WO2008054843A2

WO2008054843A2 - Improved ceramic ballistic panel construction

Info

Publication number: WO2008054843A2
Application number: PCT/US2007/064586
Authority: WO
Inventors: Ashok Bhatnagar; Lori L. Wagner; Harold Lindley Murray, Jr.
Original assignee: Honeywell International Inc.
Priority date: 2006-03-24
Filing date: 2007-03-22
Publication date: 2008-05-08
Also published as: WO2008054843A3; CN101454633A; MX2008012131A; JP2009543010A; EP1999428A2

Abstract

A ballistic resistant panel which is formed from a plurality of relatively thin ceramic layers and at least one fibrous backing layer of high tenacity fibers. The two relatively thin ceramic layers are adjacent each other, but may be separated by an additional fibrous backing layer of high tenacity fibers. The ceramic faced panel provides a desired protection level against ballistic projectiles. Different threat levels can be protected against by choosing the number of ceramic layers to be used in the panel. The relatively thin ceramic layers are simpler to manufacture than thick ceramic panels of the same overall thickness as the combined thickness of the multiple ceramic faced layers. The panels of this invention having a multiple number of ceramic layers provides substantially the same or better ballistic resistance than does a monolithic panel of substantially the same thickness and composition. Protection against various threat levels can be provided by using a desired number of performs of the relatively thin ceramic layer and the fibrous backing. This permits greater manufacturing flexibility and can reduce the inventory of panel constructions that need to be stored in order to provide protection against different threat levels.

Description

IMPROVED CERAMIC BALLISTIC PANEL CONSTRUCTION

BACKGROUND OF THE INVENTION

Field of the Invention

This invention relates to ballistic armor which includes a ceramic plate

Description of the Related Art

Various types of ballistic armor constructions have been proposed and utilized in different applications. These include armos for land vehicles, aircraft, body armor, stationary objects, and the like. In one type of known ballistic armor construction that Ls useful, for example, in land vehicles and aircraft, a ceramic plate is adhered to a layer of high tenacity fibers. The ceramic plate is designed to face outwardly in the construction, acting as the primary Saver that provides initial protection against ballistic projectiles. These structures are referred to as ceramic faced panels. These panels in general are effective in absorbing and dissipating kinetic energy from projectiles and projectile fragments.

These types of panels are designed with a particular threat level in mind. As the threat level increases, the thickness of the ceramic plate needs to increase. However, it is difficult to manufacture ballistic resistant ceramic plates that are relatively thick, which adds to the cost and complexity of the manufacturing process.

In addition, the threat levels against which a ceramic panel may be used may not be known at the time of installation, To meet a specific threat level, the manufacturer or installer of the ballistic armor plates must keep an inventory of a variety of ceramic panels that have different thicknesses, so that a particular ceramic panel is available for installation against the specific type of threat that is perceived. It would be desirable to provide an improved ceramic faced ballistic resistant panel which met the necessary ballistic requirements but which also addressed the foregoing needs.

SUMMARY OF THE INVENTION

In accordance with this i nvention, there is provided a ballistic resistant panel, the panel comprising: a first relatively thin ceram ic layer having an outer fac ing surface and an inner facing surface: a first fibrous layer comprising a network of high tenacity fibers and having an outer facing surface and an inner facing surface, the outer facing surface of the first fibrou s layer being adjacent to the inner facing surface of the ceramic lay er: and a second relatively thin ceramic layer and having an outer facing surface and an inner fac ing surface; the outer facing surface of the second ceram ic layer being adjacent to the inner facing surface of the first fibrous layer.

Preferably the panel has a bal listic resistance which is substantially equivalent to or higher than the ballistic res istance of a comparable ceramic panel construction that has only a single ceramic layer backed with a fibrous layer, which panel has an ov eral l thickness of substantial ly the same thickness as the combined th ickness of the first ceram ic layer, the first fibrous layer, the second ceramic lay er and the second fibrous layer.

There may also be provided a second fibrous layer comprising a netw ork of high tenacity fibers and having an outer facing surface and inner facing surface, the outer facing surface of the second fibrous layer bei ng adjacent to the inner facing surface of the second ceramic lay er, and the inner facing surface of the second fibrous lay er being adjacent to the outer facing surface o f the first ceramic layer.

Also in accordance with this invention, there is provided a ballistic resistant panel, the panel comprising: a first relatively thin ceramic layer having an outer facing surface and an inner facing surface: a first fibrous layer comprising a network of high tenacity fibers and having an outer facing surface and an inner facing surface, the outer facing surface of the first fibrous layer being adjacent to the inner facing surface of the ceramic layer: a second relatively thin ceramic layer and having an outer lacing surface and an inner facing surface; the outer facing surface of the second ceramic laser being adjacent to the inner facing surface of the first fibrous layer: and a second fibrous layer comprising a network of high tenacity fibers and having an outer facing surface and inner facing surface, the second fibrous layer being interposed between the first ceramic layer and the second ceramic layer, the outer facing surface of the second fibrous layer being adjacent to the inner facing surface of the second ceramic layer.

Further in accordance with this invention, there is provided in a ceramic faced ballistic resistant panel designed to protect against a certain threat level of ballistic projectiles, the improvement comprising forming the panel from a structure which comprises: a first relatively thin ceramic layer having an outer facing surface and an inner facing surface: a first fibrous layer comprising a network of high tenacity fibers and having an outer facing surface and an inner facing surface, the outer facing surface of the first fibrous layer being adjacent to the inner facing surface of the ceramic layer: and a second relatively thin ceramic layer and hav ing an outer facing surface and an. inner facing surface, the inner facing surface of the second ceramic layei being adjacent to the outer facing surface of the first ceramic layer.

