U.S. patent application number 11/048408 was filed with the patent office on 2006-08-03 for transverse-direction, elastomeric, breathable film.
Invention is credited to William T. Champion.
Application Number | 20060172137 11/048408 |
Document ID | / |
Family ID | 36756924 |
Filed Date | 2006-08-03 |
United States Patent
Application |
20060172137 |
Kind Code |
A1 |
Champion; William T. |
August 3, 2006 |
Transverse-direction, elastomeric, breathable film
Abstract
The present invention provides a multilayer film preferably
comprising two skin layers, each preferably comprising low density
polyethylene, two outer core layers, preferably comprising an
additive and a styrene block copolymer, and an inner core layer
preferably comprising an additive and a styrene block
copolymer.
Inventors: |
Champion; William T.;
(US) |
Correspondence
Address: |
MCANDREWS HELD & MALLOY, LTD
500 WEST MADISON STREET
SUITE 3400
CHICAGO
IL
60661
US
|
Family ID: |
36756924 |
Appl. No.: |
11/048408 |
Filed: |
February 1, 2005 |
Current U.S.
Class: |
428/421 ;
428/516; 428/518; 428/520 |
Current CPC
Class: |
B32B 2309/14 20130101;
B32B 2264/104 20130101; Y10T 428/31928 20150401; Y10T 428/31913
20150401; Y10T 428/249986 20150401; B32B 2250/40 20130101; Y10T
428/3192 20150401; B32B 2307/724 20130101; B32B 27/32 20130101;
Y10T 428/3154 20150401; Y10T 428/31917 20150401; Y10T 428/24998
20150401; Y10T 428/31931 20150401; B32B 2307/51 20130101; B32B
2250/24 20130101; B32B 27/18 20130101; B32B 2307/7265 20130101;
B32B 27/08 20130101; Y10T 428/31938 20150401; B32B 2307/736
20130101; B32B 2555/02 20130101; B32B 27/302 20130101; Y10T
428/31909 20150401 |
Class at
Publication: |
428/421 ;
428/516; 428/518; 428/520 |
International
Class: |
B32B 27/08 20060101
B32B027/08; B32B 27/30 20060101 B32B027/30; B32B 27/32 20060101
B32B027/32 |
Claims
1. A multilayer film comprising: a first layer comprising at least
one polyolefin polymer; and a second layer comprising an additive,
and at least one polymer compound selected from the group
consisting of high performance thermoplastic rubber, polyolefin
polymers, ethylene copolymer resins, styrene block copolymers,
fluoropolymers, polyvinylchloride, and mixtures thereof.
2. The film of claim 1 wherein said polymer compound of said second
layer comprises a metallocence-catalyzed polymer.
3. The film of claim 1 wherein said additive is a neutralizer.
4. The film of claim 3 wherein said additive is calcium
carbonate.
5. A multilayer film comprising: a first skin layer comprising at
least one polyolefin polymer; a core layer comprising an additive,
and at least one polymer compound selected from the group
consisting of high performance thermoplastic rubber, polyolefin
polymers, ethylene copolymer resins, styrene block copolymers,
fluoropolymers, polyvinylchloride, and mixtures thereof; and a
second skin layer comprising at least one polyolefin polymer,
wherein said core layer is situated between said first skin layer
and said second skin layer.
6. The film of claim 5 wherein said additive is a neutralizer.
7. The film of claim 6 wherein said additive is calcium
carbonate.
8. The film of claim 4 wherein said core layer comprises: a first
outer core layer comprising an additive, and at least one polymer
compound selected from the group consisting of polyolefin polymers,
ethylene copolymer resins, styrene block copolymers,
fluoropolymers, polyvinylchloride, and mixtures thereof, wherein
said at least one polymer compound is a metallocene-catalyzed
polymer, an inner core layer comprising an additive, and at least
one polymer compound selected from the group consisting of high
performance thermoplastic rubber, polyolefin polymers, ethylene
copolymer resins, styrene block copolymers, fluoropolymers,
polyvinylchloride, and mixtures thereof; and a second outer core
layer comprising an additive, and at least one polymer compound
selected from the group consisting of polyolefin polymers, ethylene
copolymer resins, styrene block copolymers, fluoropolymers,
polyvinylchloride, and mixtures thereof, wherein said at least one
polymer compound is a metallocene-catalyzed polymer, wherein said
inner core layer is situated between said first out core layer and
said second out core layer.
