A method for producing a cellulose product and a cellulose product

Abstract

A cellulose product (1) and a method for producing a cellulose product (1) from a cellulose material (2), wherein the method comprises the steps of; arranging the cellulose material (2) in a forming mould (3); heating the forming mould (3) to a forming temperature in the range of 100°C to 300°C, and forming the cellulose product (1) from the cellulose material in the heated forming mould (3), by moulding the cellulose material (2) with a forming pressure, where a first product section (24) of the cellulose product (1) is moulded with a first forming pressure between 4-20 MPa, and where a second product section (25) of the cellulose product (1) is moulded with a second forming pressure greater than 100 MPa, wherein the cellulose material (2) is shaped into the three-dimensional cellulose product (1), and wherein the average density of the first product section (24) is below 1,30 g / cm3 and the average density of the second product section (25) is greater than 1,30 g / cm3.

Description

A METHOD FOR PRODUCING A CELLULOSE PRODUCT AND A CELLULOSE PRODUCTTECHNICAL FIELDThe present disclosure relates to a method for producing a three-dimensional shaped cellulose product from a cellulose material, where a first section of the cellulose product is pressed with a low forming pressure and where a second section of the cellulose product is pressed with a higher forming pressure. In the method, a three-dimensional shaped cellulose product having sections with different densities is provided, where the average density of the first section is below 1,30 g / cm3 and the average density of the second section is greater than 1,30 g / cm3.BACKGROUNDCellulose fibres are often used as raw material for producing or manufacturing various products. Products formed of cellulose fibres can be used in many different situations where there is a need for having sustainable products of essentially non-flat shapes. An essentially non-flat shapes may refer to any suitable three-dimensional object shape. There is a wide range of products that can be produced from cellulose fibres and a few examples are disposable plates and cups, blank structures and packaging materials. Packages produced from cellulose fibres may for example be used for packaging of liquids, dry materials and other types of goods, where the packaging may be made in a three-dimensional shape or formed into a three-dimensional shape from a two-dimensional sheet material. Such products are often laminated with different films in order for the product to withstand liquids, grease, heat etc.Cellulose fibres are obtained by separating the cellulose fibres from a pulp derived from e.g. wood or other plants. Pulp is a lignocellulosic fibrous material that can be prepared either mechanically or chemically by separating cellulose fibres from wood or other plants. Wood pulp is e.g. obtained by grinding timber or trees in some kind of mill, e.g. a disc refiner, where the wood is ground to wood pulp. The pulp contains water, cellulose fibres, lignin and hemicelluloses. For some products, e.g. where the strength is not a key factor and / or when a low price is important, a lignocellulosic material, i.e. fibres where the lignin is not removed, can be used.There are different processes that can separate wood fibres. When preparing mechanical pulp, thermomechanical pulp or chemo-thermomechanical pulp, the fibres are separated but the lignin is not removed from the cellulose fibres. In a chemical pulp process, the lignin and some of the hemicellulose is removed more or less completely from the pulp, leaving substantially pure cellulose fibres hereinafter referred to pure cellulose fibres.One material commonly used for cellulose fibre products is wet moulded pulp. The pulp used for wet forming is often obtained from recycled paper boards and newspaper, where the cellulose fibres comprise lignin. This lowers the cost. Wet moulded pulp has the advantage of being considered as a sustainable packaging material, since it is produced from biomaterials and can often be recycled or composted after use. Consequently, wet moulded pulp has been quickly increasing in popularity for different applications. Wet moulded pulp articles are generally formed by immersing a suction mould into a liquid or semi liquid pulp suspension or slurry, while suction is applied, whereby a body of pulp is formed with the shape of the desired product by fibre deposition. The suction mould is then withdrawn from the suspension and the suction is generally continued to compact the deposited fibres while exhausting residual liquid. With all wet-forming techniques there is a need for drying of the wet moulded product, where the drying is a very time and energy consuming part of the production, which is costly. Further, this method requires a large quantity of water. The demands on aesthetical, chemical and mechanical properties of products are increasing, and due to the properties of wet-formed cellulose products, the mechanical strength, flexibility, and chemical properties are limited. It is also difficult in the wet-forming process to control the mechanical properties of the products with high precision.Another known method for producing products from cellulose material is by pressing loose cellulose fibres in a dry state, known as Dry Moulded Fibres (DMF). These products can be made in a cost-efficient way without using water as a cellulose fibre bearer and with a reduced energy need. Such products can be used to replace disposable plastic products, but are somewhat limited when it comes to strength and the possibility to vary the thickness of a product to a great extent.In a DMF process, cellulose fibres are formed with a forming pressure between 4-20 MPa in a regular compression mould. In such forming, the cellulose fibres arranged in a cellulose blank structure are drawn apart somewhat when a non-flat shape is created. Since the cellulose blank structure does not float or stretch, it is difficult to produce dry moulded cellulose products where the difference in thickness varies over the cellulose product. DMF products can be produced at the same cost as disposable plastic products.There is thus a need for improved sustainable cellulose products, where the cellulose products are having improved mechanical and chemical properties, can be manufactured with high precision, and where the production is cost-efficient and rational.SUMMARYAn object of the present disclosure is to provide a method for producing a three-dimensional cellulose product where the previously mentioned problems are avoided. This object is at least partly achieved by the features of the independent claim. The dependent claims contain further developments of the method for producing a three-dimensional cellulose product. Another object of the present disclosure is to provide a three-dimensional shaped cellulose product.The disclosure concerns a method for producing a cellulose product from a cellulose material comprising between 6 to 20% water, wherein the method comprises the steps of; arranging the cellulose material in a forming mould; heating the forming mould to a forming temperature in the range of 100°C to 300°C, and forming the cellulose product from the cellulose material in the forming mould, by moulding the heated cellulose material with a forming pressure, where a first section of the cellulose product is moulded with a first forming pressure between 4-20 MPa, and where a second section of the cellulose product is