JP2022111469A - Method for producing chemically modified microfibril cellulose fiber - Google Patents

Abstract

To provide a method for producing a chemically modified microfibril cellulose fiber having a high BET specific surface area, capable of obtaining a chemically modified microfibril cellulose fiber having a specific range of an average fiber width, and excellent in production efficiency.SOLUTION: A method for producing a chemically modified microfibril cellulose fiber includes: a chemical denaturation process in which raw pulp is chemically denatured to obtain chemically denatured pulp; and a beating process in which the chemically denatured pulp obtained in the chemical denaturation process is treated by beating under the condition of solid concentration of 15 wt.% or less, using a double disc refiner equipped with DA and DB as two discs and DM as a disc existing between them, where DA and either DB or DM are fixed and the other is rotating.SELECTED DRAWING: Figure 1

Description

The present invention relates to a method for producing chemically modified microfibril cellulose fibers.

Cellulose nanofibers and microfibril cellulose fibers obtained by refining cellulose are fine fibers with a fiber width of nano to micro order, and have functions such as high strength, high elasticity, and thixotropic properties that ordinary pulp does not have. It is expected to be used in various fields as a new material.

For example, in the field of paper manufacturing, paper strength improvers are sometimes used to improve the strength of paper, and addition of cellulose nanofibers is being studied to reinforce the effect (Patent Document 1, etc.). .

JP 2016-166444 A

However, the method described in Patent Document 1 has a problem that the cost of the resulting paper increases due to the addition of cellulose nanofibers, since cellulose nanofibers are expensive. In addition, since cellulose nanofibers have a very small fiber width, when they are added to papermaking raw materials and made into paper, they are discharged together with water due to dehydration in the wire part of the paper machine and squeezing in the press part. There is also a problem that the strength of the paper to be used is not sufficiently increased.

The inventors use microfibrillar cellulose fibers with a higher BET specific surface area than cellulose nanofibers, which are less defibrated than cellulose nanofibers, to produce low-cost, high-strength paper. I got the idea that it can be done. As a method for producing microfibril cellulose fibers with such characteristics, the use of a single disc refiner has been studied, but there has been the problem that it is difficult to increase the throughput.

An object of the present invention is to provide a method for producing chemically modified microfibril cellulose fibers with excellent production efficiency, which can obtain chemically modified microfibril cellulose fibers having a high BET specific surface area and an average fiber width in a specific range. is.

The present invention provides the following.
(1) A method for producing chemically modified microfibril cellulose fibers having a BET specific surface area of 50 m ² /g or more and an average fiber width of 500 nm or more, comprising a chemical modification step of chemically modifying raw material pulp to obtain chemically modified pulp; , the chemically denatured pulp obtained in the chemical denaturation step under conditions of a solid content concentration of 15% by weight or less, comprising DA and DB as two discs and DM as a disc existing between them, the DA and the DB or A method for producing chemically modified microfibril cellulose fibers, comprising a beating treatment step of performing beating treatment using a double disc refiner in which one of the DMs is fixed and the other is rotated.
(2) The method for producing chemically modified microfibril cellulose fibers according to (1), wherein the number of passes in the beating step is 30 or less.
(3) the chemical modification is oxidation carried out using an N-oxyl compound, a compound selected from the group consisting of bromides, iodides and mixtures thereof, and an oxidizing agent, (1) or (2); A method for producing the chemically modified microfibril cellulose fibers described.
(4) The method for producing chemically modified microfibril cellulose fibers according to (1) or (2), wherein the chemical modification is carboxymethyl modification.
(5) The double-disc refiner has a mono-flow system for raw material flow, and the blade width X1 of the first disk counted from the raw material inflow side of the DA and the DB is equal to the blade width of the second disk. The method for producing a chemically modified microfibril cellulose fiber according to any one of (1) to (4), characterized in that it is larger than X2.
(6) The double-disc refiner has a mono-flow type raw material flow system, and the blade width X1 of the first disk counted from the raw material inflow side of the DA and the DB is equal to the blade width of the second disk. The method for producing chemically modified microfibril cellulose fibers according to any one of (1) to (4), wherein the microfibril cellulose fibers are smaller than X2.
(7) The double-disc refiner has a mono-flow type raw material flow system, and the blade width X1 of the first disk counted from the raw material inflow side of the DA and the DB is equal to the blade width of the second disk. The method for producing chemically modified microfibril cellulose fibers according to any one of (1) to (4), which is the same as X2.

According to the present invention, there is provided a method for producing a chemically modified microfibril cellulose fiber having a high BET specific surface area and an average fiber width in a specific range, which is excellent in production efficiency. can be done.

It is a schematic diagram showing an example of a double disc refiner used for the manufacturing method of the present invention.

Hereinafter, the method for producing chemically modified microfibril cellulose fibers of the present invention will be described with reference to the drawings. In the present invention, "-" includes end values. That is, "X through Y" includes the values X and Y at both ends.

