Acrylonitrile-based precursor fiber for carbon fiber and method for production thereof

• US 6,428,891 B1
• Filed: 01/22/2001
• Issued: 08/06/2002
• Est. Priority Date: 07/22/1998
• Status: Expired due to Term

• Current Assignee: Mitsubishi Chemical Corporation (Mitsubishi Chemical Group Corp.)
• Original Assignee: Mitsubishi Rayon Company Limited (Mitsubishi Chemical Holdings Corporation)
• Inventors: Amakawa, Takeaki, Kageyama, Yoshitaka, Okuya, Takahiro, Hamada, Mitsuo
• Primary Examiner(s): EDWARDS, NEWTON O
• Application Number:
  US09/743,811
• Time in Patent Office: 561 Days
• Field of Search: 428/364, 428/394, 428/367, 264/206, 423/447.1
• US Class Current: 428/364
• CPC Class Codes: D01D 10/02 Heat treatment heating for finishing D02J13/00
• CPC Class Codes: D01D 5/16 using rollers, or like mechanical devices, e.g. snubbing pins
• CPC Class Codes: D01F 6/18 from polymers of unsaturated nitriles, e.g. polyacrylonitrile, polyvinylidene cyanide
• CPC Class Codes: D01F 9/22 from polyacrylonitriles
• CPC Class Codes: Y10T 428/2913 Rod, strand, filament or fiber
• CPC Class Codes: Y10T 428/2918 including free carbon or carbide or therewith [not as steel]
• CPC Class Codes: Y10T 428/2967 Synthetic resin or polymer

Abstract

This invention relates to an acrylonitrile-based precursor fiber for carbon fiber which is prepared from an acrylonitrile-based copolymer containing 96.0 to 98.5% by weight of acrylonitrile units, and which is characterized by a tensile strength of not less than 7.0 cN/dtex, an elastic modulus in tension of not less than 130 cN/dtex, an iodine adsorption of not greater than 0.5% by weight based on the weight of the fiber, a degree of crystal orientation (π) of not less than 90% as determined by wide-angle X-ray analysis, and a degree of variation in tow fineness of not greater than 1.0%. This precursor fiber has a high strength, a high elastic modulus, a high degree of denseness, a high degree of orientation, and a low degree of variation in tow fineness, and can hence be used to form a high-quality carbon fiber inexpensively by oxidation for a shorter period of time.

Claims

1. An acrylonitrile-based precursor fiber of an acrylonitrile-based copolymer containing 96.0 to 98.5% by weight of acrylonitrile units, said acrylonitrile-based precursor fiber having a tensile strength of not less than 7.0 cN/dtex, an elastic modulus in tension of not less than 130 cN/dtex, an iodine adsorption of not greater than 0.5% by weight based on the weight of the fiber, a degree of crystal orientation (π

) of not less than 90% as determined by wide-angle X-ray analysis, and, when made into a tow, a degree of variation in tow fineness of not greater than 1.0%.

2. An acrylonitrile-based precursor fiber as claimed in claim 1 wherein said acrylonitrile-based copolymer is composed of 96.0 to 98.5% by weight of acrylonitrile units, 1.0 to 3.5% by weight of acrylamide units, and 0.5 to 1.0% by weight of carboxyl-containing vinyl monomer units.

3. An acrylonitrile-based precursor fiber as claimed in claim 1 which has been formed by the wet spinning process.

4. A process for preparing an acrylonitrile-based precursor fiber as claimed in claim 1, which comprises the steps of wet-spinning an acrylonitrile-based copolymer to form a coagulated fiber, subjecting the coagulated fiber to primary drawing comprising in-bath drawing or a combination of in-air drawing and in-bath drawing, and subjecting thus obtained fiber to secondary drawing involving pressurized steam drawing, wherein the temperature of the heating roller located immediately before the introduction of the fiber into a pressurized steam drawing machine is adjusted to 120-190°

C., the degree of variation of steam pressure in said pressurized steam drawing is controlled so as to be not greater than 0.5%, and the coagulated fiber is drawn in such a way that the proportion of the secondary draw ratio to the overall draw ratio is greater than 0.2.

5. A process for preparing an acrylonitrile-based precursor fiber for carbon fiber as claimed in claim 4 wherein the overall draw ratio is not less than 13.

