Air Bag Fabric Containing Graft Polymer Thereon

The present invention relates to the field of graft polymer coatings, especially as applied to nylon and polyester yarn, fibers, woven and non-woven fabrics.

In recent years, automotive manufacturers have begun to increase the utilization of air bag safety devices in their vehicles. Therefore, there has been a continuing effort to improve the safety, performance and durability of these life-saving devices.

An automotive air bag is comprised of an inflatable/deflatable bag, an inflation device and an impact sensor. Inflation is most often provided by a sodium azide propellant positioned within the inflation device which is ignited in response to activation by an impact sensor. The combustion of this propellant yields nitrogen gas to provide rapid (about 0.2-0.5 sec) inflation of an air bag. Inflation is followed immediately with a deflation cycle. Without such an immediate deflation, the impact of a passenger upon the air bag itself could cause substantial injury.

One means of providing a deflation function for an air bag is to provide for partial air bag gas porosity. Currently, this approach is provided by utilizing a porous air bag made of uncoated fabric or non-porous fabric with vents. When utilizing such fabrics, it is required that the exhaust rate of the air bag fabric be less than the inflation rate after propellant ignition, otherwise a positive pressure would not occur within the bag. The entire inflation/deflation cycle spans approximately 0.6 seconds.

There is concern regarding several problems associated with the partial air bag porosity approach as it applies to current art on passenger and/or driver side air bags. The primary concerns centers upon the possibility that fabric yarn distortion or separation may compromise the inflation cycle. These conditions can result in an unequal volume fill of the bag, higher than acceptable gas leak rate at areas of distortion or separation, or jet stream effects that result in improper bag registration at the peak of the inflation event.

Fabric coatings have been used to provide a certain degree of yarn stability to air bag material but, at the same time, such coatings severely decrease bag porosity and increase cost. It would be highly advantageous to have an air bag material that would maintain yarn integrity during air bag inflation while providing the required air bag porosity.

The inflation/deployment of a driver side air bag; for example is both rapid (about 0.2 seconds) and aggressive, reaching a static pressure of 3 to 5 psi. The impact of the driver upon an air bag increases internal air bag pressure to about 9 to 12 psi. It is extremely important during the deployment cycle that sewn seams utilized to fabricate the bag are not compromised. It has been demonstrated that a weakness of sewn seams due to defective workmanship, fabric construction, or treatments/coatings, to fabric substrates or untreated fabric substrates could result in a condition referred to as "combing" where separation between the fibers occurs adjacent to the seam.

Stress separation during inflation and impact events resulting in separation or yarn pull-out could compromise the air bag performance or lead to catastrophic failure of the bag and/or secondary injury to the driver or passenger.

It would therefore be highly advantageous to provide an air bag fabric substrate capable of maintaining the integrity of sewn seams during packaging, compaction (for module positioning), and inflation. Preferably, such a substrate would also possess sewn seams which are capable of withstanding yarn pull-out or other catastrophic failure throughout its service life.

It is essential to provide high pliability in an air bag fabric to facilitate packageability. Furthermore, inflation time during an inflation event depends, in part, upon air bag pliability. Less pliable fabrics increase resistance to an air bag deployment resulting in a longer inflation event. Inflation times are specific to a given vehicle specification in order to provide maximum protection for the driver or passenger. It would be advantageous for a coated air bag fabric to exhibit substantially the same pliability as an uncoated air bag fabric.

Air bags are often fabricated from multiple patterns of coated or un-coated material which are sewn, bonded, or sewn and bonded. Once inflated, this manufacturing process provides a pre-selected air bag shape in accordance with interior cabin architecture and the position of the driver or passenger.

When air bag patterns are made from loom state or finished fabrics such as nylon or polyester, difficulties are encountered. These materials have a tendency to distort or fray during conventional pattern cutting operations. To avoid these problems, laser technology or hot melt dies have been employed. Since economy and high through-put are of high priority in enabling universal availability of air bags in automobiles, it would be highly desirable to provide a method for treating fabrics (such as nylon and polyester), so as to minimize fraying and distortion (filament separation in the yarn or yarn separation from the fabric). Such a method would allow economical, conventional pattern cutting technology to be utilized and would thereby help reduce the cost of air bag manufacture.

