Method of making cellulose pulp composition for moldable cellulose fibre-based webs

Abstract

The invention relates to a method for manufacturing a cellulose pulp composition for a moldable cellulose fibre-based web, the present invention relates to a process for preparing a cellulose pulp composition comprising: a) providing a cellulose pulp composition comprising at least 50 wt%, based on dry weight, of a chemical or semi-chemical wood pulp, b) subjecting the cellulose pulp composition provided in step a) to low consistency (LC) refinement at a consistency in the range of 1-7 wt% to an SR value in the range of 18-50 as determined by Standard ISO 5267-1, and c) subjecting the cellulose pulp composition provided in step a) to a low consistency (LC) refinement at a consistency in the range of 1-7 wt% to an SR value in the range of 18-50 as determined by Standard ISO 5267-1, c) subjecting the LC refined cellulose pulp composition obtained in step b) to high consistency (HC) refining at a consistency in the range of 12-40 wt% at a refining energy of at least 150 kWh / t, and d) diluting the HC refined cellulose pulp composition obtained in step c) to a consistency in the range of 0.1-10 wt%. The invention also relates to a method of manufacturing a moldable cellulosic fiber-based web and a method of manufacturing a molded cellulosic fiber-based product.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a method of manufacturing a cellulose pulp composition for a moldable cellulose fiber-based web, to a method of manufacturing a cellulose fiber-based web, and to a method of manufacturing a molded cellulose fiber-based product. BACKGROUND

[0002] Paper-based packaging materials have a growing market potential as renewable materials due to their sustainability. However, the development of new packaging concepts requires improvements in the mechanical properties of paper. High stretchability is one of these properties. Highly stretchable paper would have the potential to replace certain kinds of plastics used to form packaging by three-dimensionally (3D) shaping the sheet material into products and articles, such as deep drawing processes.

[0003] Generally, the forming processes of paper-based materials can be divided into two broad categories: slide and fixed blank processes. In forming processes using slide blanks, forming is done due to the paper sliding into the mold and the transverse contraction of the paper resulting in microfolds of the paper. In fixed blank processes, such as deep drawing, the paper is formed by straining the paper.

[0004] Generally, slide blank processes are used for producing molded products with a relatively high depth, while products produced using fixed blanks typically have a significant limitation in depth. This is due to the fact that in fixed blank processes, the tensile deformation of the paper exceeds the compressive deformation. This means that only paper grades with high stretchability, high strength, and stiffness after forming are suitable for fixed blank forming processes. Furthermore, fixed blank forming processes produce molded products with smooth and uniform edges, which enables the formed products to be hermetically sealed with barrier films. In contrast, products produced in slide blank processes have limitations in terms of sealability due to microfolds / creases, which also leads to shape instability and impaired visual appearance.

[0005] The formability of a paper-based material can be defined as the ability of the material to deform without breaking. However, formability is not a specific mechanical property, but rather a general term that can be considered to explain the degree of deformation of paper during a specific forming process. Formability can be estimated, for example, based on a 2D experimental test method simulating the process conditions in a fixed blank thermoforming process, as described in Vishtal & Retulainen, 2014 (Improving the stretchability, wet web and dry strength of paper by addition of agar, Nord Pulp Pap Res J, 29:434-443). In fixed blank processes, formability is determined by the stretchability and tensile strength of the paper. So far, fixed blank forming processes have not been widely applied in the paperboard industry.

[0006] Pulp fibers constitute the load bearing component of paper. Kraft pulp fibers are mainly composed of cellulose and hemicellulose. Cellulose is a crystalline, strong and stiff material with low extensibility, making cellulose fibers strong and stiff.

[0007] Different techniques and solutions have been proposed to improve the extensibility of paper.

[0008] To improve the formability of paper, the addition of chemicals such as thermoplastic polymers or fibers has been applied. However, there is a need to replace thermoplastic polymers or fibers with more sustainable materials.

[0009] Mechanical refining at high consistency has shown potential to improve the extensibility of paper. However, the problem with most refining methods is that they cause fiber cutting and formation of a large amount of fines. Fiber cutting and fine formation result in a decrease in the mechanical strength of the formed paper.

[0010] Paper substrates with improved extensibility can open new possibilities in the production of molded products by fixed blank forming. There is still a need to find an industrially scalable and implementable solution for improving 3D forming of fiber-based substrates on commercial machines without the risk of breakage or pinhole formation. Therefore, there is still a need for new strategies for producing paper and paperboard with improved extensibility. SUMMARY

[0011] It is an object of the present disclosure to alleviate at least some of the problems of cellulose fiber-based materials for manufacturing three-dimensional molded cellulose fiber-based products, such as by fixed blank forming.

[0012] It is a further object of the present disclosure to provide a method of manufacturing a cellulose pulp composition that can be used for manufacturing a moldable cellulose fiber-based web with improved formability, i.e. improved extensibility and strength or toughness.

[0013] It is a further object of the present disclosure to provide a method of manufacturing a cellulose pulp composition that can be used for manufacturing a moldable cellulose fiber-based web without the use of synthetic polymers.

