Note: Descriptions are shown in the official language in which they were submitted.
. WO 93/03093 PCI /US92/0~924
21 1 3627
~ .
TITLE ~ AT 8EA~ED ARTICLE:
:
:~ This application is a Continuation-In-Part
application of U.S. Application Serial No. 252,094
filed September 30, 1988 and U.S. Application Serial
No. 732,865 filed 3uly 18, 1991.
:
FIE~D OF q!~E IN~:NTION
~: 25
The present invention relates to a heat
sealed article in which the heat sealed portion of
the article is formed from interpolymers or blends
thereof. In particular, the invention relates to
the interpolymer compositions and interpolymer blend
compositions where the interpolymers have a narrow
composition distribution and a narrow molecular
weight distribution. The interpolyme.s and
especially the blends of the interpol~ers exhibit
excel~ent heat sealing and other physical
properties. The interpolymers and the blends
thereof may be used to make films, bags, pouches,
Wo93/030s3 PCT~US92/059~
~113~27 - 2 -
tubs, trays, lids, packages, containers and any
article employing a heat seal.
BAC~GRO~ND OF THæ IN~ENTION
Many articles of manufacture employing heat
s seals are currently available in the marketplace.
Generally, the seals on suoh articles may be
employed by welding two separate portions of the
article together. For example, plastic parts
usefully employed in machines and toys may be
constructed by joining together two individual
plastic pieces by heating one or both of the plastic
pieces, pressing them together, and then, allowing
them to cool. Specifically, heat sealing is very
important in packaging applications. Packages
formed by a heat seal provide for the efficient
transportation of a consumer item within the
package, provide a display of the consumer item that
.
promotes sales, and, in the food industry, the
packaging is employed to preserve the freshness of
the consumer item.
Various types of polymers are used to form
articles, which include packages, that may be joined
~ together or sealed by the application of heat and/or
; ~ pressure. Polymers or blends of polymers used to
make the articles are selected for use because they
provide a strong seal, which is easily and rapidly
formed by a single short application of heat and/or
pressure. Occasionally, the entire heat sealed
article is constructed from the same poiymer or a
blend of polymers. More often, the article is
constructed of various areas or layers of different
materials, and polymers which provide good heat
sealing properties axe utilized only in areas, or
. layers, where heat sealing will ultimately be
necessary. This type of construction is employed
because the articles, for instance multilayer films,
should have desirable physical and mechanical
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I Wos3/030s3 PCT~US92/05924
2l~ 3~2r7
- 3 -
properties such as clarity, strength, resistance to
puncture and tearing, in addition to heat sealing
properties, and should be easily processed by high
speed equipment. Many plastic materials are known
to possess good physical and mechanical properties
but often do not also possess good heat sealing
properties. ~or example, polypropylene has good
strength and clarity and is resistant to tearing,
but does not readily form good seals at the
~; 10 temperatures which are preferred in commercial
sea}ing machinery. Conversely, some polymers with
good heat sealing properties do not have adequate
strength or c}arity.
The packaging art has therefore developed
multiple layer articles such as multilayer films
incorporating one or more layers of the same or
different types of polymers that provide good
mechanical and physical properties and providing one
or more additional layers formed from polymers that
~ 20 provide the article of manufacture with good heat
-; ; sealing properties. In this way, a film may be
produced having a substrate layer of polypropylene
provided for strength and clarity, and a layer of
polyethylene to provide good heat sealing
~ 25 properties. Other articles, in addition to films,
-~ may be similarly constructed with a plurality of
materials, each material selected to contribute to
one or more of the desired properties of the final
article.
Various types of polyethylene polymers are
known in the art as having acceptable heat sealing
properties. Low density polyethylene ("LDPE") is
generally prepared at high pressure using free
radical initiators and typically has a density in
the range of 0.915-0.940 g/cm3. LDPE is also known
as "branched" polyethylene because of the relatively
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~ W093/03093 PCT/US92/059~
i
- 2
large number of long chain branches extending from
the main polymer backbone.
High density polyethylene ("HDPE") usually
has a density in the range of greater than 0.940 to
0.960 g/cm3. HDPE is prepared using a coordination
catalyst, e~g., Ziegler-Natta type catalysts, at low
or moderate pressures, but sometimes at high
~7 pressure. HDPE is generally linear without any
substantial side chain branching. HDPE is a
substantially crystalline polymer.
Linear low density polyethylene ("LLDPE")
is generally prepared in the same manner as HDPE,
but incorporates a relatively minor amount of an ~-
olefin comonomer such as butene, hexene or octene to
introduce enough short chain branches into the
otherwise linear polymer to reduce the density of
the resultant polymer into the range of that of
LDPE. The coordination catalysts used to
interpolymerize ethylene and the ~-olefins generally
produce a LLDPE with a broad composition
distribution, as hereinafter defined, and a
~ relatively broad molecular weight distribution,
7~ i.e., Mw~Mn greater than about 3, wherein Mw is the
weight average molecular weight and Mn is the number
average molecular weight.
Commercial polymerization processes produce
great numbers of polymer molecules simultaneously.
The polymer molecules produced will not all have
exactly the same molecular weight. Furthermore,
~, 30 when a comonomer is present, the resulting polymer
molecules will not all have exactly the same amount
of ~omonomer. As used herein, the terms "polymer",
"polymers", "interpolymer" and "interpolymers" are
used ~o refer to the group of polymer molecules
produced at substantially the same polymerization
conditions from catalysts having substantially the
same composition and structure. Therefore, one
I Wos3/030s3 PCT/US92/0~924
2113~27
I
- 5 -
polymer differs from another polymer when the
polymers are made from different types of catalysts,
or when the polymers are produced from the same type
of catalyst, but at different polymerization
S conditions. Polymerization conditions include the
temperature and pressure of polymerization as well
as the type and amount of comonomer present, if any,
and the amount of hydrogen present, if any.
It is known in the prior art that
interpolymers have relatively broad composition
distributions. An interpolymer with a relatively
broad composition distribution results because the
number of ~-olefin comonomer molecules incorporated
into each polymer molecule differs. Generally,
relatively low molecular weight polymer molecules
will contain a relatively high proportion of the ~-
.
olefin comonomer, and the high molecular weight
~- po}ymer molecules will contain a relatively low
proportion of a-olefin comonomer. The polymer
molecules of low comonomer content are relatively
more crystalline and have a high melting
temperature, whereas the high comonomer content
~ polymer molecules are more amorphous and melt at a
-~ lower temperature. The presence of a component with
a melting temperature that is too high is
disadvantageous in many applications, for example,
where heat sealing is required. On the other hand,
the presence of too much comonomer in the lower
melting component frequently results in a high
quantity of extractables, low mo~ecular weight
polymers that are soluble in a solvent such as
~- hexane or pentane, and this limits their use in food
contact applications.
In the past, polyethylenes such as LLDPE
also have a broad molecular weight distribution
which can be undesirable in many respects. For
example, LLDPE resins known previously in the art
j. -
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Wog3/030s3 PCT/US92/059
21 1 3~ 2 7 - 6 - ~-
contain relatively high molecular weight mblecules
that are subject to an orientation, which results in
anisotropic properties in the machine direction
compared to the transverse direction of a
fabrication process. The higher molecular weight
molecules having low comonomer content also have
less desirable heat sealing properties. On the
other hand, resins containing relatively lower
~ molecular weight molecules, in which the comonomer
i~ 10 is invariably concentrated, have better heat sealing
properties but tend to exhibit high block and
tackiness properties. These lower molecular weight,
highly branched molecules also interfere with the
proper function of certain additives compounded in
the resin, increase the percentage of extractable
polymer, and increase fouling in the polymerization
plant. The relatively high ~-olefin comonomer
content of these low molecular weight polymer
molecules causes such polymer molecules to be
generally amorphous and to exude to the surface of
fabricated parts, thereby producing an undesirable
` sticky surface.
Previously known blends of polyethylenes
designed to improve one or more of the properties of
the blend relative to its blend components or
relative to polyethylene homopolymers in the past
have also suffered from the drawbacks mentioned
above. For example, incorporating a blend component
with a high average comonomer content to reduce
crystallinity and improve heat sealability generally
results in an increase of extractables and adversely
affects other properties so that the full advantage
of the blend is not realized.
Further, International Application Wo
; 35 90/0314 published April 5, 1990 discloses
interpolymer blends made from components having a
narrow molecular weight distribution and a narrow
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,
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L~
~ Wog3/030s3 PCT/US92/059~
i~ 2113S2~i
- 7 -
composition distribution. It also mentions in
general terms that such blends may have improved
properties such as tear and tensile strength.
However, this publication by no means makes
S available or suggests the surprising and unexpected
- finding that heat sealed articles may be formed from
a select group of ethylene interpolymers and blends
under conditions of temperature and contact pressure
which enable the formation of good seals at
commercially advantageous temperatures and
processing times.
In the past, heretofore this present
invention as discussed above, no way has been found
to achieve the desired uniform distribution of
¢omonomer in polymers giving such polymers and
blends thereof excellent heat sealing properties
while maintaining other desirable physical
properties. Therefore, there is a need for a
polymer or a blend of polymers selected so as to
distribute the comonomer appropriately and uniformly
throughout all of the polymer molecules.
SUMMARY OF THE INVENTION
This invention relates to articles of
manufacture exhibiting improved heat seal properties
formed from interpolymers each having a narrow
molecular weight distribution and a composition
distribution breadth index of at leaæt 50% and
blends of these interpolymers. In particular, the
interpolymers can be ethylene interpolymers or
blends of ethylene interpolymers useful for forming
single or multilayer films used in a variety of
packaging applications. Each individual group of
ethyler.~ interpolymers has a narrow molecular weight
distribution and a narrow composition distribution.
Specifically, the particular ethylene interpolymers
and blends thereof are selected to yield superior
properties in the resulting heat sealable or heat
~7
~;
':~
W093~03093 PCT/US92/0~924
2 1 1 3 ~ 8 - ~
I sealed article of this present invention. Broadly,
¦ the blends used in articles of manufacture of this
invention comprise a plurality of linear ethylene
interpolymer components where each component has a
composition distribution breadth index (CDBI) (later
- described) of 50% or higher. The phrase "narrow
composition distribution" or "narrow CD" is used
~ herein to denote a polymer with a CDBI of 50% or
3 higher. The preferred heat sealable polymer blends
,~ 10 are substantially free of blend components having
~, both a higher average molecular weight and a lower
3 average comonomer content than that of any other
polyethylene component in the blend. Tbe components
for each blend can be selected so that the resultant
blend has plural modality with respect to molecular
weight distribution, comonomer content, or both.