The present invention provides a ballistic resistant panel that has a plurality of ceramic layers and at least one (and preferably two) fibrous backing layer in order to provide a ceramic faced panel of a desired protection level. For example, higher piotection levels are generally required to protect against armor piecing bullets rather than rifle bullets. By forming the panel from a plurality of relatively thin ceramic layers each of which are preferably backed with a fibrous backing, different threat levels can be protected against by choosing the number of layers of ceramic materials to be used in the panel. The relatively thin ceramic layers are simpler to manufacture than thick ceramic panels of the same overall thickness as the combined thickness of the multiple ceramic faced layers. Surprisingly, the panels of this invention having a multiple number of ceramic lasers provides substantially the same or better ballistic resistance than does a monolithic panel of substantially the same thickness and composition.

In addition, by manufacturing a relatively thin ceramic plate with a fibrous backing, the manufacturer or installer of the ballistic: protection needs onlj to have one type of ceramic panel, or one type of ceramic faced panel in slock. Protection against various ballistic threats can be provided by using a desired number of the reiativel} thin ceramic plates or ceramic faced plates. These multiple plates can be manufactured and assemble in a relatively simple process that can be used in the field, if desired. This permits greater manufacturing flexibility and can reduce the overall cost of the structure.

DETAILED DESCRIPTION OF THE INVENTION

As mentioned above, the ballistic panels of this invention are formed from a pluralit} of relatively thin ceramic layers and at least one. and preferably a pltirality of. fibrous layer of high tenacity fibers. The ceramic material may be in the form of a monolithic structure or in the form of individual smaller ceramic tiles that are connected together in a suitable fashion (e.g.. adhered on a support layer or on the fibrous layer(s)). Such ceramic layers which are useful in ballistic applications are known in the art.

Typical ceramic materials useful in the panels of this invention include metal and non-metal nitrides, borides. carbides, oxides and the like, and mixtures thereof. Specific materials include silicon carbide, silicon oxide, silicon nitride, boron carbide, boron nitride, titanium diboride. aluminum oxide. magnesium oxide, and the like, as well as mixtures thereof. Preferred ceramic materials include aluminum oxide, silicon carbide, boron carbide, and mixtures thereof.

The ceramic layers of this invention are relatively thin. By "relatively thin" as used herein is meant that the ceramic layers generally have a thickness of up to about 0.6 inch ( 15.2 mm), more preferably up to about 0.5 inch ( 12.7 mm) and most preferably up to about 0.4 inch (10.2 mm). The thickness of the ceramic layer mas range, for example, from about 0.05 to about 0.6 inch ( 1.3 to 15.2 mm), more preferably from about 0.1 to about 0.5 inch (2.5 to 12.5 mm) and most preferably from about 0.1 to about 0.4 inch (2.5 to 10.2 mm).

The ceramic layer may be unreinforced or reinforced such as with a fibrous material, and are available from a number of sources. For example, the ceramic layer may be bonded to or wrapped with glass fibers, graphite libers, or the like.

The ceramic layer may be of any areal density, such as from about 0.5 to about 15 psf (2.44 to 73.24 ksm). more preferably from about 1 to about !0 psf (4.88 to 48.83 ksm) and most preferably from about 2 to about 5 psf (9.77 to 24.41 ksm).

For example, a ceramic layer of aluminum oxide having a thickness of about 0, 1 10 inch (2.8 mm) typically may an area! density of about 2.30 psf ( I 1.23 ksm).

The various layers of this invention are generally of rectangular or square configuration, although other shapes may be employed, such as curved layers. The ceramic layer has an outer surface and an inner surface.

This invention provides a first relatively thin ceramic layer. The first ceramic iayer is backed with a first fibrous layer which is preferably adhered thereto. At least one other relatively thin ceramic layer is included in the ceramic panel construction. The second relatively thin ceramic layer is an outwardly facing layer (as are an} additional ceramic layers). The second relatively thin ceramic layer, and any subsequent ceramic layers, preferably has the same construction as the first ceramic layer. The second ceramic layer mas be adjacent to and preferably is adhered to the outer facing surface of the first ceramic layer. In one embodiment, the second ceramic layer is adhered directly to the first ceramic layer. In another preferred embodiment, the second ceramic layer is also is backed with a fibrous layer (the second fibrous layer), which is preferably the same as the fibrous layer that is in the first fibrous layer. However, alternatively the fibers in the second fibrous layer may be different from those in the first fibrous layer. When a second fibrous layer is employed, it is interposed between the first and second relatively thin ceramic layers. with the outer facing surface of the second fibrous layer being adjacent to the inner facing layer of the second ceramic layer, and the inner facing surface of the second fibrous layer being adjacent to the outer facing surface of the first ceramic layer. Preferably, all of the layers in the panel are adhered together.

If desired, additional ceramic layers and/or additional fibrous layers may be utilized in the panels of this invention These additional layers may be adjacent to the second ceramic layer (and therefore extend outwardly in the construction) or may be adjacent to the first fibrous layer {and therefore extend on the inward side of the structure). Preferably, these additional layers are combined layers of a relatively thin ceramic layer and another fibrous layer. For example, a third relatively thin ceramic layer may be used, which has an outer surface and an inner surface. The inner surface of the third ceramic layer is preferably adjacent to. and preferably adhered to. the outer surface of the second ceramic layer. A third fibrous layer may also be employed, which likewise has an outer surface and an inner surface. The outer surface of the third ceramic layer is adjacent to. and preferably adhered to. the inner surface of the third ceramic layer and to the outer surface of the second ceramic panel. The additional ceramic layers (e.g.. the third layer, a fourth layer, etc.) are preferably of the same type as that of the first and second ceramic layers (although they may be different if desired). The additional fibrous layers (e.g.. the third fibrous layer, a fourth fibrous layer, etc.) are preferably the same as the first and second fibrous layers (although they may be different if desired).

