US3692618A

US3692618A - Continuous filament nonwoven web

Info

Publication number: US3692618A
Application number: US865128A
Authority: US
Inventors: Oskar Dorschner; Franz Josef Carduck; Christoph Storkebaum
Original assignee: Metallgesellschaft AG
Current assignee: GEA Group AG
Priority date: 1969-10-08
Filing date: 1969-10-09
Publication date: 1972-09-19
Anticipated expiration: 1989-09-19
Also published as: DE1950669B2; ES380122A1; DE1950669C3; FR2032855A5; AU1200470A; DE1950669A1; JPS4828386B1; BE757138A; NL7006394A; IL33894A0; AT317408B; SU372832A3; CH527310A; GB1297582A; ES379169A1

Abstract

FORMATION OF A NONWOVEN WEB SUITABLE FOR THE PRODUCTION OF TEXTILE-LIKE OR PAPER-LIKE SHEET MATERIAL BY SIMULTANEOUSLY SPINNING A MULTIPLE NUMBER OF CONTINUOUS FILAMENTS OF A SYPTHETIC POLYMER SUCH AS POLYPROPLYLENE. GATHERING THE FILAMENTS INTO A STRAIGHT ROW OF SIDE-BY-SIDE, SUBSTANTIALLY EVENLY SPACED APART, UNTWISTED BUNDLES, EACH CONTAINING AT LEAST 15 FILAMENTS, SIMULTANEOUSLY DRAWING EACH BUNDLE DOWNWARDLY AT A VELOCITY OF AT LEAST 3,000 METERS PER MINUTE IN AN INDIVIDUAL SURROUNDING GAS COLUMN FLOWING AT SUPERSONIC VELOCITY, AS FOR EXAMPLE BY PASSING THE BUNDLES THROUGH A ROW OF AIR GUNS AND DIRECTING THE SAME TO IMPINGE ON A HORIZONTAL CARRIER BELT MOVING IN A DIRECTION SO THAT THE BUNDLES IN THEIR SURROUNDING GAS COLUMNS EXTEND IN A STRAIGHT ROW ACROSS THE CARRIER AT RIGHT ANGLES TO THE DIRECTION OF ITS MOVEMENT; CONTROLLING THE GAS COLUMN BY A CONTROL OF ITS DIVERGENT WIDTH AND/OR OSCILLATING THE SAME SO THAT THE LIMITS OF CONTACT OF THE EDGE OF EACH COLUMN WITH THE CARRIER OVERLAP THE LIMITS OF CONTACT OF THE EDGE OF THE ADJACENT COLUMN BY AT LEAST 50 PERCENT OF THE OVERALL WIDTH OF CONTACT OF AN INDIVIDUAL GAS COLUMN WITH THE CARRIER, AND MAINTAINING THE LAY-DOWN SPEED OF THE FILAMENTS IN RELATION TO THE SPEED OF THE CARRIER MOVEMENT SO THAT PRIOR TO AND/OR AS THE BUNDLES IMPINGE AGAINST THE CARRIER, THEY ARE DIVIDED INTO SUB-BUNDLES OF PARALLEL FILAMENTS

WHICH DEPOSIT ON THE CARRIER IN A LOOP-LIKE ARRANGEMENT EXTENDING BACK AND FORTH ACROSS THE DIRECTION OF TRAVEL OF THE CARRIER WITHIN THE LIMITS OF THE GAS COLUMN SURROUNDING THE BUNDLE, FORMING A WEB WHICH IS CHARACTERIZED BY A MULTIPLE NUMBER OF SIDE-BY-SIDE LENGTHWISE SECTIONS, EACH SECTION BEING FORMED BY THE SUBBUNDLES OF PARALLEL FILAMENTS LYING IN A LOOP-LIKE ARRANGEMENT EXTENDING BACK AND FORTH ACROSS THE WIDTH OF THE SECTION AND CONTAINING MULTIPLE OVERLAPPING SECONDARY SMALLER LOOPS AND SWIRLS WITH THE ADJACENT INDIVIDUAL SECTIONS OVERLAPPING EACH OTHER WITHOUT STRATIFICATION AND WITH THE LOOPS, SECONDARY LOOPS AND SWIRLS OF ONE SECTION RANDOMLY SUBSTANTIALLY COMPETELY INTERMINGLED WITH THE OVERLAPPING PORTION OF THE ADJACENT SECTION. THE WEB AFTER ITS LAY-DOWN MAY BE INITIALLY STABILIZED BY HEAT-SEALING, NEEDING OR TREATING WITH A BINDER SUCH LATEX AND SUBJECTED TO FURTHER TREATMENTS CONVENTIONAL IN THE NONWOVEN ART.

Description

Sept. 19, 1972 o. DoRscI-INER VET Al- 3,592,513

CONTINUOUS FILAMENT NONWOVEN WEB Filed Oct. 9. 1969 7 Sheets-Sheet 1 F/g l /0/ /00 AI-Jvwvwvvv o. DoRscHNER l-:rAL 3,692,618

CONTINUOUS FILAMENT NONWOVEN WEB Sept. 19, 1972 Filed oct. 9, 1969 7 Sheets-Sheet 4 A TTORNNS Sept. 1 9, 1972 o, DORsl-{NER EI'AL 3,692,618

CONTINUOUS FILAMENT NONWOVEN WEB Filed Oct. 9, 1969 7 Sheets-Sheet 5 l* C Fig 5a b LagA l C Hg. 5C b INVENTOR. 05m/2 DosCH/VER FRANZ ,7055/5 CAROL/CK Sept. 19, 1972 o. DoRscHNER EI'AL 3,692,618

