JP7252975B2 - Method for producing fine fibrous cellulose dispersion - Google Patents

Description

The present invention relates to a method for producing a diluted fine fibrous cellulose dispersion.

Fine fibrous cellulose obtained by finely disintegrating plant fibers includes microfibril cellulose (hereinafter sometimes referred to as "MFC") and cellulose nanofibers (hereinafter sometimes referred to as "CNF"). Fine fibrous cellulose is a fine fiber having a fiber diameter of about 1 nm to several tens of μm, and has a function of increasing strength and rigidity, so it is used for reinforcement.

Microfibrous cellulose is usually obtained in a water dispersion and has a very low solids content. Therefore, when an aqueous dispersion of fine fibrous cellulose is transported as it is, a large amount of water is transported, which poses a problem of high transport costs. For this reason, techniques for producing dried products have been developed, but once fine fibrous cellulose is dried, it is re-dispersed as fine fibrous cellulose unless dispersion treatment is performed by stirring at a high rotational speed for a long time. was difficult (Patent Document 1, etc.). There is also a problem of discoloration when heat is applied to obtain a dry product. Therefore, it is not treated as a dry product, but is transported with a high solid content.

However, since the fine fibrous cellulose dispersion with a high solid content concentration is highly viscous and in the form of a hard gel, when it is added to and mixed with the material to be reinforced as it is, the fine fibrous cellulose is not added to the material. A composition obtained by mixing without being uniformly dispersed did not have sufficient improvement in strength and the like. In addition, for the purpose of uniformly dispersing the fine fibrous cellulose dispersion with a high solid content concentration in the material to be reinforced, a conventional agitator type stirring device is used to lower the viscosity of the dispersion and make it a soft gel. However, if the gel is diluted with the gel, it cannot be uniformly diluted, and gel particles remain. Therefore, when the fine fibrous cellulose dispersion diluted by this method is added to and mixed with a material to be reinforced, it is difficult to uniformly disperse the fine fibrous cellulose in the material. . In addition, when diluting a fine fibrous cellulose dispersion with a high solid content concentration using a homogenizer capable of imparting a high shearing force, uniform dilution was possible without leaving gel particles, but shearing There is a problem that the fiber length of fine fibrous cellulose is shortened by force. Therefore, the fine fibrous cellulose dispersion diluted by this method loses the function of increasing strength and rigidity, and is inferior in reinforcing effect.

Therefore, there has been a demand for a method for producing a uniformly diluted fine fibrous cellulose dispersion by diluting a fine fibrous cellulose dispersion having a high solid content concentration so as not to cause shortening of the fiber length. .

JP 2015-134873 A

Therefore, the present invention provides a method for producing a uniformly diluted fine fibrous cellulose dispersion by diluting a fine fibrous cellulose dispersion having a high solid content concentration so as not to cause shortening of the fiber length. intended to provide

As a result of intensive studies to achieve these objects, the inventors of the present invention have found that it is extremely effective to use a specific mixing device for dispersion, and have completed the present invention.

The present invention provides the following.
(1) A step of pre-dispersing a fine fibrous cellulose dispersion having a solid content concentration of 1 wt% or more with a diluting solvent with a stirrer, and passing the mixture obtained in the pre-dispersing step through an in-line static fluid mixing device. A method for producing a diluted fine fibrous cellulose dispersion, comprising the step of main dispersing by allowing.
(2) The in-line static fluid mixing device has a tubular body, and is provided with at least two intersecting plates for causing turbulent agitation on the upstream side of the tubular body. A method for producing the described fine fibrous cellulose dispersion.
(3) The method for producing a fine fibrous cellulose dispersion according to (1) or (2), characterized in that a plurality of protrusions are provided on the tubular inner wall on the downstream side of the at least two plates.
(4) The method for producing a fine fibrous cellulose dispersion according to any one of (1) to (3), wherein the mixture is passed through the in-line static fluid mixing device at a flow rate of 2 m/sec or more.

According to the present invention, there is provided a method for producing a uniformly diluted fine fibrous cellulose dispersion by diluting a fine fibrous cellulose dispersion having a high solid content concentration so as not to cause shortening of the fiber length. be able to.

It is a schematic diagram showing a cross section of an OHR mixer that can be used in the manufacturing method of the present invention.

The present invention will now be described in detail 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 present invention is a method for producing a diluted fine fibrous cellulose dispersion, comprising a step of pre-dispersing a fine fibrous cellulose dispersion having a solid content concentration of 1 wt % or more with a diluent solvent using a stirrer; and a step of main dispersing by passing the mixture obtained in the above step through an in-line static fluid mixing device.

(Step of pre-dispersing)
In the pre-dispersion step of the present invention, a fine fibrous cellulose dispersion having a solid concentration of 1 wt % or more is pre-dispersed with a diluting solvent using a stirrer. By providing the pre-dispersing step, clogging of the sample in the pipes of the in-line static fluid mixer in the main dispersing step can be prevented.

