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Sommaire du brevet 2271482 

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Disponibilité de l'Abrégé et des Revendications

L'apparition de différences dans le texte et l'image des Revendications et de l'Abrégé dépend du moment auquel le document est publié. Les textes des Revendications et de l'Abrégé sont affichés :

  • lorsque la demande peut être examinée par le public;
  • lorsque le brevet est émis (délivrance).
(12) Demande de brevet: (11) CA 2271482
(54) Titre français: COMPOSITIONS DE POLYOLEFINE A PROPRIETES D'ETANCHEITE EQUILIBREES ET A MODULE AMELIORE ET PROCEDE CORRESPONDANT
(54) Titre anglais: POLYOLEFIN COMPOSITIONS WITH BALANCED SEALANT PROPERTIES AND IMPROVED MODULUS AND METHOD FOR SAME
Statut: Réputée abandonnée et au-delà du délai pour le rétablissement - en attente de la réponse à l’avis de communication rejetée
Données bibliographiques
(51) Classification internationale des brevets (CIB):
  • C8L 23/04 (2006.01)
  • B32B 27/32 (2006.01)
  • C8J 5/18 (2006.01)
  • C8L 23/08 (2006.01)
  • C9J 123/08 (2006.01)
(72) Inventeurs :
  • BOSIERS, LUC (Belgique)
  • DEGROOT, JACQUELYN A. (Etats-Unis d'Amérique)
  • KALE, LAWRENCE T. (Etats-Unis d'Amérique)
  • CHUM, PAK-WING STEVE (Etats-Unis d'Amérique)
  • DEKUNDER, STACI A. (Etats-Unis d'Amérique)
  • VAN DUN, JOZEF J. (Belgique)
  • OSWALD, THOMAS T. (Etats-Unis d'Amérique)
(73) Titulaires :
  • THE DOW CHEMICAL COMPANY
(71) Demandeurs :
  • THE DOW CHEMICAL COMPANY (Etats-Unis d'Amérique)
(74) Agent: SMART & BIGGAR LP
(74) Co-agent:
(45) Délivré:
(86) Date de dépôt PCT: 1997-11-13
(87) Mise à la disponibilité du public: 1998-05-22
Requête d'examen: 1999-09-30
Licence disponible: S.O.
Cédé au domaine public: S.O.
(25) Langue des documents déposés: Anglais

Traité de coopération en matière de brevets (PCT): Oui
(86) Numéro de la demande PCT: PCT/US1997/020574
(87) Numéro de publication internationale PCT: US1997020574
(85) Entrée nationale: 1999-05-12

(30) Données de priorité de la demande:
Numéro de la demande Pays / territoire Date
08/748,321 (Etats-Unis d'Amérique) 1996-11-13
08/880,006 (Etats-Unis d'Amérique) 1997-06-20

Abrégés

Abrégé français

La présente invention concerne une composition de film d'étanchéité comportant au moins deux matériaux constitutifs de polymère d'éthylène. Selon un mode de réalisation, la présente invention concerne une structure multicouches présentant des propiétés d'étanchéité équilibrées et comportant une couche d'étanchéité et une couche de polypropylène, la couche d'étanchéité comprenant une composition de polymère ou est fabriquée à partie de celle-ci, cette composition présentant des caractéristiques particulières de poids moléculaire et un second polymère d'éthylène. Selon un mode de réalisation préféré, la présente invention concerne un film polyoléfinique à densité moyenne et une composition caractérisée par un excellent équilibre entre une température d'initiation d'étanchéité et un module de film amélioré. Le film et la composition comprennent au moins un polymère d'éthylène basse densité ramifié de façon homogène et au moins un polymère d'éthylène basse densité ramifié de façon homogène ou hétérogène ou sont fabriqués à partir de ceux-ci. La présente invention est particulièrement utilisée dans des applications nécessitant des temps de prise d'étanchéité rapide et une bonne stabilité dimensionnelle d'un emballage, par exemple, emballage de cuisson, emballage rempli à chaud, sachets pour matière fluide, emballage à contenu comprimé, emballage par film rétrécissable et emballage par film barrière rétrécissable ainsi que des structures de film de polypropylène (BOPP) orientées biaxialement.


Abrégé anglais


This invention pertains to a sealant film composition comprising at least two
ethylene polymer component materials. One aspect of the invention relates to a
multilayer structure having balanced sealant properties and comprising a
sealant layer and a polypropylene layer, wherein the sealant layer comprises
and is made from a polymer composition having particular molecular weight
characteristics and a second ethylene polymer. A preferred embodiment of the
present invention pertains to a medium density polyolefinic film and
composition characterized by an excellent balance of a low seal initiation
temperature and improved film modulus. The film and composition is comprised
of and made from at least one lower density homogeneously branched ethylene
polymer and at least one higher density heterogeneously or homogeneously
branched ethylene polymer. The invention is particularly useful in those
applications requiring fast seal times and good packaging dimensional
stability such as, for example, cook-in packaging, hot-fill packaging,
flowable material pouches, compression fill packaging, shrink film packaging
and barrier shrink film packaging as well as biaxially oriented polypropylene
(BOPP) film structures.

Revendications

Note : Les revendications sont présentées dans la langue officielle dans laquelle elles ont été soumises.


We Claim:
1. A sealant film composition characterized as
comprising and made from:
from 5 to 95 weight percent, based on the total weight
of the composition, of at least one first ethylene polymer
which is a homogeneously branched substantially linear
ethylene polymer or a homogeneously branched linear ethylene
polymer, wherein the first ethylene polymer is characterized
as having:
i , melt flow ratio, I10/I2, ~ 5.63,
ii. an I2 melt index in the range of from 0.001
g/10 minutes to 2 g/10 minutes, as measured by
ASTM D-1238 Condition 190°C/2.16 kg,
iii. a density in the range of from 0.85 to 0.92
g/cc, as measured in accordance with ASTM
D-792,
iv. a molecular weight distribution, M w/M n, as
determined by gel permeation chromatography of
less than 3.5,
v. a short chain branching distribution index
(SCBDI) greater than 50 percent, as determined
using temperature rising elution
fractionation, and
from 5 to 95 weight percent, based on the total weight
of the composition, of at least one second ethylene polymer
which is a homogeneously branched ethylene polymer or a
heterogeneously branched linear ethylene polymer, wherein the
second ethylene polymer is characterized as having a density
less than 0.97 g/cc,
wherein the composition is characterized as having a
composition density of from 0.89 g/cc to 0.95 g/cc, as
measured in accordance with ASTM D-792, and the I2 melt index
of the at least one first polymer is lower than the I2 melt
index of the at least one second polymer.
-60-

2. A multilayer structure comprising a polypropylene
layer and a sealant layer, the sealant layer having balanced
properties, including excellent interlayer adhesion to
polypropylene, and characterized as comprising and made from:
(A) from 5 to 95 weight percent, based on the total
weight of the sealant layer, of at least one first
ethylene polymer which is a homogeneously branched
substantially linear ethylene polymer or a
homogeneously branched linear ethylene polymer,
wherein the first ethylene polymer is characterized
as having:
i. an I2 melt index in the range of from greater
than 0.14 g/10 minutes to less than 0.67 g/10
minutes, as measured by ASTM D-l238 Condition
190°C/2.16 kg,
ii. a density in the range of 0.85 to 0.92 g/cc,
as measured in accordance with ASTM D-792,
iii. an I10/I2 melt flow ratio in the range of from
6 to 12, as measured by ASTM D-1238 Condition
190°C/2.16 kg and Condition 190°C/10 kg,
iv. a molecular weight distribution, M w/M n, as
determined by gel permeation chromatography of
less than 3.5,
v. a single differential scanning calorimetry,
DSC, melting peak between -30 and 150°C, and
vi. a short chain branching distribution index
(SCBDI) greater than 50 percent, as determined
using temperature rising elution
fractionation, and
(B) from 5 to 95 weight percent, based on the total
weight of the sealant layer, of at least one second
ethylene polymer which is a homogeneously branched
ethylene polymer or a heterogeneously branched
linear ethylene polymer wherein the second ethylene
polymer is characterized as having a density in the
range of 0.89 g/cc to 0.965 g/cc,
wherein the sealant layer is characterized as having a
-61-

composition density of from 0.89 g/cc to 0.93 g/cc, as
measured in accordance with ASTM D-792, and an I2 melt index
in the range of from 1 g/10 minutes to 5 g/10 minutes, as
measured by ASTM D-1238 Condition l90°C12.16 kg, and wherein
the molecular weight of the at least one first polymer (A) is
higher than the molecular weight of the at least one second
polymer (B).
3. A film or film layer having improved modulus and a
composition density, the film or film layer characterized as
comprising and made from:
(C) from 20 to 60 weight percent, based on the total
weight of the film or film layer, of at least one
first ethylene polymer which is a homogeneously
branched substantially linear ethylene polymer or a
homogeneously branched linear ethylene polymer,
wherein the first ethylene polymer is characterized
as having:
i. an I2 melt index in the range of from 0.001
grams/10 minutes to 2 grams/20 minutes, as
measured by ASTM D-1238 Condition l90°C/2.16
kg,
ii. a density less than 0.89 g/cc, as measured in
accordance with ASTM D-792,
iii. a molecular weight distribution, M w/M n, as
determined by gel permeation chromatography of
less than 3.5,
iv. a short chain branching distribution index
(SCBDI) greater than 50 percent, as determined
using temperature rising elution
fractionation, and
(D) from 40 to 80 weight percent, based on the total
weight of the film or film layer, of at least one
second ethylene polymer which is a homogeneously
branched ethylene polymer or a heterogeneously
-62-

branched linear ethylene polymer, wherein the
second ethylene polymer is characterized as having
a density in the range of from 0.94 g/cc to 0.97
g/cc, as measured in accordance with ASTM D-792,
wherein the I2 melt index of the at least one first ethylene
polymer component (C) is equal to or lower than the I2 melt
index of the at least one second ethylene polymer component
(D) and the film or film layer is characterized by a
composition density in the range of from 0.915 g/cc to 0.95
g/cc, as measured in accordance with ASTM D-792.
4. A method of making a sealant film having improved
modules, the film characterized as comprising at least one
film layer, the method characterized as comprising the steps
of
providing a polymer composition comprised of or made
from:
(C) from 20 to 60 weight percent, based on the total
weight of the film, of at least one first ethylene
polymer which is a substantially linear ethylene
polymer or a homogeneously branched linear ethylene
polymer, wherein the first ethylene polymer is
characterized as having:
i. an I2 melt index in the range of from 0.001
grams/10 minutes to 2 grams/10 minutes, as
measured by ASTM D-1238 Condition 190°C/2.16
kg,
ii. a density less than 0.89 g/cc, as measured in
accordance with ASTM D-792,
iii. a molecular weight distribution, M w/M n, as
determined by gel permeation chromatography of
-63-

less than 3.5,
iv. a short chain branching distribution index
(SCBDI) greater than 50 percent, as determined
using temperature rising elution
fractionation, and
(D) from 40 to 80 weight percent, based on the total
weight of the film, of at least one second ethylene
polymer which is a homogeneously branched ethylene
polymer or a heterogeneously branched linear
ethylene polymer, wherein the second ethylene
polymer is characterized as having a density in the
range of from 0.94 g/cc to 0.97 g/cc, as measured
in accordance with ASTM D-792,
wherein the I2 melt index of the at least one first
ethylene polymer component (C) is equal to or lower
than the I2 melt index of the at least one second
ethylene polymer component (D) and the film is
characterized by a composition density in the range
of from 0.915 g/cc to 0.95 g/cc, as measured in
accordance with ASTM D-792;
extruding the polymer composition to form a film of at
least one film layer; and
collecting the film comprising at least one film layer.
5. A heat sealable composition which provides improved
film modulus, the composition characterized as comprising and
made from:
(C) from 20 to 60 weight percent, based on the total
weight of the composition, of at least one first
ethylene polymer which is a substantially linear
ethylene polymer or a homogeneously branched linear
ethylene polymer, wherein the first ethylene
polymer is characterized as having:
-64-

i. an I2 melt index in the range of from 0.001
grams/10 minutes-to 2 grams/10 minutes, as
measured by ASTM D-1238 Condition 190°C/2.16
kg,
ii. a density less than 0.89 g/cc, as measured in
accordance with ASTM D-792,
iii. a molecular weight distribution, M w/M n, as
determined by gel permeation chromatography of
less than 3.5,
iv. a short chain branching distribution index
(SCBDI) greater than 50 percent, as determined
using temperature rising elution
fractionation, and
(D) from 40 to 80 weight percent, based on the total
weight of the composition, of at least one second
ethylene polymer which is a homogeneously branched
ethylene polymer or a heterogeneously branched
linear ethylene polymer, wherein the second
ethylene polymer is characterized as having a
density in the range of from 0.94 g/cc to 0.97
g/cc, as measured in accordance with ASTM D-792,
wherein the I2 melt index of the at least one first
ethylene polymer component (C) is equal to or lower
than the I2 melt index of the at least one second
ethylene-polymer component (D) and the composition is
characterized by a composition density in the range
of from 0.9l5 g/cc to 0.95 g/cc, as measured in
accordance with ASTM D-792.
6. The composition, structure, film or film layer of any of
Claims 1-3, wherein the at least one first ethylene
polymer is a substantially linear ethylene polymer
characterized as having
i. a molecular weight distribution, M w/M n, as
determined by gel permeation chromatography
and defined by the equation:
-65-

(M w/M n) ~ <I10/I2) - 4.63,
ii. a gas extrusion rheology such that the
critical shear.rate at onset of surface melt
fracture for the substantially linear ethylene
polymer is at least 50 percent greater than
the critical shear rate at the onset of
surface melt fracture for a linear ethylene
polymer, wherein the substantially linear
ethylene polymer and the linear ethylene
polymer comprise the same comonomer or
comonomers, the linear ethylene polymer has an
I2, M w/M n and density within ten percent of the
substantially linear ethylene polymer and
wherein the respective critical shear rates of
the substantially linear ethylene polymer and
the linear ethylene polymer are measured at
the same melt temperature using a gas
extrusion rheometer.
7. The composition, structure, film or film layer of
Claim 6, wherein the substantially linear ethylene polymer
has 0.01 to 3 long chain branches/1000 carbons.
8. The composition, structure, film or film layer of
any of Claims 1-3, wherein the second ethylene polymer is a
heterogeneously branched linear ethylene polymer.
9. The composition, structure, film or film layer of
any of Claims 1-3, wherein at least one of the first ethylene
polymer or the second ethylene polymer is an interpolymer of
ethylene and at least one alpha-olefin selected from the
group consisting of 1-propylene, 1-butene, 1-isobutylene,
1-hexene, 4-methyl-1-pentene, 1-pentene, 1-heptene and
1-octene.
10. The composition, structure, film or film layer of
any of Claims 1-3, wherein at least one of the first ethylene
polymer or the second ethylene polymer is a copolymer of
-66-

ethylene and 1-octene.
11. The composition, structure, film or film layer of
any of Claims 1-3, wherein the polymer composition or layer
is prepared by mixing the first ethylene polymer and the
second ethylene polymer together by at least one of the
methods selected from the group consisting of melt extrusion,
dry blending, sequential operation of at least two
polymerization reactors and parallel operation of at least
two polymerization reactors.
12. The composition, structure, film or film layer of
Claim 11, wherein the least two polymerization reactors are
recirculating loop reactors.
13. The multilayer film structure of Claim 2, wherein
the structure is a cook-in package, hot-fill package,
flowable material pouch, compression fill package, shrink
film or barrier shrink film.
14. The multilayer film structure of Claim 2, wherein
the structure comprises a biaxially oriented polyethylene
film layer.
15. The multilayer film structure of Claim 2, wherein
the structure further comprises a barrier material or layer.
16. The multilayer film structure of Claim 15, wherein
the barrier material or layer is a polyvinylidene chloride
copolymer, polyester, polyamide, biaxially oriented
polypropylene or aluminum foil.
17. The method of Claim 4, wherein the extrusion is
-67-

accomplished by a blown film technique.
18. The method of Claim 4, wherein the extrusion step
includes combining the layer with at least one
other layer either simultaneously with the
formation of the layer or subsequent to the
formation of the layer.
-68-

Description

Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.


