Windshields key safety ingredient: PVB
By rgadmin on June 11, 2015
Windshield manufacturing is a highly technical process that involves keeping moisture and contaminants out of the process. Windshields are made up of two layers of glass with an inner layer of plastic, called Poly Vinyl Butyral, or PVB, which adheres to the glass and forms the protective mechanism that keeps glass fragments from flying into the vehicle during a collision. They are assembled in clean rooms that are controlled to tight tolerances of moisture and relative humidity. The moisture content of the PVB interlayer has a large effect on the adhesion between the glass and the PVB. In order to limit the effect of moisture, PVB is manufactured and maintained at a moisture level that must not vary by more than 5 one-hundredths of a percent (0.05%) from goal. Because the interlayer material is so sensitive to moisture, the PVB interlayer is manufactured in a controlled humidity environment, packaged in moisture-sealed systems, and shipped in refrigerated containers, just as if it were perishable vegetables. Deviation by more than this 0.05% moisture will so severely alter the way the glass sticks to the interlayer that it would likely no longer meet the federal codes for penetration resistance, nor meet the safety standards for glass adhesion.
According to the Applications Development Manager, one of the PVB manufacturers, when a windshield breaks, initial absorption of moisture from the air into the PVB interlayer occurs within minutes of exposure. Added exposure time results in the diffusion of the moisture deeper and further into the interlayer. This means that moisture entering the interlayer through a thin crack will, over time, migrate away from the line of the break. The distance the moisture migrates is a function of the amount of moisture and the temperature at which the interlayer is exposed, as well as the duration of the exposure.