SE1950981A1 - Method of producing a cellulose fiber structure and a fiber structure - Google Patents

Abstract

The invention discloses a method for producing a three dimensional molded structure from cellulose fibers, comprising the steps of:-providing an aqueous composition comprising cellulose pulp and at least one metal salt in a substantially homogeneous mixture, wherein said mixture has a solid content between 0.05-10wt%;-providing a forming tool having a three dimensional shape comprising a forming portion, and bringing said forming portion into contact with the aqueous composition so that said forming portion is covered with a wet layer of pulp;-dewatering the layer of pulp contacted by the forming tool at temperatures > 100°C to a dry content of at least 70wt% to achieve the three dimensional molded structure.

Description

METHOD OF PRODUCING A CELLULOSE FIBER STRUCTUREAND A FIBER STRUCTURE Technical fieldThe present invention relates to a method of producing athree dimensional cellulose fiber based structure by means of fiber molding.

BackgroundThere is a growing interest for producing cellulose based, three dimensional (3D) products, e.g. for use as packagingapplications for foodstuff, tableware, trays, technical products,electronic equipment and/or consumer goods. Several advantagesare associated with the use of natural fibers (such as cellulosefibers) for manufacturing packages. Being a renewable resource,natural fibers provide a sustainable alternative to other packagingmaterials such as aluminum and plastics, and furthermore naturalfibers are both recyclable and biodegradable. Natural fibers includecellulose fibers of any natural origin, such as derived from woodpulp and/or plants.

There is also a demand in packaging industry of increasingcolor, product differentiation, and novelty in addition topersonalized prints, and to provide eye catching shapes. In additionto such aesthetic considerations an element of physical protection isalso required for the goods in question.

Molding of cellulose fiber materials provides a way ofachieving renewable articles with various three dimensional shapes,which may be used to differentiate products available for sale in a given marketplace. 2 Manufacturing molded fiber products and structure can bedone by wet forming, wherein a forming tool is dipped into anaqueous pulp composition followed by compression-moldingperformed under heat, resulting in a dried fiber product having ashape complementary to the shape of the mold. Typically, said toolis perforated or porous so that water can be removed from thesuspension or wet pulp during forming during a dewatering/dryingstep. The forming tool is selected in order to control the surfaceroughness. In case of an egg box, for example, the outer surfacecan be made smooth in order to enable printed label to adhere.Preparation of a smoother surface often leads to that the reverseside is coarse. Thus, if making a smooth inner side, the outersurface will be coarse which makes direct printing difficult,especially printing of four colors (CMYK color model). Also, aproblem associated with various forming techniques is roughnessvariations of the molded product which causes problems withuneven print quality.

In US2013248130, a compression-molded tray of fibermaterial coated with a removable film is described, andWO200605761O also presents a method and a machine for makingfiber products such as food trays by means of fiber molding from astock of pulp.

In addition to designing the shape of a product or structure, itis desirable to also add colorful decorations and adornments as wellas informative content onto its surface. For example, it is commonto add a label and/or etiquette onto paper based containers andpackages as an information carrier. However, labels/etiquettesrequire additional production step and also consumes extra material in the form of label components. Direct printing is also done but 3 mostly with one color and mainly for coding or simple color printing,e.g. egg boxes.

Application of ink onto the surface of a molded article oftenleads to problems with dot resolution and that the spreading andabsorption of ink color is hard to regulate, which cause bleedingand wicking. Surface roughness and use of higher fiber content leadto reduced print density and hence greater use of colorants toattain a certain density level. Hence, there is a need forimprovements when it comes to printability of molded pulp products.

Obiects of the inventionIt is an object of the present invention, to provide a method for manufacturing a fiber based, three dimensional molded articlecomprising a surface with enhanced printability. It is also an objectof the present invention to provide a three dimensional moldedarticle which is based on cellulose fibers, and which comprises asurface with enhanced printability properties. By "enhancedprintability" means that printing a pattern onto said surface can bedone substantially without bleeding, wicking and with a highresolution and especially for 4-color (or more) prints. Low inkspreading and adjustable ink absorption is desirable for controllingboth print quality but also print durability and associated problems such as ink smearing, print thru, rub-off or hidden rub-off.

