PACKAGES

Abstract: A package (2) has a top transverse seal (8) which is designed to be opened by separating two portions (4, 6) of sheet material forming the package (2). The seal (8) has a region of weakness (20) intermediate its extremities (22) where the force required to separate the portions (4, 6) of sheet material is substantially less than that required adjacent the extremities (22). The bottom transverse seal (10) defines the profile of the interior of the package (2). The bottom seal (10) is such that there is a gradual transition (26) between each of the package sides (28, 30) and the transverse direction. Thus the product in the package (2) is encouraged to rest on the central region of the bottom seal (10) for easy accessibility.

Description: PACKAGES The present inventions relate to packaging and in particular, but not exclusively, to the packaging of food products such as snack foods. Many packages in common use such as plastics or paper bags with sealed ends are difficult to open without damaging the remainder of the package. This is a particular problem if the material packaged is a food product and especially a snack product, where the package is to be easily opened without the use of scissors, knives or the like. A problem confronting the manufacturers of such packages is that the packages should have an airtight seal and be structurally strong but at the same time be easily openable by the consumer. With known packages used for products such as potato crisps (chips) and other snack food products, the front and back sides of the bags are usually gripped by the consumer and pulled in directions away from each other so as to open the seal at the top of the bag. Unfortunately this action often results in a tear or tears running from the top of the package to the bottom. This is because initially the consumer pulls the package sides away from each other but with no effect. The consumer increases the applied force with the result that the package opens unexpectedly but force continues to be applied for a short time after opening and this can tear the package, particularly down the sides. The contents of the package can thus be spilled to the annoyance and inconvenience of the would-be consumer. The opening action may alternatively result.in a longitudinal seal of the package pulling apart, with the same consequences. In order to overcome this problem some manufacturers provide a nick, notch or score line in the top seal of the package so that when the consumer wants to open the package, he pulls the top seal in opposite directions on either side of the nick, notch or score line. This results usually in a longitudinal tear in the package. Generally the tear will be towards one side of the package through which the contents may be tipped. This may be suitable for dispensing small items such as peanuts, but such packages are not suitable for products which it is preferred to lift out of a large opening in the package such as potato crisps. Furthermore, such packages do not always tear as intended and the resulting opening may be too large and the contents of the package may be spilled. Alternatively the tear may not be in the intended direction and may for example be across the package which inevitably results in accidental spillage. Similar problems arise with packages of other materials such as powdered, granular and particulate food products which may be spilled if a package breaks when it is being opened. Breakage of the package may be particularly inconvenient where the package is to hold contents which are not intended to be used all at the same time, i.e. where the package is to act as storage for the product after opening. The problem is more acute when a package is used to contain a liquid as accidental spills can cause considerable inconvenience. Known packages such as are described above include horizontal pouches, pillow packages and bags made by a vertical form-fill seal technique. Referring firstly to horizontal pouches, these are generally formed from a roll of material such as a flexible plastics. The material is moved to a folding die which produces a U- shaped channel. Heater bars are arranged downstream of the folding die to form a side seal perpendicular to the axis of the channel. When two such seals have been formed, a pouch is defined between the seals. Product is then inserted into the defined pouch from the top of the channel. The two edges forming the top of the channel are then sealed together to close the package. The pouch forming apparatus incorporates a cutting blade which cuts through the middle of a side seal so as to separate the filled and sealed packages. A seal may also be made along the fold at the bottom of the channel for additional security. The packages can contain solids, moist products or liquids. Pillow packages are the result of a technique for wrapping products in flexible sheet material. This technique is suitable for the packaging of solid units such as for example blocks of cheese or biscuits in trays, but is also widely used for other products such as moistened tissues. The units to be packaged are placed on flexible sheets of material mainly horizontally which is wrapped around the units. A longitudinal seal is formed along the centre line and transverse seals are then made by bars so as to seal the units into individual packages. The packages are then cut in a similar operation to that used in relation to the horizontal pouches. A vertical form-fill-seal technique is particularly suitable for particulate materials and liquids and is frequently used for packaging snack food products such as potato crips (chips) . Flexible sheet material moving vertically is formed into a tube and a longitudinal seam is formed. The thus formed tube is intermittently advanced in package length increments. A transverse seal is formed which defines the lower seal for a package about to be filled, and the upper seal for an already filled package. Once the lower seal is formed the package is filled through a vertically extending pipe. The package may be inflated by air or by a gas such as nitrogen, prior to filling. Finally, the tube is advanced by a package length and the upper seal of the package is formed, simultaneously with the lower seal of a following package. The packages are separated by cutting between the seals; this may