6. A process for preparing an acrylonitrile-based precursor fiber for carbon fiber as claimed in claim 4 wherein said acrylonitrile-based copolymer is composed of 96.0 to 98.5% by weight of acrylonitrile units, 1.0 to 3.5% by weight of acrylamide units, and 0.5 to 1.0% by weight of carboxyl-containing vinyl monomer units.

7. A process for preparing an acrylonitrile-based precursor fiber for carbon fiber as claimed in claim 4, wherein, prior to drawing, the coagulated fiber has an elastic modulus in tension of 1.1 to 2.2 cN/dtex.

8. A process for preparing an acrylonitrile-based precursor fiber for carbon fiber as claimed in claim 4 wherein said pressurized steam drawing is carried out at a steam pressure of not less than 200 kPa (gauge pressure).

9. A process for preparing an acrylonitrile-based precursor fiber for carbon fiber as claimed in claim 4 wherein the fiber subjected to said pressurized steam drawing has a moisture content of not greater than 2% by weight.

10. A carbon fiber formed by oxidation and carbonizing an acrylonitrile-based precursor fiber for carbon fiber as claimed in claim 1.

11. An acrylonitrile-based precursor fiber for carbon fiber as claimed in claim 2 which has been formed by the wet spinning process.

12. A process for preparing an acrylonitrile-based precursor fiber for carbon fiber as claimed in claim 5 wherein said acrylonitrile-based copolymer is composed of 96.0 to 98.5% by weight of acrylonitrile units, 1.0 to 3.5% by weight of acrylamide units, and 0.5 to 1.0% by weight of carboxyl-containing vinyl monomer units.

13. The process for preparing an acrylonitrile-based precursor fiber for carbon fiber as claimed in claim 12 wherein, prior to drawing, the coagulated fiber has an elastic modulus in tension of 1.1 to 2.2 cN/dtex.

14. The process for preparing an acrylonitrile-based precursor fiber for carbon fiber as claimed in claim 13 wherein said pressurized steam drawing is carried out at a steam pressure of not less than 200 kPa (gauge pressure).

15. The process for preparing an acrylonitrile-based precursor fiber for carbon fiber as claimed in claim 14 wherein the fiber subjected to said pressurized steam drawing has a moisture content of not greater than 2% by weight.

16. A carbon fiber formed by oxidation and carbonizing an acrylonitrile-based precursor fiber for carbon fiber as claimed in claim 2.

17. A carbon fiber formed by oxidation and carbonizing an acrylonitrile-based precursor fiber for carbon fiber as claimed in claim 3.

18. A tow consisting of acrylonitrile-based precursor fibers prepared from an acrylonitrile-based copolymer containing 96.0 to 98.5% by weight of acrylonitrile units, said acrylonitrile-based precursor fiber having a tensile strength of not less than 7.0 cN/dtex, an elastic modulus in tension of not less than 130 cN/dtex, an iodine adsorption of not greater than 0.5% by weight based on the weight of the fiber, a degree of crystal orientation (π

) of not less than 90% as determined by wide-angle X-ray analysis, and a degree of variation in tow fineness of not greater than 1.0%.

19. A tow as claimed in claim 18 wherein said acrylonitrile-based copolymer is composed of 96.0 to 98.5% by weight of acrylonitrile units, 1.0 to 3.5% by weight of acrylamide units, and 0.5 to 1.0% by weight of carboxyl-containing vinyl monomer units.

20. A tow as claimed in claim 18 which has been formed by a wet spinning process.

21. A tow as claimed in claim 19 which has been formed by a wet spinning process.

22. An acrylonitrile-based precursor fiber of an acrylonitrile-based copolymer containing 96.0 to 98.5% by weight of acrylonitrile units, said acrylonitrile-based precursor fiber having a tensile strength of not less than 7.0 cN/dtex, an elastic modulus in tension of not less than 130 cN/dtex, an iodine adsorption of not greater than 0.5% by weight based on the weight of the fiber, a degree of crystal orientation (π

) of not less than 90% as determined by wide-angle X-ray analysis.

23. An acrylonitrile-based precursor fiber as claimed in claim 22 wherein said acrylonitrile-based copolymer is composed of 96.0 to 98.5% by weight of acrylonitrile units, 1.0 to 3.5% by weight of acrylamide units, and 0.5 to 1.0% by weight of carboxyl-containing vinyl monomer units.

24. An acrylonitrile-based precursor fiber as claimed in claim 22 which has been formed by a wet spinning process.

25. An acrylonitrile-based precursor fiber as claimed in claim 23 which has been formed by a wet spinning process.