U.S. patent application number 14/798192 was filed with the patent office on 2017-01-19 for transparent oriented polypropylene film with high moisture vapor and oxygen barrier properties.
This patent application is currently assigned to TORAY PLASTICS (AMERICA), INC.. The applicant listed for this patent is TORAY PLASTICS (AMERICA), INC.. Invention is credited to Keunsuk P. CHANG, Shichen DOU, Tracy A. PAOLILLI.
Application Number | 20170015821 14/798192 |
Document ID | / |
Family ID | 57775602 |
Filed Date | 2017-01-19 |
United States Patent
Application |
20170015821 |
Kind Code |
A1 |
DOU; Shichen ; et
al. |
January 19, 2017 |
TRANSPARENT ORIENTED POLYPROPYLENE FILM WITH HIGH MOISTURE VAPOR
AND OXYGEN BARRIER PROPERTIES
Abstract
Described are transparent oriented polypropylene films with
improved barrier properties and methods of making these films. The
films and methods include a core layer comprising polypropylene,
hydrocarbon resin, and polyethylene wax to improve moisture vapor
barrier properties, an optional barrier layer comprising polar
polymers to improve oxygen barrier properties, and optional skin
layers to improve heat sealing, winding, printing, and/or
adhesion.
Inventors: |
DOU; Shichen; (Warwick,
RI) ; PAOLILLI; Tracy A.; (East Greenwich, RI)
; CHANG; Keunsuk P.; (North Kingstown, RI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
TORAY PLASTICS (AMERICA), INC. |
N. Kingstown |
RI |
US |
|
|
Assignee: |
TORAY PLASTICS (AMERICA),
INC.
N. Kingstown
RI
|
Family ID: |
57775602 |
Appl. No.: |
14/798192 |
Filed: |
July 13, 2015 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B32B 7/12 20130101; B29C
48/91 20190201; B29K 2023/12 20130101; B29K 2023/00 20130101; B29L
2007/008 20130101; B29L 2009/00 20130101; B32B 2307/412 20130101;
B32B 27/322 20130101; B29K 2995/0026 20130101; B32B 2307/7242
20130101; B32B 2439/70 20130101; B29C 48/21 20190201; B32B 2307/31
20130101; B32B 2307/7246 20130101; B29C 48/154 20190201; B32B
2250/24 20130101; B32B 2255/10 20130101; B32B 2307/732 20130101;
B32B 27/28 20130101; B32B 2307/7244 20130101; B32B 2553/00
20130101; B32B 2307/7265 20130101; B29K 2995/0067 20130101; B32B
2307/514 20130101; B29C 48/08 20190201; B32B 27/32 20130101; B32B
2307/746 20130101; B29C 48/22 20190201; B32B 27/08 20130101; B32B
2270/00 20130101; B29L 2009/005 20130101; B32B 2255/26
20130101 |
International
Class: |
C08L 23/12 20060101
C08L023/12; B29C 47/88 20060101 B29C047/88; B29C 47/00 20060101
B29C047/00; B29C 47/06 20060101 B29C047/06; B32B 27/32 20060101
B32B027/32; B32B 27/08 20060101 B32B027/08 |
Claims
1. A film comprising: a core layer comprising high crystalline
polypropylene, 2.5-25 wt % hydrocarbon resin, and 0.5-2.0 wt %
polyethylene wax.
2. The film of claim 1, wherein the core layer further comprises a
fluoropolymer additive.
3. The film of claim 1, wherein the high crystalline polypropylene
is a highly isotactic crystalline propylene homopolymer with an
isotactic index greater than 95%.
4. The film of claim 1, wherein the hydrocarbon resin is in the
range of 5-15 wt % of the core layer.
5. The film of claim 1, wherein the hydrocarbon resin has a glass
transition temperature (Tg) from 80 to 90.degree. C.
6. The film of claim 5, wherein the polyethylene wax has a
crystallization temperature (Tc) less than the Tg of the
hydrocarbon resin of the core layer.
7. The film of claim 1, wherein the hydrocarbon resin has a
softening temperature from 135 to 145.degree. C.
8. The film of claim 1, wherein the hydrocarbon resin is a fully
hydrogenated water-white hydrocarbon resin.
9. The film of claim 1, wherein the polyethylene wax is 0.75-1.5 wt
% of the core layer.
10. The film of claim 1, wherein the polyethylene wax has a melting
temperature from 65 to 92.degree. C.
11. The film of claim 1, wherein the polyethylene wax comprises
synthetic crystalline polyethylene wax, paraffin wax,
Fischer-Tropsch wax, or combinations thereof.
12. The film of claim 1, further comprising a barrier layer
comprising polar polymers.
13. The film of claim 12, further comprising a tie-layer between
the core layer and the barrier layer.
14. The film of claim 1, further comprising a heat sealable or
winding skin layer comprising polyolefin.
15. The film of claim 1, wherein the film has a haze of less than
or equal to 5%.
16. A multi-layer film comprising: a core layer comprising high
crystalline polypropylene, hydrocarbon resin, and polyethylene wax;
a skin layer comprising polyolefin on a surface of the core layer;
and a barrier layer comprising polar polymers.
17. The film of claim 16, wherein the barrier layer is on a surface
of the core layer opposite the skin layer.
18. The film of claim 16, further comprising a tie layer on a
surface of the core layer opposite the skin layer between the core
layer and the barrier layer.
19. The film of claim 18, wherein the tie layer comprises
polyolefin homopolymers, polyolefin copolymers, maleic anhydride
grafted or copolymerized polyolefins, or combinations thereof.
20. The film of claim 16, wherein the skin layer comprises
polyolefin homopolymers, polyolefin copolymers, polyolefin
termpoloymers, maleic anhydride grafted or copolymerized
polyolefins, or combinations thereof.
21. The film of claim 20, wherein the skin layer further comprises
an antiblocking agent.
22. The film of claim 16, wherein the core layer further comprises
a fluoropolymer additive.
23. The film of claim 16, wherein the hydrocarbon resin is in the
range of 2.5-25 wt % of the core layer.
24. The film of claim 16, wherein the polyethylene wax is in the
range of 0.5-2.0 wt % of the core layer.
25. The film of claim 16, wherein the film has a total thickness in
the range of 10-60 .mu.m.
26. The film of claim 16, wherein the film has a moisture vapor
transmission rate less than 0.12 g/100 in.sup.2/day.
27. The film of claim 16, wherein the film has an oxygen gas
transmission rate less than 1.5 cc/100 in.sup.2/day.
28. The film of claim 16, wherein the film has a haze of less than
or equal to 5%.
29. A multilayer film comprising: a core layer comprising high
crystalline polypropylene, hydrocarbon resin, and polyethylene wax;
a first layer on a surface of the core layer comprising polar
polymers; and a second layer on a surface of the core layer
opposite the first layer comprising polar polymers.
30. The film of claim 29, wherein the core layer further comprises
a binding promoter.
31. The film of claim 29, wherein the binding promoter comprises
maleic anhydride grafted polypropylene.
32. The film of claim 29, comprising a skin layer on a surface of
the first or second layer opposite the core layer comprising
polyolefin.
33. A method of making a film comprising: coextruding a core layer
comprising high crystalline polypropylene, hydrocarbon resin, and
polyethylene wax with a skin layer comprising polyolefin.
34. The method of claim 33, further comprising coextruding a
barrier layer comprising polar polymers on a surface of the core
layer opposite the skin layer.
35. The method of claim 33, further comprising coating a barrier
layer comprising polar polymers on a surface of the core layer
opposite the skin layer.
36. The method of claim 35, wherein the film is oriented in the
machine direction prior to coating of the barrier layer.
37. The method of claim 36, wherein the film is oriented in the
transverse direction after coating the film with the barrier
layer.
38. The method of claim 33, further comprising coextruding a
tie-layer comprising polyolefin on a surface of the core layer
opposite the skin layer.
39. The method of claim 38, further comprising inline or offline
coating a barrier layer comprising polar polymers on a surface of
the tie-layer opposite the core layer.
40. The method of claim 38, further comprising coextruding a
barrier layer comprising polar polymers on a surface of the
tie-layer opposite the core layer.
41. The method of claim 33, further comprising heat aging the
film.
42. The method of claim 41, wherein the aging temperature is lower
than a Tg of the hydrocarbon resin and a melting temperature of the
polyethylene wax.
43. The method of claim 41, wherein the aging temperature is from
40-70.degree. C. and the aging time is from 12 to 48 hours.
Description
FIELD OF THE INVENTION
[0001] This disclosure relates to an oriented polypropylene
transparent film with improved barrier properties. More
specifically, this disclosure relates to a multi-layer oriented
transparent film that includes a core layer containing
polypropylene, hydrocarbon resin, and polyethylene wax and at least
one barrier layer containing polar polymers.
BACKGROUND OF THE INVENTION
[0002] In order to be used in packing applications, biaxially
oriented polypropylene (BOPP) films should have excellent
mechanical properties, excellent barrier properties (of moisture
vapor and/or oxygen gas), and excellent heat sealability among
other properties. In addition, BOPP films can include a promoting
layer(s) suitable for various laminating, coating, and printing
processes.
[0003] For some packaging applications, BOPP films should have both
good moisture vapor and oxygen gas barrier properties as well as
transparency. A high barrier to moisture vapor and oxygen gas can
maintain product quality in an extended shelf life, whereas
transparency provides consumers with visibility to the commodity
product in packaging.
[0004] Metallization of BOPP films via vacuum deposition of
aluminum is a well-known cost-effective method to significantly
improve the moisture and oxygen barrier properties of BOPP films;
however, the resultant films are opaque. Therefore, this technology
is not suitable for packaging applications that require
transparency.
[0005] U.S. Pat. No. 6,788,379 describes a plasma oxide coating
process via enhanced chemical vapor deposition on different polymer
sheets. The resultant oxide coated sheets demonstrated
significantly reduced transmission rate for moisture vapor and
oxygen gas. The process of aluminum oxide (AlOx) or silicon oxide
(SiOx) coating of BOPP films via roll to roll web vacuum deposition
provides a transparent thin coating layer of aluminum oxide or
silicon oxide on the substrate that gives the packaging materials
high moisture and oxygen gas barrier properties as well as
transparency. However, AlOx or SiOx coating is extremely brittle
and prone to cracking of the oxide coatings occurring in the
downstream processes of converting and packaging applications, such
that the high barrier properties of the packaging cannot be
maintained due to said cracking. In addition, the cost of such
oxide coating process is comparatively high and uncompetitive to
most other high gas barrier OPP film technologies.
[0006] U.S. Pat. No. 5,672,426 describes a process of making a
transparent liquid crystalline polymer (LCP) film via solvent
casting. The LCP is dissolved in a solvent to an appropriate
concentration and then cast into a film. Although cast LCP films
have good transparency, excellent barrier properties for both
moisture vapor and oxygen gas, and excellent mechanical properties,
the solvent casting process is very costly and not environmentally
friendly. Melt-extrudable LCPs have been known to present a
processing difficulty in making LCP films. Limitations of LCP film
extrusion include high temperature for processing, low melt
viscosity, poor adhesion to substrates, broad variations in
thickness, opaqueness to light, and uni-axial orientation due to
the unique arrangements of LCP chains in the materials. Thus, the
use of LCP packaging films is restricted to the applications of
specialty packaging since both materials and processes are
relatively expensive for general industrial packaging.
