Method for producing ultra-fine fibrous cellulose

Abstract

To provide a method for manufacturing ultra-fine fibrous cellulose in which changes in quality during the dehydration and washing processes are suppressed.SOLUTION: A method for manufacturing ultra-fine fibrous cellulose includes, in sequence, a reaction step of chemically modifying cellulose fibers to obtain chemically modified cellulose, a dehydration and washing step of dehydrating and washing a dispersion of the chemically modified cellulose, an adjustment step of adjusting the concentration of the dispersion of the chemically modified cellulose, and a fibrillation step of fibrillating the dispersion of the chemically modified cellulose by applying mechanical shear force, in which in the dehydration and washing step, the transfer of the dispersion of the chemically modified cellulose is performed without using a pump.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a method for producing microfibrillar cellulose.

Background Art

[0002] Microfibrillar cellulose obtained by defibrating cellulose fibers to a fiber width of 1000 nm or less is excellent in strength, elasticity, thermal stability, etc., and is used in industrial applications as a filler for blending with resins and rubbers. Further, an aqueous dispersion of microfibrillar cellulose is used as a viscosity modifier, a stabilizer, and the like. Microfibrillar cellulose can be obtained by defibrating pulp fibers by mechanical treatment. At that time, it is said that by introducing an ionic group into the pulp fibers and then defibrating them, the energy required for mechanical treatment can be efficiently reduced (see Patent Documents 1 and 2).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the production of microfibrillar cellulose conventionally, including the production methods described in Patent Documents 1 and 2, unexpected quality changes may occur, such as chemical modification of cellulose or changes in the water retention of microfibrillar cellulose. Therefore, an object of the present invention is to provide a method for producing microfibrillar cellulose in which quality changes in the dehydration / washing step are suppressed.

Means for Solving the Problems

[0005] The inventors of the present invention have found that by transferring the dispersion of chemically modified cellulose without using a pump in the dehydration / washing step, changes in quality in the dehydration / washing step are suppressed, and thus the present invention has been completed. The present invention relates to the following [1] to [6]. [1] A method for producing microfibrillar cellulose, which comprises a reaction step of chemically modifying cellulose fibers to obtain chemically modified cellulose, a dehydration / washing step of dehydrating and washing the dispersion of the chemically modified cellulose, an adjustment step of adjusting the dispersion concentration of the chemically modified cellulose, and a defibrillation step of applying mechanical shear force to the dispersion of the chemically modified cellulose to defibrillate it, in this order. In the dehydration / washing step, the dispersion of the chemically modified cellulose is transferred without using a pump. [2] The method for producing microfibrillar cellulose according to [1], wherein in the dehydration / washing step, the dispersion of the chemically modified cellulose is transferred using gravity without using a pump. [3] The method for producing microfibrillar cellulose according to [1] or [2], wherein the water retention capacity of the chemically modified cellulose transferred in the dehydration / washing step is 10 g / g or more and 25 g / g or less. [4] The method for producing microfibrillar cellulose according to any one of [1] to [3], wherein the reaction step is a step of introducing an ionic group into cellulose fibers. [5] The method for producing microfibrillar cellulose according to [4], wherein the ionic group is an anionic group. [6] The method for producing microfibrillar cellulose according to [5], wherein the anionic group is at least one selected from the group consisting of a phosphoxo acid group, a sulfur oxo acid group, and a carboxy group. [Advantages of the Invention]

[0006] According to the present invention, there is provided a method for producing microfibrillar cellulose in which changes in quality in the dehydration / washing step are suppressed. [Brief Description of the Drawings]

[0007]

Figure 1

Figure 2

[0008] [Method for Producing Microfibrillated Cellulose] The method for producing microfibrillated cellulose according to the present embodiment includes, in this order, a reaction step of chemically modifying cellulose fibers to obtain chemically modified cellulose, a dehydration / washing step of dehydrating and washing the dispersion of the chemically modified cellulose, an adjustment step of adjusting the concentration of the dispersion of the chemically modified cellulose, and a fibrillation step of applying mechanical shear force to the dispersion of the chemically modified cellulose to defibrillate it. In the dehydration / washing step, the dispersion of the chemically modified cellulose is transferred without using a pump. According to the present invention, there is provided a method for producing microfibrillated cellulose in which changes in quality in the dehydration / washing step are suppressed. Conventionally, in order to dehydrate and wash the chemically modified cellulose chemically modified by the reaction step, when transferring the dispersion of the chemically modified cellulose to a storage tank or to a dehydration device or the like, the dispersion of the chemically modified cellulose has been transferred using a pump. At that time, it has been found that unexpected quality changes occur, such as the chemically modified cellulose becoming fluffy, the water retention ability increasing, and as a result, the water permeability decreasing, due to an external force such as shear force being applied to the dispersion of the chemically modified cellulose. Further, as a result, the filtration efficiency in the dehydration / washing step tends to deteriorate, and there may be problems such as difficulty in transferring the dispersion of the chemically modified cellulose after the dehydration / washing step. In the present invention, in an earlier step, that is, before the fibrillation step and in a state where the viscosity of the dispersion of the chemically modified cellulose is relatively low, by transferring without using a pump, changes in the quality of the chemically modified cellulose are suppressed, and a method for producing microfibrillated cellulose excellent in filtration efficiency in the dehydration / washing step is provided. The following will describe each step in detail.

[0009] 〔Reaction step〕 The reaction step is a step of chemically modifying cellulose fibers to obtain chemically modified cellulose. In the present invention, the cellulose fibers as raw materials refer to various forms of materials mainly composed of cellulose, and are not particularly limited as the cellulose fibers as raw materials. Examples include wood pulp, non-wood pulp, and deinked pulp. Wood pulp is not particularly limited, and examples include chemical pulps such as hardwood kraft pulp (LBKP), softwood kraft pulp (NBKP), sulfite pulp (SP), dissolving pulp (DP), soda pulp (AP), unbleached kraft pulp (UKP), and oxygen bleached kraft pulp (OKP), semi-chemical pulps such as semi-chemical pulp (SCP) and chemigroundwood pulp (CGP), and mechanical pulps such as groundwood pulp (GP) and thermomechanical pulp (TMP, BCTMP). Non-wood pulp is not particularly limited, and examples include cotton-based pulps such as cotton linter and cotton lint, and non-wood-based pulps such as hemp, wheat straw, bamboo, and bagasse. Deinked pulp is not particularly limited, and examples include deinked pulp made from waste paper. The pulp raw material in this embodiment may be used alone as one of the above, or may be used as a mixture of two or more. Among the cellulose fibers used as the above raw materials, from the perspective of easy availability, for example, wood pulp and deinked pulp are preferred. Among wood pulps, from the perspective of a large cellulose ratio and a high yield of microfibrillar cellulose during defibration treatment, and from the perspective of less decomposition of cellulose in the pulp and obtaining microfibrillar cellulose of long fibers with a large aspect ratio, for example, chemical pulp is more preferred, and kraft pulp and sulfite pulp are even more preferred. Note that when using microfibrillar cellulose of long fibers with a large aspect ratio, the viscosity tends to be high.

[0010] In the present invention, when using a sheet-like cellulose raw material, it is preferably crushed into a size of about 0.5 to 5 cm square. By crushing to the above size, the cellulose raw material can be modified efficiently and uniformly in the subsequent reaction step. The method of crushing is not particularly limited, but a single-axis rotary shear crusher, a two-axis rotary shear crusher, a multi-axis screw crusher, a shredder, a guillotine cutter, etc. can be used. Among these, it is preferable to use a single-axis rotary shear crusher or a shredder from the viewpoint of crushing.

[0011] Chemical modification is performed on the cellulose fiber to obtain a chemically modified cellulose. The chemical modification is preferably carried out by introducing an ionic group (ionic substituent). That is, the reaction step is preferably a step of introducing an ionic group into the cellulose fiber. The ionic group can include, for example, either or both of an anionic group and a cationic group. In the present embodiment, it is particularly preferable to have an anionic group as the ionic group. Further, the ionic group is preferably a group introduced into the cellulose fiber via an ester bond or an ether bond, and more preferably a group introduced into the cellulose fiber via an ester bond. In this case, the ester bond is preferably formed by dehydration condensation of the cellulose fiber and a compound that becomes an ionic group.

[0012] Examples of the anionic group as the ionic group include, for example, a phosphoacid group or a substituent derived from a phosphoacid group (sometimes simply referred to as a phosphoacid group), a carboxy group or a substituent derived from a carboxy group (sometimes simply referred to as a carboxy group), a sulfur oxyacid group or a substituent derived from a sulfur oxyacid group (sometimes simply referred to as a sulfur oxyacid group), a xanthate group or a substituent derived from a xanthate group (sometimes simply referred to as a xanthate group), a phosphon group or a substituent derived from a phosphon group, a phosphine group or a substituent derived from a phosphine group, a sulfone group or a substituent derived from a sulfone group, a carboxyalkyl group, and the like. Among them, the anionic group is preferably at least one selected from the group consisting of a phosphoacid group, a substituent derived from a phosphoacid group, a carboxy group, a sulfur oxyacid group, a substituent derived from a sulfur oxyacid group, a carboxymethyl group, a carboxyethyl group, and a sulfone group; more preferably at least one selected from the group consisting of a phosphoacid group, a substituent derived from a phosphoacid group, a carboxy group, a sulfur oxyacid group, and a substituent derived from a sulfur oxyacid group; and particularly preferably a phosphoacid group. By introducing a phosphoacid group as the anionic group, defibration can be achieved with less energy. Examples of the cationic group as the ionic group include, for example, an ammonium group, a phosphonium group, a sulfonium group, and the like. Among them, the cationic group is preferably an ammonium group.

[0013] The phosphoacid group or the substituent derived from a phosphoacid group is, for example, a substituent represented by the following formula (1). A plurality of substituents represented by the following formula (1) may be introduced into each fibrous cellulose. In this case, the substituents represented by the following formula (1) introduced in plurality may be the same or different from each other.

[0014]

Chemical formula

[0015] In formula (1), a, b, and n are natural numbers, and m is an arbitrary number (provided that a = b × m). At least one of the n α and α' is O - and the rest are R or OR. Note that all of each α and α' may be O - and it doesn't matter. The n α may all be the same or each may be different. β b+ is a monovalent or higher cation composed of an organic or inorganic substance.

[0016] Each R is a hydrogen atom, a saturated - straight - chain hydrocarbon group, a saturated - branched - chain hydrocarbon group, a saturated - cyclic hydrocarbon group, an unsaturated - straight - chain hydrocarbon group, an unsaturated - branched - chain hydrocarbon group, an unsaturated - cyclic hydrocarbon group, an aromatic group, or a derivative group thereof. Also, in formula (1), n is preferably 1.

