Use of a multi-layered structure for the manufacture of gas conducts,
namely for methane
The present invention relates to use of a particular multilayer
structure for manufacturing gas ducts, and more particularly for methane
ducts.
Currently gas ducts, especially methane ducts, are made out of
rubber. These ducts, also called hoses, however have a certain number of
drawbacks among which mention may especially be made of the cost and
the weight.
An alternative to these rubber ducts is therefore sought, which is not
only advantageous from an economic point of view, but which of course
meets the demands linked to the use of such hoses for gas transport.
In particular, the primary criterion is the barrier property of the hose
with respect to the gas transported and also the criteria conventionally
imposed by user specifications, such as cold impact strength, thermal
resistance, coupling behavior, resistance to the salt (ZnCI2) etc.
It is in this context of searching for a satisfactory alternative solution
that the Applicant has observed that thermoplastic multilayer structures could
very advantageously be used for manufacturing gas ducts instead of the
current elastomeric structures.
Document US 2002/036405 in the name of the Applicant proposes a
thermoplastic multilayer structure for gas transport. This structure comprises
at least one layer composed mainly of polyethylene (which is understood as
being a homopolymer or copolymer of ethylene) and an outer layer made of
polyamide.
Although such a structure proves satisfactory from the point of view
of some of the mechanical properties (impact strength, burst strength,
windability), it has a poor coupling behavior and in addition a thermal
resistance that may be insufficient in certain applications due to the presence
of at least one layer composed mainly of polyethylene.

The invention therefore relates to the use of a multilayer structure
for manufacturing gas ducts, especially ducts for natural gas, this structure
overcoming the drawbacks of the elastomer structures and of the
thermoplastic structures taught by document US 2002/036405, and having,
inter alia and simultaneously, good barrier properties to the gas transported
and good thermal resistance properties.
The invention relates in particular to the use of a multilayer structure
for manufacturing methane ducts.
According to the invention, this use employs a multilayer structure
comprising, from the outside towards the inside, the following successive
layers, these layers adhering to their respective area of contact:
- a layer 1 comprising at least one polyamide, the polyamide being
chosen from PA-11, PA-12 and an aliphatic polyamide resulting from
the condensation of an aliphatic diamine having from 6 to 18 carbon
atoms and an aliphatic diacid having from 9 to 18 carbon atoms;
- optionally, a tie layer 2; and
- a layer 3 chosen from an EVOH layer, a layer formed from a blend of
polyamide and a polyolefin with a polyamide matrix, a PA-6 or PA-6,6
layer, a semi-aromatic polyamide or semi-aromatic copolyamide layer
and a polyphthalamide (PPA) layer, the layer 3 being intended to be
in contact with the gas transported.
The structures employed within the scope of the use according to
the present invention have a high barrier resistance to gases, such as
methane.
In the particular case of methane, it is considered to have good
barrier properties when the permeability, measured at 23°C, is below
5 cm3.mm/m2.24h.atm.
Such structures have, in addition, a high barrier resistance, while
only being able to involve a limited number of layers. Thus, structures
composed of 2 layers, or 3 layers in the case where the presence of a tie
layer proves necessary in order to ensure the adhesion of layers 1 and 3,
can indeed be envisaged.

