[Field of the invention]
The present invention relates to a multilayer pipe
comprising a functionalized fluoropolymer layer, a
polyolefin layer and a barrier layer. The polyolefin may be
a polyethylene, especially high-density polyethylene (HDPE)
or a crosslinked polyethylene (denoted by XPE). The pipe may
be used for transporting liquids, in particular hot water,
or gas. The invention also relates to the uses of this pipe.
[Technical problem]
Steel or cast iron pipes are being increasingly replaced
with equivalents made of plastic. Polyolefins, especially
polyethylenes, are very widely used thermoplastics as they
exhibit good mechanical properties, they can be easily
converted and allow pipes to be welded, together easily.
Polyolefins are widely used for the manufacture of pipes for
transporting water or town gas. When the gas is under a high
pressure (> 10 bar, or higher) , it is necessary for the
polyolefin to mechanically withstand the stresses exerted by
the pressurized gas.
In addition, the polyolefin may be exposed to an aggressive
chemical environment. For example, in the case of water
transport, the water may contain aggressive additives or
chemicals (for example, ozone, and. chlorinated derivatives
used for purifying water such as bleach, which are
oxidizing, especially when hot). These additives or
chemicals may damage the polyolefin over the course of time,
especially when the water transported is at a high
temperature (this is the case in heating circuits or else in
water systems for which the water is heated to a high
temperature in order to eliminate germs, bacteria or
microorganisms) . One problem that the invention aims to
solve is therefore to develop a chemically resistant pipe.
Another problem that the invention aims to solve is that the
pipe must have barrier properties. The term, "barrier" is

understood to mean the fact that the pipe reduces the rate
of migration into the transported fluid of contaminants
present in the external environment or else contaminants
(such as antioxidants or polymerization residues) present in
the polyolefin. The term "barrier" also means the fact that
the pipe reduces the rate of migration of oxygen or of
additives present in the transported fluid into the
polyolefin layer.
It is also necessary for the pipe to have good mechanical
properties, in particular good impact strength, and for the
layers to adhere well to one another (no delamination).
The Applicant has developed a multilayer pipe that solves
the stated problems. This pipe has, in particular, good
chemical resistance to the transported fluid and also the
abovementioned barrier properties.
[Prior art]
Document EP 1484346 published on 8 December 2004 describes
multilayer structures that include a radiation-grafted
fluoropolymer. The structures may be in the form of bottles,
tanks, containers or hoses. The structure of the multilayer
pipe according to the invention does not appear in this
document.
Document EP 1541343 published on 8 June 2005 describes a
multilayer structure based on a fluoropolymer modified by
radiation grafting in order to store or transport chemicals.
In this application, the term "chemicals" should be
understood to mean products that are corrosive or dangerous,
or else products whose purity has to be maintained. The
structure of the multilayer pipe according to the invention
does not appear in this document.
Document US 6016849 published on 25 July 1996 describes a
plastic pipe in which the adhesion between the inner layer
and the outer protective layer is between 0.2 and 0.5 N/mm.

There is no mention of a fluoropolymer modified by radiation
grafting.
Documents US 2004/0206413 and WO 2005/070671 describe a
multilayer pipe comprising a metal sheath. There is no
mention of a fluoropolymer modified by radiation grafting.
In these documents from the prior art, multilayer pipes
comprising a polyolefin layer, a functionalized
fluoropolymer layer and a barrier layer are not described.
[Brief description of the invention]
The invention relates to a multilayer pipe as defined in
claim 1, 23 or 24. It also relates to the use of the pipe in
transporting water or a gas, or a fuel, and also to a
radiant heating system comprising at least one multilayer
pipe of the invention.
The invention may be better understood on reading the
following detailed description of non-limiting illustrative
examples of the invention and on examining the appended
figure. The prior French application FR 05/10440 and also
the provisional application US 60/754887, the priorities of
which are claimed, are incorporated here for reference.
Figure
Figure 1 shows a cross-sectional view of a multilayer pipe 9
according to one of the embodiments of the invention. It is
a cylindrical pipe having several concentric layers,
referenced 1 to 8. The layers are arranged one against the
other in the order indicated from l->8:
layer 1: layer C1 comprising a. fluoropolymer;
layer 2: layer C2 comprising the functionalized
fluoropolymer + flexible fluoropolymer blend;
layer 3: adhesion tie layer C3;
layer 4: layer C4 comprising a polyolefin;
layer 5: adhesion tie layer;
layer 6: barrier layer C5;

layer 7: adhesion tie layer; and
layer 8: layer C6 comprising a polyolefin.
[Detailed description of the invention]
As regards the fluoropolymer, this thus denotes any polymer
having, in its chain, at least one fluoromonomer chosen from
compounds containing a vinyl group capable of opening in
order to be polymerized and which contains, directly
attached to this vinyl group, at least one fluorine atom,
one fluoroalkyl group or one fluoroalkoxy group.
As examples of fluoromonomers, mention may be made of vinyl
fluoride; vinylidene fluoride (VDF, CH2=CF2) ;
trifluoroethylene (VF3) ; chlorotrifluoroethylene (CTFE); 1,2-
difluoroethylene; tetrafluoroethylene (TFE);
hexafluoropropylene (HFP); perfluoroalkylvinyl ethers such
as perfluoromethylvinyl ether (PMVE), perfluoroethylvinyl
ether (PEVE) and perfluoropropyivinyl ether (PPVE);
perfluoro(1,3-dioxole); perfluoro(2,2-dimethyl-l,3-dioxole)
(PDD); the product of formula CF2=CFOCF2CF (CF3) OCF2CF2X in
which X is S02F, C02H, CH2OH, CH2OCN or CH20P03H; the product
of formula CF2=CFOCF2CF2S02F; the product. of formula
F(CF2)nCH2OCF=CF2 in which n is 1, 2, 3, 4 or 5; the product
of formula RiCH2OCF=CF2 in which Rx is hydrogen or F(CF2)2 and
z is equal to 1, 2, 3 or 4; the product of formula R3OCF=CH2
in which R3 is F(CF2)2- and z is 1, 2, 3 or 4;
perfluorobutylethylene (PFBE); 3,3,3-trifluoropropene and 2-
trifluoromethyl-3,3,3-trifluoro-1-propene,
The f luoropolymer may be a homopolymer or a copolymer; it
may also comprise non-fluorinated monomers such as ethylene.
By way of example, the fluoropolymer is chosen from:
- vinylidene fluoride homopolymers and copolymers
(PVDF) preferably containing at least 50% by weight
of VDF, the copolymer being chosen from
chlorotrifluoroethylene (CTFE), hexafluoropropylene

(HFP), trifluoroethylene (VF3) and
tetrafluoroethylene (TFE);
ethylene/TFE copolymers (ETFE);
- homopolymers and copolymers of trifluoroethylene
(VF3); and
- copolymers, and especially terpolymers, combining
the residues of chlorotrifluoroethylene (CTFE),
tetrafluoroethylene (TFE), hexafluoropropylene (HFP)
and/or ethylene units and optionally VDF and/or VF3
units.
Advantageously, the fluoropolymer is a PVDF homopolymer or
copolymer. This is because such a fluoropolymer exhibits
good chemical resistance, especially to UV radiation and to
chemicals, and is easily converted (more easily than PTFE or
ETFE-type copolymers). Preferably, the PVDF contains, by
weight, at least 50%, more preferably at least 75% and
better still at least 85% of VDF. The comonomer is
advantageously HFP.
Advantageously, the PVDF has a viscosity ranging from
100 Pa.s to 2000 Pa.s, the viscosity being measured at
230°C, at a shear rate of 100 s"1 using a capillary
rheometer. This is because these PVDFs are well suited to
extrusion and to injection molding. Preferably, the PVDF has
a viscosity ranging from 300 Pa.s to 1200 Pa.s, the
viscosity being measured at 230°C, at a shear rate of 100 s"1
using a capillary rheometer.
Thus, the PVDFs sold under the brand name KYNAR® 710 or 720
are perfectly suitable for this formulation.
As regards the flexible fluoropolymer, this is a
fluoropolymer having a tensile modulus between 50 and
1000 MPa, advantageously between 100 and 750 MPa and
preferably between 200 and 600 MPa (measured according to
the ISO R 527 standard at 23°C).

