Perforated thermoplastic sheet in which the perforation craters

Stock material or miscellaneous articles – Structurally defined web or sheet – Including aperture

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Details

428132, 428137, 428134, 6043851, 442394, 442399, 442398, 264504, 264511, 264571, A61F 1315

Patent

active

057310610

DESCRIPTION:

BRIEF SUMMARY
The present invention relates to a perforated thermoplastic sheet made in a material that is impervious to liquids and used, in particular, as a protective covering for an absorbent body, e.g. in the field of sanitary articles such as disposable diapers or nappies and sanitary napkins or towels.


BACKGROUND OF THE INVENTION

In this type of sanitary article, the absorbent wad is generally sandwiched between an outer sheet that is impervious to liquids, thereby avoiding wetting the user's clothing, and an inner protective sheet which is in contact with the skin of the user. The protective sheet must allow the liquid discharged by the user to pass through while ensuring a degree of comfort.
Proposals have already been made in document FR 2 294 656 for a disposable diaper in which the protective sheet is made of a material that is impervious to liquids and that has convergent orifices or capillaries with openings of sizes that are critical and with convergence angles that are likewise critical, the absorbent element being in intimate contact with the apexes of said convergent capillaries. The convergence angle of the capillaries is about 10.degree. to about 60.degree.. Each capillary has a base in the outer plane of the protective sheet, the size of the opening of said base is about 0.15 mm to 6.35 mm, while the size of the opening at the apex of each capillary is about 0.1 mm to 2.54 mm.
According to the teaching given in that prior document, the above-mentioned convergence and sizes allow liquid to pass from the outer surface of the protective sheet towards the absorbent body, while guaranteeing that there is no flow of liquid in the opposite direction. The convergent capillaries formed in the protective sheet act somewhat like non-return valves.


OBJECTS AND SUMMARY OF THE INVENTION

The object of the Applicant is to propose a perforated thermoplastic sheet which can be used as a protective sheet for sanitary articles and which, in known manner, includes sorts of capillaries enabling liquid to pass through the sheet while acting as non-return valves, but without being restricted as to the sizes of said capillaries.
Such a perforated sheet is made of a material that is impervious to liquids and it includes a multiplicity of craters, each having a base in the plane of the outer face of the sheet, an apex remote from said plane, and a sidewall which is inclined going from the base to the apex of the crater.
In a manner characteristic of the invention, the base of each crater has a peripheral shape including at least one zone of discontinuity, i.e., inward contraction of the peripheral curve of the crater, such that on going round the periphery of each crater, the sidewall presents an inclination that is not uniform, having angles of inclination relative to the perpendicular to the plane of the outside face of the sheet varying between positive values and negative values, said angle being negative at least in the zone of discontinuity.
For comparison with the teaching of prior document FR 2 294 656, a positive angle of inclination for the sidewall corresponds to a converging profile while a negative angle corresponds to a diverging profile. Thus, because of the presence of the zone of discontinuity and because of the particular inclination of the sidewall in said zone, it has been possible for the Applicant, surprisingly, to provide a perforated thermoplastic sheet of the invention with craters of sizes that are not restricted, while nevertheless preserving their functions of transferring liquid and of acting as a non-return valve.
Preferably, the peripheral shape of the base of the crater is the result of partially overlapping a plurality of curved geometrical shapes, in particular circles and ellipses, and the zone of discontinuity corresponds to the junction between overlapping shapes.
In a preferred embodiment, the base of each crater has a curved outline with a longitudinal axis of symmetry (EE') that is the result of partially overlapping an ellipse with at least one circle whose center lies on the lon

REFERENCES:
patent: H1575 (1996-08-01), Daugherty et al.
patent: H1579 (1996-08-01), Furio
patent: 3929135 (1975-12-01), Thompson
patent: 4324246 (1982-04-01), Mullane et al.
patent: 4342314 (1982-08-01), Radel et al.
patent: 5171238 (1992-12-01), Kajander
patent: 5567376 (1996-10-01), Turi et al.
patent: 5614283 (1997-03-01), Potnis et al.

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