UV curing, applications

Crivello and Lee have described the synthesis and characterization of a series of (4-alkoxyphenyl)phenyliodonium salts 7, which are excellent photo- and thermal-initiators for the cationic polymerization of vinyl and heterocyclic monomers [17]. Iodonium salts 7 are conveniently prepared by the reaction of alkoxyphenols 6 with [hydroxy(tosyloxy)iodo]benzene followed by anion exchange with sodium hexafluoroantimonate (Scheme 7.2). Products 7 have very good solubility and photoresponse characteristics, which make them especially attractive for use in UV curing applications. Compounds 7 with alkoxy chains of eight carbons and longer are essentially nontoxic, compared to diphenyliodonium hexafluoroantimonate, which has an oral LD50 of 40 mg kg (rats) [17]. 

Table 3. Photoinitiator Selection Chart (For Major UV-Curing Applications in the USA)... 

Each UV-curing application has a unique combination of requirements. In order to meet these requirements, the formulating chemist must carefully optimize his choice of many components including one or more photoinitiators, and their concentrations. Many properties such as surface or... 

Benzophenone is a common photosensitiser. Free radical formation by hydrogen abstraction from solvent leads to use in UV-curing applications such as inks, imaging, and clear coatings in the printing industry. By way of contrast, hydroxy benzophenones with the OH group adjacent to the carbonyl are useful photostable UV absorbers because reversible proton transfer is an efficient deactivation route leading to very short lived excited-states. 

Included among the many types of vinyl monomers that have been subjected to photoinitiated cationic polymerization are styrene," substituted styrenes, a-methylstyrenes, N-vinylcarbazole, alkyl vinyl ethers, prop-l-en-l-yl ethers, ketene acetals, and alkoxyallenes. Most useful in the crosslinking photopolymerizations employed for UV curing applications are multifunctional vinyl ethers and multifunctional prop-l-en-l-yl ethers. A number of multifunctional vinyl ether monomers are available from commercial sources, while multifunctional prop-l-en-l-yl ethers can be readily prepared by catalytic isomerization from their corresponding allyl ether precursors. The photoinitiated cationic... 

Oxetanes are slightly more basic than epoxides and have similar ring-strain energies. For this reason, oxetane monomers are also excellent candidates for use in UV curing applications. However, only monofunctional oxetane monomers were known and these were available only in small quantities from chemical supply houses. Crivello and Sasaki and Sasaki et used novel synthetic methods to prepare a series of mono- and diftmctional 3,3-disubstituted oxetane monomers that are now available on a commercial scale. In many cases, the oxetane monomers are used in combination with epoxide monomers in UV curing applications. ... 

Several volumes will be published during 2005-2007 which contain chapters linked to the chapters in Volume 1, for instance Bonding metals , Bonding composites , Epoxy adhesives , Bonding in automotive , Structural adhesives , UV curing , Application equipment , and others. 

Monomers like acrylic ester (ACE), which has a promising low volatility monoacrylate monomer for UV cure applications with an interesting cost/performance balance. 

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