Tubular container with heat seal having an inner and outer bead and method of manufacturing said container

FIELD OF THE INVENTION

The present invention relates to food containers and methods and apparatus for making food containers, and more particularly relates to tubular containers wound from at least one paperboard body ply and a liner ply.

BACKGROUND OF THE INVENTION

Food and drink products and other perishable items are often packaged in tubular containers which are sealed at both ends. These tubular containers typically include at least one structural body ply and are formed by wrapping a continuous strip of body ply material around a mandrel of a desired shape to create a tubular structure. The body ply strip may be spirally wound around the mandrel or passed through a series of forming elements so as to be wrapped in a convolute shape around the mandrel. At the downstream end of the mandrel, the tube is cut into discrete lengths and is then fitted with end caps to form the container.

Tubular containers of this type typically include a liner ply on the inner surface of the paperboard body ply. The liner ply prevents liquids such as juice from leaking out of the container and also prevents liquids from entering the container and possibly contaminating the food product contained therein. Preferably, the liner ply is also resistant to the passage of gasses, so as to prevent odors of the food product in the container from escaping and to prevent atmospheric air from entering the container and spoiling the food product. Thus, the liner ply provides barrier properties and the body ply provides structural properties.

Conventional liner plies most often include aluminum foil which has good barrier properties and also has advantageous strength properties. In particular, the liner is wound onto the mandrel prior to the winding of the body ply and must be sufficiently strong and stiff to be independently wound on the mandrel without stretching or wrinkling. Because of the support provided by the foil layer of the liner, such liners are known as "supported" liners. One or more polymeric layers are normally adhered to the foil to further improve the barrier properties of the liner and it is sometimes the case that the foil layer is not necessary for barrier properties but is included in the liner only to provide support. Such foils are expensive and thus it is desired to provide an "unsupported" liner having the requisite barrier properties without the aluminum foil layer. However, because of the problems associated with winding an unsupported liner on the mandrel, such as stretching, creasing or other misshaping of the liner, it has not been commercially feasible with conventional winding apparatus and methods to manufacture a container having an unsupported liner ply.

Another problem associated with conventional liners is excessive friction between the liner ply and the mandrel as the tubular container is wound. If the amount of friction is too high, the mandrel can suffer from overheating or premature wear. Lubricants are used although the lubricants can be expensive and may present FDA concerns. Accordingly, it would be desirable to provide a tubular container which does not create excessive friction with the shaping mandrel. In addition, the aluminum foil layer typically includes a kraft paper backing for allowing the foil layer to be adhered to the paperboard body ply. Aqueous based adhesives (or "wet adhesives") are preferably being used to adhere the liner ply to the body ply because solvent based adhesives have become disadvantageous in light of various environmental concerns. However, it has heretofore been difficult to get the aqueous adhesives to stick to the smooth and impervious surface of the aluminum foil layer. Accordingly, a kraft paper backing has been preadhered to the foil layer so that the liner can be adhered to the paperboard body ply with wet adhesives. However, the kraft paper adds further cost and thickness to the liner.

The liner ply is sealed to itself along a helical seam which is typically slightly offset from the helical seam of the body ply. Wet adhesives have typically not been able to adhere directly to the foil layer as discussed above, and thus the liner ply seam is formed with an "anaconda" fold, wherein the overlying edge of the liner ply is folded back on itself and adhered to the underlying edge. The anaconda fold allows the polymeric layers on the surface of the foil layer to be heat sealed together. Alternatively, a hot melt adhesive can be used to seal the anaconda fold of the overlying edge of the liner ply to the underlying edge. An additional advantage of the anaconda fold is that the edge of the kraft paper is not exposed to the interior of the container and thus liquids in the container will not be absorbed by the kraft paper. An example of such a fold is illustrated in U.S. Patent No. 5,084,284 to McDilda, et al.

Anaconda folds are undesirable, however, because of their increased thickness. The thickness of an anaconda fold seam is equal to three thicknesses of the liner ply and poses difficulties when attempting to hermetically seal the ends of the tubular container. Specifically, the ends of the tube are often rolled outwardly after being cut so as to form a rolled circular bead or flange on one or both ends of the tube and then end caps or covers are sealed to the bead with an adhesive sealant or compound. However, in the area where the thick anaconda fold seam forms a portion of the edge surface, the end surface of the bead or flange can be substantially non-planar thus forming hill-like and/or valley-like irregularities. Accordingly, an extra amount of adhesive sealant must be applied to the edge surface at least in the area of the anaconda fold seam to fill the discontinuities and hermetically seal the tubular container. The additional application of adhesive sealant is disadvantageous because of the extra sealant which must be used and the increased difficulty in removing the seal by the consumer due to the additional adhesive sealant.

Prior tubular containers having a liner without an anaconda fold seam include the container disclosed in U.S. Patent No. 3,520,463 to Ahlemeyer. The container disclosed therein includes a liner ply of aluminum foil which is coated on one surface to inhibit chemical attack. The liner ply web is fed to a pair of combining rolls where its uncoated surface is forced into contact with an adhesively coated surface of a body ply web. Solvent based adhesives are disclosed and include animal glue, casein-latex emulsion, vinyl-copolymer emulsion, and sodium silicate. The composite web is then spirally wound into tubular form about a mandrel to create a continuous tube. The overlapping edges of the liner ply are secured together with a hot melt adhesive.

In addition, current commercial containers often have membrane-type lids or end closures heat sealed to a beaded end of the composite container wall. The beaded end is formed by turning out the end of the container liner to position the inner layer of the liner material on the outwardly curved beaded surface. As noted above, the liner material has conventionally been a paper-backed foil liner which is spirally wound inside the composite container, examples of which are disclosed in U.S. Patent No. 3,892,351 to Johnson <i>et al.</i> and U.S. Patent No. 4,280,653 to Elias. The foil liner and paper backing are not inexpensive and have an undesirable thickness.

