Patent Publication Number: US-2010122898-A1

Title: Key base and key seat

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a key base and a key sheet for use in electronic devices such as cellular phones (including a so-called PHS), portable information terminals (personal digital assistances (PDA) or the like), portable audio devices, remote controllers for home electric appliances and keyboards. 
     2. Description of the Related Art 
     For example, in Patent Document 1, a technology is disclosed in which a key base main body is formed of a urethane sheet or a PET film (a PET sheet), and a protruding portion (a presser) made of ultraviolet (UV) curable resin is provided on the key base main body (see [0012] of the specification and FIG. 5 of Patent Document 1). Said presser is formed of the UV curable resin integrally with the key base main body on the back surface of the key base main body. 
     [Patent Document 1] Japanese Patent Application Laid-Open No. 6-5151 
     From a viewpoint of a satisfactory sense of operation during a key pressing operation, the key base main body is preferably formed of a sheet having elasticity, for example, a polyurethane sheet. However, when the key base main body is formed of the polyurethane sheet and a presser layer having the pressers is formed of electromagnetic wave curable resin such as the UV curable resin integrally with the polyurethane sheet on the back surface of this polyurethane sheet to form a key base, this polyurethane sheet is largely deformed (e.g., curled) for a reason such as contraction due to the curing of the electromagnetic wave curable resin. Therefore, it has been difficult to establish the key base and a key sheet as products. This is because the polyurethane sheet is a sheet having flexibility and elasticity. It is to be noted that as disclosed in Patent Document 1, it is also supposed that the key base main body be formed of the PET sheet instead of the polyurethane sheet. However, the PET sheet is not elastic. In a case where the key base main body is formed of the PET sheet, as compared with a case where the key base main body is formed of the polyurethane sheet, the sense of operation during the key pressing operation or the like deteriorates. Therefore, a flexible and elastic sheet such as the polyurethane sheet is to be used in the key base main body. 
     SUMMARY OF THE INVENTION 
     The present invention has been developed in view of the above respect, and an object thereof is to provide a key base and a key sheet which are established as products even in a case where a key base main body has a flexible and elastic sheet and a presser layer is formed of electromagnetic wave curable resin integrally with the key base main body on the back surface of this key base main body. 
     To achieve the above-mentioned object, a key base according to the present invention is a key base comprising: a key base main body; and a presser layer formed on the back surface of said key base main body, 
     characterized in that said key base main body has a first sheet having flexibility and elasticity, and a second sheet which is harder than said first sheet and has the front surface thereof directly or indirectly secured to the back surface of said first sheet, and 
     above-mentioned presser layer is formed of electromagnetic wave curable resin integrally with said second sheet on the back surface of said second sheet. 
     To achieve the above-mentioned object, a key sheet according to the present invention is a key sheet comprising: a key base having a key base main body and a presser layer formed on the back surface of said key base main body; and a key top corresponding to a presser which said presser layer has and secured to the front surface of said key base, 
     characterized in that said key base main body has a first sheet having flexibility and elasticity, and a second sheet which is harder than said first sheet and has the front surface thereof directly or indirectly secured to the back surface of said first sheet, 
     above-mentioned key top is secured to the front surface of said first sheet, and 
     above-mentioned presser layer is formed of electromagnetic wave curable resin integrally with above-mentioned second sheet on the back surface of said second sheet. 
     Moreover, in above-mentioned key base or above-mentioned key sheet, 
     above-mentioned first sheet is a sheet in which the thermal contraction ratio of said first sheet at a temperature at which said first sheet is heated in a case where above-mentioned presser layer is formed is different from the contraction ratio of above-mentioned electromagnetic wave curable resin during the curing of said electromagnetic wave curable resin in a case where said presser layer is formed, and 
     above-mentioned second sheet is a sheet which does not thermally contract at said heated temperature. 
     Furthermore, in above-mentioned key base or above-mentioned key sheet, 
     above-mentioned second sheet is a non-elastic sheet. 
     In addition, in above-mentioned key base or above-mentioned key sheet, 
     above-mentioned first sheet is a polyurethane sheet, and 
     above-mentioned second sheet is a PET sheet. 
