Technical field

The present invention relates to an arrangement and a method for producing a 3D molded product from pulp slurry.

There is a growing interest for producing cellulose-based articles and products, e.g. for use as bottles, containers, packaging applications for foodstuff, tableware, trays, technical products, electronic equipment and/or consumer goods. Several advantages

10 are associated with the use of natural fibers for manufacturing packages. Being a renewable resource, natural fibers provide a sustainable alternative to other packaging materials such as aluminum and plastics, and furthermore natural fibers are both recyclable and biodegradable allowing for composting. Natural fibers include cellulose fibers of any natural origin, such as derived from wood pulp and/or plants.

One way of producing items from fibers is by molding pulp. For instance in wet forming, an aqueous pulp suspension is applied onto a forming tool/drying mold to form a wet fiber layer followed by

20 compression-molding performed under elevated temperatures, resulting in a dried fiber product having a shape complementary to the shape of the mold. Typically, said molding tool is perforated or porous so that water and steam can be removed from the wet pulp during forming, such as in a dewatering/drying step. Dewatering is

25 an important part of wet forming procedures, and quick and efficient drying is advantageous in order to achieve a competetive product in terms of e.g. price and energy consumption. i An example of a molding tool is seen in W02009/105027A1, describing a device and method for compression molding a fiber tray of cellulose. Another porous drying mold is seen in W02020/141208A1, wherein a pair of molds, one being porous, presses a layer of pulp to a three-dimensional product.

It is a known problem in the field of molding pulp that the porous tools become clogged upon use and need frequent and timeconsuming cleaning. In case cleaning is neglected and the pores are plugged, the result is poor steam evacuation upon drying which may lead to steam explosions and thus to destroyed equipment and/or products. Attempts have been made to resolve this problem and avoid clogging, e.g. by using meshes or by providing only a few suction holes in the tool. However, use of meshes is expensive and results in a rough surface quality, and too few evacuation openings lead to poor drying and increased risk of steam explosions.

Object of the invention

It is an object of the present invention to provide a tool which resolves or at least minimizes the above-mentioned problems, and which enables for quick and easy drying of wet molded fiber products.

Summary of the invention

The object of the invention is obtained by means of a tool according to the appended claims.

In accordance herewith, there is provided an arrangement for drying a molded, fiber-based product comprising: -a drying mold having a front side and an opposite rear side, and a porous mold body arranged to support a fiber-based product when such a product is placed on the mold front side; and

-a suction delivery base coupled to a suction source, said suction delivery base comprising a receiving space matching said drying mold and arranged to receive said drying mold; wherein said drying mold further comprises a distancing structure at the rear side, arranged so that a distancing space is created between the mold body and the receiving space, wherein the suction delivery base upon activation of the suction source is arranged to deliver an evenly distributed suction to the front side of said drying mold via said distancing space and through said porous mold body. In one aspect of the invention, the suction delivery device comprises heating elements for heating the fiber-based product during drying, allowing for combined heating and suction of water and/or steam.

It is to be understood that the term "fiber-based" means "containing fibrous material" such as natural fibers including cellulose fibers.

It is further to be understood that the term "porous" means that the mold body is arranged with small holes, passages or pores allowing liquid I air to pass through, i.e. that the mold body is air- permeable. Further, the term "porosity" as used in this description is defined as the ratio in % of perforated front side surface area (i.e. the sum of the cross-sections of all pores at the front side surface) to total front side surface area.

It has been found that an arrangement according to the invention leads to several advantages. The air-permeable mold body can be made thin thanks to the support provided by the distancing structure, and thus the pores are not clogged upon use. Also, the porous mold body may comprise a higher porosity compared to known tools which allows for efficient steam evacuation, minimizing the risk for steam explosions thus allowing for application of higher drying temperatures and reducing the drying time. The design of the tool also leads to even suction distribution across the mold surface, i.e. meaning that a continuous suction is delivered to an equal extent across the whole surface at the same time. This in its turn leads to a uniform and speedy drying of the product. In summary, the tool according to the invention does not get clogged, it is easy to clean, the arrangement provides even and efficient drying of the fiber-layer and enables production of high-quality molded fiber products.

