AU2012212402B2

AU2012212402B2 - Sealing assembly

Info

Publication number: AU2012212402B2
Application number: AU2012212402A
Authority: AU
Inventors: Warrick CHENEY; Nick JUSTO
Original assignee: Micris Pty Ltd
Current assignee: Bemis Brisbane Pty Ltd
Priority date: 2011-02-03
Filing date: 2012-02-03
Publication date: 2016-06-30
Anticipated expiration: 2032-02-03
Also published as: AU2012212402A1; WO2012103592A1

Abstract

The invention relates to a sealing assembly (100) for sealing an inflated flexible tubular packaging material under tension in the machine direction; the sealing assembly having an upper (101) and a lower (102) sealing bar with opposed sealing faces, moveable between an open position and a closed sealing position, a flattening member (104) having a head section with a convex leading surface (106) mounted the sealing lower bar (102) for movement relative to the lower sealing bar (102), said movement being between a first position in which the leading convex surface (106) is proud of the sealing face of the lower sealing bar (102) and a second position in which the distance between the leading surface (106) of the flattening member (104) and the sealing face of said sealing bar is less than that when in the first position. The head section is in the first position when the sealing bars are in the open position and as the sealing bars travel towards the closed position the head section moves towards the second position and during such movement the leading convex surface engages the inflated tube so as to at least partially collapse the tube.

Description

SEALING ASSEMBLY

FIELD OF THE INVENTION

The present invention relates to a sealing assembly for sealing an inflated flexible tubular packaging material.

BACKGROUND OF THE INVENTION

The sealing of flexible packaging materials is known and is generally employed in packaging food and other commodities. In many cases two sides of a continuous flat sheet of flexible film are fed around a conical tube and the outer edges are sealed to form a tube of film. The seal may be formed using heat or adhesive. If the inner film layer is in contact with the product to be sealed to the outside film it is known in the art as a lap seal. If the two inside layers are sealed together it is known as a fin seal. The film is then sealed in the cross direction, known as a cross seal to form a bag into which product is inserted. A common form of sealing is known as heat sealing whereby opposed sealing bars have sealing faces that are brought together to thermally seal the inner layer of the film together. When cross seals are made at both ends on the same machine the finished package is produced. Alternatively when a seal is made at only one end, after insertion of the product the open bag may be taken to another location and remotely sealed. Remote sealing may occur for example if the product is to be vacuum sealed.

There are numerous commercial machines that use sheet film to produce a finished product as described above. If the film is fed downward while the product is inserted it is typically called a vertical form, fill seal machine (VFFS). VFFS machines are mostly used for packaging multiple small items such as grains, rice, chips cereals and the like. If the film is moved horizontally while the product is inserted typically it is known as a horizontal form fill and seal machine (HFFS). The present invention is in particular directed towards a sealing assembly for use with a HFFS machine. HFFS machines are mostly used for larger objects or those too fragile or bulky/sharp to be packaged vertically. HFFS machines feed product into the film tube by conveyor rather than feeding the product through the tube. In order to facilitate insertion of the product, the tubes are typically inflated with air.

Food products are packaged using these methods to protect and/or extend the shelf life. The films used can vary significantly depending upon the nature of the product. Properties of films that vary include modulus, thickness, moisture and oxygen barriers, toughness, shear strength and heat sealability. In many cases, the films are heat shrinkable. A particular application for heat shrink packaging is to seal perishable items such as meat products that have been vacuum sealed.

It may be appreciated that it is desirable that the seals formed in both the longitudinal and cross directions are continuous, strong and leak tight. If the package is made either on a VFFS or a HFFS in the area where the cross seal intersects with the longitudinal seal up to 4 layers of mono or multilayer film must be sealed.

It is therefore important that the seals are free of creases or other inconsistency. If the opposed faces of the film prior to sealing are not smooth and free from creases, the seal will be formed across the creases or wrinkles. This can provide a point of weakness in the seal which can at best result in a small air leak that can lead to spoilage of the packaged food and at worst failure of the package.

