PACKING CONTAINER

Abstract: Packing containers manufactured from plastic-coating paper and having a sealing fin (3) wherein the packing material is joined inside to inside in a sealed union, the material layers so joined together accomodating between them, at least along a part of the sealing fin, a tearing strip (10) inserted in the sealing fin which is sealed to the inner plastic coating of the packing material. To facilitate the pulling off of the tearing strip (10) on opening of the container, the packing material is provided at least within the region of the part of the sealing fin (3) accomodating the strip with a material layer adapted to weaken adherence which is applied between the fibrous layer and the inner plastic coating of the packing material and preferably consists of water glass.

Description: The present invention relates to a packing container of the type which is manufactured from a plastic-coated fibrous material and which has a sealing fin extending across the upper end wall of the container, wherein the packing material is joined inside to inside in a sealed union, the packing material layers so joined accomodating between them, at least along a part of the sealing fin, a tearing strip inserted in the sealing fin which comprises a pull-lug accessible from outside the container, and the said tearing strip being sealed to the inner plastic coating of the packing material. A packing container of this type is known through EP-A-83 441. A usual form of packing container for distribution of milk, fruit juice and other liquid foodstuffs is manufactured from a web of paper or cardboard, plastic-coated on both sides, this web being formed to a tube in that the longitudinal edges of the web are joined together in an overlap joint, whereafter the tube formed is filled with the intended contents and sealed transversely by means of repeated flattening and transverse sealing operations along zones located at right angles to the longitudinal direction of the tube at a distance from one another. The sealed-off portions of the tube can be separated subsequently by means of transverse cuts in the said sealing zones, whereafter a parallelepipedic shape can be imparted to the packing units formed, most frequently through pressure-forming and folding of the packing material along crease-lines provided beforehand. In the course of the folding and forming work double-walled, triangular lugs are formed at four corners of the packing container which can be doubled against, and sealed to, the side or end walls respectively of the packing container. A packing container of the type referred to here will have a longitudinal overlap joint, namely the joint which constitutes the longitudinal joint of tube, and the upper and lower end walls of the container will have transverse, finlike sealing joints in which the packing material is joined inside to inside. The said transverse and longitudinal sealing joints cross each other at the upper and lower end surface of the packing container. In packing containers of the type mentioned here generally one of the triangular corner lugs is used as an emptying opening, and the opening is done by putting up the triangular lug from its doubled position against the packing container, and by tearing or cutting off the sealing fin so that a connecting duct to the interior of the container is achieved. Since certain inconveniences may be experienced in the tearing of the said triangular corner lug along a prepared perforation line, and as a cutting off of the sealing fin presupposes the use of a tool, it has been proposed instead to solve the problem in such a manner that a tearing strip is inserted in the sealing fin from the tip of the triangular corner lug serving as a pouring opening up to, and past, the point of crossing between longitudinal and transverse joint, so that the tearing strip is accessible from the outside of the container. With the help of such a tearing strip the sealing joint in the sealing fin can thus be broken or cut up, so that a pouring opening is achieved. This form of package opening with the help of a tearing strip, where the tearing strip is intended to tear through the seal produced in order to form an emptying opening, has been found, however, not to function to complete satisfaction, in the first place because the tearing strip often fails to cut directly into the sealing joint, but instead cuts between the paper material and the plastic coating on either of the material layers, which has the effect that the raw fibre surface of the paper layer of the packing material is exposed, so that the contents on being poured out through the emptying openings come into contact with the absorbent, exposed fibre surface which rapidly swells up and loses its rigidity. Other inconveniences are that, among other things, relatively great forces are needed for tearing up the sealing joint, and it happens not infrequently that the tearing strip rips asunder the paper layer on one side of the sealing fin, that is to say "goes astray". In accordance with the present invention it has been found, however, that the inconveniences which arise in connection with known packing containers provided with tearing strips can be almost completely eliminated if the adhesive strength between the fibrous layer of the packing material and the Inner plastic