US3526526A - Nonwoven fabrics of improved opacity - Google Patents

Description

Sept 1, 1970 N. s. NEWMAN 3,526,526

NONWOVEN FABRICS OF IMPROVED OPACITY Filed Oct. 20, 1967 3,526,526 NONWOVEN FABRICS F IMPROVED OPACITY Nicholas S. Newman, West Newton, Mass, assignor to The Kendall Company, Boston, Mass., a corporation of Massachusetts Filed Oct. 20, 1967, Ser. No. 676,955 Int. Cl. 1344c 1/08 US. Cl. 117-25 13 Claims ABSTRACT OF THE DISCLOSURE The opacity and light-scattering power of nonwoven fabrics is increased by adhesively bonding to the fabric surface between 200* and 1,000 aggregates of ultra-short fibers per square inch. The ultra-short fibers are between 40 and 200 microns in length, and the aggregates are randomly distributed on a planar fabric, or concentrated at the raised surface portions of a non-planar fabric.

This invention relates to the preparation of bonded nonwoven fabrics of enhanced surface appeal. More particularly it relates to the preparation of a bonded web of unspun and unwoven textile-length fibers, at least one surface of which is characterized by having adherent thereto a multiplicity of irregularly spaced aggregates of ultra-short, non textile-length fibers.

Bonded nonwoven fabrics, comprising dry-assembled textile-length unspun and unwoven fibers bonded by polymeric binding materials, are produced 'by a variety of well-known processes and are a staple article of commerce. In additional numerous industrial applications, they are finding increasing use in such fields as disposable or limited use garments, sheets, pillowcases, draperies, and the like. Conventional nonwoven fabrics, however, are substantially planar and uniform, devoid of the surface interest associated with woven fabrics which have yarn interlacings which interrupt the surface in a regular or irregular manner.

Additionally, nonwoven fabrics of a weight range which may economically be used as disposable items are translucent, even highly so, and lack the concealing power which is generally desired.

Attempts have been made to overcome this lack of surface interest by printing a pattern or design on the surface of nonwoven fabrics, or by embossing the surface by means of patterned pressure rolls. Such expedients are expensive, and are generally ineffective in increasing the opacity of a nonwoven fabric. It has also been proposed to flock the surface of nonwoven fabrics, by the mechanical or electrostatic deposition of fibers out to 1 to 8 millimeters (LOGO-3,000 microns) in length onto a nonwoven fabric which has been provided with an adhesive coating. In conventional flocking, individual cut fibers are oriented substantially perpendicularly to the plane of a nonwoven fabric. Such a procedure does increase the opacity of nonwoven fabrics, but the surface texture developed is that characteristic of a suede 0r velvet, and not like a conventional woven fabric. Moreover, precision-cut flock is generally more expensive than the textile filaments from which it is derived.

It has now been found that a pronounced delustering and opacifying finish can be added to nonwoven fabrics if ultra-short fibers, of from 40 to 200 microns in length, are deposited on an adhesive-coated nonwoven fabric in the form of numerous and irregularly distributed fibrous aggregates, said aggregates having an average diameter of 4 to 10 times the average individual fiber length and preferably numbering 200 to 1,000 aggregates per square inch of fabric surface. Such a finish not only decreases the transmission of light through the fabric, but it greatly United States Patent 0 increases the random scattering of incident light. Since the ultra-short fibers are low in cost compared to cut flock, their use in the process of this invention provides an economical enhancement of nonwoven fabrics which renders them more suitable for disposable items where the simulation of a woven fabric is desired.

It is therefore an object of this invention to provide a low cost nonwoven fabric which simulates the surface reflectance properties of woven fabrics. It is also an object of this invention to provide a finish for a nonwoven fabric which increases its opacity and masking power without decreasing its porosity, drape, and flexibility. Other objects of the invention will be apparent from the following description and drawings, in which:

FIG. 1 represents a plan view of the surface of a typical nonwoven fabric of this invention, highly magnified.

FIG. 2 is a similar view of another embodiment of the invention.

FIG. 3 is a schematic representation of an apparatus suitable for carrying out the process of this invention.

In FIG. 1, a conventional nonwoven fabric 10 is shown as being surface-textured by aggregates of ultrashort fibers 12, said aggregates being irregularly distributed over the surface of the fabric. In the process of the invention there is a certain amount of individual fiber fall-out 14, where non-aggregated fibers are adhesively bonded to the fabric surface, but it is desirable that a substantial proportion (50% or more) of the ultra-short fibers be agglomerated in the form of aggregates distributed randomly over the surface of the product.

As base material a wide variety of nonwoven fabrics may be used, bonded by a variety of processes well known in the art.

In general, in the field of disposable articles where cost is a primary consideration, the nonwoven fabrics will weight from 15 to 40 grams per square yard, will be composed of cotton or rayon, and will be bonded by saturation with a polymeric latex binder which imparts tensile strength and toughness adequate for the desired end use. The nonwoven fabric may, if desired, be reinforced with a scrim or open-meshed woven fabric. The selection of such fibers and binders is well known to those skilled in the art, and forms no part of the present invention.

