The present invention relates to a multilayer tube
based on a polyamide and a fluoropolymer for transferring
fluids.
As examples of tubes for transferring fluids, mention
may be made of petrol pipes, in particular for carrying
petrol from the tank to the engine of motor vehicles. As
other examples of fluid transfer, mention may be made of the
fluids used in fuel cells, C02 systems for cooling, hydraulic
systems, cooling circuits and air-conditioning circuits, and
medium-pressure power transfer.
For safety and environmental protection reasons, motorvehicle
manufacturers require these tubes to have not only
mechanical properties such as burst strength and flexibility
with good cold (-40°C) impact strength and high-temperature
(125°C) strength, but also a very low permeability to
hydrocarbons and to their additives, particularly alcohols
such as methanol and ethanol. These tubes must also have
good resistance to the fuels and lubrication oils for
engines. These tubes are manufactured by coextruding the
various layers using standard techniques for thermoplastics.
The invention is particularly useful for transporting
petrol.
The content of French appln. 04-11187 filed on 20 Oct.
04, French appln. 04-11570 filed on 29 Oct. 04, French appln
04-11071 filed on 19 oct 04 and US provisionnal
specification 60/647144 filed on 26 Jan. 05 are incorporated
in the present application.
Prior art and the technical problems
Among the characteristics of the specification for
tubes carrying petrol, five are particularly difficult to
achieve simultaneously in a simple manner:
- cold (-40°C) impact strength, the tube not breaking;
- fuel resistance;
- high-temperature (125°C) resistance;
- very low permeability to petrol;
- good dimensional stability of the tube when used for
petrol.
In the multilayer tubes of various structures, the cold
impact strength remains unpredictable before the
standardized cold impact strength tests have been carried
out.
Patent EP 558 373 discloses a tube for transporting
petrol, which respectively comprises a polyamide outer
layer, a tie layer and an inner layer in contact with the
petrol and consisting of a fluoropolymer. The petrol
permeability is excellent but the shock resistance is
insufficient.
Patents EP 696 301, EP 740 754 and EP 726 926 disclose
tubes for transporting petrol, which comprise respectively a
polyamide outer layer, a tie layer, a PVDF (polyvinylidene
fluoride) layer, a tie layer and a polyamide inner layer in
contact with the petrol.
Other polyamide/PVDF-based tubes for transporting
petrol are disclosed in Patents US 5 472 784, US 5 474 822,
US 5 500 263, US 5 510 160, US 5 512 342 and US 5 554 426.
In these tubes of the prior art, complicated
compositions have been described for ensuring adhesion
between the polyamide and the PVDF.
Patent EP 1 104 526 discloses a tube having, along its
radial direction from the inside outwards, an inner layer,
based on a fluororesin (or fluoropolymer) and intended to
come into contact with a flowing fluid, characterized in
that the inner layer is formed from a blend comprising a
semicrystalline thermoplastic fluororesin (for example PVDF)
and an ABC triblock copolymer, the three blocks A, B and C
being linked together in this order, each block being either
a homopolymer or a copolymer obtained from two or more
monomers, block A being connected to block B and block B
being connected to block C by means of a covalent bond or by
an intermediate molecule linked to one of these blocks via a
covalent bond or to the other block via another covalent
bond, and in that:
-block A is compatible with the fluororesin;
-block B is incompatible with the fluororesin and is
incompatible with block A;
-block C is incompatible with the fluororesin, block A
and block B;
the outer layer of the tube being made of a polyamide.
This PVDF-based layer is impact-resistant while still
remaining a barrier to petrol. However, adhesion to the
polyamide layer remains to be provided.
A fluoropolymer-based composition has now been found
that is particularly impermeable and impact-resistant and is
able to adhere directly to substrates, such as a polyamide
substrate. The present composition exhibits excellent
solvent resistance, for example to solvents such as alcoholbased
fuels, and very low permeability.
Brief description of the invention
The present invention relates to a multilayer tube
comprising, in its radial direction from the outside
inwards:
a polyamide outer layer (1);
an inner layer (2) of a composition comprising, the
total being 100, 5 to 30% by weight of a blend (A)
comprising:
a polyethylene carrying epoxy functional groups,
an impact modifier chosen from elastomers and very
low-density polyethylenes, the said impact
modifier being completely or partly
functional!zed;
95 to 70% by weight of a blend (B) comprising:
a fluoropolymer (Bl),
a functionalized fluoropolymer (B2),
the proportion of (B2) being between 1 and 80%
(advantageously between 1 and 60%) by weight of (A)+(B), the
layers being successive and adhering to one another in their
respective contact region. The inner layer is the layer in
contact with the transported fluid.
According to one embodiment of the invention, the inner
layer (2) contains an electrically conductive material,
producing a surface resistivity of preferably less than 106
Q.
