US3293718A - Apparatus for forming non-woven web structures - Google Patents

Description

T. M. SHEETS 3,293,718

APPARATUS FOR FORMING NON-WOVEN WEB STRUCTURES Dec. 27, 1966 Filed July 1, 1963 FIGI DIRECTION COLLECTOR MOVEMENT I NVENTOR United States Patent 3,293,718 APPARATUS FOR FORMING NQN-WOVEN WEB STRUCTURES Thomas Melvin Sheets, Wilmington, DeL, assignor to E. 1. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware Fiied July 1, 1963, Ser. No. 291,945 3 Claims. (Cl. 28-1) This case relates to a novel improved process and apparatus for handling continuously forwarded fibrous elements, especially those in the form of continuous filaments of synthetic organic polymeric material. More particularly, it relates to a process for laying down a plurality of these filaments upon a collecting surface in the form of a web of substantial width and of uniform thickness, the web being comprised of filamentary elements arranged in random nonparallel array.

In the following specification and in the claims, the term fibrous elements is intended to include any filamentary material of the types appropriate to the textile art, these including any fiber, filament, thread, yarn, or filamentary structure, regardless of diameter, or composition, although in preferred form the invention relates particularly to such materials in the form of continuous filaments of synthetic organic polymeric fibrous materials.

The term web includes mats, batts, nonwoven pile fabrics, and other interfelted interentangled, or commingled fibrous products which may generally be described as coherent sheets of entangled fibers made without the fibers first being spun into yarns and the yarns later interlaced by weaving, knitting, braiding, or other means of yarn manipulation in which the ends of yarns of finite length must be handled and intertwined.

The production of non-woven webs of fibrous elements is an activity of growing commercial importance. These webs not only permit attainment of textile structures having properties equivalent to previously known fabrics of the woven and felted types and at a considerably lower cost, but also permit reaching hitherto unattainable structures having desirable properties and combinations or properties in terms of end use function and aesthetics.

It has been the experience of those skilled in the art that achieving a given desirable structure requires controlling a large number of variables. Furthermore, it has been found that the controlling parameters in their desirable ranges more often than not are mutually exclusive; attaining one object in full often seems to require missing another object completely. As a result, the nonwoven structures known in the present state of'the art are the result of prudent although not always felicitous compromises in balancing one set of objects against another.

The problems encountered in the production of nonwoven materials are particularly difiicult when forming webs of substantial widths. These may be defined as webs exceeding in width 24 inches, and more usually extending to the range of 36 inches or wider. This condition largely results from the fact that the types of apparatus employed to produce the fibrous elements are of such a nature that a web of wide width requires the combining of a plurality of such devices. Furthermore, even when it is possible to provide a source of fibrous elements capable of producing a sufficient multiplicity of elements to lay down such a wide web, it has been found that, with the vastly increased dimensions of the source, the uniformity of distribution has rapidly declined, defeating the original purpose. Thus, it is more common practice in the art to team the plurality of elements and by one means or another attempt to combine these in a manner producing the least disturbance of the final prodnet.

Patented Dec. 27, 1966 The uniformity of the final product is best measured by basis weight which, as is well known, is a measure of Weight per unit area and ordinarily expressed in terms of ounces per square yard. This then is a quantity measurement related to the major dimensions of a sheet-like structure. Variations in basis weight are frequently in excess of :L-l( As a result of this variation and in combination with peculiarities of the types of laydowns hitherto employed, directionality of physical properties in the web machine direction vs. the cross machine direction have hitherto been considerably in excess of a desirable 1:1 ratio (directionality ratio) which would, of course, be isotropic. Indeed, so difiicult has it been to avoid anisotropy, that a directional property ratio of 1.5:1 represents a condition of outstanding uniformity in the present state of the art.

Another and obvious measure of uniformity is that of variation in web thickness but this, ordinarily, is reflected in variation in basis weight.

