U.S. patent application number 10/732667 was filed with the patent office on 2004-06-24 for microwaveable latent polymer composites with rough surface texture.
Invention is credited to Zhou, Peiguang.
Application Number | 20040121144 10/732667 |
Document ID | / |
Family ID | 21694616 |
Filed Date | 2004-06-24 |
United States Patent
Application |
20040121144 |
Kind Code |
A1 |
Zhou, Peiguang |
June 24, 2004 |
Microwaveable latent polymer composites with rough surface
texture
Abstract
This invention relates to a latent polymer composite which
contains a heat-sensitive polymer material and a microwave
sensitizer. The latent polymer material is inelastic in the latent
state but can be made elastic with the addition of heat. The
microwave sensitizer is a solid material blended uniformly into the
latent polymer composite. The sensitizer absorbs microwave
radiation and heats the heat-sensitive polymer material. The
polymer composite becomes elastic under microwave radiation or
thermal energy. The latent polymer composite can bonded to a
fibrous sheet to form a latent laminate material. When exposed to
microwave radiation, the latent laminate material becomes an
elastic laminate. The latent polymer composite of the laminate
shrinks and returns to an elastic state creating an elastic
laminate material. The polymer composite of this invention has a
rough surface created by the sensitizer particles. The rough
surface of the polymer filament or film provides stronger bonding
to the fibrous sheets of the laminate.
Inventors: |
Zhou, Peiguang; (Appleton,
WI) |
Correspondence
Address: |
Pauley Petersen & Erickson
Suite 365
2800 W. Higgins Road
Hoffman Estates
IL
60195
US
|
Family ID: |
21694616 |
Appl. No.: |
10/732667 |
Filed: |
December 10, 2003 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10732667 |
Dec 10, 2003 |
|
|
|
10001147 |
Nov 30, 2001 |
|
|
|
Current U.S.
Class: |
428/323 ;
428/500 |
Current CPC
Class: |
A61F 13/4902 20130101;
Y10T 428/2913 20150115; Y10T 428/31855 20150401; C08K 3/04
20130101; Y10T 428/2982 20150115; B32B 27/12 20130101; Y10T 428/25
20150115; Y10T 428/26 20150115; Y10T 428/2978 20150115; Y10T 428/31
20150115; Y10T 428/249982 20150401; C08K 3/22 20130101; Y10T
428/249924 20150401; Y10T 428/298 20150115 |
Class at
Publication: |
428/323 ;
428/500 |
International
Class: |
B32B 005/16 |
Claims
What is claimed is:
1. A polymer composite, comprising: at least one heat-sensitive
latent polymer material; and a microwave sensitizer material
blended with the heat-sensitive latent polymer material.
2. The polymer composite according to claim 1, wherein the latent
polymer material comprises a stretched elastic polymer
material.
3. The polymer composite according to claim 1, wherein the polymer
composite comprises a polymer filament or a polymer film.
4. The polymer composite according to claim 1, wherein the polymer
material comprises one selected form the group consisting of
polyether-block amides, ethylene-vinylacetate block or random
copolymers, polyethylene-polyethylene oxide block copolymers,
polypropylene oxide-polyethylene oxide block copolymers,
polyesters, polyurethanes, polyacrylates, polyethers, and
combinations thereof.
5. The polymer composite according to claim 1, wherein the
sensitizer material comprises one selected from the group
consisting of carbon black powder, calcium chloride, aluminum
oxide, copper oxide, zinc oxide, barium ferrite, magnesium ferrite,
magnesium acetate, and combinations thereof.
6. The polymer composite according to claim 1, wherein the
sensitizer material comprises sensitizer particles comprising an
average diameter between about 0 and 25 microns.
7. The polymer composite according to claim 6, wherein the
sensitizer particles comprise an average diameter of about 5 to 10
microns.
8. The polymer composite according to claim 7, wherein the
sensitizer particles comprise an average diameter of about 1.5 to
2.5 microns.
9. The polymer composite according to claim 1, wherein the
sensitizer material is substantially uniformly blended with the
heat-sensitive polymer.
10. The polymer composite according to claim 9, additionally
comprising about 1% to 20% by weight of sensitizer material.
11. The polymer composite according to claim 10, additionally
comprising about 1% to 15% by weight of sensitizer material
12. The polymer composite according to claim 11, additionally
comprising about 2% to 8% by weight of sensitizer material
13. The polymer composite according to claim 1, additionally
comprising a rough surface texture.
14. An absorbent article comprising the polymer composite according
to claim 1.
15. A method of making the polymer composite of claim 1, the method
comprising: mixing an elastic polymer material with a microwave
sensitizer material; forming an elastic polymer composite from the
mixture of the elastic polymer material and the microwave
sensitizer material; and stretching the elastic polymer composite
to form the polymer composite comprising the latent polymer
material.
16. A method of making an elastic laminate using the polymer
composite of claim 2, the method comprising: providing the polymer
composite; bonding the polymer composite to a fibrous sheet; and
exposing the polymer composite to microwave energy.
17. A filament, comprising: a heat-sensitive latent polymer
material including a polymer selected form the group consisting of
polyether-block amides, ethylene-vinylacetate block or random
copolymers, polyethylene-polyethylene oxide block copolymers,
polypropylene oxide-polyethylene oxide block copolymers,
polyesters, polyurethanes, polyacrylates, polyethers, and
combinations thereof; and a microwave sensitizer material blended
with the heat-sensitive latent polymer material, the microwave
sensitizer material selected from the group consisting of carbon
black powder, calcium chloride, aluminum oxide, copper oxide, zinc
oxide, barium ferrite, magnesium ferrite, magnesium acetate, and
combinations thereof.
