JP4612476B2 - Method for producing zirconia fiber - Google Patents

Description

  The present invention relates to a method for producing zirconia fibers. More specifically, the present invention relates to a method for producing zirconia fibers useful as a filler or filter having excellent heat resistance.

  A ceramic fiber is a useful material used in various fields such as an electrical insulating material, a heat insulating material, a filler, and a filter by making use of properties such as electrical insulation, low thermal conductivity, and high elasticity. Ordinary ceramic fibers are produced by a melting method, a spindle method, a blowing method, or the like, and the fiber diameter is generally several μm (for example, see Patent Document 1). In particular, in the field of fillers and filters, thinner fibers have been required to increase the adhesion area with the matrix material and improve the filter efficiency.

  On the other hand, an electrospinning method is known as a method for producing fibers thinner than conventional fibers, centering on materials made of organic polymers. In the electrospinning method, a high voltage is applied to a solution in which a fiber-forming solute such as an organic polymer is dissolved, so that the solution is ejected toward the electrode, and the solvent is evaporated by the ejection. This is a method by which a structure can be obtained (see, for example, Patent Document 2).

  In addition, a method for producing a ceramic fiber by an electrospinning method is known (for example, see Patent Document 3). However, in this method, it is necessary to adjust the viscosity of the solution by the sol-gel method, and it is considered that it is very difficult to perform stable spinning, and the produced ceramic fibers are mostly composed of silica components. Therefore, it can be considered that it cannot be used for applications requiring heat resistance.

  Moreover, the method of producing a zirconia fiber by the electrospinning method is known (refer patent document 4). However, in this method, since it is necessary to perform a sol-gel reaction in order to prepare the spinning solution, there is a problem that a multi-stage preparation process has to be performed. In addition, it is necessary to add an organic polymer in order to give spinnability to the solution. Further, since the concentration of the zirconium derivative in the solution is limited by the solubility of the zirconium sol, the zirconia fiber before firing is limited. The ratio of the organic polymer contained therein is increased, so that there is a problem that the zirconia fiber after firing is likely to have a low strength.

JP 2003-105658 A JP 2002-249966 A JP 2003-73964 A International Publication No. 2005/026398 Pamphlet

  This invention is providing the manufacturing method of a zirconia fiber excellent in heat resistance and with a small fiber diameter.

As a result of intensive studies in view of the above prior art, the present inventors have completed the present invention.
That is, the object of the present invention is to
A step of dissolving a fiber-forming solute in an aqueous solution in which zirconium chloride soluble in water is dissolved, a step of spinning from the aqueous solution in which the fiber-forming solute is dissolved by an electrostatic spinning method, and the spinning. A zirconia fiber having an average fiber diameter of 50 to 1000 nm and a fiber length of 100 μm or more, comprising a step of obtaining a fiber structure accumulated on a collection substrate and a step of firing the accumulated fiber structure. This is achieved by the manufacturing method.

  Since the zirconia fiber produced by the production method of the present invention has a small average fiber diameter and a fiber length of 100 μm or more, it is effective as a filler or filter that requires heat resistance.

  In addition, the obtained zirconia fibers can be formed into various structures by processing such as weaving, and can also be used in combination with zirconia fibers other than the present invention in accordance with handleability and other requirements. it can.

Hereinafter, the present invention will be described in detail.
The zirconia fibers produced according to the present invention have an average fiber diameter of 50 to 1000 nm and a fiber length of 100 μm or more.

Here, the zirconia fiber refers to a fiber structure made of an inorganic oxide mainly composed of zirconium oxide. As inorganic oxides other than zirconium, Al ₂ O ₃ , SiO ₂ , TiO ₂ , Li ₂ O, Na ₂ O, MgO, CaO, SrO, BaO, B ₂ O ₃ , P ₂ O ₅ , SnO ₂ , K _{2 O, Cs 2 O, ZnO} , Sb 2 O 3, As 2 O 3, CeO 2, V 2 O 5, Cr 2 O 3, MnO, Fe 2 O 3, CoO, NiO, Y 2 O 3, Lu 2 O ₃ , Yb ₂ O ₃ , HfO ₂ may be mentioned.

  The addition amount of the inorganic oxide other than zirconium is preferably 1.5 to 4.5 mol% from the stabilization of tetragonal crystal, which is a metastable phase of zirconia, and more preferably 1.6 to 3. 2 mol%.

