Disposable diaper having density and basis weight profiled absorbent core

A disposable diaper wherein a central portion of its absorbent core has a higher density and higher basis weight per unit area than longitudinally spaced end portions of the absorbent core. Such absorbent cores may comprise a mixture of hydrophilic fibers and discrete particles of a highly absorbent material such as, for example, hydrogel material.

TECHNICAL FIELD 
This invention pertains to disposable absorbent products such as disposable 
diapers, and disposable briefs for incontinents. More specifically, this 
invention pertains to such products which have absorbent cores comprising 
hydrophilic fibers, or mixtures of hydrophilic fibers with discrete 
particles of highly absorbent materials such as, for example, 
water-insoluble hydrogels; and wherein the absorbent cores have central 
portions which are more dense and have higher basis weight per unit area 
than end portions of the core. As used herein, "highly absorbent 
materials" means materials which have the property to absorb water up to 
ten (10) or more times their own weights. Generally speaking such material 
will be present in particulate form in large enough particle sizes to not 
readily sift out of the fibrous matrix of the disposable diaper cores of 
interest, yet small enough particles to enable them to absorb effectively 
(e.g., sufficiently small to not have their potential absorbency 
substantially vitiated by gel blocking or analogous phenomena) and small 
enough that the diaper cores do not feel gritty. 
BACKGROUND 
A disposable diaper construction wherein the absorbent core has a thin 
dense central portion and thick, low density end portions is disclosed in 
U.S. Pat. No. 3,592,194 which issued July 13, 1971 to Robert C. Duncan; 
and a Disposable Diaper with Localized Area of Increased Density is 
disclosed in U.S. Pat. No. 4,213,459 which issued July 22, 1980 to Wayne 
C. Sigl et al., and which shows constructions having dense core areas 
which extend from the center of the crotch region to the rear edge of the 
core but which dense areas do not extend to the side edges of the core. An 
Apparatus For Continuously Making An Air-Laid Fibrous Web Having Patterned 
Basis Weight Distribution is disclosed in U.S. Pat. No. 4,388,056 which 
issued June 14, 1983 to Frankie B. Lee and Orin Jobes, Jr. Absorbent cores 
having patterned densification, and apparatus for making such cores are 
disclosed in U.S. Pat No. 4,027,672 which issued June 7, 1977 to Hamzeh 
Karami. Disposable diapers having profiled thicknesses, and compressed 
channels are disclosed in U.S. Pat. Nos. 3,766,922 which issued Oct. 23, 
1973 to Evelyn H. Krusko, and Re. 29,789 which was reissued Oct. 2, 1978 
to Charles G. Kolbach. Disposable diapers having elasticized contractable 
side portions and a variety of core shapes are shown in U.S. Pat. No. 
3,860,003 which issued Jan. 14, 1975 to Kenneth Barclay Buell. 
Additionally, U.S. Pat. No. 4,335,803 which issued June 29, 1982 to 
Virginia L. Repke discloses disposable diapers having a variety of 
plan-view shaped cores which may have densified longitudinal lines for 
improved capillarity, and which have elasticized longitudinal edge 
portions. Furthermore, U.S. Pat. No. 4,429,001 which issued Jan. 31, 1984 
to Barbara E. Kolpin et al. discloses an exemplary Sheet Product 
Containing Sorbent Particulate Material, and delineates a representative 
selection of additional patents which also disclose absorbent structures 
having particles of highly absorbent material dispersed in them. 
