MXPA00008469A - Tubular composite containers having unsupported film liners and methods and apparatus for making same - Google Patents

Abstract

A tubular composite container (10) includes a paperboard body ply (13) wrapped into a tubular shape, and a polymer film liner ply (14) wrapped into a tubular shape and adhered to the inner surface of the body ply (13). The liner ply (14) has a circumferential length when unwrapped and flat that is less than that of the body ply (13) so that the liner ply (14) is substantially uncompressed circumferentially. A strip of polymer film liner material is wrapped onto a mandrel and overlapping edge portions of the liner strip are heat sealed together by first preheating the liner strip to a temperature below the sealing temperature of the heat seal material on the edge portions of the liner strip, and then further heating the overlap region of the liner strip to at least the sealing temperature to cause heat sealing of the edge portions. A paperboard strip is coated on an inner surface with adhesive and is then wrapped about the liner and adhered thereto. The outer surface of the liner strip is surface treated by corona discharge or flame treatment prior to being wrapped on the mandrel to improve adhesion to the paperboard, and the liner strip tension is maintained less than about 1 pound per inch of width to prevent liner stretching as the liner strip is advanced to and wrapped about the mandrel. The preheating of the liner strip is performed by a heated section of the mandrel over which the liner strip passes. The overlap region is locally heated by an infrared heater.

Description

TUBULAR COMPOUND CONTAINERS THAT HAVE INTERIOR NON-REINFORCED FILM COATINGS AND METHODS AND APPARATUS TO MANUFACTURE THEM FIELD OF THE INVENTION The present invention relates to the methods and apparatus for manufacturing tubular composite containers and, more particularly, to the methods and apparatus for manufacturing said containers by wrapping an inner lining strip and at least one cardboard strip around an axis, and adhering to each other the different strips.

BACKGROUND OF THE INVENTION Sometimes food products and beverages, and other perishable items are packed in tubular containers that are sealed at both ends. Typically these tubular containers include at least one structural body layer and are formed by wrapping a continuous strip of a body layer material around a mandrel with a desired shape to create a tubular structure. The strip of the body layer can be wound spirally around the mandrel, or it can be passed through a series of forming elements so as to wrap it in a spiral shape around the mandrel. At the downstream end of the mandrel, the tube is cut into discrete lengths and then fixed with end caps, to form the container. Tubular containers of this type typically include a coating layer on the inner surface of the cardboard body layer. The coating layer prevents liquids, such as juice, from leaving the container, and also prevents liquids from entering the container and possibly contaminating the product packaged therein. Preferably the coating layer is also resistant to the passage of gases, to prevent odors of the food product that is in the container from escaping from it and to prevent atmospheric air from entering the container and spoiling the food product. In this way, the coating layer provides barrier properties and the body layer provides structural properties. Frequently, conventional coating layers include an aluminum sheet, which has good barrier qualities and also has advantageous strength properties. In particular, the coating is wound on the mandrel before the body layer is rolled up, and must be strong and stiff enough to be able to be wound on the mandrel independently without stretching or wrinkling. In addition, the aluminum sheet typically includes a kraft paper backing to allow the aluminum sheet to be adhered to the cardboard body layer. Due to the support provided to the coating by the aluminum layer reinforced with kraft paper, said coatings are known as "reinforced" coatings.

Aqueous-based adhesives (or "wet adhesives") are preferred to adhere the coating layer to the body layer, because solvent-based adhesives are no longer favored due to various environmental concerns about their use and disposal. . However, it has been difficult to cause the aqueous adhesives to stick to the smooth, impermeable surface of the aluminum foil layer. Accordingly, a kraft paper backing has been pre-adhered to the aluminum layer so that the coating can in turn adhere to the cardboard body layer with the wet adhesives. Kraft paper also adds additional costs and thickness to the coating. Normally a coating having an aluminum layer includes a polymer layer on the surface of the aluminum sheet, which faces inwardly into the interior of the resulting container. The polymeric layer prevents the product that is inside the container from coming into contact with the aluminum layer, which, in some cases, can cause a reaction that can corrode the aluminum and discolor or even adulterate the product. The polymer layer can also improve the abrasion resistance of the aluminum sheet. Often the polymer layer is also a heat-sealable material that allows a portion of the edge of the coating strip to be heat sealed to an opposite overlay portion of the strip flange. In the manufacture of tubular composite containers, a strip of coating material is wrapped around a forming mandrel and advanced along the mandrel as the tubular composite container is formed. With the line speeds currently used in the commercial manufacture of such containers, typically the coating strip is advanced at a linear speed of 121 meters / minute or more, and compressed onto the mandrel with the cardboard strips in addition to the coating, and with the band or other device that advances the tubular container along the mandrel. As a result, there is considerable friction between the mandrel and the liner, which generates heat. This heat can cause the polymer layer of the coating in contact with the mandrel to soften, resulting in the coating tending to adhere to the mandrel and "rubbing" as it proceeds along the mandrel. To help counteract this tendency to friction, a lubricant is usually applied to the interior surface of the coating. In addition, in some cases the mandrel is cooled so that its temperature is kept low enough so that the polymer layer of the coating is less prone to softening and sticking to the mandrel. However, while the polymer film layer performs the function of a heat sealing layer, a dilemma arises where a low temperature in the mandrel is preferable to reduce friction and the tendency to stick to the coating in the mandrel, while a higher temperature is preferable to facilitate the activation of the heat sealing polymer layer to form a seal.