In one preferred embodiment, the first cciamic layer and the first fibrous layer are preformed into a single unit. Likewise, the second ceramic layer and the second fibrous layer are preferably preformed into a single unit. This is also preferably extended to any third or fourth or more layers of ceramic and fibrous backing. The preformed layers are preferably adhered to one another by a suitable adhesive means. In another preferred embodiment, each of the layers is a separate layer which is then consolidated into the final structure.

Any one of the ceramic layers may be in the form of a monolithic structure or a plurality of smaller tiles separated by joints, If two ceramic layers are formed of smaller tiles, in a preferred embodiment they are stacked vertically in the structure such that the joints of the tiles in one layer are offset from the joints of the tiles in the second laser. The result is that the joints of one layer are covered by a solid portion of the ceramic layer of the other laver. Alternatively. one ceramic layer may be in the form of a monolithic structure and the other ceramic layer in the form of a plurality of smaller tiles, or both ceramic layers may be in the form of monolithic structures. If more ceramic layers are present, they can be arranged in any desired configuration,

In accordance with this invention each of the first and second fibrous layers comprise high tenacity fibers. As used herein, the term "high tenacity fibers" means fibers which have tenacities equal to or greater than about 7 g/d. Preferably, these fibers have initial tensile moduli of at least about 150 g/d and energies-to-brcak of at least about 8 J/g as measured by ASTM D2256. As used herein, the terms "initial tensile modulus", "tensile modulus" and "modulus" mean the modulus of elasticity as measured by ASTM 2256 for a yarn and by ASTM D638 for an elastomer or matrix material.

It is preferred that if a third fibrous layer or additional fibrous lay ers are employed, they likew ise comprise high tenacity fibers

Preferably, the high tenacity fibers have tenacities equal to or greater than about 10 g/d. more preferably equal to or greater than about 16 g/d. even more preferably equal to or greater than about 22 g/d. and most preferably equal to υr greater than about 28 g/d.

For the purposes of the present invention, a fiber is an elongate body the length dimension of which is much greater that the transverse dimensions of width and thickness. Accordingly, the term fiber includes monofilament, multifilament, ribbon, strip, staple and other forms of chopped, cut or discontinuous fiber and the like hav ing regular or irregular cross-section. The term "fiber" includes a plurality of any of the foregoing or a combination thereof. A yarn is a continuous strand comprised of many fibers or filaments.

The cross-sections of fibers useful herein may vary w idely . They may be circular, flat or oblong in cross-section. They may also be of irregular or regular multi-lobal cross-section having one or more regular or irregular lobes projecting from the linear or longitudinal axis of the fibers. It is preferred that the fibers be of substantially circular, flat or oblong cross-section, most preferably substantially circular.

Each of the first and second fibrous layers (and preferably as well with any additional fibrous layers) comprise a network of libers. The fibers may be in the form of woven, knitted or non-woven fabrics. Preferably, at least 50% by weight of the fibers in the fabric are high tenacity fibers, more preferabh at least about 75% by weight of the fibers in the fabric are high tenacity fibers, and most preferabh substantially all of the fibers in the fabrics are high tenacity fibers.

The yarns and fabrics used herein may be comprised of one or more different high strength fibers. The yarns may be in essentially parallel alignment, or the yarns may be twisted, over-wrapped or entangled. The fabrics employed herein may be woven with yarns having different fibers in the warp and weft directions, or in other directions.

High tenacity fibers useful in the yarns and fabrics of the invention include highly oriented high molecular weight potyolefin fibers, particularly high modulus polyethylene fibers, aramid fibers, polybenzazole fibers such as polybenzoxazole

(PBO) and polybenzothiazole (PBTB. polyvinyl alcohol fibers, polyacrylonitriie fibers, liquid crystal copolyester fibers, glass fibers, carbon fibers or basalt or other mineral fibers, as well as rigid rod polymer fibers, and mixtures and blends thereof. Preferred high strength fibers useful in this invention include polyolefin fibers, aramid fibers, polybenzoxazole fibers, and blends thereof. Most preferred are high molecular weight polyethylene fibers, aramid fibers, polybenzoxazole fibers, and blends of two or more thereof.

U.S. Pat. No. 4.457.985 generally discusses such high molecular weight polyethylene and polypropylene fibers, and the disclosure of this patent is hereby incorporated by reference to the extent that it is not inconsistent herewith. In the case of poh ethy lene, suitable fibers are those of weight average molecular weight of at least about 150.000. preferably at least about one million and more preferabh between about two million and about five million. Such high molecular weight polyethylene fibers may be spun in solution (see U.S. Pat. No. 4.137.394 and U.S. Pat. No. 4.356.138), or a filament sp.un from a solution to form a gel structure (see U.S. Pat. No. 4.413.1 10. German Off. No. 3,004. 699 and GB Patent No. 2051667). or the polyethylene fibers may be produced by a rolling and drawing process (see U.S. Pat. No. 5.702,657). As used herein, the term polyethy lene means a predominantly linear polyethy lene material that may contain minor amounts of chain branching or comonomers not exceeding 5 modifying units per 100 main chain carbon atoms, and that may also contain admixed therewith not more than about 50 vvt % of one or more polymeric additives such as alkene-1-poiymers. in particular low density polyethylene, poly propy lene or polybutylene. copolymers containing mono-olefins as primary monomers, oxidized polyolefins. graft polyolefin copolymers and polyoxymethy lenes. or low molecular weight additives such as antioxidants, lubricants, ultraviolet screening agents, colorants and the like which are commonly incorporated.

High tenacity polyethy lene fibers (also referred to as high molecular weight or extended chain polyethylene fibers) are preferred as one of the fibers useful in the fibrous layers of this invention. Such fibers are sold under the trademark SPECTRA® by Honeywell International Inc. of Morristown. New Jersey. USA.

