摘要：
The invention suggests a peelable cover panel for a lid of peel type which allows a safe sterilization of filled and closed cans in continuous autoclaves (high temperature prevailing there and a resultant high pressure in the can) avoiding risk of breaking, breaking up or detaching said plane (surface oriented) cover panel on or from the seamable annular ring. After the cooling of the can, the lid also has an acceptable appearance. Suggested therefore is a cover panel for sealing to an annular ring to provide a lid to close a can body and allow a thermally treating pasteurization or sterilization process of the closed can in a continuous autoclave. The cover panel (3) having a radially outer ring band (3a) for sealingly affixing to a flat web (6) and a remaining central portion (3b) that is surrounded by the ring band, the control portion being preformed in a bowl-shaped fashion and is for this reason stabilized. The stabilization is such that the bowl-shaped cover panel (3), during an increase in pressure during at least the pasteurization, changes from the preformed bowl-shape as first position (3b) to a second position (3b') that is bowl-shaped axially outwards, and is still able to return to the first position (3b), at least substantially during or after cooling.
权利要求：
1. Lid for a can body for receiving a foodstuff, wherein, after sealingly closing the can body, the closed can is subjectable to a pasteurization or sterilization process, thermally treating the foodstuff, - the lid (1) having an annular ring (2) for seaming to a can body edge portion and a plane or surface oriented cover panel (3;3a,3b) disposed sealingly (13) on the annular ring (2), wherein the annular ring comprises a flat web (6) that extends towards a vertical central axis (8) of the lid and is inclined upwards at an angle (11) with respect to a horizontal plane (15); - the cover panel (3) being sealingly affixed to the flat web (6), by a radially outer ring band (3a), and a remaining central portion (3b) that is surrounded by the ring band is preformed downwards in a bowl-shaped fashion and is for this reason stabilized in a manner - - so that the bowl-shaped cover panel, during an increase in pressure during at least the pasteurization, changes from the preformed first position (3b) to a second position (3b') that is bowl-shaped axially outwards, and - after a cooling - automatically returns to the preformed first position (3b).
2. Lid of claim 1, wherein the cover panel (3) consists of a material that can be hardened or stiffened by a deep-drawing deformation or comprises a layer of such a material.
3. Lid according to claim 1, in which - when referred to a horizontal plane (15) assumed to pass through a transition area (3c) between the outer ring band (3a) and the inner central portion (3b) - a first distance (10b) of a center of the central portion (3b) from the horizontal plane (15) in said outwardly bulged position of the central portion is substantially the same as a second distance (10a) in said bowl-shaped shape (3b).
4. Lid according to any of the preceding claims, in which an axial distance (10a, 10b) is dimensioned in such a way that, due to the shape change of the central portion (3b) from inside bowl to outside bowl shape upon increase in pressure, preferably 1.5 bar (0.15 MPa), an increase in volume of a headspace caused in the headspace of the closed can (1) limits a maximum pressure to a value not being detrimental to the lid during one of sterilization and pasteurization of the closed can in a continuous autoclave (retort system).
5. Lid (1) according to any of the preceding claims, wherein the angle of inclination (11) of the flat web (6) is coordinated with the distance (10a, 10b) of the center of the central portion (3b) from a horizontal plane (15, E3), which central portion is preformed in a bowl-shape in such a way that, at the maximum pressure building up during the thermal treatment in the sealing connection zone between the flat web (6) of the annular ring (2) and the outer ring band (3a) of the panel (3) at least no substantial peeling forces are acting on the outer ring band.
6. Lid (1) according to any of the preceding claims, wherein the angle of inclination (11) of the flat web (6) is selected larger than 10°, in particular smaller than 30° and larger than 20°.
7. Lid (1) according to any of the preceding claims adapted for and suitable for a can with a diameter of about 83 mm, wherein an axial distance (10a) of the centre of the preformed central portion (3b), preformed in a bowl- or dome-shape, from a horizontal reference plane (15) as "the horizontal" is between 5 mm and 6 mm, in particular about 5.6 mm.
