JP6713590B1 - Method for producing dry solid containing fine cellulose fibers - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for easily producing a dry solid material containing fine cellulose fibers which is excellent in redispersibility in a solvent such as water. A method for producing a dry solid containing fine cellulose fibers of the present invention includes a step of drying under a low pressure condition at a relatively low temperature. Since the fine cellulose fiber-containing dry solid produced in one aspect of the present invention contains fine cellulose fibers having a sulfur introduction amount of 0.5 mmol/g or more based on a sulfo group, transparency, viscosity characteristics, precipitation characteristics From the viewpoint of, the redispersibility is excellent. [Selection diagram] Figure 1

Description

The present invention relates to a method for producing a dry solid containing fine cellulose fibers, which has excellent redispersibility in water.

Cellulose nanofibers (CNFs) are microfibers obtained by subjecting plant-derived cellulose to nanoprocessing (mechanical defibration, TEMPO-catalyzed oxidation, etc.) and having a fiber width on the order of nanometers and a fiber length of several hundred nm. Since CNF has light weight, high elasticity, high strength, and low linear thermal expansion property, the use of composite materials containing CNF is expected not only in the industrial field but also in various fields such as food field and medical field. ing.

Since CNF is usually produced from plant-derived cellulose (pulp or the like) in a water-dispersed state, it is obtained in a water-dispersed state. This water dispersion contains several to several hundred times as much water as CNF in order to ensure dispersion stability, and the increase in cost due to the increase in energy and storage space during transportation, There are various problems such as the limited use of CNF.

For this reason, it is desirable to perform treatments such as drying the CNFs or aggregating them to a high concentration, but during the process of drying or concentrating, the CNFs are strongly bound to each other by hydrogen bonds, and the original CNF water dispersion is obtained. It was difficult to restore the state (hereinafter also referred to as “redispersion”) and to exhibit the original characteristics of CNF (hereinafter, this characteristic is referred to as “redispersion”). The following patent documents have tried to solve such problems.

Patent Document 1 discloses a method of treating with dry water the redispersed dry solids of cellulose nanofibers obtained by defibrating chemically modified cellulose fibers.

JP, 2017-2136, A

However, the technique of Patent Document 1 has a problem in that energy cost due to the use of hot water and a multistage process are required. Moreover, Patent Document 1 does not describe a fine cellulose fiber having a sulfo group introduced therein.
In view of the above circumstances, it is an object of the present invention to provide a simple method for producing a dry solid containing fine cellulose fibers, which is excellent in redispersibility in a solvent such as water.

According to the present invention, the following [1] to [3] are provided.
[1]
A method for producing a dried product having redispersibility, which is obtained by drying sulfonated fine cellulose fibers, wherein the amount of sulfur introduced due to a sulfo group is 0.5 mmol/g to 3.0 mmol by chemically treating pulp. /G to prepare a sulfonated pulp, a fine treatment step for finely treating the pulp after the chemical treatment step into fine cellulose fibers having an average fiber width of 1 nm to 1000 nm, A method of sequentially performing a drying step of drying a mixture obtained by dispersing the refined sulfonated fine cellulose fibers in water after the treatment step so that the water content is 80% or less, wherein the chemical treatment step is A contact step of contacting a reaction liquid in which sulfamic acid having a sulfo group and urea is dissolved in water with respect to pulp fibers constituting the pulp, and pulp after the contact step (however, in a desiccator containing anhydrous calcium chloride Is supplied to the reaction step, and in the reaction step, a step of introducing a sulfo group into a part of the hydroxyl groups of the cellulose constituting the pulp fiber is carried out in order. The reaction step is a step of heating the pulp fiber in a state where the reaction liquid after the contacting step is in contact with the reaction solution to proceed the reaction, and the reaction temperature is 100° C. to 180° C. and the reaction time is 1 minute or more. In the drying step of adjusting the temperature of the sulfonated fine cellulose fiber, the drying temperature may be one of the following (1) to (3) in relation to the amount of sulfur introduced due to the sulfo group of the sulfonated fine cellulose fiber. A method for producing a dry solid containing fine cellulose fibers, which satisfies the above condition.
(1) The mixture in which the sulfonated fine cellulose fiber having a sulfur introduction amount of 0.5 mmol/g or more and lower than 0.9 mmol/g is dispersed is dried at 40° C. or less.
(2) The mixture in which the sulfonated fine cellulose fibers having a sulfur introduction amount of 0.9 mmol/g or more and lower than 1.4 mmol/g are dispersed is dried at 70°C or less.
(3) The mixture in which the sulfonated fine cellulose fibers having a sulfur introduction amount of 1.4 mmol/g or more and 3.0 mmol/g or less are dispersed is dried at 120° C. or less.
[2]
The mixture obtained by dispersing the fine cellulose fibers after the refining treatment step in water so that the solid content concentration becomes 0.5% by mass is used as a pre-drying dispersion, and the mixture after the drying step has a solid content concentration of 0. The B-type viscosity recovery rate of the mixture after the drying step, obtained by the following formula (1), is 30% when the dispersion liquid dispersed in water so as to be 0.5% by mass is dried and then used as a redispersion liquid. The above is the method for producing a dry solid containing fine cellulose fibers according to [1].
(B type viscosity recovery rate)
B-type viscosity recovery rate (%)=(viscosity of redispersion liquid after drying)/(viscosity of dispersion liquid before drying)×100 (1)
(Viscosity: Viscosity mPa·s measured by rotating with a B-type viscometer at 25° C., rotation speed 12 rpm, 3 minutes)
[3]
The method for producing a dry solid containing fine cellulose fibers according to [1] or [2], wherein the mixture is dried under reduced pressure at 480 hPa or less.

ADVANTAGE OF THE INVENTION According to this invention, even if it does not use big heat energy and an additive, it is excellent in redispersibility and can provide the fine cellulose fiber containing dry solid obtained by a simple manufacturing method. Further, it is possible to provide a fine cellulose fiber redispersion liquid having good redispersibility, excellent transparency and viscosity characteristics when the fine cellulose fiber-containing dry solid is redispersed in a solvent.

It is a flow figure of a manufacturing method of a dry solid content containing fine cellulose fiber. FIG. 3 is a diagram showing transparency and viscosity characteristics of a sulfonated fine cellulose fiber dispersion and a fine cellulose redispersion after redispersion. It is the figure which showed the precipitation characteristic in the fine cellulose fiber redispersion liquid. It is the figure which showed the precipitation characteristic of FIG. 3 by the relationship of the sulfur introduction amount and drying temperature.

The fine cellulose fiber-containing dry solid, the method for producing the fine cellulose fiber-containing dry solid of the present embodiment, and the fine cellulose fiber redispersion liquid will be described in detail in order.

<1. Dry solids containing fine cellulose fibers>
The fine cellulose fiber-containing dry solid according to the present embodiment contains fine cellulose fibers and can be suitably produced by the production method described below. Specifically, the fine cellulosic fiber-containing dry solid is a dried product of a mixture containing fine cellulosic fibers. The fine cellulose fiber-containing dry solid can be used as a fine cellulose fiber redispersion liquid obtained by mixing and redispersing with a solvent such as water.

The water content in the dry solid containing the fine cellulose fibers is not particularly limited and may be 80% or less, preferably 80% or less and 50% or more, and more preferably measured according to JIS P 8203. It is preferably 50% or less, more preferably 30% or less, further preferably 20% or less, and particularly preferably 10% or less. When the moisture content is high, it cannot contribute to solving problems related to increase in energy and cost for transportation and space and cost for storage. The details will be described later. The formula for obtaining the water content (%) will be described later.

"Fine cellulose fibers"
The fine cellulose fibers are fine fibers obtained by subjecting a plant-derived cellulose raw material (pulp fiber) to nano-processing (mechanical defibration, TEMPO catalytic oxidation, etc.). Its properties are crystallinity with a fiber width of the order of nanometers and a fiber length of several hundred nm, and it has light weight, high elasticity, high strength, and low linear thermal expansion.

In the present embodiment, the fine cellulose fibers have a substituent introduced into a part of the hydroxyl group, and the substituent is an ionic substituent (for example, a sulfo group, a carboxyl group, a phosphoric acid group, a phosphorous acid group, and others. Anionic groups and cationic groups) are more desirable, and ionic substituents are more desirably sulfo groups. By introducing an ionic substituent, from the viewpoint that the hydrophilicity of the fine cellulose fibers is increased, and the electrostatic repulsion between the ions is generated, energy saving and dispersion in the fine cellulose fiber dispersion manufacturing process during dispersion It is easy to obtain stable dispersibility in the above step, and it is possible to contribute to water permeation into the dried solid material containing fine cellulose fibers after drying, and the redispersibility is improved.
Hereinafter, a sulfonated fine cellulose fiber in which a part of the hydroxyl groups of the fine cellulose fiber is substituted with a sulfo group will be described as a representative.

(Sulfonated fine cellulose fiber)
The sulfonated fine cellulose fiber is a fine cellulose fiber in which the cellulose fiber is finely divided, and is at least the cellulose (chain polymer having D-glucose bound to β(1→4) glycoside) constituting the fine cellulose fiber. A part of hydroxyl groups (-OH group) is substituted (sulfolated) with a sulfo group represented by the following formula (1).

