Can-like container and method for manufacturing same

Abstract: A can-like container and a method for manufacturing such a container which provides a strong structure, tight gas barrier, and no effect upon the taste of food stored in the container. The body of the container is fabricated with a multi-layer sheet composed of a metal foil layer having a thickness of no more than 40 µm and a hot-melt resin layer formed on one or both sides of the metal foil layer. The margin portions of the multi-layer material of the container body in corners thereof are either folded into two tucks at each corner or formed into vertical wrinkles upon molding the container body. A cover is joined to the container body, which cover is also composed of a metal foil layer and at least hot-melt resin layer.

Description: The present invention relates to a method for forming a container which particularly can be used for storing food for long periods of time. Metal cans suffer from various problems, including an adverse effect on the taste of the food contained therein and numerous difficulties in fabricating such cans. With the view of providing a container which is free from such defects, it has been proposed to fabricate a container from a multi-layer sheet composed of an aluminum foil base and multiple plastic layers formed on both sides of the base layer. There is known from CH-A-634 789 a container comprising a container body, said container body consisting of a multi-layer sheet composed of at least a metal foil layer and a hot-melt resin layer formed on at least one side of said metal foil layer, a cover made of a multi-layer sheet composed of at least a metal foil layer and a hot-melt resin layer, formed on one side of said metal foil layer, peripheral portions of said hot-melt resin layer of said cover being heat-sealed to said hot-melt resin layer of said container body. This known container may be satisfactory for many purposes. Nevertheless, in some cases higher mechanical stiffness of the container is desired. Higher mechanical stiffness can basically be reached with a laminated or multi-layer wall container (US-A-3 917 155) having a container body and a tray enclosing at least the lower portion of the outer surface of said container body. The tray is made of paperboard which may be a laminated structure and may include a paperboard with a plastic foil or a paper layer laminated thereto. Within the tray there may be provided a plastic liner which may be so preformed into place as to be separable from the tray. This known structure is relatively complicated and, moreover, there is the risk that the tray may be separated from the container body. There is also known from US-A-4 210 618 a can-like package or container comprising a multi-layer case-like middle-part, a bottom part and a cap both attached to the middle part. These two parts are prefabricated and attached to the middle part by inductive welding. Both the middle part and the bottom part consist of a multi-layer sheet composed of an inner layer of aluminium foil or a corresponding substantially gas-tight material and an outer plastic layer. Providing higher stiffness is not mentioned. In order to overcome the disadvantages the present invention provides a method for forming a container comprising the steps of: providing a blank sheet, said blank sheet comprising a metal foil layer having a thickness of no more than 40 µm, and a hot-melt resin layer formed on at least one side of said metal foil layer, cutting said sheet to provide a blank having dimensions established in accordance with desired dimensions of said container body, placing said blank over one side of a female mold, said female mold having a hollow central portion having dimensions established in accordance with said desired dimensions of said container, said female mold having grooves in its side wall portions pressing a male mold against said blank and into said hollow portion of said female mold thereby to provide a container body having wrinkles in side wall portions corresponding to side wall portions of said female mold; and attaching a cover to said container body, said cover comprising a metal foil layer having a hot-melt resin layer on at least one side thereof, and the step of providing a tray around said container body, said step of providing said tray comprising injection molding a resin material around a portion of said container body opposite said cover. Brief description of the drawings Figs. 1, 1A to 1C and 2 show details of containers not in accordance with the present invention, described for illustrative purposes. Figs. 3 to 9 illustrate a method of producing a cylindrical container in accordance with the present invention; and Figs. 10 and 11 show a cover according to the material of the receptacle, namely, the cover is formed by a sheet composed of a layer of metal foil having a layer of hot-melt resin provided on at least one side thereof. The cover is attached to the container body by a heat sealing step whereby the hot-melt resin of the cover is fused with the adjacent hot-melt resin layer of the container body. As shown in Fig. 1, a container comprises a cover 142 composed of a center foil layer 146 covered by two hot-melt resin layers 145 and 147 on the opposite sides thereof. The container body 141 composed of a center metal foil layer 148 covered by hot-melt resin layers 144 and 149. The layers 147 and 149, however, may be dispensed with if desired. Furthermore, a pull-top container cover of the type illustrated in Fig. 10 or 11 to be later described can be employed with equally good results. Next, results of retorting tests performed on can-like containers of the present invention will be discussed. The retorting tests were made under the following conditions, wherein a rectangular container as depicted in Fig. 1 was filled with water and covered as illustrated in Fig. 1: Retorting conditions: Temperature: 120°C Period: 20 min., and Pressure: 2 to 3 kg/cm². The material used for the container body was