18. The filament according to claim 17, wherein the latent polymer
material comprises a stretched elastic polymer material.
19. A film, comprising: a heat-sensitive latent polymer material
including a polymer selected form the group consisting of
polyether-block amides, ethylene-vinylacetate block or random
copolymers, polyethylene-polyethyle- ne oxide block copolymers,
polypropylene oxide-polyethylene oxide block copolymers,
polyesters, polyurethanes, polyacrylates, polyethers, and
combinations thereof; and a microwave sensitizer material blended
with the heat-sensitive latent polymer material, the microwave
sensitizer material selected from the group consisting of carbon
black powder, calcium chloride, aluminum oxide, copper oxide, zinc
oxide, barium ferrite, magnesium ferrite, magnesium acetate, and
combinations thereof.
20. The film according to claim 19, wherein the latent polymer
material comprises a stretched elastic polymer material.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application is a divisional of U.S. application, Ser.
No. 10/001,147, filed on 30 Nov. 2001. The co-pending parent
application is hereby incorporated by reference herein in its
entirety and is made a part hereof, including but not limited to
those portions which specifically appear hereinafter.
FIELD OF THE INVENTION
[0002] This invention relates to a microwave sensitive latent
polymer made of a blend of latent polymer material and a microwave
sensitizer. The latent polymer composites of this invention use
microwave energy to convert the latent polymer material to an
elastic form. The latent polymer composites of this invention are
useful in absorbent articles such as diapers.
BACKGROUND OF THE INVENTION
[0003] Elastic polymer materials are useful in absorbent articles.
Elastic polymer strands or films can be used, for instance, in
waist and leg regions of a wearable absorbent article such as a
diaper. The resulting elastic waist and leg regions provide a
secure fit to the user. This helps stop leaking as well as makes
the diaper more comfortable.
[0004] Absorbent articles contain many materials and the
manufacturing process can be complex and expensive. Manufacturing
methods that simplify production and reduce cost are desired. One
method of making elastic laminates involves stretching an elastic
material, such as a strand or film, and bonding the stretched
material to a fabric sheet to create an elastic laminate. Some
elastic polymers, when stretched, will maintain the stretched, or
latent, state until heat is added to restore the elasticity.
Heating latent polymers to restore elasticity is useful in
producing absorbent articles but this process can also require
numerous production steps and can become expensive.
[0005] Microwave energy has primarily been used for food
processing. Microwave sensitive materials have been used to
increase microwave heating rate and uniformity. Most microwave
sensitive materials are inorganic chemicals and are typically
coated onto a substrate to form a microwave interactive layer.
Often times there is little control over the amount of heat
produced by these materials, which can result in inadequate heating
or overheating and burning.
[0006] There is a need in the absorbent article industry for new
ways to heat latent polymer materials quickly and efficiently.
SUMMARY OF THE INVENTION
[0007] This invention relates to a latent polymer composite which
contains a heat-sensitive polymer material and a microwave
sensitizer. The latent polymer material is inelastic in the latent
state but can be converted to an elastic state with the addition of
heat. The microwave sensitizer is a solid material blended
(preferably uniformly) into the latent polymer material. The
sensitizer absorbs microwave radiation and heats the heat-sensitive
polymer material. The polymer composite becomes elastic due to the
heat from the sensitizer.
[0008] In one embodiment of this invention the latent polymer
composite is bonded to a fibrous sheet to form a laminate material.
When exposed to microwave radiation, the laminate material becomes
elastic. The latent polymer composite of the laminate shrinks and
converts to an elastic state creating an elastic laminate material.
The polymer composite of this invention has a rough surface
produced by the sensitizer particles. The rough surface provides
more surface area for the bonding material to adhere to resulting
in stronger bonding to the fibrous sheets of the laminate. The
stronger bonding in the laminate increases the creep resistance of
the laminate material. The resulting laminate is a strong, elastic
material useful in absorbent articles.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 is a photograph of a cross-section of a polymer
composite strand according to one embodiment of this invention.
[0010] FIG. 2 is a photograph of a cross-section of a polymer
composite strand according to one embodiment of this invention.
[0011] FIG. 3 is a photograph of a polymer composite strand
according to one embodiment of this invention.
[0012] FIG. 4 is a photograph of a polymer composite strand
according to one embodiment of this invention.
[0013] FIG. 5 shows a schematic diagram of creep testing.
[0014] FIG. 6 is a DSC spectra of a polymer without sensitizer
material.
[0015] FIG. 7 is a DSC spectra of a polymer without sensitizer
material stretched to 600%.
[0016] FIG. 8 is a DSC spectra of a composite according to one
embodiment of this invention.
[0017] FIG. 9 is a DSC spectra of a composite according to one
embodiment of this invention.
DEFINITIONS
[0018] Within the context of this specification, each term or
phrase below will include the following meaning or meanings.
[0019] "Absorbent article" includes diapers, training pants, swim
wear, absorbent underpants, adult incontinence products, feminine
hygiene products, absorbent wipes, medical garments, and the like.
The term "medical garment" includes medical (i.e., protective
and/or surgical) gowns, caps, gloves, drapes, face masks, blood
pressure cuffs, bandages, veterinary products, mortuary products,
and the like.