CA 02271482 1999-OS-12
WO 98/21274 PCTIUS97I20574
POLYOLEFIN COMPOSITIONS WITH BALANCED SEALANT PROPERTIES AND
IMPROVED MODULUS AND METHOD FOR SAME
This invention pertains to a sealant film composition
comprising at least two ethylene polymer components. One
( aspect of the invention relates to a multilayer structure
having balanced sealant properties and comprising a sealant
layer and a polypropylene layer, wherein the sealant layer
comprises and is made from a polymer composition having
particular molecular weight characteristics and a second
ethylene polymer. A preferred embodiment of the present
invention pertains to a medium density polyolefinic film and.
composition characterized by an excellent balance of low seal
initiation temperature and improved film modulus. The film
and composition is comprised of and made from at least one
lower density homogeneously branched ethylene polymer and at
least one higher density heterogeneously or homogeneously
branched ethylene polymer.
Although ethylene polymers have long found utility in
food packaging and food storage container applications, a
polyolefin composition with the desired balance of properties
in the form of a film, coating, lamination or coextrusion has
not been available to fabricators and packagers. For
example, an optimum ethylene polymer composition for use as a
sealant layer in packaging and storage applications would
possess a number of key performance properties such as low
heat seal and hot tack initiation temperatures, a high hot
tack strength, a broad hot tack sealing window, good
interlayer adhesion, a high softening point and low hexane
extractables levels.
Although not presently satisfied, the commercial
importance of balanced sealant properties is well understood.
That is, low heat seal and hot tack initiation temperatures
are important for improved sealing speeds and reduced energy
utilization. A broad hot tack sealing window at high hot
tack strengths (i.e., the seal temperature range where the

CA 02271482 1999-OS-12
WO 98/21274 PCT/US97/20574
hot tack strength is greater than or equal to about 46 g/cm
as measured by the Dupont spring method or greater than or
equal to about 3.3l Newton/15 mm (5.6 N/in.) as measured
using a mechanical hot tack tester such as, for example, a
Top Wave Sealing unit) is important for insuring package
integrity, sealing equipment flexibility and low package
leaker rates. Good interlayer adhesion is also important for
good package integrity as well as good package or container
aesthetics. High softening points or temperatures are
desired where goods are packaged at elevated temperatures
such as in hot-fill applications. Low hexane extractables
are required for food contact applications.
Traditionally, when attempting to achieve balanced
sealant properties, enhancement of one particular resin
property has required some sacrifice with respect to another
important property. For instance, with ethylene alpha-olefin
polymers, low heat seal and hot tack initiation temperatures
are typically achieved by increasing the comonomer content of
the resin. Conversely, high Vicat softening points and low
levels of n-hexane extractives are typically achieved by
decreasing the comonomer content of the resin. Accordingly,
improving the resin with respect to seal initiation typically
results in proportionally reduced Vicat softening temperature
and proportionally increased extractable level.
Several important multilayer packaging and storage
structures consisting of a polypropylene layer, particularly,
a biaxially oriented polypropylene (BOPP) homopolymer base or
core layer. Typically, BOPP structures utilize polypropylene
copolymers and terpolymers as sealant materials (and/or
adhesive layers) to insure good interlayer adhesion to the
BOPP base layer. While polypropylene copolymers and
terpolymers do indeed provide good interlayer adhesion to
BOPP base layers as well as good hot tack strength
performance, these copolymers and terpolymers invariably
exhibit undesirably high heat seal and hot tack initiation
temperatures.
-2-

CA 02271482 1999-OS-12
WO 98/21274 PCT/US97/20574
Other polyolefin materials have also been used as
sealant materials for multilayer packaging and storage
structures. However, in general, known polyolefin sealant
materials do not provide the desired overall property balance
and/or process flexibility desired by converters and
packagers.
Additionally, an optimum polyolefin resin composition
for use as a sealant layer in lamination or compression
filled applications has not been available because key
performance properties (i.e., a low heat seal initiation
temperature and medium-high film modulus) are mutually
exclusive for ordinary polyolefin compositions. That is,
compositions that possess the desired low seal initiation
temperature characteristic invariably possess a relatively
low film moduli. Conversely, compositions that provide the
desired medium to high film modulus are invariably
characterized by an excessively high seal initiation
temperature.
A low seal initiation temperature and a medium to high
(improved) film modulus are considered to be key performance
properties for several reasons. An improved film modulus
(film stiffness) is required to insure good film
machinability in packaging making, filling and/or sealing
operations. For example, a film with good machinability can
be cut evenly and efficiently even when cutting devices such
as knives and blades have achieved some dullness thereby
reducing waste and/or retooling requirements. A medium to
high film modulus is also required for compression filling
applications to insure good dimensional stability and thereby
permit film structures, plastic tubes and the like to stand
upright to facilitate efficient filling of the item to be
packaged.
A low seal initiation temperature is required to insure
higher packaging speeds. That is, the lower the temperature
at which strong seals can be formed, the more packaging units
per unit of time can be made to maximize productivity. Also,
-3-

CA 02271482 1999-OS-12
WO 98/21274 PCT/US97/20574
lower seal initiation temperatures permit less precise
sealing equipment temperature control as well as less seal
energy consumption.
While a variety of polyolefin compositions have been
disclosed for use as sealant materials and although
combinations consisting of coextruded or laminated film
structures are allegedly satisfactory, known compositions
(especially when used as monolayer film structures) generally
do not possess an optimum balance of key performance
properties which include a low seal initiation temperature
with a medium to high film modulus. For example, TAFMERTM
resins (supplied by Mitsui Petrochemical) are known to
provide sealants with relatively low seal initiation
TM
temperatures. However, TAFMER resins are not known to
provide the overall desired performance balance, neither as a
single component sealant material or when used as a polymer
blend component material. Nor are TAFMERTM resins known to
provide the performance characteristics of medium to high
film modulus. As another deficiency, TAFMERTM resins are also
relatively expensive and are continually in limited
commercial supply.
Relative to TAFMERTM resins, heterogeneously branched
ethylene polymers, such as linear low density polyethylene
(LLDPE) and ultra low density polyethylene (ULDPE), are
readily available. However, heterogeneously branched
ethylene polymers do not provide the desired overall property
balance for optimum use as sealant materials and they are
particularly i11-suited for BOPP structures. For example,
heterogeneously branched linear low density polyethylene
(LLDPE) (and, as such, sealant layers made from these
polymers) are particularly deficient in regards to interlayer
adhesion to polypropylene layers. Moreover, heterogeneously
branched ethylene polymers tend to possess medium to low seal
initiation temperatures and medium to low film moduli and, as
such, are not optimally suited for high speed packaging
operations where good film machinability is required.
-4-

CA 02271482 1999-OS-12.
WO 98/21274 PCT/US97/20574
Homogeneously branched ethylene polymers such as
AFFINITYTM resins supplied by The Dow Chemical Company are
also available for use as sealant materials. While
homogeneously branched ethylene polymer materials generally
exhibit improved sealing initiation performance, such
invariably possess relatively low film moduli.
U.S. Patent No. 4,429,079 to Shibata, et al. discloses
an ethylene/alpha-olefin copolymer blend composition
comprising a mixture of (A) 95-40 weight percent of a random
copolymer of ethylene and an alpha-olefin having 5 to 10
carbon atoms which has a melt index of 0.1 to 20 g/10 min., a
density of 0.9l0 to 0.940 g/cc, a crystallinity by X-rays of
0
40 to 70%, a melting point of 115 to 130 C, and an ethylene
content of 94 to 99.5 mol o; and (B) 5 to 60o by weight of a
random copolymer of ethylene and an alpha-olefin having 3 to
10 carbon atoms which has a melt index of 0.1 to 50 g/10
min., a density of 0.870 to 0.900 g/cc, a crystallinity by X-
0
rays of 5 to 400, a melting point of 40 to 100 C and an
ethylene content of 85 to 95 mol o. The (A) component
polymer is said to be produced by a titanium catalyst system
and the (B) component polymer is said to be produced by a
vanadium catalyst. Both of these catalyst systems are known
as Ziegler-Natta type catalysts which produce linear ethylene
alpha-olefin polymers. That is, the polymer will have a
linear molecular backbone without any long chain branching.
Further, the (A) component polymer will also be expected to
have a heterogeneously branched short chain distribution,
while the (B) component polymer will be expected to have a
homogeneously branched short chain distribution. The film
fabricated from the Shibata et al. composition allegedly has
good low-temperature heat sealability, heat seal strength,
pin hole resistance, transparency and impact strength.
However, Shibata et al. do not disclose films with high
ultimate hot tack strengths (i.e., values >_ 3.31 N/mm), nor
films with a medium to high moduli. Moreover, analysis of
the data disclosed in the Examples provided by Shibata et al.
-5-

CA 02271482 1999-OS-12
WO 98/21274 PCT/US97/20574
reveals the heat seal properties of the films are additive
and vary linearly with respect to the densities of the
blended component polymers.
U.S. Patent 4,981,760 to Naito et al. discloses a
polyethylene mixture having a density of from 0.900 to 0.930
g/cc and melt flow rate of from 0.1 to 100 g/10 in., which
comprises (I) from 60 to 99 parts by weight of an ethylene-a-
olefin random copolymer comprising ethylene and an a-olefin
having from 4 to 10 carbon atoms, the copolymer having an a- _.
olefin content of from 2.0 to 10 mol o and a density of from
0.895 to 0.9l5 g/cc, the programmed-temperature thermogram of
said copolymer as determined with a differential scanning
calorimeter after being completely melted and then gradually
cooled showing an endothermic peak in a range of from 75° to
100°C, with the ratio of an endotherm at said peak to the
total endotherm being at least 0.8, and (II) from 1 to,40
parts by weight of high-density polyethylene having a density
of at least 0.945 g/cc, the programmed-temperature thermogram
of said high-density polyethylene as determined with a
differential scanning calorimeter after being completely
melted and allowed to cool showing an endothermic peak at
125°C, or higher, wherein the sum of (I) and (II) amounts to
l00 parts by weight. The component polymer (I) is said to be
manufactured using a vanadium catalyst and the film allegedly
has improved heat sealability and hot tack. Naito et al. do
not disclose fabricated films comprising a component polymer
(II) with a density less than 0.945 g/cc. Also, Naito et al.
describe a film having low heat seal or hot tack initiation
temperatures when the lower density component polymer (I)
concentration is fairly high (i.e., >_ 85 parts) which is
expected to result in a lower Vicat softening point as well
as a relatively low film modulus.
U.S. Patent No. 5,206,075 to Hodgson et al. discloses a
multilayer heat sealable film comprising a base layer and a
heat sealable layer superimposed on one or both sides of the
base layer. As the base layer, Hodgson discloses a blend of:
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(a) an olefin polymer having a density greater than 0.915
g/cc; and (b) a copolymer of ethylene and a C3-C2p alpha-
monoolefin, with the copolymer (b) having a density of from
about 0.88 to about 0.915 g/cc, a melt index of from about
0.5 to about 7.5 dg/min, a molecular weight distribution of
no greater than about 3.5, and a composition distribution
breadth index greater than about 70 percent. As the heat
sealable layer, Hodgson discloses a layer comprising a
copolymer as defined in (b) with respect to the base layer.
Hodgson does not disclose the use of a blend, such as that
employed in the base layer (a), as a suitable sealing layer
and the preferred olefin polymer for component (a) of the
base layer is a copolymer of propylene with about 1-10 mole
percent ethylene. As such, this disclosure limits the
usefulness of the so-disclosed sealant material by teaching
that useful multilayer heat sealable films necessarily
comprise a base layer and sealant layer having similar olefin
chemistries.
The materials disclosed by Shibata et al., Naito et al.
and Hodgson et aI. as well as other known sealant materials
are deficient in one respect or another. These materials do
not provide balanced sealant properties that include a low
seal initiation temperature and an improved film modulus.
Nor are these materials particularly well-suited for use as
sealant materials in BOPP structures. As such, there is a
need for polymer compositions characterized by good
interlayer adhesion to polypropylene, low heat seal and hot
tack initiation temperatures, high hot tack strength and a
broad high hot tack sealing window. There is also a separate
need for a film and film composition which exhibits a low
heat seal initiation temperature and a medium to high film
modulus for use in lamination, coextrusion and compression
filled packaging applications. There is also a need for a
polymer sealant composition which has low levels of n-hexane
extractives, i.e., less than 15 weight percent, preferably
less than 10 weight percent, more preferably less than 6

