JP2015081392A - Nanofiber nonwoven fabric containing metal oxide as main component - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nanofiber nonwoven fabric containing a metal oxide as a main component that is excellent in flexibility and tensile strength.SOLUTION: The nanofiber nonwoven fabric is mainly composed of a nanofiber containing a metal oxide as a main component and having a fiber diameter of 0.2 μm to 1.0 μm, and has a flexural rigidity of 0.01 to 0.05×10NM/m and a flexural hysteresis of 0.01 to 0.20×10NM/m. The component constituting the nanofiber may have an amorphous structure or the component constituting the nanofiber may comprise a crystal phase having a crystallite diameter of 2.4 to 11.8 nm.

Description

The present invention relates to a nanofiber nonwoven fabric mainly composed of a metal oxide. Specifically, the present invention relates to a nanofiber nonwoven fabric that is rich in flexibility and has physical properties that can be used in various applications.

Metal oxide fiber has excellent properties such as heat resistance, heat insulation, and dimensional stability in high temperature atmospheres, but also has hard and brittle properties. In addition, there are drawbacks such as careful handling in the manufacture of products using metal oxide fibers. Therefore, even in a non-woven fabric that is a fabric formed of metal oxide fibers, it is difficult to form a non-woven fabric having flexibility while maintaining the tensile strength, including defects due to the characteristics of the metal oxide fibers themselves. Have difficulty.

In this respect, since the flexibility of fibers is generally improved by reducing the fiber diameter, studies have been conducted to improve the above-mentioned drawbacks by reducing the fiber diameter of metal oxide fibers to the nano level. Various proposals have been made. However, for non-woven fabrics mainly composed of metal oxides, even if the fiber diameter is reduced to the nano level, the fibers can be easily folded by applying bending stress, and the shape of the non-woven fabric is broken by breaking the fibers. It has not yet been improved on the defects caused by the basic properties of metal oxide fibers.

Patent Document 1 discloses an alumina molding having a porous structure in which alumina nanofibers having an aspect ratio of 30 to 5,000 converge and a converging body having a width of 3 to 70 mm is irregularly entangled. The body is disclosed.

In Patent Document 2, when spinning an undiluted spinning solution prepared by dissolving an inorganic salt (halide) and a polymer, and spinning to produce an inorganic fiber assembly, from the spinning process to the transporting process to a firing furnace. Is performed in an atmosphere with a relative humidity of 35% or less to prevent a decrease in physical properties of the inorganic fiber sheet.

In Patent Document 3, when spinning a spinning stock solution composed of an inorganic sol by an electrostatic spinning method, the spinning stock solution is supplied to an atmosphere having a humidity of 40% or less, and the formed gel fiber is 10% or more from the supply ambient humidity. A method is disclosed in which after being exposed to a high humidity atmosphere, the fibers are accumulated to form a fiber web, and then fired to produce an inorganic fiber sheet. This method is a method of firing after exposure to a high-humidity atmosphere in order to prevent deterioration in physical properties of the spinning atmosphere and the obtained fiber web, as in Patent Document 2.

JP 2012-36034 A JP 2009-235629 A JP 2009-263802 A

In Patent Document 1, it is described that the obtained convergent body has flexibility like paper, and as a basis for this, the flexibility of the obtained convergent body is expressed as a mandrel diameter (JIS K5600-5-1). ) And the mandrel diameter is 10 to 15 mm, so that it is excellent in flexibility. However, the mandrel diameter of 10 to 15 mm also indicates that the converging body breaks when wound around a 10 to 15 mm diameter rod. In other words, it means that the convergent body is bent by bending with a radius of curvature of 10 to 15 mm, and a problem still remains in flexibility. Moreover, in the softness | flexibility with a mandrel diameter of 10-15 mm, the convergence body will only receive the tensile stress and the bending stress, and the fiber which comprises a convergence body will occur easily. Since the tensile strength of the cut portion is also impaired, there remains a problem in terms of tensile strength.

