GB2541869A

GB2541869A - Packaging tray

Info

Publication number: GB2541869A
Application number: GB1514995.8A
Authority: GB
Inventors: Andersson Stig-Erik
Original assignee: CC PACK AB
Current assignee: CC PACK AB
Priority date: 2015-08-24
Filing date: 2015-08-24
Publication date: 2017-03-08
Also published as: GB201514995D0

Abstract

A packaging tray 1 including a paperboard layer and a plastic layer. The tray has a bottom wall 3, side wall 5 surrounding the bottom wall and a rim flange 7. The side wall has at least one curved portion 13, 15. The flange extends around an upper access opening. A central portion of the bottom wall has a first thickness (t1, fig 2), and the flange has a second thickness (t2), the second thickness being less than the first thickness. The curved portion may have several scores (103, 105, fig 4) transverse to the curved portion. The interspace between scores may form an angle (o) in the range of 1.5 to 3 degrees. The second thickness is formed by applying pressure to the tray. The tray is manufactured with use of a press tool (201, fig 5a). The overall manufacturing apparatus (400, fig 7) includes a cutting unit (420), a scoring unit (430) and a forming unit (440).

Description

PACKAGING TRAY TECHNICAL FIELD

The present disclosure relates to a packaging tray of a composite material comprising a paperboard layer and a plastic layer. The disclosure further relates to a blank, a container for foodstuff, a method, a press tool and an apparatus for manufacturing the packaging tray.

BACKGROUND

Packaging tray type containers made of a composite material comprising paperboard and plastic, e.g. a plastic-coated paperboard, are commonly used as consumer containers for food. Such containers are beneficial, since the food cannot only be stored in the container but may also be heated directly in the packaging tray in e.g. an oven or a micro-wave oven. The container is able to withstand the high temperatures, which may arise during heating of the food. Further, the container also insulates, such that the consumer may grip the container, with the warm food in it, without over-heating his or her fingers.

The packaging tray commonly comprises a bottom wall, a side wall and a rim flange. The packaging tray may be manufactured by re-shaping a flat blank. The packaging tray may be covered by a cover, membrane or lid sealed to the rim flange. It is then desirable that the connection between the packaging tray and the cover, membrane or lid is gas-tight.

It is known to provide an inert gas to the inside of the container before sealing the cover or lid, e.g. carbon dioxide or nitrogen, in order to diminish growth of bacteria and other microorganisms and/or to preserve a desired colour of the food stored in the container. An example of such a system is modified atmosphere packaging, MAP. In that case it is desirable that the material of the cover, membrane or lid is gas-tight.

Document WO 00/15431 discloses a packaging tray made of a plastic-coated paperboard. The thickness of the plastic coating is selected such that it has a certain minimum thickness. The “very thick coating” ensures a smoothing of local unevenness at the corner parts of the packaging tray.

However, the use of a “very thick coating” may increase the cost of the packaging trays.

Document WO 2007/036598 teaches that in the parts of the blank to be compressed, the blank is made thinner on its side opposite to the plastic coating, such that the plastic coating double-folds in the compressions and seals to itself.

However, the process of making the blank locally thinner resuts in an extra step in the manufacturing process.

Hence, it is desirable to provide a packaging tray, which may be gas-tightly sealed with a cover, membrane or lid and which packaging tray yet is simple and/or cost efficient to manufacture.

SUMMARY

The object of the present disclosure is to overcome or ameliorate at least one of the disadvantages of the prior art, or to provide a useful alternative.

The object above may be achieved by the subject-matter of claim 1. Embodiments are set forth in the appended dependent claims, in the following description and in the drawings.

Thus, according to the present invention there is provided a packaging tray of a composite material comprising a paperboard layer and a plastic layer. The packaging tray comprises a bottom wall, a side wall surrounding the bottom wall and a rim flange, the side wall comprising at least one curved portion. The bottom wall and the side wall form a holding volume with an upper access opening. The rim flange extends around the upper access opening. A central portion of the bottom wall has a first thickness and the rim flange has a second thickness, which is less than the first thickness.

The packaging tray is intended to be sealed by a cover, membrane or lid, e.g. in the form of a plastic film, in order to form a gas-proof container, e.g. a consumer container for foodstuff. The packaging tray may e.g. be used for modified atmosphere packaging, MAP.

The packaging tray may have a holding volume from 10 cm3 to 4 dm3.

The rim flange may have a width of at least 5 mm, preferably at least 8 mm. As an option, the rim flange may comprise one or more widened portions, which makes the packaging tray easy to grip. Purely as an example, if two widened portions are used, they may be located at opposite sides of the upper access opening. The widened portions may have a width in the range from 10 to 50 mm, preferably in the range from 20 to 30 mm.

The side walls may have a height in the range from 10 mm to 100 mm, preferably in the range from 20 mm to 70 mm, more preferably in the range from 25 to 60 mm, most preferably in the range of from 30 mm to 45 mm. These height ranges have been found to be appropriate for packaging trays intended to be used for the above-mentioned kind of consumer containers for food, wherein the food is not only stored in the container but may also be heated directly in the packaging tray in e.g. an oven or a micro-wave oven.

The bottom wall and the side wall form a holding volume with an upper access opening. The rim flange extends continuously around the upper access opening. The holding volume is adapted to receive and contain the product, e.g. foodstuff, which is to be stored in the packaging tray. The rim flange constitutes an appropriate receiving surface when the packaging tray is provided with the cover, membrane or lid, such that a gas-tight connection between the packaging tray and the cover, membrane or lid is obtainable. The tightness of the connection may be tested by a penetrant, e.g. according to the method ISO 3452: Non-destructive testing - Penetrant testing.

