Abstract:
An apparatus ( 10 ) and method for forming differentially frangible seals (FS) in a final closed pouch (FCP) are described. The method involves differential cooling a seal portions of pouch forming dies ( 15, 15 A) with a fluid directed at or in a portion of the die. The method is useful for forming pouches with dual chambers separated by a frangible seal and surrounded by a hard seal, one chamber for a liquid (L) and the other chamber for another material (M). Single pouches are also described.

Description:
GOVERNMENT FUNDING 
     None 
     CROSS REFERENCE TO RELATED APPLICATION 
     None 
     BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     The present invention relates to a method and apparatus for forming heat seals with films, particularly in pouches with a manually frangible (rupturable) seal. The frangible seal is preferably adjacent to hard seals which are not manually rupturable without destruction of the film. In particular, the present invention relates to a method and apparatus wherein a cooling fluid (gas or liquid) is used to cool portions of a die which forms the frangible seal. 
     2. Description of Related Art 
     The production of pouches with frangible seals which can be ruptured manually (by hand) to release or mix the contents of the pouch are well known to those skilled in the art. In particular, dual pouches separated by a frangible seal are well known to those skilled in the art. Illustrative are U.S. Pat. No. 2,932,385 to Bollmeier et al; U.S. Pat. No. 3,074,544 to Bollmeier et al; U.S. Pat. No. 3,608,709 to Pike; U.S. Pat. No. 3,913,789 to Miller; U.S. Pat. No. 4,266,692 to Clark; U.S. Pat. No. 4,312,473 to Hoeller; U.S. Pat. No. 4,462,224 to Dunshee et al; U.S. Pat. No. 4,537,308 to Hollander; U.S. Pat. No. 4,608,043 to Larkin; U.S. Pat. No. 4,805,767 to Newman; U.S. Pat. No. 4,872,556 to Farmer; U.S. Pat. No. 4,890,744 to Lane et al; U.S. Pat. No. 4,986,076 to Kirk et al; U.S. Pat. No. 4,923,095 to Dorfman et al; U.S. Pat. No. 4,952,068 to Flint; U.S. Pat. No. 5,131,760 to Farmer; U.S. Pat. No. 5,209,347 to Fabisiewicz et al; U.S. Pat. No. 5,263,609 to Hoshino; U.S. Pat. No. 5,287,961 to Herran; U.S. Pat. No. 5,364,486 to Falla et al; U.S. Pat. No. 5,423,421 to Inoue et al; U.S. Pat. No. 5,492,219 to Stupar; U.S. Pat. No. 5,494,190 to Boettcher; U.S. Pat. No. 5,616,337 to Kasianovitz et al; and U.S. Pat. No. 5,699,902 to Sperry et al. 
     The prior art has described the use of a lower temperature in the die to form a weaker seal which is frangible. U.S. Pat. No. 4,759,472 to Strenger discloses such a frangible seal 25 without describing how the frangible seal is produced. Frangible seals are similarly generally described in U.S. Pat. No. 4,890,744 to Lane et al., U.S. Pat. No. 5,100,028 and 5,035,348 to Siefert; and U.S. Pat. No. 5,131,760 to Farmer. 
     The inventors are unaware of any prior art which describes the use of a cooling fluid (gas or liquid) to cool a portion of the sealing die during the formation of the frangible seal. U.S. Pat. No. 5,502,952 to Wildmoser describes air cooling when the machine is stopped, but not for forming a frangible seal. U.S. Pat. No. 2,948,999 to Schlayer et al uses air to cool a bead formed as part of a hard seal. U.S. Pat. No. 5,441,345 to Garvey et al shows cooling for a timing operation. 
     The prior art has described a number of different pouch forming and filling apparatus. Illustrative are: U.S. Pat. No. 3,344,576 to Cloud et al; U.S. Pat. No. 3,478,492 to Cloud et al; U.S. Pat. No. 3,563,001 to Cloud et al; U.S. Pat. No. 3,597,898 to Cloud; U.S. Pat. No. 3,821,873 to Benner et al; U.S. Pat. No. 3,908,979 to Cloud et al; U.S. Pat. No. 4,316,566 to Arleth et al; U.S. Pat. No. 5,094,657 to Dworak et al. There is no discussion of frangible seals in these patents. 
