Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
` 2121859
TOPSHEET OF BODY FLUID ABSORPTIVE AR~ICLES
AND METHOD FOR MAKING SAME
BACKGROUND OF THE INVENTION
The present invention relates to a topsheet used for
body fluid absorptive articles such as sanitary napkins and
disposable diapers and also to a method for making the
topsheet.
It is well known to form a topsheet used for body fluid
absoptive articles, to provide this sheet with a plurality of
liquid passages each extending through the sheet from an
upper opening to a lower opening so that the upper surface
zomes in contact with a wearer's skin, and the lower openings
of the liquid passages are in contact with a liquid-absorbent
core, and thus body fluids are introduced into the liquid~
absorbent core under a capillary action occurring within the
respective liquid passages.
For example, Japanese Patent Publication No. 1982-17081
discloses a technique such that a topsheet made of
polyethylene sheet is provided with liquid passages each in
the form of truncated cone-shaped capillary tube and a lower
end of each liquid passage is arranged in close contact with
a liquid-absorbent core.
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21 21 859
Japanese patent application Disclosure No. 1992-58950
discloses a technique such that thermoplastic synthetic
fibres are melt-blown to form nonwoven fabric which is then
formed with liquid passages and fibrous fluff is formed
around lower.openings of the liquid passages to obtain a
topsheet.
In both of the above-mentioned prior techniques, the
lower end of each liquid passage should be always in close
contact with the liquid-absorbent core. However, the
topsheet which is thin and less rigid is readily wrinkled
during the practical use of the body fluid absorptive
articles and, in consequence, the lower end of each liquid
passage is separated from the liquid-absorbent core,
preventing the body fluids from being smoothly transferred
into the liquid-absorbent core.
Generally, the soft touch is indispensable to the body
fluid absorptive articles. For example, in the case of the
liquid-absorbent core formed of fluffpulp, a density thereof
is limited, since an excessively high density of the fluff
pulp would give a wearer the unpleasant stiff touch.
However, an excessively low density of the fluff pulp would
reduce the diffusibility of the body fluids. As a result, the
body fluids transferring from the liquid passages to the
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liquid-absorbent core can not rapidly diffuse laterally from
the lower openings and the body fluids stay on the topsheet
for a correspondingly longer time, giving a wearer the
discomfortable feel of wetness.
Accordingly, it is a principal object of the invention
to solve the problem encountered by the previously mentioned
prior techniques by composing a topsheet from a first sheet
and a second sheet, bonding the second sheet to the first
sheet around lower openings of respective liquid passages
formed through the flrst sheet and ad~usting a density of the
second sheet at a level of a density of a liquid-absorbent
core. ~ -
. ... :
SUMMARY OF THE INVENTION
The obJect set forth above is achieved, according to an
aspect of the invention, by a topsheet for body fluid
absorptive articles comprising this liquid-permeable
topsheet including a plurality of liquid passages each
extending therethrough from an upper opening to a lower
opening and a skin-contacting area extending continuously
around the upper openings of said liquid passages, a liquid-
impermeable backsheet and aliquid-absorbent core sandwiched
betweenth se sheets, said topsheet comprising: a first sheet
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made of thermoplasitc synthetic resinsheet and provided with
said liquid passages and said skin-contacting area; and a
second sheet underlying said first sheet and bonded thereto
around the lower openings of the respective liquid passages;
wherein said second sheet is made of mechanically intertwined
fibres only and has a density higher than a density of fibres
contained in said liquid-absorbent core.
Preferably, the second sheet of said topsheet is fibre-
oriented in the longitudinal direction of said topsheet and
the second sheet is composed of a mixture of 70 to 100~ by
weight of cellulose fibres and 30 to 0~ by weight of
thermoplastic synthetic fibres.
