ABSORBENT ARTICLES

Abstract: A diaper comprises in sequence a water-impermeable backsheet, an absorbent core, water-swellable water-insoluble polymeric material, a sheet of resilient hydrophobic material and a hydrophobic water-permeable topsheet. The resilient material is preferably a non-woven material, most conveniently a lofted non-woven material.

Description: ABSORBENT ARTICLES The present invention relates to absorbent articles including integral disposable babies' diapers, adult incontinence pads and sanitary napkins containing absorbent polymer. Integral disposable diapers and those other products generally consist of at least a water-impermeable backsheet, a layer of absorbent fluff, usually airfelt, and a topsheet which is water-permeable. Early designs of these products contained solely cellulosic fluff pulp as the absorbent. The fluid is held between the interstices/capillaries of the fibres. The problem with the early diapers is that (a) the total fluid capacity of the diapers is fairly low (b) large amounts of fluff have to be used making the diaper thick and bulky (c) under pressure the fluid is released from the fluff, back through the top sheet causing the diaper to leak onto the skin. The absorbency of these products can be improved and the bulk reduced by the incorporation of highly absorbent water-swellable, water-insoluble polymer into the diaper. It has been proposed to place the polymer into the core in various positions, eg 1. the polymer can be placed in a layer between two wads of cellulosic fluff; 2. the polymer can be mixed randomly with the cellulosic fluff pulp to form a homogenous matrix; or 3. the polymer can be placed above the fluff but just below the top sheet or a combination of any of 1, 2 and 3. Part of the function of the topsheet is to retain the other diaper components in position. Some topsheets are formed from non-woven sheet material formed from hydrophobic fibres. The use of hydrophobic materials stops liquid being retained by the topsheet so that the baby's skin, which is in contact with the topsheet, can be kept dry. Although the use of hydrophobic topsheet does help in this regard, there is always a problem with "rewet" ie the tendency of liquid to be squeezed out from the fluff through the topsheet and onto the skin of the baby when there is pressure applied. There are problems with all of the proposals for incorporation of polymer, eg in the third and, to an extent the first solution, any cellulosic fluff immediately under the topsheet holds fluid between the fibres and this fluid can still be released under pressure through the cover sheet onto the skin. In all of the proposals if a polymer of high fluid retention capacity but soft in its swollen state is used then the structure can pack down under pressure making it difficult for successive volumes of the fluid to penetrate. The polymer is generally used in the form of particles. If the particles are small then they tend to fall out of the diaper through the interstices of the non-woven topsheet and may be deposited onto the skin of the baby which is undesirable. The use of larger particles, which are less likely to be able to pass through the interstices in the non-woven topsheet, especially when in a layer immediately under the topsheet, detracts from the softness of the diaper and gives it a gritty, possibly abrasive, feel so that it is less comfortable for the baby. In EP-A-0165807 a sanitary towel comprising a water-permeable topsheet with a resilient comfort layer lying immediately underneath the topsheet is described. The absorbent core can contain ancilliary absorbent materials, eg cross-linked polyacrylate polymer particles. The resilient layer can be formed of hydrophobic fibres. IN US-A-4381783 absorbent polymer particles are incorporated into diapers in pockets. The pocket can be positioned immediately underneath the water-permeable topsheet, which comprises conventional thin non-woven materials, for instance of cellulosic fibres or of hydrophobic fibres. According to the present invention a new integral disposable absorbent product with improved rewet properties comprises in sequence a water-impermeable backsheet, a core comprising absorbent fluff, water-swellable, water-insoluble polymeric material and a water-permeable hydrophobic topsheet and is characterised in that the article comprises also a layer intermediate the topsheet and the core which comprises a sheet of a resilient water-permeable hydrophobic material having a thickness of at least 0.5mm. The presence of the resilient layer means that large particles can no longer be sensed by the baby through the topsheet. Furthermore where the polymer is in the form of small particles the resilient layer provides a physical barrier preventing the particles from passing through the topsheet, for instance onto a user's skin. The resilient layer also reduces the direct pressure on polymer in the diaper which can reduce the packing dov/n and associated problems discussed above. The absorbent article is usually for the absorbtion of bodily fluids including urine and menstrual fluid and so is usually a diaper, which term includes adult incontinence pads, or a sanitary towel. The resilient layer may be present solely in a part of the crotch region where most of the liquid is absorbed, for instance it may be in the form of a transverse strip of material across that region. Alternatively a diaper may comprise a longitudinal strip of the material along the diaper centre. For convenience of manufacture however the resilient layer preferably extends over the whole of the article. The particles of polymer used in the preferred embodiment of the diaper may be small particles or large particles or a mixture. Small particles may for instance comprise polymers particles having an average size (when dry) in the range up to 0.5mm or less, for instance up to 0.25mm. Large particles may have average size (when dry) of at least 0.5mm, for instance they may have an average size of at least 1mm. Alternatively the polymer particles may be in the form of fibres. The polymer particles are positioned immediately under the resilient layer and thus on the top