Method for producing a fiber material with improved water repellency

Abstract

The present invention relates to a method for producing a fiber material with improved dehydration behavior. The fiber material produced according to the present invention is useful, for example, in the preparation of films and coatings. The fiber material can be produced from a suspension containing MFC or highly purified pulp, a part of the solids is removed from the suspension, and subsequently, heat treatment is performed on the suspension and / or the wet web formed from the suspension.

Description

Technical Field

[0001] The present invention relates to a method for producing a fiber material with improved dehydration behavior. The fiber material produced by the present invention is useful, for example, in the preparation of films and coatings.

Background Art

[0002] Films and barrier papers containing a large amount of microfibrillated cellulose (MFC) are known in the art. Depending on how they are produced, the films can be biodegradable and renewable while having particularly advantageous strength and / or barrier properties. Films containing MFC are used, for example, in the manufacture of packaging materials and can be laminated or otherwise provided on the surface of paper or cardboard materials.

[0003] One advantage of MFC is its ability to retain water. Unfortunately, this advantage is also one of the drawbacks when making films or barriers or when using it in cardboard production. Many solutions have been proposed to improve drainage, such as a decrease in the pH of the MFC suspension, removal of hemicellulose, or enzymatic treatment of MFC for fragmentation of MFC.

[0004] The prior art further teaches that when the fibers are derivatized, i.e., chemically modified, especially before fibrillation, the resulting fibril suspension results in films with particularly improved barrier properties against gases. Therefore, when preparing the fibril suspension, it is advantageous for the suspension to contain a larger amount of individual fibrils and substantially no fibers. Another way to visualize the degree of fibrillation or the remaining amount of larger fiber fragments or coarse fibers is to determine the transparency of the suspension or, for example, the water retention value (WRV), which usually increases (decrease in turbidity, increase in water retention amount, i.e., water retention ability).

[0005] It is clear that better barrier properties can be obtained when the content of fibrils having nano dimensions is high, but it is obvious that this barrier property negatively contributes to the water drainage resistance, which is an important step in forming the barrier layer.

[0006] International Publication No. 2021 / 116988 teaches the use of hornificated particles from MFC. Various solutions for drying MFC are presented.

[0007] U.S. Patent Application Publication No. 2021 / 395949 relates to a method for fragmenting MFC to produce nanocellulose having greater uniformity in terms of nanofibril size distribution. This invention discloses an option of returning the fibers to, for example, a first or second defibrillation step.

[0008] U.S. Patent Application Publication No. 2019 / 316293 relates to a method for fragmenting a suspension containing a blend of cellulose nanofilaments or cellulose microfilaments by, for example, a dilution - fragmentation step. This method may include a washing step before the fragmentation step, and the washing can be performed at high or low pH. This document also teaches that the removal of the finest fraction has a positive effect on the tensile strength, but does not mention the role in dehydration / drainage resistance and barrier properties.

[0009] Larsson A et al. (Cellulose, 26 (2019), pages 1565 - 1575: Fragmentation of MFC for optimizing the dehydration time during film formation by filtration) teach the role of fragmentation of MFC made from bleached sulfite pulp, for example, on the filtration time and the mechanical properties of the obtained sheet. Both techniques using filtration and techniques using centrifugation were used. By increasing the concentration of fine MFC, strength properties were obtained. However, this document emphasizes that there is a significant loss of material during fragmentation.

[0010] U.S. Patent No. 9,809,655 relates to modifying nanofibrillated cellulose and reducing the viscosity of the suspension. In one embodiment, the suspension is subjected to a heat treatment in the range of 90 to 180 °C, most preferably 120 to 140 °C, which reduces the zero-shear viscosity. The applicant further claims to have found that the remaining fiber fragments are destroyed by the heat treatment and the gel structure changes, but the fibril size remains unchanged.

Summary of the Invention

[0011] Surprisingly, it has been found that when an MFC suspension or a wet web formed from the suspension is subjected to at least one heat treatment, the dehydration rate of the MFC during the preparation of the MFC film or coating can be significantly improved. A particularly surprising effect was obtained when a small fraction (fine particles) of the MFC was first removed, then the MFC was concentrated, and subsequently heat-treated.

