MXPA00009963A - Tubular container with a heat sealed lid having inner and outer sealing beads - Google Patents

Abstract

A sealed composite container for products is provided having a paperboard body ply with a liner ply (14) adhered on the inner surface thereof. One end of the container is rolled outwardly to form a rim and exposing the inner surface of the liner ply (14), which comprises a heat sealable composition. A lid (11) for the container, also having a layer of heat sealable composition, is placed adjacent to the exposed heat sealable composition of the container liner (14) and heat sealed thereto. The heat seal has both an inner and an outer bead (36,38) formed on either side of the heat sealed area, wherein the inner bead (36) comprises a larger amount of the heat seal compositions than the outer bead (38). A method and apparatus for forming the heat seal is also provided.

Description

TUBULAR CONTAINER WITH A HEAT SEAL THAT HAS NON-SYMMETRIC INTERNAL AND EXTERNAL SPHERES FIELD OF THE INVENTION The present invention relates to containers for food and methods and apparatuses for preparing containers for food, and in particular it refers to the heat seals that are used for such containers.

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 fold and are formed by wrapping a continuous strip of body fold material around a mandrel having the desired shape to create a tubular structure. The body fold 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 fold on the inner surface of the cardboard body fold. The lining fold 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 liner fold is also resistant to the passage of gases, such as oxygen and nitrogen, so as to prevent odors from the food product from escaping from the container and prevent atmospheric air from entering the container and damaging the food product. In this way, the liner fold provides barrier properties and the body fold provides structural properties. In addition, current commercial containers commonly have membrane-type covers or end seals heat-sealed to a rib of the mixed container wall to form a seal that can be peeled off. The rib is formed by flipping out the end of the container to place the inner layer of the liner material on the curved surface outward. A major difficulty in the development of a heat seal that can be used between the lid of the container and the rib of the container wall is to balance the bonding strength with the ease of opening by the end user. During transport, sealed containers experience extreme temperatures and pressures that strain the seal by heat and can lead to container rupture. The binding strength must be sufficient to withstand the rigors of transportation. In particular, when containers packed and sealed at an elevation are then subjected to lower ambient air pressure, such as during air transportation or when transported to consumers at higher locations, a relative positive pressure is created within the container that otherwise it could cause the seal between the lid and the container to break. This ability of the container to prevent rupture under such conditions is known as bursting resistance. However, as the bursting resistance increases, there is generally a concomitant increase in difficulty in opening the container, which is exhibited by peeling strength or peeling resistance of the container. The higher burst resistance indiscriminately prevents both the break during transportation and the opening by the end user. Certain types of coatings that can be heat sealed have been used in both the lids and the liners of conventional containers. For example, SURLYN® polymer, a Dupont product, is a material known in the art and is commonly used as a heat seal coating. SURLYN® polymer is an ionically interlaced polymer with low fluid characteristics when heated. Typically, the layer of the container and the layer of the membrane that make contact with each other are constructed of SURLYN® polymer, and may be covered with a wax. These two layers of SURLYN® polymer are heat sealed along the top surface of the container sphere. The two layers of SURLYN® polymer create an extremely strong bonding layer that remains relatively uniform in thickness across the seal area. However, due to the strong interlocking created by the SURLYN® polymer, the opening of the container may require a peeling force that is too high for some consumers and usually results in tearing and exposure of the other layers of the wall of the container, such as the cardboard body wall, as illustrated in the US patent No. 4,280,653 to Elias. This gives the upper part of the container bad undesirable and inadequate appearance. In copending application Serial No. 09 / 065,783, the formation of two heat seal spheres is described. The two spheres comprise an inner heat seal sphere and an outer heat seal sphere, each heat sealing sphere being formed of the heat-sealable polymers of the seal layers of the membrane and the liner. The two spheres are formed using heat and pressure to force the heat-sealable polymers to flow away from the central portion of the heat seal area and into the interior and exterior of the container. The reduction in the amount of heat seal material in the central heat seal area reduces the binding strength in the central heat seal area and allows the opening of the container without inadequately tearing the liner and exposing the cardboard layer the wall of the container. However, the formation of the spheres according to the co-pending application does not completely eliminate the difficulty of balancing burst resistance and ease of opening.

Hl ^ k ^ dwMÉÉ lMIMa It would be useful to provide a sealed container and a method for sealing a container that would combine an improved opening facility and an attractive appearance after opening with the seal and barrier strength properties required for the protection of the products. inside the container.

BRIEF DESCRIPTION OF THE INVENTION The composite container of the present invention satisfactorily balances the need for easy opening with the bursting resistance necessary to maintain a tight seal despite changes in pressure experienced during transport of a container. The present invention provides a sealed container having a larger heat seal ball on the inner side of the heat seal area than on the outer side of the heat seal. The inner heat seal sphere contains a greater amount of heat seal material and has a greater width than the outer heat seal sphere. Since it has been discovered that the inner sphere is primarily responsible for maintaining the bursting resistance and the outer sphere is primarily responsible for the peeling resistance, a larger inner sphere and a smaller outer sphere results in a good balance between the resistance to bursting and ease of opening.

