High tensile strength, high Young's modulus carbon fiber, free from holes and voids having a statistical probability of holes detected by a standard plasma etching test of less than about 2%, a tensile strength of at least about 150 kg/mm2 and a Young's modulus of at least about 15×103 kg/mm2. The carbon fiber has excellent homogeneity of internal structure and excellent reliability as a composite material.
A process is provided for producing a high performance, high quality carbon fiber having excellent productivity and operability and requiring only a short time for oxidation. The process comprises converting an organic polymeric fiber (preferably an acrylic fiber) to an oxidized fiber, comprising repeatedly bringing said fiber into contact with the surface of a heated body such as a heated roll or heated plate at about 200°-400°C in the presence of an oxidizing gas for a contact time per single contact of said fiber with the surface of the heated body of less than about 1 second, and heating the resulting oxidized fiber in an atmosphere of an inert gas at a temperature of at least about 800°C to thereby convert the oxidized fiber to a carbon fiber.
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17. A process for producing a carbonizable oxidized fiber which comprises oxidizing an organic polymeric fiber in an oxidizing atmosphere by intermittently contacting and removing said organic fiber on and from a heated body having a surface temperature from about 200° to about 400°C wherein the contact time of said organic fiber on the heated body per single contact is less than about 1 second and the temperature of said oxidizing atmosphere is maintained lower than the surface temperature of said heated body.
1. A process for producing a carbon fiber having high tensile strength which comprises oxidizing an organic polymeric fiber in an oxidizing atmosphere by intermittently contacting and removing said organic fiber on and from a heated body having a surface temperature from about 200° to about 400°C wherein the contact time of said organic fiber on the heated body per single contact is less than about 1 second and the temperature of said oxidizing atmosphere is maintained lower thn than the surface temperature of said heated body, and then carbonizing the oxidized fiber in a non-oxidizing atmosphere at a temperature above about 800°C
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This is a division of application Ser. No. 622,955, filed Oct. 16, 1975, now abandoned.
The present invention relates to a ) and 20 parts of methylethylketone wound up around a wooden frame and cured at 200°C for 30 minutes by a hot air dryer. Thereafter, a tensile test is carried out.
1. Tensile Test Conditions
| ______________________________________ |
| Chuck Air chuck(surface: soft asbestos) |
| Sample length 1. |
| 200 mm |
| Tensile speed 5mm/min |
| ______________________________________ |
2. Cross Sectional Area
A 1.5 m long carbon fiber multifilament is precisely cut and its weight W (g/m) is measured. On the other hand, the specific gravity p (g/cm3) of the multifilament is determined by Archimedes' method. Then, the cross sectional area S of the carbon fiber multifilament is: ##EQU1## 3. Tensile Strength
From the breaking load P (kg) of the tensile test, tensile strength TS is: ##EQU2## 4. Young's Modulus
The initial gradient A (kg/mm) of a "tensile strength (kg)-elongation (mm) curve" of the tensile test is determined and the Young's modulus YM is determined from the following equation. ##EQU3##
Various commercial carbon fibers having a high tensile strength and high modulus were selected to provide for the standard plasma etching test defined above.
The statistical probabilities of the hole formation being detected in the standard plasma etching test were measured and are shown in Table I.
The tensile strengths and Young's modulus are also shown in Table I.
It is shown that all of the commercially available carbon fibers have latent holes as tested in the standard plasma etch test, and their statistical probabilities were more than 2%.
