Packaging container and blank therefor

Abstract: Packing containers and packing container blanks of the type used for the packaging of e.g. milk and juice often are of the so-called gable-top type, the top closure also serving as an opening arrangement with a pouring spout which can be folded out. The parts (9, 10) forming the pouring spout (14) may be coated partly with a seal-preventing substance so as to make it possible for the pouring spout to be detached and let out in spite of the heat-sealing of the top. The seal-preventing coating (15) in accordance with the invention is covered by a film (16) which extends along the upper edge region of the packing container (1), which provides a better defined sealing strength, a tighter top seal, and protects the said coating (15) both before and after the conversion of the packing container blank (2) to packing containers (1)

Description: The present invention relates to a packing container of foldable material with a liquid-tight surface layer and with bottom walls, side walls and an openable closure which comprises two main panels sealed to one another and a bellows-fold situated between these with back-folding panels, whose surfaces facing towards the main panels comprise a coating of a seal-preventing means. The invention also relates to a blank for the manufacture of a packing container of a foldable packing material with a liquid-tight surface layer, which material by means of crease lines is divided into a number of wall panels for the formation of a bottom, side walls and an openable top closure, these wall panels comprising two main panels and back-folding panels situated between these which have a coating of a sealpreventing means. Packing containers of a flexible pecking material, e.g. paper and plastics laminate, exist in a great number of forms and are used, among other things, for the packaging of liquid foodstuffs, e.g. milk and juice. A packing container of this type occurring frequently is the so-called gable-top package which comprises four side walls, a plane bottom and a rooflike top part which has main panels inclined towards one another, whose upper parts are sealed together to a sealing fin. In the type of packing container described it is possible in general to open ports of the top part and form them to a pouring spout. The opening arrangement itself may be designed in a number of different ways, but usually the actual top seal between the upper ends of the different wall panels or fields included in the top is utilized as an opening arrangement. When the packing container is to be opened, the top seal produced in the manufacture of the packing container is then broken so that some of the panels folded in can be folded out in order to form a pouring spout. The openability of the packing container consequently will depend to a great extent on the strength of the top seal which means in practice that a choice has to be made between a good, and thus tight, top seal and an easily openable but less tight top seal. To eliminate this problem it has been proposed to separate the sealing and opening function by providing the packing material at a suitable place with another type of opening arrangement, e.g. a perforation line. This, however, means a more complicated manufacturing process and, since the perforation line has to be placed below the top seal of the packing container, the opening arrangement gets closer to the liquid surface in the packing container which is a disadvantage on opening as well as on pouring out of the liquid contents from the packing container. The original design with a combined top seal and opening arrangement is generally preferred, and it has been attempted, therefore, in recent times to optimize this design so as to obtain a good seal and tightness as well as good openability. Since the top of the packing container usually is heat-sealed by fusing together layers of thermoplastic material situated on the outside of the packing material, several of these attempts were based on a reduction of the sealing strength within the limited region of the top seal, which is used in the opening of the packing container whilst maintaining the sealing temperature and the sealing pressure. This reduction of the sealing strength may be achieved, for example, by providing the packing material within the region which is to be readily openable with an uneven surface, so that the total adhesion area within this region is reduced (EP-A-185. 325). However, this technique has proved to be subject to certain disadvantages and it has been found difficult in practice to obtain the predetermined, desired sealing strength. This disadvantage can be overcome with the help of another known technique (EP-A-270.869), according to which the region of the top seal which is to be openable is provided with a coating of a seal-preventing means which can be applied to the packing material in advance by means of a printing process. This technique provides a readily openable packing container which, however in certain combinations of seal-preventing means end plastic coating of the packing material say result in leaking packing containers. This problem is accentuated especially in packing containers of the type to be used for aseptic contents. For this type of contents and packing container the demands on tightness are extremely high, since, even a so-called microleakage impairs the sterile conditions and reduces the keeping properties of the product to an appreciable degree. Another known technique (US-A-4.712.727, US-A-4.756.426) uses laminated pieces of strip which