Abstract:
A multi-cavity coinjection mold and method for simultaneously producing a plurality of multi-layered articles comprising: a mold structure defining a plurality of mold cavities; a first supply source for supplying metered amounts of a first molding material; a second supply source for supplying metered amounts of a second molding material; a hot runner system in communication with the first and second supply sources for conveying the metered amounts of the first and the second materials separately to a region proximate each of the cavities; the region comprising having a pin controlled passage leading to proximate cavity by way of a gate having the same cross-section as the passage, the pin scavenging material from the passage and providing cavity packing.

Description:
FIELD OF THE INVENTION 
     This invention relates generally to coinjection molding and particularly relates to an improved apparatus for molding multi-layered articles which minimizes the effects of wall friction on contiguously flowing injection molding materials for supply to injection molding cavities. 
     DEFINITIONS 
     As used herein: 
     “First and second materials” is intended to cover at least two materials which are sequentially supplied to an injection mold, it being entirely possible that one or more other materials may be sequentially supplied before, between, or after the first and second materials; 
     “Balanced Hot Runner” is a temperature controlled heated uninterrupted material conveying system extending from a single input (e.g. a material source or metering valve) to a plurality of outputs (e.g. metering valves or injection mold cavities) comprising a single passage branched into a plurality of passages with each of said plurality of passages, communicating with one of the plurality of outputs, for conveying material therethrough to simultaneously supply equal quantities of the material to each of the outputs; 
     “Unbalanced Hot Runner” is a temperature controlled heated material conveying system, for the passage of material from an input (e.g. material supply source) to a plurality of outputs (e.g. metering valves for metering the material for supply of metered quantities of the material to injection mold cavities), which is not branched to provide passages of identical cross-section and length and does not divide the supplied material into equal quantities for the simultaneous supply of these quantities each to one of outputs. 
     BACKGROUND OF THE INVENTION 
     The manufacture of pure, or virgin, resin preforms for blow molding containers is well known within the prior art. But since the advent of recycling, it is now possible to manufacture preforms with materials that are compositionally less pure than virgin materials. Such degraded, or recycled, materials not only yield positive environmental benefits in an ecologically fragile era but provide manufacturers with an alternative manufacturing method which allows for substantial reductions in costs. 
     But, since recycled materials are obtained from post consumer solid waste, certain new manufacturing problems have been encountered that were heretofore previously unknown. For example, manufacturers must now provide, at increased costs, additional equipment for keeping the virgin and recycled materials separate from each other. In addition, multi-layered articles, such as preforms, that are eventually used to form containers for food stuffs, have even further impediments by way of rigid statutory guidelines. The guidelines, enacted by the Food and Drug Administration (FDA), require that certain minimums must be met, or exceeded, before the containers can be approved as “qualified” to contain food stuffs and before the foods are allowed to be distributed to the consumer population. One extremely noteworthy FDA provision enacted theretowards provides for the assurance of product “cleanliness”. 
     Currently, in order to meet the FDA cleanliness standards, a container must be configured such that only surfaces of virgin materials contact the foods and beverages therein. Other container surfaces, such as areas for contacting the human mouth, e.g. the dispensing orifice on a soda container, also require virgin material surfaces. As a result, it is economically desirable to provide manufacturers with a apparatus capable of utilizing recycled materials within containers while, at the same time, preventing recycled materials from contacting the very foods and liquids that are to be distributed to, and consumed by, the public. 
     Some advances towards the aforementioned goal have been attained by using coinjection molding techniques to manufacture multi-layered containers. The multi-layered containers thence produced have interior and exterior surfaces of the container comprised of virgin materials while the fill and support materials located within the interior of the container walls comprise the degraded, less than pure, recycled materials. Consequently, the economies and conservation of utilizing recycled materials is thereby achieved while simultaneously meeting the strict FDA statutory requirements. 
     Prior art coinjection molding techniques that produce the multi-layered containers described above, often first manufacture a multi-layered preform and then blow mold the preform into the final container. The formation of multi-layered containers are described in detail, for example, in Applicant&#39;s U.S. Pat. Nos. 4,550,043 and 5,221,507. 
