Note: Descriptions are shown in the official language in which they were submitted.
93
TOPSHEET FOR USE IN A SANITARY ABSORBENT ARTICLE
AND PRODUCTION METHOD OF THE TOPSHEET
BACKGROUND OF THE INVENTION
The present invention relates to a topsheet for use in
a sanitary article for absorbent disposal of body fluids and
to a production method of the topsheet.
A wearing article for absorbent disposal of body
fluids such as sanitary napkin , disposable diaper or the
like generally utilizes a liquid-permeable topsheet adapted
to cover an absorbent core of the article, Such topsheet
of well known art typically comprises plastic film having
openings or plastic film provided with liquid guide
capillary tubes extending from the respective openings. The
latter is disclosed, for example, in U.S. Patent No.
3,929,135 and Japanese Utility Model Application Disclosure
Gazette No. 1991-63325.
Basically, the present invention intends to develop an
improved topsheet having a fabriclike appearance provided
with liquid guide capillary tubes extending from respective
openings adapted for effective prevention of body fluids
from flowing backward and a production method of such
topsheet.
According to the above-mentioned U.S. Patent No.
3,929,135,each of the liquid guide capillary tubes is in the
form of a tapered capillary. Such tapered configuration of
the liquid guide capillary tube is based on intention to
facilitate body fluids to flow toward an underlying
absorbent core and to reduce any possible back flow of body
fluids from the absorbent core. However, it is required for
this prior art to bring the capillary end not partially but
entirely in close contact with the absorbent core and this
requirement is apt to increase an amount of undesirable back
flow. According to Japanese Utility Model Application
Disclosure Gazette No. 1991-63325, the capillary has its
lower end obliquely cut away to form a pointed tip. Certain
preventive effect against the back flow will be expected, if
only said pointed tip of the capillary is brought in contact
with the absorbent core. Regrettably, no specific method to
form such pointed tip of the capillary is disclosed and, in
addition, this proposal is not practical because the liquid
guide capillary tube is generally too fine to be readily cut
away so as to form the desired pointed tip. Moreover, most
of the opening patterns distributed on the conventional
plastic sheets have been geometric, for example, circular,
elliptical, equilaterally-triangular and the like,
disadvantageously resulting in too plasticlike appearance
which is far from a fabriclike appearance desired for a
sanitary absorptive article.
Accordingly, it is a principal object of the invention
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to provide an improved topsheet used in the sanitary
absorptive article having openings defined by combination of
straight and curved lines so as to create a fabriclike
appearance and to provide a production method of such
topsheet using a mold for plastic sheet, said mold having
asymmetrically arranged openings so that the fabriclike
appearance as well as the liquid guide capillary tubes
extending from respective top openings and terminating in
obliquely cut away bottom openings may be easily created.
SUMMARY OF THE INVENTION
The object set forth above is achieved, according to a
first aspect of the invention, by a topsheet for use in a
sanitary absorptive article having top openings formed in a
top surface of the sheet, liquid guide capillary tubes
extending downward form the respective top openings and
bottom openings defined by lower ends of the respective
liquid guide capillary tubes, wherein a plane configuration
of each top opening is defined by combination of
straight and curved lines; each pair of adjacent top
openings are separated from each other by a rib having a
width of 0.1 to 3 mm; each top opening has an area of 0.1 to
25 mm2; each bottom opening opens obliquely with
respect to the length of the associated liquid guide
capillary tube; and each bottom opening is surrounded
by an irregularly undulating peripheral edge.
The object set forth above is achieved, according to a
second aspect of the invention, by a production method of
said topsheet comprising steps of placing thermoplastic
sheet on a mold having an opening pattern formed
therethrough and heating this sheet under an air pressure to
form liquid guide capillary tubes, wherein each opening
formed through the mold has a plane configuration which is
asymmetric or has a single axis of symmetry. Preferably,
the plane configuration of each opening of the mold is
polygonal.
The topsheet of the invention has top openings each
defined by a combination of straight and curved lines so as
to present an irregular configuration and each pair of
adjacent top openings are separated from each other by a
fine rib, resulting in an irregular opening pattern which
creates a fabriclike appearance of the sheet as a whole.
