BINDER FOR A MULTILAYER STlZUCTURE
Field of the invention
The present invention relates to a binder for multilayer structures conventionally
5 comprising a metallic layer. This binder is more specifically an extrusion binder based
on cografted polyethylenes and the invention rclates to its use for malting a multilayer
structure and also to the structure obtained.
More particularly, the invention relates to a coating/lamination extrusion binder or
a coatingllamination (co)ext~usionb inder based on polyethylene comprising a mixture
10 of two types of polyethylene, one a metallocene polyethylene and the other a lowdensity
radical polyethylene, said mixture being cografted with an unsaturated
carboxylic acid and this mixture being placed in a low-density radical polyethylene
matrix.
The invention relates to the field of packagings such as sachets, bags, sacks or
15 packets made from these welded films. Nonlimiting examples that may be mentioned
include crisp;biscuit;-confectionery and coffee packets.
Prior art
Such a binder conventionally comprises a polyethylene matrix, conventionally of
20 low-density radical polyethylene type (LDPE), for its processability properties, but this
polymer alone does not adhere correctly to a metal surface, which is why an adhesion
agent that is also capable of improving the mechanical properties of the assembly,
known as a "binder", needs to be added thereto.
EP 1 136 536, filed in the name of the Applicant, is known, which discloses an
25 adhesion agent consisting of a polyethylene mixture, one consisting of a metallocene
polyethylene of particular density and the other consisting of a non-metallocene linear
low-density polyethylene (LLDPE), cografted with an unsaturated carboxylic acid and
more particularly a maleic anhydride. This adhesion agent is placed in a matrix
consisting of a polyethylene.
30 In particular, Exainples 4 and 8 present polyethylene conlpositions comprising a
linear low-density polyethylene and a metallocene polyethylene in a linear polyethylene
matrix (f radical).
Binders of this type are satisfactory from the point of view of the mechanical
properties and the adhesion to metal, but their processability in extrusion
coatingllamination, i.e. their capacity to be melt-&awn in the air gap (distance in the air
before encountering the solid substrate(s)), is very difficult and too often entails "neck-
5 in" problems (reduction of the width of the film associated with the viscoelastic
behavior of the polymer) andlor drawability problems which profoundly compromise
the production of an industrially viable film. Examples 24 and 25 of the table below
review, respectively, the examples of compositions 4 and 8 of said document EP 1 136
536.
10 WO 20041072 200 is also known, which discloses an adhesion agent consisting of
a mixture of polyolefins, one consisting of a metallocene polyethylene of particular
density and the other consisting either of a non-metallocene linear low-density
polyethylene (LLDPE) or of a polypropylene, cografted with an unsaturated carboxylic
acid or a functional derivative of this acid as a grafting monomer. This adhesion agent is
15 placed in a matrix consisting of a polypropylene.
, -
This binder does not show satisfactory adhesion properties on metal and the
processability still remains unacceptable.
Lastly, a final solution is also known, which consists in using terpolymers as
adhesion agent, especially such as an ethylene-isobutyl acrylate-methacrylic acid.
20 However, this solution requires very high installation and production costs since the
production of such a teipolymer must be performed in a high-pressure reactor.
Moreover, such terpolymers are liable to give off unpleasant odors due to the presence
of residual acrylate monomers.
Thus, at the present time, the market is lacking an econon~ic binder that can
25 satisfy all the implementation and fu~ctionality conditions, namely, firstly,
ii~eproachable processability in extrusion coatingllamination (in particular "neck-in"
and drawability limit) and melt flow index (MFI), and, secondly, excellent mechanical
characteristics and adhesion to a metal.
Brief description of the invention
The Applicant has discovered, surprisingly, in contradiction with the teachings of
the prior ai-t (processability and MFI criteria), that it is possible to prepare a mixture
containing an adhesion agent consisting of two polyethylenes of radically different
5 nature cografted with an unsaturated carboxylic acid and containing a low-density
radical polyethylene. This mixture has properties in terms of processability and
adhesion to metal that are superior to those of the con~positionso f the prior art.