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weight percent, most preferably less than 3 weight percent,
as such a composition would be useful in direct food contact
applications.
As one aspect of the present invention, we have
discovered a novel multilayer structure comprised of a
polymer composition which comprises and is made from at least
two ethylene polymer components wherein the first ethylene
polymer component is characterized as having an optimized
high molecular weight and a uniform short chain branching or
compositional distribution. The polymer composition provides
an improved sealant layer with balanced properties for use in
multilayer packaging and storage structures. The balanced
sealant properties include good interlayer adhesion to
polypropylene, low heat seal and hot tack initiation
temperatures, a broad high hot tack sealing window and, for a
given polymer density, a relatively high softening
temperature to, for example, prevent sticking to the machine
direction orientation rollers or provide good machinability.
The improved sealant is particularly useful for multilayer
structures comprising a polypropylene layer and especially a
biaxially oriented polypropylene (BOPP) film layer.
As another aspect of the invention, we also discovered a
film and film composition comprised of and made from at least
two ethylene polymer components wherein the first ethylene
polymer component is characterized as having density less
than 0.89 grams/cubic centimeter (g/cc) and the second
ethylene polymer component is characterized as having a
density in the range of from 0.99 g/cc to 0.97 g/cc. The
newly discovered film composition provides an improved
sealant film with a medium to high film modulus (i.e.,
improved modulus) for use in multilayer packaging
applications such as laminations, coextrusions and coatings.
The balance between sealant and modulus properties also
permits use as a monolayer film in various application such
as, for example, in compression filled applications where
higher speed sealing as well as good film machinability and
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dimensional stability can be realized.
The broad aspect of the p-resent invention is a sealant
film composition comprising and made from:
from 5 to 95 weight percent, based on the total weight
of the composition, of at least one first ethylene
polymer which is a homogeneously branched substantially
linear ethylene polymer or a homogeneously branched
linear ethylene polymer, wherein the first ethylene
polymer is characterized as having:
i. an Iz melt index in the range of from 0.001
g/10 minutes to 2 g/10 minutes, as measured by
ASTM D-1238 Condition 190°C/2.16 kg,
ii, a density in the range of from 0.85 to 0.92
g/cc, as measured in accordance with ASTM D-
792,
iii. a molecular weight distribution, MW/Mn~ as
determined by gel permeation chromatography of
less than 3.5,
iv. a short chain branching distribution index
(SCBDI) greater than 50 percent, as determined
using temperature rising elution
fractionation, and
from 5 to 95 weight percent, based on the total weight
of the composition, of at least one second ethylene
polymer which is a homogeneously branched ethylene
polymer or a heterogeneously branched linear ethylene
polymer, wherein the second ethylene polymer is
characterized as having a density less than 0.97 g/cc,
wherein the composition is characterized as having a
composition density of from 0.89 g/cc to 0.95 g/cc, as
measured in accordance with ASTM D-792, and the I2 melt index
of the at least one first polymer is lower than the I2 melt
index of the at least one second polymer.
A second aspect of the present invention is a multilayer
structure comprising a polypropylene layer and a sealant
layer, the sealant layer having balanced properties,
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including excellent interlayer adhesion to polypropylene, and
comprising and made from:
(A) from 5 to 95 weight percent, based on the total
weight of the sealant layer, of at least one first
ethylene polymer which is a homogeneously branched
substantially linear ethylene polymer or a
homogeneously branched linear ethylene polymer,
wherein the first ethylene polymer is characterized
as having:
15
i. an I2 melt index in the range of from greater
than 0.14 g/10 minutes to less than 0.67 g/10
minutes, as measured by ASTM D-l238 Condition
l90°C/2.16 kg,
ii. a density in the range of 0.85 to 0.92 g/cc,
as measured in accordance with ASTM D-792,
iii. an Ilp/I2 melt flow ratio in the range of from
6 to 12, as measured by ASTM D-1238 Condition
190°C/2.16 kg and Condition l90°C/10 kg,
iv. a molecular weight distribution, MW/Mn~ as
determined by gel permeation chromatography of
less than 3.5,
v. a single differential scanning calorimetry,
DSC, melting peak between -30 and l50°C, and
vi. a short chain branching distribution index
(SCBDI) greater than 50 percent, as determined
using temperature rising elution
fractionation, and
(B) from 5 to 95 weight percent, based on the total
weight of the sealant layer, of at least one second
ethylene polymer which is a homogeneously branched
ethylene polymer or a heterogeneously branched
linear ethylene polymer wherein the second ethylene
polymer is characterized as having a density in the
range of 0.89 g/cc to 0.965 g/cc,
wherein the sealant layer is characterized as having a
composition density of from 0.89 g/cc to 0.93 g/cc, as
measured in accordance with ASTM D-792, and an IZ melt index
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in the range of from 1 g/10 minutes to 5 g/10 minutes, as
measured by ASTM D-l238 Condition 190°C/2.16 kg, and wherein
the molecular weight of the at least one first polymer (A) is
higher than the molecular weight of the at least one second
polymer (B).
A third aspect of the present invention is a film or
film layer having improved modulus and a composition density,
the film or film layer comprising and made from:
(C) from 20 to 60 weight percent, based on the total
weight of the film or film layer, of at least one
first ethylene polymer which is a homogeneously
branched substantially linear ethylene polymer or a
homogeneously branched linear ethylene polymer,
wherein the first ethylene polymer is characterized
as having:
i. an Iz melt index in the range of from 0.001
grams/10 minutes to 2 grams/10 minutes, as
measured by ASTM D-1238 Condition 190°C/2.16
kg,
ii. a density less than 0.89 g/cc, as measured in
accordance with ASTM D-792,
iii. a molecular weight distribution, MW/Mn~ as
determined by gel permeation chromatography of
less than 3.5,
iv. a short chain branching distribution index
(SCBDT) greater than 50 percent, as determined
using temperature rising elution
fractionation, and
(D) from 40 to 80 weight percent, based on the total
weight of the film or film layer, of at least one
second ethylene polymer which is a homogeneously
branched ethylene polymer or a heterogeneously
branched linear ethylene polymer, wherein the
second ethylene polymer is characterized as having
a density in the range of from 0.94 g/cc to 0.97
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g/cc, as measured in accordance with ASTM D-792,
wherein the I2 melt index of the at least one first ethylene
polymer component {C) is equal to or lower than the IZ melt
index of the at least one second ethylene polymer component
(D) and the film or film layer is characterized by a
composition density in the range of from 0.915 g/cc to 0.95
g/cc, as measured in accordance with ASTM D-792.
A fourth aspect of the invention is a method of making a
sealant film having improved modulus and comprising at least
one film layer, the method comprising the steps of:
providing a polymer composition comprised of or made
from:
(C) from 20 to 60 weight percent, based on the total
weight of the film, of at least one first ethylene
polymer which is a substantially linear ethylene
polymer or a homogeneously branched linear ethylene
polymer, wherein the first ethylene polymer is
characterized as having:
i. an I2 melt index in the range of from 0.001
grams/10 minutes to 2 grams/10 minutes, as
measured by ASTM D-1238 Condition 190°C/2.16
kg,
ii. a density less than 0.89 g/cc, as measured in
accordance with ASTM D-792,
iii. a_molecular weight distribution, Mw/Mn~ as
determined by gel permeation chromatography of
less than 3.5,
iv. a short chain branching distribution index
(SCBDI) greater than 50 percent, as determined
using temperature rising elution
fractionation, and
(D) from 40 to 80 weight percent, based on the total
weight of the film, of at least one second ethylene --
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polymer which is a homogeneously branched ethylene
polymer or a heterogeneously branched linear
ethylene polymer, wherein the second ethylene
polymer is characterized as having a density in the
range of from 0.94 g/cc to 0.97 g/cc, as measured
in accordance with ASTM D-792,
wherein the IZ melt index of the at least one first
ethylene polymer component (C) is equal to or lower
than the I2 melt index of the at least one second
ethylene polymer component (D) and the film is
characterized by a composition density in the range
of from 0.9l5 g/cc to 0.95 g/cc, as measured in
accordance with ASTM D-792:
extruding the polymer composition to form a film of at
least one film layer; and
collecting the film comprising at least one film layer.
A fifth aspect of the invention is a heat sealable
composition which provides improved film modulus, the
composition comprising and made from:
(C) from 20 to 60 weight percent, based on the total
weight of the composition, of at least one first
ethylene polymer which is a substantially linear
ethylene polymer or a homogeneously branched linear
ethylene polymer, wherein the first ethylene
polymer is characterized as having:
i. an IZ melt index in the range of from 0.001
grams/10 minutes to 2 grams/10 minutes, as
measured by ASTM D-1238 Condition l90°C/2.16
kg,
ii. a density less than 0.89 g/cc, as measured in
accordance with ASTM D-792,
iii. a molecular weight distribution, MW/Mn~ as
determined by gel permeation chromatography of
less than 3.5,
iv. a short chain branching distribution index
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(SCBDI) greater than 50 percent, as determined
using temperature rising elution
fractiona-tion, and
(D) from 40 to 80 weight percent, based on the total '
weight of the composition, of at least one second
ethylene polymer which is a homogeneously branched
ethylene polymer or a heterogeneously branched
linear ethylene polymer, wherein the second
ethylene polymer is characterized as having a
density in the range of from 0.94 g/cc to 0.97
g/cc, as measured in accordance with ASTM D-792,
wherein the IZ melt index of the at least one first
ethylene polymer component (C) is equal to or lower
than the IZ melt index of the at least one second
ethylene polymer component (D) and the composition is
characterized by a composition density in the range
of from 0.915 g/cc to 0.95 g/cc, as measured in
accordance with ASTM D-792.
Surprisingly, while sealant layers made from
heterogeneously branched ethylene polymer are characterized
as having seal initiation temperatures substantially higher
than their respective softening temperature, the improved
sealant layer of the present invention is characterized as
having a comparatively high Vicat softening temperature
relative to its heat seal initiation temperature. That is,
for a minimum sealing strength of 1.8 Newtons/15 mm, the
sealant layer has a film heat seal initiation temperature
that ranges from equal to or at least 4.5°C lower than its
Vicat softening temperature and, more surprisingly, in
particular embodiments, from equal to or at least 6°C lower
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than its Vicat softening temperature.
As another surprising resent of the invention, while
ordinary sealant films are characterized as having seal
initiation temperatures which are relatively high for the
their respective densities (and/or for their respective film
modulus), the improved sealant film or film layer of the
present invention is characterized as having a comparatively
low seal initiation temperature for a given film modulus or
density. That is, relative to ordinary films, the film of
the present invention achieves a comparatively high modulus
at the same seal initiation temperature or achieves a
comparatively low seal initiation temperature at the same
film density or modulus. With the present invention, the
usual performance compromise between a relatively low seal
initiation temperature and a medium to high film modulus
simply does not exist as performance results are not additive
or based on weight fraction contributions as expected.
Without unnecessarily limiting the invention, the
present invention provides a film composition, sealant film,
sealant film layer, coating, a thermoformed article or a
molded article for packaging, storage, display and protecting
purposes. Such uses include, but are not limited to, cook-in
bags, pouches for flowable materials, barrier shrink and non-
barrier shrink films, bottle caps, lidding stock and
packaging film sealant layers.
These and other embodiments will be more fully described
in detailed herein below.
FIG. 1 is an Analytical Temperature Rising Elution
Fractionation (ATREF) curve-response for Example 1.
FIG. 2 is a Deconvoluted Gel Permeation Chromatography
(GPC) curve-response for Example 1.
FIG. 3 is a plot of hot tack strength, in Newtons/15 mm,
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as a function of the IZ melt index, in grams/10 minutes, of
the first ethylene polymer component (A).
FIG. 4 is a plot of the heat seal initiation temperature
of various inventive and comparative film examples as a
function of weight percent homogeneously branched ethylene
polymer, Component (C).
FLG. 5 is a plot of the heat seal initiation temperature
of various inventive and comparative film examples as a
function of composition density.
FIG. 6 is a plot of the heat seal initiation temperature
of various inventive and comparative film examples as a
function of film modulus.
FIG. 7 is a plot of the film modulus of various
inventive films and comparative films as a function of
composition density.
The term "composition density" as used herein means the
density of a single component polymer or a polymer
composition of a first and second ethylene polymer measured
in accordance with ASTM D-792. The term "composition
density" refers to a solid state density measurement of
pellets, film or a molding as distinguished from a melt
density determination.
The term "polymer composition" as used herein refers to
the combination of Component (A) and Component (B) or
Component (C) and Component (D). The film and composition of
the present invention comprises and is made from a polymer
composition as defined by Component A and Component and/or as
defined by properties _of the combination itself such as, for
example, composition density.
The team "polymer", as used herein, refers to a
polymeric compound prepared by polymerizing monomers, whether
of the same or a different type. The generic term "polymer"
thus embraces the terms "homopolymer," "copolymer,"
"terpolymer" as well as "interpolymer."
The term "interpolymer", as used herein, refers to
polymers prepared by the polymerization of at least two
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different types of monomers. The generic term "interpolymer"
thus includes the term "copolymers" (which is usually
employed to refer to polymers prepared from two different
monomers) as well as the term "terpolymers" (which is usually
employed to refer to polymers prepared from three different
types of monomers).
The first ethylene polymer component used in the
invention, Component (A) or Component (C), is broadly an
ethylene polymer manufactured with a homogeneous catalyst
system such as, for example, a metallocene catalyst system, a
vanadium catalyst system or a constrained geometry catalyst
system. In particular, the first ethylene polymer is at
least one homogeneously branched substantially linear
ethylene polymer or at least one homogeneously branched
linear ethylene polymer. The second component polymer is at
least one heterogeneously branched ethylene polymer or,
alternatively, at least one homogeneously branched ethylene
polymer (i.e., an ethylene polymer manufactured using a
homogeneous catalyst system). However, preferably the first
ethylene polymer component (A) or (C) is at least one
substantially linear ethylene interpolymer and the second
ethylene polymer component (B) of (D) is at least one
heterogeneously branched linear ethylene interpolymer. More
preferably, both the first and second ethylene interp~lymers
are manufactured using a continuous solution polymerization
process, especially a continuous low pressure solution
polymerization process.
Substantially linear ethylene interpolymers are
generally preferred as the first ethylene polymer component
(A) or (C) due to their improved melt extrusion
processability and unique rheological properties as described
by Lai et. al in US Patent Nos. 5,272,236 and 5,278,272, the
disclosures of which are incorporated herein by reference.
Heterogeneously branched ethylene interpolymers are preferred
as the second ethylene polymer component (i.e., components
(B) and (D) ) .
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The molecular weight of polyolefin polymers is
conveniently indicated using a melt index measurement
according to ASTM D-l238, Condition 190°C/2.1E kg (formerly
known as "Condition E" and also known as I2). Melt index is
inversely proportional to the molecular weight of the
polymer. Thus, the higher the molecular weight, the lower
the melt index, although the relationship is not linear.
For the aspect of the invention that provides a sealant
layer. with balanced sealant properties, including excellent
interlayer adhesion to polypropylene, the first ethylene
polymer component (A) has an I2 melt index in the range of
from greater than 0.14 g/10 minutes to less than 0.67 g/10
minutes, preferably from greater than or equal to 0.15 g/10
minutes to less than or equal to 0.65 g/10 minutes, more
preferably from greater than or equal to 0.16 g/10 minutes to
less than or equal to 0.6 g/10 minutes, and most preferably
from greater than or equal to 0.16 g/10 minutes to less than
or equal to 0.5 g/10 minutes.
Component (A) and component (B) will be independently
characterized by an I2 melt index. By "independently
characterized" it is meant that the I2 melt index of
component (A) need not be the same as the I2 melt index of
component (B). The second ethylene polymer component (B) may
have an I2 melt index in the range of from greater than or
equal to 0.01 g/10 minutes to less than or equal to 500 g/10
minutes, preferably from greater than or equal to 0.1 g/10
minutes to less than or equal to 50 g/10 minutes, more '
preferably from greater than or equal to 1 g/10 minutes to
less than or equal to 20 g/10 minutes, and most preferably
from greater than or equal to 1 g/10 minutes to less than or
equal to 10 g/10 minutes.
The overall melt index of the polymer composition based
on components (A) and (B) is preferably in the range of from
1 to 5 g/10 minutes, more preferably from 2 to 4 g/10
minutes.
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Other measurements useful in characterizing the
molecular weight of substantially linear ethylene
interpolymers and homopolymers involve melt index
determinations with higher weights, such as, for common
example, ASTM D-1238, Condition 190°C/10 kg (formerly known as
"Condition N" and also known as Ilp). The ratio of a higher
weight melt index determination to a lower weight
determination is known as a melt flow ratio, and for measured
Ilp and the Iz melt index values the melt flow ratio, is
conveniently designated as Ilp/I2. For the substantially
linear ethylene polymers used to prepare the films of the
present invention, the melt flow ratio indicates the degree
of long chain branching, i.e., the higher the I~p/I2 melt flow
ratio, the more long chain branching in the polymer. In
addition to being indicative of more long chain branching,
higher Ilp/I2 ratios are indicative of high extensional
viscosity.
While for balanced sealant properties, high molecular
weight, a high degree of long chain branching and/or high
extensional viscosity are generally preferred, we have
discovered that there is an optimum range with respect to
each of these polymer properties, particularly with respect
to the molecular weight of the first ethylene polymer
component (A). While the optimum molecular weight range for
the first ethylene polymer component (A) is defined above by
a specific IZ melt index range, it is believed that the
optimum range of long chain branching for the substantially
- linear ethylene polymer used in the present invention as a
first ethylene polymer component (A) and as defined by an
Ilp/I2 melt flow ratio is in the range of from greater than 6
to about less than 12 and especially from greater than 7 to
less than 10. Embodiments that meet the specified melt index
range and also meet the above Ilp/IZ range are particularly
preferred embodiments of the present invention.
The first ethylene polymer component (A) generally
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constitutes from 5 to 95 weight percent of the polymer
composition, based on the total weight of the polymer
composition, preferably from 15 to 75 weight percent, and
more preferably from 30 to 5)
The first ethylene polymer component (A) has a density
in the range of from 0.85 to 0.92 g/cc, preferably from 0.87
to 0.915 g/cc, more preferably from about 0.885 to Q.905 g/cc
(as measured in accordance with ASTM D-792). The second
ethylene polymer component (B) has a density in the range of _
from 0.90 to 0.96 g/cc, preferably from 0.91 to 0.95 g/cc,
more preferably from 0.92 to 0.93 g/cc (as measured in
accordance with ASTM D-792). Additionally, it is preferred
that the density of the at least one first ethylene polymer
component (A) is lower than the density of the at least one
second ethylene polymer component (B).
The overall density of the polymer composition based on
components (A) and (B) is preferably in the range of from
0.90 to 0.92 glcc, more preferably in the range of from 0.905
to 0.925 g/cc, and most preferably in the range of from 0.91
to 0.92 g/cc (as measured in accordance with ASTM D-792).
For the aspect of the invention that provide a sealant
layer with balanced properties and improved modulus, the
first ethylene polymer Component (C) has an I2 melt index in
the range of from 0.00l to 2 g/10 minutes, preferably-from
0.01 g/10 minutes to 1.5 g/10 minutes, more preferably from
0.01 g/10 minutes to 1.2 g/10 minutes, and most preferably
from 0.05 g/10 minutes to 1 g/10 minutes. The second
ethylene polymer Component (D) has an I2 melt index in the
range of from 0.01 g/10 minutes to 30 g/10 minutes,
preferably from 0.5 g/10 minutes to 20 g110 minutes, more
preferably from 1 g/10 minutes to 10 g/10 minutes, and most
preferably from about 1 g/10 minutes to 5 g/10 minutes.
The overall melt index of the polymer composition based
on components (C) and (D) is preferably in the range of from
0.1 to 50 g/10 minutes, more preferably from 0.5 to 20 g/10
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CA 02271482 1999-OS-12
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minutes, and most preferably in the range of from 0.7 to 6
g/10 minutes.
For the aspect of the invention that provide a sealant
layer with balanced properties and improved modulus, we have
discovered that the Ilo/I2 ratio of substantially linear
ethylene polymers should be high to maximize extrusion
processability and should be low to maximize hot tack
performance. As such, the Ilo/IZ ratio of particularly .the
first ethylene polymer component (C) should be carefully
optimized to insure a good balance between good extrusion
processability and good hot tack performance where desired.
The film or composition generally comprises (or is made
from) 20 to 60 weight percent, preferably from 20 to 55
weight percent, more preferably from 25 to 45 weight percent,
and most preferably about 25 to 90 weight percent of the
least one first ethylene polymer component (C), based on the
total weight of the film, film layer or composition.
Conversely, the film or composition generally comprises (and
is made from) 40 to 80 weight percent, preferably from 45 to
80, more preferably from 55 to 75 weight percent, and most
preferably 60 to 75 weight percent of the at least one second
ethylene polymer component (D), based on the total weight of
the film, film layer or composition.
The first ethylene polymer component (C) has a density
less than 0.89 g%cc in the range of from 0.85 to 0.89 g/cc as
measured in accordance with ASTM D-792). The second ethylene
polymer component (D) has a density in the range of from 0.94
to 0.97 g/cc, preferably from 0.94 to 0.96 g/cc, and more
preferably from D.945 to 0.955 g/cc (as measured in
accordance with ASTM D-792).
The overall density of the polymer composition based on
components (C) and (D) is preferably in the range of from
0.92 to 0.95 g/cc, more preferably in the range of from 0.925
to 0.945 g/cc, and most preferably in the range of from 0.925
to 0.99 g/cc (as measured in accordance with ASTM D-792).
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Suitable ethylene polymers for use as the second
ethylene polymer component (B) are homopolymer and
interpolymers of ethylene and include substantially linear
ethylene polymers, homogeneously branched linear ethylene
polymers, heterogeneously branched linear ethylene polymers
(i.e., linear low density polyethylene (LLDPE), medium
density polyethylene (MDPE), and high density polyethylene
(HDPE) such as those manufactured using a Ziegler-Natta
20 catalyst system), and combinations or mixtures thereof.
Substantially linear ethylene polymers are sold under
the designation of AFFINITY' and ENGAGE' resins by The Dow
Chemical Company and Dupont Dow Elastomers, respectively.
Homogeneously branched linear ethylene polymers are sold
under the designation of TAFMER'~ by Mitsui Chemical
Corporation and under the designations of EXACT and EXCEED'
resins BY Exxon Chemical Corporation. Suitable
heterogeneously branched linear ethylene polymers are sold
under the designation of D06JLEX''" by The Dow Chemical Company.
Suitable medium density polyethylene ethylene resins and high
density polyethylene resins (as interpolymers or homopolymers
of ethylene) are available from a number of resin
manufacturers including The Dow Chemical Company and Phillips
Chemical Corporation under the designation of MARLEX~' resins.
The term "homogeneously branched linear ethylene
polymer" is used herein in the conventional sense to refer to
a linear ethylene interpolymer in which the comonomer is
randomly distributed within a given polymer molecule and
wherein substantially a11 of the polymer molecules have the
same ethylene to comonomer molar ratio, The term refers to
an ethylene interpolymer that is characterized by a
relatively high snort chain branching distribution index
(SCBDI) or composition distribution branching index (CDBI).
That is, the interpolymer has a SCBDI greater than or equal
to 50 percent, preferably greater than or equal to 70
percent, more preferably greater than or equal to 90 percent.
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However, preferably the homogeneously branched ethylene
polymer is further characterized as essentially lacking a
measurable high density (crystalline) polymer fraction as
determined using a temperature rising elution fractionation
technique.
SCBDI is defined as the weight percent of the polymer
molecules having a comonomer content within 50 percent of the
median total molar comonomer content and represents a
comparison of the monomer distribution in the interpolymer to
the monomer distribution expected for a Bernoullian
distribution. The SCBDI of an interpolymer can be readily
calculated from temperature rising elution fractionation
techniques (abbreviated herein as "TREF") as described, for
example, by Wild et al., Journal of Polymer Science, Pol
Ph~s. Ed., Vol. 20, p. 44l (1982), or in US Patent 4,79B,081;
5,008,204; or by L. D. Cady, "The Role of Comonomer Type and
Distribution in LLDPE Product Performance," SPE Regional
Technical Conference, Quaker Square Hilton, Akron, Ohio,
October 1-2, pp. l07-l19 (l985), the disclosures of a11 which
are incorporated herein by reference. However, the preferred
TREE technique does not include purge quantities in SCBDI
calculations. More preferably, the monomer distribution of
the interpolymer and SCBDI are determined using 13C NMR
analysis in accordance with techniques described in US Patent
5,292,845 and by J. C. Randall in Rev. Macromol. Chem. Phys.,
C29, pp. 20l-317.
In addition to referring to a homogeneous (or narrow)
short branching distribution, the term "homogeneously
branched linear ethylene polymer" also means the interpolymer
does not have long chain branching. That is, the ethylene
interpolymer has an absence of long chain branching and a
linear polymer backbone in the conventional sense of the term
"linear." However, the term "homogeneously branched linear
ethylene polymer" does not refer to high pressure branched
polyethylene which is known to those skilled in the art to
have numerous long chain branches. Homogeneously branched
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linear ethylene polymers can be made using polymerization
processes (e. g., those described by Elston in USP 3,695,992)
which provide a uniform (narrow) short branching distribution
(i.e., homogeneously branched). In his polymerization
process, Elston uses soluble vanadium catalyst systems to
make such polymers, however others such as Mitsui Chemical
Corporation and Exxon Chemical Corporation have used so-
called single site catalyst systems to make polymers having a
similar homogeneous structure. Homogeneously branched linear
ethylene polymers can be prepared in solution, slurry or gas
phase processes using hafnium, zirconium and vanadium
catalyst systems. Ewen et al. in U.S. Pat. No. 4,937,299
describe a method of preparation using metallocene catalysts.
The term "heterogeneously branched linear ethylene
polymer" is used herein in the conventional sense in
reference to a linear ethylene interpolymer having a
comparatively low short chain branching distribution index.
That is, the interpolymer has a relatively broad short chain
branching distribution. Heterogeneously branched linear
ethylene polymers have a SCBDI less than 50 percent and more
typically less than 30 percent.
Heterogeneously branched ethylene polymers are well
known among practitioners of the linear polyethylene art.
Heterogeneously branched ethylene polymers are manufactured
using a conventional solution, slurry or gas phase
polymerization processes (at high or low pressures) in the
presence of a Ziegler-Natta type coordination metal catalysts
as described, for example, by Anderson et al. in U.S. Pat.
No. 4,076,698. These conventional Ziegler-Natta type linear
polyethylenes are not "homogeneously branched," do not have
any long-chain branching and, as such, have a linear polymer
backbone in the conventional sense of the term "linear."
Typically, the homogeneously branched linear ethylene
polymers and heterogeneously branched ethylene polymers are
ethylene/a-olefin interpolymers, wherein the a-olefin is at
least one C3-C2o a-olefin (e.g., propylene, 1-butene, 1-
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pentene, 4-methyl-1-pentene, 1-hexene, 1-octene and the like)
and preferably the at least one C3-C2o a-olefin is 1-octxene.
Most preferably, the ethylene/a-olefin interpolymer is a
copolymer of ethylene and a C3-Czo a-olefin, especially an
ethylene/C9-C6 a-olefin copolymer and most especially an
ethylenell-octene copolymer.
The term "substantially linear ethylene polymer" as used
herein refers to homogeneously branched ethylene polymers
(interpolymers and homopolymers) which possess a narrow short
chain branching distribution and contain long chain branches
as well as short chain branches attributable to homogeneous
comonomer incorporation. The long chain branches are of the
same structure as the backbone of the polymer and are longer
than the short chain branches. Substantially linear a-olefin
polymers is have from 0.01 to 3 long chain branch/1000
carbons. Preferred substantially linear polymers for use in
the invention have from 0.01 long chain branch/1000 carbons
to 1 long chain branch/1000 carbons, and more preferably from
0.05 long chain branch/1000 carbons to 1 long chain
branches/1000 carbons.
Long chain branching is defined herein as a chain length
of at least 7 carbons, above which the length cannot be
distinguished using 13C nuclear magnetic resonance
spectroscopy. The long chain branch can be as long as about
the same length as the length of the polymer backbone to
which it is attached. Long chain branches are obviously of
greater length than of short chain branches resulting from
comonomer incorporation.
The presence of long chain branching can be determined
in ethylene homopolymers by using 13C nuclear magnetic
resonance (NMR) spectroscopy and is quantified using the
method described by Randall (Rev. Macromol. Chem. Phys., C29,
V. 2&3, p. 285-297).
As a practical matter, current 13C nuclear magnetic
resonance spectroscopy cannot determine the length of a long
chain branch in excess of six-carbon atoms. However, there
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are other known techniques useful for determining the
presence of long chain branches in ethylene polymers,
including ethylene/1-octene interpolymers. Two such methods
are gel permeation chromatography coupled with a low angle
laser light scattering detector (GPC-LALLS) and gel
permeation chromatography coupled with a differential
viscometer detector (GPC-DV). The use of these techniques
for long chain branch detection and the underlying theories
have been well documented in the literature. See, for
20 example, Zimm, G.H. and Stockmayer, W.H., J. Chem. Phys., 17,
1301 (1949) and Rudin, A., Modern Methods of Polymer
Characterization, John Wiley & Sons, New York (1991) pp. 103-
112.
A. Willem deGroot and P. Steve Chum, both of The Dow
25 Chemical Company, at the October 4, 1994 conference of the
Federation of Analytical Chemistry and Spectroscopy Society
(FACSS) in St. Louis, Missouri, presented data demonstrating
that GPC-DV is a useful technique for quantifying the
presence of long chain branches in substantially linear
20 ethylene interpolymers. In particular, deGroot and Chum
found that the level of long chain branches in substantially
linear ethylene homopolymer samples measured using the Zimm-
Stockmayer equation correlated well with the level of long
13
chain branches measured using C NMR.
25 Further, deGroot and Chum found that the presence of
octene does not change the hydrodynamic volume of the
polyethylene samples in solution and, as such, one can .
account for the molecular weight increase attributable to
octene short chain branches by knowing the mole percent
30 octene in the sample. By deconvoluting the contribution to
molecular weight increase attributable to 1-octene short
chain branches, deGroot and Chum showed that GPC-DV may be
used to quantify the level of long chain branches in
substantially linear ethylene/octene copolymers.
35 deGroot and Chum also showed that a plot of Log(I2, Melt
Index) as a function of Log(GPC Weight Average Molecular
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Weight) as determined by GPC-DV illustrates that the long
chain branching aspects (but not the extent of long
branching) of substantially linear ethylene polymers are
comparable to that of high pressure, highly branched low
density polyethylene (LDPE) and are clearly distinct from
ethylene polymers produced using Ziegler-type catalysts such
as titanium complexes and ordinary homogeneous catalysts such
as hafnium and vanadium complexes.
The substantially linear ethylene polymers used in the
present invention are a unique class of compounds that are
further defined in US Patent 5,272,236, serial number
07/776,130, filed October 15, 1991 and in US patent
S,278,272, serial number 07/939,281, filed September 2, l992.
Substantially linear ethylene polymers differ
significantly from the class of polymers conventionally known
as homogeneously branched linear ethylene polymers described
above and, for example, by Elston in US Patent 3,645,992. As
an important distinction, substantially linear ethylene
polymers do not have a linear polymer backbone in the
conventional sense of the term "linear" as is the case for
homogeneously branched linear ethylene polymers.
Substantially linear ethylene polymers also differ
significantly from the class of polymers known conventionally
as heterogeneously branched traditional Ziegler polymerized
linear ethylene interpolymers (for example, ultra low density
polyethylene, linear low density polyethylene or high density
polyethylene made, for example, using the technique disclosed
by Anderson et al. in US Patent 4,076,698, in that
substantially linear ethylene interpolymers are homogeneously
branched polymers; that is, substantially linear ethylene
polymers have a SCBDI greater than or equal to 50 percent,
preferably greater than or equal to 70 percent, more
preferably greater than or equal to 90 percent.
Substantially linear ethylene polymers also differ from the
class of heterogeneously branched ethylene polymers in that
substantially linear ethylene polymers are characterized as
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essentially lacking a measurable high density or crystalline
polymer fraction as determined using a temperature rising
elution fractionation technique.
Substantially linear ethylene polymers also differ
significantly from the class of polymers known as free-
radical initiated, highly branched high pressure low density
ethylene homopolymer and ethylene interpolymers such as, for
example, ethylene-acrylic acid (EAA) copolymers and ethylene-
vinyl acetate (EVA) copolymers. That is, substantially
linear ethylene polymers do not have equivalent degrees of
long chain branching as high pressure, free-radical initiated
ethylene polymers and are made using single site catalyst
systems rather than free-radical peroxide catalysts systems.
Metallocene single site polymerization catalyst, (for
example, the monocyclo-pentadienyl transition metal olefin
polymerization catalysts described by Canich in US Patent
S,026,798 or by Canich in US Patent 5,055,438) or constrained
geometry catalysts (for example, as described by Stevens et
al. in US Patent 5,064,802) can be used to manufacture
substantially linear ethylene polymers, so long as the
manufacture and metallocene catalyst system are used
consistent with the methods described in US Patent 5,272,236
and in US Patent 5,278,272. Such polymerization methods are
also described in PCTIUS 92/08812 (filed October 15, l992).
However, the substantially linear ethylene polymers are
preferably manufactured using suitable constrained geometry
catalysts, especially constrained geometry catalysts as
disclosed in US Application Serial Nos.: 545,403, filed July
3, 1990; U.S. Pat. No. 5,132,380; U.S. Pat. No. 5,064,802;
U.S. Pat. No. 5,153,l57; U.S. Pat. No. 5,470,993; U.S. Pat.
No. 5,453,4l0; U.S. Pat. No. 5,374,696; U.S. Pat. No.
5,532,394; U.S. Pat. No. 5,494,874; U.S. Pat. No. 5,189,192.
Suitable cocatalysts for use herein include but are not
limited to, for example, polymeric or oligomeric
aluminoxanes, especially methyl aluminoxane or modified
methyl aluminoxane (made, for example, as described in US
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Patent 5,041,584, US Patent 4,544,762, US Patent 5,015,749,
and/or US Patent 5,041,585, as well as inert, compatible,
non-coordinating, ion forming compounds. Preferred
cocatalysts are inert, non-coordinating, boron compounds.
The polymerization conditions for manufacturing the
substantially linear ethylene polymers used in the present
invention are preferably those useful in the continuous
solution polymerization process, although the application of
the present invention is not limited thereto. Continuous
slurry and gas phase polymerization processes can also be
used, provided the proper catalysts and polymerization
conditions are employed. To polymerize the substantially
linear polymers useful in the invention, the single site and
constrained geometry catalysts mentioned earlier can be used,
but for substantially linear ethylene polymers the
polymerization process should be operated such that
substantially linear ethylene polymers are indeed formed.
That is, not a11 polymerization conditions inherently make
the substantially linear ethylene polymers, even when the
same catalysts are used. For example, in one embodiment of a
polymerization process useful in making substantially linear
ethylene polymers, a continuous process is used, as opposed
to a batch process.
The substantially linear ethylene polymer for use in the
present invention is broadly characterized as having
( a ) melt flow ratio, I,o/I2, >_ 5.63,
(b) a molecular weight distribution, MW/Mn, as
determined by gel permeation chromatography and
defined by the eq~lation:
(Mw/M") ~ (Ilo/I2) - 4.63,
(c) a gas extrusion rheology such that the critical
shear rate at onset of surface melt fracture for
the substantially linear ethylene polymer is at
least 50 percent greater than the critical shear
rate at the onset of surface melt fracture for a
linear ethylene polymer, wherein the substantially
linear ethylene polymer and the linear ethylene
polymer comprise the same comonomer or comonomers,
the linear ethylene polymer has an I2~ Mw/Mn and
density within ten percent of the substantially
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linear ethylene polymer and wherein the respective
critical shear rates of the substantially linear
ethylene polymer and the linear ethylene polymer
are measured at the same melt temperature using a
gas extrusion rheometer,
(d) a single differential scanning calorimetry, DSC,
melting peak between
-30° and 150°C, and
(e) a short chain branching distribution index greater
than about 50 percent.
The preferred homogeneously branched ethylene polymer
for use in this invention (and particularly as used as the
least one first ethylene polymer) are homogeneously branched
interpolymers (i.e., not homopolymers) and essentially lack a
measurable "high density" or crystalline polymer fraction as
measured by suitable TREF techniques. The preferred
homogeneously branched ethylene interpolymer is a
substantially linear ethylene polymer which have a narrow
short chain distribution (i.e., a high SCBD index).
Substantially linear ethylene interpolymers do not contain a
polymer fraction with a degree of branching less than or
equal to 2 methyls/1000 carbons. That is, substantially
linear-ethylene interpolymers, which are characterized as
consisting of uniform polymer fractions, do not contain a
high density or crystalline polymer fraction wherein a
polymer fraction characterized as having no short chain
branching or a degree of short chain branching less than or
equal to 2 methyls/1000 carbons is considered herein to be
"high density" or "crystalline." However, where a
homogeneously branched ethylene polymer is used as the second
ethylene polymer component which is specified to have a
- density in the range of from 0.99 g/cc to 0.97 g/cc and the
polymer is a homopolymer or contains very little comonomer,
the polymer of course may be characterized as having a "high
density" or "crystalline" polymer fraction by this method.
The substantially linear ethylene interpolymers for use
in the present invention are homopolymers of ethylene and
interpolymers of ethylene with at least one C3-CZO a-olefin
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and/or C9-C18 diolefin. Copolymers of ethylene and an a-
olefin of C3-CZO carbon atoms are especially preferred. The
term "interpolymer" as discussed above is used herein to
indicate a copolymer, or a terpolymer, or the like, where, at
least one other comonomer is polymerized with ethylene or
propylene to make the interpolymer. -
Suitable unsaturated comonomers useful for polymerizing
with ethylene include, for example, ethylenically unsaturated
monomers, conjugated or non-conjugated dimes, polyenes,_ etc.
Examples of such comonomers include C3-CZO a-olefins such as
propylene, isobutylene, 1-butene, 1-hexene, 4-methyl-1-
pentene, 1-heptene, 1-octene, 1-nonene, 1-decene, and the
like. Preferred comonomers include propylene, 1-butene, 1-
hexene, 4-methyl-1-pentene and 1-octene, and 1-octene is
especially preferred. Other suitable monomers include
styrene, halo- or alkyl-substituted styrenes,
tetrafluoroethylene, vinylbenzocyclobutane, 1,4-hexadiene,
1,7-octadiene, and cycloalkenes, e.g., cyclopentene,
cyclohexene and cyclooctene.
Determination of the critical shear rate and critical
shear stress in regards to melt fracture as well as other
rheology properties such as "rheological processing index"
(PI), is performed using a gas extrusion rheometer (GER).
The gas extrusion rheometer is described by M. Shida, R.N.
Shroff and L.V. Cancio in Polymer Engineering Science, Vol.
17, No. 11, p. 770 (1977), and in "Rheometers for Molten
Plastics" by John Dealy, published by Van Nostrand Reinhold
Co. (1982) on pp. 97-99. GER experiments are performed at a
temperature of about 190°C, at nitrogen pressures between 250
to 5500 psig (1.? - 37.9 Mpa) using a 0.0754 mm diameter,
20:1 L!D die with an entrance angle of about 180°. For the
substantially linear ethylene polymers described herein, the
PI is the apparent viscosity (in kpoise) of a material
measured by GER at an apparent shear stress of about 2.15 x
106 dyne/cmz. The substantially linear ethylene polymer for
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use in the invention are ethylene polymers having a PI in the
range of about 0.01 kpoise to about 50 kpoise, preferably
about 15 kpoise or less. The substantially linear ethylene
polymers used herein have a PI less than or equal to about 70
percent of the PI of a linear ethylene interpolymer (either a
conventional Ziegler polymerized interpolymer or a linear
homogeneously branched interpolymer as described by Elston in
US Patent 3, 645, 992 ) having an I2~ MW/Mn and density, each
within ten percent of the substantially linear ethylene
interpolymer.
An apparent shear stress versus apparent shear rate plot
is used to identify the melt fracture phenomena and quantify
the critical shear rate and critical shear stress of ethylene
polymers. According to Ramamurthy in the Journal of
Rheology, 30(2), 337-357, 1986, above a certain critical flow
rate, the observed extrudate irregularities may be broadly
classified into two main types: surface melt fracture and
gross melt fracture.
Surface melt fracture occurs under apparently steady
flow conditions and ranges in detail from loss of specular
film gloss to the more severe form of "sharkskin." Herein,
as determined using the above-described GER, the onset of
surface melt fracture (OSMF) is characterized at the
beginning of losing extrudate gloss at which the surf-ace
roughness of the extrudate can only be detected by 40x
magnification. The critical shear rate at the onset of
surface melt fracture for the substantially linear ethylene
interpolymers is at least about 50 percent greater than the
critical shear rate at the onset of surface melt fracture of
a linear ethylene interpolymer having essentially the same I2
and MW/Mn.
Gross melt fracture occurs at unsteady extrusion flow
conditions and ranges in detail from regular (alternating
rough and smooth, helical, etc.) to random distortions. For
commercial acceptability and optimum sealant properties,
surface defects should be minimal, if not absent. The
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critical shear stress at the onset of gross melt fracture for
the substantially linear ethylene interpolymers used in the
invention, that is those having a density less than about
0.9l g/cc, is greater than 9 x 106 dynes/cm2. The critical
shear rate at the onset of surface melt fracture (OSMF) and
the onset of gross melt fracture (OGMF) will be used herein
based on the changes of surface roughness and configurations
of the extrudates extruded by a GER. Preferably, in the
present invention, the substantially linear ethylene polymer
will be characterized by its critical shear rate, rather than
its critical shear stress.
Preferred homogeneously branched ethylene polymers, like
a11 substantially linear ethylene polymers, are further
characterized as consisting of a single polymer component
material and as having a single DSC melting peak. A single
melting peak is determined using a differential scanning
calorimeter standardized with indium and deionized water.
The method involves 5-7 mg sample sizes, a "first heat" to
140°C which is held for 9 minutes, a cool down at 10°/min. to
-30°C which is held for 3 minutes, and heat up at about
10°C/min. to 180°C for the "second heat." The single melting
peak is taken from the "second heat" heat flow vs.
temperature curve. Total heat of fusion of the polymer is
calculated from the area under the curve.
For substantially linear ethylene interpolymers having a
density of about 0.875 g/cc to about 0.91 g/cc, the single
melting peak may show, depending on equipment sensitivity, a
"shoulder" or a "hump" on the low melting side that
constitutes less than about 12 percent, typically, less than
about 9 percent, and more typically less than about 6 percent
of the total heat of fusion of the polymer. Such an artifact
is observable for other homogeneously branched polymers such
as EXACT resins and is discerned on the basis of the slope of
the single melting peak varying monotonically through the
melting region of the artifact. Such an artifact occurs
within 34°C, typically within 27°C, and more typically within
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20°C of the melting point of the single melting peak. The
heat of fusion attributable to an artifact can be separately
determined by specific integration of its associated area
under the heat flow vs. temperature curve.
The molecular weight distributions of ethylene polymers
are determined by gel permeation chromatography (GPC) on a
Waters 150C high temperature chromatographic unit equipped
with a differential refractometer and three columns of mixed
porosity. The columns are supplied by Polymer Laboratories
and are commonly packed with pore sizes of 103, 10q, 105 and
6e
10 A. The solvent is 1,2,4-trichlorobenzene, from which
about 0.3 percent by weight solutions of the samples are -
prepared for injection. The flow rate is about 1.0
milliliters/minute, unit operating temperature is about 140°C
and the injection size is about I00 microliters.
The molecular weight determination with respect to'the
polymer backbone is deduced by using narrow molecular weight
distribution polystyrene standards (from Polymer
Laboratories) in conjunction with their elution volumes. The
equivalent polyethylene molecular weights are determined by
using appropriate Mark-Houwink coefficients for polyethylene
and polystyrene (as described by Williams and Ward in 3ournal
of Polymer Science, Polymer Letters, Vol. 6, p. 621, l968) to
derive the following equation:
Mpolyethylene = a * (Mpolystyrene)b~
In this equation, a = 0.4316 and b = 1Ø Weight average
molecular weight, Mw, is calculated in the usual manner
according to the following formula: Mj - (~ wi (Mi') ) ~; where
wi is the weight fraction of the molecules with molecular
weight Mi eluting from the GPC column in fraction i and j - 1
when calculating MW and j - -1 when calculating Mn.
For the homogeneously branched substantially linear
ethylene polymers and homogeneously branched linear ethylene
polymers used in the present invention, the MW/Mn is generally
less than 3.5, preferably less than 3.0, more preferably less
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than 2.5, and especially in the range of from 1.5 to 2.5 and
most especially in the range f-rom 1.8 to 2.3.
Substantially linear ethylene polymers are known to have
excellent processability, despite having a relatively narrow
molecular weight distribution (that is, the Mw/M~ ratio is
typically less than 3.5). Surprisingly, unlike homogeneously
and heterogeneously branched linear ethylene polymers, the
melt flow ratio (Ilo/IZy of substantially linear ethylene
polymers can be varied essentially independently of the
l0 molecular weight distribution, MW/Mn. Accordingly, especially
when good extrusion processability is desired, the preferred
ethylene polymer for use in the present invention is a
substantially linear ethylene polymer, especially a
substantially linear ethylene interpolymer.
An especially preferred film, film layer or composition
of the invention will be further characterized as having a
compositional hexane extractive level of less than 15
percent, preferably less than 10 percent, more preferably
less than 6, most preferably less than 3 percent based on the
total weight of the mixture.
Still another especially preferred film, film layer or
composition of the invention will be further characterized as
having a Vicat softening point of at least 75°C, preferably
at least 85°C, and more preferably at least 90°C.
In another preferred embodiment, where good heat
strength is desired, a sealant layer of the present invention
is broadly characterized as having, at a minimum sealing
strength of 1.8 Newtons/15 mm, a seal initiation temperature
in the range from equal to or at least 4.5°C lower than the
Vicat softening temperature of the layer, more preferably, in
particular embodiments, a film heat seal initiation
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temperature in the range from equal to or at least 6°C lower
than the Vicat softening temperature of the layer and most
preferably at least 10°C lower than the Vicat softening
temperature of the layer.
Another aspect of the present invention is a process for
fabricating a monolayer or multilayer film structure or a
process for fabricating the polymer composition of the
invention into the form of a film, film layer, coating,
thermoformed or molded article. The process can include a
lamination and coextrusion technique or combinations thereof,
or can include using the polymer composition or mixture
alone, and can also specifically include blown film, cast
film, extrusion coating, injection molding, blow molding,
thermoforming, profile extrusion, pultrusion, compression
molding, rotomolding, or injection blow molding operations or
combinations thereof or like technique for fabricating a
sealant material.
The polymer composition or mixture of the invention can
be formed by any convenient method, including dry blending
individual polymer components together and subsequently melt
mixing the component polymers in a mixer or by mixing the
polymer components together directly in a mixer (e.g., a
Banbury mixer, a Haake mixer, a Brabender internal mixer, or
a single or twin screw extruder including a compounding
extruder and a side-arm extruder employed directly down
stream of a polymerization process).
The polymer composition or mixture of the invention (as
well as the at least one first ethylene polymer or the at
least one second ethylene polymer) can be formed in-situ via
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the polymerization of ethylene using a single-site catalysis,
preferably a single-siteconstrained geometry catalyst, in at
least one reactor and a single-site catalysis, preferably a
single-site constrained geometry catalyst, or a Ziegler-Natta
type catalyst in at least one other reactor. For in-situ
polymerization, the reactors can be operated sequentially or
in parallel. An exemplary in-situ polymerization process is
disclosed in PCT Patent Application 94/010S2, the disclosure
of which is incorporated herein by reference.
The polymer composition of the invention (as well as the
at least one first ethylene polymer or the at least one
second ethylene polymer) can also be formed by isolating
component (A) , (B) ( (C) and/or component (D) from a
heterogeneously branched ethylene polymer by fractionating
the heterogeneous ethylene polymer into specific polymer
fractions (or by isolating component (A) or (C) from a
homogeneously branched ethylene polymer by fractionating the
homogeneously ethylene polymer into polymer fractions),
selecting the fractions) appropriate to meet the limitations
specified for component (A), (B), (C) or(D), and mixing the
selected fractions) in the appropriate amounts with the at
least one first ethylene polymer component (A) or (C) or the
at least one second ethylene polymer component (B) or (D).
This method is obviously not as economical as the in-situ
polymerization or blender/extruder mixing technique described
above, but can nonetheless be used to obtain the polymer
composition or mixture of the present invention as well as
the at least one first ethylene polymer and the at least one
second ethylene polymer.
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However, regardless of how the polymer mixture, the at
least one first ethylene polymer or the at least one second
ethylene polymer is manufactured, the composition or
component polymer will be considered a homogeneously branched
ethylene polymer or, alternatively, a heterogeneously
branched ethylene polymer based on the above definitions that
refer to heterogeneous branching and homogeneous branching
(i.e.,~ the SCBDI) and based on specific whole composition
analysis (such as, for example, ATREF results) rather than
fractional analysis or manufacturing technique.
Additives, such as antioxidants (e. g., hindered
phenolics, such as IRGANOX'~ 1010 or IRGANOX'~ 1076 supplied by
Ciba Geigy),~phosphites (e.g., IRGAFOS'~ l68 also supplied by
Ciba Geigy), cling additives (e. g., PIB), SANDOSTAB PEPQ'
(supplied by Sandoz), pigments, colorants, fillers, anti-
stats, processing aids, and the like may also be included in
the polymer mixture of the present invention or in films
formed from the same. Although generally not required,
films, coatings and moldings formed from the polymer mixture
of the present invention may also contain additives to
enhance antiblocking, mold release and coefficient of
friction characteristics including, but not limited to,
- untreated and treated silicon dioxide, talc, calcium
carbonate, and clay, as well as primary, secondary and
substituted fatty acid amides, release agents, silicone
coatings, etc. Still other additives, such as quaternary
ammonium compounds. alone or in combination with ethylene-
acrylic acid (EAA) copolymers or other functional polymers,
may also be added to enhance the antistatic characteristics
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of films, coatings and moldings formed from the polymer
mixture of the invention and permit the use of these polymer
mixtures in, for example, the heavy-duty packaging of
electronically sensitive goods.
The film, film layer or composition of the invention may
further include recycled and scrap materials and diluent
polymers, to the extent that the balanced sealant and modulus
properties are maintained. Exemplary diluent materials
include, for example, elastomers, rubbers and anhydride
modified polyethylenes (e. g., polybutylene and malefic
anhydride grafted LLDPE and HDPE) as well as with high
pressure polyethylenes such as, for example, low density
polyethylene (LDPE), ethylene/acrylic acid (EAA)
interpolymers, ethylene/vinyl acetate (EVA) interpolymers and
ethylene/methacrylate (EMA) interpolymers, and combinations
thereof.
The film, film layer or composition of the invention may
find utility in a variety of applications. Suitable
applications are thought to include, for example, but are not
limited to, monolayer packaging films: multilayer packaging
structures consisting of other materials such as, for
example, biaxially oriented polypropylene or biaxially
oriented ethylene polymer for shrink film and barrier shrink
applications; packages formed via form/fill/seal machinery;
peelable seal packaging structures; cook-in food package s
compression filled packages; heat sealable stretch wrap
packaging film such as, for example, fresh produce packaging
and fresh red meat retail packaging; liners and bags such as,
for example, cereal liners, grocery/shopping bags, heavy-duty
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shipping sacks and trash can liners (bags), gaskets and
lidding stock.
Monolayer and multilayer biaxially oriented film
structures are used for their enhanced strength, clarity,
gloss, stiffness, barrier and/or shrink properties.
Biaxially oriented film structures find utility in various
packaging and storage applications for non-foodstuffs and
food items such as primal and subprimal cuts of meat, ham,
poultry, bacon, cheese, etc. A typical multilayer biaxially
20 oriented film structure utilizing the film, film layer or
composition of the invention may be a two to seven layer
structure including the inventive sealant film layer, an
outer layer (such as, for example, a heterogeneously branched
linear low density or ultra-low density polyethylene), and a
core layer (such as a biaxially oriented polypropylene
homopolymer or vinylidene chloride polymer) interposed
between the inventive sealant film layer and the outer layer.
Multilayer structures that include the inventive film,
film layer or composition may also include adhesion promoting
tie layers (such as PRIMACOR~ ethylene-acrylic acid (EAA)
copolymers available from The Dow Chemical Company, and/or
ethylene-vinyl acetate (EVA) copolymers. Such multilayer
structures may further include additional structural layers
such as AFFINITY" polyolefin plastomers, available from The
Dow Chemical Company, ENGAGE"' polyolefin elastomers, available
from Dupont Dow Elastomers, DOWLEXTM LLDPE, available from The
Dow Chemical Company, ATTANErM ULDPE, available from The Dow
Chemical Company, or blends of any of these polymers with
each other or with another polymer, such as an EVA copolymer.
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In general, multilayer structures that include the film,
film layer or composition of the present invention (whether
biaxiaily oriented or not) may include, but are not limited
to, barrier layers, tie layers, and/or structural layers.
Various materials can be used for these layers, with some of
them being used as more than one layer in the same multilayer
structure. Some of these materials include: foil, nylon,
ethylene/vinyl alcohol (EVOH) copolymers, polyvinylidene
chloride (PVDC), polyethylene terepthalate (PET),
l0 polypropylene (especially, oriented polypropylene (OPP) and
more especially, biaxially oriented polypropylene),
ethylene/vinyl acetate (EVA) copolymers, ethylene/acrylic
acid (EAA) copolymers, ethylene/methacrylic acid (EMAA)
copolymers, ULDPE, LLDPE, HDPE, MDPE, LMDPE, LDPE, ionomers,
graft-modified polymers (e. g., malefic anhydride grafted
polyethylene), and paper. Generally, the multilayer
structure of the present invention may comprise from 2 to
about 7 layers or any number of layers or materials or
polymers deemed required for a targeted application.
As mentioned above, the present film or composition is
thought to be particularly suitable for compression fill,
cook-in food packaging and vertical form/fill/seal
applications. Compression fill packaging typically involves
- initially fabricating a plastic tube by a blown film
technique. The tube as layflat film is then communicated or
delivered to filling machinery wherein (in continuous
operation) a bottom seal is made, compressible product items
are loaded into the tube and compressed to a reduced volume.
Subsequently to product items being loaded into the tube, a
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CA 02271482 1999-OS-12
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top seal is made to seal the packaged product. An example of
product items that may be packaged by a compression fill
technique is textiles such as, for example, but not limited
to, diapers and athletic socks.
Cook-in packaged foods are foods which are prepackaged
and then cooked. The packaged and cooked foods go directly
to the consumer, institution, or retailer for consumption or
sale. A package for cook-in must be structurally capable of
withstanding exposure to cook-in time and temperature
conditions while containing a food product. Cook-in packaged
foods are typically employed for the packaging of ham,
turkey, vegetables, processed meats, etc. Because of the
relatively high softening point to heat seal and hot tack
initiation temperature characteristic of the inventive
sealant layer, multilayer film structures comprising the
inventive sealant layer are well-suited for cook-in packaging
applications.
Form/fill/seal packages are typically utilized for the
packaging of flowable materials, such as milk, wine, powders,
etc. In a form/~ill/seal packaging process, a sheet of the
plastic film structure is fed into a form/fill/seal machine
where the sheet is formed into a continuous tube by sealing
the longitudinal edges of the film together by lapping the
plastic film and sealing the film using an inside/outside
seal or by fin sealing the plastic film using an
inside/inside seal. Next, a sealing bar seals the tube
transversely at one end to form the bottom of a pouch. The
flowable material is then added to the formed pouch. The
sealing bar then seals the top end of the pouch and either -
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CA 02271482 1999-OS-12
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burns through the plastic film or a cutting device cuts the
film, thus separating the formed completed pouch from the
tube. The process of making a pouch using form/fill/seal
machinery is generally described in U.S. Patent Nos.
4,503,102 and 4,521,437, because of the low heat seal and hot
tack initiation temperatures, the high hot tack strength and
the broad hot tack sealing window characteristics of the
inventive sealant layer, multilayer film structures
comprising the inventive sealant Layer are well-suited for
form/fill/seal packaging applications.
The heat seal initiation temperature is determined in
accordance with ASTM F 88-85. 2o secant modulus is
determined in accordance with ASTM D-882. Densities are
measured in accordance with ASTM D-792 and are reported as
grams/cubic centimeter (g/cc). The measurements reported in
the Examples below as overall densities were determined after
the polymer samples have been annealed for 24 hours at
ambient conditions in accordance with ASTM D-792.
The density and weight percent of polymer components can
be determined by an Analytical Temperature Rising Elution
Fractionation (ATREF) technique. The hardware and procedures
used for the ATREF technique have been previously described,
e.g., Wild et al, Journal of Polymer Science, Poly. Phys.
Ed., 20,41(1982), Hazlitt, et al., U.S. Patent No. 4,798,081
and Chum et al., U.S. Patent No.5,089,321.
In ATREF analysis, the film or composition to be
analyzed is dissolved in a suitable hot solvent (e. g.,
trichlorobenzene) and allowed to crystallizd in a column
containing an inert support by slowly reducing the
temperature. An ATREF chromatogram curve is then generated
by eluting the crystallized polymer sample from the column by
slowly increasing the temperature of the eluting solvent
(trichlorobenzene). The ATREF curve is also frequently
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called the short chain branching distribution (SCBD), since
it indicates how evenly the comonomer (e.g., octene) is
distributed throughout the sample in that as elution
temperature decreases, comonomer content increases.
The ATREF curve can conveniently illuminate several key
structural features of a film or composition. For example,
homogeneously branched ethylene polymers such as AFFINITY'
resins supplied by The Dow Chemical Company, ENGAGE' resins
supplied by Dupont Dow Elastomers, TAFMER~' resins supplied by
Mitsui Chemical Corporation and EXACT' resins supplied by
Exxon Chemical Corporation are known to exhibit a unique
symmetrical single elution peak (or homogeneous SCBD). In
contrast, ethylene polymers produced by a conventional
Ziegler-Natta catalyst system (such as, for example, DOLWEX~'
LLDPE resins supplied by The Dow Chemical Company) are known
to exhibit a bimodal or heterogeneous SCBD with both a broad
and a narrow peak eluting at significantly different
temperatures.
Because the uniqueness of the shape of ATREF curves and
elution temperatures correspond to polymer densities, ATREF
analysis can be used to fingerprint particular polymers. In
particular, for compositions consisting of multiple component
polymers, by integrating the ATREF curve, the weight fraction
of each component can be conveniently determined. Further,
the density of component polymers can be determined from
ATREF analysis where the composition is known from
measurement in accordance with ASTM D-792. For example, for
substantially linear ethylene polymers, calibration curves of
ATREF elution temperature versus polymer density provide
polymer density is defined by:
p =0.83494 + 9. 6l33 x 10-9 (Te)
where Te is the ATREF elution temperature of the polymer.
Given the overall composition density of the composition, the
weight fraction of the component polymer by integration of
the ATREF curve and the polymer density of the substantially
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CA 02271482 1999-OS-12
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linear ethylene polymer component, the density of the remain
component polymer can be conveniently calculated.
To further characterize the polymer composition, a
differential viscometer may be employed. The output from a
differential viscometer is the viscosity average molecular
weight, M~, which indicates the variation in molecular weight
as a function of elution volume. The M~ response can indicate
which component polymer is characterized as having a higher
molecular weight or whether the component polymers are
characterized as having substantially equivalent molecular
weights.
In summary, given the ATREF curve and composition
density of a film or composition, the weight fraction and
polymer densities of the component polymers can be
calculated. Combining ATREF analysis with a differential
viscometer (ATREF/DV) gives an indication of the relative
molecular weights of the component polymers. As such,
AFTREF/DV can be used to fingerprint the film or composition
of the present invention. The AFREF curve will show at least
two distinct elution peaks given to density differential
between the first and second ethylene polymers of the
invention and preferred embodiments will exhibit a single
elution peak associated with the first ethylene polymer
component and a second ethylene polymer component having a
higher molecular weight than the first ethylene polymer
component.
A GPC deconvolution technique can be used to determine
the melt index of individual ethylene polymer components. In
this technique, GPC data are generated using a Waters 150C
high temperature GPC chromatograph as described hereinabove.
Given empirical elution volumes, molecular weights can be
conveniently calculated using a calibration curve generated
from a series of narrow molecular weight distribution
polystyrene standards. The GPC data should be normalized
prior to running the deconvolution procedure to insure an
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CA 02271482 1999-OS-12
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area of unity under the weight fraction versus log(MW) GPC
curve.
For the deconvolution technique, homogeneously branched
ethylene polymers are assumed to follow a Bamford-Tompa
molecular weight distribution, i.e., Eq. [1],
w. ( Mr ) =1n(10) M' exp((- M' (1 + ~ )) X ( 2 + ~) Biz X I ( Mr~~n (2 + ~vz )
[ 1 ]
M" M" ~' M"
where wi is the weight fraction of polymer with molecular
weight Mi, M" is the number average molecular weight, I1(x) is
the modified Bessel function of the first kind of order one,
defined by Eq.[2],
x zn+i
Ii (x) _ ~2zn,-~b!(b+1)!
and ~ is an adjustable parameter which broadens the molecular
weight distribution, as shown in Eq.[3].
M~" =2+(, [3]
M"
For the deconvolution technique, heterogeneously
branched ethylene polymers (i.e., polymers manufactured using
a Ziegler-Natta catalyst system) are assumed to follow a log-
normal distribution, Eq.[9],
~'~'r ( Mr ) = 1 o.s eXP(- 1 ( log( Mr ) - log( M~ ) ) z )
,Q(2~c) 2
where wi is the weight fraction of polymer with molecular
weight Mi, Mo is the peak molecular weight and ~ is a
parameter which characterizes the width of the distribution.
~i was assumed to be a function of Mo, as shown in Eq. [5].
,Q = 5.70506 - 2.52383 Log( M" ) + 0.30024( Log( M" )) z [ 5 ]
The GPC deconvolution technique involves a four
parameter fit, Mn and ~, for a homogeneously branched ethylene
polymer (typically the first ethylene polymer component of
the invention), Mo for a heterogeneously branched ethylene
polymer (preferably the second component polymer of the
invention) and the weight fraction amount of the
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CA 02271482 1999-OS-12
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homogeneously branched ethylene polymer. A non-linear curve-
fitting subroutine within SigmaPlotTM supplied by Jandel
Scientific (v3.03) is used to estimate these parameters.
Given the number average molecular weight (Mn) , Eq.[3], of
the homogeneously branched ethylene polymer or the first
ethylene polymer component, its I1°/IZ melt flow ratio and its
density, its IZ melt index can be conveniently calculated
using Eq.[6].
Iz:cra = exp(62.782 - 3.8620Ln( M".) -1.7095Ln(( ~!° )F"''') _ 16.310 x
p~~P'°) [ 6 ]
2
where FCPA denotes the ethylene polymer component.
Examples
The following examples are provided for the purpose of
explanation, rather than limitation.
In an evaluation to investigate various sealant
materials, three layer (ABC) coextrusion film was
manufactured on a Bruckner cast tenter-frame BOPP film line.
The (B) layer was the core or base of the structure and was
maintained as Shell KF 6100 homopolymer polypropylene with a
slip and anti-stat additive package. The additive package
was provided by using 2.5~ by weight of Ampacet 400577
masterbatch which contains a blend of 15% by weight of anti-
static and slip agents in a 30 MFI (at 230°C with a 2.16 kg
weight ) polypropylene homopolymer carrier resin. The Shell
KF 6100 homopolymer polypropylene resin had a MFI of about 3
as measured at 230°C with a 2.l6 kg weight.
The (A) and (C) layers were produced as variable sealant
skin layers using the same sealant material for both layers
through the evaluation. An additive masterbatch containing
slip and antiblock additives was added to the sealant layers
to provide about 1250 ppm of erucamide and about 1500 ppm of
Si02. Example 1 and Comparative Examples 2-8 were the
various sealant materials investigated in this evaluation.
In this evaluation, Example 1 and comparative example 6
were prepared using an in-situ polymerization and mixture
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CA 02271482 1999-OS-12
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process, such as is disclosed in PCT Patent Application No.
94/01052. The particular production details are set forth as
follows.
The constrained geometry catalyst was prepared by
dissolving a known weight of the constrained-geometry
organometallic complex [((CH3)qC5))-(CH3)2Si-N-(t-
CqH9)]Ti(CH3)2 in IsoparT" E hydrocarbon (available from Exxon
Chemical Company) to give a clear solution with a titanium
(Ti) concentration of 9.6 x 10-4 M.. A similar solution of
the activator complex tris(perfluorophenyl)borane (3.8 x 10-3
M) was also prepared. A known weight of methylalumoxane
(available from Texas Alkyls as MMAO) was dissolved in n-
heptane to give a solution with an MMAO concentration of 1.06
x 10-2 M. These solutions were independently pumped such
I5 that they were combined just prior to being fed into the
first polymerization reactor and such that the constrained
geometry catalyst, the activator complex, and the MMAO were
in a molar ratio of 1:3.5:7.
A heterogeneous Ziegler-type catalyst was prepared
substantially according to the procedure of U.S. Patent No.
4,612,300 (Example P), by sequentially adding to a volume of
IsoparTM E hydrocarbon, a slurry of anhydrous magnesium
chloride in IsoparT" E hydrocarbon, a solution of EtA1C12 in
n-hexane, and a solution of Ti (O-iPr) q in Isopar''"' E
hydrocarbon, to yield a slurry containing a magnesium
concentration of 0.166 M and a ratio of Mg/A1/Ti of
40.0:12.5:3Ø An aliquot of this slurry and a dilute
solution of Et3A1 (TEA) were independently pumped with the
two streams being combined just prior to introduction into
the second polymerization reactor to give an active catalyst
with a final TEA: Ti molar ratio of 6.2:1.
In a two-reactor polymerization system, ethylene was fed
into the first reactor at a scaled rate of 40 lb/hr (18.2
kg/hr). Prior to introduction into the first reactor, the
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CA 02271482 1999-OS-12.
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ethylene was combined with a diluent mixture comprising
IsoparTM E hydrocarbon (available from Exxon Chemical Company)
and 1-octene. With respect to the first polymerization
reactor, the 1-octene:ethylene ratio (constituting fresh and
recycled monomer) was 0.28:1 (mole percent} and the
diluent:ethylene feed ratio was 8.23:1 (weight percent). A
homogeneous constrained geometry catalyst and cocatalyst such
as prepared above was introduced into the first
polymerization reactor. The catalyst, activator, and MMAO
scaled flow rates into the first polymerization reactor were
1.64 x 10"5 lbs. Ti/hr (7.4 x 10-6 kg Ti/hr}, 6.21 x 10-4 lbs.
activator/hr (2.82 x 10-~ kg activator/hr), and 6.57 x 10-5
lbs. MMAO/hr (3.0 x 10-5 kg MMAO/hr), respectively. The
polymerization was conducted at a reaction temperature in the
range of 70-160°C.
The reaction product of the first polymerization reactor
was transferred to the second reactor. The ethylene
concentration in the exit stream from the first
polymerization reactor was less than four percent, indicating
the presence of long chain branching as.described in U .S.
Patent No. 5,272,236.
Ethylene was further fed into the second polymerization
reactor at a scaled rate of 120 lbs./hr (54.5 kg/hr). Prior
to introduction into the second polymerization reactor, the
ethylene and a stream of hydrogen were combined with a
diluent mixture comprising Isopar''"' E hydrocarbon and 1-
octene. With respect to the second polymerization reactor,
- the 1-octene:ethylene feed ratio (constituting fresh and
recycled monomer) was 0.196:1 (mole percent), the
diluent:ethylene ratio was 5.91:l (weight percent}, and the
hydrogen: ethylene feed ratio was 0.24:1 (mole percent).
A heterogeneous Ziegler-Natta catalyst and cocatalyst as
prepared above were introduced into the second polymerization
reactor. The catalyst (Ti) and cocatalyst (TEA)
concentrations in the second polymerization reactor were 2.65
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CA 02271482 1999-OS-12
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x 10-3 and 1.65 x 10-3 molar, respectively. The catalyst and
cocatalyst scaled flow rates into the second polymerization
reactor were 4.49 x 10-9 lbs. Ti/hr (2.09 x 10-4 kg Ti/hr) and
9.l4 x 10-3 lbs. TEA/hr (4.15 x 10-3 kg TEA/hr) respectively.
The polymerization in the second reactor was conducted at a
reaction temperature in the range of 150-220°C. The
conversion and production split between the first and second
polymerization reactors was such as to yield the "weight
percent of the first ethylene polymer component (A)" value
for Example 1 and Comparative Example 6 as set forth in Table
1. That is, the weight percent of the first ethylene polymer
component (A) represents the production split between the
first and second polymerization reactors.
To the resulting polymer, a standard catalyst kill agent
25 (1250 ppm Calcium Stearate) and antioxidants (200 ppm
IRGANOX''M 1010, i.e., tetrakis [methylene 3-(3,5-di-tert=
butyl-9-hydroxy-phenylpropionate)]methane, available from
Ciba-Geigy and 800 ppm SANDOSTAB''M PEPQ, i.e., tetrakis-(2,4-
di-tert-butyl-phenyl)-4,4' biphenylphosphonite, available
from Sandoz Chemical) were added to stabilize the polymer.
Comparative example 2 was a polypropylene copolymer
having a 5 MFI as measured at 230°C with a 2.16 kg weight and
supplied by Solway under the designation of KS 4005.
Comparative example 3 was a polypropylene terpolymer having a
5 MFI as measured at 230 C with a 2.16 kg weight and supplied
by Solway under the designation of KS 300. Comparative
example 4 was a substantially linear ethylene polymer
supplied by The Dow Chemical Company under the designation of
AFFINITYTM PL 1845. Comparative example 5 was a
substantially linear ethylene polymer supplied by The Dow
Chemical Company under the designation of AFFINITYTM PL 1850.
Comparative example 7 was a heterogeneously branched linear
low density polyethylene resin supplied by The Dow Chemical
Company under the designation of DOWLEXTM 2035E. Comparative
example 8 was a heterogeneously branched ultra low density
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CA 02271482 1999-OS-12
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polyethylene resin supplied by The Dow Chemical Company under
the designation of ATTANETM SC4103.
The heat seal initiation temperature for the various
sealant layers was determined using a conventional heat seal
tester and tensiometer after seals were allowed to age far 24
hours wherein the seal initiation temperature was taken as
the temperature where a seal strength of 1.8 N/15 mm was
reached. The temperature range over which the hot tack force
exceeds 46 g/cm (using the DuPont spring-method) was taken as
the hot tack strength window.
"Sufficient interlayer adhesion" is defined herein as no
sign of delamination observed during the coextrusion
fabrication step or during sealing and seal testing.
Conversely, "poor interlayer adhesion" was taken as the onset
25 of delamination during sealing.
In this evaluation, the layer thicknesses were (A) - 1
um (micrometer), (B) - 18 um and (C) - 1 um. The side
corresponding to layer (C) was Corona treated to a level of
about 44 dynes. The materials were extruded at melt
temperatures between 245 and 275°C and at a chill roll
temperature of 25-30°C. The temperature of the machine
direction orientation (MDO) heated rollers were between 90
and 125°C. The draw ratio in the machine direction was 5:1
and in the transverse direction was 8:1. The tenter-frame
oven temperatures ranged from 180 to 160°C
The densities, melt indices, and weight percent of the
first ethylene polymer component (A), the overall melt index,
composition density and Vicat softening point of the
resultant polymer composition and the type of catalyst system
employed to manufacture the various examples as well as the
heat seal, hot tack and interlayer adhesion performance of
the examples are set forth in Table 1.
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CA 02271482 1999-05-12
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Table 1
Example ~ 1 2* 3* , 4* , 5* , 6* . 7* 8*
Overall MI, 2.7 N/A N/A 3.5 3.0 3.1 6.0 3.3
g/10 min.
: :
:
..-overall...................0 .. . ..Ø:.9i... ...Ø..... .
..
..9i........N/A'.......N/A'..... .Ø.90...... ~ 0~.~919~~~~~0.912~~
.97.9 ~~
~
Density, g/cc 8 0 2
...... ...... .... ... ~
....... .........
. .. .
... ...
..
....
.
. ... .
...............................................................................
.........................................................
....... .. .... . 90.7 82.5 99.5 105 95
. 102 ..... --
... ..
. --
.
..
overall Vicat
softening,
C ....... ..: . ... .
... .. ..... .... ....
. '... '. .
-.. .
(A~ 0 N/A N/A 3.: ...3.
......O..S7...........N/A".........N/A'......
Component : 5... Ø....
28
MI, g/10 min.
: :
:
...component ...0 .. . .... . ...Ø..90y.........N ....N.~
"-......... .8.9...... ....N/A...Ø:.9..Ø.90.... ~A'.....
N~A'... i
..
(A), Density, 8 0 2
.glcc_...............................................:......................:..
....................................:. : :
.
. .
.....................................................................
Weight $ 41..0: N/A N/A : 100.................... .. N/A
: 100.93.5 N/A
Component (A) 0 0
..............................................................._...............
..................................;................._..........................
.:.........................:......................
Catalyst Type CGC/ ..A....N/A CGC CGC CGC/ZN ZN ' -
/ ' ZN
ZN
Seal 96 120 110 95 90 95 115 110
Initiation,
C : :
...................................,.......................... ...
...............................................................................
...............:......................
Hot Tac .................................... .