In one embodiment, the present invention provides a container of sealed composite material for products having a tubular body member that includes at least one cardboard body fold. A liner fold adheres to the inner surface of the tubular body member and includes a barrier layer and a seal layer. The seal layer defines the innermost surface of the liner fold and comprises a composition that can be heat sealed. At least one end of the body member and liner fold is rolled out to form a spherical or curly rib exposing the seal layer. A cap is also provided for closing the end of the tubular body member. The cap has a barrier layer and a seal layer adjacent to the seal layer of the liner fold in the rib. The seal layer of the lid also comprises a composition that can be heat sealed. The two seal layers adhere together to form a heat seal between the lid and the liner fold. The heat seal comprises an internal sphere formed of the composition which can be heat sealed from the seal layers and faces towards the inner part of the container, and an outer sphere also formed from the compositions which can be heat sealed from the opposite side of the seal by heat. The inner sphere is larger than the outer sphere, meaning that the inner sphere comprises a greater amount of the heat seal compositions than the outer sphere. Specifically, the width of the inner sphere is about 90 to 190 microns, preferably about 130 to about 180 microns, and the width of the outer sphere is about 60 to about 140 microns, preferably about 80 to about 120 mieras In terms of percentage, the width of the inner sphere is from about 10 to about 40% larger than the width of the outer sphere, preferably about 20 to 30% greater. The heat seal additionally comprises an intermediate region between the two spheres having a width from about 0 to about 30 microns. The seal layer of the liner fold is preferably selected from the group consisting of high density polyethylene, low density polyethylene, metallocene catalyzed polyolefin and mixtures thereof. The seal layer of the lid is preferably selected from the group consisting of ethylene vinyl acetate, high density polyethylene, low density polyethylene, ethylene methyl acrylate, metallocene catalyzed polyolefins, and mixtures thereof. In a modality, the seal layer of the lid comprises about 4.53kg / 2787m2 to about 22.65kg / 2787m2 of the composition that can be heat sealed, preferably at least about 9.06kg / 2787m2. Additionally, the seal layer of the lid has a thickness of about 15.24 to about 83.82 microns. In the embodiment described above, both the liner fold and the lid include separate seal layers. However, the present invention does not require the use of two separate seal layers. At least one of said lids and said liner fold must have a seal layer comprising a heat-sealable composition that forms a heat seal between the liner fold and the liner fold, but it is not necessary that both of them Liner fold and lid, have seal layers. In one embodiment, the rib of the container defines a heat seal surface, wherein the heat seal surface has an apex portion, an inner portion that slopes away from the apex portion and toward the inner part of the container , and an outer portion that slopes from the apex portion and toward the outside of the container, the inner portion slopes from the apex portion at a rate greater than the outer portion. This rib design causes the inner rib to extend further along the heat seal surface towards the inner part of the container that the outer sphere extends along said heat seal surface towards the outside of the container . A method for making tubular containers is also provided. The method includes providing a tubular member comprising at least one cardboard body fold, an inner surface and a liner fold adhered to the inner surface of the body fold, wherein the liner fold comprises a barrier layer and a seal layer. The seal layer defines the inner surface of the liner fold and comprises a composition that can be heat sealed. At least one end of the tubular container is rolled out to form a rib that exposes the seal layer of the liner fold. A cap closing the end of the tubular container is also provided, wherein the cap comprises a barrier layer and a seal layer. The seal layer of the lid comprises a composition that can be heat sealed. The two seal layers are contacted and heated under conditions that are sufficient to provide the heat-sealable compositions of the flowable seal layers. The seal layers are also pressed to preferentially promote the fluid of the heat-sealable compositions in the direction of the inner part of the container to form an inner sphere and an outer sphere of the heat-sealable compositions, wherein the inner sphere comprises a larger quantity of compositions that can be heat sealed than the outer sphere. In this way, the lid is hermetically sealed to the liner fold. Preferably, the pressure step comprises pressing the seal layers together with an inclined surface to preferably encourage the fluid in the direction of the interior of the container. The heating step preferably comprises heating the seal layers from about 175 ° C to about 275 ° C. The pressure step preferably comprises pressing the sealing layers together for about 0.5 to about 1.75 seconds with a sealing pressure of about 2.10 to about 4.21 kg / cm2. As described above, only one seal layer is required. If only one seal layer is used, the rib and cap are placed in contact and the seal layer is heated to provide the heat-sealable composition of the flowable seal layer. The -MMdMiWÜIii rib and lid are pressed to propitiate the fluid preferably in the direction of the inner part of the container as described above. An apparatus for sealing a lid to a container is also provided. The apparatus includes a sealing head having a central axis and a sealing surface, wherein at least a portion of the sealing surface is inclined towards the central axis of the sealing head. The sealing head has a coupled climbing position and an uncoupled position. An actuator operatively connected to the sealing head displaces the sealing head between the two positions. Preferably, the sealing surface is inclined at an angle of about 2 ° to about 20 °, and most preferably at an angle of about 7 ° to about 12 °.