[0014] The above objects, as well as other objects that will be appreciated by persons of ordinary skill in the art upon reading the present disclosure, are achieved by the various aspects of the present disclosure.

[0015] According to a first aspect shown herein, there is provided a method of manufacturing a cellulose pulp composition for a moldable cellulose fiber-based web, the method comprising:

[0016] a) providing a cellulose pulp composition comprising at least 50 wt% of chemical or semi-chemical wood pulp, based on dry weight,

[0017] b) subjecting the cellulose pulp composition provided in step a) to a low consistency (LC) refining at a consistency in the range of 1-7 wt% to an SR value in the range of 18-50, determined by standard ISO 5267-1,

[0018] c) subjecting the LC refined cellulose pulp composition obtained in step b) to a high consistency (HC) refining at a consistency in the range of 12-40 wt% with a refining energy of at least 150 kWh / t, and

[0019] d) diluting the HC refined cellulose pulp composition obtained in step c) to a consistency in the range of 0.1-10 wt%.

[0020] High consistency (HC) refining of chemical or semi-chemical wood pulp can achieve a pulp suspension with a high proportion of curled fibers. Mechanical refining of chemical or semi-chemical wood pulp at high consistency has shown the potential to improve the stretchability of paper formed from the pulp. HC refining produces less fines and fiber cuts compared to LC refining, but less fibrillation. The less fibrillation in HC refining produces lower mechanical strength and more curl, in LC refining, the higher degree of fibrillation leads to more fiber bonding. On the other hand, LC refining straightens the curled fibers, and the stretch strength is improved by LC refining due to the presence of more straight fibers and less curled fibers. The present invention is based on the recognition that it is preferred to perform a low consistency (LC) refining of chemical or semi-chemical wood pulp prior to HC refining, to an SR value in the range of 18-50, determined by standard ISO 5267-1. This results in fibers with both curl and surface fibrillation.

[0021] The cellulose pulp composition provided in a) comprises at least 50 wt% of chemical or semi-chemical wood pulp, based on dry weight. In some embodiments, the cellulose pulp composition provided in a) comprises at least 60 wt%, at least 70 wt%, at least 80 wt%, or at least 90 wt% of chemical or semi-chemical wood pulp, based on dry weight. In some embodiments, the cellulose pulp composition provided in a) comprises 100 wt% of chemical or semi-chemical wood pulp, based on dry weight.

[0022] The pulp used as starting material for the preparation of the modified pulp is a chemical or semi-chemical wood pulp. Chemical pulp comprises cellulose, hemicellulose and lignin, the latter usually in very small amounts. However, unbleached and especially mechanical pulp has a significantly higher content of lignin. Mechanical pulp is not preferred in the present invention because the high content of lignin can have a negative impact on the stretchability of the paper. Therefore, webs prepared from mechanical pulp generally have a significantly lower stretchability than webs prepared from chemical or semi-chemical pulp.

[0023] In some embodiments, the chemical or semi-chemical wood pulp is a softwood pulp, preferably a pine wood pulp, a spruce wood pulp or a combination thereof. The chemical or semi-chemical wood pulp can be bleached or unbleached. The chemical or semi-chemical wood pulp is preferably unbleached. In some embodiments, the chemical or semi-chemical wood pulp has a Kappa value below 90, preferably below 70, more preferably below 50, and more preferably in the range of 0-40, determined according to standard ISO 302:2015.

[0024] In some embodiments, the chemical or semi-chemical wood pulp is from never-dried chemical or semi-chemical wood pulp. The term never-dried pulp refers to pulp fibres that have not been subjected to any drying process after being separated from its source material.

[0025] The pH value of the cellulose pulp composition is typically in the range of 5-7. In some embodiments, the pH value of the cellulose pulp composition is increased to above 7, for example above 8 or above 9, prior to the LC refi ning step in step b) or prior to the LC refi ning in step c).

[0026] The remainder of the cellulose pulp composition can comprise other types of pulp or other additives.

[0027] The cellulose pulp composition provided in step a) is subjected to a low consistency (LC) refi ning at a consistency in the range of 1-7 wt% to an SR value in the range of 18-50, determined by standard ISO 5267-1.

[0028] In some embodiments, the cellulose pulp composition in b) is subjected to LC refi ning to an SR value in the range of 20-50, determined by standard ISO 5267-1, preferably to an SR value in the range of 25-50, and more preferably to an SR value in the range of 30-50.

[0029] During LC refining, the pulp fibers are subjected to mechanical forces in the presence of water, which leads to the breakdown of fiber bundles and the separation of individual fibers. LC refining can be performed by any LC refining method known in the art. Examples of refining mills that can be used in the LC refining process include, but are not limited to, conical refining mills or disc refining mills. The temperature of the pulp composition during LC refining is typically in the range of 10-90°C, for example, in the range of 25-80°C. The consistency of the cellulose pulp composition in the range of 1-7 wt% can be achieved as needed by diluting or concentrating the composition provided in step a) using methods known in the art.

[0030] The LC-milled cellulose pulp composition obtained in step b) is subjected to high-consistency (HC) milling at a consistency in the range of 12-40 wt%, wherein the milling energy is at least 150 kWh / t.

