JPS6219527B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for making carbon yarns, particularly mesophase pitch-derived carbon yarns. Generally speaking, the usual industrial method of producing mesophase pitch-derived carbon yarns is to form a plurality of mesophase pitch fibers into a mesophase pitch yarn, heat set the mesophase pitch yarn to produce a thermoset yarn; Thereafter, the thermoset yarn is subjected to a thread line heat treatment in an inert atmosphere to pyrolyze and carbonize the thermoset yarn and produce a carbon yarn. Spry, US Pat. No. 3,503,708, describes a known method for making carbon yarn. According to prior art methods and teachings, the heat treatment step is carried out by stretching and tensioning the thermoset yarn into a line. In the prior art, this tension was found to be necessary to give the yarn good mechanical properties such as tensile strength and Young's modulus and to avoid fiber kinks and other surface defects in the yarn. are doing. The presence of surface defects on the carbon fibers in the carbon yarn adversely affects the subsequent processing leading to the industrial use of the carbon yarn. For example, a typical manufacturing operation performed on carbon yarn is to use a finishing material on the carbon yarn. Surface defects and broken fibers present in the carbon yarn tend to result in the carbon yarn retaining a relatively large amount of finish material. This makes the yarn difficult to dry and wind onto a bobbin. Additionally, most industrial applications require carbon yarns to be incorporated into composite structures with resins, and surface defects and broken fibers tend to contribute to carbon yarns retaining excessive resin loading. There is. This is not desirable. Industrial economics have prompted efforts to increase the production rate of carbon yarn. In these efforts, attempts have been made to reduce the time required for pyrolysis by increasing the speed of movement of the thermoset yarn during pyrolysis. In the present invention, it has been found that when the speed exceeds a certain speed, the occurrence of fiber breakage in the thermoset yarn increases significantly. This is thus a significant impediment to high production rates according to prior art methods. A careful and extensive analysis of the causes of breakage of thermoset yarns during pyrolysis revealed that the load-carrying capacity of thermoset mesophase pit yarns decreases considerably during pyrolysis. In particular, the thread-line breaking strength of a thermoset mesophase pit yarn decreases from its value at room temperature by about 1% of this slope as the temperature of the yarn in an inert atmosphere is increased to a temperature of about 700 to about 800°C. It was found that the value decreased to /4. Higher temperatures increase the breaking strength of the yarn. The discovery of this phenomenon represents a significant limitation on production rates according to prior art methods. In an attempt to avoid the above problem of reduced thread line breaking strength at elevated temperatures, experiments were carried out by collecting thermoset mesophase pitch yarn on a bobbin and then pyrolyzing and carbonizing the pitch yarn on the bobbin. It was implemented. The resulting carbon yarn had broken fibers and surface defects and was not considered satisfactory. Moreover, the bobbins used usually became damaged as a result of this heat treatment due to forces resulting from shrinkage of the thermoset yarn. Among the bobbins tested was one made from fine-grained graphite. This was used to obtain a bobbin compatible with yarn at elevated temperatures. In an attempt to avoid the problems that arose due to the use of bobbins, coreless packages of thermoset mesophase pitch yarn were used in the experiments described above.
package) was even used. Nevertheless, this coreless package resulted in unsatisfactory carbon yarns with surface defects. The present invention overcomes the problems of the prior art and provides many surprising benefits. The invention allows higher production rates at lower cost and with fewer problems than is possible according to prior art methods. Additionally, the heat treatment of the present invention requires less effort on the part of the manufacturer, and the present invention uses energy more efficiently than prior art methods. Even more surprising is that the present invention allows for the production of carbon yarns of exceptionally good quality compared to prior art methods and provides good control over the mechanical properties of the carbon yarns. It is what happens. Among the many benefits are the longer operating life and more stable furnace operation obtained in the through-line furnace used for one embodiment of the present invention. The term "pitch" as used herein refers to a carbonaceous residue derived from heat treatment of organic materials and consisting of a complex mixture of primarily aromatic organic compounds. Pitch is solid at room temperature and exhibits a wide melting or softening temperature range. When cooled from the melt, the pitch does not crystallize but becomes solidified. The term "mesophase" herein is synonymous with liquid crystal, ie, refers to a state of matter intermediate between a crystal and an isotropic liquid. Typically, materials in this state exhibit both anisotropic and liquid properties. The pitch can contain varying amounts of mesophase. The mesophase region in the pitch is observed to be optically anisotropic in the liquid state, and this anisotropy is maintained in the solid state. The term "mesophase pitch" as used herein means a pitch containing at least about 40% by weight mesophase. This is the lowest level at which the pitch can form a continuous anisotropic phase when dispersed by stirring or similar means. Preferably, the present invention provides at least about 70% by weight