Depending upon the formation technique, the draw ratio and temperatures, and other conditions, a variety of properties can be imparted to these fibers. The tenacity of the fibers are at least about 7 g/d. preferably at least about 15 g/d. more preferably at least about 20 g/d. still more preferably at least about 25 g/d and most preferably at least about 30 g/d. Similarly, the initial tensile modulus of the fibers, as measured by an Instron tensile testing machine, is pieferably at least about 300 g/d. more preferably at least about 500 g/d . stil! more preferably at least about 1.000 g'd and most preferably at least about 1.200 g/d. These highest values for initial tensile modulus and tenacity are generally obtainable only by employ ing solution grown or gel spinning processes. Many of the filaments have melting points higher than the melting point of the polymer from which they were formed. Thus, for example, high molecular weight polyethylene of about 150,000. about one million and about two million molecular weight generally have melting points in the bulk of 138°C. The highly oriented polyethylene filaments made of these materials have melting points of from about 7°C Io about 1 3°C higher. Thus, a slight increase in melting point reflects the crystalline perfection and higher crystalline orientation of the fi laments as compared to the bulk polv mer.

S imi larly, highly oriented high molecular weight polypropylene fibers of weight average molecular w eight at least about 200.000. preferably at least about one m i l lion and more preferably at least about two million may be used . Such extended chain polypropylene may be formed into reasonably well oriented filaments by the techniques prescribed in the various references referred to abov e, and especial ly by the technique of U.S. Pat. No. 4.413. 1 10. Since polypropylene is a much less crystal line material than poly ethylene and contains pendant methy l groups, tenaci ty values achievable with polypropylene are general ly substantial ly low er than the corresponding values for polyethylene. Λccordinglv . a suitable tenacity is ρreferably at least about 8 g/d. more preferably at least about 1 1 g/d. The initial tensi le modulus for polypropy lene is preferabh at least about 1 60 g/d, more preferably at least about 200 g/d. The melting point of the polypropylene is generally raised several degrees by the orientation process, such that the poly propylene filament preferablv has a main melting point of at least 168°C. more preferably at least 1 70°C . The particulaly preferred ranges for the above described parameters can advantageously prov ide improved performance in the final article. Employing fibers having a weight av erage molecu lar weight of at least about 200.000 coupled with the preferred ranges for the above-described parameters ( modulus and tenacity) can provide advantageously improved performance in the final article.

In the case of αram id fibers, suitable fibers formed from aromatic poly am ides are described in U.S . Pat. No. 3.671.542. wh ich is incorporated herein by re ference to the extent not inconsistent herew ith. Preferred aram id fi bers will have a tenacity of at least about 20 g-'d. an initial tensile modulus of at least about 400 g/d and an energy-to-break at least about 8 J/g. and particu larly preferred aram id fibers will have a tenacity of at least about 20 g/d and an energy -to-break of at least about 20 J/g. Most preferred aramid fibers will have a tenacity of at least about 23 g/d. a modulus of at least about 500 g/d and an energy -to-break of at least about 30 J/g. For exampie. poly(p-phenyiene terephthalamide) filaments w hich hav e moderately high moduli and teπac itv values are particularly useful in forming ba l l istic resistant composites. Examples are Twaron ® T2000 from Teijin which has a denier of 1000. Other examples are Kevlar® 29 which has 500 g/d and 22 g/d as values of initial tensile modulus and tenacity, respectively, as well as Kevlar® 129 and KM2 which are available in 400, 640 and 840 deniers from du Pont. Aram id fibers from other manufacturers can also be used in this invention. Copolymers of poly(p-phenyiene tereplithalamide) may also be used, such as co-poly(p-phen) lene terephthalamide 3.4 oxydiphenylene terephthalamide). Also useful in the practice of this invention are poly(m-phenylene isophthalamide) fibers sold by du Pont under the trade name Nomex®.

High molecular weight polyvinyl alcohol (PV-OH) fibers having high tensile modulus are described in U.S. Pat. No. 4.440.7 1 1 to Kwon et al. which is hereby incorporated by reference to the extent it is not inconsistent herew ith. High molecular weight PV-OH fibers should have a weight average molecular weight of at least about 200,000. Particularly useful PV-OH fibers should have a modulus of at least about 300 g/d. a tenacity preferably at least about IO g/d, more preferably at least about 14 g/d and most preferably at least about 17 g/d. and an energy to break of at least about 8 J/g. PV-OH fiber having such properties can be produced, for example. by the process disclosed in U.S. Pat. No. 4.599.267.

In the case of polyacry lonitrile (PAN), the PAN fiber should have a weight average molecular weight of at least about 400.000. Particularly useful PAN fiber should have a tenacity of preferably at least about 10 g/d and an energy to break of at least about 8 J/g. PAN fiber having a molecular weight of at least about 400.000, a tenacity of at least about 15 to 20 g/d and an energx to break of at least about 8 J/g is most useful: and such fibers are disclosed, for example, in U.S. Pat. No. 4.535.027.

Suitable liquid crystal copolyester fibers for the practice of this invention are disclosed, for example, in U.S. Pat. Nos. 3.975.487: 4.1 18.372 and 4.161.470.

Suitable polybenzazole fibers for the practice of this invention are disclosed, for example, in U.S. Pat. Nos. 5.286.833. 5.296.185. 5.356.584. 5.534,205 and 6.040,050. Preferably. the polybenzazole fibers are Zylon ® brand polybenzoxazole fibers from Toyobo Co. Rigid rod fibers are disclosed, for example, in U.S. Pat. Nos. 5.674.969. 5,939.553. 5.945.537 and 6,040.478. Such fibers are available under the designation M 5 ® fibers from Magellan Systems Internationa!.

The fibrous layers may be in the form of a woven, knitted or non-woven fabric, or various combinations thereof in different layers. If the fabric is a woven fabric, it may be of any desired weave, such as open weave pattern.

