GB2145970A

GB2145970A - Sanitary napkins

Info

Publication number: GB2145970A
Application number: GB08421097A
Authority: GB
Inventors: George Howarth
Original assignee: Smith and Nephew Associated Companies PLC
Current assignee: Smith and Nephew PLC
Priority date: 1983-08-26
Filing date: 1984-08-20
Publication date: 1985-04-11
Also published as: AU3222184A; GB8421097D0; GB2145970B; ZA846484B; AU563398B2; GB8322974D0

Abstract

An absorbent device suitable for use as a sanitary napkin which comprises a fluid pervious cover enclosing an elongate fluid absorbent core and a fluid impervious barrier sheet arranged between the cover and the core so that the barrier sheet covers the side of the core facing away from the body of the user and at least portions of the two longitudinal side edges of the core characterised in that the fluid impervious sheet is heat laminated over the whole of one surface thereof to a non-woven fabric fluid pervious cover is disclosed.

Description

SPECIFICATION Absorbent device The present invention relates to an absorbent device for absorbing body fluids and more particularly to a sanitary napkin in which the outer cover comprises a laminate of a fluid pervious cover material and a fluid impervious barrier sheet; and to a process for the manufacture of such absorbent devices.

Conventionally absorbent devices such as sanitary napkins comprise a generally elongate and preferably rectangular core of an absorbent hydrophilic material such as wood pulp, rayon, gauze, tissue or the like and in some instances a hydrophilic synthetic polymer. The rectangular pad or core is then usually wrapped in a cover which can be a woven fabric such as gauze or a non-woven fabric. The devices have a side which is intended to contact the body and the opposite side which is intended to contact a garment. The cover is pervious to body fluid on that side which is to contact the body. A body fluid impervious sheet is provided between the core and the cover on the garment contacting side in an effort to prevent staining and wetting of the clothing.

In use the device is positioned so that the body fluid passes through the fluid pervious cover to be absorbed into the centre of the pad. In a perfect device the fluid would then be distributed evenly throughout the core by wicking, so that any external surface would not be wetted until the pad was saturated.

Unfortunately, this perfect situation is not achieved in practice, as the elongate shape of the core means that fluid wicking wets the side edges of the core before the core is near to saturation. This means that only a small amount of absorbent is utilised and the possibility of staining clothing by leakage from the edges of the device is present.

One remedy which has been suggested is to make the body fluid impervious sheet wider than the pad so that it can be folded upwardly to cover the side edges of the pad and even to overlap part of the body contacting side of the pad. Such a system is described in United Kingdom Application No. 200390A. Such systems in which the edges of the impervious sheet remain merely folded over suffer from the disadvantages that the sheet is free to move and become misplaced within the enclosing cover thereby failing to perform its barrier function correctly and also it is found that body fluid will wick around the edge of the impervious sheet and between the cover and sheet layers thereby causing staining.This problem of side leakage has been described in United Kingdom Patent No. 2019727B. This patent describes a sanitary napkin in which a "menstrual fluid barrier seal line" is present to seal the longitudinal edge of an impervious barrier sheet to cover or wrapper. However, such lines leave the majority of the impervious sheet free to move which may place stress on the seal lines causing them to fail and also may result in rustling in wear. Such lines may not provide a complete barrier to side leakage, if fluid falls onto the pad on the wrong side of the seal line.

United Kingdom Application No. 2042901A discloses a sanitary towel comprising an outer wrap cover of the type disclosed in United Kingdom Application No. 2003390A in which the impervious barrier sheet is laminated over the whole of one surface thereof to an external fluid pervious cover material. Such a barrier sheet-cover material laminate can reduce the occurrence of side leakage found in prior art sanitary towels by preventing movement between the barrier sheet and the cover material and also by inhibiting the wicking of body fluid around the edge of the barrier sheet and between the cover and sheet layers. However the only fluid pervious cover materials disclosed in United Kingdom Application No. 2042901A comprise a woven material, a fleece material or tissue.Woven materials are generally more expensive than, for example, the non-woven fabrics used for cover layers of sanitary towels and their use for this purpose therefore, is uneconomic.

