JP2001115341A - Silicon carbide fiber and molded body - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a silicon carbide fiber which is excellent in heat resistance and strength and has excellent productivity, can reduce the apparent density as a long fiber, and can apply a papermaking method as a short fiber. The purpose is to provide. SOLUTION: Crimp degree = (ba) × 100 / b (%)
A silicon carbide fiber having a degree of crimp of 20% or more as defined by Here, a represents the fiber length when tension is applied so that the crimp of the fiber is not loose and the crimp does not elongate, and b represents the fiber length when tension is applied to the fiber. A sheet or a three-dimensional structure composed of the crimped silicon carbide fiber, wherein the apparent density is 0.01 to 0.7 g / cm ^3.
Can be produced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a silicon carbide fiber having excellent heat resistance and used for a heat insulating material, a filter material and the like.

[0002]

2. Description of the Related Art Conventionally, silicon carbide fibers have been
As described in 33681 and the like, a production method including a step of spinning an organosilicon polymer into a precursor fiber, a step of infusibilizing treatment, and a step of firing at a high temperature is known. Recently, as described in Japanese Patent Application Laid-Open No. Hei 9-118566, it has been known that it can be obtained by a method of reacting a metal silicon gas and a silicon oxide gas with activated carbon fibers as precursor fibers.

[0003] Silicon carbide fibers based on a production method using an organosilicon polymer as a precursor fiber are mainly ceramic fibers such as Tyranno fiber (trademark: Ube Industries, Ltd.) and Nicalon fiber (trademark: Nippon Carbon Co., Ltd.). Commercially available for reinforced ceramic composites. However, these commercially available fibers are characterized in that they have a large apparent density when bundled or laminated, or a sheet obtained by dispersing cut short fibers in water with an appropriate binder as a sheet on a net ( The papermaking method is difficult due to the small number of entanglements between the fibers, and it is difficult to use. Depending on the application, such as a filter with a small pressure loss or a two-dimensional or three-dimensional structure of silicon carbide fiber using the papermaking method, it is suitable for use. Did not.

On the other hand, in the process of infusibilizing the precursor fiber of the organosilicon polymer, it is known that the infusibilized precursor fiber undulates without applying tension to the fiber.
No. 681 is well known. However, simply changing the corrugated precursor fiber into silicon carbide fiber does not provide a long fiber whose apparent density when bundled or laminated is sufficiently small while maintaining the physical properties.
Further, it is not possible to obtain short fibers to which the papermaking method can be easily applied.

[0005]

SUMMARY OF THE INVENTION In view of the above circumstances, the present inventors have been able to reduce the apparent density as a long fiber which is excellent in heat resistance, strength and productivity, and An object of the present invention is to provide a silicon carbide fiber to which a papermaking method can be applied as the short fiber.

[0006]

Means for Solving the Problems A first invention of the present invention is:
A silicon carbide fiber having a degree of crimp defined by the following formula of 20% or more. Degree of crimp = (ba) × 100 / b (%) a: The fiber length when there is no looseness in the crimp of the fiber and tension is applied to the extent that the crimp does not elongate. b: Fiber length when tension is applied to the fiber. The “tension that does not extend the crimp” in the above “a” applies a tension of 5 mg for fibers of 5 denier or less and a tension of 10 mg for fibers of 5 denier or more.

A second invention of the present invention is a silicon carbide fiber obtained by siliconizing a precursor carbon fiber having a degree of crimp of 10% or more in the first invention.

[0008] A third invention of the present invention is the above-mentioned second invention, wherein the activated carbon fiber having a specific surface area of 300 to 2000 m ² / g by a BET nitrogen adsorption method is used as the precursor carbon fiber. And at least one gas selected from silicon and oxides of silicon are reacted under reduced pressure or in an inert gas atmosphere at a temperature of 1200 to 1500 ° C., and have an average diameter of 5 to 5. 20μ
m is a silicon carbide fiber having a length of 1 mm or more.

A fourth aspect of the present invention is a sheet or a three-dimensional structure comprising the silicon carbide fiber of the first aspect, wherein the sheet or the three-dimensional structure has an apparent density of 0.01 to 0.7 g / cm ^3. Body.

A fifth invention of the present invention is a composite molded product obtained by mixing the molded product of the fourth invention with ceramic powder and subjecting the mixture to a heat treatment.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The silicon carbide fiber of the present invention is characterized in that the degree of crimp is at least 20%. In particular, 20%
A degree of crimp of at least 100% is preferred. 20% crimp
If it is less than 100%, the effect is not remarkable, and if it is 100% or more, physical properties such as strength tend to decrease.

