Abstract:
A method and an apparatus are used for injection molding composite devices comprised of a plastic material and a component being at least partially embedded in the plastic material. A mold is provided having a cavity therein. The cavity has a surface and an access bore is provided in the mold which ends in the cavity surface via an opening. The component is fed through the access bore and via the opening to the cavity. The component is configured to positively cover with overlap the opening upon transition thereof while coming to rest on the surface. Molten plastic material is injected into the cavity to enclose the component, thus forming the composite device. After solidifying of the plastic material the composite device is ejected from the cavity.

Description:
FIELD OF THE INVENTION 
     This invention relates to the field of injection molding plastic material devices. More specifically, this invention is directed to a method and an apparatus for injection molding a composite device comprised of a plastic material having a component being at least partially embedded therein. 
     BACKGROUND OF THE INVENTION 
     During the injection molding of the plastic material devices one may, concurrently, provide components to be simultaneously injection molded, for example metallic components to enhance the mechanical stability, hooks, hinges and the like. Further, it is well-known in the art to injection mold so-called smart cards, i.e. plastic material cards having a module embedded therein. The module is inserted into the cavity of an injection molding machine mold prior to injecting the molten plastic material into the cavity. The term “module” is to be understood to comprise e.g. a semiconductor chip having, for example, an electric contact surface area being accessible from the outside of the card and serving to establish a single transmission line between the semiconductor chip and a card reading apparatus. 
     German patent specification 41 15 208 discloses a mold for manufacturing smart cards. Smart cards are flat devices of e.g. 50 mm width and 80 mm length and having a thickness of only about 0.6-0.8 mm. If an appropriately dimensioned cavity is provided in a plastic material injection molding mold, problems may arise due to the very narrow cross section because there might be a problem for the liquified or molten plastic material to propagate through the cavity with its very narrow cross-sectional area. This holds true the more when the extremely flat hollow cavity is, further, partially occupied by the module, the thickness of which being only a little smaller compared to the height of the cavity. If, for example, the module has a thickness of 0.6 mm and the inner height of the hollow cavity is 0.8 mm, the remaining free space “behind” the module is just a very narrow air gap of 0.2 mm width which does not allow an effective flow of the liquid plastic material. 
     The method and the apparatus disclosed in German patent specification 41 15 208 utilizes another approach. This prior art mold uses two piston-like plungers which are reciprocally operated. The plungers run in bores ending in a surface of the cavity. In the initial position the front faces of the plungers are essentially flush with that cavity surface. Therefore, in this initial position the molten plastic material may freely be injected into the practically unobstructed cross section of the hollow cavity. As long as the plastic material is still deformable, one of the plungers is advanced into the plastic material whereas the other stamp is retracted. The displacements and cross sections of the plungers are dimensioned such that during the movement of the plungers no change in volume occurs. Accordingly, when the plastic material has solidified and the device is ejected, it has a depression on that side where the first plunger had been advanced. This depression may be used for inserting a module in a subsequent operation, for example by gluing the module in place, after the plastic material device had been ejected from the mold. 
     It is, however, an inherent disadvantage of this prior art method that for mounting a module in the plastic material device a separate operational step is required after the unmolding of the device. 
     German disclosure document 41 42 410 discloses a method for producing flat plastic material devices, for example identification cards. This prior art device comprises two mold sections. The lower mold section has a prismatic, i.e. trapezoidal cross section. The lateral inclined surfaces are provided with flat hollow cavities having the shape of the identification cards to be produced. A second mold portion may be placed on top of the first mold portion, thus entirely covering the prismatic section. Moreover, channels are provided for injecting molten plastic materials into the hollow cavities. 
