WO2024094791A1

WO2024094791A1 - Method for producing cellulose fiber-based fluffboard products

Info

Publication number: WO2024094791A1
Application number: PCT/EP2023/080542
Authority: WO
Inventors: Viktor SEUNTJENS; Dominique Albert Irma VERMEIREN
Original assignee: Gate Gourmet Switzerland Gmbh
Priority date: 2022-11-03
Filing date: 2023-11-02
Publication date: 2024-05-10

Abstract

The present invention relates to a method of producing cellulose fiber- based products (103, 800), the method comprising the steps of: • (ia) providing at least two layers including one first (104a) and one second (104b) layer, and wherein said first (104a) and second (104b) layer each comprise cellulose fibers, and wherein at least one side of said first (104a) and said second (104b) layer is pre-treated (705) with a first heat curing mixture, • (ib) curing (706) said pre-treated at least two layers by exposure to elevated temperatures; • (iia) wetting said at least two cured layers; • (iib) arranging said at least two wetted layers in a superimposed relationship to each other in a forming mold (102) of a form press (101); • (iii) form pressing said stack (104) in a forming mold (102), wherein in said step (iii) said at least two layers including said one first (104a) and said one second (104b) layer are moveable with respect to each other and wherein the cellulose fibers are derived from fluffboard or fluff pulp.

Description

METHOD FOR PRODUCING CELLULOSE FIBER-BASED FLUFFBOARD PRODUCTS

FIELD OF THE INVENTION

The present invention relates to a process for cellulose fiber-based product originating from fluffboard or fluff pulp materials. Said product is typically a three-dimensional article, such as, but not limited to containers, cutlery and/or tableware, typically for single use.

BACKGROUND OF THE INVENTION

Today a vast majority of the articles for single use are still made of plastics. Plastics in general and in particular in the area of disposable articles are generating significant environmental challenges and concerns. Thus, there is an almost sky-rocketing demand for ecologically advantageous articles for single use. A low-price material having a low impact on environmental load and therefore commonly used for packaging inserts is molded pulp. Molded pulp is a packaging material, typically made from recycled paperboard and/or newsprint. It is used, for example for protective packaging such as inserts, beverage holders, protective buffer packaging etc. However, when in direct contact with food items, such as trays, plates bowls etc. molded pulp is not made of recycled material, but comes from any kind of virgin fiber like wood, bamboo, bagasse or even wheat straw. The cellulose fibers of these raw materials are dispersed in water, then formed and dried. Because the drying step is a time and energy consuming process, there is a need to circumvent this process step.

W02017/160217 and WO 2017/160218 relate to a method for manufacturing a cellulose product from a cellulose blank with less than 45 weight percent water in it, which is formed to flat or non-flat products with a pressure between 1 and 100 MPa at 100 to 200 °C in a forming mold comprising a flexible fluid impermeable membrane.

The WO 2021/0069942A1 relates to a method for producing a cellulose-based product from a multi-layer stack. During said process, the stack is formed into a single-layer configured product with a forming pressure of at least 1 MPa and a temperature between 100 and 300 °C.

While these processes provide a satisfactory product, they still require a lot of energy and a complex series of production steps. In the WO2021/148514, a first step to address the above-mentioned problems was made with the disclosed method for producing cellulose-based products. Herein, during the form pressing step included in the method, the different layer pressed together were allowed to move with respect to each other until the target pressure was reached. This allows for a relaxation of stress and strain within the material leading to a 30-40% higher stiffness of the final product. Hence, advantageously less material is required for satisfactory products lowering production cost and resource requirements.

Nonetheless, there is a need for further improved processes for producing advantageous cellulose- based products, wherein said products have satisfactory mechanical and chemical properties, can be manufactured with high precision as well as cost- and energy-efficient, and have a lowered environmental impact. In addition, such process should allow for preparing cellulose-based products that are aesthetically attractive and exhibit a number of additional performance parameters, such as low heat or cold conductivity, compostable and or recyclable and are of attractive haptic to the customer.

OBJECT OF THE INVENTION

The problem to be solved by this invention is to provide advantageous cellulose fiber-based products with a further lowered cost, energy and environmental impact profile.

SUMMARY OF THE INVENTION

It is therefore an object of the present patent application to provide an improved method for producing advantageous cellulose fiber-based products, which are stemming in this application from fluffboard or fluff pulp. The above-mentioned problems regarding the cost, energy and environmental impact profile of mostly single-use cellulose fiber-based product shall be addressed by this invention by avoiding or at least improving these points. This object is fulfilled by the process as claimed in the independent claim and the further embodiments being subject of the dependent claims.

