GB2225724A

GB2225724A - Case 1027-Hygienic absorbent device

Info

Publication number: GB2225724A
Application number: GB8828894A
Authority: GB
Inventors: Andrew John Carter
Original assignee: Smith and Nephew PLC
Current assignee: Smith and Nephew PLC
Priority date: 1988-12-10
Filing date: 1988-12-10
Publication date: 1990-06-13
Anticipated expiration: 2008-12-10
Also published as: GB8828894D0; GB2225724B

Abstract

A hygienic absorbent device which comprises a liquid pervious cover sheet, an absorbent core and a liquid pervious intermediate layer between the liquid pervious cover sheet and the body facing surface of the absorbent core. The intermediate layer comprises an apertured, contoured film of elastomeric polymer material for example a blend of ethylene vinyl acetate and an incompatible polymer.

Description

HYGIENIC ABSORBENT DEVICE This invention relates to hygienic absorbent devices generally and in particular relates to devices in the form of sanitary napkins, diapers, incontinence pads and the like.

Hygienic absorbent devices such as sanitary napkins, diapers, incontinence pads and the like normally comprise of an absorbent core which has a body facing surface and an opposed non-body facing surface.

The non-body facing surface is usually overlaid by a liquid impervious backing sheet while the body facing surface has overlaying it a liquid pervious cover sheet. The cover sheet will make direct contact with the user's skin in use. Thus any bodily fluid such as blood, urine and the like, will contact the cover sheet before being transmitted therethrough to the absorbent core. It is a common problem with hygienic absorbent devices that in use, if pressure is exerted on the device, absorbed fluid may be squeezed out of the absorbent core and be returned back to the cover sheet thereby rewetting the cover sheet and hence the skin of the user. This characteristic of such absorbent devices is undesirable as it can cause skin irritation and rashes if the contact between the bodily fluid and the skin is prolonged.An attempt has been made to solve this problem by interposing an intermediate layer between the cover sheet and the body facing surface of the absorbent core. Thus British Patent No. 1160625 teaches interposing a layer of viscose rayon or polypropylene fibres between the cover sheet and the absorbent core. However, this has not been found to be entirely satisfactory in use as viscose rayon is absorbent and retains some bodily fluid thereby facilitating rewetting of the cover sheet while polypropylene fibres being hydrophobic do not readily allow the transmission of aqueous bodily fluids so that they may remain on or in the cover sheet longer prior to being transmitted to the absorbent core. Further such wadding layers tend not to be resilient and can become compacted in use which both reduces the separation between the absorbent core and the cover sheet and may be uncomfortable.Our copending United Kingdom Patent Application No. 8521254 discloses an hygienic absorbent device in which the intermediate layer is an non-elastomeric, embossed plastics net which provides a good separation between the cover sheet and the absorbent core and has a good resistance to compaction in use, thereby providing good fluid transmission and low fluid wet back characteristics.

It has now been found that by using an intermediate layer in the form of a liquid pervious, apertured, contoured film formed from an elastomeric polymer material, the intermediate layer not only separates the cover sheet and the absorbent core and does not compact in use but also shows even better improved fluid transmission and reduced tendency to allow rewetting of the cover sheet in use. Such elastic contoured films are also soft and resilient so feel comfortable in use and are silent during movement of the user.

Accordingly the present invention provides a hygienic absorbent device which comprises a liquid pervious cover sheet, an absorbent core and a liquid pervious intermediate layer between the liquid pervious cover sheet and the body facing surface of the absorbent core characterised in that said intermediate layer comprises an apertured, contoured film of elastomeric polymer material.

Most aptly the present invention provides a hygienic absorbent device which is a sanitary napkin.

An elastomeric polymer material is a material which has a recoverable elastic strain of at least 10% and more suitably at least 15% preferably at least 20% and most preferably at least 25%.

Suitable apertured, contoured films for use in the invention can be formed from an elastomeric polymer.