[0031] In some embodiments, the cellulose pulp composition in c) is subjected to HC milling with a milling energy of at least 200 kWh / t, preferably at least 250 kWh / t and more preferably at least 300 kWh / t.

[0032] In some embodiments, the cellulose pulp composition in c) is subjected to HC milling at a temperature in the range of 70-120°C.

[0033] In HC milling, the pulp composition is milled in a concentrated form, meaning that a significant amount of the mixture consists of pulp fibers. HC milling is carried out at a consistency significantly higher than that used for LC milling. The consistency of the cellulose pulp composition in the range of 12-40 wt% can be achieved by concentrating the composition obtained in step b) as needed using methods known in the art. HC milling can be carried out by any HC milling method known in the art. Examples of refining machines that can be used in the HC milling process include, but are not limited to, conical mills, defibrators, or compactors. Conical mills are well known to those skilled in the art in pulp milling. Defibrators are high-intensity mixers equipped with rotating blades and are commonly used for the preparation of mechanical pulps. Compactors are machines commonly used to compress or compact loose biomass or other materials (e.g., sawdust) into denser and more uniform briquettes. One example of a compactor type that can be used in the HC milling process of this invention is the e-compactor as described in the published PCT patent application WO 2012 / 113990 A1. Due to the high stress transfer between fibers during HC milling, micro-compression is imparted, resulting in the formation of crimped and kinked fibers. The crimped fibers produce high flocculation, and due to mechanical interlocking, 3D short fibers exhibit relatively high strength and short fiber stretchability compared to rigid, non-crimped fibers. Those skilled in the art will understand that “crimped” refers to bent cellulose fibers, and “kinked” refers to a sharp change in the axial direction of the cellulose fiber. The crimp percentage is measured using a fiber image analyzer (e.g., Valmet FS5) and determined by measuring the profile and projected length of individual fibers. The crimp percentage is based on the length-weighted crimp of the cellulose fiber and is calculated as 100%*(1 / L), where I is the fiber profile length and L is the projected end-to-end distance of the fiber, i.e., the distance between the two furthest points on the fiber.

[0034] HC milling results in a high degree of crimp in the cellulose fibers of chemical or semi-chemical wood pulp. In some embodiments, the cellulose fibers of the resulting HC-milled cellulose pulp composition have a crimp of at least 9%, preferably at least 15%, and more preferably at least 20%. The crimp of the HC-milled cellulose pulp composition is measured using a Valmet FS5 image analyzer according to standard methods.

[0035] The inventors have discovered that subjecting a cellulose pulp composition comprising at least 50 wt% chemical or semi-chemical wood pulp based on dry weight to LC milling followed by HC milling, according to this disclosure, produces cellulose fibers that provide significantly improved formability properties when used in moldable cellulose fiber matrix sheets for forming molded products by 3D forming of a fixed blank.

[0036] Using fibers with high fiber crimp (e.g., at least 9% fiber crimp) increases the stretch of the web of fibrous cellulose material. This stretching is useful in fixed blank forming. For example, the fiber crimp of cellulose fibers from chemical or semi-chemical wood pulp can be in the range of 9-40%, for example in the range of 15-35%, or for example in the range of 20-30%.

[0037] Following HC milling, the HC-milled cellulose pulp composition obtained in step c) is diluted to a consistency in the range of 0.1-10 wt%. The diluent used for dilution is preferably water or an aqueous solution. Dilution to a consistency of 10 wt% or less allows the HC-milled cellulose pulp composition to be pumped and / or subjected to further processing. To avoid straightening of the crimped fibers formed during the HC milling of the cellulose pulp, dilution is preferably carried out without further milling of the pulp composition.

[0038] In some embodiments, the method further includes adding an anionic or nonionic polymer, based on the dry weight of the cellulose pulp composition, at a rate of 0.1-25 kg / tn, preferably 1-20 kg / tn, and more preferably 1-15 kg / tn, to the cellulose pulp composition before subjecting it to HC milling in step c). The appropriate amount of the anionic or nonionic polymer depends on the type of anionic or nonionic polymer used.

[0039] Anionic or nonionic polymers aid in HC refining by reducing friction between cellulose fibers, preventing fiber cutting, and enhancing fiber crimping.

[0040] An anionic or nonionic polymer may be added to the cellulose pulp composition before, during, or after the LC refining in step b), but before the HC refining in step c). In some embodiments, the anionic or nonionic polymer is added to the cellulose pulp composition before the LC refining in step b). In some embodiments, the anionic or nonionic polymer is added to the cellulose pulp composition during the LC refining in step b). In some embodiments, the anionic or nonionic polymer is added to the cellulose paper composition after the LC refining in step b), but before the HC refining in step c).

[0041] In some embodiments, the anionic or nonionic polymer is selected from cellulose ethers, natural gums, and anionic polyacrylamide.

