Patent Publication Number: US-2021178704-A1

Title: Rotary impulse sealer

Description:
FIELD OF THE INVENTION 
     The invention relates to a rotary impulse sealer for forming a series of discrete bonds in a bondable material. The invention also relates to a vertical form fill machine. The invention further relates to a method of forming packages for containing fluid or fluent material. 
     BACKGROUND OF THE INVENTION 
     Known packages or sachets are made from layers of plastics and/or metallic foils that are laminated together to form a sealed reservoir between adjacent layers for housing the contents of the package. 
     Such packages are typically manufactured using methods and apparatus similar to those used in the printing industry where elongate webs are passed along a line of stations. Each station performs a different function. Typically, the product to be packaged is introduced between two webs that are sealed together continuously along their opposite edges. The webs are also sealed transversely at intervals to divide the webs into separate components. Individual packages are produced by cutting the webs transversely at the transverse seals. 
     In this specification where reference has been made to patent specifications, other external documents, or other sources of information, this is generally for the purpose of providing a context for discussing the features of the invention. Unless specifically stated otherwise, reference to such external documents or such sources of information is not to be construed as an admission that such documents or such sources of information, in any jurisdiction, are prior art or form part of the common general knowledge in the art. 
     New Zealand patent specification NZ 547925 describes a sachet for storing and dispensing a fluent material. The sachet comprises a lamination of first, second and third layers. The second layer is a semi-rigid layer located between the first and third layers. A line of weakness is formed in a mid-portion of the second layer. At least a portion of the line of weakness has inter-digitated finger portions. The sachet is adapted to flex at the line of weakness on application of a compression force at the edges of the second layer. The tips of the inter-digitated finger portions cause the first layer to rupture in the vicinity of the line of weakness to form a discharge opening through which contents of the sachet may be discharged. 
     U.S. Pat. No. 7,247,219 describes a rotatable cylindrical roller for heat sealing heat sealable materials, in particular for sealing flexible packaging. The rotatable roller has at least one cooling zone and at least one heating zone. Travel of a heat sealable material over the heating zone causes the formation of a heat seal. Travel over the cooling zone allows the seal to cool in a supported state. 
     When a rotatable cylindrical roller is used to form a transverse web to seal fluent material within a package, there is a risk that the contents of the package will be displaced and/or pressurised within the package by the roller. This has the potential to distribute the contents unevenly within the packages and/or cause poor quality seals. 
     It is an object of at least preferred embodiments of the present invention to address some of the aforementioned disadvantages. An additional or alternative object is to at least provide the public with a useful choice. 
     SUMMARY OF THE INVENTION 
     In accordance with a first aspect of the invention, there is provided a rotary impulse sealer for forming a series of discrete bonds in a bondable material, the rotary impulse sealer comprising: a roller rotatable about an axis, the roller having a roller body and a plurality of seal bars extending radially outwardly from the roller and spaced apart around the roller body, at least one of the seal bars having a body and a selectively heatable heating element extending along at least a part of a length of the seal bar body, wherein the roller is rotatable through a pre-heating pressure application region in which the at least one seal bar is adapted to apply pressure to a bond area of the bondable material, followed by a heating region in which the at least one seal bar is adapted to heat the bond area, the regions being stationary with respect to the rotation of the roller. 
     The term ‘comprising’ as used in this specification means ‘consisting at least in part of’. When interpreting each statement in this specification that includes the term ‘comprising’, features other than that or those prefaced by the term may also be present. Related terms such as ‘comprise’ and ‘comprises’ are to be interpreted in the same manner. 
     In an embodiment, the roller is rotatable through a post-heating pressure application region in which the at least one seal bar is adapted to apply pressure to the bondable material. 
     In an embodiment, the pre-heating pressure application region is directly adjacent the heating region. 
     In an embodiment, the post-heating pressure application region is directly adjacent the heating region. 
     In an embodiment, the heating region is a heating and pressure application region. 
     In an embodiment, the body of the seal bar is or comprises an insulating material. 
     In an embodiment, the heating element extends substantially along the entire length of the seal bar body. 
     In an embodiment, the heating element is or comprises a conductive material. 
     In an embodiment, the roller body has a plurality of slots, each slot retaining one of the seal bars. 
     In an embodiment, at least one seal bar has a longitudinal axis that is substantially parallel to the roller axis. 
     In an embodiment, at least one seal bar has a longitudinal axis that is non-parallel with the roller axis. 
     In an embodiment, each seal bar has a body and a selectively heatable heating element extending along at least a part of a length of the seal bar body. 
