JPS6254889B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing acrylic carbon fiber,
More specifically, the present invention relates to a method for producing high-quality carbon fibers with high physical properties and shortened firing time, particularly flame resistance. Conventionally, acrylic carbon fiber, which has excellent specific strength and specific modulus, has been widely used as a variety of composite materials that use the fiber as a reinforcing material, such as aviation and space materials, and sports materials such as fishing rods, tennis rackets, and golf shafts. Furthermore, it is being used as a material for automobiles, ships, etc. The manufacturing method for this carbon fiber is generally to use acrylic fiber as a precursor fiber (precursor),
After being heated in an oxidizing atmosphere such as air at a temperature of ~400°C to convert it into oxidized or flame-resistant fiber, it is heated in an inert gas atmosphere such as nitrogen, argon, helium, etc. at a temperature of at least 1000°C to carbonize or convert it into graphite. methods have been adopted. However, in the above carbon fiber manufacturing method, in the oxidation step in which the precursor is heated in an oxidizing atmosphere, harmful decomposition gas, tar, or pitch-like substances are generated as a result of the oxidation reaction of the precursor.
This contaminates the precursor and deteriorates the physical properties of the carbon fiber resulting in fusion between single fibers due to this contamination or contamination, and partial heat accumulation due to the heat generated by the chemical reaction of the precursor in the oxidation process. It is said that this has a considerable adverse effect on the physical properties of carbon fiber. In addition, the oxidation process of the precursor requires a long heating time of several hours, which is a big disadvantage in improving productivity in carbon fiber production. It is said that shortening the time is a major problem in carbon fiber production (Japanese Patent Laid-Open No. 57-21521). As a method for shortening the oxidation time in the production of such acrylic carbon fibers, Japanese Patent Publication No. 53-22576 describes a method for preheating acrylic fibers in an oxidizing atmosphere and then maintaining the oxygen content at 300 to 500°C. but
It is disclosed that by heating for 0.3 minutes or more in an inert atmosphere of 10% or less, carbonizable fibers can be obtained in a short time required for carbonization and with relatively no decrease in carbonization yield. However, according to the studies of the present inventors, although the above method is certainly effective in shortening the carbonization time and improving the carbonization yield, it requires a long time for preliminary heat treatment in an oxidizing atmosphere, making it difficult for industrial use. It was found that this method was insufficient as a method for producing carbon fibers, and after extensive research, the present invention was developed. That is, an object of the present invention is to shorten the heating time in an oxidizing atmosphere, which has the greatest influence on the quality and performance of carbon fibers, in the production of acrylic carbon fibers. Other purposes are
The object of the present invention is to provide a method in which the mechanical properties of carbon fibers obtained by shortening the oxidation time are not impaired. The precursor acrylic fiber yarn used in the present invention has a tensile strength of at least 6 g/d, preferably 6.3 to 7.8 g/d, and an initial tensile modulus of 100 g/d.
The above is preferably within the range of 120 to 150 g/d, and the purpose is to achieve the mechanical properties of carbon fiber that can only be obtained by using acrylic fibers having such mechanical properties. This makes it possible to maintain high standards. The characteristics that the acrylic fiber yarn should have are 250
It is important that the amount of tar produced at °C is 5% by weight or less based on the weight of the yarn. In other words, when the amount of tar generated in the acrylic fiber yarn exceeds 5%, the strength of the yarn decreases significantly or fuzz occurs in the oxidation process described below, making it difficult to produce carbon fiber with excellent quality performance. be. Here, the amount of tar produced at 250°C is calculated by calculating the weight loss of the acrylic fiber yarn when heating the precursor fiber (precursor) in an oxidizing atmosphere at 250°C for 5 minutes. It is a value expressed in weight % based on weight. Further, as a method for manufacturing the acrylic fiber yarn used in the present invention, the following yarn spinning process and its conditions are employed. That is, it consists of 98% by weight of acrylonitrile (AN), the AN and 2% by weight or less of itaconic acid.
