KR0140867B1 - Improved Pitch Carbon Fiber Spinning Method - Google Patents

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Description

Improved Pitch Carbon Fiber Spinning Method

1 is a partial cross-sectional schematic of a melt spinning pack useful for practicing the present invention,

2 is a spinneret perspective view showing a rectangular opening into a spinneret.

The present invention relates to a method for producing pitch carbon fibers in which no cracks are formed in the axial direction of the fibers.

It is already well known that carbon fibers produced from pitch can be axially cracked to lower the strength of the fibers, thereby reducing their usefulness and value. The roots of the cracks were found to be due to the radial fibrous microstructures, rather than irregular or onion shell morphology. A description and drawings of the cracking phenomena and various fiber microstructures are described in US Pat. No. 4,504,454. Approaches to solving this problem are known in the art. US Patent No. 4,504,454 focuses on radiation conditions. Other references, such as US Pat. No. 4,331,620, US Pat. Nos. 4,376,747, and 4,717,331, focus on how to insert an insert that changes pitch flow within the spinneret to form the desired non-radial microstructure in the fiber. Leave. Manipulating spinnerets with movable parts on a commercial scale is very difficult. Similarly, maintaining the continuity and uniformity of fibers spun from spinnerets having a granular porous structure or a very fine porous structure inside the spinneret is very difficult on a commercial scale.

Another approach to the problem is to modify the geometry of the spinneret itself (see, for example, US Pat. Nos. 4,576,811 and 4,628,001, and Japanese Patent Laid-Open No. 61 (1986) -75820 and No. 1). Sub) 61-75821 and Japanese Patent Application No. 59 (1984) -168127). U. S. Patent No. 4,576, 811 maintains a typical spinneret configuration, but examines the effect by varying the internal angle in the region that combines the counterbore and capillary. US Pat. No. 4,628,001 describes a method for making mostly non-circular fibers that may be undesirable for some applications using non-circular spinnerets. The use of non-circular spinnerets, including some small diameter circular fibers, produces strong fibers while having manufacturing and operational difficulties. The Japanese Patent Office describes spinnerets with varying cross sections through which the pitch passes. These spinnerets can produce circular fibers, but unusual spinneret profiles can lead to difficulties in manufacturing and cleaning spinnerets.

The present invention can produce fibers that are generally circular in cross section with spinnerets that are relatively simple to manufacture and store. This fiber is high in strength thanks to its irregular microstructure that prevents axial cracking. The same is true for fibers having a large diameter. Strong continuous carbon fibers with large diameters are difficult to manufacture and have not been available until now. Accordingly, the present invention relates to a method for producing fibers that are useful for both large diameter and small fibers as well as strong continuous fibers of large diameter.

Axial cracking in a nearly circular carbon fiber can be prevented by using the arrangement of the conduits of the present invention in which the pitch is spun. The method of the present invention comprises spinning a mesophase pitch through a spinneret having a circular cross-section discharge capillary and having a high aspect ratio opening at its inlet. Openings may be trapezoidal, elliptical, parallelogram, etc., but should be long and narrow. Rectangular openings are preferred. It is preferable that aspect ratio (the value which divided opening length by width) is 3: 1 or more, and it is more preferable if aspect ratio is 5: 1 or more. The opening must be larger than the cross sectional area of the capillary. 2: 1 or more are preferable, and, as for these area ratio, 8: 1 or more are more preferable. A preferred method is to use a spinneret with an outlet opening with a counterbore larger than the capillary diameter upstream of the capillary and an opening with a larger aspect ratio cross-sectional area than the counterbore's cross-section. The area of the opening is preferably 10% to 70% of the counterbore area, more preferably in the range of 25 to 45% of the counterbore area. For rectangular openings, the shorter length of the rectangle is approximately equal to the length of the capillary diameter of the spinneret.

The method of the present invention is sufficiently effective to prevent the formation of axial cracking in the fibers and can be used to produce strong, continuous, nearly circular cross-section, large diameter carbon fibers. The diameter of these fibers is 30 to 100 µm, and the strength after stabilization and carbonization is at least 375 Kpsi minus the value of the diameter (µm) of the fibers. Preference is given to fibers having a diameter of 40 to 80 μm. Such large diameter fibers are useful as reinforcements in metal, ceramic or plastic matrices.