Certain types of heat sealable coatings have been used in both the lidding and liners of conventional containers. For example, SURLYN® polymer, a product of Dupont, is a material known in the art and is commonly used as a heat seal coating. SURLYN® polymer is an ionically cross-linked polymer with limited flow characteristics when heated. Typically, the layer of the container and the layer of the membrane which contact each other are constructed of SURLYN® polymer, and may be coated with a wax. These two layers of SURLYN® polymer are heat sealed along the top surface of the container bead. The two SURLYN® polymer layers create an extremely strong bond layer that remains relatively uniform in thickness across the seal area. Due to the strong cross-linked bond created by SURLYN® polymer, however, opening the container can require a peel force which is too high for some consumers and usually results in tearing and exposure of the other layers of the container wall, such as the paperboard body wall, as is illustrated in U.S. Patent No. 4,280,653 to Elias. This gives the top of the container a ragged, undesirable appearance.

Accordingly, it would be desirable to provide methods and apparatus for manufacturing a tubular container having an unsupported liner ply which does not include a foil layer. In addition, it would be highly desirable to provide such a container wherein the liner ply is securely adhered to the body ply with an aqueous adhesive. Such an aqueous adhesive would avoid the problems associated with solvent adhesives but should be capable of forming a sufficiently strong bond with the liner ply, a construction which has not yet been commercially feasible. In addition, it would be advantageous if the liner ply could be sealed without using an anaconda fold seam. A tubular container which could be wound without generating excessive friction with the shaping mandrel would also be very desirable.

It would also be advantageous to provide a sealed container and a method for sealing a container that combine ease of opening and an attractive appearance after opening with the seal strength and barrier properties required for protection of the products within the container.

SUMMARY OF THE INVENTION

These and other objects and advantages are met by the present invention which include methods and apparatus for manufacturing a tubular container having a paperboard body ply and a polymeric liner ply adhered thereto with a wet adhesive. In particular, the advantageous method according to the present invention includes the steps of applying an aqueous adhesive to a paperboard body ply and then heating the aqueous adhesive to evaporate at least part of the water content to render the adhesive substantially tacky. After the heating step, the paperboard body ply and a polymeric liner ply are preferably bonded together during the construction of the tubular container by winding the body ply and the liner ply around a shaping mandrel from opposite sides. Alternatively, the body ply and liner ply are passed through a pair of nip rollers to adhere the liner ply to the body ply. The body ply and the adhered liner ply are then wrapped around the shaping mandrel to create the tubular container. The body ply may be wrapped helically around the mandrel to create a spirally wound tube or wrapped longitudinally around the mandrel to create a convolute tube.

Preferably, the heating step includes subjecting the adhesive to at least about 100,000 J/m² and more preferably at least about 460,000 J/m². A sufficient amount of heat can be imparted by advancing the body ply adjacent to a heat source having the capability of generating a heat flux of at least about 50,000 W/m² for a period of less than about 3 seconds. This amount of heat will raise the temperature of the paperboard above the boiling point of water to evaporate part of the water content from the aqueous adhesive.

Another advantageous method includes advancing a continuous polymeric liner ply having first and second marginal edge portions and an adhesive layer on the first marginal edge portion of the surface of the liner ply facing the body ply. The adhesive layer includes a non-aqueous polymeric adhesive which is activated at a predetermined activation temperature. The liner ply and body ply are then passed through a pair of nip rollers and are aligned such that the first marginal edge portion of the liner ply extends beyond a first edge of the body ply.

The body ply and adhered liner ply are wrapped around the shaping mandrel and the non-aqueous adhesive layer of the liner ply is heated to a temperature above the activation temperature of the adhesive. Heating of the non-aqueous adhesive layer occurs prior to the body ply and liner ply being wrapped around the shaping mandrel, or while the plies are wrapped on the shaping mandrel, or both. The body ply is further wrapped around the shaping mandrel so that the second marginal edge portion of the liner ply is adhered to the first marginal edge portion by the non-aqueous adhesive layer, thus creating a sealed liner. Advantageously, the mandrel may also be heated.

An apparatus for manufacturing multi-ply tubular containers for food products having a paperboard body ply and an inner polymeric liner ply also forms a part of the invention. The apparatus includes a supply of continuous body ply material and an adhesive applicator adjacent to one surface of the body ply for applying an aqueous adhesive to that surface. The apparatus further includes at least one heat source downstream of the adhesive applicator for heating the aqueous adhesive and which is capable of evaporating enough water to render the adhesive substantially tacky. Preferably, the heat source comprises an infrared heater capable of generating heat flux of at least about 50,000 W/m².

The apparatus also includes a supply of continuous liner ply material and a pair of nip rollers through which the liner ply and the body ply are passed to adhere the liner ply to the body ply. In a preferred embodiment, a corona discharge element is positioned adjacent to the surface of the liner ply to promote adhesion to the body ply. The body and liner plies are wrapped around a shaping mandrel downstream of the nip rollers to form the body and liner plies into the desired tubular shape. A cutting station adjacent to the mandrel cuts the thus formed wound tube into discrete container lengths.

According to another aspect of the invention, the liner ply has a substantially smooth surface prior to the body ply being wrapped but has a wrinkled surface after being wrapped which is caused by circumferential compression of the liner ply. The peaks and valleys of the wrinkled surface cause the liner ply to move easily over the shaping mandrel, thus advantageously decreasing friction between the liner ply and the mandrel and eliminating problems of premature wear and overheating associated with conventional containers.

The body ply defines a predetermined circumferential length before being wrapped corresponding to one revolution of the body ply around the shaping mandrel when wrapped in the tubular shape. The liner ply is adhered to the inner surface of the body ply and defines a circumferential length which is equal to that of the body ply prior to being wrapped. Accordingly, the liner ply is circumferentially compressed when the body ply is wrapped into the tubular shape and the wrinkled surface is created.

The barrier layer preferably includes a layer of polyester having at least one metallized surface. In addition, the liner ply preferably has a thickness of less than about 3 mils. According to another embodiment, a second paperboard ply may be adhered to the first body ply opposite the liner ply for added strength.

