Method of forming a fibrous product

Abstract

The present invention relates to a method of forming a molded fibrous product, comprising the steps of foaming an aqueous suspension of natural fibers, optionally in combination with synthetic fibers, to provide a first fibrous foam, a surfactant may be added to aid the foaming, feeding the fibrous foam into a mold, mechanically withdrawing a part of the water contained in the foam to produce a solidified, moist fibrous composition, and evaporating water from the solidified, moist fibrous composition to produce a dry fibrous product.

Claims

1. A method of forming a molded fibrous product having a density of 5 to 100 kg/m3 and an air content of 90 to 99.5% by volume, said product containing fibers, which are bonded together essentially by hydrogen bonds and an inner part of the product is essentially free from thermoplastic bonding agents and thermoplastic fibers, said method comprising the steps of: foaming an aqueous suspension comprising natural fibers to provide a first fibrous foam, feeding the first fibrous foam into a mold, mechanically withdrawing a part of the water contained in the first fibrous foam to produce a solidified, moist fibrous composition, and evaporating water from the solidified, moist fibrous composition to produce a dry fibrous product, wherein water is removed from the fibrous foam by suction, the mold comprises an internal surface for receiving the fibrous foam and an opposite external surface, at least one side of the internal surface being made of permeable material adapted to retain fibrous material and to allow passage of water from the internal surface to the external surface, and the mold further comprising on the internal surface a protruding three-dimensional male part, covered on the internal surface with a permeable material, said male part corresponding to a cavity in the dry fibrous product, wherein the male part is covered on the internal surface with a permeable material the natural fibers have an average length of greater than 0.1 mm.

2. The method according to claim 1, further comprising foaming the aqueous suspension to a fibrous foam having an air content of more than 30% by volume of the foam.

3. The method according to claim 1, wherein the fibrous foam is provided by a method selected from: intensive mixing of the aqueous suspension of the fibers; reducing of pressure; dispersing of air into the aqueous suspension of the fibers by injection; or a combination of any of the afore-mentioned methods.

4. The method according to claim 3 wherein reducing of pressure is achieved by increasing temperature of the aqueous suspension of the fibers.

5. The method according to claim 1, wherein the consistency of the aqueous suspension is 0.1-10% based on the weight of the suspension.

6. The method according to claim 1, wherein the moist fibrous foam has a water content of up to 70% by volume of the suspension.

7. The method according to claim 1, wherein the dry fibrous product has a water content of 12% by weight or less.

8. The method according to claim 1, wherein a surfactant is incorporated into the aqueous suspension to enhance foam formation.

9. The method according to claim 1, further comprising forming a homogenous multi-phase mixture by foaming of the aqueous suspension of natural fibers.

10. The method according to claim 1, wherein the mold comprises two internal surfaces which face each other and which allow for removal of water in opposite directions.

11. The method according to claim 1, wherein the suction is applied to the fibrous foam from the external surface of the mold.

12. The method according to claim 1, wherein the suction subjects the fibrous foam to a pressure.

13. The method according to claim 1, wherein evaporation is effected by means selected from the group of microwaves, infrared waves, air impingement, air drying, and convective drying and combinations thereof.

14. The method according to claim 1, wherein a second fibrous foam of fibers is fed into the mold on top of the first fibrous foam so as to cover at least a portion of the first fibrous foam fed into the mold.

15. The method according to claim 14, further comprising feeding into the mold further fibrous foams on top of preceding fibrous foams to form a multilayered dry fibrous product.

16. The method according to claim 14, further comprising removing water and drying of the second or further fibrous foam(s).

17. The method according to claim 14, comprising: withdrawing by suction a part of the water contained in the first foam before feeding the second fibrous foam, or feeding the first and the second and further foams consecutively into the mold before applying suction in order to withdraw water from the foams.

18. The method according to claim 14, wherein the fibers of the second or further fibrous foam(s) are different from those of the first or of the preceding fibrous foam(s).

