METHOD FOR MANUFACTURED A BOX LID FROM A COMPOSITE MATERIAL

Description

[0001] The present invention relates to a method for producing a can end from a composite material comprising at least one sheet metal part, in particular aluminum or tinplate part, and at least one plastic part, in particular made of polypropylene or polyethylene terephthalate.

[0002] Can ends for beverage cans typically have an opening section separated from the rest of the can end by a weakening line, which can be moved out of the lid plane via an attached tear-open element to open the can. The opening section can be moved into the can or upwards. Resealable can ends are also known in which a sealing frame made of plastic material, which is connected to the fixed lid surface and surrounds the opening area, is connected to the metal lid area surrounding the opening area. A closing unit, which is connected to the pivoting, metal opening section of the can end, interacts with the sealing frame. The sealing frame and the closing unit are preferably made of plastic, while the can end is made of aluminum or tinplate. Similar can ends are used for food cans.It has also been reported that, instead of a line of weakness, a micro-gap is provided between the opening section and the fixed lid area. In this case, the can lid is laminated internally with a plastic film to seal the micro-gap. The plastic film is torn open when the can lid is opened, for which purpose the plastic film can also be provided with a line of weakness.

[0003] DE 20 32 928 A1 discloses a method for pretreating metal objects, in which a tear-open and closure part made of propylene polymer is bonded to a metal container end by inductive heating. US 4,397,401 A relates to an easy-to-open container closure and a method for producing the same, wherein the opening of the metal container lid is provided with a plastic edge protector. The edge protector is bonded to the lid part by hot-melt bonding using high-frequency induction heating. JP 2002 179061 A relates to a laminated lid made of metal and plastic, wherein the plastic material and the lid material are passed between two laminating rollers and bonded to one another using induction heating.

[0004] JP H05 104635A discloses the joining of a polypropylene layer and a multilayer laminate of aluminum foil and polypropylene film in a mold.

[0005] The invention is based on the object of providing a method for producing such a can lid which is as simple and cost-effective as possible.

[0006] This object is achieved by a method having the features of claim 1 and in particular by the fact that the plastic part and the sheet metal part are joined together by pressing them together and inductively heating them.

[0007] Through induction heating, the plastic part is melted, thereby creating a material bond with the sheet metal part. Induction heating has the advantage that only the sheet metal part is heated directly, since induction can only generate eddy currents in the sheet metal part. The plastic part, on the other hand, is heated indirectly by the metal part, which melts the side of the plastic part that is in contact with the sheet metal part.

[0008] Preferably, the sheet metal part and / or the plastic part are coated with an adhesion promoter before joining. This can increase the stability of the joint.

[0009] The adhesion promoter preferably contains the same plastic as the plastic part to be bonded to the sheet metal part. This results in particularly good adhesion and thus a particularly strong joint.

[0010] According to the invention, a fully formed can end element made of sheet metal is joined to a plastic film having a customized shape, in particular a thermoformed plastic film. This also results in a particularly strong joint. Furthermore, the joint can be produced with relatively little energy consumption, since conformal deformation of the plastic part is not required during joining.

[0011] To produce a resealable can end, the can end element is joined on one side to a plastic film and on the other side to a closure element covering the opening area of ​​the can end, consisting of a sealing frame and a pivotable closing unit. The closure element is made of, in particular, injection-molded plastic, in particular polypropylene or polyethylene terephthalate. Both joining processes are performed in a single step. This allows for particularly quick and easy joining. Furthermore, energy is saved because the sheet metal part of the can end only needs to be heated once.

[0012] According to a preferred embodiment of the invention, a press is used for the joining process, comprising an upper tool and a lower tool, as well as a waveguide for supplying the alternating electromagnetic field into the area of ​​the can end for inductive heating, wherein the upper tool has a shape reciprocal to one side of the can end and the lower tool has a shape reciprocal to the other side of the can end. With such a device, a particularly good joining connection can be produced. The parts to be joined are pressed together via the press so that they are in intimate contact. The alternating electromagnetic field is guided into the area of ​​the can end via the waveguide and heats the sheet metal part, the heat of which in turn leads to the melting of the plastic contacting the sheet metal part.

[0013] Particularly preferably, the waveguide has several annular or spiral sections located opposite the joining area of ​​the can lid, in particular an annular section in the edge area of ​​the can lid and a spiral section with two, three, or more turns in the central lid area. This configuration allows advantageous heating of the sheet metal part, particularly in the critical edge area, due to the waveguide's own annular section there.

[0014] According to a further advantageous embodiment of the invention, the tool located on the waveguide side is made of a dimensionally stable material, particularly plastic, and the opposite tool is made of an elastic material, particularly elastomer material. The dimensionally stable material on the waveguide side reliably protects the waveguide from forces that occur. The elastic material on the opposite side, on the other hand, allows for compensation of manufacturing tolerances, so that these do not result in excessive forces when the parts are pressed together.

