U.S. patent application number 16/597146 was filed with the patent office on 2020-04-09 for absorbent article with polymeric filler composition.
The applicant listed for this patent is The Procter & Gamble Company. Invention is credited to Torsten LINDNER, Matthias MORAND, John Andrew STRASEMEIER, Robert Haines TURNER.
Application Number | 20200108168 16/597146 |
Document ID | / |
Family ID | 70053771 |
Filed Date | 2020-04-09 |
United States Patent
Application |
20200108168 |
Kind Code |
A1 |
TURNER; Robert Haines ; et
al. |
April 9, 2020 |
ABSORBENT ARTICLE WITH POLYMERIC FILLER COMPOSITION
Abstract
An absorbent article comprising a first nonwoven material joined
to a second nonwoven material by at least one bond area, wherein a
polymeric filler composition is disposed within the bond area and
the composition comprises at least one polymer selected from the
group consisting of polypropylene homopolymers, propylene-ethylene
copolymers, and mixtures thereof, wherein the composition is
substantially free of tackifiers. It was found that such polymer
filler compositions having a Toughness of at least 25 MPa, as
measured according to the Extensional Test Method described herein,
provide bonds with good resistance to peel creep force.
Inventors: |
TURNER; Robert Haines;
(Cincinnati, OH) ; STRASEMEIER; John Andrew;
(Aurora, IN) ; LINDNER; Torsten; (Kronberg,
DE) ; MORAND; Matthias; (Sulzbach, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
The Procter & Gamble Company |
Cincinnati |
OH |
US |
|
|
Family ID: |
70053771 |
Appl. No.: |
16/597146 |
Filed: |
October 9, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62743266 |
Oct 9, 2018 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A61F 13/55105 20130101;
A61F 13/539 20130101; D04H 1/593 20130101; A61L 15/24 20130101;
A61L 15/42 20130101; A61F 2013/15325 20130101; D04H 1/587 20130101;
A61F 2013/15406 20130101; A61F 13/514 20130101; A61F 2013/5349
20130101; A61F 13/8405 20130101; A61F 2013/15861 20130101; A61F
13/515 20130101; A61L 15/24 20130101; C08L 23/12 20130101 |
International
Class: |
A61L 15/24 20060101
A61L015/24; A61L 15/42 20060101 A61L015/42; A61F 13/551 20060101
A61F013/551; A61F 13/514 20060101 A61F013/514 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 17, 2019 |
CN |
2019/082955 |
Claims
1. An absorbent article comprising: a wearer-facing surface and an
opposing garment-facing surface; a first nonwoven material; a
second nonwoven material; at least one bond area joining a portion
of the first nonwoven material and a portion of the second nonwoven
material; and a polymeric filler composition disposed within the
bond area, wherein the polymeric filler composition comprises: one
or more polymers selected from the group consisting of
polypropylene homopolymers, propylene-ethylene copolymers, and
mixtures thereof; and from 0% to less than 5% of a tackifier, by
weight of the polymeric filler composition; wherein the polymeric
filler composition has a Toughness of at least 25 MJm.sup.-3,
wherein Toughness is measured according to the Extensional Test
Method.
2. The absorbent article according to claim 1, wherein the
polymeric filler composition has a Yield Stress of at least 5 MPa,
wherein the Yield Stress is measured according to the Extensional
Test Method.
3. The absorbent article according to claim 1, wherein the
polymeric filler composition consists essentially of an unblended
polymer selected from a polypropylene homopolymer or a
propylene-ethylene copolymer.
4. The absorbent article according to claim 1, wherein the
polymeric filler composition consists essentially of a
semi-crystalline propylene-ethylene copolymer having an enthalpy of
fusion of between about 20 J/g and about 200 J/g.
5. The absorbent article according to claim 1, wherein the
polymeric filler composition consists essentially of a
semi-crystalline propylene-ethylene copolymer having an enthalpy of
fusion of at least 20 J/g.
6. The absorbent article according to claim 5, wherein a percentage
of propene monomer units in the copolymer is from about 50% to
about 99% by weight of the copolymer.
7. The absorbent article according to claim 1, wherein the
polymeric filler composition is present at a basis weight of from
about 5 gsm to about 30 gsm in the bond area.
8. The absorbent article according to claim 7, wherein the
polymeric filler composition is present at a basis weight of from
about 10 gsm to about 20 gsm in the bond area.
9. The absorbent article according to claim 1, wherein the first
nonwoven forms a portion of a nonwoven landing zone, and the second
nonwoven forms a portion of a backsheet outer cover of the
absorbent article.
10. The absorbent article according to claim 1, wherein the
absorbent article comprises an absorbent core, wherein the first
nonwoven material forms a portion of a core wrap top layer disposed
between the absorbent core and the wearer-facing surface, and
wherein the second nonwoven material forms a portion of a core wrap
bottom layer disposed between the absorbent core and the
garment-facing surface.
11. The absorbent article according to claim 10, comprising core
perimeter bonds disposed along lateral and longitudinal edges of
the absorbent core, wherein the bond area forms some of the core
perimeter bonds.
12. The absorbent article according to claim 10, wherein the
absorbent core comprises at least one channel, and wherein the bond
area forms a portion of a channel bond area.
13. The absorbent article according to claim 1, wherein the
polymeric filler composition has a viscosity at 170 deg C. from
about 1,000 mPas to about 5,000 mPas, according to the Viscosity
Test Method.
14. The absorbent article according to claim 1, wherein at least
one of the first nonwoven material and the second nonwoven material
comprise natural or recycled fibers.
15. The absorbent article according to claim 1, wherein the bond
area has a Static Peel Force Time of least 500 minutes per 10 mm
bonded length, according to the Static Peel Force Time Test
Method.
16. A package comprising a plurality of the absorbent articles
according to claim 1.
17. A nonwoven laminate for an absorbent article comprising: a
first nonwoven material; a second nonwoven material; and at least
one bond area disposed between the first nonwoven material and the
second nonwoven material, wherein a polymeric filler composition is
disposed within the bond area, and wherein the polymeric filler
composition comprises: one or more polymers selected from the group
consisting of polypropylene homopolymers, propylene-ethylene
copolymers, and mixtures thereof; and from 0% to less than 5% of a
tackifier, by weight of the polymeric filler composition; wherein
the polymer filler composition has a Toughness of at least 25
MJm.sup.-3, according to the Extensional Test Method.
18. A method of bonding a first nonwoven material to a second
nonwoven material, the method comprising the step of: applying a
polymeric filler composition to a bonding area on the first
nonwoven material, and bonding the second nonwoven material to the
first nonwoven material in the bonding area, wherein the polymeric
filler composition comprises: one or more polymers selected from
the group consisting of polypropylene homopolymers,
propylene-ethylene copolymers, and mixtures thereof; and from 0% to
less than 5% of a tackifier, by weight of the polymeric filler
composition; wherein the polymeric filler composition has a
Toughness of at least 25 MJm.sup.-3, according to the Extensional
Test Method.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit, under 35 U.S.C. .sctn.
119(e), of U.S. Provisional Patent Application Ser. No. 62/743,266,
filed on Oct. 9, 2018, and claims priority under 35 U.S.C. .sctn.
119 to Chinese Patent Application Serial No. CN/2019/082955, filed
on Apr. 17, 2019, the entire disclosures of which are hereby
incorporated by reference.
FIELD
[0002] The present application is for absorbent articles, such as
diapers, comprising one or more bond area(s) between two nonwovens.
A polymer filler composition which is substantially tackifier-free
is disposed within the bond area(s). The polymeric filler
composition comprises at least one of a polypropylene homopolymer,
a propylene ethylene copolymer, or a mixture thereof. The polymeric
filler composition is particularly useful to form nonwoven to
nonwoven (NW-NW) bonds having high peel creep requirements, such as
the bonds between the top and bottom sides of an absorbent core
wrap, or the bonds between the landing zone and the backsheet outer
cover for taped absorbent articles.