[0017] Examples of the saturated - straight - chain hydrocarbon group include a methyl group, an ethyl group, an n - propyl group, or an n - butyl group, etc., but it is not particularly limited. Examples of the saturated - branched - chain hydrocarbon group include an i - propyl group, or a t - butyl group, etc., but it is not particularly limited. Examples of the saturated - cyclic hydrocarbon group include a cyclopentyl group, or a cyclohexyl group, etc., but it is not particularly limited. Examples of the unsaturated - straight - chain hydrocarbon group include a vinyl group, or an allyl group, etc., but it is not particularly limited. Examples of the unsaturated - branched - chain hydrocarbon group include an i - propenyl group, or a 3 - butenyl group, etc., but it is not particularly limited. Examples of the unsaturated - cyclic hydrocarbon group include a cyclopentenyl group, a cyclohexenyl group, etc., but it is not particularly limited. Examples of the aromatic group include a phenyl group, or a naphthyl group, etc., but it is not particularly limited.

[0018] Also, as the derivative group in R, with respect to the main chain or side chain of the above - mentioned various hydrocarbon groups, a carboxy group, a carboxylate group (-COO -) Examples include, but are not particularly limited to, functional groups to which at least one selected from functional groups such as hydroxy groups, amino groups, and ammonium groups is added or substituted. Also, although the number of carbon atoms constituting the main chain of R is not particularly limited, it is preferably 20 or less, more preferably 10 or less. By setting the number of carbon atoms constituting the main chain of R within the above range, the molecular weight of the phosphonooxy group can be set within an appropriate range, facilitating penetration into the fiber raw material and increasing the yield of fibrous cellulose. When there are a plurality of Rs in formula (1) or when a plurality of types of substituents represented by the above formula (1) are introduced into the fibrous cellulose, the plurality of existing Rs may be the same or different from each other.

[0019] β b+ is a monovalent or higher cation composed of an organic or inorganic substance. Examples of the monovalent or higher cation composed of an organic substance include organic onium ions. Examples of organic onium ions include organic ammonium ions and organic phosphonium ions. Examples of organic ammonium ions include aliphatic ammonium ions and aromatic ammonium ions, and examples of organic phosphonium ions include aliphatic phosphonium ions and aromatic phosphonium ions. Examples of the monovalent or higher cation composed of an inorganic substance include ions of alkali metals such as sodium, potassium, or lithium, ions of divalent metals such as calcium or magnesium, hydrogen ions, ammonium ions, and the like. When there are a plurality of βs in formula (1) or when a plurality of types of substituents represented by the above formula (1) are introduced into the fibrous cellulose, the plurality of existing βs may be the same or different from each other. As the monovalent or higher cation composed of an organic or inorganic substance, sodium or potassium ions, which are less likely to cause yellowing when heating the fiber raw material containing β and are easy to use industrially, are preferred, but not particularly limited. b+ When there are a plurality of them or when a plurality of types of substituents represented by the above formula (1) are introduced into the fibrous cellulose, the plurality of existing βs b+ may be the same or different from each other. As the monovalent or higher cation composed of an organic or inorganic substance, β b+ is preferably sodium or potassium ions, which are less likely to cause yellowing when heating the fiber raw material containing β and are easy to use industrially, but not particularly limited.

[0020] Examples of the phosphooxo acid group or a substituent derived from the phosphooxo acid group include, more specifically, a phosphoric acid group (-PO3H2), a salt of the phosphoric acid group, a phosphorous acid group (phosphonic acid group) (-PO2H2), and a salt of the phosphorous acid group (phosphonic acid group). Further, the phosphooxo acid group or a substituent derived from the phosphooxo acid group may be a group in which phosphoric acid groups are condensed (e.g., a pyrophosphoric acid group), a group in which phosphonic acids are condensed (e.g., a polyphosphonic acid group), a phosphate ester group (e.g., a monomethyl phosphate group, a polyoxyethylene alkyl phosphate group), an alkylphosphonic acid group (e.g., a methylphosphonic acid group), or the like.

[0021] Further, the thiooxo acid group (a thiooxo acid group or a substituent derived from the thiooxo acid group) is, for example, a substituent represented by the following formula (2). A plurality of substituents represented by the following formula (2) may be introduced into each fibrous cellulose. In this case, the plurality of substituents represented by the following formula (2) introduced may be the same or different from each other.

[0022] [Chemical formula]

[0023] In the above structural formula, b and n are natural numbers, p is 0 or 1, and m is an arbitrary number (provided that 1 = b × m). When n is 2 or more, the plurality of p's may be the same number or different numbers. In the above structural formula, β b+is a monovalent or higher cation composed of an organic or inorganic substance. Examples of the monovalent or higher cation composed of an organic substance include organic onium ions. Examples of the organic onium ions include organic ammonium ions and organic phosphonium ions. Examples of the organic ammonium ions include aliphatic ammonium ions and aromatic ammonium ions, and examples of the organic phosphonium ions include aliphatic phosphonium ions and aromatic phosphonium ions. Examples of the monovalent or higher cation composed of an inorganic substance include ions of alkali metals such as sodium, potassium, or lithium, ions of divalent metals such as calcium or magnesium, hydrogen ions, ammonium ions, and the like. When a plurality of substituents represented by the above formula (2) are introduced into the fibrous cellulose, a plurality of β b+ may be the same or different from each other. As the monovalent or higher cation composed of an organic or inorganic substance, β b+ When the fiber raw material containing is heated, ions of sodium or potassium, which are less likely to turn yellow and are easy to use industrially, are preferred, but not particularly limited.

[0024] The introduction amount of the ionic group into the cellulose fiber is preferably, for example, 0.10 mmol / g or more, more preferably 0.20 mmol / g or more, further preferably 0.40 mmol / g or more, and particularly preferably 0.60 mmol / g or more per 1 g (mass) of the cellulose fiber. Also, the introduction amount of the ionic group into the cellulose fiber is preferably, for example, 5.20 mmol / g or less, more preferably 3.65 mmol / g or less, further preferably 3.00 mmol / g or less, still more preferably 2.50 mmol / g or less, even more preferably 2.00 mmol / g or less, still even more preferably 1.50 mmol / g or less, and particularly preferably 1.00 mmol / g or less per 1 g (mass) of the cellulose fiber. Here, the denominator in mmol / g is the counter ion of the ionic group being a hydrogen ion (H +) indicates the mass of the cellulose fiber when it is in a certain state. By setting the introduction amount of the ionic group within the above range, the fibrillation of the fiber raw material can be facilitated, and the stability of the cellulose fiber can be enhanced.

[0025] The introduction amount of the ionic group into the cellulose fiber can be measured, for example, by the neutralization titration method after subjecting the cellulose fiber to a fibrillation treatment. In the measurement by the neutralization titration method, the introduction amount is measured by determining the change in pH while adding an alkali such as an aqueous sodium hydroxide solution to the obtained slurry containing the cellulose fiber.

[0026] Figure 1 is a graph showing the relationship between the amount of NaOH dropped and the pH for a fine fibrous cellulose dispersion having phosphonooxy groups. The introduction amount of the phosphonooxy group into the cellulose fiber is measured, for example, as follows. First, ion-exchanged water is added to the target cellulose fiber to prepare a slurry with a solid content concentration of 0.2 mass%. This slurry is treated 4 times at a pressure of 200 MPa with a wet atomization device (manufactured by Sugino Machine Limited, Starburst) to obtain a fine fibrous cellulose dispersion (slurry) containing fine fibrous cellulose. Then, the fine fibrous cellulose dispersion is treated with a strongly acidic ion-exchange resin. Next, while adding an aqueous sodium hydroxide solution, observe the change in pH to obtain a titration curve as shown in the upper part of FIG. 1. In the titration curve shown in the upper part of FIG. 1, the measured pH is plotted against the amount of alkali added, and in the titration curve shown in the lower part of FIG. 1, the increment (differential value) (1 / mmol) of pH with respect to the amount of alkali added is plotted. In this neutralization titration, in the curve obtained by plotting the measured pH against the amount of alkali added, two points where the increment (differential value of pH with respect to the amount of alkali dropped) becomes maximum are confirmed. Among these, the first maximum point of the increment obtained first after starting to add the alkali is called the first end point, and the next maximum point of the increment obtained is called the second end point. The amount of alkali required from the start of titration to the first end point is equal to the amount of the first dissociable acid of the fibrous cellulose contained in the slurry used for titration, and the amount of alkali required from the first end point to the second end point is equal to the amount of the second dissociable acid of the fibrous cellulose contained in the slurry used for titration, and the amount of alkali required from the start of titration to the second end point is equal to the total amount of dissociable acid of the fibrous cellulose contained in the slurry used for titration. And the value obtained by dividing the amount of alkali required from the start of titration to the first end point by the solid content (g) in the slurry to be titrated becomes the amount of phosphonooxy group introduced (mmol / g). Note that when simply referring to the amount of phosphonooxy group introduced (or the amount of phosphonooxy group), it represents the amount of the first dissociable acid. In addition, in FIG. 1, the region from the start of titration to the first end point is called the first region, and the region from the first end point to the second end point is called the second region. For example, when the phosphonooxy group is a phosphate group and this phosphate group undergoes condensation, apparently, the amount of weakly acidic groups in the phosphonooxy group (also referred to as the amount of the second dissociable acid in this specification) decreases, and the amount of alkali required in the second region becomes less than the amount of alkali required in the first region. On the other hand, the amount of strongly acidic groups in the phosphonooxy group (also referred to as the amount of the first dissociable acid in this specification) coincides with the amount of phosphorus atoms regardless of the presence or absence of condensation. Further, when the phosphonooxy group is a phosphite group, since there is no weakly acidic group in the phosphonooxy group, the amount of alkali required in the second region may decrease or the amount of alkali required in the second region may be zero. In this case, in the titration curve, there is only one point where the increment of pH becomes maximum.

[0027] Note that since the denominator of the above-introduced amount of phosphono-oxy acid group (mmol / g) indicates the mass of the acid-form fibrous cellulose, it represents the amount of phosphono-oxy acid group possessed by the acid-form fibrous cellulose (hereinafter referred to as the amount of phosphono-oxy acid group (acid form)). On the other hand, when the counter ion of the phosphono-oxy acid group is substituted with an arbitrary cation C so as to be charge equivalent, by converting the denominator to the mass of the fibrous cellulose when the cation C is the counter ion, the amount of phosphono-oxy acid group possessed by the fibrous cellulose in which the cation C is the counter ion (hereinafter referred to as the amount of phosphono-oxy acid group (C form)) can be determined. That is, it is calculated by the following formula. Amount of phosphono-oxy acid group (C form) = Amount of phosphono-oxy acid group (acid form) / {1 + (W - 1) × A / 1000} A [mmol / g]: Total amount of anions derived from the phosphono-oxy acid group possessed by the fibrous cellulose (total amount of dissociated acids of the phosphono-oxy acid group) W: Formula weight per monovalency of the cation C (for example, 23 for Na and 9 for Al)

[0028] Figure 2 is a graph showing the relationship between the amount of NaOH dropped and the pH for a fine fibrous cellulose dispersion having a carboxy group as an ionic group. The amount of carboxy group introduced into the cellulose fiber is measured, for example, as follows. First, ion-exchanged water is added to the target cellulose fiber to prepare a slurry with a solid content concentration of 0.2% by mass. This slurry is treated 4 times at a pressure of 200 MPa with a wet atomization device (manufactured by Sugino Machine Limited, Starburst) to obtain a fine fibrous cellulose dispersion (slurry) containing fine fibrous cellulose. Then, the fine fibrous cellulose dispersion is treated with a strongly acidic ion exchange resin. Next, while adding an aqueous sodium hydroxide solution, observe the change in pH to obtain a titration curve as shown in the upper part of Fig. 2. In the titration curve shown in the upper part of Fig. 2, the measured pH is plotted against the amount of alkali added, and in the titration curve shown in the lower part of Fig. 2, the increment (differential value) (1 / mmol) of pH with respect to the amount of alkali added is plotted. In this neutralization titration, in the curve where the measured pH is plotted against the amount of alkali added, one point where the increment (differential value of pH with respect to the amount of alkali dropped) becomes maximum is confirmed, and this maximum point is called the first end point. Here, the region from the start of titration to the first end point in Fig. 2 is called the first region. The amount of alkali required in the first region is equal to the amount of carboxy groups in the dispersion used for titration. Then, by dividing the amount of alkali (mmol) required in the first region of the titration curve by the solid content (g) in the dispersion containing the fibrous cellulose to be titrated, the amount of carboxy groups introduced (mmol / g) is calculated.

