JPWO2020095577A1 - Method for Producing Fine Fibrous Cellulose Dispersion - Google Patents

Abstract

By pre-dispersing a fine fibrous cellulose dispersion having a solid content concentration of 1 wt% or more together with a diluting solvent with a stirrer, and passing the mixture obtained in the pre-dispersion step through an in-line static fluid mixing device. Including the step of main dispersion.

Description

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

Fine fibrous cellulose obtained by finely breaking plant fibers includes microfibrillose 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, and is therefore used for reinforcing applications.

Fine fibrous cellulose is usually obtained in a state of being dispersed in water and has a very low solid content concentration. Therefore, when the aqueous dispersion of fine fibrous cellulose is transported as it is, there is a problem that a large amount of water is transported and the transportation cost is high. Therefore, a technique for producing a dried product has been developed. However, once the fine fibrous cellulose is dried, it is redispersed as fine fibrous cellulose unless it is dispersed by stirring at a high rotation speed and for a long time. It was difficult (Patent Document 1 etc.). In addition, there is a problem that discoloration occurs when heat is applied to make a dried product. Therefore, instead of making it a dried product, it is transported with a high solid content concentration.

However, since the fine fibrous cellulose dispersion having a high solid content concentration has a high viscosity and is in the form of a hard gel, when it is added or mixed with the material to be reinforced as it is, the fine fibrous cellulose is added to the material. The composition obtained by mixing without being uniformly dispersed did not sufficiently improve the strength and the like. Further, for the purpose of uniformly dispersing the fine fibrous cellulose dispersion having a high solid content concentration in the material to be reinforced, a conventional agitator type agitator is used to reduce the viscosity of the dispersion to form a soft gel. When diluted by using, it cannot be diluted uniformly and gel particles remain. Therefore, when the fine fibrous cellulose dispersion diluted by this method is added and mixed with the material to be reinforced, it is difficult to uniformly disperse the fine fibrous cellulose with respect to the material. .. Further, when the fine fibrous cellulose dispersion having a high solid content concentration was diluted with a homogenizer capable of imparting a high shearing force, uniform dilution was possible without leaving any gel particles, but shearing was possible. There is a problem that the fiber length of the fine fibrous cellulose is shortened by the force. Therefore, the fine fibrous cellulose dispersion diluted by this method is inferior in the reinforcing effect because the function of increasing the strength and the rigidity is impaired.

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

Japanese Unexamined Patent Publication No. 2015-134873

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 a shortening of the fiber length. The purpose is to provide.

As a result of diligent studies to achieve such an object, the present inventors have found that it is extremely effective to disperse using a specific mixing device, and have completed the present invention.

The present invention provides:
(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 a mixture obtained in the step of pre-dispersing the mixture pass through an in-line stationary fluid mixer. A method for producing a diluted fine fibrous cellulose dispersion, which comprises a step of subjecting the mixture to the present dispersion.
(2) The in-line stationary fluid mixing device has a tubular body, and is characterized in that at least two intersecting plates for causing turbulent agitation are provided on the upstream side of the tubular body (1). The method for producing a fine fibrous cellulose dispersion according to the above method.
(3) The method for producing a fine fibrous cellulose dispersion according to (1) or (2), wherein a plurality of protrusions are provided on the peripheral wall of the tube on the downstream side of 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 stationary 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 a shortening of the fiber length. be able to.

It is the schematic which shows the cross section of the OHR mixer which can be used in the manufacturing method of this invention.

Hereinafter, the present invention will be described in detail with reference to the drawings. In the present invention, "~" includes a fractional price. That is, "X to Y" includes the values X and Y at both ends thereof.

The present invention is a method for producing a diluted fine fibrous cellulose dispersion, wherein the fine fibrous cellulose dispersion having a solid content concentration of 1 wt% or more is pre-dispersed together with a diluting solvent with a stirrer, and the pre-dispersion. This includes a step of subjecting the mixture obtained in the above step to the present dispersion by passing it through an in-line stationary fluid mixing device.

