| Résumé : |
Although they've been around almost as long as the Rolling Stones, ultraviolet- and lightcuring adhesives are now coming into their own as a value-added replacement for traditional adhesives and other fasteners in many assembly processes.
Collectively known as photocurable adhesives, UV- and light-cure adhesives have become essential to many high-tech assembly operations where high throughput and delicate components are the norm, according to Colin McLean, research associate, Ablestik Electronic Materials and Adhesives, Rancho Dominguez, Calif., which is owned by National Starch and Chemical Co., Bridgewater, N.J. Two other photocurable adhesive and coating suppliers owned by National Starch, Permabond of Englewood, N.J., and Emerson & Cuming Specialty Polymers of Lexington, Mass., say that OEMs and other assemblers are switching to light cure products for new or refurbished production lines that need lower temperature curing and faster setting adhesives and coatings.
Generally, the term photocurable denotes adhesives that cure when exposed to ultraviolet light, visible light or a combination of both. Traditional adhesives rely on chemical reactions initiated by heat, solvent evaporation, mixing of multiple components or other chemical conditions, like the presence of moisture, metal ions or the absence of oxygen to effect a cure. Photocurable adhesives require the presence of the correct wavelengths of light at sufficient intensity to form durable structural bonds.
UV- and light-cure adhesives use photoinitiators to activate the cure. Light energy is absorbed by photoinitiators in the adhesive formulation, causing them to fragment into highly reactive species that are able to polymerize or crosslink with other components of the formulation. In acrylate-based adhesives, the reactive species formed in the initiation step are known as free radicals. Another type of photoinitiator, a cationic salt, is used to polymerize epoxy functional resins, generating an acid that reacts to create the cure. |
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Photocurable adhesives : 10 tips for best performance in ADHESIVES AGE, Vol. 40, N° 12 (11/1997)
