JPH04352817A - Production of alumina continuous filament and its precursor fiber - Google Patents

Abstract

PURPOSE:To obtain the subject high-purity fiber of stabilized quality with excellent productivity by dry spinning a spinning solution composed of a water-soluble Al salt component, alumina powder and a spinning assistant such as polydisperse-based polyethylene oxide, a sintering assistant, etc. CONSTITUTION:Aluminum chloride hexahydrate is added to an aqueous solution of basic aluminum chloride and magnesium chloride and ferric chloride are further added and dissolved to prepare a solution of a water-soluble aluminum salt. A spinning solution composed of a slurry containing alumina powder, a spinning assistant composed of polydisperse-based polyethylene oxide satisfying 500000-3000000 weight-average molecular weight and >=50 polydispersity (d) (Mw/Mn) (Mn is number-average molecular weight) and, as necessary, further a sintering assistant in the aforementioned solution of the water-soluble aluminum salt is dry spun through a spinneret having >=100 spinning holes having 0.1-0.5mm hole diameter. The resultant spun precursor fiber is then passed through a spinning stack set at 35-200 deg.C maximum temperature to regulate the adhesive moisture content to 5.5-12.0wt.%. Thereby, the fiber is wound onto a bobbin at 50-400m/min speed to afford the objective fiber.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention has high tensile strength, high modulus of elasticity, excellent high temperature heat resistance, and has an alumina content of 95%.
The present invention relates to an improved method for producing continuous alumina fibers and their precursor fibers having a weight percent or higher content.

0002

BACKGROUND OF THE INVENTION Due to its excellent properties, alumina fiber is used for various purposes such as heat insulating materials and reinforcing materials for composite materials. In particular, continuous filaments have the advantage that they can be used in various forms such as ropes, nets, and textiles to suit various purposes, exhibit sufficient performance, and are easy to handle. , which are difficult to manufacture compared to short fibers, and an industrially advantageous manufacturing method is required.

[0003] Various methods have been proposed for producing alumina long fibers, but even those commonly called alumina fibers usually contain 10% by weight or more of silica, making them highly pure. Those that are not have poor heat resistance. Methods for producing high-purity alumina fibers with an alumina content of 95% by weight or more include a method of pulling single-crystalline alumina fibers from an α-alumina melt, or a slurry in which fine alumina particles are dispersed in an aqueous solution of water-soluble aluminum salt. Slurry method (Japanese Patent Publication No. 57-27210, Japanese Patent Application Laid-Open No. 63-7511)
No. 7) are known, but only the slurry method is industrially practiced.

0004

[Problems to be Solved by the Invention] The slurry method uses a water-soluble aluminum salt such as basic aluminum chloride and an inorganic component such as alumina powder as the main components, and also uses a spinning aid to improve the stringiness during spinning. Dry spinning is performed using a spinning dope to which a small amount of a water-soluble organic polymer compound is added as an agent. By the way, in the practical application of alumina fiber production, in order to improve productivity, it is desirable to use a spinneret with an increased number of spinning holes and to spin at the fastest possible speed. However, in the case of the slurry method, the main components in the spinning dope are inorganic substances, resulting in poor spinnability.In order to improve the spinnability, it is preferable to increase the amount of water-soluble organic polymer compound added. If the amount increases, it causes significant volatilization and shrinkage of components during the subsequent high-temperature heat treatment process, resulting in a decrease in fiber quality and an extreme increase in the frequency of yarn breakage. Therefore, the amount of water-soluble organic polymer compound added is limited to about 20% by weight based on the total oxide weight, and there is a limit to the improvement of spinnability by such a spinning aid. In other words, when spinning is performed using a spinning dope prepared by the conventional method, the spinning speed cannot be increased due to insufficient spinnability, the quality tends to be uneven, and the amount of spinning is also limited. In particular, when spinning is performed from a spinneret with a large number of spinning holes (several hundred or more), the discharge amount from each spinning hole varies, unevenness due to natural fall of the spinning stock solution, contact resistance with the air flow in the spinning tube, etc. Due to non-uniformity of the atmosphere inside the cylinder, such as temperature and humidity, the spinning state and drying state of each filament become non-uniform, resulting in a problem that variations in fiber diameter and denier are likely to occur. In addition, in the above-mentioned Japanese Patent Publication No. 57-27210, the spinning speed is 30 to 18 when using a spinneret having 30 to 75 spinning holes.
Although an example of spinning at a speed of 0 m/min is shown, the productivity is low and insufficient with 30 to 75 spinning holes. According to experiments conducted by the present inventors, when commercially available polyethylene oxide is used as a spinning aid, the spinning speed is at most 5 when using a spinneret with 300 spinning holes.
If the speed is up to about 0 m/min, stable spinning cannot be achieved and alumina fibers of good quality cannot be obtained. That is, the conventional methods have poor productivity and are difficult to obtain high-quality alumina fibers, so they are not satisfactory as industrial manufacturing methods.

