Chemically modified microfibrillated cellulose fiber and method for producing the same

Abstract

To provide chemical modified microfibril cellulose fibers capable of bringing both a reinforcement effect due to long fibers and density improvement / interfiber bond due to fine fibers when mixed with paper by including a relatively large amount of long fibers and including fine fibers and comparatively long fibers with sufficient balance and capable of expecting strength improvement.SOLUTION: When classifying an aqueous suspension constituted of chemicals modified microfibril cellulose fibers and having a solid content concentration of 0.25% on the conditions of a flow rate of 5.7 L / min, a water temperature of 25±1°C and the total outflow of 22 L using a fiber classification analyzer, the chemicals modified microfibril cellulose fibers have the following fiber characteristics; (a) the length distribution (%) of fibers having a length weight of 0.0-0.2 mm is 40% or more; and (b) the length distribution (%) of fibers having a length weight of 0.2-7.6 mm is 35% or more.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to chemically modified microfibrillated cellulose fibers and a method for producing the same. More specifically, it relates to chemically modified microfibrillated cellulose fibers containing fibers of a wide range of lengths.

Background Art

[0002] Chemically modified microfibrillated cellulose fibers are obtained by modifying a cellulose raw material such as pulp and then defibrating or pulverizing it, and are expected to be used as additives for improving paper strength and water retention, and as additives for foods and cosmetics.

[0003] For example, Patent Document 1 describes a microfibrillated cellulose-containing material having a viscosity of 2800 mPa·s or more and a haze value of 10% or more and 50% or less, measured at 3 rpm and 25°C using a B-type viscometer. Patent Document 2 describes oxidized microfibrillated cellulose having a Canadian standard drainage degree of less than 200 ml and an average fiber diameter of 500 nm or more. Patent Document 3 describes carboxymethylated microfibrillated cellulose fiber paper having a Canadian standard drainage degree of 200 ml or more and an average fiber diameter of 500 nm or more.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Disclosure of the Invention

Problems to be Solved by the Invention

[0005] However, the microfibrillated cellulose fibers described in Patent Documents 1 to 3 have a tendency of shortening of the fibers and a biased fiber size distribution. In such a case, for example, when mixed with paper or other materials, the effects of long fiber blending (design properties such as reinforcement effect and fiber feel and orientation) cannot be obtained. On the other hand, with ordinary pulp, improvement of paper strength with a small amount of addition like microfibrillated cellulose fibers cannot be expected. In view of the above, an object of the present invention is to provide a chemically modified microfibrillated cellulose fiber containing fibers having a wide distribution of lengths, and a method for producing the same.

Means for Solving the Problems

[0006] The inventors found that when a water-based suspension of chemically modified microfibrillated cellulose fibers with a solid content concentration of 0.25% was classified using a fiber classification analyzer under the conditions of a flow rate of 5.7 L / min, a water temperature of 25 ± 1 °C, and a total outflow volume of 22 L, the above problems can be solved by using chemically modified microfibrillated cellulose fibers having the following fiber properties. (a) The fiber length distribution (%) with a length weight of 0.0 mm to 0.2 mm is 40% or more (b) The fiber length distribution (%) with a length weight of 0.2 mm to 7.6 mm is 35% or more Therefore, the above problems are solved by the following present invention.

[0007] (1) Chemically modified microfibrillated cellulose fibers having the following fiber properties when a water-based suspension of chemically modified microfibrillated cellulose fibers with a solid content concentration of 0.25% is classified using a fiber classification analyzer under the conditions of a flow rate of 5.7 L / min, a water temperature of 25 ± 1 °C, and a total outflow volume of 22 L. (a) The fiber length distribution (%) with a length weight of 0.0 mm to 0.2 mm is 40% or more (b) The fiber length distribution (%) with a length weight of 0.2 mm to 7.6 mm is 35% or more (2) The chemically modified microfibrillated cellulose fiber according to (1), wherein the chemically modified microfibrillated cellulose fiber is a cellulose fiber having a carboxyl group. (3) The chemically modified microfibrillated cellulose fiber according to (1) to (2), wherein the chemically modified microfibrillated cellulose fiber is carboxymethylated cellulose. (4) A method for producing a chemically modified microfibrillated cellulose fiber, comprising the following steps (A) to (B): (A) A step of preparing a chemically modified cellulose; (B) A step of defibrating the chemically modified cellulose at a pH of 3 to 7 and a solid content concentration of 15% by mass or less; which comprises: A method for producing a chemically modified microfibrillated cellulose fiber, wherein the chemically modified microfibrillated cellulose fiber has the following characteristics (a) to (b). When an aqueous suspension of composite fibers with a solid content concentration of 0.3% is classified using a fiber classification analyzer under the conditions of a flow rate of 5.7 L / min, a water temperature of 25 ± 1 °C, and a total outflow volume of 22 L, (a) The fiber length distribution (%) with a length-weighted of 0.0 mm to 0.2 mm is 40% or more (b) The fiber length distribution (%) with a length-weighted of 0.2 mm to 7.6 mm is 35% or more (5) A method for producing a chemically modified microfibrillated cellulose fiber, comprising the following steps (A) to (C): (A) A step of preparing a chemically modified cellulose; (B) A step of defibrating the chemically modified cellulose at a pH of 3 to 7 and a solid content concentration of 15% by mass or less; (C) A step of adjusting the pH of the aqueous dispersion of the chemically modified microfibrillated cellulose fiber obtained by the defibrating treatment to 7 or more which comprises: A method for producing a chemically modified microfibrillated cellulose fiber, wherein the chemically modified microfibrillated cellulose fiber has the following characteristics (a) to (b). When an aqueous suspension of composite fibers with a solid content concentration of 0.3% is classified using a fiber classification analyzer under the conditions of a flow rate of 5.7 L / min, a water temperature of 25 ± 1 °C, and a total outflow volume of 22 L, (a) The fiber length distribution (%) with a length-weighted of 0.0 mm to 0.2 mm is 40% or more (b) The fiber length distribution (%) with a length-weighted of 0.2 mm to 7.6 mm is 35% or more [[Effect of the Invention]]

[0008] The chemically modified microfibrillated cellulose fibers of the present invention contain a relatively large number of long fibers, and by well-balancing fine fibers and relatively long fibers, when mixed with, for example, paper, both the reinforcing effect of the long fibers and the density improvement and fiber-to-fiber bonding by the fine fibers are considered to be brought about, and an improvement in strength is expected. Further, since there are relatively many long fibers, it is expected to exhibit characteristic design properties (fiber feel, orientation) when mixed with paints and the like.

Mode for Carrying Out the Invention

[0009] The present invention will be described in detail. In the present invention, "X to Y" includes the end values X and Y. including.

[0010] The chemically modified microfibrillated cellulose fibers of the present invention are obtained by subjecting an aqueous suspension of chemically modified microfibrillated cellulose fibers having a solid content concentration of 0.25% to a classification treatment using a fiber classification analyzer under the conditions of a flow rate of 5.7 L / min, a water temperature of 25 ± 1°C, and a total outflow volume of 22 L, and when analyzing the obtained image, (a) the fiber length distribution (%) with a length weight of 0.0 mm to 0.2 mm is 40% or more, and (b) the fiber length distribution (%) with a length weight of 0.2 mm to 7.6 mm is 35% or more. The fiber length distribution is measured, for example, by the following method. · Fiber length distribution: Dilute the slurry of chemically modified microfibrillated cellulose fibers with water so that the solid content concentration becomes 0.25%, and apply it to a fractionator twice at about 250 G each (50 g of which is used for measurement) under the conditions of a flow rate of 5.7 L / min, a water temperature of 25 ± 1°C, and a total outflow volume of 22 L, and obtain approximately 2000 images of the chemically modified microfibrillated cellulose fibers classified inside the apparatus with a CCD camera attached to the fractionator. Appropriately set the fiber analysis parameters of the analysis software IMG (Metso), analyze the obtained approximately 2000 images, and obtain data such as the fiber length distribution.