When a reinforced coating is used, this dilemma can be largely avoided by heating the coating, or at least the edge portions that are superimposed to form a seal, at a temperature above the sealing temperature for the polymer layer , just before wrapping the liner around the mandrel. The relatively large mass of the aluminum and kraft paper layers of the coating operates as a heat sink that retains heat long enough so that the edge portions of the coating can be sealed to each other with heat when the coating strip It is wrapped over the mandrel. However, aluminum sheets are expensive, and therefore it is preferred to provide a container and method for making said container, which includes a "non-reinforced" coating having the necessary barrier properties without the aluminum foil layer and Kraft paper. But when a non-reinforced coating is used, the heat sink function of the aluminum foil and kraft paper layers is eliminated. As a consequence, the relatively thin polymer film coating is difficult to heat due to its low mass which tends to rapidly dissipate heat. The use of non-reinforced coatings also presents other technical challenges. For example, due to the problems associated with winding on the mandrel of a non-reinforced coating, such as stretching, creasing or deformation of the coating, the manufacture of a container having a non-reinforced coating layer has not been economically or commercially feasible. , with the apparatus and conventional methods. However, in view of the considerable savings in material and costs offered by unreinforced coatings, it would be highly desirable to provide methods and apparatus for making composite tubular containers with unreinforced coatings. Non-reinforced coatings also offer other advantages in addition to cost and material savings. More particularly, the elimination of the kraft paper layer makes it possible to use straight overlapping seams in the coating, instead of the conventional "anaconda fold" seams traditionally used with kraft paper reinforced coatings. In an anaconda fold, the bottom edge of the coating layer bends back on itself and adheres to the overlapped edge. The anaconda fold allows the polymeric layers on the surface of the aluminum layer to be sealed to each other with heat. Alternatively, a hot melt adhesive can be used to seal the bottom edge of the coating layer to the overlapped edge. In this way the edge of the kraft paper is not exposed to the interior of the container and thus the liquids inside the container will not be absorbed by the kraft paper. An example of such a fold is illustrated in U.S. Pat. do not. 5,084,284 of McDilda, et al. However, anaconda folds are not popular due to their increased thickness. The thickness of an anaconda fold seam is equal to three times the thickness of the coating layer. For this reason, with the relatively thick reinforced coatings, the anaconda fold represents a substantial thickness and presents difficulties when it comes to hermetically sealing the ends of the tubular container. Specifically the ends of the tube are bent out after they have been cut, to form a rolled circular flange or flange at one or both ends of the tube, and then the end caps or membranes are applied and generally sealed to the flange with an adhesive sealant , seal with heat or other technique. But in the area where the thick anaconda fold seam forms a portion of the edge surface, the surface of the end flange or flange may be substantially non-planar, thus forming hill and / or valley type irregularities. For this reason an extra amount of adhesive sealant or heat seal material is required, to fill the discontinuities and hermetically seal the tubular container. The additional application of adhesive sealant or heat sealing material is a disadvantage, due to the additional sealant to be used and the increased difficulty for the consumer to remove the seal due to the additional sealant. For example, when a membrane includes a heat sealing layer, the entire heat sealing layer must be made thicker, although in reality the increased thickness is needed only around the periphery of the membrane where it contacts the membrane. flange.

Due to the aforementioned problems with respect to reinforced coatings, efforts have been made to develop methods and apparatus for making tubular composite containers having unreinforced coatings, in which the layers of aluminum foil and kraft paper are removed from the coating. In addition, methods and apparatus for making composite containers having coatings formed without anaconda fold seams have been sought. A coating formed entirely of one or more relatively thin polymer layers would be particularly beneficial because additional layers of aluminum foil and kraft paper would be eliminated along with their high costs, and the coating seam would have a relatively small protrusion at the end. bent of the container so that the problems of closing would be substantially reduced by hermetically sealing the ends of the container. Accordingly, the assignee of the present application has focused on developing practicable methods and apparatuses for making containers with said non-reinforced film coatings. For example, the applicant of the present application has developed methods and apparatuses for making composite containers with non-reinforced coatings made with polymer film and without anaconda folds, as described in co-pending US patent application no. 08 / 796,912 entitled "Polymeric coating layer for tubular containers and methods and apparatuses for manufacturing same" filed on February 6, 1997, and U.S. patent no. 5,829,669 entitled "Tubular container and methods and apparatuses for manufacturing the same", filed on November 3, 1998, both by the same owner, whose complete descriptions are included here for reference. Patent application '912 and patent' 669 describe methods and apparatuses for forming composite containers wherein, according to one embodiment, a polymeric coating strip is adhesively bonded to a cardboard strip to form the body, before wrapping it around a training mandrel. By "prelaminating" together the polymeric coating strip and the cardboard strip, the coating is effectively structurally reinforced by the cardboard strip, so that the mandrel is relatively easily advanced without unduly stretching or deforming it in the process . The polymeric coating strip is deflected relative to the cardboard to which it is adhesively bonded, such that a marginal edge portion of the coating strip extends beyond an edge of the cardboard strip. The laminated paperboard / polymer strip is wrapped around the mandrel so that the edges of the cardboard strip overlap each other and the marginal edge portions of the polymeric coating overlap each other. One of the marginal edge portions of the coating strip includes a non-aqueous adhesive layer which is activated by heat. Before and / or while the laminated paperboard / polymer strip is wrapped around the mandrel, the non-aqueous adhesive layer in the marginal edge portion is heated to at least its activation temperature, and the overlap edges are they seal with each other with heat. In this way, the resulting composite container has a polymeric coating formed without anaconda fold seams. However, the apparatus that is used to laminate the body and coating layers together before wrapping them on the mandrel, in some applications may not be the most advantageous. For example, in some cases a separate set of press rollers is needed to effect lamination. In addition, it will be convenient that the coating supply and the body layer supply rollers are located on the same side of the mandrel, which can make the placement of the supply rollers and the path of the layers towards the mandrel more complicated., of what it would be in the event that both layers of coating and body did not have to reach the mandrel from the same side. It may also be more difficult to replace the rollers when the two supply rollers are located together, as they tend to be to make the use of the space more efficient. In view of the foregoing, it would be highly preferable to provide methods and apparatus capable of making a composite container with a polymer film coating. What is more, it would be preferable to provide methods and apparatuses that would allow the formation of said container without prelaminating the body and coating layers. It would also be desirable to provide methods and apparatus that would allow the winding, either on the same side or opposite sides, of the body and liner layers on the mandrel, to increase the flexibility available to the designer and user of the apparatus, to locate the rollers. of body supply and coating.

