US 3461026 A
Description (OCR text may contain errors)
Aug. 12, 1969 M. M. SCHICK LAMINATED FIBROUS BATT" Filed June 23, 1966 BATT QF MICROCELLULAR FIBERS ,NON-CELLULAR MICROCELLULAR BATTS' OF DENSE STAPLE FIBERS STAPLE FIBERS STAPLE FIBERS PENETRATING MICROCELLULAR FIBER BATT INVENTOR MARY MARGARET SCHICK BY Q ATTORNEY United States Patent Ofiice 3,461,026 Patented Aug. 12, 1959 3,461,026 LAMINATED FIBROUS BATT Mary Margaret Schick, Wilmington, Del, assignor to E. I. du Pont de Nemours and Company, Wilmington, Del,
a corporation of Delaware Filed June 23, 1966, Ser. No. 559,839 Int. Cl. B32b 5/26, 27/08 US. (It. 161-154 9 Claims This invention relates to a resilient fibrous laminar structure. More particularly it relates to a composite fibrous structure which is suitable for cushioning uses in upholstered furniture, pillows, mattresses and the like, as Well as thermal insulating uses in garments, jackets, coats, and the like.
Prior art materials employed for cushioning purposes are of Widely diverse types ranging from metal springs to blocks of elastomeric cellular materials to batts of fibrous materials such as animal hair or feathers, straws, and batts of natural (cotton, kapok) or synthetic (polyethylene terephthalate fiber-fill, acetate) fibrous materials. Prior art insulating materials employed in quilts, sleeping bags, cold weather garments, etc. include fibrous batts of cotton, kapok, polyethylene terephthalate fiberfill, etc., feathers and down, or more recently, thin sliced sheets of synthetic polymeric foams fused or adhesively bonded to a fabric backing. Various deficiencies, pertinent to one or more of these prior art materials, include susceptibility to rot and mildew, poor durability under repeated loading, relatively high weight at filling densities sufiicient for adequate load support, high cost at filling densities sufficient for adequate load support, and, particularly in the case of foam sheet insulating material, poor drape and sensitivity to dry cleaning treatments.
In accordance with the invention there is provided a novel stutfing material which is free from the above objections. It is a resilient laminar structure comprising a first batt of randomly arranged microcellular fibers and a second batt of dense, substantially non cellular staple fibers adjacent at least one face of said first batt, said batts being mechanically joined into a coherent unit by interpenetration of the staple fibers of said second batt into said first batt, said microcellular fibers being composed of a synthetic organic polymer defining closed cells having substantially all of the polymer present as filmy elements of a thickness less than 2. microns.
The microcellular or core batt, as above described, provides most of the cushioning function of the laminar structure. If used alone, however, such a batt would prove somewhat deficient because the randomly arranged microcellular fibers thereof would be free to undergo relative movement such that upon repeated application and release of compressional forces, the fibers would tend to bunch together with consequent losses both in thickness and in comfort. The interpenetration of the staple fibers into the microcellular batt, e.g. by hydraulic entangling or analogous techniques, serves to make the latter coherent and to reduce the mobility of the individual microcellular fibers. The reinforced and structurally coherent product which results is thus able to undergo repeated exercising with excellent retention of thickness as well as load bearing properties.
The surfacing layer of dense staple fibers provides still another important advantage, particularly in the case of cushioning applications. Thus alone the microcellular fibers, being both relatively thick and firm, would produce a batt which might tend to feel rough or otherwise lacking in softness when in contact with a portion of the human body. A surfacing layer of the dense staple fibers serves as an insulator to eliminate or at least materially reduce any such rough sensation.
It will be understood that the microcellular batt may have only one of its major faces covered with a batt of dense staple fibers. In this case the staple fibers should penetrate through essentially the entire thickness of the microcellular batt in order to provide a coherent structure. If two staple fiber batts are provided so as to give a sandwich-type construction, then staple fibers from either or both may extend partially or fully through the microcellular batt so that, in any case, the latter is fully penetrated throughout its thickness.