[0015] The dimensionally stable tool is preferably associated with the plastic film. It can also be provided with ribs for introducing a weakening line into the plastic film during the joining process. This can eliminate a single work step in the production of a can end.

[0016] According to a similarly preferred embodiment of the invention, the parts to be joined are held together by negative pressure during the joining process. This ensures a precise fit. Furthermore, advantageous venting is achieved, preventing the entrapment of air bubbles between the plastic material and the sheet metal part. For can ends with a micro-gap between the opening section and the fixed lid area, the venting can act on both sides of the lid.

[0017] Particularly for the production of can ends without a micro-gap, it is advantageous to provide at least one of the tools with bulges to create free spaces designed to accommodate any trapped air. Such bulges can preferably be provided in areas where trapped air bubbles do not cause interference, for example, in the central lid area with sufficient distance from the lid edge and the opening area.

[0018] According to a further embodiment of the invention, a rotary indexing table is used to bring the individual components of the can end together for the joining process. This allows for advantageous loading of a press used in the joining process.

[0019] According to a preferred embodiment, the rotary indexing table has a vacuum supply for at least one loading station, with the vacuum supply to the individual stations being provided via valves actuated by a rotary distributor. This is particularly advantageous with regard to the distribution of the vacuum.

[0020] An embodiment of the invention is illustrated in the drawing and described below. They show, in schematic representation, Fig. 1 is a sectional perspective view of a press for use in a method according to the invention, Fig. 2 is a sectional side view of a part of the press according to the invention, Fig. 3 is a perspective view of a device of Fig. 1 inductor to be used, Fig. 4 a side view of the inductor of Fig. 3 , Fig. 5 a top view of the inductor of Fig. 3 , Fig. 6 a top view of a can lid, Fig. 7 a cross section through the can lid of Fig. 6 , Fig. 8Detail B of Fig. 7 , Fig. 9Detail C of Fig. 7 , and Fig. 10 the detail of D of Fig. 7 .

[0021] The Fig. 1The press 1 shown comprises a base frame 2 and a movable upper press part 3 as well as guide cylinders 4 for guiding the upper press part 3 during opening and closing of the press. A lower tool 5 is provided on the upper side of the base frame 2, and an upper tool 6 is provided on the underside of the upper press part 3. The lower tool 5 is made of an elastomer material and has a cavity 7 for receiving a closure element 18 (see Fig. 6 ) of a can lid 9. Furthermore, the lower tool 5 is modeled on the shape of the top side of the can lid 9. The upper tool 6 is made of a dimensionally stable plastic and is modeled on the underside of the can lid 9.

[0022] An inductor 10 is arranged in the area of ​​the press. Waveguides 11 for supplying an alternating electromagnetic field are guided from the inductor 10 into the area of ​​the upper tool 6. As can be seen in particular in the Fig. 3 to 5As can be seen, the waveguides, which are made of copper in particular, are formed into an outer ring 12 and a spiral 13 arranged within the ring with several turns. As can be seen in particular in Fig. 2 As can be seen, the outer ring 12 and the spiral 13 are arranged above the upper tool 6. They are thus opposite the surface of the can lid 9 to be joined. The copper waveguides 11 are, in particular, water-cooled.

[0023] The one in the Fig. 6 to 9 The can lid 9 shown comprises a base body 14 made of a metal sheet, in particular aluminum or tinplate. The base body 14 comprises a fixed metallic lid area 15 and a pivotable opening section 16 for releasing an opening area 8. As can be seen in particular in the Figs. 8 and 9As can be seen, the underside of the can lid 9 is laminated with a plastic film 17. On the top side of the can lid 9, however, a closure element 18 is arranged, which consists of a sealing frame 19 and a closing unit 20. The sealing frame 19 is connected to the fixed lid area 15, and the closing unit 20 is connected to the upwardly pivoting opening section 16.

[0024] For the production of the Fig. 6 to 9 The method according to the invention can be used to produce the can lid 9 shown in the Fig. 1 to 5The device shown in FIG. 1 can be used for this purpose. For this purpose, the closure element 18, which is manufactured in particular in one piece using a deep-drawing process, is inserted into the lower tool 5 such that the side facing the can lid 9 faces upward. The base body 14, which has previously been coated on its underside with the plastic film 17, is placed onto the closure element 18. The press 1 is then closed, and the induction heater 10 is switched on.

[0025] The supplied energy heats the metallic base body 14 by generating electromagnetic eddy currents therein. The heated base body 14, in turn, heats the plastic film 17 and the closure element 18, which are thereby melted. This results in a plastic welded connection between the metallic base body 14 and the plastic film 17, on the one hand, and the closure element 18, on the other hand. An adhesion promoter is preferably used to improve the plastic welded connection. The adhesion promoter can contain the same plastic used for the plastic film 17 or the closure element 18. This can be, in particular, polypropylene or polyethylene terephthalate.

