JP2010236109A - Process for producing cellulose nanofibers - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a process for efficiently producing, with low energy, a high-concentration cellulose nanofiber dispersion having excellent flowability and transparency. <P>SOLUTION: A cellulosic raw material is oxidized with an oxidant in water in the presence of (1) an N-oxyl compound and (2) a bromide, an iodide, or a mixture thereof to prepare an oxidized cellulosic raw material, and the oxidized material is subjected to a treatment with ultraviolet light and then to a fibrillation/dispersion treatment. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method capable of producing a cellulose nanofiber dispersion liquid having a lower energy and higher concentration than conventional from a cellulose-based raw material oxidized with an N-oxyl compound.

  Cellulose-based raw materials in the presence of a catalytic amount of 2,2,6,6-tetramethyl-1-piperidine-N-oxy radical (hereinafter referred to as TEMPO) and sodium hypochlorite which is an inexpensive oxidizing agent. When treated, it is possible to efficiently introduce carboxyl groups on the surface of cellulose microfibrils. Cellulosic raw materials into which these carboxyl groups have been introduced are highly viscous and transparent by performing simple mechanical processing such as with a mixer in water. It is known that it can be prepared into an aqueous cellulose nanofiber dispersion (Non-Patent Document 1).

  Cellulose nanofibers are a novel biodegradable water-dispersed material. Since the carboxyl group is introduced into the surface of the cellulose nanofiber by an oxidation reaction, the cellulose nanofiber can be freely modified with the carboxyl group as a base point. In addition, since the cellulose nanofibers obtained by the above method are in the form of a dispersion, the quality can be modified by blending with various water-soluble polymers or by combining with organic / inorganic pigments. it can. Furthermore, cellulose nanofibers can be made into sheets or fibers. Taking advantage of these characteristics of cellulose nanofibers, it is envisaged to be applied to highly functional packaging materials, transparent organic base members, high performance fibers, separation membranes, regenerative medical materials, and the like. In the future, it is expected to develop new high-functional products that are essential for the formation of a recycling-type safety and security society by making the best use of the characteristics of cellulose nanofibers.

Saito, T., et al., Cellulose Commun., 14 (2), 62 (2007)

  However, the cellulose nanofiber dispersion obtained by oxidizing the cellulose raw material using TEMPO and defibrating with a mixer is 0.3 to 0.5% (w / v). Even at low concentrations, the B-type viscosity (60 rpm, 20 ° C.) has a very high viscosity, such as about 800 to 4000 mPa · s, is not easy to handle, and its application range is actually limited. It was. For example, when a cellulose nanofiber dispersion is applied to a substrate to form a film on the substrate, the dispersion cannot be uniformly applied if the viscosity of the dispersion is too high, so the B-type viscosity of the dispersion (60 rpm, 20 ° C.) must be adjusted to about 500 to 3000 mPa · s, and for that purpose, the concentration of cellulose nanofibers in the dispersion is reduced to a low concentration of about 0.2 to 0.4% (w / v). I had to set it. However, when such a low-concentration dispersion is used, there is a problem that the application and drying must be repeated many times until the desired film thickness is achieved, resulting in poor efficiency.

  In addition, when the cellulose nanofiber dispersion is mixed with a paint containing a pigment and a binder and applied to paper or the like, the dispersion cannot be uniformly mixed if the viscosity of the dispersion is too high. However, if such a low-concentration dispersion liquid is used, the concentration of the paint becomes dilute, making it difficult to apply the sufficient viscosity necessary for application and increasing the drying load. In addition, there is also a problem that the desired function expected for the coating film such as gloss development, surface strength, and suppression of printing unevenness does not appear because the effective coating film becomes thin by the penetration of the paint into the base paper. .

  Thus, in the conventional method in which the cellulose-based raw material obtained by oxidation using TEMPO is defibrated using a mixer, the viscosity of the obtained dispersion becomes very high, causing various problems. . Further, if the viscosity is too high, the dispersion proceeds only around the stirring blades, resulting in non-uniform dispersion, resulting in a dispersion with low transparency.

