CONTAINER LID STRUCTURE AND PROCESS FOR MANUFACTURING THE SAME

Abstract: A container lid structure 1 made essentially of plastics includes a lid frame 3 and a lid plate 4. The lid plate 3 typically includes an inner layer 8 comprising a metal foil coated on the opposite sides by plastic layers and connected at the peripheral portion with the lid frame 3 and a core 10 made of a material which does not adhere to or bonds only weakly to the plastic materials for the lid frame 3 and for the inner layer 8. The core 10 is laid over the inner layer 8 with its peripheral portion in an abutting relationship with the inner periphery of the lid frame 3. A holding member 7 may be formed on the core 10 and bonded to the inner layer 8 through apertures 12 in the core. A pulling tab 5 is also formed on the core 10 and bonded to the inner layer 8 through an aperture 13 in the core.

Description: The present invention relates to a container lid structure, and more particularly to a container lid structure provided with a lid opening tab. More specifically, the present invention pertains to a container lid structure which is totally or mostly made of plastic material. A container lid structure having a finger gripping tab for opening the container has been widely adopted for example in a metal can. It has also been proposed for example by the Japanese patent laid-open application 57-163641, the Japanese patent publication 58-52897 and the Japanese patent laid-open application 59-31131 to provide a container lid structure having such a container opening tab by a plastic forming technique. The proposed container lid structure includes a lid frame adapted to be attached to a container barrel and a lid plate encircled by the lid frame, a score line being formed along a border between the lid plate and the lid frame to facilitate breakage in opening the lid. The score line is in the form of a groove formed on the upper surface of the lid structure. The score line thus formed on the upper surface of the lid is of a groove configuration having a low strength and so it can cause a deformation in the lid frame in storage or transportation of the container when the container is subjected to a shock load by being dropped or hit to another article. In a worst case, the lid may be broken at the score line causing the contents of the container to flow out. It should be noted that such problems are apt to occur when the lid structure is made of a plastic material because the plastic material has a lower strength. Since the score line is of a groove configuration exposed at the upper surface of the lid, it is likely that dust accumulates in the groove during storage of the container providing an insanitary appearance and decreasing the commercial value. It should further be noted that due to the low strength there is a further problem in that the so-called tamper resist property, that is, the property of resisting piercing by an injection needle passed through the score line, is low. Another problem experienced with a conventional plastic lid structure is that the opening tab is formed by a process which is separate from the process for the manufacture of the lid plate and is attached to the lid plate afterwards. With a conventional lid structure, the manufacturing process therefore includes a large number of steps and difficulties have been experienced in trying to decrease the manufacturing cost. In EP-A-0094359, there is disclosed a container lid structure according to the preamble of claim 1 that includes a lid plate; a lid frame encircling the lid plate and adapted to be attached to an end of a container; and a tab attached to the lid plate so that the lid plate can be removed from the lid frame by pulling the tab to form an opening. The lid plate includes an inner layer having a peripheral portion attached to the lid frame and a core arranged along an outer surface of said inner layer. The outer peripheral portion of the core of the lid plate is placed in an abutting relationship with respect to the inner peripheral portion of the lid frame, and the inner peripheral portion of the lid frame and the outer peripheral portion of the core of the lid plate are formed of materials which are connected only weakly to each other. In US-A-4155481, there is disclosed a container lid structure including a lid plate consisting of a core and an inner layer. The structure has a tab that is arranged along the upper surface of a core, and that passes through the core and is bonded to the inner layer. It is therefore an object of the present invention to solve problems inherent to a lid structure in which the whole part or a major part of the lid structure is made of a plastic material and a score line is formed on the upper surface of the lid for opening, the problems being that the lid structure is likely to be broken due to the decreased strength and dust is apt to accumulate in the score groove to reduce the commercial value of the product. A further object of the present invention is to provide a simple and less expensive than hitherto manufacturing process for manufacturing from a plastic material a container lid structure having an opening tab. According to the present invention, there is provided a container lid structure including a lid plate, a lid frame encircling the lid plate and adapted to be attached to an end of a container barrel, a tab attached to the lid plate so that the lid plate can be removed from the lid frame by pulling the tab to form an opening, said lid plate including an inner layer having a peripheral portion attached to said lid frame and a core arranged along an outer surface of said inner layer and having an outer peripheral portion placed in an abutting relationship with respect to an inner peripheral portion of said lid frame; characterised in that said outer peripheral portion of said core and said inner peripheral portion of said lid frame are formed of materials which do not adhere to each other, and in that said tab is arranged along the upper surface of said core and passes through said core to be bonded