The desirability to avoid creases and wrinkles in cross seals is well known. Generally with films of high modulus (i.e. relatively stiff films) such as nylons if the tube is partially inflated with air to expand out the sides of the film and the inflated tube is under sufficient tension in the longitudinal or machine direction, the tube may be flattened by a simple bar known as a spreader bar prior to sealing. However, when films having low modulus are used, such as films formed from low density polyethylene, Ethyl Vinyl Acetate (EVA) or other soft rubber, wrinkles are formed upon flattening. This is particularly relevant for films that need to provide excellent product drape such as is necessary for vacuum bags applications for irregular shaped product where otherwise air pockets are likely to remain and reduce shelf life. Further in films of this type, the sealant layer is chosen to enhance shrink levels. Furthermore, thin gauge films have lower amounts of sealant available to flow into pleat areas to provide an effective seal.

Sealing difficulties are more often observed with HFFS machines than VFFS in which there is generally a uniform pressure from fluid or product that behaves uniformly and repeatedly.

There have been a number of proposals to address the problem of wrinkles forming in low modulus materials. Each of these proposals relies upon mechanical methods to apply tension in the transverse or cross direction. One example is US 6,877,543 that describes a spreader mechanism having upper and lower spreading members. Each spreading member is formed from a pair of converging members that initially contact the middle of the film and then the members travel in a transverse direction so as to the spread the edges of the film outwards. Other devices rely on mechanically grabbing the edges of the film and pulling the edges away from each other. It will be appreciated that excessive tension in the transverse direction may cause thinning of the film. Further, these earlier mechanical devices are complex, expensive and require high maintenance.

It is therefore an object of the present invention to provide an alternative device for flattening a tubular packaging film prior to sealing.

SUMMARY OF THE INVENTION

According to a first broad form of the invention, there is provided sealing assembly for sealing an inflated flexible tubular packaging material under tension in the machine direction: the sealing assembly having a first and a second sealing bar with opposed sealing faces, moveable between an open position and a closed sealing position; a flattening member having a head section with a convex leading surface mounted to one of the sealing bars for movement relative to the sealing bar to which the flattening member is mounted, said movement being between a first position in which the leading convex surface is proud of the sealing face of the sealing bar to which the flattening member is mounted and a second position in which the distance between the leading surface of the flattening member and the sealing face of said sealing bar is less than that when in the first position; wherein the head section is in the first position when the sealing bars are in the open position and is moved towards the second position as the sealing bars travel towards the closed position, wherein during such movement the leading convex surface engages the inflated tube so as to at least partially collapse the tube.

The term “machine direction” is well known in the art to refer to the direction in which a film is fed through a processing or packaging machine. It may also be referred to as the longitudinal direction. A force applied at 90° to the machine direction is referred to as tension in the transverse or cross direction.

The sealing assembly may be mounted to either a VFFS or HFFS machine, and is particular suited for use with a HFFS machine. The invention will be described with particular reference to a HFFS machine which has upper and lower sealing bars. However, no limitation is intended thereby.

The flattening member has a head section with a leading convex surface. The convex surface suitably defines an arc having a radius. The length of the radius is selected so as to provide a desired degree of curvature to the head section. Thus the length of the radius will depend upon the width of the flattening member. Suitably the flattening member has substantially the same length as the sealing bar to which it is mounted. The radius is typically between about 2 to about 5 times that of the width of the sealing bar, preferably between about 2.5 to about 4.5 times, most preferably between about 2.8 to about 4 times.

Preferably, for a HFFS machine, the vertical axis of the convex surface is co-linear with the vertical axis of the tube. In this way, the leading convex surface enables the flattening member to apply a maximum vertical load to the inflated tube at the vertical axis of the tube thereby forcing the air towards the edges of the tube with continued upward movement. Applying the load at the vertical axis of the tube transfers the load to the horizontal axis of the tube, thereby causing the walls of the tube to buckle at the horizontal axis, thereby initiating a smooth collapse of the tube. Preferably, the width of the head section of the flattening member is equal to or greater than the diameter of the inflated tube.

Without being bound by theory, the present inventor believes that this mechanism of causing the tube to collapse, whereby a convex surface pushes against the machine direction tension in the film assists in smoothing out any creases or wrinkles in the film without solely relying on the requirement of mechanical application of a force in the transverse direction or by pressing the film together between spreader bars in conjunction with applying a transverse force as taught by the prior art.

The flattening member moves from a first position in which the head section is proud of the sealing bar to a second position in which the distance between the head section and the leading edge of the sealing bar is less than that when the flattening member is in the first position.

Movement of the head section in this manner can progressively reduce the tension in the machine direction prior to sealing. It is desirable that the film is under minimal tension during the actual sealing operation.