  Also, if the oxidized cellulose raw material is defibrated using a homogenizer with higher defibrating / dispersing power than the mixer, the cellulosic raw material will thicken significantly in the initial stage of dispersion, resulting in poor fluidity and dispersion treatment. There is a problem that the amount of power consumption required sometimes increases significantly, the cellulose nanofiber dispersion liquid adheres to the inside of the apparatus and the dispersion is not sufficiently performed, and operations such as taking out the dispersion liquid from the apparatus are performed. There is also a problem that the yield of the dispersion is lowered due to difficulty.

  In view of the above problems, an object of the present invention is to provide a method capable of efficiently producing a high-concentration cellulose nanofiber dispersion excellent in fluidity and transparency with low energy.

  As a result of intensive studies to solve the problems of the prior art, the present inventors have used an oxidizing agent in the presence of (1) N-oxyl compound, and (2) bromide, iodide or a mixture thereof. By oxidizing the cellulosic raw material in water to prepare an oxidized cellulosic raw material, and exposing the oxidized cellulosic raw material to ultraviolet rays before being subjected to defibration / dispersion treatment, 1 to 3% ( It has been found that a cellulose nanofiber dispersion excellent in fluidity and transparency can be efficiently produced even at a high concentration of about w / v), and the present invention has been completed.

  According to the present invention, after oxidizing the cellulosic raw material in the presence of the N-oxyl compound and bromide, iodide, or a mixture thereof, and irradiating the resulting oxidized cellulosic raw material with ultraviolet rays, By defibration / dispersion treatment, it is possible to efficiently produce a dispersion of cellulose nanofiber that is excellent in fluidity and easy to handle even at high concentrations and with excellent transparency. can do. The cellulose nanofiber dispersion obtained by the present invention is excellent in fluidity even at a high concentration.For example, when a cellulose nanofiber is applied to a substrate to form a film on the substrate, A paint containing cellulose nanofibers at a high concentration of 1 to 3% (w / v) can be prepared at a low viscosity of 500 to 3000 mPa · s (B-type viscosity, 60 rpm, 20 ° C.). There is an advantage that a film having a thickness of about 5 to 30 μm can be formed only by coating. Conventionally, in order to prepare a paint having a viscosity of about 500 to 3000 mPa · s (B-type viscosity, 60 rpm, 20 ° C.), the concentration of cellulose nanofiber is 0.2 to 0.4% (w / v). In order to produce a film having a thickness of about 5 to 30 μm, it has been necessary to repeat coating and drying many times. The feature of the cellulose nanofiber dispersion obtained by the present invention having a high fluidity at a high concentration is very excellent.

  In the present invention, a cellulose raw material oxidized by oxidizing a cellulosic raw material in water using an oxidizing agent in the presence of (1) an N-oxyl compound and (2) bromide, iodide or a mixture thereof. Prepare and subject to ultraviolet irradiation before defibration / dispersion treatment. By subjecting oxidized cellulose materials to ultraviolet irradiation before defibration / dispersion treatment, power consumption in defibration / dispersion treatment can be reduced, and cellulose nanofibers can be produced efficiently with low energy. Can do.

(N-oxyl compound)
As the N-oxyl compound used in the present invention, any compound can be used as long as it promotes the target oxidation reaction. For example, the N-oxyl compound used in the present invention includes a substance represented by the following general formula (Formula 1).

(In Formula 1, R ^{1 to} R ⁴ represent the same or different alkyl groups having about 1 to 4 carbon atoms.)
Among the compounds represented by Formula 1, 2,2,6,6-tetramethyl-1-piperidine-oxy radical (hereinafter referred to as TEMPO) and 4-hydroxy-2,2,6,6-tetramethyl-1 A compound that generates a piperidine-oxy radical (hereinafter referred to as 4-hydroxy TEMPO) is preferable. In addition, the radical of the N-oxyl compound represented by any one of the following formulas 2 to 4, that is, the hydroxyl group of 4-hydroxy TEMPO is etherified with alcohol, or esterified with carboxylic acid or sulfonic acid, and has an appropriate hydrophobicity. The imparted 4-hydroxy TEMPO derivative is particularly preferable because it is inexpensive and can provide uniform oxidized cellulose.

