Patent Publication Number: US-2018050829-A1

Title: Method for sealing a flexible package of collapsible type

Description:
FIELD OF THE INVENTION 
     The present inventive concept relates to a method for sealing packages. More specifically, the present inventive concept relates to a method for sealing a flexible package of collapsible type. 
     BACKGROUND ART 
     A package of collapsible type typically comprises a filling chamber in which a product, such as a liquid, may be contained. During a filling procedure of the package, the product may be filled by inserting a nozzle in a filling channel of the package. Subsequently, the package has to be sealed so that the product cannot escape from the filling chamber. By way of example, the sealing may be performed by means of welding, whereby the package is placed between engagement surfaces of a pair of jaws which are arranged to engage with each other and thereby exert pressure on a portion of the package for providing a seal. 
     The jaws may be heated. For example, GB943457A discloses how to form a seam between unsupported thermoplastic sheets by using heated jaws. The sheets are applied together and a seam is provided by utilizing continuously heated welding jaws. By means of additional pressing jaws, a subsequent second hot pressing is performed on a part of the width of the seam so as to remove gas bubbles or blisters which are located within the seam. 
     However, the process disclosed in GB943457A is a comparatively slow process and there is need for a faster method and device for providing seals. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present inventive concept to provide a more efficient method for sealing packages. Another object is to provide a method which provides more reliable seals on packages. 
     According to a aspect of the invention, there is provided a method for sealing a flexible package of collapsible type. The method comprises providing a first seal extending transverse a filling channel of the flexible package and providing a second seal extending transverse a filling channel of the flexible package. The second seal overlaps said first seal such that a combined seal is provided comprising a top portion formed solely by the first sealing unit, an intermediate portion formed by the first and the second sealing unit, and a bottom portion formed solely by the second sealing unit. The method further comprises setting operating parameters comprising a time parameter, a temperature parameter and a pressure parameter for providing said first seal and for providing said second seal such that a sealing characteristic below a threshold value is obtained in said top portion and said bottom portion and such that a sealing characteristic equal to or above the threshold value is obtained in said intermediate portion. 
     By a flexible package of collapsible type is here meant a package or container which may assume a collapsed state when the package is empty, i.e. non-filled. Moreover, the package is arranged to be filled by a product whereby it assumes an expanded state. The package comprises at least two flexible walls. Two opposing side walls of the package are flexible and may be joined in connecting portions to define a compartment. Preferably, the walls are thin. Additionally, there may be a bottom wall. A volume of the compartment depends on the relative position of the opposing side walls. The shape of the flexible package may correspond to the shape of the product. Optionally, there may be a handle portion provided o n the flexible package for carrying the package. Additionally, there may be gas-filled ducts provided in the connecting portions of the package for increasing the stability of the package and for improving the handling of the package. The handle portion may be formed by the gas-filled duct. 
     The material of the package may comprise several layers. For example, there may be a fluid-tight layer and a gas-tight layer. The layers may comprise materials having different melting points. 
     The material of the package may comprise at least one of a mineral, aluminium, and a plastic material, for example polymers, such as polyolefin. In a first non-limiting example, the package comprises a layer comprising plastic material and a chalk material. In a second non-limiting example, the package is solely comprised out of a plastic material. In particular, the package may comprise a recyclable material. The material of the package may comprise a filler and a binder. it is appreciated that the package may comprise other materials and that the choice of materials are not limited to the examples presented above. Preferably, however, the flexible package comprises a material which is arranged to melt above a certain melting temperature. 
     The flexible package may be filled with a product, such as a product in liquid form or in powder form. The product may be a liquid food product such as dairy products, such as milk, water, juice, wine, lemonade, a beverage, etc. It is understood that other similar products suitable for be contained in the flexible package may be used. 
     The first and/or second seals are provided for retaining the product in the flexible package. The first and/or second seals may extend transversely across the entire filling channel. In particular, at least one of the top portion, the intermediate portion and the bottom portion may extend across the entire filling channel. The first and/or second seals may extend transversely across a portion of an upper portion of the flexible package, wherein the package is provided in an upright position. Alternatively, the first and/or second seals may extend transversely across the entire upper portion of the flexible package. 