Moreover, Sample C in Table I has both visible and latent holes.
| TABLE I |
| __________________________________________________________________________ |
| Carbon fiber characteristics |
| Probability of |
| Precursor |
| Tensile Strength |
| Young's modulus |
| hole formation |
| Fiber |
| fiber (Kg/mm2) |
| (×103 kg/mm2) |
| (%) Reference |
| __________________________________________________________________________ |
| A Cellulose |
| 84 4 0 |
| B Cellulose |
| 190 35 more than 90 |
| FIG. 7 |
| C Polacrylonitrile |
| 322 19.1 19 FIG. 8 |
| D Polyacrylontrile |
| 300 22 9 |
| E Polyacrylonitrile |
| 305 21 6 FIG. 9 |
| F Polycrylonitrile |
| 280 23 more than 80 |
| FIG. 10 |
| __________________________________________________________________________ |
An acrylic fiber of 1,500 filaments which is obtained by spinning a copolymer consisting of 99 mole % of acrylonitrile and 1 mole % of 2-(hydroxybutyl)acrylonitrile is heated by intermittent contact on a heated pin of 100 mm in diameter and 100 mm in length and is converted to an oxidized fiber.
The surface temperature of the heated pin is maintained from 285° to 290°C in the oxidation step.
Table II shows the relations between contact time (T1) and the filament bonding of the oxidized fiber which resulted. The filament bonding is caused when the contact time T1 of the fiber on the surface of the heated pin is more than 1 second.
| TABLE II |
| ______________________________________ |
| Contact Time (T1) |
| (sec) Filament Bonding |
| ______________________________________ |
| more than 7 Filament bondings present |
| about 5 Filament bondings partially |
| present |
| less than 1 Filament bondings absent |
| ______________________________________ |
An acrylic fiber of 3,000 filaments obtained by spinning a copolymer consisting of 99 mole % of acrylonitrile and 1 mole % of methylacrylate, is continuously converted to oxidized fibers using an oxidation machine as shown in FIGS. 5 and 6 of the drawings. In FIGS. 5 and 6 a group of heated rollers 20, 21, 22, 23, 24, 25, 26, 27 is covered with a simple cover 29. This oxidation machine comprises four pairs of heated rollers (20,21), (22,23), (24,25) (26,27). These are stainless steel rollers, 200 mm in diameter and 300 mm in length, and have internal heating elements (hot roll). These heating elements are joined to a 220 V source and controlled electrically with a two-position control.
The surface temperature of the heated rollers is measured using an Anritsu Keiki surface thermometer, type HP-4P.
The acrylic fibers are roller over each pair of rollers, one of a pair of rollers is capable of being adjusted in the axial direction of the roller to conduct a controlled operation. At the inlet of each roller pair, yarn guides 16, 17, 18, 19 are attached in order to control the yarn line. The acrylic fibers are oxidized to form oxidized fibers at 30 meters per minute of yarn line speed, wherein the contact time T1 is 0.63 seconds. The total of the contact times T1 is 7.7 minutes, and the temperature of the atmosphere in the vicinity of the heated roller is 110°C during oxidation. The resulting oxidized fibers are pliable and have no filament bonding. The water absorbability of the oxidized fibers, as measured, was 6.7 wt %. The oxidized fibers were embedded in a resin comprising 2 parts of parafin, 1 part of ethylcellulose and one part of stearic acid, and were cut into slices of 7 microns in width using a microtome, obtained by Nippon Microtome Laboratory. They were examined under a microscope at magnifications up to 600×.
These oxidized fibers appeared to have a biconical structure as shown in FIG. 12.
The oxidized fibers were carbonized to carbon fibers in a tubular carbonizing furnace, 1000 mm in length, wherein the temperature profile of the carbonizing furnace is described in FIG. 11.
The fibers were continuously carbonized at a temperature of 1300°C and at a line speed of 1 meter per minute. The properties of the resulting carbon fibers are shown in No. 4 of Table III.
The carbon fibers were examined by the standard plasma etching test defined in the present specification.
