Method for fractionating highly purified cellulose

Abstract

The present invention relates to a method for fractionation of highly refined cellulose pulp into a fine fraction and a coarse fraction, the method comprising the steps of: a) providing a highly refined cellulose pulp suspension comprising highly refined cellulose pulp having a Shopper-Riegler (SR) number in the range of 40 to 98, as determined by ISO standard 5267-1, and a content of fibres having a length greater than 0.2 mm of at least 7 million fibres / gram based on dry weight; b) subjecting the highly refined cellulose pulp suspension to dewatering in a belt filter; c) collecting the dewatered retentate as a coarse fraction; and d) collecting the filtrate as a fine fraction, wherein the collected fine fraction contains a solids content of 2 to 50 wt. % of the highly refined cellulose pulp suspension provided in step a).

Description

[Technical Field]

[0001] This disclosure relates to a method for preparing highly purified cellulose, which is useful, for example, for producing barrier films for paper and cardboard-based packaging materials. [Background technology]

[0002] The packaging industry requires effective gas, odor, and / or moisture barriers to protect sensitive products. In particular, oxygen-sensitive products require an oxygen barrier to extend their shelf life. Oxygen-sensitive products include many foods, but also pharmaceutical and electronic products. Known packaging materials with oxygen barrier properties may consist of one or more polymer films, usually included as part of a multilayer coating structure, or fibrous paper or board coated with one or more layers of oxygen barrier polymers. Another important property for food packaging is resistance to grease and oil.

[0003] Recently, films have been developed from highly purified cellulose and microfibrillated cellulose (MFCs) in which defibrillated cellulose fibrils are suspended in water, for example, rearranged, and re-bonded together to form a continuous film. Such films have been found to offer good gas barrier properties as well as good resistance to grease and oil.

[0004] The film can be produced by applying a highly purified cellulose suspension to a porous substrate to form a web, and then dewatering the web by removing water through the substrate to form a film. Web formation can be achieved, for example, by using a paper or cardboard machine-type process. The porous substrate may be, for example, a membrane or wire mesh, or a paper or cardboard substrate.

[0005] The production of films and barrier substrates on paper machines from highly purified cellulose or MFC suspensions is difficult due to the high water retention and / or high drainage resistance of the suspension and the resulting web. For example, rapid or forced dewatering assisted by pressure or suction tends to cause high loss of fine particles from the web, or non-uniform vertical distribution of fine particles within the web, and the formation of pinholes, resulting in films with poor barrier properties. On the other hand, slowing the dewatering rate to prevent these problems requires excessively long dewatering sections.

[0006] A common problem associated with webs and films formed from highly purified cellulose or MFC suspensions is that they typically exhibit insufficient tensile and tear strength.

[0007] From a technical and economic standpoint, it would be preferable to find a solution that enables rapid dewatering while simultaneously improving the barrier and tear strength properties of the film. [Overview of the Initiative]

[0008] The object of this disclosure is to provide a method for processing highly purified cellulose pulp that mitigates at least some of the problems described above.

[0009] The object of this disclosure is to provide a method for reducing the water retention capacity of highly purified cellulose pulp and / or increasing its homogeneity.

[0010] A further object of this disclosure is to provide highly refined cellulose pulp suitable for manufacturing barrier films in paper or cardboard machine-type processes.

[0011] A further object of this disclosure is to provide highly refined cellulose pulp suitable for manufacturing barrier films based on renewable raw materials.

[0012] A further object of this disclosure is to provide highly purified cellulose pulp suitable for producing barrier films having high repulsability, which provides high recyclability for packaging products including barrier films.

[0013] The purposes described above, as well as other purposes that will be understood by those skilled in the art in light of this disclosure, are achieved by various aspects of this disclosure.

[0014] This invention is based on the recognition that a relatively small proportion of fine particles in a highly purified cellulose pulp suspension are largely responsible for the high water retention and / or high drainage resistance of the suspension and the resulting web. Traditionally, it has been considered important to retain as many fine particles as possible in the web when manufacturing barrier films, as these also greatly contribute to the barrier properties of the finished film. Therefore, previous strategies for manufacturing barrier films from highly purified cellulose focused on means of retaining the formed and dewatered fine particles within the web, such as the addition of chemical retainers.

[0015] The method of the present invention uses a belt filter, which is commonly used to wash a conventional papermaking pulp suspension to fractionate highly purified cellulose pulp and remove some of the fine particles in the pulp. Removing some of the fine particles provides highly purified cellulose, which enables more efficient production of barrier films in paper machine-type processes. Such films are useful, for example, as gas barrier films in packaging applications. These films can be used as a substitute for conventional barrier films such as synthetic polymer films or aluminum foil, which reduce the recyclability of paper or cardboard packaging products. The films of the present invention have high repulpability, providing high recyclability of the films and paper or cardboard packaging products containing these films.

