Packaging body for cellulose fine fiber wet cake

Abstract

To provide a wet cake packaging body in which cellulose fine fiber wet cake is packaged in a container and the wet cake hardly remains in the container when it is taken out from the container and thus yield is good.SOLUTION: A wet cake packaging body according to the present invention comprises a wet cake containing water and cellulose microfibers packaged within the container, wherein the compressive strength of the wet cake is 10 N or more.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a package of cellulose fine fiber wet cake. [Background technology]

[0002] Cellulose microfibers are widely used as additives to improve the strength of nonwoven sheets, filter aids to improve filtration performance, food additives, and more. In addition, the use of organic fibers such as cellulose fibers as fillers for thermoplastic resins has been investigated. Cellulose is a promising filler for environmentally friendly resin compositions because it is an environmentally friendly material, has a low specific gravity, and can have excellent physical property-enhancing effects on resin compositions. In particular, cellulose microfibers, due to their microstructure, can exhibit excellent reinforcing effects on resin compositions even in small amounts, and in recent years, their use as fillers for resin compositions has been investigated. A commonly used method for producing cellulose microfibers is to process a dilute dispersion with a low solids content using a refiner, high-pressure homogenizer, or the like. Dilute dispersions, as they are difficult to incorporate into resins as fillers, require concentration. However, cellulose microfibers are highly prone to aggregation due to hydrogen bonding between cellulose molecules, and excessive concentration reduces redispersibility (i.e., the ability to redisperse concentrated cellulose microfibers), resulting in difficulty in achieving uniform dispersion in resins. Therefore, various techniques for concentrating cellulose fine fibers have been proposed in order to achieve a state in which the cellulose fine fibers exhibit an excellent reinforcing effect and are well dispersed in a resin.

[0003] Patent document 1 describes a method for at least partially removing a solvent from a suspension containing microfibrillated cellulose, which comprises providing the microfibrillated cellulose in a solvent, applying the microfibrillated cellulose onto an at least partially apertured substrate, and exposing the microfibrillated cellulose to a vacuum while being applied onto the apertured substrate. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Special Publication No. 2022-512507 Summary of the Invention [Problem to be solved by the invention]

[0005] Wet cakes containing water and cellulose fine fibers (also referred to as cellulose fine fiber wet cakes in the present disclosure) are commercially available from several suppliers. However, the solid content of commercially available products is generally 10% by mass or less, and the volume of the wet cake is significantly larger than the net volume of the cellulose fine fibers, resulting in transportation costs. Another problem is that wet cakes with such low solid content tend to remain in the container when removed from the container. Specifically, cellulose fine fiber wet cakes tend to be easily deformed when they contain a large amount of water or when the water content is locally high. Such easily deformed wet cakes tend to remain in the container (e.g., a bag) when removed from the container, resulting in low yield. The method described in Patent Document 1 concentrates microfibrillated cellulose, but even with this method, the large solid content thickness tends to result in localized unevenness in the solid concentration. The low solid concentration portion tends to remain in the container. In particular, cellulose wet cakes are prone to mold during storage, so they are sometimes stored in small portions in airtight containers. When the amount of wet cake in the package is reduced due to the division into smaller portions, the problem of reduced yield becomes more pronounced.

[0006] One aspect of the present invention aims to solve the above-mentioned problems and provide a wet cake package in which cellulose fine fiber wet cake is packaged in a container, and the wet cake is less likely to remain in the container when removed from the container, resulting in good yield. [Means for solving the problem]

[0007] The present disclosure encompasses the following aspects. [1] A wet cake package in which a wet cake containing water and cellulose fine fibers is packaged in a container, A wet cake package, wherein the compressive strength of the wet cake is 10 N or more. [2] Item 2. The wet cake package according to item 1, wherein a water dilution of the wet cake exhibits a sedimentation rate of 1% or more and 60% or less at a solids content of 0.05% by mass. [3] 3. The wet cake package according to item 1 or 2, wherein the solid content of the wet cake is 15% by mass or more and 50% by mass or less. [4] 4. The wet cake package according to any one of items 1 to 3, wherein the average lignin content of the cellulose fine fibers in the dried wet cake is 2% by mass or less. [5] 5. The wet cake package according to any one of items 1 to 4, wherein the average hemicellulose content of the cellulose fine fibers in the dried wet cake is 8% by mass or less. [Effects of the Invention]

[0008] According to one aspect of the present invention, a wet cake package can be provided in which cellulose fine fiber wet cake is packaged in a container, and the wet cake is less likely to remain in the container when removed from the container, resulting in a good yield. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, exemplary embodiments of the present invention (hereinafter abbreviated as "present embodiments") will be described, but the present invention is not limited to these embodiments. Note that, unless otherwise specified, the characteristic values ​​of the present disclosure are values ​​measured by the methods described in the "Examples" section of the present disclosure or by methods that will be understood by those skilled in the art to be equivalent thereto.

[0010] <Wet cake packaging> One aspect of the present invention provides a wet cake package in which a wet cake containing water and cellulose fine fibers (also referred to in the present disclosure as a cellulose fine fiber wet cake or simply as a wet cake) is packaged in a container. In one aspect, the wet cake has a compressive strength of 10 N or more. The inventors have discovered that a wet cake with high compressive strength is less likely to change shape, making it easy to handle when removed from a container and less likely to remain in the container, resulting in less loss. Suppressing a decrease in yield due to loss is advantageous in reducing inconveniences such as decreased productivity and variations in the amount of material charged in the next process.

