Coated solid cellulose foam material

Abstract

The present invention relates to a coated cellulose foam material having a density in the range of 10 kg / m3 to 80 kg / m3, and a method for coating a cellulose foam. The coated cellulose foam material is formed by applying at least one coating layer of at least one coating composition on at least one outer surface of the cellulose foam.

Description

Technical Field

[0001] The present invention relates to coated solid cellulose foam materials and to a method for coating at least partially dried cellulose foam. Background Art

[0002] Different porous materials, such as foams, are commonly used in applications such as insulation in buildings and aircraft, 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 typically 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, which is 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 to produce a dry cellulosic product by first mechanically extracting a portion of the water and then evaporating the water.

[0006] In order to enable more versatile and efficient processing, foams which 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 pins. The pins need 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 because this will damage the oscillating blade.

[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] Another disadvantage of cellulose foam is that the surface characteristics of the foam in terms of smoothness are not comparable to conventional papermaking, where 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.

[0011] Therefore, there remains a need for bio-based foams that are recyclable and also enable the use of automated processes including vacuum lifting and fixing equipment.To facilitate efficient manufacturing of foams, particularly in terms of drying, it is desirable that the foams are also dimensionally stable in the wet state.

[0012] Furthermore, it is also desirable to tailor the surface properties of bio-based foams, such as surface gloss, smoothness, ink receptivity, and hydrophobicity. Summary of the invention

[0013] It is an object of the present invention to provide an improved solid 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.

[0014] Another object of the present invention is to provide a solid cellulose foam that can be used in methods involving vacuum lifting and securing equipment.

[0015] Another object of the present invention is to provide a solid cellulose foam which enables the surface properties to be tailored according to the use of the solid cellulose foam.

[0016] Another object of the present invention is to provide a solid cellulose foam which can be produced by drying wet foam without using a mold to enable a universal production method.

[0017] 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.

[0018] According to a first aspect, the present invention relates to a coated solid cellulose foam material having a density of 10 kg / m 3 Up to 80kg / m 3 within the range of; wherein the coated cellulose foam material comprises a solid cellulose foam having at least one coating on at least one outer surface, and wherein the at least one coating comprises at least one coating layer.

[0019] It has surprisingly been found that by applying a coating to at least one outer surface of the cellulose foam, the air permeability of the solid 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 coating applied can further be selected so as to provide a solid cellulose foam having not only reduced air permeability, but also other desired properties such as surface smoothness, ink absorbency, hydrophobicity, scratch resistance and surface gloss. The surface properties of the solid cellulose foam can be tailored according to the end use of the foam by applying one or more coatings.

[0020] The cellulose foam preferably comprises cellulose fibers in the range of 71 to 95 wt % based on the total weight of the solid content in the foam, a water-soluble thickener in the range of 4 to 24 wt % 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.

[0021] According to a second aspect, the present invention relates to a method for coating a cellulose foam, the method comprising the following steps:

[0022] a) providing a cellulose foam comprising at least one outer surface, and wherein the at least one outer surface is at least partially dry;

[0023] b) providing at least one coating composition;

[0024] c) applying at least one coating layer of said at least one coating composition to at least one outer surface of said cellulose foam to obtain a coated cellulose foam material;

[0025] d) drying the coated cellulose foam material to obtain a density of 10 kg / m 3 Up to 80kg / m 3 A range of coated solid cellulose foam materials.

[0026] It has surprisingly been found that the coating can be applied to a cellulose foam which is at least partially dried. This enables a versatile processing method, wherein the properties of the cellulose foam can be tailored by applying a specific coating. Since the coating can be applied to an at least partially dried foam, the properties of the cellulose foam can also be influenced during processing. The coated solid cellulose foam material according to the first aspect can be produced by the method according to the second aspect.

[0027] According to a third aspect, the present invention relates to the use of the coated solid cellulose foam material according to the first aspect in packaging, as insulation material or as building material. DETAILED DESCRIPTION

[0028] 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.

[0029] 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 cellulosic foam or a cellulose fiber foam. The cellulose foam may be wet or solid.

[0030] 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.

[0031] 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 a large extent to the shape of the wet cellulose foam. The dry content of the solid cellulose foam is at least 95 wt %, calculated based on the total 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.

