GB2258840A

GB2258840A - Topsheet for use in a sanitary absorbent

Info

Publication number: GB2258840A
Application number: GB9217530A
Authority: GB
Inventors: Masamitsu Yamamoto; Masaki Murakami
Original assignee: Unicharm Corp
Current assignee: Unicharm Corp
Priority date: 1991-08-21
Filing date: 1992-08-18
Publication date: 1993-02-24
Anticipated expiration: 2012-08-18
Also published as: JP2928665B2; JPH0549659A; AU2095392A; GB9217530D0; CA2075693A1; KR930003888A; DE59207456D1; AU666656B2; KR100221119B1; GB2258840B; EP0532937B1; CA2075693C; EP0532937A1; PH30965A

Abstract

A topsheet having openings 6 and associated liquid guide capillary tubes 8 is provided with a fabriclike appearance and oblique openings 9 are formed at the lower ends of the respective liquid guide capillary tubes 8. Top openings 6 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 6 are separated from each other by a fine rib 10. Bottom openings 9 have peripheral edges 9A 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. <IMAGE>

Description

-2 2 -3 03,3) 4 J -1 TOPSHEET- FOR USE 1N A SANITARY ABSORBENT ARTICLE AND

PRCr-'I'UCT:r-",",7 OF THE TnPSH-z-=-- The present invention relates to a topsheet for use in a sanitary art- icle for absorbent disposal'of bcdy fluids and to a production metll-.cd of the topsheet. A wearinc article for absorbent dismosal of body fluids such as sanitary napkin, disposable diaper or the like generally utilizes a liquid-permeable topsheet adapted to cover an absorbent care of the article. Such topsheet

of well known art typically comprises plastic film having openings or plastic film provided with liquid guide camillarv tubes extendIna from the respective openings. The 1 a t- 4Cer 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 1 -2 form of a tapered capillary. Such tapered configuration of the liquid gui..J3e capillary tube is based on intention to facilitate bcdv fluids to flow toward an underlying J.

absorbent core and to reduce any possible back Elow of body fluids from the absorbent core. However, it is required for this prior art to bring the capillary end dot partially but enti-relv- in close contact with the absorbent core and this reauiremen,ll-- is azt to increase an amount of undesirable back flow. According to Japanese Utility Model Application Disclosure Gazei--te No. 1991-63325, the capillary has its lower end obliquely cut away to form a pointed tip. Certain preventive.effectagainst 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 to provide an improved topsheet used in the sanitary a----o--z't-ive art- ic-l-- having openings defined by c=bination 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 exiCending from respective top openings and terminating in obliquely cut away bottom openings may be easily created.

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 tcm 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 licuid 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 -4by an irregularly undulating peripheral edge.

The objecIC set forth above is achieved, accc-rding 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 therethrouah and heating this sheet under An air pressure to form liquid guide capillary tubes, wherein each opening formed through 1Che mold has a plane configuration which is asvmmetric 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 tom 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 conficuration 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 1 -5location where the sheet bursts and relatively long along the peripher- al edges which are in the d-4-c,'L--ance 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 oi.'.: this bottom opening has an irregular undulation formed'due to the sheet burst.

The invention will be described in more detail by way of example with reference to the accompanying 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.

Fig. 1 is a perspective view showing a sanitary napkin 2 using a topsheet 1 in accordance with one embodiment of the invention as partially broken ------------------------- -6awav. The naDkin 2 has the liauid-pgrmeable topsheet 1 liquid-imper.meable backsheet 3 and an abscr-bent core 4 sandwiched there; --.et-deen. The topsheet 1 is made 0J. 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 nankin, then sealed together by a seal line 5. Longi.tudinally 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 fcr 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 91 a form the bottom opening 9 opening obliquely with respect to the length of the liquid guilde capillary tube 8. T1hi s 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 ton opening 6 has an area of 0.1 to 25 mm 17. The respective top openings may be individually of an irregular shave 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 simple geometric 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 adjacent top openings having 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 FiSs. 1 and 2, body fluidsexcreted flow into the top openings 6, then moves downward under a capillary action occurring along inner walls c-L- the liquid guide capillary tubes 8 and becins to sDread 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 amount of such back flow will be substantially reduced in comparison with the prior art in which the peripheral edge of each liauid guide capillary tube's lower end is entirely brought in contact with the absorbent core. When the user's body weight is exert-ed 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 serves. to prevent the respective bottom openings 9 from being completely blocked up, leaving certain gaps bet-deen 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 IGA 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.