SummaryThe objects of the invention are at least partially obtained by means of a method for producing a three dimensional moldedstructure from cellulose fibers according to claim 1. Said method comprises at least the steps of: providing an aqueous composition 4 comprising cellulose pulp and at least one metal salt in asubstantially homogeneous mixture, wherein said mixture has asolid content between 0.05-10wt% ; -providing a forming tool having a three dimensional shapecomprising a forming portion, and bringing said forming portion intocontact with the aqueous composition so that said forming portionis covered with a wet layer of pulp; -dewatering the layer of pulp contacted by the forming tool attemperatures >100°C to a dry content of at least 70wt% to achievethe three dimensional molded structure. Preferably, the layer ofpulp is dewatered to dry content of at least 8Owt°/0, preferably atleast 85wt%.

It has surprisingly been found that the printability of a threedimensional molded, fiber based structure is significantly improvedby means of a method and a structure according to the invention.Addition of a metal salt into the aqueous solution providesenhanced printability for inks, especially those With pigmentcolorants. The technology is suitable for inkjet but can also beapplied for flexographic or screen printing. Thanks to the invention,several advantages are achieved. In addition to enhancedprintability of the molded product, the use of expensive chemicals isavoided or at least reduced, especially fossil based ones.Furthermore, printing of primers or complex surface treatmentprocesses are not needed. Thus, the solution does not only improvefeathering and bleeding but also print density and ink adhesion.Thanks to the invention, three dimensional molded pulp productscan be decorated with more variable colored prints using multiple colors without the risk of inferior print quality, and even 3D effects can be accomplished by means of printing thanks to the enhanced printability of the substrate (i.e. the molded pulp product).

According to one aspect of the present invention, said mixturealso comprises a ce||u|ose nanomaterial such as e.g. microfibrillatedce||u|ose (MFC). The use of ce||u|ose nanomaterial enhances theretention of metal salts in the material, and it also improves thestrength of the end structure. In one aspect of the invention, MFC ispre-mixed with salt before it is added to the material composition.This enables charge reversal of MFC and it also gives a morehomogenous suspension. Herein, the term "aqueous composition"can also be referred to as "aqueous suspension".

|II The term "ce||u|ose nanomateria referred to herein is to beinterpreted as materials comprising ce||u|ose and encompassesmicrofibrillated ce||u|ose (MFC) as well as ce||u|ose nanocrystals(nanocrystalline ce||u|ose) and mixtures thereof. This means thatone dimension (diameter) of the fibers is within the scale of 1-1000nm (mean average fiber or fibril diameter). Microfibrillated ce||u|ose(MFC) or so called ce||u|ose microfibrils (CMF) shall in the context ofthe present invention mean a micro-scale ce||u|ose particle fiber orfibril with at least one average or mean dimension less than 1000nm. MFC comprises partly or totally fibrillated ce||u|ose orlignocellulose fibers. The ce||u|ose fiber is preferably fibrillated tosuch an extent that the final specific surface area of the formedMFC is from about 1 to about 500 m2/g, such as from 10 to 400m2/g or more preferably 50-300 m2/g when determined for asolvent exchanged and freeze-dried material with the BET method.Various methods exist to make MFC, such as single or multiple pass refining, pre-treatment followed by refining, or high 6 shear disintegration or liberation of fibrils. One or several pre-treatment steps are usually required in order to make MFCmanufacturing both energy-efficient and sustainable. The cellulosefibers of the pulp to be supplied may thus be pre-treatedenzymatically or chemically, for example to reduce the quantity ofhemicellulose or lignin. The cellulose fibers may be chemicallymodified before fibrillation, wherein the cellulose molecules containfunctional groups other (or more) than found in the originalcellulose. Such groups include, among others, carboxymethyl,aldehyde and/or carboxyl groups (cellulose obtained by N-oxylmediated oxidation, for example "TEMPO"), quaternary ammonium(cationic cellulose). The cellulose may also be methylated orphosphorylated. After being modified or oxidized in one of theabove-described methods, it is easier to disintegrate the fibers intoMFC.