be simultaneous with or subsequent to the sealing operation. The above mentioned packages are generally formed of a flexible sheet plastics material which can be heat sealed to form the various seals by the application of heat and pressure. Whilst longitudinal seals may be provided by rotatable wheels or the like, the transverse seals are usually formed by rectangular bars. In any event, the transverse seals extending across the packages are of uniform depth and quality in the longitudinal direction of the package, so that a sufficiently strong seal is provided uniformly across the width of the package. At least one of these transverse seals may be separated to gain access to the contents of the package, and the aforementioned problems are encountered. Accordingly the present invention relates particularly, but not exclusively, to the packaging of snack foods, fluids (such as drinks) or of other products which are to be dispensed from an initially sealed package which is to be opened by separating a transverse seal at one end; According to a first aspect of this invention there is provided a sealed package of flexible sheet material, said package having a transverse seal across one end, between two portions of sheet material, which seal is intended to be broken by separating the two portions of material so as to gain access to the interior of the package, wherein said transverse seal has a region of weakness intermediate its extremities where the force required to separate the material portions is substantially less than that required adjacent said extremities. The package may be opened in a conventional manner by pulling the front and back sides of the package apart in opposite directions. The package seal will be first broken in the region of relative weakness. The opening formed in the region of weakness is then widened gradually as the consumer continues to pull the front and back of the package in opposite directions. This encouragement of gradual opening of the package leads to a controlled opening of the package with a reduction in the likelihood of tearing. The greater strength of seal at the extremities of the transverse seal, inhibits tearing down the sides of the package. In general, the region of weakness will be of reduced seal strength relative to the strength of the transverse seal over a major, or at least substantial part, of its transverse extent. The region of weakness may have a seal strength which is less than that used for the transverse seal of a conventional package, so as to provide easier opening, and the remainder of the seal may have a seal strength equivalent to or greater than that used in conventional packages. In this manner, a strong structural and air tight seal will be provided across most of the package and this may be sufficient in practice to maintain the structural integrity of the package and the quality of the contents. However, the region of weakness may be of equivalent or even greater strength than a conventional seal, the difference relative to the rest of the package being relied upon. A consumer may have to use greater force to initiate opening if the seal strength is stronger, but with the reduced risk of tearing the package this would be acceptable. In some arrangements where the package contains a substantial body of gas such as air, carbon dioxide or nitrogen the gas may be used to open the package. In such cases, the bag is gently squeezed so as to increase the pressure of the gas. Under this pressure, the region of weakness will open first. Once an opening has been defined, the opening can easily be widened without tearing the package. If this method of opening is attempted on conventional packages, then there is a tendency towards tearing or opening along another seal with consequent spillage of the contents and, for example, the contents dropping out of the bottom of the package. Particularly with such a method of opening, where there may be a tendency for another seal to open, whether the bottom seal or e.g. a longitudinal seal, it is preferred that the region of weakness provides a region where opening occurs in preference to any point along any other seals in the package. Thus, for example, the strength of the seal in the region of weakness should preferably be less than the seal strength of any part of a transverse seal along the opposite end of the package; similarly the force required to separate the portions of material in the region of weakness should preferably be less than that required to separate the portions which form a longitudinal seal. The region of weakness may be provided in a number of ways. If the seal consists of a number of transverse sealing lines, the spacing between the lines could be increased in the region of weakness, for example by omitting portions of alternate lines. If the seal is provided by a number of discrete contact points distributed over an area, then the density of the points could be decreased in this region of weakness. Sealing enhancers such as adhesives or other binding agents could be used outside the region of weakness, or the nature of a thermal bond process altered. Preferably, instead of such arrangements - or in suitable cases in addition to one or more of them - the difference in seal strength is provided by varying the depth of the seal in a direction awa from the end of the package. Thus, preferably the region of weakness is a region where the depth of the transverse seal is less than adjacent the extremities of the seal. Preferably, the depth of the seal in such region is less than the depth of the seal over the major part of the transverse - 1 - extent of the package. There may be a gradual or step-wise increase in the depth of the seal from the region of weakness in both directions towards the extremities of the transverse seal. Indeed, with other arrangements the seal strength may increase gradually in such a fashion, for example by gradually increasing the density of sealing contact points. Preferably, the seal has a curved or V shaped profile with an apex region defining the region of weakness, and a greater seal depth at the ends of the seal, i.e. extending along the sides of the package. In most preferred arrangements, this profile will be on the inner side of the seal - i.e. defining the upper boundary of the space in the package. The upper, outer edge may then