JP2008266828A - Cellulose ultrafine fiber, fiber aggregate sheet thereof, and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cellulose ultrafine fiber in which the ultrafine fiber is uniform with an extremely small fiber diameter, ≥1 mm fiber length and low crystallinity thereof, to provide a fiber aggregate sheet thereof and to provide a method for producing the fiber aggregate sheet. <P>SOLUTION: The cellulose ultrafine fiber is obtained by carrying out electrospinning of a cellulose solution at 0.5-15 wt.% cellulose concentration, 0.01-20 wt.% polyalkylene glycol concentration and 0.01-5 wt.% surfactant concentration as a spinning solution. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an ultrafine cellulose fiber, a fiber assembly sheet thereof, and a method for producing the same.

  Cellulose is the most abundant natural polymer on the earth and has been used in various forms for a long time. In recent years, as energy problems and global environmental problems have become more serious, they are attracting attention as polymer materials that can be regenerated and have enormous potential, and are essential materials in our lives.

  Cellulose is used in many industrial fields as a fiber, but in recent years, in the fiber field, as in other fields, the nano-region is attracting a great deal of attention, and research related to nanofibers is active. . This is because fibers with a small fiber diameter (ultrafine fibers) and their fiber aggregates have very useful properties such as a very large surface area per unit weight and excellent separation performance and liquid retention performance. is there.

  As for cellulose, several production methods for obtaining ultrafine fibers have been proposed so far. For example, a cellulose fiber in a suspension such as wood pulp is refined by applying a shearing force or cutting force with a high-pressure homogenizer (see, for example, Patent Document 1), or a microorganism that produces cellulosic microfibrils. (See, for example, Patent Document 2). Cellulose fibers produced by these methods have an average fiber diameter of 0.01 to 1 μm, which is very thin, but the fiber diameter is nonuniform and the fiber length is short. Moreover, it has the characteristics that the degree of crystallinity exceeds 70% and is highly crystalline due to the manufacturing method.

  On the other hand, an electrospinning method is generally known as a method for producing ultrafine fibers. (For example, refer to Patent Document 3.) The electrostatic spinning method is a method in which a polymer solution (spinning stock solution) is discharged into a static electric field formed between electrodes using a nozzle or the like, thereby causing electrostatic force and solvent volatilization. In this spinning method, fibers and fiber aggregates can be obtained by thinning and solidifying a solution and depositing an ultrafine fibrous material on a collector.

  By using this spinning method, it is expected to produce a cellulose fine fiber having a uniform fiber diameter of nano order and a long fiber length. There are no reports of the manufacture of these products, and their proposals are expected.

JP 2000-177592 A JP 2004-270064 A JP-A 63-145465

  The present invention relates to a cellulose ultrafine fiber having a nano-sized fiber diameter, which has been impossible in the past. The nano-sized fiber diameter has good uniformity and excellent industrial productivity. An object of the present invention is to provide a fiber, a fiber assembly thereof, and a manufacturing method thereof.

  As a result of intensive studies to solve the above-mentioned problems, the inventors of the present invention have made use of an electrospinning method of a cellulose solution to obtain a cellulose ultrafine fiber having a nano-sized fiber diameter excellent in uniformity and a fiber assembly thereof. The inventors have found that production is possible, and have reached the present invention.

That is, the present invention is as follows.
(1) A cellulose ultrafine fiber having a fine fiber shape, an average fiber diameter of 0.01 to 1 μm, and a crystallinity of 0 to 70%.

  (2) The cellulose ultrafine fiber as described in (1) above, wherein the cellulose fiber is a regenerated cellulose fiber or a purified cellulose fiber.

  (3) The ultrafine cellulose fiber according to (1) or (2) above, wherein the fiber length is 1 mm or more.

  (4) The ultrafine cellulose fiber according to any one of (1) to (3), which is obtained by an electrospinning method.

(5) The ultrafine cellulose fiber according to any one of the above (1) to (4), wherein the fiber surface area per 1 dtex is 2.6 m ² or more.

(6) It is comprised from the cellulose ultrafine fiber in any one of said (1)-(5), thickness is 1-500 micrometers, and the weight per unit area is 0.1-100 g / m < ² >, A fiber assembly sheet having a particulate portion with a diameter of 3 μm or more of 500 pieces / mm ² or less.

