Note: Descriptions are shown in the official language in which they were submitted.
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1
Description
LOW PERMEABILITY AIRBAG CUSHIONS
HAVING FILM COATINGS OF EXTREMELY LOW THICKNESS
Technical Field
10 This invention relates generally to coated inflatable fabrics and more
particularly concerns airbag cushions to which very low add-on amounts of
coating
have been applied and which exhibit extremely low air permeability. The
inventive
inflatable fabrics are primarily for use in automotive restraint cushions that
require
low permeability characteristics (such as side curtain airbags).
Traditionally, heavy,
15 and thus expensive, coatings of compounds such as neoprene, silicones and
the like,
have been utilized to provide such required low permeability. The inventive
fabric
utilizes an inexpensive, very thin coating to provide such necessarily low
permeability
levels. Thus, the inventive coated inflatable airbag comprises a film
laminated on at
least a portion of the target fabric surface wherein the film possesses a
tensile strength
20 of at least 2,000 and an elongation at break of at least 180%. The film
provides a low
permeability airbag cushion exhibiting a leak-down time of at least 5 seconds
wherein
the film is present on the surface in an amount of at most 2.5 ounces per
square yard
of the fabric.
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Background Art
Airbags for motor vehicles are known and have been used for a substantial
S period of time. A typical construction material for airbags has been a
polyester or
nylon fabric, coated with an elastomer such as neoprene, or silicone. The
fabric used
in such bags is typically a woven fabric formed from synthetic yarn by weaving
practices that are well known in the art.
The coated material has found acceptance because it acts as an impermeable
barrier to the inflation medium. This inflation medium is generally a nitrogen
gas
generated from a gas generator or inflator. Such gas is conveyed into the
cushion at a
relatively warm temperature. The coating obstructs the permeation of the
fabric by
such hot gas, thereby permitting the cushion to rapidly inflate without undue
decompression during a collision event.
Airbags may also be formed from uncoated fabric which has been woven in a
manner that creates a product possessing low permeability or from fabric that
has
undergone treatment such as calendaring to reduce permeability. Fabrics which
reduce air permeability by calendaring or other mechanical treatments after
weaving
are disclosed in U.S. Patent 4,921,735; U.S. Patent 4,977,016; and U.S. Patent
5,073,418 (all incorporated herein by reference).
Silicone coatings typically utilize either solvent based or complex two
component reaction systems. Dry coating weights for silicone have been in the
range
of about 3 to 4 ounces per square yard or greater for both the front and back
panels of
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side curtain airbags. As will be appreciated by one of ordinary skill in this
art, high
add on weights substantially increase the cost of the base fabric for the
airbag and
make packing within small airbag modules very difficult. Furthermore, silicone
5 exhibits very low tensile strength and elongation at break characteristics
which do not
withstand high pressure inflation easily without the utilization of very thick
coatings.
The use of certain polyurethanes as coatings as disclosed in U.S. Patent
5,110,666 to Menzel et al. (herein incorporated by reference) permits low add
on
weights reported to be in the range of 0.1 to 1 ounces per square yard but the
material
itself is relatively expensive and is believed to require relatively complex
compounding and application procedures due to the nature of the coating
materials.
Patentees, however, fails to disclose any pertinent elasticity and/or tensile
strength
characteristics of their particular polyurethane coating materials.
Furthermore, there is
no discussion pertaining to the importance of the coating ability (and thus
con elated
15 low air permeability) at low add-on weights of such polyurethane materials
on side
curtain airbags either only for fabrics which are utilized within driver or
passenger
side cushions. All airbags must be inflatable extremely quickly; upon sensing
a
collision, in fact, airbags usually reach peak pressures within 10 to 20
milliseconds.
Regular driver side and passenger side air bags are designed to withstand this
20 enormous inflation pressure; however, they also deflate very quickly in
order to
effectively absorb the energy from the vehicle occupant hitting the bag. Such
driver
and passenger side cushions (airbags) are thus made from low permeability
fabric, but
they also deflate quickly at connecting seams (which are not coated to prevent
air
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leakage) or through vent holes. Furthermore, the low add-on coatings taught
within
Menzel, and within U.S. Patent 5,945,186 to Li et al., would not provide long-
term
gas retention; they would actually not withstand the prolonged and continuous
pressures supplied by activated inflators for more than about 2 seconds, at
the most.
The low permeability of these airbag fabrics thus aid in providing a small
degree of
sustained gas retention within driver and passenger airbag cushions to provide
the
deflating cushioning effects necessary for sufficient collision protection.
