JPH05247729A - Production of pitch-based milled carbon fiber - Google Patents

Abstract

PURPOSE:To easily obtain the subject carbon fiber sharp in fiber length distribution and very low in aspect ratio without the need for much energy by making infusibilized pitch-based fibers into milled fibers followed by carbonization or graphitization. CONSTITUTION:Optically isotropic coal-based pitch 250 deg.C in softening point is put to melt spinning into pitch fibers, which are then infusibilized in an air atmosphere at max. temp. of 310 deg.C. The resulting infusibilized fibers are made into milled fibers using a pressing machine to produce milled fibers of ca. 100mu, 60mu, and 35mu in fiber lengths, respectively. Then, these milled fibers are either raised in temperature at a rate of 5 deg.C/min to 100 deg.C and treated at this temperature for 30min into carbonized milled fibers, or treated at >=2000 deg.C into graphitized milled fibers, thus easily obtaining at low cost the objective high- quality pitch-based milled carbon fiber of <=8 in aspect ratio with narrow fiber length distribution.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a pitch-based carbon fiber mill used in many industrial fields.

[0002]

2. Description of the Related Art Carbon fibers are widely used in many industrial fields because of their excellent properties such as chemical resistance, high strength, heat resistance, electric conductivity and abrasion resistance. In particular, pitch-based carbon fiber has been attracting attention as a material having both low cost and high performance in recent years because it uses petroleum, coal, and residual tars of organic compounds as starting materials. Pitch-based carbon fibers are used as long fiber filaments, short fiber tows, or chopped fibers or milled fibers obtained by cutting these into short fibers of a certain length. The carbon fiber milled (milled fiber) is widely used as a performance enhancer for various matrices because it is easily dispersed and homogeneous.

In modifying and strengthening the matrix with a carbon fiber mill, the aspect ratio (fiber length (L) / fiber diameter (D)) of the carbon fiber mill (milled fiber) is important in addition to the characteristics of the carbon fiber. Become a factor. The aspect ratio (L / D) is used from large to small depending on the purpose of compounding.

In the prior art, a carbon fiber mill (milled fiber) is produced by spinning and then hammer-milling the carbon fiber produced by carbonizing or graphitizing the infusibilized pitch-based fiber in an oxidizing atmosphere. , A ball mill, a roll, etc. are used to cut and pulverize to a predetermined size. However, in this method, a large amount of energy must be input in order to overcome the high strength and high wear resistance characteristics of carbon fiber. In particular, if the aspect ratio (L / D) is small, even if the milling is promoted, long fiber length remains, or the fiber diameter and fiber length become unclear, and it becomes difficult to achieve stable milling. It is the current situation that a material having an aspect ratio (L / D) <8 is not manufactured.

[0005]

The problem to be solved by the present invention is to produce a pitch-based carbon fiber milled fiber (milled fiber), and the aspect ratio (L / D) which could not be practically achieved by the prior art. It is to develop a technology for manufacturing without needing a large amount of energy, including the manufacturing of an ultra-short mill of <8.

[0006]

Means for Solving the Problems As a result of intensive studies to solve these problems, the present inventors have found that pitch-based carbon fibers, after being spun, have been infusibilized in an oxidizing atmosphere ( (Hereinafter referred to as infusible fiber), or fibers that have been further heat-treated at a temperature of 600 ° C. or lower after the same treatment (hereinafter referred to as heat-treated fibers) have insufficient strength and are fragile. That can be carried out without further, the milled one can be obtained a pitch-based carbon fiber mill of sufficient physical properties by ordinary carbonization or graphitization treatment without applying any tension, that is, at the time of milling The inventors have found that a milled product having an aspect ratio (L / D) <8 can be easily manufactured despite the small input energy, and have completed the present invention.

That is, the present invention is characterized in that pitch-based carbon fibers that have been infusibilized or pitch-based fibers that have been heat treated at 600 ° C. or lower after the treatment have been milled and then carbonized or graphitized. It is in the method of manufacturing milds.