BRIEF DESCRIPTION OF THE INVENTION The present invention fulfills the aforementioned objects and achieves other advantages, including methods and apparatus for making a tubular composite container having a cardboard body strip and a non-reinforced polymer film coating strip, wherein the coating strip Not reinforced is wrapped around the mandrel without first having to be adhered or pre-laminated to the cardboard strip. According to a preferred embodiment of the invention, the coating strip includes a layer of heat-activated sealing material, covering at least a first edge section of the coating strip, and a layer of compatible polymer material which covers at least a second opposite edge portion of the coating strip. The sealing material has a predetermined sealing temperature at which the material is activated to form a bond with the compatible polymer material. The coating strip is wrapped around the mandrel, with the sealing material in the first edge portion of the facing tape facing outward, and the compatible polymer material in the second edge portion facing inward toward the mandrel. , and the first edge portion is overlapped by the second edge portion to form an overlap joint therebetween, the layer of the sealing material at the first edge portion in contact with the compatible material at the second edge portion. At least the edge portions of the coating strip are preheated to a first heating station, so that the sealing material reaches a high temperature below its predetermined sealing temperature, when the edge portions overlap to form the overlap union. Heat is then locally applied to the overlap joint of the tubular liner to a second heating station in the mandrel, to further raise the temperature of the sealing material to at least the predetermined sealing temperature, and causes the layers of the material to sealed join the compatible material. Finally a continuous strip of cardboard body is wrapped around the tubular casing that is in the mandrel, and adhered thereto to create a tubular container. In a further preferred embodiment of the invention, the preheating of the coating strip is carried out by raising the temperature of at least a portion of the mandrel, at an elevated temperature and wrapping the coating strip in the mandrel so that the The coating strip passes over the elevated temperature portion of the mandrel, before reaching the second heating station. In this way, the temperature of the mandrel can be maintained at a relatively lower temperature than would be required if all the heating to activate the sealing material was done by heating the mandrel. In this way the friction of the coating strip on the mandrel is minimized. The elevated temperature portion of the mandrel can be heated by circulating a hot fluid through the mandrel portion, by placing heating elements of strength type within the mandrel portion, or by other means known in the heating art. According to another preferred embodiment of the invention, the additional heat for activating the sealing material is applied locally to the overlap junction of the coating, heating a portion of the mandrel over which the overlap connection passes at a higher temperature than the elevated temperature portion of the mandrel. The infrared radiation is advantageously focused on the overlap joint and penetrates through the portions of the coating edge, so that the surface of the mandrel that is under the overlap joint is heated to a temperature above the sealing temperature of the sealing material. Nevertheless, other heating devices can be used in addition to, or instead of, the infrared radiator, including the hot-air driven devices directed over the overlap joint, the electric resistance heating elements disposed within the mandrel or other known heating devices in the heating technique To adhere the liner and cardboard strips, adhesive is applied to a surface of the cardboard body strip that confronts the outer surface of the tubular liner. The surface of the coating strip forming the outer surface of the tubular coating is treated to improve adhesion of the adhesive thereto. In a preferred embodiment, the treatment of the surface comprises corona discharge treatment. The structure treatment can be used alternatively. The thin films of polymer can be stretched and therefore it is preferable to control the tension of the polymer film coating strip to keep the tension sufficiently low so that the stretching of the coating strip is substantially prevented. Thus, in a preferred embodiment of the invention, the tension of the coating strip is controlled so that it is less than about 17.85 kg / m in width of the coating strip, which allows the films having a thickness as small as 0.00127 centimeters are used for the coating strip. The invention also includes apparatus for making tubular composite containers having unreinforced coatings. An apparatus according to a preferred embodiment of the invention includes an elongated mandrel having a generally tubular outer surface adapted to allow a polymer film coating strip, which has a heat sealing material, to be wrapped around the mandrel and slide on it. The apparatus also includes a first heater in heat exchange relation with a first portion of the mandrel, and which is operated to heat the first portion of the mandrel to a first elevated temperature, below a predetermined minimum sealing temperature of the sealing material with coating heat. The apparatus also includes a second heater in heat exchange relation with a second portion of the mandrel, and which is operated to heat the second portion of the mandrel to a second temperature above the predetermined minimum sealing temperature. The apparatus also comprises an adhesive applicator for applying the adhesive to a surface of a continuous strip of cardboard, which passes through the adhesive applicator. A tube conveyor engages the cardboard strip when it is wrapped around the mandrel and adhered to the coating strip on the mandrel. The tube conveyor advances the composite tube along the length of the mandrel as the tube is being formed, so that the coating strip passes over the first portion of the mandrel and then onto the second portion thereof. The first and second heaters located in the first and second mandrel portions progressively heat at least the opposite edge portions of the facing strip to the predetermined minimum sealing temperature to heat seal one of the edge portions. to the other, in an overlap formed between them. The first heater conveniently comprises a passage of fluid formed within the first portion of the mandrel to circulate a hot fluid therein, to heat the first portion to the first temperature. The second heater preferably comprises an infrared radiator positioned to direct an infrared radiation to an overlap joint of a coating strip on the mandrel. In particular where a thin coating of unreinforced polymer moves on the mandrel at high speeds of up to 121.92 meters / minutes, the coating has very little time to absorb the heat. In this way, to heat the overlap junction of the coating to the sealing point, the mandrel is used as a heat sink to absorb the infrared radiation. The non-reinforced polymer coating without the aluminum foil layer is substantially transparent for infrared radiation, and consequently the infrared radiation passes through the overlap junction of the coating strip, and heats the surface of the mandrel, which is below from the overlap junction, to the second temperature. In turn, the surface of the mandrel heats the sealing material that is in the liner to cause the edge portions of the liner to seal with each other. If the polymer film coating were heated to the sealing point without the use of the mandrel as a heat sink, the film would melt or wrinkle. The apparatus also preferably comprises a surface treatment unit that modifies the surface of the coating strip to improve wetting and adhesion of the adhesive to the coating strip. The surface treatment unit preferably comprises a corona discharge unit. However, other devices such as a flame treatment unit can be used as is known in the art. In a preferred embodiment of the invention, the apparatus also includes a tension control unit for controlling the tension of the coating strip. The tension control unit is advantageously of the type having a net accumulator which accumulates a length of coating strip material from which the coating strip is obtained at a substantially constant tension. However, other types of voltage control devices known in the art can be used. Preferably the tension control unit is operated to maintain the tension of the coating strip at less than about 17.85 kg / m in width of the coating strip, as the coating strip is wrapped around the mandrel. Accordingly, even very thin strips of unreinforced polymer film coating can be used without substantially any problem of stretching or other malformation of the strip. The invention also includes tubular containers having unreinforced polymer film coatings. According to a preferred embodiment of the invention, a tubular container comprises at least one body layer made of cardboard and wrapped in a tubular shape having an internal surface, the body layer defining a predetermined circumferential length when in a unwound, loose and flat state, and a polymeric coating layer wrapped in a tubular shape and having an outer surface adhered to the inner surface of the body layer, the coating layer defines a predetermined circumferential length when it is in a Been not wrapped, loose and flat. The circumferential length of the coating layer is smaller than that of the body layer, so that the coating layer is not substantially circumferentially pressed. Accordingly, the coating can be caused to rest smoothly against the adjacent body layer to present an attractive appearance.

