Packaging material comprising cellulose foam

Abstract

The present invention relates to a packaging material comprising a cellulose foam having a density in the range of 10 kg / m3 to 80 kg / m3 and a substrate attached to at least one outer surface of the cellulose foam.

Description

Technical Field

[0001] The present invention relates to a packaging material comprising cellulose foam and a method for producing a packaging material comprising cellulose foam. Background Art

[0002] Different porous materials, such as foams, are commonly used in applications such as insulation in buildings and vehicles, and as packaging materials for protecting various goods during storage and transportation.

[0003] Depending on the item to be protected, different types of protective packaging materials may be used. For many items, low-weight cushioning materials are used that mitigate impact shock and vibration. Common examples of such cushioning materials are petroleum-based polymer foams, such as polyurethane, polyethylene, and expanded polystyrene. The foam used should be low-weight, stable, and easy to manufacture.

[0004] Today, there is an increasing interest in replacing petroleum-based polymers with polymers from renewable resources (i.e., bio-based polymers). Cellulose is the most abundant renewable natural polymer on earth and is therefore of particular interest. For cellulose foams, recycling of the material in conventional recycling streams may be possible, depending on the composition of the foam.

[0005] There are several examples of cellulose foams prepared using different methods. Drying the wet foam composition is usually a key step. Since the stability of wet foam is typically low, a mold is usually used to prevent the foam from collapsing during drying. WO20200011587 A1 describes a porous material prepared by aerating a paste comprising cellulose fibers and gluten and depositing the aerated paste in a mold where it is dried. The dried porous material has the shape of the mold. WO2015036659 A1 describes a molded cellulosic product prepared by foaming an aqueous suspension of natural fibers combined with synthetic fibers and a surfactant, feeding the cellulosic foam to a mold and drying the foam by first mechanically extracting a portion of the water and then evaporating the water to produce a dry cellulosic product.

[0006] In order to enable more versatile and efficient processing, foams that are already dimensionally stable in the wet state are desirable.

[0007] When replacing foams from petroleum-based polymers with, for example, cellulose foams, a number of challenges associated with the manufacturing process must be overcome.

[0008] For commercial foams made from petroleum-based polymers, automated foam production and packaging lines use two main means of lifting and moving the product, namely pins and vacuum suction. The former requires a movable arm with several metal pins that can be inserted into the foam at a certain angle, allowing the machine to lift the foam. The pin process leaves small holes in the product, the size of which depends on the gauge thickness of the pin. The pin needs to be thick enough so as not to risk breaking and leaving metal residue inside the product. Another common method for lifting is vacuum suction, whereby a suction cup is pressed against the surface of the foam and the air is evacuated. This process relies heavily on having a low permeability surface in order to generate vacuum suction and sufficient lift. In addition, certain conversion equipment such as drawing tables rely on vacuum from below to hold the sample in place while cutting. In these applications, it is very important that the sample does not move, as this will damage the oscillating blade, as well as cause poor quality of the design, resulting in waste of material.

[0009] Since cellulose foams are generally highly permeable to air due to the porous structure of the foam, it is not possible to use vacuum lifting or fixing equipment during production and converting operations.

[0010] One of the most common conversion techniques for packaging materials containing foams made from petroleum-based polymers is die cutting, where blades arranged in a pattern are pressed against the foam to cut out specific shapes. The blades may be mounted to plates for conventional presses, or to rollers for continuous production lines. When cellulose foam is involved, the load-bearing and elastic properties of the foam are typically not sufficient to make die cutting an option. Also in other applications, such as in the packaging of heavy objects, the rigidity and strength of cellulose foam may be too low to make the foam a viable option.

[0011] Another disadvantage of packaging materials comprising cellulose foam is that the surface characteristics of the foam in terms of smoothness are not comparable to conventional papermaking, in which the material is pressed to produce a very smooth surface. The surface texture of cellulose foam is obtained by self-consolidation of the fibers when drying. In addition, the low density and porous nature of cellulose foam presents a large amount of capillary action for water to diffuse into it, resulting in ink bleeding when printing and lower fidelity prints. Finally, when used for hot packaging of frozen goods, the high moisture absorption of cellulose foam can present difficulties in handling condensation of water due to the fibrous and porous nature of cellulose foam.

[0012] Therefore, there remains a need for a packaging material comprising bio-based foam, wherein the packaging material is recyclable and also enables the use of automated processes including vacuum lifting and securing equipment. To facilitate efficient manufacturing of foam, particularly in drying, it is desirable that the foam is also dimensionally stable in the wet state.

[0013] Furthermore, it is also desirable to tailor the surface properties of packaging materials comprising bio-based foams, such as surface gloss, smoothness, ink receptivity, hydrophobicity, and scratch resistance.

[0014] Furthermore, it would be desirable to improve the strength and rigidity of packaging materials comprising bio-based foams without compromising the cushioning effect. Summary of the invention

[0015] It is an object of the present invention to provide an improved packaging material comprising cellulose foam which is recyclable and made from renewable sources and which obviates or mitigates at least some of the disadvantages of prior art materials.

[0016] Another object of the present invention is to provide a packaging material comprising cellulose foam that can be used in methods involving vacuum lifting and securing equipment.

[0017] Another object of the present invention is to provide a packaging material comprising cellulose foam which enables the surface characteristics to be tailored to the use of the packaging material, as well as sufficient strength and rigidity properties.

[0018] Another object of the present invention is to provide a cellulose foam material which can be produced by drying wet foam without using a mold to enable a universal production method.

[0019] The above-mentioned objects and other objects that will be appreciated by those skilled in the art from the present disclosure are achieved through various aspects of the present disclosure.