be plain although it could be shaped if desired. It will be appreciated that the profile of the seal need not be symmetric and may be defined by an asymmetric "V" or curve. Alternatively the seal profile may be such that it is a hybrid of a "V" and a curve so that on one side of the weakness, there is a substantially straight profile whilst on the other side there is substantially curved profile. The region of weakness will, as noted above, generally extend only across part of the package and the major, or at least a substantial, part of the transverse seal will be of higher strength. One reason for restricting the extent of the region of weakness is that reduced sealing not only has a mechanical effect as regards the opening force, but also leads to a greater likelihood of e.g. leakage of gas from or of air into the package. This may lead to deterioration of food products in the package. However, the region of weakness should have a lateral extent which is significant, both so that it can be identified and so that it will initiate significant separation of the sheet material along the seam. It is, for example, known to provide thin notches in the tops of bags (such as bags of peanuts) which will facilitate tearing. It is also known to provide a small hole in the top seal of a bag to enable it to be hung off a hook. Such arrangements do not provide a region of weakness which will provide the effect required, in terms of facilitating separation of the sheet material so as to provide access to the interior of the package. This invention is particularly applicable to packages of snack products made by a vertical form-fill- seal technique. However it will be appreciated that it is equally applicable to horizontal pillow and pouch packaging techniques and to other products. All of these packages can be adapted so that the upper seal of the package includes a region of weakness as set forth above. It will also be appreciated that this invention has wider applications and it may be applied to any other suitable types of packaging where a transverse seal is provided. Many types of product may be stored in packages embodying this invention and in many cases consumers will derive benefit from the opening characteristic of such a package. Preferably the package is manufactured from a suitable plastics film such as polypropylene which can be sealed to itself by means of heat and pressure. Alternatively, the package may be manufactured from a flexible paper material or foil material or laminates of any of the above-mentioned materials, such as plastics coated paper. In some cases, the seal may be made by means other than heating, such as by adhesives, bonding agents, pressure sensitive adhesives or sonic bonding. Apparatus for manufacturing packages in accordance with this invention can be in the form of modified apparatus of e.g. the pillow package, pouch, or vertical form-fill-seal type. According to a second aspect of this invention, there is provided packaging apparatus for manufacturing a sealed package of flexible sheet material, comprising sealing means for forming a transverse seal between two portions of the sheet material across one end of the package which is adapted to be broken by separating the two portions of material so as to gain access to the interior of the package, wherein the sealing means is such that the transverse seal has a region of weakness intermediate its extremities where the force required to separate the material portions is substantively less than that required adjacent said extremities. In the systems particularly referred to previously, the sealing means will generally include members between which the material portions are pressed, at least one of which members is heated. In the preferred arrangement, at least one of these members is profiled to form a seal whose depth in a region intermediate its extremities is less than that adjacent its extremities. As described earlier, the profile could be of a curve or a inverted V whose apex defines the region of weakness. Such a profile may be provided on one or both members between which the sheet portions are pressed. This invention also extends to the provision of one or more sealing members for use in the packaging apparatus. Having regard to the preferred embodiment of such apparatus, according to a third aspect of this invention, there is provided a sealing member for forming a transverse seal across an end of a package of flexible sheet material, the sealing member having a profile which defines a seal whose depth in a region intermediate its extremities is less than that adjacent its extremities. According to a fourth aspect of this invention, there is provided a process for manufacturing a sealed package of flexible sheet material in which a transverse seal is formed between two portions of the sheet material across one end of the package, the seal being adapted to be broken by separating the two portions of material so as to gain access to the interior of the package, wherein said seal is formed in such a way as to have a region of weakness intermediate its extremities where the force required to separate the material portions is substantially less than that required adjacent said extremities. The basic apparatus and process may be of any suitable type, including those used for horizontal pouch and pillow package manufacture, but suitably modified in respect of the sealing members. As known in the art, the sealing members may incorporate cutting means for cutting the packages in the region of the seal. In general, a sealing member will define not only the transverse seal for one end of a package, but also the seal for the other end. Thus, in a known manner, using a vertical form fill seal system, the sealing member will simultaneously form e.g. the top end of an already filled package, and the bottom end of a following package. The line will advance, and then the top end will be formed on this following package simultaneously with the bottom end of a further following package. The profile of the seal for the opposite end of the package may be plain, ie. a single seal of uniform depth extending across the package, or may have any desired profile. As mentioned earlier, the bottom seal is preferably stronger than the seal in the region of weakness at the top so as to prevent unwanted opening along the