JP6582111B1 - Method for producing sulfonated fine cellulose fiber and method for producing sulfonated pulp fiber - Google Patents

Abstract

A method for producing a sulfonated pulp fiber excellent in handleability and a method for producing a sulfonated fine cellulose fiber excellent in transparency are provided. A method for producing a pulp fiber in which a part of the hydroxyl group of cellulose is sulfonated from pulp includes a chemical treatment step for chemically treating the pulp, and the chemical treatment step constitutes the pulp. A contact step of bringing a sulfonating agent having a sulfo group into contact with the pulp fiber and urea or / and a derivative thereof; a reaction step of introducing a sulfo group into a part of the hydroxyl groups of cellulose constituting the pulp fiber after the contact step; Therefore, a sulfonated pulp fiber excellent in handleability can be produced. [Selection] Figure 1

Description

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

  Cellulose nanofibers (CNF) are microfibers having a fiber width of several to several tens of nanometers and a fiber length of several hundreds of nanometers (such as mechanical fibrillation and TEMPO catalytic oxidation) that are derived from plant-derived cellulose. . Since CNF has light weight, high elasticity, high strength, and low linear thermal expansibility, the use of composite materials containing CNF is expected not only in the industrial field but also in various fields such as the food field and the medical field. ing.

  When CNF is mechanically defibrated, cellulose fibers are strongly bonded by hydrogen bonds, and thus a large amount of energy is required to obtain CNF. Further, the obtained CNF has a problem that the fiber length and the like vary.

  Then, the manufacturing method which performs the chemical processing process which makes the state which loosened the cellulose fiber which comprises a pulp to some extent before performing a mechanical defibration processing process is developed (patent documents 1-4). If this manufacturing method is used, CNF can be obtained with less energy compared with a manufacturing method in which pulp is directly machined. In addition, there is an advantage that variation in the size of the obtained CNF can be suppressed.

For example, Patent Documents 1 to 3 describe a method in which pulp is chemically treated with a strong acid such as sulfuric acid, persulfuric acid, or a chlorine-based oxidizing agent, and then the obtained pulp slurry is supplied to a defibrator or the like to obtain CNF. Is disclosed.
However, in manufacturing methods such as Patent Documents 1 to 3, since sulfuric acid, persulfuric acid, and the like are used in the chemical treatment process, in addition to the complexity of handling, the problem of wastewater treatment after reaction, the piping of facilities, and the like corrode. The problem has occurred. In addition, when a chlorinated oxidant is used, there are concerns about the environmental impact of chlorine generated during the reaction.

On the other hand, Patent Document 4 discloses a production method in which pulp is chemically treated with phosphate and urea, and then the obtained pulp slurry is supplied to a defibrator or the like to obtain CNF. If such a manufacturing method is used, the problem which generate | occur | produces when using strong acids, such as a sulfuric acid, in a chemical treatment process can be eliminated. In addition, it is described that the dispersibility in an aqueous solvent can be improved because a phosphate ester can be introduced into a part of the hydroxyl groups on the surface of the obtained CNF.
Patent Document 4 describes that CNF having high transparency (haze value of 5 to 15%) can be produced by adjusting the solid content concentration to 0.2% by mass.

JP 2017-43677 A JP 2017-8472 A JP 2017-25240 A JP 2017-25468 A

  However, Patent Documents 1 to 4 do not include a technique for adjusting the water retention of the pulp fiber before defibration, and there is no description regarding handling of the pulp fiber based on the adjusted water retention.

  An object of this invention is to provide the manufacturing method of the sulfonated pulp fiber excellent in the handleability, and the manufacturing method of the sulfonated fine cellulose fiber excellent in transparency in view of the said situation.

(Method for producing sulfonated pulp fiber)
The manufacturing method of the sulfonated pulp fiber of 1st invention is a method of manufacturing the pulp fiber in which some hydroxyl groups of the cellulose were sulfonated from the pulp, Comprising: The chemical processing process of chemically processing the said pulp is included. The chemical treatment step comprises contacting a pulp fiber constituting the pulp with a reaction solution in which sulfamic acid having a sulfo group and urea are dissolved in water , and a wet pulp after the contact step. fed to the reaction step, in the reaction step, the reaction step is performed with about Engineering you introduce part sulfo group of a hydroxyl group of cellulose, in order to configure the pulp fibers, the reaction solution after the contacting step a step of heating the pulp fibers of the contacted state the reaction to proceed, the reaction temperature 100 ° C. to 180 ° C. and characterized by adjusting the reaction time to be 5 minutes or more
In the method for producing a sulfonated pulp fiber according to the second invention, in the first invention, the reaction solution is such that sulfamic acid and urea are in a concentration (g / L) ratio of 4: 1 to 1: 2.5. It is contained in.
The method for producing a sulfonated pulp fiber of the third invention is characterized in that, in the invention according to either the first invention or the second invention , the pulp supplied to the reaction step is in a state containing moisture. .
The method for producing a sulfonated pulp fiber according to a fourth aspect of the invention is the invention according to any one of the first aspect, the second aspect, or the third aspect, wherein a washing step of washing the pulp after the reaction step is performed after the reaction step. It is characterized by including.
(Method for producing sulfonated fine cellulose fiber)
The method for producing a sulfonated fine cellulose fiber of the fifth invention is a method for producing a fine cellulose fiber in which a part of the hydroxyl group of cellulose is sulfonated from the pulp, and a chemical treatment step for chemically treating the pulp; The sulfone manufactured by the manufacturing method in any one of Claims 1-4 which performs the refinement | purification process process which refines | miniaturizes the pulp after this chemical treatment process in order, The pulp after the said chemical treatment process is manufactured. The sulfonated pulp fiber has a water retention of 250% or more in the refinement treatment step .
The manufacturing method of the sulfonated fine cellulose fiber of the sixth invention is the fifth invention, wherein the sulfonated pulp fiber is a water-soluble solvent and the solid content concentration is 0.1% by mass to 20% by mass in the micronization treatment step. It is characterized by miniaturization in a dispersed state .

(Method for producing sulfonated pulp fiber)
According to the first aspect of the invention, contacting a sulfonating agent and urea having a sulfo group on pulp, by heating the reaction in a state where the moisture of the reaction solution remained in the pulp, the reaction is allowed to proceed until the internal fibers be able to. For this reason, since the sulfonated pulp fiber which has the outstanding water retention degree can be manufactured, the sulfonated pulp fiber excellent in the handleability can be manufactured . In addition, the recovery rate of the sulfonated pulp fibers can be improved. Furthermore, the production efficiency of the sulfonated pulp fiber can be improved by reacting at a predetermined temperature.
According to the second invention, by adjusting the sulfonating agent and urea to a predetermined mixing ratio, it is possible to produce a sulfonated pulp fibers having an appropriate fiber length. And since the water retention of a sulfonated pulp fiber can be controlled appropriately, the sulfonated pulp fiber according to a use can be manufactured appropriately.
According to the 3rd invention, a reaction process can be advanced appropriately.
According to the fourth invention, the handleability of the sulfonated pulp fiber can be improved.
(Method for producing sulfonated fine cellulose fiber)
According to 5th invention, a refinement | miniaturization process can be performed efficiently by making the water retention of the sulfonated pulp fiber provided to a refinement | purification process process into a predetermined value or more. Further, by reacting by contacting a sulfonating agent and urea having a sulfo group on pulp, it is possible to produce a sulfonated fine cellulose fibers having a suitable fiber length and transparency.
According to the sixth aspect of the invention, the miniaturization process can be performed appropriately.

It is a schematic flowchart of the manufacturing method of the sulfonated fine cellulose fiber of this embodiment, a sulfonated pulp fiber, and a derivative pulp. It is the figure which showed the experimental result, and is the figure which showed the characteristic table | surface of the sulfamic acid / urea processing pulp fiber corresponded to the sulfonated pulp fiber obtained by the manufacturing method of this embodiment. It is the figure which showed the experimental result, and is the figure which showed the characteristic table | surface at the time of remove | excluding the drying process of the sulfamic acid / urea process pulp fiber corresponded to the sulfonated pulp fiber obtained by the manufacturing method of this embodiment. It is the graph which showed the experimental result, and shows the amount of sulfur introduction, and the water retention. It is the graph which showed the experimental result, and shows the water retention. It is the graph which showed the experimental result, and shows the fiber length. It is the graph which showed the experimental result, and is related with reaction conditions (temperature and time). It is the graph which showed the experimental result, and is related with reaction conditions (temperature and time). It is the figure which showed the experimental result, and is the enlarged photograph of the fiber surface of the sulfamic acid / urea treatment pulp fiber corresponding to the sulfonated pulp fiber obtained by the manufacturing method of this embodiment. It is the graph which showed the experimental result, and relates to the orientation strength of the sulfamic acid / urea treated pulp fiber corresponding to the sulfonated pulp fiber obtained by the production method of this embodiment. It is the figure which showed the experimental result, and is the enlarged photograph of the fiber surface of the sulfamic acid / urea treatment pulp fiber corresponding to the sulfonated pulp fiber obtained by the manufacturing method of this embodiment. It is the figure which showed the experimental result, and is the figure which showed the defibration situation. It is the figure which showed the experimental result, and is the figure which showed the whiteness. It is the figure which showed the experimental result, and is the figure which showed the characteristic table | surface of the nano cellulose fiber equivalent to the sulfonated fine cellulose fiber obtained by the manufacturing method of this embodiment. It is the figure which showed the experimental result, and is the figure which showed the characteristic table | surface at the time of removing the drying process of the nano cellulose fiber equivalent to the sulfonated fine cellulose fiber obtained by the manufacturing method of this embodiment. It is the graph which showed the experimental result, and is related to transparency. It is the graph which showed the experimental result, and is related to transparency. It is the graph which showed the experimental result, and shows the polymerization degree. It is the graph which showed the experimental result. It is the graph which showed the experimental result, and showed the relationship between water retention and defibration. It is the graph which showed the experimental result, and showed the relationship between water retention and defibration. It is the graph which showed the experimental result, and showed the relationship between water retention and defibration. It is the figure which showed the experimental result, and is the figure which showed the solid content density | concentration at the time of defibration, and the relationship of defibration. It is the graph which showed the experimental result, and shows the relationship between the solid content concentration at the time of defibration, and defibration.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
The manufacturing method of the sulfonated pulp fiber of the present embodiment is characterized in that a sulfonated pulp fiber excellent in handleability can be manufactured.
In addition, the method for producing a sulfonated fine cellulose fiber of the present embodiment is characterized in that the sulfonated fine cellulose fiber having excellent transparency and improved entanglement between fibers can be efficiently produced. Have.
In particular, the method for producing the sulfonated fine cellulose fiber according to the present embodiment can be easily and appropriately obtained if the sulfonated pulp fiber produced by the method for producing the sulfonated pulp fiber according to the present embodiment is refined. Fiber can be produced.

