JPH0114340B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a method for producing high-performance carbon fibers using acrylic fibers having high strength and excellent adhesiveness to resin as a precursor. (Prior Art) Carbon fibers have excellent strength, elastic modulus, etc., and are therefore used as reinforcing fibers in various composite materials for aerospace applications, industrial materials, sporting goods, and the like. However, when carbon fibers are used as these composite materials, in addition to the strength and elastic modulus of the carbon fibers themselves, adhesion with matrix materials such as resins is important. Materials are obtained. Therefore, commercially available carbon fibers are usually surface-treated in some way. On the other hand, as a method for producing carbon fibers with further improved strength, many improvements in the precursor production process and in the carbonization process have been proposed. Among the improvements in the carbonization process, a method of carrying out carbonization in a special atmosphere has been proposed (Japanese Patent Publication No. 47-7686, Japanese Patent Publication No. 47-29935, Japanese Unexamined Patent Application Publication No. 1987-59).
−168129). In particular, in JP-A-59-168129, flame-retardant acrylic fibers are made with hydrogen chloride of 0.2~
It is described that carbon fibers having high strength can be obtained by heating in an atmosphere containing 10% by volume, 0.2 to 4% by volume of oxygen, and an inert gas.
According to this publication, carbon fibers obtained by heating in the above atmosphere include those heated in an atmosphere (not containing oxygen) consisting of hydrogen chloride and an inert gas, and those heated in an atmosphere consisting of hydrogen chloride and an inert gas (not containing oxygen), and carbon fibers obtained by heating in the above atmosphere. It is said that it has superior tensile strength and bending strength, and is less likely to break single filaments during the manufacturing process, compared to those heated in an atmosphere consisting of oxygen. However, when carbon fibers obtained by heat treatment in the atmosphere described in the above-mentioned publication are used as a composite material, the adhesion with the matrix resin is poor, and the interlaminar shear strength and fatigue resistance of the composite material are poor. On the other hand, Japanese Patent Publication No. 48-42812 discloses that by anodizing carbon fibers in an aqueous solution of an inorganic acid and/or an organic acid, carbon fibers with increased surface area are obtained, and as a result, carbon fibers with increased shear and bending forces are obtained. It is stated that an excellent composite material can be obtained. However, the interlaminar shear strength and fatigue resistance of the resulting composite material are not fully satisfactory. [Problems to be Solved by the Invention] As a result of extensive research into a method for producing high-performance carbon fibers that have high strength and excellent adhesion to resin, the present inventors found that the raw material carbon obtained in the carbonization process After finding out that there is a close relationship between fibers and the surface treatment process, and as a result of further investigation, we unexpectedly found that the above-mentioned Japanese Patent Application Laid-Open No. 59-168129 found that it was not desirable for obtaining high-strength carbon fibers. has been done. Carbon fibers obtained by heat-treating hydrogen chloride in an inert gas atmosphere (no oxygen) are electrolytically treated under specific conditions to achieve high strength, interlaminar shear strength, and fatigue resistance. It has been discovered that carbon fiber can be obtained that can provide a composite material with excellent properties. (Means for Solving the Problems) The present invention, when producing carbon fibers having high strength and excellent adhesion to resin using acrylic fibers as a precursor, the acrylic fibers are subjected to flame-retardant treatment and then chlorinated. Carbonization at 600-1600°C in an inert gas atmosphere containing at least 1% by volume of hydrogen and substantially oxygen-free, followed by a current of 10mA-3A at 0.1-1600°C in an alkali metal- and chlorine-free electrolyte. This is a method for producing high-performance carbon fiber, which is characterized by applying electrolytic treatment for 10 minutes and using the carbon fiber as an anode. The acrylic fiber in the present invention refers to polyacrylonitrile or other monomers that can be copolymerized with at least 90% by weight of acrylonitrile, such as acrylic esters such as methyl acrylate, acrylic acid, methacrylic acid, and itaconic acid. It refers to fibers made of copolymers with carboxylic acids such as acrylamide, allylsulfonic acid, etc. These fibers are long fibers obtained by a wet spinning method, a dry spinning method, a dry-wet spinning method, etc., and the manufacturing method thereof is not particularly limited, and conventionally known methods can be used. Conventionally known methods can be used for flame-proofing the acrylic fibers.
