KR20200073561A - Method for producing stabilized fiber for carbon fiber and preparation method of carbon fiber using the same - Google Patents

Abstract

The present invention relates to a manufacturing method of a stabilized fiber for a carbon fiber, and the stabilized fiber for the carbon fiber manufactured by the manufacturing method. According to the present invention, by applying tension to extent that a precursor fiber does not deform in a step of oxidation-stabilizing the precursor fiber for the carbon fiber, it is possible to manufacture the stabilized fiber and the carbon fiber for excellent quality carbon fiber with improved mechanical properties such as tensile strength, elastic modulus, and elongation at break. The manufacturing method of the stabilized fiber for the carbon fiber includes the following steps of: preparing the precursor fiber for carbon fiber; obtaining data on a change in shrinkage force of the precursor fiber; and stabilizing the precursor fiber.

Description

Method for producing stabilized fiber for carbon fiber and method for producing carbon fiber using the same method

The present invention relates to a method for manufacturing a stabilized fiber for carbon fiber, a method for producing a carbon fiber using the same, and a stabilized fiber for carbon fiber produced by the method.

Carbon fiber is made of construction materials, concrete structures, seismic reinforcement, civil engineering, construction fields, CNG tanks, wind power blades, centrifugal rotors, thanks to efforts to develop consistent uses that can utilize characteristics such as light weight, high strength, and high heat resistance. Constructed from aerospace fields such as alternative energy such as fly foil, green energy fields, high-speed transportation equipment fields such as ships and vehicles, deep-sea oil field mining fields in marine development, high-performance equipment, medical welfare equipment, electric conduction applications, and ultra-heat resistance The scope of application is expanding to various industries ranging from industries. Carbon fiber is growing as a material that makes the foundation for a new era as a third general-purpose material that can replace iron, aluminum, etc., taking advantage of its unique characteristics. In particular, the use of carbon fiber as an aircraft component material for the recently developed supersonic aircraft Boeing 787 and Airbus 380 is expected to increase in usage in various high-tech materials fields.

In general, carbon fibers are produced through a stabilization process in which oxidation is stabilized by applying heat in an oxidizing atmosphere to dissolve the precursor fiber, and a carbonization process in which the stabilized fibers are carbonized at a high temperature. In addition, a graphitization process may be subsequently performed. At this time, the precursor fibers of the carbon fiber include polyacrylonitrile (PAN), pitch, rayon, lignin, polyethylene, and the like. Among them, the polyacrylonitrile-based fiber has a high carbon yield of 50% or higher and a high melting point, and is an optimal precursor capable of producing high-performance carbon fiber compared to other precursors according to process condition control. Accordingly, most of the present carbon fibers are made from polyacrylonitrile-based fibers. Polyacrylonitrile-based fibers, known as the most suitable precursors for the production of carbon fibers, are subjected to a series of oxidative stabilization, carbonization, and optionally graphitization process steps and a series of surface treatment and sizing treatments. After the step, it can be finally converted to carbon fiber or graphite fiber.

The oxidation stabilization process (or flameproofing process) refers to a heat treatment process performed in a temperature range of about 200 to 400°C while applying a constant tension in an oxidizing or air atmosphere, in which polyacrylonitrile-based fibers are chemically It makes a big difference. Chemical, physical and thermally stable structures are obtained even at high heat treatment temperatures, such as subsequent partial carbonization or graphitization conditions. In the oxidation stabilization reaction, cyclization, dehydrogenation, aromatization, oxidation, and crosslinking reactions occur, and through this reaction, a ladder structure of a conjugate structure having heat resistance is formed. Through this, the oxidation stabilization step prevents the fiber from melting during the high-temperature carbonization step that follows, and greatly affects the structure and physical properties of the final product.

Japanese Patent Publication 2016-535175

An object of the present invention is to minimize the quality degradation due to excessive shrinkage and single yarn of the carbon fiber precursor fiber occurring in the oxidation stabilization step in the manufacturing process of carbon fiber, the shrinkage data generated in the precursor fiber for carbon fiber in the oxidation stabilization step It is to provide a method of manufacturing a stabilized fiber for carbon fibers, in which mechanical properties, such as tensile strength, modulus of elasticity, and elongation at break, are significantly improved by deriving an appropriate tension size from.

According to an embodiment of the present invention for solving the above problems, the present invention comprises the steps of preparing a precursor fiber for carbon fiber; Obtaining shrinkage change data of the precursor fibers generated in the oxidation stabilization process; And stabilizing oxidation while applying tension to the precursor fiber, set at two different temperatures between the temperature at which exotherm starts according to the stabilization reaction of the precursor fiber and the temperature at which exotherm indicates maximum, the first stabilization step and the second. Stabilizing step including the stabilizing step; includes,

In the first stabilization step, a force of -20% to +20% is applied to a tension at the end of the first stabilization step of the precursor fiber, and in the second stabilization step, a contraction force at the end of the second stabilization step of the precursor fiber With respect to -20% to +20% of the force is applied as a tension, the tension is a value selected from the above range is constant, provides a method for producing a stabilized fiber for carbon fiber.

