Process for preparing an ignition resistant carbonaceous material comprising a melt blowing or spunbonding step, a radiation step and a carbonizing step

#The present invention relates to a process for preparing a novel continuous, generally planar, sheet like, carbonaceous material comprised of a multiplicity of interconnected, carbonaceous fibers having a multiplicity of contact points, said fibers being integrally welded at their contact points to form said continuous, generally planar, sheet like, carbonaceous material. The carbonaceous material has a moderate to high specific resistivity, an oxygen content of less than about 2%, a carbon content of less than 92%, and a nitrogen content of from 5 to 30% and can take a variety of physical forms, including a planar, sheet like batting, fabric, panel, web, mat, and the like.

#In the process, the carbonaceous material is prepared from a meltblown or spunbonded thermoplastic polymeric precursor material. This polymeric precursor material is in the form of a multiplicity of fibers which, while in a heat softened and tacky condition, contact and adhere to each other at their contact points, thus forming a fibrous mat, web, or the like. The thus formed interconnected fibrous polymeric precursor material is then irradiated to crosslink the polymeric precursor material and heat treated in a nonoxidizing atmosphere to permanently heat set and carbonize the polymeric precursor material. The carbonaceous material of the invention provides ignition resistant, fireblocking, and thermal insulative materials.

#Textile materials can be made into a variety of different physical forms, including fibers per se, a fiber assembly such as a fiber tow, mat, web, or the like. Textile materials are further exemplified in a variety of fibrous textile structures including traditional textile fibers and fabrics and microfibrous mats, webs, or the like.

#FIG. 1 is a schematic view of a preferred apparatus of the invention wherein a polymeric precursor material is made into a nonoxo-carbonaceous material.

#In a prefered method of manufacturing, a multiplicity of polymeric precursor fibers are extruded from a conventional spunbonding or meltblowing apparatus and are deposited on a conveyor belt. Multiple extrusion heads can be spaced closely in series to build up a textile structure of the fibrous polymeric material to any desired thickness of up to 6 inches (15 cm), for example. The textile structure of the fibrous polymeric material so formed is then passed through a source of ionizing radiation, such as an electron beam, so as to stabilize the polymeric material by crosslinking. The irradiated fibrous material is then heat treated in an oven in an inert atmosphere. The heat treatment is preferably conducted by placing the fibrous precursor material on a support such as a belt so as to produce no tension on the fibrous material, to render the crosslinked fibrous material nonoxo-carbonaceous. The nonoxo-carbonaceous fibrous material is then collected on a take-up roll or in a container for further processing. While the process is preferably continuous and can be used beginning from the initial extrusion of the fibers or microfibers, it can also be readily adapted to batchwise production. That is, the process can begin by utilizing a creel of a spunbonded or meltblown fibrous polymeric precursor material, for example, polyacrylonitrile, which has been previously crosslinked by irradiation. The crosslinked fibrous precursor material can be stored and, when convenient, passed through an oven for heat treatment of the fibrous material in an inert atmosphere to obtain partial or full carbonization.

#By partial carbonization is meant that the carbon content of the fibrous polymeric precursor material is increased to greater than 65% but less than 92% by heat treating in an inert atmosphere to cause permanent chemical change in the precursor material.

#More particularly, FIG. 1 shows a typical production line for the preparation of a generally planar fibrous material 25, such as, for example, a web or mat, comprising a multiplicity of randomly oriented carbonaceous continuous microfibers which are integrally welded at their contact points. A multiplicity of polymeric microfibers 26 are extruded from a nozzle 20 of a meltblowing apparatus and are subjected to the influence of a dynamic flow of hot air from a jet 24, as described in U.S. Pat. No. 4,118,531, to form a fibrous precursor material in which the melt softened fibers are bonded to each other at their contact points. A multiplicity of contact points between individual fibers are formed due to the influence of the dynamic flow of hot air on the fibers as they transverse from the extrusion nozzel to an endless conveyor 21. The fibrous material 25 is conveyed by the endless belt conveyor 21 so as to be transported past a source 27 of electron beam radiation which is normally in a protective enclosure (not shown). The fibrous polymeric precursor material is then irradiated to crosslink and stabilize the polymeric material for the subsequent carbonizing heat treatment. One or more plies each composed of a multiplicity of the self bonded polymeric precursor fibers can be extruded over the initial fibrous material with additional nozzles and air jets followed by irradiation from further electron beam sources to form a multi-plied web or mat structure. The fibrous material is then moved into an oven 30 where it is heat treated to permanently heat set and render carbonaceous under the conditions described in U.S. Pat. Nos. 4,837,076 and 4,879,168. Preferably, the fibrous material 25 is subjected to a dynamic flow of inert non-oxidizing gas during heat treatment passing from nozzle 31 through the fibrous material, thereby improving the tenacity of the microfibers by removing interstitial oxygen from the fibrous material. Preferably, the inert non-oxidizing gas is nitrogen.