Inasmuch as the preferred form of web produced by the improved process of the instant invention is comprised of continuous filaments laid down in random nonparallel arrangement, another significant characterization is that which denotes the degree of randomness, i.e., the absence of fiber aggregates. Structures produced by the instant invention are characterized by the substantial absence of such filament aggregates and this absence may be measured by the bunching coefficient. The bunching coei'ficient, designated B.C., is defined as the ratio of the number of fiber spaces occupied by fibers relative to the total number of fiber spaces available. In this measurement the term fiber space represents the average space occupied by a fiber, and is calculated by dividing a unit distance of the nonwoven sheet structure by the total number of fibers oriented in a single direction in that unit length. The bunching coeificient concept is based on the premise that where the individual fibers disposed in the same direction are uniformly spaced from each other, each fiber space will contain one fiber and the bunching coefiicient of such a structure will be unity. In a nonwoven web which contains bunched fibers, some of the fiber spaces will contain bundles of fibers while others will be unoccupied and the bunching coeificient of such a structure will be less than one. The greater the filament aggregation, the lower the bunching coefficient. This concept was developed by D. R. Petterson, and is described in his Ph. D. thesis, On the Mechanics of Nonwoven Fabrics, presented to the Massachusetts Institute of Technology in 1958.

The basic equation is then:

Statistical analysis shows that the optimum value for bunching coefficient is approximately 0.87. The experimental determination is the same.

A process for producing nonwoven webs of fibrous elements disposed in random nonparallel arrangement is described in Belgian Patent 608,646, to Kinney. That patent describes a process in which a running multifilament bundle composed of substantially continuous synthetic organic filaments is charged electrostatically in such a manner as to separate each filament from adjacent filaments and these are thereafter collected on a receiver to form a nonwoven sheet product of the distinct type described.

The filaments may be charged by a corona discharge maintained in the vicinity, by triboelectric contact with a suitably selected guide means, or by other appropriate electrostatic methods. Ordinarily, such charging is accomplished while the filaments are under sufiicient tension that they do not separate until such tension is relieved, i.e., after they have been impelled toward the receiver whereupon they immediately separate and are then collected. In a preferred embodiment, freshly-formed melt-spun synthetic organic filaments are drawn, charged and forwarded with an aspirating jet, the action of which also serves to accelerate the charged filaments to the receiver. The output of a number of such jets may be combined to produce a wider Web.

This process is, of course, also applicable to filaments other than the synthetic organic type and with minor modifications may be employed with such filaments as glass and the like.

Where the output of a number of spaced parallel jets is combined to produce a wide web, electrostatic and aerodynamic interactions between the cone-like dispersion patterns of the individual jets produce non-uniformities, particularly across the web due to imperfect blending of the boundaries of the patterns.

One may attempt to employ mechanical means, such as contacting or deflecting surfaces, for additional distributing of the charged filaments as part of the process of combining the plurality of cone-like dispersion patterns issuing from the individual jets, so that the initially substantially parallel bundles of filaments, after being transformed into an array of cone-like dispersion pattterns, are also intermingled and edge-blended in the areas where the dispersion patterns overlap. The introduction of a surface for the purpose of distributing filaments is known in the art; for example, see the patent issued to Frickert, U.S. 2,875,503, and others of its type, in which a continuous strand is projected with a substantially high axial velocity against a deflecting surface and the deflecting surface is oscillated to sweep the resultant laydown of filaments across a collecting surface. However, such practices introduce further non-uniformities. In the instance where charged bundles of filaments are so manipulated, the product is not uniform but is characterized by an excessive number of ropey areas or, in terms of the precise characterizing criteria discussed, the product has a low bunching coetficient. Study of this occurrence has revealed that interaction between the filaments and the redistributing surface was responsible. However, recognition of the problem did not bring with it an immediate or obvious solution. It became apparent that the distributing means to be employed must of necessity be different from those known in the art, and must consider both aerodynamic interactions and electrostatic interactions such as are involved in practicing the art of the Kinney process.

