Coated solid cellulose foam material

Abstract

The present invention is 10 to 80 kg / m 3 The present invention relates to a coated cellulose foam material having a density in the range of 0.1 to 1.0 mm, 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 to at least one outer surface of a cellulose foam.

Description

[Technical Field]

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

[0002] Various porous materials, such as foams, are commonly used as insulation in buildings and aircraft, and as packaging materials used to protect various items during storage and transport.

[0003] Depending on the item being protected, various types of protective packaging materials can be used. Many items use lightweight cushioning materials to reduce shock and vibration. Common examples of such cushioning materials include polyurethane, polyethylene, and petroleum-based polymer foams such as Styrofoam. The foams used need to be lightweight, stable, and easy to manufacture.

[0004] There is growing interest in replacing petroleum-based polymers with polymers derived from renewable resources, i.e., bio-based polymers. Cellulose is the most abundant renewable natural polymer on Earth and is therefore of particular interest. Depending on the foam's composition, cellulosic foams may allow for the material to be recycled in conventional recycling streams.

[0005] There are several examples of cellulose foams, each prepared using a different method. Drying the wet foam composition is usually a critical step. Because wet foams typically have low stability, molds are commonly used to prevent the foam from collapsing during drying. WO 20200011587 describes a porous material prepared by aerating a paste containing cellulose fibers and gluten, placing the aerated paste in a mold, and drying the paste. The dried porous material has the shape of the mold. WO 2015036659 describes a molded fiber product prepared by foaming an aqueous suspension combining natural and synthetic fibers and a surfactant, feeding the fibrous foam into a mold, first mechanically extracting a portion of the water, and then drying the foam by evaporating the water to obtain a dry fiber product.

[0006] To allow for more versatile and efficient processing, foams are needed that are already dimensionally stable in the wet state.

[0007] If foams derived from petroleum-based polymers are to be replaced by, for example, cellulosic foams, many challenges related to the manufacturing process must be overcome.

[0008] For commercial foams made from petroleum-based polymers, automated foam manufacturing and packaging lines primarily use two means for product lifting and transfer: pins and vacuum suction. Pin suction involves a movable arm with multiple metal pins that can be inserted into the foam at an angle, allowing the machine to lift the foam. Pin suction creates small holes in the product, the size of which depends on the pin's gauge thickness. The pins must be thick enough to avoid breaking and leaving metal residue in the product. Another common lifting method is vacuum suction, which involves pressing a suction cup against the foam's surface to remove air. This process relies heavily on having a surface with low air permeability to generate vacuum suction and sufficient lift. Furthermore, certain conversion equipment, such as plotting tables, relies on vacuum suction from below to hold the sample in place during cutting. In these applications, it is crucial to prevent the sample from moving, as this could damage the vibrating blade.

[0009] Because cellulose foam is generally highly breathable due to the porous structure of the foam, it is not possible to use vacuum lifting or fixing devices during manufacturing and converting operations.

[0010] Another drawback of cellulose foam is that its surface properties are less smooth than those of traditional papermaking, which applies pressure to the material to create a very smooth surface. The surface texture of cellulose foam is achieved by the self-compacting fibers during drying. Furthermore, the low density and porous nature of cellulose foam makes it susceptible to moisture penetration by capillary action, leading to ink bleeding during printing and resulting in poor print quality. Finally, the fibrous and porous nature of cellulose foam makes it highly hygroscopic, which can make it difficult to handle moisture condensation when used in thermal packaging for frozen foods.

[0011] Therefore, there remains a need for bio-based foams that are recyclable and that also allow for the use of automated processes, including vacuum lifting and fixturing equipment. To facilitate efficient foam production, particularly drying, it is desirable for the foam to be dimensionally stable even in the wet state.

[0012] Additionally, it is also desirable to be able to tailor the surface properties of the bio-based foam, such as surface gloss, smoothness, ink absorbency, and hydrophobicity. Summary of the Invention

[0013] It is an object of the present invention to provide an improved solid cellulose foam that is recyclable and produced from renewable resources and that eliminates or mitigates at least some of the disadvantages of prior art materials.

[0014] It is a further object of the present invention to provide a solid cellulose foam that can be used in processes involving vacuum lift and fixation equipment.

[0015] It is a further object of the present invention to provide a solid cellulose foam that allows for customized surface properties depending on the application of the solid cellulose foam.

[0016] It is a further object of the present invention to provide a solid cellulose foam that can be produced by drying a wet foam without the use of a mold, allowing for versatile manufacturing methods.

[0017] The above objectives, as well as other objectives which will be realized by those skilled in the art in light of this disclosure, are achieved by various aspects of the present disclosure.

[0018] According to a first aspect, the present invention provides a method for manufacturing a hose having a flow rate of 10 to 80 kg / m 3wherein the coated cellulose foam material comprises a solid cellulose foam having at least one coating on at least one outer surface thereof, the at least one coating comprising at least one coating layer.

[0019] It has surprisingly been discovered that applying a coating to at least one outer surface of a solid cellulose foam reduces the air permeability of the solid cellulose foam, allowing it to be processed using vacuum lift and fixation equipment. This facilitates processing of the foam, particularly operations used in repurposing the foam for different packaging applications. The type of coating applied can also be selected to impart not only reduced air permeability to the solid cellulose foam, but also other desirable properties, such as surface smoothness, ink absorption, hydrophobicity, scratch resistance, and surface gloss. The surface properties of the solid cellulose foam can be tailored by applying one or more coatings depending on the end use of the foam.