An advantageous sealed container is also provided by the invention which allows a strong hermetic membrane-type seal, but which does not tear through the underlying layers when the membrane is removed. The seal is formed in part by a pair of inner and outer "beads" of a heat flowable polymer forming a part of the liner and membrane-type lid. In particular, a sealed composite container for products is provided having a tubular body member comprising at least one paperboard body ply and a polymeric liner ply adhered to the inner surface of the tubular body member. The polymeric liner ply preferably comprises a barrier layer and a seal layer, wherein the seal layer defines the innermost surface of the liner ply and comprises a heat flowable polymer. The barrier layer of the liner ply is adhered to the body ply with a predetermined bond strength. At least one end of the body member is preferably rolled outwardly to form a flange and expose the seal layer of the liner ply. The sealed composite container for products also includes a lid for closing the flanged end of the tubular body member, wherein the lid comprises a barrier layer and a seal layer.

The seal layer of the lid is positioned adjacent to the seal layer of the liner ply on the flange and is also comprised of a heat flowable polymer. The two seal layers are adhered together under heat and pressure to form a heat seal between the lid and the liner ply. Advantageously, the heat seal has an inner bead formed of the heat flowable polymers of the seal layers and facing the interior of the container and an outer bead formed of the heat flowable polymers on the opposite side of the heat seal from the inner bead. The heat seal further comprises a thin intermediate region between the inner and outer beads having a lower bond strength than the inner and outer beads. The intermediate region of the heat seal may even become discontinuous such that the respective barrier layers are in abutting contact.

The heat seal provides a bond strength between the barrier layer of the lid and the barrier layer of the liner ply that is less than the bond strength between the barrier layer of the liner and the tubular body member behind the barrier layer of the liner. Accordingly, when the container is opened, shearing occurs only between the barrier layers (either between the adjacent seal layers or between one of the seal layers and the adjacent barrier layer) and not through the barrier layers. The present invention thus avoids the undesirability of tearing through and/or exposing the paperboard body ply of the tubular body member.

Preferably, the lid seal layer has a lower melting point than the liner seal layer. Specifically, the melting point of the seal layer of the lid is between about 105°C to about 130°C and the melting point of the seal layer of the liner is between about 120°C and 130°C. Most preferably, the melting point of the seal layer of the lid is between about 105°C to about 125°C and the melting point of the seal layer of the liner is between about 125°C and 130°C.

The heat seal has a minimum tensile strength of about 1 lb/linear inch when pulled at a 90 degree angle relative to the top surface of the sealed container and parallel to the axis of the can. The preferred range for tensile strength is about 8 to about 12 lbs/linear inch to prevent failure of the seal at high altitude. The heat seal also has a minimum peel strength of about 1 lb/linear inch when pulled at a 135 to 180 degree angle. The preferred range for peel strength is about 5 to about 10 lbs/linear inch.

The liner seal layer is preferably constructed of a material selected from the group consisting of high density polyethylene, low density polyethylene, metallocenes and mixtures thereof. The lid seal layer is preferably constructed of a material selected from the group consisting of ethylene vinyl acetate, high density polyethylene, low density polyethylene, ethyl methyl acrylate, metallocenes and mixtures thereof. The barrier layers of the lid and liner are preferably constructed of polyester. Most preferably, the polyester used in the barrier layers is selected from the group consisting of polyethylene terephthalate, modified polyethylene terephthalate, polyethylene napthalate and mixtures thereof. The barrier layers may also be constructed of metallized polyethylene terephthalate, metallized modified polyethylene terephthalate, metallized polyethylene napthalate, metallized polypropylene, metal oxide and silicate coated polyester, metal oxide and silicate coated polypropylene, ethylene vinyl alcohol and mixtures thereof.

A method of manufacturing a sealed container for products is also provided. The method includes providing a tubular body member having at least one paperboard body ply and adhering a polymeric liner ply to the inner surface of the tubular body member. Advantageously, the liner ply has a barrier layer and a seal layer with the seal layer defining the innermost surface of the liner ply and comprising a heat flowable polymer. At least one end of the tubular body member is rolled outwardly to form a flange and expose the seal layer. The method also includes providing a lid for closing the flanged end of the tubular body member. Advantageously, the lid has a barrier layer and a seal layer with the seal layer comprising a heat flowable polymer. The method further includes contacting the seal layers of the liner ply and the seal layer of the lid and heating and pressing the seal layers together to form an inner and an outer bead of seal layer material with a thinner intermediate region of seal layer material therebetween. As a result, the lid and the liner ply are hermetically sealed. The heat seal material comprises a blend of the heat flowable polymers of the two seal layers. Preferably, the pressing is accomplished by pressing the lid and the tubular body member together using a heat sealing head.

BRIEF DESCRIPTION OF THE DRAWINGS

Some of the objects and advantages of the present invention having been stated, others will appear as the description proceeds when taken in conjunction with the accompanying drawings, which are not necessarily drawn to scale, wherein; <ul id="ul0001" list-style="none" compact="compact"><li>Figure 1 is an exploded perspective view of a tubular container according to the present invention;</li><li>Figure 2 is a fragmentary and enlarged sectional view of an end of the tubular container taken along lines 2-2 of Figure 1;</li><li>Figure 3 is an enlarged sectional view of a paperboard body ply and a polymeric liner ply taken along lines 3-3 of Figure 1;</li><li>Figure 4 is a fragmentary and enlarged sectional view of an anaconda fold seam according to the prior art;</li><li>Figure 5 is an enlarged sectional view of the anaconda fold seam of the prior art taken along lines 5-5 of Figure 4;</li><li>Figure 6 is a plan view of an apparatus according to the present invention for making a tubular container;</li><li>Figure 7 is an enlarged plan view of a section of the apparatus illustrating the alignment of the liner ply relative to the body ply;</li><li>Figure 8 is a perspective view of a section of the apparatus illustrating the winding of the body and liner plies onto a mandrel;</li><li>Figure 9A is an enlarged sectional view of the body ply taken along lines 9A-9A of Figure 6;</li><li>Figure 9B is an enlarged sectional view of the body ply and an aqueous adhesive applied thereto taken along lines 9B-9B of Figure 6;</li><li>Figure 9C is an enlarged sectional view of the body ply and the polymeric liner ply adhered thereto and taken along lines 9C-9C of Figure 6;</li><li>Figure 9D is a fragmentary and enlarged sectional view of one edge of the body ply illustrating the application of a skived edge adhesive taken along lines 9D-9D of Figure 6;</li><li>Figure 9E is a fragmentary and enlarged sectional view illustrating the application of infrared heat to the edge of the body ply taken along lines 9E-9E of Figure 6;</li><li>Figure 9F is a fragmentary and enlarged sectional view of the body ply illustrating the application of forced air heat to the edge of the body ply taken along lines 9F-9F of Figure 6;</li><li>Figure 10A is a fragmentary and enlarged sectional view of the edge of the body ply opposite the edge illustrated in Figures 9A-9F illustrating the application of forced air heat and taken along lines 10A-10A of Figure 6;</li><li>Figure 10B is a fragmentary and enlarged sectional view of adjacent body and liner plies illustrating the seams between the plies;</li><li>Figure 11 is a schematic elevational view of an apparatus for manufacturing a tubular container having two body plies according to another embodiment of the invention;</li><li>Figure 12 is a fragmentary and enlarged sectional view of one edge of the body plies adhered together in the apparatus of Figure 11;</li><li>Figure 13 is a greatly enlarged sectional view of a liner ply according to the invention adhered to the body ply;</li><li>Figure 14 is a greatly enlarged sectional view of a liner ply of another embodiment of the invention;</li><li>Figure 15 is a fragmentary perspective view of a container of the present invention illustrating the opening mechanism whereby the liner ply is not torn through to the underlying paperboard;</li><li>Figure 16 is a fragmentary and enlarged view of the sealed end of the tubular container of a preferred embodiment of the present invention illustrating inner and outer beads of heat flowable polymer;</li><li>Figure 17A is a greatly enlarged sectional view of the heat seal of the present invention taken along lines 3A-3A of Figure 15;</li><li>Figure 17B is a greatly enlarged sectional view of the heat seal of the present invention illustrating the initiation of a tear in the seal layers during opening of the container;</li><li>Figure 17C is a greatly enlarged sectional view of the heat seal of the present invention after the container has been opened; and</li><li>Figure 18 is a plan view of a preferred embodiment of an apparatus according to the present invention for making a tubular container.</li></ul>