[0029] Note that since the denominator of the above-introduced amount of carboxy groups (mmol / g) is the mass of the acid-form fibrous cellulose, it indicates the amount of carboxy groups possessed by the acid-form fibrous cellulose (hereinafter referred to as the amount of carboxy groups (acid form)). On the other hand, when the counter ion of the carboxy group is replaced with an arbitrary cation C so that the charge equivalent is achieved, by converting the denominator to the mass of the fibrous cellulose when the cation C is the counter ion, the amount of carboxy groups possessed by the fibrous cellulose with the cation C as the counter ion (hereinafter referred to as the amount of carboxy groups (C form)) can be determined. That is, it is calculated by the following formula. Amount of carboxy groups (C form) = Amount of carboxy groups (acid form) / {1 + (W - 1) × (Amount of carboxy groups (acid form)) / 1000} W: Formula weight per monovalent of cation C (for example, Na is 23, Al is 9)

[0030] In the measurement of the amount of ionic groups by titration, accurate values may not be obtained, such as when the dropping amount of one drop of an aqueous sodium hydroxide solution is too large or the titration interval is too short, resulting in a lower amount of ionic groups than normal. As appropriate dropping amounts and titration intervals, for example, it is desirable to titrate 0.1 N aqueous sodium hydroxide solution in amounts of 10 μL or more and 50 μL or less over 5 seconds or more and 30 seconds or less. Further, in order to eliminate the influence of carbon dioxide dissolved in the fine fibrous cellulose dispersion, for example, it is desirable to perform the measurement while blowing an inert gas such as nitrogen gas into the slurry from 15 minutes before the start of titration until the end of titration.

[0031] In addition, the amount of sulfur oxoacid groups and sulfone groups introduced into the fibrous cellulose is measured by ICP emission spectrometry after wet ashing the obtained fibrous cellulose using perchloric acid and concentrated nitric acid and then diluting it at an appropriate ratio. The value obtained by dividing this sulfur amount by the absolute dry mass of the tested fibrous cellulose is taken as the amount of sulfur oxoacid groups and sulfone groups (unit: mmol / g).

[0032] In order to obtain a chemically modified cellulose having an ionic group as described above, it preferably has an ionic group introduction step of introducing an ionic group into a fiber raw material (cellulose fiber) containing the cellulose described above. Examples of the ionic group introduction step include a phosphorus oxoacid group introduction step, a carboxy group introduction step, a sulfur oxoacid group introduction step, a xanthate group introduction step, a phosphonate group or phosphine group introduction step, a sulfone group introduction step, and a cationic group introduction step. Each will be described below.

[0033] <Phosphorus Oxoacid Group Introduction Step> When obtaining a chemically modified cellulose having an ionic group, it is preferable to provide a reaction step for introducing the ionic group before the fibrillation step. Examples of the reaction step include a phosphonooxy group introduction step. The phosphonooxy group introduction step is a step of allowing at least one compound (hereinafter also referred to as "compound A") selected from compounds capable of introducing a phosphonooxy group to act on cellulose fibers as a raw material by reacting with the hydroxyl groups of the cellulose fibers. By this step, cellulose fibers having a phosphonooxy group (chemically modified cellulose) can be obtained.

[0034] In the phosphonooxy group introduction step according to the present embodiment, the reaction between the cellulose fibers and compound A may be carried out in the presence of at least one selected from urea and its derivatives (hereinafter also referred to as "compound B"). On the other hand, the reaction between the cellulose fibers and compound A may be carried out in the absence of compound B.

[0035] As an example of a method of allowing Compound A to act on cellulose fibers in the co - presence of Compound B, there is a method of mixing Compound A and Compound B with cellulose fibers in a dry state, a wet state, or a slurry state. Among these, it is preferable to use cellulose fibers in a dry state or a wet state because of the high uniformity of the reaction, and it is particularly preferable to use cellulose fibers in a dry state. The form of the cellulose fibers is not particularly limited, but for example, it is preferably cotton - like or in the form of a thin sheet. For Compound A and Compound B, there are methods of adding them to the fiber raw material in a powdery form, in a solution state dissolved in a solvent, or in a state melted by heating to a temperature above the melting point. Among these, it is preferable to add them in a solution state dissolved in a solvent, particularly in an aqueous solution state, because of the high uniformity of the reaction. Also, Compound A and Compound B may be added to the cellulose fibers simultaneously, separately, or as a mixture. The method of adding Compound A and Compound B is not particularly limited, but when Compound A and Compound B are in a solution state, the cellulose fibers may be immersed in the solution to absorb the liquid and then taken out, or the solution may be dropped or sprayed onto the cellulose fibers. Further, the required amounts of Compound A and Compound B may be added to the cellulose fibers, or after adding excessive amounts of Compound A and Compound B to the cellulose fibers respectively, the excess Compound A and Compound B may be removed by pressing or filtration.

[0036] As the compound A used in this embodiment, any compound having a phosphorus atom and capable of forming an ester bond with cellulose may be used, and examples include phosphoric acid or its salts, phosphorous acid or its salts, dehydrated condensed phosphoric acid or its salts, and phosphoric anhydride (phosphorus pentoxide), but it is not particularly limited. As phosphoric acid, those of various purities can be used, for example, 100% phosphoric acid (orthophosphoric acid) or 85% phosphoric acid can be used. As phosphorous acid, 99% phosphorous acid (phosphonic acid) can be mentioned. Dehydrated condensed phosphoric acid is a compound in which two or more molecules of phosphoric acid are condensed by a dehydration reaction, and examples include pyrophosphoric acid and polyphosphoric acid. As phosphates, phosphites, and dehydrated condensed phosphates, lithium salts, sodium salts, potassium salts, ammonium salts of phosphoric acid, phosphorous acid, or dehydrated condensed phosphoric acid can be mentioned, and these can have various degrees of neutralization. Among these, from the viewpoints of high introduction efficiency of phosphoric acid groups, easier improvement of fibrillation efficiency in the fibrillation step described later, low cost, and easy industrial application, phosphoric acid, sodium salt of phosphoric acid, potassium salt of phosphoric acid, ammonium salt of phosphoric acid, or phosphorous acid, sodium salt of phosphorous acid, potassium salt of phosphorous acid, ammonium salt of phosphorous acid are preferable, and phosphoric acid, sodium dihydrogen phosphate, disodium hydrogen phosphate, ammonium dihydrogen phosphate, or phosphorous acid, sodium phosphite are more preferable.

[0037] The addition amount of compound A to the cellulose fiber is not particularly limited. For example, when the addition amount of compound A is converted to the amount of phosphorus atom, the addition amount of phosphorus atom to the cellulose fiber (dry mass) is preferably 0.5% by mass or more and 100% by mass or less, more preferably 1% by mass or more and 50% by mass or less, and even more preferably 2% by mass or more and 30% by mass or less. By setting the addition amount of phosphorus atom to the cellulose fiber within the above range, the yield of microfibrillated cellulose can be further improved. On the other hand, by setting the addition amount of phosphorus atom to the cellulose fiber below the above upper limit value, the balance between the effect of improving the yield and the cost can be achieved.

[0038] Compound B used in this embodiment is at least one selected from urea and its derivatives as described above. Examples of Compound B include urea, biuret, 1-phenylurea, 1-benzylurea, 1-methylurea, and 1-ethylurea. From the viewpoint of improving the uniformity of the reaction, Compound B is preferably used as an aqueous solution. Further, from the viewpoint of further improving the uniformity of the reaction, it is preferable to use an aqueous solution in which both Compound A and Compound B are dissolved.

[0039] The addition amount of Compound B relative to the cellulose fiber (dry mass) is not particularly limited, but is preferably, for example, 1% by mass or more and 500% by mass or less, more preferably 10% by mass or more and 400% by mass or less, and even more preferably 100% by mass or more and 350% by mass or less.

[0040] In the reaction of the fiber raw material containing cellulose and Compound A, in addition to Compound B, for example, amides or amines may be included in the reaction system. Examples of amides include formamide, dimethylformamide, acetamide, dimethylacetamide, etc. Examples of amines include methylamine, ethylamine, trimethylamine, triethylamine, monoethanolamine, diethanolamine, triethanolamine, pyridine, ethylenediamine, hexamethylenediamine, etc. Among these, triethylamine is particularly known to act as a good reaction catalyst.

[0041] In the step of introducing a phosphoacid group, it is preferable to add or mix a compound A or the like to the cellulose fiber and then perform a heat treatment on the cellulose fiber. As the heat treatment temperature, it is preferable to select a temperature at which the phosphoacid group can be efficiently introduced while suppressing the thermal decomposition and hydrolysis reactions of the fiber. The heat treatment temperature is preferably, for example, 50°C or higher and 300°C or lower, more preferably 100°C or higher and 250°C or lower, and even more preferably 130°C or higher and 200°C or lower. Further, for the heat treatment, equipment having various heat media can be used. For example, a stirring dryer, a rotary dryer, a disk dryer, a roll-type heating device, a plate-type heating device, a fluidized bed dryer, a band-type dryer, a filtration dryer, a vibration fluidized bed dryer, a pneumatic dryer, a vacuum dryer, an infrared heating device, a far-infrared heating device, a microwave heating device, or a high-frequency dryer can be used.

[0042] In the heat treatment according to the present embodiment, for example, after adding compound A to a thin sheet-like cellulose fiber by a method such as impregnation, a method of heating or a method of heating while kneading or stirring the cellulose fiber and compound A with a kneader or the like can be adopted. Thereby, it is possible to suppress the uneven concentration of compound A in the cellulose fiber and introduce the phosphoacid group more uniformly onto the surface of the cellulose fiber. This is presumably because when water molecules move to the surface of the cellulose fiber during drying, the dissolved compound A is attracted to the water molecules by surface tension and also moves to the surface of the cellulose fiber (that is, uneven concentration of compound A is caused), which can be suppressed.