DISCLOSURE OF THE INVENTION 
A disposable diaper is provided which comprises a liquid pervious topsheet, 
a liquid impervious backsheet, and an absorbent core disposed between the 
topsheet and the backsheet. The absorbent core of the disposable diaper 
comprises two longitudinally spaced end portions and a central portion 
disposed therebetween. The absorbent core comprises absorbent material 
such as cellulosic fibers which are so disposed that the central portion 
has a greater average density per unit area and a greater average basis 
weight per unit area than each of the end portions. In accordance with one 
aspect of the invention, the ratio of the average density of the central 
portion to the average density of each of the end portions is about 2:1 or 
greater; and, more preferably, 2.5:1 or greater. The central portion is 
also preferably substantially uniformly dense and of uniform basis weight 
throughout its extent. In accordance with another aspect of the invention, 
the core comprises a mixture of hydrophilic fibers and discrete particles 
of a highly absorbent particulate material such as hydrogel particulate 
material, and the mixture has a fiber-to-particulate weight ratio of from 
about 70:30 to about 98:2; and, more preferably, from about 75:25 to about 
90:10. In various other aspects of the invention: the fibers and the 
particulate of highly absorbent material are preferably uniformly 
dispersed; such particulate may be water-insoluble and may be disposed 
primarily or only in the central portion of the absorbent core; the 
absorbent cores may be configured to have laterally spaced ear regions 
which coact with either or both end portions to form a foldable waistband 
assemblage at one or both ends of the absorbent core; such waistbands may 
be of uniform density, or have thin, dense ear regions to facilitate 
folding and packaging, and to reduce bulk in the area of overlapping ear 
regions when worn by a user. In yet another aspect of the invention, the 
dense, high basis weight central portion of the absorbent core is spaced 
from the lateral side edges of the core by leg cuff portions of the core 
which are of lesser basis weight and density than the central portion; 
preferably about the same density and basis weight as the end portions of 
the core. In still other aspects of the invention, the central portions 
are more highly bonded internally and therefore are less resilient than 
the end portions of the absorbent core; and the various portions of the 
core are preferably demarked from each other by sufficiently abrupt 
thickness changes that the cores have terraced characters. 
BRIEF DESCRIPTION OF THE DRAWINGS 
While the specification concludes with claims which particularly point out 
and distinctly claim the subject matter regarded as forming the present 
invention, it is believed the invention will be better understood from the 
following description taken in conjunction with the accompanying drawings 
in which: 
FIG. 1 is a plan view of a disposable diaper embodiment of the present 
invention wherein most of the topsheet has been torn away to more clearly 
show the underlying absorbent core of the diaper. 
FIG. 2 is a longitudinal sectional view of only the absorbent core of the 
disposable diaper of FIG. 1, and taken along the medial sectional line 
2--2 thereof. 
FIG. 3 is a transverse sectional view of only the absorbent core of the 
disposable diaper of FIG. 1, and taken along sectional line 3--3 thereof 
which extends through the front waistband assemblage of the disposable 
diaper. 
FIG. 4 is a plan view of an alternate disposable diaper embodiment of the 
present invention. 
FIG. 5 is a longitudinal sectional view of the absorbent core of the 
disposable diaper of FIG. 4, and taken along sectional line 5--5 thereof. 
FIG. 5a is a fragmentary longitudinal view similar to FIG. 5 but which 
shows the absorbent core of an embodiment of the invention wherein a low 
density front end portion is thicker than the adjacent central portion of 
the core. 
FIG. 6 is a transverse sectional view of the core of the disposable diaper 
of FIG. 4, and taken along sectional line 6--6 thereof which extends 
through the front end portion of the disposable diaper. 
FIG. 7 is a plan view similar to FIGS. 1 and 4 which shows another 
alternate disposable diaper embodiment of the present invention. 
FIGS. 8, 9 and 10 are section views of only the core of the disposable 
diaper of FIG. 7, and taken along sectional line 8--8, 9--9, and 10--10 
thereof, respectively. 
FIG. 11 is a plan view of a rectilinear absorbent core which is configured 
in accordance with the present invention to be l-shaped, and to have 
transversely spaced pairs of ear regions which are thinner and more dense 
than the end portions of the core. 
FIGS. 12 and 13 are sectional views taken along sectional lines 12--12 and 
13--13, respectively, of FIG. 11. 
FIG. 14 is a plan view of an alternate embodiment, rectilinear l-shape 
absorbent core which is similar to that shown in FIG. 11 but for the 
waistband regions of the FIG. 14 embodiment being substantially uniformly 
dense and thick. 
FIGS. 15 and 16 are sectional views taken along sectional lines 15--15 and 
16--16, respectively, of FIG. 14. 
FIG. 17 is a plan view of another alternate embodiment, rectilinier l-shape 
absorbent core which is similar to the core shown in FIG. 11 except its 
dense central portion is isolated from all of the edges of the core by low 
density portions of the core. 