[0011] The compressive strength of the wet cake in one aspect is 10 N or more, preferably 12 N or more, and more preferably 15 N or more. There is no upper limit, but from the viewpoint of maintaining good dispersibility of the cellulose fine fibers, it is preferable that the compressive strength is not too high, and from this viewpoint, in one aspect, the compressive strength is 100 N or less, preferably 75 N or less, and more preferably 50 N or less. The compressive strength is a value measured using a tension-compression tester.

[0012] Samples for measuring the compressive strength of wet cake are prepared as follows: A small amount of wet cake is placed in a cylinder 50 mm in diameter and 100 mm in length, a cylinder 40 mm in diameter and 100 mm in length is placed on top, and the cake is compressed with a 2 kg weight repeatedly until the entire cylinder is filled with the cake. The compressed cake is then pushed out with a cylinder 40 mm in diameter to prepare a cylindrical compressed cake sample. The diameter and length of the obtained cylindrical sample are measured using a scale.

[0013] The sample is subjected to compression measurement using a tension and compression tester (for example, an autograph manufactured by Shimadzu Corporation) at a test speed of 5 mm / min to measure the compressive strength.

[0014] Without being bound by theory, it may be advantageous for the cellulose fine fibers to be well entangled in the wet cake in order to increase the compressive strength of the wet cake. The compressive strength can be controlled by adjusting the defibration conditions of the cellulose fiber raw material, the concentration conditions of the cellulose fine fibers, the solids concentration of the wet cake, etc.

[0015] <Cellulose microfibers> The cellulose fine fibers may be obtained from various cellulose fiber raw materials selected from natural cellulose and regenerated cellulose. Examples of natural cellulose include wood pulp obtained from wood species (broadleaf or coniferous), non-wood pulp obtained from non-wood species (cotton, bamboo, hemp, bagasse, kenaf, cotton linter, sisal, straw, etc.), and cellulose fiber aggregates produced by animals (e.g., sea squirts), algae, and microorganisms (e.g., acetic acid bacteria). Examples of regenerated cellulose include regenerated cellulose fibers (e.g., viscose, cupro, Tencel), cellulose derivative fibers, and ultrafine threads of regenerated cellulose or cellulose derivatives obtained by electrospinning. These raw materials can be mechanically beaten, fibrillated, or refined using a grinder or refiner to adjust the fiber diameter, fiber length, degree of fibrillation, etc., or can be bleached or purified using chemicals to adjust the content of components other than cellulose (e.g., acid-insoluble components such as lignin, alkali-soluble polysaccharides such as hemicellulose, etc.).

[0016] [Specific surface area] The specific surface area of ​​the cellulose fine fibers is preferably 2 m2 or less in order to obtain the effect of improving the physical properties of the cellulose fine fibers. 2 / g or more, preferably 3m 2 / g or more, preferably 5m 2 / g or more, preferably 7m 2 / g or more, preferably 10m 2 / g or more, preferably 12m 2 / g or more, preferably 15m 2 / g or more, preferably 17m 2 / g or more, preferably 20m 2 / g or more, preferably 22m2 / g or more, preferably 25m 2 / g or more, preferably 27m 2 In order to disperse the cellulose fine fibers well as desired, the cellulose fine fibers are preferably dispersed in a water-soluble polymer having a viscosity of 400 m / g or more. 2 / g or less, preferably 350m 2 / g or less, preferably 300m 2 / g or less, preferably 250m 2 / g or less, preferably 200m 2 / g or less, preferably 170m 2 / g or less, preferably 150m 2 / g or less, preferably 120m 2 / g or less, preferably 100m 2 / g or less.

[0017] The specific surface area of ​​the cellulose microfibers is measured by measuring the BET specific surface area of ​​a porous sheet of cellulose microfibers with a specific surface area / pore size distribution analyzer (e.g., Nova-4200e, manufactured by Quantachrome Instruments) using nitrogen gas. Specifically, approximately 0.2 g of the porous sheet is dried under vacuum at 120°C for 5 hours, and then the amount of nitrogen gas adsorbed at the boiling point of liquid nitrogen is measured at five points (multipoint method) in the range of relative vapor pressure (P / P0) between 0.05 and 0.2, and the BET specific surface area (m 2 / g) is calculated.

[0018] [Porous sheet] The porous sheet is produced by first adding a concentrated cake of cellulose fine fibers with a solid content of 10% by mass or more in water to tert-butanol, and dispersing it using a high-shear homogenizer (e.g., IKA Ultra-Turrax T18, processing conditions: rotation speed 15,000 rpm x 3 minutes) until no aggregates remain. The concentration is adjusted to 0.5% by mass per 0.5 g of cellulose fine fiber solids. 100 g of the resulting tert-butanol dispersion is filtered through filter paper. Without peeling the filter paper, the filtrate is sandwiched between two larger pieces of filter paper, and dried in an oven at 150°C for 5 minutes while pressing down on the edges of the larger paper with weights. The filter paper is then peeled off to obtain a porous sheet with minimal distortion. The air resistance R of this sheet is adjusted to a sheet basis weight of 10 g / m. 2 A porous sheet with a flow rate of 100 sec / 100 ml or less is used as the measurement sample. To ensure stable and reproducible measurements, a porous sheet without distortion is used.