DETAILED DESCRIPTION OF THE INVENTION

The present invention now will be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout.

A tubular container <b>10</b> according to the present invention is illustrated in Figure 1. Although illustrated as having a circular cross section, the tube may have any cross sectional shape which can be formed by wrapping the tube around an appropriately shaped mandrel. One example is a generally rectangular shaped tube having rounded corners.

The embodiment illustrated in Figure 1 is particularly advantageous for packaging potato crisps and includes a flexible lid <b>11</b>, also referred to as a membrane-type lid, and a reusable plastic end cap <b>12</b> over the seal. Various other end closures may be used, however, depending upon the type of food product which is to be packaged such as, for example, dough.

As illustrated in more detail in Figure 2, the tubular container <b>10</b> includes a wall having a body ply <b>13</b> which is preferably formed of paperboard and a liner ply <b>14</b> which is preferably formed of a polymeric material adhered to the inner surface of the body ply <b>13</b>. The upper end of the tubular container <b>10</b> is rolled over so as to form a bead <b>15</b> or flange. The lid <b>11</b> may be hermetically sealed to the top of the bead using a separate adhesive sealant <b>16</b>. The end cap <b>12</b> is then snapped over the bead <b>15</b> and may be reused after the lid <b>11</b> has been removed. A metal closure (not illustrated) can be secured to the opposite end of the container <b>10</b>.

The seams where the various plies are joined together are illustrated in Figure 3. The paperboard body ply <b>13</b> is made of a relatively thick and stiff paperboard. Accordingly, the edges are first skived and then joined together during the tube forming process with an adhesive <b>20</b> to create a strong seam. The liner ply <b>14</b> is adhered to the inner surface of the body ply <b>13</b> with a wet adhesive <b>21</b> and the overlapping edges of the liner ply are adhered together to ensure that the container <b>10</b> is completely sealed. A label ply <b>22</b> is preferably adhered to the outer surface of the body ply <b>13</b> having various indicia printed thereon regarding the product within the container.

Figures 4 and 5 illustrate conventional tubular containers which include a liner having an aluminum foil layer <b>23</b> for providing strength and barrier properties to the liner. As discussed above, because conventional wet adhesives have been unable to adhere to aluminum foil, a kraft paper layer <b>24</b> is preadhered to the aluminum foil layer <b>23</b>.

The kraft paper layer <b>24</b> cannot be exposed to the interior of the container because liquids and gasses could pass through the porous and absorbent kraft paper layer. For example, if a straight lap seam, such as that shown in Figure 3, were employed at the edges of the liner <b>14</b>, one edge of the kraft paper layer <b>24</b> would be exposed and would cause liquids in the container to wick through the kraft paper layer and leak from the container. Accordingly, an anaconda fold must be used at the seam wherein an overlying edge portion <b>25</b> of the liner is folded back on itself and then sealed to an underlying edge portion <b>26</b> of the liner as illustrated in Figure 5. The overlying liner edge portion <b>25</b> may be adhered to the underlying liner edge portion <b>26</b> by way of a hot melt adhesive (not shown). Alternatively, the aluminum foil layer <b>23</b> most often includes a thin polymeric layer (not shown) on the surface thereof facing the interior of the container which can be heat sealed to itself at the point where the overlying liner edge portion <b>25</b> contacts the underlying liner edge portion <b>26</b>.

One disadvantage of such a liner arises at the point where the anaconda fold seam extends over the bead <b>15</b> as illustrated in Figure 4. Specifically, the thick anaconda fold seam creates a pair of step discontinuities <b>30</b> along the periphery of the bead <b>15</b>. This presents difficulties when sealing the lid <b>11</b> to the bead <b>15</b> and is typically overcome by applying extra adhesive sealant <b>16</b> to the lid or the bead to fill the discontinuities <b>30</b>. The use of this added adhesive sealant <b>16</b> is disadvantageous because of the expense of the extra material used and the complexity of applying added sealant to those areas.

Two apparatus for making tubular containers which overcome the disadvantages of conventional tubular containers are illustrated in Figure 6 and Figure 18. A continuous strip of paperboard body ply material <b>13</b> is supplied to the apparatus and is first passed through a pair of opposed edge skivers <b>31</b>. As illustrated in Figure 9A, the edge skivers remove part of the square edge of the body ply <b>13</b> to create first <b>32</b> and second <b>33</b> edges having a beveled configuration.

