U.S. patent application number 11/429088 was filed with the patent office on 2007-11-08 for method and apparatus for perforating a fibrous web.
This patent application is currently assigned to PGI Polymer, Inc.. Invention is credited to Mou Chung Ngai.
Application Number | 20070256286 11/429088 |
Document ID | / |
Family ID | 38659891 |
Filed Date | 2007-11-08 |
United States Patent
Application |
20070256286 |
Kind Code |
A1 |
Ngai; Mou Chung |
November 8, 2007 |
Method and apparatus for perforating a fibrous web
Abstract
A method and apparatus are disclosed for forming a pattern of
low basis weight regions, such as apertures or perforations, in an
unbonded fibrous web. The present apparatus includes a forming
surface having a pattern of forming elements, with an unbonded web
positioned in operative association with the forming surface.
Differential air pressure is applied to the web so that a pattern
of low basis weight regions is formed corresponding to the pattern
of forming elements. The fibrous web is thereafter removed from the
forming surface, and can be further processed, if desired, such as
by application of binders or other finishes, and can be integrated
with associated components for various end uses, including medical,
industrial, and hygiene applications.
Inventors: |
Ngai; Mou Chung; (Boxmeer,
NL) |
Correspondence
Address: |
WOOD, PHILLIPS, KATZ, CLARK & MORTIMER
500 W. MADISON STREET
SUITE 3800
CHICAGO
IL
60661
US
|
Assignee: |
PGI Polymer, Inc.
|
Family ID: |
38659891 |
Appl. No.: |
11/429088 |
Filed: |
May 5, 2006 |
Current U.S.
Class: |
28/106 ;
28/104 |
Current CPC
Class: |
D04H 1/46 20130101; B26F
1/26 20130101 |
Class at
Publication: |
028/106 ;
028/104 |
International
Class: |
D04H 1/46 20060101
D04H001/46 |
Claims
1. A method of forming a fibrous web with a pattern of low basis
weight regions, comprising the steps of: providing a substantially
continuous fibrous web comprising fibrous and/or filamentary
material; providing a forming surface defining a pattern of forming
elements; directing said fibrous web onto said forming surface;
applying differential air pressure to said web to displace the
material thereof to form a pattern of low basis weight regions in
said web corresponding to said pattern of forming elements of said
forming surface; and removing said fibrous web from said forming
surface.
2. A method of forming a fibrous web in accordance with claim 1,
wherein: said forming surface comprises a forming drum, wherein
said pattern of forming elements comprises a pattern of openings
defined by said drum.
3. A method of forming a fibrous web in accordance with claim 2,
wherein: said directing step includes positioning said fibrous web
on a flexible, foraminous belt, and positioning said web between
said belt and said forming drum.
4. A method of forming a fibrous web in accordance with claim 3,
wherein: said applying step includes drawing a vacuum from within
said drum through said pattern of openings to displace fibrous
material from said web to form said pattern of low basis weight
regions.
5. A method of forming a fibrous web in accordance with claim 4,
wherein: said applying step further includes directing pressurized
air through said foraminous belt and said fibrous web, and into
said pattern of openings of said forming drum.
6. A method of forming a fibrous web in accordance with claim 4,
wherein: said applying step further includes directing pressurized
air from within said forming drum through said pattern of openings
after drawing said vacuum through said pattern of openings.
7. A method of forming a fibrous web in accordance with claim 3,
wherein: said applying step includes directing pressurized air from
within said drum through said pattern of openings to displace
fibrous material from said web to form said pattern of low basis
weight regions.
8. A method of forming a fibrous web in accordance with claim 1,
wherein: said forming surface comprises a foraminous forming drum,
wherein said pattern of forming elements comprises a pattern of
upstanding projections on the periphery of said forming drum, said
applying step including applying differential pressure to said web
of fibrous material by drawing a vacuum from within said drum so
that said web inter-engages said pattern of projections to form
said pattern of low basis weight regions corresponding to said
pattern of projections.
9. A method of forming a fibrous web in accordance with claim 8,
including: providing a cooperating female sleeve positioned in
operative relationship with said forming drum and defining a
pattern of recesses corresponding to said pattern of projections,
so that said projections are received in said recesses with said
fibrous web positioned between said forming drum and female sleeve
to form said pattern of low basis weight regions.
10. A method of forming a fibrous web in accordance with claim 9,
wherein: said applying step further includes directing pressurized
air from within said female sleeve against said fibrous web.
