|An esophageal stethoscope contains a critical dip-molded component that is used to house the sensitive internal components and electronics required to monitor temperature and sound.|
While molding process such as injection molding play a crucial part in the manufacture of medical devices and components, a lesser known, but no less important, technology is dip molding. From nasal cannulas, tubes, and Y-connectors to tissue-collection sacks, stent covers, and catheter balloons, the technique has distinct advantages over injection molding, as Chuck Brider, operations manager of Molded Devices Inc. (Riverside, CA), explains in the following conversation.
Dip molding is defined as a process by which a mold is dipped into a polymer to create a molded component. While plastisol—a suspension of PVC particles in a plasticizer—is the most commonly used dip-molding material because it is easy to process and affordable, other materials such as latex, neoprene, and urethane can also be used in dip-molding applications. In fact, latex is especially suitable for molded medical device components because it is more robust than plastisol and can tolerate a wider high-to-low temperature range. And in addition to its greater elasticity, latex can withstand more chemical abrasion than plastisol.
MPMN: What are the types of medical devices that would benefit from dip molding, and what is preferable about using dip molding in contrast to other molding processes for medical device applications?
Brider: The advantage of dip molding is that the tooling is inexpensive and that it can be used to perform short runs because of the low tooling costs. As a result, many parts can be produced for pennies apiece. The technique is also good for manufacturing thin-wall parts in a cost-effective way. Consequently, it can be used to manufacture such medical devices as balloons.
When using such materials as PVC or plastisol, dip molding can create devices with walls ranging in thickness from 0.008 to 0.010 in. When using latex, you can achieve wall thicknesses down to 0.004 or 0.005 in. Thus, the technology can make very thin-wall parts. In addition to the technology’s ability to produce thin-wall components, it works with such shape-memory stretchable, elastic materials as latex and more-rigid materials such as PVC.
MPMN: Step by step, how is the dip-molding process performed?
Brider: Dip molding is a very simple process. First, the tool has to be heated. When that step has been completed, the tool is inserted into the plastisol or latex, and then it is placed in an oven for curing. Plastisol or PVC cures much faster than latex—minutes at the most. Latex, in contrast, cures at a much lower temperature and often has to be cured overnight.
MPMN: Why would a manufacturer decide to use dip molding as opposed to a more common technique such as injection molding?
Brider: It’s a lot less expensive to use dip molding than injection molding. The equipment is pretty simple. For example, a fairly sizable oven is available for less than $50,000. In addition, water tanks, dip tanks, and tooling are relatively inexpensive. Moreover, tooling is usually available for prices in the high hundreds to the low thousands of dollars, depending on how many tools you need to make a part. While cheap injection-molding tools cost at least $10,000, expensive dip-molding tools cost perhaps $2000.
Published in MPMN, November/December 2012, Volume 28, No. 8
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