The body ply <b>13</b> is then advanced through an adhesive applicator <b>34</b> which applies an adhesive <b>21</b> to the upper surface of the body ply <b>13</b> as illustrated in Figure 9B. The adhesive <b>21</b> is advantageously an aqueous adhesive which overcomes the many problems associated with solvent based adhesives. No special equipment is needed to capture solvents which evaporate from the adhesive in order to comply with environmental regulations. Preferred adhesives are aqueous low glass transition temperature ethylene vinyl acetate (&gt;18%) materials. One preferred adhesive is No. 72-4172 which is available from the National Starch and Chemical Company. Another adhesive which may be used is No. 33-4060 which is also available from the National Starch and Chemical Company.

The body ply <b>13</b> and wet adhesive <b>21</b> applied thereto are then passed underneath a heater <b>35</b> which evaporates at least part of the water content of the aqueous adhesive <b>21</b> to render the adhesive substantially tacky. It is important that the correct amount of heat is supplied to the adhesive. Insufficient heat will not evaporate enough water in a sufficiently short period of time with the result that the adhesive will not be rendered sufficiently tacky. Conversely, too much heat will overdry the adhesive and cause the adhesive to lose tackiness. It has been discovered that at least about 100,000 J/m² is an appropriate amount of heat to render the wet adhesive tacky. More particularly, heating the adhesive with at least about 460,000 J/m² is preferred. It has been determined that, if the body ply <b>13</b> is moving at a speed of about 50 feet per minute (or is heated for less than about 3 seconds), heating the adhesive <b>21</b> with a heater <b>35</b> having a heat flux of 200,000 W/m² will raise the temperature of the paperboard body ply <b>13</b> to at least the boiling point of water (212°F at sea level), and as high as 320°F. It will be understood by one of ordinary skill in the art, however, that these parameters may change depending on various factors including the efficiency of the heat source, the speed of the body ply (line speeds up to an average of 400 ft./min. have been achieved) and the type of adhesive used. Accordingly, a sufficient amount of heat is that which causes the adhesive to become tacky in a short period of time without being overdried. A preferred type of heat source is an infrared heater although various other heat sources, <i>e.g.,</i> forced air heating or the like can be used.

After heating the adhesive <b>21</b> on the body ply <b>13</b>, Figure 18 illustrates an alternative preferred method of bonding the polymeric liner ply <b>14</b> to the body ply <b>13</b> and constructing the tubular container <b>10</b> therewith. As shown, the body ply <b>13</b> and the liner ply <b>14</b> are fed to the shaping mandrel from opposite directions. The body ply <b>13</b> is passed under a skive adhesive applicator <b>43</b> which applies the skive adhesive <b>20</b> to the beveled surface of the skived second edge <b>33</b> of the body ply <b>13</b>. The skive adhesive <b>20</b> is preferably a hot melt adhesive of the type which is conventional in the art although it could also be a water based adhesive including one or more polymers. Polyvinyl acetate and ethylene vinyl acetate are the preferred liquid adhesives. The skive adhesive <b>20</b> helps provide a stronger body ply bond especially for single body ply containers.

The surface of the liner ply <b>14</b> that contacts the body ply <b>13</b> is subjected to a corona treatment station <b>75</b>. The opposite surface of liner ply <b>14</b> is coated with lubricant from a roller <b>44</b> which allows the liner ply to slide smoothly during the winding operation.

The liner ply <b>14</b> is then passed under an infrared heater <b>45</b> which heats the second marginal edge portion <b>42</b> of the liner ply. After the infrared heater <b>45</b>, the second marginal edge portion <b>42</b> of the liner ply <b>14</b> is then passed under at least one forced air heater <b>46</b>.

The body ply <b>13</b> and the liner ply <b>14</b> are then wrapped around a shaping mandrel <b>47</b> from opposite sides of the mandrel. Each ply is first wrapped under the mandrel <b>47</b> and then back over the top in a helical fashion with the liner ply <b>14</b> wound against the surface of the mandrel. The first marginal edge portion <b>41</b> of the liner ply <b>14</b> is exposed on the mandrel <b>47</b> and is subjected to heat from a second forced air heater <b>50</b>.

As the body ply <b>13</b> is further wrapped and the first edge <b>32</b> of the body ply <b>13</b> advances back under the mandrel <b>47</b> after one complete revolution, it is brought into contact with the second edge <b>33</b> of the ensuing portion of the body ply <b>13</b> which is first coming into contact with the mandrel. The skived edges <b>32</b>, <b>33</b> become abutted together and the skive adhesive <b>20</b> adheres the edges together to form a spirally wound tube which advances along the mandrel <b>47</b>.

With regard to the liner ply <b>14</b>, the first marginal edge portion <b>41</b> is brought into an overlapping relationship with the second marginal edge portion <b>42</b> to create a sealed straight lap seam as illustrated in Figure 10B. The seal is formed by a polymeric adhesive layer <b>63</b> of the first marginal edge <b>41</b> becoming bonded to the second marginal edge <b>42</b>. However, a strip of hot melt adhesive or aqueous adhesive could alternatively be used for securing and sealing the liner overlap.

Figure 6 illustrates an alternative method of bonding the body ply <b>13</b> to the polymeric liner ply <b>14</b>. As shown, after the heater <b>35</b>, the body ply <b>13</b> is then advanced into a pair of opposed nip rollers <b>36</b>. A continuous strip of liner ply material <b>14</b> is fed from a reel <b>40</b> and is also advanced into the nip adjacent to the adhesive surface of the body ply <b>13</b>. The wet adhesive <b>21</b> is substantially tacky and thus instantaneously bonds to the liner ply <b>14</b> without sliding as they are nipped together.

The liner ply <b>14</b> is aligned through the nip with the body ply <b>13</b> such that a first marginal edge portion <b>41</b> of the liner ply extends beyond the first edge <b>32</b> of the body ply. The liner ply <b>14</b> may have the same width as the body ply <b>13</b> and thus the opposite second marginal edge portion <b>42</b> of the liner ply does not extend all the way to the second edge <b>33</b> of the body ply. Alternatively, the liner ply <b>14</b> may be wider or narrower than the body ply <b>13</b> depending on the amount of liner overlap which is desired. This configuration can be seen in the plan view of Figure 7 and the sectional view of Figure 9C.

