US3499810A - Method of making a bonded nonwoven web of staple-length filaments - Google Patents

Description

March 10, 1970 as. WAG E 3,499,810

METHOD OF MAKING A BONDED NONWOVEN WEB OF STAPLE-LENGTH FILAMENTS Filed May 31, 1967 3 Sheets-Sheet 1 POLYMER SPINNING AND COLLECTION OF FILANENTS.

FILANENTARY TOW CONERENT RIBBON CRINPINC OF 4 HLM'ENTS' TRANSVERSE OU TTINC.

CRINPEO FIBROIJS FILANENTARY TOW SECTIONS OERECISTERING OF CAROINC/ FILMIENT E ]5 REDISTRIBUTIONM 1 CRIHPEO UNBONOEO DERECISTEREO HBROUS FILANENTARY TON ASSEMBLY ANNEALINC 0F HLAIEHS' NEAT ANO COOL ANNEALEO, CRINPED BONDED OERECISTEREO uobwov FILANENTARY TON LON-NELTINC COMPONENT APPLIED BY INVENTOR DIPPING. OINMR CANPAT OLE ATTORNEY March 10, 1970 o. e. WAGLE 3,

METHOD OF MAKING A BONDED NQNWOVEN WEB STAPLE OF -LENGTH FILAMENTS Filed May 31, i967 3 Sheets-Sheet 2 FIIG.Z

CONTINUOUS- LENGTH BONDED RIBBM cumzn sEcnous UNBONDED PI ow T I HBROUS I LL ICKNG ASSEMBLY STRUCTURAL FIBERS F I 6- 3A FABRIC LOIER HELTING COMPONENT F l G- 4 FUSION BOND-LOWER HELTIHG COMPONENT INVENTOR STRUCTURAL FIBER 0mm mm mm @0444?! Q IM ATTORNEY March 10, 1 97 0 0; a. WAG LE 3 499.810

METHOD (OFMAKING 'A BONDED NONWO-V-EN WEB 0F STA LE-LENGTH FILAMENTS Filed May 31, 1967- I 3 Sheets-Sheet. 5

F I G. 5

' DRYER -4 L AIR TO SOLVENT RECOVERY CONTINUOUS LENGTH R BONDED RIBBION ANNEALED, ORINPEO OEREOISTEREO FILANENTARY TOI MR FROII SOLVENT RECOVERY INVENTOR DINKAR GANPAT WAGLE BY QM ATTORNEY United States Patent 3,499,810 METHOD OF MAKING A BONDED NONWOVEN WEB OF STAPLE-LENGTH FILAMENTS Dinkar Ganpat Wagle, Wilmington, Del., assignor to E. I. du Pont de N emours and Company, Wilmington, Del., a corporation of Delaware Continuation-impart of application Ser. No. 554,582, June 21, 1966. This application May 31, 1967, Ser. No. 646.146

Int. Cl. B32b 31/00; D04h 3/16 US. Cl. 156152 6 Claims ABSTRACT OF THE DISCLOSURE CROSS REFERENCES TO RELATED APPLICATIONS This application is a continuation-in-part of my application Ser. No. 554,582, filed June 21, 1966, now abandoned.

BACKGROUND OF THE DISCLOSURE Field of the invention This invention relates generally to the preparation of a high bulk, thermally self-bonded, fibrous product and to an unbonded assembly of crimped, stabilized filaments useful as an intermediate for the production thereof. More particularly, the present invention relates to a process embodiment leading to such products and intermediates.

Description of the prior art Various procedures have been developed in recent years involving the utilization of so-called fiber-fill in the provision of bonded fibrous batts, webs and other nonwoven products of the bulky type suitable for quilted fabric interliners, pillow-fillings and the like. Perhaps most notable among these procedures is that involving the preparation of a batt for the fiberfill and subsequent spraying of the batt with an adhesive to bond the filaments into a coherent structure. While such structures have achieved some degree of importance in the textile industry, numerous processing problems and product limitations have nevertheless arisen. In the first place these methods use spraying equipment and this is particularly disadvantageous in that a nonuniformly bonded product is obtained. Even when a thin article such as a web is to be produced, a substantially greater build-up of binder occurs on the surface than does on the inside and this inefficient utilization of binder detracts from softness or other aesthetically desirable properties and is, of course, uneconomical. For thicker webs or batts, there is a practical limit of thickness beyond which it is difficult to obtain any degree of penetration of binder into the middle thereof, at least without greatly overloading the structure with binder. Yet inadequate or nonuniform bonding throughout the structure may result in inadequate strength or inferior compressional properties.

SUMMARY OF THE INVENTION In accordance with the invention there is provided an unbonded assembly, having a density of up to about 1 3,499,810 Patented Mar. 10, 1970 lb./ft. of crimped, individually distinct staple-length filaments which have been so prepared that once formed into a desired shape, a brief exposure to heat will result in a uniformly bonded product. The assembly has the advantages of fiberfill but in addition is self-bondable. The need for spraying the nonwoven assembly is obviated because the binder is pre-afiixed to the filaments. Moreover, the binder is evenly distributed throughout the filaments, hence can be used more sparingly to give property advantages while at the same time affording superior product uniformity. Still a further advantage of the assembly is that the fibers become strongly adhered to one another by fusion bonds, yet the filaments have been prestabilized so that the assembly will undergo little or no densification during the bonding step.