The microfibrillar cellulose may contain some hemicelluloses;the amount is dependent on the plant source. Mechanicaldisintegration of the pre-treated fibers, e.g. hydrolysed, pre-swelled, or oxidized cellulose raw material is carried out withsuitable equipment such as a refiner, grinder, homogenizer,colloider, friction grinder, ultrasound sonicator, single - or twin-screw extruder, fluidizer such as microfluidizer, macrofluidizer orfluidizer-type homogenizer. Depending on the MFC manufacturingmethod, the structure might also contain fines, or nanocrystallinecellulose or e.g. other chemicals present in wood fibers or otherlignocellulosic fibers used in papermaking processes. The structuremight also contain various amounts of micron size fiber particlesthat have not been efficiently fibrillated. The amount of these fiberparticles can be determined e.g. in fiber analysator which is known for a skilled person in the art. 7 MFC can be produced from wood cellulose fibers, both fromhardwood or softwood fibers. It can also be made from microbialsources, agricultural fibers such as wheat straw pulp, bamboo,bagasse, or other non-wood fiber sources. It is preferably madefrom pulp including pulp from virgin fiber, e.g. mechanical, chemicaland/or thermomechanical pulps. It can also be made from broke orrecycled paper.

According to another embodiment, the aqueous suspensionmay comprise a mixture of different types of fibers, such asmicrofibrillated cellulose, and an amount of other types of fiber,such as kraft fibers, fines, reinforcement fibers, synthetic fibers,dissolving pulp,rejects, recycled pulp or paper packaging materials,coated or uncoated broke, TMP, CTMP or PGW.

The suspension may also comprise other process or functionaladditives, such as fillers, pigments, wet strength chemicals,retention chemicals, cross-linkers, softeners or plasticizers,adhesion primers, wetting agents, biocides, optical dyes,fluorescent Whitening agents, de-foaming chemicals,hydrophobizing chemicals such as AKD, ASA, waxes, resins etc.Other additives that may be added are various inkjet printenhancing chemicals such as cationic mordants, nanofillers etc.These will enhance the print quality effect but also provide e.g. other effects.

The term "cellulose fiber material" referred to herein is to beinterpreted as a material comprising natural cellulose-based fibers,including aqueous pulp compositions and/or fiber based sheet orweb materials. Any cellulosic fibers known in the art, includingcellulose fibers if any natural origin, such as those derived from vegetable pulp or agricultural-based pulp, can be used in the 8 cellulose fiber material. Non-limiting examples of cellulosic fiberssuitable for use in this invention are cellulose fibers derived fromsoftwoods such as pines, firs and spruces, as well as fibers derivedfrom eucalyptus, bagasse, bamboo and other ligneous and cellulose SOU FCeS.

Said press drying can be applied in one or several stepsdepending on the end structure. Also, press drying can be done bytwo complementary forming tools laminating and compressing the cellulose fiber to be dried.

According to one aspect of the invention, aqueouscomposition has a solid content between 0.05-10wt°/0.

The forming tool can be brought into contact with the saidaqueous pulp composition by means of immersion into thecomposition, whereupon cellulose fibers are drawn onto the formingportion for instance by means of vacuum suction. Next, the layer ofpulp present on said forming portion is dried and/or dewatered to adry content of at least 70%. Drying can be accomplished with orwithout heating, pressing or any other mechanical support thatimproves dewatering and formation. Combination of elevatedtemperatures and pressure is a conceivable procedure. Said"elevated temperature" is here to be interpreted as temperatures>100°C. The dried layer is removed from the forming tool toachieve a single layer three dimensional molded structure with enhanced printability.

As explained above, the aqueous composition has a solidcontent (i.e. a consistency) of preferably between 0.05 - 10 wt°/0, more preferably 0.2- 1.5wt°/0. 9 Furthermore, the layer of pulp present on said forming portionmay be press dried with a pressure between 0.2-50 bar, preferably 0.5-15 bar, more preferably 1-10 bar.