[0020] "Bonded" refers to the joining, adhering, connecting,
attaching, or the like, of two elements. Two elements will be
considered to be bonded together when they are bonded directly to
one another or indirectly to one another, such as when each is
directly bonded to intermediate elements.
[0021] "Cross direction" refers to the width of a fabric in a
direction generally perpendicular to the direction in which it is
produced, as opposed to "machine direction" which refers to the
length of a fabric in the direction in which it is produced.
[0022] "Elastic" means that property of a material or composite by
virtue of which it tends to stretch when exposed to a stretching
force, and to recover most or all of the way to its original size
and shape after removal of the stretching force. An elastic
material should be able to stretch in at least one direction by at
least 50% of its initial (unstretched) length without rupturing,
and should immediately recover more than 50% of the way to its
initial length when the stretching force is removed.
[0023] "Fibrous sheets" is used to refer to all of the woven,
knitted and nonwoven fibrous webs.
[0024] "Film" refers to a thermoplastic film made using a film
extrusion and/or foaming process, such as a cast film or blown film
extrusion process. The term includes apertured films, slit films,
and other porous films which constitute liquid transfer films, as
well as films which do not transfer liquid. The term also includes
film-like materials that exist as open-celled foams.
[0025] "Layer" when used in the singular can have the dual meaning
of a single element or a plurality of elements.
[0026] "Latent" refers to a non-elastic state of a polymer
composite. A latent polymer composite can be made by stretching an
elastic polymer composite to a certain stretched ratio at which the
polymer composite no longer has elastic characteristics. The
stretched polymer composite is in a latent state when there is
substantially less elastic recovery towards the unstreched length
or no elastic recovery at all. The latent polymer composite is
maintained in the latent state by high intermolecular forces, such
as hydrogen bonding or ionic association between polymer molecules,
and/or crystallization of polymer molecules. The polymer composite
can be made latent at about room temperature (.about.23.degree. C.)
or below, or any other temperature when the intermolecular forces
and/or crystals can form. Because latent polymer composites are in
a stretched, non-equilibrium state, they are generally temperature
sensitive. Latent polymer composites can regain elastic
characteristics when the intermolecular forces maintaining the
stretched polymer are overcome by applying thermal energy, such as
melting the crystals holding the polymer composite in the latent
state. The latent polymer composite has little or no recovery
towards the original unstretched length until the crystals are
melted by the addition of heat.
[0027] "Leg elastic" includes elastic bands, strands, ribbons,
filaments, filament bunches and the like, which are adjacent to a
garment opening that receives a wearer's leg.
[0028] "Machine direction" refers to the length of a fabric in the
direction in which it is produced, as opposed to "cross direction"
which refers to the width of a fabric in a direction generally
perpendicular to the machine direction.
[0029] "Microwave activation" refers to the use of microwave energy
to return a latent polymer to its elastic state. Microwave
activation generates heat by microwave radiation which overcomes
the hydrogen bonding, ionic association between polymer molecules,
and/or crystallization of polymer molecules that holds the polymer
in the latent state.
[0030] "Meltblown fiber" means fibers formed by extruding a molten
thermoplastic material through a plurality of fine, usually
circular, die capillaries as molten threads or filaments into
converging high velocity heated gas (e.g., air) streams which
attenuate the filaments of molten thermoplastic material to reduce
their diameter, which may be to microfiber diameter. Thereafter,
the meltblown fibers are carried by the high velocity gas stream
and are deposited on a collecting surface to form a web of randomly
dispersed meltblown fibers. Such a process is disclosed for
example, in U.S. Pat. No. 3,849,241 to Butin et al. Meltblown
fibers are microfibers which may be continuous or discontinuous,
are generally smaller than about 0.6 denier, and are generally self
bonding when deposited onto a collecting surface. Meltblown fibers
used in the present invention are preferably substantially
continuous in length.
[0031] "Nonwoven" and "nonwoven sheets" refer to fibrous materials
and webs of fibrous material which are formed without the aid of a
textile weaving or knitting process.
[0032] "Polymers" include, but are not limited to, homopolymers,
copolymers, such as for example, block, graft, random and
alternating copolymers, terpolymers, etc. and blends and
modifications thereof. Furthermore, unless otherwise specifically
limited, the term "polymer" shall include all possible geometrical
configurations of the material. These configurations include, but
are not limited to isotactic, syndiotactic and atactic
symmetries.
[0033] "Sensitizer material" refers to any material with a high
microwave absorbency that generates thermal energy as a result of
contact with microwave radiation.
[0034] "Spunbonded fiber" refers to small diameter fibers which are
formed by extruding molten thermoplastic material as filaments from
a plurality of fine capillaries of a spinnerette having a circular
or other configuration, with the diameter of the extruded filaments
then being rapidly reduced as by, for example, in U.S. Pat. No.
4,340,563 to Appel et al., and U.S. Pat. No. 3,692,618 to Dorschner
et al., U.S. Pat. No. 3,802,817 to Matsuki et al., U.S. Pat. Nos.
3,338,992 and 3,341,394 to Kinney, U.S. Pat. No. 3,502,763 to
Hartmann, U.S. Pat. No. 3,502,538 to Petersen, and U.S. Pat. No.
3,542,615 to Dobo et al., each of which is incorporated herein in
its entirety by reference. Spunbond fibers are quenched and
generally not tacky when they are deposited onto a collecting
surface. Spunbond fibers are generally continuous and often have
average deniers larger than about 0.3, more particularly, between
about 0.6 and 10.
[0035] "Thermoplastic" describes a polymer material that softens
and flows when exposed to heat and which substantially returns to a
nonsoftened condition when cooled to room temperature.
