JP7449043B2 - Alumina-based continuous fiber for inorganic composite materials and its manufacturing method - Google Patents

Description

The present invention relates to an alumina-based continuous fiber for inorganic composite materials having a coating layer consisting of a water-based organic sizing agent and inorganic fine particles, and a method for producing the same.

BACKGROUND ART Consideration has been given to the use of inorganic composite materials in high-temperature components of gas turbine engines such as aircraft, which require light weight and high durability.
Inorganic composite materials consist of inorganic fibers that serve as reinforcing materials and a matrix material, and an interfacial layer is formed at the interface between the inorganic fibers and the matrix. By preventing the propagation of cracks, the strength and toughness of inorganic composites can be increased.
In order to form this interfacial layer, it has been proposed to provide in advance a coating layer that can serve as an interfacial layer on the inorganic fibers before being composited.

Patent Document 1 proposes a method in which low-conductivity inorganic fibers are coated with a conductive polymer and further coated with a lubricating substance. However, it is necessary to perform a process of coating a conductive polymer and a lubricant substance, and an electrophoretic deposition (EPD) method is used to coat the lubricant substance, which makes the process complicated and difficult to manufacture. The cost will be high.

Patent Document 2 proposes a method of forming a coating layer on silicon carbide fibers by chemical vapor deposition (CVD). However, since silicon carbide fibers are extremely brittle, a base material is formed before the coating layer is formed, and a coating layer is formed on top of that, but this results in uniformity where the fibers overlap. There is a problem in that it is difficult to form a covering layer. In addition, before forming the coating layer, a step is required to remove the sizing agent from the fibers, and a reactor is required to perform CVD, making the process complicated and the manufacturing cost high. becomes.

Patent Document 3 also proposes a method in which inorganic fibers are sized and coated with a heat-resistant substance at the same time. However, the heat-resistant substances are short fibers, whiskers, and powder, and there is no mention of their sizes. Further, the method of Patent Document 3 aims to improve the wettability of the matrix material and ceramic and uniformly disperse continuous fibers in the composite material. Furthermore, the process is complicated, as it includes a process of vibrating a treatment liquid consisting of a sizing agent and a heat-resistant substance using ultrasonic waves.

Japanese Patent Application Publication No. 2016-156109 JP 2018-95508 Publication Japanese Unexamined Patent Publication No. 63-59473

The present invention was made in view of the problems in the conventional alumina-based continuous fibers having a coating layer for inorganic composite materials and their manufacturing method. An object of the present invention is to provide an alumina-based continuous fiber for an inorganic composite material having a coating layer consisting of a sizing agent and inorganic fine particles, and a method for producing the same.

The gist of the present invention is as follows.
1. Consisting of an aqueous organic sizing agent selected from the group consisting of polyvinyl alcohol, polyvinyl acetal, polyoxyethylene and/or aqueous polyurethane, either alone or as a mixture, and zirconia, titania, alumina, boron nitride or silicon carbide with a particle size of 10 to 200 nm. Inorganic fine particles selected from the group , and a coating layer that becomes an interface layer when composited with a matrix material is provided in advance before compositeization,
An alumina-based continuous fiber for an inorganic composite material, wherein the amounts of the water-based organic sizing agent and the inorganic fine particles in the coating layer are 0.5 to 5% by mass and 1 to 6% by mass, respectively, based on the alumina continuous fiber.
2 . Consisting of an aqueous organic sizing agent selected from the group consisting of polyvinyl alcohol, polyvinyl acetal, polyoxyethylene and/or aqueous polyurethane, either alone or as a mixture, and zirconia, titania, alumina, boron nitride or silicon carbide with a particle size of 10 to 200 nm. The alumina-based continuous fibers are continuously immersed in a treatment solution containing an aqueous dispersion having inorganic fine particles selected from the group , and the aqueous organic sizing agent and the inorganic fine particles are added to the alumina-based continuous fibers at a rate of 0.5 to 0.5, respectively. A coating that becomes an interfacial layer when the inorganic fine particles attached to the alumina continuous fibers are fixed with a sizing agent by adhering 5% by mass and 1 to 6% by mass and drying, and then composited with the matrix material on the fibers. A method for producing alumina-based continuous fibers for inorganic composite materials, characterized in that a layer is formed in advance before compositing .
3 . 2. The method for producing alumina-based continuous fibers for inorganic composite materials according to 2 above, wherein the concentration of inorganic fine particles in the treatment liquid consisting of an aqueous liquid of an aqueous organic sizing agent and an aqueous dispersion of inorganic fine particles is 4.0 to 15 % by mass.
4 . 4. The method for producing an alumina-based continuous fiber for an inorganic composite material according to any one of 2 or 3 above, wherein the aqueous dispersion of inorganic fine particles is made neutral or alkaline.