(fine fibrous cellulose)
The fine fibrous cellulose used in the present invention is fine fibers made from cellulose. Although the average fiber diameter of the fine fibrous cellulose is not particularly limited, it is about 1 nm to 10 μm. The average fiber diameter and average fiber length of fine fibrous cellulose are obtained from the results of observing each fiber using a scanning electron microscope (SEM), an atomic force microscope (AFM) or a transmission electron microscope (TEM). It can be obtained by averaging the fiber diameter and fiber length. Fine fibrous cellulose can be produced by defibrating cellulose.

The average aspect ratio of the fine fibrous cellulose used in the present invention is usually 50 or more. Although the upper limit is not particularly limited, it is usually 1000 or less. Average aspect ratio can be calculated by the following formula:
Aspect ratio = average fiber length/average fiber diameter

The cellulose raw material is not particularly limited as long as it contains cellulose. Softwood bleached kraft pulp (NBKP), hardwood unbleached kraft pulp (LUKP), hardwood bleached kraft pulp (LBKP), bleached kraft pulp (BKP), softwood unbleached sulfite pulp (NUSP), softwood bleached sulfite pulp (NBSP) thermomechanical pulp (TMP), recycled pulp, waste paper, etc.), animals (for example, sea squirts), algae, microorganisms (for example, acetobacter), microbial products, etc. Cellulose raw materials include any of these. It may be one or a combination of two or more types, preferably a plant- or microorganism-derived cellulose raw material (e.g., cellulose fiber), more preferably a plant-derived cellulose raw material (e.g., cellulose fiber ).

Although the number average fiber diameter of the cellulose raw material is not particularly limited, it is about 30 to 60 μm for softwood kraft pulp and about 10 to 30 μm for hardwood kraft pulp, which are common pulps. In the case of other pulps, those that have undergone general refining are about 50 μm. For example, in the case of refining a chip or the like having a size of several cm, it is preferable to perform a mechanical treatment with a disaggregator such as a refiner or a beater to adjust the size to about 50 μm.

Cellulose has three hydroxyl groups per glucose unit and can undergo various chemical modifications. In the present invention, from the viewpoint of promoting the progress of defibration, it is preferable to use chemically modified fine fibrous cellulose produced by defibrating a cellulose raw material (chemically modified cellulose) obtained by chemical modification.

Examples of chemical modification include oxidation (carboxylation), carboxymethylation, cationization, and esterification. Among them, oxidation (carboxylation) and carboxymethylation are more preferable.

(Chemical denaturation)
(oxidation)
In the present invention, when using oxidized fine fibrous cellulose obtained by defibrating oxidized (carboxylated) cellulose, oxidized cellulose (also called carboxylated cellulose) is obtained by oxidizing the above cellulose raw material by a known method ( carboxylation). Although not particularly limited, during oxidation, the amount of carboxyl groups should be adjusted to 0.6 to 2.0 mmol/g with respect to the absolute dry weight of the chemically modified fine fibrous cellulose. is preferable, and it is more preferable to adjust the concentration to be 1.0 mmol/g to 2.0 mmol/g.

As an example of the oxidation (carboxylation) method, a cellulose raw material is oxidized in water using an oxidizing agent in the presence of an N-oxyl compound and a compound selected from the group consisting of bromides, iodides or mixtures thereof. A method can be mentioned. This oxidation reaction selectively oxidizes the primary hydroxyl group at the C6 position of the glucopyranose ring on the cellulose surface, resulting in a cellulose fiber having an aldehyde group and a carboxyl group (-COOH) or carboxylate group ( ^-COO- ) on the surface. can be obtained. Although the concentration of cellulose during the reaction is not particularly limited, it is preferably 5% by weight or less.

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).

The amount of the N-oxyl compound to be used is not particularly limited as long as it is a catalytic amount that can oxidize the raw material cellulose. For example, it is preferably 0.01 to 10 mmol, more preferably 0.01 to 1 mmol, even more preferably 0.05 to 0.5 mmol, relative to 1 g of absolute dry cellulose. Also, it is preferably about 0.1 to 4 mmol/L with respect to the reaction system.

Bromides are compounds containing bromine, examples of which include alkali metal bromides that can be dissociated and ionized in water. Also, iodides are compounds containing iodine, examples of which include alkali metal iodides. The amount of bromide or iodide to be used can be selected within a range capable of promoting the oxidation reaction. The total amount of bromide and iodide is, for example, preferably 0.1 to 100 mmol, more preferably 0.1 to 10 mmol, even more preferably 0.5 to 5 mmol, relative to 1 g of absolute dry cellulose.

Known oxidizing agents can be used, for example, halogens, hypohalous acids, halogenous acids, perhalogenates or salts thereof, halogen oxides, peroxides and the like can be used. Among them, sodium hypochlorite is preferable because it is inexpensive and has less environmental load. The amount of the oxidizing agent used is preferably 0.5 to 500 mmol, more preferably 0.5 to 50 mmol, even more preferably 1 to 25 mmol, and most preferably 3 to 10 mmol, relative to 1 g of absolute dry cellulose. Further, for example, 1 to 40 mol is preferable per 1 mol of the N-oxyl compound.