Thus in another aspect the invention provides a hygienic absorbent device which comprises a liquid pervious cover sheet, an absorbent core and a liquid pervious intermediate layer between the liquid pervious cover sheet and the body facing surface of the absorbent core characterised in that said intermediate layer comprises an apertured contoured polymeric film formed from elastomeric polymer.

Suitable elastomeric polymers include polyether ester and polyether-polyamide block copolymers, polyurethanes, styrene-butadiene and styrene-isoprene block copolymers, polyisobutadiene and ethylene-vinyl acetate copolymers.

A favoured elastomeric polymer is an elastomeric polyether ester block copolymer. Such polymers are commercially known as Hytrels (Trade Mark). A preferred Hytrel is available as Hytrel 4056.

Another favoured elastomeric polymer is a polyether-polyamide block copolymer. Such polymer are known as Pebax (Trade Mark). A suitable Pebax is available as Pebax 2533 SN 00.

Suitable apertured, contoured films, for use in the invention can also be formed from blends of elastomeric polymers with other elastomeric or non-elastomeric polymers or fillers.

Favoured blends, however, are blends of an elastomeric polymer and an incompatible polymer. An "incompatible polymer" is a polymer which in a blend therewith is not miscible with the elastomeric polymer.

In such a blend the polymers would form separate phases and the polymer in the lower concentration (normally the incompatible polymer) would form a discrete disperse phase and the polymer present in the higher concentration (normally the elastomeric polymer) would form a continous phase. Methods of determining the compatibility of polymers is described in an article entitled "Compatibility", Encylopedia of Polymer Science and Engineering 1985, Vol 3 pages 758-775.

Preferred blends may contain from 90 to 40 parts by weight of the elastomeric polymer component.

Favoured films are made from elastomeric polymer material which is a blend of an ethylene-vinyl acetate copolymer and an incompatible polymer such as a polyolefin for example low density polyethylene or polystyrene.

Suitable blends of ethylene vinyl acetate copolymer and an incompatible polymer are disclosed in European Patent Application No. 0141592.

Preferred films are films made from a blend of ethylene vinyl acetate copolymer and polystyrene which contains 90 to 40 parts by weight of ethylene vinyl acetate copolymer.

A preferred polystyrene is high impact (rubber modified) polystyrene. An apt film for use in the invention is formed from 60 parts by weight of ethylene vinyl acetate copolymer and 40 parts by weight of high impact polystyrene.

The films of elastomeric polymer may include fillers such as chalk or whitening agents such as titanium dioxide. Suitably the fillers may be from 0 to 40% by weight of the polymer but preferably are between 1 and 10% by weight of the polymer.

The apertured film will have contours that is raised areas surrounded by troughs or flat areas. The raised areas which give rise to the contours on the apertured film may be of any shape but raised areas which are in the form of truncated square pyramids or hexagons or circular cones are preferred. Suitably the raised areas impressed in the apertured film will number per unit area 10 to 40 raised areas per sq. cm and preferably 15 to 25 raised areas per sq. cm for example 16, 20 or 24 per sq. cm.

Suitably the apertured film will contain from 30 to 150 apertures per sq. cm., more suitably will contain from 50 to 100 apertures per sq. cm. and preferably from 60 to 90 apertures per sq. cm., for example 64 apertures per sq. cm., 80 apertures per sq.

cm.

Suitably the contoured apertured film will have raised areas which have at least two apertures in the wall of each raised areas, more suitably will have from 2 to 8 apertures per raised area and preferably 2 to 4 apertures per raised area.

Favourably the area of each aperture will be from 0.01 sq. mm. to 1 sq. mm. and more favourably 0.1 sq.

mm. to 1 sq. mm. and preferably 0.25 to 0.75 sq. mm.

Suitably the open area of the apertured film will comprise from 5% to 50% of the area of the film and more suitably 10 to 40% and preferably are 20 to 30% of the area of the film.

The elastomeric polymer material film used to form the contoured, apertured film of the invention is usually formed by conventional extrusion methods of the polymer or polymer blend. Suitably the thickness of the film when extruded is from 25 to 200pm and more suitably is 30 to 150pm thick and preferably from 30 to 70pm thick.

