JP2002266216A - Nonwoven fabric sheet of silicon carbide fiber and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a nonwoven fabric sheet which is thin, has excellent processability and is obtained by using a CMC consisting essentially of silicon carbide fiber. SOLUTION: This nonwoven fabric sheet of silicon carbide fiber is characterized by comprising a silicon carbide fiber having 1-10 mm fiber length, a carbon fiber having 1-10 mm fiber length and a thermally decomposable organic binder. The sheet is impregnated with a solution in which a resin is dissolved or dispersed, dried to remove a solvent, the dried sheet is heated in a vacuum or in an inert gas and the resin is carbonized to form a carbon layer having 0.2-5 μm thickness on the surface of the silicon carbide fiber.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to ceramics, such as engines, turbines and heat exchangers, which can be used at high temperatures.
The present invention relates to a silicon carbide fiber nonwoven fabric sheet that can be used as a prepreg of a matrix-ceramic composite material (CMC).

[0002]

2. Description of the Related Art Silicon carbide materials have abrasion resistance, oxidation resistance,
It has excellent thermal shock resistance and corrosion resistance, and has high hardness, low coefficient of thermal expansion, and good thermal conductivity, and its use as a heat-resistant structural material is being studied. However, although the monolithic silicon carbide material has such excellent properties as described above, its use as a structural material is limited due to its low toughness.

As means for improving the toughness of a ceramic material, a plurality of types of ceramics having different elastic moduli are compounded, or the same type of ceramics having different elastic moduli are formed by providing a third layer at an interface thereof. It is also known. In the case of a composite material using silicon carbide as a matrix, a two-dimensional woven fabric of silicon carbide fibers having a carbon layer or a boron nitride layer on the surface, a three-dimensional woven fabric as a prepreg, an organic metal polymer impregnation method, and a method of repeating pyrolysis firing, The matrix layer is formed by a chemical vapor infiltration method (CVI method) or a reaction sintering method. The CVI method is known and described in Japanese Patent Application Laid-Open No. 9-506584.

However, when such a two-dimensional woven fabric of long fibers and a three-dimensional woven fabric are used as a prepreg, a relatively thin and small-diameter tubular structure such as a ceramic protective tube of a heat exchanger metal heat transfer tube is manufactured. This is often difficult in the production of woven fabrics.

Japanese Unexamined Patent Publication (Kokai) No. 7-172942 does not disclose a specific method, but a sheet is formed from discontinuous filaments of carbon fibers or ceramic fibers (for example, silicon carbide fibers) and impregnated with a resin. The concept of forming a carbon layer by post-mineralization is described. However, when the present inventors tried to actually produce a sheet-like prepreg of a silicon carbide fiber nonwoven fabric by a papermaking method based on this concept, a sheet composed of only silicon carbide fiber filaments has a sufficient bonding and entanglement between fibers and is insufficient. Due to lack of strength, it has been difficult to impregnate the resin or to process it into a thin and small-diameter tubular prepreg.

The concept of manufacturing a prepreg by combining silicon carbide fibers with other inorganic fibers such as carbon fibers is disclosed in
Although these are described in Japanese Patent No. 217267, the strength of each sheet is not always sufficient because the main purpose is to laminate two-dimensional woven fabrics to produce CMC. In addition, if the prepreg is rounded with a small radius, there is a problem that the fiber ends jump out from the sheet surface, and the method is not suitable for producing a thin plate-shaped prepreg or a thin and small-diameter tubular prepreg.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide a non-woven fabric sheet used for CMC mainly composed of silicon carbide fibers, which overcomes the above-mentioned various drawbacks, is thin and has excellent workability.

[0008]

The present invention adopts the following constitution as means for solving the above-mentioned problems. That is, a first aspect of the present invention is a "silicon carbide fiber nonwoven sheet comprising a silicon carbide fiber having a fiber length of 1 to 10 mm, a carbon fiber having a fiber length of 1 to 10 mm, and a thermally decomposable organic binder."

