METHOD FOR SEALING THE TOP OF A CARDBOARD TRAY COATED WITH A PLASTIC SHEET AND A CARDBOARD TRAY FOR THE SAME
Patent Information
- Authority / Receiving Office
- MX · MX
- Patent Type
- Patents
- Current Assignee / Owner
- PEKEBL BV
- Filing Date
- 2022-07-13
- Publication Date
- 2026-05-19
AI Technical Summary
Existing methods for sealing a cover sheet onto a cardboard tray lined with a plastic sheet face challenges such as irregularities on the horizontal flange leading to potential leaks, especially in modified atmosphere packaging, which can cause the contents to deteriorate due to loss of modified atmosphere.
The method involves using a compressible support edge on the lower sealing tool element, allowing the plastic sheet liner to extend beyond the horizontal flange area, ensuring direct sealing without interference from cardboard parts, and using a compressible band of rubber or plastic to accommodate thickness variations and ensure a complete seal.
This approach achieves a reliable, leak-proof seal by accommodating thickness differences and irregularities, maintaining the modified atmosphere within the packaging.
Smart Images
Figure MX433898B0
Abstract
Description
The invention relates to a method for the top sealing of a cardboard tray coated with a plastic film, said method comprising the steps of: - provide a cardboard tray having a bottom, vertical walls arranged along the periphery of the bottom and a horizontal rim arranged along the upper edges of the vertical walls, wherein the inside of the cardboard tray is lined with a plastic sheet, said plastic sheet extending at least over the horizontal rim; - arranging the cardboard tray in a lower sealing tool element having a compressible support rim, wherein at least the horizontal rim is supported by the compressible support rim of the lower sealing tool element; - place a cover sheet over the cardboard tray arranged in the lower sealing tool element to cover the tray opening defined by the upper edges of the vertical walls; - Press a sealing tool element Ref. 335787 upper heated over the lower sealing tool element, where the cover sheet, the plastic foil lining and the horizontal flange are pressed together to seal the cover sheet onto the plastic foil lining along the horizontal flange. Such a method is known, for example, from document EP 2441697. Background of the Invention When the cover film is sealed over the horizontal rim of the cardboard tray, any irregularity on the upper surface of the rim presents a risk of leakage between the cover film and the plastic liner on the rim. A leak in the seal is particularly unacceptable for modified atmosphere packaging, as the contents will not benefit from the modified atmosphere due to the leak, resulting in faster deterioration. In EP 2441697, the risk of leakage is minimized by making the horizontal flange composed of flange parts that form a flat top surface. However, even at the transition between two adjacent flange parts, a risk of leakage occurs, especially when there is a small gap between the edges of two adjacent flange parts. EP 2687360 provides an improvement to reduce the risk of leaks by leaving a portion of the plastic foil lining loose from the horizontal flange, so that when the cover sheet is sealed, the loose portion of the plastic foil lining is in better contact with the foil cover and a better seal is achieved. EP 3130548 describes another solution to reduce the risk of leaks. This publication proposes providing a protrusion on the plastic film liner, extending over the transition between two flange portions of a horizontal circumferential flange. The bulge will ensure better contact between the plastic film liner and the cover sheet, thus mitigating the potential disadvantage of a gap between the flange portions at this transition. Brief Description of the Invention However, one objective is to provide an alternative method for sealing a cover sheet onto a cardboard tray lined with a plastic film, where the risk of leaks is reduced. This objective is achieved in accordance with the invention by a method in accordance with the preamble, the ML / a / ZUZZ / UUOO 11 which is characterized in that, in view of the pressing direction, the overlap area of the plastic sheet lining, the cover sheet and the compressible support edge extends at least partially outside the area of the horizontal flange. With the method according to the invention, it is ensured that during the sealing of the cover sheet to the cardboard tray, portions of the cover sheet and the plastic film liner are pressed between the lower sealing tool element and the heated upper sealing tool element, without any other parts present, particularly cardboard pieces, that could distort the pressure on both sheets. With the method according to the invention, the cover sheet and the plastic film liner are sealed directly by the upper and lower sealing tool elements without any intervening cardboard parts of the tray. The compressible support edge of the lower member of the sealing tool allows for accommodating thickness differences in the overlapping area of the plastic sheet lining, the cover sheet, and the compressible support edge extends at least partially outside the horizontal flange area and the area that does not extend outside the horizontal flange area. It is observed that the cover sheet could also be the plastic sheet lining of another piece of cardboard, such as a lid or another cardboard tray to form the so-called clamshell container. The other piece of cardboard with a plastic film coating, which seals onto the tray as a cover sheet, could also be provided in a manner similar to the cardboard tray of the invention. The upper sealing tool should also be provided with a compressible edge, so that the plastic film coating extending beyond the cardboard area can be pressed onto