[0016] Most existing pulp fractionation methods are optimized for fractionating ordinary pulp suspensions into coarse and fine fractions. Examples include liquid centrifuges and pressure screens.

[0017] Liquid centrifuges fractionate solids based on surface area. Experimental studies have shown that liquid centrifuges separate fibers based on specific surface area, specific volume, and cell wall thickness. A problem with liquid centrifuges is that they are less efficient due to aggregation at high solid content levels, such as above 0.9 wt%.

[0018] Pressure screens separate solids based on size and flexibility. Particle acceptance is determined, in order, by fiber flexibility, length, and thickness. Fibers of equal length are accepted due to their flexibility. Chemical fibers are accepted more easily than stiff mechanical fibers. Fibers of different lengths are accepted due to their length, with shorter fibers being accepted more easily than longer fibers. During screening, smaller solid particles allow for the use of finer slits, but this requires larger machinery and is therefore less economically attractive.

[0019] Existing methods are not suitable for fractionating suspensions containing highly purified cellulose. Due to differences in size and the involvement of different physical laws, achieving good efficiency and yield with highly purified cellulose becomes more difficult.

[0020] According to a first aspect described herein, a method for fractionating highly purified cellulose pulp into fine and coarse fractions, wherein the method is a) A step of preparing a highly refined cellulose pulp suspension containing highly refined cellulose pulp having a fiber content of at least 7 million fibers / gram with a length of more than 0.2 mm, based on the Shopper-Leighler (SR) number in the range of 40 to 98 and dry weight as determined by ISO standard 5267-1; b) A step of subjecting a highly purified cellulose pulp suspension to dewatering using a belt filter; c) A step of collecting the dehydrated retained material as a coarse fraction; d) A step of collecting the filtrate as fine fractions. Includes, The collected fine fraction contains 2 to 50 wt% solids of the highly purified cellulose pulp suspension prepared in step a). A method is provided.

[0021] In this way, fine and coarse substances can be separated. In contrast to the papermaking wire / dewatering, it is preferred that the retention of fines in this system is low so that fractionation and dewatering / drainage are more efficient.

[0022] The fraction obtained by the method of the present invention can be advantageously used to prepare a barrier film in a paper machine. Conventionally, when manufacturing a barrier film, since fines also greatly contribute to the barrier properties of the finished film, it has been considered important to retain as much as possible of the fines formed and dewatered by the wire of the paper machine in the web. Therefore, previous strategies for manufacturing barrier films from highly purified cellulose have focused on means for retaining fines in the web during formation and dewatering, such as the addition of chemical retention aids.

[0023] The inventors have found that the coarse fraction obtained by the method of the present invention can be used in a pulp suspension for forming a base web on a paper machine. Since the fine particles contribute greatly to the high water retention of the pulp suspension, the reduced fine particles of the coarse fraction provide improved formation and dewatering of the web. The fine particles also contribute greatly to the barrier properties of the film formed from the pulp, so the reduced fine particle content of the coarse fraction may in some cases result in reduced barrier properties of the film formed from the coarse fraction alone. The inventors have found that this defect can be corrected by applying a coating containing cellulose fine particles or MFC to the substrate. A coating containing cellulose fine particles or MFC can cure the defects of the base web and dramatically improve the barrier properties of the web even at a very low basis weight, thus obtaining a film suitable for use as a barrier film. The fine particles used in the coating can preferably be the fine particles obtained from a fraction of highly purified cellulose pulp according to the present invention. The fine particles used in the coating can include, for example, the fine fraction obtained when preparing the coarse fraction used for the base web. Thus, in some embodiments, the fraction can also be regarded as a means of achieving redistribution of the fine particles from the bulk of the web to the surface of the web. This redistribution of the fine particles has several advantages.

[0024] The porous base web formed from the coarse fraction can be rapidly dewatered, and the porosity of the web also enables rapid dewatering and drying of the coating containing cellulose fine particles applied to the web. As a result, the method of the present invention enables rapid production of a film suitable for use as a barrier film.

[0025] Since pores and pinholes are accepted in the base web, it is possible to produce a higher basis weight film that is difficult to dewater without the formation of pinholes.

[0026] The redistribution of microparticles from the bulk to the surface, resulting in high localized concentrations of microparticles on the web surface, also allows for a reduction in the total amount of material in the barrier film while still providing similar barrier properties.

[0027] The redistribution of microparticles from the bulk to the surface has also been found to result in films with significantly higher tear strength than the corresponding films formed from highly refined pulp in which the microparticles are retained in the bulk.

[0028] A high concentration of fine particles on the web surface can also improve the surface's response to calendering.