BRIEF DESCRIPTION OF THE DRAWINGS The foregoing and other objects, features and advantages of the invention will be apparent from the following description of certain preferred embodiments thereof, when taken together with the accompanying drawings, in which: Figure 1 is a view in perspective of a tubular composite container having a non-reinforced liner, according to a preferred embodiment of the invention; Figure 2 is a cross-sectional view taken on line 2-2 of Figure 1 through the overlap joint of the container liner; Figure 3 is a schematic cross-sectional view taken on line 3-3 of Figure 2, showing the multi-layer construction of the polymer film coating; Figure 4 is a schematic view of an apparatus according to a preferred embodiment of the invention, for making tubular composite containers with unreinforced polymer film coatings; Figure 5 is a cross-sectional view taken on line 5-5 of Figure 4, showing in more detail the infrared heater and the driven air heater placed adjacent to the overlap junction of the polymer film coating to seal the overlap union; Figure 6 is a cross-sectional view similar to the figure 2, showing an overlap junction of the anaconda fold type according to a preferred alternative embodiment of the invention; Figure 7 is a schematic cross-sectional view of a container according to the present invention; and Figure 8 is a schematic view of the container of the figure 7, after having been cut longitudinally and unwrapped, so that the wall of the container is flat.

DETAILED DESCRIPTION OF THE PREFERRED MODALITIES The invention will now be explained with reference to certain preferred embodiments thereof. However, it should be understood that the invention is not limited to these embodiments, but may take other forms within the scope of the appended claims. With reference to Figures 1 and 2, there is shown a composite container 10 having a non-reinforced coating in accordance with the present invention. Although illustrated with a circular cross-section, the tubular container 10 can have any cross-sectional shape that can be formed by wrapping the tube around an appropriately configured mandrel. For example, the tube can be formed with a rectangular shape with rounded corners. The embodiment illustrated in FIG. 1 is particularly convenient for packing potato chips and includes a flexible membrane seal 11 and a plastic cap on the reusable end 12 on the seal. However, other different closures may be used for the end, depending on the type of food product that will be packaged. For example, when packing pasta, usually the end caps are made of metal and are sealed by bending over the ends of the container. As illustrated in more detail in Figure 2, the tubular container 10 includes a wall having a body layer 13 which is preferably formed with cardboard, and a coating layer 14 which is preferably formed with a polymeric material adhered to it. the inner surface of the body layer 13. The upper end of the tubular container 10 is wound to form a flange 15 or flange and the membrane seal 11 is sealed at the top of the flange with an adhesive sealant (not shown). Then the end cap 12 can be closed with pressure on the flange 15, and can be reused after having removed the membrane seal 11. At the opposite end of the container 10 a metal closure (not shown) can be secured. In Figure 2 the seams in which several layers are joined are illustrated. The cardboard body layer 13 is made with a relatively thick and stiff cardboard. Therefore in some types of containers, like self-opening containers, the edges are first thinned and then joined during the process of forming the tube with an adhesive 20 to create a strong seam. The coating layer 14 adheres to the inner surface of the body layer 13 with a wet adhesive 21 and the overlapping edges of the coating layer adhere to each other to ensure that the container 10 is completely sealed. Preferably a label layer 22 is adhered to the outer surface of the body layer 13, having several printed graphics and / or indications, related to the product that is inside the container. The apparatus used to make tubular containers according to the present invention is illustrated in Figure 4. A continuous strip of cardboard body layer material 13 is supplied to the apparatus, and is first passed through a pair. of opposite edge thinners 31. Edge thinners remove a part of the square edge of the body layer 13 to create a first 32 and a second 33 edges having a beveled configuration. In the manufacture of some types of containers where thinned edges are not needed, it will be understood that the edge thinners 31 can be omitted. Then the body layer 13 is advanced through an adhesive applicator 34, which applies an adhesive 21 to the upper surface of the body layer. The adhesive 21 is conveniently an aqueous adhesive that overcomes the many problems that are associated with solvent-based adhesives. No special equipment is needed to capture the solvents that evaporate from the adhesive, in order to comply with environmental regulations. A preferred adhesive is no. 72-4172, which is available from the National Starch and Chemical Company. Another adhesive that can be used is the no. 33-4060, which is also available from the National Starch and Chemical Company. The body layer 13 and the wet adhesive 21 are then passed over it, below a heater 35 which evaporates at least a part of the water content of the aqueous adhesive 21 to render it substantially adherent. It is important to supply the correct amount of heat to the adhesive. Insufficient heat will not evaporate enough water, in a short enough period of time resulting in the adhesive not becoming sufficiently adherent. On the contrary, excessive heat will dry the adhesive and cause it to lose adhesion. It has been found that at least about 100,000 J / m2 is an appropriate amount of heat to make the adhesive adherent. More particularly, it is preferable to heat the adhesive with at least about 460,000 J / m2. It has been determined that, if the body layer 13 moves at a speed of approximately 15.24 meters per minute (or if it is heated for less than about 3 seconds), the heating of the adhesive 21 with a heater 35 having a heat flow of 200,000 W / m2, will raise the temperature of the cardboard body layer 13 to at least the boiling point of water (100 ° C at sea level), and as high as 160 ° C. However, someone having ordinary skill in the art should understand that these parameters may change depending on various factors including the thickness of the adhesive layer, the efficiency of the heat source, the speed of the body layer (are contemplated line speeds up to approximately 121.92 m / min) and the type of adhesive used. Accordingly, a sufficient amount of heat is that which causes the adhesive to become adherent in a short period of time without drying out too much. A preferred heat source is an infrared heater in addition to other heat sources, for example heating with driven air or the like is used. In Figure 3 a preferred coating construction is illustrated, and includes a seal layer 60, a moisture barrier layer 61 and an adhesive layer 63. The barrier layer 61 is resistant to the passage of liquids and gases such as oxygen. If a barrier against liquids and also preferably against gases is needed, a preferred barrier material is polyester. For example, metallized polyethylene terephthalate (PET) provides a good barrier against the passage of liquids and gases. Some food products, however, do not need a gas barrier, such as some juices, and other barrier materials may be used (although the barrier may also be generally resistant to the passage of gases). It should be understood that various barrier materials or properties could be used, depending on the article to be packaged and the end-use requirements for the container. Barrier alternative materials include nylon, EVOH (polymer and ethylene vinyl alcohol copolymer), polyvinylidene chloride, polyethylene and propylene and the like, as will be apparent to the skilled artisan. A surface of the barrier layer 61 may include a thin metallized coating 62 to provide a metallic appearance and also to increase the barrier properties. However, the metallic coating 62, which may be made of aluminum, is significantly thinner than an aluminum foil layer, and is not necessary for strength and barrier properties in certain applications.