9. The film of claim 8 wherein the additive comprising said inner
core layer and said first and second outer core layers is a
neutralizer.
10. The film of claim 9 wherein the additive comprising said inner
core layer and said first and second outer core layers is calcium
carbonate.
11. A multilayer film comprising: a first skin layer comprising at
least one polyolefin polymer; a first outer core layer comprising
an additive and further comprising a styrene block copolymer; an
inner core layer comprising an additive and further comprising a
styrene block copolymer; a second outer core layer comprising an
additive and further comprising a styrene block copolymer; and a
second skin layer comprising at least one polyolefin polymer,
wherein said inner core layer is situated between said first and
second outer core layers, and wherein said first and second outer
core layers are situated between said first and second skin
layers.
12. The multilayer film of claim 11 wherein the at least one
polyolefin polymer in said first and second skin layers includes
low density polyethylene.
13. The multilayer film of claim 12 wherein said first and second
outer core layers further include a metallocene-catalyzed
polyolefin polymer.
14. The multilayer film of claim 13 wherein the additive in said
inner core layer and said first and second outer core layers
includes calcium carbonate.
15. The multilayer film of claim 11 wherein the additive in said
inner core layer and said first and second outer core layers
includes calcium carbonate.
16. The multilayer film of claim 12 wherein the styrene block
copolymer of said first and second outer core layers includes
styrene-ethylene/butylene-styrene elastomer.
17. The multilayer film of claim 16 wherein said first and second
outer core layers further include a metallocence-catalyzed
polyolefin polymer.
18. The multilayer film of claim 17 wherein the additive in said
inner core layer and said first and second outer core layers
includes calcium carbonate.
19. The multilayer film of claim 16 wherein the additive in said
inner core layer and said first and second outer core layers
includes calcium carbonate.
20. The multilayer film of claim 16 wherein the styrene block
copolymer of said inner core layer includes
styrene-ethylene/butylene-styrene elastomer.
21. The multilayer film of claim 20 wherein said first and second
outer core layers further include a metallocence-catalyzed
polyolefin polymer.
22. The multilayer film of claim 21 wherein the additive in said
inner core layer and said first and second outer core layers
includes calcium carbonate.
23. The multilayer film of claim 20 wherein the additive in said
inner core layer and said first and second outer core layers
includes calcium carbonate.
24. The multilayer film of claim 11 wherein the styrene block
copolymer of said first and second outer cores includes
styrene-ethylene/butylene-styrene elastomer.
25. The multilayer film of claim 24 wherein said first and second
outer core layers further include a metallocence-catalyzed
polyolefin polymer.
26. The multilayer film of claim 25 wherein the additive in said
inner core layer and said first and second outer core layers
includes calcium carbonate.
27. The multilayer film of claim 24 wherein the additive in said
inner core layer and said first and second outer core layers
includes calcium carbonate.
28. The multilayer film of claim 24 wherein the styrene block
copolymer of said inner core layer includes
styrene-ethylene/butylene-styrene elastomer.
29. The multilayer film of claim 28 wherein said first and second
outer core layers further include a metallocence-catalyzed
polyolefin polymer.
30. The multilayer film of claim 29 wherein the additive in said
inner core layer and said first and second outer core layers
includes calcium carbonate.
31. The multilayer film of claim 28 wherein the additive in said
inner core layer and said first and second outer core layers
includes calcium carbonate.
32. The multilayer film of claim 11 wherein the styrene block
copolymer of said inner core layer includes
styrene-ethylene/butylene-styrene elastomer.
33. The multilayer film of claim 32 wherein said first and second
outer core layers further include a metallocence-catalyzed
polyolefin polymer.
