JP2024028775A - Method of manufacturing fine cellulose fiber and paper containing the same - Google Patents

Abstract

To provide a method of manufacturing a fine cellulose fiber having good handling ability during manufacturing and transportation.SOLUTION: A method of manufacturing a fine cellulose fiber includes (1) a step of obtaining chemically modified pulp by chemical modification of raw material pulp and (2) a step of mechanically treating the chemically modified pulp obtained in the previous step under conditions with a solid concentration of 15 wt.% or over.SELECTED DRAWING: None

Description

The present invention relates to a method for producing fine cellulose fibers and paper containing the same.

Cellulose nanofibers and microfibrillated cellulose (hereinafter collectively referred to as "fine cellulose fibers"), which are obtained by refining cellulose, are fine fibers with fiber diameters on the nano- to micro-order, and have high strength, high elasticity, and thixotropic properties. It is expected to be used in a variety of fields as a new material that has functions that ordinary pulp does not have, such as elasticity.

Methods for producing fine cellulose fibers include a method in which cellulose fibers are made fine by mechanical shearing force (Patent Document 1), a method in which cellulose fibers are subjected to enzyme treatment or chemical modification, and then mechanically made fine (Patent Document 1). Document 2), and a method of causing microorganisms to produce fine cellulose, as typified by bacterial cellulose (Patent Document 3), are known.

Examples of chemical modification include oxidation, etherification, cationization, and esterification, and examples of substituents to be introduced include cationic groups and anionic groups. Examples of anionic groups include carboxyl groups and phosphate ester groups.

Chemically modified pulp with anionic groups introduced has low hydrophilicity in water under acidic conditions because the terminals of the anionic groups become acidic, and under alkaline conditions the terminals of the anionic groups separate and become less hydrophilic. It gets expensive. Usually, anion-modified cellulose nanofibers are produced by treating modified cellulose with alkali to convert anionic groups into salt forms, and then performing beating (pre-fibrillation) treatment as necessary to obtain microfibrillated cellulose. It is manufactured by defibrating with a dispersing machine such as an ultra-high pressure homogenizer (for example, Patent Document 4). Chemically modified pulp with anionic groups dissociated has a very high affinity with water and swells and becomes highly viscous, so it is usually beaten using a low-concentration dispersion with a solid content of 5% by weight or less. processing was being carried out. On the other hand, in order to improve the solid content concentration, there is a known method of increasing the concentration by lowering the pH of fibril cellulose that has been refined into fine particles by lowering its water retention property (Patent Document 5, 6).

By the way, paper is used in various fields such as information recording media such as printing paper and recording paper, and packaging, and in all applications, it is required to have sufficient strength during use and processing. There is. For the purpose of improving the strength and stiffness of paper, for example, Patent Document 7 discloses a paper base material to which oxidized pulp is added, and Patent Document 8 discloses a paper containing co-treated microfibrillated cellulose and an inorganic particle composition. The product is disclosed.

Japanese Patent Application Publication No. 6-10280 Japanese Patent Application Publication No. 2010-235679 Japanese Patent Application Publication No. 8-291201 International Publication 2017/057710 Special table 2017-527660 publication Special Publication No. 2015-508839 International Publication No. 2014/097929 JP2017-203243A

As described in Patent Documents 7 and 8, fine cellulose fibers are expected to be able to provide new functions in various fields including paper. However, in the conventional method for producing fine cellulose fibers, the beating treatment was performed at a low solid content concentration of 5% by weight or less, which caused problems in handling during production and transportation. The manufacturing process of fine cellulose fibers including cellulose nanofibers includes multiple steps such as oxidation, alkali treatment, beating, and fibrillation. Therefore, the inventors came up with the idea that if the processing concentration in each step could be improved, fine cellulose fibers could be advantageously produced from the viewpoint of processing amount and transportation cost. In addition, as disclosed in Patent Documents 5 and 6, it has been considered to concentrate the fine cellulose fiber slurry after micronization to increase the concentration, but the concentration of chemically modified pulp in the slurry subjected to beating has been There was no technology to improve it. Furthermore, when manufacturing microfibrillated cellulose (hereinafter also referred to as "MFC") from chemically modified pulp as a raw material, it is difficult to proceed with MFC without significantly increasing the slurry viscosity, and there are problems with handling. . In view of such circumstances, an object of the present invention is to provide a method for producing fine cellulose fibers that is easy to handle during production and transportation.

The inventors solved the above problem by mechanically treating chemically modified pulp under specific conditions. That is, the above-mentioned problem is solved by the present invention described below.
Aspect 1
(1) A step of chemically modifying raw material pulp to obtain chemically modified pulp;
(2) a step of mechanically treating the chemically modified pulp obtained in the above step at a solid content concentration of 15% by weight or more;
A method for producing fine cellulose fibers, comprising:
Aspect 2
The manufacturing method according to aspect 1, wherein the mechanical treatment is beating.
Aspect 3
The manufacturing method according to aspect 1 or 2, wherein the chemically modified pulp is an anionically modified pulp.
Aspect 4
The production method according to any one of aspects 1 to 3, wherein the chemically modified pulp has 0.3 to 2.5 mmol/g of carboxyl groups.
Aspect 5
The production method according to any one of aspects 1 to 4, comprising a step of acid-treating the chemically modified pulp.
Aspect 6
The production method according to any one of aspects 1 to 5, comprising a step of treating the chemically modified pulp with an alkali.
Aspect 7
The manufacturing method according to aspect 5, wherein the acid treatment includes adding an acid to the mixture containing the chemically modified pulp and water to adjust the pH of the mixture to 6.5 or less.
Aspect 8
The manufacturing method according to aspect 6, wherein the alkali treatment includes adding an alkali to the mixture containing the chemically modified pulp and water to adjust the pH of the mixture to above neutral.
Aspect 9
The manufacturing method according to any one of aspects 1 to 8, wherein the fine cellulose fibers are microfibrillated cellulose.
Aspect 10
The method according to any one of aspects 1 to 8, wherein the fine cellulose fibers are cellulose nanofibers.
Aspect 11
The step (2) is a step that includes performing mechanical treatment multiple times under different conditions to obtain microfibrillated cellulose, in which at least one of the mechanical treatments is performed under conditions where the solid content concentration is 15% by weight or more. The manufacturing method according to aspect 9, which is a step of performing.
Aspect 12
In the step (2), the chemically modified pulp is mechanically treated under conditions where the solid content concentration is 15% by weight or more, and then mechanically treated under conditions where the solid content concentration is less than 15% by weight to obtain microfibrillated cellulose. The manufacturing method according to aspect 11, comprising:
Aspect 13
The manufacturing method according to aspect 10, wherein the step (2) includes further subjecting the microfibrated cellulose produced by the mechanical treatment to cellulose nanofibers.
Aspect 14
The manufacturing method according to any one of aspects 1 to 13, comprising a step of treating the fine cellulose fibers produced by the mechanical treatment with an alkali.
Aspect 15
The step (2) is
(2-1) forming a cellulose fiber ball formed by entangling fine cellulose fibers by mechanically treating the chemically modified pulp at a solid content concentration of 15% by weight or more, and (2-2) the above-mentioned The manufacturing method according to aspect 9, comprising preparing microfibrated cellulose by treating cellulose fiber balls with alkali.
Aspect 16
The step (2) is
(2-1) Mechanically treating the chemically modified pulp at a solid content concentration of 15% by weight or more to form cellulose fiber balls in which fine cellulose fibers are entangled;
(2-2) preparing microfibrated cellulose by treating the cellulose fiber balls with an alkali; and (2-3) mechanically treating the microfibrated cellulose to prepare cellulose nanofibers. The manufacturing method according to aspect 10, comprising:
Aspect 17
17. The manufacturing method according to aspect 15 or 16, wherein the alkali treatment includes adding an alkali to the mixture containing the cellulose fiber balls and water to adjust the pH of the mixture to neutral or higher.
Aspect 18
preparing fine cellulose by the method of any of aspects 1 to 17;
A step of preparing a slurry containing pulp and the fine cellulose, and a step of making paper from the slurry,
Paper manufacturing method.