CONTINUOUSV FILAMENT NONWOVEN WEB Filed Oct. 9, 1969 7 Sheets-Sheet 6 Fig. 7a

o. RSCHNER ETAL 3,692,618

CONTINUOUS FILAMENT NONWOVEN WEB Filed Oct., 9. 1969 7 Sheets-Sheel'l 7 Fig 7c INVENTOR. 05m/Z UORSCHNER FRANZ JGSEF CARDUCK United States Patent O U.S. Cl. 161-72 14 Claims ABSTRACT F THE DISCLOSURE Formation of a nonwoven web suitable for the production of textile-like or paper-like sheet material by simultaneously spinning a multiple number of continuous filaments of a synthetic polymer such as polypropylene, gathering the filaments into a straight row of side-by-side, substantially evenly spaced apart, untwisted bundles, each containing at least filaments, simultaneously drawing each bundle downwardly at a velocity of at least 3,000 meters per minute in an individual surrounding gas column fiowing at supersonic velocity, as for example by passing the bundles through a row of air guns and directing the same to impinge on a horizontal carrier belt moving in a direction so that the bundles in their surrounding gas columns extend in a straight row across the carrier at right angles to the direction of its movement; controlling the gas column by a control of its divergent width and/or oscillating the same so that the limits of contact of the edge of each column with the carrier overlap the limits of contact of the edge of the adjacent column by at least 50 percent of the overall width of contact of an individual gas column with the carrier, and maintaining the lay-down speed of the filaments in relation to the speed of the carrier movement so that prior to and/or as the bundles impinge against the carrier, they are divided into sub-bundles of parallel filaments which deposit on the carrier in a loop-like arrangement extending back and forth across the direction of travel of the carrier Within the limits of the gas column surrounding the bundle, forming a web which is characterized by a multiple number of side-by-side lengthwise sections, each section being formed by the subbundles of parallel filaments lying in a loop-like arrangement extending back and forth across the width of the section and containing multiple overlapping secondary smaller loops and swirls with the adjacent individual sections overlapping each other without stratification and with the loops, secondary loops and swirls of one section randomly substantially completely intermingled with the overlapping portion of the adjacent section. The web after its lay-down may be initially stabilized by heat-sealing, needling or treating with a binder such latex and subjected to further treatments conventional in the nonwoven art.

This application is a continuation-in-part of copending applications Ser. No. 693,017, filed Dec. 22, 1967, and Ser. No. 783,556, filed Dec. 13, 1968, both now abandoned.

This invention relates to a continuous ilament nonwoven web and a process for forming the same. The invention more particularly relates to the production of nonwoven webs from continuous yfilaments of synthetic polymers such as polyolefins, polyamides, polyesters or ICC blends or copolymers thereof, which webs will be formed into textile-like, felt-like or paper-like sheet materials.

Nonwoven webs which are produced from staple fibers which are bonded together at their crossing points are well known and have found wide-spread commercial use. It is also known to produce such webs from continuous spun filaments of synthetic polymers. The production of such webs from continuous spun filaments offers the advantage of convenience and speed in production allowing a combination of the spinning and web-forming process with more or less a direct conversion of the polymer melt into the web by spinning the melt into filaments which are directly laid down as the web. The production of webs of this type, however, has presented diiiiculties in the art in that, as the filaments are spun and laid down, the same tend to retain their spinning parallelism forming ropy aggregated bundles which impart an undesirable non-uniformity to the web in both appearance and strength. Furthermore, in order to form webs with a practical width, it is necessary to form individual lengthwise sections from separate filament bundles, and the strength and uniformity of these sections varies considerably from the adjoining or overlapping portions.

It has been proposed (see U.S. Pats. 3,338,992 and 3,341,394) to avoid the above-mentioned disadvantages of filament aggregation into ropy bands by developing an electrostatic repellant charge on the individual filaments which are laid down, so that each individual filament is randomly laid down in the web with the avoidance of parallel bundles. In accordance with these patents, an attempt was made to achieve greater uniformity by complete random distribution and lack of parallelism of the individual filaments, and the webs so produced were characterized by this random distribution as measured in accordance with the patents by the coefiicient of variation of the filament separation. In accordance with the process so described, the electrostatically charged filaments had to be laid down in a manner so that the repelliug like charges could cause the same to fan out and separate from each other, which limited the production speed and could present lay-down diiiiculties. Furthermore, the strength inherent in the use of parallel bundles of filaments could not be achieved.

In some prior known processes, the filaments, after spinning, were passed through an air gun utilizing a highvelocity jet of air in order to draw the same and lay the same down as a random web on a moving carrier. In order to produce a web of practical width, it was known to lay down a number of side-by-side sections utilizing a multiple number of air guns. It was generally believed desirable to stagger the air guns one behind the other as they extend across the width of the carrier in order to achieve the desired overlap of the sections. This, however, caused what might be termed a stratification between the overlapping sections, i.e., the sections laid down by the following gun would lay down on top of the section laid down by the more advanced adjacent gun, so that the strength and uniformity between the overlapping portions did not match the strength of the individual sections themselves. This for example would occur when the web was laid down from a row of guns which would extend in a direction diagonally across the width of the carrier.

One object of this invention is a process which avoids the prior art disadvantages and which allows the formation of a nonwoven web from continuous filaments of a synthetic polymer at much higher production speeds with the obtaining of uniform web characteristics and with the retaining of the strength of parallel bundles of filaments.

A further object of this invention is a novel web which is characterized by greater strength and uniformity than the prior art webs.

These and further objects will become apparent from the following description read in conjunction with the drawings, in which:

FIG. 1 is a schematic cross-sectional representation showing the formation of the web in accordance with the invention;

FIG. 2 is flowsheet showing the process step sequence and the major apparatus components used in an embodiment of the process of the invention for producing a heat sealed web;

FIG. 3 is a cross-sectional view of an aspirator jet or air gun used to draw and project the filaments;

FIG. 4 is a detailed schematic rview of the projection of a filament bundle onto a lay-down surface;

FIG. 5 is a transverse view of the deployment of the air guns with respect to the lay-down surfare; FIG. 5A shows the placement of stationary air guns; FIG. 5B shows oscillating air guns; and FIG. 5C shows the positioning of air guns to achieve multiple overlapping;

FIG. 6 is a schematic representation of the microscopic orientation of a section formed by a filament bundle from a single pneumatic jet on the lay-down surface;

=FIG. 7 is a schematic representation of the microscopic configuration of sub-bundles into which the filament bundle is distributed and their loop-like arrangement; and

FIG 8 is a reproduction of an actual photomicrograph taken of a web made according to this invention.