In addition, the present invention comprises the steps of preparing a stabilized fiber for carbon fibers according to the above manufacturing method; And carbonizing the stabilizing fibers.

In addition, the present invention provides a stabilized fiber for carbon fibers, having a tensile strength of 0.36 to 0.6 Gpa and an elastic modulus of 10 to 20 Gpa.

According to the present invention, by applying an appropriate size of tension in the step of oxidizing and stabilizing the precursor fiber for carbon fiber, it is possible to manufacture excellent quality carbon fiber with improved mechanical properties such as tensile strength, elastic modulus, and elongation at break.

In addition, the tension is determined from the shrinkage change data of the precursor fibers for carbon fibers generated in the oxidation stabilization process. By using the size of the shrinking force of the precursor fiber bundle for carbon fiber to derive an appropriate tension size simply and quantitatively, there is an advantage that it is possible to determine the tension condition to improve the mechanical properties of the carbon fiber with high accuracy.

1 shows a device for measuring shrinkage of a precursor fiber bundle for carbon fibers according to an embodiment of the present invention.
Figure 2 shows the shrinkage change data according to the temperature of the precursor fiber for carbon fibers in Examples 1, 2 and Comparative Example 1.
Figure 3 shows the shrinkage change data according to the temperature of the precursor fiber for carbon fibers in Examples 3, 4 and Comparative Example 2.
Figure 4 shows the (a) tensile strength, (b) elastic modulus, and (c) elongation at break of stabilized fibers for carbon fibers in Examples 1 and 2 and Comparative Example 1.
Figure 5 shows the (a) tensile strength, (b) elastic modulus, and (c) elongation at break of stabilized fibers for carbon fibers in Examples 3, 4 and Comparative Example 2.

Hereinafter, the present invention will be described in more detail to aid understanding of the present invention.

Terms or words used in the description and claims of the present invention should not be construed as being limited to ordinary or dictionary meanings, and the inventor appropriately defines the concept of terms in order to describe his or her invention in the best way. Based on the principle of being able to do it, it should be interpreted as a meaning and concept consistent with the technical idea of the present invention.

When referring to "comprising" a component in the present specification, it is meant that other components may be further included instead of excluding other components, unless otherwise specified.

Before going through a high-temperature carbonization process in the carbon fiber manufacturing process using the carbon fiber precursor fiber, the precursor fiber is subjected to heat treatment with an air atmosphere (oxygen) between the temperature at which the heating starts according to the stabilization reaction and the temperature at which the exotherm indicates the maximum. This oxidation stabilization process is essential. In this process, the precursor fiber undergoes processes such as cyclization, oxidation and dehydrogenation, and cross-linking reaction, and removes low-molecular substances among the components constituting the body and causes a large chemical change. In addition, the oxidation stabilization process is an important process that significantly affects the physical and mechanical properties of the carbon fiber as a step of imparting flame retardancy and flame resistance that does not burn even when in contact with a flame.

In particular, in the oxidation stabilization step, fiber shrinkage occurs due to a change in the structure of the polymer chain. In order to obtain carbon fibers with excellent mechanical properties such as tensile strength and Young's modulus, tension is applied during the stabilization process to control shrinkage and tension within a certain range, thereby causing the polymer chain to lose orientation. Should be minimized.

Accordingly, the present inventors measured the shrinkage force of the precursor fiber for carbon fibers generated in the oxidation stabilization process according to temperature, and derived the magnitude of the appropriate tension applied in the oxidation stabilization step from the shrinkage change data. That is, in the oxidation stabilization process, the degree of shrinkage of the precursor fiber was quantitatively measured to determine the appropriate tension size by a simple method, and when performing the oxidation stabilization process of the precursor fiber for carbon fiber while applying the determined tension as described above. , It was confirmed that it is possible to manufacture carbon fibers and stabilized fibers for carbon fibers having excellent mechanical properties such as tensile strength, modulus of elasticity, and elongation at break.

One aspect of the present invention provides a precursor fiber for carbon fiber; Obtaining shrinkage change data of the precursor fibers generated in the oxidation stabilization process; And stabilizing oxidation while applying tension to the precursor fiber, set at two different temperatures between the temperature at which exotherm starts according to the stabilization reaction of the precursor fiber and the temperature at which exotherm indicates maximum, the first stabilization step and the second. Stabilizing step including the stabilizing step; includes,

In the first stabilization step, a force of -20% to +20% is applied to a tension at the end of the first stabilization step of the precursor fiber, and in the second stabilization step, a contraction force at the end of the second stabilization step of the precursor fiber With respect to -20% to +20% of the force is applied as a tension, the tension is a value selected from the above range is constant, provides a method for producing a stabilized fiber for carbon fiber.

Hereinafter, the present invention will be described in detail.

The manufacturing method of the present invention includes the step of obtaining the shrinkage change data of the precursor fiber generated in the oxidation stabilization process.