The bottom wall comprises a central portion, which typically is substantially flat. The central portion may transfer, directly or gradually, into the side wall. As an option, the bottom wall may further comprise an edge portion surrounding the central portion, which edge portion e.g. may form a recess around the central portion. The edge portion may help to increase the stability of the packaging tray. The edge portion may transfer, directly or gradually, into the side wall. As an option, the central portion, the side wall and/or the optional edge portion may be embossed with one or more embossing patterns. The first thickness is however determined in an unembossed area.

The composite material may be provided in the form of a continuous web or may be provided as individual sheets of material. The composite material may have a substantially even thickness before being formed into a packaging tray as disclosed herein.

The composite material comprises at least one paperboard layer and at least one plastic layer. The plastic layer may be a film or a coating. The plastic layer may be coated on the paperboard layer or the two layers may be laminated together. The composite material may also comprise additional layers, such as one or more extra paperboard layer(s) and/or one or more extra plastic layer(s) and/or coatings, metal foil, etc. The plastic layer may be situated facing inwards, e.g. towards the foodstuff, while the paperboard layer may be arranged facing outwards.

As used herein, a paperboard material is predominantly made from cellulose fibres or paper fibres. It may be provided in the form of a continuous web or may be provided as individual sheets of material. The paperboard material may be a single-ply or multi-ply material. It may be formed by a multi-ply headbox or by utilizing a plurality of different headboxes in a board machine.

The paperboard material may be coated, printed, embossed, etc. and may comprise fillers, pigments, binders and other additives as known in the art. The paperboard materials as disclosed herein may also be referred to as cardboard or carton materials. The paperboard material may have a thickness in the range of from 200 pm to 800 pm. Thickness is determined according to the method ISO 534: Paper and board - Determination of thickness, density and specific volume. The pending version is from 2011.

The plastic layer may include or consist of thermoplastic polymers. The plastic layer may have a thickness in the range in the range from 15 pm to 150 pm, preferably in the range from 25 pm to 100 pm, more preferably in the range from 30 pm to 75 pm.

The material of the lid, membrane or cover, which is intended to be put onto the packaging tray in order to form the container, may be gastight or gas-permeable. A gastight lid, membrane or cover may be manufactured from any material or material combination suitable for providing a gastight sealing of a compartment delimited by the lid, membrane or cover, such as aluminium foil, silicon-coated paper, plastic film, or laminates thereof. A gastight lid, membrane or cover is advantageous when the content stored in the packaging container is sensitive to air and/or moisture, and it is desirable to avoid contact of the content with ambient air. The barrier properties of the container may be designed to meet different requirements of tightness depending on the goods which is packaged in the packaging container. It may also be desirable to keep fragrances and aromas in the container and prevent the packaged contents from taking up scents and flavours from the ambient air. Gas tightness may be determined by the method ASTM F1927: Standard Test Method for Determination of Oxygen Gas Transmission Rate, Permeability and Permeance at Controlled Relative Humidity Through Barrier Materials Using a Coulo-metric Detector.

The material of the lid, membrane or cover is selected such that it is able to form the gastight connection with the material of rim flange. The material may include or consist of thermoplastic polymers, e.g. similar to those of the plastic layer of the packaging tray.

As mentioned above, the central portion of the bottom wall has a first thickness and the rim flange has a second thickness, which is less than the first thickness. The second thickness may be less than or equal to 98% of the first thickness. Preferably, the second thickness may be less than or equal to 96% of the first thickness. More preferably, the second thickness may be less than or equal to 94% of the first thickness. Most preferably, the second thickness may be less than or equal to 92% of the first thickness. The second thickness may be from 20 pm to 60 pm less than the first thickness, preferably from 30 pm to 50 pm less than the first thickness. Thickness is determined according to the method ISO 534: Paper and board - Determination of thickness, density and specific volume. The pending version is from 2011.

The side wall comprises at least one curved portion, which has a curvature direction. The curvature direction of the side wall is perpendicular to the height direction of the packaging tray. The curvature direction of the side wall extends horizontally. The radius of curvature as seen in the curvature direction may be the same for the whole curved portion. For example, there may be two curved portions each forming a semi-circle with two straight portions therebetween, giving the packaging tray a substantially oval shape. There may also be a single curved portion forming a circle giving the packaging tray a round shape. Alternatively, the radius of curvature may vary along the curvature direction, e.g. being less at the ends of the packaging tray than at a transition between curved and straight portions. The packaging tray may e.g. have the shape of an ellipse. As yet an alternative, the packaging tray may have a substantial polygonal shape, e.g. three curved portions with straight portions therebetween forming a general triangular packaging tray, four curved portions each forming 1/4-circle with four straight portions therebetween forming a general rectangular or square packaging tray, six curved portions each forming 1/6-circle with six straight portions therebetween forming a general hexagonal packaging tray, etc.

The side wall may be outwardly angled in relation to the bottom wall by an angle a, which may be in the range from 0° to 60°, preferably in the range from 8° to 45°.

The rim flange may be angled slightly upwards or downwards by an angle β, e.g. being in the range from -10° to +10°, preferably in the range from -5° to 5°. In particular, the angle β may be 0°, i.e. the rim flank is substantially horizontal.