The present invention solves these problems and provides a method for producing alumina continuous fibers and their precursor fibers, which can produce high-quality alumina continuous fibers with less unevenness with good productivity and industrial advantage. The purpose is to provide

[0006]

[Means for Solving the Problems] As a result of various studies on a method for producing high-purity alumina continuous fibers using a slurry method, the present inventors have discovered that using a specific spinning aid, spinning, drying, and It has been discovered that by performing firing, the spinning speed can be increased and high purity continuous alumina fibers of stable quality can be obtained.

That is, in the present invention, a spinning dope consisting of a slurry containing a water-soluble aluminum salt solution, alumina powder, a spinning aid, and, if necessary, a sintering aid is dry-spun to form high-purity alumina continuous fibers. In the method for producing precursor fibers, the spinning aid is a polydisperse polyethylene oxide satisfying the following formula: - Weight average molecular weight Mw = 500,000 to 3 million - Polydispersity d
(=Mw/Mn)≧50 (Mn: number average molecular weight) An amount equivalent to 5 to 20% by weight based on the total oxide weight of the fiber and a carbon number of 2
5 alcohols or aliphatic carboxylic acids having 1 to 5 carbon atoms in an amount equivalent to 10% by weight or less, or a mixture thereof. Further, the present invention is a method for producing continuous alumina fibers, which comprises firing the precursor fibers obtained by the above method for producing precursor fibers.

The greatest feature of the method of the present invention is that a spinning aid suitable for high-speed spinning is found, conditions for preparing a spinning dope using it and optimal spinning conditions are determined, and optimal conditions for each step are determined. As a result, the spinning speed was significantly improved (more than 8 times that of the conventional method). Thereby, the productivity of alumina fibers is significantly improved, and it is possible to eliminate variations in fiber diameter and denier unevenness of the obtained alumina fibers, and the homogeneity of the alumina fibers can be significantly improved.

Polyethylene oxide is commercially available in a wide range of grades with average molecular weights ranging from tens of thousands to several million, mainly for use as binders for paper manufacturing, finishing pastes for textiles, binders for molding, etc. ing. These polyethylene oxides are classified and displayed according to their average molecular weight (weight average molecular weight) estimated from their viscosity, and the molecular weight distribution is generally adjusted to be as sharp as possible. The polydispersity (d), which is expressed as the ratio of the weight average molecular weight to the number average molecular weight, has not been studied much in the past, but according to the analysis of the present inventors, the polydispersity of commercially available polyethylene oxide The degree d is usually less than 10, even if it is particularly large it is 20
It is as follows. However, the degree of polydispersity of polyethylene oxide-based spinning aids has a large effect on the stability of spinning, and it has been found that increasing the degree of polydispersity can significantly improve the spinning speed in the slurry method. It was. The degree of polydispersity can be evaluated by the difference between the respective average values of Mw, Mn, or Z average molecular weight. In particular, as an indicator, the ratio of Mw and Mn Mw/M
It was possible to find an effective relationship between the degree of polydispersity expressed by n (this is referred to as polydispersity d) and spinning stability. That is, polydisperse polyethylene oxide satisfying the following: Mw=500,000 to 3,000,000·d (=Mw/Mn)≧50 can significantly improve spinning stability. It is not clear why the spinning stability improves when a material with such a wide molecular weight distribution width is used, but the greater the polydispersity, the less entangled polyethylene oxide molecules become when passed through the spinning holes. It can be inferred that it has good fluidity and excellent spinnability.