moulded with a second forming pressure of at least 100 MPa, wherein the cellulose material is shaped into the three-dimensional cellulose product, and wherein the density of the first section is below 1,30 g / cm3 and the density of the second section is greater than 1,30 g / cm3.Advantages with these features are that the method provides an efficient manufacturing process for cellulose products with improved mechanical and chemical properties, where the cellulose product comprises a first section consisting of regular dry moulded fibre (DMF) material and a second section consisting of high density dry moulded fibre (HD-DMF) material. The advantage with this method is that a cellulose product having different density and strength properties is provided. The regular DMF section is formed with a forming pressure in the region of 4-20 MPa, and the HD-DMF section is formed with a forming pressure greater than 100 MPa. The density of the first section is below 1,30 g / cm3 and the density of the second section is greater than 1,30 g / cm3. The cellulose product may comprise several second sections.One advantage of such a product is that only one or more sections that requires a higher strength are provided with a higher density. In one example, a cutlery in the form of a knife is provided with a cutting edge having a higher density, while the rest of the knife blade and the handle is regular DMF having a density below 1,30 g / cm3. By only moulding a section of the cellulose product with a high forming pressure to a higher density, the cost is reduced since a higher pressure is costly. To produce e.g. a knife where the complete knife is moulded with a high forming pressure exceeding 100 MPa, either a larger press is required or fewer knifes can be moulded at the same time. By only pressing a section of the knife with a high forming pressure and the rest of the knife with a low forming pressure, more knifes can be moulded at the same time with a given press. In this way, a cellulose dry moulded fibre knife having a cost comparable to a disposable plastic knife can be achieved.During the moulding of the cellulose material, the cellulose fibres of the second section will assume a pseudo-liquid state during the pressing action with a forming pressure greater than 100 MPa, which means that the cellulose fibres will assume liquid-like properties during the moulding action. During the moulding action of the second section with a high forming pressure, where the second forming pressure exceeds 100 MPa, the forces acting on the cellulose fibres will not only provide a compressing force but also a shear force on the cellulose fibres when a three-dimensional product is moulded, since the cellulose fibres will be displaced somewhat in a sideway direction. In one example, the second forming pressure is higher than 150 MPa and may be higher than 200 MPa or higher, depending on the cellulose product and the cellulose material. If various additives are used in the cellulose material, this may also impact the most suitable second forming pressure.Even though a higher second forming pressure will give a cellulose product with a second section having a higher strength and a higher density, the preferred second forming pressure is a forming pressure where the desired parameters for the second section of the cellulose product are met, without exceeding these parameters. A higher second forming pressure adds a cost to the cellulose product. For this reason, it is of advantage to apply a higher forming pressure only on selected sections of a cellulose product, where a higher strength is required.One such example is cutlery. When the cellulose product is a knife, the cutting edge can be formed with a higher forming pressure to a higher density in order to provide a sharp and strong cutting edge, and where the remaining section of the knife is formed with a regular, lower forming pressure. When the cellulose product is a fork, the tines or prongs may be formed with a higher forming pressure to a higher density in order to provide sharp and pointed tines. Other cellulose products that may be provided with sections having different densities and thus different strength are e.g. trays, where a strengthening pattern of high density grooves can be implemented in order to increase the load capacity of a tray. In this way, the starting material of the tray may have a lower weight. Another advantage of using sections with a higher density is e.g. in a tray or other product where the corners should be sharp. By moulding the edges with a high forming pressure, the cellulose material at the corner regions will assume liquid-like properties which will allow the cellulose material to fill the corner regions. It has been shown that a forming pressure exceeding approximately 100 MPa will start to give the cellulose material pseudo-liquid properties.One advantage with a higher forming pressure where the cellulose fibres assume pseudo- liquid properties is that complicated shapes can be obtained, which are difficult to obtain with regular pressing of dry moulded fibres with a forming pressure between e.g. 4-20 MPa. In a regular DMF moulding, the cellulose fibres arranged in a cellulose blank structure are drawn apart somewhat when a non-flat shape is created. Since the cellulose blank structure does not float, it is difficult to produce dry moulded cellulose product where the difference in thickness varies over the cellulose product. With the inventive method, cellulose products having one or more sections with a more complicated shape can be produced, where the strength and the density of the cellulose product varies. The method can also be used for e.g. the neck of a dry moulded cellulose fibre bottle, where the neck is provided with an external thread and a smooth inner surface, and where the neck is moulded with a forming pressure exceeding 100 MPa. The rest of the bottle can be produced with a regular forming pressure of 4-20 MPa in order to save cost.The cellulose product is formed in a forming mould which comprises a first positive mould part and a second negative mould part. The forming mould parts are in one example non-flexible, preferably made from steel, and may be heated to the desired forming temperature. The forming mould is in one example heated with integrated heating elements, preferably electrical heating elements, but also liquid heating is possible. One of the forming mould parts may also comprise a solid flexible material such as silicon or rubber. A mould part intended to mould the first section of the cellulose product may be made from this flexible material. The solid flexible material may be used to even out the forming pressure acting on parts of the cellulose material during the pressing action. The mould parts intended to mould the second section of the cellulose product are made from a stiff and non-flexible material, such as steel or another stiff material.During the moulding of a three-dimensional cellulose product, different forces will act on the moulded cellulose material. When a flat cellulose product is pressed, all forming pressure forces acting on the cellulose material will be in the same direction as the forming pressure direction, i.e. perpendicular to the mould surfaces. When a three-dimensional cellulose product is pressed, some of the forces will not be parallel to the forming pressure direction, but will be perpendicular to the mould surface. Since the cellulose material does not float, the cellulose material will be pulled apart and displaced somewhat in order