Absorbent napkin, particularly for infant's diaper pads

An absorbent article comprising a base sheet of fluid impervious material, a top sheet of fluid pervious non-woven material, and an absorbent pad disposed between the top sheet and the base sheet. The top sheet is secured to the base sheet along the periphery thereof. The absorbent pad has a central portion and two side panels folded under the top sheet and over the central panel. A binder secures the side panels to the central panel to render the central panel more absorbent.

The present invention relates to absorbant napkins of fibrous material, 
such as defibered woodpulp and particularly for use as absorbant pads for 
liquid excrements in an infant's diaper or napkin. 
The latter generally includes an impermeable support sheet, for example of 
polyethylene, and an inner sheet permeable to the penetration of urine, 
for example non-woven material or a perforated film of plastics material, 
these sheets being connected to one another at their periphery and an 
absorbant pad is provided between the latter to absorb the liquid 
excrement. According to the type of diaper, this pad may be rectangular or 
may have a cut-out at the level of the crotch in a so-called anatomical 
shaped diaper. 
The material generally used to form the absorbant pads is defibered 
woodpulp in sheet form. The latter can comprise a single layer of fibrous 
material and have a rectangular shape or be cut away at the crotch. The 
napkin can comprise two layers of fibrous material superimposed on one 
another, and these layers may have an identical thickness and/or different 
weight per unit area. In these double-layer napkins, one of the layers is 
generally of rectangular shape, the other being sometimes cut-out at the 
crotch. 
The napkin can also be shaped, that is to say have volume of absorbant 
material greater at the center than at the side portions, such napkins 
being generally cut-out at the crotch. Simple rectangular napkins are also 
to be had which are folded back over the central portion so as to be 
C-shaped in cross-section. Such napkins possess poor mechanical properties 
to the extent that the fibrous material constituting them does not have 
the coherence necessary to stay in the form of an approximately homogenous 
napkin and has a tendency to crumb formation or decomposition into small 
balls. 
To try to overcome this drawback, an attempt has been made to increase the 
cohesion of the napkin by compressing the latter over particular areas, 
for example by stamping or rolling, to form crossbraces. This method is, 
in fact, only a palliative which does not provide means for increasing the 
cohesion of the napkin the latter only showing, in fact, portions of 
higher density where the fibers have a tendency to be more integral with 
one another than in the portions of lower density. The presence of such 
high density areas has the drawback of substantially reducing the 
absorbant capacity of the napkin. 
An attempt has also been made to improve the cohesion of napkins by the 
introduction of a permeable and strong sheet, for example a non-woven 
sheet, a sheet of cellulose wadding, or a thread, either in the folds of 
the napkins when the latter are folded, or between two neighboring layers 
when these napkins have several layers. The strong and impermeable sheet 
has also been used by simply enveloping the napkin. If the presence of 
such a sheet confines to a certain extent the napkin within a limited 
volume, it does not succeed in improving the mechanical characteristics, 
in that the fibrous material always shows a deficient cohesion in having 
always a tendency to crumb-formation or to be reduced to small balls or to 
become turn when it is worn by a user whose repeated movements distort the 
napkin. This leads to the creation of preferential paths through which the 
liquid flows directly without being trapped by the absorbant mass. 
This degradation of the absorbant material can occur before micturition, 
which uses beforehand the absorption capacities of the napkin. However, 
more often still, this degradation is facilitated after a first urination, 
which considerably reduces the possibilities of absorption of a second 
urination. 
The fibrous material of certain napkins may be associated with a powered 
material based on polymers, commonly called "superabsorbant", for example 
a polyacrylate. This powder may be dispersed in the mass of the fibers of 
the napkin, dusted over the surface of the napkin, dusted between two 
neighboring layers of napkin having several layers or even dusted on the 
inside of the fold of a napkin having such a fold. The powder not being 
fixed to the fibrous material, the latter has a tendency to agglomerate in 
the free areas of the infant diaper, which considerably reduces the 
possibilities of absorption that could be expected from incorporating such 
a "superabsorbant" agent. 