[0042] The anionic or nonionic polymer is preferably a natural polymer or a derivative of a natural polymer, and more preferably a natural polysaccharide or a derivative of a natural polysaccharide. In some embodiments, the anionic or nonionic polymer is selected from cellulose ethers and natural gums. Cellulose ethers are a group of polymers derived from cellulose. Cellulose ethers are produced by chemically modifying cellulose molecules, resulting in improved or altered properties that make them suitable for a variety of industrial applications. Cellulose ethers are typically water-soluble polymers. Examples of cellulose ethers that can be used as the anionic or nonionic polymers described herein include, but are not limited to, carboxymethyl cellulose (CMC), hydroxyethyl cellulose (HEC), ethyl hydroxyethyl cellulose (EHEC), hydroxypropyl cellulose (HPC), and methyl ethyl hydroxyethyl cellulose (MEHEC). These cellulose ethers can also be functionalized to increase their hydrophobicity. Natural gums are hydrocolloids derived from various plant sources. Examples of cellulose ethers that can be used as anionic or nonionic polymers in this article include, but are not limited to, gum arabic, guar gum, xanthan gum, locust bean gum, gum tragacanth, karaya gum, talac gum, alginate, carrageenan, and agar.

[0043] In some embodiments, the anionic or nonionic polymer is carboxymethyl cellulose. Carboxymethyl cellulose typically has a degree of substitution of 0.25 or more, or 0.3 or more. In some preferred embodiments, the carboxymethyl cellulose has a degree of substitution of 0.4 or more, preferably 0.6 or more, and more preferably 0.8 or more. Based on the dry weight of the cellulose pulp composition, the amount of carboxymethyl cellulose added is preferably in the range of 0.5-15 kg / tn.

[0044] In some embodiments, the method further includes adding a metal salt at a dry weight of 0.1-50 kg / tn of the cellulose pulp composition to the cellulose pulp composition before subjecting the cellulose pulp composition to HC refining in step c). In some embodiments, the metal salt is added to the cellulose pulp composition before LC refining in step b). In some embodiments, the metal salt is added to the cellulose pulp composition during LC refining in step b). In some embodiments, the metal salt is added to the cellulose paper composition after LC refining in step b) but before HC refining in step c). The metal salt is preferably added together with anionic or nonionic polymers, more preferably wherein the anionic or nonionic polymer is CMC. The metal salt is preferably CaCl2. The metal salt can improve the chemisorption of anionic or nonionic polymers (especially CMCs) on cellulose fibers.

[0045] In some embodiments, the cellulose pulp composition in c) is subjected to HC milling at a temperature in the range of 70-120°C. Without wishing to be bound by any particular scientific theory, it is believed that the elevated temperature in the range of 70-120°C during HC milling results in better chemisorption of anionic or nonionic polymers onto the cellulose fibers.

[0046] In some embodiments, the method further includes adding a polysaccharide-based strength enhancer to the cellulose pulp composition at a rate of 5-50 kg / tn, preferably 10-50 kg / tn, and more preferably 20-50 kg / tn based on the dry weight of the cellulose pulp composition after subjecting the cellulose pulp composition to HC milling in step c).

[0047] The inventors have discovered that a relatively large amount of polysaccharide-based strength enhancer can be used to achieve acceptable bonding without straightening the fibers. The polysaccharide-based strength enhancer is preferably added to the HC-milled cellulose pulp composition in a much higher amount than is typically expected when polysaccharide-based strength enhancers are used in paper / paperboard production.

[0048] After subjecting the cellulose pulp composition to HC milling in step c), a polysaccharide-based strength enhancer is added to the cellulose pulp composition. Preferably, the polysaccharide-based strength enhancer is added to the cellulose pulp composition during or after the dilution process in step d). In some embodiments, the polysaccharide-based strength enhancer is added to the cellulose pulp composition after the dilution process in step d). In some embodiments, the polysaccharide-based strength enhancer is added to the cellulose pulp composition together with the dilution water used for the dilution in step d).

[0049] In some embodiments, the polysaccharide-based strength enhancer is a cellulose-based strength enhancer, preferably selected from highly refined cellulose, cellulose fines, microfibrillated cellulose, or combinations thereof with an SR value in the range of 70-92.

[0050] As used herein, highly refined cellulose refers to cellulose that has been refined to a Schopper-Riegler (SR) value in the range of 70-92 as determined by standard ISO 5267-1. Refining or pulping cellulose refers to the mechanical treatment and modification of cellulose fibers to provide them with desired properties.

[0051] As used herein, the term cellulose fines generally refers to cellulose particles that are significantly smaller than cellulose fibers. In some embodiments, the term cellulose fines, as used herein, refers to fine cellulose particles that can pass through a 200-mesh sieve (equivalent pore size 76 μm) of a conventional laboratory grading apparatus (SCAN-CM 66:05). Two main types of cellulose fines exist: primary fines and secondary fines. Primary fines are generated during pulping and bleaching, where they are removed from the cell wall matrix through chemical and mechanical treatments. Due to their origin (i.e., complex mesothelial cells, ray cells, parenchyma cells), primary fines exhibit a lamellar structure with only a small amount of fibrillary material. Conversely, secondary fines are generated during pulping and finishing.

[0052] In the context of this patent application, microfibrillated cellulose (MFC) refers to cellulose particles, fibers or fibrils with a width or diameter of 20 nm to 1000 nm.