     Sealing may be provided by means of welding. The first and second seals may be provided by means of subjecting a portion of the flexible package to at least one of heat, pressure, etc. during a predetermined time duration. The amount of heat, the amount of pressure, and the predetermined time duration may be dependent on the type of package, the material comprised in the package, a thickness of walls of the package, the type of seal to be provided, a desired level of quality of the seal, etc. The seal may be provided by melting portions of the material of the flexible package. In a first example, a portion of a plastic material comprised in the package may melt for providing the seal. In a second example, a portion of a layer comprised in a laminate of layers of the package may melt for providing the seal. In the latter example, the different layers in the laminate may have different melting points. 
     Optionally, the seal may be cooled after heating the seal by means of a cooling unit. 
     According to a first example, the strength is constant throughout the first as well as the second seal. Thereby, the strength of the overlapping intermediate portion may also be constant. The strengths of the first and the second seal may be the same or, alternatively, different. 
     According to a second example, the strengths are varying in portions or throughout the first and/or the second seal. The strengths may be varying along a transverse direction of the package. Alternatively, or additionally, the strengths may be varying along a longitudinal direction of the package. The strength may be decreasing towards outer edges of the first and the second seal. Thereby, a smoother transition from the seal to unsealed portions of the flexible package may be provided. 
     In accordance with the inventive concept, the method is implemented by a sealing operation which is split in two separate operations by utilizing two sealing units. Indeed, the sealing operation is partly performed at the first sealing unit and is partly performed at the second sealing unit. 
     The sealing operation may be performed intermittently. The second seal may be provided on a first package already having a first seal simultaneously as the first seal is provided on a second package. Subsequently, the second seal may be provided on the second package simultaneously as the first seal is provided on a third package, etc. Thus, the inventive method may provide seals on flexible packages more efficiently. In particular, the inventive method may operate faster than known methods in the prior art. 
     Alternatively, the sealing operation may be performed continuously. 
     The sealing may be controlled by at least one parameter. The parameter may be a temperature parameter, a pressure parameter and a time parameter as will be described in more detail below. Preferably, the temperature parameter and the pressure parameter are chosen such that the flexible package does not become damaged during the sealing operation at the first and/or sealing unit. Optionally, a cooling unit for cooling the package in a region comprising the first and/or second seal may be provided. Moreover, the temperature parameter and the pressure parameter may be chosen below certain maximal temperature and maximal pressure parameter values. A typical problem in the prior art is that, even if the sealing operation itself is highly improved, it still requires more, or much more, time than any of the other operations performed by other units comprised in a production line which comprises a sealing unit for performing a sealing operation as well as additional units for performing other operations, such as a package opening operation, a filling operation, transport operations, package adjustment operations, etc. Said operations may be performed by a package opening unit, a filling unit, a transport unit, package adjustment units, etc. The operations may be performed simultaneously; for example, while the filling channel of a first package is opened up, a second package is filled and a third package is sealed, etc. In the prior art, each of the above mentioned operations are typically performed at separate, stationary stations. By splitting the sealing operation in two operations, which are performed at the first and the second sealing unit according to the present inventive concept, the downtime at the respective sealing unit may be reduced considerably. By downtime we here mean an additional time duration for performing the sealing operation exceeding the time duration of other operations in the production line. In particular, in an intermittent production line the downtime may be significant since the operation taking the longest time determines the latency in the production. According to a non-limiting example, the time duration required for sealing the package may be determined if at least one of the temperature parameter and the pressure parameter are given. 
     Operating parameters comprising a time parameter, a temperature parameter and a pressure parameter are set for providing said first and seal and for providing said second seal such that a sealing characteristic below a threshold value is obtained in said top portion and said bottom portion and such that a sealing characteristic above the threshold value is obtained in said intermediate portion. Thereby, a sufficient seal may be provided in the intermediate portion. A quality of the seal may be adjusted by adjusting the time parameter, the temperature parameter and the pressure parameter. By way of example, the seal may be improved by at least one of using a higher temperature, using a higher pressure, and by letting the first and/or the second sealing unit operate during a longer period of time. Clearly, this example is preferably subject to the restrictions explained in the above regarding keeping the flexible package undamaged. 