     OBJECTS 
     It is therefore an object of the present invention to provide a method and apparatus for forming a pressure frangible (rupturable) seal and a hard seal and a hard seal particularly between two sheets of a thermoplastic film in a pouch such that there is a significant differential between the seal strength of various hard and frangible portions of the seal. In particular, it is an object of the present invention to provide an apparatus and method whereby portions of the sealing areas of the pouch are made frangible so as to be pulled apart using novel differential cooling of a die which forms the seal. Further still, it is an object of the present invention to provide an apparatus which is relatively simple to construct and use and which is economical to operate. These and other objects will become increasingly apparent by reference to the following description and the drawings. 
     SUMMARY OF THE INVENTION 
     The present invention relates to a die for differentially heat sealing a film to another sealable material which comprises: 
     (a) a plate having a seal forming portion around a cavity, wherein a part of the seal forming portion of the plate is inletted to provide an opening around the part of the seal forming portion; and 
     (b) conduit means mounted in the plate for providing a cooling fluid to the part in the opening in the plate for cooling the part of the seal forming portion in the portion of the plate which is inletted. 
     Also the invention relates to a die which is half of a pair of dies for differentially heat sealing opposed contacting sheets of a plastic film to form a pouch defined by a peripheral seal which comprises: 
     (a) a plate having a seal forming portion around a cavity for defining an inside of the pouch, wherein a part of the seal forming portion of the plate is inletted to provide an opening around the part of the seal forming portion; and 
     (b) conduit means mounted in the plate for providing a cooling fluid to the part in the opening in the plate for cooling the part of the seal forming portion in the portion of the plate which is inletted. 
     In particular, the present invention provides a die which is preferably cooled by a cooling gas, such as air, directed at the part of the sealing area of the die which is to be cooled. 
     In particular, the present invention relates to an apparatus for differentially heat sealing a plastic film to a sealable material which comprises: 
     (a) a die for heat sealing which comprises: a plate having a seal forming portion around a cavity, wherein a part of the seal forming portion of the plate is inletted to provide an opening around the part of the seal forming portion; and conduit means mounted in the plate for providing a cooling fluid to the part in the opening in the die for cooling the part of the seal forming portion which is in the portion of the plate which is inletted; 
     (b) a fluid supply line connected to the conduit means mounted in the die; 
     (c) heating means in the pair of dies for heating the dies to provide the seal; 
     (d) motive means for closing the die against the plastic film to form the seal; and 
     (e) feed means for feeding the plastic film between the dies so that the motive means for closing the die can close the die against the film to provide the seal with the sealable material. 
     Further, the present invention relates to an apparatus for differentially heat sealing opposed contacting sheets of a plastic film to form an individual pouch defined by a peripheral seal which comprises: 
     (a) a pair of dies for heat sealing opposed contacting sheets of a plastic film to form a pouch defined by a peripheral seal, one die of which comprises: a plate having a seal forming portion around a cavity defining an inside of the pouch, wherein a part of the seal forming portion of the plate is inletted to provide an opening around the part of the seal forming portion; and conduit means mounted in the plate for providing a cooling fluid to the part in the opening in the die for cooling the part of the seal forming portion which is in the portion of the plate which is inletted; 
     (b) a fluid supply line connected to the conduit means mounted in the die; 
     (c) heating means in the pair of dies for heating the dies to provide the seal; 
     (d) motive means for closing the dies against the plastic film to form the seal; 
     (e) feed means for feeding the sheets of plastic film between the dies so that the motive means for closing the dies can close the dies to provide the seal; and 
     (f) shear means for cutting the sheets to separate multiple of the pouches formed in the sheets into individual pouches. 
