U.S. patent application number 11/165408 was filed with the patent office on 2006-12-28 for zoned stretching of a web.
This patent application is currently assigned to 3M Innovative Properties Company. Invention is credited to Byron M. Jackson.
Application Number | 20060288547 11/165408 |
Document ID | / |
Family ID | 37075510 |
Filed Date | 2006-12-28 |
United States Patent
Application |
20060288547 |
Kind Code |
A1 |
Jackson; Byron M. |
December 28, 2006 |
Zoned stretching of a web
Abstract
An apparatus and methods for stretching one or more zones of an
anisotropic web and anisotropic webs including one or more
stretched zones is provided. Each of the stretched zones in the web
is stretched in the cross-web direction, i.e., the direction
transverse to the down-web direction. The stretching can be
performed continuously as the web is advancing through the
apparatus in the down-web direction. The method for stretching an
extensible web in the cross direction generally is practiced on a
substantially continuous, extensible anisotropic web. The cross web
stretching occurs in an orientation zone established by an
orientation unit. The orientation unit moves the web out of the
plane of the web where the web is under tension, but without any
side restraints. The web moves over the orientation unit where the
degree of orientation is proportional to the cross direction
displacement of a portion of the web by the orientation unit. The
anisotropic web has a tensile strength in the downweb direction
greater than the cross direction such that the web is
preferentially displaced in the cross web direction by the
orientation unit. This can be a downweb direction tensile strength
at least 50 percent greater than the cross web direction.
Inventors: |
Jackson; Byron M.; (Forest
Lake, MN) |
Correspondence
Address: |
3M INNOVATIVE PROPERTIES COMPANY
PO BOX 33427
ST. PAUL
MN
55133-3427
US
|
Assignee: |
3M Innovative Properties
Company
|
Family ID: |
37075510 |
Appl. No.: |
11/165408 |
Filed: |
June 23, 2005 |
Current U.S.
Class: |
26/87 |
Current CPC
Class: |
B29C 55/08 20130101 |
Class at
Publication: |
026/087 |
International
Class: |
D06C 3/00 20060101
D06C003/00 |
Claims
1. A method of orienting a web in a cross machine direction
comprising, providing an anisotropic web having a width dimension
and a substantially continuous length dimension, the web having a
strength in the length dimension greater than in the width
dimension placing the web along a downweb web path under tension
less than that needed to elongate the web in the downweb direction,
moving a section of the web in the width dimension out of the web
path with an orientation unit having a diversion device, while
maintaining the web under tension along the downweb web path, so
that at least a section of the web is elongated in the width
dimension.
2. The method of orienting a web in a cross machine direction of
claim 1 wherein the web is unrestrained on either side of an
orientation zone when in the orientation unit.
3. The method of orienting a web in a cross machine direction of
claim 2 wherein the web has a strength in the downweb direction at
least 50 percent greater than in the cross direction.
4. The method of orienting a web in a cross machine direction of
claim 2 wherein the web has a strength in the downweb direction at
least 100 percent greater than in the cross direction.
5. The method of orienting a web in a cross machine direction of
claim 2 wherein the web comprises a nonwoven web or web layer.
6. The method of orienting a web in a cross machine direction of
claim 5 wherein the web is a laminate of an elastic layer and at
least one nonwoven layer.
7. The method of orienting a web in a cross machine direction of
claim 6 wherein the web the elastic layer is a film layer.
8. The method of orienting a web in a cross machine direction of
claim 2, wherein the web has high strength longitudinal zones
defining an orientation zone of relatively lower strength web
wherein the web is preferentially orientated.
9. The method of orienting a web in a cross machine direction of
claim 2 wherein the orientation unit has a degree of diversion of
from 1 to 100 cm.
10. The method of orienting a web in a cross machine direction of
claim 2 wherein the orientation unit has a degree of diversion of
from 5 to 20 cm.
11. The method of orienting a web in a cross machine direction of
claim 2 wherein the orientation unit has a diversion path with an
incline angle, from the start of diversion of the web from the web
path to an apex of the diversions device, of from 5 to 80
degrees.
12. The method of orienting a web in a cross machine direction of
claim 11 wherein the orientation unit has an incline angle of from
20 to 50 degrees.
13. The method of orienting a web in a cross machine direction of
claim 2 wherein the diversion device is a wheel.