  (7) A polyalkylene glycol having an average molecular weight of 1,000 to 4,000,000 and a surfactant are added to a cellulose solution in which cellulose is dissolved in a good solvent, and the cellulose concentration is 0.5 to 15 wt%, and the polyalkylene glycol concentration is After electrospinning a solution having a surfactant concentration of 0.01 to 20 wt% and a surfactant concentration of 0.01 to 5 wt%, the solvent, polyalkylene glycol and surfactant are removed by natural drying, solvent removal treatment and water washing. The method for producing an ultrafine cellulose fiber according to the above (1), which is dried after removing.

  (8) A polyalkylene glycol having an average molecular weight of 1,000 to 4,000,000 and a surfactant are added to a cellulose solution in which cellulose is dissolved in a good solvent, the cellulose concentration is 0.5 to 15 wt%, and the polyalkylene glycol concentration After forming a sheet of fiber aggregate by electrostatic spinning a solution with 0.01 to 20 wt% and a surfactant concentration of 0.01 to 5 wt%, natural drying, solvent removal treatment and water washing, The method for producing a cellulose fiber aggregate sheet according to (6) above, wherein the solvent, polyalkylene glycol and surfactant are removed and then dried.

  According to the present invention, the ultrafine cellulose fiber, its fiber assembly, and its production, characterized in that the fiber diameter is extremely small as nano-size, uniform, the fiber length is 1 mm or more, and its crystallinity is in a specific range A method can be provided.

  The ultrafine cellulose fiber of the present invention is obtained by an electrospinning method. As a result, the uniformity of the fiber diameter is particularly excellent in the fiber longitudinal direction or between the fibers, and the CV value has an excellent effect of 11 to 30%. Further, since the fiber aggregate composed of the ultrafine cellulose fibers is composed of extremely fine fibers, the specific surface area is extremely large and the fiber aggregate has many fine fiber voids. Can be obtained stably.

The present invention is described in detail below.
The cellulose fiber of the present invention has an extremely fine fiber shape. The extremely fine fiber shape means that there are almost no particulate portions having a diameter of 3 μm or more in the fiber. Even if most of the fibers are fibers having a fiber diameter of 0.01 to 1 μm, there are more than a certain amount of particulate portions having a diameter of 3 μm or more, for example, 500 / mm ² or more as a fiber aggregate described later. Is not an extremely fine fiber shape. As a specific example of the ultrafine fiber shape, there is a fiber as shown in FIG. 2 which is an electron microscope observation result of Example 1 described later. On the other hand, the specific example which is not an ultrafine fiber shape is a fiber as shown in FIG. 3 which is an electron microscope observation result of Comparative Example 1 described later. This is because there is a particulate portion having a remarkably large diameter of 3 μm or more with respect to the ultrafine fiber portion, and such an object is not expressed as an ultrafine fiber shape.

Such ultrafine cellulose fibers of the present invention are preferably obtained by an electrospinning method.
By using the electrospinning method, a fiber having very few particulate portions which is usually recognized in other spinning methods can be obtained. A fiber assembly composed of fibers having many particulate portions is not preferable because it is inferior in terms of specific surface area, strength and uniformity. The generation mechanism of the particulate part is not clearly understood, but due to the optimization of the spinning solution conditions (surface tension, viscoelasticity, etc.) and the equipment conditions, the injection is continuous and clogging and contamination at the nozzle tip As a result, it is considered that uniform cellulose ultrafine fibers and fiber aggregates can be obtained with few particulate portions.

  In addition, according to the electrospinning method, it is possible to control the surface structure of the fiber by controlling the solvent removal rate at the time of thinning and by the drying method. Can be produced.

  The average fiber diameter of the ultrafine cellulose fiber of the present invention is in the range of 0.01 to 1 μm. When the average fiber diameter exceeds 1 μm, the flexibility of the fiber assembly becomes poor, which is not preferable. In addition, the characteristics of the ultrafine fibers, such as the size of the specific surface area and the separation characteristics when used as a filter, are hardly exhibited. Therefore, Preferably it is 0.01-0.8 micrometer, More preferably, it is 0.01-0.5 micrometer.

  The ultrafine fiber of the present invention has a fiber length of 1 mm or more, more preferably 5 mm or more, particularly preferably 10 mm or more, and may be a continuous fiber. There is no particular upper limit, and it can be used as a raw material for short fibers or long fibers. Moreover, after manufacturing as a long fiber once, it can also cut and it can also be set as the short fiber of arbitrary length. When the fiber length is less than 1 mm, the mechanical strength of the fiber aggregate obtained thereby tends to be insufficient.

