Note: Descriptions are shown in the official language in which they were submitted.
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MULTILAYER STRUCTURE BASED ON POLYAMIDES AND GRAFT
COPOLYMERS HAVING POLYAMIDE BLOCKS
FIELD OF THE INVENTION
The present invention relates to structures based on polyamides and on graft
copolymers having polyamide blocks. They comprise, in this order, a polyamide
layer,
optionally a tie layer and a layer of graft copolymers having polyamide
blocks. These
structures are useful for producing tanks, containers, bottles, multilayer
films and tubes.
They may be manufactured by coextrusion or coextrusion-blow moulding.
Advantageously, in the above articles the layer of graft copolymers having
polyamide
blocks forms the inner layer in contact with the fluid stored or transported.
One particularly useful application relates to tubes for cooling circuits of
internal combustion engines, such as engines for cars or lorries. The cooling
liquids are
generally aqueous solutions of alcohols such as, for example, ethylene glycol,
diethylene glycol or propylene glycol. These tubes must also have good
mechanical
strength and withstand the engine environment (temperature, possible presence
of oil).
These tubes are manufactured by coextruding the various layers using standard
techniques for thermoplastics. They may be smooth (with a constant diameter)
or
annulate or have annulate parts and smooth parts.
PRIOR ART AND THE TECHNICAL PROBLEM
Patent US SSG0398 discloses tubes for a cooling circuit, these being formed
from an outer polyamide layer and an inner layer chosen from polyolefins,
fluoropolymers, polyesters and EVAs (ethylene/vinyl acetate copolymers).
Patent US 5716684 discloses tubes for a cooling circuit, these being formed
from an outer polyamide layer and an inner PVDF layer. A tie may be placed
between
these two layers.
Patent US 570G8G4 discloses tubes for a cooling circuit, these being formed
from an outer polyamide layer and an inner layer either made of PVDF or of a
polyolefin or of a polyolefin grafted by a carboxylic acid anhydride. A tie
may be
placed between these two layers.
Patent US 5850855 discloses tubes for a cooling circuit, these consisting, in
this
order, of an outer layer of a polyamide having amine terminal groups, a layer
of
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polyethylene grafted by malefic anhydride and an inner layer made of a
polyolefm or of
HDPE (high-density polyethylene) grafted by silanes. According to one
embodiment,
they consist, in this order, of an outer layer of a polyamide having amine
terminal
groups, a layer of a polypropylene grafted by malefic anhydride and an inner
layer which
is a blend of polypropylene and an EPDM elastomer (ethylene-propylene-dime
elastomer).
The tubes that have an inner layer made of a fluoropolymer are highly
resistant
to the cooling liquid but are very expensive and difficult to extrude.
Graft copolymers having polyamide blocks have now been found that are
particularly resistant to the cooling liquid even at high temperature. These
polymers are
known per se, but structures based on polyamides and on these polymers have
never
been disclosed.
Patent US 3976720 discloses graft copolymers having polyamide blocks and
their use as a compatibilizer in polyamide/polyolefm blends. The process
starts by
polymerizing caprolactam in the presence of N-hexylamine in order to obtain a
PA-6
having an amine end group and an alkyl end group. This PA-6 is then attached
to a
backbone formed from an ethylene/maleic anhydride copolymer by reacting the
anhydride with the amine end group of the PA-6. A graft copolymer having
polyamide
blocks is thus obtained, this being used in an amount from 2 to 5 parts by
weight in
order to compatibilize blends comprising 75 to 80 parts of PA-6 and 20 to 25
parts of
high-density polyethylene (HDPE). In these blends, the polyethylene is
dispersed in the
form of 0.3 to 0.5 pm nodules in the polyamide.
Patent US 3963799 is very similar to the previous one; this specifies that the
flexural modulus of the PA-6/HDPE/compatibilizer blends is around 210 000 psi
to
350 000 psi, i.e. 1 400 to 2 200 MPa.
Patent EP 1036817 discloses graft copolymers similar to those described in the
aforementioned US patents and their use as a primer or a binder for inks or
paints on a
polyolefin substrate. For these uses, the copolymers are applied as a solution
in toluene.
Patent US 5342886 discloses polymer bends comprising a compatibilizer and
more particularly polyamide/polypropylene blends. The compatibilizer is formed
from a
polypropylene backbone on which polyamide grafts are attached. This
compatibilizer is
prepared from a polypropylene homopolymer or copolymer (the backbone) onto
which
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malefic anhydride is grafted. Prepared separately is a monoamine-terminated
polyamide,
that is to say a polyamide having an amine end group and an alkyl end group.
The
monoamine-terminated polyamide is attached, by melt blending, to the
polypropylene
backbone by reaction between the amine functional group and the malefic
anhydride.
Patent application WO 0228959 discloses blends comprising, by weight, the
total being 100%, 1 to 100% of a graft copolymer having polyamide blocks
formed
from a polyolefin backbone and from, on average, at least one polyamide graft
in which:
~ the grafts are attached to the backbone by the residues of an
unsaturated monomer (X) having a functional group capable of reacting with a
polyamide having an amine end group;
~ the residues of the unsaturated monomer (X) are attached to the
backbone by grafting or copolymerization via its double bond;
~ 99 to 0% of a flexible polyolefin having an elastic modulus in
bending of less than 150 MPa at 23°C and having a crystalline melting
point of
between 60°C and 100°C.
These blends are useful for making adhesives, films, tarpaulins and
geomembranes, produced by extrusion, calendering or
thermosheathing/thermoforming,
and protective layers for electrical cables and skins using the technique of
slush
moulding.
