Patent Application
20170022658
This disclosure relates to gas barrier fabrics, and more particularly to fabrics used for inflatable structures such as aircraft evacuation slides and life rafts, inflatable watercraft, cushions, displays, recreational structures, and other inflatable structures.
Inflatable structures are often made from fabric. Although fabrics offer benefits such as strength, flexibility, and ease of assembly using multiple pieces of fabric, the fabric must often be treated in order to provide necessary levels of permeability. Additionally, many applications impose additional requirements as well. For example, aircraft evacuation slides often must meet additional requirements imposed by regulations or customer requirements.
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 barrier 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 non-permeability, 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 system 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 elastomeric polymers 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.
Fillers have been proposed for use in barrier fabric layers to inhibit permeability with a low contribution to overall fabric weight. However, some fillers can agglomerate in the coating composition, leading to coating defects that can inhibit barrier performance and flame resistance. High solvent levels in the coating composition can help reduce agglomerations, but can also cause low coating composition viscosity making the composition difficult to coat onto the fabric substrate.
In some aspects of the disclosure, a gas barrier fabric (also referred to herein as simply as a barrier fabric) comprises a fabric substrate. A heat-resistant coating layer disposed over a first side of the fabric substrate. A first gas barrier layer (also referred to herein as simply as a barrier layer) comprising a polymer is disposed over a second side of the fabric substrate. A second gas barrier layer is disposed over the first air barrier coating layer of the fabric substrate. The second barrier layer has a thickness of 5 nm to 1000 nm and comprises aligned nanoplatelets.
In some aspects of the disclosure, an inflatable structure comprises an enclosure formed from the barrier fabric and a source of inflating gas inside the enclosure or a closeable opening for introducing inflating gas from outside the enclosure.
In some aspects of the disclosure, an aircraft slide comprises tubular members formed from the barrier fabric and a slide surface, which form a self-supporting structure when inflated.
The subject matter which is regarded as the present disclosure 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 present disclosure are apparent from the following detailed description taken in conjunction with the accompanying drawings in which:
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. Carbon fiber is also a viable option but is cost prohibitive in most applications. Fiber diameters can be selected to achieve desired properties such as fiber strength, elongation and environmental resistance and other attributes. Yarns are the assembly of individual fibers and can be assembled in a fashion as to align fibers parallel to each other, twist them or spin them together to form yarns of various strength, elongation, lay length, size, and denier (a characteristic of yarn as measured in grams per 9000 meters of yarn length). Fabrics can then be further defined in terms of fiber spacing, pics per inch, yarns per inch, or total fabric weight per yard or other similar dimension. 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. Areal weight of the fabric substrate can range from 0.1 to greater than 10 oz/yd2, more specifically 1 to 10 oz/yd2, and even more specifically 2 to 8 oz/yd2.
The fiber strength of the base cloth can be increased by incorporating nanoreinforcements into the polymeric matrix of the fiber itself. The nanoreinforcements can be carbon nanotubes, carbon nanofibers, graphene nanoplatelets, graphene oxide nanoplatelets, polymeric nanofibers, metallic nanotubes or nanofibers, metal oxide nanotubes, metal oxide nanofibers, metal oxide nanoparticles, metal oxide nanoplatelets, inorganic fibers such as glass, silicon carbide, aluminum nitride, inorganic nano platelets such as montmorillonite other clay or boron nitride or a combination thereof, or combinations 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 by spinning or other fiber-forming processes. The nanoreinforcements can also be incorporated into the monomeric precursors used to synthesize the polymeric composition of the cloth fiber.
The heat-resistant (HR) coating layer is typically 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 (e.g., aluminum flakes). HR layers can contain at least 5 wt. % aluminum pigment, more specifically from 10 wt. % to 50 wt. %. 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 or heat-insulating additives such as ceramic hollow microspheres. An example formulation contains between 0.1 wt. % and 10 wt. % microspheres. A further exemplary formulation contains between 1 wt. % and 5 wt. % microspheres. All weight percentages are based on the total weight of the layer. The thickness of the HR layer can vary, for example between 0.5 μm to 50 μm, more specifically from 5 μm to 20 μm. 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.
As mentioned above, the barrier fabric also has a first gas barrier layer comprising a polymer. This layer can have a thickness ranging from 1 μm to 100 μm, more specifically from 5 μm to 50 μm. In some aspects, the first barrier layer is free of nanoplatelets, or if it includes nanoplatelets, they are not in a state of alignment as described below. The polymer used for the heat-resistant layer, and also for other polymer-containing layers on the barrier 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 or polyether) in the polyisocyanate/polyol reaction mix. In some embodiments, a polymer other than polyurethane is used, e.g., polyester. Blends of one or more of polymer resins such as those described above can also be included in a coating composition.
The coating compositions used to form the layer(s) on the barrier fabric can also contain one or more crosslinkers. For example, urethane and polyester resins can include polyfunctional alcohols (e.g., trimethylolpropane) or poly-functional alcohol reactive compounds (e.g., melamine derivatives such as hexamethoxymethylol melamine or melamine resin) or polycarbodiimides as crosslinking agents. Polyurethane resins can also include polyfunctional isocyanates (e.g., trifunctional isocyanurate compounds formed by diisocyanates such as methylenediphenyl diisocyanate (MDI) or isophorone diisocyanate (IPDI)) as crosslinkers. Polyesters can also include polyfunctional acids (e.g., tricarballylic acid) as crosslinkers. 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 coating compositions applied to form the 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 35 wt. %, based on the total weight of the coating composition.