     The present invention also relates to a method for differentially heat sealing a plastic material to a sealable material which comprises: 
     (a) a die for heat sealing which comprises: 
     a plate having a seal forming portion around a cavity, wherein a part of the seal forming portion of the plate is inletted to provide an opening around the part of the seal forming portion; and conduit means mounted in the plate for providing a cooling fluid to the part in the opening in the die for cooling the part of the seal forming portion which is in the portion of the plate which is inletted; a fluid supply line connected to the conduit means mounted in the die; heating means in the pair of dies for heating the dies to provide the seal; motive means for closing the die against the plastic material to form the seal; and feed means for feeding the plastic material between the dies so that the motive means for closing the die can close the die against the material to provide the seal with the sealable material; 
     (b) feeding sheets of plastic material between the dies and the sealable material; 
     (c) closing the die with the motive means so that the heating means seals the plastic material to the sealable material; 
     (d) removing the sealed plastic material and the sealable material from the apparatus. 
     Finally, the present invention relates to a method for forming a pouch defined by differentially heat sealed opposed sheets of a plastic material which comprises: 
     (a) heating dies for forming the seal provided in an apparatus for heat sealing opposed contacting sheets of a plastic material to form an individual pouch defined by a peripheral seal which comprises: a pair of dies for heat sealing opposed contacting sheets of a plastic material to form a pouch defined by a peripheral seal, one die of which comprises: a plate having a seal forming portion around a cavity defining an inside of the pouch, wherein a part of the seal forming portion of the plate is inletted to provide an opening around the part of the seal forming portion; and conduit means mounted in the die for providing a cooling fluid to the part in the opening in the plate for cooling the part of the seal forming portion which is in the portion of the plate which is inletted; a gas supply line connected to the conduit means mounted in the die with a gas flow rate meter in the line; heating means in the pair of dies for heating the dies to provide the seal; motive means for closing the dies against the plastic material to form the seal; feed means for feeding the sheets of plastic material between the dies so that the motive means for closing the dies can close the dies to provide the seal; and shear means for cutting the sheets to separate multiple of the pouches formed in the sheets into individual pouches; 
     (b) feeding the sheets of plastic material between the dies; 
     (c) closing the dies with the motive means so that the heating means forms the pouch wherein the gas from the gas supply means cools the part of the seal forming portion which is in the portion of the plate which is inletted; 
     (d) feeding the sheets with the pouch from between the dies; and 
     (e) shearing the pouch from the sheets wherein the pouch has differentially sealed opposed sheets forming the pouch. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a plan cross-sectional view of a pair of dies  15  and  15 A used to form a frangible seal FS in open pouch OP, wherein coolant fluid (gas or liquid) is directed at or through a bar or other exposed portion of the dies  15  and  15 A. 
     FIG. 1A is a side schematic view of the apparatus  10  for forming fluid closed pouches (FCP) containing various materials with a frangible seal using the differential cooling in dies  15  and  15 A. 
     FIG. 1B is a side view of a vertical feed apparatus as illustrated schematically in FIG.  1 . 
     FIG. 1C shows a chain drive mechanism  50  for activating pistons (not shown) in the filler manifold  14  for moving the puller  22 A in the apparatus of FIG.  1 B. 
     FIGS. 2 to  5  are schematic side views of the dies  15  and  15 A shown in FIG. 1A in cross-section, particularly illustrating the stages for going from sheets S 1  and S 2  to the open pouch OP to the closed pouch CP in the apparatus of FIGS. 1A and 1B. 
     FIG. 6 is a front view of preformed open pouches  40  (OP 1  to OP 4 ) for forming a pair of dual pouches. The dotted lines are for vertical trimming as in FIG.  8 . 
     FIG. 7 is a plan cross-sectional view of the pouch OP along line  7 — 7  of FIG.  6 . 
     FIG. 8 is a front view of the final closed pouch  41  (FCP) from FIGS. 6 and 7 after sealing illustrating dual pouches separated by a frangible seal FS and surrounded by a hard seal HS. 
     FIG. 9 is a plan cross-sectional view along line  9 — 9  of FIG.  8 . 
     FIG. 10 is a front inside view of an inside face of die  15  along line  10 — 10  of FIG. 11, particularly showing inletted portion  33  around bar or platen  24  which is cooled by air from holes  32  in tube  31  to form a frangible seal FS. FIG. 11 is a plan view showing both dies  15  and  15 A spaced apart before coming together to form the frangible seal FS along bar  34  as part of the seal portion of the dies  15  and  15 A. 
