Patent Publication Number: US-7210390-B1

Title: Buoyancy device for personnel protective plates

Description:
BACKGROUND 
   1. Field of the Invention 
   The present invention relates generally to personnel protective vests and ballistic plates associated therewith. More specifically, the present invention relates to providing personnel protective plates having enhanced buoyancy characteristics. 
   2. Background of the Invention 
   Pilots and other personnel on aircraft and other vessels and elsewhere often wear vests containing bullet resistant inserts for protection against dangers such as small arms threats and explosive fragments, etc. These inserts are often made of ceramic or hard-faced metals in combination with fiber-reinforced plastics, among other materials. 
   While reinforced plastics often have a density near that of water (approximately 1 g/cc) and are therefore virtually neutral with regard to buoyancy, the ceramics often have a density ranging from approximately 2.5 to approximately 4.0 g/cc. Metal plates are often even denser and fall into a density range of approximately 4.5 to approximately 8.5 g/cc. The previously mentioned densities are intended only to provide exemplary density ranges of some common materials. One of skill in the art will recognize that many different materials may be used in the construction of such ballistic plates and that such densities may fall outside of the stated ranges, and that the present invention relates to any material used that has a density near to or greater than that of water. 
   In cases where the personnel are forced to exit the aircraft or vessel or otherwise enter water, the plates may become a liability resulting from, for example, the negative buoyancy associated therewith. The plates under this set of circumstances could become an additional force pulling the personnel beneath the water. Due to such a liability, personnel may choose not to wear the insert during combat near water. Alternatively, personnel may choose to discard the insert or even the entire vest upon entering the water. In either situation, the personnel may be faced with choosing between ballistic protection by keeping the plate and increased buoyancy by discarding the plate. Neither of these situations is optimal. 
   BRIEF SUMMARY OF THE INVENTION 
   According to one aspect, the invention includes a personal ballistic protective device having a first layer comprised of ballistic material and a second layer comprised of buoyant material. The second layer preferably has a density sufficient to counteract a density of at least the first layer of ballistic material such that the first layer and the second layer have a combined density substantially equal to or less than the density of water. 
   According to another aspect, the invention includes a personal ballistic protective device having a first layer comprising ballistic material having a first density and a second layer comprising buoyant material having a second density. The first density preferably is sufficient to counteract at least the second density such that the first layer and the second layer have a combined density substantially equal to or less than the density of water. 
   According to yet another aspect, the invention includes a method of counteracting negative buoyancy of a personal ballistic protective device. The method includes obtaining a ballistic first layer having a first density and obtaining a positive buoyancy second layer having a second density. The method further includes combining at least the first layer with the second layer to create a personal ballistic protective device such that the second density counteracts at least the first density. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a cross-sectional view of a prior art vest having a ballistic plate and a fiber-based composite backing; 
       FIG. 2  is a cross-sectional view of a ballistic vest according to a first exemplary embodiment of the present invention; and 
       FIG. 3  is a cross-sectional view of a ballistic vest according to a second exemplary embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   As seen in  FIG. 1 , a cross-section of a typical ballistic armor insert  100  includes an outer cover  102 , a ballistic plate  104 , a backing layer  106  and two high strength cloth layers  108   a  and  108   b . As described above, ballistic plate  104  is often made of a material, such as a ceramic or metal, that has a high density, therefore causing insert  100  to have a density greater than that of water. As used herein, density of water typically refers to the standard value of 1 g/cc, but one of skill in the art will understand that the invention may be applied to specific situations where the density of water is not 1 g/cc. For example, salt water is denser than pure water and as such, the present invention may be modified for strictly saltwater applications so that the buoyancy of the personnel protective may be lower, but still more buoyant than or equally as buoyant as saltwater. By having such a density, the above-referenced and other problems may be encountered by users of insert  100 . 
     FIG. 2  is a cross-section of an exemplary ballistic armor insert  200 . As with armor insert  100 , insert  200  includes an outer cover  202 , a ballistic plate  204 , a backing layer  206  and two high strength cloth layers  208   a  and  208   b  (although it may be desirable to have no cloth layer, only one cloth layer, or more than two cloth layers as well), but also includes a buoyancy layer  210 . Outer cover  202  may be made of, for example, nylon, that substantially encloses inner portions  204 – 210 . Ballistic plate  204  may be made of, for example, ceramic material, hard-faced metals, fiber-reinforced plastics (e.g. KEVLAR™), or any combination thereof. Adjacent to high strength layer  208   b , is a backing layer  206  that may be, for example, a fiber-based composite backing that is added to further strengthen insert  200 . Adjacent to backing layer  206 , buoyancy layer  210  is included to cause the overall density of insert  200  to be substantially equal to or less than the density of water. In this manner, insert  200  may avoid many of the drawbacks associated with prior art inserts that have higher densities. 
   Buoyancy layer  210  may be comprised of a layer of closed-cell material with a high degree of inherent buoyancy, and may be preferably comprised of a lightweight foam-like structure made from materials such as, for example, polyethylene, polyurethane, polyesters, polyvinyls, other polymeric materials, natural or synthetic rubber, or other organic polymers. Buoyancy layer  210  may also be comprised of a fabricated “bubble-wrap” type structure, or similar enclosed air cellular component, Styrofoam layers, or combinations of any of the above-described materials with closed cell foams. 
   As mentioned above, the purpose of layer  210  is to offset the negative buoyancy of the rest of insert  200 . Whatever the material used for layer  210 , it will need to substantially offset at least the density of the ceramic or hard-faced metal that comprises a typical protective plate insert. The thickness of a required foam layer associated with an insert having a ceramic plate may be substantially estimated by the formula:
 