[0012] Therefore, the present invention is a method for preparing a treated fiber material in the form of a suspension or a wet web, comprising: a) providing a suspension comprising MFC or highly refined pulp, wherein the MFC or highly refined pulp is at least 50% of the solids of the suspension, and the suspension has a drainage resistance in the range of 72 to 99 SR° as measured as the Schopper-Riegler (SR) value according to EN ISO 5267-1; b) removing 2% to 25% by weight of the solids from the suspension, wherein the content of flaky fine material having a length of less than 0.2 mm in the removed fraction is at least 50% as determined as the percentage of the projected area of all the measured objects in the removed fraction using a Valmet Fiber Image Analyzer (FS5); c) adjusting the solids content of the suspension of step b) to a solids content of at least 2% by weight; d) A step of subjecting the fibrous material in the suspension of step c) to a heat treatment step, wherein the fibrous material in the suspension is subjected to a temperature in the range of 50 to 150 °C for at least 10 seconds to obtain a treated fibrous material, and the heat treatment is carried out on the suspension and / or a wet web formed from the suspension.

[0013] Accordingly, one aspect of the present invention is a treated fibrous material obtained by the method of the present invention.

[0014] The present invention also relates to the preparation of a film or a coating or a paper or a cardboard, and the treated pulp obtained according to the present invention is optionally diluted and then used to prepare a film or a coating or a paper or a cardboard by a method known in the art.

[0015] For this reason, one aspect of the present invention is a film or a coating or a paper or a cardboard prepared using the treated pulp according to the present invention.

Embodiments for Carrying out the Invention

[0016] The suspension of step a) contains MFC or highly refined pulp, and the MFC or highly refined pulp is at least 50% of the solids of the suspension, and the suspension has a Schopper - Riegler value (SR°) in the range of 72 to 99 SR°, for example 75 to 85 SR°. The Schopper - Riegler value can be determined by a standard method defined in EN ISO 5267 - 1.

[0017] MFC or highly refined pulp in the suspension can be produced using methods known in the art. For example, it may be based on kraft pulp that has been refined to achieve a desired Shopper League value. The pulp may further contain microfibrillated cellulose (MFC). The pulp may be a mixture of essentially unrefined pulp, low-refined pulp, lightly refined pulp, and / or moderately refined pulp that is mixed with highly refined pulp and / or MFC. The suspension may contain, in addition to the pulp, additives typically used in papermaking.

[0018] The suspension in step a) may contain a mixture of different types of fibers such as microfibrillated cellulose and a certain amount of other types of fibers such as kraft fibers, microparticles, reinforcing fibers, synthetic fibers, dissolving pulp, TMP or CTMP, PGW, recycled fibers / pulp. The hemicellulose content of the solids in the suspension in step a) is preferably less than 25% by weight, more preferably less than 22% by weight. The hemicellulose content of the solids in the suspension in step a) is preferably at least 2% by weight, more preferably at least 5% by weight.

[0019] The suspension in step a) may also contain fillers, pigments, wet strength chemicals, retention chemicals, crosslinking agents, softeners or plasticizers, adhesion primers, wetting agents, biocides, optical dyes, colorants, fluorescent brighteners, defoaming chemicals, hydrophobizing chemicals such as AKD, ASA, waxes, resins, and other process additives or functional additives. In one embodiment of the present invention, the suspension in step a) does not contain internal sizing agents, cationic retention and drainage chemicals, cationic fillers, or fixing agents.

[0020] The pH of the suspension in step a) is preferably in the range of 3 to 9, such as 4 to 8 or 4 to 6.

[0021] A step of removing 2% to 25% by weight of solids from the suspension of step a), wherein the content of flaky fine material having a length of less than 0.2 mm in the removed fraction is determined as a percentage of the projected area of all the measured objects in the removed fraction and is at least 50%. This step can be carried out using methods known in the art. For example, this step can be carried out using a belt washer or a Vario-Split washer (Voith GmbH). With Vario-Split, materials such as ash and / or fine particles can be removed. Preferably, at least 70% of the removed solids are flaky fine material having a length of less than 0.2 mm, determined as a percentage of the projected area of all the measured objects in the removed fraction. More preferably, at least 90% of the removed solids are flaky fine material having a length of less than 0.2 mm, determined as a percentage of the projected area of all the measured objects in the removed fraction. The characteristics of the removed fraction can be determined using a Valmet Fiber Image Analyzer (Valmet FS5). The flaky fine material having a length of less than 0.2 mm can also be described as "fine particle A" when determined using a Valmet Fiber Image Analyzer (Valmet FS5). In the case of a Valmet Fiber Image Analyzer (Valmet FS5), the version of the device can be version 2.3, and the client version can be 1.86. When determining the fraction discussed above, i.e., the "fine particle A" fraction, the Valmet Fiber Image Analyzer (Valmet FS5) determines the percentage of the projected area of the measured particles having a specified length. In one embodiment, the step of removing 2% to 25% by weight of solids from the suspension of step a) can be carried out by filtration.