As regards the functionalized fluoropolymer, this is a
fluoropolymer bearing at least one functional group chosen
from the following groups: carboxylic acid, carboxylic acid
salt, carbonate, carboxylic acid anhydride, epoxide,
carboxylic acid ester, silyl, alkoxysilane, carboxylic acid
amide, hydroxy or isocyanate. It is a copolymer comprising
at least one fluoromonomer and at least one unsaturated
monomer bearing a functional group such as defined. The
functional group is introduced into the fluoropolymer either
by copolymerization or by grafting with a monomer bearing a
functional group such as defined.
The functionalized fluoropolymer may be obtained by
copolymerizing a fluoromonomer with at least one unsaturated
monomer bearing a functional group and optionally at least
one other comonomer. For example, the functionalized polymer
may be a PVDF comprising monomer units of VDF and of a
monoesterified unsaturated diacid or vinylene carbonate such
as is described in document US 5415958. Another example of a
functionalized fluoropolymer is that of a PVDF comprising
monomer units of VDF and of itaconic or citraconic anhydride
such as is described in document US 6703465 B2 . The
functionalized fluoropolymer may be prepared by a process in
emulsion, in suspension or in solution.
The functionalized fluoropolymer may be obtained by
radiation grafting of at least one unsaturated monomer
(described later on) onto a fluoropolymer. In this case, to
simplify matters this will be referred to as a radiation-
grafted fluoropolymer.
The process for obtaining the radiation-grafted
fluoropolymer is the following.
a) The fluoropolymer is first melt-blended with the
unsaturated monomer. This is carried out by any melt-
blending technique known in the prior art. The blending step
is carried out in any blending device, such as extruders or
mixers used in the thermoplastics industry. Preferably, an

extruder will be used to make the blend in the form of
granules. The grafting therefore takes place on a blend
(throughout the mass) and not on the surface of a powder
such as is described, for example, in document US 5576106.
b) Next, the fluoropolymer/unsaturated monomer blend is
irradiated (ßor y irradiation) in the solid state using an
electron or photon source with an irradiation dose between
10 and 200 kGray, preferably between 10 and 150 kGray. The
blend may, for example, be packaged in polyethylene bags,
the air is expelled therefrom, then the bags are sealed.
Advantageously, the dose is between 2 and 6 Mrad and
preferably between 3 and 5 Mrad. It is particularly
preferred to carry out the irradiation in a cobalt-60 bomb.
The grafted unsaturated monomer content is, by weight,
between 0.1 and 5% (that is to say that the grafted
unsaturated monomer corresponds to 0.1 to 5 parts per 99.9
to 95 parts of fluoropolymer) , advantageously from 0.5 to
5%, preferably from 0.9 to 5%. The grafted unsaturated
monomer content depends on the initial content of the
unsaturated monomer in the fluoropolymer/unsaturated monomer
blend to be irradiated. It also depends on the efficiency of
the grafting, and therefore on the duration and energy of
the irradiation.
c) The unsaturated monomer that has not been grafted and
the residues released by the grafting, especially HF, may
then be optionally removed. The latter step may be necessary
if the non-grafted unsaturated monomer is liable to impair
the adhesion or else cause toxicological problems. This
operation may be carried out using techniques known to a
person skilled in the art. A vacuum degassing operation may
be applied, optionally applying heating at the same time. It
is also possible to dissolve the modified fluoropolymer in
an appropriate solvent such as, for example, N-
methylpyrrolidone, then to precipitate the polymer in a non-
solvent, for example in water or else in an alcohol, or else

to wash the modified fluoropolymer using a solvent that is
inert with respect to the f luoropolymer and the grafted
functional groups. For example, when maleic anhydride is
grafted, it is possible to wash with chlorobenzene.
One of the advantages of this radiation-grafting process is
that it is possible to obtain higher grafted unsaturated
monomer contents than with the conventional grafting
processes using a radical initiator. Thus, with this
grafting process, it is typically possible to obtain
contents of greater than 1% (1 part of unsaturated monomer
per 99 parts of fluoropolymer) , or even greater than 1.5%,
something that is not possible with a conventional grafting
process carried out in an extruder.
Moreover, the radiation grafting takes place "cold"
typically at temperatures below 100°C, or even 50°C, so that
the fluoropolymer/unsaturated monomer blend is not in the
melt state, as in the case of a conventional grafting
process carried out in an extruder, but is in the solid
state. One essential difference is therefore that, in the
case of a semicrystalline fluoropolymer (as is the case with
PVDF for example), the grafting takes place in the amorphous
phase and not in the crystalline phase, whereas homogeneous
grafting occurs in the case of melt-grafting in an extruder.
The unsaturated monomer is therefore not distributed along
the fluoropolymer chains in the same way as in the case of
radiation grafting and in the case of grafting carried out
in an extruder. The modified fluoropolymer therefore has a
different distribution of unsaturated monomer among the
fluoropolymer chains compared with a product obtained by
grafting carried out in an extruder.
During this grafting step, it is preferable to prevent
oxygen from being present. It is therefore possible to
remove the oxygen by flushing the fluoropolymer/unsaturated
monomer blend with nitrogen or argon.

The fluoropolymer modified by radiation grafting has the
very good chemical resistance and very good oxidation
resistance, and also the good thermomechanical behavior, of
the fluoropolymer before its modification.
As regards the unsaturated monomer, this has a C=C double
bond and also at least one polar functional group that may
be one of the following functional groups:
carboxylic acid;
carboxylic acid salt;
carboxylic acid anhydride;
epoxide;
carboxylic acid ester;
silyl;
alkoxysilane;
- carboxylic acid amide;
hydroxyl; and
isocyanate.
It is also possible to envisage using mixtures of 'several
unsaturated monomers.
Unsaturated carboxylic acids having 4 to 10 carbon atoms and
their functional derivatives, particularly their anhydrides,
are particularly preferred unsaturated monomers. Mention may
be made, by way of examples of unsaturated monomers, of
methacrylic acid, acrylic acid, maleic acid, fumaric acid,
itaconic acid, citraconic acid, undecylenic acid,
allylsuccinic acid, cyclohex-4-ene-l,2-dicarboxylic acid, 4-
methylcyclohex-4-ene-l,2-dicarboxylic acid,
bicyclo[2.2.1]hept-5-ene-2,3-dicarboxylic acid, x-
methylbicyclo[2.2.1]hept-5-ene-2,3-dicarboxylic acid, zinc,
calcium or sodium undecylenate, maleic anhydride, itaconic
anhydride, citraconic anhydride, dichloromaleic anhydride,
difluoromaleic anhydride, itaconic anhydride, crotonic
anhydride, glycidyl acrylate or methacrylate, allylglycidyl
ether, vinylsilanes such as vinyltrimethoxysilane,

