WO2017131035A1

WO2017131035A1 - Nanofiber and nonwoven cloth

Info

Publication number: WO2017131035A1
Application number: PCT/JP2017/002554
Authority: WO
Inventors: 竜太竹上; 邦行神長; 片井　幸祐; 幸助谷口
Original assignee: 富士フイルム株式会社
Priority date: 2016-01-26
Filing date: 2017-01-25
Publication date: 2017-08-03
Also published as: CN108495958A; KR102053562B1; US20180327932A1; JPWO2017131035A1; KR20180097721A; JP6616849B2; CN108495958B

Abstract

The present invention addresses the problem of providing: a nanofiber having excellent uniformity of fiber diameter and having a good appearance when used to produce a nonwoven cloth; and a nonwoven cloth using the nanofiber. This nanofiber contains cellulose acylate having a degree of substitution of 2.75-2.95.

Description

Nanofiber and non-woven fabric

The present invention relates to a nanofiber and a nonwoven fabric using cellulose acylate.

Nanofibers, that is, fibers with a nano-order diameter of several nanometers or more and less than 1000 nm are used as materials for products such as biofilters, sensors, fuel cell electrode materials, precision filters, electronic paper, etc. Development of applications in various fields is actively conducted.

For example, Patent Document 1 states that “a harmful substance removing material comprising a carrier composed of fibers, wherein the fiber diameter is 10 nm or more and 1 μm or less, and the pore diameter of the carrier is 100 μm or more and 1 mm or less. (Claim 1), and fibers constituting the carrier include fibers mainly composed of cellulose ester and cellulose acylate fibers ([Claim 3). ], [0019] to [0021]).

JP 2009-291754 A

The present inventors examined nanofibers produced using cellulose acylate. Depending on the type of cellulose acylate used, the uniformity of the fiber diameter of the produced nanofibers was inferior, and a nonwoven fabric was produced. It was clarified that the appearance may be inferior when

Therefore, an object of the present invention is to provide nanofibers having excellent fiber diameter uniformity and good appearance when a nonwoven fabric is produced, and a nonwoven fabric using the nanofiber.

As a result of intensive investigations to achieve the above-mentioned problems, the inventors of the present invention have a nanofiber produced using cellulose acylate having a specific substitution degree, excellent in fiber diameter uniformity, and appearance when a nonwoven fabric is produced. And the present invention was completed.
That is, it has been found that the above-described problem can be achieved by the following configuration.

[1] A nanofiber containing cellulose acylate whose degree of substitution satisfies the following formula (1).
2.75 ≦ degree of substitution ≦ 2.95 (1)
[2] The nanofiber according to [1], wherein the ratio of the average fiber length to the average fiber diameter is 1000 or more.
[3] The nanofiber according to [1] or [2], wherein the average fiber diameter is 50 to 800 nm.
[4] The nanofiber according to any one of [1] to [3], wherein the average fiber length is 500 μm or more.
[5] The nanofiber according to any one of [1] to [4], wherein the acyl group of cellulose acylate is an acetyl group.
[6] The nanofiber according to any one of [1] to [5], wherein the amount of hemicellulose in the cellulose acylate is 0.1 to 3.0% by mass.
[7] The nanofiber according to any one of [1] to [6], wherein the viscosity of a solution obtained by dissolving 6% by mass in dichloromethane is 300 mPa · s or more.
[8] A nonwoven fabric composed of the nanofiber according to any one of [1] to [7].
[9] The nonwoven fabric according to [8], which is used for a medical filter or mask.

According to the present invention, it is possible to provide nanofibers having excellent fiber diameter uniformity and good appearance when a nonwoven fabric is produced, and a nonwoven fabric using the nanofiber.

FIG. 1 is a schematic view of a nanofiber production apparatus. FIG. 2 is a cross-sectional view showing the tip of the nozzle. FIG. 3 shows a scanning electron microscope (Scanning / Electron / Microscope: SEM) image (magnification: 1800 times) of a nonwoven fabric made of nanofibers produced in Example 1. 4 shows an SEM image (magnification: 1800 times) of a nonwoven fabric made of nanofibers produced in Example 2. FIG. FIG. 5 shows an SEM image (magnification: 1800 times) of a nonwoven fabric made of nanofibers produced in Comparative Example 1.

Hereinafter, the present invention will be described in detail.
The description of the constituent elements described below may be made based on typical embodiments of the present invention, but the present invention is not limited to such embodiments.
In this specification, a numerical range expressed using “to” means a range including numerical values described before and after “to” as a lower limit value and an upper limit value.

[Nanofiber]
The nanofiber of the present invention is a nanofiber containing cellulose acylate whose degree of substitution satisfies the following formula (1).
2.75 ≦ degree of substitution ≦ 2.95 (1)
Here, “nanofiber” in the present specification refers to a fiber having an average fiber diameter of 10 nm or more and 1000 nm or less measured by a measurement method described later.

<Average fiber diameter>
An average fiber diameter means the value measured as follows.
The surface of the nonwoven fabric made of nanofibers is observed with a transmission electron microscope (TEM) image or a scanning electron microscope (SEM) image.
Observation with an electron microscope image is performed at a magnification selected from 1000 to 5000 times according to the size of the constituent fibers. However, the sample, observation conditions, and magnification are adjusted to satisfy the following conditions.
(1) One straight line X is drawn at an arbitrary position in the observation image, and 20 or more fibers intersect the straight line X.
(2) A straight line Y perpendicularly intersecting with the straight line X is drawn in the same image, and 20 or more fibers intersect with the straight line Y.
For the electron microscope observation image as described above, the width (minor axis of the fiber) of at least 20 fibers (that is, at least 40 in total) is read for each of the fibers intersecting with the straight line X and the fibers intersecting with the straight line Y. . In this way, at least three or more sets of electron microscope images as described above are observed, and fiber diameters of at least 40 × 3 sets (that is, at least 120 sets) are read.
The fiber diameters thus read are averaged to obtain the average fiber diameter.