Patent Documents 2 and 3 describe that an inorganic fiber sheet is obtained by an electrostatic spinning method. Specifically, by setting the relative humidity to 35% or less, it is possible to reduce the influence of moisture absorption of fibers, suppress the integration of fibers and film formation, and obtain an inorganic fiber sheet having a certain area. It is. In general, the fiber sheet before firing is sensitive to humidity, and the fiber surface may be dissolved. However, it is another problem that inorganic fibers having a certain area can be obtained and whether or not the obtained inorganic fiber sheets have flexibility, and these documents describe the flexibility of the obtained inorganic fiber sheets. There is no indication of performance such as sex.

In other words, from the viewpoint of handling of the nanofiber nonwoven fabric mainly composed of the obtained metal oxide, it is not sufficient to simply establish it as a nanofiber nonwoven fabric, and the nonwoven fabric has sufficient flexibility, tensile strength, and bending stress. On the other hand, it is necessary to consider whether it has a performance such as being hard to break. Moreover, it can process into the goods for various uses using this nonwoven fabric performance with the nonwoven fabric which has the said performance.

Therefore, as a result of intensive studies, the present inventors have found that a nanofiber nonwoven fabric mainly composed of a metal oxide having improved flexibility while maintaining tensile strength can be obtained by paying attention to the viscosity of the spinning dope. .

This invention is made | formed in view of the said subject, The objective is to provide the nanofiber nonwoven fabric which has a metal oxide which is excellent in a softness | flexibility and tensile strength as a main component.

A nanofiber nonwoven fabric according to an embodiment of the present invention is a nanofiber nonwoven fabric mainly composed of a nanofiber having a metal oxide as a main component and a fiber diameter of 0.2 μm to 1.0 μm, and has a flexural rigidity value of 0.00. The above-mentioned problem is solved by being 01 to 0.05 × 10 ⁻⁴ NM ² / m and the bending hysteresis value being 0.01 to 0.20 × 10 ⁻² NM / m.

Generally, the thinner the fiber diameter of the nanofiber, the more contributes to the flexibility of the nonwoven fabric. However, if the fiber diameter is too thin, the tensile strength becomes too small, which is not preferable. If it is too thick, the tensile strength increases but the flexibility is impaired. Therefore, the fiber diameter having sufficient tensile strength and flexibility is set in the range of 300 to 700 nm.

In addition, regarding the flexibility, the method for measuring the mandrel diameter (JIS K5600-5-1) described above cannot sufficiently evaluate the degree of flexibility of the nonwoven fabric, which is the subject of the present invention, and therefore a bending tester. The flexibility is evaluated by measuring the bending stiffness value and the bending hysteresis value. In general, since the bending stiffness value of fabric, paper, and yarn shows a value of 0.1 × 10 ⁻⁴ NM ² / m or more, the bending stiffness value is 0.1 × 10 ⁻⁴ NM ² / m or less. It can be said that it is 01-0.05 * 10 < ^-4 > NM < ² > / m that the softness | flexibility is improving significantly compared with a fabric, paper, and a thread | yarn.

Furthermore, the bending hysteresis value is related to the ease of wrinkles and creases, and in general, when the bending hysteresis value exceeds 0.20 × 10 ⁻² NM / m, it can be said that wrinkles and creases are likely to occur. That is, in the range of 0.20 × ¹⁰ -2 NM / m less 0.01~0.20 × ¹⁰ -2 NM / m, indicating that hardly marked with folds

The nanofiber nonwoven fabric according to an embodiment of the present invention solves the above-described problem by the metal oxide of the nanofiber having an amorphous structure.

When the crystal structure of the component constituting the nanofiber forming the nonwoven fabric is measured by XRD, it can be confirmed that the crystal state varies depending on the degree of firing. Here, in the state where sufficient crystals are not observed in the XRD measurement, in other words, when it can be said that the crystal structure of the component constituting the nanofiber forming the nonwoven fabric is an amorphous structure, the above-mentioned excellent bending rigidity And has bending hysteresis. That is, it can be said that it is a nanofiber nonwoven fabric excellent in flexibility and tensile strength.

The nanofiber nonwoven fabric which concerns on one form of this invention solves the said subject because the size of the crystallite of the metal oxide of the said nanofiber is 2.4-11.8 nm.