11. A method of forming a fibrous web in accordance with claim 1,
wherein: said forming surface comprises a foraminous belt, and said
pattern of elements comprises a pattern of relatively high-flow
regions defined by said belt, said applying step including
directing air against said fibrous web and through said foraminous
belt to form said pattern of low basis weight regions corresponding
to said pattern of high-flow regions defined by said belt.
12. A method of forming a fibrous web in accordance with claim 11,
wherein: said applying step includes drawing a vacuum through said
foraminous belt.
13. A method of forming a fibrous web in accordance with claim 1,
wherein: said forming surface comprises a foraminous belt, and said
pattern of elements comprises a pattern of relatively low-flow
regions defined by said belt, said applying step including
directing air against said fibrous web and through said foraminous
belt to form said pattern of low basis weight regions corresponding
to said pattern of low-flow regions defined by said belt.
14. A method of forming a fibrous web in accordance with claim 13,
wherein: said low-flow regions defined by said foraminous belt are
substantially impermeable.
15. A method of forming a fibrous web in accordance with claim 13,
wherein: said applying step includes drawing a vacuum through said
foraminous belt.
16. An apparatus for forming a fibrous web with a pattern of low
basis weight regions, comprising: a forming surface defining a
pattern of forming elements; and an arrangement for applying
differential air pressure to a web of fibrous material, comprising
fibrous and/or filamentary material, when said web is positioned on
said forming surface to form a pattern of low basis weight regions
corresponding to said pattern of forming elements.
17. An apparatus for forming a fibrous web in accordance with claim
16, wherein: said forming surface comprises a forming drum, wherein
said pattern of forming elements comprises a pattern of openings
defined by said drum.
18. An apparatus for forming a fibrous web in accordance with claim
17, including: a flexible, foraminous belt positioned in operative
association with said forming drum for positioning said web of
fibrous material between said foraminous belt and said forming
drum.
19. An apparatus for forming a fibrous web in accordance with claim
18, wherein: said arrangement for applying differential air
pressure to said web of fibrous material comprises an arrangement
for drawing a vacuum from within said drum through said pattern of
openings to displace fibrous material from said web to form said
pattern of low basis weight regions.
20. An apparatus for forming a fibrous web in accordance with claim
19, wherein: said arrangement for applying differential fluid
pressure to said web of fibrous material further comprises an
arrangement for directing pressurized air through said foraminous
belt and said web of fibrous material, and into said pattern of
opening in said forming drum.
21. An apparatus for forming a fibrous web in accordance with claim
19, wherein: said arrangement for applying differential air
pressure further includes an arrangement for directing pressurized
air from within said forming drum through said pattern of openings
after drawing said vacuum through said openings.
22. An apparatus for forming a fibrous web in accordance with claim
18, wherein: said arrangement for applying differential air
pressure to said web of fibrous material comprises a arrangement
for directing pressurized air from within said drum through said
pattern of openings to displace fibrous material from said web to
form said pattern of low basis weight regions.
23. An apparatus for forming a fibrous web in accordance with claim
16, wherein: said forming surface comprises a foraminous forming
drum, wherein said pattern of forming elements comprises a pattern
of upstanding projections on the periphery of said forming drum,
said arrangement for applying differential pressure to said web of
fibrous material comprising an arrangement for drawing a vacuum
from within said drum so that said web inter-engages said pattern
of projections to form said pattern of low basis weight regions
corresponding to said pattern of projections.
24. An apparatus for forming a fibrous web in accordance with claim
16, including: a cooperating female sleeve positioned in operative
relationship with said forming drum, and defining a pattern of
recesses corresponding to said pattern of projections, so that said
projections are received in said recesses with said fibrous web
positioned between said forming drum and female sleeve to form said
pattern of low basis weight regions.
25. An apparatus for forming a fibrous web in accordance with claim
24, wherein: said forming surface comprises a foraminous belt, and
said pattern of elements comprises a pattern of relatively
high-flow regions defined by said belt, said arrangement for
applying differential air pressure comprising an arrangement for
directing air pressure against said fibrous web and through said
foraminous belt to form said pattern of low basis weight regions
corresponding to said pattern of high-flow regions defined by said
belt.
26. An apparatus for forming a fibrous web in accordance with claim
24, wherein: said arrangement for applying differential air
pressure further comprises an arrangement for drawing a vacuum
through said foraminous belt.