The penetration of the staple fibers into the microcellular batt need only be at spaced intervals. For example, upon assembling the layers to the united, needling can be effected in a patterned fashion, i.e. either randomly or ordered, as is the practice in the familiar quilting operation. Thus the microcellular batt is intersected only at various intervals by the staple fibers, and the member and spacing of the penetrated areas need only be sufficient to make the composite sufficiently coherent. Areas of entanglement of the two types of fibers thus alternate with areas in which no such entanglement occurs.
The above described features will be further understood from FIG. 1 which shows in schematic form and FIG. 2 which shows in enlarged form a laminar structure of the invention in which a batt of microcellular fibers is sandwiched between batts of dense staple fibers. Spaced areas of penetration of the latter fibers into the core provide a quilted appearance.
The invention is importantly dependent upon the character of the microcellular fibers; that is, they must be of a particular closed cell variety so as to be capable of retaining gases therein. Such fibers when inflated are thus pneumatic, i.e. individual cells acting as miniature balloons, and a maximum contribution is made both with respect to load bearing abilities and to thermal insulation properties. However, the invention also contemplates laminar structures in which the microcellular filaments are initially collapsed, i.e. to less than their normal or fully expanded thickness. Such structures find unique utility in manufacturing operations where this relatively compact form facilitates handling, or where the closed cell nature of the microcellular filaments permits subsequent inplace post-inflation of the structures to their full pneumatic potential.
Microcellular filaments employed according to this invention are substantially homogeneously foamed throughout to provide closed polyhedral-shaped cells of less than about 1000 microns each in maximum transverse dimension, each cell completely enclosed by thin film-like polymeric walls less than about 2 microns thick. By substantially homogeneously foamed throughout is meant not only that there is a narrow distribution of cellsizes but also that the filament is devoid of separately identifiable skins, webs, or casings of dense polymer surrounding the foamed portion; i.e., the outer surface is composed of thin cell-walls. The density of gas-inflated microcellular filaments is in the range of 0.005 to 0.05 gm./cc. Dense polymeric skins are undesirable because they can crack upon repeated compressive flexing, because they restrict the pneumatic behavior of the enclosed foam, and because their weight per unit volume of enclosed gas is too great to obtain low densities.
Microcellular filaments must have predominantly closed foam-cells. Otherwise gases cannot be confined within the cells and a high degree of pneumaticity of the filaments cannot result. The determination of closed-cell content is ordinarily made by visual or microscopic observation. Alternatively, a gas displacement technique such as that described by Remington and Pariser in Rubber World, May 1958, p. 261, can be used if modified to operate at the lowest possible pressure differentials. A predominantly closed-cell content is qualitatively indicated if a gas-inflated microcellular filament feels pneumatic when squeezed between the fingers and recovers its original size and shape immediately thereafter.
Microcellular filaments must also be yieldable and resilient such that substantial cross-sectional deformation results from externally applied compressive loads. Generally, this requirement is satisfied if a gas-inflated filament is reduced in thickness by at least under a load of 10 p.s.i. (0.70 kg./cm. based on an area computed from the length and original diameter, the load being maintained for one second, and if there is an immediate thickness regain to at least 50%, and preferably to substantially 100%, of the original thickness on release of the load.
A particularly desirable microcellular filament for use in the products of this invention is ultramicrocellular as disclosed by Blades et al. in US. Patent No. 3,227,664. Ultramicrocellular filaments are additionally characterized in that the polymer in their thin cell-walls exhibits uniplanar orientation and uniform texture as described in said patent. These latter two properties provide the surprisingly great strength of the filaments and render their cell-walls particularly resistant to gas-permeation.
