JP7157656B2 - Method for producing fine fibrous cellulose dispersion - Google Patents

Description

The present invention relates to a method for producing a fine fibrous cellulose dispersion dispersed in a dispersion medium.

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, resulting in 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, it is added and mixed directly to the material to be reinforced, such as rubber latex, using a conventional agitator-type stirring device. In this case, the fine fibrous cellulose was not uniformly dispersed in the material, and the composition obtained by mixing was not sufficiently improved in strength and the like. In addition, when a fine fibrous cellulose dispersion having a high solid content concentration and rubber latex are mixed using a homogenizer capable of imparting a high shearing force, the rubber latex aggregates due to the shearing force of the homogenizer. was there.

Furthermore, 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. . Further, when a fine fibrous cellulose dispersion having a high solid content is diluted using a homogenizer capable of imparting a high shearing force, there is a problem that the shearing force shortens the fiber length of the fine fibrous cellulose. rice field. Therefore, the fine fibrous cellulose dispersion diluted by this method loses the function of increasing strength and rigidity, and is inferior in reinforcing effect. In addition, when diluting a fine fibrous cellulose dispersion with strong thixotropy using a disper-type high-speed stirrer or homogenizer, the stirring force is transmitted only to the periphery of the stirring blades, and the area far from the stirring blades did not flow, it was difficult to obtain a uniform dispersion.

Therefore, there is a method for producing a uniformly dispersed fine fibrous cellulose dispersion by dispersing a fine fibrous cellulose dispersion having a high solid content concentration with a dispersion medium so as not to cause shortening of the fiber length. was wanted. Further, when the dispersion medium is rubber latex, there is a demand for a method for producing a fine fibrous cellulose dispersion in which the rubber latex and the fine fibrous cellulose dispersion are uniformly dispersed without aggregating the rubber latex. rice field.

JP 2015-134873 A

Therefore, in the present invention, a fine fibrous cellulose dispersion having a high solid content concentration is dispersed with a dispersion medium so as not to cause shortening of the fiber length, and a uniformly dispersed fine fibrous cellulose dispersion is obtained. The object is to provide a manufacturing method. Furthermore, when the dispersion medium is rubber latex, the present invention provides a method for producing a fine fibrous cellulose dispersion in which the rubber latex and the fine fibrous cellulose dispersion are uniformly dispersed without aggregating the rubber latex. for the purpose.

The inventors of the present invention have made intensive studies to achieve this object, and as a result, have found that dispersion using a specific mixer is extremely effective, and completed the present invention.

The present invention provides the following.
(1) A dispersion step of dispersing a fine fibrous cellulose dispersion with a solid content concentration of 1 wt% or more together with a dispersion medium using a mixer having high-speed disper blades that revolve while rotating and low-speed blades that scrape the tank wall. A method for producing a fine fibrous cellulose dispersion dispersed in the dispersion medium, comprising:
(2) The method for producing a fine fibrous cellulose dispersion according to (1), wherein the rotation speed of the high speed disper blade is 500 to 2000 rpm and the rotation speed of the low speed blade is 5 to 10 rpm.
(3) The method for producing a fine fibrous cellulose dispersion according to (1) or (2), wherein the dispersion medium is water and/or rubber latex.

According to the present invention, a fine fibrous cellulose dispersion having a high solid content concentration is dispersed with a dispersion medium so as not to cause shortening of the fiber length, and a uniformly dispersed fine fibrous cellulose dispersion is obtained. A method of manufacturing can be provided. Further, when the dispersion medium is rubber latex, it is intended to provide a method for producing a fine fibrous cellulose dispersion in which the rubber latex and the fine fibrous cellulose dispersion are uniformly dispersed without aggregating the rubber latex. can be done.

It is a sectional view showing an outline of a mixer used for a 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 fine fibrous cellulose dispersion dispersed in a dispersion medium, wherein the fine fibrous cellulose dispersion having a solid content concentration of 1 wt % or more is rotated and revolved together with the dispersion medium by high-speed disper blades. and a low-speed blade scraping the tank wall.