The contoured apertured film itself will have a thickness as measured from the level of the plane of the film to the top of a raised area. Suitably this thickness is from 0.2 to 3mm and more suitably is 0.5 to 2mm and preferably is 0.5 to 1.5mm. The contoured apertured film when used in an absorbent device of the invention therefore provides separation between the body facing surface of the absorbent core and the cover sheet. The film after being compressed shows a resilience which maintains this separation.

The contoured apertured film may be prepared as follows: a film is formed from thermoplastic elastomeric material by, for example, conventional blending and/or extrusion methods. The film may also contain fillers, whiteners, plasticisers and the like to provide satisfactory surface characteristics and appearance to the finished film. The film may then be apertured using the normal methods of perforation such as pin moulds, heated or non-heated pins and the like.

For example, the film may be placed against a pin mould and covered by a plain polyethylene film. The film is then compressed where upon the pins of the pin mould aperture the elastomer film removing a piece of that film having the area of the pin. These pieces of film adhere to the polyethylene film along with the small pieces of elastomeric film are then removed to reveal a substantially flat apertured film of the elastomeric polymer.

The apertured film may then be contoured by placing it on the surface of a thermoplastic film, such as a polypropylene film, which has discrete raised areas for example 10 raised areas per sq. cm. The raised areas may be coated with a silicone release agent to facilitate removal of the formed contoured apertured film. The raised areas may be of any shape but either square truncated pyramids or hexagonal shapes are preferred. The apertured film is contoured by compressing it against the raised areas of the film.

Usually a resilient material, such as a foam, is present on the other side of the apertured film. The compression may be provided by a conventional press or by passing between the nip of a two rollers. It is possible that additional apertures may be placed in the already apertured film at this stage. These additional apertures are formed in the film at the tip of each of the raised areas in the thermoplastic film. The conditions of the process will depend upon the properties of the elastomeric film employed. After this treatment the contoured apertured film may be peeled off the thermoplastic film. The size of the raised areas and the pattern of bosses employed will vary depending upon the size of apertures in the elastomeric film.The raised films will be adapted in size so that at least two apertures fall in the walls of each of the raised areas formed in the apertured film during the compression process.

Alternatively the apertured film may be contoured by passing it between two rollers one or both of which may have a pattern of raised and/or depressed areas on their surface. The rollers may be heated to a suitable temperature to assist in contouring the film. In one method only one roller carries a pattern of raised areas on its surface. The other roller, the smooth roller, preferably has a soft resilient surface of rubber or foam which allows the raised areas on the other roller, which is normally made of hard material such as metal, to press into and permanently deform the apertured film. A preferred method is to use two rollers which have an intermeshing pattern of raised and depressed areas on their surface.

The absorbent material used in the invention can be any of the absorbent materials used in conventional hygienic absorbent devices. Suitable absorbent materials for such devices include comminuted/fluffed wood pulp, carded cotton webs viscose rayon fibres, tissue wadding, grafted cellulose super absorbents, polymeric super absorbents or mixtures thereof. The absorbent core can optionally contain an insert such as a tissue wadding to aid fluid distribution within the core.

The contoured, apertured film of elastomeric polymer material when used in the hygienic absorbent devices of the present invention may be placed with the raised areas in contact with the absorbent core.

Suitably this intermediate layer may be attached to the absorbent layer by suitable means, for example, a light coating of pressure sensitive adhesive may be provided on the contoured apertured film on the side which possesses the raised areas at a weight per unit area of from 2 to 15 gsm and the film adhered to the absorbent layer by slight pressure. The adhesive coating may be applied by spraying and at a weight at which transmission of fluid through the contoured film is not impeded. The contoured, apertured film may be attached over all its raised surface or only at selected bonding points.

The liquid pervious cover sheet used in the invention can be any of the cover sheets suitably used for hygienic absorbent devices. The cover sheet may be made of hydrophobic polymer such as polyolefin, for example polypropylene, high density polyethylene or polyester. Such cover sheets are less likely to retain fluid exudate at the surface of the device. The cover sheet may include, however, a hydrophilic component either as a fibre or coating on the hydrophobic fibres to facilitate initial absorption of the fluid.