The thermally self-bondable assembly of crimped, individually distinct, staple-length filaments is provided by a process comprising the steps of (1) collecting into a continuous length bundle a plurality of filaments comprising an oriented filamentary component of-a fiberforrning, synthetic, organic polymer, (2) crimping said filaments to provide an average crimp frequency of at least 3 crimps per inch and an average crimp index of at least 5%. (3) separating the crimped filaments from one another, (4) applying to said crimped, separated filaments, without substantially removing crimp therefrom, a coating of a lower-melting synthetic thermoplastic polymer component to thereby provide a continuous'ribbonlike structure, said lower-melting component having a polymer melt temperature which is at least 70 C. but is below the fiber stick temperature of the filamentary com-1 throughout the three dimensions thereof an essentially constant weight ratio of said filamentary component to' said lower-melting component, (7) it being--further:pro-

vided that at least prior to the preparation of said lowdensity assembly of step (6), above,- said filamentary component is annealed at an elevated temperature in a substantially relaxed state to provide a maximum retractive coefiicient of about 30.

In effect the fibrous assembly so obtained is ready for bonding; that is, (a) the heat-activatable binder or socalled lower-melting component has alreadybeen applied, (b) the filaments have been crimped -to'-provide bulk and/ or other properties, (0) the filaments have been stabilized (hence have a low retractive coefiicient as hereinafter defined) to minimize latent shrinkage or crimpability forces that might tend to excessively density the product upon bonding, and (4) the filaments have been redistributed, i.e. nearly all filament-to-filament bonds broken up and the filaments blended to a highly uniform low-density mass, e.g. below 1 lb./ft. usually as low as 0.6 lb./ft. or even 0.1 lb./ft. In order to make a thermally self-bonded, low-density, nonwoven product it is merely necessary to heat the unbonded assembly, prepared as described, to a'= temperature in excess of said polymer melt temperature but below said fiber stick temperature, then cool to bond the filaments.

BRIEF DESCRIPTION OF THE DRAWINGS FIGURE 1 is a flow diagram of various steps, in one sequence, leading to the unbonded fibrous assembly and then to the bonded nonwoven product.

FIGURE 2 shows schematically the ribbon cutting step of FIGURE 1 in which fibrous sections are produced.

FIGURE 3 shows schematically a pillow in which a fabric ticking has been stuffed with an unbonded fibrous assembly of the invention.

mechanically dis- FIGURE 3A shows schematically an enlarged view of the encircled portion of FIGURE 3. As shown in FIG- URE 3A individual filaments have a discontinuous coating of low melting component thereon but are not bonded to one another.

FIGURE 4 shows schematically an enlarged view of the filamentary stuffing of FIGURE 3 after bonding,

FIGURE 5 shows schematically one form of a tow coating procedure.

DETAILED DESCRIPTION Composition of the polymeric components As indicated above, the unbonded assembly of the invention utilizes two components, structural filaments and a heat-activatable adhesive referred to herein as the lowermelting component. The filaments comprise an oriented, filamentary component of a fiber-forming, synthetic, organic polymer having a relatively high fiber stick temperature. The lower-melting component comprises an unoriented synthetic thermoplastic polymer and it has a polymer melt temperature which is at least 70 C. but is below the fiber stick temperature of the filamentary component.

The filaments employed are commonly available synthetic polymer filaments of the type produced by spinning and drawing. Normally, the filaments may have a denier within a wide range, for example, from 1 to 50 denier per filament. Frequently, however, the most desirable aesthetics, e.g. softness, are achieved in bonded nonwoven products made from filaments having a denier in the range of approximately 1 to 15 denier per filament. The cross-section of the filaments will normally be round, but may be prepared so that it has other cross-sectional shapes; such as elliptical, trilobal, tetralobal, and the like shapes.

The filamentary component may comprise a variety of synthetic, organic polymers, such as polyolefins, acrylonitrile polymers and copolymers, polyesters, polyamides, vinyl polymers and copolymers, polyurethanes, polyformaldehyde, cellulose acetate and the like. It should have either a higher polymer melting temperature than the lower-melting bondable component, or should be of such a character that it has high heat stability and can be regarded as having no melting or softening point under ordinary use conditions. The general term fiber stick temperature is accordingly used. The filamentary component need not be thermoplastic but must be of fiberforming molecular weight.

By synthetic polymer is meant a material synthesized by man as distinguished from a polymeric product of nature. The class of synthetic polymers, thus excluding for example cotton and viscose rayon, has several advantages for cushioning applications over polymers of nature. They generally have a high elastic recovery; this being defined as the amount by which a fiber recovers after application and removal of a force (stress) causing deformation. Synthetic fibers usually show an elastic recovery of 90- 100% from 2% extension as compared to, for example, as little as 74% for cotton. The synthetic polymers as a class also generally exhibit superior resistance to stress decay and lower moisture regain properties.

The second or lower-melting component should comprise a thermoplastic polymer and have a polymer melt temperature above about 70 C. but below the fiber stick temperature of the filamentary component. This will ensure, first, that thermal bonding can occur without destroying the filamentary component, and, second, that the bonds will not be destroyed by moderately high temperatures of the kind normally experienced during use, i.e. usual laundering and drying procedures. Preferably, the polymer melt temperature of the lower-melting component will be within 5 to 50 C. of the fiber stick temperature of the filamentary component to facilitate the thermal bonding procedure.

The lower-melting component is lateritly bondable such that upon fabrication of the filaments into the form of the desired fibrous assembly, e.g. a batt or web, mere application of heat will cause this component to soften and/or melt. Upon cooling, bonds will thus be formed with neighboring fibers, whether or not the latter contain a bondable component associated therewith. Thus it is frequently desirable to incorporate ordinary staple filaments, either of natural fibers or of synthetic fibers, in the fibrous assembly.