     Typically, the preforms are injection molded in multi-cavity molds which may have as many as 96 cavities. These preforms are then simultaneously produced by injecting appropriate amounts of a first and second material, i.e. virgin and recycled, into each of the cavities. To this end, the mold defines a manifold arrangement to convey the two materials to each of the singular cavities. Such an arrangement, as in Applicant&#39;s prior patents, is known to convey each of the first and second materials into a singular hot runner before contiguously conveying the materials to the cavities. The combination then allows for a reduction in equipment costs due to the singular hot runner arrangement. The singular conduit repeatedly divides the materials flowing therein into a plurality of flow paths for delivery to each cavity and to thereby ultimately provide each cavity with a substantially equal amount of metered material at substantially the same temperature and at substantially the same time as every other cavity. Yet, with mold arrangements containing large numbers of cavities, such as with forty-eight and ninety-six cavities, the two materials contiguously flowing within a singular conduit have been known to have interface boundary problems between the virgin and recycled materials when conveyed over lengthy distances. 
     FIG. 1 illustrates potential interface boundary problems encountered with sequentially and contiguously flowing materials A and B in singular conduit  2 . Flow is in the direction of arrow  4  with overlapping tails  6  lagging the core flow of the materials to such an extent that a transverse cross-section (FIG. 2) of the flowing materials may contain two or more layers in a radial material distribution A-B-A (or even A-B-A-B or more) of materials A and B in lengthy conduits. This. problem complicates the injection molding of preforms for blow molding containers meeting the aforementioned FDA requirements in multi-cavity mold constructions utilizing contiguously flowing material distribution systems. 
     Other prior art multi-cavity mold apparatus, that use coinjection molding to form multi-layered preforms, utilize molds in which a completely separate manifold system for each material, i.e. virgin and recycled, is used to separately convey that specific material to the singular cavities. The separate materials are then injected sequentially into the cavities utilizing a valve arrangement closely adjacent each cavity to control the flow from the separate manifolds into multi-orifice nozzles. Such arrangements result in molds that are expensive and complex. 
     OBJECTS AND SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a more distinct division between the recycled and pure materials being contiguously conveyed within the same conduit to the individual mold cavities in order to more accurately provide a substantially equivalent amount of molding materials to each cavity. 
     It is also an object of the present invention to provide a method and apparatus that yields a delivery method for a first and second material that delivers the respective materials at substantially the same temperature and at reduced costs while conveying substantially equal amounts of the respective materials at substantially simultaneous delivery times. 
     SUMMARY OF THE INVENTION 
     According to the invention, there is provided a multi-cavity coinjection mold for simultaneously producing a plurality of multi-layered articles comprising: a mold structure defining a plurality of mold cavities; a first supply source for supplying a first molding material; a second supply source for supplying a second molding material; a hot runner system in communication with said first and second supply sources for conveying timed metered quantities of said first and said second materials separately to a region proximate each cavity; and each said region comprising a contiguous gate and adjacent passage with a reciprocal pin closely housed in the passage for movement between a fully retracted position, in which the first and second materials are conveyed contiguously through said passage and said gate to the proximate cavity, and a gate closure position, in which the pin has ejected all of the first and second materials from the passage into the proximate cavity, the passage and gate having the same cross-section and size without restriction therebetween. 
     Also according to the invention, there is provided a multi-cavity coinjection mold for simultaneously producing a plurality of multi-layered articles comprising: a mold structure defining a plurality of mold cavities; a first supply source for supplying a first molding material; a second supply source for supplying a second molding material; a hot runner system in communication with said first and second supply sources for conveying said first and said second materials separately to a region proximate each cavity; a valve mechanism per cavity for receiving said first and said second materials from said hot runner system and for sequentially supplying desired quantities of said first and said second materials contiguously to a hot runner to a region proximate each cavity, wherein each hot runner communicates with a single cavity only; and each said region comprising a contiguous gate and adjacent passage with a reciprocal pin closely housed in the passage for movement between a fully retracted position, in which the first and second materials are conveyed contiguously through said passage and said gate to the proximate cavity, and a gate closure position, in which the pin has ejected all of the first and second materials from the passage into the proximate cavity, the passage and gate having the same cross-section and size without restriction therebetween. 
