US3400188A - Method for producing reticulated film - Google Patents

Description

Sept. 3, 1968 A. R. oLsoN METHOD FOR PRODUCING RETICULATED FILM Original Filed Dec.

United States Patent O 3,400,188 METHOD FUR PRGDUCING RETICULATED FLM Arthur R. Olson, Walpole, Mass., assignor to The Kendall Company, Boston, Mass., a corporation of Massachusetts Continuation of application Ser. No. 617,719, Feb. 21, 1967, which is a division of application Ser. No. 415,338, Dec. 2, 1964. This application Aug. 31, 1966, Ser. No.

1 Claim. (Cl. 264-156) ABSTRACT OF THE DISCLOSURE This application is a division of applicationv Ser. No. 415,338, filed Dec. 2, 1964, abandoned in favor of continuation Application Ser. No. 617,719, filed Feb. 21, 1967 and now Patent No. 3,366,529.

This invention relates to needle-punched nonwoven fabrics, and more particularly to fabrics of this type which are internally reinforced by an open, porous reticulate network of thermoplastic material serving to bond the structure into a coherent, abrasion-resistant fabric.

In distinction to so-called bonded nonwoven fabrics, made by saturating an unspun and unwoven fibrous fleece with an aqueous polymeric binder, nonwoven fabrics made by a needle-loom process depend for their integrity on a mechanically-induced reorientation and interlocking of some of the fibers in a fleece. Needle nonwoven fabrics, therefore, do not suffer from the stitfening effect and the matting-down of fibers customarily associated with wet bonding. They have a soft hand and drape, easy conformability and a degree of elongation, high loft, low

density, and high insulating value, properties which render them uniquely useful in applications, such as garment linings, to which bonded nonwoven fabrics are not so well suited.

The mechanical interlocking of fibers in a needled nonwoven fabric, however, is not as strong a bond as is developed in bonded nonwoven fabrics. Therefore, `for uses where tensile strength and abrasion resistance are requisites, as in an exposed liner for boots, shoes, or other apparel, needled nonwoven -fabrics are frequently reinforced with a layer of fabric, polymeric foam, film, or combinations of such materials, as described for instance in U.S. Patent 3,059,312, to Jamieson. Combinations of needled fibrous webs with layers of other material are referred to as needled laminates in this application.

Even in the case of such laminates, Ihowever, tensile strength and, more particularly, surface durability `and abrasion resistance, leave much to` be desired. Some of the fibers are deflected by the needling operation from their normal orientation in the plane of the fabric so that they are aggregated into brous bundles extending down through the fibrous layer and through any reinforcing substrate which mayy be present. The bonds thus formed, however, are still mechanical in nature and are transient, in the sense that fibrous bundles are wedged into a substrate which yields slightly as'it receives the thrust of the fiber-laden needle, and'then recovers upon withdrawal of the needle to clasp the fibrous bundle with a firmness which varies with the elastic nature of the par- Patented Sept. 3, 1968 ticular substrate employed. Surface friction or abrasive action on the face of such needled products, such as results from body action against such a surface, gradually decreases the degree of interlocking of the fibers with each other and with the substrate if present, so that the fibers pluck out and are shed from the vnonwoven Ifabric surface.

Therefore it has been proposed to increase the internal integrity of such needled nonwoven fabrics or needled laminates by saturating with a binder. This, however, frequently alters the nature of the product so that the desirable loft and softness are lost, particularly in view of the concentration of binding agent which occurs on the surfaces due to binder migration during drying. Methods having also been advanced for the use of coagulants or gelling agents, to minimize binder migration. So far as I am aware, however, no methods previously proposed have succeeded in producing a needled nonwoven Ifabric or laminate which is soft, lofty, porous, and conformable, and which has a high degree of internal integrity enhancing the tensile strength and resistance to fiber shedding, while still preserving the desirable fleece-like free fibrous character of the surface. It is with improvements in the art of bonding together the fibers which make up needled nonwoven products that the present invention is concerned.