<Average fiber length>
The average fiber length of a cellulose fiber means the value measured as follows.
That is, the fiber length of the cellulose fiber can be determined by analyzing the electron microscope observation image used when measuring the above-described average fiber diameter.
Specifically, at least 20 fibers (that is, a total of at least 40 fibers) are read for each of the fibers intersecting with the straight line X and the fibers intersecting with the straight line Y with respect to the electron microscope observation image as described above. .
In this way, at least three or more sets of electron microscope images as described above are observed, and the fiber length of at least 40 × 3 sets (that is, at least 120 sets) is read.
The average fiber length is obtained by averaging the fiber lengths thus read.

As described above, the nanofiber of the present invention contains cellulose acylate having a degree of substitution of 2.75 or more and 2.95 or less, so that the fiber diameter is excellent in uniformity and the appearance when a nonwoven fabric is produced is good. Become.
The reason for the effect is not clear in detail, but the present inventors presume as follows.
That is, in the present invention, when a nanofiber is produced using an electrospinning method (hereinafter also referred to as “electrospinning method”), a cellulose acylate having a substitution degree of 2.75 or more and 2.95 or less is used. By using it, the crystallinity of cellulose acylate is increased, so that the spinning into droplets is suppressed, and the entanglement of cellulose acylate molecules is promoted.

In the nanofiber of the present invention, the ratio of the average fiber length to the average fiber diameter, that is, the aspect ratio (average fiber length / average fiber diameter) is 1000 because it is easy to produce a single nonwoven fabric composed of nanofibers. The above is preferable, 2500 to 20000 is more preferable, and 5000 to 20000 is particularly preferable.

In addition, the nanofiber of the present invention preferably has an average fiber diameter of 50 to 800 nm, more preferably 100 to 600 nm, because the mechanical strength of the fiber is high and a nonwoven fabric can be easily produced. In addition, when the average fiber diameter is 50 to 800 nm, effects such as a size effect, a supramolecular arrangement effect, a cell recognition effect, and a hierarchical structure effect can be expected.

In addition, the nanofiber of the present invention preferably has an average fiber length of 500 μm or more, more preferably 1 mm or more, for the purpose of preventing the fibers from fraying when a nonwoven fabric is formed. More preferably, it is 5 to 5 mm.

The nanofiber of the present invention has a further improved viscosity of a fiber diameter and a better appearance when a nonwoven fabric is produced. The viscosity of a solution in which 6% by mass is dissolved in dichloromethane (hereinafter referred to as “6% solution”). Viscosity ”) is preferably 300 mPa · s or more, more preferably 300 to 1000 mPa · s, further preferably 300 to 900 mPa · s, and 350 to 800 mPa · s. Particularly preferred.
The reason why such an effect can be obtained is that when nanofibers are produced using the electrospinning method, it is possible to suppress spinning into droplets, and also to suppress nozzle burr. Conceivable. In particular, the present inventors infer the reason why the uniformity of the fiber diameter is improved by controlling the substitution degree of cellulose acylate and the 6% solution viscosity.
First, in order to form uniform nanofibers, it is considered important to form polymer entanglements so that the nanofibers are not broken during the process of discharging the solution from the nozzle and drying. As a method for controlling the entanglement of the polymer, (a) a method for enhancing the interaction (crystallinity) between molecules (hereinafter abbreviated as “method (a)”), (b) The method of increasing the length (molecular weight) (hereinafter abbreviated as “method (b)” in this paragraph) was presumed to be useful. Therefore, in the present invention, the substitution degree of cellulose acylate is adjusted to perform the method (a), and the 6% solution viscosity is adjusted to perform the method (b). In particular, the adjustment of the degree of substitution of cellulose acylate suppresses the formation of a sudden entanglement in the late stage of drying, and the adjustment of the 6% solution viscosity controls the formation of the entanglement in the early stage of drying, which is entangled throughout the entire process. Therefore, it can be inferred that spinning into droplets can be suppressed and uniform nanofibers can be created.
In addition, in this specification, 6% solution viscosity says the value measured in the following procedures.
First, the dried cellulose acylate is precisely weighed, and a solution in which 6% by mass of cellulose acylate is dissolved in a mixed solvent in which the mass ratio of dichloromethane and methanol is 91: 9 is measured at 25 ° C. using an Ostwald viscometer. The flow time is measured and calculated by the following formula.
6% solution viscosity (mPa · s) = flowing time (seconds) × viscosity coefficient Here, the viscometer coefficient is measured using the standard solution for calibration of the viscometer in the same manner as the above solution. it can ask Te, specifically, a density (1.235g / ^cm 3) of the absolute viscosity (cps) × solution viscometer coefficient = standard solution / standard solution density of (g / ^cm 3) / standard solution It can be determined by the flow time (seconds).

Hereinafter, the cellulose acylate contained in the nanofiber of the present invention, the synthesis method thereof, and the production method of the nanofiber of the present invention will be described in detail.

[Cellulose acylate]
The cellulose acylate contained in the nanofiber of the present invention is a cellulose acylate whose degree of substitution satisfies the following formula (1).
2.75 ≦ degree of substitution ≦ 2.95 (1)
Here, “cellulose acylate” means a part of hydrogen atoms constituting the hydroxyl groups of cellulose, that is, the free hydroxyl groups at the 2nd, 3rd and 6th positions of β-1,4-bonded glucose units. Or it refers to a cellulose ester that is entirely substituted with an acyl group.
“Degree of substitution” refers to the degree of substitution of acyl groups with hydrogen atoms constituting the hydroxyl groups of cellulose, and is calculated by comparing the carbon area intensity ratio of cellulose acylate measured by ¹³ C-NMR method. can do.

<Substituent (acyl group)>
Specific examples of the acyl group include an acetyl group, a propionyl group, and a butyryl group.
Moreover, the acyl group to substitute may be only 1 type (for example, only an acetyl group), and 2 or more types may be sufficient as it.