     Moreover, in above-mentioned key base or above-mentioned key sheet, 
     above-mentioned electromagnetic wave curable resin is UV curable resin. 
     Furthermore, in above-mentioned key base or above-mentioned key sheet, 
     above-mentioned first sheet has, substantially on the whole surface thereof, a hot melt layer to secure the key top. 
     In the key base or the key sheet according to the present invention, even when the key base main body has the first sheet as the sheet having the flexibility and elasticity, but the second sheet is harder than the first sheet, and the presser layer is formed on the second sheet. Therefore, as compared with a case where the presser layer is formed on the first sheet, the deformation of the key base main body can be reduced. That is, in above-mentioned key sheet or above-mentioned key base, the second sheet is interposed between the first sheet and the presser layer, whereby even when the key base main body has the sheet having the flexibility and elasticity and the presser layer is formed of the electromagnetic wave curable resin integrally with the key base main body on the back surface of this key base main body, the key base and the key sheet are established as products. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view showing the disassembled members of a key sheet according to one embodiment of the present invention, and a substrate where this key sheet is to be arranged; 
         FIG. 2  is a perspective view showing the front surface side of the key sheet according to the embodiment of the present invention; 
         FIG. 3  is a perspective view showing the back surface side of the key sheet according to the embodiment of the present invention; 
         FIG. 4  is an enlarged sectional view showing the key sheet and the substrate in a state in which the key sheet according to the embodiment of the present invention is arranged on the substrate; 
         FIG. 5  is an enlarged sectional view showing a key sheet and a substrate in a state in which the key sheet according to another embodiment of the present invention is arranged on the substrate; 
         FIG. 6  is a diagram showing a cell phone in a case where the key sheet according to the embodiment of the present invention is assembled in the cell phone; and 
         FIG. 7  is an explanatory view showing the steps of a key base forming method according to the embodiment of the present invention, and the outline of the steps. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     One embodiment of a mode for carrying out the present invention will be described with reference to the drawings. It is to be noted that in the drawings, similar, corresponding or generic components are denoted with the same reference numerals, when described. Moreover, in a case where there are a plurality of similar, corresponding or generic components in the drawings, only a part of them is denoted with the reference numeral. 
       FIG. 1  is a perspective view showing the disassembled members of a key sheet according to one embodiment of the present invention, and a substrate where this key sheet is to be arranged, and  FIG. 2  is a perspective view showing the front surface side of the key sheet according to the embodiment of the present invention.  FIG. 3  is a perspective view showing the back surface side of the key sheet according to the embodiment of the present invention.  FIG. 4  is an enlarged sectional view showing the key sheet and the substrate in a state in which the key sheet according to the embodiment of the present invention is arranged on the substrate. 
     A key sheet  1  has a key top  3 , a cover member  4  and a key base  10 . The key sheet  1  is arranged on a substrate  6 . 
     A plurality of key tops  3  constitute keys such as a multidirectional (cursor) key, ten keys and functional keys, respectively. One or more key tops  3  may be arranged, but a plurality of key tops are usually arranged. 
     The cover member  4  is provided in order to reinforce the whole key sheet  1 , to constitute the housing of a cell phone and so on, or the like. In a case where the key tops  3  are exposed from through holes provided for the housing of the cell phone, or the like, the cover member  4  is sometimes unnecessary. In so-called narrow pitch keys in which the key tops  3  are arranged very close to each other, the cover member  4  is sometimes unnecessary. 
     Moreover, the key tops  3  and the cover member  4  are sometimes integrated and formed as one plate-like member. In this case, in the plate-like member, areas where numerals, characters, symbols, patterns or the like are depicted, areas corresponding to pressers  21  and/or the like are the key tops, and another area is the cover member. 
     Each of the key tops  3  and the cover member  4  is formed of an appropriate material such as any type of synthetic resin (e.g., hard resin), any type of glass or a metal. The synthetic resin or the glass is basically formed of a material having a property which can transmit light. The examples of the hard resin include polyethylene terephthalate (PET), polycarbonate resin, polyurethane resin, acrylic resin and silicone resin. Moreover, on the front surface and/or the back surface of the key top  3 , one or more numerals, characters, symbols, patterns, or the like are depicted by an appropriate method such as printing, painting, or the like. 