[0043] In addition, the heating device used for the heat treatment is preferably a device that can always discharge moisture held by the slurry and moisture generated by the dehydration condensation (phosphoric acid esterification) reaction between the hydroxyl groups contained in, for example, compound A and cellulose in the cellulose fiber, etc., to the outside of the device system. Examples of such a heating device include a forced-air oven. By always discharging the moisture in the device system, in addition to being able to suppress the hydrolysis reaction of the phosphoric acid ester bond, which is the reverse reaction of phosphoric acid esterification, it is also possible to suppress the acid hydrolysis of the sugar chain in the cellulose fiber. Therefore, it becomes possible to obtain microfibrillar cellulose with a high aspect ratio.

[0044] The time of the heat treatment is preferably, for example, 1 second or more and 300 minutes or less, more preferably 1 second or more and 1000 seconds or less, and even more preferably 10 seconds or more and 800 seconds or less, after substantially removing the moisture from the cellulose fiber. In this embodiment, by setting the heating temperature and the heating time within an appropriate range, the introduction amount of the phosphonooxy group can be made within a preferable range.

[0045] The phosphonooxy group introduction step may be performed at least once, but can also be repeated two or more times. By performing the phosphonooxy group introduction step two or more times, a large amount of phosphonooxy groups can be introduced into the fiber raw material.

[0046] The introduction amount of the phosphonooxy group with respect to the cellulose fiber is preferably, for example, 0.10 mmol / g or more, more preferably 0.20 mmol / g or more, even more preferably 0.50 mmol / g or more, and particularly preferably 1.00 mmol / g or more per 1 g (mass) of the cellulose fiber. Also, the introduction amount of the phosphonooxy group with respect to the cellulose fiber is preferably, for example, 5.20 mmol / g or less, more preferably 3.65 mmol / g or less, and even more preferably 3.00 mmol / g or less per 1 g (mass) of the cellulose fiber. By setting the introduction amount of the phosphonooxy group within the above range, the fibrillation of the cellulose fiber in the fibrillation treatment step can be facilitated, and the stability of the microfibrillar cellulose can be enhanced.

[0047] <Carboxy group introduction step> As the ionic group introduction step, a carboxy group introduction step may be included. The carboxy group introduction step is performed by subjecting the cellulose fiber to an oxidation treatment such as ozone oxidation, oxidation by the Fenton method, TEMPO oxidation treatment, or treatment with a compound having a group derived from a carboxylic acid or its derivative, or an acid anhydride of a compound having a group derived from a carboxylic acid or its derivative.

[0048] The compound having a group derived from a carboxylic acid is not particularly limited, and examples thereof include dicarboxylic acid compounds such as maleic acid, succinic acid, phthalic acid, fumaric acid, glutaric acid, adipic acid, and itaconic acid, and tricarboxylic acid compounds such as citric acid and aconitic acid. The derivative of the compound having a group derived from a carboxylic acid is not particularly limited, and examples thereof include imidized products of acid anhydrides of compounds having a carboxy group and derivatives of acid anhydrides of compounds having a carboxy group. The imidized product of the acid anhydride of the compound having a carboxy group is not particularly limited, and examples thereof include imidized products of dicarboxylic acid compounds such as maleimide, succinimide, and phthalimide.

[0049] The acid anhydride of the compound having a group derived from a carboxylic acid is not particularly limited, and examples thereof include acid anhydrides of dicarboxylic acid compounds such as maleic anhydride, succinic anhydride, phthalic anhydride, glutaric anhydride, adipic anhydride, and itaconic anhydride. The derivative of the acid anhydride of the compound having a group derived from a carboxylic acid is not particularly limited, and examples thereof include those in which at least some hydrogen atoms of the acid anhydride of the compound having a carboxy group are substituted with substituents such as an alkyl group and a phenyl group, such as dimethyl maleic anhydride, diethyl maleic anhydride, and diphenyl maleic anhydride.

[0050] In the step of introducing a carboxy group, when performing TEMPO oxidation treatment, for example, it is preferable to carry out the treatment under the condition that the pH is 6 or more and 8 or less. Such treatment is also referred to as neutral TEMPO oxidation treatment. The neutral TEMPO oxidation treatment can be carried out, for example, by adding cellulose fibers, a nitroxyl radical such as TEMPO (2,2,6,6 - tetramethylpiperidine - 1 - oxyl) as a catalyst, and sodium hypochlorite as a sacrificial reagent to a sodium phosphate buffer solution (pH = 6.8). Furthermore, by co - existing sodium hypochlorite, the aldehyde generated in the oxidation process can be efficiently oxidized to a carboxy group. Also, the TEMPO oxidation treatment may be carried out under the condition that the pH is 10 or more and 11 or less. Such treatment is also referred to as alkaline TEMPO oxidation treatment. The alkaline TEMPO oxidation treatment can be carried out, for example, by adding a nitroxyl radical such as TEMPO as a catalyst, sodium bromide as a co - catalyst, and sodium hypochlorite as an oxidizing agent to cellulose fibers.

[0051] The amount of carboxyl groups introduced into the cellulose fibers varies depending on the type of substituent. For example, when carboxyl groups are introduced by TEMPO oxidation, it is preferably 0.10 mmol / g or more, more preferably 0.20 mmol / g or more, further preferably 0.40 mmol / g or more, and particularly preferably 0.60 mmol / g or more per 1 g (mass) of the cellulose fibers. Also, the amount of carboxyl groups introduced into the cellulose fibers is preferably 3.65 mmol / g or less, more preferably 3.00 mmol / g or less, further preferably 2.50 mmol / g or less, even more preferably 2.00 mmol / g or less, still more preferably 1.50 mmol / g or less, and particularly preferably 1.00 mmol / g or less. In addition, when the substituent is a carboxymethyl group, the amount of carboxyl groups introduced may be 5.8 mmol / g or less per 1 g (mass) of the cellulose fibers. By setting the amount of carboxyl groups introduced within the above range, the fibrillation of cellulose fibers in the fibrillation treatment step can be facilitated, and the stability of microfibrillated cellulose can be enhanced.

[0052] <Sulfonic acid group introduction step> As the ionic group introduction step, a sulfonic acid group introduction step may be included. In the sulfonic acid group introduction step, a cellulose fiber having a sulfonic acid group (sulfonic acid group-introduced fiber) can be obtained by reacting the hydroxyl group of the cellulose fiber with a sulfur oxoacid.

[0053] In the sulfone group introduction step, instead of compound A in the above-mentioned <phosphooxo acid group introduction step>, at least one compound (hereinafter also referred to as "compound C") selected from compounds capable of introducing a sulfone group by reacting with the hydroxyl groups of cellulose fibers is used. As compound C, any compound having a sulfur atom and capable of forming an ester bond with cellulose may be used, and examples include sulfuric acid or its salts, sulfurous acid or its salts, sulfamic acid amides, etc., but it is not particularly limited. As sulfuric acid, those with various purities can be used, for example, 96% sulfuric acid (concentrated sulfuric acid) can be used. As sulfurous acid, 5% sulfurous acid solution can be mentioned. As sulfates or sulfites, lithium salts, sodium salts, potassium salts, ammonium salts of sulfates or sulfites, etc. can be mentioned, and these can have various degrees of neutralization. As sulfamic acid amides, sulfamic acid, etc. can be used. In the sulfone group introduction step, it is preferable to use compound B in the above-mentioned <phosphooxo acid group introduction step> in the same manner.

[0054] In the sulfone group introduction step, it is preferable to mix an aqueous solution containing sulfur oxoacid, urea, and / or a urea derivative with cellulose fibers and then perform a heat treatment on the cellulose fibers. As the heat treatment temperature, it is preferable to select a temperature at which the sulfone group can be efficiently introduced while suppressing the thermal decomposition and hydrolysis reactions of the fibers. The heat treatment temperature is preferably 100 °C or higher, more preferably 120 °C or higher, and even more preferably 150 °C or higher. Also, the heat treatment temperature is preferably 300 °C or lower, more preferably 250 °C or lower, and even more preferably 200 °C or lower.

[0055] In the heat treatment step, it is preferable to heat until substantially no moisture remains. For this reason, the heat treatment time varies depending on the amount of moisture contained in the cellulose fiber, the sulfur oxoacid, and the addition amount of the aqueous solution containing urea and / or a urea derivative. For example, it is preferably 10 seconds or more and 10,000 seconds or less. For the heat treatment, equipment having various heat media can be used. For example, a hot air dryer, a stirring dryer, a rotary dryer, a disk dryer, a roll type heating device, a plate type heating device, a fluidized bed dryer, a band type dryer, a filtration dryer, a vibrating fluidized dryer, a pneumatic dryer, a vacuum dryer, an infrared heating device, a far-infrared heating device, a microwave heating device, and a high-frequency dryer can be used.

[0056] The introduction amount of the sulfone group with respect to the cellulose fiber is preferably 0.05 mmol / g or more, more preferably 0.10 mmol / g or more, still more preferably 0.20 mmol / g or more, even more preferably 0.40 mmol / g or more, and particularly preferably 0.50 mmol / g or more. Also, the introduction amount of the sulfone group with respect to the cellulose fiber is preferably 5.00 mmol / g or less, more preferably 3.00 mmol / g or less. By setting the introduction amount of the sulfone group within the above range, the fibrillation of the cellulose fiber in the fibrillation treatment step can be facilitated, and the stability of the microfibrillated cellulose can be enhanced.

[0057] <Oxidation step with a chlorine-based oxidizing agent (second carboxy group introduction step)> As the ionic group introduction step, an oxidation step with a chlorine-based oxidizing agent may be included. In the oxidation step with a chlorine-based oxidizing agent, a carboxy group is introduced into the cellulose fiber by adding a chlorine-based oxidizing agent to the cellulose fiber having a hydroxyl group in a wet or dry state and carrying out a reaction.

[0058] Examples of chlorine-based oxidizing agents include hypochlorous acid, hypochlorite, chlorous acid, chlorite, chloric acid, chlorate, perchloric acid, perchlorate, and chlorine dioxide. From the viewpoints of the introduction efficiency of substituents, and thus the fibrillation efficiency, cost, and ease of handling, the chlorine-based oxidizing agents are preferably sodium hypochlorite, sodium chlorite, and chlorine dioxide. When adding the chlorine-based oxidizing agent, it may be added directly to the fiber raw material as a reagent (solid or liquid), or it may be dissolved in a suitable solvent and then added.

[0059] In the oxidation step using a chlorine-based oxidizing agent, the concentration of the chlorine-based oxidizing agent in the solution is preferably 1% by mass or more and 1,000% by mass or less, more preferably 5% by mass or more and 500% by mass or less, and even more preferably 10% by mass or more and 100% by mass or less, when converted to the available chlorine concentration, for example. The addition amount of the chlorine-based oxidizing agent with respect to 100 parts by mass of the cellulose fiber is preferably 1 part by mass or more and 100,000 parts by mass or less, more preferably 10 parts by mass or more and 10,000 parts by mass or less, and even more preferably 100 parts by mass or more and 5,000 parts by mass or less.