[0029] Due to their high surface area, fine particles bind to chemicals to a greater extent than coarser particles. The redistribution of fine particles from the bulk to the surface results in a more uniform distribution of fine particles across the entire surface area of ​​the web, and consequently, a more uniform distribution of the chemicals bound to the fine particles.

[0030] Furthermore, fractionation allows for the addition of various chemicals during the fractionation and formation processes. For example, a highly purified pulp suspension subjected to fractionation may be left without chemicals, or chemicals to aid fractionation may be added. A coarse fraction obtained for use in forming a substrate web may be given chemicals to aid in web formation, or a fine fraction may be given appropriate coating chemicals for use in coating the substrate web. In this way, overall chemical consumption can be reduced, and / or the web or film properties related to various chemicals can be improved.

[0031] The method of the present invention is carried out using a belt filter. A belt filter, also called a belt filter press, is a machine designed in conventional papermaking to process pulp and increase its consistency by removing water. The pulp and paper manufacturing industry has long used such machines to wash and concentrate pulp and paper stocks, typically for storage or other temporary processing purposes.

[0032] Belt filters are conventionally used to wash and concentrate pulp used in papermaking, but they have never been used before for fractionating highly purified cellulose pulp according to the present invention.

[0033] Exemplary belt filters include the Double Wire Press (available from Andritz-Ahlstrom); BDP (available from Baker Process); Turbodrain (1-wire), Winkelpress (2-wire), and Cascade S (both types in the series) (available from Bellmer and Corner); HC Press, Gap Washer, and TwinWire (with Paraformer headbox) (available from Metso Paper / Fiber and Phoenix Process Equipment); Salter Belt Press (available from Salter); DNT Washer (available from Thermo Black Clawson); VarioSplit (available from Voith Paper); and Osprey (available from William Jones, London).

[0034] One preferred design used in the method of the present invention is a VarioSplit type apparatus. German OS 30 05 681 and the publication “VarioSplit, eine neue Maschine zur Verbesserung von AP-Rohstoffen” in “Wochenblatt fur Papierfabrikation” Vol. 21 / 1981, pp. 787–796 describe a VarioSplit suitable for washing aqueous fiber stock suspensions obtained from paper waste, and which can also be applied to the concentration of such suspensions (OS 30 05 681, columns 2, lines 30–34, columns 2, lines 68–3, lines 41). It is stated that the typical stock suspension to be processed has a concentration of less than 1.5%, preferably 0.4–0.8% (column 3, lines 61–67).

[0035] The "VarioSplit" apparatus, according to a preferred embodiment, includes an endless wire or filter band having an outer surface that cooperates with a substantial portion of the surface of a rotating cylinder, a flat jet nozzle that forms a flat suspension jet introduced into a substantially wedge-shaped intermediate space between the outer surface of the wire band and the cylinder, a take-off roll, a catch container for the extruded water, means for collecting concentrated pulp, and three guide rolls (2nd column last row to 3rd column 41st row and single figure). To wash the stock suspension, the apparatus has a fiber web formed between the outer surface of the wire band and the cylinder with a density of 100 g / m². 2 Less than 30-70 g / m², preferably 30-70 g / m² 2 It has a weight and operates so that the wire speed and the circumferential speed of the cylinder are approximately 400 to 1200 m / min (Claim 1 and last row of column 3 to row 8 of column 4).

[0036] In the method of the present invention, the use of a belt filter enables efficient, high-volume fractionation of highly purified cellulose pulp. The use of a belt filter allows for fractionation of highly purified cellulose pulp at a scale and speed sufficient for commercial production.

[0037] In some embodiments, the belt filter is 4000 m at 100 Pa. 3 / m 2 Includes a wire belt with air permeability exceeding [number] hours.

[0038] In some embodiments, the belt of the belt filter moves at a speed of at least 50 m / min, preferably at least 100 m / min, and more preferably at least 200 m / min. The belt filter is preferably a high-speed belt filter that operates at high speed.

[0039] In some embodiments, the residence time of the highly purified cellulose pulp on the belt is less than 7 seconds, preferably less than 5 seconds, and more preferably less than 3 seconds.

[0040] In some embodiments, the belt filter is a single-wire or twin-wire type belt filter. A single-wire type belt filter removes water from the pulp suspension through a single wire. A twin-wire type belt filter places the pulp between two wires, allowing drainage through both wires.

[0041] The starting material for the method of the present invention is a highly purified cellulose pulp suspension. Purification or beating of cellulose pulp means mechanical treatment and modification of cellulose fibers to impart them desired properties. A highly purified cellulose pulp suspension is an aqueous suspension comprising a mixture of cellulose-based fibrous material and optionally non-fibrous additives suspended in water. Pulp suspensions can be produced from a variety of raw materials selected from the group consisting of, for example, bleached or unbleached softwood pulp or hardwood pulp, kraft pulp, pressurized wood pulp (PGW), thermomechanical pulp (TMP), chemothermetic pulp (CTMP), neutral sulfite semichemical pulp (NSSC), waste paper, or recycled fibers.