BRIEF DESCRIPTION OF THE INVENTION
The present invention relates to a multilayer structure based on polyamides
and
graft copolymers having polyamide blocks, comprising, in this order:
a) a first layer ( 1 ) formed from a polyamide (A) or else a polyamide
(A)/polyolefin (B) blend having a polyamide matrix;
b) optionally, a tie layer (2a);
c) a layer (2) based on a graft copolymer having polyamide blocks, formed
from a polyolefin backbone and from at least one polyamide graft in which:
~ the grafts are attached to the backbone by the residues of an
unsaturated monomer (X) having a functional group capable of reacting with a
polyamide having an amine end group;
~ the residues of the unsaturated monomer (X) are attached to the
backbone by grafting or copolymerization via its double bond;
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~ the layers (1), (2a) and (2) being successive and adhering to one
another in their respective contact region.
According to one embodiment, the structure includes a polyamide or polyolefin
layer (3), this layer being placed aside the layer (2), and an optionally tie
layer (3a)
being placed between the layer (2) and the layer (3).
These structures are useful for making tanks, containers, bottles, multilayer
films and tubes. They may be manufactured by coextrusion or coextrusion-blow
moulding.
The invention also relates to these tanks, containers, bottles, multilayer
films
and tubes.
Advantageously, in these abovementioned articles, the layer (2) of graft
copolymers having polyamide blocks or the layer (3) forms the inner layer in
contact
with the stored or transported fluid.
The invention also relates to these tanks, containers, bottles, multilayer
films
and tubes in which the layer (2) of graft copolymers having polyamide blocks
or the
layer (3) forms the inner layer in contact with the stored or transported
fluid.
One particularly useful application relates to tubes for the cooling circuits
of
internal combustion engines, such as the engines for cars or lorries.
According to another embodiment, the invention also relates to multilayer
articles such as tanks, containers, bottles, films and tubes formed from the
material of
the above layer (2).
The invention also relates to the use of these articles.
DETAILED DESCRIPTION OF THE INVENTION
With regard to the layer (1) made of polyamide (A), the term "polyamide" is
understood to mean products resulting from the condensation:
- of one or more amino acids, such as aminocaproic, 7-aminoheptanoic,
11-aminoundecanoic and 12-aminododecanoic acid or of one or more lactams, such
as
caprolactam, oenantholactam and lauryllactam;
- of one or more salts or mixtures of diamines such as hexamethylenediamine,
dodecamethylenediamine, metaxylenediamine, bis(p-aminocyclohexyl)methane and
trimethylhexamethylenediamine with diacids such as isophthalic, terephthalic,
adipic,
azelaic, suberic, sebacic and dodecanedicarboxylic acids.
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As examples of polyamides, mention may be made of PA-6 and PA-6,6.
It may also be advantageous to use copolyamides. Mention may be made of the
copolyamides resulting from the condensation of at least two alpha,
omega-aminocarboxylic acids or of two lactams or of a lactam and of an alpha,
5 omega-aminocarboxylic acid. Mention may also be made of the copolyamides
resulting
from the condensation of at least one alpha, omega-aminocarboxylic acid (or a
lactam),
at least one diamine and at least one dicarboxylic acid.
As examples of lactams, mention may be made of those which have from 3 to 12
carbon atoms on the main ring and are possibly substituted. Mention may be
made, for
example, of (3,(3-dimethylpropriolactam, a,a-dimethylpropriolactam,
amylolactam,
caprolactam, capryllactam and lauryllactam.
As examples of alpha, omega-aminocarboxylic acids, mention may be made of
aminoundecanoic acid and arninododecanoic acid. As examples of dicarboxylic
acids,
mention may be made of adipic acid, sebacic acid, isopthalic acid, butanedioic
acid,
1,4-cyclohexyldicarboxylic acid, terephthalic acid, the sodium or lithium salt
of
sulphoisophthalic acid, dimerized fatty acids (these dimerized fatty acids
have a dimer
content of at least 98% and are preferably hydrogenated) and dodecanedioic
acid
HOOC-(CH2) 10-COOH.
The diamine may be an aliphatic diamine having from 6 to 12 carbon atoms; it
may be a saturated cyclic and/or arylic diamine. As examples, mention may be
made of
hexamethylenediamine, piperazine, tetramethylenediamine, octamethylenediamine,
decamethylenediamine, dodecamethylenediamine, 1,5-diaminohexane,
2,2,4-trimethyl-1,6-diaminohexane, diamine polyols, isophoronediamine (IPD),
methylpentamethylenediamine (MPDM), bis(aminocyclohexyl)methane (BACM), and
bis(3-methyl-4-aminocyclohexyl) methane (BMACM).
As examples of copolyamides, mention may be made of copolymers of
caprolactam and lauryllactam (PA-6/12), copolymers of caprolactam, adipic acid
and
hexamethylenediamine (PA-6/6,6), copolymers of caprolactam, lauryllactam,
adipic
acid and hexamethylenediamine (PA 6/12/6,6), copolymers of caprolactam,
lauryllactam, 11-aminoundecanoic acid, azelaic acid and
hexamethylenediamine (PA-6/6,9/11/12), copolymers of caprolactam,
lauryllactam,
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11-amino undecanoic acid, adipic acid and hexamethylenediamine (PA-
6/6,6/11/12),
and copolymers of lauryllactam, azelaic acid and hexamethylenediamine (PA-
6,9/12).
Advantageously, the copolyamide is chosen from PA-6/12 and PA-6/6,6.
It is also possible to use polyamide blends. Advantageously, the relative
viscosity of the polyamides, measured as 1% solution in sulphuric acid at
20°C, is
between 1.5 and 6.
