MXPA00008470A - Tubular composite containers having folded 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). A strip of polymer film liner material is wrapped onto a mandrel and overlapping edge portions of the liner strip are heat sealed together. A paperboard strip is coated on an inner surface with adhesive and is then wrapped about the liner and adhered thereto. The liner strip includes a heat seal layer facing the body ply (13) that is formed of a heat-sealable material, and the inner surface of the liner ply (14) that contacts the mandrel is formed of a hard polymer material whose melting temperature is substantially higher than the sealing temperature at which the heat-sealable material softens and seals to itself. One edge portion of the liner ply (14) is folded inward toward the mandrel, the liner ply (14) is wrapped onto the mandrel such that the folded edge portion overlaps an opposite edge portion of the liner ply (14), and the heat seal layer on the folded edge portion is heat sealed to the heat seal layer on the opposite edge portion. In one embodiment, the liner ply (14) includes a coating of an adhesion-promoting material covering the heat seal layer except on the edge portions of the liner ply (14), the adhesion-promoting coating improving adhesion of the liner ply to the body ply (13). Where the liner is supplied with the adhesion-promoting coating covering the entire surface of the heat seal layer, the apparatus for making containers includes edge skivers for skiving off the adhesion-promoting coating from the edge portions of the liner ply (14).

Description

TUBULAR CONTAINERS OF COMPOSITE MATERIALS THEY HAVE MOVIE CLADDINGS WITHOUT SUPPORT AND METHODS AND APPARATUS TO PREPARE THEM FIELD OF THE INVENTION The present invention relates to methods and apparatus for making tubular containers of composite materials and, in particular, to methods and apparatuses for making such containers by wrapping a strip of coating and at least one strip of cardboard near an axis and adhering the various strips together.