(Dispersion process)
In the dispersing step of the present invention, a fine fibrous cellulose dispersion having a solid content concentration of 1 wt % or more is mixed with a dispersion medium using a mixer having a high-speed disper blade that revolves while rotating and a low-speed blade that scrapes the tank wall. scatter.

(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 comprises the carboxylated cellulose raw material, a cationizing agent such as glycidyltrimethylammonium chloride, 3-chloro-2-hydroxypropyltrialkylammonium halide or its halohydrin type, and an alkali metal hydroxide as a catalyst. (sodium hydroxide, potassium hydroxide, etc.) can be obtained by reacting 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. Furthermore, 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 dispersion step, is obtained by dehydrating and drying the dispersion of fine fibrous cellulose produced as described above to reduce the amount of solvent. You may get 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 dispersion step has a MFC/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, 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.

(dispersion medium)
In the present invention, the dispersion medium includes water, a water-soluble organic solvent, a mixed solvent thereof, or rubber latex. When the dispersion medium is water, a water-soluble organic solvent, or a mixed solvent thereof, it is preferable to use water from the viewpoint that a good dispersion state can easily be obtained during dispersion because the cellulose raw material is hydrophilic. The dispersion medium may be the same as the solvent for the fine fibrous cellulose dispersion having a high solid concentration before dispersion, or may be different.

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.

A rubber latex is a latex (dispersion liquid) in which a rubber component is dispersed in a dispersion medium.

The term "rubber component" refers to a raw material for rubber, which is crosslinked to form rubber. The rubber component includes a rubber component for natural rubber and a rubber component for synthetic rubber. Examples of rubber components for natural rubber include narrowly defined natural rubber (NR) without chemical modification; chemically modified natural rubber such as chlorinated natural rubber, chlorosulfonated natural rubber, and epoxidized natural rubber; hydrogenated natural rubber; Rubber; includes deproteinized natural rubber. Examples of rubber components for synthetic rubber include butadiene rubber (BR), styrene-butadiene copolymer rubber (SBR), isoprene rubber (IR), acrylonitrile-butadiene rubber (NBR), chloroprene rubber, styrene-isoprene copolymer Diene rubbers such as coalesced rubber, styrene-isoprene-butadiene copolymer rubber, isoprene-butadiene copolymer rubber; butyl rubber (IIR), ethylene-propylene rubber (EPM, EPDM), acrylic rubber (ACM), epichlorohydric Non-diene rubbers such as rubber (CO, ECO), fluorine rubber (FKM), silicone rubber (Q), urethane rubber (U), and chlorosulfonated polyethylene (CSM). Among these, NBR, NR, SBR, chloroprene rubber, and BR are preferred. The rubber component may be used singly or in combination of two or more.

Examples of the dispersion medium for rubber latex include water and organic solvents, and mixtures thereof may also be used. The content of the rubber component in the latex is preferably 10-80%, more preferably 20-70%.

The amount of the dispersion medium added to the fine fibrous cellulose dispersion having a high solid content concentration before dispersion was such that the MFC/CNF solid content concentration of the fine fibrous cellulose dispersion dispersed in the dispersion medium was 0.01 to 5 wt%. The amount is preferably 0.1 to 3 wt %, more preferably 0.1 to 3 wt %.

(mixer)
In the dispersing step of the present invention, a mixer having high-speed disper blades that revolve while rotating and low-speed blades that scrape off tank walls such as the side and bottom surfaces of the tank is used.

An example of a mixer that can be used in the present invention will be described with reference to FIG. FIG. 1 is a cross-sectional view showing an outline of a mixer. Note that the mixer that can be used in the present invention is not limited to that shown in FIG.

The mixer 2 shown in FIG. 1 includes a tank 4 containing contents, high-speed disper blades 6 that apply shearing force to the contents of the tank 4 by rotating at high speed, and power is transmitted to the high-speed disper blades 6. A high-speed stirring shaft 8, a low-speed blade 12 scraping the tank wall 10 at low speed, and a low-speed stirring shaft 14 transmitting power to the low-speed blade 12 are provided. Here, the high-speed stirring shaft 8 is connected to the low-speed stirring shaft 14 by the first arm 16 , and the low-speed blade 12 is connected to the low-speed stirring shaft 14 by the second arm 18 . The low-speed stirring shaft 14 and the high-speed stirring shaft 8 are connected to a drive unit 20 that rotates the high-speed disper blades 6 at high speed and revolves at low speed, and rotates the low-speed blades 12 at low speed.