     FIG. 12 is a front view of a single finished closed pouch  60  (FCP) with a hard seal HS and a frangible seal (cross hatched). FIG. 12A is a front view of a different pouch  70  (FCP) with a corner F.S. (cross-hatched). 
     FIGS. 13 to  18  are graphs showing the burst strength of a seal as a function of temperature for various films. FIGS. 13 to  15  show linear low density polyethylene films and FIGS. 16 and 17 are low density polyethylene at various thickness or weights per unit. FIG. 18 shows a composite film of polyethylene terphthalate, foil and BAREX™, an acrylonitrile film (48 ga PET/10.8# WLD/0.00035 Foil/10.8# EAA/3.5 mil BAREX). 
     FIG. 19 is a plan cross-sectional view of a single die  15  with a backing plate  37 . 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     FIG. 1 illustrates the basis of the present invention which relies upon the differential cooling by cooling a bar  34  or other heat sealing surface to lower the temperature at which the seal is formed. Optionally channels  37  are provided through the bar for the cooling fluid (gas or liquid). 
     The apparatus forms two open pouches OP between a frangible seal (FS) using spaced apart dies  15  and  15 A with an inletted portion  33  around the bars  34  and  34 A. Optionally a feed tube  36  can be provided in the bar and/or an air tube  31 . Coolant is provided to and from the bars  34  and  34 A as illustrated by the arms. 
     The preferred pouch forming apparatus  10  of the present invention is shown in FIGS. 1A and 1B. FIG. 1A is a schematic view of the apparatus  10  shown in FIG.  1 B. Such apparatus  10  are well known to those skilled in the art as “vertical feed” machines. Also well known are “horizontal feed” machines (not shown), such as described in U.S. Pat. No. 3,453,799 to Cloud et al, U.S. Pat. No. 4,201,031 to Wiles, U.S. Pat. No. 4,436,576 to Seiden and U.S. Pat. No. 5,181,365 to Garvey et al. Either type of machine can be used to practice the present invention on a continuous or intermittent feed basis. Also the present invention can be performed in a multistation system with separate machines which perform individual functions. 
     In the preferred vertical feed apparatus  10  as shown in FIG. 1A, dual rolls  11  and  11 A feed separate plastic materials, films or sheets S 1  and S 2  over idler rollers  12 ,  12 A,  12 B and  12 C. An electric eye sensor  13  determines the position of the sheet S 2  and holds it away from the sheet S 1 . A fill manifold  14  with one or more nozzles  14 A feeds a liquid (or other material) into an open pouch OP formed from the two sheets S 1  and S 2  by dies  15  and  15 A which are moved horizontally together and apart. Solenoid valve  14 B controls the flow of the fluid to the nozzle  14 A. The dies  15  and  15 A are a primary focus of the present invention and will be discussed in detail hereinafter. The dies  15  and  15 A are mounted on shoes  16  and  16 A and are moved by pneumatic cylinders  17  and  17 A. The dies  15  and  15 A are fed with air through meters  18 B by lines  18  and  18 A to cool portions of the dies  15  and  15 A to provide differential sealing between the sheets S 1  and S 2  as described more fully hereinafter. The dies  15  and  15 A are electrically heated by electrical wires  19  and  19 A leading to a heater (not shown) mounted on the dies  15  and  15 A. Thermocouples  20  and  20 A detect the temperature of the dies  15  and  15 A via wires  19  and  19 A, which is used to regulate the temperature of the heater. Upon closing of the dies  15  and  15 A to form the open pouch OP the dies also close a succeeding OP to form a closed pouch CP containing the material provided from the nozzle  14 A. The closed pouch CP is then trimmed on opposed sides of the pouch by side knife  21  (one shown) to produce trim T which is removed. The closed pouches CP in the machine is indexed or advanced by pneumatic cylinder  22  with puller  22 A as shown by the dotted lines. The closed pouch CP is marked with a serial number by coder  23 . The closed pouch CP is cut into individual final closed pouches FCP by cutter  24  including knife  24 A and a bar  24 B on pneumatic cylinder  24 C. The FCP is fed into a chute  25  and onto a conveyor  26  for subsequent handling. 