In the step of stabilizing the precursor fiber for carbon fiber, an oxidation reaction occurs, and shrinkage of the precursor fiber occurs due to a change in the structure of the polymer chain, which usually causes significant shrinkage. The degree of shrinkage of the precursor fiber may vary depending on the temperature at which the oxidation stabilization process is performed. Specifically, as the temperature increases, the carbon fiber precursor contracts rapidly to increase the shrinkage force, and cutting of the weak part occurs in the precursor fiber for carbon fiber or a non-uniformity phenomenon of the oxidative heat treatment tension may occur, thereby improving process stability. It becomes more difficult.

Accordingly, in the present invention, it is characterized in that the shrinkage force change data according to the temperature of the precursor fiber is obtained, and the size of the tension to be applied in the oxidation stabilization process is determined in consideration of the change in the size of the shrinkage force according to the temperature.

The shrinkage force of the precursor fiber may be measured by DMA (Dynamic Mechanical Analysis), that is, dynamic mechanical analysis.

DMA is a method of measuring the mechanical behavior of a sample by controlling the temperature while changing the load over time, and using the stress generated in the sample and the resulting deformation, resulting from the stress and deformation. It is to measure the mechanical properties of the sample to be determined.

In the present invention, the shrinkage force of the precursor fiber for carbon fiber was measured simply and quantitatively using DMA, and in particular, by using DMA, the shrinkage force of the precursor fiber bundle in which 3,000 to 24,000 strands were aggregated was measured, rather than single or tens of strands. Did.

TMA (Thermomechanical Analyzer) equipment, which has been used to measure thermal deformation (shrinkage with temperature, shrinkage, etc.) of carbon fiber in the prior art, has a small size of geometry and a low limit of force that can be used, It is impossible to measure the degree of thermal deformation in a bundle state in which the fibers are bundled into 3,000 or more strands and the bulk and shrinkage force is large, and if a large amount of even the same type of fiber is measured at once, the characteristics may vary due to variables such as interference between fibers. , There was a problem that the measurement was not performed properly.

According to an embodiment of the present invention, by measuring the shrinking force of the precursor fiber for carbon fiber using DMA, it is possible to obtain measurement values reflecting all of the various variable values when the fibers are stabilized as they are aggregated, so that the analysis is close to the actual process conditions. Since this is possible and the measurable limit is 35N, it is also possible to measure the shrinkage force of the bundle in which the fibers are 3,000 to 24,000 strands.

The precursor fiber may be a bundle in which each fiber is 3,000 to 24,000 strands.

The precursor fiber for carbon fiber of the present invention is a general purpose precursor fiber as commonly used in textile processing, which is typically produced in large tow size to be made of carbon fiber through oxidation stabilization and carbonization, resulting in very high linear density It is used as a state to cause.

Thus, in the present invention, a precursor fiber for carbon fibers in a bundle state in which 3,000 strands or more, and specifically 3,000 to 24,000 strands of precursor fibers are aggregated, is used instead of single or tens of strands of precursor fibers. The shrinkage force generated in the oxidation stabilization process was measured using the precursor fiber of.

In the stabilization process of the precursor fiber for carbon fiber, heat is generated. As the number of fiber strands included in the bundle increases, the amount of heat generated increases, and it is also more difficult to dissipate heat. Due to this, the temperature inside the bundle becomes higher than the process temperature, and the temperature deviation according to the position of the fiber also increases. Due to this, it is difficult to judge that the size of the shrinkage or shrinkage force increases uniformly as the number of fiber strands increases, and the actual shrinkage or shrinkage force size is unpredictable. Therefore, in order to predict the fiber state in the actual process, it is required to measure the shrinkage force as a bundle state as close as possible to the process conditions.

That is, in the present invention, by measuring the shrinkage force of the bundle state in which the precursor fibers are aggregated into 3,000 to 24,000 strands, not the shrinkage force of a small amount of precursor fibers in a single or tens of strands, the shrinkage force change data under similar conditions is matched to the mass production of actual carbon fibers. Was obtained, and the tension that can be suitably applied to the oxidation stabilization process was derived with higher reliability, thereby making it possible to manufacture carbon fibers having desired properties.

The manufacturing method of the present invention stabilizes the oxidation while applying tension to the precursor fiber, and is set at two different temperatures between the temperature at which exotherm starts according to the stabilization reaction of the precursor fiber and the temperature at which exotherm indicates maximum, the first stabilization Stabilizing, including a step and a second stabilization step.

In the present invention, the temperature setting for each section of the oxidation stabilization step is an important factor in determining an appropriate tension condition in that the pattern of shrinkage change of the precursor fiber generated in the oxidation stabilization process varies with each temperature.

