Formable fiber substrate with barrier layer

Abstract

The present disclosure provides a method for producing a high grammage formable fiber-based substrate with barrier layer. The method includes providing a high consistency refined pulp suspension by providing a cellulose pulp composition comprising at least 50 wt% chemical or semi-chemical wood pulp, subjecting the composition to low consistency refining, high consistency refining, and dilution. A fiber web is prepared from the pulp to a grammage above 120 gsm and below 500 gsm. At least one coated polymer layer is applied onto the substrate to provide a barrier. The resulting substrate has a CD stretch > 8%, a Water Vapor Transfer Rate (WVTR) of less than 5 g / m2 / 24h, and an oxygen transmission rate (OTR) of less than 5 cc / m2 / day.

Description

[0001] FORMABLE FIBER SUBSTRATE WITH BARRIER LAYER

[0002] FIELD OF INVENTION

[0003] The present disclosure relates to fiber-based substrates with barrier properties, and more particularly to a method for producing a high grammage formable fiber-based substrate with barrier and a package made from such a substrate.

[0004] BACKGROUND

[0005] Formable fiber webs, such as hot formable and / or deep-drawable fiber webs, have gained increasing attention in the packaging industry due to their potential for creating sustainable and recyclable packaging solutions. These materials offer the possibility of replacing traditional plastic-based packaging with more environmentally friendly alternatives. However, the development of fiber-based substrates that can meet the demanding requirements of e.g. hot forming and / or deep-drawing processes while maintaining adequate barrier properties has presented significant challenges.

[0006] In general, forming processes for paper-based materials can be divided into two main categories: sliding- and fixed blank processes. In the forming process with sliding blank, such as deep drawing, forming proceeds due to the sliding of paper into a three-dimensional mold and lateral contraction of paper that causes microfolding of the paper. In the fixed blank process, such as vacuum forming and thermoforming / hot forming, paper is formed via straining of the paper into a 3D shape.

[0007] Usually, the sliding blank process is used to produce molded products with a relatively high depth, while products produced using the fixed blank process typically have significant limitations in depth. This is due to the fact that in the fixed blank process, tensile deformation of paper prevails over compressive deformation. This means that only paper grades with high stretchability, high strength and post-forming stiffness are suitable for the fixed blank forming process. Fixed blank forming process yields molded products with smooth and even edges that enables the gas-tight sealing of formed products with barrier films. In contrast, the products produced in the sliding blank process have limitations in sealability due to microfolding / wrinkling, which also causes shape instability and impaired visual appearance.Formability of a paper-based material can be defined as the ability of a material to be deformed (such as to be stretched) without breaking. However, formability is not a specific mechanical property but can be regarded as a generic term for explaining how well the paper deforms during a particular forming process. Formability can for example be estimated on the basis of a 2D experimental test method that simulates the process conditions in a fixed blank thermoforming process as described by 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 the fixed blank process, the formability is determined by the stretchability and tensile strength of the paper. So far, the fixed blank forming process has not been widely applied in industry for paperboard.

[0008] One challenge in the development of formable fiber-based substrates is achieving the necessary stretch properties while maintaining adequate rigidity and barrier performance. Some promising solutions have emerged, such as those utilizing a combination of high consistency and low consistency refining followed by wet creping techniques like Clupak. However, these approaches have primarily been successful for low grammage substrates, and there remains a lack of information on how to improve the rigidity and barrier properties of higher grammage substrates while maintaining their stretchability. Furthermore, existing formable fiber-based substrates often struggle to achieve the high barrier properties required for modified atmosphere packaging (MAP) and vacuum skin packaging (VSP) applications. MAP is important for extending the shelflife of various food products, but traditional fiber-based materials often lack the necessary gas and moisture barrier properties to maintain a controlled atmosphere within the package.

[0009] It has been appreciated that a high grammage formable fiber-based substrate with barrier properties is needed that overcomes one or more of these problems.

[0010] SUMMARY OF INVENTION

[0011] In a first aspect, a method for producing a high grammage formable fiber-based substrate with barrier layer is provided. The method comprises: providing a cellulose pulp composition comprising at least 50 wt% chemical or semi -chemical wood pulp based on dry weight; subjecting the cellulose pulp composition to low consistency (LC) refining at a consistency in the range of 1-7 wt% to an SR value in the range of 18-50; subjecting the LC-refined cellulose pulp composition to high consistency (HC) refining or mixing at a consistency in the range of 12-40 wt% with a refining energy of at least 150 kWh / t; and diluting the HC -refined cellulose pulp composition to a consistency in the range of 0.1-10wt%; preparing a fiber web from the pulp to a grammage above 120 gsm and below 500 gsm; and applying at least one polymer layer onto a first surface of said substrate providing a barrier against at least one of liquid, moisture, grease and gas; wherein the resulting substrate has a CD stretch > 8% measured according to standard ISO 1924-3:2005, a Water Vapor Transmission Rate (WVTR) of less than 5 g / m / 24h, preferably less than 3 g / m / 24h, or less than 2 g / m / 24h as measured using ASTM F1249, and an oxygen transmission rate (OTR) of less than 5 cc / m / day measured according to ASTM D3985, 23 °C, 50 % relative humidity (RH).