Such airbag
fabrics would not function well with side curtain airbags, since, at the very
least, the
connecting seams which create the pillowed, cushioned structures within such
airbags,
as discussed in greater detail below, would not be coated. As these areas
provide the
greatest degree of leakage during and after inflation, the aforementioned
patented low
coating low permeability airbag fabrics would not be properly utilized within
side
curtain airbags.
As alluded to above, there are three primary types of different airbags, each
for
different end uses. For example, driver-side airbags are generally mounted
within
steering columns and exhibit relatively high air penmeabilities in order to
act more as
a cushion for the driver upon impact. Passenger-side airbags also comprise
relatively
high air permeability fabrics which permit release of gas either therethrough
or
through vents integrated therein. Both of these types of airbags are designed
to protect
persons in sudden collisions and generally burst out of packing modules from
either a
steering column or dashboard (and thus have multiple "sides"). Side curtain
airbags,
however, have been designed primarily to protect passengers during rollover
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crashes by retaining its inflation state for a long duration and generally
unroll from
packing containers stored within the roofline along the side windows of an
automobile
(and thus have a back and front side only). Side curtain airbags therefore not
only
provide cushioning effects but also provide protection from broken glass and
other
debris. As such, it is imperative that side curtain airbags, as noted above,
retain large
amounts of gas, as well as high gas pressures, to remain inflated throughout
the longer
time periods of the entire potential rollover situation. To accomplish this,
these side
curtains are generally coated with very large amounts of sealing materials on
both the
10 front and back sides. Since most side curtain airbag fabrics comprise woven
blanks
that are either sewn, sealed, or integrally woven together, discrete areas of
potentially
high leakage of gas are prevalent, particularly at and around the seams. It
has been
accepted as a requirement that heavy coatings were necessary to provide the
low
permeability (and thus high leak-down time) necessary for side curtain
airbags.
15 Without such heavy coatings, such airbags would most likely deflate too
quickly and
thus would not function properly during a rollover collision. As will be well
understood by one of ordinary skill in this art, such heavy coatings add great
cost to
the overall manufacture of the target side curtain airbags. There is thus a
great need to
manufacture low permeability side curtain airbags with less expensive
(preferably
20 lower coating add-on weight) coatings without losing the aging, humidity,
and
permeability characteristics necessary for proper functioning upon deployment.
To
date, there has been little accomplished, if anything at all, alleviating the
need for such
thick and heavy airbag coatings from side curtain airbags.
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Furthermore, there is a current drive to store such low permeability side
curtain airbags within cylindrically shaped modules. Since these airbags are
generally
stored within the rooflines of automobiles, and the area available is quite
limited,
5 there is always a great need to restrict the packing volume of such
restraint cushions to
their absolute minimum. However, the previously practiced low permeability
side
curtain airbags have proven to be very cumbersome to store in such
cylindrically
shaped containers at the target automobile's roofline. The actual time and
energy
required to roll such heavily coated low permeability articles as well as the
packing
volume itself, has been very difficult to reduce. Furthermore, with such heavy
coatings utilized, the problems of blocking (i.e., adhering together of the
different
coated portions of the cushion) are amplified when such articles are so
closely packed
together. The chances of delayed unrolling during inflation are raised when
the
potential for blocking is present. Thus, a very closely packed, low packing
volume,
low blocking side curtain low permeability airbag is highly desirable.
Unfortunately,
the prior art has again not accorded such an advancement to the airbag
industry.
Disclosure of Invention
In light of the background above, it can be readily seen that there exists a
need
for a low permeability, side curtain airbag that utilizes lower, and thus less
expensive,
amounts of coating, and therefore exhibits a substantially reduced packing
volume .
over the standard low permeability type side curtain airbags. Such a coated
low
permeability airbag must provide a necessarily high leak-down time upon
inflation
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and after long-term storage. Such a novel airbag and a novel coating
formulation
provides marked improvements over the more expensive, much higher add-on
airbag
coatings (and resultant airbag articles) utilized in the past.
S It is therefore an object of this invention to provide a coated airbag,
wherein
the coating is present in a very low add-on weight, possessing extremely high
leak-
down time characteristics after inflation and thus complementary low
permeability
characteristics. Another object of the invention is to provide an inexpensive
side
curtain airbag cushion. A further object of this invention is to provide an
highly
effective airbag coating formulation which may be applied in very low add-on
amounts to obtain extremely low permeability airbag structures after
inflation. An
additional object of this invention is to provide an airbag coating
formulation which
not only provides beneficial and long-term low permeability, but also exhibits
excellent long-term storage stability (through heat aging and humidity aging
testing).
