KR101586820B1 - Method of manufacturing silicon carbide fiber having uniform property by using high-speed and continuous process - Google Patents

Abstract

A method for manufacturing a silicon carbide fiber according to the present invention comprises: a winding step of winding a polycarbosilane (PCS) fiber, which is produced by the melt spinning of PCS, around a winding member; a stabilization step of rendering the winding member, which is wound with the PCS fiber, infusible in an atmosphere of iodine, air, or ozone gas; a low temperature preliminary heat treatment step of performing low temperature heat treatment on the winding member, which has completed the stabilization step, at a temperature of 200-300°C to prevent the shrinkage of the fiber and increase the strength of the fiber; a medium temperature heat treatment step of performing high-speed heat treatment on the fiber by primarily increasing the temperature from 200 or 300°C to 800-1000°C while maintaining tension of the fiber after unwinding the fiber from the winding member, which has completed the low temperature preliminary heat treatment, to separate and collect the fiber; a high temperature heat treatment step of continuously performing the high-speed heat treatment on the fiber, which has completed the medium temperature heat treatment step, by secondarily increasing the temperature from 800-1000°C to 1200-1400°C; and a step of continuously sizing the surface of a silicon carbide fiber, which is obtained by the high temperature heat treatment, with epoxy or polyvinyl alcohol resin. The method of the present invention can make uniform the quality and properties of the manufactured silicon carbide fiber and improve productivity by performing heat treatment while continuously maintaining tension after the stabilization step.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a method of producing a silicon carbide fiber having uniform physical properties by a high-speed and continuous process,

This technology is a technology in the field of ceramic fibers. Specifically, it is a technique for preventing the damage of silicon carbide fibers to be produced, inducing uniform physical properties, and for producing silicon carbide (SiC) fibers capable of high- .

Silicon carbide fibers have high strength and elasticity, and are resistant to high temperatures and oxidizing atmospheres above 1000 ° C. They are a source material expected as composite reinforcing fibers. The most widely used process for the production of silicon carbide fibers is the synthesis of Polycarbosilane (PCS) polymer by S. Yajima in 1975, which is the starting material. This polymer is an organic silicon polymer having a structure of -Si-C- as a main axis. Silicon carbide (SiC) fibers which can be used for a long period of time without losing the mechanical strength in the oxygen atmosphere under the final high temperature can be obtained by using PCS as a raw material and then through the steps of radiation, curing, and pyrolysis. PCS is composed of an oligomer (oligomer) which is oligomer. Although the fiber obtained by spinning has a circular shape, since the bond between the oligomers is weak, the fiber is hard to be cut, even when a slight load is applied , And also easily breaks into a powder form. Therefore, the so-called green fiber, which is obtained immediately after the spinning, does not maintain the shape of the fiber due to melting when heat treatment is performed at a high temperature immediately without passing through an infusibilization process. Therefore, it is a very important process to allow the PCS fiber to undergo an immiscible process before high-temperature pyrolysis or high-temperature heat treatment. Since crosslinking occurs on the surface of the PCS fiber by the above-mentioned immobilization process, Can be formed. The incompatibility of the PCS fibers is a very important characteristic in preventing the PCS fibers from being melted until the high temperature heat treatment and further obtaining the high yield ceramics. Therefore, the physical properties of the SiC fiber tend to depend largely on the conditions of the incompatibility process.

After the incompatibility process or the incompatibility process is completed, the SiC fiber can be manufactured through heat treatment to a high temperature. For example, the SiC fiber can be produced by heating the winding drum itself to a high temperature of 800 to 900 DEG C while the fiber is wound around the winding drum, and then subjected to a heat treatment step in which the fiber is heated to a higher temperature. When the heat treatment is performed in the state that the fibers are wrapped around the winding drum as described above, the infiltrated fibers turn into SiC fibers and shrinkage occurs. When the material of the winding drum is made of metal, thermal expansion occurs, Thereby cutting and damaging the fibers. Further, when the heat treatment is performed in a state of being wound up to a high temperature, there is a problem that high-speed and continuous processes are difficult to be performed.