(Sulfo group)

(−SO ₃ ⁻ ) _r ·Z ^r+ (1)

(Here, r is an independent natural number of 1 to 3, and Z ^r+ is a hydrogen ion, an alkali metal cation, an ammonium ion, an aliphatic ammonium ion, or an aromatic ammonium ion when r=1. (At least one selected from the group, and when r=2 or 3, at least one selected from the group consisting of an alkaline earth metal cation or a polyvalent metal cation.)

(Method for producing sulfonated fine cellulose fiber)
As shown in FIG. 1, the sulfonated fine cellulose fiber of the present embodiment is obtained by a chemical treatment step S1 of introducing a sulfo group into a pulp fiber and then a fine treatment step S2 of physically mechanical defibration. be able to.
On the other hand, it is also possible to produce a sulfonated fine cellulose fiber by chemically treating the pulp fiber after finely treating it, but from the viewpoint of reducing the energy required for defibration and reducing the production cost, the fiber width is small. From the viewpoint of easily obtaining uniform fine cellulose fibers, it is desirable to apply the refining treatment step S2 after introducing the sulfo group into the pulp fibers.

(Chemical treatment step S1)
The chemical treatment step S1 includes a contact step S1A in which a sulfonating agent having a sulfo group and urea or/and a derivative thereof are brought into contact with pulp fibers, and at least one hydroxyl group of cellulose contained in the pulp fibers after the contact step S1A. Reaction step S1B of introducing a sulfo group into the part.

(Reaction step S1B)
In the reaction step S1B in the chemical treatment step S1 of the method for producing a sulfonated fine cellulose fiber of the present embodiment, the sulfo group of the sulfonating agent contacted with the hydroxyl group of cellulose contained in the fiber raw material is replaced as described above, In this step, a sulfo group is introduced into the cellulose contained in the fiber raw material.
The reaction step S1B is not particularly limited as long as it is a method capable of performing a sulfonation reaction in which a hydroxyl group of cellulose is replaced with a sulfo group. For example, a sulfo group can be introduced into the cellulose contained in the fiber raw material by heating the fiber raw material impregnated with the reaction solution at a predetermined temperature.

The fiber raw material to be supplied to the reaction step S1B is not particularly limited as long as it contains water as described above. For example, the fiber raw material to be supplied to the reaction step S1B may have a high water content after the contact step S1A, or may be subjected to dehydration treatment or the like to have a low water content before being supplied to the reaction step S1B. Alternatively, as will be described later, the moisture content may be further lowered by performing a drying treatment or the like. In other words, the fiber raw material to be supplied to the reaction step S1B is not particularly limited as long as it is in a state other than that it does not contain water, that is, in a non-absolute dry state having a water content of 1% or more.

In the present specification, such a non-absolute dry fiber raw material having a water content of 1% or more is referred to as a water-containing state (that is, a wet state), and a state in which the reaction liquid is still impregnated or the like. In the present specification, not only the state of being dehydrated to some extent, but also the state of being dried to some extent is referred to as a wet state.
In the present specification, absolute dry means that the water content is lower than 1%. Then, the drying treatment step of drying to dryness refers to a step of reducing the pressure with a desiccator containing a desiccant such as calcium chloride, anhydrous calcium chloride, diphosphorus pentoxide or the like (drying under reduced pressure). .. That is, in the chemical treatment step S1 of the method for producing a sulfonated fine cellulose fiber of the present embodiment, when the fiber raw material before being fed to the reaction step S1B is subjected to dehydration treatment or drying treatment, the treatment (dehydration treatment or drying treatment) is The treatment shall be completed before such fiber raw material becomes completely dry.
The water content (%) can be calculated by the following formula.

Moisture content (%)=((mass of sample−mass of solid content of sample)/mass of sample)×100

(The mass of the sample means the mass (g) of the sample used in the measurement (for example, the fiber raw material used in the reaction step S1B in the above example). The mass of the solid content of the sample is the same as that of the sample used in the measurement. The amount of the sample was dried in an atmosphere of 105° C. for 2 hours until it became a constant weight, and the remaining solid matter (for example, in the above example, the fiber raw material used in the reaction step S1B was dried to be a constant weight state). (The latter fiber raw material) means the mass (g).)

(Reaction temperature in reaction step S1B)
The heating temperature in the reaction step S1B is not particularly limited as long as it is a temperature at which a sulfo group can be introduced into the cellulose constituting the fiber raw material while suppressing thermal decomposition or hydrolysis reaction of the fiber.
Specifically, any material capable of directly or indirectly heating the fiber raw material after the contact step S1A while satisfying the above requirements may be used. As such a thing, a well-known drier, a decompression drier, a microwave heating device, an autoclave, an infrared heating device, etc. can be mentioned. In particular, since gas may be generated in the reaction step S1B, it is preferable to use a circulating-air type dryer.

The shape of the fiber raw material after the contacting step S1A is not particularly limited, but for example, if it is heated in the form of a sheet or in a state of being loosened to some extent using the above-mentioned device or the like, the reaction can easily proceed uniformly. preferable.

The heating temperature in reaction step S1B is not particularly limited as long as it satisfies the above requirements. For example, the ambient temperature is preferably 250° C. or lower, more preferably the ambient temperature is 200° C. or lower, and further preferably the ambient temperature is 180° C. or lower. When the atmospheric temperature during heating is higher than 250° C., thermal decomposition occurs as described above, or the discoloration of the fiber proceeds faster. On the other hand, when the heating temperature is lower than 100°C, the reaction time tends to be long.
Therefore, from the viewpoint of workability, the heating temperature during heating (specifically, the ambient temperature) is 100° C. or higher and 250° C. or lower, more preferably 100° C. or higher and 200° C. or lower, and further preferably 100° C. or higher and 180° C. or lower. To adjust.

(Reaction time in reaction step S1B)
The heating time when the above heating method is adopted as the reaction step S1B is not particularly limited.
For example, the heating time in the reaction step S1B is adjusted to 1 minute or more when the reaction temperature is adjusted to fall within the above range. More specifically, it is preferably 5 minutes or longer, more preferably 10 minutes or longer, and further preferably 20 minutes or longer. When the heating time is shorter than 1 minute, it is presumed that the reaction has hardly progressed. On the other hand, even if the heating time is made too long, there is a tendency that improvement in the amount of sulfo groups introduced cannot be expected.
Therefore, the heating time when the above heating method is adopted as the reaction step S1B is not particularly limited, but from the viewpoint of reaction time and operability, it is preferably 5 minutes or more and 300 minutes or less, and more preferably 5 minutes or more and 120 minutes or less. It is good to say

(Sulfonating agent)
In the sulfonation, it is possible to introduce a sulfo group only with a sulfonating agent, but 1) the time required for introducing the sulfo group becomes long, and 2) the fibers are shortened due to the influence of the acid of the sulfonating agent. Urea and/or its derivative are used together in the chemical treatment step S1 because problems such as easy occurrence and 3) coloring of the fiber after the reaction due to the influence of the acid of the sulfonating agent may occur. Therefore, the above problems can be overcome.

The sulfonating agent used in the chemical treatment step S1 is not particularly limited as long as it is a compound having a sulfo group.
Examples thereof include sulfamic acid, sulfamic acid salt, and a sulfuryl compound having a sulfonyl group having two oxygen covalently bonded to sulfur. As the sulfonating agent, these compounds may be used alone or in combination of two or more.

The sulfonating agent is not particularly limited as long as it is a compound as described above, but has a low acidity as compared with sulfuric acid and the like, high introduction efficiency of a sulfo group, low cost, and high safety from the viewpoint of handleability. It is preferable to use sulfamic acid.

(Urea and its derivatives)
Of the urea and its derivatives in the chemical treatment step S1, the urea derivative is not particularly limited as long as it is a compound containing urea.
For example, carboxylic acid amide, a compound compound of isocyanate and amine, thiamide and the like can be mentioned. Note that urea and its derivative may be used alone or as a mixture of both. As the urea derivative, the above compounds may be used alone or in combination of two or more.

Urea and its derivative are not particularly limited as long as they are the above compounds, but it is preferable to use urea from the viewpoint of handleability such as low cost, little influence of environmental load, and high safety.

(Fiber raw material)
The fiber raw material used for producing the sulfonated fine cellulose fiber is not particularly limited as long as it contains cellulose.
For example, wood-based pulp (hereinafter simply referred to as wood pulp), dissolving pulp, cotton-based pulp such as cotton linter, straw, rice straw, bagasse, mulberry, sanpei, hemp, kenaf, and non-wood such as fruits. As the fiber raw material, it is possible to use pulps of the type: cellulose, cellulose isolated from sea squirts, seaweeds, etc.; and pulps of the waste paper type manufactured from waste newspapers, waste magazines, waste cardboard, etc. It is preferable to use wood pulp from the viewpoint of easy availability.

There are various types of wood pulp, but there is no particular limitation on the use.
Examples include chemical pulp such as kraft pulp (KP) and sulfite pulp (SP) derived from various woods, mechanical pulp such as thermomechanical pulp (TMP) and ground pulp (GP), and powdered cellulose obtained by crushing them. You can Bleached kraft pulp (NBKP, LBKP, etc.) is preferable from the viewpoint of manufacturing cost and mass production.

