U.S. patent application number 10/377470 was filed with the patent office on 2003-10-23 for fuel tank having a multilayer structure.
This patent application is currently assigned to TI Automotive Technology Center Gmbh. Invention is credited to Delbarre, Pierre.
Application Number | 20030198768 10/377470 |
Document ID | / |
Family ID | 32850487 |
Filed Date | 2003-10-23 |
United States Patent
Application |
20030198768 |
Kind Code |
A1 |
Delbarre, Pierre |
October 23, 2003 |
Fuel tank having a multilayer structure
Abstract
An automotive plastic fuel tank with a wall having a structural
layer of HDPE and a hydrocarbon fuel barrier layer of an EVOH based
material with a binder layer between them. The barrier layer
prevents the passage of hydrocarbons through the wall to the
atmosphere. The barrier layer is on an exterior face of the wall
and preferably on the interior of the tank in direct contact with
fuel therein. Preferably, the barrier includes a layer of polyamide
(A) or a mixture of polyamide (A) and polyolefin (B).
Inventors: |
Delbarre, Pierre; (Ohlungen,
FR) |
Correspondence
Address: |
REISING, ETHINGTON, BARNES, KISSELLE, P.C.
P O BOX 4390
TROY
MI
48099-4390
US
|
Assignee: |
TI Automotive Technology Center
Gmbh
|
Family ID: |
32850487 |
Appl. No.: |
10/377470 |
Filed: |
February 27, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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10377470 |
Feb 27, 2003 |
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09782485 |
Feb 13, 2001 |
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Current U.S.
Class: |
428/36.6 ;
428/35.7 |
Current CPC
Class: |
C08L 23/12 20130101;
C08L 77/00 20130101; C08L 2205/03 20130101; B60K 2015/03046
20130101; B32B 2377/00 20130101; B32B 27/306 20130101; B32B 1/02
20130101; C08L 23/06 20130101; B32B 27/32 20130101; C08L 23/14
20130101; B32B 2439/00 20130101; C08L 23/20 20130101; C08L 23/10
20130101; B32B 2323/04 20130101; B32B 27/34 20130101; Y10T 428/1379
20150115; C08L 2314/06 20130101; C09J 123/06 20130101; C08L 2205/02
20130101; C08L 2666/24 20130101; C08L 51/06 20130101; C08L 2666/06
20130101; B29K 2105/26 20130101; B32B 2323/043 20130101; C08L
2666/02 20130101; C09J 123/0815 20130101; B60K 15/03177 20130101;
Y10T 428/1352 20150115; B32B 7/12 20130101; B32B 27/08 20130101;
B32B 2329/04 20130101; C08L 23/0815 20130101; C08L 23/0815
20130101; C08L 2666/24 20130101; C08L 23/10 20130101; C08L 2666/20
20130101; C08L 77/00 20130101; C08L 2666/02 20130101; C09J 123/06
20130101; C08L 2666/06 20130101; C09J 123/06 20130101; C08L 2666/02
20130101; C09J 123/06 20130101; C08L 2666/24 20130101; C09J
123/0815 20130101; C08L 2666/06 20130101; C09J 123/0815 20130101;
C08L 2666/02 20130101 |
Class at
Publication: |
428/36.6 ;
428/35.7 |
International
Class: |
B65D 001/00 |
Claims
1. A fuel tank having a structure comprising, successively: a first
layer of high density polyethylene (HDPE), a layer of binder, and
an exposed barrier layer of an EVOH based material.
2. The fuel tank of claim 1 wherein the barrier layer also
comprises a layer of one of polyamide (A) and a mixture of
polyamide (A) and polyolefin (B).
3. The fuel tank of claim 1 wherein the binder comprises: 5 to 30
parts of a polymer (D) which itself comprises a mixture of a
polyethylene (D1) with a density of between 0.910 and 0.940 and of
a polymer (D2) chosen from elastomers, very low density
polyethylenes and metallocene polyethylenes, the mixture (D1)+(D2)
being co-grafted with an unsaturated carboxylic acid, 95 to 70
parts of a polyethylene (E) with a density of between 0.910 and
0.930, the mixture of (D) and (E) being such that: its density is
between 0.910 and 0.930, the content of grafted unsaturated
carboxylic acid is between 30 and 10,000 ppm, the MFI (ASTM D
1238--190.degree. C.-2.16 kg) is between 0.1 and 3 g/10 min, the
MFI denotes the melt flow index.
4. The fuel tank of claim 3 wherein the density of the binder is
between 0.915 and 0.920.
5. The fuel tank of claim 3 wherein D1 and E are LLDPEs which have
the same comonomer.
6. The fuel tank of claim 1 wherein the binder comprises: 5 to 30
parts of a polymer (F) which itself comprises a mixture of a
polyethylene (F1) with a density of between 0.935 and 0.980 and of
a polymer (F2) chosen from elastomers, very low density
polyethylenes and ethylene copolymers, the mixture (F1)+(F2) being
co-grafted with an unsaturated carboxylic acid, 95 to 70 parts of a
polyethylene (G) with a density of between 0.930 and 0.950, the
mixture of (F) and (G) being such that: its density is between
0.930 and 0.950, the content of grafted unsaturated carboxylic acid
is between 30 and 10,000 ppm, the MFI (melt flow index) measured
according to ASTM D 1238 at 190.degree. C.-21.6 kg is between 5 and
100.
7. The fuel tank of claim 1 wherein the binder is a polyethylene
grafted with maleic anhydride, having an MFI of 0.1 to 3, a density
of between 0.920 and 0.930 and containing 2 to 40% by weight of
insolubles in n-decane at 90.degree. C.
8. The fuel tank of claim 7 wherein the grafted polyethylene is
diluted in a non-grafted polyethylene and such that the binder is a
mixture of 2 to 30 parts of a grafted polyethylene with a density
of between 0.930 and 0.980 and from 70 to 98 parts of a non-grafted
polyethylene with a density of between 0.910 and 0.940.
9. The fuel tank of claim 1 wherein the binder is a mixture
consisting of a polyethylene of HDPE, LLDPE, VLDPE or LDPE type, 5
to 35% of a grafted metallocene polyethylene and 0 to 35% of an
elastomer, the total being 100%.
10. The fuel tank of claim 2 wherein the polyamide of the barrier
layer is a copolyamide.
11. The fuel tank of claim 2 wherein the polyolefin (B) of the
barrier layer comprises (i) a high density polyethylene (HDPE) and
(ii) a mixture of a polyethylene (C1) and a polymer (C2) chosen
from elastomers, very low density polyethylenes and ethylene
copolymers, the mixture (C1)+(C2) being co-grafted with an
unsaturated carboxylic acid.
12. The fuel tank of claim 2 wherein the polyolefin (B) of the
barrier layer comprises (i) polypropylene and (ii) a polyolefin
which results from the reaction of a polyamide (C4) with a
copolymer (C3) comprising propylene and a grafted or copolymerized
unsaturated monomer X.
13. The fuel tank of claim 2 wherein the polyolefin (B) of the
barrier layer comprises (i) a polyethylene of LLDPE, VLDPE or
metallocene type and (ii) an ethylene-alkyl (meth)acrylate-maleic
anhydride copolymer.
14. The fuel tank of claim 2 wherein the polyamide (A) of the
barrier layer is chosen from mixtures of (i) polyamide and (ii)
copolymer containing PA 6 blocks and PTMG blocks and mixtures of
(i) polyamide and (ii) copolymer containing PA 12 blocks and PTMG
blocks; the ratio of the amounts of copolymer and of polyamide by
weight being between 10/90 and 60/40.
15. The fuel tank of claim 14, wherein the polyolefin (B) of the
barrier layer comprises (i) a polyethylene of LLDPE, VLDPE or
metallocene type and (ii) an ethylene-alkyl (meth)acrylate-maleic
anhydride copolymer.
16. The fuel tank of claim 14, in which the polyolefin comprises
two functionalized polymers comprising at least 50 mol % of
ethylene units and which can react to form a crosslinked phase.
17. The fuel tank of claim 1 wherein the barrier layer is in direct
contact with fuel within the tank.
18. The fuel tank of claim 2 which also comprises a binder between
the EVOH material and the one of the layer of polyamide (A) and a
mixture of polyamide(A) and polyolefin (B) of the barrier
layer.
19. A fuel tank having a structure comprising, successively: a
first layer of high density polyethylene (HDPE), a layer of binder,
and an exposed barrier layer of an EVOH based material and a layer
of one of polyamide (A) and a mixture of polyamide (A) and
polyolefin (B).
20. The fuel tank of claim 19 wherein the barrier layer is in
direct contact with fuel within the tank.
21. The fuel tank of claim 19 which also comprises a binder between
the EVOH material and the one of the layer of polyamide (A) and a
mixture of polyamide (A) and polyolefin (B) of the barrier
layer.
22. The fuel tank of claim 19 wherein the barrier layer is on the
outside of the fuel tank and is not in direct contact with fuel
within the tank.
23. A fuel tank, comprising: a tank wall defining an interior of
the fuel tank, said tank wall having an inner layer of a polyamide
and polyolefin mixture adjacent to the interior of the fuel tank, a
barrier layer generally surrounding the inner layer, and at least
one structural layer surrounding the barrier layer.
24. The fuel tank of claim 23 wherein the tank wall is formed by a
multiple layer parison that is blow molded into its final shape and
has a pinch line in an area where the parison is closed during the
blowmolding process, and said inner layer is arranged so that a
portion of the inner layer engages another portion of the inner
layer as the parison is pinched to form a continuous inner layer of
the tank wall without a permeation window.
25. The fuel tank of claim 23 which also comprises an adhesive
layer disposed between the barrier layer and said at least one
structural layer.
26. The fuel tank of claim 23 which also comprises a damper layer
disposed between the inner layer and the barrier layer.
27. The fuel tank of claim 23 wherein the inner layer has a
continuous inner surface arranged to be in contact with fuel in the
fuel tank.
Description
REFERENCE TO CO-PENDING APPLICATION
[0001] This application is a continuation-in-part of U.S. Ser. No.
09/782,485 filed Feb. 13, 2001.
FIELD OF THE INVENTION
[0002] This invention relates to automotive fuel tanks and more
particularly to a multilayer plastic fuel tank.
BACKGROUND OF THE INVENTION
[0003] European Patent EP 742 236 describes petrol tanks consisting
of five layers which are, respectively:
[0004] high density polyethylene (HDPE);
[0005] a binder;
[0006] a polyamide (PA) or a copolymer containing ethylene units
and vinyl alcohol units (EVOH);
[0007] a binder;
[0008] HDPE.
