Production of Modular Window Gaskets Using Light Stable Polyurethanes

The advantages of modular windows with the gasket molded directly onto the glass are now well established. These windows offer aerodynamic design, variable gasket cross-section, molded-in attachments and ease of installation. This greatly increases styling and design flexibility compared to windows with conventional gaskets.

There are several choices of molded gasket material which include: PVC, post-painted polyurethane, in-mold coated Polyurethane and light stable polyurethane. Polyurethane processed by reaction injection molding (RIM) is typically selected for larger windows. Polyurethanes can be formulated to give a wide range of flexural modulus values and are readily molded into the long narrow cross-sections characteristic of window gaskets. The use of PVC is limited by the high temperatures, high injection pressures and high clamping forces needed for injection molding of thermoplastic materials.

Conventional polyurethane made with aromatic diisocyanates require a protective coating to prevent degradation by sunlight. The coating can be sprayed into the tool before the gasket is molded or the gasket can be post-painted. No protective coating is needed for an inherently light stable polyurethane formulated with an aliphatic diisocyanate. The physical properties, aging and weatherability of a series of light stable polyurethanes for modular window gaskets are described below.