Abstract:
The present invention involves bilayers that include an interlayer that incorporates at least one polymer sheet having a reduced plasticizer content relative to interlayers that are typically used in multiple layer glazing panels, and, specifically, safety glass. Bilayers of the present invention resist environmental degradation along exposed edges, and are particularly resistant to haze formation along those edges.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention is in the field of multiple layer glazing panels, and, specifically, the present invention is in the field of multiple layer glazing panels that have a single rigid substrate, such as glass or rigid plastic.  
       BACKGROUND  
       [0002]     Safety glass is a multiple layer glazing construct that typically employs a polymeric interlayer disposed between two layers of glass. Conventionally, safety glass of this type has been manufactured by placing a polymer sheet between two layers of glass and laminating the three layers by applying heat and pressure to produce a finished, multiple layer glass panel. The resulting glazing panel resists penetration of an object because the polymer sheet adheres strongly to the glass but remains flexible and energy absorbent.  
         [0003]     Many variations on this theme have been reported. For example, the interlayer can be a single polymer sheet, or it can comprise multiple polymer sheets. In addition to polymer sheets, other functional layers can be included as part of an interlayer, including, for example, a polymer film that improves one or more characteristics of the finished product.  
         [0004]     A safety glazing panel that uses only one rigid substrate, for example, a pane of glass or a pane of rigid plastic, is known in the art as a “bilayer.” In order to provide optimal optical clarity, a bilayer typically is formed with an interlayer, as described above, disposed between a rigid substrate and a relatively stiff polymer film. The polymer film provides the necessary stiffness to maintain a relatively smooth surface, which allows for optical clarity that would not be possible with only a polymer sheet.  
         [0005]     One type of bilayer is formed by laminating a polymer sheet between a glass panel and a thin polyester film. Such a construct is suitable for applications, for example, in which a full two pane safety panel is either not desired or not practical. Bilayers can be used, for example, in the side windows of vehicles, where the full thickness of a two pane glass safety panel is generally undesirable.  
         [0006]     Despite their desirability for various applications, however, conventional bilayers can present various problems that are inherent in the single rigid substrate design. For example, bilayer edges are often exposed to the environment in which the bilayer is used, which can result in delamination or haze formation at those edges. Furthermore, moisture penetration through the polyester film can result in an increase in the moisture content of the underlying polymer sheet, which can result in delamination and haze formation throughout the bilayer.  
         [0007]     Accordingly, further improved bilayer multiple layer glazing panels and methods for making those panels are needed in the art.  
       SUMMARY OF THE INVENTION  
       [0008]     The present invention involves bilayers that include an interlayer that incorporates at least one polymer sheet having a reduced plasticizer content relative to interlayers that are typically used in multiple layer glazing panels, and, specifically, safety glass. Bilayers of the present invention, through the use of polymer sheets having reduced plasticizer content, resist environmental degradation along exposed edges and throughout the entire sheet. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]      FIG. 1  represents a schematic cross sectional view of various bilayer embodiments of the present invention.  
         [0010]      FIG. 2  represents a schematic cross sectional view of various bilayer embodiments of the present invention.  
         [0011]      FIG. 3  represents a schematic cross sectional view of various bilayer embodiments of the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0012]     The present invention relates to an improved glazing bilayer. As used herein, a “bilayer” is a multiple layer glazing construct having a rigid substrate and a polymer film between which is disposed a polymer stack, wherein the polymer stack can comprise a single polymer sheet or a polymer sheet and one or more additional polymeric layers. The polymer stack is equivalent to a multiple layer interlayer in standard safety glass for which a single polymer sheet or a single polymer sheet and one or more additional polymeric layers have been combined to form the interlayer.  
         [0013]     As shown in  FIG. 1  generally at  10 , in various embodiments a bilayer comprises a rigid substrate  12  and a polymer film  16  between which is disposed a polymer stack  14 . For the embodiments shown in  FIG. 1 , the polymer stack consists of a single polymer sheet  18 , but, as mentioned above, multiple layer polymer stacks are within the scope of a bilayer of the present invention.  