[0042] As used herein, the term "highly purified cellulose pulp" refers to cellulose pulp that has been subjected to considerable purification, but not so much that all of it passes through a 200-mesh screen (equivalent hole diameter 76 μm) of a conventional laboratory fractionation apparatus (SCAN-CM 66:05). Preferably, 75% or less of the highly purified cellulose pulp passes through a 200-mesh screen of a conventional laboratory fractionation apparatus following SCAN-CM 66:05. More preferably, 50% or less of the highly purified cellulose pulp passes through a 200-mesh screen of a conventional laboratory fractionation apparatus following SCAN-CM 66:05. Thus, highly purified cellulose pulp contains a mixture of finer and coarser particles. The particle size distribution within highly purified cellulose pulp may depend on the starting materials and purification process used.

[0043] As used herein, the term highly refined cellulose pulp refers to cellulose pulp having a Schöpper-Leighler (SR) number greater than 40, as determined by ISO standard 5267-1. Highly refined cellulose pulp has a Schöpper-Leighler (SR) number in the range of 40 to 98, as determined by ISO standard 5267-1. In some embodiments, the SR number of the highly refined cellulose pulp in step a) is in the range of 50 to 98, preferably 55 to 94, and more preferably 60 to 92, as determined by ISO standard 5267-1.

[0044] Highly refined cellulose pulp has a fiber content of at least 7 million fibers / gram, preferably at least 9 million fibers / gram, and more preferably at least 15 million fibers / gram, based on dry weight, of fibers having a length greater than 0.2 mm. The fiber content having a length greater than 0.2 mm can be determined, for example, using an L&W Fiber Tester Plus instrument (L&W / ABB).

[0045] In some embodiments, highly refined cellulose pulp has an average fibril area of ​​at least 15%, preferably at least 17%, and more preferably at least 20% of fibers having a length greater than 0.2 mm. The average fibril area is determined using a Fiber Tester Plus instrument. When used herein, "average fibril area" means the length-weighted average fibril area.

[0046] The dry solids of a highly purified cellulose pulp suspension may consist solely of highly purified cellulose pulp, or it may include a mixture of highly purified cellulose pulp and other components or additives.

[0047] A highly purified cellulose pulp suspension contains highly purified cellulose as its main component, relative to the total dry weight of the pulp suspension. In some embodiments, the highly purified cellulose pulp suspension contains at least 50% by dry weight, preferably at least 70% by dry weight, more preferably at least 80% by dry weight, or at least 90% by dry weight of highly purified cellulose, relative to the total dry weight of the highly purified cellulose pulp suspension. In some embodiments, the highly purified cellulose pulp suspension contains highly purified cellulose in the range of 50 to 99% by dry weight, preferably in the range of 70 to 99% by dry weight, more preferably in the range of 80 to 99% by dry weight, and more preferably in the range of 90 to 99% by dry weight, relative to the total dry weight of the highly purified cellulose pulp suspension.

[0048] Highly purified cellulose pulp suspensions may further contain hemicellulose and / or lignin.

[0049] In some embodiments, the highly purified cellulose pulp suspension has a lignin content of 10% by weight or less relative to the total dry weight of the highly purified cellulose pulp suspension.

[0050] In some embodiments, the highly purified cellulose pulp suspension has a hemicellulose content in the range of 10 to 30% by weight relative to the total dry weight of the highly purified cellulose pulp suspension.

[0051] Highly purified cellulose pulp suspensions may further contain additives, such as natural starch or starch derivatives, cellulose derivatives, such as sodium carboxymethylcellulose, fillers, flocculants, gelatinizers, dry strength additives, softeners, crosslinking aids, sizing chemicals, dyes and colorants, wet strength resins, fixatives, defoaming aids, microorganisms and sludge adjusting aids, or mixtures thereof. The method of the present invention provides an alternative method for increasing the dewatering rate, and although this method is less dependent on the addition of retention and wastewater chemicals, small amounts of retention and wastewater chemicals may still be used. In some embodiments, the highly purified cellulose pulp suspension does not contain added retention and wastewater chemicals.

[0052] A highly purified cellulose pulp suspension preferably contains additives in a total dry weight of 20% or less relative to the total dry weight of the highly purified cellulose pulp suspension. More preferably, a highly purified cellulose pulp suspension contains additives in a total dry weight of 10% or less relative to the total dry weight of the highly purified cellulose pulp suspension.