It would not be outside the scope of the invention to replace part of the
polyamide (A) with a copolymer having polyamide blocks and polyether blocks,
that is
to say by using a blend comprising at least one of the above polyamides and at
least one
copolymer having polyamide blocks and polyether blocks.
The copolymers having polyamide blocks and polyether blocks result from the
copolycondensation of polyamide blocks having reactive ends with polyether
blocks
having reactive ends, such as, inter alias
1) polyamide blocks having diamine chain ends with polyoxyalkylene
blocks having dicarboxylic chain ends;
2) polyamide blocks having dicarboxylic chain ends with polyoxyalkylene
blocks having diamine chain ends, obtained by cyanoethylation and
hydrogenation of
aliphatic dihydroxylated alpha, omega-polyoxyalkylene blocks called
polyetherdiols;
3) polyamide blocks having dicarboxylic chain ends with polyetherdiols,
the products obtained being, in this particular case, polyetheresteramides.
Advantageously, these copolymers are used.
Polyamide blocks having dicarboxylic chain ends derive, for example, from the
condensation of alpha, omega-aminocarboxylic acids, of lactams or of
dicarboxylic
acids and diamines in the presence of a chain-stopping dicarboxylic acid.
The polyether may, for example, be a polyethylene glycol (PEG), a
polypropylene glycol (PPG) or a polytetramethylene glycol (PTMG). The latter
is also
called polytetrahydrofuran (PTHF).
The number-average molar mass M ~ of the polyamide blocks is between 300
and 1 S 000 and preferably between 600 and 5000. The mass M " of the polyether
blocks
is between 100 and 6000 and preferably between 200 and 3000.
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Polymers having polyamide blocks and polyether blocks may also include
randomly distributed units. These polymers may be prepared by the simultaneous
reaction of the polyether and polyamide-block precursors.
For example, it is possible to react polyetherdiol, a lactam (or an alpha,
omega-
amino acid) and a chain-stopping diacid in the presence of a small amount of
water. A
polymer is obtained having essentially polyether blocks and polyamide blocks
of very
variable length, but also the various reactants, having reacted in a random
fashion,
which are distributed randomly along the polymer chain.
These polymers having polyamide blocks and polyether blocks, whether they
derive from the copolycondensation of polyamide and polyether blocks prepared
beforehand or from a one-step reaction, have, for example, Shore D hardnesses
which
may be between 20 and 75 and advantageously between 30 and 70 and an intrinsic
viscosity of between 0.8 and 2.5 measured in rneta-cresol at 25°C for
an initial
concentration of 0.8 g/100 ml. The MFIs may be between 5 and 50 (235°C,
with a load
of 1 kg).
The polyetherdiol blocks are either used as such and copolycondensed with
polyamide blocks having carboxylic ends or they are aminated in order to be
converted
into diamine polyethers and condensed with polyamide blocks having carboxylic
ends.
They may also be mixed with polyamide precursors and a chain stopper in order
to
make polyamide-block and polyether-block polymers having randomly distributed
units.
Polymers having polyamide and polyether blocks are described in Patents US
4 331 786, US 4 11 S 475, US 4 195 O1 S, US 4 839 441, US 4 864 014, US 4 230
838
and US 4 332 920.
The ratio of the amount of copolymer having polyamide blocks and polyether
blocks to the amount of polyamide is, by weight, advantageously between 10/90
and
60/40. Mention may be made, for example, of blends of (i) PA6 and (ii) a
copolymer
having PA-6 blocks and PTMG blocks and blends of (i) PA-6 and (ii) a copolymer
having PA-12 blocks and PTMG blocks.
This polyamide (A) is advantageously a PA-11 or a PA-12. Advantageously, this
polyamide of the layer (1) is plasticized by standard plasticizers, such as n-
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butylbenzenesulfonamide (BBSA), the copolymers comprising polyamide blocks and
polyether blocks, and maleated EPRs and EPRs.
With regard to the layer (1) made of a polyamide (A)/polyolefin (B) blend
having a polyamide matrix, the polyamide may be chosen from the above
polyamides.
Advantageously, PA-6, PA-6,6 and PA-6/6,6 are used.
As regards the polyolefin (B) of the polyamide (A)/polyolefin (B) blend having
a polyamide matrix, this may be functionalized or unfunctionalized or may be a
blend of
at least one functionalized polyolefin and/or at least one unfunctionalized
polyolefin. To
simplify matters, functionalized polyolefins (B1) and unfunctionalized
polyolefins (B2)
are described below.
An unfunctionalized polyolefin (B2) is conventionally a homopolymer or an
alpha-olefin or diolefin copolymer, such as, for example, ethylene, propylene,
1-butene,
1-octene and butadiene. By way of example, mention may be made of
- polyethylene homopolymers and copolymers, particularly LDPE, HDPE,
LLDPE (linear low-density polyethylene), VLDPE (very low-density polyethylene)
and
metallocene polyethylene;
- propylene homopolymers or copolymers;
- ethylene/alpha-olefin copolymers, such as ethylene/propylene, EPR (the
abbreviation for ethylene/propylene rubber) and ethylene/propylene/diene
(EPDM);
- styrene/ethylene-butene/styrene (SEBS), styrene/butadiene/styrene (SBS),
styrene/isoprene/styrene (SIS) and styrene/ethylene-propylene/styrene (SEPS)
block
copolymers;
- copolymers of ethylene with at least one product chosen from salts or esters
of
unsaturated carboxylic acids, such as alkyl (meth)acrylate (for example methyl
acrylate), or vinyl esters of saturated carboxylic acids, such as vinyl
acetate (EVA), the
proportion of comonomer possibly being up to 40% by weight.