Moreover, such structures also have the advantage of being able to
be coextruded on the equipment commonly used in the field of
thermoplastics.
In particular, in the case of use of these multilayer structures in the
automotive field, the equipment manufacturers will employ, for manufacturing
gas ducts, the same equipment that they commonly use for manufacturing
multilayer structures intended, for example, for supplying petrol.
In addition, taking into account the multilayer character of these
structures, the properties of the ducts can easily be adapted as a function of
the particular applications desired and the environment into which the gas
ducts are integrated.
In one particularly preferred version of the invention, the multilayer
structures used do not comprise any layer composed of polyethylene such
as that described in document US 2002/036405.
The description that follows details the compositions of the various
layers making up the multilayer structures corresponding to the use that is
the subject of the present invention.
According to a first aspect of the invention, the multilayer structure
used for manufacturing gas ducts is formed from two or three successive
layers, layer 1, layer 2 which is optional and layer 3, the layer 3 being
intended to be in contact with the gas transported by the duct.
Layer 1
Layer 1 comprises at least one polyamide, the polyamide being
chosen from PA-11, PA-12 and an aliphatic polyamide resulting from the
condensation of an aliphatic diamine having from 6 to 18 carbon atoms and
an aliphatic diacid having from 9 to 18 carbon atoms.
As examples of aliphatic polyamides, reference may be made to the
products cited by the document US 2005/0031818 A1, especially to
paragraphs [0042] to [0047].
In particular, PA-6,12, PA-9,12, PA-10,10 or else PA-10,12 may be
used in the composition of layer 1.

The PA-11, PA-12 or aliphatic polyamide of layer 1 may in addition
comprise at least one additive chosen from plasticizers, impact modifiers,
dyes, pigments, brighteners, antioxidants, UV stabilizers and polyolefins, the
latter possibly being functionalized or unfunctionalized.
A common plasticizer is n-butylbenzenesulphonamide (BBSA). But
other plasticizers, such as those cited in paragraph [0052] of document
US 2005/0031818 A1, could also be used.
Layer 2
Layer 2 is a tie layer that enables various layers to be bonded
together in order to avoid any delamination phenomenon.
In the multilayer structure employed within the scope of the use
according to the invention, layer 2 must adhere perfectly to layers 1 and 3.
As widely described in the prior art, especially in paragraphs [0068]
to [0093] of document US 2005/0031818 A1, the tie is conventionally a
functionalized polyolefin, the functionalization of the polyolefin being
provided by a grafted or copolymerized carboxylic acid or carboxylic acid
anhydride. This functionalized polyolefin may be blended with an
unfunctionalized polyolefin.
The tie may also be a copolyamide or a blend of copolyamides.
Copolyamide-based compositions that are suitable for the multilayer
structure according to the present invention are also described in document
US 2005/0031818 A1 (paragraphs [0094] to [0111]) and also in document
US 7 063 873 (col. 5, line 3 to col. 6, line 50).
The tie may in addition comprise at least one additive chosen from
plasticizers, impact modifiers, dyes, pigments, brighteners, antioxidants, UV
stabilizers and polyolefins, the latter possibly being functionalized or
unfunctionalized.
For example, the tie may comprise an impact modifier chosen from
very low density polyethylenes and elastomers, this impact modifier being
completely or partly functionalized. Reference can be made to the document
WO 2006/066944 A1 that describes in detail the impact modifiers that are
suitable within the scope of the present invention.

This layer 2 is however optional. Indeed, with regard to limiting the
costs, this layer 2 is not inserted between layers 1 and 3, in the particular
case where the compositions of layers 1 and 3 adhere well to each other.
Layer 3
Various compositions can be envisaged for layer 3, all these
compositions enabling the use of the multilayer structure for manufacturing
gas ducts.
Layer 3 is chosen from an EVOH layer, a layer formed from a blend
of polyamide and a polyolefin with a polyamide matrix, a PA-6 or PA-6,6
layer, a semi-aromatic polyamide or semi-aromatic copolyamide layer and a
polyphthalamide (PPA) layer.
Layer 3 may be an EVOH layer, EVOH being a saponified ethylene/
vinyl acetate copolymer.
The term "EVOH layer" is understood to mean both a layer made up
of EVOH, and a layer formed from a blend comprising at least 40% by weight
of EVOH, the other constituents of the blend being then chosen from
polyolefins, polyamides and optionally functional polymers.
Compositions based on EVOH that are suitable for the multilayer
structures used within the scope of the present invention have been, in
particular, described in document US 7 063 873 (col. 7, line 18 to col. 8,
line 11).
Layer 3 may also be formed from a blend of polyamide (A) and
polyolefin (B) with a polyamide matrix.
The term "polyamide (A)" is understood to mean the condensation
products:
- of one or more amino acids;
- of one or more lactams; or
- of one or more salts or mixtures of diamines and diacids.
Copolyamides may also advantageously be used, such as those
resulting from condensation:
- of at least two alpha,omega-aminocarboxylic acids;
- of two lactams;