[0020] According to a first aspect, the present invention relates to a packaging material comprising a density of 10 kg / m 3 Up to 80 kg / m 3 A cellulose foam and a substrate within the scope of the present invention, wherein the substrate is attached to at least one outer surface of the cellulose foam.

[0021] It has surprisingly been found that by attaching a substrate to at least one side of a cellulose foam, the air permeability of the cellulose foam is reduced, allowing methods using vacuum lifting and fixing equipment to be used. This facilitates processing of the foam, particularly in terms of operations used when converting the foam for use in different packaging applications. The type of substrate may further be selected to provide the cellulose foam with other desired properties, such as surface smoothness, ink absorbency, hydrophobicity, surface gloss, improved scratch resistance, and increased strength and rigidity. Thus, the properties of the cellulose foam may be tailored according to the end use of the foam by attaching the foam to a substrate. The substrate may preferably be a paper or board substrate.

[0022] The cellulose foam preferably comprises cellulose fibers in the range of 71 to 95 wt % calculated based on the total weight of the solid content in the foam, a water-soluble thickener in the range of 4 to 24 wt % calculated based on the total weight of the solid content in the foam, and at least two surfactants. A wet foam having such a composition will be self-standing and will not require a mold or any other forming device to maintain its shape during drying.

[0023] According to a second aspect, the invention relates to a method for producing a packaging material comprising a density of 10 kg / m 3 Up to 80 kg / m 3 The method comprises the following steps:

[0024] a) providing a cellulose foam;

[0025] b) providing a substrate having a first surface;

[0026] c) attaching the first surface of the substrate to at least one outer surface of the cellulose foam to obtain a packaging material;

[0027] d) optionally drying the packaging material.

[0028] The packaging material according to the first aspect may be produced by the method according to the second aspect. DETAILED DESCRIPTION

[0029] As used herein, the term "foam" refers to a substance made by trapping air or gas bubbles inside a solid or liquid. Typically, the volume of the gas is much greater than the volume of the liquid or solid, with a thin film separating the gas pockets. In order to form a foam, three requirements must be met. Mechanical work is required to increase the surface area. This can occur by agitation, dispersing large amounts of gas into the liquid, or injecting the gas into the liquid. The second requirement is that a foam former must be present, typically an amphiphilic substance, a surfactant, or a surface-active component, to reduce the surface tension. Finally, the foam must form faster than it decomposes.

[0030] As used herein, the term "cellulose foam" refers to a foam comprising cellulose and other components such as thickeners, surfactants and additives. The main component of the cellulose foam is cellulose, such that cellulose constitutes at least 70 wt % of the dry content of the cellulose foam. The cellulose is in the form of fibers, so the foam may also be defined as a cellulose foam or a cellulose fiber foam. The cellulose foam may be wet or solid.

[0031] As used herein, the term "wet foam" or "wet cellulose foam" refers to a wet foam comprising cellulose and other components such as thickeners, surfactants, and additives. Gas bubbles are present within the wet foam. The wet foam is free-standing and behaves as a viscoelastic solid. This means that the wet foam has both viscous and elastic properties. The wet foam will behave as a solid, and therefore free-standing, unless a force large enough is applied that it begins to flow and behaves instead as a viscous material. Depending on the magnitude and time scale of any applied shear stress, the wet foam may exhibit predominantly viscous or elastic behavior.

[0032] As used herein, the term "solid cellulose foam" or "dry cellulose foam" refers to a dry porous cellulose material, i.e., a foam-formed material, that has been formed from a wet cellulose foam. During the drying process, the closed wet cellulose foam is converted into an open solid cellulose foam. The network of cellulose fibers is prevented from collapsing during drying. Therefore, the solid cellulose foam will have a shape that corresponds to the shape of the wet cellulose foam to a large extent. The dry content of the solid cellulose foam is at least 95 wt%, calculated based on the gross weight of the solid cellulose foam. The shape and density of the solid cellulose foam are also maintained in an unrestricted state. The solid cellulose foam has an open-cell structure, allowing air to occupy the pores within the foam. The solid cellulose foam may also be described as a porous material or a low-density material.

[0033] A first aspect of the present invention relates to a packaging material comprising cellulose foam. The cellulose foam is dry and may have a solid content in the range of 95 to 100 wt%, preferably 98 to 100 wt%, calculated based on the total weight of the cellulose foam. The cellulose foam is solid and has a density of 10-80 kg / m 3 , preferably 10-60 kg / m 3 , or 20-50 kg / m 3 within the range.

[0034] The cellulose foam preferably comprises cellulose fibers in the range of 71 to 95 wt%, such as 75 to 95 wt%, based on the total dry weight of the cellulose foam.