The method for producing a sulfonated pulp fiber according to the present embodiment is a method for producing a sulfonated pulp fiber by subjecting the pulp to a chemical treatment step. In this chemical treatment step, after the supplied pulp is treated in the contact step. In this method, the reaction process is performed.
Moreover, the manufacturing method of the sulfonated fine cellulose fiber of this embodiment is a method of performing in order the refinement | purification process process which refines | miniaturizes the pulp after a chemical treatment process, after using a pulp for a chemical treatment process.

  First, the outline of the sulfonated pulp fiber and the sulfonated fine cellulose fiber produced by using the sulfonated pulp fiber production method of the present embodiment and the sulfonated fine cellulose fiber production method of the present embodiment will be described.

<Sulfonated pulp fiber>
A sulfonated pulp fiber (hereinafter simply referred to as a sulfonated pulp fiber) obtained by the method for producing a sulfonated pulp fiber of the present embodiment is a pulp fiber composed of a plurality of cellulose fibers, and cellulose constituting the contained cellulose fiber. At least a part of the hydroxyl group (—OH group) of (a chain polymer in which D-glucose is β (1 → 4) glycosidic bonded) is sulfonated with a sulfo group represented by the following formula (1). .

(—SO ₃ ⁻ ) _r · Z ^{r +} (1)
(Where r is an independent natural number from 1 to 3, and Z ^{r +} is composed of hydrogen ions, alkali metal cations, ammonium ions, aliphatic ammonium ions, and aromatic ammonium ions when r = 1. And at least one selected from the group consisting of alkaline earth metal cations or polyvalent metal cations when r = 2 or 3.)

(Introduced amount of sulfo group in sulfonated pulp fiber)
The introduction amount of the sulfo group in the sulfonated pulp fiber is not particularly limited as long as it is introduced to such an extent that the pulp fiber is easily loosened.
For example, the amount of sulfur introduced per 1 g (mass) of sulfonated pulp fibers is preferably adjusted to be higher than 0.42 mmol / g, more preferably 0.42 mmol / g to 9.9 mmol / g. Yes, more preferably 0.5 mmol / g to 9.9 mmol / g, and even more preferably 0.6 mmol / g to 9.9 mmol / g.
When the amount of sulfur introduced per 1 g (mass) of the sulfonated pulp fiber is 0.42 mmol / g or less, the state in which the fine fibers constituting the sulfonated pulp fiber are strongly bonded is easily maintained. On the other hand, as the sulfur introduction amount approaches 9.9 mmol / g, there is a concern that the crystallinity is lowered, and the cost for introducing sulfur tends to increase.
Therefore, the introduction amount of the sulfo group into the sulfonated pulp fiber, that is, the introduction amount of sulfur based on the sulfo group, is preferably adjusted to be in the above range.

In particular, the amount of sulfo group introduced into the sulfonated pulp fiber is set to be higher than 0.42 mmol / g and not higher than 3.0 mmol / g from the viewpoint of facilitating dispersion of the fine fibers constituting the sulfonated pulp fiber. It is preferable to adjust, more preferably 0.5 mmol / g to 3.0 mmol / g, still more preferably 0.5 mmol / g to 2.0 mmol / g, and still more preferably 0.5 mmol / g. -1.5 mmol / g.
Moreover, it is preferable to adjust so that it may become the same range as the said range also from the viewpoint of the transparency in the fine cellulose fiber mentioned later obtained by defibrating a sulfonated pulp fiber.

(Method for measuring the amount of sulfo group introduced)
The amount of sulfur introduced into the sulfonated pulp fiber (that is, the amount of sulfo group introduced) is determined by burning a predetermined amount of the sulfonated pulp fiber and converting the sulfur content contained in the combustion product into IEC 62321 using a combustion ion chromatograph. It can be measured by a compliant method.

(Water retention of sulfonated pulp fiber)
The sulfonated pulp fiber is characterized in that it has a predetermined water retention degree in addition to the above-described amount of introduced sulfur.
Specifically, the sulfonated pulp fiber is prepared so that the water retention of the sulfonated pulp fiber, that is, the amount of water contained after centrifugal dehydration is in a predetermined state.
The range of the water retention of the sulfonated pulp fiber is not particularly limited as long as it is appropriately adjusted according to the purpose of use and use described later.
For example, the water retention of the sulfonated pulp fibers is preferably adjusted to be 150% or more. More specifically, it is preferably adjusted to be higher than 200%, more preferably 220% or more, still more preferably 250%, still more preferably 300% or more, and even more preferably. Is 500% or more.

  Here, if the water retention of the sulfonated pulp fiber is increased, the fiber is in a state of containing a large amount of moisture. In such a state, it is presumed that the moisture contained in the fiber affects the bonding force between the fine fibers constituting the sulfonated pulp fiber. That is, in the sulfonated pulp fiber prepared so as to have a high degree of water retention, the bonding between the fine fibers constituting the surface of the sulfonated pulp fiber becomes weak, and a gap is formed between adjacent fine fibers. It is inferred that moisture is easily retained by the penetration of moisture into the gap.

  For this reason, if the water retention of the sulfonated pulp fiber is adjusted to be within the above range, the sulfonated pulp fiber can be prepared according to the following purpose and application.

  For example, from the viewpoint of dewaterability in the sulfonated pulp fiber, it may be prepared so that the moisture content in the fiber is small, that is, the water retention is lowered. By lowering the water retention of the sulfonated pulp fiber, there are obtained advantages such as a reduction in transportation cost during transportation and a reduction in production efficiency and production cost when producing the sulfonated pulp fiber.

  On the other hand, from the viewpoint of refining the sulfonated pulp fiber, it may be prepared so that the moisture content in the fiber is increased, that is, the water retention is increased. This is because by increasing the water retention of the sulfonated pulp fiber, the bonding force between the fine fibers constituting the sulfonated pulp fiber can be weakened. As a result, the surface of the sulfonated pulp fiber and the portion located inward near the surface are easily fibrillated. Then, if the sulfonated pulp fiber in such a state is subjected to a defibrating machine or the like, it becomes easier to refine the pulp fiber. That is, workability and efficiency can be improved when a sulfonated pulp fiber described later is refined to prepare a refined cellulose fiber.

  When the sulfonated pulp fiber is refined, if the water retention is too high, the concentration of the refined fiber tends to be too low or the yield tends to be low. For this reason, in terms of the yield and concentration of fine fibers after the sulfonated pulp fibers are refined, it is preferable to adjust the water retention so as not to be too high. For example, the water retention is 10,000. It is desirable to adjust so that it may become less than%.

(Measurement method of water retention)
The water retention of the sulfonated pulp fiber can be determined by a general pulp fiber water retention test (for example, a method based on JAPAN TAPPI paper pulp test method No. 26: 2000).

(Average fiber length of sulfonated pulp fiber)
The length of the sulfonated pulp fiber is not particularly limited as long as the average fiber length is such that the fiber shape is maintained.
Specifically, the average fiber length may be maintained at a predetermined length before and after sulfonation of the sulfonated pulp fiber. More specifically, when comparing the average fiber length of the pulp fiber before introducing the sulfo group into the sulfonated pulp fiber and the average fiber length of the sulfonated pulp fiber after introducing the sulfo group, the latter (that is, sulfone) It is preferable to adjust so that the pulped fiber) is 50% or more compared to the former, more preferably 70% or more, and even more preferably 80% or more. In other words, the sulfonated pulp fiber is prepared so that the average fiber length is not less than a predetermined value before and after the introduction of the sulfo group, regardless of the raw material of the pulp as the raw material.

  For example, when wood-based pulp fibers are used as the raw material and the average fiber length is 2.6 mm, the average fiber length of the sulfonated pulp fibers is 50% or more of the average fiber length of the raw pulp fibers. That is, it is desirable to prepare it to be 1.3 mm or more.

(Measurement method of average fiber length)
The average fiber length of the sulfonated pulp fiber can be measured using a known fiber analyzer. As a known fiber analyzer, for example, a fiber tester (manufactured by Lorenzen & Bettley Co., Ltd.) can be cited.

(Whiteness)
The sulfonated pulp fiber is dried after a plurality of sulfonated pulp fibers are dispersed in an aqueous solution and washed. It is preferable to adjust so that the whiteness at the time of drying becomes a predetermined range.
For example, the sulfonated pulp fiber may be prepared so that the whiteness is 30% or more, and preferably 40% or more. If the degree of whiteness is 30% or more, coloring becomes inconspicuous, and handling properties can be improved.

  The whiteness of the sulfonated pulp fiber can be determined by using a known method. For example, it can be measured according to JIS P 8148: 2001 (paper, paperboard and pulp-ISO whiteness (diffuse blue light reflectance)).

  As mentioned above, if the manufacturing method of the sulfonated pulp fiber of this embodiment is used, the transparency of the fine cellulose fiber described later can be improved by adjusting the amount of sulfur introduced based on the sulfo group. become able to. In addition, by adjusting the water retention, the characteristics of the sulfonated pulp fiber can be adjusted as appropriate according to the purpose of use and application, so that the sulfonated pulp fiber with improved flexibility in handling can be manufactured. . Furthermore, by adjusting the average fiber length of the sulfonated pulp fiber to be a predetermined value or more, it becomes possible to produce a sulfonated pulp fiber with a further improved degree of freedom in handling.

<Sulfonated fine cellulose fiber>
Next, a sulfonated fine cellulose fiber (hereinafter simply referred to as a sulfonated fine cellulose fiber) obtained by the method for producing a sulfonated fine cellulose fiber of the present embodiment will be described.
The sulfonated fine cellulose fiber is a fine cellulose fiber in which the cellulose fiber is refined, and is a hydroxyl group of cellulose (a chain polymer in which D-glucose is β (1 → 4) glycosidic bond) constituting the fine cellulose fiber. At least a part of (—OH group) is sulfonated with a sulfo group represented by the above formula (1).

(Introduced amount of sulfo group in sulfonated fine cellulose fiber)
The introduction amount of the sulfo group of the sulfonated fine cellulose fiber can be represented by the introduction amount of sulfur based on the sulfo group, and the introduction amount is not particularly limited as long as the transparency and dispersibility can be maintained to some extent.
For example, the amount of sulfur introduced per 1 g (mass) of sulfonated fine cellulose fibers is preferably adjusted to be higher than 0.4 mmol / g, and more preferably 0.42 mmol / g to 9.9 mmol / g. More preferably, it is 0.5 mmol / g to 9.9 mmol / g, and still more preferably 0.6 mmol / g to 9.9 mmol / g.

