US3589956A - Process for making a thermally self-bonded low density nonwoven product - Google Patents

Abstract

A LOW DENSITY FIBROUS NONWOVEN PRODUCT IS MADE BY (A) SPINNING BICOMPONENT FIBERS, (B) CUTTING, CRIMPING, AND ANEALING THE FIBERS, (C) FORMING THE FIBERS INTO A LOW DENSITY NONWOVEN ASSEMBLY, (D) HEATING THE ASSEMBLY TO BOND THE FIBERS, AND (E) COOLING. CURRING, CRIMPING, AND ANNEALING MAY BE CARRIED OUT IN VARIOUS ORDERS, DEPENDING UPON THE NATURE OF THE BICOMPONENT FIBER. ANNEALING IS NECESSARY TO REMOVE MOST OF THE LATENT CRIMPING AND PREVENT COMPACTION AND DENSIFICATION OF THE ASSEMBLY DURING STEP (D).

Description

June 29, 1971 w KRANZ ETAL PROCESS FOR MAKING A THERMALLY SELF-BONDED LOW DENSITY NONWOVEN PRODUCT 2 Sheets-Sheet 1 Filed Sept. 22, 1967 FIG.

CRINPED EIITANGLED FIBERS INVENTOR 5 WILLIAM KRANZ WILLIAM LESTER STUMP June 29, 1971 w. KRANZ ET AL 3,589,956

PRQCESS FOR MAKING A THERMALLY SELF-BONDED LOW DENSITY NONWOVEN PRODUCT Filed Sept. 22, 1967 2 Sheets-Sheet 2 FIBER- FORMING POLYMER LOWERQIIELTI us COMPONENT BIOOIIPONENT SPINNING TOW 0F BIGOIIPONENT FILAMEIITS CRIIIP DEVELOPMENT CRIMPED FILAMENTARY TOW ANNEALING 0F FILAIIENIS ANNEALED, CRIIIPED FILMIEIITARY I0 STAPLE CUTTING STAPLE CARDING UNBOIIDED FIBRUUS ASSE II BLY HEAT AND COOL BONDED IIONWOVEII United States Patent O 3,589,956 PROCESS FOR MAKING A THERMALLY SELF- B ONDED LOW DENSITY NONWOVEN PRODUCT William Kranz, Newark, Del., and William Lester Stump, Kinston, N.C., assignors to E. I. du Pont de Nemours and Company, Wilmington, Del.

Continuation-impart of abandoned application Ser. No. 583,001, Sept. 29, 1966. This application Sept. 22, 1967, Ser. No. 675,271

Int. Cl. D04h 1/04 US. Cl. 15662.4 11 Claims ABSTRACT OF THE DISCLOSURE A low density fibrous nonwoven product is made by (a) spinning bicomponent fibers, (b) cutting, crimping, and annealing the fibers, (c) forming the fibers into a low density nonwoven assembly, ((1) heating the assembly to bond the fibers, and (e) cooling. Cutting, crimping, and annealing may be carried out in various orders, depending upon the nature of the bicomponent fiber. Annealing is necessary to remove most of the latent crimping and prevent compaction and densification of the assembly during step (d).

CROSS REFERENCES TO RELATED APPLICATIONS This application is a continuation-in-part of our US. application Ser. No. 583,001, filed Sept. 29, 1966, and now abandoned.

BACKGROUND OF THE INVENTION This invention relates to bonded fibrous nonwoven products formed of crimped, stabilized, bicomponent-spun filaments. It also relates to methods for obtaining such products.

Various techniques have heretofore been proposed for thermally bonding filaments into nonwoven products. In many cases attempts have been made to employ filaments which have been crimped so as to provide increased bulk, a soft hand, or certain other properties. While the use of bicomponent-spun or so-called composite filaments would seem advantageous for this purpose because of the ease with which a heat activatable bonding agent can be used as a component thereof, nevertheless a number of limitations have previously been encountered. Thus it has not been practical to obtain products having an extremely high bulk ad low density as would be desirable both for reasons of economics and to achieve certain aesthetics. Moreover, such products employing bicomponent-spun filaments have been attended by a distinct processing diadvantage; namely, the tendency of an unbonded filamentary product to undergo pronounced dimensional and other changes upon heating to a bonding temperature. It is in particular with these deficiencies of such prior art products that the present invention is concerned.

SUMMARY OF THE INVENTION It is a finding of this invention that prior efforts toward producing a high bulk, three-dimensionally self-bonded product composed of crimped bicomponent-spun fibers and exhibiting suitable performance properties have generally been unsuccessful for primarily one reason; namely, failure to ensure dimensional stabilization of the fibers prior to the thermal bonding treatment.

Thus, in accordance with this invention, there is provided a process for making a thermally self-bonded, lowdensity, nonwoven, fibrous product which comprises the steps:

(a) Spinning continuous strands of bicomponent filaments, said composite filaments comprising a filamentary component of a fiber-forming, synthetic, organic polymer and integral therewith along at least a portion of the exterror thereof a lower-melting, synthetic thermoplastic polymer component, said lower-melting component hav- 1ng a polymer melt temperature which is at least 70 C. but is below the fiber stick temperature of the filamentary component,

(b) Converting said continuous strands into staple length filaments having a retractive coefiicient of no more than about 30, an average crimp frequency of at least 3 crimps per inch, and an average crimp index of at least 5%, said converting being effected by the steps, in any order, of cutting, crimping and annealing said strands,

(c) Forming said staple-length filaments into a nonwtfg e/r; assembly having a density of no more than about 1 t.