Such movement of the convex head section may be compared with convex shaped jaws or members used with VFFS machines. These convex members are fixed with respect to the sealing heads. The object of these arrangements is to control the amount of product and/or remove excess air from a sealed package. In this case, it is critical to the function that there is no movement of the convex members.

The degree of movement of the head section will generally depend upon the size of the tube to be collapsed. For example, a tube having a diameter of about 300mm (typically in the range of about 200mm to about 450mm) the degree of travel is between about 10mm to about 50mm, suitably between about 15mm to about 40mm, preferably between about 20mm to about 30mm.

The flattening member may be mounted to either the upper or lower sealing bars, although the lower sealing bar is preferred.

Movement of the head section relative to the sealing bar may be achieved by any suitable means. Typically, the head section is biased towards the first position and is urged against the bias from the first to the second position as the sealing bars approach the sealing position and the tube collapses. After the tube is sealed and the sealing members return to the open position, the bias returns the head section to the first position.

The head section may be urged against the bias by the tension in the longitudinal or machine direction of the tube. The force pushing against the bias increases as the tube is collapsed. In many packaging machines, longitudinal tension is a variable that may be readily changed by an operator in response to films of different thickness and modulus and the like. In the present case, an operator may also need to select the appropriate tension to optimize operation of the sealing assembly of the present invention. This may easily be done by trial and error without any undue experimentation and is well within the ability of an average operator. Once the optimum tension has been determined for a particular film on a particular film, there ought not be any requirement for the tension to be changed.

Alternatively or in addition to, the device may include actuators for urging the head section against the bias. For example, the assembly may include a pin or pins depending from the upper sealing head that urges the head section against the bias as the flattening member is raised.

In an alternative form of the invention, the flattening member may include a pair of opposed head members that can pivot downwards in response to the tension in the film member. In such an embodiment, there may be a corresponding movement of the head members away from each other so as to provide a limited degree of transverse force to the film.

In yet a further arrangement, the flattening member may be composed of a plurality of submembers, individually mounted to the sealing bar for movement between first and second positions. In this case the upper surface of each submember is contoured such that together the upper surfaces define a convex upper surface.

The assembly may include a single flattening member. Preferably however, the device includes a pair of flattening members mounted on either side of a respective sealing bar. This allows a substantially uniform force to be applied on either side of the sealing bar. For a HFFS machine, the flattening member(s) are suitably mounted to the lower sealing bar.

In an alternative embodiment of the present invention, the flattening member is fixed relative to a respective sealing bar and flattening and spreading of the tube occurs solely as a result of the relationship between the convex upper section of the flattening member and the tension of the tube in the longitudinal tension.

According to another broad form of the invention there is provided a sealing assembly for sealing an inflated flexible tubular packaging material under tension in the longitudinal direction; the sealing assembly having sealing bars moveable between an open position and a closed sealing position and a flattening member having a convex upper surface which moves towards the inflated tube prior to sealing so as to push the tube against the tension so as to flatten the tube across the convex surface and tension isolation means for relieving tension in the material in the machine direction when the sealing bars are in the closed sealing position.

In this form of the invention, alternative methods may be used to relieve the machine direction tension prior to sealing as it is desirable that the seal is made under no or reduced tension. Such means include the use of tension isolation members in the sealing bars. The tension isolation members may be in the form of a projection in the one sealing bar that is received in a recess located in the other of the sealing bar.

According to a further broad from of the invention, there is provided a method of sealing an inflated tube of packaging material traveling horizontally under tension in the machine direction, the method comprising, providing a flattening member having a convex leading surface opposed to the inflated tube and pushing the flattening member towards the tube so as to push against the machine direction tension so as to collapse the tube, at least partially relieving the machine direction tension prior to sealing the film between opposed sealing bars.

In any of the above embodiments, the assembly may further include a tensioning bar mounted to the other of the upper or the lower sealing bar to the flattening member and extends proud of the respective sealing bar. The tensioning bar may assist in generating a desired tension in the machine direction. The tensioning bar may be rigid in which case it is suitably flat or slightly curved.

In an alternate embodiment, the convex leading surface of the flattening member is not rigid but can move between a convex conformation when the flattening member is in the first position, and a substantially flat conformation when the flattening member is in the second position. Substantially flat means that the surface may have a degree of residual convexity, flat or slightly concave The manner in which the leading surface changes shape may be by any suitable manner. In one embodiment, the flattening member may include a base section to which a plurality of submembers are individually mounted for movement between an extended position in which the leading edges of the members define a convex leading surface and a second position in which the leading edges define a substantially flat leading edge.

