CA2093810C - Method and apparatus for treating meltblown filaments - Google Patents
Method and apparatus for treating meltblown filaments Download PDFInfo
- Publication number
- CA2093810C CA2093810C CA002093810A CA2093810A CA2093810C CA 2093810 C CA2093810 C CA 2093810C CA 002093810 A CA002093810 A CA 002093810A CA 2093810 A CA2093810 A CA 2093810A CA 2093810 C CA2093810 C CA 2093810C
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- Prior art keywords
- filaments
- air
- crossflow
- filament
- orifices
- Prior art date
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- 238000000034 method Methods 0.000 title claims description 22
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- 230000003247 decreasing effect Effects 0.000 claims description 3
- 238000007599 discharging Methods 0.000 abstract description 5
- 238000012360 testing method Methods 0.000 description 18
- 239000000835 fiber Substances 0.000 description 11
- 238000002474 experimental method Methods 0.000 description 10
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- 229920001169 thermoplastic Polymers 0.000 description 4
- 239000012815 thermoplastic material Substances 0.000 description 4
- VGGSQFUCUMXWEO-UHFFFAOYSA-N Ethene Chemical compound C=C VGGSQFUCUMXWEO-UHFFFAOYSA-N 0.000 description 3
- 239000005977 Ethylene Substances 0.000 description 3
- 239000004743 Polypropylene Substances 0.000 description 3
- 229920000573 polyethylene Polymers 0.000 description 3
- 229920000098 polyolefin Polymers 0.000 description 3
- 229920005989 resin Polymers 0.000 description 3
- 239000011347 resin Substances 0.000 description 3
- 239000004416 thermosoftening plastic Substances 0.000 description 3
- 239000004698 Polyethylene Substances 0.000 description 2
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- 238000004519 manufacturing process Methods 0.000 description 2
- 229920001155 polypropylene Polymers 0.000 description 2
- 238000010791 quenching Methods 0.000 description 2
- 238000000926 separation method Methods 0.000 description 2
- 239000007921 spray Substances 0.000 description 2
- 229920000305 Nylon 6,10 Polymers 0.000 description 1
- 229920002302 Nylon 6,6 Polymers 0.000 description 1
- 239000004952 Polyamide Substances 0.000 description 1
- 239000004708 Very-low-density polyethylene Substances 0.000 description 1
- 229920006243 acrylic copolymer Polymers 0.000 description 1
- 239000003990 capacitor Substances 0.000 description 1
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- QHZOMAXECYYXGP-UHFFFAOYSA-N ethene;prop-2-enoic acid Chemical class C=C.OC(=O)C=C QHZOMAXECYYXGP-UHFFFAOYSA-N 0.000 description 1
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Classifications
-
- D—TEXTILES; PAPER
- D01—NATURAL OR MAN-MADE THREADS OR FIBRES; SPINNING
- D01D—MECHANICAL METHODS OR APPARATUS IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS
- D01D4/00—Spinnerette packs; Cleaning thereof
- D01D4/02—Spinnerettes
- D01D4/025—Melt-blowing or solution-blowing dies
-
- D—TEXTILES; PAPER
- D01—NATURAL OR MAN-MADE THREADS OR FIBRES; SPINNING
- D01D—MECHANICAL METHODS OR APPARATUS IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS
- D01D5/00—Formation of filaments, threads, or the like
- D01D5/08—Melt spinning methods
- D01D5/098—Melt spinning methods with simultaneous stretching
- D01D5/0985—Melt spinning methods with simultaneous stretching by means of a flowing gas (e.g. melt-blowing)
Abstract
A meltblowing die (11) is provided with means for discharging crossflow air (17) onto meltblown filaments (36) to disrupt their shape and flow pattern between the die and the collector (16). The disruption enhances drag forces imparted by the primary meltblowing air and results in smaller diameter filaments.
Description
WO 92!07122 ~ ~ (1 J (~ 1-~ PCT/US91/07377 hIET~00 AND APPARATUS FOR TREATING
MELT~L06~M FILAMENTS
1 Thts invention relates generally to the preparation of meltblo~ filaments and webs, In one aspect the Invention relates to a method of manufacturing meltblown webs having improded strength.
Meltblowing is a one step process in which a molten thermoplastic resin is extruded through a row of orifices to foren a plurality of polymer filaments (or fibers) while converging sheets of high velocity hot air (primary air) stretch and attenuate the hot filaments. The filaments are blown unto collector screen or conveyor where they are entangled and collected forming a nonwoven web. The converging sheets of hot air impart drag forces on the polrner strands emerging from the die causing them to elongate forming microsized filaments (typically 0.5-20 microns in diameter).
Secondary air is aspirated into the filament/air stream to cool and quench the filaments.
The meltblown webs have unique properties which make them suitable for a variety of uses such as filters, battery separators, oil rapes, cable wraps, capacitor paper, disposable liners, protective garmets, etc. One of the deficiencies, however, of the meltblown webs, is their relatively low tensile strength. One reason for the low tensile strength is the fact that the filaments have only moderate strength. Although the primary air draws down the fiibnenis, tests have shown that the polymer molecular orientation resulting therefrom is not retained.
Another reason for low strength is the brittle nature of the filaments when collected close to the die (e. g. less than 18').
Mother deficiency for many applications is a relatively broad distribution of filament sizes within a single web.
Efforts have been made to alter the properties of the web by treating the filaments between the die and the collector, but none have been directed primarily at increasing the strength of the rreb. For example, in accordance with U.S. Patent llo.
3,559,421, a liquid spray has been applied to filaments near the die discharge to rapidly quench the filmnents for the purpose of S~gS'r~i'uTE SHEET
MELT~L06~M FILAMENTS
1 Thts invention relates generally to the preparation of meltblo~ filaments and webs, In one aspect the Invention relates to a method of manufacturing meltblown webs having improded strength.
Meltblowing is a one step process in which a molten thermoplastic resin is extruded through a row of orifices to foren a plurality of polymer filaments (or fibers) while converging sheets of high velocity hot air (primary air) stretch and attenuate the hot filaments. The filaments are blown unto collector screen or conveyor where they are entangled and collected forming a nonwoven web. The converging sheets of hot air impart drag forces on the polrner strands emerging from the die causing them to elongate forming microsized filaments (typically 0.5-20 microns in diameter).
Secondary air is aspirated into the filament/air stream to cool and quench the filaments.
The meltblown webs have unique properties which make them suitable for a variety of uses such as filters, battery separators, oil rapes, cable wraps, capacitor paper, disposable liners, protective garmets, etc. One of the deficiencies, however, of the meltblown webs, is their relatively low tensile strength. One reason for the low tensile strength is the fact that the filaments have only moderate strength. Although the primary air draws down the fiibnenis, tests have shown that the polymer molecular orientation resulting therefrom is not retained.
Another reason for low strength is the brittle nature of the filaments when collected close to the die (e. g. less than 18').
Mother deficiency for many applications is a relatively broad distribution of filament sizes within a single web.
Efforts have been made to alter the properties of the web by treating the filaments between the die and the collector, but none have been directed primarily at increasing the strength of the rreb. For example, in accordance with U.S. Patent llo.
3,559,421, a liquid spray has been applied to filaments near the die discharge to rapidly quench the filmnents for the purpose of S~gS'r~i'uTE SHEET
2 0 9 3 i 1 ~ pCT/US91/07377 i . ,, ,; . '. vv.i .