These and other objects are solved by the method according to the present invention of producing a cellulose fiber-based product (103, 800), wherein the method comprises the steps of:

(ia) providing at least two layers including one first (104a) and one second (104b) layer, and wherein said first (104a) and second (104b) layer each comprise cellulose fibers, and wherein at least one side of said first (104a) and/or said second (104b) layer is pre-treated (705) with a first heat curing mixture and wherein optionally the other side is pre-treated (705) with a second heat curing mixture, wherein said first and said second heat curing mixture may be identical or different, preferably different, from each other;

(ib) curing (706) said pre-treated at least two layers by exposure to elevated temperatures;

(iia) wetting said at least two cured layers;

(iib)arranging said at least two wetted layers in a superimposed relationship to each other in a forming mold (102) of a form press (101), thereby generating a stack (104) of said at least two layers, wherein said one first (104a) and said one second (104b) layer are oriented within the stack (104) such that two sides pre-treated (705) with said first heat curing mixture face each other;

(iii) form pressing said stack (104) in a forming mold at a forming temperature of at least 50°C up to a forming end-pressure of at most 100 M Pa, into a cellulose based product (103, 800) of a predetermined shape and a single layer configuration, wherein in said step (iii) said at least two layers including said one first (104a) and said one second (104b) layer are moveable with respect to each other until said forming end-pressure is reached characterized in that the cellulose fibers are derived from fluffboard or fluff pulp.

In one embodiment the first heat curing mixture and the second heat curing mixture are waterbased dispersions and are preferably biodegradable and/or compostable and/or recyclable.

According to one embodiment the first heat curing mixture comprises at least one saccharide and the said second heat curing mixture comprises at least one saccharide and optionally an alkylated ketene dimer (AKD) and/or optionally a polyamidoamine epichlorohydrin (PAE) resin.

The area weight of an additive resulting from said first heat curing mixture and/or said second heat curing mixture ranges from 0.5 to 50 gsm, or from 2 to 25 gsm of the first and/or second layer. The first (104a) and/or second (104b) layer may comprise one or more additives that are altering the mechanical, hydrophobic, oleophobic, haptic, aesthetic properties of the cellulose fiber-based product, and wherein said first and/or second layer are constituted of cellulose fibers of from 50 to 100% dry wt, or from 60 to 100% dry wt, or from 70 to 100% dry wt, or from 80 to 100% dry wt, or from 90 to 100% dry wt and of said one or more additives of from 0 to 50% dry wt, or from 0 to 40 % dry wt, or from 0 to 30% dry wt, or from 0 to 20% dry wt, or from 0 to 10% dry wt.

The one or more additives are selected from the group consisting of starch compounds, in particular starch-based polymers, rosin compounds, polycarboxylic, in particular butanetetracarboxylic acids, gelatin compounds, alkyl ketene dimer (AKD), alkenyl succinic anhydride (ASA), wax compounds, silicon compounds, calcium compounds, sol-gels, micro- fibrilated cellulose compounds, water-based PHA compounds and fluorocarbons.

The one or more additive is added to said first (104a) and/or second (104b) layer prior to step (i).

The method of any of the preceding claims, wherein the forming mold (102) is heated to a forming temperature of from 50 °C to 250 °C, or from 100 °C to 200 °C.

In one embodiment the biodegradable additive is applied with the same or a varying thickness to at least one side of each of the cellulose fiber-based layers (104a, 104b).

Each of the first (104a) and second (104b) treated layers have an area weight ranging from 50 to 2000 gsm, or an area weight ranging of from 600 to 750 gsm.

The stack (104) comprises or consists of 2 to 10, or 2 to 7, or 2 to 5 first (104a) and second (104b) layers.

In one embodiment the total weight of the cellulose fiber based treated layer is in the range of from 650 to 2200 gsm, or in the range of from 1250 to 1550 gsm.

According to the embodiment the surface of said cellulose fiber-based product (103, 800) is dip coated or sprayed or curtain poured or brushed with a finish.

In a still further embodiment, the present invention is directed to a cellulose fiber-based cutlery and/or cellulose fiber-based tableware manufactured according to the method according to the present invention. One particular advantage of the claimed method is to be seen in the fact that the individual layers ultimately constituting the cellulose fiber-based product stay moveable with respect to each other for a comparably longtime during formation. This allows for a relaxation of stress and strain, primarily within the material between the individual cellulose fiber-based layers, occurring during formation under pressure, which in turn reinforces the so-produced product and provides the product with a high stiffness. For example, the stiffness of the final product is at least 30% higher compared to a product which was produced by pre-laminating the individual layers such that prior to form pressing the individual layers already adhere together. That is, because in the case of prelaminating before form pressing stress and strain, which results from deformation of the adhered layers during form pressing, is not released. Therefore, the individual layers do not obtain the freedom to move, slight or shift against each other while being subject to the deformations. Stiffness is hereby defined as the measure of resistance offered by the final product to mechanical deformation, e.g. deformation due to form pressing.

Therefore, further advantageously less material is necessary for product manufacture, which lowers production cost and resource requirements.

Furthermore, the layer-structure allows for the implementation of various aesthetic and/or in-use properties within the respective layers enabling the production of tailor-made products for individual customers.

In addition, the process does not need a pre-compacting step, which is disadvantageous under energy-, cost-, complexity and machine footprint aspects of the claimed process.

BRIEF DESCRIPTION OF DRAWINGS

Fig. 1 schematically shows a method for producing a cellulose fiber-based product from a stack of a first and a second layer in a form press.