FIGS. 18, 19 and 20 are sectional views taken along sectional lines 18--18, 
19--19 and 20--20, respectively, of FIG. 17. 
FIGS. 21 and 22 are plan view of T-shape absorbent cores constructed in 
accordance with the present invention: the FIG. 21 embodiment being 
generally rectilinear, and the FIG. 22 embodiment being somewhat 
curvalinear.

DETAILED DESCRIPTION OF THE INVENTION 
A disposable diaper 30 which is an exemplary embodiment of the present 
invention is shown in plan view in FIG. 1 to comprise a topsheet 31, a 
backsheet 32, an absorbent core 33, tape fasteners 34 only one of which is 
shown in FIG. 1 to be on a back corner of the diaper, and plural strands 
of elastic 35 which are affixed to the inwardly facing surface of 
backsheet 32 as by adhesive. The absorbent core 33 as shown in FIG. 1 
comprises a central portion 41, and two waistband assemblages 42 and 43 
which, in turn, comprise medial regions 44 and 45, respectively, and ear 
regions 46, 47, 48 and 49. Ear regions 46 and 47 are demarked from medial 
region 44 by edges designated 51 and 52, respectively, and ear regions 48 
and 49 are demarked from medial region 45 by edges 53 and 54, 
respectively. Medial regions 44 and 45 are alternatively designated end 
portions 44 and 45 of the absorbent core 33. Additionally, absorbent core 
33 comprises two basis weight/density transition zones 56 and 57 which are 
bounded in the plan view by arcuate lines 61, 62, 63 and 64, and by 
segments of the side edges 65 and 66 of absorbent core 33. Also, the end 
edges of the absorbent core 33 are designated end edges 67 and 68. 
In the remaining views, features and elements which are substantially 
identical are identified throughout the views by the same designations; 
and, features and elements which generally are equivalent to those of 
disposable diaper 30 are identified by the same designators along with a 
hundreds digit. For example, alternate diapers shown in FIGS. 4 and 7 are 
designated 130, and 230, respectively; and absorbent cores thereof are 
designated 133 and 134, respectively. On the other hand, the topsheets, 
backsheets, and tape fasteners of disposable diapers 30, 130, and 230 are 
designated 31, 32, and 34, respectively, for each. 
Referring now to FIG. 2, a longitudinal sectional view of only the 
absorbent core 33 of diaper 30, FIG. 1, the central portion 41 of the 
absorbent core 33 is shown to be of uniform thickness T.sub.1 ; of greater 
thickness than the thickness T.sub.2 of end portions 44 and 45; and 
substantially more dense than end portions 44 and 45. Additionally, FIG. 2 
depicts the core as being composed of fibrous material 69--preferably air 
laid, predominantly cellulosic fibrous material--having discrete particles 
70 of a highly absorbent material dispersed throughout its extent. 
FIG. 3, a transverse sectional view through the front waistband assemblage 
42 of the absorbent core 33 of diaper 30, FIG. 1, shows the ear regions 46 
and 47 to have a thickness T.sub.3 which is substantially thinner than the 
thickness T.sub.2 of medial region 44, and to be substantially more dense 
than the medial region 44. Such waistband assemblages may be made to have 
substantially uniform basis weight per unit area, and by then calendering 
the ear regions to effect the desired degrees of thickness 
reduction/densification. Such thin ear regions are particularly beneficial 
for reducing the bulk of the diaper in the side regions of users; 
particularly so if they are overlapped such as by having a front ear 
region disposed in overlapping relation with a rear ear region. 
Briefly, referring to the exemplary disposable diaper 30, FIGS. 1 through 
3, inclusive, the present invention provides a disposable diaper having an 
absorbent core 33 comprising a central portion 41 disposed intermediate 
longitudinally spaced end portions 44 and 45, and in which the central 
portion has both higher density and higher basis weight per unit area than 
the end portions: preferably having a ratio of the density of the central 
portion to the density of each of the end portions which is about equal to 
or greater than 2:1; and more preferably about 2--.5:1 or greater. Also, 
the central portion is preferably uniformly dense, and has substantially 
uniform thickness. Additionally, such cores preferably comprise a mixture 
of hydrophilic fibers 60 and discrete particles 70 of highly absorbent 
material such as, for example, a water-insoluble hydrogel wherein the 
weight ratio of the fibers to the absorbent particulate is from about 
70:30 to about 98:2; and more preferably from about 75:25 to about 90:10. 