Oxidation of cellulose allows the reaction to proceed efficiently even under relatively mild conditions. Therefore, the reaction temperature is preferably 4 to 40°C, and may be room temperature of about 15 to 30°C. Since carboxyl groups are generated in the cellulose as the reaction progresses, the pH of the reaction solution decreases. In order to allow the oxidation reaction to proceed efficiently, it is preferable to add an alkaline solution such as an aqueous sodium hydroxide solution to maintain the pH of the reaction solution at about 8-12, preferably about 10-11. Water is preferable as the reaction medium because it is easy to handle and less likely to cause side reactions.

The reaction time in the oxidation reaction can be appropriately set according to the degree of progress of the oxidation, and is usually about 0.5 to 6 hours, for example about 0.5 to 4 hours.

Moreover, the oxidation reaction may be carried out in two stages. For example, by oxidizing the oxidized cellulose obtained by filtration after the completion of the reaction in the first step, again under the same or different reaction conditions, the reaction can be efficiently It can be oxidized well.

Another example of the oxidation (carboxylation) method is a method of contacting a cellulose raw material with an ozone-containing gas. This oxidation reaction oxidizes at least the hydroxyl groups at the 2- and 6-positions of the glucopyranose ring and causes degradation of the cellulose chain. The ozone concentration in the ozone-containing gas is preferably 50-250 g/m ³ , more preferably 50-220 g/m ³ . The amount of ozone added to the cellulose raw material is preferably 0.1 to 30 parts by weight, more preferably 5 to 30 parts by weight, when the solid content of the cellulose raw material is 100 parts by weight. The ozone treatment temperature is preferably 0 to 50°C, more preferably 20 to 50°C. The ozone treatment time is not particularly limited, but is about 1 to 360 minutes, preferably about 30 to 360 minutes. When the ozone treatment conditions are within these ranges, cellulose can be prevented from being excessively oxidized and decomposed, and the yield of oxidized cellulose is improved. After the ozone treatment, additional oxidation treatment may be performed using an oxidizing agent. The oxidizing agent used in the additional oxidation treatment is not particularly limited, but examples include chlorine-based compounds such as chlorine dioxide and sodium chlorite, oxygen, hydrogen peroxide, persulfuric acid, and peracetic acid. For example, the additional oxidation treatment can be performed by dissolving these oxidizing agents in a polar organic solvent such as water or alcohol to prepare an oxidizing agent solution, and immersing the cellulose raw material in the solution.

The amount of carboxyl groups in the oxidized cellulose can be adjusted by controlling the reaction conditions such as the amount of the oxidizing agent added and the reaction time.

(Carboxymethylation)
In the present invention, when carboxymethylated fine fibrous cellulose obtained by defibrating carboxymethylated cellulose is used, the carboxymethylated cellulose is obtained by carboxymethylating the above cellulose raw material by a known method. Alternatively, a commercially available product may be used. In any case, the degree of carboxymethyl group substitution per anhydroglucose unit of cellulose is preferably 0.01 to 0.50. As an example of the method for producing such carboxymethylated cellulose, the following method can be mentioned. Using cellulose as the starting material, 3 to 20 times the weight of water and/or lower alcohol as a solvent, specifically water, methanol, ethanol, N-propyl alcohol, isopropyl alcohol, N-butanol, isobutanol, tertiary A single medium such as butanol or a mixed medium of two or more types is used. When the lower alcohol is mixed, the mixing ratio of the lower alcohol is 60 to 95% by weight. As the mercerizing agent, an alkali metal hydroxide, specifically sodium hydroxide or potassium hydroxide, is used in an amount of 0.5 to 20 times the moles of the anhydroglucose residue of the starting material. The starting material, solvent, and mercerizing agent are mixed and mercerized at a reaction temperature of 0 to 70° C., preferably 10 to 60° C., for a reaction time of 15 minutes to 8 hours, preferably 30 minutes to 7 hours. Thereafter, a carboxymethylating agent is added in an amount of 0.05 to 10.0 times mol per glucose residue, the reaction temperature is 30 to 90° C., preferably 40 to 80° C., and the reaction time is 30 minutes to 10 hours, preferably 1 hour. The etherification reaction is carried out for ~4 hours.

In this specification, "carboxymethylated cellulose", which is a kind of chemically modified cellulose used for the preparation of fine fibrous cellulose, maintains at least a part of its fibrous shape even when dispersed in water. say something Therefore, it is distinguished from carboxymethyl cellulose, which is a kind of water-soluble polymer. When an aqueous dispersion of "carboxymethylated cellulose" is observed with an electron microscope, a fibrous substance can be observed. On the other hand, no fibrous substance is observed in an aqueous dispersion of carboxymethyl cellulose, which is a type of water-soluble polymer. In addition, when "carboxymethylated cellulose" is measured by X-ray diffraction, a peak of cellulose type I crystals can be observed, but cellulose type I crystals are not observed in carboxymethyl cellulose, which is a water-soluble polymer.

