FIELD OF THE INVENTION

The present invention relates to the area of cellulose foam for packaging, more specifically to a flexible solid cellulose foam.

The invention further relates to a method for producing a flexible solid cellulose foam.

BACKGROUND INFORMATION

Plastic packaging materials such as fossil-based foams seem increasingly outdated in a society that is striving to reduce plastic usage and waste and move towards renewable materials. With regulatory bodies now driving policy towards limiting or banning fossilbased foam materials in packaging, new solutions are needed.

There are many challenges with finding foams from renewable sources. Many bio-based foams have higher cost of production and lower mechanical performance, as well as poor stability in water or high temperatures, compared to established foams from oilbased sources. Bio-based and recyclable protective materials need to have the same excellent characteristics and properties as petroleum-based protective materials for being the first choice over petroleum-based materials.

Low weight and good shock absorption of the bio-based foams are examples of crucial characteristics. Also, the ability to customize the shape and the form of the bio-based foams to the shape and form of the goods to be sheltered by the protective material is of uttermost importance. Cellulose has shown to have a special potential, as the most abundant renewable natural polymer on earth, with its crystalline structure, and the availability of methods for preparing large volumes on an industrial scale.

Several biobased foams comprising cellulose have been described. W020200011587 Al describes a porous material that is prepared by aerating a paste comprising cellulose fibres and gluten and depositing the aerated paste in a mould where it is dried. WO2015036659 Al describes a moulded fibrous product prepared by foaming an aqueous suspension of natural fibres in combination with synthetic fibres and surfactant, feeding the fibrous foam to a mould where it is dried to produce a dry fibrous product.

In packaging applications, the goods to be sheltered may often have protruding portions or have complex three-dimensional (3D) shapes that need extra protection by the packaging material during storage and transportation. In addition, the goods may be made of sensitive materials such as glass, porcelain, that need protection because of their fragile nature. Solid cellulose foams may be an interesting alternative in such applications. However, the solid cellulose foams on the market do most often not provide the necessary protection of protruding portions or complex 3D shapes due to the rigidity, inflexibility and stiffness of the bio-based foams. It is often not possible to bend solid foams around objects without the bio-based foams cracking and breaking.

There still exists a need for solid cellulose foams that can be tailored around goods of any shape and protect every part of the goods. The goods need to be so well sheltered so that any shock arising during storage and transportation will be absorbed by the surrounding cellulose foam and whereby the shock will not damage the goods.

Also, the solid cellulose foams need to be renewable, biodegradable, and fully recyclable in regular paper and board flows allowing them to be part of a circular material flow in existing packaging waste management systems. Production costs of producing the foams as well as tailoring shapes of the foams to any product shape have to be moderate in order to be a competitive choice.

In order to save raw materials there is also a need for reducing the amount of protective material used in protective packaging, as well as to minimize waste material.

There further exists a need for protective packaging materials that easily can be transported to places where goods are to be packed inside the protective packaging materials. The protective packaging materials need to offer three-dimensionally tailored protection of the goods but also take up as little space as possible during transport to the packaging places.

SUMMARY OF THE INVENTION

It is an object of the present invention to obviate at least some of the disadvantages in the prior art and to provide a flexible solid cellulose foam.

Thanks to a solution as defined in claim 1, the solid cellulose foam is provided with flexibility such that said foam may be wrapped around a curved shape of goods to be protected. Said solid cellulose foam may further be stretched, bent and twisted without any risk of cracking and breaking.

Another advantage is that said flexible solid cellulose foam is a flat material taking up very little space when stored or during transport to the place of use. Still - thanks to the possibility to stretch, bend, curve and/or twist the solid cellulose foam- said foam can be tailored around three-dimensional objects, even of complex shapes.

Another advantage is that a predetermined depth of cut DC is less than a thickness T of said cellulose foam thereby allowing said foam to remain in one piece. No waste material is cut way.

