Abstract:
In a punch and die set, the punch includes an inner section and an outer section, wherein the inner section is higher than the outer section, a cutting die for receiving the punch, and a stripper die movable within the cutting die. Because the inner section is higher than the outer section, the stripper die engages a workpiece first as the punch enters the cutting die, producing a kiss cut. The punch can further enter the die to provide a blanking cut. A pressure pad within the stripper die holds a workpiece in place for cutting.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]     This application relates to application Ser. No. 10/790,978, filed Mar. 2, 2004, entitled Dimensionally Stable Electroluminescent Lamp without Substrate, and assigned to the assignee of this invention. The entire contents of said application are incorporated by reference into this application. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     This invention relates to the manufacture of flexible, laminated sheet materials and has a particular application in the manufacturer of electroluminescent (EL) panels for separating lamps from a release layer.  
         [0003]     As used herein, and as understood by those of skill in the art, “thick-film” refers to one type of EL lamp and “thin-film” refers to another type of EL lamp. A thin, thick-film EL lamp is not a contradiction in terms and such a lamp is considerably thicker than a thin film EL lamp.  
         [0004]     As used herein, an EL “panel” is a single sheet including one or more luminous areas, wherein each luminous area is an EL “lamp.” An EL lamp is essentially a capacitor having a dielectric layer between two conductive electrodes, one of which is transparent. The dielectric layer can include phosphor particles or there can be a separate layer of phosphor particles adjacent the dielectric layer. The phosphor particles radiate light in the presence of a strong electric field, using relatively little current.  
         [0005]     A modern (post-1985) EL lamp typically includes transparent substrate of polyester or polycarbonate material having a thickness of about 7.0 mils (0.178 mm.). A transparent, front electrode of indium tin oxide or indium oxide is vacuum deposited onto the substrate to a thickness of 1000 Å or so. A phosphor layer is screen printed over the front electrode and a dielectric layer is screen printed over phosphor layer. A rear electrode is screen printed over the dielectric layer. It is also known in the art to deposit the layers by roll coating.  
         [0006]     An EL lamp constructed in accordance with the prior art is relatively stiff, even though it is typically only seven mils thick, making the lamp unsuited to some applications requiring greater flexibility, such as keypads. Layer thickness and stiffness are not directly related. The material from which the layer is made affects stiffness. Simply reducing the thickness of the substrate does not provide the desired flexibility.  
         [0007]     The above-identified application discloses a relatively flexible EL panel made on a UV-cured urethane layer on a release layer. The release layer provides substantial structural support while the lamp layers are applied. Panels made as described in the above-identified application have structural integrity but are somewhat delicate. Removing a panel from the release layer is postponed as long as possible.  
         [0008]     One technique that aids postponement is that the lamp is kiss cut while on the release layer. A kiss-cut is a cut through some but not all of the layers in an article, without cutting the substrate on which the layers were deposited. As applied to the manufacture of EL lamps, the lamp materials are cut but remain on the release layer, which is intact. The panels can then be manipulated as desired and separated just prior to applying a panel to a keyboard or keypad, for example.  
         [0009]     A convenient method for kiss cutting a group of panels is an etched die, illustrated in  FIG. 1 , having raised outlines of the panels formed on a sheet of stainless steel. Sheets of panels and the die are suitably positioned in a press and the press is actuated to kiss cut the panels. A problem with this approach is the number of panels obtainable from a die. An etched die is typically useful for 50,000 or so stampings, which may seem like a lot until one realizes that the need is one or two orders of magnitude greater, per month, and that, when one outline goes bad, the whole die-is useless.  
         [0010]     A continuous supply of die must be kept in inventory and the die are not inexpensive. Neither is the press for the die. Also, the figure given for die life is an average.. Some die last only five or six thousand stampings while other last up to one hundred thousand stampings. Thus, inventory must include several die to be sure to be able to finish just one day&#39;s production. Inventory control is made more difficult by the fact that an etched die is a specialized tool, purchased from an outside source. The die cannot be maintained internally. In fact, it is not maintained at all. It is returned to the manufacturer. It is much preferred to build or at least maintain tooling internally, thereby eliminating delivery problems and reducing costs still further.  
         [0011]     With a simple punch and die set, the punch pushes a cutting into the die. In order to remove the cutting, it is known in the art to use a stripper die, within the die, to push out the cutting prior to the next punching operation. In the prior art, a stripper die was unnecessary for a kiss cut because there was no separate cutting.  
         [0012]     In view of the foregoing, it is therefore an object of the invention to provide a long-life die for kiss cutting a laminated sheet.  
