EP3819224A1

EP3819224A1 - A method for forming a deep-drawn container comprising a stretchable paper

Info

Publication number: EP3819224A1
Application number: EP19208387.1A
Authority: EP
Inventors: Hein VAN DEN REEK; Åke REUTERHAGE
Original assignee: Billerudkorsnas AB
Current assignee: Billerud AB
Priority date: 2019-11-11
Filing date: 2019-11-11
Publication date: 2021-05-12

Abstract

The present disclosure generally relates to a method for forming a deep-drawn paper container for packaging purposes. The present disclosure also relates to a paper container comprising a stretchable paper, and to the use of such container for packaging a food product. The paper container allows for a larger storage volume and savings with respect to material and cost.

Description

TECHNICAL FIELD

The present disclosure generally relates to a method for forming a deep-drawn paper container for packaging purposes. The present disclosure also relates to a paper container comprising a stretchable paper, and to the use of such container for packaging a food product.

BACKGROUND

Plastic packaging trays are extensively used for packaging of various industrial products, such as food products. Packaging trays for cold cuts of meat, fish, cheese and other sliced food typically comprise a deep drawn, and hollow container of relatively low depth, and a plastic film enclosing the top of the tray, after the tray has been filled with food.
Plastic trays can be easily molded, stretched and produced at a relatively low cost. However, the use of plastic trays, and plastic material in general, is associated with environmental concerns.
In order to relieve the environmental burden, attempts have been made to replace plastic containers with renewable materials, such as paper.
However, paper has a number of drawbacks compared to traditional plastics. Paper is generally more permeable to gases, grease and moisture. Furthermore, normal paper is considerably less stretchable than many types of plastics, which limits the depth obtainable in the thermo forming or vacuum processing machines.
The use of paper in deep drawing processes to form commercially viable tray solutions is also subject to the risk of tearing and breaking of the paper during the process. There are also limitations with respect to the shaping of the final container.
Methods for producing trays and containers from stretchable paper are disclosed in WO 2015/082268 and EP1985437B1 .
Although the methods and packaging trays of the prior art relieve the environmental burden by replacing plastic with renewable and stretchable paper, there is still room for improvement. Particularly, it would be desirable to increase the volume for storage of the final tray or container. Furthermore, it would be desirable to enhance the flexibility with respect to methods for forming and shaping such containers.

SUMMARY

In view of the above mentioned and other drawbacks of the prior art, it is an object of the present disclosure to provide improvements with respect to methods for forming paper trays or containers, particularly with respect to increasing the flexibility of the method and the storage ability of the final container.
According to a first aspect of the present disclosure, there is provided a method for forming a deep-drawn container comprising:

a) positioning a blank of stretchable paper on a moulding cavity
b) forming a first container having a first bottom-to-wall angle, α1, by pressing at least a portion of the blank into the moulding cavity, whereby the paper in the walls of the first container is stretched
c) forming a second container having a second bottom-to-wall-angle, α2, which is smaller than said first bottom-to-wall angle, α1, by stretching the paper in the bottom of the first container.

The present inventive concept is based on the insight that the stretchability of the paper can be fully utilized if the paper is also stretched at the bottom of the paper container. With prior art methods, the paper is typically only stretched in the areas forming the walls of the final container.
By stretching the paper at all surfaces forming the final container, the full potential of the stretchable paper is utilized. By stretching the paper in the bottom such that the bottom-to-wall angle of the container is decreased, a container having steeper sidewalls is obtained, which allows for a larger storage volume of the final container. Furthermore, less material is required, which saves material and costs.
In embodiments, the second bottom-to-wall angle, α2 is from 70 to 110 degrees, preferably from 80 to 100 degrees.
In other words, the sidewalls of the second container; i.e. the final container, extend from the bottom surface of the container at an angle close to a right angle. The storage volume of the final container is thereby increased, even though the same amount of material is used.
The first bottom-to-wall angle, α1, may e.g. be from 130 to 160 degrees. Hence, the sidewalls of the first container are slanted and the bottom of the paper is substantially unstretched.
Preferably in step c), the paper in the bottom of the first container is stretched at least 5%, preferably at least 10 %.
This allows for the formation of a paper container or tray having a sharper bottom-to-wall angle. The full stretching potential of the paper is utilized, and the container can adopt a shape which allows for storage of larger volumes.
In embodiments, the paper has a stretchability according to ISO 1924-3:2005 of at least 6% in the machine direction (MD) and at least 6% in the cross direction (CD).
A high tensile strength (i.e. a high maximum force that a paper can withstand before breaking), is also desired for the paper used in the paper straw according to the present disclosure.
In embodiments, the paper has a tensile energy absorption (TEA) index according to ISO 1924-3:2005 of at least 3.5 J/g in the machine direction (MD) and/or at least 2.9 J/g in the cross direction (CD).
The high tensile strength of the paper allows the paper to withstand the forces implied during moulding and during formation of the final container.
In step b), the first container is formed by pressing at least a portion of the paper blank into the moulding cavity by:

a) applying air pressure to the paper blank, or
b) pressing a moulding tool against the moulding cavity.