     Also according to the invention, there is provided a method of multi-cavity coinjection molding for simultaneously producing a plurality of multi-layered articles comprising: a) providing a mold structure defining a plurality of mold cavities; b) providing a first supply source for supplying a first molding material; c) providing a second supply source for supplying a second molding material; d) separately conveying said first and second materials through a hot runner system from said first and second supply sources to convey timed metered quantities of said first and said second materials separately to a region proximate each cavity; wherein each said region comprising a contiguous gate and adjacent passage with a reciprocal pin closely housed in the passage, the passage and gate having the same cross-section and size without restriction therebetween; and e) and moving the pin between a fully retracted position, in which the first and second materials are conveyed contiguously through said passage and said gate to the proximate cavity, and a gate closure position, in which the pin has ejected all of the first and second materials from the passage into the proximate cavity. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will now be described, by way of example, with reference to the accompanying drawings, in which: 
     FIGS. 1 and 2 illustrate the distribution of contiguously flowing materials A and B in a relatively long conduit; 
     FIG. 3 is a diagrammatic cross-section of a multi-cavity coinjection mold system according to one embodiment of the invention; 
     FIGS. 4,  5 ,  6 ,  7  and  8  are diagrammatic views of cavity arrangements having passage and pin arrangements associated with a mold cavity, according to variations of the invention; 
     FIG. 9 is a diagrammatic illustration of a further embodiment of a mold of the present invention in which additional materials are used in the coinjection process; and 
     FIG. 10 is a variation of FIG.  4 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     With reference to the embodiment of FIG. 3, a cavity mold  8  for the sequential coinjection molding of multi-layered preforms for the blow molding of multi-layered containers comprising interior and exterior surfaces of a virgin material, e.g. polyethylene terephthalate (PET) is illustrated as having four cavity arrangements  10 . It will be appreciated by those skilled in the art that, in practice, the multi-cavity mold  8  depicted may have a greater number of cavities including both odd (e.g. 71) or even (e.g. 96) numbers. Four cavity arrangements  10  are used in this example to simplify explanation of the present invention which is applicable to molds having any number of cavities. Each cavity arrangement comprises a cavity  12  (e.g. FIG. 4) of a form is itself well known to those skilled in the art and is not described in detail herein. At the base of each cavity is a gate  14  through which passes the materials which will form the preform in that particular cavity. The particular gate cross section is a function of the properties of materials conveyed and of how much material is to be injected. All of which are well known within the art. 
     The mold  8  defines a plurality of hot runner passages  16  (e.g. FIG. 4) each for conveying timed sequential quantities of alternating first and second molding materials contiguously and simultaneously to all cavities. 
     In operation, each passage  16 , receives first and second materials through a hot runner manifold system  20  by way of hot runners  22 ,  24 . The first and second materials (A and B) are supplied by plasticizers  26  and  28  under control of ram pots  30  and  32 , respectively. So that the two materials are sequentially supplied in timed metered quantities through the passages  16  of the associated cavity (FIG.  4 ). 
     An example of a cavity arrangement  10  is diagram-matically illustrated in FIG. 4 in which one only of a plurality of cavities  12  of a multi-cavity mold is shown, the other cavities being identical as to form and material supply arrangements. In this embodiment an essentially nozzleless material supply arrangement is provided in that material A and B reach the gate  14  through a passage  16  of the same cross-section and size as the gate  14 , without the reduction in cross-section inherent in a nozzle such as the nozzles of the prior art. Hereinafter in this preferred description, the preferred cross-section of passage and gate as being circular will be referred to. 
     In this embodiment materials A and B are separately and sequentially conveyed through hot runners  22 ,  24  in timed metered quantities to passage  16  through which they are conveyed contiguously to and through gate  14  to cavity  12  for the coinjection molding of a multilayer preform as previously described. 
     A pin  30  is reciprocally mounted in passage  16  and is shown in full in its retracted position and in ghost in its gate closure position. The pin is cylindrical and has a diameter about 0.0005 inches (0.013 mm) to about 0.001 inches (0.025 mm) less than the diameter of passage  16  and gate  14 . 
     Friction of the materials A and B contiguously flowing through passage  16  causes the interfaces of materials in passage  16  to form tails adjacent the wall of passage  16  which lag the more centrally located core portions of the interfaces. These tails are undesirable as they have a potential of adversely affecting material distribution in the preform produced in the cavity  12 . The further the materials are contiguously conveyed, the worse is the adverse effect. In the embodiment of FIG. 4, the adverse effect of the tails is minimized as a result of the materials A and B being separately supplied to passage  16  and the passage  16  being kept as short as possible with the consequence that the contiguous contact of materials A and B is minimized with the consequent minimization of the tails. 