The carbon fibers did not have any holes defined in their cross sections. Photographs pursuant to this test are shown in FIG. 13.
| TABLE III |
| __________________________________________________________________________ |
| Surface Properties of Carbon Fiber |
| Line Speed |
| Contact Temperature |
| Water Tensile |
| Young's |
| Failing |
| in Oxidation |
| Time T1 |
| ΣT1 |
| of Rollers |
| Absorbability |
| Strength |
| Modulus |
| Strain |
| Refer- |
| No. m/min second |
| minute |
| °C. |
| wt % kg/mm2 |
| × 103 kg/mm2 |
| % ence |
| __________________________________________________________________________ |
| 1(control) |
| 5.3 3.56 15 285 8.4 215 21.2 1.01 |
| (Example 3) |
| 2 (control) |
| 10 1.88 10 285 ∼ 315 |
| 7.2 254 22.6 1.12 |
| (Example 4) |
| 3 20 0.94 9.8 285 ∼ 315 |
| 7.5 288 22.5 1.28 |
| (Example 5) |
| 4 30 0.63 7.7 285 ∼ 330 |
| 6.7 300 22.1 1.36 |
| (Example 2) |
| 5 77 0.25 6.0 285 ∼ 330 |
| 6.9 310 22.0 1.41 |
| FIG. 14 |
| (Example 6) |
| 6 185 0.10 5.0 285 ∼ 340 |
| 6.6 320 21.7 1.47 |
| (Example 7) |
| 7 210 0.09 5.0 285 ∼ 340 |
| 6.4 322 21.5 1.50 |
| FIG. 15 |
| (Example 8) |
| __________________________________________________________________________ |
In these examples acrylic fibers as in Example 2 were used and the oxidation procedure was similar, but instead of 30 meters per minute of yarn speed in the oxidation step the acrylic fibers were oxidized at 5.3, 10, 20, 77, 185 and 210 meters per minute.
The running conditions and the water absorbabilities of the resulting oxidized fibers are shown as Nos. 1, 2, 3, 5, 6 and 7 in Table III. After conducting the oxidation procedures, the oxidized fibers of Example 3 had filament bonding to some extent, but others were pliable and had not filament bonding (No. 1 in Table III). These oxidized fibers were carbonized up to 1300°C, as in Example 2, to produce carbon fibers.
The carbon fibers were examined by applying the standard plasma etching test, and the resulting carbon fibers did not have any holes as defined in the present invention in any case including Examples 3, 4, 5, 6, 7 and 8.
Partial photographs appearing in Examples 6 and 8 are shown in FIGS. 14 and 15, respectively.
In this example, acrylic fibers as in Example 2 were used, and the oxidation procedure was similar to Example 8, but the surface temperature of the heated rollers was maintained at from 300° to 350° C., and the total contact time T1 was 2.8 minutes. The resulting oxidized fibers were pliable and had no filament bonding, and the water absorbability of the oxidized fibers was 4.5 wt %.
These oxidized fibers were carbonized as in Example 2 to produce carbon fibers which had the properties described under No. 8 in Table IV.
The carbon fibers did not have any holes as defined above according to the standard plasma etching test.
In this example acrylic fibers as in Example 2 were used, and the oxidation procedure was similar, but the surface temperature of the heated rollers was maintained at 280°C and the total contact time T1 was 30 minutes in all. The resulting oxidized fibers were pliable and had no filament bonding, and their water absorbability was 9.3 wt %. The oxidized fibers were carbonized as in Example 2 to produce carbon fibers whose properties are shown as No. 9 in Table IV.
The carbon fibers were examined by use of the standard plasma etch test and did not have any defined holes.
The oxidation procedure was similar to Example 10, but instead of oxidizing at a surface temperature of 280°C of the heated rollers, the heated rollers were maintained at 285°C, and produced oxidized fibers which were pliable and had no filament bonding, and had a water absorbability value of 11.0 wt %.
The oxidized fibers were carbonized as in Example 2 to produce carbon fibers having properties as shown at No. 10 of Table IV.
The carbon fibers did not have any holes as defined above, according to examination using the standard plasma etch test.