The barrier may include a coating of silicon dioxide. In this way a thick and expensive layer of aluminum foil is conveniently avoided.

The coating layer 14 preferably has a total thickness of minus 15 of about 76.2 micrometers, and is preferably closer to . 4 micrometers or less in thickness. Adhesive layer 63, which is described in more detail below, comprises a material that is activated to join itself or other compatible materials when it is raised to a predetermined sealing temperature for the material. The heat seal layer 60 comprises such a compatible material that it readily adheres to the adhesive layer 63 when it is raised to its sealing temperature.

»•" - "'-' • 'Referring again to Figure 4, the liner 14 is advanced from a coating supply roll 36, through a tension control device 37 on its way to be wrapped around the mandrel 47. Various types of devices can be used to control the coating tension As can be seen, the voltage control device 37 includes a motor 38 and a brake 39 to assist and resist respectively the rotation of the supply roller. liner 36, and a net accumulator comprising a plurality of vertically spaced rollers 40, so that the liner 14 is entangled as a serpentine around the rollers 40. At least one of the rollers 40 moves vertically relative to the rollers 40. other rollers 40, in such a way that the length of the network accumulated in the network accumulator can vary.A sensor (not shown) detects the length of the network accumulated in the accumulator. and based on the signal from the sensor, the motor 38 is operated or the brake 39 is applied to maintain the length of the accumulated network within the predetermined limits. However, regardless of the specific device that was chosen to control the cladding tension, the tension control device 37 is able to adequately maintain the cladding tension to less than about 17.85 kg / m cladding width 14, and more preferably less than about 8.92 kg / m in width. For example, for a coating 14 having a width of 17.78 centimeters, the tension control device 37 will preferably maintain the tension of the coating at approximately 0.453-1.36 kg, depending on the thickness of the film, the thinner films require a lower voltage value. After the tension control device 37, the liner 14 passes through a surface treatment unit 42, which treats the outer surface of the liner 14 (i.e., the surface that will face outwardly detached from the mandrel 47 and which adheres to the cardboard body strip 13) to improve the wetting and adhesive adhesion thereof. The surface treatment unit, in a preferred embodiment of the invention, comprises a corona discharge unit. But other devices such as flame treatment devices can also be used. After passing through the surface treatment unit 42, the coating 14 passes through an optional lubrication device 44, which applies a lubricant to the interior surface of the coating 14 (i.e., the surface contacting the mandrel 47), except the edge portion that will be heat sealed, to assist in the movement of the coating 14 along the mandrel 47. In some applications the lubricant may not be necessary, and therefore the lubrication device 44 can be omitted. For example, when the liner 14 has an inner surface formed of a material with a melting temperature substantially greater than the mandrel temperature, it could not be a significant problem that the liner will wrinkle in the mandrel and therefore the lubricant is not required.

