PROCESS FOR MANUFACTURING A FIBER BASED CELLULOSE WEB FOR DRY FORMING

Abstract

The present inventive concept relates to a process for manufacturing a fiber based cellulose web for dry forming comprising. The process comprises providing a wet cellulose pulp; free drying said wet cellulose pulp to a free dried cellulose pulp, wherein said free drying provides a curl to fibres of said free dried cellulose pulp; separating said free dried cellulose pulp into individual free dried cellulose pulp fibres; and forming said individual free dried cellulose pulp fibres into a cellulose web.

Claims

1. A process for manufacturing a fiber based cellulose web for dry forming comprising: a) providing a wet cellulose pulp; b) free drying said wet cellulose pulp to a free dried cellulose pulp, wherein said free drying provides a curl to fibres of said free dried cellulose pulp, said step of free drying being performed in hot air, by using flash drying, the hot air temperature being above 100° C., preferably above 130° C., and most preferably above 150° C.; c) compacting said free dried cellulose pulp to a density between 50-500 kg/m.sup.3, or 100-400 kg/m.sup.3, or preferably between 200-300 kg/m.sup.3; d) separating said free dried cellulose pulp into individual free dried cellulose pulp fibres; e) forming said individual free dried cellulose pulp fibres into a cellulose web.

2. A process according to claim 1, wherein said free dried cellulose pulp is compacted into a bale and wherein said bale is opened before said individual free dried cellulose pulp fibres are formed into a web.

3. A process according to claim 1, further comprising adding one or more additives to said wet cellulose pulp to provide any one or a combination of hydrophobicity, strength, increased bulk properties, and debonding and to obtain a homogenous distribution of said additives.

4. A process according to claim 1, wherein air is used in said step of forming said individual free dried cellulose pulp fibres into a cellulose web, such that said cellulose web is airlaid.

5. A process according to claim 1, wherein said free drying is performed until said free-dried cellulose pulp has a moisture content of 5-20%, and preferably 7-12%.

6. A process according to claim 1, wherein said free drying is performed in less than 10 minutes and preferably less than 5 minutes.

7. A fiber based cellulose web manufactured by the process according to claim 1, for dry forming of cellulose products.

8. A fiber based cellulose web according to claim 7, wherein said cellulose web is airlaid.

9. A fiber based cellulose web according to claim 7, wherein fibres of said free dried cellulose pulp has a shape factor of less than 83%, for example 80%, when formed into a web.

10. A fiber based cellulose web according to claim 7, having an elongation at break of at least above 17%, preferably above 20%, and most preferably above 25%, measured according to ISO 12624-4: 2017.

11. The use of the fiber based cellulose web according to claim 7 in dry forming of rigid flat and/or 3D products.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0061] Non-limiting embodiments of the present disclosure will be described in greater detail with reference to the accompanying drawings in which:

[0062] FIG. 1 shows a schematic view over a continuous web formation process,

[0063] FIG. 2 shows a schematic view over a discontinuous web formation process,

[0064] FIG. 3 shows a schematic view over a continuous dry moulding process based on the web forming process described in FIG. 1, and

[0065] FIG. 4 shows a schematic view over a discontinuous dry moulding process based on the web forming process described in FIG. 2.

DETAILED DESCRIPTION

[0066] FIG. 1 shows a schematic view over a continuous web formation process. In the first step, wet cellulose pulp fibres (5) are provided. The wet cellulose pulp (5) may be provided directly from a pulp mill. Optionally, the wet cellulose pulp is impregnated with one or several additives (9) before it is subjected to free drying (50), such as flash drying. Non-limiting examples of additives are alkyl ketene dimer (AKD), Alkenyl Succinic Anhydride (ASA), rosin compounds, Sodium Carboxymethyl Cellulose (CMC), cationic polyacrylamide (C-PAM), starch compounds such as cationic starch (native or modified), Polyethyleneimine (PEI), polymaleic acid, poly-carboxylic acids such as Citric acid or butane tetracarboxylic acid (BTCA).

[0067] Free drying means that wet fibres are subjected to hot air without being subjected to restraint, i.e. dried in a free state. Thus, the free dried fibres adapt a natural curly shape. The temperature of the hot air in the free drier (50) may be above 150° C. The temperature of the hot air may be stepwise increased or stepwise decreased during the step of free drying. Alternatively, the temperature of the hot air is constant during the step of free drying. The time for free drying is preferably less than 5 minutes. During the step of free drying (50), the moisture content of the wet fibres (5) decreases to an interval of 7-12%.

[0068] In the next step, the free dried cellulose pulp (50) is transported to a separating unit (8). Non-limiting examples of separator unit for separation of the free dried cellulose pulp into individual free dried cellulose pulp fibres are hammermill and dosing unit. In the separator unit the free dried cellulose pulp is separated into individual free dried cellulose pulp fibres. The separation of individual free dried cellulose pulp fibres is advantageous to avoid an inhomogeneous distribution of cellulose pulp fibres in the cellulose web (10). After the separating unit (8), the free dried fibres are formed into a cellulose web (10) in a web formation unit. The cellulose web can be provided either as a monolayer or as part of a multilayer material matrix, supplemented by e.g. films of tissue or polymer.

[0069] This step may be used by air as carrying medium which results in a cellulose web in the form of an air laid. The curls of the free dried fibres enhance entanglement of the cellulose pulp fibres which results in a cellulose web provided with high toughness. High toughness of the cellulose web is beneficial to provide good runnability in a subsequent the step of pressure moulding. The high toughness of the cellulose web makes it possible to press complex products of 3-D shape in the pressure mould.