According to the present invention, it is possible to provide a method for producing fine cellulose fibers that is easy to handle during production and transportation.

The present invention will be explained in detail below. In the present invention, "X~Y" includes the end values of X and Y.

1. Fine cellulose fibers In the present invention, fine cellulose fibers collectively refer to cellulose nanofibers (hereinafter also referred to as "CNF") with an average fiber diameter of less than 500 nm and microfibrillated cellulose (hereinafter also referred to as "MFC") with an average fiber diameter of 500 nm or more. Refers to fiber. The average fiber diameter is a length-weighted average fiber diameter, and can be measured by observing fine cellulose fibers using, for example, a fractionator manufactured by Valmet Corporation, an optical microscope, an electron microscope, or an atomic force microscope (AFM). The lower limit of the fiber diameter is preferably 1 nm or more, and the upper limit is not particularly limited, but is about 10 mm or less, preferably 1 mm or less. In the present invention, the method for measuring the average fiber diameter is different between MFC and CNF. Therefore, first, the average fiber diameter of the obtained fine cellulose fibers is subjected to image analysis using a fiber tester manufactured by ABB Corporation, a fractionator manufactured by Valmet Corporation, etc. to determine whether it is MFC or CNF. If the obtained fine cellulose fibers are MFC, they are measured using the fractionator to determine the average fiber diameter. Furthermore, when the fine cellulose fibers are CNF, the average fiber diameter can be measured using AFM.

[MFC]
In the present invention, MFC can be produced by mechanically treating (preferably beating) chemically modified pulp so that the average fiber diameter of the resulting fine cellulose fibers is 500 nm or more. The lower limit of the average fiber diameter is preferably 1 μm or more, more preferably 10 μm or more, and the upper limit is preferably 30 μm or less, more preferably 20 μm or less. The average fiber length of the MFC is preferably 1 μm or more, more preferably 5 μm or more, and even more preferably 50 μm or more. The upper limit is preferably 2.0 mm or less, more preferably about 1.5 mm or less. In the present invention, the average fiber length is a length-weighted average fiber length.

The degree of mechanical processing differs between MFC and cellulose fibers as raw materials. The degree of mechanical treatment can be confirmed by directly observing the fibers. In addition, although it is generally not easy to quantify the degree of mechanical treatment, it is also possible to quantify it by the amount of change in freeness or water retention, or the amount of change in surface area (for example, BET) after mechanical treatment. . As an example, the case of oxidized cellulose obtained by oxidizing with an oxidizing agent in the presence of an N-oxyl compound and a substance selected from the group consisting of bromides, iodides and mixtures thereof will be described below. In this case, it is preferable that the MFC be obtained by mechanical treatment, particularly beating, to such an extent that the freeness (F ₀ ) of the pulp before defibration changes by 10 ml or more. That is, assuming that the freeness after treatment is F, the difference in freeness ΔF=|F ₀ −F| is preferably 10 ml or more, more preferably 20 ml or more, and preferably 30 ml or more. More preferred. The freeness of pulp varies depending on the degree of denaturation, but since the freeness of the pulp before mechanical treatment is used as a standard, the above definition allows the degree of mechanical treatment to be specified regardless of the degree of chemical denaturation. Since F ₀ varies depending on the degree of chemical denaturation, it is difficult to define an unambiguous upper limit for ΔF, but the freeness F after treatment will be smaller than F ₀ or the pulp will be significantly reduced by mechanical treatment. By becoming finer, it becomes larger than F ₀ (pulp passes through the mesh together with water after beating). The fibrillation rate of the chemically modified MFC thus obtained, determined using a fractionator manufactured by Valmet Corporation, is preferably 1.0% or more, more preferably 2.5% or more, and 3.5% or more. % or more is more preferable. The fibrillation rate varies depending on the type of pulp, but if it is within the above range, it is considered that mechanical treatment has been sufficiently performed.

Further, the MFC obtained in the present invention is preferably obtained by mechanically processing the pulp to such an extent that the fibrillation rate (f ₀ ) of the pulp before mechanically processing is improved by one point or more. That is, if the fibrillation rate after treatment is f, then the difference in fibrillation rate Δf = f - f ₀ only needs to exceed 0, preferably 0.2% or more, more preferably 1 point or more, More preferably, it is 2.5 points or more.

The degree of the mechanical treatment can be evaluated not only by the above-mentioned indicators but also by the absorbance and viscosity characteristics (for example, the relationship between rotational speed and viscosity) when made into a slurry.

[CNF]
In the present invention, CNF can be produced by mechanically treating (preferably defibrating) chemically modified pulp so that the average fiber diameter of the resulting fine cellulose fibers is less than 500 nm. Specifically, CNF can be manufactured by adjusting the mechanical processing equipment, intensity, number of times, and time. Alternatively, CNF can be produced by further subjecting the MFC produced as described above to mechanical treatment. The mechanical treatment in this case is also preferably defibration treatment, and the apparatus described in step (2) can be used. The CNF obtained by the present invention has performance equivalent to that of CNF produced by conventional methods. The average fiber diameter of the CNF of the present invention is preferably 100 nm or less, more preferably 50 nm or less. The lower limit is preferably 1 nm or more, more preferably 2 nm or more. The average fiber length is preferably 5 μm or less, more preferably 3 μm or less. The lower limit of the average fiber length is about 0.1 μm or more. After confirming that the obtained fine cellulose fibers are CNF as described above, the average fiber length and fiber diameter are measured using an atomic force microscope (AFM) if the diameter is less than 20 nm, and by electrolysis if the diameter is 20 nm or more. The measurement can be performed by analyzing 200 randomly selected fibers using a focused scanning electron microscope (FE-SEM) and calculating the average. Furthermore, using the values obtained in this manner, the aspect can be calculated using the following formula. The aspect ratio of the CNF of the present invention is preferably 50 or more.
Aspect ratio = average fiber length / average fiber diameter

[CFB]
In the present invention, fibrillation is promoted by beating the chemically modified pulp to form fine cellulose fibers. At this time, a cellulose fiber ball (hereinafter also referred to as "CFB"), which is a substantially spherical (spherical or ellipsoidal) material (aggregate) formed by entwining fine cellulose fibers like a pill, may be used. . That is, CFB may be formed from chemically modified pulp and fine cellulose fibers may be formed therefrom. One CFB can be formed from one fine cellulose fiber, but is preferably formed from a plurality of fine cellulose fibers.