Yet another advantage is that a direction of cut into said foam is chosen depending on the shape of the goods to be sheltered by said foam meaning that there are very good possibilities to tailor the shape of the flexible foam to the shape of the goods.

The method for producing said flexible solid cellulose foam is cost-effective to implement in existing production lines.

The method may further lead to cheaper and easier manufacture and improved product quality. The present method is also easy to perform in a large scale set up.

Further aspects and embodiments are defined in the appended claims, which are specifically incorporated herein by reference.

DETAILED AND EXEMPLIFYING DESCRIPTION OF THE INVENTION

Before the invention is disclosed and described in detail, it is to be understood that this invention is not limited to particular compounds, configurations, method steps, substrates, and materials disclosed herein as such compounds, configurations, method steps, substrates, and materials may vary somewhat. It is also to be understood that the terminology employed herein is used for the purpose of describing particular embodiments only and is not intended to be limiting since the scope of the present invention is limited only by the appended claims and equivalents thereof.

It must be noted that, as used in this specification and the appended claims, the singular forms "a", "an" and "the" include plural referents unless the context clearly dictates otherwise.

If nothing else is defined, any terms and scientific terminology used herein are intended to have the meanings commonly understood by those of skill in the art to which this invention pertains.

The expression “flat object” as used herein means an object having a height, a width and a length. Said width and length defining two surfaces and said height defining at least one side wall. Said height is so small in relation to said length and width that said object is related to as a flat object. Examples of flat objects are planks, tabletops, wall mirrors, door leaves, glass panes, solar panels. The expression “flat” refers to an object having a level surface without any protrusions or indentations.

“Plank” as used herein denotes an object that is flat and having an upper surface and a lower surface. Most often, said surfaces are parallel surfaces. “Flexible” as used herein means curvable, stretchable, twistable and/or bendable.

“Flexible material” as used herein denotes a material that may be curved, stretched, twisted and/or bent.

“Rigid” as is used herein means inflexible. A material that is rigid cannot be curved, stretched, twisted and/or bent without cracking and/or breaking into pieces.

“Predetermined depth of cut” as is used herein means that a depth of a cut is determined in advance before arranging or performing said cut.

The term “foam”, as used herein, refers to a substance made by trapping air or gas bubbles inside a solid or liquid. Typically, the volume of gas is much larger than that of the liquid or solid, with thin films separating gas pockets. Three requirements must be met in order for foam to form. Mechanical work is needed to increase the surface area. This can occur by agitation, dispersing a large volume of gas into a liquid, or injecting a gas into a liquid. The second requirement is that a foam forming agent, typically an amphiphilic substance, a surfactant or surface active component, must be present to decrease surface tension. Finally, the foam must form more quickly than it breaks down.

The term “cellulose foam”, as used herein, 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. Cellulose is in the form of fibres, and the foam can thus also be defined to be a fibrous foam or a cellulose fibre foam. The cellulose foam may be wet or solid.

The term “wet foam”, or “wet cellulose foam”, as used herein, 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 freestanding 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 thus be freestanding, unless a large enough force is applied so that it starts to flow and instead behave as a viscous material. Depending on the magnitude and timescale of any applied shear stress, the wet foam can show a predominantly viscous or elastic behaviour.

The term “solid cellulose foam”, or “dry cellulose foam”, as used herein, refers to a dry porous cellulose material that has been formed from a wet cellulose foam, i.e. a foam formed material. During the drying process, a closed wet cellulose foam is transformed into an open solid cellulose foam. The network of cellulose fibres is prevented from collapsing during drying. The solid cellulose foam will as a result have a shape that to a large extent corresponds to that of the wet cellulose foam. The dry content of the solid cellulose foam may be least 95 wt% as calculated based on the total weight of the solid cellulose foam. The shape and density of the solid cellulose foam is retained also in a non-confined state. The solid cellulose foam has an open cell structure, allowing air to occupy the pores within the foam. The solid cellulose foam can also be described as a porous material or a low-density material.