  The crystallinity of the ultrafine cellulose fiber in the present invention is in the range of 0 to 70%, more preferably 0 to 50%, and particularly preferably 0 to 30%. In the range where the degree of crystallinity is low, there are many amorphous parts of cellulose, and the processing characteristics by chemicals etc. are improved. Moreover, it has the characteristic that dyeing | staining and decomposition | disassembly are easy.

  This crystallinity is presumed to be greatly influenced by the spinning method. In the electrospinning method, the spinning solution extruded into an electrostatic field is refined by repulsion of electric charges in the solution. Along with this, abrupt desolvation occurs to form a fiber structure. Since this structure is formed when it is not sufficiently stretched, it is presumed that a fiber with low crystallinity is obtained as a result.

  On the other hand, cellulose microfibers proposed in the past use microbes that produce wood pulp or cellulosic microfibrils as raw materials, which are highly crystalline, and also have a fiber shape. Not uniform.

In the ultrafine fiber of the present invention, the fiber surface area per dtex is preferably 2.6 m ² or more. Considering the expression of the characteristics of the ultrafine fiber, it is preferably 3.3 m ² , more preferably 5.3 m ² or more. The upper limit is 266.6 m ² . When the fiber surface area per 1 dtex is in this range, it is preferable that when used as an ion exchange fiber, the contact area is large and an efficient ion exchange reaction is performed.

  The uniformity of the fiber diameter of the ultrafine fibers in the present invention is evaluated by the fiber diameter distribution of the fibers constituting the fiber assembly, that is, the CV value (S / Da) which is the ratio of the average fiber diameter Da and its standard deviation S. I can do it. The CV value indicates that the smaller the value, the smaller the fiber diameter distribution, indicating a uniform fiber diameter. The CV value of the fiber assembly of the present invention is preferably 50% or less, and more preferably 30% or less. In the examples described later, an extremely fine and uniform fiber aggregate having an average fiber diameter of 0.1 to 1 μm and a CV value of 11 to 30% is obtained.

  Having a uniform fiber diameter distribution with nano-sized fiber diameters is the greatest feature of the present invention. The present invention can be achieved by a stable spinning state based on an electrostatic spinning method, that is, by uniform discharge of a spinning solution at a constant rate. Therefore, the uniformity of the diameter in the fiber length direction and between the fibers is excellent.

In the present invention, the fiber assembly refers to a structure in which one or a plurality of fibers are irregularly laminated, and is usually formed in a sheet shape. A preferred embodiment includes a nonwoven fabric. The configuration of the nonwoven fabric is not particularly limited, although the average fiber diameter is preferably 0.01 to 0.8 μm, the basis weight is 0.1 to 100 g / m ² , and the thickness is 1 to 500 μm. Since the fibers are thin, a fabric having a relatively small basis weight and a thin thickness can be stably obtained.

  The feature of the fiber assembly of the present invention is that ultrafine fibers with nano-sized fiber diameters are densely laminated, and extremely small pores exist uniformly, and laminated with other nonwoven fabrics. It is suitable to use, and the effect can be effectively exhibited.

The fiber aggregate of the present invention preferably has a bulk density of 0.05 to 0.50 g / cm ³ and a porosity of 65 to 97%. When the bulk density is high, the porosity is lowered and the liquid holding performance is lowered. More preferably, the bulk density is 0.05 to 0.30 g / cm ³ , and the porosity is 80 to 97%. Particularly preferably, the bulk density is in the range of 0.05 to 0.20 g / cm ³ and the porosity is in the range of 87 to 97%.

The specific surface area of the fiber assembly of the present invention is 1 m ² / g or more. Considering the expression of characteristics as an aggregate of ultrafine fibers, it is preferably 5 m ² / g or more, more preferably 10 m ² / g or more.