When the amount of sulfur introduced per 1 g (mass) of the sulfonated fine cellulose fibers is 0.42 mmol / g or less, the hydrogen bond between the fibers is strong and the dispersibility tends to decrease. On the contrary, dispersibility is easily improved by making the amount of sulfur introduced higher than 0.42 mmol / g, and if it is 0.5 mmol / g or more, the electronic repulsion can be made stronger. This makes it easier to maintain a stable state. On the other hand, as the sulfur introduction amount approaches 9.9 mmol / g, there is a concern that the crystallinity is lowered, and the cost for introducing sulfur tends to increase.
Therefore, the introduction amount of the sulfo group into the sulfonated fine cellulose fiber, that is, the introduction amount of sulfur based on the sulfo group, is preferably adjusted to be in the above range.

In particular, in terms of the amount of sulfo groups introduced into the sulfonated fine cellulose fiber, from the viewpoint of the dispersibility of the fine fibers constituting the sulfonated pulp fiber, it is higher than 0.42 mmol / g and lower than 3.0 mmol / g. It is preferable to adjust, more preferably 0.5 mmol / g to 3.0 mmol / g, still more preferably 0.5 mmol / g to 2.0 mmol / g, and still more preferably 0.5 mmol / g. -1.5 mmol / g.
Moreover, it is preferable to adjust so that it may become the range similar to the said range also from a transparency viewpoint of a sulfonated fine cellulose fiber.

(Method for measuring the amount of sulfo group introduced)
The amount of sulfur introduced into the sulfonated fine cellulose fiber (that is, the amount of sulfo group introduced) is determined by burning a predetermined amount of the sulfonated fine cellulose fiber and using the combustion ion chromatograph to determine the sulfur content contained in the combustion product by IEC. It can be measured by a method based on 62321.
Further, when the above-described sulfonated pulp fiber is refined, it may be obtained from the amount of sulfur introduced into the sulfonated pulp fiber.

  If the average fiber length and average fiber width of the sulfonated fine cellulose fiber are prepared so that the fibers can be easily entangled with each other, and transparency is easily obtained when dispersed in an aqueous solvent, the length and thickness are There is no particular limitation.

(Average fiber length of sulfonated fine cellulose fiber)
The average fiber length of the sulfonated fine cellulose fiber can be indirectly represented by the degree of polymerization.

  The average fiber length of the sulfonated fine cellulose fibers is preferably adjusted so that the degree of polymerization is 280 or more, more preferably 300 to 1,000, and still more preferably 300 to 600.

If the degree of polymerization of the sulfonated fine cellulose fiber is lower than 280, the entanglement of the fiber becomes weak due to the decrease in fiber length. On the other hand, when the degree of polymerization of the sulfonated fine cellulose fiber exceeds 600, the dispersibility becomes low, and the slurry viscosity when slurried becomes too high and the dispersion stability tends to be low.
Therefore, the degree of polymerization of the sulfonated fine cellulose fiber is preferably adjusted so as to be within the above range. In particular, from the viewpoint of easy entanglement between fibers, it is preferable to prepare so that the degree of polymerization is 280 or more, and from the viewpoint of dispersibility and handleability, it is preferable to prepare so that the degree of polymerization is lower than 600. preferable.

(Measurement method of degree of polymerization)
Although the measuring method of this polymerization degree is not specifically limited, For example, it can measure by the copper ethylenediamine method. Specifically, the degree of polymerization of the sulfonated fine cellulose fiber can be measured by dissolving the sulfonated fine cellulose fiber in a 0.5 M copper ethylenediamine solution and measuring the viscosity of the solution by a viscosity method.

(Average fiber width of sulfonated fine cellulose fiber)
The average fiber width of the sulfonated fine cellulose fiber is not particularly limited as long as it is thick enough to obtain transparency when dispersed in an aqueous solvent.
For example, the average fiber width of the sulfonated fine cellulose fibers is preferably adjusted to be 1 nm to 1000 nm when observed with an electron microscope, more preferably 2 nm to 500 nm, and still more preferably 2 nm to 100 nm. More preferably, it is 2 nm-30 nm, More preferably, it is 2 nm-20 nm.
When the fiber width of the fine cellulose fiber is less than 1 nm, the cellulose is dissolved in water as cellulose molecules, so that physical properties (strength, rigidity, or dimensional stability) as the fine cellulose fiber are difficult to be expressed. On the other hand, if it exceeds 1000 nm, it cannot be said that it is a fine cellulose fiber, but is merely a fiber contained in normal pulp, and physical properties (transparency, strength, rigidity, or dimensional stability) as a fine cellulose fiber tend not to be obtained. It is in.
Therefore, it is preferable to prepare the average fiber width of the sulfonated fine cellulose fiber so as to be within the above range.
In particular, it is more preferable to prepare the sulfonated fine cellulose fiber so as to fall within the following range from the viewpoint of handling and transparency required for the sulfonated fine cellulose fiber.

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 is larger than 30 nm, it approaches 1/10 of the wavelength of visible light, and when combined with a matrix material, visible light is easily refracted and scattered at the interface, causing visible light scattering. Therefore, the transparency tends to decrease.
Therefore, the average fiber width of the sulfonated fine cellulose fiber is preferably 2 nm to 30 nm, more preferably 2 nm to 20 nm, and still more preferably 2 nm to 10 nm, from the viewpoint of handleability and transparency.
In particular, from the viewpoint of transparency, the sulfonated fine cellulose fibers are preferably prepared so that the average fiber width is 20 nm or less, more preferably 10 nm or less. If the average fiber width is adjusted to be 10 nm or less, scattering of visible light can be reduced, so that a sulfonated fine cellulose fiber having high transparency can be obtained.

(Measurement method of average fiber width)
The average fiber width of the sulfonated fine cellulose fiber can be measured using a known technique.
For example, sulfonated fine cellulose fibers are dispersed in a solvent such as pure water, and the mixed solution is adjusted to a predetermined mass%. The mixed solution is spin-coated on a silica substrate coated with PEI (polyethyleneimine), and the sulfonated fine cellulose fibers on the silica substrate are observed.
As the observation method, for example, a scanning probe microscope (for example, manufactured by Shimadzu Corporation; SPM- 9 700) can be used. The average fiber width of the sulfonated fine cellulose fibers can be determined by randomly selecting 20 sulfonated fine cellulose fibers in the obtained observation image and measuring and averaging each fiber width.

(Haze value)
The transparency of the sulfonated fine cellulose fiber can be evaluated by the haze value of the dispersion in which the sulfonated fine cellulose fiber is dispersed in the dispersion.
Specifically, the transparency when the dispersion liquid adjusted so that the solid content concentration when the sulfonated fine cellulose fiber is dispersed in the dispersion liquid becomes a predetermined concentration can be evaluated by the haze value can be evaluated. .
Although the solid content concentration of the dispersion liquid in which the sulfonated fine cellulose fibers are dispersed is not particularly limited, for example, it can be prepared to be 0.1% by mass to 20% by mass. And if the haze value of this dispersion liquid is 20% or less, it can be said that the sulfonated fine cellulose fiber of this embodiment has transparency. In other words, when the haze value of the dispersion prepared so that the solid concentration is within the above range is higher than 20%, it can be said that the transparency is hardly exhibited properly.

For example, when the solid content concentration of the dispersion liquid in which the sulfonated fine cellulose fibers are dispersed is 0.2% by mass to 0.5% by mass, the haze value of the dispersion liquid is 20% or less. It is in a state where the transparency is properly exhibited, more preferably 15% or less, and even more preferably 10% or less, and the sulfonated fine cellulose fiber has more transparency.
Therefore, the sulfonated fine cellulose fibers are preferably prepared such that the haze value of the dispersion prepared so that the solid content concentration is 0.1% by mass to 20% by mass is 20% or less, more preferably. It is preferable to prepare so that the haze value of the dispersion when the solid content concentration is adjusted to be 0.2% by mass to 0.5% by mass is in the above range.

  The dispersion is not particularly limited as long as it is an aqueous solvent. For example, as the aqueous solvent, in addition to water alone, alcohol, ketone, amine, carboxylic acid, ether, amide, or a mixture thereof can be employed.

(Measurement method of haze value)
The haze value can be measured as follows.
The sulfonated fine cellulose fiber is dispersed in the dispersion liquid described above so as to have a predetermined solid content concentration. And if this dispersion liquid is measured using a spectrophotometer based on JISK7105, the haze value which is transparency of a sulfonated fine cellulose fiber can be calculated | required.

(Measurement method of total light transmittance)
In addition, it is preferable to adjust so that the total light transmittance is 90% or more, more preferably 95% or more, in the haze value of the dispersion.
The total light transmittance can be measured as follows.
The sulfonated fine cellulose fiber is dispersed in the dispersion liquid described above so as to have a predetermined solid content concentration. And if this dispersion liquid is measured using a spectrophotometer based on JISK7105, the total light transmittance of a sulfonated fine cellulose fiber can be calculated | required.

  As described above, if the method for producing sulfonated fine cellulose fibers of the present embodiment is used, it is possible to produce sulfonated fine cellulose fibers that exhibit excellent transparency and improve the entanglement between the fibers. .

<Derivative pulp>
If a plurality of sulfonated pulp fibers manufactured using the method for manufacturing a sulfonated pulp fiber of the present embodiment are assembled, a derivative pulp containing pulp fibers into which sulfo groups are introduced can be obtained.
This derivative pulp may be a collection of only a plurality of sulfonated pulp fibers produced using the method for producing sulfonated pulp fibers of the present embodiment, or a fiber made of a material other than cellulose (for example, Polyvinyl alcohol (PVA), synthetic fibers such as polyester, natural fibers such as wool), other pulp fibers, and the like may be contained.
In addition, if it adjusts so that the content rate of the several sulfonated pulp fiber manufactured using the manufacturing method of the sulfonated pulp fiber of this embodiment may become high, it will become easy to exhibit the effect similar to the sulfonated pulp fiber mentioned above. Therefore, it is preferable.

