KR0123936B1 - Manufacturing process of high intensity carbon fiber - Google Patents

Abstract

Acrylonitrile acid or a acrylate group copolymer monomer is added in the small portion to the acrylonitrile monomer. And this monomer is mixed with dimethylsulfoxide or dimethyl formamide solution, and is polymerized for hours at 50-60 degree C to obtain a copolymer, and as this copolymer is spun and drawn, it is possible to obtain the precursor type fiber. The molecule of the precursor fiber is 200,000-500,000, and its thickness is within 12-15 micron.

Description

Manufacturing method of high strength carbon fiber

The present invention relates to a high strength carbon fiber manufacturing method, and more particularly, to a high strength carbon fiber manufacturing method for improving the carbon fiber physical properties and workability by improving the surface treatment process when manufacturing the carbon fiber.

Despite its high price, carbon fiber has been increasing in demand every year due to its excellent mechanical properties.In terms of its use, carbon fiber is used in various fields such as sporting goods, aircraft structural materials, automobile parts, civil construction, and medical equipment. In addition, the field of use is also expanding. On the other hand, carbon fiber has been trying to improve the physical properties of the fiber itself in order to meet the continuous demands of the market, and can be said that the level has reached a considerable level. However, the problem of high manufacturing cost remains, and these problems must be solved for the generalization of carbon fiber and expansion of its use, and there is a passive method of improving productivity through mass production to lower the cost of manufacturing carbon fiber. Active methods include shortening the heat treatment time by modifying the precursor fibers or improving the polymerization, spinning and heat treatment processes themselves.

The manufacturing process of the carbon fiber can be largely divided into a precursor fiber manufacturing process and a heat treatment process for producing carbon fibers by carbonizing such precursor fibers. At this time, the precursor fiber manufacturing process includes a copolymer polymerization process of polyacrylonitrile, a spinning process of spinning the copolymer of polyacrylonitrile to form precursor fibers, and a post-treatment process such as coagulation, washing, and stretching after spinning. In addition, the heat-treatment process is a flame-resistant and flame-resistant flame retarded fiber is subjected to heat stabilization of the precursor fiber prepared by this method in an oxidizing atmosphere of 20-400 ℃ for 30-90 minutes and flame retardant process of 1200-1400 ℃ It can be divided into carbonization process which carbonizes for several minutes under high temperature and inert atmosphere.

In particular, the polymerization process is a process of forming a carbon fiber raw material, and not only influences the result of a later process, but also has a decisive influence on the establishment of each process condition. In addition, the flameproofing process in the carbon fiber manufacturing process greatly influences the physical properties of the carbon fiber when producing the carbon fiber from a given precursor fiber, and most of the structural changes and chemical reactions that can be formed during the heat treatment process are performed in this process. Since the process conditions during the flameproofing process can be a great influence on the control of physical properties of the final carbon fiber.

The flameproofing process is performed in an oxidizing atmosphere, and the precursor fiber includes an exothermic reaction in which an oxidation reaction and a cyclization reaction are simultaneously performed. Such a process can shorten the reaction time by increasing the reaction rate through treatment at a high temperature. . However, when the processing speed is high, the heat of reaction in the precursor fiber bundles accumulates and the rapid progress of the reaction causes problems of cutting and firing the precursor fiber bundles. Therefore, in the case of flameproofing the precursor fiber bundle, a method of flameproofing at a low temperature for a long time has been used in order to avoid the rapid progress of the reaction, which in turn increases the manufacturing cost of the carbon fiber. To drastically reduce the manufacturing costs incurred, a more scientific approach can be found in improving process conditions that can efficiently remove or control the heat of flame-retardant reaction.