If air pressure is used to press the blank of paper into the moulding cavity, the pressure is selected such that the sheet slides into the moulding cavity and at least partially extends within the cavity. Thereby, a first, intermediate container is formed.
When the first container is formed by means of the application of air pressure, the shape of the first container may correspond to that of the moulding cavity. The pressure should be high enough to obtain a stretch of the paper in the area forming the side walls of the cavity, but low enough to prevent breakage of the paper sheet.
Alternatively, a moulding tool is pressed against the moulding cavity.
In this case, the shape of the moulding tool determines the shape of the first container. The moulding tool may be adapted to descend into the moulding cavity to form a container bottom as well as sidewalls extending from the bottom. The sidewalls are formed integral with the bottom of the container.
The shape of the moulding tool may or may not be complementary to the shape of the moulding cavity. If the shapes are complementary, both the moulding cavity and the moulding tool determine the shape of the first container.
In embodiments, the moulding tool is configured to be movable between a first, retracted configuration and a second, extended configuration, wherein the shape of the second container is complementary to the shape of the moulding tool in the extended configuration.
The transition between a retracted and extended state of the movable moulding tool allows the bottom of the paper to be stretched. Furthermore, since the shape of the moulding tool in the extended configuration is complementary to that of the second container; i.e. having generally upright sidewalls, a second container having a bottom-to-wall angle, α2 of from 70 to 110 degrees, preferably from 80 to 100 degrees can be obtained, and this shape is retained upon removal of the moulding tool.
In embodiments where the first, intermediate container is formed by means of the application of air pressure, the moulding tool is absent from step b) and may be used in the subsequent step c) to form the second container.
In embodiments, the second moulding tool comprises a moulding core defined at least by a moulding surface adapted to be pressed against the bottom surface of the moulding cavity and side walls extending from the moulding surface, wherein the angle, β1, between the moulding surface and the sidewalls in the retracted configuration of the second moulding tool is smaller than the angle, β2, between the moulding surface and the sidewalls in the extended configuration.
Accordingly, in the first, retracted configuration, the molding core comprises slanted side walls, and the angle, β1, may e.g. be from 210 to 240 degrees. In the second, extended configuration the side walls of the molding core are steeper and, the angle, β2, may e.g. be from 250 to 290 degrees, preferably from 260 to 280 degrees.
If the moulding tool is movable, the same moulding tool may be used in both steps b) and c). This may be beneficial for the purpose of simplifying the process as the same equipment may be used throughout the process. After completion of step b) wherein the first container is formed, the geometry of the moulding tool may be changed such that the tool can also be used to form the second container of step c.
The retracted configuration of the moulding tool may thus correspond to the shape of the first, intermediate, container, whereas the extended configuration of the moulding tool corresponds to the shape of the second, final container.
In embodiments, the moulding cavity has a bottom-to-wall angle, γ2, of from 70 to 110 degrees, preferably from 80 to 100 degrees.
The sharper bottom-to-wall angle of the moulding cavity, γ2, allows the paper to acquire a shape corresponding to that of the second moulding cavity. A second container having more upright sidewalls is thereby formed.
The shape of the moulding cavity may thus correspond with the shape of the second container. If a movable moulding tool is used to form both the first, intermediate container, and the second container, then the shape of the first, intermediate container is determined by the shape of the moulding tool in the retracted configuration, and the shape of the second container will be determined by the shape of the moulding tool in the extended configuration as well as the shape of the moulding cavity.
In embodiments, the moulding cavity is configured to be movable between a first, retracted configuration and a second, extended configuration, wherein in the extended configuration, the perimeter of the bottom surface of the moulding cavity is larger than the perimeter of the bottom surface of the moulding cavity in the retracted configuration.
Accordingly, when the moulding cavity moves from a retracted to an extended state, the bottom of the paper blank is stretched.
The bottom-to-wall angle, γ1, of the moulding cavity in the retracted configuration is typically larger than the bottom-to-wall angle, γ2, of the moulding cavity in the extended configuration. The bottom-to-wall angle, γ2, of the moulding cavity in the extended configuration substantially corresponds to the bottom-to-wall angle α2, of the second container. The bottom-to-wall angle, γ1, of the moulding cavity in the retracted configuration may correspond to the bottom-to-wall angle α1, of the first container.
In embodiments, the moulding tool and the moulding cavity are circumferentially movable in relation to each other.
In other words, when the moulding tool moves from the first, retracted configuration to the second, extended configuration, this may trigger the moulding cavity to move from a first, retracted configuration to a second, extended configuration, and vice versa. Hence, the sidewalls and bottom surface of the moulding cavity will adopt a shape complementary to the shape of the moulding tool in the second configuration.
The method may also comprise the step of sealing the paper container with a film. This is to provide a gas-tight sealing.
Before sealing, the paper container may be filled with the product to be packaged therein, which is typically a food product.
According to another aspect of the present disclosure, there is provided a paper container comprising a bottom surface and sidewalls extending upwardly from the bottom surface, wherein the paper package comprises a paper having a stretchability according to ISO 1924-3:2005 of at least 6% in the machine direction (MD) and at least 6% in the cross direction (CD), and wherein the angle, α2, between the bottom surface of the container and the side walls is from 70 to 110 degrees, preferably from 80 to 100 degrees.
In embodiments, the container comprises a circumferential flange portion extending outwardly from the upper edges of the side walls and a film applied to the flange portion.
According to another aspect, the present disclosure relates to the use of a container has described hereinbefore for packaging a food product.

