Fibrous webs of bi-component melt-blown fibers of thermoplastic polymers from a bi-component spinnerette assembly of multiple rows of spinning orifices

#This invention relates to an adaptation of bi-component fiber spinning to a melt-blowing process as described in U.S. Pat. No. 5,476,616, which is herewith incorporated as reference. More particularly, it relates to the improvement whereby the number of rows of spinning orifices can be extended beyond the number possible before and still maintain fiberforming spinning quality, using polymer pairs of greatly differing melt viscosities and other properties.

#It is an object of the present invention to provide a bi-component spinning system whereby a spinning nozzle fed by one type of polymer from one chamber is located inside another slightly larger spinning nozzle fed by a second chamber, said nozzle pairs being arranged in multiple rows of spinning orifices, and directing streams of gas to each row of spinning orifices.

#Another object of the invention is to provide a uniform stream of attenuating gas around each spinning nozzle by centering the nozzle pairs in round holes of gas cover plates to achieve an even gas flow around the circumference of each nozzle pair.

#A better understanding of the present invention as well as other objects and advantages thereof will become apparent upon consideration of the detailed disclosure thereof, especially when taken with the accompanying drawings, wherein like numerals designate like parts throughout; and wherein

#FIG. 1A is a partially schematic side view of a spinnerette assembly of the present invention, showing the path of gas and the two polymer flows;

#FIG. 1B is the same spinnerette where the inner nozzles 4 have been shortened by the distance 22.

#In previous bi-component spinning assemblies, side-by-side or sheath-core structures are being formed by having two polymers flow through capillaries in a laminar flow pattern without mixing before exiting the capillary and then solidifying. This limits the polymer pairs to such groups that are capable of laminar flow, i.e. have similar melt-viscosities and other properties at similar extrusion temperatures. Bi-component designs have been disclosed in U.S. Pat. Nos. 2,931,091 and 3,039,174. Most of these designs were used in traditional textile yarn spinning and are not easily adaptable to the melt-blowing process.

#In U.S. Pat. No 6,057,256 to Krueger et al. a bi-component met-blowing process is shown where the polymers are contacted with each other inside the die-body as previously described, and, by laminar flow exit the spinning orifice and are drawn down by high velocity air. This design, however, is limited to a single row of spinning orifices and consequently relatively low capacity.

#In the present invention, a bi-component melt-blowing system is shown where bi-component fibers are being spun out of multiple rows of spinning orifices, and whereby the contact time of two or more polymers inside the die-body can be controlled from zero to any finite time chosen, by having one capillary in which a first polymer flows, being fed from one polymer manifold, is surrounded by a second, larger than the first capillary, through which a second polymer fed from a second polymer manifold flows; at the exit point, each tubular nozzle is surrounded by a concentric flow of high velocity air as described in previously cited U.S. Pat. No. 5,476,616.