[0053] Various methods exist for manufacturing MFCs, such as single-pass or multi-pass milling, pre-hydrolysis followed by milling, or high-shear decomposition or fibrillation. One or more pretreatment steps are typically required to make MFC manufacturing both energy-efficient and sustainable. Therefore, the cellulose fibers used in the pulp for MFC production can be natural or enzymatically or chemically pretreated, for example, to reduce the amount of hemicellulose or lignin. Cellulose fibers can be chemically modified prior to fibrillation, where the cellulose molecules contain functional groups different from (or more than) those found in native cellulose. Such groups particularly include carboxymethyl (CM), aldehydes and / or carboxyl groups (in cellulose obtained via N-oxygen-mediated oxidation (e.g., "TEMPO")) or quaternary ammonium (cationic cellulose). After modification or oxidation using one of the methods described above, it is easier to break down the fibers into MFCs.

[0054] In some embodiments, the polysaccharide-based strength enhancer is a starch-based strength enhancer. The starch-based strength enhancer can be, for example, natural starch, cooked starch, cationic starch, chemically modified starch, physically modified polymer-grafted starch, enzyme-modified starch, anionic starch, amphoteric starch, cross-linked starch, pregelatinized starch, swollen starch, or any combination thereof. In some embodiments, the starch-based strength enhancer comprises cationic starch.

[0055] In some embodiments, the polysaccharide-based strength enhancer is a combination of a cellulose-based strength enhancer and a starch-based strength enhancer. Adding microfibrillated cellulose increases the strength enhancer loading capacity of the pulp composition. This allows for a higher total amount of strength enhancer (e.g., starch) added and bound to the pulp than is possible elsewhere.

[0056] The inventors discovered that by adding a high amount of polysaccharide-based strength enhancer to the HC-milled cellulose pulp composition, straightening of crimped fibers during subsequent processing of the HC-milled cellulose pulp composition can be avoided.

[0057] Adding such a high amount of polysaccharide-based strength enhancer to the pulp suspension allows for the retention of a higher degree of fiber crimp in the pulp composition from HC milling in the moldable cellulose fiber-based material (e.g., moldable web) formed from the pulp composition, thereby improving the stretchability properties of the moldable cellulose fiber-based web.

[0058] The cellulose pulp composition is preferably prepared without or substantially without the addition of synthetic polymers. In some embodiments, the resulting HC-milled cellulose pulp composition contains less than 2 wt%, preferably less than 1 wt%, and more preferably less than 0.5 wt% synthetic polymer based on dry weight.

[0059] In some implementations, steps a)-d) are performed as an integration process. This allows for complete control over latency and curling behavior.

[0060] The HC-milled cellulose pulp compositions obtained by the methods of this disclosure are particularly suitable for moldable webs used as precursors for preparing 3D-shaped products obtained by fixed-premise forming. As used herein, the term web generally refers to a continuous preform or sheet of paper or paperboard manufactured or in the process of manufacturing on a paper machine. As used herein, the term web also refers to a paper or paperboard substrate used for conversion into other physical forms, for example, in the preparation of molded products by fixed-premise forming.

[0061] According to a second aspect shown herein, a method for manufacturing a moldable cellulose fiber-based web is provided, the method comprising:

[0062] i) A cellulose pulp composition for manufacturing a moldable cellulose fiber-based web according to any one of the preceding claims.

[0063] ii) The wet web of the cellulose pulp composition, optionally together with other components,

[0064] iii) Dehydrate the wet fabric, and

[0065] iv) Dry the dehydrated wet web to obtain a moldable cellulose fiber-based web.

[0066] Preferably, no further refining of the cellulose composition is performed after HC refining. Further fibrillation and over-decomposition, mixing, and pumping of the HC-refined pulp are preferably avoided or minimized to prevent reduction of fiber crimp.

[0067] In some implementations, steps i)-iv) are performed as an integration process. This allows for complete control over latency and curling behavior.

[0068] The formation of the wet web in ii) can be accomplished using conventional paper or paperboard forming techniques known in the art. While those skilled in the art may envision different arrangements for carrying out the steps of the method of the invention, the method of the invention can advantageously be carried out in a paper machine, more preferably in a Fourdrinier type paper machine, i.e., a paper machine based on the principles of the Fourdrinier machine. A Fourdrinier type paper machine uses a moving dewatering fabric or woven wire (commonly referred to as a “wire mesh”) to produce a continuous web by filtering out the fibers retained in the cellulose pulp composition and producing a continuously moving wet fiber web. This wet web is then dried in the machine to produce paper or paperboard.

[0069] The formation and dewatering steps of the method of the present invention are preferably carried out in the forming section (also commonly referred to as the wet section) of the paper machine. The cellulose pulp composition is typically applied to the screen at a consistency of 0.1-1.5 wt%, and more typically below 0.5 wt%, using a so-called headbox.

[0070] The formation of the wet web in ii) may include, for example, water forming or foam forming.

[0071] In some embodiments, the formation of the wet web in ii) involves foam forming. In foam forming, fibers and other ingredient components are mixed with foam instead of water. The foam consists of water, a foaming agent, and air.