In the oxidation stabilization process, the precursor fibers change their structure in each oxidation zone due to cyclization and crosslinking reactions. The actual melting temperature of the polymer in the precursor fiber depends on the process conditions and the thermal history of the composition, but generally the fusion temperature is higher after each pass in oxidation, and the density of the fiber increases do. In order to achieve a higher oxidation rate, the temperature in the subsequent oxidation zone gradually increases. If the stabilization process is performed for a long time at a non-high temperature, the damage to the fiber is reduced, but the process takes a long time, so it is necessary to bring the process temperature high to shorten the time. However, if the temperature is excessively high in order to reduce time, deterioration of fiber properties due to melting, combustion, etc. may occur during the stabilization process. Accordingly, in the manufacturing method of the present invention, the oxidation stabilization step is divided into steps that are set to different temperatures between the temperature at which exotherm starts and the temperature at which exotherm indicates maximum, according to the stabilization reaction of the precursor fiber, and specifically, It includes a first stabilization step and a second stabilization step set at two temperatures. Specifically, the oxidation stabilization step may include a first stabilization step and a second stabilization step, which are set at two different temperatures from 200 to 300°C.

The first stabilization step may be set to a temperature within 45° C. from the temperature at which exotherm starts according to the stabilization reaction of the precursor fiber, and the second stabilization step is based on the temperature set in the first stabilization step. It may be set to 45° C., but is not limited thereto.

In addition, in the method for manufacturing a stabilizing fiber for carbon fibers of the present invention, the first stabilization step is set to two different temperatures between the temperature at which exotherm starts according to the stabilization reaction of the precursor fiber and the temperature at which exotherm indicates maximum. A first stabilization step and a first stabilization step, wherein the second stabilization step is set to two different temperatures between two different temperatures between the temperature at which exotherm starts according to the stabilization reaction of the precursor fiber and the temperature at which exotherm indicates maximum. Stabilization step and 2b stabilization step.

The stabilizing step 1a is set to a temperature within 45° C. from the temperature at which exotherm starts according to the stabilization reaction of the precursor fiber, and the stabilizing step 1b, stabilizing 2a, and stabilizing 2b are stabilizing the firsta. It may be set to 5 to 45 ℃ higher sequentially based on the temperature set in the step.

More specifically, the 1b stabilization step, the 2a stabilization step and the 2b stabilization step may be sequentially 5 to 20°C, specifically 10 to 20°C, at a high temperature based on the temperature of the 1a stabilization step, but It is not limited.

For example, the first stabilization step is 200 to 230°C, the first stabilization step is 215 to 245°C, the second stabilization step is 230 to 260°C, and the second stabilization step is 245 to 275°C, and these are based on the first stabilization step. The temperature may be increased sequentially.

According to an embodiment of the present invention, the 1a stabilization step may be 215°C, the 1b stabilization step may be 230°C, the 2a stabilization step may be 245°C, and the 2b stabilization step may be 260°C.

The temperature of each step is set to a temperature capable of satisfying the stabilization degree and density in consideration of the degree of stabilization (aroma index: AI) and density that the carbon fiber is expected to reach at each stage. The temperature of the stabilization step can be set by a person skilled in the art according to the polymerization prescription of carbon fiber, process conditions of the previous step, equipment, and the like.

In the present invention, the 1a stabilization step, the 1b stabilization step, the 2a stabilization step and the 2b stabilization step are different from each other between the temperature at which exotherm starts according to the stabilization reaction of the precursor fiber and the temperature at which exotherm indicates maximum. It is used as a meaning to distinguish each set step, and is not necessarily limited to a meaning to be divided into four sections. For example, if the step of oxidizing and stabilizing to a temperature different from the above steps between the temperature at which exotherm starts according to the stabilization reaction of the precursor fiber and the temperature at which exotherm indicates maximum, a third stabilization step, a fourth stabilization step, etc. are additionally included. can do. In this case, each stabilization step may be sequentially set to a high temperature based on the temperature set in the 1a stabilization step.

In the manufacturing method of the present invention, when the step of oxidizing and stabilizing the precursor fiber includes a first stabilization step and a second stabilization step, the first stabilization step is -20% relative to the shrinkage force at the end of the first stabilization step of the precursor fiber A force of ~20% is applied as a tension, and in the second stabilization step, a force of -20% to +20% can be applied as a tension at the end of the second stabilization step of the precursor fiber.

In addition, in the first stabilization step, a force of -15% to +15% is applied to the contraction force at the end of the first stabilization step of the precursor fiber as a tension, and in the second stabilization step, the end of the second stabilization step of the precursor fiber A force of -15% to +15% with respect to the shrinkage force of can be applied as a tension.

In addition, in the manufacturing method of the present invention, the first stabilization step is a first stabilization step and a first stabilization step set to two different temperatures between the temperature at which exotherm starts according to the stabilization reaction of the precursor fiber and the temperature at which exotherm indicates maximum. 1b stabilization step, wherein the second stabilization step is a 2a stabilization step and a 2b stabilization set to two different temperatures between the temperature at which exotherm starts according to the stabilization reaction of the precursor fiber and the temperature at which exotherm indicates maximum. If you include steps,

In the first stabilization step, a force of -20% to +20% is applied to a tension at the end of the 1b stabilization step of the precursor fiber as a tension, and in the second stabilization step, a shrinkage force at the end of the 2b stabilization step of the precursor fiber For -20% to +20% of the force can be applied as a tension.

