Abstract:
A method for heat-sealing a sheet of heat-resisting polymer to a heat-resisting polymeric fitment, which enables the fabrication of a containment and delivery system for a bulk quantity of meltable adhesive, wherein a rigid container is lined by a heat-resisting flexible envelope, with a heater interposed between them. Ports are sealed to the envelope to permit the filling and draining of molten adhesive.

Description:
FIELD OF THE INVENTION 
     The present invention relates to the packaging of hot substances including hot-melt adhesives, and in particular to packages including a flexible liner capable of withstanding such substances, without compromising package integrity. 
     BACKGROUND OF THE INVENTION 
     This invention relates to hot melt adhesives which are used in industry in a wide variety of applications, and in particular to their packaging for shipment to the user and their utilization in the user&#39;s manufacturing operations. 
     In prior art hot melt adhesive packages, considerable secondary processing of the adhesive is required. Molten adhesive at the point of production is commonly poured onto a moving chilled belt, which rapidly solidifies in the form of a ribbon. The solid ribbon is then cut into sticks and typically packed into cartons of about 50 lb (25 kg) and shipped to the customer. Other shapes such as pillows, chicklets or pellets may also be formed for shipment to the customer. At the customer&#39;s facility, the solid pieces are transferred with a worm feed or directly by hand to a vat in which the adhesive is remelted, and therefrom dispensed for use. Since in some cases the contents of a single carton may be used up quickly, constant attention is needed to ensure that the vat is replenished. In some cases the vat may be open topped, thus putting the operator at risk of being burned by hot adhesive. The use of relatively small packages results in the consumption of large amounts of packaging material which has to be disposed of by the customer. Also, in facilities which use more than one type of adhesive, the presence of large numbers of small packages increases the possibility of error. 
     SUMMARY OF THE INVENTION 
     It is an object of this invention to allow the packaging and shipping of adhesive which originates in a molten flowable state so as to minimize secondary processing, thus reducing shipping, manufacturing and handling costs. The invention comprises a package having a flexible envelope of heat resisting material, a rigid holder for the envelope, and ports sealed to the envelope to permit the filling and draining of hot melt. It further comprises an electrical heater with a temperature measuring device and a control system. Finally, the invention comprises a method for forming a durably impervious seal between the flexible envelope material and the ports. The package is filled with hot melt adhesive and allowed to cool. It is shipped to the user and the contents are reheated by activation of the heater. The use of the shipping container as the reheating vessel allows the aforementioned vat to be eliminated. Furthermore, the package, including the envelope and/or the heat, can be re-used, possibly resulting in a significant economic benefit. Optionally, instead of being allowed to cool, the adhesive can be kept in its molten state by applying the necessary heat at all stages of its handling including transportation. This allows the end user to avoid losing time in reheating the adhesive. The invention allows the shipping of adhesive in quantities of up to about 330 gallons (1245 l), with a mass of about 3300 lb (1500 kg). When such quantities are dispensed in a controlled manner, considerably less labor is required than heretofore. Furthermore, the handling of relatively few large packages reduces the risk of dispensing the wrong adhesive in error. 
     Flexible containers for liquids obviously must be formed from a flexible material. For liquids at and near room temperature, a variety of materials are available to choose from, such as polyethylene, polypropylene, paper, foil and metallized laminates. Materials for use under relatively benign thermal conditions are easily processed with regard to their ability to be shaped and to be sealed to themselves or other fitments by the use of heat-sealing or adhesive techniques. With increasing temperatures, the problem becomes more challenging. While various polymeric sheet materials which are capable of retaining their integrity at temperatures of up to about 800° F. (425° C.) are known in general, and layers of such sheets may be heat-sealed together, it has not been disclosed to form reliably impervious heat-seals between such materials and fitments which must be attached thereto. 
     Therefore, it is a purpose of this invention to provide an impervious heat-seal between a sheet of heat-resisting polymer and a rigid fitment block which selectively allows or impedes the passage of a molten substance through the sheet. 