The present invention thus relates to a binder for multilayer structures,
10 comprising:
-from 60% to 95%, by weight of the composition, of a polyethylene matrix
chosen kom low-density radical polyethylenes (LDPE),
- from 5% to 40%, by weight of the composition, of a mixture of two
polyethylenes, the first polyethylene consisting of a metallocene polyethylene, cografted
15 with an unsaturated carboxylic acid, the grafting monomer, the unsaturated carboxylic
acid grafts representing more than 0.5% by weight of the mixture, characterized in that
the second polyethylene consists of a low-density radical polyethylene (LDPE) and in
that the MFI or meltflow index (standard ASTM D 1238, at 190°C, under 2.16 kg) is
between 4 and 15 g/10 min.
20
In the text hereinbelow, the term "multilayer" is, without preference, in the plural
or in the singular and denotes a set formed from a plurality of layers.
Other characteristics or embodiments of the invention are presented below:
- advantageously, the first polyethylene is present in the mixture in a proportion of
25 fiorn 50% to 70% by weight of the polyethyle~icm ixture;
- preferably, the MFI or melt flow index of the mixture of two polyethylenes is
between 5 and 10 g/10 min;
- according to a particularly advantageous aspect, the unsaturated carboxylic acid
grafts of the mixture of iwo polyethylenes represent between 0.5% and 2%, preferably
30 between 0.6% and 1.2%, by weight of the polyethylene mixture;
- advantageously, the unsaturated carboxylic acid consists of maleic anhydride;
- according to a possibility offered by the invention, the binder conlprises between
0.1% and 5% of functional additives chosen fiom antiblocking agents, glidants,
antioxidants, fillers, pigments, colorants and processing aids, to lacilitate the
iinplementation of this extrusion-coating or extrusion-lamination composition.
5 Some of these additives may be introduced into the composition in the form of
masterbatches.
The invention especially has the advantages of being able to be performed easily,
without risk of deterioration of the film produced.
10
The present invention also relates to a multilayer structure, comprising a plurality
of adjacent layers including at least one metallic layer, characterized in that the binder
as described above is attached directly to the metallic layer.
Preferably, the metallic layer is a layer of aluminum, iron, copper, tin, nickel,
silver, chromium, gold, zinc or an alloy predominantly containing at least one of these
metals (more than 60% by weight of the alloy). In the text hereinbelow, only a support
made of aluminum was tested and presented herein, but the results collected on this
support are identical, or virtually similar, on the other supports mentioned above.
20
Finally, the invention relates to a process for manufacturing the abovementioned
multilayer structure, comprising a step of preparing the binder described above, said
binder being arranged in the form of a film between a metallic layer and a layer of
polymer, characterized in that the arrangement of said binder is produced by extrusion
25 coating/lamination or by coextrusion coating/lamination.
The description that follows is given for purely illustrative purposes and without
limitation.
Detailed description of the invention
As regards the polyethylene matrix, it is a low-density polyethylene (LDPE)
radical-polymerized at very high pressure (1800 to 3000 bar). Radical low-density
polyethylenes are by definition nonlinear polymers. Low-density polyethylenes are
products that are well known to those skilled in the art and are commercially available.
Low-density polyethylenes have densities of between 0.91 and 0.94.
As regards the first polyethylene of the polyethylene mixture, it is a metallocene
polyethylene.
5 The term "metalloeene polyethylene" denotes polymers obtained by
copolynlerization of ethylene and of alpha-olefin, for instance propylene, butene,
hexene or oetene in the presence of a single-site catalyst generally constituted of a metal
atom that may be, for example, zirconium or titanium and of two cyclic alkyl molecules
linked to the metal. More specifically, metalloeene catalysts are usually composed of
10 two eyclopentadiene rings linked to the metal. These catalysts are frequently used with
aluminoxanes as eoeatalysts or activators, preferably methylaluminoxane (MAO).
Hafnium may also be used as metal to which the eyelopentadiene is attached. Other
metallocenes may include transition metals from groups 1V A, V A and VI A. Metals of
the lanthanide series may also be used.