  The ultrafine cellulose fiber of the present invention can be obtained by electrostatic spinning of a cellulose solution in which cellulose is dissolved in a good solvent. The cellulose solution to be used is not particularly limited as long as it is a cellulose solution in which cellulose is dissolved in a good solvent. Examples of the solvent include copper ammonia, carbon disulfide, caustic soda, sulfuric acid, liquid ammonia / ammonium thiocyanate, N-methylmorpholine N-oxide, and DMAc / LiCl. In the present invention, the raw material cellulose is particularly preferably regenerated cellulose fiber or purified cellulose fiber, and for example, cupra fiber, viscose rayon fiber, polynosic fiber, or osel fiber is suitable. A particularly preferred embodiment in the present invention is an embodiment in which a copper ammonium cellulose solution is electrospun. Since the copper-an cellulose solution has moderate electrical conductivity and is an aqueous solvent, the adverse effect on the human body as observed with an organic solvent is extremely small. Further, it is preferable because the danger of ignition and explosion due to static electricity is small during spinning.

  The present invention relates to ultrafine cellulose fibers and fiber aggregates obtained by electrostatic spinning of a cellulose solution, and a manufacturing method using a copper and cellulose solution, which is a more preferable solution, will be described in detail below. .

The manufacturing method of the ultrafine cellulose fiber and fiber assembly of the present invention includes the following steps (a) to (f).
(A) Raw material cellulose is dissolved in a copper ammonia solution, 0.5 to 15% by weight of cellulose, 0.01 to 20% by weight of polyalkylene glycol having an average molecular weight of 1,000 to 4,000,000, and 0.01% of surfactant. A step of preparing a spinning dope suitable for electrospinning containing ˜5 wt%,
(B) a step of electrostatically spinning the spinning solution and depositing a fiber assembly on a collector;
(C) After the step (b), a step of coagulating and regenerating using an acidic aqueous solution containing 75 to 99% by weight of water and 1 to 15% by weight of acid,
(D) a step of washing with water after the step (c),
(E) If necessary, a step of replacing the water with an organic solvent after the step (d) using an organic solvent having a boiling point of 70 to 200 ° C. and a surface tension of 9 to 30 mN / m,
(F) After the step (d) or (e), the step of drying and removing the water or the organic solvent at a temperature in the range of 40 to 200 ° C. while restraining at least uniaxially.

First, the step (a) of the present invention will be described.
First, a copper ammonia solution having cellulose dissolving ability is prepared with a copper sulfate solution and ammonia. A purified cotton linter having a degree of polymerization of 700 to 1000 is added thereto as a cellulose source, and sufficiently stirred and dissolved to prepare a copper-an cellulose solution having a cellulose concentration of 8 to 15 wt%.

  Next, in order to obtain a copper ammonia cellulose solution suitable for electrospinning, 0.01 to 20 wt% polyalkylene glycol (hereinafter abbreviated as PAG) and 0.01 to 5 wt% surfactant are added to this solution. % And knead well so as to disperse uniformly.

  The cellulose concentration in the solution is preferably in the range of 0.5 to 15 wt%, more preferably in the range of 1 to 12 wt%, particularly preferably in the range of 2 to 10 wt%. When the cellulose concentration is less than 0.5 wt%, the solution has low dissolution stability and the product is in the form of fine particles. On the other hand, if it exceeds 15 wt%, the viscosity is remarkably high and the injection stability of electrospinning is poor.

  The PAG contained in the solution is preferably at least one of the following formulas (1) to (4). In these formulas, R and R 'are alkyl groups, and AO is an alkylene oxide. The alkylene oxide may contain 2 or more types of alkylene oxides, and may have a structure containing a branch. For example, although it does not specifically limit, polyethylene glycol, polypropylene glycol, polyethylene propylene glycol, etc. are mentioned.

RO- (AO) _n- R '(1)
RO- (AO) _n -H (2)
HO- (AO) _n- H (3)
R [—O— (AO) _n —H] ₃ (4)

  The average molecular weight of PAG is preferably in the range of 1,000 to 4,000,000, more preferably 5,000 to 2,000,000, and particularly preferably in the range of 100,000 to 1,000,000. When the average molecular weight of the PAG is within this range, it is preferable from the viewpoint that the injection stability is drastically improved due to the addition effect of the PAG. On the other hand, if the average molecular weight is less than 1,000, the effect of addition is not recognized, and if it exceeds 4 million, it is not preferable from the viewpoint of the viscosity of the spinning dope.

  The content thereof is in the range of 0.01 to 20 wt%, preferably 0.05 to 10 wt%, particularly preferably 0.1 to 5 wt%. When the content of the PAG is within this range, it is preferable from the viewpoint that the injection stability is drastically improved due to the addition effect of the PAG. On the contrary, if it is less than 0.01 wt%, the effect of adding PAG is not recognized, and if it exceeds 20 wt%, it is not preferable from the viewpoint of economy.