In case of drying the pulp present on said forming portion bymeans of applying elevated temperatures, such temperatures ispreferably between 100-350°C, preferably 120-250°C, morepreferably between 150-220°C.

It is also within the ambit of the present invention to producea mu|ti|ayer three dimensional molded structure with enhancedprintability. A "layer" can also be referred to as a "ply". According toone example, a mu|ti|ayer three dimensional molded structure maybe produced in that the surface of said forming portion of theforming tool is pre-coated with a first layer of cellulose fibers. Saidpre-coated first layer may have a different function such asproviding a certain rigidity or barrier property. A layer of metal saltcontaining pulp is thereafter applied on top of said first layer toprovide an outer surface with enhanced printability. More than twolayers are also conceivable in a multiply structure, preferably 2 - 5layers. In one embodiment, at least one of the layers in a mu|ti|ayerthree dimensional molded structure is made of MFC. A combinationof metal salts and microfibrillated cellulose enhances the effect andprovide a more even ink receptive surface. Also, addition of MFCwill not only enhance metal salt retention but also increase surface smoothness and surface strength.

According to one aspect of the invention, the metal salt- containing wet layer of pulp present on the forming portion during production of said three dimensional molded structure is 5-150 gsm in dry weight.

According to a preferred aspect of the invention, said pulp isselected from the group comprising wood pulps, non-wood pulps,unbleached chemical pulp, defibrated fiber material, bagasse,straws, bamboo, spruce CTMP, eucalyptus CTMP, spruce HT CTMP,kraft pulp, sulphate, sulphite, PGW, GW, DIP, recycled paper andboard, coated and uncoated broke, RMP, TMP, CMP, CSP NSSCnanopulp, dissolving pulp, and regenerated fibers and mixturesthereof. It is understood that other cellulosic material such aschemical or semi-chemical pulp of wood or non-wood material canbe added as part of the pulp stock. Preferably, said pulp is a pulpfiber or fiber mixture with a Schopper Riegler value above 50 measured according to the SR standard.

According to yet another aspect of the invention, the methodfurther comprises imprinting a pattern onto said three dimensionalmolded structure using a water based ink or a solvent based ink. Itis also conceivable to use an ink that comprises both solvent andwater. The ink can also be a varnish or a combination of ink andvarnish. Ink can comprises one colorant or both dye and pigment,said pigments often being anionic. According to another aspect,said metal salt is preferably added to the pulp, or in case ofcellulose nanomaterial such as MFC being present in the material,to the MFC before it is mixed with the pulp, or to the mixture ofpulp and MFC. Pre-mixing MFC and metal salt before adding to thepulp stock can be advantageous because it leads to charge reversalof MFC, and also prevents the salts from precipitating other bonding agents that may be present in the pulp. 11 According to another aspect, said metal salt is one of CaCl2,Ca(OAc)2, MgCl2 or AICI3, or mixtures thereof.

According to another aspect, the metal salt is added incombination with one or more of the following additives: a cationicpolymer, humectants, nanopigments and/or cross-linked polymers.

A possible ratio between metal salt vs additive is 1:1OO - 100:1.

According to another aspect, the dose of metal salt is 1-50kg/tn or more preferably 5-35 kg/tn measured for the outer ply incase of a multilayered ply. The skilled person understands that thesalt amount can be determined by means of ToF-SIMS or other spectroscopic of chemical analysis methods.

According to another aspect, said aqueous composition alsocomprises one or more additional functional chemicals selectedfrom the group comprising cationic polymers, nanopigments,amphoteric polymers and anonionic polymers. The salt incombination with specific cationic polymers enhance ink rubresistance and water fastness. Water fastness refers to thesensitivity of the color adhesion (once imprinted onto the surface of a material) to humidity.

According to another aspect, said aqueous compositionfurther comprises one or more co-additives selected from the groupcomprising nanoparticles, cationic mordants, cross-linkers, non-ionic polymers such as PVOH, PEG, cationic fillers, pigments or fillers with high surface area, preferably >1O g/m2. 12 According to another aspect, said cellulose nanomaterial is anionic MFC, or native MFC.