In the present invention, it is preferable that the precursor carbon fiber which has been crimped in advance is siliconized or heated while being crimped. The reason is that since the silicon carbide fiber is rigid, it is difficult to crimp the silicon carbide fiber while maintaining the strength and the like after the silicon carbide fiber becomes silicon carbide.

The precursor fiber has a specific surface area of 300 to 2 by the BET nitrogen adsorption method in consideration of availability.
A crimped activated carbon fiber of 000 m ² / g is preferred. In order to obtain a silicon carbide fiber having a desired degree of crimp, the activated carbon fiber as a precursor preferably has a degree of crimp of at least 10%, more preferably at least 20%. As a method for obtaining such a crimped carbon fiber, a method performed at the stage of the precursor of the carbon fiber is rational. That is,
In the process of spinning PAN or petroleum pitch or coal pitch, it can be crimped by winding it on a roll or applying a shearing force with a bar. Even after the fiber is cut, it can be crimped by heat treatment or mechanical treatment.

As a method for converting the precursor carbon fiber into silicon carbide, any known method may be used. From the viewpoint of production cost, Japanese Patent Application Laid-Open Publication No. HEI 9 (1998) -101605 reacts activated carbon fiber with at least one gas selected from silicon and silicon oxide under a reduced pressure or an inert gas atmosphere at a temperature of 1200 to 1500 ° C. The production method described in JP-A-9-118566 is preferred.

When a precursor fiber derived from an organosilicon polymer is used as the precursor fiber, a crimped precursor obtained by continuously applying crimps or loops to the fiber during the infusibilizing treatment of the precursor fiber is performed. By converting the fibers to silicon carbide, crimped silicon carbide fibers can be obtained.

The fiber diameter of the silicon carbide fiber of the present invention is from 1 μm to 20 μm in order to perform crimping while maintaining sufficient strength.
m is preferred. Although the fiber length varies depending on the application, it is preferably 1 mm or more where the effect of crimping appears.

The silicon carbide fiber of the present invention may be subjected to a surface treatment in order to improve heat resistance, strength and the like. As surface treatment materials for silicon carbide fibers, beryllium oxide (BeO), aluminum oxide (Al ₂ O ₃ ) or aluminum nitride (AlN), silicon oxide (SiO ₂ ) or nitride (Si) ₃ N ₄ ), group IV, V
Oxides of Group VI and Group VI transition metals (TiO ₂ , ZrO ₂ , Hf
O ₂ , Cr ₂ O _3, etc.), carbon, and boron nitride. As the method, a CVD method (Chemical Vapor Depositi) by a thermochemical reaction of an inorganic gaseous compound or the like is used.
on method), sol-gel method of precipitating ceramics from inorganic compound or polymer in liquid or colloidal solution form, or directly gasifying ceramic solids,
PVD method for depositing coatings (Physicai Vapor
Deposition method).

The crimped silicon carbide fiber can be used in the form of a long fiber, as a woven fabric, or as a three-dimensional structure, or in the form of a sheet in the form of a short fiber, and laminated three-dimensionally. It can be used as a structure. As a method of forming a sheet state, the wet papermaking method is the cheapest,
Large numbers of sheets can be manufactured. Further, a three-dimensional molded body can be formed by the Harp molding method. In these moldings, the silicon carbide fiber of the present invention may be formed into a molded body, but it is also possible to perform molding in advance at the stage of a precursor fiber and then to silicon carbide.

In order to further increase the strength, the crimped silicon carbide fiber molded body may be heat-treated with ceramic powder to be used as a silicon carbide fiber-ceramic composite material. As the ceramic powder, silicon carbide, alumina, silicon nitride and the like can be preferably used.

[0020]