When the above pulp is used as the fiber raw material, one type of the above-mentioned types of pulp may be used alone, or two or more types may be mixed and used.

(Drying Step in Chemical Treatment Step S1)
The chemical treatment step S1 of the method for producing sulfonated fine cellulose fibers of the present embodiment may include a drying step between the contact step S1A and the reaction step S1B.
This drying step is a step that functions as a pretreatment step of the reaction step S1B, and is a step of drying so that the moisture content of the fiber raw material after the contact step S1A is in an equilibrium state. The fiber raw material after the contact step S1A may be supplied to the reaction step S1B in a wet state and heated, but a part of sulfamic acid, urea or the like may be hydrolyzed. Therefore, in order to appropriately advance the sulfonation reaction in the reaction step S1B, it is preferable to provide a drying step before the reaction step S1B.
The equilibrium state of water content means a state in which the water in the atmosphere and the water in the sample in the treatment facility apparently do not come and go.

This drying step is a step of removing the solvent of the reaction solution by drying the fiber raw material in a state where the reaction solution is in contact with the reaction solution S1B at a temperature lower than the heating temperature. The apparatus and the like used in this drying step are not particularly limited, and the dryer or the like used in the above-mentioned reaction step S1B can be used.

The drying temperature in this drying step is not particularly limited.
For example, the atmospheric temperature in the heating device is preferably 100° C. or lower, more preferably 20° C. or higher and 100° C. or lower, and further preferably 50° C. or higher and 100° C. or lower. If the atmospheric temperature during heating is higher than 100° C., the sulfonating agent or the like may be decomposed. On the other hand, if the atmospheric temperature during heating is lower than 20°C, it takes a long time to dry.
Therefore, the atmospheric temperature during heating is preferably 100° C. or lower in order to appropriately carry out the above-mentioned reaction, and from the viewpoint of operability, the atmospheric temperature during heating is preferably 20° C. or higher.

(Washing process)
Further, after the reaction step S1B in the chemical treatment step of the method for producing sulfonated fine cellulose fibers of the present embodiment, a washing step of washing the fiber raw material after the introduction of the sulfo group may be included.

The surface of the fiber raw material after the introduction of the sulfo group is acidic due to the influence of the sulfonating agent. In addition, the unreacted reaction liquid is also present. Therefore, it is desirable that the reaction be surely completed and the excess reaction solution is removed to bring the reaction solution into a neutral state because the handling property can be improved.

The washing step is not particularly limited as long as the fiber raw material after introducing the sulfo group can be made almost neutral. For example, it is possible to employ a method of washing with pure water or the like until the fiber raw material after introducing the sulfo group becomes neutral.

In addition, neutralization cleaning using alkali or the like may be performed. When such neutralization cleaning is performed, examples of the alkaline compound contained in the alkaline solution include an inorganic alkaline compound and an organic alkaline compound. Examples of the inorganic alkali compound include alkali metal hydroxides, carbonates and phosphates. Examples of the organic alkaline compound include ammonia, aliphatic amines, aromatic amines, aliphatic ammonium, aromatic ammonium, heterocyclic compounds, and hydroxides of heterocyclic compounds.

(Miniaturization processing step S2)
The refining process step S2 is a step of refining the sulfonated fiber raw material into fine fibers of a predetermined size (for example, nano level). Then, in this step S2, a sulfonated fine cellulose fiber dispersion is obtained. This sulfonated fine cellulose fiber dispersion is in a state in which the sulfonated fine cellulose fibers fined in the finening treatment step S2 are dispersed in a water-soluble solvent such as water.
The processing apparatus used in the miniaturization processing step S2 is not particularly limited as long as it has the above-mentioned function. For example, a low pressure homogenizer, a high pressure homogenizer, a grinder (stone mill type crusher), a ball mill, a cutter mill, a jet mill, a short-axis extruder, a twin-screw extruder, an ultrasonic stirrer, and a household mixer can be used. The processing device is not limited to these devices. Of these, it is preferable to use a high-pressure homogenizer because it can uniformly apply a force to the material and is excellent in homogenization, but it is not limited to such an apparatus.

(Amount of sulfo group introduced)
The introduction amount of the sulfo group is not particularly limited, but is preferably 0.5 mmol/g to 3.0 mmol/g, more preferably 0.6 mmol/g to 3.0 mmol/g, and further preferably 0.8 mmol/g. ˜3.0 mmol/g, particularly preferably 1.0 mmol/g to 3.0 mmol/g.

When the introduction amount of the sulfo group is less than 0.5 mmol/g, the dispersibility of the sulfonated fine cellulose fibers when the dried solid substance containing fine cellulose fibers described later is dispersed in water or the like becomes poor, and the fine cellulose fiber-containing dried substance is dried. Redispersibility of the solid matter in a solvent such as water is also reduced. On the other hand, when the introduction amount of the sulfo group is more than 3.0 mmol/g, there is a concern that the original characteristics of the fine cellulose fiber may be lost due to the decrease in the crystallinity of the sulfonated fine cellulose fiber, and the cost for introducing the sulfo group is high. Also increases.

In particular, in the production of a dry solid containing fine cellulose fibers described below, in relation to the drying temperature at the time of drying the sulfonated fine cellulose fiber dispersion liquid containing the sulfonated fine cellulose fibers after the refining treatment step S2, From the viewpoint of the dispersibility of the dry solid containing fine cellulose fibers, it is preferable to introduce a sulfo group as follows.
For example, when the drying temperature is 40° C. or lower, the introduction amount of the sulfo group is preferably 0.5 mmol/g or more and less than 0.9 mmol/g, and the drying temperature is 70° C. or less. In the case of drying under the following conditions, the introduction amount of the sulfo group is preferably 0.9 mmol/g or more and less than 1.4 mmol/g, and when drying under the condition of the drying temperature of 120° C. or less, It is preferable that the introduced amount of the sulfo group is 1.4 mmol/g or more and 3.0 mmol/g or less.
Further, when the drying temperature for drying the mixture containing the fine cellulose fibers (the sulfonated fine cellulose fiber dispersion liquid) is the same, in order to improve the dispersibility of the dried solid containing fine cellulose fibers, It is preferable that the introduction amount of the sulfo group is large.

(Measuring method of sulfo group introduction amount)
The sulfo group introduction amount of the sulfonated fine cellulose fiber is measured by burning a predetermined amount of the sulfonated fine cellulose fiber and measuring the sulfur content in the combustion product by using a combustion ion chromatograph according to IEC 62321. can do. When the sulfonated fine cellulose fiber is prepared from the above-mentioned sulfonated fiber raw material, it may be determined from the amount of sulfur introduced into the sulfonated fiber raw material.

(Average fiber width of sulfonated fine cellulose fiber)
The average fiber width of the sulfonated fine cellulose fiber is not particularly limited, but it is 1 nm to 1000 nm as observed by an electron microscope, preferably 2 nm to 500 nm, more preferably 2 nm to 100 nm, and further preferably 2 nm to 30 nm. Yes, and more preferably 2 nm to 20 nm.

When the fiber width of the sulfonated fine cellulose fiber is less than 1 nm, it is dissolved in water as a cellulose molecule, so that the properties (strength, rigidity, or dimensional stability) as the sulfonated fine cellulose fiber are not expressed. On the other hand, if it exceeds 1000 nm, it cannot be said that it is a sulfonated fine cellulose fiber and it is only a fiber contained in ordinary pulp, so that the characteristics (transparency, strength, rigidity, or dimensional stability) as a sulfonated fine cellulose fiber are Hard to get.
Further, when the average fiber width of the sulfonated fine cellulose fibers is larger than 30 nm, the aspect ratio tends to decrease, and the entanglement between the fibers tends to decrease. Furthermore, when the average fiber width becomes larger than 30 nm, it approaches 1/10 of the wavelength of visible light, and when it is combined with a matrix material, refraction and scattering of visible light easily occur at the interface, causing visible light scattering. Therefore, the transparency tends to decrease.

Therefore, although the average fiber width of the sulfonated fine cellulose fiber is not particularly limited, it is preferably 2 nm to 30 nm, more preferably 2 nm to 20 nm, and further preferably 2 nm to from the viewpoint of the application in which handleability and transparency are required. It is 10 nm. From the viewpoint of transparency, the average fiber width is preferably adjusted to 20 nm or less, more preferably 10 nm or less. If the average fiber width is adjusted to 10 nm or less, the scattering of visible light can be further reduced, so that a sulfonated fine cellulose fiber having high transparency can be obtained (that is, having high transparency. For example, it can be said that the sulfonated fine cellulose fibers have a small average fiber width and are sufficiently fined).

(Measurement method of average fiber width)
The average fiber width of the sulfonated fine cellulose fiber can be measured by the following method.
For example, the sulfonated fine cellulose fibers are dispersed in a solvent such as pure water, and the mixed solution is adjusted so as to have a predetermined mass%. Then, this mixed solution is applied and spin-coated on a PEI (polyethyleneimine)-coated silica substrate, and sulfonated fine cellulose fibers on the silica substrate are observed. The observation can be performed using, for example, a scanning probe microscope (for example, SPM-9700 manufactured by Shimadzu Corporation). Then, 20 sulfonated fine cellulose fibers in the observed image are randomly selected, and the average fiber width of the sulfonated fine cellulose fibers can be obtained by measuring and averaging the respective fiber widths.