14. The method of orienting a web in a cross machine direction of
claim 2 wherein there are multiple orientation units located in the
downweb direction of the web.
15. The method of orienting a web in a cross machine direction of
claim 14 wherein the downweb orientation units are aligned to
orient at least in part the same cross sectional zone of the
web.
16. The method of orienting a web in a cross machine direction of
claim 14 wherein the downweb orientation units are displaced to
orient at least in part different cross sectional zones of the
web.
17. The method of orienting a web in a cross machine direction of
claim 2 wherein there are multiple orientation units located in the
cross web direction of the web.
18. The method of orienting a web in a cross machine direction of
claim 14 wherein the orientation unit diversion device is a wheel
having a variable apex's to provide variable degrees of cross web
orientation in the downweb direction in a single orientation
zone.
19. An apparatus for orienting a web in a cross machine direction
the apparatus comprising, a web path having width dimension and a
tensioning device in the downweb direction, and an orientation unit
on a portion of the web path having a diversion device for
diverting a web out of the web path wherein there are no
restraining devices for holding down opposing sections of the web
on either side of the orientation unit.
20. The apparatus for orienting a web in a cross machine direction
of claim 19 wherein the orientation unit has a degree of diversion
of from 1 to 100 cm.
21. The apparatus for orienting a web in a cross machine direction
of claim 19 wherein the orientation unit has a degree of diversion
of from 5 to 20 cm.
22. The apparatus for orienting a web in a cross machine direction
of claim 19 wherein the orientation unit has a diversion path with
an incline angle, from the start of diversion of a web from the web
path to an apex of the diversions device, of from 5 to 80
degrees.
23. The apparatus for orienting a web in a cross machine direction
of claim 22 wherein the orientation unit has an incline angle of
from 20 to 50 degrees.
24. The apparatus for orienting a web in a cross machine direction
of claim 19 wherein the diversion device is a wheel.
25. The apparatus for orienting a web in a cross machine direction
of claim 19 wherein there are multiple orientation units located in
the downweb direction of the web path.
26. The apparatus for orienting a web in a cross machine direction
of claim 25 wherein the downweb orientation units are aligned along
the web path.
27. The apparatus for orienting a web in a cross machine direction
of claim 25 wherein the downweb orientation units are displaced
along the web path.
28. The apparatus for orienting a web in a cross machine direction
of claim 19 wherein there are multiple orientation units located in
the cross direction of the web path.
29. The apparatus for orienting a web in a cross machine direction
of claim 24 wherein the orientation unit diversion device is a
wheel having a variable apex's to provide variable degrees of cross
web orientation in the downweb direction.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to the field of webs, web
processing methods, and web processing apparatus. More
particularly, the present invention provides apparatus and methods
for stretching one or more zones of a web in the cross-web
direction and webs so stretched.
BACKGROUND
[0002] It is desirable in many instances to stretch a web in the
cross-web direction during processing. For example, webs including
layers of inelastic materials, e.g., nonwoven webs, laminated or
otherwise attached to elastic layers while the elastic is not
extended typically require stretching to impart elasticity to the
web. The web is stretched so that the inelastic layers, or bonds
within the inelastic layer or layers, are broken or otherwise
disrupted allowing the elastic to freely stretch which leaves the
stretched web laminate elastic. Such stretching to impart
elasticity to a web is commonly referred to as "activation" of the
web (with the elasticity of the web being "activated" by the
stretching). Activation can be done in the machine direction of the
web or the cross direction of the web or both. Cross direction
stretching or activation can be performed by a variety of known
methods including, for example, tentering and ring rolling.
[0003] Tentering typically involves grasping the edges of a web and
stretching the web in the cross-web direction while advancing the
web in the down-web direction (i.e., along the length of the web).
Although tentering does provide the ability to vary the amount of
strain induced in the web, it also suffers from a number of
disadvantages. For example, the edges of the web must often be
discarded after tentering due to damage or inconsistent strain in
the web at the edges. Another potential disadvantage is that it may
be difficult or impossible to induce strain into selected portions
or zones of a web using tentering. Further, tentering equipment can
be both costly, complex, and may require significant amounts of
floor space to operate as the web expands in the cross direction
during the process.