k
window (temp 35 15 25 '.. ~ NoneNone None None
None i
range @ > 96 (105 (125- (115-
g/cm), C - 190) 140)
190) ' v
...............................................................
..................................................
................... ...
...
. ...
.........................,................................................
Interlayer .....
..
Adhesion to Good Good Good Good Good Good Poor Good
Homo-PP Core
CGC denotes Constrained catalyst
geometry
Z/N denotes Ziegler-Natta catalyst
*NOt an Example the ided purposesof
of present for
invention;
prov
comparison
only.
In another evaluation, various sealant layer materials
were coextruded with PP homopolymer, Shell KF 6100, on
conventional cast film equipment and were evaluated for the
heat seal and hot tack performance.
The cast coextrusion line was equipped with a 76 cm
Johnson flex-lip cast film die. The overall film thickness
of each coextruded film sample was 3.0 mils (76.2 microns).
The two-layer coextruded film structures consisted of l00
sealant and 90o PP homopolymer, Shell KF 6100. The films
were fabricated using a target line speed of 55 mlmin, a
target polypropylene homopolymer melt temperature of about
277°C, a target sealant melt temperature of 265°C and an air
gap of 12.7 centimeters.
The polymer composition of comparative example 9 was
AFFINITYTM PL 1845 supplied by The Dow Chemical Company (the
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CA 02271482 1999-OS-12
WO 98/21274 PCT/US97/20574
same as for Comparative Example 4 above). AFFINITYTM PL 1845
is a single polymer component substantially linear ethylene
polymer. The polymer compositions of Examples 11 and 12 as
well as comparative examples 10 and 13 were manufactured
using two reactors in accordance with the in situ
polymerization procedure described above as for Example 1.
The melt index of the first ethylene polymer component (A)
was determined by the GPC deconvolution routine as described
above and the density and weight percent of the first
ethylene polymer component (A) were determined by the ATREF
technique also as described above as to Example 1'.
In this evaluation, none of the samples showed any sign
of delamination of the sealant from the polypropylene layer
during coextrusion or during heat sealing operations and seal
testing.
In this evaluation, the heat seal initiation temperature
was defined as the minimum temperature at which a 1 lb./in (2
N/15 mm) seal strength was obtained. Heat seal testing was
performed on a Topwave Hot Tack Tester using a 0.5 second
dwell time with a 40 psi (0.275 MPa) seal bar pressure. The
seals are made at 5°C increments by folding the sealant layer
over and sealing it to itself. The so-formed seals are
pulled at least 24 hours after they were made using an
Instron tensiometer at a 10 in/min. (250 mm/min.) crosshead
rate .
Also in this evaluation, ultimate hot tack was defined
as the maximum hot tack strength achieved within the normal
range tested, i.e. 60-120°C. Hot tack testing was also
performed using the Topwave Hot Tack Tester set at a 0.5
second dwell, 0.2 second delay time, and 40 psi (0.275 MPa)
seal bar pressure. Hot tack seals were made at 5°C increments
by folding the sealant layer over and hot tack sealing it to
itself. The peel rate applied to the so-formed hot tack
seals was of 150 mm/sec. The tester was programmed to pull
the seals immediately after the 0.2 second delay.
-53-