[0032] A first aspect of the present invention relates to a coated solid cellulose foam material. The coated solid cellulose foam material is dry and may have a solid content of 95 to 100 wt %, preferably 98 to 100 wt %, calculated based on the total weight of the coated solid cellulose foam material. The density of the coated solid cellulose foam material is between 10 kg / m 3 Up to 80kg / m 3 , preferably 10kg / m 3 Up to 60kg / m 3 , and more preferably 20kg / m 3 Up to 50kg / m 3 within the range.

[0033] The coated solid cellulose foam material is prepared by applying at least one coating to at least one outer surface of the cellulose foam. The cellulose foam is preferably solid and may have a relative humidity of 10 kg / m 3 Up to 80kg / m 3 , preferably 20kg / m 3 Up to 50kg / m 3 And more preferably 20kg / m 3 Up to 50kg / m 3 The applied coating layer is thin and therefore has a negligible effect on the density of the coated solid cellulose foam material.

[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, the 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. The fiber length can provide different mechanical properties for the 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 the cellulose foam, and especially the bulk of the material. Higher levels of water-soluble thickeners provide stiffer materials. Therefore, water-soluble thickeners enable the mechanical properties of cellulose foams to be tailored.

[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 (myristic acid), sodium oleate, lauric acid, palmitic acid and stearic acid; glucose-based co-surfactants with aliphatic carbon tails, such as alkyl glycosides, 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. (For example and ); and polyoxyethylene lauryl ethers, such as polyethylene glycol lauryl 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 density of 140-500 kg / m 3Density and yield stress of 40-400Pa;

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

[0051] If a solid cellulose foam is not desired, the drying step can be omitted. The drying step can also be carried out only until a partially dried cellulose foam is obtained.

[0052] 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.

[0053] 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.

[0054] When aerated, the composition comprising cellulose fiber, thickener and at least two surfactants will form a highly stable wet fiber foam. Aeration can be carried out by mechanical agitation, and a large amount of air is mixed into the material. The surfactant will promote the formation of foam. By using a thickener and a surfactant combination to adjust the stability of the wet foam, a self-supporting cellulose foam can be prepared without using a crosslinking agent or fibrillated cellulose. The good stability of the foam prevents aging (i.e., the change of bubble size) and drainage. The wet foam obtained is self-supporting, and does not require a mold or a forming fabric to keep its shape when drying. Therefore, the wet foam can be formed into a self-supporting foam, which is stable enough to dry without collapse in the absence of a supporting mold. Therefore, an object can be formed and dried without using a mold.

[0055] The bubble size in the wet foam is typically below 100 μm. This provides a uniform wet foam with good stability, which does not flocculate during processing. During processing, and during the subsequent drying step, the average bubble size is largely maintained and the cellulose fibers remain well dispersed. The resulting solid cellulose foam obtained by drying the wet foam will be structurally uniform, strong, have good mechanical properties, a smooth surface and be free of defects. A smooth surface can be beneficial when a coating is to be applied on the foam.

[0056] 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 generated by the coalesced bubbles in the wet foam. Due to the defects, such solid cellulose foams are weak and have a rough surface.

[0057] 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 40-140° 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.

[0058] 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.

[0059] The solid cellulose foam may have any shape, such as a block, a cube, a cylinder or any irregular shape. Regardless of the shape, the solid cellulose foam will have at least one outer surface. The term "outer surface" as used herein refers to the outermost surface of the solid cellulose foam. It is not intended to mean the outermost surface of any final foam product. In the present invention, the outer surface of the solid cellulose foam is coated with at least one coating layer. It may be further covered with other layers, such as additional cellulose foam layers.

[0060] In one embodiment, the solid 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 have the same thickness. In embodiments where the solid 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.

[0061] The solid 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.

[0062] The densification layer comprises cellulose fibers which are more densely packed and partially differently oriented than the main body, resulting in a higher number of fiber-fiber bonds. The densification layer is formed on the outer surface of the wet foam during the drying of the wet foam body and remains on the outer surface of the solid cellulose foam when drying. The densification layer has improved mechanical stability and strength compared to the core of the solid cellulose foam. The core of the solid 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.

[0063] The densification layer thus provides increased stability and mechanical strength to the solid cellulose foam. In embodiments where the solid cellulose foam is provided in the form of a board, it is therefore preferred that during cutting of the foam board, the cutting is performed such that the thickness of the board remains the same also after cutting, thereby ensuring that the densification layer is still present on the top and bottom surfaces.