It is an object of the present invention to overcome these drawbacks by 
providing an absorbant napkin based on a fibrous material which has very 
good cohesion so as to remain stable when it is worn by a user before or 
after a first urination while preserving good absorption capacities. 
It is another object of the invention to provide a napkin comprising a 
powdered absorbant material fixed to the mass of the napkin. 
For this purpose it is an object of the invention to provide a napkin of 
the aforesaid type, characterised in that it comprises means for 
increasing its cohesion. 
According to other features: the means for increasing the cohesion comprise 
a flexible and adherent binder which extends over at least a part of the 
area of the napkin. 
It is also an object of the invention to provide a method of manufacture of 
an absorbant napkin based on a fibrous material with reinforced cohesion, 
for example of defibered woodpulp, characterised in that over a central 
portion of the napkin comprised between two lateral portions is sprayed a 
flexible and adherent binder and in that each of the lateral portions is 
folded back onto the central portion, the binder fixing these lateral 
portions to the central portion.

By incorporating a binder in the napkin, the fibers of the latter are 
bonded in the region where the binder extends, similarly to the fibers of 
an unwoven fabric. 
The binder may be deposited on at least one of the outer surfaces of the 
napkin of which both the lateral portions 1 are folded back onto a central 
portion 2 (FIG. 1), the binder 3 fixing these lateral portions 1 by gluing 
to the central portion 2. The binder may also be deposited between two 
layers 4 of a napkin comprising 2 layers (FIG. 2). 
The binder may be deposited by spraying or by application in the form of 
spots, strips or filaments. In all cases, the binder has to form over the 
area of the napkin at the level at which it extends, free spaces so as to 
permit the liquid excrements to pass through the layer of binder to become 
distributed within the whole of the absorbant mass of the napkin. 
The binder must be solid, flexible and adherent to bond the fibers together 
whilst permitting the napkin to be deformed. At the moment of its 
deposition on the napkin, the binder must have however a sufficiently 
fluid consistency so as to penetrate into at least a portion of the 
thickness of this napkin and impregnate the fibers therein. 
In the case of a folded napkin, such as that illustrated in FIG. 1, or of a 
napkin with two layers, such as that illustrated in FIG. 2, the binder 3 
has been deposited respectively, on the unfolded layer and over an area of 
one of the layers of the napkin so that in refolding it, for one of the 
lateral portions 1 on the central portion 2 and by arranging for the 
other, the second layer of the napkin on the surface of the first layer on 
which the binder has been deposited, the different parts of the napkin are 
joined by gluing by means of the binder. The latter penetrates also into 
at least a portion of the thickness of the neighboring parts of the 
napkin, that is to say into the thickness of the lateral portions 1 and of 
the central portion 2 or within the thickness of the two layers 4 of the 
napkin. 
The binder may be selected from among the following different materials; 
a thermofusible glue, for example formed from an adhesive resin, a polymer 
and a wax, deposited hot in filaments or by spraying; 
a cold glue, for example an acrylic or vinyl, used as an emulsion in water 
and sprayed. On evaporation of the water, there is coalescence of the 
droplets of glue in the emulsion which then forms a film providing free 
spaces over the sprayed surface; 
a cold glue solubilised in an organic solvent and sprayed; 
a polymer extruded or hot-sprayed, for example of polyethylene or 
polypropylene; and 
a polymer thread, for example of polypropylene or of polyethylene, or of 
thermofusible glue, this thread being melted directly on the layer to 
ensure the cohesion thereof. 
It is also possible to associate with the fibrous material of the layer 
which constitutes the basic or preponderant absorbant portion of this 
napkin, an absorbant material which will advantageously be dusted on the 
freshly deposited binder so that this powder is immobilised on the layer 
by means of the binder. 
A description will now be given with reference to FIG. 3 of the method of 
manufacturing the absorbant napkin with reinforced cohesion, according to 
the invention. 
