Electron curing

Alternatively, the same coatings can be cured by electrons from an electron accelerator without the use of photoinitiators. Electrons from a 150-600 kV accelerator are energetic enough to create free radicals on impact with the polymer molecules and curing ensues. Clear and pigmented coatings can be cured. Electron accelerators are extremely expensive, but are cheap to run. 

An Energy Sciences Electrocurtain model CB-150 equipped with a 15 cm linear cathode was used for EB curing. Electron energies of 160 KeV were employed. S unples were placed In a an aluminum tray on a variable speed conveyor (20- 235 ft/min) within the CB-150 unit. Irradiation occurred In a nitrogen atmosphere. 

EB Curing. Electron-beam accelerators (150-300 kV) used in finishing plants are of two types ... 

E-beam curing Electron beam curing for composites. 

III fact, while this correction gives the desired behaviour at relatively long separations, it doLS not account for the fact that as two nuclei approach each other the screening by the core electrons decreases. As the separation approaches zero the core-core repulsion iimild be described by Coulomb s law. In MINDO/3 this is achieved by making the cure-core interaction a function of the electron-electron repulsion integrals as follows ... 

The utihty of these adhesives arises from the electron-withdrawing character of the groups adjacent to the polymerizable double bond, which accounts for both the extremely high reactivity or cure rate and thek polar nature, which enables the polymers to adhere tenaciously to many diverse substrates. 

Cyanoacrylate adhesives (Super-Glues) are materials which rapidly polymerize at room temperature. The standard monomer for a cyanoacrylate adhesive is ethyl 2-cyanoacrylate [7085-85-0], which readily undergoes anionic polymerization. Very rapid cure of these materials has made them widely used in the electronics industry for speaker magnet mounting, as weU as for wire tacking and other apphcations requiring rapid assembly. Anionic polymerization of a cyanoacrylate adhesive is normally initiated by water. Therefore, atmospheric humidity or the surface moisture content must be at a certain level for polymerization to take place. These adhesives are not cross-linked as are the surface-activated acryhcs. Rather, the cyanoacrylate material is a thermoplastic, and thus, the adhesives typically have poor temperature resistance. 

Ra.dia.tlon. Use of radiation to affect fixation of some flame retardants is being investigated (110). Electron-beam fixation requires the selection of compounds that can be insolubilized inside or outside of the fiber with high yield in a short time. Polyunsaturated compounds, eg, Fyrol 76, have shown promise (see Radiation curing). 

Gels. Fluorosihcone fluids with vinyl functionahty can be cured using the platinum catalyst addition reactions. The cure can be controlled such that a gel or a soft, clear, jelly-like form is achieved. Gels with low (12% after 7 d) swell in gasoline fuel are useflil (9) to protect electronics or circuitry from dust, dirt, fuels, and solvents in both hot (up to 150°C) and cold (down to —65° C) environments. Apphcations include automotive, aerospace, and electronic industries, where harsh fuel—solvent conditions exist while performance requirements remain high. 

Polyimides (PI) were among the eadiest candidates in the field of thermally stable polymers. In addition to high temperature property retention, these materials also exhibit chemical resistance and relative ease of synthesis and use. This has led to numerous innovations in the chemistry of synthesis and cure mechanisms, stmcture variations, and ultimately products and appHcations. Polyimides (qv) are available as films, fibers, enamels or varnishes, adhesives, matrix resins for composites, and mol ding powders. They are used in numerous commercial and military aircraft as stmctural composites, eg, over a ton of polyimide film is presently used on the NASA shuttle orbiter. Work continues on these materials, including the more recent electronic apphcations. 

Ultraviolet Electron Beam Curing Formulations for Printing Ink, Coating and Paints, 3 Vols., SiTA Technology, London, 1991. 

The first-order decomposition rates of alkyl peroxycarbamates are strongly influenced by stmcture, eg, electron-donating substituents on nitrogen increase the rate of decomposition, and some substituents increase sensitivity to induced decomposition (20). Alkyl peroxycarbamates have been used to initiate vinyl monomer polymerizations and to cure mbbers (244). They Hberate iodine quantitatively from hydriodic acid solutions. Decomposition products include carbon dioxide, hydrazo and azo compounds, amines, imines, and O-alkyUiydroxylarnines. Many peroxycarbamates are stable at ca 20°C but decompose rapidly and sometimes violently above 80°C (20,44). 

The principal techniques for determining the microstmcture of phenoHc resins include mass spectroscopy, proton, and C-nmr spectroscopy, as well as gc, Ic, and gpc. The softening and curing processes of phenoHc resins are effectively studied by using thermal and mechanical techniques, such as tga, dsc, and dynamic mechanical analysis (dma). Infrared (ir) and electron spectroscopy are also employed. 

Small amounts of TAIC together with DAP have been used to cure unsaturated polyesters in glass-reinforced thermo sets (131). It has been used with polyfunctional methacrylate esters in anaerobic adhesives (132). TAIC and vinyl acetate are copolymerized in aqueous suspension, and vinyl alcohol copolymer gels are made from the products (133). Electron cure of poly(ethylene terephthalate) moldings containing TAIC improves heat resistance and transparency (134). 

Curing Polymers with y-Rays, X-Rays, and High Energy Electrons... 

Curing of Coatings with Electron Beams, y-Ray, X-Ray, and Planar Cathodes... 

In the electrocurtain processor, the shielding is clad direcdy to the tube housing. Housing space is relatively small, because a shielded tube 25 cm in diameter replaces the 3-m high stmcture required for the scaimed electron beam apparatus. The electrocurtain has a more flexible geometry and can be adapted more readily to many different types of curing appHcations (43). 

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