BACKGROUND OF THE INVENTION Food and drink products and other perishable items are often packaged in tubular containers that are sealed at both ends. These tubular containers typically include at least one structural body sheet and are formed by wrapping a continuous strip of body sheet material around a mandrel having the desired shape to create a tubular structure. The body sheet strip can be spirally wound around the mandrel or passed through a series of forming elements such that it wraps in a convoluted shape around the mandrel. At the downward end of the mandrel, the tube is cut into discontinuous lengths and subsequently end caps are fitted to form the container. Tubular containers of this type typically include a liner sheet on the inner surface of the cardboard body sheet. The coating sheet prevents liquids, such as juice, from leaving the container and also prevents liquids from entering the container and possibly contaminating the food product contained therein. Preferably, the coating sheet is also resistant to the passage of gases, so as to prevent odors from the food product from escaping from the container and prevents atmospheric air from entering the container and damaging the product. In this way, the coating sheet provides barrier properties and the body sheet provides structural properties. Conventional coating sheets most often include a foil laminate / paper, which has good barrier properties and also has useful strength properties. In particular, the liner is wound on the mandrel prior to winding the body sheet and must be strong and stiff enough to coil independently on the mandrel without stretching or wrinkling. Due to the support provided by the metallized paper layer of the coating such coatings are known as "supported" coatings. As mentioned, the laminate includes an aluminum metallized paper layer and a brown paper backing to allow the metallized paper layer to adhere to the cardboard body sheet. It is preferred to use water-based adhesives (or "wet adhesives") to adhere the coating sheet to the body sheet since the use of solvent-based adhesives has decreased for environmental reasons over their use and disposal. However, until now it has been difficult to obtain aqueous adhesives that stick to the smooth and impermeable surface of the aluminum foil layer. In this way, a backing of brown paper has been adhered to the metallized paper layer so that the coating can adhere to the sheet of the cardboard body with wet adhesives. However, brown paper adds greater cost and thickness to the coating. Typically, a coating formed as a paper / aluminum foil laminate includes a polymeric layer on the surface of the foil that faces inward towards the interior of the resulting container. The polymeric layer prevents the product in the container from contacting the layer of metallized paper, which in some cases can cause a reaction that can corrode the foil and discolor or adulterate the product. The polymer layer is usually a heat-sealable material that allows an edge portion of the coating strip to be heat sealed to an opposite overlap portion of the strip. The polymer layer can also improve the abrasion resistance of metallized paper, and maintains a barrier in case of small perforations in the foil. In the manufacture of composite tubular containers, a strip of coating material is wrapped around a forming mandrel and advanced along the mandrel while forming the composite tubular container. At the line speeds currently used in the commercial processing of such containers, the coating strip typically advances at a linear speed of 122 meters per minute or more and is compressed on the mandrel by the cardboard strips rolled on top. of the liner and by the tape 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 softening of the polymer layer of the coating that is in contact with the mandrel, resulting in the coating tending to adhere to the mandrel and "wear" as it moves along the mandrel. To help counteract this tenure to wear out, a lubricant is typically applied to the inner surface of the coating. Additionally, in some cases, the mandrel is cooled so that the temperature of the mandrel is kept low enough so that the coating polymer layer has a lower tendency to soften and stick to the mandrel. However, in cases where the polymer film layer performs the function of a heat sealable layer, a class dilemma arises where a low mandrel temperature is desirable to reduce wear and tack of the coating on the mandrel, while An upper mandrel temperature is desired to facilitate activation of the heat sealable polymer layer to form a seal. In cases where a support coating is used, this dilemma can be largely avoided by heating the coating, or at least the edge portions that overlap to form a seal, at a temperature above the seal temperature of the layer of polymer just before winding the coating on the mandrel. The relatively large mass of the layers of metallized paper and brown paper of the coating functions as a heat sink which keeps the heat long enough so that the edge portions of the coating can be heat sealed with one another when the coating strip is rolled up on the mandrel. However, metallized paper and brown paper are expensive and increase in thickness, therefore it is desired to provide a container and method for making such a container that includes a "non-support" polymer coating having the necessary barrier properties without Metallized aluminum foil layer and brown paper layer. However, when an unsupported coating is used, the heat dissipating function of the layers of foil and brown paper is eliminated. Consequently, the relatively thin polymer film coating is difficult to heat due to its low mass which tends to dissipate heat rapidly. The use of coatings without support also presents other technical challenges. For example, due to the problems associated with wrapping an unsupported liner on the mandrel, such as stretching, shirring, or other loss of shape of the liner, it has not been economically or commercially feasible with conventional winding apparatus and methods for processing. a container that has a lining sheet without support. However, in view of the considerable savings in material and costs offered by unsupported coatings, it would be highly desirable to provide methods and apparatus for making tubular containers of composite materials with unsupported coating. Coatings without support also offer additional advantages to material and cost savings. In particular, the removal of the layers of brown paper and metallized paper results in a significant reduction in the thickness of the fold seal, in which one edge of the coating strip is sealed to an opposite edge of the coating. With conventional support coatings anaconda folds have been necessary to allow one edge of the liner to be sealed to the opposite edge, thereby resulting in a continuous sealed liner. In an anaconda fold, the underlying edge of the lining sheet bends over itself and adheres to the overlapping edge, the anaconda fold allows the polymer layers on the surface of the foil layer to be heat sealed together. Alternatively, a hot-melt adhesive may be used to seal the underlying edge of the facing sheet to the overlapped edge. In this way the edge of brown paper is not exposed to the internal part of the container, and the liquids inside the container will not be absorbed by the brown paper. An example of such a fold is illustrated in the US patent. No. 5,084,284 to McDilda, et al. The thickness of an anaconda fold edge is equal to three times the thickness of the facing sheet. In this way, with relatively thick support coatings, the anaconda fold has a substantial thickness and presents difficulties when trying to seal the ends of the tubular container. Specifically, the ends of the tube are often rolled out after being cut such that a circular reinforced rolled edge or flange is formed on one or both ends of the tube and then end caps or