27. An apparatus for forming a fibrous web in accordance with claim
24, wherein: said forming surface comprises a foraminous belt, and
said pattern of elements comprises a pattern of relatively low-flow
regions defined by said belt, said arrangement for applying
differential air pressure including an arrangement for directing
air against said fibrous web and through said foraminous belt to
form said pattern of low basis weight regions corresponding to said
pattern of low-flow regions defined by said belt.
28. An apparatus for forming a fibrous web in accordance with claim
27, wherein: said low-flow regions defined by said foraminous belt
are substantially impermeable.
29. An apparatus for forming a fibrous web in accordance with claim
27, wherein: said arrangement for applying differential air
pressure further comprises an arrangement for drawing a vacuum
through said foraminous belt.
Description
TECHNICAL FIELD
[0001] The present invention generally relates to a method and
apparatus for perforating, or otherwise forming regions of low
basis weight, in a fibrous web, and more particularly relates to a
method and apparatus for perforating an un-bonded fibrous web
suited for products in medical, industrial, and hygiene
applications.
BACKGROUND OF THE INVENTION
[0002] Perforated nonwoven webs have found use in various
applications where a need exits for the transport of gases and
fluids. Perforations may be imparted to a fibrous web by screens
that have raised portions throughout, as described in U.S. Pat. No.
5,785,697, entitled, "Absorbent Composite Web", issued Jul. 28,
1998 to inventors Trombetta, et al. As fibers are laid down on the
screen the fibers circumscribe the raised portions projecting from
the surface of the screen, apertures are formed within the web.
Depending on the size and three-dimensional shape of the raised
portions projecting from the screen, associated apertures may be of
various shapes and sizes.
[0003] In an alternate perforating method, a forming screen and
transfer surface is employed. The forming screen includes a nob,
which may also take the form of various shapes. The method as
described in U.S. Pat. No. 6,220,999, entitled, "Method And
Apparatus For Forming An Apertured Pad", issued Apr. 24, 2001 to
inventors Kugler, et al., includes a rotatable forming screen
having a series of projections, referred to as "nobs", wherein the
nobs may be re-attachable to the screen by using threaded
fasteners. Material is deposited on the forming screen,
circumscribing the nobs to form an absorbent pad.
[0004] In yet another method for imparting perforations into a
fibrous web includes perforating the web between a pair of
compression rolls. U.S. Pat. No. 5,242,435, entitled, "Highly
Absorbent And Flexible Cellulosic Pulp Fluff Sheet", issued on Sep.
7, 1993 to inventors Murji, et al, discloses a "perf-embossing"
method involving a calendaring station. The fibrous web may be
subjected to various ranges of pressures between two rolls
including teeth to perforate the web. A subsequent step further
embosses the web.
SUMMARY OF THE INVENTION
[0005] The present invention is directed to a method and apparatus
for perforating, or otherwise forming regions of low basis weight,
in an un-bonded fibrous web suited for products in medical,
industrial, and hygiene applications. A method of forming a fibrous
web with a pattern of low basis weight regions in accordance with
the present invention, comprises the steps of providing a
substantially continuous fibrous web comprising fibrous and/or
filamentary material. The method further comprises providing a
forming surface defining a pattern of forming elements, and
directing the fibrous web onto the forming surface. The present
method contemplates applying differential air pressure to the web
to displace material therefrom to form a pattern of low basis
weight regions in the web corresponding to the pattern of forming
elements on the forming surface. Thereafter, the fibrous web is
removed from the forming surface, and can be further processed, if
desired, such as by application of binders or other finishes, and
can be integrated with associated components for end uses.
[0006] In one embodiment of the present invention, the forming
surface is provided in the form of a cylindrical forming drum,
wherein the forming elements comprise a pattern of openings defined
by the drum. In order to direct the fibrous web onto the drum, a
flexible, foraminous belt is provided, with the fibrous web
positioned between the belt and the forming drum.
[0007] Differential air pressure is applied to the web by drawing a
vacuum from within the drum through the pattern of openings, to
thereby displace fibrous material from the web, to form the pattern
of low basis weight regions. In this embodiment, it is further
contemplated that pressurized air can be directed through the
foraminous belt and the fibrous web, and into the pattern of
openings of the forming drum, thus further facilitating formation
of low basis weight regions/perforations in the fibrous web.
[0008] It is additionally contemplated that pressurized air can be
directed from within the forming drum, through the pattern of
openings, after the vacuum has been drawn from within the drum
through the pattern of openings therein. Alternately, this
embodiment can be operated without creating a vacuum within the
drum, but instead by directing pressurized air from within the drum
through the pattern of openings to displace fibrous material from
the web, thereby forming the desired low basis weight regions.
