CONTAINER AND A METHOD FOR CLOSING THE SAME

Abstract: A material portion (1) of oriented material is converted through heating in an area adjoining one boundary surface of the material portion to a layer (10) of substantially non-oriented material. A film (2) is fixed to the fixing layer (10) in that the film is pressed with the help of compression and heating means (50) to the layer (10). Through the heat supply from the means (50) the necessary heat is supplied so that the film (2) will be fixed to the fixing layer (10). Owing to the film being bonded to substantially non-­ oriented plastic material, the detachability aimed at in the bond between the film and the material portion (1) is achieved.

Description: The present invention relates to a method in the case of oriented plastic material for the detachable fixing of a foil or film to the material in a fixing area when the foil or film is made to rest against a boundary surface of the material and is fixed to it through the supply of energy, and it also relates to a closed container the opening part of which includes oriented material, where the container is closed by means of wafer of film or foil. In many applications it is necessary that one should be able to fix a foil or a film in a tight and detachable manner to a base of plastic material which mainly consists of oriented material. In the following, without any restrictive significance, the designation film is used for the foil or film which is to be fixed to the base. The structure of the film varies from occasion to occasion and is constituted in certain applications of a single-layer film, e.g. of plastic material or of metal, and in other applications of a laminated film. In laminated film the layers consists e.g. simply of plastic material when the composition of the material as a rule varies from layer to layer whilst in other applications one or more of the layers consist of e.g. metallic material, of barrier material etc. The side of the film which is to be fixed to the base, however, is always made up of a material suitable for being fixed to the base by means of heating. It has been found, surprisingly, that it is not possible in the case of certain plastic material, e.g. polyethylene terephtalate (PET) or material similar to it, to fix film to a base when this consists of oriented plastic material and to form a bond thereby which is both tight and detachable. It is found that with previously known and conventionally applied fixing techniques, where the film is pressed to the base by mechanical means and at the same time energy is supplied to the film, it is certainly possible to fix the film to the base in a tight bond, but that the tight bond aimed at is obtained only if the energy supply (heat supply) takes place on a scale which causes the film to be fixed to the base so strongly that subsequently it cannot be torn off. This means, of course, that the combination of film of the aforementioned type and oriented material in the opening part of a container of plastic material cannot be used for a package (container) where easy opening is required, i.e. containers for foodstuffs, such as dairy products. A further problem arising is that the film becomes deformed when the energy supply is so great that a tight bond is achieved. The product obtained, when e.g. a beaker with oriented material in the opening is closed by means of a film, is therefore not acceptable, since on the one hand the film is deformed to an extent which makes the container unacceptable to the consumer, whilst on the other hand the film sticks to the edge of the opening so strongly that it cannot be torn off. The present invention relates to a method and to a container where the abovementioned problem and inconveniences are eliminated. This object is achieved in that oriented material included in the prospective fixing area is heated, before the foil or film is moved to rest against the material portion, through the supply of energy, to a temperature in the region of, or exceeding, the temperature at which the orientation of the material commences to be reduced when in the said fixing area material which had been oriented before the heating is converted to a substantially non-oriented material, that the foil or film is moved so as to rest with its one boundary surface against a fixing surface of the material portion and that through heating of material in connection with the contact surfaces the film or foil is fixed to the material portion, and for the container in that oriented material of the container in an all-around opening area in a cross-section through the material has a fixing layer of substantially non-oriented material integrated with the oriented material and/or that the wafer has a fixing layer of substantially non-oriented material facing towards the oriented material for bonding the wafer to the oriented material. It is essential for the invention that in the base of plastic material a fixing layer of substantially non-oriented material should be formed, this layer constituting the connecting layer between the oriented material of the base and the film. Since this layer consists of substantially non-oriented material it is possible to apply conventional technique to the fixing of the foil to the base and achieve the desired detachability. For the formation of the fixing layer of substantially non-oriented material energy is supplied to the fixing area, which is done e.g. with the help of a mechanical means comprising a contact surface which at a temperature in the region of, or exceeding, the temperature at which the orientation of the material of the fixing layer commences to be cancelled, rests against the prospective fixing surface during a certain time interval. In other applications the heating is done in that the prospective fixing surface is subjected to a radiation of a frequency or composition chosen so that the plastic material in the fixing layer hinders the radiation from passing the fixing layer, e.g. optical radiation or thermal radiation. Heating by means of a flame is also applied in certain embodiments. In a preferred application the technique described above is used in connection with the closing of a container, e.g. a