Publication Date: 2002-Jan-23
The IP.com Prior Art Database
The processing of carbon fibers to produce the desired properties from the polymer precursor state to the final carbonized state is a complex and highly technical process. Not only are the basic properties of the carbon fiber per se important but also the application of the proper sizing. Sized fibers used in combination with the proper resin matrix, have the capability to provide a final composite structure with the maximum optimum properties.
The processing of carbon fibers to produce the desired properties from the polymer precursor state to the final carbonized state is a complex and highly technical process. Not only are the basic properties of the carbon fiber per se important but also the application of the proper fiber sizing. Sized fibers used in combination with the proper resin matrix, have the capability to provide a final composite structure with the maximum optimum properties.
Carbon fibers have found extensive and viable markets because of their excellent specific strength and specific modulus. They are being used in an ever-widening field of high strength requirement applications. The manufacture of carbon fibers is comprised of many steps, many of which are proprietary to the manufacturers. However, in a broad sense, the process essentially is the making of precursor fibers, the carbonization of those fibers and the subsequent fiber treatment prior to the specific end use application.
Precursor fibers made of polyacrylonitrile (PAN) polymer can consist of several co-polymers. One of the components can be a stabilization accelerator. Examples of these are acrylic acid, methacrylic acid, and hydroxy esters of acrylic acid. Another precursor component can be a spinning and drawing promoter. Examples of these are lower alkyl esters of acrylic acid and methacrylic acid, allylsulfonic acid, methallylsulfonic acid, styrenesulfonic acid, their alkali metal salts, vinyl acetate and vinyl chloride.
Another precursor component is the carrier solvent. The conventional ones used are dimethyl sulfoxide, dimethylformamide, dimethylacetamide, sodium thiocyanate and zinc chloride. In view of productivity, use of dimethyl sulfoxide as the solvent is preferable, since it is high in coagulation ability
The spinning method of the PAN fiber precursor can be accomplished by melt spinning, wet spinning, dry spinning or dry jet spinning. Dry jet spinning is preferable since densification of the fiber is easier and fibers with a higher strength can be more easily obtained than with the other methods. Usually a spinneret with circular holes is used to obtain coagulated fibers with a circular or similar cross sectional form.
The coagulation conditions also greatly affect the structures and tensile properties of the precursor fibers and the subsequent carbon fibers. To obtain dense coagulated fibers with fewer voids, a low coagulation rate is desirable, and therefore it is best to coagulate at a low temperature and at a high concentration.
After completion of coagulation, washing with water and drawing are carried out, and if required, there is further treatment with acid and the like.
The coagulated fibers obtained are washed with water, drawn and sized with an oil in the spinning and drawing process to produce precursor fibers. After oiling, the fibers are dried and densified. During or after completion of the spinning and drawing process, a stabilization...