Surgery – Means and methods for collecting body fluids or waste material – Absorbent pad for external or internal application and...
Reexamination Certificate
1999-12-13
2002-09-17
Lindsey, Rodney M. (Department: 3765)
Surgery
Means and methods for collecting body fluids or waste material
Absorbent pad for external or internal application and...
C604S358000
Reexamination Certificate
active
06452064
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a method of producing an apertured covering sheet for an absorbent article such as a diaper, a sanitary napkin, an incontinence protector, or the like, wherein heated needles are caused to penetrate a sheet of material comprising at least one thermoplastic component, and wherein the temperature of the needles during penetration of the sheet of material exceeds the melting temperature of the thermoplastic component.
The invention also concerns an apertured covering sheet for an absorbent article manufactured in accordance with the method, and an absorbent article provided with a covering sheet manufactured in accordance with the method.
BACKGROUND OF THE INVENTION
High demands on softness as well as dryness are put on fluid permeable covering sheets for absorbent articles of the kind which during use are intended to be in contact with the body of a user.
However, it has proven difficult to accomplish a fluid permeable covering sheet having a soft, textile-like surface which remains dry even after repeated wetting when the covering sheet is being used on an absorbent article.
In order to achieve a soft, textile-like covering sheet, it is common to use nonwoven materials. In order to more quickly lead fluid through the surface material down into a lower, absorbent material layer, it is common to perforate the material.
One such perforated nonwoven material is previously known through, for instance, EP 0,235,309. The perforated nonwoven material consists of a spunlace material having a high percentage of hydrophobic fibres. In a spunlace process, holes are formed in a fibrous material by ejecting very high pressure water jets against the material. The spunlace material is one of two layers in a topsheet-laminate and is intended to be the layer which during use is arranged closest to the user. The spunlace material consists of a higher percentage of hydrophobic fibres than the lower material layer in the topsheet. Thereby, the lower layer can drain liquid from the upper layer.
However, one problem with the described material is that holes which are formed by water jets become irregular both in shape and in size and exhibit fibres protruding from the edges of the holes, into the holes. Such protruding fibres diminish the area of the holes and will in addition act as wicks which transport liquid into the material between the holes by capillary action. The protruding fibre ends and the irregular shape and size of the holes considerably increase the risk of liquid remaining in the covering layer after wetting. Since a very small amount of liquid is sufficient for a surface material to be perceived as wet, this is evidently a considerable disadvantage with the known surface material.
A further problem with the described nonwoven material is that it is difficult to create a predetermined, well-defined hole-size. It is well known, for instance through EP 0,409,535, that the hole dimensions of a perforated material are of determining significance to obtaining an optimal inflow of liquid. For nonwoven material exhibiting some areas having a dense fibre structure and other areas having an open fibre structure, this implies that it is difficult to obtain a uniform hole size. This is due to the fact that the holes in the dense fibre areas are smaller, since they are surrounded by more fibres. Moreover, such an apertured nonwoven material exhibits a relatively low tensile strength, since the aperturing involves a decrease in the strength of the material. Since it is important that the material has sufficient strength so that no risk of breaking exists either in connection with the aperturing process, during production of the absorbent article, or during use of the finished absorbent article, naturally the decrease in the strength of the material which accompanies the aperturing is a problem.
In EP 0,214,608 a nonwoven material is apertured using hot needles which heat the nonwoven material to a temperature which is somewhat below the melting point of the material. The holes which are thus created in the material are surrounded by an edge exhibiting a densified fibre structure. The previously mentioned problems with varying hole sizes and reduced material strength are partially solved with a material which is apertured in this manner. However, the problem with liquid spreading in the nonwoven and staying in its fibre structure still remains. The denser fibre structure around the holes is intended to absorb liquid in order to transport liquid through the holes into a material layer below. However, there is a risk that a portion of the liquid is left in the denser hydrophilic fibre structure surrounding the holes. Further, liquid may spread horizontally in the plane of the nonwoven material in the fibre capillaries in the nonwoven material. Since, during use, the nonwoven material is in direct contact with the skin of the user such spreading of liquid is, of course, extremely inconvenient.
In SE 9601681-1, nonwoven material is apertured with hot needles which heat the nonwoven material to a temperature exceeding the melting temperature of at least one component in the material. Accordingly, the holes which are thus created in the material are surrounded by an edge which is at least partially melted. The melted hole edge reduces horizontal spreading of liquid via the fibre capillaries, in the plane of the nonwoven material. However, it is possible to further improve the fluid pervious covering layer as disclosed in SE 9601681-1 in order to obtain a cover exhibiting both high softness and high surface dryness. Other examples of sanitary napkins including at least one layer with a plurality of apertures are given in EP 0,165,807 and U.S. Pat. No. 4,690,679.
DESCRIPTION OF THE INVENTION
The problem with accomplishing a fluid pervious topsheet for absorbent articles, which topsheet is soft and comfortable against skin and still exhibits high surface dryness has been substantially removed by the present invention.
Accordingly, the invention provides an apertured covering sheet exhibiting high softness as well as dryness against the skin of a user.
This is accomplished in accordance with the invention by means of heated needles which are caused to penetrate a sheet of textile material comprising at least one thermoplastic component, wherein the temperature of the needles during penetration of the sheet of material exceeds the melting temperature of the thermoplastic component. The heated needles melt the thermoplastic component closest to the needles whereafter the needles are removed and the heated material is passed between at least one pair of compression rollers whereby the thermoplastic component immediately surrounding the apertures is smoothed out in the plane of the sheet of material so that a substantially smooth material surface is formed around each aperture. The thermoplastic component is then solidified.
One advantage with an apertured sheet of material produced in accordance with the invention is that it exhibits high smoothness in the plane of the material. This means that the risk of the edges of the apertures in the covering sheet rubbing against the skin of the user is practically eliminated. A further advantage with the apertured sheet of material is that the surrounding, substantially melted edge of the apertures to a higher degree can be relied upon to constitute a continuous, liquid impermeable surface. Due to the fact that the thermoplastic material surrounding the apertures in the textile material is in a molten or at least softened state when the material is passed between the compression rollers, the molten or softened thermoplastic material is pressed into and fills out cavities between optionally occurring non-thermoplastic fibres in the textile material.
A further advantage of thermally aperturing the material so that the structure surrounding the apertures melts, and thereafter passing the material through the nip of a pair of rollers is that a specific aperture size is obtained with a high degree of repeatability.
The optima
Helmfridsson Bror-Inge
Thoren Agneta
Burns Doane Swecker & Mathis L.L.P.
Grayson Angela J.
Lindsey Rodney M.
SCA Hygiene Products AB
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