JPH0323650B2 - - Google Patents

Description

[Detailed description of the invention]

[Technical Field] The present invention relates to a method for producing carbon fibers having high strength and high elasticity. [Background Art] In recent years, carbon fiber composite materials have been widely applied to sports, aerospace, industrial applications, etc., and their quantitative expansion is remarkable. In response to this situation, the performance of the carbon fibers used is also improving dramatically. If we focus on the modulus of elasticity, 10 years ago it was around 20ton/ ^mm2 , but a few years ago it became standard at 23-24ton/ ^mm2 , and more recently, the trend has been around 30ton/ ^mm2 . It has been pointed out that this may become mainstream in the future. However, if such an improvement in the elastic modulus is achieved while the strength of the carbon fiber remains constant, this will naturally lead to a decrease in the elongation of the carbon fiber, and the carbon fiber composite material This makes the composite material brittle and reduces the reliability of the composite material. Therefore, there is a strong need for carbon fibers that have high elasticity and high elongation, or in other words, carbon fibers that have both high elongation and high strength. The conventional method of improving the elastic modulus has been to increase the carbonization temperature, that is, the final heat treatment temperature. However, this method has the drawback that as the modulus of elasticity increases, the strength decreases, and therefore the elongation of the carbon fibers decreases. FIG. 1 is a correlation diagram showing the relationship between the carbonization temperature and the physical properties of the obtained carbon fiber to explain this situation. According to Figure 1, as the carbonization temperature increases, the elastic modulus increases as shown by curve A, but the strength and density of carbon fibers increase.
It decreases like B and C. For example, in order to maintain an elastic modulus of 28 ton/mm ³ , the carbonization temperature must be approximately 1800°C, but at this temperature the strength decreases by more than 100 kg/mm ³ compared to 1300°C.
High intensities are simply not achievable. This decrease in strength as the carbonization temperature rises corresponds well to the decrease in density, and is due to the generation of microscopic pores in the fibers that cause a decrease in strength during the process of increasing the carbonization temperature. It is estimated to be. [Purpose of the Invention] It is difficult to obtain carbon fibers that satisfy both high elasticity and high strength using the conventional technology of increasing the carbonization temperature to obtain high elastic fibers. It is necessary to establish a suitable firing technology. As a result of intensive studies toward this goal, the present inventors discovered a new firing method and completed the present invention. [Structure of the Invention] The gist of the present invention is to use acrylic fibers with a single fiber denier of 0.1 to 1.1 denier, and to increase the fiber density by 3% or more until the fiber density rises to 1.22 g/cm ³ .
Furthermore, after 1.22 g/ ^cm3 , an elongation of 1% or more is added to complete the flame-retardant treatment, then an elongation of 3% or more is added at a temperature of 300 to 800°C in an inert atmosphere, and a further elongation of 1300 to Processed under tension at a temperature of 1600℃, the fiber diameter is 1 to 6μ, the strand strength is 460Kg/mm2 ^or more, and the strand elastic modulus is
The object of the present invention is to provide a method for producing carbon fiber having a strand elongation of 28 t/mm ² or more, a strand elongation of 1.60% or more, and a density of 1.76 g/cm ³ or more. The present invention will be explained in more detail below. The acrylic fiber in the present invention is a fiber obtained from a homopolymer or copolymer containing 85 wt% or more of acrylonitrile (AN). Copolymerizable components refer to all monomers that can be copolymerized with AN, and representative examples include:
These include vinyl esters, acrylic esters, methacrylic esters, acrylic acids, methacrylic acids, and itaconic acids. As a method for obtaining such a homopolymer or a copolymer, homogeneous solution polymerization, redox polymerization in an aqueous solution, suspension polymerization or emulsion polymerization in a heterogeneous system, etc. can be used. It is essential that the acrylic fiber in the present invention has a fineness of 1.1 denier or less, preferably 1.0 denier or less. The present inventors have discovered that carbon fibers having the characteristics of the present invention can be obtained for the first time by using acrylic fibers having such fineness. It is known to obtain carbon fibers by firing fine acrylic fibers, for example, as disclosed in Japanese Patent Application Laid-open No. 49-94924 and Japanese Patent Application Laid-open No. 57-42934. However, in such known documents, there is no description that suggests the carbon fiber having the characteristics of the present invention and its manufacturing method. This shows that even if acrylic fibers with such a fine denier are used, carbon fibers having the characteristics of the present invention cannot be obtained if the firing conditions are inappropriate. This proves that this can only be achieved by combining acrylic fibers and the firing conditions of the present invention. The fine-grained acrylic fiber in the present invention is produced by using a conventional acrylic fiber spinning method such as wet spinning or dry spinning. For example, in normal wet spinning, after spinning, stretching, washing with water, and drying and densification, secondary stretching such as dry heat stretching or steam stretching is performed as necessary. Further, it is preferable that the acrylic fiber does not contain impurities, internal voids, and surface defects such as crazes and cracks. The acrylic fiber thus obtained is subjected to flameproofing, primary carbonization, and secondary carbonization treatments according to the firing method of the present invention. The flameproofing treatment is usually carried out in an oxygen-nitrogen mixed atmosphere such as air, or nitrogen monoxide or sulfur dioxide gas may be used. The temperature during flameproofing treatment is 200~