[0012] This method provides a high grammage fiber-based substrate with excellent barrier properties and good formability. Formability of a paper-based material can be defined as the ability of a material to deform without breaking. Materials with good formability, i.e. comprising good stretchability and tensile strength, are suitable for so-called “fixed blank process” such as vacuum forming, where a product is formed via straining a paper into a 3D-product such as a tray. The combination of LC and HC refining, followed by dilution, allows for optimal fiber development and bonding leading to high CD stretch for improved formability. Moreover, the high grammage and coated polymer layer contribute to enhanced barrier properties.

[0013] The grammage of the fiber web may be above 140 gsm, preferably above 160 gsm, more preferably above 180 gsm and below 500 gsm. Increasing the grammage within this range further improves the strength and barrier properties of the substrate while maintaining its formability. This is advantageous for manufacturing 3D-formed packages with high barrier function, e.g. modified atmosphere packages (MAP) and vacuum skin packaging (VSP) intended for food products such as meat, fish, poultry, dairy, ready meals and cheese.

[0014] The method may further comprise, after preparing the fiber web, subjecting the fiber web to a patterning treatment, where said patterning treatment preferably is a Clupak treatment or Expanda method. The patterning treatment, particularly Clupak treatment, enhances the stretchability and formability of the substrate, allowing for deeper forming also in fixed blank processes. The moisture content during the patterning treatment may be between 10-20%. Maintaining the moisture content within this range during patterning optimizes the effectiveness of the treatment, resulting in improved stretch properties without compromising the substrate's strength.

[0015] The at least one polymer layer may comprise one or more of the following polymers: polyethylene (PE), polyethylene terephthalate (PET), polyvinyl alcohol (PVOH), polyvinyl acetate (PVA),polypropylene (PP), ethyl vinyl alcohol copolymer (EVOH), and / or polyamide (PA). The selection of these polymers for the barrier layer allows for customization of barrier properties against various substances, enhancing the versatility of the substrate for different applications. The polymer layer may be applied by means of extrusion coating.

[0016] The method may comprise applying more than one polymer layer for providing barrier function against at least one of liquid, moisture, grease and gas, in which case a multilayer polymer barrier is applied onto a first side of the substrate. In one example, such a multilayer polymer barrier comprises at least three layers, wherein at least one of said three layers comprises polyethylene (PE), preferably wherein the PE is LLDPE or LDPE. In another example, the multilayer polymer barrier comprises five layers: a first innermost barrier layer comprising polyethylene (PE); a first tie layer on top of said innermost barrier layer; a second middle barrier layer comprising ethyl vinyl alcohol polymer (EVOH); a second tie layer on top of said middle barrier layer; and a third outermost barrier layer comprising polyethylene (PE), wherein the resulting substrate comprises a Water Vapor Transmission Rate (WVTR) of less than 3 g / m / 24h, as measured using ASTM F1249, and an oxygen transmission rate (OTR) of less than 2 cc / m2 / day measured according to ASTM D3985, 23 °C, 50 % relative humidity (RH).

[0017] The method may further comprise pre-adding at least one strength chemical and one friction control agent before providing the cellulose pulp composition. Pre-adding strength chemicals and friction control agents enhances the mechanical properties of the final substrate and improves processability during manufacturing.

[0018] The resulting substrate may have an MD stretch > 2% measured according to standard ISO 1924-3:2005. The high MD stretch, in combination with the high CD stretch, provides formability in multiple directions, allowing for complex shapes to be formed.

[0019] The resulting substrate may be recyclable with <15% total reject, preferably <12% total reject measured according to PTS RH 021 / 97 test method for Category II products. The high recyclability of the substrate contributes to its environmental sustainability, reducing waste and promoting circular economy principles.

[0020] The method may further comprise adding an anionic or non-ionic polymer to the cellulose pulp composition prior to subjecting it to the HC -refining, wherein the amount of polymer added is 0.1-25kg / tn, based on dry weight. The addition of anionic or non-ionic polymers before HC-refming enhances fiber bonding and improves the strength properties of the final substrate.

[0021] The method may further comprise adding a polysaccharide-based strength enhancement agent to the cellulose pulp composition after subjecting it to the HC-refming, wherein the amount of agent added is 5-50 kg / tn, based on dry weight of the cellulose pulp composition. Adding a polysaccharide-based strength enhancement agent after HC-refming further improves the mechanical properties of the substrate, particularly its strength and stiffness.

[0022] The cellulose pulp composition may be subjected to LC refining to an SR value in the range of 20-50, preferably in the range of 25-50, more preferably in the range of 30-50. Refining to these SR values optimizes fiber development, leading to improved strength and formation in the final substrate.

