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

[0001] 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.

[0002] 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.

[0003] 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.

[0004] These and other objects of the invention are achieved by directing a gas flow to the base of the spinning nozzle pair by means of baffle plates, and extending the length of the spinning nozzle pairs. The spinning nozzle pairs are guided through a family of gas cover plates providing for the centering of the round spinning nozzle pairs through round gas supply holes and supplying a uniform stream of gas to each nozzle pair and row of nozzle pairs.

[0005] 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

[0006] 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;

[0007] FIG. 1B is the same spinnerette where the inner nozzles 4 have been shortened by the distance 22.

[0008] FIG. 2A is a partial bottom view of the concentric spinning nozzles and gas cover plates, taken along the lines 23-23.

[0009] FIG. 2B is a partial bottom view of the concentric spinning nozzles and gas cover plates, taken along the lines 24-24.

[0010] FIG. 3 is a partial bottom view of a spinnerette assembly, wherein the inner nozzle is off-center and shaped in a half-circle to form side-by-side bi-component fibers.

[0011] 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.

[0012] 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.

[0013] 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.

[0014] Referring now to FIG. 1, the spinnerette assembly is mounted on the die body 1 which supplies polymer melt 2 to first supply cavity 3 feeding the spinning nozzles 4 which are mounted in the spinnerette body plate 5 wherein nozzles 4 are mounted. A second set of nozzles 6, larger than nozzles 4, having an identical mounting pattern as nozzles 4, is mounted on the die body plate 7 and is being fed with a second polymer 8 from the die body 1 and through plate 5 to cavity 9 which feeds nozzles 6. Nozzles 4 are inserted into nozzles 6, and have the same or shorter length than nozzles 4. The nozzles 4 and 6 lead through the gas cavity 10, which is fed with gas, air or other suitable fluids from gas inlet slot 11. The primary gas supply enters the spinnerette assembly through pipe 12 into the supply cavity 13. The baffle plate 14 diverts the gas stream and forces the gas through the slot 11 toward the base of nozzles 6. The nozzles 4 and 6 protrude through gas cover plate 15 through tight fitting holes 16 arranged in the same pattern as the nozzle mounts in spinnerette body plates 5 and 7. The gas cover plate family further consists of spacer plate 18 which forms a second gas cavity 19 between plate 15 and 20. The complete path of the gas is now from inlet pipe 12 into the gas supply cavity 13 through inlet slot 11 into gas cavity 19. The gas then flows through gas holes 17 of plate 15 into the gas cavity 19 and then around the nozzles 6 through holes 21, in which nozzles 6 are centered. The high velocity gas out of holes 21 accelerate and attenuate the exiting polymer melt to form fine fibers. FIGS. 2A and B show the bottom view of plates 15 and 20, respectively. FIG. 3 shows a bottom view of plate 20, wherein the inner nozzles 4 are shaped in a half circle to produce a side-by-side bi-component fiber.

[0015] The following examples are included for the purpose of illustrating the invention and it is understood that the scope of the invention is not to be limited thereby.

[0016] A 5 long spinnerette was used of the type shown in FIG. 1. The spinnerette had 12 rows of nozzles, spaced 0.060 apart, within each rows, the nozzles were also spaced 0.060 apart, resulting in a total number of nozzles of 1000. The inner nozzles 4 mounted in plate 5 had an outside diameter of 0.020 and an inside diameter of 0.010. The outside nozzles 6 mounted in plate 7 had an outside diameter of 0.035 and an inside diameter of 0.023. Air cavity 10 had a height of 0.500, air cover plate 15 a thickness of 0.063. Air holes 17 shown in FIGS. 1 and 2A had a diameter of 0.020. Air cavity 19 had a height of 0.100 and air cover plate 20 a thickness of 0.063. The air holes 21 in plate 20 had a diameter of 0.048. The resin inlets 2 and 8 were each connected to a 1 (24/1 length/diameter ratio) extruder, subsequently referred to as extruder A and B, respectively each capable of extruding approximately 10 lb/hr of polymer resin.

[0017] Extruder B (sheath polymer) was charged with high density polyethylene of Melt Index 105 (Dow Chemical Co's ASPUN 6808A) and the resin was extruded into the spinnerette at a rate of 30 gram per minute; Extruder A (core polymer ) was charges with polypropylene of MFR 70 (Melt Flow Rate, as determined by ASTM-Method D-1238-65T)(HIMONT HIH442) and extruded at a rate of 45 gram per minute, 3% of blue polypropylene color concentrate was added to the polypropylene resin to give the core fiber a blue appearance. The spinnerette temperature and the air temperature were 480 degree Fahrenheit, and the air pressure was 20 psi. 12 below the spinnerette there was a moving screen that collected a web of highly entangled blue fibers of 3 to 6 micrometer diameter. The web had a typical slick, silklike polyethylene feel, indicating that the polyethylene from extruder B was on the outside. Parallel strands of fibers were imbedded and cured into an epoxy resin, and cross sections were cut therefrom. Microscopic examination showed a concentric sheat/core fiber structure, with the blue color visible in the core section. When the fibrous web was heated to a temperature of 250 degree F, most of the point of intersection bonded by coalescence and the web formed a stiff, shape-retaining structure.

[0018] Additional experiments were conducted using polymer pairs as shown in Table 1:

TABLE 1
Experiment No.:	1	2	3	4
Polymer from	PET Polyester*	6/6 Nylon**	PBT Polyester***	Polypropylene
Extruder A	0.59 IV****	35 RV*****	0.59 IV	70 MFR
Extrusion rate	30 g/min	35 g/min	45 g/min	40 g/min
Polymer from	6,6 Nylon	PET Polyester	Nylon 6******	Nylon 6
Extruder B	35RV	0.59W	4ORV	4ORV
Extrusion rate	45 g/min	50 g/min	30 g/min	25 g/min
Spinnerette Temp. (F.)	520	520	480	470
Air Temp.(F.)	510	520	480	470
Air pressure (psi)	25	25	23	24
*Poly-(ethylene) terephthalate
**Poly-(hexamethylene adipamide)
***Poly-(butylene) terephthalate
****Intrinsic Viscosity
*****Relative Viscosity
******Poly (caproamide)

[0019] Microscopic examination of the fiber cross sections, which ranged from 3 to 7 micrometer in diameter, revealed that the sheat/core structure was concentric or near concentric.

[0020] Example I was repeated using identical polymers and process conditions, but with a spinnerette described in FIG. 1B where the inner nozzles 4 where recessed by the length 22 of 0.150. Under a microscope, the fiber cross sections showed the same concentric sheath/core structure as in Example I, with the blue polypropylene inside.

[0021] EXAMPLE I was repeated using a nozzle arrangement as shown in FIG. 3. Upon microscopic examination, the fiber cross-section showed that the two polymers had each formed a semi-circle in a side-by-side configuration.

[0022] While the invention has been described in connection with several examplary embodiments thereof, it will be under stood that many modifications will be apparent to those of ordinary skill in the art, and that this application is intended to cover any adaptations and variations thereof. Therefore, it is manifestly intended that this invention be only limited by the claims and the equivalents thereof.