[0022] Preferably, 2% to 8% by weight of the solids are removed in the step of removing a specific fraction of the solids from the suspension of step a). More preferably, 2% to 4% by weight of the solids are removed from the suspension.

[0023] The solid content of the suspension in step a) is preferably in the range of 0.1% to 1.9%, and thus 1 kg of the suspension preferably contains 1 to 19 g of solids.

[0024] The step of adjusting the solid content of the suspension of MFC or highly refined pulp to at least 2% by weight of solids can be carried out using methods known in the art to remove liquid from the suspension, for example, using a decanter, by filtration such as filtration using a porous membrane, or by centrifugation or evaporation. Preferably, the solid content is less than 10% by weight, for example less than 5% by weight.

[0025] The heat treatment in step d) is carried out on the suspension and / or the wet web formed from the suspension.

[0026] In the heat treatment step, the fiber material of the suspension is subjected to a temperature in the range of 50 to 150 °C for at least 1 minute to obtain the treated pulp. In one embodiment, the suspension is subjected to a temperature in the range of 60 to 130 °C, for example 70 to 95 °C. The duration of the heat treatment is preferably in the range of 1 to 60 minutes, for example 5 to 40 minutes or 10 to 30 minutes. The heat treatment can be carried out using methods known in the art, for example by passing steam through the suspension. In one embodiment, the heat treatment is carried out in a pressurized chamber. The heat treatment has been found to result in the keratinization of fibrils or fibrillated fibers of the suspension, or a part thereof. The heat treatment can also inactivate microbial activity and enzymes, enabling the storage of intermediates without adding biocides.

[0027] In one embodiment, the heat treatment of the fibrous material in the suspension is carried out on a wet web formed from the suspension. In this embodiment, the wet web is formed, for example, by applying the suspension onto a porous wire or onto a non-porous belt to obtain the wet web. The obtained suspension in the form of a wet web may be partially dewatered by, for example, a press, for example, by exposing one or both sides of the wet web to steam, or by using impingement drying or irradiation drying, for example drying using infrared irradiation, and is subjected to heat treatment. The solids content of the wet web during the heat treatment is preferably in the range of 5% to 98% by weight, for example, 10% to 50% by weight or 10% to 40% by weight or 10% to 30% by weight or 10% to 20% by weight. When steam is used, the temperature of the steam is preferably in the range of 100 to 150 °C, for example 100 to 120 °C. The duration of the heat treatment is preferably in the range of 10 seconds to 60 minutes, for example 1 to 15 minutes. Preferably, the basis weight of the wet web (based on the dry material) is 5 to 500 g / m 2 , more preferably 10 to 200 g / m 2 , most preferably 15 to 150 g / m 2 range.

[0028] Typically, the heat treatment according to the present invention does not change the color characteristics or the sensory characteristics of the fibrous material.

[0029] In one embodiment, the Schopper-Riegler value of the heat-treated pulp obtained in step d) is at least 2 SR° lower than the Schopper-Riegler value of the suspension in step c).

[0030] The treated pulp obtained by the method of the present invention can be used by methods known in the art. For example, the treated pulp can be used, for example, in the production of films or coatings or paper or paperboard using a paper machine or casting.

[0031] The wet web of the pulp according to the present invention can be formed, for example, by a wet laid or cast molding method. In the case of wet laid forming, the method may be carried out on a papermaking machine such as a fourdrinier paper machine, or other forming types such as a twinformer or a hybrid former. The web can be a single-layer or multi-layer web or a single or multiple webs produced by one or more head boxes.