BRIEF DESCRIPTION OF THE DRAWINGS Some objectives and utilities of the present invention have been mentioned, others will be evident from the continuation with the description taking it together with the attached drawings, which are not necessarily drawn to scale, where; Figure 1 is a perspective view of fragments of a container of the present invention illustrating the opening mechanism wherein the liner fold is not broken through the underlying paperboard; Figure 2 is an enlarged and fragmented view of the sealed end of the tubular container of an embodiment of the present invention that a ^ i iib illustrates the internal and external spheres of the composition that can be heat sealed; Figure 3A is a very enlarged sectional view of the present invention taken along lines 3A-3A of Figure 1: Figure 3B is a greatly enlarged sectional view of the heat seal of the present invention illustrating the beginning of tearing in the seal layers during the opening of the container; Figure 3C is a very enlarged sectional view of the heat seal of the present invention after having opened the container; Figure 4 is an enlarged fragmentary view of the sealed end of the tubular container of an embodiment of the present invention illustrating a preferred shape of the rib of the container; Figure 5A is an enlarged sectional view of the heat sealing apparatus of the present invention before contacting the container of the present invention; Figure 5B is an enlarged sectional view of an embodiment of the sealing head of the heat sealing apparatus of the present invention making contact with the lid of the container and forcing the compositions that can be heat sealed preferably towards the inside the container; Figure 5C is an enlarged sectional view of the sealed end of a container of the present invention after the sealing operation; Y -dbuá ^ bL- Figure 6 is a plan view of an embodiment of an apparatus for making a tubular container in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION The present invention will now be described in greater detail with reference to the accompanying drawings, wherein the preferred embodiments of the invention are shown. However, this invention can be modalized in many different forms and should not be construed as limited to the embodiments set forth herein; instead, these embodiments are provided so that this description is complete, and will fully convey the scope of the present invention to those skilled in the art. Equal numbers refer to the same elements throughout the description. A tubular container 10 in accordance with the present invention is illustrated in Figure 1. Although illustrated with a circular cross-section, the tube can have any cross-sectional shape, which can be formed by wrapping the tube around a mandrel with the proper shape . An example is a tube with a rectangular shape generally having rounded corners. The embodiment illustrated in Figure 1 is particularly useful for packing French fries and includes a flexible closure or lid 11It is also known as a membrane-type cap or closure, and a plastic end cap 12 that can be reused over the seal. However, other end closures may be used depending on the type of product to be packaged, e.g. dough. As illustrated in greater detail in Figure 2, the tubular container 10 includes a wall having a body fold 13 which preferably is formed of a cardboard liner fold 14 which is preferably formed of a polymeric material adhered to the inner surface of the body fold 13. The upper end of the The tubular container 10 is wound so as to form a ball-shaped rib 15. The lid 11 is hermetically sealed to the upper part of the rib 15 as discussed below. The end cap 12 is then snapped onto the rib 15 and can be reused after the cap 11 has been removed. A closure (not illustrated), for example a metal closure, can be secured to the opposite end of the container 10. The lid 11 is constructed of multiple layers. Optionally, the layer disposed on the outermost surface of the lid 11 away from the inner part of the tubular container 10 is a layer of paper or cardboard 18, as a sulphate paper layer. A barrier layer 20 is also provided which works as a barrier to the passage of liquids and / or gases, such as oxygen. If a barrier for liquids and gases is required, the barrier material is preferably selected from the group consisting of polyethylene terephthalate, polyethylene terephthalate, modified, polyethylene naphthalate, metallized polyester or Metallized propylene and mixtures thereof. The barrier layer 20 may also be constructed of silicate-coated metal oxide and polyester, metal oxide and polypropylene coated with silicate, ethylene vinyl alcohol and mixtures thereof. Alternatively, the barrier layer 20 comprises a layer of aluminum foil. Utilitatively, the lid 11 further includes a seal layer 22 comprising a heat-sealable composition and positioned so that the seal layer 22 of the lid 11 is adjacent to the seal layer 26 of the liner fold 14. seal layer 22 of the lid 11 preferably is constructed of a material selected from