In addition, in the first stabilization step, a force of -15% to +15% is applied to the shrinking force at the end of the 1b stabilization step of the precursor fiber, and in the second stabilization step, the end of the 2b stabilization step of the precursor fiber A force of -15% to +15% with respect to the shrinkage force of can be applied as a tension.

The tension of the size determined as described above can be continuously applied in the corresponding stabilization step. For example, when a specific value is determined by the tension of the first stabilization step, the tension of the corresponding size may be constantly applied without interruption or change from the beginning to the end of the first stabilization step.

As described above, in the present invention, the size of the tension to be applied in the oxidation stabilization process was determined based on the shrinkage of the precursor fiber at a specific point in the oxidation stabilization step.

In the oxidation stabilization process of the precursor fiber for carbon fibers, inevitably shrinkage occurs. In order to obtain carbon fibers having excellent mechanical properties such as tensile strength and Young's modulus, appropriate tension is applied during the oxidation stabilization process. In addition, it is necessary to minimize the loss of orientation of the polymer chain by controlling shrinkage and tension within a certain range.

Accordingly, in the present invention, by applying a tensile force similar to the shrinking force at the end of the stabilization step from the shrinking force change data of the precursor fiber, the polymer chain is minimized and the mechanical properties such as tensile strength, modulus of elasticity, elongation at break are improved. It is to derive the appropriate tension size.

In the present invention, when the size of the tension is outside the range determined from the shrinkage force as described above, for example, when it is less than -20% of the shrinkage force of the precursor fiber at a specific time point, the shrinkage of the precursor fiber occurs and the polymer chain loses orientation, and finally Mechanical properties, such as tensile strength, modulus of elasticity, and elongation at break, of the carbon fiber prepared as may be deteriorated.

In addition, when the size of the tension is more than +20% of the shrinkage force of the precursor fiber, tension of the precursor fiber occurs in the oxidation stabilization step, and a problem in that carbon fiber having desired mechanical properties may not be produced. In addition, a single yarn may occur beyond the tension of the precursor fiber, and during the stabilization step, atoms inside the precursor fiber move to cyclize, and if excessive tension is applied, the movement of the inner atom may be hindered to stabilize sufficiently. , Due to excessive tension of the fibers, elasticity of the finally produced carbonized fiber may be reduced (brittle), resulting in a decrease in elongation of the carbon fiber.

In addition, in the present invention, not only the size of the tension was determined based on the shrinking force of the precursor fiber at a specific time point, but also considering that the shrinking force of the precursor fiber also changes according to the temperature change, the magnitude of the tension is changed during the oxidation stabilization step.

Specifically, when the step of oxidizing and stabilizing the precursor fiber includes a first stabilization step and a second stabilization step, in the first stabilization step, a force of -20% to +20% of the contraction force at the end of the first stabilization step is constant. By applying the tension and changing the tension value at the time when the first stabilization step ends and the second stabilization step starts, a force of -20% to +20% of the contractile force at the end of the second stabilization step is constant in the second stabilization step. It was applied with tension.

In addition, the first stabilization step includes a first stabilization step and a first stabilization step set at two different temperatures between the temperature at which exotherm starts according to the stabilization reaction of the precursor fiber and the temperature at which exotherm indicates maximum, When the second stabilization step includes a 2a stabilization step and a 2b stabilization step set at two different temperatures between the temperature at which exotherm starts according to the stabilization reaction of the precursor fiber and the temperature at which exotherm indicates maximum, the second stabilization step is performed. In the first stabilization step, a force of -20% to +20% of the contraction force at the end of the first stabilization step is constantly applied as a tension, and the tension value is changed at the time when the first stabilization step ends and the second stabilization step starts, In the second stabilization step, a force of -20% to +20% of the contractile force at the end of the 2b stabilization step was constantly applied as a tension.

When a constant value is applied as a tension throughout the oxidation stabilization process, it is impossible to properly perform the change of the contraction force according to the temperature change and the shrinkage and tensile control of the fiber, thereby deteriorating the mechanical properties of the finally produced carbon fiber. Can be.

In the present invention, when the type of the precursor fiber for carbon fiber is different, the size of the tension determined according to the manufacturing method of the present invention may be different. For example, according to an embodiment of the present invention, when the oxidation stabilization step was performed using 12K polyacrylonitrile fibers, the magnitude of the tension in the 1a stabilization step at 215°C and the 1b stabilization step at 230°C. Is set to 8N, which is the contraction force at the end of the 1b stabilization step, and the magnitude of the tension at the 2a stabilization step at 245°C and the 2b stabilization step at 260°C is set to 21N, which is the contraction force at the end of the 2b stabilization step. Did. This is only an example of the present invention, and may vary depending on specific types of carbon fiber precursor fibers, manufacturing conditions, oxidation stabilization step temperature, measurement environment, and the like.

In the manufacturing method of the present invention, the step of stabilizing the precursor fiber for carbon fiber may be performed for 40 minutes to 80 minutes, and specifically, for 60 minutes.

