FORMING AND DEWATERING OF A COMPOSITE USING A DOUBLE WIRE PRESS

Abstract

A composite product comprising a fibrous material (A) and a polymer material (B), wherein the composite product is formed as a sheet, by wet web formation and wherein said web is formed from a suspension of said fibrous material and said polymer material in a double wire press (2a and 2b).

Claims

1. A method for manufacturing a composite product comprising a fibrous material and a polymer material, wherein the composite product is a sheet, formed by wet web formation, wherein said method comprises the steps of: mixing said fibrous material and said polymer material and a liquid to form a suspension; transporting said suspension to a head-box, wherein the consistency of the suspension in the head-box is from 2.0 to 10 weight-%; forming a web on wires; removing liquid from said web, to form said composite product; wherein both forming and initial dewatering is accomplished in a double wire press.

2. The method as claimed in claim 1, wherein the composite product consists of a single layer.

3. The method as claimed in claim 1, wherein the composite product is essentially homogenous in its cross-section.

4. The method of claim 1, wherein the composite produced is a multiply product.

5. The method as claimed in claim 4, wherein the head-box used is a multilayer head-box.

6. The method as claimed in claim 4, wherein more than one head-box is used.

7. The method as claimed in claim 1, wherein said head-box is pressurized.

8. The method as claimed in claim 1, wherein said head-box is equipped with means for generating turbulence in the head-box.

9. The method as claimed in claim 1, wherein the method comprises a further drying step.

10. The method as claimed in claim 1, wherein the method comprises a further step of pressing said sheet after the step of forming said sheet in the double wire press.

11. The method as claimed in claim 1, wherein said fibrous material is selected from the group of natural fibers, such as wood-derived fibers, botanical fibers and/or derivatives thereof, synthetic fibers, bacterial fibers, microfiber and/or a mixture thereof.

12. The method as claimed in claim 11, wherein said natural fiber is a cellulose fiber.

13. The method as claimed in claim 1, wherein said polymer material is a thermoplastic material selected from the group of polyethylene, polypropylene, polylactic acid, polystyrene, polycarbonate, polyvinyl chloride, acrylonitrile butadiene styrene, ethylene vinyl acetate, thermoplastic elastomers, and/or derivatives, and/or co-polymers, and/or mixtures thereof.

14. The method as claimed in claim 1, wherein the composite product further comprises at least one additive selected from the group of starch, fillers, surface-active agents, retention agents, dispersing agents, anti-foam agents, coupling agents, stabilizing agents, lubricants, flame retardants and mixtures thereof.

15. The method as claimed in claim 14, wherein the at least one additive is provided in emulsion form.

16. The method as claimed in claim 15, wherein the emulsion is precipitated on the fibers by addition of an agent that destabilizes the emulsion.

17. The method as claimed in claim 1, wherein the polymer material content is from 10 to 80 weight-% of the dry weight of the suspension of said fibrous material and said polymer material.

18. The method as claimed in claim 1, wherein said composite product has a consistency of more than 15 weight-% after being pressed in said double wire press.

19. An apparatus for forming a composite product, wherein the composite product comprises a fibrous material and a polymer material, and wherein the composite product is formed as a sheet, by wet web formation in a double wire press.

20. An apparatus according to claim 19, wherein the head-box is pressurized.

21. An apparatus according to claim 19, wherein the head-box is equipped with means for generating turbulence in the head-box.

22. A composite product obtainable by the method as claimed in claim 1.

23. The composite product as claimed in claim 22, wherein said composite product has a basis weight in the range of 100 to 10 000 g/m2.

24. The composite product as claimed in claim 23, wherein said composite product has a basis weight in the range of 1000 to 10 000 g/m2.

25. The composite product as claimed in claim 22, wherein the product is a thermo-formable sheet.

26. The composite product as claimed in claim 22, wherein the product does not absorb any substantial amount of water

27. The method as claimed in claim 1, wherein the method comprises a further step of pressing and heating said sheet after the step of forming said sheet in the double wire press.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Embodiments of the present solution will now be described, by way of example, with reference to the accompanying schematic drawing.

[0037] FIG. 1 is a schematic perspective view of an apparatus arrangement for manufacture of a composite sheet:

[0038]

TABLE-US-00001 Legend Materials stream A Fiber suspension B Polymer C Additives (optional) D Dilution water (optional) E Excess water F Humid air G Finished composite product Legend Process equipment 1 Mixer 2a Head-box 2b Pressnip(s) 3 Additional press (optional) 4 Dryer 5 Heat press

DESCRIPTION OF EMBODIMENTS

[0039] FIG. 1 illustrates an arrangement for forming the composite web and subsequent composite product in the form of a sheet or roll. In the arrangement a fiber suspension (A) and polymer (B), wherein the polymer is in the form of a dry powder or fibers or as an emulsion or a suspension, and optionally additives (C), are mixed to form a liquid suspension, for instance in a tank or mixer (1), optionally followed by dilution (D). The suspension, or intermediate or mixture suspension, is then brought to a head-box (2a) which is part of a double wire press. From the head-box the mixture suspension is subsequently brought onto the wires of the press, where a web or sheet is then directly formed and simultaneously dewatered to form the composite product.

