U.S. patent application number 09/855144 was filed with the patent office on 2002-08-29 for elastic stranded laminate with adhesive bonds and method of manufacture.
Invention is credited to Campbell, Stephen M., Dobbins, Leslie D., Fitts, James R., May, Raymond J., Welch, Howard M., Willitts, Donald V..
Application Number | 20020119722 09/855144 |
Document ID | / |
Family ID | 26899357 |
Filed Date | 2002-08-29 |
United States Patent
Application |
20020119722 |
Kind Code |
A1 |
Welch, Howard M. ; et
al. |
August 29, 2002 |
Elastic stranded laminate with adhesive bonds and method of
manufacture
Abstract
A laminated article having elastic strands or filaments
contained therein for providing elasticity to the article, are
provided. The particular adhesive pattern bonds the relatively
inelastic nonwoven layers to the more elastic continuous filaments
in a pattern that allows adhesive-to-adhesive, adhesive-to-nonwoven
layer, and adhesive-to-elastic filament bonding.
Inventors: |
Welch, Howard M.;
(Woodstock, GA) ; Dobbins, Leslie D.; (Marietta,
GA) ; Fitts, James R.; (Gainesville, GA) ;
Willitts, Donald V.; (Douglasville, GA) ; Campbell,
Stephen M.; (Winneconne, WI) ; May, Raymond J.;
(Norcross, GA) |
Correspondence
Address: |
Neil C. Jones
Nelson Mullins Riley & Scarborough
Keenan Building, Third Floor
1330 Lady Street
Columbia
SC
29201
US
|
Family ID: |
26899357 |
Appl. No.: |
09/855144 |
Filed: |
May 14, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60204300 |
May 15, 2000 |
|
|
|
Current U.S.
Class: |
442/382 ;
442/328; 442/329 |
Current CPC
Class: |
B32B 5/26 20130101; B32B
37/12 20130101; Y10T 442/601 20150401; Y10T 442/602 20150401; Y10T
442/66 20150401; D04H 3/12 20130101; D04H 3/04 20130101; A61F
13/15593 20130101; A61F 13/4902 20130101; D04H 3/14 20130101 |
Class at
Publication: |
442/382 ;
442/328; 442/329 |
International
Class: |
D04H 001/00; D04H
003/00 |
Claims
What is claimed is:
1. An laminated fabric article comprising: (a) a facing layer; (b)
a plurality of elastic filaments adjacent to a surface of the
facing layer; and (c) an adhesive component, wherein the adhesive
component is applied to the surface of the nonwoven layer in
adhesive lines, the adhesive lines intersecting both the elastic
filaments and themselves to form a bonding network comprised of
adhesive-to-elastic bonds, adhesive-to-facing layer, and
adhesive-to-adhesive bonds.
2. The laminated fabric article of claim 1 wherein said adhesive
lines intersect said elastic filaments at an angle of greater than
45.degree. and less than 90.degree..
3. The laminated fabric article of claim 1 wherein said adhesive
lines intersect said elastic filaments at an angle of between about
50.degree. and about 90.degree..
4. The laminated fabric article of claim 1 wherein said adhesive
lines intersect said elastic filaments at an angle of between about
60.degree. and about 90.degree..
5. The laminated fabric article of claim 1 wherein said adhesive
lines intersect said elastic filaments at an angle of about
60.degree..
6. The laminated fabric article of claim 1 comprising an additional
facing.
7. The laminated fabric article of claim 1 wherein said adhesive
component is about 3 to about 5 gsm in weight.
8. The laminated fabric article of claim 1 wherein said article has
a basis weight of between about 2 to about 4 osy.
9. The laminated fabric article of claim 1 wherein said facing
layer comprises a spunbonded nonwoven web.
10. The laminated fabric article of claim 6 wherein said additional
facing comprises a spunbonded nonwoven web.
11. The laminated fabric article of claim 6 wherein said continuous
filaments and said adhesive component are between said facing
layers.
12. A method of manufacturing a laminated fabric article
comprising: (a) providing a facing layer; (b) providing a plurality
of elastic filaments adjacent to a surface of the facing layer; and
(c) applying an adhesive component to bond said elastic filaments
to said facing layer in adhesive lines that intersect both the
elastic filaments and themselves to form a bonding network
comprised of adhesive-to-elastic bonds, adhesive-to-facing layer,
and adhesive-to-adhesive bonds.
13. The method of claim 12 further comprising the steps of:
providing a second facing layer and applying an adhesive component
to said second facing layer to bond said elastic filaments to said
facing layer in adhesive lines that intersect both the elastic
filaments and themselves to form a bonding network comprised of
adhesive-to-elastic bonds, adhesive-to-facing layer, and
adhesive-to-adhesive bonds.
Description
FIELD OF THE INVENTION
[0001] This invention relates to laminated composite nonwoven
articles and, in particular, to a process for producing an elastic
and/or relatively inelastic nonwoven laminate that may be used for
a variety of applications such as in diapers, athletic bandages or
other products that require a degree of elasticity.
BACKGROUND OF THE INVENTION
[0002] Composites of elastic and nonelastic materials are commonly
made by combining elastics and nonelastics in a lamination process
to provide the entire composite with a degree of stetchability or
elasticity. These elasticized composites may then be used as the
elastic components for various articles disposable personal care
products such as, for example, diapers, pads, medical bandages, and
the like.
[0003] Generally, when forming such composites, a nonelastic
material (or at least a less elastic material) is joined by bonding
to an elastic material (or at least a more elastic material) while
the elastic material or sheet is in a stretched condition. When the
tension on the more elastic material is released, the less elastic
component of the combination is allowed to gather in the spaces
between the bonding sites. The resulting composite elastic material
is stretchable to the extent that the less elastic material
gathered between the bond locations allows the more elastic sheet
to elongate. Examples of these types of composite laminate articles
and materials are set forth in U.S. Pat. Nos. 4,720,415 and
5,385,775, each of which is incorporated by reference herein.
[0004] In some stretchable laminate articles, elastic strands of
continuous filaments are bonded to relatively inelastic sheet
materials while the elastic strands are in a stretched condition.
Such elastic continuous filaments may, in certain articles, be
sandwiched between two or more relatively inelastic sheets. The
relatively inelastic sheets may include nonwoven webs formed by
meltblowing or spunbonding various polymers. Examples of such
laminates are shown in U.S. Pat. No. 5,385,775 to Wright, which is
incorporated herein in its entirety by reference thereto.