[0009] In an alternate embodiment of the present invention, a
forming surface of the apparatus is provided in the form of a
foraminous forming drum, wherein the pattern of forming elements
comprises a pattern of upstanding projections on the periphery of
the forming drum. Operation of this embodiment contemplates that
differential air pressure is applied to the fibrous web of material
by drawing a vacuum from within the drum so that the fibrous web
inter-engages the pattern of projections, to thereby form the
desired pattern of low basis weight regions/perforations
corresponding to the pattern of projections.
[0010] In one form of this embodiment of the invention, the
apparatus includes a cooperating female sleeve, positioned in
operative association with the forming drum, and defining a pattern
of recesses corresponding to the pattern of projections on the
forming drum. The projections are received in the recesses with the
fibrous web positioned between the forming drum and the female
sleeve, to thereby form the desired pattern of low basis weight
regions/perforations. In this form of the invention, it is
contemplated that pressurized air can be directed from within the
female sleeve against the fibrous web to further facilitate the
desired displacement of material for formation of the desired low
basis weight regions.
[0011] In a further embodiment of the present invention, the
forming surface is provided in the form of a foraminous belt, with
the pattern of forming element comprising a pattern of relatively
high-flow regions defined by the belt. Differential air pressure is
applied to the fibrous web positioned on the belt by directing air
pressure against the fibrous web and through the foraminous belt,
and or by drawing a vacuum through the foraminout belt. In this
fashion, the desired pattern of low basis weight regions,
corresponding to the pattern of high-flow regions defined by the
belt, is formed.
[0012] In an alternate embodiment, the forming surface is provided
in the form of a foraminous belt, with the pattern of forming
elements comprising a pattern of relatively low-flow regions
defined by the belt. After disposition of the fibrous web on the
foraminous belt, air is directed against the web and through the
foraminous belt to form the pattern of low basis weight regions
therein corresponding to the pattern of low-flow regions defined by
the belt. As in the previous embodiment, the step of directing air
pressure against the fibrous web can be provided by drawing a
vacuum through the foraminous belt. In this embodiment, the
low-flow regions defined by the foraminous belt are substantially
impermeable.
[0013] According to the present invention, a perforated web is
formed by controlling airflow through the un-bonded web and
apparatus. The method of making a perforated web is particularly
suited for constructing layered products, such as spunmelt
constructs. Other features and advantages of the present invention
will become readily apparent from the following detailed
description, the accompanying drawings, and the appended
claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 is a diagrammatic view of an apparatus for practicing
the method of the present invention;
[0015] FIG. 2 is a further diagrammatic view of the apparatus shown
in FIG. 1;
[0016] FIG. 3 is a partial, diagrammatic view illustrating a
foraminous forming drum of the apparatus shown in FIGS. 1 and
2;
[0017] FIG. 4 is a diagrammatic view of an alternate form of the
apparatus shown in FIGS. 1-3;
[0018] FIG. 5 is a diagrammatic view of an alternate apparatus for
practicing the method of the present invention;
[0019] FIG. 5a is a view of an aperture-forming projection of the
apparatus shown in FIG. 5; and
[0020] FIGS. 6a and 6b are diagrammatic views illustrating further
embodiments of an apparatus for practicing the method of the
present invention.
DETAILED DESCRIPTION
[0021] The present invention now will be described more fully
hereinafter with reference to the accompanying drawings, in which
preferred embodiments of the invention are shown. This invention
may, however, be embodied in many different forms and should not be
construed as limited to the embodiments set forth herein; rather,
these embodiments are provided so that this disclosure will be
thorough and complete, and will fully convey the scope of the
invention to those skilled in the art. Like numbers refer to like
elements throughout.
[0022] With reference to FIG. 1, therein is illustrated an
apparatus 10 for practicing the method of the present invention,
wherein un-bonded fibrous webs are formed to define perforations or
apertures, or otherwise low basis weight regions. In accordance
with the present invention, the fibrous webs are intended to
encompass those webs formed from natural and/or synthetic fibers,
and/or filamentary elements, such as spunbond filaments. This
embodiment of the present invention is particularly suited for
processing fibrous webs comprised of relatively short fibers,
typically 1-10 millimeters in length, with the present process
contemplating extracting and/or blowing fibers from non-trapped
regions of the fibrous webs, while other portions of the fibrous
webs are retained or trapped in captive relationship between a
foraminous forming belt and an associated foraminous forming drum,
which defines a pattern of openings or perforations. As will be
further described, this pattern of openings or perforations in the
foraminous drum effects formation of a like pattern of low basis
weight regions in the associated fibrous web.
