Cardboard tray for packaging food and modified atmosphere food packaging comprising said cardboard tray

Abstract

A cardboard tray (1) for packaging food comprising a tray body (10) formed from a sheet of compact cardboard and a lining film (20) disposed on the tray body (10) to come into contact with the food, wherein the tray body (10) has a lower base (11) with a continuous side wall (12) projecting vertically upwards and around the lower base (11), and wherein the continuous side wall (12) has a lower end (13) attached to the lower base (11) and an upper end (14) opposite the lower end (13), characterized in that the continuous side wall (12) has at its upper end (14) a peripheral flange (15) that is curved outwards from the cardboard tray (1).

Description

Cardboard tray for packaging food and modified atmosphere food packaging comprising said cardboard tray TECHNICAL SECTOR The present invention relates to cardboard trays used for packaging food in a modified atmosphere. PRIOR STATE OF THE ART In the food industry, it is common to package perishable foods, such as fish, meat, fruit, vegetables, cheeses, or similar products, in a modified atmosphere to keep the food fresh for a longer period of time, slowing down its decomposition and thus increasing its expiration date. In recent times, the use of flow pack technology for food packaging has increased. This technology allows food to be packaged in a modified atmosphere to extend its shelf life. A tray containing the food product is placed inside a hermetically sealed bag. Prior to sealing, a preservative gas is introduced into the bag. For example, ES2183161T3 shows a modified atmosphere package comprising an outer bag made of a flexible polymeric material, inside of which is an inner tray containing the food. The inner tray is thermoformed from a sheet of polymeric material, such as polystyrene foam, cellulose pulp, polyethylene, or polypropylene, and is coated with a liner film intended to come into contact with the food, thus preventing direct contact with the polymeric material of the tray. On the other hand, solid cardboard trays for food packaging are well-known for their good mechanical properties, enabling them to support food of a certain weight. These trays comprise a tray body formed from a sheet of solid cardboard and a lining film placed over the tray body to come into contact with the food. The tray body has a bottom base with a continuous side wall projecting vertically upwards and around the bottom base. This continuous side wall has a lower end attached to the bottom base and an upper end, opposite the lower end, terminating in a straight perimeter edge. These types of solid cardboard trays are typically coated with a food-grade transparent film, such as PVC. However, despite their good mechanical properties, they are unsuitable for modified atmosphere packaging (MAP) because the tray's straight perimeter edge has sharp edges created during the press-forming process of the solid cardboard sheet. In other words, the tray's perimeter edge ends up with irregularities caused by the various folds of the solid cardboard, inevitably producing a sharp edge that can damage the packaging material. Therefore, they cannot be used for MAP packaging. EXPLANATION OF THE INVENTION The object of the invention is to provide a cardboard tray for packaging food and a modified atmosphere food container comprising said cardboard tray, as defined in the claims. One aspect of the invention relates to a cardboard food packaging tray comprising a tray body formed from a sheet of compact cardboard and a coating film disposed on the tray body to come into contact with the food. The tray body has a lower base with a continuous side wall projecting vertically upwards and around the lower base, the continuous side wall having a lower end attached to the lower base and an upper end opposite the lower end, and wherein the continuous side wall has at its upper end a peripheral flange that is curved outwards from the cardboard tray. Another aspect of the invention relates to a modified atmosphere food container comprising a cardboard tray as defined above, and a bag that is hermetically sealed for packaging the modified atmosphere food, the cardboard tray being inside the bag. This design results in a cardboard tray with a non-cutting perimeter rim, making it suitable for packaging food in a modified atmosphere. This avoids the sharp edges inherent in conventional trays made from deep-drawn sheets of compact cardboard, which can puncture the packaging and cause gases to escape, thus eliminating the artificially extended shelf life of food products. Furthermore, the outward-curving perimeter rim of the proposed cardboard tray increases its rigidity, providing the necessary structural strength for many of the food packaging machines currently on the market. These and other advantages and features of the invention will become evident from the figures and the detailed description of the invention. DESCRIPTION OF THE DRAWINGS Figure 1 shows a top perspective view of the cardboard food packaging tray of the invention. Figure 2 shows a bottom perspective view of the cardboard tray in Figure 1. Figure 3 shows a plan view of the tray from the previous figures. Figure 4 shows an enlarged detail of the outward-curving perimeter rim of the cardboard tray. Figure 5 shows a perspective view of a modified atmosphere food container including a cardboard tray according to the invention. DETAILED EXPLANATION OF THE INVENTION The invention relates to a cardboard tray 1 for packaging food. The tray 1 comprises a tray body 10 formed from a sheet of compact cardboard and a lining film 20 arranged on the tray body 10 to come into contact with the food. There is no direct contact between the material of the tray body 10 and the food; instead, contact is established through the