membranes are applied and usually sealed to the edge reinforced with an adhesive sealant, hot-sealed or other technique. However, in the area where the thick anaconda fold edge forms a portion of the edge surface, the edge surface of the reinforced edge or flange may be substantially non-planar, thereby forming irregularities of valleys and / or slopes. In this way, an extra quantity of sealing adhesive or heat-sealable material is required to cover the discontinuities and hermetically seal the closure element in the tubular container. The additional application of the sealing adhesive or heat-sealable material is unfavorable because an additional sealing liquid must be used and has an increased difficulty for the consumer who must remove the seal, due to the additional amount of sealing liquid. For example, when a membrane includes a heat sealable layer, the entire heat sealable layer should become thicker, even when the increased thickness is actually needed only around the periphery of the membrane where it contacts the reinforced edge. Due to the problems noted above with respect to the supported coatings, efforts have been made to develop methods and apparatus for making tubular containers of composite materials having unsupported coatings wherein the layers of foil and brown paper are removed from the coating. . Additionally, methods and apparatuses have been created to make containers of composite materials having coatings formed without anaconda fold edges or with anaconda fold thicknesses greatly reduced. A coating formed entirely of one or more relatively thin polymer layers would be particularly beneficial since the additional layers of metallized paper and brown paper would be removed, as well as their accompanying costs and the coating edge would present a relatively light protrusion at the end. curling of the container, so that sealing problems with seal at the ends of the container would be substantially reduced. In this way, the assignee of the present application has devoted himself to the development of methods and apparatuses that can work in the manufacture of containers with said film coatings without support. For example, the assignee of the present application has developed methods and apparatuses for manufacturing containers of composite materials with unsupported coatings made from a polymeric film and without anaconda folds, as described in the patent application of E.U.A. with serial number 08 / 796,912 entitled "Polymeric Liner Ply for Tubular Containers and Methods and Apparatus for Manufacturing Same" filed on February 6, 1997, entitled and the patent of E.U.A. No. 5,829,669 entitled "Tubular Container and Methods and Apparatus for Manufacturing Same" issued November 3, 1998, the full descriptions of which are incorporated herein by reference. Patent application 912 and patent 699 describe methods and apparatus for forming containers of composite materials, wherein, according to one embodiment, a polymeric coating strip is adhesively bonded to a body-forming cardboard strip before being rolled up on a forming mandrel. By "pre-laminating" the polymeric coating strip and the cardboard strip together the coating is effectively supported structurally by the cardboard strip in such a way that it advances relatively easily towards the mandrel without overstretching or losing shape during the process. The polymeric coating strip is off center relative to the cardboard to which it is adhesively bonded, such that a marginal end portion of the coating strip extends beyond the edge of the cardboard strip. The laminated cardboard / polymer strip is wound onto the mandrel so that the edges of the cardboard strip overlap one another and the marginal edge portions of the polymeric coating overlap one another. One of the marginal edge portions of the coating strip includes a layer of non-aqueous adhesive that is activated by heat. Before and / or while the laminated cardboard / polymer strip is wound on the mandrel, the non-aqueous adhesive layer on the marginal edge portion is heated at least to the activation temperature, and the overlapping edges are thermally sealed together. In this way, the resulting composite container has a polymeric coating formed without anaconda fold edges. However, the apparatus used to laminate the liner and body sheets together before winding the sheets on the mandrel may not be the most useful in some applications. For example, in some cases a set of pressure rollers is needed to perform the lamination. Additionally, it will be evident that the coating feed rolls and the body sheeting rollers should be located on the same side of the mandrel, which can make it more difficult to position the feeding rollers and routing the sheets towards the mandrel. it would be in the case that the body lining sheets did not have to reach the mandrel on the same side. Replacing the rollers can also be more difficult when two nearby feed rollers are located as they will tend to make efficient use of the space. In view of such drawbacks, the assignee of the present application has also developed methods and apparatus for making tubular containers with unsupported film coating, allowing the opposite lateral winding or the same side of the coating strip on the mandrel, as described in the EUA patent application Copendent and common ignorance with serial No. 09 / entitled "Tubular Composite Containers Having Unsupported Film Liners and Methods and Apparatus for Making Same "filed on, the description of which is incorporated by reference herein In accordance with the methods and apparatus of the application, a polymer film coating is extracted from a coating supply and through an apparatus of tension control that keeps the tension of the coating sufficiently low to avoid a substantial malformation of the coating strip, and the coating strip is wound onto the mandrel before the sheet or sheets of the cardboard body are wound onto the mandrel. internal of the liner that contacts the mandrel when the tubular container advances along the mandrel comprises a heat-sealable material and a heat-sealable material also forms at least part of the outer surface of the liner that is adhesively bonded to the body sheet of cardboard by means of a water-based or "wet" adhesive. rasp an opposite edge of the coating strip so that the heat sealable material is in contact with the inner and outer surface of the strip. The portion of the mandrel over which the overlap joint passes rises to an elevated temperature just below the sealing temperature at which the heat sealable materials are activated to seal against each other, thereby preheating the overlap joint. Additional heat is locally applied by infrared and / or forced air heaters, in such a way that the temperature of the overlap joint is raised to at least the sealing temperature and thus the overlap joint is sealed. With the method of the application, the heat-sealable material on the inner surface of the coating strip is heated and softened as it passes over the heated portion of the mandrel, and this softening leads to greater friction ben the coating strip and the mandrel. To help reduce friction, a lubricant may be applied to the inner surface of the coating strip, with the exception of the edge portion to be sealed with heat, just before rolling the coating onto the mandrel. The lubricant can cool the heat sealable material and thus help to allow the edge portion to remain warmer than the rest of the heat sealable layer. However, many lubricants that are commonly used leave a sticky residue on the mandrel which can cause dust to adhere and accumulate on the mandrel, which is undesirable. Lubricants can also adversely affect the sealing of the membranes on the ends of the container. Additionally, lubricants must be approved by the FDA (Food and Drug Administration in the US) if used to make containers for food products, which limits the types and amounts of lubricants that can be used.