Fig. 2 schematically shows an embodiment, wherein a multi-layer of coated cellulose fiber-based sheet material is provided and from which two-dimensional shapes corresponding to the final three- dimensional product are cut out. These two dimensional cut out shapes are stacked in the bottom part of a forming mold of a form press. Fig. 3 schematically shows a cross sectional view of an embodiment, wherein in the bottom part of the forming mold two, two-dimensional cut outs are arranged in a stack before form pressing the stack.

Fig.4 schematically shows an embodiment where the stack of cellulose fiber-based cut outs is form pressed into a three-dimensional product by pressing the stack of cut outs into the bottom part of the mold through the top mold part approaching it, whereby the mold is successively closed.

Fig. 5 schematically shows a single layered massive structure, which is subject to a bending force F, whereas the figure serves to illustrate the tensile and yield stresses.

Fig. 6 schematically shows a detailed cross-sectional view of an embodiment of the upper mold part and the lower mold part having a first and a second layer stacked between the two mold parts. Additionally, the corresponding forces acting upon these layers when being form pressed are indicated by arrows.

Fig. 7 schematically shows the pre-treating and heat curing steps performed previous to the wetting and arranging in the forming mold.

Fig. 8 shows respective embodiments of cellulose fiber-based products. Spoon and knife are made from layers of cellulose fiber-based material obtained from fluffboard.

DETAILED DESCRIPTION OF THE INVENTION

The present application relates to a method for manufacturing a cellulose fiber-based product. The term “cellulose fiber-based product” herein refers to product that is mainly constituted of cellulose. The cellulose therein stems from fluffboard or fluff pulp. The terms “fluffboard” and “fluff pulp” refer to type of chemical pulp made from long fiber softwoods. Other commonly used names fobjefor similar materials are comminution pulp or fluffy pulp. The used materials have a weight per area in the range of from 50 to 2000 gsm, or 150 to 1800 gsm, or 300 to 1600 gsm, or 400 to 1400 gsm, or 500 to 1200 gsm, or 600 to 1000 gsm, or 600 to 800 gsm, or 650 to 700 gsm. The term “softwood” refers to wood from gymnosperm trees. Said product preferably has a three-dimensional shape. With respect to its shape, there exists in principle no limitations. The cellulose fiber-based product as prepared by the method as claimed is particularly useful for packaging of any kind of objects or to be used, in particular in combination with food items. Products, for example are trays, plates, bowls, containers and cutlery. One particular aspect with regard to the cellulose fiber-based products as prepared by the method as claimed is cutlery, in particular, cutlery for single-use, which further particular is biodegradable, compostable, recyclable and/or glue-free.

Within step (ia) of said process, at least two layers including one first and one second layer are provided. The cellulose fibers incorporated within said first and/or second layer stem from said fluffboard or fluff pulp material as defined above. The cellulose fibers thus stem from softwood as defined as well above.

The fluffboard materials are arranged to form cellulose fiber-based sheets, or paper, or board, wherein an individual sheet corresponds to a layer, e.g. a first and/or a second layer.

In a particular embodiment according to the invention, the fluffboard or fluff pulp material is not milled previous to its use as a starting material for the method according to the invention.

In one embodiment, the provided cellulose fiber-based material used in the method for manufacturing a cellulose-based product may contain more than 45 % by weight water. In particular, a cellulose blank containing less than 45 % by weight water is excluded as a starting material for the method of the present application.

In another embodiment, the cellulose fiber-based products are produced by methods excluding the dry manufacturing method as disclosed in WO 2017/160218, i.e. a method for manufacturing a cellulose product, comprising the steps: dry forming a cellulose blank (1 a) in a dry forming unit (1 1 ); arranging the cellulose blank (1 a) in a forming mould (3); heating the cellulose blank (1 a) to a forming temperature in the range of 100°C to 200°C; and pressing the cellulose blank (1 a) in the forming mould (3) with a forming pressure of at least 1 MPa is excluded.

The resulting first and/or second layers are further pre-treated with a first heat curing mixture on one side. The term “pre-treated” refers within this application to the process of applying said heat curing mixture as additive to the fluffboard material by e.g. spraying, coating, brushing, kiss roll coating, flexo coating, rotogravure coating, submerging etc. Further, the pre-treating may occur either by applying the mixture as a pre-mixed composition or by applying each component belonging to said mixtures successively. The term “successively” refers to an embodiment wherein the components of the mixture disclosed may be applied to said first and/or second layer as different solution in any order. The term “first heat curing mixture” refers within this application to a mixture which cures when heated comprising at least one saccharide, optionally at least one alkylated ketene dimer (AKD), and optionally at least one polyamidoamine epichlorhydrin (PAE) resin. The term “mixture” refers within this application to any form of aqueous systems like dispersions, suspensions, slurries, and/or solutions. The term “aqueous” thereby refers to systems containing water as liquid phase, either as a single solvent or as part of a solvent mixture, wherein the water is selected from the group consisting of tap water, deionized water demineralized water and distilled water. The solvent mixture may further comprise short chained alcohols and/or ketones.

The saccharide thereby is selected from the group consisting of starch, glucose, fructose, and cationic starch. Said first heat curing mixture comprises said saccharide in a concentration range of from 0.5% to 60 % by weight, or from 0.5% to 50% by weight, or from 1.0% to 40% by weight, or from 1.0% to 30 % by weight, or from 1.5% to 10% by weight, or from 1 .5% to 5% by weight, based on the total weight of the solution.