(d) Heating said assembly to a temperature in excess of said polymer melt temperature, but below said fiber stick temperature, and

(e) Cooling said assembly to a temperature below said polymer melt temperature to thereby produce a selfbonded low density, integral structure.

This invention also provides a new nonwoven product of exceptionally low-density which is particularly useful as fiberfill for pillows and the like. The product is a self-bonded nonwoven having a density less than 0.55 lb./ft. It is composed of staple-length, climped, bicomponent-spun filaments, one component being a polyester filamentary component and the other component being a lower melting polyester component. The lower melting component has a polymer melt temperature which is at least 70 C. but is below the fiber stick temperature of the filamentary component. These bicomponent filaments are circular in cross section, with the lower melting component forming a continuous sheath about a core of the filamentary component, the sheath and core being concentric. The product may also contain up to about by weight, based on the total weight of the fibers, of staplelength, crimped, monocomponent polyester filaments having a fiber stick temperature above the polymer melt temperature of the lower melting component. The product is bonded by fusion of the lower melting component of the bicomponent filaments at points of contact with other filaments.

This product is made by a process within the scope of this invention wherein sheath-core bicomponent continuous strands are mechanically crimped and annealed in two form, then cut to staple length and formed into a nonwoven assembly, then heated and cooled to bond. If monocomponent filaments are to be included they also must be crimped and annealed, whereby both the monocomponent and bicomponent fibers in the unbonded assembly will have a retractive coefiicient of no more than about 30, an average crimp frequency of at least 3 crimps per inch, and a crimp index of at least 5%.

BRIEF SUMMARY OF THE DRAWINGS FIG. 1 represents an enlarged, partial View of a typical unbonded, but self-bendable, batt of bicomponentspun filaments according to the prior art. The filaments, though essentially uncrimped, possess a latent capacity to crimp when subjected to a bonding temperature.

FIG. 2 shows the product of FIG. 1 following a thermal treatment to crimp the fibers and elfect bonding at cross-over points. It Will be observed that severe densification has occurred because of the intertwining and entanglements created upon crimp development.

FIG. 3 represents an unbonded fibrous batt for use in the invention. The bicomponent-spun filaments have been crimped and specially stabilized prior to formation of the batt so as to reduce the tendency for compaction and intertwining to occur during a subsequent thermal bonding treatment.

FIG. 4 shows the product of FIG. 3 following a thermal treatment to bond the fibers at cross-over points. As a result of the stabilization treatment, little densification has occurred during the bonding treatment, i.e. substantially the full dimensions of the original fibrous batt have been retained.

FIG. 5 is a flow diagram of various steps, in a preferred sequence, leading to a bonded nonwoven product in accordance with the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The bicomponent starting material The terms bicomponent-spun and bicomponent are used synonomously herein to refer to composite filaments formed by the co-spinning of at least two distinct polymer components, e.g. in sheath-core or side-by-side configuration.

The bicomponent filaments employed in the practice of the present invention contain a higher-melting filamentary component and a lower-melting component. The latter serves to render the filaments thermally selfbondable and, accordingly, can vary widely as regards its physical nature as a constituent. Thus the higher-melting component may be spun as a core with the lowermelting component being spun as the sheath surrounding the core. The two may be eccentrically or concentrically arranged, but the lower-melting component must be on the outside. Alternatively, the higher and lower-melting polymeric components may be co-spun in side-by-side relationship from spinneret plates having orifices in close proximity. Numerous examples of spinning procedures for obtaining sheath-core and side-by-side bicomponent filaments from different compositions are described in the patent literature, for example, in Breen US. 2,987,797, and 3,038,236, in Taylor US. 3,038,237 and in Zimmerman US. 3,038,235. It will be understood that the terms bicomponent-spun and bicomponent are used in their general sense to mean at least two different components. Thus it is entirely practical for some purposes to utilize filaments having three or more different components.

Bicomponent filaments can, if desired, be co-spun from two or more compositions which are so selected as to impart latent crimp characteristics to the filaments. For example, if the components diifer in the amount of shrinkage they will undergo upon heating and if they have not been co-spun in concentric arrangement, then the mere application of heat will result in the development of crimp. Thus latent crimpability as well as latent selfbondability can be built directly into the filaments.

In some cases it is advantageous to employ bicomponent fibers which, although composed of lower-melting and higher-melting components, do not possess latent crimpability characteristics. In this case the filaments are mechanically crimped in the conventional fashion for ultimate use in accordance with the invention.

The lower-melting component of the bicomponent filaments has a polymer melt temperature which is at least 70 C. but is below the fiber stick temperature of the filamentary component. This vw'll 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 at least 5 C. below the fiber stick temperature of the filamentary component to facilitate the thermal bonding procedure.