[0070] FIG. 2 shows a schematic view over a discontinuous dry moulding process. The first three steps are the same as in FIG. 1; wet pulp (15) is provided and subjected to free drying (150) with an optional addition of additives (19) before the step of free drying (150).

[0071] Thereafter, the free dried fibres are compacted (10) to the desired density and packed into a sack, truck, or a bale. It is important that the free dried cellulose pulp is compacted with a low pressure such that the curls of the free dried cellulose pulp is maintained. Compacting is preferably performed until the density of the free dried cellulose pulp is up to 500 kg/m.sup.3 and not more since this could negatively affect the curls of the free dried cellulose pulp. Compacting and bale formation enhances transportation of the free dried cellulose pulp to the web formation. Before the free dried cellulose pulp enters the web formation unit (110), the bales are opened by means of a bale opener (11) and the individual pulp fibres are separated in one or several separating units (18) as described in FIG. 1.

[0072] After the separating unit (18), the free dried cellulose pulp is formed into a cellulose web in the web formation unit (110).

[0073] FIG. 3 shows a schematic view over a continuous dry moulding process based on the web formation process described in FIG. 1. After the step of web formation (110), the fiber based cellulose web is fed to a pressure mould (12). The fiber based cellulose web may be fed to the pressure mould either continuously or discontinuously from the web formation (10). High toughness of the cellulose web makes it possible to press complex products of 3-D shape (20).

[0074] FIG. 4 shows a schematic view over a discontinuous dry moulding process based on the web formation process described in FIG. 2.

[0075] After the step of web formation (110), the fiber based cellulose web is fed to a pressure mould (112). The fiber based cellulose web may be fed to the pressure mould either continuously or discontinuously from the web formation (110). High toughness of the cellulose web makes it possible to press complex products of 3-D shape (120).

EXAMPLES

[0076] Non-limiting embodiments of the present disclosure will be described with reference to the following example.

Example 1

[0077] Tables 1, 2 and 3 comprise data derived from a reference material (air laid made from fluff pulp), test material A (air laid made from free dried pulp A), and test material B (air laid made from free dried pulp B).

[0078] As mentioned before, a cellulose web made from free dried cellulose pulp has the advantage of increased tensile strength and improved elongation at break. These measurements together indicate high toughness and ability of the cellulose web to drape.

[0079] The data shown in table 1, 2 and 3 clearly support the statement above; the tensile strength index is higher for both Test material A and Test material B in comparison to the reference material in both machine direction (MD) and in counter machine direction (CD). The Geometric Mean (GMT) is 118% higher for Test material A and 64% higher for Test material B than the reference.

[0080] In addition, the elongation at break is improved for both Test material A and Test material B in comparison to the reference material. The GMT is 118% higher for Test material A and 64% higher for Test material B than the reference.

[0081] Hereby, it is clearly shown that free drying has a positive impact on the toughness of the cellulose web.

TABLE-US-00001 TABLE 1 Test data derived from measurements in MD direction Test Test Airlaid fluff pulp material material (reference) A B Tensile strength index Nm/g 0.018 0.041 0.032 Elongation at break % 15.1 25.6 24.7 Tensile Energy J/kg 1.67 5.83 4.32 Absorption index (TEA) Increase Tensile % 0 133 83 Increase Elongation % 0 70 64 Increase TEA % 0 249 158

TABLE-US-00002 TABLE 2 Test data derived from measurements in CD direction Test Test Airlaid fluff pulp material material (reference) A B Tensile strength index Nm/g 0.023 0.047 0.034 Elongation at break % 17.2 30.4 29.0 Tensile Energy J/kg 2.42 7.91 5.39 Absorption index (TEA) Increase Tensile % 0 104 48 Increase Elongation % 0 77 69 Increase TEA % 0 226 123

TABLE-US-00003 TABLE 3 Test data derived from calculation of the geometric mean [√(MD*CD)]. Test Test Airlaid fluff pulp material material (reference) A B Tensile strength index Nm/g 0.020 0.044 0.033 Elongation at break % 16.1 27.9 26.7 Tensile Energy J/kg 2.01 6.79 4.83 Absorption index (TEA) Increase Tensile % 0 118 64 Increase Elongation % 0 73 66 Increase TEA % 0 237 140

[0082] The shape of the free dried cellulose pulp is more curled and/or more twisted than the shape of a cellulose fiber that has been subjected to restrained drying or press after drying. The curl of a fiber can be measured by calculation of shape factor; defined as the projected length of the fiber divided by its fully length when stretched out. By free drying it is possible to obtain a cellulose pulp fiber having a lower shape factor than what is possible for sheet pulp fibres or fluff pulp fibres. This is visualized in table 4 showing that the shape factor of free dried cellulose pulp fibres (whether compacted or not) have lower shape factor (80-82%) than the shape factor of fluff pulp and sheet pulp (84-86%).

[0083] Free dried cellulose pulp fibres that has been compacted is higher than the shape factor of free dried cellulose pulp that is not compacted. The former has a shape factor of 82% and the latter has a shape factor or 80%.

TABLE-US-00004 TABLE 4 Test data derived from Shape factor [%] Sheet pulp 84-86 Fluff pulp on role 86 Free dried pressed cellulose 82 pulp - bale Free dried cellulose pulp - 80 not compacted