the group consisting of ethylene vinyl acetate, high density polyethylene, low density polyethylene, ethylene methyl acrylate, metallocene catalyzed polyolefins and mixtures thereof. The seal layer 22 of the lid 11 preferably has a melting point within the range of about 70 ° C and 130 ° C. Very Preferably, the melting point of the seal layer 22 is between about 80 ° C and 110 ° C, in particular it is 83 ° C. In one embodiment, the layer 11 is formed as a laminate having a layer of cardboard 18 adhered to the barrier layer 20 using a layer of co-extruded adhesive (not shown). The adhesive layer is constructed of materials selected from the group consisting of low density polyethylene, ethylene methylacrylate (EMA), ethylene-methacrylic acid copolymers (EMAA) and mixtures thereof. The seal layer 22 is coated on the opposite surface of the barrier layer 20. The layer of A ^ i ^ iiaiK. seal 22 can be formed by extrusion coating, such as a blown film laminated by extrusion or as a blown film laminated with a thermo-adjustable adhesive. In one embodiment, the seal layer 22 is formed as a double layer by coextrusion of high density polyethylene and ethylene methacrylate copolymer. The seal layer 22 of the lid 11 is preferably between 15.24 and about 76.20 microns thick, most preferably 38.1 microns thick. The seal layer 22 comprises a heat-sealable composition weighing between about 4.5350 to about 22.67 kg / 2787 m2 and preferably about 9.07 to about 18.14 kg / 2787 m2. Preferably, the seal layer 22 has a heat-sealable composition that weighs approximately 11.33 kg / 2787 m2 or more. The relatively thick seal layer 22 avoids natural variations in the process of making the container that could affect the consistency of the seal by heat. For example, imperfections in the rib 15 and variations in the height of the container have an important effect on the sealing process. The additional heat sealing material fills any break or crevice created in the rib 15 and can also create a continuous seal around the ribs on the wall of the container, like the ribs created by anaconda folds or overlapping ribs in the lining. The additional sealing material also contributes to a better sealing compensated for slight differences in container height that could otherwise lead to a reduction in seal strength. Additionally, the increased amounts of the material of the seal layer 22 allow the creation of a heat seal despite the presence of contaminants introduced into the seal area by heat during the manufacturing process, such as wax. By using a thicker seal layer, the heat seal can be formed at lower seal temperatures. A preferred construction of the seal layer is described in the patent application of E.U.A. Serial No. 09 / 416,194, presented concurrently and entitled "Sealant Layer for Container Lid". This application is assigned to the assignee of the present application and is expressly incorporated herein by reference. The liner fold 14 is also typically constructed of multiple layers. With the exception of the outermost seal layer 26, the composition of the liner fold 14 is not important for the present invention. Preferably, one of the layers forms a barrier to moisture and / or gases depending on the application. It will be understood that various barrier materials and coating folds can be employed depending on the article to be packaged. For example, conventional coatings include a layer of paper laminated with sulphate paper backing. However, in a preferred embodiment, the liner fold 14 is substantially formed entirely of polymeric material. In particular, coating folds such as those described in the US patent may be used. No. 5,829,669 to Drummond et al and the patent of E.U.A. No. 5,846,619 to Cahill et al., Both assigned to transferee of the present invention and are incorporated by reference herein. In the embodiment illustrated in Figure 2, the liner fold 14 includes a seal layer 26, a moisture barrier layer 28 and an adhesive layer 30. The barrier layer 28 is resistant to the passage of liquids and gases, as oxygen. If a high barrier is required for liquids and gases, barrier materials such as metallized polyester or metallized polypropylene are preferred. Some food products, such as juices, do not require a gas barrier 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 may be employed depending on the article to be packaged. Alternative barrier materials include nylon, EVOH (polymer and ethylene vinyl alcohol copolymer), polyvinylidene chloride, polyethylene, polypropylene, metallized polypropylene, metal oxide and polyester coated with silicate, metal oxide and polypropylene coated with silicate and the like as will be evident for those skilled in the art. A surface of the barrier layer 28 may include a metallized coating 32 to provide a metallic appearance and also to improve the barrier properties. The metallized coating 32, which may be formed of aluminum, is much thinner than a layer of metallized paper, however it is not necessary for strength or barrier properties in certain applications.