[0023] The LC-refined cellulose pulp composition may be subjected to HC refining with a refining energy of at least 200 kWh / t, preferably at least 250 kWh / t, more preferably at least 300 kWh / t. Higher refining energies in HC refining leads to increased fibrillation and internal fibrillation of fibers, resulting in improved strength and barrier properties of the final substrate. The cellulose pulp composition may be subjected to HC refining at a temperature in the range of 70-120 °C. Refining at elevated temperatures enhances the efficiency of the refining process and can lead to improved fiber properties in the final substrate.

[0024] In a second aspect, a high grammage formable fiber-based substrate with barrier is provided, obtainable by the method of the first aspect, wherein the substrate comprises a fiber web having a grammage above 120 gsm and below 500 gsm, said fiber web optionally being patterned and having at least one extruded polymer layer, and wherein the substrate has a CD stretch > 8% measured according to standard ISO 1924-3:2005, a Water Vapor Transfer Rate (WVTR) of less than 5 g / m / 24h, preferably less than 3 g / m / 24h, or less than 2 g / m / 24h, and an oxygen transmission rate (OTR) of below 5 cc / m2 / day measured according to ASTM D3985, 23 °C, 50 % relative humidity (RH). This high grammage fiber-based substrate with barrier properties combines excellent formability with superior barrier performance against moisture and oxygen. The high CD stretch allows for three-dimensional forming such as in fixed blank process, while the low WVTR and OTR values ensure effective protection for packaged contents.In a third aspect, a method for manufacturing a 3D-molded cellulose fiber-based product is provided, comprising providing a high grammage formable substrate with barrier according to the invention, and forming a 3D molded cellulose fiber packaging product therefrom.

[0025] DETAILED DESCRIPTION

[0026] The present disclosure relates to a high grammage formable fiber-based substrate with modified atmosphere packaging (MAP) barrier properties and / or vacuum skin packaging (VSP) barrier properties. The substrate combines high stretchability with excellent barrier performance against at least one of liquids, moisture, grease, and gases. The substrate is produced using a method that involves low consistency refining followed by high consistency refining of cellulose pulp, preparation of a fiber web with a grammage above 120 gsm, and below 500 gsm, and application of at least one polymer layer applied for instance by means of extrusion coating. The resulting substrate exhibits good stretch properties in both the machine direction (MD) and cross direction (CD), while maintaining excellent barrier characteristics. The substrate may be subjected to a patterning treatment to further enhance its formability properties. The disclosed method and resulting substrate address the need for a rigid, fiber-based formable substrate that maintains barrier performance and dimensional stability without compromising recyclability.

[0027] It is to be understood that in the context of the present invention, “formable” means that the substrate exhibits properties that allow the material to be deformed, for instance by being stretched, to some extent without breaking. A formable paperboard can be subjected to 3D-forming processes, including sliding-blank as well as fixed-blank forming processes, in order to produce packaging products such as food trays.

[0028] The method for producing the high grammage formable fiber-based substrate with barrier layer involves several steps to prepare the cellulose pulp composition for subsequent use in forming the fiber web which is used for manufacturing a three-dimensional molded cellulose fiber-based packaging product.

[0029] The first step involves providing a cellulose pulp composition comprising at least 50 wt% chemical or semi-chemical wood pulp based on dry weight. In some examples, the cellulose pulp composition maycomprise softwood pulp, such as pine pulp, spruce pulp, or a combination thereof. The use of softwood pulp may contribute to the strength and flexibility of the final substrate.

[0030] Next, the cellulose pulp composition is subjected to low consistency (LC) refining. This LC refining step is performed at a consistency in the range of 1-7 wt%. The LC refining process continues until the pulp reaches an SR value in the range of 18-50, as determined by standard ISO 5267-1. In some examples, the SR value may be in the range of 20-50, 25-50, or 30-50. The LC refining step helps to fibrillate the fibers and improve their bonding potential.

[0031] Following the LC refining, the cellulose pulp composition undergoes high consistency (HC) refining. In HC refining, the pulp composition is subjected to refining in a concentrated form, meaning that a significant amount of the mixture consists of pulp fibers. This means HC refining is performed at a significantly higher consistency than the consistency used for the LC refining. In the present invention, the HC refining is conducted at a consistency in the range of 12-40 wt%. The refining energy applied during this step is at least 150 kWh / t. In some examples, the refining energy may be at least 200 kWh / t, at least 250 kWh / t, or at least 300 kWh / t. The HC refining step may be performed at a temperature in the range of 70-120 °C. This HC refining process further modifies the fiber structure, enhancing the stretch properties of the resulting substrate. A consistency in the range of 12-40 wt% of the cellulose pulp composition can be achieved by concentration of the composition obtained in step b) as required using methods known in the art. The HC refining can be performed by any of the HC refining methods known in the art. Examples of refiners useful for the HC refining process include, but are not limited to, conical refiners, wing defibrators or compactors. Conical refiners are well known to the person skilled in the art of pulp refining. Wing defibrators are high intensity mixers fitted with rotating blades, commonly used in the preparation of mechanical pulp. Compactors are machines typically used for compressing or compacting loose biomass or other materials, for example saw dust, into denser and uniform briquettes. One example of compactor type useful for HC -refining in the inventive method is an e-compactor as described in published PCT patent application WO 2012 / 113990 AL Due to high transfer of stresses between the fibers in HC refining, micro compressions are imparted leading to creation of curled and kinked fibers. Curly fibers produce high flocculation, and 3D flocks have relatively high strength and flock stretchability compared to stiff non-curly fibers due to mechanical interlocking. The skilled person understands that “curled” refers to curved cellulose fiber and “kinks” refers to sharp changes in an axial direction of a cellulose fiber. The curl % is measured by means of a fiber image analyzing instrument, such as Valmet FS5, and isdetermined by measuring individual fiber contours and projected lengths. Curl % is based on length-weighed curl of cellulose fibers and is calculated as 100% *(1 / L) where I is the fiber contour length and L is the projected end-to-end distance of the fiber, i.e. the distance between the two points on the fiber that are furthest apart.