After the nip rollers <b>36</b>, the body ply <b>13</b>/liner ply <b>14</b> laminate is passed under a skive adhesive applicator <b>43</b> which applies the skive adhesive <b>20</b> to the beveled surface of the skived second edge <b>33</b> of the body ply <b>13</b>. The skive adhesive <b>20</b> is preferably a hot melt adhesive of the type which is conventional in the art although it could also be an other polymeric-type adhesive. Liquid polyvinyl acetate and ethylene vinyl acetate are the preferred adhesives. The skive adhesive <b>20</b> helps provide a stronger body ply bond especially for single body ply containers.

The surface of the liner ply <b>14</b> may then be coated with lubricant from a roller <b>44</b> which allows the liner <b>14</b> to slide smoothly during the winding operation. If making the embodiment of the container discussed below, however, the lubricant can be advantageously eliminated or greatly reduced.

The laminate is then passed under an infrared heater <b>45</b> which heats the second marginal edge portion <b>42</b> of the liner ply <b>14</b> and also may heat the second edge <b>33</b> of the body ply <b>13</b>, as can be seen in Figure 9E. An infrared heater capable of generating a heat flux of at least about 83,000 W/m² has been determined to be sufficient. After the infrared heater <b>45</b>, the second marginal edge portion <b>42</b> of the liner ply <b>14</b> is then passed under at least one forced air heater <b>46</b>.

The body ply <b>13</b>/liner ply <b>14</b> laminate is then wrapped around a shaping mandrel <b>47</b>. The laminate is first wrapped under the mandrel <b>47</b> and then back over the top in a helical fashion with the liner ply <b>14</b> wound against the surface of the mandrel. The first marginal edge portion <b>41</b> of the liner ply <b>14</b> is exposed on the mandrel <b>47</b> and is subjected to heat from a second forced air heater <b>50</b> as can been seen in Figures 8 and 10A. As the laminate is further wrapped and the first edge <b>32</b> of the body ply <b>13</b> advances back under the mandrel <b>47</b> after one complete revolution, it is brought into contact with the second edge <b>33</b> of the ensuing portion of the body ply <b>13</b> which is first coming into contact with the mandrel. The skived edges <b>32</b>, <b>33</b> become abutted together and the skive adhesive <b>20</b> adheres the edges together to form a spirally wound tube which advances along the mandrel <b>47</b>. With regard to the liner ply <b>14</b>, the first marginal edge portion <b>41</b> is brought into an overlapping relationship with the second marginal edge portion <b>42</b> to create a sealed straight lap seam as illustrated in Figure 10B. The present invention can thus eliminate the disadvantages associated with anaconda fold seams by using a straight overlapping seam instead.

A preferred liner construction is illustrated in Figures 13 and 14 and includes a seal layer <b>60</b>, a moisture barrier layer <b>61</b> and an adhesive layer <b>63</b>. The barrier layer <b>61</b> is resistant to the passage of liquids and gasses such as oxygen. If a high barrier is required for both liquids and gasses, preferred barrier materials are metallized polyester or metallized polypropylene. Some food products, however, do not require a gas barrier, such as various juices, and other barrier materials may be used (although the barrier may also be generally resistant to the passage of gasses). It will be understood that various barrier materials or properties could be employed depending upon the item being packaged.

Alternative barrier materials include nylon, EVOH (ethylene vinyl alcohol polymer and copolymer), polyvinylidene chloride, polyethylene, polypropylene, metallized polypropylene, metal oxide and silicate coated polyester, metal oxide and silicate coated polypropylene and the like as will be apparent to the skilled artisan. One surface of the barrier layer <b>61</b> may include a thin metallized coating <b>62</b> to provide a metallic appearance and also to enhance the barrier properties. The metallized coating <b>62</b>, which may be formed of aluminum, is significantly thinner than a foil layer, however, and is not necessary for strength or barrier properties in certain applications. Thus, a thick and expensive foil sheet layer is advantageously eliminated. The liner ply <b>14</b> preferably has a total thickness less than about 3 mils and is more preferably closer to 1 mil. in thickness.

An adhesive layer <b>63</b> is below the metallized coating <b>62</b> and defines the outer surface of the liner ply <b>14</b>. The adhesive layer <b>63</b> includes a non-aqueous polymeric adhesive which is activated at a predetermined activation temperature. Such adhesives, which are also known as "dry-bond" adhesives, can include one or more of the following polymers or modified copolymers thereof; ethylene vinyl acetate, ethylene acrylic acid, ethylene methacrylic acid, ethylene methyl acrylate, ethylene butyl acrylate, metallocenes and blends with each other or lower cost polyolefins. A preferred embodiment is illustrated in Figure 14 and includes an adhesive layer having two sublayers <b>63a,b</b> which are coextruded together. The inner sublayer <b>63a</b> is preferably ethylene acrylic acid which adheres well to the polyester barrier layer <b>61</b> and the outer sublayer <b>63b</b> is preferably ethylene methyl acrylate which adheres well to the paperboard body ply <b>13</b>. The adhesive layer <b>63</b> is manufactured as part of the liner ply <b>14</b> and, because of the adhesiveness of the wet adhesive <b>21</b>, is preferably formed on only the first marginal edge portion <b>41</b> of the liner ply. A liner ply <b>14</b> wherein the adhesive layer <b>63</b> extends across the entire width of the liner such that the wet adhesive <b>21</b> is eliminated and the liner ply is adhered directly to the body ply <b>14</b> is disclosed in copending U.S. Patent Application Serial No. 08/796,912, filed February 6, 1997, which is assigned to the assignee of the present invention and is incorporated herein by reference.

A seal layer <b>60</b> may also form a part of the liner ply <b>14</b> and defines the inner surface of the liner ply. The seal layer <b>60</b> provides a surface against which the adhesive layer <b>63</b> is adhered when the first marginal edge portion <b>41</b> of the liner ply <b>14</b> is brought into an overlapping relationship with the second marginal edge portion <b>42.</b> The seal layer <b>60</b> includes a polyolefin polymer which is preferably high density polyethylene or high density polyethylene blends containing up to 30% low density polyethylene.