[0005] As shown in Wright, elastic continuous filaments may be
extruded onto a horizontally moving sheet of material. The
continuous filaments are extruded from above the horizontal plane
of sheet material and directly onto the material for bonding
thereto.
[0006] In other exemplary laminates, after bonding the elastic
continuous filaments to the sheet material, which will often be
relatively inelastic, the bonded elastic continuous
filament/inelastic nonwoven sheet material will then be stretched
and another relatively The forces that are holding the elastic
continuous filaments in a stretched condition are then released to
gather the inelastic nonwoven sheet(s) between the sheet bonding
points. In use, the product may be stretched to expand and ungather
the inelastic sheet(s), but will, upon release, return to the
shortened, gathered state.
[0007] Other lamination processes have also been developed for
forming a stretchable laminate product from elastic and inelastic
materials. For example, U.S. Pat. No. 4,910,064 to Sabee shows an
apparatus for manufacturing an integral filamentary web comprising
continuous filaments and meltblown fibers. A multiple number of
continuous filaments are spun in curtain-like form, one side of
which will have molten meltblown fibers deposited thereon and
self-bonded to fix the continuous filaments in a controlled
alignment. The process involves drawing continuous filaments either
before, during, or after the deposition of the meltblown fibers in
order to molecularly orient the continuous filaments. After
stabilizing elastic continuous filaments by bonding to the
meltblown fibers and relaxing the filaments, the elastic filaments
and the web contract to form buckles, curls, or kinks in the
non-elastic molecularly oriented permanently lengthened continuous
filaments. The patent further describes the bonding of a second
opposing meltblown web to the opposite side of the continuous
filaments after the meltblown fiber/continuous filament composite
is at least partially drawn to provide some degree of molecular
orientation.
[0008] In addition, U.S. Pat. Nos. 5,200,246 and 5,219,633, also to
Sabee, show a vertically-oriented process and apparatus for
producing a fabric that combines elongatable continuous filaments
with fibrous meltblown webs for interlocking the continuous
filaments in an integrated, fibrous, continuous filament matrix. An
extruder provides molten elastomeric continuous filaments which are
cooled, solidified, and stretched as they are drawn from the
meltblowing nozzle by counter-rotating temperature-controlled pull
rolls. The solidified continuous filaments are then subsequently
pulled into the nip of a pair of temperature-controlled deposition
rolls whereat two opposing meltblown gas-fiber streams or sprays
are simultaneously and turbulently intermingled with each other and
between the tensioned continuous elastomeric filaments. Passing the
fabric between higher velocity draw rolls may then further stretch
the composite fabric.
[0009] In the manufacture of such laminates, adhesives have been
used to hold elastic strands or filaments in place, thereby bonding
the elastic strands or filaments to nonwoven facing materials. U.S.
Pat. No. 4,880,420 to Pomparelli discloses a method of applying
adhesive to bond elastic strands to a fabric by using a
sinusoidal-shaped line of adhesive. In Pomparelli, a relatively
thick portion of adhesive is applied in a line along one or more
elastic filaments in a direction generally parallel to the elastic
filaments. However, the line of adhesive disclosed in Pomparelli
does not intersect itself at any point. Instead, the sinusoidal
adhesive line intersects a predetermined number of the same elastic
strands several times as the line winds its way across the
strands.
[0010] One problem in the manufacture of elasticized articles is
that using adhesives to bond elastic strands to a nonwoven
sometimes causes the article to be stiff, rather than soft. In
diapers, for example, excessive adhesive results in a stiff or
inflexible diaper product that is undesirable to consumers. Also,
if the adhesive is not applied in a preferred pattern, and is not
efficiently utilized, it cannot reach optimum performance to
provide the greatest bonding strength for each gram of adhesive
applied to the article. Thus, a challenge in making products of
this type is to find ways to use less adhesive, but still impart
sufficient bonding strength to securely fix elastic filaments into
a nonwoven.
SUMMARY OF THE INVENTION
[0011] The present invention provides new methods for and patterns
of applying adhesive materials to elastic strand-containing
laminate articles. The articles in which the present invention may
be utilized include various articles that require portions of
elasticity such as diapers, tampons, and absorbent garments. Such
articles will typically include one or more nonwoven layers and a
plurality of elastic filaments or strands bonded to the nonwoven
layer(s) to provide the desired degree of elasticity. Typically, an
adhesive material is used to bond the strands to the nonwoven
layer(s). In the bonding arrangement of the present invention, the
adhesive material is applied in lines that intersect the elastic
filaments to form a bonding network comprised of
adhesive-to-elastic bonds, adhesive-to-facing bonds, and
adhesive-to-adhesive bonds.
[0012] The adhesive patterns utilized in the present invention will
typically be lines that lie perpendicular or nearly perpendicular
to the elastic components. Although true 90-degree bond angles may
be desirable, the average or mean bond angle may be as small as 50
degrees, and will typically be approximately 60 degrees. A greater
bond angle will generally result in increased bonding strength
between the continuous filaments and the nonwoven layer to which
the filaments are bonded.
[0013] In the bonding arrangement of the present invention, the
adhesive-to-elastic bonds are formed at the points where the lines
of adhesive and elastic material join or intersect and the
adhesive-to-adhesive bonds are formed at the points where the lines
of adhesive intersect or join themselves.
[0014] One particular embodiment in which the present invention may
be utilized is an absorbent article (garment) or infant diaper
wherein less than 0.6 grams of adhesive is applied per article to
bond the elastic strands of the articles to the contiguous nonwoven
facing layers. This results in a product that is generally free
from unnecessary stiffness while retaining a solid and stable
bonding of elastic filaments to nonwoven facing material.
[0015] In one aspect of the invention, a process of manufacturing
an absorbent laminated article is utilized. The process comprises
providing a nonwoven layer and spraying an adhesive upon the
surface of the nonwoven layer, wherein the adhesive is applied to
the nonwoven layer in a non-random pattern that is capable of
providing predetermined strength characteristics to the laminate
structure. Further, the process includes providing a plurality of
substantially parallel elastic filaments adjacent the nonwoven
layer, the elastic filaments being extruded from a die in molten
form and then cooled. Finally, the process includes pressing the
(1) nonwoven layer, (2) elastic filaments, and (3) adhesive
together in a nip to form a laminated article.