The functionalized polyolefin (B 1 ) may be an alpha-olefin polymer having
reactive groups (functional groups); such reactive groups are acid, anhydride
or epoxy
functional groups. As an example, mention may be made of the above polyolefins
(B2)
grafted or copolymerized or terpolymerized by unsaturated epoxides such as
glycidyl
methacrylate or by carboxylic acids or the corresponding salts or esters, such
as
(meth)acrylic acid (the latter possibly being completely or partially
neutralized by
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metals such as Zn, etc.), or else by carboxylic acid anhydrides, such as
malefic
anhydride. A functionalized polyolefm is, for example, a PE/EPR blend, the
weight
ratio of which may vary widely, for example between 40/60 and 90/10, the said
blend
being cografted with an anhydride, especially malefic anhydride, with a
grafting ratio of,
for example, 0.01 to 5% by weight.
The functionalized polyolefin (B 1 ) may be chosen from the following
(co)polymers grafted with malefic anhydride or glycidyl methacrylate, in which
the
degree of grafting is, for example, from 0.01 to 5% by weight:
- PE, PP, copolymers of ethylene with propylene, butene, hexene or octene,
containing for example from 35 to 80% ethylene by weight;
- ethylene/alpha-olefin copolymers, such as ethylene/propylene, EPR (the
abbreviation for ethylene/propylene rubber) and ethylene/propylene/diene
(EPDM);
- styrene/ethylene-butene/styrene (SEBS), styrene/butadiene/styrene (SBS),
styrene/isoprene/styrene (SIS) and styrene/ethylene-propylene/styrene (SEPS)
block
copolymers;
- ethylene-vinyl acetate copolymers (EVA) containing up to 40% vinyl acetate
by weight;
- ethylene-alkyl (meth)acrylate copolymers containing up to 40% alkyl
(meth)acrylate by weight; and
- ethylene-vinyl acetate (EVA)/alkyl (meth)acrylate copolymers containing up
to
40% by weight of comonomers.
The functionalized polyolefin (B 1 ) may also be chosen from
ethylene/propylene
copolymers comprising predominantly propylene, these copolymers being grafted
by
malefic anhydride and then condensed with a monoamine polyamide (or a
polyamide
oligomer) (products described in EP-A-0 342 066).
The functionalized polyolefin (B1) may also be a copolymer or terpolymer of at
least the following units: (1) ethylene; (2) an alkyl (meth)acrylate or a
vinyl ester of a
saturated carboxylic acid and (3) an anhydride, such as malefic anhydride or
(meth)acrylic acid or epoxy such as glycidyl (meth)acrylate.
As examples of functionalized polyolefins of the latter type, mention may be
made of the following copolymers, in which ethylene preferably represents at
least 60%
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by weight and in which the termonomer (the functional group) represents, for
example,
from 0.1 to 10% by weight of the copolymer:
- ethylene/alkyl (meth)acrylate/(meth)acrylic acid or malefic anhydride or
glycidyl methacrylate copolymers;
5 - ethylene/vinyl acetate/maleic anhydride or glycidyl methacrylate
copolymers;
and
- ethylene/vinyl acetate or alkyl (meth)acrylate/(meth)acrylic acid or malefic
or
glycidyl methacrylate anhydride copolymers.
In the above copolymers, the (meth)acrylic acid may be salified with Zn or Li.
10 The term "alkyl (meth)acrylate" in (B 1 ) or (B2) denotes C 1 to C8 alkyl
acrylates
and methacrylates, these possibly being chosen from methyl acrylate, ethyl
acrylate, n-
butyl acrylate, isobutyl acrylate, 2-ethylhexyl acrylate, cyclohexyl acrylate,
methyl
methacrylate and ethyl methacrylate.
Moreover, the aforementioned polyolefms (B 1 ) may also be crosslinked by any
process or suitable agent (diepoxy, diacid, peroxide, etc.); the term
"functionalized
polyolefin" also includes blends of the aforementioned polyolefins with a
difunctional
reactant, such as a diacid, dianhydride, diepoxy, etc., capable of reacting
with them, or
blends of at least two functionalized polyolefins which can react together.
The copolymers mentioned above, (B1) and (B2), may be random copolymers or
block copolymers and have a linear or branched structure.
The molecular weight, the MFI and the density of these polyolefms may also
vary widely, as a person skilled in the art will appreciate. MFI is the
abbreviation for
Melt Flow Index, which is measured according to the ASTM 1238 standard.
Advantageously, the unfunctionalized polyolefins (B2) are chosen from
polypropylene homopolymers or copolymers and any ethylene homopolymer or
copolymer of ethylene with a comonomer of the higher alpha-olefin type, such
as
butene, hexene, octene or 4-methyl-1-pentene. Mention may be made, for
example, of
PP, high-density PE, medium-density PE, linear low-density PE, low-density PE
and
very low-density PE. These polyethylenes are known to a person skilled in the
art as
being produced according to a "radical" process, using catalysis of the
"Ziegler" type
or, more recently, using catalysis referred to as "metallocene" catalysis.
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Advantageously, the functionalized polyolefins (BI) are chosen from any
polymer comprising alpha-olefin units and units carrying polar reactive
functional
groups, such as epoxy, carboxylic acid or carboxylic acid anhydride functional
groups.