to correspond to the three-dimensional shape of the mould, and this small displacement of the cellulose material will be neglectable for a low forming pressure of 4-20 MPa. At a higher forming pressure exceeding 100 MPa, this small displacement of cellulose material will induce some shear forces on the cellulose material. Together with the high forming pressure, these shear forces will not be neglectable but will at the same time cause some local pseudo- liquid regions where the cellulose material will assume liquid-like properties.In the shown examples, the cellulose material is a dry-formed cellulose blank structure comprising loose cellulose fibres. Hence, the cellulose material is a dry-formed cellulose blank structure formed in a dry-forming process where cellulose fibres are carried and formed to the dry-formed cellulose blank structure by air as carrying medium. In the description, dry-formed cellulose blank structure is sometimes referred to as an air-laid cellulose blank structure. With an air-laid / dry-formed cellulose blank structure, the weight of the cellulose blank structure used for a regular DMF product is normally in the region between 400-800 GSM (grams per square metre). With such a material, a strong second product section of a cellulose HD-DMF product with a density exceeding 1,30 g / cm3 can be obtained, where a first section of the cellulose product is provided with a density below 1,30 g / cm3, and possible below 1,10 g / cm3.The cellulose material consists in one example of pure cellulose fibres without any additives. With pure cellulose fibres is meant cellulose fibres produced from chemical pulp where most of the lignin and the hemicelluloses are removed. The cellulose material may also include additives, where the additives are used to decrease the liquid and / or gas permeability of the cellulose product and to increase the resistance to e.g. hot and cold liquids, grease, oil etc. Such additives may also be applied to the surface of the cellulose product after the cellulose product is formed. In one example, the cellulose material comprises at least 95% cellulose fibres by dry weight, and up to 5% of suitable additives. The cellulose material may comprise up to 99% of cellulose fibres by dry weight. The purpose of the additives is to increase the resistance to liquids, grease, oxygen, etc. An additive is not a binder material. A binder material is required to create a product. An additive is a material that enhances the product, but is not required for the production of a product. A binder material will decrease the formation of hydrogen bonds between the cellulose fibres in the product.The cellulose material may comprise a first region corresponding to a first product section of the cellulose product having a weight between 400-800 GSM, and a second region corresponding to a second product section of the cellulose product having a weight that is higher than the weight of the first region. The weight of the second region may e.g. be 1000 GSM or more.One example of a cellulose product having a first section with a density below 1,30 g / cm3 and one or more second sections having a density exceeding 1,30 g / cm3 is cutlery. When the cellulose product is a knife, the cutting edge can be formed with a higher forming pressure to a higher density in order to provide a sharp and strong cutting edge, and where the remaining section of the knife is formed with a regular, lower forming pressure. When the cellulose product is a fork, the tines or prongs may be formed with a higher forming pressure to a higher density in order to provide sharp and pointed tines. Other cellulose products that may be provided with sections having different densities and thus different strength are e.g. trays, where a strengthening pattern of high density grooves can be implemented in order to increase the load capacity of a tray. Another advantage of using sections with a higher density is e.g. in a tray or another product where the corners should be sharp. By moulding the edges with a high forming pressure, the cellulose material at the corner regions will assume liquid-like properties which will allow the cellulose material to fill the corner regions. It has been shown that a forming pressure exceeding approximately 100 MPa will start to give the cellulose material pseudo-liquid properties.Another suitable cellulose HD-DMF product is a neck of a dry moulded cellulose fibre bottle, where the neck is provided with an external thread and a smooth inner surface. The rest of the bottle can be produced with a regular forming pressure of 4-20 MPa in order to save cost.The cellulose HD-DMF product is formed in the forming mould during a cycle time period in the range of 0,1 to 10 seconds, and preferably less than 5,0 seconds. A suitable holding time for the product in the forming mould is less than a second, and may be 0,3-0,7 seconds. The holding time together with the forming temperature and the forming pressure are important parameters in the forming of the cellulose product.With regard to the cellulose material, it should be noted that all cellulose based materials referred to in the application stems from lignocellulose biomass, i.e. plant dry matter. The lignocellulose material can be treated in various ways to produce chemical pulp, semi-chemical pulp or mechanical pulp, which is known per se in the art. Chemical treatment of lignocellulosic biomass removes most of the lignin and hemicellulose whereas mechanical treatment of lignocellulosic biomass produces cellulose fibres with a high content of lignin and hemicellulose. Chemical pulp has a yield of about 50% and is thus more expensive than mechanically treated lignocellulosic material which has a yield of about 90%. The DMF method described can use any type or a combination of chemical pulp, semi-chemical pulp or mechanical pulp dependent on type of product and / or type of design and / or type of use. The cellulose material can thus be in the form of pure cellulose, i.e. essentially without lignin and hemicellulose, and / or in the form of lignocellulosic material. In summary, pure cellulose is chemically treated lignocellulosic material where lignin and hemicellulose have been removed almost in its entirety. One advantage with pure cellulose is its ability to form a high amount of hydrogen bonds that bonds the fibres together to a strong and self-sustained three-dimensional product. Lignin and hemicellulose seem to form less hydrogen bonds than pure cellulose which is why pure cellulose is preferred due to a lesser need of additional material. However, for certain types of products, lignin and hemicellulose can be allowed for cost reasons without compromising quality of the product, for example by use of more fibre material in the mould.BRIEF DESCRIPTION OF DRAWINGSThe disclosure will be described in greater detail in the following, with reference to the attached drawings, in whichFig. 1 shows schematically a method for producing a cellulose product having different density sections from a cellulose blank structure according to the disclosure,Figs. 2a-b show schematically a forming mould to be used for a cellulose product having different density sections produced from a cellulose blank structure according to the disclosure,Fig. 3 shows schematically a further example of a forming mould to be used for a cellulose product having different density sections produced from a cellulose blank structure according to the disclosure,Fig. 4 shows schematically a further example of a forming mould to be used for a cellulose product having different density sections produced from a cellulose blank structure according to the disclosure,Fig. 5 shows schematically a cellulose product having different density sections produced from a cellulose blank structure according to the disclosure,Fig. 6 shows schematically a cellulose product having different density sections produced from a cellulose blank structure according to the disclosure, andFig. 