Favoured cover sheets for use in the invention include plastics nets and non-woven fabrics such as bonded non-woven fabrics for example spun bonded and thermally bonded non-woven fabrics. Preferred are bonded non-woven fabrics.

The bonded non-woven fabrics used in the invention can suitably have a weight per unit area of 2 to 40g/m2 and can preferably have a weight per unit area of 10 to 30g/m2.

Similarly, the bonded non-woven fabrics are spun bonded polypropylene fabrics, for example Lutravil VP 605 available from Lutravil Spinnvlies.

Other though less preferred sheets for use in the invention include plastics nets. Suitable plastic nets for use as a cover sheet in the invention include those disclosed in British Patent No. 1,548,865.

The liquid pervious cover sheet will normally cover the body facing side of the absorbent core. Such a sheet however, may extend around the sides and the non-body facing surface of the absorbent core to surround the core. The cover sheet may be held on the device by attachment for example by sealing means at one or both side edges, at the peripheral edge or at the non body facing side of the core.

The intermediate layer of apertured contoured film of elastomeric polymer material may cover only a portion of the surface of the absorbent core, for example the central portion of such surface. However, it is preferred that the intermediate layer of apertured contoured film covers the whole of the body facing surface of the absorbent core.

When the hygienic absorbent devices of the invention are in the form of sanitary napkins, they normally comprise an elongate absorbent core. In one embodiment the sanitary napkin may include the apertured contoured film intermediate layer around the longitudinal side edges of the core and over the non-body facing surface as well as the body facing surface to surround and thus form a wrapper for the core. However, it is not necessary that the whole of the apertured, contoured film containing wrapper is contoured to inhibit fluid wet-back. Thus in another embodiment the sanitary napkin of the invention the intermediate layer of apertured, contoured film forms part of a wrapper which surrounds the absorbent core.

The apertured contoured film of such a wrapper can conveniently be the portion of the wrapper which covers the body facing surface of the core.

Absorbent devices of the invention can optionally have a fluid impermeable barrier layer such as thin plastics barrier film, for example a polyethylene film over the non-body facing surface of the absorbent core to prevent penetration of body fluid exudate through the pad. Absorbent devices of the invention, in particular a sanitary napkin, may optionally have adhesive for example in the form of strips, on its non-body facing surface to allow attachment of the device to a supporting garment.

Suitably in the absorbent devices in which a liquid impermeable barrier is present on the non-body surface of the absorbent core, the cover sheet, apertured contoured film and barrier sheet may be sealed together around the periphery of the absorbent core by means of heat sealing or adhesive so enclosing the absorbent core.

The hygienic absorbent of this invention may be assembled by hand or by a conventional process of assembling such articles.

EXAMPLE 1 A polymer blend containing 60 parts by weight of ethylene-vinyl acetate copolymer andd 40 parts by weight of high impact polystyrene and 4% by weight of the polymer of titanium dioxide was formed by mixing the polymers in a blade mixer at 1650c. A sheet of the mixed polymers was prepared using a heated roll mill.

This sheet was allowed to cool and then granulated in a Mason cutter.

A film was prepared from the polymer blend granules by extrusion through a die to give a film of thickness 125pom.

The film was apertured by compressing it between a pin mould and a flat rigid film of polyethylene. the general configuration of the apertures was square having a side of approximately 0.5mm and hence an area 0.25 sq. mm.

The apertured film was then placed on the embossed surface of a polypropylene sheet, which had a pattern of raised discrete, hexagonal bosses on that surface: A resilient polyurethane foam was placed over the apertured film This sandwich was subjected to pressure and heat, 800c for 5 minutes. the polymer blend film had been formed into water permeable, contoured, apertured film material under the influence of the heat and pressure and could then be removed from the embossed surface of the plastics sheet.