According to another embodiment of the invention, the
inner layer (2) contains essentially no electrically
conductive material and the tube comprises a layer (2a)
placed beside the layer (2) , which layer (2a), like the
layer (2), may be based on (A) and (B) but also contains an
electrically conductive material producing a surface
resistivity of preferably less than 106 Q. This layer (2a)
may also be a f luoropolymer (Bl) or a blend of a
fluoropolymer (Bl) and an impact modifier and contains, in
addition, an electrically conductive material producing a
surface resistivity of preferably less than 106 Q. The inner
layer (2a) is the layer in contact with the transported
fluid.
One advantage of these structures is that the layer in
contact with the transported fluid (for example petrol for
motor vehicles) contains no or very few substances (for
example oligomers or plasticizers) that can pass into the
petrol. To quantify this property, an extraction fluid (for
example methanol or ethanol or even octane) is made to
circulate in a closed circuit in the tube at temperatures of
about 40 or 60°C. How much of the extraction fluid is picked
up by the tube is then measured and this measurement is
repeated for several hours in succession until a stable
value is obtained. This measurement may also be carried out
by immersing the material of the inner layer, in the form of
granules, into the extraction fluid and stirring it. The
inner layer is considered to be clean if the extraction
fluid picks up no more than 5%, advantageously 4% and
preferably 3%, by weight of products extracted from the
inner layer.
Another embodiment relates to a multilayer tube
comprising, in its radial direction from the outside
inwards:
a polyamide outer layer (1);
a layer (2) of a composition comprising, the total
being 100%, 0 to 30% by weight of a blend (A)
comprising:
a polyethylene carrying epoxy functional groups,
an impact modifier chosen from elastomers and very
low-density polyethylenes, the said impact
modifier being completely or partly
functional!zed;
100 to 70% by weight of a blend (B) comprising:
optionally, a fluoropolymer (Bl),
a functionalized fluoropolymer (B2),
the proportion of (B2) being between 10 and 100%,
advantageously 30 to 90% and preferably 40 to 75%, by weight
of (A) + (B);
a polyamide inner layer (3);
the layers being successive and adhering to each other in
their respective contact region. The inner layer is in
contact with the transported fluid.
According to one embodiment of the invention, the inner
layer (3) contains - an electrically conductive material
producing a surface resistivity of preferably less than 106
Q.
According to another embodiment of the invention, the
inner layer (3) contains essentially no electrically
conductive material and the tube comprises a layer (3a)
placed beside the layer (3), which layer (3a) is made of a
polyamide but contains, in addition, an electrically
conductive material producing a surface resistivity of
preferably less than 106 Q. Advantageously, the polyamide of
the layer (3a) is the same as that of the layer (3).
According to one advantageous embodiment, the polyamide
of the outer layer (1) is a polyamide having amine terminal
groups or comprising more amine terminal groups than acid
terminal groups.
According to one advantageous embodiment, a layer of a
polyamide having amine terminal groups or one comprising
more amine terminal groups than acid terminal groups is
placed between the outer layer (1) and the layer (2).
According to another embodiment, these two preceding
embodiments may be combined.
These tubes may have an outside diameter of 6 to 110 mm
and a thickness of around 0.5 to 5 mm.
Advantageously, the petrol tube according to the
invention has an outside diameter ranging from 6 to 12 mm
and a total thickness of 0.22 mm to 2.5 mm. In the tubes
having an inner layer (2) or (2a) , the thickness of the
outer layer (1) represents between 30 and 95% of the
thickness of the tube. In the tubes having an inner layer
(3) or (3a), the thickness of the outer layer (1) represents
between 25 and 50% of the thickness of the tube.
The tube of the present invention has a very low
permeability to petrol, especially to hydrocarbons and to
their additives, in particular alcohols like methanol and
ethanol, or even ethers such as MTBE or ETBE. These tubes
also have good resistance to fuels and to lubricating oils
for engines.
This tube exhibits very good mechanical properties at
low temperature and at high temperature.
The invention also relates to the use of these tubes
for transporting petrol.
Detailed description of the invention
The tubes having a fluoropolymer-based inner layer (2)
or (2a) will firstly be described.
With regard to the polyamide of the outer layer (1) ,
mention may be made of PA-11 and PA-12.
Mention may also be made of those of formula X, Y/Z or
6, Y2/Z in which:
X denotes the residues of an aliphatic diamine having
from 6 to 10 carbon atoms;
Y denotes the residues of an aliphatic dicarboxylic
acid having from 10 to 14 carbon atoms;
Y2 denotes the residues of an aliphatic dicarboxylic
acid having from 15 to 20 carbon atoms; and
Z denotes at least one unit chosen from the residues of
a lactam, the residues of an alpha, omega-aminocarboxylic
acid, the unit XI, Yl in which XI denotes the residues of an
aliphatic diamine and Yl denotes the residues of an
aliphatic dicarboxylic acid,
the weight ratios Z/(X-t-Y+Z) and Z/(6+Y2+Z) being
between 0 and 15%.
Mention may be made by way of example of PA-6, 10
(hexamethylenediamine and sebacic acid units), PA-6, 12
(hexamethylenediamine and dodecanedioic acid units), PA-6,
14 (hexamethylenediamine and C14 diacide), PA-6, 18
(hexamethylenediamine and CIS diacide) and PA-10, 10 (1,
10-decane diamine and sebacic acid units).