     In view of the above, the sealing operation may be made much more efficient in the production line which comprises one or several sealing operations. Also, the capacity of the production line may be increased without the need of adding additional multiple lines, such as a plurality of parallel lines. It is noted that the capacity of a filling machine which implements the operations discussed above is inter alia determined by the time required to perform these operations, and more specifically by the operation requiring the longest time to perform. 
     The sealing is performed such that neither the first nor the second seal by itself represents a sufficient seal; rather, both the first and the seals are needed to provide a sufficient seal. By sufficient seal is here meant that the seal, or combined seal, fulfils a set of seal criteria. The seal criteria may comprise a strength criterium, a width criterium, a length criterium, a thickness criterium, a criterium with respect to environmental conditions such as temperature or humidity, etc. The sealing operation is performed such that the two seals are offset, whereby a combined seal is formed in which a sufficient seal is provided. The combined seal comprises an intermediate portion wherein the first and the second seal are overlapping. In the intermediate portion the combined action of the first sealing unit and the second sealing unit is sufficient to obtain a sufficient seal. By action by a sealing unit is here meant that the flexible package is subject to a heating action and a pressure action during a time duration. 
     The first and the second seals may be perform by sealing operations during a first and a second sealing time, respectively, for forming a total sealing time. The total sealing time may be a sum of the first and the second sealing times. A sufficient seal may be provided once the total sealing time is longer than a certain time period. The time period may be predetermined. 
     The combined seal comprises three portions: a top portion having an insufficient seal, an intermediate portion having a sufficient seal, and a bottom portion having an insufficient seal. Hence, another advantage of the present inventive concept is that the device may provide a gradual transition from a strong seal to portions having no seal on the flexible package. More specifically, the intermediate portion may provide a stronger seal than the top portion and the bottom portion. Additionally, the top portion and the bottom portion may provide seals next to unsealed portions of the flexible package. As a consequence, there may be provided a seal which in a longitudinal direction of the flexible package has an unsealed portion, a bottom portion, an intermediate portion, a top portion, and an unsealed portion, thereby providing the sequence: no seal, an insufficient seal, a sufficient seal, an insufficient seal, and no seal. In particular, a direct transition from a sufficient seal to no seal may be avoided and a more gentle transition may be provided. As a consequence, the flexible package may be subject to less strain. Thereby, the device provides a more reliable seal. 
     An additional advantage of inventive method is that it provides a seal which may exhibit an improved strength. Indeed, by providing a first and a second seal, the combined seal may provide a stronger seal. 
     According to one embodiment the method further comprises transferring the flexible package from the first sealing unit to the second sealing unit. By means of this embodiment, the method may provide a seal in an even more efficient manner. By way of example, a first flexible package which has obtained a first seal may be transferred from the first sealing unit to the second sealing unit for obtaining a second seal, while a second flexible package is transferred to the first sealing unit for obtaining a first seal. The same procedure may be repeated for a plurality of flexible packages which are fed into a filling machine, or production line, comprising the device according to the present inventive concept and other units as described in the above. 
     According to one embodiment, the first seal may be provided with a width in the range of 1 to 5 millimeters. According to another embodiment, the second seal may be provided with a width in the range of 1 to 5 millimeters. According to yet another embodiment, the intermediate portion may be provided with a width in the range of 1 to 5 millimeters. The width may be measured in a longitudinal direction of the flexible package. Alternatively, the width may be measured in a transverse direction of the flexible package. By means of these embodiments, the formation of blisters may be prevented since any vapor formed by residues during the sealing operations is allowed to escape sideways. In a non-limiting example, each of the first seal and the second seal has a width of 4 millimeters and the offset is 2 millimeters, resulting in an overlapping portion of 2 millimeters. 
     According to one embodiment, the first and second seals are provided extending in parallel. Thereby, the intermediate portion, and hence a sufficient seal, may be provided transverse the entire filling channel. 
     According to one embodiment, the first and/or second seal may be provided by a sealing unit comprising a permanently heated sealing jaw. The heated sealing jaw may provide the first and/or second seal by transferring heat energy to the flexible package where the first and/or the second seal are to be located. The heat energy may be utilized for melting portions of a material comprised in the flexible package, e.g. in side walls of the package. In a non-limiting example, the permanently heated sealing jaw is formed by a metal. 