     Within the first mold portion bores are provided ending under right angles in the flat hollow cavities. Piston-like plungers run in these bores for feeding a module in a lateral direction to the hollow cavity. This is made by first retracting the plunger into an initial position and then again advancing the plunger which subsequently runs against a carrier sheet for stamping a module from that carrier sheet. While this is done molten plastic material is injected into the hollow cavity to replete same. By further advancing the plunger with the stamped-out module on top, the latter may be pressed into the liquid plastic material which is not yet solidified. 
     It is a disadvantage of this prior art apparatus that in view of the tolerances required to let the plunger run within the bore a small gap must be provided between the plunger and the surrounding bore surface. However, considering that the molten plastic material is injected under extremely high pressure, molten plastic material will also penetrate into the gap, the more as the pressure within the hollow cavity is still increased when the module is pressed into the liquid material which is not yet solidified. Therefore, when the plastic material is solidified and the plunger is retracted, the corresponding surface of the identification card has a small bulge around the module. The bulge is configured by the plastic material which has penetrated into the gap between the plunger and the bore. The bulge may be seen and felt by the user so that the identification card is defective insofar. 
     The prior art apparatus has the further disadvantage that due to the high pressure that prevails within the hollow cavity during the injection of the molten plastic material the plunger with the module resting on its front face may even be pressed back into the bore. As a result, the module will protrude from the corresponding surface of the identification card when the card has been produced. 
     Another similar process and apparatus are disclosed in German disclosure document 41 42 392. 
     It is, therefore, an object underlying the invention to provide a process and an apparatus of the kind mentioned at the outset which obviates the above-discussed disadvantages. In particular, it shall be possible to produce an entirely smooth, high-quality surface of the composite device, in particular a smart card. 
     SUMMARY OF THE INVENTION 
     The afore-mentioned and other objects are achieved by a method of injection molding a composite device comprised of a plastic material having a component being at least partially embedded therein, the method comprising the steps of: 
     providing a mold with a cavity therein, the cavity having a surface, an access bore to the cavity ending in the surface via an opening; 
     feeding the component through the access bore and via the opening to the cavity, wherein the component is configured to positively cover the opening upon transition thereof while coming to rest on the surface; 
     injecting molten plastic material into the cavity to enclose the component, thus forming the composite device; 
     ejecting the composite device from the cavity. 
     The objects are further achieved by a method of injection molding a composite device comprised of a plastic material having a component being at least partially embedded therein, the method comprising the steps of: 
     providing a mold with a cavity therein, the cavity having a surface, an access bore to the cavity ending in the surface via an opening; 
     feeding the component through the access bore to a first predetermined position within the access bore before the opening; 
     injecting molten plastic material into the cavity and into a portion of the access bore between the opening and the component at the first predetermined position; 
     displacing the component along the access bore from the first predetermined position via the opening to a second predetermined position within the cavity so as to transfer molten plastic material from the portion of the access bore into the cavity and concurrently pressing the component into the molten plastic material within the cavity; 
     ejecting the composite device from the cavity. 
     The objects are further achieved by an apparatus for injection molding a composite device comprised of a plastic material having a component being at least partially embedded therein, the apparatus comprising: 
     a mold with a cavity therein, the cavity having a surface, an access to the cavity ending in the surface via an opening; 
     means for feeding the component through the access and via the opening to the cavity, wherein the component is configured to positively cover the opening upon transition thereof while coming to rest on the surface; 
     means for injecting molten plastic material into the cavity to enclose the component, thus forming the composite device; 
     means for ejecting the composite device from the cavity. 
     The objects are further achieved by an apparatus for injection molding a composite device comprised of a plastic material having a component being at least partially embedded therein, the apparatus comprising: 
     a mold with a cavity therein, the cavity having a surface, an access bore to the cavity ending in the surface via an opening; 
     means for feeding the component through the access bore to a first predetermined position within the access bore before the opening; 
     means for injecting molten plastic material into the cavity and into a portion of the access bore between the opening and the component at the first predetermined position; 
     means for displacing the component along the access bore from the first predetermined position via the opening to a second predetermined position within the cavity so as to transfer molten plastic material from the portion of the access bore into the cavity and concurrently pressing the component into the molten plastic material within the cavity; 
     means for ejecting the composite device from the cavity. 