[0064] According to a first aspect of the invention, the solid cellulose foam is provided with at least one coating on at least one outer surface. The solid cellulose foam may be provided with a coating on one outer surface, or on several outer surfaces or on all outer surfaces. In embodiments where the solid cellulose foam is provided with a coating on more than one outer surface, the composition of the coatings on the coated outer surfaces may be the same or different. For example, the solid cellulose foam may be provided with a first type of coating on a first outer surface and with a second type of coating on a second outer surface. It is also within the scope of the invention to provide more than one coating on the same outer surface, for example, a first portion of an outer surface may be covered with a first coating and a second portion of an outer surface may be covered with a second coating.

[0065] In embodiments where the solid cellulose foam is provided in the form of a board, it may be provided with a coating on the top surface, the bottom surface and / or any side surface.

[0066] The coating is preferably provided on the outer surface of the solid cellulose foam comprising a densification layer, because the densification layer is smoother and has a less open structure than the outer surface not comprising a densification layer. In embodiments where not all outer surfaces of the solid cellulose foam comprise a densification layer, the coating may be provided both on the surface comprising the densification layer and on the outer surface not comprising the densification layer.

[0067] The adhesive layer may be provided on at least one outer surface of the cellulose foam, or on the densification layer (if present). In such an embodiment, the coating is provided on the adhesive layer. Preferably, the coating is provided directly onto the solid cellulose foam, i.e. without the use of an adhesive layer.

[0068] The coating comprises at least one coating layer, such as at least two coating layers or at least three coating layers. In embodiments where the coating comprises at least two coating layers, the compositions of the at least two coating layers may be the same or different.

[0069] In embodiments where the solid cellulosic substrate is provided with a coating on more than one outer surface, each coating may comprise at least one coating layer, such as at least two coating layers or at least three coating layers.

[0070] As used herein, the term "composition" refers to the composition of a coating in terms of its components. Compositions may differ from one another in terms of the concentration of the components, or in terms of the components present in the composition, or in terms of a combination of both.

[0071] Applying a coating on the outer surface of the solid cellulose foam will reduce the air permeability of the solid cellulose foam because the pores on the outer surface are blocked by the coating. In order to fully block all the pores on the surface, it is important that the coating is thick enough and the surface of the foam must be relatively flat. In some embodiments, the basis weight of the at least one coating is in the range of: 2 to 500 g / m 2 , for example 2 to 300 g / m 2 , or 2 to 250g / m 2 , or 10 to 200 g / m 2 , or 10 to 150g / m 2 , or 50 to 150g / m 2 , or 50 to 300 g / m 2 By reducing the air permeability of the cellulose foam by applying at least one coating on at least one outer surface, the use of the resulting coated solid cellulose foam material in automated processes involving vacuum is greatly facilitated. The coated solid cellulose foam can be used, for example, in converting and packaging processes involving steps requiring vacuum lifting and fixing.

[0072] Since the coating is thin, it has a negligible effect on the density of the coated solid cellulose material. Therefore, the density of the coated solid cellulose material is also between 10 and 80 kg / m 3 , or 10 to 60 kg / m 3 , or 20 to 50 kg / m 3 within the range.

[0073] The coating is provided by applying at least one layer of at least one coating composition to said at least one outer surface of the cellulose foam.The coating composition is preferably a liquid, such as an aqueous suspension or dispersion.

[0074] In some embodiments, the coating may include at least one particulate material. The particulate material may be selected from at least one of microfibrillated cellulose (MFC), cellulose fibers, mineral particles such as clay or calcium carbonate. Depending on the type of particulate material, the properties of the coating may be improved by adding a film-forming material. Some particulate materials, such as MFC, do not require the addition of a film-forming material to the coating.

[0075] The coating may comprise at least one particulate material and at least one film-forming material. A coating comprising at least one particulate material and at least one film-forming material will increase the coverage of the coating on the outer surface of the cellulose foam and thus reduce the risk of forming pinholes, which, if present, will adversely affect the air permeability of the cellulose foam. In addition, the smoothness and glossiness of the coated solid cellulose foam material may be improved. Furthermore, ink absorption may be improved by providing a coating, thereby allowing improved printability in terms of higher definition printing, as the ink will not penetrate into the coated solid cellulose foam material.

[0076] The coating composition may comprise at least one particulate material and at least one film-forming material. For example, the coating composition may comprise a particulate material, a film-forming material, optionally at least one additive, and water.