The present invention will be further described with reference to the drawings. 1 schematically shows a cross section of a spin pack useful in the practice of the present invention. The pack consists of a spinneret 10, a wedge 15, a distribution plate 17, and a sorting pack 19 which supports the filtration medium 20 (see US Patent No. 3,896,028 (Philips)) And filtration media are optional elements. Related support means, gasketing means, heating means and attachment means are not described in FIG. The externally supplied molten pitch (not listed) flows through the pack element in reverse order, continuously filtered through the filtration medium 20 and plurally through one of the plurality of coaxial holes 18 in the distribution plate 17. It flows toward one of the spinnerets counterbore 24, and passes through an opening 16 in the wedge 15 to allow the flow of pitch to be in the form of a ribbon. The pitch is then extruded through the spinneret capillary 22. The improvement in the spinneret 10 consists of a wide inlet 26 with a tapering neck 28 connected to the counter bore 24. The counter bore 24 is connected to the capillary 22 via an inlet 30 with a tapering neck 32. FIG. 3 of US Pat. No. 4,576,811 details the features within the capillary inlet 30 and the tapering neck 32. FIG. 2 shows in greater detail the arrangement of the openings 16 (which are preferably rectangular in this preferred embodiment) with a high aspect ratio of the wedge 15 relative to the axis of the capillary 22 in the spinneret 10. This arrangement is repeated for each of the various capillaries in the spinneret, and the molten pitch flow is in the form of a ribbon, which is advantageous during the passage from the distribution plate 17 to the spinneret 10. The pitch flow stream generally remains in a plane including the axis of the spinneret capillary 22. The figure shows a wedge plate separated from the body of the spinneret used to provide a useful fluid arrangement opening. However, other arrangements in which the high aspect ratio openings are contained within the spinneret body are also within the scope of the present invention.

The opening preferably reduces the cross-sectional area of the pitch flow by about 10 to 70%, preferably about 25 to 45%, as compared to the spinneret counter bore area. If the opening that determines the shape of the flow is too wide (i.e., the aspect ratio of the wedge opening is too small), the advantages of the present invention cannot be achieved. In addition, if the fluid limiting force is too large (ie, the wedge openings are too narrow) the process continuity will be affected. Unless the continuous flow of pitch through the opening is limited, the aspect ratio may be 25: 1 or more. The rectangular shape is the preferred flow arrangement, but other arrangements may be used that provide substantially ribbon flow. Devices used to produce pitch carbon fibers are typically empirically developed from the larger melt spinning art. Often insufficient understanding hinders this improvement. However, it is understood that the molten pitch, non-viscous liquid crystalline material has a very long relaxation time (memory) compared to conventional organic polymers and thanks to this property beneficial results are obtained by the practice of the present invention.

The long relaxation time of the pitch also seems to cause some deformation from the circular cross section observed in the fibers produced by the method of the present invention. The fibers are almost circular, but the fibers spun through the rectangular openings upstream of the circular spinneret, in particular the fibers of large diameter, are slightly elliptical. Their aspect ratio is 1.1 or less. In other words, the long dimension of the cross section is 1.1 times or less larger than the short side of the cross section.

After spinning in the manner described above, fiber stabilization, carbonization and any graphitization are carried out in a conventional manner. After producing the spun or raw filament or yarn as described above, it can be processed (temporary or permanent) for ease of handling and / or protection. Stabilization in air is carried out on a bobbin (see US Pat. No. 4,527,754) at 250 to 380 ° C., preferably according to the process described in US Pat. No. 4,576,810. Large diameter fibers require long stabilization times; A useful rule of thumb is that a stabilization time of one hour per micron of large fiber diameter is required. Thus, 30 μ fibers should be stabilized for at least about 30 hours to account for reference points in developing the optimal stabilization protocol for at least this diameter fiber. After stabilization, the yarns or fibers are hermetically stripped or precarbonized in an inert atmosphere at a temperature of 800 to 100 ° C. Subsequent carbonization can proceed more smoothly and the formation of strength limiting voids is reduced or almost eliminated. Precarbonization is generally carried out for 0.1 to 1 minute. Carbonization in an inert atmosphere is carried out at 1000 to 2000 ° C., preferably 1500 to 1950 ° C. for about 0.3 to 3 minutes. At this time, surface treatment and / or processing application is beneficial for improving fiber performance (eg adhesion) in its final application (eg composite). If desired, the graphitization can be carried out by heating at 2400 to 3300 ° C., preferably 2600 to 3000 ° C., for at least 1 minute in an inert atmosphere. During the heating step described above, treatment for longer periods of time did not appear to be harmful.

