JP5807632B2 - Method for producing fine cellulose fiber - Google Patents

Description

  The present invention relates to a method for producing fine cellulose fibers.

In recent years, materials using reproducible natural fibers have attracted attention due to the substitution of petroleum resources and the growing environmental awareness. Among natural fibers, cellulose fibers having a fiber diameter of 10 to 50 μm, especially wood-derived cellulose fibers (pulp) have been widely used as paper products so far.
As cellulose fibers, fine cellulose fibers having a fiber diameter of 1000 nm or less are also known. Various uses of fine cellulose fibers have been studied. For example, it is said that when fine cellulose fibers are blended into a resin or rubber as a reinforcing agent, the effect of improving mechanical properties is increased.
As a method for producing fine cellulose fibers, a method for refining a cellulose fiber raw material treated with ozone is known (Patent Document 1). In fine cellulose fibers, it is known that the smaller the average fiber width, the better the appearance and physical properties. In the production method described in Patent Document 1, in order to reduce the average fiber width, it is increased by centrifugation. The fiber was removed and purified.

JP 2010-254726 A

However, in the method for producing fine cellulose fibers described in Patent Document 1, the average fiber width of the obtained fine cellulose fibers has not been sufficiently reduced despite purification by centrifugation. Therefore, in order to obtain fine cellulose fibers having a sufficiently small average fiber width, increasing the number of rotations of centrifugation or extending the time of centrifugation tends to increase the energy consumption required for purification.
An object of this invention is to provide the manufacturing method of the fine cellulose fiber which can fully reduce the fiber width of the obtained fine cellulose fiber, suppressing the energy consumption required for refinement | purification.

  The method for producing fine cellulose fibers of the present invention is a fine method for obtaining a fine cellulose fiber dispersion by subjecting a cellulose fiber raw material dispersion containing cellulose fibers to a refinement treatment so that the average fiber width of the cellulose fibers is 2 to 50 nm. And a refining step of performing a second refining process after the first refining process is performed on the fine cellulose fiber dispersion, wherein the first refining process comprises It is at least one of a process of filtering with a screen having an opening of 20 μm or less and a process of centrifuging with a centrifugal force of 1000 to 5000 G. The second purification process is a fine cellulose fiber dispersion subjected to the first purification process. It is the process of centrifuging with centrifugal force 10000-20000G.

  According to the method for producing fine cellulose fibers of the present invention, the fiber width of the obtained fine cellulose fibers can be sufficiently reduced while suppressing the energy consumption required for purification.

"Fine cellulose fiber"
The fine cellulose fibers are cellulose fibers or rod-like particles having a type I crystal structure that is much finer and shorter than pulp fibers usually used in papermaking applications.
The fact that the fine cellulose fiber has a type I crystal structure is that 2θ = 14 to 17 ° in a diffraction profile obtained from a wide-angle X-ray diffraction photograph using CuKα (λ = 1.5418４) monochromatized with graphite. It can be identified by having typical peaks in the vicinity and two positions near 2θ = 22 to 23 °.
The degree of crystallinity of fine cellulose fibers determined by the X-ray diffraction method is preferably 60% or more, more preferably 65% or more, and further preferably 70% or more. If the degree of crystallinity is not less than the lower limit, further excellent performance can be expected in terms of heat resistance and low linear thermal expansion. The degree of crystallinity can be obtained by measuring an X-ray diffraction profile and using a conventional method (Segal et al., Textile Research Journal, 29, 786, 1959).

<Fiber width>
The fine cellulose fiber is cellulose having an average fiber width of 2 to 50 nm determined by observation with an electron microscope. The average fiber width of the fine cellulose fibers is preferably 2 to 30 nm, more preferably 2 to 15 nm, and further preferably 2 to 10 nm. When the average fiber width of the fine cellulose fibers exceeds the above upper limit, the characteristics as the fine cellulose fibers (high strength, high rigidity, high dimensional stability, high dispersibility when combined with resin, transparency) are obtained. Becomes difficult. If the average fiber width of the fine cellulose fibers is less than the lower limit value, the cellulose molecules are dissolved in the dispersion medium, so that characteristics (high strength, high rigidity, high dimensional stability) as fine cellulose fibers can be obtained. It becomes difficult.

Measurement of the average fiber width by observation with an electron microscope of fine cellulose fibers is performed as follows. A slurry containing fine cellulose fibers is prepared, and the slurry is cast on a carbon film-coated grid that has been subjected to a hydrophilization treatment to obtain a transmission electron microscope (TEM) observation sample. When wide fibers are included, an operation electron microscope (SEM) image of the surface cast on glass may be observed. Observation by an electron microscope image is performed at any magnification of 1000 times, 5000 times, 10000 times, 20000 times, 50000 times or 100,000 times depending on the width of the constituent fibers. However, the sample, observation conditions, and magnification are adjusted to satisfy the following conditions.
(1) One straight line X is drawn at an arbitrary location in the observation image, and 20 or more fibers intersect the straight line X.
(2) A straight line Y perpendicularly intersecting the straight line X is drawn in the same image, and 20 or more fibers intersect the straight line Y.
For the electron microscope observation image as described above, the width (minor axis of the fiber) of at least 20 fibers (that is, at least 40 in total) is read for each of the fibers intersecting with the straight line X and the fibers intersecting with the straight line Y. . In this way, at least three or more sets of electron microscope images as described above are observed, and the fiber width of at least 40 × 3 sets (that is, at least 120 sets) is read. The fiber widths thus read are averaged to obtain the average fiber width. This average fiber width is equal to the number average fiber diameter.

<Fiber length>
As for the average fiber length of a fine cellulose fiber, 0.1-5 micrometers is preferable. If average fiber length is more than the said lower limit, the strength improvement effect at the time of mix | blending a fine cellulose fiber with resin will fully be acquired. If average fiber length is below the said upper limit, the mixability at the time of mix | blending a fine cellulose fiber with resin will become more favorable. The fiber length can be determined by analyzing the electron microscope observation image used when measuring the average fiber width. That is, at least 20 fibers (that is, a total of at least 40 fibers) are read for each of the fibers intersecting with the straight line X and the fibers intersecting with the straight line Y with respect to the electron microscope observation image as described above. In this way, at least three or more sets of electron microscope images as described above are observed, and the fiber length of at least 40 × 3 sets (that is, at least 120 sets) is read. The average fiber length is obtained by averaging the fiber lengths thus read.
When the fine cellulose fiber is applied to an application where strength such as a transparent substrate is required, the fiber length is preferably long (specifically, 500 nm to 4 μm), and when blended in a resin, the fiber length Is preferably shorter (specifically, 200 nm to 2 μm).

<Anionic group, cationic group>
The fine cellulose fiber may have an anionic group and have a negative surface charge, or may have a cationic group and have a positive surface charge.
When the fine cellulose fiber has an anionic group or a cationic group, the content is preferably 0.1 to 2.0 mmol / g, more preferably 0.1 to 1.5 mmol / g, 0 More preferably, it is 2 to 1.2 mmol / g. If the content of the cationic group or the anionic group is within the above range, the hydration property of the fine cellulose fiber will not be too high, and the viscosity when slurried will be low. When the content of the anionic group or the cationic group exceeds the upper limit, the hydration property becomes too high, and the fine cellulose fiber may be dissolved.
Note that cellulose has a small amount (specifically, less than 0.1 mmol / g) of carboxy groups even without a treatment for introducing carboxy groups.

Examples of the anionic group include a carboxy group, a phosphoric acid group, and a sulfonic acid group.
The content of the anionic group is determined using a method of “Test Method T237 cm-08 (2008): Carboxyl Content of pull” of TAPPI, USA. In order to make it possible to measure the content of anionic groups over a wider range, among the test solutions used in the test method, sodium bicarbonate (NaHCO ₃ ) / sodium chloride (NaCl) = 0.84 g / 5.85 g was distilled water. According to TAPPI T237 cm-08 (2008), except that the test solution dissolved and diluted in 1000 ml was changed to 1.60 g of sodium hydroxide so that the concentration of the test solution was substantially 4-fold. Moreover, when an anion group is introduced, the difference in the measured value in the cellulose fiber before and after the introduction of the anion group is regarded as a substantial anion group content. In addition, the absolutely dry cellulose fiber used as a measurement sample is one obtained by freeze-drying in order to avoid alteration of cellulose that may occur due to heating during heat drying.
Since the anion group content measurement method is a measurement method for a monovalent anion group (carboxy group), when the anion group to be quantified is multivalent, it is obtained as the monovalent anion group content. A value obtained by dividing the obtained value by the acid number is defined as an anion group content.

  The cationic group is a group having an onium such as ammonium, phosphonium or sulfonium in the group, and is usually a group having a molecular weight of 1000 or less. Specific examples include ammonium such as primary ammonium, secondary ammonium, tertiary ammonium and quaternary ammonium, phosphonium, sulfonium, and groups having these ammonium, phosphonium or sulfonium.