In an alternative arrangement, the flattening member has a leading edge formed from a single length of a resiliency flexible material that is biased towards the convex position. The flexible material may be made of any suitable flexible metallic or plastics material. The biasing may be provided by the inherent flexibility of the material. Additional bias may be provided by a separate biasing means.

In yet a further and preferred form of the invention, the sealing assembly includes first and second flattening members in which the first flattening member is mounted to the upper or lower sealing bar and second flattening member is mounted to the other of the lower or upper sealing bar. The flattening members may be the same, however, it is preferred that the first flattening member has a convex leading surface that substantially retains its convex shape when moving to the second position and the second flattening member has a convex leading surface that has a convex shape in the first position and moves to a substantially flat position when in the second position.

Further preferred is that the assembly includes first and second pairs of flattening members, a first pair mounted to either side of the first or the second (upper or lower in the case of a HFFS machine) sealing bar and a second pair mounted to either side of the other of the second or first (lower or upper in the case of a HFFS machine) sealing bar.

The curvature of the convex shape of the flexible flattening member initially contacts the edge of the inflated tube and flattens the tube from the opposite direction to the opposite fixed flattening member, thereby facilitating flattening of the tube. At some point the respective leading surfaces of the flattening members apply force against each other with the flattened tube in between. As this force is applied, the flexible flattening member responds by moving towards a substantially flat position, which movement may assist to smooth out wrinkles or creases in the tube. This force also assists in moving the fixed flattening member against the bias towards its second position.

Typically, the flattening member having the leading surface that retains a substantially convex surface is mounted to the lower sealing bar and the flattening member with the leading surface that moves to a substantially flat leading surface.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1(a) is a schematic perspective view of a preferred sealing assembly of the present invention in which the flattening member is in the first position;

Fig. 1 (b) shows the sealing assembly of Fig. 1 in which the flattening member is in the second position;

Fig. 2(a) is a schematic perspective view of a further preferred sealing assembly of the present invention in which the flattening member is in the first position;

Fig. 2 (b) shows the sealing assembly of Fig. 2 in which the flattening member is in the second position;

Figs. 3(a) (b) and (c) show a flattening member of another preferred sealing assembly of the present invention moving from the first position in Fig 3 (a) to the second position in Fig. 3(c);

Fig. 4(a) is a front view of a preferred sealing assembly of the present invention in which the flattening member is in the first position;

Fig. 4 (b) shows the sealing assembly of Fig. 4 in which the flattening member is in the second position;

Figs 5(a), (b) and (c) show front, plan and side elevations of a further preferred flattening member;

Figs 6(a), (b) and (c) show a flattening member of another preferred sealing assembly of the present invention moving from the first position in fig 6 (a) to the second position in Fig. 6 (c);

Figs 7(a), (b) and (c) show a flattening member of another preferred sealing assembly of the present invention moving from the first position in fig 7 (a) to the second position in Fig. 7 (c);

Fig. 8 (a) is a side view of a further preferred flattening member of an alternative embodiment of the present invention; and Fig. 8(b) is a top view;

Figures 9(a) to (c) show a further preferred sealing assembly of the present invention and

Figures 10a) to e) show the sequence of a tension isolation mechanism for use in association with any one of the assemblies illustrated in figures 1 to 9.

DETAILED DESCRIPTION OF THE FIGURES

Figures 1(a) and 1(b) show a preferred sealing assembly 10 of the present invention for use with a HFFS machine.. The sealing assembly has an upper 11 and lower 12 sealing bar. The lower sealing bar 12 has parallel heating bands 13 on an upper sealing surface or face. The sealing bars move between an open position as shown in fig. 1(a) and a sealing position as shown in Figure.1(b). A flattening member 14 is mounted to the lower sealing bar 12, is urged proud of the sealing surface by a series of springs 15 extending from the base of the member 14. An identical flattening member 14 is mounted to the opposite side of the sealing bar (not shown). The flattening member 14 is formed from a solid block having a head section with an upper convex surface 16. A pair of vertical guide slots 17 that receive guide pins 18 mounted on the lower sealing bar are formed in the member 14. The flattening member 14 has two flanges 19 extending from either side thereof.