(cationization)
In the present invention, cationized fine fibrous cellulose obtained by defibrating cellulose obtained by further cationizing the carboxylated cellulose can be used. The cation-modified cellulose is obtained by adding a cationizing agent such as glycidyltrimethylammonium chloride, 3-chloro-2-hydroxypropyltrialkylammonium hydrate or its halohydrin type to the carboxylated cellulose raw material, and an alkali hydroxide as a catalyst. It can be obtained by reacting a metal (sodium hydroxide, potassium hydroxide, etc.) in the presence of water or an alcohol having 1 to 4 carbon atoms.

Preferably, the degree of cation substitution per glucose unit is between 0.02 and 0.50. By introducing cationic substituents into cellulose, the celluloses electrically repel each other. Therefore, cellulose into which cationic substituents have been introduced can be easily nano-fibrillated. If the degree of cation substitution per glucose unit is less than 0.02, sufficient nanofibrillation cannot be achieved. On the other hand, if the degree of cation substitution per glucose unit is greater than 0.50, the nanofibers may not be obtained due to swelling or dissolution. In order to defibrate efficiently, the cation-modified cellulose raw material obtained above is preferably washed. The degree of cation substitution can be adjusted by adjusting the amount of the cationizing agent to be reacted and the composition ratio of water or alcohol having 1 to 4 carbon atoms.

(Esterification)
In the present invention, esterified fine fibrous cellulose obtained by defibrating esterified cellulose can be used. The esterified cellulose can be obtained by a method of mixing the cellulose raw material with powder or an aqueous solution of the phosphate compound A, or a method of adding an aqueous solution of the phosphate compound A to a slurry of the cellulose raw material.

Phosphoric acid compound A includes phosphoric acid, polyphosphoric acid, phosphorous acid, hypophosphorous acid, phosphonic acid, polyphosphonic acid, and esters thereof. These may be in the form of salts. Among these, compounds having a phosphate group are preferred because they are low in cost, easy to handle, and can improve defibration efficiency by introducing a phosphate group into the cellulose of pulp fibers. Compounds having a phosphate group include phosphoric acid, sodium dihydrogen phosphate, disodium hydrogen phosphate, trisodium phosphate, sodium phosphite, potassium phosphite, sodium hypophosphite, potassium hypophosphite , sodium pyrophosphate, sodium metaphosphate, potassium dihydrogen phosphate, dipotassium hydrogen phosphate, tripotassium phosphate, potassium pyrophosphate, potassium metaphosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, triammonium phosphate , ammonium pyrophosphate, ammonium metaphosphate and the like. These can be used singly or in combination of two or more. Among these, phosphoric acid, sodium salt of phosphoric acid, potassium salt of phosphoric acid, phosphoric acid, from the viewpoint of high efficiency of introduction of phosphate group, easy fibrillation in the fibrillation process described below, and easy industrial application is more preferred. Sodium dihydrogen phosphate and disodium hydrogen phosphate are particularly preferred. Further, it is preferable to use the phosphoric acid-based compound A in the form of an aqueous solution, since the uniformity of the reaction is enhanced and the efficiency of introduction of the phosphoric acid group is enhanced. The pH of the aqueous solution of the phosphoric acid-based compound A is preferably 7 or less because the efficiency of introducing phosphate groups is high, but from the viewpoint of suppressing hydrolysis of pulp fibers, the pH is preferably 3 to 7.

The following method can be given as an example of the method for producing the phosphorylated cellulose. Phosphoric acid group is introduced into cellulose by adding phosphoric acid compound A to a dispersion liquid of cellulose raw material having a solid content concentration of 0.1 to 10% by weight while stirring. When the cellulose raw material is 100 parts by weight, the amount of phosphoric acid compound A added is preferably 0.2 to 500 parts by weight, more preferably 1 to 400 parts by weight, in terms of elemental amount of phosphorus. If the proportion of the phosphoric acid-based compound A is at least the lower limit, the yield of fine fibrous cellulose can be further improved. However, if the above upper limit is exceeded, the effect of improving the yield reaches a ceiling, which is not preferable from the viewpoint of cost.

At this time, in addition to the cellulose raw material and the phosphoric acid-based compound A, a powder or an aqueous solution of a compound B other than these may be mixed. The compound B is not particularly limited, but a basic nitrogen-containing compound is preferable. "Basic" herein is defined as the pink-red color of the aqueous solution in the presence of the phenolphthalein indicator or the pH of the aqueous solution being greater than 7. The basic nitrogen-containing compound used in the present invention is not particularly limited as long as the effect of the present invention is exhibited, but a compound having an amino group is preferable. Examples include, but are not limited to, urea, methylamine, ethylamine, trimethylamine, triethylamine, monoethanolamine, diethanolamine, triethanolamine, pyridine, ethylenediamine, and hexamethylenediamine. Among these, urea is preferable because it is inexpensive and easy to handle. The amount of compound B added is preferably 2 to 1000 parts by weight, more preferably 100 to 700 parts by weight, per 100 parts by weight of the solid content of the cellulose raw material. The reaction temperature is preferably 0 to 95°C, more preferably 30 to 90°C. Although the reaction time is not particularly limited, it is about 1 to 600 minutes, more preferably 30 to 480 minutes. When the esterification reaction conditions are within these ranges, cellulose can be prevented from being excessively esterified and easily dissolved, and the yield of phosphate esterified cellulose is improved. After dehydrating the obtained phosphate-esterified cellulose suspension, it is preferable to heat-treat at 100 to 170° C. from the viewpoint of suppressing hydrolysis of cellulose. Further, it is preferable to heat at 130° C. or less, preferably 110° C. or less while water is contained in the heat treatment, and heat at 100 to 170° C. after removing the water.