<Details of the method for producing the sulfonated pulp fiber of the present embodiment and the method for producing the sulfonated fine cellulose fiber of the present embodiment>
The sulfonated pulp fiber described above is manufactured using the method for manufacturing the sulfonated pulp fiber of the present embodiment.
Specifically, as described above, the pulp is subjected to the chemical treatment step, and the pulp subjected to the chemical treatment step is processed in the order of the contact step and the reaction step.
The sulfonated fine cellulose fibers are produced using the method for producing sulfonated fine cellulose fibers of this embodiment. Specifically, as described above, the pulp is processed in the order of the chemical treatment step and the refinement treatment step.

In addition, in the manufacturing method of the sulfonated fine cellulose fiber of this embodiment, the pulp fiber manufactured using the manufacturing method of the sulfonated pulp fiber of this embodiment is used as the pulp supplied to the refinement treatment step. Can do.
Below, as a manufacturing method of the sulfonated fine cellulose fiber of this embodiment, the representative of the pulp supplied with the sulfonated pulp fiber manufactured using the manufacturing method of the sulfonated pulp fiber of this embodiment to a refinement | miniaturization process process. Will be described.

  In addition, the sulfonated fine cellulose fiber is obtained by supplying the fiber raw material directly to the fine treatment step to obtain a fine cellulose fiber, and substituting at least a part of the hydroxyl groups of cellulose constituting the fine cellulose fiber with a sulfo group. The sulfonated pulp fiber manufactured by the method shown below as a representative may be refined and prepared. If the latter method is adopted, an advantage that a desired sulfonated pulp fiber can be produced only by carrying out a fine treatment step is obtained.

As described above, the derivative pulp described above can be prepared as an aggregate of a plurality of sulfonated pulp fibers manufactured using the method for manufacturing a sulfonated pulp fiber of the embodiment. Omit.
In addition, the manufacturing method shown below is only an example, and if it is a method which can manufacture the sulfonated pulp fiber and sulfonated fine cellulose fiber which have the characteristic mentioned above, it will not be limited to the following method.

(Method for producing sulfonated pulp fiber)
Each process will be specifically described in order.
First, the manufacturing method of the sulfonated pulp fiber of this embodiment is demonstrated.
As shown in FIG. 1, this sulfonated pulp fiber production method includes a chemical treatment step in which a fiber raw material containing cellulose is chemically treated by the method shown below.

(Chemical treatment process)
The chemical treatment step in the method for producing a sulfonated pulp fiber of the present embodiment 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 a fiber raw material containing cellulose, and after this contact step. And a reaction step of introducing a sulfo group into at least a part of the hydroxyl groups of cellulose contained in the fiber raw material.
That is, the method for producing a sulfonated pulp fiber of this embodiment is characterized in that urea or / and a derivative thereof is used in a method for introducing a sulfo group into cellulose contained in a fiber raw material. For this reason, the outstanding effect which was not obtained with the conventional manufacturing method as shown below is produced.

Generally, if only a sulfo group is introduced into cellulose contained in a fiber raw material, the heat treatment can be performed in a state where only the sulfonating agent is brought into contact with the fiber raw material.
However, when the reaction is carried out using only the sulfonating agent, 1) the time required for introduction of the sulfo group becomes long, 2) the fiber is easily shortened due to the influence of the acid of the sulfonating agent, and 3 ) Coloring occurs in the fiber after the reaction due to the influence of the acid of the sulfonating agent, and various chemical treatments need to be performed to treat this coloring. To do.

  On the other hand, in the method for producing a sulfonated pulp fiber of the present embodiment, as described above, a method of bringing urea or / and a derivative thereof into contact with the fiber raw material in addition to the sulfonating agent is employed. For this reason, the problems 1) to 3) and the like that occur when the reaction is carried out only with the sulfonating agent as in the prior art can be solved.

Specifically, by bringing a sulfonating agent and urea or / and a derivative thereof into contact with each other at a predetermined ratio and then reacting them,
A) The introduction amount of the sulfo group can be promoted. In other words, by making urea function as a catalyst, the reaction time can be shortened,
B) On the other hand, the action of shortening fiber by acid can be suppressed by urea. That is, it is possible to prevent the fiber from being shortened by the acid,
C) The coloring of the fiber by an acid can be suppressed by urea. In other words, the present invention is characterized in that an effect that has not been obtained in the past can be prepared, in which a fiber in which coloring to the fiber is suppressed despite treatment with an acid can be prepared.
And D) The sulfonated pulp fiber obtained also has the effect that it can adjust so that it may have a water retention as mentioned above.

  In addition, about the coloring to a fiber, it can represent with the whiteness of a fiber.

  Moreover, in the manufacturing method of the sulfonated pulp fiber of this embodiment, the following advantages are further obtained by controlling the water retention of the sulfonated pulp fiber.

When producing fine fibers such as nanofibers by refining fibers such as pulp using a defibrator or the like, the refining efficiency is very important both economically and environmentally.
In general, as a method for improving the efficiency performed in such a refinement treatment step, the degree of polymerization of the fiber before refinement is reduced (that is, the fiber length of the fiber supplied to the defibrator is shortened). A method of reducing the load on defibration or the like when supplied to a textile machine or the like is employed.
Although this method can improve the miniaturization efficiency, there is a problem that the average fiber length of the obtained fine fibers is shortened.
On the other hand, in order to increase the average fiber length of the fine fibers obtained, a defibrator or the like in a state in which the degree of polymerization of the fibers before miniaturization is maintained high (that is, the fiber length of fibers supplied to the defibrator is increased) Need to supply.
In this method, although the fiber length of the fine fiber can be increased to some extent, the fiber is in a very hard state (for example, a state in which the fine fibers constituting the fiber are firmly bonded to each other). It cannot be easily miniaturized by a fine machine or the like. For this reason, a large amount of energy (for example, when using a high-pressure homogenizer, the pressure is set to 200 MPa or more) and time (for example, a shearing device having a high-speed cutter (Cleamix, manufactured by MTechnic Co., Ltd.)) In the case of using, the problem of about 30 minutes) is required, and not only the working efficiency is deteriorated, but also the miniaturization efficiency is extremely deteriorated. Moreover, there is a problem that it is difficult to obtain fine fibers having a uniform fiber length.

  On the other hand, in the manufacturing method of the sulfonated pulp fiber according to the present embodiment, as described above, the sulfonated pulp fiber is prepared while being controlled so as to have a predetermined water retention degree. Will be able to solve.

For example, by increasing the water retention of the sulfonated pulp fiber produced by the method for producing the sulfonated pulp fiber of the present embodiment, the bonding strength between the fine fibers constituting the sulfonated pulp fiber as described above is weakened, It becomes easy to fibrillate the surface of the sulfonated pulp fiber and the portion located inward near the surface. Then, since the fiber which comprises a sulfonated pulp fiber can be made easy to loosen, the energy required when performing a refinement | miniaturization process can be made small. For example, when miniaturization is performed using a high-pressure homogenizer, the pressure can be lowered, or the number of treatments (number of passes) can be reduced. Therefore, the load on the environment due to the reduction in the amount of energy can be reduced.
In addition, since the miniaturization process can be performed smoothly, the time required for the miniaturization process can be shortened, so that productivity can be improved. In other words, the productivity can be improved, so that the manufacturing cost (production cost) can be reduced as compared with the case of manufacturing by the conventional technology.

Conversely, if the water retention of the sulfonated pulp fiber produced by the method for producing the sulfonated pulp fiber of the present embodiment is lowered, the following advantages can be obtained.
If it manufactures so that the water retention of a sulfonated pulp fiber may become low, since the moisture content in this fiber can be decreased, dewaterability can be improved. In this case, since dehydration is facilitated, a sulfonated pulp fiber having a high solid content concentration can be produced. Then, the transportation cost at the time of conveying the manufactured sulfonated pulp fiber can be suppressed.
In addition, when the production process includes a step of washing the sulfonated pulp fiber, dehydration after the washing step is facilitated, so that operability and workability can be improved. For this reason, when manufacturing a sulfonated pulp fiber for the said objective, productivity can be improved. In other words, the productivity can be improved, so that the manufacturing cost (production cost) can be reduced as compared with the case of manufacturing by the conventional technology.

  Therefore, in the manufacturing method of the sulfonated pulp fiber of this embodiment, the state of the sulfonated pulp fiber is appropriately adjusted according to the demand of the supplier by adjusting the water retention of the manufactured sulfonated pulp fiber. Can be manufactured.

In summary, the use of the method for producing a sulfonated pulp fiber of the present embodiment makes it possible to produce a sulfonated pulp fiber having the effects A) to D) as described above. Can be produced with a high recovery rate (for example, a recovery rate of 70% or more).
And since a high quality sulfonated pulp fiber can be manufactured stably, the sulfonated pulp fiber according to a desired utilization purpose and application can be produced efficiently. Furthermore, the manufacturing cost can also be suppressed.

  Hereinafter, each process of a chemical treatment process is demonstrated more concretely.

(Contact process)
The contact step in the chemical treatment step of the method for producing a sulfonated pulp fiber of this embodiment is a step of bringing a sulfonating agent and urea or / and a derivative thereof into contact with a fiber raw material containing cellulose. This contact step is not particularly limited as long as it is a method capable of causing the contact.
For example, the fiber raw material may be immersed in a reaction liquid in which a sulfonating agent and urea or / and a derivative thereof coexist to impregnate the reaction liquid, or the reaction liquid may be applied to the fiber raw material. The sulfonating agent and urea or / and derivatives thereof may be separately applied to or impregnated into the fiber raw material.
Of these methods, if a method of immersing the fiber raw material in the reaction liquid and impregnating the fiber raw material with the reaction liquid is employed, the sulfonating agent and urea or / and derivatives thereof are uniformly brought into contact with the fiber raw material. This is preferable.

(Reaction mixture ratio)
Moreover, when the method of immersing the fiber raw material in the reaction liquid and impregnating the fiber raw material with the reaction liquid is employed, the mixing ratio of the sulfonating agent and urea or / and its derivative contained in the reaction liquid is not particularly limited.

For example, the sulfonating agent and urea or / and derivatives thereof are 4: 1 (1: 0.25), 2: 1 (1: 0.5), 1: 1, 1 in a concentration ratio (g / L). : It can be adjusted to be 2.5.
For example, if the sulfonating agent and urea are dissolved in pure water and the respective concentrations are adjusted to 200 g / L and 100 g / L, the sulfonating agent: urea is 2 in the concentration ratio (g / L). : 1 reaction solution can be prepared. In other words, if urea is prepared to be 50 parts by weight with respect to 100 parts by weight of sulfamic acid, a reaction solution having a sulfonating agent: urea ratio of 2: 1 can be prepared. Further, if the sulfonating agent and urea are dissolved in pure water and the respective concentrations are adjusted to 200 g / L and 500 g / L, the sulfonating agent: urea is 1 in the concentration ratio (g / L). : 2.5 reaction solution can be prepared.