     In an embodiment, the roller axis is a stationary axis. 
     In accordance with a second aspect of the invention, there is provided a vertical form fill machine, comprising: a drive system for driving at least two sheets of bondable material that are sealed together continuously along their opposite edges through the machine; a fill product supply device for introducing fill product between the two sheets of bondable material; and a rotary impulse sealer according to any one of the preceding claims, the rotary impulse sealer adapted to make transverse seals in the at least two sheets of bondable material to form sealed reservoirs of fill product. 
     In an embodiment, the vertical form fill machine further comprises two cylindrical rollers for receiving sheets of bondable material and forming two continuous, spaced apart longitudinal seals along opposite edges of the sheets of bondable material. 
     In an embodiment, the cylindrical rollers are arranged to introduce the sheets of bondable material to the rotary impulse sealer at an angle of about 90° to a horizontal plane. 
     In an embodiment, the rotary impulse sealer is driven so that the seal bar making the seal moves at substantially the same speed as the bondable material that is being sealed. 
     In accordance with a third aspect of the invention, there is provided a method of forming packages containing fluid or fluent material comprising:
         a) continuously providing at least two sheets of bondable material having a fluid or fluent material therebetween;   b) applying pressure to a transverse bond area of the bondable material to force the fluid or fluent material away from the transverse bond area; and   c) heating the transverse bond area to form a seal.       

     In an embodiment, the method further comprises:
         d) applying pressure to the transverse bond area after step c.       

     In an embodiment, step d comprises allowing heat to dissipate from the transverse bond area. 
     In an embodiment, step c comprises simultaneously applying pressure and heat to the transverse bond area. 
     In an embodiment, step c is carried out immediately after step b. 
     In an embodiment, step d is carried out immediately after step c. 
     In an embodiment, the transverse bond area extends in a transverse direction across the width of the at least two sheets of bondable material. 
     In an embodiment, the method further comprises the step of providing a rotary impulse sealer, the rotary impulse sealer comprising a roller rotatable about an axis, the roller having a roller body and a plurality of seal bars extending radially outwardly from the roller and spaced apart around the roller body, at least one of the seal bars having a body and a selectively heatable heating element extending along at least a part of a length of the seal bar body, wherein the roller is rotatable through a pre-heating pressure application region in which the at least one seal bar is adapted to apply pressure to a bond area of the bondable material, followed by a heating region in which the at least one seal bar is adapted to heat the bond area, the regions being stationary with respect to the rotation of the roller; wherein steps b and c are performed by the rotary impulse sealer. 
     In an embodiment, the rotary impulse sealer performs step d. 
     In an embodiment, step c comprises selectively applying a current to the heating element of the seal bar. 
     In accordance with a fourth aspect of the invention, there is provided a package containing fluid or fluent material produced by the method of the third aspect. 
     In accordance with an aspect of the disclosure, there is provided a rotary impulse paddle sealer for forming a discontinuous bond in a bondable material, comprises a roller rotatable about an axis; a plurality of seal bars extending radially outwardly from the roller and spaced apart around the roller, at least one of the seal bars adapted to be selectively excited by a current during a portion of the rotation of the roller to temporarily heat the at least one seal bar, the at least one seal bar adapted to apply pressure to an area of material to be bonded during a portion of the rotation immediately preceding the portion of the rotation in which the at least one seal bar is heated. 
     In an embodiment each seal bar is adapted to apply pressure during a portion of the rotation immediately following the portion of the rotation in which the seal bar is heated. 
     In an embodiment the at least one seal bar comprises a seal bar body and a heating element extending along at least a part of a length of the seal bar body. 
     In an embodiment the heating element extends substantially along the entire length of the seal bar body. 
     In an embodiment the roller is provided with a plurality of slots adapted to retain respective seal bars, the slots shaped such that the seal bars extend radially from the roller. 
     In an embodiment at least one of the slots is substantially parallel to the axis about which the roller is rotatable. 
     In an embodiment at least one of the slots is positioned such that it is not parallel to the axis about which the roller is rotatable. 
     In an embodiment at least one of the slots is shaped such that it is not parallel to the axis about which the roller is rotatable. 
     In accordance with a further aspect of the invention, a vertical form fill machine comprises a drive system for driving at least two sheets of bondable material that are sealed together continuously along their opposite edges through the machine; a fill product supply device for introducing fill product between the two sheets of bondable material; a rotary impulse paddle sealer for forming sealed reservoirs of fill product, the rotary impulse paddle sealer adapted to apply pressure to an area to be bonded during a portion of the rotation immediately preceding a portion of the rotation in which the rotary impulse paddle sealer applies heat to form a bond. 
