U.S. patent application number 10/042822 was filed with the patent office on 2002-08-08 for dual-zoned absorbent webs.
Invention is credited to Chen, Fung-Jou, Kamps, Richard Joseph, Lake, Andrew Michael, Lindsay, Jeffrey Dean, Robinson, Mark Louis.
Application Number | 20020107495 10/042822 |
Document ID | / |
Family ID | 27124548 |
Filed Date | 2002-08-08 |
United States Patent
Application |
20020107495 |
Kind Code |
A1 |
Chen, Fung-Jou ; et
al. |
August 8, 2002 |
Dual-zoned absorbent webs
Abstract
A dual-zoned, three-dimensional, resilient absorbent web is
disclosed which is suitable as body-side liner for absorbent
articles such as feminine pads, diapers and the like. When used as
a liner in absorbent articles, the dual-zoned web combines the
advantages of apertured films and soft, nonwoven cover layers in
one structure while still being inherently hydrophilic. The liner
comprises a web of wet-resilient, hydrophilic basesheet having a
three-dimensional topography comprising elevated regions onto which
hydrophobic matter is deposited or printed and a plurality of
spaced apart depressed regions. In a preferred embodiment, the
hydrophobic matter applied to the elevated regions of the basesheet
comprises hydrophobic fibers in a contiguous nonwoven web which has
been apertured or provided with slits or other openings, such that
the apertures or openings overlay a portion of the depressed
regions. The elevated hydrophobic regions enhance dry feel and
promote fluid flow toward the lower hydrophilic regions, which
comprise the exposed depressed regions of the basesheet. The
basesheet is preferably in liquid communication with underlying
absorbent material, most preferably a stabilized airlaid cellulosic
material or compressed stabilized fluff such that the absorbent
material can wick fluid out of the basesheet by capillary action.
When soft, hydrophobic fibers are deposited on the elevated
regions, the liner also has a soft, cloth-like feel in addition to
a dry feel in use.
Inventors: |
Chen, Fung-Jou; (Appleton,
WI) ; Lindsay, Jeffrey Dean; (Appleton, WI) ;
Kamps, Richard Joseph; (Wrightstown, WI) ; Lake,
Andrew Michael; (Combined Locks, WI) ; Robinson, Mark
Louis; (Appleton, WI) |
Correspondence
Address: |
KIMBERLY-CLARK WORLDWIDE, INC.
401 NORTH LAKE STREET
NEENAH
WI
54956
|
Family ID: |
27124548 |
Appl. No.: |
10/042822 |
Filed: |
January 8, 2002 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10042822 |
Jan 8, 2002 |
|
|
|
09353278 |
Jul 14, 1999 |
|
|
|
09353278 |
Jul 14, 1999 |
|
|
|
08997287 |
Dec 23, 1997 |
|
|
|
08997287 |
Dec 23, 1997 |
|
|
|
08821483 |
Mar 21, 1997 |
|
|
|
Current U.S.
Class: |
604/365 ;
604/374 |
Current CPC
Class: |
A61F 2013/5108 20130101;
A61F 13/51121 20130101; D21H 21/16 20130101; D21H 27/02 20130101;
A61F 2013/15284 20130101; A61F 13/51305 20130101; D21H 21/22
20130101; Y10T 428/24273 20150115; Y10T 442/2221 20150401; D04H
1/495 20130101; D04H 1/49 20130101; A61F 13/512 20130101; D21H
21/20 20130101; A61F 2013/4958 20130101; D21F 11/006 20130101; A61F
13/51104 20130101; D04H 1/732 20130101; A61F 13/513 20130101; D21F
11/14 20130101; D21F 11/145 20130101; D21H 25/14 20130101; Y10T
442/2164 20150401; Y10T 156/1023 20150115 |
Class at
Publication: |
604/365 ;
604/374 |
International
Class: |
A61F 013/15; A61F
013/20 |
Claims
We claim:
1. An absorbent web having a dry feel when wet comprising: a) an
inherently hydrophilic basesheet comprising papermaking fibers and
having an upper surface and a lower surface, said upper surface
having elevated and depressed regions; and b) hydrophobic matter
deposited preferentially on the elevated regions of the upper
surface of said basesheet.
2. The absorbent web of claim 1 wherein said basesheet is a
wet-laid tissue sheet.
3. The absorbent web of claim 1 wherein said basesheet is an
airlaid structure.
4. The absorbent web of claim 1 further characterized by a Wet
Springback Ratio of about 0.7 or greater.
5. The absorbent web of claim 1 wherein the hydrophobic matter is
discontiguous.
6. The absorbent web of claim 1 further characterized by a Rewet
value of about 0.65 g or less and a Normalized Rewet value of about
0.6 or less.
7. The absorbent web of claim 1 wherein said basesheet has an
Overall Surface Depth of about 0.2 mm or greater, an In-Plane
Permeability of at least 0.5.times.10.sup.-10 m.sup.2, and a Wet
Compressed Bulk of about 5 cc/g or greater.
8. The absorbent web of claim 1 wherein said hydrophobic matter
comprises synthetic fibers fixedly attached to the upper surface of
said basesheet such that about 50% or less of the surface area of
the basesheet is covered with the synthetic fibers.
9. The absorbent web of claim 1 further comprising hydrophobic
matter on a portion of the lower surface of said basesheet.
10. The absorbent web of claim 1 wherein said web has an Overall
Surface Depth of about 0.2 mm or less while dry and an Overall
Surface Depth of about 0.3 mm or greater when wetted to a moisture
content of 100%.
11. The absorbent web of claim 1 wherein said basesheet has a
wet:dry tensile ratio of at least 0.1.
12. The absorbent web of claim 1 wherein said elevated regions
comprise from 5 to 300 protrusions per square inch having a
characteristic height of at least 0.2 mm relative to said depressed
regions.
13. The absorbent web of claim 1 wherein at least 30% of the upper
surface of said basesheet remains substantially free of hydrophobic
matter and said web has a Rewet value of 0.6 g or less.
14. The absorbent web of claim 1 wherein essentially all of said
hydrophobic matter resides above the 50% material line of a
characteristic cross-section of said web.
15. The absorbent web of claim 1 further comprising superabsorbent
particles attached to said basesheet.
16. An absorbent dual-zoned web providing a dry feel in use, said
web having an upper surface comprising a plurality of
hydrophobically treated regions surrounded by inherently
hydrophilic cellulosic regions, wherein upon wetting said web
expands such that the hydrophobically treated regions are
preferentially elevated relative to said hydrophilic regions.
17. A calendered hand towel comprising the web of claim 16.
18. An absorbent web having a Rewet value of about 1 g or less,
comprising: a) an inherently hydrophilic basesheet comprising
papermaking fibers and having an upper surface and a lower surface,
said upper surface having elevated and depressed regions with an
Overall Surface Depth of 0.2 mm or greater in the uncalendered and
uncreped state, said basesheet further having a Wet Compressed Bulk
of at least 6 cc/g; and b) hydrophobic matter deposited
preferentially on the elevated regions of the upper surface of said
basesheet.
19. The absorbent web of claim 18 wherein said basesheet is an
airlaid structure.
20. An absorbent article comprising the absorbent web of claim
18.
21. An absorbent web having a dry feel when wet, comprising: a) an
inherently hydrophilic basesheet comprising papermaking fibers and
having an upper surface and a lower surface, said upper surface
having elevated and depressed regions with an Overall Surface Depth
of about 0.2 mm or greater; b) a substantially contiguous network
of hydrophobic fibers having a plurality of macroscopic openings
attached to the upper surface of said basesheet such that a portion
of the depressed regions of the basesheet are aligned with openings
in the overlaying network of hydrophobic fibers to allow body
exudates to pass through the macroscopic openings into the
basesheet.
22. The absorbent web of claim 21 wherein said network of
hydrophobic fibers comprises a plurality of macroscopic openings
having a characteristic width of about 0.2 mm or greater.
23. The absorbent web of claim 21 wherein said basesheet is further
characterized by a wet:dry tensile strength ratio of at least about
0.1 or greater and a Wet Springback Ratio of about 0.55 or
greater.
24. The absorbent web of claim 21 further characterized by a Rewet
value of about 0.65 g or less and a Normalized Rewet value of about
0.6 or less, said basesheet further comprising about 20% or greater
by weight high yield pulp fibers.
25. The absorbent web of claim 21, wherein the superficial basis
weight of said hydrophobic matter is from about 1 to about 10 gsm
and said basesheet has a basis weight of from about 10 to about 70
gsm.
26. The absorbent web of claim 21 wherein said basesheet is an
airlaid structure.
27. The absorbent web of claim 21 wherein said basesheet is a
wet-laid web.
28. The absorbent web of claim 1 or 21, wherein said basesheet
further comprises apertures and said lower surface of the basesheet
further comprises wet-resilient protrusions adjacent said
apertures.
29. An absorbent web having a dry feel when wet, comprising: a) an
inherently hydrophilic basesheet comprising papermaking fibers and
having an upper surface and a lower surface, said upper surface
having elevated and depressed regions, said basesheet further
having a wet:dry tensile ratio of at least 0.1; and b) a contiguous
network of hydrophobic matter deposited preferentially on the
elevated regions of the upper surface of said basesheet.
30. An absorbent article with a body-side liner comprising the web
of either claim 21 or claim 29.
31. An absorbent article comprising a liquid impermeable backsheet,
a cellulosic absorbent core in superposed relation with said
backsheet, and a liquid permeable absorbent web, said absorbent web
comprising an inherently hydrophilic basesheet comprising
papermaking fibers, said basesheet having an upper surface and a
lower surface, said upper surface having elevated and depressed
regions, further comprising an apertured contiguous web of
hydrophobic nonwoven material attached to the upper surface of the
basesheet such that a portion of said apertures overlay the
depressed regions of the basesheet, wherein the basesheet is
superposed on the absorbent core with the lower surface of the
basesheet facing the absorbent core.
32. An absorbent article comprising a liquid impermeable backsheet,
a cellulosic absorbent core in superposed relation with said
backsheet, and a liquid permeable absorbent web, said absorbent web
comprising an inherently hydrophilic basesheet comprising
papermaking fibers and having a wet:dry tensile ratio of at least
0.1, said basesheet having an upper surface and a lower surface,
said upper surface having elevated and depressed regions and
hydrophobic matter deposited preferentially on the elevated
regions, wherein the basesheet is superposed on the absorbent core
with the lower surface of the basesheet facing the absorbent
core.
33. An intake material for an absorbent article comprising an
apertured nonwoven upper layer and a three-dimensional
through-dried lower cellulosic basesheet layer having a pattern of
elevated and depressed regions, wherein the apertures of the upper
layer are substantially registered with depressed regions in the
lower cellulosic layer.
34. The intake material of claim 33, wherein the nonwoven upper
layer is a hydroentangled web of synthetic fibers.
35. An absorbent article comprising the intake material of claim 33
and a densified absorbent material adjacent to the basesheet and
remote from the nonwoven upper layer, wherein said densified
absorbent material has a density greater than the density of the
basesheet.
36. A method for producing an absorbent web having a dry feel when
wet comprising the steps of a) preparing an inherently hydrophilic
basesheet comprising papermaking fibers and having an upper surface
and a lower surface, said upper surface having elevated and
depressed regions; and b) depositing hydrophobic matter
preferentially on the elevated regions of the upper surface of said
basesheet.
37. The method of claim 36, wherein said step of preparing the
basesheet comprises the steps of depositing an aqueous slurry of
papermaking fibers on a foraminous web to produce an embryonic web;
molding said web on a three-dimensional substrate; and drying said
web.
38. A method for producing an absorbent article comprising the
steps of: a) preparing a wet resilient, cellulosic basesheet having
elevated and depressed regions with an Overall Surface Depth of at
least 0.2 mm and having an upper surface and a lower surface; b)
integrally attaching a contiguous, fibrous nonwoven web having a
plurality of openings onto the upper surface of the cellulosic
basesheet such a portion of the openings are superposed over the
depressed regions of the cellulosic basesheet; c) attaching the
lower surface of the basesheet to an absorbent core and an
impervious web, such that the absorbent core is sandwiched between
the impervious web and the basesheet.
39. A method for producing an intake material for an absorbent
article, comprising the steps of a) forming an embryonic paper web
from an aqueous slurry of papermaking fibers; b) through-drying the
embryonic paper web on a three-dimensional through-drying fabric
having a pattern of elevated and depressed regions; c) completing
the drying of the web; d) aperturing a nonwoven web by means of
hydroentangling, wherein the nonwoven web overlays a carrier fabric
having substantially the same pattern of elevated and depressed
regions as the through-drying fabric of step (b); e) joining the
apertured nonwoven web with the through-dried paper web such that
the apertures of the nonwoven web are substantially aligned with
the depressed regions of the through-dried paper web.
Description
BACKGROUND OF THE INVENTION
[0001] Absorbent articles are typically used in contact with skin.
Some absorbent articles such as disposable diapers, feminine pads,
panty liners, incontinence pads and the like are held in contact
with skin to absorb body liquids or exudates, while other absorbent
materials such as paper towels, hand towels, and wipers may be held
in the hands to absorb liquid on the skin or other surfaces. In
virtually every case, it is desired that the absorbent article or
material keep liquids off the skin to provide a clean, dry feel and
to reduce skin health problems that arise from excess hydration or
from contact with harmful biological or chemical materials in the
liquid being absorbed.
[0002] While paper towels and wipers are often composed of a
homogenous material, such as an entirely cellulosic web, absorbent
articles intended to absorb body fluids typically have at least
three layers of different materials. Next to the user's skin is a
topsheet layer, sometimes herein referred to as a liner, body-side
liner or cover sheet. Beneath the topsheet is the absorbent core
that is designed to retain liquid, and beneath the absorbent core
is a fluid-impervious backsheet that prevents leakage and maintains
the integrity of the product. The topsheet should feel soft and
should have high liquid permeability to allow body fluid such as
urine, menses, or runny bowel movement to be absorbed and
transported away from the skin to reach the central absorbent core.
Ideally, the topsheet provides a "dry touch" or "dry feel" by
preventing liquid from flowing back to the skin. It is also
desirable that the topsheets have high wet resiliency to maintain
their bulk and shape when wet.
[0003] Traditional hydrophilic cover materials or topsheets in
contact with the skin can serve effectively to transport body
fluids into the absorbent core, but they cause a wet feel against
the skin of the user and may adversely affect skin health. Further,
they may wick liquid in the plane of the layer, allowing liquid to
approach the edges of the absorbent article and possibly leak or
seep out.
[0004] To achieve the goal of softness and a dry feel in topsheets
of absorbent articles, many manufacturers have turned to nonwoven
fabrics made of hydrophobic fibers for the body-contacting
topsheet. While the use of hydrophobic nonwoven fabrics may have
resulted in improved dry feel, the hydrophobic material hinders
wicking into the absorbent core, offers little absorbent capacity
and reduces liquid permeability. Further, the poor absorbency of
most hydrophobic materials causes any liquid retained therein to be
easily squeezed out by body motion of the wearer.
[0005] Others have sought to improve the poor wicking and absorbent
properties of hydrophobic materials by applying a finish comprising
surfactants on the surface of the hydrophobic fibers. This approach
may offer some benefits when the article is first wetted, but the
surfactants tend to be washed away, resulting in poorer performance
upon further wetting.
[0006] In the case of absorbent pads for feminine care, two
distinct approaches involving hydrophobic topsheets or covers are
common. One approach is to use a soft, cloth-like nonwoven
hydrophobic material, which increases comfort but has the drawback
of poor intake of menses. Another approach is to use an apertured
plastic film of hydrophobic polymer or other materials. The
hydrophobic cover material repels many body fluids, while the
apertures allow wicking away from the cover into the absorbent
material beneath.
[0007] In theory, the hydrophobic apertured material should allow
the user's skin to remain relatively dry while allowing wicking in
the z-direction (normal to the plane of the cover) into the
underlying absorbent core. In practice, hydrophobic apertured films
present a number of problems. Apertured films have the drawback of
being disliked by some users for their plastic feel and for their
poor absorbency. Their hydrophobic nature resists transport through
the material, possibly delaying wicking into the absorbent core.
Likewise, pockets or pools of liquid may form between the film and
the user's skin. In the absence of hydraulic pressure or physical
compression, menses in particular may pool on the hydrophobic
surface and not penetrate into the apertures, especially if there
is a significant interfacial gap between the cover and the
underlying absorbent material.
[0008] Therefore there is a need for an improved topsheet material
which provides the clean feel said to be characteristic of
hydrophobic topsheet materials, while also providing for rapid
z-direction (depthwise) transport of liquid through the topsheet
into the underlying absorbent core, a characteristic more typical
of hydrophilic materials. Preferably, these absorbent topsheets
also have wet resiliency and absorbency properties which persist
upon multiple insults of urine or other liquids.
SUMMARY OF THE INVENTION
[0009] The present invention pertains to composite, resilient
materials that offer the once-thought mutually exclusive benefits
of high absorbency and a clean, dry feel when used as
skin-contacting layers that absorb body fluids or other
liquids.
[0010] In copending U.S. application, Ser. No. 08/614,420, "Wet
Resilient Webs and Disposable Articles Made Therewith," by F.-J.
Chen et al., herein incorporated by reference, a novel wet-laid
tissue web is taught having unusually high bulk, wet resiliency,
in-plane permeability, and absorbency. The unusual properties of
this material are achieved through a combination of high yield
fibers, wet strength additives, and noncompressive drying of a
molded, three-dimensional structure. The three-dimensional
structure of this material does not collapse readily when wetted
and thus reduces the contact area with the skin when wet,
contributing to a relatively dry feel. It has been found that the
inherently hydrophlic material of this previous invention and
related materials can be made substantially more useful in personal
care articles by the selective addition of hydrophobic material
which can impart increased dry feel and, in some embodiments,
improved softness. With hydrophobic material deposited on the
uppermost, body-contacting regions of the three-dimensional
hydrophilic web, the highest body-contacting regions are made
substantially hydrophobic to increase the sensation of a clean, dry
feel, while a plurality of hydrophilic regions in said web remain
accessible to body fluids, allowing liquids to be wicked away from
the body and into an absorbent medium. Thus, dry feel and high
absorbency are achieved in a single unitary layer or in a single
composite structure which may be a laminate of hydrophobic and
hydrophilic materials. The hydrophobic material is bonded or
integrally attached to the basesheet. Improved disposable absorbent
articles comprising such materials include feminine pads and panty
liners, incontinence products such as diapers and liners, bed pads,
disposable diapers, pull-ups or disposable training pants,
disposable menstrual pants, poultry pads, disposable sweat bands or
pads, breast pads, odor absorbing pads for shoes, towels,
moisturized wipes, wipers, medical pads, bandages and sterile pads
for wounds, disposable garments, liners for helmets or other
protective or athletic gear, pads for use in waxing automobiles and
other surfaces, and so forth. A simple example of an absorbent
article containing a topsheet, absorbent core and a backsheet is
illustrated in U.S. Pat. No. 3,809,089 issued May 7, 1974 to
Hedstrom et al., which is hereby incorporated by reference.
[0011] In general, it has been discovered that the addition of
hydrophobic agents or materials on relatively elevated portions of
one surface of a three-dimensional, wet resilient fibrous web, said
web predominantly comprising intrinsically hydrophilic fibers, can
enhance the suitability of such webs for use in absorbent articles
by reducing the amount of fluid that can remain in contact with the
skin or flow back to the skin during use as an absorbent article,
thus resulting in an improved dry feel. Certain hydrophobic
materials such as short fine synthetic fibers can provide a
pleasant soft, fuzzy, and dry feel, while others such as
hydrophobic resins, gels, emulsions, waxes, or liquids can increase
the apparent smoothness or lubricity of the surface and improve the
tactile properties.
[0012] Suitable basesheets can be prepared from aqueous slurries of
papermaking fibers with known papermaking techniques. The fibers
may be derived from wood or other sources of cellulose and
preferably containing a portion of high yield or other wet
resilient pulp fibers and an effective amount of wet strength
agents. The basesheet can be textured by through-drying on a
three-dimensional fabric or other means known in the art and
preferably non-compressively dried to give a three-dimensional
structure. The inherent stiffness of wet resilient pulp fibers may
be reduced, if desired, by incorporation of a suitable plasticizer
such as glycerol or by mechanical treatment such as microstraining,
dry creping, or calendering.
[0013] Through-drying fabrics well suited for formation of
three-dimensional webs are disclosed in U.S. Pat. No. 5,429,686,
issued to Chiu et al., "Apparatus for Making Soft Tissue Products,"
issued Jul. 4, 1995, herein incorporated by reference. Other
methods such as wet molding, forming on three-dimensional forming
fabrics, drying on nonwoven substrates, rush transfer onto
embossing fabrics, embossing, stamping, and so forth may be used to
create useful three-dimensional structures. The basesheet may be
formed as a unitary multilayer structure in which various plies are
well bonded and intimately connected to each other. Unitary
multilayer basesheets may be formed using layered or stratified
headboxes in which two or more furnishes are provided into separate
chambers of a headbox, or they may be formed using separate
headboxes by couching the wet webs together prior to drying in
order to allow extensive hydrogen bonding to develop between the
plies during drying, or they may be formed during air-laying by
varying the composition of the fibers and additives imparted to
web. Multilayer sheets allow better control of physical properties
by tailoring the material composition of each layer. For example, a
unitary multilayer basesheet useful for the present invention would
have an upper layer, corresponding to the upper surface of the
basesheet, and at least one remaining layer below said upper layer
and integrally attached thereto, preferably through hydrogen bonds
formed between cellulosic fibers during drying, wherein said upper
layer differs from at least one remaining layer of the basesheet in
terms of material composition. The difference in material
composition may be due to differences in fiber species (for
example, percentage of hardwood versus softwood); fiber length;
fiber yield; fiber treatment with processes which change fiber
morphology or chemistry such as mechanical refining, fiber
fractionation, dispersing to impart curl, steam explosion,
enzymatic treatment, chemical crosslinking, ozonation, bleaching,
lumen loading with fillers or other chemical agents, supercritical
fluid treatment, including supercritical fluid extraction of agents
in the fiber or supercritical fluid deposition of solutes on and
into the cell wall, and the like. The difference in material
composition between the upper layer and at least one other layer in
the basesheet also may be due to differences in added chemicals,
including the type, nature, or dosage of added chemicals. The
chemicals added differentially to at least one layer of the web may
include debonding agents, anti- bacterial agents, wet strength
resins, starches, proteins, superabsorbent particles, fiber
plasticizers such as glycols, colorants, opacifiers, surfactants,
zinc oxide, baking soda, silicone compounds, zeolites, activated
carbon, and the like. In a preferred embodiment, the basesheet
structure has a wet resilient, noncompressively dried lower layer,
preferably composed of softwood fibers, preferably including at
least 10% of high yield fiber such as spruce BCTMP, and a soft
upper layer containing a portion of finer fibers such as chemically
pulped hardwoods. The multilayer basesheet structure is unitary,
meaning that the two layers are intimately connected or bonded
together. For example, a two-layer unitary basesheet could be
formed with a layered headbox or by couching together two wet
sheets prior to drying to form intimate contact and hydrogen
bonding between the two layers.
