Additives optimize medical plastics for laser-welding assembly methods

Laser welding

Chemicals company Clariant (Muttenz, Switzerland) unveiled polymers formulated for laser-based assembly methods in medical manufacturing operations at this week’s co-located Medical Design & Manufacturing (MD&M) and PLASTEC West event in Anaheim, CA. The new Mevopur materials incorporate additives that optimize the laser-welding process.

“The medical device industry is moving away from assembly methods such as solvent welding, which can leave residues, and arc welding in favor of laser welding,” Stephen Duckworth told PlasticsToday from the company’s booth. “We are seeing this across multiple application areas, from drug-delivery devices and diagnostic products to dialysis systems,” added Duckworth, who is Head of Segment Healthcare Polymer Solutions, Mevopur.

Eliminating the use of solvents and reducing liability are the twin forces driving adoption of laser welding in the medtech industry, according to Duckworth. Laser welding also brings speed and reliability to the production process and can handle complex structures, “but it raises some interesting challenges,” added Duckworth, in terms of energy absorption. “The outer surface still needs to look attractive in whatever color you have in mind, but it has to be transparent to laser energy,” he explained. Because medical devices are frequently made of transparent or translucent materials, the polymer’s ability to absorb the laser energy often needs to be enhanced using additives.

Clariant has offered these types of  additives for many years, and in 2016 the company began using them in Mevopur masterbatches and compounds for laser-marking applications. However, laser marking involves only one polymer, whereas laser welding involves two, one of which is transparent to the laser energy while the other absorbs it to create the weld. The process is further complicated by any pigments or fillers, which can change the way the plastic reacts to the laser.
“Different polymers absorb laser energy in different ways, and so this becomes a formulation exercise—understanding the basic parameters and coming up with a ‘systems approach,’” explained Duckworth. “That is what we have done.”

At MD&M West, Clariant displayed welded products that appear to involve two parts made of identical materials. In fact, two different formulations were developed to achieve laser transmission in one and absorption in the other so that they can be reliably welded together.

Another important factor in achieving a good weld is even distribution of the additive throughout the polymer matrix of the final part. In some cases, a concentrate or masterbatch can be dosed at the injection molding machine, which than mixes it into the polymer melt before molding, but this is not always ideal for dispersing the concentrate into the host polymer. In some applications, the machine, the material or the part design may cause inconsistent distribution and lead to unreliable welding, said Clariant.

To remedy this, Clariant produces compounds in which the laser-absorbing additive, along with any other pigments or additives, are optimally distributed via highly efficient compounding lines. The injection molder can use this all-in-one material without further dilution, knowing Clariant has already taken care of the formula and quality control.

Like all Mevopur masterbatch concentrates and finished compounds, the laser-friendly materials are manufactured at a dedicated facility in Lewiston, ME, and at two other sites in Malmo, Sweden, and Singapore. All three plants have been certified to ISO 13485:2016. Device manufacturers can rest easy knowing that Clariant processes are controlled, consistent and compliant from the USP Class VI, ISO 10993 pre-tested raw material ingredients to the final product, said Clariant.

Image courtesy Pixel_B/Adobe Stock.

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