Pressure-sensitive chemical release

Solid Film Paste Liquid Solvent sol, emulsion Solvent release Fusion on heating Pressure- sensitive Chemical reaction Room- temperature Elevated- temperature Bonding pressure required Bonding pressure not required... 

These two seemingly dissimilar applications have a common basis—both are examples of the pressure-sensitive release of a chemical. How are these products designed Tiny spherical capsules (microcapsules or microspheres) with a glass or polymer shell are filled with a liquid core and glued onto paper. For a scratch-and-sniff ad, the core of the microcapsules contains a liquid with the desired scent for carbonless paper, a liquid ink or dye is encapsulated within the... 

The polymer and glass microspheres employed in the pressure-sensitive release of chemicals range in size from 1 pm to 1 mm in diameter. (For comparison, a human hair is typically 80-100 pm in diameter.A scanning electron micrograph illustrating the morphology of the particles appears in color Fig. 14.2.1. ... 

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. 

The basic chemical technology of silicones and silicone elastomers is covered in Chapter 18 so the discussion here is limited to silicone resins. These materials have many applications, including use in paints and varnishes, molding compounds, encapsulants, electrical insulation, pressure-sensitive adhesives, laminates, and release coatings. Their heat stability, water repellency, and resistance to solvents and weathering favor their use in these applications. 

There are many potential causes of explosions and fires at industrial sites handling hazardous substances (a) chemical reactions that produce explosion, fire, or heat (b) ignition of explosive or flammable chemicals (c) ignition of materials due to oxygen enrichment (d) agitation of shock- or friction-sensitive compounds and (e) sudden release of materials under pressure [21,29]. 

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