CA 02271482 1999-OS-12
WO 98/21274 PCT/US97/20574
Table 2 summarizes the heat seal and hot tack data
obtained for the 3.0 mil (0.08-mm) cast film coextrusions:
Table 2
Example Heat UltimateOverallOverallFirst First First ~ First
Seal
InitiationHot MI densityethyleneethyleneethyleneethylene
Tack
T emp. Strengthdg/ dg/minpolymer polymerpolymer polymer
min
( C) lbs./in. componentcomponentcomponentcomponent
MI M" Density Fraction
(dg/min)(g/mole)(dg/ (dg/10
min) min)
Comparative88 5.6 3.5 0.910 3.5 29313 0.910 1D0
Example
9
Comparative96 6.4 3.1 0.919 0.68 96605 0.901 93.5
Example _
IO -
Example 93 7.0 2.8 0.917 0.39 55305 0.900 41.0
11 -
Example 97 7.9 2.7 0.919 0.28 62905 0.900 91.0
12
Comparative96 6.2 3.5 0.917 0.14 67159 0.891 38.4
Example
13
The data in Table 2 (and as shown in FIG. 3) indicate
that there is an optimum first ethylene polymer component (A)
molecular weight or melt index for achieving the highest hot
tack strength at a constant overall melt index. From these
data, a first ethylene polymer component (A) with an I2 melt
index .in the range of from greater than 0.14 g/10 minutes to
less than 0.68 g/10 minutes provides optimized hot tack
strength. Comparative examples 10 and 13 exhibited
insufficient hot tack strength for successful use as a
sealant layer for cast BOPP film as well as for vertical form
fill and seal (VFFS) applications, such as snack food
packaging and cereal packaging applications.
In an evaluation to investigate various sealant .
materials, melt blends of compositions made of a
substantially linear ethylene interpolymer manufactured using
a constrained geometry catalyst system and a heterogeneously
branched ethylene interpolymer manufactured using a Ziegler-
Natta catalyst system were prepared. The melt blends
included Examples 14, 15, 17, 18, 20 and 21 and 'comparative
examples 16, 19 and 22-25. The melt blends were prepared by
weighing the appropriate amount of each component polymer and
-59-