comprise layers of an adhesive and are placed on the region of the blank where a limited closing force is desired, that is to say above all on both sides of the folded-in pouring spout. However, the handling and placing of the individual pieces of strip in correct position on the blank is difficult to master and the method, moreover, is relatively expensive. It is evident from the above that it has not been possible up to now to provide a packing container of the gable-top type where on the one hand the top seal is easily openable when an opening of the packing container was intended and on the other hand a completely tight packing container could be ensured. This demand has been particularly difficult to meet in aseptic packing containers, since even very small channels through the top seal may cause the sterility to be infringed, so that the keeping properties of the product no longer can be guaranteed. It is an object of the present invention, therefore, to provide a packing container of foldable material with a top closure which is easy to open and, in spite of this, is sufficiently tight for the packing container to be used advantageously for the packaging of aseptic products. It is a further object of the present invention to provide a packing container with an opening arrangement which is not subject to the disadvantages which affected similar designs known previously. It is a further object of the present invention to provide a packing container with a top closure whose tightness and opening properties remain good even at varying sealing temperature and sealing pressure. These and other objects have been achieved in accordance with the invention in that a packing container of foldable material with a liquid-tight surface layer and with bottom walls, side walls and an openable closure which comprises two main panels sealed to one another and a bellows-fold situated between these with back-folding panels, whose surfaces facing towards the main panels comprise a coating of a seal-preventing means, has been given the characteristic that a heat-sealable film extends over the coating of seal-preventing means and is sealed to the surface layer around the coating so that the coating is screened off from the inside of the packing container in a liquid-tight manner. Preferred embodiments of the packing container in accordance with the invention have been given, moreover, the characteristics evident from subsidiary claims 2-3. A further object of the present invention is to provide a blank for the manufacture of packing containers with an openable top closure, the blank being designed and prepared so that the achievement of a top seal of the desired tightness and opening properties is assured. A further object of the present invention is to provide a blank of this type which is not subject to the disadvantages which are typical for blanks known previously. A further object of the present invention is to provide a packing container blank which is particularly well suited for the manufacture of packing containers in accordance with the present invention. These and other objects have been achieved in accordance with the invention in that a blank for the manufacture of a packing container of a foldable packing material with a liquid-tight surface layer, which material by means of crease lines is divided into a number of wall panels for the formation of a bottom, side walls and an openable top closure, these wall panels comprising two main panels and back-folding panels situated between these which have a coating of a sealpreventing means, has been given the characteristic that a film of heatsealable material extends over the coating of sealpreventing means of the back-folding panels and is sealed to the surface layer around the coating so that said coating is screened off in a liquid-tight manner. Preferred embodiments of the packing container blank in accordance with the invention have been given, moreover, the characteristics evident from subsidiary claims 5-10. By providing the packing container and the blank in accordance with the invention with a heat-sealable film which covers the coating of seal-preventing means on the one hand a well-defined and predictable sealing strength between the heat-sealable film and the seal-preventing means is obtained and on the other hand a good mutual seal between the different sealing surfaces included in the top seal covered by the heat-sealable film. Through this on the one hand a good openability is achieved and on the other hand a good seal wherein the heat-sealable film effectively contributes towards preventing the occurrence of channels and microleakage. This makes it possible to use the packing container and the blank in accordance with the invention also for the packaging of aseptic contents in sterile packages. A preferred embodiment of the packing container as well as of the blank in accordance with the invention will now be described in more detail with special reference to the schematic drawings attached which only show the details indispensable for an understanding of the invention. Fig. 1 shows a packing container blank in accordance with the invention. Fig. 2 shows a part of a packing container blank in accordance with Figure 1 is section and partly in strong enlargement. Fig. 3 shows in perspective a packing container in accordance with the invention in opened condition, parts of the packing container wall being omitted for the sake of clarity. Fig. 4 illustrated on an enlarged scale a section through a part of the packing container in accordance with Figure 3 in closed