As discussed above, the inflation of an air bag is most commonly provided by the ignition of a sodium azide propellant. The ignition of this propellant results in a highly exothermic reaction. Design considerations demand that the temperature of nitrogen gas formed by this reaction be rapidly cooled in order to prevent damage to the air bag or facial injuries to the occupant. Current air bag inflators are efficient at reducing gas temperature; however, there are still risks associated with pyrotechnic damage to the air bag. Bag damage, secondary injury, or catastrophic failure of the air bag are all potential risks which must be addressed.

1. Particulate matter (cinders)--Inflator designs include primary and secondary filter medias for the purpose of capturing solid matter resulting from the rapid combustion of the solid fuel. The efficiency of the filters are quite high; however, the potential exists for hot cinders to be propelled into the environment of the bag resulting in microscopic "pitting" of the fabric substrate. This occurrence, in itself, may not necessarily result in a decrease of the bag's performance. However, there is concern that the temperature of the cinders could ignite the fabric substrate if it does not have a measurable degree of flame retardancy.

2. Bag/manifold junctions--Air bag assemblies are normally attached to an inflator housing by means of several coated gaskets and metal "O" rings. The gaskets serve as insulators between the housing and air bag material. Since the ignition of an inflator's solid fuel results in exothermic reaction temperatures of from about 1200.degree. to 1400.degree. F., the bag/manifold junction posses a risk of transferring excessive, potentially ignition-producing heat to the air bag material. Therefore, it is of the greatest importance that the air bag fabric substrate exhibit flame retardancy.

3. Deflation drape--After an air bag deployment event, the bag will lose gas pressure and deflate and assume a limp vertical hang position from the inflator housing. In this position, it is possible for the air bag fabric to come in direct contact with hot metal parts of the inflator housing. As described above, failure of the fabric to exhibit a measurable degree of flame retardancy could result in ignition of the air bag substrate.

In view of these potential fire hazards, it would be highly desirable for the air bag to possess increased flame resistance without compromising other required air bag performance features such as permeability and pliability.

An automotive air bag system must be designed so as to endure a wide range of environmental conditions without compromise of function or performance. Air bag designs or methods must provide an air bag which is functional at environmental extremes as defined by current automotive standards for performance. Air bag fabrics must also not support microbial growth, demonstrate appreciable changes in base physical properties, show appreciable change in pliability, or compromise static and dynamic requirements of the air bag when conditioned over any given environmental event.

What is needed is a vehicular air bag comprised of a fabric exhibiting increased structural integrity effectively reducing yarn distortion, pullout and related stress failures while also providing increased resistance to seam failure and combing. Furthermore, it would be highly advantageous to provide an air bag fabric which could be effectively die-cut without filament or yarn pull-out or fraying, or fabric distortion. It would be further advantageous to provide improved flame retardance in an air bag.

Now in accordance with the present invention a method of making a vehicular air bag is provided wherein the air bag is comprised of a grafted fabric that achieves increased resistance to fraying, yarn pull-out, or distortion as compared to air bags comprised of non-grafted fabric.

In the method of the present invention, an automotive air bag is formed of a fabric structure made of filaments or yarns. A first component is grafted to the filament, yarn or fabric to provide an increase in filament or yarn integrity.

The first component may be grafted onto the filaments or yarns either before or after the forming of the fabric structure. In one embodiment of the present invention, the first component may be grafted to filaments during a spin finishing operation. Thereafter, the grafted filaments may be used to directly form grafted fabric structure or the filaments may be spun into yarn which may be incorporated into the grafted air bag fabric.

In another embodiment of the present invention, the first component is applied to filaments or staples only after formation of yarns therefrom. The first component may be grafted upon beamed yarn during a slashing operation, or applied to the yarn prior to a beaming operation. The grafted yarn is thereafter utilized to form the air bag fabric structure. The yarn may also be repackaged after the first component is grafted thereon and utilized as a fill yarn.

The first component may also be grafted directly upon staple. However, it is also possible to graft the first component to filament and thereafter cut the filament into grafted staple. The grafted staple formed in either manner may then be utilized to form grafted yarn. As discussed above, the grafted yarn may thereafter be repackaged for use in forming a fabric having a grafted warp or a grafted fill.

As discussed above, the first component may be grafted to the filaments or yarns after formation of the fabric structure. The formed fabric may be dipped into a grafting solution including the first component. However, the grafting solution may also be applied by spraying, printing or a coating operation. It is possible to selectively apply the first component to the graft fabric utilizing a screen printing or selective spraying operation. It is also possible to achieve selective application of the first component by grafting only to yarns or filaments which are formed into one of the warp or the weft of the fabric. Selective application of the first component to the air bag fabric may be utilized, as discussed below, to form an air bag with predetermined areas of varying gas permeability.