The method for producing chemically modified microfibril cellulose fibers having a high BET specific surface area and an average fiber width within a specific range according to the present invention comprises a chemically modifying step of chemically modifying a raw material pulp to obtain a chemically modified pulp, and the chemically modifying step. The obtained chemically modified pulp is provided with DA and DB as two discs and DM as a disc between them at a solid content concentration of 15% by weight or less, and either the DA and the DB or the DM. and a beating treatment step of beating using a double disc refiner in which one is fixed and the other is rotating.

(chemically modified microfibril cellulose fiber)
Microfibril cellulose fibers (hereinafter also referred to as "MFC") are fibers having an average fiber width of 500 nm or more obtained by defibrating cellulosic raw materials such as pulp. "Modified MFC") is MFC obtained by defibrating a chemically modified cellulose-based raw material. In the present invention, the average fiber width is the length-weighted average fiber width, and the fiber width can be measured with a fiber tester manufactured by ABB Corporation or a fractionator manufactured by Valmet. The lower limit of the fiber diameter is preferably 500 nm or more, and the upper limit is about 60 μm or less, although not particularly limited. MFC is obtained by defibrating or beating a cellulosic raw material relatively weakly with a beater, disperser, or the like. Therefore, MFC has a larger fiber width than cellulose nanofibers obtained by strongly fibrillating a cellulosic raw material with a high-pressure homogenizer or the like, and efficiently fluffs the fiber surface while suppressing the miniaturization of the fiber itself. It has an outer (externally fibrillated) shape.

(BET specific surface area)
The chemically modified microfibril cellulose fibers obtained by the production method of the present invention have a BET specific surface area of 50 m ² /g or more, preferably 70 m ² /g or more. When the BET specific surface area is high, when it is used as a papermaking additive, for example, it becomes easier to bind to pulp, and there are advantages such as an improvement in yield and an increase in the 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 (JISZ8830):
(1) About 2% slurry (dispersion medium: water) of chemically modified microfibril cellulose fibers is placed separately in a centrifugal container so that the solid content is about 0.1 g, and 100 mL of ethanol is added.
(2) Add a stirrer and stir at 500 rpm for 30 minutes or longer.
(3) Remove the stirrer and use a centrifuge to sediment the chemically modified microfibril cellulose fibers under the conditions of 7000 G, 30 minutes, and 30°C.
(4) Remove the supernatant while removing as little chemically modified microfibril cellulose fibers as possible.
(5) Add 100 mL of ethanol, add a stirrer, stir under the conditions of (2), centrifuge under the conditions of (3), remove the supernatant under the conditions of (4), and repeat this three times.
(6) The solvent in (5) is changed from ethanol to t-butanol, and at room temperature above the melting point of t-butanol, stirring, centrifugation and supernatant removal are repeated three times in the same manner as in (5).
(7) After removing the final solvent, add 30 mL of t-butanol, mix gently, transfer to an eggplant flask, and freeze using an ice bath.
(8) Cool in a freezer for at least 30 minutes.
(9) Attach to a freeze-dryer and freeze-dry for 3 days.
(10) Perform BET measurement using a BET measurement device (manufactured by Micromeritics) (pretreatment conditions: 105 ° C. for 2 hours under nitrogen stream, relative pressure 0.01 to 0.30, sample amount 30 mg degree).

(viscosity)
The chemically modified microfibril cellulose fibers obtained by the production method of the present invention preferably have a B-type viscosity of 1% by weight, 60 rpm, 25° C., from the viewpoint of the progress of defibration, from 10 to 6000 mPa s, or more. It is preferably 20 to 5000 mPa·s, more preferably 50 to 4000 mPa·s.

(Chemical denaturation step)
In the chemical denaturation step, raw material pulp is chemically denatured to obtain chemically denatured pulp.

(raw material pulp)
Raw material pulp includes unbleached softwood kraft pulp (NUKP), bleached softwood kraft pulp (NBKP), unbleached hardwood kraft pulp (LUKP), bleached hardwood kraft pulp (LBKP), unbleached softwood sulfite pulp (NUSP), softwood bleached sulfite pulp (NBSP), hardwood unbleached sulfite pulp (LUSP), hardwood bleached sulfite pulp (LBSP), thermomechanical pulp (TMP), pressure groundwood pulp (PGW), refiner groundwood pulp (RGP), Alkaline hydrogen peroxide mechanical pulp (APMP), alkaline hydrogen peroxide thermomechanical pulp (APTMP), linters, jute, hemp, paper mulberry, mitsumata, kenaf and other herbaceous pulps, bamboo pulps, recycled pulps, waste paper pulps, etc. include, but are not limited to.