The instant invention is an improvement over the prior art, involving a novel application of aerodynamic principles to provide the improved means and apparatus for the formation of wide non-woven sheets with superior uniformity, producing wide webs that have high bunching coefficients, indicative of substantial freedom from filamerit aggregates, combined with a maximum basis weight variation of or less and a directionality ratio of 1.5:1 or better.

Accordingly, it is an object of the present invention to provide an improved and novel process and apparatus for producing non-woven Webs characterized by a high degree of uniformity. Further, it is an object to so produce a web by simple and inexpensive, yet reliable and effective, means. Additionally, it is an object to lay down a nonwoven Web of fibrous elements in randomly distributed nonparallel array, characterized by uniformity of basis weight and uniformity of properties measured both in the direction of machine production and across that direction.

It is a still further object of the instant invention to provide improved process and apparatus for laying down webs of fibrous elements arrayed in random nonparallel arrangement, these webs being characterized by a maximum basis weight variation of no more than about 4 i10%, and by directionality of physical properties in the web machine direction vs. the cross machine direction of 1.5:1 or better and by a bunching coeflicient greater than 0.70.

And it is yet a still further object to modify and alter, in a predetermined manner, the distribution patterns of a plurality of fluid streams carrying fibrous elements, bearing electrostatic charges of the same sign and substantial magnitude, continuously forwarded by forces including aerodynamic, into a substantially uniform array of fiber elements, and to deposit such an array of filaments continuously in the form of a non-woven web of wide width and uniform properties.

These objectives are accomplished in an arrangement of process steps and means which:

Advance a plurality of electrostatically charged continuous filaments in streams of an elastic fluid from a filament supply zone toward a web-forming zone by means of a series of adjacent aligned jets to produce a series of dispersion patterns, each pattern issuing from an individual jet,

Subject each of the streams of fibers and fluid to aerodynamic transverse deflection forces, said forces being oscillatory in effect, at least partially orthogonal to the general direction of filament advances, and substantially parallel to the line formed by the series of adjacent jets, the said forces operating to intermingle the filaments of any two adjacent streams or patterns and thereby produce a laterally uniform curtain of filaments.

And deposit such curtain of filaments onto a web-forming surface in the form of a non-woven web of continuous filaments, each filament member of the curtain being deposited individually in random, loopy configuration within the web.

Preferably the oscillatory aerodynamic transverse deflection forces of this invention are provided by pairs of rotating, interacting airfoil devices diametrically opposed with respect to each stream and deriving their action from the coanda principle, discussed in detail below. In this preferred embodiment, the coanda effect, provided by each element of the pair of airfoil devices, in intermittent, and the two elements alternate substantially instantaneously in providing the rapid deflecting etfect. Since the two elements are thus opposed to one another, an oscillatory substantially instantaneously reversible deflection vector results. The oscillation causes good intermingling of the filament members of adjacent filament streams.

The invention will be more clearly understood and the advantages will become apparent by reference to the discussion below and to the figures which are given for illustrative purposes.

FIGURE 1 is a diagrammatic front elevational view of a preferred apparatus embodying the present invention.

FIGURE 2 is a front elevational View showing in detail an enlarged aspect of the preferred filament deflecting means of the present invention, and

FIGURE 3 is a top view partly in section taken at line 33 of FIGURE 2.