The lower-melting component may be selected so that it is fiber-forming, and normally this would be the case. On the other hand, it can also be non-fiber-forming, e.g. be a polymer of relatively low molecular weight. Typical thermoplastic polymers which can be used as the lowermelting component include polyolefins, acrylic resins, acrylic terpolymers, polyesters and copolyesters, polyamides and copolyamides, vinyl polymers and copolymers and the like.

For some applications it is desirable that the filaments of the assembly be provided with only small amounts, i.e. less than 15% by weight, of the lower-melting component in order to achieve certain properties such as softness of hand in the final bonded product. For other applications as much as 50% by weight or more of the lower-melting component may be used.

In a preferred embodiment of the invention the filamentary component and the lower-melting component will be derived from the same chemical class of polymers, for example, a polyester such as polyethylene terephthalate will be used to form the filamentary component whereas the lower-melting component will comprise a copolyester such as the copolymer of ethylene glycol with a mixture of isophthalic and terephthalic acids. Polyamides and copolyamides may similarly be used to advantage. The utilization of chemically related polymers in this manner is especially desirable because it gives rise to interfilament bonds of a particularly high adhesion level.

Either or both of the components may include conventional additives such as dyes, pigments, U.V. stabilizers and antistatic agents.

Preparation of unbonded assembly and bonded nonwoven In accordance with the invention, a supply of filaments is obtained by any of the usual procedures of dryspinning, wet-spinning 0r melt-spinning a fiber-forming synthetic organic polymer. Upon issuing from orifices of a spinneret into a quenching chamber the filaments are collected and drawn in the usual way. The drawing of the filaments serves to orient the polymer molecules and to provide strength and other properties. Conveniently, filaments will be obtained from a series of spinnerets, thereafter collected together into a continuous bundle of substantially parallelized filaments, e.g. a so-called tow and then drawn. As is frequently the case with freshly-drawn filaments, they may be annealed to some extent, e.g., heated above their second-order-transition temperature while substantially relaxed, following the drawing operation.

The tow of filaments may then be subjected to a crimping operation by techniques known in the art. Typical among the mechanical crimping devices which may be employed for this purpose is the co-called stufilng box type of crimper which normally produces a zig-zag crimp. Alternatively, there may be used apparatus employing a series of gears adapted to apply a gear crimp continuously to a running bundle of filaments. Certain types of filaments can also be crimped other than by mechanical means, for example polyethylene terephthalate fibers may be provided with a helical crimp by the air quenching procedure described by Kilian in US. Patent 3,050,821. In this instance the crimping step is, in effect, performed concomitant y with the spinning operation and several bundles of crimped filaments are then combined to form the tow. In any case the crimped filamentary tow so produced may be a highly compacted product in which many of adjacent filaments are in phase with one another, i.e., pairs or groups of crimped filaments contact one another for substantial distances along their lengths. Accordingly it is generally necessary to thereafter treat the tow of crimped filaments in some manner to separate adjacent filaments from one another, i.e. so adjacent filaments touch only at spaced points. Advantageously this may be effected by deregistration in which adjacent filaments are rendered out of phase with one another.

For purposes of filament separation there may be used various devices of the kind commonly employed in the tow-treating art. In one of these the tow is subjected to an explosive expansion of compressed air using a specially adapted venturi nozzle as described in Caines et al. US. Patent 3,099,594. An alternate technique for separating and deregistering filaments of a crimped tow involves the use of rolls provided with a series of rigid surfaces with serve as gripping means for displacing filaments relative to one another. Apparatus of this type is illustrated in Mahoney et al. US. Patent 3,032,829 and in Dunlap et al. US. Patent 3,156,016. Still another form of apparatus which may be used for this purpose is that illustrated in Jackson US. Patent 2,929,392 involving the use of pairs of rolls to first straighten the crimped filaments and then to suddenly relax the tow and thereby effect blooming.

The particular type of crimp, i.e. in terms of its dimensional characteristics, is not critical but rather can be selected depending upon the type of textile product to be ultimately formed. Thus the crimp may be essentially planar or zig-zag in nature or it may be a threedimensional crimp. Whatever the nature of the crimp, the filaments should attain an average crimp frequency of at least 3 crimps per inch and an average crimp index of at least 5%.

The tow may vary widely in terms of its cross-sectional dimension and the number of filaments therein. Thus a bundle may be used wherein the number of filaments is in the range of 500 to 5,000,000.

Once the crimped and separated filamentary tow is produced, it may then be annealed at this stage to reduce the so-called retractive coefficient to a suitably low level, i.e. so that it is not in excess of about 30. The low retractive coefiicient indicates that the filamentary component has been treated at some stage of its processing to remove most, if not all, of the latent crimping and shrinkage forces therefrom. During a subsequent 0 thermal bonding treatment the individual filaments will undergo little or no relative movement or other dimensional change and thus compaction and densification of the assembly will be greatly minimized. Preferably, the retractive coeflicient will be as close to zero as possible, i.e. up to or so, to ensure only very modest densification during the thermal bonding treatment. In effect, the retractive coefficient expresses a relationship between the length of the filaments before and after they are exposed to a temperature above the polymer melt temperature of the lower-melting component but below the fiber stick temperature of the filamentary component.

Continuous textile strands as initially prepared may have a relatively high retractive coefficient. This is a result of drawing treatments performed subsequent to the spinning operation in order to reduce the denier of the spun filaments and to develop strength or other properties. The drawing treatment creates internal stresses within the filaments and these often tend to result in undesirably high level shrinkage and/or crimping forces should the filaments be heated above their second-order transition temperature, i.e. of the filamentary component. In accordance with the invention the filaments are stabilized, e.g., by annealing, to relieve these tendencies and thus lower the retractive coefficient. A low-density nonwoven batt can then later be prepared in which the filaments will undergo little or no relative movement upon heating to a bonding temperature-hence individual filaments become merely bonded to one another in generally the same low-density configuration as existed in the unbonded assembly and filament intertwining or entanglements are kept at a minimum. Of course, the actual percent bulk loss in bonding can vary depending upon such factors as the unbonded batt density, filament denier, retractive coefficient level, etc.

