Electron beam curing method

A facile method by which organic thin films may be readily coated upon substrates employs the electron beam curing of materials such as of monomeric and/or oligomeric acrylates and methacrylates. The perfluorinated acrylates 2-(N-butylperfluorooctanesulfonamido)ethyl acrylate (BFOSA), 2-(N-ethylperfluorooctanesulfonamido)ethyl acrylate (EFOSA), and perfluoropolyether diacrylate (PFEDA) were obtained from the 3M corporation, St. Paul, Minnesota 1,6-Hexanediol diacrylatc (HDODA) was obtained from Interez, Inc., Louisville, Kentucky. 

It has been shown that in many cases for thermoset systems, there is a quantitative relationship between the chemical conversion of the thermoset and its Tg value, independent of the time-temperature cure history (111). This is very convenient from an applications standpoint because measurement of Tg is equivalent to a direct measurement of conversion. It implies that either the molecular structure at a given degree of conversion is the same, regardless of the reaction path, or that differences in the structures produced for different reaction paths do not affect Tg. While a Tg-degree of cure relationship has been found valid for many epoxy-amine and other thermoset materials, it has been observed not to hold in some cases, which include some epoxy-DICY, cyanate-ester, and phenolic systems. It has also been found not to hold for a given resin system cured by two different methods such as thermal and microwave (112) or thermal and electron beam cures (113). 

Abstract In this chapter, classification of adhesive and sealant materials is presented. For this purpose, various categories are considered depending on the polymer base (i.e., natural or synthetic), functionality in the polymer backbone (i.e., thermoplastic or thermoset), physical forms (i.e., one or multiple components, films), chemical families (i.e., epoxy, silicon), functional types (i.e., structural, hot melt, pressure sensitive, water-base, ultraviolet/ electron beam cured, conductive, etc.), and methods of application. The classification covers high-temperature adhesives, sealants, conductive adhesives, nanocomposite adhesives, primers, solvent-activated adhesives, water-activated adhesives, and hybrid adhesives. 

Methods 1 and 3 have been utilized in dry developed resist systems. To our knowledge, there are no resist systems commercially available that depend on post-exposure treatment other than the post-curing effect in negative electron beam resists mentioned earlier. Since such systems are still largely in the research phase we will not discuss them here but rather refer the reader to the literature for more detailed descriptions (44-50). 

Normally, the last UV unit should ensure an adequately thorough cure. This may be a problem for thick layers, particularly if they are pigmented. In such cases electron beam irradiation would be the preferred curing method. ... 

Systems using either gamma radiation from cobalt 60 or electron beams have been used for vulcanization. The electron beam method has been used for curing silicone rubbers. 

Pacansky et al. (1987) described the fabrication of dual-layer photoreceptors by radiation curing. The layers were coated with a polymerizable acrylate monomer or oligomer as the liquid component, then cured by a 175 kV electron beam or ultraviolet exposure. These methods were used for the preparation of generation layers containing bisazo and hydroxysquaraine pigments. 

Chen et al. (2006) highlight a novel calorimetric method to examine cure during electron-beam processing of epoxy resins via an energy-balance model and use of a novel experimental calorimeter. 

The development in the 1960s of extremely rapid methods of curing these coatings with ultra-violet and electron beam radiation, has led to an extension of the chemistry to compositions based on resins and monomers containing acrylic unsaturation. These coatings will also be discussed in this chapter. 

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. 

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