A range of 350°C is appropriate. In the flame-retardant treatment of the present invention, the fibers are elongated by 3% or more, preferably 10% or more, until the fiber density reaches 1.22 g/cm ³ in the flame-retardant treatment process, and then further elongated to 1.22 g/cm ^{3 .} In the subsequent density range, it is necessary to add elongation of 1% or more to complete the flame resistance treatment. By applying such elongation during the flameproofing process, flameproofing is completed without causing any disturbance to the fine structure of the fibers, making it possible to obtain the carbon fiber of the present invention. Such elongation behavior can be imparted to the fibers by, for example, bringing the fibers into contact with a number of rotating rolls and setting the speed of the rotating rolls to provide a predetermined elongation profile. The flame-resistant fibers are then heated at 300-800℃ in an inert atmosphere such as nitrogen gas or argon gas.
In the temperature range of 3% or more, preferably 5% or more, elongation is further applied during the primary carbonization treatment. In this process, the elongation rate is 3%
If it is less than that, it will be difficult to obtain a predetermined elastic modulus and strength. Furthermore, no treatment effect can be found when the temperature is below 300°C or above 800°C.
The process usually takes from several tens of seconds to several minutes. Following the first carbonization treatment, the second carbonization treatment, that is, the final heat treatment, is performed at 1300 to 1600 in an inert atmosphere.
It is preferably carried out under tension at a temperature range of 1,300 to 1,500 degrees Celsius for several tens of seconds to several minutes. In this heat treatment,
If the maximum temperature during the treatment process is less than 1300°C, it is not possible to obtain a predetermined elastic modulus. on the other hand,
When the maximum temperature exceeds 1600°C, the strength and density decrease and become below a predetermined value. In addition, the temperature profile during heat treatment is
It is preferable to set the temperature so that the temperature rises gradually from around 1000°C to reach the maximum temperature. Also,
The tension applied to the fiber during heat treatment is 250
It needs to be at least mg/denier, preferably at least 350 mg/denier. If the tension is lower than this value, it will be difficult to obtain a predetermined elastic modulus. By employing the method described above, the present invention has a fiber diameter of 1 to 6 μm and a strand strength of 460 μm.
Kg/mm ² or more, preferably 500 Kg/mm ² or more, strand elastic modulus 28t/mm ² or more, strand elongation 1.60
% or more, preferably 1.7% or more, preferably 1.8%
or more, the density is 1.76 g/cm ³ or more, preferably 1.78
Carbon fibers of g/cm ³ or more can be easily produced. Hereinafter, the present invention will be specifically explained with reference to Examples. Strand strength and strand elastic modulus are
Measured according to the method of JISR7601. Density was measured by density gradient tube method. Strand elongation is expressed as strand strength/strand elastic modulus x 100 (%). The diameter of the carbon fibers was measured by a laser method.
The degree of orientation of the acrylic fibers is determined from the half-width H1/2 (deg) of the scattering intensity distribution in the azimuthal direction in reflection at 2θ=17° (using Cu-kα radiation) using the following equation. =180−H1/2/180×100(%) Example 1 Acrylonitrile 98wt%, methyl acrylate
A polymer with a specific viscosity [ηsp] = 0.20 having a composition of 1 wt% and 1 wt% methacrylic acid was wet-spun using dimethylformamide as a solvent, and then spun on a hot water bath for 5 minutes.
Stretch it twice, wash it with water, dry it, and heat it to 1.3
An acrylic fiber with a filament count of 9000 and a fineness of 0.8 denier was obtained by stretching it twice. The degree of fiber orientation determined by X-ray diffraction was 90.3%.
When this acrylic fiber was subjected to flame-retardant treatment by passing through a hot air circulation type flame-retardant furnace with a three-step temperature profile of 220°C - 240°C - 260°C for 60 minutes, the density of the fiber was 1.22 g/cm ³ 20% to reach
, and then further elongation of 3% until reaching 1.25 g/cm ³ to complete the flame-retardant treatment. The flame-retardant fibers were then heated to 600°C in a pure _N2 stream.
A 10% elongation was applied during passing through the carbonization furnace for 3 minutes, and heat treatment was performed under a tension of 400 mg/denier in a second carbonization furnace having the maximum temperature shown in Table 1 in the same atmosphere. Carbon fibers with physical properties were obtained.