Conventional fleece materials comprise a carded web of fibres and therefore would have poor resistance to abrasions. Conventional tissue materials comprise a low weight paper which would be unstable the presence of an aqueous fluid. The body contacting surface of a sanitary towel in use however is exposed to both moist and abrasive conditions. It is therefore highly likely that in use the fleece or tissue cover materials at the body contacting surface of the outerwrap cover of a sanitary toweld disclosed in United Kingdom Application No. 2042901A would either become abraded and possibly disintegrate or become unbonded and possibly delaminate from the edges of th fluid barrier sheet or both.Furthermore it has been found that in a sanitary towel which has an outer wrap cover of the above type comprising a laminate of a tissue paper and a fluid barrier sheet, any body fluid falling on the outer wrap cover adjacent to the barrier sheet will preferentially wick into the laminated area of the cover about the side edges of the sanitary towel. The laminated outer cover of such a sanitary towel therefore does not in hi bit the wicking of fluid around the edges of the sanitary towel.

It has now been found that an absorbent device can be provided which has a cover material-fluid impervious sheet laminate outer cover which inhibits wicking of body fluids around the side edges of the device thereby reducing the possibility of leakage of fluid from the device in use.

Accordingly the present invention provides an absorbent device suitable for use as a sanitary napkin which comprises a fluid impervious cover enclosing an elongate fluid absorbent core and a fluid impervious barrier sheet arranged between the cover and the core so that the barrier sheet covers the side of the core facing away from the body of the user and at least portions of the two longitudinal side edges of the core characterised in that the fluid impervious sheet is heat laminated over the whole of one surface thereof to a non-woven fabric fluid pervious cover. Most aptly the non-woven fabric is an integral net or a bonded non-woven fabric.

Preferably the non-woven fabric is an integral net.

When used herein the term integral net means a net in which the strands or ribs and junctures are formed integrally during manufacture.

The non-woven fabrics used in the invention, due to their integral or strongly bonded structure, will be stable under moist and abrasive conditions prevalent on the body contacting side of sanitary towels in use.

The polymer for use in the non-woven fabrics employed in this invention will be a heat softenable polymer, for example a thermoplastic polymer such as polypropylene, high density polyethylene, polyamide or polyester.

It has been found that use of a heat softenable polymer in the non-woven fabric facilitates the heat lamination of the fluid pervious cover to the fluid impervious barrier sheet and enables a good bond to be formed between the cover and the sheet layers that is maintained during use of the product.

It has been found, surprisingly, that the non-woven fabrics used in the invention when bonded by heat lamination to the fluid impervious sheet have a reduced ability to wick fluids, which contrasts with the increased ability to wick fluids shown by the laminated tissue paper used in prior art devices. This advantage is particularly marked when the non-woven fabric is an integral net.

The laminated portions of the fluid pervious cover used in the invention cover the edges of the absorbent core. This cover of the sanitary towel of the invention therefore inhibits the wicking of fluids from the edges of the barrier sheet around the side edges of the absorbent core.

Suitable bonded non-woven fabrics for use in the invention include spun bonded fabrics, thermally bonded fabrics and resin bonded fabrics.

The bonded non-woven fabric used in the invention can suitably have a weight per unit area of 2 to 40 g/m2 and more suitably have a weight per unit area of 10 to 30 gim2, for example 15 to 20 g/m2.

Similarly the bonded non-woven fabrics used in the invention can suitably have a thickness of 0.025mm to 1.100mm and preferably have a thickness of 0.040mm to 0.075mm.

Favoured spun bonded fabrics include spun bonded polypropylene fabrics for example Corovin SMED (Trade Mark, available from J.H. Benecke G.m.b.H) and Lutravil VP 605 (Trade Mark, available from Lutravil Spinnvlies) and spun bonded polyamide fabrics for example Cerex fabrics available from Monsanto Textile Co.

Corovin SMED spun bonded polypropylene has a weight per unit area of 15g/m2 and a thickness of about 0.080mm. Lutravil VP 605 has spun bonded polypropylene has a weight per unit area of 15 to 20 g/m2 and a thickness of about 0.11 mm.

Favoured thermally bonded fabrics include thermally bodned polypropylene fabrics, for example Finnitex CF 10 (available from Fibre Filter OY) and Noworoll PRC (available from Kevytrakenne OY).

Finnitex CF10 thermally bonded polypropylene fabric has a weight per unit area of 1 Og/m2 and a thickness of about 0.050mm. Novoroll PRC has a weight per unit area of 10g/m2 and a thickness of about 0.065mm.