When the step of stabilizing the precursor fiber for carbon fiber includes a first stabilization step and a second stabilization step, they may be independently performed for 20 minutes to 40 minutes.

When the step of stabilizing the precursor fiber for carbon fiber includes a 1a stabilization step, a 1b stabilization step, a 2a stabilization step and a 2b stabilization step, they may be independently performed for 10 minutes to 20 minutes, Specifically, it may be performed for 15 minutes.

For example, when the step of stabilizing the precursor fiber for carbon fiber is performed over 60 minutes, the 1a stabilization step, the 1b stabilization step, the 2a stabilization step, and the 2b stabilization step can be independently performed for 15 minutes. However, it is not limited thereto.

In the manufacturing method of the present invention, when each time of the stabilization step is out of the above range, the size of the tension derived from the size of the contraction force at a specific time may be out of the appropriate range, and the advantages of the present invention may not be exhibited. The effect of improving the mechanical properties of carbon fiber may be negligible.

The time required for each section, such as the 1a stabilization step, the 1b stabilization step, the 2a stabilization step, and the 2b stabilization step, does not necessarily have to be the same, and the stabilization step depends on the type of carbon fiber precursor fiber or stabilization equipment. After appropriately setting the temperature and time, the effect of the present invention can be obtained by measuring the shrinkage force with DMA and selecting the tension condition under the corresponding conditions.

In the present invention, the step of oxidizing and stabilizing the precursor fiber may be performed in a batch type oven, or may be performed while the precursor fibers continuously pass through a plurality of ovens set at different temperatures. In addition, any method commonly used to oxidize and stabilize the precursor fiber for carbon fiber is not limited and can be used in the present invention.

In the present invention, there is no particular limitation on the type of the precursor fiber for carbon fiber as long as it can be made of carbon fiber through a carbonization step. Specifically, the precursor fiber for carbon fiber is polyacrylonitrile (PAN)-based fiber, pitch-based fiber, rayon-based fiber, lignin-based fiber, cellulose-based fiber, and polyethylene (polyethylene) ) May be one or more selected from the group consisting of fibers, but is not limited thereto.

For the purposes of the present invention, the precursor fiber for carbon fiber may be polyacrylonitrile-based fiber. The polyacrylonitrile-based fiber refers to a polymer containing acrylonitrile as a main component, and has the advantage of being able to produce fibers of various performances through process changes compared to other fibers.

In the present invention, the method for preparing the precursor fiber for carbon fiber, in particular, the polyacrylonitrile-based fiber, and the acquisition route are not limited, and the manufacturing method commonly used in the art is used, or the commercially available fiber is freely purchased. Can be used.

Another aspect of the present invention comprises the steps of preparing a stabilized fiber for carbon fibers according to the method; And carbonizing the stabilizing fibers.

Description of the method for manufacturing a stabilized fiber for carbon fiber is as described above.

The carbonization step may be a general carbonization process applied in manufacturing carbon fibers, and may be carbonization of the precursor fiber for oxidation-stabilized carbon fibers using thermal energy or microwaves, but is not limited thereto.

The carbonization step may be generally performed in an inert atmosphere, and a material for forming the inert atmosphere may be gas, such as nitrogen, argon or xenon, but is not limited thereto. In addition, the carbonization temperature in the carbonization step may be about 1,000 °C or higher, specifically 1,200 °C or higher, and an upper limit of 2,000 °C or lower, specifically 1800 °C or lower, but is not limited thereto.

Another aspect of the present invention provides a stabilized fiber for carbon fibers having a tensile strength of 0.36 to 0.6 Gpa and a Young's modulus of 10 to 20 Gpa.

The tensile strength may be 0.36 to 0.6 Gpa, preferably 0.38 to 0.6 Gpa, more preferably 0.4 to 0.5 Gpa.

The modulus of elasticity may be 10 to 20 Gpa, preferably 11 to 15 Gpa, and more preferably 12 to 14 Gpa. The stabilized fiber for carbon fiber may be manufactured according to the manufacturing method of the present invention.

When applying the method for manufacturing a stabilized fiber for carbon fibers according to the present invention, the stabilized fiber for carbon fibers prepared therefrom may have improved mechanical properties, in particular not only improved tensile strength and elastic modulus, but also elongation at break At the same time, it may be an improvement.

In addition, the carbon fiber prepared therefrom may also have excellent mechanical properties.

Example

Hereinafter, the present invention will be described in more detail by examples. However, the following examples are only for illustrating the present invention, and the scope of the present invention is not limited thereto.

<Measurement of shrinkage force according to temperature in oxidation stabilization step>

Using the 12K polyacrylonitrile-based fiber and 3K polyacrylonitrile-based fiber as a raw material, while performing an oxidation stabilization process, shrinkage force according to temperature was measured.