[0016] Other objects, advantages and applications of the present
invention will be made clear by the following detailed description
of embodiments of the invention and the accompanying drawings
wherein reference numerals refer to like or equivalent
structures.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 is a perspective view of one particular apparatus for
laminating together continuous filaments and nonwoven
facing(s);
[0018] FIG. 2A shows a cross-section of a laminated absorbent
article of the invention wherein an adhesive spray has been applied
onto the surface of one nonwoven facing;
[0019] FIG. 2B depicts a cross-section of a laminated absorbent
article of the invention wherein an adhesive spray has been applied
onto both opposing nonwoven facings;
[0020] FIG. 3A shows a bonding pattern in which the adhesive has
been applied to the elastic filaments with attenuation in the
cross-direction;
[0021] FIG. 3B shows an adhesive bonding spray or scrim
pattern;
[0022] FIG. 3C shows another adhesive bonding spray or scrim
pattern;
[0023] FIG. 3D illustrates conceptually the bond angle in a scrim
bonding pattern of this invention;
[0024] FIG. 4 shows the bonding pattern and method of calculating
the number of bonds per unit length on elastic strands or filaments
in accordance with the present invention;
[0025] FIG. 5A illustrates a swirled type of adhesive bonding
pattern;
[0026] FIG. 5B shows a randomized adhesive bonding pattern having a
majority of adhesive lines in a perpendicular orientation to the
elastic filaments;
[0027] FIG. 5C is a graphical representation of an adhesive laydown
pattern with attenuation of adhesive lines in the cross-machine
direction;
[0028] FIG. 5D shows a "chain-link fence" type pattern of adhesive
bonded to the elastic filaments; and
[0029] FIG. 6 is a schematic view of another particular apparatus
for laminating together continuous filaments and nonwoven
facing(s).
DEFINITIONS
[0030] The term "continuous filaments", as used herein, refers to
strands of continuously formed polymeric filaments. Such filaments
will typically be formed by extruding molten material through a die
head having a certain type and arrangement of capillary holes
therein.
[0031] The term "elastic" or "elasticized", as used herein, refers
to a material which, upon application of a biasing force, is
stretchable, which is elongatable to at least about 60 percent
(i.e., to a stretched, biased length which is at least about 160
percent of its relaxed unbiased length), and which will recover at
least 55 percent of its elongation upon release of the stretching
force. A hypothetical example of an elastic material would be a one
(1) inch sample of a material which is elongatable to at least 1.60
inches and which, when released, will recover to a length of not
more than 1.27 inches. Many elastic materials may be elongated by
more than 60 percent (i.e., more than 160 percent of their relaxed
length). For example, some elastic material may be elongated 100
percent or more, and many of these will recover to substantially
their initial relaxed length such as, for example, within 105
percent of their original relaxed length upon release of the
stretching force.
[0032] As used herein, the term "polymer" generally includes, but
is not limited to, homopolymers, copolymers, such as, for example,
block, graft, random and alternating copolymers, terpolymers, etc.
and blends and modifications thereof. Furthermore, the term
"polymer" includes all possible geometrical configurations of the
material, such as isotactic, syndiotactic and random
symmetries.
[0033] The term "composite nonwoven fabric", "composite nonwoven",
"laminate", or "nonwoven laminate", as used herein, unless
otherwise defined, refers to a material having at least one elastic
material joined to at least one sheet material. In most embodiments
such laminates or composite fabric will have a gatherable layer
which is bonded to an elastic layer or material so that the
gatherable layer may be gathered between bonding locations. As set
forth herein, the composite elastic laminate may be stretched to
the extent that the gatherable material gathered between the bond
locations allows the elastic material to elongate. This type of
composite elastic laminate is disclosed, for example, in U.S. Pat.
No. 4,720,415 to Vander Wielen et al., which is incorporated herein
in its entirety by reference thereto.
[0034] As used herein, the term "nonwoven web" refers to a web
having a structure of individual fibers or threads that 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, spunbonding processes and
bonded carded web processes.
[0035] 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
thermoplastic material or filaments into a high velocity gas (e.g.
air) stream which attenuates the filaments of molten thermoplastic
material to reduce their diameter, 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 disbursed meltblown fibers. Such a process
is disclosed, for example, U.S. Pat. No. 3,849,241 to Butin, which
is incorporated herein in its entirety by reference thereto.
[0036] As used herein, the term "spunbonded fibers" refers to small
diameter fibers formed by extruding a molten thermoplastic material
as filaments from a plurality of fine, usually circular,
capillaries of a spinerette with the diameter of the extruded
filaments then being rapidly reduced as by, for example, eductive
stretching or other well-known spun-bonding mechanisms. The
production of spun-bonded nonwoven webs is illustrated in patents
such as, for example, 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 incorporated herein in their entireties by
reference thereto.
[0037] As used herein, "scrim" refers generally to a fabric or
nonwoven web of material which may be elastic or inelastic, and
having a machine direction oriented along the path of manufacture
and a cross-direction.
DETAILED DESCRIPTION OF THE INVENTION
[0038] Reference now will be made to the embodiments of the
invention, one or more examples of which are set forth below. Each
example is provided by way of explanation of the invention, not as
a limitation of the invention. In fact, it will be apparent to
those skilled in the art that various modifications and variations
can be made in this invention without departing from the scope or
spirit of the invention. For instance, features illustrated or
described as part of one embodiment can be used on another
embodiment to yield a still further embodiment. Thus, it is
intended that the present invention cover such modifications and
variations as come within the scope of the appended claims and
their equivalents. Other objects, features and aspects of the
present invention are disclosed in or are obvious from the
following detailed description. It is to be understood by one of
ordinary skill in the art that the present discussion is a
description of exemplary embodiments only, and is not intended as
limiting the broader aspects of the present invention, which
broader aspects are embodied in the exemplary constructions.
[0039] As mentioned above, elastic stranded laminates are used in a
variety of personal care product applications such as waistbands,
leg cuffs, side panels, and the like in which a tight, yet
comfortable, elastic fit is needed. Products requiring such an
elastic-stranded laminate include disposable diapers, disposable
training pants, and adult-care briefs. Soft, flexible facings made
from materials such as polymer films and nonwovens surround the
strands of elastomeric polymers in these laminates. Adhesives are
commonly used to bond the facings to the strands, and the facings
to the facings.