BRIEF DESCRIPTION OF THE DRAWINGS

The various aspects of the present disclosure, including its particular features and advantages, will be readily understood from the following detailed description and the accompanying drawings, in which:

Figure 1a illustrates one embodiment of the present disclosure, wherein a blank of stretchable paper is positioned on a moulding cavity.
Figure 1b illustrates the step of forming a first, intermediate container according to one embodiment of the present disclosure.
Figure 1c illustrates the step of forming a second, final container, according to one embodiment of the present disclosure.
Figure 1d) illustrates an alternative embodiment of the present disclosure, wherein a blank of stretchable paper is positioned on a moulding cavity.
Figure 1e) illustrates the step of forming a first, intermediate container according to an alternative embodiment of the present disclosure.
Figure 1f) illustrates the step of forming a second, final container, according to an alternative embodiment of the present disclosure
Figure 2 is a top view of a moulding tool according to one embodiment of the present disclosure, seen from the moulding surface.
Figure 3 illustrates a cross-sectional view of a paper container according to an exemplary embodiment of the present disclosure.
Figure 4 illustrates a paper container according to an exemplary embodiment of the present disclosure, in which a sliced food product has been packaged.

DETAILED DESCRIPTION

The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which currently preferred embodiments of the present invention are shown. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided for thoroughness and completeness, and fully convey the scope of the present invention to the skilled person.
With reference to figure 1a-c, a method for forming a deep-drawn container (106) is schematically illustrated, the method comprising:

a) positioning a blank of stretchable paper 101 on a moulding cavity 102 (illustrated in figure 1a),
b) forming a first container 104 having a first bottom-to-wall angle, α1, by pressing at least a portion of the blank 101 into the moulding cavity 102, whereby the paper in the walls 105 of the first container 104 is stretched (see figure 1b),
c) forming a second container 106 having a second bottom-to-wall-angle, α2, which is smaller than the first bottom-to-wall angle, α1, by stretching the paper 101 in the bottom 107 of the first container 104 (see figures 1b and 1c).