19. The method according to claim 1, wherein the fibers of the first fibrous foam are selected from the group of thermomechanical pulp fibers, chemithermomechanical pulp fibers, kraft pulp fibers, sulphite pulp fibers, soda pulp fibers, dissolving pulp fibers, fluff pulp fibers, NBSK pulp fibers, SBSK pulp fibers, recycled pulp fibers, deinked pulp fibers, organosolv pulp fibers, bleached pulp fibers and mixtures thereof.

20. The method according to claim 1, further comprising producing a three-dimensional object having a smallest dimension of at least 5 mm.

21. The method according to claim 20, further comprising producing a package or package material.

22. The method according to claim 1, further comprising foaming the aqueous suspension to a fibrous foam having an air content between 50 and 90% by volume of the foam.

23. The method according to claim 1, wherein the product is essentially free from thermoplastic bonding agents or thermoplastic fibers, and the natural fibers are bonded together only by hydrogen bonds.

24. The method according to claim 1, wherein the fibers are uncut fibers.

25. The method according to claim 1, wherein all fibers of the fibrous product have an average length of greater than 0.1 mm.

26. The method according to claim 1, wherein the fibers of the fibrous product have an average length of greater than 1 mm.

27. The method according to claim 1, wherein the fibers of the fibrous product have an average length in the range of 2 mm to 100 mm.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) Next the invention will be examined more closely with the aid of a detailed description and with reference to the attached drawings, in which:

(2) FIG. 1 is a schematic flow chart showing the basic steps of a method according to the present invention of forming a moulded fibrous product;

(3) FIG. 2A shows in axonometric depiction a moulded fibrous product according to a first embodiment;

(4) FIG. 2B is another axonometric depiction of a second embodiment comprising a multilayer fibrous product;

(5) FIG. 3A shows in sideview a mould used in mechanical dewatering of a fibrous foam according to the present invention;

(6) FIG. 3B shows in sideview the mould of FIG. 3A applied to evaporation of water from a solidified moist fibrous composition; and

(7) FIG. 4 shows a multilayered moulded fibrous product of the present invention.

DESCRIPTION OF EMBODIMENTS

(8) The present invention relates to a method of forming a moulded fibrous product, comprising the steps of foaming an aqueous suspension of natural fibres, optionally in combination with synthetic fibres, to provide a first fibrous foam, a surfactant optionally being added to aid the foaming, feeding the fibrous foam into a mould, mechanically withdrawing a part of the water contained in the foam to produce a solidified, moist fibrous composition, and evaporating water from the solidified, moist fibrous composition to produce a dry fibrous product.

(9) The present moulded fibrous products are three-dimensional objects typically having a smallest dimension (e.g. thickness) of at least 1 mm, preferably at least 5 mm, in particular at least 10 mm or more, for example their smallest dimension is 20 to 100 mm. The objects can be formed by one fibrous layer or by a plurality of overlapping layers. The objects have an inner part and a surface part, the latter having a thickness or depth (normal distance from the surface area) of at least 0.1 mm. In some cases the thickness of the surface part is roughly 0.1 to 50 mm, typically about 0.1 to 10 mm. By incorporating synthetic polymers into the surface part of the objects improved mechanical properties, such as hardness or smoothness, can be achieved.

(10) FIG. 1 illustrates one exemplary embodiment of a method of forming a moulded fibrous product in which fibres, water and surfactant undergo foaming 1 to provide a fibrous foam, which is then fed into a mould. A part of the water is then withdrawn mechanically 2 from the fibrous foam to produce a solidified, moist fibrous composition. Water is then evaporated 3 from the moist fibrous composition to produce a dry fibrous product.

(11) For the purpose of the present technology the terms fibre and fibres have broad meanings.

(12) Typically, the fibre or fibres have an average aspect ratio (average length:average thickness) of 6 or more, in particular 10 or more. The average length of the fibres is greater than 0.1 mm, in particular greater than 0.5, for example greater than about 1 mm, suitably greater than about 1.5 mm, preferably in the range from about 2 up to 100 mm, such as 2 up to 50 mm. Typically at least 75%, in particular at least 80%, suitable at least 85%, of the fibres will meet those criteria, said percentage being calculated by weight of the total weight of the fibres. The composition of fibres may contain individual fibres having lengths greater than the ones mentioned above. The above ranges are applicable separately to both the natural fibres (as defined below) as well as synthetic or thermoplastic fibres. Preferably, the fibres are uncut.

