Abstract:
A laminated window assembly for a device, such as a handheld electronic device (e.g., a media player or mobile telephone), includes a window layer that preferably is glass, and a larger, substantially transparent lip-forming layer to which it is laminated, preferably by a substantially clear adhesive. Additional adhesive preferably is placed at at least portions of the edge of the window layer adjacent the lip-forming layer, especially at the corners, to resist delamination. Holes preferably are formed in the lip—e.g., at the corners—to resist the lip-forming layer peeling apart from the window layer forming layer. The holes preferably make up at most about 33% of the periphery of the window layer.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to a laminated display window, especially for a handheld electronic device, which is resistant to delamination. 
     It is desirable to provide a glass display window in a handheld electronic device such a media player or a mobile telephone. A glass window is more resistant to scratching than most plastic windows, and may be more suitable for certain types of touch-sensitive displays. 
     One way to mount a display window is to provide a lip on the window, so that the window fits into the opening of a bezel, while the bezel captures the lip to retain the window. However, it is difficult to create a glass window with such a lip. Whether the glass is molded with a lip, or ground from a larger piece of glass, there may be stresses in such a piece of glass that make it more susceptible to breakage, either in handling before assembly into the device, or if the assembled device is dropped. 
     One alternative is to laminate the window glass to a larger transparent substrate, which may be another piece of glass or a suitable plastic. The edges of the larger substrate protrude beyond the edges of the window glass to form the desired lip. However, this alternative is not without other difficulties, including, in particular, the risk of delamination. 
     Lamination is frequently accomplished using a clear adhesive. However, many adhesives, while having high shear strength, have lower peel strength. Thus, any event, such as dropping of the device, that tends to try to separate the layers at the edges may cause delamination by peeling. This is particularly true if the laminated window structure is deformed at its corner, where the peel strength is lowest. Delamination is undesirable because it may compromise the strength of the laminated window or introduce defects into the visible area of the window, or, if there is a greater degree of delamination, it may create a safety hazard. 
     It would be desirable to be able to provide a laminated display window with increased resistance to delamination. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, delamination resistance of a laminated display window is increased by reducing the susceptibility of the laminated layers to peel along the edge, in the corners, or both. Thus, in addition to whatever method is used to bond the layers to one another, an adhesive may be placed in the corners or along part or all of the periphery of the outer window layer where the lip formed by the lower layer protrudes. This adhesive strengthens the bonding along those edges or in those corners, resisting delamination. 
     Preferably, where the adhesive is used along the periphery, a channel or chamfer may be formed in which the adhesive is placed. This gives the adhesive more surface area to which to bond, and also decreases the risk of oozing of displaced adhesive. The channel or chamfer may be formed in one of the layers, and preferably in the lower, larger layer, or in the surrounding structure of the handheld device, such as in the display bezel. 
     In addition, holes or gaps may be formed in the lip adjacent the edges and/or corners of the window glass to provide strain relief. If the lip were to be deformed by an event, it would not, at least in the areas of the holes or gaps, pull on the interface between the layers, thereby avoiding peeling apart the layers. The percentage of the periphery in which such holes or gaps are formed should not be so large that the lip is unable to reliably perform its function of retaining the window in the bezel. Preferably, such holes or gaps are formed only in the corners, and in any event are not formed along more than about 33% of the periphery. 
     In another embodiment, the strain relief gaps or holes may be used alone, without the additional adhesive around the periphery. 
     Therefore, in accordance with the present invention, there is provided a laminated window assembly for a device. The assembly includes (a) a window layer of a first substantially transparent material and having a periphery, and (b) a lip-forming layer, larger than the window layer, of a second substantially transparent material. The lip-forming layer extends beyond the window layer to form a lip for engaging the device. A substantially transparent bonding layer bonds the window layer to the lip-forming layer. An adhesive bead bonds the window layer to the lip-forming layer along at least one portion of the periphery. Holes may be formed in the lip for strain relief, to help prevent deformation of the lip from delaminating the assembly. If such strain relief is provided, it may be used with or without the adhesive bead. 