1 improving the web quality (e.g. reduction 1n the fonnation of "shot'). Also, cooling water was employed 1n the process described in U.S. Patent No. 4,594,202 to prevent fiber bonding. U.S.
Patent No. 4,904,174 discloses a method for applying electrostatic charges to the filaments by erecting an electric field through which the extruded filaments pass. U.S. Patent 3,806,289 discloses a meltblowing die provided with a coanda~nozzle for depositing fibers onto a surface in a wavey pattern.
SUMMARY OF THE INVENTION
It has been discovered that by disrupting the flow of the hot polymeric filaments discharged from a meltblowing die, the drawdown of the filaments can be increased. The increased draw-down results in several improved properties of the meltblown web or mat, including improved web strength, improved filament l5 strength, more uniform filament diameter, and softer, less brittle web.
In accordance with the present invention the extruded filaments between the meitblowing die and the collector screen (or substrate) are contacted with crossflow air of sufficient intensity to disrupt the natural flow shape of the filaments.
The crossflow air causes the filaments to assume an undulating or flapping flow behavior beginning near the die discharge and extending to the collector.
Tests have shown that the undulating or flapping flow behavior results in significantly increased drawdown of the filament. ("Orawdown" as used herein means the ratio of the emerging filament diameter at the die tip to final diameter.) Although the reasons for the improved results have not been fully developed, it is believed that the disruption of the filament flow in a region near the die discharge creates a con dition for improved drag of the primary air on,the filaments. In the norm al filament flow (without crossflow air) the primary air flow is substantially parallel to filament flow, particularly near the die discharge. However by creating undulations in the fila-ment flow near the aie discharge, portions of the filament are SUBSTITUTE SHEET _ WO 92/07122 2 ~ ~ ~ g ~ p, PGT/US91/07377 1 positioned crosswise of the primary air flow thereby increasing the effects of drag thereon.
For clarity of description, the crossflow medium is referred to as "air" but other gases can be used. The water spray techniques disclosed in U:S. Patents 3,959,421 and 4,594,202 does not sufficiently disrupt the filaments to achieve the desired results. It should also be noted that the coanda discharge nozzle cannot be used as taught in ~f.S. Patent No. 3,806,289 beeause such an arrangement would not result in increased drawdown but merely pulses the filaments to one side of the coanda nozzle in providing a wavey deposition pattern of the fibers on the eollecting surf ace.
BRIEF OESCRIaTION OF THE DRAWINGS
Figure 1 is a perspective view of a meltblowing apparatus eapable of carrying out the method of the present invention.
Fia_ure 2 is a side elevation of meltblowing die, illustrating schematically the flow shape of the filaments with and without crossflow air.
As mentioned previously, the present invention relates to the application of crossflow air onto the row of filaments discharging from a meltblowing die. A meltblowing line with crossflow air chambers is illustrated in Figure 1 as Comprising an extruder 10 for delivering molten resin to a meltbtowing die 11 which extrudes molten polymer strands into converging hot air streams forming filaments. (12 indicates generally the center lines of filaments discharged from the die 11). The filament/air streaan is directed onto a collector drum or screen 15 where the filafnents are collected in a random entanglement forming a web 16. The web 16 is withdrawn from the collector 15 and may be rolled for transport and storage.
The meltblowing line also includes heating elements 14 mounted in the die 11 and an air source connected to the die 11 through valued lines 13.
SUBSTtTlITE Si-lE~t' W~ 92/07122 ~ ~ ~ ~ ~ PCT/US91/07377 1 In accordance with the present invention, the meltblowing line is pravided with air conducts 17 positioned above and/or below the row of filaments 12 discharging from the die 11.
As will be described in more detail below, each conduit 17 has a longitudinal slot far directing,~air onto the filaments 12. (The term "filament" as used herein includes both continuous strands and discontinuous fibers.) As shown in Figure 2, the meltblowing die 11 includes body members 20 and 21, an erilongate nosepiece 22 secured to the die body 20 and air plates 23 and 24. The nosepiece 22 has a converging die tip section 25 of triangular cross section terminating at tip 26. A central elongate passage 27 is formed in the nosepiece 22 and a plurality of side-by-side orifices 28 are drilled in the tip 26. The orifices generally are between 100 and 1200 microns in diameter.
The air plates 23 and 24 with the body members 20 and 21 define air passages 29 and 30. The air plates 23 and 24 have tapered inwardly facing surfaces which in combination with the tapered surfaces of the nosepiece 25 define converging air passages 31 and 32. As illustrated, the flow area of each air passage 31 and 32 is adjustable. Molten polymer is delivered from the extruder 10 through the die passages (not shown) to passage 27, and extruded as a microsized, side-by-side filaments from the orifices 28. Primary air is delivered from an air source via lines 13 through the air passages and is discharged onto opposite sides of the molten filaments as converging sheets of hot air. The converging sheets of hot air are directed to draw or attenuate the filaments in the direction of filament discharge from the orifices 28. The orientation of the orifices (i.e. their 3U axes) determine the direction of filament discharge. The included angle between converging surfaces of the nosepiece 25 ranges from about 45 to 90'. It is important to observe that the above description of the mettblowing line is by way of illustration only.
Other meltblowing lines may be used in combination with the erossflow air facilities described below.
SUBSTITUTE SHEET
WO 92/07122 2 ~ ~ ~ ~ PGT/US91/07377 1 The air conduits 1T may be tubular in construction havinc both ends closed defining an internal chamber 33. Each conduit 17 has at least one slot 34 formed therein. The slot 34 extends parallel to the axis of the eonduit 1T and traverses the full row of orifices 28 in the die 11. The slot 34 of each conduit 17 is sized to provide air discharge velocities suffi-ciently high to eontact the filaments. Velocities of at least 20 fps and between 300 and 1200 fps are preferred. Slots having a width of between .010 to 0.040 inches should be satisfactory for most applications. Flow rates through each slot of 20 to 300 SCF~9 per inch of orifice length (e.g. length of die tip 25) are preferred. The air delivery tines 18 may be connected at the ends of the conduits 17 as illustrated in Figure 1 or may connect to a midsection to provide more uniform flow through the conduits 17. The air is delivered to the conduits at any pressure but low pressure air (less than 50 psi) is preferred. The conduits may be of other shapes and construction and may have more than one slot. For example, a conduit of square, rectangular. or semicircular cross section may De provided with one, two, or three or more parallel slots. The cross sectional flaw area of each conduit may vary within a wide range; with 0.5 to 6 square inches being preferred and 0.75 to 3.5 square inches most preferred.
The conduits 1T may be mounted on a frame (not shown) to permit the following adjustments:
vertical ('a' direction in Figure 2) horizontal ('b' direction in Figure 2) angular (angle 'A' in Figure 2) The angle A is the orientation of the longitudinal axis of the slot with reference to the vertical. A positive angle A
(+A') indicates the slot 34 is positioned to discharge air in a direction away from the die and thereby provide an air velocity component tranverse or crosswise of the filament flow and a velocity ednponent in the same direction as the primary air flow.