[0020] The cellulose foam preferably comprises 71 to 95 wt. % of cellulose fibers, calculated based on the total weight of solids in the foam, 4 to 24 wt. % of a water-soluble thickener, calculated based on the total weight of solids in the foam, and at least two surfactants. Wet foams having such compositions are self-supporting and do not require a mold or other forming means to retain their shape during drying.

[0021] According to a second aspect, the present invention provides a method for producing a method comprising the steps of: a) providing a cellulose foam comprising at least one outer surface, 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 at least one coating composition to at least one outer surface of the cellulose foam to obtain a coated cellulose foam material; d) 10-80 kg / m 3 drying the coated cellulose foam material to obtain a coated solid cellulose foam material having a density in the range of The present invention relates to a method for coating a cellulose foam, comprising:

[0022] Surprisingly, it has been found that the coating layer can be applied to at least partially dried cellulose foam. This allows for a versatile processing method in which the properties of the cellulose foam can be customized by applying a specific coating. Because the coating can be applied to at least partially dried foam, it is also possible to influence the properties of the cellulose foam during processing. The coated solid cellulose foam material according to the first embodiment can be produced by the method according to the second embodiment.

[0023] According to a third aspect, the present invention relates to the use of a coated solid cellulose foam material according to the first aspect as a packaging, insulating material or building material. DETAILED DESCRIPTION OF THE INVENTION

[0024] As used herein, the term "foam" refers to a material produced by trapping air or gas bubbles within a solid or liquid. Typically, the volume of gas is much greater than the volume of the liquid or solid, with a thin membrane separating the gas pockets. For a foam to form, three requirements must be met. Mechanical work is required to increase the surface area. This can be done by agitation, dispersing a large amount of gas into the liquid, or injecting gas into the liquid. The second requirement is that a foaming agent (usually an amphiphile, surfactant, or surface-active component) must be present to reduce the surface tension. Finally, the foam must form faster than it can break down.

[0025] As used herein, the term "cellulose foam" refers to a foam containing cellulose and other components such as thickeners, surfactants, and additives. The main component of cellulose foam is cellulose, which accounts for at least 70% by weight of the dry weight of the cellulose foam. Cellulose is in the form of fibers, and therefore the foam can also be defined as a fibrous foam or a cellulose fiber foam. The cellulose foam can be in a wet or solid state.

[0026] As used herein, the terms "wet foam" or "wet cellulose foam" refer to a wet foam comprising cellulose and other components such as thickeners, surfactants, and additives. Air bubbles are present within the wet foam. The wet foam is self-supporting and behaves as a viscoelastic solid, meaning that it possesses both viscous and elastic properties. The wet foam behaves as a solid and is self-supporting unless sufficient force is applied to it, causing it to begin to flow and behave as a viscous material. Depending on the magnitude and time scale of the applied shear stress, the wet foam may exhibit primarily viscous or elastic behavior.

[0027] As used herein, the terms "solid cellulose foam" or "dried cellulose foam" refer to a dry porous cellulose material, i.e., a foam-forming material, formed from wet cellulose foam. During the drying process, the closed wet cellulose foam is converted into an open solid cellulose foam. The cellulose fiber network is prevented from collapsing during drying. As a result, the solid cellulose foam will have a shape that generally matches the shape of the wet cellulose foam. The dry content of the solid cellulose foam is at least 95% by weight, calculated based on the total weight of the solid cellulose foam. The shape and density of the solid cellulose foam are maintained even in an unconfined state. Solid cellulose foam has an open-cell structure, allowing air to enter the pores within the foam. Solid cellulose foam is sometimes referred to as a porous material or a low-density material.

[0028] 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 solids content in the range of 95 to 100% by weight, preferably 98 to 100% by weight, calculated on the total weight of the coated solid cellulose foam material. The coated solid cellulose foam material may have a dry weight of 10 to 80 kg / m 3 , preferably 10 to 60 kg / m 3 , and more preferably 20 to 50 kg / m 3 It has a density in the range of

[0029] 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 has a loading capacity of 10 to 80 kg / m. 3 , preferably 20 to 50 kg / m 3 , and more preferably 20 to 50 kg / m 3 The applied coating layer is thin and therefore has negligible effect on the density of the coated solid cellulose foam material.

[0030] The cellulose foam preferably comprises cellulose fibers in the range of 71 to 95 wt %, for example 75 to 95 wt %, based on the total dry weight of the cellulose foam.