(In formulas 2 to 4, R is a linear or branched carbon chain having 4 or less carbon atoms.)
Furthermore, the radical of the N-oxyl compound represented by the following formula 5, that is, an azaadamantane type nitroxy radical, is particularly preferable because it can produce uniform cellulose nanofibers in a short time.

(In Formula 5, R ⁵ and R ⁶ represent the same or different hydrogen or a C _{1 to} C ₆ linear or branched alkyl group.)
The amount of the N-oxyl compound used is not particularly limited as long as it is a catalyst amount that can make the cellulose-based raw material into nanofibers. For example, about 0.01 to 10 mmol, preferably 0.01 to 1 mmol, and more preferably about 0.05 to 0.5 mmol can be used with respect to 1 g of the cellulosic raw material.

(Bromide or iodide)
As the bromide or iodide used in oxidizing the cellulosic raw material, a compound that can be dissociated and ionized in water, such as an alkali metal bromide or an alkali metal iodide, can be used. The amount of bromide or iodide used can be selected as long as the oxidation reaction can be promoted. For example, 0.1 to 100 mmol, preferably 0.1 to 10 mmol, and more preferably about 0.5 to 5 mmol can be used for 1 g of cellulosic raw material.

(Oxidant)
As the oxidizing agent used for oxidizing the cellulosic raw material, the target oxidation reaction such as halogen, hypohalous acid, halous acid, perhalogen acid or salts thereof, halogen oxide, peroxide can be promoted. Any oxidizing agent can be used as long as it is an oxidizing agent. Among these, from the viewpoint of nanofiber production costs, sodium hypochlorite, which is currently most widely used in industrial processes and has low environmental impact, is particularly suitable. The amount of the oxidizing agent used can be selected within a range that can promote the oxidation reaction. For example, 0.5 to 500 mmol, preferably 0.5 to 50 mmol, and more preferably about 2.5 to 25 mmol can be used for 1 g of cellulosic raw material.

(Cellulosic material)
The cellulose-based raw material used in the present invention is not particularly limited, and kraft pulp or sulfite pulp derived from various woods, powdered cellulose obtained by pulverizing them with a high-pressure homogenizer or a mill, or chemical treatment such as acid hydrolysis. In addition to the microcrystalline cellulose powder purified by the above, plants such as kenaf, hemp, rice, bacus, and bamboo can also be used. Of these, bleached kraft pulp, bleached sulfite pulp, powdered cellulose, or microcrystalline cellulose powder is preferably used from the viewpoint of mass production and cost. In addition, it is particularly preferable to use powdered cellulose and microcrystalline cellulose powder because a cellulose nanofiber dispersion having a lower viscosity can be produced even at a high concentration.

Powdered cellulose is a rod-like particle made of microcrystalline cellulose obtained by removing a non-crystalline part of wood pulp by acid hydrolysis and then pulverizing and sieving. The degree of polymerization of cellulose in powdered cellulose is about 100 to 500, the degree of crystallinity of powdered cellulose by X-ray diffractometry is 70 to 90%, and the volume average particle size by a laser diffraction particle size distribution analyzer is preferably 100 μm. Or less, more preferably 50 μm or less. When the volume average particle diameter is 100 μm or less, a cellulose nanofiber dispersion excellent in fluidity can be obtained. As the powdered cellulose used in the present invention, for example, a fixed particle size in the form of a rod shaft produced by a method of purifying and drying an undegraded residue obtained after acid hydrolysis of a selected pulp, pulverizing and sieving. it may be a crystalline cellulose powder having a distribution, (manufactured by Nippon Paper Chemicals Co.) KC flock ^R, Ceolus ^TM (manufactured by Asahi Kasei Chemicals Corporation), a commercially available product may be used, such as Avicel ^R (FMC Corp.) .