When dispersing using the mixer 2, a fine fibrous cellulose dispersion with a high solid content concentration and a dispersion medium are put into the tank 4, and the high-speed disper blade 6 and the low-speed disper blade 12 provided in the tank 4 are operated. Start. The high-speed disper blade 6 vigorously stirs the contents in the tank 4 by rotating at high speed. Since the high-speed disper blades 6 rotate at high speed and revolve at low speed, the stirring force of the high-speed disper blades 6 is transmitted to a wide area inside the tank 4 . In addition, the low-speed blades 12 scrape off the tank wall 10 such as the side surface and the bottom surface inside the tank 4 at low speed, and the contents near the tank wall 10 are made to flow.

The rotation speed of the high-speed disper blades 6 is preferably 500 to 2000 rpm, more preferably 700 to 1800 rpm, from the viewpoint of uniform dispersion. Further, the rotation speed of the low-speed blades 12 is preferably 5 to 10 rpm, more preferably 6 to 8 rpm, from the viewpoint of efficient dispersion. In the mixer shown in FIG. 1, the revolution speed of the high-speed disper blades 6 matches the speed of the low-speed blades 12, but as long as the high-speed disper blades 6 and low-speed blades 12 do not come into contact with each other, these Mixers with different rotation speeds may also be used.

According to the production method of the present invention, even when the contents having strong thixotropic properties are stirred, the high-speed disper blade 6 revolves while rotating at high speed, so that the stirring force is transmitted to a wide area in the tank 4. be. Furthermore, since the low-speed blades 12 scrape the tank wall 10 , the flow also occurs in areas where the agitation force from the high-speed disper blades 6 would be difficult to reach without the low-speed blades 12 . As a result, uniform dispersion can be achieved.

According to the production method of the present invention, a fine fibrous cellulose dispersion having a high solid content concentration is dispersed with a dispersion medium so as not to cause shortening of the fiber length, and uniformly dispersed fine fibrous cellulose is obtained. Dispersions can be made. Furthermore, the fine fibrous cellulose dispersion uniformly dispersed in the dispersion medium obtained in this way has a low viscosity and is soft, so that it can be easily and uniformly dispersed in a material to be reinforced, such as rubber latex. .

Moreover, according to the production method of the present invention, it is not necessary to apply a high shearing force to disperse the hard gel of the fine fibrous cellulose dispersion having a high solid content. Therefore, even when rubber latex is used as a dispersion medium, it is possible to uniformly disperse the fine fibrous cellulose dispersion having a high solid content by directly mixing it with the rubber latex without aggregating the rubber latex. can.

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)
For the oxidized CNF dispersions 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 dispersion obtained in Examples and Comparative Examples, 2 drops of Bokushizuku (manufactured by Kuretake Co., Ltd., solid content 10%) were added, 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

(Evaluation method for latex cohesive stains)
For Example 2 and Comparative Example 5, after the dispersion was repeated 10 times under the conditions of Example 2 and Comparative Example 5, the inside of the dispersing device was visually observed to investigate the degree of contamination due to latex aggregates.

(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. Although the pH in the system decreased during the reaction, it 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 4.0 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 with a solid content concentration of 4.0 wt% obtained in Production Example 1 above is scraped off the high-speed disper blades and tank walls (bottom, side) that revolve while rotating with water as a dispersion medium. A mixer (manufactured by Asada Iron Works Co., Ltd., MHK-7.5) having a blade and dispersed for 10 minutes under the conditions of a rotation speed of 1000 rpm for a high-speed disper blade and a rotation speed of 10 rpm for a low-speed blade to obtain a solid content concentration. An oxidized CNF aqueous dispersion of 0.5 wt% 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.

