Note: Descriptions are shown in the official language in which they were submitted.
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Vehicle rooflining and method for producing the-same
The present invention relates to a vehicle rooflining
according to the p.re-characterising clause of Claim 1 and a
method for producing the same.
This vehicle rooflining is characterised by an especially
good acoustic behaviour and is suitable for an ultra-light
construction.
Because of their low intrinsic stab ility, large area
vehicle parts, especially vehicle roofs, tend to deform,
vibrate and oscillate during driving. This behaviour is
conventionally counter-acted by applying insulating
material, especially heavy layers of bitumen. In order to
reduce the transmitting of driving noises into the vehicle
compartment, the automotive industry has used multi-layer
sound insulating systems for some time now. As a rule,
these sound insulating systems are designed as spring-mass
systems and comprise an air-tight heavy layer coupled with
a resilient layer in order to absorb the vibrations ~f the
large area body parts and insulate sound transmission.
A sound insulation system of this kind is disclosed in EP-
0'255'332, for example, and comprise, a semi-flexible
support layer with which the rooflin:ing can be braced
against the vehicle roof in the manner of a snap
connection. A classic spring-mass system with a resilient,
sound-absorbing foam layer and a visco-elastic, closed cell
heavy layer (filled with bitumen) is pressed against the
vehicle roof with this support layer.
For example, a sound-absorbing rooflining is known from EP-
0'637'820, which essentially comprisE~s a semi-rigid PU foam
layer, approximately 5 mm - 15 mm th_Lck, and a 4 mm - 10 mm
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resilient nonwoven fabric layer, both layers being air-
permeable. In the: case of this embodiment, the foam layer
is reinforced both sides with glass fibres and has an air-
permeable decorative layer on the passenger compartment
side. The individual layers are bonded to each other with
an air-permeable adhesive, especially a PU adhesive. This
sound-absorbing rooflining is also a classic spring-mass
system.
However, it has been found with this type of rooflining
that because of the open cell construction of these sound
absorbers, their adhesive components penetrate the
decorative layer relatively quickly when these rooflinings
are made and result in visually perceptible stains and
therefore to a relatively high rejection rate. Therefore,
the use of permeable layers leads directly to an
undesirable detrimental effect on the appearance of the
rooflinings.
In addition, spring-mass constructions always lead to
resonance interference in the sound .insulation, which is
normally in the frequency range of the lower engine ordezs
and is especially undesirable there.
However, the general objective of the automotive industry
is to reduce the weight of vehicles. This has the result
that thinner and lighter body and lining parts are being
increasingly used and these can result in considerable
acoustic problems.
Therefore, it has already been suggested in FR 2 503 721,
for example, that a light rooflining be made which
essentially consists of an open cell and glass fibre-
reinforced foam layer which is covered with a decorative
layer and has an air-impermeable polyethylene foil between
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this decorative layer and the glass fibre-reinforced foam
layer to prevent the permeating of adhesive components into
the decorative layer. On account of this foil, this
suggested rooflining has a poor acoustic absorption which
could be improved at best by perforation. However,
perforation of the PE foil in this manner can lead to
visually perceptible changes in the decorative layer. In
the case of the manufacturing method disclosed in this
specification, the back layer on the roof side is
perforated, i.e. air-permeable, and therefore conflicts
with modern legal regulations concerning the design of
vehicle linings. These regulations forbid a direct air
flow between vehicle roof and passenger compartment.
Therefore, the object of the invention is to create a
rooflining which, depending on its specific use, has
optimum sound absorption and an aesthetically-resistant
appearance at the same time.
