Titanium nitride fiber, zirconium nitride fiber and manufacturing method therefor, and titanium nitride fibrous filler, zirconium nitride fibrous filler and manufacturing method therefor

Abstract

To achieve a first purpose of providing a titanium nitride fiber or a zirconium nitride fiber with excellent strength even when an average fiber diameter is of a nanometer order, and to achieve a second purpose of providing a titanium nitride fibrous filler or a zirconium nitride fibrous filler through achieving the first purpose.SOLUTION: A titanium nitride precursor fiber or a zirconium nitride precursor fiber (or a fiber web thereof) is fired together with magnesium in an atmosphere of a nitride gas or a nitrogen gas. As a result, it is possible to realize titanium nitride fibers and zirconium nitride fibers with excellent strength, as well as titanium nitride fibrous fillers and zirconium nitride fibrous fillers with excellent strength, which address the problems described.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present invention relates to titanium nitride fibers, zirconium nitride fibers, and methods for producing them. In addition, the present invention relates to titanium nitride fibrous fillers, zirconium nitride fibrous fillers, and methods for producing them.

Background Art

[0002] Metal nitrides such as titanium nitride and zirconium nitride have physical properties such as high thermal conductivity, impact resistance, and acid resistance, and are used in various industrial applications such as heat dissipation materials in the form of fabrics such as fibers, fibrous fillers, or non-woven fabrics made of such fibers.

[0003] Such metal nitrides and methods for producing them are disclosed, for example, in JP-A-2022-138397 (Patent Document 1) and JP-A-2011-202331 (Patent Document 2).

[0004] Patent Document 1 discloses preparing an aqueous solution containing an alkyl alcohol having 5 to 8 carbon atoms and a metal alkoxide and spinning it using the electrospinning method. Thereafter, it is disclosed that metal nitride fibers can be produced by firing the obtained gel-like structure in a nitride gas or an inert gas atmosphere containing a nitride. In addition, Patent Document 1 discloses that the spinning solution can be most stabilized to produce metal nitride fibers by including 0.01 to 0.27 mol of an alkyl alcohol having 5 to 8 carbon atoms per 1 mol of the metal alkoxide. In addition, Patent Document 1 lists various metal species as the metal constituting the metal alkoxide. Although titanium and zirconium are listed among them, only the production of an aluminum nitride continuous fiber sheet is disclosed in the examples of Patent Document 1.

[0005] Patent Document 2 discloses preparing an aqueous solution containing a water-soluble polymer compound (for example, an organic polymer compound soluble in water such as polyvinylpyrrolidone, polyvinyl alcohol, polyethylene glycol, poly(meth)acrylic acid, poly(meth)acrylate, etc.) and a water-soluble transition metal compound such as a transition metal salt or an organic acid transition metal salt (for example, zirconium chloride or titanium emulsion), and spinning using the electrospinning method. Thereafter, it is disclosed that titanium nitride fibers or zirconium nitride fibers can be produced by firing the obtained heat-resistant fiber precursor in a nitrogen gas or ammonia gas atmosphere. Also, Patent Document 2 discloses that by adopting the electrospinning method, metal nitride fibers with a fiber diameter on the order of nanometers can be produced.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0007] The applicant of the present application studied the prior art as disclosed in Patent Documents 1 and 2. Then, an attempt was made to produce titanium nitride fibers or zirconium nitride fibers using the production methods disclosed in these prior arts.

[0008] First, as disclosed in Patent Document 1, an attempt was made to spin an aqueous solution containing an alkyl alcohol having 5 to 8 carbon atoms and a titanium alkoxide or a zirconium alkoxide to produce titanium nitride fibers and zirconium nitride fibers. In particular, based on the disclosure of Patent Document 1 that metal nitride fibers can be produced by stabilizing the spinning solution, the amount of alkyl alcohol having 5 to 8 carbon atoms contained in the spinning solution was adjusted to an optimum amount (adjusted to 0.01 to 0.27 moles per mole of metal alkoxide). However, in reality, titanium nitride fibers and zirconium nitride fibers could not be produced.

[0009] Next, an attempt was made to spin a spinning solution containing a water-soluble polymer compound disclosed in Patent Document 2 to produce titanium nitride fibers and zirconium nitride fibers. However, the titanium nitride fibers and zirconium nitride fibers produced in this way (hereinafter sometimes referred to as metal nitride fibers according to the prior art) had a problem of inferior strength.

[0010] For example, when handling, when placing in a pouch to be used as a filler, or when kneading with resin to prepare a composite, the metal nitride fibers according to the conventional technology are easily damaged unintentionally when an external force is applied. Therefore, even if an attempt is made to produce a titanium nitride fibrous filler or a zirconium nitride fibrous filler by applying an external force to the metal nitride fibers according to the conventional technology and grinding them, the fibers are damaged unintentionally and cannot maintain their fibrous shape. As a result, it is not possible to obtain a titanium nitride fibrous filler or a zirconium nitride fibrous filler.

[0011] The problem of inferior strength in particular occurs more prominently as the average fiber diameter becomes smaller (especially when the average fiber diameter is on the order of nanometers).

[0012] The first object of the present invention is to provide titanium nitride fibers or zirconium nitride fibers having excellent strength even when having an average fiber diameter on the order of nanometers. Further, through achieving the first object, the second object is to provide a titanium nitride fibrous filler or a zirconium nitride fibrous filler.