[0032] The HC refining leads to a high degree of curl in the cellulose fibers of the chemical or semi-chemical wood pulp. In some embodiments, the cellulose fibers of the obtained HC-refined cellulose pulp composition have a fiber curl of at least 7%, preferably at least 10%, and more preferably at least 15%. The fiber curl of the HC-refined cellulose pulp composition is measured by standard methods using a Valmet FS5 image analyzer.

[0033] It has been found that subjecting a cellulose pulp composition comprising at least 50 wt% chemical or semi-chemical wood pulp based on dry weight to LC refining followed by HC refining according to the present disclosure produces cellulose fibers providing significantly improved formability properties when used in a cellulose fiber-based web for forming molded products, e.g. by fixed blank 3D forming. One reason for this improved formability is that the HC -refining generates a high fiber curl which is not destroyed by any subsequent LC refining because said LC-refining is performed in an earlier step.

[0034] Using fibers with high fiber curl, such as a fiber curl at least 9% increases the stretch of the web of the fibrous cellulosic material. This stretch is useful in fixed blank forming. For example, the fiber curl of the cellulose fibers of the chemical or semi -chemical wood pulp may be in the range of 7-30%, such as in the range of 9-25%.

[0035] In a next step, after the HC refining, the cellulose pulp composition is diluted to a consistency in the range of 0.1-10 wt%. This dilution step prepares the pulp suspension for subsequent web formation. In some examples, the method may include additional steps to enhance the properties of the pulp suspension. For instance, at least one strength chemical and one friction control agent may be added to the cellulose pulp composition before the initial step of providing the cellulose pulp composition. Another optional step involves adding an anionic or non-ionic polymer to the cellulose pulp composition prior to the HC refining step. The amount of polymer added may be in the range of 0.1-25 kg / tn, based on dry weight. In some examples, the amount may be 1-20 kg / tn or 1-15 kg / tn. The anionic or non-ionic polymer may be selected from cellulose ethers, natural gums, or anionic polyacrylamide.Additionally, a polysaccharide-based strength enhancement agent may be added to the cellulose pulp composition after the HC refining step. The amount of this agent may range from 5-50 kg / tn, based on the dry weight of the cellulose pulp composition. In some examples, the amount may be 10-50 kg / tn or 20-50 kg / tn. The polysaccharide-based strength enhancement agent may be a cellulose-based agent, such as highly refined cellulose with an SR value in the range of 70-92, cellulose fines, microfibrillated cellulose, or combinations thereof. Alternatively, the agent may be starch-based or a combination of cellulose-based and starch-based agents.

[0036] The resulting high consistency refined pulp suspension prepared through these steps forms the basis for creating the fiber web with enhanced properties for the high grammage formable fiber-based substrate.

[0037] Following the preparation of the high consistency refined pulp suspension, the next step in the method involves preparing a fiber web from the pulp. The fiber web is formed with a grammage above 120 gsm and below 500 gsm. This specific grammage range is selected to achieve the desired balance of strength, flexibility, and barrier properties in the final substrate.

[0038] The grammage of the fiber web plays a crucial role in determining the characteristics of the resulting substrate. In some examples, the grammage of the fiber web may be above 140 gsm, above 160 gsm, or above 180 gsm, while still remaining below 500 gsm. Higher grammage values within this range generally contribute to increased rigidity and strength of the substrate.

[0039] For instance, a fiber web with a grammage of 150 gsm may provide a good balance of flexibility and strength, suitable for applications requiring moderate forming capabilities. A fiber web with a grammage of 200 gsm may offer enhanced rigidity and barrier properties, making the resulting substrate more suitable for applications requiring greater structural integrity or improved barrier performance.

[0040] The process of preparing the fiber web from the pulp suspension typically involves forming the web on a paper machine. The diluted pulp suspension is deposited onto a forming fabric, where water is removed through drainage and vacuum suction. The wet web is then pressed and dried to achieve the desired moisture content and grammage.

