Patent Application
20140134355
This invention relates to air-impermeable fabrics, and more particularly, to fabrics used for emergency evacuation equipment for aircraft evacuation such as evacuation slides and life rafts, as well as other inflatable structures such as for cushions and other emergency and non-emergency applications.
The requirement for reliably evacuating airline passengers in the event of an emergency is well known. Emergencies at take-off and landing often demand swift removal of the passengers from the aircraft because of the potential for injuries from fire, explosion, or sinking in water. A conventional method of quickly evacuating a large number of passengers from an aircraft is to provide multiple emergency exits, each of which is equipped with an inflatable evacuation slide, which often doubles as a life raft in the event of a water evacuation. These evacuation slides are most commonly constructed of an air-impervious coated fabric material that is formed into a plurality of tubular members. When inflated, these tubular members form a self-supporting structure with a slide surface capable of supporting the passengers being evacuated. In addition to being air-impervious, the fabric material from which the tubular members are constructed must meet FAA specification requirements of TSO-C69c for resistance to radiant heat, flammability, contaminants, fungus and other requirements.
Although evacuation slides permit passengers to quickly and safely descend from the level of the aircraft exit door to the ground, the requirement that each aircraft exit door be equipped with an inflatable evacuation slide means that substantial payload capacity must be devoted to account for the weight of multiple evacuation slides. Accordingly, there has long existed the desire in the industry to make the inflatable evacuation slides as light as possible. A significant portion of the weight of an emergency evacuation slide is the weight of the slide fabric itself. Accordingly, various attempts have been made to reduce the weight of the slide fabric. One accepted method has been to reduce the physical size of the structural members of the slide by increasing the inflation pressure. Increased inflation pressure, however, causes greater stress on the slide fabric and, therefore, the benefit of the reduced physical size is at least partially cancelled out by the need to use a heavier gauge of slide fabric in order to withstand higher inflation pressures. Current state of the art slide fabric consists of a 72×72 yarns per inch nylon cloth made of ultra-high-tenacity nylon fibers. This 72×72 fabric by itself has a grab tensile strength of approximately 380 lbs in the warp direction and 320 lbs in the fill direction (as used herein grab tensile strength refers to the strength measured by grabbing a sample of fabric, typically 4 inches wide, between a set of one inch wide jaws and pulling to failure.) The fabric is typically coated with multiple layers of an elastomeric polymer to render it impermeable to air as well as a radiant-heat-resistant coating. This results in a strong, but heavy fabric, having a grab tensile strength of approximately 390 lbs. in the warp direction and in the fill direction, but with an areal weight that can exceed 7.0 oz/yd2. As can be determined from the foregoing, these coatings do not contribute significantly to the strength of the fabric.
Graphene nanoplatelets have been incorporated into air retention (AR) coatings for inflatable fabric structures at least in part to provide desired levels of impermeability to air at reduced weights compared to conventional AR coatings, see, e.g., published US patent application US 2012/0315407 A1. The shape of the graphene nanoplatelets and their low permeability to gas molecules are believed to enhance the air impermeability of AR coatings by creating a tortious path through the AR layer for gas molecules as they attempt to diffuse through the AR coating. However, it has now been discovered that crosslinked AR coatings containing graphene nanoplatelets can fail flammability performance requirements even when state-of-the-art flame retardant additive packages are included in the coating composition.
Although the above-described fabrics for inflatable structures have achieved widespread use in the aviation industry, the disparate requirements for strength, weight, and flame resistance, as well as other requirements, have resulted in a continuing need in the art for new fabrics.
As described in further detail below, the invention provides a new air-impermeable fabric. The air-impermeable fabric has a fabric substrate, which may also be referred to as a base fabric. Disposed over the fabric substrate is a barrier layer comprising a polymer binder and graphene nanoplatelets. The graphene nanoplatelets have been pre-treated by contacting with a liquid organophosphorus flame retardant before incorporating them into a coating composition.
In other aspects of the invention, a method of making an air-impermeable fabric is provided. According to the method, graphene nanoplatelets are first pre-treated by contacting with a liquid organophosphorus flame retardant to form treated graphene nanoplatelets. The treated graphene nanoplatelets are dispersed in a coating composition comprising a polymer resin. The coating composition is then coated over a fabric substrate, after which it can be dried or cured.
