ANISOTROPIC EXTENSIBLE NONWOVENS

Abstract

This invention relates to nonwoven fabrics in which the fibers of the fabric are laid down such that a majority of the fibers have a fiber direction making an angle substantially parallel to or within an angle in a range of +/−45° of the machine direction. The invention also relates to a nonwoven fabric bonded web having bonding points in a pattern arranged along an axis perpendicular to the machine direction spaced and more widely apart than the bonding points arranged along an axis parallel to the machine direction. The resulting nonwoven having a very low elongation in the machine direction can be elongated with relatively little force in the cross machine direction.

Description

BRIEF DESCRIPTIONS OF THE DRAWINGS

FIG. 1A is a representation of a portion of a stretch nonwoven 10 having a plurality of bonding points 20.

FIG. 1B is a representation of a portion of a stretch nonwoven 100 having a fibers 200 aligned within an angle +/−a of the machine direction MD.

FIG. 2A is flow diagram of one process for providing a stretch nonwoven according to the invention.

FIG. 2B is flow diagram of another process for providing a stretch nonwoven according to the invention.

DETAILED DESCRIPTION

According to this invention, a fully elastic nonwoven with a cloth like hand is provided by surrounding a primary spunbond elastomeric nonwoven (such as that based on EXXON VISTAMAXX® elastomeric polypropylene) by light weight layers of spun bond or melt blown hard fibers such as polypropylene, polyethylene, polyester, or polypropylene—polyethylene blends by spunbonded, meltblown and hybrid combination of the two processes. In this process, deposition of a layer of hard fiber on either side of the spunbond elastomer that is thin enough and lightly bonded enough to not hinder stretch and recovery of the center elastomeric layer. The elastic nonwoven is enhanced by using a high quality melt spun elastomer as the primary elastic layer.

According to an aspect of the invention provided are nonwoven fabrics in which the fibers of the fabric are intentionally laid down with an orientation primarily in a machine direction. The resulting nonwoven has high tensile strength and very low elongation in the machine direction, but relatively low tensile strength and can be elongated with relatively little force in the cross direction. In a process for making this nonwoven, the required fiber orientation property is obtained without a separate step “consolidation” or “necking.”

Nonwovens with substantially different properties in the cross direction versus the machine direction means that the resulting nonwoven, hereinafter an “extensible nonwoven”, is rigid with high break tenacity in the machine direction. At the same time the extensible nonwoven is easily extended in the cross direction without rupturing by application of a relatively low force. A relatively low force is an applied force of less than 1 Newton at 50% elongation.

Normally, care is taken in the production of nonwovens to randomize the direction of the fiber lay down to produce a sheet structure with similar physical properties (modulus, percent elongation and break tenacity) in all directions. However, extensible nonwovens have been shown to be useful in producing a variety of materials that utilize nonwoven sheets with cross direction.

Extensible nonwovens with cross direction stretch of 200% are well known, but are produced by a post nonwoven formation conversion process. Patent disclosures relating to this technology are assigned to TANDEC (University of Tennessee Nonwovens Research Consortium), Kimberly Clark, and BBA. According to the disclosure of U.S. Reissue Pat. No. 35,206, processes commonly known as “necking” or “consolidation” start with a nonwoven, especially spun-bond and carded thermo-bond nonwovens, which is then drawn in the machine direction to substantially align the fibers of the nonwoven in the machine direction to produce the desired properties. In addition, spun-laced (hydro-entangled) nonwovens produced by a variety of producers, including E. I. DuPont, Sheng Hung, and BBA have properties that are similar to the desired “extensible” nonwoven due, but with elongation's generally less than 100%. In this invention, an extensible nonwoven is produced directly during the nonwoven formation process without the need for post formation processing and represented by the flow charts of FIGS. 2A and 2B.

In the case of a nonwoven based on a fibrous web (in FIG. 1A), The extensible character of the nonwoven is enhanced by selecting a bonding pattern with a relative low number of bond points 20 (in FIG. 1A) and/or one in which the bond points are arranged such that bond points 20 along an axis perpendicular to the machine direction are widely spaced, e.g. having spacing A in FIG. 1A, while those on an axis parallel to the machine direction are relatively closely spaced, e.g. having a spacing B in FIG. 1A. In general, bonding point spacing satisfies the relationship A>B. More particularly, the bond point spacing is selected in order that A=1.1(B) at least, and more generally A>2(B). In the case of a spun-bond nonwoven, the bonding point pattern is accomplished by appropriate adjustment of the randomizing air jets at the fiber lay down point to produce the same fiber lay down as described above for carded thermo-bond nonwovens and also using the bonding patterns described above.

In the case of a nonwoven based on a carded web (in FIG. 1B), aligning the carded bats forming the nonwoven in such a manner that the fiber direction is either substantially parallel to or within an angle +/−a, where a is 45° of the machine direction. The coherent character of the nonwoven so-formed is enhanced by bonding using known bonding means.

Test Methods

Elongation at Break based on ASTM D 5035-90.

Claims

1. An extensible nonwoven having substantially different physical properties in the machine direction versus the cross direction, characterized in that said nonwoven has a cross direction elongation of at least about 50 percent.

2. The extensible nonwoven of claim 1 having a cross direction elongation of about 100 to about 200 percent.

3. The extensible nonwoven of claim 1 selected from the group comprising: spunbonded, melt blown, carded thermally bonded, and spunlaced structures.

4. A process for making an extensible nonwoven comprising the steps of: laying down a fibrous web and bonding the web by selecting a bonding pattern comprising a plurality of bonding points and wherein, the bonding points arranged along an axis perpendicular to the machine direction are spaced more widely apart than the bond points arranged along an axis parallel to the machine direction and wherein the bonding points are provided by thermal energy.

5. A process for making an extensible nonwoven comprising the steps of: aligning carded bats of fibers such that a majority of the fibers have a fiber direction making an angle substantially parallel to or within an angle in a range of +/−45° of the machine direction and bonding the web.

6. A process for making an extensible nonwoven comprising the steps of: laying down a fibrous web using randomizing air jets such that a majority of the fibers have a fiber direction making an angle substantially parallel to or within an angle in a range of +/−45° of the machine direction and bonding the web.