     The objects underlying the invention are thus entire achieved. 
     The fact that the transition between a gap at the transitional edge between the access bore and the surface is positively covered, i.e. covered with a certain overlap, it is entirely impossible for molten plastic material to penetrate into that area so that the formation of optically detectable bulges or the like in the surface of the produced device or smart card is entirely avoided. Moreover, by providing a certain lateral overlap between the component and the access bore opening, it is impossible to press the component back into the access bore. For this reason, too, an entirely smooth surface is generated on the device having an optimum optical quality. 
     Although the positive coverage of the transition may be effected in various ways, for example by laterally displacing the component, it is particularly preferred in an embodiment of the invention to first compress the component in a direction parallel to the surface and to then again release the component into a non-compressed state after having transitioned the opening. 
     This measure has the advantage that a simple change in the shape and dimension of the component, i.e. a relatively simple mechanical manipulation results in the required positive coverage of the transition. 
     This holds true in particular for a preferred modification of this embodiment where the component has an active element disposed on an elastic carrier, and wherein during the step of feeding the carrier is first compressed in a direction parallel to the surface and is again released into a non-compressed state after having transitioned the opening. For that purpose, the carrier may be made from an elastic material, may be provided with a lip seal at its periphery or may be shaped as a meander at its back face. 
     These measures have the advantage that due to the elasticity of the carrier the required positive coverage is effected automatically without necessitating further separate mechanisms. 
     In any event it is preferred when during the step of feeding the component is displaced along an inner surface of the access bore with the surface being configured to effect the compression and the release of the component. This holds true in particular when the access bore is at least partially configured conically with the transitional area taking the shape of a rectangle or a circle with an access bore portion being shaped as a pyramid or as a cone, respectively, at a distance from the opening or may entirely be configured as a cone. 
     These measures have the advantage that the change in shape of the carrier may simply be achieved by actually translating the carrier along the narrowing and then again widening inner surface of the access bore. If, for example, the inner surface of the access bore is entire or partially conically shaped, the carrier will impinge on that conical surface during its axial translation and will then be compressed more or less quickly in a direction parallel to the hollow cavity surface depending on the cone angle. As soon as the carrier then passes by the opening of the axis bore into the hollow cavity, i.e. passes the transition, the cross section of the axis bore suddenly widens into the hollow cavity. As a consequence, the carrier is again released automatically if it has the necessary elasticity. Depending on the particular field of application the amount of elastic release may be set such that the transition is positively covered with the required overlap. 
     In this connection it is particularly preferred in an embodiment of the inventive apparatus when the component is fed by means of a piston running in the access bore, the piston being preferably shaped at least partially in a complementary conical fashion. 
     This measure does not only have the above-discussed advantages that a deformable carrier may be compressed by simply running on a conical surface. Instead, this measure has the further advantage that the piston, when coming to rest in its terminal position constitutes a much better closure with respect to the hollow cavity surface as would e.g. be the case for a cylindrical piston or plunger in a correspondingly cylindrical access bore. In particular, when the conical piston comes to rest on the corresponding conical portion of the access bore, no annular gap is created as would be the case due to necessary tolerances in a cylindrical configuration. Instead, such peripheral gaps would only exist, when either the conical piston or the complementary conical bore would not be exactly conically shaped. 
     This embodiment of the invention has the further advantage that the piston coming to rest at its terminal position could b subjected to an appropriate closing force. The closing force could be set as high that even an extremely high injection pressure within the hollow cavity would not at the consequence to press the piston back into the access bore and, concurrently, also press back the component sitting on the piston front face. This particular feature is absent from systems utilizing a cylindrical piston or plunger in a likewise cylindrical bore because in the absence of a mechanical stop no such high closing pressure may be applied to the piston as discussed above. 