A second aspect of the present invention is the above-mentioned first aspect,
Carbon fiber is 1 to 100 parts by weight of silicon carbide fiber.
A silicon carbide fiber nonwoven fabric sheet, wherein 10 parts by weight and a thermally decomposable organic binder are 1 to 20 parts by weight.

A third aspect of the present invention is the silicon carbide fiber nonwoven fabric sheet according to the first or second aspect, wherein the thermoplastic thermally decomposable organic binder is a synthetic resin fiber.

A fourth aspect of the present invention is that in any one of the first to third aspects, the thickness is 0.2 mm or more, or the basis weight of the silicon carbide fibers contained in the sheet is 45 g / m ² or more. A silicon carbide fiber nonwoven fabric sheet characterized by the following.

A fifth aspect of the present invention is a solution prepared by dissolving or dispersing a resin in a silicon carbide fiber nonwoven sheet containing a silicon carbide fiber having a fiber length of 1 to 10 mm, a carbon fiber having a fiber length of 1 to 10 mm, and a thermally decomposable organic binder. After impregnation,
By drying to remove the solvent and heating the dried sheet in a vacuum or inert gas to mineralize the resin,
A method for producing a surface-coated silicon carbide fiber nonwoven fabric sheet, comprising forming a carbon layer having a thickness of 0.2 to 5 μm on the surface of silicon carbide fibers.

A sixth aspect of the present invention is that a silicon carbide fiber nonwoven sheet containing a silicon carbide fiber having a fiber length of 1 to 10 mm, a carbon fiber having a fiber length of 1 to 10 mm, and a thermally decomposable organic binder is three-dimensionally molded and processed. After impregnating the solution in which the resin was dissolved or dispersed in the processed body, dried to remove the solvent,
Heating the dried sheet in a vacuum or an inert gas to mineralize the resin, thereby forming a carbon layer having a thickness of 0.2 to 5 μm on the surface of the silicon carbide fiber; Production method of silicon carbide fiber molded article ".

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail. The present invention is a nonwoven fabric sheet composed of silicon carbide fibers, carbon fibers, and a thermally decomposable organic binder. Also, the method of the present invention forms a resin layer that can be mineralized on the surface of the silicon carbide fiber by impregnating the resin into the nonwoven fabric sheet, and thereafter, mineralizes the resin layer to form a carbon layer on the surface of the silicon carbide fiber. How to Accordingly, the resin is a resin that can be mineralized, and hereinafter, the operation of carbonizing the resin is also referred to as “mineralization”.

[0015] The silicon carbide fiber is a fiber substantially composed of silicon carbide, and is formed of carbon, oxygen, metal, metal salt, carbide, etc. within a range that does not impair the physical properties such as heat resistance and strength. Components other than silicon carbide may be included.

The method for producing silicon carbide fibers includes a method of firing precursor fibers obtained by spinning an organosilane polymer to form silicon carbide, a method of depositing silicon carbide on a core fiber such as titanium or carbon by a CVD method, and a method of producing activated carbon fibers. There is a known method such as a method of reacting a silicon monoxide gas using as a precursor fiber. The method for producing silicon carbide fibers is not particularly limited.
A silicon carbide fiber obtained by reacting a silicon monoxide gas with the activated carbon fiber described in Japanese Patent No. 17 as a precursor fiber is particularly preferable from the viewpoint of cost.

The fiber length of the silicon carbide fiber used in the present invention is in the range of 1 to 10 mm. When the fiber length of the silicon carbide fiber is less than 1 mm, it is difficult to form a sheet.
On the other hand, when it exceeds 10 mm, uniform dispersion becomes difficult. The diameter of the silicon carbide fiber is preferably 1 to 30 μm.
If it exceeds 30 μm, the fibers become rigid and workability is reduced. If it is less than 1 μm, handling is difficult. For the same reason, a fiber of 2 to 20 μm is more preferable.