     In an embodiment the rotary impulse paddle sealer is adapted to apply pressure during a portion of the rotation immediately following the portion of the rotation in which the rotary impulse paddle sealer applies heat to form a bond. 
     In an embodiment the rotary impulse paddle sealer is adapted to receive sheets of bondable material containing fill material at an angle greater than 0° to a horizontal plane. 
     In an embodiment the rotary impulse paddle sealer is driven at substantially the same speed as the bondable material that is being sealed. 
     In accordance with a further aspect of the invention, a method of forming packages of fluid or fluent material comprises providing a drive system adapted to drive at least two sheets of bondable material; sealing a first edge and a second edge of the sheets of bondable material together continuously; introducing a fluent material between the two sheets of bondable material; providing a rotary impulse paddle sealer adapted to apply pressure to an area to be bonded during a portion of the rotation immediately preceding a portion of the rotation in which the rotary impulse paddle sealer applies heat to form a bond. 
     The invention in one aspect comprises several steps. The relation of one or more of such steps with respect to each of the others, the apparatus embodying features of construction, and combinations of elements and arrangement of parts that are adapted to affect such steps, are all exemplified in the following detailed disclosure. 
     It is intended that reference to a range of numbers disclosed herein (for example, 1 to 10) also incorporates reference to all rational numbers within that range (for example, 1, 1.1, 2, 3, 3.9, 4, 5, 6, 6.5, 7, 8, 9 and 10) and also any range of rational numbers within that range (for example, 2 to 8, 1.5 to 5.5 and 3.1 to 4.7) and, therefore, all sub-ranges of all ranges expressly disclosed herein are hereby expressly disclosed. These are only examples of what is specifically intended and all possible combinations of numerical values between the lowest value and the highest value enumerated are to be considered to be expressly stated in this application in a similar manner. 
     To those skilled in the art to which the invention relates, many changes in construction and widely differing embodiments and applications of the invention will suggest themselves without departing from the scope of the invention as defined in the appended claims. The disclosures and the descriptions herein are purely illustrative and are not intended to be in any sense limiting. Where specific integers are mentioned herein which have known equivalents in the art to which this invention relates, such known equivalents are deemed to be incorporated herein as if individually set forth. 
     As used herein the term ‘(s)’ following a noun means the plural and/or singular form of that noun. 
     As used herein the term ‘and/or’ means ‘and’ or ‘or’, or where the context allows both. 
     The invention consists in the foregoing and also envisages constructions of which the following gives examples only. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Preferred forms of the rotary impulse paddle sealer will now be described by way of example only with reference to the accompanying figures in which: 
         FIG. 1  shows a schematic of a vertical form fill machine including a rotary impulse paddle sealer; 
         FIG. 2  shows an exemplary rotary impulse paddle sealer roller; 
         FIG. 3  shows an exemplary rotary impulse paddle sealer seal bar; and 
         FIG. 4  shows an alternative arrangement of a drive system for a vertical form fill machine. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a schematic of a continuous vertical form fill machine  100  for manufacturing packages  105  of fluid or fluent fill product  110 . The vertical form fill machine  100  includes a drive system  115  for driving at least two sheets of bondable material  120 ,  121  that are sealed together continuously along their opposite edges though the machine  100 . The drive system operates continuously. The vertical form fill machine  100  also has a fill product supply device  125  for introducing fill product  110  between the two sheets of bondable material  120 ,  12 . The vertical form fill machine  100  also has a rotary impulse sealer  130 . The rotary impulse sealer  130  is adapted to make transverse seals in the at least two sheets of bondable material for forming sealed reservoirs  135  of fill product  110 . The vertical form fill machine also has a cutting station  140  for separating the sealed reservoirs  135  into individual packages  105 . 
     The vertical form fill machine  100  is suitable for packaging fluid or fluent material or product, such as liquids or flowable powders. The size of the machine and/or components of the machine can be adapted to make packages of any size. In an embodiment, the machine  100  is adapted to produce packages having a volume of about 2 mL or about 5 mL. In another embodiment, the machine  100  is adapted to produce packages having a volume of about 1 L or more. The machine  100  may be adapted to produce packages having any other suitable volume, for example about 10 mL, about 20 mL, about 50 mL, about 75 mL, about 100 mL, about 200 mL, about 500 mL, about 750 mL or about 2 L. 