     When, in a more general aspect, components shall be fed to the cavity, one can provide one or more mechanical latches to mechanically latch the component at at least one predetermined position within the access bore. For that purpose, appropriate mechanical latch systems may be provided. 
     One can, for example, feed the component in a direction towards the hollow cavity until a first predetermined position where the component is still somewhat retracted from the hollow cavity surface. In that retracted position the component is no mechanical obstacle for the flow of molten plastic material injected into the hollow cavity. As soon as the cavity is entirely or almost entirely repleted with molten plastic material, the component may be advanced into a second predetermined position where its lower surface is flush with the corresponding surface of the hollow cavity and corresponding to the final position of the component within the cavity. By doing so the hollow cavity may be effectively repleted with molten plastic material without the problems associated with narrow cross sectional areas discussed above. Moreover, it would be possible to press the component into the still deformable plastic material and, concurrently, into its terminal position flush with the surface of e.g. the identification card. 
     If this option is used, the two predetermined positions may be mechanically defined by providing appropriate mechanical latches having the further advantage of withstanding even extremely high pressures within the hollow cavity during injection. 
     It goes without saying that these features may be used also in cases where the component which is fed to the cavity is not elastic and where the positive coverage or overlap features discussed above are not utilized. 
     It goes without saying that the afore-discussed features as well as the features which will be discussed below in connection with the description of the preferred embodiments may not be used only in the particularly given combination but also in other combinations or alone without leaving the scope of the present invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further advantages will become apparent from the description and the enclosed drawing. 
     Embodiments of the invention are shown in the enclosed drawing and will be described in more detail in the subsequent description of the preferred embodiments. 
     FIGS. 1-3 illustrate in a side elevational cross-sectional view a plastic material injection molding apparatus for producing smart cards to the prior art, in three distinct operational positions; 
     FIGS. 4 and 5 illustrate in a similar way as FIGS. 2 and 3 a first embodiment of the invention; 
     FIGS. 6-8 illustrate a second embodiment of the invention in a way similar to that of FIGS.  1 - 3 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the figures like elements are generally designated by like reference numerals. In the embodiments of FIGS. 4 and 5 “a” is added, in the embodiment of FIGS. 6-8 “b” is used as a suffix. Distinct operational positions are identified by adding one or two apostrophes. 
     In FIG. 1 reference numeral  10  as a whole indicates a plastic material injection molding tool or mold as used for the production of smart cards. Mold  11  comprises a first mold portion  11  as well as a second mold portion  12 . A hollow cavity  13  is located between mold portions  11 ,  12 . Hollow cavity  13  takes the shape of a smart card. Hollow cavity  13  may either be provided in first mold portion  11  or in second mold portion  12  or may partially be provided in both mold portions  11  and  12 . The elements required for feeding liquified or molten plastic material to hollow cavity  13  as well as the elements required for heating mold  10  etc. are not illustrated for the sake of simplicity. 
     An access bore  20  is laterally directed towards hollow cavity  13 . A plunger or piston  21  runs within bore  20  and has a front face  22  directed towards hollow cavity  13 . Access bore  20  preferably has either a rectangular or a square cross section but may also be configured cylindrically or may have an arbitrary geometric cross section. 
       23  designates the transition between access bore  20  and hollow cavity  13 . In other words, access bore  20  opens at  23  into a surface  34  of hollow cavity  13 . Surface  34  corresponds to the later flat and smooth surface of the smart card to be produced. 
     A so-called module  25 , or in a more general approach, a component is held ready on front face  22  of piston  21 . Module  25  comprises a carrier  26  as well as an integrated semiconductor chip  27  arranged on top thereof. It goes without saying that module  25  may also be an arbitrary component, for example a hinge, a reinforcing element, a handle or the like. The component had been placed on front face  22  of piston  21  previously in a mounting position (not shown), for example by means of a conventional handling system when the piston  21  is retracted far back. 