In accordance with the invention, a nonwoven web is formed by simultaneously spinning a multiple number of continuous filaments of a synthetic polymer. The spinning is effected in the conventional manner from the melt, with for example the melt of the polymer being extruded through a multiple number of downwardly directed spinning nozzles or spinnerets preferably extending in a row or multiple number of rows. The filaments as they are spun are gathered into a straight row of side-by-side, evenly spaced apart, untwisted bundles each containing at least and preferably from 50 to 150 filaments. These filament bundles are simultaneously drawn downwardly at a Velocity of at least 3,000 meters per minute, and preferably from 3,500 to 8,000 meters per minute in individually surrounding gas columns owing at a supersonic velocity and thus directed to impinge on a substantially horizontal carrier. The gathering of the filaments into the bundles and their drawing and directing to impinge on the carrier is preferably effected by passing the bundles through air guns which surround the filaments with a column or jet of air which is directed downward at supersonic velocity. The air guns are arranged so as to extend in a straight row in a direction extending across the carrier at right angles to its direction of movement, so that the bundles confined in the gas columns as the same strike the moving carrier extend in a line or row at right angles across the carrier. The carrier may be a conventional carrier used in the nonwoven art, such as an endless carrier or belt screen or the upper portion of a drum, as for example a screen drum. The filament bundles containing a number of parallel filaments are laid down on the carrier in a loop-like arrangement with primary loops extending back and forth across the Width of a section defined by the impingement of the air column from one air gun on the carrier. Before and as the parallel filament bundles impinge the carrier, they are broken up into sub-bundles containing a lesser number of parallel filaments and forming secondary smaller loops and swirls which overlap each other and those of adjacent sections to result in substantially complete intermingling with the overlapping portions of adjacent sections. The laid-down filament bundles then form a continuous uniform nonwoven web which may be consolidated and stabilized by compacting, heat-sealing, needling or treating with a binder, e.g., latex and other further treatments known in the art.

Thus, this invention involves four principal process steps, viz spinning of the polymeric filament, drawing, lay-down to forni a web, and consolidation of the web.

The polymeric fibers that may -be suitably used in the present invention are oriented crystalline or crystallizable fibers made of any thermoplastic polymer capable of forming a melt which can be spun. Illustrative polymers are the polyolefins, e. g. linear polyethylene, isotactic polypropylcne, polyisobutylene, polybutadiene, and the like; polyurethanes; polyvinyls; and the like; polyamides such as polyhexamethylene adipamide and polycaproamide; polyesters such as polyethylene terephthalate and copolyesters of ethylene glycol with a mixture of terephthalic and isoterephthalic acids; or mixed polymers, copolymers, including condensation copolymers, block graft copolymers, and the like, based on the same monomers as the polymers mentioned above.

The polymer is melted for example in an extruder and the melt delivered by pumps to the spinning equipment. The spinning of the filaments is carried out with spinning equipment capable of producing filament at a rate of at least 0.5 and up to l5 grams per orifice per minute. Suitable equipment comprises downwardly directed spinning nozzles or spinnerets which extrude molten polymer to form the desired filaments. The spinnerets are suitably arranged in a row of multiple number of rows parallel to the bank of air guns which extends transversely across the longitudinal direction of movement of the lay-down surface. Optionally, each spinneret produces at least a sufficient number of filaments to feed one air gun, i.e., at least 15 and preferably from 50 to 150 filaments, although more usually one spinneret will feed a plurality of air guns. Thus, for instance, spinnerets having from 200 to 1000 orifices can be employed. The spinneret orifices may have diameters of from 0.1 to 1.5 millimeters, preferably from 0.3 to 1.2 millimeters to produce typical filament sizes. The throughput of molten polymer generally ranges from 0.5 to 1.5 grams per minute per orifice. Spinning temperatures usually range from 250 C. to 350 C. and, of course, are dictated by the specific polymer fiber that is being extruded. The extruded filaments are cooled with cooling air.

The filaments produced by the spinning apparatus are preferably drawn to a thickness of from about 10 to 50 microns and are thus in the textile denier range, e.g., the filaments may have denier values of from about 1 to 20, although lower or higher denier filaments may be used depending on the end product to be formed. Thus, in forming a nonwoven web suitable for the production of textile-like sheet material, filaments of from l to 10 denier would be used; to make paper-like sheet material filaments of from 3 to 12 denier are suitable. For coarser products such as carpet backing material thicker filaments of from 5 to 20 denier are employed. The drawn filaments generally have an elongation at break above and a tensile strength of more than 2.5 grams/denier, e.g., from 3-7 grams/denier.

The spun filaments are gathered into a straight row of side-by-side bundles containing at least l5, and preferably from 50 to 100, filaments per bundle and drawn and projected by suitable equipment, preferably air guns, capable of producing the supersonic velocity air columns required by this invention. The gathering of the filaments into bundles after they emerge from the spinnerets may be achieved by appropriate deployment of the air jets themselves or by other suitable gathering means.

The filaments are drawn at high speeds, i.e., at from at least 3000 meters per minute and speeds as high as 8000 meters per minute can be used. The air guns that can be employed for this purpose are aspirator jets. Such an air gun has a nozzle portion through the throat of which primary aspirating air is smoothly expanded to supersonic velocities into an outwardly diverging expansion chamber. A guide tube for the filament and secondary aspirating air extends centrally through the throat and through the expansion chamber to a constant diameter draw-off tube. The primary aspirating air flows substantially parallel to the filaments issuing from the guide tubo and does not impinge on the filaments in such a manner as to cause intermingling or twisting of the filaments but flows so as to maintain good separation and preferably to allow the bundles to expand and to sub-divide into sub-bundles of parallel filaments. Substantially complete parallelism between the filaments within the filament bundle issuing from the draw-off tube is thereby obtained. A suitable air jet apparatus is shown in FIG. 3 in which the air jet consists of an upper part 2 screwed onto a lower part 1. Upper part 2 accommodates conical inlet funnel 3, for the filaments and secondary air, terminating in guide tube 4. This conical inlet opening 3 has a generating angle a of 5 to 15, preferably 7 to 11, to aid in the separation of filaments throughout their passage through the jet. The height of the inlet funnel 3 must not exceed 40 times the inside diameter of guide tube portion 4 and usually will be no more than to 20 times of the inside diameter of tube 4. The lower part 1 of the air jet assembly has a cue or two annular bores with air inlets communicating therewith for the supply of primary aspirating air and comprising annular holdback chamber 12. The holdback chamber is bound inwardly by vertical baffle walls 13 which end upwardly in a circular corner 14 connecting with funnel shaped jet cavity 15 which tapers inwardly to the narrowest point of throat 16. The cavity then enlarges outwardly to form expansion chamber 17 and ends in a cylindrical draw-ofi` tube 18. The conical enlargement of jet cavity 15 outwardly is measured by angle and this angle is generally from 8 to preferably 10 to 15. Thus, the outer wall of guide tube 4 forms with the expansion chamber at point 16 an annular throat through which the aspirating gas is accelerated to sound velocity and passed downward to expansion chamber 17. The generating angle y of jet funnel 15 should be between 20 and 50.