The degree of phosphate group substitution per glucose unit of the phosphated cellulose is preferably 0.001 to 0.40. By introducing a phosphate group substituent into cellulose, the celluloses electrically repel each other. Therefore, cellulose into which a phosphate group has been introduced can be easily nano-fibrillated. If the degree of phosphate group substitution per glucose unit is less than 0.001, sufficient nano-fibrillation cannot be achieved. On the other hand, if the degree of phosphate group substitution per glucose unit is greater than 0.40, the cellulose may swell or dissolve, and may not be obtained as fine fibrous cellulose. In order to efficiently defibrate, it is preferable that the phosphate-esterified cellulose raw material obtained above is washed by washing with cold water after boiling.

(defibration)
In the present invention, the device for defibrating the chemically modified cellulose is not particularly limited, but a device such as a high-speed rotation type, colloid mill type, high pressure type, roll mill type, ultrasonic type, etc. can be used to prepare the chemically modified cellulose aqueous dispersion. It is preferable to apply a strong shear force to In particular, for efficient fibrillation, it is preferable to use a wet high-pressure or ultrahigh-pressure homogenizer capable of applying a pressure of 50 MPa or more to the aqueous dispersion and applying a strong shearing force. The pressure is more preferably 100 MPa or higher, still more preferably 140 MPa or higher. The number of times of treatment (pass) in the fibrillation device may be one or two or more, preferably two or more.

In dispersion treatment, chemically modified cellulose is usually dispersed in a solvent. The solvent is not particularly limited as long as it can disperse the chemically modified cellulose, and examples thereof include water, organic solvents (eg, hydrophilic organic solvents such as methanol), and mixed solvents thereof. The solvent is preferably water because the cellulose raw material is hydrophilic.

The solid content concentration of the chemically modified cellulose in the dispersion is usually 0.1% by weight or more, preferably 0.2% by weight or more, and more preferably 0.3% by weight or more. As a result, the amount of liquid becomes appropriate with respect to the amount of cellulose fiber raw material, which is efficient. The upper limit is usually 10% by weight or less, preferably 6% by weight or less. Thereby, fluidity can be maintained.

Prior to defibration treatment or dispersion treatment, the chemically modified cellulose may be pretreated as necessary. Pretreatment may be performed using a mixing, stirring, emulsifying, or dispersing device such as a high-speed shear mixer.

When the chemically modified fine fibrous cellulose obtained through the fibrillation process is in a salt form, it may be used as it is, or converted into an acid form by an acid treatment using a mineral acid, a method using a cation exchange resin, or the like. You can use it. Alternatively, hydrophobicity may be imparted by a method using a cationic additive.

(Fine fibrous cellulose dispersion)
In the present invention, the fine fibrous cellulose dispersion having a high solid content concentration, which is subjected to the pre-dispersing step, is obtained by dehydrating and drying the dispersion of fine fibrous cellulose produced as described above to reduce the amount of solvent. may be obtained by A commercially available product may be used as the dispersion of fine fibrous cellulose having a high solid content.

In the present invention, the fine fibrous cellulose dispersion having a high solid content concentration to be subjected to the pre-dispersion step has a CNF solid content concentration of 1 wt% or more, preferably 2 wt% to 20 wt%, more preferably 3 to 15 wt%.

The dehydration/drying method for producing a fine fibrous cellulose dispersion having a high solid content is not particularly limited, and can be appropriately selected depending on the purpose. , freeze drying, spray drying, vacuum drying, and the like. The drying device is not particularly limited, and may be a continuous tunnel drying device, a band drying device, a vertical drying device, a vertical turbo drying device, a multi-stage disk drying device, a ventilation drying device, a rotary drying device, a flash drying device, or a spray drying device. equipment, cylindrical dryer, drum dryer, belt dryer, screw conveyor dryer, rotary dryer with heating tube, vibration transport dryer, batch type box dryer, vacuum box dryer, stirring dryer, etc. can be used alone or in combination of two or more.

(Dilution solvent)
In the present invention, the diluent solvent includes water, a water-soluble organic solvent, or a mixed solvent thereof. Since the cellulose raw material is hydrophilic, water is used from the viewpoint that a good dispersion state is easily obtained during dispersion. is preferred. As the diluting solvent, the same solvent as the solvent for the fine fibrous cellulose dispersion before dilution may be used, or a different solvent may be used.

A water-soluble organic solvent is an organic solvent that dissolves in water. Examples include methanol, ethanol, 2-propanol, butanol, glycerin, acetone, methyl ethyl ketone, 1,4-dioxane, N-methyl-2-pyrrolidone, tetrahydrofuran, N,N-dimethylformamide, N,N-dimethylacetamide, Dimethylsulfoxide, acetonitrile, and combinations thereof. Among them, lower alcohols having 1 to 4 carbon atoms such as methanol, ethanol, and 2-propanol are preferred, and from the viewpoint of safety and availability, methanol and ethanol are more preferred, and ethanol is even more preferred.

