Carbon blacks has been widely used as reinforcing agents for tires or rubbers, black pigment for printing inks or paints, coloring materials for resins, materials for dry batteries, conductive materials, etc. in various fields. Especially, those for reinforcing tires or rubbers preponderate in demands, and carbon blacks of various qualities are used as materials for the reinforcing agents.
Carbon blacks are usually produced by incomplete combustion or thermal decomposition of hydrocarbonaceous gases or oils originated from petroleum or coal, such as natural gas, petroleum gas, crude naphthalene, creosote oil, pitch oil, or the like. Known processes for the above-mentioned production are furnace method for producing furnace blacks, channel process for producing channel blacks, thermal process for producing thermal blacks, and the like.
However, these methods in which hydrocarbonaceous gases or hydrocarbonaceous oils are used as raw material have defects that the raw material situations are unstable and high cost is inevitable owing to the complicated producing processes.
On the other hand, in order to solve the defects, there was proposed a method of producing coal carbon blacks for rubber-reinforcing agents wherein a solid coal itself is thermally decomposed instead of creosote oil or crude naphthalene obtained by carbonization of coal (Japanese Patent Publication No. 16,107/1963). However, the carbon blacks for coal filler obtained by the method have a disadvantage in their use as a reinforcing agent for rubbers since they have a large ash content which decreases the modulus of rubbers and elongates vulcanization of rubbers.
The object of the present invention is to provide an economical process for producing coal fillers having excellent rubber-reinforcing properties.