7 shows schematically a cellulose product having different density sections produced from a cellulose blank structure according to the disclosure.DESCRIPTION OF EXAMPLE EMBODIMENTSVarious aspects of the disclosure will hereinafter be described in conjunction with the appended drawings to illustrate and not to limit the disclosure, wherein like designations denote like elements, and variations of the described aspects are not restricted to the specifically shown embodiments, but are applicable on other variations of the disclosure. In the present detailed description, a method for producing a cellulose product having a first section with a density below 1,30 g / cm3 and a second section having a density above 1,30 g / cm3 from a cellulose material will be described. The method is suitable for different DMF products where it is of advantage to have a section with a higher density and thus a higher strength, e.g. tensile strength. The high density section is preferably relatively small in order to reduce the required total forming pressure, which is costly. Examples of such cellulose DMF products are e.g. cutlery such as knives and forks, coffee pods, trays, snap on lids etc. In the shown examples, a knife is used as an example of a cellulose DMF product.The cellulose material used to form the cellulose DMF product is in one example pure cellulose fibres without any additives. With pure cellulose fibres is meant cellulose fibres produced from chemical pulp where most of the lignin and the hemicelluloses are removed. The cellulose material may also include additives, where the additives are used to decrease the permeability of the cellulose product and to increase the resistance to e.g. hot and cold liquids, grease, oil etc. In one example, the cellulose material comprises at least 95% cellulose fibres by dry weight and at the most 5% additives by weight. The cellulose material may also comprise some water, e.g. between 6% to 20% by weight. In one example, the water content of the second section of the cellulose blank is higher than the water content of the first section. A higher water content in the second section in combination with shear forces will increase the flowability of the cellulose fibres.Fig. 1 shows schematically a method for producing a cellulose DMF product 1 having sections with different densities from an air-laid cellulose blank structure 2. When forming the cellulose blank structure in the air-laid process, the cellulose fibres are carried and formed to the cellulose blank structure by air as carrying medium. In the air-laid process, small amounts of water or other substances may if desired be added to the cellulose material in order to change the properties of the cellulose product, but air is still used as carrying medium in the forming process. The layer of the dry-formed cellulose blank structure may have a dryness that is mainly corresponding to the ambient humidity in the atmosphere surrounding the cellulose blank structure. Additional water may be added to the cellulose blank structure, up to a water content of 20% by weight. A lower water content is possible, but may be difficult to reach due to the moisture in the ambient air. In the shown example, the cellulose blank structure 2 may comprise a first tissue layer and a second tissue layer arranged at each side of the cellulose blank structure 2. To produce the cellulose DMF products, the cellulose blank structure may be arranged as a layered continuous web. The continuous web may be formed from the layers in a continuous process step, where the continuous web is fed to the forming mould to form the cellulose products.In the shown method for manufacturing a cellulose DMF product in a cellulose product forming apparatus 6, the cellulose blank structure 2 is dry-formed, arranged in a forming mould 3, heated to a forming temperature and pressed in the forming mould 3 with a forming pressure. In a first step, the cellulose blank structure 2 is dry-formed in a dry forming unit comprising a mill 8, a forming box 9, a forming wire 12 and a compacting unit 11. The cellulose blank structure 2 is in the method formed into a three-dimensional cellulose product 1.In the mill 8, cellulose is separated into detached cellulose fibres. The cellulose material used in the mill 8 is preferably a substantially pure cellulose material, such as for example fluff pulp or the like, containing a high degree of cellulose fibres. As an example, the mill may be a conventional hammer mill. Standard virgin fluff pulp may be used as cellulose raw material and can for example be purchased on the open market in rolls 7. In Fig. 1, a roll 7 of fluff pulp is used as raw material, which is fed into the mill.The cellulose fibres are arranged onto the forming wire 12 in a conventional way. The detached cellulose fibres is drawn from the mill by a centrifugal fan and blown into the forming box 9 arranged above the forming wire 12. A vacuum box 10 may be arranged underneath the upper part of the forming wire 12. The forming box 9 may comprise a number of fibre separating rollers arranged in the forming box housing to distribute the cellulose fibres evenly onto the forming wire 12. The cellulose fibres are drawn by the vacuum in the vacuum box 10 onto the forming wire 12 in order to form a cellulose blank structure which is transported by the forming wire 12 to the compacting unit 11. The forming wire 12 may be arranged in a conventional way as an endless belt made for example from a woven mesh structure, which endless belt can be moved continuously with a constant speed when forming the cellulose blank structure. The density of the cellulose blank structure may be chosen so that it is suitable for the cellulose product to be formed.In order to form the cellulose blank structure 2, the cellulose fibres are preferably compacted or calendared in the compacting unit 11. In this way, the cellulose blank structure 2 is formed as a continuous cellulose blank structure 2. In one example, the dry forming of the cellulose blank structure 2 may be part of a continuous process, as shown in Fig. 1, in which the cellulose product is manufactured in the cellulose product forming apparatus 6. It is also possible to form the cellulose blank structure as discrete separate pieces corresponding to a cellulose product.The cellulose product is formed in a forming mould 3 which comprises a first mould part 4 and a second mould part 5. In the shown example, the first mould part is an upper positive mould part and the second mould part is a lower negative mould part. The forming mould parts may be non-flexible, preferably made from steel, and may be heated to the desired forming temperature. The forming mould is in one example heated with integrated heating elements, preferably electrical heating elements, but also liquid heating is also possible.One of the forming mould parts may also comprise a solid flexible material such as silicon rubber. The part of the mould part intended to mould the first section of the cellulose product may comprise this material. The solid flexible material may be used to even out the forming pressure