a sheet of aluminum foil laminated with ethylenepropylene block copolymer (CPP-MFR 1.1 and concentration of ethylene=9 wt%) on both sides of the aluminum foil. The thickness of the aluminum foil was 15 µm, the thickness of the outer resin layer was 30 µm, and the thickness of the inner resin layer was 70 µm. The structure of the cover was similar except that the thickness of the aluminum foil was 12 µm, the thickness of the inner resin layer was 70 µm, and the thickness of the outer resin layer was 12 µm. The results of the Retorting Tests are presented in Table 1 below: As indicated in Table 1, the amount of water charged in the container was varied from full capacity (150 cc) to 50% of full capacity (75 cc) without rupture or puncture of the container, indicating that the container had sufficient strength. As Table 1 further indicates, the use of either tucks or vertical wrinkles provides acceptable results, that is, no pin-holes are formed and no separation occurs with a container of the invention. Referring now to Figs. 1A through 1C, a further modification will be described. A cover A, formed in the same manner as the cover 142 is attached to container body B, constructed in the same manner as the container body 141, and the container body B is set in a tray C having the same general configuration as the container body B. Fig. 2 is a longitudinal cross-sectional view showing the assembly of the cover A, container body B and tray C. The tray can be made from plastics. The plastic tray is formed by injection molding of resin to the outer side of the container body B. It is preferred that the thickness of the tray be sufficient to support the container body and prevent its deformation during transportation and stacking. As shown in Fig. 2, the container body B is fitted in the tray C in such a manner that the inner side of the latter is adhered to the outer side of the former. An explanation will be now made of the method of the invention. An aluminum-plastic laminate film having an ethylene-propylene copolymer film 202 to 70 µ thickness, an aluminum foil 201 of 20 µ thickness and a polypropylene film 203 of 30 µ thickness as shown in Fig. 3B is punched out for obtaining a disc 204 as shown in Fig. 3A. The obtained disc 204 of aluminum-plastic laminate film is placed between a male mold 205 and a female mold 206 having vertical grooves 207 and 208, respectively. Then, the male mold 205 is pressed into a hollow portion of the female mold 206, thereby obtaining an aluminum foil-plastic laminate container body 209 having a cylindrical shape provided with vertical wrinkles as shown in Fig. 5. The cylindrical aluminum-plastic laminate container body 209 is set on a male mold 212 for injection molding as shown in Fig. 6. Then, a female mold 213 is aligned with the male mold 212 on which the container body 209 is mounted. Under a suitable pressure, ethylene-propylene block copolymer is injected as shown in Fig. 7. The thickness of the ethylene-propylene block copolymer layer is about 700 microns. Then, the contacting surfaces of the aluminum-plastic laminate container body 209 and the injection molded tray 214 are melt bonded intimately to each other. Thus, an integrated rigid aluminum foil-plastic composite container 215 is obtained as shown in Fig. 8. The vertical wrinkles of the container body 209 are smoothed by the resin pressure of the injection molding. Thus, the container has a smoothed inner surface. After filling the aluminum foil-plastic composite container 215 with a desired content, a laminate film 216 composed of 12 µ polyester (PET)/20 µ aluminum foil 70 µ easy peel film is placed on the container 215 as shown in Fig. 9. Then, the marginal portions are heat sealed to thereby obtain a completely sealed aluminum-plastic composite container 217. More specifically, the container body 209 and the tray 214 are heat bonded at their flanged portions to the cover 216 as shown in Fig. 9. The easy-peel film is made of blended film of ethylene-propylene block copolymer 50% and low density polyethylene 50%. In accordance with the above-described method, the aluminum-plastic composite container 217 of capacity of 120 cc which was filled with corn soup was retort processed. The following results of ability of preserving the content for a long period were obtained. Retorting conditions Temperature: 120°C Period: 20 min. Pressure: 2 to 3 kg/cm² a) Deformation of Container: none excellent b) Pinholes: none excellent c) Separation: none excellent d) Reserving Test: (35°C, 3 months, i.e., equivalent to room temperature, two years) no effect on taste excellent e) Falling Test: (Under the condition of 20°C and -5°C, the container was made fallen from 1 m height to a concrete). no crack, no damage (after ten times) excellent f) Heat Seal Strength: 2.3 kg excellent g) Easy-Peel Property: readily opened by a female person excellent With the use of a tray, the can-like container made according to the present invention is made yet more rigid, thereby making it possible to use an even thinner metal foil layer in the container body. Further, a cover structure will now be described. In Figs. 10 and 11, reference numeral 3 as before designates the cover; 58, an opening part formed by the second resin layer; 59, a peripheral part formed by the second resin layer; and 60, a slot. The slot 60 is in the form of a closed ring as shown in Fig. 10, and therefore the opening part 58 is completely separated from the peripheral part 59 by the slot 60. Further, in Figs. 10 and 11, reference numeral 11 designates a handle provided on the opening part 58; and 62, a cutting opening part 62 by a groove 63. In Fig. 11, reference numeral 64 designates a multi-layer sheet. In the case of Fig. 11, the multi-layer sheet is manufactured by forming first resin layers 66 and 67 on both sides of a gas barrier type base material. The can-like container's cover 3 is fixedly mounted on the side wall 1 of the can-like container as shown in Fig. 11. The rectangular cover 3 is opened as