[0009] A sixth layer can be added between one of the layers of
binder and one of the HDPE layers. This sixth layer consists of
manufacturing scraps following molding of the tanks, and to a much
smaller extent of non-compliant tanks. These scraps and
non-compliant tanks are then ground until granules are obtained.
This ground material is then re-melted and extruded directly at the
tank co-extrusion plant. This ground material may also be melted
and re-granulated by means of an extruding machine such as a
twin-screw extruder, before being reused.
[0010] According to one variant, the recycled product can be mixed
with the HDPE from the two extreme layers of the tank. It is
possible, for example, to mix the granules of recycled product with
granules of virgin HDPE of these two layers. It is also possible to
use any combination of these two recyclings. The content of
recycled material can represent up to 50% of the total weight of
the tank.
[0011] European Patent EP 731 308 describes a tube comprising an
inner layer comprising a mixture of polyamide and of polyolefin
with a polyamide matrix and an outer layer comprising a polyamide.
These tubes based on polyamide are useful for transporting petrol
and more particularly for bringing the petrol from the motor
vehicle tank to the motor and also, but in larger diameter, for
transporting hydrocarbons in service stations between the
distribution pumps and the underground storage tanks.
[0012] According to another form of the tube, a layer of a polymer
comprising ethylene units and vinyl alcohol units (EVOH) can be
placed between the inner and outer layers. The structure: inner
layer/EVOH/binder/outer layer is advantageously used.
[0013] The tanks described in EP 742 236 which do not have the
barrier layer in direct contact with the petrol do admittedly have
barrier properties, but they are not sufficient when very low
petrol losses are desired. EP 731 308 describes tubes whose outer
layer is made of polyamide and the barrier layer is in direct
contact with the petrol, wherein the layer made of polyamide is
necessary for the mechanical strength of the assembly. Novel
structures have now been found which have better barrier properties
and which are useful for various objects such as, for example,
petrol tanks for motor vehicles.
SUMMARY OF THE INVENTION
[0014] The present invention relates to a plastic fuel tank having
a multilayer wall structure, wherein a barrier layer forms an
exposed face of the wall and preferably is in direct contact with
the fuel contained therein. The barrier layer of the structures of
the invention constitutes one of the exposed faces of the
structure, i.e. it is not an interior layer of the wall structure.
Fuel tank structures embodying the invention have walls with
HDPE/barrier layer or HDPE/binder/barrier layer, in which "HDPE"
denotes high density polyethylene.
[0015] Preferably, the fuel tank structure comprises
successively:
[0016] a first layer of high density polyethylene (HDPE),
[0017] a layer of binder,
[0018] a second layer of EVOH or of a mixture based on EVOH,
and
[0019] optionally a third layer of polyamide (A) or a mixture of
polyamide (A) and polyolefin (B).
[0020] In the text hereinbelow, the second layer or the combination
of the second and the third layer is referred to as the "barrier
layer" and forms an exterior face of the wall structure.
[0021] The invention is particularly useful for a fluid such as
motor vehicle petrol or volatile hydrocarbon fuels such as
gasoline, by avoiding losses through the structure so as not to
pollute the environment.
[0022] Objects, features and advantages o this invention include
providing a plastic fuel tank which has significantly less
hydrocarbon fuel emissions, readily complies with stringent
environmental protection standards and requirements, is of
economical manufacture and assembly and in service has a long
useful life.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] These and other objects, features and advantages of this
invention will be apparent from the following detailed description
of the best modes, appended claims and accompanying drawings in
which:
[0024] FIG. 1 is a perspective view of an automotive plastic fuel
tank according to one presently preferred embodiment of the
invention;
[0025] FIG. 2 is a fragmentary sectional view of a wall of the fuel
tank of FIG. 1;
[0026] FIG. 3 is a fragmentary sectional view of a modified wall of
a fuel tank embodying this invention;
[0027] FIG. 4 is a fragmentary sectional view of a wall of a fuel
tank according to another presently preferred embodiment of the
invention; and
[0028] FIG. 5 is an enlarged fragmentary sectional view of a
portion of the wall of the fuel tank as in FIG. 4 in the area of a
pinch line of the fuel tank.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0029] Referring in more detail to the drawings, FIG. 1 illustrates
an automotive plastic fuel tank 10 embodying this invention with a
wall 12 having a plastic filler neck or pipe 14 with a flange 16
and a fuel pump module 18 with a cover flange 20 each heat welded
to the wall. As shown in FIG. 2, the wall 12 has an exposed outer
first layer 22 of HDPE, an inner exposed second layer 24 of EVOH
and a binder layer 26 between them which adheres the first and
second layers together. The second layer 24 is in contact with
liquid fuel in the tank 10 and provides the primary vapor barrier
and the first layer 22 provides the primary strength and structural
integrity of the tank. The adhesive layer bonds or adheres together
the dissimilar first and second layers.
[0030] FIG. 3 illustrates a modified wall 12' construction of a
fuel tank 10 with an inner first layer 22 of HDPE, an outer exposed
second layer 24 of EVOH and a binder layer 26 between them which
adheres the first and second layers together. In both forms of the
tank, the second vapor barrier layer 26 of EVOH preferably also has
a third film or layer 28 of a polyamide (A) or a mixture of a
polyamide (A) and a polyolefin (B).
[0031] Preferably, the fuel tank 10 is formed by simultaneously
co-extruding all of the layers and adhesive together into a hollow
parison which is then placed in a mold with a cavity having the
desired shape and configuration of the tank and the parison is blow
molded to form the fuel tank.
[0032] The first layer 22 is a high density polyethylene (HDPE)
which may also have some carbon black or poly black mixed therein
to provide coloration and may include a re-grind layer of HDPE
which is composed of re-ground scrap materials from the
manufacturing of the fuel tanks 10 and/or salvaged and re-ground
HDPE. The first layer 22 and any re-grind layer are preferably of
substantially the same composition. The adhesive layer may be of a
wide variety of materials and is necessary to attach the layer of
HDPE to the vapor barrier second layer and thereby increase the
structural integrity of the fuel tank 10 which is paramount for
passing various crush resistance specifications in the automotive
industry. The second vapor barrier layer is necessary to reduce the
amount of hydrocarbon vapors which would diffuse or escape through
the fuel tank wall 12 which is composed primarily of HDPE.
[0033] A typical multilayer plastic fuel tank wall 10 has a
thickness of between about 3 mm and 10 mm, with an optimal total
wall thickness of about 5-6 mm. Nominal values for the individual
layers of the multilayer plastic fuel tank 10 are as follows: the
first layer 22 comprises between about 90 to 97 percent of the
total wall thickness; the binder or adhesive layer 26 comprises
between about 1 to 4 percent of the total wall thickness; and the
vapor barrier second layer 24 or second and third layers 24,28
comprises between about 2 to 6 percent of the total wall thickness.
These ranges of the thickness of the individual layers are
illustrative only and can be readily varied during the co-extrusion
of the parison for the fuel tank wall 12 during the manufacture of
fuel tank 10.
[0034] Throughout a production run of fuel tanks 10, the thickness
of the individual layers must be controlled to assure optimum
performance and quality of the fuel tank 10 in use. The thickness
of the first layer 22 of polyethylene is important because this
layer provides structural protection of the vapor barrier layer(s)
24, 28 and also strength and structural integrity of the fuel tank
10 itself. The thickness of the adhesive layer 26 is important to
insure adequate attachment between the adjacent layers of HDPE and
the vapor barrier layer(s) 24, 28. Finally, the thickness of the
vapor barrier layer(s) 24,28 is important to prohibit the
permeation of the hydrocarbon vapors through the fuel tank 10 and
into the atmosphere.
[0035] As regards the first layer, the high density polyethylene
(HDPE) is described in Kirk-Othmer, 4th Edition, Vol. 17, pages 704
and 724-725. It is, according to ASTM D 1248-84, an ethylene
polymer with a density at least equal to 0.940. The name HDPE
relates both to ethylene homopolymers and its copolymers with small
proportions of olefin. The density is advantageously between 0.940
and 0.965. In the present invention, the MFI of the HDPE is
advantageously between 0.1 and 50. By way of example, mention may
be made of Eltex B 2008.RTM. with a density of 0.958 and an MFI of
0.9 (in g/10 min at 190.degree. C. under 2.16 kg), Finathene.RTM.
MS201B from FINA and Lupolen.RTM. 4261 AQ from BASF.
[0036] As regards the second layer, the EVOH copolymer is also
referred to as a saponified ethylene-vinyl acetate copolymer. The
saponified ethylene-vinyl acetate copolymer to be used according to
the present invention is a copolymer with an ethylene content of
from 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 %. With an ethylene content of less than 20 mol %, the
barrier properties under conditions of high humidity are not as
high as would be desired, whereas an ethylene content exceeding 70
mol % leads to reductions in barrier properties. When the degree of
saponification or of hydrolysis is less than 95 mol %, the barrier
properties are sacrificed.
[0037] The expression "barrier properties" means the impermeability
to gases, to liquids and in particular to oxygen, and to petrol for
motor vehicles. The invention relates more particularly to the
barrier to petrol or volatile hydrocarbon fuels such as gasoline
for motor vehicles.
[0038] Among these saponified copolymers, those which have melt
flow indices, under hot conditions, in the range from 0.5 to 100
g/10 minutes are particularly useful. Advantageously, the MFI is
chosen between 5 and 30 (g/10 min at 230.degree. C. under 2.16 kg),
"MFI", the abbreviation for "melt flow index" denoting the flow
rate in the molten state.
[0039] It is understood that this saponified copolymer can contain
small proportions of other comonomer ingredients, including
.alpha.-olefins such as propylene, isobutene, .alpha.-octene,
.alpha.-dodecene, .alpha.-octadecene, etc., unsaturated carboxylic
acids or salts thereof, partial alkyl esters, whole alkyl esters,
nitrites, amides and anhydrides of the said acids, and unsaturated
sulphonic acids or salts thereof.
[0040] As regards the mixtures based on EVOH, they are such that
the EVOH forms the matrix, i.e. it represents at least 40% by
weight of the mixture and preferably at least 50%. The other
constituents of the mixture are chosen from polyolefins, polyamides
and optionally functional polymers.
[0041] As a first example of these mixtures based on EVOH of the
second layer, mention may be made of the compositions comprising
(by weight):
[0042] 55 to 99.5 parts of EVOH copolymer,
[0043] 0.5 to 45 parts of polypropylene and of compatibilizer, the
proportions thereof being such that the ratio of the amount of
polypropylene to the amount of compatibilizer is between 1 and
5.