(Oxidation reaction conditions)
The method of the present invention is characterized in that the oxidation reaction can proceed smoothly even under mild conditions. Therefore, the reaction temperature may be a room temperature of about 15 to 30 ° C. In addition, since a carboxyl group produces | generates in a cellulose with progress of reaction, the fall of pH of a reaction liquid is recognized. In order to advance the oxidation reaction efficiently, it is desirable to maintain the pH of the reaction solution at about 9 to 12, preferably about 10 to 11, by adding an alkaline solution such as an aqueous sodium hydroxide solution. The reaction time in the oxidation reaction can be appropriately set and is not particularly limited, but is, for example, about 0.5 to 4 hours.

(UV irradiation)
In the present invention, the oxidized cellulosic material is irradiated with ultraviolet rays. The wavelength of the ultraviolet rays is preferably 100 to 400 nm, more preferably 100 to 300 nm. Among these, ultraviolet rays having a wavelength of 135 to 260 nm are particularly preferable because they can directly act on cellulose and hemicellulose to cause low molecular weight and shorten the fiber.

(light source)
As a light source for irradiating ultraviolet rays, a light source having a wavelength of 100 to 400 nm can be used. Specifically, a xenon short arc lamp, an ultrahigh pressure mercury lamp, a high pressure mercury lamp, a low pressure mercury lamp, a deuterium lamp, A metal halide lamp etc. are mentioned as an example, These 1 type (s) or 2 or more types can be used in arbitrary combinations. In particular, it is preferable to use a combination of a plurality of light sources having different wavelength characteristics, because ultraviolet rays having different wavelengths are simultaneously irradiated to increase the number of cut sites in the cellulose chain and hemicellulose chain, thereby promoting shortening of the fiber.

(container)
In the present invention, as a container for storing the oxidized cellulosic material at the time of ultraviolet irradiation, for example, when ultraviolet rays having a wavelength longer than 300 nm are used, those made of hard glass can be used. When using short-wavelength ultraviolet light, it is better to use quartz glass that transmits ultraviolet light more. In addition, about the material of the part which does not participate in the light transmission reaction of a container, a suitable thing can be selected from the materials with little deterioration with respect to the wavelength of the ultraviolet-ray used.

(UV irradiation conditions)
In the present invention, the concentration of the oxidized cellulose-based raw material when irradiated with ultraviolet rays is preferably 0.1% by mass or more because energy efficiency is increased, and if it is 12% by mass or less, it is preferably within the ultraviolet irradiation apparatus. It is preferable because the flowability of the cellulosic material is good and the reaction efficiency is increased. Therefore, the range of 0.1-12 mass% is preferable. More preferably, it is 0.5-5 mass%, More preferably, it is 1-3 mass%.

  The temperature of the cellulosic raw material when irradiated with ultraviolet rays is preferably 20 ° C. or higher because the efficiency of the photooxidation reaction is increased. On the other hand, if it is 95 ° C. or lower, adverse effects such as deterioration of the quality of the cellulosic raw material are caused. This is preferable because there is no fear and there is no possibility that the pressure in the reactor exceeds atmospheric pressure. Therefore, the range of 20-95 ° C is preferred. Within this range, there is also an advantage that there is no need to design a device in consideration of pressure resistance. More preferably, it is 20-80 degreeC, More preferably, it is 20-50 degreeC.

  Moreover, although pH at the time of irradiating an ultraviolet-ray does not have limitation in particular, when considering simplification of a process, it is preferable to process in a neutral region, for example, about pH 6.0-8.0.

  The degree of irradiation received by the cellulosic raw material in the ultraviolet irradiation reaction can be arbitrarily set by adjusting the residence time of the cellulosic raw material in the irradiation reaction apparatus, adjusting the amount of energy of the irradiation light source, or the like. Also, for example, by adjusting the concentration of the cellulosic material in the irradiation device by diluting with water, or by adjusting the concentration of the cellulosic material by blowing an inert gas such as air or nitrogen into the cellulosic material. The irradiation amount of ultraviolet rays received by the cellulosic material in the irradiation reaction apparatus can be arbitrarily controlled. These conditions such as residence time and concentration can be appropriately set in accordance with the quality (fiber length, cellulose polymerization degree, etc.) of the oxidized cellulose raw material after the target ultraviolet irradiation reaction.