According to another aspect, the grammage of the molded structure is preferably 5-450 gsm or more preferably 10-200 gsm.

According to another aspect, molded structure comprises adensity between 350-1500 kg/m3, preferably 400-1200 kg/m3 ormost preferably 500-900 kg/m3.

The present invention also relates to a moldable aqueoussuspension of cellulose pulp, at least one metal salt and optionally microfibrillated cellulose in a substantially homogeneous mixture.

The present invention also relates to the use of a moldableaqueous suspension comprising cellulose pulp and at least onemetal salt in a substantially homogeneous mixture, for improvingthe printability of a three dimensional molded structure made fromsaid aqueous suspension. Said aqueous suspension may optionallycomprise also cellulose nanomaterials such as MFC, and at least one metal salt in a substantially homogeneous mix.

The present invention further also relates to a three-dimensional molded pulp product comprising more than one layer,whereof at least one layer is a molded structure according to claim1 constituting an imprinting layer made from a mixture aspreviously described, further where said imprinting layer is arranged as an outer layer of said multilayer product.

Description of Embodiments The present description is directed to production of three dimensional molded pulp articles with enhanced printability. 13 Examples of a three dimensional molded pulp article include in a non-limiting way containers, trays and packages.

Although the present description relates to the context ofconventional wet forming procedures, the invention is not limitedthereto. The skilled person appreciates that the invention maycontemplate any fiber-based manufacturing method, including 3D printing techniques.

According to the invention, presence of metal salt in acellulose based molded pulp article, or at least presence of metalsalt in a surface layer of a molded article, leads to improved surface printability e.g. when using inkjet printing technology.

It is thus within the ambit of the present invention to providea 3D molded product comprising at least one outer surface or aportion of an outer surface which has been made from a pulp slurrycomprising metal salt additive/s. Production of such molded article may be done by wet molding methods.

In the following, an example of a wet molding method formanufacturing a three dimensional molded article withimproved/enhanced printability will be described in a non-limiting way.

An aqueous pulp suspension (also referred to as"composition") is provided with the consistency of O.O5-1Owt°/0. Thepulp may be any one of wood pulps, non-wood pulps, unbleachedchemical pulp, defibrated fiber material, bagasse, straws, bamboo, spruce CTMP, eucalyptus CTMP, spruce HT CTMP, kraft pulp, 14 sulphate, sulphite, PGW, GW, DIP, recycled paper and board, broke,RMP, TMP, CMP, CSP NSSC nanopulp, dissolving pulp, andregenerated fibers or mixtures thereof.

A cellulose nanomaterial such as e.g. microfibrillated cellulose(MFC) may be added to the pulp suspension. At least one metal saltis also added to the pulp and mixed to achieve a substantiallyhomogeneous suspension. The cellulose nanomaterial may be pre-mixed with the metal salt before they are added to the pulp.Furthermore, said metal salt/s may be added during fibrillation ofMFC or during disintegration of the pulp. Said MFC is preferably anionic MFC, or native MFC, or a grafted version thereof.

A 3D shaped forming tool comprising a forming portion isbrought into contact with the pulp suspension, for instance byimmersing said tool into the slurry bath. Said forming portion isarranged to represent a 3D mirror image of the article to beformed. Pulp is drawn onto the forming portion e.g. by means ofvacuum suction until a layer of desired thickness has been formed,whereupon the forming tool is removed from the slurry. At thisstage, the forming portion is covered with a wet layer of pulp, saidwet layer comprising between 5-150 gsm in dry weight. Next, thewet layer of pulp is dewatered to a dry content of at least 7Owt°/0.Dewatering and/or drying can be done in various ways. In a wetcuring procedure, the wet layer is pressed under elevatedtemperatures to be compressed and dried to a certain thickness,thereby yielding a smooth external surface for the end structure. Ina dry curing process, the wet layer is subjected to heated airthereby removing moisture, which results in an end structure with amore textured finish. This way, a single layer molded fiber product is formed.