  The surfactant contained in the solution is not particularly limited as long as it is well compatible with the solution and does not alter the solution such as gelation, and is non-ionic, anionic, cationic, Any of amphoteric and those containing two or more of these may be used. Examples thereof include polyoxyalkylene alkyl ether, polyoxyethylene alkyl ether, polyoxyethylene alkyl ester, sorbitan fatty acid ester and the like.

  The content thereof is in the range of 0.01 to 5 wt%, preferably 0.05 to 2 wt%, particularly preferably 0.1 to 1 wt%. It is preferable from the viewpoint of injection stability that the content of the surfactant is in this range. Conversely, if the content is less than 0.01 wt%, the effect of adding a surfactant is not exhibited, and if it is 5 wt% or more, it is not preferable from the viewpoint of an increase in the viscosity of the cellulose solution and economical efficiency.

Next, step (b) of the present invention will be described.
The electrospinning method is not particularly limited as long as the spinning solution obtained in the step (a) is introduced into the electrostatic field, and any convenient method can be used. For example, as shown in FIG. 1, the spinning solution 2 is put into a syringe 1, and the spinning solution is pushed out by a syringe pump 3 through a nozzle 4 at an arbitrary discharge amount. In parallel with this, a high voltage is applied to the nozzle by the high voltage generator 5 to form an electrostatic field between the nozzle and the grounded collector 6. The spinning dope extruded in the electrostatic field is refined by the repulsion of electric charges in the solution and collected as an aggregate of ultrafine fibers on the collector.

In this method, an electrostatic field may be formed between the nozzle 4 and the collector 6, and a high voltage may be applied to the collector and the nozzle may be grounded.
The magnitude of the applied voltage is preferably in the range of 5 to 100 kV. When the applied voltage is less than 5 kV, the repulsive force of the charge in the solution is too small, and the solution jumping out from the nozzle tip is not thinned. On the other hand, if it exceeds 100 kV, air breakdown tends to occur, which is not preferable. A more preferable range is 10 to 50 kV.

  The distance between the nozzle 4 and the collector 6 is preferably 5 to 20 cm. If the distance between the nozzle and the collector is less than 5 cm, the solvent may not sufficiently evaporate while the solution reaches the collector, or if the applied voltage is high, air breakdown may occur. It is not preferable. On the other hand, if it exceeds 20 cm, a very large applied voltage is required to form a fine electrostatic field, which is not preferable.

  The inner diameter of the nozzle 4 is preferably in the range of 0.1 to 3 mm, and the range of 0.1 to 1.5 mm is more preferable in consideration of the fiber diameter to be obtained.

  The fiber aggregate collected in the form of a sheet on the collector contains ammonia, copper, PAG and a surfactant in addition to cellulose, so that it is regenerated with acid and washed with water. The water is replaced with an organic solvent, followed by drying.

  The acid for regeneration in the step (c) of the present invention may be any acid that can elute copper forming a complex with cellulose, such as sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, odorous acid or hydrofluoric acid. Inorganic acids and derivatives thereof and organic acids such as acetic acid, succinic acid or tartaric acid can be used. Sulfuric acid is preferred. The concentration may be a minimum concentration at which regeneration is completed, and is preferably 15% or less in consideration of economy. The regenerating method is performed by immersing in a tank filled with an acid or spraying it using a device such as a shower.

  The water washing in the step (d) of the present invention is performed to elute the remaining copper ions and wash the regenerated solution. Similarly to the above-described regeneration method, the cleaning method is performed by immersing in a tank filled with water or spraying using a device such as a shower.

  The replacement of water with an organic solvent in the step (e) of the present invention is performed as necessary. By implementing this, it aims at maintaining the porosity and specific surface area of the fiber assembly after drying high. The organic solvent used at this time needs to have a surface tension of 9 to 30 mN / m, preferably 14 to 30 mN / m, and most preferably 19 to 30 mN / m. When an organic solvent having a surface tension exceeding 30 mN / m is used, the meaning of organic solvent substitution is reduced and the porosity of the resulting fiber assembly is lowered. On the other hand, the use of an organic solvent having a surface tension of less than 9 mN / m is not desirable because it has a poor ability to replace water and tends to be poorly miscible with other solvents.