The annular area between the end of guide tube 4 and the beginning of draw-off tube 18 (i.e. the end of expansion chamber 17) forms the annular cross-section of the expansion zone. The end of the guide tube is located somewhat below the beginning of draw-off tube 18 which is uniformly cylindrical from top to bottom.

Other air gun apparatus capable of projecting filaments at high speed while preventing mutual interference between the filaments is usable in this invention. Generally such air gun apparatus is provided with an aspirating medium which expands to supersonic velocity and reaches Mach figures of up to 3.5 and higher in flow either parallel to the direction of the filaments or slightly away from the direction of the filaments. In this way, impingement of the aspirating gas on the filaments at an angle is generally avoided by suitable construction of the expansion chamber in relation to the guide tube from which the filaments emerge. The aspirating medium is preferably cold or warm air, but steam or other suitable media may also be used. Generally, the inlet pressure of the aspirating gas is between 10 and 50 atmospheres gauge. Further description of suitable aspirating apparatus may be had by reference to copending Ser. No. 850,- 500, filed on Aug. 15, 196'9, now Pat. No. 3,655,862.

The filament bundles are projected against the carrier surface within individual surrounding gas columns generated by and expelled from the draw-off tube of the aspirator jet and directed to impinge on the carrier as shown schematically in FIG. 3. Air suction means are provided below the gas-permeable carrier surface to remove a portion of the air blown onto the carrier surface.

As a filament bundle or sub-bundle is projected against the carrier surface at high speeds the impingement of the filaments against the surface may cause the same t-ofurther break up, primarily in the form of smaller subbundles as hereinafter more fully explained, and to bounce up to form a turbulent layer of intermingled bundles and subbundles which are then laid down in the characteristic pattern hereinafter described. In the areas of overlap, turbulent filaments contained in adjacent air columns effectively interlock to form a continuous, uniform, nonstratified overlapping portion.

The manner in which lay-down is effected to result in formation of the desired uniformly strong, non-stratified web is a salient feature of this invention. Certain definitions and theoretical considerations concerning web characteristics are helpful in this connection.

A textile web can be described independently of its structure by two parameters, viz the basis weight f of the web, expressed in terms of grams of web per square meter of web, and the denier of the filament used (denier is defined as the weight in grams of a 9000 meter length of the filament). These two parameters can be combined to yield a definition for specific filament length l where l is the total filament length-deposited within a unit area:

1 .9 l @I er meters/sq. om.

The specific filament length l is independent of the the structure of the web, e.g., a given value for l might be the result of lay-down of a single filament or of a plurality of filaments emerging from one or more air guns.

The basis weight (f*) of web produced by a single air gun in the instant process can be calculated from the following variables:

and the basis weight is then defined as follows:

f* (77) ra'rn/ m t (10(0) g s sq. e er For the basis weight f of a multi-section web produced by a number of air guns, Formula 2 becomes 3) f: (m) (y.) no

where m is the number of air guns and B is the width (in meters) of the conveyor belt on which lay-down takes p ace.

If the air guns are so arranged as to result in 4the laying down of contiguous but non-overlapping sections, it is evident that f*=f, i.e. the basis weight produced by one air gun is equal to the total produced basis weight. If f* is less than f, the lay-down sections must overlap and the degree of divergence between f and f* is a measure of the degree of overlapping. Generally, the web produced according to this invention will have f/f* ratios of from 2:1 to 4: 1.

The specific filament length l can also be expressed in terms of the above variables. Since minute), combination of definitions (l), (2), and (4) resultsin grams/sq. meter Denier= (n) (Wa) (b) (v) X 104 where l* is the specific filament length produced by a single air gun. IFor the entire laid-down web, definitions (l), (3), and (4) are combined to yield:

Again, l=l* for contiguous, non-overlapping sections, and l will be greater than l* if overlapping is present, i.e. in an overlapped web the filament length deposited per unit area is greater than in a single section separately laid down by one air gun.

As pointed out above, the prior art efforts to achieve overlap of the lay-down sections involved sequential placement of air guns along the direction of longitudinal movel* (meters/sq. cm.)

(meters/sq. cm.)

ment of the lay-down surface, either by staggered banks of air guns extending across the width of the lay-down surface at various points, or by deploying the air guns diagonally across the width of the surface. In either case, it is evident that stratification must occur, i.e., that a web section laid down by one air gun is necessarily placed on top of, or below the next adjacent section inasmuch as the overlapping portion of one section is substantially completely formed before the subsequently formed overlapping portion of the next adjacent section is applied thereto. Essentially, ribboned sections are formed within the web structure wherein the ribbons are much stronger than the areas between adjacent ribbons and the strength of the overall web is therefore non-uniform. This is true even where the prior art e.g. U.S. Pat. 3,402,227, so arranged the air guns that the basis weight and specific filament length were substantially uniform throughout the web, by taking advantage of the Gaussian distribution of filaments laid down by one air gun, i.e. less filament laydown near the longitudinal borders of a section than near the center of a section, and overlapping sufiiciently t-o equalize filament lay-down over the entire width of a section. In the prior art techniques, this equalization required an overlap of from about 50 to 8O percent of one section with the adjacent section. Despite such equalization, of course, stratification still occurred with concomitant nonuniform strength of the web formed, despite relatively uniform density of the web across its width.

The present invention avoids such stratification by providing for simultaneous formation, intermingling and overlapping of filament, sub-bundles, loops, and swirls, in adjacent lay-down sections.