The present invention provides alumina-based continuous fibers having a coating layer consisting of a water-based organic sizing agent and inorganic particles, which becomes an interfacial layer of inorganic particles at the interface between the matrix and the alumina-based continuous fibers when combined with an inorganic matrix material. can do.
Furthermore, in the production method of the present invention, coating with the sizing agent and inorganic fine particles can be performed simultaneously, and no complicated steps are required to form the coating layer on the alumina continuous fibers.
In addition, by forming a coating layer using a dipping method in the state of continuous fibers, a uniform coating layer can be formed on the surface of the continuous alumina fibers.
Therefore, the coating layer can be uniformly formed on the alumina-based continuous fibers rather than forming the coating layer in a woven fabric, and the step of forming the coating layer in a woven fabric or the like can be omitted.

This is an SEM (scanning electron microscope) photograph (magnification: 6000 times) of an untreated uncoated alumina-based continuous fiber of a reference example. 1 is a SEM photograph of alumina-based continuous fibers with a coating layer obtained in Example 1. FIG. 2 is a SEM photograph of the alumina continuous fibers having the coating layer obtained in Example 1, which were heated at 1000° C. and the organic sizing agent was thermally decomposed and removed. FIG. 1 is a SEM photograph of an alumina-based continuous fiber with a coating layer obtained in Comparative Example 1. 1 is an SEM photograph of the alumina-based continuous fibers with the organic sizing agent removed when the alumina-based continuous fibers with the coating layer obtained in Comparative Example 1 were heated at 1000°C. 3 is a SEM photograph of alumina-based continuous fibers coated only with inorganic fine particles obtained in Comparative Example 2. 2 is an SEM photograph of the alumina continuous fibers obtained in Comparative Example 2, which were coated only with inorganic fine particles and were heated at 1000°C. FIG. 3 is an SEM photograph of the alumina continuous fibers obtained in Comparative Example 3, which were coated only with the organic sizing agent and were heated at 1000° C., from which the organic sizing agent had been removed. FIG.

The alumina-based continuous fiber for inorganic composite materials of the present invention is an alumina-based continuous fiber having a coating layer consisting of a water-based organic sizing agent and inorganic fine particles.
In the present invention, the water-based organic sizing agent is not particularly limited, but is water-soluble or water-dispersible, and includes, for example, polyvinyl alcohol, polyvinyl acetal, polyoxyethylene, water-based polyurethane, etc. alone or in mixtures. .
In addition, the inorganic fine particles are not particularly limited, but are preferably inorganic fine particles that do not easily react with alumina-based continuous fibers. Specifically, fine particles such as zirconia, titania, alumina, boron nitride, and silicon carbide are used. Among them, zirconia fine particles are particularly preferred.