[0019] The air resistance R was measured by measuring the basis weight W (g / m) of a porous sheet sample left to stand for one day in an environment of 23°C and 50% RH. 2 After measuring the air permeability, the air permeability resistance R (sec / 100 ml) is measured using an Oken type air permeability resistance tester (for example, manufactured by Asahi Seiko Co., Ltd., Model EG01). At this time, the air permeability resistance R (sec / 100 ml) is calculated according to the following formula: 2 Calculate the value per unit area. Weight 10g / m 2 Air resistance per unit (sec / 100ml) = R / W x 10

[0020] The specific surface area of ​​the cellulose fine fibers can be calculated by the converted fiber diameter of the cellulose fine fibers using the following formula, assuming that the cellulose fine fibers are cylindrical. The density of cellulose is 1.5 (g / cm 3 ), the volume per gram of cellulose is 6.7 × 10 -7 (m 3 / g). If the converted fiber diameter of cellulose microfibers is r (m), the average circumferential length of cellulose microfibers = πr, and the average cross-sectional area of ​​cellulose microfibers = 0.25πr 2 , so the total fiber length per 1g of cellulose fine fiber is 6.7 x 10 -7 (m 3 / g) / average cross-sectional area (=0.25πr 2 ) Total surface area = specific surface area (m 2 / g) = 6.7 × 10 -7 (m 3 / g) / average cross-sectional area (=0.25πr 2 )×average outer circumference length (=πr)=6.7×10 -7 (m 3 / g) / 0.25r = 26.68×10 -7 (m 3 / g) / r Therefore, Equivalent fiber diameter r (m) = 26.68 x 10 -7 (m 3 / g) / specific surface area (m 2 / g) For example, if the BET specific surface area of ​​the porous sheet is 40 m 2 The equivalent fiber diameter r of the cellulose fine fibers is calculated to be 66.7 nm.

[0021] In one embodiment, the equivalent fiber diameter of the cellulose fine fibers is preferably 2 to 1000 nm from the viewpoint of obtaining a good effect of improving physical properties by the cellulose fine fibers, and more preferably 4 nm or more, or 5 nm or more, or 10 nm or more, or 15 nm or more, or 20 nm or more, and more preferably 900 nm or less, or 800 nm or less, or 700 nm or less, or 600 nm or less, or 500 nm or less, or 400 nm or less, or 300 nm or less, or 200 nm or less.

[0022] The cellulose fine fibers may be chemically modified cellulose fine fibers (also referred to as chemically modified cellulose fine fibers). The cellulose fine fibers may be chemically modified with a modifying agent, for example, at the stage of raw cellulose fiber, during or after defibration treatment, or during or after preparation of a slurry as a dispersion, or during or after the drying and granulation process. Examples of chemically modified cellulose fine fibers include inorganic esters such as nitrate esters, sulfate esters, phosphate esters, silicate esters, and borate esters, organic esters such as acetylated and propionated esters, ethers such as methyl ether, hydroxyethyl ether, hydroxypropyl ether, hydroxybutyl ether, carboxymethyl ether, and cyanoethyl ether, and TEMPO oxides obtained by oxidizing the primary hydroxyl groups of cellulose. The chemical modification may contain one or more types of modifying groups.

[0023] In one embodiment, cellulose fine fibers are fine cellulose obtained by beating and fibrillating pulp or the like using mechanical force such as a beater or refiner, and then defibrating the cellulose by a pulverization method such as a high-pressure homogenizer, microfluidizer, ball mill, disc mill, or mixer (e.g., a homomixer).

[0024] In one embodiment, an example of a method for obtaining cellulose fine fibers is a method of subjecting a cellulose fiber raw material to a micronization treatment. The micronization treatment can be carried out by a known micronization treatment method. For example, when obtaining cellulose fine fibers having a number average fiber diameter or equivalent fiber diameter of less than 1000 nm (e.g., 2 nm or more and less than 1000 nm) from fibers having a number average fiber diameter or equivalent fiber diameter of 1000 nm or more, the micronization can be carried out by treatment using, for example, a grinder such as a mass colloider or a high-pressure homogenizer in water or an organic solvent.

[0025] The medium used in the micronization treatment is preferably water, but other media (for example, organic solvents, inorganic acids, bases and / or ionic liquids) may also be used, and these may be added to water.

[0026] The organic solvent is not particularly limited, but examples thereof include alcohols having 1 to 6 carbon atoms, preferably 1 to 3 carbon atoms, such as methanol, ethanol, and propanol; ketones having 3 to 6 carbon atoms, such as acetone, methyl ethyl ketone, and methyl isobutyl ketone; linear or branched saturated or unsaturated hydrocarbons having 1 to 6 carbon atoms; aromatic hydrocarbons such as benzene and toluene; halogenated hydrocarbons such as methylene chloride and chloroform; lower alkyl ethers having 2 to 5 carbon atoms; and polar solvents such as DMSO, DMF, DMAc, NMP, and diesters of succinic acid and triethylene glycol monomethyl ether. These solvents can be used alone or in combination of two or more. From the viewpoint of operability of the micronization treatment, alcohols having 1 to 6 carbon atoms, ketones having 3 to 6 carbon atoms, lower alkyl ethers having 2 to 5 carbon atoms, DMSO, DMF, DMAc, NMP, methyl triglycol succinate diester, and toluene are preferred. The cellulose fine fiber wet cake of this embodiment may also contain the above-mentioned organic solvents.

[0027] Examples of inorganic acids include hydrochloric acid, sulfuric acid, phosphoric acid, nitric acid, and boric acid. From the viewpoint of defibration efficiency and ease of handling, one or more acids selected from the group consisting of hydrochloric acid, sulfuric acid, and phosphoric acid are preferred. Examples of bases include hydroxides such as sodium hydroxide, potassium hydroxide, and calcium hydroxide; carbonates such as sodium carbonate, potassium carbonate, and calcium carbonate; and nitrogen compounds such as ammonia and organic amines (triethylamine, triethanolamine, etc.). However, from the viewpoint of defibration efficiency and ease of handling, one or more bases selected from the group consisting of hydroxides, carbonates, ammonia, and organic amines are preferred.