34. The multilayer film of claim 33 wherein the additive in said
inner core layer and said first and second outer core layers
includes calcium carbonate.
35. The multilayer film of claim 32 wherein the additive in said
inner core layer and said first and second outer core layers
includes calcium carbonate.
36. The multilayer film of claim 12 wherein the styrene block
copolymer of said inner core layer includes
styrene-ethylene/butylene-styrene elastomer.
37. The multilayer film of claim 36 wherein said first and second
outer core layers further include a metallocence-catalyzed
polyolefin polymer.
38. The multilayer film of claim 37 wherein the additive in said
inner core layer and said first and second outer core layers
includes calcium carbonate.
39. The multilayer film of claim 36 wherein the additive in said
inner core layer and said first and second outer core layers
includes calcium carbonate.
40. The multilayer film of claim 11 wherein said first and second
skin layers comprise from about 2% to about 4% by weight of said
film.
41. The multilayer film of claim 11 wherein said inner and outer
core layers comprise from about 36% to about 45% by weight of said
film.
42. The multilayer film of claim 11 wherein said inner core layer
comprises from about 48% to about 60% by weight of said film.
43. The multilayer film of claim 20 wherein said first and second
skin layers comprise from about 2% to about 4% by weight of said
film.
44. The multilayer film of claim 20 wherein said inner and outer
core layers comprise from about 36% to about 45% by weight of said
film.
45. The multilayer film of claim 20 wherein said inner core layer
comprises from about 48% to about 60% by weight of said film.
46. The multilayer film of claim 11 wherein the additive in said
first and second outer core layers and said inner core layer
comprises calcium carbonate.
47. The multilayer film of claim 11 wherein said first and second
skin layers further comprise at least one additive selected from
the group consisting of antioxidants and anti-blocking agents.
48. The multilayer film of claim 20 wherein said first and second
skin layers further comprise at least one additive selected from
the group consisting of antioxidants and anti-blocking agents.
49. A multilayer film comprising: a first skin layer comprising low
density polyethylene; a first outer core layer comprising calcium
carbonate, styrene-ethylene/butylene-styrene elastomer, and
metallocene-catalyzed linear low-density polyethylene; an inner
core layer comprising calcium carbonate and
styrene-ethylene/butylene-styrene elastomer; a second outer core
layer comprising calcium carbonate,
styrene-ethylene/butylene-styrene elastomer, and
metallocene-catalyzed linear low-density polyethylene; and a second
skin layer comprising low density polyethylene, wherein said inner
core layer is situated between said first and second outer core
layers, and wherein said first and second outer core layers are
situated between said first and second skin layers.
50. The multilayer film of claim 49 wherein said first and second
skin layers further include at least one additive selected from the
group consisting of antioxidants and antiblocking agents.
51. The multilayer film of claim 49 wherein said first and second
skin layers each comprise from about 1% to about 2%, by weight, of
said film, said first and second outer core layers each comprise
from about 18% to about 24%, by weight, of said film, and said
inner core layer comprises from about 48% to about 60%, by weight,
of said film.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates generally to synthetic films
and, more specifically, to a transverse-direction elastomeric film
having a microporous, breathable structure. The present film
preferably has a five-layer structure having generally the
following arrangement: skin/outer core/inner core/outer
core/skin.
[0002] Plastic films are used in a variety of applications. Such
films range from single-layer polymers to multilayer structures
with various tie layers and copolymers included therein. The use of
multiple layers allows for the custom adaptation of a film to meet
certain property requirements, ranging from barrier requirements to
strength requirements.
[0003] One use of such films is to provide a barrier layer in
diapers, absorbent pads, and the like. In uses wherein the product
containing the film contacts human skin for a prolonged period of
time, such as for example with diapers, the skin of the person
being so contacted is likely to develop a rash or other irritation.
Conventional films do not adequately address this problem. What is
needed, therefore, is a multilayer film adapted to provide the
physical properties desired for films used in diapers and the like,
while at the same time made breathable in order to reduce or
eliminate rashes and other irritation.