The carbon fibers reinforce the prepreg after mineralization. The carbon fiber is not particularly limited in its raw fiber and may be either pitch-based or polyacrylonitrile-based, but the fiber length is preferably 1 to 10 mm.
When the fiber length is less than 1 mm, the strength reinforcing effect is not remarkable. On the other hand, if it exceeds 10 mm, uniform dispersion becomes difficult, which is not preferable.

The amount of carbon fiber added to 100 parts by weight of silicon carbide fibers is preferably 1 to 10 parts by weight. If the amount is less than 1 part by weight, it becomes difficult to exhibit the strength reinforcing effect of the prepreg, and it becomes necessary to add a large amount of a resin for forming a carbon layer on the fiber surface to form crosslinks between fibers,
There is a possibility that the strength and oxidation resistance of CMC may be reduced due to excessive carbon. On the other hand, if the amount exceeds 10 parts by weight, the oxidation resistance of the carbon fiber is similarly lowered due to the low oxidation resistance of the carbon fiber, which is not preferable.

The nonwoven fabric sheet of the present invention contains a thermally decomposable organic binder in addition to the above-mentioned silicon carbide fibers and carbon fibers. The thermally decomposable organic binder is added for the purpose of improving the flexibility when impregnating the resin into the silicon carbide fiber nonwoven fabric sheet and at the time of molding. Organic bonds that can form bonds between silicon carbide fibers and carbon fibers by heat fusion after sheeting, and that are almost completely decomposed and disappear from the sheet when heated in a vacuum or inert atmosphere. Refers to a polymer. The thermally decomposable organic binder is not particularly limited, but olefin hydrocarbons such as polyethylene and polypropylene are preferred because of their excellent heat-fusibility and high thermal decomposability.

The addition amount of the thermally decomposable organic binder to 100 parts by weight of the silicon carbide fiber is preferably 1 to 20 parts by weight. If the amount is less than 1 part by weight, the strength of the sheet when the resin is impregnated is not sufficient. On the other hand, when the amount exceeds 20 parts by weight, unevenness of wetting of the silicon carbide fiber with the resin solution occurs during impregnation with the resin solution, which is not preferable. As a method for producing a nonwoven fabric sheet from silicon carbide fibers, carbon fibers, and a thermally decomposable organic binder, it is preferable from the viewpoint of productivity that the nonwoven fabric sheet be dispersed in water and then formed on a net. At this time, a dispersant, a flocculant, and / or a thickener may be used as needed in order to obtain a sheet having a good texture.

The thickness, basis weight, etc. of the silicon carbide fiber non-woven fabric sheet are not particularly limited depending on the application,
A thickness of 0.2 mm or more is preferred from the viewpoint of ease of sheeting, and a basis weight of silicon carbide fiber of 45 g / m ² or more is preferred.

Although the silicon carbide fiber nonwoven fabric sheet of the present invention has been described above, the present invention further impregnates the nonwoven fabric sheet with a resin solution to form a resin layer on the surface of the silicon carbide fiber, which is then vacuumed or impregnated. The method includes a method of heat-treating in an active gas to inorganicize the resin layer to form a carbon layer.

The treatment for forming a carbon layer is also referred to as a mineralization treatment. In the present invention, the purpose of the mineralization treatment is to impregnate / penetrate ceramics to produce CMC.
An object of the present invention is to reduce the adhesion between matrix ceramics and silicon carbide fibers. As a result, when the CMC is destroyed,
The direct propagation of the fracture of the matrix to the silicon carbide fibers is prevented by the surface carbon layer of the silicon carbide fibers, and the silicon carbide fibers are pulled out of the matrix ceramics, thereby exhibiting toughness. The resin is actually
It is considered that not only the surface of the silicon carbide fiber but also the surface of the carbon fiber is coated, but the carbon fiber remains carbon fiber because it is eventually carbonized.

The impregnation of the silicon carbide fiber nonwoven sheet into the resin solution is carried out under the following conditions.
This is performed in order to develop toughness in the CMC after the CVI treatment by converting into a carbon layer by a so-called mineralization treatment of heating at 0 to 1300 ° C. The thermally decomposable binder, which has maintained the sheet strength of the silicon carbide fiber nonwoven sheet before being mineralized, is decomposed by the heat of the carbonization treatment and almost all is removed.

