JP7555753B2 - Spinning apparatus and method for producing inorganic fibers - Google Patents

Description

The present invention relates to a spinning device and a method for producing inorganic fibers.

Exhaust gas emitted from internal combustion engines such as diesel engines contains particulate matter (hereinafter referred to as PM), and in recent years, the harm that this PM poses to the environment and human body has become a problem. In addition, exhaust gas also contains harmful gas components such as CO, HC, and NOx, and there are concerns about the impact that these harmful gas components have on the environment and human body.

Therefore, various exhaust gas purification devices have been proposed as exhaust gas purification devices that capture PM in exhaust gas and purify harmful gas components. The exhaust gas purification devices are composed of an exhaust gas treatment body made of porous ceramics such as silicon carbide or cordierite, a casing that houses the exhaust gas treatment body, and a retaining seal material (mat material) arranged between the exhaust gas treatment body and the casing. The main purpose of this retaining seal material (mat material) is to prevent the exhaust gas treatment body from coming into contact with the casing that covers its outer periphery and being damaged due to vibrations and impacts caused by the running of the automobile, and to prevent exhaust gas from leaking between the exhaust gas treatment body and the casing.

The mat material is usually made of inorganic fibers, etc. In order to stably hold the exhaust gas treatment body, the inorganic fibers that make up the mat material are required to have high strength.

Patent Document 1 discloses a manufacturing method for dry spinning a spinning solution containing a metal compound and an organic polymer using a blowing method.

Japanese Patent Application Publication No. 5-51806

Patent Document 1 discloses that variable costs (amount of air used) can be significantly improved by making the spinning nozzle have a specific shape. However, Patent Document 1 does not disclose in detail the conditions of the hot air for drying the drawn spinning solution. The process of drying the drawn spinning solution is extremely important. Therefore, depending on the conditions for drying the spinning solution, the spinning solution may vibrate during the drawing stage, resulting in a composite fiber in which two or more fibers are stuck together. Since composite fibers have lower strength than single fibers, conditions that can suppress the vibration of the spinning solution during the drawing stage were necessary to produce a fiber aggregate with higher strength.

The present invention was made in consideration of the above problems, and aims to provide a spinning device that can produce inorganic fibers while preventing the generation of composite fibers.

That is, the spinning device of the present invention is a spinning device having a nozzle that ejects a spinning solution containing an inorganic fiber precursor solution, an air outlet that ejects air for stretching the spinning solution, and a hot air supply mechanism that supplies hot air in a direction that collides with the air ejected from the air outlet, characterized in that the ejection direction of the spinning solution and the ejection direction of the air are approximately parallel, and the hot air is supplied from at least two directions such that the direction in which the hot air is supplied is approximately n-fold symmetric (where n is an integer of 2 or more) with respect to a nozzle extension axis that extends from the central axis of the nozzle in the ejection direction of the spinning solution.

The spinning device of the present invention has a hot air supply mechanism that supplies hot air to the air used to stretch the spinning solution. By supplying hot air to the air used to stretch the spinning solution, the stretched spinning solution can be dried to produce an inorganic fiber precursor. Furthermore, by supplying hot air from at least two directions so that the direction in which the hot air is supplied is approximately n-fold symmetric with respect to the nozzle extension axis, the hot air can be supplied to the air in a state of high symmetry with respect to the nozzle extension axis, so that the oscillation of the spinning solution can be suppressed and the content of composite fibers can be reduced.

In the spinning apparatus of the present invention, it is preferable that the temperature of the hot air at the supply port of the hot air supply mechanism is 100° C. or higher.
When the temperature of the hot air supplied by the hot air supply mechanism is 100° C. or higher, the spinning solution discharged from the nozzle can be easily dried.

In the spinning device of the present invention, in a cross section passing through a point 10 mm away from the tip of the nozzle in the discharge direction along the nozzle extension axis and perpendicular to the nozzle extension axis, it is preferable that the speed of the hot air at n points 45 mm away from the nozzle extension axis and in which the direction in which the hot air is supplied is approximately n-fold symmetrical with respect to the nozzle extension axis is 8 m/s or less at 25°C.

In the spinning device of the present invention, in a cross section passing through a point 20 mm away from the tip of the nozzle along the nozzle extension axis in the discharge direction and perpendicular to the nozzle extension axis, it is preferable that the speed of the hot air at n points 45 mm away from the nozzle extension axis and in which the direction in which the hot air is supplied is approximately n-fold symmetrical with respect to the nozzle extension axis is 4 m/s or more at 25°C.

In the spinning device of the present invention, in a cross section passing through a point 30 mm away from the tip of the nozzle in the discharge direction along the nozzle extension axis and perpendicular to the nozzle extension axis, it is preferable that the speed of the hot air at n points 45 mm away from the nozzle extension axis and in which the direction in which the hot air is supplied is approximately n-fold symmetrical with respect to the nozzle extension axis is 3 m/s or more at 25°C.

In the spinning device of the present invention, in a cross section passing through a point 40 mm away from the tip of the nozzle along the nozzle extension axis in the discharge direction and perpendicular to the nozzle extension axis, it is preferable that the speed of the hot air at n points 45 mm away from the nozzle extension axis and in which the direction in which the hot air is supplied is approximately n-fold symmetrical with respect to the nozzle extension axis is 2 m/s or more at 25°C.

In the spinning device of the present invention, the nozzles are arranged in a substantially straight line at substantially equal intervals, and it is preferable that the hot air is supplied in a direction substantially symmetrical with respect to the nozzle axis extension plane, which is a plane including the nozzle extension axes.

The method for producing inorganic fibers of the present invention includes a spinning step of preparing an inorganic fiber precursor using the spinning apparatus of the present invention, and a calcination step of calcining the inorganic fiber precursor.
By using the spinning apparatus of the present invention, it is possible to produce inorganic fibers while preventing the generation of composite fibers.

