Abstract:
The present invention is a method for making a plastic overcap using a mold tool stack. The mold tool stack has a core and a cavity plate forming a cavity therebetween. The core has a resin passageway therein with a gate in a top surface of the core. The gate has a valve proximate the top surface of the core to regulate resin flowing from the resin passageway and into the cavity. The steps of the mold method are as follows: the mold tool stack is closed to form the cavity; the valve is opened to allow resin to enter the cavity; the valve is closed; the resin is allowed to cool; and the mold tool stack is opened to allow removal of the plastic overcap from within the mold tool stack. The top side of the plastic overcap produced is blemish-free, facilitating placement of labels and other markings thereon.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This patent application is a Divisional of Co-pending U.S. patent application Ser. No. 10/619,243, filed Jul. 14, 2003, which claims priority to U.S. Patent Application No. 60/395,585, filed Jul. 12, 2002, entitled “Method For Making Plastic Overcaps Using Hot Runner Back-Gated Mold Technology”, the disclosures of which are incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     Removable protective closure systems for pharmaceutical products are generally known. U.S. Pat. No. 5,284,263 discloses a removable protective closure system for use with vials containing unit doses of medicaments, which is hereby incorporated by reference in its entirety. The closure system includes a rubber stopper, a cap seal and an overcap. Such closure systems are designed to be easily removed by a flipping motion of the thumb while the vial is held in one hand. The closure system also provide for pharmaceutical product identification which can be used at the point of application to ensure that the proper identification and other information is communicated to the nurse or other healthcare personnel.  
         [0003]     Typically, production of molded plastic overcaps  100 ′ ( FIG. 4 ) in the past has been accomplished using a cold runner top-gated mold technology ( FIG. 2 ). Referring to  FIGS. 2 and 4 , the cold runner mold technology generally comprises a series of tooling component stacks  10 ′, each stack including a core  12 ′, a core plate  14 ′, a strip plate  16 ′, a cavity plate  20 ′, a runner plate  42 ′, a runner strip plate  32 ′, and a resin injector  34 ′. The core  12 ′ is fixedly engaged with the core plate  14 ′, rising above the core plate  14 ′. The top of the core  12 ′ generally forms the bottom of a mold area cavity  22 ′ for the molded plastic overcap  100 ′. Both the core  12 ′ and the core plate  14 ′ are stationary. The strip plate  16 ′ is movable and, during molding, is in facing engagement with the core plate  14 ′. The strip plate  16 ′ has a cylindrical opening through which the core  12 ′ projects. A strip plate bushing  18 ′ is maintained within the opening of the strip plate  16 ′ to ensure sealing engagement with the core  12 ′. The movable cavity plate  20 ′ is in facing engagement with the strip plate  16 ′ during molding. A small indentation is formed in the cavity plate  20 ′ to accommodate the top of the core  12 ′ and allow for a small void to be formed between the top of the core  12 ′ and the cavity plate  20 ′, thereby forming the mold area cavity  22 ′ for the molded plastic overcap  100 ′. A cavity plate tunnel  36 ′ is formed through the cavity plate  20 ′ and ending at the center of the indentation, at which point a top outside gate  24 ′ is formed. The gate  24 ′ forms a small opening into the mold area cavity  22 ′. The cavity plate tunnel  36 ′ gradually gets wider when moving from the gate  24 ′ to the top surface of the cavity plate  20 ′ culminating in a larger opening at the top of the cavity plate  20 ′. The runner plate  42 ′ is in facing engagement with the cavity plate  20 ′ during molding. The runner plate  42 ′ has a runner plate tunnel  38 ′ therethrough, which coincides with and continues from the opening at the larger end of the cavity plate tunnel  36 ′. The runner plate tunnel  38 ′ gets wider from the smaller opening in the bottom surface of the runner plate  42 ′ to the larger opening in the top surface of the runner plate  42 ′. The runner strip plate  32 ′ is in facing engagement with the runner plate  42 ′. The runner strip plate  32 ′ has a runner strip plate tunnel  40 ′ extending therethrough through which the resin injector  34 ′ is inserted. The runner strip plate tunnel  40 ′ is of a uniform width, which is slightly less than the width of the opening of the runner plate tunnel  38 ′ in the top surface of the runner plate  42 ′.  