[0077] The particulate material may be selected from at least one of microfibrillated cellulose (MFC), cellulose fibres, mineral particles such as clay or calcium carbonate.

[0078] The film-forming material may be selected from at least one of carboxymethyl cellulose (CMC), cellulose ether, starch, polyvinyl alcohol, or synthetic latex (eg, acrylic or styrene-butadiene latex).

[0079] For example, the coating may comprise CMC, calcium carbonate and glycerol (acting as a plasticizer). The corresponding coating composition comprises CMC, calcium carbonate, glycerol and water.

[0080] In one embodiment, the coating comprises MFC. The corresponding coating composition comprises MFC and water. In the context of the present patent application, microfibrillated cellulose (MFC) shall mean cellulose particles, fibers or fibrils having a width or diameter of 20 nm to 1000 nm.

[0081] There are various methods for making MFC, such as single-pass or multi-pass refining, pre-hydrolysis followed by refining or high shear disintegration or release of fibrils. One or more pretreatment steps are usually required to make MFC manufacturing both energy-saving and sustainable. Therefore, the cellulose fibers of the pulp used in the production of MFC can be natural or enzymatic or chemically pretreated, for example to reduce the amount of hemicellulose or lignin. Cellulose fibers can be chemically modified before fibrillation, wherein the cellulose molecules contain (or more) functional groups in addition to the functional groups found in the original cellulose. Such groups especially include carboxymethyl (CM), aldehydes and / or carboxyl (cellulose obtained by N-oxyl-mediated oxidation, such as "TEMPO") or quaternary ammonium (cationic cellulose). After modification or oxidation in one of the above methods, it is easier to disintegrate the fibers into MFC.

[0082] MFC can be produced from wood cellulose fibers (both hardwood and softwood fibers). It can also be made from microbial sources, agricultural fibers such as straw pulp, bamboo, bagasse, or other non-wood fiber sources. It can be made from pulp, including pulp from virgin fibers, such as mechanical, chemical, and / or thermomechanical pulp. It can also be made from waste paper or recycled paper.

[0083] The coating comprising MFC will have excellent strength properties and good coverage of the holes in the solid cellulose foam, thereby providing improved strength and reduced air permeability for the solid cellulose foam of the coating. In addition, when it comes to the recycling of the cellulose foam material of the coating, the coating based on MFC is advantageous. In some embodiments, MFC can serve as both particulate material and film-forming material. For example, the coating can be composed entirely of MFC. In another example, the coating comprises MFC, CMC and a plasticizer, such as glycerol. The corresponding coating composition for providing the coating will comprise MFC and water; and accordingly MFC, CMC, a plasticizer and water.

[0084] In one embodiment, the coating comprises cellulose fibers. The corresponding coating composition 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.

[0085] The coating that comprises cellulose fiber can have good coverage of the hole in the solid cellulose foam.For example, the coating can comprise cellulose fiber and various additives typically used in papermaking.The corresponding coating composition that is used to provide the coating will comprise cellulose fiber, additive and water.Depending on the additive used, film-forming material may or may not be needed in the coating and the coating composition.

[0086] The coating may optionally include at least one additive, such as a dispersant, a defoamer, a UV absorber, a plasticizer, a moisture resistance additive, and a strength additive. Adding at least one additive to the coating will provide improved properties for the coating. Any suitable additive may be added, examples of additives being glycerol and polyethylene glycol (PEG).

[0087] In one embodiment, the coating comprises at least one hydrophobic agent. The corresponding coating composition comprises at least one hydrophobic agent. The hydrophobic agent can be selected from at least one of wax (e.g., beeswax or carnauba wax), alkyl ketene dimer (AKD), or alkyl succinic anhydride (ASA). In some embodiments, the coating may comprise a hydrophobic agent as well as a particulate material and a film-forming material. In such an embodiment, the hydrophobic agent may be a part of the coating layer identical to the particulate material and the film-forming material, or it may form different coating layers.

[0088] The coating composition comprising at least one hydrophobic agent may be a water-based emulsion, or it may be a solution comprising the hydrophobic agent and at least one solvent, such as an alcohol.

[0089] The at least one hydrophobic agent provides hydrophobic properties to the coating.This is particularly important in applications where improved water resistance is required, for example when the coated solid cellulose foam material is used in hot packaging solutions where condensation may cause problems.