     The key tops  3  and the cover member  4  are formed in advance separately from the key base  10 , and are secured to the front surface of the key base  10 . The key tops  3  corresponding to the pressers  21  of a presser layer  20  are secured to the front surface of the key base  10  (the front surface of a key base main body  11  (the front surface of a first sheet  12 )). 
     The key base  10  has the key base main body  11  and the presser layer  20 . The key base main body  11  has the first sheet  12  and a second sheet  13 . The presser layer  20  has the pressers  21  and a thin portion  22 . 
     The first sheet  12  is a deformably elastic sheet, and a sheet having flexibility and elasticity (e.g., an elastic film sheet having the flexibility). The second sheet  13  is a sheet (e.g., a film sheet which is harder than the first sheet  12 ) which is harder than the first sheet  12 . The second sheet  13  may be deformable or have elasticity as long as it is harder than the first sheet  12 . 
     The first sheet  12  may appropriately be such a sheet that the thermal contraction ratio of the first sheet  12  at a temperature at which the first sheet  12  is heated in a case where the presser layer  20  is formed is different from the contraction ratio of electromagnetic wave curable resin during the curing of the electromagnetic wave curable resin in a case where the presser layer  20  is formed. The second sheet  13  may be a sheet which appropriately does not thermally contract at said heated temperature. 
     The second sheet  13  may appropriately be a non-elastic sheet which does not have any elasticity. 
     The first sheet  12  is formed of one elastic film sheet such as a thermoplastic polyurethane sheet (e.g., a thickness of about 0.05 mm) or a silicone sheet (e.g., a thickness of about 0.05 mm). The second sheet  13  is formed of one non-elastic film sheet such as a PET sheet (e.g., a thickness of about 0.025 mm). 
     The first sheet  12  is a sheet which is deformed in a case where the uncured electromagnetic wave curable resin brought into contact with the first sheet  12  is cured to form the presser layer  20  integrally with this first sheet  12  on the back surface of the first sheet  12 . The second sheet  13  is a sheet which is not deformed as compared with the first sheet  12 , in a case where the uncured electromagnetic wave curable resin brought into contact with the second sheet  13  is cured to form the presser layer  20  integrally with this second sheet  13  on the back surface of the second sheet  13 . 
     Each of the first sheet  12  and the second sheet  13  is constituted of a single sheet (here a film sheet), but may have a structure constituted of a plurality of members, for example, a structure in which two or more sheets (especially, film sheets) are laminated. Each of the first sheet  12  and the second sheet  13  is constituted of a single film sheet to realize thinning. 
     The front surface of the second sheet  13  is secured to the back surface of the first sheet  12  by use of a securing layer  40  formed of an adhesive, a viscous material or the like, whereby the second sheet  13  is attached to the first sheet  12 . That is, any member or the like is not interposed between the front surface of the second sheet  13  and the back surface of the first sheet  12 , and the sheets are secured using the securing layer  40 , whereby the front surface of the second sheet  13  is directly secured to the back surface of the first sheet  12 . According to this structure, the key base main body  11  can be thinned. The key base main body  11  has the securing layer  40 . Moreover, without interposing any member or the like between the front surface of the second sheet  13  and the back surface of the first sheet  12 , both the sheets may directly be secured to each other by appropriate means such as a thermal fusion bonding. In this case, the key base main body  11  can be thinner. Moreover, any member, layer or the like may be interposed between the front surface of the second sheet  13  and the back surface of the first sheet  12  to secure the second sheet  13  to the first sheet  12  via the securing layer or the like. That is, the front surface of the second sheet  13  may indirectly be secured to the back surface of the first sheet  12 . The front surface of the second sheet  13  is directly or indirectly secured to the back surface of the first sheet  12 , before the presser layer  20  is formed. 
     It is to be noted that a member such as a sheet (especially, a polyurethane sheet) constituting the first sheet  12  and/or the second sheet  13  is appropriately processed. For example, a decorative layer (e.g., a light blocking layer or the like) is formed on this member by painting, printing or the like. In this case, this member appropriately has the formed decorative layer or the like. Moreover, a member such as the sheet (especially, a PET sheet) constituting the first sheet  12  and/or the second sheet  13  is appropriately subjected to any type of treatment (a primer treatment) or the like. In particular, in a case where the first sheet  12  is formed of the polyurethane sheet, the second sheet  13  is formed of the PET sheet and the front surface of the second sheet  13  is attached to the back surface of the first sheet  12 , the front surface of the PET sheet may preferably be subjected to the primer treatment. 
