Liquid permeable casing sheet for absorbent sanitary articles

The present invention relates to a liquid-permeable casing sheet (1) for absorbent sanitary articles, such as sanitary napkins, incontinence guards and diapers. According to the invention, the casing sheet (1) includes a first layer (2) which is corrugated across at least a central part of its surface so as to provide a row of mutually parallel waves having wave crests (3) and wave troughs (4), wherein the wave crests form an article contact surface with the wearer's body when the article is in use. The casing sheet also includes rows of through-penetrating openings (6) which extend perpendicularly to the corrugations or waves and each of which opening passes through a wave crest (3). The invention also relates to a method for producing such a casing sheet.

The present invention relates to a liquid permeable casing sheet for 
absorbent sanitary articles, such as sanitary napkins, incontinence guards 
and diapers, and to a method for producing such a casing sheet. 
Absorbent sanitary articles of the aforesaid kind normally comprise an 
absorbent core or absorbent body which is enclosed between a liquid 
impervious and a liquid permeable casing sheet. The liquid permeable 
casing sheet functions to allow liquid to pass quickly to the underlying 
absorbent body and to provide comfort to the wearer. In order for the 
sanitary article to be felt comfortable in use, it is necessary for the 
surface of the liquid permeable casing sheet that lies against the 
wearer's skin to be soft and for the wearer to feel that the article is 
dry. In order to achieve this feeling of dryness, it is necessary for the 
liquid permeable casing sheet to have good reception properties, i.e. to 
be capable of transporting all liquid quickly to the absorbent body, and 
for the article to have good rewetting properties, i.e. properties which 
prevent absorbed liquid from being pressed from the absorbent body and 
back through the casing sheet when the article is subjected to pressure. 
In order to provide a dry surface against the wearer's body, the liquid 
permeable casing sheet normally has a hydrophobic (water repellant) or 
hydrophobized apertured layer which faces the wearer in use, e.g. a 
perforated plastic film or a plastic net or a non-woven comprised of 
hydrophobic or hydrophobized fibres. It is known to form the openings or 
apertures in recesses disposed in the layer that lies proximal to the 
wearer, so as to distance the absorbent body from the wearer's body and 
therewith obtain improved rewetting properties. It is also known to 
provide such recesses and openings with the intention of favouring liquid 
flow in a direction towards the absorbent body, such as to disfavor liquid 
flow in the opposite direction. One drawback with known casing sheets or 
layers of the aforesaid kind is that they are relatively complicated to 
produce and that the apertured or perforated layer is plastically deformed 
in conjunction with producing the recesses and openings. Another drawback 
is that the recesses and openings lie close to the wearer's body, 
therewith impeding the circulation of air within the region of the 
absorbent sanitary article. 
An object of the present invention is to provide a liquid permeable casing 
sheet for absorbent sanitary articles, which has reception and rewetting 
properties that are at least equally as good as the earlier known casing 
sheet, which can be manufactured easily without plastic deformation of the 
layers in the casing sheet, and which in use allows air to circulate 
unimpeded within the area of the article in contact with the wearer's 
skin. 
This object is achieved in accordance with the invention with a liquid 
permeable casing sheet for absorbent sanitary articles, such as sanitary 
napkins, incontinence guards and diapers, which is characterized in that 
the casing sheet includes a first layer which is corrugated across at 
least a central part of its surface such as to exhibit a row of mutually 
parallel wave crests and wave troughs, wherein when the article is in use 
the wave crests form the article contact surface with the wearer's skin 
and which sheet includes several rows of through-penetrating openings that 
extend perpendicularly to the wave crests, wherein each opening passes 
through a respective wave crest. As a result of the corrugated or pleated 
surface of such a casing sheet, the absorbent body will be spaced at a 
distance which improves the rewetting properties of the article. 
Furthermore, such a sheet will present only a small contact surface with 
the wearer's skin, since only the wave crests lie against the skin and the 
openings disposed in the wave crests enable air to circulate over the full 
extent of the sheet. Liquid delivered outside the openings will run down 
into the wave troughs and hence the sheet layer that lies proximal to the 
wearer will be felt to be dry very quickly after liquid has been 
discharged. The risk of leakage due to liquid running from the casing 
sheet is extremely small. The wave troughs also function as liquid 
reservoirs in those instances when liquid is discharged more rapidly than 
the rate at which the absorbent body is able to absorb the liquid, 
therewith reducing the spread of instantaneously discharged large 
quantities of liquid in comparison with a sheet having a flat contact 
surface. 