In the present invention, the uniformity of the fiber diameter is further improved, and when the nonwoven fabric is produced, the appearance of the nonwoven fabric is better. When one kind of acyl group is used, the acyl group is preferably an acetyl group. When two or more types of acyl groups are used, it is preferable that one of the acyl groups is an acetyl group. Among these, an embodiment in which one kind of acyl group is used and the acyl group is an acetyl group is preferable.

<Degree of substitution>
The substitution degree of the acyl group is 2.75 to 2.95 as described above. However, for the reason that the uniformity of the fiber diameter is further improved and the appearance when the nonwoven fabric is produced becomes better, 2.80 to It is preferably 2.95, and more preferably 2.88 to 2.95.
The method for adjusting the substitution degree will be described in detail in the cellulose acylate synthesis method described later.

<Amount of hemicellulose>
In the present invention, the amount of hemicellulose in the cellulose acylate is 0.1 to 3.0% by mass because the uniformity of the fiber diameter is further improved and the appearance of the nonwoven fabric is improved. Preferably, the content is 0.1 to 2.0% by mass.
The reason why such an effect can be obtained is that, when nanofibers are produced by using the electrospinning method, it is possible to suppress spinning into droplets by increasing the crystallinity of cellulose acylate. Conceivable.
In the present specification, the amount of hemicellulose refers to a value calculated from sugar analysis by the alditol-acetate method (Borchadt, L. G .; Piper, C. V .: Tappi, 53, 257 to 260 (1970)).
The method for adjusting the amount of hemicellulose will be described in detail in the cellulose acylate synthesis method described below.

<Molecular weight>
The number average molecular weight (Mn) of the cellulose acylate contained in the nanofiber of the present invention is not particularly limited, but is preferably 40,000 or more, more preferably 40000 to 150,000 from the viewpoint of the mechanical strength of the nanofiber. More preferably, it is 60000-100,000.
The weight average molecular weight (Mw) of the cellulose acylate is not particularly limited, but is preferably 100,000 or more, more preferably 100,000 to 500,000, and more preferably 150,000 to 300,000 from the viewpoint of the mechanical strength of the nanofiber. More preferably.
In addition, the weight average molecular weight and the number average molecular weight in this specification are measured by the gel permeation chromatography (GPC) method under the following conditions.
・ Device name: HLC-8220GPC (Tosoh)
Column type: TSK gel Super HZ4000 and HZ2000 (Tosoh)
・ Eluent: Dimethylformamide (DMF)
・ Flow rate: 1 ml / min ・ Detector: RI
・ Sample concentration: 0.5%
Standard curve base resin: TSK standard polyester (molecular weight 1050, 5970, 18100, 37900, 190000, 706000)

The cellulose acylate content in the nanofiber of the present invention is not particularly limited, but is preferably 25% by mass or more, more preferably 40 to 100% by mass, and more preferably 60 to 100% by mass with respect to the total mass of the nanofiber. More preferably, it is 100 mass%.

[Method of synthesizing cellulose acylate]
The above-mentioned method for synthesizing cellulose acylate is disclosed in JIII Journal of Technical Disclosure (Publication No. 2001-1745, published on March 15, 2001, Invention Association) p. The description of 7 to 12 is also applicable.

<Raw material>
As a raw material of cellulose, for example, a raw material derived from hardwood pulp, softwood pulp, cotton linter and the like can be preferably mentioned. Among these, a raw material derived from cotton linter is preferable because it can produce nanofibers with a small amount of hemicellulose and further improved uniformity in fiber diameter.

<Amount of hemicellulose>
The amount of hemicellulose can be adjusted by purifying the cellulose raw material by an appropriate method.
For example, the amount of hemicellulose can be obtained by subjecting cellulose raw materials to cooking bleaching by sulfite cooking, kraft cooking, etc .; bleaching with oxygen or chlorine bleach; alkali refining; Can be adjusted.
Specifically, in the refining bleaching process combining the above-described cooking, bleaching and alkali refining processes, a 3-25% by mass strong alkaline aqueous solution is used and a low temperature of 20-40 ° C. is used when performing the alkali refining process. A method of purifying with is preferable.

<Activation>
The cellulose raw material is preferably subjected to a treatment (activation) for contacting with an activator prior to acylation.
Specific examples of the activator include acetic acid, propionic acid, and butyric acid. Among them, acetic acid is preferable.
The addition amount of the activator is preferably 5% to 10,000%, more preferably 10% to 2000%, and still more preferably 30% to 1000%.
The addition method can be selected from methods such as spraying, dropping, and dipping.
The activation time is preferably 20 minutes to 72 hours, more preferably 20 minutes to 12 hours.
The activation temperature is preferably 0 ° C. to 90 ° C., more preferably 20 ° C. to 60 ° C.
Furthermore, 0.1 to 10% by mass of an acylation catalyst such as sulfuric acid can be added to the activator.

<Acylation>
It is uniform to acylate the hydroxyl group of cellulose by reacting cellulose with a carboxylic acid anhydride using a Bronsted acid or a Lewis acid (see "Science and Chemistry Dictionary", fifth edition (2000)) as a catalyst. It is preferable for synthesizing cellulose acylate, and the molecular weight can be controlled.
The cellulose acylate can be obtained by, for example, a method of reacting two carboxylic acid anhydrides as an acylating agent by mixing or sequentially adding; a mixed acid anhydride of two carboxylic acids (for example, acetic acid and propionic acid). A method using a mixed acid anhydride; a mixed acid anhydride (for example, acetic acid and propionic acid) in a reaction system using an acid anhydride of a carboxylic acid and another carboxylic acid (for example, an acid anhydride of acetic acid and propionic acid) as a raw material A mixed acid anhydride) and a reaction with cellulose; a cellulose acylate having a degree of substitution of less than 3 is once synthesized, and the remaining hydroxyl group is further acylated using an acid anhydride or an acid halide Method; and the like.
The synthesis of cellulose acylate having a high degree of substitution at the 6-position is described in publications such as JP-A-11-5851, JP-A-2002-212338, and JP-A-2002-338601.