[0004] Ring rolling is an alternative to tentering for stretching a
web in the cross direction. Various ring rolling apparatus are
described in, e.g., U.S. Pat. No. 4,223,059 (Schwarz); U.S. Pat.
No. 4,968,313 (Sabee); U.S. Pat. No. 5,143,679 (Weber et al.); U.S.
Pat. No. 5,156,793 (Buell et al.); and U.S. Pat. No. 5,167,897
(Weber). Ring rolling or incremental stretching refers generally to
placing the web between rolls having interengaging teeth. The
engaging teeth stretch the web based generally on the size, number
and pitch of the teeth. Ring rolling can be used to stretch
selected zones in a web and stretch only in the cross direction.
However ring rolling teeth grip the web and this contact of the web
by the ring rolling apparatus can tear the web and undesirably
affect the web's appearance. The amount of strain that can be
induced in a web using ring rolling is limited by the specific ring
rolls used. Adjustment or change in the degree of stretch requires
new ring rolls to be machined. This is of course costly and
inflexible.
SUMMARY OF THE INVENTION
[0005] The present invention provides apparatus and methods for
stretching one or more zones of an anisotropic web and anisotropic
webs including one or more stretched zones. Each of the stretched
zones in the web is stretched in the cross-web direction, i.e., the
direction transverse to the down-web direction. The stretching can
be performed continuously as the web is advancing through the
apparatus in the down-web direction.
[0006] The method for stretching an extensible web in the cross
direction generally is practiced on a substantially continuous,
extensible anisotropic web. The web is traveling in a downweb
direction at a first speed under tension in the web plane. The
extensible anisotropic web has a width and substantially continuous
length in the downweb direction. The cross web stretching occurs in
an orientation zone established by an orientation unit. The
orientation unit moves the web out of the plane of the web where
the web is under tension, but without any side restraints. The web
moves over the orientation unit where the degree of orientation is
proportional to the cross direction displacement of a portion of
the web by the orientation unit. The anisotropic web has a tensile
strength in the downweb direction greater than the cross direction
such that the web is preferentially displaced in the cross web
direction by the orientation unit. This can be a downweb direction
tensile strength at least 50 percent greater than the cross web
direction.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIG. 1 is a schematic view of an apparatus for performing
the invention method of producing the invention webs.
[0008] FIG. 2 is a perspective view of an orientation zone of the
present invention.
[0009] FIG. 3 is a side schematic view of an apparatus for
performing the invention method of producing the invention
webs.
[0010] FIG. 4 is an end view of an orientation diversion wheel used
in the FIGS. 3 and 5 orientation units.
[0011] FIG. 4a is a side view of an alternative diversion
wheel.
[0012] FIG. 5 is an end view of an orientation unit diversion
device of the invention.
[0013] FIG. 6a is a graph showing the tensile to break of activated
and unactivated webs in machine direction and cross machine
direction.
[0014] FIG. 6b is a graph showing the hysteresis properties of
activated and unactivated webs.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0015] As shown in FIG. 1, web 2 is unwound from a supply source 1
which can be a roll of web material. The web 2 tension is
maintained between idler roll 3 and driven rollers 4, which
establishes the speed of the web 2 through the orientation
apparatus 12. Orientation apparatus 12 can include one or more
orientation units 7, 8, and/or 9. Nip rolls 11 can be used at
various locations to ensure that the web maintains a desired flat
profile and desired tension into and out of the orientation
apparatus 12 or between individual orientation units 7, 8, and/or
9. The zone oriented web 10 is then taken over idler rolls 5, if
needed, and collected in a suitable form, such as on a roll 6.
Generally in the above process, the web is traveling in a downweb
direction (z) at a first speed. The stretching occurs in
orientation zones established by the orientation units.
[0016] As shown in FIG. 2, there can be one, or more, orientation
zones 18 formed relative to the web in the cross direction (x).
Each orientation zone 18 is formed by orientation units 15 in
cooperation with the web being oriented. Each of these orientation
zones 18 on the web 2 could be the same or different, and there
could be different degrees of orientation within the zones 18. The
zones could also have a discrete location where orientation levels
rapidly drop or the orientation could gradually taper to zero. This
depends on the orientation unit and the properties of the web being
oriented. Orientation zones could also be arranged downweb of each
other in either an overlapping or nonoverlapping relationship. By
overlapping it is meant that the two downweb spaced orientation
units activate to some significant extent the same crossweb
(x-direction) orientation zone or region of the web sequentially.