condition. The preferred embodiment of the packing container as well as of the packing container blank in accordance with the invention which has been chosen as an illustration is a so-called gable-top package, but the invention is not limited to this type of packing container or packing container blank, but may be applied to any packing container which utilizes a sealed-in bellows-fold as an opening arrangement. The gable-top packing container 1 illustrated is in the main of a conventional type and the packing container blank 2 illustrated (which is a laminate with external thermoplastic layer of a known type) thus comprises four side wall panels 3 which are divided by vertical crease lines 4. The four side wall panels 3 at their lower ends are provided with four bottom panels 5 which in known manner can be folded in and sealed so as to form a bottom in the packing container 1, which, however, is not part of the invention and is not, therefore, described in any more detail. The four side wall panels 3 at their upper ends are separated by means of a horizontal crease line 6 from four top panels 7 which are mutually separated by means of the crease lines 4 mentioned earlier. The four top panels 7 comprise two main panels 8 and panels situated between these which by means of oblique crease lines are divided into a central, substantially triangular fold-in panel 9 and two likewise triangular back-folding panels 10 situated on either side of the same. The top panel 7 at its upper free end has an elongated sealing zone 11 whose parts corresponding to the two main panels 8 are uninterrupted and substantially rectangular and whose parts situated in between are divided by means of vertical crease lines 13 into smaller parts belonging to the respective back-folding panels 10. The blank 2, moreover, is provided in conventional manner with sealing panels and further crease lines and other details which, however, have been known previously to those versed in the art and are of no importance for the understanding of the invention. The two back-folding panels 10, which jointly with the folding-in panels 9 situated between them are intended in the finished packing container to form a pouring spout 14 which can be folded out, are provided within the sealing zone 11 with a coating 15 of seal-preventing means, e.g. silicone. The seal-preventing coating 15 in accordance with the invention is covered by a heat-sealable film 16 which may be in the form of a strip extending along the whole length of the sealing zone 11 and preferably substantially covers the same. The heat-sealable film 16 is sealed to the surface layer of thermoplastic material of the packing container blank 2 around the seal-preventing coating 15, so that on the finished packing container this coating is screened off from the Inside of the packing container in a liquid-tight manner. The upper delimitation of the seal-preventing coating 15 preferably coincides with the top edge of the packing container blank 2 as well as with the top edge of the heat-sealable film 16. On conversion of the packing container blank 2 in accordance with the invention to a packing container of the gable-top type (Fig. 3) the packing container blank is folded in a known manner along the four crease lines 4 and sealed together, so that a substantially tubular body of square cross-section is produced. Subsequently the bottom panels 5 are folded in and are hot-sealed in order to form a liquid-tight bottom seal, whereupon the packing container is filled with contents to an appropriate level and the top is closed. The closing of the top takes place in that the two main panels 8 are let down towards one another with the relevant part of the crease line as a hinge at the same time as the fold-in panels 9 and the back-folding panels 10 are folded in between the main panels 8. The sealing zones 11 of the top panels thereafter are sealed together through heating and compression and subsequent cooling, so that a liquid-tight top seal is obtained. The appearance of the top seal is illustrated in Figure 4 which is a section throiugh the upper part of the packing container in accordance with Figure 3 and shows how the upper sealing zones 11 of the two main panels 8 are sealed together to an upright sealing fin 17 which encloses the upper parts of the back-folding panels 10 included in the sealing zone 11 which are to form the pouring spout 14 and thus are coated with the seal-preventing means 15. It is evident from the Figure how the heat-sealable film 16 is situated between the different material layers included in the sealing fin 17 and contributes to increased tightness of the seal. As can be seen in particular from Figure 4, the sealing zones of the two main panels are sealed directly to one another at the top part of the sealing fin 17 which ensures a very strong and tight sealing together. At the lower part of the sealing fin 17 the folded-in pouring spout with the seal-preventing coating 15 and the heat-sealable film 16 is sealed in between the two main panels 8, which implies that the sealing strength within this region is reduced and is determined exclusively by the adhesion between the seal-preventing coating 15 and the heat-sealable film 16. By virtue of this the sealing strength within this region can be defined accurately already during the manufacture of the packing container blank so that the sealing strength is not affected appreciably by other factors, e.g. the temperature and pressure on the sealing together of the fin after the filling of the finished packing container. The presence of the