bottom, particularly if a squeezing technique is employed. In a particularly preferred embodiment the package has at its opposite end a seal which defines a bottom shape for the package which is particularly advantageous. Both seals in the preferred arrangements define the profile of the interior of the package. As regards the exterior profile, the seals at either end may have straight edges or may be angled or curved, or provided with eg. a decorative saw-tooth design. The profile will depend on the profile of the sealing member and of the cutting means. The sealing member may also be used to define a pattern on the sealed region of the package, such as ribbing. This may be achieved by the sealing surface having a plurality of ridges thereon extending in any defined direction. For example the ridges can extend perpendicular to, parallel to or at any intermediate angle to the longitudinal axis of the package. The use of ribbing may improve the strength of the seal. The sealing member may have a heating element associated therewith to heat the sealing surface. This provides the necessary energy to make a bond. However, where sonic bonding is used, for example, the sealing member may have suitable ultra sound producing means. A further problem with many packages in common use such as plastic or paper bags, is that they may be diffic lt to empty fully. Typically such packages are of generally rectangular configuration, having 90° corners at their lower ends in which material tends to be trapped. These corners are generally the junctions between the sides of the package, and a transverse seal across the lower end of the package. This can be a particular problem if the material packaged is a food product. In the case of snack products such as peanuts or small items of confectionery, entire items may be trapped in the bottom of a package. In the case of snack products which are easily broken, such as crisps or biscuits, particles may be broken off and trapped in the corners. In either case, powdered flavourings which coat the items can also be rubbed or shaken off and trapped in the corners. These problems are frequently sources of irritation for consumers of the snack products. For example, the consumer usually is able to remove most of the snack product using the forefinger and thumb. However, the removal of the last particles or last small items of snack product cause problems. Generally the consumer has two options. The first option is to invert the package to tip out the remaining contents. This is a messy process which can result in the consumer spilling the product on himself or his surroundings. Alternatively, the consumer has to attempt to remove the particles with his hand. This involves trying to force the fingers into the lower corners of the package which, as it will be appreciated, is very messy especially where the snack product has a powdered coating some of which has also collected in the corners. Problems also arise with packages of powdered soups, sauces or stuffings where there may be a tendency for the small particles - which may be made of one particular component such as an important flavouring - to settle at the corners in the bottom of a packet. Furthermore, it is frequently the case that packages are of opaque material either to prevent deterioration of the product by ultra-violet light or because of aesthetic considerations. For example it is often desired to colour the package and/or print thereon. This can make it difficult to determine whether any significant material has been trapped in the corners of the package. A further feature thus relates particularly, but not exclusively, to the packaging of products which include or consist of small items or powdered or particulate material, such as snack and other food products. Thus, preferably the transverse profile of the interior of the package adjacent its lower end may be defined by a transverse seal extending between the two sides, wherein said transverse profile is such that there is a gradual transition between each of the sides and the transverse direction. Since there is a gradual transition between the sides and the lower end of the package, trapping of material in the corners will be reduced or eliminated as the lower corners are no longer right angles. Rather, each corner will consist of e.g. a curve or of two or more obtuse angles. The gradual transition may be achieved by the lower seal having a curved inner profile with the lowest point of the curve preferably lying in the middle region of the lower seal. Of course the curve need not be symmetric nor need the lowest point of the curve be in the middle region of the lower end. In such arrangements, the curved profile may extend over substantially the entire width of the package. However, one or more portions could be straight lines. In other arrangements, a straight line portion of substantial extent could be used, for example a transverse straight line, which is joined to the sides by curved portions which provide the gradual transition. In alternative arrangements the gradual transition may be realised by at least one straight line extending downwardly from each of the sides. In some arrangements, the lines could meet at a lowest point preferably lying in the middle region of the lower seal, defining a generally "V"-shape. However, the junction could be a curved portion or a short, straight transverse portion. In other arrangements, a straight transverse line of substantial extent could be used, which is joined to the sides by the angled lines. In a case of a single straight line which meets a straight transverse line, it may be disposed symmetrically so as to provide two 135° internal angles, or asymmetrically. If two straight lines meet at the centre of the package, the angle may be relatively sharp. For example, two symmetrically disposed lines could meet at a right angle. This need not give rise to problems as it is relatively accessible, in the centre of the package. However, e.g. a curved connection portion - as discussed above - can be used if desired. In the case where there is more than one line extending from each side toward the lower edge, the lines should define a generally downward slope from each side toward the lower edge. Furthermore the defined inner profile of the sealed region need not be symmetrically arranged about the