BACKGROUND
[0003] Disposable absorbent articles, such as diapers, training
pants or adult incontinence articles, are generally manufactured by
combining several components. These components typically include a
chassis comprising a liquid-permeable topsheet, a
liquid-impermeable backsheet attached to the topsheet, an absorbent
core located between the topsheet and the backsheet, and a
plurality of bond areas holding the chassis together. When the
disposable article is worn, the liquid-permeable topsheet is
positioned next to the body of the wearer. The topsheet allows
passage of bodily fluids into the absorbent core. The
liquid-impermeable backsheet helps prevent leakage of fluids held
in the absorbent core. The absorbent core typically comprises
superabsorbent polymers (SAP) that can absorb several times their
weight of urine or other liquid, so that bodily fluids can be
transported and stored from the skin of the wearer into the
disposable absorbent article.
[0004] Frequently one or more components of a disposable absorbent
article are bonded together. For example, hotmelt adhesives have
been used to bond individual layers of the chassis of the absorbent
article, such as the topsheet and backsheet together. Hotmelt
adhesives have also been used to bond discrete components, such as
fasteners and leg elastics or cuffs, to the article. The hot melt
adhesive is often called a construction adhesive because it is used
to help construct the absorbent article from individual
components.
[0005] Common hotmelt adhesives are made by combining polymers and
additive components in a substantially uniform thermoplastic blend.
Typical additive components include tackifiers, plasticizers,
and/or waxes. While such formulations generally work, they can be
costly and their performance properties can be improved. Tackifiers
for example can comprise up to 65% of an adhesive formula, and can
be expensive and difficult to source.
[0006] Instead of using formulated adhesives, unblended polymers
have been proposed. An unblended polymer consists only of one type
of polymer (generated via its own and specific polymerization
process) rather than a blend of polymers which were made via
separate polymerization process and mixed (blended) together after
polymerization. Unblended polymers may additionally comprise minor
amount of additives such as antioxidants, perfumes and other low
molecular weight components, but is substantially free of other
polymers, mineral oils, or tackifiers.
[0007] The advantages of unblended polymers typically include
higher purity, enabling less odor, at a lower cost as the
additional steps of heating up, blending and cooling down a blend
can be avoided. Unblended polymers can have higher resistance to
degradation of the bond over time because lower molecular weight
components cannot migrate into adjacent materials. US2016/0053149A1
(Clariant) for example discloses a ready-to-use hotmelt adhesive
comprising at least 95% of one or more polyolefin copolymer waxes,
which have been prepared by means of metallocene catalysts,
characterized in that the polyolefin copolymer wax consists of
propylene and one or more further monomers selected from ethylene
and branched or unbranched 1-alkenes having 4 to 20 C-atoms and the
content of structural units derived from propylene in the copolymer
waxes amounts to 80 to 99.9% by weight, and the hot melt adhesive
has a surface tension of the melt, measured at a temperature of
170.degree. C., of at most 23 mN/m.
[0008] Some bonds in diapers need to withstand demanding
requirements related to "peel creep", i.e. exposure of a sustained
peeling force over an extended period of time, typically at body
temperature. For example, the end seal bonds of core bag should be
able to withstand the forces of the swelling SAP in use. Another
example is the landing zone material that is attached to the front
side of taped diapers and on which the back ears can be releasably
fastened. The peel creep resistance can be measured via static hang
tests. It was found that a load applied in the "Peel" configuration
is more damaging to bonds than a load applied in the "Shear"
configuration. It was also found that the required properties of
adhesives for NW-NW bonds are very different than for NW-Film
bonds.
[0009] Despite their advantages, polyolefin (PO) adhesives are
typically viscoplastic and prone to show creep in static tests.
This limits significantly their use for such bonds that require
creep resistance, and in cases where they are not completely
unsuitable requires high usages.
[0010] There is thus a need for a polymeric material, referred
herein to as polymer filler composition, that is substantially
tackifier-free and at the same time efficient to bond two nonwoven
materials, especially when these bonds are subjected to peel creep
force in an absorbent article.
SUMMARY
[0011] The present disclosure is related to an absorbent article
comprising a first nonwoven material joined to a second nonwoven
material by at least one bond area, wherein a polymeric filler
composition is disposed within the bond area and the composition
comprises at least one polymer selected from the group consisting
of polypropylene homopolymers, propylene-ethylene copolymers, and
mixtures thereof, wherein the composition is substantially free of
tackifiers, comprising less than 5% of tackifiers, by weight of the
polymeric filler composition. It was found that such polymer filler
compositions having a Toughness of at least 25 MPa, as measured
according to the Extensional Test Method described herein, provide
bonds with good resistance to peel creep force.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] The above-mentioned and other features and advantages of the
present disclosure, and the manner of attaining them, will become
more apparent and the disclosure itself will be better understood
by reference to the following description of example forms of the
disclosure taken in conjunction with the accompanying drawings,
wherein:
[0013] FIG. 1 shows a perspective view of an exemplary taped diaper
in a closed configuration as it would be when worn by a wearer;
[0014] FIG. 2 shows the garment-facing side of the diaper of FIG. 1
with the diaper flattened out;
[0015] FIG. 3 shows the wearer-facing side of the diaper of FIG. 1
with the diaper flattened out;
[0016] FIG. 4 shows a top view of an exemplary absorbent core with
the top layer partially removed;
[0017] FIG. 5 shows a longitudinal cross-section view of the
absorbent core of FIG. 4;
[0018] FIG. 6 shows transversal cross-section view of the absorbent
core of FIG. 4;
[0019] FIG. 7 is a schematic sketch showing Shear load and Peel
load applied on a bond area; and
[0020] FIG. 8 is SEM of a representative bond area.
DETAILED DESCRIPTION
Introduction
[0021] "Absorbent article", as used herein, refers to devices that
are placed against or in proximity to the body of the wearer to
absorb and contain the various exudates discharged from the body.
Absorbent articles may include baby diapers, training pants, adult
incontinence undergarments, feminine hygiene products, and the
like. As used herein, the term "body fluids" or "body exudates"
includes, but is not limited to, urine, blood, vaginal discharges
and fecal matter.
[0022] "Absorbent core" means an absorbent structure disposed
between topsheet and backsheet for absorbing and containing liquid
such as urine received by the absorbent article. The absorbent core
comprises an absorbent material, that is typically enclosed within
or sandwiched between a core wrap. The core wrap may be a single
material that is folded and attached to itself, or it may comprise
a separate top layer and bottom layer that are bonded together. The
absorbent material typically comprises superabsorbent particles
which are optionally mixed with cellulose fibers. As used herein,
"absorbent core" does not include any acquisition-distribution
systems, topsheet, or backsheet of the absorbent article. The
absorbent core may consist essentially of the core wrap, the
superabsorbent polymer particles, and the immobilizing material as
a fibrous network.
[0023] "Amorphous" refers herein to the substantial absence of
crystallinity, in particular to polymers having an enthalpy of
fusion of less than 20.0 J/g, in particular from 0 to 10 J/g, as
measured with the Enthalpy of Fusion Test Method described herein.
The amorphous nature of the polyolefin material results in a
melting point, which is not sharp or definite. Rather as the
temperature increases, amorphous polymers gradually change from a
solid to a soft and then to a liquid material. No clearly defined
glass transition or melting temperature is often noted.
[0024] "Diaper", as used herein, refers to an absorbent article
generally worn by infants and incontinent persons about the lower
torso so as to encircle the waist and legs of the wearer and that
is specifically adapted to receive and contain urinary and fecal
waste. As used herein, term "diaper" also includes "pants" which is
defined below.
[0025] "Nonwoven", as used herein, is a manufactured sheet, web, or
batt of directionally or randomly orientated fibers, bonded by
friction, and/or cohesion and/or adhesion, excluding paper and
products which are woven, knitted, tufted, stitch-bonded
incorporating binding yarns or filaments, or felted by wet-milling,
whether or not additionally needled. The fibers may be of natural
or man-made origin and may be staple or continuous filaments or be
formed in situ. Commercially available fibers have diameters
ranging from less than 0.001 mm to greater than 0.2 mm and they
come in several different forms: short fibers (known as staple, or
chopped), continuous single fibers (filaments or monofilaments),
untwisted bundles of continuous filaments (tow), and twisted
bundles of continuous filaments (yarn). Nonwoven fabrics can be
formed by many processes such as meltblowing, spunbonding, solvent
spinning, electrospinning, and carding. The basis weight of
nonwoven fabrics is usually expressed in grams per square meter
(gsm of g/m.sup.2).
