Electron beam cure adhesive formulations

The papers presented in the following chapters represent advances in pressure sensitive adhesives (ultraviolet light activated acrylate monomer - low Tg polyether formulations) photoinitiated cationic polymerization (light activated aryliodonium and arylsulfonium salts of lewis acids in epoxy resin formulations) polymer and formulation design criteria for radiation curable adhesives radiation curable composites (dynamic thermal analysis characterization of electron beam cured... 

In the past, electron beam radiation was applied to produce PSA exclusively however, recent improvements in UV curing technology (precise UV dose control, suitable photoinitiators) permit UV to be used to produce pressure-sensitive adhesives. PSA formulations can vary in consistency from low-viscosity liquids up to solids melting at 80°C (176°F). Therefore, applications may vary from screen printing to roll coating to melt extrusion. Coat weights for most PSA materials vary from 1 to 10 g/m. ... 

Their use in adhesive systems is minimal because they are relatively brittle and higher in cost than aromatic resins. However, cycloaliphatic epoxy resins are used in cationi-cally cured epoxy adhesive formulations. These are cured via uv or electron beam (EB) radiation. 

Epoxy acrylates are also commonly used as oligomers in radiation-curing coatings and adhesives. However, their name often leads to confusion. In most cases, these epoxy acrylates have no free epoxy groups left but react through their unsaturation. These resins are formulated with photoinitiators to cure via uv or electron beam (EB) radiation. The reaction mechanism is generally initiated by free radicals or by cations in a cationic photoinitiated system. The uv/EB cured epoxy formulations are discussed in Chap. 14. 

Formulation details are then presented in Chapters 11 through 14 for the various possible forms of epoxy adhesive systems room temperature and elevated-temperature curing liquids, pastes, and solids. The more or less unconventional forms of epoxy adhesives are also identified and discussed, since these are now achieving prominence in industry. These include uv and electron beam radiation curable, waterborne systems, and epoxy adhesives capable of curing via the indirect application of heat or energy. 

The yields of radiation-induced polymerizations can be very high. No additives are required, which makes it possible to synthesize very pure polymers. The initiation step is temperature independent giving rise to an easily controlled process at any desired temperature. These features account for the commercial interest in radiation polymerization. The very high speeds attainable within the layers of monomers subjected to powerful electron beams explain the wide use of this technique in radiation curing of adhesives, inks and coatings. The corresponding formulations are "solvent-free" and involve pre-polymers and monomers as reactive diluents. 

Continuous scans of modulus versus temperature utilizing the DuPont Dynamic Mechanical Analyzer (DMA) has provided a comparison of the high temperature service capabilities of radiation-cured experimental formulations of a vinyl-modified epoxy resin. Shell Epocryl-12. These scans were compared to data obtained when the same materials were applied as adhesives on aluminum test panels, radiation-cured with an electron beam, and lap shear strength tested at discrete temperatures. The DMA instrument utilizes a thin rectangular specimen for the analysis, so specimens can be cut from blocks or from flat sheets. In this case the specimens were cured as sheets of resin-saturated graphite-fibers. The same order of high temperature stability was obtained by each method. However, the DMA method provided a more complete characterization of temperature performance in a much shorter test time and thus, it can be very useful for quick analyses of formulation and processing variables in many types of materials optimization studies. The paper will present details of this study with illustrations of the comparisons. 

In summary, lEM can be used to graft vinyl functionality onto a variety of poly functional materials of both high and low molecular weight. This results in materials which can be later cured using peroxides, UV radiation, electron beam radiation and even air-dry mechanisms. Thus the use of lEM allows a variety of curing mechanisms which are especially useful for high solids or 100% solids formulation of coating and adhesive resins. 

The radiation referred to here is either UV radiation or electron beam. The UV-initiated curing mechanism requires a photoinitiator in the adhesive formulation. The adhesive formulation is otherwise made up of various components that bear reactive functional groups. 

---