Mention may also be made of polyamides of formula
X/Y,Ar in which:
• Y denotes the residues of an aliphatic diamine having
from 8 to 20 carbon atoms;
• Ar denotes the residues of an aromatic dicarboxycylic
acid;
• X denotes either the residues of aminoundecanoic acid
NH2~(CH2)1Q-COOH, of lactam 12 or of the corresponding
amino acid, or the unit Y,x remains from the
condensation of the diamine with an aliphatic diacid
(x) having between 8 and 20 carbon atoms or else the
unit Y, I remains from the condensation of the diamine
with isophthalic acid.
X/ Y,Ar denotes, for example:
- 11/10,T, which results from the condensation of
aminoundecanoic acid, 1,10-decanediamine and terephthalic
acid;
- 12/12,T, which results from the condensation of
lactam 12, 1,12-dodecanediamine and terephthalic acid;
- 10,10/10,T, which results from the condensation of
sebacic acid, 1,10-decanediamine and terephthalic acid; and
- 10,I/10,T, which results from the condensation of
isophthalic acid, 1,10-decanediamine and terephthalic acid.
The inherent viscosity of the polyamide of the outer
layer (1) may be between 1 and 2 and advantageously between
1.2 and 1.8. The inherent viscosity is measured at 20°C for
a 0.5% concentration in metacresol. The polyamide of the
outer layer (1) may contain from 0 to 30% by weight of at
least one product chosen from plasticizers and impact
modifiers per 100 to 70% of polyamide respectively. This
polyamide may contain the usual additives, such as UV
stabilizers, thermal stabilizers, antioxidants, fire
retardants, etc.
With regard to blend (A) and firstly the polyethylene
carrying epoxy functional groups, this may be a polyethylene
onto which epoxy functional groups have been grafted or an
ethylene/unsaturated epoxide copolymer.
With regard to ethylene/unsaturated epoxide copolymers,
mention may be made, for example, of copolymers of ethylene
with an alkyle (meth)acrylate and with an unsaturated
epoxide, or copolymers of ethylene with a vinyl ester of a
saturated carboxylic acid and with an unsaturated epoxide.
The amount of epoxide may be up to 15% by weight of the
copolymer and the amount of ethylene at least 50% by weight.
Advantageously, the proportion of epoxide is between 2 and
12% by weight. Advantageously, the proportion of alkyl
(meth)acrylate is between 0 and 40% by weight and preferably
between 5 and 35% by weight.
Advantageously, this is an ethylene/alkyl
(meth)acrylate/unsaturated epoxide copolymer.
Preferably, the alkyl (meth) acrylate is such that the
alkyl possesses 1 to 10 carbon atoms.
The MFI (melt flow index) may for example be between
0.1 and 50 g/10 min (190°C/2.16 kg).
Examples of alkyl acrylates and methacrylates that can
be used are especially methyl methacrylate, methyl acrylate,
ethyl acrylate, n-butyl acrylate, isobutyl acrylate and
2-ethylexyl acrylate. Examples of unsaturated epoxides that
can be used are especially:
aliphatic glycidyl esters and ethers, such as allyl
glycidyl ether, vinyl glycidyl ether, glycidyl maleate,
glycidyl itaconate, glycidyl acrylate and glycidyl
methacrylate; and
alicyclic glycidyl esters and ethers, such as 2-
cyclohexen-1-yl glycidyl ether, glycidyl cyclohexene-4,5-
dicarboxylate, glycidyl cyclohexene-4-carboxylate, glycidyl
2-methyl-5-norbornene-2-carboxylate and glycidyl endo-cisbicyclo
2.2.1] hept-5-ene-2,3-dicarboxylate.
With regard to blend (A) and now the impact modifier,
and firstly elastomers, mention may be made of SBS, SIS and
SEES block polymers and ethylene-propylene (EPR) or
ethylene-propylene-diene monomer (EPDM) elastomers. As
regards the very-low density polyethylenes, these are, for
example, metallocene polyethylenes of density between for
example 0.860 and 0.900. Acrylic elastomers are not
recommended as they cause permeability to the petrol. The
term "acrylic elastomers" denotes elastomers based on at
least one monomer chosen from acrylonitrile, alkyl
(meth)acrylates and core/shell copolymers. As regards
core/shell copolymers, these are in the form of fine
particles having an elastomer core and at least one
thermoplastic shell (usually PMMA), the size of the
particles generally being less than 1 urn and advantageously
between 50 and 300 rim. It would not be outside the scope of
the invention to use these acrylic elastomers, but this
would be to the detriment of the permeability to the petrol.
For example, 1 to 3 parts of acrylic elastomers per 5 to 10
parts of other impact modifiers may be used. Advantageously,
an ethylene-propylene (EPR) or ethylene-propylene-diene
monomer (EPDM) elastomer is used. The functionalization may
be provided by grafting or copolymerizing with an
11
unsaturated carboxylic acid. It would not be outside the
scope of the invention to use a functional derivative of
this acid. Examples of unsaturated carboxylic acids are
those having 2 to 20 carbon atoms, such as acrylic,
methacrylic, maleic, fumaric and itaconic acids. The
functional derivatives of these acids comprise, for example,
anhydrides, ester derivatives, amide derivatives, imide
derivatives and metal salts (such as alkali metal salts) of
unsaturated carboxylic acids.