follows: When the handle 15 is raised with the fingertip inserted into groove 63, the handle 15 is peeled off the multilayer sheet 64. As a result, the end 69 of the handle 1 goes inside the multi-layer sheet 64 to cut the latter. When, under this condition, the handle 15 is pulled, the multi-layer sheet 64 is cut along the slot 60 so that the opening part 58 of the cover is opened. In the container's cover the opening part 58 is completely separated from the peripheral part 59 by Ime slot 60; i.e., no bridge is provided between the parts 68 and 69. Therefore, the opening part 58 can be readily opened. This readily openable container's cover can be produced using an injection molding method. The method will be described with reference to Figs. 10 and 11. The opening part 58 and the peripheral part 59 are molded using respective gates. That is, the opening part 58 is independently molded using its gate, while the peripheral part 59 is also independently molded by using its own gate. The slot 60 is formed by the mold. At least one gate should be provided for molding the opening part 58, and similarly at least one gate should be provided for molding the peripheral part 59. The positions of the gates are indicated by reference characters 70 (G1) and 71 (G2) in Fig. 10. That is, the opening part 58 is molded using the gate 70 (G1), while the peripheral part 59 is molded using the gate 71 (G2). In the injection molding method using a plurality of gates, the moldability is excellent and the injection molding operation can be achieved readily. Therefore, materials having allowed moldability such as materials having small melting factors (MFR) resins with filters can be used in the injection molding method. As was described before, in the conventional method, it is necessary to take the moldability into consideration, i.e., it is necessary to select materials having a high fluidity, and it is difficult to use resins with filters. However, these problems have been solved by the provision of an injection molding method. Furthermore, in the molding method the molding temperature and the injection pressure are considerably low, and the productivity (molding cycle) is high. In addition, the slot is formed by the pushing action of the metal mold, and therefore, it is preferable that the mold closing pressure is suitable for increasing the durability of the metal mold preventing damage to the base material and preventing breakage of the slot. According to this method, the mold closing pressure can be low. Depending on molding conditions, sometimes a product's corner material such as an aluminum foil may be broken in the mold during injection molding. However, such a problem can be eliminated by a low injection pressure. According to this injection molding method, can-like container's body having a high adhesion strength can be obtained as described above. Especially when a multi-layer sheet having thermally meltable first resin layers on its both sides is used, the first and second resin layers are in a molten state when molded, and are then welded together. Therefore, the resultant molding is high in adhesion strength and accordingly durable in the drop test. On the other hand, the cover may suffer from the problem that the handle is also welded to the multi-layer sheet so that it cannot be peeled off the multi-layer sheet. However, this problem can be solved by applying a treatment for allowing the handle to peel off the multi-layer sheet to the part of the multi-layer sheet with which the handle is in contact. An example of the treatment is to use printing ink to form a treatment layer. Various modifications of the container of the invention can be contemplated within the scope of the present invention. For instance, although the container body is described above as having shoulders, these shoulders may be dispensed with. In this case, the cover can be heatsealed directly to the tray. Moreover, in the case that the container is to be vacuumed packed, it is recommended that a small hole be formed in the tray so that the container can be degasified to prevent the deformation thereof during the vacuum-packing process. Further, vertical wrinkles can be provided not only on the corner portions but also on the side walls. Still further, a modification is anticipated in which a resin similar to that of the outer layer of the container is directly injected over the inner surface of the container, whereby the interface between the injected resin and the container surface is smoothed.

Claims: A method for forming a container comprising the steps of: providing a blank sheet, said blank sheet comprising a metal foil layer having a thickness of no more than 40 µm, and a hot-melt resin layer formed on at least one side of said metal foil layer, cutting said sheet to provide a blank having dimensions established in accordance with desired dimensions of said container body, placing said blank over one side of a female mold, said female mold having a hollow central portion having dimensions established in accordance with said desired dimensions of said container body, said female mold having grooves in its side wall portions, pressing a male mold against said blank and into said hollow portion of said female mold thereby to provide a container body having wrinkles in side wall portions corresponding to said wall portions of said female mold; and attaching a cover to said container body, said cover comprising a metal foil layer having a hot-melt resin layer on at least one side thereof, and the step of providing a tray around said container body, said step of providing said tray comprising injection molding a resin material around a portion of said container body opposite said cover.

Inventors: MIYAUCHI OTOHIKO, OHKAWACHI MICHIHIRO, YOTSUYANAGI JUNJI, MIYAUCHI, OTOHIKO, OHKAWACHI, MICHIHIRO, YOTSUYANAGI, JUNJI
Applicants: SHOWA DENKO KK, SHOWA DENKO KABUSHIKI KAISHA
Application year: 1984
Main classification: B65D1
IPC codes: B31F1, B65D77, B29C45, B65D1, B29D22, B31B3