     It is further a purpose of the invention to provide a system comprising a flexible envelope for molten substances, the envelope having impervious heat seals with inlet and outlet fixtures and retaining its structural integrity at temperatures of up to 150° C., and preferably up to at least 200° C. The formation of such impervious seal between the envelope and the fixtures is critical for practical applications of this invention. 
     According to a first embodiment, this invention provides a receptacle for containing a molten material, comprising: a flexible envelope impervious to the molten material and including an inlet and an outlet; an inlet port imperviously sealed to the envelope at the inlet and extending outward from the inlet; and an outlet port imperviously sealed to the envelope at the outlet and extending outward from the outlet; wherein the receptacle retains its structural integrity up to a temperature of at least 150° C., and preferably up to at least 200° C. 
     According to other embodiments, the invention relates to a method for containing, transporting and dispensing a material. The method comprises: providing a receptacle that comprises a flexible envelope impervious to the material when molten and including an inlet and an outlet, a rigid holder into which the flexible inlet is disposed, and a heating element disposed between the rigid holder and the envelope, and in thermal contact with an exterior of the envelope; introducing the molten material into the envelope through an inlet port extending from the envelope inlet and an exterior of the container; closing the inlet port, and transporting the container to a desired location; activating the heating element to heat the material to a desired temperate in its molten state; and dispensing the material in its molten state from an outlet port extending from the envelope outlet and the exterior of the container; wherein the receptacle retains its structural integrity up to a temperature of at least 150° C. 
     This invention also relates to a method of forming a seal between a flexible sheet and a contact surface of a rigid block, comprising: providing a flexible sheet of a material having an aperture therethrough; providing a rigid block of material including a lower flange; inserting the rigid block through the aperture such that an upper surface of the lower flange contacts an inner surface of the flexible sheet surrounding the aperture; placing the rigid block flange surface and the flexible sheet inner surface in contact with a preheated support surface, and applying pressure for a predetermined time to form a seal between the flange and flexible sheet that is impervious to molten substances at a temperature of at least 150° C. 
     In particular, the present invention discloses regimes of temperature, pressure and time in which heat seals can be made between a sheet of heat-resisting polymer and a rigid fitment. The capability of making such heat seals enables the fabrication of flexible envelopes for receiving, containing and dispensing hot fluids at temperatures up to about 200° C., which in turn enables the fabrication of packaging systems which enable bulk quantities of such fluids to be admitted, contained, transported and dispensed. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a package for meltable adhesive. 
     FIG. 2 is a an exploded view of major components of the package. 
     FIG. 3 is a perspective view of a flexible envelope in an expanded form. 
     FIG. 4 is a perspective view of a port. 
     FIG. 5 is a partial view of the package near the port. 
     FIG. 6 is a cutaway view of the envelope. 
     FIG. 7 is a schematic representation of a sealing fixture. 
     FIG. 8 is a perspective view of work piece. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 shows a simplified perspective view of a package  10  for containing and transporting a bulk quantity of hot-melt adhesive, and FIG. 2 shows in schematic form a partial, exploded view of the same package. Package  10  comprises a rigid holder  12 , a heater  14  and a flexible impervious envelope  16 . In the illustrated embodiment, the envelope is also shown in FIG.  3 . Envelope  16  has a polyhedral shape close to that of a cube, having six facets comprising four rectangular sides  18 , a rectangular base  20  and a rectangular top  22 , each of which is orthogonal to its nearest neighbors. The top  22  has a centrally located inlet hole  24 , and one side  18  of the envelope  16  has an outlet hole  26  near to its lowest edge and centered along that edge. 
     FIG. 4 shows an inlet port  28  for installation at inlet hole  24 . Port  28  has a generally cylindrical shape, a cylindrical opening  30  through its entire length, and an interior thread  32 . A flange  34  extends outwardly from one end of port  28 , in a plane which is perpendicular to the axis of the port  28 . Immediately adjoining flange  34  is a step or flange  36  of circular cross-section having a diameter smaller than that of flange  34 . Spaced apart from step  36  is a second step or flange  38  of similar dimensions. Between steps  36  and  38 , inlet port  28  has a portion  39  which has a square cross-section of smaller size than steps  36  and  38 . Port fixture  28  illustrated in FIG. 4 may be integrally molded as a one-piece constriction. 
