Polyvinyl butyral

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: GlasNovations,BUTACITE, SAFLEX, S-Lec, TROSIFOL etc.

Applications

Automotive and architectural

Laminated glass, commonly used in the automotive and architectural fields, comprises a protective interlayer, usually polyvinyl butyral (PVB), bonded between two panels 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 laminate to the other.

Colors

PVB interlayer can be purchased in colored sheets, such as for the blue or green "shade band" at the top edge of many automobile windshields. PVB Interlayers can also be purchased in different colors for architectural laminated glass manufacture.

Solar modules

PVB has gained acceptance among manufacturers of photovoltaic thin film solar modules. The photovoltaic circuit is formed on a sheet of glass using thin film deposition and patterning techniques. PVB and a second sheet of glass (called back glass) are then placed directly on the circuit. The lamination of this sandwich encapsulates the circuit, protecting it from the environment. Current is extracted from the module at a sealed terminal box that is attached to the circult through a hole in the back glass. Another common laminant used in the solar industry is Ethylene-vinyl acetate (EVA).

Properties

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 three 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; third the viscoelastic interlayer undergoes plastic deformation during impact and under static loads after impact, absorbing energy and reducing penetration by the impacting object as well as reducing the energy of the impact that is transmitted to impacting object, e.g. a passenger in a car crash. Thus, the benefits of laminated glass include safety and security.

Production

PVB is a 70-year-old product. It has been the dominant interlayer material since the late 1930s. It is currently manufactured and marketed by a number of companies worldwide, including GlasNovations UK (KB brand, introduced in 2003), DuPont (Wilmington, Delaware, USA) ("Butacite"-brand PVB), Solutia (St. Louis, Missouri, USA) (Saflex-brand PVB), Kuraray Europe GmbH (Frankfurt, Germany) ("Trosifol"-brand PVB), and Sekisui (Kyoto, Japan).

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, 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.

Other interlayer materials

There are other types of interlayer materials in use, including polyurethanes such as Duraflex-brand thermoplastic polyurethane film, manufactured by Bayer MaterialScience, Ludwigshafen, 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."

See also

• Glass

References

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