The method of the present invention will be explained in detail below. The method of the invention can basically be carried out based on the slurry method. That is, a spinning stock solution prepared by dispersing alumina powder in a water-soluble aluminum salt solution and adding a spinning aid to a slurry to which a sintering aid is added if necessary is dry-spun using a spinneret to form high-purity alumina continuous fibers. producing precursor fibers;
This is fired to produce high-purity alumina continuous fibers. Here, high purity refers to an alumina content of 95% by weight or more.

In relation to the spinning aid according to the present invention, a preferred embodiment of the method for producing the precursor fiber is as follows: The viscosity of the spinning stock solution is adjusted to 500 to 5000 poise at 25°C, and the dry spinning is carried out with a This is carried out using a spinneret having 100 or more spinning holes of 0.1 to 0.5 mm, and the resulting spun product is passed through a spinning tube whose maximum temperature is set at 35 to 200°C to reduce the amount of attached moisture to 5. .5 to 12.0% by weight to obtain precursor fibers, which are wound onto a bobbin at a speed of 50 to 400 m/min. The precursor fibers can be stored in a wound form on a bobbin and supplied to the firing process whenever necessary. Note that long-term storage is also possible, but in this case it is preferable to store it indoors with controlled temperature and humidity.

[0012] In the above-described embodiment, the precursor fiber can be stably prepared even when the spinning speed is increased, so that productivity can be greatly improved. Furthermore, although the spinning speed is directly related to productivity, it is also related to the quality of the precursor fibers, especially the variation in quality, and increasing the spinning speed improves the productivity and reduces the variation in quality. Improvements in productivity are related to improvements in quality, and this was another unexpected effect. From this point of view, the standard for increasing the spinning speed is a spinning speed of 50 m/min or more using a spinneret having 100 or more spinning holes. If the spinning speed is less than 50 m/min, productivity will be poor, and the precursor filaments leaving the spinning hole will stretch under their own weight, and the falling speed may be greater than the winding speed, resulting in large fluctuations within the spinning tube. As a result, the fiber diameter becomes non-uniform, making it impossible to obtain high-quality fibers. Furthermore, if the number of spinning holes in the spinneret is small, the spinning properties will be stable, but the productivity will be low, so it is preferable that the number of spinning holes is 100 or more. This standard has never been achieved with conventional slurry methods. Even if the spinning speed is lower than the above, as long as an improved result is recognized in comparison with the conventional method, it is technically meaningful, and the present invention does not exclude it, but from the viewpoint of industrial productivity, the above standards are adopt.

Next, each process will be sequentially explained based on a preferred embodiment of the method for producing continuous alumina fibers of the present invention. First, in an aqueous solution of water-soluble aluminum salt, 10 to 40
Alumina powder with an average particle diameter of 0.1 μm or less equivalent to 5% to 20% by weight of a polyethylene oxide spinning aid, if necessary, an amount equivalent to 10% by weight or less of alcohols or carboxylic acid compounds, or a mixture thereof , further adding a sintering aid in an amount equivalent to 3% by weight or less if necessary,
A spinning stock solution is prepared so that the viscosity at 25° C. is 500 to 5000 poise. The aqueous solution of the water-soluble aluminum salt is preferably one in which 30% by weight or more of the salt is dissolved, and the salt used has a purity of 95% by weight or more as Al2 O3 after firing. Examples of water-soluble aluminum salts used here include basic aluminum chloride, basic aluminum nitrate, basic aluminum acetate, and basic aluminum chloroacetate. In order to improve the fluidity of the spinning raw material, reduce the volatile content during calcination and firing, and improve the fiber strength, A
The l2 O3 content is 95% by weight or more and the average particle size is 0.
Alumina powder of 1 μm or less is added in an amount equivalent to 10 to 40% by weight based on the total oxide amount in the product alumina fiber, and mixed uniformly. If the amount of alumina powder used is less than 10% by weight, the fluidity of the spinning raw material will deteriorate and shrinkage during firing will increase, which is not preferable. If the amount of alumina powder used exceeds the equivalent of 40% by weight, the fluidity of the spinning raw material becomes too large, resulting in poor spinnability, and the precursor fibers tend to dry, resulting in yarn breakage. The homogeneity and density of the fibers become poor, which is not preferable. The particle size of the alumina powder used is preferably as small as possible from the viewpoint of spinnability or making the crystal grains in the fiber after firing as fine and uniformly dense as possible, and the average particle size is 0.1μ.
m or less is preferable. Further, instead of alumina powder, an aluminum compound or alumina sol that becomes alumina by firing such as boehmite, bayerite, diaspore, or pseudoboehmite can also be used.