     The first sheet  12  has a hot melt layer  41  for securing the key top  3  and the cover member  4  substantially on the whole surface (this is an expression including the whole surface), especially substantially on the whole surface of the front surface side. For example, the polyurethane sheet constituting the first sheet  12  as described later has the hot melt layer  41  on the whole front surface of the sheet, and further has a light blocking layer on this hot melt layer  41 . The key top  3  and the cover member  4  are secured by this hot melt layer  41 . 
     The presser layer  20  is formed on the back surface of the key base main body  11 . Specifically, the presser layer  20  is formed of the electromagnetic wave curable resin integrally with the second sheet  13  on the back surface of the second sheet  13 . The material of the presser layer  20  is the electromagnetic wave curable resin. In a case where the presser layer is formed of the electromagnetic wave curable resin integrally with the second sheet  13  on the back surface of the second sheet  13 , it is meant that the presser layer  20  is secured to the back surface of the second sheet owing to a fusion bonding in the process of the curing of the electromagnetic wave curable resin, while the pressers  21  is formed owing to the curing of the electromagnetic wave curable resin in a case where the pressers  21  are formed. That is, the integral formation means that the presser layer  20  is secured to a member such as the second sheet  13  without using any securing material such as an adhesive or a viscous material. 
     The example of the electromagnetic wave curable resin is visual light curable resin, UV curable resin or the like. In particular, as the electromagnetic wave curable resin, the UV curable resin is preferable from a viewpoint of the hardness of the pressers  21 , or the like. The key base or the key sheet in which the UV curable resin is used as the electromagnetic wave curable resin is excellent. The example of the UV curable resin is acrylic resin, epoxy resin, vinyl resin, silicone resin or the like. 
     Heretofore, when the key base main body is formed of the polyurethane sheet, a sheet-like member including the pressers and made of a silicone rubber is secured to the back surface of the polyurethane sheet to form the key base. However, in the sheet-like member formed of the silicone rubber, there has been a limit to the thinning for a reason of the fluidity, strength or the like of the silicone rubber. However, in the key base  10  and the key sheet  1 , the pressers  21  are formed of the electromagnetic wave curable resin, so that such a limit is eliminated. 
     The thin portion  22  is formed together with the pressers  21  in a case where the presser layer  20  is formed. It is to be noted that the height of the presser  21  (a height from the lower surface of the thin portion  22  to the vertex of the presser  21 ) or the height of a spacer  75  described later (a height from the lower surface of the thin portion  22  to the front surface of the substrate  6  described later) needs to be the minimum height (the height of the presser  21  is, for example, 0.2 mm) for the presser  21  to press and operate a switch portion described later. Therefore, the thinning of the presser layer  20  depends on the thinness of the thin portion  22  which can be realized. 
     Here,  FIG. 5  is an enlarged sectional view showing a key sheet and a substrate in a state in which the key sheet according to another embodiment of the present invention is arranged on the substrate 
     In  FIG. 5 , any thin portion  22  is not formed. Thus, a presser layer  20  sometimes does not have any thin portion  22 . In this case, the presser layer  20  can be formed to be thinnest, and a key sheet  1  and a key base  10  can be thinned. It is to be noted that when any thin portion  22  is not formed, one or more pressers  21  only are represented as the “presser layer”  20 . 
     Turning back to  FIGS. 1 to 4 , the presser layer  20  is formed by an appropriate method such as a method using a formation mold, a jig or the like or a potting method (especially shown in  FIG. 5 ). For example, by a method described later, the presser layer  20  is formed of the electromagnetic wave curable resin integrally with the second sheet  13  on the back surface of the second sheet  13 . 
     The substrate  6  has constitution elements such as electronic elements (not shown), a circuit (not shown) and switch portions  62  mounted on a base material  61 . 
