Abstract:
A case for a mobile device with a screen. The case comprises a band arranged to surround the edge of the device. The band comprises an outer layer of a flexible polymer, an inner layer of damping material and an intermediate layer of a dissipation material between the inner and outer layers. The intermediate layer is the hardest of three layers and the inner layer is the softest.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a case for a mobile device with a screen. 
       BACKGROUND OF THE INVENTION 
       [0002]    Mobile device cases are now widely used following the explosion in use of smart phone and tablet devices. The applicant is currently producing a case which is described in WO 2015/101771. The case has an outer material of TPU which has a Shore Durometer hardness between 90 A to 95 A and an inner impact absorbing and damping material which is sold under the trade name Flexshock®. The impact absorbing material may, for example, be TPE, viscoelastic TPE, Poron or soft TPU and should preferably have a Shore Durometer hardness between 30 A and 60 A. 
         [0003]    Such a case is highly successful commercially as the two-layered structure is aesthetically pleasing and provides good impact protection. 
         [0004]    WO 2015/101771 contemplates a case in which a rigid polymer is used as an outer layer creating a three-layer structure. Other cases also use such a hard outer layer. The advantage of a hard outer layer is that it disperses the impact. The softer inner layer can then absorb this dispersed impact. However, an outer layer is prone to scratches and cracks. The hard outer material does not generally absorb energy and is generally provided just to provide a structural surface for the case. 
         [0005]    Other cases are known such as the Otterbox Defender with an outer soft material and an inner hard material. The inner hard material frames the device and provides a rigid shell for the case while the outer softer material provides absorption of impact energy. However, any impact energy which passes through the soft material and reaches the hard material is transmitted to the device. The hard inner material may also scratch the device. 
         [0006]    Obviously impact protection can be enhanced by increasing the thickness of at least one of the layers. However, thin and lightweight cases are far more desirable as they are more aesthetically pleasing, more convenient for a user to carry and have less negative effect on the radiofrequency performance of the device. 
       SUMMARY OF THE INVENTION 
       [0007]    The present invention, in one form, relates to a case for a mobile device with a screen. The case comprises a band arranged to surround the edge of the device. The band comprises an outer layer of a flexible polymer, an inner layer of damping material and an intermediate layer of a dissipation material between the inner and outer layers, wherein the intermediate layer is the hardest of three layers and the inner layer is the softest. 
         [0008]    This arrangement of three layers places the hardest dissipation layer between a soft inner layer of damping material and an outer layer of flexible polymer with an intermediate hardness. Upon impact, the outer layer with its intermediate hardness will absorb and disperse some of the impact. On reaching the dissipation material, the impact is spread across a wide portion of the band thereby reducing the localised force to be absorbed by the damping material. 
         [0009]    High speed photography has shown that such a three layer structure provides significantly enhanced impact protection as compared to the two layer band referred to in WO 2015/101771 for bands which have the same overall thickness. Further, the fact that the hard material is an intermediate layer means that it is protected from scratching and cracking, while the inner layer provides cushioning for the device itself ensuring that it does not get scratched when the device is inserted into and removed from the case. 
         [0010]    For optimum performance, the dissipation material is preferably thinner than at least one of the other layers and preferably both of the other layers for a substantial portion of the circumference of the band. As the dissipation material is a relatively hard layer, it can be made thin to effectively represent a “shell” which will adequately dissipate the impact forces without unduly increasing the thickness or mass of the case. 
         [0011]    The dissipation material is preferably fully enclosed by the other two layers for a substantial portion of the band. This protects the harder material from being scratched or cracked and also reduces the possibility of the device being scratched by the harder material. However, the dissipation material may form the inner face of the band at at least some of the regions of the band where ports and/or switches are formed. This allows the case to have greater rigidity in these regions thereby ensuring a better engagement between the case and the underlying ports and/or switches. 
         [0012]    In some regions, the flexible polymer may form the inner face of the band at at least some of the region of the band where ports and/or switches are formed. For example, the current designs of iPhone have a port for a headphone jack, a port for a lightning connector and a speaker in the bottom edge of the phone. Cases in this region are therefore required to have more open regions than other regions surrounded by the band and it is therefore awkward and unnecessary to provide more than one material in this region. 
         [0013]    Preferably, the dissipation material has a Shore Durometer hardness of 60 D to 100 D, preferably 70 D to 90 D and more preferably 80 D to 90 D. 