[0007] U.S. Pat. No. 5,139,878 describes a multilayer film
structure comprising at least one fluoropolymer layer laminated to
polyolefin or polyester layer via a tie layer or adhesive layer
through a process of coextrusion or lamination. Such a resultant
multilayer film exhibits high moisture vapor barrier and good
transparency. However, the oxygen barrier of the resultant film is
only slightly improved over the polyester film of similar
thickness. Most fluoropolymers especially
polychlorotrifluoroethylene (PCTFE) exhibit excellent moisture
barrier properties (moisture transmission rates in the range of
from 0.02 to 0.06 g/100 in.sup.2/day) and transparency; however,
the fluoropolymers usually do not provide significant oxygen gas
barrier properties. Fluoropolymer films are restricted to use in
specialty packaging since both fluoropolymers and equipment used
for fluoropolymer film production are very expensive. In addition,
fluoropolymer films during incineration generate hydrogen fluoride
(HF) which is an environmentally hazardous byproduct.
[0008] BOPP films coated with polyvinylidene chloride (PVdC)
exhibit both good moisture and oxygen barrier properties as well as
good transparency as the PVdC coating reaches a thickness level
required for the barrier properties. A few microns of PVdC coating
on BOPP substrate is usually needed to achieve good moisture vapor
and oxygen barrier properties. A costly offline coating process is
needed to apply a thick PVdC coating on a BOPP substrate. Although
PVdC coating is a good candidate for moisture vapor and oxygen gas,
it also has well-known environmental issues. Coated BOPP films
cannot be recycled into the reclaim streams of BOPP film production
due to the intrinsic characteristics of PVdC materials.
Furthermore, PVdC coating in packaging materials decomposes into
hazardous substances (for instance hydrogen chloride, HCl) as PVdC
coated films are burned by waste incinerators.
[0009] U.S. Pat. No. 5,155,160 describes a polyolefin film
structure comprising a precisely loaded paraffin wax additive in
the range of 3 to 10 wt % based on the weight of the polyolefin.
The resultant film was claimed to have improved moisture vapor
barrier. The film needed to be quenched immediately at a chill roll
temperature of about 4.degree. C. after it is extruded to avoid wax
migration. Since the molecular weight of the paraffin waxes was in
the low end range of 300 to 450 g/mole, while the loading in the
film was at a high end range of 3 to 10 wt %. Inevitably, the
paraffin waxes may migrate onto the surface of the resultant film
in downstream processes such as orientation in machine and
transverse direction, converting operations, and packaging
applications, which may lead to wax plate-out problems and
contamination of processing equipment. In addition, the resultant
film showed very limited improvements in oxygen barrier.
[0010] U.S. Pat. No. 6,033,514 describes a biaxially oriented
multilayered polypropylene film with improved moisture vapor
transmission rates (MVTR) by incorporating a crystalline
polyethylene wax additive into a core resin layer. The content of
wax additive is in the range of 1.1 to 7.5 wt %. A single core
resin layer is extruded without outer layers, coated with two
polyolefin cap layers after the orientation in machine direction,
and oriented in the transverse direction. The barrier mechanism of
the film is claimed to be that the wax additive in the core layer
migrated throughout the polyolefin cap layers to form
highly-crystalline continuous wax layers on the outer surfaces of
the polyolefin cap layers. In the cases of coextruded outer layers
or tie layers, all given examples showed no improvements in
moisture vapor transmission rates. In a production line, it is not
efficient to add two cap layers onto a single core layer at the
stages in-between the two orientation steps. Although the outer
polyolefin cap layers delayed the rate of wax migration, the wax
additive in the core layer will continue to migrate through the
polyolefin cap layers and form wax crystals on the surface, which
may cause processing issues downstream such as wax plate-out or
build-up. In addition, the resulting film showed very limited
capability to improve oxygen gas barrier which is required for some
food packaging applications.
[0011] U.S. Pat. No. 6,033,771 describes the use of waxes to
improve moisture and oxygen barrier properties of multilayer BOPP
films. In this patent, 4.5 wt % Fischer Tropsch wax is blended into
a polypropylene core layer which is cavitated to form voids. The
voids in the core layer are used to entrap the wax molecules to
prevent them to migrate to the surface, thus avoiding plate-out
problems. However, the cavitation of the intermediate layer renders
the resulting film opaque and no longer transparent.
SUMMARY OF THE INVENTION
[0012] As pointed out in the Background section, there is a need
for an economical method to improve barrier properties of
transparent BOPP films. Applicants have discovered film
formulations that result in optically clear films with both high
moisture vapor and oxygen barrier properties by utilizing a
combination of a polypropylene core layer comprising hydrocarbon
resin and crystalline polyethylene wax, and polar polymeric barrier
coatings. The resultant films can include a core layer for
improving moisture vapor barrier properties, optional barrier
layers for improving oxygen barrier properties, and optional skin
layers (also referred to as outer layers unless coated with a
barrier layer and then the barrier layer becomes the outer layer
and the skin layer becomes a tie or adhesion layer (i.e., outer
layers are exposed to air) for improving heat sealability, winding,
printing, and/or adhesion.
[0013] Described are transparent oriented polypropylene films with
improved barrier properties and methods of making these films. The
films and methods include a core layer comprising polypropylene,
hydrocarbon resin, and polyethylene wax to improve moisture vapor
barrier properties, an optional barrier layer comprising polar
polymers to improve oxygen barrier properties, and optional skin
layers to improve heat sealing, winding, printing, and/or
adhesion.
[0014] In some embodiments, the films disclosed herein comprise a
core layer that can provide the desired mechanical properties and
moisture vapor barrier properties; an optional skin layer which can
be formulated to have properties of heat sealing, winding,
adhesion, or printing; an optional barrier layer comprising polar
polymers that can improve the oxygen barrier; and an optional tie
layer (adhesion promoting layer) in between the core layer and the
barrier layer that can bond a polar barrier layer to a nonpolar
core layer. The core layer of the film can include high crystalline
polypropylene, hydrocarbon resin, and polyethylene wax.
Specifically, the core layer of the film can be a layer of highly
isotactic crystalline polypropylene (HCPP) blended with
hydrogenated hydrocarbon resins (HCR) and synthetic polyethylene
waxes (PE wax). The highly isotactic crystalline polypropylene can
have an isotactic index greater than 95%. The contents of HCR and
PE wax in the core layer can be about 2.5 to 25 wt % and about 0.5
to 2.0 wt % of the core layer, respectively. In addition, the
contents of the HCR and PE wax in the core layer can be 5 to 15 wt
% and about 0.75 to 1.5 wt % of the core layer, respectively. The
hydrocarbon resin can have a glass transition temperature (Tg) from
80 to 90.degree. C. and can have a softening temperature from 135
to 145.degree. C. In addition, the polyethylene wax can have a
crystallization temperature (Tc) less than the Tg of the
hydrocarbon resin of the core layer. The hydrocarbon resin can be a
fully hydrogenated water-white hydrocarbon resin. Furthermore, the
polyethylene wax can have a melting temperature from 65 to
92.degree. C. In addition, the polyethylene wax can comprise
synthetic crystalline polyethylene wax, paraffin wax,
Fischer-Tropsch wax, or combinations thereof.
[0015] Without being bound by any theory, it is thought that the
HCR additive with high Tg can entrap the PE wax molecules in the
core layer. Optionally, a desirable amount of fluoropolymer
additive in the range of about 100 to 1000 ppm can be added to the
core layer to improve the distribution of PE wax additives and help
further enhance the moisture barrier. Any tie layer(s) and skin
layer(s) can be coextruded with the core layer while the barrier
layer can be inline or offline applied to the outer surface of the
tie layer. In addition, the barrier layers can also be coextruded
with the core layer. Suitable polymers for the tie layers and outer
layers can include polyolefins such as homopolymers, copolymers, or
terpolymers of the monomers of ethylene, propylene, and butene, and
maleic anhydride grafted or copolymerized polyolefins. The laminate
films can be oriented either uniaxially or biaxially. The films can
be oriented biaxially in both the machine and transverse
directions. In addition, the barrier layer can be a cross-linked
product of PVOH/polyvinyl amine, or PVOH or EVOH polar polymers,
and/or blends thereof.
[0016] In some embodiments, the films disclosed herein could also
be designed only for moisture barrier application if oxygen gas
barrier is not required for a package. The laminate films could be
a multilayered laminate film comprising a core layer as described
above and two skin layers which could be formulated as layers for
the purposes of heat sealing, winding, adhesion, or printing,
respectively. In this case, the layer of polar polymers for oxygen
barrier may not be included in the laminate film structure.
[0017] In some embodiments, the films disclosed herein can comprise
a core layer comprising high crystalline polypropylene, hydrocarbon
resin, and polyethylene wax; a skin layer on a surface of the core
layer comprising polyolefin; and a barrier layer comprising polar
polymers. The core layer can also comprise a fluoropolymer
additive. In addition, the hydrocarbon resin can comprise 2.5-25 wt
% of the core layer and the polyethylene wax can comprise 0.5-2.0
wt % of the core layer. The barrier layer can be on a surface of
the core layer opposite the skin layer. The films can also include
a tie layer on a surface of the core layer opposite the skin layer
between the core layer and the barrier layer. The tie layer can
comprise polyolefins including homopolymers, copolymers, maleic
anhydride grafted or copolymerized polyolefins, or combinations
thereof. The skin layer can also comprise the same or similar
polyolefins as the tie layer. In addition, the skin layer can
include antiblocking agents. The films can have a total thickness
of about 10 to 60 .mu.m or about 15 to 25 .mu.m. In addition, the
films can have a moisture vapor transmission rate less than 0.12
g/100 in.sup.2/day and an oxygen gas transmission rate less than
1.5 cc/100 in.sup.2/day. Furthermore, the films can have a haze
less than or equal to 5%.
[0018] In some embodiments, the films disclosed herein can include
a core layer comprising high crystalline polypropylene, hydrocarbon
resin, and polyethylene wax; a first layer on a surface of the core
layer comprising polar polymers; and a second layer on a surface of
the core layer opposite the first layer comprising polar polymers.
The core layer can also comprise a binding promoter comprising
maleic anhydride grafted polypropylene. The films can also include
a skin layer on one or both surfaces of the first and second layers
opposite the core layer.
[0019] Some embodiments include methods of making the films
disclosed herein, wherein the methods can include coextruding a
core layer comprising high crystalline polypropylene, hydrocarbon
resin, and polyethylene wax with a skin layer comprising
polyolefin. The methods can also include coextruding a barrier
layer comprising polar polymers on a surface of the core layer
opposite the skin layer or inline or offline coating a barrier
layer comprising polar polymers on a surface of the core layer
opposite the skin layer. The films can be oriented in the machine
direction prior to the coating of the barrier layer and can be
oriented in the transverse direction after coating the films with
the barrier layer. In addition, the methods can include coextruding
a tie layer comprising polyolefin on a surface of the core layer
opposite the skin layer and inline or offline coating a barrier
layer comprising polar polymers on a surface of the tie layer
opposite the core layer. In addition, the barrier layer can be
coextruded on a surface of the tie layer opposite the core layer.
The methods can further include heat aging the films. The aging
temperature can be lower than a Tg of the hydrocarbon resin and a
melting temperature of the polyethylene wax. In some embodiments,
the aging temperature is 40-70.degree. C. and the aging time is
from 12 to 48 hours.
[0020] In some embodiments, the laminate films could be three-layer
films comprising a barrier layer of polar polymers for oxygen gas
barrier, a core layer for moisture vapor barrier, and an outer
non-polar layer. The layer of polar polymers can be on a surface of
the core layer. The core layer can be sandwiched between the polar
polymer barrier layer and a non-polar layer through coextrusion.