         [0004]     In order to manufacture multiple molded plastic overcaps  100 ′, multiple tooling component stacks  10 ′ are assembled as described above. The resin injectors  34 ′ of each stack are inserted within the runner strip plate tunnels  40 ′. Each resin injector  34 ′ releases heated plastic resin  28 ′ which flows through the runner plate tunnel  38 ′ and the cavity plate tunnel  36 ′, passing through the gate  24 ′ and filling the mold area cavity  22 ′. The resin injectors  34 ′ are then removed and the plastic resin  28 ′ is left to cool. Cooling is accelerated using water lines  30 ′ that run through the cavity plate  20 ′ and the core  12 ′. Cool water is circulated through the water lines  30 ′ to absorb heat from the cavity plate  20 ′ and the core  12 ′ which have absorbed heat from the heated resin  28 ′. Upon sufficient cooling, the runner strip plate  32 ′ and the runner plate  42 ′ are removed from engagement with the cavity plate  20 ′. Due to the tapered walls of the runner plate tunnel  38 ′, this movement exerts stress on the excess solidified resin that has collected within the runner plate tunnel  38 ′ and the cavity plate tunnel  36 ′. The excess resin breaks off at the point of its smallest cross-sectional area at the gate  24 ′, thereby severing the excess resin from the molded plastic overcap  100 ′. The excess resin is then collected to be recycled and subsequently reused. The cavity plate  20 ′ is then removed from engagement with the strip plate  16 ′ exposing a top side  102 ′ of the molded plastic overcap  100 ′. The strip plate  16 ′ is then removed from engagement with the core plate  14 ′, whereupon the strip plate bushing  18 ′ pushes upon a bottom side  106 ′ of an outside edge  104 ′ of the molded plastic overcap  100 ′ in order to remove the molded plastic overcap  100 ′ from the top of the core  12 ′. Pressurized air from an air line  32 ′ is also directed at the molded plastic overcap  100 ′ to facilitate its release from the top of the core  12 ′. The molded plastic overcap  100 ′, now released from the mold area cavity  22 ′, falls into a collection receptacle (not shown).  
         [0005]     There are several drawbacks inherent to the cold runner top-gated molding process of the prior art. First, because of the location of the gate  24 ′, when the excess resin is removed, a small protrusion  103 ′ of excess resin remains at the breakage point extending outwardly from the top side  102 ′ of the molded plastic overcap  100 ′. The protrusion  103 ′ presents problems when placing a label on or otherwise marking the top of the molded plastic overcap  100 ′. Second, the design of the cold runner top-gated mold technology requires the presence of the excess resin (known as a runner) during the production of each molded plastic overcap  100 ′. This necessitates the removal and recycling of the excess resin for its subsequent reuse. This process inevitably results in the loss of plastic resin. Third, because the process requires cooling time and subsequent removal of the excess resin runner before a finished molded plastic overcap  100 ′ is produced, the cycle time for the cold runner top-gated mold technology is relatively lengthy.  
         [0006]     The present invention comprises a process for making molded plastic overcaps using a hot runner back-gated mold which seeks to remedy the drawbacks of the cold runner top-gated mold technology. First, because the gate is now located at the back of the mold area, the small protrusion of excess resin gate vestige is now located on the back side of the molded plastic overcap, instead of the top side, thereby enabling the overcap to be manufactured with a flat top free from blemishes, making it easier to affix labels, custom logos, and other identification devices such as electronic or magnetic devices to or otherwise mark the top side of the overcap. Second, because the plastic resin remains in liquid form during the entire molding process, no runners are formed, and, consequently, there is no excess resin to be recycled, resulting in material savings. Third, because the process requires no cooling time and no evacuation of excess resin runners, the hot runner back-gated mold can be run at higher speeds, cutting the cycle time to less than half that of the cold runner top-gated mold.  