After passing through the lubricating device 44, the liner 14 is wrapped in a helical form around the mandrel 47 so that a marginal edge portion 45 of the liner 14 overlaps with an opposite marginal edge portion 46 of a helical turn. of the pre-wrapped liner 14, to form an overlap joint 48 (Figure 2) between them. The overlap joint 48 is sealed by heating the coating 14 to raise the temperature of the coating 14 to at least the sealing temperature of the adhesive layer 63 defining the outer surface of the coating 14. The adhesive layer 63 comprises a non-aqueous polymeric adhesive which is activated at a predetermined sealing temperature. Said adhesives, which are also known as "dry bond" adhesives, may include one or more of the following modified polymers or copolymers thereof: ethylene vinyl acetate, ethylene acrylic acid, methylene acrylic acid, ethyl methacrylate, metallocenes and mixtures thereof. the same or lower cost polyolefins. In Figure 3 a preferred embodiment is illustrated and includes an adhesive layer 63 having two sublayers 63a, b which are co-extruded together. The inner sublayer 63a is preferably methylene acrylic acid, which adheres well to the polyester barrier layer 61, and the outer sublayer 63b is preferably ethylmethylacrylate, which adheres well to the cardboard body layer 13. The adhesive layer 63 It is manufactured as part of the coating layer. A sealing layer 60 can also be part of the coating layer 14 and defines the inner surface of the coating layer.

The seal layer 60 provides a surface against which the adhesive layer 63 adheres when the first marginal edge portion 45 of the coating layer 14 enters an overlapping relationship with the second marginal edge portion 46. The sealing layer 60 includes a polyolefin polymer, which is preferably high density polyethylene or a mixture of high density and low density polyethylene. A convenient feature of the sealing layer 60 is that it has a higher melting temperature than the adhesive layer 63. As it has been noted, the first marginal portion 45 of the coating layer 14 is raised to a temperature such that the Adhesive layer 63 is activated. However, if the sealing layer 60 was made of the same polymer as the adhesive layer 63, or has a melting temperature equal to or lower than the sealing temperature of the adhesive layer 63, the sealing layer 60 will melt and tilt to stick to the mandrel 47, which would greatly impede the rolling process. The present invention does not suffer from this problem, because the sealing layer 60 has a melting temperature higher than the sealing temperature of the adhesive layer 63. An important aspect of the present invention is the method by which the edge portions Overlaps 45 and 46 of the liner 14 are activated to activate the adhesive layer 63 and form the sealed overlap joint 48. Since the liner 14 is very thin, it has a very reduced ability to retain heat. Accordingly, heating the liner 14 before it is wrapped on the mandrel 47 would be inefficient and difficult to achieve in view of the rapid cooling that would take place after the heating device and before the liner was wrapped around the mandrel. For that reason, the heating of the coating 14 according to a preferred embodiment of the present invention is carried out in a two-stage process, while the coating 14 is on the mandrel 47 so that the mandrel acts as a dissipator of heat, to efficiently heat the overlap junction of the coating. More particularly, a portion 48 of the mandrel has a fluid passage 49 through which a hot fluid is circulated to raise the temperature of the portion 48 below the sealing temperature of the adhesive layer 63 of the coating. For example, wherein the sealing temperature of the adhesive layer 63 is about 82.2-104.4 degrees C, the hot portion 48 of the mandrel is heated to about 54.4-76.6 degrees C (i.e., about 10 degrees C below the temperature of sealing of the adhesive layer). The liner 14 passes over the heated portion of the mandrel 48 as it is wrapped around the mandrel, and is thus preheated to a temperature essentially equal to that of the mandrel portion 48. Then the overlapping edge portions 45 and 46 of the coating 14 are heated further to at least the sealing temperature of the adhesive layer 63 by means of a pair of local heaters, specifically an infrared heater 50a and an air heater boosting 50b, which direct the heat locally to the overlap union 48 of the coating. Referring further to Figure 5, the infrared heater 50a directs infrared radiation to the overlap junction 48. The infrared radiation penetrates through the overlapping edge portions 45 and 46 of the sheath and locally heats a portion of the mandrel 47 that is below the edge portions 45 and 46, at a temperature at least as large, and preferably a little higher than the sealing temperature of the adhesive layer 63. The infrared heater 50a and / or the driven air heater 50b they can be elongated in the helical direction. As an alternative to the use of infrared or pulsed air heating, a laser beam can be used to locally heat the overlap joint, to seal the edge portions of the coating to one another. After the edges of the liner have been sealed together to form a polymer film tube on the mandrel 47, the cardboard strip 13 (or the multiple layers of cardboard in the case of a multi-layer body wall) it is wrapped on the liner 14 and adhered thereto by means of the adhesive 21 which is on the cardboard strip 13. The tube is then advanced along the mandrel 47 by means of a tube conveyor as a winding band 51 rolled around a pair of opposed pulleys 52. The winding band 51 not only rotates and advances the tube, but also applies a pressure to the overlapped edges of the body layer 13 and the coating layer 14 to secure a secure connection between the respective layer edges.

