Radiation-cured adhesives

Huber, H.F., Radiation cured adhesives. Beta-Gamma, 1, 3 (1992). 

Radiation curing adhesives are generally applied as solvent-free liquids. High-solids EB and uv curing liquid adhesives have been formulated from a variety of resins and elastomers. They include epoxy acrylates, epoxies, other acrylates, polyesters, blends of acrylate monomers with elastomers, and other compositions. 

Other additives used to improve the processing and performance of radiation cured adhesives are similar to those that might be found in more conventional formulations. These include antioxidants, defoamers, flow and wetting agents, and slip aids. 

Thermoplastics Cyanoacrylates, methacrylates, radiation-curing adhesives, polyurethanes (depending on the degree of crosslinkage). 

Radiation-curing adhesives for crystal clear plastics such as acrylic glass/ Plexiglas, polystyrene, polycarbonate. 

For bonded joints with crystal clear plastics like polystyrene and acrylic glass to metals, it is also possible to apply radiation-curing adhesives (Sections 4.3.2 and 9.3.3). 

Bonded Class Joints with Radiation-Curing Adhesives... 

Absorption of radiation, for example, UV rays through glass, plastics (e.g., Plexiglas) that results in a delay in curing of radiation-curing adhesives. 

Inhibitor Substance that, in low concentration, inhibits chemical reactions, for example, oxygen inhibitation of radiation-curing adhesives. 

Initiator Substance triggering a chemical reaction already in low concentration, for example, photoinitiators in UV-radiation-curing adhesives. 

Photoinitiator Substances triggering the polymerization reaction for UV or light radiation-curing adhesives. 

Radiation-curing adhesives Adhesives cured by electro-magnetic radiation, in particular by UV radiation or by visible light. 

Comparison of Thermal, Mechanical, and Spectroscopic Techniques for Characterization of Radiation-Cured Adhesives... 

Radiation cure adhesives are beconlng Increasingly Important for structural material applications. In order to obtain optimum performance and process efficiency, It Is necessary to analyze these materials using several techniques. Thin film applications have been successfully characterized by traditional methods such as Infrared spectroscopy and thermal analysis. This Investigation Includes comparison of traditional methods and mechanical spectroscopy for characterization of structural adhesive applications. In addition, mechanical spectroscopy provides viscoelastic data dependent on structure property relationships. 

Urethanes have also been used to toughen vinyl-terminated acrylic adhesives for improved impact resistance. Thus rubber-toughened urethane acrylates [79,80], water-dispersible urethane acrylates [81], and high-temperature-performance urethane-acrylate structural adhesives have been reported [82]. Polyurethanes terminated with acrylic functionality are also used for anaerobic or radiation-cured adhesives with improved toughness [83]. 

The second means of transforming a liquid adhesive entirely into a solid without the loss of a solvent or dispersion medium is to produce solidification by a chemical change rather than a physical one. Such reactive adhesives may be single-part materials that generally require heating or exposure to electron beam or UV or visible radiation (see Radiation-cured adhesives) to perform the reaction, and which may be solids (that must be melted before application), liquids or pastes. The alternative two-part systems require the reactants to be stored separately and mixed only shortly before application. The former class is exemplified by the fusible, but ultimately reactive, epoxide film adhesives and the latter by the two-pack Epoxide adhesives and Polyurethane adhesives and by the Toughened acrylic adhesives that cure by a free-radical Chain polymerization mechanism. 

Reactive acrylic adhesives generally consist of a solution of a toughening rubber (chlorosulphonated polyethylene) in a partly polymerized mixture of monomers this is mainly methylmethacrylate but ethane diol dimethacrylate is added as a cross-linking agent. The remaining monomer is polymerized in a free radical chain polymerization redox initiation involves an organic peroxide and a tertiary amine. Acrylic cements consist of a partly polymerized acrylic monomer containing an initiator. Cure is established by the thermal or UV decomposition of the initiator (see Radiation-cured adhesives). 

Radiation-cured adhesives include acrylated urethanes. 

The largest application of radiation-cured adhesives is for dental procedures (see Adhesion in dentistry restorative materials). Originally UV curable, these have given way to... 

Epoxide adhesives comprise epoxy resin, many of which are prepared from phenols and epichlorohydrin, for example, the diglycidyl ether of bis-phenol A or bis-phenol F usually, these resins are a mixtnre of molecular weights blended to fit the applications. The most-common cnratives for epoxy resins are polyanfines (used in stoichiometric amounts), usually a chain-extended primary aliphatic amine, for example, diethylene triamine or triethylene tetraamine or chain-extended equivalents, which react rapidly with the epoxy resin at room temperature. Aromatic amines react slowly at room temperature but rapidly at higher temperatures. Most epoxide adhesives also contain catalysts, typically, tertiary amines. Dicyanimide is the most-common curative for one-component high-temperature-cured epoxide adhesives. Mercaptans or anhydrides are used as curatives for epoxide adhesives for specialist applications, for example, for high-speed room-temperature cures or for electronic applications. A smaller number of epoxide adhesive are cured by cationic polymerization catalysed by Lewis acids photogenerated at the point of application. Lewis acid photoinitiators include diaryliodonium and triarly sulphonium salts. See Radiation-cured adhesives. 

Methods for the incorporation of the graft nnit may include irradiation of the base polymer and mixing with the comonomer, or reaction as solids or solntions with free radical agents and blending techniques (see Chain polymerization, Radiation-cured adhesives). 

Radiation-cured adhesives M FAKLEY Electron beam and UV curing systems advantages, disadvantages, uses... 

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