An object of the present invention is to provide a manufacturing method capable of producing silicon carbide with continuous and high-speed processes with minimized damage, uniform physical properties and excellent physical properties as the invention considered for solving the above-mentioned problems.

A method of producing a silicon carbide fiber according to an embodiment of the present invention includes a winding step of winding a polycarbosilane fiber produced by melt spinning of a polycarbosilane (PCS) on a winding member, a winding step of winding the polycarbosilane fiber A stabilizing step of immersing the member in an atmosphere of air or an atmosphere of ozone under an atmosphere of iodine in an atmosphere of an ozone gas, and a step of heat-treating the unwoven member, which has undergone the immobilization step, under an inert atmosphere at a temperature of 200 to 300 ° C A temperature lowering preliminary heat treatment step of increasing the strength of the fiber, a step of loosening the fiber from the winding member that has undergone the low temperature preheating treatment, separating and focusing the fiber, maintaining the tension, 1 and a high-speed heat treatment, and the fibers subjected to the intermediate-temperature heat treatment step are heated to 800 To a second elevated temperature from a temperature of 1000 ℃ to a temperature of 1200 to 1400 ℃ and a high temperature heat treatment step of heat-treating at a high speed.

The first elevated temperature and the second elevated temperature may be at a rate of 100 to 300 ° C / min. The mid-temperature annealing step and the high-temperature annealing step may be performed in an inert atmosphere state in which the inflow of outside air is blocked.

The incompatibility may be carried out at a temperature of from about room temperature to about 100 to 200 DEG C in two to three steps of a thermal cycle.

The low-temperature preliminary heat treatment step includes two to four sub-heating steps in which the temperature is successively increased from 200 ° C. to 300 ° C. in a heat treatment furnace, and the heat treatment is performed for each of the steps for 1 to 3 hours, It can be heated at a rate of 0.2 to 5 占 폚 / min and heat-treated.

The winding member may have a cavity formed therein and a plurality of opening patterns may be formed on the surface thereof.

The mid-temperature heat treatment step and the high-temperature heat treatment step may be a continuous process.

After the high-temperature heat treatment step, the silicon carbide fiber can be subjected to a treatment for continuously sizing the fiber surface using the polymer resin.

According to the method for producing a silicon carbide fiber according to an embodiment of the present invention, the shrinkage change of the fiber does not occur in the state that the fiber is wound around the winding member, and only the preliminary heat treatment step, It is possible to manufacture SiC fibers having uniform physical properties while preventing the fibers from being damaged because heat treatment is performed at a high temperature while being wound around the winding member.

In addition, by maintaining the tensile strength of the fibers in a heat treatment process at or above the middle temperature, the heat treatment can be performed while moving in a straight line, thereby enabling high-speed heat treatment and continuous heat treatment, ultimately improving uniform physical properties and quality of SiC fibers and maximizing productivity can do.

Further, according to the manufacturing method according to one embodiment of the present invention, it is possible to reduce the production cost and mass production, and further improve the physical properties of the resultant SiC fiber.

Further, the technical idea of the present invention is expected to be widely used in inorganic fibers of other similar processes such as pitch carbon fibers.

1 is a flow chart conceptually showing a method of manufacturing silicon carbide according to an embodiment of the present invention.

Hereinafter, a silicon carbide manufacturing technique according to the present invention will be described in detail with reference to the accompanying drawings. However, the following description is only an exemplary description of the present invention, and the technical idea of the present invention is not limited by the following description, and the technical idea of the present invention is defined by the claims that follow.

1 is a flow chart conceptually showing a method of manufacturing silicon carbide according to an embodiment of the present invention.

Referring to Figure 1, a method 100 of making silicon carbide fibers begins with a polycarbosilane (PCS) fiber precursor preparation step (S110). The PCS fiber precursor is prepared in powder form and melted in a melting chamber to prepare the spinning step. The PCS fiber precursor used in one embodiment of the present invention, that is, PCS, has a weight average molecular weight of 4000 or less and a number average molecular weight of 1,500 or less.