(Haze value)
The transparency of the sulfonated fine cellulose fiber dispersion and the fine cellulose fiber redispersion described later can be evaluated by the haze value of the dispersion.

Specifically, the haze value of the dispersion liquid adjusted to have a solid content concentration of 0.5% by mass when the sulfonated fine cellulose fibers are dispersed in the dispersion liquid has transparency when visually observed. If so, the value is not particularly limited.
For example, the haze value of the above dispersion liquid is preferably 20% or less, more preferably 15% or less, and further preferably 10% or less. When the haze value of the dispersion is higher than 20%, it becomes difficult to properly exhibit transparency.
Therefore, the sulfonated fine cellulose fiber is preferably prepared so that the haze value of the dispersion liquid adjusted to have a solid content concentration of 0.5% by mass falls within the above range.
The solid content concentration (mass %) can be calculated from the following formula.

Solid content concentration (mass %)=(solid content of sample/mass of sample)×100

(The solid content mass of the sample is the same as the sample used for the measurement, and the solid matter remaining after the sample was dried in an atmosphere of 105° C. for 2 hours until a constant weight was obtained (for example, in the above example, sulfonated fine cellulose). It means the mass (g) of the sulfonated fine cellulose fibers after drying the dispersion liquid in which the fibers are dispersed into a constant weight state, and the mass of the sample means the sample (for example, in the above example) used for the measurement. It means the mass (g) of a dispersion liquid in which sulfonated fine cellulose fibers are dispersed.)

The dispersion according to the present embodiment is a suspension in which sulfonated fine cellulose fibers or a dry solid containing fine cellulose fibers described later is dispersed in a solvent without forming large aggregates. The solvent of the dispersion liquid is not particularly limited as long as it is a water-soluble solvent (water-soluble solvent). For example, as the water-soluble solvent, not only water but also alcohols, ketones, amines, carboxylic acids, ethers, amides, etc., and mixtures thereof can be adopted.

(Total light transmittance)
The total light transmittance is preferably 90% or more, more preferably 95% or more, when the haze value of the dispersion is in the above range. When the total light transmittance of the dispersion is lower than 90%, it becomes difficult to properly exhibit the transparency.

(Method of measuring haze value and total light transmittance)
The haze value and total light transmittance can be measured as follows.

Sulfonated fine cellulose fibers are dispersed in the above-mentioned dispersion liquid so as to have a predetermined solid content concentration. Then, when this dispersion is measured using a spectrophotometer in accordance with JIS K 7105, the sulfonated fine cellulose fiber dispersion and fine cellulose fibers obtained by dispersing the fine cellulose fiber-containing dry solid described below in water or the like are obtained. The haze value, which is the transparency of the redispersion, and the total light transmittance can be determined.

As described above, excellent transparency can be exhibited by adjusting the average fiber width of the sulfonated fine cellulose fiber so as to fall within the above range. Therefore, high transparency can be exhibited in a composite material or the like using sulfonated fine cellulose fibers.

(Viscosity characteristics)
The viscosity characteristics of the sulfonated fine cellulose fiber dispersion can be evaluated by the B-type viscosity of the dispersion.
The viscosity is measured in a sulfonated fine cellulose fiber dispersion liquid in which the solid concentration of the sulfonated fine cellulose fiber is 0.5% by mass and the temperature is 25° C., and the measurement conditions are 12 rpm and 3 minutes. It is preferably 500 mPa·s or more, more preferably 1000 mPa·s, further preferably 1500 mPa·s, and particularly preferably 2000 mPa·s or more.
The commercially available thickener made of polyethylene oxide has a B-type viscosity of 100 mPa·s or more under the above conditions (temperature 25°C, thickener concentration 0.5%, 12 rpm).
Therefore, if the B-type viscosity of the sulfonated fine cellulose fiber dispersion can exhibit the large viscosity as described above, the sulfonated fine cellulose fiber dispersion can be preferably used as a thickener.

(Method of measuring B type viscosity)
The B type viscosity can be measured as follows.

Sulfonated fine cellulose fibers are dispersed in the above-mentioned dispersion liquid so as to have a predetermined solid content concentration. Then, when this dispersion liquid (sulfonated fine cellulose fiber dispersion liquid) is measured using a Brookfield viscometer in accordance with JIS Z 8803, the viscosity of the sulfonated fine cellulose fiber dispersion liquid and the fine cellulose fiber redispersion liquid described below can be calculated. You can ask.

Further, the B-type viscosity recovery rate (%) of the dry solid containing fine cellulose fibers can be calculated from the following formula based on the viscosity of the sulfonated fine cellulose fiber dispersion and the viscosity of the fine cellulose fiber redispersion. This B-type viscosity recovery rate (%) has a correlation with the precipitation characteristics of the fine cellulose fiber-containing dry solid described below, and can be evaluated as the dispersibility of the fine cellulose fiber-containing dry solid. ..

(B-type viscosity recovery rate (%))=(viscosity of fine cellulose fiber redispersion liquid)/(viscosity of sulfonated fine cellulose fiber dispersion liquid)×100

In the formula of the B-type viscosity recovery rate (%), the sulfonated fine cellulose fiber dispersion is equivalent to the “pre-drying dispersion” of the B-type viscosity recovery rate in the claims. The dispersion liquid corresponds to the “redispersion liquid after drying” having the B-type viscosity recovery rate in the claims.

<2. Method for producing dry solid containing fine cellulose fibers>
The method for producing a finely divided cellulose fiber-containing dry solid according to the present embodiment, metal ions and, without adding a dispersant such as a water-soluble polymer, the sulfonated fine cellulose fibers prepared as described above are dispersed in water. It can be obtained by drying the sulfonated fine cellulose fiber dispersion which is another dispersion so as to have the above-mentioned predetermined water content or less. That is, the sulfonated fine cellulose fiber dispersion of the present embodiment is a state in which the sulfonated fine cellulose fibers are dispersed in a water-soluble solvent such as water, the fine cellulose fiber-containing dry solid of the present embodiment, The sulfonated fine cellulose fiber dispersion (this dispersion corresponds to the "mixture" in which the finely divided fine cellulose fibers after the fine treatment step in the claims are dispersed in water) is in a dried state. .. That is, the dry solid material containing fine cellulose fibers of the present embodiment is a dried product of a mixture containing fine cellulose fibers having a predetermined average fiber width.

In addition, the fine cellulose fiber-containing dry solid obtained by drying the sulfonated fine cellulose fiber dispersion corresponds to the "dry product" obtained by drying the fine cellulose fibers in the claims.

Incidentally, drying the sulfonated fine cellulose fiber dispersion means a state in which water is removed from the sulfonated fine cellulose fiber dispersion even a little, for example, the water content of the dried fine cellulose fiber-containing dry solid. It is a concept that includes not only the state in which the ratio almost disappears, but also the state in which the dried solid substance containing fine cellulose fibers contains water as described below.

For example, the water content of the dry solid containing fine cellulose fibers after drying may be 80% or less, preferably 80% or less and 50% or more, and more preferably adjusted to 50% or less. It is preferably 30% or less, more preferably 20% or less, and particularly preferably 10% or less.
The higher the water content, the higher the production efficiency, and the fibers can be treated under mild conditions and the heating time can be shortened, so that damage to the fibers can be reduced. Therefore, the quality of the dry solid containing fine cellulose fibers can be improved. Further, by increasing the water content, the transparency of the fine cellulose fiber redispersion liquid in which the fine cellulose fiber-containing dry solid is dispersed in water or the like can be improved (see FIG. 2 ).
On the other hand, from the viewpoint of transportability and handleability, it is preferable that the water content is low. For example, the water content is preferably 50% or less, more preferably 30% or less, even more preferably 20% or less, and even more preferably 10% or less.

The water content (%) can be represented by the water content with respect to the weight of the dry solid material containing fine cellulose fibers according to JIS P8203. That is, the water content (%) can be obtained from the following equation, which is the same as the above.

Moisture content (%)=((mass of sample−mass of solid content of sample)/mass of sample)×100

(The mass of the sample means the mass (g) of the sample (for example, fine cellulose fiber-containing dry solid in the above example) subjected to the measurement. The solid content mass of the sample is the same as that of the sample subjected to the measurement. The solids remaining after drying the sample to a constant weight for 2 hours under an atmosphere of 105° C. (for example, in the above example, the fine cellulose after being dried to a constant weight by drying the fine cellulose fiber-containing dry solid). It means the mass (g) of the fiber-containing dry solid).

(Drying temperature)
The temperature at the time of drying the sulfonated fine cellulose fiber dispersion may be 120° C. or lower, from the viewpoint of reducing aggregation of the sulfonated fine cellulose fibers due to heat, and from the viewpoint of preventing discoloration after heating, which is more excellent. From the viewpoint of ensuring redispersibility, the temperature is preferably 80°C or lower, more preferably 70°C or lower, more preferably 40°C or lower, and particularly preferably 10°C or lower. In particular, when the temperature is 40° C. or lower, excellent redispersibility can be ensured even when the amount of substituent introduced into the sulfonated fine cellulose fiber is small.