The at least one curved portion of the side wall may comprise a plurality of local compressions constituting scores, which are substantially transverse to the curvature direction of the curved portion of side wall. An interspace between two consecutive scores forms an angle o being in the range from 1.5° to 3°, preferably in the range from 2° to 2.5°, the angle o being determined at an outer portion of the side wall, which outer portion faces the rim flange.

When a flat blank is pressed to form the three-dimensional packaging tray, folds or wrinkles may be formed in the composite material. By providing the scores described herein, the positions of the scores are purposely selected. Thereby, the risk of creating undesired wrinkles may be avoided, or at least considerably reduced, when forming the packaging tray. This is beneficial since such wrinkles may make it difficult to obtain the appropriate receiving surface on the rim flange providing the gas-tight connection. The characteristics of the scores e.g. number of scores, their length, width, depth, degree of compression of the composite material, and/or positions may be selected to contribute to obtaining the appropriate receiving surface for the cover, lid or membrane to provide the gas-tight connection. Thereby characteristics of the packaging tray, such as the size, the material, and the radius of curvature of the side wall may be taken into account. For example, there may be more scores present, the more the side wall is curved.

Purely as an example, there may be both long scores and short scores. The scores may be regularly distributed or irregularly distributed along the curvature direction. The terms long and short are used in a relative manner to describe the relative differences in length. The scores may be substantially transverse to the curvature direction of the at least one curved portion of the side wall of the packaging tray. The long scores may extend substantially the whole height of the side wall, while the short scores may extend only for a portion of the side wall. The short scores may have a length being in the range from 20% to 90% of the long scores, preferably in the range from 40% to 80% of the long scores, more preferably in the range from 50% to 70% of the long scores.

If using both long and short scores, there may also also another angle i determinable at an inner portion of the side wall corresponding to the interspace between the long scores. If every second score is long and every second is short, and assuming the scores are equidistantly placed, the angle i will be twice the angle o.

The above-mentioned scores are located at the at least one curved portion of the side wall of the packaging tray. There may in addition be scores located at the straight portions of the side wall, e.g. close to the transition between the curved portion and the straight portions. There are normally no scores at the bottom wall.

An inner curvature of the rim flange forming the upper access opening may have a minimum radius of curvature greater than or equal to 40 mm, preferably greater than or equal to 45 mm, more preferably greater than or equal to 50 mm, most preferably being in the range from 53 to 55 mm. These curvatures have been found appropriate in order to obtain the above-mentioned desired gas-tight sealing of the packaging tray with a cover, lid or membrane. In addition, the inner delimitation of the rim flange may comprise straight portions, e.g. if the packing tray has any of the oval, triangular, rectangular or hexagonal shapes mentioned above.

According to the present invention there is provided a blank of a composite material comprising a paperboard layer and a plastic layer, which blank is adapted for manufacturing a packaging tray as described herein. The blank may comprise a plurality of local compressions constituting scores. The composite material, as well as the scores, is/are described above in conjunction with the packing tray.

The blank may have a substantially even thickness. However, if provided with scores, the thickness may be less within the scores. As mentioned above, the composite material may be provided in the form of a continuous web or may be provided as individual sheets of material.

According to the present invention there is provided a container for foodstuff, which container comprises a packaging tray as described herein and the cover, membrane or lid, as described herein, adapted to be sealed to the rim flange, thereby providing a gas-tight connection between the cover, membrane or lid and the packaging tray.

According to the present invention there is provided a method for manufacturing a packaging tray of a composite material comprising a paperboard layer and a plastic layer. The packaging tray comprises a bottom wall, a side wall surrounding the bottom wall, and a rim flange. The bottom wall and the side wall form a holding volume with an upper access opening, with the rim flange extending around the upper access opening. The method comprises - providing a blank suitable for forming a packaging tray of the composite material, and - forming the packaging tray from the blank by applying heat and pressure, wherein the pressure is applied such that a central portion of the bottom wall is compressed to a first thickness and the rim flange is compressed to a second thickness, which is less than the first thickness.

By pressing the rim flange harder, it may be ascertained that the receiving surface for the cover, membrane or lid is flat enough to be able to provide the gas-tight connection. However, if pressing too hard, there may be a risk that the composite material is, at least partly, damaged.

The step of forming may be performed by means of a heatable press tool having a locally selectable pressure. The pressure may be applied in such a way, that a first pressure applied in a first zone, corresponding to the central portion of the bottom wall, may be less than a second pressure applied in a second zone, corresponding to the rim flange. In order to control the local pressure, the local gap width may be adjusted, e.g. by means of utilizing one or more spacers, e.g. in form of metal shims. A first gap width of the first zone is used to obtain the first thickness mentioned above and a second gap width of the second zone is used to obtain the second thickness mentioned above. However, the differences between the first and second gap widths may be larger than the difference between the first and second thicknesses, e.g. up to 200 pm.

Blanks may be prefabricated at a different location and/or at a different time from the forming of the packaging trays. Alternatively, blanks may be formed in-line with the forming of the packaging trays. In that case, the step of providing a blank suitable for forming a packaging tray of the composite material may comprise cutting and scoring the blank. The cutting and the scoring of the blank may be performed as two separate steps, but they are preferably combined into one step, such that they are performed at the same time and with the same tool.