In one preferred embodiment, the fibrous layers are in the form of a non- woven fabric, such as plies of unidirectionally oriented fibers, or fibers which are felted in a random orientation, which are embedded in a suitable resin matrix, as is known in the art. Fabrics formed from unidirectionally oriented fibers typically have one layer of fibers which are aligned parallel to one another along a common fiber direction, and a second layer of unidirectionally oriented fibers aligned parallel to one another along a common fiber direction which is 90° from the direction of the first fibers. Where the individual plies are unidirectionally oriented fibers, the successive plies are preferably rotated relative to one another, for example at angles of 0°/90°. 0°/90°/0°/90° or 0°/45°/90°/45°/0°. or at other angles. Such rotated unidirectional alignments are described, for example, in U.S. Patents 4.623.574: 4.737.402: 4.748,064: and 4.916.000.

The fibrous layer or layers are preferably in a resin matrix. The resin matrix for the fiber plies may be formed from a wide variety of elastomeric materials having desired characteristics, in one embodiment, the elastomeric materials used in such matrix possess initial tensile modulus (modulus of elasticity ) equal to or less than about 6.000 psi (41.4 MPa) as measured by ASTM D638. More preferably, the elastomer has initial tensile modulus equal to or less than about 2,400 psi ( 16.5 MPa). Most preferably, the elastomeric material has initial tensile modulus equal to or less than about 1.200 psi (8.23 MPa). These resinous materials are typically thermoplastic in nature but thermosetting materials are also useful

Alternatively, the resin matrix may be selected to have a high tensile modulus when cured, as at least about 1 x 10⁶ psi (6895 MPa). Examples of such materials are disclosed, for example, in U.S. Patent 6.642.159. the disclosure of which is expressly incorporated herein by reference to the extent not inconsistent herewith.

The proportion of the resin matrix material to fiber in the composite layers may vary widelv depending upon the end use. The resin matrix material preferably forms about 1 to about 98 percent by weight, more preferably from about 5 to about

95 percent by weight, and most preferably from about 5 to about 40 percent by weight, of the total weight of the fibers and resin matrix.

A wide variety of materials may be utilized as the resin matrix, including thermoplastic and thermosetting resins. For example, any of the following materials may be employed: polybutadiene, polyisoprene. natural rubber, ethylene-propylene copolymers. ethylene-propylene-diene terpolymers. polysuifjde polymers. thermoplastic polyurethanes. poivurethane elastomers, chlorosulfønated polyethy lene. polychloroprene. plasficized polj'viπylchloride using dioctyl phthalate or other plasticizers well known in the art. butadiene acrylonitrile elastomers, poly (isobutylene-co-isoprene). polyacrylates. polyesters, polyethers. lluoroelastomers. silicone elastomers, thermoplastic elastomers, and copolymers of ethylene, hxamples of thermosetting resins include those which are soluble in carbon-carbon saturated solvents such as methyl ethyl ketone, acetone, ethanol. methanol, isopropyl alcohol, cyclohexane. ethyl acetone, and combinations thereof. Among the thermosetting resins are vinyl esters, styrene-butadiene block copolymers, diallyi phlhalate. phenol formaldehyde, polyvinyl butyral and mixtures thereof, as disclosed in the aforementioned U.S. Patent 6.642.159. Preferred thermosetting resins for polyethylene fiber fabrics include at least one vinyl ester, dialiyl phthalate. and optionally a catalyst for curing the vinyl ester resin.

One preferred group of materials are block copolymers of conjugated dienes and vinyl aromatic copoly mers. Butadiene and isoprene are preferred conjugated diene elastomers. Styrene. vinyl toluene and t-butyl styrene are preferred conjugated aromatic monomers. Block copolymers incorporating polyisoprene may be hydrogenated to produce thermoplastic elastomers having saturated hydrocarbon elastomer segments. The polymers may be simple tri-block copolymers of the type R- (BA )_x(X=3-I 5O): wherein A is a block from a polyvinyl aromatic monomer and B is a block from a conjugated diene elastomer. A preferred resin matrix is an isoprene- styrerte-isoprene block copolymer, such as Kraton® D l 107 isoprene-styrene-isoprene block copolymer available from Kraton Polymer LLC Another preferred resin matrix is a thermoplastic polyurethane, such as a copolymer mix of polyurethane resins in water.

The resin material may be compounded with fillers such as carbon black, silica, etc and may be extended with oils and vulcanized bv sulfur, peroxide, metal oxide or radiation cure systems using methods well known to rubber technologists, Blends of different resins may also be used.

In general, the fibrous layers of the invention are preferably formed by constructing a fiber network initially and then coating the network with the matrix composition. As used herein, the term "coating" is used in a broad sense to describe a fiber network wherein the individual fibers either have a continuous layer of the matrix composition surrounding the fibers or a discontinuous layer of the matrix composition on the surfaced of the fibers. In the former case, it can be said that the fibers are fully embedded in the matrix composition. The terms coating and impregnating are interchangeably used herein. The fiber networks can be constructed via a variety of methods. In the preferred case of unidirectionally aligned fiber networks, yarn bundles of the high tenacity filaments are supplied from a creel and led through guides and one or more spreader bars into a coilimaling comb prior to coating with the matrix material. The eollimating comb aligns the filaments coplanarly and in a substantially unidirectional fashion.

The matrix resin composition may be applied in any suitable manner, such as a solution, dispersion or emulsion, onto the fibrous layer, preferably a unidirectional fiber network. The matrix-coated fiber network is then dried. The solution, dispersion or emulsion of the matrix resin may be sprayed onto the filaments. Alternatively, the filament structure may be coated with the aqueous solution, dispersion or emulsion by dipping or by means of a roll coater or the like. After coating, the coated fibrous layer may then be passed through an oven for dry ing in which the coated fiber network layer (unitape) is subjected to sufficient heat to evaporate the water or other licμiid in the matrix composition. The coated fibrous network may then be placed on a carrier web. which can be a paper or a flim substrate, or the fibers may initially be placed on a carrier web before coating with the matrix resin. The substrate and the unitape can then be wound up into a continuous roll in a known manner.