An adhesive layer 30 is preferably below the metallized coating 32 and defines the radially outermost surface of the coating ply 14. The adhesive layer 30 may have multiple or extruded layers together. The adhesive layer 30 may be selected from the group consisting of metallocene-catalyzed polyolefins, ethylene-methacrylic acid, ethylene-methyl acrylate, ethylene-butyl acrylate, ethylene-acrylic acid, ethylene vinyl acetate and combinations, mixtures and copolymers thereof. The adhesive layer 30 can also be a thermo-adjustable adhesive layer. A seal layer 26 defines the radially innermost surface of the liner fold 14. The seal layer 26 provides a surface to which the adhesive layer 30 adheres when a first marginal edge portion 41 of the liner fold 14 is placed on an overlapping relationship with a second marginal edge portion 42, as shown in Figure 6. The seal layer 26 also forms the heat seal between the lid 11 and the liner 14 together with the seal layer 22 of the lid. The seal layer 26 of the liner fold 14 is preferably constructed of a material selected from the group consisting of high density polyethylene, low density polyethylene, metallocene catalyzed polyolefins and mixtures thereof. In seal layer embodiments 26 including a polyolefin polymer, the polyolefin is preferably a high density polyethylene or a high density polyethylene blend containing up to 30% low density polyethylene. The seal layer 26 of the liner fold 14 preferably has a melting point within the range of about 110 ° C and about 140 ° C. Most preferably, the seal layer 26 has a melting point between about 120 ° C and 130 ° C. Figure 2 illustrates the sealed end of the tubular container of a preferred embodiment of the present invention, wherein the two seal layers 22, 26 are heat sealed together. As shown in greater detail in Figure 3A, a sealed container of composite material for products is provided with a heat seal between the liner fold 14 and the lid 11 in the form of an internal heat seal ball 36 and a dial. seal by external heat 38. The internal heat seal sphere 36 and the external heat seal sphere 38 are formed from the heat-sealable compositions of the seal layer 26 of the liner fold 14 and the seal layer 22 of the lid 11. The compositions that can be heat sealed from both seal layers 22, 26 move outward from the intermediate region during the heat sealing operation and subsequently cool to form the spheres 36, 38 The internal heat seal sphere 36 faces the inner part of the tubular container 10 and the seal sphere by external heat 38 is placed on the opposite side of the heat seal area from the seal sphere by internal heat 36. When cooled, the seal comprises a thin intermediate region 40 between the internal heat seal sphere 36 and the sphere of seal by external heat 38. In some places, the heat-sealable compositions can be completely displaced from between the barrier layers 20 and 28 so that the barrier layers are in splice contact. However, the internal and external spheres 36, 38, maintain double barriers against the passage of liquids and gases so that a hermetic seal is maintained. The intermediate region 40 preferably has a lower bond strength than the internal heat seal sphere 36 and the external heat seal sphere 38. The width of the intermediate region 40 is approximately 0 to about 30 microns. The term "sphere" as used herein is intended to be distinguished from the above containers by having a relatively flat heat seal where the flow of the heat seal compositions was presented at very low flow, or none at all. In addition, this embodiment is not limited to use with only coatings having a straight overlap edge, also heat seal spheres 36, 38 can be used with an anaconda fold edge. In effect, the internal heat seal sphere 36 and the external heat seal sphere 38 provide a double seal having a high or bursting resistance. The bursting resistance of the sphere seal gives the container 10 a resistant seal against forces acting against the container in a normal direction towards the heat seal (ie, normal to the plane defined by the end of the tubular container 10). Since most of the forces acting on a container during storage and transit will be normal in the heat sealing area, the high burst resistance of the internal heat sealing sphere 36 and the external heat sealing sphere 38 of the present invention is especially useful for use in product containers. The IMi? DEMtE explosion resistance can be tested using an altitude camera. Typically, the sealed container 10 is placed in the altitude chamber and subsequently subjected to an external partial vacuum for a predetermined period to determine whether the heat seal is able to withstand the differences between the internal container pressure and the external pressure of the container. air. Suitable test conditions include subjecting the container to a vacuum of 254 millimeters of Hg for 30 minutes at room temperature. The containers 10 of the present invention are capable of maintaining a hermetic seal during exposure for 30 minutes at a vacuum of 254 millimeters of Hg at room temperature. Although the high burst resistance of the heat seal formed in accordance with the present invention is relatively low, a container exhibiting a relatively easy opening results as a result. In contrast to conventional containers where two SURLYN® polymers are crosslinked and only in a relatively flat heat seal, resulting in a bond, which is sufficient to tear the liner 14 when removing the lid 11 (instead of tearing through the polymer SURLYN®). The preferred range of resistance to peeling is approximately 89.28 to 178.57 kg / m. In one embodiment, the heat seal has a breaking strength of about 124.95 kg / m to about 178.57 kg / m. In this manner, the heat seal of the present invention combines the tear resistance and the tensile strength necessary to prevent undesired ruptures of the tubular container 10 with a resistance to -tfttUtlttiMia peeling relatively low so that the consumer gets a simple opening of the container. Figures 3A-3C illustrate the opening mechanism of the container 10 of the present invention. As shown in Figures 3B and 3C, the tearing force generated during the opening of the container 10 causes a tear which propagates through the seal layer 26 of the liner fold 14 and / or the seal layer 22 of the lid 11. The seal layer 26 of the liner fold 14 and the seal layer 22 of the lid 11 provide a bonding force between the barrier layer 20 of the lid 11 and the barrier layer 28 of the liner fold 14 that is less than the bond strength between the barrier layer 28 and the liner fold 14 and the cardboard body fold 13 (or any intermediate lids such as the metallized coating 32 of the liner 14). As a result, the cut that is carried out during the opening of the tubular container 10 occurs only between, and not through, the barrier layers of the liner fold 14 and the lid 11. When the tubular container 10 of this invention opens, unexpectedly no tears are present through the barrier layer 28 of the liner fold 14. It has been found that the inner sphere 36 of the double ball seal provides a primary resistance to