Favoured resin bonded non-woven fabrics include resin bonded viscose rayon fabrics such as acrylic resin bonded viscose rayon fabrics.

The integral nets used in the invention can suitably be any of the soft integral nets conventionally used as on absorbent pads such as sanitary towels. Such nets normally comprise longitudinal filaments interconnected by thinner strand or fibre areas.

Suitably the integral nets used in the invention have a weight per unit area of 2 to 20g/m2 and preferably a weight per unit area of 4 to 12 g/m2, for example 6 to 10g/m2.

Suitably the integral nets used in the invention have a thickness of 0.030mm to 0.150mm and preferably a thickness of 0.04mm to 0.120mm, for example 0.05mm to 0.10mm. A preferred net has a thickness of 00.05mm.

Particularly favoured integral nets are those which are formed from hydrophobic polymers which include high density polyethylene (HDPE) and a blend of high density polyethylene and high impact polystyrene.

Suitable integral nets may be formed by the process described in British Patent No. 1548865 and which patent is incorporated herein by cross reference. Apt integral nets formed by this process include those available as Net 909 (Trade Mark) Grades A4, A7, H8C and DHM (available from Smith & Nephew Plastics Ltd., Giberdyke, North Humberside). Such apt nets have a weight per unit area of 5 to 11 .5g/m2 and a thickness of 0.040 to 0.120mm.

The structure of these favoured non-woven fabrics is characterised by the fact that they comprise substantially straight, parallel, smooth longitudinal ribs connected by a wholly or partly fibrillated strands.

This structure gives the fabric the strength and porosity required for use as a sanitary towel as well as a particularly soft feel. It has been found to be particularly advantageous if the fabric is laminated to the fluid impervious layer so that in the finished sanitary towel the longitudinal ribs run along the length of the device.

In this arrangement the longitudinal ribs of the laminated net cover lie in a direction which is tranverse to the width of the pad. The ribs of such a laminated net cover will therefore inhibit the spreading of body fluids from the edge portions of the barrier sheet around the side edges of the core. This arrangement also gives additional comfort to the device in wear.

The fluid impervious sheet is suitably any inert physiologically compatible plastics sheet which includes sheets made from polyethylene, polypropylene, polyamides, polyvinyl chloride, polyvinyl acetate, insoluble polyvinyl alcohol and polyurethane. Preferably the fluid impervious sheet is a polyethylene or polypropylene sheet. Suitably the sheet is from 0.005 to 0.06 mm thick and preferably is from 0.015 to 0.025mm thick.

The absorbents for use in the devices of the present invention include those which are conventionally used for sanitary towel manufacture and include cellulosics such as comminutedifluffed wood pulp, carded cotton webs, regenerated cellulose fibres, tissue paper or grafted cellulose super absorbents, polymeric super absorbents or mixtures thereof.

Optionally the devices of the present invention will also have placed between the core and the wrapper a fleece material which provides the towel with extra softness and comfort as well as contributing to the effectiveness of the wrapper to prevent cover wetness. Typically the fleece material will be positioned across the body contacting side of the device beneath the fluid permeable cover or it may extend so as to also lie between the fluid impervious sheet and the core or between the fluid impervious sheet and the wrapper along the side of the core. Suitably the fleece will be made from polyester, polypropylene, polyamide, cotton or regenerated cellulose or a mixture of these fibres. A preferred fleece material is formed from a carded viscose rayon web mixed with polyester fibre (25%).

In the absorbent devices of the present invention the non-woven fabric is heat laminated to the fluid impervious sheet over the whole of one surface of the latter.

Thus in another aspect the invention provides a process for the manufacture of an absorbent device of the invention which comprises heat laminating a fluid impervious barrier sheet over the whole of its surface thereof to a fluid pervious cover comprising a non-woven fabric and enclosing an elongate absorbent core with the laminate so that the fluid barrier sheet is between the cover and the core and covers the side of the core facing away from the body of the user and at least portions of the two longitudinal side edges of the core to leave the fluid pervious portion on the body contacting side of the device.

In a preferred process of the invention the fluid pervious cover is on an integral net comprising longitudinal ribs interconnected by fibrillated strands and the net is heat laminated to the fluid impervious barrier sheet so that the longitudinal ribs of the net extend in the longitudinal direction of the device.