[0035] Cellulose fibers suitable for use in the present invention may be derived from wood, such as softwood or hardwood, from leaves or from fiber crops (including cotton, flax and hemp). Cellulose fibers suitable for use in the present invention may also be derived from regenerated cellulose such as rayon and lyocell. Cellulose fibers suitable for use in the present invention may include lignin or hemicellulose or both, or the cellulose fibers may be free of lignin and hemicellulose. Preferably, the cellulose fibers are derived from wood, and more preferably, the cellulose fibers are pulp fibers obtained by a pulping process that releases fibers from a wood matrix. Pulp fibers may be released by mechanical pulping to obtain mechanical pulp, such as thermomechanical pulp (TMP) or chemical thermomechanical pulp (CTMP), or released by chemical pulping, such as Kraft pulp or pulp obtained by sulfite process, soda process or organic solvent pulping process. More preferably, the cellulose fibers are pulp fibers released by chemical pulping processes. The different characteristics of each cellulose fiber will affect the properties of the final cellulose foam. The length of the cellulose fibers is significantly greater than their width. The cellulose fibers may have an average width of 0.01 to 0.05 mm. The fiber length of softwood can be 2.5 to 4.5 mm, while hardwood can have a fiber length of 0.7 to 1.6 mm, and eucalyptus can have a fiber length of 0.7 to 1.5 mm. However, fiber length can vary significantly with different growing locations, etc. The cellulose fibers in the cellulose foam disclosed herein can have a length of 0.1 mm to 65 mm, or 0.1 mm to 10 mm, or 0.5 mm to 65 mm, or 0.5 mm to 10 mm, or 0.5 mm to 7 mm. Fiber length can provide different mechanical properties for foam. Due to the length of the fiber, they can be entangled with each other and give the mutual combination of fiber and fiber, which brings strength to the foam. The aspect ratio (i.e., the ratio of fiber length to fiber width) of the cellulose fiber in the cellulose foam according to the present invention can be at least 10, at least 25, at least 50, at least 75 or at least 100, which provides the preservation and stability of the foam structure during the drying procedure, so that the wet cellulose foam with a shape retention can be dried. The aspect ratio may be up to 6500, or preferably up to 2000.

[0036] The cellulose fibers may be modified to provide different properties to the final cellulose foam. For example, phosphorylated fibers or periodate-oxidized fibers may also be used when producing cellulose foams according to the present invention.

[0037] Preferably, the cellulose fibers are selected from wood pulp, such as softwood kraft bleached pulp, hardwood pulp, chemi-thermomechanical pulp, and from dissolving pulp, or a combination of one or more of these. More preferably, the cellulose pulp fibers are from softwood pulp, chemi-thermomechanical pulp or dissolving pulp. Most preferably, the cellulose pulp fibers are from softwood pulp, such as softwood kraft bleached pulp.

[0038] The cellulose foam preferably comprises cellulose fibers in a range of 71 to 95 wt%, such as 75 to 95 wt%, based on the total dry weight of the cellulose foam, a water-soluble thickener in a range of 4 to 24 wt%, such as 5 to 20 wt%, based on the total dry weight of the cellulose foam, and at least two surfactants.

[0039] The water-soluble thickener may have a molecular weight of 80 000-250 000 g / mol or 83 000-197 000 g / mol. Exemplary water-soluble thickeners are selected from carboxymethylcellulose (CMC), methylcellulose (MC), hydroxyethylcellulose (HEC), ethylhydroxyethylcellulose (EHEC), methylhydroxypropylcellulose (MHPC), starch, xanthan gum, guar gum and xyloglucan or mixtures thereof. The fact that the thickener is water-soluble facilitates the recycling of the cellulose foam.

[0040] Water-soluble thickeners can improve fiber-fiber bond strength in cellulose foams, mainly through hydrogen bonding, and therefore, the amount of water-soluble thickeners will affect the mechanical properties of cellulose foams, and especially the bulk of the material. Higher levels of water-soluble thickeners provide stiffer materials. Therefore, water-soluble thickeners enable tailoring of mechanical properties.

[0041] The cellulose foam may also contain a mixture of at least two surfactants. One of the at least two surfactants is preferably a fast-acting surfactant, and suitable surfactants for this purpose are anionic surfactants, preferably low molecular weight anionic surfactants. The anionic surfactant may have an apparent pKa of 3.2 to 3.8, preferably 3.4 to 3.6, or an apparent pKa of 3.5 in a solution having a pH of 7 to 9, preferably a pH of 8. The low molecular weight anionic surfactant may be selected from sodium dodecyl sulfate (SDS); potassium dodecyl sulfate, sodium laureth sulfate (SLES); sodium dodecylbenzene sulfonate; sodium cocoyl sarcosinate; sodium lauroyl sarcosinate. The low molecular weight anionic surfactant is preferably selected from sodium dodecyl sulfate (SDS); sodium p-n-dodecylbenzene sulfonate; sodium cocoyl sarcosinate; and sodium lauroyl sarcosinate. More preferably, the low molecular weight anionic surfactant is sodium cocoyl sarcosinate. The anionic surfactant may be biodegradable.

[0042] The other of the at least two surfactants is preferably a co-surfactant. The co-surfactant may be selected from surfactants having an apparent pKa of at least 8 or at least 9 in a surfactant solution having a pH of 7 to 9, preferably a pH of 8; and amphoteric betaines. The co-surfactant may have a maximum apparent pKa of 10. The co-surfactant preferably has a long carbon chain, more preferably a carbon chain of 14 carbon atoms (C14). The co-surfactant may be selected from high pKa fatty acids, for example selected from plant-derived raw materials such as myristic acid, sodium oleate, lauric acid, palmitic acid and stearic acid; glucose-based co-surfactants with aliphatic carbon tails such as alkyl glucosides, alkyl polyglucosides, alkyl thio-glycosides and alkyl maltosides; amphoteric betaines such as cocamidopropyl betaine (CAPB) and sodium cocoimidodipropionate (CADP); polyethylene glycol sorbitan monolaurate, i.e., Tween® (e.g., Tween® 20, Tween® 80 and Tween® 85); and polyoxyethylene lauryl ethers such as polyethylene glycol dodecyl ether, pentaethylene glycol monododecyl ether and octaethylene glycol monododecyl ether.