The object set forth above is achieved, according to
another aspect of the invention, by a method for making a
topsheet used in body fluid absorptive articles comprising
this liquid-permeable topsheet including a plurality of
liquid passages each extending therethrough from an upper
opening to a lower opening and a skin-contacting area
extending continuously around the upper openings of said
liquidpassages, aliquid-impermeablebacksheetandaliquid-
absorbent core sandwiched between these sheets, said method
comprising steps of: blowing molten fibres from a melt-blow
extruder against a forming die having a plurality of
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protrusions dimensioned substantially in a uniform height,
said protrusions having flat tops, to form melt-blown
nonwoven fabric following the configuration of said forming
die; bringing a heating element in contact with said melt-
blown nonwovqn fabric at said tops to form openings each
defined by an indented periphery; and feeding fibrous web
comprising mechanically intertwined fibres only and having
a density higher than a density of fibres contained in said
liquid-absorbent core onto said melt-blown nonwoven fabric
and thereby mechanically entwining said fibrous web around
said indented peripheries to obtain said topsheet.
Preferably, the fibrous web is fibre-oriented in the
longitudinal direction of said topsheet. The fibrous web is
preferably composed of a mixtura of 70 to 100% by weight of
cellulose fibres and 30 to 0% by weight of thermoplastic
synthetic fibres.
In the topsheet constructed in the above-mentioned
manner according to the invention, the second sheet is bonded
to the first sheet around the lower openings of the
respective liquid passages and thereby integrated with the
first sheet. Thus, the topsheet has its rigidity improved
sufficiently to prevent the topsheet from being wrinkled and
to restrict the deformation of the lower openings.
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Consequently, the liquid passages are not readily clogged.
The periphery of each lower opening is bonded to the second
sheet having a density higher than a density of the fibres
contained by the liquid-absorbent core, on one hand, and the
second sheet is in contact with the liquid-absorbent core, on
the other hand, so the body fluids having reached the lower
openings of the respective liquid passages not only can be
smoothly transferred immediately downward through the second
sheet into the liquid-absorbent core but also can be rapidly
diffused through the second sheet in the surface-direction
and then transferred into the liquid-absorbent core.
The second sheet is fibre-oriented in a desired
direction and the body fluids can be easily diffused
particularly in the direction corresponding to said fibre-
orientation. For example, said fibre-orientation may be
selected so as to coincide with the longitudinal direction of
the body fluid absorptive goods to assure that the body
fluids be rapidly diffused longitudinally of the liquid-
absorbent core and the entire liquid-absorbent core be
efficiently used.
According to the method of the invention for making the
topsheet, the openings respectively defined by the indented
peripheries can be formed by melting the protrusions formed
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2~218~9
on the melt-blown nonwoven fabric and the fibrous web is
formed by mechanically intertwined fibres so that the fibres
of this web may be easily disentangled and reliably entangled
around said peripheries. With a consequence, the melt-blown
nowoven fabric can be easily integrated with the fibrous web.
BRIEF DESCRIPTION OF THE DRAWINGS ~ `
A topsheet according to the invention and a method for ; ~
making it will be described more in detail with reference to ~ ~-
the accompanying drawing, in which:
Fig. 1 is a perspective view of a sanitary napkin; ~-
Fig. 2 is a fragmentary sectional view taken along a
line X-X in Fig. l; and
Fig. 3 is a diagram schematically illustrating a
production line for forming the topsheet.
PREFERRED EMBODIMENTS OF THE INVENTION -
Referring to Fig. 1 a sanitary napkin 1 utilizing a
topsheet 2 of the invention is shown as partially broken
away. The napkin 1 comprises the liquid-permeable topsheet
2, a liquid-impermeable backsheet 3 and a liquid-absorbent
core 4 sandwiched between these sheets 2, 3. The topsheet 2 -
entirely wraps the liquid-absorbent core 4 with overlapped
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opposite side edges thereof bonded to each other on a rear
side of the napkin 1 and with upper and lower layers of
longitudinally opposite ends thereof bonded to each other
along longitudinally opposite ends of the napkin 1,
respectively. The backsheet 3 is interposed between the
topsheet 2 and the liquid-absorbent core 4 on the rear side
of the napkin 1.