In the lay-down of the web in accordance with this invention, at least 50 percent of the Width of a section overlaps with the next adjacent section. Thus, a middle section having adjacent sections on each side must be completely overlapped. With reference to FIG. A, the overlap width c must be at least 50 percent of the laydown width b of a section. If air guns are employed which are reciprocated or oscillated in a plane transverse to or at an angle of up to 45 with the direction of movement of the lay-down surface, the section width b is measured across the broadest sweep of the air cone that is generated as shown in FIG. 5B. In FIG. 5B the shaded portions of the air cone cross-sections represent the area swept by oscillation of the air gun away from its central (unshaded) position and the overlap distance c is measured between the terminal points of the broadest sweep of adjacent overlapping air cones. It is possible to have substantially more than 50 percent overlap between adjacent sections. As shown in FIG. 5C, the overlap width c can approach the section width b so that the two widths are nearly equal. In such a case there may be lay-down portions, such as d in FIG. 5C, in which laydown is effected from at least three air guns. In any event, the overlap distance c must be at least 50 percent of section width b, and is preferably at least 70 percent of section width b, no matter whether the air guns are oscillated or not. It will be evident, however, that the use of oscillating or reciprocating air guns will generally permit a broader swept area, i.e. a greater section width b, and a greater degree of multiple overlapping (lay-down from three or more air guns in one lay-down portion). Such multiple overlapping provides particularly strong and uniform webs.

In the present invention, overlapping is achieved without stratification by arranging the air guns in a row straight across the moving carrier belt, i.e. at right angles to the direction of longitudinal movement of the carrier belt to provide an overlapping series of air columns as shown in FIG. 5. In the case of stationary, i.e., nonoscillating air guns or air cones, the overlapping between adjacent air columns generated by adjacent air guns is achieved by so choosing the distance between air gun and carrier surface that the air columns, which expand outwardly as they move downwardly from the air gun to lay-down surface generally assuming a conical form, overlap to the desired extent as they impinge on said surface. This is illustrated in FIG. 5. Since a given air gun results in an air column leaving the air gun at a natural expansion angle, e.g. from about 5 to about 10 from the vertical, the lay-down width of a section is determined solely by the distance between the drawoff tube of the air gun and the carrier surface. Generally, to achieve the degree of overlap required by this invention, a distance of 0.3 to 1.5 meters is chosen between air gun and lay-down surface where the air guns are spaced from each other at 6 centimeter intervals.

In one embodiment of this invention, the air guns are oscillated as the filament bundles are laid down. The plane of oscillation can be lateral, i.e. transverse to the direction of the longitudinally moving lay-down surface, or at an angle of up to 45 relative to the direction of movement of the lay-down surface. In either case, the air column generated by each air gun is moved from side to side across the Width of a section as illustrated in FIG. 5B. When the air guns are oscillated, especially complete intermingling of filament bundles and sub-bundles in the overlapped areas is achieved in that the filament bundles and sub-bundles contained in adjacent air columns effectively interlock in a manner analogous to shuffled cards, thereby providing strong and uniform bonding in the overlapped areas. Another advantage of using oscillating air guns is that the width of a lay-down section and the extent of overlap produced by a given lay-down apparatus assembly is variable by varying the amplitude of oscillation. In commercially useful embodiments amplitudes of oscillation of from about 5 to 30 millimeters are usable. In addition, the frequency of oscillation is variable within certain limitations and can be optimally selected to produce the desired manner of lay-down and degree of non-stratified overlapping. The maximum theoretical frequency (Lmax) possible, which would result in laydown of the filament bundles back and forth along the lay-down width with no time to form a loop upon themselves, is given by the equation:

(cycles per sec.)

where Wa is a draw-off speed of the filaments and meters per minute and b is the width of a section. Thus, for instance a draw-off speed of 4000 meters per minute and a lay-down width of 0.3 meter will permit a maximum frequency of 111 cycles per second. At frequencies approaching maximum frequency a regular primary loop pattern is formed while at lower frequencies the filaments deviate from a regular pattern by forming loops upon themselves and secondary smaller loops and swirls as shown schematically in FIG. 6. As the frequency is lowered, a higher number of crossing points of filament bundles, sub-bundles, and loops which cross each other are formed and, as a result, the strength of the web formed is increased. To produce a web according to this invention, at least ve times as much filament length must be condensed in secondary loops and swirls as would be required to form only primary loops. Thus, frequencies of oscillation of up to 0.2 of Lmax are employed in this invention. It will be appreciated that in the calculation of maximum frequency according to the above Equation 7 it was assumed that the speed of oscillation is constant. This is not strictly true because this speed is temporarily reduced to zero at the reversing points. The hold-up of such reversing points may be adjusted by suitable mechanical modification, to alter the distribution of the basis weight and thereby to equalize the basis weight throughout the width of a section. Thus, it may be desirable to somewhat slow the speed of the oscillating air gun as it moves off center to avoid unevenly high build-up of filament near the center of such section. Frequencies of 2 to 7 cycles per second have been used to advantage in preparing practically useful webs.

It is also possible to reciprocate the lay-down surface laterally, either under stationary overlap-ping air jets, or under simultaneously oscillating air jets, to enhance the intermingling effect in the overlap sections.

It will be evident that there is a critical relationship between the speed at which filament is impinged on the lay-down surface, in terms of length of filament per unit time, and the speed with which the lay-down surface is continuously advanced longitudinally. If the two speeds were the same, clearly the filament bundle emerging from an air gun would be laid down in a single straight line in the direction of carrier surface movement. If oscillating air guns are employed the minimum draw-off speed (WA) must additionally satisfy the limitation imposed by Equation 7, above, to ensure not only formation of primary loops extending back and forth across the width of the carrier surface but to provide sufiicient filament length that a substantially greater filament length is condensed in loops and swirls.

In order to obtain the characteristic lay-down pattern of the web of this invention, it is necessary (a) to maintain a relatively high filament draw-off speed and (b) to so adjust the carrier surface forwarding speed that specific fiber lengths of (1*) of at least 0.6 meter/sq. cm., yand preferably of from 5 to 100 meters/ sq. cm. are obtained. For a given draw-off speed WA and a section width b, such specific liber lengths are attained by calculating the requisite carrier belt velocity v according to Formula 5 above and maintaining such velocity during operation of the process of this invention.

For a filament of a given denier, the critical relationship of draw-off speed and carrier surface velocity can also be expressed in terms of specific fiber weight f* (grams of filament deposited per square meter of web). The specific fiber weight of web produced in accordance with this invention should be between 5 and 1500, and preferably between and 1000 grams per square meter. The specific fiber length l* can be calculated from the specific fiber weight values I(ft) for a given filament denier by applying definition (l), above, and the carrier surface velocity required for a given draw-off velocity WA can then be calculated by applying Formula 5, above. Accordingly, a given draw-off velocity and filament denier dictate the carrier surface velocity required to produce the desired specific fiber weight.