to said inner layer. A holding member may be provided along the upper surface of a core in the lid plate, the holding member being passed through the core and attached to the inner layer. The holding member may be formed integrally with an end portion of the tab. According to a preferred aspect of the present invention, the inner layer is made to provide a gas barrier by including a metallic foil coated at the opposite sides with plastic coatings. It should further be noted that, with the lid structure of the present invention it is desirable to form the opening tab at the top surface of a portion adjacent to the end portion thereof with a transversely extending groove so that the force for opening the lid can be effectively transmitted. The invention also provides a process for manufacturing a container lid structure, comprising the steps of providing a film-like inner layer whose upper surface at least is made of a plastic material; locating on said inner layer a core made of a plastic material which does not adhere to, or which bonds only weakly to, the plastic material from which the inner layer is made, the core being formed at a peripheral portion with an aperture for installation of a tab and with aperture means for installation of a holding member; and injecting a plastic material which is the same as, or which adheres well to, the plastic material from which the inner layer is formed to an area around peripheral portions of the inner layer and the core as well as at least to an area on the core covering the tab installation aperture and the holding member installation aperture means and to an area where the tab is to be formed, whereby a lid frame is formed by the plastic material injected around the peripheral portions of the inner layer and the core, whereby the holding member is formed by the plastic material injected to the area covering the tab installation aperture and the holding member installation aperture means, and whereby the tab is formed by the plastic material injected to the area where the tab is to be formed. According to the present invention, the inner peripheral portion of the lid frame and the outer peripheral portion of the lid plate are in an abutting relationship. It is therefore possible to transmit any shock load applied to a corner portion of the lid from the lid frame to the lid plate through the abutting connection between the lid frame and the lid plate without producing any local deformation at the abutting connection. It should further be noted that the lid structure is free from any groove configuration formed between the lid frame and the lid plate so that it is possible to eliminate the problem that dust accumulates in the groove configuration. In the lid structure in accordance with another aspect of the present invention, the lid plate is formed of a core and an inner layer and the inner layer is attached to the lid frame. It is therefore possible to impart a gas barrier property to the inner layer. The tab and the holding member are attached to the inner layer through the apertures in the core so that it is possible to hold the core on the inner layer even though the core is made of a material which does not adhere to or bonds only weakly to the material of the inner layer. In this lid structure, the lid is opened by breaking the inner layer at the abutting connection between the core and the lid frame. In the case where the tab is formed on the upper surface of the tip end portion with a transversely extending groove, the tab can readily be lifted in opening the lid and it is possible to use the shoulder of the groove as a fulcrum for a lever action to thereby concentrate the opening force readily to the peripheral portion of the lid plate. In this structure, the inner layer is not fixedly bonded to the core. It is therefore possible that the inner layer be deflected inwardly apart from the core. In the case where the container is filled with contents having a high temperature, there will be produced a negative pressure in the container as the temperature goes down. However, it is possible to prevent the container barrel from collapsing by forming the inner layer so as to be thinner than the container barrel so that the inner layer is deformed under the negative pressure. The inner layer may be of a type including a metallic foil. Then, it is possible to detect the deflection of the metallic foil by electromagnetic means to thereby detect the sealing condition between the lid and the container barrel. In the process for manufacturing the container lid structure in accordance with the present invention, the holding member and the tab are made by the injection of a plastic material which is the same as or can be readily bonded to the material for the lid frame and the inner layer so that the tab and the holding member securely bonded to the inner layer through the apertures formed in the core. It will therefore be understood that in accordance with the present invention it is readily possible to produce a container lid having an opening tab by use of plastic forming technology. For a better understanding of the invention and to show how the same can be carried into effect, reference will now be made by way of example only to the accompanying drawings wherein. Figure 1 is a plan view of a container lid structure in accordance with one embodiment of the present invention; Figure 2 is a sectional view of the lid structure of Figure 1; Figure 3 is a sectional view of a laminate constituting the inner layer of the lid structure; Figure 3 is a bottom view of the core of the container lid structure; Figure 4b is a plan view of the core; Figure 4c is a sectional view of the core; Figures 5 a, b, c, d, e and f are sectional views showing examples of connection between the tab and the lid plate of the container lid; Figure 6 is a plan view of the tab in accordance with another embodiment of the present invention; Figure 7 is a sectional view of the embodiment shown in Figure 6; Figure 8 is a plan view showing another embodiment of the present invention; Figure 