An absorbent core (width 60mm, length 216mm) of comminuted fluff pulp (6.6g), having a central layer insert of folded tissue wadding was placed centrally onto a strip of the apertured film (width 70mm, length 240mm) which had been lightly coated with a pressure sensitive adhesive, so that the openings in the film were in contact with and adhered to the absorbent core.

A sheet of non-woven spun-bonded polypropylene was placed in contact with the apertured contoured film. A film of liquid impervious film, polyethylene, was placed over the other side of the absorbent core and heat sealed around its edges to the apertured film and to the non-woven sheet so that the absorbent core is sandwiched between the two films.

A portion or portions of the outer facing surface of the liquid impervious film may carry a pressure sensitive adhesive layer covered by a release paper whereby in use the absorbent device in the form of a sanitary napkin may be adhered to a garment of the wearer.

Fluid Wet-Back Test Sanitary napkins prepared according to Example 1 were subjected to a fluid wet back test which was carried out in the following manner.

A 2 Kg flat weight (dimensions 10 x5 cm) was placed on the napkin and allowed to remain in place for 2 minutes and then removed. 5ml of 1% saline solution coloured with lissamine green dye was delivered onto the centre of the napkin by means of a syringe pump at a rate of 1 ml/min and at a height of 1 cm above the napkin surface formed by the contoured apertured film.

A pre-weighed stack of filter papers (Whatman No. 1 filter papers) were then placed over the wetted area of the towel and a 2 Kg flat weight (dimensions 10 x 5 cm) placed on the filter papers. After 1 minute, the filter papers were removed and weighed. The wet back expressed as grams of fluid was then calculated from the difference in weight of the filter papers before and after compression against the absorbent device. The results are the average of tests in five samples.

Sample Wet Back Sanitary napkin described in Example 1 0.02g Sanitary napkin with embossed net insert 0.22g Commercial napkin (no insert) 0.98g

Claims

Claims 1. A hygienic absorbent device which comprises a liquid pervious cover sheet, an absorbent core and a liquid pervious intermediate layer between the liquid pervious cover sheet and the body facing surface of the absorbent core characterised in that said intermediate layer comprises an apertured, contoured film of an elastomeric polymer material.
2. A device as claimed in claim 1 which is a sanitary napkin.
3. A device as claimed in either of claims 1 or 2 in which the apertured contoured film is formed from a blend of ethylene vinyl acetate copolymer and an incompatible polymer.
4. A device as claimed in claim 3 in which the blend contains 90 to 40 parts by weight of ethylene vinyl acetate copolymer.
5. A device as claimed in either of claims 3 or 4 in which the incompatible polymer is polystyrene.
6. A device as claimed in any of claims 1 to 5 in which the apertured contoured film has a thickness of 30 to 150pom.
7. A device as claimed in any of claims 1 to 6 in which the apertured contoured film has 15 to 25 raised 2 areas per cm2.
8. A device as claimed in any of claims 1 to 7 in which the apertured contoured film has raised areas in the form of truncated pyramids or cones.
9. A device as claimed in any of claims 1 to 8 in which the apertured contoured film has 2 to 8 apertures per raised area.
10. A device as claimed in any of claims 1 to 9 in which the area of each aperture in the apertured contoured film is from 0.1 to 1.0mum2
11. A device as claimed in any of claims 1 to 10 in which the open area of the apertured contoured film comprises 10 to 40% of the area of the film.
12. A device as claimed in any of claims 1 to 11 in which the apertured contoured film covers the whole of the body facing surface of the absorbent core.
13. A device as claimed in any of claims 1 to 12 in which the apertured contoured film is attached to the body facing surface of the absorbent core.
14. A device as claimed in any of claims 1 to 13 which comprises a fluid impermeable barrier film over the non-body facing surface of the absorbent core.
15. A device as claimed in claim 14 in which the apertured contoured film and the barrier film are sealed together around the periphery of the absorbent core to form a wrapper therefor.
16. A device as claimed in claim 14 in which the liquid pervious cover layer is peripherally sealed to the apertured contoured film.
17. A device as claimed in any of claims 1 to 16 in which the liquid pervious cover layer surrounds the absorbent core.