Leak Resistant Elastic Waist Diaper

FIG. 1 is a plan view, partically cut away, showing a diaper of the present invention in an as assembled configuration before the waist portions are elasticized.

FIG. 2 is similar to FIG. 1 but shows the finished diaper with elasticized waist portions.

In the description that follows, it will be understood by those skilled in the art that certain terms are relative. Most disposable diapers and adult incontinent pads are assembled in a continuous end-to-end fashion. In this case the sides of the diaper, which wrap around the upper thighs of the wearer, is the longitudinal direction. However, it is known for diapers to be manufactured in a continuous side-to-side assembly as, for example, is shown in Joa, U.S. Pat. No. 4,284,454. In this case, the ends, or waist encircling portion of the diaper is in the longitudinal direction of motion during manufacture. Thus, the terms "longitudinal" and "transverse" are relative and as used herein should not be considered as limiting to one orientation or the other.

The various embodiments of the present invention can most readily be understood by reference to the attached drawings. FIG. 1 shows a diaper 2 whose components have been fully assembled but which is as yet in an unfinished state of manufacture. This is the form of a diaper unit as they are most commonly found while under light tension in an end-to-end assembly on a diaper making machine. It comprises a moisture impervious backsheet 4 which would normally be made from a lightly textured pigmented polyethylene. Backing sheet 4 is overlaid by a moisture absorbent fluff filler pad 8. This, in turn, is overlaid at its ends by an insert strip of moisture impervious material 14, 15. In the present case this insert strip is a biaxially oriented heat shrinkable thermoplastic material. The insert is shown here in its relatively inelastic heat unstable, unshrunk state. When heat shrunk it becomes elastic having an extensibility of up to 100%, or even greater. The assembly is then covered before any heat treatment by a moisture pervious nonwoven top sheet 6. The entire assembly is bonded together by a plurality of fine hot melt adhesive lines 10. Adhesive tabs 12 are conventional and are used by the mother for attachment of the diaper to the infant.

Optionally, inserted strips 16 of the heat shrinkable latent elastic material may be inserted along longitudinal margins 20 to ultimately elasticize the leg areas. It is within the scope of the invention to use conventional rubber elastic at this location. The units are severed from a continuous assembly to form end or waist margins 18.

FIG. 2 shows the diaper of FIG. 1 in which the waist and longitudinal margins have been heat shrunk to form elastic portions. These ensure a tight fit and are important in preventing leakage when worn by an infant or adult user. The diaper of FIG. 2 is shown without any longitudinal or transverse restraint. As a result, the heat shrunk marginal areas 18', 20' will tend to form a shirred or wrinkled edge with accompanying folds. When placed on a wearer the shirred edges are generally placed under tension and the diaper surface is again drawn reasonably flat. In FIG. 2 the prime (') symbol indicates portions of the diaper of FIG. 1 which are subsequently modified by heat shrinking the inserted pieces.

The temperature to which the longitudinal edge of a diaper of the type shown in FIGS. 1 and 2 must be heated is dependent upon the particular polymeric material which is used. These temperatures will generally range between about 80.degree. to 120.degree. C. The amount of shrinkage obtained is dependent upon the temperature to which the polymeric material is heated, that time it is held at that temperature, and the degree to which it is allowed to relax while being cooled.

In the present case the transversely inserted pieces 14', 15', as shown in FIG. 2, have only the outer marginal edge 18' heat shrunk and elasticized. Inner edges 22, 23 are left unchanged. here they serve to prevent moisture leakage in the waist areas of the diaper.

The various components used in the manufacture of infant diapers or adult incontinent pads are well known within the industry. The moisture permeable top or body contacting sheet has a basis weight usually in the range of 18-26 g/m.sup.2 and may typically be a carded polyester fiber with a latex binder or spun bonded polypropylene having continuous fibers of 2-5 denier thermally bonded by patterned calendar rolls. Respective examples of these types would be Scott 6822, available from Scott Paper Company, Nonwovens Division, Philadelphia, Pennsylvania or Celestra, available from James River Corporation, Washougal, Washington. The moisture impermeable diaper backing sheet may be a low density polyethylene film having a thickness in the range of 0.02-0.04 mm (0.75-1.5 mils). This material is frequently microembossed to better retain attachment tapes. An example of such a conventional backing material would be Clopay Code 53, available from Clopay Corporation, Cincinnati, Ohio.

An alternative type of backing film is a biaxially oriented heat shrinkable elastomeric material of the type that is heat unstable and relatively inelastic in its unshrunk form and stable and relatively elastic in its heat shrunk form. This may be used either for the entire backing sheet or for ribbon-like inserts along the marginal portions of the backing sheet. One such material is Cryovac SDX-0820, available from Cyrovac Division, W. R. Grace Company, Duncan, South Carolina. This material is a biaxially oriented irradiated polyethylene that becomes heat shrinkable at temperatures generally falling within the range between 80.degree.-95.degree. C. Unrestrained shrinkage after heating this material to the above temperature range will generally be to about 50% of original dimensions. Lower shrinkage can be achieved in one of several ways. Control of the amount of stretch during film formation is one suitable way. As one example, if it is only desired to produce elasticized leg opening areas on a diaper, a uniaxially oriented film would normally be quite suitable. Control of temperature to which the film is heated, and the subsequent rate of cooling, is another way in which shrinkage can be controlled.

Flexible rapid setting hot melt adhesives, which may be used to bind separate heat shrinkable ribbons and may also be used as the fine line adhesives for uniting the entire assembly, are commonly formulated from ethylene-vinyl acetate resins used with tackifiers and other additives. These adhesives tend to be somewhat tacky and flexible at room temperature. One suitable material is available from H. B. Fuller Company, Vadnais Heights, Minnesota as Type HL 1048N.

Large sized infant diapers were made using the above components. These diapers were 495 mm long and 337 mm wide and weighed a total of 72 g. The pad was fluffed bleached kraft softwood pulp having a density in the range of 0.07-0.08 g/cm.sup.3. The polyethylene backing film had a thickness of 0.03 mm. An insert of the Cryovac film noted above is placed so as to cover the end portions of two adjacent diapers and overlap the pad portions by about 20-25 mm before the nonwoven top sheet was laid on. This film was coated on the surface facing the nonwoven with parallel fine line adhesive strips so that it was bonded to both the backsheet and topsheet. The longitudinal dimension of the film in each diaper was about 60-70 mm. After this the transverse waist areas were heated to a temperature of approximately 90.degree. C. over a width of about 15 mm and allowed to shrink freely. The ultimate diaper had an extensiblity of about 40% in the waist areas.

A series of diapers was made as in Example 1 but with the addition of strips of the Cryovac heat shrinkable elastomeric film along each longitudinal margin in the leg area. These strips were about 305 mm long and 10 mm wide. After assembly the longitudinal margins were heated at a temperature of about 95.degree. C. over their entire width using a hot roll and allowed to shrink. Subsequently the transverse waist areas were heated to a slightly lower temperature, as described above. Extensibility in the elasticized leg area approached 80% and was about 40% in the waist areas.

Another series of diapers was made as in Example 1 but here the polyethylene backing film was replaced with the Cryovac material which had a thickness of 0.03 mm.

The waist and leg areas were heated as in Example 2. The resulting diaper had a leg area extensibiliy of about 30-40% and waist area extensibility of 20-30%.

It will be readily apparent to those skilled in the art that many variations could be made without departing from the spirit of the present invention. Thus, the invention is to be considered as being limited only by the following claims.