I have found that if a fibrous fleece or batt is needled through a film composed of thermoplastic and heatretractable polymeric material, and the assembly is then subjected to a temperature above the softening point of the film but below the point at which the film becomes completely fluid, as set forth below, the film is transformed from a lightly-apertured but generally impervious layer to a very open and porous reticulate network of fused polymeric material which bonds the internal fibrous layer of the fabric into a coherent, abrasion-resistant fabric of high tensile strength. At the same time, the film substance is maintained as a discrete and self-sustaining network: it is not diffused throughout the fleece, and in cases where the film has been needled to one surface of a fibrous fleece, that surface is heat-sealing due to the Elocalized concentration of thermoplastic substance.

In Canadian Patent 680,521, to Whytlaw, a process is described in which a fibrous fleece is needle-punched into a thermoplastic film, and the assembly is subsequently heated to Within the softening range of the film, to cause the film to bond to the fibrous bundles around the peripheries of the apertures in the film through which the fibrous bundles have been thrust. It is emphasized in said patent, however, that the film is of a continuous and unbroken nature between the fibrous bundles, so that if both the film and the fibers have low moisture absorption, the fabric is said to possess moisture barrier characteristics; if the fibers are absorbent, the film base is said to serve as a moisture barrier and the punched fibers transmit air but not moisture. It is preferred by Whytlaw that the heating process be accompanied by pressure, so that the fibers are embraced by the softened film substance and the fibers and film form an integral structure. It is also known, according to British Patent 967,159, to heat such a combination of a thermoplastic film, with a fibrous fleece needled there through, until the film has become completely fluid. This has the effect, however, of Causing the film to permeate the fleece, and as set forth in said patent, the film character is lost. The diffusion of the film substance throughout the fleece causes a stiffening or bonding action to affect substantially all of the fibers, with the accompanying decrease in loft, softness, and drape.

As will be set forth more fully below, the present invention contemplates heating the film-fiber assembly'not just to the softening range, but above the softening point of the film while below the point of complete fluidity, with the unexpected formation of a unique network of fused polymeric material of very high porosity and no moisturebarrier properties.

This invention will be more clearly understood with reference to the accompanying drawings, in which:

FIGURE 1 is a magnified cross-sectional view of a fibrous ficece needled to a base film of thermoplastic and heat-retractable material.

FIGURE 2 is a magnified cross-sectional view of a fibrous fieece needled through a thermoplastic and heatretractable film and also through an underlying fabric substrate.

FIGURE 3 is a representation, magnified 4 times, of approximately one square inch of film through which a fibrous fieece has been needled, and from which the fibrous material has been dissolved out prior to heat-treatment. FIGURE 3 is not idealized, but is a tracing of an actual photograph of a film so treated.

FIGURE 4, also a tracing of an actual photograph, is a representation, magnified 4 times, of a piece of the reticulate thermoplastic network into which the film of FIGURE 3 is transformed by heating the composite film-fiber assembly above the softening point of the film substance, followed by dissolving out all the fibers.

Referring to FIGURE l, a fleece or batt of textilelength fibers is shown as having been needle-punched through an underlying film of thermoplastic and heat-retractable material 12, so that some of the fibers are gathered into the form of fibrous bundles 14 which are oriented essentially normal to the plane of the fabric and protrude through apertures 16 which have been formed in the film. By textile-length fibers is meant those fibers of length such that they can be handled and formed into a fleece 4by conventional textile equipment such as cards, garnetts, air-lay machines, and the like. Any textile fibers may be used in this invention, provided that their melting point is higher than the melting point of the film. The choice of fleece-.forming device used will depend on whether it is desired to have the fibers predominantly parallelized in the machine direction, as from a card, or isotropically arrayed as from an air-lay machine.

FIGURE 2 is similar to FIGURE 1, except that the fibrous bundles 14 pass through, an additional substrate in the form of a fabric composed of warp yarns 18 and filling yarns 20.

As film base, any polymeric material in film form may be employed, provided that it is thermoplastic and heatretractable: that is, in the softening process, the film tends to shrink and retract. Certain film-forming polymeric materials are naturally heat-retractable due to their chemical nature, while other films are retractable due to their having been unilaterally or biaxially oriented during their manufacture. Suitable films are those prepared from plasticized cellulose esters such as plasticized cellulose acetate, films prepared from vinyl polymers such as polyvinyl chloride, polyvinylidene chloride, copolymers of vinyl chloride and vinyl acetate, and polyolefine films such as polyethylene and polypropylene. The thickness of the film will depend on the degree of internal reinforcement desired. Generally, the use of a film 0.001 inch thick will at least double the strength of a needled non-woven product made according to this invention, with thicker films giving even more reinforcement and resistance to fiber shedding.