(Pre-dispersion process)
In the step of pre-dispersing the present invention, a fine fibrous cellulose dispersion having a solid content concentration of 1 wt% or more is pre-dispersed together with a diluting solvent with a stirrer. By providing the pre-dispersion step, it is possible to prevent the sample from being clogged in the piping of the in-line static fluid mixing device in the main dispersion step.

(Fine fibrous cellulose)
The fine fibrous cellulose used in the present invention is a fine fiber made from cellulose as a raw material. The average fiber diameter of the fine fibrous cellulose is not particularly limited, but is about 1 nm to 10 μm. The average fiber diameter and average fiber length of the 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. The upper limit is not particularly limited, but is usually 1000 or less. The average aspect ratio can be calculated by the following formula:
Aspect ratio = average fiber length / average fiber diameter

The cellulose raw material may contain cellulose and is not particularly limited, but for example, plants (for example, wood, bamboo, hemp, jute, kenaf, agricultural waste, cloth, pulp (conifer unbleached kraft pulp (NUKP)), Coniferous bleached kraft pulp (NBKP), broadleaf unbleached kraft pulp (LUKP), broadleaf bleached kraft pulp (LBKP), bleached kraft pulp (BKP), coniferous unbleached sulphite pulp (NUSP), coniferous bleached sulphite pulp (NBSP) Thermomechanical pulp (TMP), recycled pulp, used paper, etc.), animals (for example, squirrels), algae, microorganisms (for example, acetic acid bacteria (acetobacter)), microbial products, etc. can be mentioned. It may be a combination of two or more kinds, but it is preferably a pulp raw material derived from a plant or a microorganism (for example, cellulose fiber), and more preferably a cellulose raw material derived from a plant (for example, cellulose fiber). ).

The number average fiber diameter of the cellulose raw material is not particularly limited, but is about 30 to 60 μm in the case of softwood kraft pulp, which is a general pulp, and about 10 to 30 μm in the case of hardwood kraft pulp. In the case of other pulp, the one that has undergone general purification is about 50 μm. For example, when a chip or the like having a size of several cm is purified, it is preferable to perform mechanical treatment with a dissociator 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 denaturations. 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 chemically modifying.

Examples of the chemical denaturation include oxidation (carboxylation), carboxymethylation, cationization, esterification and the like. Of these, oxidation (carboxylation) and carboxymethylation are more preferable.

(Chemical denaturation)
(Oxidation)
In the present invention, when the oxidized fine fibrous cellulose obtained by defibrating the oxidized (carboxylated) cellulose is used, the oxidized cellulose (also referred to as carboxylated cellulose) oxidizes the above-mentioned cellulose raw material by a known method. It can be obtained by carboxylation). Although not particularly limited, at the time of 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 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 bromide, iodide or a mixture thereof. The method can be mentioned. This oxidation reaction, C6-position primary hydroxyl groups of the glucopyranose ring of the cellulose surface is selectively oxidized, and an aldehyde group on the surface, a carboxyl group (-COOH) or carboxylate groups (-COO ^-) and cellulosic fibers having a Can be obtained. The concentration of cellulose during the reaction is not particularly limited, but is preferably 5% by weight or less.

The N-oxyl compound is a compound capable of generating a nitroxy radical. As the N-oxyl compound, any compound can be used as long as it is a compound that promotes the desired oxidation reaction. For example, 2,2,6,6-tetramethylpiperidine-1-oxy radical (TEMPO) and its derivative (for example, 4-hydroxy TEMPO) can be mentioned.

The amount of the N-oxyl compound used is not particularly limited as long as it is a catalytic amount capable of oxidizing cellulose as a raw material. For example, 0.01 to 10 mmol is preferable, 0.01 to 1 mmol is more preferable, and 0.05 to 0.5 mmol is further preferable with respect to 1 g of cellulose that has been completely dried. Further, it is preferably about 0.1 to 4 mmol / L with respect to the reaction system.

The bromide is a compound containing bromine, and examples thereof include alkali metals bromide that can be dissociated and ionized in water. Further, the iodide is a compound containing iodine, and an example thereof includes an alkali metal iodide. The amount of bromide or iodide used can be selected within the range in which the oxidation reaction can be promoted. The total amount of bromide and iodide is, for example, preferably 0.1 to 100 mmol, more preferably 0.1 to 10 mmol, still more preferably 0.5 to 5 mmol, relative to 1 g of dry cellulose.

