Conair Group is teaming up with Davis Standard and Zumbach Electronics to coextrude a thermoplastic polyurethane (TPU) catheter tube at the MD&M West 2018 trade show, demonstrating how active pharmaceutical ingredients (APIs) can be incorporated in a thin layer on the outside of the plastic tube. Typical applications could include the addition of an antimicrobial outer layer to prevent formation of biofilm that can cause infection, or an anticoagulant to avoid catheter thrombosis.
MD&M West is being held at the Anaheim Convention Center, February 6 – 8. The demonstration in booth #3839 will highlight the latest technology in extrusion, sizing/cooling, gauging, cutting, and quality control.
“The same technology that can add color to the surface layer of medical tubing also can be used to apply a pharmaceutically active ingredient like silver sulfadiazine,” explains Bob Bessemer, Sales Manager, Medical Extrusion for Conair. “For the demonstration, we are using color instead of an API, but the process is exactly the same.”
The main body of the catheter tube – a single-lumen adult PICC line with an outside diameter of just 0.067 inch — is made of clear TPU delivered by the primary 3/4-inch Davis Standard extruder. A second 3/4-inch extruder delivers the blue resin representing the active layer. The inner/outer layer ratio is approximately 80/20. Each extruder feeds a positive displacement melt pump, which controls polymer flow to a cross-head co-extrusion die supplied by Guill Tool & Engineering.
“When the line includes single-screw extruders, the API would need to be pre-compounded into the resin or delivered as a masterbatch,” notes Bessemer, “but if you use a twin-screw extruder, for the pharmaceutical-layer material, you can actually combine the neat API into the polymer in-line with the rest of the process.” American Leistritz, which manufactures twin-screw extruders, is also participating in the demonstration.
As the two-layer tube exits the die, it enters a Conair MedVac™ vacuum-sizing/cooling tank. The vacuum creates pressure inside that tube that helps stabilize dimensions and prevent cooling water drooling out of the tank’s feed opening from affecting the critical surface finish of the tube. An ultrasonic gauge inside the tank monitors the wall thickness and the thickness of each of the two layers (to 0.0001 inch resolution), while a Zumbach Electronics 3-axis OD laser gauge, positioned downstream from the tank provides not only closed-loop dimensional control, but also displays the tube for concentricity adjustments. The data from these gauges is used to control melt-pump output, as well as puller speed and vacuum to maintain layer thicknesses and other critical dimensions. A vision system is also incorporated into the line to detect imperfections, including color inconsistencies, gels, surface scratches and more. The system communicates in real time with quality controls to automatically separate good vs bad tubes in-line.
Next, the tubing passes through a Conair MedLine® puller/cutter. The puller portion of the unit consistently pulls the tubing down the line during sizing and cooling. The rotary-knife cutter slices the tube precisely to the specified length. Cut lengths are then carried away on a Conair medical takeaway belt conveyer. Once on the conveyor, cut pieces that don’t meet quality standards – based on the OD/ID gauge readings and the inline machine-vision – can be removed from the production stream with a puff of compressed air. In fact, the MedLine puller/cutter has a scrap/QC mode that accepts all three inputs (from the wall-thickness gauge, the laser OD gauge and the cameras) and automatically sets a length offset so the cutter ‘knows’ when the defective piece will reach it. Then the cutter can be programmed either to cut faulty tubing differently from good product or not cut at all, or it can change the way defective section is handled by the conveyor.
MEDLINE AUXILIARIES ON DISPLAY
In addition to the downstream extrusion equipment mentioned above, the demonstration makes use of other equipment from Conair’s clean-room-ready MedLine product family. All MedLine products are based on proven Conair designs, but they have been specially sized, configured, documented and supported for use in cleanrooms and other controlled environments.
To prepare the TPU resin for extrusion, both extruders are equipped with a Conair MicroWheel MW1-0.2 dryer. With a 5.6-L (0.2-cu-ft) hopper, it is the perfect solution for processes that don’t need the capacity of a large dryer and hopper, but still need the efficiency and reliability of Conair’s desiccant-wheel drying technology. Both of the dryers are fitted with MedLine ML1 MiniLoaders. These self-contained units have an integral vacuum motor to draw resin from machine-side storage. The straight through tube loader body ensures smooth flow, even with the small quantities typical of medical molding.
Two units in Conair’s MedLine range of TW-P Thermolator temperature controls (TCUs) are supplying temperature-conditioned water to the demonstration line. One TCU is used to match the extruder feed-throat temperature to ambient conditions so that condensation does not occur and degrade the pre-dried resin. The other TCU supplies tempered (warm) water to the sizing/cooling tank to control heat removal from the tubing. Both units are configured for cleanroom operation, with one having an all stainless-steel housing and the other painted RAL 9003 white.
Providing chilled water to the TCUs is a MedLine EP1A-03 portable air-cooled chiller, which features an easy-to-clean RAL-9003-white painted housing, and nonferrous internal components (evaporator, pump, reservoir and piping) to resist corrosion. It has a compact footprint with easy-to-access interior, and a control that provides precise temperature control and extensive diagnostics.
The Conair Group (www.conairgroup.com) is a leading global supplier of auxiliary equipment for plastics processors, including resin drying systems, blenders, feeders and material-conveying systems, temperature-control equipment and granulators. Extrusion solutions include line-control systems, film and sheet scrap-reclaim systems and downstream equipment for pipe and profile extrusion. Over 450 individual products solve problems, save energy, cut waste and are easy to use. Conair is also an international company, with long-standing operations in Europe, Asia and Latin America. The industry’s most complete product line, top-flight engineering and unbeatable service, all combine to give processors the confidence they need to succeed in today’s competitive global marketplace.