[0040] One particular means of applying adhesives to the laminates
utilizes meltblown spray technology. In this technology,
meltblowing equipment presents the adhesive to the laminate layer
in a random fibrous configuration. Multiple adhesive-to-elastic
strand bonds per unit length of elastic are formed, along with
multiple facing to facing adhesive bonds per unit area. In general,
strong, flexible adhesive bonds are required to maintain the
flexibility and integrity of the laminate in use. If the
adhesive-to-elastic bonds are too few in number or are too weak,
then the elastic tension properties of the laminate will be
compromised as the tension of the elastic strands will break the
adhesive joints. The common remedy in prior art processes for
remedying this condition is to increase the number of bonding sites
by either increasing the meltspray air pressure, or by slowing the
lamination speed. As the meltspray air pressure is increased, the
resulting adhesive fiber size is reduced in these known processes,
creating weaker bonds. Increasing the amount of adhesive used per
unit area to create larger adhesive filaments usually repairs this,
but this usually increases the cost of the laminate. Lowering the
lamination speed decreases machine productivity, but negatively
impacts product cost.
[0041] FIGS. 2A and 2B illustrate the use of such meltspray webs.
In FIG. 2A, a cross-section of a laminated article produced with
the typical meltspray adhesive is shown. A laminated article 26 is
shown as having a first nonwoven facing 27 and second nonwoven
facing 28. Melt-spray adhesive layer 29 is applied between the
nonwoven facings, and continuous elastic filaments 30 are seen in
cross-section. FIG. 2B depicts a cross-section of a laminated
article 32 wherein melt-spray adhesive 29 has been applied on both
nonwoven facings 27 and 28.
[0042] The present invention, however, employs an elastic stranded
laminate where the number of bond sites per length elastic strand
are prescribed or predetermined, and the adhesive-to-elastic strand
joints are generally perpendicular in orientation to provide
enhanced strength. This allows the laminate to be made at minimal
cost by optimizing the adhesive and elastomer content to match the
product needs.
[0043] The adhesives are applied according to the present invention
in a continuous, wave-shaped pattern that intersects the elastic
strands in a predominantly perpendicular fashion. The bonding of
the continuous adhesive filaments to the elastic strands at their
intersections is also controlled to a known number per unit elastic
strand length so that predictable and controllable laminate
properties are achieved. By encapsulating high-strength adhesive to
elastic strand bonds with a perpendicular orientation and
optimizing the number of bonds per unit elastic strand length, the
elastic strand laminates of the present invention can be produced
with only a minimal amount of adhesive and elastomer. In addition,
the adhesives are applied in some embodiments of the present
invention to obtain both adhesive-to-elastic bonds and
adhesive-to-adhesive bonds as well as adhesive-to-facing bonds,
with the adhesive-to-adhesive bonding contributing to the strength
characteristics of the present invention.
[0044] Although the invention will be described and depicted in the
context of a continuous filament/nonwoven laminate forming
apparatus that is in a vertical orientation, it is to be understood
that various other apparatuses may be employed in forming the
laminates. The vertically-oriented laminate forming apparatus is
depicted in FIG. 1. This apparatus includes an extruder 15 that
forms continuous filaments 14 and then guides the continuous
filaments through a series of rollers until the filaments are
placed into position for bonding to one or more nonwoven facings.
In other embodiments, such as in FIG. 6, the series of rollers may
be eliminated. Various apparatuses may be employed in the present
invention and are described more specifically in co-pending
application owned by the present assignee and bearing Ser. No.
60/204,307 and filed on May 15, 2001, as a Provisional Application
(and later filed as a Utility application) with the title: "Method
and Apparatus for Producing Laminated Articles". That application
(both the Provisional application and the corresponding Utility
application) is incorporated herein in its entirety by reference
thereto.
[0045] Various types of compositions and various processing
conditions may be utilized to form the elastic continuous
filaments. For example, a Kraton.RTM.-brand elastic polymer may be
fed into an extruder where the polymer is melted at a controlled
temperature of between about 260.degree. and 460.degree. F., and in
certain instances at about 385.degree. F. In other embodiments,
depending on the particular polymer employed, the melt temperature
may be approximately 470.degree. F. to 480.degree. F. The polymer
is then extruded through a predetermined number of apertures in a
die head in a generally downward direction into separate continuous
filaments at a pressure of approximately 300 to 4000 psi (typically
from about 1500 to about 2000 psi).
[0046] One particular class of polymers that may be utilized in the
present process is the Kraton.RTM. G series of polymers distributed
by Shell Chemical Company (now available from Kraton Products
U.S.-LLC). Various Kraton.RTM. G polymers may be utilized.
[0047] In one embodiment, the blend used to form the elastomeric
continuous filaments as well as the facings include, for example,
from about 40 to about 80 percent by weight elastomeric polymer,
from about 5 to about 40 percent polyolefin, and from about 5 to
about 40 percent resin tackifier. For example, a particular
composition may include, by weight, about 61 to about 65 percent
KRATON.RTM. G-1657 (in one instance, about 63 percent), about 17 to
about 23 percent polyethylene NA 601-04 wax (in one instance, about
20 percent), and about 15 to about 20 percent REGALREZ.TM. 1126 (in
one instance, about 17 percent). The G-1657 is, in particular, a
styrene-ethyl butylene-styrene (S-EB-S) triblock base rubber
polymer.
[0048] In another embodiment, a polymer blend consisting of
approximately 85% A-B-A'-B' tetrablock base rubber polymer (sold as
G1730 by Kraton Products) and 15% polyethylene NA601 wax may be
employed. In this particular instance, the A and A' in the rubber
polymer may be thermoplastic blocks containing a styrene moiety and
B and B' may be elastomeric polymer blocks consisting of
poly(ethylene-propylene).
[0049] In an additional embodiment, a polymer blend consisting of
approximately 80% A-B-A'-B' tetrablock base rubber polymer, 7%
polyethylene NA601 wax, and 13% REGALREZ.TM. 1126 tackifier may be
used. As above, the A and A' in the rubber polymer may be
thermoplastic blocks containing a styrene moiety and B and B' may
be elastomeric polymer blocks consisting of
poly(ethylene-propylene).
[0050] In another embodiment, a polymer blend consisting of
approximately 70% A-B-A'-B' tetrablock base rubber polymer and 30%
polyethylene NA601 wax may be utilized. As above, the A and A' in
the rubber polymer may be thermoplastic blocks containing a styrene
moiety and B and B' may be elastomeric polymer blocks consisting of
poly(ethylene-propylene).
