BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a nonwoven web comprising arched filaments aligned within 45 degrees of a minimum tensile modulus direction axis. The present invention is useful in mechanical fastening, filtering applications, and for nonwovens utilizing bias stretch. The invention further relates to methods for making such a web.

2. Description of the Prior Art Fabrics have been used in mechanical fastening applications, typically referred to as"hook and loop"systems. Such fabrics include those sold under the trademark Velcro. In a hook and loop fastening system, one fabric comprising hooks is mechanically fastened to another fabric comprising loops via the insertion of the hooks into the loops. Prior art loops comprise a stem which projects up from the surface of the fabric and a circular loop attached to the stem. The shape of such stem and loop combinations is similar to the shape of a magnifying glass with a cylindrical handle. Such prior art hook and loop systems are expensive to produce. The gripping power of such systems is limited by the size of the loop openings.

Air filtrations systems contain a filtering media which must be sufficiently porous to allow air to pass through the filtering media while trapping undesirable particulate matter. Such filters are commonly made out of a fiberglass fabric. Such filters have limited utility and low pressure drop applications. Another drawback of conventional filtering media is that once the filter fabric becomes loaded it will cease to efficiently trap particulate matter.

SUMMARY OF THE INVENTION The apparatus of the present invention is directed towards a nonwoven web or web plane comprising a machine direction axis and an axis 0 defining a minimum initial tensile modulus direction, hereinafter referred to as the "minimum tensile modulus axis". The initial tensile modulus is defined by the slope of the stress strain curve for the nonwoven web, at that region of the curve where the web material has elastic properties. It is known to those of ordinary skill in the art, that as stress increases, the slope of the stress strain curve eventually increases, beyond that slope which defines the initial tensile modulus. The machine direction axis is defined by the direction of travel of the web plane as a machine produces it.

The invention further comprises at least one arched filament projecting out of the web plane. Each of the arched filaments comprises two base

regions attached to the web plane, a leg region attached to each of the base regions and projecting out of the web plane, and an arched central region connected to each of the leg regions. The majority of the arched filaments are positioned such that their base regions define an axis within 45 degrees of the tensile modulus direction axis 0. The phrase"within 45 degrees,"as used herein, means plus and minus 45 degrees.

In a case where the web plane comprises only one or two arched filaments, all of the arched filaments in the web plane have base regions defining an axis within 45 degrees of the minimum tensile modulus axis. The present invention is well suited to a variety of garment fastener applications, including but not limited to, diapers, pajamas, infant garments, and hospital gowns, and bulletin board.

The present invention is also directed toward methods for producing arched filaments in a nonwoven web. A method of the present invention comprises gripping a nonwoven web plane having a machine direction axis and a cross direction axis with a tensioning device, applying a tensile force and/or shear force to a nonwoven web plane which comprises a multiplicity of filaments, and heat setting. The shear force is applied along the machine direction axis in the vicinity of the web edges. The magnitude of the force will depend, in part, on the filament size and composition.

DESCRIPTION OF DRAWINGS Figure 1 is an isometric view of the web plane of the present invention.

Figure 2 is an enlarged top view of the web plane of the present invention.

Figure 3A is an enlarged top view of the web plane of the present invention resulting from shear forces.

Figure 3B is a top view of a preferred embodiment of the method of the present invention.

Figure 4 is a top view of a preferred embodiment of the method of the present invention.

Figure 5A is a block diagram of a preferred embodiment of the method the of the present invention.

Figure 5B is a block diagram of a preferred embodiment of the method of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in Figure 1, the present invention is directed towards a nonwoven web comprising a nonwoven web plane 10 having a machine direction axis 11, a cross direction axis 13 and a minimum tensile modulus axis 9. In a preferred embodiment, the minimum tensile modulus axis is tocated between 10 to 80 degrees from the cross direction axis.

The invention further comprises at least one arched filament 12, each of said filaments comprising two base regions 14 attached to the web plane, and a leg region 16 attached to each of said base regions, and projecting out of said web plane. The filaments further comprise an arched central region 18 connected to each of said leg regions wherein the majority of said arched filaments are positioned such that their base region define an axis within 45 degrees of the minimum tensile modulus axis 9.

A top view of the present invention is shown in Figure 2. The angle 0, measured relative to the minimum tensile modulus axis depicted in Figure 2, is the angle within which a majority of the base ends of said filaments define an axis. In another preferred embodiment, at least two-thirds of the arched filaments are positioned such that their base ends define an axis within 30 degrees of the minimum tensile modulus direction.

In a preferred embodiment, the web plane is formed from a thermoplastic precursor web. In another preferred embodiment, the thermoplastic precursor web is bonded. In other preferred embodiments, the thermoplastic precursor web is spunbonded or thermally bonded.