[0032] In the wet laid method, a suspension is prepared and supplied to a porous wire. Dehydration is carried out through the wire and optionally also in a subsequent press section. Drying is usually carried out using convection (cylinder, metal belt) or irradiation drying (IR) or hot air. A typical wet laid method is, for example, the fourdrinier former used in papermaking. In the cast molding method, the wet web is formed, for example, on a polymer or metal belt, and the subsequent initial dehydration is carried out mainly in one direction by evaporation using various known techniques.

[0033] The dehydration and / or drying of the web is carried out such that the water content at the end of dehydration and / or drying is preferably less than 50% by weight, more preferably less than 20% by weight, most preferably less than 10% by weight, and even more preferably less than 5% by weight. The product obtained after dehydration and / or drying of the web can be redispersed. After redispersion, the treated and redispersed pulp can be used, for example, for forming a second wet substrate for producing a film.

[0034] According to a further embodiment of the present invention, there is provided a laminate comprising paper, paperboard, or film prepared using the pulp according to the present invention. Such a laminate may additionally include, for example, a thermoplastic resin polymer (made from fossil or renewable resources) layer such as any one of polyethylene, polyvinyl alcohol, EVOH, starch (including modified starch), cellulose derivatives (such as methyl cellulose, hydroxypropyl cellulose, etc.), hemicellulose, protein, styrene / butadiene, styrene / acrylate, acrylic / vinyl acetate, polypropylene, polyethylene terephthalate, polyethylene furanoate, PVDC, PCL, PHA, PHB, and polylactic acid. The thermoplastic resin polymer layer can be provided, for example, by extrusion coating, film coating, or dispersion coating. This laminated structure can provide excellent barrier properties and can be biodegradable and / or compostable and / or repulpable. According to one embodiment of the present invention, the polyethylene may be any one of high-density polyethylene and low-density polyethylene, or a mixture or modification thereof, which can be easily selected by those skilled in the art. The paper, paperboard, or film prepared using the pulp according to the present invention can also be part of a flexible packaging material such as a stand-up pouch or bag, or can be incorporated into, for example, boxes, bags, wrapping films, cups, containers, trays, bottles, etc.

[0035] The highly refined pulp can be made from non-fragmented cellulose starting materials. The highly refined pulp may be prepared by the method disclosed in International Publication No. WO 2021 / 001751. In this embodiment, the highly refined pulp is preferably produced by: a) providing a microfibril fraction obtained by fragmenting a cellulose pulp; b) subjecting the microfibril fraction to refining to a Schopper-Riegler (SR) number in the range of 80 to 98 at a consistency in the range of 0.5 to 30% by weight as determined by ISO 5267-1 standard to obtain a highly refined pulp.

[0036] The microfibril fraction used in the preparation of highly refined pulp may be obtained, for example, by separating a cellulose pulp starting material with a pressure screen to achieve a fraction having shorter and thinner fibers. The dry weight of the microfibril fraction may include, for example, less than 75% by weight, less than 50% by weight, less than 25% by weight of the total dry weight of the non-fragmented cellulose pulp starting material used in the preparation of the highly refined pulp.

[0037] When the microfibril fraction is used in the preparation of highly refined pulp, typically, the average fiber length of the fibers is more than 0.2 mm and less than 1.7 mm (determined in accordance with ISO 16065-2), and the fiber content is at least 5 million fibers per gram with a length exceeding 0.2 mm based on the dry weight. The fiber content of the microfibril fraction with a length exceeding 0.2 mm is typically less than 10 million fibers per gram based on the dry weight.

[0038] Microfibrillated cellulose (MFC) shall mean cellulose particles, fibers, or fibrils having a width or diameter of 20 nm to 1000 nm in the context of this patent application.

[0039] There are various methods for producing MFC, such as single-pass or multiple-pass purification, pre-hydrolysis followed by fibril purification or high-shear disintegration or liberation. To achieve both energy efficiency and sustainability in the production of MFC, usually one or more pretreatment steps are required. For this reason, the cellulose fibers of the pulp used in the production of MFC may be raw or pretreated enzymatically or chemically, for example to reduce the amount of hemicellulose or lignin. The cellulose fibers may be chemically modified prior to fibrillation, at which time the cellulose molecules contain functional groups other than (or more than) those found in the original cellulose. Such groups include, inter alia, carboxymethyl (CM), aldehyde and / or carboxyl groups (cellulose obtained by N-oxyl-mediated oxidation, such as "TEMPO"), or quaternary ammonium (cationic cellulose). After modification or oxidation in one of the methods described above, it becomes easier to defibrillate the fibers into MFC.

