Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Adhesive outermost layer
Reexamination Certificate
2000-04-25
2003-03-18
Tarazano, D. Lawrence (Department: 1773)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Adhesive outermost layer
C428S515000, C428S516000, C428S523000, C525S191000, C525S222000, C525S240000
Reexamination Certificate
active
06534173
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a novel composition of metallocene plastomer and ethylene/alkyl (meth)acrylate copolymer, and to objects obtained therefrom.
Copolymers of ethylene and alpha-olefin obtained by single-site metallocene catalysis are known. As these copolymers are homogeneous in composition, it has been possible to prepare products having a density comprised, for example, between 0.905 and 0.880 g/cm
3
, known as plastomers, having good mechanical and optical properties. The molecular distribution of such plastomers is very narrow and is characterized by a polydispersity index (ratio I=Mw/Mn) which is low, in general I<3.
Consequently, if such plastomers have good mechanical and optical properties, their rheology makes them poorly suited to implementation by extrusion or injection molding, because of the following characteristics:
high specific energy due to elevated viscosity at the shearing gradients of extrusion screws;
tendency to extrusion faults;
instability of the molten material leaving the die due to poor elongational viscosity.
One consequently looks for means of modifying the rheological behavior of such ethylene metallocene (plastomer) copolymers while still preserving their mechanical and optical properties.
Several documents disclose modification of certain ethylene/alpha-olefin (co)polymers through mixing with other (co) polymers.
U.S. Pat. No. 3,176,052 discloses homogeneous mixtures comprising, by weight, (a) 25 to 95% ethylene/alpha-olefin copolymer obtained by Ziegler-Natta catalysis having a density higher than 0.92 g/cm
3
and an MFI comprised between 0.1 and 10 dg/min, which is heterogeneous in composition, and (b) 75 to 5% of a radical polyethylene having a density comprised between 0.91 and 0.94 g/cm
3
.
U.S. Pat. No. 4,623,581 discloses a homogenous mixture comprising, by weight, (a) 25 to 98% ethylene/alpha-olefin copolymer which is heterogeneous in composition with a density between 0.905 and 0.940 g/cm
3
and an MFI comprised between 0.4 and 3 dg/min, and (b) 75 to 2% of a radical polyethylene having a density comprised between 0.91 and 0.94 g/cm
3
, which has a polydispersity index above 4, said polymer having specific properties of crystallinity and alpha-olefin monomer distribution. The radical polyethylene according to that patent can be an ethylene copolymer with up to 20% by weight of an alkyl acrylate, for example 17.5% by weight butyl acrylate. There is no mention in this document of the improvement to rheological properties of the modified polymers; further, this is not the intended aim. This patent also indicates that these modified ethylene polymers do not have a polydispersity index comprised between 2.7 and 4.1 (by making reference to European patent application 0,006,110); these modified ethylene polymers consequently have a satisfactory rheology which does not need to be modified.
European patent Application 0,006,110 discloses a mixture comprising, by weight, (a) 80 to 99% of ethylene/alpha-olefin copolymer having a polydispersity index comprised between 2.7 and 4.1 and (b) 20 to 1% of a high pressure low-density homopolyethylene, the addition of low density PE being intended to overcome the defective rheology of the ethylene/alpha-olefin copolymer.
International Application WO-A-9507314 discloses packagings obtained from substantially linear ethylene/alpha-olefin copolymers having low polydispersity indexes, for example comprised between 1.5 and 2.5. This patent discloses the addition of several types of film property modifiers, including rheology modifiers, while also indicating that the ethylene/alpha-olefin copolymers are preferably employed alone. The modifiers indicated in the description include LDPE, EVA, EVOH, PB, HDPE and LLDPE. The example given in that patent mentions LDPE or a linear EP copolymer as rheology modifier. However, such rheology modifiers have very high moduli, and consequently do not allow industrial production of film having adequate properties. Another possible modifier according to that document is an EVA; nevertheless, this modifier cannot be extruded at a sufficiently high temperature as it degrades at temperatures of 220° C. or even lower.
U.S. Pat. No. 5,326,602 discloses compositions comprising an ethylene polymer with an ethylene/acrylate copolymer. The ethylene polymer is obtained by Ziegler-Natta catalysis and does not have a narrow molecular distribution. Additionally, that patent does not disclose the action of ethylene/acrylate copolymer on the processability of an ethylene polymer.
U.S. Pat. No. 5,593,747 discloses compositions comprising a particular metallocene ethylene polymer, intended for the manufacture of heat-shrinkable films. In that patent, this metallocene polymer can be mixed with a thermoplastic polymer. However, the only examples given cover addition of EVA.
European Patent Application 0,597,502 discloses compositions comprising a metallocene ethylene polymer having a density of at least 0.900 g/cm
3
, also intended for manufacture of heat-shrinkable films. In that patent, this metallocene polymer can be mixed with a thermoplastic polymer of the radical ethylene copolymer type. Although ethylene/acrylate copolymers are specifically mentioned, the only examples cover the addition of EVA.
In fact, adding EVA to a metallocene polymer does not make it possible to improve processability. Additionally, EVA is unstable at high extrusion temperatures, notably of the order of 200 to 220° C.
None of the above documents teaches nor suggests the present invention.
SUMMARY OF THE INVENTION
The invention provides a composition comprising, by weight:
(i) from 1 to 99% ethylene/alpha-olefin metallocene copolymer having a density below 0.900 g/cm
3
; and
(ii) from 99 to 1% of ethylene/alkyl (meth)acrylate radical copolymer.
In one embodiment, the ethylene (meth)acrylate radical copolymer content is comprised between 5 and 25%.
Preferably, the flexural modulus of each copolymer is comprised between 10 and 100 Mpa.
The ratio of their flexural moduli as well as their secant moduli is advantageously greater than 1.
The ethylene/alpha-olefin metallocene copolymer has a polydispersity index of for example between 2 and 5, and preferably between 2 and 3.
The ethylene/alpha-olefin metallocene copolymer has a density for example comprised between 0.900 and 0.880 g/cm
3
.
The ethylene/alpha-olefin metallocene copolymer has an MFI comprised for example between 0.5 and 10, and preferably between 0.8 and 5.
The ethylene/alkyl (meth)acrylate radical copolymer for example comprises, by weight based on the weight of said copolymer, from 5 to 40% of a C1 to C8 alkyl (meth)acrylate.
The ethylene/alkyl (meth)acrylate radical copolymer has an MFI typically comprised between 0.3 and 10.
The invention also provides a film obtained from a composition according to the invention, preferably extruded.
The invention particularly provides an adhesive stretchable film obtained from the composition of the invention.
The invention also provides a process for extruding a composition according to the invention, comprising extruding said composition at a temperature greater than or equal to 200° C., for example between 210 and 230° C., in particular for the production of film.
The invention will now be described in more detail below.
DETAIL DESCRIPTION OF THE INVENTION
The term “ethylene/alpha-olefin metallocene copolymer” as used herein refers to such copolymers obtained by metallocene catalysis and the expressions “plastomers” or “metallocene ethylene copolymer” are equivalent in the description below.
It will be recalled that such metallocene catalysis is a single-site catalysis implementing a catalyst generally constituted by a metal atom between two alkyl cycles bonded to the metal. For the metal, all the metals of transition groups IVA, VA and VIA can be used as well as the lanthanides. Preferred metals are hafnium, zirconium and titanium. For the alkyl cycle, one would generally use cyclopentadiene. Optionally, a co-catalyst or activator such as for example an aluminoxan
Baker & Botts LLP
Elf Atochem S.A.
Tarazano D. Lawrence
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