In the present invention, the inorganic fine particles in the alumina-based continuous fiber coating layer must have a particle size of 10 to 200 nm in order to ensure the smoothness of the coating layer surface when handling the alumina-based continuous fibers as a reinforcing material. is preferred.
The amount of the water-based organic sizing agent in the coating layer of the alumina continuous fibers, that is, the amount attached to the fibers, is preferably 0.5 to 5% by mass based on the alumina continuous fibers. If the amount of water-based organic sizing agent is less than 0.5% by mass, it will be difficult to fix and hold the inorganic fine particles and they will easily fall off. If it exceeds 5% by mass, it will be difficult to completely remove them by heating when composited with the matrix material. becomes.
Further, the amount of inorganic fine particles attached to the fibers in the coating layer of the continuous alumina fibers is preferably 1 to 6% by mass based on the continuous alumina fibers. If the amount of inorganic fine particles is less than 1% by mass, it is insufficient to function as an interfacial layer formed when composited with a matrix material, and if it exceeds 6% by mass, the inorganic fine particles cannot be treated with a water-based organic sizing agent. Covering and fixing is insufficient, the interfacial layer is not uniform, and the coated alumina continuous fibers become hard, making it difficult to wind up or process to form a composite base material. .

When the alumina continuous fibers for inorganic composites of the present invention are composited with a matrix material, the aqueous organic sizing agent is heated to a high temperature of 1000 to 1300°C during the composite process in the coating layer of the alumina continuous fibers. It is decomposed and removed, and the inorganic fine particles remain to form an interface layer made of inorganic fine particles at the interface between the alumina continuous fibers and the matrix.
The interfacial layer made of inorganic fine particles in the inorganic composite material prevents the alumina fibers from adhering to the matrix and reduces damage to the fibers caused by direct contact of the matrix with the alumina fibers that serve as reinforcing materials. This improves the strength of the inorganic composite material, and for example, increases the tensile strength if the composite material is a long composite material.

The alumina-based continuous fiber for inorganic composite materials of the present invention can be produced as follows.
That is, alumina-based continuous fibers are continuously immersed in a treatment liquid consisting of a water-based organic sizing agent and an aqueous dispersion of inorganic fine particles having a particle size of 10 to 200 nm, and the organic sizing agent and inorganic fine particles are attached to the alumina-based continuous fibers. By drying, the alumina continuous fibers are sized and coated with inorganic fine particles at the same time, and the inorganic fine particles attached to the alumina continuous fibers are fixed with a sizing agent to form a coating layer on the fiber surface. The purpose is to manufacture alumina-based continuous fibers for inorganic composite materials.
In the present invention, alumina-based continuous fibers are used as reinforcing fibers for inorganic composite materials, but these alumina-based continuous fibers can be applied in the form of threads with any number of single threads, and the total fineness of the threads, There is no particular restriction on the number of single threads.

For the treatment liquid consisting of a water-based organic sizing agent and an aqueous dispersion of inorganic fine particles, the above-mentioned polyvinyl alcohol, polyvinyl acetal, polyoxyethylene, water-based polyurethane, etc., singly or in combination, are used as the water-based organic sizing agent, and conventional sizing is performed. The water-based organic sizing agent may be used as long as it is water-soluble or water-dispersible, but water-dispersible and liquid sizing agents are preferably used.
Further, as the aqueous dispersion of inorganic fine particles, specifically, an aqueous dispersion containing fine particles of zirconia, titania, alumina, boron nitride, silicon carbide, etc., particularly preferably fine particles of zirconia, is used, and a treatment liquid prepared by mixing the two. It is. The inorganic fine particle aqueous dispersion is also referred to as an inorganic fine particle suspension because the fine particles contained therein are in a dispersed state.

In the inorganic fine particle aqueous dispersion used in the treatment liquid in the present invention, the particle diameter of the inorganic fine particles contained is preferably 10 to 200 nm. If the particle size of the inorganic fine particles is less than 10 nm, it is difficult to uniformly disperse them in the treatment liquid or to coat them uniformly on the alumina fibers, and if they exceed 200 nm, they will precipitate during the preparation of the treatment liquid. It is also difficult to uniformly adhere and coat alumina fibers.
In addition, when inorganic fine particles are made into an aqueous dispersion depending on the production process, the aqueous dispersion ranges from acidic to alkaline, but the aqueous dispersion of inorganic fine particles in the present invention is neutral to alkaline. It is preferable. If the inorganic fine particle aqueous dispersion is acidic, when mixed with the water-based organic sizing agent and the inorganic fine particle aqueous dispersion, depending on the sizing agent, the inorganic fine particles may aggregate, forming a uniform coating layer on the surface of the alumina fiber. It becomes difficult to do so.