     Envelope  16  contains the hot melt adhesive, and is fabricated from a sheet material which can withstand molten hot adhesive for considerable periods of time. Also, since the quantity of adhesive may be sufficient to supply several production runs, the material must also survive several heating and cooling cycles. The sheet material must be capable of being sealed to itself and to the port material. 
     For these reasons, the preferred materials for envelope  16  are nylon, and in particular a copolymer of (also known as nylon 6) and poly(epsiloncaprolactam-hexamethylene adipamide) (also known as nylon 6/66), such as the copolymers disclosed in U.S. Pat. No. 5,206,309 and those sold under the trade name Nylon 6-6. Another preferred material is a copolymer of ethylene and tetrafluoroethylene (ETFE), such as copolymers sold under the trade name Tefzel™, with the aforementioned nylon material being the most preferred. The inlet and outlet ports  28 ,  40  must be also heat resistant to the molten hot melt adhesive that flows therethrough, and are preferably fabricated from a nylon material such as the aforementioned nylon copolymers. 
     In fabricating envelope  16 , an inlet hole  24  is cut in the material for the top  22 , and outlet hole  26  is similarly cut in one of the sides  18 . The diameters of holes  24  and  26  is smaller than the diameter of flange  34 . FIG. 5 shows a section of package  10 , with inlet port  28  arranged within inlet hole  24  of envelope  16 . With flange  34  on the interior side of envelope  16 , port  28  is passed through hole  24  until flange  34  contacts envelope  16 , steps  36  and  38  being sized to pass through hole  24 . Then, flange  34  is heat-sealed to envelope  16 , according to a procedure which will be described in more detail below. An outlet port  40  is essentially identical in structure and material to inlet port  28  and is similarly installed at outlet hole  26 . Inlet port  28  accepts a closure  42 , and outlet port  40  accepts a shutoff  44 , at interior thread  32 . 
     To assemble the final cube-like structure, the sides  18 , base  20  and top  22  of the envelope are heat-sealed together along their appropriate adjoining edges, by methods generally known in the art, to form impervious seams  46 . Optionally, the sides  18 , base  20  and top  22  may be fabricated from a single piece of material appropriately folded, to reduce the number of edges which need to be heat sealed. In the assembled envelope, ports  28  and  40  are outwardly directed with their flanges  36  on the inside. 
     FIG. 6 is a cutaway view of envelope  16  in a preferred embodiment of the invention, wherein envelope  16  comprises an inner pouch  50  and a similarly structured outer pouch  52 , each pouch being impervious to molten adhesive, as a safety feature to guard against spillage in the event one of the pouches is punctured. In the heat-sealing process, the pouches  50  and  52  are sealed together along all proximate edges. In effect, the result is an envelope each of whose sides  18 , base  20  and top  22  has two thicknesses of material bonded together around its perimeter along seams  46 . The two thicknesses are also heat-sealed together at a seam  48  around inlet hole  24 , and similarly around outlet hole  26 . 
     Heater  14 , shown in FIG. 2, has a rectangular central pad  54  and four rectangular flaps  56 , each of which is foldably attached to a different edge of the central pad  54 . The heating elements in central pad  54  and the flaps  56  are electrically interconnected. 
     The heater  14  receives its power from a controller  58 , whereto it is connected by a removable conductor  60 . A second conductor  62  provides power from an electrical supply to controller  58 . Optionally the heater  14  has attached to it a thermocouple  64  for sensing its temperature and providing feedback to controller  58 , in which case thermocouple  64  connects through a removable lead  66  with controller  58 . 
     Holder  12  has four walls  68 , a base  70  and a cover  72 , and accommodates the heater  14 . The central pad  54  of heater  14  is sized to conform with the base  70 , and the flaps  56  of heater  14  are folded upwardly against walls  68  of holder  12 . To avoid excessive stress on envelope  16  when it is filled, its expanded form is slightly oversized relative to holder  12 , so that all points below the fill line are supported by holder  12 . 