The polyethylene oxide spinning aid has a weight average molecular weight Mw of 500,000 to 3,000,000, preferably 1,500,000 to 2,500,000, and a ratio of weight average molecular weight Mw to number average molecular weight Mn of Mw/Mn. A polydispersity d expressed as 50 or more and a very wide molecular weight distribution are used. Mw and Mn can be determined by gel permeation chromatography (GPC) measurement method. Polyethylene oxide with this special molecular weight distribution has better spinnability than normal polyethylene oxide, especially at 50 m
The effect of improving spinnability is large at spinning speeds of /min or higher. When polyethylene oxide has a weight average molecular weight of less than 500,000, the spinnability of the spinning dope is poor, and when it is extruded from the spinning hole, it tends to form droplet-shaped balls, and the winding speed is 50.
m/min or higher, thread breakage occurs frequently. On the other hand, polyethylene oxide with a weight average molecular weight of more than 3 million or a polydispersity d of less than 50 and a sharp molecular weight distribution has high viscoelasticity of the spinning dope, resulting in poor spinnability and a reduction in fiber diameter. I don't like it because I can't do it. To prepare such polyethylene oxide, analyze the Mw and Mn of commercially available polyethylene oxide,
By appropriately mixing them, the desired Mw and d can be achieved.

The amount of polyethylene oxide added is 5 to 20% based on the total oxide amount, taking into consideration the average molecular weight and spinning speed.
It is preferable to set it appropriately within the range of weight %. Addition amount is 5% by weight
If the spinning speed is less than 5, the effect as a spinning aid will be small, and the spinning speed will be
On the other hand, if it exceeds 20% by weight, the spinnability is good, but the amount of volatilization in the firing process exceeds 60% by weight, making it impossible to obtain high-quality alumina fibers, which is not preferable. .

[0016] In addition to the above-mentioned polyethylene oxide as a spinning aid, by adding not more than 10% by weight of alcohols having 2 to 5 carbon atoms, aliphatic carboxylic acids having 1 to 5 carbon atoms, or mixtures thereof, Furthermore, spinnability is improved. In addition, when adding, it is preferable to add it in an amount equivalent to 0.3% by weight or more. Examples of alcohols used include monohydric and polyhydric alcohols such as ethanol, propanol, butanol, ethylene glycol, propanediol, and glycerin, and carboxylic acids include formic acid, acetic acid, propionic acid, butyric acid, maleic acid, and malonic acid. Examples include acids, hydroxy acids such as lactic acid and citric acid, and salts thereof. By adding these alcohols or carboxylic acids, the spinning speed can be increased to 5
Spinnability at speeds of 0 m/min or higher is significantly improved. The reason for this is that by adding these compounds, the molecules of polyethylene oxide are untangled, the molecules are arranged in a linear chain, and the spinnability and stretchability are improved. Also,
In order to increase the spinning speed, it is necessary to dry the precursor fiber quickly, but these compounds evaporate more slowly than the water in the precursor and are effective in preventing the occurrence of cracks on the fiber surface. It is assumed that. Addition amount is 10% by weight
Exceeding this is not preferable because it may cause fusion of the precursor fibers and deteriorate the fiber properties.

[0017] If necessary, 3% by weight of oxides may be added to the spinning dope for the purpose of improving the strength of the alumina fibers.
CuO, MgO, ZrO2, PbO, C in equivalent amounts or less
A sintering aid made of an oxide such as r2 O3 or Fe2 O3 can be added. If the amount added exceeds 3% by weight, the high temperature heat resistance of the fiber will decrease, which is not preferable.

