U.S. patent application number 10/942999 was filed with the patent office on 2006-03-23 for method of producing low cost elastic web.
Invention is credited to Tze Wan Pansy Chung, Jeffrey Alan Middlesworth.
Application Number | 20060063454 10/942999 |
Document ID | / |
Family ID | 35149625 |
Filed Date | 2006-03-23 |
United States Patent
Application |
20060063454 |
Kind Code |
A1 |
Chung; Tze Wan Pansy ; et
al. |
March 23, 2006 |
Method of producing low cost elastic web
Abstract
A method for producing nonwoven webs, laminates, and composites
thereof includes activating by elongation in at least a two-stage
process wherein the first elongation is in substantially the same
direction and to substantially the same degree as the second
elongation.
Inventors: |
Chung; Tze Wan Pansy; (Fox
River Grove, IL) ; Middlesworth; Jeffrey Alan;
(Wauconda, IL) |
Correspondence
Address: |
HUNTON & WILLIAMS LLP;INTELLECTUAL PROPERTY DEPARTMENT
1900 K STREET, N.W.
SUITE 1200
WASHINGTON
DC
20006-1109
US
|
Family ID: |
35149625 |
Appl. No.: |
10/942999 |
Filed: |
September 17, 2004 |
Current U.S.
Class: |
442/327 ;
442/328; 442/409 |
Current CPC
Class: |
Y10T 442/69 20150401;
Y10T 442/60 20150401; D06C 3/00 20130101; Y10T 442/601
20150401 |
Class at
Publication: |
442/327 ;
442/328; 442/409 |
International
Class: |
D04H 5/00 20060101
D04H005/00; D04H 13/00 20060101 D04H013/00; D04H 1/00 20060101
D04H001/00 |
Claims
1. A method of activating a nonwoven web, laminate, or composite
thereof comprising: elongating a nonwoven web, laminate, or
composite thereof precursor material a first time to provide a
first elongated material; and elongating the first elongated
material a second time in substantially the same direction and to
substantially the same degree as the first elongation.
2. The method of claim 1, wherein the nonwoven web, laminate, or
composite thereof contains fibers selected from the group
consisting of polyethylene, polypropylene, acrylic, polyamide,
polyester, rayon, cellulose, nylon fibers, and combinations and
composites thereof.
3. The method of claim 1, wherein the nonwoven material in the
nonwoven web, laminate, or composite thereof precursor material has
a basis weight of 20 or less grams per square meter.
4. The method of claim 1, wherein the nonwoven material in the
nonwoven web, laminate, or composite thereof precursor material has
a basis weight of 25 or less grams per square meter.
5. The method of claim 1, wherein the laminate comprises at least
one elastic film or sheet and at least one nonwoven web.
6. A method for activating a nonwoven web, laminate, or composite
thereof precursor material comprising: elongating the nonwoven web,
laminate, or composite thereof precursor material a first time by a
first means for elongating to provide a first elongated material;
and elongating the first elongated material a second time by a
second means for elongating, the second means for elongating being
in substantially the same direction and to substantially the same
degree as in the first means for elongating.
7. The method of claim 6, wherein said first and second means for
elongating comprises sets of intermeshing gear rollers with ribs,
grooves, or teeth parallel to the axis of rotation of the
intermeshing gear rollers.
8. The method of claim 6, wherein said first and second means for
elongating comprises sets of intermeshing gear rollers with ribs,
grooves, or teeth perpendicular to the axis of rotation of the
intermeshing gear rollers.
9. The method of claim 6, wherein said first and second means for
elongating each comprises a first pair and a second pair of driven
rollers with means for frictionally engaging the nonwoven web,
laminate, or composite thereof, wherein the second pair of driven
rollers is operated at a faster linear circumferential speed than
is the first pair of driven rollers.
10. An activated nonwoven web, laminate, or composite thereof made
by the method of claim 1.
11. The activated nonwoven web, laminate, or composite of claim 10,
wherein the nonwoven web in the nonwoven web, laminate, or
composite thereof precursor material has a basis weight of 20 or
less grams per square meter.
12. The activated nonwoven web, laminate, or composite of claim 11,
wherein elongating the first and second time comprises elongating
to an activation depth of about 0.2 inches each time.
13. The activated nonwoven web, laminate, or composite of claim 12,
having a peak force of at least 8.00 Newtons per inch of sample
width.
14. The activated nonwoven web, laminate, or composite of claim 12,
having a knee elongation of at least 109% measured at the point in
the stress/strain curve at which the rate of increase of tensile
force with elongation reaches 0.1 Newtons per percent
elongation.
15. The activated nonwoven web, laminate, or composite of claim 11,
wherein elongating the first and second time comprises elongating
to an activation depth of about 0.175 inches each time.
16. The activated nonwoven web, laminate, or composite of claim 15,
having a peak force of at least 11.00 Newtons per inch of sample
width.
17. The activated nonwoven web, laminate, or composite of claim 15,
having a knee elongation of at least 93% measured at the point in
the stress/strain curve at which the rate of increase of tensile
force with elongation reaches 0.1 Newtons per percent
elongation.
18. The activated nonwoven web, laminate, or composite of claim 10,
wherein the nonwoven web in the nonwoven web, laminate, or
composite thereof precursor material has a basis weight of 25 or
less grams per square meter.
