Note: Descriptions are shown in the official language in which they were submitted.
r~
Po]yamide Fuel Lines Having a Glass Fiber
Reinforced Middle Laye_
This Application claims the benefit of the
priority of German 40 25 300.7, filed August 9, 1990.
This invention rela~es to a cold impact resistant
polyamide fuel line which is stable in length and can be
briefly thermally loaded.
BACKGROUND OF T~IE IN~ENTION
Fuel lines, so-called mono-pipes consisting of a
single homogeneous layer of polyamide 11 or 12, have been
installed in motor vehicles for a long time. An essential
disadvantage of such fuel lines resides in the
considerable absorption capacity of the polymers for
individual components of the fuels which leads to swelling
and to changes of length in the walls and wall layers.
Differing swelling in various wall parts is a particular
problem.
A further disadvantage is that there is
considerable permeation of conventional fuels through the
walls of such mono-pipes which is unreasonably high in
view of the environmental and safety considerations which
have arisen in recent years and have to be taken into
consideration.
~ ~5 ,3
Developments have therefore been made in order to
improve such mono-pipes. One possibility consists in
replacement by multi-layered pipes fabricated of polymers
of the same or different types~
A fuel line is known from DE 35 10 395 Al in which
ethylene /vinyl alcohol copolymers are laminated to
polyamide 11 or 12 layers. However, the adhesion between
these layers is so low that they delaminate easily. Also,
corrosive chemicals such as scattered salt can penetrate
between the layers at the delaminated pipe ends.
Furthermore, the adhesion to fittings with mandrel
profiles is markedly reduced. Moreover, the cold impact
resistance of such pipes is so low that they cannot
withstand cold impact tests according to ISO 7628,
DIN 73 378, and SAE J 4844d, because of the extremely
brittle polyethylene vinyl alcohol layer used as the inner
wall. The three-layer-tube as claimed in DE 38 21 723 is
made from polyamide with a polyolefin middle layer and
shows, besides low-stability in length, a limited
stability under elevated temperatures due to its
polyolefin component.
In addition, DE 38 27 092 describes a fuel line in
which thermoplastic polyester elastomers are laminated to
polyamide 6 and to a polyethylene vinyl alcohol internal
layer. As in the previously discussed case, only slight
adhesion exists between the layers so that the
above-described disadvantages arise here as well.
--2--
~ 3
Sl]MMARY OF TH~ INVENTION
_
It is therefore an object of the invention to
provide a polyamide fuel line, which is stable in length,
which exhibits sufficicnt resistance to permeation by all
conventional fuels for current environmental and safety
regulations without having the above-mentioned
disadvantages.
To achieve this object, there is provided a cold
impact resistant polyamide pipeline, which is not only
s-table in length, but also can be briefly thermally
overloaded. It consists of at least three layers of
mutually compatible polyamide polymers, wherein at least
one layer is reinforced with glass fibers.
The invention will be described in connection with
a fuel line for a motor vehicle, but its application is by
no means so limited. The fuel line according to the
invention has a permeation barrier which is adequate for
current environmental and safety regulations, is
delamination-free, and can be briefly overloaded at the
temperatures usually occurring in the engine chamber of
motor vehicles. ~oreover, it is inexpensive to produce.
Known mono-pipes cannot withstand the bursting
pressure test at 170C. On the other hand, the
multi-layered fuel lines according to the invention
withstand a bursting pressure of 7 bar even at 18~C for a
3 7 ~ ~
short time~ i.e. 1 to Z hours. This is of eonsider~le
importance for the safe~y of fuel lines in cascs wllere the
engine ov~rheats briefly, or example ;f the cooling
system begins to malfunçtion.
I
, ~
Surprisin~ly, it has been found that the stabilit~
in length of a ~ulti-layered p~lyamide pipeline is very
high i~ at least one of the polymer laycrs is reinforced,
for example with ~lass fibers. The high stabj]ity in
]en~th is also achieved if only one layer ig rcinforced.
It has been found that this can be achieved preferably by
reinfor~lng the ~elatively thin middle layer with g]ass
f ibers and can be improved by introducing impa~t strength
modifiers into th~ Iniddle layer. This combination also
cnsures good elongation at break behaYior.
i, ,.
~5 It IIAS similarly been found ~hat the fo]]owing
modified or un~odified polya~ide types, whieh mfly contain
plasticiz~rs, are suit~ble as pipe layer materials:
polyamide ll; lZ; 12,]2; ~; ~,6; polyami~e elastomers
based on polyamide 1~; and parti~lly aromatic polyamides.
~`he three last-m~ntioned polyalnides surpass the first~
entioned in their barrier e~fect against the arom~tic,
usually toxic constituents o ~uels and are,
thcrefoIe~parti~ularly preferred for use as barri~r layers
in fuel lines.
~5 A glass fiber-reinforcedg impact-modi~ied or
impac.t modi~er-~ree polyamide is co~patible Wit}l the sam~
~.,
,-,
~....
, .
..,
-4-
type of impact-modified but unreinforced polyamide. The
same applies to other layer material cornbinations such as
polyamide 6,6 with polyamide 6 on the one hand and
polyamide 11 or 12 on the other hand, as well as polyamide
6,6 with blends of copolyamides and polyamide elastomers.
It is preferred to use polyether esteramides based on the
monomers of polyamide 11 or 12; the copolyamides of the
monomers with 6, 11 or 12 carbon atoms are particularly
suitable for the above-mentioned blends. No delamination
could be observed on the pipelines from such polyamide
layers.