acting on parts of the cellulose material during the pressing action.The cellulose blank structure 2 may be arranged into the forming mould 3 in any suitable way, and as an example, the cellulose blank structure 2 may be manually arranged in the forming mould 3. Another alternative is to arrange a buffer 13 for the cellulose blank structure 2, which is transporting the cellulose blank structure 2 to the forming mould. The buffer could for example be a conveyor belt, an industrial robot, or any other suitable manufacturing equipment. As shown in Fig. 1, the cellulose blank structure may be fed to the forming mould 3 with the forming wire 12, where the buffer feeds the cellulose blank structure intermittently to the forming mould 3 when the forming wire 12 moves with a constant speed and the forming of the cellulose products in the forming mould 3 takes place in intermittent process steps.As described above, the cellulose product 1 is manufactured from cellulose fibres, and the cellulose product may comprise at least 90% by weight cellulose fibres. Sizing agents or other suitable additives may be applied to the cellulose fibres to increase the hydrophobic properties, mechanical strength and / or other properties of the cellulose blank structure 2. As an example, the cellulose product may comprise 90-98 weight percent cellulose fibres and 2-10 weight percent other substances, such as starch, sizing agents, and / or other suitable additives and substances. In order to secure that the cellulose product can be recycled after use, the added substances may be biodegradable or suitable for recycling.In order to form the cellulose product, the cellulose blank structure 2 is arranged in the forming mould 3, where the cellulose blank structure 2 is heated to a forming temperature in the range of 100°C to 300°C and pressed in the forming mould 3 with a forming pressure of at least 1 MPa. The heating of the cellulose blank structure 2 is preferably taking place in the forming mould 3 when being pressed by the pressing unit 14.When pressing the cellulose fibres with a forming pressure of at least of 1 MPa with a forming temperature in the range of 100°C to 300°C, the cellulose fibres will be bonded to each other in a way so that the resulting cellulose product will have good mechanical properties. Tests have shown that higher forming temperatures will give stronger bonding between the cellulose fibres when being pressed at a specific forming pressure. With forming temperatures above 100°C together with a forming pressure of at least 1 MPa, the cellulose fibres will be strongly bonded to each other with hydrogen bonds. A higher forming temperature will increase the fibril aggregation, water resistance, Young’s modulus and the mechanical properties of the final cellulose product. A high forming pressure is important for fibril aggregation between the cellulose fibres in the cellulose product. At temperatures higher than 300°C, the cellulose fibres will thermally degrade and therefore temperatures above 300°C should be avoided. The forming pressure and the forming temperature may be chosen to be suitable for the specific cellulose product to be produced.The forming mould comprises in one example a first mould region arranged to apply a forming pressure to the cellulose blank structure in the region between 4-20 MPa, forming a first section of the cellulose product. This forming pressure will provide a regular DMF section having an average density of below 1,30 g / cm3, and in one example between 1,00 g / cm3 and 1,10 g / cm3. The first mould region is preferably the larger part of the forming mould. The forming mould further comprises at least one second mould region arranged to apply a forming pressure to the cellulose blank structure exceeding 100 MPa, such that an average density of a second section of the cellulose product is above 1,30 g / cm3 or more. Between the first mould region and the second mould region, there may be an intermediate mould region bridging the first mould region and the second mould region. The intermediate mould region creates a transition section of the cellulose product, where the density is somewhere between the density of the first product section and the second product section.The first mould part 4 comprises a first mould surface 18, a second mould surface 19 and a fifth mould surface 22. The second mould part 5 comprises a third mould surface 20, a fourth mould surface 21 and a sixth mould surface 23. The first mould surface 18 and the third mould surface 20 are arranged facing each other, the second mould surface 19 and the fourth mould surface 21 are arranged facing each other, and the fifth mould surface 22 and the sixth mould surface 23 are arranged facing each other.The first mould region 15 is created between the first mould surface 17 of the first mould part and the third mould surface 19 of the second mould part. The first mould region will form a first product section 24 of the cellulose product, and corresponds to a regular forming mould used for regular DMF products. The distance between the first mould surface and the third mould surface in the first mould region corresponds to the thickness of the cellulose product, and may e.g. be between 0,6 to 2,0 mm depending on the actual cellulose product. The first product section will in this way obtain an average density below 1,30 g / cm3, and in one example between 1,00 g / cm3 and 1,10 g / cm3.The second mould region 16 is created between the second mould surface 18 of the first mould part and the fourth mould surface 20 of the second mould part, and is configured to apply a forming pressure exceeding 100 MPa to the cellulose blank structure, such that the created second product section 25 of the cellulose product obtains an average density above 1,30 g / cm3 or more. In one example, the distance between the second mould surface and the fourth mould surface in the second mould region may e.g. be between 0,1 to 0,6 mm depending on the actual cellulose product.The intermediate mould region 17 is created between the fifth mould surface 22 of the first mould part and the sixth mould surface 23 of the second mould part, and is configured to apply a forming pressure between 20-100 MPa to the cellulose blank structure. This will provide a transition section 26 having a density somewhere between the first product section and the second product section. Depending on the cellulose product, the transition section may be relatively small or may not be present at all.The distance between the first mould part and the second mould part in the first mould region, the second mould region and the intermediate mould region sets the thickness of the first product section, the second product section and the transition section of the cellulose product. In one example, the first mould part is flat, such that the first mould surface, the second mould surface and the fifth mould surface are arranged in the same plane. In this example, all surface variations are arranged on the second mould part.Fig. 2a shows an example of a forming mould 3 comprising a first mould part 4 and the second mould part 5 in an open state, and Fig. 2b shows the forming mould in a closed state. The shown forming mould comprises a plurality of second mould regions 16 arrange to provide a plurality of second mould sections in a cellulose product. The second mould regions 16 are arranged between first mould regions 15. In this example, the cellulose product may e.g. be a tray and the second mould sections may provide strengthening grooves