Normally, the bicomponent 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 non-woven structures made from filaments having a denier in the range of approximately 1 to 15 denier per filament. The crosssection 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 like shapes.

The filamentary component may comprise a variety of synthetic, oragnic 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 melt 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 fiber-forming 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 -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 prope ties. The lower-melting component is latently bondable such that upon fabrication of the bicomponent filaments into the form of the desired nonwoven batt, 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 employ a blend of the bicomponent staple filaments with ordinary staple filaments either of natural fibers or of synthetic fibers.

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 polymers which can be used as the thermoplastic bondable component include polyolefins, acrylic resins, acrylic terpolymers, polyesters and copolyesters, polyamides and copolyamides, vinyl polymers and copolymers, and the like. For some application it is desirable that the filaments contain 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 lowermelting component may be used.

In a preferred embodiment of the invention the filamentary component and the lower melting componet will be derived from the same chemical class of polymers. In a particularly preferred embodiment, both components are polyesters. Polyesters suitable for forming the filamentary component include: poly(ethylene terephthalate); poly(trimethylene terephthalate); poly(tetramethylene terephthalate); the polymer from 1,4-cyclohexanedimethanol and terephthalic acid; the polymer from bibenzoic acid and bis(4-hydroxymethyl cyclohexane); the polymer from bis(4-hydroxymethyl cyclohexane) and terephthalic acid; and poly(pivalolactone). Polyesters suitable as the lower melting component include poly(hexamethylene terephthalate); poly(ethylene terephthalate/hexahydroterephthalate) poly (ethylene terephthalate/isophthalate) poly (ethylene/trimethylene terephthalate); poly(trimethylene terephthalate/isophthalate); poly(ethylene terephthalate/sebacate); poly(ethylene terephthalate/azelate); and poly(ethylene/tetramethylene terephthalate). Polyamides and copolyarnides 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 adhesive level.

Both components of the bicomponent filaments may include conventional fiber additives such as dyes, pigments, U.V. stabilizers, antistatic agents, etc.

Preparation of the bonded product The process of the invention for making a thermally self-bonded nonwoven product comprises:

(1) The spinning of continuous strands of bicomponent filaments as above-described; that is, comprising a filamentary component and a lower-melting component, including drawing of the filaments;

(2) The so-called converting of the continuous strands into staple length filaments having a maximum retractive coetficient of about 30, an average crimp frequency of at least 3 crimps per inch, and an average crimp index of at least this will involve a series of steps, to be performed in any order, of cutting, crimping and annealing the continuous strands;

(3) The forming or fabrication of the staple-length filaments into a low-density nonwoven batt or other assembly of filaments;

(4) The heating of the batt to a temperature in excess of the polymer melt temperature of the lower-melting component, but below the fiber stick temperature of the filamentary component; and

(5) The cooling of the batt to a temperature below the polymer melt temperature of the lower-melting component to thereby produce a self-bonded, low density, integral structure.

The distinctive features of the foreging process primarily reside in step (2); that is, the attainment and utilization of the crimped, stabilized, staple-length bicomponent-spun filaments. Techniques for the spinning of suitable bicomponent filaments are known, and patents exemplifying such have been referred to above. Battforming techniques and bonding procedures are also generally known but these will be further discussed below with reference to the specific requirements of the present invention.

Subsequent to the spinning of the continuous strands of bicomponent filaments they must be crimped, annealed, and cut to staple length. While this particular sequence is frequently the most facile, other sequences can also be used and may be of advantage depending upon such factors as the manner in which crimp is to be developed, the melting point or other differences between the two components, and the type of batt to be produced therefrom. In some cases two of the steps can be elfected in a single operation, for example crimping and annealing when the bicomponent filaments are of the latently crimpable variety.

It will be understood that when bicomponent filaments are to be employed having a latent capacity to crimp, various techniques can be used for developing the crimp depending opon the property differences between the individual components. Thus, as described in the abovementioned Breen and Taylor patents, melt-spun bicomponent filaments can be subjected to various conditions such as dry heat, steam, hot water, heated gases, various solvating chemical agents, and the like, in order to develop the latent crimp therein.

Where the bicomponent filaments require the application of a mechanical crimp, conventional devices of the prior art may be utilized, eg a stuffing box type of crimper which normaly produces a zigzag crimp, or apparatus employing a series of gears adapted to apply a gear crimp continuously to a running bundle of filaments.

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 zigzag in nature or it may have a threedimensional crimp, such as a helical crimp as exemplified by Kilian in US. 3,050,821. Other forms of threedimensional crimp are described by Breen in US. 3,038,236 and Taylor in U.S. 3,050,237. An especially useful form of crimp is the random, three-dimensional, curvilinear crimp described in Belgian Patent 573,230. Whatever the nature of the crimp, the bicomponent filaments should attain an average crimp frequency of at least 3 crimps per inch and an average crimp index of at least 5% A critical feature of the bicomponent filaments is that they be prepared to have little or no tendency to shrink or further crimp during a subsequent thermal bonding treatment. Thus they must be prepared to have a maximum retractive coefficient of less than 30', as measured by the procedure to be described hereinafter. Preferably the retractive coefiicient will be as close to zero as possible, i.e. up to 15 or so, to ensure only very modest densi-fication during the thermal bonding treatment. In effect, the retractive coefficient expresses a relationship between the length of the filamentary structures 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, whether of the bicomponent type or not, will usually 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 filament and to develop strength or other properties. The drawing treatments create internal stresses within the filaments and these tend to result in undesirably high 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 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 essentially the same lowdensity configuration as existed in the unbonded batt and filament intertwining or entanglements are kept at a minimum.