vinyltriethoxysilane, vinyltriacetoxysilane and y-
methylacryloxypropyltrimethoxysilane.
Other examples of unsaturated monomers comprise C1-C8 alkyl
esters or glycidyl ester derivatives of unsaturated
carboxylic acids such as methyl acrylate, methyl
methacrylate, ethyl acrylate, ethyl methacrylate, butyl
acrylate, butyl methacrylate, glycidyl acrylate, glycidyl
methacrylate, monoethylmaieate, diethylmaleate, monomethyl
fumarate, dimethyl fumarate, monomethyl itaconate and
diethyl itaconate; amide derivatives of unsaturated
carboxylic acids such as acrylamide, rrtethacrylamide,
maleamide, malediamide, N-ethylmaleamide, N,N~
diethylmaleamide, N-butylmaleamide, N, N-dibutyimaleamide,
fumaramide, fumardiamide, N-ethylfumaramide, N,N-
diethylfumaramide, N-butylfumaramide and N,N-
dibutylfumaramide; imide derivatives of unsaturated
carboxylic acids such as maleimide, N-butylmaleimide and N-
phenylmaleimide; and metal salts of unsaturated carboxylic
acid such as sodium acrylate, sodium methacrylate, potassium
acrylate, potassium methacrylate and zinc, calcium or sodium
undecylenate.
Excluded from unsaturated monomers are those that have two
C=C double bonds which could result in crosslinking of the
fluoropolymer, such as for example diacrylates or
triacrylates. From this point of view, maleic anhydride just
like zinc, calcium and sodium undecylenates constitute good
graftable compounds as they have little tendency to
homopolymerize or even to cause crosslinking.
Advantageously, maleic anhydride is used. This is because
this monomer offers the following advantages:
- it is solid and may be easily introduced with the
fluoropolymer granules in order to prepare the blend
to be melted;
- it allows good adhesion properties to be obtained;

- it is particularly reactive with respect to
epoxide or hydroxyl functional groups; and
- unlike other unsaturated monomers such as
(meth)acrylic acid or acrylic esters, it does not
homopolymerize and does not have to be stabilized.
In the blend to be irradiated, the amount of fluoropolymer
is, by weight, between 80 and 99.9% per 0.1 to 20%
respectively of unsaturated monomer. Preferably, the amount
of fluoropolymer is from 90 to 99% per 1 to 10% respectively
of unsaturated monomer.
As regards the polyolefin, this term denotes a polymer
predominantly comprising ethylene and/or propylene units. It
may be a polyethylene homopolymer or copolymer, the
comonomer being chosen from propylene, butene, hexene or
octene. It may also be a polypropylene hornopolymer or
copolymer, the comonomer being chosen from ethylene, butene,
hexene or octene.
The polyethylene may especially be high-density polyethylene
(HDPE) , low-density polyethylene (LDPE) , linear low-density
polyethylene (LLDPE) or very low-density polyethylene
(VLDPE). The polyethylene may be obtained using a Ziegler-
Natta, Phillips or metallocene-type catalyst or using the
high-pressure process. The polypropylene is an isotactic or
syndiotactic polypropylene.
It may also be a crosslinked polyethylene (denoted by XPE) .
The XPE has, compared to a non-crosslinked PE, better
mechanical properties (especially good crack resistance) and
a better chemical resistance. The crosslinked polyethylene
may, for example, be a polyethylene comprising hydrolyzable
silane groups (as described in Applications WO 01/53367 or
US 2004/0127641 Al) which has then been crosslinked after
the silane groups have reacted together. The reaction
between the Si-OR silane groups results in Si-O-Si bonds
that link the polyethylene chains together. The content of

hydrolyzable silane groups may be at least 0.1 hydrolyzable
group per 100 -CH2- units (determined by infrared analysis).
The polyethylene may also be crosslinked by radiation, for
example gamma radiation. It may also be a polyethylene
crosslinked using a peroxide-type radical initiator. It will
therefore be possible to use a type-A XPE (crosslinking
using a radical initiator), a type-B XPE (crosslinking using
silane groups) or a type-C XPE (radiation crosslinking).
It may also be what is called a bimodal polyethylene, that
is to say one composed of a blend of polyethyienes having
different average molecular weights, as taught in document
WO 00/60001. Bimodal polyethylene makes it possible, for
example, to obtain a very advantageous compromise of impact
and stress-cracking resistance, good rigidity and good
pressure-withstand capability.
For pipes that have to be pressure-resistant, especially
pipes for transporting pressurized gas or for transporting
water, it may be advantageous to use a polyethylene that has
good resistance to slow crack growth (SCG) and to rapid
crack propagation (RCP). The HDPE XS 10 B grade sold by
Total Petrochemicals exhibits good (slow or rapid) crack
resistance. This is an HDPE containing hexene as a
comonomer, having a density of 0.959 g/cm3 (ISO 1183), an
MI-5 of 0.3 dg/min (ISO 1133), an HLMI of 8 dg/min
(ISO 1133), a long-term hydrostatic strength of 11.2 MPa
according to ISO/DIS 9080, a slow crack growth resistance on
notched pipes of greater than 1000 hours according to
ISO/DIS 13479.
As regards the functionalized polyolefin, this term denotes
a copolymer of ethylene and/or propylene with at least one
unsaturated polar monomer. This unsaturated polar monomer
may, for example, be chosen from:
- C1-C8 alkyl (meth)acrylates, especially methyl,
ethyl, propyl, butyl, 2-ethylhexyl, isobutyl or
cyclohexyl (meth)acrylate;

- unsaturated carboxylic acids, their salts and
their anhydrides, especially acrylic acid,
methacrylic acid, maleic anhydride, itaconic
anhydride and citraconic anhydride;
- unsaturated epoxides, especially aliphatic
glycidyl esters and ethers such as allyl glycidyl
ether, vinyl glycidyl ether, glycidyl maleate,
glycidyl itaconate, glycidyl acrylate, glycidyl
methacrylate and alicyclic glycidyl esters and
ethers; and
- vinyl esters of saturated carboxylic acids,
especially vinyl acetate or vinyl propionate.
The functionalized polyolefin may be obtained by
copolymerizing ethylene with at least one unsaturated polar
monomer chosen from the above list. The functionalized
polyolefin may be a copolymer of ethylene with a polar
monomer from the above list or else a terpolymer of ethylene
with two unsaturated polar monomers chosen from the above
list. The copolymerization takes place at high pressure,
above 1000 bar according to the high-pressure process. The
functional polyolefin obtained by copolymerization
comprises, by weight, from 50 to 99.9%, preferably from 60
to 99.9%, more preferably still from 65 to 99% of ethylene
and from 0.1 to 50%, preferably from 0.1 to 40%, more
preferably still from 1 to 35% of at least one polar monomer
from the above list.
For example, the functionalized polyolefin is a copolymer of
ethylene with an unsaturated epoxide, preferably glycidyl
(meth) acrylate, and optionally with a Ci-C8 alkyl
(meth)acrylate or a vinyl ester of a saturated carboxylic
acid. The unsaturated epoxide content, especially the
glycidyl (meth)acrylate content, is between 0.1 and 50%,
advantageously between 0.1 and 40%, preferably between 1 and
35%, more preferably still between 1 and 20%. For example,
the functionalized polyolefins may be those sold by ARKEMA
under the references LOTADER AX8840 (8% glycidyl