(13) The source of the fibres may be derived from various sources. The fibres can be natural or synthetic, animal, vegetable or mineral, or diverse mixtures of any of these sources. The fibres may be virgin fibres, the fibres may also be recycled from various sources by e.g. defibering. The fibres may be a mixture of fibres and recycled fibres.

(14) The terms fibre and fibres cover a large variety of materials including but not limited to thermomechanical pulp fibres, chemithermomechanical pulp fibres, kraft pulp fibres, sulphite pulp fibres, soda pulp fibres, dissolving pulp fibres, fluff pulp fibres, NBSK pulp fibres, SBSK pulp fibres, recycled pulp fibres, deinked pulp fibres, organosolv pulp fibres, bleached pulp fibres, as examples of natural fibres. Examples of synthetic fibres (thermoplastic polymer fibers) include but are not limited to polyester fibres, aramid fibres, acrylonitrile fibres, polylactide fibres, aromatic polymide fibres, polyamide fibres, polyurethane fibres, polyethylene fibres, polypropylene fibres and combinations thereof.

(15) A method of forming a moulded fibrous product is disclosed. In one embodiment an aqueous suspension of natural fibres, optionally in combination with synthetic fibres, is foamed to provide a first fibrous foam. The fibrous foam is fed into a mould. Part of the water contained in the foam is withdrawn mechanically to produce a solidified moist fibrous composition. Water is evaporated from the solidified moist fibrous composition to produce a dry fibrous product.

(16) For some applications only natural fibres are preferred e.g. if method of disposal is of concern, natural fibres from renewable resources are selected. By varying the proportion of synthetic fibres used in the process, the physical properties of the moulded fibrous product can be tailored according to its intended application.

(17) In an embodiment the aqueous suspension is foamed to a fibrous foam having an air content of more than 30%, preferably 50 to 90%, by volume of the foam. In a further embodiment the fibrous foam is provided by a method selected from intensive mixing of the aqueous suspension of the fibres, reducing of pressure, optionally by increasing temperature of the aqueous suspension of the fibres, dispersing of air into the aqueous suspension of the fibres by injection and a combination of any of the aforementioned methods.

(18) A further embodiment comprises producing a dry fibrous product wherein the fibres of the product are bonded together essentially by hydrogen bonds. The hydrogen bonds may be formed e.g. between hydroxyl groups on the fibres' surfaces.

(19) The bonding provided by hydrogen bonds can be supplemented by bonding achieved with synthetic fibres, which for example are melted during the production. In particular, in one embodiment, hydrogen bonds supply the bonding within the material formed by natural fibres and thermoplastic polymers achieve bonding in or on the surface of the object.

(20) Thermal bonding by melting of synthetic polymers will be discussed below.

(21) In a particular embodiment the fibre consistency of the aqueous suspension is 0.1-10%, preferably 0.5 to 5% based on the weight of the suspension. In a preferred embodiment the moist fibrous foam has a water content of up to 70% by volume, preferably 30 to 50% by volume of the suspension. In a still further embodiment the dry fibrous product has a water content of 12% by weight or less.

(22) Further embodiments disclose the incorporation of a surfactant into the aqueous suspension. In one embodiment a surfactant is incorporated into the aqueous suspension to enhance foam formation. In a further embodiment the surfactant is selected from inorganic surfactants, organic surfactants and mixtures thereof. In a particular embodiment the surfactant is selected from the group of calcium sodium 2,2,2,2-(1,2-ethanediyldinitrilo)tetraacetate (1:2:1), hexadecanol, hexadecyl palmitate, cholesterol, ethanolamine, D-fructose, gelatine, D(+) glucose monohydrate, gum arabic, D() mannitol, oleic acid, sorbitol, polyethylene glycol, polyvinyl alcohol, potassium iodate, 1,2-propanediol, sodium dodecyl sulfate, starch, sucrose, disodium dihydrogen ethylenediaminetetraacetate, wax, D(+)-xylose, azodicarbonamide (ADCA), azobisformamide (ABFA), azobisisobutyronitrile (AIBN), N,N-denitroso pentamethylene tetrarnine (DPT), P-toluenesulfonyl hydrazide (TSH), P,P-Oxybis(benzenesulfonyl hydrazide) (OBSH), ammonium carbonate and sodium hydrogen carbonate, and mixtures thereof.