The resin to be impregnated is not particularly limited, but a phenol resin, a furan resin, a pitch, or the like having a high yield when carbonized is used is preferable. For convenience, it is described as a resin solution, but is a solution in which a resin component of a resin solution is dissolved or dispersed in water or an organic solvent. Then, the resin solution may be a solution having an appropriate concentration such that when the nonwoven fabric sheet is impregnated, dried and mineralized, the thickness of the carbonized carbon layer becomes 0.2 to 5 μm.

The amount of carbon layer on the surface of the formed fiber is defined by the thickness of the carbon layer when the cross section of the fiber is observed by a scanning electron microscope (SEM), and the average thickness is 0.2 to 5 μm.
m is preferable. If less than 0.2 μm, CM
The effect of toughness on C is not sufficient. On the other hand, if it exceeds 5 μm, the oxidation resistance and strength at high temperatures are reduced due to the presence of an excessive carbon content when converted to CMC, which is not preferable. In addition, in order to enhance the processability at the time of molding and resin impregnation, it is possible to use it by bonding it to nonwoven fabric, paper, etc., which have good permeability of the resin liquid and low carbonization yield.

[0028]

The present invention will be described more specifically with reference to the following examples, but the present invention is not limited to these examples.

<Example 1> Silicon carbide fiber, carbon fiber and thermally decomposable organic binder
- Sheet (1) silicon carbide fibers, silicon carbide fibers composed of the fiber length 6 mm, specific surface area 1000
Pitch-based activated carbon fiber having a m ² / g and a fiber diameter of 13 μm (Rivenos A-10, manufactured by Osaka Gas Chemical Co., Ltd.) is used as a precursor fiber to react with silicon monoxide gas as a precursor fiber (primary). ) Silicon carbide fibers were obtained by a second treatment at 2000 ° C with a sintering aid. The average fiber length of this fiber was 5 mm, and the fiber diameter was 13 μm. The method for producing the (primary) silicon carbide fiber is based on the technique described in JP-A-6-192917.

(2) Carbon fiber The carbon fiber is a vesfite carbon fiber having a fiber length of 6.0 mm.
HTA-C6-GS (Toho Rayon Co., Ltd.) was used. (3) Thermally Decomposable Organic Binder An olefin-based synthetic pulp (trade name: SWP, Mitsui Chemicals, Inc.) was used as the thermally decomposable organic binder.

(4) Preparation of Silicon Carbide Fiber Sheet 100 parts by weight of silicon carbide fiber, 5 parts by weight of carbon fiber, and 5 parts by weight of synthetic pulp are well dispersed to obtain a silicon carbide fiber having a thickness of 0.5 mm and a basis weight of 90 g / m ² . Become JI
The sheet was formed using the hand-making apparatus described in SP-8209. Thereafter, drying was performed in a dryer at 150 ° C. for 1 hour, and the silicon carbide fiber nonwoven fabric sheet was stabilized by fusing between silicon carbide fibers with synthetic pulp.

(5) Evaluation of Resin Layer Coating of Silicon Carbide Fiber and Formability The obtained silicon carbide fiber sheet was prepared with a length of 0.5 cm and a length of 1 cm.
After being wound twice in a 0 cm wire mesh cylinder, it was impregnated with an ethanol solution of a phenol resin (trade name: Tamanol 531, Arakawa Chemical Industry Co., Ltd.). Thereafter, by drying at 120 ° C., the surface of the silicon carbide fiber was covered with a resin layer. The resin coating amount was determined by heating the silicon carbide nonwoven fabric sheet impregnated with the resin to 900 ° C. in an argon atmosphere to make the resin layer inorganic, and then observing the fiber cross section with an electron microscope to obtain an average carbon layer of 2 μm. The amount of resin was adjusted. The evaluation of the moldability of the silicon carbide fiber nonwoven sheet is such that the silicon carbide fiber nonwoven sheet can be wound around the wire mesh cylinder without being broken, and the wound silicon carbide fiber nonwoven sheet is impregnated with a phenol resin ethanol solution. Those that did not break when they were done were defined as good.
The evaluation results of the moldability are shown in Table 1.