This method is intended for the manufacture of napkins of the type of that 
of FIG. 1 which comprises two lateral portions 1 folded back onto the 
central portion 2 by being glued thereto by the central portion 2 by being 
glued thereto by means of the previously sprayed binder 3. A strip 5 of 
fibrous material, for example of defibered woodpulp, and a strong support 
sheet 5, for example of wadding, of width of the most corresponding to 
that of the strip 5, are led whilst superimposed on one another so as to 
pass under three binder spraying nozzles 7, the strip 5 extending opposite 
the nozzles 7 so that the latter deposit the binder only on the central 
portion of the strip. 
Once coated with binder, the strip 5 supported on the sheet 6 passes into a 
folding device designed to fold the lateral portions of the strip 5 and of 
the sheet 6 onto the central portion of the strip 5, the lateral portions 
1 of the strip 5 then being fixed by gluing to the central portion 2 of 
this strip by means of the freshly deposited binder. 
The folding device comprises two discs 8 movably mounted in rotation on a 
shaft 9 which extends transversely above the strip 5, the discs 8 being 
applied to the surface of the strip 5 and being spaced axially on the 
shaft 9 so that the distance to which they are spaced from one another 
corresponds approximately to the width of the central portion of the strip 
5 on which the binder is deposited. The folding device also comprises a 
backfolding fork 10 downstream of the disc 8 so that when the strip 5 and 
the strip 6 advance, this fork 10 folds back the lateral portions of the 
latter over the central portion of the strip. The discs 8 are for the 
purpose of preventing these lateral portions from folding back onto the 
strip before the passage of the fork, each lateral portion coming into 
abutment against the outer surface of the corresponding disc 8 to thus 
oblige the strip 5 to be held spread out beneath the nozzles 7 positioned 
upstream of the discs 8. 
The fork 10 comprises two prongs 11 and 12 independent of one another 
forming a V open in the direction of the nozzle 7, each prong folding 
beneath it a corresponding lateral edge of the strip 5 and of the sheet 6. 
For this purpose, one prong 12 is positioned above the other prong 11 by 
being spaced from the latter so that the corresponding lateral edges of 
the strip 5 and of the sheet 6 with which this prong 12 cooperates, may be 
able to pass between the latter and the prong 11. 
The assembly formed by the strip 5 and the sheet 6 can then be cut up at 
regular intervals along its length to provide the required absorbant 
napkins. If desired, the latter may be cut up at the level of the crotch 
(FIG. 5), in a so-called anatomic shape. 
The central portion of the napkin over which the binder extends must of 
course be as wide as possible but for the problems posed by the guiding of 
the strip from which the napkin has resulted in the course of its 
manufacture, the portion of the surface over which the binder extends, 
presents at a maximum about 80% of the total surface of the napkin (FIGS. 
4 and 5). 
Experience shows also that so that the effectiveness of the binder is not 
compromised on an anatomical shaped napkin, the width of the area of the 
latter over which the binder extends at the level of the crotch must 
represent at the minimum 50% approximately of the width of the napkin at 
the level of this crotch. 
Below are given experimental examples intended to illustrate the 
considerable adhesion of the napkins of the invention as well as their 
notable absorption power. 
Tests of tear resistance measured by means of a dynamometer were carried 
out on napkins of defibered woodpulp identical in section and in weight 
per unit surface at a traction speed of 100 mm per minute. The results are 
indicated in Table 1 below for three different binders deposited in 
variable amounts with respect to a control napkin constituted only of 
defibered woodpulp. 
Perforation strength tests were also carried out on the same napkins tested 
previously, by perforating by means of a metal cane with a hemispherical 
end and of 25 mm diameter with a perforation speed of 300 mm per minute, 
the perforation strength being measured by means of a compression 
dynamometer. The results are indicated in Table 1 below. 
An evaluation test of their intrinsic absorption capacity was also carried 
out on a series of napkins identical with those previously tested, that is 
to say the value of the absorption obtained by dipping these napkins 
horizontally into a liquid so that under these conditions, the pressure 
exerted by the liquid absorbed inside the napkin has only negligible 
influence on the absorption capacity of the latter. 
