1.  Field of the Invention
This invention relates to a laminate having an internal member responsive to stimuli; to an interlayer composite to seal the edge portions of the laminate; optionally to bus bars arranged on the internal member to eliminate hot spots at end portions of the bus bars; to methods of fabricating the laminate using the interlayer composite, and optionally the arrangement of the bus bars, and, in particular, to a heatable transparent laminate, e.g. an automotive windshield having an interlayer composite having a lead assembly to prevent ingress of air into the laminate and to provide external electrical access to bus bars optionally arranged to eliminate hot spots at end portions of the bus bars, and to methods of making the heatable laminate. 
2.  Discussion of the Technology
Automotive heatable windshields, e.g. of the type disclosed in U.S. Pat.  No.  4,820,902 include two glass sheets laminated together by a plastic interlayer, usually a sheet of polyvinyl butyral (xe2x80x9cPVBxe2x80x9d).  A pair of spaced bus bars between the glass sheets are in electrical contact with an electrically conductive member, e.g. a sputtered electrically conductive coating of the type disclosed in European Patent Application No.  00939609.4, applied to a major surface of one of the glass sheets or a plurality of electrically conductive filaments of the type disclosed in U.S. Pat.  No.  5,182,431.  Each of the bus bars is electrically accessible by an external lead to pass current from a power source through the bus bars and the coating to electrically heat the coating and heat by conduction the inner and outer surfaces of the windshield.  The heated windshield surfaces attain a temperature sufficient to remove fog, and melt snow and ice.  As can be appreciated, heatable windshields are practical, and in some geographical areas are a requirement, during the winter season. 
In the fabrication of commercially available automotive windshields, an electrically conductive coating, usually a sputtered electric conductive coating is applied to a flat piece of glass.  The flat piece of glass is cut to provide a blank.  A pair of spaced bus bars is provided on the coating by silk-screening an electrically conductive ceramic paste onto the conductive coating as discussed in U.S. Pat.  Nos.  4,654,067 and 4,718,932 or by using metal foil bus bars as discussed in U.S. Pat.  Nos.  5,418,026; 5,466,911, and 5,850,070.  A second glass blank has a black band silk-screened onto the marginal edges.  The black band shields the underlying adhesive securing the windshield to the automotive body from ultraviolet (xe2x80x9cUVxe2x80x9d) radiation that can deteriorate the adhesive and provides an aesthetically pleasing appearance. 
The coating and silk screened bus bars are normally applied to a surface of a blank that is designated as the No.  3 surface of the laminated windshield, i.e. the outer surface of the inner glass blank of the laminated windshield as mounted in the vehicle.  The black band is normally applied to a surface of a blank that is designated as the No.  2 surface of the laminated windshield, i.e. the inner surface of the outer glass blank of the laminated windshield.  The glass blank having the coating and the bus bars, and the glass blank having the black band are each shaped for a contoured windshield.  A sheet of plastic interlayer, usually polyvinyl butyral is positioned between the shaped glass sheets (referred to as a xe2x80x9cwindshield subassemblyxe2x80x9d).  When the bus bars are not silk screened on the coating, e.g. when metal foil bus bars are used, the bus bars are positioned between the interlayer and the coating. 
The edges of the windshield subassembly are edge sealed in the usual manner, e.g. moving the windshield subassembly through nipper rolls or placing a vacuum channel around the periphery of the windshield subassembly and pulling a vacuum while heating the windshield subassembly.  Thereafter the edge sealed windshield subassembly is placed in an air autoclave; heat and pressure are applied to the edge sealed subassembly to provide a laminated windshield.  The seal around the periphery of the edge sealed windshield subassembly is formed to prevent air from moving between the glass sheets during the removal of the vacuum channel after the edge sealing operation and/or during the autoclaving. 
For a general discussion regarding heatable windshields reference may be had to U.S. Pat.  Nos.  3,789,191; 3,789,192; 3,790,752; 3,794,809; 4,543,466, and 5,213,828. 
As can be appreciated, eliminating the silk screening of bus bars eliminates a manufacturing operation and all the limitations associated therewith such as the inventory of silk screens for each windshield design, handling and inventory of the ceramic conductive paste, and maintaining efficient operation of the silk-screening machines.  Using metal foil bus bars eliminates the limitations associated with silk screening bus bars; however, there are other limitations in the use of metal foil bus bars.  More particularly, the metal foil bus bars are in surface contact with the conductive coating.  A lead, usually an extension of the bus bars, extends out of the laminate to provide electrical access to the bus bars.  The surface of the lead that is a continuation of the surface of the bus bar in contact with the conductive coating and the adjacent portions of the glass sheet provide an air path.  During the removal of the channel from, and/or during the autoclaving of, the edge sealed windshield subassembly air moves through the air path between the glass blanks.  As can be appreciated by those skilled in the art of laminating windshields, the air moving between the blanks causes delamination.  Depending on the severity of the delamination, the windshield may have to be discarded or replaced. 