Fig. 2 is a fragmentary sectional view taken along a
line X-X in Fig. 1, schematically showing a state in which the
topsheet 2 is in contact with the liquid-absorbent core 4.
The topsheet 2 comprises an upper sheet 5 lying on the side of
a wearer's skin and a lower sheet 6 lying on the side of the
liquid-absorbent core 4. the upper sheet 5 has an upper
surface 7, a lower surface 8, liquid passages 10 each
extending from the upper surface 7 to the lower surface 8 over
a height of h, and a skin-contacting area 13 continuously
extending around upper openings 11 of the respective liquid-
passages 10. The lower sheet 6 has an upper surface 15, a
lower surface 16, and an exposed area 17 within the
respective liquid passages 10, and a non-exposed area 18
opposed to the skin-contacting area 13. The lower surface 16
is planar at least over the exposed area 17 or rounds out
toward the liquid-absorbent core 4, i.e., does not rise into
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the respective liquid passages 10, so the lower surface 16 is
easily brought into close contact with the liquid-absorbent
core 4. Over the non-contacting area 18, the lower surface
16 is preferably similar to the exposed area 17.
In the upper sheet 5, lower openings 12 of the liquid
passage 10 has its periphery 12A indented by plurality of
irregularities and fluffs. On the other hand, the lower
sheet 6 comprises a web formed by fibres mechanically
intertwined together and entwined also with the periphery so
as to be integrated with the upper sheet 5 and thereby to form
the topsheet 2.
The upper sheet 5 is formed by film of thermoplastic
synthetic resin or nonwoven fabric sheet of thermoplastic
synthetic fibres and hydrophobic. The synthetic resin film
may be, for example, polyethylene film having a thickness of
0.01 to 0.10 mm and the nowoven fabric sheet may be, for
example, melt blown nonwoven fabric having a weight per unit
area of 5 to 100g/m2.
The lower sheet 6 is formed by fibrous web comprising 70
to 100% by weight of cellulose fibres such as pulp or rayon
mixed with 30 to 0% by weight of thermoplastic synthetic
fibres. The lower sheet 6 is more hydrophilic than the upper
sheet 5 and has a density higher than a density of the fibres
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forming the liquid-absorbent core 4. When the liquid-
absorbent core 4 is formed, for example, by a mixture of fluff
pulp and high absorption polymer powders, it is preferred to
adjust the density of the lower sheet 6 at a level higher than
a density of said fluff pulp. Usually, the density of such
fluff pulp is selected in a range from 0.02 to 0.1 g/cm3.
Many of the fibres forming the lower sheet 6 have an
orientation longitudinal of the napkin 1 and body fluids
easily diffuse particularly in the direction corresponding
to said orientation under capillary action. If it is
desired, the lower sheet 6 primarily composed of cellulose
fibres may be added and mixed with 3096 by weight or fewer of
thermoplastic synthetic fibres to achieve the diffusibility
of body fluids higher than such diffusibility achieved by the
lower sheet formed by 100 96 by weight of cellulose fibres.
Each liquid passage 10 of the upper sheet 5 may be a
capillary tube tapered toward to the liquid-absorbent core 4,
a capillary tube tapered in the reverse direction, or a
cylindrical capillary tube of a uniform diameter. The liquid
passage 10 preferably has a length of 0.1 to 7mm. The upper
and lower openings 11, 12 may be circular, polygonal or of any
other appropriate shape and its diameter is preferably 0.3 to
7mm.
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Referring to Fig. 3, a production line for forming the
topsheet 2 is schematically illustrated. This production
line comprises a clockwise rotatabel roll 51 serving as a
forming die, a melt-blow extruder 52 opposed to the roll 51,
a heating roll 53 adapted to be ad;usted at a desired
temperature, a fibrous web feeder 54 and a take-up means 62.
The roll 51 is provided around its outer peripheral
surface with a plurality of protrusions 58 having a
substantially uniform height and each having a flat top and
indents 59 around the respective protrusions 58. The entire
periphery of the roll 51 is provided with a plurality of fine
through-holes (not shown) communicating with suction means
41 provided within the roll 51.