In Figure 1(a) the flattening member 14 is in a first position in which the upper convex surface 16 is proud of the upper sealing surface of the lower sealing bar 12. In Figure 1 (b) the flattening member 14 is shown in the second position in which the upper concave surface 16 is level with the upper surface of the lower sealing bar 12. In this position, the inflated tube has been fully collapsed (not shown) and will be draped over the lower sealing member with minimal or no creases ready for sealing.

The upper sealing member 11 has downward facing pins 9, extending from either side. As the lower sealing bar 12 moves towards the upper sealing bar 11 pins 9 meet flanges 19 that forces against the bias of springs 15, limiting or removing tension from the film just prior to sealing.

As the lower sealing member moves away from the seal position and returns to the open position, the bias of the springs 15 returns the flattening member 14 to the position shown in figure 1 (a).

Figures 2(a) and 2(b) shown an alternative flattening member 20 mounted to a lower sealing bar 21 in the first and second positions respectively. The flattening member 20 consists of 5 submembers, being two outer members 22, 23 and three inner members 24, 25, 26. Each submember is individually mounted to the lower sealing bar 21 by a spring 27. The outer submembers 22, 23 are also pivotally mounted to the lower sealing bar 21 about pivot points 28. The three inner submembers 24, 25, 26 are mounted for vertical movement.

Figure 2(b) shows the flattening member 20 in the second position in which the two outer members 22, 23 have pivoted inwardly, thereby moving the upper most part of the submembers to be level to the upper surface of the sealing bar 21. The three inner submembers have moved downwards against the bias of springs. The submembers are urged against the bias of the springs by the tension of the film. Initially the tension against the film increases as the submembers contact the film and move upwardly until a critical tension is reached, at this point the tension is progressively relieved from the center to the edges as the submembers individually move in response to the tension. As the tension is released the submembers are returned to their original position by the bias exerted by the springs 27.

Figures 3(a), (b) and (c) show still a further flattening member 30 moving between a first position in Figure 3(a) and a second position in Figure 3(c). The flattening member 30 comprises a pair of submembers 31, 32 connected by upper 33 and lower springs 34. In this case the springs do not bias the submembers against vertical movement but bias the respective upper and lower corners of each submember towards each other. The submembers are mounted to the lower sealing member (not shown) by the means of pins on the sealing bar mounted in guide slots on the submembers (not shown). A round pin 35 is mounted to the lower sealing bar between the two submembers. As the submembers are subject to tension of the film and a downward force is exerted by the collapsed tube, the submembers move downwards and are forced apart by pin 35. When the tension is released the submembers are closed by the action of springs 33, 34.

Figure 4(a) shows still a further flattening member 40 for use with the sealing assembly of the present invention. The flattening member 40 has a base 41. A plurality of finger like submembers 42 are mounted to the base 41 by means of springs 43. Also shown schematically in figure 4 is a partially collapsed inflated tube 44 of a flexible packaging material. As the tube collapse further, the upper section of the flattening member 40 will experience increased tension, thereby urging the submembers downwards, thereby progressively relieving tension from the center to the edges as the submembers move.

Figure 4 (b) shows the flattening member 40 in the second position and the tube 44 is collapsed. It may be seen that in the second position, the upper surface of the flattening member 40 has a reduced curvature compared to the first position as a result of the different levels of biasing force exerted on the individual submembers and associated springs.

Figures 5 (a), (b) and (c) show a front, plan and side view of still a further flattening member 50 of the present invention. This flattening member 50 is has two convex sections formed from a resilient material such as rubber and are mounted to either side of the lower sealing bar 51 with pins 52. As the rubber material is subjected to tension against the tube, the flexibility of the material causes the rubber to bend outwardly in the direction shown by Arrow A in figure 5 (c). This deforms the member 50 as shown in the plan view of figure 5 (b). As the tension upon the member 50 is relieved, the resilience of the material returns the member to its original position.

Figures 6 (a), (b) and (c) show yet a further flattening member 60 for use in a preferred sealing assembly of the present invention moving from a first position shown in figure 6 (a) to a second position shown in figure 6 (c), through intermediate position shown in figure 6 (b). This flattening member 60 is composed of 2 submembers 61, 62 pivotally mounted to the lower sealing bar (not shown) about pivot points 63. An identical pair of submembers is mounted to the opposite side of the lower sealing bar (not shown). Pivotal motion is limited by pins 64 in curved guide slots 65. The lower edges of the submembers 61, 62 are connected by a spring 66. As the flattening member 60 is subjected to tension from the collapsed film, the submembers 61, 62 are forced to pivot downwards in the direction shown by arrows B in Figure 6(a) and 6 (b). This pivoting movement urges against the bias of spring 66. When the tension is released, spring 65 returns the flattening member 60 to the original first position.