       BRIEF SUMMARY OF THE INVENTION  
       [0007]     Briefly stated, in one aspect, the present invention comprises a mold tool stack for making plastic overcaps from heated resin. The mold tool stack comprises a core, a cavity plate, and a resin passageway. The cavity plate is located above the core. One of the core and the cavity plate is axially movable relative to the other of the core and the cavity plate to allow the core and the cavity plate to engage with each other when the mold tool stack is in a closed position and to allow the core and the cavity plate to separate from each other when the mold is in an open position. When the mold tool stack is in the closed position, a cavity is formed between a top surface of the core and a portion of a bottom surface of the cavity plate. The portion of the bottom surface of the cavity plate corresponds to a top side of the plastic overcap. The top surface of the core corresponds to a bottom side of the plastic overcap. The portion of the bottom surface of the cavity plate is substantially flat and blemish-free. A resin passageway is located within the core with a gate in the top surface of the core. The gate has a valve proximate the top surface of the core to regulate heated resin flowing out of the resin passageway and into the cavity. The valve is proximate the top surface of the core. This allows for minimal wasted resin between the valve and the plastic overcap and further allows for a gate mark to be present on the bottom side of the plastic overcap to allow for the top side of the plastic overcap to be substantially flat and blemish-free.  
         [0008]     In another aspect, the present invention comprises a method for making a plastic overcap using a mold tool stack. The mold tool stack has a core and a cavity plate forming a cavity therebetween. The core forms a bottom of the cavity and the cavity plate forms a top of the cavity, such that the top of the cavity corresponds to a top side of the plastic overcap and the bottom of the cavity corresponds to a bottom side of the plastic overcap. The core has a resin passageway therein with a gate in a top surface of the core. The gate has a valve proximate the top surface of the core to regulate an amount of resin flowing out of the resin passageway and into the cavity. One of the core and the cavity plate is axially movable relative to the other of the core and the cavity plate. The steps of the mold method are as follows. First, the mold tool stack is closed such that the core is in contact with the cavity plate to form the cavity therebetween. Second, the valve is opened to allow resin to enter the cavity. Third, the valve is closed to stop the flow of resin into the cavity once a desired amount of resin has entered the cavity. Fourth, the resin within the cavity is allowed to cool to form the plastic overcap. Fifth, the mold tool stack is opened to allow removal of the plastic overcap from within the mold tool stack, such that the plastic overcap produced has a small protrusion of excess resin on the bottom side due to the proximity of the valve to the top surface of the core. This allows the top side of the plastic overcap to be blemish-free to facilitate placement of labels and other markings thereon. 
     
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
       [0009]     The foregoing summary, as well as the following detailed description of preferred embodiment of the invention, will be better understood when read in conjunction with the appended drawings. For the purpose of illustrating the invention, there is shown in the drawings an embodiment which are presently preferred. It should be understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown.  
         [0010]     In the drawings:  
         [0011]      FIG. 1  is a sectional elevational view of a tooling component stack of a hot runner back-gated mold in accordance with a preferred embodiment of the present invention;  
         [0012]      FIG. 2  is a sectional elevational view of a tooling component stack of a cold runner top-gated mold of the prior art;  
         [0013]      FIG. 3  is a perspective view of a molded plastic overcap manufactured using the tool component stack and the process of the present invention;  
         [0014]      FIG. 4  is a perspective view of a molded plastic overcap manufactured using the process of the prior art;  
         [0015]      FIG. 5   a  is a sectional elevational view of the tooling component stack of  FIG. 1  in a closed position with an empty cavity;  
         [0016]      FIG. 5   b  is a sectional elevational view of the tooling component stack of  FIG. 1  in a closed position with a resin-filled cavity;  
         [0017]      FIG. 5   c  is a sectional elevational view of the tooling component stack of  FIG. 1  in a partly open position;  
         [0018]      FIG. 5   d  is a sectional elevational view of the tooling component stack of  FIG. 1  in a fully open position; and  
         [0019]      FIG. 5   e  is a sectional elevational view of the tooling component stack of  FIG. 1  in a fully open position with air being forced from air lines to eject a molded plastic overcap. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0020]     Certain terminology is in the following description for convenience only and is not limiting. The words “right”, “left”, “upper”, and “lower” designate directions in the drawings to which reference is made. The terminology includes the words above specifically mentioned, derivatives thereof, and words of similar import.  