As the oxidizing agent, known ones can be used, and for example, halogen, hypohalogenic acid, subhalogenic acid, perhalogenic acid or salts thereof, halogen oxide, peroxide and the like can be used. Of these, sodium hypochlorite, which is inexpensive and has a low environmental load, is preferable. The amount of the oxidizing agent used is, for example, preferably 0.5 to 500 mmol, more preferably 0.5 to 50 mmol, still more preferably 1 to 25 mmol, and most preferably 3 to 10 mmol with respect to 1 g of dry cellulose. Further, for example, 1 to 40 mol is preferable with respect to 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. As the reaction progresses, carboxyl groups are generated in the cellulose, so that the pH of the reaction solution is lowered. 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 8 to 12, preferably about 10 to 11. Water is preferable as the reaction medium because it is easy to handle and side reactions are unlikely to occur.

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

Further, the oxidation reaction may be carried out in two steps. For example, by oxidizing the oxidized cellulose obtained by filtration after the completion of the first-stage reaction again under the same or different reaction conditions, the efficiency is not affected by the reaction inhibition by the salt produced as a by-product in the first-stage reaction. Can be oxidized well.

As another example of the oxidation (carboxylation) method, there is a method of oxidizing by contacting a gas containing ozone with a cellulose raw material. By this oxidation reaction, the hydroxyl groups at at least the 2nd and 6th positions of the glucopyranose ring are oxidized, and the cellulose chain is decomposed. Ozone concentration in the ozone containing gas is preferably 50 to 250 g / ^{m 3,} more preferably 50~220g / ^{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, it is possible to prevent the cellulose from being excessively oxidized and decomposed, and the yield of the oxidized cellulose becomes good. After the ozone treatment, the additional oxidation treatment may be performed using an oxidizing agent. The oxidizing agent used for the additional oxidation treatment is not particularly limited, and examples thereof include chlorine compounds such as chlorine dioxide and sodium chlorite, oxygen, hydrogen peroxide, persulfate, 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 the carboxyl group of cellulose oxide can be adjusted by controlling the reaction conditions such as the amount of the oxidizing agent added and the reaction time described above.

(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-mentioned cellulose raw material by a known method. Alternatively, a commercially available product may be used. In either case, the degree of carboxymethyl group substitution per anhydrous glucose unit of cellulose is preferably 0.01 to 0.50. The following method can be mentioned as an example of a method for producing such carboxymethylated cellulose. Using cellulose as a base material, 3 to 20 times by weight of water and / or lower alcohol as a solvent, specifically water, methanol, ethanol, N-propyl alcohol, isopropyl alcohol, N-butanol, isobutanol, tertiary Use a single medium such as butanol or a mixed medium of two or more kinds. When the lower alcohol is mixed, the mixing ratio of the lower alcohol is 60 to 95% by weight. As the mercerizing agent, 0.5 to 20 times mol of alkali metal hydroxide per anhydrous glucose residue of the bottoming material, specifically sodium hydroxide and potassium hydroxide is used. The bottoming material, the solvent, and the mercerizing agent are mixed, and the mercerization treatment is carried out at a reaction temperature of 0 to 70 ° C., preferably 10 to 60 ° C., and a reaction time of 15 minutes to 8 hours, preferably 30 minutes to 7 hours. Then, 0.05 to 10.0 times mol of the carboxymethylating agent is added 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 the present specification, "carboxymethylated cellulose", which is a kind of chemically modified cellulose used for preparing fine fibrous cellulose, maintains at least a part of the 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 the aqueous dispersion of "carboxymethylated cellulose" is observed with an electron microscope, a fibrous substance can be observed. On the other hand, when observing the aqueous dispersion of carboxymethyl cellulose, which is a kind of water-soluble polymer, no fibrous substance is observed. In addition, the peak of cellulose type I crystal can be observed when "carboxymethylated cellulose" is measured by X-ray diffraction, but cellulose type I crystal is not observed in the water-soluble polymer carboxymethyl cellulose.