In a particular embodiment, said mixture is biodegradable and/or compostable and/or recyclable.

In another embodiment, the components of said first heat curing mixture are applied to said first and/or second layer successively. Thereby, first starch, then optionally PAE and finally optionally AKD is added.

In another embodiment, the first heat curing mixture is added as a pre-mixed additive composition to said first and/or second layer.

Further, the other side of said first and/or second layer may be pre-treated with a second heat curing mixture as an additive. The term “second heat curing mixture” refers within this application to a mixture, which cures when heated comprising at least one saccharide, optionally at least one alkylated ketene dimer (AKD), and optionally at least one polyamidoamine epichlorhydrin (PAE) resin. The terms “pre-treated” and “mixture” are the defined as above.

The saccharide of said second heat curing mixture is selected from the group consisting of glucose, fructose, starch, and cationic starch. Said second heat curing mixture comprises said saccharide in a concentration range of from 0.5% to 60 % by weight, or from 0.5% to 50% by weight, or from 1.0% to 40% by weight, or from 1.0% to 30 % by weight, or from 1.5% to 10% by weight, or from 1.5% to 5% by weight, based on the total weight of the solution.

Said second heat curing mixture comprises an alkylated ketene dimer (AKD) in a concentration range of from 2.5% to 25 % by weight, or from 5% to 20% by weight, or from 10% to 15% by weight, based on the total weight of the solution.

Said second heat curing mixture may further comprise said at least one polyamidoamino epichlorohydrin (PAE) resin in a concentration range of from 1% to 20% by weight, or from 2.5% to 15% by weight, or from 4% to 10% by weight, based on the total weight of the solution.

In one embodiment, the said second heat curing mixture is a water-based solution comprising a polyamidoamine epichlorohydrin (PAE) resin.

In another embodiment, the components of said second heat curing mixture are applied to said first and/or second layer successively. Thereby, first starch, then PAE and finally AKD is added.

In another embodiment, the second heat curing mixture is added as a pre-mixed composition to said first and/or second layer.

In a particular embodiment, said mixture is biodegradable and /or compostable and /or recyclable.

Within step (ib) of the method according to the invention, said pre-treated first and/or second layers are cured by exposure to elevated temperature. Said elevated temperatures are reached by irradiation with IR or microwave radiation, conduction or by exposure to hot air. Said IR radiation thereby lies in the range of from 0,75 to 50 pm.

The temperature for the curing step is in the range of from 50°C to 250°C, or from 70°C to 200°C, or from 80°C to 180°C, or from 90°C to 150°C.

Within step (Ila) of the method according to the invention, said at least two layers are wetted. The term “wetted” refers to a method for applying an aqueous mixture in a way that at least one surface of each layer is covered with water. The term “aqueous” is defined as above. The mixture may further comprise short chain alcohols and/or ketones. Within step (iib) of the method according to the invention, said at least two wetted layers are arranged, e.g. positioned, in the cavity of the lower part of the forming mold of a form press, whereas the layers are stacked upon each other. The layers are thereby in loose contact with their adjacent layers. Therefore, the stacked layers are free to move, e.g. shift against each other, in particular upon deformation due to external forces acting upon the stack.

In a preferred embodiment, the layers are at least pre-treated with said first heat curing mixture, wetted, and the layers are stacked, such that between adjacent layers said first heat curing mixture is located. In this preferred embodiment, e.g. the upper most layer, which forms the top surface of the stack, i.e. the product top surface side, is formed by a side which was pre-treated with said second heat curing mixture. Additionally, the lower most surface, which is formed by the bottom surface of the stack, is as well pre-treated with said second heat curing mixture.

Within step (iii) of the method according to the invention, the stacked layers are pressed by closing the form press, e.g. the upper and the lower part of the form press mold are approaching each other. Closing of the form press will exert a forming pressure onto the stack upon which the stack is subject to deformations, which transform the stack into the tree-dimensional shape of the product. The upper and lower part of the form press may continuously approach each other during form pressing. A discontinuous movement can be thought of as well to, for example to build up a predetermined pressure profile. Depending on the elastic properties of the stacked layers, a material specific end-pressure is predetermined and ultimately reached upon form pressing. When the forming end-pressure is reached the process of form pressing is finished, e.g. if an endpressure of at most 150 MPa is reached, the upper part of the press is automatically withdrawn and the pressed stack is released. Generally, the end pressure is set to a value of 1 MPa to 100 MPa, or to 5 MPa to 75 MPa, or 5 MPa to 50 MPa, or 5 MPa to 30 MPa, or 10 MPa to 20 MPa.

