AGG - 2006 - May/June

Volume 20 • Issue 3 • May / June 2006

Glass Tech

Materials Used in Laminates

What are laminates made of? The most common glazing material used in laminated products is glass.

Plastics are the second type of glazing material used in laminated constructions. They can be composed of a natural or artificially prepared organic polymer of low extensibility. Plastics used for laminated constructions are typically extruded or molded, and are either rigid or non-rigid depending on the material type. They are relatively light and are often used in the production of bullet-resistant and other laminates requiring low deflection and rigorous impact performance. Plastics can be clear, translucent or tinted and may have an anti-scratch coating applied to one or both surfaces.

A number of materials are used as the interlayer in laminates.

Plasticized Polyvinyl Butyral (PVB) Sheet
Plasticized polyvinyl butyral sheet is made from polyvinyl butyral resin, plasticizer and proprietary chemical additives that give the interlayer unique impact and retention properties when used to laminate glass and some plastic glazings together. Typically, the raw materials are combined and extruded as sheet under stringent conditions and supplied in roll form to fabricators. The fabricators then use a sheet laminating process with properly selected interlayer and glazing to assemble the unit. When this type of interlayer is part of a laminate, it is placed between one or more plies of glass and plastic. The glazing sandwich is then exposed to heat and pressure which bonds the components into an integral unit.

There are several formulations of PVB interlayers and the architect or specifier must take care to denote the correct formulation and thickness appropriate for the design application. Interlayers tend to be classified by the primary intended use application. Formulations currently exist for acoustic damping, ballistic-resistance, decorative applications, energy control, hurricane-resistance and safety glazing. Although formulations usually are designed to cover multiple purposes, it is suggested that the interlayer manufacturer or glass fabricator be consulted to identify the appropriate formulation for the desired application. The PVB formulation should be clearly identified in the specification.

Aliphatic Polyurethane Sheet
Aliphatic polyurethanes are based on aliphatic isocyanates and mostly polyester and/or acrylic polyvols. The raw material usually is extruded as sheet under stringent conditions and supplied in roll form to fabricators. The fabricators then use a sheet lamination process with the proper interlayer and glazing to assemble the unit. When this interlayer is part of a laminate, the same process is followed with PVB. This type of interlayer is used for laminating glass-clad and all non-coated polycarbonate or acrylic (plastic) units. The interlayer is in contact with the non-coated side of the plastic, even if the opposing side contains a coating, and is available in clear, translucent and some tinted versions.

Cured Resin Interlayers
Cured resin interlayers are made from liquid formulations that react to form solid interlayers after the formulations have been introduced between two lites of glass. The compositions usually are comprised of one or more reactive polymers dissolved in reactive diluents along with other proprietary chemical additives. The polymers, which may be polyester-, urethane-, or acrylic-based, are primarily responsible for the bulk properties of the interlayer, such as tensile strength or percent elongation, while the reactive diluents serve to reduce the viscosity of the composition so that it can be easily pumped into the gap between the two pieces of glass. The chemical additives are present to help improve interlayer properties, such as adhesion to the glass.

Because a wide variety of materials can be used for the liquid interlayers, the properties of the interlayer can be tailored for specific end uses, such as safety, security, hurricane resistance, bomb blast resistance, or acoustic performance. In addition, the liquid nature of these materials enables the fabricator to add colors or effect pigments immediately prior to lamination.

For ionoplast interlayers, the raw materials typically are combined and extruded as sheet and supplied in sheet form to fabricators that use the same laminating process as with PVB. This type of interlayer is a rigid sheet and is generally used for high loads and security applications.