         [0014]     As will be described in greater detail below, a polymer sheet  18  can comprise any suitable polymer, and, in preferred embodiments, the polymer sheet  18  comprises poly(vinyl butyral). As will also be described in detail below, the polymer film  16  can be any suitable polymer film, and, in preferred embodiments, the polymer film comprises poly(ethylene terephthalate). The rigid substrate  12  can be glass, rigid plastic, or any other rigid substrate conventionally used in glazing panels.  
         [0015]     At least one polymer sheet within the polymer stack will have a relatively low plasticizer content, meaning less than 32 parts per hundred resin (phr) on a weight basis. In various embodiments, a polymer sheet in the polymer stack will comprise less than 32 phr, less than 30 phr, less than 28 phr, or less than 26 phr. In the embodiments shown in  FIG. 1 , for example, in which the polymer stack consists only of a single polymer sheet, that single polymer sheet will have the relatively low plasticizer content listed above.  
         [0016]      FIG. 2  shows other embodiments, in which the polymer stack comprises more than a single polymer sheet. As shown, a first polymer sheet  20  and a second polymer sheet  22  have been combined to form the polymer stack, which is disposed between the rigid substrate  12  and the polymer film  16 . Of course, embodiments in which three or more polymer sheets are combined to form the polymer stack are within the scope of the present invention. In embodiments with more than one polymer sheet in the polymer stack, as shown in  FIG. 2 , at least one of the polymer sheets has a relatively low plasticizer content, as described above. More than one or all of the polymer sheets in a polymer stack can have a relatively low plasticizer content as well. Further, the two or more polymer sheets in a polymer stack can be the same or different in any other respect. For example, in some embodiments two different types of polymer sheets are used, and in others, two polymer sheets having the same polymeric content are used, but each polymer sheet differs in the type and amount of additional agents that are included.  
         [0017]      FIG. 3  shows yet further embodiments in which the polymer stack, in additional to two polymer sheets, also includes a functional performance polymer film. As shown, the polymer stack  14  comprises a first polymer sheet  20  and a second polymer sheet  22  with a second polymer film  24  disposed therebetween. In these embodiments, the second polymer film  24  can be the same or different from the polymer film  16 , and, as above for the embodiments shown in  FIG. 2 , the two polymer sheets can be the same or different and at least one will have a relatively low plasticizer content.  
         [0018]     Embodiments such as those shown in  FIGS. 2 and 3  provide a means through which various agents and performance enhancing layers can be included within a polymer stack to achieve results that would be difficult or impossible with a single polymer sheet.  
         [0019]     Further included in the scope of the present invention are variations on the polymer stacks that are explicitly shown and described herein. For example, further polymer film layers and polymer sheet layers can be added to the polymer stack in many arrangements to produce a bilayer within the scope of the present invention.  
         [0020]     Further included within the scope of the present invention are polymer stacks produced through extrusion coating or coextrusion processes. For example, the polymer stack shown in  FIG. 2  can be formed by coextruding two polymers to form the two sheets shown, in addition to a conventional lamination procedure.  
         [0000]     Polymer Film  
         [0021]     As used herein, a “polymer film” means a relatively thin and rigid polymer layer that functions as a performance enhancing layer within a polymer stack or as the outside layer in a bilayer, as shown as element  16  in the Figures. Polymer films differ from polymer sheets, as used herein, in that polymer films do not themselves provide the necessary impact resistance and glass retention properties to a multiple layer glazing structure, but rather provide performance improvements, such as infrared absorption character. Poly(ethylene terephthalate) is most commonly used as a polymer film.  