     FIG. 1B shows the detail of the apparatus  10 , illustrated schematically in FIG. 1A. A feed apparatus  27  with a capability of feeding up to six tubes  28 ,  28 A,  28 B,  28 C,  28 D, and  28 E with liquid is provided. The feed apparatus  27  includes a rocker arm  27 A which moves rockers  27 B which engage pistons (not shown) which feed the tubes  28  to  28 E. A power source  29  turns the rocker arm  27 A and a pump  30  feeds the feed apparatus  27 . A pump  30  is used to feed the material to the tubes  28  to  28 E. Thus the apparatus  10  is designed to fill up to six (6) bags which are formed horizontally as six separate open pouches OP, closed pouches CP and final closed pouches FCP. The material introduced by the fill manifold  14  can be the same or different in each closed pouch CP. Also the closed pouch CP can be linked together rather than trimmed apart by the knives  21 . FIG. 1C shows a chain drive mechanism  50 . Lower and upper sprockets  51  and  52  are connected by chain  53 . The sprockets are provided with rods  51 A and  52 A connected to eccentrics  51 B and  52 B and the sprockets  51  and  52 . Drive  54  is connected to puller  22 A. Drive  54  is connected to pistons (not shown) in the fill manifold  14 . Lower sprocket  51  is driven by a motorized drive shaft (not shown). Offset on these cams allows for adjustability in speed and depth. Cutter  24 , coder  23  and dies  15  and  15 A all employ the use of a solenoid (not shown) for timing. The motor (not shown) is clutch driven and fully adjustable. The dies  15 ,  15 A, puller  22 A, coder  23  and cutter  24  are all pneumatically driven. The fill from the fill manifold  27  is by positive displacement. 
     FIGS. 2 to  5  are an exploded views showing the steps performed by the apparatus  10  at the dies  15  and  15 A. The dies  15  and  15 A are shown in cross section. A hard seal forming portion  35  and  35 A of the dies  15  and  15 A are heated to form the seal between sheets S 1  and S 2  in a U shape as shown in FIGS. 6 and 7. At least one side seal is formed as a Hard Seal HS. 
     As shown in FIGS. 6 and 7 for the open pouches  40 , the frangible seals FS indicated by cross hatch are weaker than the hard seals HS and  31 A and are not cut by the knives  21 . The frangible seals FS 1  and FS 2  are rupturable to provide a connection after the pouches are closed to provide a closed pouch CP  41  as shown in FIGS. 8 and 9. In this case OP 1  is fed a liquid L and OP 2  contains another material M. With the pouch shown in FIG. 8, when the frangible seal FS in CP  41  is ruptured the material M is reacted with or mixes with the liquid. The frangible seal FS can be ruptured by applying pressure to the pouches CP 1  or CP 2 , particularly if one contains a liquid L. The frangible seal FS can also be pulled apart by grasping the sides of the final closed pouch FCP. 
     FIGS. 10 and 11 show the details of dies  15  and  15 A used to produce the hard seal HS and the frangible FS in FIGS. 6 to  9 . In particular, air line  18  is connected to tubes  31  (one shown) with perforations or holes  32  in an open inletted portion  33  above a frangible seal FS seal forming bars  34  and  34 A which are cooled by air from the holes  32  thus reducing the temperature of the bar  34  and producing a frangible seal FS. The remaining seal forming portions  35  form the hard seal HS. The dies  15  and  15 A are mounted on shoes  16  and  16 A (FIG. 1A) by bolts in holes  36 . The result is the dual pouch FCP  41  with the frangible seal FS produced by the cooled bars  34  and  34 A shown in FIGS. 8 and 9. 
     In the preferred embodiment as shown in FIG. 10, air from line  18  through openings  32  cools the bar  34  externally. It will be appreciated that a cooling fluid could be provided inside and through the bar  34  through channels  37  (FIG.  1 ). The fluid can be a liquid or a gas which is cooled externally before being supplied through the channels  37  in the bar  34  although a cooling gas is preferred. The gas could be carbon dioxide or nitrogen and can be recycled. The liquid could be water or an oil. All of these variations will be obvious to one skilled in the art. 