As examples of such polymers, mention may be made of ethylene-alkyl acrylate-
malefic
anhydride or glycidyl methacrylate terpolymers, such as the Applicant's
LOTADER°
polymers, or polyolefins grafted by malefic anhydride, such as the Applicant's
OREVAC° polymers, and ethylene-alkyl acrylate-(meth)acrylic acid
terpolymers or
ethylenevinyl acetate-malefic anhydride terpolymers. Mention may also be made
of
polypropylene homopolymers or copolymers grafted by a carboxylic acid
anhydride and
then condensed with polyamides or monoamine polyamide oligomers.
The MFI of (A) and the MFIs of (Bl) and (B2) may be chosen within a wide
range; however, it is recommended, for facilitating the dispersion of (B),
that the
viscosities of (A) and (B) differ little.
For small proportions of (B), for example 10 to 15 parts, it is sufficient to
use an
unfunctionalized polyolefin (B2). The proportion of (B2) and (BI) in the phase
(B)
depends on the amount of functional groups present in (B 1 ) and on their
reactivity.
Advantageously, (BI)/(B2) weight ratios ranging from 5/35 to 15/25 are used.
It is also
possible to use only a blend of polyolefins (BI ) in order to obtain
crosslinking.
The polyamide (A)/polyolefin (B) blend has a polyarnide matrix. Usually it is
sufficient for the proportion of polyamide of the polyamide (A)/polyolefin (B)
blend to
be at least 40% by weight and preferably between 40 and 75% and better still
between
50 and 75% in order for there to be a polyamide matrix. This is the case of
the first three
preferred embodiments of the polyamide/polyolefm blend. In the fourth
preferred
embodiment, the polyolefin phase is crosslinked, thereby ensuring that there
is no phase
inversion and the material remains with a polyamide matrix.
According to a first preferred embodiment of the polyamide (A)/polyolefin (B)
blend having a polyamide matrix, the polyolefin (B) comprises (i) a high-
density
polyethylene (HDPE) and (ii) a blend of a polyethylene (C1) and of a polymer
(C2)
chosen from elastomers, very low-density polyethylenes and ethylene
copolymers, the
(C1) + (C2) blend being cografted by an unsaturated carboxylic acid or an
unsaturated
carboxylic acid anhydride.
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According to a variant of this first embodiment of the invention, the
polyolefin
(B) comprises (i) a high-density polyethylene (HDPE), (ii) a polymer (C2)
chosen from
elastomers, very low-density polyethylenes and ethylene copolymers (C2) being
grafted
by an unsaturated carboxylic acid, and {iii) a polymer (C'2) chosen from
elastomers,
very low-density polyethylenes and ethylene copolymers.
According to a second preferred embodiment of the polyarnide (A)/polyolefin
(B) blend having a polyamide matrix, the polyolefin (B) comprises (i)
polypropylene
and (ii) a polyolefin which results from the reaction of a polyamide (C4) with
a
copolymer (C3) comprising propylene and an unsaturated monomer X, which is
grafted
or copolymerized.
According to a third preferred embodiment of the polyamide (A)/polyolefin (B)
blend having a polyamide matrix, the polyolefin (B) comprises (i) a
polyethylene of the
EVA, LLDPE, VLDPE or metallocene type and (ii) an
ethylene/alkyl (meth)acrylate/maleic anhydride copolymer.
According to a fourth preferred embodiment of the polyamide (A)/polyolefin
(B) blend having a polyamide matrix, the polyolefin comprises two
functionalized
polymers comprising at least 50 mol% of ethylene units and able to react to
form a
crosslinked phase. According to a variant, the polyamide (A) is chosen from
blends of
(i) a polyamide and (ii) a copolymer having PA-6 blocks and PTMG blocks, and
blends
of (i) a polyamide and (ii) a copolymer having PA-12 blocks and PTMG blocks,
the
ratio of the amounts of copolymer to polyamide by weight being between 10/90
and
60/40.
With regard to the tie layers (2a) and (3a), these thus define any product
allowing good adhesion between the layers in question. The tie is
advantageously
chosen from functionalized polyolefins and from copolyamides.
As an example of ries based on functionalized polyolefins, mention may be
made o~
- polyethylene, polypropylene, copolymers of ethylene with at least one alpha-
olefin, blends of these polymers, all these polymers being grafted by
unsaturated
carboxylic acid anhydrides such as, for example, malefic anhydride, or blends
of these
grafted polymers and these ungrafted polymers;
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- copolymers of ethylene with at least one product chosen from (i) unsaturated
carboxylic acids, their salts or their esters; (ii) vinyl esters of saturated
carboxylic acids;
(iii) unsaturated dicarboxylic acids, their salts, their esters, their
semiesters or their
anhydrides; (iv) unsaturated epoxides; it being possible for these copolymers
to be
grafted by unsaturated dicarboxylic acid anhydrides such as malefic anhydride
or
unsaturated epoxides such as glycidyl methacrylate.
As regards the copolyamide-type ties, that can be used in the present
invention,
these have a melting point (DIN 53736B standard) of between 60 and
200°C and their
relative solution viscosity may be between 1.3 and 2.2 (DIN 53727 standard;
solvent:
m-cresol; concentration: 0.5 g/100 ml; temperature: 25°C; viscometer:
Ubbelohde).
Their melt rheology is preferably similar to that of the materials of the
outer layer and of
the inner layer.
The copolyamides come, for example, from the condensation of alpha,
omega-aminocarboxylic acids, of lactams or of dicarboxylic acids and diamines.
According to a first type, the copolyamides result from the condensation of at
least two alpha, omega-aminocarboxylic acids or of at least two lactams having
from 6
to 12 carbon atoms or of a lactam and of an aminocarboxylic acid not having
the same
number of carbon atoms possibly in the presence of a chain stopper which may,
for
example, be a monoamine or a diarnine or a monocarboxylic acid or a
dicarboxylic acid.