Moreover, preferably, only the central portion of the core has such highly 
absorbent particulate material dispersed in it; and, preferably, uniformly 
dispersed therein although it is not intended to thereby limit the present 
invention to constructions comprising uniformly disposed particulate 
absorbent material. Such diaper cores are so constructed that the lower 
density end portions stay dry due to the preferential capillarity of the 
central portion except when highly loaded: i.e., loaded with sufficient 
urine to sufficiently load the pores of the central portion that the 
excess urine will migrate into the lower density (large pored) end 
portions despite the fact such migration is opposite to the preferential 
capillarity of the structure. Thus, since the end portions preferably stay 
dry--i.e., their absorbency capacity not generally being utilized--they 
may be made to have very low basis weight to help hold down the cost of 
such diapers. Generally speaking, the particles of absorbent material 
dispersed throughout the fibrous matrix of the central portion of the core 
offset the potential absorbency capacity of the fibrous component thereof 
which is lost when it is compacted to give it its high density, 
preferential capillarity properties. 
An exemplary disposable diaper 33, FIG. 1 was constructed in which the 
backsheet 32 is a matte-finish polyethylene film having a nominal 
thickness of about one mil (about 0.0254 mm); the topsheet 31 is a 
non-woven, hydrophobic polypropylene having a nominal thickness of about 
three to five mils (about 0.056 mm to about 0.127 mm); an airlaid 
absorbent core 33 having a total weight of about thirty-one (31) grams; 
and weight ratio of fibers to hydrogel particles of about 85:15. The 
hydrogel particles were starch-grafted polyacrylate (e.g., Sanwet IM-1000 
made by Sanyo Chemical Industries, Japan), and had a particulate size 
range of from about fifty (50) to about nine hundred (900) microns. 
Additionally, this diaper comprises strands 35 of elastic having nominal 
unstretched thickness and width of about 0.2 and 2.4 mm, respectively, 
which had been stretched about one-hundred-twenty-five percent (125) prior 
to being adhesively secured to the backsheet, and prior to adhesively 
securing the topsheet to the backsheet whereby the longitudinal side edges 
of the topsheet/backsheet composite in the leg cuff regions of the diaper 
have nominal extensions (i.e., their available stretch as a percent of 
their elastically contracted length) of about forty-five percent or 
greater. Additionally, the core 33 is preferably enveloped with a low 
basis weight tissue paper (not shown) to provide structural integrity. A 
particular size of this exemplary disposable diaper was sized and 
configured to accommodate an exemplary embodiment of core 33 which was 
constructed to be: approximately five-and-one-quarters inches (about 13.3 
cm) wide across its central portion 41 (i.e., its crotch region); about 
eight-and-one-half inches (about 21.6 cm) wide across its waistband 
assemblages 42 and 43; about fifteen-and-one-quarter inches (about 38.7 
cm) long; and to have basis weights in its central portion 41, end 
portions 44 and 45, and ear regions 46 through 49 of 0.07, 0.03, and 0.03 
grams per square centimeter of surface area, respectively; and to have 
densities in its central portion 41, end portions 44 and 45, and ear 
regions 46 through 49 of about 0.18, 0.09, and 0.18 grams per cubic 
centimeter, respectively. Additionally, the core was configured and 
calendered so that the ear regions could be folded to overlay adjacent 
portions of their associated medial regions to form a generally 
rectangular shape, folded diaper albeit the strands of elastic pull the 
ends in somewhat. Preferably, for such folded diapers, T.sub.1 will equal 
T.sub.2 plus T.sub.3 so that the folded diaper is uniformly thick. This 
is beneficial for packaging efficiency. 
Such a core is preferably made by airlaying a thickness profiled 
core-perform of substantially uniform density; and then by calendering the 
core-preform in a fixed-gap calender wherein at least one calender roll 
has a stepped configuration to effect calendering the ear regions through 
a thinner gap than the gap through which the remainder of the core passes. 