middle of the package. In general, the gradual transition and/or the overall profile at the lower end of the package may be realised by hybrids of one or more curves and/or straight lines. In preferred arrangements, there is a central portion which is spaced a substantial distance down the package from the initial change in direction from the sides. This would be the case with a "U"- or "V- profile, but could also be the case with other arrangements. In normal use, with the package in an upright condition, small particles and so forth will then have to collect under gravity in this bottom, central region. This makes them both easier to notice and to remove. In general it is preferred that the profile should be of such a shape as to encourage small particles of product to rest away from the sides of the packag . In general, the seal will also define or follow, at least in part, the outer profile at the bottom of the package. This outer profile could match the inner profile and be curved, for example. This is not necessary, however, and the outer profile may be independent of the inner profile. It may be a conventional transverse straight line, for example. In such cases, the depth of the seal will vary across the width of the package, being greater at the sides than in the middle region. It may be important, however, for a minimum seal depth to be maintained across the package i.e. so the weakest part of the bottom seal is stronger than the weakest part of the top seal. In particular, in the central region of the package there may be a junction with a longitudinal seal and this can provide an area of weakness. The depth of the transverse seal at this point should not be reduced below that normally used in packages of conventional construction. Indeed, it may be made greater than normal. Many types of product may be stored in packages such as described above and many will benefit, from the new profile of the lower transverse seal. For example, the gradual transition may be advantageous where a viscous liquid is stored in a package, since the last portions of the volume of liquid may be more readily removed. Apparatus embodying this invention may also comprise sealing means for forming a transverse sealed region across a lower end of the package wherein, the sealing means defines a transverse interior profile adjacent said end of the package in which there is a gradual transition between the sides of the package and the transverse direction. Where the seal is provided by two sealing members, at least one of these members is profiled to form a seal, whereby there is a gradual transition between each of the sides of the package at the lower end thereof. The internal profile at the seal can be a curve or any of the above described shapes. Such a profile may be provided on one or both members between which the sheet portions are pressed. There may be provided a sealing member which is profiled not only to form the upper seal but which also forms a transverse seal across the lower end of a package, the sealing member including a profile such that a seal is defined which provides a transverse interior profile of the package adjacent said lower end, in which there is a gradual transition between the sides of the package and the transverse end. In methods embodying this invention, there may also be provided the steps of forming a transverse sealed region formed across the lower end of the package, wherein said sealed region defines a transverse interior profile adjacent said lower end of the package in which there is a gradual transition between the sides of the package and the transverse direction. The features relating to the lower end of the package are also inventive in their own right. Thus, according to a first aspect of a further invention, there is provided a package of flexible sheet material comprising an upper end, a lower end and two sides, the transverse profile of the interior of the package adjacent its lower end being defined by a transverse seal extending between the two sides, wherein said transverse profile is such that there is a gradual transition between each of the sides and the transverse direction. According to a second aspect of the further .invention, there is provided apparatus for manufacturing a package of flexible sheet material, comprising sealing means for forming a transverse sealed region across an end of the package wherein, the sealing means defines a transverse interior profile adjacent said end of the package in which there is a gradual transition between the sides of the package and the transverse direction. According to a third aspect of the further invention, there is provided a sealing member for forming a transverse seal across an end of a package of flexible sheet material, the sealing member having a profile such that a seal is defined which provides a transverse interior profile of the package adjacent said end, in which there is a gradual transition between the sides of the package and the transverse end. According to a fourth aspect of the further invention, there is provided a process for manufacturing a package of flexible sheet material, having an upper end, a lower end and two sides, in which a transverse sealed region is formed across one end of the package, wherein said sealed region defines a transverse interior profile adjacent said end of the package, in which there is a gradual transition between the sides of the package and the transverse direction. Of course, the end provided with the seal by the above apparatus, sealing member and process, is that intended to be the bottom end in use by a consumer. However, it may not be the bottom end during manufacture, storage, shipping etc. The profile of the seal for the opposite end of the package may be plain, ie. a single seal of uniform depth extending across the package, or may have any desired profile such as that in accordance with the first invention disclosed herein. It will be appreciated that whilst the packages have been defined as having upper ends at which the package is opened and lower ends on which product rest, • these terms are not to be regarded as limiting. There may be certain embodiments of the inventions where the package may be used, stored or transported in an inverted position, i.e. with the end at which the package is opened lowermost. Where the package has