[0041] The high grammage of the fiber web contributes to the overall performance of the substrate in several ways. The increased fiber content per unit area enhances the mechanical properties of the substrate, including tensile strength, burst strength, and tear resistance. Additionally, the higher grammageprovides a more substantial base for the subsequent application of the barrier layer, potentially improving the adhesion and overall barrier performance of the final substrate.

[0042] After preparing the fiber web, the method may include subjecting the fiber web to a patterning treatment. The patterning treatment is an optional step that can enhance the properties of the substrate, particularly its stretchability and dimensional stability.

[0043] In some examples, the patterning treatment is a Clupak treatment. The Clupak treatment is a mechanical process that imparts stretchability and softness to the fiber web. During the Clupak treatment, the fiber web is passed through a rubber belt and a heated cylinder. The rubber belt compresses and stretches the fibers, creating a micro-creped structure that allows for increased extensibility in both the machine direction (MD) and cross direction (CD).

[0044] The moisture content of the fiber web during the patterning treatment is a parameter that affects the effectiveness of the treatment and the resulting properties of the substrate. In some examples, the moisture content during the patterning treatment is between 10-20%. This moisture range allows for optimal fiber flexibility and rearrangement during the treatment process.

[0045] For instance, a moisture content of 12% may result in a substrate with good stretchability while maintaining sufficient strength. A moisture content of 15% may lead to increased softness and flexibility in the final substrate. At the higher end of the range, such as 18%, the treatment may produce a substrate with maximum stretchability, although care must be taken to avoid excessive weakening of the fiber structure.

[0046] The patterning treatment, particularly the Clupak treatment, contributes to the high stretch properties of the resulting substrate. The micro-creped structure created by the treatment allows the substrate to extend and conform to various shapes during 3D-forming processes. This enhanced stretchability is beneficial for applications requiring complex three-dimensional forms or packaging with intricate contours.

[0047] Additionally, the patterning treatment may improve the dimensional stability of the substrate. The rearrangement of fibers during the treatment can help reduce the tendency of the substrate to shrink or expand under varying environmental conditions, such as changes in humidity or temperature.

[0048] The combination of the high grammage fiber web produced by means of a method according to the invention and the patterning treatment results in a substrate with both rigidity and flexibility. Thisunique combination of properties allows the substrate to maintain its structural integrity while also conforming to desired shapes during forming processes.

[0049] The method for producing the high grammage formable fiber-based substrate includes applying at least one polymer layer onto a first surface of the substrate. This polymer layer provides a barrier against at least one of liquid, moisture, grease, and gas.

[0050] The coating process may be performed by means of extrusion coating involving melting the polymer material and applying it directly onto the substrate in a thin, continuous layer. The molten polymer may be extruded through a flat die and immediately pressed onto the moving substrate. The substrate and polymer layer are then cooled, solidifying the polymer and creating a strong bond between the substrate and the barrier layer.

[0051] Various polymers may be used for the extrusion coating process, depending on the desired barrier properties and end-use applications. Some examples of suitable polymers include polyethylene (PE), polyethylene terephthalate (PET), polyvinyl alcohol (PVOH), polyvinyl acetate (PVA), polypropylene (PP), ethyl vinyl alcohol copolymer (EVOH), and polyamide (PA).

[0052] In some examples, the polymer layer comprises polyethylene (PE). The PE may be low-density polyethylene (LDPE) or linear low-density polyethylene (LLDPE). The amount of PE applied may range from 30-50 gsm, with some examples using 35-45 gsm PE. For instance, a 40 gsm LDPE layer may provide good moisture and grease barrier properties while maintaining flexibility.

[0053] In other examples, multiple polymer layers may be applied to achieve specific barrier properties. For instance, a five-layer barrier structure may be used, consisting of PE + tie + EVOH + tie + PE. In this configuration, tie layers are binding the PE and EVOH-layers together, and as for functionality, the EVOH layer provides gas barrier properties, while the PE layers on either side protect the EVOH from moisture and provide heat-sealability. The tie layers may consist of modified polyethylene such as ethylene-vinyl-acetate (EVA), acid modified polyolefin, or anhydride modified polyolefin. The thickness of each layer may vary depending on the specific requirements of the application. In this five-layer structure, the PE is preferably LDPE.

[0054] The extrusion coating process may be performed at various speeds and temperatures, depending on the polymer being used and the desired coating thickness. For example, when applying a PE layer, the extrusion temperature may range from 280°C to 320°C, with the exact temperature adjusted based on the grade of PE and the desired adhesion properties.The adhesion between the polymer layer and the substrate may be influenced by several factors, including the surface properties of the substrate, the extrusion temperature, and the nip pressure applied during the coating process. In some cases, a primer or tie layer may be applied to the substrate before the polymer layer to enhance adhesion.

