JPH046154A - Production of carbon molded body - Google Patents

Abstract

PURPOSE:To obtain a carbon molded body useful as a heat insulator for a high temp. furnace, etc., at a low cost by mixing carbon fibers with pitch fibers having a prescribed rate of residual carbon under specified conditions and baking a laminate of the mixed fibers in an inert atmosphere. CONSTITUTION:Carbon fibers are mixed with pitch fibers having 0.3-0.9 rate (f) of residual carbon produced from coal pitch and/or petroleum pitch so as to regulate the product (f.r) of the weight ratio (r) of the pitch fibers to the carbon fibers and the rate (f) of residual carbon to 0.1-4.0. A laminate of the mixed fibers are baked at >=800 deg.C in an inert atmosphere such as an N2 atmo sphere.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a method for producing a molded article using carbon fibers and pitch fibers, particularly an inexpensive molded article used as a heat insulating material for high temperature furnaces, etc. .

(Prior art) Carbon materials have long been widely used as high-temperature insulation materials, but in recent years, many high-temperature furnaces have been used to manufacture advanced composite materials and new materials. Carbon materials themselves are attracting attention as heat-resistant materials or their raw materials, and demand is increasing. This is based on the fact that it has strength and dimensional stability at high temperatures, is lighter than other metals and ceramic materials, and can be used even in the ultra-high temperature range of 2000°C or higher.

Conventionally, carbon materials are made using petroleum coke or coal coke powder as aggregate, adding a binder to this, performing press molding, etc., and then firing (graphitizing at higher temperatures if necessary)
It has been processed and used as a molded body. However, in recent years, molded bodies made from carbon fiber have come into widespread use because they are lighter and less likely to break. For example, as disclosed in Japanese Unexamined Patent Publication No. 52-47014, a molded article is manufactured at the same time as carbon fiber is manufactured;
As disclosed in Japanese Patent Application Laid-Open No. 59-69410, carbon fiber fabrics are impregnated with resin, pitch, etc., heat treated, and this process is repeated several times as necessary. Law), or Tokuko Sho 5! If-38179
As disclosed in the publication, there is a method of generating and depositing carbon etc. in carbon fiber textiles by a chemical method (CVD).
=Chemical Vapor Depositsio
n method) is also available.

There is also a method of using felt, mats, textiles, etc. made only of carbon fiber as is, but unlike molded objects,
Because it lacks the ability to maintain its own shape, its use is limited to, for example, as a gap filler or coating material for other heat insulating materials.

(Problems to be Solved by the Invention) The methods disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 52-47014 etc. attempt to produce molded articles directly from pitch fibers or infusible fibers, but the raw materials and processing steps (method ) are all the same as in the production of carbon fibers, so the resulting product is just matte carbon fiber itself, and as mentioned above, lacks the ability to retain its shape, so it cannot be used in the same way as a normal carbon material molded product. It won't pass.

In the impregnation method (Japanese Unexamined Patent Publication No. 51-69410, etc.), which is the most common method for producing molded objects using carbon fibers, the raw material, such as carbon fiber fabrics, is heated using pressurization, reduced pressure, or both. It requires expensive impregnation equipment that injects pitch, resin, etc. into the product, and is difficult to scale up.Furthermore, in order to achieve uniformity of the impregnation process, the usual energy-consuming process is repeated several times. There was a drawback that the price of the molded body was high. Also, to ensure ease and uniformity of impregnation,
In order to avoid deformation of the product due to repeated firing, and because the equipment itself is expensive, thick walls and
The drawback is that it is difficult to produce large molded bodies.

On the other hand, the CVD method as seen in the above-mentioned Japanese Patent Publication No. 59-38179 is attracting attention because it can use ceramics other than carbon as a matrix, but it requires extremely expensive manufacturing using a high vacuum system. Because it requires equipment, can only produce small compacts, and is expensive, it is rarely used for general insulation materials such as high-temperature furnaces, and has limited special uses as a heat-resistant material (external walls of space rockets). Currently, the company has achieved results only in the field of materials (such as wood, etc.).

The above-mentioned methods (impregnation method, CVD method) all have the problem that it is difficult to manufacture thick-walled, large-sized products due to limitations in the manufacturing method or manufacturing equipment, and they are also expensive (incidentally, these methods The carbon fiber raw material used in the method is PA
It is a fabric made from long fibers such as N or rayon,
(As is well known, this itself is very expensive.)