- of one lactam and one alpha,omega-aminocarboxylic acid;
- of at least one alpha,omega-aminocarboxylic acid, at least
one diamine and at least one diacid; or else
- of at least one lactam, at least one diamine and at least one
diacid.
Reference can be made to document US 2005/0031818 A1, in
particular to paragraphs [0112] to [0123] that describe in detail examples of
amino acids, lactams, diamines, diacids or alpha,omega-aminocarboyxlic
acids.
Advantageously but non-limitingly, the polyamide may be chosen
from PA-6 and PA-6,6; the copolyamide may be chosen from PA-6/12,
PA-6/6,6, PA-6/12/6,6, PA-6/6,9/11/12, PA-6/6,6/11/12 and PA-6,9/12.
Blends of polyamides and/or of copolyamides may also be used.
The term "polyolefin (B)" is understood to mean a functionalized
polyolefin (B1), an unfunctionalized polyolefin (B2) or a blend of at least one
functionalized polyolefin (B1) and/or of at least one unfunctionalized
polyolefin (B2).
An unfunctionalized polyolefin (B2) is conventionally a homopolymer
or a copolymer of alpha-olefins or of diolefins.
A functionalized polyolefin (B1) is generally a homopolymer or a
copolymer of alpha-olefins having reactive units (the functionalities), these
reactive units being acid, anhydride or epoxy functional groups.
Functionalized polyolefins (B1) and unfunctionalized polyolefins (B2)
that are suitable for a layer 3 composition comprising a polyamide (A) and a
polyolefin (B) with a polyamide matrix are very broadly described in
document US 2005/0031818 A1, in particular in paragraphs [0124] to [0205].
As examples of functionalized polyolefins, mention may be made of
terpolymers of ethylene, of alkyl acrylate and of maleic anhydride or of
glycidyl methacrylate, such as Lotader®, or polyolefins grafted by maleic
anhydride, such as Orevac®, these products being sold by the Applicant.
Layer 3 may also be made of PA-6 or PA-6.6.

Layer 3 may even be made from a semi-aromatic polyamide or from
a semi-aromatic copolvamide.
Such semi-aromatic polyamides have in particular been described in
documents GB 1490 453, US 2 766 221 and more recently in document
WO 2006/108721 A1.
Mention may be made, in a non-limiting way, of the semi-aromatic
polyamides MXD-6 and MXD-10 and also the semi-aromatic polyamide, or
the semi-aromatic copolyamide in the case where Z t 0, corresponding to
the general formula MXD-10/Z in which:
- MXD-10 denotes the condensation product of a mixture of
xylylenediamines containing 70 to 100% of mefa-xylylenediamine
and sebacic acid;
- Z denotes at least one unit chosen from:
. the residues of a lactam;
. the residues of an alpha,omega-aminocarboxylic acid;
. the unit X1,Y1 in which X1 denotes the residues of an aliphatic,
arylaliphatic, cycloaliphatic or aromatic diamine and Y1 denotes
the residues of an aliphatic, cycloaliphatic or aromatic
carboxylic diaeid,
the Z/(MXD+10+Z) weight ratio being between 0 and 15%.
Preferably, the semi-aromatic copolyamide corresponds to the
general formula X/Y,Ar in which:
- Y denotes the residues of an aliphatic diamine having from 6 to 20
carbon atoms;
- Ar denotes the residues of an aromatic carboxylic diacid;
- X denotes:
. either the residues of aminoundecanoic acid NH2-(CH2)
10-COOH, of lactam-12 or of the corresponding amino acid;
. or the unit Y,x that is the residue of the condensation of the
diamine with an aliphatic diacid x having between 6 and 20
carbon atoms;