(Example 2)
The oxidized CNF aqueous dispersion having a solid content concentration of 4.0 wt% obtained in Production Example 1 above was mixed with natural rubber latex (trade name: HA latex, Resitex Co., Ltd., solid content concentration 61.5 wt%) as a dispersion medium. With water, high-speed disper blades and tank walls (bottom, side) that revolve while rotating so that CNF is 20 parts by weight in absolute dry equivalent for 100 parts by weight of absolute dry solids of natural rubber latex It is put into a mixer (MHK-7.5, manufactured by Asada Iron Works Co., Ltd.) having a scraping low-speed blade, and dispersed for 15 minutes under the conditions of a rotation speed of 750 rpm for the high-speed disper blade and a rotation speed of 10 rpm for the low-speed blade. A dispersion of oxidized CNF and natural rubber latex having a CNF solid content concentration of 1.00 wt % was obtained. The obtained dispersion of oxidized CNF and natural rubber latex was evaluated for degree of dispersion. Table 2 shows the results.
After the dispersion was repeated 10 times, no dirt due to latex aggregates was observed inside the mixer.

(Comparative example 1)
In the same manner as in Example 1, except that the rotation speed of the high-speed disper blade was changed to 250 rpm, and the rotation speed of the low-speed blade was changed to 1 rpm. An oxidized CNF water dispersion with a solid content concentration of 0.5 wt%. got 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.

(Comparative example 2)
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 an agitator was used as a dispersing device and the dispersion was performed for 30 minutes at a rotation speed of 500 rpm. 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 3)
A homogenizer (manufactured by SMTE Co., Ltd., product name: High Flex Homogenizer HF93, cutter: type 4) was used as a dispersing device, and dispersion was performed for 30 minutes at a rotation speed of 8000 rpm. An oxidized CNF aqueous dispersion of 0.5 wt% 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.

(Comparative Example 4)
Homodisper (manufactured by Primix Co., Ltd., Homodisper 2.5 type) was used as a dispersing device, and the solid content concentration was 0.5 wt% in the same manner as in Example 1 except that the dispersion was performed for 30 minutes at a rotation speed of 3000 rpm. of oxidized CNF aqueous 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.

(Comparative Example 5)
Using the same homogenizer as in Comparative Example 3 as a dispersing device, in the same manner as in Example 2 except that the dispersion was performed for 30 minutes at a rotation speed of 8000 rpm, oxidized CNF having a CNF solid content concentration of 1.0 wt% and natural rubber latex. was obtained. The obtained dispersion of oxidized CNF and natural rubber latex was evaluated for degree of dispersion. Table 2 shows the results.
After the dispersion was repeated 10 times, the inside of the homogenizer was found to be stained with aggregates of latex.

As can be seen from Table 2, a fine fibrous cellulose dispersion with a solid content concentration of 1 wt% or more is dispersed together with a dispersion medium using a mixer having high-speed disper blades that revolve while rotating and low-speed blades that scrape the tank wall. According to the method for producing a dispersion of fine fibrous cellulose dispersed in a dispersion medium, which includes a dispersion step, the resulting dispersion had a high degree of dispersion of fine fibrous cellulose. It was also confirmed that when the dispersion medium was water, the dispersion obtained by the above-described production method was suppressed in shortening of the fiber length. Moreover, when the dispersing medium was rubber latex, it was confirmed visually that there was no latex agglomeration stain in the mixer.

DESCRIPTION OF SYMBOLS 2... Mixer, 4... Tank, 6... High-speed disper blade, 8... High-speed stirring shaft, 10... Tank wall, 12... Low-speed blade, 14... Low-speed stirring shaft, 16... First arm, 18... Second arm, 20... Drive part

Claims (2)

A dispersion step of dispersing a fine fibrous cellulose dispersion with a solid content concentration of 1 wt% or more together with a dispersion medium using a mixer having high-speed disper blades that revolve while rotating and low-speed blades that scrape the tank wall,
A method for producing a fine fibrous cellulose dispersion dispersed in the dispersion medium , wherein the rotation speed of the high-speed disper blade is 500 to 2000 rpm, and the rotation speed of the low-speed blade is 5 to 10 rpm . 2. The method for producing a fine fibrous cellulose dispersion according to claim 1, wherein the dispersion medium is water or/and rubber latex.

Images