Coextrusion binder based on cografted metallocene polyethylene

Details Coextrusion binder based on cografted metallocene polyethylene Coextrusion binder based on cografted metallocene polyethylene

2001-03-26

2003-03-04

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...

C525S221000, C525S222000, C525S232000, C525S240000, C525S241000

Reexamination Certificate

active

06528587

ABSTRACT:

DESCRIPTION
The present invention relates to a coextrusion binder based on cografted metallocene polyethylene, to its use for making a multilayer structure and to the structure obtained.
The prior art EP 802 207 has already described binders based on metallocene polyethylene and on polypropylene which are cografted. In this prior art, a blend comprising at least one polyethylene and at least one polypropylene are cografted so as to compensate for the increase in viscosity of the polyethylene by the reduction in viscosity of the polypropylene due to the effect of the radical grafting initiator. This has nothing to do with the present invention, in which a blend of two polyethylenes is cografted.
The prior art WO 97/27259 describes a binder consisting of (a) a polyethylene of the HDPE, LLDPE, VLDPE or LDPE type, (b) 5 to 35% of a grafted metallocene polyethylene and (c) 0 to 35% of an elastomer, the metallocene polyethylene not being cografted.
These binders do not have sufficient hot strength—in particular, the multilayer packaging containing these binders is not good at withstanding heat treatments and thermal stresses such as, for example, pasteurization and hot welding.
The advantage of the binders of the present invention is their ability to withstand these heat treatments and the various types of thermal stresses. Another advantage of the binders of the present invention relates to their manufacture. These binders are usually made by melt grafting and melt blending, and the binder is recovered in the form of granules at the exit of an extruder or of any other equivalent device; the Applicant has found that this granulation was much easier than in the case of the binders of the above prior art.
The present invention relates to a binder comprising:
5 to 35 parts of a polymer (A) which itself consists of a blend of 80 to 20 parts of a metallocene polyethylene (A1) of relative density between 0.865 and 0.915 and of 20 to 80 parts of a non-metallocene LLDPE polyethylene (A2), the blend (A1) and (A2) being cografted by an unsaturated carboxylic acid; and
95 to 65 parts of a polyethylene (B) chosen from ethylene homopolymers or copolymers and elastomers;
the blend of (A) and (B) being such that:
the content of grafted unsaturated carboxylic acid is between 30 and 10
5
ppm,
the MFI (ASTM D 1238 standard:190° C./2.16 kg) is between 0.1 and 10 g/10 min.
According to one embodiment of the binder, the relative density of polyethylene (A2) is between 0.900 and 0.950.
According to one embodiment of the binder, the proportion of the grafting monomer is from 600 to 5000 ppm with respect to the weight of the blend of cografted A1 and A2.
According to one embodiment of the binder, the polyethylene (B) is an LLDPE of relative density between 0.910 and 0.935.
The invention also relates to a coextrusion binder consisting of a blend of 80 to 20 parts of a metallocene polyethylene (A1) of relative density between 0.865 and 0.915 and of 20 to 80 parts of a non-metallocene LLDPE polyethylene (A2), the blend of (A1) and (A2) being cografted by an unsaturated carboxylic acid; the blend of (A1) and (A2) being such that:
the content of grafted unsaturated carboxylic acid is between 30 and 10
5
ppm;
the MFI or melt flow index (ASTM D 1238 standard: 190° C./2.16 kg) is between 0.1 and 10 g/10 minutes.
The expression “unsaturated carboxylic acid” is intended to include functional derivatives as explained below.
The subject of the invention is also a multilayer structure comprising a layer which comprises the binder of any one of the preceding claims and, directly attached to the said layer, a layer (E):
of a nitrogen-containing or oxygen-containing polar resin, such as a polyamide resin, an aliphatic polyketone resin, a saponified ethylene/vinyl acetate copolymer resin (EVOH) or a polyester resin; or
of metal.