BRIEF SUMMARY OF THE INVENTION
[0004] In one embodiment of the present invention the multilayer
film of the present invention includes a first layer composed of at
least one polyolefin polymer. A second layer is also provided,
including at least one polymer compound, which may be a polyolefin
polymer, an ethylene copolymer resin, a styrene block copolymer, a
fluoropolymer, polyvinylchloride, or any other suitable polymer or
mixtures thereof.
[0005] In one alternative embodiment of the present invention, the
second layer of the multilayer film includes a
metallocene-catalyzed polymer. In another embodiment of the present
invention, the second layer further includes an additive, such as
calcium carbonate or other suitable additive.
[0006] In a preferred embodiment, the film of the present invention
has five layers, including two skin layers preferably comprising
low density polyethylene, two outer core layers, preferably
comprising and additive and a styrene block copolymer, and an inner
core layer, preferably comprising an additive and a styrene block
copolymer.
[0007] In a preferred embodiment of the invention, the skin layers
further include at least one additive, such as an antioxidant or
antiblocking agent. Further, the outer core layers preferably
include a metallocene-catalyzed polymer such as
metallocene-catalyzed linear low density polyethylene. The additive
in the inner and outer core layers is preferably calcium
carbonate.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1 is a cross-sectional view of a five-layer film
constructed in accordance with the teachings of the present
invention.
DETAILED DESCRIPTION OF THE INVENTION
[0009] The multilayer film of the present invention has a structure
that includes at least one first layer of at least one polyolefin
polymer, and at least one second layer which includes at least one
compound selected from metallocene-catalyzed polyolefin polymers,
ethylene copolymer resins, styrene-ethylene/butylene-styrene block
copolymers, and mixtures thereof. The total thickness of the film
may vary depending upon the intended application of the film. The
preferred film has a thickness of from about 1.25 mils to about 1.5
mils and, more preferably, of about 1.34 mils (about 30 g/m.sup.2).
The thickness of individual layers is preferably from about 0.025
mils to about 0.75 mils, and more preferably about 0.60 mils.
[0010] Turning now to FIG. 1, a preferred embodiment of the present
invention has five layers in the following configuration: skin
layer/outer core/inner core/outer core/skin layer. In the figure,
the skin layers are represented by the letter `B,` the outer core
layers are represented by the letter `A,` and the inner core layer
is represented by the letter `C.` In this embodiment of the present
invention, it is preferred that each skin layer comprise about
1%-2% by weight of the total film, or, preferably about 1%-1.5% by
weight of the total film or more preferably, comprise about 1% by
weight of the total film. It is also preferred, in this embodiment,
that each outer core layer comprise about 18%-24%, by weight, of
the total film, or preferably about 20%-24% by weight of the total
film, or more preferably about 24% by weight of the total film.
Finally, in this embodiment it is preferred that the inner core
comprise about 48%-60% by weight of the total film, or preferably
about 48%054% by weight of the total film, or more preferably about
48% by weight of the total film. It will be appreciated by those
skilled in the art, however, that the thickness of each individual
layer may vary from the preferred thicknesses given above.
[0011] The multilayer film of the present invention may be produced
by conventional methods used in producing multilayer films,
including coextrusion and extrusion lamination techniques. For
example, the film may be formed by coextrusion. Using this method,
melted and plasticized streams of individual layer materials are
fed into a coextrusion die. While in the die, the layers are
juxtaposed and combined, after which they emerge from the die in a
single multilayer film of polymeric material. Suitable coextrusion
techniques are fully described in U.S. Pat. Nos. 5,139,878 and
4,677,017, incorporated herein by reference to the extent permitted
by law. Coextrusion of the present film may be conducted at
temperatures of from about 400.degree. F. to about 510.degree. F.
Coextrusion techniques include the use of a feed block with a
standard die, a multi-manifold die, such as a circular die, as well
as a multi-manifold die such as used in forming flat cast films and
cast sheets. The multilayer films of the present invention may also
be made by blown film coextrusion. The film is formed using a blown
film apparatus composed of a multi-manifold circular die head
having concentric circular orifices. The multilayer film is formed
by coextruding a molten layer through a circular die, and a molten
layer on the other or each opposite side of the first layer through
additional circular dies concentric with the first circular die.