[0011] By having such fiber characteristics, for example, when mixed with paper, it is considered that both the reinforcing effect by long fibers and the density improvement and fiber - to - fiber bonding by micro - fibers are brought about, and the strength is improved.

[0012] The method for producing chemically modified microfibrillated cellulose fibers of the present invention preferably includes: (A) a step of preparing chemically modified cellulose; (B) a step of defibrating the chemically modified cellulose at a pH of 3 to 7 and a solid content concentration of 15 mass% or less.

[0013] (1) Step A <Chemically modified cellulose> The chemically modified cellulose used as a raw material for the chemically modified microfibrillated cellulose fibers of the present invention is one in which the cellulose chains constituting the fibers are chemically modified. Examples of the type of chemically modified cellulose include, but are not limited to, carboxylated cellulose into which a carboxyl group has been introduced, carboxyalkylated cellulose in which a carboxyalkyl group such as a carboxymethyl group is ether - bonded, and phosphoric acid - esterified cellulose into which a phosphate group has been introduced. Among them, oxidation (carboxylation), etherification (for example, carboxyalkylation), cationization, and esterification are preferred, and oxidation (carboxylation) and carboxyalkylation are more preferred. These production methods will be described later.

[0014] Chemically modified cellulose may take the form of a salt, and in this specification, when referring to chemically modified cellulose, it shall include salt - type chemically modified cellulose. Examples of salt - type chemically modified cellulose include those forming metal salts such as sodium salts.

[0015] The chemically modified cellulose used for the chemically modified microfibrillated cellulose fibers of the present invention is one in which at least a part of the fibrous shape is maintained even when dispersed in water. That is, when observing an aqueous dispersion of chemically modified cellulose fibers with an electron microscope or the like, fibrous substances can be observed, and when measured by X - ray diffraction, peaks of cellulose I - type crystals can be observed.

[0016] <Chemically modified microfibrillated cellulose fiber> The chemically modified microfibrillated cellulose fiber of the present invention is obtained by appropriately beating or defibrillating (fibrillating) a chemically modified cellulose raw material using a refiner or the like. The chemically modified microfibrillated cellulose fiber shows fibrillation of cellulose microfibrils on the fiber surface as compared with the chemically modified cellulose fiber that has not been beaten or defibrillated. Also, as compared with the chemically modified cellulose nanofiber, it has a larger fiber diameter and has a shape in which the fiber surface is efficiently fluffed (externally fibrillated) while suppressing the refinement (internal fibrillization) of the fiber itself.

[0017] In addition, the chemically modified microfibrillated cellulose fiber of the present invention has characteristics such as high water retention and high thixotropy due to chemical modification as compared with the microfibrillated cellulose fiber that has not been chemically modified.

[0018] Also, the chemically modified microfibrillated cellulose fiber obtained by fibrillating the chemically modified cellulose raw material of the present invention has a weaker strong hydrogen bond existing between the fibers because the cellulose fiber is chemically modified during fibrillization as compared with the one obtained by chemically modifying after beating the cellulose raw material that has not been chemically modified. Therefore, the fibers are easily loosened from each other during fibrillization and have the characteristic that the damage to the fibers is small.

[0019] The chemically modified microfibrillated cellulose fiber of the present invention has an average fiber diameter of 500 nm or more, preferably 1 μm or more, and more preferably 5 μm or more. The upper limit of the average fiber diameter is preferably 60 μm or less, more preferably 40 μm or less, still more preferably 30 μm or less, and still more preferably 20 μm or less. By performing appropriate fibrillization to such an extent that the average fiber diameter is within this range, it exhibits higher water retention as compared with the cellulose fiber that has not been defibrillated, and also provides a high strength-imparting effect and a yield-improving effect even in a small amount as compared with the finely defibrillated cellulose nanofiber.

[0020] The average fiber length of the chemically modified microfibrillated cellulose fiber is preferably 5 μm or more, preferably 10 μm or more, preferably 20 μm or more, and more preferably 30 μm or more. The upper limit of the average fiber length is not particularly limited, but is preferably 3000 μm or less, preferably 2500 μm or less, more preferably 2000 μm or less, and even more preferably 1500 μm or less. According to the present invention, since the chemically modified cellulose raw material is used for beating or defibrating, fibrillation can be promoted without extremely shortening the fibers. In addition, due to the improvement in affinity with water by chemical modification, the water retention property can be increased even when the fiber length is long.

[0021] The above average fiber diameter and average fiber length can be determined by an image analysis type fiber analyzer such as the L&W Fiber Tester Plus manufactured by ABB Ltd. or the fractionator manufactured by Valmet Corporation. Specifically, when using a fractionator, they can be determined as length-weighted fiber width and length-weighted average fiber length, respectively.

[0022] The aspect ratio of the chemically modified microfibrillated cellulose fiber is preferably 3 or more, more preferably 5 or more, and even more preferably 10 or more. The upper limit of the aspect ratio is not particularly limited, but is preferably 1000 or less, more preferably 100 or less, and even more preferably 80 or less. The aspect ratio can be calculated by the following formula: Aspect ratio = average fiber length / average fiber diameter The fibrillation rate (Fibrillation %) measured using a fractionator manufactured by Valmet Corporation for the chemically modified microfibrillated cellulose fiber is preferably 0.5% or more, more preferably 0.8% or more, and even more preferably 1.0% or more. Although the fibrillation rate varies depending on the type of cellulose raw material used, fibrillation is considered to be carried out within the above range. In addition, in the present invention, the fibrillation rate (f 0) It is preferable to perform fibrillation so as to improve. When the fibrillation rate of the fibrillated chemically modified cellulose fiber is f, the difference in fibrillation rate Δf = f - f 0 only needs to exceed 0, preferably 0.1% or more, more preferably 0.2% or more, and even more preferably 0.3% or more.

[0023] <Degree of crystallinity of cellulose type I> In the chemically modified microfibrillated cellulose fiber of the present invention, the degree of crystallinity of cellulose is 50% or more for crystalline type I, and more preferably 60% or more. The crystallinity of cellulose can be controlled by the degree of chemical modification. The upper limit of the degree of crystallinity of cellulose type I is not particularly limited. Realistically, it is considered that about 90% is the upper limit.

[0024] The method for measuring the degree of crystallinity of cellulose type I of the chemically modified cellulose fiber is as follows: Place the sample in a glass cell and measure it using an X-ray diffractometer (LabX XRD-6000, manufactured by Shimadzu Corporation). The degree of crystallinity is calculated using the method of Segal et al. Using the diffraction intensity in the range of 2θ = 10° to 30° of the X-ray diffraction pattern as the baseline, it is calculated from the diffraction intensity of the 002 plane at 2θ = 22.6° and the diffraction intensity of the amorphous part at 2θ = 18.5° by the following formula. Xc = (I002c - Ia) / I002c × 100 Xc = Degree of crystallinity of cellulose type I (%) I002c: Diffraction intensity of the 002 plane at 2θ = 22.6° Ia: Diffraction intensity of the amorphous part at 2θ = 18.5°.