The process of commercializing the carbon fiber of the required physical properties produced in this way can be referred to as a post-treatment process. The surface treatment process is a process for forming an excellent appearance to be well-filled to the consumer and improving the workability of the primary consumer. And sizing process. The surface treatment process improves the impregnation of the resin during the sizing process by introducing a functional group having good control of the roughness of the surface and introducing a reactive group through an electrolytic treatment in an oxidizing gas atmosphere, an oxidizing liquid atmosphere, or an electrolyte containing an electrolyte solution. It is a process of planning. In addition, the sizing process covers the surface treated carbon fiber with the same resin as the matrix resin to be used for the production of prepreg or composite material, thereby providing a good level of workability when working with carbon fiber. ) It is a step of expressing the effects of improvement and appearance improvement. Surface treatment of the post-treatment process is an important process that affects the properties of the final carbon fiber according to the method. Conventionally, as shown in Japanese Patent Application Laid-Open No. 62-149973, carbon fiber is electrolyzed while supplying an oxidizing gas containing nitrogen dioxide gas as an essential component in an aqueous solution of an acid or its salt, followed by deactivation. There is a method characterized by. However, this method has a disadvantage that damage to the surface of the carbon fiber due to excessive treatment may affect the appearance by causing the physical properties of the final carbon fiber or the occurrence of the wool. Further, Japanese Patent Laid-Open No. 62-149970 is characterized by strong electrolytic treatment of carbon fiber as an anode, followed by heat treatment in an inert atmosphere of at least 400 ° C while giving ultrasonic vibration in an aqueous solution of an acid or a salt thereof. This method also causes excessive damage to the surface of the carbon fiber by applying ultrasonic vibrations in an aqueous solution of an acid or its salts, thereby damaging the surface of the carbon fiber. do.

In the present invention, by improving the surface treatment during the post-treatment process to optimize the ROUGHNESS degree of the carbon fiber surface and at the same time minimize the damage of the carbon fiber surface to minimize the physical properties of the final carbon fiber workability when working with oil Its purpose is to improve.

The present invention is electrolytically treated in an aqueous solution of an inorganic acid, an organic acid or a salt thereof by the method of improving the surface treatment, and at least two or more stages (preferably 2-7 stages) of the corresponding carbon fibers during the fluorination treatment of the obtained carbon fiber surface. When heated in an inertized atmosphere divided by the above, the inertized atmosphere is characterized in that the temperature of each stage is higher than the temperature of the preceding stage by an inert gas containing nitrogen or argon.

Hereinafter, the present invention will be described in detail.

Precursor fibers used in the present invention are copolymerized for several hours at a temperature of 50-60 ° C. in a dimethyl sulfoxide or dimethylformamide solution by adding a small amount of an acid or acrylate-based copolymerization monomer to an acrylonitrile monomer. After the coalescence is obtained, it is obtained by spinning and stretching in a suitable manner. At this time, the copolymerizable monomer may be itaconic acid, acrylic acid, methacrylic acid or methyl acrylate, and the like. The precursor fiber obtained in this way has a molecular weight of 200,000-500,000, and the thickness of the precursor fiber falls within a range of 12-15 μm. It is preferable. In this case, when the molecular weight of the precursor fiber is less than 200,000, the strength of the fiber is insufficient, and when larger than 500,000, there is a problem that workability worsens in the spinning and stretching process. Moreover, when the thickness of precursor fiber is less than 12 micrometers and exceeds 15 micrometers, the carbon fiber suitable for the objective of this invention is hard to be obtained.

Ordinary precursor fibers exhibit shrinkage behavior in the longitudinal direction with respect to heat, which exhibits a primary shrinkage behavior above the glass transition temperature and a secondary shrinkage behavior at temperatures above 200 ° C. At this time, the primary contraction behavior appearing above the glass transition temperature is caused by physical contraction due to the recovery of the degree of freedom of the molecular chain, and the secondary contraction behavior appearing at temperatures higher than 200 ° C is caused by heat in the precursor fiber itself. Since the primary contraction and the secondary contraction differ in the size of the contraction and the force to contract, the tension condition applied to the precursor fiber passing through the flameproofing device during heat treatment is preferably at least two stages (preferably two-stage to seven-stage). ), It is necessary to optimize the tension conditions during the flameproofing process.