     The base  20  of envelope  16  rests on the central pad  54  of heater  14  such that each flap  56  is upwardly folded and interposed between a side  18  of the envelope  16  and a wall  68  of the holder  12 . In one flap  56  of the heater  14  and one wall  68  of the holder  12  are, respectively, holes  74  and  76  which are sized to accept the outlet port  40  from envelope  16 . Cover  72  has a hole  78  to accept inlet port  28 , which is maintained in a fixed position as will be described. Other types of heating elements may be employed, so long as the heating element is in thermal contact with the adhesive contained in the flexible envelope. 
     While holder  12  can be fabricated from any conventional rigid material, such as plywood or a heat resistant corrugated paperboard, the latter is preferred since it can easily be provided in a collapsed form and opened only as needed for use. A suitable corrugated material is available from MacMillan &amp; Bloedel. 
     Referring now to the process for sealing the envelope material to itself and to the ports, all seals must necessarily be impervious to molten substances to which they are exposed. In order to form seals that withstand aggressive thermal and chemical regimes, the preferred method is heat-sealing, whereby two surfaces are brought under pressure with the simultaneous application of heat, which causes them to flow together and merge. While flexible sheets of Nylon 6-6, Tefzel and like materials are known in the art to have been heat-sealed to each other, it has not been disclosed to form an impervious heat resistant seal between a sheet of Nylon 6-6 or Tefzel and a relatively massive fitment which acts as a heat sink. Normally, the application of sufficient heat to cause a polymeric fitment material to flow has the undesirable consequence of degrading the sheet to an unacceptable degree. Unexpectedly, a regime of temperature, pressure and time has now been discovered which permits the formation of a practical heat seal between a sheet and a massive fitment of heat-resisting polymer. 
     As shown schematically in FIG. 7, a sealing fixture  80  comprises a press  82  and an anvil  84 , which are conformed to accept a fitment with a flexible sheet. Fixture  80  has an open position when the press  82  and the anvil  84  are spaced apart, and a pressing position when they are proximate. Prior to the facets of envelope  16  being sealed together, inlet port  28  is inserted through inlet hole  24  until a contact surface  86  of the flange  34  on port  28  touches the material of the envelope top  22 , to form a work piece  88 , as shown in FIG.  8 . Press  82  and anvil  84  are preheated to a selected temperature, and the workpiece  88  placed between them in the open scaling fixture  80 , with an opposed surface  90  of flange  34  placed against the anvil  84 . The fixture  80  is next disposed into its pressing position, at a prescribed pressure which is sustained for a specified duration, until contact surface  86  has fused to the material. The fixture  80  is then opened, and the work piece is allowed to cool to solidify and then is withdrawn. In the same manner, outlet port  40  is sealed to the envelope side  18  which has outlet hole  26 . 
     In the case that the flexible sheet and the fitment are both made from a copolymer of polyepsiloncaprolactam and poly(epsiloncaprolactam-hexamethylcne adipamide), the pressing temperature is preferably at least 300° C., more preferably between 315 and 325° C., the applied pressure is preferably at least 500 kPa, more preferably between 620 and 690 kPa, and the pressure is preferably maintained for at least 60 seconds, more preferably between 80 and 100 seconds. In the case that the flexible sheet is made from an ETFE copolymer and the flexible sheet is made from a copolymer of polyepsiloncaprolactam and poly(epsiloncaprolactam-hexamethylene adipamide), the pressing temperature is preferably at least 350° C., more preferably between 375 and 385° C., the applied pressure is preferably at least 500 kPa, more preferably between 690 and 760 kPa, and the pressure is maintained preferably for at least 200 second, more preferably between 220 and 260 seconds. 