Additionally, in embodiments comprising mixtures of fibers and absorbent 
particulate material, the particulate matter is preferably added to an air 
entrained stream of fibers prior to their deposition to form the 
core-preforms to effect uniform distribution of the particulate matter 
throughout the preform: or, more preferably, added in such a way as to be 
deposited in only the central portions of the core-preforms. 
Referring now to absorbent particulate matter which may be included in 
embodiments of the present invention, hydrogel materials are very 
effective. By "hydrogel" as used herein is meant an inorganic or organic 
compound capable of absorbing aqueous fluids and retaining them under 
moderate prssures. For good results, the hydrogels should be water 
insoluble. Examples are inorganic materials such as silica gels and 
organic compounds such as cross-linked polymers. Cross-linking may be by 
covalent, ionic, vander Waals, or hydrogen bonding. Examples of polymers 
include polyacrylamides, polyvinyl alcohol, ethylene maleic anhydride 
copolymers, polyvinyl ethers, hydroxpropyl cellulose, carboxymethyl 
cellulose, polyvinly morpholinone, polymers and copolymers of vinyl 
sulfonic acid, polyacrylates, polyacrylamides, polyvinyl pyridine and the 
like. Other suitable hydrogels are those disclosed in U.S. Pat. No. 
3,901,236, issued to Assarsson et al., Aug. 26, 1975, the disclosures of 
which are incorporated herein by reference. Particularly preferred 
polymers for use herein are hydrolyzed acrylonitrile grafted starch, 
acrylic acid grafted starch, polyacrylates, and isobutylene maleic 
anhydride copolymers, or mixtures thereof. 
For the purpose of utilizing hydrogels in the present invention, it is 
essential that relatively dry hydrogel particles be used. Also, neither 
the fibers, the particles nor the mixture of fibers and particles should 
be exposed to water in its liquid form, or another solvent, at any time 
during this process or subsequent thereto. When wet hydrogel particles are 
used, the fibers tend to become entangled and/or bonded with the particles 
which result in undesirable stiffness of the absorbent structure. 
Additionally, wet hydrogel particles would obviously have less absorbency 
efficacy in the product inasmuch as their potential absorbency would 
already be diminished. 
As used herein, "dry" does not mean "absolutely water-free". For example, 
under normal storage and handling conditions, hydrogel particles take up 
some moisture. The hydrophilic fibers also take up some moisture during 
storage. Furthermore, it may be desirable to use humidified air for air 
transport of the fibers and the hydrogel particles, to avoid dusting. 
Under such process conditions, the hydrogel particles and the fibers will 
take up even more moisture, but such should be limited so that it does not 
unduly affect the practice of the present invention. 
Referring now to FIG. 4,, an alternate exemplary disposable diaper 130 is 
shown which differs from disposable diaper 30 in these respects: core 133 
of diaper 130 has a longer central portion 141 than central portion 41 of 
core 33, and the side edges 165 and 166 of central portion 141 are convex 
as compared to the straight side edges 65 and 66 of core 33; end regions 
144 and 145 of core 133 extend the full widths of the waistband portions 
of core 133, and core 133 has no ear regions comparable to the ear regions 
46 through 49 of core 33. 
As shown in FIG. 5, core 133 of disposable diaper 130, FIG. 4, has a 
terraced character by virtue of the thickness T.sub.1 of central portion 
141 being substantially greater than the thickness T.sub.2 of the end 
portions 144 and 145, and by virtue of the relatively steep slopes of the 
basis weight/density transition zones 156 and 157. FIG. 6 shows the end 
portion 144 to be substantially uniformly thick an dense throughout, which 
is also preferably the case with end portion 145. 
FIG. 5a shows a fragmentary longitudinal sectional view of a variant of 
disposable diaper core 133 which is designated 133a. FIG. 5a shows core 
133a to have a front waistband edge 167a having a thickness T.sub.2, as 
compared to the thin front waistband edge 167 of core 133, FIG. 5, having 
a thickness of T.sub.2. Indeed end portion 144a is thicker and less dense 
than central portion 141a, albeit end portion 144a is of substantially 
lesser average basis weight per unit area than central portion 141a. 