15 These metalloeene polyethylenes may also be characterized by their ratio MdMn
< 3 and prefixably < 2 in which MMI and Mn denote, respectively, the weight-average
molar mass and the number-average molar mass. The term "metalloeene polyethylene"
also denotes those with an MFR (melt flow ratio) of less than 6.53, and an Mw / Mn
ratio greater than MFR ~ninus4 .63. MFR denotes the ratio of the MFI 10 (MFI under a
20 10 kg load) to the MFI 2 (MFI under a 2.16 kg load). Other metalloeene polyethylenes
are defined by an MFR greater than or equal to 6.13 and an MMJ/ Mn ratio of less than
or equal to MFR minus 4.63.
Advantageously, the density of the first polyethylene of the mixture is between
0.900 and 0.930.
25
As regards the second polyethylene of the mixture, it is a low-density
polyethylene (LDPE) radical-polymerized at very high pressure (1800 to 3000 bar).
Radical low-density polyethylenes are by definition nonlinear polyn~ers. Low-density
polyethylenes are products that are well kno\vn to those skilled in tlie art and are
30 colnmereially available. Low-density polyethple~les have densities of between 0.91 and
0.94.
The mixture of polyethylenes, the first and the second polyethylerle described
above, is grafted with an unsaturated carboxylic acid, i.e. these two polyethylenes are
cografted. It would not constitute a departure Srom the context of the invention to use a
functional derivative of this acid.
5 Examples of unsaturated carboxylic acids are those containing 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 the
unsaturated carboxylic acids.
10 Unsaturated dicarboxylic acids containing 4 to 10 carbon atoms and functional
derivatives thereof, particularly anhydrides thereof, are particularly preferred grafting
monomers.
These grafting monomers comprise, for exan~ple, maleic acid, fumaric acid,
itaconic acid, citraconic acid, allylsuccinic acid, cyclohex-4-ene-l,2-dicarboxylic acid,
15 4-methylcyclohex-4-ene-1,2-dicarboxylic acid, hicyclo(2,2,1)hept-5-ene-2,3-
dicarboxylic acid 'dndx-methylbicyclo(2,2,l)hept-5-ene-2,3-dicarboxylic acid, maleic
anhydride, itaconic anhydride, citraconic anhydride, allylsuccinic anhydride, cyclohex-
4-ene-l,2-dicarboxylic anhydride, 4-methylenecyclohex-4-ene-1,2-dicarboxylic
anhydride, bicyclo(2,2,1)hept-5-ene-2,3-dicarboxylic anhydride and x-
20 inethylbicyclo(2,2,1)hept-5-ene-2,2-dicarboxyic anhydride.
Examples of other grafting monomers cornprise C,-Cs allcyl esters or glycidyl
ester derivatives of the unsaturated carboxylic acids such as methyl acrylate, methyl
mcthacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, butyl methacrylate,
glycidyl acrylate, glycidyl methacrylate, monoethyl maleate, dicthyl maleate,
25 ruonomethyl fumarate, dimethyl furnarate, monorncthyl itaconate and diethyl itaconate;
amidc derivatives of the unsaturated carboxylic acids such as acrylamide,
mcthacrylamide, maleic monoamide, malcic diamide, N-monoethylmaleamide, N,Ndicthylmaleamide,
N-moilobutylmaleamide, N,N-dibutylmalcrunide, fumaric
monoamide, fumaric diamide, N-inonoethylfumaramide, N,N-diethylfurnaramide, N-
30 monobutylfumaramide and N,N-dibutylfur~~aramide; imide derivatives of the
unsaturated carboxylic acids such as maleimide, N-butylmaleimide and Nphcilylinaleimide;
and rnetal salts of the unsaturated carboxylic acids such as sodium
acrylate, sodium methacrylatc, potassium acrylate and potassium methacrylate. Maleic
anhydride is preferred.
Various known processes may be used for grafting a grafting monomer onto the
mixture of the two polyethylenes.