According to the method of the invention, the opening
configuration on the mold is asymmetric or line-symmetric,
so the sheet swells and bursts under air pressure at
locations biased with respect to the peripheral edges of the
respective top openings and thereby the respective liquid
guide capillary tubes are formed. The liquid guide
capillary tubes have their walls which are relatively short
~ along the peripheral edges which are in the proximity of the
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location where the sheet bursts and relatively long along
the peripheral edges which are in the distance of the
location where the sheet bursts. Thus, the lower end of
each capillary tube wall defines a bottom opening which
opens obliquely downward. A peripheral edge of this
bottom opening has an irregular undulation formed due to
the sheet burst.
According to a further broad aspect of the
present invention there is provided a topsheet for use in
a sanitary absorptive article having top openings formed
in a top surface, liquid guide capillary tubes extending
downward from the respective top openings and bottom
openings defined by lower ends of the respective liquid
guide capillary tubes. A plane configuration of each top
opening is polygonally asymmetrically defined by a
combination of straight and curved lines. Each pair of
adjacent top openings is separated from each other by a
rib having a width of 0.1 to 3 mm. Each top opening has
an area of 0.1 to 25 mm2. Each bottom opening opens
obliquely with respect to the length of the associated
liquid guide capillary tube. Each bottom opening is
surrounded by an irregularly undulating peripheral edge.
According to a further broad aspect of the
present invention there is provided a method of producing
a topsheet for use in a sanitary absorptive article and
which comprises the steps of placing a thermoplastic
sheet on a mold having a pattern of openings formed
therethrough and heating the sheet under an air pressure
so that portions of the sheet corresponding to the
openings swell into capillary tubes extending from the
respective said openings downward toward a bottom side of
the mold and then burst, resulting in formation of top
openings in the sheet corresponding to the pattern of
openings in the mold. Upon bursting, the thermoplastic
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sheet simultaneously forms liquid guide capillary tubes
about the top openings and which extending downward from
the top openings. These capillary tubes each define a
bottom oblique opening at lower ends thereof. The plane
configuration of each of the top opening formed through
the mold is polygonally asymmetric.
According to a further broad aspect there is
provided a sanitary absorptive article which includes a
topsheet as above described.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be described more in detail
in reference with the attached drawings, in which:
Fig. 1 is a perspective view showing a sanitary
napkin as partially broken away;
Fig. 2 shows, in an enlarged scale, a part of
the topsheet in plan and sectional views;
Fig. 3 is a diagram schematically showing a
manner in which the topsheet is formed;
Fig. 4 exemplarily shows the openings formed
through the mold in plan and sectional views; and
Fig. 5 is a plan view showing a variant of the
openings formed through the mold.
PREFERRED EMBODIMENTS OF THE INVENTION
Fig. 1 is a perspective view showing a sanitary
napkin 2 using a topsheet 1 of the invention as partially
broken
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away. The napkin 2 has the liquid-permeable topsheet 1, a
liquid-impermeable backsheet 3 and an absorbent core 4
sandwiched therebetween. The topsheet 1 is made of
thermoplastic sheet, covers the absorbent core 4 as well as
the backsheet 3. The topsheet 1 has its transversely
opposite edges overlapped one upon another on the rear side
of the napkin, then sealed together by a seal line 5.
Longitudinally opposite ends of the napkin 2 are sealed
together by seal lines 7. The topsheet 1 has on its top
side a plurality of top openings 6. The backsheet 3 serves
for prevention of liquid leakage.
In Fig. 2, (A) is a partially enlarged view of the
topsheet 1 showing a plane configuration of the top opening
6 and (B) is a sectional view taken along a line PQR wherein
Q is a point corresponding to a centroid G as will be
described later. The top opening 6 is surrounded by an
irregular peripheral edge 6A defined by a combination of
straight and curved lines, and each pair of adjacent top
openings are separated from each other by a fine rib 10. A
liquid guide capillary tube 8 extends from each top opening
toward the bottom side of the topsheet 1 and terminates in a
bottom opening 9. The liquid guide capillary tube 8 has a
relatively short wall section 8A at one side and a
relatively long wall section 8B at the opposite side. These
wall sections 8A, 8B are continuous with each other so as to
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form the bottom opening 9 opening obli~uely with respect to
the length of the liquid guide capillary tube 8. This
bottom opening 9 is surrounded by a peripheral edge 9A being
irregularly undulating in the form of fluff, barb, saw-teeth
or the like and lower end of the relatively long wall
section 8B touches the absorbent core 4 and thereby form a
bridge. Each top opening 6 has an area of 0.1 to 25 mm2.