     Each of the switch portions  62  is constituted of a deformable member such as a metal dome or a polydome, and two short-circuit contacts (not shown) formed on the base material  61 . Moreover, the deformable members are fixed by a fixing member such as a film  63  (shown by a dotted line of  FIG. 1  and not shown in  FIGS. 4 and 5 ). The film  63  is formed of PET, polycarbonate resin, or the like. 
     The key tops  3 , the pressers  21  and the switch portions  62  are positioned so as to correspond to one another. When the key top  3  is pressed downward, the presser  21  moves downward, and the presser  21  presses the deformable member. The pressed deformable member is deformed to generate a sense of click, and come in contact with the two short-circuit contacts to short-circuit the two short-circuit contacts. 
     It is to be noted that the spacers  75  are appropriately arranged in the positions which are around the pressers  21  and between the key sheet  1  and the substrate  6  to prevent the influence of the movement of the key top  3  on the other key tops  3  nearby. The spacers  75  may be formed integrally with the key base main body  11  in the same manner as in the presser layer  20 , or the spacers  75  formed as a separate member may be arranged between the key sheet  1  and the substrate  6 . When the spacers  75  are formed integrally with the key base main body  11 , for example, the spacers  75  are simultaneously formed of the same material as that of the presser layer  20 . In this case, the presser layer  20  includes the spacers  75 . 
     It is to be noted that the first sheet  12  and/or the second sheet  13  may be thickened to use the first sheet  12  and/or the second sheet  13  as a guide member (so-called light guide) of light from a predetermined light source. 
     In a case where the first sheet  12  is formed of one polyurethane sheet (a thickness of 0.05 mm), the second sheet  13  is formed of one PET sheet (a thickness of 0.025 mm), the thickness of the securing layer  40  is set to 0.025 mm and the thickness of the presser layer  20  is set to 0.22 mm (the thickness of the thin portion  22  is 0.02 mm and the height of the presser  21  is 0.2 mm), the key base  10  has a total thickness of 0.32 mm. 
       FIG. 6  is a diagram showing a cell phone in a case where the key sheet according to the embodiment of the present invention is assembled in the cell phone. 
     As shown in  FIG. 6 , a cover member  4  is integrated with the housing of a cell phone  150 . 
       FIG. 7  is an explanatory view showing the steps of a key base forming method according to the embodiment of the present invention, and the outline of the steps. 
     Electromagnetic wave curable resin  80  is supplied to a formation mold  101   a  having concave portions  101   aa  in desired positions (S 701 ). 
     The electromagnetic wave curable resin  80  is supplied using, for example, a dispenser (a liquid supply device), and the electromagnetic wave curable resin  80  is discharged and supplied from a discharge nozzle  110  of the dispenser. 
     The formation mold  101   a  has one or more (usually a plurality of) concave portions  101   aa  having a predetermined shape to provide presser  21  in desired positions. Moreover, when a spacer  75  is integrally formed, the formation mold  101   a  has one or more (usually a plurality of) concave portions (not shown) having a predetermined shape to provide the spacer in a desired position. 
     The electromagnetic wave curable resin  80  may be dropped down to the concave portions  101   aa  and the concave portions (not shown), individually, by use of the dispenser or the like so that the concave portions  101   aa  and the concave portions (not shown) only are filled. In this case, any thin portion  22  is not formed. 
     The electromagnetic wave curable resin  80  supplied to the formation mold  101   a  is flattened (S 702 ). 
     As shown in  FIG. 7 , a squeegee  111  is allowed to run on the electromagnetic wave curable resin  80 . It is to be noted that at this time, the electromagnetic wave curable resin  80  other than the electromagnetic wave curable resin  80  accumulated in the concave portions  101   aa  and the concave portions (not shown) is all removed using the squeegee  111 , and then any thin portion  22  is not formed. Moreover, even if all of the electromagnetic wave curable resin  80  other than the accumulated electromagnetic wave curable resin  80  in the concave portions  101   aa  and the concave portions (not shown) is not removed, at this time, the unnecessary electromagnetic wave curable resin  80  can be removed, and the thin portion  22  can be thinned. It is to be noted that the squeegee  111  may appropriately be changed to a doctor blade, a roller or the like as long as the electromagnetic wave curable resin  80  is flattened. 