The PCS is melted in a melting chamber in a gas atmosphere at a temperature of about 300 DEG C or less and a high purity nitrogen atmosphere, and sufficiently stirred to remove air bubbles before radiation to ensure uniformity of spinning and to prevent cutting of fibers.

The bubbles are removed and the melted PCS is subjected to a spinning step and a winding step (S120) as described above. Specifically, the molten PCS is irradiated at a speed of 400 to 700 m / min at a temperature of 220 to 300 ° C. The formed continuous PCS fibers are passed through a guide for fiber focusing and wound on a winding member to form continuous PCS fibers having a diameter of 14 to 20 μm, Fibers can be obtained. During the spinning, the PCS fibers are passed through a guide for collecting several hundreds of fibers without being cut, and a separate focusing agent may be injected to reduce friction between the guide and the fibers. The spinning device may be a spinning nozzle device having about 150 to 300 nozzles and a diameter of 0.2 to 0.3 mm. The pressure during spinning is preferably varied according to the viscosity behavior of the polycarbosilane in consideration of the spinning speed of the spinning fiber and the diameter of the fiber.

The winding member for winding the PCS fiber at the time of spinning may be made of a high-temperature metal material such as stainless steel. In addition, as the winding section, a cavity in which a cavity is formed and a plurality of opening patterns are formed on the surface is used. The winding member may be, for example, a cylindrical member whose interior is empty and fine circular openings are formed on the surface. According to one embodiment of the invention, approximately the circular opening is designed to have a diameter of 1 to 3 mm. The winding member performs the subsequent infusing process and the preliminary heat treatment process in a state in which the PCS fiber is wound even after the spun off PCS fiber is wound. As described above, the winding member having the opening pattern allows the halide gas, the nitrogen gas, and the argon gas to smoothly pass through in the incompatibility step and the preliminary heat treatment step. On the other hand, the length of the PCS fiber wound around the winding member is about 500 to 2000 m.

When the spinning and winding step S120 as described above is completed, the winding member on which the PCS fiber is wound is subjected to the unfusion step S130 as it is. The infusibilization step is performed under an oxidizing atmosphere such as air or an ozone gas atmosphere under an iodine atmosphere. When the immobilization step proceeds in an ozone gas atmosphere, irradiation with ultraviolet rays or electron beams may be performed in parallel.

The PCS fiber in the wound state is subjected to a heat treatment in the step of insolubilizing. The step of insolubilization under the iodine atmosphere may be carried out at each step for 2 to 3 hours at several stages of heat cycles at a temperature range of 100 to 200 ° C. Meanwhile, the heat treatment performed under a general air atmosphere, not under an iodine atmosphere, includes a heat treatment step in which the temperature is successively raised in a temperature range of room temperature to 200 ° C, and is maintained for 1 to 5 hours.

In case of carrying out the immobilization step under the iodine atmosphere, since the PCS fiber is composed of low molecular weight and melting occurs at a low temperature, in order to maintain the fiber shape due to intermolecular crosslinking defect at the fiber surface, in the present invention, The member is placed in a heat treatment furnace such as a vacuum oven, and the iodine powder is added thereto. Thereafter, the temperature is gradually raised from 100 to 200 ° C at a rate of 0.2 to 5 ° C / min in a vacuum or an inert atmosphere at various stages so that the iodine gas reacts with the fibers Keep for 2 to 6 hours and cool to room temperature. For example, the incompatibility may be carried out at a temperature of from about room temperature to about 100 to about 200 ° C in two to three steps, and the heat treatment may be performed for about one to three hours in each cycle.

When the incompatibility step is completed, the winding member in the state in which the PCS fiber is wound is subjected to the low temperature preliminary heat treatment step (S140). The infusibilized PCS fiber is put into a heat treatment furnace and heated to a temperature of about 200 to 300 占 폚 at a rate of 0.5 to 5 占 폚 / min under a high purity nitrogen and argon atmosphere, and 2 to 4 heat treatment cycles are given, ~ 3 hours of heat treatment is carried out.