in the bottom region of the tray. The second mould part comprises a plurality of protruding fourth mould surfaces 21 arranged between third mould surfaces 20 of the second mould part 5. The first mould part 4 comprises corresponding first mould surfaces 18 and second mould surfaces 19, here arranged in the same plane.When a cellulose product is formed in the forming mould, a cellulose blank structure is positioned in the forming mould and the forming mould is closed. When the forming mould is closed, a forming pressure will be applied to the cellulose blank structure. In the first mould regions 15, the forming pressure will be in the range between 4-20 MPa and in the second mould regions, the forming pressure will be higher than 100 MPa. The achieved forming pressure is dependent on the weight (GSM, grams per square metre) of the cellulose blank structure, the geometry of the forming tool and the pressure of the pressing unit. By adjusting these parameters, a cellulose product with one or more second mould sections having an average density above 1,30 g / cm3 or more can be obtained.Fig. 3 shows a schematic example of a forming tool provided with a second mould section 16 arranged at one position of the forming mould. The larger part of the forming mould is provided with a first mould region 15 arranged between the first mould surface 18 of the first mould part and the third mould surface 20 of the second mould part. This may e.g. be used for a knife blade of a cellulose knife having regular Dry Moulded Fibre properties, such as an average density between 1,00-1,10 g / cm3 and a thickness of 0,6-1,5 mm. The second mould section 16 is arranged at one end of the forming tool and may e.g. be used for a cutting edge of a cellulose knife, where the second mould region 16 is arranged between the second mould surface 19 of the first mould part and the fourth mould surface 21 of the second mould part. An intermediate mould region is arranged between the fifth mould surface 22 of the first mould part and the sixth mould surface 23 of the second mould part. In the shown example, the second mould surface 19 and the fifth mould surface 22 are arranged in the same inclined plane. In the second mould region, a forming pressure exceeding 100 MPa will be applied to the cellulose blank structure, and in the intermediate mould region, a forming pressure starting at 100 MPa down to the forming pressure of the first mould section will be applied.Fig. 4 shows a further schematic example of a forming tool provided with a second mould section 16 arranged at one position of the forming mould. The larger part of the forming mould is provided with a first mould region 15 arranged between the first mould surface 18 of the first mould part and the third mould surface 20 of the second mould part. This may e.g. be used for a knife blade of a cellulose knife having regular Dry Moulded Fibre properties, such as an average density between 1,00-1,10 g / cm3 and a thickness of 0,6-1,5 mm. The second mould section 16 is arranged at one end of the forming tool and may e.g. be used for a cutting edge of a cellulose knife, where the second mould region 16 is arranged between the second mould surface 19 of the first mould part and the fourth mould surface 21 of the second mould part. In this example, the distance between the second mould surface and the fourth mould surface is equal over the complete second mould region. An intermediate mould region is arranged between the fifth mould surface 22 of the first mould part and the sixth mould surface 23 of the second mould part. In the second mould region, a forming pressure exceeding 100 MPa will be applied to the cellulose blank structure, and in the intermediate mould region, a forming pressure starting at 100 MPa down to the forming pressure of the first mould section will be applied.In another example, the cellulose blank structure may be provided with regions having different weights, where a second region corresponding to a second product section 25 of the cellulose product is provided with a higher cellulose blank structure weight. A first region corresponding to a first product section 24 may e.g. have a weight of 500 GSM, and a second region corresponding to a second product section may have a weight of 1500 GSM. In this way, a cellulose product having a first product section with an average density below 1,30 g / cm3 and a second product section with an average density above 1,30 g / cm3 or more can be obtained.The distance between the forming surfaces of the mould parts and / or the weight of the cellulose blank structure can be selected in order to obtain the desired cellulose product.The cellulose blank structure is according to the disclosure further heated to a forming temperature in the range of 100°C to 300°C when the cellulose product is moulded. Preferably, the forming mould is heated to the forming temperature with integrated heating elements. The cellulose product is formed from the cellulose blank structure in the heated forming mould by pressing the cellulose blank structure with a forming pressure.The forming pressure of the first mould region is preferably between 4-20 MPa, such that a first product section resembling a regular DMF product is obtained. The forming pressure in the second region is at least 100 MPa or higher, such that a second product section resembling a HD-DMF product is obtained. By heating the cellulose blank structure and pressing the cellulose blank structure in the forming mould, the cellulose product is formed, where during the forming the cellulose blank structure is shaped into a three-dimensional fibre composite structure having a first low-density section and a second high-density section.The second product section will have a higher tensile strength than the first product section, and is in one example used to provide a cutting edge of a knife. Due to the high strength, the cutting edge can be made thin and sharp, which will improve the cuttability of the knife further. There will be a transition section between the first product section and the second product section, where the density gradually increases from the first product section to the second product section. In one example, the knife is around 150 mm long with the cutting blade being around 20 mm wide. The width of the second product section may e.g. be between 1-5 mm with the transition section being a few mm wide.When pressing the cellulose fibres, the cellulose fibres will be bonded to each other in a way so that the resulting cellulose product will have good mechanical properties. Tests have shown that higher forming temperatures will give stronger bonding between the cellulose fibres when being pressed at a specific forming pressure. With forming temperatures above 100°C together with a forming pressure of 4-20 MPa, the cellulose fibres will be strongly bonded to each other with hydrogen bonds. At temperatures higher than 300°C, the cellulose fibres will be thermally degraded and therefore temperatures above 300°C should be avoided. With a forming temperature above 100°C together with a forming pressure exceeding 100 MPa, the cellulose fibres will assume liquid-like properties such that a high-density section is obtained, in which the cellulose fibres can flow some during the moulding process. The forming pressure and the forming temperature may be chosen to be suitable for the specific cellulose product to be produced. Tests have shown that when forming the first product section having regular DMF properties, forming pressure levels