(Acid anhydride)
The carboxylic acid anhydride is preferably a carboxylic acid anhydride having 2 to 6 carbon atoms, and specific examples thereof include acetic anhydride, propionic anhydride, butyric anhydride, and the like.
The acid anhydride is preferably added in an amount of 1.1 to 50 equivalents, more preferably 1.2 to 30 equivalents, and still more preferably 1.5 to 10 equivalents, relative to the hydroxyl group of cellulose.

(catalyst)
As the acylation catalyst, a Bronsted acid or a Lewis acid is preferably used, and sulfuric acid or perchloric acid is more preferably used.
The addition amount of the acylation catalyst is preferably from 0.1 to 30% by mass, more preferably from 1 to 15% by mass, and even more preferably from 3 to 12% by mass.

(solvent)
As the acylating solvent, it is preferable to use a carboxylic acid, and it is more preferable to use a carboxylic acid having 2 to 7 carbon atoms. Specifically, for example, acetic acid, propionic acid, butyric acid, and the like are used. Further preferred. These solvents may be used as a mixture.

(conditions)
In order to control the temperature rise due to the heat of reaction of acylation, it is preferable to cool the acylating agent in advance.
The acylation temperature is preferably −50 ° C. to 50 ° C., more preferably −30 ° C. to 40 ° C., and further preferably −20 ° C. to 35 ° C.
The minimum reaction temperature is preferably −50 ° C. or higher, more preferably −30 ° C. or higher, and further preferably −20 ° C. or higher.
The acylation time is preferably 0.5 to 24 hours, more preferably 1 to 12 hours, and even more preferably 1.5 to 10 hours.
The molecular weight can be adjusted by controlling the acylation time.

(Reaction terminator)
It is preferable to add a reaction terminator after the acylation reaction.
The reaction terminator may be any as long as it decomposes an acid anhydride, and specifically includes water, alcohols having 1 to 3 carbon atoms, and carboxylic acids (for example, acetic acid, propionic acid, butyric acid, etc.). A mixture of water and carboxylic acid (acetic acid) is preferred.
The composition of water and carboxylic acid is preferably 5 to 80% by mass of water, more preferably 10 to 60% by mass, and still more preferably 15 to 50% by mass.

(Neutralizer)
A neutralizing agent may be added after the acylation reaction is stopped.
Examples of the neutralizing agent include ammonium, organic quaternary ammonium, alkali metal, group 2 metal, group 3-12 metal, or group 13-15 element carbonate, bicarbonate, organic acid salt, water An oxide or an oxide can be given. Specifically, sodium, potassium, magnesium or calcium carbonate, hydrogen carbonate, acetate or hydroxide is preferably mentioned.

(Partial hydrolysis)
The cellulose acylate obtained by the acylation described above has a total degree of substitution close to about 3. However, for the purpose of adjusting to a desired degree of substitution (for example, about 2.8), a small amount of catalyst (for example, In the presence of residual acylation catalyst such as sulfuric acid) and water, the ester bond is partially hydrolyzed by keeping it at 20 to 90 ° C. for several minutes to several days, so that the acyl substitution degree of cellulose acylate is desired. Can be reduced to a degree. Note that the partial hydrolysis can be appropriately stopped by using the neutralizing agent for the remaining catalyst.

(Filtration)
Filtration may be performed at any step between the completion of acylation and reprecipitation. It is also preferred to dilute with a suitable solvent prior to filtration.

(Reprecipitation)
The cellulose acylate solution can be mixed with water or an aqueous solution of carboxylic acid (eg, acetic acid, propionic acid, etc.) and reprecipitated. Reprecipitation may be either continuous or batch.

(Washing)
It is preferable to perform a washing treatment after reprecipitation. Washing can be performed using water or warm water, and the completion of washing can be confirmed by pH, ion concentration, electrical conductivity, elemental analysis, and the like.

(Stabilization)
The cellulose acylate after washing is preferably added with a weak alkali (carbonates such as Na, K, Ca and Mg, bicarbonates, hydroxides and oxides) for stabilization.

(Dry)
It is preferable to dry the cellulose acylate to 50% by mass or less at 50 to 160 ° C.

[Production method of nanofiber]
The method for producing the nanofiber of the present invention is not particularly limited. For example, a solution in which the above-described cellulose acylate is dissolved in a solvent is taken out from the nozzle tip as a constant temperature within a range of 5 ° C. or more and 40 ° C. or less, It can be manufactured by applying a voltage between the solution and the collector and ejecting the fiber from the solution to the collector. Details will be described below with reference to the drawings.

A nanofiber production apparatus 110 shown in FIG. 1 is for producing nanofibers 46 from a solution 25 in which cellulose acylate is dissolved in a solvent. The nanofiber manufacturing apparatus 110 includes a spinning chamber 111, a solution supply unit 112, a nozzle 13, an accumulation unit 15, and a power source 65. The spinning chamber 111 accommodates, for example, the nozzle 13 and a part of the accumulating unit 15 and is configured to be hermetically sealed to prevent the solvent gas from leaking to the outside. The solvent gas is obtained by vaporizing the solvent of the solution 25.
The solvent may be a simple substance or a mixture composed of a plurality of compounds. Solvents for dissolving cellulose acylate include methanol, ethanol, isopropanol, butanol, benzyl alcohol, acetone, methyl ethyl ketone, cyclohexanone, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl formate, ethyl formate, hexane, cyclohexane, dichloromethane Chloroform, carbon tetrachloride, benzene, toluene, xylene, dimethylformamide, N-methylpyrrolidone (NMP), diethyl ether, dioxane, tetrahydrofuran, 1-methoxy-2-propanol and the like. These may be used alone or in combination depending on the type of polymer, the saturated vapor pressure Ps, the viscosity of the solution 25, and the like. In this embodiment, as a solvent, a mixture of dichloromethane and NMP, a mixture of dichloromethane and cyclohexanone, a mixture of acetone and cyclohexanenone, or the like is used.