Molten fibres 40 are blown from the melt-blow extruder
52 against the outer peripheral surface of the roll 51 under
the action of the suction means 41 to form a melt-blown
nonwoven fabric 40a following the protrusions 58 and the
indents 59.
The heating roll 53 is arranged to come in contact with
flat tops 60 of the respective protrusions 58 and melts the
nonwoven fabric 40a interposed between the heating roll 53
and the flat tops 60 on the respective flat tops 60 so as to
form openings 61.
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The fibrous web feeder 54 feeds a web 42 through a pair
of guide rolls 55 onto the nonwoven fabric 40a which has been
formed with the openings 61 under the action of the suction
means 41 and simultaneously the web 42 is entwined with the
melt-blown nonwoven fabric around the respective openings 61
under the action of a pressure roll 56. The melt-blown
nonwoven fabric 40a and the web 42 integrated in this manner
are taken up by the take-up means 62 to obtain an uncut roll
2A for the topsheet 2. This uncut roll 2A will be cut into
individual sheets dimentioned appropriatedly to be used for
individual napkins 1.
The construction of the uncut roll 2A made by the above-
mentioned method is related with the construction of the
individual topsheet 2 which is cut from the uncut roll 2A so
that the melt-blown nonwoven fabric 40a and the web 42 form
the upper and lower sheets 5, 6, respectively; the portions
deformed by the protrusions and the indents form the liquid
passages 10 and the skin-contacting area 13, respectively;
and the portions of the web overlying the respective tops 60
of the protrusions form the exposed area 17. The exposed area
17 does not rise toward the upper openings 11 in the topsheet
1 and is reliably brought in contact with the liquid-
absorbent core 4 when used in the napkin l, sincP the tops 60
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are flat.
The fibrous web 42 is formed by web comprising
mechanicallyintertwined fibres only such as randomweb, card
web, air-laid web or nonwoven fabric obtained by subjecting
any of these webs to entwinement under a high pressure of
water jet and adjusted to have a density higher than a density
of the fibers contained in the liquid-absorbent core 4 to be
actually employed. The fibrous web 42 contains hydrophilic
cellulose fibres such as pulp or rayon occupying 70 to 100%
by weight with respect to a total amount of used fibres and,
if desired, such hydrophilic fibres may be mixed with
hydrophobic thermoplastic synthetic fibres of 30 to 0% by
weight. Such web or nonwoven fabric is usually fibre-
oriented in the machine direction during its making process
and therefore the web 42 is fed and/or cut so that the fibre-
orientation may coincide with the longitudinal direction of
the napkin 1 to be manufactured.
The topsheet of the invention allows the deformation of
the liquid passages to be effectively restricted by bonding
the lower sheet to the upper sheet.
The lower sheet is ad;usted to have a density higher
than a density of the liquid-absorbent core and consequently
the body fluids, after they have reached the lower end of each
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liquid passage, not only immediately penetrate through the
lower sheet into the liquid-absorbent core but also rapidly
diffuse through the lower sheet in the surface-direction and
then penetrate therethrough downward into the liquid-
absorbent core. In this manner, with the body fluid
absorptive articles adopting the topsheet of the invention,
the body 1uids are absorbed into the liquid-absorbent core
over a ralatively large area and a time for which the body
fluids stay on the topsheet is correspondingly shortened.
With a consequence, the unpleasant feel of wetness is
alleviated.
The lower sheet may be fibre-oriented in the desired
direction to accelerate diffusion of the body fluids in this
:
direction and such diffusion may be further promoted by
mixlng the thermoplastic synthetic fibres into the lower
sheet.
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- The web comprisingmechanically intertwined fibres only
is used as the lower sheet, so the fibres easily become
disentangled and readily entwine around the indented
periphery of each liquid passage's lower opening. Such
feature facilitates the integration of the upper and lower
obeeto into the topshe-t.
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