Abstract:
A laminated glazing panel comprising at least two glass sheets and at least one plastics (preferably PVB) sheet sandwiched between the glass sheets, the plastics sheet comprising a substantially opaque strip portion extending along an edge of the plastics sheet. Usually one of the glass sheets has an opaque obscuration band extending along at least one edge leaving a thin clear area between the edge of the panel and the obscuration band. The opaque strip preferably covers the thin clear area to protect adhesives from UV degradation from sunlight and for cosmetic reasons. The glazing panel will usually be a vehicle window.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to laminated glazing panels and in particular it relates to laminated vehicle windows.  
         DESCRIPTION OF THE PRIOR ART  
         [0002]    It is common practice to provide laminated glazing panels, especially laminated vehicle windows, with an obscuration band around all or part of the periphery of the panel to protect adhesives used to glaze the panels from exposure to UV radiation in sunlight and consequent degradation and also to obscure cosmetic defects. The cosmetic defects may result from grinding of the edge of a glass sheet or be caused by uneveness in the edge of the plastics sheet.  
           [0003]    Laminated glazing panels usually comprise two glass sheets and a plastics sheet (usually of polyvinylbutyral) sandwiched between the glass sheets, i.e. the plastics sheet extends between the glass sheets and is substantially co-extensive with them. The plastics sheet is often referred to as an interlayer.  
           [0004]    Usually, obscuration bands are applied to a surface of one of the glass sheets, using a screen printing process, as a ceramic ink comprising an inorganic pigment dispersed in a glass frit. On heating the glass sheet to a high temperature, the ink fires into the glass sheet forming a durable, opaque ceramic layer. Printed obscuration bands, however, have disadvantages. As stated in GB 2,264,452 B, printing of the obscuration bands may have deleterious effects on the production and performance of laminated vehicle windows. GB 2,264,452 B proposes to solve these problems by forming an obscuration band in a laminated vehicle window by incorporating one or more separate localised areas of obscuring compatible material in the interlayer where obscuration is required. Unfortunately, the obscuration bands described in GB 2,264,452 B have a sharp edge: there is no fade-out pattern between the edge of the obscuration band and the clear portion of the window. This sharp edge may be distracting to the eye. Also, accurate assembly of the separate localised areas of obscuring compatible material is an operation which is difficult to automate.  
           [0005]    A further disadvantage of printing an obscuration band is that a thin clear area of unprinted, and thus unobscured, glass may be left between the extreme edge of the glass sheet and the obscuration band. This has not previously been a problem because, for mounting into a vehicle, the edge of the glazing panel is usually surrounded by a black, polymeric trim which covers the thin clear area. However, in new designs of vehicle glazing a trim is not used and, consequently, the thin clear area is not covered. This may have the consequence of UV degradation of glazing adhesives on exposure of the glazing panel to sunlight, and it may allow cosmetic defects at the edge of the glazing panel to be seen.  
         SUMMARY OF THE INVENTION  
         [0006]    We have discovered that the above-mentioned problems may be alleviated by using a plastics sheet including a substantially opaque portion as the interlayer in a laminated glazing panel.  
           [0007]    The present invention accordingly provides a laminated glazing panel comprising at least two glass sheets and at least one plastics sheet sandwiched between (i.e. extending between) and co-extensive with the two glass sheets characterised in that the plastics sheet comprises a substantially clear portion and a substantially opaque strip portion integral with the clear portion and extending along at least one edge of the periphery of the plastics sheet.  
           [0008]    The substantially opaque strip portion of the plastics sheets is integral with the clear portion which means that the opaque strip portion and the clear portion form a whole, i.e. the opaque strip portion is an integral part of the plastics sheet. Preferably, this is a consequence of forming the plastics sheet by co-extruding the opaque strip portion and the clear portion.  
           [0009]    In the usual embodiment of the invention at least one of the glass sheets has an obscuration band applied to at least one surface thereof and extending along at least one edge of the periphery of the glass sheet. Usually, there is a thin clear area (i.e. a narrow strip of the glazing panel which remains free of ink) between the edge of the glazing panel and the obscuration band. Preferably, the opaque strip portion of the plastics sheet covers the thin clear area between the edge of the glazing panel and the obscuration band, i.e. preferably the opaque strip portion of the plastics sheet obscures the thin clear area and thus renders it unnoticeable. This is advantageous because the edge of the glazing panel will then be obscured, blocking UV radiation which may degrade adhesive used to glaze the glazing panel, and obscuring any cosmetic defects at the edge.  
           [0010]    The opaque strip portion of the plastics sheet is preferably less than 10 cm wide, more preferably less than 3 cm wide.  
           [0011]    Where the opaque strip portion of the plastics sheet covers the thin clear area between the edge of the glazing panel and the obscuration band, it is preferable if the obscuration band is wider than the opaque strip portion of the plastics sheet (i.e. the opaque strip portion of the plastics sheet is narrower than the obscuration band). Preferably the opaque strip portion of the plastics sheet and the obscuration band are colour matched, i.e. there is little or no difference in colour between the opaque strip portion and the obscuration band, and any such difference is not readily apparent to an observer.  