A nozzle 13 is disposed in the upper part of the spinning chamber 111. The nozzle 13 is for discharging the solution 25 in a state of being charged to the first polarity by the power source 65 as will be described later. As shown in FIG. 2, the nozzle 13 is formed of a cylinder, and discharges the solution 25 from an opening 13 </ b> A (hereinafter, abbreviated as “end opening”). The tip opening 13a is an outlet through which the solution 25 exits. The nozzle 13 is made of stainless steel having an outer diameter of 0.65 mm and an inner diameter of 0.4 mm, for example, and is cut so that a tip opening edge portion 13b around the tip opening 13a is orthogonal to the cylinder center direction. The front end opening edge 13b, which is the cut surface, is polished flat.

The material of the nozzle 13 may be made of a conductive material such as an aluminum alloy, a copper alloy, or a titanium alloy instead of stainless steel. For electrospinning, the solution 25 may come into contact with the metal member at any location, be applied with a voltage, and exit from the tip opening 13a in a state of being charged to the first polarity. Therefore, the tip opening 13a does not necessarily need to be a conductive material as long as a voltage is applied at any location up to the tip opening 13a and the first opening is charged when exiting the tip opening 13a. .

As shown in FIG. 1, a pipe 32 of the solution supply unit 112 is connected to the base end of the nozzle 13. The solution supply unit 112 is for supplying the solution 25 to the nozzle 13 of the spinning chamber 111. The solution supply unit 112 includes a storage container 30, a first temperature controller 133, a pump 31, and a pipe 32. The storage container 30 stores the solution 25. The first temperature controller 133 adjusts the temperature of the stored solution 25 via the storage container 30.

The pump 31 sends the solution 25 from the storage container 30 to the nozzle 13 via the pipe 32. By changing the number of rotations of the pump 31, the flow rate of the solution 25 delivered from the nozzle 13 can be adjusted. In the present embodiment, the flow rate of the solution 25 is 3 cm ³ / hour, but the flow rate is not limited to this. When the solution 25 is sent to the nozzle 13 by the pump 31, the solution 25 exits from the tip opening 13a.

In the solution 25 of the storage container 30, the saturated vapor pressure Ps (unit: kPa) of the solvent and the concentration C (unit: g / 100 cm ³ ) of the cellulose acylate satisfy the following condition (1). The solution 25 is sent to the nozzle 13 in a state where this condition (1) is satisfied, and is discharged from the tip opening 13a. In this embodiment, the pipe 32 and the nozzle 13 are provided with temperature controllers (not shown) so that they are guided from the storage container 30 to the tip opening 13a and exit from the tip opening 13a in a state where the condition (1) is satisfied. The temperature of the solution 25 is guided to the nozzle 13 while being kept at the temperature in the storage container 30 by these temperature controllers, and is discharged from the tip opening 13a.
Ps × C ≦ 300 (1)

The saturated vapor pressure Ps (t) of the solvent at the temperature t is obtained by the following equation (2). Here, the number of components of the solvent is n (n is a natural number of 1 or more), the saturated vapor pressure of a single component i (i is a natural number of 1 to n) at temperature t is Pi (t), and the component i Let Xi be the molar fraction in the solvent. When the number of components is n, the saturated vapor pressure Ps (t) is defined by the following equation. Ps in the above condition (1) is obtained as the temperature t in the equation (2) by the temperature of the solution 25 coming out of the nozzle 13. In the present embodiment, since the temperature of the solution 25 is kept constant from the storage container 30 to the tip opening 13a, the temperature in the storage container 30 is set to the temperature t in the equation (2), thereby obtaining the saturated vapor pressure Ps. ing. Concentration C is determined by (M × 100) / V, where V (unit: cm ³ ) is the volume of solution 25 and M (unit: g) is the mass of cellulose acylate.

The saturated vapor pressure Ps is preferably in the range of 10 kPa to 50 kPa. When the saturated vapor pressure Ps is 10 kPa or higher, the solvent evaporates more easily than when the saturated vapor pressure Ps is less than 10 kPa, so that the droplets of the solution 25 and solid particles are not generated. Moreover, since it is hard to evaporate a solvent when it is 50 kPa or less compared with the case where it is larger than 50 kPa, solidification by drying of the solution 25 is suppressed.

The first temperature controller 133 adjusts the saturated vapor pressure Ps of the solvent in the solution 25 by adjusting the temperature of the solution 25. The saturated vapor pressure Ps can be adjusted by changing the mixing ratio of the solvent of the solution 25 as a mixture composed of a plurality of compounds instead of or in addition to the adjustment of the temperature of the solution 25.

The temperature of the solution 25 coming out of the nozzle 13 is preferably in the range of 5 ° C. or more and 40 ° C. or less, and in this embodiment, it is 25 ° C. ± 1 ° C. (in the range of 24 ° C. or more and 26 ° C. or less). In order to make the temperature of the solution 25 coming out of the nozzle 13 within the above range, it is preferable to store the solution 25 in the storage solution 30 by adjusting the temperature to a temperature within the range of 5 ° C. or more and 40 ° C. or less. ℃ ± 1 ℃. When the temperature of the solution 25 is 5 ° C. or higher, the solution 25 is less likely to be gelled at a low temperature than when it is less than 5 ° C., and the solution 25 is stably discharged from the nozzle 13. In addition, when the temperature of the solution 25 is 40 ° C. or lower, intense evaporation (flash) due to the solvent exceeding the boiling point is less likely to occur than when the temperature is higher than 40 ° C., and solidification due to drying of the solution 25 is suppressed. The The temperature of the solution 25 exiting from the nozzle 13 is more preferably in the range of 10 ° C. or more and 35 ° C. or less, and further preferably in the range of 15 ° C. or more and 30 ° C. or less.

