Carbonaceous or graphite articles in fibrous or film form having high anisotropy are made by selecting a substance having a particular chemical structure and properties as a carbon precursor. One known method uses pitch as a raw material which is formed into fibrous shape by melt spinning and thereafter the fibers are subjected to an infusibilization treatment and then to carbonization. Such procedures are described, for example, in U.S. Pat. Nos. 3,629,379; 4,016,247; Re. 27,794; and European Patent Application Publication No. 0026647.
It is generally desirable to use pitches having a high percentage of mesophase as the raw material in carbon fiber spinning. However, these pitches often have high softening temperatures and decompose when spinning at the temperatures encountered during processing which are about 40.degree. C. or more higher than the softening point. The preparation of neomesophase by a solvent separation technique to remove most of the non-mesophase components from the mesophase pitch is described in U.S. Pat. Nos. 4,184,942 and 4,208,267. The neomesophase pitches, however, still require a rather high spinning temperature, and may exhibit non-Newtonian flow and marginal stability.
It is conventional in fiber spinning to add a plasticizer in order to lower the melting temperature of the material being spun and thereby lower the spin temperature. Unfortunately, the small molecules that might be considered as good plasticizers are generally deleterious to the mesophase structure. The plasticizers generally form isotropic liquids and hence depress the mesophase transition temperature in the plasticizer pitch system. While the degree of disruption varies depending on the particular plasticizers, all of such materials are disruptive.
It has now been unexpectedly discovered that, if certain raw materials are treated in a particular way, the resulting product is a low melting, low molecular weight mesophase pitch which can be used as such to obtain carbon fibers by spinning or which can be used as a plasticizer with mesophase or neomesophase pitches which are used to produce carbon fibers.
Accordingly, it is the object of the present invention to provide such low melting, low molecular weight mesophase pitches and a method of preparing them. These and other objects of the invention will become apparent to those skilled in this art from the following detailed description.