The AN-based copolymer solution is wet-spun or dry-wet-spun, coagulated, washed with water, stretched (or washed with water after stretching), applied with an oil agent, dried and densified, and then subjected to secondary stretching in pressurized steam, resulting in a total stretching ratio of 11. Create ~16x drawn yarn. The thus obtained acrylic fiber yarn is brought into contact with a heating roll having a surface temperature of 150 to 240° C. for 2 seconds to 3 minutes to undergo heat treatment. The thus obtained acrylic fiber yarn having a strength of at least 6 g/d and an initial tensile modulus of 100 g/d or more is first heated above the runaway reaction initiation temperature (T _f ) in an oxidizing atmosphere of about 200 to 300°C. It is also oxidized in an oxidizing atmosphere kept at a low temperature of 10 to 30 degrees Celsius, and then oxidized at a temperature higher than the oxidizing atmosphere temperature and 300 degrees Celsius.
It is heated in an inert atmosphere within a temperature range of ~380°C to convert it into carbonizable fibers, ie so-called flame-resistant yarns. In this case, in the present invention, the oxidizing gas atmosphere temperature is within the above temperature range and is lower than the runaway reaction initiation temperature (T _f ) of the acrylic fiber yarn.
It is important to keep the temperature at a low temperature of 10 to 30 degrees Celsius,
By setting the ambient temperature in this manner, it is possible to significantly shorten the time required to heat the yarn in the oxidizing gas atmosphere and inert atmosphere and convert it into carbonizable fibers (flame resistance time). Become. In particular, the heating time in the oxidizing atmosphere can be kept within the range of 10 to 30 minutes, and in connection with the aforementioned fact that the amount of tar produced in the acrylic fiber yarn is 5% or less, the oxidizing It is possible to significantly suppress the deterioration of physical properties caused by decomposed gases, tar-like substances, etc. of the yarn in a hostile atmosphere. Here, the runaway reaction initiation temperature (T _f ) of the yarn is a value determined by the following measurement method. A needle-shaped thermocouple is inserted into an acrylic fiber thread having a length of about 30 mm, whose denier has been measured in advance, and the thread is held between the needles and suspended in an oxidizing atmosphere furnace. While blowing hot air at a speed of about 2 m/sec perpendicular to the fiber axis direction of the suspended yarn, the temperature inside the furnace is raised at a rate of about 50°C/min, and the yarn is heated with a thermocouple. Measure the temperature of. The temperature of the yarn gradually increases as the ambient temperature increases, but when the ambient temperature exceeds a certain point, the yarn temperature suddenly becomes higher than the ambient temperature. The ambient temperature when the yarn temperature reaches 10° C. higher than the oxidizing atmosphere temperature is measured, and this temperature is defined as the runaway reaction start temperature (T _f ) of the yarn. This T _f varies depending on the thickness of the yarn, the equilibrium moisture content representing the thermal history of the yarn, etc. For example, FIGS. 1 and 2 are diagrams showing the relationship between time and equilibrium moisture content when a precursor is exposed to an oxidizing atmosphere, and the relationship between equilibrium moisture content and T _f at that equilibrium moisture content, respectively ( graph).
As shown in the figure, as the oxidation or flame resistance reaction progresses, the equilibrium moisture content of the yarn increases, but the value of T _f increases accordingly. Therefore, the flame resistance time is shortened, i.e.
