Other Applications for UV Curing

Smart cards in the form of SIM cards for mobile (cell) telephones contain chip modules, and UV radiation curable epoxies have been shown to offer advanfages in fhe encapsulation of these vital components.  

Since the optical fibers are placed info locations fhat are difficult to access, the coatings are expected to last over 20 years. Tests indicated that UV cured protective coatings would be mechanically stable up to 100 years under ambient conditions. Radiation curable adhesives can also be used for end-to-end splicing, termination of bundles, construction of optical sensors, and other areas in the optical field.  

Radiation curing is an important part in the manufacture of compacf disks and digital versatile disks (DVDs). In the production of compact disks fhe replication and formation of the protective coat may be carried out with the use of UV curing. The coatings are commonly based on methacrylates. 

Schematic of the cross section of an optical fiber. (Davidson, R. S., Exploring the Science, Technology and Applications of U.V. and E.B. Curing, SITA Technology Ltd., p. 249 (1999). With permission from SITA Technology Ltd.) 

Other applications are in the manufacture of opfical lenses/ holograms/ and multilayer organic light-emitting devices/  

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Photostabilization processes have not received much attention in the last year other than a multitude of review and specialist industrial articles. These include stabilization of polypropylene fibres, new stabilizer developments, sorting of stabilizers for polyethylene, trends in UV absorbers, hindered piperidines (hindered amine stabilizers (HAS)) for polyacrylics and urethanes, new stabilizers for polyolefins, enhanced service life applications, stabilizer mas-terbatches for polyester, stabilizers for UV cured acrylic overcoats for PVC, ° stabilization of clearcoats and various commercial packages. ... 

Nearly 42% of the demand for all adhesives comes from the packaging sector. Radiation-curable adhesives are used primarily for packaging, with paper and paperboard the dominant materials used in the packaging. Radiation-curable adhesives can be used on glass, metal and some plastic materials. Other applications for radiation-curable adhesives are in healthcare, electronics, communications, pressure-sensitive tape and consumer applications. Ultraviolet (UV)-curable adhesives are best suited to small-scale applications, while electron beam (EB)-curable adhesives are more appropriate in high-volume applications (an EB system has a higher installation cost). One additional characteristic of EB-curable adhesives is that they can cure the area between two substrates. UV light-cured adhesives can also be applied on heat-sensitive substrates and are not affected by ambient temperature or humidity. 

Alternate Crosslinking Modes. In addition to the crosslinking modes previously described, (co)polymers containing 1 and 2 may be cured by other means. For example, under appropriate acidic conditions with limited availability of active hydrogen species cyclic hemiamidals 2 will lose ROH to form the enamide 9 (Scheme 5). This has been demonstrated on model systems, e.g., 2 where vinyl is replaced by methyl ). The product, N-acetylpyrroline, has in turn been converted to nonvolatile products (oligomers) under free radical catalysis. These systems may thus be considered for application in the UV/EB or catalyzed free radical cure field. 

Because of their low viscosity, cycloaliphatic epoxies are often used to dilute other epoxy resins. These resins, however, have not achieved general importance in adhesive formulations because of relatively low tensile strength and because they do not cure well at room temperature. One major application for cycloaliphatic epoxies, however, is for adhesives and coatings that can be cationically cured by exposure to uv light. 

In another commercial application of free-radical polymerization, polymerizations may be carried out in industrial coatings in the presence of air to yield a variety of coatings and structures of commercial import. This development is possible. In part, because certain vinyl monomers, particularly the acrylates, are less sensitive to retardation by oxygen compared with other monomers. It is therefore possible to produce radiation-cured coatings. UV-cured printing inks and the photopolymers are important in imaging for printing, photoresist, and related applications. 

Among the most successful of the new radiation-curable silicone coating systems are compositions Incorporating cycloaliphatic epoxyfunctional silicone polymers with compatible iodonlum salt photocatalysts (1 - S ) The syntheses, structures, UV cure response, and other properties of these materials and some of their derivatives and monomeric homologs are discussed In the balance of this chapter. Their specific application for release coatings has been described In great detail elsewhere (5.6 > and Is not the subject of this paper. 

In other industrial application sectors there is an increasing tendency to employ low-solvent paints. In furniture production, for example, waterborne, UV-curing paints are superceding high-solvent nitrocellulose lacquers. 

The UV-cured film of IV-vinyl p30 rolidone has been used as a potential bioadhesive wound-dressing matrix when blended with other polymeric materials. Skin covers and wound dressings made of PVA and PVP were produced with or without polysaccharides by the help of the gamma irradiation technique. Because of its biocompatibility and nontoxicity, PVP was also chosen as the base material for a drug-loading device. Drug release from such membrane was found to depend on the crosslinking density, composition, and membrane thickness. On the other hand, PVP has been used as a carrier in electrospun fiber applications. 

As with other techniques, the material requirements for rotogravure printing depend on the curing process. For drying (solvent removal), a viscosity of between 0.01 and 0.2 mPa s is appropriate, resulting in a film about 1 p,m thick [23], which is more than sufficient for many printed electronics applications. UV curing the film allows for thicker films, up to about 8 p,m thick. 

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