Plasticized polyvinyl butyral interlayers

DETAILED DESCRIPTION I claim: 1.
In a polyvinyl butyral sheet plasticized with a multiester of an alcohol having 2 to 4 hydroxyl groups and a C.
sub.
16 to C.
sub.
20 unsaturated fatty acid having a hydroxyl group attached to the acid molecule, the improvement which comprises, in property-improving combination with such multiester, a synergistically effective amount of a monoester of a glycol and said C.
sub.
16 to C.
sub.
20 unsaturated fatty acid, wherein the ratio of said monoester to said multiester is between about 1:1 to about 5:1.
2.
The plasticized sheet of claim 1 wherein the monoester is propylene glycol-1,2 monoricinoleate.
3.
The plasticized sheet of claim 1 wherein the monoester is ethylene glycol monoricinoleate.
4.
The plasticized sheet of claim 1 wherein said ratio is about 2:1.
5.
The plasticized sheet of claim 4 wherein the multiester is present as a castor oil component.




Description:
BACKGROUND OF THE INVENTION This invention relates to polyvinyl butyral (PVB) sheet plasticized with fatty acid esters and more particularly with a fatty acid ester blend which provides the sheet with improved penetration resistance without significant loss in its resistance to stress cracking polycarbonate or polyacrylate when in contact therewith as an interlayer in a laminated glass assembly.
In recent years sociologists and psychologists have started a movement toward prisons without bars.
Thick layers of impact resistant polycarbonate initially used in such applications were quite early determined to be inadequate since the polycarbonate could be burned or scratched or dissolved or fractured when heated or abused.
Moreover, when exposed to the elements the polycarbonate turned yellow, lost its strength and was susceptable to crazing.
Based on this early work a need was defined for a material for security applications which was strong, chemically impervious, and scratch and fracture resistant over a wide range of ambient conditions.
Thereafter laminates of one or more layers of glass with one or more layers of polycarbonate were proposed which in use were mounted with the glass layer on the outside exposed to the elements and the polycarbonate either forming the innermost surface or positioned inboard of a glass layer forming such innermost surface