In order to carry out rapid flameproofing, it is advantageous to carry out multistage flameproofing in which the temperature of the oxidizing atmosphere can be changed as the T _f value changes. Even when performing this multi-stage flameproofing, carbon fibers with excellent mechanical properties can be stabilized by controlling the oxidizing atmosphere temperature specified in the present invention to a temperature 10 to 30°C lower than T _f at the equilibrium moisture content. It can be manufactured by Next, the fiber yarn obtained by heat treatment in an oxidizing atmosphere within the temperature range of 230 to 300°C has an equilibrium moisture content of 5 to 7% by weight,
Since the flame-resistant yarn corresponds to an incompletely flame-resistant yarn that is insufficiently oxidized, it is further heated in an inert atmosphere at a temperature higher than the oxidizing atmosphere temperature and within the temperature range of 300 to 380°C to carbonize it. It is necessary to make the fiber possible. Surprisingly, the incomplete flame-retardant yarn obtained by short heat treatment in an oxidizing atmosphere as described above is a fiber that can be carbonized by heating in an inert atmosphere for about 1 to 3 minutes. can be converted into carbonizable fibers by heat treatment for up to 30 minutes throughout the oxidizing and inert atmosphere. Furthermore, the carbonizable fiber thus obtained has a tensile strength of 1 to 3 g/d, an elongation of 4 to 6%, and a modulus of elasticity of 4 to 6%.
It is within the range of 80 to 120g/d, and the heating loss when carbonized by heating in a nitrogen atmosphere at 1400℃ is 48 to 55.
%, has good stability at high temperatures, has excellent passability in the carbonization process, has little occurrence of fuzz, thread breakage, etc., and can improve quality and performance. That is, in order to improve the physical properties of carbon fibers, it is desirable that the carbonizable fibers be heated under tension or tension in an inert atmosphere at a high temperature of at least 1000°C. Even when heated under tension or elongation, there is little occurrence of fuzz or thread breakage. Moreover, in the production of carbon fibers, it is generally desirable to have a higher carbonization yield in terms of production cost or productivity, but in the present invention, the loss on heating in a nitrogen atmosphere at 1400°C is approximately 48 to 55%. This makes it possible to improve the carbonization yield, which cannot be achieved using conventional short-time flame-retardant processes. The method and conditions for carbonizing or graphitizing the carbonizable fiber yarn are not particularly limited, and various known methods and conditions may be used, for example, in an inert atmosphere of nitrogen, helium, argon, etc. at 1000 to 2000°C. about
Hold under tension of 0.1~0.5g/d and heat up rate 200~
Examples include a method of heating and carbonizing at 1600°C/min, and a method of graphitizing the obtained carbon fiber under tension at a heating rate of 1000 to 7000°C/min in the inert atmosphere at at least 2500°C. . According to the present invention, it is possible to significantly shorten the so-called flame resistance time, which has the greatest impact on the productivity and quality performance of acrylic fibers, and the quality and performance degradation due to flame resistance is small. The physical properties of carbonized fibers are relatively excellent, and even when tensioned or stretched during the carbonization process, there are no problems such as fluffing or yarn breakage, and carbon fibers with high physical properties can be manufactured stably and with good reproducibility. This method exhibits outstanding effects as an industrial manufacturing method for acrylic carbon fibers, such as exhibiting carbonization yields that exceed standards. Furthermore, the physical properties of the carbon fiber obtained by the present invention are excellent as an acrylic carbon fiber having a tensile strength of 300 Kg/mm or more and an elongation of 1.2 or more and an elastic modulus of 20 ton/mm or more, despite the remarkable shortening of the flame resistance time. It possesses sufficient physical properties. EXAMPLES Hereinafter, the present invention will be explained in more detail with reference to Examples. Example 1 A 20% dimethyl sulfoxide (DMSO) solution of an AN copolymer consisting of 99% by weight of acrylonitrile (AN) and 1% by weight of itaconic acid was discharged as a spinning stock solution into a 60% DMSO-water coagulation bath and coagulated. ,
After washing with water, it is stretched 6 times in hot water at 100℃, dried and densified, and then subjected to secondary stretching in pressurized steam at 120-150℃, with a total stretching ratio of 14 times and single yarn fineness.
1d, drawn yarn with 3000 single yarns was created. This acrylic fiber thread was heat-treated for about 2 minutes while giving 2% shrinkage on a heating roll having a surface temperature of 240°C to obtain an acrylic precursor fiber thread (precursor) having the following physical properties. Tensile strength 6.2g/d Tensile elongation 10.1% Initial tensile modulus 120g/d Tar production 3.1% T _f 277℃ This precursor was first heated to 0.7g/d in air at 260℃.