The subject matter which is regarded as the invention is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which:
As mentioned above, the invention is directed to an air-impermeable fabric. It should be noted that, as used herein, the term “impermeable” does not refer to absolute or permanent impermeability, but rather to a degree of permeability sufficiently low to meet the functional requirements needed for any particular inflatable application. The fabric substrate, or base fabric, can be formed from any type of fiber possessing desired physical properties and processability. Nylon fibers are often used, at least in part due to the strength and strength to weight ratio possessed by nylon fabrics. Various nylons, such as nylon-6, 6 or nylon-6, can be used, as well as other known nylon polymers. Other polymer fibers can also be used, such as polyester, other aromatic and/or aliphatic polyamides, liquid crystal polymers, etc. Natural fibers such as silk can also be used. Fiber diameters can be selected to achieve desired properties such as fiber spacings in woven fabric. Yarn counts can range from 30×30 yarns per inch to 90×90 yarns per inch, or higher, and more particularly from 40×40 yarns per inch to 75×75 yarns per inch. The yarn count geometry can also be asymmetric (i.e. 40×60 yarns per inch) if needed.
The fiber strength of the base cloth can also be increased by incorporating nanoreinforcements into the polymeric matrix of the fiber itself. The nanoreinforcements can be carbon nanotubes, carbon nanofibers, grapheme nanoplatelets, polymeric nanofibers, metallic nanotubes or nanofibers, metal oxide nanotubes, metal oxide nanofibers, metal oxide nanoparticles or metal oxide nanoplatelets or a combination thereof. The nanoreinforcements can be incorporated into the polymer matrix of the fiber during synthesis of the fiber matrix or processing of the matrix into fibers. For example, the nanoreinforcements can be combined with the neat polymer matrix prior to thermal processing into fibers. The nanoreinforcements can also be incorporated into the monomeric precursors used to synthesize the polymeric composition of the cloth fiber.
Graphene nanoplatelets are commercially available from sources such as XG Sciences, and can be prepared by mechanical and/or thermal exfoliation of graphite. Graphene nanoplatelets can be prepared in various sizes, and those used in the barrier layer described herein can have a thickness ranging from 2 nm to 50 nm, more particularly from 5 nm to 15 nm. The graphene nanoplatelets can have diameters ranging from 0.5 μm to 50 μm, more particularly from 5 μm to 25 μm (note that diameter on the hexagonal-shaped nanoplatelets is defined as the distance between opposite corners of the hexagon). The barrier layer can comprise various amounts of graphene nanoplatelets. In some exemplary embodiments, the barrier layer comprises 0.5 wt. % to 90 wt. % graphene nanoplatelets, based on the total weight of the barrier layer (i.e., the cured coating). In some exemplary embodiments, the barrier layer comprises 0.5 wt. % to 5 wt. %, more particularly 1 wt. % to 4 wt. %, and even more particularly 1 wt. % to 3 wt. %, of graphene nanoplatelets, the percentages based on the total weight of the barrier layer (i.e., the cured coating). In some exemplary embodiments, the barrier layer comprises 20 wt. % to 90 wt. %, more particularly 20 wt. % to 60 wt. %, more particularly 25 wt. % to 45 wt. %, and even more particularly 25 wt. % to 35 wt. % of graphene nanoplatelets, the percentages based on the total weight of the barrier layer (i.e., the cured coating).
As mentioned above, the graphene nanoplatelets are pre-treated by contacting with a liquid organophosphorus flame retardant. Organophosphorus flame retardants are commercially available, and include for example, organophosphates such as such as tris(2-propylphenyl)phosphate, triphenyl phosphate (TPP), resorcinol bis(diphenylphosphate) (RDP), bisphenol A diphenyl phosphate (BADP), and tricresyl phosphate (TCP); phosphonates such as dimethyl methylphosphonate (DMMP); and phosphinates such as aluminum diethyl phosphinate. Organic compounds can also be used that contain both phosphorus and a halogen. Such compounds include tris(2,3-dibromopropyl)phosphate (brominated tris) and chlorinated organophosphates such as tris(1,3-dichloro-2-propyl)phosphate (chlorinated tris or TDCPP) and tetrakis(2-chlorethyl)dichloroisopentyldiphosphate. The duration of pre-treatment contacting (i.e., contacting time) of the graphene nanoplatelets can vary, and in some embodiments is at least 10 minutes, more particularly at least 120 minutes, and even more particularly at least 24 hours accompanied by ultrasonic agitation. An upper duration limit is not specified, as it is limited only by process efficiency considerations. Although it is contemplated that pure liquid organophosphorus flame retardant (including substantially pure, within the limits of manufacturing and analytical capabilities) is used to pre-treat the graphene nanoplatelets, other materials can be present as well, including but not limited to other flame retardants, solvents, etc. In some embodiments, the pre-treatment liquid comprises at least 0.5 wt. % liquid organophosphorus flame retardant, more particularly at least 1.5 wt. % liquid organophosphorus flame retardant, and even more particularly at least 3.0 wt. % liquid organophosphorus flame retardant.