     Fluid or fluent materials include liquids, creams, lotions, gels, pastes, powders, lubricated powders, particulates, sauces, beverages, sunscreens, lubricants, paints, greases, oils, glues, resins, medicines, pharmaceuticals, etc. 
     The rotary impulse sealer  130  forms a series of discrete bonds in a bondable material  120 ,  121 . The rotary impulse sealer  130  has a roller  145  rotatable about an axis. In the embodiment shown, the roller axis is a stationary axis. The roller  145  has a roller body  155  and a plurality of seal bars  150 . The seal bars  150  extend radially outwardly from the roller  145  and are spaced apart around the roller body  155 . In the embodiment shown, the seal bars  150  extend axially along substantially the entire axial length of the roller  145 . 
     At least one of the seal bars  150  has a body  175  and a selectively heatable heating element  180  extending along at least a part of a length of the seal bar body  175 . In the embodiment shown, each seal bar  150  has a body  175  and a selectively heatable heating element  180  extending along at least a part of a length of the seal bar body  175 . 
     The roller  145  is rotatable through a pre-heating pressure application region or rotation portion A in which the at least one seal bar  150  is adapted to apply pressure to a bond area  154  of the bondable material  120 ,  121 . The pre-heating pressure application region A is followed by a heating region or rotation portion B in which the at least one seal bar  150  is adapted to heat the bond area  154 . The pre-heating pressure application region A and the heating region B are stationary with respect to the rotation of the roller  145 . 
     In the embodiment shown, the roller  145  is rotatable through a post-heating pressure application region or rotation portion C in which the at least one seal bar  150  is adapted to apply pressure to the bondable material. The post-heating pressure application region 
     C is stationary with respect to the rotation of the roller  145 . In an alternative embodiment, the rotary impulse sealer  130  may not have a post-heating pressure application region C and the roller may only rotate through the pre-heating pressure application region is followed by the heating region B. 
     The rotary impulse sealer  130  may be referred to as a rotary impulse paddle sealer  130 . The ‘paddles’ of the rotary impulse paddle sealer are the seal bars  150 . The seal bars  150  act as paddles to drive fill product away from a bond area, as will be described in more detail below. 
     The heating element  180  is adapted to be heated by selectively applying a current to the heating element  180  during the heating region B of the rotation of the rotary impulse paddle sealer  130 . In an embodiment, the heating element  180  of each seal bar  150  is adapted to be heated by selectively applying a current to the heating element  180 . The selectively applied current may be described as an impulse current. 
     In the preferred embodiment, two sheets of bondable material  120 ,  121  are sealed together continuously along their opposite edges to form two substantially parallel longitudinal webs. The bondable material may be polyethylene, or any other heat sealable or bondable material. The longitudinal webs may be formed by any suitable process, such as a conventional continuous heat sealing process. In the embodiment shown, the sheets of bondable material  120 ,  121  are received between two cylindrical rollers  151 ,  152 . One of the cylindrical rollers  152  has heated portions at either end (not illustrated) that apply heat to the edges of the sheets of bondable material  120 ,  121  to form the longitudinal webs. The cylindrical rollers  151 ,  152  form two continuous, spaced apart longitudinal seals along opposite edges of the sheets of bondable material  120 ,  121 . Fill product  110  is introduced between the longitudinal webs. 
     In an alternative embodiment, a sheet of bondable material is folded in half, and a single longitudinal web is formed at the open edges of the sheet. Fill product  110  is introduced between the longitudinal web and the fold. In a further alternative embodiment, fill product  110  is introduce into a tube of bondable material. The tube of bondable material may not have any longitudinal webs. 
     The drive system  115  includes a belt  116  that drives the bondable material  120 ,  121  toward the rotary impulse paddle sealer  130  at a substantially constant speed. The belt is held under tension by the cylindrical roller  151 , and two belt (lower) rollers  157 ,  158  in combination with the rotary impulse sealer  130 . One or more of the rollers  151 ,  157 ,  158  may be a driving roller that drives the belt  116 . The sheets  120 ,  121  are introduced to the rotary impulse paddle sealer  130  by the drive system  115 . 
     In the embodiment shown in  FIG. 1 , the belt rollers  157 ,  158  are located below the cylindrical roller  151 . The belt rollers  157 ,  158  are located at substantially the same height. The drive system  115  has a substantially L-shaped arrangement, with the rotary impulse sealer  130  located at the bend of the L. This arrangement provides a relatively large portion of the rotation of the rotary impulse sealer  130  in which a seal bar  150  is in contact with the bondable material  120 ,  121 . 
