Method and apparatus for sealing reclosable flexible containers without spot sealing

Abstract: An apparatus and method for manufacturing reclosable thermoplastic containers which eliminates the need for spot-sealing zipper closures (24,26) or zipper closure elements (24,26) to a web of thermoplastic film (22) prior to forming side seals (62) and zipper end seals (64) is provided. Opposing seal jaws (10,12) provide increased heat and pressure to zipper closures (24,26) in a manner which results in improved hermetic and fluid-tight side seals (62) and zipper end seals (64).

Description: The invention relates to a method and an apparatus for sealing plies of thermoplastic film having zipper closure thereon to form a reclosable container. From US-A-2 720 247 a method of sealing bags or tubes is known which comprises the following steps: subjecting a tube having intucked gusset folds at opposite sides to heat and pressure over a substantial area transverse the width of the bag and intensifying the pressure over predetermined limited, mutually spaced areas within the first mentioned area, said areas of intensified pressure overlying at least the apices of the gusset folds. This method, however, does not include any steps for forming zipper closure elements. Still, a device for welding foils is known in which two welding bars are provided perpendicularly with respect to the direction of movement of foils (EP-A-0 155 548). The foils welded by this device do not comprise zipper closure elements. In another apparatus for sealing packaging materials having thermoplastic surfaces, a pair of elongated heated jaws which are hingedly connected is provided (US-A-4 001 075). At least one of said jaws is mounted on compression springs to float into engagement with one another. Again, no zipper closure elements are provided in the thermoplastic foils manufactured by this apparatus. In a further arrangement a closable bag is provided which has two walls which are opposite to each other and connected at their lateral ends with each other (FR-A-2 630 406). Also, connecting means are provided at another end of said bag. These connecting means include profile means for opening and closing the bag. However, the manufacturing of such a bag is difficult. Finally, there is also known a method and mechanisms for preparing individual reclosable thin plastic bags with rib and groove profiles delivered in unengaged position on the finished bag (US-A-4 024 010). A separating finger must be positioned between the rib and the groove profiles along the path traveled by the facing layers of plastic bag film so that the profiles are separated during the preparation of said bags. Thus, the reclosable thin plastic bags are complicated to manufacture. It is therefore an object of the present invention to provide an apparatus and a method for manufacturing reclosable thermoplastic containers which have leak-proof zipper end seals and are easily to manufacture. The present invention meets the need for a simplified system for manufacturing flexible containers by the features of claims 1 and 15. While crushing pressure is avoided by the present invention, significant sealing pressure is positively applied to sealed zipper closures engaged between first and second seal jaws, resulting in improved side seals and zipper end seals. This sealing pressure is due, in part to the non-resilient nature of the second working surface of the first seal jaw which permits the springs supporting the second seal jaw to have the desired effect of locally increasing pressure on the area of the zipper closures to be sealed. A further advantage of the present invention is that the step of spot sealing zipper elements to the film may be eliminated. This advantage results from the formation of superior side seals and zipper end seals from increased heat and pressure brought to bear on the zipper closures areas to be sealed. Finally, another advantage of the present invention is that, in an alternative embodiment, the apparatus may be retrofitted to improve the function of existing seal jaws, or may be incorporated in new seal jaw pairs which may be installed on existing equipment. In either case, existing flexible container manufacturing or packaging equipment may be adapted to provide improved side seals and zipper end seals without need for spot-sealing the web of thermoplastic film. In order that the invention may be more readily understood, reference will now be made by example to the accompanying drawings, in which: Fig. 1 is a perspective view of the present invention, the first and second seal jaws shown in an open position; Fig. 2 is a perspective view of the first seal jaw of the present invention showing the first and second working surfaces thereof; Fig. 3 is a perspective view of the second seal jaw of the present invention showing the third working surface thereof; Fig. 4 is an elevational view of the first and second seal jaws in a closed position for sealing; Fig. 5 is a cross-section of the first and second seal jaws of Fig. 4 taken along line 5--5 in Fig. 4; Fig. 6 is a perspective view of an alternative embodiment of the first seal jaw wherein the second working surface and related heating elements are demountable; and Fig. 7 is a cross-section of the first seal jaw of Fig. 6 