The step of scoring may comprise providing a plurality of local compressions constituting scores, which in the packaging tray are substantially transverse to the curvature direction of the curved portion of the side wall, preferably an interspace between two consecutive scores forming an angle being in the range from 1.5° to 3°, preferably in the range from 2° to 2.5°, the angle being determined at an outer portion of the side wall, which outer portion faces the rim flange.

The step of scoring may comprise applying local pressure to the board layer side of the composite material at the positions corresponding to the scores. As an alternative, local pressure may be applied to the plastic layer side of the composite material at the positions corresponding to the scores, or to both sides at the same time.

The step of forming may comprise shaping the packaging tray, such that the rim flange forming the upper access opening has a minimum radius of curvature greater than or equal to 40 mm, preferably greater than or equal to 45 mm, more preferably greater than or equal to 50 mm, most preferably being in the range from 53 to 55 mm.

According to the present invention there is provided a press tool for manufacturing a packaging tray as disclosed herein from a blank as disclosed herein. The press tool comprises a first member and a second member, adapted to form a gap between each other, in which gap the packaging tray is to be formed. The gap comprises a first zone having a first gap width, adapted to form a central portion of a bottom wall of the packaging tray, and a second zone having a second gap width, at least partly being located outside of the first zone and adapted to form a rim flange of the packaging tray. At least one of the first and second members may comprise a first portion adapted to form the first zone and a second portion adapted to form the second zone, the second portion being displaceable in relation to the first portion, such that the first gap width and the second gap width are selectable independent of each other. The shapes of the first and second members are selected in order to obtain the desired three-dimensional shape of the packaging tray.

The first gap width is used to obtain the first thickness mentioned above and the second gap width is used to obtain the second thickness mentioned above. However, the differences between the first and second gap widths may be larger than the difference between the first and second thicknesses, e.g. up to 200 pm.

At least one other zone of the gap may be adapted to form an edge portion of the bottom wall and/or the side wall. Such another zone may be located in between the first and second zone. Purely as an example, a third zone being adapted to form the side wall may be located outside the first zone but inside the second zone. The third zone may the same gap width as the first zone. The side wall may be formed in contact with the first and/or second member of the press tool.

The press tool may be adapted to be heated, such that it my apply pressure and heat at the same time.

The first member may be a male member and the second member may be a female member. In that case, the male member may comprise the above-mentioned first and second portions. As an alternative, the female member may comprise the above-mentioned first and second portions. As yet an alternative, both the male and the female member may comprise the above-mentioned first and second portions.

The press tool may further comprise at least one spacer, e.g. a metal shim, which is adapted to adjust a relative position of the first portion in relation to the second portion. The spacer may be adapted to be placed between the second portion and an applied press force. As an alternative, the spacer may be placed between the first and second portions.

As an option, at least one of the first and the second member may comprise a patterning plate adapted to provide the central portion, the side wall and/or the optional edge portion with one or more patterns. The patterning plate may e.g. be in contact with the bottom of the central portion of the bottom wall the packaging tray. The patterning plate may be provided with an embossing pattern. As an alternative, the patterning plate may be flat.

The patterning plate may be exchanged without changing the rest of the press tool, in case another embossing pattern is desired.

According to the present invention there is provided an apparatus for manufacturing a packaging tray of a composite material comprising a paperboard layer and a plastic layer. The apparatus is particularly suitable for manufacturing the packaging tray as disclosed herein. The packaging tray comprises a bottom wall, a side wall surrounding the bottom wall and a rim flange. The apparatus comprises - a cutting unit, adapted for cutting a blank suitable for forming a packaging tray from the composite material, - a scoring unit, adapted to provide a plurality of local compressions constituting scores to the blank, the scoring unit preferably being combined with the cutting unit into one unit, - a forming unit, adapted to form the packaging tray from the blank by applying heat and pressure, the forming unit comprising a press tool as described herein.

The scoring unit may be shaped to provide a plurality of local compressions constituting scores as described herein.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will hereinafter be further explained by means of non-limiting examples with reference to the appended drawings wherein:

Fig. 1 is a top view of a packaging tray according to the invention,

Fig. 2 is a cross-sectional view of the packaging tray of Fig. 1 along line the ll-ll,

Fig. 3 is a cross-sectional view of the packaging tray of Fig. 1 along line the Ill-Ill,

Fig. 4 illustrates a blank for manufacturing a packaging tray according to the invention,

Fig. 5A-B illustrate a press tool for manufacturing a packaging tray according to the invention,

Fig. 5C illustrates an alternative press tool for manufacturing a packaging tray according to the invention,

Fig. 6 illustrates a method for manufacturing a packaging tray according to the invention, and

Fig. 7 illustrates an apparatus for manufacturing a packaging tray according to the invention,

It should be noted that the appended drawings are not necessarily drawn to scale and that the dimensions of some features of the present invention may have been exaggerated for the sake of clarity.

DETAILED DESCRIPTION

The invention will, in the following, be exemplified by an embodiment. It should however be realized that the embodiment is included in order to explain principles of the invention and not to limit the scope of the invention, defined by the appended claims.

Figure 1 illustrates a packaging tray 1 according to the invention. Figure 2 shows a cross-sectional view along the line ll-ll. Figure 3 shows a cross-sectional view along the line Ill-Ill. Figure 1 further illustrates a cover 35. The packaging tray 1 and the cover 35 together form a container 37 according to the invention.