The following detailed description, and the examples contained therein, are provided for the purpose of describing and illustrating certain embodiments of the invention only and are not intended to limit the scope of the invention in any way.

In a first aspect, the present invention relates to a flexible solid cellulose foam.

In a second aspect, the present invention provides a method for producing said flexible solid cellulose foam.

Said solid cellulose foam may preferably be prepared from a cellulose foam composition comprising: a) from 71-95 wt% cellulose fibres, as calculated on the total weight of solid content of the composition, b) from 4-24 wt% of a water-soluble thickener, as calculated on a total weight of solid content of the composition, and c) at least two surfactants.

Cellulose fibres suitable for use in the present invention can originate from wood, such as softwood or hardwood, from leaves or from fibre crops (including cotton, flax and hemp). The cellulose fibres suitable for use in the present invention can also originate from regenerated cellulose such as rayon and Lyocell. The cellulose fibres suitable for use in the present invention may include lignin or hemicellulose or both, or the cellulose fibres may be free from lignin and hemicellulose. Preferably, the cellulose fibres originate from wood, more preferably the cellulose fibres are pulp fibres obtained by pulping processes which liberates the fibres from the wood matrix. Pulp fibres can be liberated by mechanical pulping, obtaining mechanical pulp such as thermos mechanical pulp (TMP) or chemo thermos mechanical pulp (CTMP), or by chemical pulping such as Kraft pulp or pulps obtained by the sulphite process, soda process or organosolv pulping process. More preferably, the cellulose fibres are pulp fibres liberated by chemical pulping processes. The different characteristic of each cellulose fibre will affect the properties of the final cellulose foam. A cellulose fibre is significantly longer than it is wide. Cellulose fibres can have a mean width of 0.01 to 0.05 mm. The fibre length of softwood can be from 2.5 to 4.5 mm, while hardwood can have a fibre length from 0.7 to 1.6 mm, and Eucalyptus from 0.7 to 1.5 mm. However, the fibre length can vary considerably with different growing place etc. The cellulose fibres in the cellulose foam disclosed herein can have a length from 0.1 mm to 65 mm, or from 0.1 mm to 10 mm, or from 0.5 mm to 65 mm, or from 0.5 mm to 10 mm, or from 0.5 mm to 7 mm. The fibre lengths may provide different mechanical characteristics to the foam. Due to the length of fibres, they can entangle with each other and impart fibre to fibre interbonds that bring strength to the foam. The aspect ratio, i.e. the ratio of the fibre length to the fibre width, of the cellulose fibres 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 for preservation and stabilization of the foam structure during the drying procedure, making it possible to dry the wet cellulose foam with retained shape. The aspect ratio can be up to 6500, or preferably up to 2000. The cellulose fibres may be modified to provide different properties to the final cellulose foam. For example, phosphorylated fibres or periodate oxidized fibres could also be used when producing a cellulose foam according to the present invention.

The cellulose fibres of the cellulose foam composition may be selected from wood pulp; regenerated cellulose fibres; and plant fibres, such as fibres from bamboo, cotton, hemp, flax, and jute.

Preferably, the cellulose fibres 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.

More preferred, the cellulose pulp fibres are selected from softwood pulp, chemical- thermomechanical pulp, or dissolving pulp.

Most preferred, the cellulose pulp fibres are selected from softwood pulp, such as softwood kraft bleached pulp.

The water-soluble thickener may be present in an amount of from 4-24 wt%, or from 5- 20 wt%, as calculated on the total weight of solid content of the foam. The thickener may have a molecular weight of from 80 000-250 000 g/mol, or from 83 000-197 000 g/mol. Exemplary water-soluble thickeners are selected from carboxy methyl cellulose (CMC), methyl cellulose (MC), hydroxyethyl cellulose (HEC), ethyl hydroxyethyl cellulose (EHEC), methyl hydroxypropyl cellulose (MHPC), starch, xanthan, guar gum, and xyloglucan, or mixtures thereof.