- In another aspect, the components for the
` blend are linear ethylene interpolymers having
narrow molecular weight and narrow composition
distribution mentioned above and the blend
components are selected from one of the following
groups: (1) linear ethylene interpolymer blend
components having substantially the same average
molecular weight but different average comonomer
contents; (2) linear ethylene interpolymer blend
components having substantially the same average
comonomer content but different average molecular
weights; and (3) linear ethylene interpolymer blend
components having different average molecular
weights and comonomer contents in which the blend
components, taken serially in order of increasing
average molecular weight, have an increasing
comonomer content.
In still another aspect, the linear
ethylene interpolymer blend components have the
narrow molecular weight and composition distribution
mentioned above, and when the linear ethylene
,~ .
~ Wos3/03093 PCT/US92/0~9~
1 2 1 1 3 ~ 2 7
;, _ 9 _
interpolymer blend components are taken serially in
order of increasing average molecular weight, each
succeeding component has substantially the same or a
higher average comonomer content than each preceding
component in said series.
- In another aspect, the invention provides a
heat sealable linear ethylene interpolymer blend
having plural modality with respect to comonomer
content, a narrow molecular weight distribution such
that MW/Mn ~ 3 and an overall composition
distribution breadth index less than 50%.
In still another aspect, the invention
provides a linear ethylene interpolymer blend having
plural modality with respect to molecular weight.so
that the blend has a broad overall molecular weight
distribution such that MW/Mn ~ 3 and a CDBI > 50%.
In still another aspect, the invention
provides a blend of linear ethylene interpolymers of
: plural modality with respect to both comonomer
content and molecular weight, comprising a plurality
of components having a narrow molecular weight
distribution such that MW/Mn ~ 3 for each component,
and each component taken serially in order of
increasing average molecular weight, has an
2S increasing average comonomer content.
In a still further aspect of the invention,
there is provided a linear ethylene interpolymer
blend of plural modality with respect to both
comonomer content and molecular weight which
comprises a plurality of components having a
composition distribution breadth index of 50% or
more, wherein the components taken serially in order
of increasing comonomer content, have an increasing
. average molecular weight.
~ 35 The heat sealed article of this invention
~ may be formed by pressing at least two portions of
~ - the article together at a temperature sufficient to
. ~ ~
~ W093~03093 P~T/US92/059~
2113~27 lo-
3 soften at least one of the article portions. The
article portion which has been softened by heat is
formed from ethylene interpolymers having a CDBI of
at least 50% or from a polymer blend comprising a
plurality of the ethylene interpolymers as blend
components. Although it is sufficient if only one
of the article portions being heated and pressed to
form a heat seal is formed from the ethylene
interpolymers or blends of the ethylene
interpolymers, it is preferable for all article
portions directly involved in the heat seal to be
formed from the ethylene interpolymers or blends
thereof.
The heat sealed article so formed may, in
lS one aspect, be a sealed container comprising a body
and a sealing member secured thereto, wherein the
sealing member comprises a seal layer comprising one
of the group of ethylene interpolymers having a
narrow composition distribution and a blend of a
plurality of said ethylene interpolymers as blend
components.
~ -:
A heat sealable article in accordance with
the invention, is, in one aspect, a film comprising
eth~lene interpolymers having a CDBI of at least 50%
and a narrow molecular weight distribution or a
poly~er blend comprising a plurality of said
ethylene interpolymers as blend components.
The invention also includes the
interpolymers and interpolymer blends having heat
sealing properties for use in heat sealing
applications comprising:
- a plurality of linear ethylene interpolymer
blend component~, each component having a narrow
molec~lar weight distribution such that MW/Mn is
less than or equal to 2.5 and a composition
distribution breadth index of 50% or greater. The
blend components are selected from one of the groups
, .
~ W093/03093 PCT/US92/059~
2113~
. - 11 -
consisting essentially of blend components having
essentîally:
(1) the same average molecular weight but
different average comonomer content,
or,
(2) the same average comonomer content ~ut
different average molecular weights,
or,
; (3) different average molecular weights
and comonomer contents wherein said
components, taken serially in order
of increasing average molecular
weight have an increasing comonomer
content, or,
(4) a combination thereof;
wherein the density of the interpolymer blend is
from about 0.875 to 0.94 g/cm3.
BRI15F DE~CRIPq!ION OF TI~B ~AWING8
The foregoing aspects, features, and
; 20 advantages of the invention will become clearer and
more fully understood when the following detailed
description is read in conjunction with the
accompanying drawings, in which:
Fig. 1 is a schematic illustration of
different blends made from poly(ethylene-co-~-
olefin) blend components having narrow molecular
:
weight and composition distributions.
Fig. 2 illustrates the broad molecular
weight distribution and broad composition
distribution of a typical prior art llnPE.
Fig. 3 illustrates the narrow molecular
~ weight distribution and narrow composition
; distribution of an exemplary blend component used in
!~ the present invention.
3S Fig. 4 illustrates the molecular weight
distribution and composition distribution of an
exemplary LLDPE blend according to an embodiment of
~3
t~ Wos3Jo30s3 PCT/US92/059~
21~3.~27 - 12 -
the invention in which the blend components have
about the same molecular weight but differing
comonomer contents.
Fig. 5 illustrates the molecular weight
distribution and composition distribution of an
exemplary LLDPE blend according to another
embodiment of the invention in which the blend
components have about the same comonomer content but
differing molecular weights.
Fig. 6 illustrates the molecular weight
distribution and composition distribution of an
exemplary LLDPE blend according to yet another
embodiment of the invention in which the comonomer
contents of the blend components increases as the
molecular weight increases.
Fig. 7 is a graph of the relationship
between`seal strength and sealing temperature for
films made from prior art polymers.
Fiq. 8 is a graph of the relationship
-~ ~ 20 between seal strength and sealing temperature for
films made according to the invention.
Fig. 9 is a graph of the relationship
between seal strength and sealing temperature for
films made according to the invention.
Fig. 10 is a graph of the relationship
between seal strength and sealing temperature for
films made according to the invention.
Fig. ll is a graph of the relationship
between seal strength and sealing temperature for
films made according to the invention.
Fig. 12 is a graph of the relationship
- between seal strength and sealing temperature for
films according to the invention compared to a prior
art po~yethylene.
Fig. 13 is a cross-sectional view of a
sealed container accordin~ to the invention.
W093/03093 2 1 1 ~ ~ 2 ~ PCT/USg2/05924
- 13 -
Fig. 14 is a cross-sectional view of a
film, or lid or sealing member according to the
invention.
Fig. 15 is a graph of the solubility
distribution and composition distribution of a
copolymer (X) having a narrow SDBI and CDBI and
copolymer (Y) having a broad SDBI and CDBI.
Fig. 16 is a graph illustrating the
correlation between dissolution temperature and
composition used to convert the temperature scale to
a composition scale.
Fig. 17 is a graph illustrating the method
for calculating CDBI.
DETATLE:D DE~CRIPTION OF q~l~ INVE:NTION
The linear ethylene interpolymers of the
present invention may be homopolymers of ethylene or
higher interpolymers of a major proportion of
::
~; ethylene and a minor proportion of comonomer. If a
comonomer is used, the ethylene is generally
polymerized in a proportion of 70-99.99, typically
70-97, and often 70-80, 80-90, 83-99.99 or 90-95,
mole percent of the interpolymerized monomers with
0.01-30, typically 3-30, and often 20-30, 10-20,
0.01-17 or 5-10, mole percent comonomer.
Contemplated blend components may have a density in
the range of 0.85 to 0.96 g/cm3 and qenerally
include elastomer blend components in the density
range of about 0.875-0.900 g/cm3, very low density
polyethylene blend components in the density range
of about 0.900-0.915 g/cm3, and linear, low density
polyethylene blend components in the density range
of about 0.915-0.940 g/cm3. Ethylene interpolymers
having a density in the high density polyethylene
range above about 0.940 g/cm3 are also contemplated
as being suitably employed in the inven~ion.
Suitable comonomers interpolymerized with
the ethylene to obtain the ethylene interpolymer
:
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Wos3/03093 PCT/US92/059~
2113~7 14 -
herein generally include monomers which may be
- copolymerized with ethylene to obtain the comonomer
distribution desired in the blend component. A
preferred class of comonomers are thè ~-olefins
having 3 to about 12 carbon atoms, such as
propylene, l-butene, 1-pentene, l-hexene, 3-methyl-
l-pentene, 4-methyl-l-pentene, l-octene, l-decene,
dodecane and the like. Other suitable comonomers
include vinyl cyclohexane, norbornene, vinyl
cyclohexene, and other diene comonomers such as 1,3-
butadiene, 1,4-hexadiene, 4-methyl-1,4-hexadiene, 5-
methyl-1,4-hexadiene, l,5-hexadiene and the like.
The ethylene interpolymer may include one or more of
such comonomers, i.e. it may be copolymer,
terpolymer, etc.
The molecular weight of the ethylene
interpolymers may range from one thousand to one
million or more depending on the particular end use,
preferably 104-106, and especially 2 X 104 -
5 X 105. As used herein, the terms "average
molecular weight" and Hmolecular weight" refer to
i~ ~ weight average molecular weight unless otherwise
indicated. The molecular weight of resulting
polymers may be varied by adjusting the amount of
hydrogen gas that i8 added to the polymerization
reaction. Generally, a higher molecular weight
polymer reæults when the hydrogen concentration is
lower, and lower molecular weight polymer is
produced when the hydrogen concentration is higher.
; 30 Therefore, by selecting the proper amount of
hydrogen, one can produce polymer of desired
molecular weight.
The ethylene interpolymers preferably have
a composition distribution ("CD") such that the
composition distribution breadth index (nCDBIn) is
at least 50%, more preferably at least 60% and most
preferably at least 70%. The CDBI is defined as the
~ W093/0~93 PCT/US92/0~9~
;l 2113`~2~
~, .
- 15 -
weight percent of the ethylene interpolymer
molecules having a comonomer content within 50
percent of the median total molar comonomer content.