lining film 20, which is made of a material suitable for use in the food industry. For example, the lining film may be made of a polyethylene-based material, polypropylene, or another suitable material. The lining film 20 is arranged to at least partially cover the upper surface of the tray body 10 on which the food is placed. The tray body 10 has a lower base 11 with a continuous side wall 12 projecting vertically upwards and around the lower base 11, and said continuous side wall 12 has a lower end 13 attached to the lower base 11 and an upper end 14 opposite the lower end 13. According to the invention, the continuous side wall 12 has at its upper end 14 a perimeter flange 15 that is curved outwards from the cardboard tray 1. In this way, the upper end 14 of the continuous side wall 12 terminates in the curved perimeter flange 15, preventing the appearance of sharp edges or corners that may occur during the forming of the compact cardboard sheet, in addition to increasing the structural rigidity of the tray.For example, in a conventional compact cardboard tray, after the tray is formed, folds are generated in the cardboard, mainly at the top end 14 of the continuous side wall 12, which cause the appearance of sharp edges. As can be seen in the figures, the continuous side wall 12 is a continuous wall that extends around the entire perimeter of the tray body 10 and, therefore, the perimeter flange 15 also extends continuously around the entire perimeter of the tray body 10, increasing the structural rigidity of the tray body 10. The body of tray 10 is formed from a sheet of compact cardboard using a deep-drawing process at a temperature between 90-100°C, which facilitates folding the cardboard sheet to form the tray. For example, the press used to manufacture the cardboard trays may have a vertical feeder where sheets of compact cardboard accumulate. Transfer devices then load these sheets into a press with a first surface facing a second surface. This second surface, in use, works together to form the compact cardboard sheet and create the body of tray 10. The press surfaces have internal electrical heating elements to shape the cardboard sheet at the required temperature. Preferably, as shown in Figure 4, the perimeter flange 15 has a radius of curvature r of between 2 mm and 4 mm. Even more preferably, the radius of curvature r is 2.5 mm. This radius ensures that the folds in the cardboard produced during the forming of the compact cardboard sheet in the press do not create sharp edges or corners, and also increases the rigidity of the tray. Even more preferably, and also as shown in Figure 4, the continuous side wall 12 projects vertically from the lower base 11 at an angle of inclination X of between 15° and 80° with respect to a vertical plane Y to the lower base 11 of the tray body 10. Even more preferably, the angle of inclination X is 25°. The angle of inclination X together with the radius of curvature r are specially selected to obtain a tray with improved structural rigidity and without sharp edges. The lower base 11 of the tray body 10 may have a perimeter rib 16 projecting vertically downwards from the tray body 10 and connecting the lower base 11 to the continuous side wall 12. In this way, the perimeter rib 16 is positioned lower than the lower base 11 of the tray body 10. The rib 16 increases the structural rigidity of the continuous side wall 12 and also creates a channel around the entire perimeter of the lower base 11 that can channel away food debris from the food placed in the tray. Preferably, the perimeter rib 16 has a width V of between 4 mm and 10 mm. Preferably, the tray body 10 has a length A of between 80 mm and 405 mm and a width B of between 80 mm and 265 mm, and the lower base 11 of the tray body 10 has a length of between 73.5 mm and 398.5 mm and a width of between 73.5 mm and 258.5 mm. As shown in Figure 4, the continuous side wall 12 can have a height H of between 8 mm and 45 mm. The tray 1 shown in the example figures has a tray body 1 with a length A of 218 mm and a width B of 153 mm, a continuous side wall 12 with a height H of 10 mm, a perimeter flange 15 with a radius of curvature of 2.5 mm and an inclination angle X of 25º. The compact cardboard sheet used for the formation of the body of tray 10 has a thickness of between 0.7 mm and 1.1 mm and a grammage of between 600 g / m2 and 850 g / m2. Preferably, the compact cardboard sheet that forms the body of tray 10 comprises a multi-layer structure consisting of a printable coated top layer, an uncoated bottom layer, and a layer of cardboard fibers arranged between the coated layer and the uncoated layer. The coated top layer may be made of printable coated paper using offset printing techniques, with the food-grade coating film 20 being applied to this coated top layer. The uncoated bottom layer may comprise a white Kraft finishing material. The cardboard fiber layer comprises a mixture of recycled cardboard fibers and virgin cardboard fibers, for example with a percentage of recycled fibers of between 82-85% with respect to the total fibers. The following table shows the properties of a set of cardboard sheets that can be used for thermoforming the cardboard tray of the invention. Figure 5 shows a modified atmosphere food package comprising a cardboard tray 1 as defined in the preceding paragraphs and a bag 2 that is hermetically sealed for packaging the modified atmosphere food, the cardboard tray 1 being inside the bag 2. For food packaging, the food is first placed on cardboard tray 1 and tray 1 is inserted into bag 2. Next, a mixture of gases is introduced into bag 2 to create the modified atmosphere, and then bag 2 is hermetically sealed. Generally, the gases may include CO2, N2, and O2 to reduce oxidation, inhibit microbial growth, and maintain the freshness and color of the food contained in bag 2.