For purposes of annealing the bicomponent filaments, a temperature will normally be selected which is above the second order transition point of the filamentary component but below the polymer melt temperature of the lower-melting component. On the other hand, as will be apparent from the examples which follow, it is also possible to anneal the filaments somewhat above the polymer melt temperature of the lower-melting component. This may result in interfilament bonding to some extent but these bonds may usually be broken up by physically separating the filaments prior to annealing and then by carding after annealing. Although the annealing temperature selected will depend upon the composition of the two components, 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 temperature is sufficient for annealing the bicomponent filaments to remove the latent crimpability and shrinkage forces before further processing of the filaments. Individual filaments are, of course, under no externally applied tension during the annealing step.

Conventional techniques may be used for reducing the filaments to an ordinary staple-length, e.g. of about 1 inch to 6 inches. If a mechanical crimping method is to be used, it will precede the staple cutting step; otherwise it is entirely practicable for latent crimpability to be developed in fibers which have already been reduced to staple length.

In one highly convenient embodiment, a tow of continuous bicomponent filaments is first crimped, then annealed and finally the fibers cut to staple length before fabrication into a batt of the desired shape. Particularly when the filaments are crimped by the use of elevated temperatures, it is desirable for annealing to follow crimp development to achieve an appropriately low retractive coefiicient. In other cases, however, the order of these two steps may be reversed, as when for example crimp is developed by treatment with a chemical agent. Also when the filaments are of the type which spontaneously crimp at elevated temperatures, annealing may be simultaneously effected by making sure that the level and duration of the high temperature exposure is sufiicient to both crimp and stabilize the filaments.

Whenever the annealing temperature is high enough to soften the lower-melting component and thereby cause interfilament bonding, or the latent crimpability of the fiber is high enough to cause excessive entangling and interlocking of the filaments during annealing, an opening or deregistering step, prior to annealing, is preferred to facilitate redistributing of the filaments during formation of the nonwoven assembly. To accomplish this opening of fibers in staple form, a simple carding operation is preferred; to open fibers in tow form, a deregistration operation is preferred.

Once the filaments have been appropriately crimped, stabilized, and reduced to staple length, they may then be fabricated into a low-density assembly of predetermined dimensions and in which the filaments are arranged in the desired configuration, e.g. to be in random, onend, or on-side fiber alignment. An ordinary textile carding machine is highly suitable for this purpose because it serves to separate the filaments from one another to form a highly bulked structure which can then be directly bonded, Other well known batt-forming or laydown techniques can also be used. In any case a batt or other nonwoven assembly is produced in which the already crimped but latently-bondable filaments are in a highly loose or bulky array; that is, they contact and overlap one another but are not highly interlocked, i.e., are neither bonded nor are highly intertwined as would be the case if crimp were developed after formation of nonwoven assembly. 'Unbonded assemblies having a density of up to about 1 lb./ft. are readily obtainable, in fact those below about 0.6 lb./ft. frequently 0.3 lb./ft. are also readily obtainable.

As above-mentioned, ordinary, i.e. monocomponent, filaments may be blended with the bicomponent filaments in forming the unbonded assembly. The monocomponent filaments should have am aximum retractive coefiicient of 30, preferably 15, and a fiber stick temperature above the polymer melt temperature of the lower-melting component of the bicomponent filaments. In addition the monocomponent filaments should have an average crimp frequency of at least 3 crimps per inch and an average crimp index of at least 5%. Such ordinary filaments may comprise O to 95% by weight of the unbonded assembly.

The thusly assembled batt is then heated to a temperature above the melting point of the lower-melting component of the filaments, but below the fiber-stick temperature of the filamentary component. The lower-melting component thus softens or melts and, upon cooling, bonds are formed at fiber cross-over points throughout the three dimensions of the structure. If desired, heat need only be applied at spaced intervals, e.g. in a diamond-shaped grid pattern across the structure, to bond fibers only within particular areas-thus leaving major areas in which fibers or fiber portions are not bonded.

Characteristics of the nonwoven product and uses The product of the invention is suitable in Widely diverse applications. In this respect it is to be understood that the term nonwoven product is not intended to designate any particular geometrical shape or even any particular arrangement or size of the bicomponent-filaments therein, for these are aspects that can be appropriately selected depending upon the intended use of the product.

In one embodiment of the invention, the unbonded batt of bicomponent 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 described in Koller U.S. 3,085,922. Alternatively, an assembly of the bicomponent 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 structures may be formed into thin batts for use assuch or the webs may be stacked on top of each other to provide thick articles which are then subjected to a bonding temperature. The nonwoven structures may be formed such that the filamentary structures are arranged therein to have fiber-on-end alignment. Batts of randomly aligned filaments may be formed by processing on a Rando-Webber machine or other known air laydown machines, Le. a Duo-Form machine. Such nonwoven structures may, following thermal activation of the lowermelting component to provide a bonded structure, 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, knitted and tufted textiles for a variety of applications, but are particularly suitable for the manufacture 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.

