Radiant-cured adhesives are solvent-free adhesives that are cured when exposed to radiant energy (Ref. 4). Two of the most widely used curing systems are ultraviolet (UV) and electron beam (EB) systems. (Ref. 6) UV light-cured adhesives use photoinitiators to activate the cure. Light energy in the ultraviolet range of the spectrum (200-400 nanometers) is absorbed by the photoinitiators, causing a photochemically driven cure that is completed in seconds, throughout the bond. (Refs. 4, 11) Components of a UV light curing system include a light source that is usually a quartz lamp, power supply, reflectors to focus or diffuse the light, cooling systems to remove heat, and a conveyor to move coated substrate to and from the light source.
EB-cured adhesives, though similar in function and performance to UV light-cured adhesives, do not require the use of a photoinitiator. Instead, an electron beam within the equipment exposes the adhesives to low-energy electrons, curing the adhesive within seconds. Components of an EB curing system include a control panel, a transformer for voltage, and an electron accelerator. (Ref. 6) Adhesives cured by UV light or EB are used mainly in Europe and have not been extensively adopted in the U.S. Radiant curing technologies include UV systems, which account for 85 percent of the market for this type of adhesive, EB systems (10%), and other technologies including visible light, infrared light, and microwave systems (5%). (Ref. 10) Most radiant-cured adhesives contain 100% solids and are VOC-free.
Uses and Properties
Radiant-cured adhesives are used primarily for packaging, with paper and paperboard the dominant materials used in the packaging. (Ref. 10) Other applications for radiant-cured adhesives are in health care, electronics, communications, pressure sensitive tape, and consumer applications. (Refs. 2, 4) Table 2 describes the sectors and applications in which radiant-cured adhesives are commonly used.
|Construction||Manufacture of laminated wood panels; kitchen countertops.|
|Non-rigid Bonding||Bonding of woven and non-woven fabrics; manufacture of athletic shoes, books, and sporting goods.|
|Packaging||Manufacture of cartons, boxes and corrugated boards; bags, envelopes, disposable products (diapers, paper products); cigarettes; and labels, stamps.|
|Vehicles||Aircraft and aerospace structural assemblies; automotive, truck, boat, and bus assembly; mobile home manufacturing.|
Radiant-cured adhesives can be used on glass, metal and some plastic materials. Some specific applications of radiant-cured adhesives are glass stemware assembly, the manufacture of headlamps, architectural glass assembly, and lens to metal frame assemblies. (Ref. 12) UV light cured adhesives are best suited to small scale applications, while EB-cured adhesives are more appropriate for high volume operations (an EB system has a higher installation cost). One additional characteristic of EB-cured adhesives is that it can cure the area between two substrates. (Refs. 2, 4) UV light cured adhesives can also be applied on heat sensitive substrates, (Ref. 13) and are unaffected by ambient temperature or humidity (Ref. 14).
Radiant-cured adhesives cannot be used in all applications, and will not be a full replacement for solvent-based adhesives. (Ref. 4) For example, radiant-cured adhesives are not suitable on parts that have complex shapes and they may continue to absorb UV light even after curing. (Refs. 2, 4) Consequently, radiant-cured adhesives should be used on materials that will not be exposed to additional UV light.
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