Generally, the heat treatment is carried out in air in several stages from a low temperature side to a gradually high temperature side within the range of 200°C to 350°C. In the present invention, the carbonization step is carried out at temperatures ranging from 600℃ to 1600℃.
C. in an inert gas atmosphere containing at least 1% by volume of hydrogen chloride and substantially free of oxygen. Even if hydrogen chloride gas is supplied in a temperature range below 600°C, no substantial improvement in strength is observed, and in a temperature range between 600°C and 1600°C, strength improvement is obtained when the hydrogen chloride content is less than 1% by volume. Carbon fiber does not show any strength improvement effect. Furthermore, the upper limit of the hydrogen chloride content is approximately 20%, and even if it is contained in excess of this, it is difficult to obtain a commensurate effect, and a large amount of cost is required to treat the used exhaust gas, which is industrially disadvantageous. . Even if a small amount of oxygen gas is mixed into the atmospheric gas during carbonization, there is no problem as long as it is about 0.1% by volume or less. This approximately corresponds to the amount of oxygen brought into the carbonization furnace by the supply thread and the amount of oxygen slightly mixed in from the sealing part of the carbonization device in the case of industrial implementation. The high-strength carbon fibers obtained as described above have poor adhesion to resin as indicated by interlaminar shear strength. Therefore, in the present invention, electrolytic treatment is performed using carbon fiber as an anode in an electrolyte that does not contain alkali metals and chlorine. If an electrolyte containing an alkali metal or chlorine is used, the adhesion to the resin will be insufficient and will be highly variable. Although the reason for this is not clear, it is presumed that hydrogen chloride or chlorine adhering to the carbon fiber surface during the carbonization process has some adverse effect. Electrolytes used in the present invention include strong acids, weak acids, ammonium salts thereof, and the like. For example, sulfuric acid, nitric acid, phosphoric acid, ammonium sulfate,
Ammonium nitrate, ammonium carbonate, and mixtures thereof are useful, with nitric acid being most preferred. The concentration of these electrolytes is usually about 0.1% to 10%. The temperature of the electrolyte is generally below 70°C. Electrolysis time is about 0.1 to 10 minutes.
The electrolysis conditions are generally about 10 mA to 3 A and an electrolytic voltage of 0.5 to 20 volts, preferably a current of 50 mA to 1 A and an electrolytic voltage of 1 to 5 volts. Electrolytic conditions lower than these ranges will result in poor adhesion to the resin. On the other hand, if the electrolytic time and current are excessive, the surface treatment by electrolysis will be excessive, resulting in a significant decrease in the strength of the carbon fiber, and The adhesion with the material also begins to deteriorate. (Effect of the invention) Carbonized under specific carbonization conditions as described above,
Further, the carbon fiber obtained by processing under specific surface treatment (electrolytic treatment) conditions is a well-balanced high-performance carbon fiber that has high strength and excellent adhesiveness to resin. (Example) The method of the present invention will be specifically explained below with reference to Examples. Example 1 A polymer containing 97% by weight of acrylonitrile was wet-spun using nitric acid as a solvent according to a conventional method to obtain long fibers with a single fiber fineness of 1.3 denier and 12,000 filaments. This precursor was heat-treated in air at 240°C for 30 minutes and then in air at 260°C for 40 minutes to obtain a flame-resistant yarn. Using this flame-resistant yarn, carbon fibers were obtained under various carbonization and surface treatment conditions as shown in Table 1. Note that the electrolysis time was 1 minute. The strength of these carbon fiber strands was measured in accordance with the resin-impregnated strand test method specified in JISR7601. The same Explanation Example 2 was used for the resin formulation. The interlaminar shear strength was measured by the following method. First, carbon fibers were impregnated in a methyl ethyl ketone solution containing 100 parts by weight of tetraglycidyl diaminodiphenylmethane, 35 parts by weight of diaminodiphenyl sulfone, and 1.5 parts by weight of borosomonomethylamine trifluoride to create a unidirectional prepreg. . This prepreg is heated to 130℃.
x 60 minutes, then heated and cured at 180°C x 120 minutes to create a flat composite material. Next, the interlaminar shear strength was measured using an Instron and a three-point bending short beam method under the condition of L/D=4.