[0028] In the present disclosure, an ionic liquid refers to a liquid salt that contains an organic ion in at least one of the cation and anion moieties, and the melting point of the ion alone is 100° C. or less. The cation moiety of the ionic liquid preferably has at least one cation selected from the group consisting of imidazolium cation, pyrrolidinium cation, piperidinium cation, morpholinium cation, pyridinium cation, quaternary ammonium cation, and phosphonium cation.

[0029] The amount of water or organic solvent used in the micronization treatment is not particularly limited as long as it is an effective amount capable of dispersing the fibers before micronization, but is preferably 1 time by mass or more, more preferably 10 times by mass or more, even more preferably 50 times by mass or more, and preferably 2000 times by mass or less, more preferably 1000 times by mass or less, relative to the fibers before micronization.

[0030] Known dispersers are preferably used as the equipment for the micronization treatment. For example, a disintegrator, beater, refiner, low-pressure homogenizer, high-pressure homogenizer, ultra-high-pressure homogenizer, homomixer, grinder, mass colloider, cutter mill, ball mill, jet mill, single-screw extruder, twin-screw extruder, ultrasonic agitator, household juicer mixer, etc. can be used. The cellulose fine fibers can be recovered in the form of a dispersion in a liquid medium or in the form of a dried product. In addition to water, the liquid medium in the dispersion may further contain other liquid media (e.g., one or more of the organic solvents exemplified above) either singly or in combination.

[0031] (Cellulose microfiber wet cake) The cellulose fine fiber wet cake may be a concentrate obtained by deliquoring the cellulose fine fiber dispersion produced by defibration in the above-mentioned pulverization treatment. In one embodiment, the concentrate may be obtained by deliquoring the cellulose fine fiber dispersion produced in the above-mentioned defibration step. In a preferred embodiment, in the concentration step, the cellulose fine fiber dispersion is suction-deliquored to produce an intermediate concentrate, and the intermediate concentrate is then press-deliquored to produce a concentrate. In this manner, suction-deliquoring is performed under relatively mild conditions to produce an intermediate concentrate with a relatively low cellulose fine fiber content, and then the intermediate concentrate is further concentrated by press-deliquoring to produce a concentrate with a desired cellulose fine fiber content. When suction-deliquoring is performed under mild conditions, the cellulose fine fibers are easily entangled with each other, and an intermediate concentrate that is resistant to disintegration (i.e., strong) can be formed. Such a strong intermediate concentrate can be advantageous for producing a wet cake with high compressive strength. Furthermore, such a strong intermediate concentrate is less likely to penetrate the filtration substrate (described later), is less likely to deform during press deliquification, and is less likely to escape sideways from the press rolls (described later) (i.e., liquid pools are less likely to form on the sides of the rolls), which contributes to improving the yield of the concentrate and the process efficiency of the concentration step. The combination of suction deliquification and press deliquification is also advantageous in terms of reducing the size of the entire concentration apparatus.

[0032] In one embodiment, the mass content of cellulose fine fibers in the cellulose fine fiber dispersion supplied to the concentration step is 0.3% by mass or more, or 0.5% by mass or more, or 0.7% by mass or more, or 1.0% by mass or more, or 1.5% by mass or more, and in another embodiment, 5.0% by mass or less, or 4.0% by mass or less, or 3.0% by mass or less, or 2.5% by mass or less. When the mass content of cellulose fine fibers in the dispersion is equal to or greater than the above-mentioned lower limit, the liquid film of the dispersion is concentrated to form a concentrate, so that the film does not become too thin, making it difficult for pinholes to occur, and concentration proceeds while maintaining a uniform state. In addition, when the dispersion is concentrated on a filtration substrate described below, if the mass content of cellulose fine fibers is equal to or greater than the above-mentioned lower limit, the cellulose fine fibers are easily entangled with each other and therefore do not easily pass through the filtration substrate, forming an intermediate concentrate that is difficult to flow, which is advantageous for improving the compressive strength of the wet cake, improving the yield of the concentrate, and improving the process efficiency of the concentration step. On the other hand, when the mass content of the cellulose fine fibers is equal to or less than the upper limit, the thixotropy or viscosity of the dispersion does not become too high, so that the thickness of the dispersion tends to be uniform and the mass content of the cellulose fine fibers in the concentrate is less likely to vary. Such small variations can be advantageous for improving the compressive strength of the wet cake.

[0033] A concentrating device (more specifically, a deliquifying device) for concentrating a cellulose fine fiber dispersion is advantageously a continuous type from the viewpoint of reducing variation in the mass content of cellulose fine fibers in the concentrate of the cellulose fine fiber dispersion. The concentrating device is equipped with a concentration mechanism that receives and deliquifies the cellulose fine fiber dispersion. An example of the concentration mechanism is a combination of a filter substrate that holds the cellulose fine fiber dispersion thereon and a suction unit that deliquifies the cellulose fine fiber dispersion on the filter substrate by reducing the pressure from the filter substrate side. Other examples of concentration mechanisms include a method of deliquifying the cellulose fine fiber dispersion on the filter substrate by gravity, a method of squeezing the cellulose fine fibers between two filter substrates, a method of squeezing the cellulose fine fibers between a press roll and a press belt to perform press deliquifying, and a method of deliquifying by squeezing and shearing using a cylindrical screen and a screw inside the cylinder. The concentration mechanism, which is a combination of the filter substrate and the suction unit, is advantageous in that it is less likely to leak from the edges of the filter substrate and can concentrate even dilute dispersions with high fluidity. The concentration mechanism, which is a combination of the press roll and the press belt, is advantageous in that the concentration level can be easily adjusted and a concentrate with little variation in the cellulose fine fiber content can be produced.