Advantages summarized A most fundamental advantage of the invention is that bonded products can be obtained by mere application of heat to an unbonded batt of filaments with little or no change in shape.

Another advantage of the invention is that products can be obtained having a combination of outstanding properties. Thus they can have an exceedingly low density, and therefor they tend to be softer and have better drape properties than nonwoven textiles of the prior art. Indeed it is possible to achieve bonded products having a density of less than 1.5 pounds per cubic foot, in many cases as low as 0.2 pound per cubic foot and below.

Nonwoven, bonded products can be obtained having, by virtue of a relatively uniform distribution of bond points throughout the three dimensions of the nonwoven structure, a high degree of height retention and load support properties. In addition, the uniform bonding in the bonded nonwoven products provides excellent resistance to dimensional changes, resistance to clumping, resistance to fiber leakage, and resistance to matting after repeated washings or dry cleanings.

Test procedures 7 Retractive coefficient, RC, may be defined by the equation ture above the polymer melt temperature of the lowermelting component but below the fiber stick temperature of the structural fiber component. For purpose of the measurement, the temperature selected will usually be the minimum temperature required to sufliciently soften or melt the lower-melting component to form elfective 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 temperatures. (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.v

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 D138855T.

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 pounds 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 Ethylene glycol terephthalate polymer (abbreviation 2GT) and a copolymer formed of 79% ethylene glycol terephthalate and 21% ethylene glycol isophthalate (abbreviation 2GT/2GI) were melted separately and extruded at 292 C. through a sheath-core spinneret assembly of the type shown in FIGS. 1-5 of Breen US. 3,118,- 011. The extruded bicomponent filament was air quenched. The polyester melt was extruded through the inner tube of the spinneret and the copolyester through the outer space surrounding the tube, thus forming a sheath-core filament. The tube was located in the outer space in such a way as to produce a concentric position of the core in the sheath. After the bicomponent filaments were spun into a tow and cooled, the tow was drawn at C. to 2.8x its original length. The drawn denier per filament was 2.5. The filamentary component was 2GT having a fiber stick temperature of 230 C. whereas the lower-melting copolyester component had a polymer melt temperature of 208 C. The ratio of the two components was 50/50. A portion of the tow was treated on heated rolls at 110 C. for 9.6 seconds. Finish was added and the tow dried in a relaxed state at C. for 4 minutes in an air oven. The tow Was crimped in a stuffing box type of crimper, then cut to 2 inch lengths on a staple cutting machine.

The fibers produced had a crimp index of 13%, a crimp frequency of 10 crimps per inch, and a retractive coetficient (RC value) of 26.

A nonwoven batt was prepared from the carded fibers and then heated to 227 C. to melt the 2GT/2GI copolymer. Upon cooling, it was found that the batt had been thoroughly bonded throughout. It will be observed from the properties given in Table 1 that the bonded product so produced has undergone some compaction but the overall density was nevertheless remarkably low. Considerably greater densification would have occurred if the annealing step had been omitted.

TABLE 1 Annealing temp. C.) 110. Carding machine Sample card. Batt curing temp. C.) 227. Batt curing time (mins.) 5. Density (lbs./ft. carded 0.11. Density (lbs./ft. cured 0.35. Softness, ILD 25% (lbs.) 0.4. Drape, flex. rig. (mg-cm.) 1,522.

EXAMPLE II The procedure of Example I was repeated except that an additional annealing treatmentwas performed at a somewhat higher temperature. Thus immediately following the staple cutting step, the filaments were then annealed at 160 C. for 5 minutes in an oven. The unbonded fibers thereafter produced had a crimp index of 10%, a crimp frequency of 12 crimps per inch and an RC value of 8.

Conditions of the treatment and properties of the product are given in Table 2. It is apparent that the higher annealing temperature has made it possible to obtain a product of even lower density.

TABLE 2 Annealing temp. C.) and 160. Carding machine Garnett card. Batt curing temp. C.) 227.

Batt curing time (mins.) 15.

Density (lbs./ft. carded 0.08. Density (lbs./ft. cured 0.14. Softness, ILD 25% (lbs.) 0.4.

Drape, flex. reg. (mg-cm.) 575.

EXAMPLES III AND IV Fibers are spun and drawn according to Example I except that the draw temperature was 85 C., the drawn denier per filament 1.4, and the ratio of the two components was 70/ 30 2GT/ 2GT/ 2G1. Because of the small denier per filament, the orientation of the sheath around the core was found to be more nearly eccentric than concentric. The tow was treated in an air oven at 110 C. for 11.8 seconds. The tow was then cut to 2-inch lengths with hand shears. A portion of the filaments, Sample III, was further annealed at C. for ten minutes in a relaxed state. A second portion, Sample IV, was further annealed at 200 C. for ten min. in a relaxed state. Fiber crimp was developed during both annealing steps.