contact with said absorbent core 4 and therefore an Fig. 3 is a diagram schematically showing a forming process to produce the tcms&-.eet 1. Raw sheet 11 for the topsheet 1 is made of thermoplastic material and continuously fed onto a forming drum 12 car.rying therearound a rotatable mold 60. The mold 60 comcrises 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 radiallv 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, 641 65 are separated by partitions 69. The raw sheet 11 is guided by a guide roll 66 onto the mold 60, and then counterclockwise 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 -10 described later, under an action of vacuum untilfor-ward ends of respective swelling burst. Then, t.lhe top openings 6 substantially in conformity with.1--'-.e 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 6-5. TLI-Lereafter, the vacuumformed sheet is released from the mold and cut into a size desired for the individual tomsheets 1.

Fig. CA) is a plan view of the openings generally desianated bv the reference numeral 61 comnrising 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, 61Br 61Ci... 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 t 64.

Referring to Fig. 4(A), (B), the manner -4s illustratedl in which the raw sheet 11 is subjected 1Lc 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 perigheral edge 6A of the top opening 6 formed substantially in ccnformity 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, resnectivelv.

the sides a b, 01 Portions of the raw sheet 11 having contacted 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 sianificantly 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 c d... of the pentagon -12 this location to form the liquid guide capillary tube 8 and the bottom opening 9. Wi th respect to the opening 61 A, 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 opening 9 is oblicuely 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 limited 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 -13 nor point-symmetric figures, e.g., circle, ellinse and equilateral polygons. When ope.n-4-lgs 61 are c4rcular, th.e raw sheet 11 begins to swe-l-l at a center of each opening 61 and then bursts at this point, forming a liquid guide caDillarv tube having its wall of a substantially uniform length therearound with a bottom opening being not oblique.

When the openincs-61 are elliptic, the raw sheet 11 becins to swell at a crossing point of major and minor axes of each open-ing 61 and then bursts at this point, forming the liquid guide capillary tube 8 having its wall being relatively long at onnosite 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 de.l"-4ned 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 of the liquid guide capillary tube and the 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 capillary tube collapses under a wearer's bodv weigh"-.

Claims

-15CLAIMS

1 A topsheet for use in a sanitary absorptive article having top openi. ngs 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, 1 wherein a plane configuration of each top opening is defined by a combination of straight and curved lines; each pair of adjacent ton 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 production method of the topsheet as claimed in Claim 1, comprising steps of placing thermoplastic sheet on a mold having a pattern of openings formed therethrough and heating this 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 the bottom side of the mold and then burst, resulting in formation of said top openings corresponding to said pattern of openings, said liquid guide capillary tubes extending downward from said top openings and said bottom openings obliquely opening at lower ends of said liquid guide capillary tubes.

3. The prcduction method as claimed in Claim 2, wherein the plane configuration of each said opening formed through said mold has a single axis of symmetry.

4. The production method as claimed in Claim 2 or 3, wherein the plane configuration of each said opening formed through said mold is polygonal.

5. A sanitary absorptive article including a topsheet as claimed in claim 1.

6. A topsheet for use in a sanitary absorptive article substantially as herein described with reference to Figures 1 to 4 or 5 of the accompanying drawings.

7. A method of producing a topsheet for use in a sanitary absorptive article substantially as herein described with reference to the accompanying drawings.

8. A sanitary absorptive article substantially as herein described wih reference to the accompanying drawings.