Unsaturated dicarboxylic acids having 4 to 10 carbon
atoms and their functional derivatives, particularly their
anhydrides, are particularly preferred grafting monomers.
These grafting monomers comprise, for example, maleic,
fumaric, itaconic, citraconic, allylsuccinic, cyclohex-4-
ene-1,2-dicarboxylic, 4-methylcyclohex-4-ene-l, 2-
dicarboxylic, bicyclo[2.2.1]hept-5-ene-2, 3-dicarboxylic and
x-methylbicyclo[2.2.1]hept-5-ene-2,3-dicarboxylic acids and
maleic, itaconic, citraconic, allylsuccinic, cyclohex-4-ene-
1,2-dicarboxylic, 4-methylenecyclohex-4-ene-l,2-
dicarboxylic, bicyclo-[2.2.1]hept-5-ene-2,3-dicarboxylic and
x-methyl-bicyclo[2.2.1]hept-5-ene-2,2-dicarboxylic
anhydrides. Advantageously, maleic anhydride is used.
Various known processes may be used to graft a grafting
monomer onto a polymer. For example, this may be carried out
by heating the polymers to a high temperature, about 150 to
about 300°C, in the presence or absence of a solvent and
with or without a radical initiator. The amount of grafting
monomer may be chosen appropriately, but it is preferably
from 0.01 to 10%, better still from 600 ppm to 2%, with
respect to the weight of the polymer onto which the graft is
attached.
As regards the functionalized fluoropolymer (B2) and
firstly the fluoropolymer, this denotes any polymer having
in its chain at least one monomer chosen from compounds that
contain a vinyl group capable of opening in order to be
polymerized and that contains, directly attached to this
vinyl group, at least one fluorine atom, a fluoroalkyl group
or a fluoroalkoxy group.
As examples of monomers, mention may be made of vinyl
fluoride; vinylidene fluoride (VDF); trifluoroethylene
(VF3); chlorotrifluoroethylene (CTFE); 1,2-difluoroethylene;
tetrafluoroethylene (TFE); hexafluoropropylene (HFP);
perfluoro(alkyl vinyl) ethers, such as perfluoro(methyl
vinyl) ether (PMVE), perfluoro(ethyl vinyl) ether (PEVE) and
perfluoro(propyl vinyl) ether (PPVE).
The fluoropolymer may be a homopolymer or a copolymer;
it may also include non-fluorinated monomers such as
ethylene.
As examples, the fluoropolymer is chosen from:
- homopolymers and copolymers of vinylidene fluoride (VDF)
preferably containing, by weight, at least 50% VDF, the
copolymer being chosen from chlorotrifluoroethylene (CTFE),
hexafluoropropylene (HFP), trifluoroethylene (VF3) and
tetrafluoroethylene (TFE);
- 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.
- mention may also be made of
ethylene/tetrafluoroethylene (ETFE) copolymers.
Advantageously, the fluoropolymer is a poly(vinylidene
fluoride) (PVDF) homopolymer or copolymer. Preferably, the
PVDF contains, by weight, at least 50%, more preferably at
least 75% and better still at least 85% 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 and a shear rate of 100 s"1 using a
capillary rheometer. These PVDFs are well-suited to
extrusion and to injection moulding. Preferably, the PVDF
has a viscosity ranging from 300 Pa.s to 1200 Pa.s, the
viscosity being measured at 230°C with a shear rate of 100 s"
1 using a capillary rheometer.
By way of example of functionalized fluoropolymer mention
may be made of functionalized PVDF, that is a PVDF
comprising monomer units of VDF and of at least one
functional monomer having a least one functional group that
may be one of the following groups : a carboxylic acid, a
carboxylic acid salt, a carbonate, a carboxylic acid
anhydride, an epoxide, a carboxylic acid ester, a silyl, an
alkoxysilane, a carboxylic amide, a hydroxyl, an isocyanate.
The functionalized PVDF is prepared in suspension, in
emulsion or in solution by copolymerizing VDF with said at
least one functional monomer and optionally at least another
comonomer.
By way of example of a functionalized fluoropolymer,
mention may be made of that grafted with an unsaturated
monomer. It may be produced according to a grafting process
in which :
a) the fluoropolymer is melt-blended with the
unsaturated monomer ;
b) the blend obtained in a) is made in the form of
films, sheets, granules or powder ;
c) the products from step b) are subjected, in the
absence of air, advantageously to photon (y) or electron (p)
irradiation with a dose of between 1 and 15 Mrad; and
d) the product obtained in c) is optionally treated in
order to remove all or part of the unsaturated monomer that
has not been grafted onto the fluoropolymer.