. or else the unit Y,l that is the residue of the condensation of the
diamine with isophthalic acid.
Such copolyamides have been described in documents
EP 0 550 314, US 3 843 611, US 5 708 125 and more recently in document
US 2005/0096430 A1.
Mention may be made, in a non-limiting way, of the following semi-
aromatic copolyamides: 6,6/6,T; 6/6.T; 6.I/6.T; 12/6.T; 12.12/12.T; 10,6/10,1";
11/10.T; 12/12,T; 10,10/10,1" and 10.I/10.T.
Lastly, layer 3 may be a polyphthalamide (PPA) layer.
The PPA is an aromatic polyamide obtained by the
polycondensation of at least one phthalic acid and at least one aliphatic
diamine. The phthalic acid may be a terephthalic, isophthalic or orthophthalic
acid or else a mixture comprising at least two of said acids. The aliphatic
diamine advantageously comprises from 3 to 12 carbon atoms and
preferably from 6 to 9.
The PPA may more particularly be a polyterephthalamide, that is to
say a PPA in which terephthalic acid is used.
More preferentially, the PPA is obtained by the copolymerization of
terephthalic acid, of isophthalic acid, of at least one dicarboxylic acid,
preferably adipic acid, and of at least one aliphatic diamine.
The PPAs sold by Solvay Advanced Polymers under the trade name
AMODEL® can be used within the scope of the present invention.
According to a second aspect of the invention, the multilayer
structure used for manufacturing gas ducts is formed from three or four
successive layers, layer 1, the optional layer 2, layer 3 and layer 5, layer 5
being in contact with the gas transported by the duct.
Layers 1 to 3
The composition of each of layers 1 to 3 is identical to that
described above for the first aspect of the invention.
Layer 5
Layer 5 is a polyamide-based layer.

Layer 5 may especially comprise at least one polyamide, the
polyamide being chosen from PA-11, PA-12 and an aliphatic polyamide
resulting from the condensation of an aliphatic diamine having from 6 to 18
carbon atoms and an aliphatic diacid having from 9 to 18 carbon atoms.
Layer 5 may in addition comprise a functionalized polyolefin and/or
an unfunctionalized polyolefin.
Reference may be made to the description of the functionalized
polyolefins (B1) and unfunctionalized polyolefins (B2) given above.
Layer 5 may also comprise one or more additives, in particular those
already mentioned previously for layer 1.
Preferably, in a same multilayer structure, the polyamide-based
composition of layer 5 is identical to that described above for the composition
of layer 1.
According to a third aspect of the invention, the multilayer structure
used for manufacturing gas ducts is formed from three, four or five
successive layers, layer 1, the optional layer 2, layer 3, the optional layer 4
and layer 5, layer 5 being in contact with the gas transported by the duct.
Layers 1 to 3 and 5
The composition of each of layers 1 to 3 is identical to that
described above for the first aspect of the invention.
For the composition of layer 5, reference can be made to that which
has already been described for the second aspect of the invention
concerning layer 5.
Layer 4
As the previously described layer 2, layer 4 is optional.
This layer 4 is a tie layer inserted between layers 3 and 5 in order to
enable or to optimize the bonding of these layers 3 and 5 to each other, and
thus to avoid any delamination phenomenon.
Reference can be made to that which has been described previously
for layer 2 in order to know the compositions capable of being used for the
tie layer 4.

