Method to form a web comprising fibers

Abstract

The invention discloses a method to enable the efficient use of surfactants in web forming of a cellulose containing material, e.g. in the making of paper or paperboard. The method comprises the addition of microfibrillated cellulose (MFC) or nanocrystalline cellulose (NCC) to the white water in a web-forming process in order to form complexes with surface active agents. The formed complexes are at least partly recycled to the process. This enables the producer to have control over the concentration of surface active agents in the system.

Claims

1. A method to form a continuous web comprising fibers and/or fibrils, which method comprises the steps of: providing a furnish comprising fibers and/or fibrils and a surface active agent, applying said furnish onto a wire to form a web, draining white water from said web, adding microfibrillated cellulose (MFC) and/or nanocrystalline cellulose (NCC) to said white water, whereby said surface active agent is bonded to or physically interacting with said MFC or NCC forming a complex, recycling said complex to the furnish and/or to the web.

2. A method according to claim 1, wherein said complex, comprising the MFC or the NCC and the surface active agent, is separated from at least a part of the white water before being recycled to the furnish.

3. A method according to claim 1, wherein the MFC or NCC has a specific surface area of at least 5 m.sup.2/g.

4. A method according to claim 1, wherein a coagulant is added to the white water in addition to the MFC or NCC.

5. A method according to claim 4, wherein the coagulant is selected from the group consisting of alum, polyaluminium chloride (PAC), polydiallyldimethylammonium chloride (poly-DADMAC), polyamines and ferric sulphate.

6. A method according to claim 1, wherein the surface active agent is a cationic or an amphoteric surface active agent and the MFC or NCC is unmodified.

7. A method according to claim 1, wherein the surface active agent is an anionic surface active agents and the MFC or NCC is cationic.

8. A method according to claim 1, wherein the surface active agent is a nonionic surface active agent and the MFC or NCC is hydrophobic or native.

9. A method according to claim 1, wherein the complex is recycled to the web by the addition of the complex to a coating or surface sizing composition applied onto the web and wherein said coating or surface sizing composition further comprises a metal salt.

10. A method to form a web according to claim 1, wherein the furnish comprising the surface active agent is a foamed furnish.

11. A method to form a web according to claim 1, wherein the web is a paper or a paperboard ply.

12. A method to form a web according to claim 1, wherein the web is an MFC film.

13. A method to form a web according to claim 1, wherein the web is a nonwoven fabric.

14. A method according to claim 1, wherein the MFC or NCC has a specific surface area of at least 10 m.sup.2/g.

15. A method according to claim 1, wherein the MFC or NCC has a specific surface area of at least 15 m.sup.2/g.

16. A method according to claim 1, wherein the MFC or NCC has a specific surface area between 15-200 m.sup.2/g determined for a freeze-dried material by adsorption of nitrogen gas according to the BET method.

Description

(1) Embodiments of the invention will now be described, by way of examples, with reference to the accompanying schematic drawing.

(2) FIG. 1 shows schematically the forming section of a paper or paperboard machine.

(3) With reference to FIG. 1, and in accordance with one embodiment of the invention, a furnish comprising cellulose fibers and a surface active agent is applied on a forming wire (2) from a headbox (1).

(4) In the embodiment of manufacturing of paper or paperboard, the furnish may comprise further additives well known in the art for paper- or board making, e.g. fillers, such as clay, talc, silica, and or calcium carbonate, chemicals such as dyes, optical brightening agents, wet strength chemicals, strength chemicals, fixatives, biocides, sizing agents, drainage and retention agents etc. The furnish is a mixture of water, fibers, surface active agents and other additives and usually have a consistency of e.g. 0.5-2% in the headbox. The furnish may comprise chemical or mechanical pulp from hardwood and/or softwood fibers. It can also contained recycled pulp, deinked pulp, coated or uncoated broke or mixture of various pulps. The pulp might also contain synthetic fibers.

(5) After the furnish is applied onto the wire forming a sheet, white water is drained from the sheet through the wire (2) and, at least partly, recirculated to the furnish preparation in a circulation loop (4). In accordance with the invention, MFC or NCC is added to the white water (5), after it has been drained from the sheet, but before it is recirculated to the stock preparation. At this stage, the white water, in addition to surface treatment agents, may comprise fibers, fines and chemicals, and usually has a consistency of less than 0.5%, e.g. between 0.01-0.5% or 0.01-0.3%. At such low consistencies, the MFC or NCC added can efficiently form complexes with the surface treatment agents present in the white water.

(6) Before being recirculated to the furnish preparation, the white water passes one or several separation steps, e.g. screening, cleaning and/or flotation steps, where valuable fibers and chemicals are collected. In at least one such separation step, the formed MFC-surface active agent complex (or the formed NCC-surface active agent complex) may be separated from part of the white water. Such complex is thereafter added to the furnish in the stock preparation in a controlled amount. Alternatively, the MFC- or NCC-surface active agent complex may be recirculated directly to the stock preparation together with the white water.

(7) The method may comprise further steps known in the art to make the final paper or paperboard, such as drying, pressing, surface-sizing, coating and/or calendering.

(8) In one preferred embodiment of the invention, the method of forming the web includes foam forming, in which the web is formed from a foamed furnish suspension. This may be accomplished by turning the furnish into a foamed suspension as it is fed from the headbox to the forming wire. Foam forming gives rise to a higher bulk, which is of particular use in the making of tissue paper or paperboard. In this embodiment, a furnish comprising cellulose fibers and a surface active agent is foamed before being applied onto the wire. The foaming of the furnish may be accomplished by exposing the aqueous furnish to a vigorous shearing action, whereby air is dispersed in the furnish in the form of very small bubbles. After the foamed furnish suspension has been applied onto the wire to form a fibrous web, white water is drained from the web, to which MFC or NCC is added before it is recirculated to the stock preparation. As previously described, the thereby formed complexes of MFC- or NCC- surface active agent may be separated and recycled to the furnish in the stock preparation in a controlled amount.

(9) The method of the invention may also be used to manufacture an MFC film. In this embodiment, an MFC suspension is applied onto a wire, preferably at a consistency of 0.1-1 wt %. The suspension comprises MFC fibers, usually above 70 weight % or above 80 weight %, based on the weight of solids of the suspension, and a surface active agent. Subsequent to the web being placed onto the wire, it is dewatered to form a film. The drained white water is recircled to the preparation of the MFC suspension. A second, additional MFC is added to the drained white water before it is recircled to the preparation of the MFC suspension. Said second MFC preferably has a higher surface area than said first MFC. The film formed by the method of the invention preferably has a has an oxygen transmission rate (OTR) of less than 500 ml/m.sup.2/day, or less than 100 ml/m.sup.2/day, or less than 50 ml/m.sup.2/day, or less than 10 ml/m.sup.2/day or less than 1 ml/m.sup.2/day. The film has a basis weight of less than 50 g/m.sup.2, or preferably less than 35 g/m.sup.2, less than 25 g/m.sup.2, or less than 20 g/m.sup.2.