Photocuring advantages

For aqueous inks, the resins are water- or alkali-soluble or dispersible and the solvent is mosdy water containing sufficient alcohol (as much as 25%) to help solubilize the resin. To keep the alkah-soluble resin in solution, pH must be maintained at the correct level. Advances include the development of uv inks. These are high viscosity inks that require no drying but are photocurable by uv radiation. In these formulations, the solvent is replaced by monomers and photoinitiators that can be cross-linked by exposure to uv radiation. The advantage of this system is the complete elimination of volatile organic compounds (VOC) as components of the system and better halftone print quaUty. Aqueous and uv inks are becoming more popular as environmental pressure to reduce VOC increases. 

We chose to modify the anhydride monomers with photopolymerizable methacrylate functionalities. Methacrylate-based polymers have a long history in biomedical applications, ranging from photocured dental composites [20] to thermally cured bone cements [21]. Furthermore, photopolymerizations provide many advantages for material handling and processing, including spatial and temporal control of the polymerization and rapid rates at ambient temperatures. Liquid or putty-like monomer/initiator... 

An advantage of this type of photopolymerizations is that as they are non-radical chain polymerizations, they are insensitive to oxygen. In addition, as the cation is relatively stable, the reaction is able to continue in the dark. Applications of this chemistry may be found in the fields of coatings, adhesives, printing inks, and also for photocurable composites and microelectronic photoresists. 

Recently photoinitiators have been developed (63) which can trigger photocuring when exposed to visible light. As an industrial process, cure widi visible light offers the advantage of increased safety because it is less of an eye hazard. These visible light photoinitiators, for example 2,4-diiodo-6-butoxy fluoione (DIBF) (62a)... 

Brief reflection on the simplicity of this process reveals the many advantages of photocure over other techniques (Table 2). Of course, at the present state of development, a number of shortcomings can be cited as well and these will be discussed in a later section. 

Planar lithography techniques are not effective for precise fabrication of microdevices with hemispherical shapes (17). Drop-on-demand inkjet printing of a photocurable ink is a more appropriate approach as it takes advantage of the surface tension as well as of the delivery of a well-defined ink volume. 

The postpolymerisafion, which is known to occur just after the UV-exposure in cationic photocuring, was easily monitored by RTIR spectroscopy, as shown in Fig. 7 for DVE-3 (dashed curve). It can be seen that, after a 0.7 s exposure to UV-radiation, the vinyl ether continues to polymerise in the dark, the conversion rising from 10% to over 90% within a few seconds. One can take advantage of such an important dark curing process to assemble non-transparent foils by means of... 

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