Lamination may be achieved by any of the conventional heat lamination means such as heat sealing or ultrasonic welding. The lamination process generally involves bringing the non-woven fabric and impervious sheet together under pressure. Preferably the two layers are laminated by means of heat sealing.

The process of the invention is preferably carried out as a continuous process in which the two layers are fed between the nip of two heated rollers or belts. An apt apparatus comprises two heated belts. A favoured apparatus of this type is a laminating machine reference available from the Reliant Tooling Company.

The heat lamination process should be carried out at a temperature at which the fluid impervious sheet softens in order to obtain a good bond between the layers. The temperature used in the process however should be below the temperature at which the fluid impervious sheet loses its integrity and becomes distorted. The heat lamination process of the invention comprising a low density polyethylene film can suitably be carried out at a temperature of 80 C to 100 C. Similarly the heat lamination process of the invention comprising a polypropylene film can suitably be carried out at a temperature of 1250C to 145 C.

After bringing together the component parts of the device in a flat form, the wrapper layers are folded around the absorbent core, the edges overlapped and sealed together on the garment facing side using conventional means of heat sealing, adhesives, such as hot melt adhesives or ultrasonic welding.

The garment facing sides of the devices of the present invention will normally carry at least one area of pressure sensitive adhesive whereby the device may be adhered to a garment in use. Prior to use this area will be covered by a release paper in the conventional way.

Optionally the absorbent core may be formed of two parts and have sandwiched between the two, a folded tissue paper layer to provide extra absorption and to help to disperse the body fluid more quickly and more evenly throughout the absorbent core.

The construction of the devices of the present invention normally requires that the fluid impervious sheet is in fact in two pieces which are laminated to the cover to leave a central fluid pervious portion of the cover which forms the body contacting portion of the device when the laminate is folded to enclose the absorbent core. The lamination stage may be carried out prior to actually manufacturing the device or may occur as a stage during manufacture of the device. Thus the device may be made by delivering pre-determined lengths of the absorbent onto the preformed laminate as a flat sheet, folding the laminate around the absorbent and sealing the edges and finally cutting the strip of wrapped absorbent so formed between the pieces of absorbent and sealing across the ends to form the enclosed device.Alternatively, the cover and impervious sheet may be delivered to a sealing device just prior to delivery of the piece of absorbent.

Various forms of the absorbent article in the form of a sanitary napkin constructed in accordance with the invention and a process for their manufacture will now be described by way of example only and with reference to the accompanying drawings in which: Figure 1 is a cross-section through a sanitary napkin with a single absorbent core and laminated cover.

Figure 2 is a cross-section through a sanitary napkin which includes a tissue paper insert in the absorbent and a fleece layer.

Figure 3 is a schematic drawing of a process for forming a sanitary napkin of the present invention.

Figure 4 shows a cross-section of the abosrbent device of the present invention in the form of a sanitary napkin in which the impervious layer covers only the edges of the absorbent core.

Figure 1 shows a sanitary napkin with a unit absorbent core (1) typically of fluffed wood pulp, which is enclosed in a wrapper formed from a laminate of a bonded non-woven or integral net cover (3) laminated to a fluid impervious sheet (2). The fluid impervious sheet covers the entire garment facing surface and lies along the sides of the absorbent core and overlaps slightly onto the body facing surface but leaving a fluid pervious portion (4) through which body fluid gains access to the absorbent core. The fluid impervious sheet is in fact made up of two sheets folded together in an appropriate manner. On the garment facing surface, the ends of the wrapper are sealed together using an appropriate sealing method, that is, heat sealed or adhesive (5). The garment facing surface carries an area of pressure sensitive adhesive (6) for adhering the device to the clothing in use.Prior to use the adhesive strip (6) is covered with a conventional silicone release paper or plastic film (7).

Figure 2 shows a different type of sanitary napkin than Figure 1. In this embodiment the absorbent core (1) is conveniently formed of two superimposed parts which has a folded tissue paper (8) between the two layers. The sanitary napkin also includes a fleece (9) which is pervious to body fluid and is placed beneath the fluid pervious portion of the cover (4) and lies across the entire body facing surface and along part or even the whole of the sides of the absorbent core. The fleece lies between the absorbent core and the fluid impervious sheet.