As used herein, the term "first container" means an intermediate container formed in the method of the present disclosure. The term "second container" means the container forming the final container or the final shape of a body portion used for the packaging of products, e.g. food products. The second container is formed by "re-forming" the first container.
As used herein, the "moulding tool" means a punch or a "male tool" configured to engage with a "female tool", which in the context of the present disclosure is the moulding cavity. The moulding tool may be adapted to descend into the moulding cavity. It is however conceivable that the moulding tool is fixed, and the moulding cavity is adapted to ascend towards the moulding tool. The first container, and in embodiments, the second container, will acquire a shape complementary to the moulding tool.
The "moulding cavity" is the "female tool" configured to engage with the moulding tool. The moulding cavity may have a shape complementary to that of the second container, and, in embodiments to the shape of the first container.
As used herein, the term "bottom-to-wall angle" of the container means the angle between the inward bottom surface of the container and the sidewalls extending from the inward bottom surface.
The first bottom-to-wall angle, α1, is thus the angle measured from the inward bottom 107 of the first container and the sidewalls 105 of the first container 104. The first bottom-to-wall angle, α1, is typically from 130 to 160 degrees. The dimensions of the first container 104 in the method of the present disclosure typically correspond to the dimensions of prior art paper containers and paper containers that presently exist on the market.
The second bottom-to-wall angle, α2, is the angle measured from the inward bottom 107' of the second container 106 and the sidewalls 105 extending therefrom. The angle, α2, is smaller than the first bottom-to-wall angle, α1. The side walls 105 of the second container 106 are "steeper" than those of the first container 104.
In embodiments, the second bottom-to-wall angle, α2, is from 70 to 110 degrees, preferably from 80 to 100 degrees. Most preferably, the second bottom-to-wall angle, α2, is substantially 90 degrees.
From a storage perspective, side walls extending at a substantially right angle or close to a right angle will increase the final storage volume of the container.
The second container 106 is formed by stretching the paper 101 in the bottom 107 of the first container 104.
The stretchable properties of the entire paper are thus utilized since essentially all surfaces forming the paper container are stretched (not only the side walls). This allows for material savings and also contributes to a lower production cost.
The paper 101 in the bottom 107 of the first container 104 is preferably stretched at least 5%, preferably at least 10%.
As illustrated in figure 1b, the arrow 108 illustrates the length of the unstretched bottom 107 of the first container 104. The arrow 109 in figure 1c illustrates the length of the stretched bottom 107' of the second container 106.
The properties of the paper used are important for enabling the formation of a paper container in accordance with the present disclosure. A paper having a high stretchability and a high tensile strength is preferably used. This allows the paper to withstand the forces imparted during manufacturing.
In embodiments, the paper 101 has a stretchability according to ISO 1924-3:2005 of at least 6% in the machine direction (MD) and at least 6% in the cross direction (CD). For example, the stretchability may be at least 7% percent in both directions (MD and CD). In embodiments, the stretchability according to ISO 1924-3:2005 is at least 9% in at least one of the machine direction (MD) and the cross direction (CD).
This further improves the flexibility and extensibility of the paper container
A high tensile strength (i.e. a high maximum force that a paper can withstand before breaking), is preferred. Tensile energy absorption (TEA) is sometimes considered to be the paper property that best represents the relevant strength of a paper. The tensile strength is one parameter in the measurement of the TEA and another parameter is stretchability.
In embodiments, the paper has a tensile energy absorption index according to ISO 1924-3:2005 of at least 3.5 J/g in the machine direction (MD) and/or at least 2.9 J/g in the cross direction (CD).
In embodiments, the paper has a Gurley porosity according to ISO 5636-5 above 15 s, preferably above 20 s.
An example of a stretchable paper suitable for the method of present invention is FibreForm®, marketed by BillerudKorsnas AB.
The grammage; i.e. the basis weight of the paper used may be in the range of from 50 to 500 g/m², e.g. from 100 to 400 g/m². A grammage of 200 to 400 g/m² may be preferred as it prevents the paper from breaking and can withstand the forces implied during the deep drawing process.
If the basis weight of the paper straw is too low; i.e. below 50 g/m2, the paper may collapse or break during manufacturing, particularly in contact with the moulding tools or during stretching of the bottom of the container. However, the basis weight should not be too high as the paper container may become too thick and rigid and give rise to an unaesthetic appearance. Furthermore, a too thick paper may impair the ability of the paper container to stretch, particularly in the bottom of the paper container.
The paper container may comprise one or a plurality of plies of papers. The grammage of the paper used is dependent on the number of plies of paper utilized.
As illustrated in figure 1a-1c, the moulding cavity 102 is encircled by a circumferential rim portion 110. In the first step a) of the method of the present disclosure, the blank of paper 101 is arranged on the moulding cavity 102 such that it contacts the rim portion 110. Accordingly, in step a), the blank of paper 101 forms a "lid" on the moulding cavity 102 (see figure 1a).
In step b, the first paper container 104 is formed by pressing at least a portion of the paper blank 101 into the moulding cavity 102 by:

a) applying air pressure to the paper blank 101, or
b) pressing a moulding tool 103 against the moulding cavity 102