(Chemical denaturation)
Chemical modification is the introduction of functional groups into the pulp, and the chemical modification is preferably anion modification, ie the chemically modified pulp preferably has anionic groups. Examples of anionic groups include acid groups such as carboxyl groups, carboxyl group-containing groups, phosphoric acid groups, phosphoric acid group-containing groups, and sulfate groups. Examples of the carboxyl group-containing group include -COOH group, -R-COOH (R is an alkylene group having 1 to 3 carbon atoms), and -OR-COOH (R is an alkylene group having 1 to 3 carbon atoms). be done. Phosphate group-containing groups include polyphosphoric acid group, phosphorous acid group, phosphonic acid group, 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, there is 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. According to this method, the primary hydroxyl group at the C6 position of the glucopyranose ring on the cellulose surface is selectively oxidized to generate a group selected from the group consisting of an aldehyde group, a carboxyl group and a carboxylate group. Alternatively, an ozone oxidation method may be mentioned. According to this oxidation reaction, at least the hydroxyl groups at the 2nd and 6th positions of the glucopyranose rings constituting cellulose are oxidized, and the cellulose chains are decomposed.

An N-oxyl compound means a compound capable of generating a nitroxy radical. As the N-oxyl compound, any compound can be used as long as it promotes the desired oxidation reaction. Examples include 2,2,6,6-tetramethylpiperidine-1-oxy radical (TEMPO) and its derivatives (eg 4-hydroxy TEMPO).

An example of the method for measuring the amount of carboxyl groups is described below. Prepare 60 mL of 0.5% by weight slurry (aqueous dispersion) of oxidized cellulose, add 0.1 M hydrochloric acid aqueous solution to adjust the pH to 2.5, and then drop 0.05 N sodium hydroxide aqueous solution to adjust 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 whose electrical conductivity changes slowly.
Carboxyl group amount [mmol/g oxidized cellulose] = a [mL] x 0.05/oxidized cellulose weight [g]

The amount of carboxyl groups in the oxidized cellulose measured in this manner is preferably 0.1 mmol/g or more, more preferably 0.5 mmol/g or more, still more preferably 0.8 mmol/g, relative to the absolute dry weight. That's it. The upper limit of the amount is preferably 3.0 mmol/g or less, more preferably 2.5 mmol/g or less, still more preferably 2.0 mmol/g or less. Therefore, the amount is preferably 0.1 mmol/g or more and 3.0 mmol/g or less, more preferably 0.5 mmol/g or more and 2.5 mmol/g or less, and further 0.8 mmol/g or more and 2.0 mmol/g or less. preferable.

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

The degree of carboxymethyl substitution per glucose unit of carboxymethylated cellulose is measured, for example, by the following method. That is, 1) About 2.0 g of carboxymethylated cellulose (absolute dry) is precisely weighed and placed in a 300 mL Erlenmeyer flask with a common stopper. 2) Add 100 mL of a solution obtained by adding 100 mL of special grade concentrated nitric acid to 1000 mL of nitric acid methanol, and shake for 3 hours to convert carboxymethylcellulose salt (carboxymethylated cellulose) into hydrogen-type carboxymethylated cellulose. 3) About 1.5 g to 2.0 g of hydrogen-form carboxymethylated cellulose (absolute dry) is accurately weighed and placed in a 300 mL conical flask with a common stopper. 4) Wet hydrogen carboxymethyl 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 formula:
A = [(100 x F'- ₍ 0.1N H2SO4) ₍ mL) x F) x 0.1]/(bone dry weight of hydrogen-form carboxymethylated cellulose (g))
DS = 0.162 x A/(1 - 0.058 x A)
A: Amount of 1N NaOH (mL) required to neutralize 1 g of hydrogen-type carboxymethylated cellulose
F: Factor of _{0.1N H2SO4} F': Factor of 0.1N NaOH

The degree of carboxymethyl substitution per anhydroglucose unit in the 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 0.01 or more and 0.50 or less, more preferably 0.05 or more and 0.40 or less, and still more preferably 0.10 or more and 0.30 or less.

(Beating process)
In this step, the chemically modified pulp adjusted to a solid content concentration of 15% by weight or less is beaten using a double disc refiner. When the chemically modified pulp is subjected to a beating treatment, the fiber length and width become smaller, and fibrillation progresses, which causes the fiber to become more fluffy. In the beating treatment step of the present invention, the beating treatment using a double disc refiner may be a circulating treatment, or the beating treatment may be performed continuously using a plurality of double disc refiners as a continuous treatment. In the present invention, the number of passes of the beating treatment when the beating treatment using the double disc refiner is a circulating treatment or a continuous treatment is not particularly limited as long as the desired chemically modified microfibril cellulose fibers can be obtained. and from the viewpoint of suppressing excessive shortening of fibers and deterioration due to heat generated during treatment, the number of times is preferably 30 times or less, more preferably 20 times or less, even more preferably 10 times or less, and even more preferably 5 times or less.

In the present invention, the number of passes of the beating process when the beating process is a circulation process and a partial circulation is the number of times the raw material to be processed passes through one double disc refiner and is recovered. is multiplied by the following n.
n=1/(1−a)
where a=circulation rate. (When the circulation rate is 50%, a = 0.5, and when the circulation rate is 75%, a = 0.75.)