Among chain stoppers, mention may especially be made of adipic acid, azelaic
acid,
stearic acid and dodecanediamine. The copolyamides of this first type may also
include
units which are residues of diamines and dicarboxylic acids.
As examples of dicarboxylic acids, mention may be made of adipic acid,
nonanedioic acid, sebacic acid and dodecanedioic acid.
As examples of alpha, omega-aminocarboxylic acids, mention may be made of
aminocaproic acid, aminoundecanoic acid and aminododecanoic acid.
As examples of lactams, mention may be made of caprolactam and
lauryllactam (2-azacyclotridecanone).
According to a second type, the capolyamides result from the condensation of
at
least one alpha, omega-aminocarboxylic acid (or a lactam), at least one
diamine and at
least one dicarboxylic acid. The alpha, omega-aminocarboxylic acid, the lactam
and the
dicarboxylic acid may be chosen from those mentioned above.
CA 02461389 2004-03-19
14
The diamine may be a branched, linear or cyclic aliphatic diamine or else an
arylic diamine.
As examples, mention may be made of hexamethylenediarnine, piperazine,
isophoronediamine (IPD), methylpentamethylenediamine (MPDM), bis(aminocyclo-
hexyl)methane (BACM) and bis(3-methyl-4-aminocyclo-hexyl)methane (BMACM).
The processes for manufacturing the copolyamides are known from the prior
art and these copolyamides may be manufactured by polycondensation, for
example in
an autoclave.
According to a third type, the copolyamides are a blend of a 6/12 copolyamide
rich in 6 and of a 6/12 copolyarnide rich in 12. As regards the blend of 6/12
copolyamides, one comprising by weight more 6 than 12 and the other more 12
than 6,
the 6/12 copolyamide results from the condensation of caprolactam with
lauryllactam. It
is clear that "6" denotes the units derived from caprolactam and "12" denotes
the units
derived from lauryllactam. It would not be outside the scope of the invention
if
caprolactam were to be replaced completely or partly with aminocaproic acid,
and
likewise, in the case of lauryllactam, this may be replaced with
aminododecanoic acid.
These copolyamides may include other units provided that the ratios of the
proportions
of 6 and 12 are respected.
Advantageously, the copolyamide rich in 6 comprises 60 to 90% by weight of
6 for 40 to 10% of 12, respectively.
Advantageously, the copolyamide rich in 12 comprises 60 to 90% by weight of
12 for 40 to 10% of 6, respectively.
As regards the proportions of the copolyamide rich in 6 and of the copolyamide
rich in 12, these may be, by weight, from 40/60 to 60/40 and preferably 50/50.
These blends of copolyamides may also include up to 30 parts by weight of
other grafted polyolefins or (co)polyamides per 100 parts of the copolyamides
rich in 6
and rich in 12.
These copolyamides have a melting point (DIN 53736B standard) of between
60 and 200°C and their relative solution viscosity may be between 1.3
and 2.2 (DIN
53727; solvent: m-cresol; concentration: 0.5 g/100 ml; temperature:
25°C; viscometer:
Ubbelohde). Their melt rheology is preferably similar to that of the adjacent
layers.
These products are manufactured by standard polyamide techniques. Processes
are
CA 02461389 2004-03-19
described in the following Patents: US 4424864, US 4483975, US 4774139,
US 5459230, US 5489667, US 5750232 and US 5254641.
With regard to the graft copolymer having polyamide blocks, this may be
obtained by reaction between a polyamide having an amine end group and the
residues
5 of an unsaturated monomer X attached by grafting or copolymerization on a
polyolefin
backbone.
This monomer X may, for example, be an unsaturated epoxide or an
unsaturated carboxylic acid anhydride. The unsaturated carboxylic acid
anhydride may
be chosen, for example, from malefic, itaconic, citraconic, allylsuccinic,
cyclohex-4-ene-
10 1,2-dicarboxylic, 4-methylcyclohex-4-ene-1,2-dicarboxylic,
bicyclo[2.2.1]hept-5-ene-
2,3-dicarboxylic and x-methylbicyclo[2.2.1]hept-5-ene-2,3-dicarboxylic
anhydrides.
Advantageously, malefic anhydride is used. It would not be outside the scope
of the
invention to replace all or part of the anhydride with an unsaturated
carboxylic acid such
as, for example, (meth)acrylic acid. As examples of unsaturated epoxides,
mention may
15 be made of:
- aliphatic glycidyl esters and ethers, such as allyl glycidyl ether, vinyl
glycidyl ether, glycidyl maleate, glycidyl itaconate, glycidyl (meth)acrylate;
and
- alicyclic glycidyl esters and ethers, such as 2-cyclohex-1-yl glycidyl
ether, diglycidyl cyclohexene-4,5-dicarboxylate, glycidyl cyclohexene-4-
carboxylate,
glycidyl 2-methyl-5-norbornene-2-carboxylate and diglycidyl endo-cis-
bicyclo[2.2.1]
hept-5-ene-2,3-dicarboxylate.
With regard to the polyolefin backbone, the polyolefins may be the
unfunctionalized polyolefins mentioned above in the polyamide (A)/polyolefin
(B)
blends.
Advantageously, the polyolefin backbones on which the residues of X are
attached are polyethylenes grafted by X or ethylene-X copolymers obtained, for
example, by radical polymerization.
With regard to the polyethylenes on which X is grafted, these are understood
to
mean polyethylene homopolyrners or copolymers.
As homopolymers, mention may be made of:
CA 02461389 2004-03-19
16
- alpha-olefins, advantageously those having from 3 to 30 carbon atoms.