For purposes of annealing the filaments, a temperature will normally be selected which is above the second-ordertransition point of the filamentary component but below its fiber stick temperature. Although the annealing temperature selected will depend upon the composition of the filamentary component, usually it will exceed C. Hot air, hot water or steam may be used depending upon the type of filament. Normally, a few seconds or minutes of exposure at such a temperature is sufiicient for annealing the filaments of the tow to remove the latent crimpability and shrinkage forces before further processing of the filaments. Individual filaments are, of course, under essentially no externally applied tension during the annealing step. If the filaments are of a type which develop crimp upon heating, then crimping and annealing may be effected simultaneously.

The annealed tow of crimped, separated filaments may be then coated to form a coating of lower-melting component along the exterior of the filaments. Spraying or dipping procedures may be used for this purpose and the resulting product will thus be bonded into an integral ribbon-like structure. The bonds are adhesive bonds as contrasted to the fusion bonds to be created upon later heating the coated filaments to a bonding temperature. The adhesive bonds so obtained will be intentionally broken at later stages of processing as the filaments are redistributed to form a uniform assembly. The advantage of coating the filaments following steps of crimping and deregistration is that the adhesive bonds occur mostly at spaced points rather than as continuous lengths of bonding areas which would be dilficult to break in subsequent processing.

The bonded ribbon-like structure is obtained, in one embodiment, by causing a running length of the previously prepared tow to be momentarily immersed in a solution or dispersion of the lower-melting component. The choice of the solvent or other vehicle for this purpose is not critical, but, of course, it should be a nonsolvent for the filamentary component. Volatile inert liquids such as water, alcohols, esters, hydrocarbons, and halogenated hydrocarbons are exemplary of the many materials which can be used. Advantageously, the freshly-coated tow will then be passed through a pair of resilient, driven nip rolls to squeeze excess solution or dispersion therefrom and to uniformly distribute the lower-melting component therethrough. After drying, preferably below the polymermelt temperature of the lower-melting component, the coherent ribbon-like structure is obtained.

Spraying procedures may similarly be used in which a solution or dispersion of the lower melting-component is applied as a fine mist to the tow. Hence, for ease in processing, the use of a dip coating procedure is preferred.

The preparation of the bonded ribbon-like structure will be described in greater detail with reference to FIGURE 5. The annealed, crimped dleregistered filamentary tow is guided into the dip tank 11 and compacted to remove air by a first pair of driven squeeze rolls 12 having a film sleeve thereon of polytetrafluoroethylene. The tow from the first pair of squeeze rolls 12 is led into and out of a solution 14 of the lower-melting component as it passes about bar 13 submersed in the solution. The tow then passes through a second series of weighted, driven squeeze rolls 15 to remove excess solution therefrom and return it to the dip tank 11. The rolls 15 have a resilient rubber covering protected by a sleeve of polytetrafiuoroethylene film. The tow then passes through dryer 16 by means of driven guide rolls 17 as heated air fiows first, in the direction of tow travel and secondly, counter thereto. Finally the tow exits through driven squeeze rolls 18 and about driven guide roll 19 to be wound up or otherwise further processed.

If the solvent for the lower-melting component is a volatile liquid such as methylene chloride or 1,1,2-trichloroethane, as is preferred, then drying of the tow can be effected at a high rate of speed. For example, with air heated at about 120 C. to 160 C. or so, there is almost instantaneous drying of the tow, i.e. usually in less than about 2 seconds.

As the tow passes through the vertical dryer 16, a low amount of tension is preferably maintained on the tow to ensure that the crimped filaments are not appreciably straightened out as the lower melting component is solidified. The retention of crimp is important during the clip coating procedure in order to facilitate the subsequent carding operation. The minimum tension is provided by driving rolls 17 at a slight lower speed than squeeze rolls 15, thus ensuring that any loss of crimp, i.e. straightening, of the filaments occurring in the dip tank 11 (because of the weight of solution thereon) is restored before the lower-melting component solidifies. Tension during drying should preferably not exceed about 0.009 gram per denier. Excess tension is likewise avoided as the tow passes between rolls to minimize loss of crimp.

The amount of lower-melting component applied to the tow can be adjusted to a desired level by appropriately changing either its concentration in the solution or dispersion, the pressure applied by the squeeze rolls, or the speed of the tow being coated.

The continuous, bonded, ribbon-like structure, above described, may vary considerably in its characteristics. Usually it will be relatively dense as contrasted to the high bulk nonwoven product which can later 'be formed after thermal bonding. Densities in excess of 1 lb./ft. are not uncommon for the ribbon-like structure. Its crosssectional dimensions may vary from a few inches, or even less, to several feet in width. Normally its thickness will only be a fraction, eg one fifth or less, of the width dimension. Desirably it will at most be only a few filaments in thickness.

The coating process will result in a difference in orientation between the two components. Thus the drawn filamentary component will be relatively highly oriented whereas the lower-melting component will be a relatively unoriented coating along the exterior of the filaments. The coating may typically be non-uniform, e.g. with varying thickness, or even discontinuous. However, the term discontinuous is not meant to imply that the lower-melting component is necessarily in particulate form along the exterior of the filaments. Thus in fact it may be in the nature of a filmy coating covering large areas of the filaments-with discontinuities existing only on a microscopic scale.