The summary, with coatings having a conventional type of anaconda fold seal, requires a heat-sealable material on the inner surface of the liner on the mandrel because the liner edge is bent outward to provide the heat sealable material in a ratio opposite with the opposite overlap edge, which also has the heat sealable material on the inner surface, so that the edges can be heat sealed together. In the case of support coatings that have a brown paper backing, the anaconda fold seal is used to allow edge-to-edge sealing of the coating so that a continuous internal barrier is formed that is resistant to moisture passage. and / or gases. An alternative type of liner seam is a straight overlap seam wherein one edge of the liner overlaps the opposite edge so that the inner surface of the overlapping edge makes contact with the outer surface of the underlying rim., as it is written in the patent application. To heat seal such straight overlap seams there must be a heat-sealable material on the inner surface of the coating at least along the overlapping edge portion, and also on the outer surface of the coating at least along the portion of the underlying edge. Polymeric film coating materials having heat sealable material applied on one or both sides of a base film are typically formed by coextruding the heat sealable material and the base film material to which it is applied, and generally has the heat sealable material applied to the surface (or surfaces) complete of the base film. In this way, the heat sealable material will typically cover the entire inner surface of the coating, either with support or without support. In this way, with outwardly bent seals or straight overlap edges, the heat sealable material on the inner surface of the lining tends to wear on the mandrel when heated to the activation or sealing temperature. In view of the foregoing, it would be highly desirable to provide methods and apparatus capable of making a container of composite material with polymeric film coating without support. Additionally, it would be desirable to provide methods and apparatus that allow the formation of such a container without pre-laminating the body and liner sheets. It would also be desirable to provide methods and apparatuses that allow the reduction of the friction of the coating on the mandrel and thus accelerate the line speeds in the production of containers of composite materials having polymeric film coatings without support.