The foam preferably comprises a mixture of at least two surfactants. One of the at least two surfactants is preferably a fast-acting surfactant that during preparation of the foam quickly settle at the air-water interphase during mechanical agitation, which contributes to the formation of a foam with a high density and a high viscosity and thus enables a free-standing foam. A suitable surfactant for this purpose is an anionic surfactant, preferably a low-molecular weight anionic surfactant. The low-molecular weight anionic surfactant may be selected from sodium dodecyl sulphate (SDS); potassium dodecyl sulphate, sodium laureth sulphate (SLES); sodium dodecylbenzenesulphonate; sodium cocoyl sarcosinate; sodium lauroyl sarcosinate. The low-molecular weight anionic surfactant is preferably selected from sodium dodecyl sulphate (SDS); sodium p-n-dodecylbenzenesulphonate; 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.

The other one of the at least two surfactants is preferably a co-surfactant. The cosurfactant may be selected from high pKa fatty acids, such as from plant derived feedstock, e.g. tetradecanoic acid (myristic acid), sodium oleate, lauric acid, palmitic acid, and stearic acid; glucose based cosurfactants with an aliphatic carbon tail, such as alkyl glycosides, alkylpolyglucosides, alkyl thio-glycosides, 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.

Said foam composition may preferably be prepared by a method comprising the steps of: a) disintegrating cellulose fibres in water to obtain a slurry of cellulose fibres; b) adding the thickener to the slurry obtained in a) to obtain a mixture of thickener and cellulose fibres in water; c) adding the at least two surfactants to the mixture obtained in b) to obtain a fibre suspension; d) aerating the suspension obtained in c) to obtain a wet foam, wherein the wet foam comprises 10-38 wt% cellulose fibres, 0.5-10 wt% of the water-soluble thickener, and 0.1-2 wt% surfactants, as calculated on the total weight of the wet foam, and wherein the wet foam has a density of from MO- SOO kg/m ³ and a yield stress of from 40 to 400 Pa; e) drying the wet foam obtained in d) to obtain a dried cellulose foam. The wet foam may be dried without using a mould, i.e. the wet foam is free-standing and retains its shape during drying without the need of a mould.

The wet foam is homogenous and has a good stability due to a small bubble size (typically below 100 pm) obtained when aerating the mixture of cellulose fibres, thickener and surfactants. The wet foam does not flocculate during processing. The average bubble size is largely maintained during any subsequent processing or drying steps and the cellulose fibres remain well dispersed. The resulting solid cellulose foam obtained by drying the wet foam will be homogenous in structure, strong, have good mechanical properties, a smooth surface and no defects. In comparison, a wet cellulose foam with low stability has a larger average bubble size (i.e. typically above 100 pm) and the bubbles will coalesce faster during processing and drying such that larger bubbles are formed. In addition, the cellulose fibres will form clusters during processing and drying. This results in the wet foam collapsing during drying. The resulting solid cellulose foam will not have a homogenous structure and will also contain defects in the form of cavities resulting from the coalesced bubbles in the wet foam. Such a solid cellulose foam is, due to the defects, weak and has a rough surface.

Said dried cellulose foam obtained in step e) may be used as the solid cellulose foam.

Said dried cellulose foam obtained in step e) may be obtained by a method comprising: depositing discrete units of a cellulose foam on a surface to obtain a first foam deposition, depositing a wet cellulose foam between the discrete units to obtain a subsequent foam deposition, and drying the wet foam to obtain a solid foam wherein discrete units of a foam are embedded in a foam matrix. Said solid cellulose foam may then be used as the solid cellulose foam of claim 1 and its dependent claims.

However, said solid cellulose foam may be prepared by other methods than the above described without departing from the scope of the present invention. For example, said solid cellulose foam may be prepared by a single deposition of a wet foam into any desired shape. Optionally, any suitable restriction means, such as a mould or a frame, may be used. Said solid cellulose foam material may e.g. be prepared by depositing the foam composition on a forming portion of a conventional or, for the purpose suitably modified, paper machine for forming a foam web.