[Table] Example 2 Firing was carried out in the same manner as in Example 1, except that the elongation rate during the flameproofing treatment and the temperature and elongation rate in the first carbonization furnace were changed. The temperature of the first carbonization furnace is 550℃, the maximum temperature of the second carbonization furnace is 1450℃,
The tension was 380 mg/denier. Table 2 shows the physical properties of the obtained carbon fiber.

[Table] The flame resistant elongation rate () is determined by the fiber density.
The elongation rate is up to 1.22g/ ^cm3 , and the same ()
is the elongation rate in the range of fiber density from 1.22 to 1.25 g/cm ³ . Example 3 Acrylic fibers having the fibers shown in Table 3 were obtained in the same manner as in Example 1, except that the discharge amount of the stock solution and the stretching ratio were changed. These acrylic fibers were fired under the same conditions as in Example 1. At this time, the maximum temperature during the final heat treatment was 1450°C, and the tension was 400 mg/denier. Table 3 shows the physical properties of the obtained carbon fiber.

[Table] Example 4 In Example 1, firing was performed by changing the temperature of the first carbonization furnace, and the results shown in Table 4 were obtained.

〔Effect of the invention〕

The carbon fiber obtained by the present invention has high elasticity and high strength, so it has a wide range of applications such as primary structural materials for aircraft, sports applications such as fishing rods and golf shafts, industrial applications such as high-speed centrifuges and robots, and high-speed ground transportation vehicles. It is possible to use it for

[Brief explanation of drawings]

FIG. 1 is a correlation diagram showing the relationship with the physical properties of carbon fibers obtained at carbonization temperatures according to the conventional method. A...Modulus, B...Strength, C...Density.

Claims (1)

[Claims] 1 Using acrylic fibers with a single fiber denier of 0.1 to 1.1 denier, flame resistance is achieved by elongating 3% or more until the fiber density rises to 1.22 g/cm ³ and then elongating 1% or more after 1.22 g/cm ³ complete the conversion process,
Then, elongation of 3% or more is applied at a temperature of 300 to 800°C in an inert atmosphere, and further elongation of 1300 to 800°C in an inert atmosphere.
Treated under tension at a temperature of 1600℃, the fiber diameter is 1 to 6μ, the strand strength is 460Kg/ ^mm2 or more, the strand elastic modulus is 28t/mm2 ^or more, the strand elongation is 1.60% or more, and the density is 1.76. A method for producing high-strength and high-elasticity carbon fibers, characterized by producing carbon fibers with a weight of g/cm ³ or more.