     The key base main body  11  is supplied to the formation mold  101   a  to which the electromagnetic wave curable resin  80  has been supplied so that the back surface of the key base main body  11  faces downward (S 703 ). 
     Before or during the curing of the electromagnetic wave curable resin  80 , the electromagnetic wave curable resin  80  and the key base main body  11  are pressurized from the thickness direction of the key base main body  11 , and the electromagnetic wave curable resin  80  is cured (S 704 ). 
     Moreover, the electromagnetic wave curable resin  80  may be heated at a low temperature (e.g., about 80° C. in a case where the electromagnetic wave curable resin is UV curable resin) before curing the electromagnetic wave curable resin  80 , in order to prevent the generation of bubbles during the curing of the electromagnetic wave curable resin  80  by lowering the viscosity of the uncured electromagnetic wave curable resin  80 . In this case, the key base main body  11  which comes in contact with the heated electromagnetic wave curable resin is also heated. Furthermore, during the supplying of the key base main body  11 , the key base main body  11  is sometimes pulled from opposite ends so that the deflection of the key base main body  11  is prevented to easily form the presser layer  20 . 
     The electromagnetic wave curable resin  80  and the key base main body  11  are pressurized from the thickness direction by the formation mold  101   a  and a formation mold  101   b.  This pressurizing can allow the unnecessary electromagnetic wave curable resin  80  to overflow between the formation mold  101   a  and the formation mold  101   b,  and the thin portion  22  can be thinned. If the pressure during the pressurizing is high, the thin portion  22  can further be thinned. 
     Furthermore, after the pressurizing, the electromagnetic wave curable resin  80  is cured. For example, the upper surface of the formation mold  101   a  and/or the lower surface of the formation mold  101   b  is glass or the like, and an electromagnetic wave generation device (a UV lamp in a case where the electromagnetic wave curable resin  80  is UV curable resin) is provided at the downside or upside of this glass. Then, the electromagnetic wave curable resin  80  is irradiated with electromagnetic waves (ultraviolet rays in a case where the electromagnetic wave curable resin  80  is the UV curable resin) to cure the electromagnetic wave curable resin  80 . During the pressurizing, the electromagnetic wave curable resin  80  may be irradiated with the electromagnetic waves to cure this electromagnetic wave curable resin  80 . It is to be noted that the curing (a curing reaction) of a material might be disturbed by the pressurizing, depending on the type of the electromagnetic wave curable resin  80 . Therefore, the material is sometimes cured after the pressurizing, depending on the type of the material. 
     When the electromagnetic wave curable resin  80  is cured, the electromagnetic wave curable resin  80  in the concave portions  101   aa  constitutes the pressers  21 . Moreover, the other electromagnetic wave curable resin  80  constitutes the thin portions  22 . Then, when the electromagnetic wave curable resin  80  is cured, the electromagnetic wave curable resin  80  is integrated with the key base main body  11  (the second sheet  13 ). During the curing of the electromagnetic wave curable resin, contraction occurs owing to the curing of the electromagnetic wave curable resin. The key base main body  11  is sometimes influenced by this contraction. When the key base main body  11  is formed of the first sheet  12  only, the key base main body  11  is sometimes largely deformed with this contraction. 
     The electromagnetic wave curable resin  80  is cured, and then the key base  10  is taken out to complete the key base  10  (S 705 ). 
     When the electromagnetic wave curable resin  80  is cured, the presser layer  20  is formed of the electromagnetic wave curable resin  80  integrally with the second sheet  13  on the back surface of the second sheet  13 . 
     When the electromagnetic wave curable resin  80  is used in the presser layer  20 , during the formation of the presser layer  20 , the heating does not have to be performed. Alternatively, even when the resin is heated, the resin may be heated at the low temperature. Therefore, the first sheet  12  (especially, the polyurethane sheet) and/or the second sheet  13  of the key base main body  11  is not adversely affected. When the first sheet  12  is provided with the hot melt layer  41  in advance, the hot melt layer  41  can be prevented from changing in quality. 