       FIG. 4  shows an alternative arrangement of a drive system  1115 . The drive system  1115  is the same as the drive system  115 , except as described below. Like parts indicate like numbers, with the addition of  1000 . In this embodiment, one of the belt rollers  1158  is located below the cylindrical roller  1151 , substantially in line with the cylindrical roller  1151 , such that the rotary impulse sealer  1130  acts on a substantially vertical belt surface. This arrangement provides a relatively short portion of the rotation of the rotary impulse sealer in which a seal bar  1150  is in contact with the bondable material  1120 ,  1121 . This arrangement may be suitable for applications in which a short sealing time is required, and may enable packages to be formed very quickly. 
     In other embodiments, the relative position of the belt rollers may be chosen or designed depending on the required sealing time. For example, belt rollers may be positioned such that the belt has a U-shaped, or V-shaped configuration. In such a configuration, the sealing time may be increased compared to the sealing time of the illustrated embodiments because the belt will travel around the roller for a greater amount of time. 
     In the embodiments shown in  FIG. 1  and  FIG. 4 , the cylindrical rollers  151 ,  152  are arranged to introduce the sheets of bondable material  120 ,  121  to the rotary impulse sealer  130  at a substantially vertical orientation (about 90° relative to a horizontal plane). In alternative embodiments, the sheets of bondable material  120 ,  121  are introduced at any angle that enables the fill product to fall towards the rotary impulse paddle sealer  150  under the force of gravity. In an embodiment the angle is greater than 0° to a horizontal plane. In an embodiment the angle is less than 90° to a horizontal plane. For example, the sheets of bondable material  120 ,  121  may be introduced at an angle of about 85°, about 80°, about 70°, about 60°, about 45°, about 30° or about 15° to a horizontal plane. 
     In an embodiment, at least one of the sheets of bondable material  120 ,  121  is modified prior to being sealed to the other sheet of bondable material  120 ,  121 . For example by adding registration markers to facilitate timing of machine operations. In an embodiment, a cut and/or other line of weakness is introduced to one of the sheets of bondable material  120 ,  121  to facilitate controlled rupture of at least one of the package  105  layers prior to dispensing the package  105  contents. The line of weakness may have a zig-zag shape. Exemplary package arrangements are disclosed in NZ 547925, which is incorporated herein by reference. 
     When a seal bar  150  first contacts the bondable material  120 ,  121 , the seal bar  150  applies pressure to the bondable material  120 ,  121  through the pre-heating pressure application region A of the rotation of the roller  145 . The seal bar  150  applies pressure in a generally transverse direction across the width of the at least two sheets of bondable material  120 ,  121 . The pressure from the seal bar  150  forces the fill product  110  away from a bond area  154 . The pressure from the seal bar  150  defines a fill volume  156  between the seal bar  150  and an adjacent seal bar  150  further around the rotation path. 
     The bond area  154  extends in a transverse direction across the width of the at least two sheets of bondable material  120 ,  121 . The bond area  154  extends an angle of about 90° to the longitudinal webs. In alternative embodiments, the bond area  154  may extend between the longitudinal webs  154  at any suitable angle, for example about 75°, about 80°, about 85°, about 95°, about 100° or about 105°. 
     An impulse current is then applied to the heating element  180  of the seal bar  150  during the heating region B of the rotation of the roller  145  to heat the seal bar  150 . The heat from the seal bar  150  forms a bonded transverse web in the bondable material  120 ,  121 . In the embodiment shown, the pre-heating pressure application region A is directly adjacent the heating region B. 
     In other words, the pre-heating pressure application region A in which the seal bar  150  applies pressure to an area of material to be bonded immediately precedes the heating region B in which the seal bar  150  is heated to form a bond. 
     In an alternative embodiment, there may be a space between the pre-heating pressure application region A and the heating region B. 
     In an embodiment, the heating region B is a heating and pressure application region. In a preferred embodiment, more pressure is applied during the heating region B than during the pre-heating pressure application region A. In an alternative embodiment, less pressure is applied during the heating region B than during the pre-heating pressure application region A. 
     After the impulse current is switched off, the bond cools under pressure from the seal bar  150  during the post-heating pressure application region C of the rotation of the roller  145 . In the embodiment shown, the post-heating pressure application region C is directly adjacent the heating region B. 
     In other words, the post-heating pressure application region C in which the bond cools under pressure from the seal bar  150  immediately follows the heating region B in which the seal bar  150  is heated to form a bond. 
     In an alternative embodiment, the post-heating application may not be immediately followed by the heating region. For example, there may be another step or process between the heating region B and the post-heating pressure application region C. 