The ribbon-like structure is, as a next step, reduced to a staple-length by cutting it at intervals transversely to its longitudinal axis, as shown in FIGURE 2. As a result, socalled fibrous sections are thus produced, in each of these the parallel alignment of filaments is preserved. By this operation the filaments themselves are reduced to a highly uniform staple length. The tow may be conveniently cut by any of the well known types of staple cutters. The length of the fibrous sections, i.e. in the direction parallel to the direction of filament alignment, can be of ordinary stable fiber length, e.g. about 1 inch to 6 inches.

As will be apparent from the foregoing, an advantageous feature of the invention is that the above-described steps, starting with spinning and including that of coating, can all be performed with a continuously running tow. From the standpoint of a commercial operation this not only represents a high degree of process efiiciency, because adhesive is not applied to individual articles, but also it affords improved product uniformity.

As a next step in the preferred process embodiment of the invention, the fibrous sections are opened and the individual staple-length filaments distributed; that is, separated from one another and initimately blended. Adhesion bonds are broken but substantial portions of the lower-melting component remain afiixed to the filaments. There is thus obtained a loose, bulky assembly of individually distinct, crimped, stabilized, coated staple filaments which throughout its three dimensions is highly uniforms in terms of the ratio of filamentary component to lower-melting component. The latter characteristics, in particular, distinguish the bonded nonwoven products of the invention from attempts in the prior art to obtain bulky, adhesive coated nonwoven products. The essentially constant ratio of the two components means that bonding can also be essentially uniform such that compressional and other properties will not materially vary through the thickness of the structure. Perhaps most importantly, the uniformly bondable characteristics means than a fabricator of finished textile articles can produce a wide variety of products by the simple expedient of heating shaped assemblies.

An ordinary card or garnett card machine is particularly suitable for effecting mechanical redistribution of the filaments of the cut, staple-length fibrous sections. The combing action of the typical card cloth cylinder employed therewith serves to effect rupturing of the adhesive bonds while at the same time uniformly blending the fibers to a bulky fibrous assembly, e.g. in the form of a batt or web. Once redistributed in this or other ways, the individual filaments can be formed into a product of the desired characteristics by other techniques as well, for example batts may be processed on a Rando-Webber machine or other known air-laydown machines, i.e. a Duo-Form machine.

One advantage of this invention is that highly bulked nonwoven products can be obtained. With such low density products it is particularly important for functional purposes that the bonding be substantially uniform throughout. Bonded products having densities below 1.5 lbs./ft. in fact as low as 0.2 lb./ft. are readily obtainable. Moreover, only a relatively modest increase in density will have occurred during bonding.

The step of thermally bonding the unbonded fibrous assembly is accomplished by merely heating the assembly to a temperature is excess of the polymer melt temperature of the lower-melting component. The latter softens or melts and, upon cooling, bonds are formed at fiber cross-over points throughout the three dimensions of the structure, as indicated generally in FIGURE 4.

As above-mentioned, ordinary filaments, i.e. uncoated or monocomponent filaments, may be blended with the coated filaments in forming the unbonded assembly. The ordinary filaments would have a maximum retractive coefiicient of 30 and a fiber stick temperature above the polymer melt temperature of the lower-melting component of the coated filaments. Such ordinary filaments may comprise 0 to by weight of the unbonded assembly.

The sequence of processing steps illustrated in FIG- URE 1 and discussed above is advantageous from the standpoint of ease and economy. However, it will be apparent that numerous variations are possible, but within certain limits. In particular, the annealing step can be performed at any convenient stage of processing following drawing to reduce the retractive coefficient to a maximum of 30. In one respect it is advantageous for this step to be performed after crimping and before coating since high annealing temperatures can then be used without fusing the lower-melting component. On the other hand it is also entirely practical to effect annealing after coating. Even if the polymer melt temperature of the lower-melting component is exceeded during annealing and some fusion occurs, the bonds in the ribbon-like structure can usually be broken during a subsequent mechanical redistribution step, e.g. carding. Two or more annealing steps can also be used, for example one following drawing and another following coating. The staple cutting operation can also be performed at various stages, although it will be apparent that coating, crimping and annealing steps are more easily carried out using a continuous filament tow. Other such variations will also be evident.

Characteristics of the assembly and uses In one embodiment the product of the invention is an assembly of coated filaments which (a) are highly dissociated, i.e. the filaments are not thermally or adhesively bonded to one another but rather exist as individually distinct filaments, (b) are relatively highly crimped but nevertheless are stabilized so as to substantially prevent shrinkage and movement when subjected to a thermal bonding treatment, and (c) possess by virtue of the lowermelting component an ability to bond to themselves or to other fibers when heated above the polymer melt temperature of that component. Advantageously, at least a major proportion by weight of the assembly should comprise coated filaments as above defined-but this is not essential to all uses.

As an article of commerce the assembly is suitable in widely diverse applications. In this respect it is to be understood that the term assembly is not intended to designate any particular geometrical shape or even any particular arrangement or size of the filamentary structures therein, for these are aspects that can be appropriately selected depending upon the intended use of the assembly.

The assembly of filaments may be conveniently provided in the form of a continuous length web of staple fibers, which can be supplied to the textile industry for conversion into textile structures of the desired type, e.g. into non-woven batts, slivers, and yarns, or into knitted, tufted, and woven fabrics. For such uses the filaments of the assembly may be blended with various proportions of ordinary staple fibers which are not self-bondable themselves.