[0026] "Pant" or "training pant", as used herein, refer to
disposable garments having a waist opening and leg openings
designed for infant or adult wearers. A pant may be placed in
position on the wearer by inserting the wearer's legs into the leg
openings and sliding the pant into position about a wearer's lower
torso. A pant may be preformed by any suitable technique including,
but not limited to, joining together portions of the article using
refastenable and/or non-refastenable bonds (e.g., seam, weld,
adhesive, cohesive bond, fastener, etc.). A pant may be preformed
anywhere along the circumference of the article (e.g., side
fastened, front waist fastened). While the terms "pant" or "pants"
are used herein, pants are also commonly referred to as "closed
diapers," "prefastened diapers," "pull-on diapers," "training
pants," and "diaper-pants".
[0027] "Substantially", as used herein, means generally the same or
uniform but allowing for or having minor fluctuations from a
defined property, definition, etc. For example, small measurable or
immeasurable fluctuations in a measured property described herein,
such as viscosity, melting point, etc. may result from human error
or methodology precision. Other fluctuations are caused by inherent
variations in the manufacturing process, thermal history of a
formulation, and the like. The compositions of the present
disclosure, nonetheless, would be said to be substantially having
the property as reported.
[0028] "Superabsorbent polymer" or "SAP" refers herein to absorbent
materials, typically cross-linked polymeric materials, that can
absorb at least 10 times their weight of an aqueous 0.9% saline
solution as measured using the Centrifuge Retention Capacity (CRC)
test (EDANA method WSP 241.2.R3 (12)). The SAP may in particular
have a CRC value of at least 20 g/g, in particular of from 20 to 40
g/g. "Superabsorbent polymer particles", as used herein, refers to
a superabsorbent polymer material which is in particulate form so
as to be flowable in the dry state.
[0029] General Description of an Absorbent Article
[0030] An exemplary absorbent article according to the disclosure
in the form of a baby taped diaper 20 is represented in FIGS. 1-3.
FIG. 1 is a perspective view of the exemplary diaper in a closed
state as it would appear when worn by a wearer. This taped diaper
20 is shown for illustration purpose only as the disclosure may be
used for making a wide variety of diapers or other absorbent
articles such as baby diaper pants, adult incontinence pants or
feminine sanitary pads. In the following, the word "diaper" and
"absorbent article" are used interchangeably. The Figures are used
herein as illustration of one way to carry out the invention and
are not limiting the scope of the claims, unless specifically
indicated to do so.
[0031] The absorbent article comprises a liquid permeable topsheet
24 on its wearer-facing surface, a liquid impermeable backsheet 25
on its garment-facing surface and an absorbent core 28 between the
topsheet and the backsheet (shown in dotted line in FIGS. 2 and 3).
The topsheet typically forms the majority of the wearer-contacting
surface of the article and is the first layer that the body
exudates contact. The topsheet is liquid permeable, permitting
liquids to readily penetrate through its thickness. Any known
topsheet may be used in the present article. The backsheet
typically comprises a fluid impermeable plastic film, which may be
printed with a backsheet pattern, and a low basis weight nonwoven
outer cover glued to this impermeable film to give a nicer feel and
appearance to the backsheet.
[0032] The absorbent article may also typically comprise a fluid
acquisition layer and/or a fluid distribution layer between the
topsheet and the absorbent core, which is not represented for
simplicity but are present in most diapers, as well as outer
barrier cuffs 32 and inner barrier cuffs 34, as is known in the
art. The absorbent article may also comprise other usual components
if it is desired to increase the performance of the article, such
as transverse barrier cuffs, front and/or back elastic waistbands,
a lotion application on the topsheet, longitudinally extending
channels in the core and/or the distribution layer, a wetness
indicator, etc. . . . all these components have been extensively
described and exemplified in the art. More detailed disclosures of
example of such components are for example disclosed in
WO201493323, WO2015/183669 (both Bianchi et al), WO 2015/031225
(Roe et al.) or WO2016/133712 (Ehrnsperger et al.) to name a
few.
[0033] The absorbent article typically comprises a front edge 10, a
back edge 12, and two longitudinally-extending side (lateral) edges
13, 14. The front edge 10 is the edge of the article which is
intended to be placed towards the front of the user when worn, and
the back edge 12 is the opposite edge, and together form the waist
opening of the diaper. The lateral edges 13, 14 respectively form
the two leg openings. The topsheet 24, the backsheet 25, the
absorbent core 28 and the other article components may be assembled
in a variety of well-known configurations, in particular by gluing,
fusion and/or pressure bonding. The absorbent articles of the
present disclosure may comprise any typical layers and components
used in absorbent products of the diaper type, and which are not
necessarily represented in the simplified FIGS. 1-3. A plurality of
absorbent articles may be packaged together in a package.
[0034] General Description of an Absorbent Core
[0035] The absorbent core 28 is the component of the absorbent
article having the most absorbent capacity. An exemplary absorbent
core 28 is shown in isolation in FIGS. 4-6, in dry state (before
use). The absorbent core may typically have a generally rectangular
shape as defined by the longitudinal edges 284, 286 and transversal
front edge 280 and back edge 282. The absorbent core 28 comprises
an absorbent material 60, deposited as a layer having a generally
rectangular outline, as represented on FIG. 4. This absorbent core
represented is of course not limiting the scope of the present
disclosure as the disclosure is applicable to a wide variety of
absorbent cores. It is also common to have an absorbent material 60
layer having a non-rectangular outline ("shaped" core), in
particular the absorbent material layer may define a tapering along
its width towards the central region of the core (or "dog-bone"
shape). In this way, the absorbent material deposition area may
have a relatively narrow width in an area of the core intended to
be placed in the crotch region of the absorbent article. This may
provide for example better wearing comfort. Other shapes can also
be used such as a "T" or "Y" or "sand-hour" for the area of the
absorbent material.
[0036] The absorbent material 60 may be any conventional absorbent
material known in the art. For example, the absorbent material may
comprise a blend of cellulose fibers and superabsorbent particles
("SAP"), typically with the percentage of SAP ranging from 40% to
70% by weight of the absorbent material. The absorbent material may
also be free of cellulose fibers, as is known in so-called
airfelt-free cores where the absorbent material consists of
SAP.
[0037] Various absorbent core designs comprising high amount of SAP
have been proposed in the past, see for example in U.S. Pat. No.
5,599,335 (Goldman), EP1,447,066 (Busam), WO95/11652 (Tanzer),
US2008/0312622A1 (Hundorf), WO2012/052172 (Van Malderen). In
particular the SAP printing technology as disclosed in
US2006/024433 (Blessing), US2008/0312617 and US2010/0051166A1 (both
to Hundorf et al.) may be used. The present disclosure is however
not limited to a particular type of absorbent core. The absorbent
core may also comprise one or more glue such as auxiliary glue
applied between the internal surface of one (or both) of the core
wrap layers and the absorbent material to reduce leakage of SAP
outside the core wrap. A micro-fibrous adhesive net may also be
used in air-felt free cores as described in the above Hundorf
references. These glues are not represented in the Figures for
simplicity.
[0038] The absorbent material may be deposited as a continuous
layer within the core wrap. The absorbent material may also be
present discontinuously for example as individual pockets or
stripes of absorbent material enclosed within the core wrap and
separated from each other by material-free junction areas. A
continuous layer of absorbent material, in particular of SAP, may
also be obtained by combining two absorbent layers having matching
discontinuous absorbent material application pattern wherein the
resulting layer is substantially continuously distributed across
the absorbent particulate polymer material area. As for example
taught in US2008/0312622A1 (Hundorf), each absorbent material layer
may thus comprise a pattern having absorbent material land areas
and absorbent material-free junction areas, wherein the absorbent
material land areas of the first layer correspond substantially to
the absorbent material-free junction areas of the second layer and
vice versa.