Particularly, regarding the relationship between the dispersibility and the introduction amount of the sulfo group, as described above, when the introduction amount of the sulfo group is 0.5 mmol/g or more and less than 0.9 mmol/g, the drying temperature is Is preferably dried at a temperature of 40° C. or lower, and when the introduced amount of the sulfo group is 0.9 mmol/g or more and less than 1.4 mmol/g, the drying temperature is 70° C. or lower. When the introduced amount of the sulfo group is 1.4 mmol/g or more and 3.0 mmol/g or less, it is preferable to dry under the condition that the drying temperature is 120° C. or less.
When the introduction amount of the sulfo group is the same, the dispersibility tends to be improved by lowering the drying temperature.

(Drying method)
The method for drying the sulfonated fine cellulose fiber dispersion is not particularly limited, and the fine cellulose fiber-containing dry solid can be obtained by known methods such as natural drying, heat drying, reduced pressure drying, vacuum drying, and spray drying.

In particular, as the drying temperature is low as described above, the redispersibility of the fine cellulose fiber-containing dry solid is good, and the drying time can be shortened even in the drying under a relatively low temperature condition, under a reduced pressure atmosphere or It is desirable to adopt a method of drying in a vacuum atmosphere.
The pressure in the reduced pressure atmosphere or the vacuum atmosphere is, for example, 480 hPa or less, which is near the saturated vapor pressure of water at 80° C., more preferably 320 hPa or less, which is near the saturated vapor pressure of water at 70° C., and more preferably 40° C. A reduced pressure or vacuum condition such as 75 hPa or less, which is near the saturated steam pressure of water, and particularly preferably 15 hPa or less, which is near the saturated steam pressure of water at 10° C., can be mentioned.

In this specification, a drying method in which a device under reduced pressure is used in a dry atmosphere such as a vacuum device is referred to as reduced pressure drying, and this reduced pressure drying is a concept including vacuum drying with a lower atmospheric pressure. is there. Further, in the present specification, drying under an atmospheric pressure of 100 Pa or less that can be achieved by using a vacuum device is referred to as vacuum drying.

In addition, in the fine cellulose fiber-containing dry solid of the present embodiment, it is not necessary to add a special dispersant for exhibiting the dispersibility at the time of redispersion when drying as described above, but for example, as described above In addition to metals such as aluminum ions and calcium ions, glycerin and its derivatives, alcohols such as ethylene glycol and isopropanol may be contained as a dispersant. In this case, the redispersibility can be further improved.

(Redispersion method)
The fine cellulose fiber redispersion is obtained by adding a solvent such as water to the fine cellulose fiber-containing dry solid to obtain a fine cellulose fiber-containing dry solid-containing liquid, and then stirring the mixed liquid. Is. That is, the fine cellulose fiber redispersion liquid is a state in which the fine cellulose fiber-containing dry solid is dispersed in a water-soluble solvent such as water.

As a stirring method for performing the above stirring, manual shaking or a device having a stirring function can be used for redispersion with relatively low energy. For example, the device used for stirring includes, but is not particularly limited to, an automatic shaker, a magnetic stirrer, an ultrasonic oscillator, a household mixer, and other agitators having various agitators.

As a device having a stirring function, a device having relatively high energy such as that used when producing fine cellulose fibers may be used. For example, a grinder using a stone mill having a crushing function, a jet mill, a homogenizer. Examples thereof include a homogenizer having a functionalizing function, a high-pressure homogenizer, a static mixer that is a static stirrer, and a media mill having a dispersing function, but are not particularly limited.

<3. Fine cellulose fiber redispersion>
The fine cellulose fiber redispersion liquid according to the present embodiment is a dispersion liquid in which the fine cellulose fiber-containing dry solid matter is dispersed in a water-soluble solvent (water-soluble solvent) such as water by stirring or the like as described above.
The solid content concentration of the fine cellulose fiber-containing dry solid after redispersion in the water-soluble solvent is not particularly limited, and can be appropriately adjusted according to the application of the fine cellulose fiber redispersion liquid after redispersion.

The solvent used for redispersion is preferably water, and particularly preferably pure water, so as not to limit the use application of the fine cellulose fiber redispersion liquid.
Even if a solvent other than water is used, a suitable solvent can be selected according to the intended use, and examples thereof include polar organic solvents having no large difference in solubility parameter. Examples of the polar organic solvent include alcohols, ketones, ethers, and dimethyl sulfoxide (DMSO), but are not particularly limited.

(Evaluation of redispersibility)
The redispersibility of the fine cellulose fiber-containing dry solid is the haze value or the total light transmittance or B of the fine cellulose fiber redispersion liquid and the fine cellulose-containing solid obtained by redispersing the fine cellulose fiber-containing dry solid in water. It can be evaluated by measuring and comparing at least one item of mold viscosity or precipitation characteristics.
Good redispersibility means that
1) When the difference in total light transmittance is small as compared with that after redispersion and before drying,
2) When the difference in haze value is small by comparing after re-dispersion and before drying,
3) When the difference in viscosity between the re-dispersion and before drying is small (that is, when the recovery rate of viscosity is high),
4) It means that any one or a plurality of findings can be obtained when aggregation is not observed after redispersion in the precipitation characteristic test.

The precipitation property means that coarse fibers or a sedimented state due to aggregation of sulfonated fine cellulose fibers in a fine cellulose fiber redispersion liquid after redispersing a dry solid substance containing fine cellulose fibers in water for a certain period of time (for example, one day). It can be confirmed by observing.

Hereinafter, the present invention will be described in detail with reference to Examples, but the present invention is not limited thereto.

(Example 1)
<Production of sulfonated fine cellulose fiber dispersion>
Softwood kraft pulp (NBKP made by Marusumi Paper) was used. Hereinafter, the NBKP used in the experiment will be simply described as pulp. The pulp was washed with a large amount of pure water, drained with a 200-mesh sieve, and the solid content concentration was measured.

(Chemical treatment process)
Pulp was added to the reaction solution prepared as follows and stirred to form a slurry. The step of adding pulp to the reaction liquid to form a slurry corresponds to the contact step of the chemical treatment step of the present embodiment.

(Preparation process of reaction solution)
The sulfonating agent and urea or/and its derivative were prepared so as to have the following solid content concentrations.
In the experiment, sulfamic acid (purity 98.5%, manufactured by Fuso Kagaku Kogyo) was used as a sulfonating agent, and urea or a derivative thereof was used as a urea solution (purity 99%, manufactured by Wako Pure Chemical Industries, model number; special grade reagent). It was used. The mixture ratio of both was adjusted to be 1:2.5 in the concentration ratio (g/L) to prepare an aqueous solution.

Specifically, sulfamic acid and urea were mixed as follows.
Sulfamic acid/urea ratio ((g/L)/(g/L))=200/500

An example of preparation of the reaction solution is shown below.
100 ml of water was added to the container. Then, 20 g of sulfamic acid and 50 g of urea were added to this container to prepare a reaction liquid having a sulfamic acid/urea ratio ((g/L)/(g/L)) of 200/500 (1:2.5). .. That is, urea was added to 250 parts by weight with respect to 100 parts by weight of sulfamic acid.

In the experiment, 2 g of pulp was added to the prepared reaction liquid to an absolute dry weight. That is, in the case of the reaction solution having a sulfamic acid/urea ratio ((g/L)/(g/L)) of 200/500 (1:2.5), sulfamic acid is 1000 parts by weight with respect to 100 parts by weight of pulp. By weight, urea was adjusted to 2500 parts by weight.

The slurry prepared by adding pulp to the reaction liquid was stirred for 10 minutes using a stir bar. After stirring, the slurry was suction filtered using a filter paper (No. 2). The suction filtration was performed until the solution stopped dropping. After suction filtration, the pulp was peeled from the filter paper, and the filtered pulp was placed in a dryer (manufactured by Isuzu Seisakusho, model number: VTR-115) in which the temperature of the thermostatic chamber was set to 50°C, and the moisture content (% ) Was equilibrated to dryness.
The sample was weighed by a measuring method using a weighing bottle. An electronic balance (manufactured by Shinko Denshi KK, model number; RJ-320) was used for weighing.

Moisture content (%)=((mass of sample−mass of solid content of sample)/mass of sample)×100

Sample: Weight of pulp peeled from filter paper: Weight of pulp peeled from filter paper in a dryer (g)
Mass of solid content of sample: Pulp peeled from filter paper in the same amount as the mass (g) of pulp peeled from filter paper in a dryer is left for 2 hours under an atmosphere of 105° C. until a constant weight is obtained, and remains. It is the mass (g) of the solid matter, and the drying method was performed according to JIS P 8225.

The term "drying until the moisture content (%) reaches an equilibrium state" was defined as the end point when the moisture in the atmosphere in the treatment facility and the moisture in the sample apparently stopped coming and going. For example, after drying the sample in a weighing bottle of known weight for a predetermined time, cover the weighing bottle in the drying device, remove the sample from the dryer while the sample is still in the weighing bottle, and add the desiccant. The sample was placed in a desiccator or the like to radiate heat, and then the weight of the sample (weight of weighing bottle containing sample−weight of weighing bottle) was measured. The end point of the drying was a state in which the amount of change in the weight measured twice was within 1% of the weight at the start of drying (however, the measurement of the weight of the second time was performed in the drying time of the first time). More than half).