Manufacturing multilayered molded fiber products can beaccomplished for instance by applying more than one fibrous layeron top of each other in consecutive molding production steps. Forinstance, a layer of metal salt-containing pulp can be molded onto apre-molded pulp layer already present on the forming tool. Thevarious layers of a multilayered product may hereby providedifferent functions, such as rigidity, barrier properties, etc. In amultilayered product, the imprint-enhancing layer is to form theprinting surface, or an outer layer. According to the invention, thehot press temperature range for a wet molded procedure is around 150-220 degrees C, with a press range around 1-10 bar.

Imprinting a pattern onto the surface of the three dimensionalmolded product will now be described. The three dimensionalmolded article (produced by means of wet- or dry molding asdescribed above) is subjected to imprinting a pattern e.g. by inkjetprinting onto the metal salt-containing surface (i.e. the printingsurface). Said inkjet printing is done using one or severalprintheads, hereby using one or several colors such as four colormodel CMYK. Furthermore, printing can be done in-line, at-line oroff-line e.g. at the moulded pulp line. Printing can also be done off-line e.g. after or before packing or filling line. The printing can alsobe done using other suitable printing technologies such as screenprinting. One advantage with digital printing is, however, thepossibility for more flexible printing, variable and personalized printing and non-contact printing mode.

The preferred inks is a water based ink comprising preferablypigment based colorants. The inks typically contains multiple additives including rheology modifiers, dispersants, biocides, 16 humectants etc. It should also be understood that inks can be so-called hybrid inks comprising both dye and pigment basedcolorants. The inks can also contain one or several co-solvents in addition to water.

It is also preferred that the surface intended for printing ofsaid substrate is hydrophilic or such that the contact angle for wateris < 80 degrees or pref. < 60 degrees after 10 seconds whenmeasured with distilled water. The surface should preferably behydrophilic for rapid liquid ink carrier medium uptake. By "carriermedium" means a solvent, which could be water or water/solventmixture. Solvents could be e.g. various alcohol or e.g. glycols. Afast absorption of the carrier medium is advantageous since itreduce the risk of intercolor bleeding. At the same time, fastabsorption may also lead to too much penetration of the colorantwhich should be avoided. One way to evaluate the hydrophilicityand ability of the solvent to spread is by e.g. contact angle meaSUFementS.

Preferably, said ink is water based due to cost and safety.Solvent or co-solvent inks may also be possible but then thefixation mechanism might be different. It is believed that metalsalts electrostatically interacts with the anionic colorants in the ink.There are a number of water based inks on the market. Inks whichare especially suitable for this tye of technology are e.g. brandedunder the name ColorLok. HP Desktop Officejet 8000 is example of a printer having ink which is reactive with the metal salts.

The solution according to the invention is also suitable for useof anionic dye based inks or hybrid inks meaning dye combined with a colorant. Pigment colorants have some advantages over dye 17 based colorants such as light stability. Some properties, on theother hand, are better for the dye based colorants and therefore amix of various colorants could offer a broader technical effectcompared to a one-colorant based ink. Typically, the ink or colorants are anionicically charged, e.g. pigment colorants are anionic charged through electrostatic and/electrosteric stabilization.

The printed products can also be hybrid printed, and/orvarnished or laminated afterwards. In this context, the hybridprinting means that two or more printing techniques are combined,e.g. screen printing and inkjet printing. A problem with screenprinting is limited speed, and that personalized or variable printjobs cannot be done. On the other hand, a combinaton of screenand inkjet printing would offer different solutions to the same printjob such as variable print with inkjet and non-variable print madewith screen. It is also possible to use one or both for making varnishing including spot vanishing.

The present invention has been described with regard topreferred embodiments. However, it will be obvious to a personskilled in the art that a number of variations and modifications canbe made without departing from the scope of the invention as described herein.