         [0014]    The dissipation material preferably has outwardly projecting ribs. These serve to generate a localised increase in thickness in the hard layer to increase its rigidity without unduly increasing the mass or thickness. Further, they provide a good bonding surface between the intermediate layer and outer layer. Similarly, the dissipation material may have inwardly projecting ribs. If so, there are preferably more outwardly projecting ribs than inwardly projecting ribs. These inwardly projecting ribs are primarily provided to provide a good bonding surface to the damping material but have a less significant effect on the rigidity of the dissipation layer. 
         [0015]    Preferably the damping material has inwardly projecting ribs. This enhances the impact absorbing ability of the inner layer. Preferably the damping material extends along a substantial portion of the circumference of the band including any corners. These are the regions most vulnerable to impact as however a device is dropped, the most likely first point of impact is on one of the corners. Further, it is generally beneficial to have the damping material extending along any sides of the device away from regions of the band where ports and/or switches are formed. 
         [0016]    The damping material is preferably present in a number of discreet portions. By contrast, the flexible polymer and dissipation material are each a single continuous piece. 
         [0017]    Preferably the damping material has a Shore Durometer hardness of 35 A to 80 A and preferably 45 A to 55 A. 
         [0018]    The case may simply be a band which surrounds the four edges of the device, often referred to as a four sided case. However, preferably, the case has a back and the band forms a wall extending away from the back. This is commonly referred to as a five sided case. In this case, the back is preferably made substantially of the flexible polymer and is continuous with the outer layer. It is possible that one of the other layers, particularly the layer of damping material may extend to a limited extent across the back. 
         [0019]    Preferably the flexible polymer has a Shore Durometer from 80 A to 100 A, preferably 90 A to 100 A and more preferably 90 A to 96 A. 
         [0020]    Preferably the band has an upper lip surrounding the screen, in use, the lip being formed only of the flexible polymer in the outer layer. This provides an edge with a neat appearance. 
         [0021]    Additional features such as inserts for lens regions of the camera and the like, may be included. However, preferably, the entire band or case is made from just the three materials forming the three layers. There may be air gaps provided in the corners to provide an air cushioning effect. However, preferably there are no air gaps between the three layers as the three-layer structure provides adequate damping without requiring additional air cushioning. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]    An example of a case in accordance with the present invention will now be described with reference to the accompanying drawings, in which: 
           [0023]      FIG. 1  is a lateral cross-section through a band and the back of the case and includes a portion of the device in situ; 
           [0024]      FIG. 2  is a perspective view of the layer of dissipation material; 
           [0025]      FIG. 3  is a similar perspective view to  FIG. 2  also showing the outer layer of flexible polymer; 
           [0026]      FIG. 4  is a similar perspective view to  FIGS. 2 and 3  showing the finished case; and 
           [0027]      FIG. 5  is a schematic cross-section along the length of the band in a plane parallel to the back showing the three layer structure. 
       
    
    
     DETAILED DESCRIPTION 
       [0028]    The case  1  shown in full in  FIG. 4  has a back  2 , two side walls  3 ,  4 , a bottom wall  5  and a top wall  6 . 
         [0029]    The illustrated case is for an iPhone 6S, but the principles apply to cases for all smart phone and tablet devices as well as e-readers and the like. 
         [0030]    The back  2  is optional as the principles described here apply equally to a backless band which surrounds the edges of the device. The three layer structure forming the majority of the side wall structure is shown in  FIGS. 1 and 5 . This comprises an outer layer  10  of flexible polymer, an intermediate layer  11  of dissipation material and an inner layer  12  of damping material. 
         [0031]    The outer layer  10  of flexible polymer may be TPU, TPE or silicone. If the back  2  is present, this material will form the majority of the back, although other materials may extend to a small extent across the back. 
         [0032]    The dissipation layer  11  may be PC, ABS, PC/ABS blends, Hard TPU grades, glass and fibre-filled rigid thermoplastics, nylon, glass and fibre-filled nylons and similar materials. As shown in  FIG. 5 , the intermediate layer is provided with a plurality of outwardly extending ribs  13  which are embedded within the outer layer  10  with no air gaps. These ribs increase the rigidity and strength of the intermediate layer and form an effective increase in the thickness of the hard layer without unduly increasing the weight. The intermediate layer  11  also has a number of inwardly projecting ribs  14 . There are fewer of these than a number of outwardly projecting ribs  13  and these are provided in order to provide an improved bond with the inner layer  12 . 