Next, the spinning stock solution prepared as described above is spun into a precursor fiber. Spinning is preferably carried out using a spinning device in which a spinning tube is connected below a spinneret having a large number of spinning holes for drying the precursor fibers emitted from the spinning holes until they can be wound onto a bobbin. . Since this spinning dope has extremely good spinning properties, spinning can be performed at much higher speeds than in conventional methods.

The amount of water in the slurry, which is a uniform mixture of a water-soluble aluminum salt aqueous solution, alumina powder, a spinning aid, etc., is adjusted by means such as evaporation or addition of water, and the viscosity is adjusted to the optimum viscosity for spinning to obtain a spinning dope. shall be. The optimum viscosity varies depending on the type of raw material used, the composition of the spinning raw material, the spinning conditions, etc., but the viscosity at 25°C is 500 to 5000.
Poise range. If the viscosity of the spinning solution is lower than 500 poise, the spinnability will be poor and the solution will flow easily, resulting in non-uniform fiber shapes. Furthermore, drying in the drying process becomes insufficient, and the precursor fibers tend to fuse together. On the other hand, the viscosity is 50
If it exceeds 00 poise, it will be difficult to operate in the spinning and drying process.
Thread breakage is likely to occur inside the drying cylinder.

Next, the spinning dope prepared as described above is spun into a precursor fiber, but since this spinning dope has extremely good spinnability, it can be spun at a much higher speed than in the conventional method. spinning is possible.

[0021] The above spinning stock solution is passed through a spinneret having 100 to 5,000 spinning holes with a diameter of 0.2 to 0.5 mm.
Dry spinning is carried out at a spinning speed of 0 to 400 m/min. If the spinning speed is less than 50 m/min, productivity will be poor, and the precursor filaments leaving the spinning hole will stretch under their own weight, and the falling speed may be greater than the winding speed, resulting in large fluctuations within the spinning tube. This is not preferable because the fiber diameter becomes non-uniform and high quality fibers cannot be obtained. On the other hand, if the spinning speed exceeds 400 m/min, the strength of the precursor filament will not be able to withstand the tensile force, and yarn breakage will easily occur, which is undesirable. The precursor filament made of the spinning dope that has been shaped into a fiber after exiting the spinning hole is drawn in a spinning tube connected to a spinneret, and is dried by contacting with an air flow adjusted to an appropriate temperature and humidity. and wound onto a bobbin as a precursor fiber. The whole spinning tube is 1
Although it may be configured with one zone, it is preferable to have a configuration with two or more zones whose temperature and humidity are individually controlled. The airflow inside the spinning tube may normally be air, but
An inert gas or an oxidizing gas may be used as necessary. Furthermore, the direction of the airflow can be parallel to, countercurrent to, or cross-flowing with respect to the flow direction of the fibers. moreover,
The gas atmosphere and direction of airflow can also be changed for each zone.

[0022] Hereinafter, an example will be described in which a spinning tube is used, which is composed of an upper zone in contact with a spinneret and a lower zone connected below the upper zone. The length of the upper zone in contact with the spinneret is approximately 0.5 to 1.5 m, depending on the viscosity of the stock solution, spinning speed, humidity, etc., and the maximum temperature within the zone is within the range of 35 to 70°C. It is preferable to set it so that In this zone, the fibers are partially dried and drawn to a thickness of about 7 to 40 μm. It is preferable that the lower zone has a length of 2 m or more, and the temperature is preferably such that the maximum temperature is in the range of 40 to 200° C., and the temperature increases as it goes downward. The temperature gradient does not necessarily have to be continuous;
It is also possible to have a configuration in which the chamber is divided into three or more sections, preferably three or more sections, and the temperature is adjusted for each section. The maximum temperature in the lower zone is also related to the spinning speed, but when the spinning speed is 400 m
/min or less, the temperature is preferably 200°C or less. If the temperature exceeds 200°C, in addition to the free water content of the precursor fiber, part of the crystallized water of the water-soluble aluminum salt, which is the main component, will rapidly volatilize, and the volatilization of alcohols and carboxylic acids will become significant. This is undesirable because it becomes hard and brittle, and more fuzz is generated during winding. The degree of drying is such that the amount of free water contained in the wound precursor fiber is 5.5 to 12.0% by weight, preferably 8.5 to 12.0% by weight.
The content should be within the range of 10.5% by weight. Remaining free water has the effect of improving the handling properties of the precursor fibers and allowing further drawing treatment. Free water content is 5.
If it is less than 5% by weight, the resistance at the guides and rollers when winding at a speed of 50 m/min or more is large, and the precursor fibers are significantly damaged by bending, etc., causing fuzz. On the other hand, if it exceeds 12.0% by weight, the filaments or yarns may fuse together due to compaction when the precursor fiber is wound onto a bobbin, which is undesirable because it causes deterioration in the physical properties of the fiber.