[Table] As is clear from Table 1, the carbon fibers obtained by the method of the present invention have high strength and excellent adhesion to resin. If anodization is carried out in a non-containing atmosphere, or if anodic oxidation is carried out using an alkali metal and/or hydrochloric acid as an electrolyte, only a product with poor strength and/or adhesion to the resin will be obtained. Example 2 Using the same polymer as in Example 1, a long fiber of 6000 filaments with a single yarn fineness of 0.8 denier was obtained, and a flame-resistant yarn was obtained under the conditions of Example 1. This flame-resistant yarn was carbonized at 500℃ for 2 minutes in nitrogen gas, then carbonized at 1300℃ in nitrogen gas containing 7% by volume of hydrogen chloride gas, and then carbonized for 5 minutes.
% nitric acid as an electrolyte and a current of 120 mA was applied for 1 minute to carry out anodic oxidation. The strength of the obtained carbon fiber is
The interlaminar shear strength was 520Kg/mm ² and 14.1Kg/mm ² . Comparative Example 1 Example 1 except that the flame-resistant yarn of Example 1 was used and the carbonizing gas atmosphere was hydrogen chloride/oxygen/nitrogen.
Carbonization and electrolytic treatment were performed under the same conditions as in Experiment No. 2, and the strand strength and interlaminar shear strength were measured. The results are shown in Table-2. Furthermore, in order to clarify the differences in adhesion between these fibers, fatigue tests were conducted on the composite material. A unidirectional prepreg was made from these fibers using the same resin as in Example 1, and the angle of 67.5 degrees and -
Example 1: 10 sheets were laminated alternately in the direction of 67.5 degrees.
It was heated and cured under the same conditions as above to form a flat plate-like laminate. This was cut to a predetermined size to make a test piece, and a constant load four-point bending fatigue test was conducted. An SN (stress-fatigue frequency) curve was obtained from the results of eight tests with varying loads, and from this the fatigue frequency at a stress of 5.5 Kg/mm ² was determined to evaluate fatigue resistance. The results are shown in Table-2.

[Table] As is clear from Table 2, the fibers of the present invention exhibit excellent adhesion and fatigue resistance, whereas those containing oxygen as a carbonizing gas atmosphere both themselves and after surface treatment. It has poor adhesion to fibers and low fatigue resistance. Comparative Example 2 Example 1 except that the surface treatment time was 30 minutes.
Carbon fibers were obtained in the same manner as in Experiment No. 2. The strength and interlaminar shear strength of this carbon fiber are
371Kg/mm ² and 10.4Kg/mm ² , and Example 1-
Compared to Experiment No. 2, this value was extremely low. Comparative Example 3 A composite material fatigue test was conducted on the carbon fiber of Example 1-Experiment No. 11 by the method described in Comparative Example 2, and the fatigue resistance (number of fatigue cycles) was 39,000 times.

Claims (1)

[Claims] 1. When producing carbon fibers with high strength and excellent adhesion to resin using acrylic fibers as a precursor, the acrylic fibers are flame-retardantly treated and then treated to contain at least 1% by volume of hydrogen chloride and substantially oxygen. Carbonized at 600-1600℃ in an inert gas atmosphere free of
Subsequently, a method for producing high-performance carbon fibers is characterized in that the carbon fibers are electrolytically treated by applying a current of 10 mA to 3 A for 0.1 minutes to 10 minutes in an electrolyte that does not contain alkali metals and chlorine, using the carbon fibers as anodes.