     When the metered quantities of materials A and B, for injection molding a preform, have been conveyed to the passage  16  and cavity  12 , the passage  16  is full. At this time, the pin  30  is moved by actuator  32  in the direction of arrow  34  to drive the material remaining in passage  16  through the gate  14  to completely fill the cavity  12  with the pin  30  then closing the gate  14 . By this means, the pin  30  ejects all material from passage  16  and thus eliminates all residual tails which would otherwise remain pending the next molding cycle. With the pin  30  in this position, the cavity is full. The pin  30  then is applying and continues to apply a packing pressure (produced by actuator  32 ) to the material in the cavity  12  while that material is solidifying, thereby to ensure complete filling of the cavity  12  and formation of a complete preform therein. The pin  30  remains in this position until the next molding cycle is about to commence, at which time the pin  30  is withdrawn by actuator  32  to its fully retracted position with ports  36  and  38  fully open for the conveyance, in timed metered sequence, of materials A and B to passage  16 . It should be noted that pin  30  does not control flow of either material A and B to passage  16  as these materials are only supplied to passage  16  while the pin  30  is fully retracted. 
     It will be appreciated that while hot runners  22 ,  24  only for materials A and B (e.g. virgin and recycled PET) are shown, the provision of hot runners for the timed metered supply of a third (e.g. a barrier material) material etc. could be provided within the scope of the invention. Also while the hot runners  22 ,  24  are shown as ported into the side of passage  16 , annular or other port configurations could be used. 
     Referring now to FIG. 5 which illustrates a variation of the embodiment of FIG. 4, only distinguishing features will be described. Here a timed valve mechanism  18 , hereinafter described in more detail, supplies metered quantities of materials A and B, from hot runner systems  20  (balanced or unbalanced) for contiguous conveyance to passage  16  by way of hot runner  40 , where this contiguous supply of materials A and B is sequenced with a timed metered supply of material C (e.g. a barrier material) from a further material supply source  42  by way of hot runner  44  for the contiguous supply of materials A, B and C in a desired sequence through gate  14  to cavity  12 . 
     It will be appreciated that a further timed valve mechanism  18  (FIG.  6 ), could be employed to provide a contiguous supply of materials (e.g. C and D or C with A or B, etc.) in place of the metered supply of material C. 
     The valve mechanisms.  18  are as closely adjacent their respective cavities  12  as possible. It will be appreciated that separate conveyance of the first and second materials to the valve mechanisms proximate their respective cavities will minimize any interface boundary difficulties between the first and second materials since the two materials are not contiguous within a singular conduit prior to reaching the valve mechanisms. Once combined by the valve mechanisms  18 , the distance traveled by the contiguous first and second materials within the hot runners  40 ,  44  and passages  16  is minimal and the difficulties of lengthy contiguous travel are minimized. Simultaneously, equipment cost advantages are realized since each hot runner  40 ,  44  is a single undivided channel dedicated to a single cavity. In addition, hot runner manifold system  20  need not be a balanced conveyance system. 
     Timing control mechanism  46  facilitates the coordination of simultaneous switching of the plurality of valve mechanisms  18  so that substantially equal amounts of the materials will be supplied simultaneously to each individual cavity  12 . Actuators  32  and timing mechanism  46  may be any one of a variety of electromechanical mechanisms as will be well known to those skilled in the art and will not be described here in detail. 
     Further construction details of mold  8 , particularly its hot runners, together with the heating and cooling arrangements therefore are also conventional within this technology and will be readily apparent to those skilled in the art. Likewise, the plasticizers and ram pots are of conventional construction as are the general engineering details of valve mechanisms. Accordingly, these matters are again not described herein. in detail. 
     It will be further appreciated by those skilled in the art that the separate and distinct hot runners  22 ,  24  may be used to convey different materials from respective plasticizers  26  and  28  wherein the materials supplied from the plasticizers are of substantially different processing temperatures. Such an alternative arrangement, while providing distinct hot runners for materials. of differing temperatures, may also be used if the materials are of the same processing temperature. The conveyance of the specific materials are kept separate until conveyed to the appropriate proximate cavity regions. Conveyed first and second materials are then likewise supplied to a timed valve distribution system  18  for combining the materials into hot runners  40 , passages  16  and eventually to the appropriate individual cavities  12 . 
     FIG. 7 illustrates a cavity arrangement  10  in which valve  18  at least partially encompasses passage  16  and pin  30  and is operated by rotation about central axis  48  of pin  30 . This arrangement provides the shortest possible path for the contiguous supply of materials A and B to cavity  12  while providing for the above described operation of pin  30 . As will be seen, the hot, runners  22 ,  24  are ported to passage  16  by way of a single port  50  controlled by valve  18 . Additional hot runners could be provided for the supply of additional materials C, D, etc., to passage  16  by way of valve  18  in any desired timed metered sequence. 
