JPH0633531B2 - Carbon fiber manufacturing method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a high-performance acrylonitrile-based carbon fiber, and more specifically to a method for producing a carbon fiber at a relatively low temperature of 300 to 900 ° C. during a carbon fiber production process. The present invention relates to cleaning treatment of carbonized intermediate fiber heat-treated in an inert atmosphere.

[Conventional technology]

Carbon fiber obtained by flameproofing and carbonization treatment using acrylonitrile fiber as a precursor has high strength and elastic modulus and is light, so it is widely used as an aerospace material or as a material for sports registries such as golf shafts and fishing rods. Has been done.

With the expansion of applications of carbon fiber, higher elongation
The demand for high strength, so-called high performance carbon fibers is increasing. Various methods for producing carbon fibers satisfying such demands have been studied, and the techniques are various including those related to precursors, flame resistance, carbonization, and surface treatment. Most of these techniques are the method of controlling the final orientation of the carbon fiber, the dense structure, or the defect that becomes the starting point of the fiber (or composite) fracture by suppressing or removing the inclusion of foreign matter inside the fiber and the surface layer. It is about how to reduce points. Regarding the latter, for example, the research paper of Reynolds et al. (Phil
os.Trans.R.Soc.London, Ser.A, 294 (1980)), which states that by performing precision spinning of the spinning dope and spinning in a clean room, foreign particles such as impurity particles are removed. The strength of the carbon fiber thus obtained is greatly improved. In addition to such an example of foreign matter removal during the production of a precursor, Japanese Patent Publication No. 51-11209 discloses, in view of removal of foreign matter generated during the firing process of carbon fibers, a flame-resistant fiber after a precursor is treated with a liquid. By performing ultrasonic treatment in the medium, foreign substances such as tar-like decomposed products adhering to the fiber surface are removed, which enables subsequent uniform carbonization treatment, and makes the flame-proof treatment for a short time and strength. There is a report that carbon fibers with excellent elastic modulus can be obtained.

[Problems to be solved by the invention]

Generally, in the production of acrylonitrile-based carbon fiber,
The formation of tar-like decomposed products is most remarkable in the very early temperature range of carbonization under an inert atmosphere, that is, in the range of 300 to 500 ° C., rather than during the flameproofing process. Most of the tar-like decomposed product generated in the temperature range is released to the outside of the fiber, but part of the tar-like decomposed product remains on the fiber surface or is confined in the fiber surface layer portion as a low molecular weight substance. Such a low molecular weight decomposition product inhibits the progress of graphitization of the fiber surface layer portion in the subsequent substantial high-temperature carbonization treatment, whereby the finally obtained carbon fiber has many defects in the fiber surface layer portion. Becomes

The present invention is to find a method for producing a carbon fiber having high strength and excellent adhesion to a resin.

[Means for solving problems]

The gist of the present invention is that an acrylonitrile-based fiber is subjected to flame resistance treatment in an oxidizing atmosphere at 180 to 350 ° C.,
Then, heat treatment (low temperature carbonization treatment) is performed while imparting elongation to the fiber in an inert atmosphere of 300 to 900 ° C., and then 10
In a method for producing carbon fiber carbonized in an inert atmosphere at 00 ° C. or higher, a high-performance carbon characterized in that the surface of the fiber after low-temperature carbonization treatment is etched in the gas phase and then the fiber is washed. It is in the fiber manufacturing method.

The acrylonitrile fiber of the present invention contains at least 90% by weight or more of acrylonitrile, and contains 10% by weight or less of comonomers such as acrylic acid, methacrylic acid, acrylamide, methacrylamide, allyl acid ester, methacrylic acid ester and itaconic acid. Examples thereof include those obtained by copolymerizing at a ratio and shaping it into a fibrous shape. The single fiber strength is 0.5 to 3 denier, preferably 0.5 to 1.5 denier, and the total number of filaments is 500 to 300,000 tow.

The oxidizing atmosphere used for flameproofing the acrylonitrile fiber is an oxygen-containing atmosphere such as air at a temperature of 1
The atmosphere is 80 to 350 ° C. The density of the obtained flame resistant fiber is 1.26 to 1.45 g / cm ³ , preferably 1.30 to 1.40 g / cm ^3.
It is better to set the range. Density of flame resistant fiber is 1.26 g / cm ³
If the amount is less than the following, the progress of flame resistance is insufficient, and the fiber melts during the carbonization treatment under an inert gas atmosphere to be performed later.
The frequency of breakage increases and stable production cannot be performed. On the other hand, those having a fiber density of more than 1.40 g / cm ³ should be sufficiently stretched when the high-performance carbon fiber is produced during the low temperature carbonization treatment under the following inert gas atmosphere of 300 to 900 degrees. In addition, due to the excessive introduction of oxygen into the flame-resistant fiber, the final carbon fiber internal structure does not become dense,
It does not easily become a carbon fiber with excellent performance.

