Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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ABSORBENT DEVICE WITH IMPROVED
FUNCTIONAL SURFACE
FIELD OF T~ INVENTION
This invention relates generally to absor~ent devices having a web surface and
15 more particularly to an absorbent device and method for improving the dryness and
tactile attributes of the web surface. The invention will be specifically disclosed in
connection with a rotary screen printing method for applying a plurality of
hydrophobic projections to the web surface to improve the dryness and tactile
attributes.
BACKGROUND OF THE INVENTION
It has long been known in the disposable absorbent product art that it is
extremely desirable to construct absorptive devices, such as disposable diapers,sanitary napkins, and the like, plçs~ g a dry surface feel to the user to improve
25 wearing comfort and to l~.;.-;;~e the development of undesirable skin conditions due
to prolonged exposure to moisture absorbed within the product. Typical web
materials used in the m~nllf,.ct~lre of absorbent devices include non-woven and tissue
substrates. Non-woven and tissue substrates are problematic for web surfaces
because once the web surface, also commonly referred to as a topsheet, has been
soiled by bodily fluids such as urine or menstrual fluid, the web surface remains wet
and prolonged exposure to the fiuid absorbed by the web is experienced by the user.
With respect to tissue topsheete, surface weLness continues to be a significant
problem. With respect to non-woven topsheets, an attempt to çiimin~te surface
wetness has been addressed in U.S. Patent No. 4,041,951 issued to Sanford on
August 16, 1977 and hereby incorporated by reference. The Sanford patent discloses
a pl-~re~ed disposable diaper structure comprising a substantially planar, moisture
absorbent layer disposed between a soft topsheet and a moisture-resistant backing
sheet. The non-woven fibrous topsheet preferably comprises an integral structureco.~ g a multiplicity of depressed areas which intim~tely contact the upper mostsurface of a subst~nt~ y planar, moisture absorbent layer. The non-depressed areas
of the topsheet contact the wearer's skin in-use. The non-woven fbrous topsheet of
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the diaper disclosed in Sanford is comprised of a substantially hydrophobic material
exhibiting wet resilience such that the topsheet tends to resume its substantially three-
dimensional character upon removal of pressure applied against the topsheet by the
body movements of the wearer. The non-depressed areas of the topsheet, which aresubstantially the same density as the depressed areas, tend to isolate the wearer's skin
from moisture contained within the moisture absorbent layer, thereby providing
surface dryness and resistance to rewetting when the structure is temporarily
subjected to pressure r~slllting from the wearer's bodily movements. Although
Sanford addresses surface wetness problems with non-woven substrates, the
problems associated with surface wetness have not been totally elirninated and this
reference requires depressions subst~nti~lly through the entire thickness of the web.
Another attempt at solving surface wetness problems in absorbent devices has
been through the development of plastic film topsheets such as disclosed in U.S.Patent No. 3,929,135 issued to Thompson on December 30, 1975, and hereby
incorporated by reference. Thompson suggests a topsheet comprised of liquid-
impermeable material and is provided with tapered capillaries, the capillaries have a
base opening in the plane of the topsheet and an apex opening remote from the plane
of the topsheet. The topsheet disclosed in the Thompson patent allows the free
transfer of fluids from the body into the absorbent ~lem~nt of the device while
inhibiting the reverse flow of these fluids, resllltin~ in a relatively much dryer surface
in contact with the user than had been previously obtainable. However, Co~ ly toexpectations, it has been learned that despite the highly effective fluid transfer and
fluid isolation characteristics exhibited by plastic topsheets of the type generally
disclosed in the Thompson patent and their proven colnp~Libility with the wearer's
skin, many users find it psychologically undesirable to employ a material which is
perceivably plastic in contact with the user's genital area. It is believed that this user
reaction is due in part to the highly re~ tec~ tapered capillary pattern on the wearer-
cont~ctin~ surface of the topsheet and partly to the glossy appearance of the film.
Users are prone to view both of these characteristics negatively when dealing with
plastic films which will contact the user's skin.