The pitch-based fiber used in the present invention is made from a tar component obtained from petroleum, coal, organic compounds, etc. as a starting material. The type of pitch material used, its optical properties, and linear shape The shape is not particularly limited depending on the shape of a fiber such as a curved shape, a long fiber, or a short fiber.

[0009] The infusible fiber referred to in the present invention, the pitch-based fibers obtained by spinning the pitch for spinning, oxygen, air, ozone, 250 ° C. to 450 ° C. in an oxidizing atmosphere such as NO _X
The fiber is a surface-oxidized fiber at a temperature around it, and usually has a concentration of oxygen in the fiber of about 4 to 10% by weight and is not particularly limited by the manufacturing method or the like. The tensile strength of such infusibilized fibers is preferably 50 Kg / mm ² or less.

The heat-treated fibers referred to in the present invention, that is, the pitch-based fibers that have been heat-treated at 600 ° C. or lower, preferably 300 to 600 ° C. in a vacuum or an inert gas atmosphere after the infusibilization treatment are not yet completely carbonized. , Pitch-based fibers containing volatile components and the like. The fiber obtained by the heat treatment temperature of 600 ° C. or less has a tensile strength of 50.
Kg / mm ² or less. In the case of pitch-based carbon fiber, the strength of the fiber generally increases as the firing temperature increases,
When the strength of the fiber increases above 50 kg / mm ² , the effect of the low energy-cost production of the present invention rapidly disappears, and it becomes difficult to produce a milled product having a low aspect ratio.

On the other hand, although there are pitch-based fibers that have been spun as fibers having a tensile strength of 50 kg / mm ² or less, the pitch-based fibers that have not been treated as described above are fibers that are controlled in milling. The morphology cannot be maintained and the powder is pulverized. Therefore, in the method of the present invention, such fibers are not used as a raw material for milling.

The method of milling in the present invention includes:
Since the material to be crushed is weaker in strength than ordinary carbon fibers, a wider range of milling methods are possible, and examples thereof include hammer mills, ball mills, rolls and presses, but are not particularly limited thereto. In the method of the present invention, the L / D (fiber length / fiber diameter) ratio is 8 or less, that is, 8 to 1
It is preferable to mill up to.

As the aspect ratio (L / D ratio) becomes smaller, the pitch-based fiber of the present invention which is milled has a higher surface area ratio due to the newly formed cross section, and as a result, the infusibilizing property of the part is increased. Tends to be lower. Therefore, in the case where the fusion phenomenon of the milled product is likely to occur in the subsequent carbonization step (usually firing at 800 ° C. or higher) or graphitization step (usually firing at 2000 ° C. or higher) after milling, milling was performed. After that, a surface treatment is once performed in an atmosphere of air, ozone, NO _x, etc. at a temperature of about 200 to 400 ° C. (that is, the infusibilizing treatment as described above is performed again), and then a carbonization or graphitization step. It is necessary to enter. Here, the degree of surface treatment is sufficient to eliminate the fusion phenomenon during carbonization.

[0014]

EXAMPLES Next, the present invention will be further described with reference to examples. In the examples,% is based on weight unless otherwise specified.

Example 1 Optically isotropic coal-based pitch having a softening point of 250 ° C. was spun by a melting method to obtain pitch fibers having a diameter of 14 μm, and then subjected to infusibilization treatment in an air atmosphere at a maximum temperature of 310 ° C. An infusibilized fiber was obtained. Infusible fiber has a tensile strength of 15 kg / mm
^{Was 2} . This is milled by a press machine and about 10
0.5 kg each of 0 μm, 60 μm, and 35 μm long mills were obtained. The pressure required for milling is 20, 75 and 2 respectively.
It was 00 Kg / cm ² . Then 1 at a rate of 5 ° C / min
The temperature was raised to 000 ° C. and treated at the same temperature for 30 minutes to obtain a carbonized milled product. Except for those having an average yarn length of 35 μm, a good carbonized milled product was obtained without fusion. Average thread length 35 μm
Although the product of the present invention had some fusion and was obtained as a lump, it was easily milled in about 1 minute with a ball mill tester to obtain a non-fusion state. Average yarn diameter is 13 μm, aspect ratio is 8, 4.
5 and 3, standard deviations were 60, 35 and 20 μm.