[0039] The basis weight (amount deposited per unit of surface) of
the absorbent material may also be varied to create a profiled
distribution of absorbent material, in particular in the
longitudinal direction (as schematically illustrated in FIG. 5) to
provide more absorbency towards the center and the middle of the
core, but also in the transversal direction, or both directions of
the core. The absorbent core may also comprise longitudinally
extending channels which are substantially free of absorbent
material within the absorbent material area. The core wrap may be
bonded through these material-free areas. Exemplary disclosures of
such channels in an airfelt-free core can be found in WO2012/170778
(Rosati et al.) and US2012/0312491 (Jackels). Channels may of
course also be formed in absorbent cores comprising cellulose
fibers.
[0040] Core Wrap
[0041] The function of the core wrap is to enclose the absorbent
material. As indicated in the background, different core wrap
constructions can be used. Typical core wraps comprise two nonwoven
substrates 16, 16', which are attached to another and form
respectively the top layer 16 and the bottom layer of the core wrap
16'. These two layers may be typically attached to another along at
least part of the periphery of the absorbent core to form a seal.
Typically, neither the first nor the second substrate needs to be
shaped, so that they can be rectangularly cut for ease of
production, but other shapes are not excluded. The terms "seal" and
"enclosing" are to be understood in a broad sense. The seal does
not need to be continuous along the whole periphery of the core
wrap but may be discontinuous along part or the whole of it, such
as formed by a series of seal points spaced on a line. Typically, a
seal may be formed by gluing and/or thermal bonding.
[0042] The core wrap represented in the Figures comprises a top
layer 16 which is wider than the bottom layer 16' so that two flaps
of the top layer can be folded over the bottom layer along the
longitudinal edges 284, 286 of the core respectively to which they
are attached, typically by an adhesive to form the longitudinal
seals 284', 286'. The front edge 280 and back edge 282 may also be
sealed, for example by a sandwich seal 280', 282'. Such transversal
seals may for example made by adhesive stripes applied in machine
direction by the slot glue technique, as is known in the art.
Alternatively, is it possible to leave the transversal edges 280,
282 open without a seal. For example, there may be enough core wrap
material between the edges of the core and the absorbent material
60 to provide a buffer zone at these ends.
[0043] The present disclosure is applicable to any of these seals,
between the core wrap layers, as well as the core channel bonds 27
that will be discussed further below, as these seals or bonds are
typically subject to a peel force once the absorbent material
swells for a prolonged length of time. Alternatively, the core wrap
may be made of a single piece of nonwoven which has been folded
over itself around the absorbent material layer 60, and is bonded
to itself along a single longitudinal seal, instead of two
longitudinal seals 284' and 286' as represented in the Figures. The
present disclosure is also applicable to such a core wrap.
[0044] The top layer and the bottom layer may be made from the same
base substrate material which has been differently treated. Such
nonwoven substrate may have a basis weight within a range of from 8
to 12 gsm. The top layer may be typically a nonwoven layer made of
synthetic fibers that has been treated with a surfactant to
increase its hydrophilicity. Both layers may in particular each
comprises or consists of a nonwoven web, such as a carded nonwoven,
a spunbond nonwoven ("S") or a meltblown nonwoven ("M"), and a
multi-layer of any of these. For example, spunbond/meltblown
laminate (spunmelt) polypropylene nonwovens are commonly used and
are particularly suitable, especially those having a multi-layer
SMS, or SMMS, or SSMMS, structure. Examples are disclosed in U.S.
Pat. No. 7,744,576, US2011/0268932A1, US2011/0319848A1 or
US2011/0250413A1. Typical material used to make the synthetic
fibers are PE (polyethylene), PET (polyethylene terephthalate) and
in particular PP (polypropylene).
[0045] Spunbond, also called spunlaid, nonwovens are made in one
continuous process. Fibers are spun through a number of small
orifices in a spinneret to form fibers or filaments, which are then
directly dispersed into a web by deflectors or can be directed with
air streams on a moving foraminous surface, such as a wire mesh
conveyor. Meltblown nonwovens are produced by extruding melted
polymer fibers through a spinneret or die consisting of up to 40
holes per inch to form long thin fibers which are stretched and
cooled by passing hot air over the fibers as they fall from the
die. The diameters of the fiber are significantly reduced by hot
air which also breaks the continuous filaments into microfibers of
varying length to diameter ratio. The extremely fine fibers
(typically polypropylene) differ from other extrusions,
particularly spunbond, in that they have low intrinsic strength but
much smaller size offering key properties.
[0046] The spunbond process can be combined with the meltblown
process to form a multi-layer web having S (spunbond) layer and M
(meltblown) layer, in particular SM, SMS or SMMS webs, which are
strong and offer the intrinsic benefits of fine fibers. The
nonwovens may be consolidated using known techniques, typically
thermal point bonding. In thermal point bonding, heat is applied
locally on individual regions of the nonwoven to locally melt and
fuse the fibers together. Fusion bond patterns are for example
disclosed in US 2011/0250413 (Hu et al.) and US2014/0072767A1
(Klaska et al.). The resultant web is typically collected into
rolls at the supplier and subsequently converted to finished
products.
[0047] Core Channels
[0048] The absorbent core 28 may comprise one or more channels, in
particular at least two channels 26, within the absorbent material
layer. The channels may in particular be areas substantially free
of absorbent material, in particular areas completely free of
absorbent material (accidental minute amount of absorbent material
due to involuntary contamination of the channels due to the high
speed of the making process being disregarded).
[0049] The channels 26 may comprise a bond 27 between the top side
16 of the core wrap and the bottom side 16' of the core wrap. This
bond 27 provides for structural integrity of the channels in dry
and wet state. Any known bonding techniques known in the art may be
used to provide for this bond, in particular one selected from
adhesive bonding, thermo bonding, mechanical bonding, ultrasonic
bonding, or any combinations thereof. An adhesive may be for
example applied in the areas of the channels on the inner side of
the top side and/or the inner side of the bottom side of the core
wrap, typically by slot glue application or any other means,
followed by the application of pressure in the areas of the
channels to provide a good adhesive bonding in these areas.
Exemplary patent disclosures of such adhesive bonding processes can
be found for an airfelt or airfelt-free absorbent cores in
WO2012/170798A1 (Jackels et al.), EP2,905,000 (Jackels et al.) and
EP2,905,001 (Armstrong-Ostle et al.).
[0050] The present disclosure may be particularly useful to make
these channel bonds 27, in addition or alternatively to the core
perimeter bonds 280'-286'. Typically, the bonds 27 may generally
have the same outline and shape as the channel areas 26 in which
they are contained, but may be slightly smaller to allow for a
safety margin (e.g. by a few mm) as some deviations from the
optimal registration may happen during high speed process. It is
expected that channel bonds 27 may be more efficiently made and
stronger if they are provided in macroscopic areas with no
absorbent material (except of course accidental contamination)
compared to bonds provided in areas containing non-negligible
absorbent material.
[0051] Pant Diaper
[0052] The absorbent article may also be in the form of a pant
having permanent or refastenable side seams, which is not
represented herein but for which the invention may also apply. Pant
article comprising refastenable seams are for example disclosed in
US2014/0005020 and U.S. Pat. No. 9,421,137. Typical pant articles
comprise a chassis (sometimes referred to as a central chassis or
central panel) comprising a topsheet, a backsheet, and an absorbent
core, which may be as disclosed herein, and a front belt that
defines a front waist region and a back belt that defines a back
waist region. The chassis may be joined to a wearer-facing surface
of the front and back belts or to a garment-facing surface of the
belts. Side edges of the front belt may be joined to side edges of
the back belt to form two side seams. The side seams may be any
suitable seams known to those of skill in the art, such as butt
seams or overlap seams, for example. When the side seams are
permanently formed or refastenably closed, the absorbent article in
the form of a pant has two leg openings and a waist opening
circumference. The side seams may be permanently joined using
adhesives or bonds, for example, or may be refastenably closed
using hook and loop fasteners, for example.