As examples of unsaturated grafting monomers, mention
may be made of carboxylic acid and their derivatives, acid
chlorides, isocyanates, oxazolines, epoxydes, amines and
hydroxides. Examples of unsaturated carboxylic acids are
those having 2 to 20 carbon atoms such as acrylic,
methacrylic, maleic, fumaric and itaconic acids. The
functional derivatives of these acids comprise, for example,
anhydrides, ester derivatives, amide derivatives, imide
derivatives and metal salts (such as alkali metal salts) of
unsaturated carboxylic acids. Mention may also be made of
undecylenic acid and zinc undecylenate.
Unsaturated dicarboxylic acids having 4 to 10 carbon
atoms and their functional derivatives, particularly their
anhydrides, are particularly preferred grafting monomers.
Step a) is carried out in any blending device, such as
extruders or mixers used in the thermoplastics industry.
With regard to the proportions of the fluoropolymer and
of the unsaturated monomer, the proportion of fluoropolymer
is advantageously, by weight, from 90 to 99.9% per 0.1 to
10% of unsaturated monomer respectively. Preferably, the
proportion of f luoropolymer is from 95 to 99.9% per 0.1 to
5% of unsaturated monomer respectively.
After step a) it has been found that the
fluoropolymer/unsaturated monomer blend has lost about 10 to
50% of the unsaturated monomer that had been introduced at
the start of step a).
This proportion depends on the volatility and the
nature of the unsaturated monomer. In fact, the monomer has
been vented in the extruder or the mixer and it is recovered
in the venting circuits.
With regard to step c) , the products recovered after
step b) are advantageously packaged in polyethylene bags and
the air expelled, the bags then being sealed. During this
grafting step, it is preferable to avoid the presence of
oxygen. Flushing the fluoropolymer/graftable compound blend
with nitrogen or argon is therefore possible in order to
eliminate the oxygen.
As regards the method of irradiation, it is possible to
use, without distinction, electron irradiation, better known
as beta irradiation, and photon irradiation, better known as
gamma irradiation. Advantageously, the dose between 2 and 6
Mrad and preferably between 3 and 5 Mrad. This results in
the unsaturated monomer being grafted to an amount of 0.1 to
5 wt% (that is to say the grafted unsaturated monomer
corresponds to 0.1 to 5 parts per 99.9 to 95 parts of
fluoropolymer), advantageously 0.5 to 5 wt% and preferably
0.5 to 1.5 wt% ; better still 0.7 to 1.5 wt% ; better still
0.8 to 1.5 wt% ; better still 0.9 to 1.5 wt% ; better still
1 to 1.5 wt%. 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 grafting efficiency, and
therefore on the duration and the energy of the irradiation.
With regard to step d) , any ungrafted monomer and the
residues liberated by the grafting, especially HF can be
eliminated by any means. The proportion of grafted monomer
relative to the monomer present at the start of step c) is
between 50 and 100%. It is possible to wash with solvents
that are inert with respect to the fluoropolymer and to the
grafted functional groups. For example, when maleic
anhydride is grafted, it is possible to wash with
chlorobenzene. It is also possible, more simply, to vacuum
degas the product recovered at step c) , while optionally
heating at the same time. This operation may be carried out
using techniques known to those skilled in the art. It is
also possible to dissolve the modified fluoropolymer in a
suitable solvent, such as for example N-methyl pyrrolidone,
and then to precipitate the polymer in a non-solvent, for
example in water or in an alcohol.
As an example of a functionalized fluoropolymer,
mention may also be made of one that is grafted with an
unsaturated monomer, but via a radical route. The
unsaturated monomer may be chosen from those mentioned
above. This method is less effective than radiation grafting
- it is possible to graft no more than 0.8% of unsaturated
monomer and there is a risk of degrading the fluoropolymer.
However, this product may be suitable for simple operating
conditions.
One of the advantages of this radiation grafting
process is that it is possible to obtain higher grafted
unsaturated monomer contents than with conventional grafting
processes using a radical initiator. Thus, typically, with
the radiation grafting process, it is possible to obtain
contents of greater than 1% (one part of unsaturated monomer
per 99 parts of f luoropolymer) , or even greater than 1.5%,
whereas with a conventional grafting process carried out in
an extruder, the content is around 0.2 to 0.8%. Moreover,
the radiation grafting takes place "cold", typically at
temperatures below 100°C, or even below 70°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. One essential difference is
therefore that, in the case of a semicrystalline
f luoropolymer (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 is produced
in the case of grafting carried out in an extruder. The
unsaturated monomer is therefore not distributed along the
fluoropolymer chains in the same way in the case of
radiation grafting as in the case of grafting carried out in
an extruder. The modified fluoropolymer therefore has a
different distribution of the graftable compound along the
fluoropolymer chains compared with a product obtained by
grafting carried out in an extruder.
As examples of functionalized fluoropolymers, mention
may also be made of those in which a functional monomer or
an element carrying a functional group has been incorporated
during the polymerization. By way of example such
incorporation comes from the chain transfer agent. Such
functionalized fluoropolymers are disclosed in patents US 5
415 958, US 6 680 124 and US 6 703 465 and patent
application US 2004-0191440, the contents of which are
incorporated into the present application.