Next, a gas, typically air, is blown through a jet that is
concentric with the circular dies, thereby forming a bubble that
expands the individual layers. The bubble is collapsed onto itself
to form a pair of multilayer films attached at two opposite edges.
Usually, the pair of attached multilayer films are then cut apart
at one or more of the edges and separated into a pair of multilayer
films that can be rolled up. It is preferred that the films of the
present invention are geared from a flat cast process. An example
of the preferred process is provided below.
EXAMPLE 1
Method of Producing Films of the Present Invention
[0012] A preferred method for producing the films of the present
invention is now described. As a first step, components are blended
at a loss-in-weight blender and combined in the desired proportions
(described more fully with respect to specific films, below), then
sent to the feed portion of an extruder. This process allows for
dry-blending of ingredients, thereby avoiding the need to utilize
more expensive, fully compounded blends. Dedicated extruders mix,
melt, and meter the components to a specific film layer. A feed
block and flow plate channel three melt streams into a five layer
configuration. The three melt streams are A) the outer core; B) the
skin; and C) the inner core. The five layer configuration of the
melt streams is as follows: B-A-C-A-B. A flat, single slot die
extrudes the film onto a smooth chill cast roll, producing the flat
film product. Next, a series of pre-heat, draw, and annealing rolls
provide the film with sufficient machine-direction orientation to
induce the formation of micro voids in the structure. These pores
allow for water vapor transmission, but are too small to allow
passage of liquid. The process of machine-direction orientation
also results in minimal forces required for transverse-direction
elongation. The choice of elastomeric material helps ensure
adequate stretch and recovery, and conformance to stated physical
property requirements. Machine-direction relaxation follows, to
minimize film shrinkage in subsequent, downstream operations. The
film is allowed to retract 10%-25% prior to winding.
[0013] In the preferred film, the outer skin layers each comprise
about 1%-2% by weight of the total film, and are preferably
comprised of at least one polyolefin polymer. Preferred polyolefin
polymers include polyethylene, polypropylene, polybutenes,
polyisoprenes, copolymers thereof, terpolymers thereof,
.alpha.-olefin propylene copolymers, and mixtures thereof. Any
other suitable polyolefin polymers may be used. Suitable
polyethylenes include, in particular, low density polyethylene
(LDPE), linear low density polyethylene (LLDPE), and ultra low
density polyethylene (ULDPE). Particularly preferred is "barefoot"
grade LDPE. Preferred propylene polymers generally have a melting
point of 180.degree. C. or above. Preferred propylene polymers
further generally have a melt flow index of from about 0.5 g/10 min
to about 10 g/10 min at 230.degree. C., and a force of about 21.6N.
Isotactic propylene homopolymer having an n-heptane-soluble content
of from about 1-15% by weight, copolymers of propylene with
C.sub.4-C.sub.8 .alpha.-olefins having an .alpha.-olefin content of
10% by weight or less, and terpolymers of propylene, ethylene, and
butylene having an ethylene content of 10% by weight or less and a
butylene content of 15% by weight or less are preferred propylene
polymers. Also suitable is a mixture of propylene homopolymers,
copolymers, terpolymers, and other polyolefins. The skin layers
serve, among other functions, to protect from die buildup, and to
minimize or prevent film blocking or sticking. The skin layers may
further include additives such as antioxidants or antiblocking
agents.