methacrylate, 92% ethylene, melt index 5 according to
ASTM D1238), LOTADER AX8900 (8% glycidyl methacrylate, 25%
methyl acrylate, 67% ethylene, melt index 6 according to
ASTM D1238), LOTADER AX8950 (9% glycidyl methacrylate, 15%
methyl acrylate, 76% ethylene, melt index 85 according to
ASTM D1238).
The functionalized polyolefin may also be a copolymer of
ethylene with an unsaturated carboxylic acid anhydride,
preferably maleic anhydride, and optionally with a C1-C8
alkyl (meth)acrylate or a vinyl ester of a saturated
carboxylic acid. The content of maleic anhydride, especially
maleic anhydride, is between 0.1 and 50%, advantageously
between 0.1 and 40%, preferably between 1 and 35%, more
preferably still between 1 and 10%. For example, the
functionalized polyolefins may be those sold by ARKEMA under
the references LOTADER 2210 (2.6% maleic anhydride, 6% butyl
acrylate and 91.4% ethylene, melt index 3 according to
ASTM D1238), LOTADER 3340 (3% maleic anhydride, 16% butyl
acrylate and 81% ethylene, melt index 5 according to
ASTM D1238), LOTADER 4720 (0.3% maleic anhydride, 30% ethyl
acrylate and 69.7% ethylene, melt index 7 according to
ASTM D1238), LOTADER 7500 (2.8% maleic anhydride, 20% butyl
acrylate and 77.2% ethylene, melt index 70 according to
ASTM D1238), OREVAC 9309, OREVAC 9314, OREVAC 9307Y, OREVAC
9318, OREVAC 9304 or OREVAC 9305,
Also denoted by the term, "functionalized polyolefin" is a
polyolefin onto which an unsaturated polar monomer from the
above list is grafted by radical means. The grafting takes
place in an extruder or in solution in the presence of a
radical initiator. As examples of radical initiators, it
will be possible to use tert-butyl hydroperoxide, cumene
hydroperoxide, diisopropylbenzene hydroperoxide, di-tert-
butyl peroxide, tert-butylcumyl peroxide, dicumyl peroxide,
1,3-bis(tert-butylperoxyisopropyl)benzene, benzoyl peroxide,
isobutyryl peroxide, bis(3,5,5-trimethylhexanoyl)peroxide or
methyl ethyl ketone peroxide. The grafting of an unsaturated

polar monomer onto a polyolefin is known to a person skilled
in the art, and for further details reference may be made,
for example, to documents EP 689505, US 5235149, EP 658139,
US 6750288 B2, US 6528587 B2. The polyolefin to which the
unsaturated polar monomer is grafted may be a polyethylene,
especially high-density polyethylene (HDPE) or low-density
polyethylene (LDPE), linear low-density polyethylene (LLDPE)
or very low-density polyethylene (VLDPE). The polyethylene
may be obtained using a Ziegler-Natta, Phillips or
metallocene-type catalyst or using the high-pressure
process. The polyolefin may also be a polypropylene,
especially an isotactic or syndiotactic polypropylene. It
may also be a copolymer of ethylene and propylene of the EPR
type, or a terpolymer of ethylene, a propylene and a diene,
of the EPDM type. It may, for example, be one of the
functionalized polyolefins sold by ARKEMA under the
references OREVAC 18302, 18334, 18350, 18360, 18365, 18370,
18380, 18707, 18729, 18732, 18750, 18760, PP-C, CA100.
The polymer onto which the unsaturated polar monomer is
grafted may also be a copolymer of ethylene with at least
one unsaturated polar monomer chosen from:
- C1-C8 alkyl (meth)acrylates, especially methyl,
ethyl, propyl, butyl, 2-ethylhexyl, isobutyl or
cyclohexyl (meth)acrylate; and
- vinyl esters of saturated carboxylic acids,
especially vinyl acetate or vinyl propionate.
It may, for example, be one of the functionalized
polyolefins sold by ARKEMA under the references OREVAC
18211, 18216 or 18630.
Preferably, the functionalized polyolefin is chosen so that
the functional groups of the unsaturated monomer which is
grafted to the fluoropolymer react with those of the polar
monomer of the functionalized polyolefin. For example, if a
carboxylic acid anhydride, for example maleic anhydride, is
grafted onto the fluoropolymer, the layer of functionalized

polyolefin may be composed of a copolymer of ethylene with
an unsaturated epoxide, for example glycidyl methacrylate,
and optionally with an alkyl acrylate, the ethylene
copolymer optionally being blended with a polyolefin.
According to another example, if an unsaturated epoxide, for
example glycidyl methacrylate, is grafted onto the
fluoropolymer, the layer of functionalized polyolefin may be
composed of a copolymer of ethylene with a carboxylic acid
anhydride, for example maieic anhydride, and optionally with
an alkyl acrylate, the ethylene copolymer optionally being
blended with a polyolefin.
The multilayer pipe and all its possible variants will now
be described in greater detail.
The multilayer pipe comprises (in the following order, from
the inside of the pipe outward):
• optionally, a layer C1, comprising at least one
fluoropolymer;
• a layer C2 comprising a blend of:

- at least one copolymer comprising at least one
fluoromonomer and at least one monomer bearing a
functional group chosen from the following groups:
carboxylic acid, carboxylic acid salt, carbonate,
carboxylic acid anhydride, epoxide, carboxylic
acid ester, silyl, alkoxysilane, carboxylic acid
amide, hydroxy or isocyanaite; and
- at least one flexible fluoropolymer that has a
tensile modulus between 50 and 1000 MPa (measured
according to the ISO R 527 standard, at 23°C),
advantageously between 100 and 750 MPa and
preferably between 200 and 600 MPa;

• optionally, an adhesive tie layer C3;
• a layer C4 comprising at least one polyolefin or a
blend of at least one polyolefin with at least one
functionalized polyolefin;

• a barrier layer C5 which is a metal sheath or which
comprises EVOH or an EVOH-based blend, a PVDF or a
PGA; and
• optionally, a layer C5 comprising at least one
polyolefin.
According to one variant, layer C3 is directly attached to
layer C2. According to another variant, layer C4 is directly
attached to the optional layer C3 or else to layer C2
According to another variant, the pipe comprises a layer Clf
a layer C2, a layer C3 directly attached to layer C2, a layer
C4 directly attached to layer C3, a layer C5 and a layer Ce.
The inner layer which is in contact with the fluid is either
layer C1 or layer C2. All the layers of the pipe are
preferably concentric. The pipe is preferably cylindrical.
Preferably, the layers adhere to one another in their
respect contact regions (that is to say that two successive
layers are directly attached to one another).
Advantages of the multilayer pipe
The multilayer pipe:
• exhibits chemical resistance (via layer C1 and/or C2)
to the transported fluid;
• stops the migration of contaminants from the
external environment into the transported fluid;
• stops the migration of contaminants present in the
polyolefin from layer C4 and/or layer C6 into ■the
transported fluid;
• stops the migration of oxygen or additives present
in the transported fluid into layer C4; and
• exhibits very good adhesion between the layers (no
delamination).
Optional layer C1
This layer comprises at least one fluoropolymer (this
fluoropolymer is not modified by radiation grafting).
Preferably, the fluoropolymer is a PVDF homopolymer or

copolymer or else a copolymer based on VDF and on TFE of the
EFEP type.
Layer C2
This layer comprises a blend of at least one functionalized
f luoropolyiner and at least one flexible f luoropolymer. It
has a chemical protection role and exhibits adhesion with
layer C3 or C4., It also has a role of adhesion tie between
the polyolefin layer and the fluoropolymer layer when the
latter is present. This blend makes it possible to obtain a
very strong adhesion, which is furthermore of the cohesive
type.
The blend comprises, by weight, from 1 to 99 parts,
advantageously from 10 to 90 parts, preferably from 10 to 75
parts, more preferably still from 10 to 50 parts of a
functionalized fluoropolymer per 99 to 1 parts,
advantageously 90 to 10 parts, preferably 90 to 25 parts,
more preferably still 90 to 50 parts respectively of a
flexible fluoropolymer.
Preferably, the viscosity of the functionalized
fluoropolymer (measured with a capillary rheometer at 230°C
and 100 s-1) is between 100 and 1500 Pa.s, advantageously
bet ween 200 and 1000 Pa.s and preferably between 500 and
1000 Pa.s.
Preferably, the viscosity of the flexible fluoropolymer
(measured with a capillary rheometer at 230°C and 100 s-1) is
between 100 and 1500 Pa.s, advantageously between 200 and
1000 Pa.s and preferably between 500 and 1000 Pa.s.
Preferably, the crystallization temperature of the flexible
fluoropolymer (measured by DSC according to the ISO 11357-3
standard) is between 50 and 120°C, preferably between 85 and
110°C.