[0031] Cellulose fibers suitable for use in the present invention can be derived from wood, such as softwood or hardwood, leaves, or fiber crops (including cotton, flax, and hemp). Cellulose fibers suitable for use in the present invention can also be derived from regenerated cellulose, such as rayon and lyocell. Cellulose fibers suitable for use in the present invention can contain lignin or hemicellulose or both, or the cellulose fibers can 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 the wood matrix. Pulp fibers can be separated by mechanical pulping to obtain mechanical pulps, such as thermomechanical pulp (TMP) or chemithermomechanical pulp (CTMP), or by chemical pulping, such as kraft pulp or pulps obtained by sulfite, soda, or organosolv pulping processes. More preferably, the cellulose fibers are pulp fibers separated by a chemical pulping process. The different properties of each cellulose fiber will affect the properties of the final cellulose foam. Cellulose fibers are much longer than their width. Cellulose fibers can have an average width of 0.01 to 0.05 mm. Softwood fiber lengths can be 2.5 to 4.5 mm, while hardwood fiber lengths can be 0.7 to 1.6 mm, and eucalyptus fiber lengths are 0.7 to 1.5 mm. However, fiber lengths can vary significantly depending on the habitat and other factors. The cellulose fibers in the cellulose foams disclosed herein can have lengths of 0.1 to 65 mm, 0.1 to 10 mm, 0.5 to 65 mm, 0.5 to 10 mm, or 0.5 to 7 mm. Fiber length can provide different mechanical properties to the foam. Due to the fiber length, the fibers can intertwine with each other, resulting in fiber-to-fiber bonds and strength for the foam.The aspect ratio, i.e., the ratio of fiber length to fiber width of the cellulose fibers in the cellulose foam according to the present invention, may be at least 10, at least 25, at least 50, at least 75, or at least 100, which maintains and stabilizes the foam structure during the drying process, allowing the wet cellulose foam to dry while retaining its shape. The aspect ratio may be up to 6500, or preferably up to 2000.

[0032] Cellulose fibers can be modified to provide different properties to the final cellulose foam, for example, phosphorylated or periodate oxidized fibers can be used when making cellulose foams according to the present invention.

[0033] Preferably, the cellulose fibers are selected from wood pulps such as bleached softwood kraft pulp, hardwood pulp, chemical-thermomechanical pulp, and dissolving pulp, or a combination of one or more thereof. More preferably, the cellulose pulp fibers are derived from softwood pulp, chemical-thermomechanical pulp, or dissolving pulp. Most preferably, the cellulose pulp fibers are derived from softwood pulp, such as bleached softwood kraft pulp.

[0034] The cellulose foam preferably comprises cellulose fibers in the range of 71 to 95 wt. %, for example 75 to 95 wt. %, based on the total dry weight of the cellulose foam, a water-soluble thickener in the range of 4 to 24 wt. %, for example 5 to 20 wt. %, based on the total dry weight of the cellulose foam, and at least two surfactants.

[0035] The water-soluble thickener may have a molecular weight of 80,000 to 250,000 g / mol, or 83,000 to 197,000 g / mol. Exemplary water-soluble thickeners are selected from carboxymethyl cellulose (CMC), methyl cellulose (MC), hydroxyethyl cellulose (HEC), ethyl hydroxyethyl cellulose (EHEC), methyl hydroxypropyl cellulose (MHPC), starch, xanthan gum, guar gum, and xyloglucan, or mixtures thereof. The water-solubility of the thickener facilitates recycling of the cellulose foam.

[0036] Water-soluble thickeners can improve the bond strength between fibers in cellulose foams, primarily through hydrogen bonding. Therefore, the amount of water-soluble thickener will affect the mechanical performance of the cellulose foam, particularly the bulk of the material. A higher content of water-soluble thickener provides greater rigidity to the material. Therefore, water-soluble thickeners allow for customization of the mechanical properties of cellulose foams.

[0037] 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. A surfactant suitable for this purpose is an anionic surfactant, preferably a low-molecular-weight anionic surfactant. 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 8. The low-molecular-weight anionic surfactant may be selected from sodium dodecyl sulfate (SDS); potassium dodecyl sulfate, sodium laureth sulfate (SLES); sodium dodecylbenzenesulfonate; sodium cocoyl sarcosinate; and sodium lauroyl sarcosinate. The low-molecular-weight anionic surfactant is preferably selected from sodium dodecyl sulfate (SDS); sodium pn-dodecylbenzenesulfonate; 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.

[0038] The other of the at least two surfactants is preferably a co-surfactant. The co-surfactant can be selected from the group consisting of 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 pH 8; and amphoteric betaines. The co-surfactant can have a maximum apparent pKa of 10. The co-surfactant preferably has a long carbon chain, more preferably a carbon chain having 14 carbon atoms (C14). The co-surfactant can be selected from high pKa fatty acids from plant-derived sources, such as tetradecanoic acid (myristic acid), sodium oleate, lauric acid, palmitic acid, and stearic acid; glucose-based co-surfactants with aliphatic carbon chains, such as alkyl glycosides, alkyl polyglucosides, alkyl thioglycosides, and alkyl maltosides; amphoteric betaines, such as cocamidopropyl betaine (CAPB) and sodium cocoiminodipropionate (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.

[0039] Therefore, the at least two surfactants used in the cellulose foam preferably comprise a mixture of an anionic surfactant and a co-surfactant. The molar ratio of the anionic surfactant to the co-surfactant may be 0.2:1 to 3:1, preferably 0.5:1 to 2:1. The total amount of the at least two surfactants contained in the cellulose foam may be 0.6 to 5 wt. % or 0.8 to 2.0 wt. % calculated based on the total weight of the cellulose foam.

[0040] The cellulose foam can be redispersed in water and therefore is recyclable in the normal paper recycling stream.