The content of the cationic group is measured by the following method.
Take 0.5 g of the pulp slurry treated with the cationizing agent in terms of absolute dry mass, and dilute it with ion-exchanged water to a concentration of 1% by mass (50 g of solid). To this, 0.67 g of 30% by mass sodium hydroxide solution is added little by little with sufficient stirring, and left to stand for 2 hours. The pulp is filtered, and the pulp on the filter paper is washed with ion exchange water. The end point of washing is determined when the pH of the filtrate is 8.5 or less.
The entire amount of pulp on the filter paper is transferred to a 100 ml screw bottle, and in order to measure the amount of water in the sample, the mass of the pulp at this time is precisely weighed and recorded. Add 100 g of 0.05N hydrochloric acid solution to the precisely weighed pulp, cover the screw bottle, shake vigorously, and let stand for 1 hour.
Using a well-dried glass filter, the slurry in the screw bottle is filtered and the filtrate is received in a receiver. Transfer 3 g of the obtained filtrate to a 100 ml beaker, add 2 or 3 drops of methyl red indicator, and titrate with 0.01 N sodium hydroxide solution. The sodium hydroxide solution is dropped, and the end point of the titration is when the color of the solution changes from the original pink color to orange and yellow.
The amount of cationic group introduced is calculated according to the calculation formula shown in Equation 1. The blank value for titration is obtained by titrating 3 g of 0.05N hydrochloric acid solution.

V ₀ : Blank titration volume C _NaOH : Sodium hydroxide solution concentration W _HCl : Amount of hydrochloric acid added to sample W ₀ : Amount of blank hydrochloric acid V sample: Amount of sample titration W _sample : Amount of sample filtrate W _water : Amount of _{water in} sample _WBD-pulp : absolute dry mass of sample N: valence of substituent

"Production method of fine cellulose fiber"
The method for producing fine cellulose fibers according to the present invention for producing the fine cellulose fibers includes a refinement process for refining the cellulose fiber raw material dispersion and a purification process for subjecting the fine cellulose fiber dispersion to a purification process. .
The method for producing fine cellulose fibers of the present invention may have a chemical treatment step, a washing step, and a foreign matter removal step before the refinement step, and a concentration step and a redispersion step after the purification step. May be.

<Cellulose fiber raw material>
In the present invention, the fiber raw material containing cellulose, which is a raw material for fine cellulose fibers, includes pulp for papermaking, cotton pulp such as cotton linter and cotton lint, non-wood pulp such as hemp, straw, bagasse, sea squirt and seaweed And cellulose isolated from the above. Among these, paper pulp is preferable in terms of availability. Paper pulp includes hardwood kraft pulp (bleached kraft pulp (LBKP), unbleached kraft pulp (LUKP), oxygen bleached kraft pulp (LOKP), etc.), softwood kraft pulp (bleached kraft pulp (NBKP), unbleached kraft pulp) (NUKKP, oxygen bleached kraft pulp (NOKP), etc.), sulfite pulp (SP), chemical pulp such as soda pulp (AP), semi-chemical pulp (SCP), semi-chemical pulp such as chemiground wood pulp (CGP) In addition, mechanical pulp such as groundwood pulp (GP) and thermomechanical pulp (TMP, BCTMP), non-wood pulp using raw material such as cocoon, sardine, hemp, kenaf and the like, and deinked pulp using raw paper as a raw material. Among these, kraft pulp, deinked pulp, and sulfite pulp are preferable because they are more easily available.
A cellulose fiber raw material may be used individually by 1 type, and may be used in mixture of 2 or more types.

<Chemical treatment process>
You may use the said fiber raw material containing a cellulose as a raw material of a fine cellulose fiber as it is. However, since the miniaturization is promoted in the miniaturization step, the production method of the present invention performs a chemical treatment to contain 0.1 to 2.0 mmol / g of a substituent composed of at least one of a polar group and a bulky group. It is preferable to have a chemical treatment step.
Examples of the polar group include an anionic group (specifically, a carboxy group, a phosphoric acid group, a sulfuric acid ester group, a sulfonic acid group, a phenol group, and a nitric acid ester group), a cationic group, a carboxy group, a phosphoric acid group, and a cationic group. Groups are preferred.
Examples of the bulky group include an alkyl group, a benzyl group (benzene ring), a benzene derivative-containing group, an acyl group, a silyl group, a trityl group, and a tosyl group.

(Introduction of carboxy group)
As a method of introducing a carboxy group into a cellulose fiber raw material, a method of oxidizing a part of the hydroxyl group of cellulose to a carboxy group using an oxidizing agent can be mentioned.
Oxidizing agents include ozone, chlorine dioxide, hydrogen peroxide, peracetic acid, persulfuric acid, permanganic acid, chlorine, hypochlorous acid, chlorous acid, chloric acid, perchloric acid or an aqueous solution thereof such as six salts. Chromic acid sulfuric acid mixture, Jones reagent (acidic sulfuric acid solution of chromic anhydride), chromic acid oxidizing reagent such as pyridilinium chlorochromate (PCC reagent), activated dimethyl sulfoxide reagent used for Swern oxidation, etc., and catalytic oxidation And N-oxyl compounds such as 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) and the like. Of these, ozone, TEMPO, hydrogen peroxide, and chlorine dioxide are preferred, and ozone and TEMPO are more preferred because of the high efficiency of introducing carboxy groups into cellulose fibers.

[Treatment with ozone]
In the treatment with ozone, some hydroxyl groups of cellulose are replaced with carbonyl groups or carboxy groups. Thereby, the bond strength between the cellulose fibers is weakened, and the defibration property is improved.
Ozone can be generated by supplying an oxygen-containing gas such as air, oxygen gas, or oxygen-added air to a known ozone generator.

The treatment with ozone is performed by exposing the cellulose fiber raw material to a closed space or atmosphere in which ozone exists. If the ozone concentration in the gas containing ozone is 250 g / m ² or more, there is a possibility of explosion, so it is necessary to be less than 250 g / m ² . However, if the concentration is low, the amount of ozone used increases, so the ozone concentration is preferably 50 to 215 g / m ² . If the ozone concentration is equal to or higher than the lower limit, the handling of ozone is easy, and the effect of improving the yield of fine cellulose fibers in the refinement step is further increased.
The amount of ozone added to the cellulose fiber raw material is not particularly limited, but is preferably 5 to 30 parts by mass with respect to 100 parts by mass of the solid content of the cellulose fiber raw material. If the amount of ozone added is equal to or greater than the lower limit, the effect of improving the yield of fine cellulose fibers in the refinement step is further increased. However, exceeding the upper limit causes a decrease in yield before and after the ozone treatment and a deterioration in dewaterability. Moreover, the yield improvement effect of the fine cellulose fiber reaches a peak in the miniaturization process.

The ozone treatment temperature is not particularly limited, and is appropriately adjusted within a range of 0 to 50 ° C. Further, the ozone treatment time is not particularly limited, and is appropriately adjusted within a range of 1 to 360 minutes.
In addition, you may perform a post-oxidation process after performing an ozone process to a cellulose fiber raw material. Examples of the oxidizing agent used for the additional oxidation treatment include oxygen, hydrogen peroxide, persulfuric acid, peracetic acid, and the like, in addition to chlorine compounds such as chlorine dioxide and sodium chlorite.

Moreover, after ozone treatment, it is preferable to perform the alkali treatment which processes with the alkaline solution with respect to the processed cellulose fiber raw material. Although it does not specifically limit as a method of alkali treatment, For example, the method of immersing the cellulose fiber raw material which carried out ozone treatment in the alkaline solution is mentioned.
The alkali compound contained in the alkali solution may be an inorganic alkali compound or an organic alkali compound.

Examples of inorganic alkali compounds include alkali metal hydroxides or alkaline earth metal hydroxides, alkali metal carbonates or alkaline earth metal carbonates, alkali metal phosphates or alkaline earth metal phosphoric acids. Salt.
Examples of the alkali metal hydroxide include lithium hydroxide, sodium hydroxide, and potassium hydroxide. Examples of the alkaline earth metal hydroxide include calcium hydroxide.
Examples of the alkali metal carbonate include lithium carbonate, lithium hydrogen carbonate, potassium carbonate, potassium hydrogen carbonate, sodium carbonate, and sodium hydrogen carbonate. Examples of the alkaline earth metal carbonate include calcium carbonate.
Examples of the alkali metal phosphate include lithium phosphate, potassium phosphate, trisodium phosphate, and disodium hydrogen phosphate. Examples of alkaline earth metal phosphates include calcium phosphate and calcium hydrogen phosphate.

Examples of the organic alkali compounds include ammonia, aliphatic amines, aromatic amines, aliphatic ammoniums, aromatic ammoniums, heterocyclic compounds and their hydroxides, carbonates, and phosphates. For example, ammonia, hydrazine, methylamine, ethylamine, diethylamine, triethylamine, propylamine, dipropylamine, butylamine, diaminoethane, diaminopropane, diaminobutane, diaminopentane, diaminohexane, cyclohexylamine, aniline, tetramethylammonium hydroxide, Tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, benzyltrimethylammonium hydroxide, pyridine, N, N-dimethyl-4-aminopyridine, ammonium carbonate, ammonium hydrogen carbonate, diammonium hydrogen phosphate, etc. Can be mentioned.
The said alkali compound may be single 1 type, and may combine 2 or more types.