[0055] The combination of the LC- and HC-refined pulp substrate and the extrusion coated polymer layer results in a formable material with excellent barrier properties. The substrate provides a strong, flexible base, while the polymer layer imparts the necessary barrier characteristics against liquids, moisture, grease, and gases.

[0056] The resulting high grammage deep drawable or vacuum formable fiber-based substrate with barrier layer exhibits a combination of properties that make the substrate particularly suitable for packaging applications requiring both flexibility and barrier performance.

[0057] The substrate demonstrates excellent stretch properties in both the cross direction (CD) and machine direction (MD). The CD stretch of the substrate is > 8% measured according to standard ISO 1924-3:2005. In some examples, the CD stretch may exceed 10% or 12%. The MD stretch of the substrate is greater than 2% measured according to the same standard. In some examples, the MD stretch may also exceed 3% or 5%. These high stretch values allow the substrate to conform to complex shapes during sliding blank- and / or fixed blank forming processes without tearing or losing barrier integrity.

[0058] The substrate maintains a KIT value of 12 both before and after stretching (>10%). The KIT value, which measures the resistance to penetration by oils and greases, indicates that the substrate retains its barrier properties even when subjected to significant deformation. This characteristic is particularly valuable for packaging applications involving oily or greasy products.

[0059] The high grammage of the substrate contributes to its rigidity, which is important for maintaining package shape and structural integrity. The substrate exhibits high tensile strength, with values exceeding 15 kN / m in the MD and 8 kN / m in the CD. The tensile stiffness of the substrate is greater than 550 kN / m in the MD and greater than 270 kN / m in the CD. These properties ensure that packages made from the substrate can withstand handling and stacking without deformation.

[0060] The burst strength of the substrate exceeds 700 kPa, providing resistance to punctures and impacts. The tear strength is greater than 2 kN in both the MD and CD, with some examples exceeding 2.8 kN in the CD. These characteristics contribute to the overall durability of the packaging material.The substrate also demonstrates excellent barrier properties against moisture and gases. The Gurley value, which measures air permeability, is greater than 15, with some examples exceeding 20. This indicates low air permeability, which correlates with good barrier performance. The Water Vapor Transmission Rate (WVTR) of the substrate is less than 5 g / m / 24h, and in some examples, may be less than 3 or 2 g / m / 24h, as measured using ASTM F1249. The oxygen transmission rate (OTR) is below 5 cc / m / day, measured according to ASTM D3985 at 23 °C and 50% relative humidity. These low WVTR and OTR values indicate that the substrate provides an effective barrier against moisture and oxygen, which is crucial for preserving the quality and extending the shelflife of packaged products.

[0061] An important feature of the substrate is its recyclability. The substrate is recyclable with less than 15% total reject, and in some examples, less than 12% or even less than 8% total reject, measured according to the PTS RH 021 / 97 test method for Category II products. This high recyclability is achieved despite the presence of the polymer barrier layer, due to the unique structure and composition of the substrate.

[0062] The moisture content of the substrate after PE extrusion coating remains above 6%. This retained moisture contributes to the flexibility and processability of the substrate in subsequent converting operations.

[0063] The combination of high stretch, excellent barrier properties, rigidity, and recyclability makes this substrate particularly suitable for a wide range of packaging applications. For example, the substrate may be used in food packaging where three-dimensional forming is required to create food trays or containers with complex shapes. The high barrier properties ensure food freshness, while the rigidity maintains package integrity during transportation and storage. The recyclability of the substrate addresses growing environmental concerns in the packaging industry, making the substrate a sustainable choice for various applications.

[0064] The high grammage formable fiber-based substrate with MAP barrier and VSP barrier properties is the result of a synergistic combination of several processing steps and material selections. The interaction between the pulp preparation, fiber web formation, optional patterning treatment, and polymer layer application contributes to the unique properties of the final substrate.

[0065] The pulp preparation process, involving both low consistency and high consistency refining, plays a crucial role in developing the fiber properties necessary for the substrate's performance. The lowconsistency refining initially fibrillates the fibers, increasing their surface area and bonding potential. The subsequent high consistency refining further modifies the fiber structure, enhancing the stretch properties of the resulting web. This combination of refining steps creates a fiber network with improved flexibility and strength, which forms the foundation for the substrate's 3D formability characteristics.

[0066] The formation of a high grammage fiber web builds upon the refined pulp properties. The increased fiber content per unit area, achieved through the high grammage, provides a substantial base for the substrate. This higher fiber density contributes to the mechanical strength and barrier properties of the substrate, while also offering a more robust foundation for subsequent treatments and coatings.

[0067] The optional patterning treatment, such as the Clupak process, further enhances the stretchability of the fiber web. By creating a micro-creped structure, the patterning treatment increases the extensibility of the substrate in both the machine and cross directions. This enhanced stretchability works in concert with the refined fiber properties to allow the substrate to conform to complex shapes during 3D forming processes without compromising its structural integrity.