In a preferred embodiment, the nonwoven web further comprises a substrate 15 attached to the nonwoven web plane, as shown in Figure 1. In a preferred embodiment, the substrate comprises meltblown polymer. In a

preferred embodiment, the meltblown polymer is polypropylene, polyurethane, polyethylene, or polyester, or a copolymer of the above. In a preferred embodiment, the substrate is adhesively laminated to the web plane.

The web plane of the present invention may be made from a variety of different fibers having different filament diameters. The filament number density of the web plane is, in part, a function of the filament size. In a preferred embodiment of the present invention comprising a thermoplastic web, the web plane comprises an average arched filaments density of at least 20 arched filaments per square centimeter. Such a filament density can be achieved by practicing the method of the present invention on a nonwoven web comprising a filament density of at least 40 filaments per square centimeter.

The present invention is particularly suitable as a mechanical fastener to be used in conjunction with an article comprising hooks which are releaseably insertable into the arched filaments of the present invention. The arches of the present invention have a greater surface area than conventional "loop"fasteners having a radius which is equal to the radius of curvature of the arched filaments of the present invention. This increased surface area increases the probability that a hook from a mating strip of fastener material will engage each loop. This produces a mechanical fastener having superior

peel strength to prior art mechanical fasteners using a hook and loop type arrangement. In a preferred embodiment, the nonwoven web of the present invention has a minimum peel strength of at least 23 grams of force per centimeter wide strip of web. In a preferred embodiment, the web plane may be cut into strips which may be attached onto garments through the use of an adhesive.

The present invention is also directed toward methods for producing arched filaments in a nonwoven web, as illustrated in Figures 3B, 4,5A and 5B. The first method here of the present invention comprises heating a nonwoven web sufficiently to permit plastic deformation of its filaments in response to an applied tensile stress ; gripping a nonwoven web plane having a machine direction axis and a cross direction axis ; and applying tensile force, F, in the direction of the machine direction axis 11 or cross direction axis 13 as shown in Figure 3B and Figure 5A, blocks 60-64.

In a preferred embodiment, the heating and applying of tensile force are performed simultaneously. These steps may also be performed sequentially.

In a preferred embodiment, the force is applied by a stretching machine 22, comprising a gripping member 24 which grips the web and stretches it in the direction of the cross direction axis. The force is of sufficient magnitude

to cause an arching of one or more filaments out of the web plane as shown in block 64 of Figure 5A.

! n a preferred embodiment of the first method of the present invention, the tensile force is applied in the cross direction and it is of sufficient magnitude to produce a cross direction elongation of at least 15%, and a respective machine direction contraction of sufficient magnitude to cause-an arching of one or more filaments out of the web plane, as shown in block 64 of Figure 5A.

In a preferred embodiment, two machines located on opposite machine direction edges of the web plane are attached to the web by a gripping member such that these machines can apply a tensile force in opposite directions along the cross direction axis, as shown in Figure 3B.

In another preferred embodiment of the first method of the present invention, the tensile force is applied in the machine direction and it is of sufficient magnitude to produce a machine direction elongation of at least 15 percent, and a respective cross direction contraction of sufficient magnitude to cause an arching of one or more filaments out of the web plane, as shown in Figure 3A and in block 74 of Figure 5B.

In a preferred embodiment, a machine located on a cross direction edge of the web plane, opposite a roll of web plane, is attached to the web by

a gripping member such that the machine can apply a tensile force along the machine direction axis, as shown in Figure 3A.

A third method of the present invention is depicted in Figure 4. The first step of the third method is gripping a rectangular web plane comprising a multiplicity of filaments and at least two opposite machine direction edges and two opposite cross direction edges. The gripping occurs at a region in the vicinity of the machine direction edges. In a preferred embodiment, the third method of the present invention further comprises installing a cross direction or machine direction extension of at least 10 percent to the web. In another preferred embodiment, the nonwoven web is initially machine drawn. The phrase"opposite machine direction edges", as used herein, means two edges that define the cross direction width edges of the web plane.

The third method further comprises applying directed forces, F, in the vicinity of each gripped edge such that said web plane is subjected to a shearing stress of sufficient magnitude to install a shear deformations of at least 12 degrees and cause an arching of one or more filaments out of said web plane. This step is depicted in Figure 4. This method can be used to produce arched filaments in a web plane wherein the majority of arched filaments are positioned such that their base regions define an axis within 45

degrees of the direction of the minimum initial tensile modulus direction of the instant web product.

The foregoing disclosure and description of the invention are illustrative and explanatory thereof, and various changes in the size, shape and materials, as well as in the details of the illustrated construction, may be made without departing from the spirit of the invention.