Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Airbag and Method of Producing an Airbag
The invention relates to an air bag comprising two plies of a textile sheet
fabric, the plies facing each
other and enclosing at least one chamber that can be filled with gas, the
plies having surfaces facing
outwards, the invention also relating to a method of producing such an air
bag.
Air bag fabrics are in use whose technical properties are dictated by the
dense structure of the fabric.
To attain the needed strength and airtightness the fabric must be fabricated
suitably high set which
because of the high material consumption results in fabrication being
expensive. Fully fabricated or
one-piece woven (OPW) air bags need to satisfy the crash withstanding
performance, in other words
it is vital that the pressure in the air bag is maintained for the critical
duration, i.e. the air bags must
not leak. For this purpose such air bags are woven extremely dense, major
efforts being made to
change the weave in the transition of two-ply portions into single-ply
portions in attaining, for
example, a high fabric tear strength or comb withdrawal force.
Since in many cases the air bag fabric made in this way still fails to exhibit
an adequate leakage
resistance, additional thin films are added in an expensive process with the
sole objective of sealing
the fine pores of the fabric to achieve the necessary leakage resistance. Air
bags fabricated as such
are, on the one hand, because of the weaving method very expensive. On the
other hand, the expense
of the air bags is further increased by the complicated coating process.
Because of its high density, finishing such a fabric is a slow and thus cost-
intensive process.
Known air bag fabrics have the further drawback that because of the dense set
and involving the
slower weaving process the load on the yarn is correspondingly higher. Thus,
during the transition in
weaving the threads from the upper into the lower position and vice-versa the
threads rub against
each other all the more often and intensified because of the dense set, to the
detriment of the quality
in weaving (capillary damage, fluffing, conglomerations, thread breakage and
the like) resulting in a
high degree of spoilage. Moreover, thread damage in weaving results in many
cases in downtime of
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the weaving machine, also due to machine speeds needing to be increasingly
higher causing a
serious loss of efficiency which in turn further adds to the already high
costs of production.
Another drawback of the air bags as discussed is that due to the high set and
because of the
correspondingly high fabric thickness of the air bag fabric a certain packing
volume of the finished
air bag needs to be assured in the folded condition. Because of the high set
the fabric or air bag
becomes stiffer, further adversely influencing working the fabric.
The present invention is based on the objective of producing a low-cost air
bag in avoiding or at
least greatly diminishing the drawbacks of prior art, as well as proposing a
method for producing
such an air bag.
According to a first broad aspect of the present invention, there is provided
an air bag comprising
two gas-permeable and loosely woven plies of a textile sheet fabric, the plies
facing each other and
enclosing at least one chamber that can be filled with gas, the plies having
surfaces facing
outwardly, wherein the said two plies comprise a fabric with a loose woven set
defining an inner and
outer structure of the air bag, wherein each of the said surfaces facing
outwardly has a single leak-
resistant coating disposed thereon, and wherein the said coating strengthens
the said plies as
compared to the plies in an uncoated condition.
According to a second broad aspect of the present invention, there is provided
a method of
producing an air bag comprising two gas-permeable and loosely woven plies
facing each other and
enclosing at least one chamber that can be filled with gas, the plies having
surfaces facing
outwardly, on each of which a thermoplastics film is attached to produce a
coating for strengthening
and rendering the air bag resistant to leakage, the said method comprising the
steps of: (a) weaving
the air bag plies on a weaving machine controlled by a Jacquard device; and
(b) hot rolling the
thermoplastics film on the said surfaces, wherein keying points in the plies
are flattened by pressure
to thereby form a larger contact surface for the film.
The aforesaid objective is firstly achieved by an air bag having the features
described above. This
air bag in accordance with the invention can now be fabricated significantly
cheaper than air bags as
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known from prior art. By arranging the coating on the surfaces of the fabric
plies of the air bag
facing outwards as suitable for forming the leakage resistance and
strengthening of the air bag, the
textile sheet fabric of the air bag can now be woven relatively loosely.
Strengthening the air bag in
this sense is meant as coating the air bag to achieve particularly high
strength, leakage resistance and
keying to the fabric. The fabric itself is responsible so-to-speak for forming
the outer and inner
structure of the air bag and its at least one chamber, i.e. it not primarily
contributing towards leakage
resistance and strength of the fabric as handled namely by the coating. Now,
because of this, the set
of the fabric can be strongly redimensioned. Thus, for instance, the single-
ply portions in a one-
piece woven (OPW) can now be executed solid and tight in a (simpler) plain
weave instead of a
panama weave as hitherto. This greatly reduces the load on the fabric by shear
forces at critical
transitions from single-ply to two-ply portions with the same weave as
achieved by the plain weave
as proposed in this case, resulting in a drastic reduction in the risk of the
coating becoming detached
or damaged as arranged on the fabric, i.e. risk of leakage. By satisfying the
required airtightness the
air bag in accordance with the invention thus ensures the vital pressure
withstanding duration.
Another advantage materializes from the smoother surface of the plain weave
permitting better
adhesion of the coating in further reducing the risk of leakage. Because of
the lower set and the
resulting higher output of the weaving machine, the air bag fabric and one-
piece wovens (OPW) in
the shop and finishing can now be produced and worked to advantage
substantially cheaper. Due to
the fewer shed changes as well as due to the lesser attrition of the threads
against each other the load
on the yarn material is significantly reduced, resulting in a drastic
reduction in impairments
(capillary damage, fluffing, conglomerations, thread breakage and the like) in
thus immensely
enhancing product quality. Since this involves the weaving machine being down
far less because of
yarn impairment, efficiency is boosted substantially.