         [0033]    The inner layer  12  may be a soft elastomer, soft TPU, TPE, silicone, foam or the like. The inner layer  12  has a number of inwardly projecting ribs  15  which are configured to contact the device D such that there is generally no contact between the device and the case in the regions where the damping material is present other than through the ribs. 
         [0034]    The overall thickness of the band is intended to be compatible with our existing cases as described in WO 2015/101771. Thus, each layer should be between 0.5 mm and 0.85 mm and is preferably no thicker than 2 mm. These thicknesses apply to the general thickness of the band away from any ribs or other features. 
         [0035]    As will be apparent from  FIG. 1 , the intermediate layer  11  is fully surrounded by the outer layer  10  and inner layer  12  such that the material is protected from scratching and cracking. The outer layer  10  extends to a lip  15  which surrounds the edge of the device D. In the lip region  15 , the intermediate  11  and inner 12 layers are absent. This preserves a clean appearance to the case as only one material is visible in this region. 
         [0036]    Any impact I on the band is initially dampened and partially absorbed by the outer layer  10 . Because the outer layer  10  is not particularly hard, it is not vulnerable to cracking. The energy not absorbed in the outer layer  10  is then dissipated over a wide area by the intermediate layer  11  which spreads the impact such that the requirements of the absorbing material in the inner layer  12  are reduced. The damping material  12  absorbs much of the remaining energy. In doing so, it is assisted by the presence of the ribs  15 . 
         [0037]    The above described structure describes the band for the majority of the circumference of the case. This structure is preferred where there are no features on the case to be accommodated. In particular, this structure should be present in the four corners of the device as these are most vulnerable to impact. 
         [0038]    However, in the vicinity of any switches and ports as designated by reference numeral  20  in  FIG. 3  and  FIG. 4  the cross-sectional structure of the case is different in that the inner layer  12  of damping material is absent. In this region, the intermediate layer forms the innermost layer such that there is a relatively hard material in contact with these parts of the device. This helps to maintain the stability of the case in these regions to allow more reliable manipulation of the underlying buttons. 
         [0039]    Also, in the case of the iPhone as in many other smart phones, the lower side  5  is required to have three large ports to accommodate the speaker, lightning connector and headphone jack socket. In this region, only the outer layer of flexible polymer is present. However, the three layer structure is preserved in the corners. 
         [0040]    There are a number of ways in which the case can be manufactured. 
       1. Insert Injection Over-Moulding 
       [0041]    This is a manual loading process. The intermediate layer  11  can first be injection moulded as shown in  FIG. 2 . This component is then attached to a mould core part and inserted into a second injection mould where the outer layer  10  is over-moulded to form the sub-assembly shown in  FIG. 3 . This can either be done using a mechanical collapsible core, or the sub-assembly can be used demoulded by hand. This sub-assembly is then put into another core and inserted into a mould to over-mould the inner layer  12 . 
         [0042]    Alternatively, the intermediate layer  11  is not removed from the first stage core. Once the intermediate layer  11  is moulded, without being removed from its core, it is inserted into the second mould to over-mould the outer layer  10 . 
         [0000]    2. Multi-Shot Injection Moulding with Insert Over-Moulding 
         [0043]    This method is a semi-automated method with the intermediate layer  11  and outer layer  10  moulded in a two-shot injection moulding process with the intermediate layer  11  being the first shot and the outer layer  10  being the second. A mechanical collapsible core can be used where the sub-assembly can be removed by hand. A sub-assembly will then be put into another core and inserted into a mould to over-mould the inner layer  12 . 
       3. Multi-Shot Injection Moulding 
       [0044]    This is a fully automated process with two operational methods. 
         [0045]    Firstly, the intermediate layer  11  and outer layer  10  are moulded in a three-shot injection moulded process with the intermediate layer  11  being the first shot and the outer layer  10  being the second. A mechanical collapsible core retracts and a robotic/computer controlled arm picks up the sub-assembly and transfers the moulded component to a second injection moulding machine where the sub-assembly is inserted into another collapsible core to over-mould the inner layer  12 . This method is fully automated but requires a more complex machine to injection mould material in a three stage process.