BRIEF DESCRIPTION OF THE INVENTION The above and other objects are covered and other advantages are achieved with the present invention, which includes methods and apparatus for making a tubular container of composite material having a strip of 5 cardboard body and a polymeric film without coating strip support adhered to it, wherein the inner surface of the coating is formed of a hard polymeric material having a relatively high melting temperature that resists wear, even at elevated temperatures, the The external surface is formed of heat-sealable material having a sealing temperature substantially less than the melting temperature of the hard polymeric material. The lining of the lining is formed by folding one edge of the lining strip inwardly so that the heat-sealable material on the folded edge faces inward towards the mandrel, winding the liner strip on the mandrel in such a way that the folded edge portion overlaps an opposite edge portion of the liner strip, and heat sealing the bent edge towards the underlying opposite edge portion of the liner strip. In this way, the surface of the coating strip that contacts the mandrel is formed of hard polymeric material, which tends to slip along the mandrel more easily than the heat-sealable material, even when the mandrel is heated to promote sealing by heat of the overlapping edge portions. In accordance with the present invention, folding the edge of the liner inwardly instead of outwardly allows the heat sealable material to be removed from the inner surface of the liner. This produces several important benefits: first, having the hard polymeric material on the inner surface of the coating strip reduces the wear of the coating strip on the mandrel. Secondly, in relation to a coating having a heat-sealable material on both internal and external surfaces (as used in coatings having straight overlap edges sealed by heat), the coating thickness is reduced by an equal amount to the thickness of the heat sealable material removed from the inner surface. Third, the removal of the heat-sealable coating on the inner surface of the coating leads to a lower coating cost. According to a preferred embodiment of the invention, at least the overlapping edge portions of the coating strip are heated by passing over a heated portion of the mandrel, such that the heat-sealable material reaches an elevated temperature below its temperature. predetermined sealing temperature. By heating a portion of the mandrel over which the coating strip passes, it is possible to heat the coating strip for a longer period so that the heat sealable material has a sufficient time to reach the elevated temperature. Subsequently, additional heat is locally applied to the overlap joint of the tubular liner in a second heating station located on the mandrel to raise the temperature of the heat-sealable material to at least at a predetermined sealing temperature and causes the edge portions to increase. they are sealed together. In this way, the mandrel temperature can be maintained at a relatively low temperature that will be required where the entire amount of heating to activate the heat sealable material would be performed by heating the mandrel. Providing a hard polymer layer on the inner surface of the liner facilitates the use of mandrel heat to assist in the heat sealing operation, because the hard polymeric layer tends to slide easily even over the heated portion of the mandrel. According to another preferred embodiment of the invention, the additional heat to activate the heat sealable material is applied locally to the overlap junction of the coating by heating a portion of the mandrel surface on which the overlap bond passes at a higher temperature than the elevated temperature portion of the mandrel. Useful, the infrared radiation is focused on the overlap joint and penetrates through the facing edge portions such that the surface underlying the overlap joint of the mandrel is heated to a temperature above the sealing temperature of the heat sealable material. However, other heating devices may be used in addition to or instead of the infrared radiator, include forced hot air devices directed over the overlap junction, electric resistance heating elements disposed within the mandrel, or other heating devices known in the art. for heating. To adhere the liner and the cardboard body strips together, an adhesive is applied to a surface of the cardboard body strip facing the outer surface of the tubular liner. In a useful manner, the surface of the coating strip forming the outer surface of the tubular coating is treated to improve adhesion of the adhesive thereto. Surface treatment in the preferred embodiment comprises a corona discharge treatment. Alternatively, flame treatment may be used. To further improve the addition of the coating to the cardboard body, the coating strip according to one embodiment of the invention has a coating that improves the adhesion covering the coating of the heat sealable layer facing the cardboard body. However, the coating that improves adhesion does not cover the end portions, such that the heat sealable layer remains exposed over the edge portions. Where the coating strip is provided with the coating that improves the addition covering the entire surface of the heat sealable layer, the method according to a preferred embodiment of the invention includes the step of removing the coating from the portions of rim to expose the heat sealable layer before folding an edge portion of the liner strip inwardly and winding the liner strip onto the mandrel. The coating that improves adhesion can be removed either mechanically or by heat. The thin polymer films can be stretched and thus it is preferable to control the tension of the polymeric film coating strip to keep the tension sufficiently low so that the stretching of the coating strip is substantially avoided. Thus, in a preferred embodiment of the invention, the tension of the coating strip is controlled to be less than about 17.85 kg / m in width of the coating strip, which allows the films to have a thickness as low as 0.0012 cm to be used in the coating strip. The invention also includes tubular containers having polymer film coating without support. According to a preferred embodiment of the invention, a tubular container comprises at least one body sheet formed of cardboard and wrapped in tubular form, having an inner surface and a polymeric coating sheet wound to form a tubular coating and having a outer surface of the tubular coating adhered to the inner surface of the body sheet. The tubular liner includes at least one fold seal that extends generally along the container, the fold seal is formed by a first edge portion of the liner sheet that bends inward towards the inside of the container and second, an opposite edge portion of the facing sheet that overlaps the first folded edge portion and is sealed thereto. According to a further preferred embodiment of the invention, the coating sheet includes a heat seal layer facing the body sheet and is formed of a heat-sealable material having a sealing temperature in which the heat-sealable material is softened and it seals itself, and wherein the coating sheet includes a hard polymeric layer that forms the inner surface of the container and is formed of a polymeric material having a melting temperature substantially greater than the sealing temperature of the heat-sealable layer. The hard polymer layer of the coating sheet preferably comprises a barrier material that is substantially impermeable to moisture and gases, examples of which include but are not limited to metallized OPET and metallized OPP. The heat sealable layer preferably comprises polyester, or a mixture of polyester and a copolymer of ethylene vinyl acetate. The coating strip in one embodiment includes a coating of a material that improves adhesion applied to the surface of the heat sealable layer facing the body sheet to improve the adhesion of the coating sheet to the body sheet. The coating that improves adhesion ends adjacent to the edge portions of the coating strip such that the heat sealable layer is exposed over the edge portions. With such an unsupported coating, the edge folding method of the present invention is preferred to the use of a single turn seal, because the return seal does not provide sufficient bond strength between the heat sealable material on one side of the film and non-heat-sealable material on the other side to tolerate operations such as bending and sealing of end closures. Additionally, the crease edge portion of the liner can desirably be adhered to the remnant of the liner with the aid of a hot melt adhesive, an ethylene methylacrylate or mixtures thereof, to provide a good crease bond.