[0023] In the conventional method, it is not possible to increase the spinning speed, so differences in the drawing state between filaments occur due to air resistance and uneven temperature distribution within the spinning cylinder, resulting in variations in fiber diameter and However, according to the method of the present invention, it is possible to increase the spinning speed to 50 m/min or more, so it is possible to significantly reduce variations in fiber diameter and denier unevenness. In other words, the spinning dope has elasticity and resistance to withstand the winding force at speeds of 50 to 400 m/min, and the spun precursor fibers are pulled by the winding machine to reduce air resistance. This results in a uniform stretching state without being affected much by other factors, and a homogeneous precursor fiber can be obtained. Also,
Due to the effects of polyethylene oxide, alcohols, carboxylic acids, etc. added as spinning aids, the once wound precursor fiber can be further drawn within a range of 5% or less, and denier unevenness can be further reduced. . Note that it is also possible to install constant speed rollers with different speeds between the spinning tube and the winding machine, and to continuously apply a draft and perform a stretching operation after spinning.

The precursor fiber thus obtained can be stored in a wound form on a bobbin and supplied to the firing process whenever necessary. In addition, when storing for a long period of time, it is preferable to store it indoors with controlled temperature and humidity.

[0025] This precursor fiber is fired to obtain α-alumina fiber. The firing is preferably performed by passing the precursor fiber wound around the bobbin through a firing furnace while unwinding it. The inside of the firing furnace preferably has a temperature distribution such that the temperature increases continuously or stepwise from room temperature near the fiber supply port to the highest temperature near the exit. The maximum temperature is in the range of 1300 to 1600°C. The feeding speed of the fibers varies depending on the temperature distribution, furnace length, etc., but in order to obtain high quality alumina fibers, the limit is about 30 m/min. The residence time of the fibers in each temperature range in the furnace varies depending on the diameter and number of filaments that make up the fibers, but as a rough guide, the first half of the firing furnace is heated from room temperature to 750°C.
The temperature distribution is such that the temperature gradually increases continuously or stepwise to the maximum temperature in the range of ~1000℃, and in the latter half, the temperature rises relatively quickly to the maximum temperature in the range of 1300 to 1600℃, and then near the exit. Preferably, the temperature distribution is such that the temperature is maintained at the same temperature until then. Generally, the diameter of the precursor fibers is very small relative to the furnace opening, so it is efficient to pass a plurality of precursor fibers through the same furnace at the same time. In the method of the present invention, the spinning speed can be increased to about 400 m/min, so it is advantageous in terms of equipment costs to pass at least three or more precursor fibers in parallel during the firing process. Yes, it is practical.

The alumina continuous fiber obtained by the method of the present invention is a homogeneous high-purity α-alumina fiber with an alumina purity of 95% by weight or more with little unevenness in quality, and has excellent high temperature resistance and can be used in various heat insulating materials and composites. This material is suitable for reinforcing materials.

[0027]

EXAMPLES The method of the present invention will be explained in more detail with reference to Examples below. (Example 1) 2000 g of basic aluminum chloride aqueous solution
(Content as Al2O3: 23.5% by weight) was added with 14g of aluminum chloride hexahydrate to adjust the Al/Cl molar ratio to 1.8, and further magnesium chloride (Mg
33 g of Cl2 .6H2 O) and ferric chloride (FeC
13 .6H2 O) was added and dissolved. 165g (equivalent to 10% by weight based on total oxide) in this aqueous solution
Alumina powder having an average particle size of 0.02 μm was mixed and dispersed by stirring for 1 hour. In this slurry, while slowly stirring, a weight average molecular weight Mw of 3 as determined by GPC measurement was added.
An amount equivalent to 10% by weight based on the total oxide of polyethylene oxide prepared to have a polydispersity d of 00,000 to 3,200,000 and a polydispersity d of 250 to 290 was added and mixed. The obtained viscous slurry was further dehydrated under reduced pressure and adjusted to have a viscosity of 3000 poise at 25°C.