[0053] The highly purified cellulose pulp suspension used in the method of the present invention should have a concentration in the range of 0.1 to 1.5 wt%. Lower concentrations are not convenient for preparing a web of appropriate basis weight with a belt filter, and higher concentrations make it difficult to efficiently remove water along with the cellulose particles from the web. A concentration in the range of 0.1 to 1.5 wt% has been found to provide an appropriate balance between basis weight and efficient drainage along with the cellulose particles. In some embodiments, the concentration of the highly purified cellulose pulp suspension prepared in step a) is in the range of 0.1 to 1.5 wt%, preferably in the range of 0.1 to 1 wt%, preferably in the range of 0.2 to 0.8 wt%, and more preferably in the range of 0.2 to 0.6 wt%.

[0054] The present invention is based on the idea of ​​rapidly dewatering pulp so that the majority of the fine particles are removed from the pulp along with the filtrate. In the method of the present invention, the filtrate removed from the pulp during dewatering contains a relatively high proportion of solids from the highly purified cellulose pulp suspension. In other words, a considerable portion of the cellulose fine particles are removed from the pulp along with the filtrate. The filtrate removed from the web contains solids ranging from 0.1 to 50 wt% of the highly purified cellulose pulp suspension starting material. The collected fine fraction preferably contains 2 to 50 wt%, preferably 2 to 40 wt%, more preferably 2 to 30 wt%, more preferably at least 5 to 30 wt%, and even more preferably at least 10 to 20 wt% of the solids from the highly purified cellulose pulp suspension prepared in step a).

[0055] During dewatering in step b), it is preferable that water is removed to a concentration of at least 5 wt%. In some embodiments, the concentration of the dewatered retained material collected in step c) is at least 5 wt%, preferably at least 7.5 wt%, and more preferably at least 10 wt%.

[0056] The average particle size of the finer fraction is considerably smaller than the average particle size of the coarser fraction.

[0057] Due to the removal of fine particles during dewatering, dewatered pulp typically exhibits lower water retention than pulp in which fine particles are retained to a greater extent. In some embodiments, the collected coarse fraction has a Shopper-Leighler (SR) number of less than 95, preferably less than 90, and more preferably less than 85, as determined by ISO standard 5267-1.

[0058] As used herein, the term "fine particles" generally refers to cellulose particles that are considerably smaller in size than cellulose fibers. For example, the fine fraction collected in step d) may contain cellulose fine particles or microfibrillated cellulose (MFCs).

[0059] In some embodiments, when the term "fine particles" is used herein, it refers to fine cellulose particles that can pass through a 200-mesh screen (equivalent to a 76 μm hole diameter) of a conventional laboratory fractionation apparatus (SCAN-CM 66:05). There are two main types of fibrous fine particles, namely primary and secondary fine particles. Primary fine particles are generated during pulping and bleaching, during which they are removed from the cell wall matrix by chemical and mechanical treatment. As a result of their origin (i.e., compound middle lamella, ray cell, parenchyma cell), primary fine particles exhibit a flake-like structure and share only a small amount of fibril. In contrast, secondary fine particles are generated during pulp purification. Both primary and secondary fine particles have a negative impact on dewatering in the forming section of the paper machine. Due to their large specific surface area compared to pulp fibers, fine particles also consume a high proportion of the chemical additives used in pulp and paper production.

[0060] In some embodiments, the fine particles include microfibrillated cellulose (MFC). In patent application terms, microfibrillated cellulose (MFC) refers to cellulose particles, fibers, or fibrils having a width or diameter of 20 nm to 1000 nm.

[0061] Various methods exist for producing MFCs, such as single or multiple purification, purification after preliminary hydrolysis, or high-shear disintegration or fibril liberation. One or more pretreatment steps are usually required to make MFC production energy-efficient and sustainable. The cellulose fibers of the pulp used in producing MFCs in this way may be natural or may be pretreated enzymatically or chemically to reduce the amount of hemicellulose or lignin, for example. The cellulose fibers may be chemically modified before fibrillation, where the cellulose molecule contains (one or more) functional groups other than those found in the original cellulose. Such groups include, in particular, carboxymethyl (CM), aldehydes and / or carboxyl groups (cellulose obtained by N-oxyl-mediated oxidation, e.g., "TEMPO"), or quaternary ammonium (cationic cellulose). After modification or oxidation by one of the above methods, it is easier to disintegrate the fibers into MFCs.

[0062] MFCs can be produced from wood cellulose fibers, both from hardwood and softwood fibers. They can also be made from microbial sources, agricultural fibers, such as straw pulp, bamboo, bagasse, or other non-wood fiber sources. They can be made from pulp derived from unused fibers, such as mechanical, chemical, and / or thermomechanical pulp. They can also be made from broken or recycled paper.

[0063] The fine particles may further contain hemicellulose and / or lignin.

[0064] In some embodiments, the fine particles have a lignin content of 10% by weight or less relative to the total dry weight of the fine particles.