[0068] The application of the extrusion coated polymer layer interacts with the prepared fiber web to create the final barrier properties of the substrate. The high grammage and refined fiber structure of the web provide an excellent base for polymer adhesion. This strong bond between the substrate and the barrier layer is crucial for maintaining barrier performance during the forming process and subsequent use. The combination of the high-stretch fiber web and the flexible polymer layer results in a composite material that can maintain its barrier properties even when subjected to significant deformation during forming. The polymer layer conforms to the stretching of the fiber web, preserving the integrity of the barrier against liquids, moisture, grease, and gases.

[0069] According to the invention, a substrate obtained by a method described herein may be formed e.g. by being subjected to a fixed blank process, to form a fiber-based packaging product with barrier properties. For example, fixed blank forming may be performed with a mold depth of at least 20 mm. The formed packaging product may for example be a receptacle. Non-limiting examples of such receptacles include trays, containers, plates, bowls and cups. The receptacles may for example have a substantially square (e.g. quadratic or rectangular), substantially polygonal (e.g. hexagonal) or substantially round (e.g. circular or elliptic) geometry. The receptacle may be used, among other purposes, for storage and transport of fresh, chilled or frozen food. In some embodiments, thecontainers may also be used for conventional or microwave preparation of food. The receptacle is preferably formed from a single piece of substrate material. Within the context of this document, the phrase a "single piece of material" includes a single piece of material that comprises a single layer or multiple layers of the same material or multiple layers of different materials. These multi-layered materials could include, for example, layers of two or more paper and / or paperboard substrates completely bonded together and / or partially bonded together, such as a corrugated board material, with or without any other layer or layers of any other materials such as metal, foil, plastic, and so forth. Thus, laminates formed from two or more differing types of material are nonetheless encompassed by the phrase a "single piece of material".

[0070] The synergistic effects of these elements result in a substrate that combines high stretchability and excellent barrier properties. The refined and optionally patterned fiber web provides the necessary strength and flexibility, while the polymer layer imparts the required barrier characteristics. Together, these components create a substrate that meets the demanding requirements of modified atmosphere packaging applications and vacuum skin packaging applications, offering both functionality and sustainability.

[0071] EXAMPLE

[0072] Two furnishes comprising >50wt% pine pulp based on the total fiber content were provided: one reference furnish which had been subjected to HC refining followed by LC refining, and one test furnish which had been subjected to LC refining followed by HC refining.

[0073] The reference furnish and the test furnishes were used to prepare two respective fiber substrates with a grammage of 175 gsm. Each of the reference substrate and the test substrate was provided with a polymer barrier applied on one side, said polymer barrier comprising a coat weight of 54 gsm. The polymer barrier was an extrusion coated five-layer barrier with a structure comprising the following layers: PE + tie + EVOH + tie + PE.

[0074] The webs were evaluated with respect stretch in MD and CD, and thermoformed tray depth: the results are seen in Table 1 below.

[0075] < <

[0076] < <

[0077]

[0078] Table 1

[0079] As can be noted in Table 1, thermoforming of the test substrate resulted in an increased tray depth compared to the reference, which will lead to the benefit of increased volume capacity in case the material is used for MAP and / or VSP packages. In other words, improved material formability will allow for packages containing more food. Evaluation also showed that the barrier function was retained after thermoforming process, and adhesion between the barrier and the substrate remained intact.

[0080] Features of any of the examples or embodiments outlined above may be combined to create additional examples or embodiments without losing the intended effect. It should be understood that the description of an embodiment or example provided above is by way of example only, and various modifications could be made by one skilled in the art. Furthermore, one skilled in the art will recognize that numerous further modifications and combinations of various aspects are possible. Accordingly, the described aspects are intended to encompass all such alterations, modifications, and variations that fall within the scope of the appended claims.

Claims

CLAIMS1. A method for producing a high grammage formable fiber-based substrate with barrier layer, comprising the steps of:a) providing a cellulose pulp composition comprising at least 50 wt% chemical or semi-chemical wood pulp based on dry weight, preferably where said pulp is softwood pulp, preferably pine pulp, spruce pulp, or a combination thereofb) subjecting the cellulose pulp composition provided in step a) to low consistency (LC) refining 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% 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%;e) preparing a fiber web from the pulp to a grammage above 120 gsm and below 500 gsm; and f) applying at least one polymer layer onto a first surface of said substrate providing a barrier against at least one of liquid, moisture, grease and gas;wherein the resulting substrate comprises a CD stretch > 8% measured according to standard ISO 1924-3:2005, a Water Vapor Transmission Rate (WVTR) of less than 5 g / m2 / 24h, preferably less than 3 g / m / 24h, or less than 2 g / m / 24h as measured using ASTM Fl 249, and an oxygen transmission rate (OTR) of less than 5 cc / m2 / day measured according to ASTM D3985, 23 °C, 50 % relative humidity (RH).

2. The method of claim 1, wherein the grammage of the fiber web is above 140 gsm, preferably above 160 gsm, more preferably above 180 gsm and below 500 gsm.