It is carried out using a mesophase pitch having a mesophase of . The term "yarn" as used in the art refers to a plurality of fibers. Generally, the number of fibers will be at least about 1000 and usually about 2000. Further, the number of fibers may be 5000 or more. The term “mesophase pitch yarn” used herein
and "pitch yarn" refers to a plurality of mesophase pitch fibers forming a yarn or "as-spun" fibers. As used herein, the term "thermoset yarn" refers to pitch yarn that has undergone a heatset treatment. The terms "pyrolytic yarn" and "carbon yarn" herein refer to a thermoset yarn that has been pyrolyzed and carbonized, respectively. The term "winding angle" herein is used in connection with the winding of thermoset yarn onto a bobbin. According to its usage in the prior art, this term:
means the angle defined by that portion of the yarn wound on the bobbin and a plane perpendicular to the axis of the bobbin. The present invention is primarily directed to mesophase pitch-derived carbon yarns having an average Young's modulus of at least about 10×10 ⁶ psi for the individual carbon fibers in the carbon yarns. One embodiment of the present invention relates to a method for making a mesophase pitch-derived carbon yarn, and comprising: forming a plurality of mesophase pitch fibers into a mesophase pitch yarn; thermosetting said mesophase pitch yarn to produce a thermoset yarn; The thermoset yarn is wound onto a bobbin having a layer of carbon material that is thermally and mechanically stable and compressible and elastic at the temperatures used for pyrolysis and carbonization of the thermoset yarn; The method comprises the steps of subjecting the overlying thermoset yarn to a predetermined heat treatment in an inert atmosphere to pyrolyze and carbonize the thermoset yarn. Preferably, the mesophase pitch is at least about 70
It has a mesophase content of % by weight. Generally, the bobbin can take the form of a cylinder or a cylinder with end faces. The bobbin consists of a body made of stainless steel, high temperature alloy, ceramic, boron nitride or preferably graphite material. In addition, the bobbin may be provided with a compressible, elastic material such as carbon felt around its cylinder or cylindrical portion to absorb stresses resulting from expansion of the bobbin during heat treatment and contraction of the thermoset yarn during pyrolysis and carbonization. It is characterized by having a layer of carbon material. Typically, the cylinder or cylindrical portion of the bobbin is approximately
It can have an inner diameter of 3 inches and an outer diameter of 31/2 inches and a length of about 11 inches. The use of carbon felts for various industrial applications is well known and such materials are described in US Pat. No. 3,107,142. Preferably, the carbon felt is about 1/4 to about 1/12
It has a thickness of in. The mesophase pitch yarn includes at least about 1000 mesophase pitch fibers and typically about 2000 mesophase pitch fibers. The number of mesophase pitch fibers in the mesophase pitch yarn may be greater than that mentioned above. The invention is particularly useful for the industrial production of mesophase pitch-derived carbon yarns having approximately 2000 fibers. Difficulties in handling yarn and maintaining acceptable quality require countermeasures. Generally, the tension applied to the thermoset yarn during the winding process is from about 75 to about 300 g, preferably from about 150 to about
It is 200g. It is important to control the degree of tension that is exerted on the thermoset yarn as it is wound onto the bobbin. If the tension is too low, the resulting loosely wound bobbin will be difficult to handle in manufacturing operations, and the fibers in the yarn will not exhibit the straightness needed to obtain good mechanical properties. . If the tension is too high, the fibers near the core of the bobbin become deformed and other problems occur. In one embodiment of the invention, the temperature is about 1300°C.
The heat treatment is taught to be carried out by increasing the temperature at about 50 to about 100° C./hr to about 1 to 2 hours and maintaining this temperature for about 1 to 2 hours. Similar through-line heat treatments are known. This heat treatment is referred to in the art as "pre-carbonization," although carbonization actually occurs. The carbon yarn obtained from this treatment has a number of properties that make it suitable for a range of industrial applications. However, if it is desired to improve mechanical properties such as tensile strength and Young's modulus, a through-line treatment as used in the art is performed. This is done by unwinding the yarn and sending it to a threading line treatment at a temperature of approximately 2500°C. Surprisingly, this threading line process can be carried out using relatively high tensions with little breakage of the fibers. By using the present invention, after the pre-carbonization treatment,
It becomes possible to perform threading line processing using tensions that are generally higher than those used according to prior art methods. The use of higher tensions during threading line treatment typically results in 10 to 40
% yields carbon yarn with high Young's modulus. The use of pre-carbonization has several other benefits. During this treatment, the thermoset yarn passes through a well-known transition stage while gases are expelled from the fibers. The heating equipment must be designed to withstand these gases, as they can be corrosive and highly reactive. To some extent, the tendency for gases to be reactive at 1300°C is similar to that at 2500°C.
lower than typical high pyrolysis and carbonization temperatures such as °C. Thus, the two-stage pyrolysis and carbonization operation allows the second heating device to be less resistant to attack, and thus the second heating device does not have to be a nearly expensive device and can be used easily. The equipment generally has a long useful operating life. Typically, the mesophase pit yarn is heated to about 200 to about 400°C in air or some other oxidizing atmosphere.