[0043] Therefore, the at least two surfactants used in the cellulose foam preferably comprise a mixture of anionic surfactants and co-surfactants. The molar ratio between the anionic surfactant and the co-surfactant may be 0.2: 1-3: 1, preferably 0.5: 1 to 2: 1. The total amount of the at least two surfactants together in the cellulose foam may be 0.6-5 wt%, or 0.8-2.0 wt%, based on the total weight of the cellulose foam.

[0044] The cellulose foam is redispersible in water and can thus be recycled in conventional paper recycling streams.

[0045] The cellulose foam can be prepared using a method comprising the following steps:

[0046] - disintegrating cellulose fibers in water to obtain a slurry of cellulose fibers;

[0047] - adding a water-soluble thickener to the slurry to obtain a mixture of thickener and cellulose fibers in water;

[0048] - adding at least two surfactants to the mixture to obtain a fiber suspension; and

[0049] - aerating the fiber suspension to obtain a wet foam, wherein the wet foam comprises 10-38 wt% of cellulose fibers, 0.5-10 wt% of the water-soluble thickener and 0.1-2 wt% of a surfactant, based on the total weight of the wet foam, and wherein the foam has a viscosity of 140-500 kg / m 3density and a yield stress of 40-400 Pa.

[0050] - Drying the wet foam to obtain a dry cellulose foam.

[0051] The addition of a water-soluble thickener increases the viscosity of the slurry and enables the incorporation of sufficient air to produce a densely packed foam during aeration. Since the cellulose fibers are mixed at a high concentration, no drainage step is required, which enables the use of high concentrations of water-soluble bio-based thickeners.

[0052] Adding a fast-acting surfactant will help form a cellulose foam with high density and high viscosity because it will quickly settle at the air-water interface during aeration. This enables a free-standing wet cellulose foam to be achieved. Adding a co-surfactant together with the fast-acting surfactant will further improve the properties of the cellulose foam because it will promote the action of the fast-acting surfactant. Co-surfactants with suitable pKa and long carbon chains further contribute to stable fiber suspensions and stable wet cellulose foams.

[0053] When aerated, the composition comprising cellulose fibers, a thickener and at least two surfactants will form a highly stable wet fiber foam. Aeration can be performed by mechanical agitation, and a large amount of air is incorporated into the material. The surfactant will promote the formation of the foam. By adjusting the stability of the wet foam using a thickener and a surfactant combination, a self-supporting cellulose foam can be prepared without the use of a crosslinking agent or fibrillated cellulose. The good stability of the foam prevents aging (i.e., changes in bubble size) and drainage. The wet foam obtained is self-supporting and does not require a mold or a forming fabric to maintain its shape when drying. Therefore, the wet foam can be formed into a self-supporting foam that is stable enough to dry without collapse in the absence of a supporting mold. Therefore, objects can be formed and dried without using a mold.

[0054] The bubble size in the wet foam is typically below 100 μm. This provides a uniform wet foam with good stability that does not flocculate during processing. During processing, and during the subsequent drying step, the average bubble size is maintained to a large extent, and the cellulose fibers remain well dispersed. The resulting solid cellulose foam obtained by drying the wet foam will be uniform in structure, strong, have good mechanical properties, smooth surface and no defects. A smooth surface is beneficial when a substrate is to be attached to the foam because it promotes adhesion.

[0055] In contrast, wet cellulose foams with low stability have a larger average bubble size (i.e., typically above 100 μm), and the bubbles will coalesce more quickly during processing and drying, resulting in larger bubbles. In addition, the cellulose fibers will form clusters during processing and drying. This causes the wet foam to collapse during drying. The resulting solid cellulose foam will not have a uniform structure and will also contain defects in the form of cavities created by the coalesced bubbles in the wet foam. Due to the defects, such solid cellulose foams are weak and have a rough surface.

[0056] Due to the high solids content, the wet foam does not need to be dehydrated before it is dried. The foam can be dried by evaporation at room temperature or at an elevated temperature (e.g., a temperature of 40°C to 140°C). The dry cellulose foam may have a solids content of 10 to 80 kg / m 3 , or 10 to 60 kg / m 3 , or 20 to 50 kg / m 3 density.

[0057] In a preferred embodiment, the cellulose foam comprises cellulose fibers in a range of 71 to 95 wt%, such as 75 to 95 wt%, based on the total dry weight of the cellulose foam, a water-soluble thickener in a range of 4 to 24 wt%, such as 5 to 20 wt%, based on the total dry weight of the cellulose foam, and at least two surfactants. A wet cellulose foam having such a composition is structurally homogeneous and has good stability as described above. Such a wet cellulose foam can also be dried without prior dehydration.

[0058] The cellulose foam can be prepared by a two-step deposition. In the first deposition, the wet foam is deposited as discrete units on a surface and at least partially dried. During drying, a densification layer is formed on the outer surface of the discrete units. In the second deposition, a wet foam is deposited, which preferably has the same composition as the wet foam in the first deposition, so that it fills the space around the discrete units of the first deposition. After drying, a solid cellulose foam comprising discrete foam units embedded in a foam matrix is ​​obtained. The densification layer on the outer surface of the discrete units provides mechanical support during the drying of the foam in the second deposition and the entire cellulose foam by helping to maintain the shape of the discrete units.

[0059] The cellulose foam in the packaging material according to the first aspect may have any shape, such as a block, a cube, a cylinder or any irregular shape. Preferably, the cellulose foam has at least one flat surface. The flat surface is conducive to the attachment of the substrate. The substrate is attached to at least one outer surface of the cellulose foam. The term "outer surface" as used herein refers to the outermost surface of the cellulose foam. It is not intended to mean the outermost surface of the packaging material. The term "flat" as used herein refers to a horizontal surface without depressions or protrusions.