         [0022]     Polymer films used in the present invention can be any suitable film that is sufficiently rigid to provide a relatively flat, stable surface, for example those polymer films conventionally used as a performance enhancing layer in multiple layer glass panels. The polymer film is preferably optically transparent (i.e. objects adjacent one side of the layer can be comfortably seen by the eye of a particular observer looking through the layer from the other side), and usually has a greater, in some embodiments significantly greater, tensile modulus regardless of composition than that of the adjacent polymer sheet. In various embodiments, the polymer film comprises a thermoplastic material. Among thermoplastic materials having suitable properties are nylons, polyurethanes, acrylics, polycarbonates, polyolefins such as polypropylene, cellulose acetates and triacetates, vinyl chloride polymers and copolymers, and the like. In various embodiments, the polymer film comprises materials such as re-stretched thermoplastic films having the noted properties, for example, polyesters. In various embodiments, the polymer film comprises or consists of poly(ethylene terephthalate), and, in various embodiments, the poly(ethylene terephthalate) has been biaxially stretched to improve strength and/or has been heat stabilized to provide low shrinkage characteristics when subjected to elevated temperatures (e.g. less than 2% shrinkage in both directions after 30 minutes at 150° C.).  
         [0023]     In various embodiments, a polymer film within a polymer stack can have a thickness of 0.013 millimeters to 0.25 millimeters, 0.025 millimeters to 0.1 millimeters, or 0.04 millimeters to 0.06 millimeters. In various embodiments, a polymer film that is used as the outside polymer film (element  16  in the Figures) can have a thickness of 0.1 millimeters to 0.25 millimeters, 0.13 millimeters to 0.22 millimeters, or 0.16 millimeters to 0.20 millimeters. The polymer film can optionally be surface treated or coated with a functional performance layer to improve one or more properties, such as adhesion or infrared radiation reflection. These functional performance layers include, for example, a multi-layer stack for reflecting infra-red solar radiation and transmitting visible light when exposed to sunlight. This multi-layer stack is known in the art (see, for example, WO 88/01230 and U.S. Pat. No. 4,799,745) and can comprise, for example, one or more Angstroms-thick metal layers and one or more (for example, two) sequentially deposited, optically cooperating dielectric layers. As is also known (see, for example, U.S. Pat. Nos. 4,017,661 and 4,786,783), the metal layer(s) may optionally be electrically resistance heated for defrosting or defogging of any associated glass layers. Various coating and surface treatment techniques for poly(ethylene terephthalate) films and other polymer films that can be used with the present invention are disclosed in published European Application No.0157030. Polymer films of the present invention can also include a hardcoat and/or and antifog layer, as are known in the art.  
         [0000]     Polymer Sheet  
         [0024]     As used herein, a “polymer sheet” means any polymer composition formed by any suitable method into a thin layer that is suitable alone, or in stacks of more than one layer, for use as a polymer stack (interlayer) that provides adequate penetration resistance and glass retention properties to laminated glazing panels. Plasticized poly(vinyl butyral) is most commonly used to form polymer sheets.  
         [0025]     The polymer sheet can comprise any suitable polymer, and, in a preferred embodiment, the polymer sheet comprises poly(vinyl butyral). In any of the embodiments of the present invention given herein that comprise poly(vinyl butyral) as the polymeric component of the polymer sheet, another embodiment is included in which the polymer component consists of or consists essentially of poly(vinyl butyral). In these embodiments, any of the variations in additives disclosed herein can be used with the polymer sheet having a polymer consisting of or consisting essentially of poly(vinyl butyral).  
         [0026]     In one embodiment, the polymer sheet comprises a polymer based on partially acetalized poly(vinyl alcohol)s. In another embodiment, the polymer sheet comprises a polymer selected from the group consisting of poly(vinyl butyral), polyurethane, poly(vinyl chloride), poly(ethylene-co-vinyl acetate), partially neutralized ethylene/(meth)acrylic copolymers, ionomers, combinations thereof, and the like. In further embodiments the polymer sheet comprises poly(vinyl butyral) and one or more other polymers.  
         [0027]     Other polymers having a suitable glass transition temperature can also be used. In any of the sections herein in which preferred ranges, values, and/or methods are given specifically for poly(vinyl butyral) (for example, and without limitation, for plasticizers, component percentages, thicknesses, and characteristic-enhancing additives), those ranges also apply, where applicable, to the other polymers and polymer blends disclosed herein as useful as components in polymer sheets.  