Production of a solid cellulose foam comprises different production steps, one of which is a drying step. During said drying step outside surfaces of said foam (top surface, lower surface, side surfaces) will get an outer layer that has different properties than a bulk portion of said foam comprising a more homogeneous and porous open-cell fibre network. Said outer layer has a higher density than a density of said bulk portion because the fibres are packed more tightly and are partly oriented differently. The outer layer is called a "densified layer" or “densified outer layer”. Said densified layer will provide improved mechanical stability and improved strength to the foam.

Thanks to said densified layer having improved mechanical stability and providing strength to said foam, it may be preferred to orientate surfaces comprising said densified layer towards directions where extra stability may be needed.

The improved properties of said densified layer are used at positions of the product where they can contribute to the protective properties of said product. Although having a higher density, said densified layer is still highly porous and air permeable.

Said first aspect, said flexible solid cellulose foam, is now to be described in detail.

Said flexible solid cellulose foam comprises an upper surface and a lower surface.

Said flexible solid cellulose foam further comprises at least one side surface having a height H. Preferably, said height H corresponds to a thickness T of said solid cellulose foam. At least one of said upper surface and said lower surface of said flexible solid cellulose foam comprises at least one cutting line of a predetermined depth of cut DC, wherein said at least one cutting line is arranged to partially cut through said cellulose foam.

Said cutting line is arranged to not be a through-cut of said foam. This means that said predetermined depth of cut DC is less than said thickness T of said cellulose foam.

Said predetermined depth of cut DC of said at least one cutting line is 99% or less of said thickness T of said cellulose foam, preferably 95% or less and more preferred 90% or less.

Said at least one cutting line is arranged to cut into said cellulose foam at a cutting angle CA to said at least one of said upper surface and lower surface. Which angle is chosen depends on the circumstances, e.g. on a shape of an object to be protected by said flexible solid cellulose foam.

In some embodiments said at least one cutting line is arranged to cut into said cellulose foam in a direction that is perpendicular to said at least one of said upper surface and said lower surface.

In other embodiments, said at least one cutting line is arranged to cut into said material at a cutting angle CA that is not perpendicular to said upper surface or said lower surface. Said cutting angle CA may in these embodiments be less than 90° or greater than 90°.

Embodiments are conceivable wherein said cutting angle CA may be in an interval of 30-80° or 100-150°.

It is to be understood that in embodiments wherein said at least one cutting line is arranged oblique into said at least one of said upper surface and said lower surface and further into said foam, said predetermined depth of cut DC is a component of a vector of a cutting length of said oblique cutting line and whereby the component has the same direction as said thickness T (and most often said height H) of said foam.

Said at least one cutting line may further be arranged in a vertical direction, or a horizontal direction, or a direction between a vertical direction or a horizontal direction on at least one of said upper surface or lower surface. The direction to be chosen depends on the shape of the object to be protected by said flexible solid cellulose foam.

Said direction between said vertical direction or said horizontal direction on said at least one of said upper surface or lower surface may e.g. be a diagonal direction, i.e. 45°.

Phrased differently, said at least one cutting line is arranged to run in a direction from one edge E to an opposite edge E of said at least one of said upper surface and said lower surface, wherein said edge E is an edge E formed by at least one side surface and said upper surface or said lower surface.

Said at least one cutting line is arranged to meet said edge at an edge angle EA; said edge angle EA is in an interval of 10-170°.

In some embodiments, said at least one cutting line is arranged to meet said edge at an edge angle EA that is 90°, i.e. said at least one cutting line meets said edge E perpendicularly.

Said flexible solid cellulose foam may comprise 0.1-5 cutting lines per centimetre, preferably 0.5 to 2 cutting lines per centimetre. In some embodiments, the flexible solid cellulose foam may comprise 0.1-10 cutting lines per centimetre.