A further advantage achieved thanks to the efficient steam evacuation is the possibility of designing the mold body with a smooth top surface (i.e. the surface arranged to support the fiber product) void of large evacuation openings. This means the resulting dry molded product will acquire an even surface with very low roughness which is both aesthetically appealing and also leads to improved barrier quality in case of lamination or barrier surface coating of the end product. Uneven surface on a substrate on which a barrier is applied leads to the risk of pinholes and/or barrier rupture causing leakage when using the product e.g. for carrying food stuff.

Further features and advantages obtained thanks to the invention will be explained in the following. According to one aspect of the invention, the drying mold is made of metal, preferably aluminum. Hereby, the mold tolerates high temperatures such as temperatures above 200°C, such as above 250°C.

According to another aspect of the invention, the porous mold body comprises a wall thickness between 1 - 10mm, preferably 2 - 5mm. Thanks to the thinness of the mold body, the pores/openings are not prone to clogging, i.e. the drying mold is void of narrow passages where fines, fibers, resins and/or chemicals risk to get stuck.

According to another aspect of the invention, the porous mold body comprises a porosity between 0.1 - 50%, preferably between 0.2 - 40%, more preferably between 0.5 - 15%. Preferably, said porous mold body further comprises through-passages having a diameter between 0.1 - 1mm, more preferably between 0.2 - 0.9, even more preferably between 0.7 - 0.9 mm. The optimized porosity of the mold body ensures even and efficient evacuation of water and steam upon drying procedure, and still does not get clogged by fines, fibers and/or chemicals.

According to another aspect of the invention, said distancing structure comprises multiple, elongated bars, arranged parallel to each other at said rear side of the molding tool. In a preferred embodiment, said parallel, elongated bars do not intersect each other, meaning that no bar intersects /crosses another bar.

According to one embodiment, the distance between two parallel bars is between 2 - 15mm C-C, and the thickness (t) of each bar is between 1 - 5mm. According to another aspect, the distance between two parallel bars is between 5 - 10mm C-C, and the thickness of each bar is between 1 - 2mm. Furthermore, according to one embodiment of the invention, the distance between the mold body and said receiving space in the suction delivery base, created by said distancing structure, is at least 0.5mm, preferably at least 1mm, even more preferably at least 2mm. According to a preferred embodiment, the distance between the mold body and the surface of said receiving space does not exceed 7mm, preferably does not exceed 5mm.

According to yet another aspect of the invention, the suction delivery base comprises a suction distributing formation which, upon activation of the suction source, is arranged to distribute suction evenly across the rear side surface of the porous mold body and through the porous mold body.

According to yet another aspect of the invention, the porous mold body is manufactured by means of 3D-printing technology, preferably from aluminum material. According to one embodiment of the invention, the porous mold body and the distancing structure are manufactured in one piece.

The invention also relates to a method for producing a molded product from fiber-containing pulp slurry, comprising the steps of: a) providing a pulp slurry and wet-molding a three-dimensional fiber-based intermediate structure from said slurry wherein said intermediate structure comprises a dry content between 15-60wt%; b) transferring said intermediate structure to an arrangement according to the invention; c) placing said intermediate structure on the mold body at the front side of said drying mold while activating said suction source such that a suction is drawn through said porous mold body, thereby drying said intermediate structure to a dry content of >88wt%, preferably >94wt%, more preferably >96% thus obtaining a dried molded fiber product.

According to one aspect of the invention, step c) further comprises heating the intermediate structure to a temperature >150°C.

According to another aspect of the invention, step c) above, representing drying, may be repeated multiple, consecutive times, such as two, three, four or more times, until the end product has reached a desired dryness.

According to yet another aspect of the invention, the method further comprises providing a second drying mold matching said first drying mold and in step c) pressing said intermediate structure between said first and second molds while applying suction preferably combined with heat to evacuate water and steam.