     In an embodiment, the heating element is formed from a material that rapidly cools so that the bondable material cools to a temperature below the melting point of the bondable material when the current is no longer applied. This allows heat to dissipate in the post-heating pressure application region C. Heat may dissipate in a variety of different ways. For example, the heat may dissipate into the fill product  110 , the bondable material  120 ,  121 , and the surrounding environment. 
     In an embodiment, the seal bars  150  include a cooling system, such as a water cooling system, to assist with heat dissipation. 
     Applying pressure with the seal bar  150  prior to heating the bondable material  120 ,  121  removes fill product  110  from the area to be bonded prior to the bond being formed. This ensures a high quality bond that is free, or at least substantially free, from particles of fill product  110 . Allowing the bond to cool while still under pressure from the seal bar  150  ensures the bond sets correctly and further contributes to a high quality seal. 
     Arranging the rotary impulse paddle sealer  130  below the vertical or angled fill product  110  as shown in  FIG. 1  allows packages of liquid to be formed that have no air gaps, or at least substantially no air gaps. This is advantageous in certain applications, for example when packaging food, an absence of air gaps can improve food longevity. 
       FIG. 2  shows a perspective view of an exemplary roller  145 . The roller comprises a roller body  155 . The roller body  155  is electrically insulated from the seal bars  150 . In an embodiment the roller body  155  is made from an insulating material, for example a polymeric material such as high density polyethylene. In an alternative embodiment the roller body  155  is at least partially coated in an insulating material. The roller body  155  has an aperture  160  for receiving an axle (not shown), and a plurality of slots  165 , each slot  165  retaining one of the seal bars  150 . One seal bar  150  is shown mounted in a slot  165 . 
     In an embodiment the slots  165  are slightly narrower than the seal bars  150  so that the seals bars  150  can be retained in the slots  165  in a press fit. In an embodiment, the slots  165  include electrodes for contacting the electrodes  185 ,  186  of the seal bars  150 . The electrodes are made from tin coated copper, or any other suitably conductive material. 
     The axle of the roller  145  is driven, for example by a servo motor. In an embodiment, a control system adjusts the speed of rotation of the roller  145  to ensure the transverse webs are correctly aligned with registration markers on the bondable material. 
     Driving the roller  145  rotation ensures that the seal bar  150  making the seal is moving at substantially the same speed as the bondable material  120 ,  121  that is being sealed. This ensures a high quality seal is formed. If the roller  145  was not driven and was instead free rolling, the seal bars  150  could slip relative to the bondable material  120 ,  121 , leading to a poor quality seal. In addition, it would not be possible to accurately align the transverse webs using a control system. 
     The seal bars  150  extend outwardly from the roller  145  to define a gap that accommodates the individual reservoirs  135  of fill product  110 . In the embodiment shown, the gap is defined by substantially flat portions  170  of the roller  145  that extend between the seal bars  150 . 
     In alternative embodiments, the roller  145  could be any other suitable shape that accommodates the individual reservoirs  135  of fill product  110 . For example, the portions  170  of the roller  145  extending between the seal bars  150  could have a convex shape or a concave shape. 
     The spacing between the outer surfaces of the seal bars  150  determines the longitudinal dimension of the package  105  volume. In the embodiment shown, the rotary impulse paddle sealer  130  has eight seal bars  150  spaced about 40 mm apart from each other in a radial direction. 
     In alternative embodiments, any suitable number of seal bars having any suitable spacing may be used to achieve the desired package dimensions. In the embodiment shown, the seal bars  150  are equally spaced around the roller  145 . At least one of the seal bars  150  has a longitudinal axis that is substantially parallel to the roller axis. In the embodiment shown, all of the seal bars  150  have a longitudinal axis that is substantially parallel to the roller axis. The seal bar  150  arrangement shown in the figures produces packages that have a transverse web that is substantially perpendicular to the longitudinal webs. 
     In an alternative embodiment, the seal bars  150  are not equally spaced. 
     In an alternative embodiment, at least one of the seal bars has a longitudinal axis that is non-parallel with the roller axis. This can be achieved, for example, by providing at least one slot that is positioned such that it is not parallel to the axis about which the roller is rotatable. In an embodiment, the seal bars  150  are angled so that they form transverse webs that are not perpendicular to the longitudinal webs. 
     In an alternative embodiment, the seal bars are adapted to form a shaped transverse web. For example, the seals bars could be shaped to form a transverse web having a curved shape. This can be achieved, for example, by providing at least one slot that is shaped such that it is not parallel to the axis about which the roller is rotatable. 