For the crystal structure of the components constituting the nanofiber forming the nonwoven fabric, even when crystallization is confirmed in the XRD measurement, the observed crystallite diameter is 2.4 to 11.8 nm, In the same manner as above, the nanofiber nonwoven fabric is excellent in flexibility and tensile strength.

ADVANTAGE OF THE INVENTION According to this invention, the nanofiber nonwoven fabric which has a metal oxide which is excellent in a softness | flexibility and strength as a main component can be provided.

It is a schematic diagram which shows an example of the electrospinning apparatus used for manufacture of the nanofiber nonwoven fabric of this invention. It is a figure which shows the XRD chart at the time of baking at 700 degreeC about an example of the nanofiber nonwoven fabric of this invention, using polyvinyl alcohol (PVA) for a spinning aid. It is a figure which shows an XRD chart at the time of baking at 700 degreeC about an example of the nanofiber nonwoven fabric of this invention, using pullulan as a spinning aid. It is a figure which shows an XRD chart at the time of baking at 900 degreeC about an example of the nanofiber nonwoven fabric of this invention, using pullulan as a spinning aid. It is a figure which shows an XRD chart at the time of baking at 1000 degreeC about an example of the nanofiber nonwoven fabric of this invention, using pullulan as a spinning aid. It is a figure which shows an XRD chart at the time of baking at 1200 degreeC about an example of the nanofiber nonwoven fabric of this invention, using pullulan as a spinning aid. 1 is a scanning electron microscope (hereinafter abbreviated as “SEM”) photograph of a fiber surface when an example of the nanofiber nonwoven fabric of the present invention is obtained by using pullulan as a spinning aid and firing at 700 ° C. FIG. It is a SEM photograph of the fiber surface at the time of baking at 1000 degreeC about an example of the nanofiber nonwoven fabric of this invention, using pullulan as a spinning aid. It is a SEM photograph of the fiber surface at the time of baking at 1200 degreeC about an example of the nanofiber nonwoven fabric of this invention, using pullulan as a spinning aid. It is a photograph which shows the state which hold | gripped both ends of an example of the nanofiber nonwoven fabric of this invention by the hand, and was extended | stretched in the plane direction.

Hereinafter, embodiments of the present invention will be described in detail.

In the present invention, the nanofiber nonwoven fabric is obtained as follows. A metal organic compound aqueous solution and a spinning aid are mixed to obtain a spinning dope. The obtained spinning dope is spun by electrospinning to obtain a precursor nonwoven fabric. The obtained precursor nonwoven fabric is fired to obtain a nonwoven fabric.

Al ₂ O ₃ , SiO ₂ , or TiO ₂ is used as the metal oxide that is the main component of the nanofiber nonwoven fabric of the present invention. These metal oxides are not water soluble. Therefore, a metal organic compound aqueous solution containing Al, Si, and Ti is used as the spinning dope. As the alumina source used as the spinning dope, for example, aluminum oxychloride and aluminum isopropoxide can be used. As the silica source, for example, tetramethoxysilane or tetraethoxysilane can be used. As the titania source, for example, titanium tetraisopropoxide and titanium lactate can be used. However, it is not limited to these, What is necessary is just to contain Al, Si, and Ti on the composition, respectively, and to melt | dissolve in water.

A mixed aqueous solution of these metal organic compounds can also be used. For example, a combination of Al and Si, Al and Ti, or Si and Ti. When setting it as a 2 types mixture, it is preferable that the mixing ratio of a metal oxide component shall be 40: 60-60: 40 by weight ratio.

As the spinning aid, any compound can be used as long as it increases the viscosity of the spinning dope and enables stable spinning. Among these, water-soluble polymers and water-soluble polysaccharides that have spinnability and are not decomposed by heating during firing to leave a residue can be preferably used. Examples of the water-soluble polymer include polyvinyl alcohol, polyvinyl pyrrolidone, and polyethylene glycol. Examples of water-soluble polysaccharides include pullulan, carrageenan, sodium alginate, trihalose, polyglutamic acid, carboxymethylcellulose (CMC), and agarose. Among them, pullulan and carrageenan can be preferably used.