In the present invention, the carbon fiber that has undergone the above-described flameproofing and carbonization process is subjected to surface treatment and inactivation treatment using an electrolytic treatment method as one of post-treatment processes. Examples of the electrolytic solution used in the electrolytic treatment include inorganic acids, organic acids, or these. An aqueous solution of salt is used and the inactivation treatment is divided into 2-7 stages and is made by passing through an inactivation atmosphere in the temperature range of 200-500 ° C., wherein the temperature of each stage is configured to be higher than the temperature of the front stage. It is done. In this case, when the inactivation treatment is not given a temperature gradient (stage 1), the treatment effect is insufficient, and when it exceeds 7 stages, the treatment process is difficult and the workability is inferior. In addition, when the temperature of the inactivating atmosphere is less than 200 ° C., the treatment effect is also insufficient, and when the temperature exceeds 500 ° C., the physical properties of the carbon fibers may be deteriorated.

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

Tensile strength of the carbon fiber produced by the Examples and Comparative Examples was evaluated by the method of ASTM D3379 or JIS R7601.

Example 1

1% by weight of its copolymerized monomer was added to the acrylonitrile monomer and copolymerized at 50-60 ° C. for 5 hours in a dimethyl sulfoxide or dimethylformamide solution to obtain a copolymer, which was then spun by dry and wet spinning. Multistage stretching was carried out to obtain a final precursor fiber. The copolymer monomer used at this time is suitable for itaconic acid, acrylic acid and methacrylic acid, methyl acrylate, methyl methacrylate, etc. The molecular weight of the precursor fiber obtained in this way is 300,000, the thickness of the precursor fiber is 15μ, in boiling water Stretching was performed at 400% and 300% under pressurized water vapor to make the total draw ratio 12 times. When the precursor fiber prepared in this way was flameproofed at 250 ° C. for 40 minutes in an oxidizing atmosphere using a flameproofing device, three steps of tension conditions were set and flameproofing was performed under independent tension conditions. The range of was in the range of 200g or more and 500g or less with respect to the weight per unit length (mg / cm).

After the salt-tolerant treatment was carried out in this manner, carbonization treatment and surface treatment were carried out at 1200 DEG C for several minutes under an inert atmosphere using nitrogen and argon to finally obtain carbon fibers. In the surface treatment process, electrolytic treatment is carried out in an aqueous solution of an inorganic acid, an organic acid or a salt thereof, and the surface of the carbon fiber thus obtained is inactivated. In the inactivation treatment, the corresponding carbon fiber passes through three stages. The temperature of each stage was higher than the temperature of the front stage (200 ℃ / 300 ℃ / 400 ℃) and the residence time was 3 minutes overall. It was also heated in an inert atmosphere, where the inert atmosphere was maintained in a nitrogen atmosphere.

Physical properties of the carbon fiber prepared by the above method and the method of Comparative Examples 1,2 and 3 below are shown in Table 1.

Comparative Example 1

The surface treatment was carried out in the same manner as in Example 1 except that the inert atmosphere was set to one stage and the heating temperature was set to 400 ° C.

Comparative Example 2

The surface treatment was carried out in the same manner as in Example 1 except that the inert atmosphere was set to two stages and the temperature of the front and rear ends was the same (400 ° C./400° C.).

Comparative Example 3

The surface treatment was carried out in the same manner as in Example 1 except that the inert atmosphere was three stages and the temperature of each stage was the same (400 ° C./400° C./400° C.).

TABLE 1

Claims (1)

When producing high-strength carbon fiber through the flame resistance and carbonization process and post-treatment process of precursor fiber having a molecular weight of 200,000-500,000, carbon fiber is electrolyzed in aqueous solution of inorganic acid, organic acid or these salts by post-treatment process. A method of producing a high strength carbon fiber, characterized in that it is subjected to a surface treatment step of performing an inactivation treatment in an inactivation atmosphere that is divided into stages and the temperature of each stage is in the range of 200-500 ° C. and configured to be higher than the temperature of the front stage.