[0065] In some embodiments, the fine particles have a hemicellulose content ranging from 10 to 30% by weight relative to the total dry weight of the fine particles.

[0066] In some embodiments, finer fractions can pass through a 200-mesh screen.

[0067] The method of the present invention is useful for reducing the water retention of cellulose pulp containing fine particles. The purification process used to prepare highly purified cellulose pulp can also result in large variations in the fine particle content. Since fine particles have a significant impact on the properties of highly purified pulp and the films made from it, removing some of the fine particles can also result in a material with more uniform properties. In other words, the method of the present invention can be used to reduce the water retention and / or increase the homogeneity of highly purified cellulose pulp. To further adjust the properties of the highly purified pulp and the films made from the processed pulp, some of the fine particles removed from the pulp may be added back to the coarser fraction. If necessary, fine particles can be added to obtain a desired fine particle content in the pulp, for example, to obtain certain barrier properties in the films later made from the pulp. If necessary, fine particles can be added to compensate for variations in the fine particle content of the coarser fraction, for example, due to variations in the fine particle content of the starting material or variations in dewatering efficiency.

[0068] Therefore, in some embodiments, the method includes reducing the water retention capacity of highly purified cellulose pulp and / or increasing its homogeneity, and the method is a) A step of preparing a highly refined cellulose pulp suspension containing highly refined cellulose pulp having a fiber content of at least 7 million fibers / gram with a length of more than 0.2 mm, based on the Shopper-Leighler (SR) number in the range of 40 to 98 and dry weight as determined by ISO standard 5267-1; b) A step of subjecting a highly purified cellulose pulp suspension to dewatering using a belt filter; c) A step of collecting the dehydrated retained material as a coarse fraction; d) A step of collecting the filtrate as a fine fraction, wherein the collected fine fraction contains 2-50 wt% solids of the highly purified cellulose pulp suspension prepared in step a); e) A step of adding a portion of the cellulose fine particles obtained from the fine fraction to the coarse fraction to obtain highly refined cellulose pulp having reduced water retention and / or increased homogeneity. Includes.

[0069] In some embodiments, the amount of cellulose particles added to the coarse fraction in step e) is less than the amount of cellulose particles collected in step d), preferably in the range of 1 to 75% of the amount of cellulose particles collected in step d), and more preferably in the range of 1 to 50% of the amount of cellulose particles collected in step d).

[0070] In some embodiments, the pulp obtained in step e) has a lower Schöpper-Leighler (SR) number than the highly refined cellulose pulp prepared in step a).

[0071] In some embodiments, the pulp obtained in step e) has a lower water retention value (WRV) than the highly refined cellulose pulp prepared in step a).

[0072] Highly refined cellulose pulp is preferably produced from undried pulp. While undried pulp offers many advantages, one drawback is that it is more difficult to dehydrate compared to dried pulp. The method according to the present invention has been found to be able to dehydrate undried pulp in a good manner to produce highly refined cellulose pulp.

[0073] According to a second aspect of this specification, a purified cellulose pulp having reduced water retention and / or increased homogeneity is provided, which can be obtained by the method of the first aspect of the present invention.

[0074] The highly purified cellulose pulp obtained by the method of the present invention can be advantageously used to manufacture barrier films.

[0075] According to a third aspect shown in this specification, there is provided the use of a highly purified cellulose pulp having reduced water retention and / or increased homogeneity obtained by a method according to a first aspect in the manufacture of a barrier film.

[0076] Problems associated with webs and films formed from highly purified cellulose pulps, particularly those having a Shopper-Reigl (SR) number greater than 80, are that they typically exhibit insufficient tensile and tear strength. Now, it has been found that a web formed from a highly purified cellulose pulp having reduced fines formed according to the method of the present invention has a significantly higher tear strength than the corresponding web formed from the total pulp in which the fines are retained. In the method of the present invention, a base web having a geometric mean tear index (i.e., (tear index (md) × tear index (cd)) 2 exceeding 3.5 mNm 2 / g, preferably exceeding 4 mNm 2 / g, more preferably exceeding 5 mNm 1 / 2 ) can be formed from a highly purified pulp having an SR number greater than 80. The geometric mean tear index is typically less than 10 mNm 2 / g.

[0077] The method of the present invention enables the efficient production of a barrier film containing highly purified cellulose in a paper machine type process. Such films have been found to be very useful, for example, as gas barrier films for packaging applications. These films can be used in place of conventional barrier films such as synthetic polymer films or aluminum foils that reduce the recyclability of paper or paperboard packaging products. The films of the present invention have high repulpability and provide high recyclability of the films and paper or paperboard packaging products containing these films. <00​As used herein, the term barrier film broadly refers to a material forming a thin, continuous sheet with low permeability to gases and / or liquids. Depending on the composition of the pulp suspension, the film may also be considered as a thin paper or even a membrane.