A spinning dope using pullulan as a spinning aid greatly improves the stretchability during spinning. When the stretchability is improved, the fiber diameter can be reduced. Generally, when the fiber diameter is reduced, the flexibility of the fiber is improved. Further, by stretching during spinning, the molecules are aligned and the tensile strength is improved. Therefore, nanofibers excellent in flexibility and tensile strength can be obtained. Further, since the improvement in flexibility makes it difficult for cutting during spinning, nanofibers having an aspect ratio of at least 100 or more can be obtained.

Lactic acid can also be used as a spinning aid. Lactic acid can be preferably used when electrostatic repulsion is large during electrospinning.

In addition, when the surface tension of the spinning dope is large, more stable spinning is possible by using an alcohol having an action of lowering the surface tension of the spinning dope, for example, isopropyl alcohol as a surface tension adjusting agent.

The nanofiber nonwoven fabric of the present invention is obtained by using an electrospinning method. In FIG. 1, the schematic diagram of the electrospinning apparatus 1 is shown. First, the above-mentioned water-soluble metal organic compound and a spinning aid are mixed to prepare a metal oxide sol that is a spinning dope 2. If the concentration of the spinning dope is low, the concentration is increased by heating. The spinning dope 2 is stored in the spinning dope storage cylinder 3 of the electrospinning apparatus 1. The spinning stock solution storage cylinder 3 preferably includes a pusher 4 for extruding the spinning stock solution 2 from the spinning stock solution storage tube 3. The spinning stock solution storage cylinder 3 includes a nozzle 5 for discharging the spinning stock solution 2 on the side opposite to the presser 4. By pressing the pusher 4, pressure is applied to the spinning solution stored in the spinning solution storage cylinder 3, and the spinning solution is discharged from the nozzle 5 provided in the spinning solution storage cylinder 3. Even if the presser 4 is not necessarily provided, the spinning solution can be discharged from the nozzle 5 only by electrostatic force generated by charging the spinning solution and can be spun.

A collector 6 for forming a nanofiber nonwoven fabric is installed in the discharge direction of the nozzle 5. The spinning dope 2 and the collector 6 are applied and charged so as to have opposite polarities. That is, when a positive voltage is applied to the spinning stock solution storage cylinder 3, a negative voltage is applied to the collector 6. The reverse is also possible. A voltage of 20 to 80 kv is applied to the spinning dope 2 and the collector 6. The spinning dope 2 charged and discharged from the nozzle 5 is split into countless fine fibers by the repulsive force of electrostatic force, and the solvent is instantly evaporated to form ultrafine fibers 7 having a fine diameter. Here, the collector 6 is arranged so that the ultrafine fibers 7 can be collected in the scattering direction of the ultrafine fibers 7. The scattered ultrafine fibers 7 are collected by the collector 6 and accumulated on the collector 6. Accumulation of the ultrafine fibers 7 is synonymous with the formation of the precursor nonwoven fabric. The formed precursor nonwoven fabric can be removed from the collector 6 with bare hands. By appropriately changing the shape of the collector 6, the shape of the obtained nanofiber nonwoven fabric can be freely formed.

Next, the obtained nanofiber precursor nonwoven fabric is fired at 300 to 1200 ° C. in the air using an electric furnace to obtain a nanofiber nonwoven fabric mainly composed of a metal oxide. Here, it is not preferable that the heating and baking temperature is 300 ° C. or less because baking may be insufficient and organic substances that are not completely decomposed may remain in the nonwoven fabric. In addition, when the firing temperature is 1200 ° C. or higher, the organic matter is sufficiently decomposed, but this is not preferable because the crystallization of the metal oxide proceeds and the fiber may become brittle. Therefore, firing is preferably performed in the range of 300 to 1000 ° C, more preferably in the range of 400 to 800 ° C.

By firing the precursor nonwoven fabric, crystallization of components constituting the nanofibers constituting the nonwoven fabric proceeds, and the tensile strength and heat resistance of the nanofibers are improved. In addition, although a baking residue may remain depending on baking conditions, the main body of a nonwoven fabric is the nanofiber which has a metal oxide as a main component.