Yet another object of the invention is to provide a low permeability side
curtain airbag
possessing a very low rolled packing volume and non-blocking characteristics
for
effective long-term storage within the roofline of an automobile.
Accordingly, this invention is directed to an airbag cushion comprising a
coated fabric, wherein said fabric is laminated with a film, wherein said film
is present
in an amount of at most 2.5 ounces per square yard of the fabric; and wherein
said
airbag cushion, after long-term storage, exhibits a characteristic leak-down
time of at
least S seconds. Also, this invention concerns an airbag cushion comprising a
coated
fabric, wherein said fabric is coated with a laminate film; wherein said
laminate film
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possesses a tensile strength of at least 2,000 and an elongation of at least
180%; and
wherein said airbag cushion, after long-term storage, exhibits a
characteristic leak-
down time of at least 5 seconds.
The term "characteristic leak-down time" is intended to encompass the
measurement of time required for the entire amount of inflation gas introduced
within
an already-inflated (to a peak initial pressure which "opens" up the areas of
weak
sealing) and deflated airbag cushion upon subsequent re-inflation at a
constant
pressure at 10 psi. It is well known and well understood within the airbag
art, and
10 particularly concerning side curtain (low permeability) airbag cushions,
that retention
of inflation gas for long periods of time is of utmost importance during a
collision.
Side curtain airbags are designed to inflate as quickly as driver- and
passenger-side
bags, but they must deflate very slowly to protect the occupants during roll
over and
side impact. Thus, it is imperative that the bag exhibit a very low leakage
rate after
15 the bag experiences peak pressure during the instantaneous, quick
inflation. Hence,
the coating on the bag must be strong enough to withstand the shock and
stresses
when the bag is inflated so quickly. Thus, a high characteristic leak-down
time
measurement is paramount in order to retain the maximum amount of beneficial
cushioning gas within the inflated airbag. Airbag leakage after inflation (and
after
20 peak pressure is reached) is therefore closely related to actual pressure
retention
characteristics. The pressure retention characteristics (hereinafter referred
to as "leak-
down time") of already-inflated and deflated side curtain airbags can be
described by a
characteristic leak-down time t, wherein:
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Bag volume(ft3)
t {second) - ______________________________________________________ X3600
Volumetric leakage rate(SCFH*) at 10 Psi
*SCFH: standard cubic feet per hour.
It is understood that the 10 psi constant is not a limitation to the
invention; but merely
the constant pressure at which the leak-down time measurements are made. Thus,
even if the pressure is above or below this amount during actual inflation or
after
initial pressurizing of the airbag, the only limitation is that if one of
ordinary skill in
1 S the art were to measure the bag volume and divide that by the volumetric
leakage rate
time (measured by the amount leaking out of the target airbag during steady
state
inflation at 10 psi), the resultant measurement in time would be at least 5
seconds.
Preferably, this time is greater than about 9 seconds; more preferably,
greater than
about 1 S seconds; and most preferably, greater than about 20 seconds.
Alternatively, and in a manner of measurement with uninflated side curtain
airbags, the term "leak-down time" may be measured as the amount of time
required
for at half of the introduced inflation gas to escape from the target airbag
after initial
peak pressure is reached. Thus, this measurement begins the instant after peak
initial
pressure is reached upon inflation {such as, traditionally, about 30 psi) with
a standard
25 inflation module which continues to pump gas into the target airbag during
and after
peak initial pressure is reached. It is well understood that the pressure of
gas forced
into the airbag after peak initial pressure is reached will not remain stable
(it decreases
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during the subsequent introduction of inflation gas), and that the target
airbag will
inevitably permit escape of a certain amount of inflation gas during that
time. The
primary focus of such side curtain airbags (as noted above) is to remain
inflated for as
5 long as possible in order to provide sufficient cushioning protection to
vehicle
occupants during rollover accidents. The greater amount of gas retained, the
better
cushioning effects are provided the passengers. Thus, the longer the airbag
retains a
large amount of inflation gas, and consequently the greater the characteristic
leak-
down time, the better cushioning results are achieved. At the very least, the
inventive
10 airbag must retain at least half of its inflated gas volume 5 seconds
subsequent to
reaching peak initial pressure. Preferably, this time is 9 seconds, more
preferably IS
seconds, and most preferably 20 seconds.