A wide variety of both addition and condensation polymers can form microcellular filaments with the essential characteristics. Typical of such polymers are: polyhydrocarbons such as polyethylene, polypropylene, or polystyrene; polyethers such as polyformaldehyde; vinyl polymers such as polyvinyl chloride or polyvinylidene fluoride; polyamides such as polycaprolactam, polyhexamethylene adipamide, or polymetaphenylene iso-phthalamide; polyurethanes such as the polymer from ethylene bischloroformate and ethylene diamine; polyesters such as polyhydroxypivalic acid or polyethylene terephthalate; copolymers such as polyethylene terephthalate: isophthalate; polynitriles such as polyacrylonitrile or polyvinylidene cyanide; polyacrylates such as polymethylmethacrylate; and equivalents.
Planar molecular orientation of the polymer in the cellwalls contributes significantly to the strength of the filaments. A preferred class of polymers for forming suitable microcellular filaments is, therefore, one including those which respond to orienting operations by becoming tougher and stronger. This class includes linear polyethylene, stereo-regular polypropylene, polycaprolactam, polyethylene terephthalate, polyvinyl chloride, and the like. Further preferred is the class of polymers known to be highly resistant to gas-permeation, such as polyethylene terephthalate and polyvinyl chloride.
The microcellular filaments employed preferably contain sufficient impermeant inflatant to provide a total internal pressure within the cells of at least atmospheric pressure. An impermeant infiatant is a gas which permeates the cell-walls so slowly as compared to air that it is substantially permanently retained within the cells. The presence of impermeant inflatant within the cells creates an osmotic gradient for the inward permeation of air (or other ambient gaseous atmosphere). Thus, at equilibrium with air, the cells of microcellular filaments contain not only air at about one atmosphere but also impermeant inflatant at a given partial pressure. The combined pressure, then, is at least atmospheric and guarantees that the filaments are fully gas-inflated and turgid. Loss of air by permeation during compression is ordinarily insufiicient to prevent full reinflation immedi ately upon release of the load. If, however, full reinfiation does not result immediately, the osmotic gradient provided by the impermeant inflatant causes spontaneeous reinflation by equilibration with ambient air.
The rate of permeation for an inflatant gas through a given polymer increases as its diffusivity and solubility increase. Accordingly, impermeant infiatants should have as large a molecular size as is consistent with providing the required vapor pressure and should have very little or no solvent power for the polymer. A preferred class of impermeant infiatants is exemplified by compounds whose molecules have chemical bonds different from those found in the confining polymer, a low dipole moment, and a very small atomic polarizability.
Suitable impermeant infiatants are selected from the group consisting of sulfur hexafluoride and saturated aliphatic and cycloaliphatic compounds having at least one fluorine-to-carbon covalent bond and wherein the number of fluorine atoms preferably exceeds the number of carbon atoms. Preferably the saturated aliphatic and cycloaliphatic compounds are, respectively, perhaloalkanes and perhalocycloalkanes in which at least 50% of the halogen atoms are fluorine. Although these infiatants may contain ether-oxygen linkages, they are preferably free from nitrogen atoms, carbon-to-carbon double bonds, and reactive functional groups. Specific examples of impermeant infiatants include sulfur hexafluoride, perfluorocyclobutane, sym-dichlorotetrafiuoroethane, perfiuoro-l,3-dimethylcyclobutane, perfiuorodimethylcyclobutane mixtures, 1, 1 ,2-trichloro-1,2,2-trifiuoroethane,
chlorotrifluoromethane, and dichlorodifluoromethane. Mixtures of two or more impermeant infiatants can often be used to advantage.