In one embodiment of the invention, the assembly of filaments is used to produce a bonded block of fibers which are aligned in the same direction. This is then sliced perpendicular to the direction of the fibers to produce porous, self-supporting fiber-on-end sheets, as dedscribed in Koller US. 3,085,922. Alternatively, the assembly of filaments may be processed on a garnetting machine and then cross-lapped to entangle the fibers into a nonwoven batt structure, which may be bonded by heating the batt above the polymer melt temperature of the lower-melting component. Nonwoven products may be formed into thin batts for use as such or the batts may be stacked on top of each other to provide thick articles which are then subjected to a bonding temperature. The nonwoven products may be formed such that the filaments are arranged therein to have fiber-on-end, fiber-on-side or random alignment. Also they may, following or during bonding, be laminated to various backing materials for additional support or for further processing into still other textile products.

The products of this invention are useful for processing into a wide variety of nonwoven, woven, knitted and tufted textiles for a variety of applications, but are particularl suitable for the manaufacture of bonded, nonwoven textiles, either quilted or unquilted. They are also suitable for use in making pillow fillings, fillings for sleeping bags, cushions, quilts, comforters, coverlets, mattresses, mattress pads, mattress toppers, furniture and auto upholstery, bedspreads, pile fabrics for industrial and apparel uses, blankets, womens robes, sport jackets, car coats, interlinings, outerwear, floor covering materials, tiles, carpets, bath mats, molded articles, and the like.

For the preparation of pillows, cushions and other articles it is also entirely practicable as shown in FIG- URE 3 to use the unbonded assembly for filling a fabric,

or other covering followed by heating the entire structure to effect bonding.

Advantages summarized A most fundamental advantage of the novel assembly of the invention is that it can be formed to a desired shape by the textile converter and bonded, by mere application of heat, with little or no change in shape. Another advantage of the invention is that it provides an assembly of filaments which are specially adapted to the formation of nonwoven textile structures having a combination of outstanding properties. When the assembly is fashioned into a textile article and then subjected to the thermal activation temperature of the lower-melting component, a bonded product is obtained in which the bonds are uniformly distributed throughout the three dimensions thereof. This permits the manufacture of nonwoven products having a combination of hitherto unobtainable properties; namely, the textiles can have a lower density, and they tend to be softer and have better drape properties than nonwoven textiles of the prior art. Products having a density of less than 1.5 lbs./ft. in many cases as low as 0.2 lb./ft. and below, are obtained. By virtue of a relatively uniform distribution of bond points throughout the three dimensions thereof, a high degree of height-retention and load support properties are obtained in the product. The uniform three-dimensional bonding provides a superior resistance: to dimensional changes, resistance to clumping, resistance to fiber leakage, and resistance to matting after repeated washings or dry cleanings. The invention is also useful for making bonded yarns for woven, knitted, and tufted fabrics which will show less pilling and which will require less yarn twist in manufacture.

where L =the length of the coated filament in inches when subjected to a load of 2 mg./denier per filament, based upon the denier of only the filamentary component; and L =the length of the filament in inches under the same load after exposure to a temperature above the polymer melt temperature of the lower-melting component but below the fiber stick temperature of the structural fiber component. For purposes of the measurement, the temperature selected will usually be the minimum temperature required to sufficiently soften or melt the lower-melting component to form effective fiber-to-fiber bonds. In the examples which follow, the temperature selected will be the same as the bonding temperature. Conveniently, the measurement is made after exposure to a temperature between 1 and 20 C. above the polymer melt temperature. (Only a nominal difference in RC would be experienced Within this range.) The values of L and L,, are measured on a cathetometer while the load is applied to the filament on a Model LG Precision Balance (Federal Pacific Electric Co.). An average is taken from measurements on five filament specimens.

Polymer melt temperature, PMT, is in the case of essentially amorphous or essentially crystalline polymers, the temperature at'which a sample of the lower melting component leaves a molten trail when moved across a heated metal surface with moderate pressure. Polymers containing substantial amounts of amorphous and crystalline regions are more accurately tested for polymer melt temperature by ascertaining the melting of the last crystal of a sample when heated, e.g. on a hot stage microscope using crossed optical polarizers (in the literature this is sometimes referred to as' indicative of crystalline. melting point).

Fiber stick temperature is described in Beaman and Cramer, J. Polymer Science, 21, .228 (1956).

Crimp frequency is determined by counting, under a magnifying glass, the number of crimps in the fiber while under a tension of 2 mg./ denier. The fiber is then extended until it is just straight (observed visually) and the extended length is measured. The crimp frequency, expressed as crimps per inch, based on the extended length of the filament, is calculated. An average is taken from measurements on five filament specimens.

Crimp index is determined by measuring the length of a filament first under a tension of 2 mg./denier and then under a tension of 50 mg./denier. Crimp index is the change in length expressed as a percentage of the uncrimped length. An average is taken from measurements on five filament specimens.

Drape test, or Flexural Rigidity is measured according to ASTM D-13 88-55T.

Softness test, ILD 25 (Indentation Load Deflection at a deflection of 25%), involves measuring the load in pounds necessary to produce a 25% deflection of the sample. The load in lbs. is calculated on the basis of a 50 square inch deflection area. The testing apparatus consists of a Schiefer Compressometer (Frazier Precision Instrument Co., Silver Spring, Md.) modified for use as a dead-weight thickness gauge. The procedure consists .of placing a sample on the gauge, reading the initial thickness and then adding weights to the presser foot of the gauge until the sample is deflected 25%.

The following examples further illustrate the practice of the invention. Parts and percentages are by weight unless otherwise stated.

