COMPRESSION MOULDING TOOL AND METHOD FOR MANUFACTURING A FIBROUS PULP TRAY USING THE TOOL

Abstract

A compression moulding tool for manufacturing a fibrous pulp tray having a floor portion and walls extending from the floor portion. The tool comprises a first female mould element comprising a plurality of first recessed portions, a water permeable filter arranged in the first female mould element and configured to follow the surface of the female mould element, a second female mould element comprising a plurality of second recessed portions at locations corresponding to the first recessed portions and smaller than the first recessed portions, and a male mould element configured to press against the first and second female mould elements to compress a fibrous pulp product located therebetween, the male mould element having a surface profile free from macroscopic features at locations corresponding to the first and second recessed portions of the first and second female mould.

Claims

1. A compression moulding tool for manufacturing a fibrous pulp tray having a floor portion and walls extending from the floor portion, the tool comprising: a first female mould element having a floor and sidewalls, the first female mould element comprising a plurality of first recessed portions, each first recessed portion having a first volume; a water permeable filter arranged in the first female mould element and configured to follow the surface of the female mould element, the water permeable filter being configured to retain pulp fibers; a second female mould element having a floor and sidewalls corresponding to the first female mould element, the second female mould element comprising a plurality of second recessed portions at locations corresponding to the first recessed portions of the first female mould element, each second recessed portion having a second volume smaller than the first volume, wherein the second recessed portions are configured to form corresponding protrusions at an outer surface of the fibrous pulp tray; and at least one male mould element configured to press against the first and second female mould element to compress a fibrous pulp product located therebetween, the male mould element having a surface profile at locations corresponding to the first and second recessed portions of the first and second female mould which is free from macroscopic features.

2. The compression moulding tool according to claim 1, wherein the water permeable filter is a wire mesh comprising a plurality of recessed portions formed to fit the plurality of first recessed portions of the first female mould element.

3. The compression moulding tool according to claim 1 wherein the first recessed portions have a curved profile.

4. The compression moulding tool according to claim 1, wherein the female mould element comprises a plurality of drainage channels arranged such that each of the plurality of first recessed portions comprises at least one drainage channel.

5. The compression moulding tool according to claim 1, wherein the first and second recessed portions are located at an upper portion of corners formed by sidewalls of the first and second female mould element.

6. A method for manufacturing a fibrous pulp tray comprising: depositing a fibrous pulp suspension in a first female mould element having a floor and sidewalls, the female mould comprising a plurality of first recessed portions, each first recessed portion having a first volume, and a water permeable filter configured to retain pulp fibers arranged in in the first female mould element and configured to follow the surface of the first female mould element; pressing a male mould element against the first female mould element to dewater the fibrous pulp suspension such that a fibrous pulp product is formed therebetween and such that fibrous pulp fills the plurality of first recessions, the male mould element having a surface profile free from macroscopic features at locations corresponding to the first recessed portions of the female mould; moving the fibrous pulp product from the first female mould element to a second female mould element, the second female mould element having a floor and sidewalls corresponding to the first female mould element, the second female mould comprising a plurality of second recessed portions at locations corresponding to the first recessed portions of the first female mould element, each second recessed portion having a second volume smaller than the first volume; pressing the male mould element against the second female mould element such that a fibrous pulp product is formed therebetween and such that the fibrous pulp product fills the plurality of second recessions, thereby forming a fibrous pulp product having a floor, sidewalls and protrusions corresponding to the second recessed portions of the second female mould element.

7. The method according to claim 6, further comprising: draining water from the fibrous pulp material through drainage channels of the first female mould element.

8. The method according to claim 6, wherein depositing the fibrous pulp suspension comprises dipping the first female mould element in a container comprising a fibrous pulp suspension.

9. The method according to claim 6, further comprising laminating an inside of the fibrous pulp product with a plastic film.

10. A fibrous pulp tray obtainable by the method according to claim 1, the fibrous pulp tray comprising a floor portion and walls extending from the floor portion; wherein the outside of the tray comprises a plurality of protrusions, the protrusions being an integral part of the tray, and wherein the inside of the tray at the locations of the protrusions is free from macroscopic surface features.

