JPS58186614A - Production of graphite fiber - Google Patents

Abstract

PURPOSE:A polyacrylonitrile fiber precursor is made flame-retardant under stretching in an atmosphere for affording flame-retardance, then subjected to carbonization and graphitization to enable efficient production of graphite fiber with high toughness without fluffing and filament breakage. CONSTITUTION:The precursor made of polyacrylonitrile fiber is subjected to a treatment to make it flame-retardant in an atmosphere for affording flame- retardance from 210-250 deg.C at the start to 290 deg.C at the end which restricts the density of the flame-retardant fiber to lower than 1.28g/cm<3> under 40-100%, preferably 50-90% elongation. Further the treatment is continued under the constant length or 10% streching until the density of the fiber exceeds 1.3g/cm<3>. Finally, in an inert atmosphere, carbonization is effected up to 1,500 deg.C and graphitization up to 2,000 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing graphite fibers with excellent rigidity from polyacrylonitrile fiber precursors.

41 machine fiber precursor in an oxidizing atmosphere e.g. air for 200 min.
It is known to flame retardantly treat the graphite fibers at temperatures of up to 600 DEG C. and finally to obtain graphite fibers under tension or without tension in an inert atmosphere at temperatures of at least 2000 DEG C.

Graphite fiber is lightweight and highly rigid, and taking advantage of these characteristics, its use as a reinforcing material for composite structural materials such as sports equipment, aircraft parts, and mechanical parts is expanding. Conventionally, one way to achieve high stiffness, or high elasticity, of graphite fibers was to
It has generally been thought that it is effective to increase the orientation of fiber molecular chains by performing an elongation operation during flameproofing treatment during the firing process. However, in reality, as the degree of elongation is increased, it not only causes fuzz generation and single yarn breakage, which impairs the performance of the fiber, but also causes the equipment to be damaged due to the fuzz or cut single yarns being wrapped around rollers, etc. There was a limit to the extension operation as there was a risk of interfering with stable operation.

As a result of a detailed study of the physical property behavior of fibers during flame-retardant treatment, the present inventors found that it is possible to significantly elongate graphite fibers without generating fluff or single filament breakage, which is useful for improving the elasticity of graphite fibers. We have discovered a flame-retardant treatment method.

The present invention provides polyacrylonitrile fiber precursor with 21
The flame resistant fibers are made flame resistant by passing through a flame resistant atmosphere starting from 0 to 250°C and ending at 250 to 290°C.
9/cm3 or less to give an elongation of 40% or more and less than 100%, and then/with a constant length or elongation to 10% or less, so that the density of the flame resistant fiber is at least 1.69/cm3.
This is a method for producing graphite fiber, which is characterized by progressing flame resistance until it reaches fL3, followed by carbonization and graphitization.

Examples of the polyacrylonitrile fiber precursor include fibers made of polymers or copolymers containing polyacrylonitrile as a main component. As the copolymer component, common copolymer components such as unsaturated carboxylic acids such as acrylic acid, methacrylic acid, and itaconic acid, esters of these acids, acrylamide, and methacrylamide are used.

When carrying out the present invention, the fiber precursor to be treated is
The flame resistant fibers are passed through a flame resistant atmosphere starting at 10-250 °G and ending at 250-290 °C, with the density of the flame resistant fibers in the flame resistant atmosphere being 1.289/crr.
Pre-flame resistance treatment is performed to give elongation of 40% or more and less than 100%, limiting the elongation to L3 or less.

The ambient temperature in the initial region of the pre-flame retardant treatment is 210-250°C.
℃, preferably 220-245°C. At temperatures below this range, the progress of substantial flame resistance is slow and is industrially disadvantageous. Furthermore, if a fiber precursor is directly introduced into an atmosphere exceeding 250° C., a rapid exothermic reaction may cause fiber fusion, melting, and cutting.

The ambient temperature at the end of the pre-flame retardant treatment is 250 to 290°C.
, preferably 255-280°C. If the temperature is lower than this, fluffing or single filament breakage may occur when elongation is performed by 40% or more and less than 100% during the pre-flame resistance treatment.

At temperatures above 250°C, fluffing or single fiber breakage due to high elongation will not occur, but at temperatures above 290°C, flame resistance will rapidly progress, resulting in uneven fiber structure and the resulting graphite Fiber performance deteriorates.

As for the atmospheric temperature distribution from the initial region to the final region of the pre-flameproofing treatment, it is preferable to increase the atmospheric temperature gradually, continuously or discontinuously.

In the pre-flame-retardant treatment, the density of the flame-retardant fiber is 1.28.
9/cm3 or less to give an elongation of 40% or more and less than 100%, preferably 50 to 90%. If the density of the flame-resistant fiber exceeds 1.28 g/cm3, the laddering of polyacrylonitrile molecules progresses, making it difficult to stretch the fiber to a large extent, and forcing the fiber to stretch may cause fluff or breakage of single filaments. Cheap. If the elongation is less than 40, a sufficient effect in increasing the elasticity of graphite fibers cannot be expected. Excessive elongation of more than 100% may destroy the fiber structure, and at the same time may cause fuzzing or 9-year-old single yarns.