By maintaining the aforedescribed operating variables and lay-down conditions a characteristic web structure is formed in accordance with this invention. With reference to the macroscopic configuration of the filament bundles, FIG. 6 shows the arrangement of filament bundles across the width of a lay-down section b. It can be seen that the filament bundles impinging on the lay-down surface are distributed as a flattened loop extending back and forth over the width of the section wherein a large percentage (at least 80 percent) of the filament length is condensed in smaller loops and swirls overlapping and contacting each other. The degree of openness of the primary loop is a function of the travelling speed of the carrier in relation to the oscillations of the filament lay-down across the carrier which in turn is a function of the oscillations within the air column and of the column itself. The number of small loops formed across the width of the primary loop depends on the draw off velocity as well.

With respect to the macroscopic configuration of the web, FIG. 7 is a schematic representation of the break-up and distribution of a filament bundle containing a plurality of parallel filaments as it impinges on the carrier surface. These parallel filament bundles as they form the smaller loops described macroscopically above, are sometimes split up upon lay-down into smaller sub-bundles still containing a number of parallel filaments and occasionally some monofllaments are formed from such bundles or subbundles. It will be noted that substantial parallelism, i.e.

10 two or more filaments laid down in the same direction at substantially unchanging distance from each other, is maintained in the formation of these sub-bundles. Parallelism of the sub-bundles may be temporarily interrupted by a turning point when the outer filaments of a filament sub-bundle cross over to the inside to form the inside filament of the continuing sub-bundles. A turning point is thus formed where a number of filaments of one subbundle cross each other substantially simultaneously. With particular reference to FIG. 7A, a parallel filament bundle projected from an air gun impinges on the lay-down surface at a and may split up into several sub-bundles b each containing a lesser number of substantially parallel filaments and into a monofilament such as c. The sub-bundles form loops such as d which may cross each other at points such as e or may cross the original filament bundle or other sub-bundles at points such as g or f respectively. Similarly, a monofilament occassionally forms certain crossing points with primary bundles or sub-bundles or by crossing over by itself. It will be noted from FIG. 7B that a filament or sub-bundle b after forming a loop d may again run almost parallel to other filament sub-bundles and thereby enhance the parallelism which is a characteristic feature of the macroscopic configuration of the web of this invention. In FIG. 7C, the possibility of repeated splitting up of parallel filament sub-bundles into still further sub-bundles containing fewer parallel filaments is shown.

Once the web is completely laid down on the carrier surface in accordance with this invention, the web may be consolidated and stabilized by compacting, heat-sealing, needling and latex treating. The web is conveniently precompacted, e.g., in the nip of two pressure rollers, to form a fabric-like material which is then subjected to elevated temperature while further compacting pressure is applied thereto. For instance, according to FIG. 2, it can be passed over a heated roll and through a pressure belt machine. The temperature of the web as it passes over the heated roll should be maintained at a temperature just below the melting point of the lower limit of the melting range of the particular plastic material from which the web was formed. For instance, temperatures of from 3 C. to 50 C. below the melting point or melting range, preferably 5 to 30, under the melting point or melting range can be suitably used. Maintenance of such a temperature causes crystallization of the polymer and it has been found that such poly-crystallization results in a finished product having particularly high physical and chemical stability. The pressure applied to the web, e.g., a pressure belt machine or other suitable means, as it passes over the heated roll, should be between 2 and 50 kg. per sq. cm. or a line pressure of 10-80 kg./ cm.

The treatment time during which the web is subjected to elevated temperatures and pressures in a belt machine should be from about 2 to 30 seconds, and in an extruder type machine, less than 2 seconds.

When the webs are consolidated by the application of heat, welding together of the filament bundles is effected at filament intersections of crossing filament bundle loops lying approximately on straight lines. Such short imaginary lines are distributed over the area of the nonwoven fabric or sheeting in an isotropic pattern but are not aligned. This pattern results in the low elongation, the high dimensional stability and the unusually high tensile strength of the products according to the invention. This characteristic of the compacted nonwoven fabric or sheeting is shown in FIG. 8 which is a reproduction of an actual photomicrograph taken of a web made according to this invention.

By varying the temperature, pressure, and residence time within the above stated ranges, the nature of the consolidated web produced can be varied considerably. For instance, the use of a relatively high treatment time at high pressure and high temperature results in a paperlike sheeting wherein the polymer has an isotropic orientation. Unlike sheeting obtained by conventional proceuses, sheeting produced in accordance with such invention can be written on like conventional paper but cannot be torn by hand. In such sheeting, the fibrous nature of the web is largely eliminated, such sheeting being either translucent or transparent and having a smooth, dense surface. Webs having such paper-like characteristic are preferably made of a polymer selected from the group consisting of polyolelins, polyamides and polyesters.

On the other hand, the nonwoven fabric character of the lay-down web may be substantially preserved if the compacting and consolidation conditions are relatively rnild, i.e. if moderate pressures and temperatures and short treatment times, are used. Web consolidated under such conditions is permeable to air and water and has a fibrous structure. Such fabric may be heat-sealed on one side or on both sides.

The physical characteristics of the consolidated web may be further altered by use of a liner made of, e.g. woven fabric, and inserted between the pressure belt and applied to the web as it passes through the high pressure and temperature zone. The pattern of the liner will impress itself onto and into the web so that the appearance of the resulting consolidated web will simulate that of the material used as a liner. Thus, liners consisting of coarse, porous, woven fabrics result in a porous or perforated sheeting or fabric material. It has surprisingly been found that such properties can be impressed on the web by heat treatment on only one side of the web.

The web can also be decoratively embossed by use of appropriate liners.

The capacity of the instant process to produce a number of widely varying non-woven web products having different properties and new properties with respect to known products in itself represents a substantial advance in the art. It will be evident that a wide range of products can be made by using the same equipment and that such equipment is far simpler than conventional processing machines such as papermaking machines, drawing machines and the like.

Apparatus suitable for implementing the aforedescribed process comprises, essentially, a plurality of spinning devices, such as spinnerets, through which thermoplastic material s extruded to form filaments, draw-off means in which the filaments are pulled through pneumatic jets and blown onto a lay-down surface, such as a moving conveyor belt.