  The boiling point of the organic solvent needs to be 70 to 200 ° C, preferably 80 to 200 ° C, and most preferably 80 to 180 ° C. Use of an organic solvent having a boiling point of less than 70 ° C. is not desirable because the porosity of the resulting fiber assembly decreases. In addition, use of an organic solvent having a boiling point exceeding 200 ° C. is not desirable because energy consumption increases.

  Examples of the organic solvent having the above-described properties include ketones, alcohols, ethers, esters, nitriles, polyfunctional compounds, hydrocarbons, and halogenated hydrocarbons. Among these, in view of the ability to dissolve water, ketones, alcohols, ethers, esters, nitriles, and polyfunctional group compounds are preferable.

Examples of suitable organic solvents include ketones such as methyl ethyl ketone and diethyl ketone.
Examples of alcohols include ethanol, n-propanol, isopropanol, n-butanol, 2-butanol, and t-butanol.
Examples of ethers include 1,2-dimethoxyethane and 1,2-diethoxyethane.
Nitriles include acetonitrile and propionitrile.
Esters include ethyl acetate, n-propyl acetate and isopropyl acetate.
The polyfunctional group compound is a low molecular compound having two or more kinds of functional groups, such as 2-ethoxyethanol and 1-methoxy-2-propanol.

Furthermore, in consideration of environmental adaptability, safety, hygiene and ability to dissolve water, among the organic solvents, alcohols, ketones, and polyfunctional group compounds are preferable.
The replacement method in the present invention is performed by immersing in a tank filled with an organic solvent or spraying it using a device such as a shower.

  In the drying step of the present invention (f), it is necessary to positively heat and the drying temperature to be 40 to 200 ° C., convection heat transfer drying, radiation heat transfer drying, conduction heat transfer drying, and internal It is preferable to employ any method of exothermic drying.

Convective heat transfer drying is a method in which a hot air dryer, oven dryer, clip tenter, pin tenter, or the like is used to apply heat and supply heat by convection of air or the like.
Radiant heat transfer drying is a method of supplying heat by applying radiant heat from a temperature-controlled mold or the like.
Conductive heat transfer drying is a method of supplying heat by directly contacting a temperature-controlled mold or the like, and uses a roll dryer equipped with a temperature-controlled metal roll or the like.
Internal heat generation drying is a method of self-heating by irradiating energy rays such as microwaves.

  As described above, the drying temperature needs to be 40 to 200 ° C., and the higher the temperature, the higher the porosity of the obtained fiber assembly. When the drying temperature exceeds 200 ° C., there is no problem if it is only for a short time, but it is not desirable because the influence of thermal degradation of cellulose cannot be ignored.

  In the method for producing a cellulose fine fiber and fiber aggregate of the present invention, heat treatment, crosslinking treatment, chemical modification, or the like may be further performed depending on the purpose. Heat treatment improves dimensional stability, cross-linking improves water resistance, and chemical modification improves affinity for the liquid to be filtered.

  Most of the components of the ultrafine fiber and the fiber assembly of the present invention are composed of cellulose, but the electrospinning stock solution may contain a slight amount of polyalkylene glycol added as a spinning stabilizer.

  The composition of the spinning dope used in the present invention may further contain materials such as inorganic fillers, whiskers, filaments or short fibers, depending on the purpose. In addition, additives such as an antioxidant, an antistatic agent, a flame retardant, a lubricant and an ultraviolet absorber may be mixed.

  The fibers and fiber aggregates obtained by the present invention may be used alone, but may be used in combination with other members or other materials in accordance with other requirements such as handleability and strength. For example, it is possible to form a laminate by depositing ultrafine fibers on a nonwoven fabric, a film or paper. In addition, by combining with other materials, it is possible to develop characteristics that are not found in a single material.

  The fibers and fiber aggregates obtained by the present invention can be used for various applications such as high performance filters, various battery separators, regenerative medical media, biosensors, biochips, blood separation membranes, and precious metal collecting materials.

Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples.
Each value regarding the fiber and fiber assembly in the examples was determined by the following method. Moreover, about each evaluation in an Example and a comparative example, it is as follows.