(1) Average particle diameter The average particle diameter (D50) determined by wet measurement using a CFB laser diffraction granulometer is preferably 50 μm to 2 mm. As described later, MFC can be manufactured from CFB. However, if the average particle diameter exceeds the upper limit, it may become difficult to manufacture MFC. Furthermore, if the average particle diameter is less than the lower limit, handling may become difficult when isolating CFB in the manufacturing process. From this point of view, it is more preferable that the average particle diameter (D50) of CFB by wet measurement is 50 μm to 1.5 mm. When CFB is dispersed in a dispersion medium such as water, the average particle diameter varies depending on the pH and the like. Therefore, the average particle diameter and aspect ratio in the present invention are measured using an acidic dispersion having a pH of 6 or less.

(2) Aspect ratio (L/D)
The aspect ratio (L/D) of CFB is preferably 10 or less, more preferably 8 or less. L/D measures CFB in a dispersion of CFB in water (pH 6 or less) using any microscope, such as a fractionator manufactured by Valmet Corporation, a digital microscope (manufactured by Nikon Corporation), or a laser microscope (manufactured by Olympus Corporation). It can be measured by observation. L (the length of the major axis of the particle) and D (the length of the minor axis of the particle) are determined visually and calculated by measuring each length using image analysis software. The major axis is determined as the axis that exhibits the maximum length in the longitudinal direction of the particle, and the minor axis is determined as the axis that is perpendicular to the major axis and exhibits the maximum length (width) in that direction.

(3) Self-disintegrating property CFB has a disintegrating property in that it disintegrates into self-forming fine cellulose fibers (preferably MFC) under certain conditions. Specifically, CFB is made into a 2% by weight acidic water suspension and then disintegrated in water when the pH of the suspension is made neutral to alkaline, producing a dispersion in which fine cellulose fibers are dispersed in water. . The pH of the acidic aqueous suspension is preferably 2 or more and less than 6.5. Further, when the suspension is made neutral to alkaline, the pH is preferably 6.5 or higher. In the present invention, using this principle, fine cellulose fibers can be obtained via CFB, the details of which will be described later.

2. Manufacturing method for fine cellulose fibers (1) Step 1
[Raw material pulp]
In this step, raw material pulp is chemically modified to obtain chemically modified pulp. Raw material pulps include 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), hardwood unbleached sulfite pulp (LUSP), hardwood bleached sulfite pulp (LBSP), thermomechanical pulp (TMP), chemi-thermomechanical pulp (CTMP), pressurized groundwood pulp (PGW), Refiner ground wood pulp (RGP), alkaline hydrogen peroxide mechanical pulp (APMP), alkaline hydrogen peroxide thermomechanical pulp (APTMP), linter, jute, hemp, mulberry, mitsumata, kenaf and other herbaceous pulps, bamboo-derived pulps Examples include, but are not limited to, pulp, recycled pulp, waste paper pulp, and the like.

[Chemical denaturation]
Chemical modification refers to introducing a functional group into the pulp, and the chemical modification is preferably anionic modification, that is, the chemically modified pulp preferably has anionic groups. Examples of the anionic group include acid groups such as a carboxyl group, a carboxyl group-containing group, a phosphoric acid group, a phosphoric acid group-containing group, and a sulfuric acid ester group. Examples of the carboxyl group-containing group include -COOH group, -R-COOH (R is an alkylene group having 1 to 3 carbon atoms), -O-R-COOH (R is an alkylene group having 1 to 3 carbon atoms). It will be done. Examples of the phosphoric acid group-containing group include a polyphosphoric acid group, a phosphorous acid group, a phosphonic acid group, a polyphosphonic acid group, and the like. Depending on the reaction conditions, these acid groups may be introduced in the form of a salt (for example, a carboxylate group (-COOM, M is a metal atom)). In the present invention, chemical modification is preferably oxidation or etherification.

Oxidation can be carried out as known. For example, a method of oxidizing raw pulp in water using an oxidizing agent in the presence of an N-oxyl compound and a substance selected from the group consisting of bromides, iodides and mixtures thereof can be mentioned. According to this method, the primary hydroxyl group at the C6 position of the glucopyranose ring on the cellulose surface is selectively oxidized to produce a group selected from the group consisting of aldehyde groups, carboxyl groups, and carboxylate groups. Alternatively, an ozone oxidation method may be used. According to this oxidation reaction, at least the hydroxyl groups at the 2- and 6-positions of the glucopyranose rings constituting cellulose are oxidized, and the cellulose chain is decomposed.

An example of a method for measuring the amount of carboxyl groups will be explained below. Prepare 60 mL of 0.5% by weight slurry (aqueous dispersion) of oxidized cellulose, add 0.1M hydrochloric acid aqueous solution to adjust the pH to 2.5, and then dropwise add 0.05N sodium hydroxide aqueous solution to bring the pH to 11. Measure the electrical conductivity until the It can be calculated using the following formula from the amount (a) of sodium hydroxide consumed in the neutralization stage of the weak acid where the change in electrical conductivity is gradual.
Amount of carboxyl group [mmol/g oxidized cellulose] = a [mL] x 0.05/weight of oxidized cellulose [g]

The amount of carboxyl groups in the oxidized cellulose measured in this way is preferably 0.1 mmol/g or more, more preferably 0.3 mmol/g or more, and even more preferably 0.5 mmol/g based on the bone dry weight. Above, even more preferably 0.8 mmol/g or more. The upper limit of the amount is preferably 3.0 mmol/g or less, more preferably 2.5 mmol/g or less, even more preferably 2.0 mmol/g or less. Therefore, the amount is preferably 0.1 to 3.0 mmol/g, more preferably 0.3 to 2.5 mmol/g, even more preferably 0.5 to 2.5 mmol/g, and even more preferably 0.8 to 2.0 mmol/g. /g is even more preferred.

Etherification includes carboxymethyl (ether), methyl (ether), ethyl (ether), cyanoethyl (ether), hydroxyethyl (ether), hydroxypropyl (ether), and ethylhydroxyethyl (ether). and hydroxypropylmethyl (ether). Among these, carboxymethylation is preferred. Carboxymethylation can be carried out, for example, by mercerizing raw material pulp as a bottom forming raw material and then etherifying it.

The degree of carboxymethyl substitution per glucose unit of carboxymethylated cellulose can be measured, for example, by the following method. That is, 1) Accurately weigh about 2.0 g of carboxymethylated cellulose (absolutely dried) and place it in a 300 mL Erlenmeyer flask with a stopper. 2) Add 100 mL of methanol nitric acid (a solution obtained by adding 100 mL of special grade concentrated nitric acid to 1000 mL of methanol) and shake for 3 hours to convert carboxymethylcellulose salt (carboxymethylated cellulose) into hydrogen-type carboxymethylated cellulose. 3) Accurately weigh 1.5 g or more and 2.0 g or less of hydrogen-type carboxymethylated cellulose (absolutely dried) and place it in a 300 mL Erlenmeyer flask with a stopper. 4) Wet hydrogen carboxymethylated cellulose with 15 mL of 80% methanol, add 100 mL of 0.1N NaOH, and shake at room temperature for 3 hours. 5) Back titrate excess NaOH with 0.1N H2SO4 using phenolphthalein as indicator. 6) Calculate the degree of carboxymethyl substitution (DS) by the following formula:
A=[(100×F'-(0.1N H ₂ SO ₄ )(mL)×F)×0.1]/(absolute dry mass (g) of hydrogen-type carboxymethylated cellulose)
DS=0.162×A/(1-0.058×A)
A: Amount of 1N NaOH (mL) required to neutralize 1g of hydrogen-type carboxymethylated cellulose
F: Factor of 0.1N H ₂ SO ₄ F': Factor of 0.1N NaOH

The degree of carboxymethyl substitution per anhydroglucose unit in carboxymethylated cellulose is preferably 0.01 or more, more preferably 0.05 or more, and even more preferably 0.10 or more. The upper limit of the degree of substitution is preferably 0.50 or less, more preferably 0.40 or less, and even more preferably 0.35 or less. Therefore, the degree of carboxymethyl group substitution is preferably from 0.01 to 0.50, more preferably from 0.05 to 0.40, even more preferably from 0.10 to 0.30.