[0044] Advantageously, the ratio of the MFI of the EVOH to the MFI
of the polypropylene is greater than 5 and preferably between 5 and
25. Advantageously, the MFI of the polypropylene is between 0.5 and
3 (in g/10 min at 230.degree. C. under 2.16 kg). According to one
advantageous form, the compatibilizer is a polyethylene bearing
polyamide grafts and it results from the reaction (i) of a
copolymer of ethylene and of a grafted or copolymerized unsaturated
monomer X, with (ii) a polyamide. The copolymer of ethylene and of
a grafted or copolymerized unsaturated monomer X is such that X is
copolymerized and it can be chosen from ethylene-maleic anhydride
copolymers and ethylene-alkyl (meth)acrylate-maleic anhydride
copolymers, these copolymers comprising from 0.2 to 10% by weight
of maleic anhydride and from 0 to 40% by weight of alkyl
(meth)acrylate. According to another advantageous form, the
compatibilizer is a polypropylene bearing polyamide grafts which
results from the reaction (i) of a propylene homopolymer or
copolymer comprising a grafted or copolymerized unsaturated monomer
X, with (ii) a polyamide. Advantageously, X is grafted. The monomer
X is advantageously an unsaturated carboxylic acid anhydride such
as, for example, maleic anhydride.
[0045] As a second example of these mixtures based on EVOH of the
second layer, mention may be made of compositions comprising:
[0046] 50 to 98% by weight of an EVOH copolymer
[0047] 1 to 50% by weight of a polyethylene
[0048] 1 to 15% by weight of a compatibilizer consisting of a
mixture of an LLDPE polyethylene or metallocene and of a polymer
chosen from elastomers, very low density polyethylenes and
metallocene polyethylenes, the mixture being co-grafted with an
unsaturated carboxylic acid or a functional derivative of this
acid.
[0049] Advantageously, the compatibilizer is such that the ratio
MFI.sub.10/MFI.sub.2 is between 5 and 20, in which MFI.sub.2 is the
mass melt flow index at 190.degree. C. under a load of 2.16 kg,
measured according to ASTM D1238, and MFI.sub.10 is the mass melt
flow index at 190.degree. C. under a load of 10 kg according to
ASTM D1238.
[0050] As a third example of these mixtures based on EVOH of the
second layer, mention may be made of compositions comprising:
[0051] 50 to 98% by weight of an EVOH copolymer
[0052] 1 to 50% by weight of an ethylene-alkyl (meth)acrylate
copolymer,
[0053] 1 to 15% by weight of a compatibilizer resulting from the
reaction (i) of a copolymer of ethylene and of a grafted or
copolymerized unsaturated monomer X with (ii) a copolyamide.
[0054] Advantageously, the copolymer of ethylene and of a grafted
or copolymerized unsaturated monomer X is such that X is
copolymerized and it is a copolymer of ethylene and of maleic
anhydride or a copolymer of ethylene, of an alkyl (meth)acrylate
and of maleic anhydride. Advantageously, these copolymers comprise
from 0.2 to 10% by weight of maleic anhydride and from 0 to 40% by
weight of alkyl (meth)acrylate.
[0055] As regards the polyamide (A) and the mixture of polyamide
(A) and polyolefin (B) of the third layer, the term "polyamide"
means the following products of condensation:
[0056] of one or more amino acids, such as aminocaproic acid,
7-aminoheptanoic acid, 11-aminoundecanoic acid and
12-aminododecanoic acid of one or more lactams such as caprolactam,
oenantholactam and lauryllactam;
[0057] of one or more salts or mixtures of diamines such as
hexamethylenediamine, dodecamethylenediamine, meta-xylylenediamine,
bis(p-aminocyclohexyl)methane and trimethylhexamethylenediamine
with diacids such as isophthalic acid, terephthalic acid, adipic
acid, azelaic acid, suberic acid, sebacic acid and
dodecanedicarboxylic acid.
[0058] As examples of polyamides, mention may be made of PA 6 and
PA 6-6. It is also advantageously possible to use copolyamides.
Mention may be made of the copolyamides resulting from the
condensation of at least two .alpha.,.omega.-aminocarboxylic acids
or of two lactams or of one lactam and one
.alpha.,.omega.-aminocarboxylic acid. Mention may also be made of
the copolyamides resulting from the condensation of at least one
.alpha.,.omega.-aminocarboxylic acid (or a lactam), at least one
diamine and at least one dicarboxylic acid.
[0059] As examples of lactams, mention may be made of those
containing from 3 to 12 carbon atoms on the main ring and which can
be substituted. Mention may be made, for example, of
.beta.,.beta.-dimethylpropiolactam,
.alpha.,.alpha.-dimethylpropiolactam, amylolactam, caprolactam,
capryllactam and lauryllactam.
[0060] As examples of .alpha.,.omega.-aminocarboxylic acids,
mention may be made of aminoundecanoic acid and aminododecanoic
acid. As examples of dicarboxylic acids, mention may be made of
adipic acid, sebacic acid, isophthalic acid, butanedioic acid,
1,4-cyclohexanedicarboxylic acid, terephthalic acid, sodium or
lithium salts of sulphoisophthalic acid, dimerized fatty acids
(these dimerized fatty acids have a dimer content of at least 98%
and are preferably hydrogenated) and dodecanedioic acid
HOOC--(CH.sub.2).sub.10--COOH.
[0061] The diamine can be an aliphatic diamine containing from 6 to
12 atoms, it can be arylic and/or saturated cyclic. As examples,
mention may be made of hexamethylenediamine, piperazine,
tetramethylenediamine, octamethylenediamine, decamethylenediamine,
dodecamethylenediamine, 1,5-diaminohexane,
2,2,4-trimethyl-1,6-diaminohexane, diaminepolyols,
isophoronediamine (IPD), methylpentamethylenediamine (MPDM),
bis(aminocyclohexyl)methane (BACM) and
bis(3-methyl-4-aminocyclohexyl)met- hane (BMACM).
[0062] As examples of copolyamides, mention may be made of
copolymers of caprolactam and of lauryllactam (PA 6/12), copolymers
of caprolactam, of adipic acid and of hexamethylenediamine (PA
6/6-6), copolymers of caprolactam, of lauryllactam, of adipic acid
and of hexamethylenediamine (PA 6/12/6-6), copolymers of
caprolactam, of lauryllactam, of 11-aminoundecanoic acid, of
azelaic acid and of hexamethylenediamine (PA 6/6-9/11/12),
copolymers of caprolactam, of lauryllactam, of 11-aminoundecanoic
acid, of adipic acid and of hexamethylenediamine (PA 6/6-6/11/12)
and copolymers of lauryllactam, of azelaic acid and of
hexamethylenediamine (PA 6-9/12).
[0063] Advantageously, the copolyamide is chosen from PA 6/12 and
PA 6/6-6. The advantage of these copolyamides is that their melting
point is less than that of PA 6.
[0064] It is also possible to use any amorphous polyamide which has
no melting point.
[0065] The MFI of the polyamides and mixtures of polyamide and of
polyolefin of the present invention is measured according to the
rules of the art at a temperature of 15 to 20.degree. C. above the
melting point of the polyamide. As regards the mixtures based on PA
6, the MFI is measured at 235.degree. C. under 2.16 kg. As regards
the mixtures based on PA 6-6, the MFI is measured at 275.degree. C.
under 1 kg.
[0066] Polyamide mixtures can be used. Advantageously, the MFI of
the polyamides is between 1 and 50 g/10 min.
[0067] It would not constitute a departure from the context of the
invention to replace some of the polyamide (A) with a copolymer
containing polyamide blocks and polyether blocks, i.e. to use a
mixture comprising at least one of the above polyamides and at
least one copolymer containing polyamide blocks and polyether
blocks.
[0068] The copolymers containing polyamide blocks and polyether
blocks result from the copolycondensation of polyamide sequences
containing ends that are reactive with polyether sequences
containing reactive ends, such as, inter alia:
[0069] I) polyamide sequences containing diamine chain ends with
polyoxyalkylene sequences containing dicarboxylic chain ends.
[0070] 2) polyamide sequences containing dicarboxylic chain ends
with polyoxyalkylene sequences containing diamine chain ends,
obtained by cyanoethylation and hydrogenation of
.alpha.,.omega.-dihydroxylated aliphatic polyoxyalkylene sequences
known as polyetherdiols.
[0071] 3) polyamide sequences containing dicarboxylic chain ends
with polyetherdiols, the products obtained being, in this specific
case, polyetheresteramides. These copolymers are advantageously
used.
[0072] The polyamide sequences containing dicarboxylic chain ends
originate, for example, from the condensation of
.alpha.,.omega.-aminocar- boxylic acids, lactams or dicarboxylic
acids and diamines in the presence of a chain-limiting dicarboxylic
acid.
[0073] The polyether can be, for example, a polyethylene glycol
(PEG), a polypropylene glycol (PPG) or a polytetramethylene glycol
(PTMG). The latter is also known as polytetrahydrofuran (PTHF).
[0074] The number-average molar mass M.sub.n of the polyamide
sequences is between 300 and 15,000 and preferably between 600 and
5000. The mass M.sub.n of the polyether sequences is between 100
and 6000 and preferably between 200 and 3000.
[0075] The polymers containing polyamide blocks and polyether
blocks can also comprise randomly distributed units. These polymers
can be prepared by the simultaneous reaction of the polyether and
of polyamide block precursors.
[0076] For example, it is possible to react polyetherdiol, a lactam
(or an .alpha.,.omega.-amino acid) and a chain-limiting diacid in
the presence of a small amount of water. A polymer is obtained
essentially containing polyether blocks, polyamide blocks of very
variable length, but also various reagents which have reacted
randomly and which are distributed randomly along the polymer
chain.
[0077] Whether they originate from the copolycondensation of
polyamide and polyether sequences prepared previously or from a
one-step reaction, these polymers containing polyamide blocks and
polyether blocks have, for example, Shore D hardnesses which can be
between 20 and 75 and advantageously between 30 and 70, and an
inherent viscosity of between 0.8 and 2.5, measured in meta-cresol
at 250.degree. C. for an initial concentration of 0.8 g/100 ml. The
MFI values can be between 5 and 50 (235.degree. C. under a load of
1 kg).
[0078] The polyetherdiol blocks are either used as they are and
copolycondensed with polyamide blocks containing carboxylic ends,
or they are aminated so as to be converted into polyetherdiamines
and condensed with polyamide blocks containing carboxylic ends.