According to an embodiment of the structure, there is directly attached to the latter, on the binder side, either a polyolefin layer (F) or a layer of a resin chosen from the resins of the layer (E), or else a metal layer.
The subject of the invention is also a rigid hollow body consisting of a structure as defined above.
The invention also relates to a structure comprising a layer of polyolefin (F), a layer of the binder defined above, a layer of a polyamide resin or of a saponified ethylene/vinyl acetate copolymer (EVOH), a layer of the binder defined above and a layer of polyolefin (F), respectively.
These structures are useful for manufacturing flexible or rigid packaging, such as sachets, bottles or containers. Such packaging can be manufactured by coextrusion, lamination or coextrusion-blow molding.
The invention is also useful for coextruded hoses or pipes and for multilayer fuel tanks for motor vehicles.
The invention will now be described in detail.
With regard to (A1), the term “metallocene polyethylene” is understood to mean the polymers obtained by copolymerizing ethylene with an alpha-olefin, such as propylene, butene, hexene or octene for example, in the presence of a monosite catalyst generally consisting of an atom of a metal which may, for example, be zirconium or titanium and of two cyclic alkyl molecules attached to the metal. More specifically, the metallocene catalysts are usually composed of two cyclopentadiene rings attached to the metal. These catalysts are frequently used with aluminoxanes as cocatalysts or activators, preferably methylaluminoxane (MAO) . Hafnium can also be used as the metal to which the cyclopentadiene is attached. Other metallocenes may include transition metals of Groups IVA, VA and VIA. Metals from the series of lanthanides can also be used.
These metallocene polyethylenes may also be characterized by their ratio {overscore (M
w
)}|{overscore (M
n
)}<3 and preferably <2, in which {overscore (M
w
)} and {overscore (M
n
)} denote the weight-average molar mass and the number-average molar mass, respectively. Also termed metallocene polyethylene are polymers having an MFR (melt flow ratio) of less than 6.53 and a ratio {overscore (M
w
)}|{overscore (M
n
)} greater than the MFR less 4.63. MFR denotes the ratio of the MFI
10
(the MFI under a load of 10 kg) to the MFI
2
(the MFI under a load of 2.16 kg) . Other metallocene polyethylenes are defined by an MFR equal to or greater than 6.13 and an {overscore (M
w
)}|{overscore (M
n
)} ratio of less than or equal to the MFR less 4.63.
Advantageously, the relative density of (A1) is between 0.870 and 0.900.
With regard to polyethylene (A2), this is an ethylene/alpha-olefin copolymer of the LLDPE (linear low-density polyethylene) type which is not of metallocene origin. The alpha-olefins advantageously have from 3 to 30 carbon atoms.
Examples of alpha-olefins having 3 to 30 carbon atoms as possible comonomers comprise propylene, 1-butene, 1-pentene, 3-methyl-1-butene, 1-hexene, 4-methyl-1-pentene, 3-methyl-1-pentene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-octadecene, 1-eicocene, 1-dococene, 1-tetracocene, 1-hexacocene, 1-octacocene and 1-triacontene. These alpha-olefins may be used by themselves or as a blend of two or more of them.
The relative density of (A2) is advantageously between 0.900 and 0.950. The MFI of (A2) is between 0.1 and 8 g/10 min. (190° C./2.16 kg).
The blend of (A1) and (A2) is grafted with an unsaturated carboxylic acid, that is to say (A1) and (A2) are cografted. It would not be outside the scope of the invention to use a functional derivative of this acid.
Examples of unsaturated carboxylic acids are those having 2 to 20 carbon atoms, such as acrylic, methacrylic, maleic, fumaric and itaconic acids. The functional derivatives of these acids comprise, for example, anhydrides, ester derivatives, amide derivatives, imide derivatives and metal salts (such as alkali metal salts) of unsaturated carboxylic acids.
Unsaturated dicarboxylic acids having 4 to 10 carbon atoms and their functional derivatives, particularly their anhydrides, are particularly preferred grafting monomers.
These grafting monomers comprise, for example, maleic, fumaric, i

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