(Cationation)
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 prepared by adding a cationizing agent such as glycidyltrimethylammonium chloride, 3-chloro-2-hydroxypropyltrialkylammonium hydrite or a halohydrin type thereof 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.

The degree of cation substitution per glucose unit is preferably 0.02 to 0.50. By introducing a cationic substituent into cellulose, the celluloses are electrically repelled from each other. Therefore, cellulose into which a cation substituent has been introduced can be easily nano-defibrated. If the degree of cation substitution per glucose unit is less than 0.02, nano-defibration cannot be sufficiently performed. On the other hand, if the degree of cation substitution per glucose unit is larger than 0.50, it may not be obtained as nanofibers because it swells or dissolves. In order to efficiently perform defibration, it is preferable that the cation-modified cellulose raw material obtained above is washed. The degree of cation substitution can be adjusted by 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 a powder or an aqueous solution of a phosphoric acid compound A with the above-mentioned cellulose raw material, or a method of adding an aqueous solution of a phosphoric acid compound A to a slurry of a cellulose raw material.

Examples of the phosphoric acid-based compound A include phosphoric acid, polyphosphoric acid, phosphite, hypophosphoric acid, phosphonic acid, polyphosphonic acid, and esters thereof. These may be in the form of salts. Among these, a compound having a phosphoric acid group is preferable because it is low in cost, easy to handle, and the phosphoric acid group can be introduced into the cellulose of the pulp fiber to improve the defibration efficiency. Compounds having a phosphoric acid group include phosphoric acid, sodium dihydrogen phosphate, disodium hydrogen phosphate, trisodium phosphate, sodium phosphite, potassium phosphite, sodium hypophosphite, and 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 alone or in combination of two or more. Of these, from the viewpoints of high efficiency of introducing phosphoric acid groups, easy defibration in the following defibration steps, and easy industrial application, phosphoric acid, sodium phosphate of phosphoric acid, potassium salt of phosphoric acid, and phosphoric acid Ammonium salt is more preferred. In particular, sodium dihydrogen phosphate and disodium hydrogen phosphate are preferable. Further, the phosphoric acid-based compound A is preferably used as an aqueous solution because the uniformity of the reaction is enhanced and the efficiency of introducing the phosphoric acid group is increased. The pH of the aqueous solution of the phosphoric acid-based compound A is preferably 7 or less because the efficiency of introducing the phosphoric acid group is high, but is preferably 3 to 7 from the viewpoint of suppressing the hydrolysis of pulp fibers.

The following method can be mentioned as an example of the method for producing phosphoric acid esterified cellulose. A phosphoric acid-based compound A is added to a dispersion of a cellulose raw material having a solid content concentration of 0.1 to 10% by weight with stirring to introduce a phosphoric acid group into the cellulose. When the cellulose raw material is 100 parts by weight, the amount of the phosphoric acid compound A added is preferably 0.2 to 500 parts by weight, more preferably 1 to 400 parts by weight, as the amount of phosphorus element. When the ratio of the phosphoric acid-based compound A is at least the above lower limit value, the yield of the fine fibrous cellulose can be further improved. However, if the upper limit is exceeded, the effect of improving the yield will reach a plateau, 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, powders or aqueous solutions of other compounds B may be mixed. Compound B is not particularly limited, but a nitrogen-containing compound exhibiting basicity is preferable. "Basic" here is defined as the aqueous solution exhibiting a pink to red color in the presence of a 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 effects of the present invention are exhibited, but a compound having an amino group is preferable. For example, urea, methylamine, ethylamine, trimethylamine, triethylamine, monoethanolamine, diethanolamine, triethanolamine, pyridine, ethylenediamine, hexamethylenediamine and the like can be mentioned, but are not particularly limited. Of these, urea, which is low in cost and easy to handle, is preferable. The amount of compound B added is preferably 2 to 1000 parts by weight, more preferably 100 to 700 parts by weight, based on 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. The reaction time is not particularly limited, but is about 1 to 600 minutes, more preferably 30 to 480 minutes. When the conditions of the esterification reaction are within these ranges, it is possible to prevent the cellulose from being excessively esterified and easily dissolved, and the yield of the phosphate esterified cellulose becomes good. After dehydrating the obtained phosphoric acid esterified cellulose suspension, it is preferable to heat-treat it at 100 to 170 ° C. from the viewpoint of suppressing hydrolysis of cellulose. Further, it is preferable to heat at 130 ° C. or lower, preferably 110 ° C. or lower while water is contained in the heat treatment, remove water, and then heat-treat at 100 to 170 ° C.

