Absorbent articles having improved separator layer

An absorbent article such as a diaper has an outer layer of a porous fabric and an inner absorbent core. A separator layer of thermally bonded nonwoven fabric is positioned between the outer layer and the core to minimize rewet by liquids. The fibers of the nonwoven fabric of the separator layer have a diameter greater than 28 microns, and at least 5 crimps per extended inch, and the fabric has a porosity of about 90-95%, to provide superior rewet properties.

BACKGROUND OF THE INVENTION 
This invention relates to absorbent articles and more particularly to 
layered disposable articles used, for example, as diapers, adult 
incontinence briefs and sanitary pads, in which a porous liquid absorbing 
layer of nonwoven fabric or porous film is disposed against the body of 
the user, and an inner layer is provided for absorption of liquids. 
As originally designed, layered absorbent articles have included an inner 
or body facing cover of a porous fabric, an inner liquid absorbing layer 
or core, and an outer layer of liquid impervious film. In early products, 
the core was composed entirely of cellulose wadding or pulp, with the 
bulkiness or dry weight of the core being directly related to the maximum 
liquid absorption capacity. 
More recently, proposals have been advanced to reduce the bulk of the core 
and to reduce the overall thickness of the absorbent product for several 
reasons, such as reduced shipping cost and storage space, and better 
conformability of the absorbent article or garment to the body of the 
user. A reduced absorbent core thickness has been accomplished primarily 
by increasing the density of the absorbent core and by adding up to about 
40% by weight of a superabsorbing polymer, the latter being capable of 
absorbing many times of its weight of liquid. These changes, however, have 
inevitably led to a reduction in rate of absorption of liquid into the 
core, resulting in possible runoff and leakage of liquids. 
In order to minimize the problems of runoff and leakage in low bulk 
absorbent articles, additional proposals have been made to employ a high 
bulk fabric as the upper layer, or to incorporate a transition layer of 
nonwoven fabric between the outer layer and the core. The purpose of this 
layer, also known as a sublayer or surge layer, is to hold or retain 
excess liquid for a time sufficient to allow the core to permanently 
absorb the liquid. 
Various types of fabrics have been used as sublayers, including spunbonded 
fabrics and fabrics made of adhesively bonded fibers. Another type of 
fabric used for this purpose is low density lofty fabric having a high 
liquid void volume. These lofty fabrics, typically have a porosity of 
greater than 97 percent and are made from through-air thermally bonded 
bicomponent fibers to provide a sublayer having a high void volume. 
In addition to liquid holding properties, another important criteria of a 
sublayer is to minimize a phenomena called rewetting. Rewetting occurs 
when liquid held in the sublayer or core migrates back through the porous 
cover or body side layer under normal contact pressures to wet or hydrate 
the surface of the skin. Because of their high porosity, lofty fabrics as 
described above tend to have poor rewet properties and also tend to add 
bulk to the product. It is well known that absorbent products which have a 
wet surface in contact with the skin can cause rashes and other skin 
irritations. 
In view of the foregoing considerations, there is a continuing need to 
provide layered absorbent articles of the compact type which are not only 
capable of retaining liquid insults to be absorbed by the core, but also 
providing good separation and a significantly reduced amount of liquid or 
urine rewet to the top sheet. 
SUMMARY OF THE INVENTION 
In accordance with the present invention, an improved nonwoven fabric 
separator layer is provided for a liquid absorbent article. The absorbent 
article generally comprises a top porous sheet, an absorbent core, and the 
separator layer disposed between the top sheet and the core. 
The separator layer comprises a majority of thermally bondable polymer 
staple fibers having a fiber diameter of at least 28 microns and 
preferably at least 35 microns. The fiber has at least 5 crimps per 
extended inch and preferably at least 10 crimps per extended inch. 
The separator fabric is preferably formed by the steps of carding the 
fibers into a web on a moving conveyor and then point bonding the web by 
passage through hot calender rolls, one of which may be provided with a 
bonding pattern. The resulting fabric has a basis weight of from about 10 
to about 55 grams per square meter (gsm), and the fibers or fabric are 
preferably treated with an agent, such as a surfactant, to render them 
hydrophilic or wettable by liquids, and to allow fast penetration of 
liquid into the core. 