While applying a tension of
After heating for 2 minutes in a nitrogen atmosphere at 1300° C., carbonization was performed under a tension of 0.6 g/d in a nitrogen atmosphere at 1300°C. The physical properties of the carbon fiber thus obtained are shown in Table 1.

[Table] Comparative Example 1 In Example 1, a 20% DMSO solution of an AN-based copolymer containing 98% by weight of AN and 2% by weight of methacrylic acid was used as the spinning stock solution, and the other conditions were the same as in Example 1. A system fiber bundle was created. The physical properties of this fiber bundle were measured, and the results were as follows. Tensile strength (g/d) 5.6 Tensile elongation (%) 10.8 Initial modulus (g/d) 90 Tar production rate (%) 2.5 Fineness (d) 1 Number of filaments (pieces) 1000 Next, this fiber bundle was processed. Oxidation treatment was carried out for 21 minutes according to Example 1 to produce an oxidized fiber bundle having an equilibrium moisture content of 6%, and the rest was heated in a nitrogen atmosphere and carbonized in the same manner as in Example 1. The obtained carbon fiber had the following physical properties. Tensile strength (Kg/mm ² ) 280 Elongation (%) 1.5 Elastic modulus (ton/mm ² ) 18.5 Carbonization yield (%) 53.2 Comparative example 2 In Example 1, a heating roll with a surface temperature of 240°C was used. The physical properties of the acrylic fiber bundle before heat treatment (non-heat treatment) were measured, and the results were as follows. Tensile strength (g/d) 6.2 Tensile elongation (%) 10.3 Initial elastic modulus (g/d) 124 Tar production amount (%) 5.8 This yarn was subjected to oxidation treatment, heat treatment in a nitrogen atmosphere, and Carbonized. The physical properties of the obtained carbon fiber were as follows. Tensile strength (Kg/mm ² ) 255 Elongation (%) 1.1 Elastic modulus (ton/mm ² ) 23.2 Carbonization yield (%) 53.8 Example 2 In Example 1, the oxidation treatment temperature and time are shown in Table 2. Five types of carbon fibers were obtained by changing as shown and firing in the same manner except for the following. Table 2 shows the physical properties and carbonization yield of these carbon fibers.

【table】 [Brief explanation of the drawing]

Figure 1 shows the relationship between the heating time and the corresponding equilibrium moisture content when acrylic precursor fiber yarn is heated in an oxidizing atmosphere at 240°C, and Figure 2 shows the relationship between the heating time and the corresponding equilibrium moisture content.
The figure shows the relationship between the equilibrium moisture content of the yarn and the corresponding T _f .

Claims (1)

[Claims] 1 Wet or dry-wet spin an acrylonitrile copolymer solution composed of 98% by weight or more of acrylonitrile and 2% by weight or less of itaconic acid, and after washing the coagulated yarn with water, stretching, and applying an oil agent,
After drying and densification, secondary stretching was performed in pressurized steam at a total stretching ratio of 11 to 16, and after that the surface temperature
Acrylonitrile having a tensile strength of at least 6 g/d, an initial tensile modulus of 100 g/d or more, and a tar production amount of 5% or less at 250°C, obtained by contacting with a heating roll at 150 to 240°C. 10 below the runaway reaction initiation temperature (T _f ) of the yarn in an oxidizing atmosphere of 230 to 300°C.
After heating at a low temperature of ~30℃ for 7 to 30 minutes to convert it into a flame-resistant yarn with an equilibrium moisture content of 5 to 7% by weight, it is heated at a temperature of 300 to 380℃ at a temperature higher than the oxidizing atmosphere temperature. 1. A method for producing acrylic carbon fibers, which comprises heating in an active atmosphere for 1 to 3 minutes to convert the fibers into carbonizable fiber threads, followed by carbonization or graphitization.