Overlapping units operating on the same orientation zone 18 would
allow additional orientation to be imparted to specific regions,
for example at steadily increasing orientation levels to provide
for a gentler incremental stretching of a specific zone or region
in the web.
[0017] As shown in FIG. 2 a single orientation unit 15
preferentially orients within orientation zone 18, where zones 19
are areas where preferably (but not necessarily) little or no
orientation occurs. Although the transition between zones 18 and 19
is shown as fairly sharp it should be understood that this could be
a gradual transition. The nonpreferentually activated zones 19 are
generally where less than 50 percent orientation occurs, preferably
less than 10 percent. To help isolate the orientation to a discrete
orientation zones 18 (having a width W), in the embodiment shown in
FIG. 2 strengthened zones 16 and 17 are provided. These
strengthened zones are characterized in that they have a higher
downweb (direction Z) tensile strength than the rest of the web 2
within orientation zone 18. This higher downweb tensile strength in
strengthened zones 16 and 17 could be 100 percent higher or 200
percent higher or 300 percent higher than in the region between two
adjacent strengthened zones. The higher strength zones 16 and 17
could be provided by selectively calendaring the web in these zones
(under heat and or pressure), laminating additional materials in
these zones, folding the web in these zones, coating the webs in
these zones, or other like methods. These strengthened zones will
tend to isolate the orientation to the orientation zone 18 bounded
by these strengthened zones. With higher strength strengthened
zones this isolation effect generally increases when coupled with
higher tensions being applied to the web 2 in the downweb direction
Z.
[0018] Generally the orientation provided by the orientation units
15 is created preferentially in the cross web direction by the
overall anisotropic strength behavior of the web being oriented and
without any longitudinal side restraints holding the web on either
side of the orientation zone while the web is in the orientation
unit. This anisotropic strength can be due to strengthening zones,
as described above, or by providing the web, or one or more layers
forming the web with anisotropic strength properties such as a
strength in the downweb direction at least 50% greater than the
cross web direction or greater than 100% or 200%. The web 2 being
treated, generally has a significantly higher overall strength in
the downweb direction Z than in the crossweb direction X. This
tends to isolate the orientation induced by the orientation units
15 in the cross web or X direction orientation.
[0019] The overall anisotropic strength behavior of the web can be
created for example by an anisotropic nonwoven web or layer where
the fibers are preferentially oriented in the downweb direction.
This could also be created by a film or film layer that has induced
orientation in the downweb direction, which could be melt induced
orientation or subsequent elongational orientation created by
stretching the film. Elongational orientation can be used with
other types of web or web layers as well. Anisotropic fibrous webs
are described, for example, in U.S. Pat. No. 5,393,599, the
substance of which is incorporated by reference in its entirety,
where fibers are laid down in a carding machine to create a high
ratio of fibers extending in the machine direction verses the cross
direction. The webs described have a tensile strength ratio of at
least 4/1 and up to at least 6/1 or higher. This web can then be
joined to an elastic web, which could be a nonwoven elastic, a
elastic net or a elastic film by hydroentangling, adhesives, heat
bonding, ultrasonic bonding, extrusion bonding or the like. This
laminate could then be joined to other layers such as a
nonanisotropic nonwovens, films or the like and still have
preferential strength properties in the machine direction. Spunbond
webs can also be made anisotropic, for example by drawing the web
in the machine direction during or after web formation or by
directing the fibers downweb during web formation by use of the
directionality of the spinning device, directional air streams or
the orientation and speed of the forming wire, for example.
Anisotropic melt blown webs can be formed, for example, as
described in U.S. Pat. No. 5,366,793 by preferentially directing
the stream of meltblown fibers at an angle to the forming surface
or deflecting the stream of fibers relative to the forming surface.
These anisotropic nonwoven webs could be directly formed onto other
webs or films to directly form a multilayer anisotropic laminate.