[0051] These various compositions may be utilized to form both the
continuous filaments and the spunbond outer facing(s). However, the
present invention is not limited to these or any particular polymer
or material from which to form the continuous filaments. For
example, various materials, including the following, may be used:
polypropylene, polyethylene, polyesters, polyethylene
terephthalate, polybutane, polymethyidentene, ethylenepropylene
co-polymers, polyamides, tetrablock polymers, styrenic block
copolymers, polyhexamethylene adipamide, poly-(oc-caproamide),
polyhexamethylenesebacamide, polyvinyls, polystyrene,
polyurethanes, thermoplastic polymers, polytrifluorochloroethylene,
ethylene vinyl acetate polymers, polyetheresters, polyurethane,
polyurethane elastomerics, polyamide elastomerics, polyamides,
viscoelastic hot melt pressure sensitive adhesives, cotton, rayon,
hemp and nylon. In addition, such materials may be utilized to
extrude single-constituent, bi-constituent, and bi-component
filaments within the scope of the presently described
invention.
[0052] Other exemplary elastomeric materials that may be used
include polyurethane elastomeric materials such as those available
under the trademark ESTANE from B. F. Goodrich & Co., polyamide
elastomeric materials such as those available under the trademark
PEBAX from the Rilsan Company, and polyester elastomeric materials
such as those available under trade designation HYTREL from E. I.
DuPont De Nemours & Company.
[0053] However, the invention is not limited to only such
elastomeric materials. For example, various latent elastic
materials such as the Arnitel-brand polymers may be utilized to
provide the necessary elasticity characteristics to the continuous
filaments.
[0054] Various extruder dies may be utilized in forming the
continuous filaments. In addition, various processing steps and
parameters may be employed, depending on the characteristics
desired in the final product. For example, the die of the extruder
that forms the continuous filaments may be positioned with respect
to the first roller so that the continuous filaments meet this
first roller at a predetermined angle. The angle between the die
exit of the extruder and the vertical axis (or the horizontal axis
of the first roller, depending on which angle is measured) may be
as little as a few degrees or as much as 90.degree.. Angles such as
about 20.degree., about 35.degree., or about 45.degree. away from
vertical may be utilized.
[0055] The rollers are positioned and operated so as to cause the
continuous filaments to be stretched as they vertically flow
through the bank of rollers. Each successive roller turns in a
direction opposite to the immediately preceding roller so that the
strands of continuous filaments are handed off from roller to
roller. In addition, the speed of each successive roller may be
varied from the preceding roller so as to obtain the desired
stretching and elongation characteristics.
[0056] The number of separate rollers used to convey the continuous
filaments to the bonding location may vary depending on the
particular attributes desired in the final product. In one
particular embodiment, at least four rollers--a first chilled (or
positioning) roller, a second chilled roller, a third unchilled
roller, and a fourth unchilled roller--may be utilized. In certain
embodiments, the rollers may be plasma coated to provide good
release properties. In other embodiments, the rollers may
additionally be grooved or channeled to ensure that the extruded
continuous filaments maintain a proper separation between
individual filaments as the filaments pass over the surface of the
rolls and flow through the system. In some embodiments, smooth
rolls maybe used for one or all of the rolls. After passing through
the chill rollers (either the series or the one or two chill
rollers shown in FIG. 6) and becoming stretched, the continuous
filaments are then conveyed into a position so that a sheet
material may be bonded to the continuous filaments. In other
embodiments, the number of rollers in the series may be
substantially reduced. In fact, only one or two chilled rollers may
be necessary to achieve the products of the present invention.
[0057] In certain embodiments, this sheet material will be less
elastic than the continuous filaments. The sheet material may be
various nonwoven webs such as meltblown webs, spunbond webs, or
carded webs, various woven webs, or a film material. Certain
enhanced properties and production efficiencies, however, arise
from the use of polymeric spunbond nonwoven webs. In one particular
embodiment, a polypropylene spunbond facing having a basis weight
of approximately 0.4 ounces per square yard ("osy") may be
employed.
[0058] The materials utilized to form the continuous filaments may
also be utilized in forming the outer facings of the presently
described laminate. In particular, various webs may be utilized
that are formed from elastomeric or nonelastomeric fibers. Various
polyester elastic materials are, for example, disclosed in U.S.
Pat. No. 4,741,949 to Morman et al., which is incorporated herein
in its entirety by reference thereto. Other useful elastomeric
polymers also include, for example, elastic copolymers of ethylene
and at least one vinyl monomer such as, for example, vinyl
acetates, unsaturated aliphatic monocarboxylic acids, and esters of
such monocarboxylic acids. The elastic copolymers and formation of
elastomeric fibers from these elastic copolymers are disclosed in,
for example, U.S. Pat. No. 4,803,117, which is also incorporated
herein in its entirety by reference thereto.
[0059] The facing(s) of the present invention may be a mixture of
elastic and nonelastic fibers or particulates. For example, U.S.
Pat. No. 4,209,563 is incorporated herein in its entirety by
reference thereto and describes the process by which elastomeric
and nonelastomeric fibers are commingled to form a single coherent
web of randomly dispersed fibers. Another example of such an
elastic composite web is shown in U.S. Pat. No. 4,741,949, which is
also incorporated herein in its entirety by reference thereto
wherein an elastic nonwoven material is described as including a
mixture of meltblown thermoplastic fibers and other materials. The
fibers and other materials may be combined in the forming gas
stream in which the fibers are borne so that an intimate entangled
commingling of fibers and other materials, e.g., wood pulp, staple
fibers or particulates such as, for example, activated charcoal,
clays, starches, or hydrocolloid (hydrogel) particulates, occurs
prior to collection of the fibers upon a collecting device to form
a coherent web of randomly dispersed fibers.
[0060] Various processing aids may also be added to the elastomeric
polymers utilized in the present invention. For example, a
polyolefin may be blended with the elastomeric polymer (e.g., the
A-B-A elastomeric block copolymer) to improve the processability of
the composition. The polyolefin should be one which, when so
blended and subjected to an appropriate combination of elevated
pressure and elevated temperature conditions, is extrudable in
blended form with the elastomeric polymer. Useful blending
polyolefin materials include, for example, polyethylene,
polypropylene and polybutene, including ethylene copolymers,
propylene copolymers and butene copolymers. A particularly useful
polyethylene may be obtained from the U.S.I. Chemical Company under
the trade designation Petrothene NA 601 (also referred to herein as
PE NA 601 or polyethylene NA 601). Two or more of the polyolefins
may be utilized. Extrudable blends of elastomeric polymers and
polyolefins are disclosed in, for example, U.S. Pat. No. 4,663,220,
which is incorporated herein in its entirety by reference
thereto.