[0034] In one embodiment of packaging the cellulose fine fiber wet cake, the cellulose fine fiber wet cake discharged from the discharge section of the concentrating device is received in a container. The container is appropriately replaced to fill the cellulose fine fiber wet cake into the container. The container filled with the cellulose fine fiber wet cake may be sealed, for example, using a heat sealer. Examples of the container include a box and a bag, and the shape and dimensions are not limited. The material of the container is also not limited, and may be one or more materials, such as polymers (polyethylene, polypropylene, etc.) and aluminum (for example, as a laminate of an aluminum layer and a polymer layer). The sealing method is also not limited to a heat sealer, and sealing with sealer tape or vacuum packing, for example, can also be used. From an industrial perspective, sealing in a vacuum state, such as vacuum packing, is likely to be complicated due to the increased equipment and processes required, so a simple sealing method such as a heat sealer is preferred.

[0035] [Settling rate] The settling rate of the wet cake diluted with water at a solids content of 0.05% by mass is preferably 60% or less. When the settling rate is within this range, the fibers form a network structure and become entangled with each other, which tends to result in the wet cake exhibiting high mechanical properties (strength), particularly compressive strength, and being less prone to deformation. The settling rate is more preferably 50% or less, more preferably 40% or less, more preferably 30% or less, and most preferably 25% or less. In terms of the resistance of the wet cake to deformation, a lower settling rate is advantageous, but from the viewpoint of redispersibility, the settling rate may, in one embodiment, be 1% or more, or 1.3% or more, or 1.5% or more.

[0036] In one embodiment, the settling rate is a value measured by the following procedure. The wet cake and pure water are added to a 100 ml plastic bottle, and a dispersion treatment is performed using a high-shear homogenizer (e.g., manufactured by IKA, trade name "Ultra Turrax T18"; treatment conditions: rotation speed 15,000 rpm × 3 minutes) until no aggregates are present, producing a 1.0 mass% solids slurry. Approximately 5 g of the 1.0 mass% slurry is thinly spread using an infrared heating moisture content meter, and the solids content of the slurry is measured three times at a heating temperature of 150°C, with the average value being the solids content of the slurry. Based on this solids content, the slurry and pure water are added to a 50 ml plastic bottle, and a dispersion treatment is performed using a high-shear homogenizer to produce a 0.5 mass% slurry. The 0.5 mass% slurry is then placed in a vial, diluted exactly 10-fold with pure water, sealed, and stirred in a vortex mixer for 30 seconds to produce a 0.05 mass% slurry. 22 g of this 0.05% by mass slurry was placed in a Narika screw-cap test tube (25 mL capacity, dimensions: φ18 × 160 mm) and the liquid level was measured. The tube was then left to stand for 30 minutes, and the transparent upper part and the cloudy sediment lower part were visually distinguished, and the liquid level of the sedimented part was measured. The respective heights obtained were used to calculate the sedimentation rate using the following formula: Sedimentation rate (%) = {1 - (liquid surface height of sedimentation area after 30 minutes / liquid surface height of dispersion liquid)} x 100 During this dilution and dispensing process, concentration changes due to settling of cellulose microfibers and solid-liquid separation when using a dropper, etc., can lead to concentration variations in the 0.05% by mass slurry, so care must be taken, such as shaking the mixture before dilution or using a dropper, etc. with a diameter of φ3 mm or more.

[0037] [Solid content] The solid content of the cellulose fine fiber wet cake is preferably 15% by mass or more, or 18% by mass or more, or 20% by mass or more from the viewpoint of easily realizing the desired compressive strength of the wet cake, and is preferably 50% by mass or less, or 40% by mass or less, or 35% by mass or less from the viewpoint of obtaining good redispersibility of the cellulose fine fibers. The solid content is a value measured using an infrared moisture meter. Specifically, about 1.5 g of the wet cake is weighed out, spread thinly, and heated to 150°C to measure the solid content.

[0038] [Lignin and hemicellulose content] In one embodiment, the cellulose fine fibers may contain hemicellulose. Hemicellulose is understood by those skilled in the art as a component obtained as the alkali-soluble portion of holocellulose obtained by solvent extraction and chlorine treatment of plants (e.g., wood) (i.e., the component remaining after excluding α-cellulose from holocellulose). Hemicellulose is a polysaccharide containing hydroxyl groups, and can cause deterioration in heat resistance, physical properties, discoloration, and dispersibility in resins of the cellulose fine fibers. Therefore, it is preferable that the amount of hemicellulose in the cellulose fine fibers is small.

[0039] In the dried wet cake, the average hemicellulose content of the cellulose fine fibers is preferably 8% by mass or less, or 7% by mass or less, relative to 100% by mass of the cellulose fine fibers, from the viewpoint of maintaining good functionality of the cellulose fine fibers. A lower average hemicellulose content is advantageous, and in one embodiment it may be 0% by mass, but in one embodiment it may be 3% by mass or more from the viewpoint of ease of production of the cellulose fine fibers.

[0040] The average hemicellulose content can be determined by the method described in the non-patent literature (Wood Science Experiment Manual, edited by the Japan Wood Research Society, pp. 92-97, 2000), by subtracting the α-cellulose content from the holocellulose content (Wise method). This method is recognized in the industry as a method for measuring hemicellulose content. The alkali-soluble polysaccharide content is calculated twice for each sample, and the number average of the calculated hemicellulose contents is taken as the average hemicellulose content.