The viscosity of the solution 25 exiting from the nozzle 13 is preferably in the range of 1 mPa · s to 10 Pa · s. The viscosity of the solution 25 can be adjusted by the temperature and the components of the solution 25. When adjusting the viscosity according to the temperature of the solution 25, the temperature of the solution 25 may be adjusted by the first temperature controller 133. Examples of a method for adjusting the viscosity according to the components of the solution 25 include a method for changing the concentration C of cellulose acylate and a method for changing the solvent. As a method for changing the solvent, for example, when the solvent is composed of a simple substance, the kind of the simple substance is changed, or other ingredients are added to change the mixture, and when the solvent is a mixture, the composition ratio of the ingredients is mixed. And changing at least one of them. The viscosity of the solution 25 exiting from the nozzle 13 is more preferably in the range of 1 mPa · s to 5 Pa · s, and still more preferably in the range of 2 mPa · s to 2 Pa · s.

The nozzle 13 is preferably provided with a cover 134 that covers the tip opening 13a and a second temperature controller 135 for adjusting the temperature inside the cover 134 as in the present embodiment. In the cover 134, an opening 134 a for allowing the solution 25 to pass toward the collector 50 is formed between the tip opening 13 a and the collector 50. By adjusting the internal temperature by the second temperature controller 135, the ambient temperature Ta around the tip opening 13a (around the outlet where the solution comes out) is adjusted. The periphery is a range that covers at least the Taylor cone 44, and is preferably within a range of, for example, 20 mm from the tip opening 13a. By adjusting the atmospheric temperature Ta, it is preferable to set the difference between the temperature Ts of the solution 25 coming out of the tip opening 13a and the atmospheric temperature Ta, that is, Ts-Ta within a range of −15 ° C. to 15 ° C. When Ts-Ta is in the range of −15 ° C. or more and 15 ° C. or less, the evaporation of the solvent is moderate compared to the case where Ts-Ta is outside this range, so that solidification due to drying of the solution 25 is suppressed, and There are no occurrences of ball-like droplets of the solution 25 or solid particles. Ts—Ta is more preferably within a range of −10 ° C. to 10 ° C., and further preferably within a range of −5 ° C. to 5 ° C.

The method of adjusting the ambient temperature Ta around the tip opening 13a is not limited to the method using the cover 134 and the second temperature controller 135 of the present embodiment. Instead of the cover 134 and the second temperature controller 135, for example, a gas such as air with a constant temperature is sent to the spinning chamber 111, and the temperature of the entire interior of the spinning chamber 111 is adjusted by this feeding. Ta may be adjusted. In the present embodiment, the atmospheric temperature Ta is adjusted to 25 ° C., and the relative humidity of the atmosphere around the tip opening 13a is set to 30% RH.

The cellulose acylate concentration C in the solution 25 is preferably in the range of 0.1 g / 100 cm ³ or more and 20 g / 100 cm ³ or less. Thereby, the viscosity of the solution 25 becomes moderate, and the molecules of the cellulose acylate are appropriately entangled with each other. The concentration C is more preferably 0.5 g / 100 cm ³ or more and 15 g / 100 cm ³ or less, and further preferably 1 g / 100 cm ³ or more and 10 g / 100 cm ³ or less.

The accumulation unit 15 is disposed below the nozzle 13. The stacking unit 15 includes a collector 50, a collector rotating unit 51, a support body supply unit 52, and a support body winding unit 53. The collector 50 is for collecting the solution 25 exiting from the nozzle 13 as nanofibers 46, and in this embodiment, collects it on a support 60 described later. The collector 50 is made of an endless belt made of a band-like metal, for example, stainless steel. The collector 50 is not limited to stainless steel, and may be formed of a material that is charged by applying a voltage from the power source 65. The collector rotating unit 51 is composed of a pair of

rollers

55 and 56, a motor 57, and the like. The collector 50 is stretched horizontally around a pair of

rollers

55 and 56. A motor 57 disposed outside the spinning chamber 111 is connected to the shaft of one roller 55, and rotates the roller 55 at a predetermined speed. This rotation causes the collector 50 to circulate between the pair of

rollers

55 and 56. In this embodiment, the moving speed of the collector 50 is 10 cm / hour, but is not limited to this.

The support body 60 made of a strip-shaped aluminum sheet (aluminum sheet) is supplied to the collector 50 by the support body supply section 52. The support body 60 in the present embodiment has a thickness of approximately 25 μm. The support 60 is for obtaining the nonwoven fabric 120 by accumulating (depositing) the nanofibers 46. The support body 60 on the collector 50 is wound up by the support body winding part 53. The support body supply unit 52 has a delivery shaft 52a. A support roll 54 is attached to the core 23 of the delivery shaft 52a. The support roll 54 is configured by winding the support 60. The support winding portion 53 has a winding shaft 58. The winding shaft 58 is rotated by a motor (not shown), and the support body 60 on which the nonwoven fabric 120 is formed is wound around the core 61 to be set. The nonwoven fabric 120 is formed by integrating the nanofibers 46. As described above, the nanofiber manufacturing apparatus 110 has a function of manufacturing the nonwoven fabric 120 in addition to the function of manufacturing the nanofiber 46. The moving speed of the collector 50 and the moving speed of the support 60 are preferably the same so that friction does not occur between them. Further, the support body 60 may be placed on the collector 50 and moved as the collector 50 moves.

Note that the nanofibers 46 may be directly accumulated on the collector 50 to form the nonwoven fabric 120. However, depending on the material forming the collector 50, the surface state, and the like, the nonwoven fabric 120 may stick and be difficult to peel off. Therefore, as in this embodiment, it is preferable to guide the support body 60 on which the nonwoven fabric 120 is difficult to stick to the collector 50 and to accumulate the nanofibers 46 on the support body 60.