As mentioned above, the barrier fabric also includes a second barrier layer having a thickness of 5 nm to 1000 nm comprising aligned nanoplatelets. Nanoplatelets can be prepared in various sizes, and those used in the barrier layer described herein can have a thickness ranging from a minimum of 0.3 nm, more specifically 1 nm, and even more specifically 5 nm, up to a maximum of 100 nm, more specifically 50 nm, and even more specifically 15 nm. These maximum and minimum range limits can be combined to create ranges from any of the minimum values to any of the maximum values (e.g., 0.3-100 nm, 5-15 nm, 1-50 nm, 1-15 nm, etc.). The nanoplatelets can have diameters ranging from 0.1 μm to 50 μm, more particularly from 5 μm to 25 μm. As used herein, the term “diameter”, with respect to nanoplatelets, means an average diameter that is calculated as the diameter of a circle having an area the same as that of a flat (i.e., not including surface area in pores) surface occupying the same profile in the x-y direction as one of the faces of the nanoplatelet. The nanoplatelets can have an aspect ratio (ratio of diameter to thickness) ranging from 5:1 to 10,000:1, more specifically from 20:1 to 1000:1. In some example embodiments, the barrier layer comprises at least 30 wt. % nanoplatelets, based on the total weight of the barrier layer (i.e., the cured coating), more specifically at least 40 wt. % nanoplatelets, more specifically at least 60 wt. % nanoplatelets, more specifically at least 85 wt. % nanoplatelets. In some example embodiments, barrier layer has an upper limit on nanoplatelet content of 99.5 wt. % nanoplatelets, more specifically 90 wt. % nanoplatelets, and even more specifically 85 wt. % nanoplatelets. These maximum and minimum range limits can be combined to create ranges from any of the minimum values to any of the maximum values (e.g., 0.3-100 nm, 5-15 nm, 1-50 nm, 1-15 nm, etc.), excluding of course impossible range values where a minimum value would be higher than a maximum value.
The nanoplatelets can comprise various materials, including but not limited to clays, graphene, or graphene oxide. Examples of nanoplatelet materials include, but are not limited to graphene, phyllosilicate clays such as Montmorillonite clay, Kaolinite clay, boron nitride, mica. Nanoplatelets can be prepared from bulk materials such as graphite, bulk clays, boron nitride, mica by exfoliating the bulk material. Exfoliation can be carried out by various techniques such as ultrasonic treatment, chemical treatments to swell the bulk material to increase separation between adjacent molecular layers, and treatment with oxidants, or ion intercalation/exchange. Surface treatments, heat, or high shear mixing or mechanical work can be applied to promote exfoliation of patelet layers. Specific solvents can also be employed to reach desired exfoliation level.
The various coatings described herein can be applied using any known coating technique, including but not limited to roll coating, spray coating, dip coating, or brush coating. The nanoplatelet-containing layer can be formed at thicknesses of 5 nm to 1000 nm, more specifically from 10 nm to 800 nm by similar techniques mentioned above including but not limited to roll coating, spray coating, dip coating, or brush coating, optionally followed by processing with an air blade or physical blade to achieve the desired thickness. Coating solutions can be comprised of neat, curable polymer resin, solvent based or aqueous based coating systems. The concentrations of the coating solutions will vary depending on the required viscosity of the solution, how thick the coating is to be applied, and how many nanoplatelet layers are to be applied in one coating pass. Typically concentrations of binder and filler are very low in solvent and aqueous coating systems to allow for better alignment of filler.
As mentioned above, the nanoplatelets are aligned. As used herein, “alignment” of the nanoplatelets means that the x-y dimension of nanoplatelets is aligned parallel to the plane of the layer surface. Complete alignment of the nanoplatelets is not required, only that more of the nanoplatelets are more closely aligned in a direction parallel to the layer compared to a random alignment of the nanoplatelets. Alignment can be characterized by φp,p, with a value of 0 representing random alignment of the particles, a value of 1 representing complete alignment of the particles in the direction of layer, and a value of −½ representing complete alignment of the particles perpendicular to the direction of the layer. In exemplary embodiments, φp,p is in a range having a lower level greater than 0, more specifically 0.1, and even more specifically 0.4. The upper end of the range, for which φp,p is less than or equal to, can be 0.9, more specifically 0.8, and more specifically 0.7. Alignment of the nanoplatelets can be achieved by using known layer-by-layer self-assembly techniques where the nanoplatelets are derivatized with charged groups such as carboxyl groups that will be attracted to an oppositely-charged groups on a substrate such as a amine groups on the first barrier layer over which the nanoplatelets dispersed in a solvent are applied. In other embodiments, the nanoplatelets can be incorporated into a curable polymer coating composition, with alignment of the nanoplatelets achieved by applying physical force prior to fully curing the polymer. Examples of physical force include centrifugal force, gravity, and/or shearing force (e.g., by maintaining the coated substrate in a vertical position for a period of time) prior to curing. Derivatization techniques described above used for layer-by-layer self-assembly can also be used provide alignment in polymer coating compositions.
Turning now to the Figures,
With reference to
The entire inflatable evacuation slide assembly 10 can be fabricated from the barrier fabric described herein. 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. Of course, the depiction in
While the present disclosure has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the present disclosure is not limited to such disclosed embodiments. Rather, the present disclosure 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 present disclosure. Additionally, while various embodiments of the present disclosure have been described, it is to be understood that aspects of the present disclosure may include only some of the described embodiments. Accordingly, the present disclosure is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.