[0061] The elastomeric materials that are utilized to form the
melt-spray adhesive and/or the elastomeric filaments may have
sufficient tackiness to enhance the bonding strength of the
laminate by allowing a degree of autogenous bonding. For example,
the elastomeric polymer itself may be tacky when formed into fibers
and/or filaments or, alternatively, a compatible tackifying resin
may be added to the extrudable elastomeric compositions described
above to provide tackified elastomeric fibers and/or filaments that
autogenously bond. Various known tackifying resins and tackified
extrudable elastomeric compositions may be employed, such as those
described in U.S. Pat. No. 4,787,699, which is incorporated herein
in its entirety by reference thereto.
[0062] Any tackifier resin can be used that is compatible with the
elastomeric polymer and can withstand the extrusion processing
conditions. If the elastomeric polymer (e.g., A-B-A elastomeric
block copolymer) is blended with processing aids such as, for
example, polyolefins or extending oils, the tackifier resin should
also be compatible with those processing aids. Generally,
hydrogenated hydrocarbon resins exhibit enhanced temperature
stability and, thus, may be desirable tackifiers. REGALREZ.TM.
hydrocarbon and ARKON.TM. series tackifiers are examples of
hydrogenated hydrocarbon resins. ZONATAK.TM. 501 lite is an example
of a terpene hydrocarbon. REGALREZ.TM. hydrocarbon resins are
available from Hercules Incorporated. ARKON.TM. series resins are
available from Arakawa Chemical (U.S.A.) Incorporated. Of course,
the present invention is not limited to use of such tackifying
resins, and other tackifying resins that are compatible with the
other components of the composition and that can withstand the
processing conditions may also be used.
[0063] The adhesive employed to bond the continuous filaments to
the sheet(s) will be applied to the laminate after the continuous
filaments have been positioned on the sheet(s). The adhesive lines
may be applied by using a stationary spray head capable of forming
the predetermined pattern or by using moving nozzle(s) that are
designed to follow the predetermined pattern path required for the
adhesive line. In addition, one or two, or more, spray heads may be
utilized. Various equipment for applying the adhesive lines of the
present invention may be utilized and the invention is not limited
to any particular apparatus.
[0064] In general, the adhesive bonds anchoring the elastic strands
in the present laminate are regulated per unit area by the
application system such that key properties such as stretch and
elongation can be controlled to precisely match product performance
needs.
[0065] This invention allows for the optimization of the adhesive,
elastomer, and facings in the laminate, thus providing a preferred
match of laminate properties and laminate cost. Laminate properties
that can be more precisely adjusted with this invention include the
softness or drapability of the material--a minimal amount of
adhesive can be utilized to provide a less rigid structure.
Further, the laminate tension characteristics can be better
tailored to product requirements using this invention because the
adhesive bonds can be prescribed and/or predetermined along the
elastic strands. Thus, a minimal number of the adhesive bonds can
be used in certain embodiments to allow more flexibility in the
elastomer. Laminate elongation and retraction properties also may
be designed to meet product needs by controlling the number of
adhesive bonding sites. The level of strand slippage in the
laminate (i.e., the amount that the strands slide between the
facings among bonding sites) may be regulated to meet product needs
by also prescribing the number of adhesive bonding sites. The
amount of laminate bulk may be also be modulated since the
retraction and resulting buckling of the facings can be controlled
due in part to the ability to regulate the number of adhesive bond
sites along the elastic strands.
[0066] Adhesives are typically employed in laminates of the type
provided by the present invention because the facing materials and
elastomeric components are constructed of polymers that often do
not readily bond to each other. The use of an external
adhesive-bonding agent, however, rectifies this problem. In
addition, the elastomer utilize to form the continuous filaments
may be pre-compounded with a selective adhesive component that
readily migrates to the surface of the elastic, thus making the
continuous filaments perform more like a sheath-core filament. This
migration to the surface can provide the needed bonding agent while
preserving the elasticity of the elastomer.
[0067] Various types of adhesives may be employed in the present
invention, including those having elastomeric properties such as
Kraton.RTM.-containing adhesives that are available from the
Findley Adhesives Company (known also as Bostik Findley). Among the
various adhesives that may be employed are Findley-brand H2096 and
Findley-brand H2525A.
[0068] In the absence of autogenous bonding, the adhesives may be
used to bond the facings to the strands, and the facings to the
facings. The particular adhesive system utilized may result in a
composite fabric composite with improved texture and drape. Various
adhesives as discussed herein or that are otherwise available may
be employed in the present system. For some products, such as a
coformed stretch-bonded laminate wet wipe, the use of a high melt
flow rate metallocene-catalyzed polyethylene elastomeric resin that
has low tack may be advantageously utilized to provide improved
texture and drape. Because of its low melting temperature, such a
resin is capable of forming a physical interlock when thermally
bonded. That is, the resin can penetrate into porous facings.
[0069] Dow Chemical Company resins having a relatively low density
(between about 0.86 and about 0.88 g/cm.sup.3) may be efficiently
utilized in the adhesive system of the present invention. Other Dow
resins having lower melt flow rates have also demonstrated the
ability to create a physical interlock under thermal bonding
conditions. The resin also could be blended with a tackifier or a
lower melt flow elastomer to produce an optimized adhesive system.
High melt flow elastomers may be suitable as alternate adhesive
systems in the VFL process described herein.
[0070] The system employs nip rolls to apply pressure to the
adhesive-coating facing and the continuous filaments to result in
the necessary lamination. The outer facing is bonded together with
the continuous filaments at a fairly high surface pressure, which
may be between about 20 and about 300 pounds per linear inch
("pli"). A typical bonding pressure may be about 50 pli or about
100 pli.
[0071] The bonder, or nip roll, (sometimes referred to as
"laminator") section of the laminating apparatus performs the
primary stretching on the continuous filaments. The speed ratio of
the bonder or nip rolls relative to the chilled rolls can be
varied, and in most cases is between about 2:1 and 8:1, and in some
approximately 4:1 to 6:1.
