A light way to firm adhesion

Tom Shelley reports on an advanced adhesive aimed at higher speed production across a range of industries

A new family of single-component adhesives achieve an initial fix in as little as 5 seconds and can then be fully cured within a few more seconds under ultra violet light – offering the best of UV and instant curing technologies in one product. Target markets include loudspeakers, electronics and automotive, but many industries should find a use for these versatile new products. Traditional instant curing adhesives, which Loctite has been manufacturing since the mid 1960s, achieve a quick partial cure as soon as the substrate surfaces are pressed together. The adhesives work because they possess an acid which is able to prevent monomer molecules from polymerising. Pressing a thin film of adhesive between surfaces coated with neutral or alkaline moisture increases the pH sufficiently to allow polymerisation. The final structure, and full strength, however, is not usually achieved for 24 hours. Those who have used instant adhesives, to repair children's toys and the like, will be aware of this '24-hour limitation; while the initial repair will look firm, as soon as the toy is handed back to the child re-breakage is the usual result. The same problem can occur in manufacturing – loudspeakers bonded in this way cannot immediately be stressed by full power testing. Having to provide access for UV light to achieve a full cure is not as restrictive as it might sound. UV penetration through the adhesive is up to 5mm, more than enough to fully cure beads and fillets. Where UV light cannot penetrate under electronic components, it is possible to initiate a secondary cure using moisture or metal. The new range comprises 20cPs low viscosity, 4304 and 900 cPs high viscosity 4305 grades. Supplied as 28g or 454g packs, the adhesives are suitable for use up to 80degC. They have a fixture time of 5 to 10s when bonding ABS and 30 to 45s when used to bond steel. Target applications include the bonding of polycarbonate windows to ABS housings, sealing in electronics and bonding on logos. They are also biologically tested and approved to ISO 10993 for use in medical devices. They show a very faint green colour in thick sections. Pointers Adhesives achieve fixturing in 5 to 45s depending on substrate and application, but require only a few additional seconds exposure to UV light to achieve a full-strength cure UV light penetration is up to 5mm and maximum service temperature is 80°C