11. The fibrous pulp tray according to claim 10, further comprising a flange extending horizontally from an upper portion of the sidewalls.

12. The fibrous pulp tray according to claim 10, wherein the plurality of protrusions are located on a sidewall adjacent to the flange.

13. The fibrous pulp tray according to claim 10, wherein the sidewalls are sloped outwards.

14. The fibrous pulp tray according to claim 10, wherein the sidewalls and protrusions are configured such that the trays are stackable and such that a distance between two stacked trays is defined by the plurality of protrusions.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0029] These and other aspects of the present invention will now be described in more detail, with reference to the appended drawings showing an example embodiment of the invention, wherein:

[0030] FIG. 1 schematically illustrates a manufacturing assembly comprising a compression moulding tool according to an embodiment of the invention;

[0031] FIGS. 2-B schematically illustrate a first female mould element of a compression moulding tool according to an embodiment of the invention;

[0032] FIGS. 3-B schematically illustrate a second female mould element of a compression moulding tool according to an embodiment of the invention;

[0033] FIG. 4 schematically illustrates a male mould element of a compression moulding tool according to an embodiment of the invention;

[0034] FIG. 5 is a flow chart outlining steps of a method for manufacturing a fibrous pulp tray according to an embodiment of the invention; and

[0035] FIG. 6 is a fibrous pulp tray according to an embodiment of the invention.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

[0036] In the present detailed description, various aspects and embodiments of the present invention are mainly described with reference to a manufacturing assembly comprising a compression moulding tool for manufacturing a fibrous pulp tray suitable for food packaging.

[0037] FIG. 1 schematically illustrates selected parts of a manufacturing assembly 100 for manufacturing a fibrous pulp tray. In particular, FIG. 1 illustrates the tools used in two compression steps which preferable are performed consecutively. The manufacturing assembly 100 will be described with further reference to FIGS. 2-4 illustrating the different elements of the compression moulding tool, where FIGS. 2A-B illustrate a first female mould element 102, FIGS. 3A-B illustrate a second female mould element 104 and FIG. 4 illustrates a male mould element 106. Reference will also be made to FIG. 6 illustrating a tray 600 manufactured by the described compression moulding tool.

[0038] The illustrated compression moulding tool is configured to manufacture a fibrous pulp tray 600 illustrated in in FIG. 6 having a floor portion 602, walls 604 extending from the floor portion, and a flange 606 extending horizontally from the upper portion of the walls 604. The tray 600 can be considered to have an inner surface and an outer surface, where the upper surface of the flange 606 belong to the inner surface of the tray and the lower surface of the flange 606 belong to the outer surface of the tray 600. The described shape of the tray should be seen as an illustrative example, and the tool can be configured in many different ways to manufacture trays of different shapes, with or without a flange. Moreover, the illustrated tool comprises a 3?3 array of female and male mould elements, but any number and configuration of moulds is feasible.

[0039] The tool comprises a first female mould element 102 having a floor 108 and surrounding sidewalls 110 having an outward slope to form a substantially rectangular container with an opening having an area which is larger than an area of the floor 108. The first female mould element 102 further comprises a plurality of first recessed portions 112, each first recessed portion 112 having a first volume. The first recessed portions are here arranged at an upper portion of corners 114 formed by sidewalls 110 of the first female mould element 102. As can be seen in FIG. 2A, the corners 114 of the first female mould element 102 are rounded to form a curved transition between adjacent sidewalls 110. Moreover, the illustrated recessed portions 112 are open upwards and reaches the top portion of the sidewall. However, the recessed portions may in principle be located at any position in the first female mould element, such as at the floor portion 108.

