Vertical, form, fill and seal machine with heating element resistant to thermal cycling

Abstract

A vertical form, fill and seal machine of the type that includes at least one fill chamber for forming liquid-filled pouches of impermeable material. A heating element is fixed to a slidable sealing head. The heating element comprises a ribbon of metallic material, and an insulative base having a slot for receiving the metallic ribbon. The sealing head faces a backstop. The metallic ribbon is held at and above the upper edge of a pedestal formed in the insulative base. The insulative base is formed of mating base elements secured to one another by at least one fastener.

Description

BACKGROUND

1. Field of the Invention

The present invention relates to the production of liquid-filled pouches comprising flexible plastic sheeting by means of automated machinery. More particularly, this invention pertains to a vertical form, fill and seal machine having a heating element that is resistant to damage due to thermal cycling.

2. Description of the Prior Art

Vertical form, fill and seal machines are employed to create liquid-filled pouches for various uses and applications in, among other industries, medicine, food and beverage, and industrial fluid storage and dispensing. Such pouches offer low packaging cost, versatility and other advantages that make them attractive alternatives to bottles and cans.

The form, fill and seal machines for forming such pouches typically rely upon gravity to feed heat sealable web material from, for example, a roll, forming it into a vertically-oriented tube which surrounds a fluid delivery device such as a spigot. The roll is passed between a sealing head and a spaced-apart backstop in a sealing assembly that is located below a device for delivering the tube. The sealing assembly seals across the tube by heat pressing the two layers of web material together through the use of the moving sealing head that is energized to reciprocate toward and away from the tube opposite the backstop. Initially, a bottom seal may be formed and a quantity of liquid or other flowable material delivered to the tube. The tube may then be advanced downwardly and another seal made above the bottom seal to form a pouch between the two seals with the second seal serving as a first (or bottom) seal for the next-to-be formed pouch.

Some vertical form, fill and sealing machines operate by metering out a defined amount of liquid or other flowable material prior to formation of the second (or upper) seal while others introduce an excess amount of liquid above the first seal then form the second seal through a liquid-filled portion of the tube. Examples of vertical form, fill and seal machines of the latter type are disclosed, for example, in International patent publication WO 2005/051769 of L3 Container Corporation covering “Sealing Assembly”, U.S. Pat. No. 5,038,550 of Wirsig et al. covering “Vertical Form and Fill Machine Improvements” and U.S. Pat. No. 6,164,042 of Tobolka covering “Container With Dispensing Spout and Method For Making Same”.

The sealing head of the sealing assembly typically supports an electrically conductive heating element for applying resistance-generated heat. The heating element is typically metallic, a conductor of both electricity and heat. It may be in the shape of a metal ribbon that is mounted in a base of electrically and thermally insulative material to maintain an edge aligned with the direction of travel of the sealing head (and orthogonal to the web material as it travels through the fill chamber of the form, fill and sealing machine). As the insulative material of the base is in intimate contact with the metallic heating element, thermally-induced stresses are necessarily introduced between the metal and insulative materials as the heating element is cycled through a predetermined heating profile. The well-known differentials in coefficients of thermal expansion that exist between a metal of the type that is commonly employed for the heating element, such as titanium, and a typical thermal insulator of ceramic material can lead to stress within, and even breakage of the insulator and/or the bond between the heating element and the insulator. (Sealing and cutting temperatures may range up to, and even exceed, 500 degrees Fahrenheit.) Alternatively, suboptimal sealing (and/or separation) of filled pouches produced by a sealing apparatus may result from design of the heating profile to accommodate thermal expansion mismatches between a metallic heating element and its associated insulative base.

SUMMARY OF THE INVENTION

The present invention addresses the preceding and other shortcomings of the prior art by providing an improvement in a vertical form, fill and seal machine for forming liquid-filled sealed pouches of heat sealable web material. Such machine includes at least one fill chamber. The chamber comprises a slidable sealing head having a heating element comprising a metallic ribbon fixed to an insulative base. A backstop is aligned in opposed relation to the sealing head with the sealing head including opposed surfaces facing toward and away from the backstop. The insulative base is fixed to the surface of the sealing head that faces the backstop with the metallic ribbon being fixed to said insulative base so that an edge extends above the insulative base.

The improvement in the machine provided by the invention resides in the insulative base comprising a pair of mating base elements arranged to define a slot therebetween for receiving the ribbon.

The preceding and other features of the invention will become further apparent from the detailed description that follows. Such description is accompanied by a set of drawing figures. Numerals of the drawings, corresponding to those of the written description, point to the features of the invention with like numerals referring to like features throughout both the written description and the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top view of a fill chamber of a vertical form, fill and seal machine as taught by International patent publication WO/2005/051769;

FIGS. 2( a) and 2(b) are frontal plan and perspective views respectively of the sealing head of the vertical form, fill and seal machine of FIG. 1;

FIG. 3 is a plan view of a portion of a web of material illustrating the seams generated in a vertical form, fill and seal machine by means of a heating element in accordance with FIG. 2; and

FIGS. 4( a) and 4(b) are perspective views of a liquid-filled pouch produced in accordance with a heating element having the configuration of FIG. 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Turning now to the drawings, FIG. 1 is a top view of a fill chamber 10 of a vertical form, fill and seal machine as taught by International patent publication WO/2005/051769. A machine may include two such chambers, vertically spaced with respect to one another, whereby a tube formed of a web of impermeable material may travel downwardly through the two chambers as the requisite seams are formed to define and fill a resultant pouch.

A bottom seam is first formed in the top chamber. In a double chamber machine, the tube is then passed down into a lower fill chamber where flowable material is injected from a spigot in either a metered amount sufficient to more-than-fill the pouch so that an upper seam must be formed through the fill material. The upper seam is then formed, completing the filled pouch.

