Polyvinyl butyral
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Polyvinyl butyral (or PVB) is a resin usually used for applications that require strong binding, optical clarity, adhesion to many surfaces, toughness and flexibility. It is prepared from polyvinyl alcohol by reaction with butyraldehyde. The major application is laminated safety glass for automobile windshields. Tradenames for PVB-films include: BUTACITE, SAFLEX, S-Lec, TROSIFOL
[edit] Applications
Laminated glass, commonly used in the automotive and architectural fields, comprises a protective interlayer, usually polyvinyl butyral (PVB), bonded between two panes of glass. The bonding process takes place under heat and pressure. When laminated under these conditions, the PVB interlayer becomes optically clear and binds the two panes of glass together. Once sealed together, the glass "sandwich" (i.e., laminate) behaves as a single unit and looks like normal glass. The polymer interlayer of PVB is tough and ductile, so brittle cracks will not pass from one side of the windscreen to the other.
Annealed glass, heat-strengthened or tempered glass can be used to produce laminated glass. While laminated glass will crack if struck with sufficient force, the resulting glass fragments tend to adhere to the interlayer rather than falling free and potentially causing injury.
In practice, the interlayer provides two beneficial properties to laminated glass panes: first, the interlayer functions to distribute impact forces across a greater area of the glass panes, thus increasing the impact resistance of the glass; second, the interlayer functions to bind the resulting shards if the glass is ultimately broken. Thus, the benefits of laminated glass include safety and security.
[edit] Production
PVB has been the dominant interlayer material since the late 1930's. It is currently manufactured and marketed by a number of companies worldwide, including DuPont (Wilmington, Del.) ("Butacite"-brand PVB, introduced in 1938), Solutia (St. Louis, Mo.) (Saflex-brand PVB, introduced in 1940), Kururay Specialties Europe (Frankfort, Germany) ("Trosifol"-brand PVB), and Sekisui (Kyoto, Japan). There are, however, other types of interlayer materials in use, including polyurethanes such as Duraflex-brand thermoplastic polyurethane film, manufactured by Bayer Materials Science, Ludwigschafen, Germany. As used herein, the term "interlayer" refers to any material now known or developed in the future for manufacturing laminated glass. PVB and thermoplastic polyurethanes (TPUs) are explicitly included within the definition of "interlayer."
The market for laminated glass products is a mature one, and relatively stagnant. With only minor modifications, the PVB interlayer sold today is essentially identical to the PVB sold 30 years ago. Since its introduction in 1938 by DuPont, the worldwide market for PVB interlayer has been dominated by a handful of large chemical concerns. As a result, inventive efforts have tended toward methods of making the interlayer itself cheaper to manufacture, or making the interlayer easier to handle and less prone to material defects during the process of fabricating laminated glass panes.
PVB interlayer can be purchased in dyed sheets, such as for the blue "sun strip" at the top edge of many automobile windshields. However, discontinuous laminates of interlayer material that use colored portions of interlayer to form shapes, alpha-numeric indicia, and the like, are heretofore unknown.