     According to one embodiment, the first and/or second sealing unit comprises an abutment jaw having an engagement portion arranged to engage with the flexible package for providing the first and/or second seal. By means of this embodiment, the first and/or the second seal may be provided by pressing the flexible package between the abutment jaw and the heated sealing jaw where the first and/or the second seal are to be located. 
     The abutment jaw of the first and/or second sealing unit may comprise a tapering engagement notch. The notch may determine the width of the first and/or the second seal. In a non-limiting example, the tapering engagement notch is formed by an elastic material. In another non-limiting example, the tapering engagement notch is formed by a metal. 
     The permanently heated sealing jaw and the abutment jaw in the first sealing unit may be offset with respect to the permanently heated sealing jaw and the abutment jaw in the second sealing unit. Thereby, the first sealing unit may provide a first seal and the second sealing unit may provide a second seal, whereby the first seal is offset with respect to the second seal. The offset of the heated sealing jaw and the abutment jaw may be provided by displacing at least one of the heated sealing jaw and the abutment jaw from each other. The displacement may be carried out in a vertical direction so that the first and the second seals are offset in a longitudinal direction of the package, given that the package is sealed in an upright position. 
     According to one embodiment, the first and second sealing units are stationary. Thereby, the flexible package has to be transferred to the first and second sealing units. By way of example, the transfer may be provided by means of the transfer unit described in the above. 
     According to an alternative embodiment, the first and/or second sealing unit are movable. 
     In a first example, the first and second sealing units are provided separated in space. In a second example, the first and second sealing units are provided at the same location. 
     According to yet another embodiment, at least three sealing units are provided for providing at least three seals. The at least three seals are combined into a combined seal, thereby comprising one or several overlapping portions. According to this embodiment, the transition from the seal to the unsealed portions of the flexible package may become even more smooth. 
     It is noted that the steps of the method does not have to be performed in the exact order disclosed above. 
     Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein. All references to “a/an/the [element, device, component, means, step, etc]” are to be interpreted openly as referring to at least one instance of said element, device, component, means, step, etc., unless explicitly stated otherwise. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above, as well as additional objects, features and advantages of the present invention will be better understood through the following illustrative and non-limiting detailed description of preferred embodiments of the present invention, with reference to the appended drawings, where the same reference numerals will be used for similar elements, wherein: 
         FIG. 1  is a schematic side view of a production line comprising an embodiment of a device for sealing a flexible package according the present inventive concept. 
         FIG. 2  is a perspective view of the production line in  FIG. 1 . 
         FIG. 3  is a schematic view of the permanently heated sealing jaw and the abutment jaw comprised in the first and the second sealing units in  FIG. 1  and  FIG. 2 . 
         FIG. 4  is a schematic side view of the first and the second sealing unit comprised in the device in  FIGS. 1 and 2 . 
         FIG. 5 a    is a schematic front view of a flexible package wherein a seal has been provided in accordance with an embodiment of the inventive concept. 
         FIG. 5 b    is a schematic front view of another flexible package wherein a seal has been provided in accordance with another embodiment of the inventive concept. 
         FIG. 6  is a flow chart illustrating a method for sealing a flexible package according to an embodiment of the present inventive concept. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Next, the inventive concept will be described with reference to  FIGS. 1 and 2  which illustrate a schematic side view and a schematic perspective view, respectively, of a production line  100  for filling and sealing a plurality of flexible packages  200  of collapsible type. As will be detailed below, the production line  100  comprises an embodiment of a device for sealing a flexible package according the present inventive concept. The production line  100  may be referred to as a filling machine. 
     In the following, the wording “package”  200  and wording “flexible package”  200  will be used interchangably. 
     The plurality of flexible packages  200  may be provided from a material web according to methods well-known to a person skilled in the art. According to the present embodiment, the packages  200  are provided to the production line  100  in the form of a continuous web of packages (not shown). The web of packages are rolled up to be supplied in roll form to the production line  100 . 
     The rolls are arranged to be unwound and fed to the production line  100 . Initially, the packages  200  may be fed edgewise and subsequently the packages  200  may be fed intermittently broadwise. 