BRIEF DESCRIPTION OF THE DRAWINGS The objects, features and utilities mentioned above and others of the present invention will be apparent from the following description of some preferred embodiments thereof, when taken in conjunction with the accompanying drawings in which: Figure 1 is a perspective view of a composite tubular container having an unsupported coating in accordance with 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 construction of multiple layers of the polymeric film coating in accordance with a preferred embodiment of the present invention; Figure 4 is a schematic view of an apparatus in accordance with a preferred embodiment of the invention for making tubular containers of composite material with polymeric film coatings without support; Fig. 5 is a cross-sectional view taken through an overlap joint of a container according to another embodiment of the invention, wherein a coating for improving adhesion covers the surface of the facing facing the body sheet; and Figure 6 is a view similar to Figure 5, showing a further embodiment of the invention, wherein a sealing adhesive is applied between the crease edge portion and the coating strip and the remainder of the coating strip.

DETAILED DESCRIPTION OF THE PREFERRED MODALITIES The invention is explained below with reference to certain preferred embodiments thereof. However, it will be understood that the invention is not limited to these embodiments, since it may have other forms within the scope of the appended claims. With reference to Figures 1 and 2, a container of composite material 10 having a non-support coating in accordance with the present invention is shown. Although illustrated with a circular cross-section, the tubular container 10 can have any cross-sectional shape that can be formed by winding the tube around a mandrel in a suitable manner. For example, the tube may have a rectangular shape with rounded corners. The embodiment illustrated in FIG. 1 is particularly useful for packing potato chips and includes a flexible membrane seal 11 and a plastic end cap that can be reused 12 over the seal. However, other different ways of end closure may be used depending on the type of product that will be packed. For example, when packing dough, the end caps typically have a metal construction and are sealed by pressure to the ends of the container. As illustrated in greater detail in Figure 2, the tubular container 10 includes a wall having a body sheet 13 which is preferably formed of cardboard and a coating sheet 14 which is preferably formed of a polymeric material adhered to the inner surface of the body sheet 13. The upper end of the tubular container 10 is wound so as to form a reinforced edge 15 or flange and the membrane seal 11 is hermetically sealed to the upper part of the reinforced edge with an adhesive sealant (not shown) ) which is typically a part of the membrane. The end cap 12 is then placed on the reinforced edge 15 and can be reused after the membrane seal 11 has been removed. A metal closure (not shown) can be secured to the opposite end of the container 10. The edges where various sheets are joined are illustrated in Figure 2. The cardboard body sheet 13 is made of relatively thick rigid cardboard. In this way, in some types of containers such as self-opening containers, the edges are bevelled first and subsequently joined together during the tube forming process with an adhesive 20 to create a strong edge. The coating sheet 14 adheres to the inner surface of the body sheet 13 with a wet adhesive 21 and the overlapping edges of the coating sheet adhere to ensure that the container 10 is completely sealed. A label sheet 22 is preferably adhered to the outer surface of the body sheet 13 with various graphics and / or indicia printed thereon with information about the product that is contained within the container. The liner sheet 14 includes a fold seal 16 formed by overlapping a first fold edge portion 17 of the liner with a second opposite edge portion of the liner and sealing the overlapping edge portions together, as will be described further below. The fold edge portion 17 is bent inward towards the interior of the container, for reasons explained below. An apparatus for making tubular containers in accordance with the present invention is illustrated in Figure 4. A continuous strip of cardboard body sheet material 13 is provided to the apparatus and first passes through a pair of opposed edge bevellers 31. The edge bevels remove part of the square edge of the body sheet 13 to create first 32 and second edges 33 having a beveled configuration. The body sheet 13 is then advanced through an adhesive applicator 34, which applies an adhesive 21 to the upper surface of the body sheet. The adhesive 21 is usefully an aqueous adhesive that overcomes many problems associated with solvent based adhesives. No special equipment is required to capture solvents that evaporate from the adhesive to meet environmental standards. A preferred adhesive is number 72-4172, which is available from National Starch and Chemical Company. Another adhesive that can be used is number 33-4060, which is also available from National Starch and Chemical Company. The body sheet 13 and the wet adhesive 21 applied thereto, subsequently pass under a heater 35 which evaporates at least part of the water content of the aqueous adhesive 21 to give a substantially tacky adhesive. It is important that an adequate amount of heat is provided to the adhesive. An insufficient amount of heat will not evaporate enough water in a sufficiently short period obtaining as a result that the adhesive will not be sufficiently sticky. On the other hand, too much heat will dry the adhesive and cause the adhesive to lose stickiness. It has been found that at least about 10,000 J / m2 is an adequate amount of heat to provide a sticky wet adhesive. In particular, it is preferred to heat the adhesive with at least about 460,000 J / m2. It has been determined that, if the body sheet 13 is moved at a speed of approximately 15.24 m / min (or heated for less than about 3 seconds), by heating the adhesive 21 with a heater 35 having a heat flow of 200,000 W / m2 will raise the temperature of the cardboard body sheet 13 to at least the boiling point of water (100 ° C at sea level) and as high as 160 ° C. However, one skilled in the art will understand that these parameters may change depending on various factors, including the thickness of the adhesive layer 21, the efficiency of the heat source, the velocity of the body sheet (a velocity of the line up to approximately 121.92 m / min) and the type of adhesive used. Therefore, a sufficient amount of heat is what causes the adhesive to become sticky in a short period without overdrying. A preferred type of heat source is an infrared heater, although various other heat sources can be used, for example, heating with forced air or similar. A preferred coating construction is illustrated in Figure 3 and includes a heat sealable layer 60 and a barrier layer 61. The barrier layer 61 forms the inner surface of the coating that faces the inner part of the container and also contacts the inner surface of the container. the mandrel when the coating is wound on the mandrel, as described below. In this way, the barrier layer 61 preferably comprises a relatively hard polymer, ie, a polymer having a relatively high melting point relative to the temperature at which the heat seal layer is activated. The barrier layer 61 is preferably resistant to the passage of liquids and / or gases such as oxygen. If a barrier is required for both liquids and preferably also gases, a preferred barrier material is the metallized polyester. For example, metallized polyethylene terephthalate (PET) provides a good barrier against the passage of liquids and gases and has a relatively high melting point of approximately 176.6 ° C. However, some food products 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 gases). It will be understood that various barrier materials or properties may be employed depending on the article to be packed. Alternatively, hard barrier films include metallized OPP, metallized oriented HDPE, metallized nylon and the like, as will be apparent to those skilled in the art. A barrier layer surface 61 may include a thin metallized coating 62 to provide a metallic appearance and also to improve the barrier properties. However, the metallic coating 62, which may be formed of aluminum, is significantly thinner than a layer of metallized paper and is not necessary for strength or barrier properties in certain applications. In this way, a thick and expensive metallized paper layer is usefully removed. The barrier may include a coating of silicon dioxide. The coating sheet 14 preferably has a smaller thickness of about 50.8 microns and most preferably is closer to 25.4 microns or less in thickness. The heat sealable layer 60 comprises a heat-sealable material that softens and adheres easily to itself when the temperature rises to its sealing temperature. Examples of suitable heat sealable materials include but are not limited to polyesters, vinyl ethylene acetate copolymer (EVAC), ethylene methylacrylate, and mixtures thereof. Referring again to Figure 4, the coating 14 advances from a coating feed roller 36 through a tension control device 37 on its way to enlistment on the mandrel 47. Various types of devices can be used to control the tension of the coating. As shown, the tension control device 37 includes a motor 38 and a brake 39 to assist and resist respectively the rotation of the coating feed roller 36, and a mesh accumulator comprising a plurality of vertically spaced rollers 40, so that the liner 14 is wound as a serpentine around the rollers 40. At least one of the rollers 40 can move vertically relative to the other rollers 40, so that the length of the mesh accumulated in the mesh accumulator may vary A sensor (not shown) detects the accumulated mesh length in the accumulator, and based on the sensor signals, the motor 38 operates or the brake 39 is applied to maintain the length of the accumulated mesh within the previously determined limits . However, without taking into account the specific turning device for controlling the cladding tension, the tension control device 37 is usefully able to keep the cladding stress less than approximately 17.85 kg / m cladding width 14, and very preferably less than about 8.92 kg / m in width. For example, a liner 14 having a width of 17.78 cm, and the control device 37 will preferably maintain the coating tension approximately 0.9071 to 1.3660 kg. After the tension control device 37, the coating 14 passes through a surface treatment unit 42 that treats the outer surface of the liner 14 (i.e., the surface that will face outwardly of the mandrel 47 and adhere to the cardboard body strip 13) to improve wetting and adhesion of the adhesive to it. The surface treatment unit in a preferred embodiment of the present invention comprises a corona discharge unit. However, other devices such as flame treatment devices may be used instead. After passing through the surface treatment unit 42, the coating 14 passes through an optional lubrication device 44, which applies a lubricant to the inner surface of the coating 14 (ie, the surface that makes contact with the mandrel). 