       FIG. 3  shows an exemplary seal bar  150 . The seal bar  150  comprises a seal bar body  175 , a heating element  180  and electrodes  185 ,  186 . 
     The seal bar body  175  is adapted to slot into a slot  165  of the roller  145 . The seal bars  150  are mounted in the slots  165  using any suitable method. In the embodiment shown, the seal bar body  175  has a substantially rectangular cross section that is press fit in a slot  165  of the roller  145 . In alternative embodiments, the seal bar body  175  and roller slots  165  are shaped so that the seal bar body  175  is retained when the seal bar  150  is slid into a slot  165  in an axial direction. 
     The seal bar body  175  is or comprises an insulating material. The seal bar body  175  is made from a suitably strong material that can withstand both pressure applied by the seal bar  150  to the bondable material  120 ,  121  and heat from the heating element  180 . In an embodiment, the seal bar body  175  is formed from polyetheretherketone (PEEK). In an alternative embodiment, the seal bar body  175  is formed from a conductive material such as aluminium alloy that is at least partially coated in an insulating material. In a further alternative embodiment, the seal bar body  175  is or comprises a ceramic material. 
     The heating element  180  extends substantially along the entire length of the seal bar body  175  and folds over the ends of the seal bar body  175 . The heating element  180  is or comprises a conductive material. In an exemplary embodiment, the heating element  180  is made from a nickel chromium alloy. For example, the heating element  180  may be made from a nickel chromium alloy comprising about 60% nickel, about 16% chromium, and about 24% iron. The heating element may be made from any other suitable heating element material. In the embodiment shown in the figures, the heating element  180  extends substantially along the entire length of the seal bar body  175 . 
     In the alternative embodiment where the seal bar body  175  is or comprises a ceramic material, the heating element  180  may comprise a thin layer of conductive material, such as a layer of conductive particles. The particles may be in the form of a sand. The conductive particles may be a metal. The thin layer of conductive material may be embedded in the seal bar body  175 . The thin layer of conductive material may be coated in a thin layer of ceramic glass. 
     The electrodes  185 ,  186  overlap with the heating element  180  at the ends of the seal bar body  175  and enable current to be applied to the heating element  180 . The electrodes are made from tin coated copper, or any other suitably conductive material. Current may be applied to the electrodes via slip rings or any other suitable means. 
     A method of forming packages containing fluid or fluent material will now be described. The method comprises step a, which is to continuously provide at least two sheets of bondable material  120 ,  121  having the fluid or fluent material  110  therebetween. When the two sheets of bondable material  120 ,  121  reach the sealer, the next step, step b, comprises applying pressure to the transverse bond area  154  of the bondable material  120 ,  121 . Applying pressure to the transverse bond area  154  forces the fluid or fluent material  110  away from the bond area. 
     A subsequent step, step c, comprises heating the transverse bond area  154  to form a seal. In the preferred method, step c comprises simultaneously applying pressure and heat to the transverse bond area. 
     Step c comprises selectively applying a current to the heating element  180  of the seal bar  150  (in other words, applying an impulse current). The seal bar  150  has electrodes  185 ,  186  that overlap with the heating element  180  at the ends of the seal bar body  175 . The impulse current is applied to the seal bar electrodes  185 ,  186  via electrodes mounted in the slots  165  of the roller  145 . The electrodes  185 ,  186  are in electrical communication with slip ring that is electrically charged during a portion of the rotation of the roller  145  corresponding to the heating region B to selectively apply a current to the heating element  180 . In an alternative embodiment, the impulse current may be applied directly to the seal bar electrodes  185 ,  186 . 
     The power applied during the impulse is variable depending on the application. In an exemplary embodiment, about 10V, 80 A is applied for about 150-250 milliseconds. The power applied and/or the duration of the impulse may be varied depending on the thickness and material properties of the bondable material. For example, an impulse duration of about 50 ms may be sufficient to provide a good bond in some applications. In alternative embodiments, any suitable impulse duration may be used, such as about 60 ms, about 80 ms, about 100 ms, 1 about 20 ms, about 200 ms, or about 300 ms. 
     The heating element  180  is heated to about 300° C. when the impulse current is applied. In other embodiments, the heating element is heated to any other suitable temperature, such as about 200° C., about 220° C., about 250° C., about 270° C., about 290° C., about 310° C., about 330C° or about 350° C., for example. The temperature of the heating element may be selected depending on the properties of the sheets of bondable material  120 ,  121 . The temperature of the heating element  180  may be significantly higher than a melting temperature of the bondable material. For example, the temperature of the heating element  180  may be about twice the melting temperature of the bondable material. The relatively high temperature of the heating element  180  enables sufficient heat penetration of the bond area to create a seal during the relatively short duration of the impulse. A higher temperature of the heating element  180  may be used where the sheets of bondable material  120 ,  121  are thicker. 