the tensile forces acting on the container , as the bursting forces generated by changes in internal pressure during transport. However, the outer sphere 38 provides the primary resistance to opening by tearing the seal by The tearing heat, formed between the lid 11 and the liner fold 14. As a result, it has been discovered that the heat seal is usefully formed with a larger internal sphere 36 and a smaller external sphere 38. The resulting container exhibits an improved ease to open by virtue of a smaller outer sphere 38 and improved burst strength to withstand the rigors of transportation under the larger inner sphere 36. The heat seal of the present invention has an inner sphere 36 that has a greater width than the outer sphere 38. The width of the sphere is defined as the distance between the barrier layer 20 of the cap 11 and the barrier layer 28 of the liner fold 14 measured at the longest point through the sphere in the vertical plane as shown by the reference symbol A of Figure 3A. Note that the width measurement is defined generically as the distance between the adjacent layer next to the seal layer 22 of the lid 11 in the construction of the lid in the next layer adjacent the seal layer 26 of the liner 14 in the construction of the lining. In a preferred mode, the next adjacent layers are the barrier layers. However, in other embodiments, the following adjacent layers may be layers of other types. Specifically, the width of the inner sphere 36 is from about 90 to about 190 microns, preferably from about 130 to about 180 microns and much preferably from about 140 to about 160 microns. The width of the outer sphere 38 is from about 60 to about 140 microns, preferably about 80 to about 120 microns, and very much preferably about 95 to about 120 microns. As will be understood, the width of the spheres will depend on various factors, including the heat sealable materials that are used to form the seal layers 22, 26, the heat seal conditions and the like. In terms of relative widths of the sphere 36 and the external sphere 38, the width of the inner sphere is from about 10 to about 40% greater than the width of the outer sphere, preferably from 20 to 30% greater, and very much preferably about 22 to about 26% higher. A preferred form of the rib 15 of the container 10 is illustrated in Figure 4. As shown, the rib 15 of the container 10 is rolled out to expose the heat seal layer 26 of the cover 14. The rib 15 creates a heat seal surface that contacts the seal layer 22 of the lid 11. The heat seal surface includes an apex portion 84, an inner portion 86 that slopes from the apex portion and toward the inner portion. of the container 10, and an outer portion 88 that slopes from the apex portion and toward the outside of the container. Preferably, the inner portion 86 is inclined from the apex portion 84 at a greater rate than the outer portion 88. This rib design 15 encourages the inner sphere 36 to extend further down the heat seal surface toward the part inside the container 10 and obstructing the outer sphere 38 from extending down the surface of the seal by heat towards the outside of the container. In this way, the shape of the rib 15 affects the flow direction of the heat-sealable compositions and the relative shapes of the inner sphere 36 and the outer sphere 38. By encouraging the flow of heat-sealable compositions down from the heat seal surface towards the inner part of the container, a higher burst strength is obtained due to the anchor effect on the inner sphere 36. It is believed that the shape of the inner sphere 36 creates a resistance component of Shear stress that counteracts the forces caused by the internal pressure of the container more effectively than the higher tensile strength of the prior art designs. Additionally, peel strength is maintained at a reasonable level due to the inclination of the heat seal surface toward the outside of the can that is lesser in degree and does not promote the flow of heat-sealable compositions. in that direction. As desired, the previously described shape of the rib 15 maintains the outer sphere 38 at a relatively small size compared to the sphere 36. The desired rib shape 15 may be formed during the initial formation of the container rib or by a secondary training procedure. Alternatively, the desired rib shape 15 may be formed together with the heat sealing operation. The rib may also have a substantially flat portion as shown in Figure 4 and described in the U.S. patent application. with serial number 09 / 416,169, presented concurrently with the present and entitled "Container With Heat Seal Surface Having a Substantially Planar Portion". This application is assigned to the assignee of the present application and is expressly incorporated herein by reference. A method and apparatus for scaling a container for products is also provided. The sealing method and apparatus are illustrated in Figures 5A-5C. The heat seal can be created using any suitable apparatus known in the art. In some sealing systems, wax is applied to the rib 15 to keep the lid 11 in place before the heat seal is formed. As noted above, the relatively thick seal layer 22 of the lid 11 allows for the formation of a heat seal having sufficient bond strength despite the presence of wax in the heat seal area. The present invention also supports a sealing system that utilizes a vacuum system to initially hold the lid 11 in place prior to the heat sealing operation. The use of the apparatus, the heat sealing method of the present invention includes providing a tubular element having a cardboard layer 13 and a liner fold 14 adhered to the inner surface of the cardboard layer. As described above, the liner fold 14 includes a barrier layer 28 and a seal layer 26, the seal layer defines the innermost surface of the liner fold and comprises a heat-sealable composition. Once one end of the tubular element has been rolled to form a rib 15, a lid 11 can make contact with the ii ^ iWfkfa ^ i ^ a ^ fold of liner 14 to form the seal by heat. The lid 11 includes a barrier layer 20 and a seal layer 22, wherein the seal layer comprises a composition that can be heat sealed. The seal layer 22 of the lid 11 contacts the seal layer 26 of the liner fold 14. The two seal layers 22, 26 are subsequently heated under sufficient conditions to provide heat-sealable compositions with flowability and pressed in a manner that preferably promotes a greater flow of compositions that can be heat sealed in the direction of the inner part of the container to form an inner sphere 36 and an outer sphere 38, wherein the inner sphere contains a greater number of compositions that can be sealed by heat than the outer sphere. In a preferred embodiment, the pressure step is achieved by pressing the seal layers 22, 26 together using an inclined surface, such as the inclined heat sealing head 44. The heat sealing head 44 is preferably constructed of metal, such as aluminum , covered with copper or other heat conductive material. The heat sealing head 44 is heated by a heat source 46. The heat source can be any suitable type of heat source known in the