9 is a sectional view taken along the line IX - IX in Figure 8; and, Figure 10 is a sectional view showing a further embodiment of the present invention. Lids embodying the present invention will now be described. Referring at first to Figures 1 and 2, there is shown a container lid structure 1 which is generally formed in a circular disc shape and includes a lid frame 3 constituting a peripheral structure and a lid plate 4 which is located inside the lid frame 3. The lid frame 3 has an outer peripheral portion formed with an upright cylindrical wall 3a which is folded at an upper end into an inverted U-shape to provide a curled edge 3b. The curled edge 3b defines a groove and a container barrel has one end fitted to the groove. The lid structure 1 and the barrel 2 are connected together by means of an appropriate means such as an ultrasonic welding, high frequency welding or heat sealing. The lid plate 4 of the lid structure is adapted to be removed in an opening operation from the lid frame 3 to provide a container opening. For the opening operation, the lid plate is provided with a tab 5 which can be gripped by fingers. As shown in Figure 2, the tab 5 is provided to extend along the upper surface of the lid plate 4 and has an end tip portion 6 adjacent to the outer periphery of the lid plate 4 to be attached to the lid plate 4. The tab 6 has a free end or a rear end opposite to the tip end portion 6 and a ring 5a is provided at this free end for engagement with a finger. The lid structure 1 is opened by engaging a finger with the ring 5a of the tab and pulling the tab 5 upwardly. In the illustrated embodiment, the lid plate of the lid structure 1 comprises a laminate 8 providing an inner layer, a core 10 and a holding member 7. The laminate 8 includes as shown in Figure 3 a metallic foil 8b such as an aluminum foil and plastic layers 8a and 8c coating the opposite sides of the metallic foil 8b. The lid frame 3 is also made of a plastic material. The plastic material for the lid frame 3 is chosen from materials which are the same as or have a good bonding property with respect to the plastic material for the plastic layer 8a. For the lid frame 3 and the laminate 8, use may for example be made of polypropylene. The core is made of a plastic material which does not adhere to the plastic material for the lid frame 3. It is possible to form the core 10 from a metallic material which does not adhere to the plastic material of the lid frame 3. The core 10 is arranged along the upper surface of the laminate 8 and has an outer peripheral portion located in an abutting relationship with respect to an inner peripheral portion of the lid frame 3 to provide an abutting portion 11. The tab 5 is bonded to the plastic layer 8a of the laminate 8 through a connecting leg 5b which is passed through an aperture 13 formed in the core 10 in the vicinity of the end tip portion 6. As shown in Figure 1, the holding member 7 is of a ring shape and located along the peripheral portion of the core 10. The holding member 7 is bonded to the plastic layer 8a of the laminate 8 by means of connecting legs 7a which are passed through apertures 12 formed along the peripheral portion of the core 10. The tab 5 and the holding member 7 are made of a material which does not adhere to or has a poor bonding property with respect to the material of the core and which is the same as or has a good bonding power to the material of the plastic layer 8a of the laminate 8a. When the core 10 is formed of a plastic material and the lid frame 3 and the plastic layer 8a of the laminate 8 are made of polypropylene, the core 10 may be made of a material selected from nylon, polyester, polycarbonate, ebonite, bakelite, epoxy, phenol resin, urea-resin, melamine resin, modified polyphenylene oxide, polysulphone and polyphenylene sulfide which have melting points which are higher than that of polypropylene, or is made of a filler material such as glass fiber impregnated by such materials. When the core 10 is made of a metallic material, an iron- based material or an aluminum based alloy may be used. The tab 5 is located in the vicinity of the abutting portion 11 which is formed between the inner peripheral portion of the lid frame 3 and the outer peripheral portion of the core 10. In the opening operation, a finger is engaged with the ring 5a at the rear end portion of the tab 5 to pull the tab upward to thereby cause the end tip portion 6 of the tab 5 to be pushed down. Under this downwardly directed force, the laminate 8 is broken in the vicinity of the end tip portion of the tab 5. As the tab 5 continues to be pulled up, the laminate 8 is broken along the entire periphery of the core 10 so that the container is opened. The lid structure 1 can readily be made by a plastic forming technique. In the forming process, a laminate 8 as shown in Figure 3 is prepared as the inner layer. The laminate 8 may have the a configuration of a circular disc. A core 10 as shown in Figure 4 is further prepared. As shown in Figure 4, the core 10 has the configuration of a circular disc, having a diameter smaller than the diameter of the laminate 8. The core 10 has a peripheral portion formed at circumferentially spaced portions with apertures 12 and, at a portion where the end tip portion 6 of the tab 5 is located, with apertures 13 which are larger than the apertures 12. Further, as shown in Figures 4b and 4c, the core 10 is formed at the upper surface with two grooves 14. It should further be noted that the core 10 is formed at the peripheral portion of the lower surface with an annular groove 15 as shown in Figures 4a and 4c. Reinforcement ridges 16 are formed in the groove 15 at appropriate spacings. The core 10 is placed over the laminate 8 and located in a mould into which molten plastic material is injected. Although not shown in the drawings, the mould has a cavity for forming the lid frame 3, the tab 5 and the holding member 7 so that the lid frame 3, the tab 5 and the holding member 7 are simultaneously formed. The plastic material forming the lid frame 3 is