CA 02271482 1999-OS-12
WO 98I21274 PCT/US97/20574
tumble blending the mixture and thereafter melt extruding the
mixture using a conventional single-screw compounding
extruder at about a 350°F (177°C) melt temperature.
Comparative examples 26 and 27 were prepared by in situ
polymerization using methods and procedures such those
described in PCT Patent Application No. 94/01052.
The heat seal initiation temperature of the Examples
were determined by measuring sealant layer performance on
extrusion laminated structures consisting of 0.5 mil PET/1
mil LDPE 5004/2 mil sealant layer (Examples 14, 15, 17, 18,
and 21 and comparative examples 16, 19 and 22-27) or on a
three-layer coextruded blown film structure consisting of 1
mil (0..025 mm) Nylon 6/1 mil (0.025 mm) PRIMACOR l410/1.5 mil
(0.038 mm) sealant layer (comparative example 28). The heat
15 seal initiation temperature was defined as the minimum
temperature at which a 1 lb./in (2 N/15 mm) seal strength was
obtained. Heat seal testing was performed on a Topwave Hot
Tack Tester using a 0.5 second dwell time with a 40 psi
(0.275 MPa) seal bar pressure. The seals are made at 5°C
20 increments by folding the sealant layer over and sealing it
to itself. The so-formed seals are pulled at least 24 hours
after they were made using an Instron tensiometer at a 10
in/min. (250 mm/min) crosshead rate. The Examples listed
below in Table 3 were evaluated as sealant layers in-the
investigation. The Nylon 6 was supplied by Allied-Signal
Company. The polyester film, HOSTAPHAN 2DEF, is supplied by
American Hoechst Corporation. The PRIMACOR 1410 adhesive
polymer and the LDPE 5004 resin are supplied by The Dow
Chemical Company.
The coextruded film was fabricated on a Gloucester blown
film unit equipped with three extruders having diameters of
2, 2.5 and 2.5 inch (5.1, 6.4 and 6.4 cm). The die was an 8
inch (20.3 cm) coextrusion die set with a 70 mil (1.8 mm) die
gap. A blow-up ratio of 2:1 was maintained for a11
coextrusions. The specific output rate was 6 lbs./hr/inch
-55-