As shown in Fig. 1, a tension clamp is attached to the DMA, the polyacrylonitrile-based fibers are fitted at both ends, and two screws are tightened on each side to fix the fibers in an unfolded state as in the form of a film. Did. The fibers in the outer part of the fixing part were knotted to catch the fixing part to prevent slipping. The measuring section of the fiber was set to a length of 20 to 40 mm, while the lower clamp was fixed, and only the upper clamp was applied to the tension to pull the fiber. Specifically, during the oxidation stabilization step, the shrinkage force according to the temperature when the length of the precursor fiber was kept constant (elongation at 0%) was measured. The temperature conditions in the oxidation stabilization step were set as follows: the 1a stabilization step was 215°C, the 1b stabilization step was 230°C, the 2a stabilization step was 245°C, and the 2b stabilization step was 260°C.

The heating time from room temperature to the temperature of the stabilization step 1a took about 3 minutes, and the heating process between each step was performed at a heating rate of 50° C./min, and the time for the entire stabilization step was 60 minutes. Through the above process, the results of measuring the shrinkage force according to the temperature of the 12K and 3K polyacrylonitrile fibers are shown in FIGS. 2 and 3, respectively.

As shown in FIG. 2, when 12K polyacrylonitrile-based fibers were used, it was confirmed that the contraction force at the end of the 1b stabilization step was 8N, and the contraction force at the end of the 2b stabilization step was 21N. In addition, in the 3K polyacrylonitrile-based fiber, it was confirmed that the contraction force at the end of the 1b stabilization step was 6.8N, and the contraction force at the end of the 2b stabilization step was 8.6N.

<Oxidation stabilization of polyacrylonitrile-based fibers>

Example 1

In the same way as the oxidation stabilization step was performed to measure the shrinkage force, the oxidation stabilization process was performed using 12K polyacrylonitrile-based fibers. The tension in the first stabilization step was set to 8N, which is the contraction force at the end of the first stabilization step, and the tension in the second stabilization step was set to 21N, the contraction force at the end of the 2b stabilization step.

Example 2

The experiment was conducted in the same manner as in Example 1, except that the tension in the first stabilization step was set to 10N, and the tension in the second stabilization step was set to 24N.

Example 3

Experiments were conducted in the same manner as in Example 1, except that 3K polyacrylonitrile-based fibers were used, and the tension in the first stabilization step was set to 5.5N, and the tension in the second stabilization step was set to 7N.

Example 4

Experiments were conducted in the same manner as in Example 1, except that 3K polyacrylonitrile-based fibers were used, and the tension in the first stabilization step was set to 7.5N, and the tension in the second stabilization step was set to 9.5N.

Comparative Example 1

Experiments were carried out in the same manner as in Example 1, except that 12K polyacrylonitrile-based fibers were used, and the tension of the first and second stabilization steps was set to 8N.

Comparative Example 2

Experiments were performed in the same manner as in Example 1, except that 3K polyacrylonitrile-based fibers were used, and the tension of the first and second stabilization steps was set to 2N.

Bundle First stabilization stage tension Tension in the second stabilization phase Example 1 12K 8N (0% of the contractile force at the end of the 1b stabilization phase) 21N (0% of the contractile force at the end of the 2b stabilization phase) Example 2 12K 10N (+12.5% of the contractile force at the end of the 1b stabilization phase) 24N (+15% of the contractile force at the end of the 2b stabilization phase) Example 3 3K 5.5N (about -19% of the contractile force at the end of the 1b stabilization phase) 7N (about -18% of the contractile force at the end of the 2b stabilization phase) Example 4 3K 7.5N (+10% of the contractile force at the end of the 1b stabilization phase) 9.5N (+10% of the contractile force at the end of the 2b stabilization phase) Comparative Example 1 12K 8N (0% of the contractile force at the end of the 1b stabilization phase) Comparative Example 2 3K 2N (-71% of shrinkage at the end of the 1b stabilization phase)

<Measurement of mechanical properties of stabilized fibers>

For the stabilized fibers prepared as described above, the tensile strength, modulus of elasticity, and elongation at break of one strand of fibers were measured for 25 strands using a single fiber tester (Favimat from Textecho). Table 2 below shows the standard deviation.

Example 1 Example 2 Example 3 Example 4 Average Standard Deviation Average Standard Deviation Average Standard Deviation Average Standard Deviation Tensile strength (Gpa) 0.39 0.029 0.40 0.055 0.38 0.016 0.41 0.011 Elastic modulus (Gpa) 10.38 0.247 10.81 0.558 12.82 0.312 13.81 0.220 Elongation at break (%) 12.70 2.278 11.86 2.491 11.89 0.927 9.62 0.425

Comparative Example 1 Comparative Example 2 Average Standard Deviation Average Standard Deviation Tensile strength (Gpa) 0.33 0.031 0.354 0.028 Elastic modulus (Gpa) 9.74 0.143 11.11 0.191 Elongation at break (%) 10.79 2.600 13.21 2.751

As shown in Tables 2 and 3 and FIGS. 4 and 5, in the first stabilization step, the same tension as the end of the 1b stabilization step was applied, and in the second stabilization step, the same tension as the end of the 2b stabilization step was applied. In the case of Example 1, compared with Comparative Example 1 in which the shrinking force at the end of the first stabilization step was applied throughout the oxidation stabilization step, it was confirmed that the mechanical properties of tensile strength, elastic modulus, and elongation at break were all high.