FIG. 1 is a perspective view showing a typical example of a spinning apparatus of the present invention. FIG. 2 is a cross-sectional view for explaining an example of a process for producing inorganic fibers using the spinning apparatus shown in FIG. FIG. 3 is a cross-sectional view taken along line BB in FIG. FIG. 4 is a partial enlarged view of the nozzle tip of FIG. FIG. 5 is a perspective view showing a schematic diagram of another example of the spinning apparatus of the present invention. FIG. 6 is a cross-sectional view taken along line CC in FIG. FIG. 7 is a side view showing a schematic diagram of still another example of the spinning apparatus of the present invention. FIG. 8 is a cross-sectional view taken along line DD in FIG. FIG. 9 is a schematic diagram showing an example of inorganic fibers pulverized in the measurement of the composite ratio.

Detailed Description of the Invention
Hereinafter, the embodiments of the present invention will be described in detail. However, the present invention is not limited to the following embodiments, and can be appropriately modified and applied within the scope of the present invention.

[Spinning device]
The spinning apparatus of the present invention is a spinning apparatus having a nozzle that ejects a spinning solution containing an inorganic fiber precursor solution, an air ejection port that ejects air for stretching the spinning solution, and a hot air supply mechanism that supplies hot air in a direction in which the air collides with the air ejected from the air ejection port, characterized in that the ejection direction of the spinning solution and the ejection direction of the air are approximately parallel, and the hot air is supplied from at least two directions so that the direction in which the hot air is supplied is approximately n-fold symmetric (n is an integer of 2 or more) with respect to a nozzle extension axis that extends from the central axis of the nozzle in the ejection direction of the spinning solution.

FIG. 1 is a perspective view showing a typical example of a spinning apparatus of the present invention.
The spinning device 1 has a nozzle 10 that ejects a spinning solution, an air ejection pipe 20 equipped with an air ejection port 20a that ejects air for stretching the spinning solution, and hot air supply pipes 30, 40 that are part of a hot air supply mechanism that supplies hot air in a direction colliding with the air ejected from the air ejection port 20a.
The supply port 30a of the hot air supply pipe 30 and the supply port 40a of the hot air supply pipe 40 face each other via the nozzle extension axis _X10 . In addition, when the central axis _Y30 of the hot air supply pipe 30 passing through the central point P30 of the supply port _30a and the central axis _Y40 of the hot air supply pipe 40 passing through the central point _P40 of the supply port 40a are each extended toward the nozzle extension axis _X10 , they intersect at a point _P10 on the nozzle extension axis _X10 .

Fig. 2 is a cross-sectional view for explaining an example of a process for producing inorganic fibers using the spinning apparatus shown in Fig. 1. Fig. 2 is also a cross-sectional view of the spinning apparatus shown in Fig. 1 taken along line AA.
As shown in FIG. 2, a spinning solution 60 is discharged from a tip 10 a of the nozzle 10 .
The nozzle 10 is disposed inside the air ejection pipe 20 such that the central axis of the air ejection pipe 20 and the central axis of the nozzle 10 overlap.
The air (indicated by the arrow f in FIG. 2) discharged from the air discharge port 20a surrounds the spinning solution 60 discharged from the nozzle 10, and since the discharge direction of the spinning solution 60 and the discharge direction of the air f are approximately parallel to each other, the spinning solution 60 is stretched by the air f.

Hot air (indicated by arrow h in FIG. 2) is supplied from hot air supply pipes 30 and 40 so that it collides with the air f. By supplying the hot air h so that it collides with the air f, the spinning solution 60 is stretched and dried, and an inorganic fiber precursor is obtained.

In the spinning device of the present invention, hot air is supplied from at least two directions so that the direction in which the hot air is supplied is approximately n-fold symmetrical with respect to the nozzle extension axis, so that the hot air can be supplied to the air with high symmetry with respect to the nozzle extension axis, thereby suppressing the oscillation of the spinning solution and reducing the content of composite fibers.

Whether or not the direction in which the hot air is supplied is substantially n-fold symmetric with respect to the nozzle extension axis can be determined by the following method.
First, a reference point is determined to determine the direction in which the hot air is supplied. This reference point is one of the n points for determining the direction in which the hot air is supplied. There are no particular limitations on how the reference point is determined, and it is sufficient to select an appropriate reference point that can be confirmed to have approximately n-fold symmetry using the method described below.
Next, the remaining points (n-1 points) for determining the direction in which the hot air is supplied are determined. The remaining points are determined by the positions when the reference point is rotated by 360/n° around the nozzle extension axis in a cross section that passes through the reference point and is perpendicular to the nozzle extension axis. That is, in the case of approximately three-fold symmetry, the reference point is rotated by 120° around the nozzle extension axis twice. The positions when the reference point is rotated by 120° around the nozzle extension axis and the positions when the reference point is rotated by 240° become the other points for determining the direction in which the hot air is supplied.
Next, the direction in which the hot air is supplied at each of the n locations is measured. The measured direction is rotated around the nozzle extension axis and moved to the reference point. This operation is performed n-1 times, and the directions in which the hot air is supplied at all of the locations are moved to the reference point. With this operation, the directions in which the hot air is supplied at all of the n locations are superimposed on the reference point.
Finally, the direction in which the hot air is supplied after being moved to the reference point is compared, and the maximum angle between the directions in which the hot air is supplied is calculated. If the maximum angle is 10° or less, preferably 5° or less, it can be said that the direction in which the hot air is supplied is substantially n-fold symmetric with respect to the nozzle extension axis.

This will be specifically described with reference to FIG.
FIG. 3 is a cross-sectional view taken along line BB in FIG.
FIG. 3 shows an example in which a central point P ₃₀ of the supply port 30 a of the hot air supply pipe 30 and a central point P ₄₀ of the supply port 40 a of the hot air supply pipe 40 are used as points for determining whether the direction in which the hot air is supplied is approximately n-fold symmetric.
3, the direction in which hot air is supplied at the central point _P30 is indicated by an arrow _h30 , while the direction in which hot air is supplied at the central point _P40 is indicated by an arrow _h40 .
The central point _P30 and the central point _P40 exist on the circumference of a circle _C1 whose center is the nozzle extension axis _X10 . Therefore, when the central point _P40 is rotated 180° around the nozzle extension axis _X10 , it overlaps with the central point _P30 .
Therefore, when the direction in which hot air is supplied at the central point _P40 (direction indicated by arrow _h40 ) is rotated 180° around the nozzle extension axis _X10 , with the central point _P30 as the reference point, the direction in which hot air is supplied after the movement (direction indicated by arrow _h40 ) overlaps with the direction in which hot air is supplied at the central point _P30 (direction indicated by arrow _h30 ). In this case, the angle between the directions in which hot air is supplied is 0°.
Therefore, in the spinning apparatus 1 shown in FIGS. 1, 2 and 3, the direction in which hot air is supplied can be said to be substantially n-fold symmetric (n=2) with respect to the nozzle extension axis X ₁₀ .