     The production line  100  comprises a filling unit  110 , a first sealing unit  120 , a second sealing unit  130  and a gas-filling unit  140 . The first sealing unit  120  and the second sealing unit  130  are comprised in an embodiment of the inventive device for sealing the flexible package  200 . The packages  200  are handled at each of these units in consecutive order in a direction as indicated by the arrow X in  FIGS. 1 and 2 . The units  110 ,  120 ,  130 ,  140  are arranged along a horizontal direction which is a longitudinal direction of the production line  100 . Moreover, according to the present embodiment the units  110 ,  120 ,  130 ,  140  are arranged essentially equidistantly from each other. 
     There is also provided a transfer unit for transferring the flexible packages  200  between the units  110 ,  120 ,  130 ,  140 . In particular, the transfer unit is arranged to transfer the packages  200  from the first sealing unit  120  to the second sealing unit  130 . For clarity, the transfer unit has been left out from  FIGS. 1 and 2 . According to one example, the transfer unit is arranged to transfer the flexible packages  200  between the units  110 ,  120 ,  130 ,  140  by means of an essentially semi-circular movement, whereby the flexible packages  200  arrive at each unit  110 ,  120 ,  130 ,  140  by means of an substantially vertical motion. According to another example, the transfer unit is arranged to transfer the flexible packages  200  between the units  110 ,  120 ,  130 ,  140  by means of an essentially horizontal movement, whereby the flexible packages  200  arrive at each unit  110 ,  120 ,  130 ,  140  by means of an substantially horizontal motion. 
     In  FIGS. 1 and 2 , two pairs of flexible packages  200  are displayed, but it is understood that there may be more packages  200  in the production line  100  simultaneously. In particular, there may be a pair of flexible packages  200  at the filling unit  110  and a pair of flexible packages  200  at the gas-filling unit  140 , while the pairs of flexible packages  200  are being located at the sealing units  120  and  130 . 
     It is noted that for clarity only a part of the production line  100  is shown in  FIG. 1  and  FIG. 2 . Clearly, there may be another similar part of the production line (not shown) for providing filling and sealing of the other package  200  of the pair of flexible packages. In fact, there may be a plurality of production lines for providing filling and sealing of a plurality of flexible packages  200 . By way of example, each production line may be arranged to fill and seal a pair of flexible packages. The plurality of production lines may be provided in parallel. 
     In the following, a single package  200  will be described, but it is clear that any number of packages  200  may be treated similarly. 
     The filling unit  110  is arranged to fill the flexible package  200  with a liquid product. In a filling operation, a filling channel of the package  200  is opened by means of a suction cup, thereby forming an opening. The opening of the flexible package  200  is defined by two opposite side walls of the package. A filling nozzle (not shown) is then guided through a hole  112  formed between a first and a second gripping means into the filling channel via the opening of the flexible package  200 . More specifically, each gripping means comprises two prongs and, during the filling operation, the prongs on the first and the second gripping means are arranged to exert pressure on each other whereby the hole  112  is formed. The package  200  is filled when it assumes an upright position. The filling nozzle is introduced into the filling channel by means of a relative vertical displacement between the filling nozzle and the package  200 . 
     Before inserting the filling nozzle into the filling chamber of the package  200 , a top seal of the package  200  is arranged to be removed in order to access the filling channel of the package  200 . By way of example, this operation may be performed at a separate removal unit comprised in the production line  100 . Additionally, there is a separation unit (not shown) located before the filling unit  110  for separating the packages  200  from each other, i.e. wherein the web of packages  200  which provided on the roll are separated. In a non-limiting example, the edgewise feed referred to above may comprise the act of removing a top seal in order to open the filling channel of the package  200  as well as the act of separating the packages  200 . 
     In  FIG. 1  and  FIG. 2 , the flexible packages  200  are shown in a filled state and an unfilled state, respectively. However, with respect to  FIG. 2  it is realized that once the flexible packages  200  have passed the filling unit  110 , they have been filled with the liquid product as in  FIG. 1 , whereby the flexible packages  200  assume an expanded state wherein the side walls of each of the packages  200  are separated. 
     The first sealing unit  120  is arranged to provide a first seal to the flexible package  200 . The first sealing unit  120  comprises a first abutment jaw  122  and a first permanently heated sealing jaw  124 . Additionally, the first sealing unit  120  comprises a first protection cover  125  for keeping the flexible package  200  separated from the first permanently heated sealing jaw  124 . 