In some embodiments, said flexible solid cellulose foam may comprise 0.2-5 cutting lines per centimetre, such as 0.2-2, or 0.5-5 cutting lines per centimetre. Thus, the spacing between adjacent cutting lines in the solid cellulose foam may be from 1 mm to 10 cm, or from 2 mm to 10 cm, or from 5 mm to 2 cm, or from 5 mm to 5 cm, or from 2 mm to 2 cm.

The flexibility of the solid cellulose foam can be controlled by the number of cutting lines per centimetre and can be tailored towards specific applications. When the number of cutting lines per centimetre is high, the flexibility is high. However, the stability of the foam may be negatively impacted by a high number of cutting lines per centimetre such that the integrity of the foam is decreased which may impact the cushioning properties. Thus, there is a trade-off between high flexibility and good structural integrity of the foam. In preferred embodiments, the solid cellulose foam comprises 0.5- 2 cutting lines per centimetre. In such a range, a good flexibility is obtained while maintaining good cushioning properties of the foam.

Preferably, said flexible solid cellulose foam comprises a plurality of cutting lines, such as at least three cutting lines, or at least four cutting lines, or at least five cutting lines.

In some embodiments, two or more cutting lines may be evenly distributed on at least one of said upper and said lower surface.

In other embodiments, said two or more cutting lines are unevenly distributed on at least one of said upper and said lower surface.

The number, spacing, orientation and/or distribution of said cutting line(s) depend on the intended usage of the solid cellulose foam. A narrow spacing of cutting lines may result in an improved flexibility of the flexible solid cellulose foam. Providing cutting lines on both said upper and said lower surface may also improve the flexibility. In embodiments where cutting lines are provided on both said upper and said lower surface of the flexible solid cellulose foam, the number, spacing, orientation and/or distribution of said cutting line(s) may be the same on both surfaces, or may be different on the upper and lower surfaces. Said flexible solid cellulose foam may comprise a flat surface.

Preferably, at least one of said upper and said lower surface is a flat surface wherein said at least one cutting line is arranged on said flat surface.

It is to be understood that since said at least one cutting line is arranged to run in a direction from one edge E to said opposite edge E of at least one of said upper surface and said lower surface, said at least one cutting line also cuts said at least one side surface.

Said height H of said at least one side surface may, as earlier mentioned, be related to said thickness T of said foam.

Said height of said at least one side surface may be very small in relation to said upper and lower surface. An example of a foam material having a small height in relation to an upper surface and a lower surface is a cellulose foam plank.

An example of a flat surface may be a surface of said solid cellulose foam plank.

In some embodiments, both of said upper surface and said lower surface of said foam material comprise at least one cutting line of a predetermined depth of cut.

Said at least one cutting line of said upper surface and said at least one cutting line of said lower surface may have the same direction.

Said at least one cutting line of said upper surface and said at least one cutting line of said lower surface may have different directions.

It is further conceivable that at least one of said upper and said lower surface comprises at least two cutting lines of different directions. In one embodiment, at least one of said upper and said lower surface may comprise diagonally arranged cutting lines. At least one cutting line may be arranged at an edge angle EA of 45° while at least one other cutting line may be arranged at an angle EA of 135°; i.e. on the other diagonal of said at least one of said upper and said lower surface.

In other embodiments, at least one of said upper and said lower surface may comprise at least one horizontally arranged cutting line and at least one vertically arranged cutting line, wherein said cutting lines of the two different directions together form a grid.

It is further conceivable that said cutting angle CA may vary on said at least one of said upper and said lower surface.

It is also conceivable that in embodiments wherein both of said upper and lower surface comprise at least one cutting line, said cutting angles CA may be different on different surfaces.

In preferred embodiments, at least one of said upper surface and said lower surface of said solid cellulose foam comprises a densified outer layer.

Preferably, both of said upper and said lower surface comprise said densified outer layer.

In preferred embodiments, at least one of said upper surface and said lower surface comprising said at least one cutting line also comprises said densified outer layer.