are in the range of 4-20 MPa, and suitable temperature levels are in the range of 100°C to 300°C. However, temperature levels in the range of 140°C to 200°C are often sufficient in order to achieve DMF cellulose products with desired properties. Tests have further shown that when forming the second product section having HD-DMF properties, a forming pressure exceeding 100 MPa is required, with the same temperature levels. An even higher forming pressure, up to 200 MPa and more, may be preferred for some products.Examples of a cellulose product 1 is shown in Figs. 5 to 7, where Fig. 5 shows a knife, Fig. 6 shows a fork and Fig. 7 shows a coffee pod. The cellulose product comprises in the shown examples a first tissue layer, a dry-formed cellulose fibres layer, and a second tissue layer. One or both tissue layers may comprise an additive to increase the resistance to liquids, grease, oil etc. It is also possible to use only one tissue layer, or to use no tissue layer at all, depending on the layout of the production system.As shown in Fig. 5, a knife 27 is provided with a knife handle 28 and a knife blade 29, where the blade comprises a cutting edge 30 that may be straight or serrated. The first product section 24 comprises the handle and part of the blade, and the second product section 25 comprises the cutting edge. Between the first product section 24 and the second product section 25, there is a thin transition section 26 in which the density gradually changes from the lower density to the higher density. The handle and the blade are preferably provided with a non-flat shape in order to increase the strength of the first product section. The thickness of the cutting edge is the same as the blade at the transition section and is thinner at the outer edge of the knife, where the thickness of the cutting edge may be as thin as 0,1 mm.As shown in Fig. 6, a fork 31 is provided with a fork handle 32 and a fork head 33, where the head comprises a plurality of tines 34 extending from the head. The handle and the head are comprised in the first product section, having a lower density and resembling a regular DMF product. The tines, or at least the outer ends of the tines, are comprised in the second product section of the fork. The tines are thin and pointed, and have a higher density exceeding at least 1,30 g / cm3, such that sharp and strong tines are obtained. The tines may also comprise a transition section connecting the outer ends of the tines with the fork head.Fig. 7 shows an example where the cellulose product is a coffee pod 35, comprising a bottom portion 36, a side wall portion 37 and a rim portion 38. The bottom portion is provided with one or more grooves 39. The side wall portion, part of the bottom portion and the rim portion make up the first product section 24, and the grooves of the bottom portion makes up the second product section 25. The grooves are thinner than the regular bottom portion, and the forming pressure applied to the forming mould at the grooves will thus be higher, exceeding 100 MPa. The density of the grooves will thus be higher than the rest of the coffee pod. The grooves being thinner may e.g. be used to create a thinner section to be used when penetrating the bottom wall of the coffee pod.Another suitable cellulose product having sections with different densities is a food tray (not shown) that is provided with a bottom portion and a side wall. The bottom portion is provided with grooves that are applied in a predefined pattern over at least the bottom portion of the food tray. The pattern may e.g. be a cross pattern or may comprise parallel grooves. The grooves are formed with protrusions provided on e.g. the second lower mould part, where the protrusions form the second mould section and where the remaining second mould part forms the first mould region, such that a higher forming pressure will be applied to the grooves at the second mould region. The density of the grooves will thus be higher than the rest of the bottom portion, and will exceed 1,30 g / cm3. The grooves will help to reinforce the bottom region of the tray, such that it will be possible to use an air-laid cellulose blank structure with a lower weight to form the food tray. With the reinforcement grooves, it may e.g. be possible to reduce to weight of the cellulose blank structure from 450 GSM to 400 GSM to obtain a food tray with the same strength.The forming pressure of the second region of the forming mould is at least 100 MPa, and may be up to 200 MPa or more, depending on the required parameters of the cellulose product 1. During moulding of the cellulose product, the cellulose material in the second section of the cellulose product is exposed to the high forming pressure. During moulding of the cellulose HD-DMF section, the cellulose fibres will become pseudo-liquid due to the high forming pressure and the water comprised in the cellulose material, such that the cellulose fibres will displace some in the forming mould, filling the second forming mould region completely since the cellulose fibres will locally assume liquid properties. The pseudo-liquid behaviour will allow the cellulose fibres to fill the second forming mould region evenly.The high forming pressure, the water content and the fact that the cellulose fibres must be displaced some in the second section adds to the pseudo-liquid state of the cellulose fibres. The high pressure and the shear forces acting on the cellulose fibres creates the pseudo-liquid state. After a specified holding time, the cellulose product is ready and can be removed from the forming mould.It will be appreciated that the above description is merely exemplary in nature and is not intended to limit the present disclosure, its application or uses. While specific examples have been described in the specification and illustrated in the drawings, it will be understood by those of ordinary skill in the art that various changes may be made, and equivalents may be substituted for elements thereof without departing from the scope of the present disclosure as defined in the claims. Furthermore, modifications may be made to adapt a particular situation or material to the teachings of the present disclosure without departing from the essential scope thereof. Therefore, it is intended that the present disclosure is not limited to the particular examples illustrated by the drawings and described in the specification as the best mode presently contemplated for carrying out the teachings of the present disclosure, but that the scope of the present disclosure will include any embodiments falling within the foregoing description and the appended claims. Reference signs mentioned in the claims should not be seen as limiting the extent of the matter protected by the claims, and their sole function is to make claims easier to understand.REFERENCE SIGNS1: Cellulose product2: Cellulose blank structure3: Forming mould4: First mould part5: Second mould part6: Forming apparatus7: Pulp roll8: Mill9: Forming box10: Vacuum box11: Application rollers12: Forming wire13: Buffer14: Pressing unit15: First mould region16: Second mould region17: Intermediate mould region18: First mould surface19: Second mould surface20: Third mould surface21: Fourt mould surface22: Fifth mould surface23: Sixth mould surface24: First product section25: Second product section26: Transition section27: Knife28: Knife handle29: Knife blade30: Cutting edge31: Fork32: Fork handle33: Fork head34: Tine35: Coffee pod36: Bottom portion37: Side wall portion38: Rim portion39: Groove  