[0041] The cellulose foam is prepared by the following steps: - decomposing cellulose fibers in water to obtain a cellulose fiber slurry; - adding a water-soluble thickener to the slurry to obtain a mixture of thickener and cellulose fibers in water; - adding at least two surfactants to the mixture to obtain a fiber suspension; and - aerating a fiber suspension to obtain a wet foam, the wet foam comprising 10 to 38% by weight of cellulose fibers, 0.5 to 10% by weight of a water-soluble thickener, and 0.1 to 2% by weight of a surfactant, calculated relative to the total weight of the wet foam, and the foam has a viscosity of 140 to 500 kg / m 3 and a yield stress of 40 to 400 Pa; - drying the wet foam to obtain a solid cellulose foam The compound can be prepared using a method comprising:

[0042] 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.

[0043] The addition of water-soluble thickeners increases the viscosity of the slurry, allowing sufficient air to be entrapped during aeration to produce a tightly packed foam. Because the cellulose fibers are mixed at high concentrations, a drainage step is not necessary, allowing the use of high concentrations of water-soluble bio-based thickeners.

[0044] The addition of a fast-acting surfactant will contribute to the formation of a dense, high-viscosity cellulose foam, as it will settle quickly between the air-water phase during aeration. This allows for a self-supporting wet cellulose foam. The addition of a co-surfactant together with the fast-acting surfactant will further enhance the properties of the cellulose foam, as it will accelerate the action of the fast-acting surfactant. A co-surfactant with an appropriate pKa and long carbon chain will further contribute to the formation of a stable fiber suspension and a stable wet cellulose foam.

[0045] Upon aeration, a composition comprising cellulose fibers, a thickener, and at least two surfactants will form a highly stable wet fiber foam. Aeration can be achieved by mechanical agitation, incorporating a significant amount of air into the material. Foam formation can be facilitated by the surfactant. By adjusting the stability of the wet foam using a combination of a thickener and a surfactant, a free-standing cellulose foam can be produced without the use of crosslinkers or fibrillated cellulose. The good stability of the foam prevents ripening, i.e., changes in cell size, and drainage. The resulting wet foam is free-standing and does not require a mold or forming cloth to maintain its shape upon drying. The wet foam can be molded into a free-standing foam that is stable enough to dry without collapsing, even in the absence of a supporting mold. As a result, objects can be molded and dried without the use of a mold.

[0046] The cell size in the wet foam is usually less than 100 μm. This results in a homogeneous wet foam with good stability that does not agglomerate during processing. The average cell size is generally maintained during processing and the subsequent drying step, and the cellulose fibers remain well dispersed. The solid cellulose foam obtained by drying the wet foam has a homogeneous structure, is strong, has good mechanical properties, a smooth surface, and is free of defects. A smooth surface can be advantageous when a coating is applied to the foam.

[0047] In contrast, less stable wet cellulose foams have larger average cell sizes (i.e., typically greater than 100 μm), which result in faster cell coalescence during processing and drying, resulting in the formation of larger cells. Additionally, cellulose fibers will form clusters during processing and drying, resulting in the collapse of the wet foam during drying. The resulting solid cellulose foam will not have a homogeneous structure and will contain defects, such as voids, resulting from the coalescence of cells in the wet foam. These defects will cause the solid cellulose foam to be brittle and have a rough surface.

[0048] Due to the high solids content, the wet foam does not need to be dehydrated before drying. The foam can be dried by evaporation at room temperature or at elevated temperatures, e.g., temperatures between 40 and 140°C. The dry cellulose foam has a drying capacity of 10 to 80 kg / m 3 , or 10 to 60 kg / m 3 , or 20 to 50 kg / m 3 The density of the .mu.m particle may be .mu.m.

[0049] In a preferred embodiment, the cellulose foam comprises 71 to 95 wt. % of cellulose fibers, e.g., 75 to 95 wt. % of cellulose fibers, based on the total dry weight of the cellulose foam; 4 to 24 wt. % of a water-soluble thickener, based on the total dry weight of the cellulose foam, e.g., 5 to 20 wt. % of a water-soluble thickener, based on the total dry weight of the cellulose foam; and at least two surfactants. A wet cellulose foam having such a composition has a homogeneous structure and, as discussed above, good stability. Such a wet cellulose foam can also be dried without prior dehydration.

[0050] The solid cellulose foam can have any shape, such as a block, cube, cylinder, or irregular shape. Regardless of the shape, the solid cellulose foam will have at least one outer surface. As used herein, the term "outer surface" refers to the outermost surface of the solid cellulose foam. It is not intended to refer to the outermost surface of the 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 further be covered with other layers, such as additional layers of cellulose foam.

[0051] In one embodiment, the solid cellulose foam is provided in the form of a slab having a thickness ranging from 1 to 20 cm, preferably from 1 to 10 cm, and more preferably from 4 to 6 cm. The length and width dimensions of the slab are typically in the range of 100 to 300 cm. The slab can be cut into smaller pieces, preferably having the same thickness. In embodiments in which the solid cellulose foam is provided in the form of a slab, the exterior surfaces are present on the top, bottom, and sides of the slab.

[0052] The solid cellulose foam may have a dense layer on at least one outer surface. In embodiments in which the cellulose foam is provided in the form of a slab, the cellulose foam has a dense layer on at least the top and bottom surfaces, and optionally on the sides.