Anisotropic films can be formed directly in, for example, the melt
as described in U.S. Pat. No. 6,270,910, the substance of which is
incorporated by reference in its entirety. In this patent
anisotropic behavior is created by use of a discontinuous phase of
a higher strength material in a continuous phase. The discontinuous
phase is aligned in the machine direction by melt shear forces in
the extrusion device and/or by post formation stretching. This
technique can also be used with co-extruded films or films having
included continuous higher strength phases or layers such as
described, for example, in U.S. Pat. Nos. 5,501,675; 5,462,708;
5,354,597 or 5,344,691, the disclosures of which are incorporated
by reference in their entirety. In this case if an elastic layer or
phase is included in the film, higher strength in the machine
direction could be enhanced by stretching the film in the machine
direction. If the film has a continuous elastic layer, heat
treating the stretched film can be used to relax the elastic
material, but retaining the orientation within the elongationally
oriented inelastic material phase or layer. This would result in a
film with elastic properties in the cross direction but high
strength properties in the machine direction.
[0020] The orientation unit 15 has a web diversion device 25 shown
in FIG. 3, which has a profile that directs the web 2 out of a
webpath, in which the web is under tension, in the Y direction. The
webpath need not be straight but could be any form and could wrap
around the diversion device. The degree of diversion from the
overall webpath generally determines the amount of cross
directional stretch that can occur. However the duration of the
diversion and its rate of change from no diversion to the end
diversion (H) also can affect the orientation effect. If the
overall degree of diversion (H) is too high however there will be
greater risk of downweb orientation (Z direction) of the web and
increased risk that the web might break or suffer damage. The
diversion unit can have a profile or create a diversion path that
generally gradually increases to an apex 20 to help decrease the
strain rate and providing for gentler orientation. This diversion
device profile or diversion path increase could have an incline
angle .alpha. of from 1 to 90 degrees, but space limitations would
generally keep this incline angle at from 5 to 80 degrees, or 20 to
50 degrees.
[0021] The diversion device could be any shape or form and could
be, for example, a ramp having a gradual increase to an apex. This
ramp could be a solid stationary tool or be formed by one or more
discrete elements, wheels, rollers or the like. The diversion
device could also be provided as one or more adjacent units, which
could be integral or mechanically isolated units.
[0022] The wheel type diversion device 25, shown in FIGS. 2-5, can
rotate in a preferred embodiment, but could also be stationary. The
wheel 25 could have a land as shown in FIGS. 4 and 5, or could have
a profile in the X direction. The edge 21 of the wheel in contact
with the web preferably is rounded to avoid sharp edges tearing the
web. With a wheel type diversion device, the web material will wrap
around the wheel over some area. This wrap (.gamma.) is determined
by the direction of the web being fed onto the wheel, which is
determined by the position of the nip rolls 11 or feed rolls from
which the web is fed into the diversion device as well as the
take-up rolls onto which the oriented web is fed. This wrap could
be from 5 to 300 degrees or 10 to 90 degrees. As shown in FIG. 3,
the web path z is determined by the diversion device position,
which could be out of plane with the nip rolls 11 and/or the roll
4. The nip rolls 11 (or a driven roll), the diversion device 25 and
the roll 4 could be generally aligned as shown in FIG. 3 to form an
angle (.alpha.) of from 1 to 180 degrees or 30 to 180 degrees. With
a smaller angle (.alpha.) there will be a higher degree of wrap of
the web 2 around the wheel type diversion device 25. The height (H)
of the apex 20 of the diversion device over the web path could be
any value as long as it allows for diversion of the web but
generally would be from 1 to 100 cm, or from 5 to 20 cm, which
determines the degree of diversion.
[0023] FIG. 4a shows an alternative embodiment of a diversion
device wheel 35, where the wheel is noncircular to create regions
that have high degrees of diversion H' and low degrees of diversion
H.degree. to allow for variable degrees of cross web orientation of
the web in the downweb direction in a single orientation zone. This
effect could also be created by eccentrically mounted wheels.
[0024] The extensible web is in a preferred embodiment a laminate
of an elastically extensible web 22 and one or more relatively
inelastic web 23 as shown in FIG. 5. In this case the orientation
apparatus and methods of the present invention can be used to
"activate" zones in a web such that the activated zones exhibit
preferential cross direction elasticity after activation.