The cellulose fiber-based product may be formed in the forming mold during a forming time period in the range of 0.001 to 20 seconds. Alternatively, the forming time period may be 0.01 to 15.0 seconds or 0.1 to 10.0 seconds. The time period is chosen so that the desired properties of the cellulose fiber-based products are achieved, e.g. the stiffness being at least 30%, e.g. about 40% higher than compared to form pressing a pre-laminated stack, while resulting in good adhesion between the layers, which in turn contributes significantly to the mechanical properties and useability of the cellulose fiber-based product. During form pressing of step (iii) of the method according to the invention, the forming mold, e.g. the upper or the lower or both parts of the forming cavity are heated to the forming temperature in the range of from 50 to 250 °C, or 70 to 200 °C, or 80 to 180 °C, or from 90°C to 150°C. That is, the temperature of the forming cavity is kept constant during the form pressing at the forming temperature of, e.g. 130 °C. Heating of the forming mold may take place before arranging the stack in the forming mold or at least partly before form pressing in the forming mold. This may for example be accomplished through arranging a suitable heating unit in the manufacturing process.

The forming mold cavity, e.g. the upper and/or the lower part of the forming mold of the form press can be constructed to allow for isostatic pressing of the stack, i.e. the molding pressure is applied evenly distributed in all directions around the stack of layers. Therefore, the upper and/or the lower part of the forming mold comprises flexible, e.g. liquid like mold parts.

Within step (iii) of the method according to the invention, said stacked layers are pressed into a single layer configuration. The single layers may or may not be visible by eye to a customer. The layers are two dimensionally interconnected with each other.

The obtained product from the form pressing step (iii) of the method according to the invention forms a material with monolayer configuration in the sense that there exist a durable adhesion between the two layers. Without being bound to theory, it is believed that an interaction known as hydrogen bindings, e.g. between the at least one first and at least one second layer of the cellulose fiber-based material, is responsible for this interaction.

According to other aspects of the invention, the at least one first layer and/or the at least one second layer comprise one or more additives that are altering the properties, e.g. the mechanical, hydrophobic, and/or oleophobic properties of the cellulose fiber-based product. Each of the first layer and/or the second layer can have a material composition of from 50 to 100% dry wt, or from 60 to 100% dry wt, or from 70 to 100% dry wt, or from 80 to 100% dry wt, or from 90 to 100% dry wt cellulose fibers and from 0 to 50% dry wt, or from 0 to 40 % dry wt, or from 0 to 30% dry wt, or from 0 to 20% dry wt, or from 0 to 10% dry wt of the one or more additives. The examples of additives of the first layer and/or the second layer are starch compounds, rosin compounds, polyamidoamine epichlorohydrin (PAE), sucrose esters, modified cellulose, water-based suspensions of polyhydroxy alkanoates (PHA) butanetetracarboxylic acid, gelatin compounds, alkyl ketene dimer (AKD), Alkenyl Succinic Anhydride (ASA), wax compounds, silicon compounds, calcium compounds, sol- gels, micro-fibrillated cellulose compounds, water-based PHA compounds, and/or fluorocarbons. By using additives in the first layer and/or the second layer, the properties of the cellulose fiberbased product can be efficiently steered and controlled. The additives can alter the properties, e.g. the mechanical, hydrophobic, and/or oleophobic properties so that the cellulose fiber-based product can be used for different purposes. For example, it can be possible to create a scratch free surface by the use of a starch compound or a calcium compound, such as calcium carbonate, as an additive.

Other additives, that may be suitable for products coming into contact with food, used in the different layers are for example; carbonate salts; polysaccharides; minerals, such as silica; paraffins, such as microcrystalline waxes, low-molecular polyolefins and polyterpenes; polyvinyl alcohol; silicone oils resins or elastomers; chromium chloride complexes; aluminium, calcium, sodium, potassium, and ammonium salts; casein; mannogalactanes; sodium salt of carboxymethyl cellulose; methyl cellulose; hydroxyethyl cellulose; alginates; xanthane; copolymer structures; basic potassium zirconium carbonate; imidazolium compounds; phosphoric acid ester of ethoxylated perfluoropolyetherdiol; modified polyethylene terephthalates, perfluoropolyether dicarbonic acid; polyhexafluoropropylene oxide.

According to other embodiments of the invention, the one or more additives of the first layer and/or the second layer are added to the respective layer prior to or after said step (ia) of the process.

In a further embodiment of the present invention, the method of producing a cellulose fiber-based product defined by said steps (i) to (iii) said process can be carried out in a batch-wise or a continuous manner, preferably a continuous manner. In this embodiment the at least one first and at least one second layer(s) may be provided in the form of a continuous layer, e.g. similar to a conveyor belt, from which two dimensional cut outs corresponding to the three dimensional final product shape are continuously made. These cut outs are after being wetted in step (iia) of the method according to the invention eventually automatically fed into the cavity of the, e.g. lower forming mold and thereby automatically arranged in a superimposed relationship as it is described in step (iib) of the method according to the invention to generate the stack of first and second layers. In particular, said continuous process is particularly efficient for manufacturing the cellulose fiber-based product. In a certain embodiment, at least one of the layers of the multilayer cellulose fiber-based product is a pre-printed or a colored layer. For example, the layers which are exposed to the customers for handling the final product are colored or label imprinted. For example, preprinting or coloring is used for branding and/or content descriptions, eliminating the need for additional labels, or to obtain an attractive appearance of the cellulose fiber-based product. The layer or layers may be colored through any suitable conventional coloring method, and graphical figures or patterns may be printed on the layer or layers so that the cellulose fiber-based product will have an aesthetically appealing design.

