Wet and dry forming of multi-ply web

Abstract

According to an example aspect of the present invention, there is provided a method for manufacturing a multi-ply fibre web structure from a cellulose-based material by combining two different web layer forming technologies, a foam-laid process and a dry-laid or an air-laid process, and wet-pressing thereby formed web layers together. Also described is a multi-ply fibre web structure manufactured by such method.

Description

WET AND DRY FORMING OF MUETI-PEY WEBFIEED

[0001] The present disclosure relates to a technology for manufacturing a multi-ply fibre web structure by combining two different web layer forming technologies, targeting to reduce energy consumption of the process.BACKGROUND

[0002] In conventional papermaking process with water forming, drying is one of the most energy-intensive stages in paper production. After the paper is formed, it contains a high percentage of water. This water needs to be removed through drying to achieve the desired paper properties. Traditional drying methods involve the use of steam dryers, and this requires substantial thermal energy. Air-laid forming is utilized with dry fibres, and, depending on the bonding technology, the amount of drying energy is significantly lower than in water forming.

[0003] As an example of related prior art, GB 1595905 A is an old patent publication disclosing a process for manufacturing a multi-ply cellulosic fibrous product having its strength and stiffness concentrated in its outermost plies by utilizing properties of wet and dry-laid cellulosic webs.

[0004] Another relevant prior art patent publication is US 3,954,554, which discloses a method and apparatus for making a multi-ply paper sheet, wherein a first web is formed by wet-laying fibres and a second web is formed by dry-laying fibres, which are then combined to form a multi-ply sheet.

[0005] Also, US-patent 4,046,622 relates to the similar field than the previous, wherein a multi-ply sheet of cellulosic fibrous material is formed by combining wet and dry-laid webs.

[0006] These publications do not however disclose anything about a foam-laid process and especially combining such with a dry-laid or an air-laid process.

[0007] In the present technical field, new energy efficient solutions and technologies are needed in order to reduce the impact of even higher energy price, and also to control the CO2 emissions related to energy production.SUMMARY OF THE INVENTION

[0008] The present invention is defined by the features of the independent claims. Some specific embodiments are defined in the dependent claims.

[0009] According to an aspect of the present invention, there is provided a method for manufacturing a multiply fibre web structure, wherein at least one web layer is formed by a foam laid process and at least one web layer is formed by a dry-laid process or an airlaid process. The web layers are then pressed together for forming the structure, and dried.

[0010] This and other aspects, together with the advantages thereof over known solutions are achieved by the present invention, as hereinafter described and claimed.

[0011] The method of the present invention is mainly characterized by what is stated in the characterizing part of claim 1.

[0012] The multi-ply fibre web structure according to the present invention is characterized in claim 8.

[0013] Considerable advantages are obtained by means of the invention. The most important advantage is that energy savings are obtained since part of the material is dry and no intense thermal drying is needed. Thus, the amount of water to be evaporated in thermal drying is essentially lower than in normal papermaking, resulting a significant reduction of drying energy needed. Depending on the share of dry / foam-laid in the web, reduction reaches up to 60% of drying energy (two thirds by dry-laid), representing up to 30% of the total process energy.

[0014] Next, the present technology will be described more closely with reference to certain embodiments.EMBODIMENTS

[0015] The present technology provides means to combine two web layer forming technologies, a foam laid process and a dry-laid or an air-laid process, for forming web layers, which are (wet)pressed together to a multi-ply fibre web structure.

[0016] FIGURE 1 is a chart showing solids content (%) increase before and after wet pressing.

[0017] FIGURE 2 is a chart showing water content decrease before drying (g / m2).

[0018] In the present invention, two or more webs formed with different technologies are combined. One layer is foam-laid, i.e. an aqueous technology, and one layer is air-laid from dry fibers. The idea behind this is to bring the wet layer(s) and dry layer together and (wet)press the structure so that the water from the foam-laid layer is bringing water to the dry layer and thus bonding it. Water transfer from foam to dry layer removes the separate step for needed for bonding dry-formed web, which is usually done by for example latex application. Layers are then wet-pressed and dried thermally.