Referring to FIGURE 1, a spinning machine 1 is disposed with a plurality of spinnerets 2 so that the issuing filaments 3 pass directly to a first draw roll 4, Where the filaments are collected into the form of a ribbon, around first draw roll 4 and thence to second draw roll 4 operating at a higher speed than first draw roll 4. After wrapping around second draw roll 4', they pass through guide 5 and thence over charging target bars 6 which provide an area of unipolar ion flow for the corona discharge device '7. The corona discharge and charged target ele ments coact upon the filaments to provide an electrostatic charge upon the filaments, which are then introduced into jets 8 wherein they are advanced and emerge in a tensionfree manner, now bearing like electrostatic charges which tend to separate them. lmpelled in a downward direction by aerodynamic, electrostatic and gravitational forces, the filaments are next deflected by the aerodynamic oscillating deflection action of a pair of opposed rotating devices, 9 and 9. Detailed description of the action of these rotating devices is given below. Their action generally is based on the coanda effect, and each pair of these devices interacts to provide an oscillating separating and intermingling action to the adjacent filament streams so that these streams tend to become diverted into overlapping dispersion patterns or edge blended systems 16 in a manner producing a uniform curtain of filament which is forwarded to the collecting surface 11 under the additional attractive force of electrostatic'ally attractive surface 12 to form a web 13 of randomly disposed non parallel filaments having the desired high uniformity.

The coanda effect, named for its discoverer Henri Coanda, was first applied to a useful structure as described in U.S. 2,052,869. That patent describes an apparatus for controlling the discharge into an elastic fluid atmosphere of another elastic fluid moving at high velocity, wherein there are means for checking the flow located wholly on one side of the line of discharge. The present invention applies this principle in what is believed to be a novel way to attain an unexpected and useful result.

As illustrated in FIGURE 2, essentially, the stream of fluid as it issues from jet 8 carrying along with it the filaments 3, flows, in effect, through an asymmetric nozzle of which one wall is provided by a portion of one of the opposed rotating devices, 9 and 9' in alternating fashion. The other wall of the nozzle is fictitious, being formed by the ambient atmosphere. The fluid stream, because of its velocity, is at a pressure lower than that of the surrounding air which enables the stream to act on the surrounding air and induce it, by both surface friction, i.e. fluid shear, and also through pressure difference, to flow toward the real wall in a manner essentially perpendicular to that wall, causing the filaments to follow around the curvature essentially without touching the surface. As the kinetic energy of the stream is translated into momentum of ambient air, the filaments separate from proximity to the real wall and are borne downward in the induced flow of the large slower moving mass of secondary air under the influence of that flow combined with electrostatic and gravitational forces.

Of the two rotating devices, 9 and 9', only one is active at any given instant. The active element of the pair is that one which is momentarily presenting its layer radius grooved surface more closely to the filament-carrying air stream.

FIG. 2 illustrates in more detail the manner in which coacting aerodynamic elements are combined to bring about filament deflection and, thereby, formation of a curtain of filaments. The apparatus is positioned as shown in FIGURE 1. The pair of rotating devices, 9 and 9, each mounted on drive shafts 20 and 20' respectively, is positioned below each jet 8. Each rotating device consists essentially of a disk-like element having a thickness corresponding to the width of the fluid stream, carrying a peripheral circumferentially extending groove 14, and having portions cut away from the periphery of the disk-like element, such as portions 14 shown having reduced radial extent in the drawings. The residual groove portion 15, when suitably positioned relative to the filament aggregation, functions as a coanda device, causing filament deflection toward itself by reason of the induced air flow. The pair of elements 9, 9', and drive shafts 20, 20, are rotatably mounted on a support structure not shown, and are driven in opposed senses at the same speed by a conventional drive mechanism, not shown. Mounting of the disk elements 9, 9' is such that the residual groove portions of the two wheels are 90 out-of-phase in rotation to give a sharply alternating deflecting action. During operation, the elements 9, 9 are positioned so that the threadline passes midway between their centers or axes of rotation. As the elements 9 and 9 are rotated, alternate grooved sections approach the threadline and deflect it in accordance with coanda principles as already discussed to produce an oscillating, whipping motion as portrayed in FIGURE 2.

The process and apparatus according to the preceding descriptions produces a curtain of filaments which lays down into a non-woven web structure of extremely good uniformity. The filaments spread well and beta ray uniformities within are readily obtained. Similarly, directionality of physical properties in the web machine direction vs. the cross machine direction of 1.5 :1 or better are achieved. The process is capable of producing nonwoven webs characterized by high bunching coefficients.