Referring to the fill chamber 10, a sealing head 12 and a backstop 14 are spaced apart at opposed sides of the impermeable material comprising the tube 16 as it passes therethrough. A heating element 18 is positioned on the surface 20 of the sealing head 12 that faces the backstop 14. A motor 22 drives a ball screw 24 causing responsive movement of a plate 25 to cause, through the interactions of various mechanical linkages including shafts 26, 26′, push rods 28, 28′, rocker arms 30, 30′, outbound link arms 32, 32′ and inbound link arms 34, 34′, movement of the sealing head 12 and the backstop 14 toward and away from each other (closing and opening the gap therebetween) relative to fixed frame members 36, 38 of the sealing assembly 10.

FIGS. 2( a) and 2(b) are frontal and perspective views respectively of the sealing head 12 of the vertical form, fill and seal machine 10. The frontal plan view of FIG. 2(a) illustrates the surface 20 of the sealing head 12 that faces the backstop 14. As can be seen, the heating element 18, fixed to the surface 20 presents an edge of a metallic ribbon 40. The metallic ribbon 40, preferably formed of titanium, is held in a base 42 with sealing edge exposed to the tube of impermeable material as it passes between the sealing head 12 and the backstop 14. The base 42 is formed of electrically and thermally insulative material such as that commercially available from Corning Incorporated of Houghton Park, N.Y. under the trademark “MACOR” while the metallic ribbon 40 is contacted by, and forms an element of, an electrical circuit (not shown) that includes an energizing power source for driving resistive heating throughout the length of the ribbon 40. As mentioned above, the heated ribbon is periodically pressed against the tube of material to create seams that define the filled pouches formed by machine 10.

The base 42 comprises a mating pair of base elements 44 and 46, each being fixed to the sealing head 12 by means of a fastener, such as screws 48 and 50. As can be seen, the metallic ribbon 40 is held in place at, and extends beyond, the upper edge of a shaped pedestal formed by matching pedestal sections 52, 54 of the base components 44, 46 respectively. Pressure applied via fasteners 56 through 62 that extend through and join the pedestal sections 52, 54 together, acts to hold and maintain the position of the metallic ribbon 40 that is sandwiched between the sections 52 and 54.

FIG. 3 is a plan view of a portion of a web of material 68 illustrating seams 70 through 76 generated in a vertical form, fill and seal machine by means of a heating element 18 in accordance with FIGS. 2(a) and 2(b) while FIGS. 4(a) and 4(b) are perspective views of a completed liquid-filled pouch 78 produced in accordance therewith. The web material 68 is produced by a form, fill and seal machine comprising a vertically-stacked pair of fill chambers, each in accordance with the fill chamber 10 of FIG. 1. The two fill chambers differ insofar as the heating element of the sealing head of the lower chamber is oriented inversely with respect to that of the upper chamber. Accordingly, the seams 70 and 74, produced by the sealing head of the upper fill chamber, are oppositely-shaped from the seams 72 and 76 produced in the lower fill chamber. (Note, the web material 68, as illustrated in FIG. 3, is not completely processed, lacking the steps of filling and separation of pouches defined by the seams 70 through 76.)

Thus it is seen that the present invention provides an improvement in a vertical form, fill and seal machine comprising the provision of a heating element 18 that includes a base 42 formed of a pair of base components 44 and 46 that sandwich and hold a metallic ribbon 40 therebetween. By providing a pair of base components 44, 46, the base 42, which is formed of electrically and thermally insulative material, a degree of “give” is incorporated into the design to accommodate the different thermal expansion behavior of the thermally and electrically conductive metallic ribbon 40 when a current is passed therethrough to cause the necessary resistive heating thereof for operation of the sealing head 12.

By providing a base 42 that is capable of absorbing the differential thermal expansions of the insulative base 42 and thermally conductive metallic ribbon 40, the present invention avoids the occasional breakage experienced by the integral, single-piece bases of heating elements in accordance with the prior art.

While the invention has been described with reference to its presently-preferred embodiment, it is not limited thereto. Rather, this invention is only limited insofar as it is defined by the following set of patent claims and includes within its scope all equivalents thereof.

Claims

1. In a vertical form, fill and seal machine for forming liquid-filled sealed pouches of heat sealable web material, of the type that includes at least one fill chamber that comprises a slidable sealing head having a heating element comprising a metallic ribbon fixed to an insulative base and a backstop aligned in opposed relation to said sealing head with said sealing head including opposed surfaces facing toward and away from said backstop with said insulative base being fixed to said surface of said sealing head that faces said backstop, said metallic ribbon being fixed to said insulative base so that an edge thereof extends above said insulative base, the improvement in said machine comprising said insulative base comprising a pair of mating base elements arranged to define a slot therebetween for receiving said ribbon.

2. A vertical form, fill and seal machine as defined in claim 1 wherein said sealing head further includes at least one fastener for maintaining said base elements in intimate contact.

3. A vertical form, fill and seal machine as defined in claim 2 wherein said base further comprises; a) a pedestal, said pedestal spanning said base; andb) said slot for receiving said heating element being located within and extending above an upper surface of said pedestal.

4. A vertical form, fill and seal machine as defined in claim 3 further including: a) each of said base elements comprising a pedestal section;b) said pedestal section of each base element being located adjacent a mating edge of each of said base elements.

5. A vertical form, fill and seal machine as defined in claim 4 wherein said at least one fastener traverses mating pedestal sections of said base elements.

6. A vertical form, fill and seal machine as defined in claim 1 wherein said metallic ribbon comprises titanium.

7. A vertical form, fill and seal machine as defined in claim 1 wherein said base is of molded ceramic material.