The relatively large degree of average diameter of fiber and the degree of 
crimp in the separator or sublayer fabric has an importance influence on 
the rapid transfer of liquids to the core while significantly reducing 
wetback to the cover layer and acting as a one-way valve. The separator 
fabrics of the present invention are particularly suitable for use in 
conjunction with high density cores and also allow for significant 
reduction in rewet irrespective of the density and absorption rate of the 
core.

DETAILED DESCRIPTION 
As shown in FIG. 1, the basic components of an absorbent product of the 
present invention comprise a porous top or body facing sheet of fabric or 
porous film 10, a liquid absorbing core 14, and a separator layer of 
nonwoven fabric 12 between the top sheet and the core. 
The core 14 is conventional in nature and may comprise liquid absorbing 
cellulose fibers or pulp and/or a quantity of a superabsorbing polymer 16 
(SAP) in powder, in particulate or fiber form. Various known core 
structures are available, which are capable of permanently absorbing 
liquids, even when the core is subjected to several doses of liquids. In 
addition, it is well known to provide the outer surface of the core with a 
liquid impervious layer 18, such as a layer of film, or a semipermeable 
layer of composite material to prevent outward transfer of liquids beyond 
the core. 
The top sheet 10 is a conventional nonwoven fabric having good porosity and 
a soft surface. The top sheet 10 is preferably composed of heat bondable 
fibers, especially polyolefin fibers such as polypropylene, polyethylene, 
polybutylene, copolymers of any such polymers and mixtures and blends 
thereof It is also possible to fabricate the top sheet from thermally 
bondable bicomponent or multicomponent fibers, such as sheath-core or 
side-by-side fibers. In such case, the fiber will have a component with a 
lower melting point to allow thermal bonding. 
Various known methods can be employed to form a web of the fibers and to 
bond a web of fibers into a fabric. A particularly suitable method 
comprises the steps of first carding the polyolefin fibers into a uniform 
random web, and then consolidating the web by passage between heated 
calender rolls, with one of the rolls having a raised bonding pattern. 
Other suitable methods of consolidation include hydraulic entanglement and 
through air bonding in which heated air is passed through the web, and 
spunbonding, in which continuous filaments are formed into a web and heat 
bonded. The cover layer 10 comprises fibers having a diameter of about 
seven to about twelve microns, and the fabric has a basis weight of about 
from 10 to about 40 gsm. 
The separator fabric 12 preferably comprises at least 60% thermally 
bondable polymer fibers, preferably polypropylene fibers, with the fibers 
being treated with a surface active agent or surfactant to render it more 
hydrophilic. The fibers may be a blend of several different diameters, or 
fibers of different types and sizes may be provided in layers. Less than 
40% of the fibers may comprise polyester, nylon, rayon, acrylic or 
bicomponent fibers. 
The diameter and degree of crimp of the fibers of the separator fabric 12 
relative to the topsheet 10 is very important in order to provide an 
acceptable rate of transfer of liquid toward and into the core 14, while 
at the same time, inhibiting flow back of liquids back through the 
topsheet. The fibers in the separator should have an average diameter of 
at least 28 microns and preferably at least 35 microns and should have an 
average diameter substantially greater than the fibers in the top layer. 
The fibers of the separator layer have a minimum of five crimps per 
extended inch and preferably at least ten crimps per extended inch. The 
basis weight of the fabric is from about 10 to about 55 gsm. 
The nonwoven fabric of the separator layer 12 may be prepared by any 
suitable method, but the preferred method is by conventional carding and 
heat bonding techniques. The preferred method of bonding is by passing the 
unconsolidated web through a pair of heated calender rolls. Other possible 
consolidation methods include through air bonding and hydraulic 
entanglement, as well as spunbonding processes capable of imparting crimp 
to the filaments. 
It will be noted that the layers 10, 12 and 14 have flat facing surfaces, 
and that these surfaces are brought into substantially full contact when 
assembled as layers in an absorbent article. The separator layer 12, while 
having a somewhat lower void volume, porosity, and liquid transfer rate 
than more lofty nonwovens, has a superior ability to prevent transfer of 
absorbed liquid back through the top sheet. The void volume of layer 12 is 
in the order of 10 to 25 cm.sup.3 /g, and the porosity is in the order of 
90 to 95 percent. 