The skilled person understands that many variations of the invention are conceivable without departing from the scope of the application. For example, said distancing structure may be designed in many ways in addition to the above-described parallel, elongated bars. The distancing structure may be arranged as non-parallel bars, or the comprise discontinuous structures and/or a grid pattern or any other outline which provides the function of creating a distancing space allowing for even distribution of applied suction. Brief description of the figures

By way of non-limiting examples only, embodiments of aspects of the present disclosure will now be described with reference to the accompanying figures in which:

Fig. 1 shows in a schematic way a perspective view, partially exploded, of an arrangement according to the invention;

Fig. 2 shows in a schematic way a frontal view of a suction delivery base according to one embodiment of the invention;

Fig. 3a shows in a schematic way a cross-sectional view of an arrangement according to the invention;

Fig. 3b is a detailed view of a cross section of an assembled arrangement according to one embodiment of the invention, showing the intersection between the drying mold and the suction delivery base;

Figs. 4a-b shows in a schematic way a perspective view and a side view respectively of a drying mold according to one embodiment of the invention; and

Fig. 5 illustrates in a schematic way the set-up of an arrangement according to one embodiment of the invention.

Detailed description

The arrangement and method according to the invention will now be described with reference to the appended figures.

Fig. 1 illustrates in a schematic way an arrangement 1 according to the invention, herein seen in a partially exploded view, including a first drying mold 10 and a suction delivery base 6. Said drying mold 10 has a front side 11 and a rear side 12, wherein the front side 11 is intended for carrying and supporting a molded fiber product to be dried and the rear side 12 is arranged to face the suction delivery base 6 upon assembly of the arrangement 1. As seen in the appended figures, the drying mold 10 as pictured herein is designed to support a molded fiber product in the form of an open tray. The invention is not, however, limited to trays but can be modified in shape so as to manufacture various types of molded fiber articles such as bowls, lids, boxes, bottles, packages for electronics etc. The longitudinal direction L and the transverse direction T are indicated in Fig. 1.

The suction delivery device 6 is arranged with at least one receiving space 63 (also called "receiving cavity" 63) matching said drying mold 10 in shape and being arranged to receive said drying mold during assembly and use. In the example of Fig. 1, the suction delivery device 6 comprises two receiving spaces 63 for receiving two respective drying molds 10.

Moreover, as better pictured in Fig. 2 and Fig. 3a respectively, each receiving space 63 of the suction delivery base 6 comprises a suction distributing formation 60, which herein is in the form of a suction channel or groove extending longitudinally L along the bottom portion of the respective space 63. The suction distribution formation 60 (e.g. suction channel) connects to a number of suction outlets 64 which passes through the base 6 via through channels 61 which are, in their turn, arranged to be connected to a vacuum source I suction source 8 (a suction source 8 schematically shown in Fig. 5). The suction delivery base 6 may also comprise heating elements arranged to heat the receiving spaces 63 and transfer heat via the drying mold 10 to any fiber-based product supported by it. One way of achieving such function is by means of integrating heating rods into the base 6 via internal bores 62 extending through the structure 6.

The drying mold 10 is now to be more thoroughly described. An example of the drying mold 10 according to a preferred example of the invention is seen in Figs. 4a-c. The main body of the mold 10 is made from a porous I permeable structure, herein referred to as the porous mold body 14. The mold body 14 is preferably made of metal such as aluminum and comprises a wall thickness w between 1.5 - 3mm (see Fig. 3b). The mold body 14 has a porosity between 0.1 - 50%, preferably between 0.2 - 40%, more preferably between 0.5 - 15%. Furthermore, the porous mold body 14 is manufactured by means of 3D-printing technology, preferably from aluminum material. At the rear side 12 of the drying mold 10, seen e.g. in Fig. 4a, there is arranged a distancing structure 4 which upon assembly of the arrangement 1 creates a distancing space 5 between the rear side of said mold body 14 and the meeting surface 65 of the receiving space 63. In the example shown in the figures, the distancing structure 4 comprises multiple, elongated bars 4', arranged parallel to each other along a transversal direction T at said rear side 12 of the mold 10 so that no bar crosses another bar. In one example, the distance d between two parallel bars is between 5 - 10 mm center-to-center, and the thickness t of each bar is between 1 - 2 mm.