Next, the flame-resistant fiber thus obtained is treated at 300 to 900 degrees,
The density of the obtained fiber is 1.40 to 1.80 g / cm ³ , preferably under an inert atmosphere of 400 to 700 ° C., preferably
Heat treatment is performed from 1.45 to 1.70 g / cm ³ while imparting elongation of 3% or more and 30% or less. At this time, if the elongation rate is less than 3%, there is no elongation effect, and if it exceeds 30%, high-performance carbon fibers cannot be obtained due to frequent occurrence of fluff or cutting of fibers. If the heat treatment temperature is less than 300 ° C. or more than 900 ° C., the elongation effect of the fiber itself at that temperature may cause no elongation effect or may cause fuzz, which is not preferable.

In the present invention, the surface of the fiber which has been carbonized at a low temperature at 300 to 900 ° C. in an inert atmosphere as described above is subjected to an etching treatment in a gas phase and then to a washing treatment. The washing liquid medium at this time is water or boiling water. It is still more effective to dissolve the tar content with an organic solvent having excellent solubility for liquid tar or solid tar or an alkaline solution such as sodium hydroxide solution, and then wash with water or boiling water.

Further, by subjecting the fiber surface to an etching treatment in advance before the above-mentioned washing treatment, not only the low molecular weight decomposed product attached to the fiber surface but also the low molecular weight decomposed product intervening in the fiber surface layer portion can be removed. Examples of the etching treatment in the gas phase include ozone oxidation treatment in the gas phase. However, if the weight loss of the fiber exceeds 5% by these etching treatments, the substrate of the fiber itself is excessively left and it may cause the generation of fluff, which adversely affects the final carbon fiber substrate. The weight loss of the fibers is preferably 5% or less. By further heat-treating the thus-obtained low-temperature carbonized yarn washed yarn at a temperature of 1000 ° C. or higher, the carbon fiber targeted by the present invention can be obtained.

〔Example〕

 Hereinafter, the present invention will be described in more detail with reference to Examples.

The strand strength and the strand elastic modulus were measured according to the method of JIS R7601.

Comparative Example 1 An acrylonitrile fiber bundle consisting of 6000 filaments of a single yarn denier and 6000 filaments was subjected to a flameproofing treatment in the air at 220 to 260 ° C. while imparting 15% elongation to the fiber until the density became 1.35 g / cm ^3. Then, low-temperature heat treatment was performed in a nitrogen atmosphere at 600 ° C. while imparting 8% elongation, and finally carbonization treatment was performed in a nitrogen atmosphere having a maximum attainable temperature of 1400 ° C.
The strand strength and the strand elastic modulus of the obtained carbon fiber were 480 kg / mm ² and 26.8 ton / mm ² .

Comparative Example 2 A flame-resistant yarn obtained in the same manner as in Comparative Example 1 was heat-treated in a nitrogen atmosphere at 600 ° C. while imparting 8% elongation, and then treated with a 2% sodium hydroxide solution for 30 seconds and then in boiling water. After washing for 1 minute in the same manner, the same carbonization treatment was performed. The strand strength and elastic modulus of the obtained carbon fiber are 50 respectively.
It was 8 kg / mm ² and 26.7 ton / mm ² .

Example 1 Before the cleaning treatment of Example 1, the fibers heat-treated in a nitrogen atmosphere at 600 ° C. were irradiated with ozone in an atmosphere of 200 ° C. for 1 minute, and then treated with a sodium hydroxide solution and boiling water as in Example 1. Cleaning treatment Further carbonization treatment was performed. The strand strength and elastic modulus of the obtained carbon fiber are each 557 kg.
It was / mm ² , 27.3ton / mm ² .

〔The invention's effect〕

It is possible to greatly improve the performance of the carbon fiber by cleaning the low temperature carbonization treated yarn after the surface etching treatment.

Claims (1)

[Claims] 1. An acrylonitrile fiber is used in the range of 180 to 350.
Flameproofing in an oxidizing atmosphere at 300C, then 300-9
In a method for producing carbon fibers, which is heat-treated (low-temperature carbonization treatment) while imparting elongation to the fiber in an inert atmosphere of 00 ° C., and then carbonized in an inert atmosphere of 1000 ° C. or higher, after the low-temperature carbonization treatment, A method for producing high-performance carbon fiber, which comprises etching the surface of the fiber in a gas phase and then washing the fiber.