The concentration of inorganic fine particles in the treatment liquid consisting of an aqueous organic sizing agent and an aqueous dispersion of inorganic fine particles is preferably adjusted to 4.0 to 15% by weight. If the concentration of inorganic fine particles in the treatment solution is less than 4.0% by weight, the adhesion of inorganic fine particles to the alumina continuous fibers during immersion of the alumina continuous fibers will be insufficient, and if it exceeds 15% by weight, The inorganic fine particles tend to adhere excessively to the alumina continuous fibers, and the adhesion tends to become uneven.

Formation of the coating layer on the alumina continuous fibers is carried out by continuously immersing the alumina continuous fibers in a treatment liquid, attaching an organic sizing agent and inorganic fine particles to the alumina continuous fibers, and drying. It is later rolled up as reinforcing fiber for composite materials. During immersion in the treatment solution, the speed, tension, time, squeezing rate, etc. of the alumina continuous fibers to be supplied are adjusted as appropriate to coat the alumina fibers with a predetermined amount of the organic sizing agent and inorganic fine particles.
Alumina continuous fibers can be applied to dipping treatment with yarns of arbitrary number and fineness. During dipping treatment, a treatment liquid is infiltrated between the single yarns of the alumina continuous fibers, squeezed as appropriate, and then dried. Wind it up.

It is preferable that the organic sizing agent and the inorganic fine particles are attached to the alumina fiber in an amount of 0.5 to 5% by mass and 1 to 6% by mass, respectively, so that the organic sizing agent and the inorganic fine particles are coated. If the amount of organic sizing agent deposited is less than 0.5% by mass, it is insufficient to cover the inorganic fine particles, and if it exceeds 5% by mass, it becomes difficult to completely remove it.
In addition, if the amount of inorganic fine particles attached is less than 1% by mass, a sufficient interfacial layer cannot be formed when composited, and if it exceeds 6% by mass, the coated alumina continuous fibers become hard and the winding operation becomes difficult. Processing to form a base material becomes difficult.
In addition, the organic sizing agent contained in the treatment liquid allows the inorganic fine particles to uniformly adhere to the alumina fibers and prevents them from falling off, so that so-called sizing can prevent the fibers from coming apart.

As mentioned above, the alumina-based continuous fibers having a coating layer of an organic sizing agent and inorganic fine particles according to the present invention are used to form an inorganic composite material through a coating layer of alumina-based fibers when composited with a matrix material. Because the matrix material is coated by coating, the alumina fibers do not come into direct contact with the matrix material, so even under conditions of compositing such as high temperature heating, the fiber strength is not affected, and the inorganic composite This contributes to improving the strength of the material.
Furthermore, when the alumina continuous fibers of the present invention are composited with a matrix material, the presence of an interfacial layer of inorganic fine particles formed at the interface between the alumina continuous fibers and the matrix improves the strength of the inorganic composite material. It is something.

Hereinafter, the present invention will be specifically explained with reference to Examples. The tensile strength of the alumina fibers and the fibrous composite material was measured in accordance with the method of JIS R3420 (tensile interval 100 mm, tension speed 30 mm/min).

(Reference example)
As the alumina continuous fibers, we used alumina continuous fibers (blank fibers) with a single yarn count of 960, a total fineness of 200 tex, and a tensile strength of 6.61 kgf/yarn, which were not coated with a water-based organic sizing agent and inorganic fine particles. After applying a sol-based alumina precursor as a matrix material to alumina-based continuous fibers, the mixture was heated at 1000°C to form a composite, thereby obtaining a continuous fibrous inorganic composite material. When the tensile strength of the obtained fibrous composite material was measured, it was found that the uncoated fibers were damaged by direct contact with the matrix material during the compositing process, and as shown in Table 1, the tensile strength of this fibrous composite material was The tensile strength was 2.38 kgf/yarn, which was a 64% decrease in the tensile strength of the alumina continuous fiber that was the blank fiber.
The untreated uncoated alumina-based continuous fiber (blank fiber) of this reference example had a smooth fiber surface even when observed in an SEM photograph (see FIG. 1).