taken along line 7--7 in Fig. 6. Referring to Fig. 1, first and second seal jaws 10, 12, respectively, of the present invention are shown in an open position, representatively installed on a rotary drum machine 14 typical of those used in the manufacture of flexible containers. Shown in dashed lines, rotary drum machine 14 further includes a cam 16 in which cam follower 18 travels to open and close first and second seal jaws 10, 12 in cooperation with hinge 20. Hinge 20 is disposed in first seal jaw 10, and its position is indicated by a dashed line. As shown in Fig. 1, film web 22 is being drawn in the direction of the arrow between the seal jaws in a U-folded configuration with complementary interlocked zipper closure elements 24, 26. The film web may be of a single ply of thermoplastic material, or may be one of a number of dual or multiple ply laminates conventionally used in the art. For example, film web 22 may be a laminate of oriented polypropylene having a Saran (trademark) inner seal layer. Alternatively, film web 22 may be a laminate of nylon having an ethylene vinyl acetate copolymer inner seal layer. Referring now to Fig. 4, first and second seal jaws 10, 12 are shown in a closed position wherein their working surfaces may cooperate to engage the folded web of thermoplastic film 22 having zipper closures in the form of interlocked zipper closure elements 24, 26 (best shown in Fig. 1) for sealing. Cam 16 is designed so that the working surfaces of the seal jaws are rapidly closed on film web 22 to effect sealing and held in the closed position shown in Fig. 4 for a sufficient time, typically on the order of one second. Cam 16 then causes cam follower 18 to raise, the film web is advanced, and the cycle is repeated. First and second working surfaces 28, 30 of first seal jaw 10 are shown in more detail in Fig. 2, and third working surface 32 of second seal jaw 12 is shown in more detail in Fig. 3. As shown in Fig. 2, first working surface 28 is comprised of a resilient pressure pad, such as a tough grade of silicone rubber which is unaffected by the sealing temperatures utilized in the first and second seal jaws 10, 12. It may have a relatively flat, untextured or unpatterned surface. Second working surface 30 is comprised of a patterned, heat-conductive, non-resilient surface, such as steel or aluminum which may be coated with a heat-resistant nonstick agent such as Teflon (trademark). As can be seen, second working surface 30 is wider than the zipper closure elements and is positioned so that it will engage the zipper closure elements even if there are positional changes of the elements on the film web. This enables the present invention to be used on a number of different sizes of container webs without modification to the seal jaws. A cross-hatched pattern is preferred for second working surface 30 to promote the flow of thermoplastic material during sealing. Other suitable patterned surfaces may also be used. Referring now to Fig. 5, second working surface 30 is adjustably heated by heating elements 36, such as electrical resistance heaters, attached to a source of electrical power (not shown), and controlled by a conventional controller (not shown) and thermostats 38. As shown in Fig. 3, third working surface 32 of second seal jaw 12 is comprised of heat-conductive, non-resilient material, such as steel or aluminum which may be coated with a heat-resistant nonstick agent such as Teflon (trademark). As best shown in Fig. 5, third working surface 32 is adjustably heated by heating elements 40, such as electrical resistance heaters attached to a source of electrical power (not shown), and controlled by a conventional controller (not shown) and thermostat 42. Third working surface 32 further comprises means for gripping a web of folded thermoplastic film 22 which may be a ribbed surface pattern, as shown in Fig. 3, or which may be a complementary cross-hatched pattern which matches the pattern on second working surface 30. The provision of controllable heating elements in each of the seal jaws permits additional heat to be applied in the area of the zipper closure elements and also permits the apparatus to be adjusted for the particular film material to be sealed. For example, where the film web is a dual ply laminate of oriented polypropylene with an inner seal layer of Saran (trademark), both first seal bar 10 and second seal bar 12 are operated in the range of from 250 - 280 degrees F, (121-138 degrees Centigrade [C]) and most preferably about 260 degrees F (127 degrees C). This temperature is sufficient to melt the inner seal layer for obtaining a durable seal without causing undue deformation or shrinkage of the outer polypropylene layer. Where a nylon web material is used having a heat sealable inner layer such as a copolymer of ethylene and vinyl acetate, the temperature on second seal jaw 12 may be increased to about 400 degrees F (204 degrees C) while maintaining the temperature in the first seal jaw 10 in the range of from 250 - 280 degrees F (121-138 degrees C). This increased temperature aids in the softening and flow of the zipper closure elements and the formation of a durable seal without adversely affecting the nylon outer layer. A further aspect of the invention is shown in Fig. 4 where compressible