CA 02271482 1999-OS-12
WO 98/21274 PCT/US97/20574
(6.9 kg/hr/cm) of die and the melt temperature was between
400° and 420°F (204 and 216°C) .
The extrusion laminated structures were fabricated using
a Black-Clawson extrusion coating unit equipped with a 2.5
inch (6.4 cm), 30:1 L/D extruder. The extrusion lamination
was conducted at a melt temperature of about 550°-600°F
(288°-
316°C) and a coating rate of approximately 440 feet per
minute (134 m/min.). To effectuate the extrusion lamination,
the LDPE 5004 resin was extrusion coated onto 0.5 mil (0.013
mm) of the polyester film and a 2-mil (0.051-mm) monolayer
blown film of the sealant material was slip-sheeted onto the
LDPE 5004 resin at the extrusion nip roller. The laminated
structure was cooled by the chill roll and collected for
subsequent determination of its heat seal initiation
temperature.
The 2o machine direction (MD) modulus for the Examples
was measured on 2 mil (0.051 mm) monolayer blown film. The
monolayer films for physical testing (as well as the 2 mil
(0.051 mm) monolayer blown films used as the slip-sheeted
sealant materials in the extrusion lamination described
above) were fabricated on a Gloucester blown film unit
equipped with a 2.5 inch (6.4 cm) diameter, 24:1 L/D extruder
using a single flight, double mix polyethylene screw, a 6
inch (15.2 cm) die set to a 70 mil (1.8 mm) die gap. A blow-
up ratio of 2.5:1 was maintained for a11 examples to
fabricate the 2 mil (0.051 mm) film and the melt temperature
was set at 450°F (232°C) for a specific output rate of 6
lbs./hr/inch (6.9 kg/hr/cm) of die. Table 3 below provides
the performance data of the various Example compositions as
well as performance data for DOWLEX LLDPE resin 2045
(comparative example 28), DOWLEX LLDPE resin 2049
(comparative example 29), and DOWLEX LLDPE resin 2038
(comparative example 30). All DOWLEX resins are
heterogeneously branched ethylene interpolymers supplied by
The Dow Chemical Company.
-56-