[0036] "Waist elastic" includes elastic bands, strands, ribbons,
filaments, filament bunches and the like, which are adjacent to a
garment opening that receives a wearer's waist.
[0037] These terms may be defined with additional language in the
remaining portions of the specification.
DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS
[0038] Polymer composites of this invention are useful in personal
care absorbent articles such as diapers. Elastic polymer
composites, such as polymer strands, filaments, or films, are
especially useful in stretchable areas of absorbent articles and
are generally used to fit the absorbent article to the user. In one
embodiment of this invention elastic polymers composites are used
in the waist and/or leg regions of a diaper. The polymer composites
when in the elastic state, provide a snug fit to the user to
diminish leaking of bodily wastes held in the diaper. Using the
latent polymer composites of this invention to manufacture
absorbent articles and then activating the latent polymer material
to become elastic simplifies manufacturing and reduces cost.
[0039] Latent polymer composites of this invention can start out or
be physically changed into a latent state, which is maintainable at
a lower temperature such as room temperature, and can be converted
to an elastic state by an increase in temperature. "Latent" refers
to a non-elastic state of a polymer composite. A latent polymer
composite can be made by stretching an elastic polymer composite to
a certain stretched ratio at which the polymer composite no longer
has elastic characteristics. The stretched polymer composite is in
a latent state when there is substantially less elastic recovery
towards the unstreched length or no elastic recovery at all. The
latent polymer composite is maintained in the latent state by high
intermolecular forces, such as hydrogen bonding or ionic
association between polymer molecules, and/or crystallization of
polymer molecules. The polymer composite can be made latent at
about room temperature (.about.23.degree. C.) or below, or any
other temperature when the intermolecular forces and/or crystals
can form. Because latent polymer composites are in a stretched,
non-equilibrium state, they are generally temperature sensitive.
Latent polymer composites can regain elastic characteristics when
the intermolecular forces maintaining the stretched polymer are
overcome by applying thermal energy, such as melting the crystals
holding the polymer composite in the latent state. The latent
polymer composite has little or no recovery towards the original
unstretched length until the crystals are melted by the addition of
heat. The returning of a latent polymer composites to a state of
equilibrium, in which the polymer is elastic, is referred to as
"activation" of the latent polymer composites. Examples of polymers
that can be used to form composites that can be made latent
include, without limitation, polyethers, polyamines, polyesters,
and polyurethanes.
[0040] Latent polymer composites of this invention are blended
(preferably melt blended) with a microwave sensitizer material
before they are converted to the latent state. FIGS. 1 and 2 are
electron microscope images showing the lighter sensitizer particles
blended within the darker polymer material. Sensitizer materials
react to microwave energy and release heat. The blended polymer
composite can be stretched to form a latent polymer composite. When
microwave energy is applied to the latent polymer composite the
sensitizer material converts the microwave energy to heat. The heat
produced by the sensitizer material activates the latent polymer
composite and returns the latent polymer composite to an elastic
state. Alternatively, the latent polymer composite with blended
sensitizer material can be activated using thermal energy, such as
heat, instead of microwave energy, in the same fashion as a latent
polymer without the sensitizer is activated. Because of the
sensitizer material, activation of the latent polymer composite
with blended sensitizer material by thermal energy is also more
efficient than activation of the latent polymer composite without
blended sensitizer material.
[0041] Polymer materials useful as the latent polymer material of
this invention include thermoplastic elastomers. In one embodiment
of this invention the polymer material is a polyether-b-block
amide. Polyether-b-block amides useful in this invention are
manufactured by Elf ATOCHEM, King of Prussia, Pa., under the
general name PEBAX.RTM.. The structure of PEBAX.RTM. polymers
consist of multiple rigid polyamide blocks and flexible polyether
blocks. A generalized structure is shown by the formula:
HO--{--(CO--NH--R--NHCO).sub.a--[O--R'--O].sub.b--}.sub.n--H
[0042] Through the proper combination of polyamide and polyether
blocks, a wide range of polymers with varying performance
characteristics are possible. PEBAX.RTM. 2533 is one example of a
preferred polymer material because of its good elasticity, low
hysteresis, latency characteristics, and breathability.
[0043] Another polymer material useful in this invention is
manufactured by Exxon, Houston, Tex., under the name Exxon 601.
Exxon 601 is a proprietary polymer (U.S. Pat. Nos. 4,714,735 and
5,182,069) comprising from about 20 to about 30% by weight olefinic
elastomer, from about 60 to 75% by weight ethylene copolymer, from
about 4 to 10% by weight processing oil, and less than about 5% by
weight other additives. Other useful polymer materials include,
without limitation, ethylene-vinylacetate block or random
copolymers, polyethylene-polyethyle- ne oxide block copolymers,
polypropylene oxide-polyethylene oxide block copolymers,
polyesters, polyurethanes, polyacrylates, polyethers, and
combinations thereof.
[0044] Using latent polymer materials in manufacturing absorbent
articles instead of elastic polymers reduces manufacturing steps
and cost. Microwave activatable latent polymer materials provide
additional manufacturing benefits. The polymer material alone,
without a sensitizer material, has a low dielectric loss factor and
therefore is not easily activated by microwave energy. By adding a
sensitizer material which is interactive with microwave radiation
to the polymer material the latent polymer composites can be
quickly activated by microwave energy due to increased dielectric
loss factor.