The solvent in the alkaline solution may be either water or an organic solvent, but is preferably a polar solvent (polar organic solvent such as water or alcohol), and more preferably an aqueous solvent containing at least water. Among alkaline solutions, sodium hydroxide aqueous solution, potassium hydroxide aqueous solution, and ammonia aqueous solution are particularly preferred because of their high versatility.
The pH at 25 ° C. of the alkaline solution in which the ozone-treated cellulose fiber raw material is immersed is preferably 9 or more, more preferably 10 or more, and even more preferably 11-14. If the pH of the alkaline solution is at least the lower limit, the yield of fine cellulose fibers will be higher. However, when the pH exceeds 14, not only the handling property of the alkaline solution is lowered, but also dissolution of fine cellulose fibers occurs.

[Processing by TEMPO]
In the treatment with TEMPO, a cellulose fiber raw material is reacted with an oxidizing agent in the presence of TEMPO and an alkali halide to change a part of the hydroxyl groups of cellulose to carboxy groups. Thereby, the bond strength between the cellulose fibers is weakened, and the defibration property is improved.
The alkali halide used as an oxidation catalyst together with TEMPO is not particularly limited, and alkali iodide, alkali bromide, alkali chloride, alkali fluoride and the like can be appropriately selected and used.
The oxidizing agent is not particularly limited, and sodium hypochlorite, sodium chlorite, sodium hypobromite, sodium bromite and the like can be appropriately selected and used.

Although the usage-amount of TEMPO and an alkali halide is not restrict | limited in particular, It is preferable that it is 0.1-15 mass parts, respectively with respect to 100 mass parts of solid content of a cellulose fiber raw material. If the addition amount of TEMPO and an alkali halide is each more than the said lower limit, the yield improvement effect of the fine cellulose fiber in a refinement | miniaturization process will become higher. However, when the upper limit is exceeded, the yield improvement effect of fine cellulose fibers in the miniaturization process may reach a peak.
The amount of the oxidizing agent used is not particularly limited, but is preferably 1 to 80 parts by mass with respect to 100 parts by mass of the solid content of the cellulose fiber raw material.
The pH of the dispersion when the dispersion containing the cellulose fiber raw material is treated with TEMPO is appropriately adjusted according to the type of oxidizing agent to be used. The pH of the cellulose fiber raw material dispersion is adjusted by appropriately adding a basic substance such as potassium hydroxide or ammonia, or an acidic substance such as acetic acid or oxalic acid.
The treatment temperature for treating the cellulose fiber raw material with TEMPO is preferably in the range of 20 to 100 ° C., and the treatment time is preferably 0.5 to 4 hours.

[Treatment with carboxylic acid compound]
As a method for introducing a carboxy group into a cellulose fiber raw material, a method using a carboxylic acid compound having two or more carboxy groups in the molecule is also preferred.
In the treatment with the carboxylic acid compound, the hydroxy group of the cellulose molecule and the carboxylic acid compound undergo a dehydration reaction to form a polar group (—COO ⁻ ). Thereby, the bond strength between the cellulose fibers is weakened, and the defibration property is improved.

  Specific methods for treating the cellulose fiber raw material with the carboxylic acid compound include a method of mixing the gasified carboxylic acid compound with the cellulose fiber raw material, a method of adding the carboxylic acid compound to the dispersion of the cellulose fiber raw material, and the like. Can be mentioned. Among these, since the process is simple and the efficiency of introducing a carboxy group is high, a method of mixing a gasified carboxylic acid compound with a cellulose fiber raw material is preferable. Examples of the method for gasifying the carboxylic acid compound include a method for heating the carboxylic acid compound.

The carboxylic acid compound used in this treatment is at least one selected from the group consisting of a compound having two carboxy groups, an acid anhydride of a compound having two carboxy groups, and derivatives thereof. Of the compounds having two carboxy groups, compounds having two carboxy groups (dicarboxylic acid compounds) are preferred.
The compounds having two carboxy groups include propanedioic acid (malonic acid), butanedioic acid (succinic acid), pentanedioic acid (glutaric acid), hexanedioic acid (adipic acid), 2-methylpropanedioic acid, 2 -Methylbutanedioic acid, 2-methylpentanedioic acid, 1,2-cyclohexanedicarboxylic acid, 2-butenedioic acid (maleic acid, fumaric acid), 2-pentenedioic acid, 2,4-hexadienedioic acid, 2-methyl 2-butenedioic acid, 2-methyl-2-pentenedioic acid, 2-methylidenebutanedioic acid (itaconic acid), benzene-1,2-dicarboxylic acid (phthalic acid), benzene-1,3-dicarboxylic acid (isophthalic acid) ), Benzene-1,4-dicarboxylic acid (terephthalic acid), ethanedioic acid (oxalic acid), and the like.
Acid anhydrides of compounds having two carboxy groups include maleic anhydride, succinic anhydride, phthalic anhydride, glutaric anhydride, adipic anhydride, itaconic anhydride, pyromellitic anhydride, 1,2-cyclohexanedicarboxylic anhydride Examples thereof include acid anhydrides of dicarboxylic acid compounds such as acids and compounds containing a plurality of carboxy groups.
The acid anhydride derivative of the compound having two carboxy groups includes at least a part of the acid anhydride of the compound having a carboxy group, such as dimethylmaleic anhydride, diethylmaleic anhydride, and diphenylmaleic anhydride. The hydrogen atom is substituted with a substituent (for example, an alkyl group, a phenyl group, etc.).
Of these, maleic anhydride, succinic anhydride, and phthalic anhydride are preferred because they are industrially applicable and easily gasified.

The mass ratio of the carboxylic acid compound to the cellulose fiber raw material is preferably 0.1 to 500 parts by mass, preferably 10 to 200 parts by mass with respect to 100 parts by mass of the solid content of the cellulose fiber raw material. More preferably. If the ratio of a carboxylic acid type compound is more than the said lower limit, the yield of a fine cellulose fiber can be improved more. However, even if the upper limit is exceeded, the effect of improving the yield reaches its peak, and the carboxylic acid compound is merely used in vain.
The treatment temperature is preferably 250 ° C. or less from the viewpoint of the thermal decomposition temperature of cellulose. Furthermore, when water is contained in the treatment, the temperature is preferably 80 to 200 ° C, more preferably 100 to 170 ° C.
In this treatment, a catalyst can be used as necessary. As the catalyst, it is preferable to use a basic catalyst such as pyridine, triethylamine, sodium hydroxide or sodium acetate, or an acidic catalyst such as acetic acid, sulfuric acid or perchloric acid.
After the treatment with the carboxylic acid compound, the treated cellulose fiber raw material is preferably subjected to an alkali treatment with an alkaline solution, similarly to the treatment with ozone.

(Introduction of phosphate group)
As a method for introducing a phosphate group into cellulose, a method of mixing a powder or aqueous solution of phosphoric acid or a phosphoric acid derivative with a dry or wet cellulose fiber raw material, a phosphoric acid or phosphoric acid with a dispersion of a cellulose fiber raw material Examples thereof include a method of adding an aqueous solution of a derivative. In these methods, dehydration treatment, heat treatment, and the like are usually performed after mixing or adding a powder or aqueous solution of phosphoric acid or phosphoric acid derivative.
Examples of the phosphoric acid or phosphoric acid derivative used here include at least one compound selected from an oxo acid, a polyoxo acid or a derivative thereof containing a phosphorus atom.
Specifically, phosphoric acid; sodium salt of phosphoric acid such as sodium dihydrogen phosphate, disodium hydrogen phosphate and trisodium phosphate; sodium salt of polyphosphoric acid such as sodium pyrophosphate and sodium metaphosphate; Potassium salts of phosphoric acid such as potassium hydrogen, dipotassium hydrogen phosphate and tripotassium phosphate; potassium salts of polyphosphoric acid such as potassium pyrophosphate and potassium metaphosphate; ammonium dihydrogen phosphate, diammonium hydrogen phosphate and phosphoric acid Examples thereof include ammonium salts of phosphoric acid such as triammonium; ammonium salts of polyphosphoric acid such as ammonium pyrophosphate and ammonium metaphosphate. These may be used alone or in combination of two or more. Among the above, sodium dihydrogen phosphate and disodium hydrogen phosphate are preferable.

  The mass ratio of phosphoric acid or phosphoric acid derivative to the cellulose fiber raw material is such that phosphoric acid or phosphoric acid derivative is 0.2 to 500 parts by mass as the amount of phosphorus element with respect to 100 parts by mass of the solid content of the cellulose fiber raw material. Preferably, it is 1-400 mass parts, More preferably, it is 2-200 mass parts. If the ratio of phosphoric acid or a phosphoric acid derivative is more than the said lower limit, the yield of a fine cellulose fiber can be improved more. However, even if the upper limit is exceeded, the effect of improving the yield reaches its peak, and only phosphoric acid or phosphoric acid derivatives are used in vain.

It is preferable that the heat processing temperature is 250 degrees C or less from the point of the thermal decomposition temperature of a cellulose. Moreover, it is preferable that the heat processing temperature is 100-170 degreeC from a viewpoint of suppressing hydrolysis of a cellulose. Furthermore, regarding the heating while water is contained in the system to which phosphoric acid or a phosphoric acid derivative is added during the heat treatment, it is preferably 130 ° C. or less, more preferably 110 ° C. or less to sufficiently absorb moisture. Remove and dry. After that, it is preferable to heat-process at 100-170 degreeC. Further, when removing moisture, a vacuum dryer may be used.
After the treatment with phosphoric acid or a phosphoric acid derivative, the treated cellulose fiber raw material may be subjected to an alkali treatment, similarly to the treatment with ozone.