Likewise, the term, "after long-term storage" encompasses either the actual
storage of an inventive airbag cushion within an inflator assembly (module)
within an
1 S automobile, and/or in a storage facility awaiting installation. Such a
measurement is
generally accepted, and is well understood and appreciated by the ordinarily
skilled
artisan, to be made through comparable analysis after representative heat and
humidity
aging tests. These tests generally involve 107° C oven aging for 16
days, followed by
83° C and 95% relative humidity aging for 16 days and are universally
accepted as
20 proper estimations of the conditions of long-term storage for airbag
cushions. Thus,
this term encompasses such measurement tests. The inventive airbag fabrics
must
exhibit proper characteristic leak-down times after undergoing such rigorous
pseudo-
storage testing.
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The inventive coating, here a film, must possess a tensile strength of at
least
2,000 psi and an elongation to break of greater than about 180%. Preferably,
the
tensile strength is at least 3,000 psi, more preferably, 6,000, and most
preferably at
least about 8,000 {the high end is basically the highest one can produce which
can still
adhere to a fabric surface). The preferred elongation to break is more than
about
200%, more preferably more than about 300%, and most preferably more than
about
600%. These characteristics of the film translate to a coating that is both
very strong
(and thus will withstand enormous pressures both at inflation and during the
time after
inflation and will not easily break) and can stretch to compensate for such
large
inflation, etc., pressures. The film itself is produced prior to actual
contact with the
target airbag cushion, or fabric, surface. In order to apply such a film, a
lamination
procedure must be performed through the simultaneous exposure of heat and
pressure
over the film while in contact with the target surface. The laminate may be
applied
over any portion of the target structure, although preferably it coats the
entire cushion
or fabric. Also, more than one laminated film may be present on the target
cushion as
one type of film (possessing certain tensile strength and elongation
characteristics)
may be preferably applied to certain discrete areas of the target cushion
while a
different film with different characteristics may be selected at other
locations (such as
20 at the seams). The only requirement is that the final product exhibit the
aforementioned high leak-down properties. This film appears to act by
"cementing"
the contacted individual yarns in place and possibly preventing leakage
through open
areas between woven yarns and/or stitches. During inflation, then, the coating
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prevents leakage through the interstitial spaces between the yarns and aids in
preventing yam shifting (which may create larger spaces for possible gas
escape).
The utilization of such high tensile strength and high elongation at break
components permits the consequent utilization, surprisingly, of extremely low
add-on
weight amounts of such films. Normally, the required coatings (which are not
films,
but actual coating formulations applied to the surface which then may form non-
laminated films) on side curtain airbags are very high, at least 3.5 ounces
per square
yard (with the standard actually much higher than that, at about 4.0). The
inventive
10 airbag cushions require merely about 2.7 ounces per square yard of the
desired film
coating (preferably less, such as about 2.5, more preferably about 2.2, still
more
preferably, less than 2.2) ounces per square yard of this inventive coating to
effectuate
the desired high leak-down (low permeability). Furthermore, the past coatings
were
required to exhibit excellent heat and humidity aging stability. Unexpectedly,
even at
15 such low add-on amounts, and particularly with historically questionable
coating
materials (polyurethanes, for example), the inventive coatings, and
consequently, the
inventive coated airbag cushions, exhibit excellent heat aging and humidity
aging
characteristics. Thus, the coating compositions and coated airbags are clearly
improvements within this specific airbag art.
20 Of particular interest as the desired films are polyurethanes, although any
film
which possesses the same desired tensile strength and elongation
characteristics noted
above may function within this inventive low permeability airbag cushion.
Copolymers of polyurethanes, polyamides, and the like, may be utilized, as
merely
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one type of example. Also, such films may or may not be cross-linked on the
airbag
surface. Preferably, the film is a polyurethane and most preferably is a
polycarbonate
polyurethane or a polyurethane film based on polytetramethylene glycol diol
5 (available from Deerfield Urethane, Inc., Ivyland, PA, under the tradename
DureflexTM PT9400). This specific film exhibits a tensile strength of 8,000
psi and an
elongation at break of about 600%. Such a film may be added in an amount of as
low
as 2.2 ounces per square yard on the desired cushion and still provide the
requisite
high leak-down time characteristics. Of course, any other film meeting the
10 characteristics as noted above is encompassed within this invention;
however, the add-
on weights of other available films may be greater than this preferred one,
depending
on the actual tensile strength and elongation properties available. However,
the upper
limit of 2.5 ounces per square yard should not be exceeded to meet this
invention.