5 For example, this may be performed by heating the polyethylenes, metallocene
polyethylene and radical polyethylene, to high temperature, about 150" to about 30OoC,
in the presence or absence of a solvent, with or without radical generator. Suitable
solvents that may be used in this reaction are benzene, toluene, xylene, chlorobenzene
and eumene, inter alia. Suitable radical generators that may be used comprise t-butyl
10 hydroperoxide, cumene hydroperoxide, diisopropylbenzene hydroperoxide, di-t-butyl
peroxide, di-t-amyl peroxide, t-butylcumyl peroxide, dicumyl peroxide, 1,3-bis(tbutylperoxysopropyl)
benzene, 2,5-dimethyl-2,5-bis(t-buty1peroxy)hexane t-butyl
peroxybenzoate, t-butyl peroxy-2-ethylhexanoate, 0,O-t-butyl-0-(2-ethylhexyl)
monoperoxycarbonate, 0,O-t-amyl-0-(2-ethylhexyl) monoperoxycarbonate, acetyl
15 peroxide, dibenzoyl peroxide, isobutyryl peroxide, bis(3,5,5-trimethylhexanoyl)
peroxide and.methyl ethyl ketone peroxide.
Advantageously, the grafting process consists in extruding the polyethylelle
mixture in a corotating twin-screw extruder in the presence of a radical generator,
maleic anhydride. The temperatwe is chosen so that the reaction takes place in the
20 molten state of the polyethylene mixture and so that the radical generator decomposes
totally in the time allotted to the extrusion. It should be noted that degassing is
performed at the end of the extruder so as to remove from the polyethylene mixture the
deconlposition products of the radical generator and the unreacted monomers.
In the mixture of the iirst and second graft-modifikd polyethylenes, obtained in
25 the abovementioned mamler, the amount of grafting monomer may be chosen in an
appropriate mamler, but it is preferably from 0.5% to 2% and better still from 0.6% to
1.2% relative to the weight of grafted mixture.
The amount of grafted monomer is determilled by assaying the succinic functions
by FTIR (Fourier Transform Infra-Red) spectroscopy. The MFI of the mixture, i.e. of
30 the first and second polyethylenes that have been cografted, is 4 to 15 g110 min,
advai~tageouslyb etween 5 and 10 gI10 min.
The combination between the polyethylene matrix and the abovementioned
mixture of cografted polyethylenes is prcpared in an entirely conventional manner that
is well known to those skilled in the art, either by simple mixing of granules, or via a
step of mixing in the molten state. The thickness of the binder according to the
5 invention, in the form of a film, is generally between 5 and 30 microns (or micrometers
pm), preferably between 5 and 25 microns, more preferably between 8 and 20 microns.
The binder according to the invention may advantageously comprise additives in a
minor proportion, of the order of 0.1% to 5% by weight of the binder. These additives
10 may be antiblocking agents, glidants, antioxidants, fillers, pigments, colorants and
processing aids, to facilitate the implementation of this extrusion-coating or extrusionlamination
composition. Some of these additives may be introduced into the
composition in the form of masterbatches.
15 Production of the formulations of the test compositions:
Thcgrafted polyethylenes and the mixtures of cografted polyethylenes tested were
prepared in a ZSK26MC corotating twin-screw extruder. The grafting monomer used is
maleic anhydride supplied by the company CristalMan and the radical generator is
LuperoxO 101 from the company Arkema. The extruder is fed by means of weight
20 meters. The extrusion conditions were: delivery rate = 46 kgh, temperature = 250°C
and screw speed = 700 rpm. The amounts of malcic anhydride and of Luperox 101
introduced are adjusted as a function of the targeted maleic anhydride content and MFI
(melt flow index). The extruder is equipped with a degassing well which allowed
devolatilization of the residuals at the end of the extruder by means of a liquid-ring
25 pump (P = -0.95 bar in the degassing well). The grafted polyethylene or mixture of
cografted polyethylenes leaving the extruder is cooled on contact with water and then
granulated using a pelletizes.
The grafted polyethylenes and the mixtures of cografted polyethylenes tested were
then conlbined with a low-density polyethylene by simple mixing of granules.
30
The tested binders thus obtained are the following:
Example 1: binder not falling within the context of the invention, comprising 100% of a
low-density polyethylene LDPE2.
Example 2: binder not falling within the context of the invention, comprising 20% of an
adhesion agent consisting of an ethylene-butyl acrylate-acrylic acid tcrpolymer
combined with 80% of a low-density polyethylene LDPE2.