With regard to the fluoropolymer (Bl) , this may be
chosen from the same polymers as (B2) . (Bl) may be the same
polymer as (B2), but not functionalized, or it may be
different.
With regard to the embodiment in which the inner layer
(2) or (2a) is in contact with the transported fluid and
more particulary the proportions, those of (A) are
advantageously from 5 to 10% per 95 to 90% of (B)
respectively. The proportion of the polyethylene carrying
epoxy functional groups may be from 1 to 2 parts per 5 parts
of impact modifier. The proportion of (B2) is advantageously
between 35 and 60%, preferably between 45 and 55%, by weight
of (A) + (B) .
With regard to the preparation of the compositions of
the invention, these may be obtained by melt-blending of the
constituents using standard techniques for thermoplastics.
The (A)/(B) blends may furthermore contain at least one
additive chosen from:
dyes;
pigments;
antioxidants;
fire retardants;
UV stabilizers;
nanofillers;
nucleating agents.
With regard to the inner layer (2) containing an
electrically conductive material, mention may be made, as
examples of electrically conductive material, of carbon
black, carbon fibres and carbon nanotubes. It is
advantageous to use a carbon black chosen from those having
a BET specific surface area, measured according to the ASTM
D3037-89 standard, of 5 to 200 m2/g and DBF absorption,
measured according to the ASTM D 2414-90 standard, of 50 to
300 ml/100 g. The proportion of black is advantageously, by
weight, from 10 to 30% per 90 to 70% of the other
constituents respectively, and preferably from 12 to 23% per
88 to 77% of the other constituents respectively. These
carbon blacks are described in Patent Application
WO 99/33908, the contents of which are incorporated in the
present application.
With regard to the inner layer (2a) containing an
electrically conductive material, this layer, like the layer
(2) may consist of the blend of (A) and (B) and contains the
electrically conductive material. The proportions of (A) and
(B) and the nature of the constituents of (A) and (B) may be
the same as or different from those of the layer (2). It may
also be a fluoropolymer (Bl) or a blend of a fluoropolymer
(Bl) and an impact modifier and contains, in addition, an
electrically conductive material producing a surface
resistivity of preferably less than 106 Q. The impact
modifier may be chosen from those mentioned for the blend
(A), including acrylic elastomers. It may consist entirely
of acrylic elastomers (preferably core/shell elastomers),
since this layer does not need to be a barrier to petrol,
this function being provided by the layer (2). If the impact
modifier is not an acrylic elastomer or is a blend of an
acrylic elastomer with, for example, an EPR, this EPR is
advantageously functionalized. To make compatibilization
with (Bl) easier, it is recommended to add some
functionalized polymer (B2). The fluoropolymer (Bl) may be
the same as that of the layer (2) or be different. It is
also possible to add some functionalized fluoropolymer (B2),
which may be the same as that of the layer (2) or be
different. Advantageously, (Bl) and (B2) are PVDF
homopolymers or copolymers. The proportion of black by
weight is advantageously from 10 to 30% per 90 to 70% of the
other constituents respectively, and preferably from 12 to
23% per 88 to 77% of the other constituents respectively.
The proportion of impact modifier is advantageously from I
to 40% by weight of the combination of impact modifier,
fluoropolymer (Bl) and optional fluoropolymer (B2).
Preferably, this proportion is from 5 to 35% by weight of
the combination of impact modifier, fluropolymer (Bl) and
optional fluoropolymer (B2).
With regard to the embodiment in which the tube
includes an inner layer (3) , the polyamide of the outer
layer (1) may be chosen from the polyamides of the outer
layer (1) described above.
With regard to the layer (2), the nature of the
constituents (A) and (B) is the same as that described
above. The proportions of (A) are advantageously from 5 to
30% per 95 to 70% of (B) respectively. The proportions of
(A) are preferably from 5 to 10% per 95 to 90% of (B)
respectively. The proportion of polyethylene carrying epoxy
functional groups may be between 1 and 2 parts per 5 parts
of impact modifier. The proportion of (B2) is advantageously
between 35 and 60%, preferably between 45 and 55%, by weight
of (A) + (B) .
The polyamide of the inner layer (3) may be chosen from
the polyamides mentioned in the case of the outer layer, PA-
6 and PA-6/polyolefin blends having a PA-6 matrix and a
polyolefin dispersed phase.
In the PA-6/polyolefin blends having a PA-6 matrix and
a polyolefin dispersed phase, the term "polyolefin" denotes
both homopolymers and copolymers, and both thermoplastics
and elastomers. These include, for example,
ethylene/a-olefin copolymers. These polyolefins may be
LLDPEs, PEs, EPRs and EPDMs. They may be partly or
completely functionalized. The dispersed phase may be a
blend of one or more unfunctionalized polyolefins and one or
more functionalized polyolefins. Advantageously, the PA-6
matrix represents, by weight, 50 to 85% per 50 to 15% of
dispersed phase respectively. Preferably, the PA-6 matrix
represents, by weight, 55 to 80% per 45 to 20% of dispersed
phase respectively.