The number of passes in the beating process in the case of performing continuous treatment using a plurality of double disc refiners that perform partial circulation is calculated by the above method for each refiner and summed up.

When the beating process is a circulating process, the number of passes of the beating process in the case of performing a batch process by full circulation is the number of times the raw material to be processed passes through the double disc refiner until it is recovered.

Further, in the present invention, when the beating process is performed continuously using a plurality of double disc refiners, the number of passes of the beating process increases by 1 each time the raw material to be processed passes through one double disc refiner. and

(Disc refiner)
A disc refiner consists of discs with beating blades (disc plates (sometimes simply referred to as "discs")) facing each other at a close distance, rotating only one side or in opposite directions at a predetermined number of revolutions, It is a device that imparts the effect of pressurized beating to the slurry passing through it and the effect of continuous delivery by centrifugal force. A disc refiner with one beating gap formed by disc plates is called a single disc refiner (sometimes abbreviated as "SDR"), and the number of beating gaps formed by disc plates is two. One is called a double disk refiner (sometimes abbreviated as "DDR").

(double disc refiner)
A double disc refiner has two discs DA and DB with a disc DM between them, either one of DA and DB or DM being fixed and the other rotating, or DA and DB and DM being reversed. Take a configuration that rotates in the direction. As a double disc refiner, two discs DA and DB are fixed discs, and DM is a floating disc that freely rotates between them. Heavy Industries/Beloit (Jones) Double Disc Refiner, Ishikawajima Sangyo Kikai/Black Clawson Twin Hydra Disc, Hitachi Zosen (Hitachi Zosen Tomioka Kikai)/Escher Wyss Twin Disc Refiner, and the like.

In the present invention, a double-disc refiner is used from the viewpoint of being able to increase the throughput and to be excellent in production efficiency as compared with a single-disc refiner.

The blade width of the two discs DA and DB is preferably 0.3 to 1.5 mm, more preferably 0.5 to 1.3 mm. The groove width of DA and DB is preferably 0.5 to 2.0 mm, more preferably 0.8 to 1.7 mm. The blade width and groove width of DA and DB may be the same or different. Although the blade angle is not particularly limited, 0 to 40° is preferable, and 5 to 20° is particularly preferable.

Double disc refiners are roughly divided into two types, the mono-flow type and the duo-flow type, depending on the material flow method. In the mono-flow type, the raw material flows from the beating gap near the raw material inflow side to the other beating gap. It is a method of parallel flow. In the production method of the present invention, the mono-flow system is preferable as the raw material flow system from the viewpoint of efficient defibration.

An example of a double disc refiner that can be used in the present invention will be described with reference to FIG. FIG. 1 is a sectional view schematically showing a monoflow type double disc refiner as a material flow system. The double disc refiner that can be used in the present invention is not limited to that shown in FIG.

The double-disc refiner 2 shown in FIG. 1 has rotating discs DM8 arranged in a beating chamber 6 for beating pulp raw materials fed from a raw material inlet 4, and both surfaces of the rotating discs DM8 have a predetermined blade width and groove width. A blade with a blade is attached. A fixed disk DA10 and a fixed disk DB12 are arranged on the inner wall of the beating chamber 6 so as to face blades attached to both sides of the rotary disk DM8. A blade having a predetermined blade width and groove width is attached to fixed disk DA10 and fixed disk DB12. The rotating disk DM8 is attached to a drive shaft 14, and the drive shaft 14 is connected to a motor 16 and driven to rotate. The beating chamber 6 includes a circulation pipe 18 for circulating the beaten raw material in the beating chamber 6, an outlet 20 for discharging the beaten raw material to the outside of the beating chamber 6, and a recovery tank (see FIG. 1) from the outlet 20. (not shown) is provided, and the flow rates in the circulation line 18 and the outlet line 22 are regulated by manual valves 24 .

When the double disc refiner 2 is used to beat the pulp raw material, the pulp raw material is fed from the raw material inlet 4 of the double disc refiner 2 and sent to the beating chamber 6 . The raw material sent to the beating chamber 6 is first beaten in the beating gap formed between the fixed disk DA10 and the rotating disk DM8, and then beaten in the beating gap formed between the fixed disk DB12 and the rotating disk DM8. , part of the raw material is sent to the beating chamber 6 again via the circulation pipe 18 . The beaten raw material is discharged from the discharge port 20 and sent to the recovery tank via the outlet pipe 22 . A manual valve 24 regulates the amount of material circulating and the amount of material discharged from the outlet.

