Plastic and nonmetallic article shaping or treating: processes – Mechanical shaping or molding to form or reform shaped article – Reshaping running or indefinite-length work
Reexamination Certificate
2001-11-28
2004-10-12
Tentoni, Leo B. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Mechanical shaping or molding to form or reform shaped article
Reshaping running or indefinite-length work
Reexamination Certificate
active
06803009
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a process for making necked nonwoven webs and laminates having more uniform basis weights and stretching properties, and to necked nonwoven webs and laminates so made.
BACKGROUND OF THE INVENTION
Necked nonwoven webs, including necked spunbond webs, meltblown webs, combinations and the like, are often made using a process which is schematically illustrated in
FIG. 1. A
nonwoven web
12
having a starting width A is passed in its 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 which is faster than the first surface velocity. The surface velocity difference between the first and second nips results in formation of a narrower (“necked”) nonwoven web
22
having a necked width A′ which is less than the starting width A.
The necked nonwoven web
22
generally includes fibers which are closer together and more aligned in the machine direction than the fibers of the starting nonwoven web
12
, which can be more randomly aligned. The necking may be performed with the aid of heat applied below the melting temperature of the fibers, for instance, by placing an oven or other heat source between the first and second nips. The necked nonwoven web
22
may also be heat set, either during or after the necking process, so that the necked web becomes somewhat stable. A nonwoven web which is stable in the necked condition is said to be “reversibly necked”. A reversibly necked nonwoven web can be easily extended in the cross direction by applying a small extension force, and tends to return to its narrower, necked configuration when the extension force is released.
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
of the necking process, than the fibers in the central region
11
. Furthermore, 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 primarily in one direction, inward toward the center of the 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 may be nonuniform in the cross direction, having a higher basis weight in both edge regions than in the central region, and having greater cross-directional extendibility in both edge regions than the central region.
There is a need desire for a necking process which produces necked nonwoven webs having better cross-directional uniformity. There is also a need or desire for necked nonwoven webs, and laminates containing necked nonwoven webs, which have better cross-directional uniformity.
DEFINITIONS
As used herein, the term “recover” refers to a contraction of a stretched material upon termination of a biasing force following stretching length 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, 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 100 microns, for example, having a diameter of from about 0.5 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 entangling is 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 and/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 spinnerette 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. 4,340,563 to Appel et al., and U.S. Pat. No. 3,692,618 to Dorschner et al. The disclosures of both these patents are hereby incorporated by reference.
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 or gathering.
As used herein, the term “neckable material” means any material which can be necked.
As used herein, the “central region” of a nonwoven web is defined as the central 70% of the cross-directional width of the nonwoven web. The “edge regions” are defined as the outermost 15% of the width on both sides of the central region of the nonwoven web.
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 pre-necked dimensions, the necked and treated portions will generally recover to their necked dimensions upon termination of the force. One form of treatment is the application of heat. Generally speaking, extension
Conyer Sjon-Paul L.
Morell Charles J.
Morman Michael T.
Palmer Randall J.
Kimberly--Clark Worldwide, Inc.
Pauley Petersen & Erickson
Tentoni Leo B.
LandOfFree
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