an increased width along at least part of the "lower end", holes may be provided for suspending the package in an inverted position. Various embodiments of the inventions will now be described by way of example with reference to the accompanying drawings in which: Figure 1 shows of a front view of a package embodying the present inventions; Figure 2 shows a back view of the package of figure 1; Figure 3 shows a cross-section view along line III- III of Figure 2 ; Figure 4 shows an apparatus for making a package such as shown in Figures 1 to 3; and Figure 5 shows the end profile of a sealing member of the apparatus of Figure 4. A package embodying the present inventions will now be described with reference to Figures 1 to 3. The package 2 is generally in the form of a tube having a front face 4 and back face 6 which are sealed together at their ends by two transverse seals 8 and 10 at opposed ends of the package. The tube is completed by a longitudinal seal 12, extending along the middle of the back face 6 between the two transverse seals 8 and 10. The top transverse seal 8 has a straight outer profile 14 and an inverted V-shaped inner profile 16 as shown in Figures 1 and 2. The apex 18 of the V-shaped inner profile 16 is in a middle region of the seal 8 and defines an area of weakness 20 from which the package can be opened as described below. The apex 18 is not a sharp point but in the nature of a flattened curve, and the area of weakness extends generally between the dotted lines shown on Figure 1. The two extremities 22 of the top transverse seal 8 have a greater depth than that at the area of weakness 20 and the depth of the seal increases gradually from this area to the two extremities. To open the top transverse seal 8, so that product may be removed from the package, the front and back faces 4 and 6 ' of the package are grasped by the user in the region of the weakness 20 and pulled in opposed directions. The top transverse seal 8 opens first at the area of weakness 20 since the least opening force is required here. As the user continues to pull the faces 4 and 6 in opposite directions the rest of the seal 8 is separated so that the top of the package is open. Since the area of weakness 20 defines the region at which the package first opens, a gradual application of force can be used to open the package so that tearing can be prevented. In cases where the package has a sufficient gas content, the package may alternatively be gently squeezed so that the gas in the package exerts pressure on the top transverse seal 8. Since the area of weakness 20 defines the weakest point of that seal, the gas will be forced out of the package in this area to define an initial opening. Once this initial opening has been defined, the rest of the seal is opened by pulling the front and back faces 4 and 6 in opposite directions. The bottom transverse seal 10, like the top transverse seal 8 has a straight outer profile 21, but the inner profile is in the shape of a generally symmetric curve 24 as shown in figures 1 and 2. As can be seen, the curve 24 defines a gradual transition 26 in the interior of the package between the bottom of the package and each of the two adjacent sides 28 and 30. It should be noted that whilst this seal 10 has its narrowest depth 32 in the middle region of the seal, this depth is greater than that of the area of weakness 20 of the top seal so that area of weakness 20 is the weakest point of the package. With the bottom seal 10 shaped as shown, small pieces of product may easily be removed from the package since there are no right angled corners for the small pieces of product to get caught in. Rather the product tends to rest on the lowest part of the seal ie. the apex of the curve 24 which is in the middle region of the package so that small pieces of product can easily be removed. The longitudinal seal 12 extends between the transverse seals and is stronger than the area of weakness 20 of the top transverse seal 8. The longitudinal seal 12 is formed by inside face to inside face contact between the edges of the sheet material forming the package. The longitudinal seal 12 is then folded so as to lie flush with the back face of the package and the ends 34 of the longitudinal seal 12 are bonded to the transverse seals 8 and 10 so as to increase the strength of the longitudinal seal in these regions (traditionally a weak area in packages of this kind) . Of course, the seal can be arranged so as to provide a longitudinal seal having an inner face to outer face configuration. All of the seals include longitudinal ribs 36 along their length which increase the strength of the seals and provide a decorative effect. The package 2 is made from flexible sheet material such as polypropylene film which is in itself airtight as are the seals so that the package as a whole is airtight. Thus the freshness of the product contained in the package can be assured. Apparatus for manufacturing such a package will now be described with reference to Figures 4 and 5. This apparatus is suitable for manufacturing the package using a vertical form-fill technique and is largely conventional. Packages are formed from a continuous sheet of flexible polypropylene sheet material 40 which is vertically fed in a downward direction through die 42 which shapes the sheet material 40 into a generally tubular form. The tubular sheet material advances through a longitudinal sealing unit 44 which seals the two longitudinal sides 46 of the tubular sheet material together in inner face to inner face configuration. This sealing unit 44 comprises a rotable member 47 arranged externally of the tubular material which cooperates with a member 48 arranged internally of the tubular material. One or both of the members 47 and 48 comprising the sealing unit 44 incorporate a heating element (not shown) to form the longitudinal seal. Furthermore one or both of the members 47 and 48 may incorporate ridges to provide ribs 36. The longitudinally sealed tube is then passed to a transverse sealing and cutting unit 50 which is shaped so as to form the top transverse seal 8 of one package along with the bottom transverse seal 10 of an adjacent package. The sealing and cutting unit 50 comprises two parts 52 and 54, one arranged on either side of the tubular sheet. The first part 52 is in the form of a fixed anvil and does