[0041] In the dried wet cake, the average lignin content of the cellulose fine fibers is preferably 2% by mass or less, more preferably 1.5% by mass or less, and even more preferably 1% by mass or less, relative to 100% by mass of the cellulose fine fibers, from the viewpoint of avoiding a decrease in the heat resistance of cellulose and the resulting discoloration. A lower average lignin content is advantageous, and in one aspect, it may be 0% by mass. When a lignin-containing pulp is used, the degree of delignification (purification) may be such that the average lignin content of the cellulose fine fibers is 0.1% by mass or more.

[0042] In one embodiment, the average lignin content can be quantified by the following procedure. 3 ml of a 72% by weight sulfuric acid aqueous solution is added to 300 mg of a defatted sample, and the sample is allowed to swell in a water bath at 30°C for 1 hour. The sample is poured into a 125 ml pressure bottle with 84 ml of distilled water and autoclaved at 120°C for 1 hour to hydrolyze the sample. The sample is then suction filtered while still hot using a Shibata Chemical Co., Ltd. 1GP100 glass filter set at 105°C. The residue is suction filtered and washed using distilled water. The residue is dried at 105°C until it reaches a constant weight. A portion of the resulting dried residue is ignited in an electric furnace at 600°C for 2 hours, allowed to cool in a desiccator for 45 minutes, weighed, and the ash content is calculated using the following formula: Ash content (%) = Ashed sample (g) / Dry residue (g) × 100 The acid-insoluble lignin content is calculated from the dry weight and ash content of the defatted sample using the following formula. Acid-insoluble lignin content (%) = acid-insoluble lignin fraction (g) / dry weight of defatted sample (g) × 100 × (100 - ash content) / 100 The filtrate obtained by suction filtration after hydrolysis is diluted so that the absorbance at the maximum absorption wavelength of 205 to 210 nm in the UV spectrum is 0.3 to 0.8. The acid-soluble lignin content of the adjusted solution is calculated using the following formula. Acid-soluble lignin content (%) = d × v × (As-Ab) / a × w × 100 d: Dilution ratio v: Filtrate constant volume (L) As: absorbance of the sample solution Ab: absorbance of blank solution a: absorption coefficient of lignin w: sample amount (g) The lignin content is calculated from the acid-insoluble lignin content and the acid-soluble lignin content using the following calculation formula. Lignin content (%) = Acid-insoluble lignin content (%) + Acid-soluble lignin content (%) The number average of the lignin contents calculated for the two samples is taken as the average lignin content. [Example]

[0043] The following examples further illustrate exemplary embodiments of the present invention, but the present invention is not limited to these examples.

[0044] Evaluation Method <Wet cake compressive strength> A small amount of wet cake was placed in a cylinder 50 mm in diameter and 100 mm in length, and a cylinder 40 mm in diameter and 100 mm in length was placed on top. The cake was compressed with a 2 kg weight and the process was repeated until the entire cylinder was filled with cake. The compressed cake was extruded with a 40 mm diameter cylinder to produce a cylindrical compressed cake sample. The diameter and length of the obtained cylindrical sample were measured using a scale.

[0045] The above sample was subjected to measurement of compressive strength of the wet cake, which was performed using a tension / compression testing machine (Shimadzu Corporation, Autograph, Model AG-5000G) at a test speed of 5 mm / min.

[0046] <Settling rate> The wet cake and pure water were added to a 100 ml plastic bottle and dispersed using a high-shear homogenizer (IKA, trade name "Ultra Turrax T18"; processing conditions: rotation speed 15,000 rpm x 3 minutes) until no aggregates were present, producing a 1.0 wt% solids slurry. Approximately 5 g of the 1.0 wt% slurry was thinly spread using an infrared heating moisture content meter, and the solids content of the slurry was measured three times at a heating temperature of 150 °C. The average value was used as the solids content of the slurry. Using this solids content as a reference, the slurry and pure water were added to a 50 ml plastic bottle and dispersed using a high-shear homogenizer to produce a 0.5 wt% slurry. The 0.5 wt% slurry was then placed in a vial, diluted exactly 10-fold with pure water, sealed, and stirred in a vortex mixer for 30 seconds to produce a 0.05 wt% slurry. 22 g of this 0.05% by mass slurry was placed in a Narica screw-cap test tube (volume 25 mL, dimensions: φ18 × 160 mm), and the liquid level was measured. After that, it was left to stand for 30 minutes, and the transparent part on the top and the cloudy sediment part on the bottom were visually distinguished, and the liquid level of the sediment part was measured. The respective heights obtained were used to calculate the sedimentation rate according to the following formula. The measurement was carried out at room temperature (22°C). Sedimentation rate (%) = [1 - (liquid surface height of sedimented area after 30 minutes) / liquid surface height of dispersion] x 100 During this dilution and dispensing procedure, changes in concentration due to settling of cellulose microfibers and solid-liquid separation when using a dropper, etc., can lead to concentration variations in the 0.05 mass% slurry. Therefore, the mother liquor was shaken before dilution, and a dropper with a diameter of φ3 mm or more was used.

[0047] <Solid content> Approximately 1.5 g of the cellulose fine fiber wet cake was weighed out and spread thinly using an infrared moisture meter (manufactured by A&D, product name "heat drying moisture meter MX-50"), and the solid content was measured at a heating temperature of 150°C.