In FIG. 3, the center point of the supply port of the hot air supply pipe is used as the point for determining whether the direction in which the hot air is supplied is approximately n-fold symmetric, but other points may be used.

3 illustrates an example in which the direction in which the hot air is supplied is along a plane perpendicular to the nozzle extension axis _X10 , but the direction in which the hot air is supplied may be inclined from the plane perpendicular to the nozzle extension axis _X10 . Even if the direction in which the hot air is supplied is inclined from the plane perpendicular to the nozzle extension axis _X10 , the above determination is made by rotating the direction in which the hot air is supplied around the nozzle extension axis _X10 .

(nozzle)
The nozzle ejects a spinning solution containing an inorganic fiber precursor solution.
The cross-sectional shape of the nozzle for ejecting the spinning solution is not particularly limited, but is preferably circular.
The inner diameter of the nozzle for ejecting the spinning solution is preferably 100 μm to 500 μm.
When the cross-sectional shape of the nozzle is other than circular, the inside diameter of the nozzle is the diameter of a circle equivalent to the area determined from the inside diameter shape of the nozzle.

It is preferable that the tip of the nozzle protrudes 2 to 8 mm from the tip of the air outlet.

The spinning solution contains an inorganic fiber precursor solution.
The inorganic fiber precursor solution may be, for example, a solution containing a metal compound and a polymer compound.

The metal compounds include chlorides, inorganic acid salts such as sulfates and nitrates, organic acid salts such as acetates, hydroxides, etc., of metals such as aluminum, zirconium, silicon, magnesium, thorium, yttrium, calcium, and chromium. Specific examples include aluminum oxychloride, basic aluminum acetate, zirconium oxychloride, basic zirconium acetate, etc. Two or more of these may be used in combination.

Examples of polymeric compounds include water-soluble or water-dispersible polymers such as polyvinyl alcohol, polyethylene glycol, polyethylene oxide, polyacrylamide, starch, starch acetate, hydroxyethyl starch, methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, and carboxymethyl cellulose.

The viscosity of the spinning solution is not particularly limited, but it is preferably 1 to 100 poise.

The extrusion speed of the spinning solution is preferably 0.02 to 0.04 m/s.

(Air discharge pipe)
The air discharge pipe has an air discharge port through which air for drawing the spinning solution is discharged.

The shape of the air ejection pipe is not particularly limited, but it is preferable that the shape allows a nozzle to be placed inside.
When the nozzle is disposed inside the air ejection pipe, the outer periphery of the nozzle is surrounded by the air ejection port, so that the spinning solution ejected from the nozzle is surrounded by air, and the spinning solution can be uniformly drawn.

There may be multiple nozzles arranged inside the air discharge tube.

The shape of the air outlet can be, for example, a polygon such as a triangle, a square, or a hexagon, as well as a circle or an ellipse.

The amount of air discharged from the air discharge port is preferably 0.008 to 0.016 m ³ /min per nozzle.

(Hot air supply mechanism)
The hot air supply mechanism supplies hot air in a direction in which it collides with the air.
The hot air supply mechanism is composed of, for example, a heater that heats air, and a blower that blows the heated air to the hot air supply pipe.
The amount of hot air supplied from the hot air supply mechanism is preferably 3 to 8 m ³ /min throughout the entire spinning apparatus.

In the spinning apparatus of the present invention, hot air is supplied by the hot air supplying mechanism so as to be substantially n-fold symmetric (n is an integer of 2 or more) with respect to the nozzle extension axis.
n may be an integer of 2 or more, and examples of the symmetry include approximately two-fold symmetry, approximately three-fold symmetry, and approximately four-fold symmetry.
From the viewpoint of suppressing the fluctuation of the spinning solution during drawing, it is preferable that the symmetry of the direction in which the hot air is supplied is high, but even if it is approximately two-fold symmetry, the fluctuation of the spinning solution can be sufficiently suppressed.

The temperature of the hot air is not particularly limited, but it is preferable that the temperature of the hot air at the supply port is 100°C or higher.

It is preferable that the hot air speed is approximately the same at n points where the direction in which the hot air is supplied is approximately n-fold symmetrical with respect to the nozzle extension axis. "Approximately the same hot air speed" means that the hot air speed at all n points is 90% to 110% of the average hot air speed at the n points.

The cross-sectional shape of the hot air supply pipe and the cross-sectional shape of the supply port are not particularly limited, and may be, for example, a circle, an ellipse, a polygon such as a square or a rectangle, or an irregular shape.
The cross-sectional shape of the hot air supply pipe and the cross-sectional shape of the supply port may be the same or different from each other.

Hot air may be supplied from two or more directions using one hot air supply pipe.
For example, in the case of a ring-shaped hot air supply pipe arranged along a plane perpendicular to the nozzle extension axis, which has a plurality of circular openings arranged at approximately equal intervals on its inner surface, or a band-shaped opening that goes around the inner surface of the hot air supply pipe in the circumferential direction, hot air can be supplied from two or more directions using a single hot air supply pipe.
When a ring-shaped hot air supply pipe is arranged along a plane perpendicular to the nozzle extension axis and has a band-shaped opening that goes around the inner surface in a circumferential direction, hot air is supplied toward the nozzle extension axis from the entire inner surface of the hot air supply pipe, so that the direction in which the hot air is supplied is approximately n-fold symmetric (where n is any integer greater than or equal to 2).

In the spinning device of the present invention, it is preferable that the wind speed at a point a specified distance from the nozzle tip is within a specified range. This point will be explained using Figure 4.