The resin used for the barrier layer as well as other layers on the fabric can be chosen from various polymers. Polyurethane polymers and polyurethane-containing copolymers are often used, at least in part due their elasticity and durability. Well-known polyurethane chemistry allows for various aromatic and/or aliphatic polyisocyanates and polyols to be reacted together to provide desired coating characteristics, and such coating resins are readily commercially available. Other polymers can be readily copolymerized with polyurethanes, often through inclusion of hydroxy-terminated prepolymers (e.g., OH-terminated polyester or OH-terminated polycarbonate) in the polyisocyanate/polyol reaction mix. In some embodiments, a polymer resin other than polyurethane is used, e.g., polyester. Resins can include functional groups, such as hydroxyl, carboxyl, amino, other resin functional groups known in the art. Blends of one or more of polymer resins such as those described above can also be included in a coating composition.
The coating composition can also contain one or more crosslinkers. Crosslinkers are selected to have reactivity with the functional groups on the polymer resin, and can include, for example, polyfunctional alcohols (e.g., trimethylolpropane) polyfunctional alcohol reactive compounds (e.g., melamine), polyfunctional isocyanates (e.g., trifunctional isocyanurate compounds formed by diisocyanates such as methylenediphenyl diisocyanate (MDI) or isophorone diisocyanate (IPDI)), polyfunctional acids (e.g., tricarballylic acid), polycarbodiimides or polyazidines. The amount of crosslinker can be adjusted by those skilled in the art to achieve desired properties. In addition to accelerating cure, added crosslinker tends to increase coating hardness and decrease elasticity. The coating composition may also contain one or more volatile liquids, including water and/or various polar or non-polar organic solvents. Such volatile liquids are vaporized before or during cure and do not form part of the cured or finished coating. Reactive diluents (i.e., organic compounds that function as a solvent during application of a polymer resin-containing coating composition, but have functional groups that react with the polymer during cure so that they form part of the cured coating.
The treated graphene nanoplatelets have been demonstrated to provide enhanced flame resistance in crosslinked AR coatings. The invention described herein is not bound by any particular theory or mechanism; however, it is believed that in some exemplary embodiments, flammable side products such as alcohols, aldehydes and/or ethers released during cure are trapped in the AR layer by the nanoplatelets (e.g., blocked from diffusing out and/or absorbed by the graphene nanoplatelets). In such embodiments, pre-treatment of the graphene nanoplatelets could interfere with combustion of such side products and/or interfere with absorption of such side products by the graphene nanoplatelets. Such side products can be formed by the crosslinking reaction between functional groups on the polymer resin and alkoxymethylol-substituted amino groups on the crosslinker such as found on melamine derivatives like hexamethoxymethylol melamine (HMMM), hexabutoxymethylol melamine, etc. Of course, such melamine derivatives need not be hexa-substituted with such groups to produce such side products. Accordingly, in some exemplary embodiments, the coating composition comprises an alkoxymethylol-substituted melamine derivative crosslinking agent. In further exemplary embodiments, the coating composition comprises a hydroxy-functional polymer resin such as a hydroxy-functional polyurethane as well as additional functionalities that may permit crosslinking via other crosslinker chemistries. Curing for such crosslinkable coating compositions can be effected at an elevated temperature to promote the crosslinking reaction. In some embodiments, curing takes place at temperatures of 120° C. to 160° C., and more particularly 140° C. to 160° C., for periods of from 1 to 15 minutes, more particularly from 2 to 10 minutes. Cure temperatures and times can also be reduced by adding a para-toluene sulfonic acid-based catalyst.
