Curing radiation

One application of this technique involves infrared radiation heaters, producing an increase in the heat-transfer rate which exceeds that of oven heaters. Infrared lamps provide a useful way of removing solvents from contact adhesives prior to bonding, and are useful in the rapid heating of localized areas of a substrate. The rate of heat transfer also depends on the color of the work piece, thus the darker the part, the more rapid the heating. 

Cationic epoxies can be used to bond substrates that are not transparent. Unlike radically curing acrylic adhesives, cationic products can be sufficiently pre-activated by UV fight they will then continue to cure once the light has been removed. Cationic epoxies can be equally as effective for applications where one or more components are transparent, or none at all. 

After applying the adhesive, it needs to be activated before the other component is assembled. However, there is only a limited window for applying the second component. 

Dual curing adhesives offer more than one curing mechanism. They are designed for applications with shadow areas which are not accessible to the UV hght. Full cure in shadow areas will be achieved by anaerobic cure in the absence of oxygen with metal contact, or by adding heat. 

The systems are color-stable, weather resistant, flexible, and also adhere well to tin-free and low-tin sheet metals, as used in the manufacture of beverage and aerosol cans. Although arene-ferrocenium complexes even allow the cure of bisphenol A epoxy resins, provided postcuring takes place, these systems have not yet become important in surface protection applications. The reasons for this are inadequate color stability and weather resistance as well as the intense color of these films. 

Liquid unmodified bisphenol A-, -A/F- and -F resins produce little or no irritation of skin or muscous membranes they can however act as sensitizers and cause dermatological allergies. 

Solid epoxy resins based on bisphenol A can be categorized as effectively non-toxic they are not irritating and scarcely sensitizing. The same is true for the novolac epoxy resins although their liquid forms can have a sensitizing effect. 

Reactive diluents and low molecular mass aliphatic epoxy resins are of low viscosity, show a noticeable vapor pressure and have to be handled with care. These substances produce medium to strong irritation of skin and mucous membranes they are also sensitizers and can cause skin disorders. 

Epichlorhydrin which is used for the synthesis of epoxy resins is a suspected carcinogen in animals. Thanks to the well developed manufacturing processes, practically all the current commercially available epoxy resins contain only the smallest traces of epichlorhydrin (Occupational Hygiene Advices for Manufacturing and Processing Plastics of CIBA, Company brochure). 

Kirk-Othmer Encyclopedia of Chemical Technology (4th Edition) 

Ultraviolet light sources are based on the mercury vapor arc. The mercury is enclosed ia a quart2 tube and a potential is appHed to electrodes at either end of the tube. The electrodes can be of iron, tungsten, or other metals and the pressure ia a mercury vapor lamp may range from less than 0.1 to 1 MPa ( 1 to 10 atm). As the mercury pressure and lamp operating temperatures are iacreased, the radiation becomes more iatense and the width of the emission lines iacreases (17). 

Mechanisms of Radiation Energy—Organic Substrate Interaction 

In the case of photochemical reactions, light energy must be absorbed by the system so that excited states of the molecule can form and subsequendy produce free-radical intermediates (24,25) (see Photochemicaltbchnology). 

Relative strain at break (axial length measured at tearing) as a function of dose for branched polyethylene biaxially stretched at 70, 90, and 110 °C[7iO] 

In radiation curing, as in radiation degradation, s. Section 5.3.2.2, the irradiation dose determines the desired property changes. 

Dose-dependent increase in the insoiubie content of poiyethyiene (extraction in toiuene at 90 °C untii constant weight is reaohed) initial molecular weights and initial molecular weight distributions of branched and linear polyethylene do not match [710] 

In crosslinking semi-crystalline plastics, crosslinking takes place mainly in the amorphous, interiameiiar phase, while in the crystalline phase (the lamellae) recombination (heaiing) takes place up to higher doses. Crystallinity will undergo destruction oniy at higher doses. 

Temperature profile of shear modulus for irradiated linear polyethylene [710] 

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The major use of vinylpyrrohdinone is as a monomer in manufacture of poly(vinylpyrrohdinone) (PVP) homopolymer and in various copolymers, where it frequendy imparts hydrophilic properties. When PVP was first produced, its principal use was as a blood plasma substitute and extender, a use no longer sanctioned. These polymers are used in pharmaceutical and cosmetic appHcations, soft contact lenses, and viscosity index improvers. The monomer serves as a component in radiation-cured polymer compositions, serving as a reactive diluent that reduces viscosity and increases cross-linking rates (see... 

Higher alkyl acrylates and alkyl-functional esters are important in copolymer products, in conventional emulsion appHcations for coatings and adhesives, and as reactants in radiation-cured coatings and inks. In general, they are produced in direct or transesterification batch processes (17,101,102) because of their relatively low volume. 

Pentaerythritol and trimethylolpropane acryUc esters are usefiti in solventiess lacquer formulations for radiation curing (qv), providing a cross-linking capabihty for the main film component, which is usually an acryUc ester of urethane, epoxy, or polyester. Some specialty films utilize dipentaerythritol and ditrimethylolpropane (94,95). 

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). 

An ink is considered dry when a print does not stick or transfer to another surface pressed into contact with it. Drying is accompHshed by one or more of the following physical or chemical mechanisms absorption, evaporation, precipitation, oxidation, polymerization, cold setting, gelation, and radiation curing. 

J. P. Eouassier and J. E. Rabek, Radiation Curing in Poljmer Science andEechnology, Vols. 1 and 11, Elsevier, London, 1993. 

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