5
Example 3: binder falling within the context of the invention, comprising 10% of an
adhesion agent consisting of a mixture of polyethylene (40% of a low-density
polyethylene LDPEl + 60% of a metallocene polyethylene mPE) cografted to a
proportion of 0.68% with maleic anhydride and having an MFI of 7.1 g110 min,
10 combined with 90% of a low-density polyethylene LDPE2.
Example 4: binder falling within the context of the invention, comprising 20% of an
adhesion agent consisting of a mixture of polyethylene (40% of a low-density
polyethylene LDPEl + 60% of a metallocene polyethylene mPE) cografted to a
15 proportion of 0.68% with maleic anhydride and having an MFI of 7.1 g/10 min,
combined with 80% of a low-density polyethylene LDPE2.
Example 5: binder falling within the context of the invention, comprising 35% of an
adhesion agent consisting of a mixture of polyethylene (40% of a low-density
20 polyethylene LDPEl + 60% of a metallocene polyethylene mPE) cografted to a
proportion of 0.68% with maleic anhydride and having an MFI of 7.1 g110 min,
combined with 65% of a low-density polyethylene LDPE2.
Example 6: binder not falling within the context of the invention, comprising 45% of an
25 adhesion agent consisting of a mixture of polyethylene (40% of a low-density
polyethylene LDPEl + 60% of a metallocene polyethylene mPE) cografted to a
proportion of 0.68% with ~naleic anhydride and having an MFI of 7.1 g/10 min,
combined with 55% of a low-density polyethylene LDPE2.
30 Example 7: binder falling within the context of the invention, comprising 20% of an
adhesion agent consisting of a mixture of polyethylene (60% of a low-density
polyethylene LDPEl + 40% of a metallocene polyethylene mPE) cografted to a
proportion of 0.71% with maleic anhydride and having an MFI of 5.3 gI10 min,
combined with 80% of a low-density polyethylene LDPE2.
Example 8: binder falling within the context of the invention, comprising 20% of an
5 adhesion agent consisting of a mixture of polyethylene (20% of a low-density
polyethylene LDPEl + 80% of a metallocene polyethylene mPE) cografted to a
proportion of 0.66% with maleic anhydride and having an MFI of 9.3 gI10 min,
combined with 80% of a low-density polyethylene LDPE2.
10 Example 9: binder not falling within the context of the invention, comprising 20% of an
adhesion agent consisting of a metallocene polyethylene mPE grafted to a proportion of
0.74% with maleic anhydride and having an MFI of 9.9 gI10 min, combined with 80%
of a low-density polyethylene LDPE2.
15 Example 10: binder not falling within the context of the invention, comprising 20% of
an adhesion agent consisting of a mixture of polyethylene (40% of a linear low-density
polyethylene LLDPE + 60% of a metallocene polyethylene mPE) cografted to a
proportion of 0.69% with maleic anhydride and having an MFI of 6.5 gI10 min,
combined with 80% of a low-density polyethylene LDPE2.
20
Example 11 : binder not falling within the context of the invention, comprising 20% of
an adhesion agent consisting of a low-density polyethylene LDPE2 grafted to a
propoltion of 0.60% with maleic anhydride and having an MFI of 6.0 gll0 min,
combined with 80% of a low-density polyethylene LDPE2.
25
Example 12: binder not falling within the context of the invention, comprising 20% of
an adhesion agent consisting of a mixture of polyethylene (40% of a low-density
polyetl~ylene LDPEl + 60% of a metallocene polyethylene mPE) cografted to a
proportion of 0.68% with maleic anhydride and having an MFI of 7.1 g110 min,
30 combined with 80% of a polypropylene PP.
Exa~nplc 13: binder not falling within the context of the invention, comprising 20% of
an adhesion agent consisting of a mixture of polyethylene (40% of a low-density
polyethylene LDPEl + 60% of a metallocene polyethylene mPE) cografted to a
proportion of 0.41% with maleic anhydride and having an MFI of 9.7 gll0 min,
combined with 80% of a low-density polyethylene LDPEZ.
5 Example 14: binder falling within the context of the invention, comprising 20% of an
adhesion agent consisting of a mixture of polyethylene (40% of a low-density
polyethylene LDPEl + 60% of a metallocene polyethylene mPE) cografted to a
proportion of 0.55% with maleic anhydride and having an MFI of 8.4 g110 min,
combincd with 80% of a low-density polyethylene LDPE2.