[0090] In the embodiment that the coating comprises at least two coating layers, the composition of the at least two coating layers may be the same or different. For example, two or more coating layers of the same coating composition may be applied to cellulose foam, for example two layers of the coating composition comprising MFC. In another example, two coating layers of different coating compositions may be applied to cellulose foam, for example the first coating layer of the coating composition comprising MFC and the second coating layer of the coating composition comprising a hydrophobic agent. If it is desired to have a solid cellulose material of a coating with improved water resistance, it is advantageous to have the outermost coating layer comprising a hydrophobic agent.

[0091] In embodiments where the coating comprises at least two coating layers, a first coating layer is applied to the outer surface of the cellulose foam, and a second coating layer is applied on top of the first coating layer, and so on.

[0092] In embodiments where at least two outer surfaces of the solid cellulose foam are provided with a coating, the at least two coating layers may be the same or different. For example, one or more coating layers of a coating composition comprising MFC may be applied to all outer surfaces of the solid cellulose foam. In another example, one or more coating layers of a coating composition comprising MFC may be applied to a first outer surface of the cellulose foam, and a coating composition comprising a hydrophobic agent may be applied to a second outer surface of the cellulose foam.

[0093] In some embodiments, an additional material layer, such as a fibrous paper substrate or a second cellulose foam, is applied on top of the at least one coating so that the coating is sandwiched between the cellulose foam and the additional material layer. At least one coating may also be applied on at least one outer surface of the additional material layer.

[0094] In some embodiments, solid cellulose foam can be prepared by two-step deposition. In the first deposition, wet foam is deposited on the surface as discrete units 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 the foam matrix is ​​obtained. The densification layer on the outer surface of the discrete units provides mechanical support during the drying of the foam and the entire cellulose foam in the second deposition by helping to maintain the shape of the discrete units. A coating can be applied to at least one outer surface of a solid cellulose foam, the solid cellulose foam comprising discrete units of the foam embedded in the foam matrix. Before depositing the second deposition, a coating can also be applied to the outer surface of the discrete units. When the discrete units have been at least partially dried, a coating is applied to the outer surface of the discrete units so that when the coating is applied, the outer surface of the discrete units comprises a densification layer. In one example, a coating composition comprising MFC is applied to the outer surface of the at least partially dried discrete cells and a coating composition comprising a hydrophobic agent is applied to the outer surface of the solid cellulose foam comprising discrete cells embedded in the foam matrix, ie after the second deposition.

[0095] By selecting the type of coating applied to the cellulose foam, the properties of the resulting coated solid cellulose foam material can be carefully tailored.

[0096] The coating may be applied to the entire at least one outer surface of the cellulose foam, or only to one or more regions of the at least one outer surface of the cellulose foam. Thus, the at least one outer surface of the coated solid cellulose foam may be completely covered by the at least one coating, or the at least one outer surface of the coated solid cellulose foam may be partially covered by the at least one coating. For example, the coating may be applied in a pattern such that the outer surface comprises coated areas and uncoated areas.

[0097] In some embodiments, the at least one coating is applied in a pattern adapted to the type of vacuum equipment used in the conversion operation. For example, the at least one coating can be applied where vacuum suction is to be applied so that the air permeability of the cellulose foam is reduced primarily at the coated area.

[0098] In the embodiment that the coating comprises at least two coating layers, the at least two coating layers can cover different regions of the outer surface, or can cover the same region.For example, the at least two coating layers can be applied on the outer surface with different patterns.In an example, a coating layer is applied so that it covers the whole at least one outer surface, and the second coating layer is applied on the top of the first coating layer with a pattern.The composition of the at least two coating layers can be the same or different.

[0099] In embodiments where the coating is applied to more than one exterior surface of the cellulose foam, the coating may be applied to at least two exterior surfaces in the same pattern or in different patterns.