Means for Solving the Problems

[0013] The present invention is “(Claim 1) A metal nitride fiber having an average fiber diameter on the order of nanometers that can maintain its fiber shape after being subjected to the following (strength evaluation method), wherein the metal nitride fiber is a titanium nitride fiber or a zirconium nitride fiber. (Strength evaluation method) (1) Place 3 g of titanium nitride fibers or zirconium nitride fibers in a cylindrical tube (cross-sectional shape: an annular shape surrounding a circle with a diameter of 30 mm) that is vertically fixed on a flat plate with a smooth surface. (2) Apply a pressure of 5 kN per 225π mm 2 to the titanium nitride fibers or the zirconium nitride fibers placed in the cylindrical tube for 5 seconds. (3) After applying the pressure, check whether there is a titanium nitride fibrous filler or a zirconium nitride fibrous filler whose aspect ratio, calculated by dividing the fiber length (unit: μm) by the fiber diameter (unit: μm), is 5 or more. (4) If there is a titanium nitride fibrous filler or a zirconium nitride fibrous filler whose aspect ratio is 5 or more, it is determined that the titanium nitride fiber or the zirconium nitride fiber can maintain its fiber shape after being subjected to this measurement method. On the other hand, if there is no titanium nitride fibrous filler or zirconium nitride fibrous filler whose aspect ratio is 5 or more, it is determined that the titanium nitride fiber or the zirconium nitride fiber cannot maintain its fiber shape after being subjected to this measurement method. (Claim 2) A metal nitride fibrous filler having an average fiber diameter on the nanometer order that can maintain its fiber shape after being subjected to the (strength evaluation method) according to claim 1, wherein the metal nitride fibrous filler is a titanium nitride fibrous filler or a zirconium nitride fibrous filler. (Claim 3) (Step i) A step of preparing a metal alkoxide solution, (Step ii) A step of preparing a drawable sol solution by hydrolyzing and polycondensing the metal alkoxide in the metal alkoxide solution, (Step iii) A step of preparing metal nitride precursor fibers by spinning and firing using the drawable sol solution, (Step iv) A step of converting the metal nitride precursor fibers into metal nitride fibers by firing the metal nitride precursor fibers together with magnesium in a nitride gas or nitrogen gas atmosphere, A method for producing metal nitride fibers, comprising: wherein the metal is titanium or zirconium. (Claim 4) After (Step iv) according to claim 3, (Step v) A step of applying an external force to the prepared metal nitride fibers and pulverizing them, A method for producing a metal nitride fibrous filler, comprising: wherein the metal is titanium or zirconium. is.

Advantages of the Invention

[0014] As a result of the applicant's research, it was considered that the prior art had the following problems.

[0015] In the manufacturing method according to Patent Document 2, metal nitride fibers are to be manufactured by firing a precursor of metal nitride fibers (heat-resistant fiber precursor) containing a water-soluble polymer. Therefore, it is considered that minute voids formed during firing due to the decomposition or combustion of the water-soluble polymer exist in the manufactured metal nitride fibers. As a result, the manufactured metal nitride fibers are brittle and inferior in strength.

[0016] Incidentally, the applicant of the present application evaluated whether or not the fiber shape could be maintained after applying pressure as an external force to the (strength evaluation method) defined in the present invention so as to objectively evaluate the strength of the metal nitride fibers. As a result of subjecting the metal nitride fibers according to the prior art to the (strength evaluation method), as is clear from the comparative examples described later, they were brittle and inferior in strength and could not maintain the fiber shape.

[0017] Also, as long as the manufacturing method according to Patent Document 1 is used, in reality, titanium nitride fibers and zirconium nitride fibers could not be manufactured.

[0018] In the manufacturing method according to Patent Document 1, it is necessary to use a spinning solution containing an alkyl alcohol having 5 to 8 carbon atoms. Here, the alkyl alcohol having 5 to 8 carbon atoms has a high boiling point and has the property of being difficult to volatilize. Therefore, the alkyl alcohol having 5 to 8 carbon atoms remains in the fibers obtained by spinning using the spinning solution or in the fiber web (gel-like structure) composed of the fibers.

[0019] And in the manufacturing method according to Patent Document 1, metal nitride fibers are to be manufactured by firing the fibers containing the alkyl alcohol having 5 to 8 carbon atoms. Therefore, it is considered that minute voids formed due to the decomposition or combustion of the alkyl alcohol exist in the manufactured metal nitride fibers.

[0020] As a result, even if titanium nitride fibers and zirconium nitride fibers can be produced using the manufacturing method described in Patent Document 1, the titanium nitride fibers and zirconium nitride fibers provided based on the findings disclosed in Patent Document 1 are also considered to be brittle and inferior in strength, similar to the titanium nitride fibers and zirconium nitride fibers provided in Patent Document 2.

[0021] That is, even if titanium nitride fibers and zirconium nitride fibers can be produced using the manufacturing method described in Patent Document 1, it is not possible to provide titanium nitride fibers and zirconium nitride fibers having an average fiber diameter on the nanometer order and having the physical property of "being able to maintain the fiber shape" as defined by the present invention.

[0022] Despite the titanium nitride fibers and zirconium nitride fibers according to the first invention having an average fiber diameter on the nanometer order, they can maintain their fiber shape after being subjected to the (strength evaluation method) defined in the present invention. Therefore, they are titanium nitride fibers and zirconium nitride fibers with excellent strength.

[0023] Despite the titanium nitride fiber-shaped filler and zirconium nitride fiber-shaped filler according to the second invention having an average fiber diameter on the nanometer order, they can maintain their fiber shape after being subjected to the (strength evaluation method) defined in the present invention. Therefore, they are titanium nitride fiber-shaped fillers and zirconium nitride fiber-shaped fillers with excellent strength.

[0024] Also, the manufacturing method of titanium nitride fibers and zirconium nitride fibers according to the third invention can provide titanium nitride fibers and zirconium nitride fibers with excellent strength, which can maintain their fiber shape after being subjected to the (strength evaluation method) defined in the present invention, despite having an average fiber diameter on the nanometer order.

[0025] In the fourth invention, titanium nitride fibers and zirconium nitride fibers with excellent strength as described above are subjected to an external force and crushed to provide titanium nitride fibrous fillers and zirconium nitride fibrous fillers. Since the titanium nitride fibrous fillers and zirconium nitride fibrous fillers are derived from titanium nitride fibers and zirconium nitride fibers with excellent strength, they have excellent strength.

Brief Description of the Drawings

[0026]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Embodiments for Carrying Out the Invention

[0027] In the present invention, various configurations can be appropriately selected, such as the following configurations. Note that, unless otherwise specified, all various measurements described in the present invention are carried out under atmospheric pressure. Further, the measurements are carried out under the temperature condition of 25°C. And, unless otherwise specified, all various measurement results described in the present invention are measured up to a value one digit smaller than the required value, and the required value is calculated by rounding off the said value. As a specific example, when the value up to the first decimal place is the required value, the value up to the second decimal place is obtained by measurement, and the value up to the first decimal place is calculated by rounding off the obtained value of the second decimal place, and this value is taken as the required value. And, each upper limit value and each lower limit value exemplified in the present invention can be arbitrarily combined.

[0028] The titanium nitride fiber and zirconium nitride fiber according to the present invention (hereinafter sometimes collectively referred to as metal nitride fiber) have an average fiber diameter on the order of nanometers. Therefore, it can be suitably used for various industrial applications.

[0029] Note that the "average fiber diameter" as used in the present invention means the average value of the fiber diameters at 50 randomly selected locations where a plurality of metal nitride fibers shown in an electron micrograph taken at a magnification of 5000 times exist alone without adhering to or integrating with other metal nitride fibers. Note that the fiber diameter refers to the length in the direction perpendicular to the direction in which the metal nitride fiber shown in the electron micrograph extends continuously. And, "having an average fiber diameter on the order of nanometers" as used in the present invention means that the average fiber diameter calculated as described above is less than 1.000 μm.

