CA2075693C

CA2075693C - Topsheet for use in a sanitary absorbent article and production method of the topsheet

Info

Publication number: CA2075693C
Application number: CA002075693A
Authority: CA
Inventors: Masamitsu Yamamoto; Masaki Murakami
Original assignee: Unicharm Corp
Current assignee: Unicharm Corp
Priority date: 1991-08-21
Filing date: 1992-08-10
Publication date: 1997-09-23
Anticipated expiration: 2012-08-10
Also published as: CA2075693A1; AU2095392A; GB2258840A; GB2258840B; EP0532937B1; GB9217530D0; KR100221119B1; JPH0549659A; AU666656B2; EP0532937A1; JP2928665B2; PH30965A; KR930003888A; DE59207456D1

Abstract

A topsheet having openings and associated liquid guide capillary tubes is provided. The topsheet has a fabric-like appearance and oblique openings are formed at the lower ends of the respective liquid guide capillary tubes. Top openings of this topsheet, for use in a sanitary absorptive article, present plane configurations respectively defined by combination of straight and curved lines and each pair of adjacent top openings are separated from each other by a fine rib.
Bottom openings have peripheral edges which are irregularly undulating. A mold for the topsheet is provided with a plurality of openings each presenting an asymmetric figure or a linearly symmetric figure having a single axis of symmetry.

Description

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 Z~7~9~3 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 ; 207569 3 -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 , ~ , r 2 0 7 5 6 9 3 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 - 5a -"

2~7~Ç~9~

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 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.

2~

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 2~ 9~3 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 2~7~

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 -- 22~

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 7~

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 2~7~

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.

Claims

1. 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, wherein 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; and each bottom opening is surrounded by an irregularly undulating peripheral edge.

2. A method of producing a topsheet for use in a sanitary absorptive article comprising the steps of placing a thermoplastic sheet on a mold having a pattern of openings formed therethrough and heating said sheet under an air pressure so that portions of said sheet corresponding to the openings swell into capillary tubes extending from the respective said openings downward toward a bottom side of said mold and then burst, resulting in formation of top openings in said sheet corresponding to said pattern of openings in said mold and simultaneously forming liquid guide capillary tubes about said top openings extending downward from said top openings, said capillary tubes each defining a bottom oblique opening at lower ends thereof, and wherein the plane configuration of each said top opening formed through said mold is polygonally asymmetric.

3. A sanitary absorptive article including a topsheet 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, wherein 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; and each bottom opening is surrounded by an irregularly undulating peripheral edge.