The power source 65 is a voltage application unit that applies a voltage to the nozzle 13 and the collector 50 to charge the nozzle 13 to the first polarity, and charges the collector 50 to the second polarity opposite to the first polarity. is there. In this embodiment, the nozzle 13 is charged positively (+) and the collector 50 is negatively charged (−). However, the polarity of the nozzle 13 and the collector 50 may be reversed. By passing through the nozzle 13, the solution 25 is charged to the first polarity. In the present embodiment, the voltage applied to the nozzle 13 and the collector 50 is 30 kV.

The distance L2 between the tip opening 13a of the nozzle 13 and the collector 50 varies depending on the type of cellulose acylate and the solvent, the mass ratio of the solvent in the solution 25, etc., but is preferably in the range of 30 mm to 300 mm. In the embodiment, it is 150 mm. When the distance L2 is 30 mm or more, the spun jet 45 formed by jetting is more reliably split by repulsion due to its own charge before reaching the collector 50, compared to a case where the distance L2 is shorter than 30 mm. Therefore, the thin nanofiber 46 can be obtained more reliably. Moreover, since the solvent evaporates more reliably by splitting finely in this way, it is possible to more reliably prevent the non-woven fabric from which the solvent remains. Moreover, since the voltage to apply can be restrained low compared with the case where distance L2 is 300 mm or less and it is too long exceeding 300 mm, abnormal discharge is suppressed.

[Nonwoven fabric]
The nonwoven fabric of this invention is a nonwoven fabric comprised by the nanofiber of this invention mentioned above, for example, as above-mentioned, the nonwoven fabric 120 can be manufactured with the nanofiber manufacturing apparatus 110 shown in FIG.

The nonwoven fabric of the present invention can also be produced by peeling a nanofiber deposit obtained by an electrospinning method from a substrate and subjecting it to a heat treatment.
The contact portion between the nanofibers is strongly bonded by a curing reaction by heating, and a high-strength nonwoven fabric having excellent heat resistance and chemical resistance is obtained. The heating conditions are not particularly limited, and examples include conditions of heating at 150 to 250 ° C. for 10 minutes to 2 hours.
Further, the thickness of the nonwoven fabric of the present invention can be adjusted as appropriate by the amount of nanofibers deposited or by stacking nanofiber deposits of appropriate thickness, and is preferably about 30 nm to 1 mm. More preferably, it is about 100 nm to 300 μm.

The nonwoven fabric of this invention can be used for uses, such as a medical filter, a mask, a heat resistant bag filter, a secondary battery separator, a secondary battery electrode, a heat insulating material, a filter cloth, and a sound absorption material, for example.
Of these, cellulose acylate is preferably used as a medical filter or mask from the viewpoint of excellent biocompatibility. Moreover, when using the nonwoven fabric of this invention as a medical filter or a mask, it can be anticipated that selective separation ability will become high. This is because the nanofiber of the present invention has high uniformity of fiber diameter and high uniformity of voids, so that it has excellent physical selective separation ability. Furthermore, cellulose acylate is both hydrophilic and hydrophobic. This is because it has characteristics and has high chemical selective separation ability.
Moreover, in the case of a heat-resistant bag filter, it can be used as a bag filter for a general waste incinerator or industrial waste incinerator.
Moreover, in the case of a secondary battery separator, it can be used as a separator for a lithium ion secondary battery.
Moreover, in the case of a secondary battery electrode, it can be used as a binder for secondary battery electrode formation by using the deposit of the thermosetting nanofiber before thermosetting. Furthermore, a conductive nonwoven fabric obtained by dispersing and mixing a powder electrode material in the spinning solution of the present invention, electrospinning it, and thermosetting the deposit can also be used as a secondary battery electrode.
Moreover, in the case of a heat insulating material, it can be used as a heat-resistant brick backup material and a combustion gas seal.
In the case of a filter cloth, it can be used as a filter cloth for a microfilter by adjusting the thickness of the nonwoven fabric and the like and adjusting the size of the pores of the nonwoven fabric. By using a filter cloth, solids in a fluid such as liquid or gas can be separated.
Moreover, in the case of a sound absorbing material, it can be used as a sound absorbing material such as a wall surface sound insulation reinforcement and an inner wall sound absorbing layer.

Hereinafter, the present invention will be described in more detail based on examples. The materials, amounts used, ratios, processing details, processing procedures, and the like shown in the following examples can be changed as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be construed as being limited by the following examples.

[Example 1]
Acylation was carried out by mixing cellulose (raw material: cotton linter) with an acylating agent and sulfuric acid as a catalyst and keeping the reaction temperature at 40 ° C. or lower. The acylating agent can be selected from acetic acid, acetic anhydride, propionic acid, propionic anhydride, butyric acid and butyric anhydride, either alone or in combination depending on the desired degree of substitution. In 1, the compound was acylated using acetic acid with an acetyl group (abbreviated as “Ac” in Table 1 below).
After the cellulose as a raw material disappeared and acylation was completed, heating was further continued at 40 ° C. or lower to adjust to a desired degree of polymerization.
Next, an aqueous acetic acid solution was added to hydrolyze the remaining acid anhydride, and then partial hydrolysis was performed by heating at 60 ° C. or lower to adjust the degree of substitution.
The remaining sulfuric acid was neutralized with an excess amount of magnesium acetate. Cellulose acylate was synthesized by reprecipitation from an aqueous acetic acid solution and repeated washing with water.
The synthesized cellulose acylate, dichloromethane 90%, N-methyl-2-pyrrolidone (NMP) was dissolved in 10% of the mixed solvent, the cellulose acylate solution of 4g / 100 cm ³ was prepared, producing nanofiber shown in FIG. 1 Using the apparatus 110, a nonwoven fabric made of cellulose acylate nanofibers of 20 × 30 cm was produced.

[Examples 2 and 3]
A nonwoven fabric composed of nanofibers was produced in the same manner as in Example 1 except that the partial hydrolysis time was changed and the degree of substitution with acetyl groups was intentionally adjusted.

Example 4
A nonwoven fabric made of nanofibers was produced in the same manner as in Example 1 except that the raw material cotton linter was subjected to an alkali purification treatment and the amount of hemicellulose was intentionally adjusted.