[0040] A water permeable filter 202 is arranged in the first female mould element 102 and configured to follow the surface of the female mould element 102. The illustrated water permeable filter 202 is a wire mesh configured to retain pulp fibers while allowing water to pass through the filter 202 in a dewatering process occurring when the male mould element 106 is pressed against the first female mould element 102. Moreover, the wire mesh 202 comprises a plurality of recessed portions 204 formed to fit the plurality of first recessed portions of the first female mould element. Accordingly, the wire mesh 202 is pre-formed to have a shape corresponding to the shape of the first female mould element 102, for example by form-pressing the wire mesh 202. The first recessed portions 112 have a curved profile which has the advantage that the curved profile enhances the durability of the wire mesh 202, since sharp corners would make the wire mesh 202 more susceptible to damage.

[0041] The radius of the curvature of the first recessed portion 112 is selected based on other properties of the process, such as the characteristics of the fibrous pulp material. If the radius is too large there is a risk that the entire volume of the recessed portion is not fully filled by fibrous pulp material which would in turn result in a corresponding curvature visible on the inside of a resulting tray. Thereby, a suitable radius and depth of the first recessed portion 112 depends on a range of parameters such as properties of the fibers in the fibrous pulp suspension, mesh properties, pressing force and suction/drainage parameters. Accordingly, for a given manufacturing process, the dimensions of the first recessed portion 112 can be tailored as required to achieve the solid external protrusion 608 of the tray.

[0042] The first female mould element 102 further comprises a plurality of drainage channels 206. The drainage channels 206 are preferably arranged such that each of the plurality of first recessed portions 112 comprises at least one drainage channel 206 to improve dewatering from a fibrous pulp located in the first volume formed by the first recessed portion 112, and also to ensure that the first recessed portion 112 is filled by fibrous pulp.

[0043] FIG. 2B shows a cross section along the line A-A illustrated in FIG. 2A, where the male mould element 106 has been moved towards the first female mould element 102 to press a fibrous pulp material 208 therebetween. In FIG. 2B, it can be seen that the first recessed portion 112 is filled with the fibrous pulp material 208 which will subsequently form a protrusion in the resulting tray. Here it can also be seen that the male mould element 106 is smooth at the location of the first recessed portion 112, meaning that the male mould element 106 does not contain any macroscopic features at the location of the recessed portion 112 which would influence the resulting inner surface of the tray 600.

[0044] FIGS. 2A-B further illustrates that the first female mould element 102 comprises a flange 116 extending horizontally from an upper portion of the walls 110 so that resulting tray 600 has a corresponding flange 606. The first female mould element 102 also comprises a holder 210 arranged to hold the wire mesh 202 in place.

[0045] The second female mould element 104 illustrated in detail in FIG. 3A has a floor 302 and sidewalls 304 such that the shape of the second female mould element 104 corresponds to the shape of the first female mould element 102. The second female mould element 104 further comprises a plurality of second recessed portions 306 at locations corresponding to the locations of the first recessed portions 112 of the first female mould element 104. Each second recessed portion 306 has a second volume which is smaller than the first volume of the first recessed portion 112. The second recessed portions 306 are configured to form corresponding protrusions 608 at an outer surface of the fibrous pulp tray 600. In practice, the second female mould element 106 can have a substantially identical shape as the first female mould element 104, with the only difference being the size of the second recessed portions 306. In other words, the second recessed portions 306 have the same shape as the first recessed portions 112 but a smaller volume.

[0046] FIG. 3B shows a cross section along the line B-B illustrated in FIG. 3A, where the male mould element 106 has been moved towards the second female mould element 104 to press a fibrous pulp material 208 therebetween. In FIG. 3B, it can be seen that the second recessed portion 112 is filled with the fibrous pulp material 208 to form a protrusion 608 in the resulting tray as illustrated in FIG. 6. The fibrous pulp material 208 will be compressed in the second recessed portion 112 so that the protrusion 608 takes the shape of the second recessed portion 112. Moreover, due to the compression, the protrusion 608 can have a density which is equal to or higher than a density of the remainder of the tray 600. However, the density of both the tray 600 and of the protrusion 608 can be controlled by controlling parameters such as the volume of the first and second recessed portions 112, 306 and the properties of the fibrous pulp suspension. Further parameters that can be controlled to influence the density are the distance between the mould elements in a pressing step and the pressing force used.