(1) Evaluation of ultrafine fiber shape The surface of the obtained fiber assembly was observed and evaluated at 1000 times magnification using a scanning electron microscope (JSM-6380, manufactured by JEOL). Specifically, in the photograph (12 cm × 8 cm), the evaluation was made based on the number of particulate portions having a diameter of 3 μm or more.
○ Extremely fine fiber shape. (Number of particulate parts with a diameter of 3μ or more: within 2)
Δ: An almost ultrafine fiber shape. (Number of particulate parts with a diameter of 3μ or more: 3-5)
X It is not an extremely fine fiber shape. (Number of particulate parts with a diameter of 3μ or more: 6 or more)

(2) Average fiber diameter The surface of the obtained fiber assembly was observed with a scanning electron microscope (JSM-6380, manufactured by JEOL Ltd.) at a magnification of 10,000 times, and 50 arbitrary fibers were selected. Was selected and measured, and the average value was defined as the average fiber diameter Da.
In addition, for the fiber having a very large number of particulate portions, the above calculated value was not calculated because it greatly changed depending on the selection of one arbitrary place and did not make sense.

(3) Confirmation of presence of fibers having a fiber length of 1 mm or less A 1 cm square observation sample was cut out from the obtained fiber assembly, and the surface was magnified 1000 times using a scanning electron microscope (JSM-6380 manufactured by JEOL) Then, it was observed over the entire area, and the degree of fibers having a fiber length of 1 mm or less was evaluated.
○ Does not exist. (Number: 0)
△ A little exists. (Number: 1 to 10)
× There are many. (Number: 11 or more)

(4) Crystallinity The obtained fiber aggregate was measured using an X-ray diffractometer (RINT2200 manufactured by Rigaku), and obtained from the following formula proposed by Segal et al. From the obtained intensity curve.
Crystallinity χc (X) = (I (002) −Iam) / I (002) × 100 (%)
Here, I (002) and Iam are the diffraction peak intensity of the (002) plane and the diffraction intensity of the amorphous cellulose part, respectively.

(5) Fiber surface area per 1 dtex Calculated by the following equation.
Fiber surface area = (average fiber diameter (m) × π × 10000) / {(0.5 × average fiber diameter (m)) ² π × 10000 × 1.5 × 10 ⁶ } (m ² )

(6) Evaluation of fiber diameter distribution (CV value)
The fiber diameter distribution was evaluated based on the coefficient of variation (CV value), which is the ratio between the standard deviation S of the fiber diameter distribution of the obtained fibers and the average fiber diameter Da.
Coefficient of variation CV = (S / Da) × 100 (%)

(7) Thickness For a fiber assembly cut into a 10 cm square, using a dimatic indicator (543-450B made by Mituyo), the thickness of 9 points was measured, and the average value was determined as the thickness d (μm). did.

(8) Weight per unit area The fiber aggregate cut out to a 10 cm square was allowed to stand for 24 hours or more in an atmosphere of (23 ° C. × 60% RH), and then the weight was measured. An average value of the obtained values was converted to a unit area (m ² ) and used as a basis weight.

(9) Bulk density After measuring the thickness and basis weight, the bulk density was calculated from (weight / thickness).

(10) Porosity Calculated from the following equation.
Porosity = (1−bulk density / 1.5) × 100 (%)

(11) Specific surface area Using a specific surface area measuring device (NOVA4200e manufactured by Yuasa Ionics Co., Ltd.), measurement with nitrogen was performed, and calculation was performed by the BET method.

(Examples 1-4)
Copper ammonia cellulose solution (cellulose: 10 wt%, copper: 3.6 wt%, ammonia: 6.1 wt%, others are mostly water), aqueous ammonia (28 wt%), polyethylene glycol (hereinafter abbreviated as PEG) aqueous solution (10 wt %, Molecular weight are listed in Table 1), surfactant (trade name: Pegnol (manufactured by Toho Chemical Co., Ltd.)) was added so as to have the composition shown in Table 1, kneaded well, A spinning dope was prepared.

  This spinning stock solution is put into the syringe shown in FIG. 1, and is quantitatively discharged (2.62 ml / hr) onto a metal substrate from a metal nozzle having an inner diameter of 0.41 mm. Between the metal nozzle and the metal substrate (distance: 10 cm), Electrostatic spinning was performed by applying a voltage of 20 kV with a high-voltage power source.

  In all of the examples, the spinning state was a stable electrostatic spinning state in which the injection was almost continuous and stable, and there was almost no clogging or contamination of the spinning stock solution at the tip of the injection nozzle.