The coating compositions applied to form any of the coatings on the fabric described herein can include various additives ordinarily incorporated into coating compositions Such additives can be mixed at a suitable time during the mixing of the components for forming the composition, and include fillers, reinforcing agents, antioxidants, heat stabilizers, biocides, plasticizers, lubricants, antistatic agents, colorants, surface effect additives, radiation light stabilizers (including ultraviolet (UV) light stabilizers), stabilizers, and flame retardants. Such additives can be used in various amounts, generally from 0.01 to 5 wt. %, based on the total weight of the coating composition
In addition to the organophosphorus flame retardant used for pre-treatment, the barrier layer can include one or more other flame retardants, including but not limited to the same flame retardant used for pre-treatment. Exemplary flame retardants include phosphorous-containing compounds such as organophosphates (e.g., tris(2-butoxy)ethylphosphate (TBEP), tris(2-propylphenyl)phosphate, organophosphonates (e.g., dimethylphosphonate), organophosphinates (e.g., aluminum diethylphosphinate), inorganic polyphosphates (e.g., ammonium polyphosphate)), organohalogen compounds (e.g., decabromodiphenyl ethane, decabromodiphenyl ether, and various brominated polymers or monomers), compounds with both halogen and phosphorous-containing groups (e.g., tris(2,3-dibromopropyl)phosphate), as well as other known flame retardants. Brominated flame retardants are often used in combination with a synergist such as oxides of antimony (e.g., SbO3, Sb2O5) and other forms of antimony such as sodium antimonite. The amount of flame retardant can vary widely depending on the particular flame retardant or combination of flame retardants, with exemplary amounts ranging from 5 wt. % to 50 wt. %, more particularly from 10 wt. % to 25 wt. %.
Other coating layers can be present in addition the above-described barrier layer. In some embodiments, a heat-resistant (HR) layer is also present, often on the side of the fabric that will be the outside of the inflatable structure. HR layers can comprise a high temperature polymer resin binder and aluminum pigment. HR layers can contain at least 10 wt. % aluminum pigment. An exemplary formulation contains between 0.1 wt. % and 10 wt. % microspheres. A further exemplary formulation contains between 1 wt. % and 5 wt. % microspheres. In addition to radiant heat reflecting properties provided by the aluminum pigment, a heat-resistant layer can also include heat-absorbing additives such as ceramic microspheres. HR layers can contain at least 0.11 wt. % microspheres. An exemplary formulation contains between 0.11 wt. % and 6.2 wt. % microspheres. A further exemplary formulation contains between 1.1 wt. % and 2.1 wt. % microspheres. All weight percentages are based on the total weight of the layer. Tie coat layers can also be present. Tie coats are utilized to provide greater adhesion to the substrate than might be provided by the various functional layers. For example, a polyurethane-polycarbonate copolymer resin can be used in a tie coat applied directly to the fabric surface where its relatively low modulus of elasticity provides good conformation of the resin to the cloth morphology while the relatively higher modulus of elasticity of a polyurethane polymer resin used as binder for a barrier layer provides the necessary strength and flexibility to maintain overall coating integrity and air impermeability when subjected to deformation and stress during inflation.
Turning now to the figures,
Turning now to
With reference to
The spaced apart configuration of side rail tubes 24 and 26 is maintained by a head end transverse tube 46, a toe end transverse tube 48, a foot end transverse truss 52 and medial transverse truss 54. The bending strength of escape slide assembly 10 is enhanced by means of one or more tension straps 50 stretched from toe end 16 over foot end transverse truss 52, medial transverse truss 54 and attached proximal head end 12 of evacuation slide assembly 10. As described, evacuation slide assembly 10 provides a lightweight structure that consumes a minimum amount of inflation gas while providing the necessary structural rigidity to permit passengers to safely evacuate an aircraft under emergency conditions.
The entire inflatable evacuation slide assembly 10 can be fabricated from an air impervious material described more fully hereinafter. The various parts of the inflatable evacuation slide assembly 10 may be joined together with a suitable adhesive whereby the structure will form a unitary composite structure capable of maintaining its shape during operation. The entire structure of the inflatable evacuation slide assembly 10 can be formed such that all of the chambers comprising the structure are interconnected pneumatically, such that a single pressurized gas source, such as compressed carbon dioxide, nitrogen, argon, a pyrotechnic gas generator or combination thereof may be utilized for its deployment.
The invention is further illustrated by the following non-limiting examples.