[0053] Alternatively, instead of attaching belts to the chassis to
form a pant, discrete side panels may be attached to side edges of
the chassis. Suitable forms of pants comprising discrete side
panels are e.g. disclosed e.g. in U.S. Pat. Nos. 6,645,190;
8,747,379; 8,372,052; 8,361,048; 6,761,711; 6,817,994; 8,007,485;
7,862,550; 6,969,377; 7,497,851; 6,849,067; 6,893,426; 6,953,452;
6,840,928; 8,579,876; 7,682,349; 7,156,833; and 7,201,744.
[0054] Backsheet
[0055] The backsheet 25 is the liquid impermeable layer that
generally form the garment-facing side of the absorbent article.
The backsheet 25 prevents, or at least inhibits, the bodily
exudates absorbed and contained in the absorbent core 10 from
soiling articles such as bedsheets, undergarments, and/or clothing.
The backsheet typically comprises a liquid impermeable, or at least
substantially liquid impermeable layer, such as a thin plastic film
having a thickness of about 0.012 mm to about 0.051 mm. Suitable
backsheet materials also include breathable materials which permit
vapors to escape from the absorbent article, while still
preventing, or at least inhibiting, bodily exudates from passing
through the backsheet.
[0056] The backsheet 25 typically further comprises on its external
side a nonwoven outer cover for improving the overall feel of the
backsheet. The outer cover material (sometimes referred to as a
backsheet nonwoven) is typically a nonwoven material joined to and
covering the backsheet film. Thus the outer cover material
typically forms at least a portion of the garment-facing surface of
the absorbent article 20. The outer cover material may comprise a
bond pattern, apertures, and/or three-dimensional features.
[0057] Landing Zone
[0058] Referring to FIGS. 1 and 2, the absorbent article 20 in the
form of a taped diaper may have a discrete landing zone 44 on its
garment-facing side, typically disposed proximate the front edge 10
of the article 20. The landing zone 44 is configured to receive the
fasteners 42 and may comprise, for example, a plurality of loops
configured to be engaged with, a plurality of hooks on the
fasteners 46, or vice versa.
[0059] The landing zone 44 typically comprises one or more discrete
nonwoven materials that are attached to a portion of the outer
cover material 40 in the front waist region 12. The present
disclosure is in particular applicable to the bond area between
such a landing zone 44 and the backsheet outer cover 25. For
example, a first nonwoven may form a portion of a nonwoven landing
zone, and a second nonwoven may form a portion of a backsheet or
outer cover, wherein the at least one bond area joins a portion of
the first nonwoven and a portion of the second nonwoven.
[0060] Bond Areas
[0061] The absorbent article 20 may comprise a bond area between a
first nonwoven material and a second nonwoven material. The bond
area may be continuous or discontinuous. A polymeric filler
composition according to the present disclosure may be disposed
within the bond area. The polymeric filler composition may be the
only bonding means holding the first nonwoven material and the
second nonwoven material bonded together within the bond area.
Alternatively, the polymeric filler composition may be supplemented
by another bonding means, such as mechanical bonds or fusion bonds.
However, it is preferred that the bonding area is free of
conventional hotmelt adhesive, which comprises a substantial amount
of tackifier, e.g. more than 10% by weight of tackifiers.
[0062] While the following list is not limiting, it was found that
the polymeric filler composition of the present disclosure was
particularly efficient to form bond between nonwovens subjected to
a creep force or load during usage of the absorbent article.
Schematically, shear forces are applied to at least one of the
layers 100, 110 in a plane parallel to the bond area, while peel
forces are applied to a first layer 100 and/or a second layer 110
in a plane perpendicular to the bond area 120 (see illustration in
FIG. 7).
[0063] The present disclosure is applicable to any pair of
nonwovens of the articles where at least some peeling constraint is
applied for at least some time during the normal usage of the
article. In particular, the first nonwoven material and the second
nonwoven material can be a pair selected from the top layer 16 and
bottom layer 16' of the core wrap, or the landing zone 40 and the
outer cover of the backsheet 25.
[0064] Other nonwoven materials that may be used in the present
disclosure may be selected in the group consisting of the liquid
permeable topsheet 24, the barrier leg cuff material 32-34, any
nonwoven waist bands (not shown), an acquisition material or
secondary top sheet, or any other nonwoven materials.
[0065] The polymeric filler composition may be typically present at
a basis weight ranging from about 13 gsm to about 30 gsm within the
bond area, alternatively from about 15 gsm to about 25 gsm. The
first and/or the second nonwoven material may comprise natural or
recycled fibers.
[0066] It may be that the adhesive is applied in a way that the
bond area is not uniformly covered with the adhesive but there can
e.g. be parts of the bond area which are free of adhesive, e.g. if
the adhesive has been applied in stripes by using a slot coating
nozzle with a comb shim. In such cases, the basis weight of the
adhesive is defined as the average basis weight of the adhesive
over the bond area.
[0067] Polymeric Filler Composition
[0068] The polymer filler composition of the present disclosure
comprises at least one polymer selected from polypropylene
homopolymers, propylene-ethylene copolymers, and mixtures thereof
The polymer is at least the main component of the polymeric filler
composition, which may comprise at least 50% of the polymer by
weight of the polymer filler composition. The polymeric filler
composition may in particular comprises at least 60%, or at least
70%, or at least 80% or at least 90% and up to 100%, or up to
99.5%, or up to 99%, of the polymer, by weight of the composition.
For simplification of the compounding process, it may be
advantageous that the polymer filler composition consists
essentially of an unblended polymer.
[0069] While not wishing to be bound by theory, the inventors
believe that in order to provide for strong bonds between a first
nonwoven 100 and a second nonwoven 110, the polymeric filler
composition 130 should enable the right microscopic pattern in the
bond area 120, which can be described as a dual row entanglement of
adjacent fibers from both nonwovens (as illustrated in the electron
microscopic of FIG. 8). Ideally, the majority of the fibers is
embedded by 360.degree., or at least by 180.degree.. This creates a
mechanical lock in which the fibers are cemented. The inventors
found that the combination of such mechanical lock provided by such
structure in combination with the high Toughness of the polymer
enables a bond which is resistant against peel creep under in-use
conditions. Therefore, also pure polymers like Licocene 2502, which
are non-tacky at room temperature were found suitable for the
present disclosure at least when they are applied to the two
nonwovens in the microscopic structure described before.
[0070] While the polymers indicated above (polypropylene
homopolymers, or propylene-ethylene copolymers) can be generally
used to form such inter-fibrous locking, the present inventors have
found that not all such polymers provide the desired creep
resistance properties between two nonwoven substrates. After
testing and comparison of various polymeric filler compositions,
the inventors have found that the polymeric filler composition
should further have certain mechanical properties designated as
Toughness and Yield Stress at usage temperature (from 23.degree. C.
to 37.degree. C.), which will be illustrated below in the form of
different examples.
[0071] Crystallinity of the propylene-ethylene copolymers is
believed to be a contributor to the Toughness. The
propylene-ethylene copolymer is advantageously semi-crystalline, so
that the filler composition has an enthalpy of fusion of at least
20 J/g, as measured according to the Enthalpy of Fusion Measurement
Method described herein. However too high crystallinity can make
the polymer brittle, so the enthalpy of fusion may be
advantageously less than 100 J/g, in particular less than 50 J/g,
as measured according to the Enthalpy of Fusion Measurement Method
described herein.
[0072] Commercial example of suitable propylene-ethylene copolymers
is Clariant's Licocene.RTM. PP 2502, which has a measured enthalpy
of fusion of 29.4 J/g. On the other hand, Licocene.RTM. PP 1502
which has a measured enthalpy of fusion of 15.1 J/g or
Licocene.RTM. PP 1602 which has a measured enthalpy of fusion of
16.7 J/g, are believed to be not crystalline enough.
[0073] The enthalpy of fusion is however believed not to be the
only relevant factor to predict good peel creep resistance of the
polymers. For example, Idemitsu's L-MODU S-410 has a measured
enthalpy of fusion of only about 2 J/g but still has a good
performance. The inventors believe that the polymer filler
composition's performance is driven by a relatively high Toughness,
as measured as indicated below. This Toughness is believed to be
driven by the homopolymer nature of L-MODU S410 as well as the
relatively higher molecular weight of the polymer (45.000 g/mol).