47), with the exception of the edge portion to be heat-sealed, to assist the movement of the liner 14 along the mandrel 47. In some applications the lubricant may not be necessary and thus the lubrication device 44 may be omitted. After passing through the lubrication device 44, the liner 14 passes through an edge folder 45, which bends the downward edge portion 17 of the liner strip inwardly so that the folded edge portion 17 sees towards the mandrel 47. The liner strip is subsequently wound helically near the mandrel 47 so that the fold edge portion 17 overlaps an opposite (upward) edge portion 18 of a coiled coiled turn of the liner 14 to form a joint overlapped 16 (figure 2) between them. The overlapped junction 16 is sealed by heating the cladding 14 to raise the temperature of the cladding 14 to at least the sealing temperature of the heat sealable layer 60. A useful feature of the construction of the cladding strip 14, including the heat sealable layer 60 and the hard polymer barrier layer 61 is that the barrier layer 61 has a substantially higher melting temperature than the heat sealable layer 60. As noted above, the first edge portion 17 and the cover sheet 14 are raised to a such temperature that the heat sealable layer 60 is activated. However, the barrier layer 61 was made of the same polymer as the heat sealable layer 60 or has a melting temperature equal to or lower than the sealing temperature of the heat sealable layer 60., the barrier layer 61 will be heated and inclined to adhere to the mandrel 47, which will greatly impede the winding procedure. Because the coating 14 is very thin, it has a very low capacity to retain heat. In this way, heating the liner 14 before the liner 14 is wound on the mandrel 47 will not be efficient and will be difficult to achieve in view of the rapid cooling that will be carried out subsequent to the heating device and before the lining is rolled up. on the mandrel. In this way, heating of the liner 14, according to a preferred embodiment of the present invention, is carried out in a two-stage process while the liner 14 is made on the mandrel 47 in such a way that the mandrel acts as a heat sink. heat to efficiently heat the lapped cladding. In particular, a portion 48 of the mandrel has a fluid passage 49 through which a heated fluid circulates to raise the temperature of the portion 48 to a temperature that is below the sealing temperature of the heat seal layer 60 of the coating. For example, where the sealing temperature of the heat sealable layer 60 is about 82 to 104 ° C, the heated portion 48 of the mandrel is heated to about 54 to 76 ° C (about 28 ° C below the sealing temperature of the heat-sealable layer). The liner 14 passes over the heated mandrel portion 48 while it is wound on the mandrel and is thereby preheated to a temperature essentially equal to that of the mandrel portion 48. The overlap edge portions 17 and 18 of the liner 14 subsequently, the sealing temperature of the heat sealable layer 60 is heated by a pair of local heaters, specifically an infrared heater 50a and a forced air heater 50b, which directs the heat locally to the overlap joint 48 of the coating . The infrared heater 50a directs the infrared radiation at the overlap junction 48. The infrared radiation penetrates through the overlapping edge portions 17 and 18 of the cladding and locally heats a portion of the surface of the mandrel 47 underlying the edge portions. 17 and 18 at a temperature of at least as high and preferably greater than, the sealing temperature of the heat sealable layer 60. The infrared heater 50a and / or the forced air heater 50b may elongate in the helical direction. After the coating edges have been sealed to form a polymer film tube on the mandrel 47, the cardboard strip 13 (or the multiple sheets of cardboard, in the case of a multi-sheet body wall) is rolled over the coating 14 and adhered thereto by adhesive 21 on the cardboard strip 13. Subsequently, the tube advances down the mandrel 47 by means of a tube conveyor as a winding tape 51 wrapped around a pair of opposed pulleys 52. The tape of winding 51 not only rotates and advances the tube, it also applies pressure to the overlapping edges of the body sheet 13 and the cover sheet 14 to ensure a secure connection between the respective leaf edges. An outer label sheet 22 preferably passes over an adhesive applicator 53 and is wound around the body sheet 13. The label sheet 22 may be applied before the winding tape 51. In a cutting station 54, the continuous pipe is cut into discontinuous lengths and removed from the mandrel 47. Referring to Fig. 5, a preferred alternative embodiment of the invention is illustrated wherein the coating strip 14 includes a coating that improves adhesion 56 that covers the outer surface of the facing strip facing the body sheet 13. For example, the coating 56 can usefully be ethylene methylacrylate (EMA) a copolymer of ethylene vinyl acetate (EVAC), or a co-extruded coating comprising a layer of ethylene acrylic acid (EAA) and a layer of ethylene methylacrylate. The EMA or EVAC layer readily adheres to the wet adhesive 21 and thus provides a good bond between the coating 14 and the body sheet 13. However, it is not necessary to have the coating 56 on the edge portions 17 and 18. of the liner strip 14, and in this manner, the liner 56 preferably terminates adjacent the edge portions, as shown in Fig. 5. Where the liner strip 14 is provided with the liner 56 applied to the outer surface In addition to the entire coating strip (such as a strip formed by co-extrusion of the coating, heat-sealable layer and barrier layer), it is desirable to remove the coating 56 from the edge portions so that the heat-sealable layer (eg heat sealable layer 60 shown in FIG. Figure 3) is exposed in the edge portions. In such a case, as shown in Figure 4, the apparatus for making containers preferably includes edge bevels 58 for beveling the coating 56 along the edge portions 17 and 18. With reference to Figure 6, it is desirable to seal the folded edge portion 17 to the internal surface of the remainder of the coating strip 14 with a sealing liquid 64 such as a liquid adhesive or hot-melt adhesive which is activated by heat. For example, hot-melt adhesives with designation numbers 72-4781, 72-4667, 34-2734, or 34-2791 available from the National Starch Company may be used. In this manner, the apparatus may include a fold shutter liquid applicator 66 for applying a sealing liquid to the inner surface of the edge portion 17 of the facing strip 14. A useful feature of a container, such as the container 10 formed in accordance with the present invention, is that, by virtue of winding the coating 14 on the mandrel without first rolling it towards the body sheet 13, the coating 14 can be made in a relaxed manner (ie without tension or with substantial circumferential pressure) and lying flat against the adjacent body sheet 13, as described in the aforementioned patent application. Once the containers 10 have been formed, the ends of the containers 10 are rolled out to form the reinforced edge 15 or a flange. Another useful feature of the polymeric coating sheet according to the present invention is that the elasticity of the polymer allows the coating to be stretched and rolled more easily on a reinforced edge 15, consequently the reinforced edge has a lower probability of unwind after forming it. Conventional non-elastic laminate paper coatings have a very high tensile strength and thus may have a tendency to split during the reinforced edge forming process, and may also have a tendency to unwind the reinforced edge 15, which You may have a problem sealing the ends. After having been filled with a food product, a membrane seal 11 is preferably placed on one or both ends of the container 10. An end cap 12 can be subsequently placed on the seal 11. The non-support facing sheet 14 in accordance with the present invention is significantly thinner than conventional backing coatings and thus the fold edges are substantially thinner than an anaconda fold edge of a conventional backing with backing. In this way, many minor discontinuities occur at the point where the shore crosses the reinforced edge. In this way, the membrane seal 11 can be economically and easily sealed to the reinforced edge 15 with a minimum amount of sealing adhesive, and the fit and removal capacity of the top cover can be improved. Many modifications and other embodiments of the present invention will be apparent to those skilled in the art., to whom this invention pertains having the benefit of the teachings presented in the above descriptions and in the associated drawings. Therefore, it should be understood that the invention should not be limited to the specific embodiments described and said modifications and other embodiments were created with the intention of being included within the scope of the appended claims. For example, tubular containers in accordance with the present invention are not necessarily wound helically, and instead can be wound longitudinally to create a "convolute" tube having an axially extending edge. Furthermore, although the tubular containers according to the present invention have been described mainly together with food products, it should be understood that the containers can be used together with other products, wherein the covering sheet is useful for example to cover and fill. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.