In one preferred embodiment of the invention, the rows of openings extend 
at least in a central part of the first layer and preferably across the 
whole of said first layer. Furthermore the rows of openings have one 
opening in each wave crest and each opening also extends within a region 
of wave troughs associated with neighbouring wave crests. The first layer 
is made of an hydrophobic or hydrophobized material. The casing sheet will 
preferably include a second layer of liquid permeable material fastened to 
the wave troughs of the first layer. 
The invention also relates to a method of producing a liquid-permeable 
casing sheet for absorbent sanitary articles, such as sanitary napkins, 
incontinence guards and diapers, said method being characterized by 
pleating a first layer to a corrugated form so as to obtain a row of 
parallel waves having wave crests and wave troughs, and thereafter 
providing in the first layer a plurality of rows of through-penetrating 
openings which extend perpendicularly to the waves or corrugations and 
each of which passes through a respective wave crest. 
In one preferred embodiment, the openings are milled in the layer, and a 
second layer of liquid-permeable material is bonded to the wave troughs of 
the first layer.

The casing sheet 1 illustrated in FIG. 1 is comprised of a first corrugated 
or pleated layer 2 which exhibits transversely extending and mutually 
parallel wave-shaped folds having wave crests 3 and wave troughs 4 across 
the whole of its surface. A second layer 5 is suitably joined to the first 
layer 2, e.g. by ultrasonic welding, laser welding or by gluing. 
The first layer 2 also includes longitudinally extending rows of openings 6 
disposed in the crests 3 of the parallel wave-shaped corrugations. 
The wave crests and wave troughs of the wave-shaped corrugations need not 
have the shapes shown in FIG. 1. Conceivable alternative wave shapes are 
shown in FIGS. 2 and 3 by way of example. The wave crests 9 of the first 
layer 7 shown in FIG. 2 have the same shape as the wave crests of a 
sinusoidal wave, whereas the wave troughs 10 have flat surfaces in 
abutment with the second layer 8. This configuration may be suitable in 
ensuring that good connection is achieved between the wave troughs 10 and 
the second layer 8, which may be desirable when gluing or bonding the 
layers 7 and 8 together, for instance. In the FIG. 3, embodiment, the 
mutually parallel folds in the first layer 11 have a square wave 
cross-sectional shape, therewith providing a maximum surface for 
attachment of the wave troughs 14 to the second layer 12. The wave crests 
13 present flat contact surfaces to the user of an absorbent article 
provided with such a casing sheet. It is not essential for mutually 
sequential longitudinal pleats to be similar to one another and may be 
given mutually different wavelengths. However, the amplitude of the waves, 
i.e. the distance of the wave crests from the second layer, will 
preferably be as constant as the method of manufacture will allow, at 
least when seen locally. Seen globally, it may be desirable to have a 
greater wave amplitude within certain areas, e.g. at the wetting point of 
the absorbent article in which the inventive casing sheet is included, so 
as to generate a greater distance between the absorbent body included in 
an article provided with an inventive casing sheet and the wearer's skin 
in one particular region, therewith reducing the risk of rewetting within 
this region. 
The first layer in the aforedescribed casing sheets is comprised of a 
hydrophobic (water repellant) or hydrophobized material, e.g. a plastic 
film, a foam material, or a hydrophobic or hydrophobized non-woven 
material. The reception properties of the casing sheet are determined to a 
great extent by the open area of the first layer and particularly the open 
area at the wetting point. The open area within a first layer region is 
determined by the number of openings in this region and the size of said 
openings and is given as a percentage of the area of this region. The open 
area will preferably be between 10 and 75%, at least within the wetting 
point of the article, i.e. that region of the absorbent article casing 
sheet within which liquid is normally delivered by a wearer. 
When liquid is discharged onto a first layer according to any one of FIGS. 
1-3, liquid that does not immediately enter an opening will run down into 
the wave troughs and there collects. For this reason, at least one of the 
lower edges of the openings within at least the region of the first layer 
that lies undermost in a donned absorbent article will preferably lie at 
the same distance from the second layer as the upper side of said 
undermost part of the wave troughs so as to prevent liquid from remaining 
in the wave troughs of the upper layer. 
The flat, second layer of an inventive casing sheet is also liquid 
permeable and shall have reception properties that correspond 
substantially with the desired reception properties of the first layer. 
Because discharged liquid is able to collect in the wave troughs, as 
beforementioned, the reception properties of the second layer may be 
allowed to be somewhat poorer than otherwise desired without the casing 
sheet being felt to be wet, by virtue of the fact that only the wave 
crests of the first layer are in contact with the wearer. The second layer 
may be comprised of a plastic net, a perforated plastic film, a 
hydrophilic non-woven or a hydrophobic non-woven material having a 
sufficient open area, or a perforated hydrophobic nonwoven material. 