[0023] In accordance with this embodiment of the invention,
apparatus 10 includes an air laying unit 12, which cooperates with
an associated suction box 14 for formation of a fibrous web F on an
associated flexible, foraminous forming belt 16. Forming belt 16 is
preferably of relatively fine mesh, and may be formed from either
metallic or synthetic material. User of synthetic polymeric-type
materials is presently preferred.
[0024] The open surface area of the foraminous bent 16 is
preferably between 15 and 70 percent, with a range of 25-45 percent
presently being preferred. The foraminous belt may have a mesh
count of 5-15 elements per centimeter, with nine elements per
centimeter presently preferred. The foraminous belt may exhibit a
smooth surface, plain weave, or twill, or other weave that
facilitates maximum contact with the associated fibrous web F. This
foraminous belt should exhibit an air permeability on the order of
650-6500 l/m.sup.2/s. Typical suppliers include GKD (Gebr. Kuferath
AG) Type 40565610 or Villforth Kunststof Bonderbelt--Powerflex 4
schaft PES.
[0025] In accordance with the present invention, apparatus 10
further includes a forming surface which defines a pattern of
forming elements, which pattern corresponds to the pattern of low
basis weight regions to be formed in the fibrous web F. In this
embodiment, the forming surface is provided in the form of a
cylindrical foraminous forming drum 18 which defines a pattern of
openings (i.e., apertures or perforations) with the drum
cooperating with the foraminous belt 16 to form the desired pattern
of low basis weight regions in the associated fibrous web F. Drum
18 can be driven by belt 16, or otherwise operated for synchronous
movement therewith.
[0026] The foraminous forming drum 18 can be suitably formed from
metallic or polymeric material, with the drum provided with a wall
thickness from about 1 millimeter to about 10 millimeters,
depending upon the material from which the drum is formed. It is
presently preferred that the thickness be between about 3-6
millimeters. Formation of the drum from screen or perforated
material, or in the form of an image transfer device (ITD) having
an ablated surface, is within the purview of the present
invention.
[0027] The open area of the forming drum 18 depends on the
pattern/desired requirements for the patterned fibrous web which is
being formed. It is contemplated that the open area of the forming
drum can be varied from about 10% to about 75%, with the preferred
open area being from about 25% to about 45%. The drum diameter may
range from about 300 millimeters to about 1500 millimeters, with a
diameter on the order of about 500 millimeters presently being
preferred.
[0028] In accordance with the present invention, fibrous web F is
directed onto the forming surface of forming drum 18, with
differential air pressure applied to the web to displace material
therefrom to form the desired pattern of low basis weight regions
therein. In this embodiment, processing of the fibrous web in this
fashion is facilitated by positioning the fibrous web on the
foraminous belt 16, and thereafter positioning the web between the
belt and the exterior surface of the forming drum 18. Thus, the
forming drum and foraminous belt cooperate to retain the fibrous
web in trapped or captive relationship so that the fibrous web can
be subjected to differential air pressure for effecting formation
of the desired pattern or low basis weight regions.
[0029] In the embodiment of the apparatus illustrated in FIGS. 1-3,
differential air pressure is applied to the fibrous web F by
drawing a vacuum from within forming drum 18 through the pattern of
openings defined in its forming surface, to thereby displace
fibrous material from the web, and form the desired pattern of low
basis weight regions. To this end, a fixed position vacuum head 20
is provided within the forming drum 18. It is presently
contemplated that the vacuum head be fixed to operate over an arc
of 45.degree. within the forming drum 18, but this can be varied
depending upon the desired forming pattern and speed of operation
of the apparatus. The angle of the vacuum head is preferably
positioned such that vacuum is applied to the fibrous web F after
it is held in captive relationship between foraminous belt 16 and
forming head 18. The vacuum drawn by the vacuum head 20 can be
varied to be greater than -150 mbar, and less than -10 mbar,
depending upon the speed, opening of the pattern of openings in the
forming drum 18, the mesh/opening of the restraining foraminous
belt 16, and the setting of the associated diverting plates.