Claims (23)

1. A method for producing a three dimensional moldedstructure from cellulose fibers, comprising the steps of: -providing an aqueous composition comprising cellulose pulpand at least one metal salt in a substantially homogeneous mixture,wherein said mixture has a solid content between 0.O5-1Owt°/0; -providing a forming tool having a three dimensional shapecomprising a forming portion, and bringing said forming portion intocontact with the aqueous composition so that said forming portionis covered with a wet layer of pulp; -dewatering the layer of pulp contacted by the forming tool attemperatures >100°C to a dry content of at least 7Owt°/0,preferably at least 80% to achieve the three dimensional molded structure.

2. A method according to claim 1, wherein the aqueous composition has a solid content between O.2-1.5wt°/0.

3. A method according to any one of claims 1 or 2, whereinthe layer of pulp present on said forming tool is dewatered by means of press-drying.

4. A method according to any one of the previous claims, wherein the wet layer of pulp is 5-150 gsm in dry weight.

5. A method according to claim 3 or 4, wherein press drying isperformed at temperatures >100°C, preferably at temperaturesbetween 120-250°C or more preferably between 150-220°C. 19

6. A method according to any one of the previous claims,further comprising imprinting a pattern onto said three dimensional molded structure using a water based ink.

7. A method according to claim 6, wherein said imprinting is performed by any one of inkjet, flexographic or screen printing.

8. A method according to claim 6 or 7, wherein the imprintingis performed using any one of pigment based colorant ink, anionic dye based ink or hybrid ink.

9. A method according to any one of the previous claims,wherein said aqueous composition also comprises microfibrillatedce||u|ose (MFC).

10. A method according to any one of the previous claims,wherein said ce||u|ose pulp is selected from the group comprising:wood pulps, non-wood pulps, unbleached chemical pulp, defibratedfiber material, bagasse, straws, bamboo, spruce CTMP, eucalyptusCTMP, spruce HT CTMP, kraft pulp, sulphate, sulphite, PGW, GW,DIP, recycled paper and board, broke, RMP, TMP, CMP, CSP NSSCnanopulp, dissolving pulp, and regenerated fibers and mixtures thereof

11. A method according to any one of the previous claims,wherein said metal salt is preferably pre-mixed With microfibrillatedce||u|ose into a mixture, whereafter said mixture is added to the aqueous composition.

12. A method according to any one of the previous claims,wherein said metal salt is selected from the group comprising:CaCl2, Ca(OAc)2, MgCl2 or AlCl3, or mixtures thereof.

13. A method according to any one of the previous claims,wherein the dose of metal salt is 1-50 kg/tn or more preferably 5-35 kg/tn.

14. A method according to any one of the previous claims,wherein said material also comprises one or more additionalfunctional chemicals selected from the group comprising cationicpolymers, nanopigments, amphoteric polymers and anonionic polymers.

15. A method according to any one of the previous claims,wherein said mixture also comprises one or more co-additivesselected from the group comprising nanoparticles, cationicmordants, cross-linkers, non-ionic polymers such as PVOH, PEG,cationic fillers, pigments or fillers with high surface area preferably with a surface area >10 g/m2.

16. A method according to any one of claims 9-15, wherein said MFC is preferably anionic MFC, or native MFC.

17. A method according to any one of the previous claims,wherein the grammage of the molded structure is preferably 5-450 gsm or more preferably 10-200 gsm.

18. A method according to any one of the previous claims,wherein said molded structure comprises a density between 350-1500 kg/m3, preferably 400-1200 kg/m3 or most preferably 500-900 kg/m3. 21

19. A moldable aqueous suspension of cellulose pulp,microfibrillated cellulose and at least one metal salt in a substantially homogeneous mix.

20. Use of a moldable aqueous suspension of cellulose pulpand at least one metal salt in a substantially homogeneous mix, forimproving the printability of a three dimensional molded structure made from said aqueous suspension.

21. Use according to claim 20, wherein said aqueous suspension further comprises microfibrillated cellulose.

22. A three-dimensional molded pulp structure made by means of a method according to any one of claims 1 - 18.

23. A three-dimensional molded pulp structure comprisingmore than one layer, whereof at least one layer is an imprintinglayer made by means of a method according to any one of claims 1- 18, further where said imprinting layer is arranged as an outer layer of said multilayer structure.