If the moulding tool 1 03 is used to form the first container 104, the shape of the moulding tool 103 will determine the general shape of the first container 104. This is illustrated in figure 1b, wherein the moulding tool 103 has been removed from the moulding cavity 102 after shaping of the first container 104.
In embodiments, the moulding cavity 102 has a shape complementary to the shape of the moulding tool 1 03. In this case, the shape of the moulding cavity 102 will also determine the final shape of the first container and aid in retaining the shape of the first container 104 in step b) (see e.g. figure 1e).
If air pressure is used to form the first container 104, the air pressure is selected such that the paper blank 101 partly slides into the moulding cavity 102 and partly extends within the cavity 104.
The air pressure should be high enough to obtain a stretch of the paper at the sidewalls of the first container, but low enough to prevent breakage of the paper blank. The pressure may be in the range of 1-25 bar, e.g. 1-15 bar.
A higher pressure may provide for a smoother paper surface and a better distribution of micro creases. However, if the pressure is too high, the paper may break as it is prevented from sliding into the cavity.
The moulding tool 103 may be arranged to descend into the moulding cavity 102. Alternatively, the moulding cavity 102 is arranged to ascend towards the moulding tool 103.
The moulding tool 103 may comprise a second rim portion 111 encircling the moulding core 113 of the moulding tool 1 03. The second rim portion 111 is arranged to contact the first rim portion 110 of the moulding cavity 102 when the tools are pressed against each other in step b), and/or step c).
The rim portions 110 and 111 hold the paper in position when the paper blank is pressed into the moulding cavity 102. This way, the paper in the walls 105 of the first container 104 is stretched. Furthermore, the first rim portion 110 of the cavity forms a flange portion 112; i.e. a generally flat surface onto which a sealing film may subsequently be attached.
In embodiments, the moulding tool 103 is configured to be movable between a first, retracted configuration and a second, extended configuration, wherein the shape of the second container 106 is complementary to the shape of the moulding tool 103 in the extended configuration.
Figure 1b) illustrates the moulding tool 103 in the first, retracted configuration.
Figure 1c) illustrates the moulding tool 103 in the extended configuration after having been removed from the moulding cavity 102. As illustrated by the arrow 109, the part of the paper that was previously unstretched (see 108 in figure 1b) has now been stretched.
The moulding tool 103 may comprise a moulding core 113 defined at least by a moulding surface 114 adapted to be pressed against the bottom surface 115 of the moulding cavity 102 and side walls 116 extending from the moulding surface 114. The angle, β1, between the moulding surface 114 and the sidewalls 116 in the retracted configuration of the moulding tool is smaller than the angle, β2, between the moulding surface 114 and the sidewalls 116 in the extended configuration.
The angle, β1, may be from 210 to 240 degrees in the retracted configuration. In the second, extended configuration the side walls of the molding core are steeper and, the angle, β2, may e.g. be from 250 to 290 degrees, preferably from 260 to 280 degrees
In embodiments, the perimeter of the moulding surface 114 of the moulding tool 103 in the second, extended configuration is larger than the perimeter of the moulding surface 114 of the moulding tool 103 in the first configuration (see figure 1b and 1c).
As used herein, the term "moulding surface" refers to the surface of the moulding tool adapted to be pressed against the bottom surface of the moulding cavity.
The moulding tool 103 may comprise at least one extendable or movable part. This is to enable the moulding tool 103 to move between the first and second configuration. For example, the moulding tool may comprise a moulding core defined by a moulding surface, sidewalls and an upper surface. At least a part of the sidewalls 116 and/or the moulding surface 114 of the moulding tool 1 03 may be extendable in order to adopt the second configuration. The moulding tool 103 may also comprise means to lock the moulding tool 103 in the first, and second position, respectively.
The moulding tool 103, the cavity 102, and consequently the formed container 106 may be rectangular, circular, square, or oval shaped.
Figure 2 illustrates a top view of a circular moulding tool 203 (seen from the moulding surface 214. The moulding tool may comprise a plurality of moulding segments 219, each of which is movable in relation to a center piece of the tool 203, and in relation to each other. The segments 219 may be adapted to expand when the moulding tool 203 moves from its retracted to its extended configuration. After stretching of the bottom of the first container, the moulding tool 203 may return to its retracted configuration, and subsequently be removed from the moulding cavity.
The moulding tool 103 forms the second container bottom inwardly, whereas the moulding cavity 102 forms the container bottom outwardly.
As illustrated in figure 1a-c), the moulding cavity may have a bottom-to-wall angle, γ2, of from 70 to 110 degrees, preferably from 80 to 100 degrees.
This is to facilitate the formation of a second container 106 with generally upright sidewalls, such that the storage volume is increased.
As used herein, the term "first bottom-to-wall angle of the moulding cavity" means the angle between the bottom surface of the moulding cavity and the cavity walls extending from the bottom of the moulding cavity. In embodiments, the bottom-to-wall angle, γ2, of the moulding cavity corresponds to the bottom-to-wall angle α2, of the second container 106. The sharper bottom-to-wall angle, γ2, allows the paper to acquire a corresponding shape; i.e. a container having more upright sidewalls.