[0040] MFC can be produced from wood cellulose fibers from both hardwood and softwood fibers. MFC can also be manufactured from microbial sources, agricultural fibers such as wheat straw, bamboo, bagasse, or other non-wood fiber sources. MFC can be made from pulp containing pulp derived from virgin fibers, such as mechanical pulp, chemical pulp, and / or thermomechanical pulp. MFC can also be made from waste paper or recycled paper.

Example

[0041] Highly fibrillated bleached kraft pulp was prepared by fibrillating bleached softwood kraft pulp at low consistency to a drainage resistance of °SR95. After suspending the fibrillated cellulose at a consistency of about 0.1 wt%, a wet substrate or wet film was made.

[0042] By treating the sample in a DDJ (dynamic drainage jar) equipped with 200-mesh wire, the refined pulp was further subjected to fine particle removal, thereby removing 14 wt% of the fine particles. When the pH was adjusted to 5 before fibrillation, the amount of depleted fine particles was 24 wt%. The removed material was analyzed using a Valmet FS5 Fiber Image Analyzer. It was found that approximately 94% of the removed solid material was "fine particle A", i.e., flaky fine material with a length of less than 0.2 mm, determined as the percentage of the projected area of all measured objects in the removed fraction.

[0043] The values of fine particle A and fine particle B (lamellar fine particles, particles with a width of less than 10 μm and a length of more than 0.2 mm) in the highly fibrillated bleached kraft pulp were determined to be approximately 47% and 45%, respectively, using a Valmet FS5 Fiber Image Analyzer.

[0044] A 30 gsm film was prepared from the resulting suspension. In the following examples, the dehydration time was determined and a 30 gsm film was formed as follows.

[0045] The MFC suspension was diluted to a consistency of 0.1 wt% with reverse osmosis purified water and subjected to rod mixing (for 30 seconds) and magnetic stirring (for 2 minutes). 125.6 g of the diluted and mixed suspension was poured into the funnel of a vacuum filtration device equipped with a membrane filter (Durapore®, pore size 0.65 μm). The diameter of the circular filtration area was 73 mm. Immediately after pouring the suspension into the funnel, the vacuum was switched on and the time recording was started. The dehydration time recorded during filtration was the time required for all visible water to disappear from the top of the filter cake. The wet filter cake was removed from the filtration device together with the membrane filter and placed between two sheets of blotting paper. Subsequently, the filter cake (i.e., the film) was couched and subjected to a wet press at 410 kPa for 5 minutes and dried in a drum dryer at 80 °C for at least 90 minutes. The dried film was weighed after conditioning at 23 °C / 50% RH. To obtain the specific dehydration value (seconds / g), the recorded dehydration time (seconds) was divided by the weight (g) of the dried film. Four replicates were performed for each sample.

[0046] Example 1 - Comparative Example The highly fibrillated cellulose suspension was subjected to rod mixing (twice for 30 seconds) and dehydrated on a membrane to form a wet substrate, during which the water resistance or dehydration time was recorded according to the above procedure.

[0047] Example 2 - Comparative Example In this case, the highly fibrillated cellulose suspension was subjected to a dehydration step on a membrane to form a wet substrate, which was then couched between blotting papers. The solids content after blotting was approximately 25 - 30 wt%. After couching, the wet substrate was redispersed with a rod mixer and subjected to a second dehydration. The dehydration time ("dehydration time 1") during the formation of the wet substrate before couching was measured, and further, the dehydration time ("dehydration time 2") during the formation of the second wet substrate after couching and redispersion was measured.

[0048] Example 3 - Comparative Example In this case, the highly fibrillated cellulose was subjected to two dehydration steps in the same manner as in Example 2, but a pressing step was performed after the beating step, and this step is similar to mechanical pressure dehydration at a load of about 400 kPa.

