US 3806289 A
Apparatus for producing a randomly mixed fibrous web of high strength and opacity. A thermoplastic polymer is extruded through a die having slots of varying length and cross-sectional area. Air at about the polymer melt temperature is impinged angularly on the fibers and allowed to expand thus cooling the fibers and breaking them up into varying dimensions as they are deposited on a carrier. In a preferred embodiment a controlled Coanda effect is applied so as to provide an overall wavy pattern of randomly mixed fibers.
Description (OCR text may contain errors)
United States Patent [191 Schwarz APPARATUS FOR PRODUCING STRONG AND HIGHLY OPAQUE RANDOM FIBROUS WEBS  V Inventor: Eckhard C. A. Schwarz, Neenah,
 Assignee: Kimberly-Clark Corp., Neenah,
 Filed: Apr-5, 1972 [211 Appl.No.:241,373
 US. Cl 425/72, 264/115, 425/461  Int. Cl B29f 3/08  Field of Search 425/72, 83, 461; 264/115,
[ 56] References Cited 1 UNITED STATES PATENTS 12/1953 12/1962 10/1970 Stalego 264/121 X White et al. 264/121 X FOREIGN PATENTS OR APPLICATIONS 3/1969 Great Britain 264/210 R Pukacz 264/121 x [4 1 Apr.23, 1974 61,192 5/1948 Netherlands 425/72 437,193 11/1967 Switzerland 264/115 Primary ExaminerR. Spencer Annear Attorney, Agent, or FirmDaniel J. I-lanlon, Jr.; William D. Herrick; Raymond J. Miller 57 ABSTRACT Apparatus for producing a randomly mixed fibrous web of high strength and opacity. A thermoplastic polymer is extruded through a die having slots of varying length and cross-sectional area. Air at about the polymer melt temperature is impinged angularly on the fibers and allowed to expand thus cooling the fibers and breaking them up into varying dimensionsas they are deposited on a carrier. In a preferred embodiment a controlled Coanda effect is applied so as to' provide an overall wavy pattern of randomly mixed fibers. v
7 Claims, 8 Drawing Figirres LINEAR v POLYMER H EAT TO EXTRUDABLE MELT EXTRUDE THROUGH SLOTTED DIE WITH VARYING SLOTS IMPINGE FIBERS wITH AIR HIGH VELOCITY PULSED HEATED GAS COANDA EXPAND GAS COOL FIBERS COLLECT FIBRIDS AND Fl LAM ENTS FIG. I
PATENTEU APR 23 m4 SHEET 2 [1P4 FIG. 3
APPARATUS FOR PRODUCING STRONG AND HIGHLY OPAQUE RANDOM .FIBROUS WEBS BACKGROUND OF THE INVENTION 1. Field of the Invention The invention relates generally to nonwoven fibrous webs. More particularly, the invention relates-to extrusion apparatus that produce webs characterized by high Strength and opacity.
2. Description of the Prior Art It is known to form fibrous webs by drawing fibers from an extruder and depositing them on a moving carrier such as a rotating screen or moving wire. It is further known to perform the drawing step by impinging a current of air against the fibers. U. S. Pat. No. 3,509,009 to I-Iartmann, for example, discusses such methods and apparatus for carrying them out including extruder dies formed by grooves in wedges which are placed together so that the grooves are juxtaposed. As
the polymer is extruded, the mass is blown into fine fibers through the use of aircurrents and forms a web on a moving carrier. This patent teaches, however, that it is preferred to draw continuous filaments by entraining them in a gas stream directed into the filament path and depositing them on a foraminous support.
It is also known and disclosed in U. S. Pat. No. 3,488,819 to Jackson, for example, that the Coanda effect of a divergent nozzle may be utilized to oscillate an airjet causing an entrained yarn to be deposited on a carrier in continuous crosswise movement. In addition, the prior art contains teachings of the use of dies for extrusion having various shapes and configurations of spinneret holes; such are disclosed, for example, in U. S. Pat. Nos. 3,249,669 and 3,528,129.
SUMMARY OF THE INVENTION The present invention has as a primary object to provide improvements in apparatus for-producing nonwoven fibrous webs of exceptional strength and' opacity for a given weight. Other objects and advantages will be apparent upon reference to the drawings and to the detailed description below. r
In accordance with the invention the improved webs are formed by heating a thermoplastic polymer to produce an extrudable melt, extruding the melt through a slotted film die having slots of correspondingly varying length and cross section, drawing the melt into fibers by impinging a gas at the melt temperature at an angle to the extruding polymer, cooling the gas and fibers by al lowing the gas to expand thereby causing the fibers to break up in varying lengths, and collecting the broken fibers into a web. In a preferred embodiment the apparatus includes means for providing a Coanda effect and angular deposition in an interlocking crosswise wave pattern.