8. Process for providing tightness of can closures during sterilization or pasteurization of at least one can filled with foodstuff, the process operating in a continuous autoclave or retort system having no counterpressure, said can being closed with a lid (1) comprising an annular ring (2) and a lid panel (3; 3a, 3b), which is affixed with an outer ring band (3a) on an inner flat web (6) that is axially outwardly and downwardly inclined at an angle (11) with respect to a horizontal plane (15), wherein prior to attaching the lid (1) to the filled can, a central portion (3b) of the lid panel (3) bounded by the outer ring band (3a) is pre-shaped into a smooth bowl shape or a bowl shape with a plane surface having no steps, the shaping performed by a deep-drawing step and, by this step the material of this portion (3b) is one of solidified, stiffened or hardened so that it changes - under an increased pressure in a headspace of the closed can during the can's passage through the autoclave or retort system - into an axially outwardly bulged shaped that is mirror-inverted to the pre-shaped form, but automatically returns to the original bowl shape with the same surface area upon the subsequent cooling of the closed can.
9. Process according to claim 8, wherein a stress in a sealing area (13) as a fastening place connecting outer ring band (3a) and web (6), depends on the load or tensile stress of the central portion having given thickness and given differential pressure on the central portion (3b).
10. Process according to claim 8 or 9, wherein a stress on the central portion (3b) upon application of surface pressure can be changed by selecting a width of a sealing area (13) implemented as a sealing seam on the flat web (6).
11. Process according to any of claims 8 to 10, wherein the radial flat web (6) of the annular seaming ring (2) is imparted an inclination at an angle (11), which is coordinated to an axial depth (10a, 10b) of two layers (27a, 27b; 3b, 3b') of the central portion in such a way that applying a maximal pressure during the passage of the filled and closed can through the continuous autoclave, this pressure provides no peeling effect in the sealing portion (13) of the ring band (3a) on the flat web (6) of the annular ring (2).
12. Process according to any of claims 8 to 11, wherein the central portion (3b) of the lid panel (3) is deep drawn prior to or after sealing the lid panel to the flat web (6) of the annular ring (2).
13. Process according to any of claims 8 to 12, wherein the ring band (3a) is attached to the flat web (6) by hot sealing, in particular using an induction process.
14. Process according to any of claims 8 to 12, wherein the pressure in the headspace (H) does not exceed substantially 1 bar (0.1 MPa), and this up to a sterilization temperature during sterilization.
15. Process according to any of claims 8 to 14, wherein the angle (11) is between substantially 22° and 25° or greater than 10°.
16. Process according to claim 8, wherein an inner tensile stress of the central portion (3b) is reduced by deep drawing said portion, in order to create a reduced stress or load of the fastening place (13) between ring band (3a) and inclined flat web (6) at a pressure load with a surface pressure on the central portion (3b) during the passage through the autoclave station (retort station).
17. Process according to claim 16 or 8, wherein the central portion is brought into a shape by deep-drawing, which is determined by an inner space of the annular ring (for seaming to the can body), radially further inside than the flat web and reaching - exposed to thermally caused surface pressure - a deflection (depth; 10b) which subjects the central portion within its material and likewise the fastening place (13) on the flat web (6) to tensile stress, said tensile stress being below a stress limit of the central portion, thus avoiding a plastic deformation, in particular avoiding tearing or cracking.
18. Process according to any of the preceding claims 8 to 17, wherein the angle of inclination (11) of the flat web (6) is shaped to be larger than 20°, in particular smaller than 30°.
19. Process according to any of the preceding claims 8 to 18 for a can body with a diameter of about 83 mm, wherein an axial distance (10a) of the center of the central area (3b) preformed in a bowl-shaped fashion is downwardly shifted due to the reshaping from a horizontal reference plane (15) as the "horizontal" by between 5 and 6 mm, in particular by about 5.6 mm.
20. Process according to any of the preceding claims 8 to 19, wherein the solidification or hardening is distributed or acts across substantially the entire central area (3b).
21. Process of claim 8, wherein the autoclave being a continuous autoclave, preferably having at least no substantial counter-pressure upon sterilizing the closed cans.
22. Process of claim 8 or 21, wherein counter-pressure in the continuous autoclave being below 1.6 bar (0.16 MPa).