JPS5971417A - Manufacture of graphite fiber - Google Patents

Abstract

PURPOSE:To manufacture a graphite fiber having high specific strength and specific elastic modulus, and high performance as a reinforcing material for composite material, by heat-treating a flame-resistant yarn under specific rate of temperature increase of the yarn to be treated in a low-temperature range. CONSTITUTION:A flame-resistant fiber (preferably a fiber obtained by making an acrylonitrile fiber precursor flame-resistant, and carbonizing at >=800 deg.C in a non-oxidizing atmosphere) is treated at >=2,000 deg.C to obtain a graphite fiber. In the above process, the rate of the temperature increase of the fiber to be treated is adjusted to >2,000 deg.C/min and <=5,000 deg.C/min in the temperature range of 1,300-2,000 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing graphite fibers, and more particularly to a method for producing high-performance graphite fibers with high specific strength and specific modulus.

After making it flame resistant by treating it in an oxidizing atmosphere at a temperature of usually 00°C to 300°C, it is treated at a temperature of 800°C or higher to 1300°C in a substantially non-oxidizing atmosphere.
It is known to carbonize the carbon fibers at temperatures below 2000 DEG C. and further treat the carbon fibers in an inert atmosphere at temperatures of at least 2000 DEG C. to give graphite fibers.

In recent years, graphite fibers have attracted attention as reinforcing materials for composite materials, largely because they not only have excellent elastic modulus and strength, but also are lightweight. That is, the material properties are extremely heavy in terms of strength and specific strength and specific modulus, which are the ratios of elastic modulus and density, compared to other reinforcing materials such as glass fiber, alumina fiber, boron fiber, silicon carbide fiber, steel, etc. This is because it is far superior in comparison.

In the process of heat-treating carbon fiber at a higher temperature, graphite crystallization progresses, and the fiber density of graphite fiber becomes even higher than that of carbon fiber. An increase in graphite fiber density is undesirable. However, it has been said that it is extremely difficult to obtain graphite fibers with improved specific strength and specific modulus by reducing the fiber density without impairing mechanical properties such as strength and elastic modulus. Ta.

Therefore, the present inventors have completed the present invention as a result of intensive studies to find a method for producing graphite fibers that are excellent in specific strength and specific modulus, which are extremely important material properties.

The gist of the present invention is to make a flame-resistant system, especially an acrylonitrile-based fiber precursor, flame-resistant, and then to
When producing graphite fibers by processing at a temperature of ooo°C, the heating rate of the treated fiber in the processing temperature range of 1300°C to 200°C exceeds 2000°C/min to 5000°C.
The present invention provides a method for producing graphite fiber, which is characterized in that the processing time is less than 1 minute.

The flame-retardant system used in carrying out the present invention includes organic fiber precursors such as acrylonitrile-based fibers, cellulose-based fibers, and phenol-based fibers that have been flame-retardantly treated, or pitch-based fibers. In order to produce graphite fibers with high specific strength and specific modulus by the method of the present invention, it is preferable to use an acrylonitrile fiber precursor.

Graphite fibers made using acrylonitrile-based fiber precursors have excellent performance in composite materials when used as reinforcing materials. Acrylonitrile fibers are fibers made of polymers or copolymers whose main component is acrylonitrile, and the copolymer components include unsaturated carboxylic acids such as acrylic acid, methacrylic acid, and itaconic acid, and esters of these acids. Commonly used copolymerization components such as , acrylamide, and methacrylamide are used.

When carrying out the present invention, it is necessary that the acrylonitrile fibers be at least flame-resistant treated, and preferably carbonized in a non-oxidizing atmosphere at a temperature of 80° C. or higher.

When graphitizing at a desired temperature of 2000°C or higher, the fibers to be treated will necessarily undergo heat treatment at a low temperature of 2000°C or lower. The feature of the present invention is that in this low-temperature heat treatment region, by regulating the heating rate of the heat history that the treated fibers undergo, graphite fibers with lower density than conventional methods can be obtained without reducing the elastic modulus and strength. The point is that we have discovered that it can be done. Among these low-temperature heat treatment areas, the temperature increase rate has a remarkable effect on the density in 130
The temperature ranges from 0°C to 200°C. No significant effect is observed in a temperature range outside the above range.

Furthermore, the temperature increase rate within the above temperature range is 2000℃/
more than 5000°C/min, preferably 2500°C
It is preferable to carry out the reaction at a rate of 4500° C./min to 4500° C./min.

It is difficult to reduce the density of graphite fibers at a heating rate of 2000°C/min or less, and even if the heating rate exceeds 5000°C/min, it is difficult to reduce the density of graphite fibers.
Not only is it not possible to achieve a much lower density than in the case where the graphite fibers are less than 10 minutes, but the strength of the obtained graphite fibers is significantly reduced, and as a result, only fibers with low specific strength can be obtained.