[0060] In some embodiments, the cellulose foam may have at least one non-planar surface, such as a surface having protrusions, to which the substrate is attached.

[0061] In one embodiment, the cellulose foam is provided in the form of a board having a thickness in the range of 1-20 cm, preferably 1-10 cm, more preferably 4-6 cm. The length and width dimensions of the board are typically in the range of 100 to 300 cm. The board can be cut into smaller pieces, but preferably also have the same thickness after cutting. In embodiments where the cellulose foam is provided in the form of a board, the outer surface is therefore present on the top surface, the bottom surface and the side surface of the board.

[0062] The cellulose foam may have a densification layer on at least one outer surface. In embodiments where the cellulose foam is provided in the form of a board, the cellulose foam has a densification layer on at least the top and bottom surfaces, and optionally on the side surfaces.

[0063] The densification layer comprises cellulose fibers that are more densely packed and partially differently oriented than the main body. The densification layer is formed on the outer surface of the wet foam during the drying of the wet foam and remains on the outer surface of the dried cellulose foam. The densification layer has improved mechanical stability and strength compared to the core of the cellulose foam. The core of the cellulose foam comprises a uniform open-cell fiber network. The core is highly porous, and even though the densification layer has a denser structure than the core, it is still porous.

[0064] The densification layer thus provides increased stability and mechanical strength to the cellulose foam. In embodiments where the cellulose foam is provided in the form of a board, it may therefore be advantageous that during cutting of the foam board, the cutting is performed such that the thickness of the board also remains the same after cutting, thereby ensuring that the densification layer is still present on the top and bottom surfaces. However, in other applications, the board may be cut such that no densification layer is present after cutting.

[0065] The substrate may be attached to the outer surface of a cellulose foam that includes a densification layer, or it may be attached to the outer surface of a cellulose foam that does not include a densification layer.

[0066] According to a first aspect of the invention, a substrate is attached to at least one outer surface of the cellulose foam.

[0067] Any suitable substrate can be used, such as a plastic film, a metal foil or a cellulosic substrate. Preferably, the substrate is selected from paper or paperboard. The air permeability of the substrate may be lower than the air permeability of the cellulose foam. The substrate can therefore be selected so that it has a sufficiently low air permeability depending on the application.

[0068] By attaching the substrate to the cellulose foam, the air permeability of the cellulose foam can be reduced because the holes on the outer surface are covered by the substrate. By attaching the substrate on at least one outer surface to reduce the air permeability of the cellulose foam, the use of the resulting packaging material in automated methods involving vacuum is greatly promoted. The packaging material can be used, for example, in conversion and packaging processes involving steps that require vacuum lifting and fixing. Lower air permeability also improves the performance of the packaging material in hot packaging.

[0069] Attaching the substrate to the cellulose foam can also improve other properties of the packaging material, such as stability, rigidity and strength. For example, when a rigid substrate is attached to the cellulose foam, the load-bearing properties are improved because the pressure can be distributed over a wider area to minimize the compression under pressure, which enables the use of die cutting. By attaching the substrate to the cellulose foam, the rigidity of the substrate can be combined with the cushioning properties of the foam so that the packaging material has a customizable property for different applications (including heavier products). When using cellulose foam sheets, handling is greatly facilitated by attaching the substrate to the foam. The risk of tearing thin foam pieces is also reduced.

[0070] The substrate preferably has a flat shape, for example in the form of a sheet, film or foil. The substrate comprises at least a first surface and a second surface. The substrate comprises a first surface at least partially attached to the cellulose foam.

[0071] As used herein, the term "attach" refers to the process of permanently attaching two objects, in this case the cellulose foam and the substrate.

[0072] In some embodiments, the area of ​​the first surface of the substrate has the same dimensions as the area of ​​the outer surface of the cellulose foam to which the substrate is attached. Thus, in such embodiments, the entire first surface of the substrate is attached to the cellulose foam.

[0073] In some embodiments, the area of ​​the first surface of the substrate attached to the cellulose foam has a larger or smaller size than the area of ​​the outer surface of the cellulose foam to which the substrate is adhered. Thus, in such embodiments, the first surface of the substrate is partially attached to the cellulose foam.

[0074] In some embodiments, the substrate is attached to one outer surface of the cellulose foam. For example, paperboard can be attached to a cellulose foam board, with the first surface of the paperboard having an area having approximately the same dimensions as the outer surface of the board.

[0075] In some embodiments, the substrate is attached to at least two outer surfaces of the cellulose foam. In such embodiments, the substrate can be folded along at least one fold line so that it can be attached to at least two outer surfaces of the cellulose foam. For example, the paperboard can be provided with fold lines corresponding to the edges of the cellulose foam board. By folding the paperboard along the fold lines, the cellulose foam can be attached to the paperboard on all sides.

[0076] In some embodiments, the substrate may be a plastic film or a metal foil. The plastic film may, for example, be selected from polyethylene, cellophane, or polylactic acid. The metal foil may, for example, be an aluminum foil. The plastic film and the metal foil must be thin enough so that the packaging material can be recycled in a conventional paper recycling stream. When the plastic film or the metal foil is attached to the outer surface of the cellulose foam, the air permeability of the cellulose foam is reduced.

[0077] In some embodiments where the substrate is a plastic film or a metal foil, the plastic film and metal foil are preferably, but not necessarily, thin enough so that the packaging material can be recycled in conventional paper recycling streams.