[0053] The dense layer contains more densely packed, partially differently oriented cellulose fibers compared to the bulk, resulting in an increased number of bonds between fibers. The dense layer forms on the outer surface of the wet foam during drying and remains on the outer surface of the solid cellulose foam after drying. The dense layer has improved mechanical stability and strength compared to the core of the solid cellulose foam. The core of the solid cellulose foam contains a homogeneous open-cell fiber network. The core is highly porous, while the dense layer has a denser structure than the core, but is still porous.

[0054] The dense layer thus provides the solid cellulose foam with improved stability and mechanical strength. Thus, in embodiments in which the solid cellulose foam is provided in the form of a slab, it is preferred that when cutting the foam slab, the cut is made so that the thickness of the slab remains the same after cutting, thus ensuring that the dense layer is still present on the top and bottom surfaces.

[0055] According to a first aspect of the present invention, a solid cellulose foam is provided with at least one coating on at least one exterior surface. The solid cellulose foam can be provided with a coating on one exterior surface, multiple exterior surfaces, or all exterior surfaces. In embodiments in which the solid cellulose foam is provided with coatings on multiple exterior surfaces, the coating compositions of the coated exterior surfaces can be the same or different. For example, the solid cellulose foam can be provided with a first type of coating on a first exterior surface and a second type of coating on a second exterior surface. It is also within the scope of the present invention to apply multiple coatings to the same exterior surface, e.g., covering a first portion of the exterior surface with a first coating and a second portion of the exterior surface with a second coating.

[0056] In embodiments where the solid cellulose foam is provided in the form of a slab, the coating can be applied to the top, bottom, and / or either side.

[0057] The coating is preferably applied to the outer surface of the solid cellulose foam that includes a dense layer, since the dense layer is smoother and less open than the outer surface that does not include the dense layer. In embodiments in which not all outer surfaces of the solid cellulose foam include a dense layer, the coating can be applied to both the surface that includes the dense layer and the outer surface that does not include the dense layer.

[0058] An adhesive layer may be applied to at least one outer surface of the cellulose foam, or to the dense layer, if present. In such embodiments, the coating is applied over the adhesive layer. Preferably, the coating is applied directly to the solid cellulose foam, i.e., without the use of an adhesive layer.

[0059] The coating comprises at least one coating layer, e.g., at least two coating layers, or at least three coating layers. In embodiments in which the coating comprises at least two coating layers, the compositions of the at least two coating layers can be the same or different.

[0060] In embodiments in which the solid cellulosic substrate has coatings on multiple outer surfaces, each coating can include at least one coating layer, such as at least two coating layers or at least three coating layers.

[0061] As used herein, the term "composition" refers to the composition of the coating in terms of components. Compositions can differ from one another in terms of the concentration of the components, in terms of the components present in the composition, or a combination of both.

[0062] Applying a coating to the exterior surface of a solid cellulose foam will reduce the breathability of the solid cellulose foam because the pores on the exterior surface will be blocked by the coating. It is important that the coating be thick enough to adequately block all of the pores on the surface, and that the surface of the foam be relatively flat. In some embodiments, at least one coating has a thickness of 2 to 500 g / m 2 , for example, 2 to 300 g / m 2 , or 2 to 250 g / m 2 , or 10 to 200 g / m 2 , or 10 to 150 g / m 2 , or 50 to 150 g / m 2 , or 50 to 300 g / m 2The cellulose foam has a basis weight in the range of 0.01 to 0.01. By reducing the air permeability of the cellulose foam by applying at least one coating to at least one outer surface, the resulting coated solid cellulose foam material is much easier to use in automated processes involving vacuums. The coated solid cellulose foam can be used, for example, in converting and packaging processes that involve steps requiring vacuum lifting and fixation.

[0063] Because the coating is thin, its effect on the density of the coated solid cellulose material is negligible. Therefore, the density of the coated solid cellulose material is also limited to 10-80 kg / m. 3 , or 10 to 60 kg / m 3 , or 20 to 50 kg / m 3 is within the range.

[0064] The coating is provided by applying at least one layer of at least one coating composition to at least one outer surface of the cellulose foam. The coating composition is preferably a liquid, such as a water-based suspension or dispersion.

[0065] 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, and 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. For some particulate materials, such as MFC, the addition of a film-forming material to the coating is not necessary.

[0066] The coating can include at least one particulate material and at least one film-forming material. A coating including at least one particulate material and at least one film-forming material can enhance the coverage of the coating on the outer surface of the cellulose foam and reduce the risk of pinhole formation, which, if present, would adversely affect the breathability of the cellulose foam. Additionally, the smoothness and gloss of the coated solid cellulose foam material can be improved. Furthermore, applying a coating can improve ink absorption, thereby preventing ink from seeping through the coated solid cellulose foam material, improving printability in terms of high-resolution printing.

[0067] The coating composition can include at least one particulate material and at least one film-forming material. For example, the coating composition can include a particulate material, a film-forming material, optionally at least one additive, and water.

[0068] The particulate material may be selected from at least one of microfibrillated cellulose (MFC), cellulose fibers, mineral particles such as clay or calcium carbonate.

[0069] The film-forming material may be selected from at least one of carboxymethyl cellulose (CMC), cellulose ethers, starch, polyvinyl alcohol, or synthetic latexes such as acrylic or styrene butadiene latexes.