A calendaring operation may be utilized to further decrease the gas permeability of the grafted air bag. The calendaring operation may be utilized with either the selectively grafted air bag fabric or a uniformly grafted fabric depending upon the desired gas permeability properties to be achieved. Thus, one can achieve a fabric having a gas porosity which is substantially equivalent to a coated air bag fabric, while, at the same time, maintaining fabric pliability substantially equivalent to uncoated fabric.

The methods of the present invention provide increased pliability in an air bag fabric as compared to coated air bag fabrics of the prior art. It has been found that by calendaring a graft fabric made in accordance with the methods of the present invention an increase in pliability of the grafted fabric may be achieved. Furthermore, it has been found that fabrics such as nylon that are otherwise resistant to calendaring, may be effectively calendared by utilizing the methods of the present invention to graft a first component to nylon fibers or yarns prior to the calendaring operation.

In the method of the present invention, it is preferred that the fabric structure is formed of filaments or yarns comprised of polyamide, polyester, polyaramid or mixtures thereof. Natural fibers or yarns, or combinations of natural and synthetic yarns, may also be used, if desired.

In an alternative embodiment of the above-described methods, a second component may be grafted onto the filaments or yarns of the fabric structure or onto the first component. The second component, as discussed below, provides an increase in the quantity and length of soft segments within the first component to provide greater pliability to the grafted fabric. It is preferred that the first component be a water dispersible polymer and that the second component be a monomer having a molecular weight of about 1200 or less. A flame retardant agent may also be advantageously added to the grafted fabric structure increase its flame retardancy, while an antioxidant, antiozonant or other stabilizer may be included to increase the resistance of the grafted fabric to heat aging, or other environmental deterioration effects.

In yet another embodiment of the present invention, a method for making an air bag fabric is provided wherein a fabric comprised of filaments or yarns is selected. Thereafter, a graft solution is contacted with the filaments or yarns to provide a grafted yarn or filament having increased structural integrity to the filaments and yarns. Fabric structures formed of the grafted filaments or yarns achieve increased resistance to distortion, fraying and pull-out during manufacture or use of the fabric.

The graft solution includes water, a graft initiator for activating sites on the filaments or yarns, a catalyst for activating or regenerating the graft initiator, and a first component that has a functional group for reaction and covalent bonding with an active site on the filaments or yarns. The graft solution may advantageously include a second component which, upon contact with the filaments or yarns, grafts upon either the first component or the filaments or yarns. It is preferred that the first component be a water-dispersible polymer such as, for example, a polyurethane, a thermoplastic, or a natural or synthetic elastomer, such as aliphatic or aromatic polyester polyurethane, polyvinyl chloride, or neoprene. It is especially preferred that the water-dispersible polyurethane includes sufficient soft segments, as discussed below, so as to provide a predetermined pliability to the air bag fabric substrate. It is preferred that the second component be a monomer having a molecular weight of about 1200 or less. It is especially preferred that the monomer is an acrylate or methacrylate monomer. It is most preferred that the monomer is a diacrylate compound of about 600 a.m.u.

The graft solution may be contacted to the filaments or yarns either before or after forming the fabric therefrom. Furthermore the solution may be contacted with staple prior to formation of yarn therefrom. Dipping, coating, spraying or printing may be utilized to contact the filaments or yarns with the graft solution. The grafting solution may be selectively applied to the filaments or yarns to obtain a desired fabric porosity profile. Furthermore, selective application may be used to provide increased resistance to fraying, pull-out, and distortion only in predetermined areas of the fabric substrate wherein pattern or mechanical die cutting will occur or where seams will be located. Furthermore, the fabric may be calendared after contacting the filaments or yarns with the graft solution so as to provide a decrease in the gas permeability of the fabric. However, it is also within the scope of the present invention to calendar the fabric prior to contact thereof with the grafting solution.

The present invention also provides an air bag fabric having increased resistance to fraying, filament or yarn pull-out, or distortion as compared to air bag fabric which has not been grafted. After the air bag fabric has been mechanically die-cut, the patterns are joined together with sewn, bonded or sewn/bonded seams to form an air bag of a predetermined configuration. The first component, or the first and second components, may also be selectively applied only to those areas of the air bag fabric which are to be utilized to form seams. Therefore, increased resistance to fabric failure due to combing, pull-out and distortion may be provided at seam areas especially subject to such failures while simultaneously conserving graft solution.