Thickness of Foam=Thickness of Ceramic Plate×((ρCeramic/ρWater)−1)
 
   where ρ=density in g/cc. 
   The weight of the buoyancy layer can range from very light weight (˜0.1 psf) up to approximately 0.5 to approximately 0.8 psf (or any other weight that suitably counteracts the density of the ballistic plate or the rest of the insert). The layer or layers of buoyant material may also provide an additional benefit of providing a blunting of the ballistic impact via shock wave dispersion of the foam cells. Such dispersion could mitigate trauma often associated with non-penetrating projectile impacts (blunt force trauma). 
   Unlike prior art devices, buoyancy layer  210  actually alters the buoyancy characteristics of armor insert  200  itself rather than including, for example, the addition of inflation devices or other buoyant components to the vest to make the entire vest assembly more buoyant. The degree of buoyancy may be controlled by thickness or size of the passive buoyant layer. Another advantage of the present invention is that it does not require any significant alteration of the overall vest assembly, thus allowing current vests to be used with the improved insert  200 . Additionally, unlike prior art solutions, insert  200  does not require any active components, such as gas canisters, to provide buoyancy for the insert. Because insert  200  has an approximately positive buoyancy, the plate need not be removed from the vest assembly upon entry into the water as with prior art inserts. Also, personnel may maintain substantially the same, if not better, degree of ballistic protection as afforded by prior art plate/vest assemblies. 
   Another alternative, exemplary embodiment of an armor insert  300  cross-section according to the present invention is depicted in  FIG. 3 . Insert  300  includes outer cover  302  enclosing layers similar to that of insert  200 , except that the placement of the components is slightly altered. As with insert  200 , insert  300  includes a ballistic layer  304 , a backing layer  306  and two cloth layers  308   a  and  308   b . Insert  300  also includes a buoyancy layer  310 , but instead of being adjacent to the backing layer  308 , as is done with insert  200 , layer  310  is on the opposite side of insert  300  adjacent cloth layer  308   a . One of skill in the art will understand that the various layers, including the buoyancy layer, may be in any configuration that provides suitable ballistic protection along with the desired buoyancy characteristics described herein. 
   An armor insert as described herein may be made by several methods, some exemplary ones of which are described below. For example, a layer (or layers) of buoyant material may be attached to the front (or back, or both) surface(s) of a manufactured insert. This assembly may be achieved, for example, by use of a film contact adhesive applied between the insert and the buoyant layer. Liquid adhesives, as well as any other suitable securing mechanism device or method, may also be used to bond the two components. 
   According to another exemplary method, the buoyancy layer may be included as a part of the interior insert assembly, as depicted in  FIGS. 2 and 3 . In other words, the buoyancy layer would be internal to the final fabricated insert assembly, and would be interior to the final outer containment (e.g., a ballistic nylon cover). In yet another method, a cavity in may be built into insert. Foam may then be injected into the cavity either before or during assembly. For example, with reference to  FIG. 2 , ballistic layer  204  may include a depression/cavity that can be filled with a buoyancy-providing foam or other similar material. Such a cavity or depression would preferably not significantly decrease the ballistic qualities of the insert. 
   In yet another method of construction, a separate, unattached foam layer may be inserted into the vest assembly either behind or in front of the insert to provide increased buoyancy to counteract any negative buoyancy of the insert. Additionally a cloth pocket may be provided on the insert to allow such a foam layer to be added to the insert. Such pocket may be included on either the front or the back of the insert. 
   An insert as described herein, preferably provides buoyancy to all levels of protective inserts, such as NIJ levels III and IV, as well as other plates designed against specific threats outside of the standard NIJ or other United States government designations. 
   The foregoing disclosure of the preferred embodiments of the present invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Many variations and modifications of the embodiments described herein will be apparent to one of ordinary skill in the art in light of the above disclosure. The scope of the invention is to be defined only by the claims appended hereto, and by their equivalents. 
   Further, in describing representative embodiments of the present invention, the specification may have presented the method and/or process of the present invention as a particular sequence of steps. However, to the extent that the method or process does not rely on the particular order of steps set forth herein, the method or process should not be limited to the particular sequence of steps described. As one of ordinary skill in the art would appreciate, other sequences of steps may be possible. Therefore, the particular order of the steps set forth in the specification should not be construed as limitations on the claims. In addition, the claims directed to the method and/or process of the present invention should not be limited to the performance of their steps in the order written, and one skilled in the art can readily appreciate that the sequences may be varied and still remain within the spirit and scope of the present invention.