     Similarly, the second sealing unit  130  is arranged to provide a second seal to the flexible package  200 . The second sealing unit  130  comprises a second abutment jaw  132  and a second permanently heated sealing jaw  134 . Additionally, the second sealing unit  130  comprises a second protection cover  135  for keeping the flexible package  200  separated from the second permanently heated sealing jaw  134 . 
     According to present embodiment, the first  120  and the second  130  sealing unit comprises the same components.  FIG. 3  is a schematic view of the first  122  and the second  132  abutment jaw and the first  124  and the second  134  permanently heated sealing jaw which are comprised in the first  120  and the second  130  sealing units in  FIGS. 1 and 2 . It is understood that the abutment jaws  122 ,  132  and the permanently heated sealing jaws  124 ,  134  have an extension in a transverse direction, i.e. in a direction normal to the cross-sectional planar surface displayed in  FIG. 3 . In  FIG. 2  it may be seen that, according to the present embodiment, a width of the abutment jaws  122 ,  132  as well as a width of the permanently heated sealing jaws  124 ,  134  substantially correspond to a width of an upper portion of the package  200 . 
     Clearly, according to an alternative embodiment, the first  120  and the second  130  sealing unit may comprise different components. For example, the abutment jaws and/or the sealing jaws may be designed differently. 
     The first abutment jaw  122  comprises a first tapering engagement notch  126  and the second abutment jaw  132  comprises a second tapering engagement notch  136 . The notch  126  and  136  determine a width of the first and the second seal, respectively. According to the present embodiment, the tapering engagement notches  126 ,  136  are formed by an elastic material. 
     In  FIG. 4  there is illustrated a schematic side view of the first sealing unit  120  to the left and the second sealing unit  130  to the right. It is also illustrated how to provide a combined seal  300  of the flexible package  200  extending transverse the filling channel of the flexible package  200  at the upper portion thereof. The resulting combined seal  300  comprises a first seal  302  and a second seal  304 . 
     Incidentally, note that the positions of the first  120  and second  130  sealing units in  FIG. 4  have been interchanged as compared to  FIGS. 1 and 2 . 
     As shown in the enlargement  4   a  in  FIG. 4 , the first sealing unit  120  is arranged to provide the first seal  302  on the flexible package  200  by means of the first abutment jaw  122  and the first permanently heated sealing jaw  124 . More specifically, in operation the first abutment jaw  122  is pressed towards the first permanently heated sealing jaw  124  whereby the first seal  302  is provided on an upper portion of the flexible package  200 , which in operation is placed between the first abutment jaw  122  and the first permanently heated sealing jaw  124 . A first portion of the material in the upper portion of the package  200  is melted by the action of the first abutment jaw  122  and the first permanently heated sealing jaw  124  for forming the first seal  302 . 
     Moreover, in the enlargement  4   b  in  FIG. 4  it is shown that the second sealing unit  130  is arranged to provide the second seal  304  on the flexible package  200  by means of the second abutment jaw  132  and the second permanently heated sealing jaw  134 . Analogously to the first sealing unit  120 , in operation the second abutment jaw  132  is pressed towards the second permanently heated sealing jaw  134  whereby the second seal  304  is provided on an upper portion of the flexible package  200 , which in operation is placed between the second abutment jaw  132  and the second permanently heated sealing jaw  134 . A second portion of the material in the upper portion of the package  200  is melted by the action of the second abutment jaw  132  and the second permanently heated sealing jaw  134  for forming the second seal  304 . Part of the second portion overlaps with the first portion. 
     The second seal  304  is offset with respect to the first seal  302 . More specifically, the second seal  304  is displaced in a longitudinal direction of the flexible package  200  with respect to the first seal  302 . This offset is implemented by displacing the second sealing unit  130  by a distance D with respect to the first sealing unit  120  in a vertical direction as shown in  FIG. 4 . 
     Moreover, the offset is such that the first  302  and the second  304  seals are overlapping in a region of the upper portion of the package  200 , thereby forming an intermediate portion  316 . Hence, the combined seal  300  comprises three portions: a top portion  312  formed solely by the first sealing unit  120 , a bottom portion  314  formed solely by the second sealing unit  130 , and an intermediate portion  316  formed by the first sealing unit  120  as well as the second sealing unit  130 . 