(Example 1)
A polyurethane aqueous dispersion was used as the water-based organic sizing agent, and a zirconia fine particle aqueous dispersion (particle size 60 to 100 nm, pH 7.0 to 8.3) was used as the inorganic fine particle aqueous dispersion, and both were mixed to achieve a zirconia fine particle concentration of 13.5. A treatment solution of % by mass was prepared. The alumina-based continuous fibers of the blank fibers shown in the reference example (number of single yarns: 960, total fineness: 200tex) were continuously immersed in this treatment solution, polyurethane and zirconia fine particles were attached to the alumina-based continuous fibers, and extra treatment was performed using a roller. The liquid was squeezed out, air-dried at room temperature, and wound up to obtain an alumina-based continuous fiber having a coating layer composed of polyurethane and zirconia fine particles.
The amount of polyurethane and the amount of zirconia fine particles in the coating layer of the obtained continuous alumina fibers were 0.89% by mass and 4.41% by mass, respectively, based on the fibers.
The amounts of polyurethane and zirconia fine particles in the coating layer of the alumina continuous fibers were determined from the amount of each adhered to the entire fiber.
The tensile strength of this alumina-based continuous fiber having a coating layer made of polyurethane and zirconia fine particles was 8.41 kgf/yarn, which was an increase of 27% compared to the blank fiber of the reference example.

In order to confirm whether the obtained coating layer of alumina-based continuous fibers functions as an interface layer in a composite material, the following composite material form was evaluated.
A sol-based alumina precursor was applied as a matrix material to the alumina-based continuous fibers having the obtained coating layer, and then heated at 1000° C. to integrate the composite to obtain a continuous fibrous inorganic composite material.
When the tensile strength of the obtained fibrous composite material was measured, as shown in Table 1, the tensile strength of this fibrous composite material was 6.55 kgf/yarn, which was a 1% decrease compared to the blank fiber of the reference example. It just became.
Table 1 also shows a comparison between the tensile strength of the blank fiber in the reference example and the tensile strength of the fibers and fibrous composite materials in this example, example 2, and comparative examples 1 to 3. .
The coating layer of the alumina continuous fibers obtained in this example changes into an interface layer during the process of making the composite material, and the resulting interface layer sufficiently functions as an interface layer in the composite material to reduce damage to the fibers. It was confirmed that the tensile strength of the fibrous composite material was improved.

When the surface of the alumina continuous fiber having the coating layer obtained in Example 1 was observed using a SEM photograph, it was found that the zirconia fine particles were covered with the organic sizing agent polyurethane and were not seen on the coated surface of the fiber surface. (See Figure 2).
The organic sizing agent polyurethane in the coating layer was thermally decomposed and removed when heated at 1000°C, and the zirconia fine particles covered by the polyurethane appeared, and the zirconia fine particles were uniformly coated on the fiber surface. (See Figure 3).

(Example 2)
Example 1 except that a solution-based alumina precursor was applied as a matrix material to the alumina-based continuous fiber (tensile strength 8.41 kgf/yarn) having a coating layer made of polyurethane and zirconia fine particles obtained in Example 1. Compositeization was performed in the same manner to obtain a continuous fibrous inorganic composite material.
When the tensile strength of the obtained fibrous composite material was measured, as shown in Table 1, the tensile strength of this fibrous composite material was 6.72 kgf/yarn, which was an increase of 1% compared to the blank fiber of the reference example. It was confirmed that even if the matrix material was changed, the interfacial layer formed by changing from the alumina continuous fiber coating layer functioned satisfactorily as an interfacial layer.

