EP1119471A1

EP1119471A1 - Low permeability airbag cushions having film coatings of extremely low thickness

Info

Publication number: EP1119471A1
Application number: EP00941468A
Authority: EP
Inventors: Shulong Li
Original assignee: Milliken and Co
Current assignee: Milliken and Co
Priority date: 1999-06-17
Filing date: 2000-06-15
Publication date: 2001-08-01
Also published as: CA2340939A1; EP1119471A4; BR0006932A; WO2000078578A1; CN1159179C; CN1320090A; AU5617400A; JP2003513841A; MXPA01001743A; JP4657547B2

Abstract

Coated inflatable fabrics (26), more particularly airbags to which very low add-on amounts of coating have been applied, are provided which exhibit extremely low air permeabilities. The fabrics are primarily for use in automotive restraint cushions which require low permeability characteristics (such as side curtain airbags). The fabric utilizes an inexpensive, very thin coating to provide such necessary low permeability levels. Thus, the inventive coated airbag possesses a coating of at most 2.5 ounces per square yard, most preferably about 0.8 ounces per square yard, and exhibits a leak-down time of at least 7 seconds. All coatings, in particular elastomeric, nonsilicon coatings, and coated airbags, meeting these criteria are intended to reside within the scope of this invention.

Description

LOW PERMEABILITY AIRBAG CUSHIONS

HAVING FILM COATINGS OF EXTREMELY LOW THICKNESS

Technical Field

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,

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

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. Background Art

Airbags for motor vehicles are known and have been used for a substantial

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 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

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 correlated

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

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 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 permeabilities 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 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

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.

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

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. 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,

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 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.

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 5 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 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

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

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

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: 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

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 15 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

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 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

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

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 15

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

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

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. 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

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 prevents leakage through the interstitial spaces between the yarns and aids in

preventing yarn 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

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

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.

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, maybe utilized, as merely 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

(available from Deerfield Urethane, Inc., Ivyland, PA, under the tradename

Dureflex™ 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

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 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,

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 first layer, the desired film is then laminated through heat and pressure to the 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

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-

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

films) are heat stabilizers, flame retardants, primer adhesives, and materials for

protective topcoats. A potentially preferred thickener is marketed under the trade

designation NATROSOL™ 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

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 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 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

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

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 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

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

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

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

certain polyester and polyether-containing elastomers), 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 Irganox® 565, 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

rubbers, and the like, as long as the elastomer composition (including the topcoat)

does not exceed the 2.5 ounces per square yard (preferably much less than that, about

1.5 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

formed from yarns comprising synthetic fibers, such as polyamides or polyesters.

Such yarn preferably has a linear density of about 105 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

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

machines as disclosed in U.S. Patents 5,503,197 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 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.,

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

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

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 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

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

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

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

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 effect. However, such one-piece woven structures permit extremely low add-on

amounts of elastomeric coatings for low permeability effects. In 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

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 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

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 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

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

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

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

container, the necessary volume of such a container would equal about 830 cm³. (with the volume calculated as 2[Pi]radius ) 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 characteristics). Thus, the required cylindrical container volume would be at least 980

cm . 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

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

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.

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 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

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

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:

EXAMPLE

First, an adhesive primer formulation was produced having the composition:

Component Parts by weight

Desmoderm® 43195 (Bayer Corporation, polyurethane resin) 25 grams

Dimethylformamide (Aldrich, solvent) 75 grams Desmodur® 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 preferred embodiments within United States Patent Application Ser. No. 09/406,264, to 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

(Dureflex™ PT9400) was then laminated on both sides of the primer coated airbag

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

characteristic leak-down time was an astounding amount, greater than 80 seconds.

Description of the Drawings

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

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

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 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

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.

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.

Claims

CLAIMSWHAT IS CLAIMED IS:

1. An airbag cushion comprising a coated fabric, wherein said fabric is coated

with a laminate film in an amount of at most 2.7 ounces per square yard of the fabric;

and wherein said airbag cushion exhibits a characteristic leak-down time after

inflation of at least 5 seconds.

2. The airbag cushion of Claim 1 wherein said film is silicone free.

3. The airbag cushion of Claim 1 wherein said film composition comprises

polyurethane.

4. The airbag cushion of Claim 1 wherein said coated fabric is woven from

polyamide yams.

5. The airbag cushion of Claim 4 wherein said polyamide yarns are formed from

nylon 6,6 fiber.

6. The airbag cushion of Claim 4, wherein said polyamide yams are multifilament

yams characterized by a linear density of about 210-630 denier.

7. The airbag cushion of Claim 6, wherein wherein said multifilament yams are

characterized by a filament linear density of about 7 denier per filament or less.

8. The airbag cushion of Claim 1 wherein said film is present on said

airbag fabric surface in an amount of at most 2.5 ounces per square yard.

9. The airbag cushion of Claim 8 wherein said film is present on said airbag

fabric in an amount of at most 2.2 ounces per square yard.

10. An airbag cushion comprising a coated fabric, wherein said fabric is coated

with a laminate film; wherein said film possesses a tensile strength of at least 2,000

and an elongation at break of at least 180%; and wherein said airbag cushion exhibits

a leak-down time after inflation of at least 5 seconds.

11. The airbag cushion of Claim 9 wherein said film comprises polyurethane.

12. The airbag cushion of Claim 10 wherein said coated fabric is woven from

polyamide yams.

13. The airbag cushion of Claim 11 wherein said polyamide yams are formed from

nylon 6,6 fiber.

14. The airbag cushion of Claim 12, wherein said polyamide yams are

multifilament yams characterized by a linear density of about 210-630 denier.

15. The airbag cushion of Claim 13, wherein said multifilament yams are

16. The airbag cushion of Claim 10 wherein said film is present on said airbag

fabric surface in an amount of at most 2.5 ounces per square yard.

17. The airbag cushion of Claim 16 wherein said film is present coated on said

airbag fabric surface in an amount of at most 2.2 ounces per square yard.