connected to the upper surface of the laminate 8 at the peripheral portion thereof. A portion of the plastic material for forming the tab 5 flows through the aperture 13 to the groove 15 on the reverse of the core 10 to be bonded to the plastic layer 8a of the laminate 8. A portion of the plastic material for forming the holding member 7 flows through the apertures 12 to the groove 15 at the reverse of the core 10 to be bonded to the plastic layer 8a of the laminate 8. Thus, there is formed a lid structure 1 wherein the lid frame 3, the lid plate 4 and the tab 5 are integrated. The tab 5 may be formed at a portion adjacent to the groove 14 with a reinforcement ridge. The configuration of the lid frame 3 and the lid plate 4 at the abutting portion 11 may be appropriately determined as shown in Figures 5a, 5b, 5c, 5d, 5e and 5f. Figures 6 and 7 show another embodiment of the present invention. In this embodiment, the tab 5 is formed at the upper surface of a portion adjacent to the end tip portion with a transversely extending groove 5c. With the aid of the groove 5c, the tab 5 can be raised for the opening operation with a relatively small effort. In the opening operation, the shoulder portions 5d and 5e approach each other and when the tab 5 is actuated further from this situation, the end tip portion 6 of the tab 5 is applied with a force which pushes the peripheral portion of the core 10 strongly downwardly. It is therefore possible to carry out the opening operation more easily. Figures 8 and 9 show a further embodiment of the present invention. In this embodiment, the holding member 7 is formed integrally with the tip end portion 6 of the tab 5 and has a plurality of circumferentially spaced bridge pieces 20 which are extending radially outwardly toward the lid frame 3. The bridge pieces 20 extend as shown in Figure 9 from the holding member 7 across the abutting portion 11 between the core 10 and the lid frame 3 over the upper surface of the lid frame 3. According to this embodiment, the bridge pieces 20 thus formed serve to prevent the lid plate 4 from being pushed inwardly under an external shock load which may be applied to the lid during transportation possibly causing failure of the lid. Figure 10 shows a further embodiment of the present invention. In this embodiment, the core 10 is not of a circular disc shape but of a ring shape. Inside a ring of core-forming material 10, there is formed a disc 21 made of a plastic material which is the same as the material for the tab 5. Results of comparative tests on lid structures in accordance with embodiments of the present invention and conventional lid structures having score lines will now be described. Comparative Test (drop test) Tests were conducted with the following sample lids. A lid structure embodying the present invention included a laminate 8 comprising a 70µm polypropylene film constituting the plastic layer 8c, a 30 µm aluminum foil constituting the metallic foil 8b and a 50µm polypropylene film constituting the plastic layer 8a. The laminate 8 was placed in a mould. A core 10 0.65 mm thick was separately prepared from nylon resin containing 30 % of glass fibers and laid over the laminate 8. Then, polypropylene resin was injected into the mould to produce a lid structure 0.8 mm thick. Comparative test samples were prepared using laminates which are the same as the laminate for the lid structure embodying the present invention. The laminate was placed in a mould and polypropylene resin was injected into the mould to produce a lid structure having a score line 1.0 mm wide and 0.65 mm deep along the entire periphery of the lid plate. Each of the test samples was attached to a container barrel of 65 mm inner diameter and 105 mm high which was filled with 300 ml of water. the container was sealed by attaching the lid structure to the barrel by high frequency welding. The container was then subjected to a retort sterilization treatment at a temperature of 125 °C for 30 minutes to prepare a specimen for a drop test. The specimens were subjected to drop tests from various heights to observe damage. The results are shown in Table 1. The values in the table show the number of test specimens in which the lids were broken as the results of the drop tests, 10 specimens having been put into each test. In Table 1, it will be noted that with the specimens embodying the present invention failure of the lid structure is seen at a drop height of more than 90 cm. In contrast with the comparative specimen, failure is seen even at a drop height of 60 cm. Thus, the lid structure embodying the present invention has a higher drop strength. Comparative Test (Opening Tests) Specimens prepared as in the previous tests were subjected to opening tests by 12 women testers. The observations of the testers are shown in Table 2. In the Table 2, o shows the invention whereas shows the prior art In Table 2, it will be noted that the lid structure in accordance with the present invention is comparable to conventional lid structures in respect of ease of opening. In other words, the lid structure of the present invention has an openability which is equivalent to that in a conventional lid structure having a score line. As described above, in the lid structure in accordance with the present invention, the inner peripheral portion of the lid frame and the outer peripheral portion of the lid plate are laid in an abutting relationship. It will therefore be understood that any shock load which may be applied to the container in storage or transportation will be transmitted from the lid frame through the abutting portion to the lid plate. Thus, it will not be likely as in a conventional structure having a score line that a local deformation is produced in the area of the score line. It should further be noted that as no groove such as a score line is externally exposed, it is possible to avoid the problem that dust is accumulated in the groove. Further, according to the present invention, it is possible to produce a lid closure by plastic forming in a small number of steps.