Activation is stretching a web such that inelastic layers, or bonds
within the inelastic layer or layers, are broken or otherwise
disrupted, thereby leaving the stretched portion of the web elastic
due to, e.g., the elastic materials or layers located within the
laminate, which recover after the activation stretching. The
inelastic layer or layers which are now broken or otherwise
disrupted do not provide significant resistance to subsequent
elastic extensions of the web. As used herein, an inelastic zone in
a web is "activated" if it has been stretched such that, after
stretching, the stretched zone of the web exhibits at least some
elastic behavior. By elastic behavior, it is meant that, after
stretching of an activated zone, the activated zone returns at
least in part to its relaxed dimension in the absence of any
constraining forces.
[0025] An orientation unit used to stretch portions of a web in
accordance with the invention can be used in-line with other web
processing equipment or easily be placed in an existing
multifunctional line such as a diaper line. For example, the
orientation unit may be located downstream of an apparatus that
may, for example, process a pre-existing web by, e.g., heating,
cooling, calendaring, applying materials to an existing web (e.g.,
laminating a material by heat, ultrasonics, hot melt or pressure
sensitive adhesives), etc. In some instances the apparatus may
manufacture a web (by, e.g., extrusion, spun-bonding, carding, melt
blowing, weaving, laminating a nonwoven or other inelastic web to
an elastic web, etc.) that is then directed as is, or in a
laminated form, into an orientation unit according to the present
invention.
[0026] The orientation unit according to the present invention may
also be located upstream of another processing apparatus that acts
on the web after portions of the web have been stretched according
to the principles of the present invention. For example, apparatus
for slitting, perforating, and/or aperturing the web at one or more
locations or apparatus for laminating materials to the web (e.g.,
such as attaching fastener materials such as hooks) die cutting,
etc. An orientation unit, in accordance with the invention could
easily be placed in an assembly line, such as a diaper assembly
line; to specifically orient or activate certain predetermined
cross direction zones.
EXAMPLES
[0027] The following examples are provided to enhance understanding
of the present invention. The examples are not intended to limit
the scope of the invention.
Test Methods
Tensile Strength/Hysteresis:
[0028] The tensile strength and hysteresis properties of the
elastic/nonwoven laminates were measured. For tensile strength at
break testing, a 50 mm wide by 100 mm long piece of laminate was
mounted in a tensile testing machines (INSTRON Model 55R1122,
available from Instron Corp.) with the upper and lower jaws 40 mm
apart. Line contact jaws were used to minimize slip and breakage in
the jaws. The jaws were then separated at a rate of 51 cm/minute
until sample breakage occurred. The results are shown in FIG. 6a
where each curve represents an average of 2 replicates. FIG. 6a
graphically shows the anisotropic character of the laminate. When
tested in the machine direction, the sample breaks at high tensile
force and low elongation relative to the cross machine direction.
For hysteresis properties a 50 mm wide by 100 mm long piece of
laminate was mounted in a tensile testing machine (INSTRON Model
55R1122, available from the Instron Corp.) with the upper and lower
jaws 40 mm apart. Line contact jaws were used to minimize slip and
breakage in the jaws. The jaws were then separated at a rate of 51
cm/minute until a load of 15 Newtons was recorded. The jaws were
then held stationary for 1 second after which they returned to the
zero elongation position. The jaws were again held stationary for 1
second and then separated at the same rate until a load of 16
Newtons was recorded. The cycle was repeated twice more for a total
of 3 cycles. Two (2) replicates were tested with the results shown
in FIG. 6b. The unstretched laminate was tested as a control and
also the stretched laminate (Example 1) as described below. FIG. 6b
shows that the stretching process resulted in a laminate having
significantly higher extension at a given load as evidenced by
comparing the curves labeled 1', 2' and 3' with the curves labeled
1, 2 and 3. The stretched material also had a significantly flatter
(lower slope) stress-strain (hysteresis) curve than the unstretched
material which is a desirable feature for an elastic material in
many applications.
Example 1
[0029] An elastic/nonwoven laminate web was prepared using the
method disclosed in PCT publication WO 2004/082918.