[0072] In foam forming, a large amount of air is added to the cellulose pulp composition in the presence of a foaming agent. The resulting bubbles prevent fiber flocculation, enhance dehydration, and enable the production of lightweight structures. Foam forming is also expected to maintain fiber crimp in a better manner than conventional waterforming, resulting in better stretchability of the formed web.

[0073] As used herein, the terms foam and foaming refer to substances made by trapping air or bubbles within a solid or liquid. Typically, the volume of a gas is much larger than that of a liquid or solid, with a thin film separating the gas pockets. For foam to form, three requirements must be met. First, mechanical work is required to increase the surface area. This can occur by stirring, dispersing a large amount of gas into a liquid, or injecting gas into a liquid. Second, a foam-forming agent must be present, typically an amphiphilic substance, surfactant, or surface-active component, to reduce surface tension. Finally, the foam must form faster than it decomposes.

[0074] In some embodiments, a foam generator is used to achieve the foaming required for foam formation. The pulp suspension can be pumped through the foam generator once or multiple times to achieve the desired gas content or foam density. In some embodiments, the pulp suspension is pumped through a high-shear mixer or refiner that generates the foam. The foam can be generated offline or online on the paper machine.

[0075] Based on the volume of the foam, the typical air content is in the range of 50-70 vol%. The bubbles prevent fibers from flocculating in the headbox. In some embodiments, the foam is made to have an air content of 60-70 vol% before being applied to the formed fabric. The consistency of the foamed cellulose pulp composition is typically in the range of 2-5 wt%.

[0076] Foam is formed and stabilized using a foaming agent present in the slurry suspension. The foaming agent can be a small-molecule surfactant or a polymeric foaming agent, or a mixture thereof. The amount of foaming agent in the foam is typically in the range of 0.005 to 30 wt% based on the total dry weight of the foam, but this can be readily determined by those skilled in the art. An example of a small-molecule surfactant that can be used for foam forming is sodium dodecyl sulfate (SDS). The amount of SDS in the foam is typically in the range of 0.005 to 10 wt% based on the total dry weight of the foam, for example, about 0.02 wt%. Examples of polymeric foaming agents that can be used for foam forming include polyvinyl alcohol (PVOH) and partially hydrolyzed polyvinyl acetate (PVOH / Ac). The amount of polyvinyl alcohol (PVOH) or partially hydrolyzed polyvinyl acetate (PVOH / Ac) in the foam is typically in the range of 0.01 to 30 wt% based on the total dry weight of the foam, for example, about 5 wt%.

[0077] When using foam forming, the cellulose pulp composition can be applied to the screen at a consistency significantly higher than that typically found in water forming (0.1-1.5 wt%). When using foam forming, the cellulose pulp composition is preferably applied to the screen at a consistency of 2-5 wt%.

[0078] The wet web material first undergoes dehydration on the screen. Dehydration on the screen can be assisted by various dehydration devices, such as blades, tables and / or foil elements, suction boxes, frictionless dehydration, ultrasonic-assisted dehydration, couch rolls, or watermark rolls.

[0079] Dewatering typically further includes pressing the wet web to squeeze out as much water as possible. Dewatering may, for example, involve passing the formed wet web through the press section of a paper machine, where the wet web passes between large rolls loaded under high pressure to squeeze out as much water as possible. The removed water is typically received by the fabric or felt. In some embodiments, the dry solids content of the dewatered wet web is in the range of 15-65 wt%, preferably in the range of 18-60 wt%, and more preferably in the range of 22-55 wt%.

[0080] The drying step may, for example, involve drying the dehydrated wet fabric by passing it through a series of heated drying drums. Drying typically reduces the water content in the fabric to about 1-15 wt%, preferably to about 2-10 wt%.

[0081] In some embodiments, the drying in step iv) results in a drying shrinkage rate of at least 4% in the transverse (CD) direction, preferably in the range of 5-20%, and more preferably in the range of 6-12%.

[0082] The moldable cellulose fiber-based web obtained according to the invention preferably has properties such as basis weight, thickness and stretchability, which makes the material suitable for conversion into molded packaging products by 3D forming techniques (e.g., fixed blank forming, including molding and / or deep drawing techniques).

[0083] In some embodiments, the obtained 3D-formable cellulose fiber-based web has a density of 50 g / m². 2 -500g / m 2 Within the range, or at 120g / m 2 -200g / m 2 Or 150g / m 2 -200g / m 2 The weight in grams, i.e., the basis weight, is within the range of 120 to 200 g / m³. 2 The weight between these values ​​is preferred because it will be less prone to breakage and can withstand the forces inherent in the 3D forming process.

[0084] In some embodiments, according to standard ISO 1924-3:2005, the obtained moldable cellulose fiber matrix web has at least 5% stretchability in the longitudinal direction (MD) and at least 9% stretchability in the transverse direction (CD). For example, the stretchability is at least 6% in both directions (MD and CD). In another example, the stretchability is at least 10% or at least 12% in the transverse direction (CD). In yet another example, according to standard ISO 1924-3:2005, the stretchability in the CD direction is between 8% and 15%, preferably between 10% and 14%.

[0085] In some embodiments, the resulting moldable cellulose fiber web, based on dry weight, contains less than 2 wt%, preferably less than 1 wt%, and more preferably less than 0.5 wt% of a synthetic polymer.