[0060] In the oxidation step using a chlorine-based oxidizing agent, the reaction time with the chlorine-based oxidizing agent can vary depending on the reaction temperature, but is preferably 1 minute or more and 1,000 minutes or less, more preferably 10 minutes or more and 500 minutes or less, and even more preferably 20 minutes or more and 400 minutes or less, for example. The pH during the reaction is preferably 5 or more and 15 or less, more preferably 7 or more and 14 or less, and even more preferably 9 or more and 13 or less. Also, it is preferable to maintain a constant pH (for example, pH 11) while appropriately adding hydrochloric acid or sodium hydroxide at the start of the reaction and during the reaction. Further, after the reaction, excess reaction reagents, by-products, etc. may be washed and removed by filtration or the like.

[0061] <Zanthate group introduction step> The manufacturing process of microfibrillar cellulose may include a xanthate group introduction step as a reaction step. In the xanthate group introduction step, by substituting the hydroxyl group of cellulose fibers with a xanthate group represented by the following formula (3), cellulose fibers having a xanthate group (xanthate group-introduced fibers) can be obtained. -OCSS - M + ……(3) Here, M + is at least one selected from a hydrogen ion, a monovalent metal ion, an ammonium ion, an aliphatic or aromatic ammonium ion.

[0062] In the xanthate group introduction step, first, an alkali treatment is performed in which the above cellulose fibers are treated with an alkali solution to obtain alkali cellulose. Examples of the alkali solution include an aqueous solution of an alkali metal hydroxide and an aqueous solution of an alkaline earth metal hydroxide. Among them, the alkali solution is preferably an aqueous solution of an alkali metal hydroxide such as sodium hydroxide or potassium hydroxide, and particularly preferably a sodium hydroxide aqueous solution. When the alkali solution is an aqueous solution of an alkali metal hydroxide, the concentration of the alkali metal hydroxide in the aqueous solution of the alkali metal hydroxide is preferably 4% by mass or more, more preferably 5% by mass or more. Also, the concentration of the alkali metal hydroxide in the aqueous solution of the alkali metal hydroxide is preferably 9% by mass or less. By setting the alkali metal hydroxide concentration to the above lower limit value or more, mercerization of cellulose can proceed sufficiently, the amount of by-products generated during subsequent xanthation can be reduced, and as a result, the yield of the xanthate group-introduced fibers can be increased. Thereby, the fibrillation treatment described later can be performed more effectively. Also, by setting the alkali metal hydroxide concentration to the above upper limit value or less, while allowing mercerization to proceed, it is possible to suppress the penetration of the alkali metal hydroxide aqueous solution into the crystal region of cellulose, so that the crystal structure of cellulose I is easily maintained, and the yield of microfibrillar cellulose can be further increased.

[0063] The time of the above alkali treatment is preferably 30 minutes or more, more preferably 1 hour or more. Also, the time of the alkali treatment is preferably 6 hours or less, more preferably 5 hours or less. By setting the time of the alkali treatment within the above range, the final yield can be increased and the productivity can be enhanced.

[0064] It is preferable to subsequently perform solid-liquid separation on the alkali cellulose obtained by the above alkali treatment to remove the aqueous solution component as much as possible. Thereby, the water content during the subsequent xanthation treatment can be reduced and the reaction can be promoted. As the method of solid-liquid separation, for example, general dehydration methods such as centrifugation and filtration can be used. Note that the concentration of the alkali metal hydroxide contained in the alkali cellulose after solid-liquid separation is preferably 3% by mass or more and 8% by mass or less with respect to the total mass of the alkali cellulose after solid-liquid separation.

[0065] In the xanthate group introduction step, a xanthation treatment step is performed after the alkali treatment. In the xanthation treatment step, carbon disulfide (CS2) is reacted with the alkali cellulose to convert the (-O - Na + ) group into a (-OCSS - Na + ) group to obtain xanthate group-introduced fibers. Note that, in the above, the metal ion introduced into the alkali cellulose is typically described as Na + , but the same reaction proceeds with other alkali metal ions.

[0066] In the xanthation treatment, it is preferable to supply carbon disulfide in an amount of 10% by mass or more based on the absolutely dry mass of cellulose in the alkali cellulose. Further, in the xanthation treatment, the contact time between carbon disulfide and alkali cellulose is preferably 30 minutes or more, and more preferably 1 hour or more. When carbon disulfide comes into contact with alkali cellulose, xanthation proceeds rapidly. However, since it takes time for carbon disulfide to penetrate into the interior of the alkali cellulose, it is preferable to set the reaction time within the above range. On the other hand, the contact time between carbon disulfide and alkali cellulose may be 6 hours or less, whereby sufficient penetration can proceed even with respect to the mass of the alkali cellulose after dehydration, and xanthation that enables reaction can be almost completed.

[0067] The reaction temperature in the xanthation treatment is preferably 46°C or lower. By setting the reaction temperature within the above range, it becomes easier to suppress the decomposition of alkali cellulose. Further, by setting the reaction temperature within the above range, it becomes easier to react uniformly, so that the generation of by-products can be suppressed, and furthermore, the removal of the generated xanthate groups can also be suppressed.

[0068] The amount of xanthate groups introduced in the xanthate group introduction step is preferably 0.60 mmol / g or more, more preferably 0.70 mmol / g or more, still more preferably 0.80 mmol / g or more, even more preferably 1.00 mmol / g or more, and particularly preferably 1.20 mmol / g or more per 1 g (mass) of cellulose fibers. Further, the amount of xanthate groups introduced is preferably 5.00 mmol / g or less, more preferably 3.00 mmol / g or less per 1 g (mass) of cellulose fibers, for example. By setting the amount of xanthate groups introduced within the above range, microfibrillar cellulose excellent in fibrillation properties and transparency can be obtained.

[0069] <Phosphonate group or phosphine group introduction step (phosphoalkylation step)> As the ionic group introduction step, it may include a phosphon group or phosphine group introduction step (phosphoalkylation step). In the phosphoalkylation step, as essential components, a compound having a reactive group and a phosphon group or phosphine group (compound E A ), an alkali compound as an optional component, and compound B selected from the aforementioned urea and its derivatives are added to a fiber raw material having a hydroxyl group in a wet or dry state and reacted, whereby a phosphon group or phosphine group is introduced into the cellulose fiber.

[0070] Examples of the reactive group include an alkyl halide group, a vinyl group, an epoxy group (glycidyl group), etc. Compound E A Examples of compound E A include vinylphosphonic acid, phenylvinylphosphonic acid, phenylvinylphosphine acid, etc. From the viewpoints of the introduction efficiency of substituents, and thus the defibrillation efficiency, cost, and ease of handling, compound E is preferably vinylphosphonic acid.

[0071] Compound E A When adding compound E

[0072] it may be added directly to the cellulose fiber as a reagent (solid or liquid), or it may be dissolved in a suitable solvent and added. The cellulose fiber is preferably alkali-celluloseized in advance or alkali-celluloseized simultaneously with the reaction. The method of alkali-celluloseization is as described above.

[0073] Compound E AThe addition amount is preferably 1 to 100,000 parts by mass, more preferably 2 to 10,000 parts by mass, and even more preferably 5 to 1,000 parts by mass, based on 100 parts by mass of the cellulose fiber.

[0074] The reaction time can vary depending on the reaction temperature. For example, it is preferably 1 minute or more and 1,000 minutes or less, more preferably 10 minutes or more and 500 minutes or less, and even more preferably 20 minutes or more and 400 minutes or less. After the reaction, excess reaction reagents, by-products, etc. may be washed and removed by filtration or the like with water.

[0075] <Sulfone group introduction step (sulfalkylating step) (second sulfone group introduction step)> As the ionic group introduction step, a sulfone group introduction step (sulfalkylating step) may be included. In sulfalkylating, as essential components, a compound having a reactive group and a sulfone group (compound E B ) and, as optional components, an alkali compound and compound B selected from the aforementioned urea and its derivatives are added to cellulose fibers having hydroxyl groups in a wet or dry state and reacted, whereby a sulfone group is introduced into the cellulose fibers.

[0076] Examples of the reactive group include a halogenated alkyl group, a vinyl group, an epoxy group (glycidyl group), etc. Compound E B Examples of compound E B include sodium 2-chloroethanesulfonate, sodium vinylsulfonate, sodium p-styrenesulfonate, 2-acrylamido-2-methylpropanesulfonic acid, etc. Among them, from the viewpoints of the introduction efficiency of substituents, and thus the defibrillation efficiency, cost, and ease of handling, compound E is preferably sodium vinylsulfonate.

[0077] Compound EB When adding it, it may be added directly to the cellulose fibers as a reagent (solid or liquid), or it may be dissolved in a suitable solvent and then added. The cellulose fibers are preferably alkalized cellulose in advance or alkalized cellulose simultaneously with the reaction. The method of alkalizing cellulose is as described above.

[0078] The temperature during the reaction is preferably, for example, 50°C or higher and 300°C or lower, more preferably 100°C or higher and 250°C or lower, and even more preferably 130°C or higher and 200°C or lower.

[0079] Compound E B The addition amount of it to 100 parts by mass of the cellulose fibers is preferably 1 part by mass or more and 100,000 parts by mass or less, more preferably 2 parts by mass or more and 10,000 parts by mass or less, and even more preferably 5 parts by mass or more and 1,000 parts by mass or less.

[0080] The reaction time can vary depending on the reaction temperature. For example, it is preferably 1 minute or more and 1,000 minutes or less, more preferably 10 minutes or more and 500 minutes or less, and even more preferably 15 minutes or more and 400 minutes or less. Also, after the reaction, excess reaction reagents, by-products, etc. may be washed with water and removed by filtration or the like.

[0081] <Carboxyalkylation step (third carboxy group introduction step)> As a reaction step, a carboxyalkylation step may be included. As an essential component, a compound having a reactive group and a carboxy group (Compound E C ) and, as an optional component, an alkali compound and Compound B selected from the above-mentioned urea and its derivatives are added to the cellulose fibers having a hydroxyl group in a wet or dry state to carry out a reaction, whereby a carboxy group is introduced into the cellulose fibers.

[0082] Examples of the reactive group include an alkyl halide group, a vinyl group, an epoxy group (glycidyl group), etc. Compound E CAs for [the compound], monochloroacetic acid, sodium monochloroacetate, 2-chloropropionic acid, 3-chloropropionic acid, sodium 2-chloropropionate, and sodium 3-chloropropionate are preferable from the viewpoints of the introduction efficiency of the substituent, and thus the fibrillation efficiency, cost, and ease of handling. Furthermore, as an optional component, it is also preferable to similarly use Compound B in the above-described <phosphooxo acid group introduction step>, and it is preferable that the addition amount is also as described above.

[0083] Compound E C When adding [Compound E], it may be added directly to the cellulose fiber as a reagent (solid or liquid), or it may be dissolved in an appropriate solvent and then added. It is preferable that the cellulose fiber is alkalicelluloseized in advance or is alkalicelluloseized simultaneously with the reaction. The method of alkalicelluloseization is as described above.

[0084] The temperature during the reaction is preferably, for example, 50°C or higher and 300°C or lower, more preferably 100°C or higher and 250°C or lower, and even more preferably 130°C or higher and 200°C or lower.

[0085] Compound E C The addition amount of [Compound E] with respect to 100 parts by mass of the cellulose fiber is preferably 1 part by mass or more and 100,000 parts by mass or less, more preferably 2 parts by mass or more and 10,000 parts by mass or less, and even more preferably 5 parts by mass or more and 1,000 parts by mass or less.