[0072] In certain embodiments, one or more additional facings may
be bonded to the other unattached surface of the stretched
continuous filaments so as to achieve a stretchable article wherein
the continuous filaments are sandwiched between at least two outer
facings. Various bonding techniques may be utilized to form this
two-layer/continuous filament laminate. The adhesive line
techniques of the present invention may be employed or known
melt-spray techniques may be employed, depending on the particular
characteristics desired in the final product. The requirement of
the present invention is that at least one of the facings is bonded
to the continuous filaments utilizing the described predetermined
patterns.
[0073] Several patents describe various spray apparatuses and
methods that may be utilized in supplying the meltspray adhesive to
the outer facing(s) or, when desired, to the elastic strands
themselves. For example, the following United States patents
assigned to Illinois Tool Works, Inc. ("ITW") are directed to
various means of spraying or meltblowing fiberized hot melt
adhesive onto a substrate: U.S. Pat. Nos. 5,882,573; 5,902,540;
5,904,298. These patents are incorporated herein in their
entireties by reference thereto. The types of adhesive spray
equipment disclosed in the aforementioned patents are generally
efficient in applying the adhesive onto the nonwoven facings in the
process of this invention. In particular, ITW-brand Dynatec spray
equipment, which is capable of applying about 3 gsm of adhesive at
a run rate of about 1100 fpm, has been used successfully in the
melt-spray adhesive applications contemplated by the present
inventive process.
[0074] After bonding of the facing(s) to the continuous filaments
to form a spunbond/elastomeric continuous filament/spunbond
laminate, the laminate is then allowed to relax and contract to an
unstretched or less stretched, condition. The laminate is then
wound onto a take-up roll via a surface driven winder. The speed
ratio of the winder relative to the bonder rollers results in
relaxation of the stretched continuous filaments and a retraction
of the laminate into a gathered state as the laminate is wound onto
the roll. The contraction of the continuous filaments results in a
gathered, stretchable laminate article where the outer facing(s) is
gathered between the bonding points.
[0075] The overall basis weight of the laminate can vary, but in
some applications is between about 2 and about 4 ounces per square
yard ("osy"). In one particular embodiment, the basis weight is
between about 2.85 and about 3.2 osy.
[0076] FIG. 1 illustrates an exemplary vertically-configured
apparatus 11 for forming the continuous filament/spunbond laminates
of the present invention. An extruder 15 is mounted for extruding
continuous molten filaments 14 downward from a die at a canted
angle onto chilled positioning roller 12. Chilled positioning
roller 12 ensures proper alignment through the remainder of the
system as it spreads the filaments. As the filaments travel over
the surface of chilled positioning roller 12, they are cooled and
solidified as they travel towards and over the chilled surface of
first chilled roller 13. The filaments then travel downward in an
"s-shaped" progression, in this particular embodiment, to second
roller 16 and then across the surface of third roller 17, fourth
roller 18 and into the nip formed by nip roller 19 and nip roller
20.
[0077] The continuous filaments may be combined at the nip with
various types of facings. In the embodiment depicted in FIG. 1, a
first non-woven spunbond facing 22 and second non-woven spunbond
facing 24 are combined on opposing surfaces of the continuous
filaments to form a bonded laminate 25. In some embodiments, only
one facing may be used, and in other embodiments it is possible to
combine the elastic continuous filaments with three, four, or more
layers of facing material.
[0078] Bonding of the facings to the continuous filaments typically
occurs by utilizing an adhesive as described above. The adhesive
may be applied with a stationary spray head 23 that delivers
adhesive to the surface of at least one of the non-woven spunbond
facings in a predetermined adhesive line pattern or may be applied
with a moving adhesive nozzle (not shown) that is guided on the
apparatus to follow the predetermined bonding pattern. As shown in
FIG. 1, stationary spray head 23 may be positioned on the back side
of the point where facing 22 will meet with continuous filaments
14. Nip rollers 19 and 20 may be aligned so that adhesive 50 can be
applied to the continuous filaments 14 and facing 22 as they are
brought together into the laminating nip section. A second
adhesive-applying spray head or nozzle (not shown) may be employed
in some embodiments to provide an adhesive line to the other facing
24 to allow bonding to the other surface of the continuous
filaments.
[0079] Alternatively, the adhesive may be applied to the surface of
the nonwoven sheet material prior to the sheet material being
placed into contact with the continuous filaments. In this
embodiment, the facing carries the adhesive lines until the
continuous filaments are brought into adhering contact at the
adhesive bonding points.
[0080] In another embodiment of the present system, the
aforementioned series of s-wrap rollers may be eliminated as shown
in FIG. 6. In this Figure, as in FIG. 1, an exemplary apparatus is
depicted in order to carry out the above-described process. The VFL
system 111 is vertically configured. An extruder 115 is mounted for
extruding continuous molten filaments 114 downward from a die at a
canted angle onto chilled positioning roller 112. Chilled
positioning roller 112 ensures proper alignment through the
remainder of the system as it spreads the filaments. As the
filaments travel over the surface of chilled positioning roller
112, they are cooled and solidified as they travel towards and over
the chilled surface of chilled roller 113. As in other embodiments,
the filaments then travel downward toward the laminator section of
the system comprising a nip formed by nip roller 119 and nip roller
120, but in this instance, do so without the need for the series of
s-wrap rollers described above. The continuous filaments in this
embodiment may also be combined at the nip with various types of
facings. In the embodiment depicted in FIG. 6, a first non-woven
spunbond facing 122 and a second non-woven spunbond facing 124 are
combined on opposing surfaces of the continuous filaments to form a
bonded laminate 125. The spunbond facings 122 and 124 are provided
to the nip by first outer facing roll 127 and second outer facing
roll 128.
[0081] Bonding of the facings to the continuous filaments is
accomplished in this embodiment by the use of two spray-type
adhesive applicators. A spray head 123 delivers adhesive to the
surface of at least one of the non-woven spunbond facings 122 prior
to compression and lamination at the nip; and a second spray head
152 applies adhesive to the other non-woven spunbond facing
124.
[0082] Take-up roll 21 (shown in FIG. 1) may be employed for
receiving and winding the bonded spunbond/continuous
filament/spunbond laminate 25 for storage.
[0083] FIG. 3A illustrates one exemplary adhesive pattern useful in
the present invention in which the adhesive has been applied to the
elastic filaments with attenuation of the adhesive lines in the
cross-machine direction. Pattern 35 includes adhesive lines 36 and
elastic filaments 30. This pattern utilizes only
adhesive-to-elastic bonds.