[0086] In some implementations, the total rejection rate of the obtained moldable cellulose fiber web, according to the PTS RH 021 / 97 test method for Class II products, is less than 10%, and preferably less than 5%.

[0087] In some implementations, the moldable cellulose fiber matrix is ​​formed as a single layer of a multilayer moldable cellulose fiber matrix.

[0088] According to a third aspect shown herein, a method for manufacturing three-dimensional (3D) cellulose fiber-based products is provided, the method comprising:

[0089] i) A cellulose pulp composition for manufacturing moldable cellulose fiber-based webs according to any one of claims 1-14

[0090] ii) The wet web of the cellulose pulp composition, optionally together with other components,

[0091] iii) Dehydrate the wet fabric.

[0092] iv) Drying and dehydrating the wet web to obtain moldable cellulose fiber-based web, and

[0093] v) Forming molded cellulose fiber-based products from moldable cellulose fiber-based webs, for example by forming a fixed blank.

[0094] In some implementations, steps i)-v) are performed as an integration process. This allows for complete control over latency and curling behavior.

[0095] In some embodiments, after step iv) and before product formation in step v), the dehydrated web is compacted in a Clupak unit. In this case, the web contains 20-50% moisture during Clupak compaction. As known to those skilled in the art, the Clupak method is an in-plane compaction treatment of wet fiber layers, resulting in improved ductility of the material. The production process involves running the web through the gaps in a compactor, whereby the web is subjected to recoil from an elastic surface (e.g., an endless rubber surface), resulting in compaction of the web and thus mechanically increasing the web's stretchability. It has been noted that foam-formed webs are particularly well resistant to Clupak treatment due to the improved stretchability described above. Therefore, in one embodiment, the web to be subjected to Clupak compaction is foam-formed.

[0096] In some embodiments, fixed blank forming is performed with a die depth of at least 20 mm. In some embodiments, fixed blank forming is deep drawing.

[0097] Molded products can be, for example, molded receptacles. Non-limiting examples of such receptacles include trays, containers, plates, bowls, and cups. Receptacles can have, for example, substantially square (e.g., quadratic or rectangular), substantially polygonal (e.g., hexagonal), or substantially circular (e.g., circular or elliptical) geometries. Among other purposes, receptacles can be used for the storage and transport of fresh or frozen foods. In some embodiments, containers can also be used for the conventional or microwave preparation of food. Receptacles are preferably formed from a piece of substrate material. In the context of this document, the phrase "piece material" includes a piece material comprising one or more layers of the same material or multiple layers of different materials. These multilayer materials can include, for example, layers of two or more paper and / or cardboard substrates that are completely bonded together and / or partially bonded together, such as corrugated cardboard material, or any other layer or multiple layers with or without any other material (e.g., metal, foil, plastic, etc.). Therefore, laminated materials formed from two or more different types of materials are still covered by the phrase "piece material."

[0098] The molded product is preferably prepared using a moldable cellulose fiber matrix web obtained according to the second aspect via a fixed blank forming technique. In a preferred embodiment, the molded three-dimensional product is formed from a single piece of moldable cellulose fiber matrix web. In a preferred embodiment, the molded product is formed from a single piece of moldable cellulose fiber matrix web, wherein the basis weight of the web is 120 g / m². 2 Above, or at 150g / m 2 above.

[0099] Although the methods of the present invention described herein are primarily intended for fixed-formation, it should be noted that the method, as well as the cellulose pulp composition and moldable cellulose fiber matrix web obtained by the method, can also be used with other forming techniques, such as hydroforming, thermoforming, and compression forming. Therefore, in any aspect or embodiment described herein, fixed-formation may be replaced by and / or include deep drawing, hydroforming, thermoforming, or compression forming.

[0100] The methods of the present invention described herein are primarily intended for the manufacture of cellulose pulp compositions and moldable cellulose fiber-based webs for the production of 3D molded cellulose fiber-based products. However, the tensile strength and tensile properties of the moldable cellulose fiber-based webs are also useful in other applications where these properties are desired. Specifically, the resulting cellulose pulp compositions and moldable cellulose fiber-based webs can also be used to manufacture cellulose-based capping films for agricultural applications. The moldable cellulose fiber-based webs can be used as an alternative to conventional synthetic polymer capping films.

[0101] While the invention has been described herein with reference to various exemplary embodiments, those skilled in the art will understand that various changes can be made and elements thereof can be substituted with equivalents without departing from the scope of the invention. Furthermore, many modifications can be made to adapt particular situations or materials to the teachings of the invention without departing from the essential scope of the invention. Therefore, it is intended that the invention be limited to the specific embodiments disclosed as the best mode for carrying out the invention, but that the invention will include all embodiments falling within the scope of the appended claims.

Claims

1. A method of manufacturing a cellulose pulp composition for a moldable cellulosic fibrous web, the method comprising: a) providing a cellulose pulp composition comprising at least 50 wt% of chemical or semi-chemical wood pulp, based on dry weight, b) subjecting the cellulose pulp composition provided in step a) to a low consistency (LC) refining at a consistency in the range of 1-7 wt% to an SR value in the range of 18-50 determined by standard ISO 5267-1, c) subjecting the LC refined cellulose pulp composition obtained in step b) to a high consistency (HC) refining at a consistency in the range of 12-40 wt% with a refining energy of at least 150 kWh / t, and d) diluting the HC refined cellulose pulp composition obtained in step c) to a consistency in the range of 0.1-10 wt%.