When the raw material flow system is a mono-flow system, the blade width (X1) of DA, which is the first disk counted from the raw material inlet 4 side, and the blade width (X1) of the second disk among the two disks DA and DB There are the following merits depending on the relation of the edge width (X2) of a certain DB.
X1=X2: The obtained MFC tends to have uniform fiber width and fiber length.
X1>X2: Since the raw material is beaten and fibrillated on the wide blades and then beaten and fibrillated by the narrow blades, the cutting progresses, so that the raw material becomes difficult to pass through as it is unfibrillated.
X1<X2: After the raw material is beaten with narrow blades and cutting proceeds, it is beaten with wide blades and fibrillated, so fine fibers with advanced fibrillation are likely to be obtained.

When the material flow system is a mono-flow system, the groove width (Y1) of DA, which is the first disk counted from the material inlet 4 side, and the second disk out of the two disks DA and DB. The following merits are obtained depending on the groove width (Y2) of the disk DB.
Y1=Y2: The obtained MFC tends to have uniform fiber width and fiber length.
Y1>Y2: Since the raw material passes through a narrow beating gap after passing through a wide beating gap, an excessive load is less likely to be applied, making it suitable for treating highly viscous materials.
Y1<Y2: When passing through the first narrow beating gap, fibrillation progresses and the viscosity tends to increase, but the next wide beating gap is passed, and the raw material can pass without delay.

In the production method of the present invention, as operating conditions when using a double disc refiner, the clearance between DA and DM and between DB and DM is preferably 0.6 mm or less, more preferably 0.4 mm or less, and 0.2 mm or less. More preferred. Although the lower limit is not particularly limited, it is preferably 0.02 mm or more in order to avoid metal touch. The operating temperature is preferably 5 to 120°C. The flow rate, treatment time, other conditions, etc. are appropriately adjusted so as to obtain chemically modified microfibril cellulose fibers having a desired fiber width.

In the production method of the present invention, the solid content concentration of the chemically modified pulp subjected to the beating treatment step is 15% by weight or less, preferably 0.3 to 10% by weight, and 0.5 to 6% by weight from the viewpoint of transferring the pulp slurry. % is more preferred. If the solid content concentration is too low, the blades of the plate do not reach the plate during beating, resulting in poor beating efficiency. The solid content concentration may fluctuate during the mechanical treatment including the beating treatment, but in the present invention, the solid content concentration at the start of the beating treatment is referred to as the solid content concentration in the beating treatment process.

A method for adjusting the solid content concentration of the chemically modified pulp to 15% by weight or less includes dilution.

The pH of the chemically modified pulp to be subjected to the beating step is preferably 6 or higher, more preferably 7 or higher, from the viewpoint of ease of defibration. Examples of methods for adjusting the pH to the above range include adding chemicals such as NaOH, KOH and sodium bicarbonate, or reducing the amount of acidic chemicals added after chemical modification. Although the pH of chemically modified pulp may fluctuate during mechanical treatments including beating, in the present invention, the pH at the start of beating is defined as the pH in the beating step.

The chemically modified pulp to be subjected to the beating treatment step may be one subjected to alkali treatment. Arbitrary alkalis, such as NaOH and KOH, can be used for this alkali treatment. When the chemically modified pulp used in the present invention is anionically modified pulp, the addition of an alkali converts the ends of the modifying groups to Na-type or the like, increasing the repulsion between fibers. Therefore, the electrostatic repulsion of fibers can be utilized to efficiently proceed with mechanical treatments such as beating, defibration, and fibrillation.

The chemically modified pulp to be subjected to the beating treatment step may be one subjected to an acid treatment. When the chemically modified pulp used in the present invention is anionically modified pulp, the end of the modified group becomes H-type by acid treatment, and the affinity for water is lowered.

In addition, in the production method of the present invention, one or more mechanical treatment steps using a device other than the double disc refiner are included before and after the beating treatment step using the double disc refiner. can be Moreover, before and after the beating treatment step, a mechanical treatment step may be provided in which the chemically modified pulp having a solid content concentration higher than 15% by weight is mechanically treated.

In the present invention, mechanical treatment refers to mixing fibers and further miniaturizing or fibrillating, and includes beating, defibration, dispersion, kneading, and the like. Here, the mechanical treatment under conditions where the solid content concentration is higher than 15% by weight is sometimes 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, the mechanical treatment under the condition that the solid content concentration is 15% by weight or less is sometimes called "low-concentration mechanical treatment", and in particular, when the mechanical treatment is beating, it is also called "low-concentration beating". In the present invention, the mechanical treatment may be performed multiple times as long as the beating treatment step of beating at a low concentration using a double disc refiner is performed at least once.

In the present invention, the mechanical treatment may be a circulation operation (batch treatment), a partial circulation operation, or a continuous treatment in which mechanical treatments are continuously performed using a plurality of devices. A high-concentration mechanical treatment and a low-concentration mechanical treatment may be combined, and when these mechanical treatments are combined, the order of treatment is not limited. It is preferable to carry out the treatment first. For example, after subjecting chemically modified pulp to high-concentration mechanical treatment, the chemically-modified pulp obtained by the treatment is diluted to 15% by weight or less, and subjected to low-concentration beating treatment using a double disc refiner to remove MFC. Obtainable.