The respective top openings may be individually of an
irregular shape or may be of a combination of regular shapes
which appear respectively at relatively; long interval so
that the arrangement of these top openings 6 presents no
slmple geometrlc pattern. The rib 10 has a width of 0.1 to
3 mm and the capillary tube wall 8 extends over 0.3 to 7 mm
between the top and bottom openings of the liquid guide
capillary tube. The top openings 6 and the arrangement
thereof such that each pair of the ad~acent top openings
havlng their respective irregular shapes are separated from
each other by the fine rib 10 create a desired fabriclike
appearance which has never been obtained by a conventional
topsheet having a geometric pattern of top openings. If
desired, the ribs 10 may be subjected to creping or matting
treatment to obtain a further improved fabriclike
appearance.
In use of the topsheet 1, as will be apparent from
Figs. 1 and 2, body fluids~excreted flow into the top
.,
openings 6, then moves downward under a capillary action
occurring along inner walls of the liquid guide capillary
tubes 8 and begins to spread itself into the absorbent core
4 via the bridge formed by the lower ends of the capillary
tube wall sections 8B in contact with the absorbent core 4.
Any back flow from the absorbent core 4 should necessarily
occur along the capillary tube wall sections 8B being in
contact with said absorbent core 4 and therefore an amount
of such back flow will be substantially reduced in
comparison with the prior art in which the peripheral edge
of each liquid guide capillary tube's lower end is entirely
brought in contact with the absorbent core. When the user's
body weight is exerted on the napkin 2, the capillary tube
wall sections 8B and the adjacent zones may collapse inward.
However, the indentation or undulation along the peripheral
edges 9A ser~es. to prevent the respective bottom openings 9
from being completely blocked up, leaving certain gaps
between the peripheral edges 9A and the absorbent core 4 so
that body fluids may flow into the absorbent core 4.
Additionally, said indentation or undulation of the
peripheral edges 9A facilitates the topsheet 1 to be
anchored on fibrous material of the ~absorbent core 4 and
thereby prevents the topsheet 1 and the absorbent core 4
from being relatively displaced, eliminating discomfort
during use of the napkin 2.
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Fig. 3 is a diagram schematically showing a forming
process to produce the topsheet 1. Raw sheet 11 for the
topsheet 1 is made of thermoplastic material and
continuously fed onto a forming drum 12 carrying therearound
a rotatable mold 60. The mold 60 comprises a cylinder
having a smooth peripheral surface, through which there is
formed an opening pattern including a plurality of openings
61 as will be described later, and capillary tubes
62 radially extending from the respective openings 61 toward
the drum center. The forming drum 12 has a suction zone 64
corresponding to a sector of the mold 60 under which there
is provided a vacuum source, a heating zone 63 corresponding
to a sector of the mold 60 defined upstream of said suction
zone 64, above which there is provided a hot air blower
directed to the raw sheet 11 and a cooling zone 65
corresponding to a sector of the mold 60 defined behind said
suction zone 64, above which there is provided a cold air
blower directed to the raw sheet 11. The respective zones
63, 64, 65 are separated by partitions 69. The raw sheet 11
is guided by a guide roll 66 onto the mold 60, and then
conouterclockwise rotated in close contact with the mold 60.
During this rotation, the raw sheet 11 is softened by hot
air as the raw sheet 11 travels along the heating zone 63
and enters the suction zone 64 along which the raw sheet 11
swells into the respective capillary tubes 62, which will be
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described later, under an action of vacuum until forward
ends of respective swelling portions burst. Then, the top
openings 6 substantially in conformity with the openings 61
of the mold and the associated liquid guide capillary tubes
8 as well as the bottom openings 9 defined by the lower ends
of the respective liquid guide capillary tubes which have
burst in the preceding suction zone 64 are formed as the raw
sheet 11 is cooled in the cooling zone 65. Thereafter, the
vacuumformed sheet is released from the mold and cut into a
size desired for the individual topsheets 1.
Fig. 4(A) is a plan view of the openings generally
designated by the reference numeral 61 comprising individual
openings 61A, 61B, 61C, ... forming together the opening
pattern. Fig. 4(B) is a sectional view of the opening 61A
along a line XGY, showing a capillary tube 62A, which
corresponds to the general reference numeral 62. Each
opening 61 presents a polygonal asymmetric configuration
having a centroid (center of figure) G. For example, the
opening 61A is of an asymmetric pentagon a b c d e with the
centroid which is located near the side a e and far from the
side c d of the pentagon. The respective openings 61A,
61B, 61C, ... are separated from one another by the
respective ribs 65. The capillary tubes 62 extending from
the respective openings 61 have their lower ends opened and
are subjected to the action of vacuum in the suction zone
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64.
