JP2020097733A - Fine cellulose fiber-containing dry solid, and fine cellulose fiber re-dispersion liquid - Google Patents

Abstract

To provide a fine cellulose fiber-containing dry solid having excellent re-dispersibility in solvent such as water, and provide a fine cellulose fiber re-dispersion liquid having excellent transparency and viscosity properties.SOLUTION: A fine cellulose fiber-containing dry solid contains a fine cellulose fiber with an amount of sulfur introduction in terms of a sulfo group of 0.5 mmol/g or more. A fine cellulose fiber re-dispersion liquid has the fine cellulose fiber re-dispersion liquid and water and has excellent re-dispersibility in terms of transparency, viscosity properties, and precipitation properties.SELECTED DRAWING: Figure 1

Description

The present invention relates to a fine cellulose fiber-containing dry solid having excellent redispersibility in water and a fine cellulose fiber redispersion liquid using the fine cellulose fiber-containing dry solid.

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, an object of the present invention is to provide a fine cellulose fiber-containing dry solid having excellent redispersibility in a solvent such as water and a fine cellulose fiber redispersion liquid having excellent transparency and viscosity characteristics.

The fine solid cellulose fiber-containing dry solid of the first invention is a dry product of a mixture containing fine cellulose fibers in which cellulose fibers are finely divided to have an average fiber width of 1 nm to 1000 nm and water, wherein the fine cellulose fibers have hydroxyl groups. A sulfonated fine cellulose fiber in which a sulfo group is partially introduced, the amount of sulfur introduced due to the sulfo group is 0.5 mmol/g or more and 3.0 mmol/g or less, and the dried product is water. Of 50% or less, and the dried product is dispersed in water so that the solid content concentration of the fine cellulose fibers is 0.5% by weight. The viscosity is 500 mPa·s or more, which is measured by rotating at 25° C., a rotation speed of 12 rpm for 3 minutes.
The fine cellulose fiber-containing dry solid matter of the second invention is the dry matter of the first invention, wherein the dry matter is dispersed in water such that the solid content concentration of the fine cellulose fiber is 0.5% by weight. In this state, the haze value of the dispersion is 20% or less.
The fine cellulose fiber-containing dry solid matter of the third invention is the dry matter according to the first invention or the second invention, wherein the dry matter is water so that the solid content concentration of the fine cellulose fiber is 0.5% by weight. The total light transmittance of the dispersion is 95% or more in the state of being dispersed.
The fine cellulose fiber redispersion liquid of the fourth invention is characterized in that the fine cellulose fiber-containing dry solid described in any one of the first invention, the second invention or the third invention is dispersed in water. ..

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.

FIG. 3 is a diagram showing transparency and viscosity characteristics of a fine cellulose fiber dispersion and a fine cellulose fiber redispersion after redispersion. It is the figure which showed the precipitation characteristic in the fine cellulose fiber redispersion liquid.

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. 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 fine cellulose fibers is not particularly limited and is preferably 50% or less, more preferably 30% or less, still more preferably 20% or less, particularly preferably, measured according to JIS P8203. Is 10%. 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.

"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 the like). Anionic groups and cationic groups) are more desirable, and ionic substituents are more desirably sulfo groups. By introducing an ionic substituent, from the viewpoint of increasing the hydrophilicity of the fine cellulose fibers, from the viewpoint of causing electrostatic repulsion between the ions, in the dispersion of fine cellulose fiber dispersion energy saving and 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.

(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)
The sulfonated fine cellulose fiber of the present embodiment can be obtained by a chemical treatment step of introducing a sulfo group into the pulp fiber, and then a fine treatment step of physically mechanical defibration.
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. In addition, from the viewpoint of easily obtaining uniform fine cellulose fibers, it is desirable to apply the refining treatment step after introducing the sulfo group into the pulp fibers.

(Chemical treatment process)
The chemical treatment step includes a contact step in which a sulfonating agent having a sulfo group and urea or/and a derivative thereof are brought into contact with pulp fibers, and a sulfo group is added to at least part of hydroxyl groups of cellulose contained in the pulp fibers after the contact step. And a reaction step of introducing a group.

(Reaction process)
The reaction step in the chemical treatment step of the method for producing a sulfonated fine cellulose fiber of the present embodiment, as described above, by substituting the sulfo group of the sulfonating agent in contact with the hydroxyl group of cellulose contained in the fiber raw material, the fiber raw material Is a step of introducing a sulfo group into the cellulose contained in.
This reaction step 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 substituted 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.

(Reaction temperature in reaction step)
The heating temperature in the reaction step 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, it is sufficient that the fiber raw material after the contacting step can be heated directly or indirectly while satisfying the above requirements. 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 a gas may be generated in the reaction step, it is preferable to use a circulating-air type dryer.

The shape of the fiber raw material after the contacting step is not particularly limited, but for example, it is preferable to heat it using a sheet-shaped material or the above-mentioned device in a state of being loosened to a certain degree because the reaction can easily proceed uniformly. ..