A negative angle A (-A'), on the other hand, indicates the slot 34 is positioned to discharge air toward the die to provide an air SUBSTITUTE SHEET
WO 92/Q7122 2 0 9 3 ~ 10 p~'/US91/07377 i 1 velocity component transverse or crosswise the filament flow and a velocity component opposite the flow of the primary air, A zero angle A, of course, indicates the slot is positioned to discharge air at right angles to the direction of filament discharge (e. g.
to the direction of orientation of the orifices 28). The reference to horizontal and vertical are merely for purposes of description. The relative dimensions a, b, and A will appiy in any orientation of the extrusion die 11.
As mentioned previously, the main function of the erossflow air discharging fran the slots 34 is to disrupt and alter the natural flow pattern or sh ape of the filaments discharging from the die 11. It is preferred that the cross flow air contact the filaments as close to the die 11 as possible (i.e. within 1/4 the distance between the die 11 and the collector 15) and still provide for a generally uniform filament flow to the collector 15.
Optimally, the erossflow air should disrupt the filaments within ~1", preferably within 1/2", and most preferably within 1l4" from the orifices. The conduits 17 are mounted, preferably, one above and one below the filament/air, having the following positions.
Preferred Best Broad Range Range Mode a 1/8 to 2 1/2" 1/8 to 1 1/2" 1/8 to 1/4"
b 0 t0 8" 0 t0 S' 0 t0 1/2"
A -40' to 70' -35 to 45 -20 to lU
The two conduits 17 may be positioned symmetrically on each side of the filament/air stream or may be independently operated or adjusted. Thus, the apparatus may include one or two conduits Figure 2 illustrates the flow pattern of a filament 36a without the use of the crassflow conduits 17. As illustrated the filament 36 flows in a relatively straight line for a short distance (in the order of 1 inch) after discharge from the orifices 28 due to the drag fortes exerted by the primary air flow.
SUBSTi'1UTE SHEET
WO 92107122 2 0 9 3 g 10 p~/US91/07377 _7_ 1 At about 1 inch from the die, the filament 36a flow shape begins to undulate reaching a region of violent flapping motion after about 3 to 6 inches. This flapping motion is believed to result in increased drawdown of the filament 36a.
The onset and behavior of the flapping motion is dependent on several factors including die slat width, nosepiece design, set back, operating temperatures, primary air flow rate, and polymer flow rate. Because so many variables are involved, it is not believed possible to control these variables with a high degree of certainty to achieve a desired amount of filament flapping, It appears to be an inherent behavior for a particular set of parameters. It is known, however, that in Lhe initial region, the primary air flow is generally parallel to the filament flow so little or no flapping occurs in this region.
In accordance with the present invention, crossflow air is impinged on the filaments to initiate the onset of filament trosswise or flapping flow shape much closer to the die outlet.
This earlier onset of flapping filament flow increases drawdown because the filament assumes an attitude crosswise of the primary air flow permitting a more efficient transfer of fortes by the primary air flow. hbreover, the filaments are hotter and may even be in the molten or semimolten state during the early stages of the flapping flow behavior, Using air conduits 17 to deliver cross flaw air where a was 1/2", b was 1', and angle A was 0', the filament 36 had the flow behavior, also depicted in Figure 2. The crossflow air disrupted the filament flow almost immediately upon leaving the die 11 and is characterized by a larger region of high amplitude wave motion and much longer flapping region. Tests have shown that the induced fiapping motion of the filament in accordance with the present inventian decreases filament diameter signifi-cantly over conventional meitblowing (without crossflaw airj under the same operating conditions. It is preferred that the crossflow air produced diameter decreases in the arder of 10 to 70x, mast preferably in the order of 15 to 60x. The resultant increased in SUBSTITUTE SHEET
1 polymer orientation increases the filament strength and the web strength. Tests indicate that the filaments have a more uniform size (diameter) distribution and the collected webs are stronger and tougher.
S O~erat ion In carrying out the method of the present invention, the conduits 17 are placed over and/or under the die outlet and adjusted to the Desired "a", "b", and angle "A" settings. The meltblowing line is operated to achieve steady state operation s.
the crossflow air then is delivered to the conduits 17 by a conventional compressor at the desired pressure. Some minor adjustments may be necessary to achieve optimum results.
It is important to note that the air conduits may be added to on any meltblowing die. For example, the die 11 may 1S De as disclosed in U.S. Patent 4,818,463 or U.S. Patent 3,978,185.
Thermoplastic materials suitable for the process of th a invention include polyolefins such as ethylene and propylene homopolymers, copolymers, terpolymers, etc. Suitable materials include polyesters such as poly(methytmethacrytate) and poly (ethylene terephthate). Also suitable are polyamides such as poly (hexamethylene adipamide), poly(omega-caproamide), and poly (hexamethylene sebacamide). Also suitable are polyvinyls such as polystrene and ethylene acrylates including ethylene acrylic copolymers. The polyolefins are preferred. These include homo-polymers and copolymers of the f ami 1 i es of- polypropyl eves, polyethylenes, and other, higher polyolefins. The polyethylene s include LOPE, HDPE, LLOPE, and very low density polyethylene.
Blends of the above thermoplastics may also be used. Any thermoplastic polymer capable of being spun into fine fibers by meltblowing may be used.
A broad range of process conditions may be used according to the process of the invention depending upon thermoplastic material chosen and the type of web/product properties needed. Any operating temperature of the thermoplastic C 1 1 f? cTrn "-r- ... . _ ..._ WO 92107122 2 0 9 3 81 ~ POf/US91/07377 .g-1 material is acceptable so long as the materials is extruded from the die so as to form a nonwoven product. M acceptable range of temperature for the thermoplastic material in the die, and consequently the approximate temperature of the diehead around the material is 350'-900°F. A preferred range is 400°-150°F.
For polpropylene, a highly preferred range is 400°-65U°F.
Any operating temperature of the air is acceptable so long as it permits production of useable non-woven product. An acceptable range is 350°-900°F.
The flow rates of thermoplastic and primary air may vary greatly depending on the thermoplastic material extruded, the distance of the die from the collector (typically b to 18 inches), and the temperatures employed. M acceptable range of the ratio of pounds of primary air to pounds of polymer is about 20-500, more commonly 30 - 100 for polypropylene. Typical polymer flow rates vary from about 0.3 - 5.0 grams/hole/minute, preferably about 0.3-1.5.
EXPERIMENTS
Experiments were carried out using a one-Inch extruder with a standard polypropylene screw and a aie having the following description:
no. of orifices 1 orifice sire (d) 0.015 inches nosepiece included angle 6U' orifice land length 0.12 inches Air slots (defined by air plates) 2 mm opening and 2 mm neg. set back Other test equipment used in Series I Experiments included an air conduit semicircular in shape and having one longitudinal slot formed in the flat side thereof. The air conduits in the other Experiment were in the form of slotted pipes 1 inch in diameter.
_Series I Experiments The resin and operating conditions were as follows:
SUBSTITUTE SHEET
1 Resin: 800 MFR PP (ExxorrT~~ 3495G) Grade 01e Temp.: 430'F
Melt Temp.: 430'F
Primary Air Temp.: 460'F
Primary Air Rate: 1b.5 SCFM per . of in die width Polymer Rate: 0.8 gms/min.
Slot opening: 0.030 in.
Web collector; screen 12 inchesfrom the die The a, b, and angle A values for the tests this of series were 1", 1 1/2", and , respectively.The dataare +30' shown in Table I.