[0014] The portion of the surface area treated with hydrophobic
materials should be great enough to provide an effective
improvement in comfort, which will in part depend on the specific
product. Accordingly, the fraction of the basesheet surface covered
by hydrophobic material can be about 5% or greater, more
specifically about 10% or greater, more specifically about 20% or
greater, more specifically about 30% or greater, and still more
specifically from about 40% to about 75%. The portion of the
surface area of the basesheet that remains essentially hydrophilic
can be about 10% or greater, more specifically about 20% or
greater, more specifically about 30% or greater, more specifically
about 40% or greater, more specifically from about 20% to about
90%, and still more specifically from about 50% to about 90%. For
effective fluid removal, the lateral width of the depressed
hydrophilic regions should be about 0.1 mm or greater, more
specifically about 0.5 mm or greater, and still more specifically
about 1 mm or greater. The spacing between depressed hydrophilic
regions can be about 0.4 mm or greater, more specifically about 0.8
mm or greater, and still more specifically about 1.5 mm or greater.
The minimum width of the elevated regions can be about 0.5 mm or
greater, more specifically about 1 mm or greater, and still more
specifically from about 1 to about 3 mm.
[0015] In one preferred embodiment, the hydrophobic matter
comprises a substantially contiguous network of hydrophobic fibers
having a plurality of macroscopic openings such that a portion of
the depressed regions of the basesheet are aligned with openings in
the overlaying network of hydrophobic fibers to allow body exudates
to pass through the macroscopic openings into the basesheet. A
macroscopic opening is defined as an opening that is large relative
to the intrinsic pore size of the material. In a typical spunbond
or bonded carded web, for example, a macroscopic opening would
appear to the eye to be a deliberately introduced hole or void in
the web rather than a characteristic pore between adjacent fibers,
and specifically could have a characteristic width of about 0.2 mm
or greater, about 0.5 mm or greater, about 1 mm or greater, about 2
mm or greater, about 4 mm or greater, about 6 mm or greater, or
from about 1 mm to about 5 mm. The characteristic width is defined
as 4 times the area of the aperture divided by the perimeter.
[0016] The nonwoven web may be made from synthetic fibers, as is
known in the art, and may be a spunbond web, a meltblown web, a
bonded carded web, or other fibrous nonwoven structures known in
the art. For example, a polyolefin nonwoven web such as a low basis
weight spunbond material could be provided with apertures through
pin aperturing; perf embossing and mechanical stretching of the
web; die punching or stamping to provide apertures or holes in the
web; hydroentangling to impart apertures by rearrangement of the
fibers due to the interaction of water jets with the fibrous web as
it resides on a patterned, textured or three-dimensional substrate
that imparts a pattern to the web; water knives that cut out
desired apertures or holes in the web; laser cutters that cut out
portions of the web; patterned forming techniques, such as air
laying of synthetic fibers on a patterned substrate to impart
macroscopic openings; needle punching with sets of barbed needles
to engage and displace fibers; and other methods known in the art.
Preferably, the openings are provided in a regular pattern over at
least a portion of the topsheet of the absorbent article.
[0017] Preferably, the openings in the network of hydrophobic
fibers are spaced and registered with respect to the structure of
the basesheet such that a predetermined fraction of the openings
are largely superposed over depressed regions of the basesheet. An
opening is said to be largely superposed over a depressed region if
at least half of the area of the macroscopic opening resides over a
depressed region of the basesheet. The predetermined fraction of
the openings that are largely superposed over depressed regions can
be about 0.25 of greater, 0.4 or greater, 0.5 or greater, 0.7 or
greater, 0.8 or greater, or from about 0.4 to about 0.85. The
contiguous network of hydrophobic matter is laminated to or
otherwise physically joined with the underlying basesheet.
Preferably, the network of hydrophobic fibers is attached to the
basesheet by means of adhesives and related agents, including hot
melts, latexes, glues, starch, waxes, and the like, which adhere or
join the upper regions of the basesheet with adjacent portions of
the overlaying network of hydrophobic fibers. Preferably, adhesives
are applied only to the most elevated portions of the basesheet to
effect the bonding between the hydrophilic basesheet and the
network of hydrophobic fibers with macroscopic openings therein,
leaving the depressed regions substantially free of adhesives.
Adhesive application can be through meltblown application of hot
melt glues and thermoplastic materials, spray or swirl nozzles of
melted or dissolved adhesives, printing of adhesive material onto
one or both surfaces before joining, and the like. If adhesives are
applied directly to the basesheet by means of spray, mist, aerosol,
or droplets in any form, prior to contact of the basesheet with the
hydrophobic matter, then it is desirable to use a template or
patterned shield to prevent application of adhesive to the
depressed regions of the basesheet and to ensure that adhesives are
preferentially applied to the elevated portions of the
basesheet.
[0018] For improved comfort, the network of hydrophobic fibers use
in the above-mentioned embodiment preferably is one that is
perceived as soft and conformable when next to the skin.
[0019] For optimum efficiency in the embodiment comprising a
nonwoven web, the apertures or openings in the web should be
arrayed in a pattern corresponding to the array of depressed
regions in the tissue basesheet, or should correspond to a subset
of the depressed regions of the basesheet. Applicant have found a
useful means for providing apertures in a nonwoven web in a pattern
which corresponds geometrically to the depressed regions of a
molded, three-dimensional basesheet wherein the basesheet was
molded on a foraminous textured substrate such as a
three-dimensional through-drying fabric. The method involves
hydroentrangling, which is a well known principle involving the use
of high pressure water jets to modify a fibrous surface. Basic
principles of hydroentangling are disclosed by Evans in U.S. Pat.
No. 3,485,706 issued in 1969, and in U.S. Pat. No 3,494,821 issued
in 1970, both of which are herein incorporated by reference.
Hydroentangling, as is known in the art, can be used to impart
apertures to a nonwoven web. In one well known technique, the
nonwoven web is carried on a textured, permeable carrier fabric.
The action of water jets on the nonwoven web as it resides on the
textured fabric causes fibers to be moved away from the elevated
portions of the carrier fabric on which the nonwoven web reside,
resulting in apertures where the carrier fabric was elevated. If a
nonwoven web is placed on the same kind of throughdrying fabric
that was used to mold a three-dimensional through-dried sheet,
preferably an uncreped or only lightly creped sheet in order to
preserve texture in the basesheet, then the high places on the
carrier TAD fabric will become apertured regions in the nonwoven
basesheet. The high portions of the TAD fabric will correspond to
the depressed regions on the fabric side of the through-dried
sheet. Alternatively, if the nonwoven web is hydroentangled against
the backside of a three-dimensional TAD fabric, the elevated
regions of the TAD fabric's backside will generally correspond to
the depressed in the air side of the sheet that is through dried on
the TAD fabric. In either case, a nonwoven web can be created
having apertures that align with the real physical structure of the
TAD fabric, namely, with the depressed regions of a through-dried
sheet. When the apertured nonwoven material is then attached to the
through-dried basesheet, the apertures can be aligned with the
depressed regions of the basesheet using techniques known in the
art, such as photoelectric eyes or high speed CCD cameras which can
view the position of apertures in the nonwoven web relative to the
position of the through-dried fabric as the two are brought
together, whereupon the position of one material can be adjusted
both in the cross-direction and the machine direction (e.g., by
controlling the speed of one layer or by machine direction motion
of an unwind roll of one material) for proper placement of the two
layers together.
[0020] In embodiments comprising contiguous nonwoven webs with
spaced apart openings for fluid access to the hydrophilic
basesheet, Applicants have found excellent fluid intake and
absorbency results when the absorbent web is superposed on a
separate layer of densified fluff pulp or an air laid cellulosic
web, preferably an air laid web stabilized with thermosetting
materials or crosslinking chemistry such as Kymene wet strength
resin. With a densified cellulosic web beneath the basesheet and
hydrophobic matter of the present invention, an insult of fluid
that enters the hydrophilic basesheet can be pulled out of the
hydrophilic basesheet by capillary suction provided that the local
pore size of the underlying absorbent layer is small enough.
Experiments with dyed water and also with an aqueous egg white
mixture have shown that the combination of a hydrophobicly treated
cellulosic basesheet resting on a densified airlaid web can result
in greatly improved intake, with fluid being largely directed into
the air laid material and not spreading significantly laterally in
the basesheet.
[0021] It has also been discovered that highly calendered versions
of such webs are suitable as hand towels. The hydrophobic,
originally uppermost regions are made relatively flat, offering
significant hydrophilic areas initially in contact with the wet
skin for rapid intake of fluid, but also having the ability to
expand after wetting to provide improved dry feel as the wet,
hydrophilic areas retract from the skin relative to the more
hydrophobic, elevated regions. Webs so treated can achieve the once
mutually exclusive goals of having high density for economical
dispensing and low density once wetted for high absorbency, while
also having a dry feel in use.
[0022] Hence, in one aspect, the invention resides in an absorbent
web having a dry feel when wet, comprising: (a) an inherently
hydrophilic basesheet comprising papermaking fibers and having an
upper surface and a lower surface, said upper surface having
elevated and depressed regions; and (b) hydrophobic matter
deposited preferentially on the elevated regions of the upper
surface of said basesheet.
[0023] In another aspect, the invention resides in an absorbent
dual-zoned web providing a dry feel in use, said web having an
upper surface comprising a plurality of hydrophobically treated
regions surrounded by inherently hydrophilic cellulosic regions,
wherein upon wetting said web expands such that the hydrophobically
treated regions are preferentially elevated relative to said
hydrophilic regions.
[0024] In another aspect, the invention resides in an absorbent web
having a Rewet value of about 1 g or less, comprising: (a) an
inherently hydrophilic basesheet comprising papermaking fibers and
having an upper surface and a lower surface, said upper surface
having elevated and depressed regions with an Overall Surface Depth
of 0.2 mm or greater in the uncalendered and uncreped state, said
basesheet further having a Wet Compressed Bulk of at least 6 cc/g;
and (b) hydrophobic matter deposited preferentially on the elevated
regions of the upper surface of said basesheet.
[0025] In another aspect, the invention resides in an absorbent web
having a dry feel when wet, comprising: (a) an inherently
hydrophilic basesheet comprising papermaking fibers and having an
upper surface and a lower surface, said upper surface having
elevated and depressed regions with an Overall Surface Depth of
about 0.2 mm or greater; and (b) a substantially contiguous network
of hydrophobic fibers having a plurality of macroscopic openings
attached to the upper surface of said basesheet such that a portion
of the depressed regions of the basesheet are aligned with openings
in the overlaying network of hydrophobic fibers to allow body
exudates to pass through the macroscopic openings into the
basesheet.
[0026] In another aspect, the invention resides in an absorbent web
having a dry feel when wet, comprising: (a) an inherently
hydrophilic basesheet comprising papermaking fibers and having an
upper surface and a lower surface, said upper surface having
elevated and depressed regions, said basesheet preferably having a
wet:dry tensile ratio of at least 0.1; and (b) a contiguous network
of hydrophobic matter deposited preferentially on the elevated
regions of the upper surface of said basesheet.
[0027] In another aspect, the invention resides in an absorbent
article comprising a liquid impermeable backsheet, a cellulosic
absorbent core in superposed relation with said backsheet, and a
liquid permeable absorbent web, said absorbent web comprising an
inherently hydrophilic basesheet comprising papermaking fibers and
having a wet:dry tensile ratio of at least 0.1, said basesheet
having an upper surface and a lower surface, said upper surface
having elevated and depressed regions and hydrophobic matter
deposited preferentially on the elevated regions, wherein the
basesheet is superposed on the absorbent core with the lower
surface of the basesheet facing the absorbent core.
[0028] In another aspect, the invention resides in an absorbent
article comprising a liquid impermeable backsheet, a cellulosic
absorbent core in superposed relation with said backsheet, and a
liquid permeable absorbent web, said absorbent web comprising an
inherently hydrophilic basesheet comprising papermaking fibers,
said basesheet having an upper surface and a lower surface, said
upper surface having elevated and depressed regions, further
comprising an apertured contiguous web of hydrophobic nonwoven
material attached to the upper surface of the basesheet such that a
portion of said apertures overlay the depressed regions of the
basesheet, wherein the basesheet is superposed on the absorbent
core with the lower surface of the basesheet facing the absorbent
core.
[0029] In another aspect, the invention resides in calendered, low
density structures of previously three-dimensional resilient webs
having hydrophobic matter on the once uppermost regions of one or
both sides of the web. Without limitation, such articles may serve
as suitable hand towels by providing high initial uptake of fluid
by the plurality of hydrophilic regions in the plane of the flat
paper during initial wicking, followed by an enhanced dry feel as
the dry-feeling treated areas rise out of the plane of the sheet
during wetting. The hydrophobic matter in such articles may also be
used to increase the apparent softness or lubricity of the article
and be applied in contiguous or discontiguous forms.
[0030] In another aspect, the invention resides in a method for
producing an intake material for an absorbent article, comprising
the steps of (a) forming an embryonic paper web from an aqueous
slurry of papermaking fibers; (b) through-drying the embryonic
paper web on a three-dimensional through-drying fabric having a
pattern of elevated and depressed regions; (c) completing the
drying of the web; (d) aperturing a nonwoven web by means of
hydroentangling, wherein the nonwoven web overlays a carrier fabric
having substantially the same pattern of elevated and depressed
regions as the through-drying fabric of step (b); and (e) joining
the apertured nonwoven web with the through-dried paper web such
that the apertures of the nonwoven web are substantially aligned
with the depressed regions of the through-dried paper web.
[0031] In stating that hydrophobic matter is preferentially
deposited on elevated portions of the basesheet, the term
"preferentially" implies that more hydrophobic matter is deposited
on the elevated regions rather than in the depressed regions, in
terms of a mass per unit area basis, such that the depressed
regions have a significantly lower amount of hydrophobic matter
present than the elevated regions. It is preferred that the
percentage of the hydrophobic material deposited on the elevated
regions be at least about 60 percent, more specifically at least
about 70 percent, and still more specifically at least about 80
percent of the total amount deposited. The hydrophobic matter can
comprise fine fibers, powders, resins, gels, and other materials,
preferably applied with an average superficial basis weight of less
than 10 gsm, more specifically from about 1 to about 10 gsm. When
used as the skin-contacting layer of absorbent articles, said
absorbent web serves as an absorbent improvement over nonabsorbent,
plastic apertured films or other inherently hydrophobic materials.
The elevated regions of said basesheet preferably comprise between
about 5 and about 300 protrusions per square inch having a height
relative to the plane of the basesheet, as measured in the
uncalendered state, of about 0.1 mm or greater, preferably about
0.2 mm or greater, more preferably about 0.3 mm or greater, and
most preferably from about 0.25 to about 0.6 mm.
[0032] Definition of Terms and Test Procedures
[0033] In describing the webs of this invention and their
fluid-handling characteristics, a number of terms and tests are
used which are described below.
[0034] As used herein, "high yield pulp fibers" are those
papermaking fibers of pulps produced by pulping processes providing
a yield of about 65 percent or greater, more specifically about 75
percent or greater, and still more specifically from about 75 to
about 95 percent. Yield is the resulting amount of processed fiber
expressed as a percentage of the initial wood mass. High yield
pulps include bleached chemithermomechanical pulp (BCTMP),
chemithermomechanical pulp (CTMP) pressure/pressure
thermomechanical pulp (PTMP), thermomechanical pulp (TMP),
thermomechanical chemical pulp (TMCP), high yield sulfite pulps,
and high yield Kraft pulps, all of which contain fibers having high
levels of lignin. The preferred high yield pulp fibers can also be
characterized by being comprised of comparatively whole, relatively
undamaged fibers, having a freeness of 250 Canadian Standard
Freeness (CSF) or greater, more specifically 350 CSF or greater,
and still more specifically 400 CSF or greater, and low fines
content (less than 25 percent, more specifically less than 20
percent, still more specifically less that 15 percent, and still
more specifically less than 10 percent by the Britt jar test). In
addition to common papermaking fibers listed above, high yield pulp
fibers also include other natural fibers such as milkweed seed
floss fibers, abaca, hemp, kenaf, bagasse, cotton and the like.
[0035] As used herein, "wet resilient pulp fibers" are papermaking
fibers selected from the group comprising high-yield fibers,
chemically stiffened fibers and cross-linked fibers. Examples of
chemically stiffened fibers or cross-linked fibers include
mercerized fibers, HBA fibers produced by Weyerhaeuser Corp., and
those such as described in U.S. Pat. No. 3,224,926, "Method of
Forming Cross-linked Cellulosic Fibers and Product Thereof," issued
in 1965 to L. J. Bernardin, and U.S. Pat. No. 3,455,778, "Creped
Tissue Formed From Stiff Cross-linked Fibers and Refined
Papermaking Fibers," issued in 1969 to L. J. Bernardin. Though any
blend of wet resilient pulp fibers can be used, high-yield pulp
fibers are the wet resilient fiber of choice for many embodiments
of the present invention for their low cost and good fluid handling
performance when used according to the principles described
below.
[0036] The amount of high-yield or wet resilient pulp fibers in the
basesheet can be at least about 10 dry weight percent or greater,
more specifically about 15 dry weight percent or greater, more
specifically about 30 dry weight percent or greater, still more
specifically about 50 dry weight percent or greater, and still more
specifically from about 20 to 100 percent. For layered basesheets,
these same amounts can be applied to one or more of the individual
layers. Because wet resilient pulp fibers are generally less soft
than other papermaking fibers, in some applications it is
advantageous to incorporate them into the middle of the final
product, such as placing them in the center layer of a
three-layered basesheet or, in the case of a two-ply product,
placing them in the inwardly-facing layers of each of the two
plies.
[0037] "Water retention value" (WRV) is a measure that can be used
to characterize some fibers useful for purposes of this invention.
WRV is measured by dispersing 0.5 grams of fibers in deionized
water, soaking at least 8 hours, then centrifuging the fibers in a
1.9 inch diameter tube with a 100 mesh screen at the bottom of the
tube at 1000 G for 20 minutes. The samples are weighed, then dried
at 105.degree. C. for two hours and then weighed again. WRV is (wet
weight--dry weight)/dry weight. High yield pulp fibers can have a
WRV of about 0.7 or greater and characteristically have a WRV of
about 1 or greater and preferably from about 1 to about 2.
Low-yield, cross-linked fibers typically have a Water Retention
Value of less than about 1, specifically less than about 0.7 and
more specifically still less than about 0.6.
[0038] "Rewet" is a measure of the amount of liquid water which can
be wicked out of a moistened web into an adjacent dry filter paper
and is intended to estimate the tendency of a moistened web to wet
the skin. The Rewet test is performed by cutting a sample of a
tissue web to a rectangle of dimensions 4 in.times.6 in. The test
is performed in a Tappi conditioned room (50% RH, 73.degree. F.).
The initial air dry weight of the conditioned sample is recorded,
then deionized water is sprayed onto both sides of the tissue
sample to uniformly wet it, bringing the total wet mass of the
tissue to a value of 4 times the previously recorded initial air
dry weight of the sample, thus bringing the "apparent moisture
ratio" of the sample to a value of 3.0 grams (.+-.0.15 g) of added
water per gram of conditioned air dry fiber. The process of
repeatedly spraying and weighing the sample until the proper mass
has been reached should take no more than 2 minutes. Once the
sample is wetted, a single dry Whatman #3 filter, whose mass has
been measured and recorded, is placed on the center of the wet
tissue sample and a load is immediately placed on the filter disk.
The load is a cylindrical disk of aluminum having a diameter of 4.5
inches and a thickness of 1 inch for a mass of 723 g. The aluminum
disk should be centered about the filter disk. The filter paper on
the wet sample remains under load for 20 seconds, at which time the
load and the filter paper are immediately removed. The filter paper
is then weighed, and the additional mass relative to the initial
air dry mass is reported in grams as the Rewet value.
[0039] "Normalized Rewet" is the Rewet value of a sample divided by
the conditioned dry mass of the sample.
[0040] "Absorbency at 0.075 psi" is a measure of basesheet
absorbent capacity under a load of 0.075 psi. The test requires two
metal plates cut to a length of 6 inches and a width of 4 inches. A
lower plate is 0.125-inches thick and the upper plate is 3/4-inch
thick aluminum having a mass of 813 g, which imparts a load of
0.075 psi when placed flat on a tissue sample. The center of the
upper plate has a cylindrical hole 0.25-inches in diameter. To
perform the test, 4-in.times.6-in samples of dry tissue are cut,
with the 6-in length being aligned with the machine direction.
Multiple tissue plies are stacked to achieve a tissue stack weight
as close to 2.8 grams as possible. The tissue stack is placed
between the two horizontal plates, which lie flat in a larger tray.