Then preferably an outer label layer 22 is passed over an adhesive applicator 53 and wrapped around the body layer 13. The label layer 22 could be applied before the winding band 51. In a cutting station 54 , the continuous tube is cut into discrete lengths and removed from the mandrel 47. A convenient feature of a container like the container 10 made in accordance with the present invention is that, by virtue of the coating 14 being wrapped on the mandrel, Laminating it first to the body layer 13, the covering 14 can be made to be loose (ie not in substantial tension or circumferential compression) and to be flat against the adjacent body layer 13. This feature is explained by taking FIGS. 7 and 8, which schematically describe a container 10 in sectioned end view, with the thickness of the covering 14 shown disproportionately large in relation to that of the body layer 13 for clarity. Figure 7 represents the container 10 in its normal state. In Figure 8, the container 10 is cut longitudinally in a circumferential location, and has been unwrapped so that the side wall of the container is flat. In Figure 7 it will be noted that the inner radius RL of the sheath 14 is inevitably smaller than the inner radius RB of the body layer 13, and is specifically smaller by the thickness of the sheath 14 plus the thickness of the adhesive (does not appear in the Figures 7 and 8, but you can see the reference figures 21 in Figure 2) which adheres the coating to the body layer. Accordingly, the liner 14 must necessarily have a circumferential length of 2pRL which is smaller than the circumferential length 2pRB of the body layer 13. The same should apply to any container having a coating adhered to the inner surface of a body layer . However, in the container 10 made in accordance with the present invention, the circumferential length of the coating 14 is still smaller than that of the body layer 13 even when the container is cut and extended, and the coating 14 and the body layer 13 are loosened as shown in Figure 8. In order to achieve the state of the layers shown in Figure 8, it must be assumed that the liner 14 is not adhered to the body layer 13 and is therefore free to slip relative to the body layer 13 when the container is unwrapped. The method of the present invention essentially represents an inversion of the wrapping operation described above. That is, the liner 14 is first wrapped around the mandrel and is in a generally circumferential compression-free state (and is in fact under slight tension as it is controlled by the tension control device 37), and then the layer of body 13 carrying adhesive on its inner surface, it is wrapped around the mandrel on the coating so that it is in a generally circumferential compression-free state (and in fact it is also under a tension caused by the friction of several rollers and devices through which the body layer passes on its way to the mandrel). Since the liner 14 and the body layer 13 are wrapped separately on the mandrel, instead of being prelaminated in a flat condition, and then wrapped around the mandrel, the liner and the body layer are able to withstand relative movement for that the coating can lie flat against the body layer in an unpressed state. In contrast, when the body layer and the liner are prelaminated and then wrapped, unless there is a subsequent relative movement between the liner and the body layer, the lining must necessarily be reduced in a circumferential direction because the lining and the layer of body have the same length in the flat state. Accordingly, such prelamination methods can sometimes cause the coatings to not lie flat and smooth against the body layer. Nevertheless, the present invention makes it possible for the coating to be flat and smooth against the body layer in a substantially circumferential compression-free state. Once the containers 10 have been formed, the ends of these are rolled out to form a flange 15 or flange. Another convenient feature of the polymeric coating layer according to the present invention is that the elasticity of the polymer causes the flange 15 to be secured in place once it is wound up. Conventional non-elastic sheet coatings may have a tendency to unwind the flange 15 or fracture, which can be a problem when sealing the ends.

After having been filled with the food product, preferably a seal membrane 11 is sealed at one or both ends of the container 10. An end cap 12 can then be placed on the seal 11. The non-reinforced coating layer 14 of In accordance with the present invention, it is significantly thinner than conventional aluminum foil coatings and a straight overlap splice can be used instead of the anaconda fold seam. Therefore, much less discontinuities occur at the point where the seam intersects the flange. In this way, the membrane seal 11 can be economically and easily sealed to the flange 15 with a minimum amount of sealant, and can improve the fit and the removability of the lid. The invention is not limited to containers in which the liner has a straight overlap seam, but also applies to containers in which the liner has a fold seam similar to an anaconda fold. Figure 6 describes a cross section taken through the overlap area of an alternative preferred embodiment of a container 10"according to the invention, wherein a folded edge edge portion 45 'of the liner 14' is overlapped by a portion of Opposite marginal edge 46 'of the coating and is sealed thereto It will be appreciated that the inner surface of the marginal edge portion 46' is thus in contact with the inner surface of the folded portion of the other marginal edge portion 45". Thus, if the liner 14 'is constructed with a seal layer forming the interior surface of the liner 14"similar to the seal layer 60 of the liner 14 of Figure 3, the overlap joint 48' is sealed by raising the temperature of the coating in the overlap region, at least the sealing temperature of the sealing layer.The heat sealing layer can be applied only on the inner surfaces of the marginal edge portions 45 'and 46', and not in the remainder of the inner surface of the liner 14 'to minimize the friction problems of the lining that would otherwise arise when the heat seal layer rises to its sealing temperature.These marginal heat seal layers could be made by the co-extrusion of the coating material or with blow-molded films Alternatively, a heat-activated adhesive, similar to the adhesive layer 63 of the coating, could be applied 14, to the inside surface of the folded portion of the edge 45 ', while not being applied to the rest of the interior surface of the liner 14'. Many modifications and other embodiments of the invention will come to the mind of one of ordinary skill in the art to which this invention pertains, having the benefit of the teachings that are presented in the foregoing descriptions and associated drawings. Therefore, it should be understood that the invention is not limited to the specific embodiments described, and that modifications and other embodiments are intended to be included within the scope of the appended claims. For example, the tubular containers in accordance with the present invention are not necessarily helically wound, but may also be rolled longitudinally to create a "spirally wound" tube having an axially extending seam. Furthermore, although the tubular containers according to the present invention were described mainly in connection with food products, it should be understood that the containers could be used in relation to other products where the coating layer is suitable such as, for example, ink or caulk . Although specific terms are used here, they are used in a generic and descriptive sense only and not for the purpose of limiting.

Claims (15)

NOVELTY OF THE INVENTION CLAIMS

1. - A method for manufacturing multi-layer tubular containers for products, characterized in that it comprises the steps of: advancing a continuous strip of non-reinforced polymer film facing towards a forming mandrel, the coating strip includes a layer of sealing material which is activated by heat covering at least a first edge portion of the coating strip, and a layer of a compatible polymer material to which the sealing material can adhere covering at least a second portion of opposite edge of the strip of coating, the sealing material having a predetermined sealing temperature at which said material is activated to join the compatible polymer material; wrapping the liner strip around the mandrel with the sealing material in the first edge portion of the liner strip facing outward, and the compatible polymer material in the second edge portion facing inward toward the mandrel, and overlapping the first edge portion with the second edge portion to form an overlap joint therebetween, the sealing material at the first edge portion having contact with the compatible polymer material at the second edge portion, the rolled coating strip forming a tubular coating having an outer surface; preheating at least the edge portions of the coating strip in a first heating station, so that when the edge portions overlap to form the overlap joint, the sealing material reaches an elevated temperature which is below the predetermined sealing temperature; applying heat locally to the overlap joint of the tubular liner in a second heating station to further raise the temperature of the sealing material, to at least the predetermined sealing temperature and cause the sealing material to bond to the compatible polymer material; and wrapping a continuous strip of cardboard body around the tubular liner and adhering the body strip thereto to create a tubular container.