[0078] In a preferred embodiment, the substrate is a cellulosic substrate. The cellulosic substrate preferably comprises cellulose fibers. The cellulose fibers may be selected from wood pulp; regenerated cellulose fibers; and plant fibers, such as fibers from bamboo, cotton, hemp, flax and jute. Preferably, the cellulose fibers are selected from wood pulp, such as softwood pulp, hardwood pulp, chemical-thermomechanical pulp, and from dissolving pulp, or a combination of one or more of these.

[0079] The cellulosic substrate may preferably be selected from paper or paperboard. For example, the cellulosic substrate may be paperboard, cardboard or corrugated board.

[0080] The term "paper" as used herein generally refers to a material made in sheets or rolls from pulp of wood or other cellulosic substances containing cellulose fibers, which is used, for example, for writing, drawing or printing, or as packaging material. Paper may be bleached or unbleached, coated or uncoated, and produced in various thicknesses, depending on the end-use requirements.

[0081] The term "board" as used herein generally refers to a strong, thick paperboard or cardboard comprising cellulose fibers, which is used, for example, as a flat substrate, tray, box and / or other types of packaging. Paperboard can be bleached or unbleached, coated or uncoated, and produced in various thicknesses, depending on the end use requirements.

[0082] An advantage of using paper or paperboard as a substrate is that the packaging material comprising a cellulose foam attached to paper or paperboard is redispersible in water and will therefore be easily recycled in conventional paper recycling streams. By attaching a paper or paperboard substrate to the cellulose foam, air permeability is also reduced and the stability of the foam can be increased.

[0083] The basis weight of the cellulosic substrate is preferably at least 20 g / m 2 , or at least 80 g / m 2 The basis weight of the cellulosic substrate is preferably less than 500 g / m 2 , or less than 400 g / m 2 The basis weight of the cellulosic substrate can be between 20 and 500 g / m 2 , or 80 to 500 g / m 2 , or 120 to 500 g / m 2 within the range.

[0084] The substrate may be selected so as to infer desirable properties in addition to a reduction in air permeability and an increase in strength and stability of the packaging material. For example, if the packaging material is to be printed during a converting process, it is advantageous to attach a substrate that improves printability by minimizing ink bleed. The substrate may also be selected to change the look and feel of the packaging material, with respect to properties such as gloss and texture. In applications where it is important for the packaging material to have improved water resistance, a substrate may be selected that has hydrophobic properties.

[0085] In some embodiments, the substrate is a second cellulose foam material. Such an embodiment provides a layered cellulose foam material. The second cellulose foam may have a composition that is the same or different from the composition of the cellulose foam. The second cellulose foam may be further selected to provide certain desired properties to the packaging material, as discussed further above.

[0086] In some embodiments, the substrate is a different foam material, such as a starch foam.

[0087] In some embodiments, the second substrate is attached to at least one outer surface of the cellulose foam. The second substrate may be the same or different from the substrate. The substrate and the second substrate may be attached to the same outer surface of the cellulose foam, or may be attached to different outer surfaces. In a preferred embodiment, the substrate and the second substrate are attached to the relative outer surfaces of the cellulose foam so that the cellulose foam is sandwiched between the substrate and the second substrate. For example, cardboard may be placed on the top and bottom sides of the cellulose foam.

[0088] By attaching a second substrate to the cellulose foam, strength and rigidity are further improved. By selecting a second substrate that is different from the substrate, a packaging material can be provided that has different properties on different sides. For example, the aesthetics on the top side of the cellulose foam can be improved, while the foam is provided with improved strength on the back side.

[0089] The second substrate may be further defined as outlined above with reference to the substrate.

[0090] In some embodiments, the cellulose foam comprises at least two separate blocks of cellulose foam, and wherein the substrate is attached to at least one outer surface of all of the at least two separate blocks. The composition of the cellulose foam in the at least two separate blocks may be the same or different. Other properties of the at least two separate blocks, such as density, size and shape may be the same or different. By providing at least two separate blocks of cellulose foam and attaching the substrate to at least one outer surface on each of the two separate blocks of at least cellulose foam, a highly versatile packaging material is provided. By selecting a cellulose foam block with a defined shape and property and attaching it to the substrate, a packaging material with customized rigidity and cushioning properties according to the application can be provided.

[0091] In some embodiments, the packaging material is included in an adhesive layer between the at least one outer surface of the cellulose foam and the substrate. The substrate is attached to the at least one outer surface of the cellulose foam by the adhesive layer. The adhesive layer can include any suitable adhesive, such as hot melt adhesive, wood adhesive, starch-based glue, carboxymethyl cellulose (CMC), polyvinyl acetate, ethylene vinyl acetate, casein, latex, polyurethane, dextrin and gum, such as guar gum and xanthan gum. The adhesive is preferably water-based and / or bio-based.

[0092] In some embodiments, the adhesive layer is a double-sided tape.

[0093] In embodiments where the cellulose foam comprises CMC, the adhesive layer may comprise water. The water will partially dissolve the outer surface of the cellulose foam and provide adhesive properties by exposing the CMC. The substrate may be attached to the partially dissolved outer surface.

[0094] In some embodiments, the adhesive layer may comprise a thin layer of wet cellulose foam. Using a thin layer of wet foam as the adhesive layer is particularly suitable when the substrate is a second cellulose foam, thereby producing a layered material comprising only cellulose foam.

[0095] In some embodiments, the packaging material comprises at least two adhesive layers. The composition of the adhesive layers may be the same or different.

[0096] In embodiments where the second substrate is attached to the cellulose foam, the second substrate may be attached via an adhesive layer as defined above.