[0045] Most known sensitizer materials are made from inorganic
chemicals such as aluminum, copper, zinc, oxides of aluminum,
copper, and zinc, and various ferrites including without limitation
barium ferrite, magnesium ferrite, and carbon black. Many known
sensitizer materials generally offer little control of how much
heat is generated and how quickly. Sensitizer materials are
generally coated onto a surface of an object to be heated and the
heat generated slowly permeates the object from the surface inward.
Because the sensitizers heat the surface first, the heating is not
typically uniform throughout the object. Using sensitizer material
in this regard is not unlike the heating done by hot air, where the
hot air heats a surface of an object first and then the energy
gradually permeates the object while raising its overall
temperature. It has been discovered that some sensitizers can be
uniformly blended in solid form with polymer materials to create a
latent polymer/sensitizer composite which, in the presence of
microwave energy, will generate proper, uniform amounts of heat to
activate the latent polymer material. The heat generation by the
blended sensitizers throughout the composite increases the rate of
composite heating and lowers the overall energy necessary to heat
the composite.
[0046] Sensitizer materials useful in this invention include
calcium chloride and carbon black powder. Other sensitizer
materials useful in this invention include, without limitation,
metal particles, metal oxides such as aluminum, copper, zinc, and
their oxides, various ferrite containing materials such as barium
ferrite and magnesium ferrite, magnesium acetate, and combinations
thereof. Polymer composites of this invention contain between about
1% and 20% by weight sensitizer material, more suitably between
about 1% and 15% by weight sensitizer material, and desirably
between about 2% and 8% by weight sensitizer material.
[0047] In one embodiment of this invention a polymer material is
blended with a sensitizer material and the blend is extruded into
polymer filaments. In one embodiment the sensitizer material is
blended into melted polymer material before forming a filament or
film. In one embodiment the polymer-sensitizer blend is mixed by
twine extruder during a melting process and formed into pellets.
The pellets of the compound are extruded by a twine extruder into
filaments. The filaments are then stretched by vertical filament
laminate process to create latent polymer filaments at or below
room temperature. The vertical filament laminate process includes
stretching the extruded filaments using one or more series of
stretch rolls. Each series of stretch rolls may include one or more
individual stretch rolls, and desirably at least two stretch rolls.
Where more than one series of stretch rolls are used, a latter
series of stretch rolls rotates at a speed greater than the speed
of a former series of stretch rolls, thereby stretching the
nonwoven fabric.
[0048] In one embodiment, each successive roll rotates at a speed
greater than the speed of the previous roll. For example, a first
stretch roll may rotate at speed "x"; a second stretch roll rotates
at a speed greater than "x", for example about "1.1x"; a third
stretch roll rotates at a still greater speed, for example about
"1.15x"; and a forth stretch roll rotates at a still greater speed,
for example about "1.25x" to about "2x." As a result, filaments can
be stretched by about 100% to about 800% of an initial length, or
by about 200% to about 700% of an initial length. The stretching
process can be done using various rolls at various speeds or using
other filament stretching processes known in the art.
[0049] Polymer composites of this invention are elastic at room
temperature (.about.23.degree. C.) and must be stretched to a
certain length to place the polymer strands in the non-elastic
latent state. Elastic composites of this invention are generally
stretched at least about 100-800% of the initial non-stretched
length to create a latent polymer composite. The latent polymer
strands are then used as desired in manufacturing an absorbent
article. The latent polymer strands can be activated by exposure to
microwave energy at any time as desired depending on the
manufacturing process and the type of absorbent article made.
Polymer strands of this invention may have a thickness of between
about 0.1 mm and 2.0 mm when in the latent state.
[0050] In one embodiment of this invention the polymer composite
compound is formed into a latent polymer film. The latent polymer
film can be made by any method known in the art such as cast or
blown film extrusion. Polymer composite films of this invention are
formed from molten polymer composite, cooled, and then stretched by
various techniques at about room temperature (.about.23.degree. C.)
to obtain a latent polymer film. Latent polymer strands and films
can be used in the manufacture of absorbent articles and returned
to an elastic state by either microwave energy, thermal energy, or
combinations thereof. The thickness of the elastic polymer films or
filaments can vary depending upon the final use of the films or
filaments. Production of films according to this invention is done
by using a extruder with a film die instead of a filament die.
[0051] In one embodiment of this invention at least one latent
polymer filament is placed between fibrous sheets, such as
thermoplastic nonwoven sheets including without limitation spunbond
or meltblown nonwoven sheets, and bonded to the nonwoven sheets
with or without hot melt adhesive, provided the hot melt adhesive
is not too hot (a temperature below the melting point of the
polymer is generally useable) so the adhesive does not activate the
latent polymer filament, to form latent polymer laminates. The
laminates can be activated either by microwave energy or thermal
energy to return the latent polymer material to an elastic state.
The resulting elastic laminates are useful in absorbent articles.
In one embodiment of this invention the elastic laminates are used
in at least one of a waist region and leg regions of a diaper.
Latent polymer films can also be used to create laminates with
nonwoven sheets.
[0052] Microwave energy is an electromagnetic energy which has
wavelengths from 1.0 centimeters to 1.0 meters corresponding to
frequencies in the range of 3.times.10.sup.8 to 3.times.10.sup.10
hertz. Frequencies suitable for use in this invention for
activating latent polymer composites are either 2415 megahertz or
915 megahertz. Generally, microwave energy is absorbed by molecules
through the polarization or dipole reorientation of the functional
groups, and/or by ionic movements, which is translated into thermal
energy. As a result, materials can be heated using microwave
irradiation at the molecular level. The heat is generated within
each molecule and thereby a uniform heating pattern can be created
in the material. In this manner, the material can be heated very
efficiently as compared to conventional heating.