2. The method according to claim 1, further characterized in that the step of preheating comprises raising the temperature of at least a portion of the mandrel, at an elevated temperature and wrapping the coating strip on the mandrel in such a way that the Overlap bond pass over the elevated temperature portion of the mandrel, before reaching the second heating station.

3. The method according to claim 2, further characterized in that the step of raising the temperature of the mandrel comprises circulating a hot fluid through at least the high temperature portion of the mandrel.

4. The method according to claim 1, further characterized in that the step of locally heating the overlap joint comprises heating a localized region of the mandrel over which the overlap connection passes, at a higher temperature than the rest of the mandrel .

5. The method according to claim 1, further characterized in that the step of locally heating the overlap junction comprises at least one of the steps of irradiating the overlap junction and a portion of the mandrel that is below the junction of overlap with infrared radiation, and direct a stream of hot air over the overlap junction.

6. The method according to claim 1, further characterized in that it further comprises the step of treating the surface of the coating strip forming the outer surface of the tubular coating, to improve adhesion of the cardboard strip thereto, surface treatment comprises one of the following surface treatments: corona discharge treatment and flame treatment.

7. The method according to claim 1, further characterized by additionally comprising the step of controlling the tension of the facing strip advancing towards the mandrel, to maintain the tension at less than about 17.85 kg / m of the width of the coating strip.

8. The method according to claim 1, further characterized in that the step of advancing the coating strip comprises advancing a strip formed of a layer with polymer base, so that an internal surface of the base layer polymer is facing the mandrel, and an outer surface of the polymer-based layer is facing outwardly from the mandrel, the sealing material that is on the first edge portion being adjacent to the outer surface of the base layer polymer, and the compatible polymer material that is in the second edge portion comprises the material of the polymer-based layer that forms the inner surface of the second edge portion, and because the step of wrapping the coating strip around the The mandrel comprises wrapping the liner strip in an unfolded condition around the mandrel with the inner surface of the liner strip against the liner. dril, and the second edge portion overlapping the first edge portion.

9. The method according to claim 1, further characterized in that the step of advancing the coating strip comprises advancing a strip formed with a polymer-based layer with an inner surface of the polymer-based layer facing towards the mandrel, and an outer surface of the polymer-based layer facing outwardly from the mandrel, the coating strip having a single layer of sealing material applied to the inner surface or outer surface of the polymer-based layer, the advancing step further comprises folding an edge portion of the coating strip onto itself, so that the sealing material that is on the folded edge portion faces outward from the other surface of the polymer based layer in the rest of the coating strip, and in that the step of wrapping the coating strip comprises wrapping the coating strip around the mandrel. and overlapping the strip in such a manner that the layer of the sealing material which is in the folded edge portion contacts the layer of the sealing material which is in an opposite edge portion of the coating strip.

10. A multi-layer tubular container characterized in that it comprises: at least one body layer formed of cardboard and wrapped in a tubular shape having an inner surface, the body layer defining a predetermined circumferential length when in a state not wrapped and flat; and a polymeric coating layer wrapped in a tubular shape and having an outer surface adhered to the inner surface of the body layer, the coating layer defining a predetermined circumferential length when in a non-wrapped and flat state; the circumferential length of the coating layer being less than that of the body layer, so that the coating layer is not substantially circumferentially pressed.

11. The container according to claim 10, further characterized in that the coating layer includes overlapping the first and second edge portions, the first edge portion having an outer surface facing the body layer, and the second portion of edge having an inner surface facing outwardly from the body layer, and in that the inner surface of the second edge portion is heat sealed to the outer surface of the first edge portion.

12. The container according to claim 11, further characterized in that the coating layer comprises a layer of polymer barrier film that is substantially impermeable to moisture and gases, and has exterior and interior surfaces facing towards, and from the body layer, respectively, a layer of heat-sealing material covering at least the first edge portion of the outer surface of the barrier film layer, and a layer of a polymer material compatible with the which is to adhere the heat sealing material covering at least the second edge portion of the inner surface of the barrier film layer, and is heat sealed to the layer of heat sealing material that is in the first edge portion.

13. The container according to claim 12, further characterized in that the layer of barrier film comprises metallized polyester.

14. The container according to claim 12, further characterized in that the layer of heat sealing material covers substantially the entire outer surface of the barrier film layer.

15. The container according to claim 12, further characterized in that the compatible polymer material contains high density polyethylene. SUMMARY OF THE INVENTION A tubular composite container that includes a cardboard body layer wrapped in a tubular shape, and a polymer film coating layer wrapped in a tubular shape and adhered to the inner surface of the body layer. The coating layer has a circumferential length when it is not wrapped and is flat, which is less than that of the body layer, so that the coating layer is not substantially circumferentially pressed. A strip of polymer film coating material is wrapped on a mandrel and the overlapping edge portions of the coating strip are sealed to each other with heat, first preheating the coating strip to a temperature below the temperature of sealing the heat sealing material that is in the edge portions of the coating strip, and then further heating the overlap region of the coating strip to at least the sealing temperature to cause heat sealing of the layers. Edge portions. A strip of cardboard is coated on an interior surface with an adhesive and then wrapped around the coating and adhered thereto. The outer surface of the coating strip is surface treated by corona discharge or flame treatment before being wrapped on the mandrel, to increase adhesion to the board, and the tension of the coating strip is maintained at least about 17.85 kg / m of width to prevent the liner from stretching as the liner strip advances and wraps around the mandrel. The preheating of the coating strip is carried out by a hot section of the mandrel on which the coating strip passes. The overlap region is heated locally by an infrared heater. GGC / gvd * P00 / 1118