  Next, it will be described that the average fiber diameter is 50 to 1000 nm. When the average fiber diameter of the zirconia fiber of the present invention exceeds 1000 nm, the flexibility of the zirconia fiber becomes unfavorable. On the other hand, if it is smaller than 50 nm, the strength of the zirconia fiber becomes very low, which is not preferable. Moreover, when it uses as a filler, since a fiber diameter is small and a specific surface area becomes large, since an adhesion area with a matrix material increases, it is preferable. More preferably, it is in the range of 100 to 600 nm, and still more preferably in the range of 150 to 500 nm.

  Next, it will be described that the fiber length is 100 μm or more. When the fiber length of the zirconia fiber of the present invention is 100 μm or less, the mechanical strength of the zirconia fiber aggregate obtained thereby is insufficient. The fiber length is preferably 150 μm or more, more preferably 1 mm or more.

  The method for producing a zirconia fiber of the present invention includes a step of dissolving a fiber-forming solute in an aqueous solution in which water-soluble zirconium chloride is dissolved, and an electrostatic spinning method from the aqueous solution in which the fiber-forming solute is dissolved. Spinning, a step of obtaining a fiber structure accumulated on the collection substrate by spinning, and a step of firing the accumulated fiber structure.

First, water-soluble zirconium chloride will be described. In the production method of the present invention, water-soluble zirconium chloride is used as a ceramic raw material for zirconia fibers. Here, the term “soluble in water” refers to a compound having a solubility of 50 or more, and examples of the zirconium chloride soluble in water include chlorinated zirconium oxide.
The concentration of zirconium chloride soluble in water is preferably 10 to 200 parts by weight, more preferably 50 to 150 parts by weight with respect to 100 parts by weight of the water solvent.

  Next, the step of dissolving the fiber-forming solute will be described. In the production method of the present invention, it is necessary to dissolve a fiber-forming solute in order to give the solution a string. The fiber-forming solute is not particularly limited as long as the zirconia fiber is produced, but an organic polymer having a molecular weight of 10,000 to 10,000,000 is necessary because of handling and firing. preferable. Examples thereof include polyethylene glycol, polyvinyl alcohol, polyvinyl ester, polyvinyl ether, polyvinyl pyridine, polyacrylamide, ether cellulose, pectin, and starch. Polyethylene glycol is particularly preferred.

  When the molecular weight of the organic polymer is low, the addition amount of the organic polymer is increased, and the amount of gas generated by firing increases, which increases the possibility of defects occurring in the structure of the zirconia fiber, which is not preferable. In the case of polyethylene glycol, the preferred molecular weight is in the range of 100,000 to 8,000,000, more preferably 100,000 to 600,000.

  Next, the addition amount of the fiber-forming solute is preferably as small as possible in the concentration range in which the fibers are formed, from the viewpoint of improving the denseness of the zirconia fibers, but is in the range of 0.01 to 5% by weight. Preferably, it is 0.01 to 2 weight%.

  Next, the solvent used in the present invention will be described. In the present invention, water is used as a solvent. From the viewpoint of improving the stability of the solution and improving the stability of spinning, the solvent may be a solvent other than water, for example, alcohols, ketones, amines, amides, carboxylic acids. It is also possible to add a salt such as ammonium chloride. Next, the electrostatic spinning method will be described. In the present invention, zirconia fibers are produced by an electrospinning method. In the electrospinning method, a solution in which a fiber-forming substrate is dissolved is discharged into an electrostatic field formed between electrodes, and the solution is directed to the electrodes. The fibrous material is obtained by accumulating the fibrous material formed on the collection substrate, and the fibrous material is a solvent that dissolves the fiber-forming substrate. And not only the state which is a fiber laminated body but the state in which the said solvent is contained in the fibrous substance is also shown.

  Ordinary electrospinning is performed at room temperature, but the temperature of the spinning atmosphere and the temperature of the collection substrate can be controlled as necessary, such as when the solvent is not sufficiently volatilized. It is.

Next, an apparatus used in the electrostatic spinning method will be described.
The above-described electrode can be used as long as it has conductivity, and any metal, inorganic, or organic material has a thin film of conductive metal, inorganic, or organic material on an insulator. May be.

  The electrostatic field is formed between a pair or a plurality of electrodes, and a high voltage may be applied to any of the electrodes. This includes, for example, the case where two high-voltage electrodes with different voltage values (for example, 15 kV and 10 kV) and a total of three electrodes connected to ground are used, or when more than three electrodes are used. Shall also be included.