Flame retardant agents such as cyclic phosphonate esters, halogenated compounds and thiourea-formaldehyde compounds, or mixtures thereof are especially preferred, as are the conventional antioxidants, antiozonants, or other stabilizers, which are utilized in polyurethane formulations.

The present invention provides, in still another embodiment, a vehicular air bag restraint system including an air bag having a reduced predetermined range of gas permeability and increased resistance to filament or yarn tear-out, fraying or fabric distortion. The restraint system of the present invention comprises an inflatable air bag formed of a grafted air bag fabric described above and a means for inflating the inflatable air bag with a gas upon the occurrence of a collision. Upon inflation, the air bag is inflated to the predetermined shape to protect the occupants of the vehicle.

It is known in the art that both natural and synthetic fibers are utilized in the formation of fabric materials. Staple is a relatively short fiber which must be spun into a yarn. Filament may also be spun into yarn. However, longer synthetic filaments may by used as a monofilament for forming fabric directly.

The method of the present invention contemplates contacting fibers and yarns with a grafting solution at any stage of yarn or fabric production. Thus, the grafting solution may be applied to staple or filament fibers, yarns or formed fabric.

As discussed above, the grafting solution may be applied selectively to yarn utilized either for the warp or the weft of a formed fabric. Generally, warp yarns run in a machine direction while a weft or filling yarns run across the machine direction.

It is still further contemplated that the fibers or yarns may be contacted with graft solution either before or after chemical or mechanical production operations such as spin finishing, lubricant application or sizing. Furthermore, the graft solution may be applied to the yarns or fibers after formation of a fabric therefrom. The fabric may be contacted with Grafting solution either before, during, or after chemical and mechanical finishing operations such as the application of fabric softeners or calendaring operations. The terms fiber, yarn, filament, staple and fabric are well known to those skilled in the textile art. Also, the finishing and treatment operations referred to above are well known. However, each of these terms and operations are described in the McGraw-Hill Encyclopedia of Science & Technology, 6th Edition, vol 18, pages 246-254, which is hereby expressly incorporated by reference.

The grafting of the first component or the first and second component onto filaments or yarns either before or after forming an air bag fabric allows for the manufacture of an air bag fabric providing a predetermined reduced fabric porosity as compared to fabric substrate which has not been grafted. Furthermore, grafted filament and yarns form a fabric achieving increased structural integrity such as resistance to pull-out, distortion and increased seam strength.

Air bag fabric made in accordance with the methods of the present invention provide increased ease of manufacture since increased fabric integrity allows mechanical die-cutting without fabric distortion, pull-out and related defects. Furthermore it has been found that air bag fabric made in accordance with the methods of the present invention exhibit pliability which is similar to an untreated or uncoated fabric substrate.

The methods of the present invention require a grafting solution comprised of water, a catalyst for activating or regenerating a graft initiator in the presence of the fibers or yarns, a graft initiator which, upon activation or regenerating by the catalyst renders the fibers or yarns receptive to bonding with a first component by producing an active site on the fibers or yarns, and at least one first component having a functional group that reacts with and bonds to the fibers or yarns at the active site thereon. When the grafting solution contains a second component, covalent bonding of the first and second components or bonding of the second component with an active site on the fibers or yarns occurs when the grafting solution contacts the fibers or yarns. It is preferred that the first component comprises at least one water dispersible polymer which includes at least one functional group, e.g., a carboxyl, hydroxyl, NH.sub.2, or acrylic group. Water dispersible polyurethane polymers are especially preferred. These polymers are ideally suited for incorporation into the present grafting solution since they may include, as discussed below, sufficient soft segments so as to result in a highly flexible graft polymer, and thus a pliable air bag fabric.

It is preferred that the second component is at least one monomer having a molecular weight of less than 1200. It is especially preferred that the at least one monomer has a molecular weight of from about 200 to 800. As used in the present specification, the term "monomer" refers to low molecular weight polymer chains of less than 1200 amu. It is most preferred that the grafting solution include at least one monomer having a molecular weight of at least 600. The use of a 600 m.w. monomer in the solution, as is explained in greater detail below, increases the chain length of the graft polymer. As is known to the art, increasing the soft segment polymer length increases polymer "softness" or flexibility.