  In addition, when the ultraviolet irradiation treatment in the present invention is performed in the presence of an auxiliary such as oxygen, ozone, or peroxide (hydrogen peroxide, peracetic acid, sodium percarbonate, sodium perborate, etc.), photooxidation is performed. Since the efficiency of reaction can be improved more, it is preferable.

  In the present invention, particularly when ultraviolet rays having a wavelength region of 135 to 242 nm are irradiated, ozone is generated because air is usually present in the gas phase around the light source. In the present invention, while continuously supplying air to the periphery of the light source, the generated ozone is continuously extracted, and this extracted ozone is injected into the oxidized cellulosic raw material, so that the outside of the system is removed. Without supplying ozone, ozone can be used as an auxiliary for the photo-oxidation reaction. Furthermore, by supplying oxygen to the gas phase around the light source, a larger amount of ozone can be generated in the system, and the generated ozone can be used as an auxiliary agent for the photooxidation reaction. As described above, in the present invention, it is also a great advantage that ozone generated by the ultraviolet irradiation reactor can be used.

  In the present invention, the ultraviolet irradiation treatment can be repeated a plurality of times. The number of repetitions can be appropriately set according to the relationship with the target quality of the oxidized cellulosic raw material and the post-treatment such as bleaching. For example, although not particularly limited, ultraviolet rays of 100 to 400 nm, preferably 135 to 260 nm, are irradiated 1 to 10 times, preferably about 2 to 5 times, for a length of about 0.5 to 3 hours per time. be able to.

(Defibration / dispersion processing)
In the present invention, the oxidized cellulose-based raw material is irradiated with ultraviolet rays and then subjected to defibration and dispersion treatment. Examples of types of defibrating / dispersing devices include high-speed rotation type, colloid mill type, high pressure type, roll mill type, ultrasonic type, etc. Cellulose nanofiber dispersion liquid with excellent transparency and fluidity can be efficiently used. In order to obtain, it is preferable to treat with a wet high pressure or ultra high pressure homogenizer that can be dispersed under conditions of 50 MPa or more, preferably 100 MPa or more, and more preferably 140 MPa or more.

(Cellulose nanofiber)
The cellulose nanofiber produced by the present invention is a single microfibril of cellulose having a width of 2 to 5 nm and a length of about 1 to 5 μm. In the present invention, “to form a nanofiber” means that a cellulose-based raw material is processed into cellulose nanofiber which is a single microfibril of cellulose having a width of about 2 to 5 nm and a length of about 1 to 5 μm.

  The cellulose nanofiber dispersion obtained by the present invention has a B-type viscosity (60 rpm, 20 ° C.) at a concentration of 1.0% by mass (w / v) of 1000 mPa · s or less, preferably 800 mPa · s or less, more preferably It is 500 mPa · s or less, and the light transmittance (660 nm) at a concentration of 0.1% by mass (w / v) is 90% or more, preferably 95% or more. Cellulose nanofibers produced according to the present invention are excellent in fluidity and transparency, and are also excellent in barrier properties and heat resistance, and thus can be used for various applications such as packaging materials.

  In the present invention, the B-type viscosity of the cellulose nanofiber dispersion can be measured using a normal B-type viscometer commonly used by those skilled in the art, for example, TV-10 type viscosity of Toki Sangyo Co., Ltd. Using a meter, it can be measured at 20 ° C. and 60 rpm.

  The light transmittance of the cellulose nanofiber dispersion can be measured with an ultraviolet / visible spectrophotometer.

(Operation of the present invention)
In the present invention, cellulose nano-materials excellent in fluidity and transparency even at high concentrations are obtained by irradiating ultraviolet rays on cellulose-based raw materials oxidized using an N-oxyl compound, and then defibrating and dispersing. A fiber dispersion can be obtained with low power consumption. The reason is guessed as follows. Carboxyl groups are localized on the surface of the cellulose-based raw material oxidized using the N-oxyl compound, and a hydrated layer is formed. Therefore, it is considered that there is a microscopic gap between the raw materials which is not found in ordinary pulp due to the action of the charge repulsive force between the carboxyl groups. When the raw material is irradiated with ultraviolet rays, active oxygen species having excellent oxidizing power such as ozone are generated from oxygen dissolved in the hydration layer on the surface of the raw material or pore water of the raw material, and the cellulose chain is efficiently formed. It is considered that the fiber is oxidized and decomposed, and finally the shortening of the cellulose-based raw material is promoted. By shortening the cellulose-based raw material, it is considered that the B-type viscosity of the dispersion in the defibration / dispersion treatment in the next step is significantly reduced, and the fluidity of the dispersion is improved. Moreover, it is thought that the cellulose nanofiber dispersion liquid excellent in transparency is obtained by shortening the fiber of a cellulose raw material.