of any other absorbent material such as airfelt (or other material) core. In this position there is a very great improvement in rewet properties provided by the combination of resilient layer and absorbent polymer that is on application of pressure on a wet product liquid is not squeezed back from the airfelt core on to the outside of the topsheet and from there into contact with the user's skin, as it would be in an embodiment wherein other absorbent material was provided between the polymer and resilient layer. The polymer may be provided over part only of the article's surface area, eg solely in the crotch region, or may be spread across the whole area of the article. The polymer may be formed of any of the materials described in EP-A-268,498 or EP-A-269 ,393. Other monomer mixtures may be used, for instance copolymers of maleic acid with an olefin such as isobutylene for instance croεslinked through an external polyhydroxy crosslinker. The polymer may be cationic, anionic or non-ionic. The airfelt or fluff forming the bulk of the absorbent material in the diaper is of the usual type. It may comprise additional absorbent polymer, in the form of fibres, particles or as a sheet. The resilient material must be water-permeable in order to allow passage of liquid waste through into the absorbent part of the diaper, ie into the absorbent polymer and the airfelt below. The material is hydrophobic in order that it does not retain liquid but allows liquid to pass very easily through it. Also the layer allows fluid to enter the diaper and spread into the core rapidly, thereby keeping the skin drier at the initial expulsion of liquid onto the article. The resilient material is preferably formed of fibres although may be formed of hydrophobic open-cell sponge material. A material formed of fibres is rendered resilient by the orientation of the fibres in the material such that they do not all lie in the plane of the web. The resilient layer preferably is formed of a non-woven material, the fibres of which are preferably formed of polyester, polypropylene or polyethylene. The material conveniently consists of a lofted non-woven material. By lofted we mean that the material as supplied for the diaper manufacturing process is in the form of a relatively thin non-woven material which, when i is heated, expands to form the thicker resilient sheet. Such materials are made originally as thick resilient powder-bonded non-woven sheets which are then calendered to form thinner sheets. The heating process used in the manufacturing step allows the material to find its original, thicker and resilient form. Such material is particularly convenient to use from the manufacturers' point of view. It is provided as a thin material so can be supplied on rolls with adequate web length, and is then heated for the lofting during the manufacturing operation. The resilient material is preferably at least 1mm thick and often is 2 to 3mm thick. The layer may be integral with the topsheet ie permanently bonded to it, either before, eg during manufacture of the non-woven sheet, or during the diaper or other manufacturing process. Thus the resilient layer and non-woven topsheet could form a dual layer in the product. The topsheet may be a thin layer of a non-woven material, for instance a hydrophobic material of the type used for disposable diapers in existing products. The fibres in the topsheet, in contrast to the material used in the resilient layer, lie mainly in the plane of the web. Alternatively it may comprise an apertured thermoplastic film, such as of embossed polyethylene. Such film-type topsheets are more commonly used in sanitary napkins than diapers or incontinence pads. There is also provided in the invention a new process for producing the novel products, in which the step of introducing the resilient layer into the product comprises unreeling a web of calendered non-woven material in unlofted form and then heating the material to loft it and form the resilient material which the said sheet is from. The heating step is usually carried out prior to the material being placed in position in the product and is preferably carried out immediately before the material is introduced into the diaper. The heating could possibly be carried out after the material had been positioned and fixed into the diaper. The use of the lofted non-woven material is particularly convenient since it allows the material as supplied to the manufacturer to be fairly thin, since otherwise if the material was supplied in the lofted, resilient form the length of material on a reel would be very short which would be inconvenient for manufacturing purposes. The resilient material is thus held in place in the diaper either by virtue of it being sandwiched between the topsheet and the fluff, or it may be welded or bonded into position by adhesive for instance at its edges. The other features of the product's construction are conventional eg the backsheet material, fastening devices, such as, adhesive tabs, elasticated leg side flaps, waistband etc. The following example illustrates the invention. Example Two test diapers of the invention were made up by dismantling a commercial product by removal of the topsheet (which was a thermally bonded polyester non-woven having a weight of 21 g per m 2 ) and tissue layer immediately under the topsheet, followed by sprinkling though a 180 x 90 mm template arranged over the centralised longitudinal area 4 gm of particulate polymer and then applying a dual layer topsheet in the usual topsheet's position. Two products were formed, one (A) with a dual layer (ie laminated) topsheet of polyester non-woven material with a thin soft outer layer (10 g/m a ) and a medium thickness resilient lofted inner layer (28 g/m 2 ) Ultrasoft PlO/Ultraloft P28 (lofted) and the second (B) being similar but having a thicker resilient layer (50 g/m 2 ) (Ultrasoft PlO/Ultraloft P50 (lofted) both from Bonar Carelle Ltd) . These products were compared with the non-altered control product (no polymer) and five other commercially available diapers, all containing superabsorbent polymer, and one of these having the polymer located on the top of the