[0086] The reaction time can vary depending on the reaction temperature, but is preferably, for example, 1 minute or more and 1,000 minutes or less, more preferably 3 minutes or more and 500 minutes or less, and even more preferably 5 minutes or more and 400 minutes or less. Further, after the reaction, excess reaction reagents, by-products, etc. may be washed and removed by filtration or the like.

[0087] <Cationic group introduction step (cationization step)> As an essential component, a compound having a reactive group and a cationic group (Compound E D) By adding, as an optional component, an alkali compound and Compound B selected from the above-described urea and its derivatives to cellulose fibers having hydroxyl groups in a wet or dry state and carrying out a reaction, a cationic group is introduced into the cellulose fibers.

[0088] Examples of the reactive group include an alkyl halide group, a vinyl group, an epoxy group (glycidyl group), and the like. Examples of the cationic group include an ammonium group, a phosphonium group, a sulfonium group, and the like. Among them, the cationic group is preferably an ammonium group. Compound E D From the viewpoints of the introduction efficiency of the substituent, and thus the defibrillation efficiency, cost, and ease of handling, glycidyltrimethylammonium chloride, 3-chloro-2-hydroxypropyltrimethylammonium chloride, etc. are preferable. Furthermore, as an optional component, it is also preferable to use the same Compound B as in the above-described <phosphonooxy acid group introduction step>. The addition amount is also preferably the same as described above.

[0089] Compound E D When adding Compound E, it may be added directly to the cellulose fibers as a reagent (in solid or liquid form), or it may be dissolved in a suitable solvent and then added. The cellulose fibers are preferably alkalicelluloseized in advance or alkalicelluloseized simultaneously with the reaction. The method of alkalicelluloseization is as described above.

[0090] The temperature during the reaction is preferably, for example, 50°C or higher and 300°C or lower, more preferably 100°C or higher and 250°C or lower, and even more preferably 130°C or higher and 200°C or lower.

[0091] Compound E D The addition amount of Compound E with respect to 100 parts by mass of the cellulose fibers is preferably 1 part by mass or more and 100,000 parts by mass or less, more preferably 2 parts by mass or more and 10,000 parts by mass or less, and even more preferably 5 parts by mass or more and 1,000 parts by mass or less.

[0092] The reaction time can vary depending on the reaction temperature, but it is preferably, for example, 1 minute or more and 1,000 minutes or less, more preferably 5 minutes or more and 500 minutes or less, and even more preferably 10 minutes or more and 400 minutes or less. After the reaction, excess reaction reagents, by-products, etc. may be washed and removed with water by filtration or the like.

[0093] After the reaction step as described above, it is preferable to have a dehydration / washing step, an alkali treatment step (neutralization step), and a fibrillation treatment step in this order, and in addition to the washing step, an acid treatment step may be included. 〔Dehydration / Washing Step〕 The dehydration / washing step is a step of washing the obtained dispersion of chemically modified cellulose with water or an organic solvent after dehydration treatment, and this step is an essential step for obtaining microfibrillar cellulose with few impurities. The washing is preferably carried out with water. Also, the dehydration / washing step may be carried out after each of the steps described below, and the number of washing times carried out in each washing step is not particularly limited. In this step, a dehydration device of the centrifugal separation type, vacuum dehydration type, or pressure dehydration type can be used. Specifically, centrifugal separation type: (Tanabe Ultitech centrifuge, Kokusan centrifuge, etc.), vacuum dehydration type: drum type vacuum dehydrator, Tsukishima Machinery horizontal belt filter, pressure dehydration type: filter press, tube press, screw press, belt press horizontal belt filter, poly disk filter, vibrating screen, etc. Among these, since dehydration can be carried out without applying a strong shearing force to the dehydration raw material, the pressure dehydration type (filter press, tube press), centrifugal separation type (Tanabe Ultitech centrifuge, Kokusan centrifuge, etc.), and vacuum dehydration type (drum type vacuum dehydrator, Tsukishima Machinery horizontal belt filter) are preferable. Also, a combination of a plurality of these can be used.

[0094] In this embodiment, in the dehydration and washing process, the dispersion of the chemically modified cellulose is transferred without using a pump. Examples of the transfer of the dispersion of the chemically modified cellulose include the transfer of the prepared dispersion of the chemically modified cellulose to a storage tank and the transfer from the storage tank to a filtration device. In the dehydration and washing process, it is preferable to transfer the dispersion of the chemically modified cellulose using gravity without using a pump. The method of transferring using gravity is not particularly limited, but an example is a method in which the dispersion of the chemically modified cellulose is stored in a storage tank provided above the above-described dehydration device used in the dehydration and washing process, and is transferred to the dehydration device using gravity. When transferring using gravity, it is preferable to control the flow rate by adjusting the opening degree of a valve provided at the outlet of the storage tank, in the pipe, etc. The valve may be an electromagnetic valve or an air valve, and is not particularly limited, but from the viewpoint of the operating speed at the time of opening and closing, it is preferably an air valve.

[0095] When transferring the dispersion of the chemically modified cellulose using gravity, the distance from the storage tank to the dehydration device is preferably 20 cm or more, more preferably 30 cm or more, still more preferably 50 cm or more as the vertical distance, and from the viewpoint of transfer efficiency, it is preferably 300 cm or less, more preferably 250 cm or less, still more preferably 200 cm or less.

[0096] Also, the method is not limited to the method of transferring using gravity, and an example is also a method of pressurizing the inside of the storage tank for transfer. When transferring by pressurizing the inside of the storage tank, it is preferable to control the flow rate by adjusting the pressure inside the storage tank, and in addition to adjusting the pressure inside the storage tank, the opening degree of a valve provided at the outlet of the storage tank, in the pipe, etc. may be adjusted. When pressurizing the storage tank, the pressure in the storage tank is preferably 0.005 MPa or more, more preferably 0.01 MPa or more, still more preferably 0.02 MPa or more, from the viewpoint of suppressing clogging and obtaining a sufficient transfer rate, and preferably 1.0 MPa or less, more preferably 0.8 MPa or less, still more preferably 0.5 MPa or less, from the viewpoint of reducing the load on the storage tank.

[0097] The size of the transfer pipe immediately before the dehydration device is preferably 200A or less, more preferably 150A or less, still more preferably 125A or less, from the viewpoint of adjusting the flow rate, and preferably 32A or more, more preferably 40A or more, still more preferably 50A or more, from the viewpoint of obtaining a sufficient flow rate.

[0098] The viscosity of the dispersion of the chemically modified cellulose to be transferred is preferably 10 mPa·s or more, more preferably 20 mPa·s or more, still more preferably 30 mPa·s or more, at 23°C, from the viewpoint of suppressing the liquid delivery amount during transfer, and preferably 5000 mPa·s or less, more preferably 1000 mPa·s or less, still more preferably 500 mPa·s or less, at 23°C, from the viewpoint of transferring without using a pump. The viscosity of the dispersion of the chemically modified cellulose is the value measured at a concentration of 2% by mass and a rotational speed of 3 rpm with a rotational viscometer.

[0099] The water retention capacity of the chemically modified cellulose to be transferred is preferably 5 g / g or more and 27 g / g or less, more preferably 10 g / g or more, still more preferably 15 g / g or more, and more preferably 26 g / g or less, still more preferably 25 g / g or less. When the water retention capacity is within the above range, it is preferable because the filtration efficiency is excellent and the production efficiency is excellent. Also, when the water retention capacity is within the above range, it is preferable because the dispersion spreads uniformly on the dehydrator and the uniformity of filtration on the dehydrator is improved. Here, the water retention capacity is an index indicating the ability of the fiber to retain water and can be determined as follows. Ion-exchanged water is added to the dispersion of chemically modified cellulose to prepare 40 mL of a slurry (medium: water) with a solid content of 0.3% by mass. Let the mass of this slurry be A. Then, the entire amount of the slurry is centrifuged for 30 minutes at 30 °C and 25,000 G using a high-speed cooling centrifuge to separate the aqueous phase and the sediment. Let the mass of the sediment at this time be B. Also, the aqueous phase is placed in an aluminum cup and dried at 105 °C for one day and night to remove water, and the mass of the solid content in the aqueous phase is measured. Let the mass of the solid content in this aqueous phase be C. The water retention capacity is calculated using the following formula: Water retention capacity = (B + C - 0.003×A) / (0.003×A - C). As shown in the above formula, the water retention capacity corresponds to the mass of water in the sediment with respect to the mass of the solid content of the fibers in the sediment. The larger the value, the higher the ability of the fibers to hold water. When the water retention capacity is high, it tends to be inferior in water permeability. In particular, when the water retention capacity increases due to transfer, the filtration efficiency tends to decrease. Therefore, in this embodiment, it is preferable to suppress the increase in the water retention capacity due to transfer. More specifically, the change in the water retention capacity due to transfer is preferably 5 g / g or less, more preferably 4 g / g or less, and even more preferably 3 g / g or less.

[0100] Note that an alkali treatment step and an acid treatment step may be provided between the above dehydration / washing step and the preparation step described later. Also, the above dehydration / washing step may be provided before and after the alkali treatment step and the acid treatment step. <Alkali treatment step> An alkali treatment step may be provided between the reaction step and the adjustment step. The method of alkali treatment is not particularly limited, and examples include immersing chemically modified cellulose, preferably chemically modified cellulose into which an ionic group has been introduced (ionic group-introduced cellulose), in an alkali solution.

[0101] The alkali compound contained in the alkali solution is not particularly limited and may be an inorganic alkali compound or an organic alkali compound. In the present embodiment, since it has high versatility, it is preferable to use, for example, sodium hydroxide or potassium hydroxide as the alkali compound. Further, the solvent contained in the alkali solution may be either water or an organic solvent. Among these, the solvent contained in the alkali solution is preferably a polar solvent including water or a polar organic solvent exemplified by alcohol, and more preferably an aqueous solvent containing at least water. As the alkali solution, since it has high versatility, for example, an aqueous sodium hydroxide solution or an aqueous potassium hydroxide solution is preferable.

[0102] The temperature of the alkali solution in the alkali treatment step is not particularly limited, but it is preferably, for example, 5°C or higher and 80°C or lower, and more preferably 10°C or higher and 60°C or lower. The immersion time of the chemically modified cellulose in the alkali solution in the alkali treatment step is not particularly limited, but it is preferably, for example, 5 minutes or longer and 30 minutes or shorter, and more preferably 10 minutes or longer and 20 minutes or shorter. The amount of the alkali solution used in the alkali treatment is not particularly limited, but it is preferably, for example, 100% by mass or more and 100,000% by mass or less with respect to the absolute dry mass of the chemically modified cellulose, and more preferably 1,000% by mass or more and 10,000% by mass or less.

[0103] In order to reduce the amount of the alkali solution used in the alkali treatment step, the chemically modified cellulose may be washed with water or an organic solvent after the reaction step and before the alkali treatment step. After the alkali treatment step and before the fibrillation step, from the viewpoint of improving handleability, it is preferable to wash the chemically modified cellulose subjected to the alkali treatment with water or an organic solvent.

