Abstract:
A security film for shatter-proofing windows comprises a polyurethane stratum interposed between a pair of polyester strata, each of which is self supporting, the film being bonded to the inner face of the window by a pressure sensitive adhesive.

Description:
RELATED APPLICATIONS 
     The present application is a continuation-in-part of application Ser. No. 113,426, filed Feb. 8, 1971, now U.S. Pat. No. 3,775,226, issued Nov. 27, 1973, and is a division of application Ser. No. 295,816, filed Oct. 10, 1972, now U.S. Pat. No. 3,899,621, issued Aug. 12, 1975. 
    
    
     BACKGROUND AND SUMMARY 
     The present invention relates to a security film for shatter-proofing windows against impact or explosion, and, more particularly, to security film for application to one face of a window as a shield to prevent fragmentation of glass notwithstanding its splintering or cracking when damaged. Prior security films, when adhered to window faces, have tended to rip in the event of impact or explosion to the accompanyment of flying glass, which is the primary danger that safety film is intended to prevent. 
     The object of the present invention is to provide, as a security film for shatterproofing ordinary window panes, a laminated assemblage in which at least one polyurethane stratum is interposed between at least a pair of polyester strata, each of the latter of which are self supporting, and one of the latter of which is provided with a pressure sensitive surface. It has been found that such an assemblage, when adhered to the inner or outer face of an ordinary window pane, is characterized by an unusual ability to absorb energy without rupture, possibly because of the microstructure of the polyester which is devoid of surface discontinuities, the tenacity with which polyurethane can be bonded to polyester and the energy redistribution of which the entire assemblage is capable when incrementally under stress. 
     Another object of the present invention is to provide a process for applying such an assemblage to the inside or outside of an ordinary window pane, by wetting the pressure sensitive adhesive with an aqueous detergent, which permits the assemblage to be slipped into optically clear contact with the window pane face and which then evaporates through the assemblage, which fortuitously is moisture permeable, and via its edges to permit activation of the pressure sensitive adhesive. 
     Other objects of the present invention are to provide, in an assemblage of the present invention: a vapor deposited aluminum coat on at least one of the polyester strata for reduction of infrared transmission; and/or an ultra-violet absorbing pigment for reduction of ultraviolet transmission. 
     Further objects of the present invention will in part be obvious and will in part appear hereinafter 
     The invention accordingly comprises the products and processes of the present invention, together with their components, steps and interrelationships, which are referred to in the present disclosure, the scope of which will be indicated in the appended claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a fuller understanding of the nature and objects of the present invention, reference is made to the following detailed description, taken in connection with the accompanying drawing wherein: 
     FIG. 1 is a flow diagram illustrating a security film, in exaggerated cross section, undergoing a process of the present invention; 
     FIG. 2 illustrates a window incorporating the present invention; 
     FIG. 3 is an alternative product, in exaggerated cross section, analogous to the product of FIG. 1; 
     FIG. 4 is another alternative product embodying the present invention; and 
     FIG. 5 is a further alternative product embodying the present invention. 
    
    
     DETAILED DESCRIPTION 
     Generally, the security film of FIG. 1, which is flexible, comprises, in laminated sequence, a moisture permeable polyester stratum 12, an elastomeric polyurethane bonding stratum 14, a moisture permeable polyester stratum 16 and a pressure sensitive adhesive stratum 18. All of these strata are optically clear and transparent. Typically polyester strata 12 and 16 are of the type sold by Dupont under the trademark Mylar or by I.C.I. under the trademark Melinex. Typically polyurethane bonding stratum 14 is formed as an elastomer by casting a mixture of an isocyanate containing component and a hydroxyl containing component on one of the faces of polyester strata 12, 16, then superposing another of the faces thereon and compressing the two strata during heat curing. Typically pressure sensitive adhesive 18 is composed of a mixture of synthetic and natural rubbers, e.g. neoprene and latex, a tackifier such as terpene, and an organic solvent such as toluene or methyl ethyl ketone. This pressure sensitive adhesive is optically clear and transparent. 
     Preferably, polymeric strata 12 and 14 each ranges in thickness from 0.5 to 5 mils, elastomeric bonding stratum 14 ranges in thickness from 0.2 to 0.4 mils and pressure sensitive adhesive 18 ranges in thickness from 0.5 to 1.5 mils. 
     As shown in FIG. 1, following stripping of a silicone release stratum 20 from pressure sensitive adhesive stratum 18, a clear aqueous detergent 22 is applied to pressure sensitive stratum 18 in order to deactivate the pressure sensitive adhesive during application of the film shown at 10, to a window 24. During such superposition, the aqueous detergent coat serves as a lubricant to permit smoothing of the film and elimination of air pockets between the film and the window. Following application of the film to the window, the aqueous detergent diffuses through the edges of the interface between the film and the window and through the film itself. In order to facilitate such evaporation, preferably all of the strata of the film are selected for their vapor permeability, the pressure sensitive adhesive in particular being vapor permeable but insoluable with respect to water. In other words, the detergent is polar and the pressure sensitive adhesive is non-polar. 
     The alternative embodiment of FIG. 3 comprises, in laminated sequence, a moisture permeable polyester stratum 32, an elastomeric polyurethane bonding stratum 34, a moisture permeable polyester stratum 36, a pressure sensitive adhesive stratum 38, and a release stratum 42, all analogous to their counterparts in the embodiment of FIG. 1. In addition, this alternative embodiment comprises a vapor deposited aluminium coat 40 that is characterized by a visible light transmission of 5% to 60% and a thickness of no more than 300 angstrom units. In a modification of the embodiment of FIG. 2, one or both of the polyester strata contains an ultraviolet absorbent, for example, a dispersed substituted benzophenone of the type sold by Antara Chemicals under the trademark Uvinul. 
     Alternative heavier duty security films embodying the present invention are shown in FIGS. 3 and 4. The security film of FIG. 4 comprises in laminated sequence a polyester stratum 46, a polyurethane stratum 48, a polyester stratum 50, a polyurethane stratum 52, a polyester stratum 54, a pressure sensitive adhesive stratum 56 and a release stratum 58. The security film of FIG. 5 comprises all of the strata of FIG. 4, designated 60, 64, 66, 68, 70, 72, and 74, and additionally an interposed vapor deposited aluminum coat 62. In FIGS. 4 and 5, the polyester strata, polyurethane strata, vapor deposited strata, pressure sensitive strata and release strata are analogous to their counterparts in FIGS. 1 and 3. 
     In operation of each of the security films of FIGS. 1, 3 and 4, the security film is applied at 76 to the inside or outside face of a window pane 78. When in position, the security film of FIGS. 1 or 4 is capable of preventing fragmentation of window 78 when it is cracked or otherwise damaged by an external impact or explosion at a position 80. When in position, the security film of FIG. 2 or 5, in addition to serving the function of that of FIG. 1 or 4, serves as a solar control window for reduction of transmission of infrared, visible and ultraviolet radiation. 
     The present invention accordingly comprises a security film for application to an ordinary window pane in order to render it splinter proof. Since certain changes may be made in the foregoing disclosure without departing from the scope of the invention herein involved, it is intended that all matter shown in the accompanying drawing or described in the foregoing specification be interpreted in an illustrative and not in a limiting sense.