[0025] <Degree of anionicization> The degree of anionicity (anionic charge density) of the chemically modified microfibrillated cellulose fiber of the present invention is usually 2.50 meq / g or less, preferably 2.30 meq / g or less, more preferably 2.00 meq / g or less, still more preferably 1.50 meq / g or less, and even more preferably 1.00 meq / g or less. Thereby, compared with chemically modified cellulose fibers having a higher degree of anionicity, it is considered that the chemical modification is made more uniform over the entire cellulose, and it is considered that the effects peculiar to chemically modified cellulose fibers such as water retention can be obtained more stably. The lower limit is usually 0.08 meq / g or more, preferably 0.10 meq / g or more, more preferably 0.30 meq / g or more, but is not particularly limited. Therefore, 0.08 meq / g or more and 2.50 meq / g or less are preferable. The degree of anionicity is the equivalent of anions per unit mass of the chemically modified microfibrillated cellulose fiber, and can be calculated from the equivalent of diallyldimethylammonium chloride (DADMAC) required to neutralize anionic groups in the chemically modified microfibrillated cellulose fiber per unit mass. In the present invention, the method for measuring the degree of anionicity is as follows: Disperse the chemically modified microfibrillated cellulose fiber in water to prepare an aqueous dispersion with a solid content of 10 g / L, and stir at 1000 rpm for 10 minutes or more using a magnetic stirrer. After diluting the obtained slurry to 0.1 g / L, collect 10 ml, and titrate with diallyldimethylammonium chloride (DADMAC) of 1 / 1000 normal concentration using a streaming current detector (Mutek Particle Charge Detector 03). Using the added amount of DADMAC until the streaming current becomes zero, calculate the degree of anionicity by the following formula.: q=(V×c) / m q: Degree of anionicity (meq / g) V: Added amount of DADMAC until the streaming current becomes zero (L) c: Concentration of DADMAC (meq / L) m: Mass of the chemically modified microfibrillated cellulose fiber in the measurement sample (g)

[0026] <Water retention capacity> The water retention capacity of the chemically modified microfibrillated cellulose fiber of the present invention is preferably 15 or more as measured by the following method. The method for measuring the water retention capacity is as follows: Prepare 40 mL of a slurry (medium: water) with a solid content of 0.3% by mass of the chemically modified microfibrillated cellulose fiber. Let the mass of the slurry at this time be A. Next, centrifuge the entire amount of the slurry at 30 °C and 25,000 G for 30 minutes using a high-speed cooling centrifuge to separate the aqueous phase and the sediment. Let the mass of the sediment at this time be B. Also, put the aqueous phase in an aluminum cup and dry it at 105 °C for one day and night to remove water, and measure the mass of the solid content in the aqueous phase. Let the mass of the solid content in this aqueous phase be C. Use the following formula to calculate the water retention capacity: Water retention capacity = (B + C - 0.003×A) / (0.003×A - C).

[0027] As shown in the above formula, the water retention capacity corresponds to the mass of water in the sediment relative to the mass of the solid content of the fiber in the sediment. The larger the value, the higher the ability of the fiber to retain water. The water retention capacity of the fibrillated chemically modified cellulose fiber of the present invention is preferably 15 or more, more preferably 20 or more, and even more preferably 30 or more. The upper limit is not particularly limited, but it is considered to be about 200 or less in reality.

[0028] Note that the above method for measuring the water retention capacity is for fibrillated fibers, and it is not usually applicable to non-fibrillated or defibrated fibers or cellulose nanofibers defibrated to single microfibrils. If an attempt is made to measure the water retention capacity of non-fibrillated or defibrated cellulose fibers by the above method, a dense sediment cannot be formed under the above centrifugation conditions, and it is difficult to separate the sediment and the aqueous phase. Also, cellulose nanofibers hardly sediment under the above centrifugation conditions.

[0029] <B-type viscosity> In the present invention, the method for measuring the B-type viscosity is as follows: Weigh the chemically modified microfibrillated cellulose fibers into a polypropylene container, disperse them in 160 ml of ion-exchanged water, and adjust the aqueous dispersion to a solid content of 1% by mass. Adjust the aqueous dispersion to 25°C. Then, in accordance with the method of JIS-Z-8803, use a B-type viscometer (manufactured by Toki Sangyo Co., Ltd.) to measure the viscosity after 1 minute at a rotational speed of 60 rpm.

[0030] The upper limit of the B-type viscosity (25°C, 60 rpm) of the chemically modified microfibrillated cellulose fibers of the present invention is 4,000 mPa·s or less, preferably 3,000 mPa·s or less, more preferably 2,000 mPa·s or less. The lower limit is 10 mPa·s or more, preferably 20 mPa·s or more, more preferably 50 mPa·s or more.

[0031] <Others> The chemically modified microfibrillated cellulose fibers of the present invention preferably have an electric conductivity of 500 mS / m or less when made into an aqueous dispersion with a solid content concentration of 1.0% by mass. More preferably, it is 300 mS / m or less, still more preferably 200 mS / m or less, still more preferably 100 mS / m or less, still more preferably 70 mS / m or less. The lower limit of the electric conductivity is preferably 5 mS / m or more, more preferably 10 mS / m or more. The electric conductivity can be measured by the following method: Prepare 200 g of an aqueous dispersion with a solid content concentration of 1.0% by mass of the chemically modified microfibrillated cellulose fibers and stir well. Then, use an electric conductivity meter (ES-71 type manufactured by HORIBA) to measure the electric conductivity.

[0032] The chemically modified microfibrillated cellulose fibers of the present invention preferably have a BET specific surface area of 30 m 2 / g or more, more preferably 50 m 2 / g or more, still more preferably 70 m 2is / g or more. When the BET specific surface area is high, for example, when used as an additive for papermaking, it is easy to bind to pulp, and there are advantages such as improved yield and enhanced effect of imparting strength to paper. The BET specific surface area can be measured by the following method with reference to the nitrogen gas adsorption method (JIS Z 8830): (1) Take out about 2% slurry of chemically modified microfibrillated cellulose fiber (dispersion medium: water) so that the solid content is about 0.1 g and put it into a centrifuge container, and add 100 ml of ethanol. (2) Add a stirrer and stir at 500 rpm for 30 minutes or more. (3) Take out the stirrer and sediment the chemically modified microfibrillated cellulose fiber under the conditions of 7000 G, 30 minutes, and 30 °C with a centrifuge. (4) Remove the supernatant while trying not to remove the chemically modified microfibrillated cellulose fiber as much as possible. (5) Add 100 ml of ethanol, add a stirrer, stir under the conditions of (2), centrifuge under the conditions of (3), and remove the supernatant under the conditions of (4), and repeat this 3 times. (6) Change the solvent in (5) from ethanol to t-butanol, and repeat stirring, centrifuging, and removing the supernatant 3 times in the same manner as in (5) at room temperature above the melting point of t-butanol. (7) After the final solvent removal, add 30 ml of t-butanol, mix gently, then transfer to a eggplant flask and freeze using an ice bath. (8) Cool in a freezer for 30 minutes or more. (9) Attach to a freeze dryer and freeze dry for 3 days. (10) Perform BET measurement (pretreatment conditions: 105 °C for 2 hours under a nitrogen stream, relative pressure 0.01 - 0.30, sample amount about 30 mg).