The fibers produced from Sample III had a crimp index of 14%, a crimp frequency of 18 crimps per inch,

I 1 and a retractive coefiicient (RC value) of 24. The fibers produced from Sample IV had a crimp index of 12%, a crimp frequency of crimps per inch, and a retractive coefficient of 4.

Nonwoven batts were prepared separately from Samples III and IV and the batts were heated to 218 C. to melt the 2GT/2GI copolymer. Upon cooling, it is found that the batts have been thoroughly bonded throughout. It will be observed from the properties given in Table 3 that both bonded products have exceptionally low densities although that of Sample IV is superior owning to the higher annealing temperature.

l Sample card.

EXAMPLE V Bicomponent nylon side-by-side filaments were meltspun using polyhexamethylene adipamide (abbreviated 66) as the filamentary component and a copolyamide (abbreviated 66/ 6) as the second component. The copolyamide was composed of hexamethylene adipamide and caproamide units in an 85/15 ratio. The two components were melted separately and extruded at 295 C. through a side-by-side spinneret assembly of the type shown in FIGS. 6 and 7 of Breen US. 3,118,011 to provide filaments containing 66 and 66/ 6. The extruded filaments were air quenched and, after cooling, were drawn to 3.28 times their original length at 9 6 C. The drawn denier per filament was 20. The structural fiber component, 66, had a fiber stick temperature of 235 C. and the lower melting component, 66/ 6, had a polymer melt temperature of 219 C.

The filaments were cut to 2-inch staple length with hand shears and then treated by immersing in boiling water for 20 seconds to develop latent crimp characteristics. The fibers were then centrifuged to remove excess water and air dried. The crimped fibers were then separated by forming into a batt by a conventional carding operation. Thereafter, they were annealed to remove residual crimp and shrinkage forces by heating in an air oven at a temperature of 215 C. for four minutes (below bonding temperature).

The retractive coefficient of the filamentary structures was 19, the average crimp frequency was 12, and the crimp index was 44%. The filamentary structures were carded on a sample card into a batt having a density of 0.59 lbs./ft. The carded assembly of fibers was then placed in an air oven which had been preheated to 220 C. After a temperature of 220 C. was again attained, the oven was opened, the assembly turned over, and the heating cycle repeated.

A bonded article was obtained upon cooling which had a density of 0.97 lbs./ft. and excellent drape and softness properties.

EXAMPLE VI This example illustrates a comparison between a product of the invention, Sample VI, versus a Control Sample in which crimp developed during the batt bonding step.

Bicomponent nylon side-by-side filaments were meltspun and drawn according to the first paragraph of Example V.

The filaments were cut to 2-inch staple length with hand shears and divided into two portions. A portion as the Control Sample received no further treatment except to be carded into a batt on a sample card.

A portion as Sample VI was treated by immersing in boiling water for 20 seconds to develop latent crimp characteristics. These fibers were then centrifuged to remove excess water and air dried. The crimped fibers were then separated by forming into a batt by a conventional carding operation. Thereafter, they were annealed to remove residual crimp and shrinkage forces by heating up to 220 C. (slightly above PMT temperature) in an air oven and then removing them. The fibrous batt was then recarded to break the bonds and separate the filaments.

The fibers of the Control Sample had a crimp index of 2%, a crimp frequency of 2 crimps per inch and a retractive coefficient of 59. The annealed fibers of Sample VI had a crimp index of 16%, a crimp frequency of 6 crimps per inch and a retractive coefficient of 12.

The Control Sample batt was immersed in boiling water for 20 seconds and then bonded in an air oven at 220 C. for a total of 8 minutes. The Sample VI batt was bonded in an air oven at the same conditions. Properties of the batts are summarized in Table 4.

It will be apparent from Table 4 that a product of entirely diflierent characteristics is obtained by utilization of the annealing step and by fully developing crimp in the fibers before a batt is formed of unbonded fibers.

TABLE 4 Sample Control VI Amlealing temp. C.) None 220 Batt density (lbs/itfi), carded 0. 6 0. 6 Batt density (lbs./ft. bonded- 4. 0 0. 9 Percent of carded bulk retained after bonding- 15 67 Softness, ILD 25% (lbs.) 112. 2 0. 6 Drape, fiexural rigidity (mg-cm.) 16, 560 73 EXAMPLE VII The procedure of Example IV is repeated except that the bicomponent fiber has an extrusion temperature of 285 C., a draw temperature of 95 C., a draw ratio of 4.0 a drawn denier per filament of 3.5, a ratio of 75/ 25 2G-T//2G-T/2GI (/20) 1 and crimp is applied with a stufiing box type of crimper. The bicomponent is annealed as shown in Table 5. A nonwoven batt is formed of a mixture of the bicomponent fibers with monocomponent 2G-T fibers of Z-inch (5.1 cm.) staple length and 4 denier per filament which are annealed as shown in Table 5. Blends containing 40%, 80% and of the monocomponent fibers are used and very soft, lightlybonded, low-density structures are obtained. Fiber and batt properties are shown in Table 5.

