Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2000-01-20
2001-11-20
Nutter, Nathan M. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S232000, C525S240000
Reexamination Certificate
active
06319989
ABSTRACT:
This invention relates to an ethylene interpolymer composition characterized as having broad molecular weight distribution (MWD) and improved compositional uniformity. The invention also relates to a process for making such a composition and fabricated articles made from the novel composition. The novel composition exhibits good processibility and improved toughness properties, especially excellent film tear and impact resistance, and is particularly well-suited for use in applications such as high performance trash can liners and heavy duty shipping bags.
In the manufacture of ethylene interpolymers such as ethylene interpolymerized with at least one unsaturated comonomer, a number of polymerization methods and procedures are known. For example, single site and constrained geometry catalyst systems have been disclosed for manufacturing olefin polymers with high compositional uniformity and relatively narrow molecular weight distributions.
Variations in the reactor systems used to manufacture ethylene interpolymers are also known. For example, while single site catalysis systems are disclosed to provide compositionally uniform, narrow MWD products (e.g., EXACT plastomers supplied commercially by Exxon Chemical Corporation) when employed in a high pressure polymerization system and conversely products with decreased homogeneity with respect to the short chain branching distribution and a broader molecular weight distribution (e.g., EXCEED resins supplied commercially by Exxon Chemical Corporation) when employed in a low pressure gas phase polymerization process.
While the art is replete with various products and manufacturing techniques, the known range of manufacturing capabilities still do not permit the manufacturing of ethylene interpolymer compositions characterized as having good processability and excellent toughness properties such as excellent film tear and impact resistance. That is, known ethylene interpolymer compositions (either as single reactor products, multiple reactor products or polymer blends) do not exhibit the desired balance of good processability (i.e., sufficient extrusion processing characteristics to avoid, for example, objectionable melt fracture during blown film fabrication with sufficient melt strength to permit, for example, good bubble stability to maximize output rates) and excellent toughness.
The traditional polyethylene solution for achieving improved toughness properties involves manufacturing products with narrow molecular weight distributions as broad molecular weight distributions are known to yield reduced toughness properties. Beyond providing a narrow molecular weight distribution, linear polyethylenes are known to provide improved toughness properties relative to highly branched LDPE. Beyond a narrow molecular weight distribution and a linear polymer backbone, compositional uniformity has been offered for enhanced toughness properties. However, while the combination of a narrow molecular weight distribution, a linear polymer backbone and compositional uniformity may provide enhanced toughness, this combination of polymer properties invariably provides poor processability (e.g., the occurrence of melt fracture).
In contrast to the combination of a narrow molecular weight distribution, increased compositional uniformity and a linear polymer backbone, to achieve the balance of good processability (i.e., resistance to melt fracture and improved melt strength) and toughness properties, Lai et al. disclose in U.S. Pat. No. 5,272,236, the disclosure of which is incorporated by reference, substantially linear ethylene polymers characterized as having narrow molecular weight distribution, high compositional uniformity and long chain branching.
Other proposed solutions for achieving the desired property balance include polymer blends such as those disclosed by Kale et al. in U.S. Pat. No. 5,210,142 and Hazlitt et al. in U.S. Pat. No. 5,370,940, the disclosures of both of which are incorporated by reference. However, while such polymer blends exhibit good handling properties and processability, known polymer blends inevitably exhibit insufficient compositional uniformity to provide the desired toughness properties.
Because no known ethylene interpolymer composition provides the desired balance of good to excellent processability, melt fracture resistance, melt strength and toughness as demonstrated by high tear and impact resistance, there is a need for an improved ethylene interpolymer composition. There is also a need for a process for making an improved ethylene interpolymer composition with the desired property balance. There is also a need for a process for making an improved ethylene interpolymer composition wherein the process involves polymerization using multiple reactors and the process is characterized by improved flexibility such that a broad range of product molecular weights and/or densities can be economically manufactured. There is also a need for a blown film with good extrusion processability and high tear and impact resistance. These and other objects will become apparent from the detailed description of the present invention provided herein below.
We have discovered an ethylene interpolymer composition which is characterized by a broad molecular weight distribution and yet also possesses a relatively high compositional uniformity respecting its short chain branching distribution or fractional crystallinity. One aspect of the invention is a process and ethylene polymerization system,
the system comprising at least two injection points and at least two polymerization reactors, each reactor having a reaction stream or zone wherein at least one catalyst system and make-up feed is injected and wherein the make-up feed comprises ethylene and optionally at least one unsaturated comonomer,
the process comprising continuously operating the at least two polymerization reactors and separately injecting the catalyst system and the make-up feed into the reaction stream or zone of at least one reactor.
A second aspect of the invention is a process and polymerization system for making an ethylene polymer composition, the composition comprising ethylene interpolymerized with at least one unsaturated comonomer and characterized as having:
a) a melt flow ratio, I
10
/I
2
, from 8 to 10.4,
b) a M
w
/M
n
of greater than 4 as determined by gel permeation chromatography,
c) a melt index, I
2
, greater than 0.1 gram/10 minutes,
d) a composition density less than 0.945 gram/cubic centimeter, and
e) based on the total weight of crystallizable polymer portions, a weight percent at the dominant peak temperature above 75° C., as determined using crystallization analysis fractionation in the range of 20 to 100° C., equal to or greater than the mathematical product of 1.7946×10
−28
×10
(31.839×composition density)
for composition density in grams/cubic centimeter,
the system comprising at least two injection points and at least two polymerization reactors, each reactor having a reaction stream or zone wherein at least one catalyst system and make-up feed is injected and wherein the make-up feed comprises ethylene and optionally at least one unsaturated comonomer,
the process comprising continuously operating the at least two polymerization reactors and separately injecting the catalyst system and the make-up feed into the reaction stream or zone of at least one reactor.
A third aspect of the invention is a polymer composition comprising ethylene interpolymerized with at least one unsaturated comonomer, wherein the composition is characterized as having:
a) a melt flow ratio, I
10
/I
2
, from 8 to 10.4,
b) a M
w
/M
n
of greater than 4 as determined by gel permeation chromatography,
c) a melt index, I
2
, greater than 0.1 gram/10 minutes,
d) a composition density less than 0.945 gram/cubic centimeter, and
e) based on the total weight of crystallizable polymer portions, a weight percent at the dominant peak temperature above 75° C., as determined using crystallization analysis fractionation in the range of 20 to 100° C., equal to
Anderson Kenneth W.
Chum Pak-Wing S.
Eversdyk David A.
Hazlitt Lonnie G.
Jain Pradeep
Nutter Nathan M.
The Dow Chemical Company
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