Fig. 4 is a partially enlarged view of the nozzle tip of Fig. 2. Moreover, the arrows f and h indicating the flow of air and hot air, and the spinning solution, which are shown in Fig. 2, are omitted in Fig. 4.
The planes passing through points (points _a1 , _b1 , _c1 , and _d1 ) that are 10 mm, 20 mm, 30 mm, and 40 mm away from the tip 10a of the nozzle 10 along the nozzle extension axis _X10 in the discharge direction and that are perpendicular to the nozzle extension axis _X10 are indicated by dashed lines a, b, c, and d, respectively.

The cross section taken along the broken line a is a cross section passing through a point _a1 10 mm away from the tip 10a of the nozzle 10 along the nozzle extension axis _X10 and perpendicular to the nozzle extension axis _X10 .
The points _a2 and _a3 shown in Fig. 4 are each 45 mm away from the point _a1 , which is a point on the nozzle extension axis _X10 . In addition, as shown in Fig. 2, the hot air supply pipes ₃₀ and 40 are arranged on the left and right of the nozzle extension axis X10 so as to face each other via the nozzle extension axis _X10 , so that at the points _a2 and _a3 , the direction in which the hot air h is supplied is substantially n-fold symmetric (n = 2) with respect to the nozzle extension axis _X10 .
Therefore, points _a2 and _a3 shown in FIG. 4 correspond to _{two points that are 45 mm away from the nozzle extension axis X10 and have a direction in which the hot air h is supplied that is substantially two-fold symmetrical with respect to the nozzle extension axis X10 in a cross section that passes through point a1 that is} 10 mm away from the tip 10a of the nozzle ₁₀ in the discharge direction along the nozzle extension axis X10 and is perpendicular to the nozzle extension axis _X10 .
The speed of the hot air at points _a2 and _a3 is preferably 8 m/s or less at 25° C.

The cross section taken along the broken line b is a cross section passing through a point _b1 that is 20 mm away from the tip 10a of the nozzle 10 along the nozzle extension axis _X10 and perpendicular to the nozzle extension axis _X10 .
The points _b2 and _b3 shown in Fig. 4 are each 45 mm away from the point _b1 , which is a point on the nozzle extension axis _X10 . In addition, as shown in Fig. 2, the hot air supply pipes ₃₀ and 40 are arranged on the left and right of the nozzle extension axis X10 so as to face each other via the nozzle extension axis _X10 , so that at the points _b2 and _b3 , the direction in which the hot air h is supplied is approximately n-fold symmetric (n = 2) with respect to the nozzle extension axis _X10 .
Therefore, points _b2 and _b3 shown in FIG. 4 correspond to _two points that are 45 mm away from the nozzle extension axis _X10 and have a direction in which the hot air h is supplied that is substantially two-fold symmetrical with respect to the nozzle extension axis _X10 in a cross section that passes through point b1 that is 20 mm away from the tip 10a of the nozzle ₁₀ in the discharge direction along the nozzle extension axis X10 and is perpendicular to the nozzle extension axis _X10 .
The speed of the hot air at points _b2 and _b3 is preferably 4 m/s or more at 25° C.

The cross section taken along the broken line c is a cross section passing through a point _c1 that is 30 mm away from the tip 10a of the nozzle 10 along the nozzle extension axis _X10 and perpendicular to the nozzle extension axis _X10 .
The points _c2 and _c3 shown in Fig. 4 are each 45 mm away from the point _c1 , which is a point on the nozzle extension axis _X10 . In addition, as shown in Fig. 2, the hot air supply pipes ₃₀ and 40 are arranged on the left and right of the nozzle extension axis X10 so as to face each other via the nozzle extension axis _X10 , so that at the points _c2 and _c3 , the direction in which the hot air h is supplied is approximately n-fold symmetric (n = 2) with respect to the nozzle extension axis _X10 .
Therefore, points _c2 and _c3 shown in FIG. 4 correspond to _two points that are 45 mm away from the nozzle extension axis _X10 and have a direction in which the hot air h is supplied that is substantially two-fold symmetrical with respect to the nozzle extension axis _X10 in a cross section that passes through point c1 that is 30 mm away from the tip 10a of the nozzle ₁₀ in the discharge direction along the nozzle extension axis X10 and is perpendicular to the nozzle extension axis _X10 .
The speed of the hot air at points _c2 and _c3 is preferably 3 m/s or more at 25° C.

The cross section taken along the broken line d is a cross section passing through a point _d1 that is 40 mm away from the tip 10a of the nozzle 10 along the nozzle extension axis _X10 and perpendicular to the nozzle extension axis _X10 .
The points _d2 and _d3 shown in Fig. 4 are each 45 mm away from the point _d1 , which is a point on the nozzle extension axis _X10 . In addition, as shown in Fig. 2, the hot air supply pipes ₃₀ and 40 are arranged on the left and right of the nozzle extension axis X10 so as to face each other via the nozzle extension axis _X10 , so that at the points _d2 and _d3 , the direction in which the hot air h is supplied is approximately n-fold symmetric (n = 2) with respect to the nozzle extension axis _X10 .
Therefore, points _d2 and _d3 shown in FIG. 4 correspond to _{two points that are 45 mm away from the nozzle extension axis X10 and have a direction in which the hot air h is supplied that is substantially two-fold symmetrical with respect to the nozzle extension axis X10 in a cross section that passes through point d1 that is} 40 mm away from the tip 10a of the nozzle ₁₀ in the discharge direction along the nozzle extension axis X10 and is perpendicular to the nozzle extension axis _X10 .
The speed of the hot air at points _d2 and _d3 is preferably 2 m/s or more at 25° C.

The hot air speed at each point converted to 25°C can be determined by operating the spinning device with the heater of the hot air supply mechanism turned off under conditions of an ambient temperature of 25°C, and measuring the air speed at each point with an anemometer.

Methods for adjusting the speed of the hot air at each of the above-mentioned points include adjusting the amount (supply speed) of hot air supplied from the hot air supply mechanism, or changing the position of the supply port through which the hot air is supplied.
An example of a method for adjusting the hot air supply speed is to adjust the aperture of the supply port while keeping the amount of hot air supplied fixed.

In the spinning device of the present invention, the hot air supply mechanism may have three or more supply ports for supplying hot air.
An example of a spinning apparatus having three supply ports for supplying hot air will be described with reference to FIG.

