Processing ultraviolet cure

The UV technology alluded to above holds out the promise of even more superior labels. In this process, ultraviolet cured inks are used as the printing medium. These are cured by exposure to industrial type UV mercury vapor lamps in either a non-inert system (air environment) or in an inert (oxygen-free) system. The result is excellent adhesion to vinyls, polyesters, polycarbonates, butyrates and acetates and a cured elongation of between 20 and 40% to avoid embrittlement of the substrate. Initial testing has exhibited little sign of degradation and excellent chemical resistance after three years of exterior exposure. Such UV labels as well as other techniques should be considered whenever use demands extended label performance. 

Ultraviolet curing grades of "aerobic" acrylic adhesives, however, have been developed to provide structural bonds within seconds at room temperature on a wide variety of substrates. Parts may be precisely positioned and then structurally joined "on demand" at a time convenient to the assembly process. 

Excitation ek- Sl- ta-shon (14c) n. In ultraviolet curing, the first state of the polymerization process, in which the photo-initiator, such as benzophenone amine, is stimulated by UV into a singlet or triplet state, with subsequent formation of free radicals. 

Ultraviolet curing (or UV curing) n. (1) Conversion of a wet coating or printing ink film to a solid film by the use of ultraviolet radiation. (2) The process by which certain polymers or coatings are cured, with the aid of a photoinitiator, by exposure to ultraviolet radiation. One such polymer system is the oligomer tris(2-hydroxymethyl) isocyanurate triacrylate with an initiator... 

If the outer (female) substrate had been transparent in Figure 5.12, it may have been possible to use an ultraviolet-curing adhesive. The benefit of UV adhesives is that the product will only cure on demand and so there will be plenty of time to rotate the component parts to ensure full joint coverage. Where the assembly process is horizontal, the chamfer is not always necessary but the male part may require to be rotated to ensure full joint coverage. 

Binders and Resins. The choice of binder is the most important ingredient choice in the formulation process because the binder affects the performance properties of a paint more than any other single ingredient (3). The physical properties of binders required for paints include the abiHty to dry or cure under various ambient conditions, good adhesion to various substrates, abrasion resistance, washabiHty, flexibiHty, water resistance, and ultraviolet light resistance. The balance of these required properties is mosdy dependent on whether the paint is being developed for interior or exterior appHcations. 

Curing with Ultraviolet, Visible, and Infrared Processing Equipment... 

The free-radical cure mechanism of the vinyl ester resins is well understood. In most respects, it is similar to that of the unsaturated polyester resins. To initiate the curing process, it is necessary to generate free radicals within Ike resm mass. Organic peroxides are tlie most common source of free radicals. These peroxides will decompose under the influence of elevated temperatures or chemical promoters, e.g., organometallics or tertiary amines, to form free radicals. Generation of free radicals also can be effected by ultraviolet or high-energy radiation applied directly to the resin system. The free radicals thus formed react to open the double bond... 

But vitrification may be a problem when the cure is started at room temperature and no external heat source is provided (the only source of heat generation is the polymerization reaction). This is the case of UV (ultraviolet radiation), EB (electron beam), or X-ray curing processes. 

Although the basis and end result of the radiation curing process is essentially the same using either electron or ultraviolet energy, the mechanisms are quite different. This is because the energy of electrons is about 50,000 times... 

The main disadvantage is that web temperatures of 275-325° F are required to cure the film. These temperatures affect the paper properties adversely, and therefore higher-quality, more-expensive paper must be used. Even so, blisterii or cracking in the folder may be a problem. Moreover, the solvent emission, although reduced significantly, is not eliminated, and, as with the ultraviolet light-cured inks, paper printed with these thermally-catalyzed inks cannot be recycled in the currently used processes (8, 9). 

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