[0033] The chemically modified microfibrillated cellulose fiber of the present invention preferably has a transparency (transmittance of light at 660 nm) of less than 60% when it is made into an aqueous dispersion with a solid content of 1% by mass, more preferably 40% or less, still more preferably 30% or less, and even more preferably 20% or less. The lower limit is not particularly limited and may be 0% or more. When the transparency is within such a range, the degree of fibrillation is appropriate and the effects of the present invention can be easily obtained. The transparency can be measured by the following method.: Prepare an aqueous dispersion of the chemically modified microfibrillated cellulose fiber (solid content 1% (w / v), dispersion medium: water), and using a UV-VIS spectrophotometer UV-1800 (manufactured by Shimadzu Corporation), measure the transmittance of light at a wavelength of 660 nm using a rectangular cell with an optical path length of 10 mm.

[0034] When water is used as the dispersion medium, the chemically modified microfibrillated cellulose fiber of the present invention forms a semi-transparent to white gel, or a cream-like or paste-like substance at a solid content concentration of about 2% or more.

[0035] The chemically modified microfibrillated cellulose fiber may be in the state of the dispersion obtained after production, but may be dried if necessary, or redispersed in water. The drying method is not limited at all, and for example, known methods such as freeze-drying method, spray-drying method, shelf drying method, drum drying method, belt drying method, method of thinly spreading on a glass plate etc. and drying, fluidized bed drying method, microwave drying method, heat-generating fan type vacuum drying method can be used. After drying, if necessary, it may be pulverized with a cutter mill, hammer mill, pin mill, jet mill, etc. Also, the method of redispersion in water is not particularly limited, and known dispersion devices can be used.

[0036] The uses of the chemically modified microfibrillated cellulose fibers of the present invention are used in various applications. Also, since the degree of fibrillation is not too strong and an appropriate fiber diameter is maintained, it is considered that they can be particularly optimally used in applications that require fiber strength or applications that require a high yield of fibers. However, they may also be used in other applications. The fields in which the chemically modified microfibrillated cellulose fibers are used are not limited, and various fields in which additives are generally used, for example, food, beverages, cosmetics, pharmaceuticals, papermaking, various chemical products, paints, sprays, agricultural chemicals, civil engineering, construction, electronic materials, flame retardants, household goods, adhesives, detergents, fragrances, lubricating compositions, etc., can be used as thickeners, gelling agents, pastes, food additives, excipients, paint additives, adhesive additives, papermaking additives, abrasives, rubber / plastic compounding materials, water retention agents, shape retention agents, mud conditioners, filter aids, sludge prevention agents, etc.

[0037] <Method for producing chemically modified microfibrillated cellulose fibers> The chemically modified microfibrillated cellulose fibers of the present invention can be produced by first preparing a chemically modified cellulose raw material and then fibrillating it. As the types of chemical modification, as described above, for example, carboxylation of cellulose, carboxyalkylation, phosphoric acid esterification, etc. can be mentioned, but it is not limited thereto. As the chemically modified cellulose raw material to be subjected to fibrillation, commercially available ones may be used, or for example, the cellulose raw material described later can be produced by chemically modifying it by the method described later.

[0038] <Cellulose raw material> The cellulose used as a raw material for the chemically modified microfibrillated cellulose fiber of the present invention is not particularly limited, and examples thereof include those derived from plants, animals (e.g., tunicates), algae, microorganisms (e.g., acetic acid bacteria (Acetobacter)), and microbial products. Examples of those derived from plants include wood, bamboo, hemp, jute, kenaf, agricultural waste residues, cloth, pulp (softwood unbleached kraft pulp (NUKP), softwood bleached kraft pulp (NBKP), hardwood unbleached kraft pulp (LUKP), hardwood bleached kraft pulp (LBKP), softwood unbleached sulfite pulp (NUSP), softwood bleached sulfite pulp (NBSP), thermomechanical pulp (TMP), softwood dissolving pulp, hardwood dissolving pulp, recycled pulp, waste paper, etc.). Further, cellulose powder obtained by pulverizing the above-mentioned cellulose raw material may be used. Any one or a combination of these may be used as the cellulose raw material, but preferably cellulose fibers derived from plants or microorganisms, more preferably cellulose fibers derived from plants, and still more preferably lignocellulosic pulp.

[0039] In order to maintain a crystallinity of 50% or more of cellulose I in the chemically modified microfibrillated cellulose fiber, it is preferable to use cellulose having a high crystallinity of cellulose I as a raw material. The crystallinity of cellulose I of the cellulose raw material is preferably 70% or more, and more preferably 80% or more. The method for measuring the crystallinity of cellulose I is the same as that described above.

[0040] <Carboxylation of Cellulose Raw Material> As an example of a chemically modified cellulose raw material, a carboxylated (introduction of carboxyl groups into cellulose, also referred to as "oxidation") cellulose raw material can be used. As the carboxylated cellulose raw material (also referred to as "oxidized cellulose raw material"), commercially available ones may be used, or the above cellulose raw material may be produced by carboxylating (oxidizing) it by a known method. The amount of carboxyl groups is preferably 0.1 to 2.5 mmol / g, more preferably 0.6 mmol / g to 2.5 mmol / g, and even more preferably 1.0 mmol / g to 2.0 mmol / g with respect to the absolute dry mass of the carboxylated cellulose fiber.

[0041] The amount of carboxyl groups in the carboxylated cellulose can be measured by the following method. Prepare 60 ml of a 0.5 mass% slurry (aqueous dispersion) of carboxylated cellulose, add 0.1 M hydrochloric acid aqueous solution to adjust the pH to 2.5, then dropwise add 0.05 N sodium hydroxide aqueous solution and measure the electrical conductivity until the pH reaches 11. From the amount of sodium hydroxide (a) consumed in the neutralization stage of the weak acid where the change in electrical conductivity is gentle, it is calculated using the following formula.

[0042] Amount of carboxyl groups [mmol / g carboxylated cellulose] = a [ml] × 0.05 / mass of carboxylated cellulose [g] The amount of carboxyl groups in the carboxylated cellulose raw material before fibrillation and the amount of carboxyl groups in the carboxylated cellulose fiber after fibrillation are usually the same.

[0043] As an example of the carboxylation (oxidation) method, a method of oxidizing a cellulose raw material in water using an oxidizing agent in the presence of an N-oxyl compound and a compound selected from the group consisting of bromides, iodides, and mixtures thereof can be mentioned. By this oxidation reaction, the primary hydroxyl group at the C6 position of the glucopyranose ring on the cellulose surface is selectively oxidized, and an aldehyde group and a carboxyl group (-COOH) or carboxylate group (-COO -A cellulose raw material having [specific content] can be obtained. The concentration of the cellulose raw material during the reaction is not particularly limited, but preferably 5% by mass or less.

[0044] The N-oxyl compound refers to a compound capable of generating a nitroxyl radical. As the N-oxyl compound, any compound can be used as long as it promotes the target oxidation reaction. For example, 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO) and its derivatives (such as 4-hydroxy TEMPO) can be mentioned. The amount of the N-oxyl compound used only needs to be a catalytic amount capable of oxidizing the cellulose raw material and is not particularly limited. For example, for 1 g of absolutely dry cellulose raw material, 0.01 mmol to 10 mmol is preferred, 0.01 mmol to 1 mmol is more preferred, and 0.05 mmol to 0.5 mmol is even more preferred. Also, about 0.1 mmol / L to 4 mmol / L is good for the reaction system.

[0045] The bromide is a compound containing bromine, and examples thereof include alkali metal bromides that can dissociate and ionize in water. The iodide is a compound containing iodine, and examples thereof include alkali metal iodides. The amount of the bromide or iodide used can be selected within a range capable of promoting the oxidation reaction. The total amount of the bromide and iodide is, for example, preferably 0.1 mmol to 100 mmol, more preferably 0.1 mmol to 10 mmol, and even more preferably 0.5 mmol to 5 mmol with respect to 1 g of absolutely dry cellulose raw material.