Next, the present invention will be described in more detail with reference to Examples.
Explain, but the invention is not limited to these examples
Not something. <Example 1> BET nitrogen commercially available from Osaka Gas Chemical Co., Ltd.
Specific surface area by adsorption method is 1000m ^Two/ G pitch
Activated carbon fiber (brand name Ribenos A-10)
When the degree of crimp was measured. 15%. Average fiber
Dry activated carbon fiber (20g) cut to 5cm in length
Metallic silicon powder 60g (Reagent 1st grade, manufactured by Wako Pure Chemical Industries, Ltd.)
And 130 g of silica powder (reagent grade 1 Wako Pure Chemical Industries, Ltd.)
Powder), a mud having an inner diameter of 64 mm installed in a tubular furnace.
Mullite furnace with an inner diameter of 64 mm installed in a light tube furnace
The heart tube was filled over a length of 150 mm. This furnace
Argon gas (purity: 99.99% by volume) was introduced into the heart tube.
While flowing at 0 ml / min, from room temperature to 900 ° C
Temperature for 3 hours, and then to 1350 ° C for 1 hour
And kept at 1350 ° C. for 4 hours. Then to room temperature
For 5 hours. This mixture of fiber and powder
From the stirrer in 50 liters of water (product
Name: Agitator, manufactured by Shimazaki Co., Ltd.)
Dispersed. This dispersion is passed through a 149 μm sieve.
The fibers are collected on a sieve and passed through running water.
The fibers were washed. Washed fiber in air dryer at 120 ° C
For 5 hours. The weight of the recovered fiber is 25 g
Was. The average fiber length of this fiber is 4.5 cm and the fiber diameter is
13 μm. When the degree of crimp was measured, it was 30%.
Met. 5 g of the silicon carbide fibers are bundled and oriented.
And the apparent density was measured to be 0.2 g / cm^ThreeIn
Was. The results are shown in Table 1.

<Example 2> Short fibers obtained by cutting 2 g of the above-mentioned silicon carbide fiber having a crimp degree of 30% to an average fiber length of 3 mm were used as a binder, 0.2 g of unbeaten bleached softwood kraft pulp, and PEO- as a viscosity improver. 18 (trademark, Sumitomo Seika Co., Ltd.) was dispersed in 0.5 L of water together with 2 g of a 1 w / v% aqueous solution, and then formed into a sheet using a hand-making apparatus described in JIS P8209. However, in order to prevent the silicon carbide fiber from breaking, do not use a coach roll after wetting and place the blotter paper on the silicon carbide wet paper, hold it lightly on the coach plate and make the blotter paper adhere to the silicon carbide wet paper. To transfer the silicon carbide wet paper onto the blotting paper. After drying with a blast dryer, a uniform and strong silicon carbide short fiber sheet having an apparent density of 0.06 g / cm ³ was obtained. In addition, JIS P9
The results were summarized in Table 2 by determining the breaking length according to 113.

<Comparative Example 1> Nicalon fiber (type NL-20) manufactured by Nippon Carbon Co., Ltd., which is a commercially available silicon carbide fiber
When the degree of crimp of the single fiber of 1) was measured, it was less than 2%. When the apparent density was measured in the same manner as in Example 1, it was 0.8 g / cm ³ . The results are shown in Table 1.

<Comparative Example 2> Using the fiber of Comparative Example 1 to form a sheet in the same manner as in Example 2, the binder and the silicon carbide fiber were separated and a uniform sheet could not be produced, and the sheet was transferred to blotting paper. Sometimes the wet paper broke and separated. Table 2 shows the results
It described in.

[0024]

[Table 1]

[0025]

[Table 2]

[0026]

As described above, the silicon carbide fiber having a high degree of crimp according to the present invention can easily reduce the apparent density of the fiber bundle, and can be used in various applications such as a filter. Are more suitable than rigid silicon carbide fibers. Further, the present invention has made it possible to easily apply silicon carbide fibers to a papermaking method, which is a method of manufacturing a sheet-like structure excellent in cost performance, which has been difficult so far.

Claims (5)

[Claims] 1. A silicon carbide fiber having a degree of crimp defined by the following formula of 20% or more. Degree of crimp = (ba) × 100 / b (%) a: The fiber length when there is no looseness in the crimp of the fiber and tension is applied to the extent that the crimp does not elongate. b: Fiber length when tension is applied to the fiber. 2. The silicon carbide fiber according to claim 1, which is obtained by siliconizing a precursor fiber having a degree of crimp of 10% or more. 3. An activated carbon fiber having a specific surface area of 300 to 2000 m ² / g by a BET nitrogen adsorption method is used as said precursor fiber, and said activated carbon fiber and at least one selected from silicon and oxides of silicon are used. The seed gas is reduced to 1200 to 1500 under reduced pressure or an inert gas atmosphere.
The average diameter obtained by reacting under a temperature condition of 5 ° C. is 5 to 5.
3. A fiber having a length of 20 μm and a length of 1 mm or more.
The silicon carbide fiber according to the above. 4. A sheet or a three-dimensional structure comprising the silicon carbide fiber according to claim 1, wherein the molded article has an apparent density of 0.01 to 0.7 g / cm ³ . 5. A composite molded article obtained by mixing the molded article according to claim 4 with ceramic powder and heat-treating the mixture.