The invention will be described in greater detail in the following, with reference to the attached drawings according to Figs. 1 to 8.

In the embodiments of Figs. 1 to 8 during arrangement of the first 104a and the second 104b layer in a superimposed manner in the lower forming mold 102b the layers 104a, 104b have an essentially flat shape. However, other initially non-flat layers can alternatively be arranged in the lower 102b or likewise upper part 102a of the forming mold 102. The multi-layer stack 104 positioned in the forming mold 102 of the form press 101 presents a shape similar to the shape of the final product 103, 800 desired.

A flat shape may refer to a generally two-dimensional shape, such as for example the shape of a sheet material initially provided, and essentially non-flat shapes may refer to any suitable three- dimensional shape. The cellulose fiber-based product 103, 800 may have complex shapes with different thicknesses, or portions having holes or openings. For instance, the cellulose fiber-based product 103, 800 can comprise creases, shaped text, hinges, threads, handles or surface patterns.

Previous to arranging, said first 104a and/or second 104b layer is pre-treated 705 with a first and/or a second heat curing mixture. Said pre-treating 705 with said first and/or second heat curing mixture may applied thereby at once as one composition or the components of said first and/or second heat curing mixture may be applied successively. After said pre-treating 705, said first 104a, 704a and/or second 104b, 704b are heat cured 706 at elevated temperatures. Further after heat curing 706, the layers are wetted and arranged in the forming mold 102.

Fig. 1 schematically shows an embodiment of a method of producing a cellulose fiber-based product 103 from two cellulose fiber-based layers 104a, 104b. Most preferably the layers 104a, 104b are essentially made of cellulose fibers obtained from fluffboard material and the two layers 104a, 104b are arranged in a superimposed relationship to each other in the bottom part 102b of a forming mold 102 of a form press 101 , thereby generating a stack 104 of layers 104a, 104b. After positioning of these layers 104a, 104b in the bottom of the forming mold 102b, the upper part 102a of the forming mold 102 approaches the stacked layers 104 from top, whereas a forming pressure builds up, which acts onto the stack 104 and thus onto the individual layers 104a, 104b. At some point in time after initializing the pressing motion the end-pressure is reached, which is a predetermined pressure of e.g. 100 MPa, whereas upon reaching the end-pressure the upper part 102a of the form press 101 preferably automatically withdraws from the bottom part 102b of the forming mold 102. Upon withdrawal of the forming parts 102 the pressed three-dimensional predetermined product shape is at least partially exposed to temperatures below the forming temperature and the compact single layer configuration is cured due to the ability of cellulose fibers to build hydrogen bridges between the fibers when wetted and pressed. Generally, the end pressure is set to a value of 1 MPa to 100 MPa, or to 5 MPa to 75 MPa, or 5 MPa to 50 MPa, or 5 MPa to 30 MPa, or 10 to 20 MPa.

As schematically shown in Fig. 2, the initially provided cellulose based layers 204 are prior to positioning pre-shaped by cutting a two-dimensional shape 205, which corresponds to the final three-dimensional product shape, out of the initially provided sheet like layers 204, e.g. the shape of a spoon. That is, these cutouts 205 are arranged in the lower part 102b of the forming mold 102. Thereby the initially provided cellulose based layers 204 are cut individually or, in order to increase efficiency, the layers are cut in a single process step. That is, cutting of the layers can be done by punching, for example an initially provided sheet material from top to down. In a preferred embodiment, the downwards movement also pushes the cutout 205 into a cavity 206, which eventually will be the lower part 102b of the press forming cavity of the mold 102.

Fig. 3 schematically shows arranging the cellulose fiber- based layers 304a, 304b, 304c in the lower part 302b of the press forming cavity of the forming mold 302. In this superimposed relationship the at least first and second layer 304a, 304b are arranged in loose contact with each other, which is indicated in Fig. 3 by drawing the stacked layers 304 slightly separated from each other. In the superimposed relationship of the stack 304, the layers 304a, 304b are arranged on top of each other so that the layers 304a, 304b are in contact but are still able to move against each other, i.e. the layers 304a, 304b are able to shift along each other’s adjacent surfaces, when a force, e.g. the press forming force is acting upon the layers 304a, 304b or upon an individual layer 304a. The layers are arranged as discrete pieces. The layers 304a, 304b are arranged in the lower mold part 302b manually or automatically, e.g. layer by layer by hand, or the first, the second layer 304a, 304b, etc. are supplied by a conveyor belt or in a robotics-assisted manner known to those skilled in the art. In one embodiment said layer(s) 304a, 304b are supplied continuously, e.g. by a conveyor belt and the cutout geometries 205 of the final product 103, 800 are essentially automatically punched out and arranged in the lower part of the forming mold 302b such that the production process is a continuous one step process. The forming mold may 302 be arranged in a suitable forming mold unit comprising high pressure tools and other necessary pressing equipment.