The yarns useful in the fibrous layers may be of any suitable denier, such as from about 50 denier to about 3000 denier. The selection is governed by considerations of desired properties and cost. Finer yarns are more costly to manufacture and to weave, but can produce better properties (such as greater ballistic effectiveness per unit weight). The yarns are preferably from about 200 denier to about 3000 denier. More preferably, the yarns are from about 650 denier to about 1500 denier. Most preferably, the yarns are from about 800 denier to about 1300 denier.

Each of the first, second and any additional fibrous layers may be formed from fibers of the same composition, or they may be in the form of hybrid layers of fibers having two or more different compositions. That is. one or more fibrous layers may be formed from at ieast two layers of different fiber materials that are adhered together, or from a mixture of different fiber materials in the same layer.

The thickness of each fibrous layer is preferably the same but may be different, and may vary depending upon the specific application, and weight and cost limitations. Typical thicknesses of such fibrous layers may range from about 0.1 to about 0.8 inch (2.54 to 20.32 mm), more preferably from about 0.2 to about 0.6 inch (5.08 to 15.24 mm), and most preferably from about 0.3 to about 0.5 inch (7.62 to 12.70 mm).

In one preferred embodiment the first fibrous layer is formed from high molecular weight polyethylene fibers, aramid fibers and/or polybenzoxazole fibers in the form of a unidirectional non-woven fabric or a woven fabric, and the second fibrous layer is formed from the same fibers as are in the first fibrous layer that arc either in the form of a woven fabric or in the form of a unidirectional non-woven fabric. In another preferred embodiment the first fibrous layer is formed from high molecular weight polyethylene fibers or aramid fibers that are either in the form of a woven fabric or in the form of a unidirectional non-woven fabric and the second fibrous fayer is formed from the same fibers as are in the first fibrous layer that are either in the form of a unidirectional non-woven fabric or a woven fabric.

Also, preferably the first and second fibrous layers (as well as any additional fibrous layers) are formed of a plurality of plies which have been laminated together. The number of plies in each layer is dependent on the desired area! density, thickness, protection level and the like. For example, when the fibrous layer is formed from either high molecular weight polyethylene fibers, arnmid fibers or polybenzoxa/ole libers, the number of individual plies may range from about 2 to about 200. more preferably from about 10 to about 150. and most preferably from about 50 to about 100. it should be recognized that the individual plies may be preformed into a multiply prepreg. For example, if the prepreg is formed from 4 plies, then the number of plies mentioned previously would be reduced to one-quarter of the amounts stated.

The individual plies are also preferably in the form of subassemblies of two or four units which include cross-plied, preferably at 0°/90° for a two ply unit and ai 0°/90°/0790° for a four ply unit. The fibrous layers may be formed from a plurality of such cross-plied units.

Laminates of two or more plies that form the fibrous layers of the invention are preferably produced from continuous rolls of unidirectional prepregs. using a continuous cross-ply operation. One such method is described in U.S. Patents 5.173.138 and 5.766.725. hereby incorporated by reference to the extent not incompatible herewith. Alternatively, the plies may be laved up by hand, or by any- other suitable means. The plies (for example, two plies) are consolidated by the application of heat and pressure in the cross-plying process. Temperatures may range from about 90° to about 160° C. and pressures may range from about 100 to about 2500 psi (69 to 17.0000 kPa). depending upon the type of fibers and matrix sheet that is employed. By "consolidating" is meant that the matrix material and the fibrous plies are combined into a single unitary layer. Consolidation can occur by drying, cooling, heating, pressure or a combination thereof. Assembl ies of the various plies that constitute the fibrous layers of this invention may comprise rigid assemblies or flex ible assemblies. Rigid assem bl ies are usually formed by stacking and consol idating the plies in a press, such as under the conditions mentioned above. Flexible assemblies may be formed by loosely stacking the plies, in which the plies are either unattached or attached only at one or more edges by stitching, for example.

One or more plastic fi lms can be included in the fibrous layers, for example to perm it different layers to slide over each other for ease of form ing into a desired shape. These plastic films may typical ly be adhered to one or both surfaces of each fi brous !ayer or each consolidated prepreg two- or four-plies that form the fibrous layers. Any suitable plastic film may be employed, such as films made of polyolefins. e.g.. linear low density polyethylene ( LLDPE) films and ultrahigh molecular weight poly ethylene (UHMWPE) films, as well as polyester films, nylon films. poly carbonate films and the like. These films may be of any desirable thickness. Typical thicknesses range from about 0. 1 to about 1 .2 mils (2.5 to 30 μm). more preferably from about 0.2 to about I mi l (5 to 25 μm ). and most preferably from about 0.3 to about 0.5 m ils (7.5 to 12.5 μm). Most preferred are films of LLDPE.

In addition to the fibrous layers of high tenac ity fibers that are present in the composite material of this invention, there may also be employed other lay ers. For example, a fiber glass composite and/or a graphite composite may be interposed between the two ceramic layers. Such composites may be formed with a desi red resin, such as a thermosetting epoxy resin. A lternatively, such composite materials may be present in other locations in the article of this invention.

In one particularly preferred embodiment of this invention, the ceram ic layers are formed from alum inum oxide and the fibrous layers are formed from aramid fibers or high molecular weight polyethylene fibers.