2. The method according to claim 1, wherein the chemical or semi-chemical wood pulp is softwood pulp, preferably pine wood pulp, spruce wood pulp or a combination thereof.

3. The method according to any one of the preceding claims, further comprising adding to the cellulose pulp composition 0.1-25 kg / tn, preferably 1-20 kg / tn and more preferably 1-15 kg / tn of an anionic or non-ionic polymer, based on dry weight, prior to subjecting the cellulose pulp composition to HC refining in step c).

4. The method according to claim 3, wherein the anionic or non-ionic polymer is selected from the group consisting of cellulose ethers, natural gums and anionic polyacrylamides.

5. The method according to claim 4, wherein the anionic or non-ionic polymer is selected from the group consisting of cellulose ethers and natural gums.

6. The method according to any one of the preceding claims, further comprising adding 5-50 kg / tn, preferably 10-50 kg / tn and more preferably 20-50 kg / tn of a polysaccharide-based strength enhancer to the cellulose pulp composition, based on dry weight of the cellulose pulp composition, after subjecting the cellulose pulp composition to HC refining in step c).

7. The method according to claim 6, wherein the polysaccharide-based strength enhancer is a cellulose-based strength enhancer, preferably selected from the group consisting of highly refined cellulose having an SR value in the range of 70-92, cellulose fines, microfibrillated cellulose and combinations thereof.

8. The method according to claim 6, wherein the polysaccharide-based strength enhancer is a starch-based strength enhancer.

9. The method according to claim 6, wherein the polysaccharide-based strength enhancer is a combination of a cellulose-based strength enhancer and a starch-based strength enhancer.

10. The method according to any one of the preceding claims, wherein the cellulose pulp composition in b) is subjected to LC refining to an SR value in the range of 20-50, preferably to an SR value in the range of 25-50 and more preferably to an SR value in the range of 30-50.

11. The method according to any one of the preceding claims, wherein the cellulose pulp composition in c) is subjected to HC refining with a refining energy of at least 200 kWh / t, preferably at least 250 kWh / t, and more preferably at least 300 kWh / t.

12. The method according to any one of the preceding claims, wherein the cellulose pulp composition in c) is subjected to HC refining at a temperature in the range of 70-120 °C.

13. The method according to any one of the preceding claims, wherein the cellulose fibres of the obtained HC refined cellulose pulp composition have a fibre curl of at least 9 %, preferably at least 15 %, and more preferably at least 20 %.

14. The method according to any one of the preceding claims, wherein the obtained HC refined cellulose pulp composition comprises less than 2 wt%, preferably less than 1 wt%, and more preferably less than 0.5 wt% of synthetic polymers, based on dry weight.

15. A method of manufacturing a mouldable cellulose fibre-based web, the method comprising: i) manufacturing a cellulose pulp composition for a mouldable cellulose fibre-based web according to any one of the preceding claims, ii) forming a wet web of the cellulose pulp composition, optionally together with further components, iii) dewatering the wet web, and iv) drying the dewatered wet web to obtain a mouldable cellulose fibre-based web.

16. The method according to claim 15, wherein the obtained moldable cellulosic fibrous base web has a dry basis weight in the range of 50-500 g / m2 2 or 120-200 g / m2 2 or 150-180 g / m2 2 .

17. The method according to any one of claims 15-16, wherein the drying in step iv) results in a drying shrinkage in the cross direction (CD) of at least 4 %, preferably in the range of 5-20 %, and more preferably in the range of 6-12 %.

18. The method of any one of claims 15-17, wherein, The obtained mouldable cellulose fibre-based web has a stretchability in the machine direction (MD) of at least 5 % and in the cross direction (CD) of at least 9 % according to standard ISO 1924-3:2005.

19. The method of any one of claims 15-18, wherein, The obtained mouldable cellulose fibre-based web comprises less than 2 wt%, preferably less than 1 wt%, and more preferably less than 0.5 wt% of synthetic polymers, based on dry weight.

20. The method of any one of claims 15-19, wherein, The obtained mouldable cellulose fibre-based web has a total reject rate of less than 10 %, and preferably less than 5 % according to PTS RH 021 / 97 test method for class II products.

21. A method of manufacturing a moulded cellulose fibre-based product, the method comprising: i) manufacturing a cellulose pulp composition for a mouldable cellulose fibre-based web according to any one of claims 1-14, ii) forming a wet web of the cellulose pulp composition, optionally together with further components, iii) dewatering the wet web, iv) drying the dewatered wet web to obtain a mouldable cellulose fibre-based web, and v) forming a three-dimensional moulded cellulose fibre-based product from the mouldable cellulose fibre-based web.

22. A mouldable cellulose fibre-based web obtainable by the method according to any one of claims 15-16.

23. A moulded cellulose fibre-based product obtainable by the method according to claim 21.