Another problem associated with the use of tissue, non-woven or plastic film
topsheets is that the tactile hllple~sion (or softness) of the topsheet is less than
desirable. Considering that tissue or non-woven substrates consist of natural fibers
such as wood pulp or synthetic fibers, the tactile impression of these substrates needs
to be ~;x~ lllely soft when applied to the delicate tissues of the genital area. Although
the tactile hll~.ression created by plastic film topsheets has proven to be quite good,
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S the psychological problems of a plastic material creates in some users the illlples~ion
that the softness of the plastic film is not sati~f~ctory
Yet another problem associated with web substrates consisting of tissue, non-
woven or plastic film materials is that once these topsheets are soiled, the topsheets
are ineffective at m~ckinsg the bodily fluid collected by the absorbent device. These
topsheets remain dirty due to a phenomenon referred to as fluid hangup. Fluid
hangup is a phenomenon where the bodily fluid sits on the surface of the topsheet and
does not pass through the topsheet and into the absorbent component located below
the topsheet. When the bodily fluid is menstrual fluid, components of the menstrual
fluid such as blood clots and body tissue is of a consistency which prevents those
components from passing through the topsheet and into the absorbent component.
Also fluid contained within the storage component can be seen through the topsheet.
Therefore, there exists a need for an absorbent device having improved dryness
and tactile attributes when the web surface comprises a non-woven or tissue
substrate. There also exists a need for an absorbent device having improved tactile
attributes when the web surface conlplises a plastic film. There also exists a need for
an absorbent device having either tissue, non-woven or plastic film web surfaceshaving improved m~cking capabilities.
SUMMARY OF TE~ IN~IENTI~N
The present invention provides an absorbent device and a method of improving
the surface dryness and tactile attributes of the absorbent device. The present
invention subst~nti~lly reduces the surface wetness problems associated with prior
absorbent devices having tissue or a non-woven material topsheet and provides these
substrates with a surface dryness e~ual to that of a formed film topsheet. The
invention also addresses the psychological problems associated with formed film
topsheets by improving the tactile h.lples~ion of the formed film topsheet. The
invention also provides improvement in the m~king characteristics of an absorbent
device having web types of tissue, non-woven or formed film materials.
The improved abso,l/elll device of the present invention is provided by a
method of joining small regular or random patterned hydrophobic projections on the
surface of the web without ~h~ngin~ any of the fluid h~n~lling ch~nn~ of the webmaterial. The plurality of projections are adapted to contact the user and to separate
the user from the body facing surface of the topsheet. The hydrophobic projections
further define a plurality of fluid containment areas between the projections for
collecting and temporarily co,.~ g bodily fluid ~orn~n~ting from the user. The
hydrophobic projections separate the fluid from the user to improve the dryness
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S attributes, and improve the tactile impression of the absorbent device by hllpa"illg
comfort properties to the user.
The material that can be joined to the web surface can be any hydrophobic
material that can be printed or sprayed. These include, but are not limited to, thermal
plastics and hot melt resins. The material can be joined by any printing or spraying
10 method, wherein rotary screen printing is p-e~lled. Other appal~L~Is and processes
suitable for use with the claimed invention is exemplified by that disclosed in U.S.
Patent No. S,058,247 issued to Thomas, et al. on October 22, 1991; U.S. Patent No.
5,116,563 issued to Thomas, et al. on May 26, 1992; and U.S. Patent No. 5,230,851
issued to Thomas on July 27, 1993, said patents being hereby incorporated by
15 reference. The apparatus and processes disclosed in the Thomas, et al. patents can be
utilized as an alternative to the pl erel l ed rotary screen printing process.
The rotary screen printing process comprises the steps of pumping molte~
hydrophobic fluid into a cylindrical-shaped screen which is supported above a back-
up roll. The back-up roll supports the web which is passed between the rotary screen
20 and the back-up roll. The cylindrical screen in~ludes a doctor blade which receives
the hydrophobic material and fills the holes within the cylindrical screen. The holes in
the screen are small enough and the hydrophobic material is of sufficient viscosity
that the hydrophobic material will not flow through the holes in the screen on its
own. The doctor blade forces the hydrophobic material to fill up the screen holes
25 such that a mPni.cc~ of material hangs down from the screen toward the back-up roll.