After the water content reached an equilibrium state, a heating reaction was performed. For the heating reaction, a dryer (manufactured by Isuzu Seisakusho, model number: VTR-115) was used. The reaction conditions are as follows.
Temperature of constant temperature bath: 120℃, heating time: 20 minutes

After the heating reaction, the reacted pulp is diluted with pure water so as to have a solid content of 1% by mass or less, neutralized by adding an excess amount of sodium hydrogen carbonate, and thoroughly washed with pure water. A sulfamic acid/urea treated pulp suspension was prepared.

(Miniaturization process)
The sulfamic acid/urea-treated pulp was defibrated using a high-pressure homogenizer (N2000-2C-045 type manufactured by Kos Nijuichi) to prepare a sulfonated fine cellulose fiber dispersion. The processing conditions of the high pressure homogenizer were as follows.

The sulfamic acid/urea-treated pulp was supplied to a high-pressure homogenizer prepared so that the solid content concentration was 0.5% by mass. The number of passes was repeated until the coarse fibers could not be visually observed. The pressure at that time was 60 MPa.

(Drying process)
50 g of the sulfonated fine cellulose fiber dispersion having a solid content concentration of 0.5% by mass (0.25 g in terms of absolute dry weight) was dispensed on a petri dish and placed in a vacuum device (vacuum pump ultimate pressure is 10 Pa). Then, it was dried (corresponding to vacuum drying of the present embodiment) until the water content became equilibrium (water content of 10% or less) to obtain a dry solid material containing fine cellulose fibers. The drying conditions are as follows.

Vacuum device vacuum gauge pointer value: -0.1 MPa or less Ambient temperature in vacuum device: 40°C
Sample temperature: 10℃

(Redispersion process)
Put the whole amount of the obtained dry solids containing fine cellulose fibers in a vial, add pure water so that the solid content concentration becomes 0.5% by mass, leave it for 30 minutes, and shake it for 10 minutes with strong manual shaking. A fine cellulose fiber redispersion liquid was obtained by redispersing the dry solid material containing cellulose fibers.
The evaluation described below was carried out after the dispersion liquid was allowed to stand still for 24 hours.

"Evaluation"
(Elemental analysis of pulp after chemical treatment (sulfur))
The sulfur content contained in the pulp after the chemical treatment was determined by a combustion ion chromatograph. The measurement method was performed according to the measurement conditions of IEC 62321.

Combustion device: Mitsubishi Chemical Analytech, model number; AQF-2100H
Ion chromatography: Thermo Fisher Science Co., model number; ICS-1600

(Measurement of haze value and total light transmittance of sulfonated fine cellulose fiber dispersion and fine cellulose fiber redispersion)
For the measurement of the haze value and the total light transmittance, the sulfonated fine cellulose fiber dispersion liquid was prepared with pure water so that the solid content concentration was 0.5% by mass. Then, the prepared solution was sampled and measured using a spectrophotometer (manufactured by JASCO Corporation, model number: V-570). The measuring method was based on the method of JIS K 7105.

(Viscosity measurement of sulfonated fine cellulose fiber dispersion and fine cellulose fiber redispersion)
The viscosities of the sulfonated fine cellulose fiber dispersion and the fine cellulose fiber redispersion prepared by the method described below were measured with a B-type viscometer (LVDV-I Prime, manufactured by Eiko Seiki Co., Ltd.).
Specifically, each of the measurement samples had a solid content concentration of 0.5 mass% and a temperature of 25° C., the measurement conditions were a rotation speed of 12 rpm and 3 minutes, and the spindle was an attached LV spindle.

The B-type viscosity recovery rate was calculated from the following formula.

(B-type viscosity recovery rate (%))=(viscosity of fine cellulose fiber redispersion liquid)/(viscosity of sulfonated fine cellulose fiber dispersion liquid)×100

(Precipitation characteristics of fine cellulose redispersion liquid)
The fine cellulose fiber-containing dry solid (absolute dry weight of 0.25 g) was placed in a vial, pure water was added, and the fine cellulose fiber-containing dry solid was adjusted to have a solid content concentration of 0.5% by mass. The mixture was manually shaken and left overnight to obtain a fine cellulose fiber redispersion liquid. The state of precipitation of the obtained dispersion was visually confirmed and evaluated as follows.

⊚: Transparent with almost no coagulation ○: Partially coagulated fibers are seen with some cloudiness, but no sedimentation ×: Aggregated fibers are seen and further sedimentation

(Example 2)
In the drying step, it was carried out in the same manner as in Example 1 except that heat drying was carried out by a dryer in which the temperature of the constant temperature bath was set to 40°C.

(Example 3)
In the step of preparing the reaction solution, the reaction solution adjusted so that the sulfamic acid/urea ratio ((g/L)/(g/L))=200/200 was used, and sulfamine was added to 100 parts by weight of pulp. It was carried out in the same manner as in Example 1 except that the acid was adjusted to 1000 parts by weight and the urea was adjusted to 1000 parts by weight.

(Example 4)
In the drying step, it was carried out in the same manner as in Example 3 except that heat drying was carried out by a dryer in which the temperature of the constant temperature bath was set to 40°C.

(Example 5)
In the drying step, it was carried out in the same manner as in Example 3 except that heat drying was carried out with a dryer in which the temperature of the constant temperature bath was set to 70°C.

(Example 6)
In the step of preparing the reaction solution, the sulfamic acid/urea ratio ((g/L)/(g/L))=200/300 pulp to 100 parts by weight, the sulfamic acid was 1000 parts by weight, and the urea was 1500 parts by weight. Was prepared. Further, in the heating step, the same procedure as in Example 1 was carried out except that the reaction temperature was 160° C. and the reaction time was 1 hour.

(Example 7)
In the drying step, it was carried out in the same manner as in Example 6 except that heat drying was carried out by a dryer in which the temperature of the constant temperature bath was set to 40°C.

(Example 8)
In the drying step, it was carried out in the same manner as in Example 6 except that heat drying was carried out with a dryer in which the temperature of the constant temperature bath was set to 70°C.

(Example 9)
In the drying step, it was carried out in the same manner as in Example 6 except that heat drying was carried out by a dryer in which the temperature of the constant temperature bath was set to 105°C.

(Example 10)
As the pulp, softwood kraft pulp (NBKP manufactured by Marusumi Paper Co., Ltd.) was used as in Example 1. The pulp was washed with a large amount of pure water, drained with a 200-mesh sieve to a solid content concentration of 20% by weight, and used for the experiment.
The reaction liquid was prepared so that 200 g of sulfamic acid and 200 g of urea were added to 1 L of pure water. That is, they were mixed as follows.
Sulfamic acid/urea ratio ((g/L)/(g/L))=200/200

The pulp was weighed to an absolute dry weight of 10 g, and 1000 parts by mass of the reaction liquid was impregnated with 100 parts by mass of the pulp. Specifically, the pulp was dried to a dry weight of 10 g so that the solid content of the reaction liquid was 100 g, and the pulp was kneaded to uniformly impregnate the chemical liquid. The pulp slurry impregnated with the above reaction solution was dried in a drier having a temperature of 50° C. in a constant temperature bath until the weight change disappeared (until the water content reached an equilibrium state). This dried pulp was subjected to a heating reaction (sulfonation reaction) under the following reaction conditions.
Temperature of constant temperature bath: 140℃, heating time: 30 minutes

After the heating reaction, the pulp was washed using a 300 mesh sieve. Specifically, the sulfonated pulp was washed with a large amount of pure water, then neutralized with a saturated sodium hydrogen carbonate solution, and then washed again with a large amount of water.

The sulfonated pulp after this washing was prepared so that the solid content concentration was 0.5% by mass, and subjected to a refining treatment.
A high-pressure homogenizer was used for the miniaturization treatment. The pressure of the high pressure homogenizer was 60 MPa. The number of passes is until the coarse fibers can no longer be visually observed. A sulfonated fine cellulose fiber was obtained.
The redispersibility test and evaluation of the dry solid containing fine cellulose fibers prepared by drying the obtained sulfonated fine cellulose fibers were carried out in the same manner as in Example 1.

That is, in Example 10, the reaction liquid was made to be 1000 parts by mass as the solid content weight with respect to 100 parts by mass as the dry weight of pulp, and after the reaction liquid was impregnated in the pulp, dehydration by suction filtration was performed. Example 3 was carried out in the same manner as in Example 3, except that the heating reaction was performed without heating, the temperature during the heating reaction was 140° C., and the heating reaction time was 30 minutes.

(Example 11)
In the drying step, it was carried out in the same manner as in Example 10 except that heat drying was carried out with a dryer in which the temperature of the constant temperature bath was set to 40°C.

(Example 12)
In the drying step, it was carried out in the same manner as in Example 10 except that heat drying was carried out with a dryer in which the temperature of the constant temperature bath was set to 70°C.

(Example 13)
In the drying step, it was carried out in the same manner as in Example 10 except that heat drying was carried out with a dryer in which the temperature of the constant temperature bath was set to 105°C.

(Example 14)
In the drying step, heat drying was performed with a dryer in which the temperature of the constant temperature bath was set to 105° C., and the moisture content of the dried solid fine cellulose fiber-containing solid was adjusted to 43%. It carried out similarly.