The curtain of filaments produced in accordance with the process of this invention is preferably deposited on a foraminous surface, such as a cloth or wire screen 11. The surface may be in the form of a continuous moving belt. If desired, further control of filament deposition and isotropy of filament arrangement in the web can be obtained by the use of suction devices placed under the surface below the area of deposition in any part or all of that area.

As described in the Kinney patent previously referred to, the products of this process are extremely useful in a great variety of end uses, not only replacing previously woven materials with an economic advantage as in substrates for tent and tarpaulin fabrics but also replacing other non-woven materials such as felts employed in filter cloths, as well as producing a variety of hitherto unobtainable non-woven structures.

While a preferred embodiment of the invention has been disclosed in detail, many changes and modifications within the spirit of the invention will occur to those skilled in the art. Such changes and modifications are intended to fall within the scope of the following claims.

I claim:

1. In an arrangement for combining, in an elastic fluid atmosphere, a plurality of laterally spaced and aligned parallel moving streams of an elastic fluid having a plurality of fibrous elements dispersed therein and collecting the fibrous elements from the combined streams in the form of a unitary coherent non-woven web structure having uniform thickness, density, and directional properties, the improvement comprising stream combining and controlling apparatus, said apparatus comprising means for aerodynamically rapidly diverting each stream in an oscillating manner along a general lateral line of direction transverse to the path of stream movement, said general lateral line substantially coinciding with the plane defined by said parallel moving streams to cause the diverted streams to merge and form a single combined evenly blended continuous laterally extending moving stream of fluid and fibrous elements, said means comprising a set of movable members positioned in opposed positions adjacent each stream, said members constructed and arranged with respect to each stream to alternately check at opposed sides of said stream the flow of the elastic fluid atmosphere induced by said stream, each set of movable members comprising a pair of diametrically opposed rotatable elements each having an axis of rotation, each of said rotatable elements comprising a first portion spaced from said axis of rotation and rotatable into position closely adjacent said stream to check said induced flow, and a second portion spaced a lesser distance from said axis and inoperative to check said induced flow upon r0- tation of said element, the elements of each pair rotated in predetermined phase relationship to each other so that said induced flow is substantially instantaneously alternately checked by said first portions of each element at opposite sides of said stream to rapidly divert said stream in said oscillating manner.

2. The arrangement of claim 1 in which each of said rotatable elements comprises a disk structure having a thickness corresponding to the width of said stream and having a periphery with diametrically opposed portions cut away to form said second portions spaced a lesser distance from said axis of rotation, and said periphery between said cutaway portions being provided with a circumferentially extending channel.

3. In an arrangement for combining, in an elastic fluid atmosphere, a plurality of laterally spaced and aligned parallel moving streams of an elastic fluid having a plurality of fibrous elements dispersed therein and collecting the fibrous elements from the combined streams in the form of a unitary coherent non-woven Web structure having uniform thickness, density, and directional proper ties, the improvement comprising stream combining and controlling apparatus, said apparatus comprising means for aerodynamically rapidly diverting each stream in an oscillating manner along a general lateral line of direction transverse to the path of stream movement, said general lateral line substantially coinciding with the plane defined by said parallel moving streams to cause the diverted streams to merge and form a single combined evenly blended continuous laterally extending moving stream of fluid and fibrous elements, said means comprising a set of movable members positioned in opposed positions adjacent each stream, said members constructed and arranged with respect to each stream to alternately check at opposed sides of said stream the flow of the elastic fluid atmosphere induced by said stream, each set of movable members comprising a pair of diametrically opposed elements each having a curved surface movable into position closely adjacent said stream to check said induced flow while its diametrically opposed element is further from said stream and inoperative to check said induced flow, said elements operated in predetermined phase relationship so that each in turn presents a curved surface adjacent to a side of the fluid stream whereby said induced flow is substantially instantaneously alternately checked by each element at opposite sides of said stream to rapidly divert said stream in said oscillating manner.