They can also be mixed with polyamide precursors and a
chain-limiter in order to make polymers containing polyamide blocks
and polyether blocks having randomly distributed units.
[0079] Polymers containing polyamide and polyether blocks are
described in U.S. Pat. Nos. 4,331,786; 4,115,475; 4,195,015;
4,839,441; 4,864,014; 4,230,838 and 4,332,920.
[0080] The ratio of the amount of copolymer containing polyamide
blocks and polyether blocks to the amount of polyamide is, on a
weight basis, advantageously between 10/90 and 60/40. Mention may
be made, for example, of mixtures of (i) PA 6 and (ii) copolymer
containing PA 6 blocks and PTMG blocks and mixtures of (i) PA 6 and
(ii) copolymer containing PA 12 blocks and PTMG blocks.
[0081] As regards the polyolefin (B) of the mixture of polyamide
(A) and polyolefin (B) of the third layer, it can be functionalized
or non-functionalized or can be a mixture of at least one
functionalized and/or of at least one non-functionalized. For
simplicity, functionalized polyolefins (B 1) and non-functionalized
polyolefins (B2) have been described below.
[0082] A non-functionalized polyolefin (B2) is conventionally a
homopolyrner or copolymer of .alpha.-olefins or of diolefins such
as, for example, ethylene, propylene, 1-butene, 1-octene or
butadiene. By way of example, mention may be made of:
[0083] polyethylene homopolymers and copolymers, in particular
LDPE, HDPE, LLDPE (linear low density polyethylene), VLDPE (very
low density polyethylene) and metallocene polyethylene.
[0084] propylene homopolymers or copolymers.
[0085] ethylene/.alpha.-olefin copolymers such as
ethylene/propylene, EPR (abbreviation for
ethylene-propylene-rubber) and ethylene/propylene/diene (EPDM).
[0086] styrene/ethylene-butene/styrene (SEBS),
styrene/butadiene/styrene (SBS), styrene/isoprene/styrene (SIS) or
styrene/ethylene-propylene/styre- ne (SEPS) block copolymers.
[0087] copolymers of ethylene with at least one product chosen from
unsaturated carboxylic acid salts or esters, such as alkyl
(meth)acrylate (for example methyl acrylate), or saturated
carboxylic acid vinyl esters, such as vinyl acetate, it being
possible for the proportion of comonomer to be up to 40% by
weight.
[0088] The functionalized polyolefin (B1) can be an .alpha.-olefin
polymer containing reactive units (functionalities); such reactive
units are acid, anhydride or epoxy functions. By way of example,
mention may be made of the above polyolefins (B2) grafted or co- or
terpolymerized with unsaturated epoxides such as glycidyl
(meth)acrylate, or with carboxylic acids or the corresponding salts
or esters such as (meth)acrylic acid (it being possible for the
latter to be totally or partially neutralized with metals such as
Zn, etc.) or alternatively with anhydrides of carboxylic acids such
as maleic anhydride. A functionalized polyolefin is, for example, a
PE/EPR mixture, in which the weight ratio can vary within a wide
range, for example between 40/60 and 90/10, the said mixture being
co-grafted with an anhydride, in particular maleic anhydride,
according to a degree of grafting of, for example, from 0.01 to 5%
by weight.
[0089] The functionalized polyolefin (B1) can be chosen from the
following (co)polymers, grafted with maleic anhydride or glycidyl
methacrylate, in which the degree of grafting is, for example, from
0.01 to 5% by weight:
[0090] PE, PP, copolymers of ethylene with propylene, butene,
hexene or octene containing, for example, from 35 to 80% by weight
of ethylene;
[0091] ethylene/.alpha.-olefin copolymers such as
ethylene/propylene copolymers, EPR (abbreviation for
ethylene-propylene-rubber) and ethylene/propylene/diene (EPDM)
copolymers.
[0092] styrene/ethyhlene-butene/styrene (SEBS),
styrene/butadiene/styrene (SBS), styrene/isoprene/styrene (SIS) or
styrene/ethylene-propylene/styre- ne (SEPS) block copolymers.
[0093] ethylene-vinyl acetate (EVA) copolymers containing up to 40%
by weight of vinyl acetate;
[0094] copolymers of ethylene and of alkyl (meth)acrylate,
containing up to 40% by weight of alkyl (meth)acrylate;
[0095] ethylene-vinyl acetate (EVA) and alkyl (meth)acrylate
copolymers, containing up to 40% by weight of comonomers.
[0096] The functionalized polyolefin (BI) can also be chosen from
ethylene/propylene copolymers predominantly containing propylene
grafted with maleic anhydride and then condensed with monoamino
polyamide (or a polyamide oligomer) (products described in EP-A-0
342 066).
[0097] The functionalized polyolefin (B1) can also be a co- or
terpolymer of at least the following units: (1) ethylene, (2) alkyl
(meth)acrylate or saturated carboxylic acid vinyl ester and (3)
anhydride such as maleic anhydride or (meth)acrylic acid or epoxy
such as glycidyl (meth)acrylate. Examples of functionalized
polyolefins of the latter type which may be mentioned are the
following copolymers, in which ethylene preferably represents at
least 60% by weight and in which the termonomer (the function)
represents, for example, from 0.1 to 10% of the weight of the
copolymer:
[0098] ethylene/alkyl (meth)acrylate/(meth)acrylic acid or maleic
anhydride or glycidyl methacrylate copolymers;
[0099] ethylene/vinyl acetate/maleic anhydride or glycidyl
methacrylate copolymers;
[0100] ethylene/vinyl acetate or alkyl (meth)acrylate/(meth)acrylic
acid or maleic anhydride or glycidyl methacrylate copolymers.
[0101] In the preceding copolymers, the (meth)acrylic acid can be
salified with Zn or Li.
[0102] The term "alkyl (meth)acrylate" in (B 1) or (B2) denotes C1
to C8 alkyl methacrylates and acrylates and can be chosen from
methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl
acrylate, 2-ethylhexyl acrylate, cyclohexyl acrylate, methyl
methacrylate and ethyl methacrylate.
[0103] Moreover, the abovementioned polyolefins (B 1) can also be
crosslinked by any suitable process or agent (diepoxy, diacid,
peroxide, etc.); the expression "functionalized polyolefin" also
comprises mixtures of the abovementioned polyolefins with a
difunctional reagent such as diacid, dianhydride, diepoxy, etc.
which can react with the latter or mixtures of at least two
functionalized polyolefins which can react together.
[0104] The copolymers mentioned above, (B1) and (B2), can be
copolymerized in a random or block manner and can have a linear or
branched structure.
[0105] The molecular weight, the MFI index and the density of these
polyolefins can also vary within a wide range, which a person
skilled in the art will appreciate. MFI, the abbreviation for melt
flow index, is the flow rate in the molten state. It is measured
according to ASTM standard 1238.
[0106] Advantageously, the non-functionalized polyolefins (B2) are
chosen from polypropylene homopolymers or copolymers and any
homopolymer of ethylene or copolymer of ethylene and of a comonomer
of higher .alpha.-olefinic type such as butene, hexene, octene or
4-methyl-1-pentene. Mention may be made, for example, of PPs, high
density PEs, medium density PEs, linear low density PEs, low
density PEs and very low density PEs. These polyethylenes are known
by those skilled in the art as being produced according to a
"radical-mediated" process, according to a catalysis of "Ziegler"
type or, more recently, according to a so-called "metallocene"
catalysis.
[0107] Advantageously, the functionalized polyolefins (B1) are
chosen from any polymer comprising .alpha.-olefinic units and units
bearing reactive polar functions such as epoxy, carboxylic acid or
carboxylic acid anhydride functions. As examples of such polymers,
mention may be made of the terpolymers of ethylene, of alkyl
acrylate and of maleic anhydride or of glycidyl methacrylate, such
as the products Lotader.RTM. from ELF Atochem S.A. or polyolefins
grafted with maleic anhydride, such as the products Orevac.RTM.
from ELF Atochem S.A., as well as terpolymers of ethylene, of alkyl
acrylate and of (meth)acrylic acid. Mention may also be made of
polypropylene homopolymers or copolymers grafted with a carboxylic
acid anhydride and then condensed with polyamides or monoamino
polyamide oligomers.
[0108] The MFI of (A) and the MFI of (B1) and (B2) can be chosen
within a wide range, but it is recommended, in order to facilitate
the dispersion of (B), that the MFI of (A) be greater than that of
(B).
[0109] For small proportions of (B), for example 10 to 15 parts, it
is sufficient to use a non-functionalized polyolefin (B2). The
proportion of (B2) and (B1) in the phase (B) depends on the amount
of functions present in (B1) as well as their reactivity.
Advantageously, (B1)/(B2) weight ratios ranging from 5/35 to 15/25
are used. For small proportions of (B), it is also possible to use
only one mixture of polyolefins (B1) to obtain crosslinking.
[0110] According to a first preferred form of the invention, the
polyolefin (B) comprises (i) a high density polyethylene (HDPE) and
(ii) a mixture of a polyethylene (C1) and a polymer (C2) chosen
from elastomers, very low density polyethylenes and ethylene
copolymers, the mixture (C1)+(C2) being co-grafted with an
unsaturated carboxylic acid.
[0111] According to a second preferred form of the invention, the
polyolefin (B) comprises (i) polypropylene and (ii) a polyolefin
which results from the reaction of a polyamide (C4) with a
copolymer (C3) comprising propylene and a grafted or copolymerized
unsaturated monomer X.
[0112] According to a third preferred form of the invention, the
polyolefin (B) comprises (i) a polyethylene of LLDPE, VLDPE or
metallocene type and (ii) an ethylene-alkyl (meth)acrylate-maleic
anhydride copolymer.
[0113] According to a fourth preferred form of the invention, the
polyamide (A) is chosen from mixtures of (i) polyamide and (ii)
copolymer containing PA 6 blocks and PTMG blocks and mixtures of
(i) polyamide and (ii) copolymer containing PA 12 blocks and PTMG
blocks; the ratio of the amounts of copolymer and of polyamide by
weight being between 10/90 and 60/40. According to a first variant,
the polyolefin (B) comprises (i) a polyethylene of LLDPE, VLDPE or
metallocene type and (ii) an ethylene-alkyl (meth)acrylate-maleic
anhydride copolymer; according to a second variant, the polyolefin
comprises two functionalized polymers comprising at least 50 mol %
of ethylene units and which can react to form a crosslinked
phase.