3. The method of claim 1 or 2, wherein, after step e) subjecting the fiber web to a patterning treatment, where said patterning treatment preferably is a Clupak treatment or Expanda.

4. The method of claim 3, wherein the moisture content during the patterning treatment is between 10-20%.

5. The method of any one of claims 1 to 4, wherein the at least one polymer layer comprises one or more of the following polymers: polyethylene (PE), polyethylene terephthalate (PET), polyvinylalcohol (PVOH), polyvinyl acetate (PVA), polypropylene (PP), ethyl vinyl alcohol copolymer (EVOH), and / or polyamide (PA).

6. The method of any one of claims 1 to 4, wherein the at least one polymer layer comprises 30-50 gsm polyethylene (PE), preferably 35-45 gsm PE, preferably wherein the PE is LLDPE or LDPE.

7. The method of any one of claims 1 to 6, wherein in step f), a multilayer polymer barrier is applied onto a first surface of said substrate, providing barrier function against at least one of liquid, moisture, grease and gas, wherein said multilayer polymer barrier preferably comprises at least three layers, wherein at least one of said three layers comprises polyethylene (PE), preferably wherein the PE is LLDPE or LDPE.

8. The method of any one of claims 1 to 6, wherein in step f), a multilayer polymer barrier is applied onto a first surface of said substrate, providing barrier function against at least one of liquid, moisture, grease and gas, wherein said multilayer polymer barrier comprises a first innermost barrier layer comprising polyethylene (PE), a first tie layer on top of said innermost barrier layer, a second middle barrier layer comprising ethyl vinyl alcohol polymer (EVOH), a second tie layer on top of said middle barrier layer, and a third outermost barrier layer comprising polyethylene (PE), wherein the resulting substrate comprises a Water Vapor Transmission Rate (WVTR) of less than 3 g / m / 24h, as measured using ASTM Fl 249, and an oxygen transmission rate (OTR) of less than 2 cc / m / day measured according to ASTM D3985, 23 °C, 50 % relative humidity (RH).

9. The method of any one of claims 1 to 8, further comprising pre-adding at least one strength chemical and one friction control agent before step a).

10. The method of any one of claims 1 to 9, wherein the resulting substrate has an MD stretch > 2% measured according to standard ISO 1924-3:2005.

11. The method of any one of claims 1 to 10, wherein the resulting substrate is recyclable with <15% total reject, preferably <12% total reject measured according to PTS RH 021 / 97 test method for Category II products.

12. The method of any one of claims 1 to 11, further comprising:adding an anionic or non-ionic polymer to the cellulose pulp composition prior to subjecting it to the HC-refining in step c), wherein the amount of polymer added is 0.1-25 kg / tn, based on dry weight, preferably 1-20 kg / tn, more preferably 1-15 kg / tn.

13. The method of claim 12, wherein said anionic or non-ionic polymer is selected from the group consisting of cellulose ethers, natural gums, and anionic polyacrylamide.

14. The method of any one of claims 1 to 13, further comprising:adding a polysaccharide-based strength enhancement agent to the cellulose pulp composition after subjecting it to the HC -refining in step c), wherein the amount of agent added is 5-50 kg / tn, based on dry weight of the cellulose pulp composition, preferably 10-50 kg / tn, more preferably 20-50 kg / tn.

15. The method of claim 14, wherein said polysaccharide -based strength enhancement agent is a cellulose based strength enhancement agent, 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.

16. The method of claim 14, wherein said polysaccharide -based strength enhancement agent is a starch-based strength enhancement agent.

17. The method of claim 14, wherein said polysaccharide -based strength enhancement agent is a combination of a cellulose based strength enhancement agent and a starch-based strength enhancement agent.

18. The method of any one of claims 1 to 17, wherein the cellulose pulp composition in b) is subjected to LC refining to an SR value in the range of 20-50, preferably in the range of 25-50, more preferably in the range of 30-50.

19. The method of any one of claims 1 to 18, 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, more preferably at least 300 kWh / t.

20. The method of any one of claims 1 to 19, wherein the cellulose pulp composition in c) is subjected to HC refining at a temperature in the range of 70-120 °C.

21. A high grammage formable fiber-based substrate with barrier, obtainable by the method of any of claims 1-20, wherein the substrate comprises:a fiber web having a grammage above 120 gsm and below 500 gsm, said fiber web optionally being patterned and having at least one extruded polymer layer, and wherein the substrate has a CD stretch > 8% measured according to standard ISO 1924-3:2005, a Water Vapor Transfer Rate (WVTR) of less than 5 g / m2 / 24h, preferably less than 3 g / m2 / 24h, or 2 g / m2 / 24h as measured using ASTM F1249, anoxygen transmission rate (OTR) of below 5 cc / m / day measured according to ASTM D3985, 23 °C, 50 % relative humidity (RH).

22. A method for manufacturing a 3D-molded cellulose fiber-based product, comprising providing a high grammage formable substrate with barrier according to claim 21, and forming a 3D molded cellulose fiber packaging product therefrom.

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