Apparatuses that can be used for low-concentration mechanical treatment include, for example, high-speed rotary, colloid mill, high-pressure, roll-mill, ultrasonic, and other types of apparatuses, including high-pressure or ultrahigh-pressure homogenizers, conical refiners, Refiners, Beaters, PFI Mills, Kneaders, Dispersers, Top Finers, Seven Finers, Beat Finers, Twin Beat Finers, Henschel Mixers, Homomic Line Mills, etc. Alternatively, a method using friction between pulp fibers, or a method that disperses or defibrates pulp fibers by cavitation, water flow, or water pressure can be used.

Apparatuses that can be used for high-concentration mechanical treatment include, for example, high-speed rotary, colloid mill, high-pressure, roll-mill, ultrasonic, and other types of apparatus, including high-pressure or ultra-high pressure homogenizers, refiners, A beater, a PFI mill, a kneader, a disperser, a topfiner, or the like, in which a metal or blade acts on pulp fibers around a rotating shaft, or a method in which pulp fibers are rubbed against each other can be used.

According to the present invention, there is provided a method for producing a chemically modified microfibril cellulose fiber having a high BET specific surface area and an average fiber width in a specific range, which is excellent in production efficiency. can be done.

In the production method of the present invention, chemically modified pulp is used as a raw material, and electrostatic repulsion of the substituents introduced by chemical modification occurs. MFC can be obtained.

The chemically modified microfibril cellulose fibers obtained by the production method of the present invention are made from chemically modified pulp, and since functional groups are arranged on the fiber surface, they have various functionalities derived from the functional groups. For this reason, the chemically modified microfibril cellulose fibers obtained by the production method of the present invention can be used in various applications, and in various fields where additives are generally used, such as thickening agents, gelling agents, sizing agents, food products, etc. Additives, Excipients, Paint Additives, Adhesive Additives, Abrasives, Compounding Materials for Rubber and Plastics, Water Retaining Materials, Form Retainers, Mud Control Agents, Filter Aids, Anti-Overflow Agents, Admixtures etc. can be used. The fields include food, beverages, cosmetics, pharmaceuticals, paper manufacturing, various chemical products, paints, sprays, agricultural chemicals, civil engineering, construction, electronic materials, flame retardants, household goods, adhesives, cleaning agents, fragrances, lubricating compositions. things, etc.

EXAMPLES The present invention will be described in more detail below with reference to Examples, but the present invention is not limited to these.

(Example 1)
<Preparation of chemically modified pulp 1>
40 kg (absolutely dry) of bleached unbeaten kraft pulp derived from softwood (85% whiteness: manufactured by Nippon Paper Industries Co., Ltd.) was brominated with 312 g of TEMPO (manufactured by Sigma Aldrich) (0.05 mmol relative to 1 g of absolutely dry cellulose). It was added to 4000 L of an aqueous solution in which 4112 g of sodium (1.0 mmol per 1 g of absolute dry cellulose) was dissolved, and stirred until the pulp was uniformly dispersed. An aqueous sodium hypochlorite solution was added to the reaction system so that sodium hypochlorite was 5.5 mmol/g, and an oxidation reaction was initiated at room temperature. The pH in the system decreased during the reaction, but was adjusted to pH 10 by successively adding 3M sodium hydroxide aqueous solution. The reaction was terminated when the sodium hypochlorite was consumed and the pH in the system stopped changing. After adjusting the pH to 2 by adding hydrochloric acid to the reaction mixture, the pulp was thoroughly washed with water by repeating dehydration and dilution with water. (TEMPO oxidized pulp) was obtained. The pulp yield was 90% and the carboxyl group content was 1.41 mmol/g.

The resulting TEMPO oxidized pulp was dispersed in tap water, sodium hydroxide was added, and the mixture was stirred to obtain an aqueous dispersion of TEMPO oxidized pulp having a pH of 7.7 and a solid content concentration of 1.1% by weight.

<Beating>
3000 kg of the resulting aqueous dispersion of TEMPO oxidized pulp was passed through a monoflow double disc refiner (AWN20 manufactured by Aikawa Iron Works Co., Ltd., plate: blade width (X1): 0.8 mm, groove width (Y1): 1.3 mm, blade Width (X2): 0.6 mm, groove width (Y2): 1.0 mm), clearance: 0.4 mm or less, circulation rate 75.5%. The oxidized pulp was MFC. The pass number of the beating treatment was 8.1 times. The MFC was then evaluated by the method described below. Table 1 shows the results.