By the above treatment, the cellulose has phosphoric acid-derived groups (—PO ₄ ²⁻ , —PO ₄ H ⁻ ). Cellulose may have two or more phosphoric acid-derived groups. For example, cellulose may have two types of phosphoric acid derived from different numbers of hydrogen ions.

(Introduction of cationic groups)
As a method for introducing a cationic group into a cellulose fiber raw material, a method using a cationizing agent having a quaternary ammonium group and a group reactive with a hydroxyl group of cellulose is applied.
By reacting the cationizing agent in the presence of an alkali metal hydroxide (such as sodium hydroxide or potassium hydroxide) as a catalyst, the cellulose is cationized and the electric repulsion between the cations is strengthened. Thereby, the bond strength between the cellulose fibers is weakened, and the defibration property is improved.
Specific examples of the cationizing agent include glycidyltrialkylammonium halides such as glycidyltrimethylammonium chloride and 3-chloro-2-hydroxypropyltrimethylammonium chloride or halohydrin type compounds thereof.

Although the usage-amount of a cationizing agent is not restrict | limited in particular, It is preferable that it is 10-1000 mass parts with respect to 100 mass parts of solid content of a cellulose fiber raw material. If the usage-amount of a cationizing agent is more than the said lower limit, the yield improvement effect of the fine cellulose fiber in a refinement | miniaturization process will become higher. However, when the upper limit is exceeded, the yield improvement effect of fine cellulose fibers in the refinement process may reach its peak.
The treatment temperature in the cationizing agent treatment is preferably in the range of 30 to 90 ° C., and the treatment time is preferably 1 to 3 hours.

(Enzyme treatment)
The cellulose fiber raw material used in the present invention does not necessarily have the above polar group or bulky group, but when it does not have the above polar group or bulky group, the cellulose fiber raw material is produced by an enzyme collectively referred to as so-called cellulase. Is preferably processed. Cellulase is an enzyme having cellobiohydrolase activity, endoglucanase activity, and beta-glucosidase activity.
As the enzyme used in the enzyme treatment, an enzyme having the above activity may be mixed and used in an appropriate amount, or a commercially available cellulase preparation may be used.
Commercially available cellulase preparations include Trichoderma, Acremonium, Aspergillus, Phanerochaete, Trametes, Humicola, and Humicola. Cellulase preparations derived from the above.
Commercially available products of such cellulase preparations are all trade names, for example, cellulosin T2 (manufactured by HIPI), mecerase (manufactured by Meiji Seika Co., Ltd.), Novozyme 188 (manufactured by Novozyme), multifect CX10L (manufactured by Genencor) ) And the like.
In addition, many commercially available cellulase preparations have hemicellulase activity as well as various cellulase activities described above.

  In the enzyme treatment, in addition to cellulase, a hemicellulase-based enzyme may be used alone, or a cellulase and a hemicellulase-based enzyme may be used in combination. Among hemicellulase enzymes, it is preferable to use xylanase, which is an enzyme that degrades xylan, mannanase, which is an enzyme that degrades mannan, and arabanase, which is an enzyme that degrades araban. In addition, pectinase, which is an enzyme that degrades pectin, can also be used as a hemicellulase-based enzyme.

The pH of the dispersion during the enzyme treatment is preferably maintained in a range where the activity of the enzyme used is high. For example, in the case of a commercially available enzyme derived from Trichoderma, the pH is preferably between 4-8.
Further, the temperature of the dispersion during the enzyme treatment is preferably maintained within a range in which the activity of the enzyme used is increased. For example, in the case of a commercially available enzyme derived from Trichoderma, the temperature is preferably 40 ° C to 60 ° C. If the temperature is less than the lower limit, the enzyme activity decreases and the treatment time becomes longer. If the temperature exceeds the upper limit, the enzyme may be deactivated. The treatment time for the enzyme treatment is preferably in the range of 10 minutes to 24 hours. If the treatment time of the enzyme treatment is less than 10 minutes, the effect of the enzyme treatment is hardly exhibited. If it exceeds 24 hours, the decomposition of the cellulose fiber is too advanced by the enzyme, and the average fiber length of the resulting fine cellulose fiber may be too short.
It should be noted that when the enzyme remains active for a predetermined time or longer, the decomposition of cellulose proceeds excessively as described above. Therefore, when the predetermined enzyme treatment is completed, it is preferable to perform an enzyme reaction stop process. . The enzyme reaction is stopped by washing the enzyme-treated dispersion with water, removing the enzyme, adding sodium hydroxide to the enzyme-treated dispersion to a pH of about 12, and then adding the enzyme. Examples thereof include a method for inactivation and a method for inactivating the enzyme by raising the temperature of the dispersion treated with the enzyme to a temperature of 90 ° C.

<Washing process>
The washing step is a step of removing chemicals used in the chemical treatment step and decomposition products of the cellulose fiber raw material. Specifically, in the washing step, various washing machines usually used for washing pulp, for example, a filter washing machine, a drum washing machine, a belt washing machine, a diffuser washing machine, a filter press, a screw press, and the like may be used. it can. However, when the cellulose fiber raw material used in the present invention contains at least one of a polar group and a bulky group in an amount of 0.1 to 2.0 mmol / g, water drainage is poor and washing and dehydration are difficult. Therefore, among the above washing machines, press washing machines such as a filter press and a screw press are preferable.
In the washing process using the press washer, the cellulose fiber raw material dispersion containing the chemicals to be washed away and the decomposition product of the cellulose fiber raw material is dehydrated with the press washer, and then the cellulose fiber raw material is diluted with the washing water and pressed again. Repeat the operation of dehydrating with a washing machine to wash.

<Foreign matter removal process>
The foreign matter removing step is a step of subjecting the cellulose fiber raw material dispersion to a foreign matter removing process.
Usually, the cellulose fiber raw material contains various kinds of foreign matters. For example, when wood-derived raw materials are used, bark that should have been peeled off and removed before pulping may be included as foreign matter. In the case where the cellulose fiber raw material is a chemical pulp for papermaking, undigested pieces that are not sufficiently digested and remain in the shape of the original wood raw material may be included as foreign matter. When the cellulose fiber raw material is mechanical pulp, undefibrated fibers that are not sufficiently pulped in the mechanical pulping step may be included as foreign matter. In the case where the cellulose fiber raw material is deinked pulp, an adhesive, vinyl, poly string, hot melt, etc. contained in the used waste paper or the like may be included as foreign matters. Moreover, as a foreign material contained in common with all the raw materials, a stone piece, sand, rust, a metal piece, etc. are mentioned. Usually, the process for producing the cellulose fiber raw material includes a process for removing foreign substances, but it is substantially impossible to completely remove the foreign substances, so that some foreign substances remain more or less.
If these foreign substances are brought into the miniaturization process, wear and damage of the miniaturization apparatus tends to occur and the life of the apparatus tends to be shortened, and the frequency of maintenance must be increased. Moreover, when the foreign material is contained, the foreign material remains in the obtained cellulose fiber, causing deterioration of the appearance and deterioration of various physical properties. In particular, since foreign matters become fracture nuclei, the dispersion and reduction in strength are likely to occur, and when cellulose fibers are used for applications where strength is important, residual foreign matters are not desirable.
However, in the present invention, by having a foreign matter removing step, not only can the abrasion and damage of the miniaturization processing apparatus be prevented, but also the quality and appearance of the resulting cellulose fibers can be kept high.

The foreign matter removing process in the foreign matter removing process may be any process that separates and removes foreign substances from the cellulose fiber raw material. As a foreign substance removal device used for foreign substance removal processing, because of its high foreign substance removal property, a screen that separates foreign substances according to the difference in shape and size from cellulose fibers, and a cleaner that separates foreign substances according to differences in specific gravity from cellulose fibers. preferable. These may be used singly or a plurality of different types may be combined. A plurality of the same devices may be combined.
When combining two foreign substance removal devices, for example, the reject discharged from the first device is supplied to the second device, the second reject is discharged outside the system, and the first unit is accepted. And a multi-stage system for collecting the second accept can be applied. Also, apply a multiple system in which the first reject is discharged outside the system, the accept is supplied to the second, the second reject is also discharged outside the system, and the second accept is recovered. You can also. In addition, a cascade system that collects the first accept, supplies the first reject to the second, returns the second accept to the first, and discharges the second reject outside the system. It can also be applied. The “accept” is discharged from the foreign matter removing apparatus as a collected portion, and the “reject” is discharged as a foreign matter containing portion from the foreign matter removing device.
In any of the above multistage system, multiplex system, and cascade system, it is possible to use three or more foreign substance removing devices.

There are two types of screens, an open-type vibrating screen and a pressure-sealed screen, and either type may be used in the present invention.
The screen is classified according to the shape of the eye hole, and specifically, a round hole screen and a slit screen can be mentioned.
In the present invention, only one of the round hole screen and the slit screen may be used. For example, when there are few large foreign substances in the cellulose fiber raw material, only the slit screen may be used.
In the present invention, both a round hole screen and a slit screen may be used. When both the round hole screen and the slit screen are used, it is preferable to remove the large foreign matter with the round hole screen and then remove the small foreign matter with the slit screen.