The desired films may be added in multiple layers if desired as long the
required
15 thickness for the overall coating is not exceeded. Alternatively, the
multiple layer
film/coating system may also be utilized as long as at least one film
possessing the
desired tensile strength and elongation at break is utilized and the requisite
low
permeability is exhibited.
Other possible components present within or on these films are thickeners,
20 antioxidants, flame retardants, coalescent agents, adhesion promoters, and
colorants.
In accordance with the potentially preferred practices of the present
invention, a
primer adhesive coating is first applied to the target cushion surface. Upon
drying of
this f rst layer, the desired film is then laminated through heat and pressure
to the
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selected areas of the target surface for a sufficient time to effectuate
lamination.
Preferably, the preferred film (or films) will not include any silicone, due
to the
extremely low tensile strength (typically below about 1,500 psi)
characteristics
S exhibited by such materials. However, in order to provide effective aging
and non-
blocking benefits, such components may be applied to the film as a topcoat as
long as
the add-on weight of the entire film and topcoat does not exceed 2.5 ounces
per square
yard. Additionally, elastomers comprising polyester or polyether segments or
other
similar components, are undesirable, particularly at very low add-on weights
(i.e., 0.8-
10 1.2 oz/yd2) due to stability problems in heat and humidity aging
(polyesters easily
hydrolyze in humidity and polyethers easily oxidize in heat); however, such
elastomers may be utilized in topcoat formulations as long, again, as the 2.5
ounces
per square yard is not exceeded.
Among the other additives particularly preferred within or on the film (or
1 S films) are heat stabilizers, flame retardants, primer adhesives, and
materials for
protective topcoats. A potentially preferred thickener is marketed under the
trade
designation NATROSOLT"' 250 HHXR by the Aqualon division of Hercules
Corporation which is believed to have a place of business at Wilmington,
Delaware.
In order to meet Federal Motor Vehicle Safety Standard 302 flame retardant
20 requirements for the automotive industry, a flame retardant is also
preferably added to
the compounded mix. One potentially preferred flame retardant is AMSPERSE F/R
51 marketed by Amspec Chemical Corporation which is believed to have a place
of
business at Gloucester City New Jersey. As noted above, primer adhesives may
be
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utilized to facilitate adhesion between the surface of the target fabric and
the film
itself. Thus, although it is preferable for the film to be the sole component
of the
entire coating in contact with the fabric surface, it is possible to utilize
adhesion
promoters, such as isocyanates, epoxies, functional silanes, and other such
resins with
adhesive properties, without deleteriously effecting the ability of the film
to provide
the desired low permeability for the target airbag cushion. A topcoat
component, as
with potential silicones, as noted above, may also be utilized to effectuate
proper non-
blocking characteristics to the target airbag cushion. Such a topcoat may
perform
10 various functions, including, but not limited to, improving aging of the
film (such as
with silicone) or providing blocking resistance due to the adhesive nature of
the
coating materials (most noticeably with the preferred polyurethane
polycarbonates).
Airbag fabrics must pass certain tests in order to be utilized within
restraint
systems. One such test is called a blocking test which indicates the force
required to
15 separate two portions of coated fabric from one another after prolonged
storage in
contact with each other (such as an airbag is stored). Laboratory analysis for
blocking
entails pressing together coated sides of two 2 inch by 2 inch swatches of
airbag fabric
at 5 psi at 100°C for 7 days. If the force required to pull the two
swatches apart after
this time is greater than 50 grams, or the time required to separate the
fabrics utilizing
20 a 50 gram weight suspended from the bottom fabric layer is greater than 10
seconds,
the coating fails the blocking test. Clearly, the lower the required
separating shear
force, the more favorable the coating. For improved blocking resistance (and
thus the
reduced chance of improper adhesion between the packed fabric portions),
topcoat
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components may be utilized, such as talc, silica, silicate clays, and starch
powders, as
long as the add-on weight of the entire elastomer composition (including the
topcoat)
does not exceed 2.5 ounces per square yard (and preferably exists at a much
lower
S level, about 1.5, for instance).
Two other tests which the specific coated airbag cushion must pass are the
oven (heat) aging and humidity aging tests. Such tests also simulate the
storage of an
airbag fabric over a long period of time upon exposure at high temperatures
and at
relatively high humidities. These tests are actually used to analyze
alterations of
10 various different fabric properties after such a prolonged storage in a hot
ventilated
oven (>100°C) (with or without humid conditions) for 2 or more weeks.