The relationship between the firing temperature of the precursor nonwoven fabric and the crystallization of the components constituting the nanofiber and the relationship with the crystallite diameter will be described using the measurement results of XRD. Here, the case where alumina is used as the metal oxide will be described.

In the description, an example of the nanofiber nonwoven fabric of the present invention will be described with reference to FIG. 2 which shows an XRD chart when PVA is used as a spinning aid and fired at 700 ° C. Moreover, about an example of the nanofiber nonwoven fabric of this invention, the XRD chart at the time of using a pullulan for a spinning aid is shown in FIGS. 3-6, and is demonstrated. 3 to 6 show different firing temperatures, FIG. 3 shows a case of firing at 700 ° C., FIG. 4 shows a firing temperature of 900 ° C., FIG. 5 shows a firing temperature of 1000 ° C., and FIG.

Furthermore, the crystal phase and the crystallite diameter of the component which comprises the nanofiber which forms a nonwoven fabric at the time of using a pullulan for a spinning aid are shown in Table 1-Table 3, and are demonstrated. Tables 1 to 3 have different firing temperatures, Table 1 shows a case of 900 ° C, Table 2 shows a case of 1000 ° C, and Table 3 shows a case of firing at 1200 ° C. And the said FIG. 4 and Table 1, FIG. 5 and Table 2, FIG. 6 and Table 3 have a corresponding relationship, respectively, and shows the case of the same nonwoven fabric. Hereinafter, each case will be described.

FIG. 2 is an XRD chart of a nanofiber nonwoven fabric mainly composed of alumina obtained by firing a precursor nonwoven fabric obtained by using PVA as a spinning aid at 700 ° C. as described above. From FIG. 2, although a weak peak can be confirmed at a position of 2θ = 67 °, a peak cannot be confirmed in other ranges, and a strong peak as a whole cannot be confirmed. Therefore, it can be seen that the proportion of crystals in the entire material constituting the nanofiber nonwoven fabric is low. This is considered to indicate an amorphous structure. That is, it can be said that the nanofiber nonwoven fabric containing alumina as a main component when PVA is used as a spinning aid and fired at 700 ° C. has an amorphous structure.

FIG. 3 is an XRD chart of a nanofiber nonwoven fabric mainly composed of alumina obtained by firing a precursor nonwoven fabric using pullulan as a spinning aid at 700 ° C. as described above. From FIG. 3, a continuous weak peak can be confirmed in the vicinity of 2θ = 25 ° or at a position of 2θ = 25 ° to 2θ = 35 °, and a weak peak can also be confirmed at a position around 2θ = 58 ° or 2θ = 62 °. However, as in the case of FIG. 2, a strong peak as a whole cannot be confirmed. Therefore, it can be said that the nanofiber nonwoven fabric mainly composed of alumina when it is fired at 700 ° C. using pullulan as a spinning aid shows an amorphous structure.

The nanofiber nonwoven fabric in this case has been confirmed in advance to be excellent in flexibility and tensile strength. However, the component of the nanofiber forming the nonwoven fabric has an amorphous structure, which affects the flexibility of the nanofiber. I think to do. In the case of an amorphous structure, it is considered that molecular bonding becomes flexible and flexibility can be obtained.

FIG. 4 is an XRD chart of a nanofiber nonwoven fabric mainly composed of alumina obtained by firing a precursor nonwoven fabric obtained using pullulan as a spinning aid at 900 ° C. as described above. Table 1 shows the crystal phase and crystallite diameter in this case as described above.

First, it can be confirmed from Table 1 that the crystal phase is aluminum oxide, and the crystallite diameter is in the range of 2.41 nm to 11.78 nm (24.06 to 117.80 mm). It can be confirmed that it is a mixture. Further, from FIG. 4, peaks can be confirmed around 2θ = 46 ° and 2θ = 68 °, and peaks can also be confirmed around 2θ = 37 °. However, since a sufficiently strong peak cannot be confirmed in other ranges, it is considered that crystallization has not progressed completely.

The nanofiber nonwoven fabric in this case has also been confirmed in advance to be excellent in flexibility and tensile strength. However, the crystallite diameter of the component constituting the nanofiber forming the nonwoven fabric is small, and crystallization proceeds completely. This is thought to affect the ability to obtain excellent flexibility.