[0053] Microwave heating of a material is dependent on the
dielectric properties of the material. The dielectric properties of
a material can be described by two parameters, the dielectric
constant and the dielectric loss factor. If the dielectric loss
factor is too low, the material will not absorb microwave
radiation, regardless of microwave power. The higher the dielectric
loss factor of the material, the higher the heating rate can be.
Generally, it is desired that a sensitizer material of this
invention will permit the microwave power to be greater than about
800 watts, more desirably to be greater than about 3.0 kilowatts,
and most desirably greater than 6.0 kilowatts. The greater the
dielectric loss factor of the sensitizer material and the greater
amount of sensitizer material, the greater the amount of heat
released and the greater the rate and degree of shrinking capacity.
Polymer composites of this invention suitably contain between about
10% and 20% by weight sensitizer material, more suitably between
about 10% and 15% by weight sensitizer material, and desirably
between about 2% and 8% by weight sensitizer material.
[0054] Desirably the sensitizer material is activated using a high
speed microwave activation process. The process desirably uses a
microwave oven set at a power of 900 watts and a frequency of about
2450 megahertz. Conventional microwave ovens can be used to
activate the sensitizer material.
[0055] Blending solid particles of a microwave material into a
polymer material to create a polymer filament or film has an
additional benefit in that the resulting strand or film has a rough
surface texture. As shown in FIG. 3, a PEBAX.RTM. polymer filament
has a smooth surface texture both in a latent state and a elastic
state. As shown in FIG. 4, a PEBAX.RTM. polymer filament having a
microwave sensitizer material according to this invention has a
rough surface texture. In one embodiment of this invention the
rough surface texture of the latent polymer filament having a
sensitizer material provides a stronger bonding to nonwoven sheets.
The rough surface of the latent polymer filament allows better
bonding of an adhesive material and results in a stronger polymer
strand/nonwoven sheet laminate.
[0056] Latent polymer composites of this invention have sensitizer
materials distributed fairly uniformly throughout the latent
polymer composite. In one embodiment of this invention the amount
of sensitizer material in the latent polymer composite is suitably
at least about 0.1 grams sensitizer material/gram polymer material.
Suitably the amount of sensitizer material in the latent polymer
composite is about 10% to 20% by weight. The uniform distribution
provides even heating of the latent polymer composite when exposed
to microwave energy and a uniform rough surface texture provides
better bonding with adhesive materials. Uniform heating can also be
influenced by sensitizer particle size. Sensitizer particle
diameter can vary and is suitably in a range from sub-micron to
about 10 microns. In one embodiment of this invention the suitable
average diameter of the sensitizer particles is about 0 and 25
microns, more suitably between about 5 and 10 microns, and
desirably between about 1.5 and 2.5 microns.
[0057] In one embodiment of this invention, an activated laminate
has improved elastic composite creep resistance. "Activated
laminate" refers to a laminate material having at least one latent
polymer composite with sensitizer material as one layer of the
laminate, and wherein the latent polymer composite has been
activated by thermal or microwave energy to return to an elastic
state. When the polymer composites of the laminate material are
latent polymer composites then the laminate material is referred to
as a latent laminate material.
[0058] It is fairly difficult to securely bond a pure PEBAX.RTM.
latent strand in a laminate by conventional hot melt adhesive. Upon
activation the PEBAX.RTM. strand loses adhesion due to structure
and morphology changes. Due to the lost adhesion, the activated
polymer strands move within the laminate. This movement is referred
to as "creeping." Activated PEBAX.RTM. strands, as an example,
typically exhibit more than 50% creep when used in a nonwoven
laminate. It has been discovered that a latent polymer composite
having a blended sensitizer material not only has a faster
microwave and hot air activation speed, but also exhibits less
creep than a latent polymer composite without a sensitizer
material. Less creep of the polymer composites of this invention is
due in part to the bonding improvement of the rough surface texture
and the surface tension change.
[0059] A sample creeping test is shown in FIG. 5. Elastic strands
30 are spaced apart approximately 2.5 mm in the cross-direction,
each elongated approximately 150% to 300% and adhesively attached
and sandwiched between two 4-inch wide continuous polypropylene
spunbonded layers 34 to form a laminate. The laminate is fully
extended by hanging a weight (about 500 grams or higher) at one end
of the laminate, and a first machine-direction length 40 is then
marked. The laminate is then released, such that the first
machine-direction length 40 is snapped back to a second
machine-direction length 45, whereupon the second machine-direction
length 45 is marked. The laminate is then stapled to a piece of
cardboard at the second machine-direction length 45. The marked
length of the laminate is then cut to release tension in the
elastic strands 30, and the snapback length 50 of the strands is
measured.
[0060] Initial creep percentage is calculated by first determining
the difference between the second machine-direction length 45
(second length) and the snapback length 50, then dividing the
difference by the second machine-direction length 45 and
multiplying the quotient by 100, as shown in the following
equation:
Initial Creep %=(second length-snapback length)/second
length.times.100
[0061] The sample is then placed in an oven at 100.degree.
Fahrenheit, or other suitable temperature, for 90 minutes to
measure aging creep. Aging creep percentage is then calculated by
determining the difference between the second machine-direction
length 45 and that snapback length 50, then dividing the difference
by the second machine-direction length 45 and multiplying the
quotient by 100, as shown in the following equation:
Aging Creep %=(second length-aged snapback length)/second
length.times.100
[0062] Snapback length readings used in the calculations can be an
average of the snapback length of multiple samples.