The degree of phosphate group substitution per glucose unit of the phosphoric acid esterified cellulose is preferably 0.001 to 0.40. By introducing a phosphate group substituent into cellulose, the celluloses are electrically repelled from each other. Therefore, the cellulose into which a phosphate group has been introduced can be easily nano-defibrated. If the degree of phosphate substitution per glucose unit is less than 0.001, nano-defibration cannot be sufficiently performed. On the other hand, if the degree of phosphoric acid group substitution per glucose unit is larger than 0.40, it swells or dissolves, so that it may not be obtained as fine fibrous cellulose. In order to efficiently perform defibration, it is preferable that the phosphoric acid esterified cellulose raw material obtained above is washed by boiling and then washing with cold water.

(Defibration)
In the present invention, the apparatus for defibrating the chemically modified cellulose is not particularly limited, but the above-mentioned aqueous dispersion of the chemically modified cellulose is used by using an apparatus such as a high-speed rotary type, a colloid mill type, a high pressure type, a roll mill type, and an ultrasonic type. It is preferable to apply a strong shearing force to the. In particular, in order to efficiently defibrate, it is preferable to use a wet high-pressure or ultra-high 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 more, still more preferably 140 MPa or more. The number of treatments (passes) in the defibrator may be once, twice or more, and preferably twice or more.

In the 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, an organic solvent (for example, a hydrophilic organic solvent such as methanol), and a mixed solvent thereof. Since the cellulose raw material is hydrophilic, the solvent is preferably water.

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 the cellulose fiber raw material, which is efficient. The upper limit is usually 10% by weight or less, preferably 6% by weight or less. This makes it possible to maintain liquidity.

Prior to the defibration treatment or the dispersion treatment, the above-mentioned chemically modified cellulose may be pretreated, if necessary. The 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 defibration step is a salt type, it may be used as it is, or it may be used as an acid type by an acid treatment using a mineral acid or a method using a cation exchange resin. You may use it. Further, the 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 to be subjected to the step of pre-dispersion dehydrates and dries the fine fibrous cellulose dispersion produced as described above, and reduces the amount of solvent. It may be obtained by. As the dispersion of fine fibrous cellulose having a high solid content concentration, a commercially available product may be used.

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

The dehydration / drying method for producing a fine fibrous cellulose dispersion having a high solid content concentration is not particularly limited and may be appropriately selected depending on the intended purpose. For example, spray drying, squeezing, air drying, hot air drying. , Freeze-drying, spray-drying, vacuum-drying and the like. The drying device is also not particularly limited, and is a continuous tunnel drying device, a band drying device, a vertical drying device, a vertical turbo drying device, a multi-stage disk drying device, an aeration drying device, a rotary drying device, an air flow drying device, and a spray drying device. Equipment, cylindrical drying equipment, drum drying equipment, belt drying equipment, screw conveyor drying equipment, rotary drying equipment with heating tube, vibration transport drying equipment, batch type box type drying equipment, vacuum box type drying equipment, stirring drying equipment, etc. Can be used alone or in combination of two or more.

(Diluting solvent)
In the present invention, examples of the diluting solvent include water, a water-soluble organic solvent, and a mixed solvent thereof. Since the cellulose raw material is hydrophilic, water is used from the viewpoint that a good dispersion state can be easily obtained at the time of dispersion. Is preferable. Further, as the diluting solvent, the same solvent as that of the fine fibrous cellulose dispersion before dilution may be used, or a different solvent may be used.