19. The activated nonwoven web, laminate, or composite of claim 18,
wherein elongating the first and second time comprises elongating
to an activation depth of about 0.2 inches each time.
20. The activated nonwoven web, laminate, or composite of claim 19,
having a peak force of at least 10 Newtons per inch of sample
width.
21. The activated nonwoven web, laminate, or composite of claim 19,
having a knee elongation of at least 102% measured at the point in
the stress/strain curve at which the rate of increase of tensile
force with elongation reaches 0.1 Newtons per percent
elongation.
22. The activated nonwoven web, laminate, or composite of claim 18,
wherein elongating the first and second time comprises elongating
to an activation depth of about 0.175 inches each time.
23. The activated nonwoven web, laminate, or composite of claim 22,
having a peak force of at least 15 Newtons per inch of sample
width.
24. The activated nonwoven web, laminate, or composite of claim 22,
having a knee elongation of at least 86% measured at the point in
the stress/strain curve at which the rate of increase of tensile
force with elongation reaches 0.1 Newtons per percent
elongation.
25. An absorbent article comprising the activated nonwoven web,
laminate, or composite thereof of claim 10.
26. The absorbent article in claim 25, wherein the nonwoven web in
the nonwoven web, laminate, or composite thereof precursor material
has a basis weight of less than or equal to 20 grams per square
meter.
27. The absorbent article in claim 25, wherein the nonwoven web in
the nonwoven web, laminate, or composite thereof precursor material
has a basis weight of less than or equal to 25 grams per square
meter.
28. The absorbent article in claim 25, wherein the laminate
comprises at least an elastic film and a nonwoven web.
Description
FIELD OF THE INVENTION
[0001] Embodiments relate generally to methods for activating
nonwoven webs, laminates, and composites thereof. More
particularly, embodiments relate to the activation of nonwoven
webs, laminates, and composites thereof for use in, for example,
diapers, articles for the control of the effects of incontinence,
bandages, and other hygiene articles.
BACKGROUND OF THE INVENTION
[0002] Nonwoven fabrics, especially inexpensive polymer-based
nonwoven fabrics, have found increasing use in the textile market.
Nonwoven fabrics typically are webs, batts, mats, sheets, or films
of fiber networks. They are commonly referred to simply as
"nonwoven webs" or "webs." Many different natural, synthetic, and
semi-synthetic polymer fibers are used to create nonwoven webs.
Nonwoven webs may consist of one type of fiber, several different
types of fibers, laminates of different fibers, and composites. The
fibers may be staple (short fibers) or filaments (long fibers).
Nonwoven webs often are combined with other materials to form
laminates or composites. If desired, the fibers that comprise the
nonwoven web may be bonded to one another using, for example, a
chemical binder. Otherwise, the nonwoven webs usually are
mechanically bonded through fiber entanglement.
[0003] One obstacle to the use of nonwoven fabrics has been the
relatively inelastic nature of some nonwoven webs. Inelastic fabric
often is rough and uncomfortable and therefore of limited utility
as a textile. Nonwoven webs may be made more elastic, however, and
therefore softer in feel, by a process known as activation.
"Activating" a nonwoven web involves stretching or elongating the
web in one or more directions beyond the elastic limit of the web.
As the nonwoven web is elongated beyond its elastic limit, some of
the fibers, inter-fiber bonds, and intra-fiber bonds are believed
to be broken. It is believed that breaking of the fibers and bonds
of the nonwoven web results in increased elasticity and softness in
the web, at least to the degree of elongation.
[0004] Typically, activation of nonwoven webs is accomplished by
one of two processes. U.S. Pat. No. 3,849,526, the disclosure of
which is incorporated herein by reference in its entirety,
describes one of the processes in relation to a method of making
webs of filter material. The web is stretched by a pair of rollers
with transverse ribs across the length of the rollers arranged
parallel to the axis of rotation. The transverse ribs of the
rollers intermesh similar to the two teethed wheels of a gear but
without coming into contact with one another. The web is stretched
in the direction of travel, otherwise referred to as the "machine"
direction, as it passes through the nip between the pair of
rollers.
[0005] U.S. Pat. No. 5,167,897, the disclosure of which is
incorporated herein by reference in its entirety, describes an
alternative stretching process in relation to a method for
incrementally stretching a laminate web to impart elasticity. The
method described involves transverse stretching whereby the
nonwoven web is stretched by passing it through the nip of
interdigitating corrugated or grooved rollers with ribs
substantially perpendicular to the axis of rotation. The degree of
overlap of the opposing ribs on the corrugated rollers may be
adjusted to control the degree of stretching or elongation of the
web. In this way, the nonwoven web is stretched in the "transverse"
direction (i.e. perpendicular to the direction of travel) as it
passes through the nip between the rollers.
[0006] U.S. Pat. No. 4,223,059, the disclosure of which is
incorporated herein by reference in its entirety, describes a
process of stretching a nonwoven web comprised of an orientable
polymeric fiber. The fibers are selectively stretched in
incremental portions to form a bi-axially stretched web in first
and second stations wherein the first and second stations are
provided with sets of rollers having grooves parallel and
perpendicular, respectively, to the axis of each set of
rollers.