A detailed understanding of apparatus utilizable in this invention and of the following examples may be had by reference to FIG. 1 which shows the formation of the web in accordance with this invention and to FIG. 2 which is a flow sheet showing the process step sequence and the major apparatus components used in the process of the invention; in FIG. 3 an aspirator jet used to draw and project the filaments is shown.

With reference to FIG. l, thermoplastic material is introduced into and melted and extruded in extruder 100 which is driven by motor 101. The extruded material is supplied by pump 103 to the spinnerets 1. The resultant filaments are drawn through an air jet 2 which is continuously supplied with propellant gas under pressure through inlet 2a. In air jet 2, the aspirating gas flows substantially parallel to the filaments issuing from a guide tube therein and does not impinge on the filaments in such a Way as to cause intermingling of the filaments, but flows so as to maintain good separation between the filaments, and, preferably, in such a way as to spread the filaments to form sub-bundles, i.e. to sub-divide the bundles into sub-bundles of substantially parallel filaments. The thus-formed sub-bundles then impinge on lay-down receiver belt 3 which is supported and actuated by rollers 4. The lay-down receiver is partially surrounded by baffle means 104 disposed between the exit of the air jet 2 and the lay-down receiver 3 and additionally is disposed above exhaust chamber 105 in which the air blowing onto the receiver 3 from the air jet 2 is at least partially removed.

With reference to FIG. 2, molten thermoplastic material is extruded through spinneret l to form a bundle of filaments which are drawn through an air jet 2 which is continuously supplied with air under pressure through air inlet 2a. The bundle of filaments is projected from the mouth of the air jet at high velocity against continuously moving conveyor belt 3 which is supported and actuated by rollers 4. The projected filaments are laid down in spirals from the air jet mouth against the moving belt to form a fiat-loop fabric web extending across the width of the air cone generated by the air jet as projected against the belt. The belt, with the filaments deposited thereon, is passed through the nip of a pair of pressure rolls S and the fabric web is then stripped from the belt and taken up by stripper roller 6 and may be passed through a machine in which the crude fabric web is heated and firmly compressed. The pressure belt machine shown in FIG. 2 comprises a heated roll 7, a pair of guide rollers 9 and a tensioning roller 10 which activate the pressure belt 8 to press the fabric Web against the heated roll 7. Usually, the guide rolls 9 are so arranged with respect to the heated roll 7 that from 30-80 percent of the circumference of heated roll 7 is contacted with the continuously moving pressure belt pressing against the fabric web. In order to prevent sticking of the fabric web to the heated roll 7, it may be desirable to interpose a moving liner between heated roll 7 and the moving fabric web, for instance, by means of liner dispensing roll 13- and liner take-up roll 14 supplying and withdrawing liner 15 to and from the heated roll 7. The liner may be made of suitable non-sticking material, such as a woven fabric. After passing through the pressure belt machine, the finished b fabric web is stripped from the pressure belt and taken up by a second stripper roller 11 and then wound up on take-up roller 12 as finished product.

FIG. 3 shows how an air cone containing the filament bundle being projected is formed by the air emitted at high velocity from the mouth of the air jet 2. The air cone has a true round conical shape if the air jet mouth is circular or it may have a pyramidal shape if the air jet mouth is square or rectangular. The width b of the length-Wise section of fabric web being laid down depends on the degree of divergence of the air cone emanating from the air jet mouth and on the distance h between the air jet mouth and the lay-down surface.

The following examples are illustrative:

EXAMPLE 1 Polypropylene granules were melted in an extruder having an extruder screw which had a diameter of 45 millimeters and a length of 28 times its diameter. The polypropylene had a crystalline melting range of 160- 164 C., a density of 0.906 gram per cubic centimeter and melt index i5 at 230 C. of about 5 before extruding. Extrusion was effected under a pressure of 35 kilograms/sq. cm. and the melt had a temperature of 310 C. at the outlet. The spinneret had 300 orifices. The throughput per hole was 0.66 gram per hole per minute. The polypropylene filaments emerging from the spinneret were cooled to below 60 C. and drawn in bundles of 30 monofilaments each by ten air jets arranged with even spacing in a row transverse to the direction of movement of a conveyor belt located 1.3 meters below the nozzles. The air jets were operated at a pressure of 22 atm. The air consumption was 30 In.3 per hour per air jet. The dimensions of the air jets were 2.0 mm. diameter at the inlet and 4.3 mm. diameter of the outlet tube. The filaments were drawn through the air jets by an air stream having a velocity of flow of about 520 meters per second. The air jets were oscillated at a frequency of 2 cycles per second. The draw-off speed of the filaments driven by the air stream was 4000 meters per minute which results in a titer of 1.5 denier. The tenacity of the filaments of 1.5 denier was 4.3 grams per denier. The basis weight of the web was grams per sq. meter of laid down web, corresponding to a throughput rate of 13 10.8 4kilograms per hour. The belt was moved at a speed of about 3 meters per minute. Bundles of continuous filaments were blown onto the moving conveyor belt in randomly overlapping sub-bundles, each containing from 3 to 5 substantially parallel filaments, to form a nonwoven web. The resulting web was formed of a plurality of side-by-side lengthwise sections of polypropylene filaments distributed in a form of small sub-bundles of substantially parallel filaments in a loop-like arrangement extending back and forth across a section in a section width of 0.25 meter with a filament length of 5 meters being condensed across a section in a loop-like arrangement as multiple overlapping secondary smaller loops and swirls. The adjacent individual sections overlapped without stratification by 65 to 70 percent of their width. The loops and swirls of one section were completely intermingled with those of the adjacent sections. The basis weight of any given web segment did not deviate by more than 7 percent from the average Weight of the entire web. The resulting web had a width of 70 centimeters and a very uniform structure. To facilitate the handling of the web, the latter was slightly compacted by two pressure rolls. The slightly compacted web was then drawn in at a speed of 3 meters per minute (i.e. equal to the laydown belt speed) between the belt and roll of a pressure belt machine.