     The final closed pouches FCP can also be formed by trimming between each individual pouch at the frangible seal FS. In this event, both the HS and FS are cut as the pouches are formed. In this event, the pouches  60  and  70  have a single frangible seal FS as shown in FIGS. 12 and 12A. 
     As can be seen from FIGS. 13 to  18 , the strength of the frangible seal FS for the sheets or films is directly related to the temperature of the sealing dies  15  and  15 A. The pressure of the die or dies insures that there is intimate contact of the films S 1  and S 2 . LLDPE is linear low density polyethylene. BAREX™ is an acrylonitrile film available from Greenway Plastic Industry Corporation, Wayne, N.J. The seal strength is measured in grams per inch (or centimeter) necessary to separate the frangible seal FS using a Tinius Olsen, tensile strength testing (ASTM D-882) apparatus. Preferably the seal strength is between 200-1500 gm/inch. The present invention permits 1) creation of a cool zone which allows a single die to make both frangible and hard seals; and 2) the target seal strength varies with relatively small swings in sealing die temperature. Many sealing die control systems have a temperature variation of ±15 degrees fahrenheit. The present invention can reduce this variation significantly. The present invention enables seal strength management. Preferably the seal strength of a given film can be maintained at a 300 gram per inch range while maintaining seal strength. This seal strength range is managed by sealing films with known seal strength characteristics in the sealing die that has differential sealing temperatures across the surface area of the dies. Sealing temperatures are controlled by regulated heat sources used in conjunction with the application of cooling fluid used to cool portions of the die which forms the frangible seal. Application of cooling fluids may be controlled by regulators, flow meters or other flow control valves or methods. The curves are quite steep, so that maintaining the temperature differential in the method and apparatus of the present invention provides the necessary control over the formation of the FS and HS seals. The temperature differential in a sealing die from FS to HS in a single sealing die can be between 50 to 75° F. which in a single die  15  would be impossible without the present invention. 
     The plastic materials, films or sheets can be any of sheet stock, roll stock, film or formed parts or any other forms of packaging materials well known by those skilled in the art. The thermoplastic polymers used in the present invention are well known to those skilled in the art and are previously noted in the patents listed. These polymers soften as a function of the temperature achieved by the film and bond or weld to other films which can be of the same or different thermoplastic composition. The polymers can be natural or synthetic. Sometimes the term “thermoplastic resins” is used in the art for “thermoplastic polymers” and it is intended that they be treated the same. The thermoplastic polymers are contrasted with “thermoset” polymers which decompose but do not soften upon heating. However, there are numerous hybrid and mixed polymers which are the equivalent of the thermoplastic polymers for the purpose of the present invention. Preferred polymers are the polyalkylene oxide polymers (polyethylene, polypropylene, polybutylene, the terphthalate polymers (PET) and polyolefins, such as vinyl resins such as vinyl acetate, vinyl chloride, and styrene. 
     Rotary sealing systems are described in Packaging Technology and Engineering, Jul. 28 to 30, 1999. Unlike platen or flat sealing die systems, rotary sealing systems utilize heated wheels to produce side seals on pouches. These wheels have a continuous or intermittent motion. The cross seals on these machines can be formed by continuous motion wheels or dies activated by mechanical index or by use of a photocell. Pressure is applied by tension springs or controlled pneumatic cylinders. The seal is formed by passing the packaging film between heated wheels or between a heated wheel and a non-heated backer plate or wheel. The present invention includes such rotary wheel sealing apparatus. 
     The term “die” as used herein with the differential heating seal portions encompass a curved rotary wheel sealing which is heated or a flat sealing die as described in detail herein. Also in these systems a single die can be used, as shown in FIG. 19, with a backing plate  37  against which the die  15  moves with the heat sealable films between them. All of these variations will become apparent to those skilled in the art. The term “platen”, “bar” or “sealing jaw” are sometimes used in the art and are dies. 
     It is intended that the foregoing description be only illustrative of the present invention and that the present invention be limited only by the hereinafter appended claims.