TABLE 5 Bicom- Monocomponent 1 ponent 2 Fiber properties:

Crimps per inch 14 12 Oriinps per centimeter 5. 5 4. 7 Crimp index (percent) 13 26 C 11 13 Batt density 40/60 blend 80/20 blend 95/5 blend Lbs Gm./ Lbs./ Gm./ Lbs./ Gm./ ft. cm. ftfi cm. ft. cmfi Carded 0. 21 0. 003 0. 21 0. 003 0. 21 0. 003 Bonded O. 24 0. 004 0. 33 0.005 0.30 0.005

1 Annealed at 200 C. for 10 min. Annealed at C. for 2 min., cooled to room temperature, then annealed again at 200 C. for 10 mm.

When this type of code is used herein ilt is to be un(lor stood that the number preceding the first pair of slashes represents the Weight percent of the first polymer, lthat is, the polymer preceding the second pair of slashes in the bicomponenzt fiber, and the number just following the first pair or slashes represents the weight percent of the second polymer (or copolymer, whichever the case may be), that is, the polymer following the second pair of slashes in the bicomponent fiber. The ratio in patrenltheses represents the weight percent of each monomeric llllilt in the copolymer, 0g. 80 weight pew cent polyethylene tereplrthnlate units and 20 weight percent polyethylene isophthalwte units.

EXAMPLES VIII-IX Bicomponent fibers are spun, drawn and crimped as in Example VII. The fibers are carded to separate the filaments and the resulting mass is then divided into three portions. Two of these portions are annealed at 180 and 220 C., respectively, by placing the portion in an air oven, heating to the appropriate temperature and then removing the sample from the oven. The third portion, Control Sample B, receives no annealing. Each fiber portion is then carded into a batt on a sample carding machine and then heat-bonded at 220 C. in an air oven. The properties of the fibers and batts are listed in Table 6. Densification of the control batt occurs on bonding while the batts of the present invention remain relatively open.

EXAMPLES XXI Bicomponent fibers are prepared as in Example VII except that the extrusion temperature is 291 C.; draw temperature is 90 C.; draw ratio is 3.9; drawn denier per filament is 4.3 and homopolymer (core)/polymer (sheath) ratio is 85/15. The fibers, in tow form, are divided into three portions. One portion is annealed at 180 C. The second portion is first annealed at 180 C., then opened by a suitable tow-opening machine to separate the filaments and the tow is then annealed at 220 C. for five minutes. The third portion, Control Sample C, receives no annealing. Each item is cut to 2-inch (5.1 cm.) staple with hand shears, carded into a batt on a sample carding machine and heat-bonded at 218 C. for five minutes in an air oven. The properties of the fibers and the batts produced from them are listed in Table 7.

Carded 0. 22 0. 004 Bonded 0. 0.

EXAMPLES XII-XIII The procedure of Examples XXI and Control Sample C (above) is followed except that extrusion temperature is 289" C., draw ratio is 4.0, drawn denier per filament is 4.0, homopolymer/copolymer ratio is 90/10, and the tow is opened and deregistered on a suitable tow opener. Fiber and batt properties are listed in Table 8.

EXAMPLE XIV Fibers are spun, drawn and cut to staple as in Example V. The fibers are then carded to separate the filaments, divided into two portions, annealed at the temperature listed in Table 10, recarded and bonded at 220 C. in an air o'ven. Properties of the fibers and batts are listed in Table 9.

TABLE 9 Example No XIV Control E Fiber annealing temp. 0.)..- 220 None Fiber properties:

Crimps per inch 9 2 Crimps per cm 3. 5 0. 8 Crimp index (percent) 13 12 R 21 64 Batt density Lbs/ft. Gin/cc. Lbs/it. GmJcc.

Carded 0. 6 0.010 0. 6 0. 010 Bonded 1. 5 0. 024 3. 5 O. 056

EXAMPLE XV The procedure of Example XIV is followed except that the two components are spun through a concentric sheathcore spinneret, extrusion temperature is 285 C., composition is 75% 66 nylon for the core and 25% 66/6 (/15) nylon copolymer for the sheath, draw ratio is 3.5, draw temperature is 75 C., drawn denier per filament is 3.5 and the filaments are crimped in a stuffing-box type of crimping machine and annealed at 180 C. Properties of the annealed fibers and the batts produced therefrom are shown in Table 10.

TABLE 10 Fiber properties:

Crimps per inch (per cm.) 12 (4.7) Crimp index (percent) 6 RC. 5

Batt density, l bs/ft. g./ cc.)

Carded 0.60 (0.010) Bonded 0.72 (0.012)

EXAMPLE XVI This example illustrates the preparation of a fiber-onend structure.

A blend is made of the following fibers:

Item 1: 27% of 4 denier per filament, 2-inch (5.1 cm.) polyethylene terephthalate produced according to Kilian US. Pat. 3,050,821 having helical crimp along its length and asymmetric birefringence across its diameter, annealed at 160 C. for 1 minute.

Item 2: 40% of 1 /2 denier per filament, 1.5-inch (3.8 cm.) polyethylene terephthalate having stuffer-box crimp, annealed at 145 C. for 1 minute.