(2) Process 2
In this process, chemically modified pulp is mechanically treated. In the present invention, mechanical treatment refers to mixing fibers and further making them fine or fibrillated, and includes beating, fibrillation, dispersion, kneading, and the like. Refinement refers to a decrease in fiber length, fiber diameter, etc., and fibrillation refers to an increase in the fluffiness of the fibers. Devices used for mechanical processing are not limited, but include, for example, high-speed rotation type, colloid mill type, high pressure type, roll mill type, and ultrasonic type devices, such as high-pressure or ultra-high pressure homogenizers, refiners, beaters, PFI Mills, kneaders, dispersers, high-speed disintegrators, top finers, and other devices in which pulp fibers interact with metal or cutlery around a rotating shaft, or devices that use friction between pulp fibers can be used. In the present invention, the mechanical treatment is preferably beating using a refiner or kneader, since fibrillation of the fibers can be efficiently promoted.

Mechanical treatment (preferably beating) is carried out using a mixture containing a chemically modified pulp and a dispersion medium, with a solids concentration of 15% by weight or more. The dispersion medium is not limited, and an organic solvent or water can be used, but preferably water is used. The solid content concentration is the concentration of solid content in the mixture subjected to mechanical treatment, and is usually the concentration of chemically modified pulp. By beating the chemically modified pulp under high conditions such as a solid content concentration of 15% by weight or more, benefits such as improved processing efficiency and improved handling properties can be obtained. Mechanical treatment at this concentration is also referred to as "high concentration mechanical treatment." Handling characteristics include, for example, the ability to transport the high concentration without dilution after high concentration mechanical treatment, and the fact that the viscosity of the MFC dispersion that has undergone high concentration mechanical treatment is not high and can be easily pumped. In addition, the dispersion has good transport efficiency, and the dispersion hardly sticks to the storage container. Furthermore, when another treatment step is performed after the high-concentration mechanical treatment, the efficiency of transporting the dispersion liquid to the next step is also good. The reason why the viscosity of the MFC dispersion of the present invention is difficult to increase is not clear, but it is believed that when chemically modified pulp is treated at a high concentration, the fibers tend to become short and the viscosity tends to decrease. It is inferred. The viscosity of the MFC dispersion is evaluated by the B-type viscosity when the anionic group terminal is a Na atom (Na type) (the pH of the dispersion is 6 or more) at a solid content concentration of 1% and a temperature of 25°C. be able to.

The solid content concentration is 15% by weight or more, preferably 18% by weight or more, and more preferably 20% by weight or more. If the solid content concentration is too high, the efficiency of mechanical treatment will decrease, so the upper limit of the solid content concentration is preferably 60% by weight or less, more preferably 45% by weight or less. Although the solid content concentration may vary during the mechanical treatment, in the present invention, the solid content concentration at the start of the mechanical treatment is referred to as the solid content concentration in the treatment. Further, the treatment time, conditions, etc. are adjusted as appropriate so that fine cellulose fibers with a desired fiber diameter can be obtained.

In the present invention, the mechanical treatment may be performed multiple times. In this case, it is sufficient to carry out at least once under the condition that the solid content concentration is 15% by weight or more. As mentioned above, mechanical treatment under these conditions is also referred to as "high-concentration mechanical treatment," and in particular, when the mechanical treatment is beating, it is also referred to as "high-concentration beating." Similarly, mechanical treatment under conditions where the solid content concentration is less than 15% by weight is also referred to as "low concentration mechanical treatment", and particularly when the mechanical treatment is beating, it is also referred to as "low concentration beating". Therefore, high-concentration mechanical treatment and low-concentration mechanical treatment may be combined. When these mechanical treatments are combined, the order of the treatments is not limited, but from the viewpoint of ease of concentration, it is preferable to perform the high-concentration mechanical treatment first. For example, MFC can be obtained by subjecting chemically modified pulp to a high concentration mechanical treatment and then subjecting the resulting chemically modified pulp to a low concentration mechanical treatment. From the viewpoint of easy dehydration or concentration of the chemically modified pulp as a raw material, it is preferable that the chemically modified pulp to be subjected to high concentration mechanical treatment is of the acid type, in which the terminal anionic group is H. After dehydration or concentration in this state, it may be converted into a dissociated form and subjected to high-concentration mechanical treatment. The chemically modified pulp subjected to low-concentration mechanical treatment may be an acid type in which the anionic group terminal is H, or a dissociation type in which the terminal is a metal atom (such as Na). From the viewpoint of improving mechanical processing efficiency by utilizing repulsion due to electric charges, it is preferable that the material be of a dissociative type.

Examples of equipment used for low-concentration beating include high-speed rotation type, colloid mill type, high-pressure type, roll mill type, and ultrasonic type equipment, including high-pressure or ultra-high-pressure homogenizers, refiners, beaters, PFI mills, and kneaders. , dispersers, high-speed disintegrators, etc. that act on pulp fibers with metal or cutlery around a rotating shaft, or that use friction between pulp fibers, or that disperse or defibrate pulp fibers by cavitation, water flow, or water pressure. can be used.

In this step, MFC or CNF is produced from the chemically modified pulp. As mentioned above, MFC may be produced from chemically modified pulp via CFB. Furthermore, the obtained MFC can be subjected to mechanical treatment to form CNF.

Examples of combinations of high concentration mechanical treatment and low concentration mechanical treatment are not limited, but include the following. In this case, the above two treatments may be combined with the acid or alkali treatment described below.
1) Perform high concentration mechanical treatment with the anionic group in the acid form, then dilute and perform low concentration mechanical treatment. 2) Perform concentration mechanical treatment with the anionic group in the acid form, then dilute. 3) After obtaining CFB by performing high-concentration mechanical treatment with the anionic group in the acid form, dilution is performed. 4) Add alkali and perform low-concentration mechanical treatment while the anionic group is in the acid form (preferably Na-type) by adding alkali to the dissociation-type state. type (preferably Na type), then diluted and subjected to low concentration mechanical treatment

(3) Acid or alkali treatment In the present invention, acid or alkali treatment is performed before step (2) or for the purpose of increasing the concentration (dehydration) of pulp or fine cellulose slurry, changing the properties of cellulose fibers, and improving treatment efficiency. ) Acid or alkali treatment can be carried out at any stage. Acid or alkali treatments may be performed multiple times in any combination. The acid or alkali used in the treatment is not limited, but inorganic acids such as hydrochloric acid, sulfuric acid, and phosphoric acid, and organic acids such as acetic acid can be used, and any alkali such as NaOH and KOH can be used. . Acid treatment includes adding an acid to a mixture containing chemically modified pulp and water to adjust the pH of the mixture to 6.5 or less. In addition, the alkali treatment includes adding an alkali to a mixture containing chemically modified pulp and water to adjust the pH of the mixture to above neutrality (over 6.5). The apparatus for carrying out the acid or alkali treatment may be separate from the apparatus for carrying out the mechanical treatment, but the same apparatus may be used to carry out both at the same time or in succession. In addition to the acid or alkali, other types of chemicals may be added, such as oxidizing agents such as hydrogen peroxide, dispersants, penetrants, hydrophobizing agents, and the like.

