Modification of Cationic Curable Silicone Release Coating - Formulation with Oxetane Derivatives -

UV-cationic curabTe silicone release coatings, which are based on cycloaliphatic epoxy-functional polydimethylsiloxane (CE-PDMS) in combination with onium salts, can be counted as well-established commercial products. Despite their good performance, such as not subjecting to oxygen inhibition and high throughput based on their high curing speeds, they are still niche products due to their high system cost relative to conventional thermal cured silicones. For the cost reduction, blends of inexpensive organic compound have been proposed. In the UV-cationic formulations, vinyl ether monomers, exhibiting rather low viscosity with high safety, had been evaluated as reactive diluent. High compatibility both with CE-PDMS or onium salts and good properties as silicone release coatings was reported. The cationic polymerization of vinyl ether monomer, however, tends to cause yellowing and odor problem based on a generation of hemiacetal unit by atmospheric water. In addition, the formulation of vinyl ethers and cycloaliphatic epoxides results in the mixture of homo- and block-polymers of them (9). Because of the difference in the active species, alternative co-polymerization does not occur, which makes the formulation design difficult. Thus, another low viscous, safe and co-polymerizable monomer has been desired. Oxetane was found to possess quite different polymerization characteristics from those for epoxides in the UV cationic polymerization (10). Formulating with epoxy monomer, highly reactive UV cationic curable oxetane resins have been proposed by our laboratory (11, 12). In addition to the high reactivity of oxetanes, another interesting property is a safety. Oxetane monomers synthesized and tested so far, were all AMES test negative (12). Taking an advantage of this safety, low molecular weight oxetane monomers possessing low viscosity and high compatibility with other ingredients can be designed and used safely, which enable formulators to explore wide latitude for the formulations. Introduction of linear alkyl chains should be effective for improved miscibility to non-polar monomers, such as PMDS. Employing 3-ethyl-3-(2-ethylhexyloxy)methyl oxetane (EHOX) and 3-Ethyl-3-{(3-ethyloxetan-3-yl)methoxymethyl}oxetane (DOX), preliminary survey for the modification of CE-PDMS was carried out and good performance as diluent was found, however, the curing speed was reduce with high amount of EHOX added.