10
Example 15: binder falling within the context of the invention, comprising 20% of an
adhesion agent consisting of a mixture of polyethylene (40% of a low-density
polyethylene LDPEl + 60% of a metallocene polycthylene mE'E) cografted to a
proportion of 1.12% with maleic anhydride and having an MFI of 6.6 g110 min,
15 combined with 80% of a low-density polyethylene LDPE2.
Example 16: binder falling within the context of the invention, comprising 20% of an
adhesion agent consisting of a mixture of polyethylene (40% of a low-density
polyethylene LDPEl + 60% of a metallocene polyethylene mPE) cografted to a
20 proportion of 1.28% with maleic anhydride and having an MFI of 6.3 gI10 min,
combined with 80% of a low-density polyethylene LDPE2.
Example 17: binder falling within the context of the invention, comprising 20% of an
adhesion agent consisting of a mixture of polyethylene (40% of a low-density
25 polyethylene LDPEl + 60% of a metallocene polyethylene mPE) cografted to a
propoi-tion of 1.83% with maleic anhydride and having an MFI of 5.5 g110 min,
combined with 80% of a low-density polyethylene LDPE2.
Example 18: binder not falling within the context of the invention, comprising 20% of
30 an adhesion agent consisting of a mixture of polyethylene (40% of a low-density
polyethylene LDPEl + 60% of a metallocene polyethylene mPE) cografted to a
propoltion of 2.18% with ~naleic anhydride and having an MFI of 5.1 g110 min,
combined with 80% of a low-density polyethylene LDPE2.
Exanrplc 19: binder not falling within the context of the invention, comprising 20% of
an adhesion agent consisting of a mixture of polyethylene (40% of a low-density
polyethylene LDPEI + 60% of a metallocene polyethylene mPE) cografted to a
5 proportion of 0.72% with maleic anhydride and having an MFI of 3.1 gI10 min,
combined with 80% of a low-density polyethylene LDPE2.
Example 20: binder falling within the context of the invention, comprising 20% of an
adhesion agent consisting of a mixture of polyethylene (40% of a low-density
10 polyethylene LDPEl + 60% of a metallocene polyethylene mPE) cografted to a
proportion of 0.71% with maleic anhydride and having an MFI of 5.2 gI10 min,
combined with 80% of a low-density polyethylene LDPE2.
Example 21: binder falling within the context of the invention, comprising 20% of an
15 adhesion agent consisting of a mixture of polyethylene (40% of a low-density
polyethylene LDPEI + 60% of a metallocene polyethylene mPE) cografted to a
proportion of 0.62% with maleic anhydride and having an MFI of 8.7 gI10 min,
combined with 80% of a low-density polyethylene LDPE2.
20 Example 22: binder falling within the context of the invention, comprising 20% of an
adhesion agent consisting of a mixture of polyethylene (40% of a low-density
polyethylene LDPE2 + 60% of a metallocene polyethylene mPE) cografted to a
proportion of 0.72% with maleic anhydride and having an MFI of 11.3 gI10 min,
combined with 80% of a low-density polyethylene LDI'E2.
25
Example 23: binder falling within the context of the invention, comprising 20% of an
adhesion agent consisting of a mixture of polyethylene (40% of a low-density
polyethylene LDPE2 + 60% of a metallocene polyethylene mPE) cografted to a
propoi-tion of 0.67% with maleic anhydride and having an MFI of 13.8 gI10 min,
30 combined with 80% of a low-density polyethylene LDPE2.
Exalnple 24: binder not falling within the context of the invention, comprising 20% of
an adhesion agent consisting of a nlixture of polyethylene (40% of a low-density
polyethylene LDPE2 + 60% of a metallocene polyethylene mPE) cografted to a
propoition of 0.61% with maleic anhydride and having an MFI of 17.4 gilO min,
combined with 80% of a low-density polyethylene LDPE2.
The binders tested were coextruded to give 37 pd10 pd50 pm/50 pm
aluminum/binder/LDPE2/PE film structures so as to evaluate their properties of
adhesion to aluminum. These structures were prepared on a collina brand extruder in
extrusion lamination configuration. The extruder is equipped with a "feed block" (2-
layer configuration) and a flat die with a 300 pm air gap and a width of 25 cm (LO).