(Example 2)
The TEMPO-oxidized pulp having a solid content concentration of 20% by weight obtained in Example 1 was dispersed in tap water, and sodium hydroxide was added and stirred to obtain a TEMPO-oxidized pulp having a pH of 7.6 and a solid content concentration of 1.1% by weight. An aqueous dispersion of pulp was obtained.
3000 kg of this aqueous dispersion of TEMPO oxidized pulp was applied to a plate with blade width (X1): 0.6 mm, groove width (Y1): 1.0 mm, blade width (X2): 0.6 mm, groove width (Y2): 1. MFC was obtained by beating treatment in the same manner as in Example 1, except that the diameter was changed to 0.0 mm. The MFC was then evaluated by the method described below. Table 1 shows the results.

(Example 3)
The TEMPO-oxidized pulp having a solid content concentration of 20% by weight obtained in Example 1 was dispersed in tap water, and sodium hydroxide was added and stirred to obtain a TEMPO-oxidized pulp having a pH of 7.6 and a solid content concentration of 1.1% by weight. An aqueous dispersion of pulp was obtained.
3000 kg of this aqueous dispersion of TEMPO oxidized pulp was placed on a plate with blade width (X1): 0.6 mm, groove width (Y1): 1.0 mm, blade width (X2): 0.8 mm, groove width (Y2): 1. An MFC was obtained by beating treatment in the same manner as in Example 1, except that it was changed to 0.3 mm. The MFC was then evaluated by the method described below. Table 1 shows the results.

(Comparative example 1)
The TEMPO-oxidized pulp having a solid content concentration of 20% by weight obtained in Example 1 was dispersed in ion-exchanged water, and sodium hydroxide was added and stirred to obtain a TEMPO-oxidized pulp having a pH of 8.8 and a solid content concentration of 2% by weight. was obtained.
74 kg of this TEMPO oxidized pulp aqueous dispersion was treated with a single disc refiner (14 inch lab refiner (RF-14 type) manufactured by Aikawa Iron Works Co., Ltd., plate: blade width: 0.6 mm, groove width: 1.0 mm), and clearance Circulation was performed for 10 minutes under the conditions of 0.23 to 0.25 mm, followed by beating treatment to obtain TEMPO-oxidized MFC. The MFC was then evaluated by the method described below. Table 1 shows the results.

(Comparative example 2)
The TEMPO-oxidized pulp having a solid content concentration of 20% by weight obtained in Example 1 was dispersed in ion-exchanged water, and sodium hydroxide was added and stirred to obtain a TEMPO-oxidized pulp having a pH of 8.6 and a solid content concentration of 4% by weight. was obtained.
58 kg of this TEMPO oxidized pulp aqueous dispersion was treated with a single disc refiner (14-inch laboratory refiner (RF-14 type) manufactured by Aikawa Iron Works Co., Ltd., plate: blade width: 0.8 mm, groove width: 1.5 mm), and the clearance Circulation was performed for 10 minutes under the conditions of 0.23 to 0.25 mm, followed by beating treatment to obtain TEMPO-oxidized MFC. The MFC was then evaluated by the method described below. Table 1 shows the results.

As can be seen from Table 1, a chemical denaturation step to obtain chemically denatured pulp by chemically denaturing the raw material pulp, and the chemically denatured pulp obtained in the chemical denaturation step under conditions of a solid content concentration of 15% by weight or less as two discs. a beating treatment step of performing beating treatment using a double-disc refiner comprising DA and DB, and DM as a disk existing between them, wherein one of said DA and said DB or said DM is fixed and the other is rotated; Compared to the method using a single ^disc refiner, the method for producing chemically modified microfibril cellulose fibers containing Chemically modified microfibril cellulose fibers with a width of 500 nm or more could be produced.

Physical properties and characteristics were evaluated as follows.
<Average fiber length, average fiber width (measurement method A)>
A slurry of chemically modified microfibril cellulose fibers was diluted with water so that the solid content concentration was 0.25%, and about 250 g each ( Approximately 2000 images of the chemically modified microfibril cellulose fibers classified by the flow rate were obtained inside the apparatus with a CCD camera attached to the fractionator.
The fiber analysis parameters of the analysis software IMG (Metso) were set as shown in Tables 2 to 4, and about 2000 images were analyzed to obtain data such as average fiber length, average fiber width, and fiber length distribution. . The average value obtained by performing the measurement and analysis twice was used as the measurement data.

・平均繊維長（Length）：長さ加重平均繊維長
・平均繊維幅（Width）：長さ加重平均繊維幅
・繊維長分布（Fraction percentage of length weighted distribution）：長さ加重繊維長分布（各フラクションの設定は表２に記載した通り。）

・ Average fiber length (Length): Length weighted average fiber length ・ Average fiber width (Width): Length weighted average fiber width ・ Fiber length distribution (Fraction percentage of length weighted distribution): Length weighted fiber length distribution (each fraction are set as shown in Table 2.)

<Average fiber length, average fiber width (measurement method B)>
Measurement conditions were the same as in A except that the fiber analysis parameters of the analysis software IMG (Metso) were set as shown in Tables 5-7.