The packaging tray 1 is made of a composite material comprising at least one paperboard layer and at least one plastic layer. The plastic layer may be coated on the paperboard layer or the two layers may be laminated together. The plastic layer may have a thickness in the range in the range from 15 pm to 150 pm, preferably in the range from 25 pm to 100 pm, more preferably in the range from 30 pm to 75 pm. The composite material may also comprise additional layers, such as one or more extra paperboard layer(s) and/or one or more extra plastic layer(s).

The packaging tray 1 comprises a bottom wall 3, a side wall 5 surrounding the bottom wall 3 and a rim flange 7.

The bottom wall 3 comprises a central portion 9, which is substantially flat and an edge portion 11 surrounding the central portion 9. In the illustrated embodiment, the edge portion 11 forms a recess around the central portion 9, which helps to make the packaging tray 1 more stable. As an option, not illustrated, the central portion 9 and/or the edge portion 11 may be embossed with one or more patterns.

The side wall 5 comprises at least one curved portion, which has a curvature direction, denoted by curved arrows in Figure 1. The curvature direction is perpendicular to the height direction of the packaging tray 1. The curvature direction extends horizontally. In the illustrated embodiment, there are two curved portions 13, 15 with two straight portions 17, 19 therebetween, since the packaging tray 1 has a substantially oval shape. Each curved portion 13, 15 substantially forms a semi-circle. When seen as a cross-section through the packaging tray 1, the changeover from the edge portion 11 of the central portion 9 to the side wall 5 occurs at the point P wherein the side wall 5 protrudes from an imaginary surface S, on which the packaging tray 1 is resting. See Figure 2. The side wall 5 thus includes a vertically curved transition portion 21. The side wall 5 is outwardly angled by an angle a of about 12°. Therefore the curvature of the vertically curved transition portion 21 corresponds to the angle a. The angle a may be in the range from 0° to 60°, preferably in the range from 8° to 45°.

As an alternative shape for the packaging tray, there could be a single curved portion of the side wall substantially forming a circle or an ellipse without any straight portion. As yet an alternative, there could be three curved portions with straight portions therebetween forming a general triangular packaging tray, four curved portions each forming 1/4-circle with four straight portions therebetween forming a general rectangular or square packaging tray, six curved portions each forming 1/6-circle with six straight portions therebetween forming a general hexagonal packaging tray, etc.

The bottom wall 3 and the side wall 5 form a holding volume 23 with an upper access opening 25. The rim flange 7 extends continuously around the upper access opening 25. The holding volume 23 is adapted to receive and contain the product, e.g. foodstuff, which is to be stored in the packaging tray 1. The rim flange 7 constitutes an appropriate receiving surface when the packaging tray 1 is provided with a cover 35, membrane or lid, such that a gas-tight connection between the packaging tray 1 and the cover 35, membrane or lid is obtainable.

In the illustrated embodiment, the rim flange 7 is angled slightly downwards by an angle β of 5°. See Figure 2. The changeover from the side wall 5 to the rim flange 7 occurs at the point Q. The rim flange 7 has a substantially flat surface, which is beneficial when forming the receiving surface for the cover 35, membrane or lid. The angle β may be in the range from -10° to +10°, preferably in the range from -5° to 5°. As an example, the angle β may be 0°, i.e. the rim flank is substantially horizontal.

The rim flange 7 may be used to grip the packaging tray 1. This may be practical, when e.g. the content of the packaging tray 1 has been warmed up in an oven or a micro-wave oven in order not to over-heat one’s fingers. As an option, not illustrated, the rim flange 7 may comprise one or more widened portions, e.g. at the ends of the oval shape, which makes the packaging tray 1 easy to grip.

The central portion 9 of the bottom wall 3 has a first thickness U and the rim flange 7 has a second thickness t2, which is less than the first thickness h, i.e. t2 < U. This may be a result of the composite material having been harder pressed, i.e. more compressed, at the rim flange 7 than at the central portion 9 of the bottom wall 3, which is further described below in conjunction with Figures 5A-C. By pressing the rim flange 7 harder, it may be ascertained that the receiving surface for the cover 35, membrane or lid is flat enough to be able to provide the gas-tight connection. However, if pressing too hard, there may be a risk that the composite material is, at least partly, damaged. It has been found advantageous if t2 < 0.98 ti, preferably t2 < 0.96 h, more preferably t2< 0.94 h, most preferably t2 <0.92 ti.

The curvature of the curved portions 13, 15, see arrows in Figure 1, is selected such that the holding volume 23 can hold the desired content and yet sharp corners are avoided. It has been found to be advantageous if an inner curvature 33 of the rim flange 7 forming the upper access opening 25 has a minimum radius of curvature greater than or equal to 40 mm, preferably greater than or equal to 45 mm, more preferably greater than or equal to 50 mm, e.g. being in the range from 53 to 55 mm.

The packaging tray 1 is manufactured from a blank 101, see Figure 4. The blank 101 comprises the composite material described above. The blank 101 may be cut from a sheet of the composite material or from a roll of composite material, as is further described below. The blank 101 has a flat shape adapted to form the desired three-dimensional shape of the packaging tray 1. Therefore also the blank 101 depicted in Figure 4 has a generally oval shape corresponding to the generally oval shape of the packaging tray 1, as seen in Figure 1.