     Thereby, the intermediate portion  316  provides a stronger part of the combined seal  300  than the top portion  312  and the bottom portion  314 . In particular, the intermediate portion  316  has been pressed and heated by the first  120  and second  130  sealing units during a longer time as compared to the top portion  312  and the bottom portion  314  which have been pressed solely by the first sealing unit  120  and the second sealing unit  130 , respectively. 
     In  FIG. 5 a    there is shown a schematic front view of a flexible package  200  in an upright position wherein a combined seal  300  has been provided on an upper portion of the flexible package  200  in accordance with an embodiment of the inventive concept. It is noted that the dimensions of the combined seal  300  have been exaggerated for illustrative purposes. According to this embodiment, the combined seal  300  extends across the entire package  200  in the transverse direction of the package. In particular, the combined seal  300  transverse a filling channel  210  of the package  200 , thereby sealing the product within a compartment  202  of the package  200  which is defined by the broken lines in  FIG. 5 a   . In particular, the intermediate portion  316  transverses the filling channel  210  of the package  200  for forming a sufficient seal. According to the embodiment in  FIG. 5 a   , the filling channel  210  also operates as an opening portion of the package  200 . 
     In  FIG. 5 b    there is shown a schematic front view of a flexible package  200  in an upright position wherein a combined seal  300  has been provided on an upper portion of the flexible package  200  in accordance with another embodiment of the inventive concept. The tilted lines in  FIG. 5 b    indicate a cross-sectional view of the package  200 . It is understood that the combined seal  300  comprises a first  302  and a second  304  seal as explained above, and thereby a top portion  312 , a bottom portion  314  and an intermediate portion  316 . The combined seal  300  transverses the filling channel  210  of the package  200 , thereby sealing the product within the compartment  202  of the package  200 . In particular, the intermediate portion  316  transverses the filling channel  210  of the package  200  for forming a sufficient seal. 
     It is clear that  FIG. 5 b    indicates an exemplary position of the combined seal  300  and that, according to alternative embodiments, the combined seal  300  may be located at different positions. For example, the combined seal  300  may be located closer to or farther away from the top of the package  200 . Also, the combined seal  300  may be shifted to the left or the right in  FIG. 5 b   . However, it is important that the combined seal  300  transverse the filling channel  210  within the package  200  for providing sufficient sealing of the package  200 . 
     The flexible package  200  according to the embodiment in  FIG. 5 b    further comprises a handle portion  220  which is formed by a gas-filled duct  222 . Moreover, the package  200  comprises an opening portion  230  comprising a tab which may be torn apart for allowing a user to access the product from the package  200 . 
     The gas-filling unit  140  is arranged to fill the package  200  with gas, such as air, in the duct  222  for forming the handle portion  220  of the package  200  in  FIG. 5 b   . The gas-filling unit  140  comprises a nozzle (not shown) for introducing air into the duct  222 . The gas-filling unit  140  is also arranged to seal the duct  222  at an upper portion thereof for containing the gas in the handle portion  220 . 
     Next, a method for sealing the flexible package  200  will be described according to an embodiment of the present inventive concept with reference to the flow chart in  FIG. 6 . The method may be implemented in the production line  100  which in particular comprises the first sealing unit  120  and the second sealing unit  130  as has been described in the above. The flexible package  200  is provided to the production line  100  from a web of packages as has been described above. 
     First, the flexible package  200  is transferred by means of the transfer unit (not shown) to the filling unit  110 . At the filling unit  110 , the flexible package  200  is filled with a product, such as a liquid product (Box  410 ). More specifically, a top seal is first removed from the package  200  for accessing the filling channel  210  of the package  200 . Thereafter, the filling channel  210  is opened by means of the suction cup, thereby forming an opening, and the filling nozzle is inserted into the filling channel  210  and the compartment  202  is filled with the product. The filling nozzle is subsequently removed from the filling channel  210 . 
     Thereafter, the flexible package  200  is transferred by the transfer unit from the filling unit  110  to the first sealing unit  120  (Box  420 ). Once at the first sealing unit  120 , the first seal  302  is provided on the package  200  (Box  430 ) according to the above. The first seal  302  is provided to the package  200  during a first sealing time t 1 . 
