MANUFACTURING PROCESS FOR PRODUCING HERMETIC SINGLE-USE FOOD CONTAINERS USING A SEALING HEAD HAVING A SPECIFIC PROFILE WITH A RIB

Abstract

The invention concerns a manufacturing process for producing hermetic single-use food containers, including: forming a container body (30) having an peripheral rim (31), placing the container body in a sealing head having a first die (2) and a second die (8) having cooperating annular sealing surfaces (4, 10) facing the rim (31), sealing a closing lid (34) placed over the container body with the rim (31) by applying the first die (2) and the second die (8) one against the other. According to the invention, the first die (2) is provided with a continuous annular rib (6) in its sealing surface (4), the rib having a height (h) which is at least equal to a maximum depth of wrinkles that might appear on the rim upon forming the container body, whereby a sealing groove (12) is formed by the rib (6) in a side of the rim during the sealing.

Claims

1. Manufacturing process for producing hermetic single-use food containers, including: forming a container body having a peripheral rim, placing the container body in a sealing head having a first die and a second die, at least one of which being mobile, the first die and the second die having cooperating annular sealing surfaces facing the rim, applying a closing lid over the container body, sealing the closing lid with the rim of the container body by applying the first die and the second die one against the other, and the first die is provided with an annular rib in its sealing surface, the rib having a height which is at least equal to a maximum depth of wrinkles that might appear on the rim upon forming the container body, whereby a sealing groove is formed by the rib in a side of the rim when sealing the closing lid to the container body, the closing lid being bound to the rim in front of the sealing groove.

2. Manufacturing process according to claim 1, wherein the container body is made from a sheet of paper/PLA laminate.

3. Manufacturing process according to claim 2, wherein the container body is made from a sheet of PLA-PVOH-PLA of 50 μm laminated with a formable paper of 130 g/m.sup.2 and wherein the closing lid is made from a sheet including a PLA barrier laminated with a paper of 30 g/m.sup.2.

4. Manufacturing process according to claim 1, wherein the first die is a lower die of a vertical press and the second die is an upper die, whereby the sealing groove is engraved is in an underside of the rim.

5. Manufacturing process according to claim 1, wherein the sealing surface of the second die is flat and rigid.

6. Hermetic single-use food container, including a container body with a peripheral rim, and a closing lid closing the container body comprising: the container body is made in a paper-laminated material and has wrinkles at least at the rim, the wrinkles extending essentially radially, and the hermetic single-use container shows an annular sealing groove engraved on a side of the rim which extends continuously essentially in a circumferential direction all around the rim and which has a depth at least equal to a maximum depth of the wrinkles whereby the wrinkles are flattened by the sealing groove, the closing lid being bound to the rim of the container body at least in the region of the sealing groove.

7. Hermetic single-use food container according to claim 6, wherein the closing lid has a top surface which is flat at least at the rim.

8. Hermetic single-use food container according to claim 6, wherein the sealing groove engraved in the rim is formed in an underside of the rim.

9. Hermetic single use food container according to claim 6, wherein the sealing groove engraved in the rim has a width comprised between 0.15 mm and 5 mm, and a height of between 0.05 mm and 3 mm.

10. Hermetic single use food container according to claim 6, wherein the container body is made from a sheet of paper/PLA laminate.

11. Hermetic single use food container according to claim 10, wherein the container body is made from a sheet of PLA-PVOH-PLA of 50 μm laminated with a formable paper of 130 g/m.sup.2 and wherein the closing lid is made from a sheet including a PLA barrier laminated with a paper of 30 g/m.sup.2.

12. Coffee pod that includes a hermetic single-use food container including forming a container body having a peripheral rim, placing the container body in a sealing head having a first die and a second die, at least one of which being mobile, the first die and the second die having cooperating annular sealing surfaces facing the rim, applying a closing lid over the container body, sealing the closing lid with the rim of the container body by applying the first die and the second die one against the other, and the first die is provided with an annular rib in its sealing surface, the rib having a height which is at least equal to a maximum depth of wrinkles that might appear on the rim upon forming the container body, whereby a sealing groove is formed by the rib in a side of the rim when sealing the closing lid to the container body, the closing lid being bound to the rim in front of the sealing groove.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Additional features and advantages of the present invention are described in, and will be apparent from, the description of the presently preferred embodiments which are set out below with reference to the drawings in which:

[0050] FIG. 1 is a schematic view in perspective of a container body according to the invention or to the prior art.

[0051] FIG. 2 is a schematic cross-section of single-use food container according to the invention.

[0052] FIG. 3 is a schematic cross-section of a forming device that can be used in a manufacturing process according to the invention.

[0053] FIG. 4 is a schematic cross-section of a portion of an embodiment of a sealing head according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0054] The first step of the manufacturing process according to the invention aims to produce a 3D container body such as the container body 100 shown at FIGS. 1 and 2, from a 2D blank 10 illustrated in FIG. 3. The forming process used in the manufacturing process according to the invention can be chosen from known sliding blank processes (where the sliding of the blank into the mould and the lateral contraction of the blank cause the micro-folding of the blank) such as stamping processes or deep-drawing processes, or from known fixed blank processes (where the container is formed essentially via straining of the blank) such as air forming/vacuum forming processes and hot pressing processes, depending on the desired shape (in particular the desired depth) for the container body, the material of the blank, etc.