As the screen and back-up roll rotate, the screen contacts the web substrate at the
point of the back-up roll and transfers the hydrophobic material out of the screen hole
and onto the web substrate.
The holes in the cylindrical screen can be varied to produce patterns of printed30 hydrophobic material in the shape of dots. circles, lines, dimples, hairs, fil~ments7 or
any combination of patterns. The printed pattern typically is raised .05 to 3
millimeters above the web surface. The height of the printed material provides a void
area for quickly collecting fluid, but it is dry to the touch because the top surface of
the hydrophobic printed material retains no fluid. The printed pattern of hydrophobic
35 material improves the tactile i,l~plession by creating a surface which is soft to the
touch. Dyes or fillers can be added to the hydrophobic material to improve the fluid
m~CLing attributes of the web surface by ~ sgllising the soiling pattern of the
absorbent device created by bodily fluids.
Consequently, it is an object of the invention to provide an absorbent device
40 having improved dryness and tactile attributes of the topsheet web when the topsheet
web comprises a tissue or a non-woven material. It is yet another object of the
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invention to provide an absorbent device having an improved tactile impression of the
topsheet when the topsheet comprises a formed film material.
It is still another object of the invention to provide an absorbent device having
improved m~cking and fluid acquisition characteristics of the topsheet when the
topsheet consists of tissue, non-woven or formed film material.
Other objects and advantages of the invention will become apparent upon
reading the following detailed description and upon reference to the drawings, in
which it is understood to be illustrated by a sanitary napkin, but generally applicable
to all disposable absorbent devices.
BRIEF DESCRIPTION OF THE DRAW~GS
Fig. 1 is a perspective view of an absorbent device;
Fig. 2 is a top view of a fluid absorbing web structure of the absorbent devicç
of Fig. 1;
Fig. 3 is a side view of the web structure of Fig. 2,
Fig. 4 is a side view of an alternative embodiment of the web structure of ~ig.
2;
Fig. 5 is a second alternative embodiment of the web structure of Fig. 2;
Fig. 6 is a photograph of the web structure of Fig. 3;
Fig. 7 is a photograph of the web structure of Fig. 4;
Fig. 8 is a photograph ofthe web structure of Fig. 5; and
Fig. 9 is a sch~m~tic illustration of the method for producing the web structureof Fig. 2.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The present invention provides for an absorbent device and a method of
improving the dryness and tactile attributes of the web substrate which is in contact
with the skin of a user. Fig. 1 illustrates the invention as incorporated into a sanitary
napkin 10. The sanitary napkin generally comprises a web substrate 12, commonly
referred to as a topsheet, a backsheet 14, and a storage component 16 located inbetween topsheet 12 and backsheet 14. Although the present invention is illustrated
in Fig. 1 as a s~lila-y napkin, it is to be understood that the invention is not so limited
to applications of sanitary napkins, but is equally applicable to all absorbent devices
including for ~Y~mple diapers and incontinence products.
Topsheet 12 has been cutaway to more clearly show the storage component 16
of the sanitary napkin 10. Topsheet 12 can be made from a web material such as
tissue, non-woven or formed film materials. Tissue and non-woven topsheets can
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S contain all natural fibers, such as wood pulp, or synthetic fibers, or any combination
of natural and synthetic fibers. The exact formulation of fibers is not critical to the
present invention and can be generally any co",bination which provides a fluid-
pervious topsheet which are well known in the absorbent device art. A formed film
topsheet is exemplified by that disclosed in U.S. Patent No. 4,342,314 issued toRadel, et al. on August 3, 1982, said patent being hereby incorporated by reference.
Storage component 16 similarly can comprise natural, synthetic or any
combination of natural and synthetic fibers well known in the art. Rackcheet 14 can
be any of a number of plastic materials, also well known in the art which generates
the properties of being fluid-impervious to prevent the absorbed bodily fluid from
15 migrating out of the absorbent device.