Table 1 CRUSS-FLOW AYG.
tEST CHAMBER WEIGHT TYPE Of CITlf1 UIAMETER2DIA.
STD.
H0.CONOITIOH PRESS. GM/M2 Web MICRONS DEYIATIOH
m N/TEX
- -~ -1-1Base Case 0 44.30 Brittle 10.5 7.93 2.93 1-2' 0 41.77 "
2-1Crossflow Device 0 39.90 ' 15.6 1.57 2.80 In Place 2-2' 0 37.30 ' 13.5 3-1'+ Secondary Air 0 40.80 ' 13.4 8.33 3.67 Taped Off 3-2' 0 40.80 " 12.4 _ 4-1Crossflow Device 5 37.30 Tough, 19.4 6.59 2.20 In Place Soft 4-2' S 37.30 " 17.7 5-1" 14 33.80 ' 22.3 6.52 1.87 5-2' 14 33.80 " 16.8 f-1'+ Secondary Air 14 31.60" 19.3 6.87 2.18 Taped Off b-2' 14 37.30 " 17.8 7-1' S 32.90 ' 19.6 7.65 2.26 7-2" 5 32.30 ' 17.7 et ~oG~TtTt ~T~ e~ur-r-T
WO 92/07122 ~ ~ ~ ~ ~ ~ PCT/US91/07377 ~ 11 -1 11-TEtiACITY was measured by cutting 1" wide strips and testing in an Instron tensile tester with zero separation between ,)aws. Jaw separation speed was 1.0 inJmin.
2Average fiber diameter yeas measured by optical microscope with an overall magnification of 400. The microscope was focused an a sample of the web and every fiber within the view area was measured using a reticulated ocular. Several different focus areas were selected at random to give a total fiber count of 50. The average reported is a simple number average of all io fiber measursnents for each sample.
3The air velocities for 5 and 14 psi were 705 fps and 1030 fps, respectively.
The Table I data demonstrate that the crossflow air resulted in the following 1; (a) The diameter of the filaments was decreased.
(b) The filament diameter distribution was more uniform.
(c) The web strength eras improved.
(d) The quality of the web was improved.
ZC Series lI Experiments:
These tests employed the same line and polymer but with one tubular air conduits permitting adjustment of the a, b, and angle A settings. Table 2 presents the data for Series II
Experiments.
$U~$'TI'TU~'i~ ~~1EET -WO 92/07122 ~ Q 9 ~ ~ ~ O PCT/US91/07377 1 Tabte 2 CROSSFLOW1 AYG.
CHAM$ER FIBER
TESTSETTINGS PRESSURE OIAM.STD.
ANGLE
N0. a b psi A OEVIAT10N
1 _ _ _ - 10.853.79 2 1/2"1/2" 2 -35' 8.48 2.93 103 ~~ ~~ 4 " 7.06 2.65 4 " " 8 8.72 3.49 3/8"5/8" 2 -20' 6.36 2.61 6 " " 4. 6.17 2.16 7 " " 8 " 8.16 2.9 1'8 1/4"7!8" 2 0' 8.6 2.4 . " " 4 " 7 2. 65 ,g .
" " 8 " 9.58 2.05 11 3/8"1' 2 20' 9.0 3.12 12 " " 4 8.96 2.65 2013 " g 9.22 3.23 14 1/2"5/4 Z 45 9.22 2.48 " " 4 ' 8.66 3.0 16 " " 8 " 8.47 1.98 25lAirvelocities psi e 476 fps, 654 at wer fps, 761 2, 4, 6, and fps,and859 respectively.
fps, These data indicate that for all a, b, ana A settings the filaonent avg. diameters were reduced and the size distributions 30 ire decreased. The 0 to negative angle settings (0 to -35') gave the best results and are therefore preferred. Table 2 data indicates that Lhe optimum crossflow chamber pressure or velocity depend on the geometry.
~u~~~ u~~~
WO 92/071ZZ ~ ~ ~ J V ~ ~ PGT/US91/07377 1 Series III Experiments:
These tests employed only one crossflow conduit (under the filament discharge) having a, b, and A settings of 3/8", 5/8", and -20, respectively. The primary air flog rate (at a temp. of 530') was varied and the die and melt temperatures were 500°. The other conditions were the same as in Series I and II tests. The data for Series III tests are shown in Table 3.
Table 3 CROSSFLUNAVERAGE
CHAMBER FILAMEMT
TEST PRIMARY AIR PRESSURE DIAMETERSTD.
N0. RATE (SCFMJ~psi DEVIATION
1 11 - 8.77 3.33 2 18 - 5.07 2.56 3 27 - 3.77 2.22 4 18 2 2.83 1.11 5~ 18 4 3.16 1.06 6 18 ~ 3.72 1.33 7 27 2 2.7 1.36 8 27 d 2.4 0.89 9 27 8 3.58 1.44 *per inch of die width Test Runs 1-3 in this table show the effect on fiber diameter by increasing primary air rate with no crossfiow air used. The use of crossflow air gives a significant reduction in diameter and diameter standard deviation at both tow and high primary air rates. Again, an optimum crossflow air rate was observed. Highest crossflow air (8 spi) produced larger diameter filaments than medium crossflow air (4 psi), although still smatter than for the 0 crossflow air base case.
Best results appear to be obtained at crossf)ow velocities between 476 fps (2 psij and 859 fps (8 psi). Tests have shown that chamber pressure as low as 1 psi can produce improved results.
SUBSTITUTE SHEET
2~193g10 WO 92/07122 P(.'T/US91/07377 1 Series IY Ex~riments:
These tests were conducted wtth two crossflow conduits illustrated in Figure 2. Each conduit was.ad3usted independently of the other to provide different crossflow contact areas. The upper conduit had a, b, and A settings of l/2", 3/4", and +30', respectively; and the lower conduit had a, b, and A settings of 1/Z', 1", and -20, respectively. The data for Series III
Experiments are presented in Table 4.
Table 4 CROSSFLOw CHAhIBER AYG.
TEST PRESSURE FI8ER STD.
N0. PSI DIAMETER DEYIATION
upper lower 1 0 0 5.69 2.58 2' ~ 0 2 3 .45 1.19 3 2 2 3.9 1.53 .
4 6 2 3.23 1.0 S 4 4 3.95 1.58 6 8 4 3.64 1.37 These data indicate that the settings of the upper and lower conduits can be varied and still provide improved results.
It is significant to note that Test No. 2 using only the lower eonduit gave better results than all but one of the other Series IV
Experiments.
.. In summary, the method of the present invention may be viewed as a two stage air treatment of extruded filaments: the prfwary air contacts the filaments at an angle of between about 22' to about 45' to to impart drag forces on the filaments in the direction of filament extrusion, the crossflow air contacts the extruded filaments at a point down stream of the contact point of the primary air and at a contact angle of at least 10' greater than the contact angle of the primary air on the same side of plane 12 to impart undulating flow shape to the extruded filaments. As viewed in Figure 2 the contact angle of the primary air is SUBSTITUTE SHEET
WO 92/07122 2 ~ 9 3 ~ ~. J PGT/US91/07377 ~ 15 -1 determined by the eenter line of the passages 31 and 32 with plane 12. fie contact angle of the crossflow air from conduit 1T above plane 12 (defined Dy the focus of slot 34 and plane 12) is at least 10' larger than the contact angle of the primary air from passage 31 as measured clockw5~e. Likewise, the contact angle of crossflow air from the conduit 17 below the plane 12 is at least 10' larger than the contact angle of the primary air fro;a passage 32 as measured counterclockwise in Figure 2. The crossflow ai,r has a major velocity component perpendicular to the direction of filament extrusion and a minor velocity component parallel to the direction of filbnent extrusion.
