What’s the dose?
An advantage of UV is that complete cure is achieved in the bondline in seconds. In order for this to happen, it’s important that the adhesive receives the correct dose of UV light, as well as the right wavelengths. Most UV curing adhesives start curing once exposed to the correct light, and will stop if the light is removed, so it is important to ensure a full cure is achieved in the exposure process
Manufacturers should test their process to determine the minimum light dose to achieve optimal cure for their application; dose is a combination of light intensity or power, and exposure time. Once the minimum dose is empirically established, best practice suggests that a safety factor (perhaps 25 per cent) is added to arrive at a robust process. High performance UV curing adhesives designed for use in industrial applications will require a minimum activation energy level of 50 mW/cm2 in order to properly establish cross-linking and effect a good cure.
Higher intensity lights will result in faster cures and process efficiency; more energy will help to give a better cure, improving performance. Manufacturers can use a radiometer to check the light intensity and your technical contact at your adhesives supplier can recommend a radiometer for your application.
UV light is hazardous. However, protecting operators from the light using integral shielding or by equipment design is straightforward. For manual, hand-held curing operations, a common sense approach would be to consider how you would look after yourself on a sunny day at the beach — cover up exposed skin and protect eyes. A good supplier will deliver safety eyewear with each lamp and will help with any further PPE needed, as well as the risk assessment. Training is recommended for everyone involved in the process. A radiometer can be used to check levels of UV light near the equipment, and to give colleagues better understanding of any hazard.
About the author:
Peter Swanson is Managing Director at adhesives specialist Intertronics -www.intertronics.co.uk