     In the preferred embodiment, the method further comprises step d, which comprises applying pressure to the transverse bond area  154  after the step of heating the transverse bond area. This step occurs during the post-heating pressure application region C of the rotation of the roller. Applying pressure after heating step c may help the bond to set correctly. In an alternative embodiment, the method may not include step d. 
     Either during, or before step d, heat is no longer applied to the transverse bond area. The heat is no longer applied by the impulse current ceasing. Accordingly, during step d, the heat from the transverse bond area is allowed to dissipate from the transverse bond area. For example, heat may dissipate into the fluid or fluent material  110 , the bondable material  120 ,  121 , and the surrounding environment. 
     The heating element  180  cools to less than 120° C. as the heat dissipates. The heating element  180  may cool to any suitable temperature, depending on the material that is being bonded. For example, the heating element may cool to about 60° C., about 80° C., about 100° C., about 140° C. or about 160° C. 
     Step d is preferably carried out immediately after step c. In an alternative embodiment, there may be a gap between carrying out step c and step d. 
     In the preferred method, pressure is applied continuously throughout steps b, c, and d. In an embodiment, the amount of pressure applied increases during step b and reaches a maximum during step c. The amount of pressure applied then decreases during step d. In an alternative embodiment, the amount of pressure may be applied relatively constant throughout a substantial part of steps b, c and d. In alternative embodiments, step c may comprise applying the same amount of pressure as step b, or less pressure than step b. In a preferred embodiment, step c comprises applying more pressure than step b. In alternative embodiments, step c comprises applying the same amount of pressure as step d, or less pressure than step d. 
     The method is preferably carried out using the rotary impulse sealer  130 . In the preferred method, the rotary impulse sealer  130  performs steps b, c, and d. In an alternative embodiment, the rotary impulse sealer  130  may perform steps b and c, and not step d. Step b corresponds to the pre-heating pressure application region A of the roller. Step c corresponds to the heating region B of the roller. Step d corresponds to the post-heating pressure application region C of the roller. 
     In an exemplary embodiment, pressure is applied during the pre-heating pressure application region A for about 400 milliseconds. Pressure may be applied during the pre-heating pressure application region A for any suitable period of time. The optimum amount of time may be different for different fluid or fluent materials. For example, pressure may be applied for about 50 milliseconds, about 60 milliseconds, about 80 milliseconds, about 100 milliseconds, about 150 milliseconds, about 200 milliseconds, about 250 milliseconds, about 300 milliseconds, about 350 milliseconds, about 450 milliseconds, about 500 milliseconds, about 550 milliseconds or about 600 milliseconds. 
     In an exemplary embodiment, pressure is applied during the post-heating pressure application region C for about 400 milliseconds. Pressure may be applied during the post-heating pressure application region C for any suitable period of time. The optimum amount of time may be different for different materials. For example, pressure may be applied for about 50 milliseconds, about 60 milliseconds, about 80 milliseconds, about 100 milliseconds, about 150 milliseconds, about 200 milliseconds, about 250 milliseconds, about 300 milliseconds, about 350 milliseconds, about 450 milliseconds, about 500 milliseconds, about 550 milliseconds or about 600 milliseconds. 
     The rotation speed of the roller  145  and/or the timing and location of the impulse current is/are controlled by a control system. In an exemplary embodiment, the impulse current is applied at a point of the rotation of the roller  145  corresponding to the start of the heating region B. In an exemplary embodiment, the impulse current is applied during a portion of the rotation of the rotary impulse paddle sealer  130  in which maximum pressure is applied to the bondable material  120 ,  121  by the seal bar  150 . The location and length of the portion of the rotation where the impulse current is applied is adjustable via the control system. For example, a single rotation of the roller  145  is divided into a number of counts. A sensor associated with the axle of the roller  145  determines a nominal starting point for the rotation. The control system applies current to each seal bar  150  at a different number of counts such that current is initially applied to each seal bar  150  at a point of the rotation of the roller  145  corresponding to the start of the heating region B. Current is applied to each seal bar  150  for a duration of time set by a user. 
     Preferred embodiments of the invention have been described by way of example only and modifications may be made thereto without departing from the scope of the invention.