     It is to be noted that the first sheet  12  is a sheet having flexibility and elasticity, and the second sheet  13  is a sheet harder than the first sheet  12 . In the key sheet  1  or the key base  10 , the presser layer  20  is formed on the second sheet  13  which is harder than the first sheet  12 , so that the deformation of the key base main body  11  due to the contraction caused by the curing of the electromagnetic wave curable resin during the formation of the presser layer  20  can be reduced as compared with the presser layer  20  is formed integrally with the first sheet  12 . That is, the second sheet  13  is interposed between the first sheet  12  and the presser layer  20 , whereby even when the key base main body  11  has a sheet having the flexibility and elasticity and the presser layer  20  is formed of the electromagnetic wave curable resin integrally with the key base main body  11  on the back surface of the key base main body  11 , the key sheet  1  or the key base  10  is the key sheet or the key base established as a product. 
     Moreover, in a case that when the presser layer  20  is formed of the electromagnetic wave curable resin integrally with the key base main body  11  on the back surface of this key base main body  11 , the electromagnetic wave curable resin  80  is heated at a low temperature (e.g., about 80° C. in a case where the electromagnetic wave curable resin is UV curable resin) in order to prevent the generation of bubbles during the curing of the electromagnetic wave curable resin  80  by lowering the viscosity of the uncured electromagnetic wave curable resin  80 , the key base main body  11  which comes in contact with the heated electromagnetic wave curable resin is also heated. In a case where this presser layer  20  is formed, when the first sheet  12  only constitutes the key base main body  11 , the first sheet  12  is heated to thermally contract. Moreover, when this presser layer  20  is formed, the electromagnetic wave curable resin is cured and hence contracts. At this time, the thermal contraction ratio of the first sheet  12  (the thermal contraction ratio of this first sheet  12  at the temperature at which the first sheet  12  is heated during the formation of the presser layer  20 ) is different from the contraction ratio during the curing of the electromagnetic wave curable resin (the contraction ratio of the electromagnetic wave curable resin during the curing of the electromagnetic wave curable resin in a case where the presser layer  20  is formed), so that the key base  10  is deformed. In a case where the second sheet  13  is a sheet which does not thermally contract at said temperature at which the second sheet  13  is heated, the second sheet  13  is not deformed at said heated temperature. Therefore, owing to the presence of the second sheet, the key sheet  1  or the key base  10  is the key sheet or the key base which can be established as a product. 
     It is to be noted that in a case where it is described that the sheet “does not thermally contract”, this description includes not only a case where the sheet completely does not thermally contract but also a case where the sheet slightly contracts to such an extent that the degree of the contraction can be ignored. 
     Furthermore, when the presser layer  20  is formed of the electromagnetic wave curable resin integrally with the key base main body  11  on the back surface of this key base main body  11 , to prevent the deflection of the key base main body  11  and facilitate the forming of the presser layer  20 , the key base main body  11  is sometimes pulled from the opposite ends. Thus, in a case where the key base main body  11  is constituted of the first sheet  12  only and the first sheet  12  has the elasticity, when the key base main body  11  is pulled, the key base main body  11  expands, and the key base main body  11  contracts after the formation of the presser layer  20 . It is also supposed that the contraction of this key base main body  11  sometimes causes the deformation of the key base  10 . Even in a case where the first sheet  12  is an elastic sheet, when the second sheet  13  is non-elastic sheet, the expansion and contraction of this key base main body  11  can be suppressed. Therefore, the key sheet  1  or the key base  10  constitutes the key sheet or the key base established as a product. Moreover, when the first sheet  12  has the elasticity and the second sheet  13  is not elastic, a poor sense of operation in a case where the key base main body  11  is formed of the non-elastic sheet can be compensated by the elasticity of the first sheet  12 . 
     As described above, in the key base  10  and the key sheet  1  in which the key base main body  11  has the first sheet  12  and the second sheet  13 , the defect of the first sheet  12  can be compensated by the second sheet  13 , and the defect of the second sheet  13  can be compensated by the first sheet  12 . 
     Moreover, it is preferable that the first sheet  12  is formed of the polyurethane sheet and that the second sheet  13  is formed of the PET sheet. The UV curable resin is preferably used as the electromagnetic wave curable resin. 
