Patent Application
20130040098
Polymer based structures have been used in a number of applications. Polymers can have some favorable properties that make them ideal for radar applications like radomes. Radomes, for example, can be constructed from low dielectric materials that have high environmental performance capabilities. Often radomes are used in harsh climates such as on ships at seas, on airplanes traveling at high speeds, or on wind swept mountains. Radomes should sufficiently protect the radar equipment from the environment, while maintaining stable mechanical performance and radar transmission.
Embodiments of the invention include benzoxazine structures that can include a benzoxazine face skin and a low density core material. The core material, for example, can be a foam. The benzoxazine face skins, for example, can include a reinforcement material such as fibers, meshes, or particulates as well as a benzoxazine polymer. Such benzoxazine structures can be used in a number of applications such as, for example, radomes.
The following detailed description together with the accompanying drawings will provide a better understanding of the nature and advantages of the present invention.
Embodiments of the invention include benzoxazine structures that can include a benzoxazine face skin and a low density core material. The core material, for example, can be a foam or honeycomb. The benzoxazine face skins, for example, can include a reinforcement material such as fibers, meshes, or particulates as well as a benzoxazine polymer. Such benzoxazine structures can be used in a number of applications such as, for example, radomes.
As used throughout this disclosure the term “benzoxazine material” is any material that includes benzoxazine. The term “benzoxazine composite material” is a benzoxazine material with some type of reinforcement material. And the term “benzoxazine composite structure” is a structure that includes at least one layer of a benzoxazine composite material and a second layer of another material. Benzoxazine composite structures can include benzoxazine sandwich panels that include two outer layers sandwiching an inner core layer. One or both of the two outer layers can include a benzoxazine material layer, a non-benzoxazine material layer, and/or a benzoxazine composite material.
Some embodiments of the invention employ benzoxazine materials in a number of structural applications that will be described below. Benzoxazine is a bicyclic heterocycle consisting of a benzene ring fused with an oxazine. Benzoxazine materials, for example, can be formed from the reaction product of an amine, a phenol, and formaldehyde.
Benzoxazine materials can be combined or hybridized with any number of materials. A number of materials are listed herein as examples of materials that can be used to hybridize with benzoxazine. But any material can be used whether described herein or not. Benzoxazine can be hybridized with a material based on the specific application to improve the structural, electrical, thermal, mechanical, and/or environmental performance, etc.
Benzoxazine can be combined or hybridized with polymers, cynates (e.g., cynate ester), olifins (e.g., Cyclic Olefin Copolymer), epoxies, polypropylene, etc. Other materials can be used such as Vinyl esters, Bismaleimides, methacrylates, phenolics, POSS, liquid silanes, siloxanes, thermoplastics, thermosets, and/or reactive rubbers. Various fillers may also be used to hybridize, such as nanoclay, core shell rubbers, glass microballoons, ceramic particles or microballoons, phenolic or other polymeric particles or microballoons, fumed silica, wollastonite, and/or duralite.
Benzoxazine materials can exhibit a number of properties that can be useful for various applications such as, for example, flame retardance, high modulus, high glass transition temperature, low curing shrinkage, low water absorption (e.g., less than 10%, 8%, 5%, 3%, 2%, 1% water absorption by weight), low dielectric constant (e.g., at RF frequencies), low dissipation factors (e.g., below 0.05 at RF frequencies, erosion resistivity, shear strength, impact resistance, high temperature resistance, bending resistivity, compressive strength, and/or stable thermal mechanical properties.
Benzoxazine Composite Material
Benzoxazine composite materials are used in various embodiments of the invention. Benzoxazine composite materials generally include a benzoxazine with a reinforcement material such as a fiber, yarn, mesh, fabric, weave, etc. In some embodiments, carbon fibers or metallic fibers can be used. In some embodiments, a metallic mesh or surface etching in a particular orientation or grid pattern can provide frequency-selective surface (FSS) properties.
For purposes of this disclosure, the term “fiber” encompasses a structure that exhibits a length that exceeds the largest cross-sectional dimension (e.g., the diameter for round fibers). Thus, the term “fiber” differs from other structures such as plaques, containers, sheets, films and the like that can be extruded, blow-molded or injection molded. The term “fiber” does encompass, however, structures including monofilament fibers, multi-filament fibers, yarns, tape fibers, and the like.
The term “multi-filament yarn” is intended to encompass a structure that includes at least three filaments that have been individually formed such as via extrusion through a spinneret prior to being brought in proximity to one another to form a single yarn structure that can then be incorporated into a fabric.
High modulus fibers suitable for use in the present invention can generally have a modulus as measured according to ASTM D2256-02, which is incorporated herein by reference, greater than about 8 GPa (100 grams/denier). In one embodiment, the fibers can have a modulus greater than about 10 GPa, for example, greater than about 12 GPa, or greater than about 16 GPa. In addition, the fibers of the present invention can have a high tenacity, for example greater than about 400 MPa (5 grams/denier) in some embodiments as measured according to ASTM D2256-02. In one embodiment, the fibers can have a tenacity greater than about 500 MPa, or greater yet, greater than about 560 MPa (7 grams/denier). The fibers can also have a low density, for example, less than about 1.3 g/cm3, in one embodiment. In another embodiment, the fibers can have a lower density, for instance less than about 1.0 g/cm3
In some embodiments of the invention, benzoxazine composite structures can include reinforcement materials in the form of fibers, yarns, or meshes that can include glass materials, ceramics, polymers, or hybrids thereof. These multiple reinforcement materials can be woven or braided together.