[0100] According to a second aspect, the present invention relates to a method for coating cellulose foam. Step a) of the method according to the second aspect comprises providing a cellulose foam comprising at least one outer surface. The cellulose foam provided in step a) is at least partially dry. In the context of the present invention, at least partially dry means that at least the outer surface of the cellulose foam is dry so that a coating can be applied thereto. In a preferred embodiment, the cellulose foam provided is dry and may have a solid content of 95 to 100 wt %, preferably 98 to 100 wt %, calculated on the total weight of the cellulose foam. Therefore, preferably, a solid cellulose foam is provided in step a). The density of the solid cellulose foam may be between 10 and 80 kg / m 3 , for example 10 to 60 kg / m 3 , or 20 to 50 kg / m 3 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 comprises providing at least one coating composition. The coating composition is preferably a liquid, such as an aqueous dispersion, a suspension or an emulsion. Other suitable solvents other than water may also be used. The coating composition 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 applying at least one coating layer of the at least one coating composition to at least one outer surface of the cellulose foam to obtain a coated cellulose foam material. The coating composition can be applied using any suitable method for coating, such as roller coating, blade / knife coating, brush coating, flexographic roller coating and spraying. In embodiments where more than one coating layer is applied, the coating composition of each coating layer can be applied using the same coating method or different coating methods. Depending on the desired properties of the coated cellulose foam material, different combinations of coating layers can be applied, as further described above with reference to the first aspect.

[0103] The coating layer may be applied to the entire at least one outer surface, or only to some areas of the at least one outer surface, as further explained above with reference to the first aspect.

[0104] Step d) of the method according to the second aspect comprises drying the coated cellulose foam material to obtain a density between 10 kg / m 3 Up to 80kg / m 3 , for example 10kg / m 3 Up to 60kg / m 3 , or 20kg / m 3 Up to 50kg / m 3 The coated solid cellulose foam material may be dried by evaporation at room temperature or at an elevated temperature, such as a temperature of 40° C. to 140° C. Any suitable drying equipment may be used, such as an oven or infrared heating.

[0105] In embodiments where at least two coating layers are applied, the first coating layer may be dried prior to applying the second coating layer. If a third coating layer is to be applied, the second coating layer may be dried prior to applying the third layer, and so on. In an alternative embodiment, the first coating layer is not dried prior to applying the second coating layer.

[0106] Example

[0107] Example 1 - Preparation of Foam

[0108] A homogeneous wet paste containing 12 wt% cellulose pulp (softwood bleached kraft pulp) and 1.2 wt% thickener (CMC) in water is prepared. The wet paste is aerated with a surfactant mixture (myristic acid and sodium cocoyl sarcosinate) until the desired wet foam density is obtained. Discrete units of the foam are deposited on a flat surface using a cylindrical mold having dimensions of 2.5 cm high and 6.6 cm in diameter. The mold is used only to deposit the wet foam in the desired shape and size and is removed before the foam is dried. The molded foam is dried in a conventional convection oven at 120°C until completely dry. The density of the dry cellulose foam is 30 kg / m 3 .

[0109] Example 2

[0110] A cylindrical dry cellulose foam prepared as described in Example 1 was coated with an aqueous solution containing microfibrillated cellulose (2 wt%). The coating was applied on all sides of the cellulose foam using a brush, and it was ensured that the coating layer applied was thick enough to cover the surface of the foam. The MFC coating was applied on the densified layer on the outer surface of the foam.

[0111] The air permeability of the cellulose foam is reduced by the MFC coating. In addition, the smoothness of the surface of the foam is improved by the coating. In addition, the strength of the densified layer is improved by the coating. This is obvious because the properties during the impact test are better than the foam without the MFC coating. The degradation of the foam with the MFC coating over time is also less compared to the foam without the coating. Compare with the foam according to Example 1.

[0112] Example 3

[0113] A cylindrical dry cellulose foam prepared as described in Example 1 was coated with an aqueous coating comprising CaCO3 and CMC. The coating solution was prepared by dispersing calcium carbonate in an 8% (w / w) CMC aqueous solution so that the final solid content was 40% (w / w). The coating was applied on all sides of the foam using a brush, and ensuring that the coating layer applied was thick enough to cover the surface of the foam. The coated foam was dried in an oven at 120°C until completely dry.

[0114] The air permeability of the cellulose foam was reduced by the coating and it was apparent that the coating blocked the pores on the surface and the air permeability was reduced. It was also apparent that the surface of the foam became smoother after the coating was applied.

[0115] Example 4

[0116] Same as Example 3, but glycerol (8 w / w) was added to the CMC coating solution. The coating was modified by adding glycerol, and the air permeability of the cellulose foam after the coating was applied was further reduced compared to the coating in Example 3.