[0104] <Acid treatment step> In the reaction step, an acid treatment step may be provided between the step of introducing an ionic group and the adjustment step. For example, the reaction step, acid treatment, alkali treatment, and fibrillation treatment may be performed in this order.

[0105] The method of acid treatment is not particularly limited. For example, a method of immersing chemically modified cellulose in an acidic solution containing an acid can be mentioned. The concentration of the acidic solution to be used is not particularly limited, but for example, it is preferably 10% by mass or less, and more preferably 5% by mass or less. Further, the pH of the acidic solution to be used is not particularly limited, but for example, it is preferably 0 or more and 4 or less, and more preferably 1 or more and 3 or less. As the acid contained in the acidic solution, for example, inorganic acids, sulfonic acids, carboxylic acids, etc. can be used. Examples of inorganic acids include sulfuric acid, nitric acid, hydrochloric acid, hydrobromic acid, hydroiodic acid, hypochlorous acid, chlorous acid, chloric acid, perchloric acid, phosphoric acid, boric acid, etc. Examples of sulfonic acids include methanesulfonic acid, ethanesulfonic acid, benzenesulfonic acid, p-toluenesulfonic acid, trifluoromethanesulfonic acid, etc. Examples of carboxylic acids include formic acid, acetic acid, citric acid, gluconic acid, lactic acid, oxalic acid, tartaric acid, etc. Among these, it is particularly preferable to use hydrochloric acid or sulfuric acid.

[0106] The temperature of the acid solution in the acid treatment is not particularly limited, but for example, it is preferably 5°C or more and 100°C or less, and more preferably 20°C or more and 90°C or less. The immersion time in the acid solution in the acid treatment is not particularly limited, but for example, it is preferably 5 minutes or more and 120 minutes or less, and more preferably 10 minutes or more and 60 minutes or less. The amount of the acid solution used in the acid treatment is not particularly limited, but for example, it is preferably 100% by mass or more and 100,000% by mass or less with respect to the absolute dry mass of the chemically modified cellulose, and more preferably 1,000% by mass or more and 10,000% by mass or less.

[0107] 〔Adjustment step〕 In the present embodiment, in order to efficiently perform the following fibrillation step, the concentration of the dispersion of chemically modified cellulose is adjusted. In the adjustment process, for example, it is preferable to dilute chemically modified cellulose with a dispersion medium to form a slurry. As the dispersion medium, one or more selected from water and organic solvents such as polar organic solvents can be used. The polar organic solvent is not particularly limited, but for example, alcohols, polyhydric alcohols, ketones, ethers, esters, aprotic polar solvents, etc. are preferable. Examples of alcohols include methanol, ethanol, isopropanol, n-butanol, isobutyl alcohol, etc. Examples of polyhydric alcohols include ethylene glycol, propylene glycol, glycerin, etc. Examples of ketones include acetone, methyl ethyl ketone (MEK), etc. Examples of ethers include diethyl ether, tetrahydrofuran, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol mono n-butyl ether, propylene glycol monomethyl ether, etc. Examples of esters include ethyl acetate, butyl acetate, etc. Examples of aprotic polar solvents include dimethyl sulfoxide (DMSO), dimethylformamide (DMF), dimethylacetamide (DMAc), N-methyl-2-pyrrolidone (NMP), etc. Among these, it is preferable to use water.

[0108] The solid content concentration of the dispersion of chemically modified cellulose in the adjustment process can be set as appropriate. The solid content concentration of the dispersion of chemically modified cellulose is preferably 0.1% by mass or more and 10% by mass or less. The solid content concentration of the dispersion of chemically modified cellulose is more preferably 0.2% by mass or more, still more preferably 0.3% by mass or more, and preferably 10% by mass or less, more preferably 6% by mass or less. If the solid content concentration is too low, the amount of liquid becomes too large relative to the amount of chemically modified cellulose to be treated, resulting in poor efficiency. If the solid content concentration is too high, the fluidity becomes poor. In addition, the dispersion of chemically modified cellulose may contain solids other than ionic group-introduced pulp such as hydrogen-bonding urea.

[0109] 〔Fibrillation process〕 In this embodiment, the fibrillation process is a process of fibrillating chemically modified cellulose by applying mechanical shear force to a dispersion of the chemically modified cellulose. In the fibrillation process, for example, a fibrillation treatment device can be used. The fibrillation treatment device is not particularly limited, and for example, a high-speed fibrillator, a grinder (stone mill type crusher), a high-pressure homogenizer or an ultra-high pressure homogenizer, a high-pressure impact type crusher, a ball mill, a bead mill, a disk type refiner, a conical refiner, a twin-screw kneader, a vibration mill, a homomixer under high-speed rotation, an ultrasonic disperser, or a beater can be used. Among the above fibrillation treatment devices, it is more preferable to use a high-speed fibrillator, a high-pressure homogenizer, or an ultra-high pressure homogenizer that is less affected by grinding media and has less risk of contamination.

[0110] The fibrillation process may be carried out in one step using the above-mentioned fibrillation treatment device, or may be carried out in two steps including a rough fibrillation step and a fine fibrillation step. When the fibrillation process is carried out in two steps, in the rough fibrillation step, it is preferable to carry out fibrillation using a refiner, and the refiner performs preliminary fibrillation on the chemically modified cellulose. A refiner is a device that beats chemically modified cellulose, and by applying shear force to the chemically modified cellulose by beating while applying a load, it causes fluffing on the chemically modified cellulose and makes the fibers flexible to perform preliminary fibrillation.

[0111] The refiner is not particularly limited as long as it can beat chemically modified cellulose, and known ones can be used. As the refiner, a conical type, a double disk refiner (DDR), or a single disk refiner (SDR) is preferable from the viewpoints of efficiently applying shear force to the chemically modified cellulose and being able to proceed with preliminary fibrillation.

[0112] In the fibrillation process, it is preferable to use a high-pressure homogenizer. The high-pressure homogenizer is used to refine the chemically modified cellulose in the slurry and is used as a disperser that discharges the slurry and the like at high pressure from pores. The high-pressure homogenizer refers to a homogenizer having the ability to discharge the slurry at a pressure of, for example, 10 MPa or more, preferably 100 MPa or more. By treating the pulp with introduced ionic groups using a high-pressure homogenizer, collisions between fibers of the chemically modified cellulose, pressure differences, microcavitation, etc. act, and fibrillation occurs effectively. As a result, the number of treatment times in the refinement process can be reduced (shortened), and the production efficiency of microfibrillated cellulose can be further increased.

[0113] <Microfibrillated cellulose> The microfibrillated cellulose obtained by the production method of this embodiment is fibrillar cellulose having a fiber width of 1,000 nm or less. The fiber width of the fibrillar cellulose can be measured, for example, by electron microscope observation. The fiber width of the microfibrillated cellulose is 1,000 nm or less. The fiber width of the microfibrillated cellulose is preferably, for example, 2 nm or more and 1,000 nm or less, more preferably 2 nm or more and 100 nm or less, even more preferably 2 nm or more and 50 nm or less, and particularly preferably 2 nm or more and 10 nm or less. By setting the fiber width of the microfibrillated cellulose to 2 nm or more, dissolution in water as cellulose molecules can be suppressed, and the effects of improving the strength, rigidity, and dimensional stability by the microfibrillated cellulose can be more easily expressed.

[0114] The average fiber width of the microfibrillar cellulose is, for example, 1,000 nm or less. The average fiber width of the microfibrillar cellulose is preferably 2 nm or more and 1,000 nm or less, more preferably 2 nm or more and 100 nm or less, even more preferably 2 nm or more and 50 nm or less, and particularly preferably 2 nm or more and 10 nm or less. By setting the average fiber width of the microfibrillar cellulose to 2 nm or more, dissolution in water as a cellulose molecule can be suppressed, and the effects of improving the strength, rigidity, and dimensional stability by the microfibrillar cellulose can be more easily expressed. Note that the microfibrillar cellulose is, for example, single-fiber cellulose.

[0115] The average fiber width of the microfibrillar cellulose is measured, for example, using an electron microscope as follows. First, an aqueous suspension of fibrillar cellulose with a concentration of 0.05% by mass or more and 0.1% by mass or less is prepared, and this suspension is cast onto a carbon film-coated grid that has been hydrophilized to obtain a sample for TEM observation. When the sample contains wide fibers, the SEM image of the surface cast on glass may be observed. Next, observation is performed on the electron microscope image at any one of magnifications of 1,000 times, 5,000 times, 10,000 times, or 50,000 times according to the width of the fiber to be observed. However, the sample, observation conditions, and magnification are adjusted to satisfy the following conditions. (1) Draw a straight line X at an arbitrary position within the observation image, and 20 or more fibers intersect this straight line X. (2) Draw a straight line Y that intersects perpendicularly to the straight line within the same image, and 20 or more fibers intersect this straight line Y.

[0116] For the observation image that satisfies the above conditions, visually read the widths of the fibers that intersect the straight line X and the straight line Y. In this way, obtain 3 or more sets of observation images of surface portions that do not overlap with each other at least. Next, for each image, read the widths of the fibers that intersect the straight line X and the straight line Y. As a result, at least 20 × 2 × 3 = 120 fiber widths are read. Then, the average value of the read fiber widths is taken as the average fiber width of the fibrillar cellulose.

[0117] The fiber length of the microfibrillar cellulose is not particularly limited, but is preferably, for example, 0.1 μm or more and 1,000 μm or less, more preferably 0.1 μm or more and 800 μm or less, and even more preferably 0.1 μm or more and 600 μm or less. By setting the fiber length within the above range, destruction of the crystalline regions of the microfibrillar cellulose can be suppressed. Also, it becomes possible to set the slurry viscosity of the microfibrillar cellulose within an appropriate range. Note that the fiber length of the microfibrillar cellulose can be determined, for example, from image analysis by TEM, SEM, or AFM.

[0118] The microfibrillar cellulose preferably has an I-type crystal structure. Here, the fact that the microfibrillar cellulose has an I-type crystal structure can be identified from the diffraction profile obtained from a wide-angle X-ray diffraction photograph using graphite-monochromatized CuKα (λ = 1.5418 Å). Specifically, it can be identified from the fact that typical peaks are present at two positions near 2θ = 14° or more and 17° or less and near 2θ = 22° or more and 23° or less. The proportion of the I-type crystal structure in the microfibrillar cellulose is preferably, for example, 30% or more, more preferably 40% or more, and even more preferably 50% or more. Thereby, further excellent performance can be expected in terms of heat resistance and manifestation of a low linear thermal expansion rate. Regarding the crystallinity, an X-ray diffraction profile is measured, and it is determined by a conventional method from the pattern (Seagal et al., Textile Research Journal, Vol. 29, page 786, 1959).

[0119] The axial ratio (fiber length / fiber width) of the microfibrillar cellulose is not particularly limited, but is preferably, for example, 20 or more and 10,000 or less, more preferably 50 or more and 1,000 or less. By setting the axial ratio to be equal to or higher than the above lower limit value, it becomes easy to form a sheet containing the microfibrillar cellulose. Also, sufficient thickening property is easily obtained when preparing a solvent dispersion. By setting the axial ratio to be equal to or lower than the above upper limit value, it is preferable, for example, in terms of ease of handling such as dilution when treating the microfibrillar cellulose as an aqueous dispersion.

