Adhesives Highlight Fast Processing Times

March 1, 2003

6 Min Read
Adhesives Highlight Fast Processing Times

Originally Published MPMN March 2003


Adhesives Highlight Fast Processing Times

Epoxies offer functionality and quick curing

Zachary Turke

Many medical devices are held together by one or more types of adhesive. And in today's world of specialization, it should come as no surprise that there are unique epoxies for almost every application. Whether you're trying to bond a cannula to a syringe hub, cement a lens in an endoscope, or produce disposables, chances are that some company makes an adhesive especially for that purpose. The following examples describe recent advances in adhesives that may be of particular interest to our readers.

For further information on these and other products, see the accompanying Buyers Guide. It provides a comprehensive listing of suppliers with complete contact information and highlights their core competencies

Adhesive improves syringe safety

The single-component 4E98 epoxy from Permabond improves adhesion strength between needle and hub.

In what is just one example of its many uses, an adhesive offered by Permabond has been employed to create a syringe that prevents reuse. In traditional syringe designs, the needle assembly is formed by bonding a steel cannula to a plastic hub. But the strength offered by conventional adhesives is not enough to prevent a determined party from separating the components for reuse, a practice that can spread disease. To overcome this shortcoming, Permabond's 4E98 adhesive was used to permanently bond a cannula directly to the syringe. Coupled with a novel plunger, this connection is enough to ensure that a syringe and its needle are rendered usable only once.

The 4E98 adhesive is a single-component epoxy that offers a tensile strength of 41.4 MPa and tensile lap shear of 14 MPa. Suited for bonding stainless-steel, polycarbonate, nylon, and polyimide substrates, the material is noncytotoxic and features a hardness of 85 Shore D. It withstands gamma irradiation, EtO, E-beam, and limited autoclaving sterilization, and is suited for manual, semiautomatic, and fully automatic application.

But according to its manufacturer, one of the epoxy's most appealing features is that it cures quickly at low temperatures. "The majority of heat-curable adhesives require temperatures of at least 90° to 100°C," explains business development executive Laurie Gibbons. "But many plastics used in medical devices can't withstand these high temperatures, and those that can often experience problems with adhesive flow," she adds. The 4E98 adhesive cures fully after 60 minutes at a temperature of 80°C. This feature can improve throughput and lower energy expenditures for device manufacturers.

In addition to needle bonding, product applications for the 4E98 adhesive include scalpels, catheters, surgical instruments, and other medical devices.

Optically clear epoxy eliminates birefringence

Dymax Corp. supplies the OP–series of epoxies that do not distort during curing.

Supplied by Dymax Corp., a light-curable epoxy for lens-bonding applications remains optically clear after curing to eliminate birefringence. "Birefringence is a form of distortion that can be caused by the adhesive curing too quickly," says Richard Golebiewski, vice president of medical products. "In the past, this problem was solved by curing slowly using low-intensity UV equipment, but this hurt production output."

Dymax's OP-series adhesive offers another solution to this dilemma. Its formulation allows the use of high-intensity UV equipment to cure in times as small as fractions of a second without negatively affecting clarity. Suited for bonding glass, metals, and quartz substrates, the adhesive also features a shrinkage rate of 0.02%. Depending on the specific formulation, it also offers a viscosity ranging from 200 to 25,000 cP and an elongation of 120 to 175%. Other product benefits include moisture resistance, minimized outgassing, and thermal resistance.

Applied using manual, semiautomatic, and fully automatic methods, the adhesive's applications include bonding, mounting, bundling, splitting, laminating, and fixturing. Doublets, lenses, prisms, fiber optics, and endoscopes are just a few of the products for which it is useful. A UV-blocking formulation of the adhesive is available by request.

Light-curable adhesive features increased elongation

Suited for bonding dissimilar substrates, the 3381 adhesive from Loctite Corp. can be elongated to 330%.(click to enlarge)

A resilient single-component adhesive offers increased elongation for bonding dissimilar substrates. Suited for potting and sealing applications, the 3381 adhesive from Loctite Corp. is designed for use on components that must withstand thermal cycling or environmental exposure. "This single-component adhesive is particularly suited for these situations because it can safely be elongated to 330%," says medical market manager Christine Salerni. "Also, it has a hardness of 72 Shore A, which means it's tough and durable," she adds.

Cured using ultraviolet radiation, the 3381 adhesive can be applied using manual or automatic methods. Acceptable substrates for bonding include thermoplastic, glass, and metal materials. When bonding two glass substrates, the epoxy offers a strength of 607 psi. If used to join two polycarbonate materials, the bond strength is rated to 1430 psi. The material withstands sterilization by EtO, gamma radiation, hydrogen peroxide, and limited autoclaving, but should not be used in pure-oxygen or oxygen-rich systems.

Because it is certified to ISO 10993 standards for biocompatibility, the Loctite adhesive can be used to produce medical disposables. "So far, we've had companies use it to produce fluid-collection devices, tube sets, anesthesia masks, and respiratory-care products," says Salerni.

Syringe-dispensable epoxy suited for die attachment

Distributed by Creative Materials Inc., a syringe-dispensable electrically insulating adhesive is designed for die attachment, PCB fabrication, and coating applications. According to the manufacturer, the 122-33(SD) epoxy offers thermal stability and chemical resistance, and produces no voids during curing. It is shipped ready to use and cures fully when exposed to temperatures of 155°C for 30 minutes.

Constructed with an aluminum-oxide filler, the 122-33(SD) adhesive has a viscosity of 135,000 cP. It can be used in temperatures that span from –55° to 230°C, but retains thermal stability to 325°C. When cured fully, it provides a lap shear strength of 1800 psi. Other product features include a dielectric constant of 4.1 and a dissipation factor of 0.027. The material has a shelf life of two weeks when stored at a temperature of 25°C.

One-part adhesive offers unlimited working times

SC 2000–series adhesives from Devcon require no mixing and offer unlimited working times at room temperature. The four formulations of single-component adhesive are heat cured and self-leveling. The materials provide thermal stability and corrosion resistance, and are suited for filling gaps and bonding metal, ceramic, and glass substrates.

Withstanding service temperatures of –40° to 300°F, the SC 2001 formulation has a viscosity of 250,000 cP, making it suited for potting and encapsulation. This material may be cured using induction or traditional heat curing.

The SC 2002 adhesive is particularly suited for use on steel and aluminum. Offering a viscosity of 65,000 cP, it has been used to secure steel screens, seal bottom plates, and pot end caps in metal filter applications.

A more viscous version of the SC 2002 adhesive, the SC 2003 epoxy is formulated for applications that require greater sag and run resistance. The material has a service temperature range of –40° to 300°F.

The SC 2004 adhesive offers resistance to aluminum-sulfate solutions. It has a 285,000-CP viscosity and withstands service temperatures of –60° to 300°F.

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