A titrating burette with 50 ml of deionized water is aligned
directly above the hole in the upper plate. The burette is opened
and water is allowed to slowly enter the hole in the upper plate
such that the hole is filled with a column of water that is
maintained as high as possible without rising above or spilling
onto the upper surface of the plate. This is done until the sample
is apparently saturated. Apparent saturation is the point at which
water begins to leave any edge of the sample. The mass of water
that has been removed from the burette is taken as the value for
"Horizontal Absorbency at 0.075 psi." At that point, the tray
containing the plates is tilted at a 45.degree. angle for 30
seconds to allow some of the liquid in the sample to drain. The
mass of any liquid that drains out is subtracted from the previous
"Horizontal Absorbency at 0.075 psi" value to yield "Tilted
Absorbency at 0.075 psi." For the basesheet, the horizontal
absorbency at 0.075 psi can be about 5 g or greater, or
alternatively 7 g or greater, 9 g or greater, 11 g or greater, or
from about 6 g to about 10 g. The tilted absorbency at 0.075 psi
may be about 4 g or greater, about 6 g or greater, about 8 g or
greater, about 10 g or greater, or from about 6 to about 10 g. The
tilted absorbency of the cover may be about 5 to 40% less than that
off the basesheet alone, while the horizontal absorbency may be
greater or lower than that off the basesheet.
[0041] "Fabric side" of a through-air dried paper web is the side
of the web that was in contact with the through-air dryer fabric
(TAD fabric) during through-drying. Typically the fabric side of a
through-dried sheet offers the most pleasant tactile properties for
contact with skin.
[0042] "Air side" of a through-air dried paper web is the side of
the web that was not in contact with the through-air dryer fabric
(TAD fabric) during through-drying. Typically the air side of a
through-dried sheet feels somewhat more gritty than the fabric side
of the same sheet.
[0043] "Density" can be determined by measuring the caliper of a
single sheet using a TMI tester (Testing Machines, Inc.,
Amityville, N.Y.) with a load of 0.289 psi, e.g., using a TMI Model
49-70 with an enlarged platen. Density is calculated by dividing
the caliper by the basis weight of the sheet. The basesheets useful
for the purposes of this invention can have low, substantially
uniform densities (high bulks), which is preferred for wet laid
structures, or may have a distribution of zones of varying density,
which is preferred in airlaid basesheets. Substantial density
uniformity is attained, for example, by throughdrying to final
dryness without differentially compressing the web. In general, the
density of the basesheets of this invention can be about 0.3 gram
per cubic centimeter (g/cc) or less, more specifically about 0.15
g/cc or less, still more specifically about 0.1 g/cc or less and
can be from about 0.05 to 0.3 g/cc or from about 0.07 to 0.2 g/cc.
It is desirable that the basesheet structure, once formed, be dried
without substantially reducing the number of wet-resilient
interfiber bonds. Throughdrying, which is a common method for
drying tissues and towels, is a preferred method of preserving the
structure. Basesheets made by wet laying followed by throughdrying
typically have a density of about 0.1 gram per cubic centimeter,
whereas airlaid basesheets normally used for diaper fluff typically
have densities of about 0.05 gram per cubic centimeter. All of such
basesheets are within the scope of this invention.
[0044] As used herein, "dry bulk" is measured with a thickness
gauge having a circular platen 3 inches in diameter such that a
pressure of 0.05 psi is applied to the sample, which should be
conditioned at 50% relative humidity and at 73.degree. F. for 24
hours prior to measurement. The basesheet as well as the
uncalendered web can have a dry bulk of 3 cc/g or greater,
preferably 6 cc/g or greater, more preferably 9 cc/g or greater,
more preferably still 11 cc/g or greater, and most preferably
between 8 cc/g and 28 cc/g.
[0045] "Wet strength agents" are materials used to immobilize the
bonds between the fibers in the wet state. Typically the means by
which fibers are held together in paper and tissue products involve
hydrogen bonds and sometimes combinations of hydrogen bonds and
covalent and/or ionic bonds. In the present invention, it is
desirable to provide a material that will allow bonding of fibers
in such a way as to immobilize the fiber to fiber bond points and
make them resistant to disruption in the wet state. In this
instance the wet state usually will mean when the product is
largely saturated with water or other aqueous solutions, but could
also mean significant saturation with body fluids such as urine,
blood, mucus, menses, runny bowel movement, lymph and other body
exudates.
[0046] There are a number of materials commonly used in the paper
industry to impart wet strength to paper and board that are
applicable to this invention. These materials are known in the art
as "wet strength agents" and are commercially available from a wide
variety of sources. Any material that when added to a paper web or
sheet results in providing the sheet with a wet geometric tensile
strength:dry geometric tensile strength ratio in excess of 0.1
will, for purposes of this invention, be termed a wet strength
agent. Typically these materials are termed either as permanent wet
strength agents or as "temporary" wet strength agents. For the
purposes of differentiating permanent from temporary wet strength,
permanent will be defined as those resins which, when incorporated
into paper or tissue products, will provide a product that retains
more than 50% of its original wet strength after exposure to water
for a period of at least five minutes. Temporary wet strength
agents are those which show less than 50% of their original wet
strength after being saturated with water for five minutes. Both,
classes of material find application in the present invention. The
amount of wet strength agent added to the pulp fibers can be at
least about 0.1 dry weight percent, more specifically about 0.2 dry
weight percent or greater, and still more specifically from about
0.1 to about 3 dry weight percent based on the dry weight of the
fibers.
[0047] Permanent wet strength agents will provide a more or less
long-term wet resilience to the structure. In contrast, the
temporary wet strength agents would provide structures that had low
density and high resilience, but would not provide a structure that
had long-term resistance to exposure to water or body fluids. The
mechanism by which the wet strength is generated has little
influence on the products of this invention as long as the
essential property of generating water-resistant bonding at the
fiber/fiber bond points is obtained.
[0048] Suitable permanent wet strength agents are typically water
soluble, cationic oligomeric or polymeric resins that are capable
of either crosslinking with themselves (homocrosslinking) or with
the cellulose or other constituent of the wood fiber. The most
widely-used materials for this purpose are the class of polymer
known as polyamide-polyamine-epichl- orohydrin (PAE) type resins.
These materials have been described in patents issued to Keim (U.S.
Pat. Nos. 3,700,623 and 3,772,076) and are sold by Hercules, Inc.,
Wilmington, Del., as KYMENE 557H. Related materials are marketed by
Henkel Chemical Co., Charlotte, N.C. and Georgia-Pacific Resins,
Inc., Atlanta, Ga.
[0049] Polyamide-epichlorohydrin resins are also useful as bonding
resins in this invention. Materials developed by Monsanto and
marketed under the SANTO RES label are base-activated
polyamide-epichlorohydrin resins that can be used in the present
invention. These materials are described in patents issued to
Petrovich (U.S. Pat. No. 3,885,158; U.S. Pat. No. 3,899,388; U.S.
Pat. No. 4,129,528 and U.S. Pat. No. 4,147,586) and van Eenam (U.S.
Pat. No. 4,222,921). Although they are not as commonly used in
consumer products, polyethylenimine resins are also suitable for
immobilizing the bond points in the products of this invention.
Another class of permanent-type wet strength agents are exemplified
by the aminoplast resins obtained by reaction of formaldehyde with
melamine or urea.
[0050] Suitable temporary wet strength resins include, but are not
limited to, those resins that have been developed by American
Cyanamid and are marketed under the name PAREZ 631 NC (now
available from Cytec Industries, West Paterson, N.J.). This and
similar resins are described in U.S. Pat. Nos. 3,556,932 to Coscia
et al. and 3,556,933 to Williams et al. Other temporary wet
strength agents that should find application in this invention
include modified starches such as those available from National
Starch and marketed as CO-BOND 1000. It is believed that these and
related starches are disclosed in U.S. Pat. No. 4,675,394 to
Solarek et al. Derivatized dialdehyde starches, such as described
in Japanese Kokai Tokkyo Koho JP 03,185,197, may also provide
temporary wet strength. It is also expected that other temporary
wet strength materials such as those described in U.S. Pat. No.
4,981,557; U.S. Pat. No. 5,008,344 and U.S. Pat. No. 5,085,736 to
Bjorkquist would be of use in this invention. With respect to the
classes and the types of wet strength resins listed, it should be
understood that this listing is simply to provide examples and that
this is neither meant to exclude other types of wet strength
resins, nor is it meant to limit the scope of this invention.
[0051] Although wet strength agents as described above find
particular advantage for use in connection with this invention,
other types of bonding agents can also be used to provide the
necessary wet resiliency. They can be applied at the wet end of the
basesheet manufacturing process or applied by spraying or printing,
etc. after the basesheet is formed or after it is dried.
[0052] "Noncompressive drying" refers to drying methods for drying
cellulosic webs that do not involve compressive nips or other steps
causing significant densification or compression of a portion of
the web during the drying process. Such methods include through-air
drying; air jet impingement drying; non-contacting drying such as
air flotation drying, as taught by E. V. Bowden, E. V., Appita J.,
44(1): 41 (1991); through-flow or impingement of superheated steam;
microwave drying and other radiofrequency or dielectric drying
methods, water extraction by supercritical fluids; water extraction
by nonaqueous, low surface tension fluids, infrared drying; drying
by contact with a film of molten metal; and other methods. It is
believed that the three-dimensional basesheets of the present
invention could be dried with any of the above mentioned
noncompressive drying means without causing significant web
densification or a significant loss of their three-dimensional
structure and their wet resiliency properties. Standard dry creping
technology is viewed as a compressive drying method since the web
must be mechanically pressed onto part of the drying surface,
causing significant densification of the regions pressed onto the
heated Yankee cylinder. Technology to noncompressively dewater and
dry tissue webs with an air press and optionally with a Yankee
dryer operated without creping is disclosed in the following
commonly owned copending applications: U.S. patent application Ser.
No. unknown, "Method of Producing Low Density Resilient Webs" by F.
G. Druecke et al., Attorney Docket No. 13,504, filed Oct. 31, 1997;
U.S. patent application Ser. No. unknown, "Low Density Resilient
Webs and Methods of Making Such Web" by S. Chen et al., Attorney
Docket No. 13,381, filed Oct. 31, 1997; U.S. patent application
Ser. No. 08/647,508 filed May 14, 1996 by M. A. Hermans et al.
titled "Method and Apparatus for Making Soft Tissue;" and U.S.
patent application Ser. No. unknown filed Oct. 31, 1997 titled "Air
Press for Dewatering a Wet Web" by F. Hada et al., all of which are
herein incorporated by reference. Also of potential value for the
tissue making operations useful in the present invention is the
paper machine disclosed in U.S. Pat. No. 5,230,776 issued Jul. 27,
1993 to I. A. Andersson et al.; and the capillary dewatering
techniques disclosed in U.S. Pat. Nos. 5,598,643 issued Feb. 4,
1997 and 4,556,450 issued Dec. 3, 1985, both to S. C. Chuang et
al., all of which are incorporated herein by reference. The
dewatering concepts disclosed by J. D. Lindsay in "Displacement
Dewatering to Maintain Bulk," Paperija Puu, 74(3): 232-242 (1992)
are also of potential value.
[0053] As used herein, the "wet:dry ratio" is the ratio of the
geometric mean wet tensile strength divided by the geometric mean
dry tensile strength. Geometric mean tensile strength (GMT) is the
square root of the product of the machine direction tensile
strength and the cross-machine direction tensile strength of the
web. Unless otherwise indicated, the term "tensile strength" means
"geometric mean tensile strength." The basesheets of this invention
preferably have a wet:dry ratio of about 0.1 or greater, more
specifically about 0.15 or greater, more specifically about 0.2 or
greater, still more specifically about 0.3 or greater, and still
more specifically about 0.4 or greater, and still more specifically
from about 0.2 to about 0.6. Tensile strengths can be measured
using an Instron tensile tester using a 3-inch jaw width, a jaw
span of 4 inches, and a crosshead speed of 10 inches per minute
after maintaining the sample under TAPPI conditions for 4 hours
before testing. For enhanced wet resiliency and integrity, the
basesheets of this invention also preferably have a minimum
absolute ratio of dry tensile strength to basis weight of about 1
gram/gsm, preferably from about 2 grams/gsm, more preferably about
5 grams/gsm, more preferably about 10 grams/gsm and still more
preferably about 20 grams/gsm and preferably from about 15 to 50
grams/gsm.
[0054] "Overall Surface Depth". A three-dimensional basesheet or
web is a sheet with significant variation in surface elevation due
to the intrinsic structure of the sheet itself. As used herein,
this elevation difference is expressed as the "Overall Surface
Depth." The basesheets useful for this invention possess
three-dimensionality and have an Overall Surface Depth of about 0.1
mm. or greater, more specifically about 0.3 mm. or greater, still
more specifically about 0.4 mm. or greater, still more specifically
about 0.5 mm. or greater, and still more specifically from about
0.4 to about 0.8 mm.
[0055] The three-dimensional structure of a largely planar sheet
can be described in terms of its surface topography. Rather than
presenting a nearly flat surface, as is typical of conventional
paper, the molded sheets useful in producing the present invention
have significant topographical structures that, in one embodiment,
may derive in part from the use of sculptured through-drying
fabrics such as those taught by Chiu et al. in U.S. Pat. No.
5,429,686, previously incorporated by reference. The resulting
basesheet surface topography typically comprises a regular
repeating unit cell that is typically a parallelogram with sides
between 2 and 20 mm in length. For wetlaid materials, it is
preferred that these three-dimensional basesheet structures be
created by molding the moist sheet or be created prior to drying,
rather than by creping or embossing or other operations after the
sheet has been dried. In this manner, the three-dimensional
basesheet structure is more likely to be well-retained upon
wetting, helping to provide high wet resiliency and to promote good
in-plane permeability. For air-laid basesheets, the structure may
be imparted by thermal embossing of a fibrous mat with binder
fibers that are activated by heat. For example, an air-laid fibrous
mat containing thermoplastic or hotmelt binder fibers may be heated
and then embossed before the structure cools to permanently give
the sheet a three-dimensional structure.
[0056] In addition to the regular geometrical structure imparted by
the sculptured fabrics and other fabrics used in creating a
basesheet, additional fine structure, with an in-plane length scale
less than about 1 mm, can be present in the basesheet. Such a fine
structure can stem from microfolds created during differential
velocity transfer of the web from one fabric or wire to another
prior to drying. Some of the materials of the present invention,
for example, appear to have fine structure with a fine surface
depth of 0.1 mm or greater, and sometimes 0.2 mm or greater, when
height profiles are measured using a commercial moir interferometer
system. These fine peaks have a typical half-width less than 1 mm.
The fine structure from differential velocity transfer and other
treatments may be useful in providing additional softness,
flexibility, and bulk. Measurement of the surface structures is
described below.
[0057] An especially suitable method for measurement of Overall
Surface Depth is moir interferometry, which permits accurate
measurement without deformation of the surface. For reference to
the materials of the present invention, surface topography should
be measured using a computer-controlled white-light field-shifted
moir interferometer with about a 38 mm field of view. The
principles of a useful implementation of such a system are
described in Bieman et al. (L. Bieman, K. Harding, and A.
Boehniein, "Absolute Measurement Using Field-Shifted Moir," SPIE
Optical Conference Proceedings, Vol. 1614, pp. 259-264, 1991). A
suitable commercial instrument for moir interferometry is the
CADEYES.RTM. interferometer produced by Medar, Inc. (Farmington
Hills, Mich.), constructed for a 38-mm field-of-view (a field of
view within the range of 37 to 39.5 mm is adequate). The
CADEYES.RTM. system uses white light which is projected through a
grid to project fine black lines onto the sample surface. The
surface is viewed through a similar grid, creating moir fringes
that are viewed by a CCD camera. Suitable lenses and a stepper
motor adjust the optical configuration for field shifting (a
technique described below). A video processor sends captured fringe
images to a PC computer for processing, allowing details of surface
height to be back-calculated from the fringe patterns viewed by the
video camera.
[0058] In the CADEYES moir interferometry system, each pixel in the
CCD video image is said to belong to a moir fringe that is
associated with a particular height range. The method of
field-shifting, as described by Bieman et al. (L. Bieman, K.
Harding, and A. Boehnlein, "Absolute Measurement Using
Field-Shifted Moir," SPIE Optical Conference Proceedings, Vol.
1614, pp. 259-264, 1991) and as originally patented by Boehnlein
(U.S. Pat. No. 5,069,548, herein incorporated by reference), is
used to identify the fringe number for each point in the video
image (indicating which fringe a point belongs to). The fringe
number is needed to determine the absolute height at the
measurement point relative to a reference plane. A field-shifting
technique (sometimes termed phase-shifting in the art) is also used
for sub-fringe analysis (accurate determination of the height of
the measurement point within the height range occupied by its
fringe). These field-shifting methods coupled with a camera-based
interferometry approach allows accurate and rapid absolute height
measurement, permitting measurement to be made in spite of possible
height discontinuities in the surface. The technique allows
absolute height of each of the roughly 250,000 discrete points
(pixels) on the sample surface to be obtained, if suitable optics,
video hardware, data acquisition equipment, and software are used
that incorporates the principles of moir interferometry with
field-shifting. Each point measured has a resolution of
approximately 15 microns in its height measurement.
[0059] The computerized interferometer system is used to acquire
topographical data and then to generate a grayscale image of the
topographical data, said image to be hereinafter called "the height
map." The height map is displayed on a computer monitor, typically
in 256 shades of gray and is quantitatively based on the
topographical data obtained for the sample being measured. The
resulting height map for the 38-mm square measurement area should
contain approximately 250,000 data points corresponding to
approximately 500 pixels in both the horizontal and vertical
directions of the displayed height map. The pixel dimensions of the
height map are based on a 512.times.512 CCD camera which provides
images of moir patterns on the sample which can be analyzed by
computer software. Each pixel in the height map represents a height
measurement at the corresponding x- and y-location on the sample.
In the recommended system, each pixel has a width of approximately
70 microns, i.e. represents a region on the sample surface about 70
microns long in both orthogonal in-plane directions). This level of
resolution prevents single fibers projecting above the surface from
having a significant effect on the surface height measurement. The
z-direction height measurement must have a nominal accuracy of less
than 2 microns and a z-direction range of at least 1.5 mm. (For
further background on the measurement method, see the CADEYES
Product Guide, Medar, Inc., Farmington Hills, Mich., 1994, or other
CADEYES manuals and publications of Medar, Inc.)
[0060] The CADEYES system can measure up to 8 moir fringes, with
each fringe being divided into 256 depth counts (sub-fringe height
increments, the smallest resolvable height difference). There will
be 2048 height counts over the measurement range. This determines
the total z-direction range, which is approximately 3 mm in the
38-mm field-of-view instrument. If the height variation in the
field of view covers more than eight fringes, a wrap-around effect
occurs, in which the ninth fringe is labeled as if it were the
first fringe and the tenth fringe is labeled as the second, etc. In
other words, the measured height will be shifted by 2048 depth
counts. Accurate measurement is limited to the main field of 8
fringes.
[0061] The moir interferometer system, once installed and factory
calibrated to provide the accuracy and z-direction range stated
above, can provide accurate topographical data for materials such
as paper towels (Those skilled in the art may confirm the accuracy
of factory calibration by performing measurements on surfaces with
known dimensions.) Tests are performed in a room under Tappi
conditions (73.degree. F., 50% relative humidity). The sample must
be placed flat on a surface lying aligned or nearly aligned with
the measurement plane of the instrument and should be at such a
height that both the lowest and highest regions of interest are
within the measurement region of the instrument.
[0062] Once properly placed, data acquisition is initiated using
Medar's PC software and a height map of 250,000 data points is
acquired and displayed, typically within 30 seconds from the time
data acquisition was initiated. (Using the CADEYES.RTM. system, the
"contrast threshold level" for noise rejection is set to 1,
providing some noise rejection without excessive rejection of data
points.) Data reduction and display are achieved using CADEYES.RTM.
software for PCs, which incorporates a customizable interface based
on Microsoft Visual Basic Professional for Windows (version 3.0).
The Visual Basic interface allows users to add custom analysis
tools.
[0063] The height map of the topographical data can then be used by
those skilled in the art to identify characteristic unit cell
structures (in the case of structures created by fabric patterns;
these are typically parallelograms arranged like tiles to cover a
larger two-dimensional area) and to measure the typical peak to
valley depth of such structures. A simple method of doing this is
to extract two-dimensional height profiles from lines drawn on the
topographical height map which pass through the highest and lowest
areas of the unit cells. These height profiles can then be analyzed
for the peak to valley distance, if the profiles are taken from a
sheet or portion of the sheet that was lying relatively flat when
measured. To eliminate the effect of occasional optical noise and
possible outliers, the highest 10% and the lowest 10% of the
profile should be excluded, and the height range of the remaining
points is taken as the surface depth. Technically, the procedure
requires calculating the variable which we term "P10," defined at
the height difference between the 10% and 90% material lines, with
the concept of material lines being well known in the art, as
explained by L. Mummery, in Surface Texture Analysis: The Handbook,
Hommelwerke GmbH, Muhlhausen, Germany, 1990. In this approach,
which will be illustrated with respect to FIG. 7, the surface 31 is
viewed as a transition from air 32 to material 33. For a given
profile 30, taken from a flat-lying sheet, the greatest height at
which the surface begins--the height of the highest peak--is the
elevation of the "0% reference line" 34 or the "0% material line,"
meaning that 0% of the length of the horizontal line at that height
is occupied by material. Along the horizontal line passing through
the lowest point of the profile, 100% of the line is occupied by
material, making that line the "100% material line" 35. In between
the 0% and 100% material lines (between the maximum and minimum
points of the profile), the fraction of horizontal line length
occupied by material will increase monotonically as the line
elevation is decreased. The material ratio curve 36 gives the
relationship between material fraction along a horizontal line
passing through the profile and the height of the line. The
material ratio curve is also the cumulative height distribution of
a profile. (A more accurate term might be "material fraction
curve.")