Fig. 4 schematically shows an embodiment where a stack 404 consisting of a first and a second heat curing mixture coated layer 404a, 404b is pressed into the lower part of the forming mold cavity 402b by a pressing motion of the upper mold part 402a. Upon this pressing motion, the stack 404 begins to deform from its initial two dimensional cut out shape 205 into the desired three- dimensional product shape. Due to the curvature of the final product shape the initial pressing force F_o is to some extend translated into shear forces F_s acting upon each layer 404a, 404b. The shear forces F_s can vary over the thickness of the stack 404 depending on the degree of deformation. For example, depending on the product shape or product design, the radius of curvature of a spoon on its top surface, e.g. the upper most layer 404a of the stack 404, distinguishes more or less from the radius of curvature of its bottom surface, the bottom layer 404b of the stack 404.

This context is further illustrated in detail in Fig. 5. Fig. 5 shows an initially straight massive structure 500, e.g. a cross section of a part of a spoon, upon which an external bending force F is acting and which then bends the structure. A dotted middle line 505 is shown, which separates the structure into an upper part “Upp” and into a lower part “Low”. Further, a dashed symmetry line 506 separates the bended structure into a left “L” and right section “R”. Two radii of curvature r_t and r_b are measured from the symmetry line 506, whereas r_t refers to the top of the structure and r_b, refers to the bottom of the structure 500. Because the radii of curvature distinguish from each other through bending, “Upp” is subject to yield stress, which is indicated by F_y, whereas “Low” is subject to tensile stress indicated by Ft. The two counteracting forces F_y and Ft cancel each other out only at the intersecting point between the symmetry line 506 and the middle line 505. The counteracting forces thus destabilize the internal of the bended structure 500. Therefore, in order to reduce the degree of destabilization by these internal forces, the structure is split apart into individual layers 504a, 504b, e.g. separating the massive structure 500 between “Upp” and “Low”. Upon deformation caused by the external bending force F, the lower part “Low” and the upper part “Upp” would then shift against each other, as it is for simplicity reason only indicated on the one side “R” of Fig 5 by an amount characterized as dX, thereby releasing some of the tension caused by bending the two layers 504a, 504b.

In the following the forces acting between the individual layers 504a, 504b are further considered. That is the external bending force is not perpendicular pressing onto a layer but mimics the three- dimensional shape of the final product 103, 800. Thus, the bending forces are split into smaller forces acting in different directions upon the layers 504a, 504b.

Fig. 6 schematically shows a detailed view of the upper mold part 602a and the lower mold part 602b with a first 604a and a second 604b layer stacked in between the two mold parts 602, wherein the corresponding forces are indicated by arrows. The forces appear when form pressing the stacked layers 604. In detail, when the upper part 602a of the form press 101 approaches the top layer 604a of the stack 604, i.e. the layer 604a, which faces towards the upper part 602a of the mold 602, compression of the stacked layers 604 commences. This pressing force F_o thus initially acts upon the top layer 604a of the stack 604, whereas the first layer 604a transmits the pressing force Fo towards the further underlying layers 604b, i.e. the second layer 604b. The force F_o is shown split apart in Fig. 4 into a normal force FN and a shear force Fs. The normal force FN points normally onto the lower part 602b of the form press mold 602. The shear force points along a shear line 605 as shown indicated with dotted points in Fig. 6 and which is located between the two layers 604a, 604b. The shear force direction thus corresponds to the curvature of the upper 602a, lower 602b form part respectively. Expressed in more general terms, the direction of the shear force vector essentially points along the curvature of the upper 602a/lower 602b part of the form press mold 602. Because the stacked layers 604 are moveable with respect to each other, the shear forces are only absorbed due to mechanical friction between the layers 604a, 604b. The strength of the friction scaled with the forming pressure and thus friction between the layers 604a, 604b increases during form pressing. Consequently, friction between the layers 604a, 604b is initially low, and thus, the emerging shear forces only couple to some extend into the individual layers 604a, 604b, which allows the layers 604a, 604b to shift or move or migrate against each other. Hence, stress which occurs during formation is reduced and not fully incorporated into the final cellulose fiber-based product 103, 800, leaving the final product 103, 800 with higher mechanical stiffness. Because respective layers 604a, 604b are arranged to have at least one coated side of a layer 604a, 604b located between each other, friction between the individual layers 604a, 604b also depends on the properties of the additive. Fig. 7 schematically shows the pre-treating 705 and heat curing 706 steps. Thereby, either said first 104a and/or said second 104b layer are treated previous to the arrangement of said first 104a and/or said second 104b layers in a superimposed relationship in the forming mold 102. In the embodiment depicted in Fig. 7, the heat curing mixture is applied as additive during pre-treating 705 by spraying but is not limited to this. Other embodiments are dip coating or curtain pouring. The heat curing 706 with elevated temperatures is reached by irradiation with IR or microwave radiation, conduction or by exposure to hot air. After said heat curing 706 and previous to arranging said first 104a and/or said second 104b layer in a superimposed relationship in a forming mold 102, said first 104a and/or second 104b layers are wetted.

Fig. 8 shows respective embodiments of cellulose fiber-based products 700. Spoon and knife are made from layers of cellulose fibers obtained from fluffboard material.