[0040] According to one embodiment this product may be further pressed in a subsequent additional press operation (3) to remove excess water before it is dried in a dryer (4), forming the non-consolidated fiber polymer composite as a sheet or roll. The step of removing liquid from the web may thus also include a further pressing step, or if the web has a desired consistency after passing through the double wire press, it may be directly transferred to a dryer for further removal of liquid from the web to form a substantially dry composite product. The heating or drying, i.e. the further increase of the dry content, may be performed by any conventional means, such as by heating against a hot surface (hot rolls or condebelt), by applying hot gas, by applying microwaves, infrared radiation or a mixture of different heating techniques, known to the skilled person. After drying, the composite is preferably taken through a heat-pressing step of temperatures above the melting point of the polymer and pressures above 200 kPa where the polymer material melts and is pressed into the voids between the fibers to form a matrix and the resulting product is consolidated and essentially homogenous and does not absorb any substantial amounts of water. The product is essentially impermeable to water. In one embodiment this consolidation can take place simultaneously with the thermo-forming operation. The double wire press (2a and 2b), may be of a conventional type known to the skilled person. It may also be modified to achieve the composite sheet product according to the present invention. The speed of the double wire press can be adjusted as required to obtain the desired basis weight of the product. The speed is typically less than 60 m/min, considerably lower than in a typical papermaking process.

[0041] The mixing can be performed in any type of mixer, for instance in a tank (1) or stand-pipe, but also in special mixers.

[0042] The composite product is thus simultaneously formed and dewatered in the double wire press (2a and 2b). The new type of composite product formed has an increased or higher basis weight, i.e. being thicker, than sheet-like composites made through a conventional paper making process, comprising a wire section and subsequent pressing and drying steps. This means that the process takes up less space than a conventional paper making machine, and also that the equipment may be cheaper than conventional paper making machines both in investment and operational cost.

[0043] The composite product may be in the form of a roll or a sheet, i.e. a substantially flat or plane product, depending on the desired use of the end product composite. It is possible to form sheets having a large size of up to 2 to 3 meters wide and up to 5 or 6 meters long.

[0044] The fibrous material may be selected from the group comprising natural fibers, such as wood-derived fibers including spun and regenerated cellulose, botanical fibers and/or derivatives thereof, synthetic fibers, bacterial fibers, microfiber and/or a mixture thereof. The natural fibers may also be a nanofibrillated polysaccharide such as for instance microfibrillated cellulose (MFC), microfibrillated lignocelluloses (MLC) or nanocrystalline cellulose (NCC). The fibrous material may comprise fibers of any suitable length, depending on the desired characteristics of the end product. It may also comprise fines material or micro- or nanofibrillar or crystalline material. This fibrous material may include bacterial cellulose or nanocellulose spun with either traditional spinning techniques or with electrostatic spinning. The fibers can also be formed by other means using e.g. ionic liquids or membrane techniques (precipitation or coagulation of dissolved cellulose) and thus either a form of regenerated cellulose or liberated fibrils obtained by selective dissolving liquids. In these cases, the material is preferably a polysaccharide but not limited to solely a polysaccharide. Also microcrystalline cellulose, whiskers and nanocellulose crystals could be used. The said component can also be a mixture of the presented materials or combination between organic and synthetic nanofibers. The microfibrillated cellulose (MFC) is also known as nanocellulose. It is a material typically made from wood cellulose fibers, both from hardwood or softwood fibers. It can also be made from microbial sources, agricultural fibers such as wheat straw pulp, bamboo or other non-wood fiber sources. In microfibrillated cellulose the individual microfibrils have been partly or totally detached from each other. A microfibrillated cellulose fibril is normally very thin (20 nm) and the length is often between 100 nm to 10 m. However, the microfibrils may also be longer, for example between 10-200 m, but lengths even 2000 m can be found due to wide length distribution.

[0045] MFC or nanocellulose or nanocrystalline cellulose can be made with different means such as mechanically or chemically or enzymatically or by using bacteria or by combining e.g. chemical and mechanical treatment steps.

[0046] Different types of spinning and precipitation processes can also be used. In this case, the starting material for making a nanofiber or MFC can be a polysaccharide.

[0047] The polymer material may, according to one embodiment be a thermoplastic material selected from the group comprising polyethylene, polypropylene, polylactic acid, polystyrene, polycarbonate, polyvinyl chloride, acrylonitrile-butadiene-styrene (ABS), ethylene vinyl acetate (EVA), thermoplastic elastomers, polyamides, and/or co-polymers, and/or derivatives, and/or mixtures thereof.

[0048] The thermoplastics materials must be processable in later production steps at a temperature below 250 C., preferably below 220 C.

