Adhesives that are specially formulated for medical devices can introduce design benefits, achieve better performance and quality, improve assembly rates, and prove cost effective, writes Bob Goss. Basically, adhesives for the medical industry fall into four categories:
Instant adhesives - Cyanoacrylate (CA) adhesives cure in seconds and are available in viscosities ranging from water-thin liquids to thixotropic gels. They provide excellent adhesion to a wide variety of substrates including ABS, PVC, latex, polycarbonate, styrene, acrylic and thermoset plastics. By using a primer, even difficult to bond materials such as polypropylene, polyethylene and other low-energy rubbers and plastics can be bonded. Typical applications include bonding balloon to multi-lumen tubes in angioplasty, thermo dilution foley and high pressure catheters. They can also be employed to bond needles to tubing in winged infusion sets and fistulas.
Light-curing instant adhesives - These combine the fast cure of CA with the advantage of cure-on-demand UV technology. This is especially helpful where a secondary moisture cure is required – allowing the adhesive to harden in shadowed areas. They are used for join stainless steel cannulae to non-transparent hubs and syringes, bonding catheters, oxygen concentrators, blood gas analysers and filters.
UltraViolet and Visible Light Curing - One component, solvent-free adhesives that are available in viscosities ranging from 100 to 10,000mPa.s and which cure rapidly on demand. They are designed for automatic dispensing systems where high strength, clear bondlines and a total seal are required. Applications include cannulae/hubs, glass assemblies, sub-assemblies in blood pressure transducers, surgical masks, blood collection devices (illustrated), tubing in IV sets and bonding insulin glass syringes to metal needles.
Structural Adhesives - High peel and shear strength is provided on a variety of plastics, metals and glass. When cured these thermoset plastics provide outstanding thermal and chemical resistance, alongside high cohesive strength and minimal shrinkage. These are used for bonding/sealing endoscopes, catheters, artherectomy devices and dental instruments.
Bob Goss is with Henkel Loctite