FIG. 5 is a perspective view showing a schematic diagram of another example of the spinning apparatus of the present invention.
The spinning device 2 shown in Figure 5 has a nozzle 11 that ejects the spinning solution, an air ejection pipe 21 equipped with an air ejection port 21a that ejects air for stretching the spinning solution, and hot air supply pipes 31, 41, and 51 that are part of a hot air supply mechanism that supplies hot air in a direction colliding with the air ejected from the air ejection port 21a.
The nozzle 11 is disposed inside the air discharge pipe 21 .
The hot air supply pipes 31, 41, 51 all pass through a point a predetermined distance away from the tip of the nozzle 11 along the nozzle extension axis _X11 and exist on a plane perpendicular to the nozzle extension axis _X11 . The supply port 31a of the hot air supply pipe 31, the supply port 41a of the hot air supply pipe 41, and the supply port 51a of the hot air supply pipe 51 all face the nozzle extension axis _X11 . When the central axis _Y31 of the hot air supply pipe 31, the central axis _Y41 of the hot air supply pipe 41, and the central axis _Y51 of the hot air supply pipe 51 are each extended toward the nozzle extension axis _X11 , they intersect at a point _P11 on the nozzle extension axis _X11 .

FIG. 6 is a cross-sectional view taken along line CC in FIG.
As shown in FIG. 6, the angles at which the central axis Y ₃₁ , the central axis Y ₄₁ , and the central axis Y ₅₁ intersect at a point P ₁₁ on the nozzle extension axis X ₁₁ are each 120°.
The directions in which hot air is supplied to the center point P ₃₁ of the supply port 31a, the center point P ₄₁ of the supply port 41a, and the center point P ₅₁ of the supply port 51a are indicated by arrows h ₃₁ , h ₄₁ , and h ₅₁ , respectively.
The central point _P31 , the central point _P41 , and the central point _P51 exist on the circumference of a circle _C2 centered on the nozzle extension axis _X11 . Therefore, when the central point _P41 is rotated 120° clockwise around the nozzle extension axis _X11 , it overlaps with the central point _P31 . Also, when the central point _P51 is rotated 120° counterclockwise around the nozzle extension axis _X11 , it overlaps with the central point _P31 .
Therefore, when the direction in which hot air is supplied at the central point _P41 (direction indicated by arrow _h41 ) and the direction in which hot air is supplied at the central point _P51 (direction indicated by arrow _h51 ) are rotated around the nozzle extension axis _X11 and overlapped with the central point _P31 , which is the reference point, the direction in which hot air is supplied at the central point _P41 (direction indicated by arrow _h41 ) and the direction in which hot air is supplied at the central point _P51 (direction indicated by arrow _h41 ) overlap with the direction in which hot air is supplied at the central point _P31 (direction indicated by arrow _h31 ).
Therefore, in the spinning device 2 shown in FIG. 5, the direction in which hot air is supplied can be said to be substantially n-fold symmetric (n=3) with respect to the nozzle extension axis _X11 .

The spinning apparatus of the present invention may include a plurality of nozzles.
When a plurality of nozzles are provided, the plurality of nozzles are preferably arranged at substantially equal intervals in a substantially linear manner. In this case, it is preferable that the hot air is supplied in a direction substantially symmetrical with respect to a nozzle axis extension plane that is a plane including the plurality of nozzle extension axes.
At this time, hot air is supplied by the hot air supply mechanism to all the nozzles so that the directions in which the hot air is supplied are substantially two-fold symmetrical with respect to the nozzle extension axis that extends from the nozzle in the discharge direction.

FIG. 7 is a side view showing a schematic diagram of still another example of the spinning apparatus of the present invention.
The spinning device 3 shown in FIG. 7 includes a plurality of nozzles 12a, 12b, 12c, 12d, 12e, and 12f, an air discharge pipe 22 having an air discharge port 22a that discharges air for drawing the spinning solution, and hot air supply pipes 32, 33, 34, 42, 43, and 44 that are part of the hot air supply mechanism.
The nozzles 12a, 12b, 12c, 12d, 12e, and 12f are arranged at approximately equal intervals in an approximately straight line so as to protrude from the inside of the air discharge pipe 22. The air discharge port 22a is also provided in a straight line along the same direction as the multiple nozzles 12a, 12b, 12c, 12d, 12e, and 12f are arranged in an approximately straight line.

In the spinning device 3 shown in FIG. 7, when a nozzle axis extension plane S is assumed to be a plane including the nozzle extension axes Xa, Xb, Xc, Xd, Xe, and Xf obtained by extending the nozzles 12a, 12b, 12c, 12d, 12e, and 12f in the direction of ejection of the spinning solution, the supply port 32a of the hot air supply pipe 32 and the supply port 42a of the hot air supply pipe 42, the supply port 33a of the hot air supply pipe 33 and the supply port 43a of the hot air supply pipe 42, and the supply port 34a of the hot air supply pipe 34 and the supply port 44a of the hot air supply pipe 44 are each opposed to each other via the nozzle axis extension plane S.

Whether or not the direction in which the hot air is supplied is substantially symmetrical with respect to the nozzle axis extension plane can be determined by the following method.
First, the nozzle extension axis is obtained for each nozzle, and a nozzle axis extension plane that includes all the nozzle extension axes is defined.
Next, three pairs of two reference points are determined, each pair being equally spaced from the nozzle axis extension plane and facing each other across the nozzle axis extension plane. Two pairs of reference points are disposed at positions facing each other across the nozzle extension axis of an end nozzle that has only one adjacent nozzle. At this time, the shortest distance from each reference point to the nozzle axis extension plane is all set to be equal. By this operation, two pairs of reference points are determined.
The remaining pairs of reference points are placed at the midpoints of lines connecting the reference points that are not paired with each other among the already determined reference points.
Next, the direction in which the hot air is supplied is measured at each reference point.
Next, the direction in which the hot air is supplied at one of the paired reference points is moved so as to be mirror symmetric (plane symmetric) with respect to the nozzle axis extension plane, and is superimposed on the other reference point to determine the angle between the directions in which the hot air is supplied. If the angle between all pairs of reference points is 5° or less, it can be said that the direction in which the hot air is supplied is approximately plane symmetric with respect to the nozzle axis extension plane.