     Reference numeral  30  in FIG. 1 indicates that a molten plastic material may be injected laterally into hollow cavity  13 , as indicated by an arrow  31 . In FIG. 1 the lead of molten plastic material  13  has not yet reached access bore  20 . Piston  21  with module  25  is still in a retracted position. 
     In a somewhat later operational position as shown in FIG. 2 piston  21 ′ has been advanced upwardly as indicated by an arrow  32 . Module  25  in this situation has almost reached surface  34 . As indicated by an arrow  31 ′, the lead of molten plastic material  30 ′ has now essentially passed access bore  20 . 
     FIG. 3 shows the terminal operational position. Piston  21 ″ is in its upper end position in which its front face  22 ′ is flush with surface  34 . Module  25 ″ has been impressed into solidifying molten plastic material  30 ′″. Carrier  26 ″ is now in a position where its lower surface is also flush with surface  34 . 
     However, as can be seen from a blown-up section  40  in FIG. 3, a gap  42  exists between a peripheral surface  41  of piston  21  and the inner surface of access bore  20  due to the necessary clearance between piston  21  and access bore  20  making movement of piston  21  and access bore  20  possible and, further, in view of the unavoidable tolerances. Molten plastic material  30 ″ during injection under high pressure penetrates into gap  42  and forms a protrusion which takes the shape of a peripheral bulge  43  on the smart card after it has been unmolded. Peripheral bulge  43  is visible by the eye and palpable, thus constituting a significant quality defect. 
     In the embodiment of the invention shown in FIGS. 4 and 5 things are different insofar as in that case carrier  26   a  is configured elastically, i.e. may consist of an elastic material. Carrier  26   a,  however, may also be provided at its peripheral edge with some kind of lip seal. As an alternative, carrier  26   a  on its side facing away from hollow cavity  13  may be provided with a meander over a substantial portion of its thickness for effecting a compressibility in a radial direction. In the position shown in FIG.  4  and corresponding to the position in the prior art of FIG. 2 module  25   a ′ is located shortly below surface  34  in a position identified on the left hand side of FIG. 4 by “A”. Carrier  26   a ′ in that position engages the wall of access bore  20  under laterally directed pressure, as symbolized by arrows  46 . This means that at least a rim  47 ′ of carrier  26   a ′ is compressed in a direction parallel to surface  34 . 
     The compression of rim  47  or of the entire carrier  26   a,  respectively, may, for example, be effected by providing a ramp  48  or a conical section as shown in FIG. 4 below access bore  20 . Carrier  26   a  during the upwardly directed movement of piston  21   a  runs on ramp  48  in the direction of an arrow  32   a  and is, hence, compressed in the direction of arrows  46 . 
     As soon as piston  21   a  has reached the position identified by “B” in FIG. 4 carrier  26   a ′ passes the transition  23   a  between axis bore  20  and surface  34 . As shown in FIG. 5, the laterally compressed carrier  26   a ″ may, hence, release and widen outwardly, thus concurrently overlapping transition  23   a  in surface  34 . 
     As can clearly be seen from the blown up section  40   a  in FIG. 5, rim  47 ″ now overlaps transition  23   a,  so that gap  42   a  is positively covered with respect to plastic material  30 ″. Therefore, no plastic material  30   a ″ may penetrate into gap  42   a.  The lower surface of module  25   a ″ or carrier  26   a ″, respectively, hence lie flush with surface  34   a  and an entirely smooth surface of the smart card is generated. 
     On the left hand side of FIG. 5 it is further shown that piston  21 ″ in its illustrated terminal end position may be mechanically latched. For that purpose piston  21 ″ as well as the corresponding mold portion  12   a  are provided with bores  50 ,  51  which are flush to each other in the position of FIG.  5 . By means of a pin  52  inserted into both bores  50  and  51  piston  2 l a ″ may thus be latched in an axial direction. As a consequence, even if an extremely high pressure prevails in hollow cavity  13   a,  piston  21   a  may not be displaced backwardly, i.e. downwardly. 