[0046] As the oxidizing agent, known ones can be used. For example, halogen, hypohalous acid, halous acid, perhalic acid or their salts, halogen oxides, peroxides, etc. can be used. Among them, sodium hypochlorite, which is inexpensive and has a low environmental impact, is preferred. The appropriate amount of the oxidizing agent used is, for example, preferably 0.5 mmol to 500 mmol, more preferably 0.5 mmol to 50 mmol, even more preferably 1 mmol to 25 mmol, and most preferably 3 mmol to 10 mmol with respect to 1 g of absolutely dry cellulose raw material. Also, for example, 1 mol to 40 mol is preferred with respect to 1 mol of the N-oxyl compound.

[0047] Even under relatively mild conditions, the oxidation process of the cellulose raw material can proceed efficiently. Therefore, the reaction temperature is preferably 4°C to 40°C, and it may also be at room temperature of about 15°C to 30°C. As carboxyl groups are generated in the cellulose chain as the reaction progresses, a decrease in the pH of the reaction solution is observed. In order to efficiently proceed the oxidation reaction, it is preferable to add an alkaline solution such as an aqueous sodium hydroxide solution to maintain the pH of the reaction solution at 8 to 12, preferably about 10 to 11. The reaction medium is preferably water in terms of ease of handling and difficulty in causing side reactions. The reaction time in the oxidation reaction can be appropriately set according to the degree of progress of oxidation, and is usually 0.5 hours to 6 hours, for example, about 0.5 hours to 4 hours.

[0048] Also, the oxidation reaction may be carried out in two steps. For example, the oxidized cellulose obtained by filtration after the completion of the first-stage reaction is oxidized again under the same or different reaction conditions, so that it can be efficiently oxidized without being inhibited by the reaction of by-produced sodium chloride in the first-stage reaction.

[0049] As another example of the carboxylation (oxidation) method, a method of oxidizing by bringing a gas containing ozone into contact with the cellulose raw material can be mentioned. By this oxidation reaction, the hydroxyl groups at least at the 2-position and 6-position of the glucopyranose ring are oxidized, and the decomposition of the cellulose chain occurs. The ozone concentration in the gas containing ozone is preferably 50 g / m 3 ~250 g / m 3 and preferably 50 g / m 3 ~220 g / m 3It is more preferable. When the solid content of the cellulose raw material is 100 parts by mass, the ozone addition amount to the cellulose raw material is preferably 0.1 part by mass to 30 parts by mass, and more preferably 5 parts by mass to 30 parts by mass. The ozone treatment temperature is preferably 0°C to 50°C, and more preferably 20°C to 50°C. The ozone treatment time is not particularly limited, but is about 1 minute to 360 minutes, and preferably about 30 minutes to 360 minutes. When the ozone treatment conditions are within these ranges, it is possible to prevent the cellulose raw material from being excessively oxidized and decomposed, and the yield of oxidized cellulose becomes good. After the ozone treatment, a post-oxidation treatment may be performed using an oxidizing agent. The oxidizing agent used for the post-oxidation treatment is not particularly limited, and examples thereof include chlorine-based compounds such as chlorine dioxide and sodium chlorite, oxygen, hydrogen peroxide, persulfuric acid, peracetic acid, and the like. For example, these oxidizing agents can be dissolved in a polar organic solvent such as water or alcohol to prepare an oxidizing agent solution, and the post-oxidation treatment can be performed by immersing the cellulose raw material in the solution.

[0050] The amount of carboxyl groups in the carboxylated cellulose raw material can be adjusted by controlling the reaction conditions such as the addition amount of the above-mentioned oxidizing agent and the reaction time.

[0051] <Carboxyalkylation of Cellulose Raw Material> As an example of the chemically modified cellulose raw material, a cellulose raw material having a carboxyalkyl group such as a carboxymethyl group ether-bonded thereto (a carboxyalkylated cellulose raw material) can be used. Such a raw material may be a commercially available one, or may be produced by carboxyalkylating the above-mentioned cellulose raw material by a known method. The carboxyalkyl substitution degree per anhydroglucose unit of cellulose is preferably from 0.01 to 0.50. The upper limit is preferably 0.40 or less. When the carboxyalkyl substitution degree exceeds 0.50, dissolution in water tends to occur, and the fibrous form cannot be maintained in water. In order to obtain the effect of carboxyalkylation, it is necessary to have a certain degree of substitution degree. For example, when the substitution degree is less than 0.02, depending on the application, the advantages of introducing a carboxyalkyl group may not be obtained. Therefore, the carboxyalkyl substitution degree is preferably 0.02 or more, more preferably 0.05 or more, still more preferably 0.10 or more, still more preferably 0.15 or more, even more preferably 0.20 or more, and even more preferably 0.25 or more. The carboxyalkyl substitution degree can be adjusted by controlling the addition amount of the carboxyalkylating agent to be reacted, the amount of the mercerizing agent, the composition ratio of water and the organic solvent, and the like.

[0052] In this specification, the anhydroglucose unit means an individual anhydroglucose (glucose residue) constituting cellulose. Further, the carboxyalkyl substitution degree (also referred to as the degree of etherification) indicates the ratio of the hydroxyl groups in the glucose residue constituting cellulose that are substituted with carboxyalkyl ether groups (the number of carboxyalkyl ether groups per glucose residue). Note that the carboxyalkyl substitution degree may be abbreviated as DS.

[0053] The method for measuring the carboxyalkyl substitution degree is as follows: Weigh accurately about 2.0 g of the sample and place it in a 300 mL Erlenmeyer flask with a stopper. Add 100 mL of nitric acid-methanol (a solution prepared by adding 100 mL of special grade concentrated nitric acid to 1000 mL of methanol), shake for 3 hours to convert the salt form of carboxyalkylated cellulose to the hydrogen form of carboxyalkylated cellulose. Weigh accurately 1.5 - 2.0 g of the hydrogen form of carboxyalkylated cellulose (absolutely dry) and place it in a 300 mL Erlenmeyer flask with a stopper. Moisten it with 15 mL of 80% methanol, add 100 mL of 0.1N-NaOH, and shake at room temperature for 3 hours. Using phenolphthalein as an indicator, back-titrate the excess NaOH with 0.1N-H 2 SO 4 and calculate the degree of carboxyalkyl substitution (DS value) according to the following formula. A = [(100×F’ - 0.1N-H 2 SO 4 (mL)×F)×0.1] / (absolute dry mass of hydrogen form carboxyalkylated cellulose (g)) Degree of carboxyalkyl substitution = 0.162×A / (1 - 0.058×A) F’: Factor of 0.1N-H 2 SO 4 F: Factor of 0.1N-NaOH.

[0054] The degree of carboxyalkyl substitution in the carboxyalkylated cellulose raw material before fibrillation and the degree of carboxyalkyl substitution in the carboxyalkylated cellulose fiber after fibrillation are usually the same.

[0055] As an example of a method for producing a carboxyalkylated cellulose raw material, an example of the production of a carboxymethylated cellulose raw material is described below.

