Originally Published EMDM November/December 2002
PRODUCT UPDATE
Light-Cure Cyanoacrylates Optimize Device AssemblyRapid cure rates and shadow curing capabilities are among the reasons that device manufacturers are bonding with UVCAs.
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| Light-cure cyanoacrylates can be dispensed in a variety of ways, but they are especially prized for high-speed assembly processes because of their rapid curing properties. |
Introduced in 1999, ultraviolet-light-cure cyanoacrylate (UVCA) adhesives were initially developed to bond needle assemblies. Since then, the adhesives have been used in several other medical applications where rapid tack-free cures, high bond strength, biocompatibility, and shadow curing properties are desirable. Christine Salerni, medical market manager for Loctite Corp. (Rocky Hill, CT, USA), published a technical article on the use of UVCAs for medical device assembly in the June 2002 issue of our sister publication Medical Device & Diagnostic Industry. (The article can be viewed on-line at www.devicelink.com/mddi.) Salerni discussed some of the issues she addressed in her piece during a recent interview with EMDM.
An alternative to traditional adhesives, UVCAs combine the advantages of cyanoacrylates and light-cure adhesives with few of their limitations, according to Salerni. "Because they were designed to overcome the limitations of those types of adhesives, UVCAs have very few drawbacks," she adds.
"Light-cure materials are probably the most widely used adhesives in the medical device manufacturing market," says Salerni. "But if you have an application in which the light can't get to the bond line, that adhesive will never cure. Because UVCAs are similar to traditional CAs, they will cure between small gaps in opaque parts, but they can still be cured in exposed areas by the use of UV light," explains Salerni. This takes on significance when parts with exposed and shadowed areas are being bonded. "In the past, manufacturers would have had to use two different adhesives. With a UVCA, they can accomplish both tasks with one product," says Salerni. She cites the assembly of an infusion device as an example.
To bond a semiflexible, clear PVC tube to an angled stainless-steel cannula with an approximate engagement of 0.75 in., a light-cure acrylic adhesive is used to expedite processing and minimize work-in-process time. The tube-and-cannula assembly is then positioned through the internal diameter of an opaque white butterfly hub and secured with a cyanoacrylate adhesive to ensure cure, even in shadowed areas. By using a UVCA material, both assembly operations can be accomplished with one adhesive, reducing handling and overall production time.
Preventing Blooming
The rapid cure time of UVCAs eliminates the need for accelerators, which are traditionally used with cyanoacrylates to prevent blooming or frosting (the formation of a white haze or powdery residue on the bond line). Catheters are susceptible to blooming, notes Salerni, and the materials' rapid fixture and ease of use have made UVCAs the adhesive of choice for securing latex balloons to either rigid PVC or polyurethane tubing.
Catheters are packaged immediately after assembly, often resulting in excessive blooming within the sealed container, says Salerni. "The blooming is caused by adhesive that has squeezed out of the bond joint. Replacing traditional cyanoacrylates with UVCAs makes it easier for the manufacturer to maintain the rapid assembly process without worrying about the potential for blooming," according to Salerni.
In her article, Salerni also cites an application involving surgical pressure transducers, where the use of UVCAs accelerates assembly and enhances aesthetics. "PVC cabling is usually bonded to the polycarbonate housing of the transducer with traditional light-cure adhesives," she writes. In some applications, however, the adhesive can migrate into shadowed areas where it does not cure. To prevent this, manufacturers may use a traditional cyanoacrylate adhesive in conjunction with an accelerator to speed the cure. The problem that arises, according to Salerni, is that the accelerator creates a secondary operation and often produces a whitening of the bond line. By switching to a light-cure CA, "transducer assembly can be accomplished rapidly with a single adhesive and without the aesthetic problem presented by the accelerator," she explains.
Performance Benefits
Although UVCAs are well suited for manual and semi- and fully automated dispensing methods, their rapid curing capability without the use of heat or parts racking results in significant performance benefits for high-speed assembly processes. In addition, UVCAs provide a high bond strength to commonly used device plastics, says Salerni.
"Bonding polyolefins, for example, is challenging because they are such chemically inert materials," explains Salerni. Unlike typical light-cure acrylics, UVCAs react positively to specialty primers developed to enhance bond strength, she adds. "Primers can increase adhesion to those types of substrates tenfold. You can go from a strength of 50 psi to more than 1000 psi with the aid of primers on those hard-to-bond plastics."
As with any adhesive, Salerni recommends caution when considering the use of UVCAs on a device that will be repeatedly autoclaved. A maximum of two cycles is recommended to maintain the material's performance properties. UVCAs will maintain their performance characteristics following exposure to all other forms of sterilization, says Salerni.
Currently, only two viscosities are available, but the product line will almost certainly be expanded in the near future. "We are doing further development work in the UVCA field," says Salerni, "but I can't say whether it will be related to more viscosity versions or to detection issues."
For more news about developments in light-cure cyanoacrylates, as well as other solutions for device assembly, keep reading. Medical-grade adhesives from several leading suppliers are described in the following pages of this section.
More Products:
Panacol-Elosol GmbH
Devcon
Adhesives Research Ltd.
Loctite Corp.
Wellomer GmbH
Collano AG
Norgesplaster A/S
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