Toughness is believed to be increased with the molecular
weight.
[0074] The polymer comprises propene monomer units. In copolymers,
the percentage of propene monomer units may range for example from
50% to 99% by weight of the copolymer. If the percentage of propene
monomer units is not known, it may be determined by a suitable
method, such as nuclear magnetic resonance or infrared
spectroscopies, as known to those of skill in the art.
[0075] The polymers of the present disclosure can be prepared using
a metallocene catalysts. The polymer can be for example prepared by
the methods described in US2016/0053149A1("Ready-to-use hot melt
adhesive having an improved property profile"). The polymer can be
prepared into a final polymeric filler composition by heating the
primary polymer to elevated temperatures (e.g., about 135 to about
175.degree. C.) that melts the polymer. Once molten, one or more
optional ingredients (e.g., additive or other polymers components)
can be added to the primary polymer. A mixer can be used to mix the
components together into a final polymeric filler composition. See
for example U.S. Pat. No. 5,723,546, which discloses such
blending.
[0076] According to the present disclosure, the polymeric filler
composition comprises less than 5%, alternatively less than 3%,
alternatively less than 2%, alternatively less than 1%,
alternatively less than 0.5%, and alternatively less than 0.1% of a
tackifier, by weight of the polymer filler composition. Exemplary
tackifiers can include aliphatic hydrocarbon resins, aromatic
modified aliphatic hydrocarbon resins, hydrogenated
poly-cyclopentadiene resins, poly-cyclopentadiene resins, gum
rosins, gum rosin esters, wood rosins, wood rosin esters, tall oil
rosins, tall oil rosin esters, poly-terpenes, aromatic modified
poly-terpenes, terpene-phenolics, aromatic modified hydrogenated
poly-cyclopentadiene resins, hydrogenated aliphatic resins,
hydrogenated aliphatic aromatic resins, hydrogenated terpenes and
modified terpenes, and hydrogenated rosin esters. The polymeric
filler composition can be free of a tackifier.
[0077] There are significant advantages to minimizing or avoiding
the use of a tackifier as it may reduce the cost of the polymeric
filler composition, as well as eliminate an additional ingredient
and potential issues that may be associated with supplying the
additional ingredient. Furthermore, tackifiers may impart
undesirable odor in disposable articles and can also act as
carriers of low molecular weight plasticizers (e.g., process oils
that are used in SBC based adhesives) that may weaken the
polyethylene back sheet materials used in absorbent articles and
textile articles.
[0078] The polymeric filler composition may optionally comprise
additives such as an antioxidant, UV stabilizer, brightener,
colorant, fragrance etc. . . . . The polymeric filler composition
may comprise less than 5% by weight of such additives. Any
antioxidant known to a person of ordinary skill in the art may be
used in the adhesion composition.
[0079] Non-limiting examples of suitable antioxidants include
amine-based antioxidants such as alkyl diphenyl amines,
phenyl-naphthylamine, alkyl or aralkyl substituted
phenyl-naphthylamine, alkylated p-phenylene diamines,
tetramethyl-diaminodiphenylamine and the like; and hindered phenol
compounds such as 2,6-di-t-butyl-4-methylphenol;
1,3,5-trimethyl-2,4,6-tris(3',5'-di-t-butyl-4'-hydroxybenzyl)benzene;
tetra kis
[(methylene(3,5-di-t-butyl-4-hydroxyhydrocinnamate)]methane (e.g.,
IRGANOX.TM. 1010, from Ciba Geigy, New York);
octadecyl-3,5-di-t-butyl-4-hydroxycinnamate (e.g., IRGANOX.TM.
1076, commercially available from Ciba Geigy) and combinations
thereof. The amount of the antioxidant in the polymeric filler
composition may be equal to or less than 1%, alternatively from
about 0.05% to about 0.75%, and alternatively from about 0.1% to
about 0.5%, by weight of the polymeric filler composition.
[0080] The polymeric filler composition may optionally comprise a
UV stabilizer, that may prevent or reduce the degradation of the
composition by radiation. Any UV stabilizer known to a person of
ordinary skill in the art may be used in the polymeric filler
composition. Non-limiting examples of suitable UV stabilizers
include benzophenones, benzotriazoles, aryl esters, oxanilides,
acrylic esters, formamidine carbon black, hindered amines, nickel
quenchers, hindered amines, phenolic antioxidants, metallic salts,
zinc compounds, and combinations thereof. Where used, the amount of
the stabilizer in the polymeric filler composition can be less than
1%, alternatively from about 0.05% to about 0.75%, and
alternatively from about 0.1% to about 0.5%, by weight of the
polymeric filler composition
[0081] The polymeric filler composition may optionally comprise a
brightener, colorant, and/or pigment. Any colorant or pigment known
to a person of ordinary skill in the art may be used in the
polymeric filler composition. Non-limiting examples of suitable
brighteners, colorants, and/or pigments include fluorescent
materials and pigments such as triazine-stilbene, coumarin,
imidazole, diazole, titanium dioxide and carbon black,
phthalocyanine pigments, and other organic pigments such as
IRGAZINB, CROMOPHTALB, MONASTRALB, CINQUASIAB, IRGALITEB, ORASOLB,
all of which are available from Ciba Specialty Chemicals,
Tarrytown, N.Y. Where used, the amount of the brightener, colorant,
and/or pigment in the polymeric filler composition can be less than
10%, alternatively from about 0.01% to about 5%, and alternatively
from about 0.1% to about 2%, by weight of the polymeric filler
composition.
[0082] The polymeric filler composition may optionally comprise a
fragrance such as a perfume or other odorant. Such fragrances may
be retained by a liner or contained in release agents such as
microcapsules that may, for example, release fragrance upon removal
of a release liner from or compression on the adhesive composition.
Where used, the amount of the fragrance in the polymeric filler
composition can be less than 3%, alternatively less than 2%,
alternatively less than 1%, alternatively from about 0.05% to about
0.75%, and alternatively from about 0.1% to about 0.5%, by weight
of the polymeric filler composition.
Examples & Data
[0083] Exemplary Nonwoven-Nonwoven Laminates were Made as
Follows.
[0084] A first nonwoven material and a second nonwoven material are
bonded via a specified slot coating process using a bonding
material to form a laminate. The bonding material may be a
polymeric filler composition as claimed or a comparative example
such as a tackifier-containing adhesive composition. The first
nonwoven material and the second nonwoven material used to form the
laminate are 15 gsm polypropylene spunbond (SSS) with a thermal
bond pattern matching that of U.S. Design Pat. No. D714,560 that
covers approximately 13-15% of first nonwoven material and the
second nonwoven material. The first nonwoven material and the
second nonwoven material are provided in roll stock form and are
230 mm in width.
[0085] The bonding material is slot coated onto the first nonwoven
material at a speed of 114 m/min and the total tension at the point
of application is 0.5 lbs (10.5 N/m tension per unit width). The
bonding material is slot coated onto the first nonwoven material
using an ITW Dynatec APEX Slot Die, from ITW Dynatec,
Hendersonville Tenn., USA, or equivalent). The shim of the die is
0.15 mm thick and cut such that a coating of bonding material is
applied in the cross-machine direction of 27 mm width and
continuous in the machine direction. The bonding material flow rate
for the nozzle is set such that the applied basis weight can be
chosen, in the present examples at 10.+-.0.1 gsm.
[0086] The bonding material is maintained at a temperature
.+-.5.degree. C. at all points up to and including the applicator
such that the viscosity of the of bonding material at the
maintained temperature is within the range of 1,500 mPas to 10,000
mPas.
[0087] The overall slot coating process is performed at an ambient
temperature of 21.+-.2.degree. C. The bonding material is applied
to the first nonwoven material with the slot coat die by bringing
the slot coat die into contact with the first nonwoven material
supported between two non-driven web-support idlers that co-rotate
with the moving first nonwoven material. Each web-support idler has
a 50 mm diameter. The spacing of the web-support idlers is set to
200 mm, center to center, and the bonding material applicator's
exit is set at a point 150 mm from the downstream idler's center.