(23) One embodiment discloses forming a homogenous multi-phase mixture by foaming of the aqueous suspension of natural fibres, which optionally contains synthetic fibres.

(24) A further embodiment discloses removing water from the fibrous foam by suction.

(25) In one embodiment the mould comprises an internal surface for receiving the fibrous foam and an opposite external surface, at least one side of the internal surface being made of a permeable material adapted to retain fibrous material and to allow passage of water from the internal surface to the external surface. In a further embodiment the mould comprises two internal surfaces which face each other and which allow for removal of water in opposite directions. In a particular embodiment the mould comprises on the internal surface a protruding three-dimensional male part corresponding to a cavity in the dry fibrous product. In a suitable embodiment the male part is covered on the internal surface with a permeable material.

(26) The above embodiment is particularly suitable for producing packages in particular cushioning packages. Examples include packages for fragile products which can be placed in the cavity. Such a cavity efficiently cushions the product.

(27) In one embodiment the suction is applied to the fibrous foam from the external surface of the mould. In a preferred embodiment the suction subjects the fibrous foam to a pressure.

(28) In a still further embodiment evaporation is effected by means selected from the group of microwaves, infrared waves, air impingement, air drying, and convective drying and combinations thereof.

(29) Further embodiments disclose feeding further fibrous foams into the mould. In one embodiment a second fibrous foam of fibres is fed into the mould on top of the first fibrous foam so as to cover at least a portion of the first fibrous foam fed into the mould. In a further embodiment further fibrous foams are fed into the mould on top of preceding fibrous foams to form a multilayered dry fibrous product.

(30) One embodiment comprising removing water and drying of the second or further fibrous fibrous foam(s) is disclosed. A further embodiment comprises withdrawing by suction a part of the water contained in the first foam before feeding the second fibrous foam or feeding the first and the second and further foams consecutively into the mould before applying suction in order to withdraw water from the foams.

(31) In a preferred embodiment the fibres of the first fibrous foam are selected from the group of thermomechanical pulp fibres, chemithermomechanical pulp fibres, kraft pulp fibres, sulphite pulp fibres, soda pulp fibres, dissolving pulp fibres, fluff pulp fibres, NBSK pulp fibres, SBSK pulp fibres, recycled pulp fibres, deinked pulp fibres, organosolv pulp fibres, bleached pulp fibres and mixtures thereof, optionally in combination with synthetic polymer fibres, such as thermoplastic polymer fibres.

(32) Examples of synthetic fibres which can be used in the first fibrous foam(s) include polyester fibres, aramid fibres, acrylonitrile fibres, polylactide fibres, aromatic polymide fibres, polyamide fibres, polyurethane fibres, polyethylene fibres, polypropylene fibres and combinations thereof.

(33) In a further embodiment the fibres of the second or further fibrous foam(s) are selected from the group of thermomechanical pulp fibres, chemithermomechanical pulp fibres, kraft pulp fibres, sulphite pulp fibres, soda pulp fibres, dissolving pulp fibres, fluff pulp fibres, NBSK pulp fibres, SBSK pulp fibres, recycled pulp fibres, deinked pulp fibres, organosolv pulp fibres, bleached pulp fibres and mixtures thereof, optionally in combination with synthetic polymer fibres, such as thermoplastic polymer fibres.

(34) Examples of synthetic fibres which can be used in the second fibrous foam(s) include polyester fibres, aramid fibres, acrylonitrile fibres, polylactide fibres, aromatic polymide fibres, polyamide fibres, polyurethane fibres, polyethylene fibres, polypropylene fibres and combinations thereof.