TEST PROCEDURES 
The following tests were employed to evaluate the liquid acquisition rate 
and rewet value of an absorbent article. 
Unless otherwise specified, the same commercial diaper type (Ultrathin 
Huggies for Him Step 3, Kimberly-Clark, Dallas, Tex.) was employed. The 
core of these diapers contains a high ratio of superabsorbent polymer to 
pulp. The product has a top spunbonded nonwoven cover fabric having a 
basis weight of 22 gsm and a lofty sublayer of through-air bicomponent 
nonwoven fabric having a basis weight of 60 gsm. 
The elastic members are removed from the diapers to allow the article to 
lie flat. With the exception of the control diapers, the topsheet and 
sublayer in these Huggies diapers were removed and the location of the 
sublayer was marked. The test separator materials were cut to the same 
dimension as the Huggies sublayer and were placed on top of the absorbent 
core at the same location of the Huggies sublayer. A thermal bonded 
polypropylene carded web (18 gsm) sold under the trade brand of 6788 by 
PGI Nonwovens was placed on top of the test separator layer. A pressure 
loading of 0.5 psi is applied to the middle of the test sublayer sample. 
An opening area of 0.8 square inch is provided and located at the center 
of the pressure load to allow a simulated urine solution to be introduced 
into the diaper core through the topsheet and test separator samples. The 
simulated urine was product JA-00131-000-01 supplied by Endovations Inc. 
of Reading, Pa. A funnel is positioned on top of the opening area of the 
pressure load and a total of 100 ml of simulated urine was introduced into 
the diaper core. The time for the liquid to completely enter the absorbent 
structure is then measured and is termed the "first insult strike-through" 
of the sample. 
The 0.5 psi pressure load is continued applied on the diaper for 5 minutes. 
The pressure is momentarily removed, a preweighed sample of absorbent 
filter paper (Eaton-Dikeman Filter Paper #631) approximately 5".times.5" 
is inserted on top of the topsheet around the test area, and the 0.5 psi 
pressure loading is reapplied to the sample for a period of 2 minutes. The 
filter paper is removed and reweighed, and the amount of liquid absorbed 
by the fiber paper is termed the "first insult rewet" of the sample. 
The above procedure was repeated two more times to obtain the second and 
third insult strikethrough and rewet of the sample. 
The following examples 1-7 are designed to illustrate particular 
embodiments of the present invention and to teach one of ordinary skill in 
the art the manner of carrying out the present invention. 
EXAMPLES 1-3 
In Example 1, the Huggies sample is tested in its original condition 
without alteration. In Example 2, the Huggies topsheet was removed and 
replaced with the above 6788 fabric. The original thru-air bond carded web 
sublayer remained in the diaper during testing. In Example 3, both the 
original topsheet and sublayer were removed. A layer of brand 6788 is 
placed on top of the absorbent core. In this situation, the diaper is 
tested without a sublayer. The tests results are listed in Table 1. 
EXAMPLE 4 
A 40 gsm basis weight bonded carded web comprising 31 micron, crimped 
staple fibers under the trade brand of Hi Comfort Philip available from 
Danaklon Americas of Athens, Ga., was made using a carding machine. The 
fibers had an average length of 1.5 inches. The fibers had a natural 
helical crimp ranging from about 7 to about 11 crimps per extended inch 
counting 1 crimp per repeat cycle of the helical fibers in accordance with 
ASTM D-3937. The line speed of the carding machine was 400 feet per 
minute. The carded web was fed through a pair of heat calender rolls. The 
pattern has a bond area of about 24% and a pin density of 400 pins per 
square inches. The fabric had a porosity of 90.3%. The fabric was then 
tested as the separator layer with the Huggies core. 
EXAMPLE 5 
A 40 gsm basis weight bonded carded web comprising 37 micron, crimped 
staple fibers under the trade brand of Hi Comfort Philic available from 
Danaklon Americas, Inc. of Athens, Ga., was made using a carding machine. 
The fibers had an average length of 1.5 inches. The fibers had a natural 
helical crimp ranging from about 7 to about 11 crimps per extended inch, 
counting 1 crimp per repeat cycle of the helical fibers in accordance with 
ASTM D-3937. The line speed of the carding machine was 400 feet per 
minute. The carded web was fed through a pair of heated calender rolls. 