[0014] In the preferred film, the outer core layers each comprise
about 18%-24%, and preferably about 24%, by weight of the film as a
whole. Each outer core layer preferably comprises about 67% by
weight of a neutralizer, such as CaCO.sub.3 (preferably provided in
the form of a calcium carbonate super concentrate, described
below), about 26% by weight of a styrene-ethylene/butylene-styrene
(SEBS) polymer, such as, for example, Kraton 1657 available from
Kraton Polymers (Houston, Tex.), and about 7% by weight of a
metallocene-catalyzed polyolefin polymer, such as, for example, the
ethylene .alpha.-olefin resin Dow PL 1280, available from Dow
Chemical Company (Midland, Mich.). Other suitable elastomers may be
used in place of the SEBS polymer described above, such as Kraton
6571 and Kraton 6936. Likewise, other suitable
metallocene-catalyzed polymers may be used in place of the
metallocene-catalyzed polyolefin polymers described above. The
outer core layers serve, among other functions, to provide
breathability, some elastomeric performance, durability (with
metallocene-catalyzed polymer), and block-resistant qualities.
[0015] In the preferred film, the inner core layer comprises
approximately 48%-60% by weight of the film. The inner core layer
preferably comprises about 67% by weight of a neutralizer such as
CaCO.sub.3 (preferably provided in the form of a calcium carbonate
super concentrate, described below), and about 33% by weight of a
high SEBS block copolymer, such as, for example, Kraton G1657.
Other suitable compounds, such as
styrene-ethylene/butylenes-styrene thermoplastic elastomers, or
high performance thermoplastic rubbers may also be used. The inner
core serves, among other functions, to provide breathability and
elastic performance to the film.
[0016] The calcium carbonate additive in the inner and outer core
layers of the present invention may be provided in any suitable
manner, but is preferably provided in the form of a calcium
carbonate super concentrate. This super concentrate preferably
contains about 75% Omya 2SST calcium carbonate with stearic acid
coating, about 0.18% B-900 antioxidant (available from Ciba
Specialty Chemicals, Tarrytown, N.Y.), about 12.41% Dowlex 2517
LLDPE, and about 12.41% Dowlex 2035 LLDPE.
[0017] It will be appreciated by those skilled in the art that
additives may be added to one or more layers of the film of the
present invention in order to improve certain characteristics of
the particular layer. Preferred additives include color
concentrates, neutralizers, process aids, lubricants, stabilizers,
hydrocarbon resins, antistatics, and antiblocking agents. A color
concentrate may be added to yield a colored layer, an opaque layer,
or a translucent layer. Preferred color concentrates include color
formulations, including black, white, and other colors suitable for
the film of the present invention. Preferred color concentrates
include Ampacet.RTM. white PE masterbatch, available from Ampacet
Corporation (Tarrytown, N.Y.). The carrier resin of Ampacet.RTM.
white PE masterbatch is a LLDPE having a melt index of 20 g/10 min
and a density of 0.92 g/cc. This concentrate has a nominal specific
gravity of 2.06, a melt index of 3-23 g/10 min, and nominally
contains 75% ash. Another preferred color concentrate includes
Ampacet.RTM. white HDPE masterbatch, the carrier resin of which is
a HD/LLDPE having a nominal melt index of 10 g/10 min and a density
of 0.96 g/cc. This concentrate has a nominal specific gravity of
1.54, a melt index of 9-15 g/10 min, and a pigment composed of 50%
TiO.sub.2.
[0018] Suitable neutralizers include calcium carbonate, as
indicated above, and calcium stearate. Preferred neutralizers have
an absolute particle size of less than 10 .mu.m and a specific
surface area of at least 40 m.sup.2/g. Polymeric processing aids
may also be used in a layer. Fluoropolymers, fluoropolymer blends,
and fluoroelastomers are particularly preferred, but any processing
aid known in the art for use in polymer films is suitable. A
particularly preferred processing aid is Ampacet.RTM. Process Aid
PE masterbatch, having an LLDPE carrier resin with a nominal melt
index of 2 g/10 min and a density of 0.918 g/cc. The concentrate
therein has a nominal specific gravity of 0.91, a nominal melt
index of 1-3 g/10 min, and contains 3% ash.
[0019] Lubricants that may be used in accordance with the present
invention include higher aliphatic acid esters, higher aliphatic
acid amides, metal soaps, polydimethylsiloxanes, and waxes.