In alternative embodiments, as illustrated in figures 1d-1e, the moulding cavity 102 is configured to be movable between a first, retracted configuration and a second, extended configuration, wherein in the extended configuration, the perimeter of the bottom surface 115' of the moulding cavity 102 is larger than the perimeter of the bottom surface 115 of the moulding cavity 102 in the retracted configuration.
In this case, as illustrated in figures 1d-1f, a paper blank 101 is first positioned on the moulding cavity 102. Either air pressure or a moulding tool 103 may be used to form the first, intermediate container 104 with sloping side walls 105.
The circumferential extension of the bottom surface 115 of the moulding cavity 102 in the extended configuration is larger than that in the retracted configuration (see figures 1e-f)).
The arrow 108 in figure 1e illustrates the unstretched bottom surface 107 of the paper blank, whereas the arrow 109 in figure 1f illustrates the bottom surface 107' of the paper blank 101 after it has been stretched.
The circumferential extension of the bottom surface 115 of the moulding cavity in the extended configuration may correspond to the distance by which the bottom surface 107' of the paper 101 is stretched. This distance, or degree of stretching, may vary depending on the size of the container to be produced.
The moulding cavity 102 may comprise hinging means 117. Hinges 117 may e.g. be applied at the interface between the rim portion 110 and the side walls 118 of the moulding cavity 102 and/or at the interface between the bottom surface 115 and the sidewalls 118 of the moulding cavity 102.
The bottom surface 115 of the moulding cavity 102 may e.g. comprise a plate configured to extend to form a cavity bottom surface 115' with a larger perimeter. This allows the bottom of the paper of the container to be stretched.
For example, the bottom surface 115 may comprise a plurality of segments, each of which is movable in relation to a centerpiece of the plate and in relation to each other. In other words, the bottom surface of the moulding cavity may have a similar configuration as the moulding surface illustrated in figure 2.
The transition between the retracted and extended configuration of the moulding cavity 102 causes the bottom of the first container 104 to stretch. A second container 106 with steeper sidewalls 105 is thereby obtained, which may be removed from the cavity and subsequently packed with a food product and sealed.
Alternatively, the moulding cavity 103 may comprise a thermally deformable material which allows the cavity to adopt a different shape, e.g. when exposed to the force and/or pressure from a moulding tool 103.
The bottom-to-wall angle of the moulding cavity in the retracted configuration, γ1, is larger than that the bottom-to-wall angle of the moulding cavity in the extended configuration, γ2. The bottom-to-wall angle, γ1, in the retracted configuration may correspond to the bottom-to-wall angle α1, of the first container 104 (see e.g. fig 1e)).
In embodiments, the moulding tool 103 and the moulding cavity 102 are circumferentially movable in relation to each other.
Thus, when the moulding tool 103 moves from the first configuration to the second, extended configuration, the sidewalls 105 of the moulding cavity 102 may deform or adopt a shape complementary to the shape of the moulding tool 1 03 in the second configuration.
For example, the movement from the first to the second moulding tool configuration may trigger the moulding cavity 102 to move from a first, retracted configuration into a second, extended configuration. Alternatively, when the moulding cavity 102 is switched from a first to a second, extended configuration, this may trigger the moulding tool 103 to move from its first to its second, extended configuration. In other words, the sidewalls 118 and bottom surface 115 of the moulding cavity 102 will adopt a shape complementary to the shape of the moulding tool 1 03 in the second configuration.
In embodiments, when the moulding tool 103 is switched to a second, extended configuration, a force may be exerted on the sidewalls of the moulding cavity 102, which causes these to deform or adopt a different shape.
Upon sliding or movement from the first to the second configuration, the paper forming the bottom of the container is stretched accordingly.
In embodiments, the moulding cavity is a first moulding cavity, and an additional, second moulding cavity is utilized in step c) of the method. Accordingly, the first container may be formed in a first moulding cavity (step b), and the first container may then be transferred to a second moulding cavity in order to form the second container (step c).
During step b) and/or step c), a lubricant may be applied to the paper blank and/or the tools. The lubrication may facilitate the desired sliding in the mould cavity. The lubricant is preferably food-approved. The food-approved lubricant may for example be a vegetable oil.
The method may further comprise the step of sealing the paper container with a film.
The flange portion 112 formed from the upwardly extending sidewalls 105 of the second container 106 may form a surface for liquid- and/or gas-tight sealing. The flange portion 112 typically protrudes outwardly, e.g. radially, from the upper edges of the side walls 105, and thereby provides for a flat, horizontal surface onto which a gas-tight film may be applied. The flange portion 112 may be coated prior to sealing in order to facilitate sealing.