Preferably, the functionalized fluoropolymer is a radiation-
grafted fluoropolymer. Preferably, it is a radiation-grafted
PVDF. Advantageously, the radiation-grafted PVDF is obtained
from a PVDF comprising, by weight, at least 80%,
advantageously at least 90%, preferably at least 95%, more
preferably still at least 98% of VDF. Most preferably, it is
a PVDF homopolymer (that is to say with 100% VDF).
Preferably, the flexible fluoropolymer is a PVDF copolymer,
more particularly a VDF/HFP copolymer.
Optional layer C3
Layer C3 which is positioned between layer C2 and layer C4
has the role of increasing the adhesion between these two
layers. It comprises an adhesion tie, that is to say a
polymer which has the role of improving the adhesion between
these two layers.
The adhesion tie may, for example, comprise at least one
functionalized polyolefin optionally blended with a
polyolefin. In the case where a blend is used, this blend
comprises, by weight, from 1 to 99%, advantageously from 10
to 90%, preferably from 50 to 90% of functionalized
polyolefin per 99 to 1%, advantageously 90 to 10%,
preferably 50 to 10% respectively of polyolefin. The
polyolefin which is used for the blend with the
functionalized polyolefin is preferably a polyethylene since
these two polymers exhibit good compatibility. Layer C3 may
also comprise a blend of two or more functionalized
polyolefins. For example, it may be a blend of a copolymer
of ethylene with an unsaturated epoxide and optionally with
an alkyl (meth) acrylate and a copolymer of ethylene with an
alkyl (meth)acrylate.
Layer C4
Layer C4 comprises at least one polyolefin. It may also
comprise at least one polyolefin as a blend with at least
one functionalized polyolefin. In this case, the blend

comprises, by weight, from 1 to 99%, advantageously from 10
to 90%, preferably from 10 to 50% of functionalized
polyolefin per 99 to 1%, advantageously 90 to 10%,
preferably 90 to 50% respectively of polyolefin. The
polyolefin which is used for the blend with the
functionalized polyolefin is preferably a polyethylene since
these two polymers exhibit good compatibility.
In the case of such a blend, layer C3 may be eliminated if a
functionalized polyolefin which has functional groups
capable of reacting with the functional groups grafted onto
the fluoropolymer is used. Thus, for example, if anhydride
functional groups are grafted onto the fluoropolymer, the
functionalized polyolefin will advantageously comprise
epoxide or hydroxyl functional groups. For example too, if
epoxide or hydroxyl functional groups are grafted onto the
fluoropolymer, the functionalized polyolefin advantageously
comprises anhydride functional groups. Similarly, this is
also true for the functionalized polyolefin of layer C3. The
multilayer pipe therefore comprises (in the following order,
from the inside of the pipe outward):
• optionally a layer Cα of at least one fluoropolymer;
• a layer C2 comprising a blend of at least one
functionalized fluoropolymer and at least one
flexible fluoropolymer;
• a layer C4 of at least one blend of a polyolefin. and
of at least one functionalized polyolefin which has
functional groups capable of reacting with the
functional groups grafted onto the fluoropolymer;
• a barrier layer C5 which is a metal sheath or which
comprises EVOH or an EVOH-based blend, PVDF or PGA;
and
• optionally, a layer Cs of a polyolefin.
Barrier layer C5
The role of the barrier layer is to prevent contamination of
the fluid which flows, especially transported water or gas,
by contaminants. Oxygen and chemicals such as hydrocarbons,

for example, are contaminants. In the more specific case of
gases, moisture may be a contaminant.
The barrier layer may be a metal sheath. Besides its barrier
function, the metal sheath also has the role of increasing
the mechanical strength of the pipe. Another advantage of
using a metal sheath is being able to bend or deform the
pipe without it returning to its initial position under the
effect of the mechanical stresses created by the layers of
thermoplastic polymers. The metal may be steel, copper or
aluminum or an aluminum alloy. It is preferably aluminum or
an aluminum alloy for reasons of corrosion resistance and
flexibility. The metal sheath is manufactured according to
one of the processes known to a person skilled in the art.
Reference may especially be made to the following documents
which describe processes enabling composite plastic/metal
pipes to be produced: US 6822205, EP 058X208 Al,
EP 0639411 Bl, EP 0823867 Bl, EP 0920972 Al. Preferably, use
is made of the process consisting in:
• shaping a metal strip so as to go around the already
coextruded thermoplastic polymer layers (i.e. layers
C1 to C4) , said metal strip having longitudinal edges
that are angled toward a common side and placed so
as to bear against one another, extending
approximately parallel to the longitudinal axis of
the plastic pipe; and
• the longitudinal edges are then welded together.
They therefore form a longitudinal weld seam.
After having welded the longitudinal edges of the metal
strip, a tubular metal sheath is therefore obtained.
To improve the adhesion of the barrier layer C5, an adhesion
tie layer is advantageously positioned between the barrier
layer C5 and the polyolefin layer C4 and/or between the
barrier layer C5 and the optional polyolefin layer C6. The
adhesion tie is, for example, a functionalized polyolefin.
It is advantageously a polyolefin, grafted onto which is a

carboxylic acid or a carboxylic acid anhydride, for example
(meth)acrylic acid or maleic anhydride. It may therefore be
a polyethylene onto which (meth)acrylic acid or maleic
anhydride is grafted - or a polypropylene onto which
(meth)acrylic acid or maleic anhydride is grafted. Mention
may be made, by way of example, of the functionalized
polyolefins sold by ARKEMA under the references OREVAC
18302, 18334, 18350, 18360, 18365, 18370, 18380, 18707,
18729, 18732, 18750, 18760, PP-C, CA100 or by UNIROYAL
CHEMICAL under the reference POLYBOND 1002 or 1009
(polyethylene onto which acrylic acid is grafted).
The barrier layer C5 may also comprise a barrier polymer, for
example:
• EVOH or an EVOH-based blend;
• a PVDF; or
• poly(glycolic acid) (PGA).
EVOH is also referred to as saponified ethylene/vinyl
acetate copolymer. This is a copolymer having an ethylene
content of 20 to 70 mol%, preferably from 25 to 70 mol%, the
degree of saponification of its vinyl acetate component not
being less than 95 mol%. EVOH constitutes a good oxygen
barrier. Advantageously, EVOH has a melt flow index between
0.5 and 100 g/10 min (230°C/2.26 kg), preferably between 5
and 30. It is understood that EVOH may contain small amounts
of other comonomer ingredients, including α-olefins such as
propylene, isobutene, α-octene, unsaturated carboxylic acids
or their salts, partial alkyl esters, full alkyl esters,
etc.
For EVOH-based blends, the EVOH forms the matrix, that is to
say represents at least 40%, and preferably at least 50%, by
weight of the blend.
PGA denotes poly(glycolic acid), that is to say a polymer
containing, by weight, at least 60%, advantageously 70%,
preferably 80% of the following units (1):

(Formula Removed)
This polymer may be manufactured by heating 1,4-dioxane-2,5-
dione at a temperature between 120 and 250°C in the presence
of a catalyst such as a tin salt, for example SnCl4. The
polymerization takes place in bulk or in a solvent. The PGA
may contain the other following units (2) to (6):
(Formula Removed)
where n is an integer between 1 and 10 and m is an integer
between 0 and 10;
(Formula Removed)
where j is an integer between 1 and 10;
(Formula Removed)
where k is an integer between 2 and 10 and R1 and R2 each
denote, independently of one another, H or a C1-C10 alkyl
group;
(Formula Removed)
or
(Formula Removed)
PGA is described in European Patent EP 925 915 Bl.
Optional layer C6