(35) In addition to the above-disclosed synthetic polymer material fibres, which typically comprise only one polymer material, it is also possible to use bicomponent fibres. Such fibres are typically formed by a first polymer material forming a core of the fibre and being surrounded by a second polymer material.

(36) Preferably, the first material has a first melting point and the second has a second melting point, which is different from the first melting point. Usually the first material has a higher melting point that the second material surrounding it, whereby the fibre essentially maintains its shape during melting.

(37) By applying heat to the material, the synthetic fibres (or the surface layer thereof) will melt and achieve bonds within the material formed by the natural fibres, thus improving interfibre bonding. Suitably the bicomponent fibres are located in the surface part of the objects to achieve stronger bonds and a tougher or harder surface.

(38) Naturally, it is possible to enhance bonding by incorporating chemical binding agents, such as latexes, or nanocellulose.

(39) The present three-dimensional objects can be given a hard surface by heating the surface optionally in combination with pressing, or by building structures having several overlapping layers.

(40) The methods used for evaporation can also be used for melting of the synthetic (thermoplastic) polymer portion. Thus, in particular microwaves, infrared waves, air impingement, air heating, and convective heating and combinations thereof can be used.

(41) The weight ratio of natural to synthetic fibres is generally about 1000:1 to 1:100, in particular 500:10 to 10:100, for example 100:10 to 100:100.

(42) In a suitable embodiment the fibres of the second or further fibrous foam(s) are different from those of the first or of the preceding fibrous foam(s). In a preferred embodiment the fibres of the first fibrous foam are selected from chemical fibres which optionally are bleached.

(43) Further embodiments disclose a lightweight moulded fibrous product. One embodiment discloses a moulded fibrous product having a density of 5 to 100 kg/m.sup.3 and an air content of 90 to 99.5% by volume, said product containing fibres, which are bonded together essentially by hydrogen bonds. In an embodiment the product is essentially free from thermoplastic bonding agents. In a suitable embodiment the product comprises bonding agents selected from the group of chemical bonding agents, nanocellulose and a mixture thereof. However, as discussed above, the product may contain at least some synthetic fibres, such as thermoplastic fibers for achieving improved bonding, e.g. in the surface layer thereof.

(44) In one embodiment the product comprises at least a first layer, particularly a second layer, suitably multiple layers. In a further embodiment at least one layer comprises mechanical pulp fibres, selected from the group of mechanical pulp fibres, thermomechanical pulp fibres, chemithermomechanical pulp fibres, and a combination thereof. In a particular embodiment at least one layer comprises chemical pulp fibres, selected from the group of chemithermomechanical pulp fibres, kraft pulp fibres, sulphite pulp fibres, soda pulp fibres, dissolving pulp fibres, fluff pulp fibres, NBSK pulp fibres, SBSK pulp fibres, recycled pulp fibres, deinked pulp fibres, organosolv pulp fibres, bleached pulp fibres, polyester fibres, aramid fibres, acrylonitrile fibres, polylactide fibres, aromatic polymide fibres, polyamide fibres, polyurethane fibres, polyethylene fibres, polypropylene fibres and a combination thereof.

(45) FIG. 2A illustrates an exemplary embodiment of a moulded fibrous product of the invention suitable for use as a packaging material, comprised of a single layer 11 of moulded fibres, said single layer 11 of moulded fibres comprising an upper surface 10 and a lower surface (not shown), the upper surface characterised in that it comprises a moulded cavity having a lower surface 12 and side surfaces 13, said lower surface 12 and side surfaces 13 having a form appropriate to an item or items that is(are) to be packed.

(46) FIG. 2B illustrates a further embodiment of a moulded fibrous product of the invention suitable for use as a packaging material, comprised of a first layer 18 of moulded fibres and a second layer 15 of moulded fibres, said second layer 15 aligned with said first layer 18 providing a moulded fibrous product with one upper surface 14 and one lower surface (not shown). The upper is surface characterised in that it comprises a moulded cavity having a lower surface 16 and side surfaces 17, said lower surface 16 and side surfaces 17 having a form appropriate to an item or items that is(are) to be packed.