heat-sealable film 16 in the sealing zoene brings about also that further thermoplastic material is provided which results in increased tightness, since the material can fill out better the channels and the recesses which may occur during the sealing. This enhanced tightness is particularly essential in order to prevent bacteria from penetrating into aseptic packages, but may also represent an advantage in respect of cost, since it may be possible to reduce the thickness of the liquid-tight thermoplastic layer of the packing material asthis now simply has a liquid-tightening function. As mentioned earlier, the packing container blank 2 preferably consists of a laminated material which comprises a central layer 18 of paper (Figure 2) which is coated on either wide with thin, liquid-tight layers 19 of thermoplastic material. On the side of the packing container blank which Is intended to be facing inwards and thus cove into contact with the contents, the material is provided, moreover, with a barrier layer 20 of preferably aluminium foil, whose surface is covered by a further layer 19 of thermoplastic material. From the enlarged region in Figure 2 it is evident moreover that the inner thermoplastic layer 19 is covered partially by the seal-preventing coating 15 which in turn is covered by the heat-sealable film 16. The heat-sealable film 16 preferably comprises a heat-sealable material, e.g. polythene which on the side facing towards the seal-preventing coating has a layer of a material sealable to the inside of the packing laminate. With an inside coating of thermoplastic material, usually LDPE, the said layer may consist appropriately of a polymer or copolymer based on acrylic acid, and a typical film of this type thus is a co-extruded film which has a layer of a polymer or copolymer based on acrylic acid intended for heat-sealing to the polythene layer of the packing laminate and a polythene layer. The total thickness is approx. 25 µm whereof the thickness of the LDPE Layer Constitutes approx. 75%. When the packing container is intended for the aseptic packaging of sterile contents or when specially high demands are made on gas-tightness, the heat-sealable film moreover may comprise a layer of a barrier plastics, e.g. nylon or polyester. The heat-sealable film in this instance naturally also comprises the further layers which say be necessary for bonding together the layers included in the film, that is to say any suitable adhesive material. A typical film for this purpose in accordance with the invention (reckoned from the side sealable to the packing laminate and facing towards the seal-preventing coating) comprises a layer of a polymer or copolymer based on acrylic acid, an layer of bonding agent, a layer of barrier plastics (nylon, polyester etc.), a further layer of bonding agent and a heat-sealable material layer, e. g. polythene. When during the manufacture of the packing container blank 2 the heat-sealable film 16 is applied along the sealing zone 11 the film is heat-sealed to the inside layer of the packing laminate along the whole length of the film. The heat-sealable film 16 then will be strongly bonded to the said inside layer whilst the seal to the seal-preventing coating 15 will be weaker and will be determined exclusively by the chosen combination of seal-preventing coating and the material type of the film 16 facing towards the coating 15. When the packing container blank after the conversion to packing containers is to be top-sealed, the sealing strength between the seal-preventing coating 15 and the heat-sealable film 16 will not be altered or influenced by the sealing temperature end the sealing pressure, which ensures that the adhesion force defined through the said choice of material is maintained. During the sealing of the top port of the package the part of the heat-sealable film 16 situated above the seal-preventing coating will be sealed strongly to adjoining ports of the sealable film 16, i.e. the parts of the sealing film 16 which cover the adjoining halves of the two main panels. When the packing container is to be opened the relatively strong seal between the two main panels 8 formed on the upper port of the sealing fin 17 is broken first, whereafter the seal between the coating 15 and the film 16 is broken , so that the two back-folding panels 10 forming the pouring spout 14 can be folded out. The port of the heat-sealable film 16 applied over the seal-preventing coating 15 will remain on the said adjoining ports of the two main panels 8, so that the seal-preventing coating 15 is exposed along the pouring edge of the pouring spout. As a result the pouring out of the contents present in the packing container can take place over a clean and even surface, which has no torn-off parts or residual shreds from the seal. In the region below the seal-preventing coating 15, however, residual shreds or remains of the heat-sealable film 16 may be left, but these shreds are at a relatively great distance from the pouring edge of the pouring spout 14 and in practice do not affect the pouring. Since the packing material, as mentioned earlier usually consists of a laminate which, among other things, has an outer layer of thermoplastic material (i.e. a layer which subsequently adjoins the contents), this thermoplastic layer may be used, of course, in accordance with an alternative embodiment of the invention, as the heat-sealable film (16) instead of a separately applied striplike film. In this instance, obviously, the seal-preventing coating 15 has to be applied directly below the external thermoplastic layer