  The hole size of the round hole screen is preferably 0.1 to 10 mm, more preferably 1 to 5 mm. The slit size of the slit screen is preferably 0.05 to 2.0 mm, more preferably 0.1 to 0.5 mm, in the short direction. The size of the holes in these screens greatly affects the removal rate of foreign matters. In order to remove even small foreign substances, it is preferable to reduce the size of the hole. However, if the size of the hole is made smaller than the above range, the cellulose fiber raw material is difficult to pass through, and the screen is operated by closing the hole. May be difficult. On the other hand, if the size of the hole is larger than the above range, the cellulose fiber raw material is easy to pass through, so that it is possible to avoid the difficulty of operating the screen, but it is easy to pass through the foreign matter, so the foreign matter removal rate is descend.

There are two types of cleaners, a forward type and a reverse type, and either can be used in the present invention. Usually, the cleaner is provided with a conical container, and the object to be treated (in the present invention, cellulose fiber raw material dispersion) is pumped to the bottom of the conical container, and the object to be treated is rotated along the inner surface in the container. The foreign matter having a specific gravity different from that of the cellulose fiber is removed by utilizing the centrifugal force generated at that time.
The forward type cleaner separates and removes heavy foreign matter that collects at the tip and inner wall of the container, and the reverse type cleaner removes light foreign matter that collects at the bottom and center of the container. These may use only one according to the kind of the foreign material contained in a cellulose fiber raw material, and may use both together.
It is important to set the differential pressure between the inlet pressure and the outlet pressure in both the forward type and reverse type cleaners. That is, the cleaner removes the foreign matter by forcibly applying a centrifugal force to the foreign matter having a specific gravity different from that of the cellulose fiber raw material. Therefore, the higher the inlet pressure and the larger the differential pressure, the stronger the centrifugal force becomes. It becomes easy to separate. However, when the differential pressure is increased, the power consumption of the pressure feed pump that supplies the object to be processed is increased, resulting in an increase in energy cost. Since them, as the differential pressure set value is preferably ^{0.5~10kg / cm 2, 1~5kg / cm} 2 is more preferable.

<Refining process>
The refinement step is a step of obtaining a fine cellulose fiber dispersion containing fine cellulose fibers by subjecting the cellulose fiber raw material dispersion to a fine treatment so as to obtain fine cellulose fibers having an average fiber width of 2 to 50 nm. .
In the refining treatment in the present invention, the cellulose fiber raw material dispersion is subjected to a first refining treatment using a pressure disperser, and then a second refining using a high-speed rotary disperser. It is preferable to carry out a miniaturization treatment. Such a miniaturization process can be sufficiently miniaturized while suppressing energy consumption required for the miniaturization.

The pressure disperser used in the first refinement process is a homogenizer including a homovalve and a homovalve seat. In miniaturization using a homogenizer, a homovalve and a homovalve seat are arranged so that a narrow gap is formed between them, and the cellulose fiber raw material dispersion is supplied to the gap at a high pressure and then discharged from the gap. To release the pressure to near atmospheric pressure. Thereby, a strong shearing force is applied to the cellulose fiber raw material dispersion to refine the cellulose fiber raw material.
Specific examples of the homogenizer include a high pressure homogenizer, an intermediate pressure homogenizer, and an ultrahigh pressure homogenizer.

  The supply pressure (gauge pressure) of the cellulose fiber raw material dispersion to the pressure disperser is preferably 50 to 250 MPa, more preferably 60 to 180 MPa, and still more preferably 70 to 150 MPa. If the supply pressure of the cellulose fiber raw material dispersion to the pressure disperser is equal to or higher than the lower limit value, the cellulose fiber raw material can be sufficiently refined, and if it is equal to or lower than the upper limit value, energy consumption can be further suppressed. .

The high-speed rotary disperser used in the second miniaturization treatment is provided with a rotor provided with stirring blades and a screen arranged outside the stirring blades. In this high-speed rotary disperser, the cellulose fiber raw material dispersion is rotated at high speed with a stirring blade to form a discharge flow of the cellulose fiber raw material dispersion, and the discharge flow is passed through a screen by rotating the rotor. A strong shearing force is applied to the fiber material. Thereby, a cellulose fiber raw material is refined | miniaturized.
As the type of the stirring blade, a paddle blade, a turbine blade, a propeller blade, or the like can be used.
The shape of the eye holes of the screen may be circular or slit. When the shape of the screen hole is circular, the hole diameter is preferably 0.05 to 5 mm, and when the shape of the screen hole is slit, the opening width in the short direction is 0. 0 mm. It is preferable that it is 05-5 mm. If the hole diameter or the opening width in the lateral direction is within the above range, it can be sufficiently miniaturized.
There is no restriction | limiting in particular as a shape of a screen, For example, it may be conical shape which can accommodate a stirring blade, and cylindrical shape which can insert a stirring blade may be sufficient.
The rotational peripheral speed of the rotor is preferably 20 to 60 m / second, more preferably 25 to 50 m / second, and further preferably 30 to 40 m / second. Here, the rotational peripheral speed of the rotor is the peripheral speed of the outermost part of the stirring blade. If the rotational peripheral speed of the rotor is equal to or higher than the lower limit value, it can be sufficiently fined, and if it is equal to or lower than the upper limit value, excessive energy consumption can be further prevented.
The gap between the outermost part of the stirring blade and the screen is preferably 0.05 to 1 mm, and more preferably 0.1 to 0.6 mm. If the gap between the outermost part of the stirring blade and the screen is equal to or greater than the lower limit value, the stirring blade and the screen can be easily arranged, and if the gap is equal to or smaller than the upper limit value, the size can be sufficiently reduced.

It is preferable that the solid content concentration of the cellulose fiber raw material dispersion supplied to the micronization treatment is 0.1 to 20% by mass, and more preferably 0.5 to 10% by mass. If the solid content concentration of the cellulose fiber raw material dispersion is equal to or higher than the lower limit, the efficiency of the refining treatment is improved, and if it is equal to or lower than the upper limit, blockage in the refining treatment apparatus can be prevented.
Examples of the dispersion medium for dilution include water, an organic solvent, and a mixture of water and an organic solvent.

In the micronization step, the cellulose fiber raw material dispersion is subjected to a rotary blade and a fixed blade or a rotary blade arranged outside the rotary blade, such as a refiner, beater, and PFI mill, before the first micronization process. You may refine | miniaturize by the provided beating machine.
Further, in the miniaturization step, the miniaturization process may be performed by a disperser other than the pressure disperser, the high-speed rotary disperser, and the beater. Examples of other dispersers include a grinder, a collision grinder, a ball mill, a bead mill, a vibration mill, an ultrasonic disperser, and a twin screw extruder. Miniaturization by another disperser may be performed at any point in the miniaturization process.

<Purification process>
A refinement | purification process is a process of refine | purifying a fine cellulose fiber dispersion liquid after a refinement | miniaturization process. Specifically, in the refining process in the present invention, the fine cellulose fiber dispersion is subjected to the first refining process and then the second refining process. In this purification step, coarse fibers remaining without being refined and fibers that have not been sufficiently refined are removed, and the average fiber width of the fine cellulose fibers is preferably 2 to 50 nm, more preferably 2 to 30 nm. To be purified.

The first purification process is at least one of a process of filtering the fine cellulose fiber dispersion with a screen and a process of centrifuging.
The centrifugal force in the case of applying centrifugation in the first purification treatment is 1000 to 5000 G, and preferably 2000 to 4000 G. If the centrifugal force in the first purification treatment is less than the lower limit, purification becomes difficult, and if it exceeds the upper limit, energy consumption required for purification becomes excessively large.
In the centrifugation in the first purification treatment, a decanter is preferably used in that the centrifugal force can be easily within the above range. A centrifuge can also be used.
After centrifugation, the supernatant is recovered and subjected to a second purification process.

When filtration by a screen is applied in the first purification treatment, a screen having an opening of 20 μm or less, preferably 15 μm or less is used. When the mesh of the screen exceeds the upper limit, it becomes difficult to obtain fine cellulose fibers having a small average fiber width.
On the other hand, the opening of the screen is preferably 0.01 μm or more, and more preferably 0.1 μm or more. If the opening of the screen is less than the lower limit, it may be clogged and filtration may be difficult.
Except for the mesh opening, the same screen as that used in the foreign matter removing step can be used as the screen. However, in terms of easy opening to the mesh, a wire mesh, a filter medium in which yarns are densely packed, and the like are preferable. .

The second purification process is a process of further centrifuging the fine cellulose fiber dispersion subjected to the first purification process. After centrifugation, the supernatant is collected.
The centrifugal force in the second purification treatment is 10,000 to 20000 G, and preferably 10,000 to 15000 G. When the centrifugal force in the second refining treatment is less than the lower limit value, it becomes difficult to obtain fine cellulose fibers having a small average fiber width, and when the upper limit value is exceeded, the energy consumption required for refining is excessively increased.
In the centrifuge in the second purification treatment, a centrifuge is preferably used in that the centrifugal force can be easily within the above range.