(47) FIG. 3A illustrates mechanical dewatering of a fibrous foam in a mould comprising an upper opening, a water tight wall 21, a first water permeable wall 22 and a second water permeable wall 23 positioned about a three-dimensional male part intruding the mould, the mould further comprising a third water permeable wall 24 fitted around the three-dimensional male part. Water is withdrawn mechanically through the water permeable walls 22, 23, 24 by e.g. suction or gravity or a combination thereof, to give a moist fibrous composition.

(48) FIG. 3B illustrates the evaporation of water from a moist fibrous composition in a mould comprising an upper opening, a water tight wall 21, a first water permeable wall 22 and a second water permeable wall 23 positioned about a three-dimensional male part intruding the mould, the mould further comprising a third water permeable wall 24 fitted around the three-dimensional male part. Water is evaporated from the moist fibrous composition through the upper opening of the mould by e.g. microwaves, infrared waves, air impingement, air drying, and convective drying or combinations thereof, to give a dry fibrous product.

(49) As disclosed herein, embodiments of the present technology provide for composition comprising natural fibres mixed with synthetic fibres. The latter ones can be dispersed evenly throughout the fibrous bulk formed by the natural fibres. The synthetic fibers may also be located primarily on the surfaces of the three-dimensional objects. The objects are typically dried and hardened.

(50) Thus, based on the above, the present products can be comprised of natural fibres and synthetic fibres, which are evenly mixed to form objects which have a uniform density throughout the object, optionally with the exception of the surface layers which can have a higher content of synthetic fibres for improved surface properties (e.g. hardness).

(51) The present products may also be comprised of layered structures formed by overlapping layers on one hand consisting of natural fibres and on the other hand consisting of synthetic fibres, respectively. The number of layers is typically 2 to 50.

(52) Finally the present products may also be comprised of layered structures which contain a plurality of layers, for example 2 to 50 layers, of mixtures of natural fibres and synthetic fibres interspersed by layers (typically 1 to 40) consisting of natural fibres.

LIST OF REFERENCE NUMBERS

(53) 1 Foaming 2 Mechanical withdrawal of water 3 Evaporation of water 10 Upper surface of moulded fibres 11 Single layer of moulded fibres 12 Lower surface of moulded cavity 13 Side surface of moulded cavity 14 Upper surface of moulded fibrous product 15 Second layer of moulded fibres 16 Lower surface of moulded cavity 17 Side surface of moulded cavity 18 First layer of moulded fibres 21 Water tight wall 22 First water permeable wall 23 Second water permeable wall 24 Third water permeable wall

(54) The following non-limiting examples are intended to merely illustrate the methods and products according to the preferred embodiments of the invention.

EXAMPLES

Example 1

(55) Into 8-10 liters of water was mixed 250 g of unground long fibre cellulose to form a suspension. Into the suspension was added 2 g/l of sodium dodecyl sulphate (SDS) and the suspension was foamed. A first layer of the foamed suspension was poured into a mould with dimensions 500 mm500 mm. The first layer of the foamed suspension was provided with a blue surface by impregnation of the foam with a dye by suction (15 s). A second layer of the foamed suspension was poured into the mould. After the addition of the second foam, aearation was carried out for 10 seconds. The mould was then placed into a fan-assisted oven at 90 C. for 15-20 hours overnight and the mould was opened the following morning. The moulded fibrous product was then cut to size.

INDUSTRIAL APPLICABILITY

(56) Industries in which the present invention may be applied include packaging, sound proofing and thermal insulation.

(57) As will appear from the above, the present technology is particularly suitable for producing containers, packagings, wrappings and packages, including packages as such as (for example cushioning packages), well as blanks for packages.

(58) In one embodiment, the present technology provides for packages. Particularly interesting packages are formed by relatively thick layers of material. Suitable thicknesses of the layers are 5 mm or more, in particular 7.5 mm up to about 1000 mm, for example 10 mm to 500 mm.

CITATION LIST

Patent Literature

(59) 1. GB 2 303 630 2. JP 5 263 400 3. US2002117768 4. JP2010215872 5. WO2012006714