Cyanoacrylate adhesives are one-part acrylate adhesives that cure instantly on contact with mated surfaces through a reaction with surface moisture. Cyanoacrylates are often called super glues. Cyanoacrylate adhesives have high strength, excellent adhesion to a wide variety of substrates, especially plastics. Poor shock or impact resistance (brittleness) and poor gap filling abilities are potential disadvantages of cyanoacrylate adhesives. Rubber or elastomer modified cyanoacrylates and accelerators have overcome some of these problems.
Important specifications to consider when selecting between cyanoacrylate adhesives include viscosity, initial set time, gap fill, tensile strength (UTS), and use temperature. Viscosity is a measurement of a fluids resistance to flow. Water is lower in viscosity than oil or honey. Oil is lower in viscosity than tar or molasses. Depending on the application method, the viscosity controls the amount of cyanoacrylate adhesives dispensed onto a substrate. Working, assembly or initial set time is the amount of time an adhesive, sealant or cement can be applied and repositioned or removed before extensive setting or curing and results in hardening of the bond joint. After this time, further movement or assembly adjustments would be difficult and possibly damage the finished bond. Gap fill is the spacing or gap between the substrate that the cyanoacrylate adhesive can accommodate and still maintain a functional, full strength bond. The ultimate tensile strength (UTS) is the amount of applied stress required to cause failure in a control specimen of the material under tensile load conditions. Use temperature is the range that the cyanoacrylate adhesive can be exposed to without degradation of structural or other required end-use properties.
Cyanoacrylate adhesives are available in a number of dispensable forms, each of which provides distinct advantages for specific applications. These include gels, liquids, and pastes. Gel cyanoacrylate adhesives are more run resistant during application. Liquid cyanoacrylate adhesives can be used to fill deep gaps more effectively than other adhesive forms, however, they have a higher likelihood of flowing beyond the desired application area requiring greater clean-up potential. Paste adhesives are very resistant to running, but greater force is required to dispense and spread the adhesive paste on the surface. Paste adhesive may contain high filler content.
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