EXAMPLE I Polyethylene terephthalate polymer (abbreviated 26- T) is melt-spun, drawn and crimped in accordance with Kilian US. Patent 3,050,821 to produce filaments of 4 denier/filament. The procedure involves air quenching the filaments as they exit from orifices of a spinneret, drawing the filaments in superheated steam and then relaxing the tension. U-pon release of the tension of drawing, it is observed that the filaments exhibit a high level of three-dimensional crimp, referred to as a reversing helical crimp. The filaments from several spinnerets are combined to produce a filamentary tow having a total denier of about 50,000.

After crimping, the tow is annealed in an air oven at 160 C. for one minute to relax the filaments, to eflect further crimping and to lower the retractive coefficient. The tow is then opened by hand from a cylindrical to generally fiat tow. This is then deregistered to separate filament groups. For this purpose, there are used two sets of positively driven nip rolls of the type more particularly described in Dunlap et a1. U.S. Patent 3,156,016. These pressure nip rolls have a diameter of 2 /8 inches and are 14 inches long. In each set of rolls, one has a series of helical threads whose ridged surfaces are 0.017 inch wide. The other is a smooth-surfaced elastomer covered roll. Upon pulling the tow under tension through the nips of the rolls, married groups of adjacent filaments are rendered out of phase with one another to deregister the crimps.

The deregistered tow is then given a second annealing treatment at 227 C. for 15 minutes in an air oven. This is just below the fiber stick temperature of the 2G-T which is 230 C. and well above the second-order-transition temperature of 80 C.

The opened and deregistered tow is then passed through a dip tank containing a by-weight solution of a copolyester in 1,1,2 trichloroethane and then squeezed free of excess solution. Apparatus generally similar to that of FIGURE 5 is used for this purpose. The copolyester has a polymer melt temperature of 208 C. and is a copolymer of 79 parts by-weight ethylene glycol terephthalate and 21 parts ethylene glycol isophthalate (abreviated 2G-T/2G-I). The tow is found to pick up 10% of the lower-melting copolyester component, based on filament plus copolyester. The tow is dried at 65 C. under minimal tension to produce an integral, flat bonded ribbon-like structure which is continuous in length and has a cross-section dimension of 5 by 0.1 inches.

The ribbon-like structure is next reduced to 2 inch length sections by cutting it in the transverse direction using a Pacific Converter. The filaments at this stage have a crimp index of 20, a crimp frequency of 14 crimps per inch and a retractive coefficient of only 6.

The adhesive-bonded fibrous sections are next treated to mechanically distribute the filaments, break the bonds and thereby obtain a highly uniform, low-density assembly of individualy distinct, staple-length filaments. For this purpose, carding of the fibrous sections is effected on a commercial garnett carding machine.

The unbonded assembly of filaments produced by carding is cross-lapped to form a batt whose dimensions are 23 by 17 by 0.79 inches. The batt is then bonded in an air oven under the conditions indicated in Table 1. As further indicated therein, only modest densification occurs during the bonding step-the overall density being extremely low. Mostimportantly, the bonded nonwoven product so obtained is uniformly bonded throughout such that its properties are also constant in all portions.

TABLE 1 Batt bonding temp. C.) 227 Batt bonding time (mins) 15 Density (lbs./ft. )-carded 0.11 Density (lbs./ft. )-bonded 0.18 Softnes, ILD 25% (lbs) 0.6 Drape, flex. rig (mg-cm.) 312 EXAMPLES II-V A bonded ribbon-like structure is produced as in Example I except that both before deregistration and after clipping (omitting annealing at 227 C.) the tow is annealed at 221 C. for 5 minutes under minimal tension in an air oven rather than at 227 C. for 15 minutes. The ribon-like structure is then cut to 3-inch long fibrous sections on a Beria cutter.

The fibers have a crimp index of 26%, a crimp frequency of 15 crimps per inch and a retractive coefiicient of 3.

The fibrous sections are opened using a Kirschner opener having a three-blade beater bar.

The annealed staple fibers are then carded into a web on a Proctor & Schwartz 740 carding machine to effectively break up interfilament bonds and evenly distribute the filaments. The card web is then fed onto a card cloth cylinder which separates the fibers in the web from one another. The fibers are then transferred from the cylinder to an air stream by jets of air and collected on a perforated belt having a vacuum slot underneath it. Four batts of varying density are prepared.

The air-laid batts are then bonded at 218 C. for five minutes in an oven having forced air directed upward against the batt so as to minimize the tendency for compaction to occur. The properties of the carded batts and bonded structures are shown in Table 2.

EXAMPLES VI-VII Helically crimped, deregistered 2G-T filaments are produced in accordance with Example I except that the drawn 13 tow has a total denier of about 860,000 and no heat is applied to the fibers after drawing. The tow is then sprayed with a 6% solution of 79/21 2G-T/2G-I in 1,1,2 trichloroethane to produce a bonded tow structure having a 2GT/2GI content of 9% based on the total weight of fiber and 2G-T/2G-I. The bonded tow is then divided into two parts a Control and VI/VII. The Control part receives no heat treatment and part VI/VII is annealed at 215 C. for 10 minutes under minimal tension in an air oven. Both parts are then cut to 2" long fibrous sections using hand shears.

The Control part filaments, which have had no annealing, have a crimp index of 15%, a crimp frequency of 9 crimps per inch and a retractive coefiicient of 37. The part VI/VII filaments have a crimp index of 28%, a crimp frequency of 13 crimps per inch and a retractive coetficient of 3. The bonded fiber sections from each of the parts are separately carded into batts on a sample card to uniformly distribute the staple filaments and to break up the filament-to-filament bonds. A pair of batts are formed from the Control part item to have a density of 0.3 and 0.6 lb./ft. respectively, after carding. A similar pair of batts is formed from the part VI/VII item.