Claims (15)

NOVELTY OF THE INVENTION CLAIMS

1. - A method for making multi-sheet tubular containers for products, comprising: advancing an unsupported polymer film coating strip having inner and outer surfaces towards a forming mandrel, the inner surface of the coating strip being formed of a polymer material with a relatively high melting point, and at least opposite edge portions of the outer surface of the coating strip being formed of a heat-activated heat-sealable material having a predetermined sealing temperature, in which the said material is activated to bind itself, the sealing temperature of the heat sealable material being substantially less than the melting temperature of the high melting point polymer material; folding an edge portion of the facing strip inwardly such that the heat sealable material on an edge portion faces towards the mandrel; enlisting the liner strip around the mandrel with the high melting polymer material on the inner surface of the liner strip against the mandrel, and overlapping the fold edge portion on the other edge portion of the liner strip to form an overlap joint between these with a heat-sealable material on one edge portion in contact with the heat-sealable material on the other edge portion, the coating strip wound into a tubular coating having an outer surface; heating at least the overlapping edge portions of the coating strip to a temperature equal to at least the predetermined sealing temperature to heat seal the edge portions against each other; and winding a continuous cardboard body strip around the tubular liner and adhering the body strip thereto so that a tubular container is created.

2. The method according to claim 1, wherein further the step of advancing the coating strip comprises advancing a strip formed of a layer of a high-melting polymer material laminated to a layer of the heat-sealable material such that the heat sealable material forms the entire outer surface of the coating strip.

3. 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 of a heat-sealable material, a layer of high-melting polymer material laminated on one side of the heat-sealable material layer and a layer of a coating material covering the other side of the heat-sealable material layer with except along the edge portions thereof, the coating material improves the adhesion of the Coating strip of the cardboard body strip.

4. The method according to claim 1, further comprising the step of applying an adhesive between the crease edge portion of the liner strip and the inner surface of the liner strip, on which the portion is folded of crease edge, such that the folded edge portion adheres to the inner surface.

5. The method according to claim 1, wherein further the heating step comprises raising the temperature of at least a portion of the mandrel to a high temperature and winding the coating strip on the mandrel, so that the union overlap passes over the elevated temperature portion of the mandrel.

6. The method according to claim 5, wherein further the step of raising the mandrel temperature comprises circulating a heated fluid through at least the elevated temperature portion of the mandrel.

7. The method according to claim 4, wherein further the step of heating the overlap unit comprises at least one of the steps of irradiating the overlap joint and a portion of the mandrel underlying the overlap joint with a infrared radiation and direct a flow of hot air towards the overlap junction.

8. The method according to claim 1, wherein it further comprises the step of controlling the tension of the facing strip that is advancing towards the mandrel in such a manner as to maintain the lower tension approximately 17.8579 kg / m in width of the coating strip.

9. - A multi-sheet tubular container comprising: at least one body sheet formed of cardboard and wrapped in a tubular shape having an internal surface; and a polymeric coating sheet wound to form a tubular coating having an outer surface of the tubular coating adhered to the inner surface of the body sheet, the tubular coating including at least one fold seal extending generally along the container, the fold seal being formed by a first edge portion of the facing sheet that is bent inward towards the inner part of the container and a second opposite edge portion of the facing sheet that overlaps the first folding edge portion and It is sealed to this one.

10. The container according to claim 9, further characterized in that the coating sheet includes a heat-sealable layer that covers at least the portions of the coating sheet adjacent to the edges thereof, the heat-sealable layer is facing the sheet of body and is formed of a heat sealable material having a sealing temperature at which the heat-sealable material softens and seals itself, and wherein the coating sheet includes a layer of hard polymer that forms the inner surface of the container and is formed of polymer material having a melting temperature substantially greater than the sealing temperature of the heat sealable layer.

11. The container according to claim 10, further characterized in that the hard polymer layer of the coating sheet comprises a barrier material that is substantially impermeable to moisture and gases, the barrier material comprises a metallized polyester and polyethylene terephthalate.

12. The container according to claim 10, further characterized in that the heat sealable layer comprises polyester.

13. The container according to claim 10, further characterized in that the heat sealable layer comprises a mixture of polyethylene and a vinyl ethylene acid copolymer.

14. The container according to claim 10, further characterized in that the coating strip further comprises a coating of a material that improves the adhesion applied to the surface of the heat-sealable layer facing the body sheet to promote adhesion of the lining sheet towards the body leaf.

15. The container according to claim 14, further characterized in that the coating improving adhesion ends adjacent to the edge portions of the coating strip so that the heat sealable layer is exposed to the edge portions. SUMMARY OF THE INVENTION Disclosed is a composite tubular container that includes a cardboard body sheet rolled into a tubular shape, and a polymer film coating sheet wound into a tubular shape and adhered to the inner surface of the body sheet; a strip of polymer film coating material is wound onto a mandrel and overlapping edge portions of the coating strip are heat sealed; a strip of cardboard is coated on an internal surface with adhesive and subsequently rolled onto the coating and adhered thereto; the coating strip includes a heat-sealable layer facing the body sheet which is formed of a heat-sealable material, and the inner surface of the coating sheet which contacts the mandrel is formed of hard polymer material whose melting temperature is substantially greater than the sealing temperature at which the heat-sealable material softens and seals itself; An edge portion of the liner sheet is bent inward toward the mandrel, the liner sheet is wound onto the mandrel such that the folded edge portion overlaps an opposite edge portion of the liner sheet, and the layer heat sealable on the bent edge portion is heat sealed to the heat sealable layer on the opposite edge portion; in one embodiment, the coating sheet includes a coating of a material that improves the adhesion that covers the heat sealing layer with the exception of the edge portions of the coating sheet, the coating improves the adhesion of the coating sheet to the body leaf; wherein the coating is provided with a coating that improves the adhesion that covers the entire surface of the heat-sealable layer, the container-making apparatus includes bevelers for chamfering the coating that improves adhesion from the edge portions of the coating sheet. HL / aom * kra * sff * yac * pbg * igp * jtr * P00 / 1102