         [0028]     For embodiments comprising poly(vinyl butyral), the poly(vinyl butyral) can be produced by known acetalization processes that involve reacting poly(vinyl alcohol) with butyraldehyde in the presence of an acid catalyst, followed by neutralization of the catalyst, separation, stabilization, and drying of the resin.  
         [0029]     As used herein, “resin” refers to the polymeric (for example poly(vinyl butyral)) component that is removed from the mixture that results from the acid catalysis and subsequent neutralization of the polymeric precursors. Resin will generally have other components in addition to the polymer, for example poly(vinyl butyral), such as acetates, salts, and alcohols.  
         [0030]     Details of suitable processes for making poly(vinyl butyral) resin are known to those skilled in the art (see, for example, U.S. Pat. Nos. 2,282,057 and 2,282,026). In one embodiment, the solvent method described in Vinyl Acetal Polymers, in Encyclopedia of Polymer Science &amp; Technology,  3 rd edition, Volume 8, pages 381-399, by B. E. Wade (2003) can be used. In another embodiment, the aqueous method described therein can be used. Poly(vinyl butyral) is commercially available in various forms from, for example, Solutia Inc., St. Louis, Mo. as Butvar™ resin.  
         [0031]     In various embodiments, the polymer sheet comprises poly(vinyl butyral) having a molecular weight greater than 30,000, 40,000, 50,000, 55,000, 60,000, 65,000, 70,000, 120,000, 250,000, or 350,000 grams per mole (g/mole or Daltons). Small quantities of a dialdehyde or trialdehyde can also be added during the acetalization step to increase molecular weight to greater than 350,000 Daltons (see, for example, U.S. Pat. Nos. 4,874,814; 4,814,529; and 4,654,179). As used herein, the term “molecular weight” means the weight average molecular weight.  
         [0032]     Any suitable plasticizers can be added to the polymer resins of the present invention in order to form the polymer sheets. Plasticizers used in the polymer sheets of the present invention can include esters of a polybasic acid or a polyhydric alcohol, among others. Suitable plasticizers include, for example, triethylene glycol di-(2-ethylbutyrate), triethylene glycol di-(2-ethylhexanoate), triethylene glycol diheptanoate, tetraethylene glycol diheptanoate, dihexyl adipate, dioctyl adipate, hexyl cyclohexyladipate, mixtures of heptyl and nonyl adipates, diisononyl adipate, heptylnonyl adipate, dibutyl sebacate, polymeric plasticizers such as the oil-modified sebacic alkyds, mixtures of phosphates and adipates such as those disclosed in U.S. Pat. No. 3,841,890 and adipates such as those disclosed in U.S. Pat. No. 4,144,217, and mixtures and combinations of the foregoing. Other plasticizers that can be used are mixed adipates made from C 4  to C 9  alkyl alcohols and cyclo C 4  to C  10  alcohols, as disclosed in U.S. Pat. No. 5,013,779, and C 6  to C 8  adipate esters, such as hexyl adipate. In preferred embodiments, the plasticizer is triethylene glycol di-(2-ethylhexanoate).  
         [0033]     Polymer sheets other than those having a relatively low plasticizer content, as detailed above, can comprise 20 to 60, 25 to 60, 20 to 80, 10 to 70, or 5 to 100 parts plasticizer phr. Of course other quantities can be used as is appropriate for the particular application. In some embodiments, the plasticizer has a hydrocarbon segment of fewer than 20, fewer than -15, fewer than 12, or fewer than 10 carbon atoms.  
         [0034]     Adhesion control agents (ACAs) can also be included in the polymer sheets of the present invention to impart the desired adhesiveness. Any of the ACAs disclosed in U.S. Pat. No. 5,728,472 can be used. Additionally, residual sodium acetate and/or potassium acetate can be adjusted by varying the amount of the associated hydroxide used in acid neutralization. In various embodiments, polymer sheets of the present invention comprise, in addition to sodium acetate and/or potassium acetate, magnesium bis(2-ethyl butyrate)(chemical abstracts number 79992-76-0). The magnesium salt can be included in an amount effective to control adhesion of the polymer sheet to glass.  