the plastic film coating of the cardboard tray of the invention. In a preferred embodiment of the method according to the invention, the compressible support edge of the lower sealing tool is a compressible rubber or plastic band. Such a compressible band of rubber or plastic deforms easily and accommodates changes in thickness and even allows relatively small areas extending outside the horizontal flange area to be sufficiently supported by the lower member of the sealing tool to allow a reliable seal of the plastic sheet lining with the cover sheet. In another preferred embodiment of the method according to the invention, when the upper sealing tool element is pressed onto the lower sealing tool element, the compressible rubber or plastic strip abuts against the plastic liner sheet where, in view of the direction of pressure, the overlap area of the plastic liner sheet, the cover sheet, and the compressible support edge extend at least partially outside the area of the horizontal flange. If, for example, the plastic film lining extends around all sides of the tray beyond the outer circumference of the horizontal flange, a completely closed peripheral seal is obtained between the cover sheet and the plastic film lining, a seal that is not affected by any irregularity in the cardboard of the horizontal flange. The invention further relates to a cardboard tray for use in the method according to the invention, said cardboard tray comprising: - a fund; - vertical walls arranged along the periphery of the bottom; - a horizontal flange arranged along the upper edges of the vertical walls; and - plastic sheet coated against the inside of the cardboard tray, plastic sheet extending at least over the horizontal flange and extending, in a direction perpendicular to the horizontal flange, at least partially outside the area of the horizontal flange. In a preferred embodiment of the cardboard tray according to the invention, the plastic film extends from the inside of the cardboard tray, over the horizontal flange, and at least partially beyond the outer edge of the horizontal flange. With this embodiment, a completely closed peripheral seal between the cover film and the plastic film lining can be obtained using the method of the invention. In another preferred embodiment of the cardboard tray according to the invention, the cardboard tray is folded from a piece of cardboard, wherein the horizontal flange is composed of horizontal flange portions, each of which is disposed on the upper edge of a respective vertical wall. Folding a cardboard tray from a piece of cardboard allows the tray to be formed, filled with contents, and sealed with a cover sheet all in a single production line. Preferably, the cardboard piece is folded by pushing it into a mold, after which a heated plastic sheet is laminated onto the folded cardboard piece using a pressure differential, as described, for example, in EP 2441697. Due to the cuts and folds in the cardboard tray, low pressure can build up beneath the heated plastic sheet, while higher pressure is present above it. This allows the plastic sheet to be drawn into the cardboard tray once a sufficient pressure differential exists.When specific suction ports are not provided, the cuts can function as pressure valves, so that low pressure enters the cardboard tray suddenly, once a certain threshold is reached. However, it is also possible to form the cardboard tray by gluing cardboard parts together, whether completely separate parts or single-piece parts. In another preferred embodiment of the cardboard tray according to the invention, at the transition from one horizontal flange portion to an adjacent horizontal flange portion, an opening is provided in the horizontal flange, and the plastic sheet lining covers such an opening. The main dimension of the opening is substantially larger than the small gap created when two horizontal flanged parts meet. The main dimension of the opening is preferably greater than 5 millimeters. This opening allows the compressible support edge of the lower sealing tool element to penetrate the opening and hold the plastic film liner covering it, thus achieving a good seal with the cover film. In yet another embodiment of the cardboard tray according to the invention, between two vertical walls with a horizontal flange portion disposed therein, a vertical wall without a horizontal flange portion is provided and wherein at least part of the upper edge of the vertical wall without a horizontal flange portion is separated from the horizontal flange, so that an opening is provided between the vertical wall and the horizontal flange. The opening formed between the vertical wall and the horizontal flange also allows the compressible support edge to penetrate the opening to support the plastic sheet lining that covers this opening and allow a reliable seal with the cover sheet. In a still further preferred embodiment of the cardboard tray according to the invention, in view of a direction perpendicular to the bottom, the shape of the bottom is an octagon having four sets of parallel edges of equal length. In yet another preferred embodiment of the cardboard tray according to the invention, at least one of the vertical walls is provided with a flap disposed on the edge of the vertical wall bordering an adjacent vertical wall, wherein the flap overlaps and rests on such adjacent vertical wall, wherein the flap is provided with an opening, which is covered by the plastic sheet lining, such that the plastic sheet lining is joined to the adjacent vertical wall through the opening in the flap. The opening in the flap allows for positional locking of the flap against the vertical wall it overlaps. This positional locking is achieved by the plastic film liner, which is laminated to the inside of the cardboard tray and thus extends over