The procedure of Example 2 was repeated to examine the effect of atmospheric temperature in the vicinity of the heated rollers. The oxidation procedure was similar to Example 2, except that the damper in the duct attached on the cover was almost closed.
The resulting oxidized fibers were pliable and had no filament bonding and their water absorbability was 6.9 wt %.
During oxidation the atmospheric temperature in the vicinity of heated rollers was measured as 160°C, which value is higher than that of Example 2.
This procedure saved about 10% of the electricity consumption in comparison with Example 2.
The resulting oxidized fibers were also carbonized up to 1300°C as in Example 2 to produce carbon fibers the properties of which are shown in No. 11 of Table IV.
In this example the oxidation procedure was similar to Example 6, except that the surface temperature of the heated rollers was maintained at 300°C throughout.
The resulting oxidized fibers were pliable and had no filament bonding. The water absorbability of the oxidized fibers was 5.2 wt %.
The carbon fibers were carbonized as described as in Example 2 and their properties are shown in No. 12 Table IV. These carbon fibers did not have any holes as defined above according to examination by the standard plasma etch test.
Partial photographs resulting from this test are shown in FIG. 16.
In this example the oxidation procedure was similar to Example 6, except that the surface temperature of the heated rollers was maintained at 305°C
The resulting oxidized fibers were pliable and had no filament bonding. Their water absorbability was 5.6 wt %.
The oxidized fibers were carbonized as in Example 2 to produce carbon fibers whose properties are shown in No. 13 of Table IV.
The carbon fibers did not have any holes as defined above according to examination by the standard plasma etch test.
Partial photographs resulting from this test are shown in FIG. 17.
1500 filaments of acrylic fibers obtained from spinning a copolymer consisting of 99.2 mole % of acrylonitrile and 0.8 mole % of itaconic acid were used in this example.
The oxidation procedure was similar to Example 2. The resulting oxidized fibers were pliable and had no filament bonding.
The water absorbability of the oxidized fibers and the properties of the carbon fibers are shown in No. 14 of Table IV. The carbon fibers did not have any holes as defined by examination using the standard plasma etch test.
| TABLE IV |
| __________________________________________________________________________ |
| Surface Properties of Carbon Fiber |
| Line Speed Temperature |
| Water Young's |
| Failing |
| Oxidation |
| Contact Time T1 |
| ΣT1 |
| of Rollers |
| Absorbability |
| Tensile Strength |
| Modulus |
| Strain |
| No. |
| m/min second minute |
| °C. |
| wt % kg/mm2 |
| × 103 kg/mm2 |
| % |
| __________________________________________________________________________ |
| 8 210 0.09 2.8 300 ∼ 350 |
| 4.5 279 19.0 1.47 |
| 9 30 0.63 30 280 9.3 284 23.1 1.23 |
| 10 30 0.63 30 285 11.0 280 23.6 1.19 |
| 11 30 0.63 7.7 285 ∼ 330 |
| 6.9 303 21.4 1.42 |
| 12 77 0.25 6.0 300 5.2 294 20.7 1.42 |
| 13 77 0.25 6.0 305 5.9 290 20.1 1.44 |
| 14 30 0.63 7.7 285 ∼ 330 |
| 7.2 294 21.7 1.35 |
| __________________________________________________________________________ |
Carbon fibers obtained by the method of Example 2 were heated up to 2400°C in a nitrogen atmosphere using a 1 meter graphitizing furnace. This process was continuously conducted at 0.7 meters per minute of line speed.
The properties of the resulting graphitized fibers are shown by the following Table V.
| TABLE V |
| ______________________________________ |
| Tensile Strength 248 kg/mm2 |
| Young's modulus 39.2 × 103 kg/mm2 |
| Failing strain 0.63% |
| ______________________________________ |
Carbon fibers obtained from the method of Example 2 were conducted to be oxidized by the procedure of electrolysis well known in the prior art.
