Pressure sensitive adhesive silicone rubber

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. 

Pressure-sensitive adhesives (PSAs) based on acrylic, natural rubber and silicone are employed primarily for ease of application. To name Just a few applications, PSAs bond decals to surfaces, interior decorative surfaces to interior panels, interior trim pieces in place directly or hook and loop tape for the same purpose, structural shims in place during manufacturing and acoustic (sound deadening) materials to body skin interior surfaces. Tape products with pressure-sensitive adhesive on one or both surfaces are used for such functions as cargo compartment sealing, as a fluid barrier to prevent spills and leaks in the lavatories and... 

The primary mode of bonding for a pressure-sensitive adhesive is not chemical or mechanical but rather a polar attraction to the substrate. This always requires pressure to achieve sufficient wet-out onto the surface thereby providing adequate adhesion. The four main varieties of pressure-sensitive adhesives are derived from rubber-based, acrylic, modified acrylic and silicone formulations. Release liners are used to carry the sticky label and enable it to be printed. The release liners are normally paper, treated with a very thin silicone coating to allow the label to be peeled away easily without tearing. Some transfer of the silicone into the adhesive is inevitable. 

FDA approved under 21CFR175.125 - pressure sensitive adhesives 175.300 - resinous and polymeric coatings 175.390 -zinc-silicon dioxide matrix coatings, 177.1210 - closures with sealing gaskets for food containers 177.2600 - rubber articles intended for repeated use and 178.2010 - antioxidants and/or stabilizers for polymers. 

The fourth and fifth papers have to do with properties of pressure-sensitive adhesives. In particular, the matter of how the materials composing pressure-sensitive adhesives (rubbers and resins) interact and phase separate to produce the phenomenon of tack or pressure-sensitivity is addressed. Both studies use dynamic mechanical measurements to uncover phasing - one in a silicone and the other in natural and styrene-butadiene rubber systems tackified with various resins. 

Adhesives as materials can be classified in a number of ways such as chemical structure or functionality. In this book, adhesives have been classified into two main classes natural and synthetic. The natural group includes animal glue, casein- and protein-based adhesives, and natural rubber adhesives. The synthetic group has been further divided into two main groups industrial and special compounds. Industrial compounds include acrylics, epoxies, silicones, etc. An example of the specialty group is pressure-sensitive adhesives. 

Applications requiring low adhesion take advantage of the surface properties of the methyl groups (see Mould adhesion and fouling). They include liquid silicone rubber (LSR) used in moulding applications, silicone Release coatings to dispense organic Pressure-sensitive adhesives (PSA) and silicone PSAs. 

The raw materials used for pressure-sensitive adhesives are natural and synthetic rubbers in conjunction with modified rosins, phenol - formaldehyde resins, or hydrocarbon resins. In addition to rubber, polyacrylates, polymethacrylates, poly(vinyl ethers), and polyisobutenes also are used frequently, again mostly in combination with resins. Silicone resins are used for special applications. 

Pressure-sensitive adhesives (PSAs) are typically used to hold objects together by bringing the surfaces into contact under pressure, applied briefly at room temperature. Natural rubber, styrenebutadiene (SBR), butadiene-acrylonitrile rubber, thermoplastic adhesives, polyacrylates, and silicones are the typical materials used for pressure-sensitive adhesive applications. These materials have viscous properties to provide flow while resisting excessive flow, partial elastic behavior to be able to carry some load, the ability to store energy to provide peel and tack, and the capability to dissipate energy during usage. Tack may be obtained by the use of resinous softeners such as pine tar or rosin esters, by the use of mineral fillers and various coal tar or petroleum derivatives. 

Pressure sensitive and contact adhesives are made from a variety of polymers including acrylic acid esters, polyisobutylene, polyesters, polychloroprene, polyurethane, silicone, styrene-butadiene copolymer and natural rubber. With the exception of acrylic acid ester adhesives which can be processed as solutions, emulsions, UV curable 100% solids and silicones (which may contain only traces of solvents), all remaining rubbers are primarily formulated with substantial amounts of solvents such as hydrocarbon solvents (mainly heptane, hexane, naphtha), ketones (mainly acetone and methyl ethyl ketone), and aromatic solvents (mainly toluene and xylene). 

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