It would be advantageous therefore to use metal foil bus bars to eliminate the drawbacks of silk screening while eliminating the present drawbacks of metal foil bus bars. 
This invention relates to an interlayer composite having a plastic sheet with a predetermined shape, a pair of spaced bus bars mounted on a major surface of the sheet, e.g. by a pressure sensitive adhesive and a lead assembly having an air barrier associated with each of the bus bars.  The lead assemblies provide external electrical access to the bus bars and prevent air from moving around the leads during the laminating process (the edge sealing of the subassembly and autoclaving of the edged sealed subassembly).  In one non-limiting embodiment, each of the bus bars and the lead associated therewith are a contiguous metal foil, e.g. a copper foil having a xe2x80x9cTxe2x80x9d shape.  The bus bars, the first elongated or horizontal member of the xe2x80x9cTxe2x80x9d, is secured on the major surface of the plastic sheet, and the leads, the second elongated or vertical member of the xe2x80x9cTxe2x80x9d extends away from the bus bars beyond the periphery of the sheet.  In another non-limiting embodiment of the invention, a sleeve is provided over a portion of the lead to electrically isolate the lead and prevent damage to the sleeve from handling, e.g. a polyamide sleeve; a first air barrier is provided between inner walls of the sleeve and the surface portions of the lead in the sleeve, and a second air barrier, e.g. a thermo-set adhesive layer is provided on an outer surface portion of the sleeve to prevent air from moving over the outer surface portion of the sleeve during use of the composite in the laminating process. 
The invention further relates to a heatable laminate such as an automotive transparency, e.g. an automotive windshield.  The laminate in one non-limiting embodiment includes a first substrate, e.g. a first glass sheet, having a major surface and a periphery; an electric conductive member over a potion of the major surface of the first substrate; a pair of spaced bus bars, each bus bar having a major surface defined as a first surface and an opposite surface defined as a second surface, with the first surface in electrical surface contact with the electric conductive member.  A second substrate, e.g. a second glass sheet, has a major surface, over and facing the electric conductive member and the second surface of the pair of bus bars.  A plastic sheet having opposed major surfaces is between the second substrate and second surface of the pair of spaced bus bars.  One of the major surfaces of the plastic sheet defined as the first surface of the plastic sheet is adhered to a portion of the conductive member and the second surface of the pair of bus bars, and the other major surface of the plastic sheet defined as the second surface of the plastic sheet is adhered to surface portions of the major surface of the second substrate.  One of a pair of leads is connected to one of the pair of bus bars, and the other lead connected to the other one of the bus bars.  Each of the leads has an end extending beyond the periphery of the first glass sheet to provide external electrical access to the bus bars.  A sleeve is over a portion of each of the leads with an end portion of the sleeve between the glass sheets and the other end portion of the sleeve extending beyond the periphery of the first and second glass sheets, terminating short of the end of the lead outside the glass sheets.  A first air barrier is provided between inner surface of the sleeve and the surface portion of the lead within the sleeve, and a second air barrier, e.g. an adhesive layer is between the outer surface portions of the sleeve and portions of the major surface of the first glass sheet. 
In further non-limiting embodiments of the invention, the conductive member is a conductive coating applied to a surface of a sheet.  The coating has a perimeter spaced from the edges of the sheet to provide the sheet with a non-conductive strip.  Hot spots in the ends of the bus bar are minimized, if not eliminated by extending the end portions of the bus bars from the coating into the non-conductive strip.  Additional non-limiting features of the invention to minimize if not eliminate hot spots at the end portions of bus bars include one or more of the following. ( 1) A pair of spaced bus bars having different lengths, one of the bus bar extends along the topside of the conductive coating and the other one of the bus bars extends along the bottom side of the conductive coating.  The portions of the coating between the bus bars do not extend beyond the ends of the longer bus bar. ( 2) The windshield has a vision area having a top edge and a bottom edge; the coating has a top edge extending beyond the top edge of the vision area and a bottom edge extending below the bottom edge of the vision area.  The bus bars are mounted on the coating and are outside of the vision area.  The xe2x80x9cvision areaxe2x80x9d is defined as the see through area of the windshield available to the driver and/or passenger.  The top bus bars is adjacent the top edge of the coating and the bottom bus bar is adjacent the bottom edge of the coating.  The bottom edge of the coating is spaced a greater distance from the bottom edge of the vision area than the bottom bus bar, and the top edge of the coating is spaced a greater distance from the top edge of the vision area than the top bus bar. 
In other non-limiting embodiments of the invention, the interlayer composite described above may be used between the two substrates other than glass sheets, and the conductive member may be any member that is responsive to electric or heat stimuli, e.g. changes in transmittance as current is moved through the member. 
The invention also relates to methods of making the laminates using the composite and optionally, the bus bar arrangement to minimize, if not eliminate, hot spots.