In addition, in the first stabilization step, 10N, which is about 12.5% higher than the contractile force at the end of the 1b stabilization step, is added as a tension, and in the second stabilization step, 24N, which is about 15% higher than the shrinkage force at the end of the 2b stabilization step, is applied as a tension. Similarly, the tensile strength, modulus of elasticity, and elongation at break were all high.

That is, according to the present invention, when deriving the magnitude of the tension from the shrinkage change data of the precursor fiber and applying it to the oxidation stabilization step, the tensile strength, the elastic modulus, the elongation at break are all improved evenly, and the stabilized fiber for carbon fiber with excellent mechanical properties It was found that can be prepared.

Claims (13)

Preparing a precursor fiber for carbon fiber;
Obtaining shrinkage change data of the precursor fibers generated in the oxidation stabilization process; And
The first stabilization step and the second stabilization step are set to two different temperatures between the temperature at which exotherm starts according to the stabilization reaction of the precursor fiber and the temperature at which exotherm indicates the maximum, while stabilizing the oxide while applying tension to the precursor fiber. Stabilizing, including the step; includes,
In the first stabilization step, a force of -20% to +20% is applied to a tension at the end of the first stabilization step of the precursor fiber as a tension,
In the second stabilization step, a force of -20% to +20% is applied to a tension at the end of the second stabilization step of the precursor fiber as a tension,
The tension is a method selected from the above range, the constant value is applied, the method for producing a stabilized fiber for carbon fiber.
The method according to claim 1,
In the first stabilization step, a force of -15% to +15% is applied as a tension to the shrinking force at the end of the first stabilization step of the precursor fiber,
In the second stabilization step, a method of manufacturing a stabilization fiber for carbon fibers, wherein a force of -15% to +15% is applied as a tension to the shrinking force at the end of the second stabilization step of the precursor fiber.
The method according to claim 1,
The first stabilization step is set to a temperature within 45° C. from the temperature at which exotherm starts according to the stabilization reaction of the precursor fiber, and the second stabilization step is 5 to 45 based on the temperature set in the first stabilization step. A method of manufacturing stabilized fibers for carbon fibers, which is set at a high temperature.
The method according to claim 1,
The step of stabilizing the precursor fiber is to be performed for 40 minutes to 80 minutes, the method for producing a stabilized fiber for carbon fibers.
The method according to claim 1,
The first stabilization step and the second stabilization step, each of which is performed independently for 20 minutes to 40 minutes, the method for producing a stabilized fiber for carbon fibers.
The method according to claim 1,
The first stabilization step includes a first stabilization step and a first stabilization step set at two different temperatures between a temperature at which exotherm starts according to a stabilization reaction of the precursor fiber and a temperature at which exotherm indicates maximum,
The second stabilization step includes a 2a stabilization step and a 2b stabilization step set at two different temperatures between a temperature at which exotherm starts according to a stabilization reaction of the precursor fiber and a temperature at which exotherm indicates maximum,
In the first stabilization step, a force of -20% to +20% is applied as a tension to the shrinking force at the end of the first stabilization step of the precursor fiber,
In the second stabilization step, a method of manufacturing a stabilizing fiber for carbon fibers, wherein a force of -20% to +20% is applied to a tension at the end of the 2b stabilization step of the precursor fiber.
The method according to claim 6,
In the first stabilization step, a force of -15% to +15% is applied to the contractile force at the end of the first stabilization step of the precursor fiber as a tension,
In the second stabilization step, a method of manufacturing a stabilizing fiber for carbon fibers, wherein a force of -15% to +15% is applied as a tension to the shrinking force at the end of the 2b stabilization step of the precursor fiber.
The method according to claim 6,
The stabilizing step 1a is set to a temperature within 45° C. from the temperature at which exotherm starts according to the stabilization reaction of the precursor fiber, and the stabilizing step 1b, stabilizing 2a, and stabilizing 2b are stabilizing the firsta. Method of manufacturing a stabilized fiber for carbon fibers, which is sequentially set to 5 to 20°C higher based on the temperature set in the step.
The method according to claim 6,
The 1a stabilization step, the 1b stabilization step, the 2a stabilization step and the 2b stabilization step are each independently performed for 10 minutes to 20 minutes, a method for producing a stabilized fiber for carbon fibers.
The method according to claim 1,
The shrinking force is measured by DMA (Dynamic Mechanical Analysis), a method for producing stabilized fibers for carbon fibers.
The method according to claim 1,
The precursor fiber is a method for producing stabilized fibers for carbon fibers, wherein each fiber is in a bundle state of 3,000 to 24,000 strands.
Preparing a stabilized fiber for carbon fibers according to any one of claims 1 to 11; And
Carbonizing the stabilizing fiber; containing,
Carbon fiber manufacturing method.
A tensile strength of 0.36 to 0.6 Gpa, and an elastic modulus of 10 to 20 Gpa.

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