Claims

1. A cardboard tray (1) for packaging food comprising a tray body (10) formed from a sheet of compact cardboard and a lining film (20) disposed on the tray body (10) to come into contact with the food, wherein the tray body (10) has a lower base (11) with a continuous side wall (12) projecting vertically upwards and around the lower base (11), and wherein the continuous side wall (12) has a lower end (13) attached to the lower base (11) and an upper end (14) opposite the lower end (13), characterized in that the continuous side wall (12) has at its upper end (14) a peripheral flange (15) that is curved outwards from the cardboard tray (1).

2. A tray according to claim 1, wherein the peripheral flange (15) has a radius of curvature (r) of between 2 mm and 4 mm. 3.Tray according to claim 2, wherein the perimeter rim (15) has a radius of curvature of 2.5 mm.

4. Tray according to any of the preceding claims, wherein the continuous side wall (12) projects vertically from the lower base (11) at an angle of inclination (X) of between 15° and 80° with respect to a vertical plane (Y) to the lower base (11) of the tray body (10).

5. Tray according to the preceding claim, wherein the continuous side wall (12) projects vertically from the lower base (11) at an angle of inclination (X) of 25° with respect to the vertical plane (Y) to the lower base (11) of the tray body (10).

6. Tray according to any of the preceding claims, wherein the lower base (11) has a perimeter rib (16) projecting vertically downwards and connecting the lower base (11) to the continuous side wall (12). 7.Tray according to the preceding claim, wherein the perimeter rib (16) has a width (V) of between 4 mm and 10 mm.

8. Tray according to any of the preceding claims, wherein the tray body (10) has a length (A) of between 80 mm and 405 mm, and a width (B) of between 80 mm and 265 mm.

9. Tray according to any of the preceding claims, wherein the lower base (11) of the tray body (10) has a length of between 73.5 mm and 398.5 mm, and a width of between 73.5 mm and 258.5 mm.

10. Tray according to any of the preceding claims, wherein the continuous side wall (12) has a height (H) of between 8 mm and 45 mm.

11. Tray according to any of the preceding claims, wherein the tray body (10) formed from the compact cardboard sheet has a thickness of between 0.7 mm and 1.1 mm. 12.Tray according to any of the preceding claims, wherein the tray body (10) formed from the compact cardboard sheet has a basis weight of between 600 g / m² and 850 g / m².

13. Tray according to any of the preceding claims, wherein the tray body (10) comprises a multi-layer structure formed by a coated upper layer, an uncoated lower layer, and a layer of cardboard fibers disposed between the coated and uncoated layers.

14. Modified atmosphere food packaging comprising a cardboard tray (1) according to any of the preceding claims and a hermetically sealed bag (2), the cardboard tray (1) being inside the bag (2).