This object is achieved according to the invention by a
lining with the features of Claim 1 ,and especially in that
a semi-permeable and migration-resistant barrier layer is
provided between an air-permeable de~~orative layer and a
mufti-layer structure element. The mufti-layer structure
element is also air-permeable and has a support layer,
especially a PU foam layer, which is provided both sides
with an air-permeable reinforcement layer especially made
from glass fibres. These layers are bonded together in a
known way. The decorative layer may consist of a non-woven
fabric or another air-permeable material, e.g. a knitted
glass fabric. The semi-permeable and migration-resistant
barrier layer used according to the :invention is
impermeable for and migration-resist<~nt against the
adhesive used, or their components or_ additives on the one
hand and is micro-porous on the other, i.e. air-permeable,
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and has a thickness of 0.1 < d < 1.0 mm and is designed in
such a way as to produce an air flow resistance of 500Nsm-
3, < Rl < 2500Nsm-'3, especially of 900Nms-3 < R1 < 1900Nsm-
3. It is important: for optimising the acoustic
effectiveness of the vehicle rooflining that the air flow
resistance on the passenger compartment side is in the
desired range. In addition, the air--permeable, i.e. open
cell barrier layer, is made from a material which is semi-
permeable and migration-resistant and especially prevents
the penetration or permeation and / or migration of the
adhesive used, or its components and / or the softeners
used, the decomposition products caused by ageing and / or
the additives from the PU foam layer or the adhesive
layers. These barrier layers are ava_Llable on the market
and are made from chemically-bonded cellulose and polyester
fibres, for example.
One preferred method for making a lining according to the
invention provides for depositing re_Lnforcement fibres,
e.g. glass fibres or polyester fibres, on a continuously
unwound bottom layer or back layer, especially, in
polyethylene, and applying a continuously unwound support
layer, especially a PU foam layer, to it. This layer
sequence in the form of a sheet is impregnated with the
first component of an adhesive, especially a PU adhesive.
According to a preferred embodiment, this layer sequence is
transported as sheet through a bath filled accordingly. In
order to be able to control the amount of the first
adhesive component applied, this impregnated layer sheet is
transported through a pair of squeezing rollers.
Reinforcement fibres are again applied to the layer sheet
treated in this way and a second
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adhesive component is sprayed on before a semi-permeable
and migration-resistant barrier layer is applied and
pressed onto the other layers. A de;:orative layer, e.g. a
100 g/m2 PE non-woven fabric, is applied to this barrier
layer.
The sheet made in this way is then cut into suitable pieces
and shaped in a known way, i.e, with heated moulding press
dies, in order to obtain the vehicle rooflinings wanted. _
Naturally, the materials for this lining and the chemicals
needed to make this lining are not limited to the selection
disclosed here as an example. A person skilled in the art
will choose suitable materials and chemicals depending on
the range of application of the product according to the
invention. Naturally, the continuous manufacturing method
disclosed above may also be carried out sheet by sheet or
step by step.
The invention is explained in more dE~tail below on the
basis of the diagrams and an example of an embodiment,
where
Fig: 1 shows a diagramatic secti0I1 diagram of the
construction of a lining part according to the
invention;
Fig. 2 a diagramatic section of the method for making a
lining according to the invention.
Fig. 3 a comparative graph of the frequency-related
sound absorption of the lining according to the
invention.
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Figure 1 shows a diagram of the construction of a lining
according to the invention. This lining has a central
support layer 3, which consists of a.n air-permeable
material, preferably an open cell PU foam. In a preferred
embodiment, this foam layer 3 has a thickness of
approximately 5 mm. to 30 mm, especially 20 mm, and has a
volume of 20 kg/m2 to 60 kg/m2. A reinforcement layer 4 and
is disposed on each side of support layer 3,
respectively. Preferably, these reinforcement layers are
made from glass fibres and are bonded to the support layer
3 with an adhesive 7. According to a preferred embodiment,
a glass fibre layer with a weight per unit area of
approximately 50 g/m2, whose thickness corresponds
approximately to 1 to 3 times the diameter of the fibres,
is used on both sides. Naturally, other suitable
materials, i.e. rigid materials, may be used for the
reinforcement layers. It is essential for the present
invention that the aforementioned individual layers are
air-permeable and that adhesive 7 also allows an air flow
through these layers. An air-impermeable back layer 9,
preferably in polyethylene, is provided on the vehicle roof
side. This back layer 9 prevents air from being able to
flow from the passenger compartment through the air-
permeable lining 1 into the space between the vehicle roof
2 and the lining 1. An air-permeable decorative layer 6,
e.g. a 100 g/m2 heavy PE non-woven fabric, is applied on
the passenger compartment side. According to the
invention, a micro-porous, semi-permeable and migration-
resistant barrier layer 8 lies between the decorative layer
6 and the support layer 3. In a preferred embodiment, this
barrier layer 8 is made from cellulose and polyester fibres
banded together and is gas-permeable, especially air-
permeable, on the one hand but impermeable on the other,
i.e. impermeable for at least the li~~uid or viscous
substances used when making the lining, especially adhesive
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components, and therefore acts as a barrier layer for the
adhesive 7 used. In addition, this barrier layer 8 is made
from a material which prevents the rnigration of adhesive
components, any softeners, decompos_Ltion products caused by
ageing and / or chemical additives. The air-permeability
is achieved by the micro-porous and air-permeable structure
of this barrier layer 8. The air f7_ow-resistance through
this layer 8 can be pre-determined especially through the
choice of fibre diameter, barrier layer density and its
thickness. In a preferred embodiment, this barrier layer 8
has a thickness of 0.1 < d < 1.0 mm and is designed in such
a way to produce an air flow resistance of 500Nsm-3 < Rl<
2500Nsm-3, especially 900 Nsm-3 < R1 < 1900 Nsm-3 in the
lining layers on the passenger compartment side. The
surfaces of this barrier layer 8 car., be treated, i.e.