not move during either the cutting or sealing action. The second part 54 is reciprocably movable by means of e.g. a hydraulic actuator 56, although both parts 52 and 54 could be movable if desired. One or both of the parts 52 , 54 have an end profile 55 (sealing face) which defines a shape as shown in Figure 5, corresponding to the bottom seal shape of one package and the top seal shape of another, either side of a separating line 58. When the plastics material is pressed between the two faces, a top seal is formed on one package whilst a bottom seal is formed on an adjacent package. The second part 54 also incorporates a blade (not shown) which is normally flush or below the plane of its sealing face. When the first and second parts 52 and 54 are urged together so that the desired seals are formed, the blade is arranged so as to move toward the sealing face 55 of the first part 52 to thereby cut the formed seal in two, along the separating line 58 to separate a formed package from the adjacent package which is still in the process of being formed. The blade is withdrawn to its original position (ie. a non-cutting position) when the cutting operation is completed. The movement of the second part 54 and the blade is controlled by conventional means. One or both of the two parts of the sealing and cutting unit 50 have associated heating elements so as to heat the sealing faces in order to form the transverse seals. The apparatus has a conduit 60 through which product is able to pass, in the direction of arrow 62, down toward a partially formed package. The inner diameter of the conduit 60 is such that the product to be packaged is able to easily pass through the conduit 60. The apparatus may also incorporate means (not shown) for injecting a volume of gas into the package just before it is formed such that the gas is retained in the package after it is fully sealed. The gas may be air, nitrogen, carbon dioxide or any other suitable gas. The following steps are carried out when-using the apparatus as described above in order to form a package. Firstly the sheet material is folded into a tubular form by die 42. A longitudinal seal is the made along the tubular sheet material to form the back seal 12 of the package. At the next stage, the bottom seal 10 is formed by the sealing and cutting unit 50 and using conduit 60 the partially formed package is filled with product. The package is moved stepwise through the apparatus so that the top transverse seal 8 can be formed. The bottom seal 10 of the adjacent bag is simultaneously formed as that top transverse seal. The package is then cut between the top transverse seal 8 of one package and the bottom seal 10 of the next package. The completely formed package can then be removed from the apparatus. It will be apparent to the man skilled in the art that various modifications to the design of the package and the apparatus can be carried out within the scope of the invention. For example the package may be formed by the horizontal pouch or pillow pouch technique as opposed to the described vertical form-fill technique. For example, in the case of the horizontal pouch technique the following steps would be carried out: a) forming a U-shaped channel from flexible sheet material; b) forming two parallel seals, the axes of which are perpendicular to the longitudinal axis of the channel; c) filling a compartment of the channel formed by the two parallel seals with product; and d) sealing the open end of the product filled compartment to thereby form a package, wherein at least one of the seals formed in steps b) or d) is such that the seal is formed between two portions of the sheet material, the seal being adapted to be broken by separating the two portions of sheet material to gain access to the interior of the package, said seal being formed in such a way as to have a region of weakness intermediate its extremities where the force required to separate the material portions is substantially less than that required adjacent the extremities, and/or wherein at least one of the seals formed in steps b) or d) is such that the seal forms a transverse sealed region across one end of the package, said sealed region defining a transverse interior profile adjacent said end of the package, in which there is a gradual transition between the sides of the package and the transverse direction. Alternatively in the case of the pillow pouch technique, the following steps would be carried out; a) placing product on flexible sheet material; b) forming a tube about the product; c) sealing the tube along a longitudinal seam thereof formed by overlapping edges of the sheet material; d) forming seals transverse, with respect to the longitudinal axis, on either side of the product to form the package, wherein at least one of the transverse seals is adapted to be broken by separating two portions of sheet material to gain access to the interior of the package, the seal being formed in such a way as to have a region of weakness intermediate its extremities where the force required to separate the material portions is substantially less than that required adjacent the extremities, and/or wherein at least one of the transverse seals forms a transverse sealed region across one end of the package, wherein said sealed region defines a transverse interior profile adjacent said end of the package in which there is a gradual transition between the sides of the package and the transverse direction. In both of these techniques as well as the vertical form-fill technique described earlier, the cutting means may be associated with the relevant sealing means or may alternatively be provided as a separate unit downstream of the sealing means. It will also be appreciated that the shape of the seals can be varied so as to be asymmetric and may have any suitable shape. Furthermore the point of weakness may not necessarily be defined in terms of a least depth but may be defined in terms of least bond strength by for example varying the quantity of adhesive used in the region of weakness or in the case of heat sealing, the intensity of heat applied to the. seal may be less in one region to define area of weakness. Instead of the inside face to inside face configuration of the longitudinal seal, it will be appreciated that an inside face to outside face configuration is also possible.