         [0035]     Additives may be incorporated into the polymer sheet to enhance its performance in a final product. Such additives include, but are not limited to, plasticizers, dyes, pigments, stabilizers (e.g., ultraviolet stabilizers), antioxidants, flame retardants, other IR absorbers, UV absorbers, anti-block agents, combinations of the foregoing additives, and the like, as are known in the art.  
         [0036]     Agents that selectively absorb light in the visible or near infrared spectrum can be added to any of the appropriate polymer sheets. Agents that can be used include dyes and pigments such as indium tin oxide, antimony tin oxide, or lanthanum hexaboride (LaB 6 ).  
         [0037]     One exemplary method of forming a poly(vinyl butyral) layer comprises extruding molten poly(vinyl butyral) comprising resin, plasticizer, and additives, and then forcing the melt through a sheet die (for example, a die having an opening that is substantially greater in one dimension than in a perpendicular dimension). Another exemplary method of forming a poly(vinyl butyral) layer comprises casting a melt from a die onto a roller, solidifying the melt, and subsequently removing the solidified melt as a sheet. As used herein, “melt” refers to a mixture of resin with a plasticizer and, optionally, other additives. In either embodiment, the surface texture at either or both sides of the layer may be controlled by adjusting the surfaces of the die opening or by providing texture at the roller surface. Other techniques for controlling the layer texture include varying parameters of the materials (for example, the water content of the resin and/or the plasticizer, the melt temperature, molecular weight distribution of the poly(vinyl butyral), or combinations of the foregoing parameters). Furthermore, the layer can be configured to include spaced projections that define a temporary surface irregularity to facilitate the de-airing of the layer during lamination processes after which the elevated temperatures and pressures of the laminating process cause the projections to melt into the layer, thereby resulting in a smooth finish.  
         [0038]     In various embodiments, the polymer stacks of the present invention can have total thicknesses of 0.1 to 3.0 millimeters, 0.2 to 2.0 millimeters, 0.25 to 1.75 millimeters, and 0.3 to 1.5 millimeters, although other thicknesses, including greater thicknesses, are within the scope of the present invention. The individual polymer sheets of a multiple layer polymer stack can have, for example, approximately equal thicknesses that, when added together, result in the total thickness ranges given above. Of course, in other embodiments, the thicknesses of the layers can be different, and can still add to the total thicknesses given above.  
         [0039]     Bilayers of the present invention can be formed through any suitable process. In various embodiments, a bilayer is formed by stacking and then laminating the following layers: glass//polymer sheet//polymer film//glass. Lamination of this stack can be performed by any appropriate laminating process in the art, including known autoclave procedures. After lamination, the pane of glass that is in contact with the polymer film can be peeled off of the polymer film, leaving a single pane of glass having a polymer sheet disposed thereon with a polymer film disposed on the polymer sheet. Any multiple layer polymer stack of the present invention can be substituted for the polymer sheet in these methods (i.e. glass//polymer stack//polymer film//glass).  
         [0040]     The present invention also includes methods of manufacturing any of the bilayers of the present invention comprising using a vacuum non-autoclave process. In various embodiments of the present invention, a bilayer of the present invention is manufactured using a vacuum deairing non-autoclave process embodiment described in U.S. Pat. No. 5,536,347. In various other embodiments, a nip roll non-autoclave process embodiment described in published U.S. application US 2003/0148114 A1 is used.  
         [0041]     The present invention also includes methods of making a bilayer, comprising disposing a polymer stack of the present invention between a rigid substrate and a polymer film, and laminating the construct to form a bilayer.  
         [0042]     The present invention also includes glazing panels comprising any of the bilayers of the present invention.  
         [0043]     The following paragraphs describe various techniques that can be used to measure the characteristics of the polymer sheet.  