The blank 101 comprises a plurality of local compressions of the composite materials constituting scores. In the illustrated example, the scores are alternating long scores 103 and short scores 105, such that every second score is long and every second score is short. The scores 103, 105 are regularly distributed. The terms long and short are used in a relative manner to describe the relative differences in length between the scores 103 and 105. The scores 103, 105 are adapted to be substantially transverse to the curvature direction of the at least one curved portion 13, 15 of the side wall 5 of the packaging tray 1. The long scores 103 extend substantially down to the transition portion 21 of the side wall 5, while the short scores 105 extend only for a portion of the side wall 5. The short scores 105 may have a length being in the range from 20% to 90% of the long scores 103, preferably in the range from 40% to 80% of the long scores 103, more preferably in the range from 50% to 70% of the long scores 103.

There is an interspace between two consecutive long scores 105 forming an angle i being in the range from 3° to 6°, preferably between 4° and 5°. In the illustrated example the angle i is about 4.5°. The angle i may be determined at a portion of the blank 101, which is to constitute an inner portion of the side wall 5. There is further an angle o between a long score 103 and its adjacent short score 105. The angle o may be in the range from 1.5° to 3°, preferably between 2° and 2.5°. In the illustrated example, the angle o is half of the angle i, since every second score is short and every second long. The angle o may be determined at a portion of the blank 101, which is to constitute an outer portion of the side wall 5 or the rim flange 7 in the packaging tray 1.

In the illustrated embodiment, the scores 103, 105 are located at the at least one curved portion 13, 15 of the sidewall 5 of the packaging tray 1. There may in addition, as is illustrated in Figure 4, be scores 107 located at a portion of the blank 101, which is to constitute the straight portions 17, 19 of the side wall 5, e.g. close to the transition between the curved portion 13, 15 and the straight portions 17, 19. There are no scores at the bottom wall 3.

When the flat blank 101 is pressed to form the three-dimensional packaging tray 1, folds or wrinkles may be formed in the composite material. By providing the scores 103, 105, 107 described herein, the positions of the scores are purposely selected. Thereby, the creation of undesired wrinkles may be avoided, or at least considerably reduced, when forming the packaging tray 1. This is beneficial since wrinkles may make it difficult to obtain the appropriate receiving surface on the rim flange 7 providing the gas-tight connection. The characteristics of the scores 103, 105, 107, e.g. number, length, width, depth, degree of compression of the composite material, and/or their positions may thus be selected to contribute to obtaining the appropriate receiving surface for the cover 35, membrane or lid to provide the gas-tight connection. Thereby characteristics of the packaging tray 1, such as the size, the material, and the radius of curvature of the side wall may be taken into account. For example, there may be more scores present, the more the side wall is curved.

Figure 5A and B illustrate a cross-section through a press tool 201 according to the invention. The press tool 201 is used for manufacturing a packaging tray from a blank, e.g. for manufacturing the packaging tray 1 illustrated in Figures 1-3 from the blank 101 illustrated in Figure 4.

The press tool 201 comprises a first member 203 and a second member 205, adapted to form a gap 207 between each other, in which gap 207 the packaging tray 1 is to be formed. In the illustrated embodiment, the first member 203 forms a male member and the second member 205 forms a female member. The gap 207 comprises a first zone 209 having a first gap width wi, adapted to form the central portion 9 of the bottom wall 3 of the packaging tray 1, and a second zone 211 having a second gap width w2, adapted to form the rim flange 7 of the packaging tray 1. The first gap width wi and the second gap width w2 are advantageously selected to obtain the relation between first thickness ^ and the second thickness t2 as described herein. However, the differences between the first and second gap widths may be larger than the difference between the first and second thicknesses, e.g. up to 200 pm.

At least one of the first 203 and second 205 members, in this case the first member 203, comprises a first portion 213 adapted to form the first zone 209 and a second portion 215 adapted to form the second zone 211. The second portion 215 is displaceable in relation to the first portion 213, denoted by arrows in Figure 5A, such that the first gap width wi and the second gap width w2are selectable independent of each other. In the illustrated embodiment, the second portion 215 forms a ring surrounding the first portion, corresponding to the rim flange 7 surrounding the side wall 5 in the packaging tray 1.

Other zones 217, 219 of the gap 207 are adapted to form the edge portion 11 of the bottom wall 3 and to form the side wall 5. In the illustrated embodiment these other zones 217, 219 are formed in the gap between the first portion 213 of the first male member 203 and the second female member 205. These other zones 217, 219 are located in the gap 207, between the first zone 209 and the second zone 211.

Figure 5A further illustrates an exemplary way of how the control the first gap width wi independent from the second gap width w2. One or more spacers, illustrated as a metal shim 221, are used to control the position of the second portion 215 in relation to the first portion 213. The spacer 221 is in the illustrated embodiment placed between the second portion 215 and the applied pressure, i.e. below the second portion 215 in Figure 5A.

In the illustrated embodiment of Figure 5A, the second member 205 comprises, as an option, a patterning plate 223. The patterning plate 223 is in contact with the bottom of the central portion 9 of the bottom wall 3 the packaging tray 1. The patterning plate 223 may be provided with an embossing pattern resulting in an at least partly embossed central portion 9. As an alternative, the patterning plate 223 may be flat resulting in an unembossed central portion. The patterning plate 223 may be exchanged without changing the rest of the press tool 201, in case another embossing pattern is desired.

Figure 5C illustrates an alternative press tool 201’ according to the invention. Many elements of the alternative press tool 201’ are similar to those of the press tool 201 illustrated in Figure 5A and therefore not described again. However, in the alternative press tool 20T, the female member 205’ comprises the first portion 213’ and the second portion 215’, which have a selectable relative position, such that the first gap width wi and the second gap width w2 may be selected to obtain the relation between first thickness U and the second thickness t2 as described herein. This may be obtained by placing a spacer 221’ between the first portion 213’ and the second portion 215’.

