This invention relates to plasticized polyvinyl butyral interlayers for use in laminated glazing units. More particularly it relates to polyvinyl butyral interlayers plasticized with a blend of plasticizers which together exhibit a desirable range of properties that make such interlayers useful in the production of laminated glazing units for architectural purposes.
The major property required of a plasticized polyvinyl butyral interlayer suitable for the production of laminates for architectural purposes is edge stability, that is, its ability to resist delamination at the edges of the laminate, particularly after many years of exposure to a humid environment. Laminates for architectural purposes must meet an exceptionally high standard of edge stability not demanded of laminates used in automotive windshields which have a shorter expected life span than architectural laminates.
Edge stability of closely related to compatibility in the sense that if the plasticizer is incompatible with the polymer, it will readily be lost at the laminate edge by, for example, exudation or displacement by water. Thus unless the plasticizer has outstanding compatibility, a laminate employing as the interlayer a polyvinyl butyral plasticized with that plasticizer is unlikely to exhibit a sufficiently high degree of edge stability to permit its use for architectural purposes.
Another characteristic that is highly desirable in an architectural glass laminate is an adequate impact strength. It is known that some plasticizers have a disastrous effect on the impact strength, especially at low temperatures, of laminates incorporating an interlayer plasticized thereby. The plasticizer combinations of the present invention however are capable of being used to produce laminates which also meet the necessary impact strength criteria for use as architectural glass.