In one embodiment, the first ceramic layer and the first fibrous layer are adhered together to form a preformed unit. Any suitable means can be used to attach the layers together, such as a solid adhesive film, a liquid adhesive, etc. Adhesive films are preferred, such as polyurethane adhesives, epoxy adhesives, polyethylene adhesives. and the like. These layers may be bonded to each other in a suitable press. such as a match-die press or autoclave. The layers are combined under suitable temperatures and pressures. For example, if a liquid adhesive is employed, the layers may be bonded together at room temperature conditions. Alternatively, the layers may be bonded together using an adhesive film or liquid under suitable pressures and temperatures. If heat and pressure are used to bond the layers together, preferably the temperatures employed are preferably about 20 to about 30° F ( 11.1 to I6.7°C) lower than the temperature used in the consolidation of the fibrous layers mentioned above, or about 20 to about 30° F ( 11.1 to I6.7°C) lower than the melting point of the fibers used in the fibrous backing layers. Pressures can be lower than those used in the consolidation of the fibrous layers, such as about 20 to about 500 psi (0.14 to 3.4 MPa). If an autoclave is employed, the pressures may range, for example, from about 50 to about 250 psi (0.34 to 1.7 MPa).

Likewise, the second ceramic layer and the second fibrous layer (if present) may be adhered together in a similar fashion by a similar adhesive. If additional layers of ceramic and fibers are used, they are also preferably adhered together by an adhesive means.

The various preformed combined layers of the first ceramic layer and the first fibrous layer, together with the second ceramic layer and the second fibrous layer (and any additional ceramic and/or fibrous layers) may be stacked in a suitable press w ith interleaving layers of adhesive film. The press may be an autoclave or a match-die high pressure press. The adhesive may be the same or different than what is used to bond the first ceramic layer to the first fibrous layer. The stacked preformed layers are combined into a consolidated article preferably under heat and pressure. The same pressures and temperatures that are employed to form each of the preformed layers may be employed to form the entire panel of the invention, or other pressures and temperatures may be used,

Alternatively, all of the layers may be in the form of individual layers (ceramic layer, fibrous layer, ceramic layer, fibrous layer, etc.) that are bonded to each other in a single step, such as being stacked in a press and bonded under suitable heat and pressure. The following non-limiting examples arc presented to provide a more complete understanding of the invention. The specific techniques, conditions. materials, proportions and reported data set forth to illustrate the principles of the invention are exemplary and should not be construed as limiting the scope of the invention.

EXAMPLES

Example 1 (Comparative)

A ceramic faced panel was prepared from a ceramic tile. The tile was an aluminum oxide ceramic (AD-90 from CoorsTek) having dimensions of 4 x 4 inches ( 101.6 x 101 .6 mm) and a thickness of 0.4 inch ( 10.16 mm). The ceramic layer had an areal density of 7.41 psf (36.17 ksm). The ceramic was backed w ith molded SPECTRA SHIELD® PCR. a two ply non-woven composite formed from high molecular weight polyethy lene libers (from Honeywell International Inc.). This material was a non-woven unidirectionally oriented structure, with a matrix resin (20% by weight of Kratonll Dl 107 isoprene-styrene-isoprene block copolymer available from Kraton Poly mer LLC). The 2-ply structure included individual plies that were cross-plied 0790°. The SPECTRA ® polyethylene fibers have a tenacit) of 30 g/d. a tensile modulus of 850 g^;d and an energy-to-break of 45 g/d.

The fibrous layer contained 148 layers of the SPECTRA SHIELDS product and had an areal density of 4 psf ( 19.5 ksm). These lavers were formed as a separate consolidated layer by stacking the layers in a 200 ton hydraulic press, and molding by preheating at 240°F ( 1 16°C) ior 10 minutes, followed by molding at 240T ( 1 16°C) under a pressure of 1500 psi ( 10.3 MPa) for 10 minutes, followed by a cool dow n under pressure to 150°F (66°C). The fibrous layer was in the form of a 12 x 12 inch (30.5 x 30.5 cm) sheet.

The ceramic layer was adhered to the preformed fibrous layer of high molecular weight polyethj lene fibers under room temperature conditions using a spray adhesive (H1-9 from 3M Company). The ceramic layer was placed in the center of the fibrous layer, with the adhesive film (of approximately the same area as the ceramic layer) between the ceramic layer and the fibrous iayer. The resultant panel had a total areal density of 1 1.4 J psf (55.7 ksm).

The panel was tested for ballistic performance in accordance with National

Institute of Justice (NU) Standard 0101.04 level IV armor. The projectile was an armor piercing 0.50 caliber. 710 grain APM2 bullet, with a steel jacket and steei core. The results are shown in Table 1, below .

Example 2

Example I was repeated except that two of the combined ceramic-fibrous panels of Example 1 were empkned. Each panel was prepared as in Example 1. The individual panels were then adhered together in the same manner as in Example I .

The panel had two layers of ceramic and two lavers of SPECTRA SHIELD® PCR non-woven fabric of high molecular weight polyethylene fibers. The panel was tested for ballistic properties, as in Example 1. The results are shown in Table 1. below.

As can be seen in comparing Examples 1 and 2. a single layer of combined ceramic and consolidated non-woven fibers failed the test, with the bullet penetrating the armor at the indicated exit velocity, in contrast, when two layers of ceramic and two layers of the consolidated non-woven fibers v\ere used, the armor passed the test. with the bullet having been stopped. Thus, an increased velocity of threat can be defeated by adding a ceramic layer, and there is no need to change the entire ceramic plus composite backing system and replace it with a thicker ceramic and composite backing system.

Example 3

A ceramic faced panel was prepared. The ceramic layers were formed from plates of alumina (AD-96 from CoorsTek) having dimensions of 3.985 .\ 3.985 inch ( 101.219 x 101.219 mm), and a thickness of 0.1 10 inch (2.794 mm). The areal density of each ceramic layer was 2.30 psf ( 1 1.23 ksm).