Conventional stabilizing compounds for polymers of ethylene,
propylene, and other .alpha.-olefins are preferably employed in the
present invention. In particular, alkali metal carbonates, alkaline
earth metal carbonates, phenolic stabilizers, alkali metal
stearates, and alkaline earth metal stearates are preferentially
used as stabilizers for the composition of the present
invention.
[0020] Hydrocarbon resins and, in particular, styrene resins,
terpene resins, petroleum resins, and cyclopentadiene resins have
been found to be suitable as additives in order to improve
desirable physical properties of the film. These properties may
include water vapor permeability, shrinkage, film rigidity, and
optical properties. In particular, adhesive resins are preferred. A
particularly preferred adhesive resin is sold under the trademark
Bynel.RTM. by DuPont Corporation and is primarily composed of
maleic anhydride modified polyolefin with some residual maleic
anhydride and may also contain small amounts of stabilizers,
additives and pigments.
[0021] Preferred antistatics include substantially straight-chain
and saturated aliphatic, tertiary amines containing an aliphatic
radical having 10-20 carbon atoms that are substituted by
.omega.-hydroxy-(C.sub.1-C.sub.4)-alkyl groups, and
N,N-bis-(2-hydroxyethyl)alkylamines having 10-20 carbon atoms in
the alkyl group. Other suitable antistatics include ethoxylated or
propoxylated polydiorganosiloxanes such as polydialkysiloxanes and
polyalkylphenylsiloxanes, and alkali metal alkanesulfonates.
[0022] Preferred antiblocking agents include organic polymers such
as polyamides, polycarbonates, and polyesters. Other preferred
agents include calcium carbonate, aluminum silicate, magnesium
silicate, calcium phosphate, silicon dioxide, and diatomaceous
earth.
[0023] In the preferred embodiments of the film of the present
invention described hereinabove, the film structure is a five-layer
structure. The five-layer construction allows the highest content
of elastomer to be buried inside the inner core layer. This permits
other components to function as a protective outer core layers to
minimize or prevent layers of film from sticking or blocking by
minimizing the content of tacky, sticky elastomer in the outer
core, and also permits the use of metallocene-catalyzed polyolefin
polymer in outer core layers in order to encapsulate the inner core
and provide film toughness. Finally, the five-layer configuration
permits the use of a thin, protective LDPE outer skin to provide
protection from die build up during the film casting process.
Because of these advantages, the five-layer embodiment of the
present film described above it preferred. It will, however, be
appreciated by those skilled in the art upon reading this
disclosure that an alternate number of layers could also be
used.
[0024] The present invention is further illustrated by the
following examples, which are not to be construed in any way as
imposing limitations upon the scope thereof. On the contrary, it is
to be clearly understood that various other embodiments,
modifications, and equivalents which, after reading the description
herein, may suggest themselves to those skilled in the art, may be
used without departing from the spirit of the present invention
and/or the scope of the appended claims.
EXAMPLES OF FILM STRUCTURES IN ACCORDANCE WITH THE PRESENT
INVENTION
[0025] A five-layer film having a total thickness of about 1.5 mils
was produced using the formula set forth in Table 1. TABLE-US-00001
TABLE 1 Formulation A - 5 Layer Formulation Percent (w) Layer of
Film Polymer Additive Metallocene 1 (skin) 1% LDPE 0 0 2 (outer
core) 18% 23% SEBS 67% CaCO.sub.3 7% ethylene .alpha.- olefin resin
3 (inner core) 62% 33% SEBS 67% CaCO.sub.3 0 4 (outer core) 18% 23%
SEBS 67% CaCO.sub.3 7% ethylene .alpha.- olefin resin 5 (skin) 1%
LDPE 0 0
[0026] The specific products used in the manufacture of the Table 1
film are provided in Table 2, below. TABLE-US-00002 TABLE 2
Formulation B - 5 Layer Formulation Percent (w) Layer of Film
Polymer Additive Metallocene 1 (skin) 1% LDPE 0 0 2 (outer core)
18% 23% Kraton 67% CaCO.sub.3 7% Dow 1657 PL1280 3 (inner core) 62%
33% Kraton 67% CaCO.sub.3 0 G1657 4 (outer core) 18% 23% Kraton 67%
CaCO.sub.3 7% Dow 1657 PL1280 5 (skin) 1% LDPE 0 0
[0027] The films described in tables 1 and 2 were produced by the
following process. The film was produced by a coextrusion method,
with LDPE present in the skin layer extruder such that a 1% LDPE
skin layer was produced on either side of the film. Casting began
at a chill roll speed of about 50 meters/minute (about 150
feet/min), with the chill roll speed being gradually increased to a
speed of up to about 75 meters/min (225 f/min). Unstretched film
thickness was calculated to be about 3.4 mils. MDO temperature was
adjusted to 130.degree. F. in preheat, 125-130.degree. F. in
stretch zones, and 170-175.degree. F. in the final two rolls in the
MDO in order to anneal the film. A stretch ratio of about
3.85.times. to about 4.times. was used to observe film stretching
and check film properties. The film was retracted approximately 18%
in the MDO.