The bonding material applicator is pressed into the tensioned first
nonwoven material between the idlers, such that the first nonwoven
material is deflected 3-4 mm at the exit point of the bonding
material from the slot coat die, with respect to the plane made by
the first nonwoven material under tension when the bonding material
applicator is absent. The angle made between the slot coat die's
shim plane and the plane of the tensioned first nonwoven material
when the bonding material applicator is not engaged is the pitch
angle. This angle is described to be zero pitch when the planes are
perpendicular to each other. During application of the bonding
material to the first nonwoven material, the angle is set to zero
pitch. In other words, the plane of the shim relative to the plane
of the tensioned first nonwoven material when the bonding material
applicator is not engaged is 90.degree. on the side of the
downstream web-support idler. The bonding material coating is
centered along the length of the first nonwoven material by
centering the width of the slot coat die on the cross-machine width
of the first nonwoven material.
[0088] The coated first nonwoven material is then brought into
contact with the second nonwoven material 165 mm after the point of
coating with the bonding material to create a laminate. A
compression nip is used to compress the laminate at a point 955 mm
from the point of coating with the bonding material. The
compression nip consists of a steel roll and a rubber coated steel
roll that coaxially counter rotate while in contact with each other
to create pressure between them. The steel roll and rubber roll
diameters are 100 mm and the rubber coating is 20 mm thick with a
Shore A hardness of 100. The steel roll and rubber coated steel
roll are forced together to develop a constant pressure of 70 psi
in the nip. The laminate travels through the nip and is subjected
to this pressure as it travels. The laminate speed and the
resulting bonded laminate is maintained at 114 m/min. After passing
through the compression nip, the bonded laminate is wound onto a
roll for sampling at 1.5 lbs winding tension. Laminated test panels
are immediately cut from the wound roll of bonded laminate. The
laminated test panels are equilibrated at 21.+-.2.degree. C. and
40% relative humidity for a minimum of 24 hours before further
preparation and testing.
[0089] Performance
[0090] Laminates obtained as described above using commercial
compositions were tested according to Static Peel Force Time test
described below, in which a constant peel force is exerted by a
weight of ca. 200 g on one layer of the laminate. Toughness and
Yield Stress were also measured for each composition according to
Extensional Test Method described below.
[0091] Table 1 below shows the values measured for various
tackifier-free compositions. Licocene designates a range of
metallocene-technology based propylene-ethylene copolymer. L-MODU
designates a range of metallocene catalyst homopolymer
polypropylene from Idemitsu. RT designates a range of Amorphous
Poly Alpha Olefin (APAO) from Rextac.
TABLE-US-00001 TABLE 1 Performance [min/10 mm Toughness Yield
Stress Polymer Source bonded length] [MJm.sup.-3] [MPa] Licocene
Clariant >740.7 * 28.0 9.0 2502 L-MODU Idemitsu >740.7 * 84.7
7.5 S410 Licocene Clariant Not measured 26.1 4.7 1602 RT2830 Rextac
3.1 22.9 2.9 Licocene Clariant n.a. ** 2.9 4.8 1302 Licocene
Clariant n.a. ** 9.1 2.5 1502 * testing stopped as no failure
observed; ** not measured, these materials are very soft with low
crystallinity (low enthalpy of fusion) and are expected to be not
suitable a peel resistant filler composition;
[0092] The Static Peel Force Time test was also conducted with
commercially available tackifier-containing hotmelt adhesives, as
shown in Table 2 below.
TABLE-US-00002 TABLE 2 Performance [min/10 mm Toughness Yield
Stress Polymer Source bonded length] [MJm.sup.-3] [MPa] DM3800
Henkel 7.6 40.5 0.8 2401 Bostik 135.6 n.a. n.a.
[0093] The inventors believe that the polymer filler composition
should have a Toughness of at least 25 MJm.sup.-3 and preferably a
Yield Stress of at least 5 MPa in order to provide the bond with a
long Static Peel Force Time, especially a lower basis weight (10-20
gsm). Toughness and Yield Stress parameters, characterize the
behavior of the bonding composition submitted to a high strain, as
opposed to previous methods describing adhesives using oscillatory
rheology (e.g. the storage modulus G'). The inventors have found
that these large are critical to predict the adhesive behavior
according to the static test method (hang time), which again is
needed to predict the performance of the bonds in use in the
diaper.
[0094] The Toughness of the polymer filler composition may be at
least 27 MJm.sup.-3. The Toughness may also be up to 200
MJm.sup.-3, or up to 150 MJm.sup.-3 or up to 100 MJm.sup.-3 or up
to 60 MJm.sup.-3.
Test Methods
[0095] Extensional Test Method
[0096] The Extensional Test Method is used to determine the Yield
Stress and the Toughness for a specimen of a polymer composition. A
thin film specimen formed of polymer composition is analyzed with a
rotational rheometer fitted with a specialized fixture with counter
rotating rollers, and the stress associated with extensional strain
imparted is measured and recorded.
[0097] Instrumental Setup
[0098] A rotational rheometer (ARES G2, TA Instruments, New Castle,
Del., USA, or equivalent) is fitted with a fixture that has counter
rotating cylindrical rollers specifically designed for the
interrogation of extension deformation of films. An example of a
suitable fixture is the Extensional Viscosity Fixture, or EVF (EVF,
TA Instruments, or equivalent). The rheometer is further fitted
with a forced-convection oven FCO (FCO, TA Instruments, or
equivalent) and cooling system (ACS 2, TA Instruments, or
equivalent) capable of controlling temperate from at least -50 to
250.degree. C. to a within a tolerance of 0.5.degree. C.
[0099] Specimen Preparation
[0100] Approximately 6 g.+-.2 g of the polymer composition is
placed in a circular polytetrafluoroethane (PTFE) bowl with a flat
bottom (diameter of 60 mm.+-.2 mm) and introduced into a vacuum
oven held at 170.degree. C. After 15 minutes at ambient pressure,
the pressure is lowered to 10 mbar, and the polymer composition is
subsequently held at 170.degree. C. and at 10 mbar for 45 minutes
to remove air bubbles from the polymer composition. If 170.degree.
C. is insufficient to melt the polymer compositions a temperature
30.+-.10.degree. C. above the melting temperature of the polymer
material composition is used. The polymer composition is removed
from the vacuum oven and allowed to cool to ambient lab conditions
(23.+-.2.degree. C.) for 90.+-.30 minutes, at which point the
polymer composition is removed from the PTFE bowl and placed
between 2 sheets of siliconised paper (such as product number
114918, Mondi Group, Hilm, Austria, or equivalent). A metal shim
500.+-.30 .mu.m in thickness is used in the heated press as a
spacer to obtain a film thickness of 500 .mu.m when pressed with a
heated press at 90.degree. C. for 60 seconds at a pressure
sufficient to form a polymeric film. If 90.degree. C. is
insufficient to press a uniform flat film, a temperature
approximately 10.+-.5.degree. C. below the melting point of the
sample material composition such that the sample material
composition is in a semi-solid state is used. The film is stored at
least 120 hours in the laboratory at 23.+-.2.degree. C. prior to
testing. From the film individual specimens for measurement are
punched with a sample cutter to the final specimen dimensions of
20.0 mm by 10.0 mm by 500 .mu.m.
[0101] Measurement
[0102] To secure the film to the cylinders of the EVF, the
cylinders are heated to 50.degree. C. for 90.+-.30 s in the
forced-convection oven of the rheometer. After opening the oven, a
specimen of polymer composition is briefly pressed onto the
cylinders of the EVF to secure it to the cylinder surface. The
specimen is placed perpendicular to the axis of rotation of the
cylinders.
[0103] The specimen mounted on the EVF is then placed in the forced
convection oven of the rheometer for thermal conditioning and is
kept isothermal at 23.+-.1.degree. C. for 300.+-.10 s. After this
time has elapsed, the specimen is mechanically conditioned. To
mechanically condition the specimen, the torque transducer is
zeroed, and the sample is put under a pre-stretch rate of 0.001
s.sup.-1 for 0.30 s and then allowed to relax for 60 s (in this
method, all strain is expressed in terms of Hencky strain, also
known as "true strain" or "logarithmic strain.").