[0070] For example, the coating can include CMC, calcium carbonate, and glycerol (which acts as a plasticizer). A corresponding coating composition includes CMC, calcium carbonate, glycerol, and water.

[0071] In one embodiment, the coating comprises MFC. A corresponding coating composition comprises MFC and water. Microfibrillated cellulose (MFC) is intended in the context of the patent application to mean cellulose particles, fibers, or fibrils having a width or diameter of 20 nm to 1000 nm.

[0072] There are various methods for producing MFC, including single-pass or multi-pass purification, prehydrolysis followed by purification, or shear dispersion or fibril release. To ensure that MFC production is both energy-efficient and sustainable, one or several pretreatment steps are typically required. The cellulose fibers of the pulp used in MFC production can be natural or can be enzymatically or chemically pretreated, for example, to reduce the amount of hemicellulose or lignin. Cellulose fibers can also be chemically modified before fibrillation, so that the cellulose molecules contain functional groups other than (or more than) those found in the original cellulose. Such groups include, among others, carboxymethyl (CM), aldehyde and / or carboxyl groups (cellulose obtained by N-oxyl-mediated oxidation, e.g., "TEMPO"), or quaternary ammonium (cationic cellulose). After modification or oxidation by one of the above methods, the fibers are more easily degraded into MFC.

[0073] MFC can be produced from wood cellulose fibers, both hardwood and softwood. It can also be produced from microbial sources, agricultural fibers such as wheat straw pulp, bamboo, bagasse, or other non-wood fiber sources. It can be produced from pulp from virgin fibers, including mechanical, chemical, and / or thermomechanical pulps. It can also be produced from shredded or recycled paper.

[0074] Coatings containing MFC will not only have excellent strength properties but also good coverage of the pores of the solid cellulose foam, resulting in a coated solid cellulose foam with improved strength and reduced breathability. Additionally, MFC-based coatings are advantageous when it comes to recycling coated cellulose foam materials. In some embodiments, MFC can act as both a particulate material and a film-forming material. For example, a coating can consist entirely of MFC. In another example, the coating includes MFC, CMC, and a plasticizer (e.g., glycerol). The corresponding coating compositions used to apply the coating would include MFC and water; and MFC, CMC, a plasticizer, and water, respectively.

[0075] In one embodiment, the coating comprises cellulose fibers. The corresponding coating composition comprises cellulose fibers. The cellulose fibers can be selected from wood pulp; regenerated cellulose fibers; and plant fibers, such as fibers derived 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 dissolving pulp, or a combination of one or more thereof.

[0076] Coatings containing cellulose fibers can provide good coverage of the pores in solid cellulose foams. For example, the coating can include cellulose fibers and various additives commonly used in the paper industry. The corresponding coating composition used to apply the coating will include cellulose fibers, additives, and water. Depending on the additives used, the coating and coating composition may or may not require a film-forming material.

[0077] The coating may optionally include at least one additive, such as, for example, a dispersant, an antifoaming agent, a UV absorber, a plasticizer, a moisture resistance additive, and a strength additive. The addition of at least one additive to the coating provides the coating with improved properties. Any suitable additive may be added, and examples of additives include glycerol and polyethylene glycol (PEG).

[0078] In one embodiment, the coating includes at least one hydrophobic agent. The corresponding coating composition includes at least one hydrophobic agent. The hydrophobic agent can be selected from, for example, at least one of a wax, such as beeswax or carnauba, an alkyl ketene dimer (AKD), or an alkyl succinic anhydride (ASA). In some embodiments, the coating can include the hydrophobic agent as well as particulate matter and a film-forming material. In such embodiments, the hydrophobic agent can be part of the same coating layer as the particulate matter and film-forming material, or can form a different coating layer.

[0079] The coating composition comprising at least one hydrophobic agent may be an aqueous emulsion or may be a solution comprising the hydrophobic agent and at least one solvent, such as an alcohol.

[0080] The at least one hydrophobic agent provides hydrophobic properties to the coating, which is particularly important in applications where improved water resistance is required, such as when the coated solid cellulose foam material is used in thermal packaging solutions where condensation can be a problem.

[0081] In embodiments in which the coating comprises at least two coating layers, the compositions of the at least two coating layers can be the same or different. For example, two or more coating layers of the same coating composition (e.g., two layers of a coating composition comprising MFC) can be applied to the cellulose foam. In another example, two coating layers of different coating compositions can be applied to the cellulose foam, e.g., a first coating layer of a coating composition comprising MFC and a second coating layer of a coating composition comprising a hydrophobic agent. When a coated solid cellulose material with improved water resistance is desired, it is advantageous to have an outermost coating layer comprising a hydrophobic agent.

[0082] 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, a second coating layer is applied over the first coating layer, and so on.

[0083] In embodiments in which at least two outer surfaces of a solid cellulose foam are coated, the at least two coatings can be the same or different. For example, one or more coating layers of a coating composition comprising MFC can 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 can be applied to a first outer surface of the cellulose foam, and a coating composition comprising a hydrophobic agent can be applied to a second outer surface of the cellulose foam.

[0084] In some embodiments, an additional layer of material, such as a fibrous substrate or a second cellulosic foam, is applied over the at least one coating, with the coating sandwiched between the cellulosic foam and the additional layer of material. The at least one coating can also be applied to at least one outer surface of the additional layer of material.

