the case 1 shown in full in fig4 has a back 2 , two side walls 3 , 4 , a bottom wall 5 and a top wall 6 . 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 . 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 fig1 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 . 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 . 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 fig5 , 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 . 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 . 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 . as will be apparent from fig1 , 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 . 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 . 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 . however , in the vicinity of any switches and ports as designated by reference numeral 20 in fig3 and fig4 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 . 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 . there are a number of ways in which the case can be manufactured . this is a manual loading process . the intermediate layer 11 can first be injection moulded as shown in fig2 . 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 fig3 . 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 . 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 . 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 . 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 .
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 .