beaker, whose opening edge or opening flange consists of oriented material. As a result the properties imparted to the material through orientation, and hence the properties of the container, are preserved also in the opening area at the same time as the closing of the container can be done by means of a detachable film or foil. In the subsidiary claims further preferred embodiments of the invention are indicated. The invention is described in greater detail in connection with a number of figures, wherein Fig. 1 is a cross-section through a portion of oriented material, Fig. 2 is a cross-section corresponding to Fig. 1 where the plastic material has an upper fixing layer of substantially non-oriented material, Fig. 3 is a cross-section corresponding to Figs. 1 and 2 where a mechanical heating means rests against the oriented material, Fig. 4 is a cross-section through a portion of plastic material with a beam transmitter or a burner nozzle directed towards one boundary surface of the plastic material, Fig. 5 is a cross-section where a film rests against the fixing layer and for the bonding of the film a mechanical means presses the film against the boundary surface, Fig. 6 is a cross-section of an opening part of a container limited by an upper flange whose surface facing upwards constitutes the upper boundary surface of a fixing surface and Fig. 7 is a cross-section corresponding to Fig. 5 where the opening part is provided with a closing film. In the Figures which show preferred embodiments of the invention Fig. 1 illustrates a portion 1 of plastic material 7 with an upper boundary surface 3 and a lower boundary surface 4. The plastic material is monoaxially or biaxially oriented. Fig. 2 shows a cross-section corresponding to Fig. 1 through the portion 1 of plastic material, but there the plastic material forms two layers 7 and 10 respectively, the layer 7 corresponding to the bulk of the oriented plastic material according to Fig. 1 and the other layer 10 corresponding to the remaining part of the oriented material in the portion 1 which has been converted so as to constitute an upper layer of substantially non-oriented material, referred to as a rule hereinafter as fixing layer 10. The outer boundary surface of the fixing layer corresponds to the upper boundary surface 3 in Fig. 1 and bears the reference designation 11. Fig. 3 shows a mechanical heating means 30 provided with ducts 32 for the transport of heat transfer medium. The heating means has a contact surface 31 facing towards a holding-up means 35 whose contact surface facing towards the heating means bears the reference designation 36. The holding-up means is provided with ducts 37 for the transport of heat transfer medium. The material portion 1 rests against the contact surface 31 of the heating means 30 for the transfer of heating energy to the material portion. The irregular line in the portion 1 marks a transition area 8 between material which is heated by the heating means 30 and material which is not heated. In Fig. 5 is shown an arrangement corresponding to that in Fig. 3 where a mechanical compression and heating means 50 and a holding-up means 55 are included in the arrangement, both provided with ducts 52 and 57 respectively, for the transport of heat transfer medium. The reference numerals 51 and 56 mark the contact surfaces facing one another of the compression and heating means 50 and of the holding-up means 55, respectively. Between the compression and heating means 50 and the holding-up means 55 is to be found a portion 1 of plastic material consisting of a layer 7 of oriented plastic material and a fixing layer 10 integrated therewith of substantially non-oriented material. In Figs. 3 and 5 the arrows A and B respectively, indicate that the heating means 30 and the compression and heating means 50 respectively, are movable to and from with the help of driving means (not shown in the Figures) between the opening position and the operating position shown in the Figures. It is evident to those versed in the art that alternatively the holding-up means 35 and 55 may be provided with driving means for movement corresponding to what has been described for the means 30, 50 and/or that the heating means as well as the holding-up means may be adapted for relative movement so as to occupy positions corresponding to the opening positions or operating positions. In Fig. 5 too the portion 1 is shown according to Fig. 2 constituted of the layer 7 of oriented plastic material and the layer 10 (the fixing layer) of substantially non-oriented material. A foil or film 2, hereinafter generally referred to as film, is placed between the contact surface 51 of the mechanical compression and heating means 50 and the fixing layer 10 and thus rests against the contact surface 11 of the fixing layer. One boundary surface 5 of the film faces towards the compression and heating means whereas the other boundary surface 6 faces towards the fixing layer 10. Fig. 4 shows a heating means 40 provided with a lens 41 for the converging of a beam 45 of e.g. light towards the surface 3 of the portion 1 of oriented material situated at a distance. The radiation is of a frequency or a composition selected so that the plastic material substantially prevents the radiation from passing through it. As a rule the lens 41 is of a design selected so that the beam refracted towards the surface 3 of the portion 1 is of a bandlike appearance. The heating means 40 and the portion 1 are adapted to be moved with the help of driving means (not shown in the Figures) in relation to one another whilst largely maintaining the concentration of the beam 45 against the boundary surface 3 of the portion 1. The reference numeral 10 marks the fixing layer of substantially non-oriented material being in the process of formation. In certain applications the heating means 40 is constituted of a burner, e.g. a gas burner, from which originates a flame 45 directed towards the portion 1 of oriented plastic material. Figs. 6 and 7 show a cross-section through the opening area of a container 13. The container has an opening part 16 provided with an all-around opening area 14 of oriented material 7 which is delimited by the