the flap and the opening. The plastic film liner adheres to the vertical walls, the bottom, the flap, and, through the opening in the flap, to the portion of the vertical wall covered by the flap. This ensures that the tray's shape is reliably retained by the plastic film liner, without the need to separately adhere the flaps to the vertical walls. Brief Description of the Figures These and other features of the invention will be explained together with the accompanying figures. Figures 1A-1C schematically show the steps of one modality of the method in accordance with the invention. Figures 2A and 2B show respectively a perspective view and a cross-section of a first embodiment of a cardboard tray according to the invention. Figures 3A and 3B show respectively a perspective view and a cross-section of a second modality of a cardboard tray in accordance with the invention. Figures 4A and 4B show respectively a perspective view and a cross-section of a third modality of a cardboard tray according to the invention. Detailed Description of the Invention Figure 1A shows a first stage of one embodiment of the method according to the invention. In this stage, a cardboard tray 1 is provided. The cardboard tray 1 has a bottom 2, vertical walls 3, and a horizontal flange 4 disposed on the upper edges of the vertical walls 3. The inside of tray 1 is lined with a plastic sheet 5, which extends over the bottom 2, the vertical walls 3, the horizontal rim 4 and extends beyond the outer edge of the horizontal rim 4. In Figure IB, the cardboard tray 1 rests with its horizontal flange 4 on a lower sealing tool member 6, which is provided with a compressible support edge 7 made of a compressible rubber band. At this stage, a cover sheet 8 is placed over the cardboard tray 1 and a heated top sealing tool element 9 is placed there. Figure 1C shows the next step of the method according to the invention. The heated upper sealing tool member 9 is pressed down onto the cover sheet 8, the plastic sheet lining 5, the horizontal flange 4, and the lower sealing tool member 6. Due to the pressure exerted by the upper sealing tool element 9, the compressible rubber band 7 will deform and ensure that the portion of the plastic film lining 5 that extends beyond the outer edge of the horizontal flange 4 is also pressed against the cover sheet 8, so that a reliable seal is obtained between the plastic film lining 5 and the cover sheet 8. Figure 2A shows a perspective view of a first embodiment of a cardboard tray 20 according to the invention, which is folded from ML / a / ZUZZ / UUOO 11 a piece of cardboard. The tray 20 has a bottom 21 with vertical walls 22, 23 arranged along the periphery 24 of the bottom 21. A horizontal flange 25, 26 is composed of horizontal flange portions 25, 26, which are arranged on the upper edge of a respective vertical wall 22, 23. The vertical wall 22 is provided with a flap 27, which has an opening 28. The flap 27 overlaps and rests on the adjacent vertical wall 23. Figure 2B shows a cross-section of the cardboard tray 20 arranged in a sealing tool with a heated upper sealing tool element 9 and a lower sealing tool element 6 with a compressible rubber band 7, as described in Figures 1A-1C. The cardboard tray 20 is lined on the inside with a plastic sheet 29, which extends over the horizontal flange 25 and beyond its outer edge. Due to the compressible rubber band 7, the plastic sheet 24 also rests outside the horizontal flange 25, thus achieving a reliable seal with the cover sheet 30. Figure 3A shows a perspective view of a second embodiment of a cardboard tray 40 according to the invention. The tray 40 is folded from a piece of cardboard and has a bottom 41, vertical walls 42, and horizontal rim portions 43, similar to the embodiment of Figures 2A and 2B. At the transition 44 of the adjacent horizontal flange portions 43, an opening 45 is provided. As shown in Figure 3B, this opening 45 is covered by a plastic sheet lining 46, which extends from the bottom 41, over the vertical walls 42 and the horizontal flange 43. When the cardboard tray 40 is compressed together with a cover sheet 47 between the lower and upper members of the sealing tool 6, 9, the compressible rubber band 7 is deformed in the opening 45, so that the part of the plastic sheet lining 46 covering the hole 45 is also sufficiently supported to obtain a reliable seal with the cover sheet 47. Figure 4A shows a perspective view of a third embodiment of a cardboard tray 50 according to the invention. The cardboard tray 50 has an octagonal bottom 51 with vertical walls 53, 54, 55 along its periphery 52. A horizontal flange portion 59, 60 is arranged on the upper edge 56, 58 of the vertical walls 53, 55 respectively. The vertical wall 54, arranged adjacent to both vertical walls 53, 55, does not have a horizontal flange portion, so that an opening 63 is formed. The vertical wall 53 has a flap 61 with an opening 62, which overlaps and butts against the vertical wall 54. As shown in Figure 4B, the inside of the tray 50 is lined with a plastic sheet 64, which also runs over the flap 61 and adheres through the opening 62 to the underlying vertical wall 54, so that the folded cardboard retains its shape. When the cardboard tray 50 is placed in a sealing tool having a heated upper sealing tool element 9 and a lower sealing tool element 6 with a compressible rubber band 7, the rubber band 7 will deform at the opening 63. As a result, the deformed rubber band 7 will also support the plastic film liner 64 extending over the opening 63, so that a good seal with the cover film 65 is also obtained in this position. It is hereby stated that, as of this date, the best method known to the applicant for putting the aforementioned invention into practice is the one that is clear from the present description of the invention.