- ~ SUBSTITUTE SHEET
1 improving the web quality (e.g. reduction 1n the fonnation of "shot'). Also, cooling water was employed 1n the process described in U.S. Patent No. 4,594,202 to prevent fiber bonding. U.S.
Patent No. 4,904,174 discloses a method for applying electrostatic charges to the filaments by erecting an electric field through which the extruded filaments pass. U.S. Patent 3,806,289 discloses a meltblowing die provided with a coanda~nozzle for depositing fibers onto a surface in a wavey pattern.
SUMMARY OF THE INVENTION
It has been discovered that by disrupting the flow of the hot polymeric filaments discharged from a meltblowing die, the drawdown of the filaments can be increased. The increased draw-down results in several improved properties of the meltblown web or mat, including improved web strength, improved filament l5 strength, more uniform filament diameter, and softer, less brittle web.
In accordance with the present invention the extruded filaments between the meitblowing die and the collector screen (or substrate) are contacted with crossflow air of sufficient intensity to disrupt the natural flow shape of the filaments.
The crossflow air causes the filaments to assume an undulating or flapping flow behavior beginning near the die discharge and extending to the collector.
Tests have shown that the undulating or flapping flow behavior results in significantly increased drawdown of the filament. ("Orawdown" as used herein means the ratio of the emerging filament diameter at the die tip to final diameter.) Although the reasons for the improved results have not been fully developed, it is believed that the disruption of the filament flow in a region near the die discharge creates a con dition for improved drag of the primary air on,the filaments. In the norm al filament flow (without crossflow air) the primary air flow is substantially parallel to filament flow, particularly near the die discharge. However by creating undulations in the fila-ment flow near the aie discharge, portions of the filament are SUBSTITUTE SHEET _ WO 92/07122 2 ~ ~ ~ g ~ p, PGT/US91/07377 1 positioned crosswise of the primary air flow thereby increasing the effects of drag thereon.
For clarity of description, the crossflow medium is referred to as "air" but other gases can be used. The water spray techniques disclosed in U:S. Patents 3,959,421 and 4,594,202 does not sufficiently disrupt the filaments to achieve the desired results. It should also be noted that the coanda discharge nozzle cannot be used as taught in ~f.S. Patent No. 3,806,289 beeause such an arrangement would not result in increased drawdown but merely pulses the filaments to one side of the coanda nozzle in providing a wavey deposition pattern of the fibers on the eollecting surf ace.
BRIEF OESCRIaTION OF THE DRAWINGS
Figure 1 is a perspective view of a meltblowing apparatus eapable of carrying out the method of the present invention.
Fia_ure 2 is a side elevation of meltblowing die, illustrating schematically the flow shape of the filaments with and without crossflow air.
As mentioned previously, the present invention relates to the application of crossflow air onto the row of filaments discharging from a meltblowing die. A meltblowing line with crossflow air chambers is illustrated in Figure 1 as Comprising an extruder 10 for delivering molten resin to a meltbtowing die 11 which extrudes molten polymer strands into converging hot air streams forming filaments. (12 indicates generally the center lines of filaments discharged from the die 11). The filament/air streaan is directed onto a collector drum or screen 15 where the filafnents are collected in a random entanglement forming a web 16. The web 16 is withdrawn from the collector 15 and may be rolled for transport and storage.
The meltblowing line also includes heating elements 14 mounted in the die 11 and an air source connected to the die 11 through valued lines 13.
SUBSTtTlITE Si-lE~t' W~ 92/07122 ~ ~ ~ ~ ~ PCT/US91/07377 1 In accordance with the present invention, the meltblowing line is pravided with air conducts 17 positioned above and/or below the row of filaments 12 discharging from the die 11.
As will be described in more detail below, each conduit 17 has a longitudinal slot far directing,~air onto the filaments 12. (The term "filament" as used herein includes both continuous strands and discontinuous fibers.) As shown in Figure 2, the meltblowing die 11 includes body members 20 and 21, an erilongate nosepiece 22 secured to the die body 20 and air plates 23 and 24. The nosepiece 22 has a converging die tip section 25 of triangular cross section terminating at tip 26. A central elongate passage 27 is formed in the nosepiece 22 and a plurality of side-by-side orifices 28 are drilled in the tip 26. The orifices generally are between 100 and 1200 microns in diameter.
The air plates 23 and 24 with the body members 20 and 21 define air passages 29 and 30. The air plates 23 and 24 have tapered inwardly facing surfaces which in combination with the tapered surfaces of the nosepiece 25 define converging air passages 31 and 32. As illustrated, the flow area of each air passage 31 and 32 is adjustable. Molten polymer is delivered from the extruder 10 through the die passages (not shown) to passage 27, and extruded as a microsized, side-by-side filaments from the orifices 28. Primary air is delivered from an air source via lines 13 through the air passages and is discharged onto opposite sides of the molten filaments as converging sheets of hot air. The converging sheets of hot air are directed to draw or attenuate the filaments in the direction of filament discharge from the orifices 28. The orientation of the orifices (i.e. their 3U axes) determine the direction of filament discharge. The included angle between converging surfaces of the nosepiece 25 ranges from about 45 to 90'. It is important to observe that the above description of the mettblowing line is by way of illustration only.
Other meltblowing lines may be used in combination with the erossflow air facilities described below.
SUBSTITUTE SHEET
WO 92/07122 2 ~ ~ ~ ~ PGT/US91/07377 1 The air conduits 1T may be tubular in construction havinc both ends closed defining an internal chamber 33. Each conduit 17 has at least one slot 34 formed therein. The slot 34 extends parallel to the axis of the eonduit 1T and traverses the full row of orifices 28 in the die 11. The slot 34 of each conduit 17 is sized to provide air discharge velocities suffi-ciently high to eontact the filaments. Velocities of at least 20 fps and between 300 and 1200 fps are preferred. Slots having a width of between .010 to 0.040 inches should be satisfactory for most applications. Flow rates through each slot of 20 to 300 SCF~9 per inch of orifice length (e.g. length of die tip 25) are preferred. The air delivery tines 18 may be connected at the ends of the conduits 17 as illustrated in Figure 1 or may connect to a midsection to provide more uniform flow through the conduits 17. The air is delivered to the conduits at any pressure but low pressure air (less than 50 psi) is preferred. The conduits may be of other shapes and construction and may have more than one slot. For example, a conduit of square, rectangular. or semicircular cross section may De provided with one, two, or three or more parallel slots. The cross sectional flaw area of each conduit may vary within a wide range; with 0.5 to 6 square inches being preferred and 0.75 to 3.5 square inches most preferred.
The conduits 1T may be mounted on a frame (not shown) to permit the following adjustments:
vertical ('a' direction in Figure 2) horizontal ('b' direction in Figure 2) angular (angle 'A' in Figure 2) The angle A is the orientation of the longitudinal axis of the slot with reference to the vertical. A positive angle A
(+A') indicates the slot 34 is positioned to discharge air in a direction away from the die and thereby provide an air velocity component tranverse or crosswise of the filament flow and a velocity ednponent in the same direction as the primary air flow.