For the
purposes of this invention, this test was used basically to analyze the air
permeability
of the coated side curtain airbag by measuring the characteristic leak-down
time (as
discussed above, in detail). The initially produced and stored inventive
airbag cushion
1 S should exhibit a characteristic leak-down time of greater than about 5
seconds (upon
re-inflation at 10 psi gas pressure after the bag had previously been inflated
to a peak
pressure above about 15 psi and allowed to fully deflate) under such harsh
storage
conditions. Since polyurethanes, the preferred elastomers in this invention,
may be
deleteriously affected by high heat and humidity (though not as deleteriously
as
20 certain polyester and polyether-containing elastomefs), it may be prudent
to add
certain components within a topcoat layer and/or within the elastomer itself.
Antioxidants, antidegradants, and metal deactivators may be utilized for this
purpose.
Examples include, and are not intended to be limited to, Irganox~ 1010 and
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Irganox~ S6S, both available from CIBA Specialty Chemicals. This topcoat may
also
provide additional protection against aging and thus may include topcoat aging
improvement materials, such as, and not limited to, polyamides, NBR rubbers,
EPDM
S rubbers, and the like, as long as the elastomer composition (including the
topcoat)
does not exceed the 2.S ounces per square yard (preferably much less than
that, about
l .S at the most) of the add-on weight to the target fabric.
The substrate to which the thin film coatings are applied to form the airbag
base fabric in accordance with the present invention is preferably a woven
fabric
10 formed from yarns comprising synthetic fibers, such as polyamides or
polyesters.
Such yarn preferably has a linear density of about l OS denier to about 840
denier,
more preferably from about 210 to about 630 denier. Such yarns are preferably
formed from multiple filaments wherein the filaments have linear densities of
about 7
denier per filaments or less, more preferably about 6 dpf or less, and most
preferably
1 S about 4 dpf or less. In the more preferred embodiment such substrate
fabric will be
formed from fibers of nylon, and most preferred is nylon 6,6. It has been
found that
such polyamide materials exhibit particularly good adhesion and maintenance of
resistance to hydrolysis when used in combination with the coating according
to the
present invention. Such substrate fabrics are preferably woven using fluid jet
weaving
20 machines as disclosed in U.S. Patents S,S03,197 and 5,421,378 to Bower et
al.
(incorporated herein by reference). Such woven fabric will be hereinafter
referred to
as an airbag base fabric. As noted above, the inventive airbag must exhibit
extremely
low permeability and thus must be what is termed a "side curtain" airbag. As
noted
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previously and extensively, such side curtain airbags (a.k.a., cushions) must
retain a
large amount of inflation gas during a collision in order to accord proper
long-duration
cushioning protection to passengers during rollover accidents. Any standard
side
curtain airbag may be utilized in combination with the low add-on coating to
provide
a product which exhibits the desired leak-down times as noted above. Most side
curtain airbags are produced through labor-intensive sewing or stitching (or
other
manner) together two separate woven fabric blanks to form an inflatable
structure.
Furthermore, as is well understood by the ordinarily skilled artisan, such
sewing, etc.,
10 is performed in strategic locations to form seams (connection points
between fabric
layers) which in turn produce discrete open areas into which inflation gasses
may flow
during inflation. Such open areas thus produce pillowed structures within the
final
inflated airbag cushion to provide more surface area during a collision, as
well as
provide strength to the bag itself in order to withstand the very high initial
inflation
15 pressures (and thus not explode during such an inflation event). Other side
curtain
airbag cushions exist which are of the one-piece woven variety. Basically,
some
inflatable airbags are produced through the simultaneous weaving of two
separate
layers of fabric which are joined together at certain strategic locations
(again, to form
the desired pillowed structures). Such cushions thus present seams of
connection
20 between the two layers. It is the presence of so many seams (in both
multiple-piece
and one-piece woven bags) which create the aforementioned problems of gas loss
during and after inflation. The possibility of yarn shifting, particularly
where the
yarns shift in and at many different ways and amounts, thus creates the quick
deflation
CA 02340939 2001-02-16
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19
of the bag through quick escaping of inflation gasses. Thus, the base airbag
fabrics do
not provide much help in reducing permeability (and correlated leak-down
times,
particularly at relatively high pressures). It is this seam problem which has
primarily
5 created the need for the utilization of very thick, and thus expensive,
coatings to
provide necessarily low permeability in the past.