[0055] For example, the forming of the container body can be carried on by deep-drawing with a press as illustrated at FIG. 3, comprising a male die 20 while the female mould can be absent, present as a counter holder 21 as illustrated or used to emboss the under of the shape. The 2D blank 10 is placed into the forming machine where it is clamped by a blank holder 24 with a predetermined force F; subsequently, the male die 20 starts a downward movement towards the counter holder 21 along a forming cavity 22, which is where the actual forming occurs. Finally, the shape is released from the forming device. The forming cavity is preferably surrounded by heating elements 23. Heating elements 23′ can also be provided in the male die 20.

[0056] The whole forming sequence can be as short as a couple of seconds. The selection of forming parameters such as the die force, the blank holding force F, the forming gap or clearance (which is the lateral distance between the edge of the forming cavity and the edge of the male die) is performed empirically.

[0057] As to the forming gap, it can be noted that this distance is varied, among others, according to the thickness of the material from which the blank is made. Too small a forming gap increases the out-of-plane and in-plane shear and forces. This can lead to the formation of cracks and eventual failure of material in the formed shape. Typically, the gap is around 0.7 times the thickness of the paperboard (it can be noticed that dimensions and ratios are not respected at FIG. 3, which is very schematic). On the other hand, too large a forming gap leads to the poor appearance of the shape and to significant wrinkles that create voids which restrict the possibility of gas-tight sealing of such shapes.

[0058] As a negative consequence of the forming process, the container body 100 exhibits wrinkles 103 (see FIG. 1) essentially in the rim 102 and at the junction between the rim 102 and the sidewall 101 and on a large part of the sidewall 101.

[0059] To close the container body thus obtained, a closing lid (not shown at FIG. 1) is later sealed on the upper surface of the rim 102 after the container body 100 has been filled with food. The wrinkles 103 compromise the perfect sealing of the closing lid with the rim and a hermetic seal cannot be obtained. In particular, the wrinkles formed at the surface of the rim are oriented in the radial direction of the container body 100, and their impair the correct flatness of the rim. Therefore, when the upper lid is sealed onto said rim, radial channels are created along the wrinkles, through which oxygen and moisture are able to circulate from outside the container, into the internal compartment of said container, hence rapidly degrading the quality of the food contained therein.

[0060] To solve this problem, the invention proposes to use a sealing head one die of which has a sealing surface with a specific profile. An example of a sealing head according to the invention is partially represented at FIG. 4 with a container body 30 and a closing lid 34 therein. The sealing head includes a fixed lower die (first die) 2 with an annular top sealing surface 4 and a movable upper die (second die) 8 with a bottom sealing surface 10, the cooperating sealing surfaces 4 and 10 being circular and having a width that corresponds to the width of the rim 31 of the container body 30.

[0061] The sealing surface 4 of the first die 2 includes a circular rib 6, while the sealing surface 10 of the second die 8 is flat (planar). The rib 6 causes a sealing groove 12 in the underside of the rim that erases the wrinkles (such wrinkles are not represented at FIG. 4). More precisely, the formation of the groove 12 in a direction which is orthogonal to the direction of the wrinkles, “flattens” and therefore recloses the wrinkles by pushing the material of the rim back into the empty space of each wrinkle. As a consequence, all wrinkles on the periphery of the rim are eliminated by deformation of the material, at least in the region of the groove. In a highly preferred embodiment of the invention, the groove is formed on the underside of the rim (as illustrated in FIG. 4), although the wrinkle-removing groove could be formed on the upper surface of the container rim. By forming the groove on the underside of the rim as shown in FIG. 4, the upper surface of the rim is preserved and more than that, the entire surface of said rim is in principle kept entirely flat. As a result, it is much easier to seal a top lid afterwards, preserving the seal integrity of the resulting container.

[0062] The rib 6 has dimensions h (height) and w (width) chosen such that the height of the sealing groove 12 engraved in the rim is comprised between 0.1 mm to 3 mm and the width of the sealing groove 12 is comprised between 0.15 mm to 5 mm. The dimensions of the rib 6 may be slightly higher than the dimensions of the desired sealing groove 12 depending on the elasticity of the material constituting the container body. Moreover, the width of the rib 6 is preferably less than three times its height. In any case, according to the invention, the height of the rib 6 and the height of the sealing groove 12 should be higher than a maximum depth of the wrinkles of the container body 30, the wrinkles depth depending, among others, on the dimensions, the material and the forming conditions of the container body.

[0063] It should be understood that various changes and modifications to the presently preferred embodiments described herein will be apparent to those skilled in the art. Such changes and modifications can be made without departing from the spirit and scope of the present invention and without diminishing its attendant advantages. It is therefore intended that such changes and modifications be covered by the appended claims.