     With respect to the polyurethane sheet, there are many securing materials such as an adhesive and a viscous material that have satisfactory compatibility (that can easily be secured). Therefore, when the first sheet  12  is the polyurethane sheet, the key top  3  and the cover member  4  can be secured to this polyurethane sheet by use of a securing layer using this securing material having the satisfactory compatibility such as the hot melt layer. In consequence, the key top  3  (especially made of polycarbonate resin) and the cover member  4  (especially made of polycarbonate resin) can firmly be secured to the front surface of the key base. Moreover, with respect to the polyurethane sheet, there are many materials having satisfactory compatibility, for example, ink, whereby the polyurethane sheet facilitates processing such as the forming of a decorative layer (e.g., a light blocking layer or the like) on the front surface of this polyurethane sheet by printing or the like. Thus, the polyurethane sheet has many advantages in a case where the sheet is used as the constitution element of the key base  10 . Therefore, it is supposed that the polyurethane sheet is preferable as the first sheet  12 . 
     The PET sheet is not easily subjected to the above-mentioned processing as compared with the polyurethane sheet. Moreover, owing to the reason that there is not any or many securing materials having satisfactory compatibility with the PET sheet, to the property of the PET sheet itself, and the like, the securing strength between the PET sheet and the key top is smaller than that between the polyurethane sheet and the key top. However, the PET sheet has properties that the PET sheet is harder than the polyurethane sheet and that the PET sheet does not thermally contract (has a small contraction ratio) at a temperature at which the sheet is heated during the formation of the presser layer  20 . The PET sheet also has the non-elastic property and the like. Therefore, even in a case where the presser layer  20  is formed of the UV curable resin integrally with the PET sheet on the back surface of the PET sheet, as compared with a case where the layer is formed on a urethane sheet, the deformation of the key base  10  can be reduced. In consequence, the PET sheet is preferable as the second sheet  13 . 
     As described above, in the key base  10  or the key sheet  1  in which the first sheet  12  is formed of the polyurethane sheet, the second sheet  13  is formed of the PET sheet and the electromagnetic wave curable resin is the UV curable resin, the defect of the polyurethane sheet can be compensated by the PET sheet, and the defect of the PET sheet can be compensated by the polyurethane sheet. That is, in this key base  10  or key sheet  1 , even in a case where the key base main body  11  has the polyurethane sheet and the presser layer  20  is formed of the UV curable resin integrally with the key base main body  11  on the back surface of the key base main body  11 , there can be provided the remarkably excellent key base  10  or key sheet  1  provided with the following advantages; the key base or the key sheet can be established as a product; the key tops  3  can firmly be secured to the front surface of the key base; the front surface of the key base main body is easily processed; the key base or key sheet can be thinned; the pressers  21  having a satisfactory hardness or the like can be obtained; and the like. 
     Moreover, the first sheet  12  has, substantially on the whole surface thereof, the hot melt layer  41  for securing the key tops  3  and the cover member  4 , whereby the whole back surface of the key top  3  or the cover member  4  can be secured to the front surface of the first sheet, and any gap is not generated between the key top  3  or the cover member  4  and the first sheet  12  (the whole back surface of the key top  3  or the cover member  4  can be bonded to the first sheet  12 ). Therefore, it can be prevented that the key top  3  or the cover member  4  peels from this gap. Moreover, a sheet (e.g., the polyurethane sheet provided with the hot melt layer  41  as described later) provided with the hot melt layer  41  on the whole front surface thereof and having the flexibility is commercially available. When this sheet is used, a step of forming the hot melt layer  41  can be omitted. Moreover, the hot melt layer  41  is formed on the side of the first sheet  12 , whereby the viscous material or the like does not have to be used in securing the cover member  4 . This facilitates the forming of the key sheet  1 . When the hot melt layer is formed on the back surface of the key top  3  or the cover member  4 , the step of forming the hot melt layer become complicated as the hot melt layer need to be formed on the respective key tops  3  and cover member  4 . However, when the hot melt layer  41  is formed on the side of the first sheet  12 , or the sheet provided with the hot melt layer  41  on the whole front surface thereof and having the flexibility is used, the step of forming the hot melt layer can be simplified or omitted. 
     The key sheet according to the present invention is not limited to above-mentioned embodiment only, and needless to say, above-mentioned embodiment can appropriately be modified without departing from the scope of the present invention.