[0104] The measurement is performed in the FCO oven at 23.degree.
C..+-.0.5.degree. C. The strain rate extension for the measurement
is 1 s.sup.-1, and the strain at maximum extension is 4.0. After
measurement, the specimen is checked for rupturing. If it has
ruptured, the location of the break is noted. If the rupture is
approximately in the middle between the two cylinders of the EVF,
the data collected are deemed acceptable. Otherwise, if the
polymeric film break is at or close to the rotating cylinders, the
results are discarded, and the measurement performed again on a
replicate specimen.
[0105] Analysis
[0106] For the extensional stress calculation, a constant volume is
assumed. From the raw torque versus angular displacement data
recorded by the rheometer, extensional stress (in megapascals, or
MPa) versus Hencky strain data are calculated. The data are plotted
in semilogarithmic fashion with Hencky strain on the abscissa
(linear scale) and extensional stress on the ordinate (logarithmic
scale). A linear range is sought in this plot. If a linear range
above a strain of 0.3 can be identified and this range can be fit
with a positive slope with an R.sup.2 value of 0.98 or greater, the
value of the fitted line at a Hencky strain of zero (that is, the
y-intercept), is defined as the Yield Stress, which is reported in
MPa to the nearest kilopascal. Otherwise, the maximum value of
extensional stress recorded during the measurement is reported as
the Yield Stress, again reported in MPa to the nearest
kilopascal.
[0107] The extensional stress (MPa) versus Hencky strain data
calculated above are again plotted, but this time in linear fashion
with Hencky strain on the abscissa (linear axis) and extensional
stress on the ordinate (linear axis). The integral of extensional
stress with strain (that is, the area under the extensional stress
curve as a function of strain) is calculated from a strain of zero
to the strain at which the sample ruptured (or, in the case it did
not rupture during the measurement, to a strain of 4.0) and is
reported as the Toughness, which is reported in units of megajoules
per cubic meter, or MJ m.sup.-3
[0108] Static Peel Force Time Test Method
[0109] The Static Peel Force Time Test Method is used to determine
the time required for an adhesive bond to completely delaminate in
an approximate 180.degree. peel geometry under constant load and at
fixed temperature. Multiple specimens of a representative sample
are analyzed for a given sample polymer filler material to
establish the Static Peel Force Time.
[0110] Sample Preparation
[0111] If, for a sample polymer filler of interest, an exemplary
laminate is available the preparation of which is described above,
ten specimens measuring 25.4 mm in the machine direction are taken
at random from the equilibrated roll stock. The laminate cross
direction (the direction parallel to which the peel is performed in
this method) is 27 mm. If, for a sample polymer filler material of
interest, an exemplary laminate is not available, two-layer
laminate bond specimens of one or more different geometries excised
from available materials may be measured. For example, if bond
containing filler of interest is present on finished absorbent
articles, ten specimens of bonds rectangular in shape may be
extracted from ten individual like articles selected at random from
a commercially sourced package of diapers. In this case, specimens
must contain bonds that measure at least 10 mm parallel to the axis
along which the peel will be performed and 25.4 mm transverse to
the axis. For each specimen, the dimension of the bonded area
parallel to the axis along with the peel is measured to the nearest
1 mm and recorded. Specimens must further have sufficient unbonded
material in both laminate layers on at least one side of the bonded
area along the axis of peel such that material can be affixed to
wooden dowel rods as discussed below.
[0112] Regardless of whence specimens for peel analysis are
sourced, each of the unbonded layers at the edge of the laminate is
separately folded over a small round wooden dowel rod 2 mm in
diameter and approximately 40 mm long and the wrapped dowels are
secured with a 2 inch wide bulldog clip. The clip is placed over
the wrapped dowel and clamped onto the doubled layer of material
such that the material does not slip or pull out of the clip.
[0113] Measurement
[0114] With clips attached, the test specimens are placed in
preconditioned incubator (at 38.+-.1.degree. C.) for about 2 hours
before testing. After 2 hours, each sample is suspended in the
chamber by the clip attached to one laminate layer, and a weight is
attached to the other laminate layer's clip, hanging therefrom. The
hanging weight, the bulldog clip, and the dowel have a total mass
of 200.+-.2 g.
[0115] The specimen is suspended such that the bottom of the
attached weight is located high enough above the bottom of the
chamber so that the entire laminate can peel apart, and the weight
can freely fall to the bottom of the chamber through some remaining
distance. A timer is used to measure the time between the time at
which the hanging weight is attached and the time at which the
bonded area of the test laminate fully delaminates. For each
specimen, this time to failure is recorded to the nearest
second.
[0116] Analysis and Reporting
[0117] For each specimen, the time to failure is normalized to a 10
mm bond dimension to establish that specimen's normalized hang
time, recorded for each specimen to the nearest second.
Normalized hang time [ min ] = 10 mm Bond dimension [ mm ] parallel
to axis of peel .times. time to failure [ min ] ##EQU00001##
[0118] The arithmetic mean of the normalized hang time values for
the ten specimens is calculated and reported as the Static Peel
Force Time in minutes to the nearest minute.
[0119] Viscosity Test Method
[0120] The Viscosity Parameter of the polymer filler composition is
determined using the Viscosity Parameter Test Method, which
consists of performing ASTM D3236-15 with the following additional
guidance. A Brookfield RVT viscometer with spindle SC 4-27
(Brookfield Engineering, Middleboro, Mass., USA), or equivalent, is
used. The sample temperature is maintained at 170.0.+-.1.0.degree.
C., unless otherwise specified, throughout the measurement. The
sample is preheated for 10 minutes and stirred with the measurement
spindle for 30 min. The spindle is rotated at 20 rpm throughout the
measurement. The resulting apparent viscosity, as described in
section 10, is reported as the "viscosity" in units of
millipascal-seconds to the nearest 100 mPas.
[0121] Enthalpy of Fusion Measurement Method
[0122] The Enthalpy of Fusion of a hot-melt adhesive composition is
determined using the Enthalpy of Fusion Test Method, which consists
of performing ASTM D3418-15 with the following additional guidance.
Hot-melt specimen(s) are preferably extracted from molded or
pelleted raw material adhesive composition. If raw material is not
available, specimen(s) of adhesive are extracted from bonds of
interest in an absorbent article using techniques known to those of
skill in the art. Dry nitrogen is used as the purge gas in the
differential scanning calorimeter (DSC). The rate of increase of
temperature in the DSC is 10.degree. C./min, and the rate of
decrease of temperature in the DSC is 1.degree. C./min. The
mass-normalized enthalpy of fusion is calculated as specified in
section 11.4 based on the curve corresponding to decreasing
temperature (at 1.degree. C./min) and is reported as the "Enthalpy
of Fusion" in units of joules per gram (J/g) to the nearest 0.1
J/g.
[0123] The dimensions and values disclosed herein are not to be
understood as being strictly limited to the exact numerical values
recited. Instead, unless otherwise specified, each such dimension
is intended to mean both the recited value and a functionally
equivalent range surrounding that value. For example, a dimension
disclosed as "40 mm" is intended to mean "about 40 mm."
[0124] Every document cited herein, including any cross referenced
or related patent or application and any patent application or
patent to which this application claims priority or benefit
thereof, is hereby incorporated herein by reference in its entirety
unless expressly excluded or otherwise limited. The citation of any
document is not an admission that it is prior art with respect to
any invention disclosed or claimed herein or that it alone, or in
any combination with any other reference or references, teaches,
suggests or discloses any such invention. Further, to the extent
that any meaning or definition of a term in this document conflicts
with any meaning or definition of the same term in a document
incorporated by reference, the meaning or definition assigned to
that term in this document shall govern.
[0125] While particular embodiments of the present disclosure 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 present
disclosure. It is therefore intended to cover in the appended
claims all such changes and modifications that are within the scope
of this present disclosure.
* * * * *