[0030] Since the thinner the average fiber diameter, the more suitable it is for various industrial applications, the average fiber diameter of the metal nitride fiber can be 950 nm or less, 900 nm or less, 800 nm or less, 700 nm or less, 600 nm or less, 500 nm or less, 400 nm or less, 300 nm or less, 200 nm or less. On the other hand, although the lower limit value of the average fiber diameter of the metal nitride fiber can be adjusted as appropriate, it is realistic to be 10 nm or more, and it can be 100 nm or more.

[0031] The metal nitride fiber of the present invention is preferably a substantially continuous fiber so as to have excellent thermal conductivity. Note that the metal nitride fiber being "substantially continuous fiber" means that at both ends of the majority of the metal nitride fibers shown in the electron micrograph taken at a magnification of 500 times, they cannot be confirmed. Such a substantially continuous fiber metal nitride fiber can be prepared by using a direct spinning method such as an electrospinning method or a blow method described later.

[0032] Alternatively, the metal nitride fiber may be a short fiber cut to a specific length so that it is easy to disperse when kneaded with a resin to prepare a composite, and also easy to put into a pouch. Such short fibers can be prepared by cutting the metal nitride fiber to a specific length. The average fiber length of the short fibers can be adjusted as appropriate, but it can be 200 μm or less, 100 μm or less, 50 μm or less, 10 μm or less, 5 μm or less. On the other hand, although the lower limit value of the average fiber length can be adjusted as appropriate, it is realistic to be 1 μm or more, and it can be 3 μm or more. Note that the "average fiber length" referred to in the present invention means the average value of the fiber lengths of 50 randomly selected metal nitride fibers from a plurality of metal nitride fibers shown in the electron micrograph taken at a magnification of 500 times. Note that the fiber length refers to the length in the direction in which the metal nitride fiber shown in the electron micrograph continues and extends.

[0033] The cross-sectional shape of the metal nitride fiber of the present invention may be an irregular cross-section other than a substantially circular or elliptical shape. In addition, as fibers having an irregular cross-section, a hollow shape, a polygonal shape such as a triangular shape, an alphabetic character type shape such as a Y shape, an irregular shape, a multi-leaf shape, a symbol type shape such as an asterisk shape, or a cross-sectional shape such as a shape in which a plurality of these shapes are combined may be used.

[0034] The mass percentage of titanium nitride in the mass of the titanium nitride fiber and the mass percentage of zirconium nitride in the mass of the zirconium nitride fiber can be adjusted as appropriate. However, in order to be suitably used for various industrial applications, these mass percentages are preferably 70% by mass or more, preferably 80% by mass or more, preferably 90% by mass or more, and it is preferable that the titanium nitride fiber is composed only of titanium nitride or the zirconium nitride fiber is composed only of zirconium nitride. In addition, in the production method according to the present invention described later, titanium nitride fibers or zirconium nitride fibers can be produced without using a water-soluble polymer compound or an alkyl alcohol having 5 to 8 carbon atoms.

[0035] In order to be excellent in strength, the average value of the crystallite size of titanium nitride constituting the titanium nitride fiber and the average value of the crystallite size of zirconium nitride constituting the zirconium nitride fiber are preferably larger than 75 Å. In order to be more excellent in strength, the average value of the crystallite size described above is preferably 100 Å or more, preferably 200 Å or more, preferably 300 Å or more. On the other hand, the upper limit value of the average value of the crystallite size can be adjusted as appropriate, but it is realistic that it is 1000 Å or less.

[0036] The "average value of the crystallite size" in the present invention means the crystallite size obtained from the half-value width using the Scherrer method based on the result of measurement (measurement conditions: 2θ measurement range +3 to 140°, tube voltage: 30 kV, tube current: 15 mA) by supplying the metal nitride fiber to be measured to an X-ray diffractometer (desktop X-ray diffractometer MiniFlex50, manufactured by Rigaku Corporation).

[0037] That is, the half-value width of the plane with the strongest diffraction intensity and the highest uniformity in the metal nitride fiber is substituted into the following Scherrer's formula to obtain the crystallite size. Note that LaB6 is used as the standard substance. Scherrer's formula: D = K × λ / (β × cosθ) D: Crystallite size (Å) K: Scherrer constant (K = 0.94) λ: Measured X-ray wavelength (Å) β: Spread of the diffraction line due to the crystallite size (rad) θ: Bragg angle of the diffraction line

[0038] The titanium nitride fiber and zirconium nitride fiber according to the present invention have the physical property that they can maintain the fiber shape after being subjected to the following (strength evaluation method). This measurement method is for objectively evaluating the strength of the metal nitride fiber, and this measurement method will be described with reference to FIG. 1.

[0039] (Strength evaluation method) (Step 1) Prepare 3 g of the metal nitride fiber to be measured. When the metal nitride fiber is in the form of a fabric such as a non-woven fabric, prepare 3 g of the fabric. (Step 2) Stand a cylindrical tube (20, cross-sectional shape: an annular shape surrounding a circle (21) with a diameter of 30 mm) on the main surface of a plate (10) with a smooth surface, and fix the cylindrical tube (20) on the main surface (11) of the plate (10) with a smooth surface. At this time, one end of the cylindrical tube (20) is in contact with the main surface (11) of the plate (10) with a smooth surface. (Step 3) Place 3 g of the metal nitride fiber or the metal nitride fiber in the form of a fabric into the cylindrical tube (20). At this time, the metal nitride fiber is placed in a cylindrical space surrounded by the main surface of the plate (10) and the cylindrical tube (20) and having a bottom surface that is a circle (21) with a diameter of 30 mm. (Step 4) Apply a pressure of 5 kN per 225π mm 2 to the metal nitride fiber placed in the cylindrical tube (20) (pressure: 5 kN / 225π mm 2) is allowed to act for 5 seconds. In addition, in order to apply pressure to the metal nitride fiber, a cylinder (not shown) can be inserted into the inside of the cylindrical tube (20). (Step 5) Check whether the aspect ratio calculated by dividing the average fiber length (unit: μm) by the average fiber diameter (unit: μm) of the metal nitride fiber filler present after applying pressure is 5 or more. Note that the metal nitride fiber filler is formed by the metal nitride fiber being crushed under the action of pressure and the fiber length being shortened. (Step 6) When the aspect ratio of the metal nitride fiber filler is 5 or more, it is determined that the metal nitride fiber subjected to the measurement can maintain its fiber shape after the measurement and is excellent in strength. On the other hand, when the aspect ratio of the metal nitride fiber filler is less than 5, it is determined that the metal nitride fiber subjected to the measurement cannot maintain its fiber shape after the measurement and is inferior in strength.