         [0021]     Referring to the drawings in detail, wherein like numerals indicate like elements throughout, there is shown in  FIG. 1 a  preferred embodiment of a hot runner back-gated mold tool stack, indicated generally at  10 , in accordance with the present invention. It is preferred that the present invention has a plurality of tool stacks  10  in order to increase production, and, although only a single tool stack  10  is described below, all tool stacks  10  of the present invention are substantially similar. The tool stack  10  has a core  12 , a core plate  14 , a strip plate  16 , a strip plate bushing  18 , and a cavity plate  20 , all of which are made of a high strength, light weight material such as tool steel, for example. The core  12  is fixedly maintained within an opening in the core plate  14 . The core  12  forms a generally cylindrical protrusion extending upwardly from a top surface of the core plate  14 . Preferably, both the core  12  and the core plate  14  are stationary.  
         [0022]     The strip plate  16  is in facing engagement with the core plate  14 . The strip plate  16  is movable in a vertical direction and has an opening therethrough to accommodate the core  12  when in facing engagement with the core plate  14 . The strip plate bushing  18  is maintained within the opening in the strip plate  16  in order to ensure a sealing engagement with the core  12 .  
         [0023]     The cavity plate  20  is in facing engagement with the strip plate  16 . The cavity plate  20  has an indentation in a bottom surface in order to accommodate the amount of the core  12  that extends beyond a top surface of the strip plate  16 . The cavity plate  20  is movable in the vertical direction.  
         [0024]     The tool stack  10  is in a closed position ( FIG. 5   a ) when the cavity plate  20  and the strip plate  16  and strip plate bushing  18  are stacked in their respective lowest positions. The tool stack  10  is in an open position ( FIG. 5   e ) when the cavity plate  20  and the strip plate  16  and strip plate bushing  18  are raised to their respective highest positions above the core  12 .  
         [0025]     When in the closed position, a small mold area cavity  22  is formed by the tool stack  10  between a portion of the bottom surface of the cavity plate  20  and a top surface of the core  12 , within which a molded plastic overcap  100  is formed for each cycle of the tool stack  10 . The portion of the bottom surface of the cavity plate  20  corresponds to a top side  102  of the plastic overcap  100  ( FIG. 3 ), and the top surface of the core  12  corresponds to a bottom side  106  of the plastic overcap  100 .  
         [0026]     Within the core  12  is a resin passageway  26  leading from a resin source (not shown) to the mold area cavity  22 . The resin passageway  26  is preferably located through the center of the core  12 . A plastic resin  28  enters the mold area cavity  22  from the resin passageway  26  through a gate  24  at the top surface of the core  12 , preferably in the center of the top surface of the core  12 . A valve  52  is within the gate  24  to regulate the amount of resin  28  flowing out of the resin passageway  26  and into the mold area cavity  22 . The valve  52  is proximate the top surface of the core  12  to allow for minimal wasted resin  28  between the valve  52  and the plastic overcap  100 . The placement of the valve  52  proximate the top surface of the core  12  further allows for a gate mark to be present on the bottom side  106  of the plastic overcap  100  to allow the top side  102  of the plastic overcap  100  to be substantially flat and blemish-free. Heating coils  50  are preferably located around the resin passageway  26  up to the gate  24  in order to keep the resin  28  within the resin passageway  26  heated at all times throughout a mold cycle.  
         [0027]     Air jets  32  are preferably located within the strip plate bushing  18 , although it is within the spirit and scope of the present invention for the air jets  32  to be located within the core  12 . Air is forcibly ejected from the air jets  32  and directed against the bottom side  106  of the plastic overcap  100  to facilitate removal of the plastic overcap  100  from within the tool stack  10  at the end of the mold cycle ( FIG. 5   e ).  
         [0028]     At least one tube  30  is located within the cavity plate  20  through which cool water or other fluid flows in order to keep the cavity plate  20  cool and subsequently facilitate the cooling of the resin  28  within the mold area cavity  22  during the mold cycle. Although only one tube  30  is portrayed, it is within the spirit and scope of the present invention that there be a network of tubes  30  located within the cavity plate  20  in order to more evenly and more quickly cool the resin  28  within the mold area cavity  22  at the end of the mold cycle.  