[0064] Once the material ratio curve is established, one can use it
to define a characteristic peak height of the profile. The P10
"typical peak-to-valley height" parameter is defined as the
difference 37 between the heights of the 10% material line 38 and
the 90% material line 39. This parameter is relatively robust in
that outliers or unusual excursions from the typical profile
structure have little influence on the P10 height. The units of P10
are mm. The Overall Surface Depth of a material is reported as the
P10 surface depth value for profile lines encompassing the height
extremes of the typical unit cell of that surface. "Fine surface
depth" is the P10 value for a profile taken along a plateau region
of the surface which is relatively uniform in height relative to
profiles encompassing a maxima and minima of the unit cells.
Measurements are reported for the most textured side of the
basesheets of the present invention, which is typically the side
that was in contact with the through-drying fabric when air flow is
toward the through-dryer. FIG. 8 represents a profile of Example 13
of the present invention, discussed below, having an Overall
Surface Depth of about 0.5.
[0065] Overall Surface Depth is intended to examine the topography
produced in the basesheet, especially those features created in the
sheet prior to and during drying processes, but is intended to
exclude "artificially" created large-scale topography from dry
converting operations such as embossing, perforating, pleating,
etc. Therefore, the profiles examined should be taken from
unembossed regions if the basesheet has been embossed, or should be
measured on an unembossed basesheet. Overall Surface Depth
measurements should exclude large-scale structures such as pleats
or folds which do not reflect the three-dimensional nature of the
original basesheet itself. It is recognized that sheet topography
may be reduced by calendering and other operations which affect the
entire basesheet. Overall Surface Depth measurement can be
appropriately performed on a calendered basesheet.
[0066] The "Wet Wrinkle Recovery Test" is a slight modification of
AATCC Test Method 66-1990 taken from the Technical Manual of the
American Association of Textile Chemists and Colorists (1992), page
99. The modification is to first wet the samples before carrying
out the method. This is done by soaking the samples in water
containing 0.01 percent TRITON X-100 wetting agent (Rohm &
Haas) for five minutes before testing. Sample preparation is
carried out at 73.degree. F. and 50 percent relative humidity. The
sample is gently removed from the water with a tweezers, drained by
pressing between two pieces of blotter paper with 325 grams of
weight, and placed in the sample holder to be tested as with the
dry wrinkle recovery test method. The test measures the highest
recovery angle of the sample being tested (in any direction,
including the machine direction and the cross-machine direction),
with 180.degree. representing total recovery. The Wet Wrinkle
Recovery, expressed as a percent recovery, is the measured recovery
angle divided by 180.degree., multiplied by 100. Basesheets of this
invention can exhibit a Wet Wrinkle Recovery of about 60 percent or
greater, more specifically about 70 percent or greater, and still
more specifically about 80 percent or greater.
[0067] "Wet compressive resiliency" of the basesheets is defined by
several parameters and can be demonstrated using a materials
property procedure that encompasses both wet and dry
characteristics. A programmable strength measurement device is used
in compression mode to impart a specified series of compression
cycles to an initially dry, conditioned sample, after which the
sample is carefully moistened in a specified manner and subjected
to the same sequence of compression cycles. While the comparison of
wet and dry properties is of general interest, the most important
information from this test concerns the wet properties. The initial
testing of the dry sample can be viewed as a conditioning step. The
test sequence begins with compression of the dry sample to 0.025
psi to obtain an initial thickness (cycle A), then two repetitions
of loading up to 2 psi followed by unloading (cycles B and C).
Finally, the sample is again compressed to 0.025 psi to obtain a
final thickness (cycle D). (Details of the procedure, including
compression speeds, are given below). Following the treatment of
the dry sample, moisture is applied uniformly to the sample using a
fine mist of deionized water to bring the moisture ratio (g water/g
dry fiber) to approximately 1.1. This is done by applying 95-110%
added moisture, based on the conditioned sample mass. This puts
typical cellulosic materials in a moisture range where physical
properties are relatively insensitive to moisture content (e.g.,
the sensitivity is much less than it is for moisture ratios less
than 70%). The moistened sample is then placed in the test device
and the compression cycles are repeated.
[0068] Three measures of wet resiliency are considered which are
relatively insensitive to the number of sample layers used in the
stack. The first measure is the bulk of the wet sample at 2 psi.
This is referred to as the "Wet Compressed Bulk" (WCB). The second
measure is termed "Wet Springback Ratio" (WS), which is the ratio
of the moist sample thickness at 0.025 psi at the end of the
compression test (cycle D) to the thickness of the moist sample at
0.025 psi measured at the beginning of the test (cycle A). The
third measure is the "Loading Energy Ratio" (LER), which is the
ratio of loading energy in the second compression to 2 psi (cycle
C) to that of the first compression to 2 psi (cycle B) during the
sequence described above, for a wetted sample. The final wet bulk
measured at the end of the test (at 0.025 psi) is termed the "final
bulk" or "FB" value. When load is plotted as a function of
thickness, loading energy is the area under the curve as the sample
goes from an unloaded state to the peak load of that cycle. For a
purely elastic material, the springback and loading energy ratio
would be unity. Applicants have found that the three measures
described here are relatively independent of the number of layers
in the stack and serve as useful measures of wet resiliency. Also
referred to herein is the "Compression Ratio", which is defined as
the ratio of moistened sample thickness at peak load in the first
compression cycle to 2 psi to the initial moistened thickness at
0.025 psi.
[0069] In carrying out the foregoing measurements of the wet
compressive resiliency, samples should be conditioned for at least
24 hours under TAPPI conditions (50% RH, 73.degree. F.). Specimens
are die cut to 2.5".times.2.5" squares. Conditioned sample weight
should be near 0.4 g, if possible, and within the range of 0.25 to
0.6 g for meaningful comparisons. The target mass of 0.4 g is
achieved by using a stack of 2 or more sheets if the sheet basis
weight is less than 65 gsm. For example, for nominal 30 gsm sheets,
a stack of 3 sheets will generally be near 0.4 g total mass.
[0070] Compression measurements are performed using an Instron 4502
Universal Testing Machine interfaced with a 286 PC computer running
Instron Series XIl software (1989 issue) and Version 2 firmware.
The standard "286 computer" referred to has an 80286 processor with
a 12 MHz clock speed. The particular computer used was a Compaq
DeskPro 286e with an 80287 math coprocessor and a VGA video
adapter. A 1 kN load cell is used with 2.25" diameter circular
platens for sample compression. The lower platen has a ball bearing
assembly to allow exact alignment of the platens. The lower platen
is locked in place while under load (30-100 lbf) by the upper
platen to ensure parallel surfaces. The upper platen must also be
locked in place with the standard ring nut to eliminate play in the
upper platen as load is applied.
[0071] Following at least one hour of warm-up after start-up, the
instrument control panel is used to set the extensionometer to zero
distance while the platens are in contact (at a load of 10-30 lb).
With the upper platen freely suspended, the calibrated load cell is
balanced to give a zero reading. The extensionometer and load cell
should be periodically checked to prevent baseline drift (shirting
of the zero points). Measurements must be performed in a controlled
humidity and temperature environment, according to TAPPI
specifications (50%.+-.2% RH and 73.degree. F.). The upper platen
is then raised to a height of 0.2 in. and control of the Instron is
transferred to the computer.
[0072] Using the Instron Series XII Cyclic Test software with a 286
computer, an instrument sequence is established with 7 markers
(discrete events) composed of 3 cyclic blocks (instructions sets)
in the following order:
[0073] Marker 1: Block 1
[0074] Marker 2: Block 2
[0075] Marker 3: Block 3
[0076] Marker 4: Block 2
[0077] Marker 5: Block 3
[0078] Marker 6: Block 1
[0079] Marker 7: Block 3.
[0080] Block 1 instructs the crosshead to descend at 1.5 in./min.
until a load of 0.1 lb. is applied (the Instron setting is -0.1
lb., since compression is defined as negative force). Control is by
displacement. When the targeted load is reached, the applied load
is reduced to zero.
[0081] Block 2 directs that the crosshead range from an applied
load of 0.05 lb. to a peak of 8 lb. then back to 0.05 lb. at a
speed of 0.4 in./min. Using the Instron software, the control mode
is displacement, the limit type is load, the first level is -0.05
lb., the second level is -8 lb., the dwell time is 0 sec., and the
number of transitions is 2 (compression, then relaxation); "no
action" is specified for the end of the block.
[0082] Block 3 uses displacement control and limit type to simply
raise the crosshead to 0.2 in. at a speed of 4 in./min., with 0
dwell time. Other Instron software settings are 0 in first level,
0.2 in second level, 1 transition, and "no action" at the end of
the block.
[0083] When executed in the order given above (Markers 1-7), the
Instron sequence compresses the sample to 0.025 psi (0.1 lbf),
relaxes, then compresses to 2 psi (8 lbs.), followed by
decompression and a crosshead rise to 0.2 in., then compress the
sample again to 2 psi, relaxes, lifts the crosshead to 0.2 in.,
compresses again to 0.025 psi (0.1 lbf), and then raises the
crosshead. Data logging should be performed at intervals no greater
than every 0.02" or 0.4 lb. (whichever comes first) for Block 2 and
for intervals no greater than 0.01 lb. for Block 1. Preferably,
data logging is performed every 0.004 lb. in Block 1 and every 0.05
lb. or 0.005 in. (whichever comes first) in Block 2.
[0084] The results output of the Series XII software is set to
provide extension (thickness) at peak loads for Markers 1, 2, 4 and
6 (at each 0.025 and 2.0 psi peak load), the loading energy for
Markers 2 and 4 (the two compressions to 2.0 psi previously termed
cycles B and C, respectively), the ratio of the two loading
energies (second cycle/first cycle), and the ratio of final
thickness to initial thickness (ratio of thickness at last to first
0.025 psi compression). Load versus thickness results are plotted
on the screen during execution of Blocks 1 and 2.
[0085] In performing a measurement, the dry, conditioned sample is
centered on the lower platen and the test is initiated. Following
completion of the sequence, the sample is immediately removed and
moisture (deionized water at 72-73.degree. F.) is applied. Moisture
is applied uniformly with a fine mist to reach a moist sample mass
of approximately 2.0 times the initial sample mass (95-110% added
moisture is applied, preferably 100% added moisture, based on
conditioned sample mass; this level of moisture should yield an
absolute moisture ratio of about 1.1 g. water/g. oven dry
fiber--with oven dry referring to drying for at least 30 minutes in
an oven at 105.degree. C.). (For the uncreped throughdried
materials of this invention, the moisture ratio could be within the
range of 1.05 to 1.7 without significantly affecting the results).
The mist should be applied uniformly to separated sheets (for
stacks of more than 1 sheet), with spray applied to both front and
back of each sheet to ensure uniform moisture application. This can
be achieved using a conventional plastic spray bottle, with a
container or other barrier blocking most of the spray, allowing
only about the upper 10-20% of the spray envelope--a fine mist--to
approach the sample. The spray source should be at least 10" away
from the sample during spray application. In general, care must be
applied to ensure that the sample is uniformly moistened by a fine
spray. The sample must be weighed several times during the process
of applying moisture to reach the targeted moisture content. No
more than three minutes should elapse between the completion of the
compression test on the dry sample and the completion of moisture
application. Allow 45-60 seconds from the final application of
spray to the beginning of the subsequent compression test to
provide time for internal wicking and absorption of the spray.
Between three and four minutes will elapse between the completion
of the dry compression sequence and initiation of the wet
compression sequence.
[0086] Once the desired mass range has been reached, as indicated
by a digital balance, the sample is centered on the lower Instron
platen and the test sequence is initiated. Following the
measurement, the sample is placed in a 105.degree. C. oven for
drying, and the oven dry weight will be recorded later (sample
should be allowed to dry for 30-60 minutes, after which the dry
weight is measured).
[0087] Note that creep recovery can occur between the two
compression cycles to 2 psi, so the time between the cycles may be
important. For the instrument settings used in these Instron tests,
there is a 30 second period (.+-.4 sec.) between the beginning of
compression during the two cycles to 2 psi. The beginning of
compression is defined as the point at which the load cell reading
exceeds 0.03 lb. Likewise, there is a 5-8 second interval between
the beginning of compression in the first thickness measurement
(ramp to 0.025 psi) and the beginning of the subsequent compression
cycle to 2 psi. The interval between the beginning of the second
compression cycle to 2 psi and the beginning of compression for the
final thickness measurement is approximately 20 seconds.
[0088] The utility of a web or absorbent structure having a high
Wet Compressed Bulk (WCB) value is obvious, for a wet material
which can maintain high bulk under compression can maintain higher
fluid capacity and is less likely to allow fluid to be squeezed out
when it is compressed.
[0089] High Wet Springback Ratio values are especially desirable
because a wet material that springs back after compression can
maintain high pore volume for effective intake and distribution of
subsequent insults of fluid, and such a material can regain fluid
during its expansion which may have been expelled during
compression. In diapers, for example, a wet region may be
momentarily compressed by body motion or changes in body position.
If the material is unable to regain its bulk when the compressive
force is released, its effectiveness for handling fluid is
reduced.
[0090] High Loading Energy Ratio values in a material are also
useful, for such a material continues to resist compression (LER is
based on a measure of the energy required to compress a sample) at
loads less than the peak load of 2 psi, even after it has been
heavily compressed once. Maintaining such wet elastic properties is
believed to contribute to the feel of the material when used in
absorbent articles, and may help maintain the fit of the absorbent
article against the wearer's body, in addition to the general
advantages accrued when a structure can maintain its pore volume
when wet.
[0091] The hydrophobically-treated absorbent webs of this invention
and the untreated, inherently hydrophilic basesheets useful in
producing this invention can exhibit one or more of the foregoing
properties. More specifically, said absorbent webs and basesheets
can have a Wet Compressed Bulk of about 6 cubic centimeters per
gram or greater, more specifically about 7 cubic centimeters per
gram or greater, more specifically about 8 cubic centimeters per
gram or greater, and still more specifically from about 8 to about
13 cubic centimeters per gram. The Compression Ratio can be about
0.7 or less, more specifically about 0.6 or less, still more
specifically about 0.5 or less, and still more specifically from
0.4 to about 0.7. Also, they can have a Wet Springback Ratio of
about 0.6 or greater, more specifically about 0.7 or greater, more
specifically about 0.85, and still more specifically from about 0.8
to about 0.93. The Loading Energy Ratio can be about 0.6 or
greater, more specifically 0.7 or greater, more specifically still
about 0.8 or greater, and most specifically from about 0.75 to
about 0.9. Final bulk can be about 8 cubic centimeters per gram or
greater or preferably about 12 centimeters per gram or greater.
[0092] "In-Plane Permeability". An important property of porous
media, particularly for absorbent products, is the permeability to
liquid flow. The complex, interconnected pathways between the solid
particles and boundaries of a porous media provide routes for fluid
flow which may offer significant flow resistance due to the
narrowness of the channels and the tortuosity of the pathways.
[0093] For paper, permeability is commonly expressed in terms of
gas flow rates through a sheet. This practice is useful for
comparing similar sheets, but does not truly characterize the
interaction of flowing fluid with the porous structure and provides
no direct information about flow in a wet sheet. The standard
engineering definition of permeability provides a more useful
parameter, though one less easily measured. The standard definition
is based on Darcy's law (see F. A. L. Dullien, Porous Media: Fluid
Transport and Pore Structure, Academic Press, New York, 1979),
which, for one-dimensional flow, states that the velocity of fluid
flow through a saturated porous medium is directly proportional to
the pressure gradient: 1 V = K P L ( 1 )
[0094] where V is the superficial velocity (flow rate divided by
area), K is the permeability, .mu. is the fluid viscosity, and
.DELTA.P is the pressure drop in the flow direction across a
distance L. The units of K are m.sup.2. In Equation (1), the
permeability is an empirical proportionality parameter linking
fluid velocity to pressure drop and viscosity. For a homogeneous
medium, K is not a function of .DELTA.P, sample length, or
viscosity, but is an intrinsic parameter describing the flow
resistance of the medium. In a compressible medium, permeability
will be a function of the degree of compression. Darcian
permeability is a fundamental parameter for processes involving
fluid flow in fibrous webs.
[0095] Darcian permeability has units of area (m.sup.2) and for
simple uniform cylindrical pores is proportional to the cross
sectional area of a single pore. However, the permeability of most
real materials cannot be predicted from an optical assessment of
pore size. Permeability is determined not only by pore size, but
also pore orientation, tortuosity, and interconnectedness. Large
pores in the body of an object may be inaccessible to fluid flow or
accessible only through minute pores offering high flow resistance.
Even with a full three-dimensional description of the pore space of
a material from x-ray tomography or other imaging techniques, it is
difficult to predict or calculate the permeability. Permeability
and pore size determinations are related but distinct pieces of
information about a material. For example, a sheet of metal with
discreet, nonoverlapping holes punched in it may have very large
pores (the holes), while still having negligible In-Plane
Permeability. Swiss cheese has many large pores, but typically has
negligible permeability in any direction unless sliced so thin that
individual holes can extend from one face to the other of the
cheese sample.
[0096] Most studies of permeability in paper have focused on flow
in the z-direction (normal to the plane of the sheet), which is of
practical importance in wet pressing and other unit operations.
However, paper is an anisotropic material (for example, see E. L.
Back, "The Pore Anisotropy of Paper Products and Fibre Building
Boards," Svensk Papperstidning, 69: 219 (1966)), meaning that fluid
flow properties are a function of direction. In this case,
different flow directions will appear to have different apparent
permeabilities. The many possibilities of flow direction and
pressure gradients in such a medium can be encompassed with a
multidimensional form of Darcy's law, 2 v _ = - K = P , ( 2 )
[0097] where {overscore (v)} is the superficial velocity vector
(volumetric flow rate divided by cross-sectional area of the flow),
.mu. is the viscosity of the fluid, {double overscore (K)} is a
second-order tensor and .gradient.P is the pressure gradient. If a
Cartesian coordinate system is chosen to correspond with the
principal flow directions of the porous medium, then the
permeability tensor becomes a diagonal matrix (see Jacob Bear,
"Dynamics of Fluids in Porous Media.," American Elsevier, New York,
N.Y., 1972, pp. 136-151): 3 K = = [ K x 0 0 0 K y 0 0 0 K z ] , ( 3
)
[0098] where K.sub.x, K.sub.y, and K.sub.z are the principal
permeability components in the x-, y-, and z-directions,
respectively. In paper, these directions will generally correspond
to the cross-direction (taken here as y) and the machine-direction
(taken as x, the direction of maximum In-Plane Permeability) in the
plane, and the transverse or thickness direction (z). Thus, the
anisotropic permeability of typical machine-made paper can be
characterized with three permeability parameters, one for the
machine-direction, one for the cross-direction, and one for the
z-direction. (In some cases, as when there are unbalanced flows in
the headbox of the paper machine, the direction of maximum
permeability may be slightly off from the machine direction; the
direction of maximum In-Plane Permeability and the direction
orthogonal to that should be used for the x- and y-directions,
respectively, in that case.) In handsheets, there may be no
preferential direction of orientation for fibers lying in the
plane, so the x- and y-direction permeability values should be
equal (in other words, such a sheet is isotropic in the plane).
[0099] In spite of the past focus on z-direction permeability in
paper, In-Plane Permeability (both K.sub.x and K.sub.y are in-plane
factors) is important in a variety of applications, especially in
absorbent articles. Body fluids or other liquids flowing into the
absorbent article usually enter the article in a narrow, localized
region. Efficient use of the absorbent medium requires that the
incoming fluid be distributed laterally through in-plane flow in
the absorbent article, otherwise the local capacity of the article
to handle the incoming liquid may be overwhelmed resulting in
leakage and poor utilization of the absorbent core. The ability of
fluid to flow in the plane of the article is a function of the
driving force for fluid flow, which can be a combination of
capillary wicking and hydraulic pressure from fluid source, and of
the ability of the porous medium to conduct flow, which is
described in large part by the Darcian permeability of the
material. Two-phase flow and non-Newtonian liquids or suspensions
complicate the physics, but the in-plane permeability of the porous
medium is a critical factor for rapid in-plane distribution of
liquid insults. Especially in the case of urine management, where
liquid flow rates may occur far in excess of the ability of
capillary forces, high In-Plane Permeability is needed in the
intake layer to allow the fluid to be distributed laterally rather
than to leak.
[0100] While many past studies of liquid permeability in paper
focused exclusively on measuring K.sub.z for z-direction flow, more
recently, methods have been taught for measuring permeability in
the plane of a paper sheet. J. D. Lindsay and P. H. Brady teach
methods for in-plane and z-direction permeability measurements of
saturated paper in "Studies of Anisotropic Permeability with
Applications to Water Removal in Fibrous Webs: Part I," Tappi J.,
76(9): 119-127 (1993) and "Studies of Anisotropic Permeability with
Applications to Water Removal in Fibrous Webs: Part II," Tappi J.,
76(11): 167-174 (1993). Related methods have been published by K.
L. Adams, B. Miller, and L. Rebenfeld in "Forced In-Plane Flow of
an Epoxy Resin in Fibrous Networks," Polymer Engineering and
Science, 26(20) 1434-1441 (1986); J. D. Lindsay in "Relative Flow
Porosity in Fibrous Media: Measurements and Analysis, Including
Dispersion Effects," Tappi J., 77(6): 225-239 (June 1994); J D.
Lindsay and J. R. Wallin, "Characterization of In-Plane Flow in
Paper," AlChE 1989 and 1990 Forest Products Symposium, Tappi Press,
Atlanta, Ga. (1992), p. 121; and D. H. Horstmann, J. D. Lindsay,
and R. A. Stratton, "Using Edge-Flow Tests to Examine the In-Plane
Anisotropic Permeability of Paper," Tappi J., 74(4): 241
(1991).