(Reaction liquid contact amount)
Moreover, the quantity of the reaction liquid contacted with a fiber raw material is not specifically limited.
For example, in the state where the reaction liquid and the fiber raw material are in contact, the sulfonating agent contained in the reaction liquid is 1 part by weight to 20,000 parts by weight with respect to 100 parts by weight of the dry weight of the fiber raw material. Can be prepared such that urea or / and a derivative thereof is 1 to 100,000 parts by weight with respect to 100 parts by weight of the dry weight of the fiber raw material.

  In addition, a water retention degree can be calculated | required with the general test methods (For example, the method based on JAPAN TAPPI paper pulp test method No.26: 2000) as mentioned above.

(Reaction process)
The reaction step in the chemical treatment step of the method for producing the sulfonated pulp fiber of the present embodiment replaces the sulfo group of the sulfonating agent brought into contact with the hydroxyl group of cellulose contained in the fiber raw material, as described above, to the fiber raw material. This is a step of introducing a sulfo group into the contained cellulose.
This reaction step is not particularly limited as long as it is a method capable of sulfonation reaction in which a sulfo group is substituted for a hydroxyl group of cellulose. For example, if a fiber raw material impregnated with the reaction liquid is heated at a predetermined temperature, a sulfo group can be introduced into cellulose contained in the fiber raw material.

(Reaction temperature in the reaction process)
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 and hydrolysis reaction of the fiber. Specifically, any material that can heat the fiber raw material after the contacting step directly or indirectly while satisfying the above requirements may be used. As such a thing, a well-known dryer, a vacuum dryer, a microwave heating apparatus, an autoclave, an infrared heating apparatus etc. are employable. In particular, since a gas may be generated in the reaction process, it is preferable to use a circulation blower type dryer.

  The shape of the fiber raw material after the contacting step is not particularly limited, but for example, heating in the form of a sheet or using the above equipment in a somewhat loosened state is preferable because the reaction can easily proceed uniformly. .

The heating temperature in the reaction step is not particularly limited as long as the above requirements are satisfied.
For example, the atmospheric temperature is preferably 250 ° C. or lower, more preferably the atmospheric temperature is 200 ° C. or lower, and further preferably the atmospheric temperature is 180 ° C. or lower. When the atmospheric temperature at the time of heating is higher than 250 ° C., as described above, thermal decomposition occurs or the progress of discoloration of the fibers is accelerated. On the other hand, when the heating temperature is lower than 100 ° C., the reaction time tends to be longer. 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. Adjust as follows.

(Reaction time in the reaction process)
Moreover, the heating time at the time of employ | adopting the said heating method as a reaction process is not specifically limited. For example, the heating time in the reaction step is adjusted to be 1 minute or longer when the reaction temperature is adjusted to be in the above range. More specifically, it is preferably 5 minutes or more, more preferably 10 minutes or more, and further preferably 20 minutes or more.
When the heating time is shorter than 1 minute, it is assumed that the reaction hardly proceeds. On the other hand, even if the heating time is too long, improvement in the amount of sulfo group introduced tends not to be expected.
Accordingly, the heating time when the above heating method is adopted as the reaction step is not particularly limited, but is preferably 5 minutes or more and 300 minutes or less, more preferably 5 minutes or more and 120 minutes or less from the viewpoint of reaction time or operability. It is good to do.

(Sulfonating agent)
The sulfonating agent in the reaction step is not particularly limited as long as it is a compound having a sulfo group. Examples thereof include sulfamic acid, sulfamate, and a sulfuryl compound having a sulfonyl group having two oxygens covalently bonded to sulfur.
In addition, as a sulfonating agent, these compounds may be used independently and may be used in mixture of 2 or more types.
The sulfonating agent is not particularly limited as long as it is a compound as described above. However, from the viewpoint of handleability, the acidity is low compared to sulfuric acid and the like, the introduction efficiency of sulfo group is high, the cost is low, and the safety is high. It is preferable to employ sulfamic acid.

(Urea and its derivatives)
Of urea and derivatives thereof in the reaction step, the urea derivative is not particularly limited as long as it is a compound containing urea. For example, carboxylic acid amide, a composite compound of isocyanate and amine, thiamide, and the like can be given. Urea and its derivatives may be used alone or in combination. As the urea derivative, the above compounds may be used singly or in combination of two or more.
Urea and its derivatives are not particularly limited as long as they are compounds as described above, but it is preferable to employ urea from the viewpoint of handling because it is low in cost, has little influence on environmental impact, and has high safety.

(Textile raw material)
The fiber raw material used for the manufacturing method of a sulfonated pulp fiber will not be specifically limited if it contains a cellulose.
For example, wood-based pulp (hereinafter simply referred to as “wood pulp”), cotton-based pulp such as dissolving pulp and cotton linter, straw, bagasse, straw, sardine, hemp, kenaf, and non-wood-based fruits such as fruits Pulp such as cellulose isolated from pulp, sea squirts, seaweed, etc., and waste paper pulp produced from waste newspaper, magazine waste paper, cardboard waste paper, etc. can be used as the fiber raw material. In addition, it is preferable to use a wood pulp from a viewpoint of availability.

There are various types of wood pulp, but there are no particular limitations on the use. Examples thereof include papermaking pulp such as coniferous kraft pulp (NBKP), hardwood kraft pulp (LBKP), and thermomechanical pulp (TMP).
In addition, when using the said pulp as a fiber raw material, 1 type of pulp of the kind mentioned above may be used independently, and 2 or more types may be mixed and used.

(Drying process)
The chemical treatment process of the manufacturing method of the sulfonated pulp fiber of this embodiment may include a drying process between the contact process and the reaction process.
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 moisture 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 and heated in a wet state, but some of sulfamic acid, urea and the like may be hydrolyzed. For this reason, 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 material in contact with the reaction solution at a temperature lower than the heating temperature in the reaction step. The apparatus etc. which are used for this drying process are not specifically limited, The dryer etc. which are used by the reaction process mentioned above can be used.

The drying temperature in this drying process is not particularly limited. For example, the heating temperature is preferably an atmospheric temperature of 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., drying takes time.
Accordingly, the atmospheric temperature during heating is preferably 100 ° C. or lower for appropriately performing the above-described reaction, and the atmospheric temperature during heating is preferably 20 ° C. or higher from the viewpoint of operability.

(Washing process)
Moreover, after the reaction process in the chemical treatment process of the manufacturing method of the sulfonated pulp fiber of this embodiment, you may include the washing | cleaning process which wash | cleans the fiber raw material after introduce | transducing a sulfo group.

  The fiber raw material after introducing the sulfo group has an acidic surface due to the influence of the sulfonating agent. Further, unreacted reaction liquid is also present. For this reason, it is desirable that the reaction can be surely completed and the excess reaction solution is removed to a neutral state, so that the handleability can be improved.

This 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, a method of washing with pure water or the like until the fiber raw material after introducing the sulfo group becomes neutral can be employed.

  Further, neutralization washing using an alkali or the like may be performed. In the case of performing such neutralization washing, examples of the alkali compound contained in the alkali solution include an inorganic alkali compound and an organic alkali compound. Examples of the inorganic alkali compound include alkali metal hydroxides, carbonates, and phosphates. Examples of the organic alkali compound include ammonia, aliphatic amine, aromatic amine, aliphatic ammonium, aromatic ammonium, heterocyclic compound, and heterocyclic compound hydroxide.

(Method for producing sulfonated fine cellulose fiber)
As shown in FIG. 1, the sulfonated fine cellulose fiber is supplied by supplying the sulfonated pulp fiber prepared as described above to the refinement treatment step in the method for producing the sulfonated fine cellulose fiber of the present embodiment. can get.

(Miniaturization process)
The refinement treatment step in the method for producing the sulfonated fine cellulose fiber of the present embodiment is a step of making the sulfonated pulp fiber finer into a predetermined size (for example, nano-level) fine fiber.
The processing apparatus used for this refinement | miniaturization process process will not be specifically limited if it has the said function. For example, a low pressure homogenizer, a high pressure homogenizer, a grinder (stone mill type grinder), a ball mill, a cutter mill, a jet mill, a short screw extruder, a twin screw extruder, an ultrasonic stirrer, a household mixer, etc. can be used. The processing apparatus is not limited to these apparatuses.
Of these, it is desirable to use a high-pressure homogenizer in terms of being able to apply force evenly to the material and being excellent in homogenization, but is not limited to such an apparatus.

When a high-pressure homogenizer is used in the refinement treatment step, the sulfonated pulp fiber obtained by the above-described production method is supplied in a state dispersed in a water-soluble solvent such as water. Hereinafter, a solution in which sulfonated pulp fibers are dispersed is referred to as slurry.
The solid content concentration of the sulfonated pulp fiber of this slurry is not particularly limited. For example, the solution adjusted so that the solid content concentration of the sulfonated pulp fiber in the slurry may be 0.1% by mass to 20% by mass may be supplied to a processing apparatus such as a high-pressure homogenizer.

  For example, if a slurry adjusted so that the solid content concentration of the sulfonated pulp fiber is 0.5% by mass is supplied to a processing apparatus such as a high-pressure homogenizer, the sulfonated fine cellulose fiber having the same solid content concentration becomes a water-soluble solvent. A dispersion in a dispersed state can be obtained. That is, in this case, a dispersion liquid adjusted so that the solid content concentration of the sulfonated fine cellulose fiber is 0.5% by mass can be obtained.

Moreover, the water retention of the sulfonated pulp fiber supplied in a refinement | purification process process will not be specifically limited if it is adjusted so that it may be easily refined with the said apparatus.
For example, it is desirable to use a sulfonated pulp fiber prepared so as to increase the water retention level from the viewpoint of reduction in processing efficiency and reduction in energy consumption. From such a viewpoint, it is preferable to adjust the water retention of the sulfonated pulp fiber to be 150% or more. In particular, it is preferable to use one prepared to be higher than 200%, more preferably 220% or more, further preferably 250%, still more preferably 300% or more, and still more preferably. It is preferable to use one prepared so as to be 500%.
However, when the water retention is higher than 10,000%, the recovery rate of the sulfonated pulp fiber after the sulfonation treatment tends to be lowered.
Therefore, from the viewpoint of the refinement efficiency and the recovery rate, the water retention of the sulfonated pulp fiber when supplied to the refinement treatment step is preferably 150% to 10,000%, more preferably 200% to 10%. 1,000%, more preferably 220% to 10,000%, even more preferably 250% to 5,000%, and even more preferably 250% to 2,000%.