The microcellular filaments are deposited in a random fashion to build up a core batt to the desired area and thickness. When the microcellular fibers are fully inflated, this core is resilient and recoverable from deformation through at least two mechanisms. First, the filaments themselves are pneumatic in view of their closed cell thinwalled gas-containing structure, so that they recover from deformation by virtue of the recovery forces of the compressed confined gas in the cells. Secondly, the turgid microcellular filaments exhibit an appreciable resistance to bending from their normal extended configuration so that when such distortions are imposed by gross compression of the batt, this bending provides a recovery force both to resist the compression and to restore the batt to its original shape when the external compressive force is removed. Both of these recovery forces depend on the continued presence of the entrapped gas in the cells, so that the preferred microcellular filaments for the cushioning structures have a diameter in excess of A (so that the gas is not readily lost by outward diffusion from the internal cells). Diameters up to 0.25 inch or so are advantageous in this respect. On the other hand, for improved surface aesthetics and uniformity, smaller diameter microcellular filaments are preferred for the thinner thermal-insulation batts useful for example as interliners. In either case, however, the preferred filaments contain a quantity of an impermeant gas in each cell as described previously.
The fully-inflated microcellular filaments exhibit very low density, generally in the range from 0.05 to 0.005 g./ cc. (3 to 0.3 lb./ft. However, since these filaments are deposited in a random array to form the core batt, an appreciable fraction of the volume of the batt exists as interfibrillar voids so that the overall apparent density of the microcellular batt is of the order of only a few tenths of a lb./ft. even when the filaments are packed in sufiicient proximity to support loads up to several lb./in. as are commonly encountered in seat cushion and mattress applications. Adequate load support at such low bulk densities, with adequate residual resilience, is not provided by common prior art structures.
The core batts of pneumatic microcellular filaments described above have a degree of coherence, by virtue of surface-frictional engagement between the randomly deposited neighboring filaments, just sufficient to permit a minimum of gentle handling. Furthermore, although the batts provide sufficient resilience under sitting loads, their surfaces generally are judged somewhat too firm and lumpy (the preferred large diameter filaments are individually perceptible even through a ticking cover). This invention therefore provides for surfacing the core batt with a batt, e.g. a carded or garnetted batt, of resilient dense staple fibers such as cotton or polyethylene terephthalate fiberfill. The dense fiber batt is then joined or locked to the foam filament core batt by needle punching, hydraulic entangling, or similar means, operating from the dense fiber batt side. This results in a penetration of the ends of some of the dense staple fibers into the microcellular filament core where they become entangled, thus not only binding the layers together, but reinforcing and immobilizing the whole structure to an extent permitting subsequent handling such as stuffing into ticking or other surface covering fabrics. In order that this binding and reinforcing function be adequately performed, the length of the staple fibers in the dense fiber batts should average at least 1", and lengths of 2 /2" or more are preferred.
The pneumatic microcellular filament core batt can vary from a thin sheet-like structure only two or three fiber diameters thick, up to a batt several inches thick, depending on the requirements of the particular end-use for which it is intended. For example, the thicker batts are more desirable for luxurious cushioning uses such as deep upholstery and mattresses, while the thinner batts are more suitable for thermal-insulating uses such as jacket or coat interlinings. In this latter case a unique 3- layer laminate is often useful: a thin microcellular filament batt is sandwiched between a fabric base and the dense fiber staple batt overlay. The subsequent needle punching or hydraulic entangling step binds all three layers together, and the fabric base layer then serves as the inner-facing layer when the interliner is incorporated in a garment. Similar composites, backed with cheesecloth or burlap, are suitable for furniture or mattress topper pads. For the thin thermal-insulating structures, light weight surfacing layers of dense fibers are preferred, such as 0.3 oz./yd. fiberfill, while for cushioning structures where a very soft resilient luxurious surface is important, thicker batts up to 5 or oz./yd. are preferred.