[0028] Using the slurry thus prepared as a spinning dope, a spinning device was used in which a spinning tube of 5 m in length was connected to a spinneret having 1000 spinning holes with a diameter of 0.3 mm, and an evaluation test for spinning properties was carried out. I did it. The test method is first 20
Start at a spinning speed of m/min, then gradually increase the spinning speed, and perform spinning while controlling so that the free moisture content of the precursor fiber is approximately 9% by weight and the filament diameter is 15 μm, causing yarn breakage. The maximum spinning speed at which stable spinning could be achieved without any problems was determined. During this time, the temperature at the top of the spinning tube is adjusted within the range of 30 to 70°C while monitoring the spinning condition, and the temperature at the bottom of the spinning tube is adjusted to within a range of 30 to 70℃ while monitoring the drying condition of the precursor fiber.
The temperature was adjusted within the range of 0 to 250°C. The results are shown in Table 1, and the polydispersity d of polyethylene oxide was 25.
In the range of 0 to 290, by adjusting Mw to the range of 500,000 to 3 million, the spinning speed is 50 m/min.
Stable spinning was possible with the above conditions.

[0029]

[Table 1] (Example 2) The weight average molecular weight Mw of the polyethylene oxide used was about 2 million, and the polydispersity d was 50 to 90.
The spinnability test was conducted in the same manner as in Example 1 except that the spinnability was changed between 0 and 0. The results are shown in Table 2, and M
When using polyethylene oxide with w adjusted to about 2 million, it is possible to spin at around 30 m/min even if d is less than 50, but in order to obtain a spinning speed of 50 m/min or more, d must be increased. 50 or more, further 100m/
It can be seen that it is necessary to set d to 100 or more in order to obtain a spinning speed of min. In addition, the spinning speed is 5
If the speed was smaller than 0 m/min, not only was the productivity low, but as shown in Example 4, the variation in quality was significantly large.

[0030]

[Table 2] (Example 3) As a spinning aid, the weight average molecular weight Mw is 20
A spinnability test was carried out in the same manner as in Example 1, except that polyethylene oxide having a polydispersity d of 80,000 and a polydispersity d of 408 was used, and the alcohols or carboxylic acids shown in Table 3 were added. Note that alcohols or carboxylic acids were added before adding polyethylene oxide. In addition, the precursor fibers obtained at each of the highest stable spinning speeds were fired at a maximum temperature of 1500°C in a firing furnace divided into two stages, the first and second stages, each 4 m in length, to form filaments. Diameter approx. 10
μm α-alumina fibers were produced and their tensile strength and tensile modulus were measured. The results are shown in Table 3 (tensile strength and tensile modulus are average values of 300 filaments). Table 3
From the results, it was found that the spinning speed could be further improved by adding alcohols or carboxylic acids in addition to polyethylene oxide. Furthermore, based on the physical properties of the obtained alumina continuous fibers, the optimum amount of alcohols or carboxylic acids added is in the range of 0.3 to 10% by weight; if it exceeds 10% by weight, thread breakage occurs frequently during firing. I understand.

[0031]

[Table 3] (Example 4) 5% by weight of ethylene glycol in Example 3
In the example in which 10% was added, precursor fibers spun at different spinning speeds were fired in the same manner as in Example 3.
300 filaments were randomly sampled from α-alumina fibers consisting of 00 filaments, and variations in fiber diameter and tensile strength were examined. Also, spinning speed 100m
Similarly, variations in fiber diameter and tensile strength were also examined for the precursor fibers obtained by drawing the precursor fibers at 2%. The results are shown in Table 4, and it can be seen that the higher the spinning speed and the further stretching, the smaller the variations in fiber diameter and tensile strength.

[0032]

[Table 4] (Example 5) Polyethylene oxide with a weight average molecular weight Mw of 2,020,000 and a polydispersity d of 281, and for comparison, polyethylene oxide with a weight average molecular weight Mw of 1,830,000 and a polydispersity d of 11 were used. Otherwise, spinning stock solutions A and B were prepared in the same manner as in Example 1.

