METHOD FOR PRODUCING A THERMALLY SELF- BONDED LOW DENSITY NONWOVEN PRODUCT

3,449,486

METHOD FOR PRODUCING A THERMALLY SELFBONDED LOW DENSITY NONWOVEN PRODUCT

Rastamikant Maganlal Contractor and Robert Evans Kern, Wilmington, Del., assignors to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware

Continuation-in-part of application Ser. No. 554,550, June 1, 1966, which is a continuation-in-part of application Ser. No. 410,766, Nov. 12, 1964. This application May 31, 1967, Ser. No. 649,778 Int. CI. D04h 3/16, 1/58; B32b U.S. CI. 264—115 5 Claims

ABSTRACT OF THE DISCLOSURE

A bonded, low density, nonwoven fibrous product is made by preparing an assembly of binder-coated, crimped, annealed, staple-length, synthetic fibers, mechanically working (e.g. carding) the assembly to break fiber-to-fiber bonds and to uniformly distribute the binder, then heating to fuse the binder at fiber cross-over points.

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CROSS-REFERENCES TO RELATED
APPLICATIONS

This application is a continuation-in-part of our application Ser. No. 554,550, filed June 1, 1966, which is in turn a continuation-in-part of our application Ser. No. 410,766, filed Nov. 12, 1964, both now abandoned.

BACKGROUND OF THE INVENTION

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Field of the invention

This invention relates 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.

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 of 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. Even when a thin article such as a web is to be produced, a substantially greater buildup 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. 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 of crimped, staple-length filaments which have been so prepared that once formed into a 5 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-affixed to the filaments. Moreover, the 10 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 15 by fusion bonds, yet the filaments have been prestabilized so that the assembly will undergo little or no densification during the bonding step.

In one embodiment of the invention there is provided an unbonded assembly, having a density of up to about 20 1 lb./ft.3, of individually distinct, staple-length filaments, said filaments comprising an oriented filamentary component of a fiber-forming, synthetic, organic polymer and integral therewith as a coating along at least a portion of the exterior thereof an unoriented, lower-melting, synthetic thermoplastic polymer component, 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, the weight ratio of said filamentary component to said lower-melting component being essentially constant throughout the three dimensions of the assembly, said filaments having an average length of at least one inch, being characterized by a retractive coefficient of no more than about 30 and being crimped so as to provide an average crimp frequency of at least 3 crimps per inch and an average crimp index of at least 5%.

In effect the fibrous assembly as above-described is ready for bonding; that is, (a) the heat-activatible binder 40 or so-called "lower-melting" component has already been applied, (b) the filaments have been crimped to provide bulk and/or other properties, (c) the filaments have been stabilized (hence have a low "retractive coefficient" as hereinafter defined) to minimize latent shrinkage or crimp45 ability forces that might tend to excessively densify the product upon bonding, and (d) 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.3, usually as low as 0.6 lb./ft.3 or even 0.1 lb./ft.3. Various methods for producing the unbonded fibrous assembly and bonded nonwoven products therefrom will be discussed below.

BRIEF DESCRIPTION OF THE DRAWINGS

55 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 pro

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

FIGURE 3A is an enlarged representation of the en05 circled portion of FIGURE 3 and shows that the indi

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