[0007] U.S. Pat. No. 5,143,679, the disclose of which is
incorporated herein by reference in its entirety, describes a
method and apparatus for incrementally stretching "zero strain"
stretch laminate webs to impart elasticity. The mechanical
stretching operation is carried out by passing the laminate web
between multiple pairs of meshing corrugated rollers, each pair of
rollers exhibiting a greater degree of meshing than the preceding
pair, to sequentially stretch the web in stages. The patent states
that more gradual stretching of the web is believed to minimize
damage to the web.
[0008] Because nonwoven webs often are combined with materials to
form laminates or composites, the activation step can likewise be
performed on the laminate or composite containing the nonwoven web
rather than the nonwoven web by itself. For example, U.S. Pat. No.
5,861,074, the disclosure of which is incorporated herein in its
entirety, describes using a diagonal intermeshing stretcher, cross
direction intermeshing stretcher, machine direction intermeshing
stretcher, or incremental stretching technique to stretch the
laminate.
[0009] One of the disadvantages of activation of nonwoven webs and
laminates or composites thereof is that the process is destructive
of the structure of the nonwoven web. This may necessitate use of a
high quality and expensive precursor nonwoven web in order to
maintain a viable structure in the activated product. For example,
typical basis weights (weight of a unit area of fabric) of 25 grams
per square meter (gsm) or greater often are used commercially.
[0010] The description herein of problems and disadvantages of
known apparatus, methods, and devices is not intended to limit the
embodiments to the exclusion of these known entities. Indeed,
embodiments may include one or more of the known apparatus,
methods, and devices without suffering from the disadvantages and
problems noted herein.
SUMMARY OF THE EMBODIMENTS
[0011] In the embodiments, a method for activating a nonwoven web,
laminate, composite thereof is described, wherein a nonwoven web,
laminate, or composite thereof precursor material is elongated by a
first means for elongation to provide a first elongated material.
The first elongated material then is elongated by a second means
for elongation in substantially the same direction and to
substantially the same degree of elongation as in the first means
for elongation.
[0012] In the embodiments, a method for activating a nonwoven web,
laminate, or composite thereof is described that includes a first
means for elongating the nonwoven web, laminate, or composite
thereof precursor material to provide a first elongated material,
and a second means for elongating the first elongated material in
substantially the same direction and to substantially the same
degree of elongation as in the first means for elongation. The
first and second means for elongation may be, for example, sets of
intermeshing gear rollers with ribs, grooves, or teeth either
parallel or perpendicular to the axis of rotation of the gear
rollers.
[0013] In a further embodiment, an activated nonwoven web,
laminate, or composite thereof is provided, whereby the material is
produced by elongating the nonwoven web, laminate, or composite
thereof precursor material a first time to provide a first
elongated material, and then elongating the first elongated
material a second time in substantially the same direction and to
substantially the same degree as the first time. The nonwoven web,
laminate, or composite thereof may possess superior mechanical
properties compared to webs activated by other methods.
[0014] In another embodiment, an absorbent article is provided that
includes an activated nonwoven web, laminate, or composite thereof
produced by elongating a nonwoven web, laminate, or composite
thereof precursor material a first time to provide a first
elongated material, and then elongating the first elongated
material a second time in substantially the same direction and to
substantially the same degree as the first time.
[0015] Still further embodiments are identified in the ensuing
description, with reference to the drawings identified below.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 is a drawing of an exemplary machine direction
elongation means.
[0017] FIG. 2 is a drawing of an exemplary transverse direction
elongation means.
[0018] FIG. 3 is a drawing of another exemplary machine direction
elongation means.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0019] The terminology used herein is for the purpose of describing
particular embodiments only, and is not intended to limit the scope
of the claims. As used throughout this disclosure, the singular
forms "a," "an," and "the" include plural reference unless the
context clearly dictates otherwise.
[0020] Unless defined otherwise, all technical and scientific terms
used herein have the same meanings as commonly understood by one of
ordinary skill in the art to which the embodiments belong. Although
any methods and materials similar or equivalent to those described
herein can be used in the practice or testing of the embodiments,
the preferred methods, devices, and materials are now described.
All publications mentioned herein are cited for the purpose of
describing and disclosing the various webs, films, laminates,
processing methods and articles that are reported in the
publications and that might be used in connection herewith. Nothing
herein is to be construed as an admission that such disclosures are
prior art.
[0021] Embodiments include the possibility of using a less
expensive precursor nonwoven web and still producing an activated
nonwoven web, laminate, or composite thereof with acceptable end
use properties by carrying out the activation in two procedures,
wherein the two activations are carried out in substantially the
same direction to the substantially the same degree of activation.
Tensile and elastic properties in the finished product are as good
as, or superior to, more expensive nonwoven webs, laminates, or
composites thereof that undergo single activation steps, or double
activation steps that are more severe in terms of the degree of
elongation that is applied to the web, or where the second
activation step applies a higher degree of elongation to the
material than does the first.
[0022] The term "substantially" means that a given property or
parameter (such as direction) may vary by about 10% from the stated
value. Preferably, the property or parameter varies by less than 5%
of the stated value, and most preferably less than 3%.
[0023] The term "permeability" denotes the ability of the vapor or
liquid to permeate through the substrate.