[0028] A five-layer film having a total film thickness of about
1.50 mils was produced using the formula set forth in Table 3.
TABLE-US-00003 TABLE 3 Formulation C - 5 Layer Formulation Percent
(w) Layer of Film Polymer Additive Metallocene 1 (skin) 1% LDPE 0 0
2 (outer core) 18% 23% Kraton 67% CaCO.sub.3 7% Dow 1657 PL1280 3
(inner core) 62% 33% Kraton 67% CaCO.sub.3 0 Blend (20% 1657 + 80%
other SEBS thermoplastic elastomer) 4 (outer core) 18% 23% Kraton
67% CaCO.sub.3 7% Dow 1657 PL1280 5 (skin) 1% LDPE 0 0
[0029] A five-layer film having a total film thickness of about 1.5
mils was produced using the formula set forth in Table 3.
TABLE-US-00004 TABLE 4 Formulation D - 5 Layer Formulation Percent
(w) Layer of Film Polymer Additive Metallocene 1 (skin) 1% LDPE 0 0
2 (outer core) 18% 23% Kraton 67% CaCO.sub.3 7% Dow 1657 PL1280 3
(inner core) 62% 33% Kraton 67% CaCO.sub.3 0 Blend (40% 1657 + 60%
other SEBS thermoplastic elastomer) 4 (outer core) 18% 23% Kraton
67% CaCO.sub.3 7% Dow 1657 PL1280 5 (skin) 1% LDPE 0 0
[0030] The film was tested for elastic performance and
breathability. For elasticity, a two cycle test was used to
determine load loss and percent set. The two cycle test was done up
to 70% elongation. The sample size was three inches in the machine
direction by six inches in the transverse direction. The grip size
was three inches in width. The grip separation was four inches. The
samples were loaded such that the transverse direction of the
sample was in the vertical direction. The preload was of
approximately 10-15 grams set. During the test, the film was pulled
at 20 inches/min (500 mm/min) to 70 percent elongation (2.8 inches
in addition to the 4 inch gap), and then immediately returned to
the zero point (the 4 inch gauge separation). The term "percent
set" refers to the measure of the amount of the material stretched
from its original length after being cycled. Percent set is defined
as the point at which the retraction curve crossed the elongation
axis. The "load loss" value was calculated as follows: cycle
.times. .times. 1 .times. .times. extension .times. .times. tension
- cycle .times. .times. 2 .times. .times. tension cycle .times.
.times. 1 .times. .times. extension .times. .times. tension .times.
100 .times. % ##EQU1## where the extension tension for both cycles
is determined at 50% elongation.
[0031] The foregoing description of the embodiments of the
invention has been presented for purposes of illustration and
description, and is not intended to be exhaustive or to limit the
invention to the precise form disclosed. The description was
selected to best explain the principles of the invention and
practical application of these principles in order to enable others
skilled in the art to best utilize the invention in various
embodiments and with such modifications as are suited to the
particular use contemplated. It is intended that the scope of the
invention not be limited by the specification, but be defined by
the claims as set forth below.
* * * * *