Yet another advantage of the air bag in accordance with the invention
materializes from the reduced
packing volume in the folded condition. The reduction in set as made possible
by the invention now
makes it possible to reduce the cover factor and result in a fabric with a
softer feel with added
flexibility. As a result of this, the fabric coming from the weaving machine
can now be worked
much better in the subsequent steps in the process.
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Further features and advantages of the invention follow below.
The aforesaid objective is further achieved by the method as previously
described. For this purpose,
particular mention is made to the advantages of hot rolling thermoplastic film
to the surfaces,
resulting in the keying points in the fabric being flattened by the pressure
in thus providing a more
expansive receiving surface for the roll-applied film. In other words, this
technique now makes it
possible to achieve a smoother surface for better keying between film and
fabric.
As a rule the surfaces of e.g. woven, non-woven fleece, knitted or netted
textile sheet fabrics as
representing the aforementioned surfaces, for example, are not smooth in
structure but "bumpy",
resulting in no continuous flat contact surface being available for a coating,
e.g. applied in the form
of a film. The threads of the textile sheet fabric merely "ripple" from the
surface thereof in a bumpy
structure, whereby in a knit, for example, the peaks of the loops protrude
from the surface whilst the
valleys of the loops are located deeper in the knit.
It is known to coat textile sheet fabrics with fluids, films, film-like
materials or laminates and the
like, serving e.g. to enhance the resistance to ageing and/or leakage and/or
to reduce permeability
and/or friction, etc. When such textile sheet fabrics are overtaxed
mechanically, hydraulically or
pneumatically the key between the textile sheet fabric and the coating is
disrupted which may even
result in a total malfunction of the textile sheet fabric.
In another advantageous aspect of the method in accordance with the invention,
a low-cost method
of coating textile sheet fabrics, especially where wovens, air bag wovens and
air bags are involved
in achieving a better adhesion between the textile sheet fabrics and their
coating. A substantial
improvement in the adhesion of the textile sheet fabric is achieved both by
corona treatment and by
plasma treatment as well as by fluorination. In the corona and plasma
processes as described and
discussed e.g. in German utility model DE 298 05 999 U1 electrostatic forces
of attraction are
activated to greatly enhance the adhesion of the substances applied to the
textile sheet fabric. In
fluorination of a textile sheet fabric, a reproducible, dry chemical reaction
takes place at the surface
in which hydrogen atoms are substituted by fluorine, creating a longer-active
surface permitting
mechanical and chemical bonding.
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In still another advantageous aspect of the method in accordance with the
invention the textile sheet
fabric is coated with a film of silicone whose surface facing away from the
textile sheet fabric is
treated with fluorine gas. This fluorination produces a near totally smooth
surface practically
cancelling any silicone/silicone adhesion.
This advantage is put to use particularly for air bags to be folded, since it
does away with the need
for a parting agent as required hitherto.
The invention will now be briefly explained in the following by way of an
example embodiment
with reference to the drawing in which:
FIG. 1 is a diagrammatic cross-section through a fabric ply of an air bag in
accordance with the
invention.
FIG. 2 is a diagrammatic illustration of how thermoplastic films are rolled on
to a fabric ply for
producing a textile sheet fabric for the air bag in accordance with the
invention.
Referring now to FIG. I there is illustrated a fabric including weft threads 6
and (not shown true to
scale) warp threads 7. Indicated are so-called keying points 2 to which a film
1 optimized as to
adhesion, resistance to leakage and strength is applied to a fabric 3 formed
by weft and warp threads
6 and 7 respectively. Due to the fabric 3 being compressed by a pair of nip
rollers 4 (Figure 2) as
shown in FIG. 2 the warp threads 7 are squeezed together so that they become
elliptical cross-
sectionally. Likewise evident from the arrangement as shown in FIG. 1 is how
the keying "points" 2
become flattened between film and fabric.
Referring now to FIG. 2 there is illustrated a pair of nip rollers 4 between
which the film 1 as cited
above and the backing fabric 3 thinned in the thread densities is guided and
keyed. The resulting key
of film and fabric is achievable, chemically, thermally or mechanically,
resulting in so-to-speak a
textile-strengthened plastics surface 5 according to embodiments of this
invention which can be
additionally compounded by making use of bicomponent yams. In a loose fabric
setting the
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undulation of the fabric is less. The keying points 2 (Figure 1) of the
textile-strengthened plastics
surface 5 are flattened by the pressure in rolling and offer a larger contact
surface for the film 1.
With reference to other embodiments of the present invention, the fabric 3 may
be a knit or a non-
woven fleece. The film 1 may be keyed to the surfaces of the fabric 3 either
chemically, thermally
or mechanically. The film 1 may also consist of a layer of plastics-sheathed
threads of the plies of
fabric 3.
The air bag according to the present invention may be produced by weaving the
plies for same on a
weaving machine controlled by a Jacquard device. A thermoplastic film is
deposited on the
outwardly facing surfaces of the plies as aforesaid by hot rolling, wherein
keying points in the fabric
plies are flattened by pressure to thereby form a larger contact surface for
the film.
The said surfaces of fabric 3 and the film 1 may be prepared at least in part
by a corona treatment,
by a plasma treatment or by fluorination before the said step of hot rolling.
The film 1 may be
selected from the group consisting of polyamide, polyester, silicone, neoprene
or polyurethane.
Moreover, the said surfaces of fabric 3 may be provided with a film of
silicone which is in turn
treated with fluorine gas.
The air bag may also be configured as it reads from claim 3, whereby the
advantages as discussed
with reference to claim 1 are likewise provided. By thermally treating the air
bag after weaving the
necessary leakage resistance and strength are attainable due to cross-linking
of the components of
the plastics sheathing the threads of the fabric plies.