Said at least one cutting line is arranged to cut through said densified outer layer and into at least one of said upper and said lower surface and further into a core of said solid cellulose foam material until said predetermined depth of cut DC is reached.

Said predetermined depth of cut DC may be 99% or less of said thickness T of said cellulose foam material, more preferred 90% or less and most preferred 80% or less. In some embodiments, said at least one cutting line is arranged to cut through said densified outer layer of at least one of said upper surface and said lower surface and further into said core and all the way to - but not through - said densified outer layer of the other one of at least one of said upper surface and said lower surface. Said predetermined depth of cut is in these embodiments less than a thickness of said densified outer layer such that said predetermined depth of cut may be formulated as the thickness T of said foam minus a thickness of said densified outer layer of the other one of at least one of said upper surface and said lower surface.

It is conceivable that said densified outer layer has a different thickness depending on which surface said densified outer layer is arranged on.

It is further conceivable that said densified outer layer may have the same thickness irrespective of on which surface said densified outer layer is arranged on.

Embodiments are conceivable wherein said at least one cutting line is arranged into at least one of said upper surface and lower surface not comprising said densified outer layer.

Said second aspect, the method for producing said flexible solid cellulose foam material, is now to be described in detail.

Said method comprises the steps of:

- providing said cellulose foam material comprising said upper surface and said lower surface;

- arranging said at least one cutting line of said predetermined depth of cut DC into at least one of said upper surface and said lower surface, whereby further arranging at least one cutting line to partially cut through said cellulose foam material.

Said method further comprises arranging said at least one cutting line to partially cut through said cellulose foam material such that said predetermined depth of cut DC is less than said thickness T of said cellulose foam material. Cutting is performed by providing a cutting tool and arranging said cutting tool to be in contact with said at least one of said upper surface and said lower surface. Said cutting tool is then forced into said at least one of said upper surface and said lower surface and further into said core of said cellulose foam material thereby arranging said at least one cutting line to partially cut through said cellulose foam material.

Said predetermined depth of cut DC of said at least one cutting line is preferably 99% or less of said thickness T of said cellulose foam, more preferred 90% or less and most preferred 80% or less.

In some embodiments said method further comprises arranging said at least one cutting line to partially cut into said cellulose foam material in a direction that is perpendicular to at least one of said upper surface and said lower surface.

In other embodiments of the method said at least one cutting line is arranged to cut oblique into said material. Said at least one cutting line cuts into said material at a cutting angle CA to said upper surface or said lower surface, wherein said cutting angle is less than 90° or greater than 90°.

Said at least one cutting line is arranged to run in a direction from one edge E to an opposite edge E of said respective upper surface or lower surface; said at least one cutting line thereby forming an angle EA with said edge E.

Said angle EA may be 90°, so that said at least one cutting line meets said edge E perpendicularly or said angle EA may be less than 90° or greater than 90°.

Or, rephrasing the above aspects concerning said angle EA, said method further comprises arranging said at least one cutting line in a vertical direction, or a horizontal direction, or a direction between a vertical direction or a horizontal direction on at least one of said upper surface or lower surface. According to the method said flexible solid cellulose foam is arranged to comprise 0.1-5 cutting lines per centimetre, preferably 0.5-2 cutting lines per centimetre. In some embodiments, the flexible solid cellulose foam may comprise 0.1-10 cutting lines per centimetre.

In some embodiments, said flexible solid cellulose foam may comprise 0.2-5 cutting lines per centimetre, such as from 0.2-2, or from 0.5-5 cutting lines per centimetre.

Preferably, said flexible solid cellulose foam comprises a plurality of cutting lines, such as at least three cutting lines, or at least four cutting lines, or at least five cutting lines.

Preferably, said method further comprises arranging at least one cutting line of a predetermined depth of cut into both of said upper surface and said lower surface.

It is to be understood that said predetermined depth of cut DC may be the same on both sides or may be different on different surfaces of said foam.