For example, the flange portion 112 may be coated with a coating comprising a thermoplastic material, such as polyethylene, and may serve to even out the flange surface without leaving air pockets. The coating may be applied by roller coating, stamping, spraying or spreading. The coating is preferably food approved.
Figure 3 illustrates a cross-sectional view of the paper container 300 of the present disclosure comprising a bottom surface 307 and sidewalls 305 extending upwardly from the bottom surface 307, wherein the paper container 300 comprises a paper having a stretchability according to ISO 1924-3:2005 of at least 6% in the machine direction (MD) and at least 6% in the cross direction (CD), and wherein the angle, α2, between the bottom surface 307 and the side walls 305 is from 70 to 100 degrees, preferably from 80 to 90 degrees.
The sidewalls 305 are formed integral with the bottom surface 307.
The paper container of the present disclosure combines the advantages associated with plastic containers, and with environmentally friendly paper containers.
In embodiments, the stretchability according to ISO 1924-3:2005 is at least 7% percent in both directions (MD and CD). For example, the stretchability according to ISO 1924-3:2005 may be at least 9% in at least one of the machine direction (MD) and the cross direction (CD).
This further improves the flexibility and extensibility of the paper container.
In embodiments, the paper has a tensile energy absorption index according to ISO 1924-3:2005 of at least 3.5 J/g in the machine direction (MD) and/or at least 2.9 J/g in the cross direction (CD).
An example of a stretchable paper suitable for the paper container of present invention is FibreForm®, marketed by BillerudKorsnas AB.
The shelf life of fresh foods is typically short and a leak proof and air-tight sealing is often required.
Therefore, the paper container 300 may comprise a circumferential flange portion 312 extending outwardly from the upper edges 320 of the side walls 305 and a film 321 applied to the flange portion 312.
The paper container 300 and the flange portion 312 are formed from the same paper blank. The flange portion 312 is formed integral with the upper edges 320 of the sidewalls 305, and extends completely around the perimeter of the container 300.
The flange portion 312 protrudes outwardly such that it forms a substantially horizontal and flat surface onto which a film 321 is applied.
The film 321 may be a plastic layer comprising a film-forming polymeric material, e.g. polyamide, polyethylene, or polyester such as polyethylene terephthalate (PET). It may also comprise a polymer coated paper board. The film may comprise one or several layers. The film 321 is preferably transparent such that the contents of the container 300 can be seen.
The depth, d, of the container 300 may be at least 10 mm, such as at least 15 or 20 mm.
The width, w, is the shortest distance between opposing sidewalls 305 forming the container 300. In other words, if the container 300 is circular, the width is the diameter of the bottom surface 307 of the container 300.
The depth-to-width ratio of the container 300 may be at least 1:8. Preferably, the depth to width ratio of the container 300 is at least 1:7, such as at least 1:6, 1:5, 1:4 or 1:3.
The container 300 of the second aspect of the present disclosure may be produced by the method of the first aspect of the present disclosure. The embodiments and benefits of the first aspect apply to the second aspect mutatis mutandis.
In order to preserve the quality of the food product to be packed in the container, the inside and/or the outside of the container 300 may comprise a barrier coating, such as an oxygen or moisture barrier coating. The coating material preferably has a low permeability or transmission rate for oxygen and/or moisture.
For example, the container 300 may be coated with a material having an oxygen transmission (OTR) value of less than 10 ml/m^2∗24h^∗i atm, such as less than 8, 5 or 3 ml/m^2∗24h^∗i atm.
In embodiments, the container 300 of the present disclosure may also comprise a second container sealed to it, e.g. such that a clam shell capsule is formed (not shown).
As a third aspect, there is provided the use of the container 300 for packaging a food product. A sealed food container may be produced by arranging a food product in the paper container of the present disclosure and then sealing the filled container. These two operations may be carried out in the same process line or machine.
Figure 4 illustrates a container 400 comprising a film 421, e.g. a transparent polymer film. The film 421 may be heat sealed to the flange portion 412 of the container 400. The film 421 is preferably gas-tight and liquid-tight. In figure 4, the container 400 is partially opened by peeling the film 421 from the corners of the container 400 to access the food product 422, which, as illustrated in figure 4 may be sliced cheese.
The paper container 400 may be used as a consumer package for any kind of ready-made foods, sliced cheese, meat and fish products, vegetables, chocolates etc.
The container is also useful for consumer packages of products other than food.
The paper container is not limited to a particular shape, but any general shape is conceivable within the scope of the present disclosure.
Even though the present disclosure has been described with reference to specific exemplifying embodiments thereof, many different alterations, modifications and the like will become apparent for those skilled in the art.
Variations to the disclosed embodiments can be understood and effected by the skilled addressee in practicing the present disclosure, from a study of the drawings, the disclosure, and the appended claims. Furthermore, in the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality.