Contrary to the prior art it will be noted that there is no lateral movement of the submembers such that lateral tension is not applied to the inflated tube during collapse of the tube.

Figures 7 (a), (b) and (c) show a similar flattening member 70 to that shown in figure 6. Flattening member 70 consists of two pairs of sub members 71,72 mounted to either side of the lower sealing bar (not shown). The submembers are mounted to the sealing bar by inner and outer pins 73, 74 mounted within curved guide slots 75, 76. A spring 77 connects the lower edges of the submembers 71,72.

Figures 8(a) and 8(b)show side and plan views of a further assembly in which a single flattening member 80 is fixed to both sides of the lower sealing bar 81 by bolts 82. In this embodiment, relief of the machine direction tension is accomplished by an arrangement of film tensioners located within the sealing heads. As shown in Figure 10.

It may be seen that with each of the flattening members as illustrated in figures 1 to 8 that the convex upper section of the flattening member applies an upwards force that is met by the film tension in the material direction. The convex shape of the upper section of the flattening member forces air towards the outer edges of the tube as the tube is collapsed by the rising flattening member. This movement of air serves to smooth out any wrinkles or creases.

When the tube is fully collapsed, the upper surface of the flattening member is under maximum tension. In figures 1 to 7, this is relieved by various mechanisms by a downward movement of the flattening member to a second position in which the upper surface is level with or below that of the upper surface of the lower sealing bar. This leaves the collapsed film draped over the lower sealing bar ready for sealing. Significantly there is no or minimal tension applied to the film in the lateral dimension.

Figures 9(a) to (c) show a preferred sealing assembly of the present invention. The sealing assembly has an upper 101, and lower sealing bar 102. The lower sealing bar 102 has parallel heating bands 103. The sealing bars move between the open position shown in fig 9a) to through to a sealing position shown in Figure 9c). A bottom flattening member 104, is mounted to the lower sealing bar 102, is urged proud of the sealing band by a series of springs 105 extending from the base of the member 104. An identical flattening member 104 is mounted to the opposite side of the sealing bar (not shown). The flattening member 104 is formed from a solid block having a head section with an upper convex surface 106. .A pair of vertical guide slots 107 that receive guide pins 108 mounted on the lower sealing bar are formed in the member 104.

Attached to the top sealing bar is a flexible flattening member 111. This is attached to a movable pin 112, that is spring loaded 113, against a bush 114, that is mounted to the upper sealing bar 101. The flexible flattening member 111, is also retained by locating guides 115 and 116.

In Figure 9(a) the bottom flattening member 104 is in a first position in which the upper convex surface 106 is proud of the top surface lower sealing bar 102. In Figure 9 (c) the flattening member 104 is shown in the second position in which the upper concave surface 106 is level with the upper surface of the lower sealing bar 102. The flexible flattening member 111 changes from a marked convex shape in Figure 9a) to a slightly concave shape in Figure 9(c). The combined action of the film tension and the flexible flattening member 111, assist with urging the bottom flattening member 104 downwards In this position against the bias of the springs 105. Similarly the combined action of the film tension and resistance provided from the bottom flattening member 104, urge the flexible flattening member 111 to an upper position where its shape is changed from convex to slightly concave. The inflated tube has been fully collapsed (not shown) and will be draped over the lower sealing member with minimal or no creases ready for sealing.

As the lower sealing member moves away from the seal position and returns to the open position, the bias of the springs 105 returns the bottom flattening member to the position shown in figure 9(a). At the same time, the bias of spring 113 returns the flexible flattening member 111 to the position shown in figure 9(a).

Figure 10 shows an arrangement of isolating the tension in the film prior to sealing for use on conjunction with the sealing assembly as shown in figure 8. Figure 10 shows upper 120 and lower sealing bars 121. The lower bar 121 has parallel heating elements 123. The upper sealing bar 122 has a silicone rubber backing member 124. The upper sealing bar 122 has a downwardly extending pretensioner 125 that is receivable within an opposed recess 1266 in the lower sealing bar 121. The upper sealing bar 120 also has film gripping members 127, 128, 129 on either side of the silicone rubber. The gripping members are downwardly biased by springs 130. A cutting blade 131 is located between gripping members 128 and 129.