fixing layer 10 of substantially non-oriented material with a fixing surface 11. In a preferred application the all-around opening area 14 is designed to have an opening edge flange 15. In certain applications the opening edge flange is absent when the opening edge is finished by a layer of substantially non-oriented materials forming the fixing layer of the opening part. Fig. 7 shows how a wafer 17 of foil or film is bonded to the fixing layer 10 for the tight closing of the container. In the application of the invention, in a preferred embodiment of the same, the fixing layer 10 is formed in that the oriented plastic material 7 in connection with the prospective fixing surface 11 is heated to a temperature in the region of, or exceeding, the temperature at which the orientation of the material commences to be reduced. In the case of PET e.g. in a preferred embodiment, the contact surface of the heating means 30 is of a temperature exceeding 190°C. In applications where the fixing layer should consist of substantially amorphous material the material is heated to melting, the heating means being of a temperature which at least slightly exceeds the melting temperature of the material. In the process a layer of the material which had been oriented before the heating is converted to a substantially non-oriented material which forms the fixing layer 10. As a rule the heating time is limited so that the higher temperature is attained only in a relatively thin area of material which in cross-section will thus be continued by oriented material. The heating for the formation of the fixing layer 10 described in the foregoing section takes place in certain embodiments with the help of the mechanical heating means 30, whereas in other embodiments the radiation means 40 or the burner 40 is used. In certain embodiments a heating means designed as a cylinder corresponding to the mechanical heating means 30 shown in Fig. 3 is included. The foil or film or alternatively the oriented material area roll over the cylinder so as to be heated locally for the formation of a fixing layer 10. As a rule the environment provides sufficient cooling to cool the fixing layer rapidly to a temperature so low that the material in the same becomes substantially amorphous. In certain applications where a relatively thick fixing layer is required, the equipment is supplemented by a means for the forced cooling of the heated fixing layer. Such a cooling is done in certain applications by a jet or curtain of cool air whereas in other applications the material provided with fixing layer passes a cooling cylinder. The oriented material area and the film (foil) thereafter is placed between the holding-up means 55 and the compression and heating means 50 when at least the oriented material area or the film, at least in the prospective fixing area, are delimited by the fixing layer 10. The placing of the same is such that it forms the boundary of the material area or of the film where the material area and the film rest against one another. The compression and heating means 50 and the holding-up means 55 are then moved towards one another so that the film 2 is pressed by the heating means to the material area at the same time as heat is supplied from the means 50. The fixing layer 10 on the material area or the film causes the film to stick to the material area and the desired bond against substantially non-oriented plastic material to be achieved. For the fastening of the film to the actual material portion the material or the film in certain applications are coated with an adhesive whose fixing effect is activated on supply of heat. In certain applications where heating means 30 with the help of which the fixing layer 10 is formed is replaced by the compression and heating means which, in a first operating step rests directly against the upper boundary surface 3 of the portion 1 for the formation of the fixing layer 10, whereupon the contact ceases as the means and the material portion 1 are moved in relation to one another so that the distance of the means to the boundary surface (fixing surface) 11 is increased in order to allow insertion of the film 2. In a second step the compression and heating means 50 is used for the fastening of the film to the fixing layer 10 according to the technique described above. The basic technique illustrated in Figs. 3 and 5 for the fastening of the film to a base of oriented material, which has been provided with the fixing layer 10, is also applicable, of course, to the embodiments shown in Figs. 6 and 7 where the fixing layer 11 constitutes a boundary of an all-around opening area 14 on a container. The technique thus makes it possible to join by conventional methods the wafer 17 to the opening edge of a container 13 also in applications where the opening edge mainly consists of oriented material 7. In accordance with the invention the effect of the energy supply or the intensity of the radiation is relatively great. Since the plastic material has a relatively small thermal conductivity a rapid heating of material occurs in an area near the surface of the layer (the prospective fixing surface) at the same time as the low thermal conductivity gives rise to the temperature gradient being great in relation to the underlying oriented material. The supply of energy is stopped after a period which is determined by the thermal conductivity of the material and as a rule is chosen so that only a thin layer of material below the fixing surface, referred to earlier as fixing layer, attains temperatures so high that the orientation of the material is substantially cancelled. The remaining part of the material, seen in a cross-section through the same, is heated only to a small extent and retains therefore its orientation, and constitutes a dimension-determining supporting layer for the fixing layer. Since the orientation of the supporting layer remains intact, the properties of the supporting layer concerning strength, thermal resistance, dimensional stability etc. too are determining for a product on which a film is attached to the supporting layer in accordance with the procedure specified above. In applications where it is desired that the material in