When a mixed solvent is used, the amount of the water-soluble organic solvent in the mixed solvent is preferably 10% by weight or more, more preferably 50% by weight or more, and even more preferably 70% by weight or more. Although the upper limit of the amount is not limited, it is preferably 95% by weight or less, more preferably 90% by weight or less. Moreover, the water-based solvent may contain a water-insoluble organic solvent to the extent that the effect of the invention is not impaired.

The amount of the diluting solvent added to the fine fibrous cellulose dispersion before dilution is preferably such that the solid content concentration of the diluted fine fibrous cellulose dispersion is 0.01 to 5 wt %. More preferably, the amount is 1 to 3 wt %.

(mixer)
As the stirrer used in the pre-dispersion step of the present invention, a stirrer capable of crushing hard gel lumps to a size that does not cause clogging of pipes without shortening the fiber length of fine fibrous cellulose with a high shearing force is appropriately selected. can be used. For example, an agitator or the like can be used. The conditions for preliminary dispersion using a stirrer are not particularly limited, but are, for example, 100 to 1500 rpm for about 15 seconds to 30 minutes.

(Main dispersing step)
In the main dispersing step of the present invention, the mixture of the fine fibrous cellulose dispersion obtained in the pre-dispersing step and the diluent solvent is passed through an in-line stationary fluid mixer.

(Inline static fluid mixer)
The in-line static fluid mixer used in the present invention is not particularly limited as long as it can dilute the above mixture uniformly without leaving gel particles. Examples include static mixers, OHR mixers, and MSE static mixers. A mixer and the like can be mentioned, and it is preferable to use an OHR mixer from the viewpoint of dispersibility.

A static mixer is a fluid mixing device in which right-handed and left-handed spiral elements are arranged alternately in a tube with one end perpendicular to the other. It is a device.

An OHR mixer is a fluid mixing device that promotes mixing and agitation by providing a plurality of projections on the inner peripheral wall surface of the tube to increase cavitation in the fluid.

MSE static mixer is a fluid mixing device in which a stack of mixing elements having a large number of small through holes and a large through hole in the center is arranged in a pipe, or such a mixing element is installed in the pipe and used A fluid mixing device.

In the main dispersing step, the flow rate for passing the mixture through the inline static fluid mixing device is preferably 2.0 to 10.0 m / sec, more preferably 3.0 to 10.0 m / sec, from the viewpoint of dispersibility. is more preferred.

A pump with sufficient liquid delivery capacity is preferably used to introduce the mixture into the in-line static fluid mixing device at the desired flow rate. Examples of the pump include, but are not limited to, vortex pumps, mono pumps, and the like.

The number of times the mixture is passed through the in-line static fluid mixing device is not particularly limited, and may be one time or two or more times.

An example of using an OHR mixer as an in-line static fluid mixer will be described with reference to FIG. FIG. 1 is a schematic diagram showing a cross section of an OHR mixer. Note that the in-line static fluid mixer that can be used in the present invention is not limited to that shown in FIG.

The OHR mixer 2 shown in FIG. are fixed to the inner wall of the tubular body 4 . In addition, a plurality of protrusions 8 are provided on the inner peripheral wall of the tubular body 4 on the downstream side of the plate 6 . In FIG. 1, the direction of passage of the mixture is indicated by an arrow.

When the mixture is introduced into the OHR mixer 2 at a flow rate above a certain level, the two plates 6 act to turn the mixture into a spiral flow with a strong twist. At this time, the mixture is abruptly divided by the two plates 6 and changes the flow, thereby generating a mechanical shearing force. Then, turbulent agitation occurs and is agitated. The mixture is sent further downstream through the tubular body and collides with the protrusions 8 while being stirred, thereby being more vigorously mixed and dispersed, thereby obtaining a diluted fine fibrous cellulose dispersion. .

The number and shape of the plates 6 provided on the upstream side of the tubular body 4 are not limited as long as they can cause turbulent stirring, but the number is preferably 2 to 8 from the viewpoint of increasing the number of times of shearing. , is more preferable. Moreover, the shape is preferably semi-elliptical from the viewpoint of stirring efficiency.

The shape of the protrusions 8 on the inner peripheral wall of the tubular body 4 is not particularly limited, but is preferably mushroom-shaped from the viewpoint of enhancing the mixing efficiency.

According to the production method of the present invention, a fine fibrous cellulose dispersion having a high solid content concentration is diluted so as not to cause shortening of the fiber length, and a uniformly diluted fine fibrous cellulose dispersion is produced. can do.

EXAMPLES The present invention will be described in more detail below with reference to Examples, but the present invention is not limited to these. In addition, when the method of measurement/calculation of each numerical value in each example is not specifically described, it is measured/calculated by the method described in the specification.