Briefly, depending on the propensity of the constituents of the core to 
become bonded to different extents when calendered to different degrees, a 
core preform as described hereinbefore which has a thicker and heavier 
basis weight central portion than its end portions may be selectively 
calendered to precipitate either thin end portion embodiments as 
represented by core 133, FIG. 5, or thick end portion embodiments as 
represented by core 133a, FIG. 5a. In embodiments comprising materials 
which hydrogen bond under pressure, moisture content of the core 
constituents may be controlled to precipitate the desired profile upon 
calendering. In general, relatively low moisture levels would enable 
precipitating the FIG. 5 type profile upon uniformly calendering the above 
described preform through a fixed-gap; and, relatively higher moisture 
levels would enable precipitating the FIG. 5a type profile. 
Turning now to FIGS. 7 through 10, an additional alternate exemplary 
disposable diaper 230 which is an embodiment of the present invention is 
shown to be different from disposable diaper 30, FIGS. 1 through 3, by 
virtue of its central portion 241 being an island of high density, and 
high basis weight which is isolated from the edges of the core by: the 
combination of the end portions 244 and 245, and portions 259 and 260 
which are hereby denominated leg cuff portions 259 and 260 of core 233; 
and by the race-track shaped portion 258 which is hereby denominated the 
basis weight/density transition zone 258 of core 233. Additionally, 
particulate absorbent material 70 is disposed only in the central portion 
241 of core 233 to illustrate selective disposition thereof. However, it 
is not intended to thereby limit the present invention to such selectively 
disposed absorbent particulate material, or to limit the utility of such 
selective deposition of absorbent particulate matter to only cores of the 
configuration of core 233. In use, disposable diapers comprising such 
cores having high density/high basis weight island-shape central portions 
which are isolated from all of the core edges by portions having lower 
density and lower basis weight, tend to retain urine in the dense central 
portions and to remain dry or drier along all of its edges due to the 
preferential capillarity of the dense portion. This, of course, helps to 
obviate leakage around the edges of such diapers. 
Additional alternate absorbent cores which are configured and constructed 
in accordance with the present invention are designated 333, 433, 533, 
633, and 733 in FIGS. 11, 14, 17, 21 and 22, respectively. Broadly 
speaking: cores 333, 433 and 533 are rectilinear l-shape counterparts of 
the generally curvalinear-shape cores 33 (FIG. 1), 133 (FIG. 4), and 233 
(FIG. 7), respectively. Additionally, core 33 is shown in FIG. 2 to have 
thinner and less dense end portions 344 and 345 (thickness T.sub.2) 
relative to central portion 341 (thickness T.sub.1); and, in FIG. 3, to 
have ear regions 346 and 347 which are more dense and thinner (thickness 
T.sub.3) than end portion 344 (thickness T.sub.2). Preferably, T.sub.1, 
T.sub.2 and T.sub.3 are so related that T.sub.1 is equal to the sum of 
T.sub.2 and T.sub.3 to enable efficient folding (of the ear regions over 
the central portions) and packaging as described hereinbefore. Also, 
albeit end portions 344 and 345 are shown to be equally thick and dense, 
it is not intended to thereby limit the invention; and, albeit it is 
preferably that end portions and ear regions have the same basis weight 
for, among other reasons, simplicity of manufacturing, it is also not 
intended to thereby limit the present invention. 
Absorbent cores 633 and 733, FIGS. 21 and 22, respectively, are T-shape 
cores which, but for not having ear regions on their front end portions 
are generally the equivalents of core 233, FIG. 11, and core 33, FIG. 1, 
respectively. Accordingly, further descriptions thereof are not included 
to avoid undue redundancy. 
While particular embodiment of the present invention have been illustrated 
and described, it would be obvious to those skilled in the art that 
various other changes and modifications can be made without departing from 
the spirit and scope of the invention. In particular, while disposable 
diapers 30, 130 and 230, and absorbent cores 33, 133 and 233 thereof, 
respectively are shown to be somewhat hourglass shape, it is not intended 
to exclude rectangular or other shapes from the scope of the present 
invention. It is intended to cover in the appended claims all such changes 
and modifications that are within the scope of this invention.