Release coatings, silicones

Silicone release coatings are the workhorses of the easy release industry because the very nature of the molecule fulfills most requirements for low adhesion. When well cured, silicone networks are fairly inert and present a very low sur-... 

Among all the low energy interactions, London dispersion forces are considered as the main contributors to the physical adsorption mechanism. They are ubiquitous and their range of interaction is in the order 2 molecular diameters. For this reason, this mechanism is always operative and effective only in the topmost surface layers of a material. It is this low level of adhesion energy combined with the viscoelastic properties of the silicone matrix that has been exploited in silicone release coatings and in silicone molds used to release 3-dimensional objects. However, most adhesive applications require much higher energies of adhesion and other mechanisms need to be involved. 

Jones, J.D. and Peters, Y.A., Silicone release coatings. In Handbook of Pressure Sensitive Adhesive Technology. Satas Donatas Ed., Van Nostrand Reinhold, New York, 1989, pp. 601-626. 

Stein, J. and Eckberg, R.P., UV Curable silicone release coatings and controlled release additives. J. Coat. Fabr., 20, 24 (1990). 

R. P. Eckberg, "Chemistry and Technology of Radiation Curable Silicone Release Coatings," in D. Satas, ed.,. Advances in Pressure Sensitive Adhesives, Satas Associates, Warwick, R.I., 1992. 

The silicone release coating is applied on the paper or film in a liquid form and is then cured, generally by heating. 

Silicone release coated papers and films, when laminated to pressure-sensitive adhesive (PSA) coated materials, such as adhesive coated labels and tapes, provide both protection for the adhesive coated product (such as in preparation for slitting, die-cutting, and the like) and they provide subsequent easy release of the release coated paper or film from the adhesive surface immediately prior to its intended final use... 

The backing material and release liner can be fabricated from a variety of materials including polyvinylchloride, polyethylene, polypropylene, ethylene-vinyl acetate and aluminium foil. The most important property of these materials is that they are impervious to both drug and formulation excipients. The most useful backing materials conform with the skin and provide a balanced resistance to transepidermal water loss, which will allow some hydration of the stratum corneum, yet maintain a healthy subpatch environment. The release liners are usually films or coated papers and must separate easily from the adhesive layer without lifting off any of the pressure-sensitive adhesive. Silicone release coatings are used with acrylate and rubber-based adhesive systems, and fluorocarbon coatings with silicone adhesives. 

Typical substrates for silicone release coatings are supercalendered kraft paper, glassines, and thermally sensitive films such as polyethylene and polypropylene. Ideal curing conditions are 150°C or lower, and line speeds are as fast as 460 m/min. Key properties for release coatings are cure speed, integrity of cure, and stable release values. 

Epoxies can be modified to have low energy surfaces so that they can function in conjunction with silicone-release coatings. For this application, three types of block copolymers (53), each of which consisted of two blocks, were used as surface modifiers. One bloek was a random copolymer of methyl methacrylate (MMA) and 2,3-epoxypropyl methacrylate (GMA), the other was a polymer of lH,lH,2H,2H-heptadecafluorodeeyl acrylate (PFA) which has the following structure. 

Jones, D.J., Factors Affecting the Selection and Performance of Silicone Release Coatings. Dow Coming Corp., 1997. 

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