(Comparative example 1)
An alumina-based continuous fiber having a coating layer was obtained in the same manner as in Example 1, except that the treatment liquid in Example 1 was changed to a treatment liquid having a zirconia fine particle concentration of 19.5% by mass. The amount of polyurethane and the amount of zirconia fine particles in the coating layer of the obtained continuous alumina fibers were 1.14% by mass and 8.13% by mass, respectively, based on the fibers.
The tensile strength of this alumina-based continuous fiber having a coating layer made of polyurethane and zirconia fine particles was 8.19 kgf/yarn, which was 24% higher than that of the blank fiber of the reference example.
A continuous fibrous inorganic composite material was obtained in the same manner as in Example 1 using the alumina continuous fibers having a coating layer containing a large amount of zirconia fine particles obtained in Comparative Example 1. When the tensile strength of the obtained fibrous composite material was measured, as shown in Table 1, the tensile strength of this fibrous composite material was 5.86 kgf/yarn, which was a decrease of 11% compared to the blank fiber of the reference example. Met.
This composite material was extremely hard and difficult to handle because white powder, which appeared to be fine zirconia particles, fell off when touched.
In addition, when the surface of the alumina-based continuous fiber having the coating layer obtained in Comparative Example 1 was observed using an SEM photograph, it was found that there were so many zirconia fine particles that they could not be covered with the organic sizing agent polyurethane, resulting in large lumps. was also observed (see Figure 4).
When this alumina-based continuous fiber was heated at 1000°C in the same manner as in Example 1, the organic sizing agent polyurethane was thermally decomposed and removed, and zirconia fine particles covered with polyurethane appeared, but a large amount of aggregates remained. (See Figure 5).

(Comparative example 2)
Alumina continuous fibers were prepared in the same manner as in Example 1, using only a zirconia fine particle aqueous dispersion (particle size 60 to 100 nm, pH 7.0 to 8.3, fine particle concentration 3% by mass) as the inorganic fine particle aqueous dispersion as a treatment liquid. was immersed in this treatment solution and dried to obtain an alumina-based continuous fiber having a coating layer consisting only of zirconia fine particles.
The amount of zirconia fine particles adhered to the obtained alumina continuous fiber was 1.15% by mass based on the fiber. Further, the tensile strength of the alumina-based continuous fiber having a coating layer consisting only of zirconia fine particles was 6.69 kgf/yarn, which was 1% higher than that of the blank fiber of the reference example.
Using the obtained alumina-based continuous fibers, a continuous fibrous inorganic composite material was obtained in the same manner as in Example 1, except that the same solution-based alumina precursor used in Example 2 was used as the matrix material.
When the tensile strength of the obtained fibrous composite material was measured, as shown in Table 1, the tensile strength of this fibrous composite material was 5.86 kgf/yarn, which was a decrease of 11% compared to the blank fiber of the reference example. Met.
The surface of the alumina continuous fiber obtained in Comparative Example 2 was observed using a SEM photograph, and although zirconia fine particles were attached to the fiber surface, it was not uniform and the entire fiber was not covered (see Figure 6). . When this alumina-based continuous fiber was heated at 1000°C, although zirconia fine particles were attached to the fiber surface, the adhesion was not uniform as before heating, and a decrease in the amount of zirconia fine particles attached was observed (Figure 7 reference).
Furthermore, it was observed that a large portion of the matrix had peeled off from the surface of the obtained fibrous composite material.