BRIEFDESCRIPTION OF THE DRAWINGS showing means for provid- FIG. 8 schematically illustrates aformed web portion.
DETAILED DESCRIPTION OF THE INVENTION The apparatus of the invention will now be described in detail with particular reference to the preferred embodiments illustrated in the drawings.
Turning to FIG. 1, the process involves first the selection of a suitable thermoplastic polymer. Many such polymers capable of extrusion in fiber form are avail-' able, and the particular one to be utilized is a matter of choice based usually on considerations such as cost, melt temperature, fiber properties, and extrusion properties, as well as desired web characteristics. Examples of polymers contemplated for use in the invention include the following: polyolefins, nylons, polyesters, and
polyacetals. However, it will be recognized that other I slots with correspondingly varying slot length and cross sectional area dimensions. The phrase correspondingly varying" is used to indicate that the length and cross section area dimensions must vary in the same mannerl 'lhat is, the larger the slot length, the larger will be its cross sectional area. In general, 'each slot is preferably of uniform dimensions which are different from those of adjacent slots..The fibers emerging from the die are impinged by high velocity air at about, the melt temperature directed at an angle of from about 10 to 45 to the fiber orientation direction. The gas is thereafter allowed to expand rapidly causing cooling and fracturing of many of the fibers into a mixture of fibrids, short fibers and filaments of widely varying di mensions. In, the terms of this invention the words frbrids, short fibers and filaments are defined as follows: filaments aresubstantially continous strands generally of l to 20 denier, short fibers are discontinuous strands Vi inch to 3 inches inlength andgenerally of V: to 3 denier, and fibrids are short strands of less than V4 inch in length and generally less than A denier. This mixture is collected on a moving carrier such as a screen or the like and forms a strong, opaque web which may be removed and wound into rolls with apparatus conventionally used for such purposes. By
opaque" it is meant that the web has high opacity for As indicated by the flow diagram, FIG. I, an alternative embodiment includes the step of using a Coanda arrangement to direct the fibers. across the receiving carrier. Pulsed air may be used to cause the fibers to deposit in wavy patterns across the carrier surface. This manner of deposition increases the interlocking nature of the random pattern of the fiber-filament-fibrid mixture thus augmenting strength and opacity.
Turning nowto FIGS. 2 to 5, the invention willbe described in terms of the embodiment illustrated therein.
where particularly suitable for use with polyolefins, e.g., polypropylene, and results in a web having the previously I mentioned advantages of strength, opacity, and gross uniformity of formation. Of course, the particular dimensionsselected involve largely a matter of choice depending upon the desired fiber characteristics in the web and will, in some cases, differ widely from the example recited. In particular, the specific slot crosssection shape need not be as shown since it is recognized that the filaments, fibers, and fibrids will tend to become round in cross-section as cooling takes place.
It is only critical that the slots 20 exhibit significant variation in both length and cross-sectional area across the lip 16 of die 10. The ratio of length to cross section is preferably selected for each polymer to result in generally equal shear stresses for each slot. Thus, the conditions are such that in all cases,
Pa=sCL P die pressure, psi;
C slot cross sectional circumference, in.
s shear stress, lbs./in.
a slot cross section, in.
L slot length, in. thus, s/P constant= a/CL for each slot. While the circumference of the slots depends on the cross sectional sharia. sheath s me. h p is. s fer a." slots, it
will vary in proportion to V5. Hence, it is preferred that the individual slot lengths be proportioned'according to V5 to maintain a constant value of 'a/CL. By keeping the shear stress generally equal in all slots, flow through each one'is assured. The particular slot cross section shape depends upon the desired properties and end use. It may be round, rectangular, or triangular, for example. A dog-bone shape may be used to produce an effect of high luster.
. The number of teeth 18 per inch of width will simi-' larly be dependent upon desired fiber properties such as denier as well as web properties such as basis weight. However, it is contemplated that the typical ranges for these dimensions for producing a web with paper-like strength and opacity will be as follows: length of groove (L,L) 0.008 to 0.5 inch; cross sectional area of groove 0.0001 in. to 0.0025 in., preferably 0.0002 in. to
0.0015 in.; and number of grooves from about 5 to 100 within chamber 22.As shown in cross-section the housing. includesdual air manifolds 24 which direct air flow frpm a source "at elevated temperature (not shown) down the beveled edges of die 10 to lip 16 and out through nozzle 26. In accordance with the invention in a preferred embodiment, nozzle 26 includes an outlet 28 having a nearly symmetrical Coanda configuration which has been exaggerated in the drawing for illustrative purposes. By avoiding complete symmetry it is possible to produce higher stability on one side of nozzle 26 to which the fibers will naturally be drawn as they are formed; in the illustrated case the preferred side will be side 30 which has a slightly smaller, by about 1 to 10 per cent, for example, radius of curvature when compared to the radius of side 36. Channel 32 is pro vided in side 30 and connected to a source (not shown) of pulsed air. Such sources are well known and, in
longer fibers. The upper limit of 2 1,600 yards per minute has been selected as representing sonic velocity. It is recognized; however, that with special orifice designs, higher rates are obtainable; when available, these higher air rates may also be utilized with the present invention.
