Process for producing a high tensile strength, high Young's modulus carbon fiber having excellent internal structure homogeneity

Abstract

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/mm 2 and a Young's modulus of at least about 15×10 3 kg/mm 2 . 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.

I claim the following: 
     
       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.]. .Iadd.than .Iaddend.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. 
     
     
       2. A process according to claim 1, wherein the temperature of said oxidizing atmosphere is maintained within the range from room temperature to about 200° C. 
     
     
       3. A process according to claim 1, wherein said oxidizing atmosphere fed to oxidation step is air at room temperature. 
     
     
       4. A process according to claim 1, wherein the contact time per single contact of said organic fiber on the heated body is within the range from about 0.001 seconds to about 0.7 seconds. 
     
     
       5. A process according to claim 1, wherein the total contact time for converting said organic fiber to the oxidized fiber is less than about 30 minutes. 
     
     
       6. A process according to claim 5, wherein the total contact time is within the range from about 2 minutes to about 20 minutes. 
     
     
       7. A process according to claim 1, wherein said heated body is a heated roller. 
     
     
       8. A process according to claim 1 wherein said heated body is a heated plate. 
     
     
       9. A process according to claim 7, wherein the diameter of said heated roller is about 50 mm to about 1000 mm. 
     
     
       10. A process according to claim 1, wherein said organic fiber is a fiber of a polymer comprising at least 85 mole % of acrylonitrile. 
     
     
       11. A process according to claim 10, wherein said polymer comprises acrylonitrile and at least one kind of vinyl monomer which is copolymerizable with said acrylonitrile. 
     
     
       12. A process according to claim 1, wherein the water absorbability of said oxidized fiber is about 3.5 to about 15%. 
     
     
       13. A process according to claim 1, wherein the water absorbability of said oxidized fiber is about 5 to about 10%. 
     
     
       14. A process according to claim 1, wherein the carbonized fiber is subsequently heated to .[.more than about 3000° C. in a non-oxidizing atmosphere.]. .Iadd.up to about 3000° C. in a non-oxidizing atmosphere. .Iaddend. 
     
     
       15. A process according to claim 1, .[.wherein.]. .Iadd.further comprising .Iaddend.the step of spinning the organic fiber .[.is.]. .Iadd.and .Iaddend.directly .[.connected.]. .Iadd.connecting said spinning step to .Iaddend.the oxidizing step .[.in which.]. .Iadd.whereby .Iaddend.said organic fiber obtained from the spinning step is converted continuously to an oxidized fiber. 
     
     
       16. A process according to claim 15, wherein the line speed of the organic fiber in the oxidizing step is more than at least 20 meters per minute and substantially equal to the line speed of the organic fiber in the spinning step. .Iadd. 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. .Iaddend..Iadd. 18. A process according to claim 17, wherein the temperature of said oxidizing atmosphere is maintained within the range from room temperature to about 200° C. .Iaddend..Iadd. 19. A process according to claim 17, wherein said oxidizing atmosphere fed to said oxidation step is air at room temperature. .Iaddend..Iadd. 20. A process according to claim 17, wherein the contact time per single contact of said organic fiber on the heated body is within the range from about 0.001 seconds to about 0.7 seconds. .Iaddend..Iadd. 21. A process according to claim 17, wherein the total contact time converting said organic fiber to the oxidized fiber is less than about 30 minutes. .Iaddend..Iadd. 22. A process according to claim 21, wherein the total contact time is within the range from about 2 minutes to about 20 minutes. .Iaddend. .Iadd. 23. A process according to claim 17, wherein said heated body is a heated roller. .Iaddend..Iadd. 24. A process according to claim 17, wherein said heated body is a heated plate. .Iaddend..Iadd. 25. A process according to claim 23, wherein the diameter of said heated roller is about 50 mm to about 1000 mm. .Iaddend..Iadd. 26. A process according to claim 17, wherein said organic fiber is a fiber of a polymer comprising at least 85 mole % of acrylonitrile. .Iaddend..Iadd. 27. A process according to claim 26, wherein said polymer comprises acrylonitrile and at least one kind of vinyl monomer which is copolymerizable with said acrylonitrile. .Iaddend..Iadd. 28. A process according to claim 17, wherein the water absorbability of said oxidized fiber is about 3.5 to about 15%. .Iaddend..Iadd. 29. A process according to claim 17, wherein the water absorbability of said oxidized fiber is about 5 to about 10%. .Iaddend..Iadd. 30. A process according to claim 17, further comprising the step of spinning the organic fiber and directly connecting the spinning step to the oxidizing step whereby said organic fiber obtained from the spinning step is converted continuously to an oxidized fiber. .Iaddend..Iadd. 31. A process according to claim 30, wherein the line speed of the organic fiber in the oxidizing step is more than at least 20 meters per minute and substantially equal to the line speed of the organic fiber in the spinning step. .Iaddend.