means, such as springs 44a, 44b, support second seal jaw 12, and impose, in compression, a skewed or asymmetric loading profile upon second seal jaw 12. At least two compressible springs are preferred, as shown. Second seal jaw 12 may be displaced against springs 44a, 44b into housing 46, shown typically in Figs. 4 and 1. Springs 44a and 44b are designed to have the same effective length, but different spring constants. Thus, when compressed, spring 44b, which has the higher spring constant, reacts with greater force than spring 44a, enhancing the sealing pressure upon zipper closures 24, 26. Other compressible means, such as unmatched pneumatic pistons or air shocks may be used to achieve the same results. However, springs are preferred. For typical films used in commercial applications, the seal jaws 10, 12, in conjunction with springs 44a and 44b, are designed to place up to about 75-100 psi (5.17x10⁶ - 6.89x10⁶ degrees/cm²) of pressure initially onto the zipper closure area of the film web while placing only about 15-20 psi (1.03x10⁶ - 1.38x10⁶ degrees/cm²) of pressure onto the remaining areas of the web. This very high initial pressure on the zipper closure area of the film web, in conjunction with the heat supplied by the heating elements in the seal jaws, provides a rapid softening and flow of polymer to form durable, fluid tight side seals and zipper end seals. For purposes of illustration only, the present invention is shown in Figs. 1 and 4 as being installed, on rotary drum machine 14. The present invention may also find use on vertical or horizontal flexible container manufacturing or packaging equipment. Likewise, while the means of opening and closing first and second seal jaws 10, 12 are shown as comprising a hinge 20, with cam 16 and cam follower 18, this arrangement is also merely representative. While this construction is preferred for use of the invention on rotary drums, other means of opening and closing first and second seal jaws 10, 12 may be suitable for installations of the present invention on other types of equipment, as discussed above. An alternative embodiment of the present invention is shown in Figs. 6 and 7. As shown, the present invention may be configured as a demountable second working surface 50 which may be retrofitted to existing flexible container manufacturing or packaging equipment. Demountable second working surface 50 is attached to first seal jaw 10 by conventional means (not shown), and has the same characteristics as second working surface 30. Demountable second working surface 50 includes heating elements 56 and thermocouples 58 connected and controlled in the same manner as previously described with respect to heating elements 36 and thermocouples 38. As further shown in the alternative embodiment of Figs. 6 and 7, first seal jaw 10 of the present invention may further comprise a slot 48 having a cutting means, such as a knife 60, slidably disposed therein. So disposed, knife 60 may be reciprocated by conventional means known in the art to sever the side seals and zipper end seals formed by first and second seal jaws 10, 12 and thereby form individual flexible containers. In operation, the present invention advantageously increases the heat and pressure in the area of the zipper closures to be sealed. Additional heat introduced to the seal jaws by heating elements 36 causes the thermoplastic material of the film web to soften and flow into voids between zipper closure elements 24, 26 and film 22 and form a durable seal, as well as causing the ends of zipper closure elements 24, 26 to fuse to each other. Intermeshing cross-hatched patterns, preferred on second and third working surfaces 30, 32, also promote the flow of the thermoplastic material and strengthen the resulting side seals and zipper end seals. The sealing pressure on zipper closure elements 24, 26 is further enhanced by springs 44a, 44b. Finally, in accordance with the method of the present invention, flexible container manufacturing or packaging equipment, such as rotary drum 14, may be supplied with a web of thermoplastic film having zipper closure elements 24, 26 attached thereto without spot-sealing. Laminates of thermoplastic film known in the art are typically used in manufacturing flexible containers, and, in particular, for packaging foodstuffs. The film is folded, zipper closure elements 24, 26 brought into opposing, engagable or, alternatively, interlocked relationship, the folded web of thermoplastic film 22 is engaged between first and second seal jaws 10, 12 to form a first side seal and first zipper end seal, and then advanced to form a second side seal and second zipper end seal. In Fig. 1, first and second side seals are shown typically as side seal 62 and first and second zipper end seals are shown typically as zipper end seal 64. Seal time is typically in the range of 1 second. Film 22 is thereafter severed along the length of these first and second seals 62, generally along the center thereof, to form individual flexible containers or packages. In accordance with the alternative embodiment of present invention shown in Figs. 6 and 7, the step of severing may be accomplished after the first and second side seals 62 and first and second zipper end seals 64 are formed by inserting knife 60 through slot 48.

