Photocuring

Photocurable materials for photographic films contain pentaerythritol and dialkylamino and/or nitrile compounds, which have good adhesion and peelabihty of the layers, and produce clear transfer images (97,98). 

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. 

Table 8. Photocurable Polymer Systems For Photoresist Applications...

Photoinitiation with a high quantum yield of radical production in the visible light is of practical importance for photocuring processes [5,6]. 

Photocuring of commercial unsaturated polyester-styrene mixture was effectively done in the presence of the VOL2CI photoinitiator complex. The chlorine atom produced by the scission of V—Cl bond in the VOL2CI complex is proven to be the initiating species for the photocuring process 168]. 

TABLE 3 Photocurent Observed in a System Using Porous Membranes Covered with BR Film Deposited by the Usual LB Technique and Electric Field-Assisted Technique... 

Mitra, S. B. (1989). Photocurable ionomer cement systems. European Patent Application 0 323 120 A2. 

Nakanishi, H., Namikawa, N., Norisuye, T. and Tran-Cong-Miyata, Q. (2006) Autocatalytic phase separation and graded co-continuous morphology generated by photocuring. Soft Matter, 2, 149—156. 

The cured polymer samples used for physical property testing were prepared by photocuring 12 mil thick sheets of degassed and photosensitized monomer mixtures, using a mold composed of glass plates lined with polyester film and separated by a double thickness of vinyl electrical tape. A GE sunlamp was used for Illumination, and Darocure 1173 (E. Merck) was used as the photoinitiator. Hydrocarbon monomers were used as received from the manufacturers. All the vinyl group-containing compounds were stored at -5°C until use. 

Thermal and Dynamic Mechanical Analyses. The thermal and mechanical properties of the new photocured films were evaluated by DMA and TGA. The initial DMA scan of the photocured polymer (prepared from a 3 1 blend of 4-allyloxystyrene DVE-3) to ensure crosslinking on UV exposure shows two transitions at 62°C and 232°C, as shown in Figure 4, scan a. The low temperature transi-... 

Alkenyloxystyrene monomers such as 4-allyloxystyrene are useful components of photocured cationically polymerizable compositions. Used alone or in combination with divinyl ethers they provide low viscosity formulations, which are excellent solvents for commercial onium salt photoinitiators. Photocuring rates are comparable to vinyl ether monomers and the initially photocured alkenyloxystyrene polymers may be further heat processed to yield crosslinked phenolic type resins having outstanding thermal resistance properties. The new materials have good adhesive properties and are potentially useful where a combination of ease of processability and high performance is required. 

In order for maleimide/vinyl ether photoinitiator free photopolymerization to be useful, it is important that the cured films have good thermal/UV stability. Since there are no small molecule photoinitiators added to the uncured mixture initially, there is no residual small molecule photo initiator present in the final crosslinked film. This accounts for the enhanced UV stability we have observed for cured maleimide/vinyl ether films. In addition, TGA thermograms of photocured films of the MPBM/CHVE mixture (Figure 8) exhibit excellent thermal stability, with decomposition occurring at higher temperatures than for a simple UV cured HDDA film with 3 weight percent DMAP photoinitiator. (Such thermal stability would be... 

Fouassier, J.P. Photoinitiation, Photopolymerization, and Photocuring, 1995, Hanser Publishers, New York, NY. 

Temperature Profiles of Adiabatic Polymerizations. Experiments were conducted to characterize the adiabatic temperature profiles of photocured composites... 

Figure 10. Flexural modulus as a function of illumination time for photocured composites with fiber loadings of 0, 25, and 50 wt.%.

Para-t-butylphenyl glycidyl ether BPGE had a similar viscosity and C/O ratio as those of NA and had the best properties of the photocurable epoxies that were surveyed, but this monomer dewetted from Si substrates immediately after spin coating and formed a puddle at the substrate center. Other monofunctional epoxies exhibited the same behavior. Mixtures of BPGE with multifunctional aromatic epoxies wetted Si substrates and could be used as planarizing layers. 

Soucek, M. D. Wu, S. Chakrapani, S. Synthesis, Characterization, and Evaluation of Siloxane-Gontaing Modifiers for Photocurable Epoxy Coating Formulations. In Silicones and Silicone-Modified Materials-, Glarson, S. J., Fitzgerald, J. J., Owen, M. J., Smith, S. D., Eds. ACS Symposium Series 729 American Chemical Society Washington, DC, 2000 pp 516-532. 

---