For instance if the median total molar comonomer
content of a certain group of ethylene interpolymers
found to be 4 mole percent, the CDBI of that
group of interpolymers would be the weight percent
of ethylene interpolymers having a molar comonomer
concentration from 2 to 6 mole percent. If 55 wt%
of the ethylene interpolymers had a molar comonomer
content in the 2 to 6 mole percent range, the CDBI
would be 55%. The CDBI of linear homopolymer
polyethylene, which does not contain a comonomer, is
defined to be 100%. The CDBI of a copolymer is
readily c lculated by data obtained from techniques
known in the art, such as, for example, temperature
rising elution fractionation as described, for
example, in U.S. Patent 5,008,204 or in Wild et al.,
,
. Polv. ~Çi, Poly. phys. Ed., vol. 20, p. 441
(1982), both of which are hereby fully incorporated
herein by reference.
Solubility Distribution is measured using a
column of length 164 cm and 1.8 cm ID (inner
diameter) is packed with non-porous glass beads (20-
30 mesh) and immersed in a temperature programmableoil bath. The bath is stirred very vigorously to
minimize temperature gradients within the bath, and
the bath temperature is measured using a platinum
resistance thermometer. About 1.6 g of polymer is
placed in a sample preparation chamber and
repeatedly evacuated and filled with nitrogen to
remove oxygen from the system. A metered volume of
tetrachlorethylene solvent is then pumped into the
sample preparation chamber, where it is stirred and
heated under 3 atmospheres pressure at 140-C to
obtain a polymer solution of about 1 percent
concentration. A metered volume of this solution,
WO 93/03093 PCI-/US92/05924
'
2113~27 - 16 -
100 cc is then pumped into the packed column
thermostated at a high temperature, 120-C.
The polymer solution in the column is
subsequently crystallized by cooling the column ~o
oC at a cooling rate of ~20 C/min. The column
temperature is then maintained at this temperature
for 25 min. at O C. The elution stage is then begun
by pumping pure solvent, preheated to the
temperature of the oil bath, through the column at a
flow rate of 27 cc/min. Effluent from the column
passes through a heated line to an IR detector which
is used to measure the absorbance of the effluent
stream. The absorbance of the polymer carbon-
hydrogen stretching bands at about 2960 cm 1 serves
as a continuous measure of the relative weight
percent concentration of polymer in the effluent.
After passing through the infrared detector the
;~ temperature of the effluent is reduced to about
llO-C, and the pressure is reduced to atmospheric
pressure before passing the effluent stream into an
automatic fraction collector. Fractions are
collected in 3~C intervals. In the elution stage
pure tetrachloroethylene solvent is pumped through
the column at O-C at 27 cc/min for 25 min. This
2S flushes polymer that has not crystallized during the
cool-ing stage out of the column so that the percent
of uncrystallized polymer (i.e. the percent of
polymer soluble at O'C) can be determined from the
infrared trace. The temperature is then programmed
upward at a rate of l.O-C/min. to 120-C. A
solubility distribution curve, i.e. a plot of weight
- fraction of polymer solubilized as a f~nction of
temperature, is thus obtained.
' The procedure for calculatin~ the
Solubility Distribution Breadth Index (SDBI) is set
forth below.
W093/03093 PCT/US92/059
211.3627
` - 17 -
Solubility distributions of two ethylene
interpolymers are shown in Figure 15. Here, for
illustration purposes only, Sample X has a narrow
solubility distribution and elutes over a narrow
temperature range compared to Sample Y, which has a
- broad solubility distribution. A solubility
distribution breadth index (SDBI) is used as a
measure of the breadth of the solubility
distribution curve. Let w(T) be the weight fraction
of polymer eluting (dissolving) at temperature T.
The average dissolution temperature, T ave, is given
by
: /
Tave = ~ T w(T)dT, where ~ w(T)dT = 1.
SDBI is calculated using the relation:
SDBI(-C) = 4 ~(T - Tav~)4w(T)dT.
(SDBI is thus analogous to the standard
deviation of the solubility distribution curve, but
; it involves the fourth power rather than the second
power to T - TaVe)~ Thus, for example, the narrow
solubillty distribution Sample X and the broad
solubility diætribution Sample Y in Figure 15 have
~ SDBI values equal to 14.6 and 29.4-C, respectively.
- The preferred values of SDBI are less than
28-C and more preferred less than 25-C and evern
more preferred less than 20-C.
The composition distribution (CD) of a
crystalline interpolymer is determined as follows.
~ The composition and number average molecular weight,
- Mn~ of fractions collected in various narrow
temperature intervals for several poly(ethylene-co-
butene)'s was determined by C13 NNR and size
; exclusion chromatography, respectively. Figure 16
i8 a plot of mole percent comonomer vs. elution
:
7 W093/03093 PCTIUS92/059~
2 1 1 3 ~ 2 1 - 18 -
temperature for fractions having Mn ~ 15,000. The
curve drawn through the data points i8 used to
correlate composition with elution temperature for
temperatures greater than O C. The correlation
between elution temperature and composition becomes
less accurate as the Mn f a fraction decreases
below 15,000. Such errors can be eliminated by
direct measurement of the composition of effluent
fractions by C13 NMR. Alternatively, the elution
temperature-composition calibration for high
molecular weight fractions given in Figure 16 may be
corrected based on the Mn f effluent fractions and
an experimentally established correlation between Mn
and elution temperature that applies for Mn <
15,000. However, it is assumed that such low
molecular weight molecules are present to a
negligible extent and that any errors caused are
negligible. A correlation curve such as the one in
Figure 16 is applicable to any essentially random
poly(ethylene-co-~-olefin) provided, however, that
the a-olefin is not propylene.
The temperature scale of a solubility
distribution plot can thus be transformed to a
composition scale, yielding a weight fraction of
polymer vs. composition curve. As seen from the
composition scale in Figure 16, Sample X contains
molecules spanning a narrow composition range,
whereas Sample Y contains molecules spanning a wide
composition range. Thus, Sample X has a narrow
composition distribution whereas Sample Y has a
broad composition distribution.
A guantitative measure of the breadth of
the composition distribution is provided by the
Compogition Distribution Breadth Index (CDBI). CDBI
is defined to be the percent of polymer whose
composition is within 50% of the median comonomer
composition. ~t is calculated from the composition
~ W093/0~93 2 1 1 3 ~ 2 1 PCT/US92/059~
i~i 1 9
distribution cure and the normalized cumulative
integral of the composition distribution curve, as
illustrated in Figure 17. The median composition,
} Cmed, corresponds to the composition at the poin~
where the cumulative integral equals 0.5. The
difference between the values of the cumulative
integral at compositions 0.~ Cmed and 1.5 Cmed (71 -
29, or 42%, in this example~ is the CDBI of the
copolymer . CDBI values fall between zero and one,
with large values indicating narrow CD and low
values indicating broad CD. Thus, now referring
bac~ to Figure 15, the narrow and broad CD
copolymers have CDBI's equal to 95.5% and 42%,
respectively. It is difficult to measure the CD and
CDBI of copolymers having very low comonomer content
with high accuracy so the CDBI of polyethylenes with
densities greater than 0.94 g/cc is defined to be
equal to 100%. Unless otherwise indicated, terms
such as "comonomer content", "average comonomer
content~ and the like refer to the bulk comonomer
content of the indicated ethylene interpolymer on a
molar basis.
The ethylene interpolymers of this present
invention preferably have a narrow molecular weight
distribution (MWD). The term "narrow MWD" means
~; that the ratio of the weight average molecular
; weigbt (Mw) to the number average molecular weight
- ~ (Mn) is less than or equal to 3Ø Particularly
preferred are the ethylene interpolymers having a
very narrow MWD, i.e. MW/Mn less than or equal to
2.5, and especially about equal to 2. Molecular
- weiqht distributions of ethylene interpolymers are
readily determined by techniques known in the art,
such as, for example, size exclusion chromatography.
A graphical illustration of an exemplary
narrow MWD, narrow CD ethylene interpolymer is seen
in Fig. 3. In this three-dimensional figure, the Y-
,
:
;
~,~
W093/03~3 PCT/US92/059~
2 1 1 3 6 2 7 - 20 -
axis is the molecular weight, the X-axis is the
molar comonomer content, and the Z-axis represents
the incidence or weight proportion of molecules. As
can be seen, the MWD and the CD of the ethylene
S interpolymer are narrow and appear as relatively
- sharp peaks in Fig. 3. In ~ontrast, the MWD/CD
diagram for a typical conventional LLDPE, seen in
Fig. 2, shows a broad MWD and a broad CD, and the
comonomer content tends to decrease as the molecular
weight increases. In each blend of the present
- invention, one or more of the properties of the
blend are improved by appropriate selection and
combination of narrow CD and narrow MWD ethylene
interpolymer blend components. In one embodiment,
for example, tear strength may be controlled by
blending linear polyethylene resins having about the
;~ same average molecular weight but with different
average comonomer contents. Such a blend is
illustrated as line B in Fig. 1. In another
embodiment, the comonomer contents of the linear
polyethylene blend components are the same, but
: :
~-~ molecular weights are varied, as illustrated by
line C in Fig. 1. In still further embodiments
illustrated by lines D, E and F in Fig. 1, the blend
components taken serially in order of increasing
molecular weight, or in order of increasing molar
comonomer content, have the same or higher comonomer
content or molecular weight, respectively.
As used herein, two or more blend
components have substantially the same molecular
weight if the resulting MWD of the blend thereof is
~ siailarly narrow to the MWD of each blend component,
- i.e. the value of MW/Mn f the resulting blend is
less than or equal to about 3.0, preferably less
than about 2.5. Conversely, two or more blend
components have a different average molecular weight
if the overall MW/Mn f the resulting blend is
W093/03~93 2 1 1 3 ~ 2 7 PCT/US9~/059~
- 21 -
relatively greater than for each such blend
component, i.e., the MW/Mn of the blend is greater
than 3Ø
A~ used herein, two or more blend
components have a dif~erent comonomer content if the
overaii CDBI of the resulting blend is relatively
less than that of each such blend component, i.e.,
the overall CDBI of the blend is less than 50%.
Conversely, two or more blend components have
substantially the same molar comonomer content if
the resulting CD of the blend thereof is similarly
narrow with respect to each blend component, i.e.,
the resulting blend has a CDBI of 50~ or greater.