FIG. 5 is an XRD chart of a nanofiber nonwoven fabric mainly composed of alumina obtained by firing a precursor nonwoven fabric obtained using pullulan as a spinning aid at 1000 ° C. as described above. Table 2 shows the crystal phase and crystallite diameter in this case as described above.

First, it can be confirmed from Table 2 that the crystal phase is a mixed phase of η-alumina phase and corundum (α-alumina) phase. It can be confirmed that the crystallite diameter is in the range of 5.68 to 56.91 nm (56.81 to 569.07 mm). Further, it can be confirmed from FIG. 5 that the portion showing a strong peak is also a portion of the corundum phase. Compared with the nanofiber nonwoven fabric fired at 900 ° C., the flexibility is relatively inferior, but it is not a nonwoven fabric that can be easily folded and has no problem in handling. This is thought to be due to the fact that the fiber diameter of the nanofibers constituting the nanofiber nonwoven fabric is sufficiently thin.

FIG. 6 is an XRD chart of a nanofiber nonwoven fabric mainly composed of alumina obtained by firing a precursor nonwoven fabric obtained using pullulan as a spinning aid at 1200 ° C. as described above. Table 3 shows the crystal phase and crystallite diameter in this case as described above.

First, it can be confirmed from Table 3 that the crystal phases are all corundum (α-alumina) phases and the crystallite diameter is in the range of 29.66 to 79.64 nm (296.57 to 796.44 mm). It can be said that crystallization is completely advanced. Moreover, it can confirm that a crystalline phase shows a strong peak from FIG. This indicates that the nanofiber is hard and brittle.

The nanofiber nonwoven fabric in this case has been confirmed in advance to be inferior in flexibility and tensile strength compared to the conventional cases, and when the degree of crystallization progresses to some extent, the nanofiber becomes hard and brittle. Conceivable.

The SEM photograph of the fiber surface of an example of the nanofiber nonwoven fabric of this invention is shown in FIGS. Among these, FIG. 7 (a) shows a fiber surface of a nanofiber nonwoven fabric mainly composed of alumina obtained by firing a precursor nonwoven fabric obtained by using pullulan as a spinning aid at 700 ° C. by a factor of 5000. FIG. 7B is an enlarged SEM photograph in which numerical values are displayed for a part of the fiber diameter. FIG.7 (c) expanded the fiber surface of the nanofiber nonwoven fabric obtained by baking at 700 degreeC similarly to FIG.7 (a), (b) by 10000 time, and numerically displayed about some fiber diameters. It is a SEM photograph.

From the SEM photographs of FIGS. 7A to 7C, nanofibers having a fiber diameter of at least 0.27 μm (270 nm) to 0.69 μm (690 nm) can be confirmed. Moreover, 0.97 micrometer (970 nm) nanofibers can also be confirmed in terms of the scale in the SEM photograph.

FIG. 8 (a) enlarges the fiber surface of a nanofiber nonwoven fabric mainly composed of alumina obtained by firing a precursor nonwoven obtained using pullulan as a spinning aid at 1000 ° C. by a factor of 5000, FIG. 8B is an SEM photograph showing numerical values for a part of the fiber diameters. FIG. 8B is an SEM showing the same nanofiber nonwoven fabric as FIG. It is a photograph.

From the SEM photographs of FIG. 8A and FIG. 8B, nanofibers having a fiber diameter of at least 0.24 μm (240 nm) to 0.71 μm (710 nm) can be confirmed.

FIG. 9 (a) is an SEM in which the fiber surface of a nanofiber nonwoven fabric mainly composed of alumina obtained by firing a precursor nonwoven fabric obtained using pullulan as a spinning aid at 1200 ° C. is magnified 5000 times. It is a photograph. Moreover, FIG.9 (b) is the SEM photograph which expanded the fiber surface of the same nanofiber nonwoven fabric as Fig.9 (a) by 10000 time, and FIG.9 (c) shows numerical display about a part of fiber diameter to this. It is the SEM photograph which was done.

From the SEM photographs of FIGS. 9A to 9C, nanofibers having a fiber diameter of at least 0.22 μm (220 nm) to 0.30 μm (300 nm) can be confirmed.