Figure 6 illustrates a method 300 for manufacturing a packaging tray from the composite material, e.g. for manufacturing the packaging tray 1 illustrated in Figures 1-3. The method comprises: 310: Providing a blank suitable for forming a packaging tray of the composite material. 320: Forming the packaging tray from the blank by applying heat and pressure, wherein the pressure is applied such that the central portion of the bottom wall is compressed to the first thickness h and the rim flange is compressed to the second thickness t2, which is less than the first thickness.

Blanks may be prefabricated at a different location and/or at a different time from the forming of the packaging trays. Alternatively blanks may be formed in-line with the forming of the packaging trays. In that case, the step of providing a blank suitable for forming a packaging tray of the composite material may comprise cutting and scoring the blank. The cutting and the scoring of the blank may be performed as two separate steps, but they are preferably combined into one step, such that they are performed at the same time and with the same tool.

The step of scoring may comprise providing a plurality of local compressions constituting scores 103, 105, 107, which in the packaging tray 1 are substantially transverse to the curvature direction of the curved portion 9 of the side wall 5, as is described in conjunction with Figure 4.

The forming of the packaging tray 1 may be performed by means of a heated press tool having a locally selectable pressure, such as the press tool 201 as described herein, cf Figure 4. The two different degrees of compressions may be obtained by applying a first pressure in the first zone 209, corresponding to the central portion 9 of the bottom wall 3, which first pressure is less than a second pressure applied in the second zone 209, corresponding to the rim flange 7.

The step of forming may comprise shaping the packaging tray 1, such that the rim flange 7 surrounding the upper access opening 25 has an inner curvature 33 with a minimum radius of curvature as described above in conjunction with Figures 1-3.

Figure 7 illustrates an apparatus 400 for manufacturing a packaging tray from the composite material, e.g. for manufacturing the packaging tray 1 illustrated in Figures 1-3. The apparatus comprises: - a means 410 for providing the composite material, - a cutting unit 420, adapted for cutting a blank suitable for forming a packaging tray from the composite material, - a scoring unit 430, adapted to provide a plurality of local compressions constituting scores to the blank, and - a forming unit 440, adapted to form the packaging tray from the blank by applying heat and pressure.

The means 410 for providing the composite material may comprise a reel stand, if the composite material is supplied as a roll, ora sheet feeder, if the composite material is supplied as a stack of sheets.

The cutting unit 420 is preferably combined with the scoring unit 430 into one unit, which is able to perform both cutting and scoring of the blank, seen as a dashed line in Figure 7. The scoring unit 430 may be adapted to provide the blank with a plurality of local compressions constituting scores 103, 105, 107, which in the packaging tray are substantially transverse to the curvature direction of the curved portion 9 of the side wall 5, as is described in conjunction with Figure 4.

The forming unit 440 is adapted to reshape the flat blank into the three-dimensional packaging tray. The forming unit 440 may comprise the press tool 201 as described herein.

Further modifications of the invention within the scope of the appended claims are feasible. As such, the present invention should not be considered as limited by the embodiments and figures described herein. Rather, the full scope of the invention should be determined by the appended claims, with reference to the description and drawings.

Claims

1. A packaging tray (1) of a composite material comprising a paperboard layer and a plastic layer, which packaging tray (1) comprises a bottom wall (3), a side wall (5) surrounding said bottom wall (3), and a rim flange (7), said side wall (5) comprising at least one curved portion (13, 15), said bottom wall (3) and said side wall (5) forming a holding volume (23) with an upper access opening (25), said rim flange (7) extending around said upper access opening (25), characterized in that a central portion (9) of said bottom wall (3) has a first thickness U and said rim flange (7) has a second thickness t2, which is less than said first thickness U.

2. The packaging tray (1) according to claim 1, wherein said second thickness t2 < 0.98 of said first thickness L, preferably t2 < 0.96 L, more preferably t2< 0.94 L, most preferably t2< 0.92 U.

3. The packaging tray (1) according to any one of the preceding claims, wherein said at least one curved portion (13, 15) of said side wall (5) comprises a plurality of local compressions constituting scores (103, 105), which are substantially transverse to a curvature direction of said curved portion (13, 15) of said side wall (5), an interspace between two consecutive scores (103, 105) forming an angle (o) being in the range from 1.5° to 3°, preferably in the range from 2° to 2.5°, said angle (o) being determined at an outer portion of said side wall (5), which outer portion faces said rim flange (7).

4. The packaging tray (1) according to any one of the preceding claims, wherein an inner curvature (33) of said rim flange (7) forming said upper access opening (25) has a minimum radius of curvature greater than or equal to 40 mm, preferably greater than or equal to 45 mm, more preferably greater than or equal to 50 mm, most preferably being in the range from 53 to 55 mm.

5. The packaging tray (1) according to any one of the preceding claims, wherein said plastic layer has a thickness in the range from 15 pm to 150 pm, preferably in the range from 25 pm to 100 pm, more preferably in the range from 30 pm to 75 pm.