[0085] In some embodiments, the solid cellulose foam can be prepared by a two-stage deposition. In the first deposition, wet foam is deposited on a surface as individual units and at least partially dried. During drying, a dense layer forms on the outer surfaces of the individual units. In the second deposition, a wet foam, preferably having the same composition as the wet foam in the first deposition, is deposited to fill the space around the individual units of the first deposition. After drying, a solid cellulose foam is obtained, comprising individual foam units embedded within a foam matrix. The dense layer on the outer surface of the individual units provides mechanical support by helping the individual units maintain their shape during drying of the foam and the entire cellulose foam in the second deposition. A coating can be applied to at least one outer surface of the solid cellulose foam comprising individual foam units embedded within a foam matrix. A coating can also be applied to the outer surface of the individual units before depositing the second deposition. The coating is applied to the outer surface of the individual units after the individual units have at least partially dried, so that the outer surface of the individual units comprises a dense layer when the coating is applied. In one example, a coating composition comprising an MFC is applied to the outer surface of the at least partially dried individual units, and a coating composition comprising a hydrophobic agent is applied to the outer surface of the solid cellulose foam comprising the individual units embedded in a foam matrix (i.e., after the second deposition).

[0086] 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.

[0087] The coating can be applied to the entire at least one exterior surface of the cellulose foam, or to only one or more regions of the at least one exterior surface of the cellulose foam. Thus, the at least one exterior surface of the coated solid cellulose foam can be completely covered by the at least one coating, or the at least one exterior surface of the coated solid cellulose foam can be partially covered by the at least one coating. For example, the coating can be applied in a pattern such that the exterior surface includes coated and uncoated regions.

[0088] In some embodiments, the at least one coating is applied in a pattern that is compatible with the type of vacuum device used in the converting operation. For example, the at least one coating can be applied in locations where vacuum suction is applied, such that the breathability of the cellulose foam is reduced primarily in the coated areas.

[0089] In embodiments where the coating comprises at least two coating layers, the at least two coating layers may cover different areas of the exterior surface or the same area. For example, the at least two coating layers may be applied to the exterior surface in different patterns. In one example, one coating layer is applied to cover the entire at least one exterior surface, and a second coating layer is applied in a pattern on top of the first coating layer. The compositions of the at least two coating layers may be the same or different.

[0090] In embodiments in which the coating is applied to multiple exterior surfaces of the cellulose foam, the coating layers can be applied to at least two exterior surfaces in the same pattern or in different patterns.

[0091] According to a second aspect, the present invention relates to a method for coating a 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 dried. In the context of the present invention, "at least partially dried" means that at least the outer surface of the cellulose foam is dry and can have a coating applied thereon. In a preferred embodiment, the provided cellulose foam is dry and may have a solids content in the range of 95 to 100 wt. %, preferably 98 to 100 wt. %, calculated relative to 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 is 10 to 80 kg / m. 3 , e.g., 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 embodiment.

[0092] 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, suspension, or emulsion. Suitable solvents other than water may also be used. The coating composition may be further defined as described above in relation to the first aspect.

[0093] Step c) of the method according to the second aspect involves applying at least one coating layer of 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 coating method, such as roller coating, blade / knife coating, brushing, flexographic roller, and spray coating. In embodiments where multiple coating layers are applied, the coating composition of each coating layer can be applied using the same coating method or different methods. As further described above with respect to the first aspect, different combinations of coating layers can be applied depending on the desired properties of the coated cellulose foam material.

[0094] The coating layer may be applied to the entire at least one exterior surface, or to only a partial area of ​​the at least one exterior surface, as further described above with respect to the first embodiment.

[0095] Step d) of the method according to the second aspect is to dry the coated cellulose foam material to a density of 10 to 80 kg / m 3 , e.g., 10 to 60 kg / m 3 , or 20 to 50 kg / m 3 The method includes obtaining a coated solid cellulose foam material having a density in the range of 0.05 to 0.15 mm. The coated cellulose foam material can be dried by evaporation at room temperature or at elevated temperatures, for example, at temperatures of 40 to 140° C. Any suitable drying device can be used, such as an oven or infrared heating.

[0096] In embodiments where at least two coating layers are applied, the first coating layer can be dried before applying the second coating layer. If a third coating layer is applied, the second coating layer can be dried before applying the third layer, etc. In alternative embodiments, the first coating layer is not dried before applying the second coating layer. [Example]

[0097] Example 1 - Foam Preparation A homogeneous wet paste containing 12% by weight cellulose pulp (softwood bleached kraft pulp) and 1.2% by weight thickener (CMC) was prepared in water. The wet paste was aerated with a surfactant mixture (myristic acid and sodium cocoyl sarcosinate) until the desired wet foam density was obtained. A cylindrical mold measuring 2.5 cm in height and 6.6 cm in diameter was used to place individual foam units on a flat surface. The mold was used only to deposit the wet foam in the desired shape and dimensions and was removed before the foam dried. The formed foam was dried at 120°C in a conventional convection oven until completely dry. The dried cellulose foam had a density of 30 kg / m². 3 The density was .gtoreq.1.