     A device incorporating such a window assembly also is provided. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further features of the invention, its nature and various advantages, will be apparent upon consideration of the following detailed description, taken in conjunction with the accompanying drawings, in which like reference characters refer to like parts throughout, and in which: 
         FIG. 1  is a perspective view of a laminated display window in accordance with the present invention; 
         FIG. 2  is a cross-sectional view, taken from line  2 - 2  of  FIG. 1 , of the laminated display window of  FIG. 1 ; 
         FIG. 3  is a fragmentary cross-sectional view of a device in which the laminated display window according to the present invention is mounted; 
         FIG. 4  is a schematic view showing placement of adhesive at the corners of the laminated display window according to a preferred embodiment of the present invention; 
         FIG. 5  is a schematic view showing placement of adhesive around the periphery of the laminated display window according to the present invention; 
         FIG. 6  is a fragmentary cross-sectional view showing provision of a channel in one layer of a laminated display window in accordance with an embodiment of the present invention; 
         FIG. 7  is a fragmentary cross-sectional view showing provision of a channel in one layer of a laminated display window in accordance with another embodiment of the present invention; 
         FIG. 8  is a fragmentary perspective view showing provision of a channel in a bezel adjacent the laminated display window in accordance with an embodiment of the present invention; 
         FIG. 9  is a fragmentary cross-sectional view showing provision of a channel in a bezel adjacent the laminated display window in accordance with an embodiment of the present invention; and 
         FIG. 10  is a fragmentary perspective view showing provision of strain relief in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     A laminated display window assembly  10  with which the present invention may be used is shown in  FIGS. 1 and 2 . Assembly  10  includes a window layer  11 , and a larger lip-forming layer  12  which is bonded to layer  11  by bonding layer  20 . For the reasons stated above, window layer  11  preferably is made of glass, although it may be made from a plastic material, and particularly from a high-molecular-weight plastic material that has many of the desirable characteristics of glass, such as scratch resistance. Other scratch-resistant clear materials, such as sapphire or quart crystal, also may be used. 
     Lip-forming layer  12  preferably is made from a plastic material, which is more resistant to breakage than glass, but could also be made from glass. Lip-forming layer  12  preferably is sufficiently larger than window layer  11  to form a lip  120  large enough to securely retain assembly  10  in the device in which it is used. 
     Although both window layer  11  and lip-forming layer  12  are preferably clear, either or both may include printing or decoration on either of its respective surfaces. 
     Bonding layer  20  could be any suitable clear bond. For example, if both layers are plastic materials, the two layers could be heat-bonded to one another. However, where, as is preferred, at least one layer is glass, then preferably bonding layer  20  is a clear adhesive, and in particular a clear pressure-sensitive adhesive, or a clear liquid adhesive. 
     Window layer  11  may be a flat glass sheet, preferably between about 0.50 mm and about 0.75 mm in thickness. Suitable glass sheets are available from Asahi Glass Co. Ltd., of Tokyo, Japan, and may be ground if necessary to a desired thickness, although other glass sheets may be used. In some embodiments, the final thickness of window layer  11  may be either 0.55 mm or 0.70 mm. In these embodiments, lip-forming layer  12  may be a 0.30 mm polycarbonate sheet available from Mitsubishi Engineering Plastics Corporation, of Tokyo, Japan (part number MR05GH), although another material could be used, and it may have another thickness. Finally, in this embodiment, bonding layer  20  may be a clear pressure-sensitive adhesive available from 3M Company, of St. Paul, Minn. (part number 8167 or 9483), although another clear pressure-sensitive or liquid adhesive could be used. These are only exemplary and any combination of materials, thicknesses and adhesives providing the desired properties—i.e., strength, clarity, etc.—may be used. 
     It should be noted in this regard that while any material used for window layer  11  or lip-forming layer  12  should be as scratch-resistant as possible, the provision of a scratch-resistant coating or “hard coat” may decrease the adhesion between layers  11  and  12 . Therefore, it may be desirable to omit such coatings on the mating faces of layers  11  and  12 , with the understanding that the risk of scratching prior to assembly would be increased unless extra care to avoid scratching is taken. 
     The fragmentary cross-sectional view of  FIG. 3  shows how window assembly  10  is retained in an exemplary device  30 . A bezel  31 , affixed to casing  32 , has an extension  310  that extends over lip  120  to retain assembly  10 . Beneath assembly  10  there may be a display module  33  (e.g., a liquid crystal display), while space  34  may contain other components of the device (circuitry, batteries, etc.). A gasket  35  may be provided between bezel  31  and module  33 . 
