Carbon fibers having improved strength and modulus and an associated method and apparatus for preparing same

Abstract

The invention is directed to carbon fibers having high tensile strength. The invention also provides a method and apparatus for making the carbon fibers. The method comprises advancing a precursor fiber through a plurality of passes through an oxidation oven, where stretching during the initial passes is minimized or eliminated entirely, or made negative, followed by controlled stretching over a series of passes, using rollers of increasing speed.

That which is claimed: 
     
         1 . A method of making a carbon fiber, the method comprising:
 advancing a carbon fiber precursor polymer through an oxidation oven to produce an oxidized fiber, the oven having an oxidizing atmosphere at a temperature between about 175 to 300° C.;   wherein said advancing comprises
 (i) subjecting the fiber to a first plurality of passes, wherein each of said first plurality of passes has a stretch % which is less than or equal to 0.5%; and 
 (ii) subjecting the fiber to a second plurality of passes, wherein each of said second plurality of passes has a stretch % which is greater than 0.5%. 
   
     
     
         2 . The method of  claim 1 , wherein the stretch in each of said first plurality of passes is between 0 and 0.1%, inclusive. 
     
     
         3 . The method of  claim 1 or 2 , wherein the stretch in each of said first plurality of passes is 0%. 
     
     
         4 . The method of any one of  claims 1-3 , wherein the stretch in at least one of said first plurality of passes is negative. 
     
     
         5 . The method of any one of  claims 1-4 , wherein each of said first plurality of passes has an identical stretch %. 
     
     
         6 . The method of any one of  claims 1-5 , wherein in said second plurality of passes, each successive pass has a % stretch which is greater than that of the immediately preceding pass. 
     
     
         7 . The method of any one of  claims 1-6 , wherein the fiber exits the oxidation oven as part of a pass. 
     
     
         8 . The method of any one of  claims 1-7 , wherein the fiber comprises one or more comonomers selected from the group consisting of acrylonitrile, methyl acrylate, methacrylic acid, sodium methallylsulfonate, and itaconic acid. 
     
     
         9 . The method of any one of  claims 1-8 , wherein the precursor fiber has a denier between about 0.6 to 1.53 dpf. 
     
     
         10 . The method of  claim 9 , wherein the precursor fiber has a denier between about 0.6 to 0.8 dpf. 
     
     
         11 . The method of  claim 9 , wherein the precursor fiber has a denier between about 1.2 to 1.4 dpf. 
     
     
         12 . The method of any one of  claims 1-11 , wherein the fiber is introduced into a plurality of oxidation ovens and wherein each successive oven includes an oxidizing atmosphere that is at a temperature that is as least as great as a preceding oxidation oven. 
     
     
         13 . The method according to any one of  claims 1-12 , wherein said first plurality of passes comprises at least two passes. 
     
     
         14 . The method according to any one of  claims 1-13 , wherein said first plurality of passes comprises at least four passes. 
     
     
         15 . The method according to any one of  claims 1-14 , wherein said second plurality of passes comprises at least four passes. 
     
     
         16 . The method according to  claim 15 , wherein said second plurality of passes comprises at least six passes. 
     
     
         17 . The method of any one of  claims 1-16 , further comprising passing the oxidized carbon fiber through a low-temperature furnace at a temperature between about 350 and 800° C.; and
 subsequently carbonizing the oxidized carbon fiber by passing the oxidized carbon fiber through a carbonizing furnace. 
 
     
     
         18 . The method according to  claim 17 , wherein the carbonization furnace is at a temperature between about 1150 and 2000° C. 
     
     
         19 . The method according to  claim 18 , wherein the carbonization furnace is at a temperature between about 1300 and 1500° C. 
     
     
         20 . The method according to any one of  claims 17-19 , wherein the low-temperature furnace is at a temperature between about 300 and 900° C. 
     
     
         21 . The method according to  claim 20 , wherein the low-temperature furnace is at a temperature between about 400 and 800° C. 
     
     
         22 . The method of any one of  claims 17-21 , further comprising the steps of surface treating and sizing the precursor fiber. 
     
     
         23 . The method according to any one of  claims 1-22 , wherein the oxidation oven is at a temperature between about 150 to 600° C. 
     
     
         24 . The method according to  claim 23 , wherein the oxidation oven is at a temperature between about 175 to 300° C. 
     
     
         25 . The method according to any one of  claims 1-24 , wherein upon exiting the oxidation oven, the fiber has an average diameter that is between 0 and 50% less than the fiber's original diameter prior to entering the oxidation oven. 
     
     
         26 . The method according to any one of  claims 1-25 , wherein the fiber comprises a fiber bundle having between about 1,000 and 50,000 individual filaments. 
     
     
         27 . The method according to any one of  claims 1-26 , wherein the fiber comprises improved tensile strength and/or modulus of elasticity compared to a fiber prepared using an idled roll scheme with an identical total stretch. 
     
     
         28 . A carbon fiber prepared according to the method of any one of  claims 1-27 . 
     
     
         29 . The carbon fiber of  claim 28 , wherein the carbon fiber has a tensile strength greater than about 4500 MPa. 
     
     
         30 . The carbon fiber of  claim 28 , wherein the carbon fiber has a tensile strength greater than about 5500 MPa.