Referring to Fig. 2, a plurality of hydrophobic projections 18 are positioned onweb 20. It is to be understood that web 20 can consist of tissue, non-woven or
formed film material. Hydrophobic projection 18 can be any material that can be
printed or sprayed, and incllld~, but are not limited to, thermal plastics and hot melts
20 resins. Preferred resins for application on formed films are resins produced by the
H.B. Fuller Company of Vadnais Heights, Minnesota, specifically Resin Numbers
E~1412-X and ~1424-X. Preferred resins for applying to non-woven or tissue
webs are resins produced by either Century International Adhesives and Coatings,Inc. of Columbus, Ohio, specifically Resin Number CA X 1064-1, or F~tm~n
25 Chemical Products, Inc. of Kingsport, Tennessee, specifically Resin Eastobond A-3.
With respect to formed film webs such as polyethylene, polypropylene polyester, or
other thermal plastic films, the surface tension of the resin to be applied must be
lower than the surface tension of the formed film web. Additionally the melting point
of the formed film should be at least 10~ C higher than the melting point of the resin
30 which is joined to the film to ensure that the film is not melted when the hydrophobic
m~t~ l iS applied.
The hydrophobic projections 18 are arranged to create land areas 22 on the
web, between individual projections, for collection and absorbing of bodily fluid.
Because the hydrophobic projections do not absorb fluid, they funnel fluid towards
35 the land area increasing the fluid acquisition rate of web 20. Bodily fluid can have a
tendency to sit on the surface of a web or roll off the sides of the web before it can be
absorbed, and the hydrophobic projections deter fluid from moving laterally on the
surface of the web 20 by forming barriers and thereby allowing the fluid to be
absorbed by web 20. For tissue and non-woven webs consisting of natural or
40 synthetic fibers, the closeness of the fibers in the web dictates how the web will
absorb and move bodily fluids into the storage component. Consequently, the
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5 hydrophobic projections 18 are positioned only on the surface of web 20 such that
the projections do not penetrate into the web and affect fluid wicking ch?~nnçl~between individual fibers in the web.
As shown in Fig. 3 projections 18 are raised .05 to 3 millimetçrs above the
surface 24 of web 20. By raising projections 18 above the surface 24 of web 20,
10 valleys or void areas 26 are created between individual projections for collecting
bodily fluid to be absorbed. The dry attributes of web 20 are improved because
bodily fluid is ~ d in valley 26 temporarily before being absorbed, and away
from the skin of the user. Consequently, projections 18 separate the fluid from the
user and keep the user dry and clean. By applying hydrophobic projections 18 on the
15 surface of tissue and non-woven webs, the individual web fibers at their tipS which
are in contact with the user, becomes hydrophobic thereby directing the bodily fluid
through the web and into the storage component without ,~...~;..;l~g on the we~
surface. In addition by joining the hydrophilic projections to the web surface as a
separate component, as opposed to being integral, projections of hydrophobic
material can be used in conjunction with hydrophilic webs such as tissue or non-woven material. Also projections with varying degrees of hydrophobicity can be
used in conjunction with webs exhibiting varying degrees of hydrophobic or
hydrophilic characteristics. Preferably the density of the projections on the web
surface range from about 1,600 to about 10,000 projections per square inch.
As shown in Figs. 2, 3 and 6, hydrophobic projections 18 can be applied as
dots. It is to be understood, however, that hydrophobic projections 18 can be
applied as dots, circles, lines, dimples, hairs, fil~m~ntc or any co-l-l)inaLion of ~val~e~l~s.
The patterns can be distributed uniformly over the web surface 24, or randomly.
When hydrophobic projections are applied as dimples, they can be in any shape, such
as oval, round, diamond, pyramidal, or square shaped. In any shape or pattern, the
hydrophobic projections provide a void area for quickly collecting fluid, but remain
dry to the touch because the top surface of the projections retain no fluid.
Softness of web 20, commonly referred to as tactile i.--~lession, is improved bypl~cem~nt of the hydrophobic projections on the surface in regular or random pattern
form. Although hydrophobic projection 18 applied as dots increase the tactile
impression of the web 20, the preft;ll~d form of hydrophobic projections 18 for the
greatest tactile il~pression is achieved when hydrophobic projections 18 are formed
as hairs 28 as shown in Figs. 4 and 7. Hairs 28 as shown in Fig. 7 extend
perpendicularly, as well as non-perpendicularly away from web surface 24. The
advantage achieved with hairs is that a larger number of projections can be applied to
the surface 24 of web 20 thereby gene.~ g a softer feel. Hair projections, unless
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5 applied in a very thick caliper can collapse when placed in contact with the user.