Fig. 3a illustrates a cross sectional view of an assembled arrangement 1 according to the invention, wherein a drying mold 10 is positioned in a receiving space 63 of a suction delivery body 6. As seen in the detailed view of Fig. 3b, the distancing bars 4' of the drying mold 10 creates an open distancing space 5 between the rear wall surface of the mold body 14 and the meeting surface 65 of the respective receiving space 63. In a preferred embodiment, when assembled, the distance referred to as "X" between the rear wall surface of the mold body 14 and said meeting surface 65 is between 3 - 7 mm, or between 3 - 5 mm. In such a preferred embodiment, said distance X does not exceed 7 mm, or optionally does not exceed 5 mm. When the arrangement 1 is assembled, the distancing structure 4, e.g. in the form of bars 4', is resting on the surface 65 of the receiving space 63 thus forming a support structure for the mold.

Furthermore, in assembled configuration, the distancing structure 4 of the mold 10 is arranged so that suction drawn via the suction outlets 64 and the suction channels 60 respectively is allowed to be spread evenly across the entire rear side 12 of the mold 10. In the example seen in the appended Figures, this is achieved in that the suction distribution channel 60 is extending perpendicular compared to the extension direction of the distancing bars 4'. See e.g. Fig. 3a. This way, suction will reach the entire distancing space 5 created between the mold body 14 and the meeting surface 65 of the respective receiving space 63 by said bars 4'. As understood by the skilled person, other ways of achieving the same result are conceivable.

The method and function of the present invention will now be described. For this purpose, reference is made to Fig. 5 which shows an example of the arrangement 1 according to the invention in a schematic way. In one example, the invention is used for drying a fiber product that has been formed in a previous step by means of wet forming procedure. In wet forming, a pulp slurry is provided which contains natural fibers such as cellulose fibers, and a forming mold is brought into contact with said slurry to wet-form an intermediate three-dimensional (3D) structure 3 which may be dewatered by compression to a dry content between 15-60wt% based on the total fiber content, or between 20 - 35wt%. The hereby obtained semiwet intermediate 3D structure is subsequently transferred to a downstream drying station in which an arrangement 1 according to the invention is used for further drying. As illustrated in Fig. 5, the intermediate fiber-based structure 3 is placed on the porous / permeable body 14 at the front side 11 of the mold 10, which mold 10 is then brought into assembled position in the receiving space 63 of the suction delivery base 6 (as seen in Fig. 3a). Activation of the suction source 8 then leads to that an evenly spread suction is created at the rear side 12 of the mold 10 drawing water and steam through the porous mold body 14 via said distancing space 5 and said suction channel 60, out through the suction outlets 64. Preferably, drying is performed by means of drawing vacuum through the drying mold and at the same time applying a pressure and heat on the fiber layer 3 present on the mold front surface 11. Application of pressure can be achieved in various ways, such as using a permeable or impermeable physical pressing member as seen in Fig. 5 in the form of a second drying mold 20. Other pressing methods can be used such as compressed air, a flexible pressing membrane, heated compressed air or superheated steam for pressing the fiber-based article against the respective drying mold. Preferably, the fiber structure 3 is heated to between 100-300°C during drying operation. In this manner, the intermediate 3D structure 3 is dried to a dry content of >88wt%, preferably >94wt% based on the total fiber content, more preferably >96% thus obtaining a final, dry fiber product having a three-dimensional shape. The drying step as described herein may be repeated several times, wherein the dry content of the fiber-based product is increased stepwise for each round.

The foregoing description of the preferred embodiments of the present invention is provided for illustrative and descriptive purposes. It is not intended to be exhaustive or to restrict the invention to the variants described. Many modifications and variations will obviously be apparent to one skilled in the art. The embodiments have been chosen and described in order best to explain the principles of the invention and its practical applications and hence make it possible for specialists to understand the invention for various embodiments and with the various modifications appropriate to the intended use.