It is rsadily appreciated that the CD and MWD of a
blend can depend on the relative proportions of each
blend component employed therein. It is
specifically contemplated that blend components may
have the "same" molecular weight for purposes of one
- blend, but not for the purpose of another blend,
~ 20 e.g., wherein the components would result in the
- blend having an NWD less than or greater than 3.0
depending on the proportion of each blend component.
Similarly, blend components may have a "different"
comonomer content for purposes of one blend, but not
for the purposes of another blend, e.g., wherein the
components would result in the final blend having
CDBI less than or greater than 50% depending on the
proportion of each blend component.
The molecular weight and composition
distribution of a bimodal blend of the invention is
illustrated graphically in Fig. 4. It is seen from
this MWD/CD diagram that the comonomer content of
each of the blend components is different, while the
molecular weight of each blend component iæ about
the same. The comonomer content of ethylene
interpolymers may be varied by adjusting the amount
of comonomer fed to the polymerization reactor. If
.
~,
,
, .,. . ., . .. , . , . , . . , - ..
i wo93/o3os3 PCT/USg2tOS9
2 11 3 6 27 22
more comonomer is fed to the reactor, more comonomer
will be incorporated in the resulting interpolymer.
The comonomer content of resulting interpolymers may
be measured directly by NMR spectroscopy or
correlated by density. Generally, when more
comonomer is incorporated in the resulting polymer,
the density of the polymer will decrease.
The blend of Fig. 4 corresponds to line B
of Fig. 1. In contrast, a similar graph for typical
conventional LLDPE is seen in Fig. 2, and line A of
Fig. 1. These figures show that the lower molecular
weight fractions contain more of the comonomer than
the higher molecular weight fractions. The lower
molecular weight molecules which contain relatively
high comonomer concentrations as in this
conventional LLDPE can cause undesirable effects
such as poor surface properties, high block and
tackiness, cling development, high levels of
- extractables, and fouling of polymerization plants.
In the present invention, such effects are minimized
and properties are enhanced by providing heat sealed
articles comprising ethylene interpolymers or
comprising ethylene interpolymer blends of the type
illustrated in Curve B, C, D, E, and F.
As an example of the embodiment of Curve B,
it has been found that a 50-50 blend of a first
- LLDPE having a 6.4 moleS l-butene content and a Mw
~;~ of 80,400 (MW/Mn = 2.3; CDBI z67%; MI (melt index)
- 4.0 dg/min; density - 0.9042 g/cm3) with a HDPE
having a 0.0 mole% l-butene content and a ~w f
76,700 (MW/Mn = 2.8; CDBI ~100%; MI - 5.0 dg/min;
density - O.9552 g/cm3) has an Elmendorf tear
strength of 210 g/mil. Surprisingly, this blend is
enhanced in contrast to the tear strengths of 111
and 48 g/mil for the respective first and second
blend components. Further, a 25-75 blend of these
same components has a further enhanced Elmendorf
::
:
~ W093/03093 PCT/US92/059~
3 2113~2~
- 23 -
tear strength of 227 g/mil. This result is quite
surprising and unexpected because including a higher
proportion of the second LLDPE resin with the lower
tear strength in the blend increases the tear
strength of the resulting blend, rather than
~ decreasing the tear strength as would be expected
- from polyethylene produced according to the prior
art.
In another embodiment exemplified in Fig. 5
and line C of Fig. 1, a multimodal MWD is obtained
by blending linear polyethylene components each
having narrow molecular weight and composition
distributions, and about the same comonomer content,
but differing molecular weights. The MWD of such
blends improves the melt processability and
- rheological characteristics thereof, for example,
the blends may be formulated to have high extrusion
; rates, high bubble stability, high shear
sensitivity, and reduced draw resonance. On the
other hand, the optical, mechanical and surface
properties of individual blend components are
~ generally substantially retained or improved in the
-~ blends, for example tear strength, modulus, yield
strength, clarity, gloss, haze, heat sealability,
~- ; 25 hot tack and the like are improved and blocking is
reduced. Moreover, such blends have lower portions
of solvent extractable polymer molecules than prior
art copolymers having similar molecular weight
distribution. Desirable molecular weight and
composition distributions may be obtained by
separately making the appropriate et~ylene
interpolymer components and then blending the
different components together, or by polymerization
of the blend components simultaneously in the same
reactor or in multiple reactors.
.
The higher molecular weight fraction
containing relatively less comonomer in conventional
.
~ W093/03093 PCT~US92/0~9~
2113~27 `
- 24 -
LLDPE may cause an anisotropic morphology durin~
fabrication processing known as "row nucleated" or
"shi~h-ka-bob" morphology. This anisotropic
morphology is believed to contribute to poor
toughness in articles crystallized from flowing
melts. In the present invention, the anisotropy may
be minimized by providing a blend with lower
concentrations of such higher molecular weight
molecules with a relati~ely low comonomer content
and by incorporating the comonomer in the blend
components as indicated in blends B, C, D, E and F.
In another embodiment as exemplified by
Fig. 6 and line D of Fig. 1, the blend includes
components having narrow molecular weight and
composition distributions, but differing average
molecular weights and average comonomer contents.
However, in contrast to conventional LLDPE as
illustrated in line A of Fig. 1 and in Fig. 2, the
blend of this embodiment has a greater comonomer
content in the higher molecular weight fractions or
blend components than in the lower molecular weight
fractions or blend components. These distributions
are obtained, for example, by blending narrow MWD,
narrow CD linear polyethylene resins which, taken
serially in order of increasing molecular weight,
have an increasing comonomer content. It is also
contemplated that the blend may include two or more
blend components having the same molecular weight as
illustrated by line F in Fig. 1, in which case such
components would be included in the serial ordering
secondarily in order of their increasing average
comonomer content. Also, the presence of two or
more blend components having the same comonomer
conte ffl is also contemplated as being within the
purview of this embodiment, as illustrated by line E
in Fig. 1, provided that there is included either at
least one blend component having a higher comonomer
W093/03093 2 1 ~ 3 ~ ~ 7 P~T/US92/059~
- 25 -
content and molecular weight or at least one blend
component having a lower comonomer content and lower
molecular weight than any of the blend components
having the same comonomer content. In this
embodiment, the blend is preferably substantially
free of blend components having both a higher
molecular weight and a lower comonomer content than
any component present in the blend.
Such a blend has heat sealing properties
which are significantly superior to prior art blends
and conventional LLDPE resins in which the comonomer
content generally decreases in proportion to
increasing molecular weight components or fractions.
The isotropy and toughness of films made from such
blends are also improved by minimizing the
anisotropic shish-ka-bob or row-nucleated morphology
ordinarily caused by a low concentration of
comonomers present in the higher molecular weight
molecules of conventional LLDPE resins. Moreover,
such blends have other desirable properties such as,
for example, reduced blocking, reduced coefficients
of friction, and lower extractables, in comparison
to conventional heat sealable LLDPE resins.
Preferred blends according to the invention
generally have a density in the range of 0.88 to
o.94 g/cm3, and a melt index ~MI) (MI by ASTM D-
~ - 1238) in the range of 0.5 to 2Ø Particularly, one
;~ preferred blend may be prepared by combining two
different ethylene interpolymer components. The
first component i8 a high molecular weight ethylene
interpolymer with a density of 0.88 to 0.92 g/cm3
and a MI of 0.05 to 2. The second component is a
low molecular weight ethylene interpolymer with a
density of 0.91 to 0.96 g/cm3 and a MI of 50 to
~, 35 1000. The combination of 50 to 70 wt% of the first
5~ component with 30 to 50 wt~ of the second component
will result in an excellent heat sealing blend.
:
WO 93~03093 PCI'/US92/05924
~ 1 ~ 3 & 2 ~ 2 6
The linear polyethylene blend components of
the invention may be prepared by use of catalyst
sy~tems of the metallocene type known to provide
ethylene interpolymers with both narrow CD and
narrow MWD. Cyclopentadienylide catalyst systems
using a metallocene complex in conjunction with an
alumoxane cocatalyst or reaction product thereof are
suitable for preparing the ethylene interpolymers
utilized individually or as blends in the invention.
The metallocene catalyst may be represented by the
general formula (Cp)mMRnR'p wherein Cp is a,
substituted or unsubstituted cyclopentadienyl ring;
M is a Group IVB, or VB transition metal; R and R'
are independently selected halogen, hydrocarbyl
group, or hydrocarboxyl groups having 1-20 carbon
atoms; m = 1-3, n = 0-3, p - 0-3, and the sum of
m + n ~ p equals the oxidation state of M. Various
forms of the catalyst system of the metallocene type
~ .
may be used for polymerization to prepare the
polymer components of the present invention
including those of the homogeneous or the
heterogeneous, supported catalyst type wherein the
catalyst and alumoxane cocatalyst are together
supported or reacted together onto an inert support
for polymerization by gas-phase, high pressure,
slurry, or solution polymerization.