Through the preliminary heat treatment step (S140), the fibers wound on the winding member can have a strength enough to maintain the tension. As described above, the low-temperature preliminary heat treatment step (S140) allows the fiber to be heat-treated in a subsequent heat treatment step by imparting strength to the fiber within a range that does not cause damage or shrinkage of the fiber. In the present invention, after the low-temperature preliminary heat treatment step (S140), the fibers are moved in a straight line tension to move The heat treatment proceeds at a high speed.

In the present invention, in order to minimize the damage of the PCS fiber wound on the specially designed winding member, the winding member is directly subjected to the infusibilization treatment, and after the preliminary heat treatment, the wound fibers are loosened and transported in a straight line, Thereby continuously producing SiC fibers at a high speed.

A known technique employs a method of winding spun PCS fibers onto an aluminum or plastic tube followed by carefully unwinding the fibers wound in a winder and placing them on a mesh such as a stainless steel mesh. In the process of loosening the wrapped PCS fiber, a very fragile fiber is subjected to a lot of cuts and the fiber-fiber is attached and the fiber bundle is completely cut off and is no longer usable. Furthermore, it takes a long time and manpower to loosen the fiber of 1000m. In the present invention, since the fibers wound on the winding drum have a low strength, there is a high possibility that the fibers fail to be loosened without breaking the fibers of several hundreds of meters or more, and when the fibers are loosened, the filament of the fiber bundle is cut off, The problem of dropping can be prevented.

In this case, since the fiber bundle is not placed in a certain circular shape, when the radius of curvature is small, the fiber is not shrunk to a certain degree, The nonwoven fabric has uneven mechanical properties throughout the fiber. The manufacturing method of the present invention can eliminate such nonuniformity of fibers.

The fiber after the low-temperature preliminary heat treatment step (S140) is released from the winding member and is separated and transferred to the tubular heat treatment furnace for the intermediate-temperature heat treatment step. After completion of the low-temperature preliminary heat treatment step (S140), the bundle of two to ten fibers can be bundled into one bundle using a winding device, or the bundle of bundles that have been previously unpacked can be directly bundled into a bundle while being transported directly into the tubular bundle . Before the coalesced fibers enter the tubular furnace, the bundle of fibers is straightened and tensioned as it passes through two or three rollers. (S150) is performed in a tubular furnace at a rate of 100 to 300 ° C / min from 200 ° C to 300 ° C, while the temperature is sequentially increased from 800 ° C to 1000 ° C. In the tubular heat treatment furnace, there are a plurality of sections having different temperatures to be applied in each section, and the rate of temperature increase is causally related to the conveying speed of the fibers to be conveyed while maintaining the tension. At the time of transport, use a winding machine to apply some tension to the fibers. The PCS fiber reacts easily with oxygen in the air at high temperature and oxidation occurs. Therefore, in order to prevent this, the air inlet and shutoff device is installed in three places in the tubular furnace, and the flow rate of the high-purity inert gas is controlled to flow the air to prevent the air from entering by the pressure difference.

After the intermediate-temperature heat treatment step (S150) is completed, a high-temperature heat treatment step (S160) is performed in which the temperature is raised to a high temperature of 1200 to 1400 ° C and heat-treated. In the high-temperature heat treatment step (S160), the heating rate is maintained in the range of 100 to 300 占 폚 / min as in the intermediate-temperature heat treatment step (S150).

Since the heat treatment is performed through the high-speed movement in the intermediate temperature and high-temperature heat treatment steps (S150 and S160), the productivity can be improved by shortening the time considerably. In addition, after the low-temperature preliminary heat treatment step (S140), since the heat treatment can be performed while being transferred in a straight line, the continuous process can be performed, thus simplifying the process. Further, in such a continuous transfer step, since the fiber amount is small, each of the fiber filaments can be treated at a uniform heat treatment temperature, and it is possible to manufacture a fiber having uniform physical properties.

In the mid-temperature heat treatment step (S150) and the high-temperature heat treatment step (S160), when the heat treatment is performed under a nitrogen gas atmosphere, high purity nitrogen gas (99.999% or more) If used, quality improvement can be achieved.