_5 j_
Table 3
~o
_. _
00
.
wa
Example 14 i 15 16* 17 18 19* 20 21 22* 23* 24* 25* 26*
27* 28* 29* 30*
- t
......;........................................................t...............
..........................................s...................t................
.........................................................................-.
..........................................................~....................
..................................-...
Flra t s ....
..................
SLEP = SLEPSLED SLEP SLEP SLED SLEP SLED SLEP SLEP SLED i

Component (A) SLED SLEP
SLEP None None None
Polymer . Type.. ... .

..........................:...................;.................
.;...................~...................;..................-
;................; ; ; ;
.. . . ......... ...;................. . ;
.....
.......... ...;..... . ;

. ....
. .
........ .
.... ................... . ..
..........................................
First ... ..
'................................
. ............
.. ..................
..
.
Component (A) 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.3 1).19 ,6 N/N 0.3
0.5 N/A N/t~ ; N/l1
Ii melt index,
g/10 min.

... .......-
...............................................:...................:..
........ .:...................;. -;-.. .: : t :

.............. ................. .............

;. .. . ........
. . .
.. .
.
. . ...... .. . .. .................... ..
...;.......................................
F rat . .... ... ....:..
....................................................................
... ... ..
.. .
... .
..
.
Component (A 0.885 0.885 0.885i 0.8700.870 0.8700.920 0.8950.8965'
0.918 .,' N/A i N/A y
~ 0.885 0.885 i 0.890 0.887 N/A

j
Density, g/cc

~ ~
.......................................................-
.........................~.....................................................
.......................
...............................................................................
.................................... ... .. o
Second .......'...........................
= .
.....................................................N
;
1 Component Z/N Z/N Z/N Z/N Z/N Z/N Z/N Z/N ?Z/N Z/N Z/N Z/N 'Z/N
ZIN Z/N Z/N 2/N
(8)

Polymer Type i
'
i
V

..........._............................. - . . . ..
....................' . .................... .-
.......... . .. .. ............. .
...............................................................................
....................................
I Second ' .......... . .... ................ _ ..................
; ~ s ..
. . .. .. .. ; .................
...
. ...... . .........

. .. .

.. .
_ .... .
.. s
...
..
Component (8) 1.0 ' 1.0 1.0 1.0 S ; 9.0 4.0 0.9 N/D ; 1.6
0.05 1.0 2.0 = 1.0
1.0 1.0 1.0 ' 1.0

Iz melt index,: s

g/10 min. s ~ ;

: :
L
....._......................................................
......................................................
................................ .................. ... .................
. ..
Second ................ .-.. ...........
...................... . ...................... ....
...............
... .... . ....................
; ' '_, .......
Component (8) 0.952 0.952 0.9S2~ 0.9520.952 0.952' 0.952 ? 0.9520.957
~ ~ 0.920' 0.935
; 0.952 0.952 ' 0.952 0.994 0.942
0.926
Density, g/cc

...............................................................................
...............................................................................
......................; .;............: : : :
.........................................
.... ................. . :
.... .
.
..
..
:
.... ....-- . . .. ..
Wssight 6 First35 25 i 17 95 55 13.5 25 95 60 21 U ..
........................................................................n~
.. 30 0 i i 0
. 0
..
.
....
35 30
Component (A)

...............................................................................
..............................................................................:
............................,.........;....................................
..................................-. .v
r s s s . . .

s s ..........
.. . ..................
Weight sh _
... . ........................
r ... .........

Second 65 75 83 55 95 86.5 75 55 90 79 70 65 70
70 100 100 100
Component (8) i

; ; ; :

. ..... .. .... . .~.

. ..... :...381. .'. :...i63.';.. . ..Ø 9317..... .....
....,
Ø931.. ....929".Ø:.9.29.3 ..;..o....5.. ..... '.. ....91.....
i...o.....90......0:........Ø920-..:...0,.926...9...0:.'95_
.Compoaition~ :..o. 9 0.993....., . 0.9 . D~.9.Ø9
. .
9 : ~0~.9 ....9...... 65~' 9 : 6 926'.

' . ~0.9
4 ~~0.
162
Density, g/cc i ' '

' ; ; ; j i ; ' ' ' ~
'
; ; L
................................................................
j........................................................................
-..............,.... ..................................... .
.............,......
Seal ..................... 85Ø =
..........................................................................3
.....................................
106.5 i 123.3 i 127.4.................... 120.0 125.0 ~
116.0105.9~ ~ N/D
= 116.8 70.9 i 106.2 120.0 ',s 115.5 N/D

: 66.6 129.5
Initiation ; ;
' s
Temp., C
f 1 3 v
; , ~
...... ... ....... ,.. .....

~9~8~~B25~~~69~~309~~ .. .... ... . .3..... . .. ..... .... .
: ~~ "0
2~~1~~~Secant~: 59~ ?~~ 8 ~~~ " ~ ~3 .. ..... . 1 5 5 )_.
. . ~39 51
~ 221~ ~ ~ 951 38 31 ....2. 59 4 ~ ~~
~~~9 . 790 894
, ~ ~ . ~~71~4 ~ 20 ~ 580 ~~2 ~ 41, 22~ ~
. . 3 69 69, . 5 , . 0 89 . ~ B 368 ,

389 ~28, ( 0 . , , 5, S . ,
3
_
Modnlus, pai
n
SLED denotes y ear
lyst stem.
a substantiall lin ethylene
sy
polymer
manufactured
using
a
constrained
geometry
cata
Z/N denotes ly anched polymer Ziegler-Natta

a heterogeneous br ethylene manufactured catalyst

using system.
a
N/A denotes N/D denotesnot termined.
J
not applicable. de

*Not an Example ent nvention: ided for

of the pres i prov purposes

of comparison
only.
N
J
.P

CA 02271482 1999-OS-12
WO 98/21274 PCT/US97/20574
From the data set forth in Table 3, various plots were
generated. FIG. 4 is a plot of the heat seal initiation
temperature of various inventive and comparative film
examples as a function of weight-percent homogeneously
-5 branched ethylene polymer, Component (C). Surprisingly, FIG.
4 indicates that for the range of about 20 to about 60 weight
percent substantially linear ethylene polymer as the first
ethylene polymer component (C), Examples 14, 15, 17, 18, 20
and 21 exhibit a lower seal initiation temperature than
comparative films examples comprised of a homogeneously
branched ethylene polymer having a density greater than 0.89
glcc. The seal initiation temperature of Examples is
especially lower than comparable comparative examples for
weight percentages greater than or equal to 35 weight
percent, based on the total weight of the two component
composition the film is made from.
Even more surprisingly, FIG. 5 indicates that the seal
initiation temperature of the Examples is substantially lower
than that of comparative examples at equivalent composition
densities. Likewise, FIG. 6 indicates that the Examples
exhibit a lower seal initiation temperature at an equivalent
film modulus relative to comparative film Examples. That is,
while the comparative examples exhibit a relatively high film
modulus and a relatively high seal initiation, the Inventive
Examples have a relatively low seal initiation temperature
for their given film modulus.
Finally, FTG. 7 indicates that although the Inventive
Examples exhibit a relatively low seal initiation temperature
for their given film modulus, their film modulus at a given
composition density is surprisingly higher than that of
single component heterogeneously branched ethylene polymer at
equivalent densities. Hence, collectively, FIG. 4-7 indicate
that the Inventive Examples exhibit seal initiation
temperatures equivalent to lower density ethylene polymers
while maintaining the film modulus of medium to higher
density ethylene polymers. As such, these data demonstrate
-58-

CA 02271482 1999-OS-12
WO 98/21274 PCTlU897/20574
the present invention surprisingly and unexpectedly overcomes
the traditional compromise between heat seal performance and
film stiffness.
-59-

Dessin représentatif
Une figure unique qui représente un dessin illustrant l'invention.
États administratifs

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Description Date
Inactive : CIB de MCD 2006-03-12
Inactive : CIB de MCD 2006-03-12
Demande non rétablie avant l'échéance 2003-11-13
Le délai pour l'annulation est expiré 2003-11-13
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Réputée abandonnée - omission de répondre à un avis sur les taxes pour le maintien en état 2002-11-13
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Inactive : Lettre de courtoisie - Preuve 1999-11-23
Lettre envoyée 1999-10-29
Exigences pour une requête d'examen - jugée conforme 1999-09-30
Toutes les exigences pour l'examen - jugée conforme 1999-09-30
Requête d'examen reçue 1999-09-30
Inactive : Transfert individuel 1999-09-13
Inactive : Page couverture publiée 1999-08-04
Inactive : CIB attribuée 1999-06-30
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Inactive : CIB en 1re position 1999-06-30
Inactive : Lettre de courtoisie - Preuve 1999-06-15
Inactive : Notice - Entrée phase nat. - Pas de RE 1999-06-11
Demande reçue - PCT 1999-06-09
Demande publiée (accessible au public) 1998-05-22

Historique d'abandonnement

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2002-11-13

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Historique des taxes

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Enregistrement d'un document 1999-09-13
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Titulaires au dossier

Les titulaires actuels et antérieures au dossier sont affichés en ordre alphabétique.

Titulaires actuels au dossier
THE DOW CHEMICAL COMPANY
Titulaires antérieures au dossier
JACQUELYN A. DEGROOT
JOZEF J. VAN DUN
LAWRENCE T. KALE
LUC BOSIERS
PAK-WING STEVE CHUM
STACI A. DEKUNDER
THOMAS T. OSWALD
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Document 
Date
(yyyy-mm-dd) 
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Dessin représentatif 1999-08-03 1 4
Description 1999-05-11 59 2 832
Abrégé 1999-05-11 1 75
Revendications 1999-05-11 9 318
Dessins 1999-05-11 4 70
Page couverture 1999-08-03 2 84
Rappel de taxe de maintien due 1999-07-13 1 112
Avis d'entree dans la phase nationale 1999-06-10 1 194
Accusé de réception de la requête d'examen 1999-10-28 1 179
Courtoisie - Certificat d'enregistrement (document(s) connexe(s)) 2000-01-20 1 115
Courtoisie - Certificat d'enregistrement (document(s) connexe(s)) 2000-01-20 1 115
Courtoisie - Certificat d'enregistrement (document(s) connexe(s)) 2000-01-20 1 115
Courtoisie - Certificat d'enregistrement (document(s) connexe(s)) 2000-01-20 1 115
Courtoisie - Certificat d'enregistrement (document(s) connexe(s)) 2000-01-20 1 115
Courtoisie - Lettre d'abandon (taxe de maintien en état) 2002-12-10 1 176
Courtoisie - Lettre d'abandon (R30(2)) 2003-01-22 1 167
PCT 1999-05-11 8 278
Correspondance 1999-06-14 1 32