375-D로 요약된다, 이 방정식에서, S는 강도(Kpsi)이고, D는 섬유직경(㎛)이다.The graph of tensile strength versus diameter for the preceding carbon fiber decreases with increasing fiber size, showing a curve with large tensile strength if the fiber is small. When the fiber diameter exceeds 30 mu m, the curve becomes flat, but it tilts downward as the fiber diameter increases. The graph from the data for the macrofibers of the present invention shows a curve that is almost similar to that of the prior art fibers, but the tensile strength is greater, if the graph for a diameter of 30 μm or less is treated with a straight line, The strength-to-diameter relationship for diameter fibers is approximately equation S

Summarized as 375-D, in this equation, S is strength (Kpsi) and D is fiber diameter (μm).

The present invention is intended to be more fully understood by reference to the following non-limiting examples.

(Example 1)

Midcontinent refinery decant oil is topping at atmospheric pressure to obtain a residue above 454 ° C. Analysis of the residue by C ¹³ NMR showed 91.8% carbon, 6.5% hydrogen, 35.1% Conradson carbon residue and 81.6% aromatic carbon. The light oil residue is thermally immersed at 393 ° C. for 6.3 hours and then vacuum deoiled to obtain the thermally immersed pitch. This pitch is tested in 16.4% tetrahydrofuran insolubles 1 g pitch in 20 ml THF).

The pitch obtained by the above method is pulverized and then dissolved in toluene (solvent: pitch weight ratio 1: 1) by heating to reflux for about 1 hour. The solution was passed through a 1 μ filter and then mixed with a sufficient amount of toluene / heptane (98: 2) (antisolvent) such that a) the volume ratio of the toluene / heptane mixture was 99: 1 and b) the volume of mixed solvent / pitch The weight ratio should be 8: 1.

After refluxing for 1 hour, the mixture is cooled to ambient temperature and the precipitated solid is centrifuged. The cake is washed with additional anti-solvent and then dried in a rotary vacuum oven. Several of these batches are mixed, melted at about 400 ° C., then passed through a 2 μ filter and extruded to obtain pellets. At this time, the pitch pellet is 100% mesophase containing less than 0.1 weight% of quinoline insoluble matter (ASTM 75 degreeC) as measured by the polarization microscope method.

The pellet is placed in a screw extruder with an exit temperature of 350 ° C. and remelted and spun at about 360 ° C. through 480 spinnerets with 4 in diameter holes. The holes are arranged in a circle of five concentric circles (96 holes per circle), located 1/2 inch outside the surface of the spinneret. Each hole is US Patent 4,576,811 (especially Riggs et al. , As specified in Example 2), a counter bore with a diameter of 0.055 inches, consisting of a capillary tube with a diameter of 200 microns and a length of 800 microns (L / D = 4) and an inflow angle of 80/60 degrees. Insert a wedge of 0.005 in thickness between the spinneret and the distribution plate. The wedge has a number of 0.008 x 0.10 in grooves aligned with each spinneret hole as shown in FIG. These grooves allow the pitch to flow in ribbon form into the spinneret.

The spinneret is externally heated to about 360 ° C. and the spinner cell comprises an outer quench tube, about 6 inches in diameter and 5 ft in length, screened 6 inches at the top for quench air at room temperature. Aspiration is performed with a 4 in. Long tapered (3 to 2 · ½ in) central column. Air-cooled, wound at a rate of 550yd per minute in a spool described in US Patent No. 4,527,754 to Flynn, a silicone oil processing product sold by Takemoto oil and Fat Co. To the spun filament or raw fiber.

Several spool packages, each containing about 1 lb of yarn, are heated in air to batch stabilize. Then all are heated to 170 ° C. for 80 minutes. The temperature is then increased to 245 ° C. in several steps over several hours and then held at 245 ° C. for an additional about 2 hours.

The carbonization was combined from six stabilized packages fixed on the krill and passed through a pre-carbonization oven at a temperature of 600 to 800 ° C. and a 3 ft length at a speed of 12 ft / min under tension of its own weight (about 150 g), A 2880 filament tow (usually 3K) is formed by passing a 19 ft long carbonaceous oven comprising an inlet zone of 1000 to 1200 ° C., a carbonization zone of 1950 ° C., and an outlet zone of 1000 to 1200 ° C. The fibers are held at the carbonization temperature for about 1 minute. The carbonized yarn is passed through a 19-foot chamber containing dry room temperature air mixed with 0.098% (980 ppm) of ozone supplied at a rate of 1 cfm. 1% solution of epoxy resin in water (CMD-W55-5003, commercially available from Celanese Corporation) using the method and apparatus described in Bell, Jr., US Pat. No. 4,624,102. To be processed. The yarn thus treated is cured at 350 ° C. and then cleaned by passing through a guide as described in Winkler, US Pat. No. 4,689,947. Ten representative bobbins of carbonized yarn thus obtained were selected and single fibers with a gauge length of 1 '' according to the method of ASTM 3379 on ten samples from each bobbin (average diameter 9.4μ). The tensile property of the is measured. The average physical properties obtained were 478 Kpsi in strength, 52 Mpsi in modulus and 0.9% elongation. Less than 1% of the filaments observed in optical micrographs of yarn bundles show longitudinal cracking. The microstructure of the individual filaments is irregular in all cases, and the degree of microstructure control and homogeneity differs from usual.