[0101] The basic method used in most of these publications is
injection of fluid into the center of a paper disk that is
constrained between two flat surfaces to force the fluid flow to be
in the radial direction, proceeding from the injection point at the
center of the disk to the outer edge of the disk. This is
illustrated in FIG. 9, which depicts a sheet 41 in which a central
hole 42 has been punched and into which fluid is injected by means
of an injection port of the same size as the punched hole. Fluid is
forced to flow to the outer radial edge 43. For a liquid-saturated
sheet of constant thickness subject to steady radial fluid flow in
the manner described in the work of Lindsay and others, the
equation relating average In-Plane Permeability to fluid flow is: 4
K r K x + K y 2 = Q ln ( R o / R i ) 2 L p P , ( 4 )
[0102] where R.sub.o is the radius of the paper disk 41, R.sub.i is
the radius of the central hole 42 in the sample into which fluid is
injected through an injection port; L.sub.p is the thickness of the
paper; .DELTA.P is the constant pressure above atmospheric pressure
at which fluid is injected into the disk (the gauge pressure at the
injection pore); Q is the volumetric flow rate of liquid, and
K.sub.r is the In-Plane Permeability, technically the average
radial permeability, defined as the average of the two in-plane
permeability components. The disk diameter is 5 inches. The central
inlet hole 42 was consistently 0.375 inches (3/8 inch) and was
created using a paper punch tool The test apparatus for In-Plane
Permeability measurements is depicted in FIG. 10 and FIG. 11, which
is similar in principle to the apparatus taught by Lindsay and
Brady, previously cited. Tubing 45 connects water from a water
reservoir to an injection port drilled into a 1-inch thick
Plexiglas support plate 45. (The support plate is transparent to
permit viewing of the wetted sample, especially in cases when an
aqueous dye solution is injected into the sample. A mirror at a 45
degree angle below the support plate facilitates viewing and
photography.) The water reservoir 51 provides a nearly constant
hydraulic head 49 for fluid injection during the test. The
volumetric flow rate is obtained by noting the change in water
reservoir mass as a function of time, and converting the water mass
flow rate to a volumetric flow rate. Vacuum-deaerated deionized
water at room temperature is used.
[0103] In using the apparatus, a paper disk 41, cut to be 5-inches
in diameter and having a central hole diameter of 0.375-inches, is
placed on the support plate 46 over the injection port 44 (0.375
inches diameter also) and is then saturated with water. The fluid
injection line 45 and the injection port 44 should be filled with
water and efforts should be taken to avoid air bubbles being
trapped in the sheet or in the injection area. To help eliminate
air pockets, the sample 41 should be bent gently in the center as
it is placed on the wet support plate to initiate liquid contact in
the center of the sample; the edges can then be lowered gradually
to create a wedge-like motion of the liquid meniscus to sweep air
bubbles out from under the sheet. Multi-ply stacks of sheets can be
handled in the same way, although preliminary sample wetting may be
needed to remove interply air bubbles. The goal in removing air
bubbles is to reduce the flow blockage that trapped air bubbles can
cause.
[0104] Once the wetted sample is in place, a cylindrical metal
platen 47, 5-inches in diameter, is gently lowered on top of the
sample to provide a constant compressive load and to provide a
reference surface on its top for thickness measurement with
displacement gauges 48. Three displacement gauges 48 are used,
spaced approximately evenly around the edge of the top of the metal
cylinder 47, in order to measure the average thickness of the sheet
41. The sample thickness is taken as the average of the three
displacement values relative to a zero point when no sample is
present. A suitable thickness gauge is the Mitutoyo Digimatic
Indicator, Model 543-525-1, with a 2-inch stroke (traveling
distance of the contacting spindle) and a precision of 1
micrometer. The thickness gauges are rigidly mounted relative to
the support plate. The contacting spindles of the thickness gauges
can be raised and lowered (without changing the position of the
body of the gauge) by use of a cable to provide clearance for
moving the metal platen onto the sample. The small force applied by
the thickness gauges 48 should be added to the weight of the metal
platen 47 to obtain the total force applied to the sample 41; this
force, when divided by the cross sectional area of the sample and
platen, should be 0.8 psi.
[0105] A hydraulic head of 13 inches is used to drive the liquid
flow. The head is the vertical distance 49 between the water line
50 of the supply reservoir 51 and the plane of the sample 41. This
head is achieved by placement of a water bottle 51, filled to a
specified level 50, on a mass balance 52 at a fixed height relative
to the support plate 46 on which the sample rests. As the sample is
being placed on the support plate, the water reservoir is at such a
height that the water level 50 in the reservoir is nearly the same
as (or slightly greater than) the support plate 46 on which the
sample rests. When the sample has been moistened and placed under
the compressive load of the metal platen, the water reservoir is
then raised and placed on a mass balance 52 such that the water
level is 13 inches above the support platen. A timer is activated
and the water reservoir mass is recorded at 20 seconds or 30
seconds intervals for a least 90 seconds. The thickness readings of
the three gauges is also recorded regularly during the test. To
reduce creep, the saturated sample should be allowed to equilibrate
under the compressive load for at least 30 seconds before the water
bottle is raised and forced flow through the sample begins.
[0106] The change in water reservoir mass as a function of time
gives the mass flow rate, which can easily be converted to a
volumetric flow rate for use in Equation 4. Normal engineering
principles should be used to ensure that the proper units
(preferably SI units) are used in applying Equation 4.
[0107] In performing In-Plane Permeability measurements, it is
important that the sample be uniformly compressed against the
restraining surfaces to prevent large channels or openings that
would provide paths of least resistance for substantial liquid flow
that could bypass much of the sample itself. Ideally, the liquid
will flow uniformly through the sample, and this can be ascertained
by injecting dyed fluid into the sample and observing the shape of
the dyed region through the transparent support plate. Injected dye
should spread out uniformly from the injection point. In isotropic
samples, the shape of the moving dye region should be nearly
circular. In materials with in-plane anisotropy due to fiber
orientation or small-scale structural orientation, the shape of the
dye region should be oval or elliptical, and nearly symmetric about
the injection point. A suitable dye for such tests is Versatint
Purple II made by Milliken Chemical Corp. (Inman, S.C.). This is a
fugitive dye that does not absorb onto cellulose, allowing for easy
visualization of liquid flow through the fibrous medium.
[0108] As will be illustrated in the Examples, the webs and
basesheets of this invention possess very high In-Plane
Permeability. The In-Plane Permeability can be about
0.1.times.10.sup.-10 square meters or greater, more specifically
about 0.3.times.10.sup.-10 square meters or greater, more
specifically about 0.5.times.10.sup.-10 square meters or greater,
still more specifically from about 0.5.times.10.sup.-10 to about
8.times.10.sup.-10 square meters, and still more specifically from
about 0.8.times.10.sup.-10 to about 5.times.10.sup.-10 square
meters.
BRIEF DESCRIPTION OF THE DRAWINGS
[0109] FIG. 1 is a cross-section of an absorbent web comprising a
contoured, resilient basesheet having zones of hydrophobic
material.
[0110] FIG. 2 depicts the absorbent web of FIG. 1 in contact with
an underlying absorbent fibrous layer.
[0111] FIG. 3 depicts the absorbent web of FIG. 1 attached to an
inverted basesheet having similar topography.
[0112] FIG. 4 depicts a paper machine suitable for producing the
contoured, resilient basesheet of the present invention shown in
FIG. 1.
[0113] FIG. 5 depicts a version of FIG. 2 in which the low regions
of the basesheet are provided with apertures.
[0114] FIG. 6 depicts a pattern of hydrophobic material printed
onto a hydrophilic basesheet.
[0115] FIG. 7 depicts a height profile and several material lines
to illustrate the definition of material surface curve and the P10
height.
[0116] FIG. 8 depicts a CADEYES profile from Sample 13 of the
present invention.
[0117] FIG. 9 portrays the flow pattern in a paper disk during an
In-Plane Permeability measurement (angle view).
[0118] FIG. 10 is a side view of the In-Plane Permeability
apparatus.
[0119] FIG. 11 is a top view of the brass platen and thickness
gauges in the In-Plane Permeability apparatus.
[0120] FIG. 12 depicts the grayscale height map of a section of
uncreped tissue basesheet showing relatively high regions as light
gray and lower regions as darker gray or black.
[0121] FIG. 13 is a graph of mean Rewet values and 95% confidence
intervals for samples of Example 1.
[0122] FIG. 14 is a table of physical property results for Examples
3-6.
[0123] FIG. 15 is a table of physical property results for Examples
7-10.
BRIEF DESCRIPTION OF THE DRAWINGS
[0124] FIG. 1 shows a cross section of a contoured, inherently
hydrophilic basesheet 1, preferably a resilient cellulosic tissue
sheet, onto which hydrophobic material 2 has been deposited on the
uppermost regions 3 of the contoured basesheet to form a composite
absorbent web. The upper side of the web having the hydrophobic
material 2 can serve as the skin-contacting layer of a topsheet or
liner in an absorbent article. The hydrophobic material preferably
resides only on the elevated regions of the basesheet as shown,
preferably penetrating into no more than about 50% of the thickness
of the basesheet, more specifically no more than about 20% of the
thickness of the basesheet, and most preferably no more than about
10% of the thickness of the basesheet. For some products, it may be
desirable that the hydrophobic material lie almost exclusively on
the upper (outer) surface of the fibers on the upper surface of the
basesheet, with very little penetration into the basesheet itself.
The hydrophobic material deposits generally have a thickness that
rises some distance above the underlying hydrophilic basesheet. In
some embodiments, the distance above the underlying hydrophilic
basesheet can be less than 3 mm, less than 0.5 mm, less than 0.1
mm, less than 0.05 mm, or between 0.05 and 0.5 mm. In some
preferred embodiments, the thickness of the hydrophobic deposits
relative to the local thickness of the hydrophilic basesheet can be
less than 50%, alternatively less than about 20%, alternatively
less than about 10%, or between about 5% and 25%.
[0125] For best performance in terms of liquid absorption, the
density of the basesheet preferably should be substantially uniform
throughout any characteristic cross-section of the basesheet, as is
characteristic of uncreped, through-air dried tissues and other
paper sheets that have been dried by largely noncompressive means.
Such a basesheet is relatively free of regions having low
permeability and low absorbent capacity and tends to be more
resilient when wet. The depressed regions 4 of the basesheet are
substantially hydrophilic and can serve much as apertures do in an
apertured film by providing pore space to receive liquids and by
providing regions in the midst of hydrophobic material where liquid
can be wicked into an absorbent medium, the medium being the
hydrophilic basesheet itself and optionally an underlying absorbent
core preferably in liquid communicating contact with the composite
web. The underlying absorbent core is preferably a fibrous mat such
as a mat of fluff pulp. One such embodiment is depicted in FIG. 2,
where the inherently hydrophilic basesheet 1 is in direct contact
with a fibrous mat 5. For enhanced transport of liquid out of the
composite web into the fibrous mat, the fibrous mat 5 may be
provided with a heterogeneous structure having high density regions
with small pores to provide high capillary pressure to pull liquid
out of the composite web, while still having a significant amount
of low density regions to provide adequate pore space to hold large
quantities of fluid and to provide high permeability regions. A
heterogeneously densified fibrous mat 5 can have a relatively dense
upper layer in contact with the basesheet 1, or it can have a
pattern of densified regions imparted by embossing or other means,
preferably with at least some of the densified regions in direct
contact with the lower hydrophilic portions 4 of the basesheet
1.
[0126] As shown in FIG. 3, the inherently hydrophilic basesheet 1
can also be in contact 9 with a web of similar topography having
depressions 7 to form a multi-ply structure with significant
interply pore space 8. Preferably, the web provides a combination
of desired material properties: wet resiliency, to maintain shape
and bulk when wet; absorbency and good capillary structure to
provide rapid intake of fluid in the hydrophilic areas, softness on
the upper surface on the body side for improved comfort;
flexibility for comfort during use; and a three-dimensional contour
to reduce contact area against the body, thus resulting in less of
a wet feel when wet.
[0127] The inherently hydrophilic basesheet can be produced by a
wide variety of methods. Preferably, the basesheet, prior to any
calendering that may be desired, is characterized by a low-density
three-dimensional structure created in substantial part before the
sheet reaches a solids level (dryness level) of about 60% or higher
and preferably about 70% or higher. Suitable low-density
three-dimensional structures can be achieved by a variety of means
known in the arts of papermaking, tissue production, and nonwoven
web production, including but not limited to the use of specially
treated high-bulk fibers such as curled or chemically treated
fibers as an additive in the furnish, including the fibers taught
by C. C. Van Haaften in "Sanitary Napkin with Cross-linked
Cellulosic Layer," U.S. Pat. No. 3,339,550, issued Sep. 5, 1967,
which is hereby incorporated by reference; mechanical debonding
means such as differential velocity ("rush") transfer between
fabrics or wires, hereafter described; mechanical straining or "wet
straining" of the moist web, including the methods taught by M. A.
Hermans et al. in U.S. Pat. No. 5,492,598, "Method for Increasing
the Internal Bulk of Throughdried Tissue," issued Feb. 20, 1996,
herein incorporated by reference, and M A Hermans et al. in U.S.
Pat. No 5,411,636, "Method for Increasing the Internal Bulk of
Wet-Pressed Tissue," issued May 2, 1995, herein incorporated by
reference; molding of the fiber onto a three-dimensional wire or
fabric, such as the fabrics disclosed by Chiu et al. in U.S. Pat.
No. 5,429,686, "Apparatus for Making Soft Tissue Products," issued
Jul. 4, 1995, which is hereby incorporated by reference, including
differential velocity transfer onto or from said three-dimensional
wire or fabric; wet embossing of the sheet; hydroentanglement of
fibers; wet creping; and the optional use of chemical debonding
agents. Inherently hydrophilic basesheets may also be produced from
composites of synthetics and pulp fibers, with one embodiment
disclosed in commonly owned U.S. Pat. No. 5,389,202, "Process for
Making a High Pulp Content Nonwoven Composite Fabric," issued Feb.
14, 1995 to Cherie H. Everhart et al., hereby incorporated by
reference.
[0128] Air laid mixtures of cellulosic and synthetic fibers are
within the scope of the present invention. Pulp fibers for air
laying may be prepared by comminution, as by a hammermill, or other
means known in the art. Methods of forming air laid materials are
well known in the art, including, for example, the methods
disclosed by Dunning and Day in U.S. Pat. No. 3,976,734, issued
Aug. 24, 1976, and U.S. Pat. No. 5,156,902, issued Oct. 20, 1992 to
Pieper et al., both of which are herein incorporated by reference.
Suitable papermaking fibers for air laying may include hardwood or
softwood, low or high yield fibers, and chemically treated fibers
such as mercerized pulps, chemically stiffened or crosslinked
fibers, sulfonated fibers, and the like. Useful fiber preparation
methods include those of Hermans et al. disclosed in U.S. Pat. No.
5,501,768, issued Mar. 26, 1996, and U.S. Pat. No. 5,348,620,
issued Sep. 20, 1994, both of which are herein incorporated by
reference. Fiber softening methods known in the art may also be
employed, including the compounds disclosed by Smith et al. in U.S.
Pat. No. 5,552,020, issued Sep. 3, 1996, herein incorporated by
reference. The pulp fibers may be entrained in air or steam and
combined or commingled with newly formed, hot synthetic fibers from
a meltblown or spunbond process, or the pulp fibers may be mixed
with a stream of relatively short, cut synthetic fibers (preferably
less than 22 mm in length) entrained in air. Bonding agents and
adhesives may be used to impart stability and wet strength to the
air laid structure, or heat may be applied to partially melt some
of the synthetic fibers to provide bonding. One embodiment
comprises mixtures of papermaking fibers and meltblown polymers
known as "coform" as taught in U.S. Pat. No. 4,100,324 issued to
Anderson et al.; U.S. Pat. No. 4,879,170 issued to Radwanski et
al.; and U.S. Pat. No. 4,931,355 issued to Radwanski et al., all
herein incorporated by reference. For the purposes of this
invention, steps should be taken to impart appropriate texture to
the web. Such steps may include forming on a screen having a
pattern of low and high permeabilities to produce a web of
patterned basis weight and thickness, spot bonding, pattern
bonding, embossing, pulling out regions of the web in the
z-direction to disrupt the surface in a predetermined pattern,
ultrasonic pattern bonding, web disruption with hydraulic jets of
liquid, and so forth. Desirably, inherently hydrophobic synthetic
fibers may be treated to increase wettability with respect to
water, urine or menses, using methods such as surfactant coating,
supercritical fluid deposition of surfactants or other surface
active agents on the fiber surface, deposition of protein or
amphiphilic protein, corona discharge treatment, ozonation, coating
with hydrophilic matter, and the like. When synthetic fibers are
used in the production of the basesheet, they may constitute 70% or
less by weight of the basesheet, preferably 40% or less, more
preferably 20% or less, more preferably still 10% or less, and most
preferably between about 1% and about 10%. Alternatively, the web
may comprise between about 1% and about 10% synthetic fibers.
Alternatively, the web may comprise between about 1% and 50% of
synthetic polymer fibers. A lower content of synthetic fiber is
generally desirable to reduce cost, although other factors may be
more important in determining the optimum fiber mix for a specific
product. Other suitable materials for incorporation in absorbent
articles of the present invention include the soft webs of Tanzer
et al. in U.S. Pat. No. 5,562,645, issued Oct. 8, 1996, herein
incorporated by reference.
[0129] In a preferred embodiment, the basesheet is a wet-laid
tissue produced without creping and dried by non-compressive means.
Techniques for producing such sheets are disclosed by S. J. Sudall
and S. A. Engel in U.S. Pat. No. 5,399,412, "Uncreped Throughdried
Towels and Wipers Having High Strength and Absorbency," issued Mar.
21, 1995; R. F. Cook and D. S. Westbrook in U.S. Pat. No.
5,048,589, "Non-creped Hand or Wiper Towel," issued Sep. 17, 1991;
and J. S. Rugowski et al., "Papermaking Machine for Making Uncreped
Throughdried Tissue Sheets," U.S. Pat. No. 5,591,309, Jan. 7, 1997;
all herein incorporated by reference.
[0130] A preferred method for producing the basesheet for the
present invention is depicted in FIG. 4. For simplicity, the
various tensioning rolls schematically used to define the several
fabric runs are shown but not numbered. It will be appreciated that
variations from the apparatus and method illustrated in FIG. 4 can
be made without departing from the scope of the invention. Shown is
a twin wire former having a layered papermaking headbox 10 which
injects or deposits a stream 11 of an aqueous suspension of
papermaking fibers onto the forming fabric 13 which serves to
support and carry the newly-formed wet web downstream in the
process as the web is partially dewatered to a consistency of about
10 dry weight percent. Additional dewatering of the wet web can be
carried out, such as by vacuum suction. while the wet web is
supported by the forming fabric. The headbox 10 may be a
conventional headbox or may be a stratified headbox capable of
producing a multilayered unitary web. For example, it may be
desirable to provide relatively short or straight fibers in one
layer of the basesheet to give a layer with high capillary
pressure, while the other layer comprises relatively longer,
bulkier, or more curled fibers for high permeability and high
absorbent capacity and high pore volume. It may also be desirable
to apply different chemical agents to separate layers of a single
web to optimize dry and wet strength, pore space, wetting angle,
appearance, or other properties of a web. Multiple headboxes may
also be used to create a layered structure, as is known in the
art.
[0131] The wet web is transferred from the forming fabric to a
transfer fabric 17 preferably traveling at a slower speed than the
forming fabric in order to impart increased stretch into the web.
This is commonly referred to as "rush" transfer. One useful means
of performing rush transfer is taught in U.S. Pat. No. 5,667,636,
issued Mar. 4, 1997 to S. A. Engel et al., herein incorporated by
reference. The relative speed difference between the two fabrics
can be from 0-80 percent, preferably greater than 10%, more
preferably from about 10 to 60 percent, and most preferably from
about 10 to 40 percent. Transfer is preferably carried out with the
assistance of a vacuum shoe 18 such that the forming fabric and the
transfer fabric simultaneously converge and diverge at the leading
edge of the vacuum slot.
[0132] The web is then transferred from the transfer fabric to the
throughdrying fabric 19 with the aid of a vacuum transfer roll 20
or a vacuum transfer shoe, optionally again using a fixed gap
transfer as previously described. The throughdrying fabric can be
traveling at about the same speed or a different speed relative to
the transfer fabric. If desired, the throughdrying fabric can be
run at a slower speed to further enhance stretch. Transfer is
preferably carried out with vacuum assistance to ensure deformation
of the sheet to conform to the throughdrying fabric, thus yielding
desired bulk and appearance. Suitable throughdrying fabrics are
described in U.S. Pat. No. 5,429,686 issued to Kai Chiu et al.,
previously incorporated by reference.
[0133] In a preferred embodiment, the fabric comprises a sculpture
layer superposed on or integrally connected to a load bearing
layer, said sculpture layer comprising elongated, raised elements
having an aspect ratio of at least 4, preferably at least 6, more
preferably at least 10, more preferably still at least 20, and most
preferably between about 8 and about 50. The fabric may be woven or
nonwoven. In one embodiment, the fabric is a woven fabric wherein
the load bearing layer comprises interwoven machine-direction warps
and cross-direction chutes and the sculpture layer comprises
additional warps or chutes interwoven in the weave of the load
bearing layer, wherein the highest knuckles of the sculpture layer
may be higher than the highest knuckles of the load bearing layer
by about 0.1 mm or greater, preferably 0.2 mm or greater, more
preferably 0.5 mm or greater, and most preferably between about 0.4
mm and about 2 mm. For purposes of imparting improved
cross-direction stretch of the basesheet, the elongated, raised
elements of the sculpture layer should be preferentially oriented
in the machine direction.