A negative angle A (-A'), on the other hand, indicates the slot 34 is positioned to discharge air toward the die to provide an air SUBSTITUTE SHEET
WO 92/Q7122 2 0 9 3 ~ 10 p~'/US91/07377 i 1 velocity component transverse or crosswise the filament flow and a velocity component opposite the flow of the primary air, A zero angle A, of course, indicates the slot is positioned to discharge air at right angles to the direction of filament discharge (e. g.
to the direction of orientation of the orifices 28). The reference to horizontal and vertical are merely for purposes of description. The relative dimensions a, b, and A will appiy in any orientation of the extrusion die 11.
As mentioned previously, the main function of the erossflow air discharging fran the slots 34 is to disrupt and alter the natural flow pattern or sh ape of the filaments discharging from the die 11. It is preferred that the cross flow air contact the filaments as close to the die 11 as possible (i.e. within 1/4 the distance between the die 11 and the collector 15) and still provide for a generally uniform filament flow to the collector 15.
Optimally, the erossflow air should disrupt the filaments within ~1", preferably within 1/2", and most preferably within 1l4" from the orifices. The conduits 17 are mounted, preferably, one above and one below the filament/air, having the following positions.
Preferred Best Broad Range Range Mode a 1/8 to 2 1/2" 1/8 to 1 1/2" 1/8 to 1/4"
b 0 t0 8" 0 t0 S' 0 t0 1/2"
A -40' to 70' -35 to 45 -20 to lU
The two conduits 17 may be positioned symmetrically on each side of the filament/air stream or may be independently operated or adjusted. Thus, the apparatus may include one or two conduits Figure 2 illustrates the flow pattern of a filament 36a without the use of the crassflow conduits 17. As illustrated the filament 36 flows in a relatively straight line for a short distance (in the order of 1 inch) after discharge from the orifices 28 due to the drag fortes exerted by the primary air flow.
SUBSTi'1UTE SHEET
WO 92107122 2 0 9 3 g 10 p~/US91/07377 _7_ 1 At about 1 inch from the die, the filament 36a flow shape begins to undulate reaching a region of violent flapping motion after about 3 to 6 inches. This flapping motion is believed to result in increased drawdown of the filament 36a.
The onset and behavior of the flapping motion is dependent on several factors including die slat width, nosepiece design, set back, operating temperatures, primary air flow rate, and polymer flow rate. Because so many variables are involved, it is not believed possible to control these variables with a high degree of certainty to achieve a desired amount of filament flapping, It appears to be an inherent behavior for a particular set of parameters. It is known, however, that in Lhe initial region, the primary air flow is generally parallel to the filament flow so little or no flapping occurs in this region.
In accordance with the present invention, crossflow air is impinged on the filaments to initiate the onset of filament trosswise or flapping flow shape much closer to the die outlet.
This earlier onset of flapping filament flow increases drawdown because the filament assumes an attitude crosswise of the primary air flow permitting a more efficient transfer of fortes by the primary air flow. hbreover, the filaments are hotter and may even be in the molten or semimolten state during the early stages of the flapping flow behavior, Using air conduits 17 to deliver cross flaw air where a was 1/2", b was 1', and angle A was 0', the filament 36 had the flow behavior, also depicted in Figure 2. The crossflow air disrupted the filament flow almost immediately upon leaving the die 11 and is characterized by a larger region of high amplitude wave motion and much longer flapping region. Tests have shown that the induced fiapping motion of the filament in accordance with the present inventian decreases filament diameter signifi-cantly over conventional meitblowing (without crossflaw airj under the same operating conditions. It is preferred that the crossflow air produced diameter decreases in the arder of 10 to 70x, mast preferably in the order of 15 to 60x. The resultant increased in SUBSTITUTE SHEET
1 polymer orientation increases the filament strength and the web strength. Tests indicate that the filaments have a more uniform size (diameter) distribution and the collected webs are stronger and tougher.
S O~erat ion In carrying out the method of the present invention, the conduits 17 are placed over and/or under the die outlet and adjusted to the Desired "a", "b", and angle "A" settings. The meltblowing line is operated to achieve steady state operation s.
the crossflow air then is delivered to the conduits 17 by a conventional compressor at the desired pressure. Some minor adjustments may be necessary to achieve optimum results.
It is important to note that the air conduits may be added to on any meltblowing die. For example, the die 11 may 1S De as disclosed in U.S. Patent 4,818,463 or U.S. Patent 3,978,185.
Thermoplastic materials suitable for the process of th a invention include polyolefins such as ethylene and propylene homopolymers, copolymers, terpolymers, etc. Suitable materials include polyesters such as poly(methytmethacrytate) and poly (ethylene terephthate). Also suitable are polyamides such as poly (hexamethylene adipamide), poly(omega-caproamide), and poly (hexamethylene sebacamide). Also suitable are polyvinyls such as polystrene and ethylene acrylates including ethylene acrylic copolymers. The polyolefins are preferred. These include homo-polymers and copolymers of the f ami 1 i es of- polypropyl eves, polyethylenes, and other, higher polyolefins. The polyethylene s include LOPE, HDPE, LLOPE, and very low density polyethylene.
Blends of the above thermoplastics may also be used. Any thermoplastic polymer capable of being spun into fine fibers by meltblowing may be used.
A broad range of process conditions may be used according to the process of the invention depending upon thermoplastic material chosen and the type of web/product properties needed. Any operating temperature of the thermoplastic C 1 1 f? cTrn "-r- ... . _ ..._ WO 92107122 2 0 9 3 81 ~ POf/US91/07377 .g-1 material is acceptable so long as the materials is extruded from the die so as to form a nonwoven product. M acceptable range of temperature for the thermoplastic material in the die, and consequently the approximate temperature of the diehead around the material is 350'-900°F. A preferred range is 400°-150°F.
For polpropylene, a highly preferred range is 400°-65U°F.
Any operating temperature of the air is acceptable so long as it permits production of useable non-woven product. An acceptable range is 350°-900°F.
The flow rates of thermoplastic and primary air may vary greatly depending on the thermoplastic material extruded, the distance of the die from the collector (typically b to 18 inches), and the temperatures employed. M acceptable range of the ratio of pounds of primary air to pounds of polymer is about 20-500, more commonly 30 - 100 for polypropylene. Typical polymer flow rates vary from about 0.3 - 5.0 grams/hole/minute, preferably about 0.3-1.5.
EXPERIMENTS
Experiments were carried out using a one-Inch extruder with a standard polypropylene screw and a aie having the following description:
no. of orifices 1 orifice sire (d) 0.015 inches nosepiece included angle 6U' orifice land length 0.12 inches Air slots (defined by air plates) 2 mm opening and 2 mm neg. set back Other test equipment used in Series I Experiments included an air conduit semicircular in shape and having one longitudinal slot formed in the flat side thereof. The air conduits in the other Experiment were in the form of slotted pipes 1 inch in diameter.
_Series I Experiments The resin and operating conditions were as follows:
SUBSTITUTE SHEET
1 Resin: 800 MFR PP (ExxorrT~~ 3495G) Grade 01e Temp.: 430'F
Melt Temp.: 430'F
Primary Air Temp.: 460'F
Primary Air Rate: 1b.5 SCFM per . of in die width Polymer Rate: 0.8 gms/min.