[0049] Example 4 - Comparative Example In this case, the highly fibrillated cellulose was first subjected to fine particle removal, and then, after the pressing step, it was subjected to two dehydration steps in the same manner as in Example 3 above.

[0050] Example 5 - Comparative Example The highly fibrillated cellulose was first subjected to fine particle removal, and then, after reducing the pH of the suspension to 5, the procedure was carried out in the same manner as in Example 4.

[0051] Example 6 The highly fibrillated cellulose was subjected to fine particle removal, and then the pH (5) was adjusted to form a wet substrate. The wet substrate was further press-dehydrated and then subjected to steam treatment (100 - 120 °C) for 10 minutes. Then, after redispersing the wet film, a second wet substrate was formed.

[0052] Example 7 - Comparative Example In this case, the highly fibrillated cellulose was subjected to heat treatment (90 °C, 30 minutes) and then subjected to the first and second dehydration steps according to the same procedure as used in Example 3. In this experiment, removal of the fine particle material was not performed.

[0053] Example 8 - Comparative Example In this case, the highly fibrillated cellulose was subjected to fine particle removal and then heat treatment (90 °C, 30 minutes) in the form of a suspension with a solid content of 0.15% by weight, and then the treatment was carried out as in Example 7.

[0054] Example 9 In contrast to the treatment steps of Example 6, the pH adjustment was performed before the fine particle removal and subsequent wet substrate formation. After preparing the wet substrate, this substrate was subjected to steaming (10 minutes, steam temperature 100 °C), and then the treatment was carried out in the same manner as in Example 6.

[0055] Result Table I summarizes the influence of various treatment steps on the dehydration resistance or drainage resistance according to the present invention. When normalizing the dehydration time or drainage resistance, it becomes clear that the treatment is most efficient when both pH adjustment and particulate depletion are carried out. After dehydration and steaming, changes in fibril and fiber properties due to wet keratinization are confirmed. Dehydration in the second dehydration stage was significantly improved, and the roles of both the solid content increase and steaming in keratinization were confirmed (see Example 9).

[0056] Furthermore, it is confirmed that in Sample 6, the dehydration resistance decreases, particularly in the second dehydration step, due to the removal of particulates after pH adjustment and further steaming. TIFF2025519676000001.tif64170TIFF2025519676000002.tif116170

[0057] Considering the above detailed description of the present invention, other modifications and variations will be apparent to those skilled in the art. However, it is clear that such other modifications and variations can be achieved without departing from the spirit and scope of the present invention.

Claims

1. A method for preparing a processed fiber material in the form of a suspension or a wet web, a) A step of providing a suspension comprising MFC or highly purified pulp, wherein the MFC or highly purified pulp constitutes at least 50% of the solids of the suspension, and the suspension has dewatering resistance in the range of 72 to 99 SR° as measured as a Schöpper-Leighler (SR) value according to EN ISO 5267-1, b) A step of removing 2% to 25% by weight of solid matter from the suspension, wherein the content of flake-like fine material less than 0.2 mm in length in the removed fraction is at least 50% as determined by Valmet Fiber Image Analyzer (FS5) as a percentage of the total projected area of ​​all measured objects in the removed fraction. c) A step of adjusting the solid content of the suspension from step b) to a solid content of at least 2% by weight, A method comprising the steps of: d) subjecting the fibrous material in the suspension of step c) to a heat treatment step, wherein the suspension is subjected to a temperature in the range of 50 to 150°C for at least 10 seconds to obtain a treated fibrous material, and the heat treatment is performed on the suspension and / or a wet web formed from the suspension.

2. The method according to claim 1, wherein the pH of the suspension in step a) is in the range of pH 4 to 8.

3. The method according to claim 1, wherein the duration of the heat treatment in step c) is in the range of 1 minute to 1 hour.

4. The method according to claim 1, wherein a wet web is formed on a polymer or metal belt by casting.

5. The method according to claim 1, wherein the heat treatment is performed on a wet web.

6. The method according to claim 5, wherein the heat-treated wet web is dehydrated and / or dried to obtain a film.

7. A processed fiber material obtainable by the method described in claim 1.

8. A film obtainable according to claim 7.

9. Paper, cardboard, or film comprising the processed fiber material described in claim 7.

10. A packaging material comprising paper, cardboard, or film as described in claim 9.