One advantageous feature of the seal layer <b>60</b> is that it has a higher melting temperature than the adhesive layer <b>63</b>. As noted above, the first marginal portion <b>41</b> of the liner ply <b>14</b> is raised to a temperature (whether heated before reaching the mandrel <b>47</b> or while on the mandrel <b>47</b>) such that the adhesive layer <b>63</b> is activated. However, if the seal layer <b>60</b> was made of the same polymer as the adhesive layer <b>63</b> or had a melting temperature equal to or less than the melting temperature of the adhesive layer, the seal layer would be melted and inclined to stick to the mandrel <b>47</b>, which would greatly impede the winding process. This problem would be especially acute with the apparatus according to the present invention because the mandrel <b>47</b> is preferably heated to minimize heat loss from the liner ply <b>14</b> to the mandrel. The present invention does not suffer from this problem, however, because the seal layer <b>60</b> has a melting temperature higher than the activation temperature of the adhesive layer <b>63</b>.

The tube is then advanced down the mandrel <b>47</b> by a conventional winding belt <b>51</b> which extends around a pair of opposed pulleys <b>52</b>. The winding belt <b>51</b> not only rotates and advances the tube, but also applies pressure to the overlapping edges of the body ply <b>13</b> and liner ply <b>14</b> to ensure a secure bond between the respective ply edges.

An outer label ply <b>22</b> is then preferably passed over an adhesive applicator <b>53</b> and wrapped around the body ply <b>13</b>. The label ply <b>22</b> could be applied before the winding belt <b>51</b>. At a cutting station <b>54</b>, the continuous tube is cut into discrete lengths and removed from the mandrel <b>47</b>.

The ends of the containers <b>10</b> are then rolled outwardly to form the bead <b>15</b> or a flange. Another advantageous feature of the polymeric liner ply according to the present invention is that the elasticity of the polymer causes the bead <b>15</b> to be locked in place once rolled. Conventional inelastic foil liners may have a tendency to unroll the bead <b>15</b> or crack which can present a problem when sealing the ends. Thus, with the liner of the present invention, "tighter" beads or flanges having reduced radii of curvature can be formed.

After being filled with the food product, a lid <b>11</b> preferably is sealed on one or both ends of the container <b>10</b>. The unsupported liner ply <b>14</b> according to the present invention is significantly thinner than conventional foil liners and a straight lap seam can be used instead of an anaconda fold seam. Accordingly, much smaller discontinuities are presented at the point where the seam crosses the bead, and the lid <b>11</b> can be cheaply and easily sealed to the bead <b>15</b> with a minimum amount of adhesive sealant <b>16</b>. An end cap <b>12</b> can then be placed over the lid <b>11</b>.

Figures 15-17C illustrate further desirable features of the invention relating to the seal at the end of the container with the lid. The lid <b>11</b> is constructed of multiple layers. Optionally, the layer disposed on the outermost surface of the lid <b>11</b> away from the inside of the tubular container <b>10</b> is a paperboard layer <b>67</b>. A barrier layer <b>65</b> is also provided that serves as a barrier to the passage of liquids and/or gases such as oxygen. If a barrier is required for both liquids and gases, the barrier material is preferably selected from the group consisting of polyethylene terephthalate, modified polyethylene terephthalate, polyethylene napthalate, metallized polyester or metallized polypropylene and mixtures thereof. The barrier layer may also be constructed of metal oxide and silicate coated polyester, metal oxide and silicate coated polypropylene, ethylene vinyl alcohol and mixtures thereof.

Advantageously, the lid <b>11</b> further includes a seal layer <b>66</b> comprised of a heat flowable polymer and positioned such that the seal layer <b>66</b> of the lid <b>11</b> is adjacent to the seal layer <b>60</b> of the liner ply <b>14</b>. The seal layer <b>66</b> of the lid <b>11</b> is preferably constructed of a material selected from the group consisting of ethylene vinyl acetate, high density polyethylene, low density polyethylene, ethyl methyl acrylate, metallocenes and mixtures or blends thereof. The seal layer <b>66</b> of the lid <b>11</b> preferably has a melting point within the range of about 105°C and 130°C. Most preferably, the melting point of the seal layer <b>66</b> is between about 105°C and 125°C.

For purposes of this embodiment, the seal layer <b>60</b> of the liner ply <b>14</b> is preferably constructed of a material selected from the group consisting of high density polyethylene, low density polyethylene, metallocenes and mixtures or blends thereof. The seal layer <b>60</b> of the liner ply <b>14</b> preferably has a melting point within the range of about 120°C and about 130°C. Most preferably, the seal layer <b>60</b> has a melting point between about 125°C and 130°C.

Figure 16 illustrates the sealed end of the tubular container of a preferred embodiment of the present invention wherein the seal layers, <b>60</b> and <b>66</b>, are heat sealed together. As shown in Figure 17A, this embodiment provides a sealed composite container for products having a heat seal between the liner ply <b>14</b> and the lid <b>11</b> in the form of an inner heat seal bead <b>68</b> and an outer heat seal bead <b>69</b>. The inner heat seal bead <b>68</b> and the outer heat seal bead <b>69</b> are formed of the heat flowable polymers of the seal layer <b>60</b> of the liner ply <b>14</b> and the seal layer <b>66</b> of the lid <b>11</b>. In particular, the seal layers <b>60</b>, <b>66</b> are heated and pressed together with a heat seal head. The heat flowable polymers of both seal layers are displaced outwardly from the intermediate region and are cooled to form the beads <b>68</b>, <b>69</b>. The inner heat seal bead <b>68</b> faces the interior of the tubular container <b>10</b> and the outer heat seal bead <b>69</b> is disposed on the opposite side of the heat seal area from the inner heat seal bead <b>68</b>. When cooled, the heat seal comprises a thin intermediate region <b>70</b> between the inner heat seal bead <b>68</b> and the outer heat seal bead <b>69</b>. In certain places, the heat flowable polymers may be completely displaced from between the barrier layers <b>61</b> and <b>65</b> such that the barrier layers are in abutting contact. However, the inner and outer beads <b>68</b>, <b>69</b> maintain double barriers against the passage of liquids and gases so that a hermetic seal is maintained. The intermediate region <b>70</b> preferably has a lower bond strength than the inner heat seal bead <b>68</b> and the outer heat seal bead <b>69</b>. The term "bead" as used herein is intended to be distinguished from prior containers having SURLYN® polymer layers heat sealed together where very little, if any flowing of the polymers occurs. In addition, this embodiment is not limited to use with only liners having a straight overlapping seam, but the heat seal beads <b>68</b>, <b>69</b> could also be used with a folded anaconda seam.