The films can be oriented uniaxially or biaxially. The layer of
polar polymers can also be added to one surface of the core layer
(in case of 2-layer coextruded laminate film) through a process of
inline or offline coating. The non-polar outer skin layer can
function as a heat sealable layer or a layer to be formulated for
the purpose of winding, adhesion, or printing. A desirable amount
of polar maleic anhydride grafted polyolefins can also be added
into the core layer to achieve strong bond strength between the
interface of the core layer and the barrier layer of polar
polymers, as a discrete tie layer for promoting adhesion may not be
included in this specific film structure. Suitable polar polymers
can include maleic anhydride (MAH) grafted polypropylene.
[0021] In some embodiments, the coextruded oriented laminate film
could be a two-layer film comprising a core layer described above
and an outer skin layer. The outer skin layer could function as a
heat sealable layer or a layer formulated for the purpose of
winding, adhesion, or printing. The side of the core layer opposite
the skin layer could be corona discharge-treated to allow for
higher surface energy for the suitability to receive coatings,
inks, or to laminate to another substrate with adhesives.
[0022] In some embodiments, the laminate film is a four-layered or
five-layered oriented film. The polar polymers for oxygen barrier
enhancement could be incorporated into the structure of a
multilayered laminate film as one intermediate layer or tie layer,
preferably two intermediate layers or tie layers, on at least one
surface of the core layer. The intermediate layer(s) could be
coextruded with the core layer and outer layers of the laminate
film and then oriented. Suitable polar polymers can include
extrudable EVOH or PVOH or blends thereof and/or other extrudable
polar polymers with excellent oxygen barrier properties. Polar
polymeric compatibilizers or tie-resins can be added into both the
skin layers and the core layer to achieve strong bond strength
between the interfaces of intermediate layers and other layers.
Suitable polymeric compatibilizers can include maleic anhydride
(MAH) grafted polyolefin homopolymers and copolymers, as well as
maleic anhydride copolymerized copolymers or terpolymers,
preferably with a MAH grafting rate of from 0.5 to 2.0 wt %. With
two polar intermediate layers immediately next to the core layer,
possible wax migration can be avoided or substantially minimized
even if the wax content in the core layer is slightly higher, since
the polar intermediate layers will repel the non-polar wax and keep
it from migrating out of the core layer.
[0023] Various specific embodiments, examples, definitions and
descriptions are adopted in the art for understanding the
invention. The details in the art are only used to provide specific
preferred embodiments and exemplary to those skilled in the art.
The scope of the invention will refer to any one or more in the
appended claims, but not necessarily all, of the invention defined
by the claims.
[0024] It is understood that aspects and embodiments of the
invention described herein include "consisting" and/or "consisting
essentially of" aspects and embodiments. For all methods, systems,
compositions, and films described herein, the methods, systems,
compositions, and films can either comprise the listed components
or steps, or can "consist of" or "consist essentially of" the
listed components or steps. When a system, composition, or film is
described as "consisting essentially of" the listed components, the
system, composition, or film contains the components listed, and
may contain other components which do not substantially affect the
performance of the system, composition, or film, but either do not
contain any other components which substantially affect the
performance of the system, composition, or film other than those
components expressly listed; or do not contain a sufficient
concentration or amount of the extra components to substantially
affect the performance of the system, composition, or film. When a
method is described as "consisting essentially of" the listed
steps, the method contains the steps listed, and may contain other
steps that do not substantially affect the outcome of the method,
but the method does not contain any other steps which substantially
affect the outcome of the method other than those steps expressly
listed.
DETAILED DESCRIPTION OF THE INVENTION
[0025] Described are films and methods of making and using
transparent polypropylene films with improved moisture vapor and/or
oxygen barrier properties. Efforts to enhance the moisture vapor
barrier of transparent BOPP films in a cost-effective manner have
often involved the methods of adding the additives of HCR or PE
waxes into the core layer of the multi-layer BOPP film.
Hydrogenated hydrocarbon resin (HCR) can be used in making BOPP
films with improved moisture barrier properties. A typical BOPP
film modified with hydrocarbon resin exhibits moisture transmission
rates about 1.5 to 2 times better than the moisture barrier
properties of a non-HCR-modified BOPP film. An HCR-modified BOPP
film has better moisture barrier, and its transparency can be
maintained at the same level as its unmodified counterpart. The
oxygen gas transmission rate (O2TR) of the HCR-modified film can be
reduced to about 50% of its original 02TR. Thus, hydrocarbon resins
can improve the barrier properties of BOPP films; however, the
improved barrier to both moisture vapor and oxygen gas is often not
enough for demanding applications where the product shelf life
needs to be significantly extended.
[0026] To improve the oxygen barrier properties of transparent BOPP
films, polar polymers as coatings or coextruded layers are usually
applied to a tie-layer bonded to a polypropylene substrate through
an inline or offline process. However, the polar polymers such as
polyethylene vinyl alcohol (EVOH), polyvinyl alcohol (PVOH), or
polyhydroxyaminoether (PHAE) or other polar polymers with high
oxygen barrier properties are often inadequate for moisture vapor
barrier, since these polar polymers absorb moisture and allow polar
water molecules to diffuse through them easily. Moreover, the
process of moisture absorption due to strong polar molecular
attractions (for instance, hydrogen bonding) swells the structure
of relatively hydrophilic EVOH or PVOH in high humidity conditions
and deteriorates gas and vapor barrier properties. Cross-linking of
EVOH and PVOH or other polar polymers by crystallites or chemical
reaction can lessen the swelling or plasticization of
moisture/water to the film structure. In comparison, the aromatic
structure of relatively hydrophobic PHAE resists water absorption
and swelling. Therefore, the moisture vapor barrier of BOPP films
cannot be achieved through the coatings of coextruded layers of
polar polymers.
[0027] However, HCR and PE wax additives as moisture barrier
promoters are often not combined together in a polypropylene core
layer; instead, either a HCR resin or a PE wax resin is
incorporated into the core layer to improve the moisture barrier of
the film. As described in the art, the moisture vapor transmission
rate of a HCR modified BOPP film is about 1.5-2 times lower than
that of a non-HCR modified BOPP film. However, the improved
moisture vapor barrier is not enough for severe packaging
applications and the situation of long extended shelf-life
properties. Where a PE wax additive was used, the moisture vapor
transmission rate was reduced significantly to 0.10 g/100
in.sup.2/day or less, which is lower than that which can be
obtained from using HCR modification alone. However, the prior art
either adds a significant amount of waxes in the range of 3 to 10
wt % in the core layer or adds a special capping process to both
surfaces of the core layer between MDO and TDO to avoid undesirable
wax migration to the surfaces of the film. In practice, these
methods are extremely inefficient for a state-of-the-art BOPP line,
and the wax migration to the surface of production equipment
(plate-out) cannot be avoided.
[0028] Without being bound by any theory, the mechanism behind the
films disclosed herein is as follows. The simplest way of
understanding the diffusion of an individual penetrant is to look
at its path through space or through a medium. It is believed that
the transmission rate of moisture vapor in a polymer crystal
(lamellar) is a few orders of magnitude lower than that in the
amorphous phase of the polymer. The transmission rate of an
individual penetrant in a polymer film is thus dominated by its
transmission rate in the amorphous phase structure of the polymer
film; the transmission rate of an individual penetrant through
polymer crystals (lamellae) is usually ignored due to its low
orders in magnitudes. Herein, an individual penetrant (water
molecule) is considered to diffuse only in the amorphous phase
through tortuous pathways. For a BOPP film to have high moisture
barrier, the film needs to have two important factors: high
crystallinity and low free volume in the amorphous phase. High
moisture barrier of a BOPP film can be reached by a good balance of
the two factors. In the films disclosed herein, hydrogenated
hydrocarbon resins and synthetic polyethylene waxes can be added
into the core layer of a BOPP film to reduce the free volume of PP
chain segments in the amorphous phase. The content of PP crystals
in the core layer of the films can decrease accordingly with
increasing content of HCR and PE wax resins (since the volume of
the HCR and wax displaces a corresponding volume of isotactic
crystalline PP), while the content of the free volume of the
amorphous region in the core layer can decrease with increasing
entrapping effects of added HCR resin to PP chain segments in the
amorphous phase. The crystallinity of the highly isotactic
polypropylene can maintain its initial crystallinity prior to the
addition of the two additives.
[0029] Crystallization of highly isotactic crystalline
polypropylene resin in the core layer during cooling is a two-step
process: 1) formation of nucleation centers (nuclei) and 2)
formation of lamellae (crystal growth). One part of a polypropylene
chain (crystallizable long molecule) stacks on the nuclei to form
lamellae, another part of the polypropylene chain tends to
transverse through multiple lamellae, forming interlamellar links,
which are random coil structures or entangled amorphous chain
segments. Molten HCR and PE waxes (non-crystallizable at the
crystallization temperature of polypropylene) do not stack into
compact lamellar phase. Instead, they can be phased into the
amorphous phase of the core layer, which includes random coils and
entanglements of polypropylene chain segments at the
crystallization temperature of HCPP resin. PE waxes at low content
are miscible in hydrocarbon resin at the extrusion temperature of
the core layer or even a lower temperature, forming a homogeneous
mixture with HCR and HCPP.
[0030] At stretching temperatures, block slippage can occur within
HCPP lamellae, followed by a stress-induced fragmentation and
recrystallization. The molten HCR and PE waxes can reduce the
viscosity of the semi-molten blend and make the process of
reorganizing polypropylene chains easier.
[0031] As the films are cooled from the Tc of HCPP to the Tg of
HCR, secondary crystallization outside of the stacked lamellae can
take place to form more perfect lamellae. The cohesion of molten
HCR, PE waxes, and PP chain segments in the amorphous phase can
reduce to some extent the formation of nanovoids (empty space),
which could have been generated in a BOPP film without the addition
of HCR. The miscibility of HCR, PE waxes, and PP chain segments in
the amorphous phase can decrease with decreasing cooling
temperature. As the temperatures reach the Tg of HCR, HCR can
solidify to form partially connected HCR domains with entrapped PP
chain segments and PE wax molecules, depending on the content of
HCR in the core layer. Since solidified HCR resin makes PP chain
segments and PE wax molecules entrapped in the amorphous phase due
to initial cohesion and change in miscibility, some PP chain
segments and PE wax molecules can become entrapped in the
solidified HCR phase. These entrapped PE wax molecules can be
released from the solidified HCR phase slowly at elevated
aging/annealing temperatures. The released PE waxes could form
small wax crystals in the nanovoids existing in the amorphous phase
at the temperatures lower than the Tc of PE waxes.
[0032] Below the Tg of HCR and the Tc of PE waxes (which can be
less than the Tg of HCR), some of the un-entrapped amorphous PP
chain segments can be free to move locally to some extent within
the constraints of the solidified HCR molecules. The un-entrapped
mobile PE waxes can move slowly to occupy the nanovoids existing in
the amorphous phase to form PE wax crystals. Therein, below the Tg
of HCRs, there can exist connected or unconnected nanovoids newly
formed in the amorphous phase due to the motion of amorphous PP
chain segments, recrystallization, and shrinkage. Mobile PE wax
molecules can move into these nanovoids and form small wax
crystals. The PE wax crystals block the tortuous pathways of
moisture vapor diffusion, therein the MVTR can be further reduced
to a lower level in comparison with the MVTR of adding hydrocarbon
resin alone. The small PE wax crystals can grow to large sizes at
elevated temperatures (aging/annealing) due to secondary
recrystallization. Aging or annealing the films at elevated
temperatures can facilitate the release of trapped PE wax molecules
and the crystallization and secondary recrystallization of PE wax
crystals in the nanovoids.