  Thereafter, the obtained fiber aggregate was subjected to natural drying, solvent removal treatment and water washing to remove the solvent, PEG and surfactant, and then dried to obtain a cellulose fiber aggregate. When the surface was observed with a scanning electron microscope, it was a very thin and uniform fiber with very few particulate portions. The observation result of Example 1 is shown in FIG. Other values and evaluation are shown in Table 1.

(Comparative Example 1)
Copper ammonia cellulose solution (cellulose: 10 wt%, copper: 3.6 wt%, ammonia: 6.1 wt%, most others are water), ammonia water, surfactant (trade name: Pegnol (manufactured by Toho Chemical Co., Ltd.)) ) Was added so as to have the composition shown in Table 1, and kneaded well to prepare a spinning dope for electrospinning.

  This spinning stock solution is put into a syringe, and is quantitatively discharged onto a metal substrate from a metal nozzle having an inner diameter of 0.41 mm. A voltage of 20 kV is applied between the metal nozzle and the metal substrate (distance: 10 cm) by a high-voltage power source, Spinning was performed.

  In the spinning state, the injection was discontinuous, and after a few minutes from the start of spinning, the nozzle tip was contaminated, and after a while, it solidified and clogged.

  Thereafter, the obtained fiber aggregate was subjected to natural drying, solvent removal treatment and water washing to remove the solvent, PEG and surfactant, and then dried to obtain a cellulose fiber aggregate. When the surface was observed with a scanning electron microscope, many small particulate portions were confirmed. The observation result of Comparative Example 1 is shown in FIG. Other values and evaluation are shown in Table 1.

  The ultrafine cellulose fiber and fiber aggregate of the present invention have the original characteristics of cellulose, such as heat resistance, hydrophilicity and biodegradability, and the fiber diameter is extremely small and uniform, and there are few particulate portions, and the fiber length Is 1 mm or more, and the degree of crystallinity is 0 to 70%.

It is a schematic diagram which shows the one aspect | mode of the electrospinning method. 2 is a result of observation with a scanning electron microscope of the fiber assembly sheet obtained in Example 1. FIG. 4 is a scanning electron microscope observation result of the fiber assembly sheet obtained in Comparative Example 1. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Syringe 2 Spinning undiluted solution 3 Syringe pump 4 Nozzle 5 High voltage generator 6 Collector 10 Particulate part

Claims (8)

  A cellulose ultrafine fiber, which is an ultrafine fiber having an average fiber diameter of 0.01 to 1 μm and a crystallinity of 0 to 70%.   The cellulose fine fiber according to claim 1, wherein the cellulose fiber is a regenerated cellulose fiber or a purified cellulose fiber.   The cellulose ultrafine fiber according to claim 1 or 2, wherein the fiber length is 1 mm or more.   The cellulose ultrafine fiber according to any one of claims 1 to 3, which is obtained by an electrostatic spinning method. The ultrafine cellulose fiber according to any one of claims 1 to 4, wherein a fiber surface area per 1 dtex is 2.6 m ² or more. It is comprised from the cellulose ultrafine fiber in any one of Claims 1-5, The thickness is 1-500 micrometers, The weight per unit area is 0.1-100 g / m < ² >, The diameter of 3 micrometers or more particle shape A fiber assembly sheet having a portion of 500 pieces / mm ² or less.   A polyalkylene glycol having an average molecular weight of 1,000 to 4,000,000 and a surfactant are added to a cellulose solution in which cellulose is dissolved in a good solvent, the cellulose concentration is 0.5 to 15 wt%, and the polyalkylene glycol concentration is 0.00. After electrospinning a solution having a concentration of 01 to 20 wt% and a surfactant concentration of 0.01 to 5 wt%, after removing the solvent, polyalkylene glycol and surfactant by natural drying, solvent removal treatment and water washing The method for producing ultrafine cellulose fibers according to claim 1, wherein drying is performed.   A polyalkylene glycol having an average molecular weight of 1,000 to 4,000,000 and a surfactant are added to a cellulose solution in which cellulose is dissolved in a good solvent, the cellulose concentration is 0.5 to 15 wt%, and the polyalkylene glycol concentration is 0.00. Electrospinning a solution having a concentration of 01 to 20 wt% and a surfactant concentration of 0.01 to 5 wt% to form a fiber assembly sheet, followed by natural drying, solvent removal treatment and water washing, The method for producing a cellulose fiber aggregate sheet according to claim 6, wherein the alkylene glycol and the surfactant are removed and then dried.