It is also possible to utilize as starting material a very lightly bonded or even an unbonded web, as disclosed in my copending application Ser. No. 444,536, filed Apr. 1, 1965. In such cases, the tensile strength of the fibrous base may not be sufficient to withstand the saturation step disclosed in FIG. 3, and recourse is had to spraying the web with binder, or saturating it while it is supported between two screens, as is understood in the art.

As ultra-short fibers it has been found that a length of between 40 and 200 microns, in the case of cellulosic fibers, is a desirable range for the promotion of fibrous aggregates. Regular commercial flock, of LOGO-8,000 microns in length, does not form coherent aggregates, but tends to be dposited in the form of individual fibers oriented perpendicularly to the fabric surface. This is true whether the flock-deposition process is mechanical or electrostatic, or a combination of both. The result is a smooth and uniform pile-like surface, as set forth above. The clumping which gives the characteristic frosted and irregularly-reflective surface appearance desired in the products of this invention appears to be related to fiber length, for reasons which are not entirely understood. It may be that as the length of a fibrous particle begins to approach its diameter, the less effectively are the particles oriented perpendicularly to the nonwoven fabric surface, particularly in the case of electrostatic flocking.

For reasons of economy, it is preferred to use ultra- 3 short cellulosic fibers, such as ground (and preferably bleached) wood pulp or ground cotton. Other ultra-short fibers may be used provided that they tend to agglomerate in a flocking operation rather than disperse into a uni form, pile-like distribution.

The application of such ultra-short fibered aggregates to a nonwoven fabric may be effected conveniently by a flocking range of conventional design, shown schematically in FIG. 3. A supply roll 20 of nonwoven fabric is provided with a polymeric latex coating, either by a saturation and squeeze as shown at 22, or by spraying, or by knife or roller coating or similar means. The ultrashort fibered aggregates are applied at stage 24, where the aggregates are deposited on the adhesively-coated nonwoven fabric from a screen 26. Beater bars 28 assist in the distribution and anchorage of the aggregates, and the process may optionally be coupled with the driving power of electrostatic forces as is well known in the art. A vacuum source 30 removes a considerable part of the excess unanchored ultra-short fibered aggregates, after which the assembly is dried at stage 32. This may be carried out by a heated oven, steam cans, infrared lamps, and the like. A brushing stage 34, to remove final traces of unanchored aggregates, is followed by a windup 36.

Particularly interesting results are obtained when the nonwoven fabric base contains a layer of scrim or is otherwise reinforced with yarns or pseudo-yarns, or is embossed or locally deformed to cause a patterned protrusion on the nonwoven fabric surface. Such a structure is shown in FIG. 2, where a base nonwoven fabric 11 has been reinforced, during its manufacture, with an openmeshed scrim comprising warp yarns 16 and filling yarns 18. There is a minor amount of individual ultra-short fibrous coverage 14, but the preponderance of the fibers are in the form of aggregates 12 which are concentrated chiefly along the yarn-like pattern which protrudes from the surface of the fabric. The reason for a disproportionate number of aggregates being found distributed in a scrim-like pattern may lie in the fact that those areas immediately overlying the yarns have a higher capillarity, and higher adhesive concentration, than the balance of the nonwoven fabric. Or the reason may be a purely physical one, since it is known that especially when electrostatic forces are used, a charged particle tends to travel the shortest path and to direct its course to the highest points on the oppositelycharged surface to which it is attracted.

The process of this invention offers an economical and expedient method for increasing the opacity of nonwoven fabrics, for increasing the light-scattering characteristics of the surface of the fabric, and for increasing the weight and absorbency of the fabric without the sacrifice in softness and flexibility associated with processes which increase the weight by adding more textile-length fibers. It will be illustrated by the following example.

EXAMPLE I A bonded nonwoven fabric of 74% rayon, 13% nylon, and 13% acetate fibers, all of textile length, was prepared by carding a blend of said fibers into a fleece weighing 26 grams per square yard. This fleece was saturated with an acrylic binder in latex form to add 21 grams of dry binder to each square yard of material after drying.

Using the process illustrated in FIG. 3, this bonded fabric was saturated with an adhesive acrylic latex polymer, and ultra-short cellulosic fibers were deposited thereon in a mechanical flocking operation using beater bars and without the aid of electrostatic forces. The ultra-short fibers were Solka-Floc BW-200, a trademarked fiber of the Brown Paper Company. After drying and brushing the product weighed 65 grams per square yard and had bound thereto 15% of ultra-short fibers, principally in the form of fibrous aggregates distributed randomly over the surface, which resembled FIG. 1. The product reflected light in an irregularly scattered fashion appearing opaque and delustred in comparison with the base fabric. The machine direction tensile strength had increased over the base fabric by 27%; the cross-directional strength by and the cross-directional tear resistance by 58%.

