Slit neck spunbond process and material

Details Slit neck spunbond process and material Slit neck spunbond process and material

2002-04-24

2004-09-07

Vanatta, Amy B. (Department: 3765)

Textiles: cloth finishing

Expanding device for textile webs

C026S099000, C028S170000, C264S289300

Reexamination Certificate

active

06785937

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to a process for making necked nonwoven materials and laminates having edge regions with higher basis weight and increased extendibility relative to a central region, and to necked nonwoven materials produced by such process.
BACKGROUND OF THE INVENTION
Necked nonwoven webs, including necked spunbond webs, meltblown webs, combinations and the like, and laminates including nonwoven webs such as spunbond film laminates, are often made using a process which is schematically illustrated in
FIG. 1. A
nonwoven web
12
having a starting width is passed in a machine direction between a first nip
16
, which can be a first pair of nip rollers traveling at a first surface velocity, and a second nip
26
, which can be a second pair of nip rollers traveling at a second surface velocity greater than the first surface velocity. The surface velocity difference between the first nip and the second nip results in formation of a necked or narrowed nonwoven web
22
having a necked width which is less than the starting width.
The starting nonwoven web
12
includes edge regions
13
and
15
, and a central region
11
. The necked nonwoven web
22
includes edge regions
23
and
25
, and a central region
21
. Because the necking causes the nonwoven fibers to become closer together and more aligned, without noticeably stretching or narrowing the individual fibers, the necked nonwoven web
22
generally has a higher basis weight than the starting nonwoven web
12
.
As can be easily seen from
FIG. 1
, the nonwoven fibers in the edge regions
13
and
15
of the starting nonwoven web travel a greater distance between the first nip
16
and the second nip
26
during the necking process, than the fibers in the central region
11
. Further, the cross-directional stresses in the central region
11
are at least partially counteracted, because these stresses are applied in both cross directions. The cross-directional stresses in each of the edge regions
13
and
15
are in one direction, inward toward the central region
11
of the nonwoven web. This results in increased fiber gathering and necking in the edge regions. Consequently, the fibers in the edge regions
23
and
25
of the necked nonwoven web are generally more aligned and closer together than the fibers in the central region
21
. As a result, the necked nonwoven web becomes nonuniform in the cross direction, having greater gathering and thus a higher basis weight and extendibility in both edge regions than in the central region. If this necked web is then slit into a desired number of slits, the slits including each edge portion of the necked nonwoven web will have different properties, edge to edge, than the center slits.
There is a need or desire for a necking process which produces similar or identical slit necked nonwoven strips, each having a substantially similar cross-directional profile in basis weight and extendibility.
Definitions
As used herein, the term “comprising” opens the claim to inclusion of additional materials and/or process steps other than those recited.
As used herein, the term “recover” refers to a contraction of a stretched material upon termination of a biasing force following stretching of the material by application of the biasing force. For example, if a necked material having a relaxed, unbiased width of one (1) inch is elongated 50 percent in the cross direction by stretching to a width of one and one half (1.5) inches the material would be elongated 50 percent (0.5 inch) and would have a stretched width that is 150 percent of its relaxed width. If this exemplary stretched material is relaxed, and is recovered to a width of one and one tenth (1.1) inches after release of the biasing and stretching force, the material would have recovered 80 percent (0.4 inch) of its one-half (0.5) inch elongation. Recovery may be expressed as [(maximum stretched dimension minus final sample dimension)/(maximum stretched dimension minus initial sample dimension)]×100.
As used herein, the term “nonwoven web” means a web that has a structure of individual fibers of threads which are interlaid, but not in an identifiable repeating manner. Nonwoven webs have been, in the past, formed by a variety of processes such as, for example, spunbonding processes, meltblowing processes and bonded carded web processes.
As used herein, the term “microfibers” means small diameter fibers having an average diameter not greater than about 75 microns, for example, having a diameter of from about 0.5 microns to about 75 microns, more specifically microfibers may also have an average diameter of from of from about 4 microns to about 40 microns.
As used in herein, the term “interfiber bonding” means bonding produced by thermal bonding or entanglement between the individual nonwoven fibers to form a coherent web structure. Fiber contact bonding and entangling are inherent in the meltblown processes but may be generated or increased by processes such as, for example, hydraulic entangling or needle punching. One or more thermal bonding steps are employed in most processes for forming spunbond webs. Alternatively or additionally, a bonding agent can be utilized to increase the desired bonding and to maintain structural coherency of the web. For example, powdered bonding agents and chemical solvent bonding may be used.
As used herein, the term “meltblown fibers” means fibers formed by extruding a molten thermoplastic material through a plurality of fine, usually circular, die capillaries as molten threads or filaments into a high velocity gas (e.g. air) stream which attenuates the filaments of molten thermoplastic material to reduce their diameters, which may be to microfiber diameter. Thereafter, the meltblown fibers are carried by the high velocity gas stream and are deposited on a collecting surface to form a web of randomly dispersed meltblown fibers. Such a process is disclosed, for example, in U.S. Pat. No. 3,849,241 to Butin, the disclosure of which is hereby incorporated by reference.
As used herein, the term “spunbonded fibers” refers to small diameter fibers which are formed by extruding a molten thermoplastic material as filaments from plurality of fine, usually circular, capillaries in a spinneret with the diameter of the extruded filaments then being rapidly reduced, for example, by eductive drawing or other well-known spun bonding mechanisms. The production of spun-bonded nonwoven webs is illustrated in patents such as, for example, in U.S. Pat. No. 3,802,817 to Matsuki et al., U.S. Pat. No. 4,340,563 to Appel et al., and U.S. Pat. No. 3,692,618 to Dorschner et al. The disclosures of these patents are hereby incorporated by reference.
“Necked” or “neck stretched” are interchangeable terms and refer to a method of elongating a nonwoven fabric, generally in the longitudinal, or machine direction, to reduce its width in a controlled manner to a desired amount. The controlled stretching may take place under cool, room temperature or greater temperatures and is limited to an increase in overall dimension in the direction being stretched up to the elongation required to break the fabric, which in many cases is about 1.05 to 1.7 times. When relaxed, the web returns toward its original dimensions. Such a process is disclosed, for example, in U.S. Pat. Nos. 4,443,513 to Meitner and Notheis; U.S. Pat. Nos. 4,965,122, 4,981,747 and 5,114,781 to Morman; and U.S. Pat. No. 5,244,482 to Hassenboehler Jr. et al.
As used herein, the term “necked material” refers to any material which has been constricted in at least one dimension by processes such as, for example, drawing.
As used herein, the term “neckable material” means any material which can be necked.
As used herein, the term “reversibly necked material” refers to a necked material that has been treated while necked to impart memory to the material so that, when a force is applied to extend the material to its prenecked dimensions, the necked and treated portions will generally recover to their necked dimensions upon termination of the f

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