[0134] The number of elongated, raised elements per square inch of
the fabric should be between about 5 and about 300, more preferably
between about 10 and about 100. The resulting throughdried
basesheet will have elevated regions preferably comprising between
about 5 and about 300 protrusions per square inch having a height
relative to the plane of the basesheet, as measured in the
uncalendered state and uncreped state, of about 0.1 mm or greater,
preferably 0.2 mm or greater, more preferably about 0.3 mm or
greater, and most preferably from about 0.25 to about 0.6 mm. When
the basesheet structure comprises a relatively planar portion with
both protrusions and depressions departing therefrom, the
relatively planar portion is taken as the plane of the basesheet.
In some structures, a basesheet plane may not be well defined. In
such cases, the protrusion height can be measured relative to the
characteristic depth of the deepest depressions. In any case, the
protrusion height relative to the characteristic depth of the
deepest depressions, as measured in the uncalendered state and
uncreped state, can be about 0.1 mm or greater, preferably 0.3 mm
or greater, more preferably about 0.4 mm or greater, more
preferably still about 0.5 mm or greater, and most preferably from
about 0.4 to about 1.2 mm. In one specific embodiment, the elevated
regions of the basesheet correspond to elevated machine-direction
knuckles from a sculpture layer of a three-dimensional
throughdrying fabric used to produce an uncreped throughdried web.
Webs formed in this manner have unusually high values of
cross-direction stretch prior to failure, as measured in standard
tensile tests, of 6% or greater, preferably 9% or greater, and more
preferably 12% or greater, due to the high cross-direction
topography imparted by the elevated machine-direction elements on a
throughdrying fabric. The machine direction stretch can be enhanced
by rush transfer and can be at least as great as the
cross-direction stretch and preferably at least 10% and more
preferably at least 14%
[0135] The level of vacuum used for the web transfers can be from
about 3 to about 15 inches of mercury (75 to about 380 millimeters
of mercury), preferably about 5 inches (125 millimeters) of
mercury. The vacuum shoe (negative pressure) can be supplemented or
replaced by the use of positive pressure from the opposite side of
the web to blow the web onto the next fabric in addition to or as a
replacement for sucking it onto the next fabric with vacuum. Also,
a vacuum roll or rolls can be used to replace the vacuum
shoe(s).
[0136] While supported by the throughdrying fabric, the web is
final dried to a consistency of about 94 percent or greater by the
throughdryer 21 and thereafter transferred to a carrier fabric 22.
The dried basesheet 23 is transported to the reel 24 using carrier
fabric 22 and an optional carrier fabric 25. An optional
pressurized turning roll 26 can be used to facilitate transfer of
the web from carrier fabric 22 to fabric 25. Suitable carrier
fabrics for this purpose are Albany International 84M or 94M and
Asten 959 or 937, all of which are relatively smooth fabrics having
a fine pattern. Although not shown, reel calendering or subsequent
off-line calendering can be used to improve the smoothness and
softness of the basesheet.
[0137] The basesheet may be slitted, perforated, or provided with
apertures formed by cutting, stamping, or the piercing action of
fine water jets. Such perforations or apertures may assist in the
transfer of fluid into an underlying absorbent core. Preferably,
the apertures are provided near or within depressed areas of the
contoured basesheet that serve as hydrophilic zones. FIG. 5 depicts
a cross-section of one such embodiment in which the basesheet 1 has
been provided with perforations 27 in the low, hydrophilic
regions.
[0138] Co-aperturing of the nonwoven material with the underlying
basesheet, wherein the nonwoven web and the basesheet are
simultaneously apertured as with pin aperturing of a two-layer
structure, is possible within the scope of the present invention
but is not preferred. Co-aperturing tends to place hydrophobic
matter from the nonwoven web over the hydrophilic matter of the
basesheet in the apertures, such that fluid entering the aperturing
might encounter a hydrophobic barrier between it and the basesheet.
It is desired that fluid entering the apertures be able to flow
into the basesheet. Apertures in the basesheet may enhance
subsequent transport into the underlying core, but the hydrophobic
properties of the basesheet should contribute positively to the
fluid handling performance of the composite cover material.
[0139] FIGS. 7 to 11 have been previously discussed.
[0140] FIG. 12 shows a representative portion of a grayscale height
map of a basesheet structure of potential value in the present
invention, acquired by the CADEYES moir interferometer (Medar, Inc.
Farmington Hills, Mich.) having a 38-mm field of view. The tissue
is an uncreped through-air dried structure having a surface depth
of about 0.3 mm. Preferably, the basesheet is textured or molded
prior to complete drying to impart an Overall Surface Depth in the
dried structure of about 0.1 mm. or greater, more preferably about
0.3 mm. or greater, still more preferably about 0.4 mm. or greater,
still more preferably about 0.5 mm. or greater, and most preferably
from about 0.4 to about 0.8 mm. In another preferred embodiment,
the basesheet further contains at least 10% by weight of high yield
or other wet resilient pulp fibers and an effective amount of wet
strength resin such that the wet:dry tensile ratio is at least
about 0.1. The uppermost, elevated regions of the basesheet
preferably offer relatively smooth and flat plateaus in order to be
placed against skin with relatively little sense of grittiness or
abrasion.
[0141] The hydrophobic material 2 on the basesheet as shown in FIG.
1 is preferably deposited on relatively elevated regions of the
web, such as the light gray or white regions on the height map of
FIG. 12, in order to place hydrophobic regions in contact with the
user's body when the web is used as a topsheet in an absorbent
article. The hydrophobic material is preferably deposited over a
large enough portion of the basesheet to render a distinct
improvement in dry feel while still allowing liquid transport by
wicking in the z-direction (thickness direction, normal to the
plane of the web) in multiple hydrophilic regions. The proper
application of hydrophobic matter to a fraction of the upper
surface of the hydrophilic basesheet will generally result in a
decrease of Rewet value relative to the untreated basesheet
(meaning an improvement in the dry feel) of at least about 10%,
more specifically at least about 20%, more specifically at least
about 30%, still more specifically at least about 40%, and most
specifically from about 10% to about 50%. The resulting Rewet value
is preferably less than about 1 g, more specifically less than
about 0.65 g, more specifically less than about 0.5 g, still more
specifically less than about 0.4 g, and most specifically less than
about 0.3 g. The resulting Normalized Rewet value is preferably
less than about 1, more specifically less than about 0.7, more
specifically less than about 0.5, still more specifically less than
about 0.4, and most specifically less than about 0.3. In one
embodiment, there is essentially no hydrophobic matter present
below the 50% material line of a characteristic profile of the web,
or below the midplane of a typical cross section of contoured
web.
[0142] In one embodiment, the hydrophobic matter is applied in a
manner designed to limit lateral (in-plane) wicking of liquids to
prevent seepage or leakage from the edges of an absorbent article
while also improving the dry feel. Producing this embodiment
normally requires that hydrophobic material or materials be added
to the upper surface of the hydrophilic basesheet in two ways such
that some of the hydrophobic matter penetrates substantially into
the basesheet to establish a barrier region to inhibit in-plane
wicking, while the remainder of the hydrophobic matter is applied
more lightly to avoid substantial penetration into the basesheet.
The barrier regions may also use hydrophobic matter to fill in the
depressions of the web to prevent flow of liquid along surface
channels or pores. Different hydrophobic materials and application
means may be used for the two or more regions of differing
penetration depth or differing basis weight of application. One
approach suitable for use in absorbent articles such as feminine
pads or incontinence pads is to apply longitudinal bands of a
hydrophobic material in liquid form, such as a melted wax or
polymeric compound, applied heavily enough to permeate into the
basesheet for a significant portion of the thickness of the
basesheet. with said bands being near the edges of the absorbent
article to limit seepage from the edge. The remaining portion of
the basesheet may be treated with hydrophobic matter applied more
superficially to be less penetrating.
[0143] Suitable hydrophobic materials may comprise compounds which
are solid or highly viscous at room temperature but become liquid
or significantly less viscous at elevated temperature, enabling
application of the liquid at elevated temperature by gravure
printing, spray, brush application, or other means, whereupon the
liquid solidifies, gels, or becomes substantially immobile at room
temperature or body temperature. The hydrophobic agent may also be
dissolved, dispersed, or emulsified in a liquid carrier, such as
water, and applied to the web by means such as coating, spraying,
or printing, whereafter part of the liquid carrier is removed by
evaporation, sorption, or other means to leave a hydrophobic
coating or impregnation on the web. The hydrophobic agent may also
comprise solid particles such as PTFE, polyolefins, or other
polymers that have been ground and formulated into a viscous grease
or paste. Additionally, the hydrophobic matter may be in solid
form, such as fibers or particles that are attached adhesively to
the basesheet or attached by entanglement, hydroentanglement,
electrostatic attraction, and so forth.
[0144] Suitable hydrophobic materials include silicone compounds,
fluorocarbons, PTFE, waxes, wax emulsions, polyurethane emulsions,
fats and fatty acid derivatives, polyolefins, nylon, polyesters,
glycerides, and the like, as well as mixtures of the same. Several
suitable materials containing solidified mixtures of waxes and oils
are disclosed in commonly owned U.S. Pat. No. 5,601,871, "Soft
Treated Uncreped Throughdried Tissue," issued Feb. 11, 1997 to D.
Krzysik et al., herein incorporated by reference. Disclosed therein
are compounds containing oil, wax, and optionally fatty alcohols,
said compositions having melting points between about 30.degree. C.
to about 70.degree. C. When distributed relatively uniformly over
an uncreped tissue, said compositions significantly reduce liquid
intake rates and reduce friction against the skin. It is believed
that the hydrophobic compositions disclosed by Krzysik et al. could
also be used advantageously in the present invention through a
macroscopically nonuniform application of said compositions to a
portion of the most elevated regions of a three-dimensional,
resilient, hydrophilic basesheet in such a manner as to avoid
significant reduction of liquid intake rates.
[0145] As disclosed by Krzysik et al., suitable oils include, but
are not limited to, the following classes of oils: petroleum or
mineral oils, such as mineral oil and petrolatum; animal oils, such
as mink oil and lanolin oil; plant oils, such as aloe extract,
sunflower oil, and avocado oil; and silicone oils, such as
dimethicone and alkylmethyl silicones. Suitable waxes include, but
are not limited to the following classes: natural waxes, such as
beeswax and carnauba wax; petroleum waxes, such as paraffin and
ceresine wax; silicone waxes, such as alkyl methyl siloxanes; or
synthetic waxes, such as synthetic beeswax and synthetic sperm wax.
Useful silicone compounds and methods of application are known in
the art, including those of Kasprzak in U.S. Pat. No. 5,302,382,
issued Apr. 12, 1994, and Kaun in U.S. Pat. No. 5,591,306, issued
Jan. 7, 1997, both of which are herein incorporated by
reference.
[0146] The amount of fatty alcohol, if present, in the compositions
of Krzysik et al. can include those having a carbon chain length of
C.sub.14-C.sub.30, including cetyl alcohol, stearyl alcohol,
behenyl alcohol, and dodecyl alcohol.
[0147] For some embodiments of the present invention, it is desired
that the hydrophobic material have a melting point well above
typical body temperatures since absorbent articles containing the
web of the present invention may be worn against the body under hot
conditions, and any melting of the hydrophobic material may
interfere with the performance of the absorbent article and
eliminate the advantage of a dry feel. For such articles containing
the compositions of Krzysik et al. and other compositions, said
compositions should have a melting point above about 35.degree. C.,
specifically above 40.degree. C., more specifically above about
45.degree. C., and more specifically still above 50.degree. C.
[0148] Other suitable hydrophobic compositions comprise up to 30
weight percent oil and from about 50 to about 100 weight percent
wax, said compositions having a melting point of from about
40.degree. C. to about 200.degree. C., more specifically from
70.degree. C. to about 160.degree. C., more specifically above
75.degree. C., and more specifically still from about 85.degree. C.
to 140.degree. C. For purposes herein, "melting point" is the
temperature at which the majority of the melting occurs, it being
recognized that melting actually occurs over a range of
temperatures. Hydrophobic materials may also be used which do not
melt or which degrade or decompose prior to or during melting.
[0149] Examples of water repellent agents which are potentially
useful in the present invention include polyurethane emulsions such
as Aerotex 96B of American Cyanamid; fluorochemical agents such as
FC 838, FC 826, and the SCOTCHGARD compounds sold by Minnesota
Mining and Manufacturing and Milease F-14 and Milease F-31X, sold
by ICI. Also desirable are high molecular weight cationic
fluorocarbons which can be formed into aqueous emulsions for ease
of application and handling. An example of a potentially useful wax
emulsion is Phobotex, sold by Ciba. A variety of other
water-repellent materials that can be applied to paper webs are
reviewed and disclosed in U.S. Pat. No. 5,491,190, issued Feb. 13,
1996 to Paul E. Sandvick and Calvin J. Verbrugge, incorporated
herein by reference. Sandvick and Verbrugge focus primarily on the
use of mixtures of fatty acids and polymers for repulpable paper
sheets. Various wax and polymer compositions of potential value for
the present invention are disclosed in U.S. Pat. No. 3,629,171 to
Kremer et al.; U.S. Pat. No. 3,417,040 to Kremer; U.S. Pat. No.
3,287,149 to Dooley et al.; U.S. Pat. No. 3,165,485 to Ilnyckyj et
al.; and U.S. Pat. No. 2,391,621 to Powell, et al., all of which
are herein incorporated by reference. Mixtures of hydrophobic latex
and wax may also be used, including those taught in U.S. Pat. No.
4,117,199 to Gotoh et al., herein incorporated by reference.
British Pat. No. 1,593,331 to Vase teaches a method for treating
paper and paperboard to make them water resistant by coating them
with an aqueous latex coating composition. The latex coating
composition is an acrylic polymer and a metal stearate or wax where
the wax is at least 20% by weight of the total acrylic polymer and
metal stearate present. The metal stearate is preferably calcium
stearate. Latex emulsions, latex foams, and water absorbing
polymers may be used, including those disclosed in U.S. Pat. No.
5,011,864, issued Apr. 30, 1991 to Nielsen and Kim, herein
incorporated by reference, which also discloses combinations
containing chitosan. Potentially useful latexes also include those
disclosed by Stanislawczyk in U.S. Pat. No. 4,929,495, and the
anionic latex compounds are disclosed in U.S. Pat. No. 4,445,970,
issued May 1, 1984, both of which are herein incorporated by
reference. After application, the coating is dried or cured on the
paper. For the present invention, the composition would be applied
nonuniformly to the upper surface of a basesheet.
[0150] Other examples of aqueous emulsions and emulsifiable
compositions for coating paper and the like are found in U.S. Pat.
No. 3,020,178 to Sweeney et al. and U.S. Pat. No. 3,520,842 to
Crean (aqueous mixtures of petroleum wax, a polymeric olefin
material and a fatty acid are added to water containing an amine
soap-forming agent such as an alkanolamine, followed by agitation
and homogenization to form an aqueous emulsion coating
composition). The hydrophobic matter may also comprise formulations
intended to promote skin wellness and comfort. For example, the
hydrophobic matter may include a hydrophobic base such as mineral
oil, waxes, petrolatum, cocoa butter, and the like, combined with
effective amounts of skin wellness additives or pharmaceutical
agents such as antibiotics and or anti-bacterial agents,
anti-fungal agents, Vitamin E (alpha tocopherol), lanolin, silicone
compounds suitable for skin care, cortisone, zinc oxide, baking
soda, corn silk derivatives, avocado oil, emu oil, other natural
plant and animal oils, and the like.
[0151] Hydrophobic material may also be applied in fibrous or
particulate form and attached to the basesheet through thermal
fusion, chemical binding through the use of a binder agent or
adhesive, preferably a water-repellent binder, entanglement
(resulting from high velocity impact against a porous web),
electrostatic attachment, and the like. In a preferred embodiment,
the hydrophobic material, whether applied as fibers, as particles,
or as a liquid or slurry, may be contiguously deposited to form an
interconnected network, such as the network of lines shown in FIG.
6, in which case the hydrophilic regions are isolated from one
another. In addition to materials previously described, useful
particulate hydrophobic agents include talcum powder and lycopodium
powder.
[0152] Preferably, the hydrophobic material is applied to the
desired regions with an area-averaged local dry basis weight in the
range of from about 0.5 to about 50 gsm, more specifically in the
range of from about 1 to about 10 gsm, more specifically about 5
gsm or less, and most specifically about 3 gsm or less. The
hydrophobic matter preferably comprises about 30% or less of the
total mass of the dry absorbent web, more specifically about 20% or
less, more specifically about 10% or less, and most specifically
from about 1% to about 15% of the total mass of the dry absorbent
web. The basis weight of the underlying basesheet can be from about
10 to about 200 gsm, more specifically from about 15 to about 70
gsm, and most specifically from about 15 to about 40 gsm. For
multi-ply tissue structures, it is preferred that the basis weight
be less than about 40 gsm and more specifically less than about 30
gsm.
[0153] In addition to hydrophobic matter, other agents may be
suitably added to the basesheet in accordance with this invention,
including superabsorbent particles or fibers. Superabsorbent
material may be deposited or attached in the depressed regions of
the upper surface of the basesheet, or preferably may be
incorporated within the fibrous structure of the basesheet,
attached to the lower surface of the basesheet, or incorporated
between the basesheet and an attached absorbent core. Other
chemical agents may be added to either surface or both surfaces, or
dispersed throughout the basesheet, applied to inner or outer
layers of the basesheet, or applied to selected surface regions of
the basesheet, including application in a regular pattern as by
gravure printing. Such chemical agents include emollients, lotions,
chemical softeners, opacifiers, optical brighteners, wet strength
agents, quaternary ammonium salts, proteins, crosslinking agents,
virucides, bactericides, perfumes, dyes, chemical debonders,
plasticizers for high yield fibers, zeolites or other agents for
odor control, and the like. Chitosan and related derivatives may be
incorporated in the articles of the present invention for their
anti-bacterial or other health benefits; triclosan and other
anti-bacterial agents may likewise be incorporated.
[0154] Various mechanical and physical treatments may be applied to
the basesheet before or after addition of hydrophobic material to
improve the mechanical properties, softness, or functionality of
the web. Such treatments include brushing, differential velocity
transfer between belts or fabrics, penetration by high velocity air
jets, needling, hydroentanglement, calendering, soft nip
calendering, thermal gradient calendering, corona discharge
treatment, electret formation, microstraining, dry creping,
embossing, slitting, and aperturing. Preferably, the basesheet is
not co-apertured with the topsheet.
[0155] Also within the scope of the present invention are absorbent
webs in which both sides of the web have been treated with
hydrophobic material. Such an embodiment may be useful for
absorbent towels and other materials where absorption may occur on
either surface. In that case, it is preferred that hydrophobic
material be placed on the most elevated regions of both surfaces,
the elevated regions being the highest regions when the respective
surface is facing up. Since the depressions on the upper surface
will generally correspond to elevated regions on the lower surface
when the lower surface is facing up, especially when the web has
substantially uniform thickness throughout its cross section, the
hydrophobic material on one surface will generally not be
superposed directly over other hydrophobic material on the other
surface but the hydrophobic regions on the two surfaces will tend
to be in a staggered relationship to each other. The type of
hydrophobic material, its method of application, and the amount
applied may differ on both sides. Likewise, multiple applications
of different hydrophobic materials may be performed on a single
surface to achieve desired properties or a desired visual
appearance, including the use of mutlicolored fiber patches,
colored adhesives, and the like.
[0156] The scope of the present invention also includes multi-ply
basesheet structures and laminates with one or more layers being
the dual-zoned absorbent webs described above. For example, the
traditional fluff pulp absorbent core used in many absorbent
articles may be replaced by a series of resilient basesheet layers,
such as the wet resilient uncreped, through-air dried basesheets
described in Examples 7-10 below, and a dual-zoned absorbent web
containing hydrophobic material could be placed in superposed
relation on said series of resilient basesheet layers. All or some
of the multiple plies may be further provided with apertures,
slits, embossments, and the like. Multiple plies may be fixedly
attached to each other through adhesives, sewn thread, entanglement
by needling or fluid jets, embossing, and the like.
[0157] An excellent hand towel can be made by taking advantage of
the unusually high wet resiliency of uncreped, non-compressively
dried basesheets, especially those containing resilient fibers such
as high-yield fibers and containing wet strength agents. The
fiber-fiber bonds of such sheets comprise hydrogen and covalent
bonds which are formed during non-compressive drying while the
sheet is in a molded, three-dimensional structure. While
calendering may flatten such a basesheet, many of the bonds are
undisturbed. When the basesheet is later wetted, the swelling
fibers can be relieved of the stresses imparted by calendering and
can return to the structure achieved during drying. In a sense, the
bonds have locked in a memory of the basesheet structure achieved
during drying and curing of wet strength resins. Thus it is
possible to prepare a calendered, flat basesheet which can return
to a bulkier, three-dimensional state upon wetting, as disclosed in
commonly owned copending application Ser. No. 60/013,308 filed Mar.
8, 1996 to D. Hollenberg et al., herein incorporated by reference.
Such a "thin when dry, thick when wet" material can be used
advantageously in the present invention. By adding hydrophobic
material to the elevated regions of a basesheet and then
calendering the basesheet, or alternatively, by adding hydrophobic
material to the previously-high spots after calendering, a
relatively thin, flat absorbent web is produced which has
hydrophilic and hydrophobic regions in essentially the same plane.
That structure can absorb fluids well upon contact because
hydrophilic regions are in contact with the fluid. However, after
wetting, the absorbent web expands such that the wet-feeling,
hydrophilic regions are no longer in direct contact with the skin
while the dry-feeling, hydrophobic regions become elevated to
contact the skin. Such an absorbent web desirably has an Overall
Surface Depth of about 0.2 mm or less while dry and about 0.3 mm or
greater when wetted to a moisture content of 100%. Alternatively,
the calendered absorbent web can have an Overall Surface Depth of
about 0.3 mm or less while dry and about 0.4 mm or greater, more
specifically about 0.5 mm or greater, when wetted to a moisture
content of 100%.
