UV Cured Silicone Release Coatings

Silicone release liners are used as a nonadhering surface to which adhesive materials, such as, for example, pressure-sensitive adhesives, can be laminated. UV curable release coatings are based on poly(dimethylsiloxane) oligomers functionalized with acrylate or epoxy groups and are mostly coated onto papers or thin films. 

The coat weights are critical for fhe release properties of the liner. They are typically in the 0.7 to 1.0 g/m range and are applied most frequently by multiroll reverse coating systems or by offset gravure rolls. 

The chemistry involved depends on the oligomer used silicone acrylates cure by radical mechanism epoxy-silicones require cationic curing systems. Silicone 

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Silicone with vinyl-terminal groups is commonly UV-cured for release coatings. These materials have been combined with silicate tackifiers and acrylate monomers to make PSA compositions as well [55]. 

Among the most successful of the new radiation-curable silicone coating systems are compositions Incorporating cycloaliphatic epoxyfunctional silicone polymers with compatible iodonlum salt photocatalysts (1 - S ) The syntheses, structures, UV cure response, and other properties of these materials and some of their derivatives and monomeric homologs are discussed In the balance of this chapter. Their specific application for release coatings has been described In great detail elsewhere (5.6 > and Is not the subject of this paper. 

Chem. Descrip. Dimethicone/mercaptopropyl methicone copolymer Uses Release agent for plastics arid nrbber internal lubricant and release agent for sulfur and peroxide cure nrbber coreactant in vinyl polymerization synthesis of orgysilicone copolymers heat stabilizer for dimethyl silicone fluids corrosion inhibitor in coatings UV and EB cured inks and coatings ingred. cosmetic and personal care applies, incl. hair care... 

Uses Corrosion inhibitor in coatings release agent for plastic and rubber internal lubricant, release agent for sulfur- and peroxide-cure rubber coreactant in vinyl polymerization synthesis of organic/silicone copolymers ingred. in UV- and EB-cure inks and coatings heat stabilizer in dimethyl silicone fluids... 

UV-cured acrylate functionahsed silicones have been successfully used as release coatings [125,129,134]. They consist of either acrylate end-capped linear polydimethylsiloxanes or of sdicone chains containing pendent acrylate groups. 

With all of the aforementioned variables, hundreds of Pt-curable silicone products are available including heat-cured rubber, liquid injection moldable products and release coatings. There are also many curable products based on chemistry other than platinum condensation cure RTV, peroxide-cured and UV-cured epoxy silicones. With other functional groups and/or molecular weights, even more products are... 

The release layer is ordinarily a vinyl carbamate or a silicone (see Fig. 15.14). The primary requirements for good release are (1) the complete incompatibility between the adhesive and release layer, and (2) the lack of specific interactions or covalent bonding across the interface. For cured silicones, the likely presence of some unreacted groups such as acrylate ends (UV cured) or hydrosilane (Si-H) groups (hydrosilation cure) must be considered. The side chains of the vinyl carbamate release coatings are uniform in length which allows them to crystallize to... 

Chem. Descrip. Silicone oil-tree modified polymer Uses Air release agent tor nonaq. high-solids coatings (alkyds, epoxies, PU, acrylics, PVC, UV/EB-cured coatings) and printing inks Properties Gardner 2 color dens. 6.9 Ib/gal vise. 65 cps VOC 73.8% (EPA Method 24) 100% act., 22.9% solids Use Level 0.1-0.5% on total wt. 

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