In particular, when the chemically modified pulp used in the present invention is an anionically modified pulp, acid treatment reduces the number of dissociative anionic groups in the chemically modified pulp and increases the number of acidic anionic groups. That is, the acid type anionic groups occupy more of the total anionic groups, and the hydrophilicity of the chemically modified pulp decreases. For example, when the anionic group is a carboxyl group, -COOM (M is a metal atom) decreases and -COOH increases with respect to all carboxyl groups in the acid-treated chemically modified pulp. The degree of affinity for water depends on the proportion of dissociable anionic groups, and as the number of acidic anionic groups increases, the affinity for water decreases, making it possible to increase the concentration of chemically modified pulp. On the other hand, when alkali treatment is performed, the ends of the anionic groups become separated due to the addition of alkali, increasing the repulsion between the fibers. Therefore, mechanical treatments such as beating and fibrillation can be carried out efficiently by utilizing the electrostatic repulsion of the fibers. Therefore, it is preferable that alkali treatment for the purpose of improving beating and defibration efficiency be performed before or during high concentration mechanical treatment.

Below, the acid or alkali treatment in the MFC formation step will be explained in detail when the anion modification is TEMPO oxidation or carboxymethylation.

[MFC conversion of TEMPO oxidized pulp]
Immediately after the oxidation reaction, the carboxyl groups of the TEMPO oxidized pulp are in the dissociated type (Na type) and have high water retention, making dehydration difficult. Therefore, for the purpose of improving dehydration efficiency, it is preferable to add an acid to form an acid form. Preferably, the high concentration mechanical application of the present invention is performed after acid treatment and dehydration. The high-concentration mechanical treatment may be performed at least once, and the fiber length and fibrillation degree of the produced MFC can be adjusted depending on the degree of treatment. Further, after the acid treatment and dehydration, the carboxyl group may be made into a dissociated form by successively performing an alkali treatment, and the dissociated form may be subjected to high-concentration mechanical treatment. An alkaline treatment may be performed during the high concentration mechanical treatment.

[Converting CM pulp to MFC]
Since CM pulp is generally manufactured by performing etherification after mercerization as described above, it is strongly alkaline after the reaction, and the carboxymethyl group is a dissociated type (Na type). In the present invention, the obtained CM pulp can be further subjected to the steps of acid addition, dehydration, and drying to obtain a dried product, or can be subjected to a high-concentration mechanical treatment after drying and then pulverized. The carboxymethyl group of the CM-formed pulp after drying is a dissociated type (Na type).

The conversion of the CM pulp into MFC is carried out in the same manner as the conversion into MFC of the TEMPO oxidized pulp described above. Unlike TEMPO oxidized pulp, dried or dry-milled CM pulp has a high solid content concentration (low water content), so it can be directly subjected to the high-concentration mechanical treatment of the present invention, or it can be solidified as appropriate by adding water. After adjusting the concentration, it may be subjected to high-concentration mechanical treatment. At the time of the dilution, an acid or an alkali may be added, but if an acid is added and a high concentration mechanical treatment is performed in an acid form, the above-mentioned CFB may be formed. be. The high-concentration mechanical treatment may be performed at least once, and the fiber length and fibrillation degree of the produced MFC can be adjusted depending on the degree of treatment. The obtained CFB is composed of MFC, and as with TEMPO-oxidized CFB, MFC in a dispersed state can be obtained by adding an alkali.

[Alkali treatment of CFB]
By performing high-concentration mechanical treatment, MFC with advanced short fibers and fibrillation is formed, but as mentioned above, if the treatment is strengthened under acidic conditions (anionic groups become acid form), CFB is formed. When CFB is treated with alkali, the CFB fiber mass is unraveled and MFC in a dispersed state is obtained. Although the reason why the fiber mass unravels is not clear, it is presumed that the addition of alkali causes the anionic group to become a dissociated type (Na type) and the repulsion between the fibers becomes stronger, causing the fiber mass to unravel. The alkali treatment includes adding an alkali to the mixture containing the particles and water to adjust the pH of the mixture to above neutral. Since divalent ions may inhibit fiber dispersion due to crosslinking, from this viewpoint, it is preferable that the alkali used in this treatment contains monovalent metal ions. Examples of the alkali include KOH, NaOH, and the like.

Therefore, in one embodiment, step (2) includes forming a CFB from chemically modified pulp and treating the CFB with an alkali to prepare an MFC. In yet another embodiment, step (2) includes the step of mechanically treating the MFC thus obtained to prepare CNF.

In the fiber length distribution of MFC in the MFC dispersion obtained by disintegrating CFB, it is preferable that the proportion of fibers of 0.6 mm or less is 15% or more. This is because if the ratio is less than 15%, the fibers will not be sufficiently refined by beating, and the MFC function will not be fully exhibited. The upper limit of the ratio is not limited and is preferably 100% or less. Since the fiber length distribution cannot be measured by directly analyzing CFB, the fiber length distribution measured in this manner may be regarded as the fiber length distribution of the fine cellulose fibers constituting the CFB.

The magnitude of the charge density is a (meq./g) when the pH of the CFB suspension is acidic (preferably pH 4.5), and the charge density when the pH of the CFB suspension is neutral to alkaline (preferably pH 7.5). When the size of is b (meq./g), ba is preferably 0.1 (meq./g) or more. If the difference is within this range, the proportion of the dissociated type of anionic groups in the chemically modified cellulose is sufficiently high, and the terminals of the anionic groups dissociate, causing the cellulose to electrically repel each other, making it easy for CFB to collapse. . The upper limit of ba is not limited, but is preferably 1 (meq./g) or less. Charge density is the density of charge per predetermined amount of cellulose fiber, and for example, the cation demand is measured using a particle surface charge measuring device (MUTEK, Particle Chargedetector, PCD03), and the anion charge density is calculated. It is measured in

3. Applications The fine cellulose fibers obtained by the present invention are made from chemically modified pulp and have functional groups on the fiber surface, so they have various functionalities derived from the functional groups. Therefore, the fine cellulose fibers of the present invention can be used for various purposes. The fine cellulose fibers of the present invention can be used as thickeners, gelling agents, glues, food additives, excipients, paint additives, and adhesive additives in various fields where additives are generally used. It can be used as an abrasive, a compounding material for rubber and plastics, a water retaining material, a shape retaining agent, a muddy water conditioner, a filter aid, a mud flooding prevention agent, an admixture, etc. The fields include food, beverages, cosmetics, pharmaceuticals, paper manufacturing, various chemical supplies, paints, sprays, agricultural chemicals, civil engineering, architecture, electronic materials, flame retardants, household goods, adhesives, cleaning agents, fragrances, and lubricating compositions. Examples include things.

4. Paper Manufacturing Method The paper manufacturing method of the present invention includes a step of preparing fine cellulose, a step of preparing a slurry containing pulp and the fine cellulose, and a step of making paper from the slurry. Finely divided cellulose is prepared as described above.