The pipe may optionally include a layer C6 comprising at
least one polyolefin. The polyolefins of layers C4 and C6 may
be identical or different. Layer C6 makes it possible to
mechanically protect the pipe (e.g. against impacts on the
pipe when it is installed), in particular to protect layer C4
or barrier layer C5 when the latter is present. It also makes
it possible to mechanically reinforce the entire pipe, which
may make it possible to reduce the thicknesses of the other
layers. In order to do this, layer C6 may include at least
one reinforcing agent, for example a mineral filler.
Owing to its good thermomechanical properties, XPE is
advantageously used for layer C4 and/or for layer C6.
Each of the layers of the multilayer pipe, especially the
polyolefin layer or layers, may contain additives commonly
blended into thermoplastics, for example antioxidants,
lubricants, colorants, fire retardants, mineral or organic
fillers, antistatic agents such as, for example, carbon
black or carbon nanotubes. The pipe may also comprise other
layers, for example an insulating outer layer.
Multilayer pipe according to a preferred variant (best mode)
The multilayer pipe comprises (in the following order, from
the inside of the pipe outward):
• optionally, a layer C1 comprising at least one PVDF
homopolymer or copolymer;
• a layer C2 comprising a blend of at least one PVDF
homopolymer or copolymer onto which maleic anhydride
has been radiation-grafted and of at least one
flexible PVDF;
• an adhesion tie layer C3;
• a layer C4 comprising at least one polyethylene,
preferably of XPE type;
• a barrier layer C5; and
• optionally, a polyethylene layer C6, preferably of
the XPE type.

The adhesion tie preferably comprises at least one
functionalized polyolefin which has functional groups
capable of reacting with the maleic anhydride, optionally
blended with a polyolefin. Advantageously, this is a
functionalized polyolefin having epoxide or hydroxyl
functional groups. For example, it may be a copolymer of
ethylene, an unsaturated epoxide, for example glycidyi
methacrylate, and optionally an alkyl acrylate.
Preferably, the barrier layer C5 is a metal sheath.
Thickness of the layers
Preferably, layers C:L, C2, C3 and C5 each have a thickness
between 0.01 and 30 mm, advantageously between 0.05 and
20 mm, preferably between 0.05 and 10 mm. The polyolefin
layers C4 and C6 preferably each have a thickness between 0.1
and 10 000 mm, advantageously between 0.5 and 2000 mm,
preferably between 0.5 and 1000 mm. The layer or layers
comprising the adhesion tie have a thickness between 0.001
and 30 mm, advantageously between 0.001 and 10 mm.
Production of the pipes
The pipes without a metal sheath are manufactured by
coextrusion. When the polyolefin of layer C4 and/or of
optional layer C6 is a type-B XPE (crosslinking via silane
groups), the process starts by extruding the uncrosslinked
polyolefin. The crosslinking is carried out after the
coextrusion of layers C2 and C4, and optionally layers C1 and
C3, has finished, by heating the extruded pipes, for example
by immersing them in a bath of hot water. When the
polyolefin of layer C4 and/or optional layer Ce is a type-A
XPE (crosslinking using a radical initiator) , the
crosslinking is carried out using a radical initiator which
is thermally activated during the extrusion.
The pipes with a metal sheath are manufactured after
coextrusion of layers C1 to C4, and of the optional adhesion
tie layer between layer C5 and layer C4, then a metal strip

is wound around the layers thus obtained. The longitudinal
edges may be welded together to form a longitudinal weld
seam. It is then possible to extrude layer C6 and optionally
an adhesion tie layer between layer C5 and layer C6. When the
polyolefin of layer C4 and/or of optional layer C6 is a type-
B XPE, the crosslinking takes place by heating the pipes,
for example by immersing them in a bath of hot water.
Uses of the pipe
The multilayer pipe may be used for transporting various
fluids. The pipe is suitable for transporting water,
especially hot water, in particular for transporting mains
hot water. The pipe may be used for transporting hot water
for heating (temperature above 60°C, or even 90°C). One
advantageous application example is that of radiant floor
heating in which the pipe used for conveying the hot water
is placed beneath the floor. The water is heated by a boiler
and flows through the pipe. Another example is that in which
the pipe is used to convey hot water to a radiator. The pipe
can therefore be used for radiant water heating systems. The
invention also relates to a network heating system
comprising the pipe of the invention.
The chemical resistance of the pipe is adapted to water
containing chemical additives (generally in small amounts,
of less than 1%) which may impair the polyolefins,
especially polyethylene, in particular when hot. These
additives may be oxidizing agents such as chlorine and
hypochlorous acid, chlorinated derivatives, bleach, ozone,
etc.
For applications in which the water flowing in the pipes is
a potable water, a water intended for medical or
pharmaceutical applications or a biological liquid, it is
preferable to have a layer of an unmodified fluoropolymer as
a layer in contact with the water (layer C1). Microorganisms
(bacteria, germs, molds, etc.) have little tendency to grow
on a fluoropolymer, especially on PVDF. Furthermore, it is

preferable for the layer in contact with the water or the
biological liquid to be a layer of unmodified fluoropolymer
rather than a layer of modified fluoropolymer in order to
prevent the migration of ungrafted (free) unsaturated
monomer into the water or the biological liquid.
The barrier properties of the pipe make it usable for
transporting water in contaminated ground by stopping the
migration of contaminants into the transported fluid. The
barrier properties are also useful for preventing the
migration of oxygen into the water (DIN 4726), which may be
damaging in the case where the pipe is used to transport hot
water for heating (the presence of oxygen is a source of
corrosion of steel or iron components of the heating
installation). It is also desirable to stop the migration of
contaminants present in the polyolefin layer (antioxidants,
polymerization residues, etc.) into the transported fluid.
More generally, the multilayer pipe can be used for
transporting chemicals, especially those capable of
chemically degrading polyolefins.
The multilayer pipe may also be used for transporting a gas,
especially a pressurized gas. When the polyolefin is a
polyethylene of the PESO or PE100 type, it is especially
suitable for withstanding pressures above 10 bar, or even
above 20 bar, or even still above 30 bar. The gas may be of
varying nature. It may be, for example:
• a gaseous hydrocarbon (for example, town gas, a
gaseous alkane, especially ethane,. propane or
butane, a gaseous alkene, especially ethylene,
propylene or butene);
• nitrogen;
• helium;
• hydrogen;
• oxygen; or
• a gas that is corrosive or capable of degrading
polyethylene or polypropylene. For example, it may

be an acidic or corrosive gas, such as H2S or HC1 or
HF.
Mention will also be made of the advantage of these pipes
for applications associated with air-conditioning, in which
the gas flowing in the pipes is a cryogen. It may be C02,
especially supercritical C02, an HFC or HCFC gas. The
optional layer C1 or else layer C2 exhibits good resistance
to these gases, as it is a f luoropolymer. Preferably, the
f luoropolymer of layers C1 and C2 is PVDF, as it is
particularly resistant. It is possible for the cryogen to
condense at certain points in the air-conditioning circuit
and to be liquid. The multilayer pipe can therefore also
apply to the case in which the cryogenic gas has condensed
into liquid form.
The fluid may also be a fuel, for example a petrol
The multilayer pipe may also be used for transporting a
fuel, for example a petrol, especially a petrol that
contains an alcohol. The petrol may be, for example, the M15
petrol (15% methanol, 42.5% toluene and 42.5% isooctane),
Fuel C (50% toluene, 50% isooctane), CE10 (10% ethanol and
90% of a mix containing 45% toluene and 45% isooctane} . It
may also be MTBE.
[Examples]
The examples which follow illustrate the improved adhesion
when a blend of a flexible fluoropolymer and a
functionalized fluoropolymer is used.
Products used
KYNAR® 720: a PVDF homopolymer from ARKEMA with a melt flow
index of 20 g/10 min (230°C/5 kg) and a melting point of
around 170°C.
KYNAR® 710: a PVDF homopolymer from ARKEMA with a melt flow
index of 25 g/10 min (230°C/5 kg) and a melting point of
around 17 0°C.