The SiC fiber can be obtained by subjecting the SiC fiber to a high-temperature heat treatment step (S160). After the SiC fiber is subjected to the sizing step (S170) with the polymer resin for protecting the surface of the fiber, the final SiC fiber is manufactured and wound.

Hereinafter, the production method of the present invention will be described in more detail with reference to concrete examples.

[Example]

Example 1

The PCS used in the present invention had a weight average molecular weight of 3400 and a number average molecular weight of 1400 PCS powder in a melting chamber and melted in a high purity nitrogen atmosphere at about 250 ° C to remove low molecular weight bubbles generated in the stirrer, A constant pressure was maintained during the spinning. In the spinning block, a metal powder was used to filter impure or gel-free PCS in the molten PCS. The number of spinning holes was 300, and a nozzle of 0.25 mm diameter was used. A guide roller was installed to concentrate the 300 fibers in the spinning, and a bundling agent was flowed in order to reduce the friction between the roller and the fiber and to eliminate the cut of the fiber. The radiated PCS fibers were wound in a winding drum at a speed of 450 to 550 m / min. The winding drum is made of stainless steel, and holes of 2 mm in diameter are drilled at intervals of 2 mm so that the stabilization gas and the inert gas can pass through during the unfusion (stabilization process) and heat treatment. The length of the PCS fiber wound around the winding drum is about 1000 to 1500 m, and the diameter of the spinning fiber is about 20 m or less. Iodine powder was put in a vacuum oven with a PCS wrapped in a vacuum oven. The temperature was raised from room temperature to 120 ° C at a rate of 1 to 5 ° C / min for 3 hours, and maintained at 0.2 ° C / min And maintained for 1 to 3 hours, and then cooled to room temperature to be subjected to an immobilization treatment. The infiltrated wound roll was placed in a heat treatment furnace and heated at a rate of 1 to 2 占 폚 / min from room temperature to 150 占 폚 in a high-purity nitrogen atmosphere, held for 1 hour, heated to 150 to 200 占 폚 at a heating rate of 0.5 占 폚, The temperature was raised from 0.2 to 300 ° C at a rate of 0.2 ° C / min, and then the temperature was maintained at the room temperature for 3 hours. The strength of the preliminarily heat treated stabilized fibers reached 60-100 MPa, which gave them sufficient strength for subsequent treatment. Five preliminarily heat-treated winding rollers were installed in a fiber unloading workbench, and the bundle of fibers was loosely pulled while rotating each of the winding rollers and piled up on a separate plate. In this way, the grass was uniformly wound around the winding tube to combine five fiber bundles into one bundle. Another method is to combine the five bundles of fibers unfrozen on the plate in advance into one bundle while directly feeding into the tubular using the transfer jig. Five plates with previously unbonded thermally treated fiber or fiber prepared in advance are installed so that they can be transferred to the heat treatment equipment. The prepared fiber bundle was not directly conveyed into the tubular furnace, but was passed through two or three rollers so that the fibers were aligned in a straight line, and tension was applied during conveyance. The tubular furnace consisted of 6 heating zones and the length was 300mm. The mid-temperature heat treatment temperature range of preheated fibers was 300 ~ 1000 ℃. The fiber was fed at a speed of 0.5 m / min. Since the fiber reacts with oxygen in the air at high temperature during the heat treatment, oxidation occurs. Therefore, in order to prevent air from the outside from flowing into the tubular body when the fiber is transferred, And a device for blowing nitrogen gas into the tubular furnace so as to maintain an inert atmosphere in the tubular furnace was installed near the inlet of the tubular furnace. At this time, the flow rate of the nitrogen gas was adjusted by controlling the flow rate of the nitrogen gas The role of blocking the air inflow and allowing the reaction gas to flow quickly to the outlet. The heat-treated fibers were allowed to pass through the roller while leaving the tubular structure, so that the fibers were maintained in tension. In addition, since the gas generated in the tubular furnace stays for a long time, it reacts with the fiber again and causes damage to the fiber surface. Therefore, a device for removing gas generated at the tubular outlet is installed. After the heat treatment at mid temperature, the fibers were immediately transferred into the tubular furnace for the final high temperature heat treatment. The high temperature heat treatment temperature is in the range of 1100 ~ 1300 ℃. The tubular furnace consisted of six heating zones, and the length of the confinement zone was 300 mm. The feed rate was 0.5 m / min. During the heat treatment, several rollers were passed through the tubular inlet so that high tension was applied to the fibers. In the high temperature heat treatment such as the mid-temperature heat treatment condition, the air flow rate was controlled by setting the air shutoff device at three places because the inflow of air caused a serious damage to the physical properties of the fiber. Even in the case of high temperature heat treatment, it was performed in a high purity nitrogen gas atmosphere. The high temperature heat treated fiber becomes SiC fiber. The SiC fiber from the hot tubular furnace was also provided with several stages of rollers outside the tubular outlet to maintain the tensile strength during the heat treatment. The fiber bundle made of the final SiC fiber was subjected to a sizing treatment process for coating the fiber surface to protect the fiber surface from dust and foreign matter and to prevent damage from the outside. As a sizing agent, polyvinyl alcohol (PVA) resin was diluted and coated at 0.5 wt%. The coating allowed the SiC fibers to pass through the PVA tubing while allowing the coating of the fibers to pass, while the excess resin was removed as it passed through the squeeze rollers. The coated SiC fibers cured the coated resin while passing through a tubular tube maintained at 150 < 0 > C. Finally, the sized SiC fibers were wound on a Woyt-viewb in a winding machine to produce a silicon carbide fiber product. The SiC fiber filaments prepared in this example were subjected to a tensile test under an air atmosphere at 1100 ° C. As a result, SiC fibers having a tensile strength of 2.1 GPa, a modulus of elasticity of 190 GPa and an oxygen content of 8 wt% were obtained. The change in the physical properties of the obtained SiC fiber was 1.5%, and the product obtained by the process developed in the present invention had a very high uniformity, and the manufacturing time was shortened compared with other processes due to the continuous coalescence.