Next, a step of obtaining a fiber structure accumulated on the collection substrate will be described.
In the production method of the present invention, since the spinning is performed by the electrostatic spinning method, the fiber structure is laminated on the electrode that is the collection substrate. If a flat surface is used for the collection substrate, a planar nonwoven fabric can be obtained. However, by changing the shape of the collection substrate, a structure having a desired shape can be produced.
In addition, when the uniformity is low, such as when the fiber structure is concentrated and laminated at one place on the substrate, the substrate can be swung or rotated.

  Next, the step of firing the fiber structure will be described. In the present invention, it is necessary to fire the fiber structure produced by spinning. For firing, a general electric furnace can be used, but if necessary, an electric furnace capable of replacing the gas in the firing atmosphere may be used. The firing temperature is preferably 800 ° C. or higher in order to produce a ceramic fiber having excellent heat resistance, and when fired at 1400 ° C. or higher, grain growth in the zirconia fiber is increased or the melting point is low. Since the material melts, the mechanical strength decreases, which is not preferable. A more preferable firing temperature is 900 ° C to 1300 ° C.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to these examples. The evaluation items in the following examples and comparative examples were carried out by the following methods.

Average fiber diameter:
The surface of the obtained zirconia fiber was photographed with a scanning electron microscope (S-2400, manufactured by Hitachi, Ltd.) (magnification: 2000 times), and 20 filaments were randomly selected from the photograph to measure the diameter of the filament. The average value of all the fiber diameters (n = 20) was obtained and used as the average fiber diameter of zirconia fibers.

Confirmation of the presence of fibers having a fiber length of 100 μm or less:
A photograph obtained by photographing the surface of the obtained zirconia fiber with a scanning electron microscope (S-2400, manufactured by Hitachi, Ltd.) (magnification 400 times) is observed, and it is confirmed whether a fiber having a fiber length of 100 μm or less exists. did.

[Example 1]
Zirconium chloride oxide octahydrate (manufactured by Wako Pure Chemical Industries, Ltd., special grade) 50 parts by weight, yttrium nitrate n hydrate (manufactured by Wako Pure Chemical Industries, Ltd., special grade) 1.3 parts by weight, polyethylene oxide (Sigma Aldrich) A solution was prepared by mixing 1 part by weight of an average molecular weight of 2,000,000) and 50 parts by weight of ion exchange water at room temperature (25 ° C.). A fiber structure was produced from the spinning solution using the apparatus shown in FIG. The inner diameter of the ejection nozzle 1 was 0.4 mm, the voltage was 15 kV, and the distance from the ejection nozzle 1 to the electrode 4 was 15 cm. The obtained fiber structure was heated to 1000 ° C. in 1.8 hours using an electric furnace in an air atmosphere, and then held at 1150 ° C. for 2 hours to produce zirconia fibers. When the obtained zirconia fiber was observed with an electron microscope, the fiber diameter was 400 nm, and a fiber having a fiber length of 100 μm or less was not observed. Electron micrographs are shown in FIGS.

It is the figure which showed typically the manufacturing apparatus for performing the manufacturing method of this invention. 2 is a photograph obtained by photographing (400 times) the surface of a zirconia fiber obtained by the operation of Example 1 with a scanning electron microscope. FIG. 2 is a photograph obtained by photographing the surface of the zirconia fiber obtained by the operation of Example 1 with a scanning electron microscope (magnification 2000 times). FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Solution ejection nozzle 2 Solution 3 Solution holding tank 4 Electrode 5 High voltage generator

Claims (3)

  A step of dissolving a fiber-forming solute in an aqueous solution in which zirconium chloride soluble in water is dissolved, a step of spinning from the aqueous solution in which the fiber-forming solute is dissolved by an electrostatic spinning method, and the spinning An average fiber diameter of 50 to 1000 nm and a fiber length of 100 μm or more, including a step of obtaining a fiber structure accumulated on the collection substrate and a step of firing the accumulated fiber structure; Production method.   The method for producing zirconia fibers according to claim 1, wherein the fiber-forming solute is an organic polymer having a molecular weight of 10,000 to 10,000,000.   The method for producing zirconia fibers according to claim 2, wherein the organic polymer is polyethylene glycol.

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