This will be specifically described with reference to FIG.
FIG. 8 is a cross-sectional view taken along line DD in FIG.
As shown in FIG. 8, among nozzles 12a, 12b, 12c, 12d, 12e, and 12f, nozzles 12a and 12f have only one adjacent nozzle, and therefore are also nozzles located at the ends (also called end nozzles).
Reference points _P32 and P42 are provided at points spaced apart by an equal distance (the distance indicated by the double arrow _L1 and the distance indicated by the double arrow _L2 ) via the nozzle extension axis Xa of the nozzle _12a , which is the end nozzle. The reference point _P32 coincides with the center point of the supply port 32a of the hot air supply pipe 32, and the reference point _P42 coincides with the center point of the supply port 42a of the hot air supply pipe 42.
Further, a reference point _P34 and a reference point P44 are provided at points spaced apart by an equal distance (the distance indicated by the double arrow _L1 and the distance indicated by the double arrow _L2 ) via the nozzle extension axis Xf of the nozzle _12f , which is an end nozzle. The reference point _P34 coincides with the center point of the supply port 34a of the hot air supply pipe 34, and the reference point _P44 coincides with the center point of the supply port 44a of the hot air supply pipe 44.
The reference point _P32 and the reference point _P42 , and the reference point _P42 and the reference point _P44 , which are spaced apart by an equal distance via the nozzle axis extension plane S, respectively constitute two pairs of reference points.
Furthermore, point _P33 , which is the midpoint between reference point _P32 and reference point _P34 , which are not paired with each other, and point _P43 , which is the midpoint between reference point _P42 and reference point _P44 , which are not paired with each other, form the final pair of reference points.
8, the reference point _P33 coincides with the center point of the supply port 33a of the hot air supply pipe 33. Also, the reference point _P43 coincides with the center point of the supply port 43a of the hot air supply pipe 43.

Next, the direction of the hot air at the reference point is moved so as to be mirror-symmetric with respect to the nozzle axial extension plane S.
In FIG. 8 , when the central axis _Y32 of the hot air supply pipe 32, the central axis _Y33 of the hot air supply pipe 33, and the central axis _Y34 of the hot air supply pipe 34 are each extended toward the nozzle axis extension plane S, they overlap with the central axis _Y42 of the hot air supply pipe 42, the central axis _Y43 of the hot air supply pipe 43, and the central axis _Y44 of the hot air supply pipe 44 on the nozzle axis extension plane S, respectively.
Therefore, the direction in which hot air is supplied at reference point _P32 (direction indicated by arrow _h32 ), the direction in which hot air is supplied at reference point _P33 (direction indicated by arrow _h33 ), and the direction in which hot air is supplied at reference point _P34 (direction indicated by arrow _h34 ), and the direction in which hot air is supplied at reference point _P42 (direction indicated by arrow _h42 ), the direction in which hot air is supplied at reference point _P43 (direction indicated by arrow _h43 ), and the direction in which hot air is supplied at reference point _P44 (direction indicated by arrow _h44 ) can be said to be opposite directions to each other across the nozzle axis extension plane S.
Therefore, when the direction in which the hot air is supplied at the reference point _P42 (direction indicated by the arrow _h42 ) is moved so as to be mirror-symmetrical with respect to the nozzle axis extension plane S, it overlaps with the direction in which the hot air is supplied at the reference point _P32 (direction indicated by the arrow _h32 ). Similarly, when the direction in which the hot air is supplied at the reference point _P43 (direction indicated by the arrow _h43 ) is moved so as to be mirror-symmetrical with respect to the nozzle axis extension plane S, it overlaps with the direction in which the hot air is supplied at the reference point _P33 (direction indicated by the arrow _h33 ), and when the direction in which the hot air is supplied at the reference point _P44 (direction indicated by the arrow _h44 ) is moved so as to be mirror-symmetrical with respect to the nozzle axis extension plane S, it overlaps with the direction in which the hot air is supplied at the reference point _P34 (direction indicated by the arrow _h34 ). In this case, the angles between the directions in which the hot air is supplied are all 0°.
Therefore, in the spinning device 3 shown in FIG. 7, the direction in which the hot air is supplied is approximately symmetrical with respect to the nozzle axis extension plane S.

Note that Figures 7 and 8 illustrate an example in which the direction in which the hot air is supplied is along a plane perpendicular to the nozzle extension axis (Xa, Xb, Xc, Xd, Xe, Xf), but the direction in which the hot air is supplied may be inclined from the plane perpendicular to the nozzle extension axis.
If the direction in which the hot air is supplied at the reference point is inclined from a plane perpendicular to the nozzle extension axis, the above judgment is made by moving the direction in which the hot air is supplied so that it is mirror-symmetric with respect to the nozzle axis extension plane S.

Note that, although FIG. 8 illustrates an example in which the reference point and the center point of the supply port coincide, the reference point and the center point of the supply port do not have to coincide. Therefore, the reference point may be a predetermined distance away from the supply port. Furthermore, the reference point does not have to be on the central axis of the hot air supply pipe.

When the spinning device of the present invention is equipped with multiple nozzles, it is preferable that the spacing between the nozzles is 1 mm or more.

The composite ratio of the fibers obtained by the spinning apparatus of the present invention is preferably 15% or less, more preferably 10% or less, and even more preferably 5% or less.

The fiber composite ratio can be determined by observing the crushed fibers under a scanning electron microscope (SEM). Specifically, the crushed fibers are observed under an SEM at 1000x magnification, and all fibers present in the field of view are classified as single fibers or composite fibers, and the number of fibers is counted. This is performed for a total of four fields of view, and the composite ratio is calculated by dividing the number of composite fibers by the total number of fibers x 100 (%).

FIG. 9 is a schematic diagram showing an example of inorganic fibers pulverized in the measurement of the composite ratio.
As shown in FIG. 9, by observing the inorganic fibers under a scanning electron microscope after crushing them, it is possible to distinguish between the single fibers 70 present in the region α and the composite fibers 80 present in the region β.

