Ultraviolet light cured inks

The use of solventless inks avoids the emission of solvents during drying. The development of such inks has been a major goal of the printing ink industry for the past several years and has resulted in tiie development of several different types 1. ultraviolet light-cured inks ... 

Ultraviolet Light-Cured Inka Ultraviolet light-cured inks are a distinct d rture from conventional printing inks in that fiieir mechanism of... 

Electron Beam-Cured Inks. Electron beam-cured inks are similar in principle to ultraviolet light-cured inks except that no photoinitiator is needed. Vinyl polymerizations may be initiated Iqr any form of ionizing radiation, e. g., neutrons, a-particles, y-rays, and x-rays, as well as by high-energy electrons ( 5-rays). The mechanism of initiation is more complex than that of photochemical initiation in that radiation of vinyl monomers gives cations and anions as well as free radicals however, most radiation-initiated polymerizations are radical-initiated because the cations and anions formed are not stable at the temperature of polymerization and therefore dissociate to form radicals. 

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). 

The formulations of ultraviolet light-cured inks are proprietary, and at present, the best source of information as to their composition is the rapidly-growing patent literature. However, it is risky to infer the composition of inks used in tiie field from those described in the patent literature because only a small proportion of patented compositions ever become commercial products, and the compositions used in the field imy be the subject of patent applications not yet granted, or may be held as technical secrets without applying for patents. Nevertheless, the patent... 

Theoretical Aspects. Ultraviolet light-cured inks are cured by free radical-initiated vinyl addition polymerization. The photochemical initiation of vinyl polymerization has been the subject of many investigations dating back more than 30 years, to the first systematic studies of polymerization kinetics. Photochemical initiation offered a reproducible source of radicals that is not dependent upon temperature as is the thermal decomposition of free radical initiators. However, despite these early studies of its mechanism and kinetics, only recently has photochemical initiation become of practical interest, mainly because of the recent development of ultraviolet lamps suitable for production curing of printing inks and coatings. 

Practical Aspects. The foregoing theoretical relationships are difficult to apply to the curing of ultraviolet light-cured printing inks for several reasons. First, the polymerization kinetics of the complex monomers and prepolymers used in flie ink formulations have not yet been investigated under conditions that can be correlated with theory (i. e., low concentrations of reactants, constant temperature, simple model formulations). Second, the ultraviolet light-cured inks are polymerized in bulk to high conversion tiie polyfunctional nature of the... 

The foregoing results illustrate the complexily of these sterns and emphasize the importance of studying the ultraviolet light-cured ink system in addition to its individual components. 

Inevitably, the cost of ultraviolet light-cured inks is higher than that of the conventional solvent-based inks they are designed to replace. 

It is difficult to specify Ihe increased cost of thse ultraviolet light-cured inks with any accuracy. For example, in one case, the cost of the ink was estimated to be 30-50% higher (7), but an estimate made in 1971 cannot be expected to apply today when raw material costs are increased on a monthly or even we ly basis. In anolher case, the overall cost of... 

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