JPS6250574B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing high-strength carbon fibers that are easy to handle. Traditionally, as an atmosphere for the carbonization process to obtain high-strength carbon fibers, for example,
In a vacuum or a non-oxidizing atmosphere such as hydrogen as described in Japanese Patent Publication No. 44-24692, in an atmosphere of acid vapor such as hydrochloric acid gas as described in Japanese Patent Publication No. 44-24692, or in a halogenated atmosphere as described in Japanese Patent Publication No. 47-40575. It is known to carry out the reaction in a hydrogen atmosphere and in a hydrogen chloride-water-inert gas atmosphere as described in Japanese Patent Publication No. 53-19047. However, carbon fibers obtained by carbonization in these atmospheres all have problems in handling during the manufacturing process, and have the disadvantage of being prone to "fluff" or "single yarn breakage." For this reason, sizing is carried out by applying a small amount of synthetic resin to the surface, but usually the type and amount of resin used for sizing must be adjusted appropriately according to the handling conditions of the carbon fiber, so sizing is carried out. The appearance of carbon fiber that is easy to handle has been desired. An object of the present invention is to provide a method for producing carbon fibers that are easy to handle and have high strength, eliminating the drawbacks of the prior art. After heating with hydrogen chloride to make it flame resistant,
A method for producing carbon fibers, characterized by heating in an atmosphere containing 0.2 to 10% by volume, 0.2 to 4% by volume of oxygen, and an inert gas. Hereinafter, the present invention will be specifically explained in detail. The polyacrylonitrile fiber (hereinafter referred to as PAN fiber) used in the present invention is a polyacrylonitrile homopolymer or a combination of polyacrylonitrile of 85% by weight or more and an ethylenically unsaturated compound, such as methyl acrylate, methyl methacrylate, or vinyl acetate. esters, vinyl chloride,
Copolymers and mixtures with halogens such as vinylidene chloride, acids such as acrylic acid, methacrylic acid, and itaconic acid, and amides such as acrylamide and methacrylamide can be used. Spinning can be performed by any dry spinning method, and rhodanate, nitric acid, dimethylformamide, dimethylacetamide, and dimethylsulfoxide can be used as the solvent. As the fiber bundle, a fiber bundle consisting of tens to hundreds of thousands of filaments with a single fiber density of 0.1 to 10 denier per filament (dpf) is usually used, but filaments of 1 to 5 dpf are preferably used. This PAN fiber is heated to 300℃ or less, preferably 230℃ or less.
Heat at 280°C in an oxidizing atmosphere such as oxygen, halogen gas, air, etc. for 0.5 to 3 hours to make it flame resistant. At this time, it is preferable to apply tension to an extent that causes contraction of several percent or less or slight elongation with respect to the fibril length. The flame-resistant fibers are then heated to 300-1500° C. in an atmosphere containing 0.5-10% by volume of hydrogen chloride, 0.2-4% by volume of oxygen, and an inert gas such as nitrogen or argon. The carbon fiber thus obtained can be further heat-treated to 2,000 to 3,000°C to form graphite fiber, if necessary. The reason why the proportions of hydrogen chloride and oxygen are limited as described above in the present invention is as follows. In a hydrogen chloride-oxygen-inert gas atmosphere,
If hydrogen chloride is less than 0.2% by volume and oxygen is less than 0.2% by volume, no effect on preventing "single thread breakage" is observed, and if hydrogen chloride exceeds 10% by volume and oxygen is 4% by volume, "single thread breakage" occurs. increases, and the strength also decreases. Therefore, in carbonization, heating may be performed in an atmosphere containing hydrogen chloride content of 0.2 to 10% by volume, oxygen content of 0.2 to 4% by volume, preferably 0.3 to 3% by volume, and an inert gas. desirable. According to conventional methods, the presence of hydrogen chloride is said to be effective in shortening carbonization time and improving strength, and the amount of hydrogen chloride in the atmosphere has been considered to be preferably 10% by volume or more. However, the presence of a large amount of hydrogen chloride poses a difficult problem in the treatment of exhaust gas, and as described in Japanese Patent Publication No. 53-19047, instead of suppressing the amount of hydrogen chloride to 0.3 to 30% by volume, water 0.5
The method of adding ~6% by volume also had problems in terms of corrosion of the heat treatment equipment. Furthermore, a major problem with carbon fibers obtained using conventional methods is that the single fibers that make up the fiber bundle break when they are wound onto a bobbin, taken out from the bobbin, aligned to be combined with plastic, etc., or woven. Problems such as ``single thread breakage'' and tangles were likely to occur. Carbon fiber obtained by conventional methods does not cause "single thread breakage" even when sizing
could not be prevented. According to the method of the present invention, the amount of hydrogen chloride can be kept low, making it extremely easy to treat the exhaust gas, and since no moisture is present, there are fewer problems of equipment corrosion. Furthermore, carbonization in an atmosphere using a combination of hydrogen chloride and oxygen has the effect of significantly reducing the occurrence of "single fiber breakage" in the resulting carbon fibers. Therefore, the high-strength carbon fiber obtained by the present invention can be used without sizing even under severe handling conditions.
Alternatively, it can be fully used without special sizing. The present invention will be specifically described below based on Examples and Comparative Examples. Examples 1 to 12 and Comparative Examples 1 to 13 Acrylonitrile content 95%, 9000 denier,
0.1g/6000 filament PAN fiber in air
After heating at 250° C. for 1 hour under d tension to make it flame resistant, it was heated to 1400° C. and carbonized at various hydrogen chloride and oxygen concentrations in the HCl-O ₂ -N ₂ atmosphere shown in Table 1. The time required for carbonization was 2 minutes. The properties of the obtained carbon fibers are shown in Table 1. The number of occurrences of "single thread breakage" is as shown in Figure 1.
The carbon fiber bundle 2 is pulled out from the center of the bobbin 1 and guided to the guide roll 3 located L = 50 cm away from the center of the bobbin 1.
A load of 500 g was applied using a weight 4, and then an air flow of 20 m/sec (at room temperature) was blown onto the center of the carbon fiber bundle 2 from a position of m = 10 cm using a blower 5 for 30 seconds. The number of occurrences was measured.

【table】

[Table] As shown in Table 1, carbon fibers heat-treated in hydrogen chloride concentration, oxygen concentration, and inert gas atmosphere within the range of the present invention are different from carbon fibers heat-treated under other conditions. In comparison, it has excellent tensile strength and bending strength, and has fewer "single thread breaks." As is clear from the above explanation, the carbon fiber obtained by the method of the present invention in which polyacrylonitrile fiber is made flame resistant in an oxidizing atmosphere and then heated in an HCl-O ₂ -inert gas atmosphere at a specific concentration is Compared to the conventional method, it has excellent strength and the number of occurrences of "single yarn breakage" is significantly lower, indicating that it is easier to handle.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a method for measuring "single yarn breakage." 1: bobbin, 2: carbon fiber bundle, 3: guide roll, 4: weight, 5: blower.

Claims (1)

[Claims] 1. Polyacrylonitrile fibers are heated in an oxidizing atmosphere to make them flame resistant, and then heated in an atmosphere containing 0.2 to 10% by volume of hydrogen chloride, 0.2 to 4% by volume of oxygen, and an inert gas. Carbon fiber manufacturing method.