. The deposition process “pre-treats” one of the clear mating parts with a biocompatible laser absorber comprised of pigment dyes or carbon black microparticles suspended in a carrier fluid like isopropyl alcohol or acetone.

The laser absorber can be delivered to the surface of one of the clear mating parts through a variety of methods. It can be master-batched in the resin prior to molding, applied using a pad printing process or, for the greatest precision, spray-deposited on one of the plastic parts using ultrasonic spray-deposition equipment. In the latter case, the laser-absorbing dye gets deposited on the surface of one of the parts using a spray pattern as small as 0.5 mm in width.

By applying a solvent-based laser absorber to the mating surface of one part, laser welding technology can now join clear-on-clear parts with exceptional aesthetic and functional results.

Operation of the process “clear-on-clear”

During welding, the particles absorb laser energy and release heat that conducts through the weld zone of the two parts and bonds them together under a precisely controlled clamp force.
The ultrasonic spray-deposition system is described as being “designed to deposit minute quantities of pigment dye, measured in microliters, with coating thicknesses that are evaluated in the hundreds of nanometers on the surface of the coated parts.”
The new spray-deposition process used to deposit ultra-thin, ultra-precise coatings on medical stents. The laser-absorbing properties of the new biocompatible solvent and pigment dye combination light-absorbing coatings used on photovoltaic cells. This new technology involved an iterative process that transitioned the coating/deposition/weld process from absorptive-to-transmissive materials, culminating in the final transmissive-to-fully-transparent materials.
The microfluidic parts used in today’s medical devices must be reliably bonded while maintaining precise, consistent dimensions along minute flow paths. To develop the technology required for such a precise bonding process. The new clear-on-clear plastic laser-welding technology can reliably produce complex fluid paths.

Two clear mating parts can now be laser-welded using an innovative new welding process that can reliably produce complex fluid paths while maintaining superior aspect ratios.