Embodiments with Hydrophobic Fibers
[0158] FIG. 13. depicts a form of a preferred set of embodiments
wherein the hydrophobic material comprises groups or tufts of thin
polyolefin fibers 50 or other hydrophobic fibers in order to
provide a soft, clothlike feel. The fibers may comprise a variety
of fiber lengths and types 50a and 50b, or may be primarily short
fibers 50c with a fiber length smaller than the characteristic
length of the elevated regions of the basesheet or may be primarily
long fibers 50c with a length near or greater than the
characteristic length of the elevated regions of the basesheet. In
one embodiment, the tufts may be patches of short synthetic fibers
attached preferentially to the elevated regions of the upper
surface of the basesheet such that less than 80%, preferably less
than 50%, and more preferably less than about 25% of the surface
area of said basesheet is covered by the attached synthetic fibers.
Such fibers may be applied by adhesives, thermal bonding,
ultrasonic binding, electrostatic attraction, needling,
entanglement, hydroentanglement or through the use of adhesives or
binders, including water-repellent binders. The adhesives or
binders may include hydrophilic agents such as polyvinyl alcohol,
starch, cationic latexes, proteins, and the like, provided that the
hydrophobic effect of the adhered fibers is not destroyed or
severely reduced by the use of such adhesives. To ensure
hydrophobic activity, water-repellent binders may be desirable,
including materials such as polybutyl acrylate, styrene-acrylic
copolymer, acrylic vinyl chloride copolymer, ethylene-acrylic acid
copolymer, ethylene-vinyl acetate copolymer, ethylene-vinyl
chloride copolymer, acrylic copolymer latex, styrene-butadiene
latex, and vinyl chloride latex. Suitable repellent binders which
may be utilized are Geon 580X83 and Geon 580X119, sold by Goodrich
(consisting of vinylchloride latex); Emulsion E1497, and Emulsion
El 847, sold by Rohm & Haas (consisting of an acrylic
emulsion); and Rhoplex NW-1285, sold by Rohm & Haas (consisting
of an acrylic emulsion); Airflex 120 and Airflex EVLC 453, sold by
Air Products (consisting of ethylene vinyl chloride emulsions);
Nacrylic 78-3990, sold by National Starch (consisting of an acrylic
emulsion) and Primacor, sold by Dow Chemical (consisting of an
ethylene/acrylic acid copolymer).
[0159] As shown in FIG. 13, a densified absorbent material 51
preferably is in contact with the lower side of the hydrophilic
basesheet 1 wherein the densified absorbent material has a pore
size smaller than the characteristic pore size of the basesheet 1
or a density greater than the density of the basesheet 1 and
preferably has a density of about 0.1 g/cc or less, and more
preferably about 0.2 g/cc or less. The densified absorbent material
can be an airlaid web or a densified fluff pulp layer or other
layers of cellulosic tissue. Preferably the densified absorbent
material is stabilized to prevent excessive expansion or loss of
absorbent capacity upon wetting. Stabilization can be achieved
through the addition of thermosetting fibers or particles followed
by heat treatment, by the addition of crosslinking agents followed
by proper curing or heat treatment, by the addition of adhesives in
the web, or other means known in the art. When fluid enters the
basesheet 1, capillary forces can then wick the fluid into the
absorbent material. If the material is stabilized, it will be less
likely to lose its capillarity upon wetting but can continue to
wick and retain fluids effectively.
[0160] The hydrophobic fibers 50 may be applied in isolated or
interconnected patches along the uppermost surfaces of the
hydrophilic basesheet, or, in the case of a relatively flat
basesheet, they may be applied in a specific pattern to provide
either isolated or interconnected patches of such material, or a
combination of isolated and interconnected regions, preferably
elevated relative to the surrounding untreated basesheet such that
skin adjacent to the cover material will preferentially contact and
sense the soft hydrophobic regions. Preferably, the fibers have a
denier less than about 9, more specifically less than about 6, more
specifically less than about 5, and most specifically from about 1
to about 5. Suitable polymers include ethylene/propylene
copolymers, polyester copolymers, low-density polyethylene,
acrylic, ethylene/vinyl acetate copolymer, polyethylene,
polypropylene, chlorinated polyethylene, polyvinyl chloride,
polyamide, high density polyethylene, linear low-density
polyethylene, and the like. Conjugate fibers such as bicomponent
sheath/core or bicomponent side-by-side fibers may also be used.
Bicomponent fibers with a relatively low melting point material and
a higher melting point material in a single fiber may be used by
heating the fibers in contact with the basesheet such that the low
melting point material melts and adheres the unmelted higher
melting point material to the basesheet. Although continuous
filaments of fibers may be employed, the preferred fibers have
lengths of from about 0.3 mm to about 10 mm, more specifically from
about 0.5 mm to about 5 mm, more specifically less than about 3 mm,
and most specifically less than about 2 mm. Preferably the attached
fibers have at least one end which is free and can deform or
deflect under shear to provide a soft, velvety feel. The fibers
should be fixedly attached such that they do not readily fall off
or slough off excessively in use. The attached fibers may be
applied to form a layer approximately one fiber diameter in depth
or a layer having a plurality of fiber diameters in thickness,
including 2 to 100 fiber diameters, more specifically 3 to 50 fiber
diameters or more specifically still 3 to 10 fiber diameters in
depth.
[0161] The fibers may part of a preformed nonwoven web or may be
loose fibers deposited through air laying and subsequent bonding,
preferably using a patterned vacuum surface to apply the fibers in
a desired pattern, or else by applying a fairly uniform mat of
short fibers onto the surface of the basesheet and bonding only the
fibers on the uppermost regions of the surface of the basesheet.
The latter process may include a heated nip in which the raised
regions on the basesheet force better contact between the deposited
fibers and a textured heated surface, such that fibers become
thermally bonded to the web only at the highest points on the
basesheet. The high spots on the textured heating surface or
heating roll provide spot welding of the fibers onto the
basesheet.
[0162] A useful method of attaching hydrophilic fibers requires
first printing or depositing binder material or adhesive onto the
uppermost regions of a textured basesheet, such as by gravure
printing, followed by exposure of the basesheet to loose fibers
entrained in air, as in an air laying process, such that the fibers
are retained by the binder material on the printed regions but not
retained elsewhere on the basesheet. Unadhered fibers could then be
removed by blowing of air or by vacuum, and then recycled. In this
manner thin mats of loose, fluffy fibers could be deposited and
attached on the desired locations on the basesheet, preferably with
minimal sheet penetration by the adhesive.
[0163] Fibers may be formed directly on the basesheet or deposited
immediately after formation using melt blown or spun bond
processes, adapted to provide fibers only in desired regions.
Alternatively, a continuous thin, soft, bulky layer of a preformed
melt blown or spun bond fibers may be cut to have apertures over
the low regions of the tissue web and then positioned properly on
the web and attached by thermal bonding or other means. In another
embodiment, the fibers may be incorporated into a dilute aqueous
slurry and applied onto the basesheet. This may be done during the
formation of the basesheet itself with a layered headbox, resulting
in a unitary basesheet containing a portion of soft, hydrophobic
fibers embedded in the upper layer of an otherwise cellulosic
basesheet. Additional application of water-repellent agents at the
uppermost regions of the contoured surface of the basesheet may
then be needed to ensure that said uppermost regions are
sufficiently hydrophobic.
[0164] Applicants have found that a contiguous web of hydrophobic
fibers, such as spunbond or meltblown nonwoven web of synthetic
fibers, can be especially advantageous for use as the hydrophobic
matter of the present invention, offering economical processing and
excellent comfort. For effective removal of menses, mucous, runny
bowel movement, and other viscous fluids, the nonwoven web should
be provided with macroscopic apertures, slits, or other openings as
shown in FIG. 14 to provide good access to the hydrophilic
basesheet for body exudates. The openings or apertures 61 in the
nonwoven web 60 should overlay a portion of the depressed regions
in the hydrophilic basesheet such that fluid is repelled by the
most elevated portions of the surface contacting the skin and drawn
toward depressed regions that are not in direct contact with the
skin.
[0165] Openings in a nonwoven web can be provided through pin
aperturing; perf embossing and mechanical stretching of the web;
die punching or stamping; hydroentangling to impart apertures by
rearrangement of the fibers; water knives that cut out desired
apertures or holes in the web; laser cutters that cut out portions
of the web; patterned forming techniques, such as air laying of
synthetic fibers on a patterned substrate to impart macroscopic
openings, as disclosed by F. J. Evans in U.S. Pat. No. 3,485,706,
issued Dec. 23, 1969, and U.S. Pat. No. 3,494,821, issued Feb. 10,
1970, both incorporated herein by reference; needle punching with
sets of barbed needles to engage and displace fibers; and other
methods known in the art. Pin aperturing of nonwoven materials is
described in commonly owned U.S. Pat. No. 5,188,625, issued Feb.
23, 1993 to Van Iten, et al., herein incorporated by reference.
[0166] Openings or apertures can be created in a way that permits
excellent registration of apertures 61 with the depressed regions
of a three-dimensional through-dried tissue web. A modified form of
hydroentangling may be especially useful in this regard. Such a
process comprises placement of a nonwoven web 60 on the same type
of through-drying fabric that is used to mold the associated
basesheet during through drying. With the nonwoven web on the
through-drying fabric, hydroentangling can be applied to drive
fibers away from the elevated portions of the through-drying
fabric, which will typically correspond to the depressed regions of
the fabric-side of the through-air dried sheet. If the tissue web
is to be used with the air-side toward the body in the absorbent
article, then the nonwoven web should be placed on the backside of
the through-drying fabric and then hydroentangled, for the elevated
portions of the backside of the through-drying fabric will
generally correspond to the depressed regions of the other side on
which the tissue web is molded.
[0167] After hydroentangling on a through-drying fabric has
provided the nonwoven web 60 with a pattern of apertures 61, the
web can be registered with the through-dried tissue to put the
apertures over the depressed regions to result in effective intake
into the hydrophilic depressions while maintaining hydrophobic
material on the elevated portions of the basesheet. Registration
can be achieved with photoeyes and image analysis software or other
mechanical means known in the art to control the position of the
nonwoven web as it is placed on the molded basesheet by automated
equipment.
[0168] Preferably, the openings are provided in a regular pattern
over at least a portion of the topsheet of the absorbent
article.
[0169] Wicking of fluids into the apertures toward the hydrophilic
basesheet can be enhanced by modification of the surface chemistry
of the hydrophobic nonwoven web in the area of the apertures, such
as by addition of surfactants to the nonwoven web in the vicinity
of apertures or oxidation of fibers by plasma or other treatment.
Alternatively, cellulosic fibers or other hydrophilic matter could
be added to the region of the apertures to enhance wicking. For
example, cellulosic fibers could be added to the periphery of the
apertures to enhance wicking.
EXAMPLES
Example 1
[0170] To demonstrate an example of a textured, wet resilient
absorbent web with improved dry feel, a suitable basesheet was
prepared and modified by addition of hydrophobic material in the
form of paraffin. The basesheet was produced on a continuous tissue
making machine adapted for uncreped through-air drying, similar to
the machine configuration shown in FIG. 4. The machine comprises a
Fourdrinier forming section, a transfer section, a through-drying
section, a subsequent transfer section and a reel. A dilute aqueous
slurry at approximately 1% consistency was prepared from 100%
spruce bleached chemithermomechanical pulp (BCTMP), pulped for 20
minutes at about 4% consistency prior to dilution. The spruce BCTMP
is commercially available as Tembec 525/80, produced by Tembec Corp
of Temiscaming, Quebec, Canada. Kymene 557LX wet strength agent,
manufactured by Hercules, Inc., Wilmington, Del., was added to the
aqueous slurry at a dosage of about 20 pounds of Kymene per ton of
dry fiber. The slurry was then deposited on a fine forming fabric
and dewatered by vacuum boxes to form a web with a consistency of
about 12%. The web was then transferred to a transfer fabric
(Lindsay Wire 952-505) using a vacuum shoe at a first transfer
point with no significant speed differential between the two
fabrics. The web was further transferred from the transfer fabric
to a woven through-drying fabric at a second transfer point using a
second vacuum shoe. The through drying fabric used was a Lindsay
Wire T-116-3 design (Lindsay Wire Division, Appleton Mills,
Appleton, Wis.), based on the teachings of U.S. Pat. No. 5,429,686
issued to Kai F. Chiu et al. The T-116-3 fabric is well suited for
creating molded, three-dimensional structures. At the second
transfer point, the through-drying fabric was traveling more slowly
than the transfer fabric, with a velocity differential of 2.8%. The
web was then passed over a hooded through-dryer where the sheet was
dried. The hood temperature was approximately 200.degree. F. The
dried sheet was then transferred from the through-drying fabric to
another fabric, from which the sheet was reeled. The pilot paper
machine for producing the uncreped paper was operated at a speed of
approximately 20 feet per minute. The basis weight of the dry
basesheet was approximately 39 gsm (grams per square meter). The
sheet had a thickness of 0.64 mm when measured with a platen gauge
at 0.05 psi, for a dry bulk of 16.4 cc/g. The Surface Depth is
about 0.42 mm.
[0171] Samples of the basesheet were conditioned under Tappi
environmental conditions for several days, then cut to a number of
6 in.times.12 in sheets which were then treated with paraffin wax
using a variety of methods. A rectangular slab of Gulfwax.TM.
paraffin for home canning was used to apply a small quantity of wax
on the fabric side surface of the uncreped basesheet produced as
described above. Several basesheet samples were heated individually
on a Corning PC-351 hot plate set at a low power level of 2.5. The
samples were held in light contact with the heated surface by hand
for 5 to 10 seconds, then removed and placed on a table. The slab
of wax was them immediately dragged over the heated sample surface
to deposit a small quantity of wax on the most elevated regions of
the upper surface. In one version, the fabric side of the basesheet
was in contact with the heated surface, while in a second version,
the air side of the basesheet was heated. In applying the wax, the
slab was held at about a 30.degree. angle relative to the plane and
the lower end of the slab was placed on the basesheet. The slab was
then dragged with light force (estimated at about 0.5 to 1 pound)
over one entire surface of the basesheet such that the contacting
end of the slab was the trailing edge. Care was taken to apply the
wax uniformly. The objective was to avoid melting the wax since the
melted wax would impregnate the basesheet and not remain on the
surface, but to facilitate the deposition of wax onto the basesheet
through heat. Heating and wax treatment was done successively on
sections about 3-inches square or 6-inches square until the entire
basesheet sample was treated. The wax slab was weighed before and
after application. The typical amount of wax applied to the 6
in.times.12 in basesheet was about 0.06 g.
[0172] Upon subsequent wetting of the resulting absorbent web,
minute upper sections of the wax-treated web appeared slightly
lighter than untreated regions, as if the wax had trapped some air
next to the fibers. Based on the physical appearance, it was
evident that wax was preferentially distributed on the uppermost
regions of the basesheet surface, occupying a small fraction of the
total surface area estimated to be about 10%.
[0173] Mean Rewet values for untreated and wax-treated samples are
shown in Table 1. Also listed are mean Normalized Rewet values
(Rewet divided by the conditioned dry mass of the sample). The
graph in FIG. 15 depicts the mean values and the 95% confidence
intervals about the means (1.96 * standard deviation/square root of
sample size). The treatment with paraffin resulted in a significant
decrease in Rewet. The decrease in Rewet value is assumed to be
indicative of a dryer feel if the tissue were wetted in contact
with skin, for less fluid could pass through the local, elevated
hydrophobic barriers to contact the skin. The wax-treated samples
also felt slightly less gritty than the untreated samples,
apparently due to some degree of lubricity afforded by the paraffin
on the highest portions of the treated surface.
1TABLE 1 Rewet Values for Example I Normalized Rewet Treatment
Method Rewet Value, g (Rewet/Dry Mass) Untreated 0.446 0.706 Wax,
air-side heat 0.390 0.629 Wax, fabric-side heat 0.363 0.564
Example 2
[0174] In order to further illustrate this invention, uncreped
throughdried tissue basesheet was produced using the method
substantially as described in Example 1. More specifically,
single-layer, single-ply tissue was made from unrefined northern
softwood bleached chemithermomechanical pulp (BCTMP) fibers. After
pulping and dilution of the BCFMP fibers, Kymene 557LX was added at
20 kilograms per metric ton of pulp. The forming fabric in this
case was an Appleton Wire 94M fabric and the first transfer fabric
was a Lindsay 956 fabric. Rush transfer was performed at the first
transfer point, during the transfer from the forming fabric to the
Lindsay 956 transfer fabric. The degree of rush transfer was 35%.
The differential velocity transfer process used the vacuum shoe
geometry taught in U.S. Pat. No. 5,667,636, issued Mar. 4, 1997 to
S. A. Engel et al., previously incorporated by reference. At this
second transfer point, from the transfer fabric to the through-air
drying, both fabrics were running at substantially the same speed
of about 40 feet per minute. The web was then transferred to a
throughdrying fabric (Lindsay Wire T116-3). The throughdrying
fabric was traveling at a speed substantially the same as the
transfer fabric. The web was then carried over a throughdryer
operating at a hood temperature of about 315.degree. F. and dried
to final dryness of about 94-98 percent consistency. The basis
weight of the web was 60 gsm.
[0175] The resulting uncreped throughdried tissue basesheet was
used in measurements of In-Plane Permeability using a stack of two
disks, yielding a value of 1.87.times.10.sup.-10 m.sup.2 Wet
resiliency testing gave a WCB (Wet Compressed Bulk) value of 9.65
cc/g, a Springback of 0.889, and an LER of 0.824. The bulk measured
at 0.1 psi was 16.2 cc/g.
[0176] After several weeks of storage under Tappi environmental
conditions, the basesheet was then treated with paraffin wax
essentially as described in Example 1. Two strips were prepared, 12
inches.times.6 inches. For each strip, the fabric side of a 6-inch
square region was heated in contact with the Corning PC-351 hot
plate at a power setting of 2.5 for about 5 seconds, then removed
and placed fabric-side up on a flat surface. A slab of paraffin wax
was then dragged over the surface to deposit about 0.06 g of wax on
the surface of the first strip and 0.07 g of wax on the surface of
the second. The two strips were then cut into 4-inch.times.6-inch
segments. All segments from the first strip (labeled 1A, 1B, and
1C) were tested for Rewet and one segment from the second strip was
tested in addition to 3 similar untreated strips of the same
basesheet (labeled 3, 4, and 5). Results are shown in Table 2.
Rewet values for the waxed segments were significantly lower than
the untreated samples, with the exception of segment 1A, which had
a value similar to untreated samples. This sample was excessively
wet, beyond the recommended range for the test, so the additional
available moisture may have inflated the Rewet value. However, it
is suspected that the waxing operation may have been performed
poorly in the region that would later be in contact with the
Whatman filter paper during testing. The mean Rewet for the waxed
samples, excluding sample 1A, is 0.467 g compared to the untreated
mean of 0.689 g, an apparent reduction of 32%. Normalized Rewet
also drops significantly due to hydrophilic treatment. Here, Rewet
values less than 0.68 g are taken as evidence of improved dry
feel.
2TABLE 2 Rewet Values for Example 2 Dry Wet Normalized Rewet Sample
Treatment Mass Mass Rewet, g (Rewet/Dry Mass) 1A Waxed 0.93 3.95
0.628 0.675 1B Waxed 0.94 3.82 0.438 0.466 1C Waxed 0.98 4.06 0.525
0.536 2 Waxed 1.01 4.14 0.437 0.433 3 Unwaxed 0.97 3.98 0.680 0.701
4 Unwaxed 1.00 4.06 0.692 0.692 5 Unwaxed 1.03 4.26 0.695 0.675
[0177] To determine if the small amount of presumably dominantly
surface wax applied to the textured basesheets had any adverse
effect on total absorbent capacity, the tested segments were fully
immersed in tap water and then held by a corner and allowed to drip
for 60 seconds, then weighed. The "Dripping Wet Mass" for untreated
samples 3 and 5 was 7.8 and 8.3 g, respectively. The "Dripping Wet
Mass" for samples 1A, 1B, and 1C was 7.44, 7.55, and 7.9 g,
respectively. For sample 2, it was 8.00 g. Given the variability
and overlap of the data ranges for treated and untreated samples,
there is no clear evidence of a significant decrease in absorbent
capacity of the waxed samples.
Examples 3-6
[0178] In order to further illustrate a method of making absorbent
webs of this invention, basesheets were produced using non-wet
resilient northern softwood kraft fibers (NSWK), with and without a
wet strength agent (20 lbs Kymene/ton of fiber), and wet resilient
fibers (spruce BCTMP), with and without a wet strength agent (20
lbs Kymene/ton of fiber), using an uncreped throughdried process
substantially as shown in FIG. 4.
[0179] The fiber was pulped at 4% consistency in the hydropulper
for 30 minutes. The fiber was pumped into a stock chest and diluted
to 1.0% consistency. 20#/ton of Kymene 557 LX was added to the
stock chest and allowed to mix for 30 minutes. A single-layer,
blended sheet of 30 gsm dry weight was formed on an Albany 94M
forming fabric and dewatered with 5 inches (127 millimeters) of
mercury vacuum. The forming fabric was traveling at 69 fpm (0.35
meters per second). The sheet was transferred at a 15% rush
transfer to a Lindsay 952-S05 transfer fabric traveling at 60 fpm
(0.30 meters per second). The vacuum in the transfer between the
forming fabric and transfer fabric was 10 inches (254 millimeters)
of mercury.
[0180] The sheet was vacuum transferred at 12 inches (305
millimeters) of mercury to a throughdryer fabric (Lindsay T116-1)
traveling at the same speed as the transfer fabric, 60 fpm (0.30
meters per second). The sheet and throughdryer fabric traveled over
a fourth vacuum at 12 inches (305 millimeters) of mercury just
prior to entering a Honeycomb throughdryer operating at 200.degree.
F. (93.degree. C.) and dried to a final dryness of 94-98%
consistency.