[0056] First, a cellulose raw material is mixed with a solvent and a mercerizing agent, and mercerization of the cellulose raw material is carried out at a reaction temperature of 0 to 70°C, preferably 10 to 60°C, and a reaction time of 15 minutes to 8 hours, preferably 30 minutes to 7 hours. Next, a carboxymethylating agent is added in an amount of 0.05 to 10.0 moles per mole of glucose residue, and carboxymethylation is carried out at a reaction temperature of 30 to 90°C, preferably 40 to 80°C, and a reaction time of 30 minutes to 10 hours, preferably 1 hour to 4 hours.

[0057] As the solvent, 3 to 20 times by mass of water or an organic solvent or a mixture thereof can be used. Examples of the organic solvent include, but are not limited to, alcohols such as methanol, ethanol, N-propyl alcohol, isopropyl alcohol, N-butanol, isobutanol, and tertiary butanol, ketones such as acetone, diethyl ketone, and methyl ethyl ketone, and dioxane, diethyl ether, benzene, dichloromethane, and the like. Among these, monohydric alcohols having 1 to 4 carbon atoms are preferable, and monohydric alcohols having 1 to 3 carbon atoms are more preferable because of their excellent compatibility with water. As the mercerizing agent, an alkali metal hydroxide in an amount of 0.5 to 20 moles per mole of anhydroglucose residue of the cellulose raw material, specifically sodium hydroxide or potassium hydroxide, is preferably used. Examples of the carboxymethylating agent include monochloroacetic acid, sodium monochloroacetate, methyl monochloroacetate, ethyl monochloroacetate, and isopropyl monochloroacetate. Among these, monochloroacetic acid or sodium monochloroacetate is preferable in terms of easy availability of the raw materials. The amount of the carboxymethylating agent used is not particularly limited, but in one embodiment, it is preferably added in the range of 0.5 to 1.5 moles per anhydroglucose unit of cellulose. The lower limit of the above range is more preferably 0.6 mole or more, still more preferably 0.7 mole or more, and the upper limit is more preferably 1.3 moles or less, still more preferably 1.1 moles or less. The carboxymethylating agent can be added to the reactor, for example, as an aqueous solution of 5 to 80% by mass, more preferably 30 to 60% by mass, or can be added in a powdered state without dissolution.

[0058] When using monochloroacetic acid or sodium monochloroacetate as the carboxymethylating agent, the molar ratio of the mercerizing agent to the carboxymethylating agent (mercerizing agent / carboxymethylating agent) is generally 0.90 to 2.45. The reason is that if it is less than 0.90, the carboxymethylation reaction may be insufficient, and unreacted monochloroacetic acid or sodium monochloroacetate may remain, resulting in waste. And if it exceeds 2.45, side reactions may proceed due to the excess mercerizing agent and monochloroacetic acid or sodium monochloroacetate, and there is a risk of generating an alkali metal salt of glycolic acid, which may be uneconomical.

[0059] When performing carboxymethylation of a cellulose raw material, there are usually a method of performing both mercerization and carboxymethylation under a water-based solvent (aqueous medium method) and a method of performing both mercerization and carboxymethylation under a mixed solvent of water and an organic solvent (solvent method). However, in the present invention, a water-based solvent may be used for mercerization, and a mixed solvent of an organic solvent and water may be used for carboxymethylation. By doing so, even when maintaining the crystallinity of cellulose at 50% or more, a carboxymethylated cellulose raw material in which carboxymethyl groups are introduced uniformly rather than locally (that is, the absolute value of the degree of anionicization is small) can be obtained economically.

[0060] Using water as the main solvent (solvent mainly composed of water) means a solvent containing water at a ratio higher than 50% by mass. The water in the solvent mainly composed of water is preferably 55% by mass or more, more preferably 60% by mass or more, still more preferably 70% by mass or more, still more preferably 80% by mass or more, even more preferably 90% by mass or more, and even more preferably 95% by mass or more. Particularly preferably, the solvent mainly composed of water is 100% by mass of water (i.e., water). The greater the proportion of water during mercerization, the advantage of more uniform introduction of carboxymethyl groups into cellulose can be obtained. As the solvent other than water (used in mixture with water) in the solvent mainly composed of water, the organic solvents described above can be used. The amount of the organic solvent in the solvent mainly composed of water is preferably 45% by mass or less, more preferably 40% by mass or less, still more preferably 30% by mass or less, still more preferably 20% by mass or less, even more preferably 10% by mass or less, even more preferably 5% by mass or less, and more preferably 0% by mass.

[0061] Simultaneously with the addition of the carboxymethylating agent, or before or immediately after the addition of the carboxymethylating agent, an organic solvent or an aqueous solution of an organic solvent is appropriately added to the reactor, or an organic solvent other than water during the mercerization treatment is appropriately reduced by means of reduced pressure or the like to form a mixed solvent of water and an organic solvent, and it is preferable to carry out the carboxymethylation reaction under this mixed solvent of water and an organic solvent. The timing of the addition or reduction of the organic solvent may be between after the completion of the mercerization reaction and immediately after the addition of the carboxymethylating agent, and is not particularly limited. For example, within 30 minutes before and after the addition of the carboxymethylating agent is preferable.

[0062] The proportion of the organic solvent in the mixed solvent during carboxymethylation is preferably 20% by mass or more, more preferably 30% by mass or more, still more preferably 40% by mass or more, still more preferably 45% by mass or more, and particularly preferably 50% by mass or more, based on the total of water and the organic solvent. The higher the proportion of the organic solvent, the easier it is for uniform substitution of carboxymethyl groups to occur, and thus the quality of the obtained carboxymethylated cellulose raw material is stabilized. The upper limit of the proportion of the organic solvent is not limited and may be, for example, 99% by mass or less. Considering the cost of the organic solvent to be added, it is preferably 90% by mass or less, more preferably 85% by mass or less, still more preferably 80% by mass or less, and still more preferably 70% by mass or less.

[0063] The reaction medium (a mixed solvent of water and an organic solvent, etc., not containing cellulose) during carboxymethylation preferably has a lower proportion of water (in other words, a higher proportion of the organic solvent) than the reaction medium during mercerization. By satisfying this range, it becomes easier to maintain the crystallinity of the obtained carboxymethylated cellulose raw material, and the fibers of the present invention can be obtained more efficiently. Further, when the reaction medium during carboxymethylation has a lower proportion of water (a higher proportion of the organic solvent) than the reaction medium during mercerization, there is also an advantage that a mixed solvent for the carboxymethylation reaction can be formed by a simple means of adding a desired amount of the organic solvent to the reaction system after the completion of the mercerization reaction when shifting from the mercerization reaction to the carboxymethylation reaction.

[0064] In carboxymethylation, the effective utilization rate of the carboxymethylating agent is preferably 15% or more. More preferably, it is 20% or more, still more preferably 25% or more, and particularly preferably 30% or more. The effective utilization rate of the carboxymethylating agent refers to the ratio of the carboxymethyl groups introduced into cellulose among the carboxymethyl groups in the carboxymethylating agent. By using a solvent mainly composed of water during mercerization and a mixed solvent of water and an organic solvent during carboxymethylation, a carboxymethylated cellulose raw material can be obtained with a high effective utilization rate of the carboxymethylating agent (that is, economically without significantly increasing the amount of the carboxymethylating agent used). The upper limit of the effective utilization rate of the carboxymethylating agent is not particularly limited, but in reality, it is about 80% as the upper limit. Incidentally, the effective utilization rate of the carboxymethylating agent may be abbreviated as AM.

[0065] The calculation method of the effective utilization rate of the carboxymethylating agent is as follows: AM = (DS × number of moles of cellulose) / number of moles of carboxymethylating agent DS: Degree of carboxymethyl substitution (the measurement method will be described later) Number of moles of cellulose: pulp mass (dry mass when dried at 100 °C for 60 minutes) / 162 (162 is the molecular weight per glucose unit of cellulose).