In an advantageous version, in a same multilayer structure, the
polyamide-based composition of layer 5 is identical to that described above
for the composition of layer 1.
In a particularly advantageous version of the invention, the
compositions of layers 2 and 4 on the one hand and layers 1 and 5 on the
other hand, of a same multilayer structure, are identical.
The multilayer structure used within the scope of the present
invention, whether it comprises two, three, four or five layers, may in addition
include a protective layer 1', placed on layer 1.
This protective layer 1' may be a layer for protecting against heat, a
flame-retardant layer, an abrasion-resistant layer, an oxidation-resistant layer
or else a layer having several of these properties simultaneously.
The multilayer structure described above is advantageously shaped
so as to be in the form of a hollow body, preferably in the form of a tube or a
pipe.
In particular, the tubes are manufactured by the technique of
coextrusion, hence the need to have perfect adhesion between the various
coextruded layers forming the structure.
When the multilayer structure is a tube, this tube can be moulded so
as to obtain a smooth tube or on the other hand, a ringed tube.
The present invention will now be illustrated by various examples for
which the methane permeability has been measured at 23°C.
The products used were the following:
PA-11: PA-11 of reference BESN TL;
PA-11 p: PA-11 of reference BESNO P40 TL with a plasticizer
(BBSA);
Tie: PLATAMID®1 (50%) and PLATAMID®2 (50%),
PLATAMID®1 being a 6/12 (40/60) copolyamide and

terms of methane barrier properties, the measured permeability being well
below 5 cm3.mm/m2.24h.atm.
It is stated that all the documents cited in the present description, in
particular the passages picked out from these documents, are incorporated
by way of reference.

Claims
1. Use of a multilayer structure comprising, from the outside towards the
inside, the following successive layers:
- a layer 1 comprising at least one polyamide, the polyamide being
chosen from PA-11, PA-12 and an aliphatic polyamide resulting from
the condensation of an aliphatic diamine having from 6 to 18 carbon
atoms and an aliphatic diacid having from 9 to 18 carbon atoms;
- optionally, a tie layer 2; and
- a layer 3 chosen from an EVOH layer, a layer formed from a blend of
polyamide and a polyolefin with a polyamide matrix, a PA-6, PA-6,6,
MXD-6 or MXD-10 layer and a semi-aromatic copolyamide layer,
for manufacturing gas ducts, in particular methane ducts, the layer 3 being
intended to be in contact with the gas transported.
2. Use according to Claim 1, characterized in that the layer 1 in addition
comprises at least one additive chosen from plasticizers, impact modifiers,
functionalized or unfunctionalized polyolefins , dyes, pigments, brighteners,
antioxidants and UV stabilizers.
3. Use according to Claim 1 or 2, characterized in that the layer 3 is
coated by the following successive layer(s):

- optionally, a tie layer 4; and
- a polyamide-based layer 5, the layer 5 being in contact with the gas
transported.
4. Use according to Claim 3, characterized in that the layer 5 comprises
at least one polyamide, the polyamide being chosen from PA-11, PA-12 and
an aliphatic polyamide resulting from the condensation of an aliphatic
diamine having from 6 to 18 carbon atoms and an aliphatic diacid having
from 9 to 18 carbon atoms.

5. Use according to Claim 3 or 4, characterized in that the layer 5 in
addition comprises a functionalized polyolefin and/or an unfunctionalized
polyolefin.
6. Use according to any one of Claims 1 to 5, characterized in that the
multilayer structure in addition comprises a protective layer 1', placed on the
layer 1.
7. Use according to any one of Claims 1 to 6, characterized in that the
multilayer structure is a tube.
8. Use according to Claim 7, characterized in that the tube is smooth.
9. Use according to Claim 7, characterized in that the tube is ringed.

The present invention relates to the use of a multi-layered structure for the manufacture of gas conducts, namely for methane. The multi-layered structure comprises, from the inside to the outside, the following successive layers: a layer containing at least one polyamide, wherein the polyamide is chosen from PAH, PA12 and an aliphatic polyamide obtained from condensation
reaction of an aliphatic diamine having 6 to 18 carbon atoms and an aliphatic diacid having 9 to 18 carbon atoms; optionally, abinding 2 layer; and a layer 3 chosen from an EVOH layer, a layer formed of a mixture of polyamide and a polyolefin with a polyamide matrix, a layer of PA6.PA6-6, MXD.6 or MXD. 10 and a layer of semi-aromatic copolyamide, the layer 3 being intended to be in contact with the transported gas.