The 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, Included are dimethyl sulfoxide, acetonitrile, and combinations thereof. Among them, lower alcohols having 1 to 4 carbon atoms such as methanol, ethanol and 2-propanol are preferable, methanol and ethanol are more preferable, and ethanol is further preferable from the viewpoint of safety and availability.

In the case of using a mixed solvent, 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, still more preferably 70% by weight or more. The upper limit of the amount is not limited, but is preferably 95% by weight or less, and more preferably 90% by weight or less. Further, the aqueous 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 an amount 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 a hard gel mass to a size that does not cause pipe clogging without shortening the fiber length of the fine fibrous cellulose with a high shearing force is appropriately used. Can be used. For example, an agitator or the like can be used. The conditions for pre-dispersion using a stirrer are not particularly limited, but are, for example, about 15 seconds to 30 minutes at 100 to 1500 rpm.

(Main dispersion process)
In the present dispersion step of the present invention, a mixture of the fine fibrous cellulose dispersion obtained in the above-mentioned pre-dispersion step and a diluting solvent is passed through an in-line stationary fluid mixing device.

(In-line stationary fluid mixer)
The in-line stationary fluid mixing device used in the present invention can be used without particular limitation as long as the above mixture can be uniformly diluted so as not to leave gel particles. For example, a static mixer, an OHR mixer, and MSE static can be used. Examples thereof include a mixer, and it is preferable to use an OHR mixer from the viewpoint of dispersibility.

A static mixer is a fluid mixture in which right-twisted spiral elements and left-twisted spiral elements are arranged alternately so that one end is perpendicular to the other end. It is a device.

The OHR mixer is a fluid mixing device that promotes mixing and stirring by providing a plurality of protrusions on the peripheral wall surface inside the tube and increasing cavitation in the fluid.

The MSE static mixer is a fluid mixing device in which a laminate 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 and used in a pipe. It is a fluid mixer.

In the main dispersion step, the flow velocity for passing the mixture through the in-line stationary fluid mixer is preferably 2.0 to 10.0 m / sec, and 3.0 to 10.0 m / sec from the viewpoint of dispersibility. Is more preferable.

It is preferable to use a pump with sufficient liquid delivery capacity to introduce the mixture into the in-line stationary fluid mixer at the desired flow rate. The pump is not particularly limited, and examples thereof include a vortex pump, a mono pump, and the like.

The number of times the mixture is passed through the in-line stationary fluid mixer is not particularly limited, but may be once or more than once.

An example in which an OHR mixer is used as the in-line stationary fluid mixer will be described with reference to FIG. FIG. 1 is a schematic view showing a cross section of an OHR mixer. The in-line stationary fluid mixing device that can be used in the present invention is not limited to the one shown in FIG.

The OHR mixer 2 shown in FIG. 1 is provided with a pipe body 4 through which a mixture is passed and two intersecting plates 6 for causing turbulent agitation on the upstream side of the pipe body 4. Is fixed to the inner wall of the tubular body 4. Further, 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 passage direction of the mixture is indicated by an arrow.

When the mixture is introduced into the OHR mixer 2 at a flow rate of a certain level or higher, the mixture becomes a spiral flow with a strong twist due to the action of the two plates 6. At this time, the mixture generates a mechanical shearing force due to abrupt division and current transformation by the two plates 6. Then, turbulent stirring occurs and is stirred. The mixture is fed further downstream through the tube and collides with the protrusions 8 while being stirred, so that the mixture is mixed more vigorously and the dispersion is promoted to obtain 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 agitation, but the number is preferably 2 to 8 from the viewpoint of increasing the number of shears. Two or two are more preferable. Further, the shape is preferably a semi-elliptical shape from the viewpoint of stirring efficiency.

The shape of the protrusion 8 on the inner peripheral wall of the tubular body 4 is not particularly limited, but is preferably mushroom-shaped from the viewpoint of increasing 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 a shortening of the fiber length to produce a uniformly diluted fine fibrous cellulose dispersion. can do.

Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited thereto. When the measurement / calculation method of each numerical value in each embodiment is not particularly described, it is measured / calculated by the method described in the specification.