  Next, based on an Example, this invention is demonstrated still in detail.

  5 g (absolutely dried) bleached unbeaten sulfite pulp (Nippon Paper Chemical Co., Ltd.) derived from coniferous tree was added to 500 ml of an aqueous solution in which 78 mg (0.5 mmol) of TEMPO (Sigma Aldrich) and 755 mg (7 mmol) of sodium bromide were dissolved, Stir until the pulp is uniformly dispersed. After adding 18 ml of an aqueous sodium hypochlorite solution (effective chlorine 5%) to the reaction system, the pH was adjusted to 10.3 with an aqueous 0.5N hydrochloric acid solution to initiate the oxidation reaction. During the reaction, the pH in the system was lowered, but a 0.5N aqueous sodium hydroxide solution was successively added to adjust the pH to 10. After reacting for 2 hours, it was filtered through a glass filter and washed thoroughly with water to obtain oxidized pulp. 2 L of 1% (w / v) slurry of oxidized pulp was treated with a 20 W low-pressure mercury lamp that irradiates ultraviolet rays of 254 nm for 6 hours. When the oxidized pulp slurry treated with ultraviolet rays was treated 10 times with an ultra-high pressure homogenizer (treatment pressure 140 MPa), a transparent gel dispersion was obtained. The B-type viscosity (60 rpm, 20 ° C.) of the obtained 1% (w / v) cellulose nanofiber dispersion was measured using a TV-10 viscometer (Toki Sangyo Co., Ltd.) and 0.1% ( The w / v) cellulose nanofiber dispersion transparency (660 nm light transmittance) was measured using a UV-VIS spectrophotometer UV-265FS (Shimadzu Corporation), and the power consumption required for defibration / dispersion treatment. Was obtained by (power during processing) × (processing time) ÷ (amount of sample processed). The results are shown in Table 1.

  A nanofiber dispersion was obtained in the same manner as in Example 1 except that ultraviolet rays having a wavelength range of 260 to 400 nm and having a main peak at 310 nm were irradiated using a 20 W low-pressure mercury lamp. The results are shown in Table 1.

  A nanofiber dispersion was obtained in the same manner as in Example 1 except that ultraviolet rays having a wavelength range of 340 to 400 nm and having a main peak at 360 nm were irradiated using a 20 W low-pressure mercury lamp. The results are shown in Table 1.

  A nanofiber dispersion was obtained in the same manner as in Example 1 except that the treatment pressure of the ultrahigh pressure homogenizer was 100 MPa. The results are shown in Table 1.

  A nanofiber dispersion was obtained in the same manner as in Example 1 except that the treatment pressure of the ultrahigh pressure homogenizer was 50 MPa. The results are shown in Table 1.

  A nanofiber dispersion was obtained in the same manner as in Example 1 except that the treatment pressure of the ultrahigh pressure homogenizer was 30 MPa. The results are shown in Table 1.

  A nanofiber dispersion was obtained in the same manner as in Example 1 except that powdered cellulose (Nippon Paper Chemical Co., Ltd., particle size 75 μm) was used as the cellulose-based material. The results are shown in Table 1.

  A nanofiber dispersion was obtained in the same manner as in Example 5 except that powdered cellulose (Nippon Paper Chemical Co., Ltd., particle size 75 μm) was used as the cellulose-based material. The results are shown in Table 1.

  A nanofiber dispersion was obtained in the same manner as in Example 6 except that powdered cellulose (Nippon Paper Chemical Co., Ltd., particle size 75 μm) was used as the cellulose-based material. The results are shown in Table 1.