TABLE 1 
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Intrinsic* 
Tear* Perforation* 
Absorption 
Strength 
Resistance 
+ 
+ + (g/g) 
(N) (N) ++ 
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Napkin of pure defibered 
0.9 2.0 12.4 
woodpulp 
Napkin of defibered 
woodpulp with increase 
in the cohesion by a 
thermofusible glue: 
N.degree. 1 about 10 g/m.sup.2 
5.7 7.2 11.7 
about 20 g/m.sup.2 
8.0 18.3 12.5 
N.degree. 2 about 10 g/m.sup.2 
3.0 10.5 11.6 
about 20 g/m.sup.2 
4.0 9.5 11.1 
For an acrylic glue: 
about 10 g/m.sup.2 
5.6 8.2 -- 
about 20 g/m.sup.2 
7.8 13.1 11.8 
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*Average result of ten tests. 
++ These values are not significantly different 
These results show the substantial improvement in the cohesion of the 
napkins of the invention. 
The increase in the cohesion of a napkin with a binder does not in fact 
diminish significantly the space between the fibers of the latter and 
hence the absorption capacity, which is exactly the reverse of the results 
obtained with the napkins of which certain regions have been compressed to 
increase the cohesion thereof. 
Below are given the results of experimental tests to determine the 
effective absorption capacity, that is to say before rupture, of napkins 
based on defibered woodpulp of comparable cross sections and mass per unit 
surface. This experiment is a comparison of the effective absorption 
capacity of napkins with different binders and the different amounts of 
binder with respect to a napkin of pure defibered woodpulp. 
The experimental conditions used were for the purpose of imitating the 
absorption of a napkin in use, that is to say suspended vertically so that 
the fluid absorbed tends to reduce the absorption capacity of the napkin 
with respect to the hydrostatic pressure. 
Each napkin is hence suspended vertically on a support and urine is poured 
on the upper portion of the napkin by means of a tube sending a pulsed jet 
of 30 ml in 5 seconds. This volume of 30 ml and this flow rate of 6 ml/s 
correspond to the average urological data of an infant of 9 months hence 
of weight about 9 kg. 
To avoid the jet perforating the napkin, a piece of unwoven fabric is fixed 
at the point of impact and the urination operation (a jet of 30 ml in 5 
seconds) is repeated every minute, until rupture under its own weight of 
the soaked napkin. The time of one minute is sufficient to insure complete 
distribution of the volume poured on each occasion. 
The results are given in Table II below. 
TABLE II 
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Effective Absorption 
in g/g Remarks 
______________________________________ 
Napkin of pure The pads rupture 
defibered woodpulp 
3.6 before 
saturation 
Napkin of defibered 
woodpulp with 
increase in the 
cohesion by a 
thermofusible glue: 
N.degree. 1 about 10 g/m.sup.2 
7.3 The pads rupture 
at the limit of 
N.degree. 2 about 20 g/m 
7.8 saturation 
For an acrylic glue: The pads do not 
rupture but are 
about 10 g/m.sup.2 
6.3 less saturated. 
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These simple tests establish the fact that on wearing a napkin based on 
defibered woodpulp whose cohesion has not been increased by means of a 
binder, a degradation of the napkin frequently occurs when a certain level 
of saturation in absorption is reached whereas, in the case of napkins 
whose cohesion is increased with a binder, the degradation by rupture only 
occurs after saturation or even does not happen. 
The effective overall absorption of the napkin with reinforced cohesion of 
the invention is greater than that of the prior art to the extent that 
there is better use of the absorbant mass of the napkin as a whole. Thus, 
for an equal effective absorption capacity, the napkins of the invention 
call upon a smaller absorbant mass than conventional napkins whose 
cohesion is not increased with a binder. 
The invention hence enables the cohesion of napkins to be very 
substantially improved whether the latter are dry or wet. Better use of 
the absorbent mass available is made and there is not, on the one hand, 
degradation before the first urination and, on the other hand, less 
degradation between the first and the second urinations. 
The napkins also preserve a correct appearance whether they are worn dry or 
wet.