Figure 3 is a schematic drawing of a process for forming the absorbent devices of the present invention in the form of a sanitary napkin. At the lefthand side of the drawing the absorbent core (11) is formed by bringing together two continuous batts of fluffed wood pulp and cutting to a pre-determined length by means which are conventional in the art. This system allows, when desired, a tissue layer to be introduced between the two parts of the absorbent core in a simple manner. The absorbent core is actually delivered onto the cover - fluid impervious sheet laminate. The laminate is formed continuously by bringing together the two pieces of fluid impervious sheet (12, 13) with the cover (14) under heat and pressure. The laminate so formed having had the correct length of absorbent core delivered to it is then folded around the absorbent core and the edges sealed (15).The strip of absorbent enclosed with the wrapper (16) is cut across its width between the pieces of absorbent core and the open ends heat sealed (not shown). A strip of pressure sensitive adhesive may then be applied to the side which is intended to contact a garment in use and covered with a conventional release paper.

Figure 4 shows a cross-section of a further sanitary napkin of the present invention. In this embodiment the absorbent core (1) is enclosed by a laminate of a fluid permeable bonded non-woven or integral net cover (2) and a fluid impervious sheet (3), the fluid impervious sheet does not overlap onto the body contacting surface of the napkin but extends so as to only cover the longitudinal edges of the absorbent core.

On the garment facing side of the sanitary napkin the edges of the impervious sheet (10) do not overlap as shown in the napkins of Figures 1 and 2. The edges of the cover still form an overlap and are adhered to each other by penetration of the pressure sensitive adhesive used to form the garment adhering strip (6) through the two overlapping edges of the cover.

The invention will now be illustrated by reference to the following Examples: Example 1 Preparation of laminated cover Two 50mm wide strips of low density polyethylene film (0.025mm thick) were heat laminated to the longitudinal side edge portions of a 1 80mum wide strip of integral net which comprised longitudinal ribs interconnected by fibrillated strands (weight per unit area 5.8g/m2, thickness 0.048mm), to leave a central longitudinal area (60mm) unlaminated. One of the strips was laminated adjacent to one edge and the other strip was laminated inset (20mm) from the other edge of the integral net to provide an unlaminated edge portion to assist the sealing of the Cover.The heat lamination was carried out on a laminating press (Reliant ) at a laminating temperature of 85 C. The film strips were found to be well bonded to the integral net.

Preparation of absorbent device (sanitary towel) An elongate absorbent pad strip (length 1 80mm, width 60mm, thickness 1 0mum) consisting of a batt of fluff wood pulp wrapped in tissue was fed onto the central longitudinal unlaminated area of the cover strip as prepared above. The longitudinal sides of the cover strip were then folded around the longitudinal sides of the pad and the overlapping portions of the cover strip at the back face of the pad and sealed by application of an adhesive to the unlaminated edge portion. The folded strip was then cut to suitable length and the overlapping portions at the ends of the pad were heat-sealed to form a sanitary towel of the invention.

In the sanitary towel so formed the fluid impervious film of the laminated cover covered the back face, the longitudinal side edges and the side edge margins (5mm wide) of the top face of the absorbent core and the longitudinal ribs of the integral net were in the length direction of the device.

Example 2 A sanitary towel was formed in the same manner as Example 1 except that carded thermally bonded polypropylene fabric (Finntex CF10, weight per unit area 1 Og/m2, thickness 0.050mm) was used instead of an integral net and the heat lamination process was carried out at 90 C. The polyethylene film strips were found to be well bonded to the polypropylene fabric.

Example 3 A sanitary towel was formed in the same manner as Example 2 using a carded thermally bonded polypropylene fabric (Noworoll PRC, weight per unit area 10g/m2, thickness 0.065mm) and the heat lamination process temperature of 85 C. The polyethylene film strips were found to be well bonded to the polypropylene fabric.

Example 4 A sanitary towel was formed in the same manner as Example 1 using a spun bonded polypropylene fabric Lutravil VP 605, weight per unit area 15g/m2, thickness 0.065mm) instead of the integral net, a propylene-ethylene copolymer film strip (0.025mm) instead of a polyethylene film strip. The heat lamination process was carried out at a temperature of 140 C. The film strips were found to be well bonded to the polypropylene fabric.