[Slurry preparation process]
In this step, a slurry containing pulp and the fine cellulose is prepared. As the pulp, the same pulp as the above-mentioned "raw material pulp" can be used. For example, this step can be carried out by mixing the pulp slurry prepared in advance with the mixture of fine cellulose and water obtained in the previous step. Mixing can be performed as known. For example, a slurry can be prepared by mixing both using a known mixer or the like. The mixture of fine cellulose and water obtained when preparing fine cellulose can be used as is in this step, but from the viewpoint of improving the dispersibility of fine cellulose in the pulp, the concentration of fine cellulose in the mixture should be adjusted. It is preferable that The concentration is preferably 60% by weight or less, more preferably 30% by weight or less from the viewpoint of dispersibility, and still more preferably 10% by weight or less. Moreover, from the viewpoint of improving dispersibility, it is preferable that the fine cellulose is subjected to this step without being dried.

The concentration of fine cellulose in the slurry containing pulp and fine cellulose is preferably 0.01 to 20% by weight based on the solid content of the pulp and fine cellulose combined. If the upper limit exceeds this value, the dispersion of fine cellulose may become insufficient, resulting in undispersed matter occurring in the dispersion, or the viscosity of the dispersion becoming too high, resulting in poor handling. . From this point of view, the upper limit of the fine cellulose concentration is more preferably 10% by weight or less, and the lower limit is preferably 0.1% by weight or more. The B-type viscosity of the slurry (1%, 25°C, 60 rpm) may be within the range that can be transferred by pipes and pumps used in normal papermaking processes, and from the viewpoint of fluidity and dispersibility of fine cellulose in the slurry. to 600 mPa·s or less is preferable, and 200 mPa·s or less is more preferable. Fillers and additives commonly used in paper manufacturing can be added to the slurry. In addition, since the MFC of the present invention increases the water retention (water retention) of pulp slurry, the water retention tends to increase as the amount added increases, while the freeness (Canadian standard freeness, etc.) tends to decline.

[Paper making process]
In this step, paper is obtained by making paper from the slurry. Paper making can be carried out in a known manner, for example, using a known paper machine such as a fourdrinier wet paper machine, a twin wire paper machine, a Yankee paper machine, a cylinder paper machine, a cylinder/short screen combination paper machine, etc. . The paper may also be made by hand.

[Other processes]
The manufacturing method of the present invention may include a coating step of providing a pigment coating layer or a clear coating layer containing no pigment on the base paper. Furthermore, the manufacturing method of the present invention may include a step of surface treating the paper. These methods can be performed as known.

[Paper containing fine cellulose]
The paper containing fine cellulose obtained in the present invention has excellent strength and air resistance. Patent Document 7 discloses paper containing oxidized pulp. The oxidized pulp does not have sufficient dispersibility in the slurry used for paper making, and the reinforcing effect and air permeation resistance of the paper are also not at a sufficient level. Further, Patent Document 8 discloses a paper containing MFC obtained by mechanically treating unmodified pulp with inorganic particles. However, the MFC does not have sufficient dispersibility in the slurry, and the air permeation resistance of the paper is also not at a sufficient level. Furthermore, since paper to which MFC, which is co-treated with the inorganic particles, is added, inevitably contains a certain amount of inorganic particles, there is also the problem that it is difficult to control the ash content. On the other hand, chemically modified cellulose can loosen cellulose fibers more efficiently than untreated cellulose due to the electrostatic repulsion of introduced functional groups. Therefore, when chemically modified cellulose is beaten, MFC with advanced fibrillation and short fiber formation can be obtained compared to when cellulose that is not chemically modified is beaten. In particular, the MFC obtained in the present invention has more advanced short fibers, so when added to the slurry, the MFC has good dispersibility, and the paper obtained from the slurry has excellent mechanical strength. , and has a higher degree of air permeation resistance.

[Example 1]
<Preparation of chemically modified pulp 1 (TEMPO oxidation)>
5.00 g (absolutely dry) of bleached unbeaten kraft pulp derived from coniferous trees (whiteness 85%, manufactured by Nippon Paper Industries Co., Ltd.), and 39 mg (0.05 mmol per 1 g of absolutely dry cellulose) of TEMPO (manufactured by Sigma Aldrich). and 514 mg of sodium bromide (1.0 mmol per 1 g of bone-dried cellulose) were added to 500 mL of an aqueous solution, and the mixture was stirred until the pulp was uniformly dispersed. An aqueous sodium hypochlorite solution was added to the reaction system so that the sodium hypochlorite concentration was 5.5 mmol/g, and the oxidation reaction was started at room temperature. During the reaction, the pH in the system decreased, but the pH was adjusted to 10 by successively adding a 3M aqueous sodium hydroxide solution. The reaction was terminated when the sodium hypochlorite was consumed and the pH within the system stopped changing. Hydrochloric acid was added to the reaction mixture and the mixture was filtered through a glass filter to separate the pulp, which was thoroughly washed with water to obtain a chemically modified pulp (carboxylated cellulose). The pulp yield was 90%, the time required for the oxidation reaction was 90 minutes, the pH was 5, and the amount of carboxyl groups was 1.59 mmol/g.

<beating>
The resulting mixture of chemically modified pulp and water was dehydrated to a pulp solid content concentration of 25% by weight, and subjected to beating treatment seven times using a 14-inch laboratory refiner (manufactured by Aikawa Iron Works Co., Ltd.) to obtain CFB. High-concentration mechanical processing with a 14-inch laboratory refiner is a batch process in which raw materials are fed into the equipment, mechanically processed, recovered, and then subjected to mechanical processing multiple times, so the degree of processing is determined by the number of processing times. adjusted.

<pH adjustment from neutral to alkaline>
Ion-exchanged water was added to the obtained CFB to make a mixture with a CFB solid concentration of 2% by weight, which was made acidic and then the pH of the mixture was adjusted to 7.5, resulting in a dispersion in which MFC was dispersed in water. was gotten. The MFC was evaluated by the method described below. The results are shown in Table 1.

[Example 2]
Chemically modified pulp 2 with a COOH group content of 1.42 mmol/g was prepared in the same manner as in Example 1, except that an aqueous sodium hypochlorite solution was added so that the sodium hypochlorite concentration was 4.9 mmol/g. I got it. A dispersion of MFC was obtained in the same manner as in Example 1, except that the resulting mixture of chemically modified pulp and water was dehydrated to a pulp solid content concentration of 30% by weight, and the number of treatments was twice. However, in this example, no CFB was formed.

[Example 3]
A dispersion of MFC was obtained in the same manner as in Example 1 except that the number of treatments was changed to three times. However, in this example, no CFB was formed.

[Example 4]
A mixture of chemically modified pulp 2 and water was dehydrated so that the pulp solid content concentration was 30% by weight. The mixture was subjected to treatment with a 14-inch laboratory refiner (manufactured by Aikawa Tekko Co., Ltd.), and the beating treatment was performed twice. NaOH and H ₂ O ₂ were added to the treated mixture to convert the COOH groups into salt form and to bring the pulp solids concentration to 4% by weight. The mixture was subjected to Top Finer (manufactured by Aikawa Iron Works Co., Ltd.) and treated for 20 minutes. The treated mixture was not subjected to pH adjustment, but only diluted with ion-exchanged water to obtain an MFC dispersion.