(Means for Solving the Problems) The present invention provides a synthetic material made of carbon fibers without using expensive equipment such as impregnation equipment or CVD equipment and which has restrictions on increasing the size of the equipment itself and the product. is produced at low cost by laminating mixed fibers obtained by mixing carbon fibers and pitch fibers, or by alternately laminating carbon fiber layers and pitch fiber layers and firing them in an inert atmosphere. be.

The raw material carbon fiber is pitch-based or PAN-based.

Rayon-based, other forms are chopped and matte.

Felt, woven fabrics, etc. can be relied upon, but from the point of view of producing cheaper molded products, pitch-based short fiber carbon fibers, etc.
It is desirable from the viewpoint of raw material cost and ease of handling.

The raw material for pitch fibers may be petroleum or coal, and pitch fibers may or may not be produced as raw materials for carbon fibers. Further, from the viewpoint of ease of handling, it is desirable that the fiber diameter is 5 to 100 μm and the fiber length is 5IIIn or more. However, the pitch fiber used needs to have a residual carbon ratio f in the range of 0.3 to 0.9 for reasons described later.

In addition, regarding the amount of both carbon fiber and pitch fiber used, the weight ratio r = of pitch fiber weight - 7 (g) and carbon fiber weight - PIAc (g") and the remaining C carbon ratio f of pitch fiber. The value of the product r-r must be within the range of 0.1 to 4.0.However, the value of f-r should be around the center of the above (for example, f-r = 2.0). This value is not more desirable, and changes in this value will change the characteristics of the molded product produced, so this value may be selected within the above range depending on the purpose.In other words, f-r <1.0. In this range, the raw material carbon fiber felt, mat,
A molded product with high elasticity and workability (easily deformable and cuttable) that strongly retains the shape of the chop, etc., and conversely has a large value such as f-r > 3.0. A hard molded product with excellent shape retention ability can be obtained. (Here, "residual carbon percentage f" refers to the initial pitch fiber weight [ha
Cg) J and the residue U left after carbonization.

The ratio of weight [W, (g)] is called the residual coal ratio.

)what.

The method for producing a molded article according to the present invention is as follows.

(a) Chopped carbon fiber (fiber length 5-100100O
and pitch fiber chips (5 mm or more) as mentioned above.
They are mixed uniformly so that the value falls within the specified range, and are laminated to the required thickness.

(b) Or use carbon fiber chips, felt mats, woven fabrics, etc. and pitch fiber chops, felt, mats, etc.
An arbitrary number of sheets are alternately stacked so that the value of r falls within a specified range.

(c) The laminate of mixed fiber layers or the laminate of carbon fiber layers and pitch fiber layers prepared in (a) or (b) above can be used as is, or after being compressed and densified using rolls, etc. A molded body is obtained by performing firing treatment at a high temperature of 800° C. or higher in an inert atmosphere while maintaining a pressurized state by placing a weight on the molded body.

The firing temperature when performing the above firing treatment may be 800°C or higher, but if the product molded body is used at a high temperature of 800°C or higher, the firing treatment may be performed at a high temperature of 800°C or higher.
Desirable for the purpose of increasing product life and suppressing gas generation during use.

According to the method of the present invention, molded bodies can be produced at low cost since expensive impregnation equipment, CD equipment, etc. are not required. Moreover, since the carbon fibers and pitch (fibers) are uniformly mixed or alternately layered before firing, there is no problem with impregnation, and the product can be easily made thicker and larger. In addition, since the manufacturing equipment is only a firing furnace, there is an advantage that the cost increase due to enlargement is extremely small and it is technically easy.

(Function) It is well known that the carbon fiber itself does not change in any way in the inert atmosphere during the firing treatment in the method of the present invention, but when the value of f-r is small (especially when the r value is If the pitch is small), the viscosity of the pitch that melts when the temperature rises in the firing process is low, so it has high fluidity, and it selectively adheres to and remains at the contact points of carbon fibers or at places with small gaps, and carbonizes. The molded product produced by this method has a large proportion of carbon fiber, so it retains the flexibility of the raw material carbon fiber (and its mats, felts, etc.) and has excellent workability.
The bonding at the intersections between the carbon fibers is strong, and a molded article having sufficient shape retention ability can be obtained.