[0026] The upper tool 6 can also have ribs (not visible here), through which a line of weakness is introduced into the plastic film 17 during the pressing and joining process. In addition, bulges can be provided in the upper tool 6 to create free spaces between the plastic film 17 and the metallic base body 14. This allows trapped air to be collected in predetermined areas of the can end 9, in particular in areas where air bubbles do not cause interference, such as in the area between the edge of the can end and its opening area 8. Additionally or alternatively, the press 1 can be provided with a vacuum supply, which on the one hand holds the parts to be joined together and on the other hand can at least largely prevent air from being trapped. In the case of can ends with a micro-gap between the fixed lid area 15 and the pivotable opening section 16, this applies to both sides of the can end.

[0027] A rotary indexing table with several stations for assembling the individual parts of the can end can be provided for loading press 1. Instead of a rotary indexing table, a linear feeder can also be provided for press 1.

[0028] After the plastic film 17 and the closure element 18 have been welded to the metallic base body 14, the press is opened and the finished can end 9 is removed. List of reference symbols

[0029] 1 Press 2 Base frame 3 Upper press part 4 Guide cylinder 5 Lower tool 6 Upper tool 7 Cavity 8 Opening area 9 Can end 10 Inductor 11 Waveguide 12 Outer ring 13 Spiral 14 Base body 15 Fixed end area 16 Opening section 17 Plastic film 18 Closure element 19 Sealing frame 20 Closing unit

Claims

1. A method of manufacturing a can lid (9) composed of a composite material comprising at least one sheet metal part (14), in particular an aluminum part or a tin plate part, and at least one plastic part (17, 18), in particular composed of polypropylene or polyethylene terephthalate, wherein the plastic part (17, 18) and the sheet metal part (14) are joined together by pressing together and by inductive heating, characterized in that a fully formed can lid part (14) composed of sheet metal is joined together with a plastic film (17) having a matched shape, wherein the can lid part (14) is joined together with the plastic film (17) on its one side and with a closure element (18) on its other side that covers an opening region (8) of the can lid (9) and that is composed of plastic, and wherein both joining processes take place in one workstep.

2. A method according to claim 1, characterized in that the sheet metal part (14) and / or the plastic part (17, 18) is / are coated with a bonding agent before the joining.

3. A method according to claim 2, characterized in that the bonding agent includes the same plastic as the plastic part (17, 18) to be connected to the sheet metal part (14).

4. A method according to any one of the preceding claims, characterized in that the can lid part (14) is joined together with a thermally shaped plastic film.

5. A method according to any one of the preceding claims, characterized in that the can lid part (14) is joined together with a closure element (18) composed of injection molded plastic, in particular polypropylene or polyethylene terephthalate.

6. A method according to any one of the preceding claims, characterized in that a press (1) is used for the joining process having a top tool (6) and a bottom tool (5) as well as a hollow conductor (11) for supplying an electromagnetic alternating field into the region of the can lid (9) for its inductive heating, with the top tool (6) having a shape reciprocal to one side of the can lid (9) and the bottom tool having a shape reciprocal to the other side of the can lid (9).

7. A method according to claim 6, characterized in that the hollow conductor (11) comprises a section which is disposed opposite the reception region of the can lid (9) to be joined, in particular a ring-shaped region (12) in the marginal region of the can lid (9) and a spiral region (13) disposed within the ring-shaped region (12) and having two, three, or more windings in the middle region of the can lid (9).

8. A method according to claim 7, characterized in that the tool (6) located at the side of the hollow conductor (11) comprises shape-stable material, in particular plastic, and the oppositely disposed tool (5) comprises elastic material, in particular elastomeric material.

9. A method according to claim 8, characterized in that the shape-stable tool (6) is associated with the plastic film (17).

10. A method according to claim 9, characterized in that the tool (6) associated with the plastic film (17) has ribs for introducing a weakening line into the plastic film (17) during the joining process.

11. A method according to any one of the preceding claims, characterized in that at least one of the tools (5, 6) has indentations for producing free spaces for receiving possibly enclosed air.

12. A method according to any one of the preceding claims, characterized in that the parts (14, 17, 18) to be joined are held together by vacuum during the joining process.

13. A method according to any one of the preceding claims, characterized in that a rotary indexing table is used to join together the individual components (14, 17, 18) of the can lid (9) for the joining process.

14. A method according to claim 13, characterized in that the rotary indexing table has a vacuum supply for at least one charging station, with the vacuum supply of the individual stations being able to be switched on and off via valves which are supplied with vacuum by a round distributor.