Referring to Fig. 4(A), (B), the manner is illustrated,
in which the raw sheet 11 is subjected to the forming
process by which the sheet 11 is vacuumformed with the top
and bottom openings 6, 9 as well as the liquid guide
capillary tubes 8. In Fig. 4(A), the peripheral edge 6A of
the top opening 6 formed substantially in conformity with
the opening 61A is indicated by an imaginary line and in
Fig. 4(B), the swelling state 11B and the ruptured state 11C
of the raw sheet 11 are indicated by imaginary lines,
respectively. Portions of the raw sheet 11 having contacted
the sides a b, c d, ... of the pentagon are formed into
straight lines 6B but portions of the raw sheet 11 having
contacted the corners a, b, c, ... are formed into curved
lines 6C since these portions are not conformable with mold.
Consequently, the peripheral edge 6A as a whole comprises a
combination of these straight and curved lines 6B, 6C, i.e.,
it is difficult to conform each top opening 6 with the
corresponding opening 61 of the mold. These straight and
curved lines significantly change depending on even slight
variations in thickness of the raw sheet 11 as well as in
the forming condition and the same opening 61 often results
in uneven, indeterminate top opening 6. Swelling of the raw
sheet 11 begins at a location corresponding to the centroid
G of each opening 61, and then the raw sheet 11 bursts at
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this location to form the liquid guide capillary tube 8 and
the bottom opening 9. With respet to the opening 61A, for
example, the capillary tube wall section 8A formed adjacent
the side a e is relatively short and the capillary tube wall
section 8B formed adjacent the side c d is relatively long.
The capillary tube wall sections 8A, 8B are continuous with
each other, so the bottom openlng 9 is obliquely directed
relative to the length of the liquid guide capillary tube 8.
The peripheral edge 9A of the bottom opening 9 has irregular
undulation such as fluff-, barb-, or sawtooth-like
undulation caused by bursting of the raw sheet 11.
Fig. 5 is a plan view of the opening 61, each being
symmetric with respect only to an axis Z-Z. For example,
the opening 61A is shaped in a trapezoid a b c d having the
centroid G on the axis of symmetry Z-Z nearer to the side
c d than the side a b. From such opening configuration, it
is possible to obtain the topsheet 1 having the liquid guide
capillary tubes whose bottom openings have irregularly
undulating edges 9A.
While a plane configuration of each opening 61 is not
lim1ted to polygons but can be also defined only by a curved
line, it will be difficult in this case to define the
corresponding top opening 6 by a combination of straight and
curved lines. It should be understood that the openings 61
include neither figures having two or more axes of symmetry
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nor point-symmetric figures, e.g., circle, ellipse and
equilateral polygons. When the openings 61 are circular,
the raw sheet 11 begins to swell at a center of each opening
61 and then bursts at this point, forming a liquid guide
capillary tube having its wall of a substantially uniform
length therearound with a bottom opening being not oblique.
When the openings 61 are elliptic, the raw sheet 11 begins
to swell at a crossing point of major and minor axes of each
opening 61 and then bursts at this point, forming the liquid
guide capillary tube 8 having its wall being relatively long
at opposite ends of the major axis and being relatively
short at opposite ends of the minor axis.
The topsheet 1 may be produced from thermoplastic
material such as polyethylene, polypropylene or the like
having a thickness of 0.01 to 0.2 mm.
The mold 60 may be an electroformed mold.
The topsheet produced from thermoplastic material by
the method of the invention has the top openings each
defined by a combination of straight and curved lines so as
to provide an indeterminate shape and separated from one
another by the fine ribs. Such arrangement allows the
topsheet of the invention to present the desired fabriclike
appearance. Each liquid guide capillary tube terminates in
the bottom opening opening downward obliquely with respect
to the length or the liquid guide capillary tube and the
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lowermost pointed tip of said capillary tube is brought in
contact with the absorbent core to improve a back flow
preventing effect of the liquid guide capillary tube. The
method of the invention to produce the topsheet adopts the
mold having the opening pattern comprising a plurality of
asymmetric polygons or polygons each having a single axis of
symmetry so that the topsheet can be provided with a
fabriclike appearance and the bottom opening of each liquid
guide capillary tube can be obliquely opened. Undulation
along the peripheral edge of the bottom opening serves to
prevent the bottom opening from being completely blocked up,
even if the liquid guide capillarly tube collapses under a
wearer's body weight.
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