Recently, a move has been made away from both the multiple-piece side
curtain airbags (which require great amounts of labor-intensive sewing to
attached
woven fabric blanks) and the traditionally produced one-piece woven cushions,
to
10 more specific one-piece woven fabrics which exhibit substantially reduced
floats
between woven yarns to substantially reduce the unbalanced shifting of yarns
upon
inflation, such as in Ser. No. 09/406,264, to Sollars, Jr., the specification
of which is
completely incorporated herein. These one-piece woven bags are generally
produced
on dobby or jacquard fluid jet looms, preferably the utilized one-piece airbag
is made
15 from a jacquard weaving process. With such an improvement, the possibility
of high
leakage at seams is substantially reduced. These airbags provide balanced
weave
constructions at and around attachment points between two layers of fabrics
such that
the ability of the yarns to become displaced upon inflation at high pressures
is reduced
as compared with the standard one-piece woven airbags. Unfortunately, such
20 inventive one-piece woven bags are still problematic in that the weave
intersections
may be displaced upon high pressure inflation such that leakage will still
most likely
occur at too high a rate for proper functioning. As a result, there is still a
need to coat
such one-piece woven structures with materials which reduce and/or eliminate
such an
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effect. However, such one-piece woven structures permit extremely low add-on
amounts of elastomeric coatings for low permeability effects. 1n fact, these
inventive
airbags function extremely well with low add-on coatings below 1.5 and as low
as
about 0.8 ounces per square yard.
Furthermore, although it is not preferred in this invention, it has been found
that the inventive coating composition provides similar low permeability
benefits to
standard one-piece woven airbags, particularly with the inventive low add-on
amounts
of high tensile strength, high elongation, non-silicone coatings; however, the
amount
10 of coating required to permit high leak-down times is much higher than for
the
aforementioned Sollars, Jr. inventive one-piece woven structure. Thus, add-on
amounts of as much as 1.5 and even up to about 2.7 ounces per square yard may
be
necessary to effectuate the proper low level of air permeability for these
other one-
piece woven airbags. Even with such higher add-on coatings, the inventive
coatings
15 themselves clearly provide a marked improvement over the standard,
commercial,
prior art silicone, etc., coatings (which must be present in amounts of at
least 3.0
ounces per square yard).
Additionally, it has also been found that the inventive film coating
compositions, at the inventive add-on amounts, etc., provide the same types of
20 benefits with the aforementioned sewn, stitched, etc., side curtain
airbags. Although
such structures are highly undesirable due to the high potential for leakage
at these
attachment seams, it has been found that the inventive coating provides a
substantial
reduction in permeability (to acceptable leak-down time levels, in fact) with
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21
correlative lower add-on amounts than with standard siliconeand neoprene
rubber
coating formulations. Such add-on amounts will approach the 2.7 ounces per
square
yard limit, but lower amounts have proven effective (2.2 ounces per square
yard, for
5 example) depending on the utilization of a sufficiently high tensile
strength and
sufficiently stretchable elastomeric component within the film coating
composition
directly in contact with the target fabric surface. Again, with the ability to
reduce the
amount of coating materials (which are generally always quite expensive),
while
simultaneously providing a substantial reduction in permeability to the target
airbag
10 structure, as well as high resistance to humidity and extremely effective
aging
stability, the inventive coating composition, and the inventive coated airbag
itself is
clearly a vast improvement over the prior airbag coating art.
Of particular importance within this invention, is the ability to pack the
coated
airbag cushions within cylindrical storage containers at the roof line of a
target
15 automobile in as small a volume as possible. In a rolled configuration (in
order to
best fit within the cylindrical container itself, and thus in order to best
inflate upon a
collision event downward to accord the passengers sufficient protection), the
inventive
airbag may be constricted to a cylindrical shape having a diameter of at most
23
millimeters. In such an instance, with a 2 meter long cylindrical roofline
storage
20 container, the necessary volume of such a container would equal about 830
cm3.(with
the volume calculated as 2[Pi]radius2) Standard rolled packing diameters are
at least
25 millimeters for commercially available side curtain airbag cushions (due to
the
thickness of the required coating to provide low permeability
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22
characteristics). Thus, the required cylindrical container volume would be at
least 980
cm3. Preferably, the rolled diameter of the inventive airbag cushion during
storage is
at most 20 millimeters (giving a packed volume of about 628 cm3) which is
clearly
well below the standard packing volume. In relation, then, to the depth of the
airbag
cushion upon inflation (i.e., the length the airbag extends from the roofline
down to its
lowest point along the side of the target automobile, such as at the windows),
the
quotient of the inventive airbag cushion's depth (which is standard at
approximately
17 inches or 431.8 millimeters) to its rolled packed diameter should be at
least about
10 18.8. Preferably this quotient should be about 21.6 (20 millimeter
diameter), and, at
its maximum, should be about 24 (with a minimum diameter of about 18
millimeters).