[0030] In this regard, apparatus 10 includes an air diverting plate
22, positioned generally in operative association with the vacuum
head 20, generally at the exterior of foraminous belt 16. The air
diverting plate 22 can be configured in the nature of an adjustable
blind or baffle, including a plurality of adjustable slats whereby
speed and direction of air directed through the foraminous belt 16
and against the fibrous web F can be selectively controlled.
[0031] As illustrated in FIG. 3, apparatus 10 further includes an
arrangement for directing pressurized air from within forming drum
18 through the pattern of openings therein, and against the fibrous
web F. This arrangement includes an air-blowing device 24
positioned within the forming drum, with the preferred arrangement
further including a deflector 26 positioned in operative
association with the blowing device 24 exteriorly of the forming
drum 18.
[0032] The provision of blowing device 24 desirably acts to improve
the clarity of perforations or apertures formed in fibrous web F by
directing pressurized air to the perforated areas after the
application of suction from vacuum head 20. Typically, compressed
air is directed through the blowing device, with the provision of
the blowing device desirably acting to ensure that the perforated
fibrous web F is laying on the foraminous belt 16, thus
facilitating separation of the fibrous web F from the forming drum
18. It is contemplated that blowing device 24 can be operated at a
pressure between about 0.5 bar to about 15 bar, per blowing
element. While the minimum number of blowing elements, or jet
rolls, is one, depending upon the weight of the fibrous web and
desired hole design, a plurality of the jet rolls may be required
to achieve the desired level of aperture clarity. While space
limitations within the foraminous drum 18 can limit the number of
jet rolls of the blowing device, it is presently contemplated that
2-4 of the jet rolls can be provided within the foraminous drum
18.
[0033] Air deflector 26 preferably cooperates with the blowing
device 24, with the deflector exhibiting a diamond-shaped surface
deflector opposite the jet rolls of the blowing device 24. The
deflector is intended to function to maximize the performance of
air directed from the blowing device 24, with the gap of the
deflector to the forming drum 18, the perforated web F, and the
foraminous belt 16 being adjustable to maximize the required effect
of web transfer, hole clarity and/or profile surface around the
fibrous web.
[0034] FIG. 4 illustrates an alternate embodiment of this form of
the present apparatus, wherein a blowing device 24 is positioned
within forming drum 18, with only the compressed air delivered by
the blowing device acting to create the desired low basis weight
regions in the associated fibrous web F. As will be observed, this
embodiment of the present invention does not include an arrangement
for drawing a vacuum from within the forming drum 18, but rather
can include a plurality of nozzles or slots from which air is
delivered, through the pattern of openings in the forming drum 18,
for cooperation with the exterior deflector 26. Thus, this
embodiment of the present invention acts to direct pressurized air
from within the forming drum 18 through the pattern of openings
defined thereby to displace fibrous material from the fibrous web
F, to thereby form the desired pattern of low basis weight regions
(e.g., perforations or apertures) in the fibrous web F.
[0035] With reference to FIG. 5, therein is illustrated an
alternate embodiment for practicing the method of the present
invention, whereby a fibrous web F is provided with a pattern of
low basis weight regions (e.g., apertures, perforations), again by
applying differential air pressure to the web to displace material
to form the desired pattern therein. This embodiment includes a
forming surface in the form of a foraminous forming drum 28,
wherein the forming surface includes a pattern of forming elements
in the form of a pattern of upstanding projections 30 on the
periphery of the forming drum 28. It is contemplated that this form
of apparatus for practicing the present invention is particularly
suited for carded fibrous webs, with fiber lengths from about 10 to
about 100 millimeters, and is also suitable for processing
non-bonded spun-melt webs, and may also be suitable for use in
processing webs formed from short fibers delivered by air-former
systems, or combinations thereof.
[0036] The projections 30 provided about the periphery of
foraminous drum 28 are preferably provided in a generally tapered
configuration, and may be provided with a helical recess 31
machined into the external surface of the projections (see FIG.
5a).
[0037] As the fibrous web F is directed onto the forming surface of
foraminous forming drum 28, differential air pressure is applied
thereto by drawing a vacuum from within the drum by the provision
of a vacuum head 32 positioned within the drum 28. By this
arrangement, the fibrous web interengages the pattern of
projections 30 on the drum to form the desired pattern of low basis
weight regions, especially perforations or projections,
corresponding to the pattern of projections 30.