     Package  10  is assembled and used in the following manner. Holder  12 , which can be stored in a collapsed form, is opened up and placed on a pallet  92 , which provides clearance from floor level and allows the use of a forklift vehicle to transfer package  10  as necessary to a transportation vehicle. A guard  94 , which is provided in a collapsed form, is unfolded and placed around the walls  68  of holder  12  near its base  70 . Heater  14  is disposed within holder  12  so that its central pad  54  contacts base  70  of the holder, and flaps  56  are opened up against walls  68 , with hole  74  of the heater aligned with hole  76  of holder  12 . Guard  94  has an opening  96  which is also aligned with holes  74  and  76 . Envelope  16  is placed within holder  12  such that outlet port  40  passes through holes  74  and  76  and opening  96 . While cover  72  is closed at the top of holder  12 , inlet port  28  is positioned to project upward through hole  78  of cover  72 , with step  36  generally flush with the cover, and step  38  to the outside of the cover. To secure inlet port  28  in this position, a u-shaped clip  98  is placed astride the square portion  39  of port  28  and frictionally engaged between steps  36  and  38 , as is shown in FIG.  5 . Outlet port  40  may be similarly secured to a wall  68 . Shutoff  44  is engaged with the interior thread  32  of outlet port  40 . Guard  94  has sufficient thickness so that shutoff  44  is recessed within opening  96 , and is therefore protected from accidental impacts. 
     With closure  42  removed and shutoff  44  closed, envelope  16  is filled through inlet port  28  with molten adhesive from a supply source. When sufficient melt has been added, closure  42  is put in inlet port  28 , and the melt allowed to cool. Package  10  is transferred to a shipping area with a fork lift or other suitable device, onto a transport vehicle and conveyed to a customer&#39;s facility, whereat it is moved to a point of use. 
     At some time prior to hot adhesive being required, thermocouple lead  66  and conductor  60  are connected with the package  10 , and the heater  14  is activated, with controller  58  at a desired temperature setting. When the appropriate temperature is reached, shutoff  44  is opened and adhesive is dispensed as required. The adhesive may be dispensed until it is exhausted from the envelope, or in increments between which it may be allowed to cool and then be reheated. A further advantage of preferred embodiments of this invention is that many hot melt adhesives are homogenous materials, in which case mixing of the material in the container is not required while the material is being remelted for dispensing. 
     Optionally, instead of being allowed to cool once it has been received into the package, the adhesive may be kept in the molten state while being shipped to the customer, so as to save the time involved in remelting the solid. In such a case, an electrical supply and controller  58  can be provided on the transportation vehicle. 
     After the envelope  16  is drained, the power is turned off, shutoff  44  is closed and controller  58  disconnected from package  10 , which is ready to be returned for refilling. Optionally, the same envelope  16  may be re-used, or it may be substituted by another one. A further option is to discard the entire package and use a fresh one. The option selected would be determined by economic and environmental considerations. 
     We have described an invention the primary purpose of which is to provide a convenient means to contain, ship and dispense substances which are solid at room temperature, but which must be molten at the point of dispensation and use. While the invention can clearly be applied to relatively low-melting solids such as paraffin wax, the ability to form an envelope of heat-resisting materials, and in particular to heat seal fitments to such materials, is what enables the invention to be applied to substances with melt temperatures as high as about 400° F. (200° C.), such as for example required for dispensing hot-melt adhesives. Flexible sheet materials which can survive such temperatures include hcat-resisting organic polymers such as a polyaromatic amide, as is sold for example under the trade name Kevlar™; a polyimide, as is sold for example under the trade name Kapton™; an ethylene-tetrafluoroethylene copolymer known as ETFE, as is sold under the trade name Tefzel™; and a nylon such as a copolymer of polyepsiloncaprolactam and poly(epsiloncaprolactam-hexamethylene adipamide) as is sold under the trade name Nylon 6-6. We have shown that, preferably, the aforementioned ETFE and, most preferably, the aforementioned nylon can be used to form seals with a fitment fabricated from a nylon such as Nylon 6-6. 
     While the invention has been described with reference to preferred embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation of material to the teachings of the invention without departing from the scope of the invention. Therefore, it is intended that the invention not be limited to the particular embodiments disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope and spirit of the appended claims.