From the above, according to the SEM photographs of FIGS. 7 to 9, nanofibers having a fiber diameter of 0.2 μm to 1.0 μm can be confirmed. Moreover, when the aspect ratio was calculated from the fiber length in all the SEM photographs of FIGS. 7 to 9, it can be confirmed that the aspect ratio is at least 100 or more.

FIG. 10 shows a photograph showing a state in which one end of a nanofiber nonwoven fabric as an example of the nanofiber nonwoven fabric of the present invention and the other end facing the nanofiber nonwoven fabric are gripped by hand and stretched in the plane direction. The nanofiber nonwoven fabric of FIG. 10 is a nanofiber nonwoven fabric mainly composed of alumina obtained by firing a precursor nonwoven fabric obtained using pullulan as a spinning aid at 900 ° C. The nanofiber nonwoven fabric did not break even when stretched until the wrinkles on the surface of the nanofiber nonwoven fabric were completely eliminated. That is, it can be said that the nanofiber nonwoven fabric has sufficient tensile strength. Moreover, since it is excellent also in a softness | flexibility, it can process into the goods which can be used for the various uses which utilized this characteristic.

Hereinafter, the present invention will be described specifically by way of examples. The nanofiber nonwoven fabric mainly composed of alumina is hereinafter referred to as “alumina nanofiber nonwoven fabric”, and the nanofiber nonwoven fabric mainly composed of PVA is hereinafter referred to as “PVA nanofiber nonwoven fabric”.

[Example 1] (Alumina nanofiber nonwoven fabric; firing temperature 700 ° C.)
As a water-soluble organometallic compound of aluminum, 11.8 g of aluminum oxychloride and 0.9 g of pullulan as a spinning aid were mixed to prepare a spinning dope. In order to perform spinning by electrospinning and obtain a nanofiber nonwoven fabric, an apparatus having the same configuration as the electrospinning apparatus shown in FIG. 1 was used as the spinning dope.

Here, when the distance between the nozzle and the collector was 20 cm and a voltage of 23 kv was applied between the nozzle and the collector, the spinning stock solution was discharged from the nozzle toward the collector, and the dried precursor nonwoven fabric was accumulated on the collector. The obtained precursor nonwoven fabric was removed from the collector and baked for 1 hour in an electric furnace heated to 700 ° C. in air to obtain an alumina nanofiber nonwoven fabric.

It was confirmed that the obtained alumina nanofiber nonwoven fabric was very flexible and had a tensile strength that would not be torn even if pulled by hand.

[Comparative Example 1] (PVA nanofiber nonwoven fabric)
PVA having an average polymerization degree of 2000 and a saponification degree of 98% was made into an aqueous solution having a concentration of 10 wt% to prepare a spinning dope. As with the alumina nanofiber nonwoven fabric, the precursor nonwoven fabric was obtained by performing the same conditions using the apparatus used for the production of the alumina nanofiber nonwoven fabric for spinning by the electrospinning method. The obtained precursor nonwoven fabric was sandwiched between two iron plates, put into a dryer, and heat treated at 200 ° C. for 1 minute to obtain a PVA nanofiber nonwoven fabric.

Various physical properties of the alumina nanofiber nonwoven fabric of Example 1 were measured using the PVA nanofiber nonwoven fabric, glass filter paper, and cellulose filter paper of Comparative Example 1 as comparative objects.

The following samples were used for the measurement. Sample A is the alumina nanofiber nonwoven fabric of Example 1 (thickness 94 to 96 μm, basis weight 167 g / m ² ). Moreover, the PVA nanofiber nonwoven fabric of Comparative Example 1 (thickness: 45 to 53 μm, basis weight: 6.6 g / m ² ) is designated as sample B. The glass filter paper as a sample C (Whatman GF / A, thickness 240 .mu.m, basis weight 54 g / m ^2), using the cellulose filter paper (ADVANTEC5A, thickness 200 [mu] m, basis weight 103 g / m ²⁾ as a sample D. Each sample was cut into a strip shape having a width of 10 mm and a length of 20 mm.