[0063] Activated laminates having polymer strands having blended
sensitizer materials according to this invention exhibit less
creeping than activated laminates having polymer strands without
sensitizer materials. Activated laminates having polymer strands
having blended sensitizer materials according to this invention
generally exhibit a creeping percentage less than about 50%, more
suitably less than about 30%, more suitably less than 20%, and most
suitably less than 10%. Laminates made with PEBAX.RTM. not having
blended sensitizer material typically creep about 50% to 70% and
laminates made with PEBAX.RTM. having blended sensitizer material
according to this invention creep at about less than 30% and
typically about 10% to 15%.
[0064] To further illustrate the invention and demonstrate some of
the advantages the following examples were prepared. The examples
are not intended to limit the invention and it should be understood
that variations of these examples are available which would also
demonstrate the invention.
EXAMPLES
[0065] A blend of PEBAX.RTM. 2533 (92% by weight) and calcium
chloride, CaCl.sub.2.2H.sub.2O, (8.0% by weight) was premixing
manually and then compounded by a Brabender twine extruder
available from C.W. Brabender Instruments, Inc., New Jersey, in the
temperature range of about 200-235.degree. C. Thermal analysis of
PEBAX.RTM. 2533 (PEBAX) and the blends (PEBAX/CaCl.sub.2 blend) was
performed by differential scanning calorimetry (DSC) and
thermogravimetric analysis (TGA).
[0066] Thermogravimetric analysis measurements were carried out
using TA Instruments 951 Thermal Gravimetric Analyzer connected to
a 2100 Controller. The samples were heated from room temperature to
450.degree. C. with a heating rate of 10.degree. C./min under a
dynamic atmosphere of air with air flow of approximately 80 ml/min.
A separate control sample PEBAX was analyzed at 10.degree. C./min
under a dynamic atmosphere of nitrogen (N.sub.2) with a flow of 80
ml/min. The flow rate was monitored with a flow cell having a scale
of 0 to 100 ml/min.
[0067] The thermal and oxidation stability of PEBAX and the
PEBAX/CaCl.sub.2 blend were evaluated by TGA in nitrogen and air
separately. Thermograms for PEBAX showed oxidation degradation in
air occurring at about 195.degree. C. and thermal degradation in a
nitrogen atmosphere at about 350.degree. C. Thermograms for the
PEBAX/CaCl.sub.2 blend showed degradation in air at about
350.degree. C., representing an increased oxidative stability in
air over pure PEBAX. The enhanced thermal oxidative stability of
PEBAX/CaCl.sub.2 blend may be due to physical crosslinking in which
the Ca.sup.+2 associated with the carbonyl or ether groups of PEBAX
and limited oxygen penetration into the blend.
[0068] Differential Scanning Calorimetry analysis was performed
using a TA Instruments 2920 Differential Scanning Calorimeter (DSC)
with both a single sample cell and a dual sample cell. The samples
tested included PEBAX pellets, PEBAX strands stretched to 400%,
600%, and 800%, PEBAX/CaCl.sub.2 blend pellets, and
PEBAX/CaCl.sub.2 blend strands stretched to 700%. The samples were
heated from--100.degree. C. to 250.degree. C. at a rate of
10.degree. C./min under a dynamic atmosphere (50 ml/min) of
nitrogen for the PEBAX samples and air for the PEBAX/CaCl.sub.2
blend samples.
[0069] FIG. 6 shows a DSC spectrum for PEBAX pellets. FIG. 7 shows
a DSC spectrum for PEBAX strands stretched to 600%. The DSC spectra
of PEBAX strands stretched to 400%, 600%, and 800% clearly
indicated that latency of a PEBAX strand is due to stress inducing
crystallization. The DSC spectra of the stretched PEBAX strands
showed the crystallization peak in the range of about 40.degree. C.
to 45.degree. C. for each stretch ratio. Taking into account
instrument error, one can see the melting point of the PEBAX is not
substantially related to the stretch ratio. Furthermore, the DSC
spectra showed the enthalpy of melting (.DELTA.H J/g) was increased
as the stretching percent increased, which indicated more
crystallization of the polymer chains occurred at a higher stretch.
Table 1 summarizes the stress-induced crystallization and melting
points of PEBAX strands under different stretching ratios.
1TABLE 1 Stress-induced Stretch crystallization Melting (%)
(.DELTA.H J/g) Point (.degree. C.) 400 46.1 43.4 600 54.4 41.2 800
86.1 45.8
[0070] PEBAX/CaCl.sub.2 blend pellets and strands stretched to
about 700% original size were also tested by DSC. FIG. 8 shows a
DSC spectrum of PEBAX/CaCl.sub.2 blend pellets. FIG. 9 shows a DSC
spectra for PEBAX/CaCl.sub.2 blend strands stretched to 700%. As
shown in FIG. 8 the melting point of the PEBAX/CaCl.sub.2 blend
pellets was at about 30.degree. C. (the peak at about 9.54.degree.
C. is the melting point of the polyether block of the PEBAX) as
compared to the melting point of the PEBAX pellets of about
7.52.degree. C. As shown in FIG. 9 the melting point of the
PEBAX/CaCl.sub.2 blend is at about 28.50.degree. C. as compared to
about 41.2 the PEBAX strand at 600%. In addition to having lower
melting points the PEBAX/CaCl blend samples exhibited a lower
enthalpy of melting. The lower melting point and lower enthalpy of
melting of the PEBAX/CaCl.sub.2 blend than the PEBAX results in
less energy required for activation.