           [0012]    In any embodiment of the invention it is preferred that the opaque strip portion of the plastics sheet is evenly coloured along its length and across its width. Preferably the opaque strip portion of the plastics sheet is of a dark, more preferably a very dark colour. Most preferably the opaque strip portion of the plastics sheet is black.  
           [0013]    The plastics sheet may be formed of any suitable material, for example polymers such as polyvinyl chloride or polyurethane. However, preferably, the plastics sheet comprises polyvinyl butyral (PVB).  
           [0014]    The plastics sheet may be employed as a single layer of a polymeric material in direct contact with both glass sheets, but alternatively, it may be desirable that the plastics sheet is part of a laminate comprising a multiplicity of layers other than glass. Thus, the plastics sheet may be part of a plastics laminate having a multiplicity of layers, said layers comprising, in sequence, a layer of polyvinyl butyral, a layer of polyethylene terephthalate (PET) and a layer of polyvinyl butyral (PVB). This is advantageous because the laminated glazing panel may then be conveniently provided with solar control properties by, for example, depositing a solar control coating on the PET layer. Thus, preferably, the layer of polyethylene terephthalate has an infra-red reflective coating deposited thereon. The infra-red reflective coating will usually comprise thin layers of a reflective metal (for example silver) and anti-reflection layers of dielectric materials (for example zinc oxide or tin oxide).  
           [0015]    Preferably, the opaque strip portion extends along the top edge of the glazing panel (i.e. that edge which is uppermost when the glazing panel is installed). However, the opaque strip portion may instead, or additionally, extend along at least one other edge of the glazing panel (e.g. the bottom edge and/or one or more side edges of the glazing panel).  
           [0016]    Laminated glazing panels of the present invention are useful as laminated vehicle windows (in particular as laminated vehicle windscreens). Thus, in a preferred embodiment, the present invention provides a laminated vehicle window comprising two glass sheets and at least one plastics sheet sandwiched between and co-extensive with the two glass sheets, wherein at least one of the glass sheets has a substantially opaque ceramic obscuration band applied to at least one surface thereof and extending along at least one edge of the periphery of the glass sheet and wherein there is a thin clear area between the edge of the glazing panel and the ceramic obscuration band and wherein said plastics sheet comprises a substantially clear portion and a substantially opaque strip portion integral with the clear portion and extending along at least one edge of the periphery of the plastics sheet and wherein said opaque strip portion covers the thin clear area between the edge of the glazing panel and the ceramic obscuration band.  
           [0017]    In a second aspect, the present invention provides a method of producing a laminated glazing panel which comprises providing at least two glass sheets and at least one plastics sheet comprising a substantially clear portion and a substantially opaque strip portion integral with the clear portion and extending along at least one edge of the periphery of the plastics sheet, sandwiching the plastics sheet between the two glass sheets, and laminating the glass sheets and the plastics sheet. Preferably, the plastics sheet comprising the substantially clear portion and the substantially opaque strip portion is formed by co-extrusion.  
           [0018]    In a further aspect the present invention provides a laminated vehicle window comprising a multiplicity of plies including at least two glass plies and at least one plastics ply wherein one ply has a first obscuration means in the form of a substantially opaque band applied to one surface and extending along at least one edge of the periphery of the ply, characterised in that a second obscuration means in the form of a substantially opaque band having substantially uniform opacity is applied to one surface and extends along at least one edge of the periphery of a different ply.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]    Some illustrative embodiments of the invention will now be disclosed by way of example by reference to the accompanying drawings in which:  
         [0020]    [0020]FIG. 1 illustrates a schematic plan view of a laminated vehicle windscreen known in the prior art.  
         [0021]    [0021]FIG. 2 illustrates a section on A-A of FIG. 1.  
         [0022]    [0022]FIG. 3 illustrates a schematic plan view of a laminated vehicle windscreen according to the invention.  
         [0023]    [0023]FIG. 4 illustrates a section on B-B of FIG. 3.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0024]    Referring to FIG. 1, a known laminated vehicle windscreen  1  comprises an outer glass sheet  3 , a polyvinyl butyral sheet (not shown) and an inner glass sheet (not shown). Around the four edges of the periphery of the windscreen there is provided an opaque ceramic obscuration band  5 . The ceramic obscuration band  5  is applied as a ceramic ink to the outer surfaces of the outer glass sheet  3  by a screen printing process and fired by heating at high temperature before assembly of the laminated windscreen  1 . The equipment used to apply the ceramic obscuration band is such that a thin clear area of unobscured laminate  7  is left around the periphery of the windscreen between the edge of the windscreen and the ceramic obscuration band.  
         [0025]    Referring to FIG. 2, in section the known windscreen is seen to comprise an outer glass sheet  9  and an inner glass sheet  11 . Sandwiched between the glass sheets is a polyvinyl butyral sheet  13 . An opaque ceramic obscuration band  15  is provided on the outer surface of the outer glass sheet  9  leaving a thin clear area  17  of unobscured laminate at the edge of the windscreen.  