Examples were mentioned above. These alpha-olefins may be used by themselves
or as
a mixture of two or more than two of them;
- unsaturated carboxylic acid esters, such as for example
alkyl(meth)acrylates,
the alkyls possibly having up to 24 carbon atoms; examples of alkyl acrylates
or
methacrylates are especially methyl acrylate, ethyl acrylate, n-butyl
acrylate, isobutyl
acrylate and 2-ethylhexyl acrylate;
- vinyl esters of saturated carboxylic acids, such as for example vinyl
acetate or
vinyl propionate;
- dimes such as, for example, 1,4-hexadiene;
- the polyethylene may include several of the above comonomers.
Advantageously, the polyethylene, which may be a blend of several polymers,
comprises at least 50% and preferably more than 75% (in mols) of ethylene and
its
density may be between 0.86 and 0.98 g/cm3. The MFI (viscosity index of
190°C/2.16 kg) is advantageously between 5 and 100 g/10 min.
As examples of polyethylenes, mention may be made of
- low-density polyethylene (LDPE);
- high-density polyethylene (HDPE);
linear low-density polyethylene (LLDPE);
- very low-density polyethylene (VLDPE);
- polyethylene obtained by metallocene catalysis;
- EPR (ethylene - propylene rubber) elastomers;
- EPDM (ethylene-propylene - dime monomer) elastomers;
- blends of polyethylenes with an EPR or an EPDM;
- ethylene/alkyl (meth)acrylate copolymers possibly containing up to 60% by
weight, preferably 2 to 40%, of (meth)acrylate.
Grafting is an operation known per se.
With regard to the ethylene/X copolymers, that is to say those in which X is
not
grafted if they are copolymers of ethylene with X and optionally with another
monomer
possibly chosen from the comonomers mentioned above in the case of the
ethylene
copolymers intended to be grafted.
CA 02461389 2004-03-19
17
Advantageously, ethylene/maleic anhydride copolymers and
ethylene/alkyl(meth)acrylate/maleic anhydride copolymers are used. These
copolymers
comprise from 0.2 to 10% by weight of malefic anhydride and from 0 to 40%,
preferably
from 5 to 40%, by weight of alkyl(meth)acrylate. Their MFI is between 5 and
100
(190°C/2.16 kg). The alkyl(meth)acrylates have already been described
above. The
melting point is between 60 and 100°C.
Advantageously, there are on average at least 1.3 mol, preferably from 1.3 to
and better still from 1.3 to 7 mol, of X per mole of chain attached to the
polyolefin
backbone. A person skilled in the art may easily determine the number of these
moles of
10 X by FTIR analysis.
With regard to the polyamide having an amine end group, the term "polyamide"
is understood to mean products resulting from the condensation:
- of one or more amino acids, such as aminocaproic, 7-aminoheptanoic,
11-aminoundecanoic and 12-aminododecanoic acid or of one or more lactams, such
as
caprolactam, oenantholactam and lauryllactam;
- of one or more salts or mixtures of diamines such as hexamethylenediamine,
dodecamethylenediarnine, metaxylylenediamine, bis(p-aminocyclohexyl)methane
and
trimethylhexamethylenediamine with diacids such as isophthalic, terephthalic,
adipic,
azelaic, suberic, sebacic and dodecanedicarboxylic acids;
- or mixtures of several monomers, resulting in copolyamides.
Polyamide/copolyamide blends may be used. Advantageously, PA-6, PA-11,
PA-12, the copolyamide having 6 units and 11 units (PA-6/11), the copolyamide
having
6 units and 12 units (PA-6/12) and the copolyamide based on caprolactam, I1-
amino
undecanoic acid and lauryllactam (PA-6/ 11 / 12) are used. The advantage of
copolyamides is that it is thus possible to choose the melting point of the
grafts.
Advantageously, the grafts are homopolymers or copolymers consisting of
residues of caprolactam, 11-amino-undecanoic acid and dodecalatam, or
copolyamides
consisting of residues chosen from at least two of the three above monomers.
The degree of polymerization may vary widely; depending on its value, this is
a
polyamide or a polyamide oligomer. In the rest of the text, the two
expressions for the
grafts will be used without distinction.
CA 02461389 2004-03-19
In order for the polyamide to have a monoamine terminal group, all that is
required is to use a chain stopper of formula:
R1 _ NH
I
R2
in which:
Rl is hydrogen or a linear or branched alkyl group containing up to 20 carbon
atoms;
R2 is a linear or branched, alkyl or alkenyl, group having up to 20 carbon
atoms, a saturated or unsaturated cycloaliphatic radical, an aromatic radical
or a
combination of the above. The chain stopper may, for example, be laurylamine
or
oleylamine.
Advantageously, the polyamide having an amine end group has a molar mass
of between 1 000 and 5 000 g/mol and preferably between 2 000 and 4 000 g/ml.
The preferred amino acid or lactam monomers for synthesizing the monoamine
aligomer according to the invention are chosen from caprolactam, 11-amino-
undecanoic
acid or dodecalactam. The preferred monofunctional polymerization stoppers are
laurylamine and oleylamine.
The polycondensation defined above is carried out using standard known
processes, for example at a temperature generally between 200 and
300°C, in a vacuum
or in an inert atmosphere, with stirring of the reaction mixture. The average
chain length
of the oligomer is determined by the initial molar ratio of the
polycondensable monomer
or the lactam to the monofunctional polymerization stopper. To calculate the
mean
chain length, it is usual practice to count one chain limiter molecule per
oligomer chain.
The addition of the monoamine polyamide oligomer to the polyolefin backbone
containing X is effected by an amine functional group of the oligomer reacting
with X.