[0038] In order to ensure the desired clarity of apertured formed
in the fibrous web F, it is presently preferred that this
embodiment of the present apparatus includes a female sleeve 34,
positioned in operative association with the forming drum, and
which cooperates with forming drum 28, such that the fibrous web F
is directed between the forming drum 28 and the female sleeve 34.
The sleeve defines a pattern of recesses or apertures corresponding
to the pattern of projections 30 on the drum 28, such that the
projections are received in the recesses when the fibrous web is
positioned between the forming drum and the female sleeve to form
the desired pattern of low basis weight regions in the form of
apertures or perforations. The provision of the female sleeve 38 is
believed to be particularly desirable for processing relatively
heavy weight staple fiber webs, as well as webs formed from
spun-melt materials. In this regard, it is particularly preferred
to direct pressurized air from within the female sleeve against the
fibrous web, with an air slot 36 provided within the sleeve 34 for
this purpose.
[0039] Features of the embodiment illustrated in FIG. 5 facilitate
its efficient operation for handling fibrous webs of varying
characteristics. The foraminous forming drum 28 may include a
suitable internal supporting frame for the internal circumference
thereof, with the exterior fine mesh screen pre-mounted with the
desired projections 30, preferably in the form of the
afore-described helically-grooved pins. While metallic mesh screen
is presently preferred for this application, it is within the
purview of the present invention that a synthetic polymeric-type
mesh may be employed, or a combination of polymer and
metallic-types. One screen found to be suitable for this
application is type ND 20 from GKD (Gebr. Kufferath AG). The ND 20
screen has a 31 warp by 20 weft with wire thickness of 0.18 mm by
0.205 mm, exhibiting an air permeability of 7400 l/m.sup.2/s.
[0040] As noted, the screen for the foraminous drum can be
pre-mounted with the projections 30, but it is also possible that
the projections can be mounted on the internal supporting frame for
the drum, with the exterior screen provided with openings through
which the pins project. While it is contemplated that the
projections 30 be provided in the form of helically-grooved pins,
as illustrated in FIG. 6a, it will be understood that a similar
effect can be achieved with non-grooved pins.
[0041] In this regard, the pins which provide projections 30 are
designed to have a helical or spiral shape to facilitate the
unbonded fibrous web F to be perforated with clear openings during
processing. In particular, the fibers around the helically-grooved
projections 30 are desirably twisted around during the perforation
process.
[0042] Suitable material for the projections 30 include metallic
and synthetic polymeric materials, or combinations thereof. Because
the fibrous material of the web F is unbonded, it has been found
that forming the projections from synthetic material is presently
preferred, since such materials typically exhibit lower friction
than metallic materials.
[0043] It should be noted that the pins which provide projections
30 on the forming drum 28 can be a combination of different
diameters, with preferred diameters being in the range from about 8
mm to about 25 mm. The projections 30 can protrude to a height from
about 5 mm to about 25 mm, depending on the weight of the unbonded
fibrous web F, with the preferred height being on the order of
about 7 mm to about 12 mm.
[0044] The vacuum head 32 positioned within the foraminous forming
drum 28 can be operated to provide a vacuum level between about
-150 mbar, and about -10 mbar, depending on the speed of operation,
fiber cohesion, types of webs and web weight, fiber length, or
continuous filaments, etc.
[0045] As noted, the provision of female sleeve 34 is particularly
desirable for processing relatively heavy fibrous webs, and webs
formed from melt-spun elements. It is also believed that the
provision of female sleeve 34 can be desirable for processing
lighter weight webs which exhibit good fiber adhesion. The
provision of air slot 36 within the female sleeve 34 facilitates
formation of perforations in the fibrous web, particularly if the
fibrous web is partially positioned on the projections 30, and not
fully seated on the foraminous surface of drum 28.
[0046] In the preferred form, a tension/vacuum transfer roll 38 is
provided upstream of the forming drum 28, and desirably ensures
that sufficient tension is created in the fibrous web to facilitate
the perforation which is effected of the unbonded fibrous web by
the action of the projections 30 on the foraminous forming drum 28.
Roll 38 also desirably acts to facilitate transfer of the fibrous
web F from the associated transfer belt positioned upstream of the
perforation apparatus.
[0047] In the illustrated embodiment, another tension/vacuum roll
40 is provided positioned downstream of the foraminous forming drum
28. This roll facilitates removal of the now-perforated web from
the drum 28, such as for integration with associated components of
a composite structure.