[0040] As a result of this measurement, it means that the higher the aspect ratio of the metal nitride fiber filler, the better the strength of the metal nitride fiber subjected to the measurement. Therefore, as a result of this measurement, it is preferable that the metal nitride fiber has a measurement result with an aspect ratio of 5 or more, and more preferably a measurement result with an aspect ratio of 6 or more, and more preferably a measurement result with an aspect ratio of 10 or more, and more preferably a measurement result with an aspect ratio of 20 or more, and more preferably a measurement result with an aspect ratio of 30 or more, and more preferably a measurement result with an aspect ratio of 40 or more, and more preferably a measurement result with an aspect ratio of 50 or more. Note that the upper limit value of the aspect ratio is preferably 100 or less.

[0041] The titanium nitride fiber filler and zirconium nitride fiber filler according to the present invention (hereinafter sometimes collectively referred to as metal nitride fiber fillers) have an average fiber diameter on the order of nanometers, similar to the aforementioned metal nitride fibers. Therefore, it can be suitably used for various industrial applications.

[0042] Since the smaller the average fiber diameter, the more suitable it is for various industrial applications, the average fiber diameter of the metal nitride fibrous filler can be 950 nm or less, can be 900 nm or less, can be 800 nm or less, can be 700 nm or less, can be 600 nm or less, can be 500 nm or less, can be 400 nm or less, can be 300 nm or less, can be 200 nm or less. On the other hand, although the lower limit value of the average fiber diameter of the metal nitride fibrous filler can be adjusted as appropriate, it is realistic to be 50 nm or more, and can be 100 nm or more.

[0043] In addition, the fiber diameter and average fiber diameter of the metal nitride fibrous filler are measured and obtained by reading "metal nitride fiber" as "metal nitride fibrous filler" in the measurement method of the fiber diameter and average fiber diameter of the metal nitride fiber.

[0044] Also, the "fibrous filler" referred to in the present invention means one having an aspect ratio calculated by dividing the average fiber length (unit: μm) by the average fiber diameter (unit: μm) of 5 or more and less than 1000. Note that those with an aspect ratio of 1000 or more can be judged as fibers.

[0045] The aspect ratio of the metal nitride fibrous filler is adjusted as appropriate so that it can be suitably used for various industrial applications. However, it is a metal nitride fibrous filler having an aspect ratio of 5 or more, preferably having an aspect ratio of 6 or more, preferably having an aspect ratio of 10 or more, preferably having an aspect ratio of 20 or more, preferably having an aspect ratio of 30 or more, preferably having an aspect ratio of 40 or more, preferably having an aspect ratio of 50 or more. The upper limit value of the aspect ratio is adjusted as appropriate, but is preferably 100 or less.

[0046] The average fiber length of the metal nitride fibrous filler can be adjusted as appropriate, but it can be 100 μm or less, 90 μm or less, 80 μm or less, 70 μm or less, or 60 μm or less. On the other hand, the lower limit value of the average fiber length can be adjusted as appropriate, but it is practical to be 1 μm or more, and it can be 5 μm or more or 10 μm or more.

[0047] Note that the fiber length and average fiber length of the metal nitride fibrous filler are measured and determined by substituting "metal nitride fibrous filler" for "metal nitride fiber" in the measurement method of the fiber length and average fiber length of the metal nitride fiber.

[0048] The mass percentage of titanium nitride in the mass of the titanium nitride fibrous filler and the mass percentage of zirconium nitride in the mass of the zirconium nitride fibrous filler can be adjusted as appropriate. However, in order to be suitably used for various industrial applications, these mass percentages are preferably 70% by mass or more, preferably 80% by mass or more, preferably 90% by mass or more, and it is preferable that the titanium nitride fibrous filler is composed only of titanium nitride or the zirconium nitride fibrous filler is composed only of zirconium nitride.

[0049] In order to have excellent strength, the average value of the crystallite size of titanium nitride constituting the titanium nitride fibrous filler and zirconium nitride constituting the zirconium nitride fibrous filler is preferably greater than 75 Å. In order to have more excellent strength, the average value of the above-described crystallite size is preferably 100 Å or more, preferably 200 Å or more, preferably 300 Å or more. On the other hand, the upper limit value of the average value of the crystallite size can be adjusted as appropriate, but it is practical to be 1000 Å or less.

[0050] The "average value of the crystallite size" in the present invention is measured and determined by supplying a metal nitride fibrous filler to the above-described X-ray diffractometer (desktop X-ray diffractometer MiniFlex50, manufactured by Rigaku Corporation) instead of the metal nitride fiber.

[0051] Note that the metal nitride fibrous filler can be crushed and its fiber length can be shortened by receiving an external force such as pressure. That is, the metal nitride fibrous filler can be turned into a metal nitride fibrous filler with a small aspect ratio or a metal nitride filler without a fibrous shape by receiving an external force such as pressure.

[0052] The titanium nitride fibrous filler and zirconium nitride fibrous filler according to the present invention have the physical property of being able to maintain the fibrous shape after being subjected to the above-described (strength evaluation method). This measurement method is for objectively evaluating the strength of the metal nitride fibrous filler, and is measured and obtained by providing the metal nitride fibrous filler instead of the metal nitride fiber to the above-described (strength evaluation method).

[0053] Even after being subjected to the pressure applied to this measurement, the higher the aspect ratio of the metal nitride fibrous filler, the more excellent the strength of the metal nitride fibrous filler provided for the measurement. Therefore, as a result of this measurement, it is preferable that the metal nitride fibrous filler has a measurement result with an aspect ratio of 5 or more, and more preferably a measurement result with an aspect ratio of 6 or more, and more preferably a measurement result with an aspect ratio of 10 or more, and more preferably a measurement result with an aspect ratio of 20 or more, and more preferably a measurement result with an aspect ratio of 30 or more, and more preferably a measurement result with an aspect ratio of 40 or more, and more preferably a measurement result with an aspect ratio of 50 or more. Note that the upper limit value of the aspect ratio is preferably 100 or less.

[0054] The titanium nitride fiber according to the present invention can be produced, for example, using the following method. (Step i) A step of preparing a titanium alkoxide solution (Step ii) A step of preparing a drawable sol solution by hydrolyzing and polycondensing titanium alkoxide in the titanium alkoxide solution. (Step iii) A step of preparing a titanium nitride precursor fiber by spinning and baking using the drawable sol solution. (Step iv) A step of converting the titanium nitride precursor fiber into a titanium nitride fiber by baking the titanium nitride precursor fiber together with magnesium in a nitride gas or nitrogen gas atmosphere. A method for producing titanium nitride fiber, comprising the above steps.