Acrylic and diacrylic monomers having a functional group such as a carboxyl, hydroxyl or NH.sub.2 are especially preferred. These preferred monomers include, for example, hydroxy ethyl or propyl methacrylate, a dimethyl or diethyl amino ethyl acrylate or methacrylate, methyl, ethyl and butyl acrylates and methacrylate, glycidyl methacrylate or mixtures thereof. Diacrylates are especially preferred whereas higher acrylate functionality such as triacrylates may result in undesirable crosslinking.

As discussed above, the grafting solution requires a graft initiator in order to provide an active site on the fibers or yarns for reaction and covalent bonding with the first and/or second component. The graft initiator is selected to abstract an active hydrogen from a substrate filament or yarn to which a graft polymer will be bonded.

Hydrogen abstraction, as discussed below, produces an activated position on a substrate which bonds with the first component. It is preferred that the initiator is a metal ion provided by the ionization of a metal salt. Silver ions provided by the ionization of silver salts are especially preferred although ferrous and ferric ions abstracted from iron salts as well as other metal salts may also be advantageously utilized.

When a silver salt such as silver nitrate, silver perchlorate and silver acetate is utilized to activate the graft initiator, such salts are preferably present in the graft solution in an amount of from about 0.001% to about 0.01% by weight of the solution.

In order to ionize the metal salts to provide an activating metal ion, the graft solution includes a catalyst. A wide variety of catalysts may be utilized in the method of the present invention. Peroxide, peracid, or a perbenzoate are preferred catalysts. Peroxide catalysts of urea, hydrogen and benzoyl peroxides are especially preferred. Specifically, urea peroxide, hydrogen peroxide, benzoyl peroxide, peracetic acid or tertiary butyl perbenzoate are the most advantageous. The catalyst functions to ionize metal salts such as silver or iron salts described above so as to provide silver and iron ion graft initiators. The grafting solution also advantageously includes a flame retardant and an antioxidant, antiozonant or other stabilizer.

In one embodiment of the present invention, the grafting solution additionally comprises from about 3 to 6 parts per weight of an antioxidant, antiozonant or other stabilizer. Antioxidants of the sterically hindered phenol class such as, for example, Irganox 1076, may be advantageously included in the grafting solution. U.V. stabilizers of the amine class may also be added to the grafting solution. It is preferred to utilized sterically hindered amines such as, for example, Tinuvin 292 as a U.V. stabilizer. However, U.V. absorbers of the oxalanilide class, such as, for example, Sanduvor VSU may also be utilized. Thus the grafted substrate is provided with increased resistance to heat, U.V. and age degradation.

A preferred grafting solution comprises by dry weight from about 5 to 45 weight percent of a first component, from about 45 to 5 weight percent of the second component, from about 25 to 65 weight percent of the flame retardant, from about 0.001 to 0.01 weight percent of the catalyst, and from about 0.0001 to 0.001 weight percent of the graft initiator. The grafting solution can operate with as little as 1 weight percent solids and 99 weight percent water, but typically includes from about 5 to about 95 and preferably, about 10 to 60 weight percent water as a vehicle to carry these solids.

In the method of the present invention chemical grafting of a natural or polymeric filament or yarn substrate is initiated with the contact of a graft initiator ("GI") with an "active hydrogen" of the substrate. An active hydrogen is a hydrogen which is relatively easily removed from the substrate by the graft initiator. A tertiary carbon, for example, maintains a weaker covalent bond with a hydrogen atom than a secondary carbon, and that hydrogen atom would be one type of active hydrogen. Other types includes N--H, --OH, --COOH, --COOR--H, etc.

Graft initiators are able to remove:

1. An active hydrogen alone, resulting in the formation of a cation position;

2. An active hydrogen with one electron resulting in a substrate free radical position; or

3. An active hydrogen and both electrons resulting in the formation of an anion position on the substrate.

Although there are many components which do not react with a free radical substrate position, the present invention provides for the production of all three species of activated substrate sites listed above. Therefore, it is possible to use a wide range of monomers, polymers and mixtures thereof which are selected according to the desired properties that they will contribute to the grafted substrate.

As discussed above, the method of the present invention utilizes a grafting solution which includes a first component having a functional group. Optionally, a second component polymer may be included to bond with the first component or directly graft upon the filaments or yarns comprising, or which will comprise, the fabric substrate.

It is especially preferred that the first component be a water dispersible or water based polyurethane such as, for example, an aliphatic polyester polyurethane (Dispercoli 442); aromatic polyurethane (Witcobond 160 and 170); aromatic polyurethane (Neorex R940) and aliphatic polyurethane (NeoRez R960, R962); aliphatic polyurethane (Witcobond 232); and aromatic polyester polyurethane (NeoRez R9431).