Of course, this range of quotients does not require the depth to be at a
standard of 17
inches, and is primarily a function of coating thickness, and thus add-on
weight.
While the invention will be described and disclosed in connection with certain
15 preferred embodiments and practices, it is in no way intended to limit the
invention to
those specific embodiments, rather it is intended to cover equivalent
structures
structural equivalents and all alternative embodiments and modifications as
may be
defined by the scope of the appended claims and equivalence thereto.
20 Detailed Description of the Preferred Embodiment of the Invention
Surprisingly, it has been discovered that any film with a tensile strength of
at
least 2,000 psi and an elongation at break of at least 180% coated onto and
over both
sides of a side curtain airbag fabric surface at a weight of at most 2.7
ounces per
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23
square yard, and preferably below about 2.5, more about 2.2, and most
preferably less
than about 2.2 ounces per square yard, provides a coated airbag cushion which
exhibits extremely low and extended permeability upon and after inflation.
This
5 unexpectedly beneficial type and amount of film coating thus provides an
airbag
cushion which will easily inflate after prolonged storage and will remain
inflated for a
sufficient amount of time to ensure an optimum level of safety within a
restraint
system. Furthermore, it goes without saying that the less film coating
composition
required, the less expensive the final product. Additionally, a lower required
amount
10 of film coating composition will translate into a decrease in the packing
volume of the
airbag fabric within an airbag device. This benefit thus improves the
packability for
the airbag fabric.
The preferred airbag cushion of this invention was produced in accordance
with the following Example:
15
EXAMPLE
First, an adhesive primer formulation was produced having the composition:
20
Component parts by
wei~~ht
Desmoderm~ 43195 (Bayer Corporation, polyurethane resin) 25 grams
Dimethylformamide (Aldrich, solvent) 75 grams
25 DesmodurC~7 CB-75N (Bayer, polyisocyanate adhesion promoter) 4 grams
This primer coating was applied to both sides of a 2.5 liter size Jacquard
woven nylon
airbag (of 440 denier fibers), made in accordance with the Figures and prefer
ed
embodiments within United States Patent Application Ser. No. 09/406,264, to
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24
Sollars, Jr., previously incorporated by reference. The primer coating was
dried at
about 160°C for about 2 minutes to obtain a dry coating weight of about
0.25 ounces
per square yard on each side. Subsequently, a 2 mil thick polyurethane film
(DureflexTM PT9400) was then laminated on both sides of the primer coated
airbag
5 utilizing a hotpress providing about 80 psi pressure at about 188°C
with a residence
tim eof about 1 minute. The total polyurethane film add-on weight on each side
of the
airbag was about 2.2 ounces per square yard. The airbag was then rapidly
inflated to
30 psi air pressure. More than 28 seconds elapsed before the air pressure
leaked down
to 8 psi. The leakage rate was thus measured at 10 psi to be about 4 SCFH. The
10 characteristic leak-down time was an astounding amount, greater than 80
seconds.
Description of the Drawings
15 FIG. 1 depicts the side, inside view of a vehicle prior to deployment of
the
inventive side curtain airbag.
FIG. 2 depicts the side, inside view of a vehicle after deployment of the
20
inventive side curtain airbag.
Detailed Description of the Drawings
As depicted in FIG. 1, an interior of a vehicle 10 prior to inflation of a
side
curtain airbag (not illustrated) is shown. The vehicle 10 includes a front
seat 12 and a
25 back seat 14, a front side window 16 and a back-side window 18, a roofline
20, within
which is stored a cylindrically shaped container 22 comprising the inventive
side
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curtain airbag (not illustrated). Also present within the roofline 20 is an
inflator
assembly 24 which ignites and forces gas into the side curtain airbag (26 of
FIG. 2)
upon a collision event.
FIG. 2 shows the inflated side curtain airbag 26. As noted above, the airbag
26
S is coated with at most 2.5 ounces per square of a coating formulation (not
illustrated),
preferably polyurethane polycarbonate. The inventive airbag 26 will remain
sufficiently inflated for at least 5 seconds, and preferably more, as high as
at least 20
seconds, most preferably.
10 There are, of course, many alternative embodiments and modifications of the
present invention which are intended to be included within the spirit and
scope of the
following claims.
20
