Curing adhesive challenges
Peter Swanson, managing director of adhesives specialist Intertronics, explains how medical device manufacturers can use UV light curing systems to achieve a repeatable, validatable and productive bonding process.
Ultraviolet (UV) curing adhesives can be used to assemble medical devices such as catheters, reservoirs and housings, needles and syringes, medical electronics, tube sets and fittings, facemasks, and many more. When assembling these devices, UV light curing systems may be a good option because they help achieve process reliability, repeatability and validation.
Medical device manufacturers face specialised adhesive needs: the material must bond to the parts, withstand the rigours of the product end-use, and comply with the industry’s particular regulatory needs. Medical device manufacturers want assurance that the process is verifiably and consistently in control; it must be efficient, reliable and repeatable.
Adhesives may be cured by a variety of mechanisms, but UV light curing is popular for medical device applications due to speed and process control advantages. Light curing adhesives are solvent-free, offer a full cure in seconds and are sterilisable. They are designed to adhere to the typical substrates used in medical devices, for example, PEEK, PVC, PEBAX and ABS. Furthermore, they can be biocompatibility tested in accordance with ISO 10993 and/or USP Class VI (typical test results provided include ISO 10993-4 Hemolysis, ISO 10993-5 Cytotoxicity, ISO 10993-6 Implantation 14 Days, ISO 10993-10 Intracutaneous and ISO 10993-11 Systemic Toxicity), making them suitable for medical device applications where proof of non-toxicity is an industry requirement.
UV curing adhesives are process friendly. Being single part, only curing on demand and with a range of viscosity choices, application is relatively straightforward, with methods ranging from simple syringe dispense under time/pressure control right up to sophisticated volumetric positive displacement pumps.
UV curing equipment
It is important to select UV curing equipment that matches the adhesive of choice. UV curing lamps are primarily based on two quite different types of technology: mercury arc lamps and LED-based UV curing lamps.
Traditional mercury arc lamps produce a broad spectrum of light and have been used successfully for decades. Mercury arc lamps, however, typically have less than 2,000 hours of bulb operating life, and the intensity of the lamp degrades over time, which creates a process variable that can affect output. The warm-up and cool down time associated with broad spectrum lamps often mean that manufacturers choose to leave them running all day, increasing operating costs.
LED-based UV curing lamps are a more recent technology and, unlike mercury arc lamps, produce a narrow spectrum of light. They offer numerous advantages compared with traditional technology, including no output degradation over time, no bulbs to replace and cooler cures. With instant on/off capability and no warm-up time, medical device manufacturers can turn them on as and when needed, thereby removing the need for mechanical shutters, and reducing running and energy costs.
Because LED UV curing lamps offer a narrow spectrum of output, they may not optimally cure an adhesive that has been formulated to work with broad spectrum mercury arc lamp technology. It is recommended that the adhesive chosen is designed to cure with narrow spectrum UV LED lamps — as is usually the case with newer products. If this is not possible, then practical testing and verification with production parts should be undertaken to ensure that the LED lamp and the chosen chemistry provide a satisfactory result.
Improving productivity with LED UV curing
UV curing systems offer several productivity advantages. For example, fast curing can reduce work-in-progress (WIP) and release factory space, employees and other resources so they can be reallocated to parts of the manufacturing process that add more value.
There are also UV curing products available that offer inline quality inspection to help reduce defects and waste; for example, products that change colour when fully cured. Co-optimising adhesives and equipment can also shorten cycle times, leading to reduced work in progress.
Improving productivity doesn’t have to be about big leaps; it could be about increasing manufacturing output or decreasing operating costs or input by small incremental amounts. For example, LED UV curing lamps offer a consistent output compared with that of a broad-spectrum lamp, which allows medical device manufacturers to achieve process stability and uniform results. This facilitates superior process control, increased manufacturing throughput and lower operating costs, resulting in an increase in productivity.
Automating improvements
There is no room for inconsistency in medical device manufacturing. With a manual process, operators can introduce process variability that may lead to problems with quality; for example, if too much or not enough adhesive is applied.
UV curing adhesive processes can be readily automated to improve productivity and eliminate inconsistencies — benchtop and gantry robots can be integrated with dispensing, curing or surface preparation equipment.
Case study
One successful customer example is Brandon Medical, a UK manufacturer and designer of technology for operating theatres. The company was experiencing production bottlenecks due to extended curing times when bonding three polycarbonate lenses together to make the large front lens of its Quasar eLite operating theatre lamp.
Intertronics supplied Brandon Medical with the Dymax 3225-T-SC single-part UV light curing adhesive and a Phoseon LED UV curing lamp with a 50 x 20-mm emitting window. The lamp’s 396 nm intensity output provided enough light energy to give Brandon Medical a fast cure, with less heat introduced compared with traditional broad-spectrum lamps. The application was automated using a benchtop robot, integrating both the dispensing and the curing process, saving time in the production process.
Conclusion
With any medical device, the manufacturing process must be validatable, by establishing evidence that a process is capable of consistently delivering quality products. Each step of the manufacturing process is controlled to assure that the finished product meets all design characteristics and quality attributes including specifications. UV curing processes and equipment such as LED-based UV curing lamps reduce process variability, facilitating the establishment and maintenance of a validated production.