[0084] FIG. 3B illustrates another exemplary scrim pattern 38
having adhesive lines 39 applied to elastic strands 30 and the
adhesive lines 39 themselves. This pattern takes advantage of
additional bonding at the adhesive-to-adhesive points. In fact, the
adhesive overlaps itself in a generally perpendicular fashion to
provide greater bonding strength. The bond angle is very high,
approaching 90.degree. at the intersection between the adhesive and
the elastic filaments.
[0085] FIG. 3C illustrates another scrim pattern 41 having adhesive
lines 42 and continuous elastic strands 30. This embodiment
utilizes adhesive-to-adhesive bonding, but not to the extent of the
pattern illustrated in FIG. 3B.
[0086] FIG. 3D illustrates the relatively high bond angle that may
be employed in products produced according to the present
invention. In particular, lay down angle 44 is shown as the angle
formed by the adhesive line 48 and the elastic strand 30.
Adhesive/elastic angle 46 and adhesive/elastic angle 45 are shown
as being less than 90.degree..
[0087] FIG. 4 utilizes an exemplary bonding pattern to conceptually
illustrate the measurement for determining the number of bonds per
unit length on elastic strands or filaments. By employing specified
bonds per unit length, various desirable characteristics can be
obtained.
[0088] FIG. 5A shows another exemplary bonding pattern employing
adhesive-to-adhesive bonding wherein a swirled type of
configuration is employed. FIG. 5B illustrates a more randomized
pattern wherein a large percentage of adhesive lines are in a
perpendicular, or almost perpendicular, orientation to the elastic
filaments. FIG. 5C is another exemplary embodiment of a bonding
pattern having no adhesive-to-adhesive bonds, but numerous
adhesive-to-elastic strand bonds.
[0089] FIG. 5D illustrates another exemplary bonding pattern that
has both adhesive-to-adhesive and adhesive-to-elastic strand bonds.
The configuration shown in FIG. 5D is similar to the design of a
chain-link fence and provides excellent bonding strength.
[0090] The present invention may be better understood by reference
to the Examples below. However, it is to be understood that the
invention is not limited thereto.
EXAMPLE 1
[0091] In this Example, an ITW-brand nozzle having 17 holes per
inch was employed for creating and analyzing various spray pattern
characteristics. In particular, an adhesive polymer melt
(Findley-brand H2525A) was employed at various fiber diameters,
basis weights, and nozzle pressures to determine percent coverage
and orientation (i.e., "anisotropy"). Orientation is the tangent of
the average orientation of the spray pattern. In Table 1, when the
orientation is less than 1.000, then orientation of the adhesive
spray was in the machine direction and when the orientation is more
than 1.000, then orientation of the adhesive spray was in the
cross-machine direction. When the orientation has a value of 1.00,
then the orientation is 45.degree., meaning that the orientation is
neither dominant in the machine direction nor in the cross-machine
direction. In addition, coverage is the ratio of adhesive presence
to no adhesive presence. "%COV" equals 100(standard deviation/mean
of the percent-area histogram), with the smaller % coverage
exhibiting better overlap of the adhesive to form the
adhesive-to-adhesive bonds. "Formation" is the coefficient of
variation for formation. The fiber diameter is the average fiber
size in micro-milliliters.
1TABLE 1 Fiber Basis Diameter, Orientation Formation, % Coverage,
Weight PSI mean (.mu.m) (Tan .theta.) Coverage % Area 3 20 85.4
1.20 33.5 14.2 3 40 53.9 1.18 23.6 16.9 4 40 79.9 1.16 29.5 20.8 3
60 65.1 1.13 16.5 23.7 3 80 55.6 0.89 13.6 23.1
EXAMPLE2
[0092] In this Example, an ITW-brand nozzle having 5 holes per inch
was employed for creating and analyzing various spray pattern
characteristics. In particular, an adhesive polymer melt
(Findley-brand H2525A) was employed as described above at various
fiber diameters, basis weights, and nozzle pressures.
2TABLE 2 Fiber Basis Diameter, Orientation Formation, % Coverage,
Weight PSI mean (.mu.m) (Tan .theta.) Coverage % Area 3 16 139 1.18
41.9 11.9 3 30 120 1.37 34.3 12.2 4 16 152 1.49 27.6 14.6
EXAMPLE 3
[0093] In this Example, an ITW-brand nozzle having 14 holes per
inch was employed for creating and analyzing various spray pattern
characteristics. In particular, an adhesive polymer melt consisting
of Findley-brand H2096 was employed at various fiber diameters,
nozzle pressures, and basis weights as above to determine percent
coverage and orientation. The temperature of the adhesive was
360.degree. F. and the temperature of the air was 420.degree. F.
The height of the nozzle above the laydown materials was 1.25
inches. As with Table 1, when the orientation is less than 1.000,
then orientation of the adhesive spray was in the machine direction
and when the orientation is more than 1.000, then orientation of
the adhesive spray was in the cross-machine direction. In addition,
"%COV" equals 100(standard deviation/mean of the percent-area
histogram), with the smaller % coverage exhibiting better overlap
of the adhesive to form the adhesive-to-adhesive bonds.
[0094] The lines speeds of the various samples were varied. The
first four samples employed a line speed of 500 feet per minute;
the next three samples employed a line speed of 1000 feet per
minute; and the last seven samples employed a line speed of 1500
feet per minute.
3TABLE 3 Fiber Basis Diameter, Orientation Formation, % Coverage,
Weight PSI mean (.mu.m) (Tan .theta.) Coverage % Area 1.5 11 128
1.095 48.1 15.6 1.5 17 116 1.19 37.7 19.6 3.0 11 153 1.439 33.5
24.8 3.0 17 135 1.488 25.7 24.8 1.5 17 134 1.259 37.1 14 3.0 17 157
1.12 37.5 17.6 3.0 17 158 1.425 48.1 18.2 1.5 17 139 0.807 29.4
25.6 1.5 17 129 0.869 36.7 24.8 1.5 23 139 0.996 45.2 14.2 1.5 23
135 1.118 39.3 13.8 3.0 17 160 0.913 34.3 34.4 3.0 17 163 0.944
29.2 33.2 3.0 23 160 1.007 17.8 14.6
[0095] It is understood by one of ordinary skill in the art that
the present discussion is a description of exemplary embodiments
only, and is not intended as limiting the broader aspects of the
present invention, which broader aspects are embodied in the
exemplary constructions. The invention is shown by example in the
appended claims.
* * * * *