PVDF-1: KYNAR© 720 onto which maleic anhydride had been
radiation-grafted. The grafting was carried out by blending
KYNAR® 720 in a twin-screw extruder with 2 wt% of maleic
anhydride. The blend was granulated and then bagged in
aluminum-lined bags, then the bags and their blend were
irradiated to 3 Mr ad using a cobalt-60 bomb for 17 hours.
The product was recovered and vacuum-degassed in order to
remove the ungrafted residual maleic anhydride. The content
of grafted maleic anhydride was 1% (by infrared
spectroscopy) . The MFR (melt flow rate) of the PVDF-1 was
13 g/10 min (230°C/5 kg) .
PVDF-2: KYNAR© 710 onto which maleic anhydride had been
radiation-grafted. The grafting was carried out by blending
KYNAR® 710 in a twin-screw extruder with 2 wt% of maleic
anhydride. The blend was granulated and then bagged in
aluminum-lined bags, then the bags and their blend were
irradiated to 3 Mrad using a cobalt-60 bomb for 17 hours.
The product was recovered and vacuum-degassed in order to
remove the ungrafted residual maleic anhydride. The content
of grafted maleic anhydride was 1% (by infrared
spectroscopy) . The MFR (melt flow rate) of the PVDF-2 was
16 g/10 min (230°C/5 kg).
LOTADER® AX8840: a copolymer of ethylene (92%) and glycidyl
methacrylate (8%) from ARKEMA, having a melt index of 5
according to the ASTM D1238 standard.
XPE: the layer XPE was obtained from a blend containing 95%
of the BORPEX® ME-2510 grade and 5% of the MB-51 grade sold
by BOREALIS.
The examples relate to multilayer pipes having the following
structure:
KYNAR® 720/layer comprising a functionalized
fluoropolymer/LOTADER® AX8840/XPE

The KYNAR® 720 layer is the inner layer and the XPE layer is
the outer layer. XPE denotes a crossiinked polyethylene
obtained from a polyethylene bearing silane functional
groups. The XPE layer is obtained by extruding a blend of
two products sold by BOREALIS (95 wt% of BORPEX® ME-2510
which is the polyethylene bearing silane functional groups
and 5% of MB-51), then by crosslinking the blend by putting
the pipes into a bath of hot water (70°C) for 5 days.
Example 1 (comparative)
A multilayer pipe having the following structure was
manufactured:
KYNAR® (120µm)/PVDF-1 (50 µm) /LOTADER® AX8840 (50 µm) /XPE
(780 µm)
The pipes were obtained by coextruding a layer of
polyethylene modified by silane groups (extrusion
temperature of around 230°C), a layer of LOTADER® AX8840
(extrusion temperature of around 250°C), a layer of PVDF-1
and a layer of KYNAR® 720 (extrusion temperature of around
250°C) . Next, the pipes were placed in a heated bath in
order to obtain the XPE.
The respective thickness of the layers was (for a pipe
having an outer diameter of 14 mm) 0.78 mm of XPE, 50 µm of
LOTADER® AX8840 and 50µm of modified KYNAR® 720 and 120 µm
of KYNAR® 720. The XPE layer was the outer layer. All the
layers adhered to one another.
The adhesion between the grafted KYNAR and LOTADER® AX8840
layers, 5 days after the extrusion, was measured by
circumferential peel to be 15 N/cm. The adhesion was of the
adhesive failure type.
Example 2 (according to the invention)
The conditions from Example 1 were repeated but the PVDF-1
layer was replaced, by a layer of a blend comprising 50% of

PVDF-1 and 50% of a VDF/HFP copolymer containing 16% HFP and
having a viscosity at 230°C of 900 Pa.s at 100 s_1.
The adhesion between the grafted KYNAR and LOTADER® AX8840
layers, 5 days after the extrusion, was measured by
circumferential peel to be 42 N/cm. The adhesion was of the
cohesive failure type.
Example 3 (according to the invention)
The conditions from Example 1 were repeated but the PVDF-1
layer was replaced by a layer of a blend comprising 50% of
PVDF-2 and 50% of a VDF/HFP copolymer containing 16% HFP and
having a viscosity at 230°C of 900 Pa.s at 100 s-1.
The adhesion between the grafted KYNAR and LOTADER© AX8840
layers, 5 days after the extrusion, was measured by
circumferential peel to be 45 N/cm. The adhesion was of the
cohesive failure type.
Example 4 (comparative)
The conditions from Example 1 were repeated but the PVDF-1
layer was replaced by a layer of a blend comprising 50% of
PVDF-2 and 50% of a VDF/HFP copolymer containing 16% HFP and
having a viscosity at 230°C of 2300 Pa.s at 100 s'1.
The adhesion between the grafted KYNAR and LOTADER© AX8840
layers, 5 days after the extrusion, was measured by
circumferential peel to be 20 N/cm. The adhesion was of the
adhesive failure type.
Example 1 shows that when the functionalized fluoropolymer
(here, a radiation-grafted PVDF) is not diluted, the layer
of this polymer has an adhesion with the LOTADER® AX8840
layer of around 15 N/cm. This adhesion is very substantially
improved (Example 2) when the grafted fluoropolymer is
diluted in a flexible fluoropolymer. The adhesion is further
improved when a flexible fluoropolymer is used in the
presence of a more fluid grafted fluoropolymer (Example 3).

Table I

(Table Removed)

WE CLAIM:
1. A multilayer pipe comprising (in the following order,
from the inside of the pipe outward):
• optionally, a layer C1 comprising at least one
fluoropolymer;
• a layer C2 comprising a blend of:

- at least one functionalized fluoropolymer; and
- at least one flexible fluoropolymer that has a
tensile modulus between 50 and 1000 MPa (measured
according to the ISO R 527 standard at 23°C),
advantageously between 100 and 750 MPa and
preferably between 200 and 600 MPa;

• optionally, an adhesive tie layer C3;
• a layer C4 comprising at least one polyolefin or a
blend of at least one polyolefin with at least one
functionalized polyolefin;
• a barrier layer C5; and
• optionally, a layer C6 comprising at least one
polyolefin.

2. The multilayer pipe as claimed in claim 1,
characterized in that the barrier layer C5 is a metal sheath
or comprises EVOH or an EVOH-based blend, a PVDF or a PGA.
3. The multilayer pipe as claimed in claim 1 or 2,
characterized in that the functionalized fluoropolymer is a
copolymer comprising at least one fluoromonomer and at least
one unsaturated monomer bearing a functional group chosen
from the following groups: carboxylic acid, carboxylic acid
salt, carbonate, carboxylic acid anhydride, epoxide,
carboxylic acid ester, silyl, alkoxysilane, carboxylic acid
amide, hydroxy or isocyanate.
4. The multilayer pipe as claimed in one of claims 1 to 4,
characterized in that the functionalized fluoropolymer is
obtained by irradiation-grafting of at least one unsaturated
monomer onto a fluoropolymer.