Slot opening: 0.030 in.
Web collector; screen 12 inchesfrom the die The a, b, and angle A values for the tests this of series were 1", 1 1/2", and , respectively.The dataare +30' shown in Table I.
Table 1 CRUSS-FLOW AYG.
tEST CHAMBER WEIGHT TYPE Of CITlf1 UIAMETER2DIA.
STD.
H0.CONOITIOH PRESS. GM/M2 Web MICRONS DEYIATIOH
m N/TEX
- -~ -1-1Base Case 0 44.30 Brittle 10.5 7.93 2.93 1-2' 0 41.77 "
2-1Crossflow Device 0 39.90 ' 15.6 1.57 2.80 In Place 2-2' 0 37.30 ' 13.5 3-1'+ Secondary Air 0 40.80 ' 13.4 8.33 3.67 Taped Off 3-2' 0 40.80 " 12.4 _ 4-1Crossflow Device 5 37.30 Tough, 19.4 6.59 2.20 In Place Soft 4-2' S 37.30 " 17.7 5-1" 14 33.80 ' 22.3 6.52 1.87 5-2' 14 33.80 " 16.8 f-1'+ Secondary Air 14 31.60" 19.3 6.87 2.18 Taped Off b-2' 14 37.30 " 17.8 7-1' S 32.90 ' 19.6 7.65 2.26 7-2" 5 32.30 ' 17.7 et ~oG~TtTt ~T~ e~ur-r-T
WO 92/07122 ~ ~ ~ ~ ~ ~ PCT/US91/07377 ~ 11 -1 11-TEtiACITY was measured by cutting 1" wide strips and testing in an Instron tensile tester with zero separation between ,)aws. Jaw separation speed was 1.0 inJmin.
2Average fiber diameter yeas measured by optical microscope with an overall magnification of 400. The microscope was focused an a sample of the web and every fiber within the view area was measured using a reticulated ocular. Several different focus areas were selected at random to give a total fiber count of 50. The average reported is a simple number average of all io fiber measursnents for each sample.
3The air velocities for 5 and 14 psi were 705 fps and 1030 fps, respectively.
The Table I data demonstrate that the crossflow air resulted in the following 1; (a) The diameter of the filaments was decreased.
(b) The filament diameter distribution was more uniform.
(c) The web strength eras improved.
(d) The quality of the web was improved.
ZC Series lI Experiments:
These tests employed the same line and polymer but with one tubular air conduits permitting adjustment of the a, b, and angle A settings. Table 2 presents the data for Series II
Experiments.
$U~$'TI'TU~'i~ ~~1EET -WO 92/07122 ~ Q 9 ~ ~ ~ O PCT/US91/07377 1 Tabte 2 CROSSFLOW1 AYG.
CHAM$ER FIBER
TESTSETTINGS PRESSURE OIAM.STD.
ANGLE
N0. a b psi A OEVIAT10N
1 _ _ _ - 10.853.79 2 1/2"1/2" 2 -35' 8.48 2.93 103 ~~ ~~ 4 " 7.06 2.65 4 " " 8 8.72 3.49 3/8"5/8" 2 -20' 6.36 2.61 6 " " 4. 6.17 2.16 7 " " 8 " 8.16 2.9 1'8 1/4"7!8" 2 0' 8.6 2.4 . " " 4 " 7 2. 65 ,g .
" " 8 " 9.58 2.05 11 3/8"1' 2 20' 9.0 3.12 12 " " 4 8.96 2.65 2013 " g 9.22 3.23 14 1/2"5/4 Z 45 9.22 2.48 " " 4 ' 8.66 3.0 16 " " 8 " 8.47 1.98 25lAirvelocities psi e 476 fps, 654 at wer fps, 761 2, 4, 6, and fps,and859 respectively.
fps, These data indicate that for all a, b, ana A settings the filaonent avg. diameters were reduced and the size distributions 30 ire decreased. The 0 to negative angle settings (0 to -35') gave the best results and are therefore preferred. Table 2 data indicates that Lhe optimum crossflow chamber pressure or velocity depend on the geometry.
~u~~~ u~~~
WO 92/071ZZ ~ ~ ~ J V ~ ~ PGT/US91/07377 1 Series III Experiments:
These tests employed only one crossflow conduit (under the filament discharge) having a, b, and A settings of 3/8", 5/8", and -20, respectively. The primary air flog rate (at a temp. of 530') was varied and the die and melt temperatures were 500°. The other conditions were the same as in Series I and II tests. The data for Series III tests are shown in Table 3.
Table 3 CROSSFLUNAVERAGE
CHAMBER FILAMEMT
TEST PRIMARY AIR PRESSURE DIAMETERSTD.
N0. RATE (SCFMJ~psi DEVIATION
1 11 - 8.77 3.33 2 18 - 5.07 2.56 3 27 - 3.77 2.22 4 18 2 2.83 1.11 5~ 18 4 3.16 1.06 6 18 ~ 3.72 1.33 7 27 2 2.7 1.36 8 27 d 2.4 0.89 9 27 8 3.58 1.44 *per inch of die width Test Runs 1-3 in this table show the effect on fiber diameter by increasing primary air rate with no crossfiow air used. The use of crossflow air gives a significant reduction in diameter and diameter standard deviation at both tow and high primary air rates. Again, an optimum crossflow air rate was observed. Highest crossflow air (8 spi) produced larger diameter filaments than medium crossflow air (4 psi), although still smatter than for the 0 crossflow air base case.
Best results appear to be obtained at crossf)ow velocities between 476 fps (2 psij and 859 fps (8 psi). Tests have shown that chamber pressure as low as 1 psi can produce improved results.
SUBSTITUTE SHEET
2~193g10 WO 92/07122 P(.'T/US91/07377 1 Series IY Ex~riments:
These tests were conducted wtth two crossflow conduits illustrated in Figure 2. Each conduit was.ad3usted independently of the other to provide different crossflow contact areas. The upper conduit had a, b, and A settings of l/2", 3/4", and +30', respectively; and the lower conduit had a, b, and A settings of 1/Z', 1", and -20, respectively. The data for Series III
Experiments are presented in Table 4.
Table 4 CROSSFLOw CHAhIBER AYG.
TEST PRESSURE FI8ER STD.
N0. PSI DIAMETER DEYIATION
upper lower 1 0 0 5.69 2.58 2' ~ 0 2 3 .45 1.19 3 2 2 3.9 1.53 .
4 6 2 3.23 1.0 S 4 4 3.95 1.58 6 8 4 3.64 1.37 These data indicate that the settings of the upper and lower conduits can be varied and still provide improved results.
It is significant to note that Test No. 2 using only the lower eonduit gave better results than all but one of the other Series IV
Experiments.