[0055] In addition, the zirconium nitride fiber according to the present invention can be produced, for example, by using the following method. (Step i) A step of preparing a zirconium alkoxide solution. (Step ii) A step of preparing a drawable sol solution by hydrolyzing and polycondensing zirconium alkoxide in the zirconium alkoxide solution. (Step iii) A step of preparing a zirconium nitride precursor fiber by spinning and baking using the drawable sol solution. (Step iv) A step of converting the zirconium nitride precursor fiber into a zirconium nitride fiber by baking the zirconium nitride precursor fiber together with magnesium in a nitride gas or nitrogen gas atmosphere. A method for producing zirconium nitride fiber, comprising the above steps.

[0056] Specifically, first, a titanium alkoxide solution or a zirconium alkoxide solution (hereinafter sometimes collectively referred to as a metal alkoxide solution) is prepared. At this time, it is not necessary to include a water-soluble polymer compound (an organic polymer compound soluble in water) or an alkyl alcohol having 5 or more carbon atoms (a poorly water-soluble or water-insoluble alcohol) disclosed in the prior art in the metal alkoxide solution.

[0057] The metal alkoxide solution can contain a solvent (such as alcohols like ethanol or water-soluble organic solvents like dimethylformamide), water for hydrolyzing the titanium alkoxide or zirconium alkoxide contained in the metal alkoxide solution, and a catalyst (such as tetrabutylammonium hydroxide).

[0058] Furthermore, the metal alkoxide solution may contain inorganic or organic fine particles. Examples of the inorganic fine particles include yttrium oxide, titanium nitride, manganese dioxide, copper oxide, silicon dioxide, activated carbon, and metals (such as platinum), and examples of the organic fine particles include dyes or pigments. Also, the average particle size of the fine particles is not particularly limited, but is preferably 0.001 to 1 μm, more preferably 0.01 to 0.1 μm.

[0059] Next, a drawable sol solution is prepared by hydrolyzing and polycondensing the titanium alkoxide or zirconium alkoxide in the metal alkoxide solution.

[0060] The amount of water for hydrolyzing the titanium alkoxide or zirconium alkoxide contained in the metal alkoxide solution varies depending on their molecular structures and is not particularly limited. For example, the amount of water is preferably 4 times the molar amount or less of the titanium alkoxide or zirconium alkoxide.

[0061] Also, the reaction temperature of the solution when hydrolyzing the titanium alkoxide or zirconium alkoxide in the metal alkoxide solution can be adjusted as appropriate. By lowering the reaction temperature of the solution, the hydrolysis rate can be reduced and the growth of the sol into a high dimension can be suppressed. Since it becomes easier to produce titanium nitride fibers or zirconium nitride fibers even when fired at a low temperature, 30°C or lower is preferable, and 25°C or lower is more preferable. On the other hand, if the reaction temperature of the solution is too low, the water vapor contained in the air in the reaction kettle or flask used during the reaction may liquefy into water, and the water may mix into the solution, causing the hydrolysis reaction to proceed rapidly. Therefore, 0°C or higher is preferable.

[0062] Furthermore, the reaction temperature of the solution during polycondensation following hydrolysis only needs to be higher than the temperature during hydrolysis, and is not particularly limited. However, if it is carried out at 25°C or higher, polycondensation can be carried out efficiently. The presence or absence of "drawability" can be determined under the conditions shown in the following (Determination Method).

[0063] (Determination Method) (1) Adjust the solution obtained by hydrolyzing and polycondensing the metal alkoxide so that the solid content concentration becomes 10 to 50 wt% to obtain a spinning solution. While discharging the spinning solution from a metal nozzle (inner diameter: 0.4 mm) arranged horizontally with respect to an earthed metal plate (discharge amount: 0.5 to 1.0 g / hr), apply a voltage to the nozzle (electric field strength: 1 to 3 kV / cm, polarity: positive application or negative application), and continuously spin for 1 minute or more without causing solidification of the solution at the tip of the nozzle, and accumulate the fibers on the metal plate. (2) Take a scanning electron micrograph of the accumulated fibers, observe, and if there are no droplets and there are conditions under which fibers with an average fiber diameter (arithmetic mean value of 50 points) of 5 μm or less and an aspect ratio of 1000 or more can be produced, the spinning solution is judged to have "drawability". On the contrary, when changing the above conditions (i.e., concentration, discharge amount, electric field strength, and / or polarity), no matter how they are combined, if there are droplets, if the fiber form is not an oil-like and constant form, if the average fiber diameter exceeds 5 μm, or if the aspect ratio is less than 1000 (for example, particulate), and there are no conditions under which the above fibers can be produced, the spinning solution is judged to have "no drawability".

[0064] Next, spinning is carried out using the drawable sol solution. The method of spinning using the drawable sol solution is not particularly limited. For example, well-known direct spinning methods such as the electrospinning method and the method (blow method) of discharging gas in parallel to the spinning solution discharged from the liquid discharge part and applying a shearing force in a straight line to the spinning solution to fiberize, as disclosed in JP-A-2009-287138, can be adopted. Among these, according to the electrospinning method, it is easy to form fibers having an average fiber diameter on the order of nanometers, which is preferable.

[0065] When directly spinning this drawable sol solution, the viscosity of the drawable sol solution is preferably 0.01 to 10 Pa·s, more preferably 0.05 to 5 Pa·s, and even more preferably 0.1 to 3 Pa·s so as to enable efficient spinning. This is because when the viscosity exceeds 10 Pa·s, it is difficult to spin fine fibers, and when it is less than 0.01 Pa·s, the fiber shape itself tends not to be obtained. When spinning the drawable sol solution using a nozzle, by setting the atmosphere at the tip of the nozzle to the same solvent gas atmosphere as the solvent of the metal alkoxide solution, it may be possible to spin a drawable sol solution with a viscosity exceeding 10 Pa·s.

[0066] By collecting the fibers spun in this way onto a collector, a fiber web in which the fibers are randomly dispersed can be prepared.

[0067] In addition, by firing the spun fibers or fiber web, zirconium nitride precursor fibers or titanium nitride precursor fibers (or fiber webs thereof) can be prepared. The firing temperature can be adjusted as appropriate, but can be 500°C to 2000°C and can be 800°C to 1500°C. Also, the firing time can be adjusted as appropriate, but can be 1 to 5 hours. And the firing can be carried out in an oxygen atmosphere or an air atmosphere. The titanium nitride precursor fibers prepared in this way contain titania, and the zirconium nitride precursor fibers contain zirconia.