The heating temperature in the reaction step 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)
The heating time when the above heating method is adopted as the reaction step is not particularly limited.
For example, the heating time in the reaction step 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 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. Good to do.

(Sulfonating agent)
In the sulfonation, it is possible to introduce a sulfo group with only a sulfonating agent, but 1) the time required for the introduction of the sulfo group becomes long,
2) Shortening of the fiber is likely to occur due to the influence of the acid of the sulfonating agent, and 3) there is a problem that the fiber after the reaction is colored due to the influence of the acid of the sulfonating agent. Therefore, the above problems can be overcome by subjecting urea or/and its derivative to the chemical treatment step together.

The sulfonating agent used in the chemical treatment step 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 urea and its derivatives in the chemical treatment step, the derivative of urea 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 process)
The chemical treatment step of the method for producing sulfonated fine cellulose fibers of the present embodiment may include a drying step between the contacting step and the reaction step.
This drying step is a step that functions as a pretreatment step of the reaction step, and is a step of drying so that the water content of the fiber raw material after the contacting step is in an equilibrium state. The fiber raw material after the contacting step may be supplied to the reaction step in a wet state and heated, but there is a possibility that 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, it is preferable to provide a drying step before the reaction step.

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 at a temperature lower than the heating temperature in the reaction step. 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 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 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 introducing 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 process)
The refining treatment step is a step of refining the sulfonated fiber material into fine fibers of a predetermined size (for example, nano level). The processing apparatus used in this miniaturization processing step 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 fine cellulose fibers in the fine cellulose fiber-containing dried body dispersion liquid is deteriorated, and the redispersion of the fine cellulose fiber-containing dried body in a solvent such as water. Sex 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 deterioration of the crystallinity of the fine cellulose fiber, and the cost for introducing the sulfo group also increases. To do.

(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 fine cellulose fibers is less than 1 nm, the fine cellulose fibers are dissolved in water as cellulose molecules, and the properties (strength, rigidity, or dimensional stability) as the fine cellulose fibers are not expressed. On the other hand, if it exceeds 1000 nm, it cannot be said that it is a fine cellulose fiber, and it is only a fiber contained in ordinary pulp, so that it becomes difficult to obtain the characteristics (transparency, strength, rigidity, or dimensional stability) as a fine cellulose fiber.
Further, when the average fiber width of the 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 it is a fine cellulose fiber having a small average fiber width and 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 sulfonated 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 dispersion according to the present embodiment is a suspension in which fine cellulose fibers are 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. When this dispersion is measured using a spectrophotometer in accordance with JIS K 7105, the haze value and total light transmission of the sulfonated fine cellulose fiber dispersion and the fine cellulose fiber redispersion described below are transparent. You can calculate the rate.

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 fine cellulose fiber dispersion liquid in which the solid content concentration of the sulfonated fine cellulose fibers is 0.5% by mass and the temperature is 25° C., and the measurement conditions are 12 rpm and 3 minutes, preferably, It is 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 fine cellulose fiber dispersion can be made to exhibit the large viscosity as described above, the 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, the viscosity of the sulfonated fine cellulose fiber dispersion and the fine cellulose fiber redispersion described later can be determined by measuring this dispersion with a Brookfield viscometer in accordance with JIS Z8803.

<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, the metal ion and, without adding a dispersant such as a water-soluble polymer, the sulfonated fine cellulose fiber dispersion, the predetermined moisture content described above. It can be obtained by drying so as to become the following.
The dried solid material containing fine cellulose fibers obtained by drying the sulfonated fine cellulose fiber dispersion corresponds to the dried product obtained by drying the fine cellulose fibers in the claims.

Drying the sulfonated fine cellulose fiber dispersion means a state in which moisture is removed from the sulfonated fine cellulose fiber dispersion even a little, for example, the moisture content of the dried solid fine cellulose fiber-containing dry solid. It is a concept that includes not only a state in which it almost disappears but also a state in which the dried solid substance containing fine cellulose fibers after drying contains water as described below.
For example, the water content of the dried solid fine cellulose fiber-containing dried solid is preferably adjusted to be 50% or less, more preferably 30% or less, further preferably 20% or less, and particularly preferably Is 10% or less. On the other hand, 50% or less is preferable from the viewpoint of transportation.
The water content can be represented by the water content based on the weight of the dried solid material containing fine cellulose fibers after drying, according to JIS P8203.

(Drying temperature)
The temperature at the time of drying the fine cellulose fiber dispersion may be 120° C. or lower from the viewpoint of reducing aggregation of the fine cellulose fibers due to heat, and also from the viewpoint of preventing discoloration after heating. From the viewpoint of ensuring the above, 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, if the temperature is 40° C. or lower, excellent redispersibility can be ensured even when the amount of substituent introduced into the fine cellulose fiber is small.

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

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 is, for example, 480 hPa or less, which is near the saturated steam pressure of water at 80° C., more preferably 320 hPa or less, which is near the saturated steam pressure of water at 70° C., and further preferably saturated water vapor at 40° C. A reduced pressure or a vacuum condition such as 75 hPa or less, which is near the pressure, particularly preferably 15 hPa or less, which is near the saturated vapor pressure of water at 10° C., can be mentioned.