[0097] The packaging material may also include an additional layer. The type of material in the additional layer is not particularly limited. It may be, for example, a cellulose foam, which may be paper or paperboard, a plastic film or a metal foil. For example, the additional layer may be attached to the other side of the substrate. In one example, a corrugated paperboard substrate is attached to the cellulose foam, and another cellulose foam is attached to the opposite side of the corrugated paperboard, so that the corrugated paperboard is sandwiched between two layers of cellulose foam. In another example, a plastic film is attached to a paperboard substrate, which in turn is attached to the cellulose foam.

[0098] According to a second aspect, the present invention relates to a method for producing a packaging material comprising a density of 10 to 80 kg / m 3 , for example 10 to 60 kg / m 3 , or 20 to 50 kg / m 3 Step a) of the method according to the second aspect involves providing a cellulose foam. The cellulose foam provided may be wet or dry. If a wet cellulose foam is provided, it may be applied on top of a substrate and then dried. Alternatively, a substrate may be attached on top of the wet foam before drying the wet foam. The density of the wet foam may be in the range of 140 to 500 kg / m 3 Due to the viscoelasticity of the wet foam of the present invention, it will be self-supporting and thus have an outer side to which a substrate can be attached.

[0099] In embodiments where the cellulose foam is provided as a solid cellulose foam, the solids content of the foam may be in the range of 95 to 100 wt%, preferably 98 to 100 wt%, based on the total weight of the cellulose foam.The cellulose foam has at least one outer surface.

[0100] The cellulose foam may be further defined as described above with reference to the first aspect.

[0101] Step b) of the method according to the second aspect involves providing a substrate. The substrate is preferably dry. The substrate comprises a first surface and at least one second surface. Preferably, the substrate is in the form of a sheet, a film or a foil. The substrate may be further defined as described above with reference to the first aspect.

[0102] Step c) of the method according to the second aspect comprises attaching the first surface of the substrate to at least one outer surface of the cellulose foam.The attaching step may comprise applying an adhesive layer on the first surface of the substrate and / or on the at least one surface of the cellulose foam.

[0103] The step of attaching the first surface of the substrate to at least one outer surface of the cellulose foam comprises bringing the first surface of the substrate and the at least one outer surface of the cellulose foam into intimate contact with each other. In some embodiments, an adhesive layer is located between the outer surface of the cellulose foam and the first surface of the substrate.

[0104] In some embodiments, pressure is applied when the first surface of the substrate is attached to the at least one outer surface of the cellulose foam. By applying pressure during the attachment step, it is ensured that the substrate and the cellulose foam are in close contact with each other to ensure a firm attachment. Any suitable pressing device can be used to apply pressure. For example, a pressing device such as a roller, a rod or a plate can be used. Pressure can be applied to the substrate or the cellulose foam or both. For example, after the substrate has been placed on the cellulose foam, the structure can pass under the roller that applies pressure so that the substrate is firmly attached to the cellulose foam.

[0105] The attachment step typically involves placing the cellulose foam on the substrate manually or automatically, or vice versa. Any suitable equipment known to those skilled in the art can be used. For example, the adhesive layer is first applied to the outer surface (typically the top surface) of the cellulose foam, and then the cardboard is placed on the outer surface. The cardboard can be supplied from a roller, and the roller can also apply pressure when the cardboard is placed on the cellulose foam to ensure a firm attachment. Alternatively, pressure can be applied by a second roller.

[0106] Depending on the substrate and the attachment means, elevated temperatures may be used during the attachment step. For example, in embodiments where the substrate is a plastic film, the plastic film and / or the cellulose foam may be heated during the attachment step so that the plastic film is laminated to the cellulose foam. Certain adhesives may also require heating. In embodiments where pressure is applied during the attachment step, heat may be supplied by a pressing means, such as by using heated rollers.

[0107] Any suitable method for coating (e.g., roller coating, blade / knife coating, brush coating, flexographic roller, and spray coating) can be used to apply the adhesive layer on the first surface of the substrate and / or on the outer surface of the cellulose foam. In some embodiments, before the substrate is attached to the cellulose foam, the adhesive layer is applied to the first substrate of the substrate. In some embodiments, before the substrate is attached to the cellulose foam, the adhesive layer is applied to the outer surface of the cellulose foam. In some embodiments, before the substrate is attached to the cellulose foam, the adhesive layer is applied to both the first surface of the substrate and the at least one outer surface of the cellulose foam. By applying the adhesive layer to both the substrate and the cellulose foam, the attachment can be more secure and more durable.

[0108] In some embodiments, the method includes the additional steps of providing a second substrate and attaching the substrate to at least one outer surface of the cellulose foam. The first surface of the substrate is attached to at least one outer surface of the cellulose foam. The second substrate is preferably attached by applying an adhesive layer on the first surface of the second substrate and / or on at least one outer surface of the cellulose foam. The second substrate may be further defined as described above with reference to the first aspect.

[0109] In embodiments involving a second substrate, the second substrate can be attached to the cellulose foam simultaneously with the substrate, or after the substrate has been attached to the cellulose foam. Attachment of the second substrate can involve an adhesive layer, pressure, and / or elevated temperature, as further outlined above with respect to the step of attaching the substrate.

[0110] The adhesive layer may comprise more than one adhesive sublayer, for example at least two adhesive sublayers, or at least three adhesive sublayers. The adhesive composition in the at least two sublayers may be the same or different. The adhesive and adhesive layer may be further defined as described above with reference to the first aspect.

[0111] Step d) of the method according to the second aspect comprises an optional step of drying the packaging material. The packaging material may be dried by evaporation at room temperature or at an elevated temperature (e.g. a temperature of 40 to 140° C.). Any suitable drying equipment may be used, such as an oven or infrared heating.