[0079] Barrier films can be used on their own or in combination with one or more other layers. For example, a film is useful as a barrier layer in cardboard-based packaging materials. A barrier film may also be a barrier layer of glassine paper, greaseproof paper, or thin packaging paper, or constitute such a layer.

[0080] Although different arrangements may be conceivable by those skilled in the art to carry out the steps of the present invention, the present invention will be advantageously carried out in a paper machine, more preferably a screen printing machine.

[0081] According to a fourth aspect described herein, a barrier film is provided which is formed from highly purified cellulose pulp that can be obtained by the method of the present invention according to the first aspect. [Modes for carrying out the invention]

[0082] While the present invention has been described in relation to various exemplary embodiments, as will be understood by those skilled in the art, various modifications may be made without departing from the scope of the invention, and equivalent elements may be substituted. Furthermore, many modifications can be made to adapt the teachings of the invention to specific situations or materials without departing from the essential scope of the invention. Thus, the present invention is not limited to the specific embodiments disclosed as the best possible mode for carrying out this invention, but is intended to encompass all embodiments that fall within the scope of the appended claims. [Examples]

[0083] Example 1 (Comparison) Highly purified softwood pulp, purified to an SR value of >90 and possessing a fibril area of ​​approximately 20% (>0.2 mm) and a fiber density of approximately 15 million fibers per gram of sample (>0.2 mm), as determined using an L&W Fiber Tester Plus instrument (L&W / ABB), was prepared at a pH of approximately 7 and a concentration of 1.7 wt% and processed on a pilot paper machine. The specific formation was relatively good at 0.51, and the tensile index ratio (md / cd) of the formed film was approximately 2. The results are shown in Table 1.

[0084] This example demonstrates that while high-density barrier films can be prepared from highly refined pulp, the pulp's drainage resistance is very high, requiring the machine speed to be kept extremely low (30 m / min), and therefore resulting in very slow web production.

[0085] Example 2 (Comparison) Highly purified softwood pulp, purified to an SR value of >90 and possessing a fibril area of ​​approximately 20% (>0.2 mm) and a fiber content of approximately 15 million / gram sample (>0.2 mm) as determined using an L&W Fiber Tester Plus instrument (L&W / ABB), was prepared at a pH of approximately 7 and a concentration of 1.7 wt% and processed on a full-scale paper machine with a long-wire paper machine layout. The ratio formation was approximately 0.7 and the tensile index ratio was approximately 2.

[0086] The machine speed had to be reduced to approximately 130 m / min due to the high drainage resistance of the pulp. The amount of solids removed through the dewatering wire was approximately 2 wt% of the solids content of the highly refined cellulose pulp used as the starting material.

[0087] The results in Table 1 below show that while high-density sheets can be produced, the manufacturing speed is low due to high drainage resistance, and the base formation and uniformity are also negatively affected.

[0088] Example 3 Highly purified softwood pulp, purified to an SR value of over 90 and possessing a fibril area of ​​approximately 20% (>0.2 mm) and a fiber content of approximately 15 million / gram sample (>0.2 mm) as determined using an L&W Fiber Tester Plus instrument (L&W / ABB), was prepared, diluted to a concentration of 0.5–0.6 wt%, and subjected to a twin-wire hybrid former at a speed of 500 m / min at a pH of 6.5–8 and a temperature in the range of 37–44°C.

[0089] The concentration of solids in the white water removed from the pulp during dewatering was approximately 0.05 wt%, which means that the amount of solids removed through the wire during dewatering was approximately 10 wt% of the solids in the highly purified cellulose pulp used as the starting material.

[0090] This example demonstrates that a web containing a large amount of highly purified pulp can be dewatered at high speed, resulting in a web with increased air permeability due to the removal (i.e., fractionation) of a considerable proportion of fine solids from the pulp.

[0091] Interestingly, the ratio formation was 0.43, which is extremely good, and the tensile index ratio was 3.75, which is very high. Furthermore, the tear resistance was extremely good, supporting the idea that using pulp fractionation has a positive effect on web strength.

[0092] Example 4 (Comparison) Coniferous pulp, purified to 82 SR and having a fibril area of ​​approximately 17% (>0.2 mm) and a fiber content of approximately 11 million / gram (>0.2 mm) as determined using an L&W Fiber Tester Plus instrument (L&W / ABB), was prepared into sheets using a Formette apparatus (laboratory apparatus). The basis weight of the formed sheets was 30 gsm. The OTR of the sheets, determined at 23°C / 50% RH, was 189 cc / m². 2 This is based on the fact that the sheet has some barrier properties, but not at the same level as in Comparative Example 1. This is mainly due to the slightly coarser fibrous material compared to Example 1.