A wide variety of fabric substrates may be used, if desired, in the practice of this invention, varying from openmeshed lightweight cotton gauze to heavy nylon monofilament screening. In place of fabric, added insulating value may be realized through the use of foamed polymeric material such as polyurethane foam, or both foam and fabric may be used. Novelty is not claimed for any particular pre-assemblage of textile fibers with a reinforcing substrate or substrates, but resides in the uniquely porous configuration of the thermoplastic and heat-retract- 4 able film after processing, together with its bonded union to the fibrous fieece and substrate, if the latter is used.

The above-described fibrous fieece is superimposed upon the thermoplastic film plus any additional substrates desired, and the assembly is then needle-punched, preferably in a continuous operation, by passing it through a needle loom. Such devices are well-known in the art and are not shown. The result of such an operation is to thrust fibrous bundles down through apertures formed in the film, so that the lower face of the assembly is studded with fibrous bundles protruding from said face. The tracing of FIGURE 3, magnified 4 times, was made by needling, in a Hunter loom, a layer of rayon fibers superimposed upon a layer of polyethylene film 0.001 inch thick, both superimposed on a layer of 32 x 28 cotton gauze. The assembly was passed through the loom twice, at a rate of about 160 strokes per square inch per passage, making a total of somewhat over 300 penetrations per square inch of lm. Both the rayon fibers and the cotton gauze were dissolved away by solvent and swelling techniques not affecting the film, to leave the base film 12 of FIGURE 3 perforated with minute apertures 16. In this condition, the base film is still essentially non-porous, being or more continuous film with the apertured area constituting 25% or less of total film.

In the fiber-free apertured film of FIGURE 3 is now heated to its softening point while free from restraint, the film area as a whole will undergo some shrinkage and the holes will be substantially closed. In combination with needled fibrous bundles thrust through the film, however, the film is not free to shrink in area, but is restrained by the presence of the bundles. Heating of the film to its softening point causes the film to draw together around the fibrous bundles, particularly if pressure is employed. By this process, the fibrous bundles are more firmly bound to the film, but the film remains continuous and unbroken between the punched fibers, forming a imoisture barrier.

I have found that quite different and unexpected results are obtained if the assembly of film and fibers, plus substrates if used, is heated not just up to the softening point but actually into or beyond that point but below the point at which the film becomes completely fiuid. FIGURE 4 represents the fiber-film fabric assembly from which the lm of FIGURE 3 was produced, after heating to 115 C., a figure above the softening point of polyethylene, and after removal of fiber and fabric as before. In FIGURE 4, the film substance 12 is no longer in the form of a lcontiuous film, but has retracted into an open, porous reticulate network marked by large and irregular holes 22. The .film has been converted from 75 or more closed area to 75% or more open area. The number of openings in the film has decreased by over 50%, and their laverage size has greatly increased. At the same time, the thickness of the network of FIGURE 4 is about 0.012 inch, measured by a Starrett gauge No. 170, as compared with a thickness of 0.001 inch for the film of FIGURE 3. In this softening and retracting process, there is pronounced bonding of the fibers, reinforcing the integrity of the fabric, and a greatly increased resistance to delamination or fiber shredding without any sacrifice in the desirable loft, softness and porosity of the material.

The invention will be illustrated by the following examples:

Example 1 A fibrous web of 1.5 denier viscose rayon fibers, weighing 168 grams per square yard, was needled through a polyethylene film 1 mil thick by passing twice through a Hunter needle loom at a total needle penetration rate of about 300 per square inch. The product was then heated to 320 F. for one minute in an oven.

Before heat treatment, the fibers could readily lbe separated from the film by pulling, and the tensile strength was 6.3 pounds per inch wide strip. The air porosity was low. After heating, the fibers resisted removal from the glm by pulling, the tensile strength was 23.5 pounds per inch wide strip, and the porosity was substantially equal to the porosity of a similar needled sample containing no film.