[0114] As regards the first form, the proportions are
advantageously as follows (by weight):
[0115] 60 to 70% of polyamide,
[0116] 5 to 15% of the co-grafted mixture of (C1) and (C2)
[0117] the remainder being high density polyethylene.
[0118] As regards the high density polyethylene, its density is
advantageously between 0.940 and 0.965 and the MFI between 0.1 and
5 g/10 min (190.degree. C., 2.16 kg).
[0119] The polyethylene (C1) can be chosen from the polyethylenes
mentioned above. Advantageously, (C1) is a high density
polyethylene (HDPE) with a density of between 0.940 and 0.965. The
MFI of (C1) is (under 2.16 kg-190.degree. C.) between 0.1 and 3
g/10 min.
[0120] The copolymer (C2) can be, for example, an
ethylene/propylene elastomer (EPR) or ethylene/propylene/diene
elastomer (EPDM). (C2) can also be a very low density polyethylene
(VLDPE) which is either an ethylene homopolymer or a copolymer of
ethylene and of an .alpha.-olefin. (C2) can also be a copolymer of
ethylene with at least one product chosen from (i) unsaturated
carboxylic acids, salts thereof, esters thereof, (ii) vinyl esters
of saturated carboxylic acids, (iii) unsaturated dicarboxylic
acids, their salts, their esters, their hemiesters and their
anhydrides. Advantageously, (C2) is an EPR.
[0121] Advantageously, 60 to 95 parts of (C 1) are used per 40 to 5
parts of (C2).
[0122] The mixture of (C 1) and (C2) is grafted with an unsaturated
carboxylic acid, i.e. (C1) and (C2) are co-grafted. It would not
constitute a departure from the context of the invention to use a
functional derivative of this acid. Examples of unsaturated
carboxylic acids are those containing from 2 to 20 carbon atoms,
such as acrylic acid, methacrylic acid, maleic acid, fumaric acid
or itaconic acid. The functional derivatives of these acids
comprise, for example, the anhydrides, the ester derivatives, the
amide derivatives, the imide derivatives and the metal salts (such
as the alkali metal salts) of unsaturated carboxylic acids.
[0123] Unsaturated dicarboxylic acids containing 4 to 10 carbon
atoms and functional derivatives thereof, particularly their
anhydrides, are grafting monomers that are particularly preferred.
These grafting monomers comprise, for example, maleic acid, fumaric
acid, itaconic acid, citraconic acid, allylsuccinic acid,
4-cyclohexene-1,2-dicarboxylic acid,
4-methyl-4-cyclohexene-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, maleic
anhydride, itaconic anhydride, citraconic anhydride, allylsuccinic
anhydride, 4-cyclohexene-1,2-dicarboxylic anhydride,
4-methylene-4-cyclohexene-1,2-dicarboxylic anhydride,
bicyclo(2,2,1)hept-5-ene-2,3-dicarboxylic anhydride and
x-methylbicyclo(2,2,1)hept-5-ene-2,2-dicarboxylic anhydride. Maleic
anhydride is advantageously used.
[0124] Various known processes can be used to graft a grafting
monomer onto the mixture of (C1) and (C2). For example, this can be
carried out by heating the polymers (C1) and (C2) to high
temperature, about 150.degree. C. to about 300.degree. C., in the
presence or absence of a solvent with or without a
radical-generator.
[0125] In the mixture of (C1) and (C2) modified by grafting,
obtained in the abovementioned manner, the amount of the grafting
monomer can be chosen in an appropriate manner, but is preferably
from 0.01 to 10%, better still from 600 ppm to 2%, relative to the
weight of grafted (C1) and (C2). The amount of the grafted monomer
is determined by assaying the succinic functions by FTIR
spectroscopy. The MFI of (C1) and (C2) which have been co-grafted
is from 5 to 30 g/10 min (190.degree. C.-2.16 kg), preferably 13 to
20.
[0126] Advantageously, the mixture of co-grafted (C1) and (C2) is
such that the MFI.sub.10/MFI.sub.2 ratio is greater than 18.5,
MFI.sub.10 denoting the flow rate at 190.degree. C. under a load of
10 kg and MFI.sub.2 denoting the flow rate under a load of 2.16 kg.
Advantageously, the MFI.sub.20 of the mixture of co-grafted
polymers (C 1) and (C2) is less than 24. MFI.sub.20 denotes the
flow rate at 190.degree. C. under a load of 21.6 kg.
[0127] As regards the second form of the invention, the proportions
are advantageously as follows (by weight):
[0128] 60 to 70% of polyamide,
[0129] 20 to 30% of polypropylene
[0130] 3 to 10% of a polyolefin which results from the reaction of
a polyamide (C4) with a copolymer (C3) comprising propylene and a
grafted or copolymerized unsaturated monomer X.
[0131] The MFI of the polypropylene is advantageously less than 0.5
g/10 min (230.degree. C.-2.16 kg) and preferably between 0.1 and
0.5. Such products are described in EP 647 681.
[0132] The grafted product of this second form of the invention is
now described. To begin with, (C3) is prepared, which is either a
copolymer of propylene and of an unsaturated monomer X or a
polypropylene onto which is grafted an unsaturated monomer X. X is
any unsaturated monomer which can be copolymerized with the
propylene or grafted onto the polypropylene and which has a
function that can react with a polyamide. This function can be, for
example, a carboxylic acid, a dicarboxylic acid anhydride or an
epoxide. As examples of monomers X, mention may be made of
(meth)acrylic acid, maleic anhydride and unsaturated epoxides such
as glycidyl (meth)acrylate. Maleic anhydride is advantageously
used. As regards the grafted polypropylenes, X can be grafted onto
polypropylene homo- or copolymers, such as ethylene-propylene
copolymers predominantly containing propylene (in moles).
Advantageously, (C3) is such that X is grafted. The grafting is an
operation which is known per se.
[0133] (C4) is a polyamide or a polyamide oligomer. Polyamide
oligomers are described in EP 342 066 and FR 2 291 225. The
polyamides (or oligomers) (C4) are the products of condensation of
the monomers already mentioned above. Mixtures of polyamides can be
used. PA-6, PA-11, PA 12, the copolyamide containing units 6 and
units 12 (PA-6/12) and the copolyamide based on caprolactam,
hexamethylenediamine and adipic acid (PA-6/6.6) are advantageously
used. The polyamides or oligomers (C4) can contain acid, amine or
monoamine endings. In order for the polyamide to contain a
monoamine ending, it suffices to use a chain-limiter of formula
R.sub.1--NH.vertline.R.sub.2 in which:
[0134] R.sub.1 is hydrogen or a linear or branched alkyl group
containing up to 20 carbon atoms,
[0135] R.sub.2 is a group containing up to 20 linear or branched
alkyl or alkenyl carbon atoms, a saturated or unsaturated
cycloaliphatic radical, an aromatic radical or a combination of the
above. The limiter can be, for example, laurylamine or
oleylamine.
[0136] Advantageously, (C4) is a PA-6, a PA-11 or a PA-12. The
proportion of C4 in C3+C4 by weight is advantageously between 0.1
and 60%. The reaction of (C3) with (C4) is preferably carried out
in the molten state. For example, (C3) and (C4) can be blended in
an extruder at a temperature generally of between 230 and
250.degree. C. The average residence time of the molten material in
the extruder can be between 10 seconds and 3 minutes and preferably
between 1 and 2 minutes.
[0137] As regards the third form, the proportions are
advantageously as follows (by weight):
[0138] 60 to 70% of polyamide,
[0139] 5 to 15% of an ethylene-alkyl (meth)acrylate-maleic
anhydride copolymer.
[0140] The remainder is a polyethylene of LLDPE, VLDPE or
metallocene type; advantageously, the density of this polyethylene
is between 0.870 and 0.925, and the MFI is between 0.1 and 5
(190.degree. C.-2.16 kg).
[0141] Advantageously, the ethylene-alkyl (meth)acrylate-maleic
anhydride copolymers comprise from 0.2 to 10% by weight of maleic
anhydride, up to 40% and preferably 5 to 40% by weight of alkyl
(meth)acrylate. Their MFI is between 2 and 100 (190.degree. C.-2.16
kg). The alkyl (meth)acrylates have already been described above.
The melting point is between 80 and 120.degree. C. These copolymers
are commercially available. They are produced by radical-mediated
polymerization at a temperature which can be between 200 and 2500
bar.
[0142] As regards the fourth form, the proportions are
advantageously as follows (by weight):
[0143] According to a first variant:
[0144] 60 to 70% of the mixture of polyamide and of copolymer
containing polyamide blocks and polyether blocks,
[0145] 5 to 15% of an ethylene-alkyl (meth)acrylate-maleic
anhydride copolymer,
[0146] The remainder is a polyethylene of LLDPE, VLDPE or
metallocene type; advantageously, its density is between 0.870 and
0.925, and the MFI is between 0.1 and 5 (190.degree. C.-2.16
kg).
[0147] Advantageously, the ethylene-alkyl (meth)acrylate-maleic
anhydride copolymers comprise from 0.2 to 10% by weight of maleic
anhydride, up to 40% and preferably 5 to 40% by weight of alkyl
(meth)acrylate. Their MFI is between 2 and 100 (190.degree. C.-2.16
kg). The alkyl (meth)acrylates have already been described above.
The melting point is between 80 and 120.degree. C. These copolymers
are commercially available. They are produced by radical-mediated
polymerization at a pressure which can be between 200 and 2500
bar.
[0148] According to a second variant:
[0149] 40 to 95% of the mixture of polyamide and of copolymer
containing polyamide blocks and polyether blocks,
[0150] 60 to 5% of a mixture of an ethylene-alkyl
(meth)acrylate-maleic anhydride copolymer and of an ethylene-alkyl
(meth)acrylate-glycidyl methacrylate copolymer.
[0151] The copolymer with the anhydride was defined in the first
variant. The ethylene/alkyl (meth)acrylate/glycidyl methacrylate
copolymer can contain up to 40% by weight of alkyl (meth)acrylate,
advantageously from 5 to 40%, and up to 10% by weight of
unsaturated epoxide, preferably 0.1 to 8%. Advantageously, the
alkyl (meth)acrylate is chosen from methyl (meth)acrylate, ethyl
acrylate, n-butyl acrylate, isobutyl acrylate and 2-ethylhexyl
acrylate. The amount of alkyl (meth)acrylate is preferably from 20
to 35%. The MFI is advantageously between S and 100 (in g/10 min at
190.degree. C. under 2.16 kg) and the melting point is between 60
and 110.degree. C. This copolymer can be obtained by
radical-mediated polymerization of the monomers.