[0033] Without the HCR in the core layer, PE waxes can be
immiscible with HCPP resin, and the local motion of PP chain
segments (it is believed that the Tg of PP resin is lower than
15.degree. C.) in the amorphous phase can be constrained at ambient
temperatures. The PE wax molecules in the core layer tend to
migrate to the surface of the films at temperatures above the Tm of
PE waxes or below the Tm of PE waxes for the uncrystallized PE
waxes. Although low temperature quenching (at 4.degree. C.) was
applied to cool the surface of the cast film for the purpose of
eliminating wax migration as described in the prior art (U.S. Pat.
No. 5,155,160), molten PE waxes can easily migrate to the surface
of the films during MDO and TDO. Even if some PE waxes stay in the
amorphous phase, since there is no constraint to the local motion
of the amorphous PP chain segment, PE waxes may have very limited
contribution to the reduction of free volume in the amorphous
phase. The PP chain segments in the amorphous phase can be movable
locally (dynamically) at a scale much larger than with the
constraints of added HCR. Added PE waxes may not reduce the
effective free volume of the amorphous phase in the core layer.
Relatively high free volume in the amorphous phase of the core
layer can allow for moisture vapor to diffuse through a film at a
higher transmission rate. Thus, the MVTR barrier improvements seen
in the prior arts (U.S. Pat. Nos. 5,155,160 and 6,033,514) greatly
rely on the wax migration to the surface of the films. Two
comparative examples in the art, with 2.0% PE wax added in to the
core layer but no HCR, showed a much higher moisture vapor
transmission rate than that of the examples with both added HCR and
PE waxes.
[0034] PE waxes at low contents can be miscible in hydrocarbon
resins at the extrusion temperature of the core layer or even a
lower temperature, forming a homogeneous mixture with HCR and HCPP.
Polypropylene resins can solidify from molten state due to
crystallization as temperature decreases. PE waxes and hydrocarbon
resins can be phased into the amorphous phase of the core layer.
The PE waxes in the amorphous phase can crystallize at temperatures
much lower than that of polypropylene resins and thus can form
small PE crystals in the unconnected or interconnected nanovoids,
therein blocking the tortuous pathways for moisture vapor diffusion
leading to a significant decrease in moisture vapor transmission
rate.
[0035] The films disclosed herein can incorporate both HCR and PE
waxes into the core layer of film to improve moisture vapor
barrier. A desirable amount of high Tg HCR resin (Tg>70.degree.
C.) not only can constrain the mobility of the PE waxes and the
mobility of the chain segments of PP in the amorphous phase of the
core layer, but it also can occupy the nanovoids existing in the
amorphous phase of the core layer, leading to a reduction in the
free volume of the core layer. Although the mobility of
non-crystallizable PE waxes and amorphous PP chain segments
(Tg<15.degree. C.) can be restricted to a low extent, they are
still locally mobile. The mobile PE waxes can fill into the
nanovoids existing in the amorphous phase of the core layer. A
desirable amount of PE waxes can be added into the core layer and
filled into the nanovoids in the amorphous phase of polypropylene.
PE waxes can be small crystalline molecules that can crystallize in
the nanovoids. If the content of PE waxes in the core layer exceeds
a desirable amount, PE waxes could migrate to the surface of the
film or equipment (plate-out) as the processing temperature
decreases. As the film temperature decreases with cooling, the
miscibility of PE waxes in hydrocarbon resin can also decrease. At
low wax content, any mobile single wax molecule can move to tunnels
connecting the closest PE wax dominated domains and then stack on
the surface of PE crystals, forming larger PE wax crystals. PE wax
crystals in nanovoids, surrounded by high Tg hydrocarbon resin or
PP chain segments constrained from moving due to existing PP
crystals and HCR domains, can block the tortuous path of moisture
vapor diffusion. Thus, by using a combination of hydrocarbon resin
and wax additives, two mechanisms can be exploited to improve
moisture vapor barrier properties.
[0036] The films disclosed herein can also incorporate at least one
layer of polar polymers as a coating/barrier or coextruded layer(s)
on the substrate of the coextruded laminate film for improving
oxygen gas barrier. Therein, the films can have desirable enhanced
barrier properties to both moisture vapor and oxygen gas.
[0037] The core layer of the films described herein can comprise a
crystalline propylene homopolymer (preferably high crystalline) and
a desirable amount of hydrogenated hydrocarbon resins and synthetic
polyethylene wax. Suitable examples of highly isotactic crystalline
polypropylenes (HCPP) can include LyondellBasell's HP2409, or
Phillips 66's CH020XK, Total Petrochemical's LX10903 or 3270
grades. Typically, these HCPP resins can have a melt flow rate in
the range of about 1.5 to 3.5 g/10 min., a melting point in the
range of about 160-167.degree. C., and a density of about 0.90-0.92
g/cm.sup.3. Typical isotactic content of these high crystalline PP
resins can be above about 95%, and preferably about 96-98%,
measured via .sup.13C NMR spectra obtained in
1,2,4-trichlorobenzene solutions at 130.degree. C. The % percent
isotactic can be obtained by the intensity of the isotactic methyl
group at 21.7 ppm versus the total (isotactic and atactic) methyl
groups from 22 to 19.4 ppm.
[0038] Suitable examples of hydrogenated hydrocarbon resins can
include Plastolyn.TM. R1140 and Eastotac.TM. H-142W provided by
Eastman Chemicals; Oppera.TM. PR100A provided by ExxonMobil; and
Sukorez.RTM. SU-640 provided by Kolon Industries. Typically, these
hydrocarbon resins can be fully hydrogenated water-white amorphous
materials having a softening point of about 130 to 150.degree. C.;
a glass transition temperature (Tg) in the range of about 75 to
90.degree. C.; a weight-average molecular weight (Mw) in the range
of about 500 to 1000 g/mole; and a polydispersity index (PDI) of
about 1.7 to 2.0 as determined using size exclusion chromatography
(SEC). The hydrocarbon resins can be derived by thermally
polymerizing olefins of aliphatic C5 feedstocks, aromatic C9
feedstocks, or a combination of C5/C9 feedstocks obtained from
refinery industries, followed by a process of hydrogenation. The
core layer of the films disclosed herein can comprise about 2.5 to
25 wt % of the hydrocarbon resins. Preferably, the content of the
hydrocarbon resins is in the range of from about 5 to 15 wt % of
the core layer. In some embodiments, the core layer includes at
most about 25 wt %, about 20 wt %, about 15 wt. %, about 10 wt. %,
about 5 wt. %, or about 2.5 wt. % hydrocarbon resins.
[0039] Suitable examples of waxes can include synthetic
polyethylene waxes, paraffin waxes, and Fischer Tropsch waxes,
which can have a melting temperature (Tm) in the range of about 60
to 95.degree. C. and a number-average molecular weight in the range
of about 400 to 655 g/mole. Preferably, the melting point can be in
the range of about 65 to 92.degree. C. Characteristics of the wax
additives can include an ethylene backbone and highly crystalline
aptitude. Examples can include synthetic polyethylene waxes
provided by Baker Hughes such as Polywax.TM. 400, Polywax.TM. 500,
Polywax.TM. 600, and Polywax.TM. 655. Other examples of
polyethylene wax can be synthetic paraffin wax products, such as
grades of WAX#178P, WAX#275P, and WAX#504 provided by Koster
Keunen. More examples of polyethylene waxes can be crystalline
Fischer Tropsch waxes, such as Sasolwax.RTM. C80 (Tm=ca. 80 to
85.degree. C.) provided by Sasol Wax North America Corporation. The
core layer of the films disclosed herein can comprise about 0.5 to
2.0 wt % of synthetic polyethylene wax. Preferably, the PE wax in
the core layer can be in the range of about 0.75 to 1.5 wt %. In
some embodiments, the core layer includes at most about 2 wt %,
about 1.75 wt %, about 1.5 wt. %, about 1.25 wt. %, about 1 wt. %,
about 0.75 wt. %, or about 0.5 wt. % synthetic polyethylene
wax.
[0040] The core layer of the films disclosed herein can thus
comprise high crystalline propylene homopolymer, hydrocarbon resin,
and polyethylene wax to provide a transparent, high moisture vapor
barrier propylene-based and oriented film.
[0041] The outer skin layers of the laminate films disclosed herein
can include polyolefin resins for the application of heat-sealing,
winding, adhesion, or printing. These skin layers can be coextruded
with the core layer to form coextruded laminate films. The
polyolefin resins can include ethylene homopolymer, propylene
homopolymer, ethylene or propylene-based copolymers and terpolymers
(e.g. ethylene-propylene, ethylene-butene, propylene-butene,
ethylene-propylene-butene), or blends thereof. Modified polar
polyolefin resins such as grafted polar polyolefins or
copolymerized polar polyolefin resins can be added into the outer
layers to promote adhesion, particularly as a tie-resin or
tie-layer for receiving polar polymer coatings or coextruded
layers.
[0042] Polar polymers as coatings or coextruded layers can be
applied to a tie-layer bonded to a polypropylene-based substrate
through an inline or offline process for improving oxygen gas
barrier. The polar polymers can include ethylene vinyl alcohol
(EVOH), polyvinyl alcohol (PVOH), or modified polyvinyl
alcohol/polyvinyl amine copolymer (PV-Am), and
polyhydroxyaminoether (PHAE) or other polar polymers with high
oxygen barrier properties, and blends thereof. The layer of polar
polymers can be cross-linked to lessen the moisture absorption and
swelling due to strong polar molecular attractions. Cross-linking
of EVOH, PVOH, PV-Am (or blends thereof) or other polar polymers by
crystallites or chemical reaction can eliminate the swelling or
plasticization of moisture vapor/water to the film structure.
Examples of oxygen barrier coating compositions can include the
solutions of Selvol.TM. (aka Celvol.RTM.) 502 PVOH resin provided
by Sekisui Specialty Chemicals of America, LLC.; Excelval.RTM.
RS-2117 EVOH resin provided by Kuraray America Inc.; Freechem.RTM.
40 DL glyoxal cross-linker provided by Emerald Performance
Materials; solutions of PVOH/PVA Selvol.TM. Ultiloc.RTM. 5003 BRS
polyvinyl alcohol-polyvinyl amine (PV-Am) copolymer provided by
Sekisui Specialty Chemicals; Polycup.RTM. 9200 epichclorohydrin,
provided by Hercules, Inc., and citric acid provided by Duda
Energy, LLC. as suitable crosslinkers for the PV-Am. Examples of
coextrudable EVOH resins can include modified EVOH resin with
ethylene content in the range of 27 to 48 mol %, preferably 38 to
48 mol %, such as Soarnol.TM. EVOH grades provided by Nippon
Gohsei.
[0043] An optional but desirable amount of fluoropolymer additive
can be included in the core layer to improve the distribution of PE
waxes and help the moisture vapor barrier. The content of the
fluoropolymer additive can be in the range of about 100-1000 ppm of
the core layer, preferably about 300-600 ppm of the core layer.
This fluoropolymer can be typically available as a processing aid
in a masterbatch form and can be typically polymerized from two
monomers--hexafluoropropylene and vinylidene fluoride--to form a
poly(vinylidene) fluoride-co-hexafluoropropylene polymer
(1,1-difluoroethylene-1,1,2,3,3,3-hexafluoro-1-propene copolymer).