EXAMPLE 2 Nylon 6 was melted in the extruder described in Example 1. The viscosity of the molten material was 2.6 11,51 and the temperature of the melt was 283 C. The pressure of the extruder was 60 atm. The spinneret had 150 orifices with a diameter of 0.6 mm. each. The throughput per hole was 1.1 grams per hole per minute. The nylon filaments were drawn off with the air jets and under the operating conditions of Example 1. The resulting filament draw-off speed was 3300 meters per minute which corresponds to a titer of 3.0 denier. The basis weight of the laid down web was 350 grams per sq. meter. The laid down web was needle punched under the following conditions:

Type of needles 36 Punching depth mm 13 Stitches per cm.Z 90

Strokes per minute 410 EXAMPLE 3 A polyester containing 0.4 percent by weight of titanium dioxide was melted in an extruder and processed according to the following conditions:

Spinning conditions Extruder: 45 mm. diameter; length 1'26 cm. (28 d.) Spinneret: 300 orifices Spinning temperature: 275 C.

Number of air jets:

Throughput: 1.1 grams per hole per minute Draw-ofi speed of the filaments: 4500 meters per minute Titer: 2.2 denier Air supply pressure for air jets: 25 atm.

Inlet diameter of air jet: 2.5 mm.

Outlet diameter of air jet: 5.10 mm.

Basis weight: 100 grams per m? This resulting laid down web was heat sealed at a temperature of 102 C. with slight application of pressure, and embossed on both sides.

EXAMPLE 4 Polypropylene resin was processed in the following equipment at the following conditions according to the general procedure set forth in Example 1:

Extruder diameter: 120 mm. Length: 360 cm. Melt temperature: 286 C.

14 Number of spinneret holes: 1412 (14 sections with 108 holes each) Number of air jets: 14 Throughput: 1.5 grams per hole per minute Titer: 3 denier Draw-off speed: 3800 meters per minute Filament tenactiy: 3.6 grams per denier Elongation at break: 129% Air jets:

Pressure: 22 atm.

Inlet diameter: 3.0 mm.

Outlet diameter: 6.6 mm. Air consumption: m per hour Basis weight of the web: grams per m.2

EXAMPLE 5 The web produced as described in Example 4 was consolidated and then fed between the pressure belt and the roll of a heat sealing machine. The steel roll was heated to C. and the pressure applied by the tensioned belt was atmospheres. The steam-heated steel roll was 700 millimeters in diameter and was contacted by the pressure belt on 65% of its circumference.

The web was heat sealed on both sides in two passes to yield the following web properties:

Strip strength: Elongation at break, percent Parallel (1.82 kg./mm.2) 19 Transverse (1.5 kg./mm.2) 12 Tongue tear: Kg./g./m.2 Parallel 0.056

Transverse 0.057

EXAMPLE 6 The web produced as described in Example 4 was passed through the heat sealing machine in only one pass at a temperature of 158 C. of the steel roll and a pressure of 150 atmospheres. The resulting web had the following properties:

Strip strength: Elongation at break, percent Parallel (2.6 kg./mm.2) 38 Transverse (2.2 kg./mm.2) 32 Tongue tear: Kg./g./m.2 Parallel 0.030

Transverse 0.026

EXAMPLE 7 The following table shows how the draw-off speed, which can be influenced by the design and the operating conditions of the air jet, influences the characteristics of the resulting filaments:

Product=Polypropylene Spinning hole diameter=0.6 mm. Length of capillary=2 times diameter Tenaety Elongation Titer Draw-ofi speed (rm/min.) (g./den.) (percent) (denier) EXAMPLE 8 A web produced under the conditions described in Example 4 but having a lower basis weight of 80 grams per m.2 (produced by correspondingly increasing the laydown belt speed) was latex treated using a commercial latex (No. 9210) produced by Synthomer Chemie, Germany. The basis Weight of the web after latex treatment 15 was 192 grams per m and the web had the following mechanical properties:

Latex Treatment What is claimed is:

1. A nonwoven web formed of a multiple number of sidebyside lengthwise sections each section being formed from a bundle of at least 15 continuous spun and drawn synthetic polymeric filaments distributed in the form of smaller sub-bundles of substantially parallel filaments in a loop-like arrangement extending back and forth across the width of the section with a substantially greater filament length of at least 500% being condensed in said loop-like arrangements as multiple overlapping secondary smaller loops and swirls, the adjacent individual sections overlapping each other without stratification by at least 50% of their Width with the loops, secondary loops and swirls of one section randomly substantially completely intermingled with those of the overlapping portion of the adjacent section, the weight of the web at the overlapping portions of the sections not varying from the overall weight of the web by more than 20%, the individual filaments forming the web being of between 1 and 20 denier having a tenacity of 0.5 to 6 grams per denier and the web having a weight of between 10 and 1500 grams per square meter.

2. Nonwoven web according to claim 1 in which said filaments are oriented polyolefin filaments.

3. Nonwoven web according to claim 2 in which said filaments are oriented polypropylene filaments.

4. Nonwoven web according to claim 2 in which said filaments are polyethylene filaments.

5. Nonwoven web according to claim 2 in which said filaments are polybutylene filaments.

6. Nonwoven web according to claim 1 in which said filaments are polyamide filaments.

7. Nonwoven web according to claim 1 in which said filaments are polyester filaments.

CII

16 8. Nonwoven web according to claim 1 in which said filaments are copolymers of polyolefins.

9. Nonwoven web according to claim 1 in which said filaments are blends of polyolefins, polyamides or polyesters.

10. Nonwoven web according to claim 1 having at least 5 parallel overlapping sections each section having a width of between and 300 mm., the adjacent overlapping portions of the sections having a width of between about 35 and 240 mm.

11. Nonwoven web according to claim 1 having at least 35 parallel overlapping sections each section having a width of between 180 and 300 mm., the adjacent overlapping portions of the sections having a width of between about and 240 mm.

12. Nonwoven web according to claim 1 in which a substantial number of said sub-bundles of substantially parallel filaments are welded together at their crossing points.

13. Nonwoven web according to claim 1 containing a binder binding a substantial number of said sub-bundles of substantially parallel filaments together at their crossing points.

14. Nonwoven web according to claim 1 in which said loop-like arrangement is formed of flattened loops extending back and forth across the width of the section, the length of the parallel bundles of filaments forming said flattened loops being condensed as multiple secondary loops and swirls.

References Cited UNITED STATES PATENTS 2,671,745 3/ 1954 Slayter ll-DIG 4 2,855,634 10/1958 Smart 161-169 3,394,046 7/ 1968 Smock et al. 161-72 3,402,227 9/ 1968 Knee 28-72 NW ROBERT F. BURNETT, Primary Examiner R. L. MAY, Assistant Examiner U.S. Cl. X.R.