The cyclopentadienyls of the catalyst may
be unsubstituted or substituted with hydrogen or
hydrocarbyl radicals. The hydrocarbyl radicals may
include alkyl, alkenyl, aryl, alkylaryl, arylalkyl,
and like radicals containing from about 1-20 carbon
atoms or where 2 carbon atoms of cyclopentadienyl
are joined together to form a C4-C6 ring. Exemplary
hydrocarbyl radicals include methyl, ethyl, propyl,
butyl, amyl, isoamyl, hexyl, isobutyl, heptyl,
octyl, nonyl, decyl, cetyl, 2-ethylhexyl, phenyl and
the like. Exemplary halogen substituents include
:
W093/030g3 2 1 ~ 3 ~ 2 7 PCT/US92/059~
- 27 -
chlorine, bromine, fluorine and iodine. Of these
halogen atoms, chlorine is preferred. Exemplary
hydrocarboxy radicals are methoxy, ethoxy, propoxy,
butoxy, amyloxy and the like. Illustrative, but
non-limiting examples of the metallocene catalyst
useful in preparing the polymers of the present
~: invention include bis(cyclopentadienyl)titanium
dimethyl, bis(cyclopentadienyl)titanium diphenyl,
bis(cyclopentadienyl)zirconium dimethyl,
bis(cyclopentadienyl)zirconium diphenyl,
bis(cyclopentadienyl)hafnium dimethyl and diphenyl,
bis(cyclopentadienyl)titanium di-neopentyl,
bis(cyclopentadienyl)zirconium di-neopentyl,
bis(cyclopentadienyl)titanium dibenzyl,
. 15 bis(cyclopentadienyl)zirconium dibenzylt
bis(cyclopentadienyl)vanadium dimethyl; the mono
alkyl metallocenes such as
bis(cyclopentadienyl)titanium methyl chloride,
bis(cyclopentadienyl)titanium ethyl chloride,
bis(cyclopentadienyl)titanium phenyl chloride,
bis(cyclopentadienyl)zirconium methyl chloride,
bis(cyclopentadienyl)zirconium ethyl chloride,
bis(cyclopentadienyl)zirconium phenyl chloride,
bis(cyclopentadienyl)titanium methyl bromide,
bis(cyclopentadienyl)titanium methyl iodide,
b~is(cyclopentadienyl)titani~m ethyl bromide,
bis(cyclopentadienyl)titanium phenyl bromide,
bis(cyclopentadienyl)titanium phenyl iodide,
bis(cyclopentadienyl)zirconium methyl bromide,
bis(cyclopentadienyl)zirconium methyl iodide,
bis(cyclopentadienyl)zirconium methyl iodide,
bis(cyclopentadienyl)zirconium ethyl bromide,
bis~cyclopentadienyl)zirconium ethyl iodide,
- : bis(cyclopentadienyl)zirconium ethyl bromide,
bis(cyclopentadienyl)zirconium ethyl bromide,
:~ bis(cyclopentadienyl)zirconium ethyl iodide,
bis(cyclopentadienyl)zirconium ethyl iodide,
: ~:
:
I WO93fo30s3 PCT/US92/059~
~ 2113~7 - 28 - `~
bis(cyclopentadienyl)zirconium phenyl bromide,
bis(cyclopentadienyl)zirconium phenyl iodide; the
trialkyl metallocenes such as
cyclopentadienyltitanium trimethyl, cyclopentadienyl
zirconium triphenyl, and cyclopentadienyl zirconium
trineopentyl, cyclopentadienylzirconium trimethyl,
cyclopentadienylhafnium triphenyl,
cyclopentadienylhafnium trineopentyl, and
cyclopentadienylhafnium trimethyl.
~;~ 10 Other metallocenes which may be usefully
employed to prepare the polymer components of the
invention include the monocyclopentadienyls
titanocenes such as, pentamethylcyclopentadienyl
titanium trichloride, pentaethylcyclopentadienyl
titanium trichloride;
bis(pentamethylcyclopentadienyl) titanium diphenyl,
:` the carbene represented by the formula
bis(cyclopentadienyl)titanium=CH2 and derivatives of
~ .
this reagent such as bis(cyclopentadienyl)Ti=CH2 -
Al(CH3)3 ~ (CP2TicH2)2 , Cp2TiCH2CH(CH3)CH2 , Cp2Ti-
: ~ CHCH2CH2 wherein Cp represents a cyclopentadienyl;
~ substituted bis(cyclopentadienyl)titanium (IV)
-~ compounds such as: bis(indenyl)titanium diphenyl or
: dichloride, bis(methylcyclopentadienyl)titanium
diphenyl or dihalides; dialkyl, trialkyl, tetra-
. alkyl and penta-alkyl cyclopentadienyl titanium
compounds such as bis(l,2-
dimethylcyclopentadienyl)titanium diphenyl or
dichloride, bis(l,2-diethylcyclopentadienyl)titanium
diphenyl or dichloride and other dihalide complexes;
silicon, phosphine, amine or carbon bridged
; cyclopentadiene complexes, such as dimethyl
silyldicyclopentadienyl titanium diphenyl or
dichloride, methyl pho~phine dicyclopen~adienyl
~: 35 titaniu~ diphenyl or dichloride,
methylenedicyclopentadienyl titanium diphenyl or
:
~ W093/03093 2 1 1 3 ~ 2 7 PCT/US92/0~924
- 29 -
dichloride and other dihalide complexes and the
like.
Additional zirconocene catalysts useful
according to the present invention include
s bis(cyclopentadienyl) zirconium dimethyl;
bis(cyclopentadienyl) zirconium dichloride,
- bis(cyclopentadienyl) zirconium methylchloride,
pentamethylcyclopentadienyl zirconium trichloride,
pentaethylcyclopentadienyl zirconium triahloride,
~o bis(pentamethylcyclopentadienyl)zirconium diphenyl,
the alkyl substituted cyclopentadienes, such as
~-~ bis(ethylcyclopentadienyl)zirconium dimethyl, bis(A-
phenylpropylcyclopentadienyl)zirconium dimethyl,
bis(methylcyclopentadienyl)zirconium dimethyl,
bis(n-butyl-cyclcopentadienyl)zirconium dimethyl,
bis(cyclohexylmethylcyclopentadienyl)zirconium
d~imethyl, bis(n-octyl-cyclopentadienyl)zirconium
dimethyl, and haloalkyl and dihalide complexes of
the above; di-alkyl, trialkyl, tetra-alkyl, and
penta-alkyl cyclopentadienes, such as
;~ : bis(pentamethylcyclopentadienyl)zirconium di-methyl,
bis(l,2-dimethylcyclopentadienyl)zirconium dimethyl
and dihalide complexes Qf the above; silicon,
phosphorus, and carbon bridged cyclopentadiene
complexes such as dimethylsilyldicyclopentadienyl
zirconium dimethyl or dihalide, and methylene
dicyclopentadienyl zirconium dimethyl or dihalide,
and methylene dicyclopentadienyl ethylene bridged
bis(tetrahydroindenyl) zirconium dimethyl or
d~halide, carbenes represented by the formula
Cp2Zr-CHP~C6Hs)2CH3, and derivatives of these
compound~ such as Cp2ZrCH2CH(CH3)CH2 .
Bis(cyclopentadienyl)hafnium dichloride,
~; bis(cyclopentadienyl)vanadium dichloride,
bis(cyclopentadienyl)vanadium dichloride and the
like are illustrative~ of other metallocenes.
:~
: ~:
; W093/03093 PCT/US92/059~
~ 21 1362~ 30 _ ~
The alumoxanes are polymeric aluminum
compounds which can be represented by the general
formula (R-Al-O)n which is a cyclic compound and
R(R-Al-O-)nAlR2 , which is a linear compound. In
the general formula R is a Cl-Cs alkyl group such
as, for example, methyl, ethyl, propyl, butyl and
pentyl and n is an integer from 2 to about 20.
Generally, in the preparation of alumoxanes from,
for example, aluminum trimethyl and water, a mixture
of the linear and cyclic compounds is obtained.
The alumoxane can be prepared in various
ways. Preferably, alumoxane is prepared by
contacting water with a solution of aluminum
trialkyl, such as, for example, aluminum trimethyl,
lS in a suitable organic solvent such as benzene or an
aliphatic hydrocarbon. For èxample, the aluminum
~; - alkyl is treated with water in the form of a moist
solvent. In an alternative method, the aluminum
alkyl such as aluminum trimethyl can be desirably
contacted with a hydrated salt such as hydrated
- copper sulfate.
~ Preferably, the alumoxane is prepared in
-~ the presence of a hydrated ferrous sulfate as
-~ described in U.S. Patent 4,665,208 incorporated
herein by reference. The method comprises treating
a dilute solution of aluminum trimethyl in, for
example, toluene, with ferrous sulfate represented
by the general formula FeS04 2 7H20. The ratio of
ferrous sulfate to alu~inum trimethyl i~ desirably
about 1 mole of ferrous sulfate for 6 to 7 moles of
aluminum trimethyl. The reaction is evidenced by
the evolution of methane.
The ratio of aluminum in the alumoxane to
total metal in the metallocenes can be in the range
of about 0.5:1 to about 10,000:1, and preferably
about 5:1 to about 1000:1.
~ W093/03093 2113~2~1 PCT/US9~/0S9~
~ - 31 -
i
Various inorganic oxide supports may be
used for supported catalyst s~stems to prepare
interpolymers and blend components of the present
invention. The polymerization is generally carried
out in the temperature range of about 0-160-C, or
even higher. This temperature range is not meant to
be exclusive for preparing the interpolymer and
blend components of the invention. They may be
prepared by any technique resulting in the structure
set forth. Atmcspheric, sub-atmospheric, or super-
atmospheric pressure conditions have been used for
the polymerization using the metallocene catalyst
described above~ It is generally preferred to use
catalyst compositions at a concentration so as to
provide from about 1 ppm to about 5000 ppm, most
preferably 10 ppm to 300 ppm, by weight of
transition metal based on the weight of monomers in
the polymerization of the ethylene polymers.
A slurry polymerization process generally
uses super-atmospheric pressures and temperatures in
the range of 40-llO-C. In a slurry polymerization,
a suspension of solid, particulate polymer is formed
in a liquid polymerization medium to which ethylene
and comonomers and often hydrogen along with
catalyst are added. The liquid employed in the
polymerization medium can be alkane or cycloalkane,
or an aromatic hydrocarbon such as toluene,
ethylbènzene or xylene. The medium employed should
be liquid under the conditions of polymerization and
relatively inert. Preferably, hexane or toluene is
employed.
In a modification, the po~ymer components
of the present invention may be formed by gas-phase
polymèrization. A gas-phase process utilizes super-
atmospheric pressure and temperatures in the rangeof about 50--120-C. Gas-phase polymerization can be
performed in a stirred or fluidized bed of catalyst
~' .
W093/03093 ; PCT/US92/059~
~ 211~62~ - 32 -
and product particles in a press~re vessel adapted
to permit the separation of product particles from
unreacted gases. Ethylene, comonomer, hydrogen and
an inert diluent gas such as nitrogen can be
; 5 introduced at a controlled constant temperature or
recirculated so as to maintain the particles at a
temperature of 50--120-C. Triethylaluminum may be
added as needed as a scavenger of water, oxygen, and
other impurities. Polymer product can be withdrawn
continuously or semi-continuously at a rate such as
to maintain a constant product inventory in the
reactor. After polymerization and deactivation of
the catalyst, the product polymer can be recovered
by a suitable means. In commercial practice, the
polymer product can be recovered directly from the
gas phase reactor, separated from residual monomer
with a nitrogen purge, and used without further
; deactivation or catalyst removal. The polymer
obtained can be extruded into water and cut into
pellets or other suitable comminuted shapes as is
known in the art. Also known in the art, pigments,
antioxidants and other additives may be added to the
,:~
-; polymer.