The pattern had a bond area of about 24% and a pin density of 400 pins per 
square inches. The fabric has a porosity of 91.5%. The fabric was then 
tested as separator layer with the Huggies core. 
EXAMPLE 6 
A 40 gsm basis weight bonded carded web comprising 43 micron, crimped 
staple fibers under trademark Hi Comfort Philic available from Danaklon 
Americas of Athens, Ga., was made using a carding machine. The fibers had 
an average length of 1.5 inches. The fibers have a natural helical crimp 
ranging from about 7 to about 11 crimps per extended inch, counting 1 
crimp repeat cycle of the helical fibers in accordance with ASTM D-3937. 
The line speed of the carding machine was about 94 feet per minute. The 
carded web was fed through a pair of heat calender rolls. The pattern has 
a bond area of about 24% and pin density of 400 pins per square inch. The 
fabric had a porosity of 93.3%. The fabric was then tested as a sublayer 
material. The results of the tests of the fabrics of Examples 4-6 are also 
shown in Table I. 
TABLE I 
______________________________________ 
Example 
Strike-Through (Sec) 
Rewet (gm) 
No. 1st insult 
2nd 3rd 1st insult 
2nd 3rd Total 
______________________________________ 
1 69.5 79.5 87.3 0.10 0.12 3.34 3.56 
2 73.6 78.9 88.6 0.14 2.06 5.53 7.73 
3 213.5 199.8 217.4 0.19 2.61 7.7 10.56 
4 111.1 134.8 155.8 0.16 0.23 1.56 1.95 
5 84.8 113.1 131.3 0.21 0.22 0.33 0.76 
6 122.1 140.1 164.5 0.15 0.21 0.39 0.75 
______________________________________ 
From a review of Examples 1-6, which use the same commercial core, the 
separator fabric resent invention allows a significant reduction in rewet, 
with an average of less than two of rewet liquid, and usually less than 
one gram, after three 100 ml liquid insults in on. 
EXAMPLE 7 
An expanded study including a broader range of fiber sizes and compositions 
confirms that fibers exceeding five (5) denier (or having a diameter of 28 
microns or more) for a consoldated carded staple fiber fabric obtains the 
claimed performance improvement in rewet. 
The results of the tests of the fabrics of Example 7 are summarized in 
Table II below according to increasing fiber denier per filament (dpf) and 
fiber diameter (in microns) relative strike-through time (in seconds) and 
third rewet (in grams). The testing is more fully set forth in FIG. 2 and 
is based on an average of three (3) diaper testing. 
For purposes of analyzing Example 7, the commercial competitive sample from 
the leading brand Huggies was again used as a competitive benchmark. The 
test method used substantially the same as described above, except that a 
pressure loading of 0.5 psi was not applied to the middle of the test 
sublayer sample. Rather, a simulated urine solution, here saline solution, 
was poured onto the diaper core through a tube onto the topsheet and test 
separator sheet samples. A total of 80 ml of simulated urine was 
introduced into the diaper core. The time for the liquid to completely 
enter the absorbent structure was measured as the "first insult 
strike-through" of the sample. As shown, the Huggies brand resulted in a 
third insult rewet of 10.2 grams. Therefore, any result below 8 grams of 
rewet on the third insult, representing a nominal 20% improvement in 
performance on a leading commercial product, was considered a significant 
improvement. 
TABLE II 
__________________________________________________________________________ 
Bulk, Bond pattern, fiber type 
denier & fiber finish included on summary 
Sample 
total 
per filament 
fiber diameter, u 
Diaper 
Strike through, sec. 
Rewet, grams 
Code BW fiber #1 
fiber #2 
fiber #1 
fiber #2 
Wt. 1st 
2nd 
3rd 
1st 
2nd 
3rd 
__________________________________________________________________________ 
6853-0 
15.0 
3.0 17.5 44.4 
18.9 
20.0 
25.6 
0.1 
0.70 
7.9 
Amer/NW 
19.0 
3.0 17.5 43.8 
15.8 
17.6 
20.4 
0.2 
0.6 
12.1 
6714-8 
15.0 
4.4 26.2 41.610 
20.3 
25.5 
43.0 
0.1 
0.5 
8.1 
156-189-6 
20.0 
5.0 28.0 40.8 
22.3 
20.5 
24.8 
0.2 
1.8 
9.5 
meltblown 
35.0 
5.0 28.0 41.7 
13.0 
16.0 
31.9 
0.1 
3.73 
10.6 
Hugg/Cont. 