As used herein, dense fiber refers to normal noncellular or non-foamy textile fibers wherein the fiber density is at least 0.5 g./ cc. or greater. The surfacing of the core batt with the dense fiber batt may refer to covering only the top surface of the core batt, top and bottom surfaces only, or top, bottom and edges of the core batt, depending on the intended use of the completed cushioning structure. The microcellular filaments in the core batt may be either continuous filaments or staple filaments of suificient length, e.g. a length-to-diameter ratio of at least about 10, to be piddled or otherwise randomly deposited to form an entangled fibrous web. Needle punching is an art recognized term referring to the process of repeatedly inserting a bank of needles through the surface into the structure, and in the case of the present invention, results in the ends of some of the staple fibers in the surface batt being carried down into the core fiber batt and becoming entangled therewith. Hydraulic entangling refers to a related process where fine streams of fluid (water) under high pressure are traversed across the surface of the structure, the impact pressure being sufiicient to drive portions of the fibrous filaments from the surface batt into the core batt where they become entangled.
A convenient continuous process for making the composite fibrous structures of the present invention comprises depositing a random batt of the microcellular filaments transported directly from the spinning machine onto a moving belt, covering one or both surfaces of the moving batt with a batt of dense staple fibers moving at the same velocity, and passing this composite through a needle punching or hydraulic entangling device where the layers are fastened together, and cutting off segments suitable for individual cushions, pillows, panels, etc. Where desirable, the composite batts may be impregnated with elastic adhesives to further enhance batt endurance and minimize fiber packing. Flame-proofing agents and similar additives may also be applied either by spray or dipping techniques.
This invention is further illustrated by the following examples. Examples I to V employ ultramicrocellular filaments having the various characteristics described above.
Example I A one liter pressure vessel is charged with 400 grams polyethylene terephthalate (dried at 210 C.), 300 ml. methylene chloride (dried over calcium hydride), 54 grams of fluorotrichloromethane and 46 grams perfiuorocyclobutane (impermeant infiatant). The vessel is rotated end-over-end while being heated at 220 C., then cooled at 210 C., positioned vertically, and connected to a source of nitrogen gas at 1200 p.s.i.g., and the solution extruded through 12 holes 0.003 diameter x 0.006" long. The ultramicrocellular fibers thus generated are passed directly through an air venturi jet and pulled at minimum tension across a slowly rotating magnesium bar to electrostatically charge the filaments. They are then deposited onto a sheet of paper covering a 2 x 3 aluminum plate. The plate is moved during the deposition to allow random build-up of the batt to a uniform thickness. After several layers of fibers are deposited over the entire surface, water is sprayed onto the batt to weigh down the fibers and facilitate further accumulation. In this way a batt having a thickness of 1" is built up. The batt is then placed in an air oven at C. to remove water and to cause the filaments to become fully inflated. The batt thickness thus increases to 1 /2". The density of the individual inflated ultramicrocellular continuous filaments is approximately 0.03 g./cc. and their average diameter is about 0.15 cm.
- A thin layer of carded and garnetted polyethylene Example II Another portion of polyethylene terephthalate ultramicrocellular filaments is prepared by a process similar to that described in Example I, using 400 grams polymer, 215 ml. methylene chloride and 45 ml. (70 grams) 1,1,2- trichloro-1,2,2-trifiuoroethane. The extrusion occurs under an applied nitrogen pressure of 800 p.s.i.g. through a 24- hole spinneret, each hole 0.004" diameter by 0.008" long. The filaments issue at a velocity estimated to be about 1100 y.p.m., are collected in a random pile and dried 20 mins. in a circulating air oven at 110 C. These fully inflated pneumatic filaments now have a density of about 0.03 g./cc., a relative viscosity of 42, a tenacity of 0.45 g.p.d., and a denier of 39 d.p.f. (4.3 tex.). In order to demonstrate preparation of the composite cushioning structures of this invention from collapsed closed cell filaments, a portion of these polyethylene terephthalate ultramicrocellular filaments is subjected to a deflation treatment comprising about a 4 minute immersion in boiling methylene chloride. The filaments are removed from the bath, spread out and air dried, the product being collapsed filaments having a stable density of about 0.3 gram per cc.