Test samples were prepared by coating a 60×60 yarns per inch ultra-high-tenacity nylon fabric with a coating composition comprising a polycarbonate polyurethane resin (Stahl Permuthane SU21-591), a flame retardant additive package comprising decabromodiphenylethane (DBDPE) and an SbO3 synergist. A crosslinker (hexamethoxymethylol melamine (HMMM), Stahl XR91-110) was included in the coating composition on some of the samples, as indicated in Table 1. Graphene nanoplatelets (XG Sciences, Grades M5, M15 and M25, with mean particle diameters of approximately 5, 15 and 25 microns) were also included in the coating composition for some of the samples, with the GNP are either untreated or treated by mixing for a minimum of 60 minutes with a 1-20 wt. % solution of tri(2-propylphenyl)phosphate in toluene, dimethylformamide, 2-propanol or other solvent compatible with the polyurethane resin. Individual or a mixture of the solvents can be utilized as shown in Table 1. The samples were tested for flame resistance using a 12 second vertical flammability test according to ASTM D-6413 “Standard Test Method for Flame Resistance of Textiles, and for adhesion according to an adapted version of ASTM D4651. The results are shown in Table 1.
As shown in Table 1, the control sample D without graphene nanoplatelets passed both the flammability test and the adhesion test. However, when graphene nanoplatelets were introduced for payload weight and air retention purposes, the sample (B) failed the adhesion test unless crosslinker with 160° C. cure was added. However, the crosslinked sample A failed the flammability test. The graphene nanoplatelet-containing sample with the crosslinker and pre-treated graphene nanoplatelets passed both the flammability and adhesion tests. The beneficial results provided by treated graphene nanoplatelets are of course not limited to crosslinked coatings, and may provide flammability benefits in non-crosslinked coatings under different testing protocols than those used for this particular application.
Additional test samples were prepared by coating a 60×60 yarns per inch ultra-high-tenacity nylon fabric on one side with first and second air retentive layers (Layer1 and Layer2) as shown in Table 2, and on the other side with an aluminum pigment-containing radiant heat resistant coating. Individual layers were applied to yield a final areal weight about 0.20-0.60 oz./yd2 per layer. Samples F, G, and H differed in the grade, version, or source of organophosphate and/or Sb synergist. Samples J and K also differed in the grade, type, or source of organophosphate and/or Sb synergist. The air retentive coatings for samples F through L were formulated using two individual premixes, premix A containing the graphene nanoplatelets and the organophosphate/solvent blend and premix B incorporating all remaining components. After the premixes were mixed sufficiently, premix A incorporating the graphene nanoplatelets is added to premix B. For sample M, graphene nanoplatelets were pre-treated for 120 minutes in the specified solution of toluene solvent and phosphorus-based flame retardant, following which the mixture of GNP's with toluene and flame retardant (Premix A) were mixed with the other components of the coating composition (Premix B).
The samples were subjected to flammability testing according to an adapted version of ASTM 6413. The results are shown in Table 3.
As shown in Table 3, the addition of SbO3 synergist and the accompanying higher amounts of bromine-based flame retardant (samples J and K) provided a significant benefit in time to extinguish and burn length. However, these samples did not include a crosslinking agent, which is often needed in order to meet coating adhesion or other physical property requirements. Sample L included such a crosslinking agent, but exhibited significantly worse results in both time to extinguish and burn length. Sample M, which utilized GNPs pre-treated in phosphorous-base flame retardant provided significant benefits in both time to extinguish and burn length even when a crosslinking agent is present.
As used herein, the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise, and “or” means “and/or”. The modifier “about” used in connection with a quantity is inclusive of the stated value and has the meaning dictated by the context (e.g., includes the degree of error associated with measurement of the particular quantity). The terms “front”, “back”, “bottom”, and/or “top” are used herein, unless otherwise noted, merely for convenience of description, and are not limited to any one position or spatial orientation. The endpoints of all ranges directed to the same component or property are inclusive and independently combinable (e.g., ranges of “less than or equal to 25 wt %, or 5 wt % to 20 wt %,” is inclusive of the endpoints and all intermediate values of the ranges of “5 wt % to 25 wt %,” etc.). The suffix “(s)” is intended to include both the singular and the plural of the term that it modifies, thereby including at least one of that term (e.g., “the colorant(s)” includes a single colorant or two or more colorants, i.e., at least one colorant). “Optional” or “optionally” means that the subsequently described event or circumstance can or can not occur, and that the description includes instances where the event occurs and instances where it does not. Unless defined otherwise, technical and scientific terms used herein have the same meaning as is commonly understood by one of skill in the art to which this invention belongs.
While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.
This is a continuation-in-part of U.S. patent application Ser. No. 13/490,083, filed Jun. 6, 2012, the disclosure of which is incorporated herein by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 61494759 | Jun 2011 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 13490083 | Jun 2012 | US |
| Child | 14158574 | US |