Figure 10 (a) shows the sealing bars 120, 121 in the open position in which a tube of film is being fed between the sealing bars 120, 121 under tension in the direction of arrow A. As the sealing bars 120, 121 travel towards each other, the pretensioner 125 presses the film into recess 126. The film gripping members 127, 128, 129 clamp the film in the position shown in figure 10 (b). When the film is clamped, the pretensioner 126 is raised as is shown in Figure 10(c). The tube is then sealed and the blade is lowered to cut the film as shown in Figure 10(d). After the tube is cut, the blade 131 is raised. The sealing bars 121, 123 then return to the open position shown in figure 10(a).

It may be appreciated that the sealing mechanisms of the present invention provide a means for collapsing an inflated flexible material prior to sealing with minimization of wrinkles and creases in the film.

It will be appreciated that various changes and modifications may be made to the invention as described and claimed herein without departing from the spirit and scope thereof. In particular, each of the devices may be used on one or both sides of the sealing bar, and may or may not be used in concert with a flexible flattening member such as that depicted in Figure 9.

Claims

1. A sealing assembly for sealing an inflated flexible tubular packaging material under tension in the machine direction: the sealing assembly having a first and a second sealing bar with opposed sealing faces, moveable between an open position and a closed sealing position, a flattening member having a head section with a convex leading surface mounted to one of the sealing bars for movement relative to the sealing bar to which the flattening member is mounted, said movement being between a first position in which the leading convex surface is proud of the sealing face of the sealing bar to which the flattening member is mounted and a second position in which the distance between the leading surface of the flattening member and the sealing face of said sealing bar is less than that when in the first position; wherein the head section is in the first position when the sealing bars are in the open position and is moved towards the second position as the sealing bars travel towards the closed position and during such movement the leading convex surface engages the inflated tube so as to at least partially collapse the tube.

2. The sealing assembly of claim 1, wherein the first sealing bar is a lower sealing bar and the second sealing bar is an upper sealing bar.

3. The sealing assembly of claim 2, wherein the flattening member is mounted to the lower sealing bar.

4. The sealing assembly of claim 2 or claim 3, wherein the center vertical axis of the convex surface is aligned vertically with the vertical axis of the inflated tube.

5. The sealing assembly of any one of claims 1 to 4, wherein the head section is biased towards the first position.

6. The sealing assembly of claim 5, wherein the head section is urged against the bias as the sealing bars travel towards the sealing position.

7. The sealing assembly of any one of claims 1 to 6 comprising two flattening members mounted to both sides of said sealing bar.

8. The sealing assembly of any one of claims 1 to 7, wherein the leading convex surface moves from a convex conformation in the first position to a substantially flat conformation when in the second position.

9. The sealing assembly of any one of claims 1 to 7, wherein the leading convex surface retains its convex conformation between the first and second positions.

10. The sealing assembly of any one of claims 1 to 9 having a first flattening member(s) mounted to the first or second sealing bar and a second flattening member(s) mounted to other of the second or first sealing bar.

11. The sealing assembly of claim 10 wherein the leading convex surface of the first flattening member(s) retains its convex conformation between the first and second positions and the leading convex surface of the second flattening member(s) surface moves from a convex conformation in the first position to a substantially flat conformation when in the second position.

12. The sealing assembly of claim 11, wherein the flattening member(s) with the leading convex surface that moves to a substantially flat conformation is mounted to a sealing bar that is an upper sealing bar.

13. The sealing assembly of any one of claims 1 to 9, wherein the flattening member comprises at least two submembers.

14. The sealing assembly of claim 13, wherein each submember is individually biased towards the first position.

15. A sealing assembly for sealing an inflated flexible tubular packaging material under tension in the longitudinal direction; the sealing assembly having upper and lower sealing bars and a flattening member having a convex leading surface which moves towards the inflated tube prior to sealing so as to push the tube against the tension so as to flatten the tube across the convex surface.

16. A method of sealing an inflated tube of packaging material traveling horizontally under tension in the machine direction, the method comprising, providing a flattening member having a convex upper surface beneath the inflated tube and pushing the flattening member upwards towards the lower most part of the tube so as to push against the machine direction tension so as to collapse the tube, at least partially relieving the machine direction tension prior to sealing the film between opposed sealing bars.