[0024] The term "extensibility" of a web refers to the amount of
strain (in percent relative to the zero strain state) that can be
applied to a web by a tensile force without breakage of fibers,
bonds between fibers, or undue distortion of the web structure. For
a nonwoven web to be extensible in any given direction means that
when a tensile force is applied to the web in that direction, the
web expands in that direction, and a strain is induced in the web,
substantially without breakage of fibers or of bonds between
fibers.
[0025] The extensibility of a creped web has two components. One is
the "intrinsic extensibility" of the web, that refers to the
extensibility of the web in its natural, uncreped, state. The
second component is the "crepe induced extensibility", that refers
to the strain that can be applied to extend the web in a given
direction by virtue of the creping structure. It can be seen, for
example, that after a creped web has been stretched to the point of
"crepe induced extensibility," the web is predominantly in its
uncreped state.
[0026] As used herein, the expression "absorbent articles" means
articles that absorb and contain body fluids and other body
exudates. More specifically, an absorbent article includes garments
that are placed against or in proximity to the body of a wearer to
absorb and contain the various exudates discharged from the
body.
[0027] The expression "knee elongation" refers to the inflexion in
the stress/strain tensile curve of a material that occurs when the
rate of application of stress required to incrementally stretch the
material beyond its current point of tension increases
significantly. For the purposes of this disclosure, the knee
elongation refers to the point in the stress/strain curve of the
material at which the rate of increase of tensile force with
elongation reaches and thereafter exceeds 0.1 Newtons/% elongation,
measured on a sample with a width of one inch (25.4 millimeters).
The significance of "knee elongation" is that it defines a point at
which it becomes progressively more difficult in terms of applied
stress to stretch the web. For a soft structure, therefore, it is
preferable that the knee elongation be as high as possible, so that
the web subjectively feels stretchable.
[0028] The expression "peak force" refers to the maximum force that
is seen in the tensile curve of the material, referred to in
Newtons per inch of sample width (N/in). A minimum peak force of
8.0 N/in is desirable to ensure that the material has sufficient
strength in use.
[0029] In an exemplary embodiment, there is provided a method of
activating a nonwoven web, laminate, or composite thereof. The
method comprises elongating the nonwoven web, laminate, or
composite thereof a first time to provide a first elongated
material, and then elongating the first elongated material a second
time in substantially the same direction and to substantially the
same degree as in the first time.
[0030] The nonwoven web, laminate, or composite thereof may be
comprised of any appropriate fiber. For example, polyethylene,
polypropylene, acrylic, polyamide, polyester, rayon, cellulose,
nylon, and combinations of such fibers are all appropriate for use
in the nonwoven web. The nonwoven web in the embodiments also may
be the product of any process for forming the same. For example,
the nonwoven web may be carded, spun-bonded, wet-laid, air-laid and
melt-blown as such processes are well known in the art. One
knowledgeable in the art will appreciate the myriad ways in which a
nonwoven web made be created from its constituent fibers and the
many different types of fibers that might be utilized, using the
guidelines provided herein. In one embodiment, the web is a
spun-bonded material made of polypropylene fiber.
[0031] If desired, the nonwoven web may be laminated with another
film or otherwise formed into a composite structure. For example,
apertured films, where the film has a plurality of holes that
extend from one surface to a second surface, may be formed with at
least one layer of a nonwoven web. The apertured films may be
two-dimensional films, where there is no three-dimensional
structure in the holes that connect the first surface of the film
to the second surface of the film, or three-dimensional films,
where protuberances are found on the surface of the film. The
protuberances are preferably in the shape of polygons, for example,
squares, hexagons, pentagons, ellipses, circles, ovals, slots,
etc., in a regular or random pattern.
[0032] The film also may be a monolayer film, coextruded film,
coated film, or composite film. Coated films are films comprising a
monolayer or coextruded film that are subsequently coated, (e.g,
extrusion coated, impression coated, or printed) with a thin layer
of the same or different material to which it is inseparably
bonded. Composite films are films comprising more than one film
where at least two films are combined in a bonding process. Bonding
processes may incorporate adhesive layers between the film
layers.
[0033] The film used in the laminate may be of any appropriate
material. For example, the film may be made of an elastomeric
polymer. The elastomeric film may be of the polyolefin type that is
processable into a film for direct lamination by melt extrusion
onto the nonwoven web. Suitable elastomeric polymers also may be
biodegradable or environmentally degradable. Suitable elastomeric
polymers for the film include, but are not limited to
poly(ethylene-butene), poly(ethylene-hexene),
poly(ethylene-octene), poly (ethylene-propylene),
poly(styrene-butadiene-styrene), poly(styrene-isoprene-styrene),
poly(styrene-ethylene-butylene-styrene), poly(ester-ether),
poly(ether-amide), poly(ethylene-vinylacetate),
poly(ethylene-methylacrylate), poly(ethylene-acrylic acid),
poly(ethylene butylacrylate), polyurethane,
poly(ethylene-propylene-diene), ethylene-propylene rubber,
polyisoprene, and butadiene-styrene copolymers. A new class of
rubber-like polymers also may be employed that are generally
referred to as polyolefins produced from single-site catalysts. The
most preferred catalysts are metallocene catalysts whereby
ethylene, propylene, styrene and other olefins may be polymerized
with butene, hexene, octene, etc., to provide elastomers suitable
for use in accordance with the principles herein, such as
poly(ethylene-butene), poly(ethylene-hexene),
poly(ethylene-octene), poly(ethylene-propylene) and/or polyolefin
terpolymers thereof. In certain preferred embodiments, the
elastomeric materials may comprise high performance elastomeric
materials such as elastomeric block copolymers. An example of a
suitable elastomeric block copolymer is KRATON.RTM. (commercially
available from Kraton Polymers of Houston, Tex.).