The resulting oxidized carbon fibers were impregnated in an epoxy resin comprising 100 parts by weight of "Epikote 828" (manufactured by Shell Oil Co.) and 3 parts of the complex of boron trifluoride and monoethylamine.
The impregnated fibers were laid into a mold, the mold was closed, and the product was precured for 1 hour at 170°C followed by postcuring for 2 hours at 170°C The resulting composite had fiber volume fractions of 61%. The specimens were cut from the composite and their mechancial properties were measured using an Instron Type 1114 tester (Instron Corporation). The results are shown in Table VI.
For comparison purposes, a commercially available carbon fiber having a tensile strength of 280 kg/mm2 and a Young's modulus of 23×103 kg/mm2, which was obtained by the usual oxidation procedure using a hot air oven, was impregnated with a similar resin and cured as described above.
The resulting composite specimen was found to have fiber volume fractions of 65% and its mechanical properties were measured and determined as shown in Table VI.
These commercially available carbon fibers were examined by use of the standard plasma etching test. They were found to have 9% of latent hole formations, according to this test.
| TABLE VI |
| ______________________________________ |
| Example 17 |
| Control |
| Obtained by |
| Commercial |
| Carbon fiber Example 2 Carbon Fiber |
| ______________________________________ |
| Fiber volume |
| 61 65 |
| fraction of |
| composite (%) |
| 169 151 |
| Flexible |
| Mechanical |
| strength |
| properties |
| (kg/mm2) |
| of Interlaminar |
| 8.1 7.5 |
| composite |
| shear strength |
| (kg/mm2) |
| Tensile strength |
| 170 148 |
| (kg/mm2) |
| ______________________________________ |
The acrylic fibers used in Example 2 were heated for 15 minutes residence time in an oven in which hot air was circulated, and its temperature was maintained at 300°C
The resulting oxidized fibers were brittle and had some filament bondings.
The oxidation procedure was similar to Comparative Example 2, except that the air temperature was maintained at 305°C
In this example, a vigorous exthothermic reaction occurred during oxidation and the acrylic fibers burned out.
In this example the process of spinning acrylic fibers was continuously connected to the process of the oxidation. A strand of 1500 filaments of acrylic fibers was spun, using a copolymer consisting of 99 mole % of acrylonitrile and 1 mole % of 2-(hydroxybutyl)acrylonitrile. The strand was washed with hot water, stretched, dried, drawn from dryer at a line speed of 120 meters per minute, and then continuously followed by a process of oxidation, wherein said acrylic fibers were heated on the surfaces of three pairs of hot rollers at a line speed of 120 meters per minute. This speed corresponded to the above speed of the yarn when drawn from the dryer. In the process of oxidation the surface temperatures of three pairs of heated rollers were maintained at 285°, 290° C. and 305°C respectively.
The contact time T1 of the acrylic fibers on the surfaces of the heated rollers was 0.24 seconds, and the total contact time T1 was 9.6 minutes during the oxidation procedure.
The resulting oxidized fibers were pliable and did not have any filament bonding. The water absorbability of the oxidized fibers was 7.5 wt %. These oxidized fibers were carbonized to carbon fibers in a carbonizing furnace heated up to 1300°C in a nitrogen atmosphere, using a procedure similar to Example 2. The properties of the resulting carbon fibers are shown in the following Table VII.
| TABLE VII |
| ______________________________________ |
| Tensile strength 295 kg/mm2 |
| Young's modulus 22.1 × 103 kg/mm2 |
| Failure strain 1.33% |
| ______________________________________ |
Various modifications, changes, alterations and additions can be made in the present method and product. All such modifications, substitutions, additions and the use of equivalent components, ingredients or method steps form a part of the present invention as defined in the appended claims.
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| Executed on | Assignor | Assignee | Conveyance | Frame | Reel | Doc |
| May 10 1979 | Toray Industries, Inc. | (assignment on the face of the patent) | / |
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