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

(Measurement method of dispersion)
For the oxidized CNF aqueous dispersion 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.
Two ink droplets (manufactured by Kuretake Co., Ltd., solid content 10%) were appropriately added to 1 g of the oxidized CNF aqueous dispersion obtained in Examples and Comparative Examples, and a vortex mixer (manufactured by IUCHI, device name: Acoustic Lab-mixer HM) was added. The scale of the rotation speed of -10H) was set to the maximum, and the mixture was stirred for 10 seconds. Next, the mixture containing ink droplets was sandwiched between two glass plates so that the film thickness was 0.15 mm, and the magnification was magnified using an optical microscope (digital microscope KH-8700 (manufactured by Hirox Co., Ltd.)). It was observed at 100 times.

In the above observation, the major axis of the agglomerates existing in the range of 3 mm × 2.3 mm was measured, and the observed agglomerates were measured 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 = (extra-large number x 512 + large number x 64 + medium number x 8 + small number x 1) / 2 x CNF concentration coefficient The CNF concentration coefficient is shown in Table 1.

(Evaluation criteria for dispersion)
⊚: CNF variance index is less than 1600 ○: CNF variance index is 1600 or more and less than 3200 Δ: CNF variance index is 3200 or more and less than 6400 ×: CNF variance index is 6400 or more

(Manufacturing Example 1)
5.00 g (absolutely dry) of bleached unbeaten kraft pulp (whiteness 85%) derived from coniferous trees, 39 mg (0.05 mmol per 1 g of absolute dry cellulose) of TEMPO (Sigma Aldrich) and 514 mg of sodium bromide (absolutely dry). It was added to 500 mL of an aqueous solution in which 1.0 mmol) was dissolved in 1 g of cellulose, and the mixture was stirred until the pulp was uniformly dispersed. An aqueous sodium hypochlorite solution was added to the reaction system so that the sodium hypochlorite content was 6.0 mmol / g, and the oxidation reaction was started. Although the pH in the system decreased during the reaction, a 3M aqueous sodium hydroxide solution was sequentially added to adjust the pH to 10. The reaction was terminated when sodium hypochlorite was consumed and the pH in the system did not change. The mixture after the reaction was filtered through a glass filter to separate the pulp, and the pulp was thoroughly washed with water to obtain oxidized pulp (carboxylated cellulose). The pulp yield at this time 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 three times with an ultra-high pressure homogenizer (20 ° C., 150 MPa) to obtain an aqueous dispersion of cellulose oxide nanofibers. The obtained cellulose oxide nanofibers had an average fiber diameter of 3 nm and an average fiber length of 650 nm.

(Measuring method of carboxyl group amount)
60 mL of a 0.5 wt% slurry (aqueous dispersion) of carboxylated cellulose was prepared, and a 0.1 M hydrochloric acid aqueous solution was added to adjust the pH to 2.5, and then a 0.05 N sodium hydroxide aqueous solution was added dropwise to adjust the pH to 11. The electric conductivity was measured until
Amount of carboxyl groups [mmol / g carboxylated cellulose] = a [mL] x 0.05 / weight of carboxylated cellulose [g]

(Example 1)
The aqueous CNF oxide dispersion obtained in Production Example 1 having a solid content concentration of 3 wt% was put into an agitator together with water and pre-dispersed (500 rpm, 30 minutes) to carry out a pre-dispersion (500 rpm, 30 minutes), and a slurry having a solid content concentration of 0.5 wt%. Was produced. This slurry is sent using a pump at a flow rate of 3.0 m / sec, and is an OHR mixer (MX-F8 manufactured by OHR Fluid Engineering Laboratory Co., Ltd., MX-F8, outlet disconnection), which is an in-line static fluid mixer connected to the pump. This dispersion was carried out by passing the area: 50.2 mm ² ) once to obtain an aqueous CNF oxide dispersion having a solid content concentration of 0.5 wt%. The obtained aqueous CNF oxide dispersion was evaluated for the degree of dispersion and the average fiber length was measured. The results are shown in Table 2.