art. The heat sealing head 44 does not have to be heated. The heat seal layers 22, 26 could be heated independently using a separate heat source. The heat sealing head 44 has a sealing position engaged in contact with the lid 11 and a decoupled position. The heat sealing head 44 is displaced between the two positions by an actuator 48. The actuator 48 may be of any type of actuator known in the art, including mechanical, pneumatic and the like. The angle of the inclined surface of the heat sealing head 44 affects the amount of material flowing to form the spheres as well as the relative size of the spheres. The angle of the inclined surface of the heat sealing head 44 is from about 2 to about 20 °, preferably about 7 to about 12 °. In one embodiment, the angle of the inclined surface is about 10 °. In another mode, the angle is close to 3 ° C. The inclined surface of the head 44 causes the fused polymer of the seal layers to move towards the bottom of the container to form the inner sphere. When this movement occurs, the fused polymer usefully "fills" any irregularities in the liner and lid surfaces, thereby improving seal integrity. The heat sealing conditions, such as temperature, pressure and time, depend on several factors, including the heat sealable compositions that are used and the thickness of the heat seal layers. In one embodiment, the heat seal layers are heated to between about 175 ° C to about 275 ° C, preferably about 205 ° C to about 230 ° C, and most preferably about 210 ° C to about 225 ° C. In one embodiment, the heat sealing temperature is about 218 ° C. The heat sealing pressure is from about 2.10 to about 4.21 kg / cm2, preferably about 2.81 to about 3.51 kg / cm2. In one embodiment, the heat sealing pressure is about 3.16 kg / cm2. The sealing time t ± A by heat, meaning the period during which heat seal pressure is applied is from about 1.5 to about 1.75 seconds, preferably about 0.9 to about 1.5 seconds, and very much preferably about 1.15 to about 1.35 seconds In one embodiment, the heat sealing time is about 1.25 seconds. Although the embodiments of the container discussed above include two seal layers, 22 and 26, the present invention does not require the use of two seal layers. At least one liner and cover must include a seal layer to provide the necessary heat seal spheres 36 and 38, as described above. However, two seal layers are not necessary to practice the present invention. In case of using a single heat sealing layer, the heat seal layer may be constructed of high density polyethylene, low density polyethylene, ethylene vinyl acetate, ethylene methyl acrylate, metallocene catalyzed polyolefins and mixtures thereof. The containers 10 of the present invention can be made by the process illustrated in Figure 6. As shown, a continuous strip of cardboard body folding material 13 is provided to the apparatus and first passes through a pair of thinners of opposite edge 50. The edge thinners remove part of the square edge of the body fold 13 to create first 52 and second edges 54 having a beveled configuration. The body fold 13 subsequently advances through an adhesive applicator 56, which applies a tt ^ it adhesive METHOD 21 to the upper surface of the body fold. The adhesive 21 is usefully an aqueous adhesive that overcomes many problems associated with solvent based adhesives. No special equipment is necessary to capture solvents that evaporate from the adhesive to comply with the 5 environmental standards. Preferred adhesives are aqueous ethylene vinyl acetate (> 18%) materials with low glass transition temperature. 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 adhesive 21, as well as other adhesive layers used to construct the container 10, can be applied in the form of a foam, as described in the copending U.S. patent application. with serial number 09 / 197,275 entitled "Composite Container Having Foamed Adhesive", which is assigned to the assignee of the present invention and is incorporated herein by reference. The body fold 13 and the wet adhesive 21 applied thereto, subsequently pass under a heater 58 which evaporates at least part of the water content of the aqueous adhesive 21 to give a substantially tacky adhesive. It is important that a adequate amount of heat 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 contrary, too much heat will dry the adhesive and cause the ri ^ MHMn iaM || jto ^^? t? ? G ?? you, m? adhesive lose stickiness. A preferred type of heat source is an infrared heater, although various other sources of heat may be used, for example, heating with forced air or the like. After heating the adhesive 21 on the body fold 13, the body fold 13 and the liner fold 14 are fed to the formed mandrel! from opposite directions. The body fold 13 passes under a thinned adhesive applicator 60 which applies the thinned adhesive 24 to the beveled surface of the second thinned edge 54 of the body fold 13. The thinned adhesive 24 is preferably a hot melt adhesive of the conventional type. the technique, although a water-based adhesive may also be used including one or more polymers. The liquid adhesives that are preferred are polyvinyl acetate and ethylene vinyl acetate. The thinned adhesive helps to provide a stronger body fold joint especially for single body crease containers. The surface of the liner fold 14 contacting the body fold 13 is subjected to a corona treatment station 62. The opposite surface of the liner fold 14 is coated with a lubricant from a cylinder 64, which allows the fold of liner glides smoothly during the winding operation. The liner fold 14 subsequently passes under an infrared heater 66, which heats the second marginal edge portion 42 of the liner fold. After the infrared heater 66, the second edge portion .tte .... . ..... jm ....! .- .-, .. marginal 42 of the liner fold 14 passes under at least one forced air heater 68. The body fold 13 and the liner fold 14 are subsequently wound around a forming mandrel 70 from opposite sides of the mandrel. Each fold is first wrapped under the mandrel 70 and subsequently over the top in a helical shape with the liner fold 14 wound against the surface of the mandrel. The first marginal edge portion 41 of the liner fold 14 is exposed on the mandrel 70 and is subjected to heat from a second forced air heater 72. While the body fold 13 is further wrapped and the first edge 52 of the body fold 13 back under mandrel 70 after a complete revolution, it comes into contact with the second edge 54 of the next portion of the body fold 13 that first makes contact with the mandrel. The recessed edges 52, 54 are spliced and the thinned adhesive 24 adheres to the edges together to form a spirally wound tube advancing along the mandrel 70. With respect to the skin fold 14, the first marginal edge portion 41 is puts in an overlap relationship with the second marginal edge portion 42 to create a sealed straight overlap edge. The seal is formed by a polymeric adhesive layer 30 of the first marginal edge 41 joining the second marginal edge 42. However, a strip of hot melt adhesive can alternatively be used to fix and seal the liner overlap.