         [0029]     In operation, referring to  FIGS. 1, 3 , and  5   a - 5   e , the tool stack  10  is assembled as described above in the closed position ( FIG. 5   a ). The valve  52  is opened in the resin passageway  26 , allowing heated resin  28  to pass from the resin source through the gate  24  and into the mold area cavity  22 . Upon filling of the mold area cavity  22 , the valve  52  is closed, cutting off the flow of resin  28  at the gate  24 , as seen in  FIG. 5   b . The tubes  30  through the cavity plate  20  circulate cool water or other fluid throughout the tooling stack  10  in order to keep the mold area cavity  22  cool. The heating coils  50  immediately below the gate  24  around the resin passageway  26  keep the resin  28  heated. In this way, the resin  28  within the mold area cavity  22  cools quickly, while the resin  28  remaining within the resin passageway  26  remains heated. Referring specifically to  FIG. 5   c , the cavity plate  20  is then raised vertically from the strip plate  16  and strip plate bushing  18 , opening the mold area cavity  22  and exposing the top side  102  of the molded plastic overcap  100  formed within. Referring now to  FIG. 5   d , both the strip plate  16  and the cavity plate  20  are raised vertically from the core  12  such that the tool stack  10  is in the open position. In so doing, the strip plate bushing  18  engages with a bottom of a side skirt  104  of the molded plastic overcap  100  pushing the plastic overcap  100  and removing it from engagement with the top surface of the core  12 . Removal of the overcap  100  from within the tool stack  10  is facilitated by air forcibly ejected from the air jets  32  and directed against the bottom side  106  of the plastic overcap  100 . The finished plastic overcap  100  then drops from the tool stack  10  into a waiting collection receptacle (not shown). The cavity plate  20 , the strip plate  16 , and the strip plate bushing  18  are then lowered into a stack to place the tool stack  10  in the closed position, and the mold cycle is repeated.  
         [0030]     Referring now to  FIG. 3 , the plastic overcap  100  produced with the tool stack  10  of the present invention is comprised of a single circular disk having the top side  102 , the bottom side  106 , and the side skirt  104 . The side skirt  104  extends downwardly from the outside edge of the bottom side  106 . The top side  102  is substantially flat and blemish-free to facilitate writing on or placement of labels on the top side  102  of the plastic overcap  100  in order to properly identify a medicament within a medicament container (not shown). The bottom side  106  has a small cylindrical ring  108  extending downwardly therefrom. Although it is preferable that the cylindrical ring  108  be located at the center of the bottom side  106  of the plastic overcap  100 , it is within the spirit and scope of the present invention for the cylindrical ring  108  to be located anywhere on the bottom side  106 . The cylindrical ring  108  is appropriately sized to insert into and engage with an opening in the cap seal, in a manner well understood by those of ordinary skill in the art. Extending slightly downwardly from the bottom side  106  within the cylindrical ring  108 , the plastic overcap  100  has a gate mark  103 , in the form of a small protrusion (shown in phantom in  FIG. 3 ). The gate mark  103  is on the bottom side  106  of the plastic overcap  100  so as not to disrupt the substantially flat and blemish-free top side  102 . Also, the gate mark  103  is preferably inside the cylindrical ring  108  so as to be out of contact with the cap seal in order to avoid improper sealing of the medicament container. Although the plastic overcap  100  of the present invention is used with a closure system preferably for the sealing of medicament containers, it is within the spirit and scope of the present invention that the plastic overcaps  100  be used with closure systems for the sealing of different types of containers and is not limited to medicament containers.  
         [0031]     The hot runner back-gated mold tool stack  10  of the present invention overcomes several problems inherent in the prior art. First, the location of the gate  24  allows the mold area  22  to be filled with resin  28  from the back, causing the gate mark  103  of excess resin  28  to form on the bottom side  106  of the plastic overcap  100 . This allows the top side  102  to be free from blemishes so that labels and other markings can be more easily affixed thereto. Second, because the resin  28  remains heated and in liquid form within the resin passageway  26  and because the valve  52  cuts off the supply of resin  28  immediately proximate the mold area cavity  22 , there are no excess resin runners to be recycled and reused, resulting in material savings. Third, because there is little required cooling time and no evacuation of excess resin runners required, the tool stack  10  can be run at higher speeds than was possible in the prior art, resulting in cycle times of the present invention that are less than half those of the prior art.  
         [0032]     It will be appreciated by those skilled in the art that changes could be made to the embodiment described above without departing from the broad inventive concept thereof. It is understood, therefore, that this invention is not limited to the particular embodiment disclosed, but it is intended to cover modifications within the spirit and scope of the present invention.