Using this spinning dope, a spinnability test was conducted in the same manner as in Example 1, except that the number of spinning holes in the spinneret was changed. The results are shown in Table 5, and when Mw is 20
In the method of the present invention using polyethylene oxide with a polydispersity d of 20,000 and 281, even if a spinneret with 3,000 spinning holes is used, the spinning speed is 120 m/min, and the spinning speed with 100 spinning holes is The spinneret allows spinning at a high speed of 300 m/min. On the other hand, in the case of the conventional method using polyethylene oxide with Mw of 1.83 million and polydispersity d of 11, even if a spinneret with 100 spinning holes is used, the spinning speed is only about 50 m/min. I know it can't be done.

[0034]

[Table 5]

[0035]

Effects of the Invention When producing precursor fibers of alumina continuous fibers by dry spinning a slurry in which alumina powder is added to an aqueous solution of a water-soluble aluminum salt using a conventionally known spinning aid, the When continuous spinning is performed from a spinneret having spinning holes, the spinning speed at which stable spinning can be achieved is at most about 50 m/min, which is problematic as an industrial production method. On the other hand, according to the method of the present invention, it is possible to spin at a high speed of 50 m/min or more, reaching a maximum of 400 m/min from a spinneret having 100 or more spinning holes, and the α -The quality of alumina continuous fibers has also been stabilized, and productivity has improved significantly.

The greatest feature of the method of the present invention is that a spinning aid suitable for high-speed spinning is found, conditions for preparing a spinning dope using it and optimal spinning conditions are determined, and optimal conditions for each step are determined. As a result, the spinning speed has been increased by more than eight times compared to the conventional method. As a result, the productivity of alumina continuous fibers has been significantly improved, and the uniformity of the alumina continuous fibers has been significantly improved, as the fiber diameter variation and denier unevenness of the obtained alumina continuous fibers has been eliminated. An advantageous manufacturing method has been established.

Claims (6)

[Claims] Claim 1: Dry spinning a spinning dope consisting of a slurry containing a water-soluble aluminum salt solution, alumina powder, a spinning aid, and, if necessary, a sintering aid, to obtain precursor fibers of high-purity alumina continuous fibers. A method for producing a precursor fiber, characterized in that at least a polydisperse polyethylene oxide satisfying the following formula is used as the spinning aid.・Weight average molecular weight Mw = 500,000 to 3 million ・Polydispersity d
(=Mw/Mn)≧50 (Mn: number average molecular weight) 2. Polydisperse polyethylene oxide as a spinning aid is used in a range of 5 to 50% based on the total oxide weight of the alumina continuous fibers.
20% by weight equivalent and 10% by weight of alcohols having 2 to 5 carbon atoms or aliphatic carboxylic acids having 1 to 5 carbon atoms.
The method for producing precursor fibers according to claim 1, characterized in that less than or equal to a considerable amount or a mixture thereof is used. Claim 3: The viscosity of the spinning dope is 50 at 25°C.
Adjust the poise to 0 to 5000, and dry spin the pore size to 0.1 to 5000 poise.
The process is carried out using a spinneret having 100 or more spinning holes of 0.5 mm, and the resulting spun product is heated at a maximum temperature of 35 to 200 mm.
Passed through the spinning tube set at ℃ to reduce the amount of attached moisture to 5.5
~12.0% by weight to obtain a precursor fiber, which was reduced to 50~12.0% by weight
2. The method for producing a precursor fiber according to claim 1, wherein the precursor fiber is wound onto a bobbin at a speed of 400 m/min. 4. A method for producing continuous alumina fibers, which comprises firing precursor fibers obtained by the method for producing precursor fibers according to any one of claims 1 to 3. 5. The method for producing continuous alumina fibers according to claim 4, wherein the precursor fibers are stretched in a range of 5% or less and then fired. 6. A polydisperse polyethylene oxide that satisfies the following formula and is used in the method for producing a precursor fiber according to claim 1.・Weight average molecular weight Mw = 500,000 to 3 million ・Polydispersity d
(=Mw/Mn)≧50 (Mn: number average molecular weight)