[0068] Thereafter, the prepared titanium nitride precursor fibers or zirconium nitride precursor fibers (or fiber webs thereof) are fired together with magnesium in a nitride gas or nitrogen gas atmosphere. The manufacturing method according to the present invention is characterized in that the precursor fibers are fired together with magnesium in a nitride gas or nitrogen gas atmosphere.

[0069] In the present invention, the "nitride gas" refers to a gas containing a molecule having a nitrogen atom and another atom bonded to the nitrogen atom in the molecule. Examples thereof include gases such as ammonia, hydrazine, and diethanolamine. In particular, ammonia gas and hydrazine gas are preferred because by-products are less likely to be generated.

[0070] The applicant of the present application has found that by firing the precursor fiber together with magnesium in an atmosphere of a nitride gas or a nitrogen gas, high-purity titanium nitride fibers and zirconium nitride fibers can be easily prepared. On the other hand, when the precursor fiber is simply fired as it is in an atmosphere of a nitride gas or a nitrogen gas, or when it is simply fired together with activated carbon in an atmosphere of a nitride gas or a nitrogen gas, titanium nitride fibers and zirconium nitride fibers cannot be prepared.

[0071] The amount of magnesium used in this step is appropriately adjusted so that high-purity metal nitride fibers can be easily prepared. Preferably, 1 mol or more of magnesium is used per 1 mol of titania or zirconia contained in the precursor fiber, more preferably 3 mol or more, and still more preferably 5 mol or more.

[0072] The firing temperature is appropriately adjusted. However, by firing at 1300 °C or lower, it is preferable to easily produce metal nitride fibers having an average crystallite size of 75 Å or more. This firing can be carried out using, for example, an oven or a firing furnace. When the firing temperature is low, the growth of crystallites can be suppressed, and metal nitride fibers with a small crystallite size can be realized. Therefore, the firing temperature is more preferably 1200 °C or lower, and still more preferably 1150 °C or lower. The lower limit of the firing temperature is preferably 50 °C or higher. The firing time is appropriately adjusted, but specifically, it is preferably 1 to 5 hours, and more preferably 1 to 3 hours.

[0073] By firing in this way, titanium nitride fibers or zirconium nitride fibers (or non-woven fabrics thereof) can be prepared.

[0074] The titanium nitride fibrous filler or zirconium nitride fibrous filler according to the present invention can be prepared by applying an external force such as pressure to the titanium nitride fibers or zirconium nitride fibers (or non-woven fabrics thereof) prepared as described above and pulverizing them.

[0075] The method of applying an external force to the metal nitride fibers or the non-woven fabric of metal nitride fibers and pulverizing them can be appropriately selected. For example, a method of feeding the metal nitride fibers or the non-woven fabric of metal nitride fibers to a press machine and pulverizing them, a method of applying ultrasonic waves to the metal nitride fibers or the non-woven fabric of metal nitride fibers and pulverizing them, etc. can be adopted. The pressure exerted by the press machine can be adjusted as appropriate, but it can be 5 MPa or more, it can be greater than 5 MPa, and it can be 10 MPa or more.

[0076] In particular, when adopting the method of feeding the non-woven fabric of metal nitride fibers to a press machine and pulverizing them, by uniformly applying pressure to the entire metal nitride fibers constituting the non-woven fabric of metal nitride fibers, a metal nitride fibrous filler with a desired aspect ratio can be prepared. In addition, it is preferable to feed the non-woven fabric in a state where a plurality of sheets are laminated to the press machine and pulverize it so as to improve the productivity of the metal nitride fibrous filler.

Examples

[0077] Hereinafter, the present invention will be specifically described by way of examples, but these do not limit the scope of the present invention.

[0078] (Comparative Example 1) An aqueous solution of zirconium chloride (manufactured by Matsumoto Fine Chemical Co., Ltd., trade name: Organicx (registered trademark) ZB-126) and a 10% by mass aqueous solution of polyvinyl alcohol (average degree of polymerization: 150, saponification degree: 99%) were mixed at a ratio of 40 parts by mass of zirconium chloride: 5 parts by mass of polyvinyl alcohol to obtain a spinning solution. The spinning solution thus prepared was spun by electrospinning under the following conditions and collected on a drum collector to prepare a fiber web. (Spinning conditions) · Discharge amount from nozzle: 1 g / hour · Distance between the nozzle tip and the drum collector: 10 cm · Temperature and humidity inside the spinning container: 25°C / 30% RH · Applied voltage to the nozzle: +10 kV Then, the prepared fiber web was fed into a firing furnace and fired under a nitrogen atmosphere at a firing temperature of 1300°C for 1 hour, and then allowed to cool, thereby preparing a non-woven fabric (average fiber diameter: 0.50 μm) composed of fibers containing 70% by mass of zirconium nitride and 30% by mass of zirconium chloride nitride. The non-woven fabric thus prepared was subjected to (strength evaluation method). As a result, the fibers containing zirconium nitride and zirconium chloride nitride that make up the non-woven fabric could not maintain their fiber shape. The results of being subjected to (strength evaluation method) are shown in Figure 2.

[0079] (Comparative Example 2) A spinning solution was obtained in the same manner as in Comparative Example 1, except that an aqueous 2-propanol solution of emulsified titanium (manufactured by Matsumoto Fine Chemical Co., Ltd., product number: TC-310, content of emulsified titanium: 35 - 45% by mass, content of 2-propanol: 40 - 50% by mass, content of water: 10 - 20% by mass) was used instead of the aqueous zirconium chloride solution. Using the spinning solution thus prepared, electrospinning was carried out in the same manner as in Comparative Example 1 to spin the fibers, and the fibers were collected on a drum collector to prepare a fiber web. Then, the prepared fiber web was fed into a firing furnace and fired under a nitrogen atmosphere at a firing temperature of 1300°C for 1 hour, and then allowed to cool, thereby preparing a non-woven fabric (average fiber diameter: 0.80 μm) composed of titanium nitride fibers. The non-woven fabric thus prepared was subjected to (strength evaluation method). As a result, the titanium nitride fibers that make up the non-woven fabric could not maintain their fiber shape. The results of being subjected to (strength evaluation method) are shown in Figure 3.

[0080] (Comparative Example 3) To the nonwoven fabric of fibers containing zirconium nitride and zirconium nitride chloride prepared in Comparative Example 1, a pressure of 5 kN per 225π mm 2 was applied for 5 seconds to attempt to pulverize and prepare fibrous fillers. However, the fibers containing zirconium nitride and zirconium nitride chloride after the pressure was applied were unintentionally pulverized into powder, and fibrous fillers with an aspect ratio of 5 or more and less than 1000 could not be obtained.