Claims: 1. A container lid structure (1) including a lid plate (4), a lid frame (3) encircling the lid plate (4) and adapted to be attached to an end of a container barrel (2), a tab (5) attached to the lid plate (4) so that the lid plate (4) can be removed from the lid frame (3) by pulling the tab (5) to form an opening, said lid plate (4) including an inner layer (8) having a peripheral portion attached to said lid frame (3) and a core (10) arranged along an outer surface of said inner layer (8) and having an outer peripheral portion placed in an abutting relationship (11) with respect to an inner peripheral portion of said lid frame (3); characterised in that said outer peripheral portion of said core (10) and said inner peripheral portion of said lid frame (3) are formed of materials which do not adhere to each other, and in that said tab (5) is arranged along the upper surface of said core (10) and passes through said core (10) to be bonded to said inner layer (8). 2. A structure (1) in accordance with claim 1, which includes a holding member (7) arranged along said upper surface of the core (10) of said lid plate (4), said holding member (7) passing through said core (10) and being bonded to said inner layer (8). 3. A structure (1) in accordance with claim 2, in which said holding member (7) is formed integrally with an end portion of said tab (5). 4. A structure (1) in accordance with claim 2 or 3, in which said holding member (7) and said tab (5) are made of a material which bonds well to the surface of said inner layer (8). 5. A structure (1) in accordance with any preceding claim, in which at least said inner peripheral portion of said lid frame (3) and said outer peripheral portion of said lid plate (4) are formed of plastic materials. 6. A structure (1) in accordance with any preceding claim, in which said tab (5) is formed at an upper surface in the vicinity of an end portion of said tab (5) with laterally extending groove means (14). 7. A structure (1) in accordance with any preceding claim, in which said core (10) is of a circular disc shape. 8. A structure (1) in accordance with any preceding claim, in which said core (10) is of a ring shape. 9. A structure (1) in accordance with any preceding claim, in which said lid frame (3) is made of a plastic material at least at the inner peripheral portion, said core (10) being made of a metallic material. 10. A structure (1) in accordance with any preceding claim, in which said inner layer (8) includes a metallic foil (8b) coated at the opposite sides with plastic (8a, 8c). 11. A structure (1) in accordance with any preceding claim, in which a plurality of circumferentially spaced bridge pieces (20) are provided integrally with an upper surface of said core (10) to extend from said core (10) towards and over said lid frame. 12. A process for manufacturing a container lid structure (1), comprising the steps of providing a film-like inner layer (8) whose upper surface at least is made of a plastic material; locating on said inner layer (8) a core (10) made of a plastic material which does not adhere to or which bonds only weakly to, the plastic material from which the inner layer (8) is made, the core (10) being formed at a peripheral portion with an aperture for installation of a tab (5) and with aperture means for installation of a holding member (7); and injecting a plastic material which is the same as, or which adheres well to, the plastic material from which the inner layer (8) is formed to an area around peripheral portions of the inner layer (8) and the core (10) as well as at least to an area on the core (10) covering the tab installation aperture and the holding member installation aperture means and to an area where the tab (5) is to be formed, whereby a lid frame (3) is formed by the plastic material injected around the peripheral portions of the inner layer (8) and the core (10), whereby the holding member (7) is formed by the plastic material injected to the area covering the tab installation aperture and the holding member installation aperture means, and whereby the tab (5) is formed by the plastic material injected to the area where the tab (5) is to be formed.

Inventors: IGOTA, SHOJI C/O AJINOMOTO CO., INC., KOBAYASHI, YUKIO C/O AJINOMOTO CO., INC., SASAKI, HITHOSHI C/O AJINOMOTO CO., INC.
Applicants: AJINOMOTO CO., INC.
Application year: 1988
Main classification: B65D17
IPC codes: B29C45, B65D17, B29C65