[0047] The compression moulding tool 100 further comprises at least one male mould element 106 illustrated in FIG. 4. The male mould element 106 is configured to press against the first and second female mould elements 102, 104 to compress a fibrous pulp product located therebetween. The male mould element 106 has a smooth surface profile at least at locations corresponding to the first and second recessed portions 112, 306 of the first and second female mould. In the illustrated example, the male mould element 106 has an entirely smooth surface profile following the shape of the first and second female mould elements 102, 104 except for the recessed portions 112, 306. However, the male mould element may be configured to have protrusions and/or recessed portions at other locations and for other purposes, such as for imprinting a trademark, logotype or the like in the tray.

[0048] In FIG. 1, only one set of male mould elements 106 is illustrated since it is possible to use the same male mould element 106 for both of the described pressing steps. However, it would equally well be possible to use two separate sets of male mould elements, which may or may not be identical. Moreover, even though the second female mould element 104 and the male mould element 106 are illustrated herein without drainage channels, they may still comprise drainage channels if so desired. For example, a male mould element used in a first pressing step may comprise drainage channels while a male mould element used in a second pressing step may be without drainage channels.

[0049] Furthermore, all mould elements 102, 104, 106 are illustrated as solid elements made in one piece. However, one or more of the mould elements 102, 104, 106 may consist of a plurality of separate pieces which can be joined together to form the mould element. It would also be possible to form the mould elements from a porous material such as from porous aluminum.

[0050] FIG. 5 is a flow chart outlining the general steps of a method of manufacturing a fibrous pulp tray 600 according to an embodiment of the invention. The method comprises depositing 500 a fibrous pulp suspension in the first female mould element 102, for example by dipping the first female mould element 102 in a container containing the fibrous pulp suspension.

[0051] The following step comprises pressing 502 the male mould element 106 against the first female mould element 102 to dewater the fibrous pulp suspension such that a fibrous pulp product is formed between the first female mould element 102 and the male mould element 106 and such that fibrous pulp fills the plurality of first recessions 112. The first pressing step 502 further comprises draining water from the fibrous pulp material through drainage channels 206 of the first female mould element 102.

[0052] Next, the fibrous pulp product is moved 504 from the first female mould element 102 to the second female mould element 104, for example by using vacuum to lift the fibrous pulp product from one station to the next.

[0053] Finally, the method comprises pressing 506 the male mould element 106 against the second female mould element 104 such that a fibrous pulp tray 600 is formed therebetween and such that fibrous pulp fills the plurality of second recessions 306, thereby forming a fibrous pulp product 600 having a floor 602, sidewalls 604 and protrusions 608 having a shape corresponding to the second recessed portions 306 of the second female mould element 104. The second pressing step 506 may also comprise dewatering the fibrous pulp product if required. In that case the second female mould element 104 and/or the male mould element 106 may comprise dewatering channels.

[0054] FIG. 6 illustrates a fibrous pulp tray 600 made by the above described tool and method, the tray comprising protrusions 608 on the outside of the tray 600 with no visible correspondence of the protrusions at the inside 610 of the tray 600. Thereby, stackable trays 600 are formed where the protrusions 608 define the distance between adjacent stacked trays 600. The protrusion 608 may also be referred to as a spacer configured to form a space between stacked trays. The illustrated container is a rectangular tray 600 with rounded corners and having a horizontal flange 606, but containers of many different shapes may be formed using the described method and tool, such as square, round or even polygonal containers.

[0055] The method may further comprise laminating an inside of the fibrous pulp tray 600 with a plastic film by arranging a plastic film over the tray and heating the film so that it softens and adapts to the shape of the inner surface of the tray 600. By means of the smooth inner surface of the tray, the occurrence of pinholes and other defects of the laminated film can be significantly reduced compared to for an inner surface comprising depressions, recesses protrusions or any other structure deviating from a smooth surface profile.

[0056] Even though the invention 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. Also, it should be noted that parts of the described tool and method may be omitted, interchanged or arranged in various ways, the tool and method yet being able to perform the functionality of the present invention.

[0057] Additionally, variations to the disclosed embodiments can be understood and effected by the skilled person in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. 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. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.