This fluoropolymer typically can have a weight average molecular
weight M.sub.w of about 400,000 to 455,000 g/mol; a number average
molecular weight M.sub.n of about 110,000 to 130,000 g/mol; a
melting point of about 135-140.degree. C.; a melt flow rate of
about 4-10 g/10 min. at 230.degree. C.; a viscosity of about 20,000
to 25,000 poise at 230.degree. C. and 100 sec.sup.-1; and a density
of about 1.78 g/cm.sup.3. A suitable supplier of the fluoropolymer
masterbatch is Ampacet Corporation with suitable grades such as
Ampacet 401198 (a 3 wt % loading of fluoropolymer in a propylene
homopolymer carrier resin) or Ampacet 402810 (a 5.0 wt % loading of
fluoropolymer in a propylene homopolymer carrier resin). These
masterbatches typically can have a density of about 0.90-0.92
g/cm.sup.3 and a melt flow rate of 3-12 g/min. at 230.degree.
C.
[0044] In some embodiments, the laminate film can comprise a first
layer (A), a core layer (B), a second skin layer (C), and a polar
polymer coating layer (D). The first layer (A) and the second skin
layer (C) can be coextruded onto the sides of the core layer (B); a
typical configuration is to have the skin layers (A) and (C) each
on opposite surfaces of the core layer (B). A layer of polar
polymers (D) can be coated on the first layer (A) opposite the
second skin layer (C) through said inline or offline coating
process. In this case, the first layer (A) is a tie-layer, and the
polar coating layer (D) is an outer layer and provides the
afore-mentioned high oxygen gas barrier property. In some
embodiments, the film comprises only core layer (B). In some
embodiments, the film comprises core layer (B) and first layer (A).
In some embodiments, the film comprises core layer (B) and second
skin layer (C). In some embodiments, the film comprises core layer
(B), first layer (A), and second skin layer (C). In some
embodiments, the film comprises core layer (B) and polar polymer
coating layer (D), wherein polar polymer coating layer (D) is
coated on a surface of core layer (B). In some embodiments, the
film comprises core layer (B), first layer (A), and polar polymer
coating layer (D), wherein polar polymer coating layer (D) is
coated on first layer (A). In some embodiments, the film comprises
core layer (B), second skin layer (C), and polar polymer coating
layer (D), wherein polar polymer coating layer (D) is coated on a
surface of the core layer (B) opposite second skin layer (C). In
some embodiments, the first layer (A) and/or second skin layer (B)
are not co-extruded with the core layer. In some embodiments, polar
polymer layer (D) can also be coextruded with the core layer. In
some embodiments, there are two polar polymer layers (D), one on
each side of the core layer. The multiple polar polymer layers can
also be on a surface of a tie layer that is on a surface of the
core layer.
[0045] The first layer (A) can comprise an isotactic propylene
homopolymer or "mini-random" ethylene-propylene copolymer (an EP
copolymer with a fractional amount of ethylene content, e.g. less
than 1 wt % ethylene co-monomer, preferably about 0.3-0.6 wt %) or
maleic anhydride-grafted (MAH-g) polyolefins, or blends thereof. A
composition blended with a desirable amount of MAH-g-polypropylene
can enhance the bond adhesion between the layer (A) and polar
coatings or inks compared to that with no added polar polymeric
compatibilizer. The core layer (B) can comprise highly isotactic
highly crystalline polypropylene, synthetic polyethylene wax,
hydrocarbon resin, and an optional fluoropolymer additive. Upon one
side is contiguously attached the first layer (A), and upon the
other side is contiguously attached the second skin layer (C) with
functionalities of heat sealing or winding, etc. as desired. The
second skin layer (C) can comprise a blend of heat sealable
ethylene-propylene-butene terpolymer, ethylene-propylene copolymer,
propylene-butene copolymer, or blends thereof.
[0046] The core layer (B) can include a desirable amount of
crystalline polyethylene wax in an amount of about 0.5-2.0 wt % of
the core layer. Preferably, the amount of crystalline polyethylene
can be between about 0.75-1.5 wt % of the core layer. Suitable
crystalline polyethylene waxes can include wax grades available
from Baker Hughes and Koster Keunen as previously described in the
art. High wax content in the core layer can be undesirable (e.g.
greater than about 3 wt %) since the miscibility of PE waxes in the
hydrocarbon resin phase and amorphous PP segments decreases with
cooling temperature such that wax migration and plate-out on
processing equipment can occur.
[0047] A desirable amount of hydrocarbon resin can also be included
in the core layer to further improve moisture barrier properties.
Hydrocarbon resin can also help in orientation of stretching the
high crystalline polypropylene and in preventing uneven stretch and
film breaks. Suitable loadings of hydrocarbon resin can be up to
about 25 wt % of the core layer. Preferably, hydrocarbon resin in
the core layer can be in the range of about 7.5-15 wt % to achieve
the optimal balance of high content of PP crystals and low free
volume in the amorphous phase of the core layer. The optimal
balance can be evidenced by the saturation in moisture vapor
barrier of the laminate films. The suitable hydrocarbon resins
should be fully hydrogenated after polymerization. Examples of
suitable hydrocarbon resins can include ExxonMobil Oppera.TM.
PR100A, Eastman Chemical company's Plastolyn.TM. R1140 and
Eastotac.TM. H-142W, and Kolon Industries' Sukorez.RTM. SU-640 as
described previously.
[0048] A desirable optional amount of fluoropolymer additive can be
also included in the core layer to help distribute PE waxes and
further enhance the moisture vapor barrier. A desirable amount of
optional fluoropolymer additive can be about 100-1000 ppm of the
core layer, preferably about 300-600 ppm of the core layer.
[0049] The outermost skin layers (A and C) on both sides of the
core layer (B) can have a thickness after biaxial orientation
between about 0.1 and 5 .mu.m, preferably between about 0.5 and 3
.mu.m, and more preferably between about 0.5 and 1.5 .mu.m. It is
well-known to those skilled in the art that there can be a need to
add inorganic or organic anti-blocking agents into the outermost
skin layers to improve processability in film-making and handling.
A desirable amount of anti-blocking agents may be added up to about
10,000 ppm to these outer layers, depending on their functionality.
Preferably about 300-5000 ppm of anti-blocking agents may be added.
Suitable inorganic anti-blocking agents can include those such as
inorganic silicas and sodium calcium aluminosilicates. Suitable
organic anti-blocking agents can include those such as cross-linked
spheres of polymethylsilsesquioxane and polymethylmethacrylate.
Typically, useful particle sizes of these anti-blocking agents can
be in the range of about 1-12 .mu.m, preferably in the range of
about 2-4 .mu.m. Suitable anti-blocking agents may also include
migratory slip agents. Examples of migratory slip agents can
include fatty amides and silicone oils of low molecular weight
molecules, and/or combinations thereof. Examples of--but not
exclusive of--fatty amides can be stearamide, erucamide,
behenamide, and/or combinations thereof.
[0050] If the second outer skin layer (C) of the films are to be
heat sealable, the heat-sealable layer can be any polyolefin that
has a lower melting point than that of the isotactic crystalline
propylene-based resin of the core layer. Such polyolefins can
include polyethylene, copolymers of propylene, ethylene, butene,
and blends thereof. Preferably, the polyolefin can be a copolymer
of propylene, either ethylene-propylene or butylene-propylene, and
preferably comprises a ternary ethylene-propylene-butene copolymer,
or blends thereof. Examples of suitable heat-sealable terpolymer
resin can include Sumitomo SPX78R6 and WF345R2 which have a melt
flow rate of about 9 g/10 min. at 230.degree. C. and a melting
temperature of about 128 to 134.degree. C. Examples of suitable
heat-sealable ethylene-propylene copolymers can include Total 8573
with a melt flow rate of about 8 g/10 min. at 230.degree. C.,
ExxonMobil Vistamaxx.TM. 3588FL with a melt flow rate of about 9
g/10 min. at 230.degree. C., or LyondellBasell Adsyl.TM. 7416 XCP
with a melt flow of about 7.5 g/10 min. at 230.degree. C.
[0051] If the second outer skin layer (C) of the films is not
designed for heat sealing but for winding purposes, this layer can
comprise a crystalline polypropylene or a blend of polypropylene
and ethylene-propylene copolymer with anti-blocking and/or slip
additives. Preferably, the surface of the winding layer can be
corona discharge-treated to provide a functional surface with
higher surface energy for lamination or coating with adhesives
and/or inks.
[0052] Additionally, the second outer layer (C) can also be
formulated to have a matte finish by adding a block copolymer blend
of polypropylene and one or more other polymers (e.g. polyethylene)
to provide a roughened and low gloss surface during the step of
film formation. This matte surface can also be corona
discharge-treated as desired, or could also be formulated with
propylene copolymers to impart a heat sealable matte layer.
Antiblock and slip additives as described previously may also be
added to this layer for control of coefficient of friction
(COF).
[0053] In some embodiments, the films or coextruded films can be
five-layered films comprising a core layer (B) blended with HCPP,
HCR, PE waxes, and an optional polar polymer compatibilizer.
Preferably, the compatibilizer can be a maleic anhydride-grafted
polypropylene resin. Additionally, two intermediate layers (E) of
polar polymers for oxygen gas barrier properties can be on each
surface of the core layer (B), and two outermost layers (F and G)
can be on each surface of an intermediate layers (E) opposite the
core layer (B). The layers (F and G) can be formulated for the
purpose of printing, adhesion, winding, heat sealing, and coating,
etc. The two polar polymer layers (E) can provide oxygen barrier
and block the potential of any migrations of wax molecules to the
outermost surfaces of the films.
[0054] For a typical 3-layer coextruded film embodiment as
described previously, the coextrusion process can include a
three-layered compositing die. The polymeric core layer (B) can be
sandwiched between the skin layer (A) and the heat-sealable or
winding layer (C). The outer layer (A) of a three layer laminate
sheet can be cast onto a chilling or casting drum with a controlled
temperature in the range of ca. 15 to 45.degree. C. to solidify the
non-oriented laminate sheet, followed by a secondary cooling on
another chilling drum with a controlled temperature. The
non-oriented laminate sheet can be stretched in the machine
direction at about 95 to 165.degree. C. at a ratio of about 4 to 6
times of the original length and then heat set at about 50 to
100.degree. C. to obtain a uniaxially oriented laminate sheet with
minimal thermal shrinkage. The uniaxially oriented laminate sheet
can be introduced into a tenter and preliminarily heated between
about 130.degree. C. and 180.degree. C., stretched in the
transverse direction at a ratio of about 7 to 10 times of the
original length, and heat-set to give a biaxially oriented sheet
with minimal thermal shrinkage. This biaxially oriented sheet may
be used in a process of offline coating to impart the oxygen
barrier polar polymer coating upon the desired side of the sheet
for the resultant laminate film for moisture vapor and oxygen gas
barrier final product. If a process of inline coating is used for
the resultant laminate film, the inline coating station can be
typically and preferentially located between the machine direction
orientation unit and the transverse direction orientation unit
(tenter). The MD-oriented sheet's surface of the outer layer of the
first layer (A) of the laminate can be preferably corona
discharge-treated to raise surface energy. A stretchable aqueous
coating of the desired polar polymer can be provided by the inline
coater through a process of gravure coating or rod coating (or
other wet coating means well known in the art). It can then be
added onto the (optionally) discharge-treated outer surface of the
first layer (A). The wet-coated uniaxially oriented laminate sheet
can be introduced into a tenter and preliminarily heated between
about 130.degree. C. and 180.degree. C., stretched in the
transverse direction at a ratio of about 7 to 10 times of the
original length, and heat-set to give a biaxially oriented sheet
with minimal thermal shrinkage. The tenter oven can also function
as a means to dry the aqueous coating. The dried polar polymer
coating can be typically about 0.1-2.0 G (0.025-0.5 .mu.m) in
thickness, preferably about 0.5-1.0 G (0.125-0.25 .mu.m). The
overall coated and biaxially oriented film can have a total
thickness between about 10 and 60 .mu.m, preferably between about
15 and 25 .mu.m.