[0048] FIGS. 6a and 6b illustrate a further apparatus for practice
of the present invention, with this embodiment including a forming
surface defining a pattern of forming elements in the form of a
foraminous belt which exhibits regions of relatively high and low
air flow.
[0049] FIG. 6a illustrates an embodiment of a forming surface which
can be formed by integrating two foraminous or mesh belts with each
other so as to form a composite belt structure 42 exhibiting a
pattern of relatively low-flow regions, which pattern corresponds
to the pattern of low basis weight regions to be formed in an
associated fibrous web. To this end, the "dual belt" structure can
be formed by providing a normal fine mesh belt of substantially
continuous configuration, with another fine mesh belt, having
either a finer or coarser mesh, with the second belt including
cut-out regions or openings. The integrated belt structure 42 thus
defines regions of relatively high-flow corresponding to the
cut-out regions of the second mesh belt. In this embodiment,
differential air pressure is applied to the associated fibrous web,
such as by drawing a vacuum through the composite foraminous belt
structure.
[0050] In the embodiment of FIG. 6b, a forming surface in the form
of a foraminous belt 44 is provided with a pattern of forming
elements 46 which comprise a pattern of low-flow regions defined by
the foraminous belt. Formation of this belt is effected by
covering/welding, or otherwise coating the desired pattern on the
foraminous surface of the belt, again with differential air
pressure applied to the associated web such as by drawing a vacuum
through the foraminous belt. In this embodiment, it is contemplated
that the low-flow regions defined by the foraminous belt are
substantially impermeable, such as by securing polymeric elliptical
elements 46 to the foraminous belt. By this arrangement, attendant
to application of differential air pressure to a fibrous web
positioned on the belt, the desired pattern of low basis weight
regions is formed in the web, with the pattern corresponding to the
pattern of low-flow regions of the foraminous belt.
[0051] Fibrous webs exhibiting a pattern of low basis weight
regions formed in accordance with the present invention can be
advantageously employed in a wide variety of applications.
Apertures/perforated areas in cellulose-based carded webs or
air-formed webs, or combinations thereof, are particularly suitable
as a "sandwich" layer in between associated spun-melt
constructions, or as part of a spun-melt construction to provide
absorbent regions, and relatively less absorbent regions, from the
perforated areas, for extra breathability, and dry-feeling comfort
in apparel applications. Such a construction can be particularly
suitable for medical protection articles, such as caps, isolation
gowns, scrub suits, drapes, and the like.
[0052] It will be noted that multi-layered composite constructions
can be provided with non-continuous layers of cellulose-based
fibrous webs positioned between associated spunbond (S) and
meltblown (M) webs. In a construction wherein such a
cellulose-based web is positioned between associated spunbond
layers, a composite structure is provided which is particularly
suited for surgical scrub suits and caps, as well as for
general-purpose applications, in view of the desired enhancement of
wearer comfort provided by the liquid repellant but well-ventilated
properties of the composite construction.
[0053] The provision of a cellulose-based fibrous web formed in
accordance with the present invention in association with plural
spunbond and meltblown layers can be particularly suitable for use
in medical applications, as well as for special industrial
applications where it is desired to reduce static characteristics
is low humidity environments.
[0054] A medical drape material formed from a composite including a
non-continuous cellulose-based web, formed in accordance with the
present invention, positioned in association with meltblown and
spunbond layers can be designed such that a spunbond layer
configured to exhibit hydrophilicity can be positioned next to the
cellulose-based fibrous web formed in accordance with the present
invention.
[0055] Bonded fabrics, with one side exhibiting a profile shape,
made from a combination of layer or layers of a perforated web, and
layer or layers of non-perforated webs, can deliver specific
delayed liquid run-off properties, as can be desirable for
medical-drape fabrics. Bonded fabrics from two or more layers of
perforated webs formed in accordance with the present invention can
be provided with low basis weight, open areas, which are
non-aligned on opposite surfaces, to thus deliver unique features
for application such as wipes, as well as hygiene, medical, and
industrial applications.
[0056] Apertures and perforations formed in spun-melt composite
constructs, before bonding, can also provide unique properties for
medical devices, and applications such as wipes, hygiene products,
and industrial products.
[0057] From the foregoing, it will be observed that numerous
modifications and variations can be effected without departing from
the true spirit and scope of the novel concept of the present
invention. It is to be understood that no limitation with respect
to the specific embodiment illustrated herein is intended or should
be inferred. The disclosure is intended to cover, by the appended
claims, all such modifications as fall within the scope of the
claims.
* * * * *