[0152] Catalysts can be added to accelerate the reaction between
the epoxy and anhydride functions. Among the compounds capable of
accelerating the reaction between the epoxy function and the
anhydride function, mention may be made in particular of:
[0153] tertiary amines such as dimethyllaurylamine,
dimethylstearylamine, N-butylmorpholine,
N,N-dimethylcyclohexylamine, benzyldimethylamine, pyridine,
4-dimethylaminopyridine, 1-methylimidazole,
tetramethylethylhydrazine, N,N-dimethylpiperazine,
N,N,N',N'-tetramethyl-1,6-hexanediamine, a mixture of tertiary
amines containing from 16 to 18 carbon atoms, known under the name
dimethyltallowamine,
[0154] tertiary phosphines such as triphenylphosphine
[0155] zinc alkyldithiocarbamates
[0156] acids.
[0157] The preparation of the mixtures of the third layer can be
carried out by mixing together the various constituents in the
molten state in the apparatus usually used in the thermoplastic
polymer industry.
[0158] The first layer can consist of a layer of virgin HDPE and a
layer of recycled polymers obtained from scraps from the
manufacture of the transfer or storage devices or of these
non-compliant devices as explained in the prior art already
mentioned. This recycled layer is located on the binder layer side.
In the text herein below these two layers will be denoted for
simplicity by the term "first layer".
[0159] The thickness of the first layer can be between 2 and 10 mm,
that of the second layer between 30 and 500 .mu.m and that of the
third layer between 30 .mu.m and 2 mm. The total thickness is
usually between 3 and 10 mm.
[0160] A layer of binder can also be placed between the second and
the third layer. By way of examples of binders, mention may be made
of the functionalized polyolefins (B 1) described above. The binder
between the first and second layer and that between the second and
third layer may be identical or different. In the descriptions
below of binders, the term "polyethylene" denotes both homopolymers
and copolymers; such products have been described earlier in the
polyolefins of the third layer.
[0161] As a first example of a binder, mention may be made of the
mixture of co-grafted (C1) and (C2) described above in the first
preferred form of the third layer.
[0162] As a second example of a binder, mention may be made of
mixtures comprising:
[0163] 5 to 30 parts of a polymer (D) which itself comprises a
mixture of a polyethylene (D1) with a density of between 0.910 and
0.940 and of a polymer (D2) chosen from elastomers, very low
density polyethylenes and metallocene polyethylenes, the mixture
(D1)+(D2) being co-grafted with an unsaturated carboxylic acid,
[0164] 95 to 70 parts of a polyethylene (E) with a density of
between 0.910 and 0.930,
[0165] the mixture of (D) and (E) being such that:
[0166] its density is between 0.910 and 0.930,
[0167] the content of grafted unsaturated carboxylic acid is
between 30 and 10,000 ppm,
[0168] the MFI(ASTM D 1238-190.degree. C.-2.16 kg) is between 0.1
and3 g/10 min.
[0169] The MFI denotes the melt flow index.
[0170] The density of the binder is advantageously between 0.915
and 0.920. Advantageously, (D1) and (E) are LLDPEs, and preferably
have the same comonomer. This comonomer can be chosen from
1-hexene, 1-octene and 1-butene.
[0171] As a third example of a binder, mention may be made of
mixtures comprising:
[0172] 5 to 30 parts of a polymer (F) which itself comprises a
mixture of a polyethylene (F) with a density of between 0.935 and
0.980 and of a polymer (F2) chosen from elastomers, very low
density polyethylenes and ethylene copolymers, the mixture
(F1)+(F2) being co-grafted with an unsaturated carboxylic acid,
[0173] 95 to 70 parts of a polyethylene (G) with a density of
between 0.930 and 0.950,
[0174] the mixture of (F) and (G) being such that:
[0175] its density is between 0.930 and 0.950 and advantageously
between 0.930 and 0.940,
[0176] the content of grafted unsaturated carboxylic acid is
between 30 and 10,000 ppm,
[0177] the MFI (melt flow index) measured according to ASTM D 1238
at 190.degree. C.-21.6 kg is between 5 and 100.
[0178] As a fourth example of a binder, mention may be made of
polyethylene grafted with maleic anhydride, having an MFI of 0.1 to
3, a density of between 0.920 and 0.930 and containing 2 to 40% by
weight of insolubles in n-decane at 90.degree. C. To determine the
insolubles in n-decane, the grafted polyethylene is dissolved in
n-decane at 140.degree. C., the solution is cooled to 90.degree. C.
and products precipitate; the mixture is then filtered and the
insolubles content is the percentage by weight which precipitates,
and is collected by filtration at 90.degree. C. If the content is
between 2 and 40%, the binder has good resistance to petrol.
[0179] Advantageously, the grafted polyethylene is diluted in a
non-grafted polyethylene and such that the binder is a mixture of 2
to 30 parts of a grafted polyethylene with a density of between
0.930 and 0.980 and from 70 to 98 parts of a non-grafted
polyethylene with a density of between 0.910 and 0.940, preferably
between 0.915 and 0.935.
[0180] As a fifth example of a binder, mention may be made of
mixtures comprising:
[0181] 50 to 100 parts of a polyethylene homo- or copolymer (J)
with a density of greater than or equal to 0.9,
[0182] 0 to 50 parts of a polymer (K) chosen from polypropylene
homo- or copolymer (K1), poly(1-butene) homo- or copolymer (K2) and
polystyrene homo- or copolymer (K3),
[0183] the amount of (J)+(K) being 100 parts,
[0184] the mixture of (J) and (K) being grafted with at least 0.5%
by weight of a functional monomer,
[0185] this grafted mixture itself being diluted in at least one
polyethylene homo- or copolymer (L) or in at least one polymer of
elastomeric nature (M) or in a mixture of (L) and (M).
[0186] According to one form of the invention, (J) is an LLDPE with
a density of 0.91 to 0.930, the comonomer containing from 4 to 8
carbon atoms. According to another form of the invention, (K) is an
HDPE advantageously with a density of at least 0.945 and preferably
from 0.950 to 0.980.
[0187] Advantageously, the functional monomer is maleic anhydride
and its content is from 1 to 5% by weight of (J)+(K).
[0188] Advantageously, (L) is an LLDPE in which the comonomer
contains from 4 to 8 carbon atoms and, preferably, its density is
at least 0.9 and preferably 0.910 to 0.930.
[0189] Advantageously, the amount of (L) or (M) or (L)+(M) is from
97 to 75 parts per 3 to 25 parts of (J)+(K), the amount of
(J)+(K)+(L)+(M) being 100 parts.
[0190] As a sixth example of a binder, mention may be made of
mixtures consisting of a polyethylene of HDPE, LLDPE, VLDPE or LDPE
type, 5 to 35% of a grafted metallocene polyethylene and 0 to 35%
of an elastomer, the total being 100%.
[0191] As a seventh example of a binder, mention may be made of
mixtures comprising:
[0192] at least one polyethylene or an ethylene copolymer,
[0193] at least one polymer chosen from polypropylene or a
propylene copolymer, poly(l-butene) homo- or copolymer, polystyrene
homo- or copolymer and preferably polypropylene,
[0194] this mixture being grafted with a functional monomer, this
grafted mixture itself optionally being diluted in at least one
polyolefin or in at least one polymer of elastomeric nature or in a
mixture thereof. In the above mixture which is grafted, the
polyethylene advantageously represents at least 50% of this mixture
and preferably 60 to 90% by weight.
[0195] Advantageously, the functional monomer is chosen from
carboxylic acids and derivatives thereof, acid chlorides,
isocyanates, oxazolines, epoxides, amines or hydroxides and
preferably unsaturated dicarboxylic acid anhydrides.
[0196] As an eighth example of a binder, mention may be made of
mixtures comprising:
[0197] at least one LLDPE or VLDPE polyethylene
[0198] at least one elastomer based on ethylene chosen from
ethylene-propylene copolymers and ethylene-butene copolymers
[0199] this mixture of polyethylene and of elastomer being grafted
with an unsaturated carboxylic acid or a functional derivative of
this acid
[0200] this co-grafted mixture optionally being diluted in a
polymer chosen from polyethylene homo- or copolymers and styrene
block copolymers
[0201] the binder having
[0202] (a) an ethylene content which is not less than 70 mol %
[0203] (b) a content of carboxylic acid or of its derivative of
from 0.01 to 10% by weight of the binder and
[0204] (c) an MFI.sub.10/MFI.sub.2 ratio of from 5 to 20, in which
MFI.sub.2 is the mass melt flow index at 190.degree. C. under a
load of 2.16 kg, measured according to ASTM D 1238, and MFI.sub.10
is the mass melt flow index at 190.degree. C. under a load of 10
kg, according to ASTM D 1238.
[0205] The various layers in the structure of the invention,
including the layers of binder, can also contain at least one
additive chosen from:
[0206] fillers (mineral fillers, flame-retardant fillers,
etc.);
[0207] fibres;
[0208] dyes;
[0209] pigments;
[0210] optical brighteners;
[0211] antioxidants;
[0212] UV stabilizers.
EXAMPLES
[0213] The following products were used:
[0214] EVOH D: ethylene-vinyl alcohol copolymer containing 29 mol %
of ethylene, MFI 8 (210.degree. C.-2.16 kg), melting point
188.degree. C., crystallization temperature 163.degree. C., Tg
(glass transition temperature) 62.degree. C.
[0215] Mixtures were prepared of polyamide and of polyolefin for
the third layer, known as Orgalloy.RTM., and were made from the
following products:
[0216] Polyamides (A)
[0217] PA 1: Copolyamide 6/6-6 of medium viscosity with a melting
point of 196.degree. C. and a flow index of 4.4 g/10 min according
to ASTM 1238 at 235.degree. C. under a weight of 1 kg.
[0218] PA 2: Copolyamide 6/6-6 of medium viscosity with a melting
point of 196.degree. C. and a flow index of 6.6 g/10 min according
to ASTM 1238 at 235.degree. C. under a weight of 1 kg.
[0219] Polyolefins (B2)
[0220] LLDPE: Linear low density polyethylene with a density of
0.920 kg/l according to ISO 1872/1 and a flow index of 1 g/10 min
according to ASTM 1238 at 190.degree. C. under a weight of 2.16
kg.
[0221] HDPE: High density polyethylene with a density of 0.952 kg/l
according to ISO 1872/1 and a flow index of 0.4 g/10 min according
to ASTM 1238 at 190.degree. C. under a weight of 2.16 kg.