On the other hand, when the f-r value is large (particularly when compression treatment or pressure firing is performed), pitch fibers are melted and carbonized to fill the gaps between carbon fibers, resulting in a process similar to that produced by the impregnation method. A high-density and hard molded body can be obtained.

It has already been mentioned that in the present invention, there are restrictions on the value of the residual carbon percentage f of the pitch fiber used and the value of the product of the ratio r and f of the pitch fiber and carbon fiber, but this is due to the following reasons. be.

If pitch fibers with an f value of less than 0.3 are used, the fluidity during melting is good, but the problem is that carbides derived from the pitch fibers segregate in the product molded product, making it impossible to obtain a good molded product. occurs. On the other hand, if the value of f is larger than 0.9, the pinched fibers will not melt during the firing process, or even if they are melted, they will not exhibit sufficient fluidity, resulting in the problem that a uniform molded product cannot be obtained. . Also, the value of fr is 0.1
If the size is smaller, the amount of carbide derived from the pitch fibers required for adhesion between carbon fibers will not be formed, resulting in a molded product lacking in shape retention (this is because the method of the present invention will cause the molded product to The main reason for this is that the amount of carbide derived from pitch fibers is usually much smaller than the value expected from the residual carbon ratio f). If the value of f-r is greater than 4.0, there is a problem that gases generated from the molten pitch phase during the firing process do not escape easily and remain as bubbles in the molded product, resulting in an uneven product.

(Example) Next, the present invention will be explained by examples.

Fruit 1" 1- Chopped product of coal pitch carbon fiber manufactured by centrifugal spinning method (average diameter 16 μm, average length 80 mm) 1.00
0g, and chopped pitch fiber (average diameter 18μ) manufactured from the same pitch fiber as the raw material for this carbon fiber.
m, average length 40 mm, residual coal rate 0.7) 1,000
2. OOOmmX 500mm
They were stacked on a tray to form a flat plate with a thickness of 200 mm.

This was heated as it was in a N2 atmosphere from room temperature to 900°C.
The molded product shown in Table 1 (1) was obtained by firing under the conditions of 0 minute and 900° C. for 5 minutes.

Carbon fiber chopped product 1,000 g used in Example 1
and 3,000 g of chopped pitch fibers were uniformly mixed in a dry method, stacked on a 2.000 mm x 500 mm tray, and then formed into a flat plate with a thickness of 80 mm using a roller press.

This was fired as it was in a N2 atmosphere under conditions of heating from room temperature to 1000°C for 45 minutes and holding at 1000'C for 5 minutes to obtain a molded body as shown in (2) in Table 1.

Felt manufactured from the carbon fiber used in Example 1 (fabric weight 200 g/m2) and pitch fiber chops manufactured from coal-based pitch for electrode impregnation (average diameter 14 μm, average length 3
0 mm, residual carbon ratio 0.5), 10 layers each (total 2
0 layer) is stacked to form a flat plate with an area of 500m x 500mm, and on top of that is a 500mm x 500mm layer made of alumina.
10 plates (weighing 7.5 kg) are placed on top of each other.
When baked from room temperature to 1200℃ for 60 minutes without holding under a pressure of 0.3kg/cm2, the results shown in Table 1 (
A molded article as shown in 3) was obtained.

(Effects of the Invention) According to the manufacturing method of the present invention, a large molded body made of carbon fiber and suitable for a heat insulating material for a high temperature furnace can be manufactured at low cost without using any special equipment.

Claims (1)

[Claims] 1. Pitch fibers and pitch fibers manufactured from coal-based pitch and/or petroleum-based pitch and having a carbon residual ratio f in the range of 0.3 to 0.9; A laminate of mixed fibers obtained by mixing so that the value of the product f・r of the weight ratio r of 1. A method for producing a carbon molded body, characterized by performing a firing treatment. 2. Carbon fibers and pitch fibers manufactured from coal-based pitch and/or petroleum-based pitch and having a residual carbon percentage f in the range of 0.3 to 0.9 are combined with the weight ratio r of pitch fibers and carbon fibers and the above f. Pitch fibers and carbon fibers are alternately laminated so that the value of the product f/r is in the range of 0.1 to 4.0, and then fired in an inert atmosphere at a temperature of 800°C or higher. A method for producing a carbon molded body.