The blends of the present invention are
prepared by blending the desired components in the
desired proportions using conventional blending
techniques and apparatus, such as, for example,
screw-type extruders, Banbury mixers, and the like.
Alternatively, the blends may be made by direct
polymerization, without isolation of the blend
components, using, for example, two or more
catalysts in one reactor, or by using a single
catalyst and two or more reactors in series or
parallel. The blend may also be compounded with
various conventional additives known in the art such
as, for example, antioxidants, W stabilizers,
pigments, fillers, slip additives, block additives,
I W093/03093 2 ~ 1 3 6 r~ 7 PCT/US92/059
!
- 33 -
and the like. The blend preferably does not contain
any blend components in proportions which would
significantly adversely affect any improved
properties desired to be obtained by blending the~
LLDPE resins.
Ethylene interpolymers with narrow CD and
narrow MWD may be formed as described above. The
ethylene interpolymers may be used to form articles
with particularly desirable heat sealing properties.
In particular, the ethylene interpolymers may be
processed into films which will possess particularly
desirablè heat sealing and other physical
characteristics. Different ethylene interpolymer
components, each having a narrow CD and narrow MWD,
may be combined to form a polymer blend of ethylene
interpolymers having particularly preferred heat
sealing characteristics. The ethylene interpolymers
are individually se}ected so that the resulting
blend is essentially free of blend components having
both a higher average molecular weight and a lower
average comonomer content than that of any other
blend component.
A blend ha~ing a narrow CD and a narrow MWD
` is made by blending two or more et~ylene
interpo}ymers selected so that the blend has a CDBI
of at least 50% and a MWD (MW/Mn) S 3. A blend
having ~ narrow CD and a broad NWD is made by
blending two or more ethylene interpolymers selected
so that the blend has a CDBI of at least 50% and a
MWD > 3. A blend having a broad CD and a narrow MWD
is made by blending two or more ethylene
interpoly~ers selected so that the blend has a CDBI
of less than 50% and a MWD < 3. Also, an
interpolymer having a narrow CD and a narrow MWD can
be blended with a polymer having a CDBI of less than
50% and a NWD > 3Ø
~,:
~,
~ W093~03093 PCT/US92/05g~
~ 2~13~27 _ 34 -
The ethylene interpolymers may be used to
form any commercial article where heat sealing is
important or necessary. For example, the ethylene
interpolymers and blends thereof may be used to form
films which are in turn formed into bags or pouches
by heat sealing techniques known in the art. The
heat sealable film may also be used in packaging as
the sealing material, for example, the film may be
; placed over the opening of a container, and then
secured to the container by the application of heat.
This technique may be used to seal perishable items,
such as food, into paper, plastic, glass, ceramic or
metallic containers. The technique may also be used
to package consumer items in attractive sales
displays and to secure items for transportation.
The articles described herein are said to
be formed from ethylene interpolymers and blends
thereof. The articles may comprise other materials,
~. ~
especially in portions of the article that will not
be utilized for heat sealing. In the portions of
the article that are used for heat sealing, the
language "formed from" is intended to mean
"comprising." All articles or portions of articles
described herein may also be constructed to consist
essentially of the inventive ethylene interpolymers
or blends thereof, in more preferred embodiments.
In other words, the heat sealing portion of any
article described herein may consist essentially of
the inventive ethylene interpolymers and blends
thereof.
The ethylene interpolymers may be formed
~nto films by methods well known in the art. For
ex~ple, the polymers may be extruded in a molten
state through a flat die and then cooled.
Alternatively, the polymers may be extruded in a
molten state through an annular die and then blown
and cooled to form a tubular film. The tubular film
:
;~
~'
~ W093/03093 2 1 13~2 ~ PCT/US92/059~
~ - 35 -
.,
may be axially slit and unfolded to form a flat
film. The films of the invention may be unoriented,
uniaxially oriented or biaxially oriented.
The films of the invention may be single
layer or multiple-layer films. The multiple-layer
films may consist of one or more layers formed from
ethylene interpolymers and blends thereof. The
films may also have one or more additional layers
formed from other materials such as other polymers,
polypropylene, polyester and EVoH for instance,
metal foils, paper and the like.
Multiple-layer films may be formed by
methods well known in the art. If all layers are
polymers, the polymers may be coextruded through a
coextrusion feedblock and die assembly to yield a
film with two or more layers adhered together but
differing in composition. Multiple-layer films may
also be formed by extrusion coating whereby a
substrate material is contacted with the hot molten
~ 20 polymer as the polymer exits the die. For instance,
-~ an alre~dy formed polypropylene film may be
extrusion coated with an ethylene interpolymer film
as the latter i8 extruded through the die.
Extrusion coating is particularly useful when the
; ; 25 ethylene interpolymer heat seal layer iæ to be
applied to substrates that are woven or knitted from
natural or synthetic fibers or yarns, e.g.,
textiles, or substrates made from non-polymer
materials such as glass, ceramic, paper or metal.
Multiple-layer films may also be formed by
combining two or more single layer films prepared as
describ-d above. For instance, a polypropylene
substrate film may be combined with an ethylene
interpolymer heat seal film yielding a two layer
film that would have the strength properties of
polypropylene and the heat sealing characteristic of
the ethylene interpolymer film. The two layers of a
W093~03093 ~;i PCT/US92/059~
2113627 - 36 - ''
film so formed may be adhered together with an
adhesive or by the application of heat and pressure.
There are several important characteristics
of a good heat sealing polymer. One important
S characteristic is the heat seal initiation
temperature. This is the temperature to which the
polymer must be heated before it will undergo usef~ll
bonding to itself under pressure. Therefore, heat
sealing temperatures above the seal initiation
temperature result in heat seals with considerable
and measurable seal strength. Relatively lower heat
sea~ initiation temperatures are desirable in
commercial heat sealing equipment. The lower
temperatures provide for faster operation of the
equipment because the polymer need not be heated to
as great a temperature to make the seal. Also,
cooling of the seal to attain adequate strength will
be faster.
Another important characteristic is the
seal strength plateau on-set temperature. This is
the lowest temperature to which the polymer must be
heated to obtain a seal with the maximum strength
after cooling that is possible with the particular
;~` materials being sealed., As heat sealing temperature
' 25 is gradually raised above the seal initiation
temperature, the resulting seals are stronger. The
seal strength continues to increase with increasing
,
sealing temperature up to a point where increased
~ealing,temperature no longer provides increased
; 30 ~eal strength. This temperature is the seal
strength plateau on-set temperature. More
importantly, the se81 strength plateau on-set
temperature is usually the lowest heat sealing
temperature that will yield a heat sesl that fails
solely by tearing and not by peeling alone or by
peeling and tearing. When a heat seal fails by
peeling, the two sealed surfaces separate cleanly.
W093/03093 2 1 1 3 ~ 2 7 PCT/US92/059~
- 37 -
When a seal fails in this manner, the ~eal strength
is usually low. When a seal fails by peeling and
tearing the two sealed surfaces undergo considerable
stretching or elongation during separation. When a
seal fails by tearinq, the failure occurs not in the
~eal itself but in the material around the seal.
The maximum seal strength is reached when failure is
solely by tearing. Since the mode of seal failure
changes at the seal strength plateau on-set
temperature, a visual indication of the seal failure
modes may be used to determine the plateau on-set
temperature. Commercial sealing equipment may be
operated at higher speeds if the seal strength
plateau on-set temperature is lower for the same
reasons discussed above with respect to seal
initiation temperature.
A third important characteristic~is the
sealing window which is the range of temperatures
acceptable for forming a seal. The sealing window
determines the acceptable range of operating
temperatures where seal strength remains essentially
constant. The low temperature in the range is the
p}ateau on-set temperature and the upper temperature
in the range is the temperature where the seal
2S strength begins to decrease or the polymer begins to
-~ degrade. Since it is often difficult or impossible
to maintain commercial sealing equipment at exactly
the sa~e temperature throughout a commercial sealing
run, a broader range of acceptable sealing
temperatures makes it easier to assure that all heat
~eals made will have acceptable strength.
The heat sealed article ~ay be formed by
pressing at least two portions of the article
together at a temperature sufficient to soften at
least one of the article portions. The article
portion which has been softened by heat is formed
from ethylene interpolymers having a CDBI of at
W093/03093 PCT/US92/059~
2113~27 38 -
least 50% or from a polymer blend comprising a
plurality of the ethylene interpolymers as blend
components. Although it is sufficient if only one -
of the article portions being heated and pressed to `
form a heat seal is formed from the ethylene
interpolymers or blends of the ethylene
interpolymers, it is preferable for all article
portions directly involved in the heat seal to be
formed from the ethylene interpolymers or blends
thereof. Other portions of the article may be
constructed of other materials. `
The heat sealing temperature must be high
enough to soften the interpolymers so that they will
stick to the material to which they are being
sealed. The heat sealing temperature may range as
high as the melting temperature of the interpolymers
or even higher, but at temperatures this high the
sealing contact time must be shortened.
The seals are formed by heating one or both
of the article portions to the necessary
temperature, pressing the article portions together
for a time sufficient to cause them to meld
together, at least partially, and then cooling the
seal. The presæure needed to join the portions will
depend on the article shape, the thickness of the
sealing layer, the composition of the sealing layer
and the temperature at which the seal is made. The
heat sealed article ~o formed may be a sealed
container comprising a body and a sealing member
- 30 secured thereto, wherein the sealing member
comprises a seal layer comprising one of the group
of ethylene interpolymers having a narrow t
composition distribution and a blend of a plurality
of said ethylene interpolymers as blend components.
The body, as described previously, may be
constructed with any number of different materials
such as paper, plastic, glass, ceramics, metals and
wo93/03093 ~ 27 PCT/US9~/OS9~
- 39 -
textiles. The body can be constructed with walls
that are impervious to liquids and/or gasses or the
body may be constructed to allow the passage of
liquids and/or gasses. The body may also be
constructed with one or more portals to allow
passage of small items through the body wall or to
allow the consumer ~o inspect the item stored in the
container without removing the item from the
container. Figure 13 represents a cross-section of a
sealed container, showing a container body 132 and a
sealing member 134 which define a sealed chamber
136. The sealed container may also have a flange
138, to provide extra surface area for making a heat
seal.