[0093] Example 5 This example was performed to demonstrate the effect of coating a substrate web formed from highly purified cellulose pulp with a coating containing fine cellulose cell material in the form of microfibrillated cellulose (MFC).

[0094] This example used the same purified softwood pulp as in Example 4. A 25gsm sheet was formed from the pulp using a Formette apparatus, and then a 5gsm MFC layer was applied to the sheet using a spray apparatus. The MFC was prepared by treating the softwood fibers with an enzyme (cellulase) before high-pressure fluidization. The MFC coating was applied to the substrate web after dehydration but before drying. The basis weight of the substrate web was 25gsm, and the amount of MFC applied to the web was 5gsm. The OTR of the coated sheet, determined at 23°C / 50%RH, was 3, confirming the effect of applying fine MFC to the sheet surface.

[0095] Example 6 Example 1 was repeated on a pilot paper machine, but this time 30% unrefined softwood pulp was added to highly refined cellulose pulp. This gave a highly porous substrate web with no barrier properties.

[0096] Subsequently, the MFC coating used in Example 5 was applied to the dehydrated but not dried web by wet curtain coating.

[0097] The OTR of the coated substrate, determined at 23°C / 50%RH, was 565 cc / m². 2 This was / day. This relatively low OTR supported the fact that the MFC coating could close the surface despite the very high particle / fiber size distribution within the substrate web, which is represented by the addition of 30% unrefined fibers to the highly refined pulp. TIFF0007880890000001.tif255170TIFF0007880890000002.tif34170

Claims

1. A method for fractionating highly purified cellulose pulp into fine and coarse fractions, wherein the method is a) To provide a highly refined cellulose pulp suspension containing highly refined cellulose pulp having a fiber content of at least 7 million fibers / gram having a length of more than 0.2 mm, based on the Shopper-Leighler (SR) number in the range of 40 to 98 and dry weight as determined by ISO standard 5267-1; b) subjecting a highly purified cellulose pulp suspension to dehydration in a belt filter; c) Collecting the dehydrated retained material as a coarse fraction; d) Collecting the filtrate as fine fractions; Includes, The collected fine fraction contains 2-50 wt% solids of the highly purified cellulose pulp suspension provided in step a). method.

2. The method according to claim 1, wherein the highly refined cellulose pulp provided in step a) has a Schöpper-Leighler (SR) number in the range of 50 to 98 as determined by ISO standard 5267-1.

3. The method according to claim 1 or 2, wherein the collected fine fraction contains 5 to 40 wt% solids of the highly purified cellulose pulp suspension provided in step a).

4. The method according to any one of claims 1 to 3, wherein the collected fine fraction contains at least 10 to 30 wt% solids of the highly purified cellulose pulp suspension provided in step a).

5. The method according to any one of claims 1 to 4, wherein the concentration of the highly purified cellulose pulp suspension provided in step a) is in the range of 0.1 to 1.5 wt%.

6. The method according to any one of claims 1 to 5, wherein the concentration of the dehydrated retained material collected in step c) is at least 5 wt%.

7. The method according to any one of claims 1 to 6, wherein the coarse fraction has a Shopper-Leighler (SR) number of less than 95 as determined by ISO standard 5267-1.

8. The method according to any one of claims 1 to 7, wherein fine fractions can pass through a 200-mesh screen.

9. The belt filter is 4000m at 100 Pa. ３ / m ２ The method according to any one of claims 1 to 8, comprising a wire belt having air permeability exceeding 1 / hour.

10. The method according to any one of claims 1 to 9, wherein the belt of the belt filter moves at a speed of at least 50 m / min.

11. The method according to any one of claims 1 to 10, wherein the residence time of highly purified cellulose pulp on the belt is less than 7 seconds.

12. The method according to any one of claims 1 to 11, wherein the belt filter is a single-wire or twin-wire type belt filter.

13. The method according to any one of claims 1 to 12, wherein the amount of cellulose particles added to the coarse fraction is less than the amount of cellulose particles collected in step d).

14. The method according to any one of claims 1 to 13, wherein the amount of cellulose particles added to the coarse fraction is in the range of 1 to 75% of the amount of cellulose particles collected in step d).

15. The method according to any one of claims 1 to 14, wherein the amount of cellulose particles added to the coarse fraction is in the range of 1 to 50% of the amount of cellulose particles collected in step d).

16. The method according to any one of claims 13 to 15, wherein the pulp obtained after adding a portion of cellulose fine particles has a lower Schöpper-Leighler (SR) number than the highly purified cellulose pulp provided in step a).

17. The method according to any one of claims 13 to 16, wherein the pulp obtained after adding a portion of cellulose fine particles has a lower water retention value (WRV) than the highly purified cellulose pulp provided in step a).

18. A barrier film formed from highly purified cellulose pulp, which can be obtained by the method described in any one of claims 1 to 17.

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