It is also to be understood that said at least one cutting line of said upper surface and said at least one cutting line of said lower surface may be arranged to have same directions or to have different directions.

Said method further comprises arranging at least one of said upper surface or said lower surface of said solid cellulose foam to comprise said densified outer layer; and preferably arranging both of said at least one of said upper surface or said lower surface to comprise said densified outer layer.

MATERIALS AND MATERIAL PROPERTIES

The cellulose fibres comprised in said solid cellulose foam are preferably selected from wood pulp; regenerated cellulose fibres; and plant fibres; preferably selected from softwood pulp, chemi-thermo mechanical pulp (CTMP) and dissolving pulp or a combination thereof. Said solid cellulose foam preferably comprises: d) from 71-95 wt% cellulose fibres, as calculated on the total weight of solid content of said foam, e) from 4-24 wt% of a water-soluble thickener, as calculated on the total weight of solid content of said foam, and f) at least two surfactants.

A density of said solid cellulose foam may be in the interval of 10-80 kg/m ³ , preferably 10-60 kg/m ³ and more preferred 20-50 kg/m ³ .

At least one of said upper surface or said lower surface of said solid cellulose foam comprises a densified outer layer. Preferably, both said upper and said lower surface comprise said densified outer layer.

Said cellulose foam may have a thickness in an interval of 5-200 mm, more preferred 10-100 mm, or 10-50 mm.

An example of a conceivable dimension is a solid cellulose foam plank having a thickness of 40-60 mm, preferably around 50 mm.

Said dimensions only serve as examples and should not be seen as limiting the inventive product to said dimensions.

EXAMPLES OF DIFFERENT EMBODIMENTS

Example 1

A flexible solid cellulose foam plank comprising vertically arranged cutting lines on a top surface and horizontally arranged cutting lines on a bottom surface thereby making possible to wrap said foam material around an object while still maintaining the protective characteristics of said foam material.

Example 2 A flexible solid cellulose foam plank comprising diagonally arranged cutting lines in one direction on a top surface and diagonally arranged cutting lines in another direction on a bottom surface thereby making possible to curve and twist the foam material.

A flexible solid cellulose foam plank comprising vertically or horizontally arranged cutting lines on a top surface and diagonally arranged cutting lines on a bottom surface thereby making possible to curve and stretch the foam material.

Example 4

A flexible solid cellulose foam comprising vertically arranged cutting lines on the top surface and horizontally arranged cutting lines on the bottom surface. Said foam according to this example may be wrapped around the object to be protected, e.g. around a bottle.

In all examples 1-4, a solid cellulose foam plank with a thickness of 5 cm was cut manually using a knife. The cutting lines were arranged to cut through said cellulose foam material to a depth corresponding to 2/3 of the thickness of the foam. The distance between adjacent cutting lines was in the range of from 1 to 2 cm.

The cellulose foam plank was dry, had a density in the range of from 32 to 35 kg/m ³ and comprised from 83 to 88 wt% cellulose fibres (softwood bleached Kraft pulp), from 10 to 15 wt% thickener (CMC) and about 2 wt% surfactant (mixture of myristic acid and sodium cocoyl sarcosinate).

Said top and bottom surfaces of said flexible solid cellulose foam in the above examples comprise said densified outer layers.

As will be understood by those skilled in the present field of art, numerous changes and modifications may be made to the above described and other embodiments of the present invention, without departing from the scope of the present invention as defined in the appending claims. For example, said at least one cutting line may be of other forms than a straight line. Said cutting line may e.g. be a curved cutting line, a zigzagshaped cutting line etc.

Said flexible solid cellulose foam may comprise compressed regions.

At least one of said upper surface and lower surface may be a curved surface.

It should be noted that the above described aspects may be the subject for its own protection, as such in a separate divisional application. Hence, it is foreseen that this aspect of the invention may require a protection by its own, e.g. since it may be applicable per se also in other concepts than that defined by the independent claim in this application.