An additional advantage derived from the process of this invention lies in the -fact that products made with no secondary substrate, as in Example l, are heat sealable. When the product of Example l was folded upon itself with the faces bearing the polyethylene network facing each other and the two layers were pressed with' a hot sealing iron, a very strong bond was formed, and the two layers could not be separated without total destruction of the fabric. After removal of the rayon fibers with sulfuric acid, there was left two layers of polyethylene film, strongly sealed together, each resembling the reticulated plastic network of FIGURE 4. Since both networks are very porous, a heat-sealed bond of this type is also very porous, transmitting air .and moisture vapor very readily.

The process of this invention, therefore, is advantageous when it is desired not just to increase the tensile `strength of a needled nonwoven product, but to render the product capable of heat-sealing to itself or to other materials with the formation of a bond that is tenacious and air perme-l able` The air-permeable heat-sealed bond appears to be due to the fact that once the punctured film has been transformed into a reticulated network, the properties of which are described more fully below, so much film substance has been retracted into the peripheries 12 of the large and irregular openings 22 (FIGURE 4) that there is little or no tendency for the openings to become closed over under the infiuence of heat and normal heat-sealing pressures. In the field of needle-punched non-woven blankets, for example, this allows the heat-sealed application of inexpensive selvages, or of decorative patterns of other materials to the blanket surface, or of the anchoring of heating filaments between the layers of the product of Example 1 to produce an inexpensive electric blanket.

Example2 This was similar in all respects to Example 1 except that the fibrous fieece was 156 grams per square yard of 3 denier acrylic fibers. The unheated sample had a tensile strength of 5.7 pounds per inch wide strip` The heated sample was much more resistant to fiber shredding and had a tensile strength of 12.8 pounds per inch wide strip.

IExample 3 A fibrous web of 5.5 denier rayon fibers, Weighing 165 grams per square yard, was needled through a layer of 1.5 mil polyethylene film and through a layer of 32 x 28 cotton gauze which underlaid the film. The needling operation was conducted as in Examples l and 2.

When the fibrous layer and the gauze-film layer were placed separately in the jaws of an Instron machine, the needled assembly showed a delamination strength of 1.8 pounds per inch wide strip. After heating the product as in Example l, the delamination strength was 5.0 pounds per inch wide strip.

Before heating, the product had a porosity of only 42 cubic feet of air per square Afoot per minute at one-half inch pressure drop, most of the transmission being through the needled fibrous bundles disposed in their individual apertures. After heating the product to above the melting point of the film, the air porosity increased almost tenfold, to 398 cubic feet of air per minute.

All three of the above products were soft, strong, porous, and conformable, with a textile drape and hand.

Example 4 A fibrous web of 3 denier polyethylene terephthlate fibers weighing 76 grams per square yard Was needled through a layer of l mil polyethylene film and through a layer of nylon mesh screening underlaying the film. The

nylon screen was composed of woven nylon monofilaments, in a 24 x 20 count, and weighed 200 grams per square yard. Needling was as in Example l.

In the material as prepared, the fibrous layer could be more or less readily pulled away from the film-nylon mesh substrates. After heating as in Example l, it was impossible to separate the fibrous layer from the substrates without breaking a substantial percentage of the fibers. The air porosity was 335 cubic feet of air per minute.

In each of the above examples, dissolving out all ingredients except the polyethylene left a porous, openmeshed network of polymeric thermoplastic filaments, irregular in contour and interconnected to define irregularly shaped apertures. The filaments of the network (12 in FIGURE 4) were from five to ten or more times as thick as the thickness of the film from which they had been derived, but the network was so open and porous that it was quite flexible, and did not detract from the softness and the drape of the reinforced needled nonwoven fabrics and laminates. The needled fibrous bundles extending downwardly through the fibrous fleece and through the film, and through the substrate if present, are not individually disposed each through a separate and discrete aperture with unbroken film extending between apertures, as is the case before treatment, but are anchored firmly to the edges of the polymeric filaments which compose the irregular network. In the case of Examples 3 and 4, where a fabric substrate was used, the polymeric network was in turn firmly bonded to the fabric substrate, and could not be mechanically removed therefrom without destroying the network or the fabric. If the fabric substrate is removed by solvent or swelling action, the pattern of the fabric is found to be engraved in intaglio on the underside of the porous polymeric network derived from the film, the pattern being actually undercut in places attesting to the flow of film substance around the yarns of the fabric substrate.