(Method for measuring average fiber length)
The fiber length was measured from an atomic force microscope image (3000 nm×3000 nm) of the cellulose nanofiber fixed on the mica section, and the number average fiber length was calculated. The fiber length was measured in the range of 100 nm to 2000 nm using image analysis software WinROOF (Mitani Corporation).

(Method for measuring degree of dispersion)
Regarding the oxidized CNF water dispersions having a solid content concentration of 0.5 wt% obtained in Examples and Comparative Examples, the CNF dispersion index was calculated as follows, and the degree of dispersion was evaluated according to the following criteria.
To 1 g of the oxidized CNF aqueous dispersion obtained in Examples and Comparative Examples, 2 drops of Bokushizuku (manufactured by Kuretake Co., Ltd., solid content 10%) were dropped, and a vortex mixer (manufactured by IUCHI, equipment name: Automatic Lab-mixer HM -10H) was stirred for 10 seconds by setting the rotation speed scale to the maximum. Next, the mixture containing Bokushizuku was sandwiched between two glass plates so that the film thickness was 0.15 mm, and an optical microscope (Digital Microscope KH-8700 (manufactured by Hilox Co., Ltd.)) was used to magnify the mixture. Observed at 100x magnification.

In the above observation, the major axis of the aggregates present in the range of 3 mm × 2.3 mm was measured, and the observed aggregates were classified as extra large: 150 µm or more, large: 100 µm or more and less than 150 µm, medium: 50 µm or more and less than 100 µm, small: It was classified into 20 μm or more and less than 50 μm, the number of classified aggregates was counted, and the CNF dispersion index was calculated by the following formula.

CNF dispersion index = (number of extra-large x 512 + number of large x 64 + number of medium x 8 + number of small x 1)/2 x CNF concentration factor Table 1 shows the CNF concentration factor.

(Evaluation Criteria for Degree of Dispersion)
◎: CNF dispersion index is less than 1600 ○: CNF dispersion index is 1600 or more and less than 3200 △: CNF dispersion index is 3200 or more and less than 6400 ×: CNF dispersion index is 6400 or more

(Production example 1)
5.00 g (bone dry) of bleached unbeaten kraft pulp (85% whiteness) derived from softwood was mixed with 39 mg (0.05 mmol per g of cellulose of absolute dry) of TEMPO (Sigma Aldrich) and 514 mg of sodium bromide (bone dry). 1.0 mmol for 1 g of cellulose) was added to 500 mL of an aqueous solution and stirred until the pulp was uniformly dispersed. An aqueous sodium hypochlorite solution was added to the reaction system so that sodium hypochlorite was 6.0 mmol/g to initiate an oxidation reaction. 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. The mixture after the reaction was filtered through a glass filter to separate pulp, and the pulp was thoroughly washed with water to obtain oxidized pulp (carboxylated cellulose). At this time, the pulp yield was 90%, the time required for the oxidation reaction was 90 minutes, and the amount of carboxyl groups was 1.6 mmol/g. This was adjusted to a CNF solid content concentration of 3.0 wt% with water, and treated with an ultrahigh pressure homogenizer (20°C, 150 MPa) three times to obtain an oxidized cellulose nanofiber aqueous dispersion. The obtained oxidized cellulose nanofibers had an average fiber diameter of 3 nm and an average fiber length of 650 nm.

(Method for measuring carboxyl group content)
60 mL of a 0.5% by weight slurry (aqueous dispersion) of carboxylated cellulose was prepared, and 0.1 M aqueous hydrochloric acid solution was added to adjust the pH to 2.5. It was calculated from the amount of sodium hydroxide (a) consumed in the neutralization step of the weak acid, where the change in conductivity is gradual, using the following formula:
Carboxyl group amount [mmol/g carboxylated cellulose] = a [mL] x 0.05/carboxylated cellulose weight [g]

(Example 1)
The oxidized CNF aqueous dispersion having a solid content concentration of 3 wt% obtained in Production Example 1 above is put into an agitator together with water, pre-dispersed (500 rpm, 30 minutes), and a slurry having a solid content concentration of 0.5 wt%. was made. This slurry is sent using a pump at a flow rate of 3.0 m / sec, and the OHR mixer (MX-F8, manufactured by OHR Fluid Engineering Laboratory Co., Ltd., outlet cut off), which is an in-line static fluid mixing device connected to the pump. Area: 50.2 mm ² ) was passed through once for main dispersion to obtain an oxidized CNF aqueous dispersion with a solid content concentration of 0.5 wt%. The resulting oxidized CNF aqueous dispersion was evaluated for degree of dispersion and measured for average fiber length. Table 2 shows the results.

(Example 2)
An oxidized CNF water dispersion with a solid content concentration of 0.5 wt% was obtained in the same manner as in Example 1 except that the main dispersion was performed by passing through the OHR mixer twice. In addition, for this oxidized CNF aqueous dispersion, the evaluation of the degree of dispersion and the measurement of the average fiber length were performed. Table 2 shows the results.

(Example 3)
An oxidized CNF water dispersion with a solid content concentration of 0.5 wt% was obtained in the same manner as in Example 1 except that the main dispersion was performed by passing through the OHR mixer three times. In addition, for this oxidized CNF aqueous dispersion, the evaluation of the degree of dispersion and the measurement of the average fiber length were performed. Table 2 shows the results.