6. A blank (101) of a composite material comprising a paperboard layer and a plastic layer, which blank (101) is adapted for manufacturing a packaging tray (1) according to any one of the preceding claims, wherein said blank (101) comprises a plurality of local compressions constituting scores (103, 105), which are adapted to be substantially transverse to a curvature direction of said curved portion (13, 15) of said side wall (5), an interspace between two consecutive scores forming an angle (o) being in the range from 1.5° to 3°, preferably in the range from 2° to 2.5°, said angle (o) being determined at a portion of said blank (101) adapted to form an outer portion of said side wall (5), which outer portion faces said rim flange (7).

7. A container (37) for foodstuff, said container comprising - a packaging tray (1) according to any one of claims 1-5, - a cover (35), membrane or lid, adapted to be sealed to said rim flange (7), thereby providing a gas-tight connection.

8. A method (300) for manufacturing a packaging tray (1) of a composite material comprising a paperboard layer and a plastic layer, which packaging tray (1) comprises a bottom wall (3), a side wall (5) surrounding said bottom wall (3), and a rim flange (7), said bottom wall (3) and said side wall (5) forming a holding volume (23) with an upper access opening (25), said rim flange (7) extending around said upper access opening (25), said method comprising - providing a blank (101) suitable for forming a packaging tray (1) of said composite material, - forming said packaging tray (1) from said blank (101) by applying heat and pressure, characterized in that said pressure is applied such that a central portion (9) of said bottom wall (3) is compressed to a first thickness U and said rim flange (7) is compressed to a second thickness t2, which is less than said first thickness U.

9. The method according to claim 8, wherein a first pressure applied in a first zone (209), corresponding to said central portion (9) of said bottom wall (3), is less than a second pressure applied in a second zone (211), corresponding to said rim flange (7).

10. The method according to claim 8 or 9, wherein said step of forming is performed by means of a heatable press tool (201) having a locally selectable pressure.

11. The method according to any one of claims 8-10, wherein the step of providing a blank (101) suitable for forming a packaging tray (1) of said composite material comprises cutting and scoring the blank (101).

12. The method according to claim 11, wherein the step of scoring comprises - providing a plurality of local compressions constituting scores (103, 105), which in said packaging tray (1) are substantially transverse to said curvature direction of said curved portion (13, 15) of said side wall (5), preferably an interspace between two consecutive scores forming an angle (o) in the range from 1.5° to 3°, preferably in the range from 2° to 2.5°, said angle (o) being determined at an outer portion of said side wall (5), which outer portion faces said rim flange (7).

13. The method according to any one of claims 11 or 12, wherein the step of scoring comprises applying local pressure on said board layer side of said composite material in order to form said scores (103, 105).

14. The method according to any one of claims 8-13, wherein the step of forming comprises shaping said packaging tray (1), such that an inner curvature (33) of said rim flange (7) forming said upper access opening (25) has a minimum radius of curvature greater than or equal to 40 mm, preferably greater than or equal to 45 mm, more preferably greater than or equal to 50 mm, most preferably being in the range from 53 to 55 mm.

15. A press tool (201, 20T) for manufacturing a packaging tray (1) from a blank (101), said press tool (201, 20T) comprising a first member (203, 203’) and a second member (205, 205’), adapted to form a gap (207) between each other, in which gap (207) said packaging tray (1) is to be formed, said gap (207) comprising a first zone (209) having a first gap width (wi), adapted to form a central portion (9) of a bottom wall (3) of said packaging tray (1), and a second zone (211) having a second gap width (w2), at least partly being located outside of said first zone (209) and adapted to form a rim flange (7) of said packaging tray (1), characterized in that at least one of said first and second members (203, 205’) comprises a first portion (213, 213’) adapted to form said first zone (209) and a second portion (215, 215’) adapted to form said second zone (211), said second portion (215, 215’) being displaceable in relation to said first portion (213, 213’), such that said first gap width (w^ and said second gap width (w2) are selectable independent of each other.

16. The press tool (201, 20T) according to claim 15, wherein said first member (203, 203’) is a male member and said second member (205, 205’) is a female member.

17. The press tool (201, 20T) according to claim 15 or 16, wherein said press tool further comprises at least one spacer (221, 22T), e.g. a metal shim, said spacer (221, 22T) being adapted to adjust a relative position of said first portion (213, 213’) in relation to said second portion (215, 215’).

18. The press tool (201, 20T) according to claim 15, 16 or 17, wherein said second portion (215, 215’) forms a ring surrounding said first portion (213, 213’).

19. An apparatus (400) for manufacturing a packaging tray (1) of a composite material comprising a paperboard layer and a plastic layer, which packaging tray (1) comprises a bottom wall (3), a side wall (5) surrounding said bottom wall (3), and a rim flange (7), said apparatus (400) comprising - a cutting unit (420), adapted for cutting a blank (101) suitable for forming a packaging tray (1) from said composite material, - a scoring unit (430), adapted to provide a plurality of local compressions constituting scores (103, 105) to said blank (101), said scoring unit (430) preferably being combined with said cutting unit (420) into one unit, - a forming unit (440), adapted to form said packaging tray (1) from said blank (101) by applying heat and pressure, said forming unit (440) comprising a press tool (201) according to any one of claims 15-18.

20. The apparatus according to claim 19, wherein said scoring unit (430) is shaped to provide a plurality of local compressions constituting scores (103, 105), which are substantially transverse to a curvature direction of said curved portion (13, 15) of side wall (5), preferably an interspace between two consecutive scores (103, 105) forming an angle (o) being in the range from 1.5° to 3°, preferably in the range from 2° to 2.5°, said angle (o) being determined at an outer portion of said side wall (5), which outer portion faces said rim flange (7).