Claims

A method for producing a deep-drawn container (106, 300, 400) comprising:
a) positioning a blank of stretchable paper (101) on a moulding cavity (102),

b) forming a first container (104) having a first bottom-to-wall angle, α1, by pressing at least a portion of said blank (101) into said moulding cavity (102), whereby the paper in the walls (105) of said first container (104) is stretched,

c) forming a second container (106) having a second bottom-to-wall-angle, α2, which is smaller than said first bottom-to-wall angle, α1, by stretching the paper (101) in the bottom (107) of said first container (104).
The method according to claim 1, wherein said second bottom-to-wall angle, α2, is from 70 to 110 degrees, preferably from 80 to 100 degrees.
The method according to claim 1 or claim 2, wherein in said step c), said paper (101) in said bottom (107) of said first container (104) is stretched at least 5%, preferably at least 10 %.
The method according to any one of the preceding claims, wherein said paper (101) has a stretchability according to ISO 1924-3:2005 of at least 6% in the machine direction (MD) and at least 6% in the cross direction (CD).
The method of any one of the preceding claims, wherein said paper (101) has a tensile energy absorption (TEA) index according to ISO 1924-3:2005 of at least 3.5 J/g in the machine direction (MD) and/or at least 2.9 J/g in the cross direction (CD).
The method according to any one of the preceding claims, wherein in said step b), said first paper container (104) is formed by pressing at least a portion of said blank (101) into said moulding cavity (102) by:
a) applying air pressure to said paper blank (101), or

b) pressing a moulding tool (103) against said moulding cavity (102).
The method according to any one of the preceding claims, wherein said moulding tool (103) is configured to be movable between a first, retracted configuration and a second, extended configuration, wherein the shape of said second container (106) is complementary to the shape of said moulding tool (103) in said extended configuration.
The method according to 7, wherein said moulding tool (103) comprises a moulding core (113) defined at least by a moulding surface (114) adapted to be pressed against the bottom surface (115) of said moulding cavity (102) and side walls (116) extending from said moulding surface (114), wherein the angle, β1, between the moulding surface (115) and the sidewalls (116) in said retracted configuration of said moulding tool (103) is smaller than the angle, β2, between the moulding surface (115) and the sidewalls (116) in said extended configuration.
The method of any one of the preceding claims, wherein said moulding cavity (102) has a bottom-to-wall angle, γ2, of from 70 to 110 degrees, preferably from 80 to 100 degrees.
The method according to any one of the preceding claims, wherein said moulding cavity (102) is configured to be movable between a first, retracted configuration and a second, extended configuration, wherein in said extended configuration, the perimeter of the bottom surface (115) of said moulding cavity (102) is larger than the perimeter of the bottom surface (115) of said moulding cavity (102) in said retracted configuration.
The method according to any one of claims 6-10, wherein said moulding tool (103) and said moulding cavity (102) are circumferentially movable in relation to each other.
The method according to any one of the preceding claims, further comprising the step of sealing said paper container (106) with a film.
A container (300, 400) comprising a bottom surface (307) and sidewalls (305, 405) extending upwardly from said bottom surface (307), wherein the container comprises a paper having a stretchability according to ISO 1924-3:2005 of at least 6% in the machine direction (MD) and at least 6% in the cross direction (CD), and wherein the angle, α2, between said bottom surface (307) and said side walls (305, 405) is from 70 to 100 degrees, preferably from 80 to 90 degrees.
A paper container (300, 400) according to claim 13, wherein said container comprises a circumferential flange portion (312, 412) extending outwardly from the upper edges (320) of said side walls (305) and a film (321, 421) applied to said flange portion (312, 412).
Use of a container (300, 400) according to claim 13 or claim 14 for packaging a food product.