coating is weakened, at least within the region of the part of the sealing fin accomodating the strip, so that it becomes less than the adhesive strength between the inserted tearing strip and the packing material. On tearing the tearing strip, consequently, the parts of the inner plastic coating of the packing material which are sealed with good adherence to the tearing strip will relatively easily let go of the fibrous layer and accompany the tearing strip as it is withdrawn, without roughening or exposing any absorbent raw paper fibres in the torn region of the sealing fin. In accordance with the invention the said weakening of the strength of adherence is brought about by the features defined in the characterizing part of claim 1. This layer of material adapted to weaken adherence may consist of any material among the range of known materials with the capacity of reducing the adhesive power between Plastic and fibrous layers, e.g. surlyn- dispersion (Du Pont 56220), sodium carboxymethyl cellulose (Blanose 7LFD, Hercules) etc., but among the materials known at present water glass (sodium silicate) is preferred as this has been found to function particularly well and advantageously. Apart from water glass being physiologically compatible, inexpensive and easy to apply, it also has the advantage that, at least partly, it penetrates and impregnates the fibrous layer and thus imparts an effective moisture barrier on the uncovered fibrous layer after withdrawal of the tearing strip. Practical experiments have shown that a water glass layer in an amount of approx. 4-5 g dry weight/m² functions well. The requirement made on a tearing strip functioning well is, of course,that it should be made of a material of sufficiently high tensile strength so that it does not break on opening of the container, and the tearing strip, therefore, consists preferably of a plastic material of relatively small extensibility, e.g. polyester. Polyester material or other plastic material of comparable strength characteristics and extension characteristics as a rule has a melting range which lies higher than the melting range for e.g. polythene, which is the most commonly used coating material on a packing material, and it is therefore difficult to heat-seal a tearing strip of polyester directly to a polythene layer. To facilitate the heat-sealing of the tearing strip to the plastic coating of the packing material it is appropriate, therefore, to provide the polyester strip with more readily melting outer sealing coatings of polythene. To facilitate withdrawal of the tearing strip on opening of the container it may be suitable, moreover, to provide the part of the tearing strip accessible from the outside of the container with a loop or grip-ring. The invention will now be described in greater detail with special reference to the attached drawings, wherein Figure 1 shows the top part of a packing container in accordance with the invention not yet opened, Figure 2 shows the packing container during tearing, and Figures 3 and 4 show cross-sections of the packing container in accordance with Figures 1 and 2 along the section lines I-I and II-II respectively. The packing container 1 shown in Figure 1 and 2 is of the type which has been described previously, that is to say it is manufactured from a web folded up to a tube, which thereafter is filled with contents and transversely sealed. The packing container 1 has a longitudinal sealing joint 2 of the overlap type and a sealing fin 3 which extends along the upper end wall 4 of the packing container 1. As is evident, the packing container has a triangular, double-walled lug 5, which is intended to function as an emptying opening, and in Figure 1 the triangular lug 5 has been detached and partially raised up from the side wall 6 of the packing container against which it is normally sealed. In the crossing point 7 between the longitudinal overlap joint 2 and the transverse sealing fin 3 the edge of the overlapping material has been cut obliquely along the region 8 and in the crossing point 7 projects a part 9 of a strip 10 inserted into the fin 3. The strip part 9 thus projecting appropriately may be in the form of, or be provided with, a grip-ring or loop by means of which the withdrawal of the strip 10 can be facilitated. As is evident from Figure 3 and partly also from Figure 4, which show greatly enlarged cross-sections of the packing container 1 along the lines I-I and II-II respectively, the packing container 1 is manufactured from a packing laminate consisting for one thing of a central carrier layer 11 of paper or cardboard imparting stiffness, and for another of thin layers 12 and 13 of liquid-tight plastic material, preferably polythene laminated to both sides of the carrier layer. The material layers of the sealing fin 3 facing one another accomodate between them the strip 10 inserted in the sealing fin along a region which extends from the tip 5a of the double-walled triangular lug 5 to the crossing point 7 between the longitudinal joint 2 and the sealing fin 3 from which the strip 10 is accessible from the outside by means of the projecting free strip portion 9 which preferably is in the form of a loop. In the example shown here the strip 10 consists of a laminated material including a central layer 14 of a plastic material strong in tension, preferably