Claims: Claims 1. A sealed package of flexible sheet material, said package having a transverse seal across one end, between two portions of sheet material, which seal is intended to be broken by separating the two portions of material so as to gain access to the interior of the package, wherein said transverse seal has a region of weakness intermediate its extremities where the force required to separate the material portions is substantially less than that required adjacent said extremities. 2. A package as claimed in claim 1, wherein said region of weakness is defined by a reduced seal strength relative to the strength of the transverse seal over at least a substantial part of its transverse extent. 3. A package as claimed in claim 1 or 2 , wherein said region of weakness provides a region where opening of the package occurs in preference to any point along any other seals in the package. 4. A package as claimed in any preceding claim, wherein the region of weakness is provided by a region of decreased bonding strength of the seal. 5. A package as claimed in any of claims 1 to 4 wherein the region of weakness is defined by a region where the depth of the transverse seal is less than adjacent the extremities of the seal. 6. A package as claimed in claim 5, wherein the transverse seal has a curved or V-shaped profile with an apex region defining the region of weakness. 7. A package as claimed in any preceding claim, wherein the transverse profile of the interior of the package adjacent its lower end is defined by a transverse seal extending between the two sides, wherein said transverse profile is such that there is a gradual transition between each of the sides and the transverse direction. 8. A package as claimed in claim 7, wherein the gradual transition is provided by the lower seal having a curved inner profile. 9. A package as claimed in claim 8, wherein the lowest point of the curve lies in the middle region of the lower seal. 10. A package as claimed in claim 7, wherein the gradual transition is provided by at least one straight line extending downwardly from each side. 11. A package as claimed in any one of claims 7 to 10, wherein there is provided a central portion spaced a substantial distance down the package from the start of each gradual transition whereby in normal use, product tends to* collect in this central portion. 12. A package as claimed in any one of claims 7 to 11, wherein the weakest part of the bottom seal is equal to or greater in strength than the weakest part of the transverse seal forming the top seal. 13. A package as claimed in any preceding claim wherein said sheet material comprises one of the following materials: plastics film for example polypropylene, paper, foil material or laminates of any one or more of the preceding materials. 14. A package as claimed in any preceding claim, wherein the or each seal is formed by means of heat and/or pressure. 15. Packaging apparatus for manufacturing a sealed package of flexible sheet material, comprising sealing means for forming a transverse seal between two portions of the sheet material across one end of the package which is adapted to be broken by separating the two portions of material so as to gain access to the interior of the package, wherein the sealing means is such that the transverse seal has a region of weakness intermediate its extremities where the force required to separate the material portions is substantially less than that required adjacent said extremities. 16. A process for manufacturing a sealed package of flexible sheet material in which a transverse seal is formed between two portions of the sheet material across one end of the package, the seal being adapted to be broken by separating the two portions of material so as to gain access to the interior of the package, wherein said seal is formed in such a way as to have a region of weakness intermediate its extremities where the force required to separate the material portions is substantially less than that required adjacent said extremities. 17. A sealing member for forming a transverse seal across an end of a package of flexible sheet material, the sealing member having a profile which defines a seal whose depth in a region intermediate its extremities is less than that adjacent its extremities. 18. A sealing member as claimed in claim 17, wherein said member is arranged to simultaneously form a bottom transverse seal of one package and a top transverse seal of an adjacent package. 19. Apparatus for manufacturing a package of flexible sheet material comprising a pair of sealing members as claimed in any one of claims 17 or 18. 20. A package of flexible sheet material comprising an upper end, a lower end and two sides, the transverse profile of the interior of the package adjacent its lower end being defined by a transverse seal extending between the two sides, wherein said transverse profile is such that there is a gradual transition between each of the sides and the transverse direction. 21. A package as claimed in claim 20, wherein the gradual transition is provided by the lower seal having a curved inner profile. 22. A package as claimed in claim 21, wherein the lowest point of the curve lies in the middle region of the lower seal. 23. A package as claimed in claim 20, wherein the gradual transition is provided by at least one straight line extending downwardly from each side. 24. A package as claimed in any one of claims 20 to 23, wherein there is provided a central portion spaced a substantial distance down the package from the start of each gradual transition whereby in normal use, product tends to collect in this central portion. 25. A package as claimed in any one of claims 20 to 24, wherein the weakest part of the bottom seal is equal to or greater in strength than the weakest part of a transverse seal forming a top seal. 26. A package as claimed in any one of claims 20 to 25, wherein said sheet material comprises one of the following materials: plastics film for example polypropylene, paper, foil material or laminates of any one or more of the preceding materials. 27. A package as claimed in any one of claims 20 to 26, wherein the lower seal is formed by means of heat and/or pressure. 28. Apparatus for manufacturing a package of flexible sheet material, comprising sealing means for forming a transverse sealed region across an end of the package wherein, the sealing means defines a transverse interior profile adjacent the end of the package in which there is a gradual transition between the sides of the package and the transverse direction. 29. A process for manufacturing a package of flexible sheet material, having an upper end, a lower end and two sides, in which a transverse sealed region is formed across one end of the package, wherein said sealed region defines a transverse interior profile adjacent said end of the package, in which there is a gradual transition between the sides of the package and the transverse direction. 30. A sealing member for forming a transverse seal across an end of a package of flexible sheet material, the sealing member having a profile such that a seal is defined which provides a transverse interior profile at the package adjacent said end, in which there is a gradual transition between the sides of the package and the transverse end. 31. A sealing member as claimed in claim 30, wherein said member is arranged to simultaneously form a bottom transverse seal of one package and a top transverse seal of an adjacent package. 32. Apparatus for manufacturing a package of flexible sheet material comprising a pair of sealing members as claimed in claim 30 or 31.

Inventors: BATCHEN DAVID, PALMER CHRISTOPHER, PALMER MARTIN, BATCHEN, DAVID, PALMER, CHRISTOPHER, PALMER, MARTIN
Applicants: DALGETY SPILLERS FOODS, DALGETY SPILLERS FOODS LIMITED
Application year: 1992
Main classification: B65D75
IPC codes: B65B9, B65B51, B65B61, B65D75