[0049] In the suspension of fiber and polymer, it is further possible to add other additives, such as starch, fillers, surface-active agents, retention agents, dispersing agents, anti-foam agents, coupling agents, stabilizing agents, lubricants, flame retardants, anti-oxidants, UV-stabilizers, and mixtures thereof.

[0050] Preferably a compatibility agent (also referred to as coupling agent) is provided or added, such as for instance a maleic anhydride grafted polymer or similar substances, in order to improve the adhesion between fibers and polymer matrix in the composite.

[0051] The head-box consistency, i.e. the proportion of solids in the suspension may be from 2.0 to 10 weight-% or from 2.4 to 10 weight-% such as from 3 to 10 weight-% or from 4 to 10 weight-%. Solids include fibrous material, polymer and potentially other components such as additives to the extent the other components such as additives are insoluble in the liquid of the suspension. The polymer material content of the dry weight of the suspension of said fibrous material and said polymer material may be from 10 to 80 weight-% such as from 30 to 60 weight %. Thus the fiber content of the dry weight of the suspension of said fibrous material and said polymer material may be from 20 to 90 weight-%.

[0052] According to one embodiment the composite product may have a consistency of more than 15 weight-%, such as 20 weight-% or 25 weight-% after being pressed in said double wire press.

[0053] The composite product may have a basis weight in the range of from 100 to 10 000 g/m.sup.2, such as from 100 to 5 000 g/m.sup.2 or from 1 000 to 10 000 g/m.sup.2 or from 500 to 5 000 g/m.sup.2 or from 250 to 5000 g/m.sup.2 or from 250 to 10 000 g/m.sup.2 or from 2 000 to 10 000 g/m.sup.2.

[0054] According to one embodiment the head-box (2a) may be a multilayer head-box. By using a multilayer head-box it is possible to provide a multilayer or multiply composite product in a very efficient way. Through the double wire press (2) it would then be possible to form and dewater the web easily, but yet achieving a composite product having higher basis weight than conventionally laid multiply papers. After drying and heating, each layer of the multiply composite product is consolidated and essentially homogenous and does not absorb any substantial amounts of water. The multiply composite product is essentially impermeable to water.

Examples

[0055] Composite sheets were formed on a modified double wire press Multibelt M1500 from Hedemora Verkstder, Hedemora Sweden. The press was equipped with a closed, pressurized headbox attached on a crossbeam in close proximity to the wire gap. The headbox was designed with an adjustable lip opening which during the trials was set to 3 mm. To save material in the trials, the headbox was considerably narrower than the wire. The furnish was prepared in a 40 m.sup.3 mixing tank equipped with a side fitted mixing propeller operating at 220 rpm. The furnish was withdrawn from the tank by a centrifugal mixing pump which could also be set to recirculation for additional pre-mixing of the furnish.

[0056] For the examples 6.0 m.sup.3 of bleached DIP, with a measured consistency of 4.1%, from the Stora Enso Hylte Mill DIP-line was filled into the mixing tank. 30 I of Aquaseal X 2196 (supplied by Paramelt Veendam B.V., Veendam, The Netherlands) was added and mixed in for ten minutes. Subsequently 50 I of a 0.3% solution of Drewfloc 413NS (Solenis Sweden AB, Gteborg, Sweden) was added and mixed in for ten minutes. After this 220 kg of polypropylen homopolymer (Borealis HG 385 MO) ground into powder form was mixed into the fibre suspension. Finally an additional 2.0 m.sup.3 of water was added to the furnish and this mixed for an additional 10 min. The final total consistency of the furnish led to the headbox was measured to be 6.0%.

[0057] The press was run at a constant rate of feeding of the furnish but different wire speeds and samples of approximately 4050 cm were collected. These were pressed at approximately 750 kPa between pieces of press felts in a hand operated veneer press to further increase the dry content. After this they were dried in a heating cabinet at 105 C. overnight. A4 sized pieces were cut out for the gram mage determination and for measurement of caliper. To consolidate the composite 1212 cm pieces were finally cut out and heat pressed at 200 C. and approximately 730 kPa for 18 min with 5 or 10 min of pre-heating at pressing temperature. Caliper was also measured on those pieces. The results are presented in the table below:

TABLE-US-00002 Dry content Original Caliper after Wire speed out of press Grammage caliper heat press Sample (m/min) (%) (g/m.sup.2) (mm) (mm) 1 4.4 20 2450 5.7 0.3 2.9 0.2 2 5.4 n.m. 1780 4.1 0.3 2.0 0.05 3 6.1 n.m. 1540 3.5 0.2 1.9 0.05 4 7.8 n.m 1440 3.3 0.2 1.7 0.05

[0058] In view of the above detailed description of the present invention, other modifications and variations will become apparent to those skilled in the art. However, it should be apparent that such other modifications and variations may be effected without departing from the spirit and scope of the invention.