An inventive casing sheet also provides good rewetting properties to an 
absorbent article provided with such a casing sheet, since the user 
contacting surface will be located relatively far from the wearer. 
The wave-shaped corrugations of the first layer will suitably extend 
transversely across the full width of the article in which said layer is 
included. This allows ambient air to circulate freely and therewith 
ventilate the wearer's skin within the region of a donned absorbent 
article. Perspiration and the like can thereby be ventilated away from the 
skin, giving the wearer an extra feeling of dryness in comparison with an 
article having a flat wearer abutment surface. Small quantities of liquid 
present on the surface of the first layer can also be ventilated away, eg. 
small quantities of liquid remaining in the wave troughs. 
The inventive casing sheet also provides good security against leakage due 
to liquid running from the article, since liquid can not readily flow past 
the wave troughs. Further, solids which may be present in menstrual fluid 
can easily be trapped in the wave troughs of the first layer. This also 
applies to discharged excretion when using such a casing layer in diapers. 
FIG. 4 illustrates schematically an arrangement for manufacturing an 
inventive casing sheet from two webs of material 15, 16 stored on storage 
reels 17 and 18 respectively. The webs are mutually joined in a device 
that includes two rotatable cylinders 19, 20, for instance by causing a 
laser beam from a laser source 21 to fall intermittently on the nip 
between the cylinders 19, 20 and therewith produce a weld joint. 
The web 15 may be comprised of polyethylene film and the web 16 comprised 
of polypropylene-based nonwoven material. 
Prior to its entry into the nip defined between the cylinders 19, 20, the 
web 15 is pleated or corrugated between the cylinder 19 and a further 
cylinder 22, these cylinders having undulating peripheral surfaces which 
mutually engage one another in the manner of two mutually coacting toothed 
wheels. Subsequent to their passage through the cylinders 19, 20, the 
composite web comprising said webs 15, 16 will consist of an upper 
corrugated web 15 whose wave troughs are joined to an underlying flat web 
16. 
It is pointed out in this context that the laser source generates a row of 
laser rays which are incident to the nip between the cylinders 19, 20 in a 
direction at right angles to the plane of the paper in FIG. 4. The laser 
source used may be of the kind described in Swedish Patent Application No. 
9600096-3, filed on Jan. 11, 1996. Naturally, other methods of joining the 
webs 15, 16 together are conceivable within the scope of the invention. 
For instance, the apparatus may include a glue applicator which coats the 
web 16 with glue or applies transversal glue strings prior to the web 
passing through the cylinders 19, 20. Alternatively, the web 16 may be 
heated prior to entering the nip between the cylinders 19, 20, e.g. by 
incorporating a heat source in the cylinder 20. 
The composite web is thereafter passed through a milling cylinder 23 which 
has a plurality of axially separated rows of peripherally extending 
cutters 24. When passing the milling cylinder 23 longitudinally extending 
rows of openings corresponding to the rows of cutters 24 will be cut out 
of the composite web. The cylinder 23 is suitably set so that the depth of 
cut will be smaller than the height of the wave-shaped web 15, such as to 
ensure that no material will be cut from the other web 16. However, the 
cutting depth may be conceivably be set so that through-penetrating 
openings or partially penetrating openings are cut from the underlying web 
16, for instance when this web is comprised of imperforate plastic film or 
when the reception properties of said web material need to be improved for 
some reason or other. 
Subsequent to passage by the milling cylinder 23, individual casing sheets 
are cut from the composite web in a suitable manner, not shown. 
An inventive casing sheet can thus be produced in a very simple way and its 
reception properties can be readily changed by altering the cutting depth 
of the miller or replacing the milling tool, therewith enabling the 
dimensions of individual openings and the number of rows of openings to be 
readily varied. The wetting properties of the casing sheet can also be 
readily altered, by varying the peripheral speed of the cylinders 22 and 
the undulating wave shape of the peripheral surface of the cylinder 19. 
Because the corrugations, or wave shapes, and the openings are formed by 
mechanical means, the corrugated layer will not be deformed plastically, 
meaning that the thickness of layers included in the casing sheet will not 
be changed in the manufacturing process and enables the strength 
properties of the casing sheet to be predicted more readily. 
It will be understood that the described and illustrated embodiments can be 
modified within the scope of the invention. For instance, the second layer 
may comprise the upper surface of the absorbent body of an absorbent 
article which includes an inventive casing sheet, provided that the 
absorbent body is sufficiently well-bonded. Furthermore, the first layer 
may be provided with openings prior to being pleated, although this is not 
preferred for reasons of a manufacturing/technical reason. The invention 
is therefore solely restricted by the contents of the following claims.