[0117] Example 5

[0118] A homogeneous wet paste containing 12 wt% cellulose pulp (softwood bleached kraft pulp) and 1.2 wt% thickener (CMC) in water was prepared. The wet paste was aerated with a surfactant mixture (myristic acid and sodium cocoyl sarcosinate) until the desired wet foam density was obtained. A 27*37*5 cm mould was filled with the aerated wet foam and the surface was scraped to remove any extra foam and leveled to the height of the frame. Finally, the foam was dried at 120°C in a normal convection oven until completely dry. The density of the dry cellulose foam was 30 kg / m 3 .

[0119] The coating solution was prepared by dispersing calcium carbonate (24% (w / w)), PEG (0.8% (w / w)) and glycerol (23.25% (w / w)) in an aqueous CMC solution so that the final solid content was 52% (w / w). PEG and glycerol acted as plasticizers.

[0120] The coating was applied using a brush on the top side of the foam and only on one quarter of the surface, and ensuring that the coating layer applied was thick enough to cover the surface of the foam. The coated foam was dried in an oven at 120°C until completely dry.

[0121] The air permeability of cellulose foam is greatly reduced by the coating on the coated area of ​​the foam. The effectiveness of the coating was tested by lifting the foam board using vacuum suction. When the vacuum suction cup was applied to the uncoated foam area, no sufficient suction effect was achieved and the foam board could not be lifted. However, when the vacuum suction cup was used on the coated area of ​​the foam, the board could be lifted.

[0122] 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. Coated solid cellulose foam material with a density of 10 kg / m 3 Up to 80kg / m 3 within the range of; wherein the coated cellulose foam material comprises a solid cellulose foam having at least one coating on at least one outer surface, and wherein the at least one coating comprises at least one coating layer.

2. The coated solid cellulose foam 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 solid cellulose foam.

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

4. A coated solid cellulose foam material according to any one of the preceding claims, wherein at least one outer surface of the solid cellulose foam comprises a densification layer.

5. A coated solid cellulose foam material according to claim 4, wherein the at least one coating is provided on the densification layer.

6. The coated solid cellulose foam material according to any one of the preceding claims, wherein the at least one coating comprises at least two coating layers, and wherein the composition of the at least two coating layers may be the same or different.

7. A coated solid cellulose foam material according to any one of the preceding claims, wherein the coating comprises at least one particulate material and at least one film-forming material.

8. A coated solid cellulose foam material according to any one of the preceding claims, wherein the coating comprises microfibrillated cellulose (MFC).

9. A coated solid cellulose foam material according to any one of the preceding claims, wherein the coating comprises at least one hydrophobic agent.

10. A coated solid cellulose foam substrate according to any one of the preceding claims, wherein the basis weight of the coating is in the range of 2 to 300 g / m 2 within the range.

11. A method for coating a cellulose foam, the method comprising the steps of: a) providing a cellulose foam comprising at least one outer surface, and wherein the at least one outer surface is at least partially dry; b) providing at least one coating composition; c) applying at least one coating layer of said at least one coating composition to at least one outer surface of said cellulose foam to obtain a coated cellulose foam material; d) drying the coated cellulose foam material to obtain a density of 10 kg / m 3 Up to 80kg / m 3 A range of coated solid cellulose foam materials.

12. The method of claim 11, wherein the cellulose foam comprises cellulose fibers in an amount ranging from 71 wt% to 95 wt% based on the total dry weight of the cellulose foam.

13. The method according to any one of claims 11 or 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, a water-soluble thickener in the range of 4 wt% to 24 wt% based on the total dry weight of the cellulose foam, and at least two surfactants.

14. The method according to any one of claims 11 to 13, wherein the at least one coating composition is provided in the form of a liquid.

15. The method according to any one of claims 11 to 14, wherein at least two coating layers are applied, and wherein the coating compositions in the at least two coating layers may be the same or different.

16. The method according to any one of claims 11 to 15, wherein the cellulose foam provided has a density of 10 kg / m 3 Up to 80kg / m 3 A range of solid cellulose foams.

17. The method of any one of claims 11-16, wherein the at least one coating composition comprises at least one particulate material and at least one film-forming material.

18. The method of any one of claims 11-17, wherein the at least one coating composition comprises MFC.

19. The method according to any one of claims 11 to 18, wherein the at least one coating composition comprises at least one hydrophobic agent.

20. Use of a coated solid cellulose foam material according to any one of claims 1 to 10 as packaging material, as insulating material or as building material.