(Example 2)
By passing through the OHR mixer twice, an aqueous CNF oxide dispersion having a solid content concentration of 0.5 wt% was obtained in the same manner as in Example 1 except that this dispersion was carried out. Moreover, about this oxide CNF aqueous dispersion, the degree of dispersion was evaluated and the average fiber length was measured. The results are shown in Table 2.

(Example 3)
By passing through the OHR mixer three times, an aqueous CNF oxide dispersion having a solid content concentration of 0.5 wt% was obtained in the same manner as in Example 1 except that this dispersion was carried out. Moreover, about this oxide CNF aqueous dispersion, the degree of dispersion was evaluated and the average fiber length was measured. The results are shown in Table 2.

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

(Example 5)
This dispersion was performed by using a static mixer (two units of Noritake Company Limited 3 / 8-N30-232-F type connected) instead of the OHR mixer, and by passing the static mixer twice. An aqueous dispersion of CNF oxide having a solid content concentration of 0.5 wt% was obtained in the same manner as in Example 1 except for the above. The obtained aqueous CNF oxide dispersion was evaluated for the degree of dispersion and the average fiber length was measured. The results are shown in Table 2.

(Example 6)
The aqueous CNF oxide dispersion obtained in Production Example 1 having a solid content concentration of 3 wt% was concentrated with a blower dryer to obtain an aqueous CNF oxide 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 having a solid content concentration of 0.5 wt%. This slurry is sent at a flow rate of 10.0 m / sec using a pump, and is an OHR mixer (MX-F8 manufactured by OHR Fluid Engineering Laboratory Co., Ltd., MX-F8, outlet disconnection), which is an in-line static fluid mixer connected to the pump. This dispersion was carried out by passing the area: 50.2 mm ² ) 5 times to obtain an aqueous CNF oxide dispersion having a solid content concentration of 0.5 wt%. The obtained aqueous CNF oxide dispersion was evaluated for the degree of dispersion and the average fiber length was measured. The results are shown in Table 2. The average fiber length of the physical properties of the oxidized CNF dispersion before dilution shown in Table 2 is a value measured using an aqueous CNF oxide dispersion having a solid content concentration of 3 wt% before concentration.

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

(Comparative Example 2)
The flow velocity of the oxidized CNF aqueous dispersion having a solid content concentration of 3 wt% obtained in Production Example 1 together with water having a solid content concentration of 0.5 wt% using a pump without predispersing. This dispersion was performed by feeding the liquid at 3.0 m / sec and passing it once through the same OHR mixer as in Example 1 connected to the pump, but the solid content concentration was 0.5 wt% because the OHR mixer was clogged. An aqueous dispersion of CNF oxide could not be obtained.

(Comparative Example 3)
Pre-dispersion was carried out in the same manner as in Example 1 to prepare a slurry having a solid content concentration of 0.5 wt%. For this slurry, the degree of dispersion was evaluated and the average fiber length was measured without performing the main dispersion. The results are shown in Table 2.

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

As can be seen from Table 2, the step of pre-dispersing the fine fibrous cellulose dispersion having a solid content concentration of 1 wt% or more with a stirrer together with the diluting solvent and the mixture obtained in the step of pre-dispersing are mixed in-line static fluid. According to a method for producing a diluted fine fibrous cellulose dispersion, which comprises a step of main dispersion by passing through an apparatus, the obtained dispersion has a high degree of dispersion of fine fibrous cellulose and a fiber length. The 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 diluting solvent with a stirrer.
A method for producing a diluted fine fibrous cellulose dispersion, which comprises a step of main-dispersing the mixture obtained in the pre-dispersion step by passing it through an in-line stationary fluid mixing device. The fineness according to claim 1, wherein the in-line stationary fluid mixing device has a tubular body, and at least two intersecting plates for causing turbulent agitation are provided on the upstream side of the tubular body. A method for producing a fibrous cellulose dispersion. The method for producing a fine fibrous cellulose dispersion according to claim 1 or 2, wherein a plurality of protrusions are provided on the peripheral wall of the tube body on the downstream side of 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 stationary fluid mixing device at a flow rate of 2 m / sec or more.

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