     The flexible package  200  is then transferred by the transfer unit from the first sealing unit  120  to the second sealing unit  130  (Box  440 ). At the second sealing unit  130 , the second seal  304  is provided on the package  200  (Box  450 ) according to the above. The second seal  304  is provided to the package  200  during a second sealing time t 2 . 
     The total sealing time is given by the sum of the first and second sealing times, i.e. t=t 1 +t 2 . The total sealing time t is chosen to be longer than or equal to a critical sealing time t cri t which is sufficiently long for obtaining a sufficient seal. Additionally, the applied pressure P to the package  200  between the abutment jaws  122 ,  132  and the permanently heated sealing jaws  124 ,  134  and temperature T of the permanently heated sealing jaws  124 ,  134  are chosen suitably for obtaining a sufficient seal. In other words, P≧P crit  and T≧T ‘C”′t , where Pent and T crA  is a critical pressure and a critical temperature, respectively. 
     Thus, operating parameters are set for providing the first and the second seals  302 .  304 . These operating parameters comprise a time parameter, a temperature parameter and a pressure parameter. The operating parameters for providing the first seal may be different from the operating parameters for providing the second seal. 
     The operating parameters are set such that a sealing characteristic below a threshold value is obtained in said top portion and in said bottom portion and such that a sealing characteristic equal to or above the threshold value is obtained in said intermediate portion. 
     The threshold value corresponds to the sealing characteristics of a seal having been exposed to a proper sealing process in order to form a sufficient or functional seal. The proper sealing process for a given material and material thickness is dependent on the operating parameters: time, temperature and pressure. 
     In accordance with the inventive concept, it is only the intermediate portion, formed by the first and second seals overlapping each other, that is exposed to a proper sealing process, i.e. that has a sealing characteristic equal to or above the threshold value. 
     Lastly, the package  200  is transferred away from the second sealing unit  130  (Box  460 ). Thereafter, the package  200  may be further processed. By way of example, the package  200  may be transferred to the gas-filling unit  140 . At the gas-filling unit  140 , the duct  222  may be gas-filled by a gas such as air, cf. the package in  FIG. 5 b   . According to the embodiment in  FIG. 5 b   , the gas-filled duct  222  forms a volume formed by two opposing side walls. By means of the gas-filled duct  222 , the rigidity of the package  200  increases. 
     Moreover, after the package  200  has been provided with a gas-filled handle portion  220 , it may be transferred to other units in the production line  100 . For example, the package  200  may be transferred to a packing unit wherein the package  200  becomes packed in a box (not shown). Before being packed, the package  200  may be adjusted or aligned to a suitable position and orientation, by performing a rectilinear displacement of the package  200  and by rotating the package  200  around one or several axes. 
     According to an alternative embodiment, however, the package  200  is not provided with a duct  222  and there is no need for a gas-filling unit  140  in the production line  100 . A non-limiting example of such a package  200  is provided in  FIG. 5   a.    
     It is understood that the method described above may be repeated for a plurality of packages  200 . As described in the above, the packages  200  may be provided to a production line  100  in a row. Moreover, multiple packages  200  arranged side-by-side may be provided to the production line  100 . For example, there may be a pair of packages  200  provided side-by-side as shown in  FIG. 2 . Additionally, it is clear that there may be a plurality of production lines  100  arranged side-by-side. In these cases, a separation unit (not shown) may be located before the filling unit  110  for separating the plurality of packages  200  from each other. 
     The invention has mainly been described above with reference to a few embodiments. However, as is readily appreciated by a person skilled in the art, other embodiments than the ones disclosed above are equally possible within the scope of the invention, as defined by the appended patent claims. For example, the particular order of the various units included in the production line  100  may be varied. In relation to this, the steps comprised in the method may also be varied. Additionally, the particular form of the sealing units described must be considered as non-limiting as there are other ways of designing the sealing units. For example, the shape and/or the material of the abutment jaw may be different. Also, according to alternative embodiments, the sealing jaw does not have to be permanently heated. For example, there may be a separate heating member arranged next to the sealing jaw and/or abutment jaw for providing an improved sealing by means of intermittent heating.