Claims: An apparatus for sealing plies of thermoplastic film having zipper closures (24, 26) thereon to form a reclosable container comprising: opposing first and second seal jaws (10, 12) for engaging said thermoplastic film (22) in an area to be sealed, said area including said zipper closures (24, 26); said first seal jaw (10) having first and second working surfaces (28, 30, 50), said first working surface (28) comprising resilient means for engaging said area to be sealed, excluding said zipper closures; said second working surface (30, 50) comprising a patterned, heat-conductive surface positioned to engage said zipper closures (24, 26) in said areas to be sealed; and means for heating (36, 56) said second working surface (30, 50) for sealing said zipper closures (24, 26) in said areas to be sealed; said second seal jaw (12) having a third working surface (32), and means for heating (40) said third working surface for sealing said areas to be sealed, including said zipper closures (24, 26); said third working surface (32) including means for gripping said thermoplastic film and means for engaging said zipper closures (24, 26) in said areas to be sealed. An apparatus as recited in claim 1, characterized in that said third working surface (32) on said second seal jaw (12) includes a patterned surface which intermeshes with said pattern on said second working surface (30, 50) of said first seal jaw (10). An apparatus as recited in claim 1, characterized in that said second working surface (50) and said means for heating (56) said second working surface (50) are removably attached to said first seal jaw (10). An apparatus as recited in claim 1 characterized in that said means for heating (36,56) said second working surface (30,50) comprises at least one electrical resistance heating element (36,56), and at least one thermocouple 38,58) adapted to adjustably control thermal input to said second working surface (30,50); and means for supplying electrical power to said at least one heating element (36,56) and said at least one thermocouple (38,58). An apparatus as recited in claim 1 characterized in that said means for heating (40) said third working surface (32) comprises at least one electrical resistance heating element (40), and at least one thermocouple adapted to adjustably control thermal input to said third working surface (32); and means for supplying electrical power to said at least one electrical heating element (40) and said at least one thermocouple (40). An apparatus as recited in claim 1 characterized in that said means for gripping of said third working surface (32) comprise ribs oriented generally perpendicular to the direction of movement of said thermoplastic film (22). An apparatus as recited in claim 2 characterized in that said intermeshing patterns of said second working surface (30,50) and said third working surface (32) comprise a cross-hatched pattern. An apparatus as recited in claim 1 further characterized by means for cyclically reciprocating (16,18,20) said first seal jaw (10) into sealing cooperation with said second seal jaw (12). An apparatus as recited in claim 8 characterized in that said cyclically reciprocating means (16,18) comprises a hinge (20) on said first seal jaw (10), a cam (16), and a cam follower (18) engagable in said cam (16) and disposed at the end of said first seal jaw (10) opposite said hinge (20). Apparatus as recited in claim 1 further characterized by compressible means (44a,44b) for supporting said second seal jaw (12), said compressible means (44a,44b) adapted to impose an asymmetric sealing pressure profile upon said second seal jaw (12) with greater sealing pressure on said zipper closures (24,26) in said area to be sealed. An apparatus as recited in claim 10 characterized in that said compressible means (44a,44b) comprises two or more springs (44a, 44b) having different spring constants. An apparatus as recited in claim 1 characterized in that said first seal jaw (10) further comprises means for severing (60) thermoplastic film (22) engaged in said first and second seal jaws (10,12). An apparatus as recited in claim 12 characterized in that said severing means (60) comprises a slot (48) disposed in said first seal jaw (10), a knife-edge (60) slidably disposed in said slot (48), and means for cyclically reciprocating said knife-edge (60) in said slot (48). An apparatus as recited in claim 1, characterized in that said working surface (30, 50) is non-resilient, said first seal jaw (10) comprises at least one heating element for adjustably heating said second working surface (30, 50) and said third working surface (32) has a patterned surface for preventing slippage of said thermoplastic film (22). A method for manufacturing reclosable thermoplastic containers comprising the steps of: providing a folded web of thermoplastic film (22) having opposing plies with engaged zipper closure elements (24, 26) attached thereto without spot sealing; engaging said plies of said folded web of thermoplastic film (22) between first and second seal jaws (10, 12) to form a first side seal (62) and first zipper end seal (64) of a flexible container, said step of engaging comprising subjecting said plies, excluding said zipper closure elements (24, 26), to heat and pressure between a resilient first working surface (28) of said first seal jaw (10) and a heated third working surface (32) of said second seal jaw (12); and subjecting said zipper closure elements (24, 26) to heat and pressure between a heated, non-resilient, patterned second working surface (30, 50) of said first seal jaw (10), and said heated, patterned third working surface (32) of said second seal jaw (12) such that the pressure applied to said zipper closure elements (24, 26) exceeds the pressure applied to the remainder of said plies; advancing said film (22); engaging said plies of said folded web of thermoplastic film (22) between said first and second seal jaws (10, 12) to form a second side seal (62) and a second zipper end seal (64) of a container in the same manner as said first side seal (62) and zipper end seals (64) were formed; and severing said plies of said folded web of thermoplastic film (22) along the length of said first and said second side seals (62, 62) to form individual containers. A method for manufacturing reclosable flexible containers as recited in claim 15, characterized in that said step of severing is performed while said plies of said folded web of thermoplastic film (22) are engaged in said first and second seal jaws (10, 12).

Inventors: BAUER MARK D, BOECKMANN HUGO, VAN ERDEN DON L, BAUER, MARK D., BOECKMANN, HUGO, VAN ERDEN, DON L.
Applicants: ILLINOIS TOOL WORKS, ILLINOIS TOOL WORKS, INC.
Application year: 1990
Main classification: B29C65
IPC codes: B29C65