     In a further embodiment as shown in FIG. 8 a plurality of cavity arrangements  10  each have a. cavity  12 , gate  14  and passage  16  with a pin  30  actuated by one or more actuators  32  (two being shown, one for each of two cavities  12 ). As the pins  30  may operate synchronously, one actuator  32  could be used to operate a plurality of pins  30 . There may be two, three, four or more cavities  12  in this plurality (depending on available space) each fed with timed metered quantities of materials A and B conveyed contiguously through hot runners  52  and passages  16  to the cavities  12  by way of gates  14 . There is one hot runner  52  and one passage  16  for each cavity with all hot runners  52  being identical and all passages  16  and pins  30  being identical. The hot runners  52  are each supplied with equal timed metered contiguous quantities of materials A and B (and possible additional materials C, D, etc.) through a hub  54  from a valve mechanism  18  rotatable about axis  48  to selectively convey the materials A and B from hot runners  22 ,  24  sequentially in the timed metered amounts to the associated cavities. 
     An additional or alternatively other material or contiguous timed metered quantities of materials, etc. could be conveyed to passages  16  for contiguous supply with materials A and B to the cavities and these may be provided through a balanced hot runner system or through one or more valve mechanisms  18  in similar manner to valve mechanism  18  of FIG. 8 or with one valve serving each cavity or a plurality of valves serving groups of cavities differing from those enumerated with reference to FIG.  8 . 
     In all embodiments disclosed, it will be appreciated that passages  16  are hot runners suitably temperature controlled, as is the hot runner system  20  and hot runners  22 ,  24 ,  40 ,  44 ,  52 ,  54 , etc. by temperature controllers  56  and appropriate insulation  58  (these being shown diagrammatically only in FIGS. 3,  4  and  10 ). 
     Referring now to FIG. 9, four plasticizers  70 ,  72 ,  74  and  76  which may each be associated with a ram pot (not shown in FIG. 9) separately supply a plurality of up to four different materials by way of one or both of balanced and unbalanced hot runner system to supply cavities  12  of cavity arrangements  10  with time metered contiguous quantities of materials A, B, etc. in accordance with the above described embodiments. 
     In an embodiment employing an unbalanced hot runner and a balanced hot runner the plasticizers may provide three different materials, for example, virgin PET recycled PET and another material, such as a barrier material. Alternatively, two of the plasticizers could supply virgin PET. In either circumstance virgin PET is supplied separately by way of the unbalanced hot runner to the valve mechanisms of the assemblies  10  while the other materials are metered by a diverter valve to the balanced hot runner for contiguous flow therethrough to supply the materials simultaneously and sequentially in equal quantities to the valve mechanisms of the assemblies  10  for metering, with the virgin PET from the unbalanced hot runner, to provide the contiguous supply of the materials from the valve mechanisms of the assemblies  10 . Operation of all of the valves is preferably synchronized to ensure appropriate material metering. 
     In the event of the material from two of the materials both being virgin PET, this arrangement can advantageously be used to supply virgin PET through an unbalanced hot runner to valve mechanisms of the assemblies  10  without any possible contamination by the recycled PET, thereby to facilitate the formation of the inner surface of a multi-later article molded in the cavities and to supply virgin and recycled PET through a balanced hot runner for use in the article where contamination of the virgin PET is less critical. 
     It will be appreciated that, for example, a single plasticizer could be used to supply the same material to both the unbalanced hot runner and the diverter valve of the balanced hot runner and that similar variations are possible in other embodiments. In addition the balanced hot runners may be identical, in order to balance the contiguous supply of metered material therethrough, or may be different from each other and/or controlled at different temperatures to provide desired characteristics of material flow to the cavities. 
     The valve mechanisms may be provided with an “off” or closed position as well as a position for the supply of each material sequentially and contiguously. 
     Of course it will be appreciated that diverter valve operation could be adjusted, if injection molding in different cavity groups is unbalanced thereby causing non-uniform layers and or parts from cavity group to cavity group, by sequentially operating the valves and/or changing valve timing to adjust material flow from one cavity group to another, for example, so that cavity groups that would receive the most material would have their diverter valve operation delayed to compensate and balance the flow of material to the groups. 
     One of the materials may be recycled PET or a barrier material e.g. ethylene vinyl alcohol (EVOH) disposed intermediate polyester layers of the article. 
     FIG. 10 shows a variation of FIG. 4 in which hot runners  22 ,  24  conveying materials A and B are increased in cross-sectional area upstream of the ports  36 ,  38  in order to reduce frictional effects on the material flows. A similar increase in cross-sections material supply hot runner could be utilized in other embodiments of this invention.