the fixing layer should consist mainly or at least in the area adjoining the fixing surface, of substantially amorphous material or of material with low thermal crystallization, the heating of the fixing layer is done so that the material melts whereupon the material in the fixing layer, immediately after the heating, is cooled down rapidly to a temperature below the crystallization temperature. This is done, e.g. by the use of mechanical means which are in contact with the material of the fixing layer and which at least in the contact areas consist of material zones of good thermal conductivity. With the help e.g. of cooling ducts these material zones on the mechanical means are kept at a low temperature, e.g. at 0°C. The technique is also usable in applications where e.g. an aluminium layer is provided with a layer of material suitable after heating to constitute a bonding agent between the aluminium foil and the opening edge of the beaker. In certain applications it is permissible for the fixing layer, seen in cross-section, to consist at least partly of crystallized material. Especially in an area of the fixing layer which in cross-section lies relatively far away from the fixing surface the poor thermal conductivity of the material entails that the heated material retains a temperature suitable for crystallization for such a long time that the thermal crystallization continues so long that in certain applications the material in this area becomes opaque. The technique in accordance with the invention is also applicable of course when a film or a foil of oriented material needs to be provided with a fixing layer of substantially non-oriented material. This embodiment of the invention is particularly appropriate to be used for a wafer of relatively great thickness and especially in applications where e.g. an opening edge of the container consists of a material, and is of a design, which makes it possible to allow energy from the compression and heating means to pass through the material of the opening edge to the material of the wafer adjoining the contact surfaces between the wafer and the opening edge. In the preceding description reference was made to a limited number of embodiments of the invention only, but it will be readily evident to those versed in the art that the invention embraces a large number of embodiments within the scope of the following claims.

Claims: A method for fixing a foil or film (2) to a material portion (1) of oriented material so as to form a fixing area when the foil or film is made to rest against a boundary surface (3) of the material and when the film or foil is fixed to the material through the supply of energy to the fixing area, characterized in that oriented material included in the prospective fixing area is heated, before the foil or film (2) is moved to rest against the material portion (1), through the supply of energy, to a temperature in the region of, or exceeding, the temperature at which the orientation of the material commences to be reduced, when in the said fixing area material which had been oriented before the heating is converted to a substantially non-oriented material, that the foil or film (2) is moved so as to rest with its one boundary surface (6) against a fixing surface (11) of the material portion (1) and that through heating of material in connection with the contact surfaces (6 and 11) the film or foil is fixed to the material portion. A method in accordance with claim 1, characterized in that the heating for the conversion of the oriented material to a substantially non-oriented material takes place in a relatively thin fixing layer (10), located below the fixing surface. A method in accordance with claim 2, characterized in that after heating of the fixing layer (10) the same is cooled down rapidly so as to form a layer of substantially amorphous material. A method in accordance with claim 2 or 3, characterized in that the heating of the material of the fixing layer (10) is done with the help of a mechanical means (30) comprising a contact surface (31) which at a temperature in the region of, or exceeding, the melting temperature of the material of the fixing layer (10) during a predetermined time interval rests against the fixing surface. A method in accordance with claim 2 or 3, characterized in that the heating is done by means of radiation which is of a frequency or composition chosen so that the plastic material in the fixing layer (10) substantially prevents the radiation from passing through the fixing layer, or that the heating is done by means of a flame which is directed against the fixing surface of the fixing layer (10). A method in accordance with anyone of claims 1-5, characterized in that an all-around opening area (14) on a container (13) is heated so as to form the fixing layer (10). A method in accordance with claim 6, characterized in that the fixing layer is formed on an opening flange (15) of the container. A container (13) of plastic material closed by means of a wafer (17) formed by a film or foil (2) and where oriented material is included in the opening part (16) of the container, characterized in that oriented material of the container (13) in an all-around opening area (14) in a cross-section through the material has a fixing layer (10) of substantially non oriented material integrated with the oriented material and/or that the wafer has a fixing layer (10) facing towards the oriented material of substantially non-oriented material for the fastening of the wafer (17) to the oriented material. A container in accordance with claim 8, characterized in that the wafer (17) is detachably bonded to the container. A container in accordance with claim 8 or 9, characterized in that the container is provided with an opening flange (15) wherein the fixing layer (10) forms an all-around boundary surface (11) or that the container is provided with an opening flange (15) whereon the fixing layer (10) constitutes an upper boundary layer to which the wafer is fixed.

Inventors: OEHLENSCHLAEGER, ULLA, PEDERSEN, JAN RUNE, SOERENSEN, ERLING, Sörensen, Erling
Applicants: PLM AB
Application year: 1987
Main classification: B65D77
IPC codes: B65B7, B65D77, B65D17, B29C65