         [0013]     Another object of the invention to provide a die for kiss cutting and blanking an article from a laminated sheet.  
         [0014]     A further object of the invention is to provide a method for kiss cutting and blanking an article from a laminated sheet.  
         [0015]     Another object of the invention is to provide an improved die for blanking flexible EL lamps.  
         [0016]     A further object of the invention is to provide an improved kiss cut die that is more easily maintained than an etched die.  
         [0017]     Another object of the invention is to reduce the cost of cutting articles from a laminated strip.  
       SUMMARY OF THE INVENTION  
       [0018]     The foregoing objects are achieved by this invention by a punch and die set in which the punch includes an inner section and an outer section, wherein the inner section is higher than the outer section, a cutting die for receiving the punch, and a stripper die movable within the cutting die. Because the inner section is higher than the outer section, the stripper die engages a workpiece first as the punch enters the die, producing a kiss cut. The punch can further enter the die to provide a blanking cut. A pressure pad within the stripper die holds a workpiece in place for cutting. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]     A more complete understanding of the invention can be obtained by considering the following detailed description in conjunction with the accompanying drawings, in which:  
         [0020]      FIG. 1  is a plan view of a etch die constructed in accordance with the prior art;  
         [0021]      FIG. 2  is a cross-section of a thin, thick film, flexible EL lamp;  
         [0022]      FIG. 3  is a plan view of a release layer containing graphics for referencing the orientation of a panel;  
         [0023]      FIG. 4  is a plan view of a finished lamp panel;  
         [0024]      FIG. 5  is a cross-sectional view of a press constructed in accordance with a preferred embodiment of the invention; and  
         [0025]      FIG. 6  is a top view of a portion of the system illustrated in  FIG. 5 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0026]      FIG. 2  is a cross-section of an EL lamp constructed as described in the above-identified application. Lamp  20  includes release layer  21  with insulating layer  22  deposited thereon, e.g. by screen printing or other technique known in the art. The release layer is a coated paper or a plastic sheet, such as polyethylene terephthalate (PET), supplied in rolls, which facilitates handling the lamps and integrating the lamps into appliances or molding apparatus. None of the layers is drawn to scale. Layer  21 , for example, is about 1-5 mil. (0.025-0.127 mm) thick. The phosphor layer and the dielectric layer are each about 1 mil thick.  
         [0027]     Electrode  23  is carbon/PEDOT/PSS (Poly-3,4-ethylenedioxythiophene/polystyrenesulfonic acid) (Orgacon™ EL-P 4010; Agfa-Gevaert N.V.) , a conductive polymer composite thatis screen printed on layer  22 . Dielectric layer  25  overlies electrode  23  and phosphor layer  26  overlies the dielectric layer. Electrode  27  is made by screen printing a transparent PEDOT/PSS ink (Orgacon™ EL-P 3040; Agfa-Gevaert, N.V.) on phosphor layer  26 . Electrode layers  23  and  27  can be patterned to define lit areas of the lamp in a graphic design. Insulating layer  28  overlies electrode  27 .  
         [0028]     Other layers could be added to the embodiment shown in  FIG. 2 , such as graphic overlays and protective layers. Any lamp layer can be split to form a plurality of lamps in a single panel.  
         [0029]      FIG. 3  illustrates section  31  of a strip or roll containing graphics for orienting a user to the location of lamps in a panel formed on the strip. The strip corresponds to release layer  21  in  FIG. 2 .  FIG. 4  illustrates a panel as it might appear on section  31 . Because a protective layer is typically used, the panel is featureless, which is why the graphics are used on the substrate. Given a roll or strip containing a plurality of sections like section  31 , the problems is how to separate the panel from the release layer and separate the panels from the strip.  
         [0030]      FIG. 5  is a cross-section of a press constructed in accordance with a preferred embodiment of the invention. Press  50  includes a first die attached to movable platen  51  and a punch is attached to fixed platen  52 . Obviously, motion is relative and either or both platens can be movable.  
         [0031]     Punch  54  includes outer section  56  and inner section  58 . While illustrated as separate pieces, a single piece having a raised central section could be used instead.  FIG. 6  is a top view of punch  54 , showing the outline of an EL panel more clearly. The stippled area corresponds to the upper surface of outer section  56 . The white area represents the upper surface of inner section  58 . In  FIG. 5 , inner section  58  extends above the top surface of outer section  56  by height  57 , indicated by arrows. In one embodiment of the invention, the height  57  was  7  mils (0.178 mm.) or slightly more than the thickness of a panel. The amount for any given application depends upon the properties of the material.being kiss cut and is readily determined experimentally. Punch  54  is located by guide  59 , which can move downward toward platen  52  during operation.  