As discussed above, the second component is preferably a monomer. As used in the present specification, the term "monomer" refers to low molecular weight polymer chains of 1200 m.w. or less and preferably from about 200 to 800 m.w. Monomers especially suited to the practice of the present invention include acrylic monomers including hydroxyl, carboxyl, epoxy, amino, hydride and glycidyl functional groups, i.e., hydroxy ethyl or propyl methacrylate, dimethyl and diethyl amino ethyl acrylates and methacrylate, methyl, ethyl and butyl acrylates and methacrylate, glycidyl methacrylate. Any of the foregoing monomers can be used alone or in combination. Although mono and diacrylates are preferred as the second component, triacrylics should not be used in large amounts because they can cause cross-linking of polymer chains resulting in an undesirable stiffening of the air bag fabric.

The formula below represents a grafting process in accordance with the present invention. CH.sub.2 .dbd.CHX represents a vinyl component wherein X is a functional group. The first formula below illustrates the formation of a graft polymer in accordance with the methods of the present invention upon a segment of a polypropylene fiber substrate. The tertiary hydrogens represent active hydrogens. The second formula listed below illustrates the abstraction of hydrogen from polypropylene by means of the graft initiator. The asterisk represents either a free radical, an anion or a cation as discussed above. The third formula illustrates covalent bonding of a first component or a second component to the polypropylene fiber substrate. Since the linkage between the grafted polymer and the substrate is covalent, the graft polymer cannot be leached from the substrate. ##STR1##

As discussed above, it is important to maintain high pliability in air bag applications. Therefore, the graft polymer method of the present invention must provide a grafted air bag substrate exhibiting similar pliability to an uncoated substrate.

It is known in urethane chemistry that polymer softness can be improved by increasing the length of the soft segment portions of the polymer (simple, linear, alkyl chain sections). See H. Saunders and K. C. Frisch, Polyurethanes, Chemistry and Technology, Krieger Publ. Co. 1983, pp. 477 et seq. By analogy, it has now been discovered that by increasing the molecular weight of the second component (which may bond to the first component as a chain extender), or by using a larger molar ratio second component (CH.dbd.CHXR chain extender), a flexible graft polymer can be provided. Therefore, a particular chain extender and/or ratio may be preselected for use in a graft polymer solution in accordance with the present method to provide a graft polymer achieving high pliability. Therefore, it is now possible to have pliability in a grafted polymer fabric which is similar to that of uncoated fabric substrate.

By increasing the percentage of monomer (second component) in the grafting solution relative to the first component, a higher percentage of simple, straight chained monomer units will be incorporated into the polyurethane. These relatively linear segments of the polyurethane, known to the art as soft segments, increase the flexibility of the polymer chain. Cyclic and highly branched sections of a polyurethane are known as hard segments and increase chain stiffness. Therefore, by either increasing the amount of monomer incorporated into the polyurethane chain, or by increasing the percentage of monomer/polymer incorporated, increased flexibility of the grafted polymer can be attained. It has been found that a monomer to polymer ratio of about at least 2:1 and preferably 5:1 or more is especially useful for forming a flexible polymer. However, as the ratio of monomer is increased beyond this range, the grafted polymer begins to become tacky and thus undesirable for use on a vehicular air bag fabric. It has also been found that a molecular weight of about 600 is preferred to provide optimum polymer soft segments.

The relative percentages of monomer to polymer will also influence which component grafts directly to the polymer fiber substrate. However, it must also be considered that the relative reactivity of the functional groups incorporated within each component with the substrate will also influence the rate of grafting.

As discussed above, during the graft initiation stage, an active hydrogen is abstracted from a yarn or filament substrate (RH) by a graft initiator (e.g. Ag.sup.+).

The active site R may now react with a first component or a second component in a chain propagation step.

From this stage, the grafted chain extender can (A) react with an adjacent active site R terminating chain growth or (B) may react with additional first or second components to form a grafted polymer. As explained above, greater percentage of monomer bonding to the chain will result in a softer polymer.

