Medical devices are frequently coated with lubricants, drugs, or other fluids, and the best way to apply these fluids may be with low-volume, low-pressure (LVLP) coating systems. They are accurate, precise, cost effective, and can handle different coatings and viscosities. Typical tasks include lubricating syringes so the plungers slide smoothly, dispensing solutions onto point-of-care test strips, and applying coatings to membranes.

Common problems

Most coating methods involve dipping the device into a coating, airbrushing it on, or using standard spray valves. While these methods can turn out acceptable results, manufacturers often report several shortcomings, such as:

• A lack of process control. For many medical devices, coating placement, volume, and thickness are critical. Manual processes or spray systems with only coarse adjustment may not give the controlled, consistent coverage needed for predictable results and dependable device performance.

• Low production rates. Prototypes and short production runs that might be made in a lab or R&D facility rather than a production line mean spending extra time fine-tuning the coating equipment for acceptable results.

• Unacceptable reject rates. Rejects, lower yields, and reduced profitability can stem from uncoated or partially coated areas, variations in thickness, or unintended application on nearby components.

• Waste, downtime, and maintenance. Overapplying expensive coatings increases costs and requires extra cleanup time. Standard coating systems can be difficult to set up and adjust, may not turn out uniform results, and often contain seals and O-rings that wear out and leak. Some spray systems clog frequently. Any of these can waste time and money.

How LVLP works

LVLP systems use a precision spray valve, a microprocessor-based valve controller, and a fluid reservoir. They operate on compressed air and electricity, and control the amount of material applied by controlling valve-open time, fluid pressure, and stroke setting.

The air-actuated needle valve has two separate air inputs: One for valve actuation and one for fluid distribution. A low fluid-flow rate needs low air pressure (typically only 1 to 3 psi) to apply fluids in a controlled spray. This ensures high transfer efficiency (the amount of material deposited on the substrate, compared to the amount of material leaving the nozzle) and minimizes overspray or mist. And changing the valve nozzle and air cap creates different spray patterns.

The valve controller simplifies setup, regulates the valve, and allows adjusting nozzle pressure for best results with different materials and viscosities. Another advantage of a dedicated valve controller is that adjustments are quick and done at the dispensing station without having to reprogram a distant controller.

When operating, air lifts a piston inside the valve, retracting the needle from its nozzle seat, letting fluid flow leave the nozzle. Low-pressure nozzle air simultaneously flows through an annulus around the nozzle, creating a pressure drop that breaks the fluid into a spray of fine droplets.

At the end of the dispensing cycle, actuating air is shut off and the needle drops down into its seat, halting the fluid flow. Nozzle air flows for a few milliseconds longer to ensure a clean cutoff and prevent clogging.

How to cut coating problems

The technology's advantages include:

• Better process control. The combination of precisely regulated nozzle pressure, calibrated stroke control, and high transfer efficiency creates an even, consistent coating.

  Applications can be either timed or continuous. For timed applications, spray periods can be adjusted in increments as small as 0.001 seconds. In addition, nozzles with a variety of configurations are available to accommodate different substrates and spray patterns.

  In addition, all dispensing parameters can be documented and easily duplicated, so results are uniform.

• Faster production, fewer rejects. Consistent coating placement and thickness means fewer rejects, at speeds of to 400 parts/min.

• Less waste. LVLP's high transfer efficiency places material only where it is needed, without waste or overspray on surrounding areas.

• Less downtime and maintenance. LVLP systems are simple to set up and install, and feature a wear-resistant, low-maintenance design. Using a microprocessor-based controller to regulate valve operation minimizes setup time and allows making adjustments quickly at the coating station, without stopping production.

• A cleaner, safer work environment. LVLP equipment provides a sealed system, eliminating operator contact with the fluid, minimizing mist and vapors, and keeping material off surrounding surfaces.

  LVLP technology offers medical-device manufacturers an accurate, cost-effective coating method to increase yields, reduce costs, and improve control. The systems are simple to install and operate, and can improve a wide variety of coating processes.

Make Contact
EFD Inc., (800) 556-3484, efd-inc.com