According to a preferred embodiment, the
PA-6/polyolefin blends having a PA-6 matrix comprise, the
total being 100%:
50 to 90% (advantageously 60 to 80%) of PA-6;
1 to 30% (advantageously 10 to 25%) of HDPE;
5 to 30% (advantageously 10 to 20%) of at least one
polymer PI chosen from impact modifiers and polyethylenes,
at least one of the HOPE and of PI being completely or
partly functionalized.
Advantageously, the impact modifier is chosen from
elastomers and very low-density polyethylenes.
With regard to the impact modifier and firstly the
elastomers, mention may be made of SBS, SIS, SEES block
copolymers and ethylene-propylene (EPR) and ethylenepropylene-
diene monomer (EPDM) elastomers. As regards the
very low-density polyethylenes, these are for example
metallocene polyethylenes having a density for example
between 0.860 and 0.900.
It is advantageous to use an ethylene-propylene (EPR)
or ethylene-propylene-diene monomer (EPDM) elastomer. The
functionalization may be provided by grafting or
copolymerizing with an unsaturated carboxylic acid. It would
not be outside the scope of the invention to use a
functional derivative of this acid. Examples of unsaturated
carboxylic acids are those having 2 to 20 carbon atoms, such
as acrylic, methacrylic, maleic, fumaric and itaconic acids.
The functional derivatives of these acids comprise, for
example, anhydrides, ester derivatives, amide derivatives,
imide derivatives and metal salts (such as alkali metal
salts) of unsaturaded carboxylic acids.
Unsaturated dicarboxylic acids having 4 to 10 carbon
atoms and their functional derivatives, particularly their
anhydrides, are particularly preferred grafting monomers. It
is advantageous to use maleic anhydride.
The proportion of functionalized HDPE and/or
functionalized PI relative to all of the functionalized and
unfunctionalized HDPE and functionalized and
unfunctionalized PI may be between 0 and 80%, advantageously
between 5 and 70% and preferably between 20 and 70% by
weight.
The PA-6/polyolefin blends having a PA-6 matrix may be
prepared by melt-blending the various constituents in
standard equipment used in the thermoplastic polymer
industry.
According to a first embodiment of these
PA-6/polyolefin blends having a PA-6 matrix, the HOPE is not
grafted and PI is a grafted elastomer/ungrafted elastomer
blend.
According to another embodiment of these
PA-6/polyolefin blends having a PA-6 matrix, the HOPE is
ungrafted and PI is a grafted polyethylene, optionally
blended with an elastomer.
With regard to the inner layer (3) or (3a) containing
an electrically conductive material, mention may be made, as
examples of electrically conductive material, of carbon
black, carbon fibres and carbon nanotubes. It is
advantageous to use a carbon black chosen from those having
a BET specific surface area, measured according to the ASTM
D3037-89 standard, of 5 to 200 m2/g and DBP absorption,
measured according to the ASTM D 2414-90 standard, of 50 to
300 ml/100 g. The proportion of black is advantageously, by
weight, from 16 to 30% per 84 to 70% of the other
constituents respectively, and preferably from 17 to 23% per
83 to 77% of the other constituents respectively. These
carbon blacks are described in Patent Application
WO 99/33908, the contents of which are incorporated in the
present application.
Examples
The following polymers were used:
Kynar® ADX 120 : a functional PVDF homopolymer grafted with
maleic anhydride, from Arkema, with an MVI (Melt Volume
Index) of 7 cm3/10 min (230°C/5 kg).
Kynar® 740 : a PVDF homopolymer from Arkema with an MVI
(Melt Volume Index) of 1 cm3/10 min (230°C/5 kg) .
LOTADER® 8840 : an ethylene/glycidyl methacrylate copolymer
from Arkema with an MVI (Melt Volume Index) of 5 cm3/10 min
(190°C/2.16 kg) and containing 92% ethylene and 8% glycidyl
methacrylate by weight.
EXXELOR® VA 1803 : an EPR elastomer grafted with maleic
anhydride, with an MFI of 3 g/10 min (230°C-2.16 kg).
Rilsan MA.4411 : an impact-modified plasticized nylon-12 from
Arkema.
Conductive nylon-12: a composition similar to Rilsan MA4411®
but containing in addition 20% carbon black (to the
detriment of nylon-12).
Example 1 :
A Kynar 740 (38 wt%)/Kynar ADX 120 (50 wt%)/LOTADER
8840 (2 wt%) /EXXELOR VA 1803 (10 wt%) blend was produced at
230°C in a Werner 40-type extruder. This blend, once
produced, has a nodular morphology, the mean size of the
dispersed phase being less than 5 (j,m.
A two layer tube 1 mm in thickness and 8 mm in outside
diameter, composed of Rilsan MA4411 as external layer (800
Vim) and the above PVDF alloy as internal layer (200 urn) , was
extruded on a McNeil line at 230°C.
The peel force needed to separate the internal layer
from the external layer at 50 mm/min was 50 N/cm.
24
This tube passed the -40°C impact test according to the
SAEJ 2260 standard.