[0181] The basesheets were aged for over 5 days at less than 50%
humidity at 70.degree. F. (21.degree. C.). The basesheets were
tested for physical characteristics in a controlled environment of
50%.+-.2% humidity and 23.degree. C..+-.1.degree.. The wet and dry
strength were Instron tested with a 3-inch (7.62 cm) sample width,
4-inch (10.16 cm) jaw span at 10 in/min (25.4 cm/min) crosshead
speed. Caliper was measured with the TMI tester at 0.289 psi.
[0182] Physical property results are shown in the table of FIG. 16.
Example 6 exhibited substantially greater wet resiliency, as
measured by the Wet Wrinkle Recovery Test, than the other three
samples. In addition, Example 6 also showed a high wet:dry ratio.
The properties of Example 6 in particular make it suitable for use
as a basesheet that can be calendered and later recover much of its
original bulk upon wetting. When treated with hydrophobic materials
such as silicones or talcum powder, such a calendered absorbent web
can provide high absorbency and a dry feel when the hydrophilic
regions rise from the remainder of the sheet after wetting.
Examples 7-10
[0183] Further examples were carried out similar to those described
in Examples 3-6, but for the purpose of exploring the basis weight
effect on a bulky, absorbent, wet resilient structure. Four basis
weight levels of 30, 24, 18 and 13 gsm of 100% Spruce BCTMP with
20#/ton Kymene were produced.
[0184] The fiber was pulped at 4% consistency in the hydropulper
for 30 minutes. The fiber as pumped into a stock chest and diluted
to 1.0% consistency. 20#/ton of Kymene 557 LX was added to the
stock chest and allowed to mix for 30 minutes. A single-layer,
blended sheet was formed on an Albany 94M forming fabric and
dewatered with 4 inches (102 millimeters) of mercury vacuum. The
forming fabric was traveling at 69 fpm (0.35 meters per second).
The sheet was transferred at a 15% rush transfer to a Lindsay
952-S05 transfer fabric traveling at 60 fpm (0.30 meters per
second). The vacuum in the transfer between the forming fabric and
transfer fabric was 7 inches (178 millimeters) of mercury. The 13
gsm sample was produced without a rush transfer, the forming fabric
was traveling at 60 fpm (0.30 meters per second), the same as the
transfer fabric and throughdryer fabric.
[0185] The sheet was vacuum transferred at 10 inches (254
millimeters) of mercury to a throughdryer fabric (Lindsay T116-1)
traveling at the same speed as the transfer fabric, 60 fpm (0.30
meters per second). The sheet and throughdryer fabric traveled over
a fourth vacuum at 11 inches (279 millimeters) of mercury just
prior to entering a Honeycomb throughdryer operating at 260.degree.
F. (127.degree. C.) and dried to a final dryness of 94-98%
consistency.
[0186] The basesheets were aged for over 5 days at less than 50%
humidity at 70.degree. F. (21.degree. C.). The basesheets were
tested for physical characteristics in a controlled environment of
50%.+-.2% humidity and 23.degree. C..+-.10. The wet and dry
strength were Instron tested with a 3-inch (7.62 cm) sample width,
4 inch (10.16 cm) jaw span at 10 in/min (25.4 cm/min) crosshead
speed. The caliper was measured with the TMI tester at 0.289
psi.
[0187] Physical property results are summarized in the table of
FIG. 17. As shown, examples 7-10 exhibited high wet resiliency as
determined by the Wet Wrinkle Recovery Test and the Compressive Wet
Resiliency tests. Materials such as the web of Example 10 are
especially suitable as a basesheet to receive hydrophobic matter in
the production of a dense, calendered absorbent web that can
rapidly absorb liquid and then spring back to a bulkier structure
having hydrophilic material on the uppermost regions to provide a
clean, dry feel. Typical commercial tissue and paper towels
generally have Wet Springback Ratios of less than 0.7, WCB values
less than 6, and LER values less than 0.7. Likewise, such materials
tend to have In-plane Permeability values below
0.4.times.10.sup.-10 m.sup.2.
Examples 11 and 12
[0188] For Examples 11 and 12, the fabric side of the basesheet of
Example 1 was treated with adhesive sprays to create scattered
hydrophobic regions, some of which were further treated with
hydrophobic powder. For Example 11, a spray can of 3M #72 Pressure
Sensitive Adhesive was used to randomly cover about 30% of the
surface area of the basesheet with the blue, flexible, soft, and
low-tack adhesive material. Tack was further reduced by sprinkling
a small quantity of lycopodium powder (also known as club moss
spores, commercially available from EM Science, Gibbstown, N.J.) on
one portion of the web and talc powder on another portion to
selectively adhere to the adhesive and remove the tacky sensation.
Unattached powder was shaken off. For Example 12, the spray
adhesive used was 3M #90 High Strength Adhesive, which was randomly
and lightly sprayed to yield scattered patches about 1/2 to 1 inch
in diameter containing adhesive on the upper surface. Tack was
again reduced by sprinkling talk or lycopodium powder on various
portions of the web and removing excess powder. When the webs were
wetted, the hydrophobic regions containing adhesive and hydrophobic
powder felt somewhat drier than the untreated regions. The
adhesive-containing regions of Example 12 were noticeably stiffer
than the surrounding basesheet and would be unsuitable for many
products. The lower viscosity of the adhesive used in Example 12
also resulted in relatively more penetration of the adhesive into
the absorbent web relative to Example 11, so the adhesive patches
of Example 12 appeared lighter than the surrounding untreated
regions when the absorbent web was fully wetted with water.
Example 13
[0189] Additional uncreped, through-air dried basesheets were made
according to Example 2. Example 13 differed in having 10 pounds of
Kymene per ton of dry fiber in the furnish, had 15% rush transfer,
and comprised 75% northern softwood kraft fibers and 25% spruce
BCTMP. As with Example 2, the basis weight was 60 gsm and the
through-air drying fabric was a Lindsay Wire T116-3 fabric. The
measured Wet Springback Ratio was 0.839, WCB was 7.5 cc/g, and LER
was 0.718. In-plane Permeability was 0.84.times.10.sup.-10
m.sup.2.
[0190] The basesheet of Example 13 could be made into a web of the
present invention by blade coating the upper surfaces of the fabric
side of the basesheet with a flexible, hydrophobic, low-tack hot
melt adhesive at elevated temperature immediately followed by air
laying fine synthetic fibers having an average length of about 1 mm
on the adhesive-containing side of the web, followed by light air
jets to blow off and recover unattached fibers. Cooling jets may be
desired to remove tack of the adhesive before reeling. Tack
reduction of exposed adhesive may also be accomplished by the
addition of particulates entrained in air jets applied to the
treated web, said particulates comprising talc, baking soda,
titanium oxide, zinc oxide, miscellaneous fillers known in
papermaking, and the like.
[0191] The foregoing examples serve to illustrate possible
approaches pertaining to the present invention in which improved
dry feel and other properties are achieved through novel
combinations of resilient, textured basesheets with hydrophobic
matter. However, it will be appreciated that the foregoing
examples, given for purposes of illustration, are not to be
considered as limiting the scope of this invention which is defined
by the following claims and all equivalents thereto.
Example 14
[0192] A 0.6 osy polyethylene spunbond nonwoven web was laminated
with construction adhesive to the fabric side of a 40 gsm uncreped,
through-air dried web comprising 100% BCTMP spruce fibers and
textured by through drying on a Lindsay Wire T-216-3 fabric. A
strip of airlaid cellulosic web was prepared that had been
densified and stabilized with about 1% thermoplastic fibers which
melted during heating to hold the strip at a constant density of
about 0.2 g/cc. The 1-inch wide strip was placed underneath the
uncreped basesheet with the attached nonwoven web on top. Fluid
intake was tested by placing drops of dyed water on the upper
surface. The water rapidly penetrated into the tissue basesheet and
then into the airlaid strip, resulting in the majority of the fluid
being held by the airlaid material. When colored drops of water
were placed on the laminated web without an underlying airlaid
absorbent, the fluid spread over a much greater area in the
basesheet than when the airlaid strip was present.
[0193] A mixture of about equal parts egg white and water, with
some green commercial food coloring added, was prepared to simulate
the intake of viscoelastic fluids such as mucous or menses. The
solution was gently stirred to establish a uniform consistency. The
solution was then applied as drops of about 0.3 ml to about 1 ml to
the surface of the intake material with the airlaid strip
underneath. Intake seemed very slow or even completely impeded by
the nonwoven material. The tip of a knife blade was then used to
scratch away a small portion of the nonwoven web, resulting in an
aperture about 0.2 mm wide and 2 mm long. A drop of the egg white
solution applied to the aperture penetrated into the hydrophilic
within a few seconds, much more rapidly than without the aperture,
yet still more slowly than the less viscous and non-viscoelastic
colored water.
Example 15
[0194] To demonstrate the potential of apertured nonwoven fabrics
in the present invention, three polyethylene nonwoven spunbond webs
were acquired having basis weights of 0.4, 0.6, and 0.8 ounces per
square yard (osy). The webs were apertured using a roll device for
twin aperturing. Metallic pins were mounted in holes in curved
metal plates that could be bolted onto the midsection of an upper
roll. Matching metal plates with holes mounted to the lower roll
received the upper tapered portion of the pins in the upper roll.
Two different pin diameters were used, 0.109-inches and
0.187-inches. The holes for receiving and holding pins were arrayed
in a bilaterally staggered grid. The 0.187-inch pins were placed
into every hole in the array over a two-inch wide strip around the
upper roll. Roll perimeter is 36 inches. The 0.187-inch pins were
thus spaced apart at about 0.25-inch intervals from center to
center along any row. The 0.109-inch pins were spaced apart over a
4-inch wide strip of bilaterally staggered holes, with pins loaded
only in alternating rows and in any row containing pins, loaded
only into every other hole of that row. With 11 pins in each 4-inch
wide row, the loaded 0.109-inch pins are spaced apart by about
0.4-inches from center to center. To improve the quality of the
aperturing, the upper roll containing the pins is heated to about
200.degree. F. and the lower roll, which contacts the nonwoven web,
is electrically heated to 150.degree. F. These are temperatures
measured inside the roll. Using a surface thermocouple, the upper
surface temperature of the upper roll was measured at
150-158.degree. F. Using the 0.109-inch pins first, the aperturing
device was driven at 50 fpm and used to aperture lengths of
polyethylene spunbond material having a basis weight of 0.4, 0.6,
and 0.8 osy (ounce per square yard). Then the plates containing
pins were switched to permit aperturing with the 0.187-inch
diameter pins, also at 50 fpm and all three spunbond basis weight
materials were apertured. The apertured nonwoven web appeared soft
and suitable for use as a feminine care material. Samples of the
nonwoven webs were then cut and placed on sections of uncreped,
through-dried material made according to Wendt et al., previously
incorporated by reference, and textured on three-dimensional
through drying fabric from Lindsay Wire according to Wendt et al.
and Chiu et al., also previously incorporated by reference.
[0195] Though 3M pressure sensitive spray adhesive was used at one
point to join the tissue basesheet and the nonwoven web, joining
the apertured nonwoven to the textured uncreped tissue web was
simplified by a natural mechanical affinity of the tissue surface
for the loopy nonwoven surface. Engagement of fibrils apparently
allows the nonwoven layer to adhere reasonably well, though it IS
preferred to create a more intimately bonded structure through any
of adhesive bonding, ultrasonic bonding, thermal bonding, and the
like.
Example 16
[0196] Composite topsheet structures were prepared by adhering the
apertured webs of Example 15 to textured, uncreped, through air
dried basesheets, similar to those described in Examples 1-10.
Adhesion was achieved with a specialty adhesive transfer paper
comprising a coated release paper printed with dots of adhesive,
such that the dots could be transferred to other surfaces by mild
application of pressure. A hot melt construction adhesive was used,
National Starch #5610, printed on a coated release paper via screen
printing with a New England Rotary screen, 40-NERO-SF0001. To join
an apertured nonwoven web to the textured tissue paper, the
adhesive transfer paper was placed with the adhesive dots in
contact with textured tissue and then pressed lightly with a rubber
roller at a load of less than 0.5 pounds per linear inch such that
the web was not substantially flattened by the roller and such that
a portion of the adhesive dots transferred to the most elevated
portions of the web. The apertured nonwoven web was then superposed
on the tissue. In placing the nonwoven web on the tissue web, the
side of the nonwoven web that contacted the tissue was the side
which was away from the roll holding the pins during the pin
aperturing process. This tissue-facing side of the nonwoven web had
protrusions surrounding each aperture where the pin had forced some
of the polyolefin material out of the plane of the nonwoven web
during the pin aperturing process. In some cases, it may be
preferably that such protrusions should reside primarily in
depressed regions of the underlying tissue web to provide a nearly
continuous material bridge from the body-facing side of the
nonwoven web to the tissue surface, such that fluid does not need
to cross any significant interfacial gaps between the two or more
layers of the topsheet.
[0197] For these examples, only 0.4 osy basesheet nonwoven spunbond
webs were used. The basesheets were all unlayered, uncreped,
through-air dried tissue webs made according to the principles
given in Examples 1-10, with the exception that basis weight, fiber
type, rush transfer, and fabric types were varied. "High texture"
refers to webs made with about 30% rush transfer onto a Lindsay
Wire T-116-3 fabric as the transfer fabric, followed by through
drying on a T-216-3 fabric. "Flat" tissue was through dried on a
traditional flat through drying fabric lacking high surface depth.
"Medium texture" refers to webs made with 8% rush transfer onto a
Lindsay Wire T-216-3 fabric as the transfer fabric, followed by
through drying on a Lindsay Wire T-116-3 fabric. All webs had about
20 lb Kymene per ton of fiber added for wet strength. The following
combinations of nonwoven and basesheet were tested:
3TABLE 3 Composites tested for intake. Sample Aperturing Basesheet
1 none 30 gsm, 100% BCTMP, high texture 2 0.109" pins 30 gsm, 100%
BCTMP, high texture 3 0.187" pins 30 gsm. 100% BCTMP, high texture
4 0.187" pins 30 gsm, 100% BCTMP, flat 5 0.187" pins 30 gsm, 100%
BCTMP, high texture 6 0.187" pins 50 gsm, 50% bleached northern
softwood, 50% mercerized bleached southern softwood, medium texture
7 0.187" pins 30 gsm, 100% BCTMP, flat
[0198] In some cases, the cover material was combined with a thin
absorbent layer consisting of another uncreped, through-air dried
sheet or an air-laid strip. These absorbent layers include:
[0199] Abs. A: a "high texture" 100% BCTMP web (Sample 1 of Table
3)
[0200] Abs. B: a "flat" 100% BCTMP web (Sample 4 of Table 3);
[0201] Abs. C: a 100% BCTMP uncreped web through-dried on a Lindsay
Wire 134-10 fabric;
[0202] Abs. D: a "medium texture" web comprising bleached softwood
(Sample 6 of Table 3)
[0203] In addition, the airlaid strip of Example 14, having a basis
weight of about 200 gsm, was also used in some tests. The absorbent
layer was simply placed beneath the composite cover and was not
joined mechanically or with adhesives. In some cases, light
adhesive might be desirable to hold the cover onto the absorbent
core.
[0204] To demonstrate the suitability of the apertured webs of
Example 15 for intake of menses, a simple menses simulant was used.
The simulant was a 50:50 mixture of fresh egg whites and water,
with added fugitive dye. The mixture was prepared by separating the
egg whites from the yolks for two large eggs (Sparboe Farms,
Litchfield, Minn.) that had been removed from refrigeration and
placed in a room with a temperature of approximately 72.degree. F.
for six hours. The egg white mass was 60.0 g. An additional 60 g of
deionized water was added to the egg whites in a 250 ml beaker and
stirred vigorously in the beaker with a laboratory spatula for
about 3 minutes, taking care to prevent froth formation. The
resulting mixture appeared slightly turbid and still showed signs
of proteinaceous strands in the fluid having a different refractive
index that other parts of the solution. An additional 2 ml of a dye
solution was stirred in gently. The dye solution was prepared by
adding 40 ml of Versatint Purple II due (Milliken Chemical, Inman,
S.C.) to 1000 ml of deionized water.
[0205] The colored egg white solution was applied to the surface of
the composite topsheet material with an Eppendorf pipette set to
apply 0.5 ml droplets. The droplet was applied to the upper surface
of the topsheet within a 3 second interval, taking care to apply
the drop gently and smoothly. Initially the drop balled up, resting
on the nonwetting surface as a flattened sphere several millimeters
in diameter, broad enough to engage at least one aperture,
typically regardless of where the drop was placed. Then visual
observation was used to identify the time required for wicking to
occur in the plane of the underlying basesheet, and the additional
time after the onset of wicking for the drop to be substantially
removed from the surface of the nonwoven web, such that essentially
no remaining liquid remained noticeably elevated above the plane of
the nonwoven web. The first time, the time for visible wicking to
begin, is termed the "entry time," and was detected when colored
fluid could be seen extending horizontally in the basesheet beyond
the margins of the drop on top. The second time, the time for
substantial removal of the liquid from drop on the nonwoven surface
is the "wicking time." The sum of the two times is the "intake
time." Results are shown for several trials in Table 4. Best
results were obtained with the larger pin apertures. With the
smaller apertures, the hydrophobic fibers in the protrusion on the
back side of the web formed during aperturing may have become
flattened to partially close off apertures during attachment to the
uncreped tissue web.
4TABLE 4 Intake results for egg-white solutions for the composites
of Table 3. Run Sample Entry time (s) Wicking time (s) Intake time
(s) 1 1 >500 NA >500 2 2 >500 NA >500 3 3 70 90 160 4 3
+ Abs. A 20 80 100 5 4 + Abs. B 10 50 60 6 4 + Abs. B 0 25 25 7 5 +
Abs. C 10 30 40 8 5 + Abs. C 0 40 40 9 6 + Abs. D 5 35 40 10 7
about 200 about 200 about 400 11 4 + air laid 10 150 160 12 4 + air
laid >500 NA >500 13 5 + Abs. C 10 70 80 14 6 + air laid 5
200 205 15 6 + air laid >500 NA >500
[0206] It is believed that intake rates could be increased
significantly by increasing the exposed area of the basesheet.
[0207] By placing drops of the egg white solution directly on BCTMP
and bleached softwood uncreped sheets, it was observed that BCTMP
offers more rapid intake, apparently because of the more open pore
structure of the BCTMP sheet. Densified air laid strips with a
density of about 0.2 cc/g also gave rapid intake of the
solution.
Example 17
[0208] The ability of the present invention to serve as an
improvement over apertured films can be envisioned in this example,
wherein a moist hydrophilic basesheet is provided with a non-planar
apertured structure and then noncompressively dried to impart high
wet resiliency, followed by printing or coating of hydrophobic
matter on the most elevated regions of the body-contacting side of
the apertured web, resulting in a composite material having
hydrophilic apertures and a hydrophobic upper surface. In
particular, a soft, flexible web of basis weight from about 10 gsm
to about 100 gsm, more preferably from about 20 gsm to about 50
gsm, during manufacture is apertured before the web has dried to
above about 60% solids, and preferably before the web has dried
above about 40% solids. The web may be relatively flat or textured
prior to aperturing. Aperturing can be done by protrusions on a
roll contacting the body side of the web while residing on a
surface having mating depressions, such that intermeshing of the
protrusions and the depressions causes apertures to descend away
from the body-contacting side of the web to create a non-planar,
three-dimensional topography with regions of the web adjacent the
apertures having some z-direction fiber orientation. Apertures in
the basesheet can also be created by needling, perf-embossing,
stamping, or differential air pressure. Differential air pressure
can be used when the web resides on a perforated but otherwise
low-permeability carrier. The weak, moist web residing on a
perforated surface permits air pressure to cause portions of fibers
over the perforations to deflect and break free from the plane of
the web and to descend partly in the z-direction. After the 3-D
apertures are created in the moist state, the web should be dried
to completion without significantly disrupting the perforated or
apertured state it has achieved. The structure of the web will then
have high wet resiliency, particularly if low yield fibers or wet
strength additives are used. As a result, the basesheet is provided
with apertures and the lower surface of the basesheet is provided
with fibrous protrusions descending from the basesheet which are
adjacent to the apertures and may surround or partially surround
the apertures, forming hydrophilic aperture walls. The protrusions
or aperture walls, by virtue of being dried in their
three-dimensional state, also have good wet resiliency, or a
tendency to maintain the form and orientation in which they were
dried even after being wetted, especially if high yield fibers or
wet strength agents were used in making the web. Preferably, the
apertures have an open area of at least 15% and more preferably at
least 30%, and have a characteristic or effective diameter
preferably of from about 0.2 mm to about 4 mm, more specifically
from about 0.3 mm to about 2 mm, and most specifically about 0.5 mm
or greater.
[0209] After non-compressive drying, the body-contacting side of
the web (the side remote from the descending sides of the
apertures) is treated with hydrophobic matter. This may be printed
onto the web in discontiguous drops or fine spaced apart regions.
Alternatively, the web may be coated or printed by a smooth
printing surface having a film of the hydrophobic matter in the
molten, liquid state, or slurry state. Waxes or mixtures of wax,
oil, and opacifiers may be especially preferred. The resulting
structure has hydrophobic elevated regions while the walls of the
apertures descending away from the hydrophobic matter are still
hydrophobic. The hydrophobic matter is intimately bonded to the
surface of the hydrophilic web. Because the basesheet is providing
structural integrity, the hydrophobic matter can be continues but
weak or discontiguous, and generally would not be expected to be
capable of being removed from the basesheet without being severely
damaged or disintegrating. It provides a dry feel adjacent the body
and, if properly selected, can enhance the soft, pleasant feel of
the cover. The underlying basesheet provides excellent absorbency
and provides conduits like traditional apertured films for flow
direct to the absorbent core. However, in-plane wicking and flow
channels underneath the basesheet will provide for good fluid
handling and absorbent capacity.
[0210] It will be appreciated that the foregoing examples, given
for purposes of illustration, are not to be construed as limiting
the scope of this invention, which is defined by the following
claims and all equivalents thereto.
* * * * *