[0081] (Comparative Example 4) To the nonwoven fabric of titanium nitride fibers prepared in Comparative Example 2, a pressure of 5 kN per 225π mm 2 was applied for 5 seconds to attempt to pulverize and prepare fibrous fillers. However, the titanium nitride fibers after the pressure was applied were unintentionally pulverized into powder, and fibrous fillers with an aspect ratio of 5 or more and less than 1000 could not be obtained.

[0082] (Example 1) Zirconium tetra-n-butoxide, acetoacetic acid as a ligand, hydroxylammonium chloride as a catalyst, water, and 2-propanol were stirred at room temperature for 15 hours so as to have a molar ratio of 1:1.5:0.025:1.5:22 to hydrolyze zirconium tetra-n-butoxide. Then, after concentration by an evaporator until the zirconia concentration became 20 mass%, the viscosity was increased until it became 2100 to 2800 mPa·s to obtain a drawable sol solution. Using the drawable sol solution thus prepared as a spinning solution, electrospinning was carried out in the same manner as in Comparative Example 1, and collected on a drum collector to prepare a fiber web. Then, the prepared fiber web was placed in a firing furnace and fired under the conditions of a firing temperature of 800 °C for 2 hours in an air atmosphere and then allowed to cool to prepare a fiber web of zirconium nitride precursor fibers containing zirconia. Subsequently, a fiber web of zirconium nitride precursor fibers and magnesium powder (manufactured by High Purity Chemical Research Institute, purity: 99.9%, particle size: 150 mesh) were mixed using an agate mortar while loosening the fiber web so that the zirconia:magnesium in the fiber web was 1 mol:5 mol to prepare a mixture. The prepared mixture was fed into a firing furnace and fired under a nitrogen atmosphere at a firing temperature of 1200 °C for 1 hour. After cooling, magnesium oxide as a by-product was removed using 1 M nitric acid, washed with water and ethanol, and then dried to prepare zirconium nitride fibers (average fiber diameter: 0.65 μm). As a result of subjecting the zirconium nitride fibers prepared in this way to (strength evaluation method), fibrous fillers with an aspect ratio of 5 or more (average fiber diameter: 0.65 μm, average fiber length: 10 μm) were obtained. Therefore, as a result of subjecting the zirconium nitride fibers to (strength evaluation method), they could maintain their fiber shape and were excellent in strength. The results of subjecting to (strength evaluation method) are shown in Figure 4.

[0083] (Example 2) Titanium tetra-n-butoxide, ethyl lactate as a ligand, hydroxylammonium chloride as a catalyst, water, and 2-propanol were stirred at room temperature for 15 hours so that the molar ratio was 1:1:0.025:1.5:22 to hydrolyze titanium tetra-n-butoxide. Then, it was concentrated by an evaporator until the titania concentration reached 30 mass%, and then thickened until the viscosity reached 2100 - 2800 mPa·s to obtain a drawable sol solution. Using the drawable sol solution prepared in this way as a spinning solution, electrospinning was carried out in the same manner as in Comparative Example 1, and collected on a drum collector to prepare a fiber web. Then, the prepared fiber web was fed into a firing furnace and fired under an air atmosphere at a firing temperature of 800 °C for 2 hours, and cooled to prepare a fiber web of titanium nitride precursor fibers containing titania. Subsequently, a fiber web of titanium nitride precursor fibers and magnesium powder (manufactured by High Purity Chemical Laboratory, purity: 99.9%, particle size: 150 mesh) were mixed using an agate mortar while disintegrating the fiber web so that the ratio of titania:magnesium in the fiber web was 1 mol:5 mol to prepare a mixture. The prepared mixture was fed into a firing furnace and fired under a nitrogen atmosphere at a firing temperature of 1200 °C for 1 hour. After cooling, magnesium oxide as a by-product was removed using 1 M nitric acid, washed with water and ethanol, and then dried to prepare titanium nitride fibers (average fiber diameter: 0.80 μm). As a result of subjecting the titanium nitride fibers thus prepared to (strength evaluation method), fibrous fillers with an aspect ratio of 5 or more (average fiber diameter: 0.80 μm, average fiber length: 5 μm) were obtained. Therefore, as a result of subjecting the titanium nitride fibers to (strength evaluation method), they were able to maintain their fiber shape and were excellent in strength. The results of subjecting to (strength evaluation method) are shown in FIG. 5.

[0084] (Example 3) The zirconium nitride fibers prepared in Example 1 were crushed by applying a pressure of 5 kN per 225π mm 2 for 5 seconds to attempt to prepare fibrous fillers. The zirconium nitride fibers were not inadvertently pulverized into powder, and fibrous fillers with an aspect ratio of 5 or more (average fiber diameter: 0.65 μm, average fiber length: 10 μm) could be obtained. Also, as a result of subjecting the zirconium nitride fibrous fillers thus prepared to (strength evaluation method), they were able to maintain their fiber shape and were excellent in strength.

[0085] (Example 4) The titanium nitride fibers prepared in Example 2 were crushed by applying a pressure of 5 kN per 225π mm 2 for 5 seconds to attempt to prepare fibrous fillers. Titanium nitride fibers were able to obtain fibrous fillers with an aspect ratio of 5 or more (average fiber diameter: 0.8 μm, average fiber length: 5 μm) without being inadvertently pulverized into powder. Moreover, as a result of subjecting the titanium nitride fibrous filler prepared in this way to (the method for evaluating strength), it was able to maintain its fiber shape and was excellent in strength.

[0086] (Comparative Example 5) Attempts were made to prepare zirconium nitride fibers in the same manner as in Example 1, except that magnesium powder was not used. However, the zirconium nitride precursor fibers did not become zirconium nitride fibers.

[0087] (Comparative Example 6) Attempts were made to prepare titanium nitride fibers in the same manner as in Example 2, except that magnesium powder was not used. However, the titanium nitride precursor fibers did not become titanium nitride fibers.

[0088] (Comparative Example 7) Attempts were made to prepare zirconium nitride fibers in the same manner as in Example 1, except that activated carbon was used instead of magnesium powder. However, the zirconium nitride precursor fibers did not become zirconium nitride fibers.

[0089] (Comparative Example 8) Attempts were made to prepare titanium nitride fibers in the same manner as in Example 2, except that activated carbon was used instead of magnesium powder. However, the titanium nitride precursor fibers did not become titanium nitride fibers.