[0222] Polyolefins (B1)
[0223] B1-1: This is a carrier PE with a content of 3000 ppm of
maleic anhydride and having a flow index of 1 g/10 min according to
ASTM 1238 at 190.degree. C. under a weight of 2.16 kg.
[0224] Antioxidants
[0225] Anti 1: Antioxidant of hindered phenolic type.
[0226] Anti 2: Secondary antioxidant of phosphite type.
[0227] The copolyamide, the polyolefin and the functional
polyolefin are introduced, via three independent weight-metering
devices (or by simple dry-premixing of the various granulates),
into the hopper of a Werner-Pfleiderer co-rotating twin-screw
extruder with a diameter of 40 mm, L/D=40 (9 sleeves+4 struts, i.e.
a total length of 10 sleeves). The total flow rate of the extruder
is 50 kg/h and the spin speed of the screws is 150 rpm and the
material temperatures at sleeves 3/4, 6/7 and 7/8 and at the die
outlet are, respectively, 245, 263, 265 and 276.degree. C. The
extruded rods are granulated and then oven-dried under vacuum for 8
hours at 80.degree. C. The compositions are given in Table 1 below
(proportions by weight):
1TABLE 1 Product Orgalloy C1 Orgalloy C2 Orgalloy C3 Orgalloy C4
PA1 64.3 64.3 PA2 64.3 64.3 LLDPE 27 27 HDPE 27 27 B1-1 8 8 8 8
Anti 1 0.5 0.5 0.5 0.5 Anti 2 0.2 0.2 0.2 0.2
[0228] Orgalloy.RTM.1: mixture of polyamide 6 and of polyolefin
corresponding to the third preferred form of the third layer and
consisting (by weight) of:
[0229] 65 parts of PA 6
[0230] 25 parts of linear low density polyethylene of MFI 0.9 g/10
min and density 0.920,
[0231] 10 parts of a copolymer of ethylene, of butyl acrylate and
of maleic anhydride in proportions by weight of 91/6/3 and of MFI 5
(190.degree. C.-2.16 kg)
[0232] The binders described in the section "Second example of a
binder" are referred to as binder 2a-binder 2d, and their details
are given in Table 2 below.
2 TABLE 2 Formulations of the binders Binder 2a Binder 2b Binder 2c
Binder 2d Polyethylene Comonomer 1-octene 1-butene 1-hexene
1-octene D1 Density (g/cm.sup.3) 0.919 0.917 0.918 0.919 MFI (g/10
min; 2.16 kg) 4.4 2.5 3 4.4 % by weight D1/D1 + D2 75 90 80 75
Polyethylene Comonomer propylene 1-butene 1-octene 1-octene D2
Density (g/cm.sup.3) 0.880 0.900 0.870 0.870 MFI (g/10 min; 2.16
kg) 0.2 2.8 5 5 % by weight D2/D1 + D2 25 10 20 25 Co-grafted
Maleic anhydride content 3800 7500 4000 8000 mixture D (ppm) % by
weight D/D + E 20 10 15 15 Polyethylene Comonomer 1-octene 1-butene
1-hexene 1-octene E Density (g/cm.sup.3) 0.919 0.919 0.921 0.920
MFI (g/10 min; 2.16 kg) 1.1 1 0.5 1 Mixture D + E Density
(g/cm.sup.3) 0.917 0.919 0.919 0.918 MFI (g/10 min; 2.16 kg) 1.0
0.8 0.5 1.1 Maleic anhydride content 760 750 600 1200 (ppm)
[0233] Next Presently Preferred Embodiment
[0234] As best shown in FIG. 4, another presently preferred
embodiment of a multi-layer plastic fuel tank 50 having a tank wall
52 that includes six layers of polymeric material. Starting from
the outside of the tank and progressing toward the interior, the
fuel tank has an outer layer 54 preferably formed of HDPE, an
intermediate layer 56 preferably formed of salvaged and reground
material, an adhesive layer 58, a barrier layer 60 preferably
formed of EVOH, another adhesive or damper layer 62, and an inner
layer 64 that is preferably formed of a polyamide or a polyamide
and polyolefin mixture or alloy such as ORGALLOY.RTM. which may
have a composition generally as described previously. Likewise, the
HDPE, regrind, adhesive, damper and EVOH layers may also be of the
compositions described previously.
[0235] The HDPE may comprise FINATHENE.RTM. MS201 having a density
on the order of about 0.950. The adhesive and adhesive/damper
layers 58 and 62, respectively, may be a maleic anhydride linear
low density polyethylene, such as that sold under the trade name
OREVAC.RTM. 18334. The barrier layer 60 may be an EVOH copolymer
such as that sold under the trade name SOARNOL.RTM. DT2903,
distributed by ATOFINA in Europe and SOARUS in the United
States.
[0236] The regrind layer 56 is preferably salvaged and reground
scrap material which is thus a blend of the various materials
forming the fuel tank 50. If necessary, to maintain compatibility
with the HDPE outer layer 54, the regrind may be diluted with HDPE
so that the regrind layer 56 does not have an ORGALLOY.RTM. matrix.
Advantageously, when the regrind is diluted, an excess of regrind
may be produced which may be used for other applications, such as
for various valve housings, supports or other arrangements wherein
the ORGALLOY.RTM. or nylon-based matrix may be beneficial, for
example, by way of its increased resistance to permeation of
hydrocarbon vapor therethrough.
[0237] The damper layer 62 is provided between the barrier layer 60
and the inner layer 64 to improve the mechanical integrity of the
fuel tank, as may be tested with various impact tests known in the
art. The damper layer 62 may be, although is not necessarily, of
the same material as the adhesive layer 58, although it is not
necessary to provide an adhesive between the ORGALLOY.RTM. and EVOH
layers since they readily adhere to each other. It has been found
that directly connecting the ORGALLOY.RTM. and EVOH layers can
reduce the structural integrity of the fuel tank in at least some
designs, because the ORGALLOY.RTM. layer does not dissipate impact
energy sufficiently to protect the relatively brittle and thin EVOH
layer. Therefore, the damper provided between the EVOH and
ORGALLOY.RTM. layers may be provided primarily to dissipate energy
and thereby increase the structural integrity of the fuel tank
against impacts or collisions.
[0238] For ease of processing and compatibility with exciting
extrusion and blow molding tools, the various layers may have
thicknesses similar to those in a conventional six-layer fuel tank,
having an outer layer of HDPE, a regrind layer adjacent to the
outer layer, an adhesive layer between the regrind layer and a
barrier layer of EVOH, and another adhesive layer between the
barrier layer and an inner layer of HDPE. In view of the large
capital cost for the extrusion and blow molding equipment for fuel
tanks, it is desirable that the equipment currently used to form
conventional 6-layer fuel tanks can also be used to form the
multi-layer fuel tank 50 as described. Accordingly, the inner layer
64 of ORGALLOY.RTM. may comprise 30% of the total fuel tank wall 52
thickness, the damper layer 62 may be on the order of 5% of the
fuel tank wall thickness, the barrier layer 60 may be 3% of the
total thickness, the adhesive layer 58 may be 3% of the total
thickness, the regrind layer 56 may be about 40% of the total
thickness, and the outer layer 54 may be around 19% of the total
thickness. Of course, these thicknesses are merely illustrative of
one presently preferred embodiment, and may be changed as desired
within the range of current tools, or may be changed more if new or
different tooling is employed. Through experimentation, it has been
found that the hydrocarbon barrier properties of the ORGALLOY.RTM.
inner layer 64 are not significantly changed over a range of about
10%-40% of the fuel tank wall thickness providing some flexibility
in the design of the fuel tank 50. Desirably, the ORGALLOY.RTM.
material may be extruded with the same extrusion equipment suitable
for polyethylene as in conventional 6-layer fuel tanks, so the
processing and manufacturing of the multi-layer fuel tank 50 is
very flexible and highly adaptable to current processing machines
with the same tools and without requiring any significant
changeover.
[0239] When constructed in the manner described, the multi-layer
fuel tank 50 exhibits exceptional hydrocarbon barrier performance
compared to conventional six layer fuel tanks. This is due in large
part to the ORGALLOY.RTM. inner layer 64 which is itself an
excellent barrier against hydrocarbon permeation, and is far more
resistant to permeation of hydrocarbons than HDPE. Thus, the fuel
tank has a first barrier layer which includes the ORGALLOY.RTM.
inner layer 64, and also has a second barrier layer including the
EVOH barrier layer 60. These layers 60,64 are provided in series,
greatly improving the overall resistance to permeation of
hydrocarbons of the fuel tank 50. Both the EVOH barrier layer 60
and the ORGALLOY.RTM. inner layer 64 are at least substantially
continuous thereby reducing or eliminating permeation windows in
the fuel tank 50.
[0240] In fact, as shown in FIG. 5, even in the area of the pinch
line 70 of a blow-molded fuel tank 50, the inner layer 64 is
continuous, which greatly reduces permeation of hydrocarbon vapors
along the pinch line 70. Blow molded fuel tanks are formed by
enclosing a parison in a blow mold, closing the mold, and inflating
the parison into the mold. Closing the mold also closes the parison
and forms a pinch line where the parison is closed between the
molds. Permeation along the pinch line is a problem with
traditional six layer fuel tanks since the EVOH barrier layer is
not continuous in the area of the pinch. Because in conventional
six layer fuel tanks the EVOH barrier layer does not seal on itself
in the pinch area, a permeation window is defined in the gap
between portions of the barrier layer through which hydrocarbon
vapors more readily escape. In the multi-layer fuel tank described
herein, even if a similar window or gap exists in the barrier layer
60 (as diagrammatically shown in FIG. 5), there is no corresponding
window or gap in the inner layer 64, so the extent of hydrocarbon
permeation through the pinch line 70 is greatly reduced. Without
wishing to be held to any particular theory or numerical range, it
is currently believed that approximately 20% to 30% of the
hydrocarbon emissions from conventional 6-layer fuel tanks occur
through the area of the pinch line. Therefore, the continuous inner
layer 64 in the fuel tank 50, even in the area of the pinch line
70, greatly reduces hydrocarbon emission from the fuel tank 50.
