Stock material or miscellaneous articles – Composite – Of addition polymer from unsaturated monomers
Reexamination Certificate
1998-10-14
2003-07-15
Harlan, Robert D. (Department: 1713)
Stock material or miscellaneous articles
Composite
Of addition polymer from unsaturated monomers
C442S062000, C442S155000, C442S164000, C442S168000, C442S171000, C524S128000, C526S348000, C526S351000
Reexamination Certificate
active
06593004
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to novel extrusion coating compositions containing certain polypropylene polymers and solid substrates extrusion coated with such compositions.
BACKGROUND OF THE INVENTION
Solid substrates extrusion coated with polypropylene resins are known in the art. However, polypropylene resins have heretofore been found to be deficient when used alone in extrusion coating process and thus require blending with other resins and/or additional treatment of the substrate. U.S. Pat. No. 3,418,396 teaches blending polyethylene with polypropylene for improving extrusion coating onto Kraft paper. Additionally, U.S. Pat. No. 3,887,640 describes extrusion coating of blends of ethylene-propylene impact copolymers and polyethylene.
SUMMARY OF THE INVENTION
This invention relates to novel extrusion coating compositions containing certain high melt flow, narrow molecular weight distribution impact or random polypropylene copolymers and to substrates extrusion coated with such compositions. The novel coating compositions can be directly extrusion coated onto a substrate without blending with polyethylene or other polymers and without special preparation or treatment of the substrate. A good balance of properties including adhesion, edge weaving, surging and neck-in is achieved in the process of extrusion coating such compositions onto a suitable substrate.
DETAILED DESCRIPTION OF THE INVENTION
Extrusion Coating Compositions
The novel coating compositions of the present invention contain a propylene polymer selected from the group consisting of high melt flow, narrow molecular weight distribution versions of certain high impact polypropylene copolymers and certain propylene-ethylene random copolymers. These polypropylene polymers may be used alone without blending with other polymers such as polyethylene to achieve satisfactory results in the preparation of extrusion coated composite structures. In addition to the polypropylene polymers, the novel extrusion coating compositions of this invention preferably contains a particular combination of additives as is described in more detail below.
The homopolymer phase of the high impact copolymers useful in the compositions of present invention is preferably a propylene homopolymer, but it is understood that it may contain up to 5%w of comonomer, including but not limited to, C
2
and C
4
-C
8
alpha-olefins, such as 1-butene and ethylene, and dienes, such as 5-ethylidene-2-norbornene (ENB), and 7-methyl-1,6 octadiene. The mole ratio of olefin to propylene in this homopolymer phase is about 0 to about 0.06 and, preferably, when present, is about 0.015 to about 0.04.
The rubber phase of the high impact copolymers useful in the present invention is a copolymer of ethylene and propylene. The ethylene content (E
c
) of the rubber phase is between about 50%w to about 60%w, more preferably between about 50%w and about 55%w. The amount of rubber phase (F
c
) in the high impact copolymer ranges between about 10%w to about 35%w and preferably about 20%w to about 30%w based on the total weight of the impact copolymer. The melt flow (MF) of the high impact copolymer is between about 30 dg/min to about 70 dg/min, (as determined by ASTM D-1238, Cond. L) preferably about 40 dg/min to about 50 dg/min, produced either in the reactor or by controlled rheology (cracking or visbreaking) modes.
The ratio of intrinsic viscosity of the rubber phase to the intrinsic viscosity of the homopolymer phase referred to as the intrinsic viscosity ratio or beta/alpha ratio, &bgr;/&agr;, should be between about 1.1 to about 2.0 and preferably about 1.4 to about 2.0. The intrinsic viscosity ratio may be calculated as follows:
&bgr;/&agr;=1+(1/fc) [(MF homopolymer/MF copolymer)
0.213−
1.0] where fc is the fraction of rubbery copolymer in the impact copolymer.
The random copolymers for use herein contain from about 1 to about 10 weight percent of an alpha-olefin comonomer, e.g., ethylene or 1-butene. Preferably the comonomer content is from about 3 to about 4 weight percent. The melt flow of the random copolymer is between about 15 dg/min to about 70 dg/min.
The polypropylene impact copolymers and random copolymers which are useful in the present invention have a narrow molecular weight distribution, i.e. polydispersity index Q of less than 6.5 where Q is defined as M
w
/M
n
where M
w
is weight average molecular weight and M
n
is number average molecular weight. Q is measured by gel permeation chromatography (GPC) as will be understood by those skilled in the art.
The polypropylene polymers useful in the present invention can be produced in slurry polymerization processes conducted in inert hydrocarbon solvents, in bulk polymerization processes conducted in liquefied monomers such as liquefied propylene, and in stirred-bed or fluidized-bed gas phase polymerization processes. Gas phase processes using a fluidized-bed are preferred. Impact copolymers are advantageously made in a two reactor system wherein the propylene homopolymer phase is made in a first reactor and the contents of that reactor are conveyed to a second reactor where a comonomer is added and polymerized to produce a copolymer rubber phase. Such a process provides for in situ blending of the homopolymer phase and the copolymer rubber phase. U.S. Pat. Nos. 4,379,759; 4,728,705; 5,338,790 and 5,674,630 describe processes which could be used to produce propylene polymers which could be cracked to produce the high MF polymers useful in this invention
Commonly used catalysts for such systems include:
A. Ziegler-Natta catalysts, including titanium based catalysts such as those described in U.S. Pat. Nos. 4,376,062, 4,379,758 and 5,066,737. Ziegler-Natta catalysts are typically magnesium/titanium/electron donor complexes used in conjunction with an organoaluminum cocatalyst and an external selectivity control agent, such as an alkoxy silane, and
B. Metallocene catalysts, i.e., organometallic coordination complexes of one or more ligands in association with a metal atom.
The propylene polymers used in this invention are prepared in accordance with olefin polymerization processes which are well known in the art. Typically in these processes, discrete portions of the catalyst components continually are fed to the reactor in catalytically effective amounts together with the propylene (and possibly comonomer) while the polymer product is continually removed during the continuing process. Fluid bed reactors useful for this purpose are described, e.g., in U.S. Pat. Nos. 4,302,565, 4,302,566 and 4,303,771.
For example, in the preparation of impact copolymers, propylene or a mixture of propylene and a small amount of at least one olefin having 2 to 8 carbon atoms is introduced together with hydrogen and catalyst into the first reactor. The mole ratio of hydrogen to propylene alone or combined propylene and olefin is in the range of about 0.001 to about 0.45 and is preferably about 0.004 to about 0.1.
A mixture of homopolymer or copolymer of propylene with active catalyst embedded in the polymer matrix is produced in the first reactor. This mixture from the first reactor is transferred to the second reactor in which no additional solid catalyst need be added. Additional cocatalyst and/or electron donor optionally may be added to the second reactor. In the second reactor, ethylene and propylene are maintained at a gas phase composition in a range of mole ratio of about 0.1 to about 10 moles of ethylene per mole of propylene, and preferably about 0.1 to about 5.0 moles of ethylene per mole of propylene.
The propylene polymers useful in the present invention may be produced directly in the polymerization reactor using metallocene catalysts or by cracking reactor products to achieve the desired higher melt flows and narrow molecular weight distribution. The cracking or vis-breaking of polymers is a well known technique and involves thermally or chemically degrading the polymers to obtain a lower molecular weight product. Representative processes for cracking polyolefin resins
Harlan Robert D.
Union Carbide Chemicals & Plastics Technology Corporation
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