[Example 5]
<Preparation of chemically modified pulp 4 (carboxymethylation)>
130 parts by weight of water and 20 parts by weight of sodium hydroxide dissolved in 100 parts by weight of water were added to a twin-screw kneader whose rotational speed was adjusted to 100 rpm, and hardwood pulp (manufactured by Nippon Paper Industries Co., Ltd., LBKP) was added. The dry weight (after drying at 100° C. for 60 minutes) was 100 parts by weight. A mixed and mercerized cellulose raw material was prepared by stirring at 30° C. for 90 minutes. Further, while stirring the contents, 100 parts by weight of isopropanol (IPA) and 60 parts by weight of sodium monochloroacetate were added, and after stirring for 30 minutes, the temperature was raised to 70° C. and a carboxymethylation reaction was performed for 90 minutes. The concentration of IPA in the reaction medium during the carboxymethylation reaction was 30% by weight. After the reaction, the contents were neutralized by adding acetic acid to a pH of about 7, deliquified, and dried to produce carboxymethylated pulp with a carboxymethyl substitution degree of 0.21 and a cellulose I type crystallinity of 72%. Obtained. The effective utilization rate of the carboxymethylating agent was 29%. The method for measuring the degree of carboxymethyl substitution was as described above, and the crystallinity of cellulose type I and the effective utilization rate of the carboxymethylating agent were determined by known methods.

<beating>
The beating treatment was carried out in the same manner as in Example 3, except that hydrochloric acid was added to the obtained mixture of carboxymethylated pulp and water to adjust the pH to 5, and the solid content concentration of the dehydrated pulp was set to 30% by weight. A dispersion of MFC was obtained. No CFB was formed in this example.

[Example 6]
A mixture of carboxymethylated pulp and water was subjected to beating treatment without adding hydrochloric acid, and after beating treatment, pH adjustment was not performed and only dilution with ion-exchanged water was performed. An MFC dispersion was obtained.

[Comparative example 1]
An MFC dispersion was obtained in the same manner as in Example 1, using unmodified NBKP and changing the beating conditions as shown in Table 1.

[Comparative example 2]
An MFC dispersion was obtained in the same manner as in Example 1 using Chemically Modified Pulp 1 and changing the beating conditions as shown in Table 1. The low-concentration mechanical treatment in the 14-inch laboratory refiner was performed by connecting the tank and refiner with a pipe to perform circulation treatment, so the degree of treatment was adjusted by the treatment time.

[Comparative example 3]
Comparative example except that the beating treatment was performed without adding hydrochloric acid, the beating treatment was performed for 5 minutes with a 14-inch laboratory refiner, and the pH was not adjusted after the beating treatment and only dilution with ion-exchanged water was performed. A dispersion of MFC was obtained in the same manner as in 2.

Physical properties and characteristics were evaluated as follows.
1) Average fiber length and average fiber diameter Deionized water was added to the beaten mixture to prepare a 0.25% by weight slurry, and the slurry was measured using a Valmet fractionator.
2) Fibrillation rate Ion-exchanged water was added to the beaten mixture to prepare a 0.25% by weight slurry, and the slurry was measured using a Valmet fractionator.
3) Charge Density Charge density was measured as follows using a particle surface charge measuring device (Particle Charge Detector PCD03, manufactured by MUTEK) and an automatic titration device ([Model Titrino702] manufactured by Mutek).
i) A sample and ion-exchanged water were mixed to prepare a solution with a sample concentration of 0.01% by weight.
ii) 10 mL of the solution was titrated with a cationic polymer electrolyte (Polydimethyl diallyl ammonium chloride, 1/1000N) solution, and the amount consumed up to the zero charge point was measured.
iii) The magnitude of charge density (cation requirement) was determined according to the following formula.
Size of charge density (μeq/g) = (V x c x 1000)/m
V: titrant consumption (mL), c: titrant concentration (mol/L=eq/L), m: sample amount (g)
4) Handling property The following items were evaluated for the MFC dispersion obtained by diluting after beating.
(item)
i) Does it have high concentration and good transport efficiency?
ii) Does it have low viscosity and does not stick to transportation containers, etc.?
(standard)
a: Good
b: Slightly inferior
c: Poor 5) Type B viscosity An aqueous dispersion having an MFC concentration of 1% by weight was prepared, the pH was adjusted to 6 or more, and the measurement was performed at 25° C. and 60 rpm.

[Example A1]
<Preparation of chemically modified pulp 1 (TEMPO oxidation)>
Chemically modified pulp 1 was obtained in the same manner as in Example 1.

<beating>
The resulting mixture of chemically modified pulp and water was dehydrated to a pulp solid content concentration of 25% by weight, and subjected to beating treatment three times using a 14-inch laboratory refiner (manufactured by Aikawa Tekko Co., Ltd.) to form a mixture of MFC and water. I got it.

<Paper manufacturing>
A pulp slurry was prepared by adding sulfuric acid, cationized starch, MFC obtained in the above step, PAM, and a retention agent to deinked waste paper pulp (manufactured by Nippon Paper Industries Co., Ltd.) in this order, and then adding water. As MFC, the mixture obtained in the above step was added to the pulp as it was. The blending amounts were as follows.
Deinked waste paper pulp: 96 parts by weight MFC: 4 parts by weight Sulfate band: 0.9% by weight based on the total of deinked waste paper pulp and MFC (pulp-based raw materials)
Cationized starch: 0.3% by weight based on pulp raw materials
PAM: 0.06% by weight based on pulp raw materials
Retention agent: 200ppm based on pulp raw materials

Using the obtained papermaking slurry, handmade sheets were produced and evaluated.

[Comparative example A1]
A handmade sheet was produced and evaluated in the same manner as in Example A1, except that MFC was not used.

[Comparative example A2]
A handmade sheet was produced and evaluated in the same manner as in Example A1, except that MFC was prepared with a pulp solid content concentration of 4% by weight during beating and a beating treatment time of 3 minutes.

[Comparative example A3]
A handsheet was produced in the same manner as in Example A1, except that NBKP was used instead of chemically modified pulp 1, the pulp solids concentration at the time of beating was 4% by weight, and the processing time was 9 minutes to prepare MFC. and evaluated. The results are shown in Table 2.

[Example B1]
<Preparation of chemically modified pulp 5 (TEMPO oxidation)>
Chemically modified pulp 5 was obtained in the same manner as in Example 1, except that an aqueous sodium hypochlorite solution was added so that the sodium hypochlorite concentration was 4.7 mmol/g. The amount of carboxyl groups was 1.37 mmol/g.

<beating>
The resulting mixture of chemically modified pulp and water was dehydrated to a pulp solid content concentration of 28% by weight, and subjected to beating treatment five times using a 14-inch laboratory refiner (manufactured by Aikawa Iron Works Co., Ltd.), so that the CFB was dissolved in water. A dispersed mixture was obtained. When a NaOH aqueous solution was added to the mixture and the pH of the mixture was adjusted to 8, a mixture in which MFC was dispersed in water was obtained.

<Paper manufacturing>
A pulp slurry was prepared by adding each component other than MFC and water to pulp (undeinked pulp, manufactured by Nippon Paper Industries Co., Ltd.) under the same conditions as in Example A1. A slurry for paper making was prepared by mixing this slurry with the above-mentioned pH-adjusted mixture of MFC dispersed in water. Using the obtained papermaking slurry, handmade sheets were produced and evaluated.