References Cited by the Examiner UNITED STATES PATENTS 2,721,371 10/1955 Hodkinson et al 28-21 2,786,637 3/1957 Russell et al.

2,854,059 9/1958 Palmer 22697 X 2,874,446 2/1959 Sellers 28.72 2,881,906 4/1959 Griset 226--7 2,927,621 3/1960 Slayter et al. 19-155 X 3,031,733 5/1962 Ljung et al. 281 3,035,327 5/1962 Agren 281 3,040,412 6/1962 Russell 28-72 3,059,308 10/1962 Friedel 2821 3,117,055 1/1964 Guandique et al. 161-470 2,117,056 1/1964 Katz et al. 161-170 FOREIGN PATENTS 242,895 1/ 1963 Australia.

ROBERT R. MACKEY, Primary Examiner.

DONALD W. PARKER, Examiner.

Claims (1)

1. 3. IN AN ARRANGEMENT FOR COMBINING, IN AN ELASTIC FLUID ATMOSPHERE, A PLURALITY OF LATERALLY SPACED AND ALIGNED PARALLEL MOVING STREAMS OF AN ELASTIC FLUID HAVING A PLURALITY OF FIBROUS ELEMENTS FROM THE COMBINED STREAMS IN THE THE FIBROUS ELEMENTS FROM THE COMBINED STREAMS IN THE FORM OF A UNITARY COHERENT NON-WOVEN WEB STRUCTURE HAVING UNIFORM THICKNESS, DENSITY, AND DIRECTIONAL PROPERTIES, THE IMPROVEMENT COMPRISING STREAM COMBINING AND CONTROLLING APPARATUS, SAID APPARATUS COMPRISING MEANS FOR AERODYNAMICALLY RAPIDLY DIVERTING EACH STREAM IN AN OSCILLATING MANNER ALONG A GENERAL LATERAL LINE OF DIRECTION TRANSVERSE TO THE PATH OF STREAM MOVEMENT, SAID GENERAL LATERAL LINE SUBSTANTIALLY COINCIDING WITH THE PLANE DEFINED BY SAID PARALLEL MOVING STREAMS TO CAUSE THE DIVERTED STREAMS TO MERGE AND FORM A SINGLE COMBINED EVENLY BLENDED CONTINUOUS LATERALLY EXTENDING MOVING STREAM OF FLUID AND FIBROUS ELEMENTS SAID MEANS COMPRISING A SET OF MOVABLE MEMBERS POSITIONED IN OPPOSED POSITIONS ADJACENT EACH STREAM, SAID MEMBERS CONSTRUCTED AND ARRANGED WITH RESPECT TO EACH STREAM TO ALTERNATELY CHECK AT OPPOSED SIDES OF SAID STREAM THE FLOW OF THE ELASTIC FLUID ATMOSPHERE INDUCED BY SAID STREAM, EACH SET OF MOVABLE MEMBERS COMPRISING A PAIR OF DIAMETRICALLY OPPOSED ELEMENTS EACH HAVING A CURVED SURFACE MOVABLE INTO POSITION CLOSELY ADJACENT SAID STREAM TO CHECK SAID INDUCED FLOW WHILE ITS DIAMETERICALLY OPPOSED ELEMENT IS FURTHER FROM SAID STREAM AND INOPERATIVE TO CHECK SAID INDUCED FLOW, SAID ELEMENTS OPERATED IN PREDETERMINED PHASE RELATIONSHIP SO THAT EACH IN TURN PRESENTS A CURVED SURFACE ADJACENT TO A SIDE OF THE FLUID STREAM WHEREBY SAID INDUCED FLOW IS SUBSTANTIALLY INSTANTANEOUSLY ALTERNATELY CHECKED BY EACH ELEMENT AT OPPOSITE SIDES OF SAID STREAM TO RAPIDLY DIVERT SAID STREAM IN SAID OSCILLATING MANNER.

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