[0034] Polyethylene is a preferred material for production of the
film. For example, low density polyethylene (LDPE), linear low
density polyethylene (LLDPE), or a blend of LDPE and LLDPE,
polypropylene, and combinations thereof are useful. In one
embodiment, the film is made from a mixture of at least about 10%
by weight, or about 10% to about 50% by weight of medium density
polyethylene (MDPE), and the remainder is LDPE, LLDPE or a blend of
LDPE and LLDPE. The film also may be made from a mixture of at
least 10% by weight, or about 10% to about 50% by weight of high
density polyethylene (HDPE) and the remainder is LDPE, LLDPE or a
blend of LDPE and LLDPE. A particularly preferred film material is
a coextruded film with skin layers composed of metallocene LLDPE,
blended with LDPE, where the core material is a styrenic polymer,
preferably a styrene butadiene rubber blend. Each of the material
formulations may include additional materials, usually in small
percentages relative to the polymer, such as processing aids,
colorants (e.g, whiteners), and surfactants. The use of the term
LLDPE herein also includes those LLDPE's that are made using
metallocene catalysts and are commonly referred to as mLLDPE.
[0035] The film may be produced by any appropriate method
including, but not limited to, cast or blown extrusion processes.
Extrusion processes are well known in the art, and any suitable
extrusion process can be used to prepare a molten sheet of polymer,
using the guidelines provided herein. These extrusion processes
usually comprise mechanisms for feeding materials to the extruder,
mechanisms for melting and mixing materials, mechanisms for
transporting the molten materials to a forming die, and mechanisms
for cooling the molten sheet of polymer to form a polymer film. In
case a second film or nonwoven web is laminated to the molten
sheet, the second film or web may participate in the cooling
process.
[0036] Methods and apparatus suitable for feeding the raw materials
to the extruder generally are known in the art. A preferred feeding
mechanism comprises a conveying mechanism such as a vacuum pump
connected to a vacuum pipe, the pipe being submerged in a reservoir
of polymer material. In a controlled manner, the pump generates
vacuum in the pipe causing the pipe to suction polymer from the
reservoir and deposit the polymer in a feed hopper. The feed hopper
typically contains a metering device that deposits accurately
controlled amounts of polymer into the extruder receiving cavity.
Multiple cavities and feed hoppers may be present in a single
extruder thereby enabling feeding of multiple components.
Additionally, antistatic and vibratory devices can be positioned at
or near the feed hoppers to assist in accurately dosing the
polymer. Other feeding mechanisms known to those skilled in the art
or later discovered are also contemplated for use herein.
[0037] A preferred melt forming die is a cast die, but other types
of dies are possible such as blown film dies. The die forms a
molten polymer sheet that is subsequently cooled to create a film
or a laminate structure.
[0038] In an alternative embodiment, the molten polymer exits the
extruder through a pelletizing die (a flat, cylindrical plate with
multiple small openings). As the polymer passes through the die, it
forms strings of polymer. The strings may be subsequently cooled
and cut by a rotating knife. The cut strings are called "compounded
pellets." Compounded pellets can then be transported to a second
extruder where they are melted again, transported to a die, and
formed into a sheet that is subsequently cooled to form a film or
laminate structure. In certain embodiments, the compounded pellets
are combined with other polymer pellets in the second extruder.
[0039] Cooling mechanisms also are well known in the art, and any
cooling mechanism now known or later discovered can be used. A
primary cooling mechanism can include an embossing station
comprising two cooled rollers that are pressed against each other.
The molten polymer is caused to pass between the embossing rollers
(called engraving and anvil rollers, respectively) where it is
cooled by contact with the cooler rollers. Alternatively, the
rollers can both be smooth chill rollers without an engraving or
embossing roll. Another well known cooling device comprises passing
the polymer sheet over a single roll and applying an air or cool
water curtain to the molten polymer to cause it to contact the
single cooling roll. Both the air or water curtain and the contact
with the roll contribute to cooling.
[0040] Another well known cooling mechanism comprises passing the
polymer sheet over an apertured screen while in the presence of
vacuum. Vacuum causes the polymer sheet to come into close contact
with the screen, causing the polymer to cool. In one embodiment the
vacuum and screen combination causes the polymer sheet to conform
to the shape of the apertured screen surface, forming protrusions
in the film. The side of the film that contacts the screen is
called the formed film inner surface, and the side of the film that
is opposite the inner surface is called the formed film outer
surface. The protrusions can be apertured, or they can be
unapertured. Forming apertured polymer films in this manner is well
known in the art, as exemplified by U.S. Pat. Nos. 3,045,148;
4,155,693; 4,252,516; 4,508,256; and 4,509,907; the disclosures of
which are incorporated by reference herein in their entirety.