[0048] <Preparation of degreased samples> The cellulose microfibers were air-dried, crushed in a Willey mill, and then sieved to a particle size of approximately 200-500 μm to prepare a crushed sample. 10-20 g of the crushed sample was extracted with a Soxhlet extractor using an ethanol-benzene mixed solvent for 6 hours. The extracted sample was then further extracted with alcohol for 4 hours. The extracted sample was then dried to prepare a defatted sample.

[0049] <Holocellulose content> To calculate the holocellulose content, 2.0 g of the defatted sample prepared as described above was added to approximately 150 ml of distilled water, 1.0 g of sodium chlorite, and 0.2 ml of acetic acid and heated at 70–80°C for 1 hour. This process was repeated 3–4 times until the sample was decolorized to white. The mixture was then suction filtered using a Shibata Chemical 1GP100 glass filter set at 105°C. The residue was washed with cold water and acetone. It was dried at 105°C to a constant weight and weighed. A portion of the resulting dried residue (as the holocellulose fraction) was ignited in an electric furnace at 600°C for 2 hours, cooled in a desiccator for 45 minutes, and weighed. The ash content was calculated using the following formula: Ash content (mass%) = Ashed sample (g) / Dry residue (g) × 100 The holocellulose content was calculated from the dry weight and ash content of the defatted sample using the following formula. Holocellulose content (%) = holocellulose fraction (g) / dry weight of defatted sample (g) × 100 × (100 - ash content) / 100

[0050] <α-cellulose content> To 1.0 g of the holocellulose fraction, 25 ml of 17.5% by mass NaOH aqueous solution at 20°C was added, covered with a watch glass, and left for 3 minutes. The mixture was lightly crushed with a glass rod until swollen, then again covered with a watch glass and left. 30 minutes after adding the NaOH aqueous solution, 25 ml of distilled water was added, stirred for 1 minute, and left at 20°C for 5 minutes. Suction filtration was performed using a Shibata Chemical Co., Ltd. 1GP100 glass filter set at 105°C and washed until the filtrate was neutral. The residue was suction filtered using 40 ml of 10% by mass acetic acid aqueous solution, followed by suction filtration with 1 L of boiling water. The residue was dried to a constant weight at 105°C and weighed. A portion of the resulting dried residue (as the α-cellulose fraction) was ignited in an electric furnace at 600°C for 2 hours, cooled in a desiccator for 45 minutes, and weighed. The ash content was calculated using the following formula: Ash content (mass%) = Ashed sample (g) / Dry residue (g) × 100 The α-cellulose content was calculated from the dry weight and ash content of the defatted sample using the following formula. α-cellulose content (mass%) = α-cellulose fraction (g) / dry weight of defatted sample (g) × 100 × (100 - ash content) / 100

[0051] <Average hemicellulose content> The hemicellulose content was calculated from the holocellulose content and α-cellulose content obtained by the above procedure using the following calculation formula. Hemicellulose content (mass%) = holocellulose content (mass%) - α-cellulose content (mass%) The value obtained from two samples (i.e., n=2) was taken as the average hemicellulose content.

[0052] <Evaluation of the likelihood of cellulose fine fiber wet cake remaining> Approximately 50 g of cellulose microfiber wet cake was weighed and placed in a Unipack K-8 bag manufactured by Seiichi Corporation, the zipper closed, and the cake was shaken. The cake was then transferred to another unused Unipack K-8 bag and shaken again. This process was repeated five times, and the weight of the remaining cake was measured. The likelihood of residue was expressed as the weight loss rate and calculated using the following formula: Ease of retention (%) = {1 - (remaining cake weight (g) / initially added cake weight (g))} × 100

[0053] ≪Materials used≫ <Cellulose> Refined cotton linter pulp Cotton linter pulp sheets obtained from Marubeni Corporation were used.

[0054] <Production Example 1> (Production of cellulose fine fiber dispersion) One part purified cotton linter pulp was dispersed with 49 parts water (solids content: 2% by mass) using a pulper manufactured by Aikawa Iron Works Co., Ltd., and then diluted with 66.7 parts water to prepare a dispersion (solids content: 1.5% by mass). The dispersion was then passed through the discs 30 times using an Aikawa Iron Works SDR14 Lab Refiner (disc blade: blade width: 0.8 mm, groove width: 1.5 mm) with a 0.25 mm inter-disc clearance to obtain a beaten dispersion. The beaten dispersion was then processed three times using a high-pressure homogenizer (NS3015H manufactured by Niro Soavi) at a pressure of 80 MPa or less to obtain a cellulose fine fiber dispersion (aqueous dispersion) with a solids content of 1.5% by mass.

[0055] <Production Example 2> (Production of cellulose fine fiber dispersion) 49 parts by mass of water was added to 1 part by mass of purified cotton linter pulp and dispersed using a pulper manufactured by Aikawa Iron Works Co., Ltd. (solid content: 2% by mass), and then 66.7 parts by mass of water was added to dilute the mixture to prepare a dispersion (solid content: 1.5% by mass). Then, using an SDR14 Lab Refiner manufactured by Aikawa Iron Works Co., Ltd. (disc blade: blade width: 0.8 mm, groove width: 1.5 mm) as a disc refiner device, the dispersion was passed between the discs 30 times for beating treatment with an inter-disc clearance of 0.02 mm, to obtain a cellulose fine fiber dispersion (aqueous dispersion) with a solid content concentration of 1.5% by mass.