Chain Termination

A: R--CH.sub.2 --CHX+R.fwdarw.R--CH.sub.2 --CHX--R

Further Chain Propagation

B: R--CH.sub.2 --CHX+(CH.sub.2 .dbd.CHX).sub.n .fwdarw.R--CH.sub.2 --CHX--(CH.sub.2 --CHX).sub.n-1 --CH.sub.2 --CHX

Chain Termination

R--CH.sub.2 --CHX--(CH.sub.2 --CHX.sub.n-1)--CH.sub.2 CHX+R.fwdarw.R--CH.sub.2 --CHX--(CH.sub.2 --CHX).sub.n-1 --CH.sup.2 --CHX--R

As can be seen in stage B illustrated above, further reaction between the chain extenders before termination will result in longer grafted polymers. By providing a relatively large percentage of chain extender (monomer) in a grafting solution formulated in accordance with the methods of the present invention, extended chain propagation occurs incorporating soft segments prior to chain termination. Thus the present method provides a means of obtaining similar pliability to that of an uncoated fabric substrate in a grafted polymer fabric.

The formula sequence illustrated below is representative of the grafting method of the present invention as applied to polyester substrate.

In the case of polyester, the active hydrogen is the hydrogen of the carboxyl group.

1. Radical formation--The active hydrogen may be abstracted by a graft initiator to form a free radical carbonyl group located in the polyester chain.

2. Initiation/extension--The free radical carbonyl group thereafter reacts with either a first component or a second component (e.g. CH.sub.2 .dbd.CH--X), so as to graft the component as a free radical upon the polyester chain.

3. Propagation--the grafted free radical component may now, covalently bond to additional components of the same or different species thereby activating additional components to a free radical state, or

4. Termination--may react with another free radical to terminate the polymerization process. Peroxide, for example may be converted by graft initiator to a free radical state for bonding with activated monomer. ##STR2##

Natural, polyester or nylon fabric may serve as the substrate in accordance with the present invention. The graft initiator abstracts an active hydrogen from the nylon or natural substrate to form a free radical in the same manner as it does for polyester.

In one method of the present invention, polyester or nylon fabric is treated with a solution of a first component water dispersible polyurethane, a second component acrylic monomer, a peroxide catalyst, a silver nitrate graft initiator, a flame retardant, an antioxidant and other ingredients of the composition. The hydroxyl, carboxyl and acrylic groups in the solution polymerize to form a polymeric structure which is chemically bound to the fabric.

The grafting solution is a system that contains selected polymers and monomers along with other ingredients of the formulation.

In one embodiment of the present invention, a predetermined amount of urethane polymer or a combination of urethane polymers is added to monomer(s), catalyst, graft initiator, and other ingredients of the solution. The grafting solution thus prepared is then used to treat polyester or nylon fabric either by dipping, spraying, printing or other methods known in the art. The treated fabric is dried to provide a grafted polymer fabric.

It has now been found that the above described grafting method may be utilized to reduce the gas permeability range of a fabric substrate. Fabric substrate ordinarily exhibit a wide range of gas permeability due to inconsistent fabric integrity. Fabric failures caused by die-cutting, seam failure during inflation or other forces applied to conventional air bag material result in a wide range of fabric porosity. The method of the present invention has been found to increase the structural integrity of the fabric substrate, e.g., by reducing yarn pull-out, distortion and combing. The increased fabric integrity provided by the present invention allows die-cutting to be applied to the grafted fabric without the above-described fabric defects. Thus, increased fabric stability results in a more predictable, reduced range of gas permeability.

In an alternative embodiment of the present invention, the graft polymer solution is selectively applied to those areas of a yarn or filament substrate along which a pattern cut is to be made to effectively lock yarn fibers together thereby preventing fraying, distortion, or yarn pull-out during conventional pattern cutting.

Selective application of the graft polymer to fabric substrate in accordance with the methods of the present invention may be accomplished by utilizing a rotary screen printing method. Also, discrete spraying devices can effect selective graft application. In addition, a spray head or series of spray heads may be used to deposit a particular graft pattern .

In FIG. 1 there is illustrated a means of applying graft polymer through the use of a rotary screen printing device.

In FIG. 2 there is illustrated a selectively coated fabric.

In FIG. 1 there is illustrated a means of applying the graft polymer upon only specific areas of the fabric substrate through the use of a rotary screen printing device 50. First, the fabric substrate 12 is mounted on unwind roll 60 and roll 65 which feeds the fabric to the rotary screen roller 70 which selectively, in a predetermined pattern, applies the grafting composition to the fabric substrate 12. The selectively grafted fabric 10 is then fed on roller 72, 73, and 74 to the cutting station where the knife 75 cuts the selectively grafted fabric at a predetermined length 76. These predetermined lengths 76 are stacked one on top of the other until a predetermined number are stacked as illustrated at 77. The predetermined lengths of selectively grafted fabrics are then transported to a die-cutting station where the die 78 performs the final cutting or trimming operation resulting in a fully trimmed selectively grafted fabric 15 from which the air bag is formed by folding, gluing, bonding and/or stitching into the desired configuration.