         [0044]     The clarity of a polymer sheet can be determined by measuring the haze value, which is a quantification of the light scattered by a sample in contrast to the incident light. The percent haze can be measured according to the following technique. An apparatus for measuring the amount of haze, a Hazemeter, Model D25, which is available from Hunter Associates (Reston, Va.), can be used in accordance with ASTM D1003-61 (Re-approved 1977)-Procedure A, using Illuminant C, at an observer angle of 2 degrees. In various embodiments of the present invention, percent haze is less than 5%, less than 3%, and less than 1%.  
         [0045]     The visible transmittance can be quantified using a UV-Vis-NIR spectrophotometer such as the Lambda 900 made by Perkin Elmer Corp. by methods described in international standard ISO 9050:1990. In various embodiments, the transmittance through a polymer sheet of the present invention is at least 60%, at least 70%, or at least 80%.  
         [0046]     Pummel adhesion can be measured according to the following technique, and where “pummel” is referred to herein to quantify adhesion of a polymer sheet to glass, the following technique is used to determine pummel. Two-ply glass laminate samples are prepared with standard autoclave lamination conditions. The laminates are cooled to about −17.8° C. (0° F.) and manually pummeled with a hammer to break the glass. All broken glass that is not adhered to the poly(vinyl butyral) layer is then removed, and the amount of glass left adhered to the poly(vinyl butyral) layer is visually compared with a set of standards. The standards correspond to a scale in which varying degrees of glass remain adhered to the poly(vinyl butyral) layer. In particular, at a pummel standard of zero, no glass is left adhered to the poly(vinyl butyral) layer. At a pummel standard of 10, 100% of the glass remains adhered to the poly(vinyl butyral) layer. Poly(vinyl butyral) layers of the present invention can have, for example, a pummel value of between 3 and 10.  
       Example 1  
       [0047]     Two bilayers are constructed having three layers—glass//poly(vinyl butyral)//poly(ethylene terephthalate). The glass layers are 2.3 millimeters thick. The poly(ethylene terephthalate) layers are 0.18 millimeters thick with a hardcoat (available from CPFilms, Inc.). The poly(vinyl butyral) layer in the first bilayer is 0.76 millimeters thick and has a plasticizer (triethylene glycol di-(2-ethylhexanoate)) content of 38 phr. The poly(vinyl butyral) layer in the second bilayer is 0.76 millimeters thick and has a plasticizer (triethylene glycol di-(2-ethylhexanoate)) content of 30 phr. Both poly(vinyl butyral sheets) also contain adhesion control salts and UV absorbers.  
         [0048]     Measurements are taken immediately after lamination and then again after the panels are exposed to an environment of 70° C. and 100% relative humidity for one week. Results are shown in the table, below:  
                                                                     First Bilayer (38 phr   Second Bilayer (30 phr           plasticizer)   plasticizer)                                        Initial Moisture %   0.4   0.3           Final Moisture %   3.6   3.5           Initial % Haze   1.4   1.7           Final % Haze   29.0   11.6                      
 
         [0049]     By virtue of the present invention, it is now possible to provide bilayers having improved edge stability character for use as glazing panels, such as laminated glass panels for windshields and architectural windows.  
         [0050]     While the invention has been described with reference to exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiments disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.  
         [0051]     It will further be understood that any of the ranges, values, or characteristics given for any single component of the present invention can be used interchangeably with any ranges, values, or characteristics given for any of the other components of the invention, where compatible, to form an embodiment having defined values for each of the components, as given herein throughout. For example, a polymer sheet can be formed comprising any of the relatively low plasticizer contents as well as various residual hydroxyl contents to form many permutations that are within the scope of the present invention but that would be exceedingly cumbersome to list.  
         [0052]     Any figure reference numbers given within the abstract or any claims are for illustrative purposes only and should not be construed to limit the claimed invention to any one particular embodiment shown in any figure.  
         [0053]     Figures are not drawn to scale unless otherwise indicated.  
         [0054]     Each reference, including journal articles, patents, applications, and books, referred to herein is hereby incorporated by reference in its entirety.