(Example 4)
An oxidized CNF aqueous dispersion with a solid content concentration of 0.5 wt% was obtained in the same manner as in Example 1, except that the slurry feeding speed was changed to a flow speed of 5.5 m / sec. The resulting oxidized CNF aqueous dispersion was evaluated for degree of dispersion and measured for average fiber length. Table 2 shows the results.

(Example 5)
Instead of the OHR mixer, a static mixer (two 3/8-N30-232-F type manufactured by Noritake Co., Ltd. are connected) was used, and the static mixer was passed twice to perform the main dispersion. An oxidized CNF aqueous dispersion with a solid content concentration of 0.5 wt% was obtained in the same manner as in Example 1 except that. The resulting oxidized CNF aqueous dispersion was evaluated for degree of dispersion and measured for average fiber length. Table 2 shows the results.

(Example 6)
The oxidized CNF aqueous dispersion having a solid content concentration of 3 wt% obtained in Production Example 1 was concentrated with a blower dryer to obtain an oxidized CNF aqueous dispersion having a solid content concentration of 20 wt%. This was put into an agitator together with water and pre-dispersed (500 rpm, 30 minutes) to prepare a slurry with a solid content concentration of 0.5 wt %. This slurry is fed at a flow rate of 10.0 m / sec using a pump, and an OHR mixer (MX-F8, manufactured by OHR Fluid Engineering Laboratory Co., Ltd., outlet cut off), which is an in-line static fluid mixing device connected to the pump. Area: 50.2 mm ² ) was passed through five times for main dispersion to obtain an oxidized CNF aqueous dispersion with a solid content concentration of 0.5 wt%. The resulting oxidized CNF aqueous dispersion was evaluated for degree of dispersion and measured for average fiber length. Table 2 shows the results. In addition, the average fiber length of the pre-dilution oxidized CNF dispersion physical properties described in Table 2 is a value measured using an oxidized CNF aqueous dispersion having a solid content concentration of 3 wt% before concentration.

(Comparative example 1)
An oxidized CNF aqueous dispersion with a solid content concentration of 0.5 wt% was obtained in the same manner as in Example 1, except that the flow rate of the slurry was changed to 1.0 m / sec. The resulting oxidized CNF aqueous dispersion was evaluated for degree of dispersion and measured for average fiber length. Table 2 shows the results.

(Comparative example 2)
The oxidized CNF aqueous dispersion with a solid content concentration of 3 wt% obtained in Production Example 1 above is mixed with water in an amount to make the solid content concentration 0.5 wt%, without pre-dispersing, using a pump at a flow rate of The main dispersion was carried out by feeding the liquid at 3.0 m/sec and passing it once through the same OHR mixer as in Example 1 connected to a pump. An oxidized CNF water dispersion could not be obtained.

(Comparative Example 3)
Preliminary dispersion was performed in the same manner as in Example 1 to prepare a slurry having a solid content concentration of 0.5 wt %. Evaluation of degree of dispersion and measurement of average fiber length were performed on this slurry without carrying out main dispersion. Table 2 shows the results.

(Comparative Example 4)
The oxidized CNF aqueous dispersion having a solid content concentration of 3 wt% obtained in Production Example 1 and water were charged into a homogenizer and stirred at 8000 rpm for 30 minutes to obtain a solid content concentration of 0.5 wt%. An oxidized CNF water dispersion was obtained. The resulting oxidized CNF aqueous dispersion was evaluated for degree of dispersion and measured for average fiber length. Table 2 shows the results.

As can be seen from Table 2, a step of pre-dispersing a fine fibrous cellulose dispersion having a solid content concentration of 1 wt% or more together with a diluent solvent with a stirrer, and the mixture obtained in the pre-dispersing step was subjected to in-line static fluid mixing. According to the method for producing a diluted fine fibrous cellulose dispersion comprising the step of main dispersion by passing through an apparatus, the obtained dispersion has a high degree of dispersion of fine fibrous cellulose and a long fiber length. Shortening was suppressed.

Claims (4)

A step of pre-dispersing a fine fibrous cellulose dispersion having a solid content concentration of 1 wt% or more with a diluent solvent using a stirrer;
A method for producing a diluted fine fibrous cellulose dispersion, comprising the step of main dispersing the mixture obtained in the pre-dispersing step by passing it through an in-line static fluid mixing device. 2. The microfluidic mixer according to claim 1, wherein said in-line static fluid mixing device has a tubular body, and at least two intersecting plates for generating turbulent agitation are provided upstream in said tubular body. A method for producing a fibrous cellulose dispersion. 3. The method for producing a fine fibrous cellulose dispersion according to claim 1 or 2, wherein a plurality of protrusions are provided on the tubular inner peripheral wall on the downstream side of the at least two plates. The method for producing a fine fibrous cellulose dispersion according to any one of claims 1 to 3, wherein the mixture is passed through the in-line static fluid mixing device at a flow rate of 2 m/sec or more.

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