[0041] Other means of perforation include passing the film over a
perforating roll with projecting pins or blades that enter the film
and produce holes as the film passes over the roll. In these
methods, a backing roll is generally used that holds the film in
place against the perforating roll. The actual perforation then
takes place in the nip between the perforating roll and the backing
roll.
[0042] Activating a nonwoven web, laminate, or composite thereof
using certain embodiments enables the use of relatively lower
quality fibers without sacrificing the strength, elasticity, and
other important characteristics of the activated nonwoven web.
Therefore, in one embodiment the nonwoven web precursor material
has a basis weight of 25 or less grams per square meter. In another
embodiment, the nonwoven web precursor material has a basis weight
of 20 or less grams per square meter.
[0043] Another embodiment provides a method for activating a
nonwoven web, laminate, or composite thereof. The method includes a
first means for elongating the nonwoven web, laminate, or composite
thereof to provide a first elongated material. The method further
includes a second means for elongating the first elongated material
in substantially the same direction and to substantially the same
degree as in the first means.
[0044] The first and second means for elongating the nonwoven web,
laminate, or composite thereof, for example, may be an intermeshing
gear (IMG) machine where elongation is accomplished by stretching
the film through a gear-like pair of rollers, as is exemplarily
illustrated in FIG. 1. To accomplish elongation of the nonwoven web
in the machine direction, the rollers 1 have ribs, grooves, or
teeth 2 that extend parallel to the axis of rotation of the
rollers. Those skilled in the art will appreciate that the
embodiment illustrated in FIG. 1 is only an approximate depiction,
and that the roller arrangement may have a variety of alternative
configurations.
[0045] To accomplish elongation of the nonwoven web in the
transverse direction, the rollers have ribs, grooves, or teeth that
extend perpendicular to the axis of rotation of the rollers, as is
exemplarily illustrated in FIG. 2. The intermeshing gears 10 may be
described as an alternating stack of two different diameter disks
11 and 12. Disks that are larger in diameter 11 alternate on the
rollers with disks that are smaller in diameter 12. The two rollers
are aligned so that the larger diameter disks 11 of one roller are
opposite the smaller diameter disks 12 of the other roller. In this
way, the ribs, grooves, or teeth that extend perpendicular to the
axis of rotation of the rollers intermesh.
[0046] The shafts where the rollers may be mounted can be
positioned between two machine side plates, the first shaft being
located in fixed bearings and the second shaft being located in
bearings in slidable members. The position of the slidable members
is adjustable by means of wedge shaped elements operable by
adjusting screws or other devices. Screwing the wedges out or in
will move the vertically slidable member respectively down or up to
further engage or disengage the gear-like teeth of the second
intermeshing roll with the first intermeshing roll. Micrometers
mounted to the side frames indicate the depth of engagement of the
teeth of the intermeshing roll.
[0047] Air cylinders may be employed to hold the slidable members
in their engaged position firmly against the adjusting wedges to
oppose the opposing force exerted by the material being stretched.
These cylinders also may be retracted to disengage the upper and
lower intermeshing rollers from each other for purposes of
threading material through the intermeshing equipment or in
conjunction with a safety circuit that would open all the machine
nip points when activated.
[0048] A drive means typically is utilized to drive the stationery
intermeshing roll. If the intermeshing rollers are to remain in
constant engagement, the second intermeshing roller typically need
not be driven because torque will be transferred from the driven
roller through the nonwoven web, laminate, or composite thereof to
the second roller. The teeth preferably are not designed to
transmit rotational torque and do not contact metal-to-metal in
normal intermeshing stretching operation.
[0049] In the case of rollers with ribs, grooves, or teeth parallel
to the axis of rotation of the rollers, it may be preferable to
incorporate an anti-backlash gearing arrangement to facilitate
disengagement of the second intermeshing roller from the driven
roller. An anti-backlash gearing arrangement assures that upon
reengagement, the teeth of one intermeshing roller always fall
between the teeth of the other intermeshing roller. This feature
avoids potentially damaging physical contact between addendums of
intermeshing teeth. If the intermeshing rolls are to remain in
constant engagement, the second intermeshing roll typically need
not be driven. Driving the second roll may be accomplished by the
driven intermeshing roll through the material being stretched. The
teeth are not designed to transmit rotational torque and do not
contact metal-to-metal in normal intermeshing stretching
operation.
[0050] In the case of rollers with ribs, grooves, or teeth
perpendicular to the axis of rotation of the rollers, it may be
preferable to incorporate a means for causing the shafts of the two
intermeshing rollers to remain parallel when the movable second
shaft is raising or lowering. This is necessary to assure that the
teeth of one intermeshing roller falls between the teeth of the
other intermeshing roller to avoid potentially damaging physical
contact between the intermeshing teeth. This parallel motion may be
assured, for example, by a rack and pinion arrangement wherein a
stationary gear rack is attached to each side frame in
juxtaposition to the vertically slidable members. A gear resides on
each end of this shaft and operates in engagement with the racks to
produce the desired parallel motion.