Example 2 The same infusible fiber as described above was used, and this was heated at 5 ° C. in a nitrogen gas atmosphere.
Heat treatment by increasing the temperature at 1 / min and holding at 550 ° C for 30 minutes
Thread is made (tensile strength is 40 kg / mm ²). This
This is milled with a press machine, and approximately 200 μm, 100
0.5 kg each of μm and 50 μm long milled products were obtained. Mildo
The pressure required for the conversion is 20, 50, and 160 Kg /
cm²Met. After that, 1000 ℃ at a speed of 5 ℃ / minute
The temperature was raised to and treated at the same temperature for 30 minutes to obtain a carbonized milled product.
All samples were obtained in good milled condition. Average thread diameter
13 μm, aspect ratios of 16, 8, and 4, standard
The deviations were 165, 70, and 28 μm.

Example 3 Optically anisotropic petroleum pitch having a softening point of 230 ° C. was spun by a melting method to obtain pitch fibers having a diameter of 12 μm, and then subjected to infusibilizing treatment at a maximum temperature of 300 ° C. in a NO ₂ atmosphere. The infusible fiber was obtained. Tensile strength of infusible fiber is 10kg / c
It was m ² . This is milled with a press machine and about 1
00μm, 60μm, 35μm long milled 0.5kg each
Got The pressures required for milling were 15, 70, and 180 Kg / cm ² , respectively. Then average yarn length 60μ
With respect to m and 35 μm, the surface oxidation treatment was carried out by holding in air atmosphere at a maximum temperature of 320 ° C. for 30 minutes. Next, these three samples were heated to 1000 ° C. at a rate of 5 ° C./min and treated at the same temperature for 30 minutes to obtain a carbonized milled product. All samples were obtained in good milled condition. Average thread diameter 13μ
m, aspect ratios were 8, 4.5, and 3, respectively, and standard deviations were 55, 32, and 18 μm.

Comparative Example 1 The same infusible fiber as in Example 1 was heated at 2 ° C./minute to 900 ° C. and treated at the same temperature for 30 minutes to obtain carbon fiber. The tensile strength of the obtained carbon fiber was 70 Kg / mm ² . Milled with the same press machine as in Example 1 to give about 20
0.5 kg each of 0 μm and 100 μm long milled products was obtained. The pressure required for milling is 120 and 200 kg /
It was cm ² . Milled yarns with an average yarn length of 100 μm or less
Pressurized up to 250 Kg / cm ² , but could not be obtained. The obtained milled (aspect ratio 16, 8) had standard deviations of 195 and 90 μm.

[0019]

EFFECT OF THE INVENTION In the method of the present invention in which the infusibilized pitch-based fiber or the pitch-based fiber which is heat-treated at 600 ° C. or lower after the treatment is milled, and then carbonized or graphitized to obtain a carbon fiber milled, A low aspect ratio milled product is obtained and the manufacturing energy required for it is low.
In addition, even with a low aspect ratio, a high-quality milled product having a small fiber length distribution can be obtained at low cost.

Claims (6)

[Claims] 1. A method for producing a pitch-based carbon fiber mill, which comprises milling infusibilized pitch-based fibers and then carbonizing or graphitizing. 2. The method according to claim 1, wherein the infusible treated fiber having a fiber strength of 50 kg / mm ² or less is milled. 3. An infusibilized pitch-based fiber is further added to 60.
A method for producing a pitch-based carbon fiber mill, which comprises heat-treating at 0 ° C. or lower, milling, and then carbonizing or graphitizing. 4. The method according to claim 3, wherein the heat-treated fiber having a fiber strength of 50 kg / mm ² or less is milled. 5. The production method according to claim 1, wherein the L / D (fiber length / fiber diameter) ratio is milled to 8 or less. 6. The manufacturing method according to claim 1, 2, 3, 4, or 5, which is subjected to surface oxidation treatment after milling and then carbonized or graphitized.