[0019] One aspect of the present invention is, thus, hydrogen bonding, which enables the dry web layer and the wet web layer to attach to each other. Energy savings are obtained since part of the raw material is dry and thus no intense thermal drying is needed.

[0020] According to one embodiment of the present invention, the present method for manufacturing a multi-ply fibre web structure from a cellulose-based material comprises at least the following steps: forming at least one web layer from moist cellulose fibres by a foam-laid process, forming at least one web layer from dry cellulose fibres by a dry-laid or an air-laid process,(wet)pressing the formed web layers together and thereby forming the multi-ply web structure, and(thermally) drying the multi-ply web structure.

[0021] According to one embodiment, the cellulose-based material is lignocellulosic fibres, such as wood fibres, or biobased staple fibres, such as viscose, or a combination thereof.

[0022] According to one embodiment, the multi-ply fibre web structure is manufactured by joining together at least two layers, for example three layers i.e. a top layer, a middle layer and a backing layer.

[0023] According to one embodiment, at least one layer is formed by a foam laid process and at least one layer is formed by a dry-laid or an air-laid process.

[0024] According to one embodiment, a top layer and a backing layer are formed by a foam laid process and a middle layer is formed by a dry-laid or an air-laid process.

[0025] According to one embodiment, the layers are wet-pressed before joining the layers together. This increases the solids content of the final layered sheet structure to above 80%.

[0026] According to one embodiment, the web layer formed by the foam-laid process is manufactured from bleached and unrefined SW kraft and the web layer formed by the dry-laid or air laid process is manufactured from bleached chemi-thermomechanical pulp (CTMP).

[0027] According to one embodiment, the CTMP share of the total weight of the multi-ply structure is at least 50%, more preferably at least 60% and more suitably about 67%. For example, if there are two webs of equal basis weight combined, a dry and a foam laid, there is approximately 50% less water to be removed and respective reduction in drying energy need is expected.

[0028] According to one embodiment, the forming of web layers increases the solids content at least 50%, more suitably at least 100%, and the wet-pressing increases the solids content of the multi-ply web structure at least 20%, more suitably at least 40%.

[0029] According to one embodiment, the web-layers are attached to each other(s) mainly by hydrogen bonds.

[0030] According to a further embodiment, the web layers are attached to each other(s) by hydrogen bonds. Ply bond may be further improved by an additional adhesive agent, selected from for example cationic starch, carboxymethylcellulose (CMC), cellulose nanofibers, cellulose microfibers, trimethylphosphine, polyvinyl alcohol and chemicals for polyelectrolyte layering, or by any combination thereof.

[0031] According to one embodiment, a multi-ply fibre web structure, which has solids content after wet pressing of at least 50%, preferably at least 65% and more preferably at least 80% also belongs to the scope of the present invention. An example of such structure / product is folding boxboard.

[0032] According to one embodiment, the multi-ply fibre web structure comprises at least two web layers wet-pressed together, wherein one web layer is a dry-laid or an airlaid formed CTMP layer and one layer is a foam-laid formed SW kraft layer.

[0033] According to a further embodiment, the multi-ply fibre web structure comprises three web layers wet-pressed together: a top layer and a backing layer of foam- laid formed SW kraft and a middle layer of dry-laid or air-laid formed CTMP.

[0034] According to one embodiment, the forming of the web layers increases the solids content at least 50%, more suitably at least 100%, and that the wet-pressing increases the solids content of the multi-ply fibre web structure at least 20%, more suitably at least 40%.

[0035] According to one embodiment, the multi-ply fibre web structure is recyclable and / or biodegradable.

[0036] Reference throughout this specification to one embodiment or an embodiment means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Where reference is made to a numerical value using a term such as, for example, about or substantially, the exact numerical value is also disclosed.

[0037] As used herein, a plurality of items, structural elements, compositional elements, and / or materials may be presented in a common list for convenience. However, these lists should be construed as though each member of the list is individually identified as a separate and unique member. While the forgoing examples are illustrative of the principles of the present invention in one or more particular applications, it will be apparent to those of ordinary skill in the art that numerous modifications in form, usage and details of implementation can be made without the exercise of inventive faculty, and without departing from the principles and concepts of the invention. Accordingly, it is notintended that the invention be limited, except as by the claims set forth below.