Example 2 :
A three-layer tube of 1 mm thickness and 8 mm outside
diameter, composed of Rilsan MA4411 as external layer
(400 jam) , ADX120 as intermediate layer (200 pirn) and
conductive nylon-12 as internal layer (400 |im) , was extruded
on a McNeil line at 230°C.
The peel force needed to separate the internal or
external layer from the grafted PVDF layer at 50 mm/min was
50 N/cm.
This tube passed the -40°C impact test according to the
SAEJ 2260 standard.
The surface resistivity measured on the tube according
to the SAEJ 2260 standard was less than 106 ohms.sq.
This tube had a CE10 permeability at 40°C of less than
5 g/m2/day (CE10 petrol contains 45% isooctane, 45% toluene
and 10% ethanol by volume).

WE CLAIM:
1. Multilayer tube comprising, in its radial direction
from the outside inwards:
a polyamide outer layer (1);
an inner layer (2) of a composition comprising, the
total being 100%, 5 to 30% by weight of a blend (A)
comprising:
a polyethylene carrying epoxy functional groups,
an impact modifier chosen from elastomers and very
low-density polyethylenes, the said impact
modifier being completely or partly
functionalized;
95 to 70% by weight of a blend (B) comprising:
a fluoropolymer (Bl),
a functionalized fluoropolymer (B2),
the proportion of (B2) being between 1 and 80%
(advantageously between 1 and 60%) by weight of (A)+(B),
the layers being successive and adhering to one another
in their respective contact region.
2. Tube according to Claim 1, in which the inner layer (2)
contains an electrically conductive material.
3. Tube according to Claim 1, in which the inner layer (2)
contains essentially no electrically conductive material and
the tube comprises a layer (2a) placed beside the layer (2),
which layer (2a) is, like the layer (2) based on (A) and (B)
but contains, in addition, an electrically conductive
material.
4. Tube according to Claim 1, in which the inner layer (2)
contains essentially no electrically conductive material and
the tube comprises a layer (2a) placed beside the layer (2),
which layer (2a) is a blend of a fluoropolymer (Bl) and an
impact modifier, and contains in addition an electrically
conductive material producing a surface resistivity of
preferably less than 106 Q.
5. Multilayer tube comprising, in its radial direction
from the outside inwards:
a polyamide outer layer (1);
a layer (2) of a composition comprising, the total
being 100%, 0 to 30% by weight of a blend (A)
comprising:
a polyethylene carrying epoxy functional groups,
an impact modifier chosen from elastomers and very
low-density polyethylenes, the said impact
modifier being completely or partly
functional!zed;
100 to 70% by weight of a blend (B) comprising:
optionally, a fluoropolymer (Bl),
a functionalized fluoropolymer (B2),
the proportion of (B2) being between 10 and 100% by weight
of (A) + (B);
a polyolefin inner layer (3) ;
the layers being successive and adhering to each other in
their respective contact region.
6. Tube according to Claim 5, in which the proportions of
(A) are from 5 to 30% per 95 to 70% of (B) respectively.
7. Tube according to Claim 5 or 6, in which the inner
layer (3) contains an electrically conductive material.
8. Tube according to Claim 5 or 6, in which the inner
layer (3) contains essentially no electrically conductive
material and the tube comprises a layer (3a) placed beside
the layer (3), which layer (3a), like the layer (3), is a
polyamide layer but also contains an electrically conductive
material.
9. Tube according to any one of the preceding claims, in
which the polyamide of the outer layer (1) is a polyamide
having amine terminal groups or comprising more amine
terminal groups than acid terminal groups.
10. Tube according to any one of the preceding claims in
which a layer of a polyamide having amine terminal groups or
one comprising more amine terminal groups than acid terminal
groups is placed between the outer layer (1) and the layer
(2). •
11. Tube according to any one of the preceding claims, in
which the impact modifier of the blend (A) is an EPR grafted
with maleic anhydride or an EPDM grafted with maleic
anhydride.
12. Tube according to any one of the preceding claims, in
which the functionalized fluoropolymer (B2) is a PVDF
homopolymer or copolymer grafted with maleic anhydride.
13. Tube according to any one of the preceding claims, in
which the fluoropolymer (Bl) is a PVDF homopolymer or
copolymer.
14. Tube according to any one of Claims 1 to 4 and 6 to 13,
in which the proportions of (A) are from 5 to 10% per 95 to
90% of (B) respectively.
15. Tube according to any one of the preceding claims, in
which the proportion of the polyethylene carrying epoxy
functional groups is from 1 to 2 parts per 5 parts of impact
modifier.
16. Tube according to any one of the preceding claims, in
which the proportion of (B2) in the blends of (A) and (B) is
between 35 and 60% by weight of (A)+(B).
17. Tube according to Claim 16, in which the proportion of
(B2) in the blends of (A) and (B) is between 45 and 55% by
weight of (A)+(B) .
18. Use of the tubes according to any one of the preceding
claims for transporting petrol.
19. Multilayer tube, substantially as hereinbefore
described with reference to the foregoing examples.