Examples

[0120] Examples and comparative examples are given below to more specifically explain the features of the present invention. The materials, amounts used, ratios, treatment details, treatment procedures, etc. shown in the following examples can be appropriately changed as long as they do not depart from the spirit of the present invention. Therefore, the scope of the present invention should not be construed in a limited manner by the specific examples shown below.

[0121] <Measurement> [Measurement of the amount of phosphonooxy groups] The amount of phosphonooxy groups in the microfibrillar cellulose was measured by performing titration with an alkali after treating a fibrillar cellulose-containing slurry prepared by diluting a microfibrillar cellulose dispersion containing the target microfibrillar cellulose with ion-exchanged water so that the content became 0.2% by mass with an ion-exchange resin. The treatment with the ion-exchange resin was carried out by adding a strongly acidic ion-exchange resin (Amberjet 1024; Organo Corporation, conditioned) having a volume of 1 / 10 to the above fibrillar cellulose-containing slurry, performing a shaking treatment for 1 hour, and then pouring it onto a mesh with an opening of 90 μm to separate the resin and the slurry. Also, the titration using an alkali was carried out by measuring the change in the pH value shown by the fibrous cellulose-containing slurry after treatment with an ion-exchange resin while adding 10 μL of a 0.1 N aqueous sodium hydroxide solution to the slurry every 5 seconds. Note that the titration was carried out while blowing nitrogen gas into the slurry from 15 minutes before the start of the titration. In this neutralization titration, two points where the increment (the differential value of the pH with respect to the amount of alkali added) becomes maximum are observed in the curve plotting the measured pH against the amount of alkali added. Among these, the first maximum point of the increment obtained first after starting to add the alkali is called the first end point, and the next maximum point of the increment is called the second end point (Figure 1). The amount of alkali required from the start of the titration to the first end point is equal to the amount of the first dissociating acid in the slurry used for the titration. Also, the amount of alkali required from the start of the titration to the second end point is equal to the total amount of dissociating acid in the slurry used for the titration. Note that the value obtained by dividing the amount of alkali (mmol) required from the start of the titration to the first end point by the solid content (g) in the slurry to be titrated was defined as the amount of phospho-oxo acid groups (mmol / g).

[0122] As the raw material pulp, softwood kraft pulp manufactured by Oji Paper Co., Ltd. (solid content 93 mass%, basis weight 245 g / m 2 in sheet form, disintegrated, and having a Canadian Standard Freeness (CSF) measured in accordance with JIS P 8121-2:2012 of 700 mL) was used.

[0123] The phospho-oxidation treatment of this raw material pulp was carried out as follows. First, an aqueous mixed solution of ammonium dihydrogen phosphate and urea was added to 100 parts by mass (dry mass) of the above raw material pulp and adjusted to 45 parts by mass of ammonium dihydrogen phosphate, 120 parts by mass of urea, and 150 parts by mass of water to obtain an impregnated pulp with chemicals. Next, the obtained impregnated pulp with chemicals was heated in a hot air dryer at 165 °C for 250 seconds to introduce phosphate groups into the cellulose in the pulp and obtain a phosphorylated pulp.

[0124] The obtained phosphorylated pulp was measured for infrared absorption spectrum using FT-IR. As a result, 1230 cm -1Absorption based on P=O of phosphate groups was observed nearby, and it was confirmed that phosphate groups were added to the pulp. Further, when the obtained phosphorylated pulp was tested and analyzed with an X-ray diffractometer, typical peaks were confirmed at two positions near 2θ = 14° or more and 17° or less and near 2θ = 22° or more and 23° or less, and it was confirmed that it had cellulose I-type crystals. The amount of phosphate groups (the amount of the first dissociation acid) measured by the measurement method described in [Measurement of the amount of phosphooxo acid groups] described later was 2.35 mmol / g.

[0125] <Water retention capacity> Ion-exchanged water was added to the dispersion of the chemically modified cellulose to prepare 40 mL of a slurry (medium: water) with a solid content of 0.3% by mass. Let the mass of this slurry at this time be A. Next, the entire amount of the slurry was centrifuged at 30 °C and 25,000 G for 30 minutes using a high-speed cooling centrifuge to separate the aqueous phase and the sediment. Let the mass of the sediment at this time be B. Also, the aqueous phase was placed in an aluminum cup and dried at 105 °C for one day and night to remove water, and the mass of the solid content in the aqueous phase was measured. Let the mass of the solid content in this aqueous phase be C. The water retention capacity was calculated using the following formula: Water retention capacity = (B + C - 0.003×A) / (0.003×A - C). The water retention capacity corresponds to the mass of water in the sediment with respect to the mass of the solid content of the fibers in the sediment as per the above formula. The larger the value, the higher the ability of the fibers to hold water, which means poorer filtration efficiency.

[0126] <Example 1> The washing treatment of the phosphorylated pulp was carried out as follows. The obtained phosphorylated pulp was diluted to a concentration of 2%, and a chemically modified cellulose dispersion A (water retention capacity of chemically modified cellulose = 23 g / g) was obtained. 250 g of the chemically modified cellulose dispersion A was poured into a suction filtration device equipped with a circular quantitative filter paper (manufactured by ADVANTEC, No. 2, 90 mm φ) using gravity without using a pump, and suction filtration was carried out under the condition of -30 kPa. The time from the start of suction until sufficient dehydration occurred and the entire surface of the pulp mat became white was measured. The chemically modified cellulose remaining on the filter paper was recovered, and 100 g of ion-exchanged water was added. After stirring to disperse uniformly, filtration and dehydration were carried out under the same conditions, and the time from the start of suction until sufficient dehydration occurred and the entire surface of the pulp mat became white was measured.

[0127] Next, the chemically modified cellulose remaining on the filter paper was recovered, and 166 g of a 0.3N aqueous sodium hydroxide solution was added. After stirring to disperse uniformly, filtration and dehydration were carried out under the same conditions, and the time from the start of suction until the filtrate stopped dropping was measured. Then, the chemically modified cellulose remaining on the filter paper was recovered, and 400 g of ion-exchanged water was added. After stirring to disperse uniformly, filtration and dehydration were carried out under the same conditions, and the time from the start of suction until sufficient dehydration occurred and the entire surface of the pulp mat became white was measured. The total time from the start of suction until the filtrate stopped dropping in each filtration treatment was 60 seconds.

[0128] Ion-exchanged water was added to the washed chemically modified cellulose to prepare a chemically modified cellulose dispersion with a solid content concentration of 2% by mass. It was treated twice with the pressure of a wet atomization device (manufactured by Sugino Machine Limited, Starburst) set at 200 MPa to obtain a microfibrillated cellulose dispersion containing microfibrillated cellulose. The processing speed of the wet atomization device was 30 L / h. When the fiber width of the obtained microfibrillated cellulose was measured using a transmission electron microscope, it was 3 - 5 nm.

[0129] <Comparative Example 1> The washing treatment of the phosphorylated pulp was carried out as follows. After diluting the obtained phosphorylated pulp to a concentration of 2%, the slurry was passed through a Mono Pump (Model 3NUL10) manufactured by Heishin Sobi Co., Ltd. twice at a flow rate of 1.5 L / min to obtain a chemically modified cellulose dispersion B (water retention capacity of chemically modified cellulose = 28 g / g). Passing the pump twice was considered in view of the transfer of the phosphorylated pulp dispersion to the storage tank and the transfer to the filtration device in the actual machine. 250 g of the chemically modified cellulose dispersion B was poured into a suction filtration device equipped with a circular quantitative filter paper (manufactured by ADVANTEC, No. 2, 90 mm φ), and suction filtration was carried out under the condition of -30 kPa. The time was measured from the start of suction until sufficient dehydration occurred and the entire surface of the pulp mat became white. The chemically modified cellulose remaining on the filter paper was recovered, and 100 g of ion-exchanged water was added. After stirring to disperse uniformly, filtration and dehydration were carried out under the same conditions, and the time was measured from the start of suction until sufficient dehydration occurred and the entire surface of the pulp mat became white.

[0130] Next, the chemically modified cellulose remaining on the filter paper was recovered, and 166 g of a 0.3 N aqueous sodium hydroxide solution was added. After stirring to disperse uniformly, filtration and dehydration were carried out under the same conditions, and the time was measured from the start of suction until sufficient dehydration occurred and the entire surface of the pulp mat became white. Then, the chemically modified cellulose remaining on the filter paper was recovered, and 400 g of ion-exchanged water was added. After stirring to disperse uniformly, filtration and dehydration were carried out under the same conditions, and the time was measured from the start of suction until sufficient dehydration occurred and the entire surface of the pulp mat became white. The total time from the start of suction until the filtrate stopped dropping in each filtration treatment was 90 seconds.

[0131] Ion-exchanged water was added to the washed chemically modified cellulose to prepare a chemically modified cellulose dispersion with a solid content concentration of 2% by mass. The pressure of a wet atomization device (manufactured by Sugino Machine Limited, Starburst) was set to 200 MPa and processed twice to obtain a microfibrillated cellulose dispersion containing microfibrillated cellulose. The processing speed of the wet atomization device was 30 L / h. When the fiber width of the obtained microfibrillated cellulose was measured using a transmission electron microscope, it was 3 to 5 nm.

[0132] As shown in the examples and comparative examples, in Example 1 where no pump was used for the dispersion of chemically modified cellulose, the water retention capacity of the chemically modified cellulose was 23 g / g and the total filtration time was 60 seconds. In contrast, in Comparative Example 1 where the pump was passed through twice, the water retention capacity of the chemically modified cellulose increased to 28 g / g and the filtration time was 90 seconds. This is considered to be because the use of the pump caused the chemically modified cellulose to fluff due to shear force etc., improving the water retention property, and thus increasing the time required for filtration.

Claims

1. A reaction step of chemically modifying cellulose fibers to obtain chemically modified cellulose, A dehydration / washing step of dehydrating and washing the dispersion of the chemically modified cellulose, An adjustment step of adjusting the concentration of the dispersion of the chemically modified cellulose, A fibrillation step of applying mechanical shear force to the dispersion of the chemically modified cellulose to defibrillate it, A method for producing microfibrillated cellulose, comprising the above steps in this order, In the dehydration / washing step, the dispersion of the chemically modified cellulose is transferred without using a pump, A method for producing microfibrillated cellulose.

2. The method for producing microfibrillated cellulose according to Claim 1, wherein in the dehydration / washing step, the dispersion of the chemically modified cellulose is transferred using gravity without using a pump.

3. The method for producing microfibrillated cellulose according to Claim 1, wherein the water retention capacity of the chemically modified cellulose transferred in the dehydration / washing step is 10 g / g or more and 25 g / g or less.

4. The method for producing microfibrillated cellulose according to Claim 1, wherein the reaction step is a step of introducing an ionic group into cellulose fibers.

5. The method for producing microfibrillated cellulose according to Claim 4, wherein the ionic group is an anionic group.

6. The method for producing microfibrillated cellulose according to Claim 5, wherein the anionic group is at least one selected from the group consisting of a phosphono group, a sulfono group, and a carboxy group.

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