     The method illustrated in FIGS. 4 and 5 may be still more refined if piston  21   a ′ when it is in the position indicated by “A” is briefly stopped as long as the liquid molten plastic material  30   a ′ flows into hollow cavity  13   a.  The position A shown must, however, be understood only as an example. Of course, piston  21   a ′ may be advanced a little bit more so that the upper surface of carrier  26   a ′ is flush with surface  34   a′.  In any event position A is selected such that molten plastic material  30   a ′ may freely flow into hollow cavity  13   a  without being obstructed by an obstacle. 
     In second step piston  21   a ′ is now advanced into its terminal position B and, hence, module  25   a ′ is pressed into molten plastic material  30   a′,  as indicated in FIG. 5 by  25 ″ and  30   a′.    
     By impressing module  25   a ″ according to FIG. 5, one can, further, apply the necessary pressure which would otherwise be required for compensating for the shrinkage occurring in the plastic material during solidifying. 
     In the further embodiment of the invention shown in FIGS. 6-8 there is a modification insofar as access bore  20   b  within mold portion  12   b  is now made entirely conical, i.e. becomes narrower in an upward direction and may, for example, take the shape of a pyramid or a cone. As a consequence, piston  21   b  in a lower section in FIG. 6 is configured cylindrically, whereas a front section  56  is configured conically. The conical shape of section  56  is complementary to the conical shape of access bore  20   b.    
     Carrier  26   b  again, is made from an elastic material. Its rim  47   b  slightly protrudes over front face  22   b  of piston  21   b.    
     As one can easily see from FIG. 6, carrier  26   b  has a somewhat larger cross section as compared to an opening  60  in access  20   b  within surface  34   b.  As indicated by arrows  61 , carrier  26   b  comes into contact with conical access bore  20   b  prior to reaching transition  23   b.  As soon as elastic carrier  26   b  impinges on conical access bore  20   b  along arrows  61 , the backward space of access bore  20   b  is tightly sealed towards hollow cavity  13   b.  This corresponds to the above-discussed first position A of FIGS. 4 and 5 in which piston  21   b  may be briefly stopped. The molten plastic material  30   b  may now be injected into hollow cavity  13   b.  When flowing into hollow cavity  13   b  it is obstructed by module  25   b  because module  25   b  is positioned at least partially below surface  34   b.  On the other hand side a penetration of molten plastic material  30   b  into the back section of access bore  20   b  is prevented because, as mentioned above, access bore  20   b  is sealed towards hollow cavity  13   b.    
     As soon as hollow cavity  13   b  is now partially or entirely repleted with molten plastic material  30   b,  piston  21   b′,  may now be displaced upwardly as shown in FIG. 7 where the condition of maximum compression (arrows  46   b ) is attained because rim  47   b  is now compressed to the narrowmost cross section in the area of transition  23   b.    
     As soon as hollow cavity  13   b  is now entirely repleted with molten plastic material, as shown by reference numeral  30   b ″ in FIG. 8, piston  21   b ″ is displaced into its terminal position of FIG.  8 . Rim  47   b ″ now jumps over transition  23   b  or opening  60 , respectively, and positively covers or overlaps gap  42   b.  Gap  42   b  to a certain extent is unavoidable for reasons of practical design, for example because in the area of transition  23   b  between conical axis bore  20   b  and flat surface  34   b  a certain rounding is necessary. 
     From FIG. 8 one may, further, take that conical section  56 ″ snugly fits into conical access bore  20   b.  Therefore, it is possible to exert an axial closure force from below on piston  21   b ″ in its position of FIG.  8 . Such axial closure force prevents that piston  21   b ″ is pressed back and downwardly by the inherent pressure within liquid plastic material  30   b″.