In effect, the inner heat seal bead <b>68</b> and the outer heat seal bead <b>69</b> provide a double seal having a high tensile strength. The tensile strength of the bead seals gives the container <b>10</b> a strong seal against forces acting upon the container in a direction normal to the heat seal (i.e., normal to the plane defined by the end of the tubular container <b>10</b>). Since most forces acting upon a container during storage and transit will occur normal to the heat seal area, the high tensile strength of the inner heat seal bead <b>68</b> and outer heat seal bead <b>69</b> of the present invention is especially advantageous for use with product containers. The heat seal has a minimum tensile failure strength of about 1 lb/linear inch when pulled at a 90 degree angle relative to the top surface of the sealed container and parallel to the axis of the can. The preferred range for tensile failure is about 8 to about 12 lbs/linear inch to prevent failure of the seal at high altitude.

Notwithstanding the high tensile strength, the peel strength of the heat seal formed according to the present invention is relatively low, resulting in a container that exhibits relative ease of opening. This is in contrast to conventional containers where two SURLYN® polymers are ionically cross-linked together, resulting in a bond which is sufficient to tear the liner <b>14</b> when removing the lid <b>11</b> (rather than tearing through the SURLYN® polymer). The heat seal also has about a 1 lb/linear inch minimum peel failure strength when pulled at a 135 to 180 degree angle. The preferred range for peel strength is about 5 to about 10 lbs/linear inch. Thus, the heat seal of the present invention combines the tensile strength necessary to prevent unwanted breaches of the tubular container <b>10</b> with a relatively low peel strength for ease of opening by the consumer.

Figure 15 illustrates the opening mechanism for container <b>10</b> of the present invention. As shown by Figures 17B and 17C, the shearing force generated during opening of the container <b>10</b> causes a tear to propagate through the seal layer <b>60</b> of the liner ply <b>14</b> and/or the seal layer <b>66</b> of the lid <b>11</b>. The seal layer <b>60</b> of the liner ply <b>14</b> and the seal layer <b>66</b> of the lid <b>11</b> provide a bond strength between the barrier layer <b>65</b> of the lid <b>11</b> and the barrier layer <b>61</b> of the liner ply <b>14</b> that is lower than the bond strength between the barrier layer <b>61</b> of the liner ply <b>14</b> and the paperboard body ply <b>13</b> (or any other intermediate layers such as the metallized coating <b>62</b> of the liner <b>14</b>). As a result, shearing that takes place during the opening of the tubular container <b>10</b> occurs only between, and not through, the barrier layers of the liner ply <b>14</b> and lid <b>11</b>. When the tubular container <b>10</b> of the present invention is opened, unsightly tears through the barrier layer <b>61</b> of the liner ply <b>14</b> do not occur.

Another advantageous feature of the present invention is the wrinkled or "matte" surface of the liner ply <b>14</b> which can be seen in Figures 1 and 2. The wrinkled surface is provided by the method and apparatus illustrated in Figure 6 which causes equal lengths of the body ply <b>13</b> and liner ply <b>14</b> to be adhered together before being wrapped around the mandrel <b>47</b>. As the plies are wrapped around the mandrel <b>47</b>, the much stiffer body ply <b>13</b> causes the liner ply <b>14</b> to become compressed. In other words, the body ply <b>13</b> initially defines a circumferential length corresponding to one revolution around the mandrel <b>47</b> and the liner ply <b>14</b> has an initial length per revolution equal to that of the body ply <b>13</b>. However, when wrapped, the liner ply <b>14</b> is forced into a circular section having a slightly smaller radius than the radius of the circle defined by the body ply <b>13</b>. As such, the liner ply <b>14</b> is circumferentially compressed relative to the body ply <b>13</b>.

The circumferential compression is advantageous if certain types of liner ply <b>14</b> are used because the compression may cause an initially smooth liner ply to have a wrinkled or matte surface once wrapped. The wrinkled surface finish has an "alligator skin" type appearance caused by many small peaks and valleys in the surface of the liner ply <b>14</b>. The wrinkled surface is highly advantageous because it dramatically decreases the amount of winding friction between the liner ply <b>14</b> and mandrel <b>47</b>. While not wishing to be bound by theory, it is believed that the decreased friction is due to the decreased surface area of the liner ply <b>14</b> (caused by the peaks and valleys thereof) which is in frictional contact with the mandrel <b>47</b>. The friction is decreased so much that the lubricant and lubricant roller <b>44</b> can preferably be eliminated. One preferred material for the liner ply <b>14</b> includes a polyester barrier layer <b>61</b> which becomes wrinkled with circumferential compression.

An alternative embodiment of the tubular container <b>10</b> according to the present invention is illustrated in Figure 12 and includes two overlying body plies <b>13a</b>, <b>13b</b>. This embodiment is advantageous if additional strength is necessary. A first body ply <b>13a</b> is adhered to the liner <b>14</b> in the fashion discussed above and passed through the pair of nip rollers <b>36</b>. A second body ply <b>13b</b> is coated with a wet adhesive and then brought into engagement with the underside of the first body ply <b>13a</b> so that they will be adhered together. The heating equipment used in connection with the first body ply <b>13a</b> is not necessary with the second body ply <b>13b</b> because the water in the adhesive on the second body ply can escape from the bond area after the body plies have been adhered together because both adjoining plies are made of pervious paperboard.

Many modifications and other embodiments of the invention will come to mind to one skilled in the art to which this invention pertains having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the invention is not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. For example, the tubular containers according to the present invention are not necessarily helically wound but may instead be longitudinally wrapped to create a "convolute" tube having an axially extending seam. In addition, although the tubular containers according to the present invention have been described primarily in connection with food products, it is to be understood that the containers could be used in connection with other products where the liner ply is advantageous such as, for example, ink or caulk. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.