Advantageously, X carries an anhydride or acid functional group; amide or
imide links
are thus created.
The oligomer having an amine end group is added to the polyolefin backbone
containing X preferably in the melt state. Thus, it is possible, in an
extruder, to mix the
oligomer with the backbone at a temperature generally between 180° and
250°C. The
mean residence time of the melt in the extruder may be between 15 seconds and
5 minutes, preferably between 1 and 3 minutes. The efficiency of this addition
is
CA 02461389 2004-03-19
19
evaluated by selective extraction of the free polyamide oligomers, that is to
say those
that have not reacted to form the final graft copolymer having polyamide
blocks.
The proportion of polyolefin backbone containing X (abbreviated to PO) to the
proportion of polyamide having an amine end group (abbreviated to PA) is such
that:
PO/PA is between 55/45 and 90/120 and advantageously between 60/40 and 80/20.
The preparation of such polyamides having an amine end group and their
addition to a polyolefin backbone containing X is described in Patents US
3976720, US
3963799, US 5342886 and FR 2291225.
The graft copolymers having polyamide blocks of the present invention are
characterized by a nanostructured organization with polyamide lamellae having
a
thickness of between 10 and 50 nanometres.
With regard to the embodiment in which the structure comprises a layer (3),
the
polyamide of this layer may be chosen from the polyamide or the
polyamide/polyolefin
blends having a polyamide matrix of the layer (1). It may be identical to or
different
from the layer (1). The polyolefin of this layer (3) may be chosen from the
abovementioned functionalized or unfunctionalized polyolefins in the layer
(1). If this
layer (3) is advantageously a polyolefin, it is propylene.
More particularly with regard to tubes for cooling circuits, these may, for
example, have an inside diameter of 5 to 100 mm and a thickness of 1 to 10 mm.
As
regards the thicknesses of the layers, these are advantageously 30 to 95% of
the total
thickness in the case of the layer 1, 5 to 60% in the case of the layer 2, 5
to 30% in the
case of each layer 2 and 3a and 5 to 40% in the case of the layer 3, the total
being 40%.
EXAMPLES
Example 1
An ethylene/butyl acrylate/maleic anhydride terpolymer containing 5 to 7%
acrylate and 2.8 to 3.4% malefic anhydride by weight, having a melt index of 6
g/ 10 min
(at 2.16 kg/190°C) was mixed in a Leistritz~ corotating twin-screw
extruder equipped
with several mixing zones, having a temperature profile between 180 and
220°C, with a
PA-11 of 2 500 g/mol molecular mass having an amine end group, synthesized
according to the method described in Patent US 5342886. This terpolymer
contained on
average between 1 and 3 anhydride groups per chain. The proportions introduced
into
CA 02461389 2004-03-19
the extruder were such that the polyolefin of the backbone/polyamide having an
amine
end group ratio was 80/20 by weight.
We therefore produced plaques by compression moulding using an
ENERPAC~ press using the following conditions:
5 - before each compression, the granules were placed for about 10 minutes in
an
oven at 100°C.
We produced 3 plaques of this specimen, each plaque required at least two
passes (in order to avoid any bubbles) with, between each pressing, a cutting
(into 4), an
oven annealing operation (at 100°C) and juxtaposition of the pieces.
10 All the test pieces were therefore separated into 2:
~ a 1St part (control) for determining the properties before ageing;
~ a 2°d part for determining the properties after 1 000 hours at
130°C in a 50/50 water/glycol mixture.
Thus, we placed the second part of the test pieces in a "bomb"-type autoclave
15 reactor capable of withstanding the pressure containing a 50/50
water/ethylene glycol
mixture by weight, and this reactor was also placed in an oven at
130°C.
Creep:
Before carrying out the creep tests (ISO 899 Standard) we had to condition the
products so as in the end to obtain test pieces of the "IFC (abbreviation for
d'Institut
20 Fran~ais du Caoutchouc) [French Rubber Institute]) type" and we therefore
cut these
test pieces into plaques. The creep tests consisted in imposing a constant
stress on a
material at a given temperature and in monitoring its deformation over time.
The initial
stress (constant force) was proportional to the area of the central cross
section of the test
piece. Then, after 15 minutes, the test piece was recovered and the elongation
with
respect to the initial reference length after cooling was measured and the
creep
deformation was thus obtained.
Stress at break, elongation at break ahd flexural modulus:
For these measurements, the tension/compression machine used was an MTS
Systems DY 21 B No. 525", the standard was the "ISO 527-2" reference and the
test
pieces were of the "Type SA" (cut from the plaques). The measurements were
carried
out with a pull rate of 100 mm/min.
CA 02461389 2004-03-19
21
Res~~ltl~ .
We therefore measured the creep in our tests (before and after ageing) at
120°C'
under a stress of 2 bar:
,~.sC~e~
-
1 000 h at
130C~ in
Conditioning ~ Control
water/glycol
~ .~: . , , -,;,E ~, x..
0~/~
;. ,
0'~~ II
The tests after ageing gave the same creep characteristics a5 the base.
Each specimen was also tested in tension before measuring the stress and
elongation break and the modulus of elasticity. The results are given in the
following
table:
~oxt ~ ~ ~ ~ ~ ~-~' ' ~ ,~4".~v.
,~ , ~ ~ ~ ~ 7(
~ ~, 'G
:Y.",
~., T'
MPa Mpa /, ~ ~,
aMPa
j
Control _ 1 ~.~.___ i (i. _._.__. __
~ -__._ 3.1 ~ r__ 24.3
__~__ -__
After ageinb
19.5 1 ).3 302 23.8
in lycr~l