According to the invention, therefore,
multi-layered polyamide pipelines are provided,the
external layer of which consists of impact-modified
polyamides which may contain plasticizers and of which the
glass fiber-reinforced middle layer consists of
impact-modifier-free or impact-modified polyamide,
preferably of polyamide 6, polyamide 12, or polyamide
6,6. The glass fiber-reinforced middle layer of such
pipelines preferably consists of polyamide 6 or 12 which
can also contain impact-modifiers.
~unctionalized homopolyolefins or copolyolefins
are used as impact-modifiers. These modifiers are present
in amounts of 5% to 30% by weight and the glass fibers
constitute 15% to 50% by weight. The ratio of the two
additives is not critical and can be varied according to
the requirements of the specific applications.
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Combinations which consist internally and
externally of impact-modified polyamide 6 or
impact-modified polyamide 12 are preferred. A further
preferred embodiment has roughly the same layer thickness
in the internal and external layers, which is between 0.2
and 1.0 mm in practice. Thicknesses of 5~ to 25% of the
total wall thickness are sufficient for the glass fiber-
reinforced middle layers. Thicknesses of 0.1 to 0.5 mm
are, therefore, particularly preferred for the glass fiber-
reinforced middle layer.
The polyamide pipelines according to the invention
can obviously be made up from more than three layers if
the principle of an impact-modified external layer and at
least one reinforced layer, preferably between the
internal and external layers is respected and the
compatibility of the layer materials is ensured.
The multi-layered polyamide pipelines accordin to
the invention are preferably produced by combining streams
of melt in a coextrusion device. Such coextruded
polyamide pipelines according to the invention have been
tested with respect to their cold impact strength
according to SAE J 844d, DIN 73 378, and IS0 7628, with
respect to fuel permeation, and with respect to their
stability in length.
v~ 3
1~ ~
¦ Tlle reslllts of ~h~ ~old impa~t tes~s are
repro~uced in 'I'a~le l. They have been carried out on
pip~s l~aving an external diameter of B mm a wa~ thickness
~ o~ 1 mm, and the layer str~tures al~e ~l~o indicated in
¦ 5 ~he sa~e Table, The polyamides mentioned are:
,
.....
GRILO~ XF31~s an impact-~odified PA 6
...
.
GRII,AMl~ X}s3]48 an impact-modified PA l~ with
plasticizer
1. '.
GRtLON PYZ ~H an impact-modified PA 6 ~ith 30%
glass fiber
.,', ,
1.. .
GRI~AMID ~.Y~ ~ an impact modifier~frcc ~A 12 with
50~ ~lass fiber
~, .
" .
.. .
The ~bove-mentioned polyamides are produced by
~` ~MS-~H~MI~ AG, Zurich, Swit~crland. The sa~e applies to
. .
~
~ 15 GRILON T300 GM ~n impac~modifier-free PA 66
~.,
~ GRILAMID ~LY20NZ an impact-modified po)y~ide
.
~ elastomer
}
GRIJ,ON CA6E an amorphous eopolyamidc based on
~ caprolactam/laurolact~m
i~
~ -7-
i~ ~
GRILON R47HW a high-viscosity, impact-modified
PA 6 with a defined plasticizer
content
GRILAMID L25W20 a polyamide 12 with a defined
plasticizer content
GRILAMI`D L25W40 a polyamidc 12 with a defined
(higher) plasticizer content
which have additionally been used for comparison tests
according to Table 1 and Figures 2 to 5.
In the accompanying drawings, constituting a part
hereof and in which like reference characters indicate
like parts,
Figure 1 is a diagrammatic view of a permeability
testing device;
Figures are bar graphs indicating the
2-4 permeability of various polyamide resins
to various fuels; and
Figure 5 is a graph similar to Figures 2-4
showing permeability at different
temperatures.
~ 3
The apparatus used for the permeation tests is
shown in Figure 1. The fuel flows in fuel circuit 1 which
contains an air chamber 3 and passes through heater 4 and
a portion of pipe 5 of a pipeline to be tested. Pressure
tank 2 communicates with the air chamber 3 and serves to
maintain a pressure of 4 bar in fuel circuit l. The fuel
flows in the fuel circuit 1 at about 10 liters/h and is
heated to 70C by heater ~.
The apparatus also includes carrier circuit 6
which is connected to both ends of pipe 5. Carrier
circuit 6 also has array 7 of activated carbon filters.
The fuel which has permeated through the wall of pipe 5 is
conveyed in carrier circuit 6 with 100 ml/min of nitrogen
over activated carbon filter array 7, and its weight after
300 hours is determined. Like the impact measurements,
these permeation tests were carried out on pipes having an
external diameter of 8 mm and a wall thickness of 1 mm.
The length stability of the pipes according to the
invention was determined by measuring the change in length
of pipeline portions having an external diameter of 8 mm
and a wall thickness of 1 mm while fuel flowed
therethrough for 300 hours in an apparatus similar to the
permeation apparatus of Figure 1.
The results of the length stability tests are to
be found in Table 1. The results of the permeation tests
are reproduced in Figures 2 to 4, while Figure 5 relates
to the analysis of aromatic substances.
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~ M is a bl~nd of 50% ~luol, 30% isooct~ne, 15%
isobutene, 5~ ethanol.
F~M 15 in Yigure 5 is a blend of 84,5~ l~AM, 0,5%
wa t ~ r, and l S ~ me thano 1 .
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