  In addition, when the water retention degree of the sulfonated pulp fiber used for a refinement | miniaturization process process is high, the following advantages can also be acquired.

The higher the water retention of the sulfonated pulp fiber that is subjected to the micronization treatment step, the more the fiber expands, so the fiber is more easily loosened. For this reason, as described above, there is an advantage in that the occurrence of problems such as clogging of fibers in the defibrator to be used can be suppressed as well as the efficiency of the defibrator used in the defibrating process is improved. For this reason, since smooth refinement | miniaturization (defibration) can be performed, a higher concentration pulp fiber can be processed with a defibrating machine etc.
In addition, since smooth refinement (defibration) can be performed, the time required for the refinement process can be further shortened. For example, when a defibrator is used, it can be refined with a small number of passes.

  It was confirmed that sulfonated fine cellulose fibers and sulfonated pulp fibers can be produced by using the production method of the present invention.

(Experiment 1)
In Experiment 1, softwood kraft pulp (NBKP) (average fiber length of 2.6 mm) was used as a fiber raw material. Below, NBKP used for experiment is demonstrated only as a pulp.
The pulp was washed with a large amount of pure water, drained with a 200-mesh sieve, measured for solid content, and then subjected to an experiment without drying.

(Chemical treatment process)
The pulp was added to the reaction solution prepared as follows and stirred to form a slurry.
In addition, the process of adding a pulp to a reaction liquid and making it into a slurry form is equivalent to the contact process in the chemical treatment process of the manufacturing method of the sulfonated pulp fiber of this embodiment.

(Preparation of reaction solution)
The sulfonating agent and urea or / and derivatives thereof were prepared to the following concentrations.
In Experiment 1, sulfamic acid (purity 98.5%, manufactured by Fuso Chemical Industries) was used as a sulfonating agent, and urea solution (purity 99%, manufactured by Wako Pure Chemical Industries, model number; special grade reagent) as urea or a derivative thereof. )It was used.
The mixing ratio of the two is 4: 1 (1: 0.25), 2: 1 (1: 0.5), 1: 1, 1: 2.5 in the concentration ratio (g / L). The aqueous solution was prepared by mixing.

Specifically, sulfamic acid and urea were mixed as follows.
Sulfamic acid / urea ratio ((g / L) / (g / L)) = 200/50, 200/100, 200/200, 200/500, 50/25, 100/50, 200/100
An example of the preparation of the reaction solution is shown below.
100 ml of water was added to the container. Next, 20 g of sulfamic acid and 10 g of urea were added to this container to prepare a reaction solution having a sulfamic acid / urea ratio ((g / L) / (g / L)) of 200/100 (1: 0.5). . That is, urea was added to 50 parts by weight with respect to 100 parts by weight of sulfamic acid.

In Experiment 1, 2 g (dry weight) of pulp was added to the prepared reaction solution.
That is, in the case of a reaction solution having a sulfamic acid / urea ratio ((g / L) / (g / L)) of 200/100 (1: 0.5), the amount of sulfamic acid is 1000 with respect to 100 parts by weight of pulp. Part by weight and urea were prepared to be 500 parts by weight.

As Comparative Examples A and A2, a comparative sample (sulfamic acid / urea ratio ((g / L) / (g / L)) = 200/0) in which the reaction solution was sulfamic acid concentration 200 g / L and urea was not added was used. Prepared. The same operation as in the other experimental examples was performed except that urea was not added.
Moreover, NBKP which was not made to contact the reaction liquid was used as a blank pulp.

The slurry prepared by adding pulp to the reaction solution was stirred for 10 minutes using a stirring bar. After stirring, the slurry was suction filtered using a filter paper (No. 2). Suction filtration was performed until no solution dropped.
After suction filtration, the pulp is peeled off from the filter paper, and the filtered pulp is put into a dryer (model number: VTR-115, manufactured by Isuzu Seisakusho) in which the temperature of the thermostatic bath is set to 50 ° C. and dried until the water content becomes an equilibrium state. . That is, the thing dried before the heating reaction was supplied to the next process. In the following, the conditions under which the drying is performed are simply referred to as “conditions for drying process”.
In addition, the process of drying the pulp after this filtration is equivalent to the drying process in the chemical treatment process of the manufacturing method of the sulfonated pulp fiber of this embodiment.

After the water content reached an equilibrium state, a heating reaction was performed.
A drying machine (manufactured by Isuzu Seisakusho, model number: VTR-115) was used for the heating reaction.
The reaction conditions are as follows.
Temperature of constant temperature bath: 100 ° C., 120 ° C., 140 ° C., heating time: 5 minutes, 25 minutes, 60 minutes, 120 minutes Note that this heating reaction is a chemical treatment step of the method for producing sulfonated pulp fibers of this embodiment. This corresponds to the reaction step in.

  After the heating reaction, the reacted pulp was washed with pure water until neutrality to prepare a sulfamic acid / urea treated pulp.

In addition, the process of wash | cleaning the reacted pulp with a pure water until it becomes neutral corresponds to the washing | cleaning process in the chemical treatment process of the manufacturing method of the sulfonated pulp fiber of this embodiment.
Further, the sulfamic acid / urea-treated pulp corresponds to the derivative pulp of this embodiment, and the reactive pulp fiber constituting the sulfamic acid / urea-treated pulp is a sulfonated pulp obtained by the method for producing a sulfonated pulp fiber of this embodiment. Corresponds to fiber.

  In addition, when omitting a drying process, what peeled the pulp from the filter paper after suction filtration was used for the heating reaction as it was. In other words, the drying as described above was not performed before the heating reaction, and was directly supplied to the heating reaction in the next step. The reaction conditions for the heating reaction in the next step were the same as described above. In the following, the condition in which the drying is not performed is simply referred to as “drying process unconditional”.

(Miniaturization process)
A sulfamic acid / urea-treated pulp was nanosized by using a high-pressure homogenizer (manufactured by GEA Niroso-Avi Corp., model number: Panda Plus 200) to prepare nanocellulose.
The processing conditions of the high pressure homogenizer were as follows.
The sulfamic acid / urea-treated pulp was prepared so as to have a solid content concentration of 0.5% by mass and supplied to a high-pressure homogenizer. The pressure was 120 to 140 MPa.
Each sulfamic acid / urea-treated pulp was subjected to 3-pass treatment with a high-pressure homogenizer to obtain nanocellulose fibers.

  Note that the defibrating operation using this high-pressure homogenizer corresponds to the refinement treatment step in the method for producing the sulfonated fine cellulose fiber of the present embodiment. And the obtained nano cellulose fiber is corresponded to the sulfonated fine cellulose fiber obtained with the manufacturing method of the sulfonated fine cellulose fiber of this embodiment.

(Pulp yield)
The yield of pulp before and after chemical treatment was determined from the following formula.
The pulp after chemical treatment was collected using a 300 mesh wire.

Yield = solid weight of pulp recovered after chemical treatment step / solid weight of pulp charged before chemical treatment step

(Elemental analysis (sulfur))
The sulfur content contained in the pulp after chemical treatment was determined by combustion ion chromatography. The measurement method was based on the measurement conditions of IEC 62321.
Combustion device: manufactured by Mitsubishi Chemical Analytech, model number: AQF-2100 H
Ion chromatography: manufactured by Thermo Fisher Science Co., model number: ICS-1600

(Measurement of water retention)
The water retention of the fiber after chemical treatment was measured using TAPPI No. 26.

(Observation of fiber form using FE-SEM)
The surface of the pulp after chemical treatment was observed using FE-SEM (manufactured by JEOL Ltd., model number: JSM-7610). The sample was subjected to observation by substituting the solvent of the fine fiber dispersion with t-butyl alcohol and coating the lyophilized product with osmium.

(Measurement of fiber orientation)
Image analysis of the FE-SEM image of the pulp was performed to evaluate the fiber orientation.
FiberOri8s03 was used as the image analysis software. This software is also used for academic evaluation of fiber orientation on the paper surface.

(Measurement of whiteness)
The whiteness was measured according to JIS P 8148: 2001 paper, paperboard and pulp-ISO whiteness (diffuse blue light reflectance).
As the sample used for the measurement, the pulp after chemical treatment was washed with water and lyophilized.

(Observation of fiber form and measurement of fiber width using SPM)
The sulfonated fine cellulose fibers after the high-pressure homogenizer treatment were prepared with pure water to a solid content concentration of 0.001 to 0.005% by mass, and spin-coated on a silica substrate coated with PEI (polyethyleneimine).
The observation of nano-cellulose on the silica base, a scanning probe microscope (manufactured by Shimadzu Corporation, model number; SPM- 9 700) was performed using.
The fiber width was measured by randomly selecting 20 fibers in the observed image.

(Measurement of haze value and total light transmittance)
For the measurement of the haze value and the measurement of the total light transmittance, sulfonated fine cellulose fibers were prepared with pure water so as to have a solid content concentration of 0.5% by mass to obtain a measurement solution.
In the pulverization treatment step, in the sulfonated fine cellulose fiber obtained by supplying the sulfamic acid / urea-treated pulp prepared so that the solid content concentration becomes 0.5% by mass to the high-pressure homogenizer, it was obtained. Since the concentration of the dispersion liquid in which the sulfonated fine cellulose fibers were dispersed was the same as the solid content concentration before the supply, it was directly subjected to measurement as a measurement solution.
The measurement solution was collected and measured using a spectrophotometer (manufactured by JASCO Corporation, model number: V-570). In addition, the measuring method was performed based on the method of JISK7105.
In addition, the said measurement solution corresponds to the dispersion liquid in the manufacturing method of the sulfonated fine cellulose fiber of this embodiment.

(Measurement of degree of polymerization)
According to JIS P 8215 (1998), the intrinsic viscosity of the sulfonated fine cellulose fiber was measured. Thereafter, the degree of polymerization (DP) of the sulfonated fine cellulose fiber was calculated from the intrinsic viscosity (η) by the following formula. This degree of polymerization is sometimes referred to as “viscosity average degree of polymerization” because it is an average degree of polymerization measured by the viscosity method.