Next, the elongation is limited to a constant length or 10% or less to suppress the occurrence of fuzz or single filament breakage, and flame resistance is continued until the density of the flame resistant fiber reaches at least 1.3 g/cm3. In order to perform the carbonization process stably after flameproofing is completed,
The density of the flame-retardant fibers must be at least 1.397 cm3. If it is less than 1.5 g/min, the formation of a flame-resistant structure is insufficient, which may lead to melting and cutting of the fibers during carbonization. After the pre-flame-proofing treatment, the ambient temperature when flame-proofing is to be continued is preferably 250 to 290'C.

To determine the density of the flame-resistant fibers, take a group of 20 to 60 fibers from a fiber bundle, shape it into a ring with a diameter of 2 to 3 ml, and dry it at 100'C for 6 hours. It is determined by vacuum degassing in a carbon tetrachloride-toluene system and then immersing in a density gradient tube liquid at a temperature of 25°C.

After completion of flameproofing, carbonization is carried out in a substantially inert atmosphere by conventional methods at a maximum temperature of 1500'C or less, and further treated at a temperature of at least 2000'C.
Graphite fibers are obtained.

According to the method of the present invention, by concentrating the elongation operation at a relatively early stage of flame resistance, and by adopting effective elongation conditions to suppress elongation after flame resistance, the flame resistance treatment, which is a disadvantage of the conventional method, can be performed. It is possible to industrially advantageously produce highly elastic graphite fibers while suppressing the occurrence of fuzz, fiber breakage, etc. that are caused by high elongation operations.

Example 1 Polyacrylonitrile fiber (single yarn denier 1.5, number of filaments 6000) was heated at 265°C-255°C-26
In air with a three-step ambient temperature of 5°C, the original length is stretched by 60% and then subjected to pre-flame resistant treatment, resulting in a flame resistant fiber density of 1.26! i'/cm3, and then flame-proofing was completed under constant length at 265° C. in air to give a final flame-proofing fiber density of 1.55 ji/6m3.

The fibers were carbonized in a nitrogen atmosphere at a maximum temperature of 1250'C, followed by carbonization in a nitrogen atmosphere at a maximum temperature of 2530'C.
It was graphitized with C. After the obtained graphite fibers were impregnated with an epoxy resin and cured, the tensile elastic modulus and tensile strength were measured using a tensile tester using a growth test of 200 mm. As a result, the tensile modulus was 42.8 ton/mi2, and the tensile strength was 253 kg/mm2. The graphite fiber had a good appearance with no fluff or single fiber breakage.

Comparative Example 1 Graphite fibers were obtained in the same manner as in Example 1, except that the elongation rate during the pre-flame resistance treatment was set to 25% of the original length. The obtained graphite fiber has a tensile modulus of 39.1 ton/H.
2. The tensile strength was 250 kg/mm2, and the elastic modulus was particularly poor.

Comparative Example 2 A pre-flame resistant treatment was performed using the same method as in Example 1, and the flame resistant fiber density after the pre-flame resistant treatment was 1.30! j / 6m3
When the temperature was increased to 100%, fluffing and single yarn breakage occurred frequently, which wrapped around the rollers, making it impossible to continue operating the flameproofing device.

Therefore, the flame resistant fiber density after the pre-flame resistant treatment was lowered to 1.26 ji/6 m3, which is the same as in Example 1, and the operation was restarted. After the operation became stable, the final density of the flame-resistant fiber was gradually lowered to 1.3597 cm3 in the case of Example 1, and 5 hours after restarting the operation, melting and cutting of the treated fiber occurred in the carbonization treatment furnace. Ta. The final density of the flame-resistant fiber at this time was 1,2897 cm3.

Example 2 The same polyacrylonitrile fiber as in Example 1 was
Pre-flame resistant treatment was performed in air with a 6-step ambient temperature of °G-255 °G-270 °C while elongating 80% of the original length, and the density of the flame-resistant fiber was made 1.2597 cm3. Flame resistance was completed under constant length at 270° C. in air, and the final flame resistance fiber density was 1.359/cIrLS. This fiber was carbonized and graphitized by the same method as in Example 1, and the tensile modulus and tensile strength of the graphite fiber obtained were measured, and the results were 44 and 817 g, respectively.
1.2 and 255 kllJ/mm” and the strength is that of Example 1.
It is equivalent to , but the elastic modulus is further improved. The appearance of the graphite fibers was as good as in Example 1.

Comparative Example 6 In Example 2, the ambient temperature during the pre-flame retardant treatment was set to 24
When the temperature was gradually lowered from 0°C to 245°G to 245°C, fiber breakage occurred in a short period of time during the pre-flame resistance treatment process. Therefore, the ambient temperature during the pre-flameproofing treatment was set to 260'C.
The temperature was set to -265°C-270°C and operation was restarted. The obtained graphite fibers showed fusion between the fibers and could not be used for performance evaluation. This rapidly heats the precursor to 260°C.
This is thought to be due to the introduction of the flame-retardant atmosphere.

Applicant: Mitsubishi Rayon Co., Ltd. Agent: Patent attorney Masao Kobayashi

Claims (1)

[Claims] Polyacrylonitrile fiber precursor, 210 to 250
It is made flame resistant by passing it through a flame resistant atmosphere starting at 250-290 degrees Celsius, at which time the density of the flame resistant fibers in the atmosphere is first adjusted to 1.28 fl /
The density of the flame-retardant fiber is at least 1.37 while elongation is limited to 40% or more and less than 100% with a limit of cm3 or less, and then elongation is performed at a constant length or to 10% or less! /cm3
A method for producing graphite fiber, which is characterized by making it flame resistant until it becomes flame resistant, followed by carbonization and graphitization.