Claims

1. A method for producing a three-dimensional cellulose Dry Moulded Fibres product (1) from a cellulose material (2), wherein the method comprises the steps of; arranging the cellulose material (2) in a forming mould (3);heating the forming mould (3) to a forming temperature in the range of 100°C to 300°C; andforming the cellulose product (1) from the cellulose material in the heated forming mould (3), by moulding the cellulose material (2) with a forming pressure, where a first product section (24) of the cellulose product (1) is moulded with a first forming pressure between 4-20 MPa, and where a second product section (25) of the cellulose product (1) is moulded with a second forming pressure of at least 100 MPa, wherein the cellulose material (2) is shaped into the three-dimensional cellulose product (1), and wherein the average density of the first product section (24) is below 1,30 g / cm3 and the average density of the second product section (25) is greater than 1,30 g / cm3.

2. A method according to claim 1, wherein the second forming pressure is at least 150 MPa.

3. A method according to claim 1, wherein the second forming pressure is at least 200 MPa.

4. A method according to any of the preceding claims, wherein the cellulose material is a dry-formed cellulose blank structure (2) formed in a dry-forming process where cellulose fibres are carried and formed to the dry-formed cellulose blank structure (2) by air as carrying medium.

5. A method according to any of the preceding claims, wherein the cellulose material comprises a first region corresponding to a first product section (24) of the cellulose product (1) having a weight between 400-800 GSM, and a second region corresponding to a second product section (25) of the cellulose product (1) having a weight that is higher than the weight of the first region.

6. A method according to any of claims 1 to 5, wherein the forming mould (3) comprises a first mould part (4) and a second mould part (5), where the forming mould (3) is provided with a first mould region (15) arranged to mould the first product section (24) of the cellulose product (1), and a second mould region (16) arranged to mould the second product section (25) of the cellulose product (1).

7. A method according to any of the preceding claims, wherein the cellulose material comprises at least 95% cellulose fibres by dry weight.

8. A method according to any of the preceding claims, wherein the cellulose material contains substantially only cellulose fibres.

9. A three-dimensional cellulose product (1) formed from a cellulose material (2), c h a r a c t e r i z e d i n that the cellulose product (1) comprises a first product section (24) having a density below 1,30 g / cm3 and a second product section (25) having a density greater than 1,30 g / cm3.

10. A product according to claim 9, wherein the second product section (25) is arranged at a side edge of the cellulose product (1).

11. A product according to claim 9 or 10, wherein the thickness of the second product section (25) is thinner than the thickness of the first product section (24).

12. A product according to any of claims 9 to 11, wherein the first product section (24) of the cellulose product (1) is formed with a forming pressure between 4-20 MPa, and wherein the second product section (25) of the cellulose product (1) is formed with a forming pressure exceeding 100 MPa.

13. A product according to any of claims 9 to 12, wherein the cellulose material is a dry-formed cellulose blank structure.  

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