[0055] The films disclosed herein can be better understood with
reference to the following examples, which are intended to
illustrate specific embodiments within the overall scope of the
invention.
Example 1
[0056] Example 1 represents a comparative example to describe the
experimental conditions of making the same. A 3-layer coextruded
film was made on a nominal 1.6 m wide biaxial orientation line,
comprising of a core layer (B), a skin layer (A) on one side of the
core layer, and a heat-sealable skin layer (C) on the other side of
the core layer opposite that of the skin layer (A). The core layer
comprised of about 100 wt % Total Petrochemical Co.'s LX10903 HCPP
resin. The skin layer (A) comprised of about 99.4 wt % Admer.RTM.
QF500A MAH-g-PP supplied by Mitsui Chemical Corporation and about
0.6 wt % ABVT19NSC antiblock masterbatch purchased from A.
Schulman. (ABVT19NSC is masterbatch of Silton.RTM. JC-30 in
ethylene-propylene copolymer with a blend ratio of 5/95
respectively. Silton.RTM. JC 30 is an anti-blocking agent with
nominal 3 .mu.m particle size of a spherical sodium calcium
aluminum silicate manufactured by Mizusawa Industrial Chemicals,
Co., Ltd.) The skin layer (C) is comprised of about 100 wt % of
ethylene-propylene-butene terpolymer sealant Sumitomo SPX78R6 which
also contained about 4000 ppm of a nominal 2 .mu.m particle size of
a spherical cross-linked silicone polymer (Momentive Performance
Materials' Tospearl.RTM. 120). The total thickness of this 3-layer
coextruded film substrate after biaxial orientation was nominal 70
G (17.5 .mu.m). The thickness of the skin layer (A) and sealant
skin layer (C) after biaxial orientation was nominal 4 G (1 .mu.m)
and 6 G (1.5 .mu.m), respectively. The thickness of the core layer
(B) is nominal 60 G (15 .mu.m). The skin layer (A) and core layer
(B) were melt-extruded at about 230-260.degree. C. The sealant
layer (C) was melt-extruded at 230-255.degree. C. The 3-layer
coextrudate was passed through a flat die to be cast on a chill
drum of about 20-26.degree. C. The formed cast sheet was passed
through a series of heated rolls at about 100-124.degree. C. with
differential speeds to stretch in the machine direction (MD) to a
4.75 stretch ratio. This was followed by transverse direction (TD)
stretching to an 8.0 stretch ratio in the tenter oven at about
150-170.degree. C. in a tenter oven. Inside the tenter oven, there
are three zones for the purposes of heating, stretching and
heat-setting. The temperatures of first, second and third zones are
ca. 165, 155, and 150.degree. C., respectively. After transverse
stretching, the film was heat-set in the third zone to minimize
thermal shrinkage, followed by a 5% relax in the transverse
direction. The resultant laminate film was corona discharge-treated
upon the surface of the outer layer opposite the outer skin layer
(C) before it was wound into a roll form. The film was then tested
for appearance, optical properties, oxygen gas/moisture vapor
barrier properties. The film was also forced-heat-aged by placing
it in a conditioning oven at an elevated temperature of about
50.degree. C. for 12 hrs in order to further reduce the free volume
in the amorphous phase of the core layer.
[0057] The three layer film was tested for barrier properties as
shown in Table 1. The sample has a poor moisture vapor transmission
rate of about 0.340 g/100 in.sup.2/day before aging, and about
0.321 g/100 in.sup.2/day after aging, respectively. Aging the film
sample did not significantly improve the moisture vapor barrier.
The sample also had a poor oxygen transmission rate of about 115
cc/100 in.sup.2/day. The O2TR barrier was tested without aging the
sample.
Examples 2-4
[0058] Example 2 was made using the same conditions as that of
Example 1. However, the recipe of the core layer was changed to
comprise about 90 wt % Total LX10903 HCPP resin and about 10 wt %
Oppera.TM. PR100A hydrocarbon resin (HCR, supplied by ExxonMobil).
The hydrocarbon resin was compounded into a masterbatch with Total
LX10903 HCPP resin at a ratio of 50/50 for easily feeding into the
hopper of an extruder.
[0059] Table 1 indicates that the resultant laminate film with 10%
HCR in the core layer (Ex 2) has an oxygen gas transmission rate of
about 82.4 cc/100 in.sup.2/day and a moisture vapor transmission
rate of about 0.231 g/100 in.sup.2/day. The oxygen barrier is about
1.4 times better than the comparative film made in Example 1 and
the moisture vapor is about 1.5 times better than the comparative
film of Example 1.
[0060] Examples 3-4 present a process to prepare coated films by
coating a polar polymeric layer (D) on the outer surface of the
layer A of Example 2 through inline gravure coating after machine
direction orientation (base film recipe was listed in Table 1). The
exposed surface of uniaxially oriented film was corona
discharge-treated first and then an aqueous liquid coating solution
for improving oxygen barrier properties was continuously coated
onto the treated surface of the layer (A) of Example 2 (base film)
using a direct gravure roll coating system 45 BCM (billion cubic
microns). The sheet with coated solution on it then was fed at a
line speed of about 15.5 ft/min. into a tenter oven with three
temperature control zones. The wet coating was dried to remove
solvent water in the pre-heating zone with a temperature range
measured in the range of about 80 to 90.degree. C. The dried
barrier coating layer after further heating was stretched to about
8.0 times of the initial dimension in transverse direction. Coating
weight (thickness) can be controlled by adjusting the solid content
of the coating solution according to machine engraving coating
chart. In this BOPP film, B5K and B18 are examples of polar
polymeric coating compositions that were used to improve oxygen
barrier properties. A coating thickness of about 0.70 G (0.175
.mu.m) after TD stretch was targeted for all coated films to
achieve an optimal balance in cost and barrier performance.
[0061] B5K is an oxygen barrier coating solution of a composition
after drying of about 58.6 wt % polyvinyl alcohol (Selvol.TM. 502
PVOH resin provided by Sekisui Specialty Chemicals of America),
about 28.25 wt % ethylene vinyl alcohol (Excelval.RTM. RS-2117 EVOH
resin provided by Kuraray America Inc.), about 12.27 wt % glyoxal
(Freechem.RTM. 40 DL cross-linker provided by Emerald Performance
Materials), and about 0.87 wt % defoamers/surfactants
(Surfynol.RTM. 420 anti-foamer/leveling surfactant provided by Air
Products and Chemicals, Inc.). B18 is another oxygen barrier
coating solution of a composition after drying of about 84.63 wt %
PVOH/PVA (Selvol.TM. Ultiloc.RTM. 5003 BRS, provided by Sekisui
Specialty Chemicals of America, Dallas, Tex.), about 0.85 wt %
epichlorohydrin (Polycup.RTM. 9200 epichclorohydrin, provided by
Hercules, Inc.), and about 13.82 wt % citric acid (food grade,
provided by Duda Energy, LLC), and about 0.71 wt %
defoamers/surfactants (Surfynol.RTM. 420 anti-foamer/leveling
surfactant provided by Air Products and Chemicals, Inc.).
[0062] After coated with the polar polymeric barrier coating, the
resultant laminate films showed significant improvements in oxygen
gas barrier properties. The oxygen gas transmission rates of the
resultant films coated with B5K and B18 are about 1.67 cc/100
in.sup.2/day and about 0.035 cc/100 in.sup.2/day, respectively.
These values of oxygen transmission rates are two orders of
magnitude for B5K and four orders for B18 better than that of the
uncoated base film (Example 2). B18 coating composition in oxygen
barrier improvement is further significantly better than B5K.
However, no significant moisture vapor barrier improvement was
observed for these coated film Examples 3 and 4 in comparison with
the MVTR values of uncoated film (Example 2) measured before and
after aging.
Examples 5-10
[0063] Examples 5-10 were made using the same conditions as that of
Examples 3 and 4. There was no change in the layers of (A), (C) and
(D). The composition of the core layer (B) was changed to improve
moisture vapor barrier properties. The core layer comprised of
about 10 wt % Oppera.TM. PR100A, about 1.0 wt % synthetic
polyethylene wax (PE wax), and about 600 ppm fluoropolymer additive
(shown in Table 1). The content of Total LX10903 HCPP resin was
adjusted accordingly to match a total weight ca. 100% in the core
layer. The synthetic polyethylene wax additives are Baker Hughes
Polywax.TM. 400 (Tm=ca. 81.degree. C.), 500 (Tm=ca. 88.degree. C.),
and 655 (Tm=ca. 99.degree. C.), respectively. The wax additives
were compounded into a masterbatch with Total LX10903 HCPP resin at
a ratio of 25/75 for easily feeding into the hopper of the core
layer. The fluoropolymer additive in this invention was used as a
masterbatch (gradename 402810) obtained from Ampacet which contains
5 wt. % fluoropolymer and 95 wt % ethylene-propylene copolymer.
[0064] The resultant laminate films demonstrated a significant
moisture vapor barrier improvement in comparison with the MVTR
values of the films in Examples 2-4. Specifically, the moisture
vapor barrier properties were further improved by heat aging the
films at elevated temperature of about 50.degree. C. for about 12
hrs. The improvement of PE wax additives to the moisture vapor
barrier follows the order of wax molecular weight of the
Polywax.TM. grades 400>500>655, probably due to the order of
the increasing crystallization temperature (Tc) of the PE waxes.
The Polywax.TM. 400 has the lowest Tc at ca. 73.degree. C. (peak
temperature) which is the closest to the aging temperature of about
50.degree. C. (the crystallization of Polywax.TM. 400 starts at
around 50.degree. C.). For the wax additives with higher Tc,
increasing aging temperature helped decrease the MVTR of the
resultant film due to the formation of more perfect PE wax crystals
at higher aging temperature. As expected, the oxygen gas barrier
properties of the resultant films coated with B5K or B18 were not
improved by adding PE wax and fluoropolymer additives in the core
layer. The thickness and performance of polar polymeric coatings
dominated the oxygen gas barrier properties of the resultant
laminate films.
Comparative Examples 1-3
[0065] Comparative Examples (CEx) 1-3 were made using the same
conditions as that of Examples 5-10. The composition of the core
layer (B) was changed to evaluate the influence of fluoropolymer
additive on the moisture vapor barrier properties of the resultant
laminate films. The PE wax additive in the core layer of all
Comparative Examples 1-3 was about 1.0 wt % Polywax.TM. 500. The
Comparative Example 1 comprised of about 600 ppm fluoropolymer in
the core layer while the Comparative Examples 2-3 did not contain
fluoropolymer additive (as shown in Table 1).
[0066] The resultant laminate films with added fluoropolymer
additive in the core layer did not show significant improvements in
moisture vapor barrier properties, by comparing the MVTR of Ex 7,
Ex 8, and CEx 1 with that of CEx 2 and CEx 3. All examples after
forced heat-aging had a value of MVTR in the range of about 0.153
to about 0.161 g/100 in.sup.2/day.