Example 5 A sanitary towel was formed in the same manner as Example 1 using a single ply of bleached tissue (grade DD 84/72 available from British Tissues) instead of an integral net. The heat lamination process was carried out at 90 C. The film strips were found to be well bonded to the tissue.

Wicking Test The sanitary towels of Examples 1 to 5 were subjected to a wicking test in which a drop (0.5ml) of fluid (1.0% aqueous saline solution containing a lissamine green dye) was allowed to fall on the cover, on the body facing side of the sanitary towel, adjacent to the edge of a laminated film portion. After approximately 60 seconds the area of spread of the fluid into both the non-laminated and laminated portions of the cover was measured and the results expressed as the ratio: Area of fluid spread in laminated portion Area of fluid spread in non-laminated portion The results obtained were as follows: Example No.Spreading Ratio 1 0.4 2 0.4 3 0.5 4 0.4 5 (comparative) 1.5 The results show that sanitary towels of the invention (Examples 1-4) which have an integral net or bonded non-woven fabric-fluid barrier sheet laminate outer cover have a spreading ratio of less than one whereas the comparison sanitary towel which has a tissue paper-fluid barrier sheet laminate outer cover has a spreading ratio of greater than one. The results thus indicate that the laminated portions of the integral net or bonded non-woven fabric cover material used in the invention inhibit the spreading or wicking of aqueous body fluids whereas the laminated portions of the cover material (tissue paper) used in prior art comparative example promote the spreading or wicking of such aqueous body fluids. The test therefore shows that the outer covers used in a sanitary towel of the invention inhibits the wicking of body fluids from edge portions of the barrier sheet around the side edges of these sanitary towels thereby reducing the possibility of leakage from these sanitary towels in use. Furthermore, it was found in the test that the longitudinal ribs of the laminated integral net cover of the sanitary towel of example 1 tended to spread the fluid in the length direction of the ribs which also lie in the length direction of the sanitary towel and to limit the spreading of fluid in the transverse direction of the ribs. Such ribs of the laminated integral net - fluid barrier cover used in the sanitary towel of the invention will therefore further inhibit the wicking of body fluids from the edge portions of the barrier sheet around the side edges of the sanitary towel.

Claims

1. An absorbent device suitable for use as a sanitary napkin which comprises a fluid pervious cover enclosing an elongate fluid absorbent core and a fluid impervious barrier sheet arranged between the cover and the core so that the barrier sheet covers the side of the core facing away from the body of the user and at least portions of the two longitudinal side edges of the core characterised in that the fluid impervious sheet is heat laminated over the whole of one surface thereof to a non-woven fabric fluid pervious cover.

2. An absorbent device as claimed in claim 1 in which the fluid pervious cover is an integral net.

3. An absorbent device as claimed in claim 2 in which the inegral net comprises longitudinal ribs connected by fibrillated strands.

4. An absorbent device as claimed in claim 3 in which the longitudinal ribs of the net extend in the length direction of the device.

5. An absorbent device as claimed in any of claims 1 to 4 in which the inegral net comprises a blend of high density polyethylene and high impact polystyrene.

6. An absorbent device as claimed in claim 1 in which the bonded non-woven fabric is a spun bonded fabric.

7. An absorbent device as claimed in claim 1 in which the bonded non-woven fabric is a thermally bonded fabric.

8. An absorbent device as claimed in either of claims 6 or 7 in which the bonded non-woven fabric comprises polypropylene.

9. An absorbent device as claimed in any of claims 1 to 8 in which the fluid impervious sheet comprises polyethylene.

10. A process for the manufacture of the absorbent device of claims 1 to 9 which comprises heat laminating a fluid impervious barrier sheet over the whole of its surface thereof to a fluid pervious cover comprising a non-woven fabric and enclosing an elongate absorbent core with the laminate so that the fluid impervious barrier sheet is between the cover and the core and covers the side of the core facing away from the body of the user and at least portions of the two longitudinal side edges of the core to leave a fluid pervious portion on the body contacting side of the device.

11. A process as claimed in claim 10 in which the fluid pervious cover is an integral net comprising longitudinal ribs interconnected by fibrillated strands and the net is heat laminated to the fluid impervious barrier sheet so that the longitudinal ribs of the net extend in the length direction of the device.