The compressive breaking strength of an inorganic fiber is the pressure required to break the fiber when the fiber is compressed in a direction perpendicular to the axial direction of the inorganic fiber.
Specifically, first, one single fiber is selected from the inorganic fibers fixed on a pressure plate using an optical microscope (magnification: about 10 to 50 times). At this time, the fiber diameter is also measured. Next, the selected fiber is pressed with an indenter. The value obtained by dividing the load at which the fiber breaks by the contact area with the indenter is the compression breaking strength of the single fiber.
The same procedure is carried out on 10 randomly selected single fibers, and the average value obtained is regarded as the compressive breaking strength of the single fiber.
The average diameter of the inorganic fibers can be determined by observing the pulverized fibers with a scanning electron microscope (SEM). Specifically, the pulverized fibers are observed with a SEM at a magnification of 1000 times, and the diameters of all the single fibers present in the field of view are measured. This is performed for a total of four fields of view, and the average value is taken as the average fiber diameter.

If composite fibers are present in the field of view, one composite fiber is then selected from the inorganic fibers fixed on the pressure plate using an optical microscope (magnification: about 10 to 50 times). At this time, the fiber diameter of the composite fiber is also measured. The cross-sectional area of the composite fiber is calculated from the fiber diameters of all the single fibers constituting the composite fiber, and the fiber diameter is the diameter of the projected area circle corresponding to the cross-sectional area. The same operation is performed on 10 randomly selected composite fibers, and the average value calculated is the average fiber diameter of the composite fiber. Next, the selected composite fiber is pressed with an indenter. The load at which the composite fiber breaks divided by the contact area with the indenter is the compressive breaking strength of the composite fiber. The compressive breaking strength of the entire inorganic fiber is calculated by the following formula.
Compressive breaking strength of all inorganic fibers = [compressive breaking strength of single fiber x (100 - composite ratio)] + [compressive breaking strength of composite fiber x composite ratio]

The compressive breaking strength of the inorganic fibers produced by the spinning apparatus of the present invention is preferably 1.0 GPa or more.

[Method of manufacturing inorganic fibers]
The method for producing inorganic fibers of the present invention is characterized by comprising a spinning step of preparing an inorganic fiber precursor using the spinning apparatus of the present invention, and a calcination step of calcining the inorganic fiber precursor.
By using the spinning apparatus of the present invention, it is possible to produce inorganic fibers while preventing the generation of composite fibers.

The spinning process is a process for preparing an inorganic fiber precursor using the spinning device of the present invention, so a detailed explanation will be omitted.

In the calcination step, the inorganic fiber precursor is calcined.
The firing conditions may be appropriately changed depending on the composition of the inorganic fiber precursor, but an example is a method of firing at 1000° C. to 1600° C. for 30 minutes to 6 hours.

Before calcining the inorganic fiber precursor, the inorganic fiber precursor may be subjected to a needling treatment.

(Example)
EXAMPLES Hereinafter, examples that more specifically disclose the present invention will be described, however, the present invention is not limited to these examples.

Example 1
(a) Preparation of spinning solution: 124 g of a 30 wt % silica sol solution and 93 g of a 10 wt % aqueous polyvinyl alcohol solution were added to 400 g of an aqueous aluminum oxychloride solution prepared to have an Al content of 75 g/L and an Al:Cl ratio of 1:1.8 (atomic ratio), and the mixture was then concentrated at 50° C. to prepare a spinning solution having a viscosity of 20 poise and an alumina-silica content of 30 wt %.

(b) Drawing of the spinning solution (spinning process)
Using the spinning apparatus shown in FIG. 1, the spinning solution was discharged and drawn under predetermined conditions, and the inorganic fiber precursor was collected on a conveyor provided at a position 3 m away from the nozzle.
A nozzle (inner diameter: 300 μm) for discharging the spinning solution was arranged inside the air outlet for discharging air for stretching the spinning solution, and the direction of the spinning solution discharged from the nozzle was parallel to the direction of the air discharged from the air outlet. The tip of the nozzle was protruded 6 mm from the air outlet.
Furthermore, the hot air supply mechanism supplied hot air in a direction colliding with the air discharged from the air discharge port. The hot air supply mechanism had two hot air supply ports, and the positions of the supply ports were adjusted so that the two supply ports faced each other across the nozzle extension axis in a cross section perpendicular to the nozzle extension axis. The temperature of the hot air at the supply ports was 100°C. The speed of the hot air at the supply port of the hot air supply mechanism was 25.0 m/s.
The direction in which the hot air was supplied was two-fold symmetrical with respect to the nozzle extension axis in a cross section perpendicular to the nozzle extension axis.

(c) Calcination of the inorganic fiber precursor (calcination step)
The obtained inorganic fiber precursor was calcined in air at 1200° C. for 30 minutes to obtain alumina fibers.

[Wind speed measurements at each point]
The spinning apparatus was operated under the same conditions as in Example 1, except that the heater provided in the hot air supply mechanism was stationary, and the wind speed was measured at two points that passed through points 10 mm, 20 mm, 30 mm, and 40 mm away from the tip of the nozzle along the nozzle extension axis in the discharge direction, 45 mm away from the nozzle extension axis in a cross section perpendicular to the nozzle extension axis, and the direction in which the hot air is supplied is approximately two-fold symmetrical with respect to the nozzle extension axis. The room temperature at this time was 25°C. This is the speed of the hot air converted to 25°C at the same point when the heater provided in the hot air supply mechanism was operated. The results are shown in Table 1. In Table 1, each point is shown corresponding to the points _a1 , _a2 , _a3 , _b1 , _b2 , _b3 , _c1 , _c2 , _c3 , _d1 , _d2 , and _d3 shown in FIG. 4.

(Examples 2 to 4)
The hot air velocity at the supply port and the shape of the supply port were not changed, and the symmetry of the direction in which the hot air was supplied was maintained, but the position of the supply port was changed to change the air velocity at each point as shown in Table 1. Except for this, an inorganic fiber precursor was prepared and calcined in the same manner as in Example 1 to obtain alumina fiber.

(Comparative Example 1)
Except for the fact that the spinning solution was stretched while hot air was supplied to only one of the supply ports, an inorganic fiber precursor was produced and calcined to obtain an alumina fiber in the same manner as in Example 1. The amount of hot air supplied from one of the supply ports and the amount of air discharged from the air discharge port were the same as in Example 1.