10 These productions were made at a temperature of 290°C for a line speed of 25 dmin.
Starting materials for the test compositions:
LDPE1: radical low-density polyethylene, with an MFI (190°C, 2.16 kg) :)oT 7.5
g110 rnin and a density of 0.920.
15 LDPE2: radical low-density polyethylene, with an MFI (19OoC, 2.16 kg) of 4 g110
min and a density ,of 0.925.
rnPE1: ethylene-hexene metallocene copolymer, with an MFI (19O0C, 2.16 kg) of
20 g1lO min and a density of 0.915.
d E 2 : ethylene-octene metallocene copolymer, with an MFI (190°C, 2.16 kg) of
20 1 g110 min and a density of 0.870.
mPE3: ethylene-octene metallocene copolymer, with an MFI (19OoC, 2.16 kg) of
1 g110 min and a density of 0.890.
LLDPEI : ethylene-hexene non-metallocene copolymer, with an MFI (1 9OoC, 2.16
kg) of 3.0 g110 min and a density of 0.920.
25 LLDPE2: ethylene-butene non-metallocene copolymer, with an MFI (190°C, 2.16
kg) of 3.0 gI10 min and a density of 0.920.
LLDPE3: ethylene-butene non-metallocene copolyn~erw, ith an MFI (19O0C, 2.16
kg) of 3.0 g110 min and a density of 0.930.
LLDPE4: ethylene-butene non-metallocene copolymer, with an MFI (19OoC, 2.16
30 kg) of 3.0 g110 min and a density of 0.910.
PP: propylene-ethylene copolymer, with an MFI (23OoC, 2.16 kg) of 7 gI10 mi11
and a density of 0.905.
Terpolymer: ethylene-isobutyl acrylate-methacrylic acid terpolymer, with an MFI
(19OoC, 2.16 kg) of 11 gIl0 min and a density of 0.920.
Tests performed:
5 Adhesion test
All the abovementioned con~positions, considered to be of identical thickness,
were tested according to exactly the same referential, namely on the same support and
in the same standardized adhesion test (in accordance with standard IS0 11339).
Strips 15 mm wide were cut from the center of the width and in the direction of
10 extrusion. The polymer coating was separated manually fiom the support over a
distance of a few centimeters, and the two arms thus fieed (aluminum and polymer
coating, respectively) were then each placed in one of the two jaws of a Synergie 200
tensile testing machine from MTS. The peel strength was then evaluated with a peel
speed of 200 mmlmin. Five specimens were tested per adhesive reference. The tests
15 were performed within 15 minutes of implementation (peeling at to) and also after
conditioiiing for 8 days at 23OC and 50% relative humidity (peeling at t8d). Thus, the
adhesion is measured with regard to a peel force.
Processability test
20 Tests were performed on a Dr Colliil brand extruder in coating configuration, in which
the test binder is coated onto an aluminum foil (37 pm). All of these tests were
performed with a temperature profile of 280°C.
An identical screw speed and air gap are chosen for all the tests, filming is then started
and a line speed of 5 mlmin is set. Under these conditions, the width (Lf) and thickness
25 (tf) of the coated filin are noted.
Once thesc paran~eters have been noted, the line speed is increased until the first
instabilities are observed. These instabilities may be in several forms: "melt" rupture or
"draw" resonance, which are well known to those skilled in the art (visible instability on
the edges of the film which leads to a variation on the width). These observations are
30 performed thee times in succession, so as to confirm the results, and a mean value of
this series is taken for exploitatioil of the results.
Drawability limit (nllmin) = line speed at which the start of the instabilities (draw
resonance or melt rupture) appears.