         [0032]     Die  71  is attached to upper platen  51  by suitable means (not shown). Also omitted for clarity from  FIG. 5  are stop blocks, guide pins, index pins, actuators, and other details well known to those of ordinary skill in the art of tool making. Die  71  includes a cylindrical opening in which stripper die  73  is located. Shoulder  74  within die  71  engages a corresponding shoulder on the outside of stripper die  73  to limit the downward travel of the stripper die. The cross-sectional (in a plane perpendicular to the plane of the drawing) shape of stripper die  73  is the same as that of outer section  56 . Stripper die  73  is tubular or cylindrical and contains pressure pad  75 , which has a cross-sectional shape corresponding to inner section  58 . The press is operated by a suitable actuator (not shown) that engages rubber strip  81 , which prevents the press from jamming by cushioning platen  51  from the actuator.  
         [0033]     During operation, a strip of panels, represented by dashed line  60 , is inserted into the press and rests on inner section  58 . Press  50  is closed, lowering platen  51 . As the platen is lowered, pressure pad  75  comes to rest on strip  60 . Because strip  60  is squeezed slightly between pressure pad  75  and inner section  58 , the squeezed portion of the strip remains flat and dimensionally stable during subsequent cutting.  
         [0034]     As platen  51  continues to descend, pressure pad  75  slides upwardly within stripper die  73  while pressure pad  75  maintains pressure on strip  60  as determined by the compression rate of spring  82 , which is resiliently coupled to pressure pad  75  by movable pin  83 . As pressure pad  75  moves upwardly, lower edge  84  of stripper die  73  moves past corner  85  on the upper surface of inner section  58 . The shear force provides a kiss cut in the lamp layers on strip  60 . The strip is-not completely cut because height  57  is not sufficient to cause a complete cut. Thus, stripper die  73  is used as a cutting die.  
         [0035]     At this point the kiss cut is complete, the press can be opened, and strip  60  can be indexed to the next position or removed.  
         [0036]     In a preferred embodiment of the invention, the kiss cut is combined with a blanking cut to produce individual panels on substrates. For a blanking cut, platen  51  is lowered further. Pressure pad  75  and stripper die  73  move together upwardly until outer corner  87  of outer section  56  moves past inner corner  88  of die  71 . The motion is somewhat greater than the thickness of strip  60 , sufficient to produce a through cut, thereby blanking out an EL panel. Guide  59  engages die  71  and is moved downward. The lower limit on the downward movement of guide  59  is shoulder  89  on outer section  56 . As previously noted, guide rods, return springs, and the like, for guide  59  have been omitted for clarity.  
         [0037]     After a panel is blanked from strip  60 , press  50  is opened by raising platen  51 . As platen  51  is raised, spring  81  lowers stripper die  73  and pressure pad  75 , ejecting the blanked panel. Shoulder  74  in die  71  limits the downward travel of stripper die  73 . Bolt  91  limits the downward travel of pressure pad  75  Strip  60  is moved to the next index position and the process is repeated. An EL panel is easily removed from the release layer, by a vacuum pickup for example.  
         [0038]     The invention thus provides a long-life die for kiss cutting a laminated sheet. A punch and dies constructed as illustrated in  FIG. 5  and made from tool steel are expected to last for at least 6,000,000 cycles, which greatly reduces the cost of the tooling. The pressure pad can be tool steel or common steel, case hardened if desired. The invention also provides a die for kiss cutting and blanking an article from a laminated sheet in a single operation and, in particular, for kiss cutting and blanking flexible EL lamps. The punch and dies are easily maintained with conventional die making tools, such as grinders and polishers. Thus, the tooling can be maintained in-house, which further reduces cost. The apparatus can be used on single panel sheets, strips having a plurality of EL panels, or on rolls of EL panels.  
         [0039]     Having thus described the invention, it will be apparent to those of skill in the art that various modifications can be made within the scope of the invention. For example, inner section  58  need not have a completely flat upper surface but can be recessed or domed to suit a particular application. Similarly, while illustrated as square, corners  85  and  87  can be acute angles for improved cutting. A right angle is preferred and is much easier to machine and maintain. As previously noted, motion is relative. In the following claims, the recitation of one part as movable or another part as fixed is merely to provide a frame of reference for understanding the claim, not as a structural limitation.