It is thermally cured by applying a temperature of . Winding of thermosetting yarn onto a bobbin can be carried out using a range of winding angles. It has been found that a relatively wide range of angles from about 15 DEG to about 30 DEG can be used in conjunction with bobbins without edges for the pre-carbonization process described above using maximum temperatures of about 1300 DEG C. For bobbins with ends, 0° or parallel winding should be used to avoid yarn falling off the ends of the bobbin. When a bobbin with parallel windings is heat treated to about 3000℃, ^the
Good quality yarns can be produced with strengths greater than or equal to about 100 x 10 ⁶ psi and Young's modulus greater than about 100 x 10 6 psi. The present invention is particularly directed to carbon yarns having at least 2000 carbon fibers since the industrial problems are overcome and avoided. However, the present invention provides a method of forming mesophase pitch fibers, thermosetting the mesophase pitch fibers, winding the thermoset fibers onto a bobbin, and applying the thermoset fibers on the bobbin in an inert atmosphere. The present invention also relates to a method for producing mesophase pitch-derived carbon fibers comprising the steps of subjecting the thermoset fibers to a predetermined heat treatment to pyrolyze and carbonize the fibers. Further objects and advantages of the invention will become apparent from the following detailed description and claims. For a fuller understanding of the nature and objects of the invention, reference should be made to the following detailed description taken in conjunction with the accompanying drawings. Certain embodiments are chosen to illustrate the practice of the invention in the accompanying drawings and detailed description. Next, FIGS. 1 to 4 will be explained. FIG. 1 shows the main steps in the industrial production of carbon yarn from mesophase pitch. Spinning device 5
are 2000, each with a diameter of approximately 13 microns
The mesophase is used to spin pitch fibers.
These mesophase pitch fibers form mesophase pitch yarn 6 and enter a thermosetting device 7.
The thermosetting yarn 8 is produced by a thermosetting device 7 and transferred to a pyrolysis and carbonization device 9 for heat treatment to produce a carbon yarn 11, which is wound onto rolls in a collecting device 12. .
Typically, the thermosetting yarn 8 between the devices 7 and 9 is subjected to winding operations onto a paperboard bobbin and unwinding operations therefrom. Attempting to pass the thermosetting yarn 8 through the apparatus 9 at relatively high speeds resulted in load fluctuations on the thermosetting yarn 8, which produced carbon yarns 11 of poor quality. FIG. 2 shows a spinning apparatus 13 for producing 2000 mesophase pitch yarns to form mesophase pitch yarn 14. FIG. The mesophase pitch yarn 14 enters a thermosetting device 16 which produces thermoset yarn 17. A collecting device 18 collects the thermoset yarn 17 onto a bobbin. Figures 3A and 3B illustrate two embodiments of bobbins suitable for practicing the present invention. The bobbin 19 includes a body 21 and a carbon felt material 22 wrapped around the body 21 and having a beveled portion 23 to provide a smooth continuous bond. Carbon felt material 22 can be attached to body 21 with adhesive or even with "masking" tape 24. Since the tape 24 carbonizes at high temperatures,
This is only used to hold the carbon felt material 22 in place for an hour until the thermosetting yarn is wound onto the bobbin 19. Typically, the inside diameter of body 21 is about 3 inches and the length of body 21 is about 11 inches. Carbon felt material 22 has a thickness of approximately 1/4 inch. FIG. 3B shows a bobbin 25 that can be used in connection with the present invention. Bobbin 25 differs from bobbin 19 in that it has an end plate 26. The bobbin 25 is a thermosetting yarn.