[0112] In embodiments where the cellulose foam provided is a wet cellulose foam, drying is required to obtain the packaging material. In embodiments involving an adhesive layer, drying may also be beneficial.

[0113] Example

[0114] Example 1 - Preparation of cellulose foam

[0115] A homogeneous wet paste comprising cellulose pulp fibers (bleached softwood kraft pulp), thickener (CMC) and water was prepared. The solid concentration of the wet paste was 13.2 wt%. After the addition of surfactant (a mixture of myristic acid and sodium cocoyl sarcosinate), the paste was aerated by mechanical mixing until a density of 226 kg / m 3 The composition of the wet foam is shown in Table 1. The wet foam is then used to fill the wooden frame. Once the frame is completely filled with the wet foam, the extra foam is scraped off to obtain a smooth surface. The foam is dried in an oven at 120°C until it is completely dry. The density of the dry cellulose foam is 30 kg / m 3 The foam has a flat shape and a thickness of 5 cm.

[0116] Table 1.

[0117]

[0118] Example 2 - Preparation of packaging material

[0119] The cellulose foam board of Example 1 was used to prepare a packaging material. An adhesive layer comprising a CMC solution (10 wt % in water) was applied to the top and bottom surfaces of the foam board. 2 The adhesive layer was applied in an amount of dry material. A single layer of recycled corrugated cardboard was attached to the top and bottom surfaces of the foam board to obtain a packaging material in which the cellulose foam board was sandwiched between two layers of corrugated cardboard. The dimensions of the corrugated cardboard were the same as those of the foam board. Attaching the corrugated cardboard to the foam improved the mechanical properties of the foam. The thickness of the corrugated cardboard was 2.5 mm, and the basis weight of the corrugated cardboard was 70 g / m 2 , the basis weight of the kraft lining is 50 g / m 2 .

[0120] In view of the above detailed description of the invention, other modifications and variations will become apparent to those skilled in the art. However, it should be apparent that such other modifications and variations can be implemented without departing from the spirit and scope of the invention.

Claims

1. Packaging materials, which contain density of 10 kg / m 3 Up to 80 kg / m 3 A cellulose foam and a substrate within the scope of the present invention, wherein the substrate is attached to at least one outer surface of the cellulose foam.

2. The packaging material according to claim 1, wherein the cellulose foam comprises cellulose fibers in the range of 71 wt% to 95 wt%, based on the total dry weight of the cellulose foam.

3. The packaging material according to any one of claims 1 or 2, wherein the cellulose foam comprises: cellulose fibers in a range of 71 wt% to 95 wt% based on the total dry weight of the cellulose foam, a water-soluble thickener in a range of 4 wt% to 24 wt% based on the total dry weight of the cellulose foam, and at least two surfactants.

4. A packaging material according to any one of the preceding claims, wherein the substrate is a cellulosic substrate.

5. Packaging material according to any one of the preceding claims, wherein the substrate is selected from paper or paperboard.

6. The packaging material according to any one of the preceding claims, wherein the substrate is a second cellulose foam, and wherein the second cellulose foam may have a composition that is the same as or different from the composition of the cellulose foam.

7. The packaging material according to any one of the preceding claims, wherein the cellulose foam comprises at least two separate pieces of cellulose foam, and wherein the substrate is attached to at least one outer surface of all of the at least two separate pieces.

8. The packaging material according to any one of the preceding claims, wherein the packaging material comprises an adhesive layer between the at least one outer surface of the cellulose foam and the substrate.

9. A packaging material according to any one of the preceding claims, wherein the second substrate is attached to at least one outer surface of the cellulose-based foam.

10. A method for producing a packaging material comprising a density of 10 kg / m 3 Up to 80 kg / m 3 The method comprises the following steps: a) providing a cellulose foam; b) providing a substrate having a first surface; c) attaching the first surface of the substrate to at least one outer surface of the cellulose foam to obtain a packaging material; d) optionally drying the packaging material.

11. The method according to claim 10, wherein the cellulose foam has a density of 140 kg / m 3 Up to 500 kg / m 3 A range of wet foams are available.

12. The method according to any one of claims 10, wherein the cellulose foam is provided as a solid cellulose foam having a density of 10 kg / m 3 Up to 80 kg / m 3 within the range.

13. The method of any one of claims 10-12, wherein the cellulose foam comprises cellulose fibers in the range of 71 wt% to 95 wt% based on the total dry weight of the cellulose foam.

14. The method according to any one of claims 10-13, wherein the cellulose foam comprises: cellulose fibers in a range of 71 wt% to 95 wt% based on the total dry weight of the cellulose foam, a water-soluble thickener in a range of 4 wt% to 24 wt% based on the total dry weight of the cellulose foam, and at least two surfactants.

15. The method of any one of claims 10-14, wherein the substrate is a cellulosic substrate.

16. The method according to any one of claims 10 to 15, wherein the substrate is selected from paper or paperboard.

17. The method of any one of claims 10-16, wherein the substrate is a second cellulose foam, and wherein the second cellulose foam can have a composition that is the same as or different from the composition of the cellulose foam.

18. The method of any one of claims 10-17, wherein the cellulose foam is provided as at least two separate pieces of cellulose foam, and wherein the substrate is attached to at least one outer surface of all of the at least two separate pieces.

19. The method according to any one of claims 10-18, wherein the step of attaching the substrate to the at least one surface of the cellulose foam comprises applying an adhesive layer on the first surface of the substrate and / or on the at least one surface of the cellulose foam.

20. The method of any one of claims 10-19, wherein the method comprises the additional steps of providing a second substrate and attaching the second substrate to at least one outer surface of the cellulose foam.

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