(Measurement of tensile strength)
Using Sample A, Sample B and Sample C, the tensile strength was measured. Each sample was cut out as a strip sample having a width of 10 mm and a length of 20 mm. The tensile strength was measured using an RTG-1310 type Tensilon manufactured by A & D Co., Ltd. at a tensile speed of 30 mm / min. The measurement results are shown in Table 4.

From Table 4, it was confirmed that the alumina nanofiber nonwoven fabric of Sample A had sufficient tensile strength.

(Measurement of ventilation resistance)
Using Sample A, Sample B, Sample C, and Sample D, the airflow resistance was measured. For the measurement of the ventilation resistance, a testing machine manufactured by Kato Tech Co., Ltd., KES-F8-API was used. The measurement of the airflow resistance was performed for each sample with one sheet and two sheets. The measurement results are shown in Table 5.

From the measurement results in Table 5, it was confirmed that the ventilation resistance of the alumina nanofiber nonwoven fabric (Sample A) was small.

[Example 2] (Alumina nanofiber nonwoven fabric; firing temperature 1000 ° C.)
An alumina nanofiber nonwoven fabric was obtained in the same manner as in Example 1 except that it was fired in an electric furnace heated to 1000 ° C. for 1 hour. Sample A is the alumina nanofiber nonwoven fabric of Example 2 (thickness 94 to 96 μm, basis weight 167 g / m ² ).

(Measurement of flexibility)
Using Sample A, Sample B, Sample C, Sample D, and Sample E, the flexibility was measured. Flexibility was measured in terms of bending stiffness. For measurement of bending rigidity, an automated pure bending tester, KES-FB2-AUTO-A, manufactured by Kato Tech Co., Ltd. was used. The measurement results are shown in Table 6.

The larger the value is, the more difficult the bending rigidity is to bend, and the larger the value is, the lower the hysteresis is, the lower the recovery is (Nm is torque). In the case of a fabric, it is rare that the bending rigidity value is 1.0 × 10 ⁻⁴ NM ² / m or less and the bending hysteresis is 0.20 × 10 ⁻² NM / m or less. In view of this point, from Table 6, it was confirmed that the alumina nanofiber nonwoven fabric of Sample A was provided with extremely high flexibility, and it was confirmed that it was difficult to bend due to the low bending hysteresis value. On the other hand, the alumina nanofiber nonwoven fabric of Sample E has a larger bending rigidity value than Sample A, but it has been confirmed that it has sufficient flexibility. However, since the bending hysteresis value exceeded 0.1 × 10 ⁻² NM / m, it was confirmed that it was easy to be wrinkled or creased as compared with Sample A.

The metal oxide originally has excellent properties such as heat resistance, heat insulation, and dimensional stability in a high temperature atmosphere as described above, and in addition to this, the nanofiber nonwoven fabric of the present invention is extremely excellent in flexibility, In addition, since it has excellent tensile strength and low ventilation resistance when gas is permeated, it can be processed into products for various applications. In particular, technical fields that utilize the characteristics of excellent heat resistance and large specific surface area of nanofibers, such as heat insulating materials, soundproofing materials, adsorbents, filters, catalyst carriers, various fields such as exhaust gas filters and dust masks Application expansion to can be expected.

DESCRIPTION OF SYMBOLS 1 ... Electrospinning apparatus 2 ... Spinning stock solution 3 ... Spinning stock solution storage cylinder 4 ... Pusher 5 ... Nozzle 6 ... Collector 7 ... Extra fine fiber

Claims (3)

A nanofiber nonwoven fabric mainly composed of nanofibers having a metal oxide as a main component and a fiber diameter of 0.2 μm to 1.0 μm,
Nanofiber nonwoven fabric characterized by a bending stiffness value of 0.01 to 0.05 × 10 ⁻⁴ NM ² / m and a bending hysteresis value of 0.01 to 0.20 × 10 ⁻² NM / m. .   The nanofiber nonwoven fabric according to claim 1, wherein the component constituting the nanofiber has an amorphous structure.   The nanofiber nonwoven fabric according to claim 1, wherein a crystallite diameter of a component constituting the nanofiber is 2.4 to 11.8 nm.