wetted, for the adhesives interacting with the surfaces,
whereas the centre area of this barrier layer 8 can have a
pronounced repellent effect for these adhesives. Suitable
surface treatments, e.g, scarfing, with chemical primer or
corona treatment, are kncwn to a person skilled in the art.
The wetting capability of these barrier layer surfaces is
chosen in such a way that these surfaces enter into
adhesion with the adhesives used, but these adhesives
cannot form any closed, air-impermeable film. In this
preferred embodiment, a barrier layer of polyester and
cellulose fibres with a weight per unit area of 20 g/m3 to
60 g/m2, especially 40 g/m2 is used. The weight of the
adhesive necessary is approximately 60 g/m2. A lining with
a total weight of approximately 800 g/m2 and a thickness of
approximately 22 mm can be made with this.
The method illustrated in Fig. 2 for making a lining
according to the invention uses a than back layer 9 which
is taken down continuously from a roll. Preferably, this
back layer consists of polyethylene and serves as an
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impermeable under layer to which the other materials are
applied. In a first method step, reinforcement fibres 11,
especially glass fibres, are strewn loosely over this back
layer 9. A support layer 3, especially a PU foam layer, is
then placed on these glass fibres 11. This support layer 3
may also be drawn down from a roll. In a further step of
the method, these three layers 9, 11, 3 are transported
through a bath 13 which contains a first adhesive
component. To be able to control the amount of this
adhesive component: applied, this impregnated layer sequence
is transported between two first squeezing rollers 14.
After this squeezing process, reinforcement fibres 15,
especially glass fvibres, are scattered on again and then
sprayed with a second adhesive component 16. The micro-
porous, semi-permeable and migration-resistant barrier
layer 8 is applied to the material sheet treated in this
way and pressed with the aid of a second pair of squeezing
rollers 17. A decorative layer 6 is applied in a next
method stage. This material is then cut to size and
transformed into the required shape :in a heated press die.
Naturally; the continuous manufacturing method disclosed
here as an example may be simply modified by a person
skilled in the art. to form a discontinuous, i.e. step-by-
step manufacturing' method.
The curves shown in Fig. 3 show the acoustic effectiveness
of the lining according to the invention. In this case,
curve A represents a sound absorption behaviour of a
vehicle rooflining without barrier layer 8 according to the
invention. It is evident from this curve that an
absorption of more than 0.8 can be achieved through the
open cell construction of the layers on the passenger
compartment side. However, such high absorption
coefficients are undesirable in the vehicle acoustics
range, because this greatly prejudices the intelligibility
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of speech in the passenger compartment. The path of this
curve (a) also shows inadequate absc>rption of the vehicle
rooflining in the range below 1500 Hz. On the other hand,
curve (b), characterising the absorb>tion behaviour of the
lining according to the invention with micro-porous barrier
layer, shows that this rooflining already has satisfactory
absorption at frequencies of 800 Hz and the absorption
coefficient for higher frequencies fluctuates in the range
between 0.7 and 0.8. This comparison illustrates the .
advantages obtained with the vehicle rooflining according
to the invention.
Naturally, other embodiments of this vehicle rooflining are
within the range of the normal technical scope of a person
skilled in the art.. With his knowledge, a person skilled
in the art will especially choose suitable materials and
adhesives for making a vehicle rooflining according to the
invention. The special fashioning or shaping of the
rooflining also belongs to the normal technical scope of a
person skilled in the art.