[0056] <Production of cellulose fine fiber wet cake> Example 1 The cellulose fine fiber dispersion obtained in Production Example 1 was dehydrated and concentrated using a continuous concentrator. 3 The mixture was poured into a tank and stirred at a peripheral speed of 0.7 m / sec to maintain a uniform dispersion. The circulating filter substrate (material: nylon) was pumped at a speed of 1.5 m / min, and the dispersion was pumped at a rate of 15 L / min using a mono pump. The dispersion was then temporarily stored and supplied to the filter substrate. The cellulose fine fibers were then deliquored in the suction section, resulting in a layer of concentrated cellulose fine fibers, yielding an intermediate concentrate. This intermediate concentrate was then sandwiched between a press roll and a press belt while still on the filter substrate, and deliquored to produce a cellulose fine fiber wet cake. The wet cake was then scraped off with a scraper at the exit of the press roll and collected in a Unipack K-8 (Seinichi Co., Ltd.).

[0057] <Example 2> The cellulose fine fiber dispersion obtained in Production Example 1 was dehydrated and concentrated using a continuous concentrator. 3 The mixture was poured into a tank and stirred at a peripheral speed of 0.7 m / sec to maintain a uniform dispersion. A circulating filter substrate (material: nylon) was pumped at a speed of 1.0 m / min, and the dispersion was pumped at a rate of 10 L / min using a mono pump. The dispersion was then temporarily stored and supplied onto the filter substrate. The cellulose fine fibers were then deliquored in the suction section, resulting in a layer of concentrated cellulose fine fibers, yielding an intermediate concentrate. This intermediate concentrate was then sandwiched between a press roll and a press belt while still on the filter substrate, and deliquored to produce a cellulose fine fiber wet cake. The wet cake was then scraped off with a scraper at the exit of the press roll and collected in a Unipack K-8 (Seinichi Co., Ltd.).

[0058] Example 3 The cellulose fine fiber dispersion obtained in Production Example 2 was dehydrated and concentrated using a continuous concentrator. 3The mixture was poured into a tank and stirred at a peripheral speed of 0.7 m / sec to maintain a uniform dispersion. The circulating filter substrate (material: nylon) was pumped at a speed of 1.5 m / min, and the dispersion was pumped at a rate of 15 L / min using a mono pump. The dispersion was then temporarily stored and supplied to the filter substrate. The cellulose fine fibers were then deliquored in the suction section, resulting in a layer of concentrated cellulose fine fibers, yielding an intermediate concentrate. This intermediate concentrate was then sandwiched between a press roll and a press belt while still on the filter substrate, and deliquored to produce a cellulose fine fiber wet cake. The wet cake was then scraped off with a scraper at the exit of the press roll and collected in a Unipack K-8 (Seinichi Co., Ltd.).

[0059] <Comparative Example 1> The cellulose fine fiber dispersion obtained in Production Example 1 was dehydrated and concentrated using a continuous concentrator. 3 The mixture was poured into a tank and stirred at a peripheral speed of 0.7 m / sec to maintain a uniform dispersion. The circulating filter substrate (material: nylon) was pumped at a speed of 3.5 m / min, and the dispersion was pumped at a rate of 60 L / min using a mono pump. The dispersion was supplied to the filter substrate via a temporary storage section, and the cellulose fine fibers were concentrated in a layer at the suction section to obtain an intermediate concentrate. This intermediate concentrate was then sandwiched between a press roll and a press belt while still on the filter substrate and pressed for deliquification to produce a cellulose fine fiber wet cake. The cellulose fine fiber wet cake was scraped off with a scraper at the exit of the press roll and collected in a Unipack K-8 (Seinichi Co., Ltd.).

[0060] <Comparative Example 2> Daicel Miraize Co., Ltd.'s Celish (product number: KY-100G) was opened and transferred to Seinichi Co., Ltd.'s Unipack K-8.

[0061] The cellulose fine fiber wet cakes produced in Examples 1 to 3 and Comparative Examples 1 and 2 were subjected to the above-described procedures for measuring the settling rate, solid content, and average hemicellulose content, and for evaluating the likelihood of cake residue. The results are shown in the table below.

[0062] [Table 1]

[0063] As can be seen from the evaluation results shown in Table 1, it was confirmed that in Comparative Examples 1 and 2, in which the compressive strength of the wet cake was low, the wet cake was likely to remain in the container. On the other hand, it was confirmed that in Examples 1 to 3, in which the compressive strength of the wet cake was high, the amount of wet cake remaining in the container was suppressed. [Industrial Applicability]

[0064] In the wet cake package of the present disclosure, the cellulose fine fiber wet cake has high compressive strength, so the wet cake is resistant to deformation, has little residue in the container when removed from the container, and is highly redispersible. Such wet cake can be suitably applied to a wide range of applications that utilize resin compositions reinforced with cellulose fine fibers, such as industrial machine parts, general machine parts, automobile, railway, vehicle, ship, and aerospace related parts, electronic and electrical parts, building and civil engineering materials, daily necessities, sports and leisure goods, housing components for wind power generation, containers and packaging components, etc.

Claims

1. A wet cake package in which a wet cake containing water and cellulose fine fibers is packaged in a container, A wet cake package, wherein the compressive strength of the wet cake is 10 N or more.

2. The wet cake package according to claim 1, wherein the wet cake diluted with water exhibits a settling rate of 1% or more and 60% or less at a solids content of 0.05% by mass.

3. The wet cake package according to claim 1 or 2, wherein the solid content of the wet cake is 15% by mass or more and 50% by mass or less.

4. The wet cake package according to claim 1 or 2, wherein the average lignin content of the cellulose fine fibers in the dried wet cake is 2 mass% or less.

5. 3. The wet cake package according to claim 1, wherein the average hemicellulose content of the cellulose fine fibers in the dried wet cake is 8% by mass or less.

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