[0071] The morphology of strands and pellets of the PEBAX and
PEBAX/CaCl.sub.2 blend was studied by scanning electron microscopy
(SEM). Each sample was sectioned to provide a smooth, flat surface
for electron imaging. Visualization of the calcium chloride
particles within the PEBAX matrix was optimized using atomic number
contrast imaging in the SEM. Backscatter electron images were
collected from the planed block faces using a Galileo Electronics
microchannel plate electron detector (MOP) in a JEOL 6400 scanning
electron microscope at 1.4 kV for direct imaging of the sample
(without coating covered). Bright phase particle imaging and X-ray
analysis confirmed the uniform displacement of the calcium chloride
particles in the PEBAX. The average particle size was measured by a
PGT MIX microanalyzer system.
[0072] The PEBAX and PEBAX/CaCl.sub.2 blend were used to make
laminates for testing differences in activation rates by microwave
and hot air and also for creep testing. The PEBAX laminate was used
as a control to see the benefits of the PEBAX/CaCl.sub.2 blend.
Laminates were made by attaching one of PEBAX or PEBAX/CaCl.sub.2
blend to 0.4 osy polypropylene spunbond fabric by hot melt
adhesives H2800 and H2096, available from AtoFindley Adhesives,
Inc., Milwaukee, Wis. PEBAX and PEBAX/CaCl.sub.2 blend strands were
made by a vertical filament lamination extrusion system. The
filaments were extruded and stretched 700% between the nips of two
rollers and had a final basis weight of 50-70 gsm. The stretched
latent filaments were then sandwiched and glued between two 0.4 osy
spunbond layers with 12 gsm hot melt adhesive H-2096. The laminate
size was 55.times.200 mm with about 11-12 strands in each laminate.
The resulting laminate was maintained in a flat, non-elastic state
with minimal relaxation before activation.
[0073] Microwave energy and conventional hot air were each used to
activate both the PEBAX and PEBAX/CaCl.sub.2 blend laminates. A
conventional microwave-cooking oven (Sharp Mode Carousel) was used
as a screen tool for primary evaluation of microwave sensitivity of
the laminates. The output power of the microwave oven was 900 W
with a frequency of 2450 MHZ and the microwave had a Teflon support
plate to minimize microwave energy absorption by the glass plate.
Hot air activation of the laminates was done using a forced-air
oven at both 60.degree. C. and 75.degree. C. at time periods to get
maximum shrinkage as a comparison to the microwave activation
process.
[0074] Activation of the laminate samples were carried out in both
the conventional oven and a microwave oven separately. The results
of the percent shrinkage of the laminates at various times during
activation are summarized in Table 2. Percent shrinkage of the
laminates at a given time is equal to the original length minus the
length after activation divided by the original length. The greater
the percent shrinkage the more activation of the laminates has
occurred. A higher shrinkage of the laminate by one activation
method than another at the same activation time indicates higher
efficiency of that activation method. The results in Table 2
indicate that both microwave and hot air activation of the
PEBAX/CaCl.sub.2 blend are more efficient than those of pure PEBAX
strands stretched at the same ratio.
2 TABLE 2 Time (seconds) 3 4 5 10 15 30 Microwave 0 0 0 23% 30% 47%
PEBAX Microwave .about.35% .about.45% .about.50% .about.50% PEBAX
Blend 75.degree. C. Hot Air 42% 54%* 56% 58% PEBAX 75.degree. C.
Hot Air 60% 62%* 62% 62% PEBAX Blend 60.degree. C. Hot Air 45% 50%
PEBAX 60.degree. C. Hot Air 56% 60% PEBAX Blend (*these results
were recorded at 8 seconds)
[0075] The PEBAX and PEBAX/CaCl.sub.2 blend laminates were then
tested according to a creeping test. The laminates were in the
nonelastic latent state originally, then activated either by
microwave or hot air to gain maximum elasticity (activation). The
activated laminates had about a 100 mm length. The activated
laminates were fully extended and released back 25% (to a length of
about 130-135 mm), stapled to a piece of cardboard, marked at 100
mm, the original length, and cut at the marked length. Initial
creep percent was taken by measuring the snapback length from the
original 100 mm mark after cutting, and divided by the original
length 100 mm. The sample was then placed in an oven at 100.degree.
F. for 90 minutes to measure aged creeping. Aging creep percent was
then calculated by measuring the snapback length of the strands and
dividing by 100 mm.
[0076] Not only did the PEBAX/CaCl.sub.2 blend exhibit a much
faster microwave and hot air activation rate, the PEBAX/CaCl.sub.2
blend also showed greater creeping resistance than the pure PEBAX
strands. The pure PEBAX strands had an initial creep of about
50-60% and an aged creep of about 55%-60%. The PEBAX/CaCl.sub.2
blend had an initial creep of 15-25% and an aged creep of about
25-30%. The greater creep resistance of the PEBAX/CaCl.sub.2 blend
is most likely due to the rough surface and surface tension change
created by the calcium chloride particles, resulting in better
bonding to the substrate.
[0077] While the embodiments of the invention described herein are
presently preferred, various modifications and improvements can be
made without departing from the spirit and scope of the invention.
The scope of the invention is indicated by the appended claims, and
all changes that fall within the meaning and range of equivalents
are intended to be embraced therein.
* * * * *