Further, in the purification step, a purification process other than the first purification process and the second purification process may be performed at an arbitrary time.
As other purification treatments, centrifugal treatment under centrifugal conditions other than the first purification treatment and the second purification treatment, filtration treatment using a screen having an opening of more than 20 μm and less than 100 μm, purification treatment using a cleaner, For example, a flotation separation using a difference in specific gravity using a floatator or a pressurized flotation device may be mentioned.
A centrifuge can be used for centrifugation in other purification processes. When the centrifugal force is low (less than 1000 G), a decanter can be used.
As the screen, the same screen as that used in the first purification treatment can be used except for the mesh. If the aperture of the screen used in other purification processes is 20 μm or less, the first purification process overlaps, and if it is 100 μm or more, the intended purification may be difficult.
As the cleaner, the same cleaner as that used in the foreign matter removing step can be used, but a forward type cleaner is preferred. The forward type cleaner is used for separating and removing a large specific gravity, and is suitable for separating and removing a large cellulose fiber.

  The fine cellulose fiber dispersion to be purified is preferably adjusted in advance so that the solid content concentration of the fine cellulose fiber is 0.01 to 10% by mass, and the concentration is adjusted to be 0.1 to 5% by mass. More preferably. If the solid content concentration of the fine cellulose fiber dispersion is equal to or higher than the lower limit value, purification treatment is facilitated. If the solid content concentration is equal to or lower than the upper limit value, blockage in the apparatus for purification treatment can be prevented.

<Concentration process>
When transporting or storing the fine cellulose fiber dispersion obtained by the purification process without immediately using it, it has a concentration process for concentrating the fine cellulose fiber dispersion to reduce transportation costs and storage costs. It is preferable to obtain a fine cellulose fiber-containing material. As will be described later, the fine cellulose fiber-containing material is re-dispersed in the dispersion medium after completion of transportation or storage.
Examples of the concentration method in the concentration step include a method having an aggregation step and a filtration step (hereinafter referred to as “first concentration method”) and a method having a heating step (hereinafter referred to as “second concentration method”). It is done. The 1st concentration method is preferable at the point from which the fine cellulose fiber containing material with high redispersibility is obtained easily.
The fine cellulose fiber dispersion used in the concentration step preferably has a fine cellulose fiber content of less than 6% by mass and more preferably 3.0% by mass or less from the viewpoint of dispersion stability. The fine cellulose fiber content of the fine cellulose fiber dispersion to be subjected to the concentration step is preferably 0.2% by mass or more and 0.5% by mass or more from the viewpoint of productivity of the fine cellulose fiber-containing product. More preferably.
Moreover, in a concentration process, it is preferable to make content of the fine cellulose fiber in the fine cellulose fiber containing material obtained into 6-80 mass%, It is more preferable to set it as 10-50 mass%, It is 12-30 mass% More preferably. If the content of the fine cellulose fiber after concentration is not less than the above lower limit value, the transportation cost and the storage cost can be further reduced, and if it is not more than the above upper limit value, the fine cellulose fiber-containing material can be produced easily and in a short time. .

(First concentration method)
The aggregation step in the first concentration method is a step of aggregating the fine cellulose fibers contained in the fine cellulose fiber dispersion.
Examples of the method for aggregating the fine cellulose fibers include a method of adding at least one of an aggregating agent containing a polyvalent metal salt and an acid to the fine cellulose fiber dispersion when the surface charge of the fine cellulose fibers is negative. It is done. When the surface charge of the fine cellulose fiber is positive, a method of adding at least one of a flocculant containing a polyvalent metal salt and an alkali to the fine cellulose fiber dispersion may be mentioned.

When the flocculant is added, the addition amount is preferably 0.5 to 300 parts by mass, more preferably 1.0 to 50 parts by mass with respect to 100 parts by mass of the solid content of the fine cellulose fiber. More preferably, it is 2-30 mass parts. If the amount of the flocculant added is equal to or greater than the lower limit, the fine cellulose fibers can be easily aggregated. However, adding more than the above upper limit is useless because the cohesion is hardly improved.
When adding an acid, it is preferable to make pH of the fine cellulose fiber containing material obtained into 4.0 or less, and it is more preferable to set it as 3.0 or less. When an acid is added so that the pH is not more than the above upper limit, negatively charged fine cellulose fibers can be easily aggregated, the filtration time can be shortened, and a fine cellulose fiber-containing material can be obtained in a short time. However, when the amount of the acid added is small and the pH exceeds the upper limit, the aggregation of the negatively charged fine cellulose fibers is weak and it is difficult to remove the dispersion medium during filtration in the next step.
When adding an alkali, it is preferable to make pH of a fine cellulose fiber containing material 10.0 or more, and it is more preferable to make it 12.0 or more. When alkali is added so that the pH is equal to or higher than the lower limit, positively charged fine cellulose fibers can be easily aggregated, the filtration time can be shortened, and a fine cellulose fiber-containing material can be obtained in a short time. However, when the amount of alkali added is small and the pH is less than the lower limit, the aggregation of the positively charged fine cellulose fibers is weak and it is difficult to remove the dispersion medium during filtration in the next step.

The filtration step in the first concentration method is a step of removing the dispersion medium by filtering the fine cellulose fiber dispersion after the aggregation step.
As a filtration method in the filtration step, a known filtration method using a filter medium such as filter paper, filter cloth, or resin filter can be applied.
The opening diameter of the filter medium is preferably 100 to 3000 nm, and more preferably 200 to 1000 nm, from the viewpoint of the separation property of the dispersion medium and the filtration time.

(Second concentration method)
The heating step in the second concentration method is a step of heating the fine cellulose fiber dispersion to volatilize and remove the dispersion medium.
As a heating method, a container with an open top is filled with a fine cellulose fiber dispersion, the container is heated, a bowl with an open top is heated, and a fine cellulose fiber dispersion is poured into the bowl, The method etc. which heat a fine cellulose fiber dispersion directly are mentioned.
The heating temperature is preferably 40 to 120 ° C, more preferably 60 to 105 ° C. If the heating temperature is at least the lower limit, the dispersion medium can be volatilized quickly, and if it is not more than the upper limit, the cost required for heating and the decomposition of cellulose due to heat can be suppressed.

<Redispersion process>
The fine cellulose fiber-containing material obtained by the concentration step is returned to the fine cellulose fiber dispersion by the redispersion step. Specifically, in the redispersion step, a dispersion medium is added to the fine cellulose fiber-containing material to prepare a fine cellulose fiber-containing liquid, and the fine cellulose fiber-containing liquid is subjected to a dispersion treatment to obtain a fine cellulose fiber dispersion. Remanufacture.
In the redispersion step, the fine cellulose fiber content of the fine cellulose fiber dispersion is preferably 0.1 to 10% by mass, and more preferably 0.2 to 3% by mass. If the fine cellulose fiber content of the fine cellulose fiber dispersion is not less than the lower limit, the dispersion stability of the fine cellulose fibers will be high, and if it is not more than the upper limit, the viscosity of the fine cellulose fibers will not be too high, Handling becomes relatively easy.
The fine cellulose fiber content of the fine cellulose fiber dispersion can be adjusted by the addition amount of the dispersion medium. The more the addition amount of the dispersion medium, the lower the fine cellulose fiber content.

  Further, in the redispersion step, redispersibility becomes higher. Therefore, when the surface charge of the fine cellulose fibers is negative, it is preferable to add an alkali to the fine cellulose fiber-containing liquid. When the surface charge of the fine cellulose fiber is positive, it is preferable to add an acid. The alkali added in the redispersion step is the same as the alkali used in the alkali treatment in the concentration step. The acid is the same as the acid used in the concentration step.

  When the surface charge of the fine cellulose fibers is negative, the pH (23 ° C.) of the fine cellulose fiber-containing liquid is preferably 7 or more, more preferably 9 or more, by addition of alkali, more preferably 11 or more. More preferably. If the pH of the fine cellulose fiber-containing liquid is set to the above lower limit or more, the redispersibility of the fine cellulose fibers becomes higher. When the surface charge of the fine cellulose fibers is positive, it is preferable to adjust the pH (23 ° C.) of the fine cellulose fiber-containing liquid within the range of 4 to 7 by adding an acid. If it is in the said range, the redispersibility of a fine cellulose fiber will become higher.

As a dispersion apparatus used for the dispersion process, for example, the same apparatus as the refinement process apparatus used in the above-described refinement process can be used. One type of miniaturization processing apparatus may be used alone, or two or more types may be used in combination. When two or more kinds of the dispersing devices are used in combination, one by one may be used in sequence or at the same time.
It is preferable to use an ultrasonic disperser as a dispersing device in that the fine cellulose fibers can be easily redispersed even in a fine cellulose fiber-containing liquid having a high content of fine cellulose fibers.