allows zero angle or parallel winding of the yarn without encountering problems with it falling off the ends of the yarn. In FIG. 4, the bobbin with thermosetting yarn is
It undergoes heat treatment in a pyrolysis and carbonization device 27. In one embodiment of the invention, no additional heat treatment is performed. In another embodiment, yarn 28 is subjected to thread line processing in carbonizer 29 at about 2400°C. This produces carbon yarn 30 which is transferred to a collection device 31 where it is wound onto other bobbins for storage and handling. In the following examples, the bobbins used were made from commercially available fine-grained graphite. Examples 1-8 Mesophase pitch yarns having 2000 pitch fibers, each approximately 13 microns in diameter, were prepared and heat set according to conventional methods. The thermoset yarn was collected onto a bobbin made from fine grained graphite and having an inner diameter of about 3 inches, a length of about 11 inches, and a layer of carbon felt about 1/4 inch thick. The bobbin had no end faces and the winding tension was about 150 g. A winding angle of approximately 20° was used. For each sample in these examples, the yarn collected was approximately 6000 ft in length, and the pyrolysis and carbonization treatment increased the temperature at a rate of approximately 50°C/hr until it reached 1300°C. The test was carried out in a nitrogen atmosphere by holding for about 2 hours. The temperature was allowed to return to room temperature and the pyrolyzed yarn was then passed through a through-line carbonizer for further carbonization. This carbonization device has a nitrogen atmosphere and has a
It had a furnace temperature of 2400℃. The average linear tension in the carbonizer was about 800 g. Table 1 shows the tensile strength and Young's modulus of each example.

TABLE Examples 1-8 exhibited excellent mechanical properties and yielded carbon yarns that were well parallelized and virtually unraveled. Example 9 Make a mesophase pitch yarn as in Example 1,
The pitch yarn was then wound around a bobbin having end faces but otherwise similar to the bobbin used in Example 1. Parallel winding was used with a tension of about 200 g. The heat treatment rate was the same as in Example 1 except that the final temperature was approximately 3000°C. No loading line treatment was used. The resulting carbon yarn had a tensile strength of about 400×10 ³ psi and a Young's modulus of greater than 100×10 ⁶ psi. Although the configuration of the present invention has been specifically illustrated and described above, it should be understood that the present invention is not intended to be limited to these specific examples, as many changes and modifications can be made by those skilled in the art.

[Brief explanation of the drawing]

FIG. 1 is a schematic block diagram of an industrial operation for producing carbon yarn, with 6 indicating mesophase pitch yarn, 8 thermosetting yarn and 11 carbon yarn. FIG. 2 is a block diagram illustrating some of the steps of the present invention, with 14 indicating mesophase pitch yarn and 17 indicating thermosetting yarn. Figures 3A and 3B show two specific examples of bobbins for use in the present invention, with reference numerals 19 and 25 indicating the bobbins. FIG. 4 is a schematic block diagram of the invention after the step shown in FIG. 2, with reference numeral 28 indicating the carbon yarn and 30 indicating the carbon yarn having undergone threading line processing.

Claims (1)

[Scope of Claims] 1. A plurality of mesophase pitch fibers are formed into a mesophase pit yarn, the mesophase pit yarn is thermally cured to produce a thermoset yarn, and the thermoset yarn is subjected to pyrolysis and pyrolysis of the thermoset yarn. winding onto a bobbin having a layer of carbon material that is thermally and mechanically stable and compressible and elastic at the temperatures used for carbonization, and applying the thermoset yarn on the bobbin in an inert atmosphere. A method for producing a mesophase pitch-derived carbon yarn comprising the steps of subjecting the thermoset yarn to a predetermined heat treatment to pyrolyze and carbonize the yarn. 2 The tension exerted on the thermosetting yarn between the windings is approximately
75 to about 300 g. 3 The tension exerted on the thermosetting yarn between the windings is approximately
3. The method of claim 2, wherein the amount is from 150 to about 200 g. 4. The method of claim 1, wherein the heat treatment comprises raising the temperature of the thermoset yarn to about 1300C. 5. Heat treatment is performed by increasing the temperature to approximately 50~1300℃.
5. The method of claim 4 carried out by increasing the temperature at about 100°C/hr and then maintaining the temperature at about 1300°C for the predetermined time. 6. The method of claim 5, wherein the temperature of about 1300<0>C is maintained for about 1 to about 2 hours. 7. The method of claim 1, wherein the winding step is carried out at a winding angle of about 15 to about 30 degrees. 8. The method according to claim 1, wherein the winding step is performed in substantially parallel winding. 9. The method of claim 1, wherein the mesophase pitch yarn comprises at least about 1000 mesophase pitch fibers. 10. The method of claim 1, wherein the mesophase pitch yarn comprises at least about 2000 mesophase pitch fibers. 11 The mesophase pitch yarn contains about 2000 mesophase pitch fibers, the tension applied to the thermoset yarn during winding is about 75 to about 300 g, and the winding process is about 15
The winding angle is ~30°, and the heat treatment is
Claim 1 carried out by increasing the temperature at about 50 to about 100°C/hr to about 1300°C and then maintaining the temperature at about 1300°C for about 1 to about 2 hours. the method of.