Examples 11-16
[0067] A process similar to Example 3 was repeated to make nominal
80 G (20 .mu.m) laminate films (Ex 11-16 shown Table 2). The
thickness of the core layer was increased from nominal 60 G to 70 G
(15-17.5 .mu.m), therein, the resultant laminate films have total
thickness of nominal 80 G (20 .mu.m). The recipe of the core layer
(B) for this set of experiments is listed in Table 2 except for a
small variation in the content of Total LX10903 HCPP resin to match
a total weight ca. 100 wt % in the core layer. B18 was the only
barrier coating solution used to coat the uniaxially oriented
laminate film.
[0068] As expected, a thicker core layer (70 G or 17.5 .mu.m) of
the resultant films provided a better moisture vapor barrier in
comparison with that of 60 G (15 .mu.m) core layer in the art.
Example 12 showed a typical MVTR value (about 0.175 g/100
in.sup.2/day) for the type of laminate films with HCR modification
but no PE wax additive added into the core layer. After heat aging,
the MVTR was only slightly reduced to the value of about 0.172
g/100 in.sup.2/day. If about 1.0 wt % Polywax.TM. 400 was added
into the core layer (Ex 12), the MVTR of the resultant laminate
film was reduced to about 0.159 g/100 in.sup.2/day before aging and
about 0.131 g/100 in.sup.2/day after nominal 50.degree. C. and 12
hrs heat-aging, respectively. For comparison, fluoropolymer
additive and polar polymeric coating did not show good improvements
in the moisture barrier of the resultant laminate film as shown in
Ex 13 and Ex 14. Similar reduction in MVTR values was also observed
for the resultant laminate film with ca. 1.0 wt % Polywax.TM. 500
added into the core layer (Ex 15 and Ex 16).
Comparative Examples 4-5
[0069] A process similar to Example 12 was repeated to make the
nominal 80 G (20 m) resultant laminate films (CEx 4 and CEx5). The
recipe of the core layer (B) comprised of about 3000 ppm
fluoropolymer additive (about 6 wt % Ampacet 402810 masterbatch in
the core layer), about 10 wt % Oppera.TM. PR100A hydrocarbon resin,
and about 84 wt % Total LX10903 HCPP resin. There was no PE wax
additive added into the core layer. A base film was made and then
B18 barrier coating solution was used to coat the uniaxially
oriented laminate film after MDO.
[0070] As shown in Table 2, the MVTR (about 0.195 g/100
in.sup.2/day) of the resultant films with added 3000 ppm
fluoropolymer additive but no added PE wax additive (CEx 4 and CEx
5) was slightly higher than the MVTR (about 0.175 g/100
in.sup.2/day) of the control film (Ex 12) before heat-aging. After
heat-aging, the resultant films showed some improvements in
moisture vapor barrier according to the result of about 0.146 g/100
in.sup.2/day for uncoated film or about 0.164 g/100 in.sup.2/day
for coated film. The extent of MVTR improvement after force-aging
was comparable with that obtained from Polywax.TM. 500 at about 1.0
wt % loading.
Examples 17-24
[0071] A process similar to Example 12 was repeated to make the
nominal 80 G (20 .mu.m) resultant laminate films of Examples 17-24
shown in Table 3. The recipe of the core layer (B) comprised of
about 10 wt % Oppera.TM. PR100A but no fluoropolymer additive. The
content of Polywax.TM. 400 in the core layer varied in the range of
about 0 wt % to about 2.0 wt %. LX 10903 HCPP resin was added to
match a total weight ca. 100% in the core layer. A base film was
made and then B18 barrier coating solution was used to coat the
uniaxially oriented laminate film after MDO.
[0072] As shown in Table 3, the MVTR of the resultant laminate
films was significantly reduced from about 0.175 g/100 in.sup.2/day
(Ex 17, no wax) to about 0.098 g/100 in.sup.2/day (Ex 24, 2.0 wt %
Polywax.TM. 400) with increasing content of Polywax.TM. 400. After
heat aging (ca. 50.degree. C./12 hrs), the MVTR of the resultant
laminate films was reduced to a lower value of about 0.074 g/100
in.sup.2/day. However, the O2TR of the coated resultant laminate
films was slightly increased from about 0.36 cc/100 in.sup.2/day to
about 1.2 cc/100 ln.sup.2/day with increasing content of
Polywax.TM. 400 in the core layer, which was probably due to the
formation of pin holes in the coating layer potentially caused by
light wax migration. No obvious hazy spots underneath the polar
polymeric coating layer were observed for those coated films with
Polywax.TM. 400 additive, the extent of wax migration should be at
a low level which does not impact the appearance of the resultant
laminate films.
Examples 25-26
[0073] A process similar to Example 12 was repeated to make the
nominal 80 G (20 .mu.m) resultant laminate films of Examples 25-26
shown in Table 3. The recipe of the core layer (B) comprised of
about 10 wt % Oppera.TM. PR100A and about 1.5 wt % Polywax.TM. 500
and about 88.5 wt % LX 10903 HCPP resin. Oxygen gas barrier coating
solution was B18.
[0074] Before heat aging, the MVTR of the resultant laminate films
was reduced slightly from about 0.175 g/100 in.sup.2/day (Ex 17) to
about 0.157 g/100 in.sup.2/day (Ex 25). After heat aging
(50.degree. C./12 hrs), the MVTR of the resultant laminate film was
reduced to a significantly low level in the range of about
0.102-0.117 g/100 in.sup.2/day. The O2TR of the coated laminate
film with added 1.5 wt % Polywax.TM. 500 was comparable to that of
the coated laminate film with added Polywax.TM. 400. The appearance
of the coated laminate film was comparable to that of the uncoated
laminate films with added Polywax.TM. 500.
Comparative Examples 6-9
[0075] A process similar to Example 23 was repeated to make the
nominal 80 G (20 .mu.m) resultant laminate films of CEx 6-9 shown
in Table 3. The recipe of the core layer (B) comprised of about 2.0
wt % Polywax.TM. 400 (CEx 6 and CEx 7) and Polywax.TM. 500 (CEx 8
and CEx 9), respectively. LX 10903 HCPP resin in the core layer was
about 98 wt %. No hydrocarbon resin was added into the core layer.
A base film was made and the oxygen gas barrier coating solution
B18 was coated on the base film after MDO.
[0076] The two uncoated base films (CEx 6 and CEx 8) had good
appearance and showed no hazy wax spots, while hazy wax spots were
observed for the two coated films (CEx 7 and CEx 9). Both
Polywax.TM. 400 and 500 waxes migrated to the top surface of the
uncoated films in the tenter oven, and then after migration, the
waxes vaporized (smoked in the TD stretch oven), giving a clear
appearance. No hazy wax spots could be seen for those uncoated
films. With a polar top coating (a capping layer (D)) over the top
surface of the layer (A), the top polar coating blocked the
pathways of the vaporization of the migrated wax molecules trapped
in between the layer (A) and layer (D), wax molecules formed
crystals which could be seen visually and led to a poor appearance
to the resultant laminate films. Without hydrocarbon resin in the
core layer, PE wax molecules could more easily migrate to the top
surface of the resultant laminate films in the tenter oven, leading
to the formation of hazy wax crystals seen for the coated laminate
films.
[0077] As is evidenced by the results in Table 3, the MVTR of the
coated and uncoated resultant laminate films with about 2.0 wt %
Polywax.TM. 400 or 500 in the core layer showed very limited
improvements in the moisture barrier properties in comparison with
the MVTR of Ex 1 (about 100 wt % HCPP resin in the core layer)
before heat aging. After heat aging, the MVTR of the resultant
films was about 0.150 g/100 in.sup.2/day for CEx 7 (2.0 wt %
Polywax.TM. 400) and to about 0.199 g/100 in.sup.2/day for CEx 9,
(2.0 wt % Polywax.TM. 500), respectively. Polywax.TM. 400 had
slightly better effects on the moisture vapor barrier improvement
than Polywax.TM. 500. The MVTR values of those films with only PE
wax additives in the core layer were much higher than that of the
resultant laminate films with a combination of hydrocarbon resin
and PE waxes in the core layers. The O2TR of the coated resultant
films were about twice higher than that of the resultant film with
added hydrocarbon resin in the core layer (Ex 24) due to pin holes
induced from severe wax migration.
Examples 27-35
[0078] A process similar to Example 18 was repeated to make the
nominal 80 G (20 .mu.m) resultant laminate films of Examples 27-35
shown in Table 4. The recipe of the core layer (B) comprised of
about 10-12.5 wt % hydrocarbon resin (ExxonMobil Oppera.TM. PR100A,
HCR) or about 10.0 wt % hydrocarbon resin (Eastman Eastotac.TM.
H-142W, named as HCR1 in Table 4). The content of synthetic
polyethylene waxes in the core layer was in the range of from about
0.5 to 1.5 at %, selected from Polywax.TM. 400, 500 and 600
supplied by Bake Hughes or synthetic paraffin wax Wax#178P (Tm=ca.
78-83.degree. C.) and WAX#201P (Tm=ca. 96-100.degree. C.) supplied
by Koster Keunen. Both hydrocarbon resins and waxes were compounded
into a masterbatch with Total LX10903 HCPP resin at a ratio of
50/50 and 25/75, respectively, for easily feeding into the hopper
of an extruder. Oxygen gas barrier coating solution was B18.
[0079] As shown in Table 4, the resultant laminate film of Ex 27
with ca. 12.5 wt % Oppera.TM. PR100A in the core layer, higher than
the ca. 10.0 wt % HCR content of Examples Ex 11 and 17, does not
show moisture barrier improvement before aging. After aging, the
MVTR of resultant laminate film was reduced slightly from about
0.184 to about 0.164 g/100 in.sup.2/day. Increasing the content of
Polywax.TM. 400 from about 0.0 to about 0.5-1.0 wt %, the MVTR of
the resultant films of Examples Ex 28 and Ex 29 was reduced from
about 0.184 to about 0.176-0.159 g/100 in.sup.2/day, especially,
after the laminate films were heat aged at ca. 50.degree. C. for
about 12 hrs, the MVTR of the resultant laminate films was reduced
further from about 0.164 to about 0.136-0.124 g/100 in.sup.2/day.
The O2TR of the resultant laminate films of Examples Ex 27, Ex 28
and Ex 29 was reduced slightly with increasing wax content in the
core layer.
[0080] In Ex 30 and Ex 31, the hydrocarbon resin in the core layer
was replaced by about 10.0 wt % Eastotac.TM. H-142W, and the
content of Polywax.TM. 500 varied from about 1.0 to 1.5 wt %. The
MVTR of the resultant laminate films was higher than that of Ex 27
to 29 as shown in Table 4, however, after heat aging at 50.degree.
C. for about 12 hrs, the MVTR of the resultant laminate films was
reduced to a significant low level of about 0.151 and 0.128 g/100
in/day, respectively. To compare with Ex 30, the hydrocarbon resin
of Ex 32 was changed to about 10.0 wt % Oppera.TM. PR100A. The MVTR
of the resultant laminate film of Ex 32 was slightly lower than
that of Ex 30 before heat aging, however, the MVTR of Ex 30 and
Ex32 showed little difference after heat aging. The O2TR of the
resultant laminate films of Ex 30 and Ex 31 increased about one
fold with increasing wax content in the core layer.