The ratio (%) of fibers having a fiber length of 0 to 0.2 mm in the fiber length distribution (length weighted) was evaluated by measurement method A. The ratio (%) of fibers with a fiber width of 0 to 5 μm in the fiber width distribution (weighted length) was evaluated by measurement method A.

<Viscosity>
Add ion-exchanged water to the dispersion after treatment to prepare a 1% by weight slurry, leave at 25° C. for 3 hours, stir with PRIMIX Homo Disper (3000 rpm) for 5 minutes, and immediately after stirring, use a B-type viscometer (manufactured by Toki Sangyo Co., Ltd.), No. Using an appropriate rotor from 1 to 4, the viscosity was measured after 1 minute at 60 rpm.

<BET specific surface area>
The BET specific surface area was measured by the following method with reference to the nitrogen gas adsorption method (JIS Z 8830):
(1) To the dispersion after treatment, deionized water is added as necessary to prepare an about 2% slurry (dispersion medium: water), which is separated so that the solid content is about 0.1 g and centrifuged. and added 100 mL of ethanol.
(2) A stirrer was added, and the mixture was stirred at 500 rpm for 30 minutes or more.
(3) The stirrer was taken out, and the fibrillated chemically modified cellulose fibers were sedimented in a centrifuge at 7000 G for 30 minutes at 30°C.
(4) The supernatant was removed while trying not to remove fibrillated chemically modified cellulose fibers as much as possible.
(5) Add 100 mL of ethanol, add a stirrer, stir under the condition of (2), centrifuge under the condition of (3), remove the supernatant under the condition of (4), and repeat this three times.
(6) The solvent in (5) was changed from ethanol to t-butanol, and at room temperature above the melting point of t-butanol, stirring, centrifugation and supernatant removal were repeated three times in the same manner as in (5).
(7) After the final removal of the solvent, 30 mL of t-butanol was added, mixed gently, transferred to an eggplant flask, and frozen using an ice bath.
(8) Cooled in a freezer for 30 minutes or more.
(9) Attached to a freeze dryer and freeze-dried for 3 days.
(10) BET measurement was performed using a BET measurement device (manufactured by Micromeritics) (pretreatment conditions: 105 ° C. for 2 hours under nitrogen stream, relative pressure 0.01 to 0.30, sample amount 30 mg).

<Productivity>
Productivity was determined according to the following formula.
Productivity (BDkg/h) = Amount processed (physical kg) x Concentration during processing (%) x 0.01 ÷ Processing time (h)

<Electricity intensity>
The electric power consumption rate was calculated according to the following formula.
Basic unit of electric power (kwh/BDT) = load during processing (kw) / productivity (BDkg/h) x 1000

2 Double disc refiner 4 Raw material inlet 6 Beating chamber 8 Rotating disc DM 10 Fixed disc DA 12 Fixed disc DB 14 Drive shaft 16 Motor 18 Circulation pipe 20 Outlet, 22... Outlet piping, 24... Manual valve

Claims (7)

A method for producing chemically modified microfibril cellulose fibers having a BET specific surface area of 50 m ² /g or more and an average fiber width of 500 nm or more,
a chemical denaturation step of chemically denaturing raw material pulp to obtain chemically denatured pulp;
The chemically denatured pulp obtained in the chemical denaturation step is provided with two discs, DA and DB, and a disc, DM, at a solid content concentration of 15% by weight or less, wherein the DA and the DB or the above A method for producing chemically modified microfibril cellulose fibers, comprising a beating treatment step of performing beating treatment using a double disc refiner in which one of the DMs is fixed and the other is rotated. 2. The method for producing chemically modified microfibril cellulose fibers according to claim 1, wherein the number of passes in the beating step is 30 or less. 3. The chemically modified microstructure according to claim 1 or 2, wherein said chemical modification is oxidation carried out using an N-oxyl compound, a compound selected from the group consisting of bromides, iodides and mixtures thereof, and an oxidizing agent. A method for producing fibril cellulose fibers. The method for producing chemically modified microfibril cellulose fibers according to claim 1 or 2, wherein the chemical modification is carboxymethyl modification. The double-disc refiner has a monoflow flow system for the raw material, and the edge width X1 of the first disk counted from the raw material inflow side of the DA and the DB is larger than the edge width X2 of the second disk. The method for producing chemically modified microfibril cellulose fibers according to any one of claims 1 to 4, characterized in that the fibers are large. The double-disc refiner has a monoflow flow system for the raw material, and the edge width X1 of the first disk counted from the raw material inflow side of the DA and the DB is larger than the edge width X2 of the second disk. The method for producing chemically modified microfibril cellulose fibers according to any one of claims 1 to 4, characterized in that they are small. The double-disc refiner has a mono-flow system for raw material flow, and the edge width X1 of the first disk counted from the raw material inflow side of the DA and the DB is the same as the edge width X2 of the second disk. The method for producing chemically modified microfibril cellulose fibers according to any one of claims 1 to 4, characterized in that:

Images