[Example B2]
The treatment in a 14-inch laboratory refiner with a pulp solid content of 28% by weight in Example B1 was changed to treatment with a four-screw kneader (manufactured by Aikawa Tekko Co., Ltd.) with a pulp solid content of 30% by weight, and the treatment time was 10%. A mixture of MFC and water was obtained in the same manner as in Example B1, except that the mixture was divided into 50%. Using the MFC, a handmade sheet was manufactured and evaluated in the same manner as in Example B1.

[Example B3]
When an alkali was added during the treatment with the four-screw kneader in Example B2 and ion-exchanged water was added to the treated mixture without adjusting the pH, MFC was dissolved in water without going through CFB. A dispersed mixture was obtained. Using the MFC, a handmade sheet was manufactured and evaluated in the same manner as in Example B1.

[Example B4]
The treated material obtained by processing with the four-axis kneader in Example B3 was diluted so that the pulp solid content concentration was 4% by weight, and then treated with a 14-inch laboratory refiner for 10 minutes, without passing through the CFB. A mixture of MFC dispersed in water was obtained. Using the MFC, a handmade sheet was manufactured and evaluated in the same manner as in Example B1.

[Example B5]
The beating treatment in a 14-inch laboratory refiner at a solid content concentration of 28% by weight in Example B1 was changed to 3 times, and the treated product was diluted to a pulp solid content concentration of 4% by weight, and then beaten in a top finer. A mixture in which MFC was dispersed in water was obtained in the same manner as in Example B1, except that the treatment was carried out for 10 minutes. Using the MFC, a handmade sheet was manufactured and evaluated in the same manner as in Example B1.

[Comparative example B1]
A handmade sheet was produced and evaluated in the same manner as in Example B1, except that MFC was not used. These results are shown in Table 3.

[Example C1]
<Preparation of chemically modified pulp 4 (carboxymethylation)>
Chemically modified pulp 4 (degree of carboxymethyl substitution: 0.21) was obtained in the same manner as in Example 5.

<beating>
The resulting mixture of chemically modified pulp and water was dehydrated to a pulp solid content concentration of 28% by weight, and subjected to beating treatment seven times using a 14-inch laboratory refiner (manufactured by Aikawa Iron Works Co., Ltd.) to form a mixture of MFC and water. I got it.

<Paper manufacturing>
Using the mixture of MFC and water obtained in the above process, a handmade sheet was manufactured and evaluated in the same manner as in Example A1.

[Example C2]
The treatment with the 14-inch laboratory refiner in Example C1 was carried out three times, and ion-exchanged water was added to the mixture after the treatment to make the pulp solid content concentration 4% by weight, and this was treated with the 14-inch laboratory refiner for 10 minutes. A mixture in which MFC was dispersed in water was obtained. Using the mixture, a handmade sheet was produced and evaluated in the same manner as in Example C1.

[Example C3]
A handmade sheet was produced in the same manner as in Example C2, except that the treatment with a 14-inch laboratory refiner at a solid content concentration of 4% by weight in Example C2 was changed to a top refiner treatment at a solid content concentration of 4%. evaluated.

[Comparative example C1]
A handmade sheet was produced and evaluated in the same manner as in Example C1, except that MFC was not used. These results are shown in Table 4.

[Evaluation method]
Basis weight: According to JIS P 8124:2011.
Average fiber length and average fiber diameter: Deionized water was added to the beaten dispersion to prepare a 0.25% by weight slurry, and measured using a Valmet fractionator.
Paper thickness and density: according to JIS P 8118:2014.
Ash content: According to JIS P 8251:2003.
Air permeability resistance: Measured using an Oken type smoothness air permeability tester in accordance with JIS P8117:2009.
Breaking length: According to JIS P 8113:1998.

The paper obtained by the manufacturing method of the present invention has excellent air permeability resistance and tear length. The papers of Example B using alkali-treated MFC and Example C using CM-modified MFC have particularly excellent air permeability resistance and tear length.

Claims (18)

(1) A step of chemically modifying raw material pulp to obtain chemically modified pulp;
(2) a step of mechanically treating the chemically modified pulp obtained in the above step at a solid content concentration of 15% by weight or more;
A method for producing fine cellulose fibers, comprising: The manufacturing method according to claim 1, wherein the mechanical treatment is beating. The manufacturing method according to claim 1 or 2, wherein the chemically modified pulp is an anionically modified pulp. The manufacturing method according to any one of claims 1 to 3, wherein the chemically modified pulp has 0.3 to 2.5 mmol/g of carboxyl groups. The manufacturing method according to any one of claims 1 to 4, comprising the step of acid-treating the chemically modified pulp. The manufacturing method according to any one of claims 1 to 5, comprising a step of treating the chemically modified pulp with an alkali. The manufacturing method according to claim 5, wherein the acid treatment includes adding an acid to the mixture containing the chemically modified pulp and water to adjust the pH of the mixture to 6.5 or less. 7. The manufacturing method according to claim 6, wherein the alkali treatment includes adding an alkali to the mixture containing the chemically modified pulp and water to adjust the pH of the mixture to above neutral. The manufacturing method according to any one of claims 1 to 8, wherein the fine cellulose fibers are microfibrillated cellulose. The method according to any one of claims 1 to 8, wherein the fine cellulose fibers are cellulose nanofibers. The step (2) is a step that includes performing mechanical treatment multiple times under different conditions to obtain microfibrillated cellulose, in which at least one of the mechanical treatments is performed under conditions where the solid content concentration is 15% by weight or more. The manufacturing method according to claim 9, which is a step of performing. In the step (2), the chemically modified pulp is mechanically treated under conditions where the solid content concentration is 15% by weight or more, and then mechanically treated under conditions where the solid content concentration is less than 15% by weight to obtain microfibrillated cellulose. The manufacturing method according to claim 11, comprising: The manufacturing method according to claim 10, wherein the step (2) includes further subjecting the microfibrated cellulose produced by the mechanical treatment to a mechanical treatment to obtain cellulose nanofibers. The manufacturing method according to any one of claims 1 to 13, comprising a step of treating the fine cellulose fibers produced by the mechanical treatment with an alkali. The step (2) is
(2-1) forming a cellulose fiber ball formed by entangling fine cellulose fibers by mechanically treating the chemically modified pulp at a solid content concentration of 15% by weight or more, and (2-2) the above-mentioned The manufacturing method according to claim 9, comprising preparing microfibrated cellulose by treating cellulose fiber balls with alkali. The step (2) is
(2-1) Mechanically treating the chemically modified pulp at a solid content concentration of 15% by weight or more to form cellulose fiber balls in which fine cellulose fibers are entangled;
(2-2) preparing microfibrated cellulose by treating the cellulose fiber balls with an alkali; and (2-3) mechanically treating the microfibrated cellulose to prepare cellulose nanofibers. The manufacturing method according to claim 10, comprising: The manufacturing method according to claim 15 or 16, wherein the alkali treatment includes adding an alkali to the mixture containing the cellulose fiber balls and water to adjust the pH of the mixture to neutral or higher. preparing finely divided cellulose by the method of any one of claims 1 to 17;
A step of preparing a slurry containing pulp and the fine cellulose, and a step of making paper from the slurry,
Paper manufacturing method.