An embodiment of this invention in which the process is carried out on an unbonded web or fleece is illustrated by Example II.

EXAMPLE II An unbonded assembly was prepared consisting of two carded webs, each 7 grams per square yard, of 1.5 denier 1%, inch rayon fibers, separated by a layer of 8 x 8 scrim weighing 10 grams per square yard.

Using a double-screen saturating process, this assembly was saturated with about 250% of a 25% solution of an adhesive acrylic polymer, and the same ultra-short cellulosic fibers as in Example I were deposited in a mechanical flocking operation using beater bars and without the aid of electrostatic forces. After drying and brushing the product weighed 55 grams per square yard and contained 30% flock adherent to its surface principally in the form of fibrous aggregates as illustrated in FIG. 2, with a preponderance of the aggregates distributed along lines defined by the yarns in the layer of scrim. The product had a pleasingly irregular or frosted surface appearance.

A similar nonwoven fabric base was prepared using the same type of scrim, but increasing the weight of the rayon webs so that the final bonded fabric weighed the same as the fabric above, 55 grams, but without the addition of ultra-short fibrous aggregates. The surface appearance of this plain fabric was planar, lacking in interest, and without the diffusing effect on incident light displayed by the fabric of Example I.

The flexibility of the two fabrics was measured by the cantilever principle based on the Fabrics Research Laboratory Tester (Federal Specification CCC-T-191b). In this test, rigidity is expressed in centimeters, lower readings indicating greater softness or drape.

Rigidity in centimeters Machine direction Cross direction Example I 2. 4 3. 6 Plain fabric 8. 3 4. 4

fabric of equal weight.

Having thus described by invention, I claim:

1. The process for enhancing the surface of a nonwoven fibrous assembly which comprises applying a coating of adhesive to at least one surface of the assembly,

applying to the coated surface in random distribution a plurality of aggregates of ultra-short fibers,

said ultra-short fibers being between 40 and 200 microns in length,

the average diameter of the fibrous aggregates being between 4 and 10 times the average fiber length, and drying said fibrous assembly.

2. The process according to claim 1 in which the fibrous assembly is a bonded nonwoven fabric.

3. The process according to claim 1 wherein between 200 and 1,000 fibrous aggregates are applied to each square inch of surface of the assembly.

4. The process according to claim 1 in which the ultrashort fibers are cellulosic.

5. The process for enhancing the surface of a yarnreinforced nonwoven fibrous assembly which comprises applying a coating of adhesive to at least one face of a fibrous assembly which comprises yarns which 6 cause a protruding pattern on the face of the as- 11. A nonwoven fabric of enhanced opacity, flexibility, sembly, and surface texture which comprises applying to the coated surface a plurality of aggregates a base layer of nonwoven fabric with a protruding pat of ultra-short fibers, tern on at least one face of said fabric,

said ultra-short fibers being between 40 and 200 microns 5 to which face is adhesively united a plurality of agin length, gregates of ultra-short fibers,

the average diameter of the fibrous aggregates being said aggregates being predominately concentrated on betWeen 4 and 10 times the average fiber g and in the immediate vicinity of said protruding and drying said fibrous assembly, pattern,

whereby a preponderan e of Said fi r ll aggr gates 10 the fibers comprising said aggregates being between 40 are caused to adhere to the fibrous assembly on and d 200 microns in length, in the immediate Vicinity of the protruding Pattern the average diameter of the fibrous aggregates being caused by the yarns. between 4 and 10 times the average fiber length.

The Process according to Claim 5 wherein between 12. The product according to claim 11 wherein there 200 and 1,000 fibrous aggregates are pp 10 each 15 are between 200 and 1,000 fibrous aggregates per square square inch of surface of the fibrous assembly. i h f nonwoven fabri surface,

The PrOeeSS according to Claim 5 in which the ultra- 13. The product according to claim 11 wherein the short fibers are cellul si ultra-short fibers are cellulosic.

8. A nonwoven fabric of enhanced opacity, flexibility, and surface texture which comprises References Cited a base layer of nonwoven fabric,

TES PAT NTS to at least one face of which is adhesively united a UNITED STA E 3 X plurality of aggregates of ultra-short fibers, 3,356,521 12/1967 e g 117 3 said aggregates being distributed over said surface, 3,434,858 3/1969 Dlckmson 117 33 X the fibers comprising said aggregates being between 40 3,459,579 8/1969 Newman 117-33 and 200 microns in length, the average diameter of the fibrous aggregates being WILLIAM MARTIN Pnmary Exammer between 4 and 10 times the average fiber length. P. ATTAGUILE, Assistant Examiner 9. The product according to claim 8 wherein there are between 200 and 1,000 fibrous aggregates per square inch US. Cl. X.R. of nonwoven fabric surface. 117-33; 161-64 10. The product according to claim 8 in which the ultra-short fibers are cellulosic.

Images