[0051] An example of a particularly useful embodiment employs IMG
rollers that can be temperature controlled from about 50.degree. F.
to about 210.degree. F., and more preferably in a range of from
about 70.degree. F. to about 190.degree. F. The roll temperature
may be maintained through the use of an internal flow of a heated
or cooled liquid, an electrical system, an external source of
cooling/heating, combinations thereof, and other temperature
control and maintenance methods that will be apparent to those of
ordinary skill in the art. The preferred temperature control method
is internal flow through the rollers of a heated or cooled
liquid.
[0052] The depth of engagement of the roller teeth determines the
degree of elongation to which the web is subjected. A balance
usually is drawn between the depth of engagement of the roller
teeth and the precursor web composition, as these affect many
important physical properties of the web. Some of the factors
affecting the choice of pitch, teeth depth, and depth of engagement
include the composition of the web, desired final properties
(breathability, absorbency, strength, cloth-feel), and the width
and diameter of the IMG rollers. The final application of the
nonwoven web, laminate, or composite thereof also affects these
choices because it determines desired final properties.
[0053] The width of the IMG rollers presents economic and technical
limitations--as the width increases the weight of the rollers also
increases and so does the amount of deflection experienced by the
rollers. Deflection creates variation not only in the process of
stretching, but also in the process of making the rollers,
particularly as the pitch and tooth depth increases. Those skilled
in the art are capable of designing a suitable means for elongation
in the transverse direction depending on the myriad factors noted
above, using the guidelines provided herein.
[0054] Another embodiment involves incrementally stretching the
webs without using IMG rollers. In this embodiment, there is a
first means for elongating the nonwoven web, laminate, or composite
thereof and a second means for elongating the nonwoven web,
laminate, or composite, thereof, as illustrated in FIG. 3. Those
skilled in the art will appreciate that the embodiment illustrated
in FIG. 3 is only an approximate depiction, and that the first
means and second means may have a variety of alternative
configurations, following the guidelines provided herein.
[0055] FIG. 3 generally depicts a series of rollers (first pair and
second pair of rollers 33, 34, and first pair and second pair of
rollers, 35, 36) rotating at different circumferential speeds. The
first means 30 for elongating the nonwoven web, laminate, or
composite thereof comprises a first pair 33 of rollers and a second
pair 34 of rollers. The second means 31 for elongating the nonwoven
web, laminate, or composite thereof also comprises a first pair 35
of rollers and a second pair 36 of rollers. The rollers on each
pair of rollers 33, 34, 35, and 36 may have frictional engaging
means 32 for frictionally engaging the nonwoven web, laminate, or
composite thereof. The frictional engaging means may be similar to
sand paper or other means as will be appreciated by one of ordinary
skill in the art, using the guidelines herein.
[0056] The second pair of driven rollers 34 of the first means 30
for elongating the nonwoven web, laminate, or composite thereof is
operated at a faster linear circumferential speed than is the first
pair of driven rollers 33 of the first means 30. If the coefficient
of friction between the nonwoven web, laminate, or composite
thereof and the frictional engaging means 32 is sufficiently high,
the web is forced to stretch in the gap between the first pair 33
and second pair 34 of driven rollers, resulting in machine
direction elongation. The second pair of driven rollers 36 of the
second means 31 for elongating the nonwoven web, laminate, or
composite thereof likewise is operated at a faster linear
circumferential speed than is the first pair of driven rollers 35
of the second means 31. If the coefficient of friction between the
nonwoven web, laminate, or composite thereof and the frictional
engaging means 32 is sufficiently high, the nonwoven web, laminate,
or composite thereof again is forced to stretch in the gap between
the first pair 35 and second pair 36 of driven rollers, resulting
in machine direction elongation. The degree of elongation of the
nonwoven web, laminate, or composite thereof in the first means 30
of elongation is substantially the same as in the second means 31
of elongation.
[0057] Another embodiment provides an activated nonwoven web,
laminate, or composite thereof made by a process comprising
elongating a precursor nonwoven web, laminate, or composite thereof
a first time to provide a first elongated material. The method
further includes elongating the first elongated material a second
time in substantially the same direction and to substantially the
same degree as the first time to produce the activated nonwoven
web, laminate, or composite thereof.
[0058] In certain embodiments, the activated nonwoven web,
laminate, or composite thereof is prepared from a nonwoven
precursor having a basis weight of 25 or less grams per square
meter. Use of such a low basis weight precursor material may make
production of the activated nonwoven web, laminate, or composite
thereof less expensive than that produced by previously known
methods. Nevertheless, the activated nonwoven web, laminate, or
composite thereof has excellent strength and elasticity
characteristics.
[0059] For example, a sample of a nonwoven web/elastic laminate
precursor material (nonwoven basis weight of 25 gsm) that has been
activated twice, each time to a depth of 0.2 inches, had a peak
force of 10.52 Newtons per inch of sample width. Comparatively, the
identical precursor material incrementally activated once at 0.175
inches and a second time at 0.2 inches had a peak force of 8.54
Newtons per inch of sample width. In addition, the same precursor
material activated twice, each time to a depth of 0.2 inches, had a
knee elongation value at 0.1 Newtons/percent elongation of 102.87%.
Comparatively, the same precursor sample activated once at 0.2
inches had a knee elongation value at 0.1 Newtons/percent
elongation of 63.8%.