         [0026]    Referring to FIG. 3, a laminated vehicle windscreen  18  according to the invention comprises an outer glass sheet  19 , a polyvinyl butyral sheet (not shown) and an inner glass sheet (not shown). Around the four edges of the periphery of the windscreen there is provided an opaque ceramic obscuration band  21  and there is a thin clear area of unobscured laminate  23 . The polyvinyl butyral sheet (not shown) is provided with an opaque strip portion  25  of 10 cm width integral with the plastics sheet and extending along the top edge  24  of the periphery  22  of the windscreen covering the thin clear area  23  along the top edge of the windscreen. The strip portion  25  and the ceramic obscuration band  21  are colour matched and black in colour.  
         [0027]    Referring to FIG. 4, in section the windscreen according to the invention is seen to comprise an outer glass sheet  27  (e.g. 2 mm thick) and an inner glass sheet  29  (e.g. 1.6 mm thick). Sandwiched between the glass sheets is a polyvinyl butyral sheet  31  (e.g. 0.8 mm thick). An opaque ceramic obscuration band  37  is provided on the outer surface of the outer glass sheet  27  leaving a thin clear area  35  of unobscured laminate at the edge of the windscreen. More usually, the obscuration band  37  will be provided on the inner surface of the inner glass sheet  29  (the inner glass sheet  29  being that glass sheet on the inside of a vehicle when the windscreen  18  is installed in the vehicle), or on a surface of a glass sheet adjacent to, and in contact with, the polyvinyl butyral sheet  31 . The top edge of the polyvinyl butyral sheet  31  is provided with an opaque, black strip portion  33  which extends all the way to the edge of the windscreen. It therefore, covers and obscures the thin clear area  35  when viewed from the inside of the vehicle, and obscures it and renders it unnoticeable from the outside of the vehicle.  
         [0028]    The thicknesses of the glass sheets and polyvinyl butyral (PVB) sheet are not critical. In other designs the outer or inner glass can, for example, be in the range 1.6 mm to 3 mm and the PVB in a range 0.38 mm to 1.52 mm. The PVB sheet can also be replaced with a sheet of other plastics material for example polyvinyl chloride or polyurethane, with thicknesses typically being in the same range as for the PVB. In other examples it can be possible to incorporate layers of other plastics materials such as polyethylene terephthalate (PET) into the laminate, sandwiching this PET between two sheets of PVB. This PET sheet may incorporate a reflective solar control film.  
         [0029]    A laminated vehicle windscreen according to the invention is produced in the following manner. Two glass sheets (alternatively referred to as glass plies) of the same size and shape are cut. A black ceramic obscuration band is applied to the innermost surface (that is the surface intended to be on the interior of the vehicle into which the windscreen is to be glazed) of the inner glass sheet using a standard screen printing method for windscreens and Cerdec ink IR 14205 (manufactured by and obtained from Degussa). This ink is typical of a wide variety of products available in the industry to perform this function. This printing helps to improve the aesthetic appearance of the manufactured article and to mask all those items that preferably are not visible (for example, electric connections and the structure of the vehicle) after assembling of the windscreen onto the car.  
         [0030]    As a result of a limitation of the screen printing application process commonly used by the industry to apply this ink, it usually occurs that the ink does not extend all the way to the edge of the glass. The edge of the printed area is typically one to two millimeters from the edge of the glass. When the two glasses are laminated with the clear PVB it is possible to see a thin clear area along the edge of the glazing.  
         [0031]    After printing, the glass sheets are heated to a temperature of around 650° C. and shaped, using a process well known in the art. The high temperatures for shaping fire the ceramic ink into the glass surface. The thickness of the ceramic obscuration band after heating is about 16 to 18 microns, but may be between about 10 and 40 microns depending on the specific ink type used.  
         [0032]    The PVB used to laminated the glass sheets was obtained from HT Troplast (Cologne, Germany) in the form of a roll having a width of about 85 cm and a thickness of about 0.8 mm. Approximately 75 cm of the width of the PVB roll was clear PVB and the top 10 cm was black and substantially opaque. The PVB was produced by a co-extrusion process in a similar way to that used to produce blue or green transparent shade bands. The PVB sheet used for lamination was cut from the roll so that the black band was at the top of the sheet. Before lamination the cut sheet of PVB is preferably shaped so that the black band in the PVB follows the curvature of the top edge of the glass. This shaping is preferably sufficiently precise so as to ensure that the strip portion of the PVB does not extend over the area of the glass that is intended to be unobscured but does cover the glass edge.  
         [0033]    The two glass sheets (the outer 2 mm thick and the inner 1.6 mm thick) were laminated with the sheet of PVB in an autoclave using sets of temperature and pressure conditions which are well known in the art. These conditions may be altered to meet the particular requirements of the alternate materials described above.