  In the redispersion step, the average fiber width B of the fine cellulose fibers contained in the remanufactured fine cellulose fiber dispersion and the average fiber width A of the fine cellulose fibers contained in the fine cellulose fiber dispersion subjected to the concentration step Dispersion treatment conditions, alkali or acid addition conditions are selected so that the ratio (B / A) is preferably 0.5 to 2.0, more preferably 0.5 to 1.0. If B / A is within the above range, the average fiber width of the fine cellulose fibers contained in the regenerated fine cellulose fiber dispersion is the fiber width of the fine cellulose fibers contained in the fine cellulose fiber dispersion subjected to the concentration step. It is almost the same as or thinner. Therefore, the fine cellulose fibers contained in the re-produced fine cellulose fiber dispersion have the characteristics as the original fine cellulose fibers (high strength, high rigidity, high dimensional stability, high dispersibility when combined with resin, transparent Easy to obtain).

<Effect>
In this invention, since a fine cellulose fiber dispersion liquid is refine | purified by a refinement | purification process and a coarse fiber is removed, the external appearance of a fine cellulose fiber can be made favorable and a physical property can be improved. In a composite material in which fine cellulose fibers are blended with resin, rubber or the like, coarse fibers are likely to be the starting point of destruction. For this reason, by removing coarse fibers by the refining step, the starting point of destruction is reduced, so that a decrease in strength and variation of the composite material can be prevented.
In addition, when the present inventors investigated, it was not possible to sufficiently purify by the process of filtering with a screen having a pore diameter of 20 μm or less or the first purification process of centrifuging at a centrifugal force of 1000 to 5000 G, but the energy consumption was small. It was. On the other hand, in the 2nd refinement | purification process centrifuged by the centrifugal force 10000-20000G, although it can fully refine | purify, the energy consumption increased.
In the present invention, fine cellulose fibers can be smoothly refined because they are coarsely refined by the first refining process with low energy consumption and then refined by the second refining process. Therefore, the fiber width of the obtained fine cellulose fiber can be sufficiently reduced while suppressing the energy consumption required for purification.

  Examples of the present invention will be described below, but the present invention is not limited to the following examples.

<Example 1>
(Chemical treatment process)
As a cellulose fiber raw material, 20 g of hardwood bleached kraft pulp (LBKP) having a carboxy group content of 0.06 mmol / g, a solid content concentration of 30% by mass (water content of 70% by mass), and an absolute dry mass conversion was prepared. The LBKP was placed in a container, and 30 L of an ozone / oxygen mixed gas having an ozone concentration of 200 g / m ³ was introduced into the container and shaken at 25 ° C. for 2 minutes. The ozone addition rate at this time was 30 mass% with respect to the pulp dry mass. After standing for 6 hours, ozone and air in the container were removed, and the ozone oxidation treatment was completed. After the treatment, the operation of suspending in ion-exchanged water, dehydrating at a pressure of 0.5 kg / cm ² using a pressure filtration device, and suspending again in ion-exchanged water and dehydrating is performed. Was repeated until 6 or more, and an ozone-oxidized pulp having a solid content concentration of 20% by mass was obtained. This operation was repeated 10 times, and they were mixed to obtain 200 g of ozone-oxidized pulp in terms of absolute dry mass.
Next, 1000 g of ozone-oxidized pulp (200 g in terms of absolute dry mass), 2000 g of 0.3 mass% sodium chlorite aqueous solution adjusted to pH 4 to 5 with hydrochloric acid (relative to the absolute dry mass of cellulose fibers) , Equivalent to 3% by mass as sodium chlorite) and reacted at 70 ° C. for 3 hours for additional oxidation treatment. After completion of the post-oxidation treatment, the operation of suspending in ion exchange water, dehydrating with a pressure filtration device, suspending again in ion exchange water and dehydrating is repeated until the pH of the washing water reaches 6 or higher. A treated pulp was obtained.
Ion exchange water was added to the oxidized pulp (200 g in terms of absolute dry mass) to prepare a dispersion having a solid content concentration of 2% by mass. Sodium hydroxide was added to this dispersion so that the sodium hydroxide concentration was 0.3% by mass, and the mixture was stirred for 5 minutes and then allowed to stand at room temperature for 30 minutes. After the treatment is completed, the suspension is suspended in ion-exchanged water, dehydrated with a pressure filtration device, suspended in ion-exchanged water and dehydrated again until the pH of the washing water reaches 6 or higher. A dispersion containing was obtained.

(Foreign substance removal process)
Next, the dispersion liquid containing the alkali-treated pulp was put into a test flat screen manufactured by Kumagai Riki Kogyo Co., Ltd., which is an open vibration type screen. As the screen, a screen having a slit-type eye with a slit width of 0.25 mm was used.
Next, the dispersion liquid that passed through the screen was collected and dehydrated with a pressure filtration device to obtain a dispersion liquid that had been subjected to foreign matter removal treatment.

(Miniaturization process)
Subsequently, ion-exchange water was added to the dispersion liquid containing the alkali-treated pulp which performed the foreign material removal process, and the cellulose fiber raw material dispersion liquid with a cellulose fiber density | concentration of 1.0 mass% was prepared. From this cellulose fiber raw material dispersion, 500 g (5 g in terms of absolute dry mass) was taken out and subjected to a 120 MPa × 1 pass treatment with a high-pressure homogenizer (“Panda Plus 2000” manufactured by NiroSoavi). By repeating this operation 20 times and mixing them, 10000 g (100 g in terms of absolute dry mass) of a dispersion subjected to 120 MPa × 1 pass treatment was obtained. Next, the dispersion was used for 1 minute under the conditions of a rotor rotational speed of 21,500 rpm and a rotor rotational peripheral speed of 34 m / second using a high-speed rotary disperser (CL Technique-2.2S manufactured by M Technique Co., Ltd.). The fine cellulose fiber dispersion liquid was obtained by refinement treatment.

(Purification process)
After adding ion-exchanged water to the obtained fine cellulose fiber dispersion to adjust the cellulose concentration to 0.5% by mass, the concentration-adjusted 2400 ml dispersion is centrifuged (centrifugated) at a centrifugal force of 3,000 G for 1 minute. Machine: “H-2000B” manufactured by Kokusan Co., Ltd.). The supernatant thus obtained was recovered, and the supernatant was centrifuged at a centrifugal force of 12,000 G for 1 minute using the same centrifuge to recover the supernatant.

<Example 2>
In the purification step, instead of centrifuging for 1 minute at a centrifugal force of 3,000 G, the same procedure as in Example 1 was conducted except that a fine cellulose fiber dispersion having a cellulose concentration of 0.5 mass% was filtered using a screen having a pore diameter of 10 μm. A supernatant was obtained.

<Example 3>
(Chemical treatment process)
1.69 g of sodium dihydrogen phosphate dihydrate and 1.21 g of disodium hydrogen phosphate are dissolved in 3.39 g of water to obtain an aqueous solution of a phosphoric acid compound (hereinafter referred to as “phosphorylation reagent”). It was. The pH of this phosphorylating reagent was 6.0 at 25 ° C.
LBKP similar to that used in Example 1 was diluted with ion-exchanged water so that the water content was 80% by mass to obtain a cellulose fiber raw material dispersion. To 200 g of this cellulose fiber raw material dispersion, 83.9 g of the phosphorylating reagent (20 parts by mass as the amount of phosphorus element with respect to 100 parts by mass of dried pulp) is added, and the mixture is 15 by a blow dryer (Yamato Scientific Co., Ltd. DKM400) at 105 ° C. It was dried until the mass became constant while kneading once a minute. Subsequently, it heat-processed with the 150 degreeC ventilation drying machine for 1 hour, and introduce | transduced the phosphate group into the cellulose.
Next, 4000 ml of ion-exchanged water was added to the cellulose into which phosphate groups had been introduced, and the mixture was stirred and dehydrated using a pressure filtration device. This operation was repeated three times. The dehydrated pulp was diluted with 4000 ml of ion-exchanged water, and 70 ml of 1N sodium hydroxide aqueous solution was added little by little with stirring to obtain an alkali-treated pulp dispersion having a pH of 12 to 13. Thereafter, the operation of dehydrating this alkali-treated pulp dispersion with a pressure filtration device, adding ion-exchanged water again and dehydrating with a pressure filtration device is repeated until the pH of the washing liquid becomes 7 or less, and the cellulose fiber raw material A dispersion was obtained.

(Foreign substance removal process, refinement process, purification process)
The supernatant of the fine cellulose fiber dispersion was obtained in the same manner as in Example 1, except for the foreign matter removing step, the finening step, and the purification step.

<Example 4>
(Chemical treatment process)
The same LBKP as used in Example 1 was dried at 105 ° C. for 3 hours to obtain a dry pulp having a moisture content of 3% by mass or less. Next, 200 g of the dried pulp and 200 g of maleic anhydride (100 parts by mass with respect to 100 parts by mass of the dried pulp) were filled in an autoclave and treated at 150 ° C. for 2 hours. Next, 4000 g of ion-exchanged water was added to the pulp treated with maleic anhydride and dehydrated using a pressure filtration device. This operation was repeated three times. The dehydrated pulp was dispersed in 4000 ml of ion exchange water to obtain a maleic anhydride treated pulp dispersion.
Next, while stirring the maleic anhydride-treated pulp dispersion, 500 mL of 4N sodium hydroxide aqueous solution was added little by little to adjust the pH to 12-13, and the pulp was alkali-treated. Thereafter, the pulp after the alkali treatment was washed using a pressure filtration device until the pH became 8 or less to obtain a cellulose fiber raw material dispersion.