Collapsed projections may interfere with fluid absorption and the dryness attributes at
the web 20.
To maxirnize both the dryness and tactile attributes of web 20, the hydrophobic
projections preferably are applied as fil~ment~ 30 as shown in Figs. 5 and 8.
10 Fil~ments 30 are çesenti~lly shorter, thicker hairs which remain perpendicular to web
surface 24. Fil~m~nt.e 30 are more resistant to being compressed by the user because
they are thicker and shorter than hair projections 28.
Masking capabilities of web 20 can be ~nh~n~e~ by the addition of a dye or
filler to the hydrophobic projections 18. Suitable m~sking agents could be tit~ni~lm
15 dioxide (TiO2) or calcium carbonate (CaCO3). The hydrophobic projections
themselves, as well as the fillers aid in the m~C~ing of bodily fluids absorbed by the
web and retained in the storage component. The m~el~ing agent creates a clea~
appearance because the user cannot see through the web.
Referring to Fig. 9, the p~ ed method for applying the hydrophobic
20 projections to the web surface is by a rotary screen printing method. Although the
preferred method for applying the hydrophobic projection is h~ehldner discussed
with respect to the rotary screen printing method, it is to be understood that other
methods of printing or spraying hydrophobic projections are contemplated by the
invention. Such methods include spiral spraying, mist spraying or line spraying,25 gravure printing, and flexographic plill~ g. Rotary screen printing is the most
~;rt;l-ed because the method can be pe.rolllled at high web line speeds.
Rotary screen printing is accomplished by passing web 20 from a stock roll 32
of web material between a rotary screen cylinder 34 and a back-up roll 36. Web 20 is
unwound from stock roll 32 by drive cylinder 38. Rotary screen cylinder 34 is loaded
30 with hydrophobic material such as molten resin through slot extruder 40 attached to
screen cy~inder 34. Doctor blade 42 forces the hydrophobic material from slot
extruder 40 into holes in rotary screen 34. Rotary screen 34 has a thickness of
app.u~ ately 4 to 7 millimeters. The doctor blade fills the small screen holes with
the hydrophobic material, which is of sufflcient viscosity that it will not flow right
35 through the screen holes, and forces enough hydrophobic material into the screen
such that a meniscus of fluid extends downwardly from the screen holes as the screen
rotates. As the web passes between rotary screen cylinder 34 and back-up roll 36,
which is also rotating, the rotary screen contacts the web at the point of the back-up
roll and the m~ c~ . of hydrophobic material transfers from the screen onto web 20.
40 The hydrophobic material is literally pulled out of the screen by the web as it passes
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between the rotary screen and the back-up roll. The holes in the rotary screen are
continuously refilled by doctor blade 42.
f To print the dot pattern of hydrophobic projections on the web 20, the web line
speed is equal to the speed at which the rotary screen rotates. To print the hair
J pattern of hydrophobic projections, the web line speed is increased one-half to one
10 percent above the rotational speed of the rotary screen. Since the web is moving
faster than the rota~y screen, the web will pull the hydrophobic material out of the
screen such that the hair pattern is formed. To form the filament hydrophobic
pattern, cold air is pumped from nozle 44 directly onto the web immediately after
the hydrophobic material is transferred from the rotary screen cylinder onto the web.
15 The cold air freezes the hydrophobic material in the fil~mPnt pattern, thereby
preventing the hydrophobic material from forming the hair pattern. Alternatively,
back-up roll 36 can be chilled to freeze the hydrophobic material into the fi1~m~r~
pattern instead of pumping cold air through a nozzle.
While the invention has been described in conjunction with an absorbent device
20 having improved dryness and tactile attributes, it is to be understood that alternatives,
modifications and variations ~,vill be apparen~ to those skilled in the art in light of the
foregoing description. Acco~ gly, the invention is int~n-ie~l to embrace all such
alternatives, modifications, and variations as fall within the spirit and broad scope of
the appended claims.