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.

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 a fine cellulose fiber-containing dry solid substance is dispersed in a water-soluble solvent (water-soluble solvent) such as water.
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 is to observe coarse fibers or a sedimentation state due to aggregation of fine cellulose fibers in a fine cellulose fiber redispersion liquid after re-dispersing a dry solid substance containing fine cellulose fibers in water (for example, one day and one night). This can be confirmed.

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 off 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 dried until the moisture content became equilibrium. ..

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 weight 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 the high-pressure homogenizer prepared so that the solid content concentration was 0.5% by weight. 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 obtained 0.5 wt% sulfonated fine cellulose fiber dispersion (0.25 g in dry weight) was dispensed on a petri dish, and the water content was equilibrated in a vacuum device (vacuum pump ultimate pressure was 10 Pa). It was dried until it became (water content 10% or less) to obtain a fine cellulose fiber-containing dry solid. 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 weight, 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 fine cellulose fiber dispersion and fine cellulose fiber redispersion liquid)
The haze value and the total light transmittance were measured by preparing sulfonated fine cellulose fibers with pure water so that the solid content concentration was 0.5%. 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 fine cellulose fiber dispersion and fine cellulose fiber redispersion)
The viscosities of the fine cellulose fiber dispersion liquid and the fine cellulose fiber redispersion liquid prepared by the method described below were measured by a B-type viscosity.
Specifically, the measurement samples were each 0.5 mass %, the temperature was 25° C., and the measurement conditions were a rotation speed of 12 rpm and 3 minutes.

The B-type viscosity recovery rate was calculated as follows.

(B-type viscosity recovery rate (%))=(fine cellulose fiber redispersion liquid)/(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 bottle, pure water was added, and the fine cellulose fiber-containing dry solid was adjusted to 0.5% by weight, and manually adjusted. The mixture was 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 under the condition of 40°C.

(Comparative Example 1)
In the drying step, it was carried out in the same manner as in Example 1 except that it was heated and dried at 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 carried out under the condition of 105°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 under the condition of 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 under the condition of 70°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 under the condition of 105°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 under the condition of 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 under the condition of 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 under the condition of 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 in Comparative Example 4 except that heat drying was carried out under the condition of 40°C.

(Comparative example 6)
In the drying step, it was carried out in the same manner as in Comparative Example 4 except that heat drying was carried out under the condition of 70°C.

(Comparative Example 7)
In the drying step, it was carried out in the same manner as in Comparative Example 4 except that heat drying was carried out under the condition of 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, it was carried out in the same manner as Comparative Example 8 except that the heat drying was carried out under the condition of 40°C.

(Comparative Example 10)
In the drying step, it was carried out in the same manner as Comparative Example 8 except that the heat drying was carried out under the condition of 70°C.

(Comparative Example 11)
In the drying step, it was carried out in the same manner as Comparative Example 8 except that the heat drying was carried out under the condition of 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 the substrate was overheated 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.

(result)
The transparency and viscosity characteristics of the fine cellulose fiber dispersions of Comparative Example 4, Example 1, Example 3 and Comparative Example 8 and the fine cellulose fiber redispersion after redispersion are shown in FIG.
The precipitation characteristics of the fine cellulose fiber redispersions of Examples 1 to 9 and Comparative Examples 1 to 13 are shown in FIG.

As shown in FIG. 1 and FIG. 2, in the present invention, no sedimentation of aggregated fibers after redispersion is observed despite the fact that additives such as dispersants are not used. Also, it can be seen that the viscosity characteristics and the transparency (total light transmittance, haze value) are not significantly lowered, and that the redispersibility is excellent.

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 (4)

A dried product of a mixture containing fine cellulose fibers and water, wherein the cellulose fibers are finely divided to have an average fiber width of 1 nm to 1000 nm,
The fine cellulose fibers are
A sulfonated fine cellulose fiber in which a sulfo group is introduced into a part of the hydroxyl groups,
The amount of sulfur introduced due to the sulfo group is 0.5 mmol/g or more and 3.0 mmol/g or less,
The dried product is
The moisture content is 50% or less,
In a state where the dried product was dispersed in water so that the solid content concentration of the fine cellulose fibers was 0.5% by weight, using a B-type viscometer of the dispersion, 25° C., rotation speed 12 rpm, A dry solid containing fine cellulose fibers, characterized in that the viscosity measured by rotating for 3 minutes is 500 mPa·s or more. The dried product is
The haze value of the dispersion is 20% or less when the dried product is dispersed in water so that the solid content of the fine cellulose fibers is 0.5% by weight. A dry solid containing fine cellulose fibers according to claim 1. The dried product is
When the dried product is dispersed in water such that the solid content of the fine cellulose fibers is 0.5% by weight, the total light transmittance of the dispersion is 95% or more. The dry solid containing fine cellulose fibers according to claim 1 or 2. A fine cellulose fiber redispersion liquid, which is obtained by dispersing the fine cellulose fiber-containing dry solid matter according to any one of claims 1 to 3 in water.

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