[0241] Further, as shown in FIGS. 5 and 6, the ORGALLOY.RTM. inner
layer 64 has a different rheology than the HDPE inner layer of the
conventional six layer fuel tanks. Desirably, the ORGALLOY.RTM.
inner layer consistently provides a flat interior surface 72 in the
area of the pinch line 70 which greatly reduces or eliminates
problems that can be encountered with the conventional six layer
fuel tank. In the conventional six layer fuel tank, the flow of
material during the pinching process is somewhat unpredictable and
difficult to control. It is common for a notch or indention to form
in the interior surface of the inner layer of HDPE in the area of
the pinch line. This notch can reduce the structural integrity of
the fuel tank to such things as, for example, internal pressure
whereby a fracture or crack may be initiated in the area of the
notch. Empirical data has shown that the multi-layer fuel tank 50
has superior mechanical performance including internal pressure
resistance as demonstrated by a significant improvement in the
burst test performance of the fuel tank. Some empirical testing
conducted to date shows that the fuel tank 50 has exhibited
increased internal pressure resistance on the order of 20-35%
greater then the conventional six layer fuel tank. In addition to
forming a continuous, relatively flat inner surface 72, the
rheology of the ORGALLOY.RTM. layer, which has a lower viscosity
then polyethylene, does not affect the thickness or integrity of
the EVOH barrier layer in the area of the pinch line 70 to the same
extent that is found in conventional six layer fuel tanks.
Desirably, in the area of the pinch line 70 the barrier layer 60 of
the multi-layer fuel tank does not become as thin as in
conventional six layer fuel tanks. This results in still further
improved resistance to permeation of hydrocarbon vapors, even in
the area of the pinch line 70 of the multi-layer fuel tank 50.
[0242] The greatly improved resistance to permeation of hydrocarbon
exhibited by the multi-layer fuel tank 50 over conventional six
layer fuel tank, enables the multi-layer fuel tank 50 to meet the
very stringent emissions standards enacted or contemplated, for
example, in the State of California. These standards include, for
example, LEV II and PZEV which require significantly reduced
vehicle emissions. While some designs of conventional six layer
fuel tanks may meet the requirements of LEV II they will not meet
the requirements of the more restrictive regulations of PZEV. The
multi-layer fuel tank 50 of the embodiment disclosed provides
vastly superior resistance to permeation of hydrocarbons, and can
be readily designed to meet the PZEV requirements. In general
numbers, to relate the barrier performance of various materials in
the polymeric fuel tanks in non-alcoholic or low alcohol fuels such
as CARB Ph II, if HDPE is assigned a general permeation rate of
1,000, ORGALLOY.RTM. would have a permeation rate of about 1.5,
over 600 times lower than the rating for HDPE. For comparison, EVOH
may have a permeation rate of 0.6. Therefore, it can be seen that
ORGALLOY.RTM. by itself, is a vastly superior barrier to
hydrocarbon emissions than is HDPE. While nylon based, and hence
somewhat susceptible to fuels containing alcohol, ORGALLOY.RTM.
still provides far superior resistance to hydrocarbon permeation
than HDPE. Using similar general ratings, HDPE may have a
permeation rate of 1,000 in high alcohol fuels like the test fuel
TF1 which contains 10% ethanol, while ORGALLOY.RTM. has a
permeation rate of only about 225. Therefore, even in high alcohol
fuels, ORGALLOY.RTM. has a more than 4 times lower permeation rate
than HDPE.
[0243] When employed in a fuel tank constructed in the manner
described, the overall resistance to hydrocarbon permeation of the
multi-layer fuel tank 50 is on the order of 21/2 to 3 times better
than conventional six-layer fuel tanks for non-alcohol or low
alcohol fuels. By way of general relative numbers, if the
conventional six-layer fuel tank is rated with a permeation rate of
100 in such fuels, the multi-layer fuel tank 50 has a permeation
rate on the order of 30-40. Likewise, the multilayer fuel tank 50
has a permeation rate about 1/2 that of the conventional six-layer
fuel tanks in high alcohol fuels, like TF1. If a conventional
six-layer fuel tank has a permeation rating of 100 in high alcohol
fuel, the multi-layer fuel tank 50 has a comparative permeation
rating of about 45-55. Further, test results have shown that the
multi-layer fuel tank 50 is able to provide greatly reduced
emissions of about 4 to 7 mg/day in CARB Ph II with an average of
about 5 mg/day, and 7 to 10 mg/day in TF1 with an average of about
8 mg/day. These results came from an 80-week soak test at
40.degree. C. of 70 liter fuel tanks. The tanks had a surface area
of about 2.1 m.sup.2, and a pinch line length of about 2 meters.
Under similar test conditions with similar size conventional fuel
tanks, the permeation rates for conventional six layer fuel tanks
were more than double for CARB Ph II fuel and typically over 60%
higher for TF1. It is believed that the permeation rate will not
significantly change over the designed life of the fuel tank of 15
years or more.
[0244] Desirably, the multi-layer fuel tank dramatically reduces
the emissions of the greatest pollutants, generally designated as
aromatics. Aromatics typically include, by way of example without
limitation, benzene, Toluene, Ethyl Toluene, Xylene and heavy
aromatics. Even in high alcohol fuels, while the overall permeation
rate of the multi-layer fuel tank 50 is about 1/2 half that of a
conventional six-layer fuel tank, the emission of aromatics from
the multi-layer fuel tank 50 is {fraction (1/10)} that of the
conventional six-layer fuel tank. Accordingly, emission of the
greatest pollutions is drastically reduced in the multi-layer fuel
tank 50. The emission of alcanes and oxygenates is also greatly
reduced in the multi-layer fuel tank 50.
[0245] Further, since the inner layer 64 provides a consistent,
thick and continuous interior barrier layer, the resistance to
hydrocarbon permeation in the multi-layer fuel tank 50 is very
consistent from tank-to-tank, day-to-day and month-to-month. There
is very little variation in the process and formation of the
multi-layer fuel tank 50. Conversely, in the conventional six-layer
fuel tank, variations of the thickness in the EVOH layer in any
part of the fuel tank can drastically degrade its hydrocarbon
permeation performance. Since the EVOH is relatively expensive and
brittle, control of the thickness of the EVOH throughout the entire
fuel tank is important to the conventional 6-layer fuel tanks which
rely on the EVOH layer almost entirely for the resistance to
permeation of hydrocarbons. Accordingly, even if some conventional
six-layer fuel tanks can be made to meet some of the increasingly
strict emission standards, due to process variations including
equipment, environment, human influence, and the like, it is
unlikely that all or even a significant number of conventional
six-layer fuel tanks would meet these increased standards for a
given production run.
[0246] Still further, the ORGALLOY.RTM. inner layer 64, and the
multi-layer fuel tank 50 in general, have superior mechanical
performance at higher temperatures as compared to HDPE and fuel
tanks employing an inner layer of HDPE as in conventional six layer
fuel tanks. The ORGALLOY.RTM. inner layer 64 has a significantly
higher melting point, generally in the range of about 375.degree.
F. to 400.degree. F., then that of HDPE, which may have a melting
point in the range of about 255.degree. F. to 275.degree. F.
Therefore, the multi-layer fuel tank 50 experiences less deflection
of its walls 52 when temperature increases, and greatly reduces or
eliminates any risk of melting of the inner layer 64 by even very
hot fuel returned to the fuel tank 50, such as from an engine fuel
rail. By way of example, without limitation, in some diesel fuel
systems, fuel may returned at temperatures up to about 255.degree.
F., which is in the range for melting point for the HDPE, and
thereby may melt the HDPE or may adversely affect its structural
integrity, at least locally and temporarily. In contrast, fuel
returned at temperatures of 255.degree. F. does not cause any
significant degradation of the ORGALLOY.RTM. inner layer 64 since
it has a much higher melting temperature. Also, the structural
integrity of the multi-layer fuel tank 50, such as may be measured
by impact testing, is also better than that of conventional 6-layer
fuel tanks, at least in certain temperature ranges, especially
higher temperatures. Because the multi-layer fuel tank 50 may
exhibit improved structural integrity, there is the potential to
reduce the thickness of the fuel tank wall 52 thereby achieving
weight and cost savings.
[0247] While generally described with reference to a blow molded
fuel tank having a pinch line, the fuel tank construction described
herein may be advantageously employed in a thermoforming operation
wherein two halves of a fuel tank are generally separately formed
and thereafter joined together, such as by welding. The
ORGALLOY.TM. inner layer 64 will still be continuous since the
inner layer from one tank half will be welded to the inner layer of
the other tank half, to reduce or eliminate permeation windows. In
a thermoformed tank, the weld line extends around the entire
periphery since the fuel tank is formed in two separate halves.
Accordingly, in conventional thermoformed fuel tanks, this weld
line between the two tank halves can be a significant source of
hydrocarbon emissions. This source of hydrocarbon emissions can be
greatly reduced or eliminated with the fuel tank constructed in the
manner described, due at least in part to the reduction or
elimination of any permeation window and the continuous inner layer
of a material that greatly retards hydrocarbon permeation through
the tank walls 52.
[0248] Persons of ordinary skill in the art will recognize that the
above description of several presently preferred embodiments is
provided in terms of illustration of these embodiments and not
limitation of the invention. Various substitutions and
modifications may be made without departing from the spirit and
scope of the invention as defined in the appended claims. For
example, without limitation, the outer layer 54 of HDPE may not be
necessary if the re-grind layer 56 has a nylon-based matrix, since
the HDPE and re-grind layers may not be compatible. To facilitate
welding other components, such as vent valves or the flange of a
fuel pump module to the nylon matrix outer layer (in the case where
the outer HDPE layer is not employed), these components may be
formed from a nylon based material. Further, while the barrier
layers of the last disclosed embodiment were set forth as being
formed from EVOH and ORGALLOY.RTM., other materials may be used.
The EVOH may be removed or replaced by other materials resistant to
permeation of hydrocarbons, and likewise, the inner layer may be
formed of a polyamide or a different mixture of polyamide and
polyolefin than ORGALLOY.RTM.. As another example, without
limitation, the EVOH material described with reference to the
barrier layer 60 may be replaced by another polyamide or a mixture
of polyamide and polyolefin such as, for example, ORGALLOY.RTM..
This may be more desirable when the multi-layer fuel tank is used
with non-alcoholic or low alcohol fuels, since materials like
polyamide or mixtures of polyamide and polyolefin such as
ORGALLOY.RTM. are good barriers against hydrocarbon permeation,
especially in non-alcoholic fuels. As still another example,
without limitation, while blowmolding and thermoforming techniques
were discussed, the multi-layer fuel tank 50 may be made by any
suitable process such as by overmolding with polyethylene or the
like a film having layers of hydrocarbon barrier material. Of
course, in whatever process used to form the fuel tank, other
materials may be used as desired for a particular application, and
other substitutions or modifications are possible in accordance
with the spirit and scope of the invention.
* * * * *