FIG. 2 illustrates a selectively coated fabric 15 which has been selectively coated to construct a coated fabric having a desired overall permeability as well as a permeability rate in certain locations of the fabric that has been selectively prearranged to provide the desired permeability of the final product. The selectively coated fabric 15 has uncoated areas 20 and coated areas 25.

In still another embodiment of the present invention, graft solution is selectively applied to a fabric substrate in order to provide a predetermined pattern for desired gas permeability. Therefore, it is possible to design an air bag having areas of differential inflation and deflation.

The following examples disclose the composition of various graft solutions prepared in accordance with the present invention.

Five grafting solutions formulated in accordance with the methods of the present invention are illustrated in Table 1. Each of the five grafting solutions were applied to individual nylon fabric substrate samples. The factor varied in the illustrated experiment is the amount of diacrylate monomer included in each subsequent grafting solution test. A description of each of the listed components is indicated in Table 2 below.

After a sufficient time was allowed for drying of the solution treated fabric substrates, the flame resistance, handling and die-cutability of the fabrics were tested. An informal grading system utilizing the symbols "+" equivalent to fully acceptable, "(+)" equivalent to marginal performance, and "-" equivalent to unacceptable performance are listed in Table 1.

As illustrated in Table 1, as the diacrylate is increased relative to the polyurethane and acrylic polymers, the drape of the grafted fabric improves. As discussed above, higher percentages of monomer: first component allows increased percentage of monomer incorporation into a grafted polymer chain. Thus a softer grafted polymer and more pliable grafted fabric will result. A "+" drape notation indicates fabric pliability substantially equal to untreated fabric substrate, e.g. before contacting the fabric with the grafting solution.

As noted in the last two rows of Table 1, the die-cutability of fabrics grafted with each of the five listed solutions was acceptable. Acceptable die-cutability means that the grafted fabric substrate underwent mechanical die-cutting without significant fabric distortion, yarn pull-out or fraying. Furthermore, the flame resistance of all treated fabrics satisfied current automotive industry standards.

The following examples are preferred grafting solutions for polyester and nylon substrate fabric respectively. Each example is described in terms of parts per weight.

The graft solution of Example 2 is especially adapted for polyester substrates. Fabrics comprised of polyester yarns and filaments contacted with this solution achieved pliability substantially equivalent to untreated substrate, flame resistance satisfying current automotive industry standards, as well as excellent die-cut characteristics. As noted above, the term "die-cut characteristics" or "die-cutability" refers to the ability of a fabric grafted in accordance with the methods of the present invention to undergo mechanical die-cutting without exhibiting substantial yarn pull-out, fraying or other fabric distortion.

The graft solution of Example 3 is especially adapted for nylon substrate. Fabric comprised of nylon yarns and filament contacted with this solution achieved excellent pliability, flame resistance as well as excellent die-cut characteristics.

Table 2 describes the various trade names utilized in the examples above and below.

Table 3 below lists 6 grafting solutions formulated (by percentage weight) in accordance with the present invention. Formulations F and G are useful on Polyester substrates. Formulations H, I, J, and K are useful on nylon substrates.

Table 5 illustrates the results of laboratory testing of a grafted polyester air bag fabric utilizing a grafting solution comprised of the formulation, listed in parts by weight in Table 4.

As discussed above, an antioxidant, antiozonant or other stabilizer is advantageously added to the grafting solution of the present invention in order to increase the heat and/or aging resistance of grafted fibers, yarns or fabrics comprised thereof. Table 6 below illustrates 4 grafting solutions of the present invention, (L, M, N, and O) incorporation Sanduvor VSU, Tinuvin 292, Irganox 1076 and Triphenyl Phosphate as antioxidants respectively.

While it is apparent that the invention herein disclosed is well calculated to fulfill the objects above stated, it will be appreciated that numerous modifications and embodiments may be devised by those skilled in the art, and it is intended that the appended claims cover all such modifications and embodiments as fall within the true spirit and scope of the present invention. For example, it is within the scope of this invention to apply the grafting solution to a seamless air bag formed from one continuous piece of fabric.