Claims (5)

A winding step of winding a polycarbosilane fiber produced by melt spinning of polycarbosilane (PCS) on a winding member;
A stabilizing step of immersing the winding member in which the polycarbosilane fiber is wound in an atmosphere of iodine in an atmosphere of air or in an atmosphere of ozone gas;
A low-temperature preliminary heat treatment step of heat-treating the take-up member having undergone the stabilization step at a temperature of 300 ° C or lower to increase the strength of the fiber;
Temperature heat treatment step of loosening, separating and focusing the fibers from the winding member that has undergone the low-temperature preliminary heat treatment, maintaining the tension, heating the fiber from a temperature of from room temperature to 300 ° C to a temperature of from 800 to 1000 ° C, And
And a high-temperature heat treatment step of maintaining the tensile strength of the fiber subjected to the intermediate-temperature heat treatment step to a second temperature elevation from a temperature of 800 to 1000 ° C to a temperature of 1200 to 1400 ° C, followed by heat treatment.
The method according to claim 1,
The low-temperature preliminary heat treatment step is sequentially heated to a temperature of 200 ° C to 300 ° C in a heat treatment furnace, and the low-temperature preliminary heat treatment step includes a sub-heating step of 2 to 4 stages, and is maintained for 1 to 3 hours Wherein the heat treatment is performed at a rate of 0.2 to 5 ° C / min, and the heat treatment is performed.
The method according to claim 1,
Wherein the middle temperature heat treatment step or the high temperature heat treatment step is performed in the presence of an inert gas in a state in which the inflow of external air is blocked.
The method according to claim 1,
Wherein the winding member has a cavity formed therein and a plurality of opening patterns formed on a surface thereof.
The method according to claim 1,
Wherein the first temperature elevation and the second temperature elevation are performed at a rate of 100-300 DEG C / min. The method of manufacturing a silicon carbide fiber according to claim 1, wherein the intermediate temperature heat treatment step and the high temperature heat treatment step are continuous processes.

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