5. The multilayer pipe as claimed in claim 4, in which the
unsaturated monomer grafted to the fluoropolymer has a C=C
double bond and also at least one polar functional group
which may be a carboxylic acid, carboxylic acid salt,
carboxylic acid anhydride, epoxide, carboxylic acid ester,
silyl, alkoxysilane, carboxylic acid amide, hydroxy or
isocyanate functional group.
6. The multilayer pipe as claimed in claim 5, in which the
unsaturated monomer grafted to the fluoropolymer is an
unsaturated carboxylic acid having 4 to 10 carbon atoms and
functional derivatives thereof, preferably an anhydride.
7. The multilayer pipe as claimed in claim 5, in which the
unsaturated monomer which is grafted is methacrylic acid,
acrylic acid, maleic acid, fumaric acid, itaconic acid,
citraconic acid, undecylenic acid, allylsuccinic acid,
cyclohex-4-ene-l,2-dicarboxylic acid, 4-methylcyclohex-4-
ene-1,2-dicarboxylic acid, bicyclo[2.2.1]hept-5-ene-2,3-
dicarboxylic acid, x-methylbicyclo[2.2.1]hept~5~ene-2,3-
dicarboxylic acid, zinc, calcium or sodium undecylenate,
maleic anhydride, itaconic anhydride, citraconic anhydride,
dichloromaleic anhydride, difluoromaleic anhydride, itaconic
anhydride, crotonic anhydride, glycidyl acryiate or
methacrylate, allylglycidyl ether, vinylsilanes, preferably
vinyltrimethoxysilane, vinyltriethoxysilane, vinyltri-
acetoxysilane and y-methylacryloxypropyltrimethoxysilane.
8. The multilayer pipe as claimed in any one of the
preceding claims, characterized in that the viscosity of the
functionalized fluoropolymer (measured with a capillary
rheometer at 230°C and 100 s-1) is between 100 and 1500 Pa.s,
advantageously between 200 and 1000 Pa.s and preferably
between 500 and 1000 Pa.s.
9. The multilayer pipe as claimed in any one of the
preceding claims, characterized in that the viscosity of the

flexible fluoropolymer (measured with a capillary rheometer
at 230°C and 100 s-1) is between 100 and 1500 Pa.s,
advantageously between 200 and 1000 Pa.s and preferably
between 500 and 1000 Pa.s.
10. The multilayer pipe as claimed in any one of the
preceding claims, characterized in that the crystallization
temperature of the flexible fluoropolymer (measured by DSC
according to the ISO 11357-3 standard) is between 50 and
120°C, preferably between 85 and 110°C.
11. The multilayer pipe as claimed in any one of the
preceding claims, in which the fluoropolymer of layer C1
and/or of layer C2 is a polymer having, in its chain, at
least one monomer chosen from compounds containing a vinyl
group capable of opening in order to be polymerized and
which contains, directly attached to this vinyl group, at
least one fluorine atom, one fluoroalkyl group or one
fluoroalkoxy group.
12. The multilayer pipe as claimed in any one of the
preceding claims, in which the fluoropolymer of layer C1
and/or of layer C2 is a VDF1 homopolymer or copolymer
containing at least 50% by weight of VDF, or else an EFEP.
13. The multilayer pipe as claimed in any one of the
preceding claims, in which the fluoropolymer onto which the
unsaturated monomer is grafted, is a VDF homopolymer or
copolymer containing at least 50% by weight of VDF, or else
an EFEP.
14. The multilayer pipe as claimed in one of the preceding
claims, characterized in that layer C3 is directly attached
to layer C2.
15. The multilayer pipe as claimed in one of the preceding
claims, characterized in that layer C4 is directly attached
to the optional layer C3 or else to layer C2.

16. The multilayer pipe as claimed in one of claims 1 to
13, comprising (in the following order, from the inside of
the pipe outward) a layer C1, a layer C2, a layer C3 directly
attached to layer C2, a layer C4 directly attached to layer
C3, a layer C5 and a layer C6.
17. The multilayer pipe as claimed in any one of the
preceding claims, in which the layers adhere to one another
in their respective contact regions.
18. The multilayer pipe as claimed in any one of the
preceding claims, in which the adhesion tie comprises at
least one functionalized polyolefin optionally blended with
a polyolefin.
19. The multilayer pipe as claimed in claim 18,
characterized in that the functionalized polyolefin of the
adhesion tie has functional groups capable of reacting with
the functional groups grafted onto the fluoropolymer.
20. The multilayer pipe as claimed in one of claims 1 to
17, in which when layer C3 is absent and layer C4 is in
direct contact with layer C2, the functionalized polyolefin
of the blend has functional groups capable of reacting with
the functional groups grafted onto the fluoropolymer.
21. The multilayer pipe as claimed in any one of the
preceding claims, in which the polyolefin of layer C4 and/or
of layer C6 is a polymer predominantly comprising ethylene
and/or propylene units.
22. The multilayer pipe as claimed in claim 21, in which
the polyolefin is a polyethylene homopolymer or copolymer or
a polypropylene homopolymer or copolymer.
23. The multilayer pipe as claimed in claim 22, in which
the polyolefin is an XPE.

24. A multilayer pipe comprising (in the following order,
from the inside of the pipe outward):
• optionally a layer C1 comprising at least one
fluoropolymer, preferably such as defined in one of
claims 12;
• a layer C2 comprising the blend such as defined in-
one of claims 1 to 13;
• a layer C4 comprising a blend of at least one
polyolefin and of at least one functionalized
polyolefin which has functional groups capable of
reacting with the functional groups grafted onto the
fluoropolymer;
• a barrier layer C5 which is a metal sheath or which
comprises EVOH or an EVOH-based blend, PVDF or PGA;
and
• optionally, a layer C6 comprising at least one
polyolefin.
25. A multilayer pipe comprising (in the following order,
from the inside of the pipe outward):
• optionally, a layer C1 comprising at least one PVDF
homopolymer or copolymer;
• a layer C2 comprising at least one PVDF homopolymer
or copolymer onto which maleic anhydride has been
radiation-grafted;
• an adhesion tie layer C3;
• a layer C4 comprising at least one polyethylene,
preferably of XPE type;
• a barrier layer C5 which is a metal sheath; and
• optionally, a polyethylene layer C6, preferably of
the XPE type.
26. The multilayer pipe as claimed in either of claims 24
and 25, in which the layers adhere to one another in their
respective contact regions.

27. The multilayer pipe as claimed in either of claims 25
and 26, in which the adhesion tie comprises at least one
functionalized poiyolefin having functional groups capable
of reacting with maleic anhydride, optionally blended with a
poiyolefin.
28. The multilayer pipe as claimed in claim 27, in which
the functionalized poiyolefin has epoxide or hydroxy
functional groups.
29. The multilayer pipe as claimed in either of claims 27
and 28, in which the functionalized poiyolefin is a
copolymer of ethylene, of an unsaturated epoxide, for
example glycidyl methacrylate, and optionally of an alkyl
acrylate.
30. The multilayer pipe as claimed in. any one of the
preceding claims, in which the adhesion tie layer is
positioned between C5 and C4 and/or between C5 and C6.
31. The use of a pipe such as defined in any one of claims
1 to 30, for transporting water, especially hot water,
chemicals or a gas.
32. The use of a pipe such as defined in any one of claims
1 to 30, for conveying a fuel.
33. The use of a pipe such as defined in any one of claims
1 to 30, for conveying hot water in an under-floor radiant
heating system or for conveying hot water to a radiator.
34. The use of a pipe such as defined in any one of claims
1 to 30, in radiant heating systems.
35. The use as claimed in claim 31, characterized in that
the gas is a gaseous hydrocarbon, nitrogen, helium,
hydrogen, oxygen, a corrosive gas or a gas capable of
degrading polyethylene or polypropylene, or a cryogen.

36. A process for manufacturing a multilayer pipe such as
defined in one of claims 1 to 30, having at least one type-C
XPE layer, in which:
• the various layers of the multilayer pipe are
coextruded; and then
• the multilayer pipe thus formed is exposed to
radiation in order to crosslink the polyethylene
layer or layers.

37. A radiant heating system comprising at least one
multilayer pipe, as claimed in any one of claims i to 30.
38. A multilayer pipe, substantially as hereinbefore
described with reference to the foregoing examples and
accompanying drawing.
39. A process for manufacturing a multilayer pipe,
substantially as hereinbefore described with reference to
the foregoing examples and accompanying drawing.