(Foreign substance removal process, refinement process, purification process)
The supernatant of the fine cellulose fiber dispersion was obtained in the same manner as in Example 1, except for the foreign matter removing step, the finening step, and the purification step.

<Example 5>
(Chemical treatment process)
200 g of LBKP similar to that used in Example 1 was prepared in terms of absolute dry mass. This was dispersed in 17000 ml of ion-exchanged water in which 20 g of sodium bromide, 3.2 g of TEMPO catalyst (2,2,6,6-tetramethylpiperidine-1-oxy radical) was dissolved. 580 ml of 64.5 g / L sodium hypochlorite aqueous solution was adjusted to pH 10 with 0.1 M hydrochloric acid, and this was added to LBKP dispersed in ion-exchanged water containing a TEMPO catalyst to initiate the reaction. . The reaction was performed at room temperature. During the reaction, the pH decreased, but the pH was maintained at 10 while adding a 20 g / L aqueous sodium hydroxide solution as needed. After 4 hours from the start of the reaction, the pH was not lowered, so the reaction was terminated at this point. After completion of the reaction, the operation of suspending in ion exchange water, dehydrating with a pressure filtration device, adding ion exchange water again and dehydrating with a pressure filtration device was repeated until the pH of the washing solution became 7 or less. Thereby, TEMPO oxidized pulp was obtained.
180 g of sodium chlorite, 600 g of acetic acid, and 7000 ml of ion-exchanged water were added to the TEMPO oxidized pulp, and the pH was adjusted to 4.5 with a 20 g / L aqueous sodium hydroxide solution. The reaction was held for 48 hours at room temperature. After completion of the reaction, suspend in ion-exchanged water, dehydrate in a pressure filtration device, repeat the operation of adding ion-exchanged water again and dehydrating in a pressure filtration device until the pH of the cleaning solution becomes 6 or more, A cellulose fiber raw material dispersion was obtained.

(Foreign substance removal process, refinement process, purification process)
The supernatant of the fine cellulose fiber dispersion was obtained in the same manner as in Example 1, except for the foreign matter removing step, the finening step, and the purification step.

<Example 6>
(Chemical treatment process)
200 g of LBKP similar to that used in Example 1 was prepared in terms of absolute dry mass. The LBKP was diluted with ion-exchanged water to a concentration of 3% by mass, adjusted to pH 6 with 0.1% by mass sulfuric acid, and warmed in a water bath until 50 ° C. was reached. Next, the enzyme optimase CX7L (manufactured by Genencor) was added to the liquid containing warm LBKP by 3% by mass with respect to the pulp (in terms of solid content), and reacted with stirring at 50 ° C. for 1 hour to perform the enzyme treatment. . Then, it heated at 95 degreeC or more for 20 minutes, the enzyme was deactivated, and the enzyme treatment dispersion liquid was obtained. The enzyme-treated dispersion is repeatedly suspended in ion-exchanged water and dehydrated with a pressure filtration device until the conductivity at a cellulose content of 1% by mass is 10 μS / cm or less, and the cellulose fiber raw material dispersion Got.

(Foreign substance removal process, refinement process, purification process)
The supernatant of the fine cellulose fiber dispersion was obtained in the same manner as in Example 1, except for the foreign matter removing step, the finening step, and the purification step.

<Example 7>
(Chemical treatment process)
LBKP similar to that used in Example 1 was beaten with a Niagara beater (capacity: 23 liters, manufactured by Tozai Seiki Co., Ltd.) for 200 minutes to obtain a pulp dispersion (pulp concentration: 2% by mass). The obtained pulp dispersion was drained with a centrifugal dehydrator (manufactured by Kokusan Co., Ltd.) under the conditions of 12000 rpm and 15 minutes, and the pulp concentration was concentrated to 25% by mass. Next, in a stirrer (manufactured by IKA) whose rotation speed is adjusted to 800 rpm, the concentrated dispersion is 60 parts by mass by dry mass, 7 parts by mass of sodium hydroxide, 2352 parts by mass of isopropyl alcohol (IPA), 588 parts by mass of water was charged. Subsequently, after mixing and stirring at 30 ° C. for 30 minutes, the temperature was raised to 80 ° C., and 120 parts by mass of glycidyltrimethylammonium chloride as a cationizing agent was added in terms of effective amount. And after making it react for 1 hour, the reaction material was taken out, neutralized, wash | cleaned, and concentrated, and the cellulose fiber raw material dispersion liquid containing the cationized pulp of a 25 mass% density | concentration was obtained.

(Foreign substance removal process, refinement process, purification process)
The supernatant of the fine cellulose fiber dispersion was obtained in the same manner as in Example 1, except for the foreign matter removing step, the finening step, and the purification step.

<Comparative Example 1>
In the purification step, a supernatant of a fine cellulose fiber dispersion was obtained in the same manner as in Example 1 except that centrifugation at 12,000 G for 1 minute was omitted.

<Comparative example 2>
In the purification step, a supernatant of a fine cellulose fiber dispersion was obtained in the same manner as in Example 2 except that the centrifugation at 12,000 G for 1 minute was omitted.

<Comparative Example 3>
In the purification step, a supernatant of a fine cellulose fiber dispersion was obtained in the same manner as in Example 1 except that the centrifugation at 3,000 G for 1 minute was omitted.

<Comparative example 4>
In the purification step, the supernatant of the fine cellulose fiber dispersion was obtained in the same manner as in Example 1 except that the centrifugation at 12,000 G for 1 minute was omitted and the centrifugation at 3,000 G for 1 minute was made 10 minutes. Obtained.

<Comparative Example 5>
In the purification step, the supernatant of the fine cellulose fiber dispersion was obtained in the same manner as in Example 1 except that the centrifugation at 3,000 G for 1 minute was omitted and the centrifugation at 12,000 G for 1 minute was made 10 minutes. Obtained.

<Comparative Example 6>
Example 1 except that in the purification step, instead of centrifuging at 3,000 G for 1 minute and then at 12,000 G for 1 minute, centrifuging at 1,000 G for 1 minute and then centrifuging at 3,000 G for 1 minute In the same manner as above, a supernatant of a fine cellulose fiber dispersion was obtained.

<Comparative Example 7>
In the purification step, the order of centrifugation at 3,000 G for 1 minute and that at 12,000 G for 1 minute were changed, and the mixture was centrifuged at 12,000 G for 1 minute and then centrifuged at 3,000 G for 1 minute. In the same manner as in Example 1, a supernatant of a fine cellulose fiber dispersion was obtained.

(Evaluation)
The average fiber width of fine cellulose fibers contained in the supernatant was measured by the method described in paragraph 0009 above. The measurement results are shown in Table 1.
In addition, only when the average fiber width of the obtained fine cellulose fibers is 50 μm or less, the basic unit of electric power required to produce 1 kg of fine cellulose fibers in the purification process is determined by the amount of fine cellulose fibers and the consumption of the centrifuge. Obtained from the amount of electric power. The results are shown in Table 1. In addition, “-” in the column of the power consumption unit in Table 1 means that it has not been measured.

In Examples 1 to 7, which were subjected to 12000 G centrifugation after 3000 G centrifugation in the purification step, the average fiber width of the fine cellulose fibers could be sufficiently reduced, and the power consumption required for purification was small.
In Comparative Example 1 in which the 12000 G centrifugation was not performed after the 3000 G centrifugation in the purification step, the average fiber width of the fine cellulose fibers could not be sufficiently reduced.
In Comparative Example 2 in which 12000 G centrifugation was not performed after filtration through a screen in the purification process, the average fiber width of the fine cellulose fibers could not be sufficiently reduced.
In Comparative Example 3 in which the 12000 G centrifugation was performed without performing the 3000 G centrifugation in the purification step, the average fiber width of the fine cellulose fibers could not be sufficiently reduced.
In Comparative Example 4 in which centrifugation at 3000 G was performed only for 10 minutes in the purification step, the average fiber width of the fine cellulose fibers could not be sufficiently reduced.
In Comparative Example 5, in which the 12,000 G centrifugation was performed for 10 minutes in the purification step, the average fiber width of the fine cellulose fibers could be sufficiently reduced, but the power consumption required for purification was large.
In Comparative Example 6, in which the centrifugal separation of 3000 G was performed after the centrifugal separation of 1000 G in the purification process, the average fiber width of the fine cellulose fibers could not be sufficiently reduced.
In Comparative Example 7 in which the 12000G centrifugation was performed before the 3000G centrifugation, the average fiber width of the fine cellulose fibers could not be sufficiently reduced.

Claims (1)

A refinement step for obtaining a fine cellulose fiber dispersion by subjecting the cellulose fiber raw material dispersion containing cellulose fibers to a refinement treatment so that the average fiber width of the cellulose fibers is 2 to 50 nm, and the fine cellulose fiber dispersion A purification step of performing a second purification treatment after the first purification treatment,
The first purification process is at least one of a process of filtering the fine cellulose fiber dispersion with a screen having an opening of 20 μm or less, and a process of centrifuging with a centrifugal force of 1000 to 5000 G.
The second purification treatment is a method for producing fine cellulose fibers, which is a treatment of centrifuging the fine cellulose fiber dispersion subjected to the first purification treatment with a centrifugal force of 10,000 to 20,000 G.