polyester, and outer coatings 15 of sealable plastic material, preferably polythene. Moreover, the strip 10 thus inserted is sealed with good adhesive strength to the surrounding material layers of the sealing fin 3 through surface fusion between the outer plastic coatings 15 of the strip and the oppositely situated inner plastic coatings 12 of the material layer. To make possible an easy tearing away of the tearing strip 10 the packing material comprises within a region corresponding at least to the region of the sealing fin 3 accomodating the strip a thin layer 16 of a material which is applied directly to the fibrous layer 11 and adapted to weaken the strength of adherence, preferably water glass, between the carrier layer 11 and the inner plastic coating 12 of the packing material. The application of the thin material layer 16 brings with it that the strength of adherence between the carrier layer 11 and the inner plastic coating of the packing material is thus less, preferably much less, within the region accomodating the strip than within the remaining region of the packing material. When the packing container 1 is to be opened, this is done in the manner which is evident from Figures 1 and 2. The opening takes place in that in the first place the double-walled triangular lug 5 sealed against the side wall 6 is raised, so that it lies essentially in the same plane as the upper end surface 4 of the packing container, as shown in Figure 1. Thereafter the end 9, freely projecting at the crossing point 7, is seized, and the strip 10 is pulled upwards and backwards, towards the right in Figure 2, as a result of which the strip 10 is withdrawn, carrying along with it the plastic coating 12, sealed with good strength of adherence against the outer coatings 15 of the strip, which readily lets go of the carrier layer 11 of the packing material along the region of the sealing fin with weakened strength of adherence, to uncover an emptying opening 17. Practical experiments have shown that a packing container 1 in accordance with the invention is very easy to open in the manner described above with the help of the inserted tearing strip 10, without excessive expenditure of force and without any rish of delamination or going astray of the tearing strip. Furthermore, It has been found that the inner plastic coating 12 of the packing material very readily lets go of the carrier layer 11 within the region adapted to weaken the strength of adherence without roughening or exposing any absorbent raw paper or cardboard fibres in the region opened. In particular it has been found that a material layer 16 weakening the strength of adherence which consists of water glass is particularly effective, since water glass, at least partially, penetrates into, and impregnates,the carrier layer 11 thus imparting a moisture-protecting impregnating outer layer to the carrier layer 11 which contributes to reducing the risk of roughening and exposing absorbent fibres in the emptying opening.

Claims: A packing container of the type which is manufactured from a plastic-coated fibrous material and which has a sealing fin (3), extending across the upper end wall (4) of the container, wherein the packing material is joined inside to inside in a sealed union, the packing material layers so joined accomodating between them, at least along a part of the sealing fin, a tearing strip (10) inserted in the sealing fin which comprises a pull-lug (9) accessible from outside the container, and the said tearing strip being sealed to the inner plastic coating (12) of the packing material, characterized in that the packing material, at least within the region of the part of the sealing fin accomodating the strip, has a material layer (16) which is applied directly to the fibrous layer (11) and adapted to weaken the strength of adherence between the fibrous layer (11) and the inner plastic coating (12) of the packing material, the adhesive strength between the fibrous layer (11) and the inner plastic coating (12) of the packing material being less than the adhesive strength between the tearing strip (10) and the inner plastic coating (12) of the packing material within this region of weakened adherence of the sealing fin. A packing container in accordance with claim 1, characterized in that the tearing strip (10) comprises a central layer (14) of a material strong in tension, preferably polyester, and outer coatings (15) of sealable plastics, the seal between the tearing strip (1) and the packing material being brought about through surface fusion between plastic coatings (15) of the tearing strip (10) and the inner plastic coating (12) of the packing material. A packing container in accordance with claim 1 or 2, characterized in that the projecting pull-lug (9) of the tearing strip (10) is in the form of, or is provided with, a grip-ring or loop. A packing container in accordance anyone of the preceding claims, characterized in that the material layer (16) adapted to weaken adherence consists of a thin coating of water glass applied directly to the fibrous layer (11) of the packing material. A packing container in accordance with claim 4, characterized in that the water glass coating amounts to 4-5 g dry weight/m².

Inventors: KJELGAARD, TOM
Applicants: ROBY TEKNIK AB
Application year: 1988
Main classification: B65D5
IPC codes: B65D5