     Although window layer  11  is shown as a single clear sheet that fits within the opening of bezel  31 , it may be desirable to include one or more separate pieces that serve a decorative or functional purpose. For the purposes of this description and the claims that follow, any such collection of multiple pieces bonded to lip-forming layer  12  and fitting within the opening in bezel  31  may be considered collectively as window layer  11 . 
     In accordance with the present invention, the risk of delamination of window assembly  10 —e.g., in case of a drop event—may be reduced by providing additional adhesive at the edge of window layer  11  adjacent lip-forming layer  12 . In one preferred embodiment  40  shown in  FIG. 4 , adhesive  41  is applied at the corners of window layer  11 , providing additional adhesion where the peel strength is lowest. At the other extreme, in another preferred embodiment  50  shown in  FIG. 5 , a bead  51  of additional adhesive extends completely around the periphery of window layer  11  adjacent layer  12 . In an intermediate embodiment (not shown), a plurality of shorter beads of adhesive may be provided along selective stretches of the edge of window layer  11 —less than the complete periphery as in  FIG. 5 , but more than just the corners as in  FIG. 4 . A suitable adhesive may be DP460 epoxy adhesive available from 3M Company and sold under the trademark SCOTCH-WELD®. 
     In two variants  60 ,  70  of embodiment  50 , a channel may be provided in lip-forming layer  12  in which adhesive bead  51  is placed. This gives the adhesive more surface area to which to bond, and also decreases the risk of oozing of displaced adhesive. In embodiment  60  ( FIG. 6 ), channel  61  has an arcuate cross section, while in embodiment  70  ( FIG. 7 ), channel  71  has a rectangular cross section. To avoid compromising the integrity of lip  120 , the depth of channel  61 / 71  preferably should not exceed about one-half of the thickness of lip  120 . 
     Instead of providing a channel in lip-forming layer  12 , the channel may be provided in device  30 , and particularly in the portion adjacent window assembly  10 , which in the embodiments shown is bezel  31 . In the fragmentary perspective view of  FIG. 8 , looking from the underside of window assembly  10  and bezel  31 , with part of window assembly  10  cut away, a rectangular channel  80  can be seen in bezel  31  for receiving adhesive bead  51 . Channel  80  also is shown in phantom in  FIG. 9 , which primarily shows the provision, as an alternative to channel  80 , of a chamfer  90  to receive adhesive bead  51 . 
     In addition to, or instead of, providing adhesive  41 / 51 , the risk of delamination of window assembly  10  can be reduced by providing strain relief features to reduce the peel forces resulting from deformation of lip  120 .  FIG. 10  shows the provision of a hole or gap  100  in lip  120  adjacent corner  110  of window layer  11 . The effect of providing hole or gap  100  is that in the case of flexing of lip  120 , as indicated by arrows  101 , no force is transmitted to adhesive interface  20  in the area of hole or gap  100 . 
     Thus, in the case of flexing as shown in  FIG. 10 , although there is transmission of peeling forces at locations  102  adjacent hole or gap  100 , there is no transmission of peeling force at corner  110 , where peel strength is lowest. It should be noted, however, the holes or gaps  100  could be provided in one or more locations elsewhere along the periphery of window layer  11 , instead of, or in addition to, corners  110 . One limitation is that the total amount of holes or gaps  100  should not be so great as to compromise the structural integrity of lip  120 . Generally, for that reason, holes or gaps  100  should occupy no more than about 33% of the periphery of window layer  11 . 
     As noted above, strain relief holes or gaps  100  could be used instead of, or in addition to, adhesive  41 / 51  to reduce the risk of delamination of window assembly  10 . It will be appreciated, however, that if both adhesive  41 / 51  and strain relief holes or gaps  100  are used, then adhesive preferably should not be placed in holes or gaps  100 , lest force be transmitted across holes or gaps  100  by the adhesive, defeating the strain relief function. Thus, if holes or gaps  100  are placed in corners  110  as in  FIG. 10 , then embodiment  40  of  FIG. 4 , where adhesive  41  is present in corners  110 , should not be used. 
     Thus it is seen that a laminated display window with increased delamination resistance has been provided. It will be understood that the foregoing is only illustrative of the principles of the invention, and that various modifications can be made by those skilled in the art without departing from the scope and spirit of the invention, and the present invention is limited only by the claims that follow.