84.0 
5.0 27.5 42.5 
11.0 
11.0 
13.4 
0.1 
0.8 
10.2 
6829-0 
43.0 
6.0 24.8 42.5 
9.9 
10.8 
13.1 
0.1 
1.0 
5.9 
143-177-9 
30.0 
9.0 37.5 41.2 
14.0 
13.7 
15.9 
0.1 
1.0 
6.8 
67CSO 35.0 
9.0 37.5 41.5 
15.0 
14.0 
15.9 
0.1 
0.3 
4.7 
143-177-9 
62.0 
9.0 37.5 42.9 
10.6 
10.6 
11.7 
0.1 
0.1 
2.2 
156-195-10 
50.0 
9.9 6.0 39.3 
30.6 
42.3 
13.8 
12.3 
14.6 
0.1 
0.2 
1.2 
Bauschvlies 
40.0 
2.0 6.0 17.7 
30.6 
42.2 
16.1 
17.2 
18.5 
0.2 
4.3 
13.3 
156-177-9 
20.0 
3.0 9.0 21.7 
37.5 
42.6 
19.7 
20.9 
25.1 
0.1 
0.5 
8.3 
Fiberweb 
40.0 
5.0 17.0 
28.0 
41.7 
40.6 
12.9 
13.7 
20.9 
0.2 
1.4 
8.10 
6710.0 
29.0 
6.0 2.0 30.6 
17.7 
40.7 
15.6 
16.9 
20.3 
0.1 
1.8 
8.9 
4138.0 
40.0 
3.0 10.0 
21.7 
32.0 
42.1 
8.80 
8.60 
9.50 
0.4 
0.5 
5.50 
4147.0 
40.0 
3.0 10.0 
21.7 
32.0 
42.8 
7.90 
8.50 
10.5 
0.2 
0.6 
4.4 
4141.0 
52.0 
3.0 10.0 
21.7 
32.0 
40.5 
11.9 
12.8 
14.4 
0.3 
1.4 
10.1 
__________________________________________________________________________ 
As contemplated by the present invention, a blend of fibers used to create 
the sublayer should have one of the fibers of at least 5 denier and crimp. 
Additionally, if the sublayer or separator layer is made of two individual 
layers, one of the individual layers should have fiber deniers greater 
than 5. The data set forth in FIG. 2 and Table II indicates that the 
benefits of the present invention are independent of the method of web 
consolidation, that is, either pattern bonded or through air. Crimp is 
also important to fabric performance. While samples with high crimp and 
low denier failed to achieve superior performance, it was observed that a 
high denier, low crimp fabric did not obtain the desired exceptional 
performance, supporting the need for crimping. For example, Meltblown 
Sample Nos. 1 and 2, were at 25 and 5.2 microns, well above the fiber size 
expected to offer the desired exceptional performance. However, these 
sample have no crimp and did not obtain the desired exceptional 
performance (only 10.6 and 9.2 gram at third insult rewet, respectively). 
Referring to FIG. 3, the results are plotted according to increasing fiber 
diameter, in microns. It can be observed that all samples perform 
similarly after the first and second rewets. Substantial difference in 
performance occurs after the third insult. Again using 8 grams of rewet as 
the desired exceptional performance, all samples falling below that value 
fit the predictive model of the present invention. Although a single 
sample, No. 6710, fits the model of higher fiber thickness and crimp 
without providing the significant improvement in performance, the model is 
still supported by 18 other examples obtained from industry as well as 
internal samples. 
To confirm that basis weight differences were not overwhelming the 
sensitivity of the model, third insult rewet is presented against sublayer 
basis weight in FIGS. 4 and 5. Again, using 8 grams of rewet as 
exceptional performance, one notes first that the best performance is for 
fabrics greater than 20 gsm. However, there are several examples at the 35 
gsm and 40 gsm level where the superior performance at a given basis 
weight is demonstrated only by fabrics that fit the limitations of the 
present invention. Finally, one of the worst performers is the Huggies 
sample, which coincidentally has the highest sublayer basis weight of all 
samples tested.