[0038] The verbs “to comprise” and “to include” are used in this document as open limitations that neither exclude nor require the existence of also un-recited features. The features recited in depending claims are mutually freely combinable unless otherwise explicitly stated. Furthermore, it is to be understood that the use of "a" or "an", that is, a singular form, throughout this document does not exclude a plurality.INDUSTRIAL APPLICABILITY

[0039] The present technology can be used for example for manufacturing paper or carton boards, such as folding boxboards.EXAMPLESMethods and materials with reference to table 1 :■ SW kraft (bleached, unrefined) top and backing, CTMP (CSF 600 ml / min, bleached spruce) for middle ply■ Reference: water formed 40+120+40 g / m2■ Two preparation procedures for samples 1 and 2: joining of layers• after forming• after wet pressing the top and backing layers■ Wet-laid sheet preparation (for reference) according to standard method using laboratory sheet mould. Foam-laid sheet preparation with an in-house sheet mould. Air-laid sheet prepared with laboratory scale air-laid sheet mould. Wet pressing with hydraulic platen press, drying with laboratory drum dryer.■ Sheet properties were measured according to standards.Total 6 conditions, with three parallel samplesTable 1.Results and observations with reference to figures 1-2:■ Reference sheet (all water formed layers) solids content ~18-19% before wet pressing and 47-49% after pressing.■ Combining water laid SW layers with air-laid CTMP results in 40% solids before wet pressing and 65-67% after wet pressing• CTMP share of total weight is 60% (200 gsm sheet) or 67% (240 gsm sheet), and resulting solids increases reflect higher water retention value of SW kraft.■ If the top and backing layers are wet pressed before joining, the solids of layered sheet exceeds 80%.• Solids of wet pressed S W layers 41 % before joiningCITATION LISTPatent literatureGB 1595905US 3,954,554US 4,046,622

Claims

CLAIMS:

1. A method for manufacturing a multi-ply fibre web structure from a cellulose-based material, characterized in comprising at least the following steps: forming at least one web layer from moist cellulose fibres by a foam-laid process, forming at least one web layer from dry cellulose fibres by a dry-laid or an air-laid process, wet-pressing the formed web layers together and thereby forming the multi-ply web structure, and drying the multi-ply web structure.

2. The method according to claim 1, characterized in that the cellulose-based material is lignocellulosic fibres, such as wood fibres, or biobased staple fibres, such as viscose, or a combination thereof3. The method according to claim 1 or 2, characterized in that the multi-ply fibre web structure is manufactured by joining together at least two layers.

4. The method according to claim 3, characterized in that at least one layer is formed by a foam laid process and at least one layer is formed by a dry-laid or an air-laid process.

5. The method according to claim 3 or 4, characterized in wet-pressing the layers before joining the layers together.

6. The method according to any of the preceding claims, characterized in that the web layer formed by the foam-laid process is manufactured from bleached and unrefined SW kraft and the web layer formed by the dry-laid or air laid process is manufactured from bleached chemi-thermomechanical pulp (CTMP).

7. The method according to any of the preceding claims, characterized in that the web layers are attached to each other(s) by hydrogen bonds.

8. A multi-ply fibre web structure, which has solids content after wet pressing of at least9. The multi-ply fibre web structure according to claim 8, which comprises at least two web layers wet-pressed together, wherein one web layer is a dry-laid or an air-laid formed CTMP layer and one layer is a foam-laid formed SW kraft layer.

10. The multi-ply fibre web structure according to claim 8 or 9, which comprises three web layers wet-pressed together: a top layer and a backing layer of foam-laid formed SW kraft and a middle layer of dry-laid or air-laid formed CTMP.

11. The multi-ply fibre web structure according to any of claims 8 to 10, characterized in being recyclable and / or biodegradable.

12. The multi-ply fibre web structure according to any of claims 8 to 11, which is manufactured according to the method of any of claims 1 to 7.

13. Use of the method according to any of claims 1 to 7 for manufacturing paper or carton boards, such as folding boxboards.

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