(Comparative example 3)
A polyurethane aqueous dispersion having the same concentration of 1.5% by mass as used in Example 1 as a water-based organic sizing agent was used as the treatment liquid, and the same alumina-based continuous fibers used in Example 1 were immersed in this treatment liquid and dried. Then, alumina-based continuous fibers sized with polyurethane were obtained, which were coated with only polyurethane. The amount of polyurethane adhered to the obtained alumina-based continuous fibers was 1.88% by mass based on the fibers.
Further, the tensile strength of this alumina-based continuous fiber coated only with polyurethane was 7.39 kgf/yarn, which was 12% higher than the blank fiber of the reference example.
Using the obtained alumina-based continuous fibers, a continuous fibrous inorganic composite material was obtained in the same manner as in Example 1, except that the same sol-based alumina precursor as used in Example 1 was used as the matrix material. When the tensile strength of the obtained fibrous composite material was measured, as shown in Table 1, the tensile strength of this fibrous composite material was 4.81 kgf/yarn, which was a decrease of 27% compared to the blank fiber of the reference example. Met.
The alumina continuous fibers coated only with polyurethane obtained in Comparative Example 3 were heated at 1000°C, but the surface of the alumina continuous fibers from which the polyurethane had been removed remained as smooth as before (Figure 8 reference).

(Comparative example 4)
The same water-based polyurethane used in Example 1 was used as the water-based organic sizing agent, and a zirconia fine particle aqueous dispersion (particle size 60 to 100 nm, pH 2.5 to 3.8) different from that used in Example 1 was used as the inorganic fine particle aqueous dispersion. Although an attempt was made to prepare a processing liquid containing zirconia fine particles by mixing the two, the zirconia fine particles agglomerated and precipitated during mixing, making it impossible to obtain a good processing liquid. Furthermore, it has not been possible to obtain alumina-based continuous fibers having a uniform coating layer consisting of polyurethane as an organic sizing agent and zirconia fine particles as inorganic fine particles.

The alumina-based continuous fiber for inorganic composite materials of the present invention is used as a reinforcing material in inorganic composite materials used in parts that require light weight and high durability as high-temperature components of gas turbine engines such as aircraft. It is possible to provide continuous fibers that can increase the strength and toughness of the fibers. Further, according to the present invention, it is possible to commercially advantageously obtain the alumina-based continuous fiber for inorganic composite materials without any complicated steps.

Claims (4)

Consisting of an aqueous organic sizing agent selected from the group consisting of polyvinyl alcohol, polyvinyl acetal, polyoxyethylene and/or aqueous polyurethane, either alone or as a mixture, and zirconia, titania, alumina, boron nitride or silicon carbide with a particle size of 10 to 200 nm. Inorganic fine particles selected from the group , and a coating layer that becomes an interface layer when composited with a matrix material is provided in advance before compositeization,
An alumina-based continuous fiber for an inorganic composite material, wherein the amounts of the water-based organic sizing agent and the inorganic fine particles in the coating layer are 0.5 to 5% by mass and 1 to 6% by mass, respectively, based on the alumina continuous fiber. Consisting of an aqueous organic sizing agent selected from the group consisting of polyvinyl alcohol, polyvinyl acetal, polyoxyethylene and/or aqueous polyurethane, either alone or as a mixture, and zirconia, titania, alumina, boron nitride or silicon carbide with a particle size of 10 to 200 nm. The alumina-based continuous fibers are continuously immersed in a treatment solution containing an aqueous dispersion having inorganic fine particles selected from the group , and the aqueous organic sizing agent and the inorganic fine particles are added to the alumina-based continuous fibers at a rate of 0.5 to 0.5, respectively. A coating that becomes an interfacial layer when the inorganic fine particles attached to the alumina continuous fibers are fixed with a sizing agent by adhering 5% by mass and 1 to 6% by mass and drying, and then composited with the matrix material on the fibers. A method for producing an alumina-based continuous fiber for inorganic composite materials, characterized in that a layer is formed in advance before compositing . The method for producing alumina-based continuous fibers for inorganic composite materials according to claim 2 , wherein the concentration of inorganic fine particles in the treatment liquid consisting of an aqueous aqueous organic sizing agent liquid and an aqueous dispersion of inorganic fine particles is 4.0 to 15 % by mass. . The method for producing an alumina-based continuous fiber for an inorganic composite material according to claim 2 or 3, wherein the aqueous dispersion of inorganic fine particles is made neutral to alkaline.