List of References

101 Form press; 102 Forming mold; 102a - 602a Upper part of the forming mold; 102b - 602b Lower part of the forming mold; 103, 800 Cellulose based product; 104 - 604 Stack; 104a - 604a First layer; 104b - 604b Second layer; 105 Forming cavity; 204 Initial cellulose fiber-based layer; 205 Cutout; 206 Cavity; 500 Structure; 505 Middle line; 506 Symmetry line; 605 Shear line; 705 pre-treating; 706 heat curing.

Claims

1. A method of producing a cellulose fiber-based product (103, 800), wherein the method comprises the steps of:

(ia) providing at least two layers including one first (104a) and one second (104b) layer, and wherein said first (104a) and second (104b) layer each comprise cellulose fibers, and wherein at least one side of said first (104a) and said second (104b) layer is pretreated (705) with a first heat curing mixture and wherein optionally the other side is pre-treated (705) with a second heat curing mixture, wherein said first and said second heat curing mixture may be identical or different, preferably different, from each other,

(iia) wetting said at least two cured layers;

(iib)arranging said at least two wetted layers in a superimposed relationship to each other in a forming mold (102) of a form press (101), thereby generating a stack (104) of said at least two layers, wherein said one first (104a) and said one second (104b) layer are oriented within the stack (104) such that two sides pre-treated with said first heat curing mixture face each other;

(iii) form pressing said stack (104) in a forming mold (102) at a forming temperature of at least 50°C up to a forming end-pressure of at most 100 M Pa, into a cellulose fiberbased product (103, 800) of a predetermined shape and a single layer configuration, wherein in said step (iii) said at least two layers including said one first (104a) and said one second (104b) layer are moveable with respect to each other until said forming end-pressure is reached characterized in that the cellulose fibers are derived from fluffboard or fluff pulp; wherein the cellulose fiber-based products are produced by methods excluding the dry manufacturing method as disclosed in WO 2017/160218.

2. The method of claim 1 , wherein said first heat curing mixture and said second heat curing mixture are water-based dispersions and are preferably biodegradable and/or compostable and/or recyclable.

3. The method of claim 1 or 2, wherein the said first heat curing mixture comprises at least one saccharide and the said second heat curing mixture comprises at least one saccharide and optionally an alkylated ketene dimer (AKD) and/or optionally a polyamidoamine epichlorohydrin (PAE) resin.

4. The method of any of the preceding claims, wherein said pre-treatment of said at least one side of said first (104a) and/or said second (104b) layer with said first heat curing and/or second heat curing mixture is carried out such that respective components of said first heat curing mixture and/or second heat curing mixture are applied to said first and/or second layer successively to each other.

5. The method of any of the preceding claims, wherein the area weight of an additive resulting from said first heat curing mixture and/or said second heat curing mixture ranges from 0.5 to 50 gsm, or from 2 to 25 gsm of the first (104a) and/or second (104b) layer.

6. The method of any of the preceding claims, wherein said first (104a) and/or second (104b) layer comprise one or more additives that are altering the mechanical, hydrophobic, oleophobic, haptic, aesthetic properties of the cellulose fiber-based product, and wherein said first and/or second layer are constituted of from 50 to 100% dry wt, or from 60 to 100% dry wt, or from 70 to 100% dry wt, or from 80 to 100% dry wt, or from 90 to 100% dry wt cellulose fibers and from 0 to 50% dry wt, or from 0 to 40 % dry wt, or from 0 to 30% dry wt, or from 0 to 20% dry wt, or from 0 to 10% dry wt of said one or more additive.

7. The method of claim 6, wherein said one or more additives are selected from the group consisting of starch compounds, in particular starch-based polymers, rosin compounds, polycarboxylic, in particular butane tetracarboxylic acids, gelatin compounds, alkyl ketene dimer (AKD), alkenyl succinic anhydride (ASA), wax compounds, silicon compounds, calcium compounds, sol-gels, micro-fibrillated cellulose compounds, water-based polyhydroxy alkanoates (PHA) compounds and fluorocarbons.

8. The method of claim 5 or 6, wherein said one or more additive is added to said first (104a) and/or second (104b) layer prior to step (i).

9. The method of any of the preceding claims, wherein the forming mold (102) is heated to a forming temperature of from 50 °C to 250 °C, or from 100 °C to 200 °C.

10. The method of any of the preceding claims, wherein the additive is applied with the same or a varying thickness to at least one side of each of the cellulose fiber-based layers (104a, 104b).

11. The method of any of the preceding claims, wherein each of said first (104a) and second (104b) coated layers have an area weight ranging from 50 to 2000 gsm, or an area weight ranging from 600 to 750 gsm.

12. The method of any of the preceding claims, wherein said stack (104) comprises or consists of 2 to 10, or 2 to 7, or 2 to 5 first (104a) and second (104b) layers.

13. The method of any of the preceding claims, wherein the total weight of the cellulose fiberbased coated layer is in the range of 650 to 2200 gsm, or in the range of 1250 to 1550 gsm.

14. The method of any of the preceding claims, wherein the surface of said cellulose fiber-based product (103, 800) is dip coated or sprayed or curtain poured or brushed with a finish.

15. Cellulose fiber-based cutlery and/or cellulose fiber-based tableware manufactured according to the method according to any of the preceding claims; wherein the cellulose fiber-based products are produced by methods excluding the dry manufacturing method as disclosed in WO 2017/160218.