[0066] <Phosphorylation of Cellulose Raw Material> As an example of a chemically modified cellulose raw material, a cellulose raw material esterified with phosphoric acid can be used. Examples of the esterification method include a method of mixing a powder or aqueous solution of a compound having a phosphate group with the cellulose raw material, a method of adding an aqueous solution of a compound having a phosphate group to a slurry of the cellulose raw material, and the like. Examples of the compound having a phosphate group include phosphoric acid, sodium dihydrogen phosphate, disodium hydrogen phosphate, trisodium phosphate, sodium phosphite, potassium phosphite, sodium hypophosphite, potassium hypophosphite, sodium pyrophosphate, sodium metaphosphate, potassium dihydrogen phosphate, dipotassium hydrogen phosphate, tripotassium phosphate, potassium pyrophosphate, potassium metaphosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, triammonium phosphate, ammonium pyrophosphate, ammonium metaphosphate, and the like. One or more of these can be used in combination to introduce a phosphate group into the cellulose raw material. Among these, phosphoric acid, sodium salts of phosphoric acid, potassium salts of phosphoric acid, and ammonium salts of phosphoric acid are preferred from the viewpoints of high efficiency of phosphate group introduction, easy fibrillation in the following fibrillation step, and easy industrial application. Particularly preferred are sodium dihydrogen phosphate and disodium hydrogen phosphate. Further, since the reaction can proceed uniformly and the efficiency of phosphate group introduction is high, it is desirable to use the compound having a phosphate group as an aqueous solution. The pH of the aqueous solution of the compound having a phosphate group is preferably 7 or less from the viewpoint of high efficiency of phosphate group introduction, but preferably pH 3 to 7 from the viewpoint of suppressing hydrolysis of the fiber.

[0067] Examples of the method for producing a cellulose raw material esterified with phosphoric acid include the following method. A compound having a phosphate group is added to a suspension of a cellulose raw material having a solid content concentration of 0.1 to 10% by mass while stirring to introduce a phosphate group into the cellulose. When the cellulose raw material is 100 parts by mass, the addition amount of the compound having a phosphate group is preferably 0.2 to 500 parts by mass, more preferably 1 to 400 parts by mass, in terms of the amount of phosphorus element.

[0068] After dehydrating the suspension of the obtained phosphorylated cellulose raw material, from the viewpoint of suppressing the hydrolysis of cellulose, it is preferable to perform heat treatment at 100 to 170 °C. Further, while water is contained during the heat treatment, it is preferably heated at 130 °C or lower, preferably 110 °C or lower, and after removing the water, it is preferably heat-treated at 100 °C to 170 °C.

[0069] The degree of substitution of phosphate groups per glucose unit of the phosphorylated cellulose raw material is preferably 0.001 or more and less than 0.40. The degree of substitution of phosphate groups in the phosphorylated cellulose raw material before fibrillation and the degree of substitution of phosphate groups in the phosphorylated cellulose fiber after fibrillation are usually the same.

[0070] (2) Step B In Step B, chemically modified cellulose microfibril fibers are obtained by defibrating or beating the chemically modified cellulose raw material. Defibrating or beating in fibrillation is preferably carried out wet (that is, in the form of a dispersion using water or the like as a dispersion medium) using a refiner such as a disk type, conical type, cylinder type, etc., a high-speed defibrator, a shear type stirrer, a colloid mill, a high-pressure jet disperser, a beater, a PFI mill, a kneader, a disperser, etc., but is not particularly limited to these devices, and any device that imparts mechanical defibrating force wet may be used.

[0071] The solid content concentration of the raw material in the dispersion of the chemically modified cellulose raw material to be subjected to fibrillation is preferably 15% by mass or less, more preferably 10% by mass or less. Further, as the lower limit of the concentration, 0.1% by mass or more is preferable, 0.5% by mass or more is more preferable, 1.0% by mass or more is more preferable, and 2.0% by mass or more is more preferable.

[0072] When fibrillating, the pH of the aqueous dispersion of the chemically modified cellulose raw material is preferably 7 or less, more preferably 6 or less, during mechanical treatment. The lower limit of the pH is not particularly limited, but is usually 2 or more, preferably 3 or more, more preferably 4 or more. The pH can be adjusted, for example, by adding an acid (e.g., hydrochloric acid, sulfuric acid) or an alkali (e.g., sodium hydroxide) to the aqueous dispersion.

[0073] Before preparing the dispersion for fibrillation, the chemically modified cellulose raw material obtained by the above method may be dried and pulverized in advance. Subsequently, the dry-pulverized chemically modified cellulose raw material may be dispersed in a dispersion medium and subjected to fibrillation (wet). The apparatus used for dry pulverization of the raw material is not particularly limited, and examples thereof include impact mills such as hammer mills and pin mills, media mills such as ball mills and tower mills, and jet mills.

[0074] As described above, fibrillation is carried out in a range that maintains an average fiber diameter of 500 nm or more, preferably 1 μm or more, more preferably 2 μm or more. The upper limit of the average fiber diameter is preferably 60 μm or less, more preferably 40 μm or less, further preferably 30 μm or less, and still further preferably 20 μm or less. By performing appropriate fibrillation to such an extent that the average fiber diameter is within this range, a higher water retention property is exhibited compared to unfibrillated cellulose fibers, and a high strength imparting effect and a yield improvement effect can be obtained even in a small amount compared to more finely fibrillated cellulose nanofibers.

[0075] (3) Step C Optionally, a step C of adjusting the pH of the chemically modified microfibrillated cellulose fiber suspension obtained in step B to 7 or more may be provided. By adjusting the pH to 7 or more, the proportion of the modified terminals of the chemically modified microfibrillated cellulose fibers being in the separated type (salt type) can be increased. By doing so, the degree of anionicization of the chemically modified microfibrillated cellulose fibers increases, so when blended into paper or the like, the expression of charge control in the paper stock, strength development due to interaction with chemicals, and good dispersibility due to charge repulsion are expected.

Examples

[0076] Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples, but the present invention is not limited thereto. Unless otherwise specified, "parts" and "%" indicate parts by mass and mass%, respectively.

[0077] <Measurement Procedure for Physical Properties of Chemically Modified Microfibrillated Cellulose Fibers> (Chemical Properties) · Amount of carboxyl (COOH) groups: 60 ml of a 0.5 mass% aqueous dispersion of the sample was prepared, and 0.1 M hydrochloric acid aqueous solution was added to adjust the pH to 2.5. Then, 0.05 N aqueous sodium hydroxide solution was added dropwise, and the electrical conductivity was measured until the pH reached 11. From the amount of sodium hydroxide (a) consumed in the neutralization stage of the weak acid with a gentle change in electrical conductivity, it was calculated using the following formula: Amount of carboxyl groups [mmol / g carboxylated cellulose] = a [ml] × 0.05 / mass of carboxylated cellulose [g]. · Measurement method of anionic degree: Chemically modified microfibrillated cellulose fibers were dispersed in water to prepare an aqueous dispersion with a solid content of 10 g / L, and stirred at 1000 rpm for 10 minutes or more using a magnetic stirrer. The obtained aqueous dispersion was diluted to 0.1 g / L, 10 ml was taken, and titrated with 1 / 1000 normal degree of diallyldimethylammonium chloride (DADMAC) using a streaming current detector (Mutek Particle Charge Detector 03). Using the added amount of DADMAC until the streaming current became zero, the anionic degree was calculated by the following formula: q = (V × c) / m q: Anionic degree (meq / g) V: Added amount of DADMAC until the streaming current becomes zero (L) c: Concentration of DADMAC (meq / L) m: Mass of chemically modified microfibrillated cellulose fibers in the measurement sample (g).