(Example 15)
In the drying step, heat drying was performed with a dryer in which the temperature of the constant temperature bath was set to 105° C., and the moisture content of the dried solid fine cellulose fiber-containing solid was adjusted to 77%. It carried out similarly.

(Example 16)
As the pulp, softwood kraft pulp (NBKP manufactured by Marusumi Paper Co., Ltd.) was used as in Example 1. The pulp was washed with a large amount of pure water, drained with a 200-mesh sieve to a solid content concentration of 20% by weight, and used for the experiment.

The reaction solution was prepared so that 200 g of sulfamic acid and 500 g of urea were added to 1 L of pure water. That is, they were mixed as follows.
Sulfamic acid/urea ratio ((g/L)/(g/L))=200/500

The pulp was weighed to an absolute dry weight of 10 g, and 150 parts by mass of the reaction liquid was impregnated with 100 parts by mass of the pulp. Specifically, the mixture was mixed so that the dry weight of the pulp was 10 g and the solid content of the reaction liquid was 15 g, and the pulp was kneaded so that the chemical liquid was uniformly impregnated into the pulp.
The pulp slurry impregnated with the reaction solution was dried in a dryer in a thermostatic chamber at a temperature of 50° C. until there was no change in weight (until the moisture content reached an equilibrium state). This dried pulp was subjected to a heating reaction (sulfonation reaction) under the following reaction conditions.
Temperature of constant temperature bath: 120°C, heating time: 25 minutes

After the heating reaction, the pulp was washed using a 300 mesh sieve. Specifically, the sulfonated pulp was washed with a large amount of pure water, then neutralized with a saturated sodium hydrogen carbonate solution, and then washed again with a large amount of water. Other operations were the same as in Example 1 to obtain a sulfamic acid/urea-treated pulp (also referred to as a sulfonated pulp).
The resulting sulfamic acid/urea-treated pulp was not dried but the above treatment was repeated once to obtain a sulfonated pulp treated twice.
The resulting twice-treated sulfonated pulp was again reacted with sulfamic acid/urea.

The reaction liquid was prepared so that 200 g of sulfamic acid and 200 g of urea were added to 1 L of pure water. That is, they were mixed as follows.
Sulfamic acid/urea ratio ((g/L)/(g/L))=200/200

The pulp was weighed to an absolute dry weight of 10 g, and 150 parts by mass of the reaction liquid was impregnated with 100 parts by mass of the pulp. Specifically, the mixture was mixed so that the dry weight of the pulp was 10 g and the solid content of the reaction liquid was 15 g, and the pulp was kneaded so that the chemical liquid was uniformly impregnated into the pulp. The pulp slurry impregnated with the above reaction liquid was dried in a drier having a temperature of 50° C. in a constant temperature bath until there was no change in weight (that is, until the moisture content was in an equilibrium state). This dried pulp was subjected to a heating reaction (sulfonation reaction) under the following reaction conditions.
Temperature of constant temperature bath: 120°C, heating time: 25 minutes

After the heating reaction, the pulp was washed using a 300 mesh sieve. Specifically, the sulfonated pulp was washed with a large amount of pure water, then neutralized with a saturated sodium hydrogen carbonate solution, and then washed again with a large amount of water. Other operations were the same as in Example 1 to obtain a sulfonated pulp.

The sulfonated pulp after the washing, which had been treated three times, was prepared so as to have a solid content concentration of 0.5% by mass, and subjected to a micronization treatment.
A high-pressure homogenizer was used for the miniaturization treatment. The pressure of the high pressure homogenizer was 60 MPa. Further, the number of passes was repeated until the coarse fibers could not be visually observed to obtain sulfonated fine cellulose fibers.
The redispersibility test and evaluation of the dried solid containing fine cellulose fibers prepared by drying the obtained sulfonated fine cellulose fibers were carried out in the same manner as in Example 1.

That is, in Example 16, the first and second treatments were carried out by impregnating the reaction liquid into the pulp by adjusting the reaction liquid to 150 parts by mass as the solid content relative to 100 parts by mass as the dry weight of the pulp. After that, a sulfonated pulp was prepared in the same manner as in Example 1 except that it was subjected to a heating reaction without being dehydrated by suction filtration.
In the third treatment, the reaction liquid was made to be 150 parts by mass as the solid content with respect to 100 parts by mass as the dry weight of the pulp, and the pulp was impregnated with the reaction liquid and then dehydrated by suction filtration. A sulfonated pulp was obtained in the same manner as in Example 1, except that the heating reaction was performed without heating and the heating reaction time was 25 minutes.

(Example 17)
In the drying step, it was carried out in the same manner as in Example 16 except that heat drying was carried out with a dryer in which the temperature of the constant temperature bath was set to 40°C.
In this experiment, the fine cellulose fiber-containing dry solid obtained after the drying process after the micronization treatment was prepared so that the water content was 10% or less.

(Example 18)
In the drying step, it was carried out in the same manner as in Example 16 except that heat drying was carried out with a dryer in which the temperature of the constant temperature bath was set to 70°C.
In this experiment, the fine cellulose fiber-containing dry solid obtained after the drying process after the micronization treatment was prepared so that the water content was 10% or less.

(Example 19)
In the drying step, it was carried out in the same manner as in Example 16 except that heat drying was carried out with a dryer in which the temperature of the constant temperature bath was set to 105°C.

(Example 20)
In the drying step, the drying process was performed in the same manner as in Example 17, except that the drying process was carried out by heating with a dryer in which the temperature of the constant temperature bath was set to 105° C., and the moisture content after drying was 46%.

(Example 21)
In the drying step, the drying was carried out in the same manner as in Example 17, except that the drying was performed with a dryer in which the temperature of the constant temperature bath was set to 105° C., and the moisture content after drying was 75%.

(Comparative Example 1)
In the drying step, it was carried out in the same manner as in Example 1 except that heat drying was carried out by a dryer in which the temperature of the constant temperature bath was set to 70°C.

(Comparative example 2)
In the drying step, it was carried out in the same manner as in Example 1 except that heat drying was performed by a dryer in which the temperature of the constant temperature bath was set to 105°C.

(Comparative example 3)
In the drying step, it was carried out in the same manner as in Example 3 except that heat drying was carried out by a dryer in which the temperature of the constant temperature bath was set to 105°C.

(Comparative Example 4)
In the step of preparing the reaction liquid, the same procedure as in Example 1 was carried out except that sulfamic acid was 250 parts by weight and urea was 125 parts by weight with respect to 100 parts by weight of pulp.

(Comparative example 5)
In the drying step, it was carried out in the same manner as Comparative Example 4 except that the drying was carried out by a dryer in which the temperature of the constant temperature bath was set to 40°C.

(Comparative example 6)
In the drying step, it was carried out in the same manner as in Comparative Example 4 except that the drying was carried out by a dryer in which the temperature of the constant temperature bath was set to 70°C.

(Comparative Example 7)
In the drying step, the drying was performed in the same manner as in Comparative Example 4 except that the drying was performed with a dryer in which the temperature of the constant temperature bath was set to 105°C.

(Comparative Example 8)
(Preparation of phosphate esterified fine cellulose fiber-containing material)
Using the same NBKP as that used in Example 1, it was squeezed to 100 parts by mass of NBKP as an absolute dry mass of 56 parts by mass of ammonium dihydrogen phosphate and 150 parts by mass of urea to obtain a chemical-impregnated pulp. .. The chemical liquid-impregnated pulp was dried in an atmosphere of 105° C., and then heated in an atmosphere temperature of 140° C. for 20 minutes as a reaction step to introduce a phosphate group, and the same procedure as in Example 1 was carried out.

(Measurement of phosphate group introduction amount)
The amount of phosphoric acid groups in the obtained phosphoric acid esterified fine cellulose fibers was measured by alkali titration. Specifically, it was carried out as follows. As a pretreatment, the phosphoric acid esterified fine cellulose fiber slurry was diluted with pure water so that the solid content concentration was 0.2% by mass, and then 10% by volume of a strongly acidic ion exchange resin was mixed with the slurry. The mixture was shaken for 1 hour, and only the slurry was separated with a wire net having a mesh of 90 μm.

Alkali titration was performed using the slurry separated by the above pretreatment. The alkaline solution used was an aqueous sodium hydroxide solution, and its concentration was 0.1N. Specifically, the electrical conductivity is measured for each alkali drip, the titer of the inflection point is read from the alkali titer and the plot of the electrical conductivity, and the value of the phosphate esterified fine cellulose fiber used for the measurement is read. The amount of phosphate group was calculated by dividing by the solid content weight. (Note that the phosphoric acid group has a strongly acidic group and a weakly acidic group, and there are two inflection points due to this, but in this experiment, the amount of the strongly acidic group is expressed as the amount of the phosphoric acid group. .)

(Comparative Example 9)
In the drying step, the drying was performed in the same manner as in Comparative Example 8 except that the drying was performed with a dryer in which the temperature of the constant temperature bath was set to 40°C.

(Comparative Example 10)
In the drying step, it was carried out in the same manner as Comparative Example 8 except that heat drying was carried out by a dryer in which the temperature of the constant temperature bath was set to 70°C.