[0098] Example 2 A cylindrical, dried cellulose foam prepared as described in Example 1 was coated with an aqueous solution containing microfibrillated cellulose (2 wt %). The coating was applied to all sides of the cellulose foam using a brush, ensuring that the applied coating layer was thick enough to cover the surface of the foam. The MFC coating was applied to a dense layer on the outer surface of the foam.

[0099] The breathability of the cellulose foam was reduced by the MFC coating. In addition, the coating improved the surface smoothness of the foam. Furthermore, the coating improved the strength of the dense layer. This was evident from the better properties during the impact test compared to the foam without the MFC coating. The foam with the MFC coating also showed less degradation over time than the foam without the coating. A comparison is made with the foam from Example 1.

[0100] Example 3 Cylindrical dried cellulose foams prepared as described in Example 1 were coated with an aqueous coating containing CaCO3 and CMC. The coating solution was prepared by dispersing calcium carbonate in an 8% (w / w) aqueous CMC solution to a final solids content of 40% (w / w). The coating was applied to all sides of the foam using a brush, ensuring that the applied coating layer was thick enough to cover the foam surface. The coated foams were dried in an oven at 120°C until completely dry.

[0101] The breathability of the cellulose foam was reduced by the coating, but it was clear that the coating blocked the surface pores, reducing breathability. It was also clear that the surface of the foam became smoother after the coating was applied.

[0102] Example 4 Similar to Example 3, but with the addition of glycerol (8 w / w) to the CMC coating solution, the addition of glycerol improved the coating and further reduced the breathability of the coated cellulose foam compared to the coating in Example 3.

[0103] Example 5 A homogeneous wet paste containing 12% by weight cellulose pulp (softwood bleached kraft pulp) and 1.2% by weight thickener (CMC) was prepared in water. 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 x 37 x 5 cm mold was filled with the aerated wet foam, the surface was scraped to remove excess foam, and the surface was leveled to the frame height. Finally, the foam was dried at 120°C in a conventional convection oven until completely dry. The dried cellulose foam had a density of 30 kg / m². 3 The density was .gtoreq.1.

[0104] 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 to a final solids content of 52% (w / w). PEG and glycerol act as plasticizers.

[0105] The coating was applied to only the top and top quarter of the foam using a brush, ensuring that the applied coating layer was thick enough to cover the surface of the foam. The coated foam was dried in an oven at 120°C until completely dry.

[0106] The breathability of the cellulose foam was significantly reduced by the coated areas of the foam. The effectiveness of the coating was tested by using vacuum suction to lift the foam plank. Applying a vacuum suction cup to the uncoated areas of the foam did not achieve sufficient suction to lift the foam plank. However, using a vacuum suction cup on the coated areas of the foam allowed the plank to be lifted.

[0107] It will be apparent to those skilled in the art in view of the above detailed description of the invention that other modifications and variations will be apparent to those skilled in the art, and that such other modifications and variations are possible without departing from the spirit and scope of the invention.

Claims

1. 10 to 80 kg / m ３ 1. A coated solid cellulose foam material having a density in the range of 0.1 to 1.0 mm, wherein the coated cellulose foam material comprises a solid cellulose foam having at least one coating on at least one outer surface thereof, the at least one coating comprising at least one coating layer.

2. 10. The coated solid cellulose foam material of claim 1, wherein the cellulose foam comprises in the range of 71 to 95 weight percent cellulose fibers, based on the total dry weight of the solid cellulose foam.

3. 3. The coated solid cellulose foam material of claim 1, wherein the solid cellulose foam comprises 71 to 95 wt. % cellulose fibers based on the total dry weight of the solid cellulose foam, 4 to 24 wt. % water-soluble thickener based on the total dry weight of the solid cellulose foam, and at least two surfactants.

4. 4. The coated solid cellulose foam material of claim 1, wherein at least one outer surface of the solid cellulose foam comprises a dense layer.

5. 5. The coated solid cellulose foam material of claim 4, wherein at least one coating is disposed on the dense layer.

6. 6. The coated solid cellulose foam material of claim 1, wherein at least one coating comprises at least two coating layers, and the compositions of the at least two coating layers may be the same or different.

7. 7. The coated solid cellulose foam material of claim 1, wherein the coating comprises at least one particulate material and at least one film-forming material.

8. 8. The coated solid cellulose foam material of claim 1, wherein the coating comprises microfibrillated cellulose (MFC).

9. 9. The coated solid cellulose foam material of claim 1, wherein the coating comprises at least one hydrophobic agent.

10. The coating is 2 to 300 g / m ２ 10. The cellulose foam substrate of claim 1 having a basis weight in the range of

11. 1. A method for coating a cellulose foam, comprising: a) providing a cellulose foam comprising at least one outer surface, 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 at least one coating composition to at least one outer surface of the cellulose foam to obtain a coated cellulose foam material; d) 10-80kg / m ３ drying the coated cellulose foam material to obtain a coated solid cellulose foam material having a density in the range of A method comprising:

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

13. 13. The method of claim 11 or 12, wherein the cellulose foam comprises cellulose fibers in the range of 71 to 95 wt. % based on the total dry weight of the cellulose foam, a water-soluble thickener in the range of 4 to 24 wt. % based on the total dry weight of the cellulose foam, and at least two surfactants.

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

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

16. The provided cellulose foam has a melting point of 10 to 80 kg / m ３ 16. The method of claim 11, wherein the solid cellulose foam has a density in the range of

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

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

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

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

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