A 2.3 oz./yd. random batt of these collapsed polyethylene terephthalate filaments is covered on both surfaces with a carded batting (1.15 oz./yd. of polyethyl ene terephthalate fiberfill of 4.75 denier per filament. This structure is hydraulically entangled on both sides in a 2" block pattern with a jet of high pressure water. This quilted batting is sufliciently entangled to be durable to subsequent handling including post-inflation of the collapsed ultramicrocellular fibers. Postinflation is accomplished by immersing the composite batt for 15 minutes in a boiling 50/50 (by volume) bath of methylene chloride/ 1,1,2-trichloro-1,2,2-trifluoroethane followed by a 15 minute drying in a circulating air oven at 100 C. This treatment inflates the ultramicrocellular filaments to a stable density of about 0.03 g./ cc. Follow-ing this treatment, the thickness of the composite batt is 1.60" and the bulk density 0.20 lb./ft. This product has utility as an insulating interlining which provides insulation equivalent to prior art fibrous battings at only to as great a basis weight. v
A unique interlining structure is prepared in similar fashion wherein a l oz./yd. random batting of collapsed ultramicrocellular fibers having a density of about 0.3 g./cc. is covered on one surface with a 1 oz./yd. carded batting of polyethylene terephthalate fiberfill of 4.75 denier per filament and on the other surface with a rayon taffeta interlining fabric. A high pressure jet of water traversed across the fiberfill surface pushes the ends of some of the staple fibers through both the ultramicrocellular core batt and the rayon fabric, effectively securing the laminae together in a 2" block pattern. This batting is sufficiently entangled so that it can be postinflated as above (except that the immersion time is reduced to 4 minutes to minimize damage to the rayon fabric). The thickness of the structure after post-inflation of the ultramicrocellular fibers is 1.0", and the bulk density, excluding the fabric backing is 0.17 lb./ft. This resilient composite structure is directly useful as an interlining material where an exterior fabric is applied over the fiberfill surface and the rayon fabric surface serves directly as the exposed inner face.
Example III Filaments are produced as Example II except that the 1,1,2-trichloro-1,2,2-trifluoroethane component is omitted. The resulting ultramicrocellular fibers, which spontaneously deflate to a density of about 0.3 g./cc. are chopped to a length of about 6 inches and are deposited as a random batt on a thin polyethylene terephthalate fiberfill batt. This is covered with a second fiberfill batt and the sandwiched structure is hydraulically entangled as in Example II to make a coherent structure. Post-inflation is then effected as in Example II.
Example IV A composite cushioning structure is prepared by covering a random batt core of continuous polyethylene terephthalate ultramicrocellular collapsed filaments of the type described in the above examples with a fiber batt of dense cellulose acetate staple. The surfacing batt is attached to the core batt by an hydraulic entangling process wherein the composite batt is supported on a 10 mesh wire screen and passed under fluid jets of water supplied at 1500 p.s.i.g. through 2.8 mil holes. Suflicient staple fibers from the surface batt are thus entangled in the core batt to produce an integral unit of suflicient coherence to survive subsequent handling including post-inflation of the collapsed cellular filaments. The resulting coherent structure is useful in cushioning applications where the pneumatic ultramicrocellular continuous filament core batt provides load support at very low bulk density while the dense acetate fiber surfacing batt provides soft desirable aesthetics.
Example V Collapsed polyethylene terephthalate ultramicrocellular filaments of density 0.3 g./cc. and 50 d.p.f. are supplied as a thin batt of continuous filaments. A thin surfacing batt of carded polyethylene terephthalate fiberfill staple is placed on top of the core batt and the two layers joined by a hand operated needle punching technique employing a knitting needle to simulate a mechanical needle punching operation. Adequate entanglement is achieved to provide a coherent composite batt which can be handled and post-inflated.