Glass reinforcement materials can include E-glass, S-glass, S2-glass, NE-glass, and/or D-glass. Ceramic reinforcement materials can include Nextel products and/or Al2O3 fibers. Other reinforcement materials can include quartz, basalt, thermoplastic hybrids, thermoplastic/glass hybrids (e.g., 940 Innegra S), polypropylene (PP), high molecular weight polypropylene (HMPP), ultra high molecular weight polyethylene (UHMWPE), polyphenylene oxide (PPO), Cyclic Olefin Copolymer (COC), Polyether Imide (PEI), and Polyetheretherketone (PEEK). As another example, Aramid fibers such as Kevlar can also be used.
Any number of processes known in the art can be used to construct a benzoxazine composite material. For example, the pre-impregnation process or the resin transfer molding process may be used.
Benzoxazine Composite Structures
A simple benzoxazine composite structure can include benzoxazine and a reinforcement material. As shown in the cross section in
In some embodiments, a benzoxazine composite structure can include a benzoxazine layer (with or without reinforcement material) and one or more face sheets. A face sheet can be a thin active or passive layer. In
In some embodiments, a benzoxazine composite structure can include a benzoxazine layer (with or without reinforcement material) with a tunable layer. Some embodiments of the invention can be used in radar applications. In such applications an electrically conductive mesh can be embedded within a benzoxazine composite structure to provide frequency filtering (see
Core 104 can be a foam or honeycomb material; for example, a plastic foam or honeycomb material. Core 104 can be a low density thermoplastic such as, for example, polyvinyl chloride (PVC), polyetherimide (PEI), styrene butadiene styrene (SBS), acrylonitrile butadiene styrene (ABS), or chemical combinations thereof. The honeycomb construction can be a fiber reinforced resin shaped to have hexagonally arranged ridges throughout.
Benzoxazine composite structure can be used for any number of applications. In one application, the benzoxazine composite structure can be manufactured into large sheets (e.g., about 5 feet long and/or wide). These sheets can be constructed with any size or dimension. These sheets can then be used to construct various structures. Domes and other structures may also be constructed from a benzoxazine composite structure.
For example, the aperture size or grid line width of a metallic mesh layer can control the frequency response. Various types of frequency-selective filters can be used including meshes and/or semiconductors. The embodiments of the invention are not limited by use of a frequency-selective filter let alone use of a specific frequency-selective filter. A tunable frequency-selective filter can be used. Moreover, metamaterials can be used with the frequency-selective filter.
In some embodiments of the invention, a frequency-selective filter can include a semiconductor layer (e.g., GaN, GaP, GaAs, SiC, Si, MgF2, ZnS) or a polymer layer with a frequency-selective surface (e.g., a metallic layer) etched within the semiconductor layer. The frequency-selective surface can be etched, for example, using a chemical etching technique, ablated using a laser, or any other technique.
Radomes
In some embodiments of the invention, benzoxazine composite structures can form the structural elements of a radome. A radome is a structural, weatherproof enclosure that protects communication equipment such as a microwave antenna, a radar antenna, a GPS antenna, etc. The design constraints for a radome can vary depending on the application. And radomes can be used in various applications including ground-based, air-based, and marine-based applications. Moreover radomes can be used in mobile and stationary applications. A radome can be constructed of material that minimally attenuates the electromagnetic signal transmitted or received by the antenna. In other words, the radome is largely transparent to radar or radio waves. Radomes protect the antenna surfaces from the environment (e.g., wind, rain, ice, sand, and ultraviolet rays) and/or conceal antenna electronic equipment from public view. They also protect nearby personnel from being accidentally struck by quickly-rotating antennas.
Radomes can be used in terrestrial, space, flight, and/or oceanic application. Radomes can be constructed in several shapes, for example, spherical, polyhedron, geodesic, dome, planar, etc. depending upon the particular application. Various construction techniques can be used to build a radome from Benzoxazine composite structures.
For example, a radome can be formed during manufacturing of the benzoxazine composite structure in the shape of the radome.
For example, benzoxazine composite structures can be formed in flat or non-flat panels of various sizes and/or shapes. A radome can be constructed from a number of these panels. Large radomes in particular may be constructed from a number of smaller panels. For example, radome 400 shown in
Benzoxazine composite structures can also be used to construct missile radomes.
Composite structures are easy to design and build into any shape. Various processes can be used to lay the various layers that make up the composite structures described herein. For example, benzoxazine composite structures can be laid up using pre-preg, autoclave molding, co-curing, compression molding, hand lay-up, vacuum assisted resin transfer molding (VARTM), vacuum bag molding, molding, etc. Composite material layers can be laid up in any shape or size as needed. For example, radomes can have any shape such as geodesic, polyhedron, globe, etc.
Various other structures can be constructed from benzoxazine composite structures. For example, in ships all or parts of the hull, decks, quarters, top deck structures, etc. can be constructed from benzoxazine composite structures. Moreover, any structure that is commonly constructed from metal can be replaced with benzoxazine composite structures. In some embodiments, such structures can act as radomes while performing their structural functions. In aircraft, the nozzle, fuselage, wings, tails, fins, etc. can be constructed using benzoxazine composite structures. In some embodiments, such aircraft components can act as radomes while performing their structural functions.
Thus, although the invention has been described with respect to specific embodiments, it will be appreciated that the invention is intended to cover all modifications and equivalents within the scope of the following claims.
This is a non-provisional application that claims the benefit of commonly assigned U.S. Provisional Application No. 61/521,331, filed Aug. 8, 2011, entitled “Benzoxazine Structures,” the entirety of which is herein incorporated by reference for all purposes.
| Number | Date | Country | |
|---|---|---|---|
| 61521331 | Aug 2011 | US |