Except for those made from other batches of the same type of pitch without grooved fine wedges, ten representative bobbins manufactured and characterized as described above exhibit the following average properties. Diameter of 9.3μ, strength of 418Kpsi, modulus of 53Mpsi and 0.7% elongation, which are discernible differences. In addition, 33% of the filaments observed in the optical microscope limb cross section at an hour show cracks in the longitudinal direction. The observed microstructures are typically radial structures.

(Example 2)

Example 1 is repeated except that different batches of the same type of pitch are used and different amounts of antisolvent are used to achieve a toluene / heptane mixture with a volume ratio of 90:10.

This change results in an expected spinning temperature of 355 ° C to 346 ° C for the pitch used in Example 1. Expected spinning temperature refers to the temperature at which the pitch represents a melt viscosity of 630 p (POISE) as measured using an Instron capillary viscometer. The spinneret also has 500 holes for 480 holes and an inlet angle of 135 for 80/60.

After carbonizing the fibers as in Example 1, the same equipment was graphitized to operate at a maximum temperature (2550 ° C.) with a residence time of about 30 seconds. The resulting graphite fibers have on average (25 breaks / 2 bobbins) 609 kPSI strength, 135 Mpsi modulus and elongation of 0.55%. No longitudinal cracking was observed, and the microstructure was irregular.

(Example 3)

Example 1 is repeated as follows. A pitch similar to the pitch used in Example 1 is used. The spinneret holes are the same shape as in Example 1 but twice the size (ie, the capillary diameter is 0.016 inches). The wedge opening is rectangular with a width of 0.010 inches. The diameter of the spun fiber is 48 μm and the strength exceeds 327 Kpsi. Microscopic observation of the fiber cross section shows irregular microstructures and the fibers have little or no axial cracking.

Claims (14)

A method of spinning a nearly circular carbon fiber from a pitch by extruding a molten mesophase pitch through a spinneret having a circular cross-section discharge capillary, wherein the molten pitch has a large aspect ratio and an area much larger than the cross-sectional area of the capillary. Flow firstly through the opening. The method of claim 1 wherein the aspect ratio of the openings is at least 3: 1. The method of claim 1 wherein the aspect ratio of the openings is at least 5: 1. The method of claim 3 wherein the opening is rectangular. The method according to any one of claims 1 to 4, wherein the ratio of the area of the opening to the area of the capillary is at least 2: 1. The method of any one of claims 1 to 4, wherein the ratio of the area of the opening to the area of the capillary is at least 8: 1. 5. The spinneret of claim 1, wherein the spinneret has a counterbore upstream of the capillary and downstream of the opening, the counterbore having a diameter larger than the capillary and the opening area at the inlet of the spinneret is counterbore. 10 to 70% of the cross-sectional area, wherein the ratio of the area of the opening to the area of the capillary exceeds 2: 1. The spinneret according to any one of claims 1 to 3, wherein the spinneret has a counterbore upstream of the capillary and downstream of the opening, the counterbore having a diameter larger than that of the capillary, and the opening at the inlet of the spinneret is rectangular, with an area of the counterbore. 25 to 45% of the cross-sectional area, wherein the ratio of the area of the opening to the area of the capillary exceeds 8: 1, and the small rectangular opening is about the same as the diameter of the capillary. The method according to any one of claims 1 to 4, wherein the diameter of the fiber after stabilization is 30 to 100 µm. The method according to any one of claims 1 to 4, wherein the diameter of the fiber after stabilization is 40 to 80 µm. A continuous carbon fiber having a circular cross section in general, having a diameter of 30 to 100 µm and having a strength of 375 Kpsi or more minus the value of the fiber diameter (µm). The fiber of claim 11 having a diameter of 40 to 80 μm. The molten mesophase pitch is produced by first passing through an opening having a large aspect ratio and an area much larger than the cross-sectional area of the capillary of the spinneret, and then spinning through a spinneret having a circular cross-section discharge capillary, the cross section being generally circular and having a diameter Continuous carbon fiber of 30 to 100 μm. The fiber of claim 11 having a diameter of 40 to 80 μm.

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