(Comparative Example 11)
In the drying step, it was carried out in the same manner as Comparative Example 8 except that the drying was carried out by a dryer in which the temperature of the constant temperature bath was set to 105°C.

(Comparative Example 12)
<Production of carboxylated CNF>
In the same NBKP as used in Example 1, 2,2,6,6-tetramethyl-1-piperidine-oxy radical (hereinafter referred to as TEMPO) and bromide were used as catalysts in the presence of hypochlorite. A carboxy group was introduced into NBKP.

Specifically, 78 mg of TEMPO (Sigma Aldrich) and 754 mg of sodium bromide were dissolved in water to prepare an aqueous solution, and then 5 g of NBKP as an absolute dry weight was added and stirred until uniform, and a pulp slurry containing a catalyst component was prepared. Got After adding 16.25 mL of 2M sodium hypochlorite aqueous solution to the obtained pulp slurry, 0.5N hydrochloric acid aqueous solution was added and it adjusted to pH 10.3 and started the oxidation reaction. During the oxidation reaction, the pH decreased with time, but the decrease in pH could not be confirmed after 3 hours. Therefore, the reaction was considered to be completed at this point, and the pulp was thoroughly washed with water to obtain carboxylated pulp. The same procedure as in Example 9 was carried out except for the step of obtaining the above-mentioned carboxylated pulp.

(Measurement of the amount of carboxyl groups)
The carboxy group in the obtained carboxylated fine cellulose fiber was measured by alkali titration of the carboxylated pulp before the grain refining treatment. Specifically, it was carried out as follows. Carboxylated pulp having an absolute dry weight of 0.3 g was precisely weighed and diluted with pure water so that the solid content concentration became 0.5%. The obtained carboxylated pulp slurry was adjusted to pH 2.5 with 0.1 M hydrochloric acid aqueous solution, and then subjected to alkali titration. The alkaline solution used was a 0.05 N sodium hydroxide aqueous solution, and the electrical conductivity was measured each time the alkaline solution was dropped until the pH reached 11, thereby obtaining a plot of the alkaline titration amount and the electrical conductivity. .. The amount of carboxy groups was calculated by reading the titration amount at the inflection point from the obtained plot and dividing the value by the weight of the solid content of the carboxylated pulp used for the measurement.

(Comparative Example 13)
(Preparation of Phosphite Esterified Fine Cellulose Fiber-Containing Material)
Using the same NBKP as that used in Example 1, the reaction chemicals were added to 100 parts by mass of pulp, 130 parts by mass of sodium hydrogen phosphite pentahydrate, 108 parts by mass of urea, and a reaction step. Was carried out in the same manner as in Example 9 except that it was heated at an ambient temperature of 180°C.

(Measurement of phosphite group introduction amount)
The amount of phosphite groups in the obtained phosphorous acid esterified fine cellulose fiber dispersion was measured in the same manner as in Comparative Example 10.

In the above-mentioned Examples and Comparative Examples, fine cellulose fiber dispersions were dried without using additives such as dispersants.

(Comparative Example 14)
A fine solid cellulose fiber (BiFiFi-s, FMa-1002, manufactured by Sugino Machine Co., Ltd.) that had not been chemically modified was dispersed in water, and the dispersion was subjected to a drying step to prepare a dry solid. The redispersibility test and evaluation of this prepared dry solid were carried out in the same manner as in Example 1.
Specifically, the fine cellulose fibers manufactured by Sugino Machine Ltd. (the solid content concentration at the time of product shipment is 2% by mass) are mixed with pure water so that the solid content concentration becomes 0.5% by weight, and the mixture is homogenized. Shaking until left overnight. The dispersion liquid after standing overnight was subjected to a drying step to prepare a dried solid substance.

(Comparative Example 15)
In the drying step, it was carried out in the same manner as Comparative Example 14 except that the drying was carried out by a dryer in which the temperature of the constant temperature bath was set to 105°C.

(Comparative Example 16)
In the drying step, the drying was performed in the same manner as in Comparative Example 15 except that the drying was performed by a dryer in which the temperature of the constant temperature bath was set to 105° C. and the moisture content after drying was 85%.

(result)
FIG. 2 shows the measurement results of Comparative Example 4, Example 1, Example 3, Example 10 to Example 16, Example 18 to Example 21, Comparative Example 8, and Comparative Example 14 to Comparative Example 16 (fine cellulose). The transparency and viscosity characteristics of the fiber dispersion and the redispersed fine cellulose fiber are shown.
FIG. 3 shows the results of evaluation tests of Examples and Comparative Examples.
In FIG. 4, the evaluation test results are shown by the relationship between the sulfo group introduction amount (sulfur introduction amount) and the drying temperature. In FIG. 4, “◯” indicates an example and “x” indicates a comparative example.

As shown in FIG. 2 and FIG. 3, in the present invention, even though no additive such as a dispersant is used, no sedimentation of aggregated fibers after redispersion is observed, and further, after redispersion, Also, it can be seen that the viscosity property and the transparency (total light transmittance, haze value) are not significantly lowered, and that they have excellent redispersibility.
As shown in FIG. 2, in the case of the fine cellulose fibers not chemically modified as shown in Comparative Examples 14 to 16, all the evaluation tests of the redispersed liquid in which the dried solid matter is dispersed are performed. The result was "x" and "agglomerated fibers were seen and further settled". Moreover, the same evaluation was made when the water content of the dried solid was adjusted to 85%. For this reason, the transparency (total light transmittance and haze value) and the viscosity of the redispersion liquid in which any of the dry solids is dispersed could not be appropriately measured.

The fine cellulose fiber-containing dry solid of the present invention, and the fine cellulose fiber redispersion can be suitably used for various applications in various fields such as the industrial field, the food field, the medical field, and the cosmetic field. It can also be suitably used as a raw material of a composite material used in the field of. In particular, the fine cellulose fiber redispersion liquid of the present invention ensures excellent transparency even after redispersion, and can be suitably used as a transparent substrate such as a transparent film and an optical display. .. Further, since it has a high viscosity, it can be suitably used as a thickener for cosmetics, foods, pharmaceuticals, paints, inks, cements, and other household products and industrial products.

Claims (3)

A method for producing a dried product having redispersibility obtained by drying a sulfonated fine cellulose fiber,
A chemical treatment step of chemically treating the pulp to prepare a sulfonated pulp such that the amount of sulfur introduced due to the sulfo group is 0.5 mmol/g to 3.0 mmol/g ;
A refining treatment step of refining the pulp after the chemical treatment step into fine cellulose fibers having an average fiber width of 1 nm to 1000 nm;
A drying step of drying the mixture obtained by dispersing the finely divided sulfonated fine cellulose fibers in water after the fine treatment step so that the water content is 80% or less;
Is done in order,
The chemical treatment step,
A contacting step of contacting a sulfamic acid having a sulfo group and urea with a reaction liquid dissolved in water with respect to the pulp fibers constituting the pulp;
The pulp after the contacting step (however, except the absolutely dried pulp which has been dried under reduced pressure in a desiccator containing anhydrous calcium chloride) is supplied to the reaction step, and in the reaction step, the cellulose constituting the pulp fiber is removed. The step of introducing a sulfo group into a part of the hydroxyl groups, and sequentially,
The reaction step is
In the step of heating the pulp fibers in a state where the reaction liquid is in contact with the reaction solution after the contacting step, to proceed the reaction,
The reaction temperature is adjusted to 100° C. to 180° C. and the reaction time is adjusted to 1 minute or more,
In the drying step of drying the mixture,
The drying temperature is, in relation to the sulfur introduced amount due to sulpho groups of the sulfonated fine cellulose fibers, the following (1) to (3) either condition is satisfied fine cellulose fiber-containing, wherein the Method for producing dried solid matter.

(1) The mixture in which the sulfonated fine cellulose fiber having a sulfur introduction amount of 0.5 mmol/g or more and lower than 0.9 mmol/g is dispersed is dried at 40° C. or less.
(2) The mixture in which the sulfonated fine cellulose fibers having a sulfur introduction amount of 0.9 mmol/g or more and less than 1.4 mmol/g are dispersed is dried at 70°C or less.
(3) The mixture in which the sulfonated fine cellulose fibers having a sulfur introduction amount of 1.4 mmol/g or more and 3.0 mmol/g or less are dispersed is dried at 120° C. or less. The mixture obtained by dispersing the fine cellulose fibers after the refining treatment step in water so that the solid content concentration becomes 0.5% by mass is used as a pre-drying dispersion, and the mixture after the drying step has a solid content concentration of 0. The B-type viscosity recovery rate of the mixture after the drying step, obtained by the following formula (1), is 30% when the dispersion liquid dispersed in water so as to be 0.5% by mass is used as a redispersion liquid after drying. It is above, The manufacturing method of the dry solid material containing a fine cellulose fiber of Claim 1 characterized by the above-mentioned.

(B type viscosity recovery rate)
B-type viscosity recovery rate (%)=(viscosity of redispersion liquid after drying)/(viscosity of dispersion liquid before drying)×100 (1)
(Viscosity: Viscosity mPa·s measured by rotating with a B-type viscometer at 25° C., rotation speed 12 rpm, 3 minutes) The method for producing a dry solid containing fine cellulose fibers according to claim 1 or 2, wherein the mixture is dried under reduced pressure at 480 hPa or less.

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