Neck-in (%) = (width of the die - width of the coated film) I width of the die x 100 =
(Lo-Lf)/L" x 100
5
Test results:
NECK-IN (%)
Peel force at to
(N115 mm)
Peel force at
t8d W115 mm)
8
0,4
8
2.2
1.9
9
2.2
1.9
9
2.5
2.9
9
2.7
3
10
2.8
3.1
9
2.2
2.1
9
2.3
2.1
14
2.1
2.3
15
2.1
1.9
8
2.2
2.1
18
1.6
0.4
---
I I
1.9
1.5
10
2.1
1.9
Casnpositions Example 20
content of
grafted lnaleic
anhydride 0.62
(mass%)
Ml'l (gIl0 min
at 190°C under 8.7
2.16 kg)
Example 24
20%
50% mPE2
+ 50%
LI.DPE2
Example 25
20%
50% mPE3
+ 50%
LLDPE3
Drau-ability
limit (t~drnin)
NECK-R\I (%)
Pecl force at 10
(N115 inm)
32
10
2.4
29
13
2.6
27
14
2.5
21
16
2.3
4
20
2 0
3
20
1.9
In general, the following results for the various tests must be obtained in order for
Pcel force at
tad ( N i l 5 mm)
a composition to be satisfactory in the envisaged application:
The drawability limit must be greater than 25 dmin and more preferentially
5 greater than 30 dmin (meters per minute).
The neck-in must be less than 15% and more preferentially less than 10%.
The peel force at to must be greater than 2 N/15 mm (newtons per millimeter) and
more preferentially greater than 2.2 N/15 mm.
The peel force at t 8 days (after eight days) must be greater than 1.8 Nil5 mm and
10 more preferentially greater than 2.3 Nl15 mm.
2'7 3 2.9 2.6 1 .S 1.8
CLAIMS
1. A binder for multilayer structures, comprising:
-from 60% to 95%, by weight of the composition, of a polyethylene matrix
5 chosen fiom low-density radical polyethylenes (LDPE),
-from 5% to 40%, by weight of the composition, of a mixture of two
polyethylenes, the first polyethylene consisting of a metallocene polyethylene, cografted
with an unsaturated carboxylic acid, the grafting monomer, the unsaturated carboxylic
acid grafts representing more than 0.5% by weight of the mixture, characterized in that
10 the second polyethylene consists of a low-density radical polyethylene (LDPE) and in
that the MFI or meltflow index (standard ASTM D 1238, at 190°C, under 2.16 kg) is
between 4 and 15 g/10 min.
2. The binder as claimed in claim 1, characterized in that the first polyethylene is
15 present in the mixture in a proportion of from 50% to 70% by weight of the
polyethylene mixture.
3. The binder as claimed in claim 1 or 2, characterized in that the MFI or melt
flow index of the mixture of two polyethylenes is between 5 and 10 g/10 min.
20
4. The binder as claimed in any one of the preceding claims, characterized in that
the unsaturated carboxylic acid grafts of the mixture of two polyethylenes represent
between 0.5% and 2%, preferably between 0.6% and 1.2%, by weight of the
polyethylene mixture.
25
5. The binder as claimed in any one of the preceding claims, characterized in that
the unsaturated carboxylic acid consists of lnaleic anhydride.
6. The binder as claimed in any one of the preceding claims, characterized in that
30 it comprises between 0.1% and 5% of functional additives chosen fiom antiblocking
agents, glidants, antioxidants, fillers, pigments, colorants and processing aids, to
facilitate the implementation of this extrusion-coating or extrusion-lan~ination
coml~osition. Some of tliese additives liiay be introduced into the co~nposition in tlie
fornl of n~asterbatclies.
7. A multilayer structure, co~nprising a plurality of adjacent layers islcluding at
5 least one metallic layer, cl~aracterized in that the binder as claimed in any one of the
receding claims is attached directly to the nictallic layer.
8. The inultilayer structure as claiiiied ui tlie preceding claim, characterized in
that the metallic layer is a layer of aluminum, iron, copper, tin, 17iclce1, silver, chomium,
10 gold, zinc or an alloy corltaining at least one of these metals.
9. A process for mariulicturi~iga ~nultilayers tructure as claimed in claim 7 or 8,
coinprising a step of preparing the hinder as claimed iii any one of claiins I to 6, said
binder tlie~bi eing a~migedin tile form of a filn between a metallic layer arid a layer of
15 polymer, characterized in that the anangement of said hinder is produced by exbusion
coalinglla~iiinatroi r by coextrusioil coatingllamination.