Best of both worlds

Permabond UV7220 (black) and Permabond UV7221 (clear) are epoxy resins that cure when exposed to 365nm UV light; and they can also cure with heat, like standard epoxy resins, or by using a combination of the two: UV + heat.

“Unlike UV adhesives based on acrylic chemistry, these cationic epoxies continue curing even when the UV light is removed,” says Permabond. “This means they can cure in shadow areas. Other benefits include excellent chemical and temperature resistance, low shrinkage, reduced odour and tack-free surfaces.”

Electronics applications

The tack-free nature of Permabond’s cationic epoxy/UV adhesives makes them particularly well suited to electronics applications, such as bonding SMDs (surface mounted devices) onto PCBs and glob top/semiconductor chip encapsulation. “In the automotive industry, they also have a proven track record in applications such as sensor sealing, lens bonding and sealing glass filled PBT or PBT-PC cameras,” adds the company.

“Their low shrinkage means precision parts can be accurately aligned and not suffer movement over time and the glossy-tack free adhesive surface will not attract dust, which is very important for the optical properties of these applications.”

The ability of these adhesives to cure using either UV light or heat, and their cationic nature, where cure continues even after UV light or heat has been removed, means that, in many applications, production processes can be significantly accelerated, reducing costs and increasing productivity.

Key features and benefits

Key features and benefits of cationic epoxy/UV adhesives highlighted by Permabond include:

• Single component – no need to measure / mix or use mixing nozzles
• Delayed cure – allows time to position or align parts correctly
• Parts can be ‘flashed’ with UV light, then assembled, allowing cure in shadow areas
• Optically clear (UV7221), good transparency – ideal for bonding sensors and optical parts
• Low shrinkage, compared with regular UV-cure adhesives
• Tack-free surface – low odour, low skin irritation, will not attract dust and fluff
• Good thermal and environmental resistance
• Contain no solvents
• Will bond to a wide variety of surfaces including plastics, metals, glass, composite materials.