of the laminate, i.e. between this and the underlying layer which, depending on the type of packing material, say be a further (internal) thermoplastic layer, a barrier layer or, if the barrier layer is lacking, the central carrier layer 18 of paper. The application of the seal-preventing medium on this occasion is made within the intended region before the heat-sealable film is applied over the whole surface of the packing material. When the packing container is to be opened, then, as in the embodiment of the invention described earlier, the seal between the coating and the heat-sealable film (the thermoplastic layer) will be broken, so that the pouring spout can be folded out. The thermoplastic layer will rupture along the lower edge of the coating, but any adhering remains or shreds which may be produced in the process do not interfere with the pouring out of the contents. Through the application of a heat-sealable film over the seal-preventing coating of the pouring spout primarily two advantages are obtained. In the first place the sealing strength in the opening region can be determined in advance end be defined in such a manner during the manufacture of the packing container blank that it is not affected by operations carried out subsequently, e.g. the top sealing of the packing container. The sealing strength will be independent of the quality and the type of the coating layer which the packing container blank has on the side facing towards the inside of the packing container, and will not be affected either by other factors such as changing material quality, contaminations or mechanical ruptures. The top seal, moeover, is influenced positively, since the heat-sealable film serves as an auxiliary material whih provides a stronger and more homogeneous seal so that microleakage can be prevented, which is a substantiaol advantage when the arrangement in accordance with the invention is to be used on packing containers of the aseptic type. The seal-preventing coating 15 as well as the heat-sealable film 16 are simple to apply in connection with the manufacture of the material. The seal-preventing coating can be applied in an exact pattern at the desired location by means of a relatively simple printing process, whilst the heat-sealable film can be applied in the form of a continuous, prefabricated strip which is heat-sealed to the inside layer of the packing material.

Claims: A packing container (1) of foldable material with a liquid-tight surface layer (19) and with bottom walls, side walls and an openable closure which comprises two main panels (8) sealed to one another and a bellows-fold situated between these with back-folding panels (10), whose surfaces facing towards the main panels comprise a coating (15) of a seal-preventing means, characterized in that a heat-sealable film (16) extends over the coating (15) of seal-preventing means and is sealed to the surface layer (19) around the coating (15) so that the coating (15) is screened off from the inside of the packing container in a liquid-tight manner. A packing container in accordance with claim 1, characterized in that the heat-sealable film (16) is in the shape of a strip of thermoplastic material, this strip extending along the upper edge of the packing container where in closed position of the packing container (1) it is sealed in between the main panels (8) and the back-folding panels (10). A packing container in accordance with claim 1 or 2, characterized in that the heat-sealable film (16) is in the form of a layer of thermoplastic material, which covers the whole inside of the packing container (1). A blank for the manufacture of a packing container of a foldable packing material with a liquid-tight surface layer (19), which material by means of crease dines is divided into a number of wall panels for the formation of a bottom, side walls and an openable top closure, these wall panels comprising two main panels (8) and back-folding panels (10) situated between these which have a coating (15) of a sealpreventing means, characterized in that a film (16) of heatsealable material extends over the coating (15) of sealpreventing means of the back-folding panels (10) and is sealed to the surface layer (19) around the coating (15) so that said coating (15) is screened off in a liquid-tight manner. A blank in accordance with claim 4, characterized in that the heat-sealable film (16) is constituted of a strip which extends over parts of the main panels (8) as well as of the back-folding panels (10). A blank in accordance with claim 4 or 5, characterized in that the film (16) is heat-sealed to the surface layer (19) along one edge of the blank (2). A blank in accordance with one or more of claims 4-6, characterized in that the film (16) substantially covers a sealing zone (11) situated at the upper edge of the main panels (8) as well as of the back-folding panels (10). A blank in accordance with one or more of claims 4-7, characterized in that the heat-sealable film (16) comprises a layer facing towards the seal-preventing coating (15) of a material which is sealable to the inside of the packing laminate. A blank in accordance with claim 8, characterized in that the said layer comprises a polymer or copolymer based on acrylic acid. A blank in accordance with claim 8 or 9, characterized in that the film moreover comprises layers of a barrier plastics.

Inventors: ANDERSSON THORBJOERN, RYDH NIKLAS, ANDERSSON, THORBJOERN, RYDH, NIKLAS, Andersson, Thorbjörn 
Applicants: PROFOR AB, AKTIEBOLAGET PROFOR
Application year: 1989
Main classification: B65D5
IPC codes: B65D5