Item 3: 33% of bicomponent fiber spun and drawn as in Example III except that the draw temperature is 85 C., the staple length is 1.5 inches (3.8 cm.) and the tow is treated in an air oven at C. for 11.8 seconds and then crimped in a stuffer-box type of crimping machine.

Fiber properties are listed in Table 11.

The fibrous blend is carded on a sample carding machine, annealed at 216 C. for 15 minutes, then recarded. The carded sliver is rolled into batts by hand and placed into a 9-inch x 9-inch x 2-inch (22.9 x 22.9 x 5.1 cm.) mold so that the fibers are aligned in the same general direction with the fiber ends directed toward the top and bottom of the mold. The density of the nonwoven at this point is 0.90 lbs/ft. (0.014 g./cm. The mold is then placed in an air oven and heated to 230 C. for 30 minutes. After this bonding step, the density is still 0.90 lbs/ft. (0.014 g./cm. indicating that no shrinkage of the nonwoven occurred during the bonding step. The bonded nonwoven is useful for preparation of wafers for lamination to backing fabrics.

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 this invention to produce coated substrates, laminates, bonded felts and the like.

'We claim:

1. Process for making a thermally self-bonded, low density, nonwoven, fibrous product comprising:

(a) spinning continuous strands of bicomponent filaments of substantially circular cross-section, said composite filaments comprising a filamentary core component of a fiber-forming, synthetic, organic polymer and integral therewith a continuous sheath concentric with the core of a lower-melting, synthetic thermoplastic polymer component, said lower-melting sheath component having a polymer melt temperature which is at least 70 C. but is below the fiber stick temperature of the filamentary core component;

(b) converting said continuous strands into staple length filaments having a retractive coeificient of no more than about 30, an average crimp frequency of at least 3 crimps per inch, and an average crimp index of at least 5%, said converting being effected by the steps, in any order, of cutting, mechanically crimping and annealing said strands;

(c) forming said staple-length filaments into a nonwoven assembly having a density of no more than about 1 lb./ft.

(d) heating said assembly to a temperature in excess of the melt temperature of said sheath component, but below the fiber stick temperature of said core component; and

(e) cooling said assembly to a temperature below the melt temperature of said sheath component to thereby produce a self-bonded low density, integral structure.

2. Process according to claim 1 wherein, in part (b) thereof, said converting is effected by mechanically crimping a continuous bundle of said continuous strands,

1 3 annealing the filaments of said bundle at a temperature above the second-order transition temperature of said filamentary core component, but below the fiber stick temperature of said sheath component, and cutting the resultant fibers to staple length.

3. Process according to claim 2 wherein, in part (0) thereof, the said assembly has a density below about 0.6 lb./ft.

4. Process according to claim 3 wherein, after part (b) thereof, said bicomponent filaments have a retractive coeificient of no more than about 15 and wherein the bonded product has a density less than 1 pound per cubic foot.

5. Process according to claim 4 wherein said filamentary core component and said lower-melting sheath component are both polyesters, and wherein said bonded product has a density of no bore than 0.5 lb./ cu. ft.

6. Process according to claim 5 wherein, prior to part (0) thereof, said bicomponent filmaments are blended with monocomponent polyester filaments having a retractive coefiicient of less than 15, and average crimp frequency of at least 3 crimps per inch, and an average crimp index of at least 5%, the weight of said bicomponent fibers being at least 5% of the total weight of the fibers in said blend.

7. Process of claim 6 wherein both said bicomponent filaments and said monocomponent filaments have a denier per filament of about 1 to about 15.

8. Process of claim 5 wherein said bicomponent fibers have a denier per filament of about 1 to about 15.

9. Process according to claim 1 wherein, prior to part (c) thereof, said bicomponent filaments are blended with monocomponent staple filaments having (1) a fiber stick temperature above said polymer melt temperature of the lower melting component of said bicomponent filaments, (2) a retractive coefficient of no more than about 30, (3) an average crimp frequency of at least 3 crimps per inch, and (4) an average crimp index of at least 5%, the weight of said bicomponent fibers being at least 5% of the total weight of the fibers in the blend.

10. Process of claim 9 wherein both said bicomponent filaments and said monocomponent filaments have a denier per filament of about 1 to about 15.

11. Process of claim 1 wherein said bicomponent fibers have a denier per filament of about 1 to about 15.

References Cited UNITED STATES PATENTS 2,774,129 12/1956 Secrist 161157X 2,994,617 8/1961 Proctor 161159X 3,017,686 1/1962 Breenet al. 16l--173X 3,117,055 1/1964 Guandique et a1 161170 3,449,486 6/1969 Contractor et a1. 161-170X 2,880,057 3/1959 Cuculo 161--l72X FOREIGN PATENTS 643,420 8/1964 Belgium 161l50 1,073,181 6/1967 Great Britain 161150 ROBERT F. BURNETT, Primary Examiner R. L. MAY, Assistant Examiner US. Cl. X.R.

2 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No .W34589 E256 Dated June 291L 19Yl lliam Lester Stump It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Inventofls) Claim 5, last line, "bore" should be more and "0.5 lb./cu. ft." should be 0.55 lb./cu. ft.

Claim 6, line 2, "filaments" was improperly printed.

Signed and sealed this 5th day of December 1972.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents

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