.. In summary, the method of the present invention may be viewed as a two stage air treatment of extruded filaments: the prfwary air contacts the filaments at an angle of between about 22' to about 45' to to impart drag forces on the filaments in the direction of filament extrusion, the crossflow air contacts the extruded filaments at a point down stream of the contact point of the primary air and at a contact angle of at least 10' greater than the contact angle of the primary air on the same side of plane 12 to impart undulating flow shape to the extruded filaments. As viewed in Figure 2 the contact angle of the primary air is SUBSTITUTE SHEET
WO 92/07122 2 ~ 9 3 ~ ~. J PGT/US91/07377 ~ 15 -1 determined by the eenter line of the passages 31 and 32 with plane 12. fie contact angle of the crossflow air from conduit 1T above plane 12 (defined Dy the focus of slot 34 and plane 12) is at least 10' larger than the contact angle of the primary air from passage 31 as measured clockw5~e. Likewise, the contact angle of crossflow air from the conduit 17 below the plane 12 is at least 10' larger than the contact angle of the primary air fro;a passage 32 as measured counterclockwise in Figure 2. The crossflow ai,r has a major velocity component perpendicular to the direction of filament extrusion and a minor velocity component parallel to the direction of filbnent extrusion.
- ~ SUBSTITUTE SHEET
Claims (11)
1. In a meltblowing method comprising extruding a polymer melt through a plurality of parallel orifices arranged in a row to form a plurality of filaments, contacting the extruded filaments with sheets of air converging from opposite sides of the row of filaments to impart drag forces on the filaments forming a filament/air stream, and depositing the filaments on a collector or substrate, the improvement comprising contacting the filaments in the filament/air stream with crossflow air to disrupt the normal flow shape of the filaments, the crossflow air being of sufficient velocity and rate to create or increase undulations in the flow shape of the filaments thereby increasing the drawdown of the filaments and decreasing the average diameter of the filaments by at least 10% over that attainable without the crossflow air under the same operating conditions.
2. The method of claim 1 wherein the step of contacting the filaments with the crossflow air is carried out by directing air flow onto the extruded filaments in a region between the orifice discharge and 1/4 the distance between the orifice discharge and the collector or substrate, the crossflow air flow being perpendicular to, or having a major velocity component perpendicular to, the axes of the orifices and a minor velocity component toward or away from the direction of filament discharge.
3. The method of claim 1 wherein the orifices of the meltblowing die have centerlines which lie in the same plane, and the crossflow air is in the form of a sheet, the direction of which forms an angle with said plane, said angle ranging from +45 degrees to -35 degrees with respect to the vertical where (+) indicates an angle. away from the orifices and (-) indicates an angle toward the orifices.
4. The method of claim L wherein the crossflow air disrupts the normal flow patterns of the filaments within 1 inch from the discharge of the orifices.
5. The method of claim 1 wherein the crossflow air has a flow rate of between 20 to 300 SCFM per inch of the row of orifices and a velocity of between 200 to 1200 fps.
6. The method of claim 1 wherein the direction of the crossflow air has a major velocity component perpendicular to the direction of filament extrusion and a minor velocity component parallel to the direction of filament discharge.
7. The method of claim 1 wherein the orifices have a diameter between 100 to 1200 microns and the filaments deposited. on the collector or substrate have a diameter of between 0.5 to 20 microns.
8. The method of claim 1 wherein the crossflow air disrupts the flow of the filaments within a region beginning within 1/2 inch of the orifice discharge.
9. The method of claim 1 wherein the step of contacting the filaments with crossflow air is carried out by directing crossflow air from a source positioned on one side of the filaments/air stream.
10. In a meltblowing method comprising extruding a polymer melt through a plurality of parallel orifices arranged in a row to form a plurality of filaments, contacting the extruded filaments with sheets of air converging from opposite sides of the row of filaments to impart drag forces on the filaments forming a filament/air stream, and depositing the filaments on a collector or substrate, the improvement comprising contacting the filaments in the filament/air stream with crossflow air to disrupt the normal flow shape of the filaments, the crossflow air being continuous and at the same rate and being of sufficient velocity and rate to create or increase undulations in the flow shape of the filaments thereby increasing the drawdown of the filaments.
11. The method of claim 1 or 10 wherein the direction of said crossflow air is at least 10 degrees greater than the angle of the converging air sheet on the same side of the row of orifices.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US596,057 | 1990-10-11 | ||
| US07/596,057 US5075068A (en) | 1990-10-11 | 1990-10-11 | Method and apparatus for treating meltblown filaments |
| PCT/US1991/007377 WO1992007122A1 (en) | 1990-10-11 | 1991-10-03 | Method and apparatus for treating meltblown filaments |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2093810A1 CA2093810A1 (en) | 1992-04-12 |
| CA2093810C true CA2093810C (en) | 2001-10-02 |
Family
ID=24385812
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002093810A Expired - Fee Related CA2093810C (en) | 1990-10-11 | 1991-10-03 | Method and apparatus for treating meltblown filaments |
Country Status (6)
| Country | Link |
|---|---|
| US (1) | US5075068A (en) |
| EP (1) | EP0552285B1 (en) |
| JP (1) | JP3037420B2 (en) |
| CA (1) | CA2093810C (en) |
| DE (1) | DE69115920T2 (en) |
| WO (1) | WO1992007122A1 (en) |
Families Citing this family (48)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5273565A (en) * | 1992-10-14 | 1993-12-28 | Exxon Chemical Patents Inc. | Meltblown fabric |
| US5405559A (en) * | 1993-12-08 | 1995-04-11 | The Board Of Regents Of The University Of Oklahoma | Polymer processing using pulsating fluidic flow |
| CA2190957C (en) * | 1994-05-26 | 1999-04-06 | Martin H. Beck | Polyester insulation |
| US5688468A (en) * | 1994-12-15 | 1997-11-18 | Ason Engineering, Inc. | Process for producing non-woven webs |
| US5591335A (en) * | 1995-05-02 | 1997-01-07 | Memtec America Corporation | Filter cartridges having nonwoven melt blown filtration media with integral co-located support and filtration |
| US5652048A (en) * | 1995-08-02 | 1997-07-29 | Kimberly-Clark Worldwide, Inc. | High bulk nonwoven sorbent |
| US5667749A (en) * | 1995-08-02 | 1997-09-16 | Kimberly-Clark Worldwide, Inc. | Method for the production of fibers and materials having enhanced characteristics |
| US5711970A (en) * | 1995-08-02 | 1998-01-27 | Kimberly-Clark Worldwide, Inc. | Apparatus for the production of fibers and materials having enhanced characteristics |
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-
1990
- 1990-10-11 US US07/596,057 patent/US5075068A/en not_active Expired - Fee Related
-
1991
- 1991-10-03 CA CA002093810A patent/CA2093810C/en not_active Expired - Fee Related
- 1991-10-03 JP JP03518293A patent/JP3037420B2/en not_active Expired - Lifetime
- 1991-10-03 EP EP91919720A patent/EP0552285B1/en not_active Expired - Lifetime
- 1991-10-03 WO PCT/US1991/007377 patent/WO1992007122A1/en active IP Right Grant
- 1991-10-03 DE DE69115920T patent/DE69115920T2/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| JPH06504094A (en) | 1994-05-12 |
| DE69115920D1 (en) | 1996-02-08 |
| EP0552285B1 (en) | 1995-12-27 |
| WO1992007122A1 (en) | 1992-04-30 |
| CA2093810A1 (en) | 1992-04-12 |
| US5075068A (en) | 1991-12-24 |
| JP3037420B2 (en) | 2000-04-24 |
| DE69115920T2 (en) | 1996-08-14 |
| EP0552285A1 (en) | 1993-07-28 |
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| EEER | Examination request | ||
| MKLA | Lapsed |