The four batts are then bonded in an air oven at 218 C. for minutes. As shown in Table 3, the Control part lbatts, whose fibers had no annealing, lose 25-50% of their bulk during bonding. However, the part VI/VII batts, Whose fibers were annealed at 215 0., show little or no densification during bonding.

TABLE 3 Control Part VI/V II Annealing temp. C.) None 215 Bonding C.) 218 218 SampleA SampleB SampleVI SampleVII The procedure of Example I is repeated except that a sample carding machine is used to form the non-woven batt and just before carding, quantities of monocomponent 2G-T staple which had been annealed at 175 C. for 2 minutes then again at 227 C. for 15 minutes, in tow form, prior to its being out, are blended with the coated staple. The monocomponent 2G.T fibers are of 2-inch (5.08 cm.) staple length, are 4'denier per filament, and have a crimp index of 32, a crimp frequency of 11 and a retractive coetficient of 1. Blends containing 40%, 80% and 95% of the monocomponent fibers are used and very soft, lightly-bonded, low-density structures are obtained. Batt densities are shown in Table 6.

Nylon (66) tow having a filament denier of three total denier of 430,000 and a stufiing-box type of crimp is deregistered on the threaded-roll machine of Example I, then sprayed with a 5% solution of a copolyester dissolved in two parts methylene chloride and one part 1,1,2- trichloroethane to provide a content of 15 by weight, of the copolyester. The composition of the copolyester (abbreviated 2G-T/2G10) is a 55/45 weight ratio of ethylene terephthalate and ethylene sebacate units and its polymer melt temperature is 159 C. The tow is then cut to 2-inch (5.08 cm.) staple, annealed at 180 C. for 5 minutes in an air oven and carded on a sample carding 14 machine. The properties of the fiber are listed in Table 7. The carded batt is bonded at 160 C. for 5 minutes; batt properties are shown in Table 7.

The procedure of Example IX is repeated except that conventional polyacrylonitrile tow (fiber stick temperature is 231 C.) having a filament denier of 3 and a total denier of about 500,000 is used. Fiber and batt properties are listed in Table 8.

TABLE 8 Fiber properties:

Crimps per inch 9 Crimp index (percent) 9 RC. 5 Batt density, lb./ft. (g./cm.

Carded 0.22 (0.004) Bonded 0.40 (0.006)

EXAMPLE XI The procedure of Example VI is repeated except that the lower-melting component is a copolymer of vinyl chloride and vinyl acetate (about 87:13 weight ratio, polymer melt temperature of 136 C.) and the temperature used for the tow annealing :and batt-bonding steps is C. Carded and bonded batts having density properties similar to those obtained in Example VI are produced.

EXAMPLE XII The procedure of Example XI is repeated except that the lower-melting component is an alcohol soluble terpolymer (polymer melt temperature of C.) formed by condensing caprolactam, hexamethylene diamine, adipic acid and sebacic acid, such that there are substantially equal portions of polycaproamide, polyhexamethylene adipamide and polyhexamethylene sebacamide in the terpolymer, the solvent is an 80/20 ethanol/Water mixture by volume and the temperature used for the fiber-annealing and batt-bonding steps is C. Results similar to Example XI are obtained.

The invention has been particularly described with reference to applications in which the bonded product is used for cushioning and filling purposes and as a pile fabric. In these or other uses natural or synthetic resins or elastomers may be applied by suitable methods to the self-bonded products of the invention to produce coated substrates, laminates, bonded felts and the like.

'What is claimed is:

1. Method for producing a thermally self-bendable assembly of individually distinct, staple-length filaments comprising the steps of (1) collecting into a continuous length bundle a plurality of filaments comprising an oriented filamentary component of a fiber-forming, synthetic, organic polymer (2) crimping said filaments to provide an average crimp frequency of at least 3 crimps per inch and an average crimp index of at least 5%, (3) separating the crimped filaments from one another, (4) applying to said crimped, separated filaments, without substantially removing crimp therefrom, a coating of a lower-melting synthetic thermoplastic polymer component to thereby provide a continuous ribbon-like structure, said lowermelting component having a polymer melt temperature which is at least 70 C. but is below the fiber stick temperature of the filamentary component, (5) transversely cutting said continuous ribbon-like structure to Provide fibrous sections of staple-length filaments, (6) opening said sections, mechanically distributing said staple-length filaments and providing a low-density assembly of in dividual- 1y distinct filaments having throughout the three dimensions thereof an essentially constant weight ratio of said filamentary component to said lower-melting component, (7) it being further provided that at least prior to the preparation of said low-density assembly of step (6), above, said filamentary component is annealed at an elevated temperature in a substantially relaxed state to provide a maximum retractive coeflicient of about 30.

2. Method according to claim 1 wherein the said annealing temperature is in excess of the second-order transition temperature of said filamentary component.

3. Method according to claim 1 wherein said lowermelting component is applied by dipping said bundle in a solution of said lower-melting component.

4. Method according to claim 1 wherein said polymer melt temperature is Within 5 to 50 C. of said fiber stick temperature and said retractive coefiicient does not exceed about 15.

5. Method according to claim 1 wherein said filamentary component is polyethylene terephthalate andsaid temperature in excess of said polymer melt temperature but below said fiber "stick temperature and cooling said assemblyto thereby bond said filamentary components.

References Cited UNITED STATES PATENTS 3,391,048 7/1968 Dyer et al. 156-181 XR 3,177,644 4/1965 Aspy et a1. 28-75 XR 3,255,506 6/1966 Fritz;

PHILIP DIER, Primary Examiner US. ,Cl. X.R.

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