Example 5
A nonwoven fabric made of nanofibers was produced in the same manner as in Example 1 except that the raw material was changed from cotton linter to hardwood pulp.

[Examples 6 and 7]
A nonwoven fabric composed of nanofibers was produced in the same manner as in Example 1 except that the reaction time in acylation was changed and the molecular weight was intentionally adjusted.

Example 8
A nonwoven fabric made of nanofibers was produced in the same manner as in Example 1 except that the acyl group was changed from an acetyl group to a propionyl group (abbreviated as “Pr” in Table 1 below).

Example 9
A nonwoven fabric made of nanofibers was produced in the same manner as in Example 1 except that the acyl group was changed from an acetyl group to a butyryl group (abbreviated as “Bu” in Table 1 below).

[Comparative Examples 1 and 2]
A nonwoven fabric composed of nanofibers was produced in the same manner as in Example 1 except that the partial hydrolysis time was changed and the degree of substitution with acetyl groups was intentionally adjusted.

[Comparative Example 3]
A nonwoven fabric composed of nanofibers was produced in the same manner as in Example 8, except that the partial hydrolysis time was changed and the degree of substitution with the propionyl group was intentionally adjusted.

[Comparative Example 4]
A nonwoven fabric composed of nanofibers was produced in the same manner as in Example 9, except that the partial hydrolysis time was changed and the degree of substitution with the butyryl group was intentionally adjusted.

For each synthesized cellulose acylate, the degree of substitution, hemicellulose amount, 6% solution viscosity, number average molecular weight (Mn), weight average molecular weight (Mw), and molecular weight distribution (Mw / Mn) were measured by the methods described above. The results are shown in Table 1 below.

<Evaluation>
Each produced nonwoven fabric was observed visually and using a scanning electron microscope (S-4300, magnification: 1800 times, manufactured by Hitachi, Ltd.), and the uniformity of the nonwoven fabric was evaluated in five stages according to the following criteria. The results are shown in Table 1 below. Two or more points can be used in practice.
Moreover, from the SEM image of each nonwoven fabric, the average fiber length and average fiber diameter of the nanofiber were measured by the method described above, and the aspect ratio (average fiber length / average fiber diameter) was calculated from these values. The results are shown in Table 1 below.
In addition, SEM images obtained by observing the nonwoven fabrics produced in Examples 1 and 2 and Comparative Example 1 are shown in FIGS.
5 points: No defects are observed by visual observation or SEM observation.
4 points: Defects are not visually observed, but a part of the fiber diameter is not uniform in SEM.
3 points: Defects are not visually observed, but many portions with nonuniform fiber diameters are observed with SEM.
Two points: Some defects are visually observed, and many portions with non-uniform fiber diameters are observed with SEM.
1 point: Many non-uniform | heterogenous parts are seen by both visual observation and SEM.

From the results shown in Table 1, it was found that when cellulose acylate having a substitution degree of less than 2.75 was used, the uniformity was inferior regardless of the type of substituent, the amount of hemicellulose, the 6% solution viscosity, etc. ( Comparative Examples 1 to 4).
On the other hand, it was found that when cellulose acylate having a degree of substitution of 2.75 or more and 2.95 or less was used, the fiber diameter of nanofibers was excellent in uniformity and the appearance of the nonwoven fabric was improved (implementation) Examples 1-9).
In particular, from the comparison of Examples 2, 4 and 5, when the amount of hemicellulose is in the range of 0.1 to 3.0, the uniformity of the fiber diameter of the nanofiber becomes better and the appearance of the nonwoven fabric becomes better. I understood that.
In addition, from the comparison between Examples 2, 6 and 7, it is found that when the 6% solution viscosity is 300 mPa · s or more, the uniformity of the fiber diameter of the nanofibers becomes better and the appearance of the nonwoven fabric becomes better. It was.
Further, from the comparison of Examples 1 to 3, it can be seen that when the degree of substitution is 2.80 to 2.95, the uniformity of the fiber diameter of the nanofiber becomes better and the appearance of the nonwoven fabric becomes better, It was found that when the degree of substitution was 2.88 to 2.95, the uniformity of the fiber diameter of the nanofibers was further improved, and the appearance of the nonwoven fabric was further improved.

13 Nozzle 13a Tip opening 13b Tip opening edge 15 Accumulation part 23 Core 25 Solution 30 Storage container 31 Pump 32 Pipe 44 Taylor cone 45 Spinning jet 46 Nanofiber 50 Collector 51 Collector rotating part 52 Support supply part 52a Delivery shaft 53 Support Body winding part 54 Support body roll 55 Roller 56 Roller 57 Motor 58 Winding shaft 60 Support body 61 Core 65 Power source 110 Nanofiber production apparatus 111 Spinning chamber 112 Solution supply part 120 Non-woven fabric 133 First temperature controller 134 Cover 134a Opening 135 Second temperature controller P Pump M Motor L2 Distance

Claims

A nanofiber containing cellulose acylate having a substitution degree satisfying the following formula (1).
2.75 ≦ degree of substitution ≦ 2.95 (1)
The nanofiber according to claim 1, wherein the ratio of the average fiber length to the average fiber diameter is 1000 or more.
3. The nanofiber according to claim 1 or 2, wherein the average fiber diameter is 50 to 800 nm.
The nanofiber according to any one of claims 1 to 3, wherein the average fiber length is 500 µm or more.
The nanofiber according to any one of claims 1 to 4, wherein the acyl group of the cellulose acylate is an acetyl group.
6. The nanofiber according to claim 1, wherein the cellulose acylate has a hemicellulose content of 0.1 to 3.0% by mass.
The nanofiber according to any one of claims 1 to 6, wherein the viscosity of a solution obtained by dissolving 6% by mass in dichloromethane is 300 mPa · s or more.
A nonwoven fabric comprising the nanofiber according to any one of claims 1 to 7.
The nonwoven fabric according to claim 8, which is used for medical filters or masks.