The rate of temperature increase of the fiber to be treated in the above treatment temperature range is determined by the temperature gradient of the furnace and the running speed of the fiber to be treated, but the temperature gradient of the furnace is not particularly limited and is determined by the temperature of the fiber to be treated as desired. The running speed is set so as to satisfy the temperature increase rate range.

The method of the present invention will be specifically explained below with reference to Examples, but the present invention is not limited thereto. However, the method for measuring fiber density used in the present examples and comparative examples is to take out a group of 20 to 30 fibers from a fiber bundle, form it into a ring shape with a diameter of 2 to 3 wn, and dry it at 100 ° C. for 3 hours. After vacuum defoaming in an immersion liquid with a density close to that of the fiber to be measured, the temperature was 5.
It was determined by immersing it in a density gradient tube solution (carbon tetrachloride-ethylene bromide system) at ℃.

Example 1 Polyacrylonitrile fiber (single denier 1.5, number of filaments 3000) was made flame resistant in air at 250°C, further carbonized at 1250°C in a nitrogen atmosphere, and then heated at the maximum temperature in a nitrogen atmosphere. Graphitize in a furnace at 2300°C. At that time, 1300℃ to 20℃ during graphitization heating process.
Temperature increase rate of treated fiber in the temperature range of 00°C: 3500°C/
The speed of the fibers to be processed and the temperature distribution of the furnace were controlled to obtain graphite fibers.

The graphite fiber obtained by the above treatment was impregnated with an epoxy resin and after hardening, the tensile strength and tensile modulus were measured using a tensile tester using a trial test of 200 deafness. Further, the density of the graphite fibers was measured by the method described above. The obtained performance was tensile strength of 290/J and tensile modulus of 33.6 t.
The on/-1 density was 1.74 f/c4, the specific strength determined from these was 1.67 x 108 cm, and the specific elastic modulus was excellent, 1.93 x 10''.

Comparative example 1゜Example 1. The same polyacrylonitrile fiber used in Example 1 was subjected to flame resistance and carbonization treatment under the same conditions as in Example 1.
After that, Example 1. Graphitization treatment was performed in the same 2300°C furnace. At that time, the temperature increase rate in the temperature range of 1300°C to 2000°C was regulated to 1500°C/min. As shown below, its properties were poor in specific strength and specific modulus.

Tensile strength 300Kg/- Tensile modulus 33.7 tons/-Density
1832/cr/l specific strength 1
．． 64 x 10Fm specific elastic modulus 1.84 x
1010 Darkness Example 2゜Example 1. The same polyacrylonitrile fiber used in Example 1. Flameproofing and carbonization treatments were performed under the same conditions as above, and then graphitization treatment was performed in a furnace with a maximum temperature of 2600°C. At that time, the temperature increase rate in the temperature range of 1300°C to 2000°C was regulated to 3000°C/min. As shown below, its properties were excellent in specific strength and specific modulus.

Tensile strength 270 to 9/J Tensile modulus 42 ton/7 Density 1.79 f/cr & Specific strength 1.51 x 10'm specific modulus
2.35 x 10" Dark Comparative Example 2 The same polyacrylonitrile fibers used in Example 1 were made flame resistant under the same conditions as in Example 1, and then carbonized to obtain carbon fibers. Graphitization treatment was carried out in the same 2600°C furnace.
The temperature increase rate in the temperature range of 0°C was set to 1500°C/min.

The properties of the obtained graphite fiber were as follows (the specific modulus was poor).

Tensile strength 280 to 9/- Tensile modulus 42 ton /4 Density 1.86 g/atl specific strength 1.51 x 108wn specific modulus
2.25 x 10" Gourd Comparative Example 3゜The same polyacrylonitrile fiber used in Example 1 was made flame resistant under the same conditions as in Example 1, and then carbonized, and the obtained carbon fiber was used in Example 2. Graphitization treatment was carried out in the same 2600℃ furnace as ゜.
The temperature increase rate in the temperature range at 00℃ is 5500℃/
Minutes and regulated and processed.

The properties of the graphite fibers obtained were poor in specific strength as shown below.

Tensile strength: 200 ton/- Tensile modulus: 41 ton/, i Density
1.79 f/crtl specific intensity
1.12×108 Specific modulus 2.29×10101o From these results, the specific strength and specific modulus of the graphite fiber obtained under conditions outside the scope of the present invention are the same as those of the graphite fiber obtained by the method of the present invention. It is clear that the strength and specific modulus of elasticity are inferior.

Patent applicant: Mitsubishi Rayon Co., Ltd. Representative Patent Attorney 1) Taketoshi Mura

Claims (2)

[Claims] (1) Flame-resistant yarn is treated at a temperature of at least 200°C to 1300°C to 200°C to produce graphite fibers.
1. A method for producing graphite fibers, characterized in that the heating rate of the fiber to be treated in a treatment temperature range of 000°C is more than 2000°C/min and less than 5000°C/min. (2) The method for producing graphite fibers according to claim 1, wherein a flame-resistant acrylonitrile fiber precursor is used as the flame-resistant yarn.