[0060] In another embodiment, the activated nonwoven web, laminate,
or composite thereof is prepared from a nonwoven precursor material
having a basis weight of 20 or less grams per square meter. Again,
use of a lower quality precursor web may make production of the
activated product less expensive without unduly sacrificing
strength or elasticity characteristics. For example, a sample of a
nonwoven web/elastic laminate precursor material (nonwoven basis
weight of 20 gsm) that has been activated twice, each time to a
depth of 0.2 inches, had a peak force of 8.77 Newtons per inch of
sample width. Comparatively, the same precursor incrementally
activated once at 0.175 inches and a second time at 0.2 inches had
a peak force of 7.43 Newtons per inch of sample width. In addition,
the same precursor material activated twice, each time to a depth
of 0.2 inches, had a knee elongation value at 0.1 Newtons/percent
elongation of 109.29%. Comparatively, the same precursor sample
activated once at 0.2 inches had a knee elongation value at 0.1
Newtons/percent elongation of 65.42%.
[0061] Another embodiment provides an absorbent article including
an activated nonwoven web, laminate, or composite thereof made by
the process of the embodiments. In certain useful embodiments, the
absorbent article is made of an activated laminate of a nonwoven
web and an elastic film. The nonwoven web and elastic film may be
made from any of the polymers mentioned herein or other polymers as
will be appreciated by someone of ordinary skill in the art using
the guidelines herein. It is preferred that the activated material
be included as part of the topsheet, backsheet, fastening elements,
side panels, and other extensible elements of the absorbent
article. The elongation means utilized to elongate the nonwoven
web, laminate, or composite thereof may be any of the means
described herein or other applicable means as will be appreciated
by persons of ordinary skill in the art, using the guidelines
herein.
EXAMPLE
[0062] Samples of nonwoven (Sofspan.RTM. 200 supplied by BBA
Nonwovens, One Lakeview Place--Suite 204, Nashville, Tenn. 37124
USA) and elastomeric formed film (Flexaire.RTM., 40 gsm supplied by
Tredegar Film Products, 1100 Boulders Parkway, Richmond, Va. 23225
USA) were vacuum bonded and activated between a pair a finned
rollers produced by BIAX Fiberfilm (Biax-Fiberfilm Corporation,
N992 Quality Drive, Suite B, Greenville, Wis. 54942 USA). The
activation pattern as indicated in the tables refers to the depth
of engagement of the teeth of the gear rollers. This is the maximum
depth at which the ribs, grooves, or teeth of one activation roller
penetrate between the ribs, grooves, or teeth of the opposing
activation roller. For example, a 200 activation depth refers to a
laminate being activated once, and to a depth of 200 mils
(thousandths of an inch). A 200/200 pattern refers to a laminate
being activated twice, to depths of 200 mils each time.
[0063] Samples with a gauge length of 2 inches (50.8 millimeters)
were stretched on a Synergie.RTM. 200 tensile tester (commercially
available from MTS Systems Corp, 14000 Technology Drive, Eden
Prairie, Minn. 55344 USA) at a rate of 500 mm/minute. Numbers
quoted are the average of 4 trials.
[0064] Table 1 illustrates the effect of nonwoven basis weight and
activation pattern on the peak force and knee elongation of the
laminate. A double activation yields a superior knee elongation
value, but at the cost of some loss of peak force. TABLE-US-00001
TABLE 1 Peak Force Basis Weight (Newtons/inch (grams per Activation
Depth of Knee Elongation square meter) (thousandth of inch) sample
width) at 0.1 N/% 25 200 20.67 63.8 25 200/200 10.52 102.87 20 200
16.66 65.42 20 200/200 8.77 109.29
[0065] Table 2 demonstrates an advantage of embodiments over the
use of a process where the second activation is to a greater degree
than the first. TABLE-US-00002 TABLE 2 Basis Weight (grams per
Activation Depth Peak Force Knee Elongation square meter)
(thousandth of inch) (Newtons/inch) at 0.1 N/% 20 175/200 7.43
113.44 25 175/200 8.54 113.9 20 200/200 8.77 109.29 25 200/200
10.52 102.87 20 175/175 11.42 93.55 25 175/175 15.72 86.8
[0066] All of the samples that use a 200 mil depth of engagement
for the second activation have similar knee elongation values. Of
these samples, the double activation samples that use a lesser
depth of engagement followed by the greater one at 200 mils
actually yield inferior peak force values compared to samples where
two equal depths of engagement were used. Double activation of the
sample at 200 mils for both activations using a 20 gsm nonwoven
yields an acceptable product.
[0067] A particularly useful embodiment is exemplified by the
example above designated basis weight of 20 and activation depth of
175/175.
[0068] The examples of the embodiments are limited to webs
subjected to two activation procedures. However, embodiments are
not limited to two activation procedures, and it will be understood
by one skilled in the art that a process characterized by further
activation, for example three or more, falls within the scope of
the appended claims.
[0069] While the description presented above has been described
with reference to particularly preferred embodiments, it is
recognized that similar advantages may be obtained by other
embodiments. It will be evident to those skilled in the art that
various changes and modifications can be made without departing
from the spirit and scope of the embodiments. All such
modifications are intended to be encompassed within the scope of
the appended claims.
* * * * *