[0081] In Ex 33 to 35, the core layer contained ca. 10.0 wt %
hydrocarbon resin Oppera.TM. PR100A, and ca. 1.5 wt % wax additive
selected from Polywax.TM. 600 and synthetic paraffin WAX#178P and
WAX#201P provided by Koster Keunen. The MVTR of the resultant
laminate films after heat aging was significantly reduced to about
0.140, 0.128 and 0.141 g/100 in.sup.2/day, respectively. The O2TR
of the resultant laminate films was reduced to the range of from
about 0.026 to 0.041 cc/100 in.sup.2/day.
[0082] Optical properties of all resultant laminate films in the
art depended on the recipes and experimental condition setup of
each set of experiment. The data of optical properties of the
resultant laminate films shown in each table was obtained from
measuring the film samples made with the same single experiment
setup, starting with a control example listed on the top of each
table. No attempts were applied to improve the optical properties
of each example during the process of making the same. No obvious
wax hazy spots underneath the polar polymeric coating layer were
observed for those coated films with both wax additive and
hydrocarbon resin in the core layer, wax migration at a level did
not appear to impact the appearance of the resultant laminate
films. However, without adding hydrocarbon resin into the core
layer, heavy hazy wax spots underneath the polar polymeric coating
layer due to wax migration were observed for the coated resultant
films.
[0083] Thus, Applicants have discovered a solution to provide
significantly improved moisture vapor barrier and oxygen gas
barrier for transparent BOPP films by utilizing a combination of
hydrocarbon resin, crystalline polyethylene wax, and polar
polymeric barrier coatings. Such an inventive combination of
additives also maintained high transparency (low haze), high gloss,
and good printability, and wetting tension properties of the
film.
[0084] The barrier properties of the Examples ("Ex") and
Comparative Examples ("CEx") are shown in Tables 1, 2, 3 and 4.
Table 1 summarizes the core layer formulations, oxygen barrier
coatings, moisture vapor transmission rate (MVTR), oxygen gas
transmission rate (O2TR) and optical properties of the nominal 70 G
(17.5 .mu.m) resultant laminate films of Examples 1-10 and
Comparative Examples 1-3. Table 2 summarizes the core layer
formulations, oxygen barrier coatings, moisture vapor transmission
rate and optical properties of the nominal 80 G (20 .mu.m)
resultant laminate films of Examples 11-16 and Comparative Examples
4-5. Table 3 summarizes the core layer formulations, oxygen barrier
coatings, moisture vapor transmission rate, oxygen gas transmission
rate and optical properties of the resultant laminate films of
Examples 17-26 and Comparative Examples 6-9. Table 4 summarizes the
core layer formulations, oxygen barrier coatings, moisture vapor
transmission rate and optical properties of the resultant laminate
films of Examples 27-35.
TABLE-US-00001 TABLE 1 MVTR (g/ Polywax Polywax Polywax MVTR (g/
100 in.sup.2/day) O2TR Gloss Gloss HCR 400 500 655 FP 100 in.sup.2/
aged at (cc/ (60.degree.) (20.degree.) Example (%) (%) (%) (%)
(ppm) Coating day) 50.degree. C./12 hrs 100 in.sup.2/day) cast side
sealant side Haze Ex1 0 0.345 0.321 115 120 86 2.9 Ex2 10 0.231
0.223 82.4 119 77 4.6 Ex3 10 B5K 0.232 0.190 1.67 128 88 3.7 Ex4 10
B18 0.226 0.217 0.035 131 93 3.2 Ex5 10 1.0 600 B5K 0.145 0.121
1.55 123 80 3.8 Ex6 10 1.0 600 B18 0.182 0.136 0.027 125 82 3.8 Ex7
10 1.0 600 B5K 0.167 0.159 1.73 126 87 3.7 Ex8 10 1.0 600 B18 0.177
0.158 129 88 3.6 Ex9 10 1.0 600 B5K 0.206 0.982 126 83 3.6 Ex10 10
1.0 600 B18 0.191 0.176 0.047 122 74 3.2 CEx1 10 1.0 600 0.204
0.161 118 80 4.6 CEx2 10 1.0 0.231 0.154 117 81 4.3 CEx3 10 1.0 B5K
0.197 0.153 1.35 126 86 3.7
TABLE-US-00002 TABLE 2 Polywax Polywax MVTR Gloss Gloss HCR 400 500
FP MVTR (g/100 in2/day) (60.degree.) (20.degree.) Example (%) (%)
(%) (ppm) Coating (g/100 in2/day) aged at 50.degree. C./12 hrs cast
side sealant side Haze Ex11 10.0 0.175 0.172 104 68 4.7 Ex12 10.0
1.0 0.159 0.131 101 59 4.7 Ex13 10.0 1.0 600 0.168 0.129 103 61 4.8
Ex14 10.0 1.0 600 B18 0.136 114 69 4.1 Ex15 10.0 1.0 600 0.167
0.143 103 51 5 Ex16 10.0 1.0 600 B18 0.154 110 60 4.5 CEx4 10.0
3000 0.195 0.146 109 66 4.6 CEx5 10.0 3000 B18 0.164 114 72 4
TABLE-US-00003 TABLE 3 Polywax Polywax MVTR Gloss Gloss HCR 400 500
MVTR (g/100 in2/day) O2TR (60.degree.) (20.degree.) Example (%) (%)
(%) Coating (g/100 in2/day) aged at 50.degree. C./12 hrs (cc/100
in2/day) cast side sealant side Haze Ex17 10 0.175 73.5 108 64 4.1
Ex18 10 B18 0.172 0.165 0.368 105 58 4.1 Ex19 10 1.0 0.139 0.104
103 54 4.2 Ex20 10 1.0 B18 0.158 0.109 0.362 116 73 3.2 Ex21 10 1.5
0.118 0.101 59.9 103 55 4.2 Ex22 10 1.5 B18 0.133 0.103 1.18 114 67
3.3 Ex23 10 2.0 0.127 0.078 102 52 4.4 Ex24 10 2.0 B18 0.098 0.074
1.18 112 63 3.7 Ex25 10 1.5 0.157 0.117 98 48 4.9 Ex26 10 1.5 B18
0.172 0.102 1.02 112 66 3.4 CEx6 2.0 0.234 0.179 93 53 4.9 CEx7 2.0
B18 0.304 0.150 2.57 133 110 2.4 CEx8 2.0 0.198 0.279 90 46 5.1
CEx9 2.0 B18 0.261 0.199 2.20 131 103 2.6
TABLE-US-00004 TABLE 4 MVTR (g/ 100 in2/ MVTR day) O2TR Gloss
Polywax Polywax Polywax WAX# WAX# (g/ aged at (cc/ Gloss
(60.degree.) HCR HCR1 400 500 600 178P 201P 100 in2/ 50.degree. C./
100 in2/ (20.degree.) seatant Example (%) (%) (%) (%) (%) (%) (%)
Coating day) 12 hrs day) cast side side Haze Ex27 12.5 B18 0.184
0.164 0.088 103 47 4.4 Ex28 12.5 0.5 B18 0.176 0.136 0.055 116 69 3
Ex29 12.5 1.0 B18 0.159 0.124 0.041 112 61 4 Ex30 10.0 1.0 B18
0.230 0.151 0.078 102 44 4.2 Ex31 10.0 1.5 B18 0.212 0.128 0.153
103 45 4.2 Ex32 10.0 1.0 B18 0.190 0.139 0.022 104 50 3.9 Ex33 10.0
1.5 B18 0.189 0.140 0.026 99 45 4 Ex34 10.0 1.5 B18 0.186 0.123
0.040 102 48 3.9 Ex35 10.0 1.5 B18 0.252 0.141 0.041 103 50 4
Test Methods
[0085] The various properties in the above examples were measured
by the following methods:
[0086] Moisture vapor transmission rate (MVTR) of the films was
measured by using a Mocon.RTM. Permatran 3/31 unit measured
substantially in accordance with ASTM F1249. In general, the
preferred value can be an average value equal to or less than about
0.17 g/100 in.sup.2/day (2.64 g/m.sup.2/day).
[0087] Oxygen gas transmission rate (O2TR) of the films was
measured with a Mocon.RTM. Oxtran.RTM.2/20 Oxygen Permeability
Testing Apparatus (manufactured by Mocon Inc.) substantially in
accordance with ASTM D3985. In general, the preferred value can be
an average value equal to or less than about 2.0 cc/100
in.sup.2/day (31.0 cc/m.sup.2/day); and more preferably, less than
about 1.0 cc/100 in.sup.2/day (15.5 cc/m.sup.2/day).
[0088] Films for MVTR analysis were tested directly without
lamination to other substrates. Films for O2TR analysis were
laminated to a substrate of PATCO 502A low density
polyethylene/acrylic adhesive pressure sensitive tape (Berry
Plastics, Bristol, R.I.) adhered to the outer surface of the layer
(A) for uncoated film or to the outer surface of the coating layer
(D).
[0089] Forced heat-aging of the test films was conducted as
follows: several 81/2''.times.11'' cut-sheet samples of the
exemplary films (e.g. about a dozen sheets of one of the respective
film variables) were stacked or cut from a slab sample with the
corona discharge-treated surface of the cut-sheet film samples
facing in the "up" position. This stack of film samples were then
placed between two smooth, flat steel plates (ordinary office
printer paper was placed over the top film sheet sample and on top
of the bottom steel plate to separate the film samples from direct
contact with the steel plates), and this construction was then
placed inside a conditioning oven. A 30-lbs weight was placed on
top of the uppermost steel plate. The conditioning oven was set for
about 40-70.degree. C. for about 12-48 hours as desired. If aging
at a lower temperature, the aging time should be extended, e.g. if
40.degree. C. aging temperature is used, the aging time should be
extended to about 24-48 hours. Preferably, the aging time can be
about 12 hours and aging temperature used can be about 50.degree.
C. for the Examples of this invention. After aging, the stack of
film samples was removed and allowed to cool to room temperature.
The weight and upper steel plate were removed, and the office paper
and the first sheet of the film sample stack were discarded. The
remaining film sheet samples were carefully separated for moisture
vapor transmission rate test.
[0090] Haze of the film was measured using a BYK Gardner
Instruments "Haze-Gard Plus" haze meter substantially in accordance
with ASTM D1003. Preferred haze values can be about 5% or less for
a single sheet.
[0091] Gloss of the film was measured using a commercially
available gloss meter such as available from BYK Gardner
Instruments "Mirror-Tri-Gloss" and measured substantially in
accordance with ASTM D2457. Gloss was measured on both sides of the
film, at an angle of 60.degree. for the cast side (coated or not
coated side) and an angle of 20.degree. for the opposite side (heat
sealable or functional side). Preferred values for cast side
60.degree. gloss were about 95 or higher (preferably ca. 100 or
higher); preferred values for the heat sealable side 20.degree.
gloss can be about 40 or higher (preferably ca. 50 or higher).
[0092] This application discloses several numerical ranges in the
text and figures. The numerical ranges disclosed inherently support
any range or value within the disclosed numerical ranges even
though a precise range limitation is not stated verbatim in the
specification because this invention can be practiced throughout
the disclosed numerical ranges.
[0093] The above description is presented to enable a person
skilled in the art to make and use the invention, and is provided
in the context of a particular application and its requirements.
Various modifications to the preferred embodiments will be readily
apparent to those skilled in the art, and the generic principles
defined herein may be applied to other embodiments and applications
without departing from the spirit and scope of the invention. Thus,
this invention is not intended to be limited to the embodiments
shown, but is to be accorded the widest scope consistent with the
principles and features disclosed herein. Finally, the entire
disclosure of the patents and publications referred in this
application are hereby incorporated herein by reference.
* * * * *