DP = 1.75 × [η]

(Experimental result)

(Experimental results of sulfamic acid / urea treated pulp)
2 and 3 are characteristic tables of sulfamic acid / urea-treated pulp fibers.
FIG. 2 is a characteristic table of sulfamic acid / urea-treated pulp fibers under the condition of drying before heating reaction (conditions with a drying step).
FIG. 3 is a characteristic table of sulfamic acid / urea-treated pulp fibers under conditions where drying was not performed before the heating reaction (unconditional drying process).
4 to 8 specifically show the characteristics of sulfamic acid / urea-treated pulp fibers.
FIG. 4 shows the amount of sulfur introduced (mmol / g) and water retention (%) of the sulfamic acid / urea-treated pulp fiber obtained under the conditions of the drying process and the sulfamic acid / urea ratio ((g / L) of the reaction solution) It is the figure which showed the relationship with / (g / L)).
FIG. 5 shows the water retention (%) of the sulfamic acid / urea-treated pulp fiber obtained without the drying step and the sulfamic acid / urea ratio ((g / L) / (g / L)) of the reaction solution. It is the figure which showed the relationship.
FIG. 6A shows the pulp fiber length (mm) of the sulfamic acid / urea-treated pulp fiber obtained under the drying process conditions and the sulfamic acid / urea ratio ((g / L) / (g / L) of the reaction solution. 6 (B) shows the fiber length maintenance rate (%) before and after chemical treatment of the sulfamic acid / urea-treated pulp fiber obtained under the drying process conditions and the reaction solution. It is the figure which showed the relationship with sulfamic acid / urea ratio ((g / L) / (g / L)).
FIG. 7 is a graph showing the relationship between the amount of sulfur introduced (mmol / g) and reaction temperature of sulfamic acid / urea-treated pulp fiber obtained under conditions with a drying process.
FIG. 8 (A) is a diagram showing the relationship between the fiber length (mm), reaction temperature, and treatment time of sulfamic acid / urea-treated pulp fibers obtained under the drying process conditions, and FIG. It is the figure which showed the relationship between the fiber length maintenance factor (%) before and behind the chemical treatment of the sulfamic acid / urea-treated pulp fiber obtained on the conditions with a drying process, reaction temperature, and processing time.

From the experimental results, by adjusting the mixing ratio of urea in the concentration ratio of sulfamic acid and urea, the amount of sulfur introduced into the sulfamic acid / urea-treated pulp fiber (see, for example, FIG. 4) is 0.56 mmol / g to 0.97 mmol. It was confirmed that it was possible to adjust to / g.
Moreover, as shown in FIG. 4 or FIG. 5, by adjusting the mixing ratio of urea in the concentration ratio of sulfamic acid and urea, the water retention of sulfamic acid / urea-treated pulp fiber is in the range of 250% to 4600%. It was confirmed that adjustment was possible.
That is, it was confirmed that by adjusting the concentration ratio of sulfamic acid and urea, the amount of sulfur introduced and the water retention of the sulfamic acid / urea-treated pulp fiber can be controlled.

  As shown in FIGS. 4 and 5, the sulfur introduction amount and water retention of the sulfamic acid / urea-treated pulp fiber tend to be similar, and therefore there is some relationship between the two. Inferred.

  As shown in FIG. 6, it was confirmed that the fiber length of the sulfamic acid / urea-treated pulp fiber can be increased as compared with Comparative Example A in which urea was not mixed. In other words, it was confirmed that the shortening of fibers by sulfamic acid can be prevented by mixing urea. Moreover, it was confirmed that the fiber length of the sulfamic acid / urea-treated pulp fiber can be maintained at substantially the same length as before the reaction.

As shown in FIGS. 7 and 8, it was confirmed that the amount of sulfur introduced and the fiber length could be controlled by adjusting the heating temperature and the heating time.
As shown in FIG. 7, in order to make the sulfur introduction amount of the sulfamic acid / urea-treated pulp fiber 0.5 mmol / g or more, it may be 15 minutes or more under the condition of 120 ° C. or 140 ° C. However, it was confirmed that the temperature should be 35 minutes or longer under the low temperature condition of 100 ° C.
Moreover, as shown in FIG. 8, in order to lengthen the fiber length of a sulfamic acid / urea processing pulp fiber, it has confirmed that the thing of the conditions with low temperature is preferable.

FIG. 9 is an enlarged photograph of the surface of sulfamic acid / urea-treated pulp fiber (with drying process, reaction condition: temperature 120 ° C., time 25 minutes).
9A to 9D show that the sulfamic acid / urea ratio is 200/50 (1: 0.25), 200/100 (1: 0.5), 200/200 (1: 1), 200, respectively. It is a surface enlarged photograph of / 500 (1: 2.5).
FIG. 9E is an enlarged surface photograph of NBKP shown as a comparative example.

The sulfur introduction amounts of the sulfamic acid / urea-treated pulp fibers in FIGS. 9A to 9D are (A) 0.56 mmol / g, (B) 0.84 mmol / g, and (C) 0.97 mmol / g, respectively. (D) 0.65 mmol / g.
The water retention of the sulfamic acid / urea treated pulp fibers of FIGS. 9A to 9D was (A) 980%, (B) 1920%, (C) 1120%, and (D) 250%, respectively.

FIG. 10 is a diagram showing the degree of orientation of the surface fibers of the sulfamic acid / urea-treated pulp fiber, and FIG. 11 shows the sulfamic acid / urea-treated pulp fiber (with drying process, reaction condition: temperature 120 ° C., time 25 minutes). It is a surface enlarged photograph.
11 (A) to 11 (D) show that the sulfamic acid / urea ratio is 200/50 (1: 0.25), 200/100 (1: 0.5), 200/200 (1: 1), 200, respectively. It is a surface enlarged photograph of / 500 (1: 2.5).
FIG. 11E is an enlarged photograph of the surface of NBKP shown as a comparative example.
The orientation degrees of the sulfamic acid / urea treated pulp fibers of FIGS. 11 (A) to (D) are (A) 1.18, (B) 1.04, (C) 1.10, and (D) 1.30, respectively. Met.

  In this measurement method, an orientation degree (orientation strength) of 1.1 or less is non-oriented, 1.1 to 1.2 is slightly oriented, and 1.2 or more is judged to be strongly oriented. ing.

  From this experimental result, the orientation ratio of the fibers on the surface of the sulfamic acid / urea-treated pulp fiber can be made random by reducing the mixing ratio of urea in the reaction solution in the concentration ratio of sulfamic acid and urea. Was confirmed. On the contrary, it was confirmed that when the mixing ratio of urea was increased, the fiber orientation on the surface of the sulfamic acid / urea-treated pulp fiber could be made uniform. That is, it was confirmed that the fiber orientation on the surface of the sulfamic acid / urea-treated pulp fiber can be controlled by adjusting the concentration ratio of sulfamic acid and urea.

  Further, from this experimental result, it was confirmed that the degree of orientation of the surface fibers of the sulfamic acid / urea-treated pulp fiber can be used as an index indicating the degree of fibrillation of the sulfamic acid / urea-treated pulp fiber. And since it was confirmed that the orientation degree and the water retention degree show the same tendency (for example, see FIG. 4 and FIG. 10), the fibrillation of the sulfamic acid / urea treated pulp fiber can be achieved by adjusting the water retention degree. It was confirmed that it can be controlled.

FIG. 12 is a diagram confirming the ease of defibration treatment of sulfamic acid / urea-treated pulp fibers.
It was confirmed that the sulfamic acid / urea-treated pulp fiber could have an average fiber width of 20 nm or less after 3 times of defibration (3 passes).
On the other hand, fine fibers not subjected to chemical treatment (that is, NBKP of blank pulp) have an average fiber width of 30 nm to 50 nm even when defibrated 20 times (20 passes), and the average fiber width is set to 20 nm or less. could not.

  In addition, the photograph of FIG. 12 shows the measurement condition of the fiber width in an observation image, observing the fine fiber after defibration with FE-SEM. An enlarged photo of 50,000 times was used for the measurement of the fiber width. As a method of measuring the fiber width in the image (for example, the fiber width indicated by the white arrow in FIG. 12), two diagonal lines are drawn on the observation image, and two straight lines passing through the intersection of the diagonal lines are arbitrarily drawn. The width of the fiber intersecting with these straight lines was measured visually. The average fiber width was determined from the average value of 50 fibers.

FIG. 13 is a graph showing the whiteness of sulfamic acid / urea-treated pulp fibers.
It was confirmed that the coloration of the fiber by sulfamic acid can be suppressed by mixing urea with the reaction solution.
It was also confirmed that the whiteness of the sulfamic acid / urea-treated pulp fiber can be controlled by adjusting the mixing ratio of urea in the concentration ratio of sulfamic acid and urea.

(Experimental results of nanocellulose fibers)
14 and 15 are characteristic tables of nanocellulose fibers.
FIG. 14 is a characteristic table of nanocellulose fibers obtained under the condition of drying (conditions for drying process).
FIG. 15 is a characteristic table of nanocellulose fibers obtained under the condition where drying was not performed (the drying process was unconditional).
16 to 18 specifically show the characteristics of nanocellulose.
FIG. 16 shows the total light transmittance (%) and haze value (%) of the nanocellulose fiber obtained under the drying process conditions and the sulfamic acid / urea ratio ((g / L) / (g / L) of the reaction solution. It is the figure which showed the relationship with)).
FIG. 17 shows the total light transmittance (%) and haze value (%) of the nanocellulose fiber obtained without any drying process and the sulfamic acid / urea ratio ((g / L) / (g / L) of the reaction solution. It is the figure which showed the relationship with)).
FIG. 18 shows the degree of polymerization of nanocellulose fibers obtained under the drying process conditions (that is, equivalent to the average fiber length of nanocellulose fibers) and the sulfamic acid / urea ratio ((g / L) / ( It is the figure which showed the relationship with g / L)).

  In addition, as Comparative Example B and Comparative Example C, the reaction solution was set to a sulfamic acid concentration of 200 g / L, and a comparative sample without adding urea (sulfamic acid / urea ratio ((g / L) / (g / L)) = 200/0. ) Was prepared. The same operation as in the other experimental examples was performed except that urea was not added.

As shown in FIG. 14, it was confirmed that the average fiber width of the nanocellulose fibers can be adjusted to 20 nm or less.
In addition, as shown in FIGS. 14, 15, 16, and 17, when prepared so that the solid content concentration of the nanocellulose fiber of the measurement solution (that is, the dispersion) was 0.5% by mass, It was confirmed that a nanocellulose fiber having a light transmittance (%) of 90% or more and a haze value (%) of 15% or less can be prepared.
That is, it was confirmed that nanocellulose fibers having improved dispersibility in the dispersion and having very high transparency can be prepared.

  In addition, in the commercially available resin film in which transparency is required, the total light transmittance (%) of the film made of methacryl having high transparency is about 90%, and the haze value of the polyethylene film which is a general-purpose resin Since (%) is about 20%, it was confirmed that the nanocellulose fibers obtained in the experiment had the same or higher quality as the conventional commercial products.