(6) Preparation of CMC by CVI method Five sheets of a silicon carbide fiber nonwoven fabric sheet impregnated with a resin in an amount to form a carbon layer having a thickness of 2 μm in the same manner as described above are laminated and heated to 150 ° C. by hot pressing. By doing so, integration was performed as a silicon carbide fiber nonwoven sheet laminate. At this time,
Apparent density of silicon carbide fiber nonwoven sheet laminate 0.5
g / cm ³ . Thereafter, the resin layer was mineralized in the same manner as described above, and the surface of the silicon carbide fiber was covered with a carbon layer to obtain a prepreg. The CVI treatment for the prepreg is performed by a known method disclosed in Japanese Patent Application Laid-Open No. 9-506585. That is, 800 ° C to 900 ° C
A mixed gas of methyltrichlorosilane and hydrogen is diffused inside the pores of the prepreg placed in a heated chamber, and silicon carbide deposits are formed as a matrix inside the prepreg by decomposition of methyltrichlorosilane by the reducing power of hydrogen. Produced a CMC. The apparent density of CMC was about 1.8 g / c.
I went until the m ^3.

(7) Strength Measurement The strength of the obtained CMC was determined by cutting out a test piece having a width of 5 mm, a height of about 3 mm, and a length of 40 mm.
It was measured as point bending strength. Also, the presence or absence of toughness was determined from the relationship between strain and stress at that time. The results are shown in Table 1.

<Comparative Example 1> (Sheet composed of silicon carbide fiber and thermally decomposable organic binder) (1) Preparation of non-woven silicon carbide fiber sheet Under the same conditions as in Example 1, 100 parts by weight of silicon carbide fiber, synthesized 5 parts by weight of pulp were well dispersed to prepare a silicon carbide fiber nonwoven sheet having a thickness of 0.5 mm. Then 150 ° C
The drying was performed in a dryer for 1 hour, and the silicon carbide fiber non-woven fabric sheet was stabilized by fusing between the silicon carbide fibers with synthetic pulp.

(2) Evaluation of moldability The moldability was confirmed in the same manner as in Example 1 and found to be good. The results are summarized in Table 1. (3) Production of CMC by CVI method In the same manner as in Example 1, a resin-impregnated silicon carbide fiber nonwoven sheet laminate was used to make the resin layer mineralized. Could not do. The results are summarized in Table 1.

<Comparative Example 2> (Sheet composed of silicon carbide fiber and thermally decomposable organic binder) (1) Preparation of non-woven silicon carbide fiber sheet and formation of resin layer on silicon carbide fiber surface The sheet was formed with a resin layer on the surface of the silicon carbide fiber in the same manner as in Example 1. The resin impregnation amount was adjusted so that the carbon layer became 8 μm as a carbon layer so that the carbon layer would crosslink between fibers in order to prevent the prepreg from collapsing after the mineralization treatment.

(2) Evaluation of Formability Evaluation was made in the same manner as in Example 1, and it was good. The results are summarized in Table 1.

(3) Preparation of CMC by CVI Method and Measurement of Strength The same procedure as in Example 1 was used to prepare a silicon carbide nonwoven fabric sheet laminate from a resin-impregnated silicon carbide fiber nonwoven fabric sheet, and then mineralized to prepare a prepreg. Unlike the comparative example 1, this prepreg was durable and could be subjected to the CVI treatment, so that the prepreg had an apparent density of 1.8 g /
The matrix was filled up to the size of cm ³ to prepare a CMC.
The bending strength and toughness of the obtained CMC were measured in the same manner as in Example 1. The results are shown in Table 1.