[Measurement of Compressive Breaking Strength and Average Fiber Diameter]
The inorganic fibers obtained in each of the Examples and Comparative Examples were subjected to measurement of compressive breaking strength and average fiber diameter.
The methods for measuring the compressive breaking strength and the average fiber diameter are as explained in the description of the present invention. The results are shown in Table 1.

[Measurement of the composite ratio]
The composite ratio of the inorganic fibers obtained in each of the Examples and Comparative Examples was measured.
The method for measuring the composite ratio is as explained in the description of the present invention. The results are shown in Table 1.

From the results in Table 1, it is understood that by using the spinning apparatus of the present invention, the generation of composite fibers can be prevented and inorganic fibers with a low composite ratio can be obtained.
In Comparative Example 1, the conjugation rate exceeded 15% and the compressive breaking strength was less than 1 GPa. This is thought to be because the direction in which the hot air was supplied was not substantially n-fold symmetric with respect to the nozzle extension axis, so the symmetry of the direction in which the hot air was supplied was low, causing the spinning solution (fiber) to oscillate during drawing, resulting in the formation of a large number of conjugated fibers.

1, 2, 3 Spinning device 10, 11, 12b, 12c, 12d, 12e Nozzle 12a, 12f Nozzle (end nozzle)
10a Nozzle tip 20, 21, 22 Air discharge pipe 20a, 21a, 22a Air discharge port 30, 31, 32, 33, 34, 40, 41, 42, 43, 44, 51 Hot air supply pipe (part of hot air supply mechanism)
30a, 31a, 32a, 33a, 34a, 40a, 41a, 42a, 43a, 44a, 51a Supply port 60 Spinning solution 70 Short fiber 80 Composite fiber _a1 Point _a2 , a3 10 mm away from the tip of the nozzle along the nozzle extension axis in the discharge direction Point a1 Point _b1 Point _b2 , b3 20 mm away from the tip of the nozzle along the nozzle extension axis in the discharge direction Point _b1 Point _c1 Point _c2 , _c3 30 mm away from the tip of the _nozzle along the nozzle extension axis in the discharge direction Point _c1 , _C2 Circle centered on _the nozzle extension axis _d1 Point _d2 , _d3 40 mm away from the _tip of the _nozzle along the nozzle extension axis in the discharge direction Point f 45 mm away from _d1 Air h Hot air _h30 , _h31 , _h32 , _h33 , _h34 , _h40 , _h41 , _h42 , _h43 , _h44 , _{h51 Arrows L1} , _L2 indicating the direction in which hot air is supplied Shortest distance S from the nozzle axis extension plane to a reference point Nozzle axis extension plane _P10 , _P11 Points on the nozzle extension axis _P30 , _P31 , _P40 , P41, _P51 Center point of the supply port _P32 , _P33 , _P34 , _P42 , _P43 , _P44 Reference point _X10 , _X11 , Xa, Xb, Xc, Xd, Xe, Xf Nozzle extension axis _Y30 , _Y31 , _Y32 , _{Y33 , Y34} , _Y40 , _Y41 , _Y42 , Y ₄₃ , Y ₄₄ , Y ₅₁ Central axis α, β region of hot air supply pipe

Claims (8)

A nozzle for discharging a spinning solution containing an inorganic fiber precursor solution;
an air outlet for injecting air for drawing the spinning solution;
a hot air supplying mechanism for supplying hot air in a direction in which the hot air collides with the air discharged from the air discharge port,
The ejection direction of the spinning solution and the ejection direction of the air are approximately parallel to each other,
The spinning apparatus is characterized in that the hot air is supplied from at least two directions so that the directions in which the hot air is supplied are approximately n-fold symmetric (n is an integer of 2 or more) with respect to a nozzle extension axis that is an extension of the central axis of the nozzle in the discharge direction of the spinning solution. The spinning device according to claim 1, wherein the temperature of the hot air at the supply port of the hot air supply mechanism is 100°C or higher. The spinning device according to claim 1 or 2, wherein in a cross section passing through a point 10 mm away from the tip of the nozzle along the nozzle extension axis in the discharge direction and perpendicular to the nozzle extension axis, the hot air velocity at n points 45 mm away from the nozzle extension axis and in which the direction in which the hot air is supplied is approximately n-fold symmetric with respect to the nozzle extension axis is 8 m/s or less at 25°C. The spinning device according to any one of claims 1 to 3, wherein in a cross section passing through a point 20 mm away from the tip of the nozzle along the nozzle extension axis in the discharge direction and perpendicular to the nozzle extension axis, the speed of the hot air at n points 45 mm away from the nozzle extension axis and in which the direction in which the hot air is supplied is approximately n-fold symmetric with respect to the nozzle extension axis is 4 m/s or more at 25°C conversion. The spinning device according to any one of claims 1 to 4, wherein in a cross section passing through a point 30 mm away from the tip of the nozzle along the nozzle extension axis in the discharge direction and perpendicular to the nozzle extension axis, the speed of the hot air at n points 45 mm away from the nozzle extension axis and in which the direction in which the hot air is supplied is approximately n-fold symmetric with respect to the nozzle extension axis is 3 m/s or more at 25°C. The spinning device according to any one of claims 1 to 5, wherein in a cross section passing through a point 40 mm away from the tip of the nozzle along the nozzle extension axis in the discharge direction and perpendicular to the nozzle extension axis, the speed of the hot air at n points 45 mm away from the nozzle extension axis and in which the direction in which the hot air is supplied is approximately n-fold symmetric with respect to the nozzle extension axis is 2 m/s or more at 25°C. A plurality of the nozzles are arranged substantially linearly at substantially equal intervals,
The spinning device according to any one of claims 1 to 6, wherein the hot air is supplied so that the direction in which the hot air is supplied is approximately symmetrical with respect to a nozzle axis extension plane, which is a plane including the plurality of nozzle extension shafts. A spinning step of preparing an inorganic fiber precursor using the spinning apparatus according to any one of claims 1 to 7;
and a calcination step of calcining the inorganic fiber precursor.

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