In commercial applications, the open
chamber 136 is filled with the item to be packaged
and the sealing member 134 is then pressed against
the flange 138. The sealing member 134, the flange
138 or both may be preheated prior to contact or one
or both may be heated after contact. In any event,
the sealing member 134 is pressed against flange 138
at a temperature suffi ient to soften the sealing
member 134. After sealing member 134 has been
pressed against flange 138 under heat and pressure
sufficient to form a heat seal, the heat and
~- pressure are removed and the sealed area is cooled.
The resulting article is a sealed container with the
consumer item sealed in chamber 136.
As discussed above, the sealing member may
be constructed solely from the inventive ethylene
interpolymers and blends thereof, or the sealing
me~er may be a multilayer film. If the sealing
member is constructed from more than one material,
the inventive ethylene interpolymers, or blends
~ 35 thereof, need be utilized only in the areas where
- the heat seal will be formed. For exampIe, the
sealing member may be constructed as shown in Figure
W093/03~93 PCT/US92/059~ `
2113~27 - 40 -
14, which is a cross-section of a two-layer film.
The sealing member 144 may be constructed of a
substrate layer 143 and a heat sealing layer 145.
~SF15R15NTTAI. ~:~CAMPLE:8
In order to provide a better understanding
of the present invention including representative
advantages thereof, the following referential
examples are offered as related to actual tests
performed in the practice of this invention, and
illustrate the surprising and unexpected heat seal
property of the interpol~lmers and blends thereof of
this present invention and are not intended as a
- limitation on the scope of the invention.
E~AMP~ I
An ethylene copolymer resin was prepared
according to the prior art and is identified herein
as Sample No. A. Sample A was prepared in a
fluidized bed gas phase reactor employing a titanium
transition metal catalyst as described below. The
gas phase reaction was carried out at 83-C reaction
temperature, an ethylene pressure of 130 psia, a
hydrogen/ethylene mole ratio of 0.0556, a
butene/ethylene mole ratio of 0.0263 and a residence
time of 2.4 hours. A comonomer of 4.82 mole %
butene was incorporated in the resulting polymer.
A second copolymer known in the art was
prepared in a liguid slurry phase reaction and
designated as Sample No. B. The slurry phase
reaction temperature used to prepare Sample No. B
was 83-C, the pressure of ethylene in the reactor
was 130 psia, the hydrogen/ethylene mole ratio in
the reactor was 0.0556, and the residence time was
2.4 hours. A comonomer of 3.2 mole ~ butene was
incorporated in the resu}ting polymer. The prior
art transition metal catalyst was prepared in
accordance with procedures outlined in U.S. patent
4,719,193 which is incorporated herein by reference.
W093/0~93 PCTJUS92/059~
2 1 1 3 ~ ~ 7
- 41 -
Silica was calcined at 600 C and then treated with
triethylaluminum in a mixture of isopentane at 25-C.
Nagnesium dichloride was then reacted with titanium
trichloride in the presence of aluminum trichloride
and tetrahydrofuran (THF) solvent at 60-C. The
resulting reaction product was contac~ed in THF
solvent at 50 C with the treated silica prepared as
noted above. The resulting product was treated with
a mixture of diethylaluminum chloride and tri n-
Hexyl aluminum in isopentane at 50 C to yield the
catalyst used to prepare Sample B.
The physical properties of the resulting
polymers are set forth in Table I below. The melt
index (MI) is measured according to ASTM D-1238 and
is the number of grams of polymer ex*ruded in ten
minutes under a weight of 2.16 kg at a temperature
of 190-C.
The tear resistance (TR) is measured by the
Elmendorf Pendulum method according to ASTM D-1922
(PL-007). Tear resistance is measured in (Kg/cm) in
the machine direction (ND) and in the transverse
directions (TD) because the films show different
behavior in different directions. Intrinsic tear
(IT) is measured according to ASTM 922.
Dart impact resistance (DIR) is measured by
the free falling dart method according to ASTM D-
1709-75, Method A (PL-002). Dart impact resistance
i8 ~easured in (gm/mil).
Haze is measured according to ASTM D-1003-
61 Procedure A and Gloss is measured accordinq to
ASTM D-2457-70, AST D-523-80. Both Haze and Gloss
are mea~ured by percent (t). Haze is not the same
as Gloss. Gloss is the shine of the film seen by
reflected light. The Haze of a film is inversely
related to the clarity of the film.
Hexane Extractables (HE) is measured
according to the procedure set forth by the Food and
WO 93/03093 PCI`/US92/05924
2113~27 42-
0 _ I ~ ~ o ,~
_ o~ o~ o a~
I I I
o ~ ~ CO o
~ O V~0 N U~
e 3 1 I D~ " oo ~ . r ~
~ ~ ~ ~ N ~0 N
0~ ~
~B ~ X ' ~ N _I V 0
~. o 8 s ~ I ~ S S S ~ ;~ S c: ~ S :: S
~ r r N ~ r
0 8 ~ ~ N N t~ - N ~
~
V 11~ ~ Il N N
o o o o o o o ~ r~
O ~ ~ o o
C~
v rl n ~
0 o~ o
wo93/o3os3 PCT/US92/059~
2 1 1 3 ~ ,L~ r~
.: .~.... ~ . .
- 43 -
Drug Administration as described in 21 CFR (
1.77.1520(d)(3)(ii) measured in percent (%).
ESAMPL~ TI
A silica supported transition metal
catalyst according to the invention was prepared in
the following manner. About 100 grams of high
surface area (Davison 952) silica, was dehydrated by
heating the silica to 800-C for about five hours and
maintaining a flow of dry nitrogen over the silica.
The dry silica was then slurried with 500 ml of dry
toluene at 25-C under a nitrogen atmosphere in a
2500 ml round-bottom flask equipped with a magnetic
; stirrer. Thereafter, 250 ml of methyl alumoxane in
toluene (1.03 mole/liter in aluminum) was added
dropwise over about 15 minutes with constant
stirring of the silica slurry. Stirring was
subsequently continued for 30 minutes while
maintaining the temperature of the flask at 25-C. A
toluene so}ution containing 2.00 grams of bis(n-
butylcyclopentadienyl)zirconium dichloride was added
to the alumoxane treated silica slurry dropwise over
15 minutes. Stirring was maintained constantly
during the addition and for one additional half hour
while maintaining the temperature of the slurry at
~ 25 65-C. Thereafter, toluene was decanted and the
-~ solids were recovered and dried under a vacuum for
four hours. Analysis of the catalyst indicated that
it contained 4.5 wt% aluminum and 0.63 wt%
zirconium.
Catalysts prepared in the manner described
above was then used for a gas phase reaction under
the conditions indicated in Table II. During each
polymerization reaction, the indicated amount of
ethy}ene mixed with nitrogen was added to the
reactor along with the indicated amount of hydrogen.
The reaction time to make each polymer was about two
to four hours. The reaction temperature was
W093/03093 PCT/US92~059~
2113627
- 44 -
maintained as indicated in Table II and the
indicated amount of comonomer was added at the start
of the reaction. After each reaction, polymer
particles were separated from t~e rest of the
reaction mixture. The resulting molecular weight
and density of each blend component is also set
forth in Table II and properties of the blends are
set forth in Table I.
Samples A and B described above in Example
I and have a comonomer distribution in relationship
to molecular weight as represented by line A of
Figure 1. Sample 1 was prepared to have a narrow CD
and a broad MWD and contain a majority of high
molecular weight component. The distribution of
comonomer in relation to molecular weight for Sample
1 would lie along line C of Figure 1.
Sample 2 was blended to have a broad CD and
a broad MWD with a minority of h~gh molecular
weight, low density component. A distribution plot
for Sample 2 would lie along line D of Figure 1.
Sample 3 was blended to have a narrow CD,
and a broad MWD and have a majority of high
molecular weight component. The distribution figure
for Sample 3 would lie along line C of Figure l.
Sample 4 has a narrow CD, and a broad MWD
and contains a minority of high molecular weight
component. A representation of the comonomer
distribution would appear as line C in Figure 1.
Sample 5 has a broad composition
distribution and a bxoad molecular weight
distribution and comprises a minority of high
molecular weight high density component. This
sample was blended to mimic prior art polymers. The
distribution for Sample 5 would lie along line A of
3S Figure 1.
Sample 6 has a broad CD and a broad MWD and
contains a majority of a high molecular weight, low
W093/03093 2 11 3 5 2 I PCT/US92/0~9~
_ 45 _
density component. A distribution for Sample 6
would lie alon line D in Figure 1.
Sample 7 has a broad CD and a narrow MWD
and equal amounts of high and low density
components. The distribution for Sample 7 would lie
along line B of Figure l.
Sample 8 has a narrow CD and a narrow MWD
and has only one interpolymer component of 80,000
molecular weight and 0.9049 density.
Sample 9 is a single interpolymer with a
narrow CD and a narrow MMD. Sample 9 has a high
molecular weight of about 96,500 and a 0.9104
density.
Sample lO is also a single interpolymer
component sample with a narrow CD and a narrow MWD.
Sample 10 has a 84,300 molecular weight and a 0.9147
density.
..
~: :
WO 93/03093 . PCI'/US92/0~924
2:113~27 46-
o o .. ~ :.
~_ ,,,VI,,I,. I~,I,I
a ~ ~ N
oq ~ ..
C~ ~ ~o r
~ .
~.^
:~ ~ E ~ r ~ ~ o~ ~ N O ~ 0 ~ 1~ O U~
111 t~ ~1 0 t~ ~ O ~ _I O 0 ~ ~ ~ O N O ~ ~1
O C ~ ~ ~ a~ o o~ ~ o O~ ~ ~ ~ o~ ~ ~ O~ a a~
~- O ~
~a- o o o o o o o o o o o o o o o o o
;:
-:
V -
~I ..
C ~` ~ o U~ ~ ,.
l O ~ O ~ ~ ~ rl ~ ~ ~ 'O ~ . .
O S ~ ~ o~ ~- ~ ~ ~ ~ ~ r ~ I~ I` I` o ~o ~
h x ,~ ~ 0 ~ 0 -:
_
~0 ~1 ~ ~ N 'O ~ r 'O ~ ~ o S
C _ ~ ~ ~ O Cl~ ~1 0 ~
O O
O O ~ ~` ~ ~ ~ U~
`
~J
::
~ .