Example VI Partially collapsed polypropylene microcellular filaments are prepared by blending in a heated extruder equal parts by weight of isotactic polypropylene (Hercules Pro-Fax 6223) and fluorodichloromethane. The resulting solution is extruded at 170 C. and 1250 p.s.i.g. through a cylindrical orifice 4.5 mil diameter x 8 mils long to generate a microcellular filament as the superheated solvent flashes off. These microcellular filaments are comprised of polyhedral cells defined by textured walls less than 2 microns thick. After equilibrium with ambient air is established, the filaments are in a partially deflated condition with a density of 0.0249 g./cc., a diameter of 14 mils, and a tenacity of 0.4 g.p.d. These filaments are collected beneath the extrusion orifice as a batt of 2.3 oz./sq. yd. basis weight comprised of randomly deposited continuous filaments.
This partially collapsed microcellular filament batt is employed as the filling in a sandwich structure whose bottom layer is a 1 oz./ sq. yd. batting of 1.5 d.p.f. polyethylene terephthalate dense staple in a 70/30 garnetted blend of 1 /2" staple/ .41" staple, chosen to contribute particularly desirable surface aesthetics. The top layer is a 2 oz./ sq. yd. batting of the same polyethylene terephthalate staple blend which had been previously hydraulically entangled by exposing the batting, supported on a 14 x 14 backing screen of approximately 45% open area, to Water jets issuing through 7 mil diameter holes drilled 20 holes per inch along the length of a supply pipe providing water at 500 p.s.i.g. The 3-layer sandwich structure is consolidated by a hydraulic entangling step applied from the top layer in a 3" block pattern employing the same equipment with water pressures up to 850 p.s.i.g. The resulting dense fiber surfaced composite is coherent enough to withstand an inflation treatment.
Complete inflation of the microcellular fibers comprising the core of the structure is accomplished by exposing the composite sandwich structure for 30 minutes to perfluorocyclobutane vapor in equilibrium with the liquid phase at 55 C. in a closed pressure-vessel. Subsequently the sample is transferred directly to a circulating air oven at C. and held there for 15 minutes. This treatment fully inflates the polypropylene microcellular filaments to a density of only 0.0132 g./cc., while the thickness of the composite cushioning structure simultaneously increases to 1 /8" and a bulk density of 0.35 lb./cu. ft.
What is claimed is:
1. A resilient laminar structure comprising a first batt of randomly arranged microcellular fibers and a second batt of dense, substantially non-cellular staple fibers adjacent at least one face of said first batt, said batts being mechanically joined into a coherent unit by interpenetration of the staple fibers of said second batt into said first batt, said microcellular fibers being composed of a synthetic organic polymer defining closed cells having substantially all of the polymer present as filmy elements of a thickness less than 2 microns.
2. The structure of claim 1 wherein said polymer is crystalline and said microcellular fibers are ultramicrocellular fibers exhibiting uniplanar orientation and uniform texture.
3. The structure of claim 2 wherein said ultramicrocellular fibers are continuous-length fibers and are composed of polyethylene terephthalate.
4. The structure of claim 3- wherein said dense, substantially non-cellular staple fibers are composed of poly ethylene terephthalate.
5. The structure of claim 1 wherein said microcellular fibers are fully inflated.
6. The structure of claim 1 wherein said microcellular fibers are collapsed.
7. The structure of claim 6 wherein the cells of the ultramicrocellular fibers contain an impermeant inflatant.
8. The structure of claim 1 wherein the microcellular fibers are composed of polyhedral-shaped cells having an average transverse dimension of less than 1,000 microns and which contain an impermeant inflatant, said microcellular fibers having a density of less than about 0.05 gram/ cc. and a diameter of less than about 0.25 inch.
9. The structure of claim 1 wherein the interpenetration of said staple fibers into said first batt are at spaced intervals so as to define a pattern of areas of entanglement alternating with areas of no entanglement.
References Cited UNITED STATES PATENTS ROBERT F. BURNETT, Primary Examiner R. L. MAY, Assistant Examiner U.S. Cl. X.R.