[0078] (Fiber Properties) · Fiber length distribution: The slurry of chemically modified microfibrillated cellulose fibers was diluted with water to a solid content concentration of 0.25%, and passed through a fractionator twice at approximately 250 G each (50 g of which was used for measurement) under the conditions of a flow rate of 5.7 L / min, a water temperature of 25 ± 1 °C, and a total effluent volume of 22 L. Approximately 2,000 images of the chemically modified microfibrillated cellulose fibers classified inside the apparatus were obtained using the CCD camera attached to the fractionator. The fiber analysis parameters of the analysis software IMG (Metso) were set as shown in Tables 1 and 2, and approximately 2,000 acquired images were analyzed to obtain data such as the average fiber length, average fiber width, and fiber length distribution. The average value obtained from two measurements and analyses was adopted as the measurement data. · Average fiber length: Length-weighted average fiber length Lc (l) mm · Average fiber width: Fiber width μm Length-weighted fiber width · Fiber length distribution: Fraction percentage of length weighted distribution

[0079]

Table 1

[0080]

Table 2

[0081] · Aspect ratio: Calculated from the measured values of fiber width and fiber length using the following formula. Aspect ratio = average fiber length / average fiber diameter

[0082] ·B-type viscosity (25°C, 60 rpm): After standing for more than 1 day after fibrillation, it was measured by the following method. After diluting to a solid content of 1%, it was left standing in a water bath adjusted to 25°C for 3 hours, and then the viscosity measurement was started (60 rpm) using a TOKIMEC B-type viscometer (manufactured by TOKIMEC, Inc.), and the viscosity value after 1 minute was recorded.

[0083] ·Electrical conductivity: 200 g of an aqueous dispersion with a solid content concentration of 1.0 mass% of chemically modified microfibrillated cellulose fibers was prepared and stirred well. Then, the electrical conductivity was measured using an electrical conductivity meter (ES-71 type manufactured by HORIBA, Ltd.).

[0084] [Example 1] 5.00 g (absolute dry) of bleached unbeatened kraft pulp (NBKP, manufactured by Nippon Paper Industries Co., Ltd., whiteness 85%) derived from softwood was added to 500 ml of an aqueous solution in which 39 mg of TEMPO (manufactured by Sigma Aldrich) (0.05 mmol per 1 g of absolute dry cellulose) and 514 mg of sodium bromide (1.0 mmol per 1 g of absolute dry cellulose) were dissolved, and stirred until the pulp was uniformly dispersed. An aqueous sodium hypochlorite solution was added to the reaction system so that the sodium hypochlorite became 5.5 mmol / g, and the oxidation reaction was started at room temperature. During the reaction, the pH in the system decreased, but a 3M aqueous sodium hydroxide solution was sequentially added to adjust the pH to 10. The reaction was terminated when the sodium hypochlorite was consumed and the pH in the system no longer changed. After adding hydrochloric acid to the mixture after the reaction to adjust the pH to 2, it was filtered through a glass filter to separate the pulp, and the separated pulp was washed thoroughly with water to obtain TEMPO-oxidized pulp. The pulp yield at this time was 90%, the time required for the oxidation reaction was 90 minutes, the amount of carboxyl groups was 1.42 mmol / g, and the pH was 4.5. [Microfibrillation] An aqueous dispersion with a solid content concentration of 4.0 mass% and a pH of 4.5 of the obtained TEMPO-oxidized pulp was prepared, and it was treated for 10 minutes using a top finisher (manufactured by Aikawa Iron Works Co., Ltd.) to prepare chemically modified microfibrillated cellulose (TEMPO-oxidized MFC). The physical property values of the obtained chemically modified microfibrillated cellulose are shown in Table 1. The measurement methods for each physical property value are as described above.

[0085] [Example 2] Chemically modified microfibrillated cellulose was prepared in the same manner as in Example 1, except that a 5% aqueous NaOH solution was added after treatment with a top finisher to adjust the pH to 8.1. The physical property values of the obtained chemically modified microfibrillated cellulose are shown in Table 1.

[0086] [Comparative Example 1] Chemically modified microfibrillated cellulose was prepared in the same manner as in Example 1, except that a 5% aqueous NaOH solution and sodium hydrogen carbonate were added before treatment with a top finisher to adjust the pH to 8.3. The physical property values of the obtained chemically modified microfibrillated cellulose are shown in Table 1.

[0087] [Comparative Example 2] The TEMPO-oxidized pulp obtained in the same manner as in Example 1 was dehydrated until the solid content concentration reached 30% by mass, and then treated 7 times using a 14-inch laboratory refiner (manufactured by Aikawa Iron Works Co., Ltd.). The obtained product was a substantially spherical (spherical or ellipsoidal) material (cellulose fiber ball) formed by entanglement of fine cellulose fibers. The physical property values of the obtained cellulose fiber ball are shown in Table 1.

[0088] [Comparative Example 3] The TEMPO-oxidized pulp obtained in the same manner as in Example 1 was dehydrated until the solid content concentration reached 30% by mass, and then treated 7 times using a 14-inch laboratory refiner (manufactured by Aikawa Iron Works Co., Ltd.). Next, water and a 5% aqueous NaOH solution were added and stirred to prepare chemically modified microfibrillated cellulose with a pH of 7.2 and a solid content concentration of 2%. The physical property values of the obtained chemically modified microfibrillated cellulose are shown in Table 1.

[0089] [Comparative Example 4] Water was added to the TEMPO-oxidized pulp obtained in the same manner as in Example 1 and stirred to adjust the pH to 4.5 and the solid content concentration to 2%. The physical property values of the TEMPO-oxidized pulp are shown in Table 1.

[0090]

Table 3

[0091] As shown in Examples 1 and 2, by defibrating chemically modified cellulose at pH 3 to 7 and a solid content concentration of 15% by mass or less, a fiber length distribution (%) of 0.0 mm to 0.2 mm in length-weighted is 40% or more, and a fiber length distribution (%) of 0.2 mm to 7.6 mm in length-weighted is 35% or more, chemically modified microfibrillated cellulose having such fiber properties could be obtained.

Claims

【Claim 1】 A method for producing a chemically modified microfibrillated cellulose fiber, comprising the following steps (A) to (C): (A) A step of preparing carboxylated cellulose oxidized in the presence of an N-oxyl compound selected from TEMPO and its derivatives as the chemically modified cellulose; (B) A step of defibrating the chemically modified cellulose at a pH of 3 to 7 and a solid content concentration of 10% by mass or less; (C) A step of adjusting the pH of the aqueous dispersion of the chemically modified microfibrillated cellulose fiber obtained by the defibrating treatment to 7 or more. The method for producing a chemically modified microfibrillated cellulose fiber, wherein the chemically modified microfibrillated cellulose fiber has the following characteristics (a) to (b). When an aqueous suspension of composite fibers with a solid content concentration of 0.3% is classified using a fiber classification analyzer under the conditions of a flow rate of 5.7 L / min, a water temperature of 25 ± 1 °C, and a total outflow volume of 22 L, (a) The fiber length distribution (%) with a length weighted average of 0.0 mm to 0.2 mm is 40% or more. (b) The fiber length distribution (%) with a length weighted average of 0.2 mm to 7.6 mm is 35% or more.

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