As shown in FIG. 18, it was confirmed that the nanocellulose fibers can be prepared to have a polymerization degree of 386 to 478. It was confirmed that this value can be increased as compared with the nanocellulose fiber (Comparative Example B) obtained under the condition of only sulfamic acid. That is, it was confirmed that the polymerization degree (that is, fiber length) of the nanocellulose fiber can be improved by mixing urea in the reaction solution. In other words, it was confirmed that nanocellulose fibers that are easily entangled between fibers can be prepared.
It was confirmed that nanocellulose fibers having a fiber length of about 200 nm could be prepared when the degree of polymerization was 400 and the length of one glucose molecule in the axial direction was about 5 mm (about 0.5 nm).

FIG. 19 is a diagram showing experimental results when a compound similar to sulfamic acid is used as a reaction solution.
In the experiment, sulfate (ammonium hydrogen sulfate) was used as a compound similar to sulfamic acid. As an experimental method, the same method was used except that ammonium hydrogen sulfate was used instead of sulfamic acid.
As shown in FIG. 19, the sulfate (ammonium hydrogen sulfate) / urea-based pulp fiber could not be defibrated when the number of defibration was three times (three passes).
From these experimental results, urea does not exhibit or does not exhibit the same function (for example, function as a catalyst) as the sulfamic acid / urea system in sulfonation using sulfate (ammonium hydrogen sulfate). It was confirmed that it was not functioning sufficiently.
Therefore, in the sulfamic acid / urea system, the efficiency of refinement can be improved and the degree of sulfonation can be improved as compared to sulfonation using sulfate (ammonium hydrogen sulfate). Was confirmed.

(Experiment 2)
In Experiment 2, it was confirmed that defibration can be facilitated by adjusting the water retention of the sulfamic acid / urea-treated pulp.

In Experiment 2, a slurry prepared by adjusting the sulfamic acid / urea-treated pulp obtained in Experiment 1 to a solid content concentration of 0.2% by mass was supplied to a high-pressure homogenizer, and the resulting nanocellulose fiber dispersion was obtained. The easiness of defibration was evaluated based on the fiber residual ratio contained in the.
Further, the total light transmittance (%) and haze value (%) at the solid content concentration were also confirmed.
Using a high-pressure homogenizer (manufactured by Kos Nijuichi Co., Ltd., model number: N2000-2C-045 type), pre-defibration was performed twice at a treatment pressure of 10 MPa and once at 50 MPa. This preliminary defibrating was defibrated. In the defibrating treatment, the treatment pressure was set to 60 MPa, which is about half of Experiment 1.
The apparatus used in Experiment 1 was used as the apparatus other than the high-pressure homogenizer.
In the measurement method of Experiment 2, the description overlapping with Experiment 1 is omitted.

(Fiber remaining rate (%))
The proportion of undefibrated fibers contained in the dispersion of nanocellulose fibers obtained after defibrating with a high-pressure homogenizer was calculated by the following method.
The fiber residual ratio (%) of undefibrated fibers was calculated based on measured fibers in a solid content of 0.05 g before and after defibrating treatment.
The apparatus used is a fiber tester (manufactured by Lorenzen & Bettley Co., Ltd.).

First, fibers that can be measured in a solid content of 0.05 g from a slurry in which the sulfamic acid / urea-treated pulp before defibration treatment is prepared to have a solid content concentration of 0.2% by mass using the above-described apparatus. Measured how many are present.
Next, using the above apparatus, the number of measurable fibers in a solid content of 0.05 g was measured from the dispersion of nanocellulose fibers after defibration treatment.
And fiber residual ratio (%) = (measured value after defibrating treatment / measured value before defibrating treatment) × 100 was obtained.

(Experimental result)
FIG. 20 is a graph showing the relationship between the water retention (%) of the sulfamic acid / urea-treated pulp, the fiber residual ratio (%), and the number of passes of the high-pressure homogenizer.
When the fiber residual ratio (%) was 10% or less, the fibers contained in the dispersion could not be confirmed by visual observation.

  As shown in FIG. 20, it was confirmed that the higher the water retention (%) of the sulfamic acid / urea-treated pulp, the lower the fiber residual ratio (%). Then, it was confirmed that nanocellulose fibers having high transparency can be prepared in one pass under a treatment pressure of 60 MPa with sulfamic acid / urea treated pulp having a water retention (%) of 980%, 1120% and 1920%. Moreover, it was confirmed that nanocellulose fibers having high transparency can be prepared by two passes even in the case of sulfamic acid / urea-treated pulp having a water retention (%) of 250%.

Further, as shown in FIG. 21, if the water retention (%) of the sulfamic acid / urea-treated pulp is higher than that of Comparative Example D, the nanocellulose fiber having a high total light transmittance (%) in one pass. It was confirmed that can be prepared.
Furthermore, as shown in FIG. 22, it was confirmed that nanocellulose fibers having a haze value (%) of 15% or less can be prepared by two passes. In particular, when the water retention (%) of the sulfamic acid / urea-treated pulp was 1000% or more, it was confirmed that nanocellulose fibers having a haze value (%) of 5% or less could be prepared in one pass.

In Comparative Example D, the dispersion obtained after the defibrating treatment was cloudy with a large amount of precipitates. And as shown in FIGS. 21 and 22, the haze value (%) of Comparative Example D was almost 100%, and the total light transmittance (%) was 40% or less. It was confirmed that the defibration cannot properly defibrate Comparative Example D.
In addition, when defibration was performed by increasing the number of passes, Comparative Example D did not provide a sufficient defibration result.

From the experimental results of Experiment 2, by adopting a manufacturing method in which urea is mixed into the reaction solution, sulfamic acid / urea treatment can be easily performed even at a defibration pressure that was not assumed in the prior art. It was confirmed that the pulp could be prepared.
Moreover, the water retention (%) of the sulfamic acid / urea-treated pulp is made higher than 180% of the comparative example, and the sulfur introduction amount of the sulfamic acid / urea-treated pulp is made higher than 0.42 mmol / g of the comparative example. It was confirmed that nanocellulose fibers having high transparency can be easily prepared (manufactured).
In particular, if the water retention (%) of the sulfamic acid / urea-treated pulp is adjusted to be 1000% or more, nano particles having a haze value (%) of 5% or less can be easily obtained in one pass under a defibration pressure of 60 MPa. It was confirmed that cellulose fibers could be prepared.

(Effects of solid content of sulfamic acid / urea-treated pulp and resulting nanocellulose fibers)
FIG. 23 and FIG. 24 confirm the influence of the solid content concentration of the sulfamic acid / urea-treated pulp in the slurry supplied to the high-pressure homogenizer and the resulting nanocellulose fibers.
In this experiment, the above-described manufacturing method (with a drying step, using a reaction solution having a sulfamic acid / urea ratio ((g / L) / (g / L)) of 200/100 (1: 0.5)) described above. Slurry prepared with sulfamic acid / urea-treated pulp prepared under reaction conditions: temperature 120 ° C., time 25 minutes, water retention level 1920%) so that the solid content concentrations are 0.5 mass% and 0.2 mass%, respectively. Was fed to a high pressure homogenizer. And the quality of the obtained nano cellulose fiber was evaluated by total light transmittance (%), haze value (%), and the number of undefibrated fibers after defibration.

  The number of undefibrated fibers is determined by measuring the undefibrated fibers in 0.05 g of solid content after defibrating treatment with a fiber tester (manufactured by Lorenzen & Bettley Co., Ltd.). The number of measurable fibers was measured.

(Experimental result)
As shown in the experimental results of FIGS. 23 and 24, the total light transmittance (%) is about 100% and the haze value (%) is 5 in both the 1-pass treatment and the 2-pass treatment during defibration. % And below. Further, in the number of undefibrated fibers, all were 30 or less in one pass treatment, and a large difference could not be confirmed.
Therefore, the solid content concentration of the sulfamic acid / urea-treated pulp in the slurry supplied to the high-pressure homogenizer does not affect the ease of defibration within the range of 0.2% by mass to 0.5% by mass. I was able to confirm. And also in the obtained nano cellulose fiber, it has confirmed that the quality was not affected.

The production method of the sulfonated pulp fiber and the production method of the sulfonated fine cellulose fiber of the present invention can be suitably used for many applications in various fields such as the industrial field, food field, medical field, cosmetic field, It is suitable as a method for producing a composite material used in these fields.

Claims (6)

A method for producing a pulp fiber in which a part of hydroxyl groups of cellulose is sulfonated from pulp,
A chemical treatment step for chemically treating the pulp,
The chemical treatment step is
Contacting with a reaction solution in which sulfamic acid having a sulfo group and urea are dissolved in water with respect to pulp fibers constituting the pulp; and
Pulp in a wet state after the contacting step is fed to the reaction step, performed in said reaction step, and as engineering you introduce a sulfo group in a part of the hydroxyl groups of the cellulose constituting the pulp fibers, the order
The reaction step includes
It is a step of heating the pulp fiber in a state where the reaction liquid after the contact step is in contact to advance the reaction,
A method for producing a sulfonated pulp fiber, wherein the reaction temperature is adjusted to 100C to 180C and the reaction time is adjusted to 5 minutes or more . The reaction solution is
The method for producing a sulfonated pulp fiber according to claim 1, wherein sulfamic acid and urea are contained so as to have a concentration (g / L) ratio of 4: 1 to 1: 2.5. The method for producing a sulfonated pulp fiber according to claim 1 or 2, wherein the pulp supplied to the reaction step contains moisture . The method for producing a sulfonated pulp fiber according to claim 1, 2 or 3, further comprising a washing step for washing the pulp after the reaction step after the reaction step. A method for producing fine cellulose fibers in which a part of hydroxyl groups of cellulose is sulfonated from pulp,
A chemical treatment step for chemically treating the pulp, and a refinement treatment step for refining the pulp after the chemical treatment step, in order,
The pulp after the said chemical treatment process contains the sulfonated pulp fiber manufactured with the manufacturing method in any one of Claims 1-4 ,
In the miniaturization process,
The method for producing a sulfonated fine cellulose fiber, wherein the sulfonated pulp fiber has a water retention value of 250% or more . In the miniaturization process,
The sulfone according to claim 5, wherein the sulfonated pulp fiber is refined in a state in which the sulfonated pulp fiber is dispersed in a water-soluble solvent so as to have a solid content concentration of 0.1% by mass to 20% by mass. For producing modified fine cellulose fiber.