fluff pad. Two tests were carried out, one on "puddling time" and the other on "wet back" . The puddling time test measured the time required for 60 ml of synthetic urine to penetrate into the centre of a diaper under a load of 1 g/cm 2 . Similar tests are done under low and high loads (8 g/cm 2 and 35 g/cm 2 respectively) . Repeat puddling time tests are carried out which give the time for successive aliquots of 60 ml synthetic urine applied at 20 minute intervals. The wet back tests measure the amount of synthetic urine in grams which emerges back through the topsheet of a diaper under zero (1 g/cm 2 ) low (8 g/cm 2 ) and high (35 g/cm 2 ) load, from the original entry area over a period of 2 minutes, immediately after 60 mis of synthetic urine have penetrated into the diaper, measured by placing a wade absorbent pad over the topsheet. Likewise repeat wet backs are tested after successive 60 ml aliquots are applied at 20 minute intervals. The results show that for the initial puddling time tests (ie initial aliquot) the performance of both test diapers under zero load was slightly worse than all of the commercially available products, including those with and without superabsorbent polymer. However under both low and high headings the puddling time was very considerably reduced in the products of the invention, whereas for all of the commercial products the time increased. At high loading the initial puddling time of the products of the invention was lower than under zero loading but higher than under the low loading, but again was much lower than all of the commercially available products. The thickness of the resilient layer did not appear to make any significant difference in initial puddling time. Tests on the repeat puddling times showed that under low load the second and third aliquots had very low puddling time for the products of the invention, the times being left on a third of the initial puddling time. However for all of the commercial products the successive aliquots have increased puddling times. Under low and high loads the puddling time of the products of the invention does increase for the second and third aliquots but to a much lower extent than for all of the commercially available products. The puddling time of the third aliquot, for the products of the invention, is far lower than for each of the commercially available products, under zero, low and high loadings. For the wet back tests, the presence of superabsorbent polymer in all of the products, both the commercially available and the products of the invention gave a very greatly improved wet back property to the nappy. The initial wet back of the products of the invention under zero loading was approximately the same as that of the best of the commercially avialable products (Pampers) , indeed the wet back under low and high loads was approximately equivalent to the Pampers results. These results were hugely improved over all of the other commercially available products. The products of the invention however showed dramatically improved wet back properties in the "repeat" experiments, that is where successive aliquots of synthetic urine were applied. In these tests the wet back remained low for the products of the invention, even under the fairly high loads. For all of the commercially available products the wet back after successive aliquots increased, often to high values. For the zero load the wet back of the best commercially available diaper was ten times that of the diapers according to the invention. These properties were apparent under any of the loading conditions tested. These results clearly show the greatly improved properties of the products of the invention, believed to be due to the combination of the resilient topsheet with superabsorbent polymer. The experiments also showed that the thinner resilient layer (28 g/m 2 ) gave adequate properties, not significantly different from the thicker (50 g/m 2 ) . The improvement was not related solely to the positioning of the polymer with respect to the pad, as the properties of the commercial product with polymer between the airfelt core and topsheet were far worse than the products of the invention.

Claims: CLAIMS 1. An integral disposable absorbent product which comprises in sequence a water-impermeable backsheet, a core comprising absorbent fluff, water-sellable water-insoluble polymeric material and a water-permeable hydrophobic topsheet, characterised by comprising also a layer intermediate the topsheet and the core which comprises a sheet of a resilient water-permeable hydrophobic material having a thickness of at least 0.5mm. 2. An article according to claim 1 which is a diaper or a sanitary towel. 3. An article according to claim 1 or 2 in which the resilient layer is at least 1mm, preferably at least 2mm thick. 4. An article according to any preceding claim in which the resilient layer comprises a non-woven material, preferably formed from polyester, polypropylene or polyethylene fibres. 5. An article according to claim 4 in which the resilient material is a lofted non-woven material. 6. An article according to any preceding claim in which the water-swellable polymeric material is present in the form of particles, preferably having average dry sizes of at least 0.5mm. 7. An article according to any of claims 1 to 5 in which the water-swellable polymeric material is present in the form of fibres. 8. An article according to any preceding claim in which the water-swellable polymeric material is spread across substantially the whole area of the article. 9. A Process for producing a product according to claim 5 in which the step of introducing the resilient layer into the product comprises unreeling a web of calendered non-woven material in unlofted form and then heating the material to loft it and form the resilient material which the said sheet is formed. 10. A process according to claim 9 in which the heating step is carried out immediately before the material is introduced into the diaper.

Inventors: MARSHALL DAVID, MARSHALL, DAVID
Applicants: ALLIED COLLOIDS LTD, ALLIED COLLOIDS LIMITED
Application year: 1990
Main classification: A61F13
IPC codes: A61F13