[0030] A 40 mm diameter twin screw extruder fitted with a gear pump
was used to deliver 75 grams/meter.sup.2 of a molten elastomeric
polymer blend consisting of a styrene-ethylenebutylene-styrene
block copolymer (70%, KRATON G-1657, Kraton Polymers Inc., Houston,
Tex.) and ultra low density polyethylene (30%, Engage 8452, Exxon
Polymers Inc., Houston, Tex.) at a melt temperature of
approximately 246.degree. C. to a die. The die was positioned such
that a film of molten polymer was extruded vertically downward into
the interface region of a heated doctor blade and a cooled forming
roll. The doctor blade was maintained at a temperature of
246.degree. C. and the forming roll was maintained at a temperature
of 30.degree. C. by circulating chilled water through the interior
of the roll. The doctor blade was held against the forming roll
with a pressure of 450 pounds per lineal inch (788 Newtons/lineal
cm).
[0031] Approximately 10 cm in width of the exterior surface of the
forming roll was chemically etched so as to have a series of
elliptically shaped posts arranged around the periphery of the
roll. The posts were 1.6 mm wide and spaced 3.2 mm apart
circumferentially (downweb) around the roll and 5 mm apart axially
(crossweb) along the roll. The height of the posts was 63 microns.
The tops (or lands) of the posts were the same height as the
non-machined outermost areas of the roll such that when the doctor
blade wiped extrudate from the roll, no extrudate was left on the
lands of the posts resulting in an apertured polymeric film 10 cm
in width. The extrudate was transferred from the forming roll to a
lightly bonded high extension carded (HEC) nonwoven polypropylene
substrate (Product FPN 332D) with a basis weight of 27
grams/meter.sup.2 and a width of 22 cm from BBA Nonwovens
(Simpsonville, S.C.) at a nip formed with a conformable backup roll
(a steel core with a rubber cover having a durometer of 75 Shore
A). The core of the backup roll was chilled by circulating water at
a temperature of 5.degree. C. The pressure exerted on the nip
between the forming roll and the backup roll was 14 pounds per
lineal inch (25 Newtons/lineal cm). To enhance the bond between the
extrudate and the nonwoven, the nonwoven was sprayed in a swirl
pattern with a hot melt adhesive (4.5 grams/meter.sup.2, H9388,
Bostik, Wauwatosa, Wis.) across the full width (22 cm) of the
nonwoven. The 10 cm of extrudate was centered onto the 22 cm wide
nonwoven, resulting in approximately 6 cm of outermost edge zones
without elastomer. A second layer (22 cm width) of the same type of
nonwoven, also sprayed with adhesive, was then laminated to the
elastomer side of the previously created laminate using a rubber
roll/steel roll nip, resulting in a 3 layer laminate in the middle
10 cm of the web and a 2 layer laminate in the outermost 6 cm of
the web.
[0032] The laminate was then stretched in the cross-direction using
an apparatus similar to that shown in FIG. 3. Rolls 4 and 11 were
polyurethane rubber coated steel rolls (30 durometer) 6.3 cm in
diameter and 25.4 cm long. The web diversion device was a steel
stretching wheel 25, having a diameter d of 7.6 cm and a thickness
t of 6.4 mm mounted on a 1.6 cm shaft as shown in FIG. 4. The
outermost edge of the wheel was machined as shown in FIG. 4 with a
land `q` of approximately 3.2 mm. The web was positioned such that
the stretching wheel 25 was centered on the elastic containing
region of the laminate. Rolls 4 and 11 were driven rolls and wheel
25 rotated based on web tension only. The web 2 was stretched by
pulling the web over the wheel 25 using a roll 4 speed of 3.7
meter/min and a roll 11 speed of 3.0 meter/min. The 23% overspeed
created a machine direction tension on the web which then
translated into a cross-direction force as the web was pulled down
over the wheel 25. The innermost 2.5 cm of web centered on the
stretching wheel was stretched approximately 250%. The regions of
elastic-containing laminate (approximately 3.8 cm on each side)
immediately adjacent to the region that was draped over the
stretching wheel did not incur as much tension/force and therefore
did not stretch as much.
[0033] As briefly addressed above, the present invention can be
used to process any suitable extensible web, including homogenous
webs, monolayer webs, multilayer webs and composite webs. This
would include assembled articles, which had specific zones or
regions that were extensible.
[0034] The preceding specific embodiments are illustrative of the
practice of the invention. This invention may be suitably practiced
in the absence of any element or item not specifically described in
this document. The complete disclosures of all patents, patent
applications, and publications are incorporated into this document
by reference as if individually incorporated in total.
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