AGG - 2006 - March/April

Volume 20 • Issue 2 • March/April 2006

Glass Tech

Design Considerations for Laminated Glazing Even Out

Laminated glazing materials consist of multiple plies of glass, interlayers, resins and/or plastic glazing materials (such as polycarbonate sheet or acrylic), which are often complex in nature. Design professionals should be aware of the following considerations when selecting and specifying laminated glazing constructions.

Aesthetic Color

Commercial clear float glass is nearly colorless, however, a green or blue-green tint, which is faint in thin glass, may become noticeable in glazing applications where the glass thickness exceeds 3/8 inch (10 mm).

Laminated glazing materials, utilized for their impact resistance to ballistics, blast and physical attack and for additional applications such as zoo exhibits and large aquariums, incorporate numerous plies of transparent glazing materials. In these applications, the thickness of the glass portion of the laminate often results in a more apparent degree of green. In some instances, the green tint is not as pronounced, as it can be disguised by the blue color of the water or the color of painted walls in an aquarium. The green tint also may not be as apparent in certain constructions such as glass-clad polycarbonate laminates that contain more polycarbonate than glass.

However, in certain applications, the green tint may be regarded as aesthetically displeasing to a designer and owner.

For projects that require the highest level of color clarity, low-iron clear float glass should be considered. Low-iron clear float glass may also assist the designer in providing a closer color match to a less thick glass that is in proximity to the laminated glazing. Many laminated glazing components are designed to block ultraviolet light (energy wavelengths from 280 nm to 380 nm); however, these components also block a portion of the visible light spectrum (wavelengths from 380 nm to 420 nm) with a result that there may be a slight yellow appearance.

This yellow appearance, not visible in single or thin multiple layers, may become noticeable when these materials are used in thicker or a greater number of multiple layers. This color, the result of the physics of spectral energy, should be considered in conjunction with color imparted by the glass itself.

There are also design considerations, which must be taken into account when a low-E or reflective coating is used in the construction of a laminate. When the coating, applied to the glass substrate, is placed in contact with the PVB, the refractive index of the coating is changed and will result in a perceived color shift. This means that a coating in an insulating glass unit may appear a different color than the same coating in a laminate.

Iridescence

When viewing laminated glazing constructions, under certain conditions, a pattern of iridescent spots or darkish shadows may become visible. This is commonly referred to as the strain pattern of the heat-treated glass and is related to the stresses introduced in the cooling process of the glass fabrication. While not normally visible, the strain pattern may become more evident by reflectance and in transmittance when viewing the glazing material at severe angles or under polarized light conditions. The potential of the iridescence becoming more pronounced is enhanced as the thickness of the laminated glazing material increases. The strain pattern is inherent in those heat-treated components and is not a result of discoloration or non-uniformity.

This material is excerpted from the Glass Association of North America’s (GANA) Informational Bulletin: Design Considerations for Laminating Glass Applications. The complete bulletin may be downloaded from the GANA Web site, www.glasswebsite.com. It is under the Publications category. Material© GANA 2005.