Claims
1. A method for the top sealing of a cardboard tray lined with a plastic film, comprising the steps of: - providing a cardboard tray having a bottom, vertical walls arranged along the periphery of the bottom, and a horizontal flange arranged along the upper edges of the vertical walls, wherein the interior of the cardboard tray is lined with a plastic film, the plastic film extending at least over the horizontal flange; - placing the cardboard tray in a lower sealing tool element having a compressible support edge, wherein at least the horizontal flange is supported by the compressible support edge of the lower sealing tool element; - placing a cover sheet over the cardboard tray disposed in the lower sealing tool element to cover the opening of the tray defined by the upper edges of the vertical walls;- pressing a heated upper sealing tool element onto the lower sealing tool element, wherein the cover sheet, the plastic film lining and the horizontal flange are pressed together to seal the cover sheet onto the plastic film lining along the horizontal flange, characterized in that, in view of the direction of pressure, the overlap area of the plastic film lining, the cover sheet and the compressible support edge extends at least partially outside the area of the horizontal flange.
2. Method according to claim 1, characterized in that the compressible support edge of the lower sealing tool is a compressible rubber or plastic band.
3. Method according to claim 2, characterized in that, when the upper element of the sealing tool is pressed upon the lower element of the sealing tool, the compressible rubber or plastic strip abuts against the plastic lining sheet in view of the direction of pressure, the overlapping area of the plastic sheet lining, the cover sheet and the compressible support edge extend at least partially outside the area of the horizontal flange.
4. Cardboard tray for use in the method according to any of the preceding claims, characterized in that it comprises: - a bottom; - vertical walls arranged along the periphery of the bottom; - a horizontal flange arranged along the upper edges of the vertical walls; and - a plastic sheet coated against the inside of the cardboard tray, the plastic sheet extending at least over the horizontal flange and extending, in a direction perpendicular to the horizontal flange, at least partially outside the area of the horizontal flange.
5. Cardboard tray according to claim 4, characterized in that the plastic sheet extends from the inside of the cardboard tray, over the horizontal flange and at least partially beyond the outer edge of the horizontal flange.
6. Cardboard tray according to claim 4 or 5, characterized in that it is folded from a piece of cardboard, wherein the horizontal flange is composed of horizontal flange portions, each of which is arranged on the upper edge of a respective vertical wall.
7. Cardboard tray according to claim 6, characterized in that at the transition from a horizontal flange portion to an adjacent horizontal flange portion an opening is provided in the horizontal flange, and wherein the plastic sheet lining covers such opening.
8. Cardboard tray according to claim 6, characterized in that between two vertical walls with a horizontal flange portion disposed therein, a vertical wall without a horizontal flange portion is disposed and wherein at least part of the upper edge of the vertical wall without a horizontal flange portion is separated from the horizontal flange, so that an opening is provided between the vertical wall and the horizontal flange.
9. Cardboard tray according to any of the preceding claims 4-8, characterized in that, viewed from a direction perpendicular to the bottom, the shape of the bottom is an octagon having four sets of parallel edges of equal length.
10. Cardboard tray according to any of the preceding claims 4-9, characterized in that at least one of the vertical walls is provided with a flap disposed on the edge of the vertical wall bordering an adjacent vertical wall, wherein the flap overlaps and rests on such adjacent vertical wall, wherein the flap is provided with an opening, which is covered by the plastic sheet lining, such that the plastic sheet lining is joined to the adjacent vertical wall through the opening in the flap.