[0090] (Comparative Example 9) Zirconium tetra-n-butoxide, acetoacetic acid as a ligand, hydroxylammonium chloride as a catalyst, water, 2-propanol, and 1-hexanol were stirred for 15 hours at room temperature in an atmosphere so as to have a molar ratio of 1:1.5:0.025:1.5:22:0.01 to hydrolyze zirconium tetra-n-butoxide. Then, it was concentrated by an evaporator until the zirconia concentration reached 20 mass%, and then thickened until the viscosity reached 2100 - 2800 mPa·s to obtain a drawable sol solution. Preparation of zirconium nitride fibers was attempted in the same manner as in Example 1, except that the drawable sol solution prepared in this way was used as a spinning solution and magnesium powder was not used. However, the zirconium nitride precursor fibers did not become zirconium nitride fibers.

[0091] (Comparative Example 10) Zirconium tetra-n-butoxide, acetoacetic acid as a ligand, hydroxylammonium chloride as a catalyst, water, 2-propanol, and 1-hexanol were stirred for 15 hours at room temperature in an atmosphere so as to have a molar ratio of 1:1.5:0.025:1.5:22:0.27 to hydrolyze zirconium tetra-n-butoxide. Then, it was concentrated by an evaporator until the zirconia concentration reached 20 mass%, and then thickened until the viscosity reached 2100 - 2800 mPa·s to obtain a drawable sol solution. Preparation of zirconium nitride fibers was attempted in the same manner as in Example 1, except that the drawable sol solution prepared in this way was used as a spinning solution and magnesium powder was not used. However, the zirconium nitride precursor fibers did not become zirconium nitride fibers.

[0092] (Comparative Example 11) Titanium tetra-n-butoxide, ethyl lactate as a ligand, hydroxylammonium chloride as a catalyst, water, 2-propanol, and 1-hexanol were stirred for 15 hours at room temperature in an atmosphere so as to have a molar ratio of 1:1:0.025:1.5:22:0.01 to hydrolyze titanium tetra-n-butoxide. Then, after concentrating with an evaporator until the titania concentration reached 30 mass%, the viscosity was increased until it reached 2,100 to 2,800 mPa·s to obtain a drawable sol solution. Preparation of titanium nitride fibers was attempted in the same manner as in Example 2, except that the drawable sol solution prepared in this way was used as a spinning solution and magnesium powder was not used. However, the titanium nitride precursor fibers did not become titanium nitride fibers.

[0093] (Comparative Example 12) Titanium tetra-n-butoxide, ethyl lactate as a ligand, hydroxylammonium chloride as a catalyst, water, 2-propanol, and 1-hexanol were stirred at room temperature for 15 hours so as to have a molar ratio of 1:1:0.025:1.5:22:0.27 to hydrolyze titanium tetra-n-butoxide. Then, after concentrating with an evaporator until the titania concentration reached 30 mass%, the viscosity was increased until it reached 2,100 to 2,800 mPa·s to obtain a drawable sol solution. Preparation of titanium nitride fibers was attempted in the same manner as in Example 2, except that the drawable sol solution prepared in this way was used as a spinning solution and magnesium powder was not used. However, the titanium nitride precursor fibers did not become titanium nitride fibers.

[0094] The physical properties of the metal nitride fibers and the metal nitride fiber-like fillers prepared as described above are summarized in Tables 1 to 2. Note that since the metal nitride fiber-like fillers could not be obtained, the results of Comparative Examples 3 to 4 are not described in Table 2. Also, since the metal nitride fibers themselves could not be obtained, the results of Comparative Examples 5 to 12 are not described in the table.

Table 1

Table 2

Industrial Applicability

[0095] The titanium nitride fibers, zirconium nitride fibers, titanium nitride fibrous fillers, and zirconium nitride fibrous fillers according to the present invention have physical properties such as high thermal conductivity, impact resistance, and acid resistance, and can be used in various industrial applications such as heat dissipation materials.

Explanation of Signs

[0096] 10: Plate with a smooth surface 11: Main surface of the plate with a smooth surface 20: Cylindrical tube 21: Circle with a diameter of 30 mm

Claims

1. A metal nitride fiber having an average fiber diameter on the order of nanometers, which can maintain its fiber shape after being subjected to the following (strength evaluation method), The metal nitride fibers are titanium nitride fibers or zirconium nitride fibers. (Strength evaluation method) (1) 3 g of titanium nitride fibers or zirconium nitride fibers are placed inside a cylindrical tube (cross-sectional shape: annular shape surrounding a circle with a diameter of 30 mm) fixed upright on a plate with a smooth surface. (2) 225πmm to the titanium nitride fiber or the zirconium nitride fiber contained in the cylindrical tube ２ A pressure of 5 kN is applied per second for 5 seconds. (3) After applying pressure, confirm whether or not titanium nitride fibrous filler or zirconium nitride fibrous filler is present, the aspect ratio of which, calculated by dividing the fiber length (unit: μm) by the fiber diameter (unit: μm), is 5 or more. (4) If titanium nitride fibrous filler or zirconium nitride fibrous filler having an aspect ratio of 5 or more is present, it is judged that the titanium nitride fibers or zirconium nitride fibers are capable of maintaining their fiber shape after being subjected to this measurement method. On the other hand, if titanium nitride fibrous filler or zirconium nitride fibrous filler having an aspect ratio of 5 or more is not present, it is judged that the titanium nitride fibers or zirconium nitride fibers are unable to maintain their fiber shape after being subjected to this measurement method.

2. A metal nitride fibrous filler having an average fiber diameter on the order of nanometers, which can maintain a fiber shape after being subjected to the (strength evaluation method) according to claim 1, The metal nitride fibrous filler is a titanium nitride fibrous filler or a zirconium nitride fibrous filler.

3. (step i) preparing a metal alkoxide solution; (Step ii) preparing a spinnable sol solution by hydrolyzing and polycondensing the metal alkoxide in the metal alkoxide solution; (Step iii) preparing a metal nitride precursor fiber by spinning the spinnable sol solution and calcining the spinnable sol solution; (Step iv) calcining the metal nitride precursor fiber together with magnesium in a nitride gas or nitrogen gas atmosphere to convert the metal nitride precursor fiber into a metal nitride fiber; A method for producing a metal nitride fiber, comprising: The method for producing metal nitride fibers, wherein the metal is titanium or zirconium.

4. After (step iv) according to claim 3, (Step v) applying an external force to the prepared metal nitride fiber to pulverize it; A method for producing a metal nitride fibrous filler, comprising: The method for producing a metal nitride fibrous filler, wherein the metal is titanium or zirconium.

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