  A nanofiber dispersion was obtained in the same manner as in Example 1 except that a high shear mixer (circumferential speed: 37 m / s, Nippon Seiki Seisakusho) equipped with a rotating blade as a dispersing device was used instead of the ultrahigh pressure homogenizer. The results are shown in Table 1.

  A nanofiber dispersion was obtained in the same manner as in Example 1 except that 1% (w / v) of hydrogen peroxide was added to the oxidized pulp during UV irradiation. The results are shown in Table 1.

  A nanofiber dispersion was obtained in the same manner as in Example 1 except that a 20 W low-pressure ultraviolet lamp that simultaneously irradiates ultraviolet rays of 254 nm and 185 nm was used. The results are shown in Table 1.

[Comparative Example 1]
A nanofiber dispersion was obtained in the same manner as in Example 1 except that ultraviolet rays were not irradiated. The results are shown in Table 1.

[Comparative Example 2]
A nanofiber dispersion was obtained in the same manner as in Comparative Example 1 except that a high shear mixer (circumferential speed: 37 m / s, Nippon Seiki Seisakusho) equipped with a rotary blade as a dispersing device was used instead of the ultrahigh pressure homogenizer. The results are shown in Table 1.

  In Examples 1 to 12, in which oxidized pulp was subjected to ultraviolet irradiation treatment, cellulose nanofibers having a low B-type viscosity and high transparency can be obtained with low power consumption as compared with Comparative Examples 1 and 2 in which ultraviolet irradiation was not performed. Recognize. Therefore, according to the method for producing cellulose nanofibers of the present invention, a cellulose nanofiber dispersion having high fluidity and transparency can be obtained at a high concentration and with high efficiency.

  A 1% (w / v) cellulose nanofiber dispersion produced in Example 1 was applied to one side of a polyethylene terephthalate film (thickness 20 μm) with a hand-painted bar (bar No. 16) at 50 ° C. Dried to form a film. The thickness of the film was about 5.9 μm.

  A 1% (w / v) cellulose nanofiber dispersion produced in Example 2 was applied to one side of a polyethylene terephthalate film (thickness 20 μm) with a hand-painted bar (bar No. 16) at 50 ° C. Dried to form a film. The thickness of the film was about 7.8 μm.

  The 1% (w / v) cellulose nanofiber dispersion produced in Example 7 was applied to one side of a polyethylene terephthalate film (thickness 20 μm) with a bar (bar No. 16) dedicated to hand coating, at 50 ° C. Dried to form a film. The thickness of the film was about 7.8 μm.

[Comparative Example 3]
The concentration of the 1% (w / v) cellulose nanofiber dispersion produced in Comparative Example 1 was adjusted to have a B-type viscosity of 600 mPa · s (60 rpm, 20 ° C.). The cellulose nanofiber concentration at this time was 0.4% (w / v). This dispersion was coated on one side of a polyethylene terephthalate film (thickness 20 μm) with a bar (bar No. 16) dedicated to hand coating, and dried at 50 ° C. to form a film. The film thickness was about 2.0 μm. In order to form a 5.9 μm film having the same thickness as in Example 13, it was necessary to repeat coating and drying at least twice.

Claims (5)

(A) oxidizing the cellulosic material using an oxidizing agent in the presence of (1) an N-oxyl compound and (2) a compound selected from the group consisting of bromide, iodide or a mixture thereof;
(B) irradiating the cellulosic material from (A) with ultraviolet light; and
(C) Nanofiberization by defibrating and dispersing the cellulosic material from (B),
The manufacturing method of the cellulose nanofiber containing this.   The method for producing cellulose nanofiber according to claim 1, wherein the wavelength of the ultraviolet light is 100 to 400 nm.   The method for producing cellulose nanofiber according to claim 1 or 2, wherein the ultraviolet irradiation is performed in the presence of an oxidizing agent.   The method for producing cellulose nanofiber according to any one of claims 1 to 3, wherein the ultraviolet light source comprises a plurality of light sources having different wavelength characteristics.   The method for producing cellulose nanofiber according to any one of claims 1 to 5, wherein the fibrillation / dispersion treatment is performed under a pressure of 50 MPa or more.