OC
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~: ~U ~- u~ ~ ~ O ~
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O ~ D ~ O O ~ 'O ~-~ O
~C~ .~...................... ~
U O C 1~ ~1 0 N N Ir r~ N In O ~ ~1 ~ ~1
o E S S S ~ S ~ S ~
O ~ ~ o o o o o o o r~ ~ o ~ o
U ~ r N N N N ~I N N ~i rl 0~ r~l N r N
W `
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. ,. _ ,,
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W093/03093 2 1 1 3 ~ 2 7 PCT/US92/0~9~
- 47 -
EXAMPL~ III
The films made from Samp'es A and B were
made on a 1 inch Egan Blown Film Line, (Tower
Flight Model) with a blown ratio of 4:1. The films
produced each had a thickness of approximately 2.0
mils (50 microns). The blends for samples numbered
1-8 were each homogenized on a large Werner
Pfleiderer model ZSK-57 twin screw compounding
extruder. Films from each of the resins so blended
were then made on a l-inch Killion Mini Cast Film
Line, Model KLB 100 into films having a thickness of
1.5 to 2.0 mils (37.5 to 50 microns) in thickness.
Samples 9 and 10 each comprised only one polymer
component and therefore did not require blending.
Films from Samples 9 and 10 were made on a 2-inch
Collin Film Cast Line.
Heat seals were made from the films on a
laboratory scale Theller Model EB heat sealer. A
dwell time of about one second and a sealing
pressure of 50 N/cm2 was used for making the seals.
The seals on the films were made in the transverse
direction for both the blown and cast films and the
heat sealing anvils were insulated from the heat
sealing film by a Mylar film. The Mylar film is
2S very stable at normal heat sealing temperatures and
is easily removed from the heat sealing polymer
after the seal has been made. The seals were aged
for 24 hours before testing them for strength.
For the strength test, the sealed samples
were cut into 1 inch t2.54 cm) wide pieces and then
strength tested using an Instron instrument at a
strain rate of 508 mm/min and a 2 inch (5.08 cm) jaw
separation. The free ends of the sample are fixed
in jaws, and then the jaws are separated at the
strain rate until the seal fails. The peak load at
seal break is measured and the seal strength is
Wog3/030s3 PCTtUS92/059~
2113~27 - 48 -
calculated by dividing the peak load by the sample
width.
The heat seal initiation temperature was
determined by measuring the seal strenqths of each
s sample sealed at various temperatures and then
extrapolating from a plot of seal strength versus
-- temperature to find the lowest temperature at which
some seal strength is present~ This same plot can
be used to determine the temperature at which a seal
strength of 2 N/cm occurs. The plot can also be
used to determine the plateau on-set temperature and
the sealing temperature window. Values for these
measured properties of prior art and inventive heat
sealed films are given in Table III.
A qualitative rank of the performance of
each of the samples further indicates the advantages
of heat seals made from the inventive interpolymers
over those of the prior art. Prior art type
polymers are represented by Samples No. A and B and
rank at the top of the order depicted in Table IV.
The samples at the top of the Table require the
highest heat sealing temperatures for the indicated
level of seal strength. They are therefore the
least desirable of the samples ranked in Table IV.
Samples at the bottom of the Table require the
lowest heat sealing temperature required for
achieving the indicated level of seal strength and
are therefore most desirable. Sample No. 5 was
blended to mimic the composition distribution of
prior art polymers, and as can be seen from
Table IV, the properties of Sample No. 5 are about
as poor as those of prior art polymers.
The 2 N/cm seal strength, while chosen
arbitrarily, does provide some indication of the j~
minimum temperature necessary to provide
commercially useful heat seals. As Tables III and
IV show, the invention provides seals with 2 N/cm
W093/03093 PCT/US92/059~
21~ 3627
- 49 -
seal strengths at heat sealing temperatures of 95 C
or less, 90 C or less, or even 85 C or less. The
prior art samples A and B, and sample 5 blended to
mimic the prior art required heat sealing -
temperatures of greater than 95 C in order to
produce a seal of 2 N/cm seal strength. All of the
inventive blends required 95-C or less. These
temperatures are significantly below the
temperatures required for sealing prior art
polymers, even though in absolute terms they differ
by only a few degrees Centigrade. This small
reduction in absolute heat sealing temperature can
result in significant improvement in commercial heat
sealing processes. As mentioned before, the lower
seal temperature provides for faster sealing and
gr-a~er productivity per heat s-aling machine.
,~ .
WO 93/03093 PCI /US92/0~924
- 50 - -
2113627
_~ ~ :
C--o, ~ I` O U~ U~ ~ O U~ O 0~ CD 1`
~o.
~ .o o
U~ C ,~
~,, ~
o ~ o ~ o ~ ~ ,
H -
: . H ` ;
O 0~ 0 o~ o co co a~
Z ~
~:
CC~
O~
~O
o o ~r u~ r~ In ~ ~ ~1
~ ~ o o~ o o CD a~
_~ C
E
U~
~ z o
:: a
,:~ tn
-
WO 93/03093 PCI`/US92/05924
Sl- 21~3~.27
:: ~ C
cn ~ u~ ~: ~ 'D m o~ ,I r ~ ~ o a~
~ ~'
~ ~ _ . ~
~U '
m ~ ~r o ~c~ co ,~ ~ ~
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n
.~I ~.~ 3
.C o
~;:
WO93~030s3 PCT/US92/059
21 1 3~ 27 ~ 52 -
Although all of the resins according to the
invention provide improved heat sealing properties,
samples numbered 1, 3, 6, 7, 8 and 9 are far
superior than the prior art polymers as indicated by
the data in Tables III and IV. They form seals of 2
N/cm strength at sealing temperatures of 90 C or
less. Samples 3 and 9 form such seals at 85-C or
less. A further indication of the superiority of
the inventive heat seals made from the particularly
described polymers is graphically indicated in
Figures 7-12. Figure 7 represents the sealing curve
of two prior art polymers, Samples A and B. The
graphs represent the seal strength of a heat seal
measured in N/cm with respect to the temperature
(-C) at which the seal was made. For comparison,
the curve for Sample A appears in all of the Figures
7-11.
Figure 8 represents the curves for samples
numbered 1, 2 and 3 and graphically depicts the
advantages of samples 1, 2 and 3 over the prior art.
The curves for the inventive samples begin at lower
temperatures, thus indicating the lower seal
initiation temperature achieved through the use of
the narrow CD and narrow MWD polymers or blends
thereof. The strength of the seal formed with these
inventive polymers is greater at the same heat
sealing temperature as compared to the prior art
polymer A. For example, in Figure 8, at lOO-C
sealing temperature, it is apparent that samples
numbered 1, 2 and 3 have remarkably higher seal
strength than the prior art polymer of Sample A.
For instance, the seal strength of Sample A at lOO'C
as determined from the figure is less than 1 N/cm,
whereas the seal strength for Sample No. 3 is above
6 N/cm. This Figure shows the remarkably improved
seal strength of a film according to the invention
at a relatively low sealing temperature.
W093/03093 2 1 1 3 ~ 2 ~ PCT/US92/059~
- 53 -
Figure g represents samples numbered 4, 5
and 6 compared to Sample A. This figure shows
further that Sample No. 5, which was blended to
mimic prior art type polymers, has a sealing curve
substantially the same as that of prior art
polymers. In comparison, samples numbered 4 and 6
exhibit the beneficial properties as described in -~
the specification. Namely, samples numbered 4 and 6 '!
have greater seal strength at the same sealing
temperature in comparison to the prior art polymers
represented by Sample A. For instance, at lOO C,
the seal strength for Sample No. 6 is above 4 N/cm
while the seal strength for Sample No. A is below 1
N/cm.
Figure 10 represents the advantages of
samples numbered 7 and 8 compared to the prior art
polymer. The figure shows that samples 7 and 8
exhibit the same desirable qualities as described in
this application. Namely, low seal initiation
temperature and a greater seal strength at lower
- sealing temperatures. Again for comparison, the
inventive polymers exhibit remarkably higher seal
strength at lOO-C sealing temperature than is
exhibited by the prior art polymer. The inventive
resins have seal strengths of 4 N/cm or greater
compared to less than 1 N/cm for the prior art
polymer.
Figure 11 represents the seal strength data
for samples numbered 9 and 10 in comparison with the
prior art Sample A. The same advantages for samples
9 and 10 are apparent and include xemarkably higher
seal strength at a sealing temperature of lOO-C.
Samples numbered 9 and 10 have a seal strength of
almost 6 N/cm at lOO-C compared to less than 1 N/cm
for the prior art polymer.
Figure 12 represents the seal strength data
for samples numbered 1, 3 and 9 in comparison with
W093/03093 PCT/US~2/0~9~
~113627 - 54 ~
prior art Sample B. This plot shows the same heat
sealing advantages of the invention, i.e. lower heat
seal initiation temperature and greater seal
strength at a given heat sealing temperature, in
S comparison to the prior art.
The commercial advantages to be obtained
through the use of the inventive type of heat
sealing articles is apparent from the figures. The
inventive articles may be adequately sealed at
temperatures of less than 120-C, llO-C, or lOO-C,
and yet retain adequate strength in the seal thus
formed. In comparison prior art polymers sealed at
lOO-C, llO C or even 120 C and higher may not yield
seals of substantial strength. It is therefore
possible to use the inventive materials in
commercial lines operating at a sealing temperature
as low as 100-C or less. An operating temperature
of lOO-C is substantially lower than normal
commercial sealing operating temperatures. With
sealing temperatures as low as lOO-C, substantial
increases in heat sealing speed may be achieved and
therefore the output of a heat sealing unit may be
remarkably increased by use of the inventive heat
sealing materials. At the higher heat sealing
temperatures used for sealing prior art materials,
the invention provides the advantage of faster
sealing. Since the properties of the interpolymers
or blends of interpolymers provide for faster heat
sealing, greater numbers of seals may be made on
existing heat sealing equipment.
While the present invention has been
described and illustrated by reference to particular
embodiments thereof, it will be appreciated by t~ose
of ordinary skill in the art that the invention
lends itself to variations not necessarily
illustrated herein. For instance, the catalyst
system may comprise various other transition metal
W093/03093 2 1 1 3 ~ ~ 7 PCTI~s92/osg24
!. -; `
metallocenes that are activated by alumoxane and/or
ionic activators as the cocatalyst to produce :
interpolymers having a narrow molecular weight
distribution and narrow composition distribution.
~: 5 For this reason, then, reference should be made
- solely to the appended claims for purposes of
~ determining the true scope of the present invention.
:, ~
: ::
:
:~