The tube then advances down the mandrel 70 by a conventional winding tape 74 which extends around a pair of opposed pulleys 76. The winding tape 74 not only rotates and advances the tube, it also applies pressure to the overlapping edges of the body fold 13 and the skin fold 14 to ensure a secure connection between the respective fold edges. An outer label fold 16 preferably passes over an adhesive applicator 78 and is wound around the body fold 13. The label fold 16 can be applied prior to the winding tape 74. In a cutting station 80, the continuous pipe is cut into discontinuous lengths and removed from the mandrel 70. The ends of the containers 10 are subsequently wound outward to form the rib 15 and the lid 11 is subsequently heat sealed as described above. An end closure, such as a metal closure, is attached to the other end of the container 10. Typically, the lid 11 and the end closure 12 are applied to one end of the container 10 before filling the container. After filling, an end closure is applied to the opposite end. 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 foregoing descriptions and associated drawings. Therefore, it should be understood that the invention should not be limited to ^^^^ specific modalities described and such modifications and other modalities 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. ^ ^ u ~ .. *,. .., ...,.

Claims (9)

NOVELTY OF THE INVENTION CLAIMS

1. - A container of sealed composite material for products comprising: a tubular body element comprising at least one crease of cardboard body (13) and having an internal surface; a liner fold (14) adhered to the inner surface of said tubular body member and comprising a barrier layer (28), at least one end of said body member and said liner fold being rolled outward to form a rib (15) and exposing said liner fold; and a lid 11 operatively positioned adjacent said rib and heat sealed thereto, said lid comprising a barrier layer (20); wherein at least one of said lid and liner fold further comprises a seal layer comprising a heat-sealable composition, said seal layer forming a heat seal between said lid and said liner fold comprising an inner sphere (36) formed of the composition that can be heat sealed and facing the inside of the container and an outer sphere (38) formed of the composition that can be heat sealed on the opposite side of the seal by heat from the inner sphere, in wherein said internal sphere comprises a large number of the compositions that can be heat sealed in cross section to said outer sphere.

2. - A container according to claim 1, wherein the width of the sphere is from about 90 to about 190 microns and the width of the outer sphere is from about 60 to about 140 microns.

3. A container according to claim 2, wherein the width of the sphere is from about 130 to about 180 microns and the width of the outer sphere is from about 80 to about 120 microns.

4. A container according to claim 1, wherein said heat seal provides a bonding force between said barrier layer of said cover and said barrier layer of said lining fold; said binding force being less than the bonding strength between said barrier layer of said liner fold and said tubular body member behind said barrier layer so that, when opened, a tear occurs only between the barrier layers .

5. A container of sealed composite material for products comprising: a tubular body element comprising at least one crease of cardboard body (13) and having an internal surface; a liner fold (14) adhered to the inner surface of said tubular body member and comprising a barrier layer (28), at least one end of said body member and said liner fold being rolled outward to form a rib (15) said rib defining a heat seal surface having an apex portion (84), an inner portion (86) that slopes from said apex portion and toward the interior portion of the container, and an outer portion (88) that is tilted from ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ and a cap (11) operatively positioned adjacent said rib and heat sealed thereto, said cap comprising a barrier layer (20); wherein at least one of said lid and liner fold further comprises a seal layer comprising a heat-sealable composition, said seal layer forming a heat seal between said lid and said liner fold comprising an inner sphere (36) formed of the composition that can be heat sealed and facing towards the inside of the container and an outer sphere (38) formed of the composition that can be heat sealed on the opposite side of the seal by heat from the inner sphere, in wherein said inner sphere further extends along said heat seal surface toward the interior of the container said said outer sphere extends along said heat seal surface towards the outside of the container.

6. A container according to claim 5, wherein the width of said inner sphere is from about 10 to about 40% greater than the width of said outer sphere.

7. A container according to claim 6, wherein the width of said inner sphere is from about 20 to about 30% greater than the width of said outer sphere.

8. A method for making a sealed container for products comprising: providing a tubular element comprising at least one crease of a cardboard body having an internal surface and a lining fold adhered to the internal surface of the body crease, the lining fold comprises a barrier layer; winding out at least one end of the tubular element to form a rib; providing a cap for closing the end of said tubular element, the cap comprising a barrier layer, at least one of said cap and said liner fold additionally comprising at least one seal layer comprising a composition that can be heat sealed , the seal layer being operatively placed to form a heat seal between the lid and the liner fold; make the rib and lid contact; heating the seal layer under conditions sufficient to provide the heat-sealable composition of the seal layer that can flow; pressing the rib and the lid together to preferably promote the flow of the heat-sealable composition in the direction of the interior of the container to form an internal sphere and an outer sphere of the composition that can be heat sealed, the inner sphere comprises a greater amount of the composition that can be sealed by heat in cross section than the outer sphere, sealing in a sealed manner in this way the lid to the liner fold.

9. A method according to claim 8, wherein said pressing step comprises pressing the rib and the lid together with an inclined surface to preferably promote the fluid of the composition that can be heat sealed in the direction of the inside of the container.