Apart from its utility in strengthening needled nonwoven fabrics and rendering them heat-scalable, as set forth above, a reticulated plastic network as illustrated in FIGURE 4 has independent utility in its own right as for example a replacement for film which has been locally slit and then expanded, or pressure-embossed and then stretched, to form an apertured plastic film used for packaging or decorative purposes. Such products are well known in the packaging art, and are made by mechanically stretching a suitable plastic film into which a patterned set of discontinuities has been introduced into the film substance. The process of this invention provides a reticulate plastic network in a relatively simple manner and without the need for expanding tenters or other stretching devices, as illustrated by the following example.

Example 5 A sheet of l mil polyethylene film was run through a needle loom and punctured at a rate of approximately 300 penetrations per square inch. If such a film is heated While free to move, it will shrivel and shrink in overall area, and the majority of the perforations will tend to become smaller.

If, however, the film is restrained from exerting any substantial overall area shrinkage during the heating process, as by confining it between two wire metal screens of 14 x 14 mesh, with a highly crimped weave, while heating to 320 F. for three minutes, the reticulate structure of FIGURE 4 is obtained. In said structure, the minute punctures of FIGURE 3 have been replaced by a pleasingly irregular pattern of larger openings, fewer in number, and rimmed at their peripheries by interconnected plastic filaments of substantial strength and thickness compared to the original film.

It is desirable in this process that the restraint against shrinkage be applied locally over the face of the punctured film, so that it is exerted at a multiplicity of points within the area of the film. The use of peripheral restraint alone is liable to lead to the formation of a very few large openings and a product of decreased utility. The use of layers of wire screen, or similar rough surfaces, seems to afford a multiplicity of discrete points across the face of the film, at which points the shrinkage tendency is locally impeded, so that the punctures in the film do not seal up while the film is passing through the retraction-temperature zone, but instead the film regions around the punctures are locally tensioned, this tension plus the surface tension of the softened film drawing the polymer into the desired configuration shown in FIGURE 4.

Although the above examples illustrate a needling operation conducted in one direction, it will be apparent to those skilled in the art that needling through both the upper and lower surfaces of a laminate may often be desirable. This is especially true when it is desired to attach a fibrous web or fleece to both faces of a film, as in the formation of a blanket material such as is illustrated in the following example:

Example 6 Two fibrous webs of 3 denier randomly-arrayed viscose fibers weighing 12() grams per square yard were needled, one web on each face, into a polyvinylidene film one mil thick by two passes through the Hunter loom as in previous examples, needling first from one face of the assembly and then from the reverse face. The laminate thus formed had a tensile strength of 5.7 pounds per inchwide strip, and was difficult to breathe through. After heating to 375 F. for one minute, the material had a tensile strength of 13.7 pounds per inch-wide strip, and was substantially as easy to breathe through as a pair of needled webs containing no film.

Such a characteristic degree of attachment of needled brous webs to a substrate is exceptional, especially when combined with a high air porosity, making such products eminently suited for use as garment linings, porous supportive elements for the foundation garment and brassiere trades, blankets, and the like.

Having thus described my invention, I claim:

1. 'I'he process of making an open-meshed reticulate net- Work of filamentary plastic material from a continuous heat-retractable thermoplastic polymeric film which comprises:

puncturing said film at a multiplicity of points,

and subsequently decreasing the number of original apertures in said film by at least and substantially increasing the thickness of said film by heating said film above its softening point,

but below the point at which said film becomes completely fluid,

while holding said tilm under restraint and preventing said film from retracting in overall area,

said restraint being applied at a multiplicity of discontinuous points across the face of said film.

References Cited UNITED STATES PATENTS 1,955,083 4/1934 Mller 161-109 2,294,966 9/1942 Dreyfus 16l-l09 2,361,369 10/1944 Grebe et al 264-156 XR 3,092,439 6/ 1963 Harrison 264-230 XR 3,146,283 8/1964 Da Valle 264--156 3,216,882 11/1965 Feldt et al 161--109 3,218,381 11/1965 Such et al 264-156 XR ROBERT F. BURNETT, Primary Examiner.

R. H. CRISS, Assistant Examiner.

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