w The samba the fibers warlidaamriany tend to take due to the slight dissymetryof the Coanda configuration is illustrated by arrow A of FIG. 6,. As the air expands, rapid cooling of the polymer filaments 34 takes place causing them to separate into the various lengths forfilaments, short fibers, and fibrids. Air under pressure of about 0.1 to l psig, for example, is pulsed through channel 32 and, when air is flowing in the channel, causes displacement of the fiber flow towards side 36. Channel 32 is preferably positioned so that the excited pulsed air moves generally at a tangent to the outlet-curve of side 36 on nozzle 26, thus tending to urge the fibers in that direction as well, as indicated by arrow B. When air is not flowing in channel 32, the fibers will tend to resume the original flow direction A. The result, indicated by arrow C, is a generally sine wave deposition path in the direction of travel of carrier 38 with afrequency that depends upon the pulsing frequency. This frequency maybe, for example, in the range of 2 to 600 cycles per second. In a critically designed system, for example, an oscillating diaphragm of an earphone placed in channel 32 could beused to replace the air pulses and induce vibrations and fiber deposition at'a desired frequency.
deposited by nozzle 26. As shown, it is preferred thatdie 10 be disposed'angularly with respect to the lateral direction of movement of surface 38. The angle, a, se lected is not critical and preferably may vary, for exarnq In operation, the polymer is extruded through die 10 pie, between 30 and 60. It has been found that this angular deposition in combination with the controlled Coanda effect results in wavy motion of the fibers in the direction of movement of surface 38. The fibers are caught in this interlocking pattern as a random mixture of oriented filaments, short fibers and fibrids. The rapid cooling caused by the nozzle expansion prevents deorientation of the fiber molecules and shrinking of the fiber ends which has previously resulted in balling and lumping producing poor formation characteristics.
FIG. 8 schematically illustrates the web 40 formed on surface 38 which may be subsequently treated by methods and for purposes that are well known. For example calendaring may be used, and the resulting sheet will display increased stength and density due to the fibrids intermixedbetween the fibers.,These fibrids also increase the total inner surface area thus providing in- Y I forcing material for tapes. Other uses for specific combinations will be apparent to those skilled in this art.
In summary, the invention comprises an improved apparatus for use in a methodfor producing strong, opaque fibrous webs including the steps of extruding a polymer through a die having slotsof corresponding varying dimensions and impinging the fibers at an angle with heated, high velocity air. The fibers are cooled by rapid air expansion and collected on a carrier to form a web. A controlled Coanda may-be used and the fibers deposited at an angle with respect to the carrier in preferred arangements. The apparatus of the invention includes a die having a lip with slots of correspondingly varying dimensions as well as means for applying a con trolled Coanda effect and angular deposition in the preferred embodiments.
, I claim: i
LApparatus for producing a high strength opaque web of random filaments, fibers. and fibrids; from I a thermoplastic polymer comprising, in combination,
a. means for providing the polymer in extrudable form; b. an extruder adapted to receive said polymer and having a slotted die with slots of correspondingly varying length and cross sectional area dimensions selected to result in generally equal shear stresses for each slot;
c. means for providing high velocity air at about the extrusion temperature of said. polymer;
d. conduits for said air causing impingement with-the extruding polymer as it emerges from the extruder, said impingement being from opposing sides at an angle of from about l0 to 45 to the fiber'direction and tending to draw and orient said emerging fibers; j
e. adiverging nozzle configuration for rapidly expanding and cooling said air and-extruding polymers; and
f. means for collecting said extruding polymer as it is formed into filaments and fibrids.
2. Apparatus of claim 1 wherein said extruder and die are disposed angularly with respect to the collecting means. i
3. Apparatus of claim 1 further including means for providing a Coanda effect wherein said diverging nozzle has a nearly symmetrical Coanda configuration and pulsing means are provided to disturb the Coanda cf feet with the result that said extruding polymer is deposited on said collecting means in aninterlocking wave pattern. 7
4..Apparatus of claim 1 wherein said die slots vary regularly in length .inthe range of from about 0.008
inch to 0.500 inch andin cross sectional area in the range of from 0.0001 in. to about 0.0025in. with from five to slots per inch providing generally equal shear stresses ineach slot.- n
5. The apparatus of claim 3 wherein said pulsing means is a conduit for pulsed air at a pressure slightly 7. The apparatus of claim 5' wherein said pulsing means includes an oscillating diaphragm.
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