<Comparative Example 3> (Sheet composed of silicon carbide fiber and carbon fiber) (1) Preparation of non-woven fabric sheet of silicon carbide fiber As in Example 1, 100 parts by weight of silicon carbide fiber and 5 parts by weight of carbon fiber were used. It was dispersed and formed into a sheet having a thickness of 0.5 mm and a basis weight of 90 g / m ² as silicon carbide fibers. Then, the silicon carbide fiber nonwoven sheet 15
It was dried in a dryer at 0 ° C.

(2) Evaluation of Formability The formability of the silicon carbide fiber nonwoven sheet obtained in the same manner as in Example 1 was evaluated. When the sheet was wound around a tube, many fibers were missing from the sheet surface, and the phenol resin was removed. When impregnated with an ethanol solution, breakage was extremely easy to occur, so it was judged that moldability was not good. This result is shown in Table 1.
Summarized in

[0042]

[Table 1]

As shown in Table 1, as shown in FIG.
The silicon carbide fiber non-woven fabric sheet made of carbon fiber and synthetic pulp (Example 1) was used for resin impregnation, moldability and CM.
The physical properties of C were also excellent. On the other hand, in the case of a silicon carbide fiber nonwoven fabric sheet composed of silicon carbide fiber and synthetic pulp (Comparative Example 1 and Comparative Example 2), a prepreg that can withstand the CVI method cannot be produced with a carbon layer (Comparative Example 1) having the same thickness as that of Example 2. , Need to increase carbon layer to be formed (Comparative Example 2)
As a result, the strength was reduced. The subsequent process could not be performed on the silicon carbide fiber nonwoven sheet composed of only silicon carbide fibers and carbon fibers (Comparative Example 3) because the sheet collapsed during resin impregnation.

[0044]

The present invention has made it possible to produce a thin sheet-shaped prepreg excellent in workability, which was impossible with conventional two-dimensional fabrics and three-dimensional fabrics. by this,
This is extremely significant because thin-walled tubular CMC such as a metal heat transfer tube of a heat exchanger can be extremely easily manufactured.

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Claims (6)

[Claims] 1. A silicon carbide fiber having a fiber length of 1 to 10 mm,
A silicon carbide fiber nonwoven sheet comprising carbon fibers having a fiber length of 1 to 10 mm and a thermally decomposable organic binder. 2. With respect to 100 parts by weight of silicon carbide fiber,
The silicon carbide fiber nonwoven sheet according to claim 1, wherein the carbon fiber is 1 to 10 parts by weight and the thermally decomposable organic binder is 1 to 20 parts by weight. 3. The silicon carbide fiber nonwoven fabric sheet according to claim 1, wherein the thermally decomposable organic binder is a thermoplastic synthetic resin fiber. 4. The method according to claim 1, wherein the thickness is 0.2 mm or more, or the basis weight of the silicon carbide fibers contained in the sheet is 45 g / m ² or more. Silicon carbide fiber nonwoven sheet. 5. A silicon carbide fiber having a fiber length of 1 to 10 mm,
After impregnating a solution in which a resin is dissolved or dispersed in a silicon carbide fiber nonwoven sheet containing a carbon fiber having a fiber length of 1 to 10 mm and a thermally decomposable organic binder, the solvent is removed by drying, and the dried sheet is placed in a vacuum or A method for producing a surface-coated silicon carbide fiber nonwoven fabric sheet, comprising forming a carbon layer having a thickness of 0.2 to 5 μm on the surface of silicon carbide fibers by carbonizing the resin by heating in an inert gas. . 6. A silicon carbide fiber having a fiber length of 1 to 10 mm,
A silicon carbide fiber non-woven fabric sheet containing a carbon fiber having a fiber length of 1 to 10 mm and a thermally decomposable organic binder is three-dimensionally formed and processed, and the processed body is impregnated with a solution in which a resin is dissolved or dispersed. By removing the dried sheet and heating the dried sheet in a vacuum or an inert gas to mineralize the resin, a thickness of 0.2 to 5 μm
A method for producing a surface-coated silicon carbide fiber molded body, comprising forming a carbon layer of