The fibrous backing material was SPKCTRA SHIELD® PCRw. a 4-ply non-woven composite formed from high molecular weight polyethylene fibers (from Honeyvveil International Inc.). This material was a non-woven unidirectional ly oriented structure, with a matrix resin 16% by weight of Kraton ® D l 107 isoprcne- styrene-isoprene block copolymer available from Kraton Polymer LLC). The 4-ply structure included individual plies that were cross-plied 0°/90°/0°/90°. The fibers had the same properties as in Example I . The fibrous backing materials was formed from 40 layers of the SPECTRA SHIELD® product, and consolidated under heat and pressure under the same conditions as Example I . The consolidated fibrous layer was in the form of a 12 x 12 inch (30.5 x 30.5 cm) sheet. The areal density of this layer was 2.00 psf (9.76 ksm).

The ceramic layer was adhered to the fibrous layer using an adhesive film. The adhesive film was a polyether aliphatic polyurethane available from Stevens

Urethane which has a melting range of 120 to 140°C. an elongation at break of 450% and a specific gravity of 1 ,07g/cc. The ceramic layer was placed in the middle of the fibrous laver. A second ceramic layer of the same type as the first layer was adhered to the outer surface of the first layer using the same type of adhesive film. The combined three layers were bonded to each other in an autoclave under the following conditions: vacuum of 14.7 psf (71.7 ksm). pressure of 250 psi (1.72 MPa). temperature of 240⁰F (II6°C). duration of 2 hours of process followed by cooling down to 150⁰F (66°C).

The panel was tested for ballistic performance in accordance with National Institute of Justice (NIJ) Standard 0101.04. level IV armor. The projectile was a armor piercing 0.30 caliber. 162 grain M2AP bullet, with a steel jacket and a steel core. The results are shown in Table 2. below.

Example 4 (comparative)

Example 3 was repealed except that the second ceramic la\er was not employed. The areal density of the soie ceramic layer was 2.8 psf (13.67 ksm) and the total areal density of the structure was 4.8 psf (23.43 ksm).

The panel was tested for ballistic performance as in Example I. The lowest velocity bullet that could be fired was 1580 fps (482 mps). The bullet completel} penetrated the panel.

Example 5

Example 3 was repeated using three of the ceramic layers of Example 3 that were bonded together. The fibrous backing layer was formed of 42 layers of the 4-ply material of Example 3. The areal densitv of the fibrous layer was 2.15 psf (10.49 ksm).

The structure was bonded logether under the same conditions as in

Example 3.

The panel was tested for ballistic properties, as in Example 3. The results are shown in Table 2. below. Example 6

Example 4 was repeated sung four of the ceramic layers of Example 3. The fibrous backing iayer was the same as in Example 4.

The panel was tested for ballistic properties, as in Example 3. The results are shov\n in Table 2. below.

When comparing Examples 3 and 4. it can be seen that the use of an additional relativell thin ceramic iayer provides a structure that meets the threat level whereas the single layer structure had no stopping resistance to the type of bullets used. Also as can be seen from Table 2. additional relatively thin ceramic layers can be added to the front face of the panel to provide even higher levels of protection w ithout requiring the replacement of the panel by a thicker ceramic/fibrous backing material panel. Accordingly, it can be seen that the present invention provides a ballistic resistant panel that has a plurality of ceramic layers and at least one {and preferably two) fibrous backing layer in order to provide a ceramic faced panel of a desired protection level. By forming the panel from a plurality of relatively thin ceramic layers with at least one fibrous backing, different threat levels can be protected against by choosing the number of layers of ceramic materials to be used in the panel. The relatively thin ceramic layers are simpler to manufacture than thick ceramic panels of the same overall thickness as the combined thickness of the multiple ceramic faced layers. Surprisingly, the paneis of this invention having a multiple number of ceramic layers provides substantially the same or better ballistic resistance than does a monolithic panel of substantially the same thickness and composition.

Protection against various threat levels can be provided by using a desired number of preforms of the relatively thin ceramic layer and the fibrous backing. This permits greater manufacturing flexibility and can reduce the inventors of panel constructions that need to be stored in order to provide protection against different threat levels.

The panels of this invention are particularly useful for ballistic protection of land vehicles and aircraft. The} also useful as inserts for body armor, such as vests and helmets, in stationary devices as well as in homeland security applications.

Having thus described the invention in rather full detail, it will be understood that such detail need not be strictly adhered to but that further changes and modifications may suggest themselves to one skilled in the art. all falling within the scope of the invention as defined by the subjoined claims.

Claims

What is claimed is:

I . A ballistic resistant panel, said panel comprising: a first relatively thin ceramic layer having an outer facing surface and an inner facing surface; a first fibrous layer comprising a network of high tenacity fibers and having an outer facing surface and an inner facing surface, said outer facing surface of said first fibrous layer being adjacent to said inner facing surface of said ceramic layer: and a second relatively thin ceramic layer and hav ing an outer facing surface and an inner facing surface: said inner facing surface of said second ceramic layer being adjacent to said outer facing surface of said first ceramic layer, said second ceramic layer facing outwardly of said panel.

2. The panel of claim 1 further comprising a second fibrous layer comprising a network of high tenacity fibers and having an outer facing surface and inner facing surface, said second fibrous layer being interposed between said first ceramic layer and said ceramic layer, with said outer facing surface of said second fibrous la}er being adjacent to said inner facing surface of said ceramic Iayer and said inner facing surface of said second fibrous layer being adjacent to said outer facing surface of said first ceramic layer.

3. The panel of claim 1 wherein said panel has a ballistic resistance which is substantially equivalent to or higher than the ballistic resistance of a comparable ceramic panel construction that has only a single ceramic layer backed with a fibrous layer, which single ceramic layer has an overall thickness of substantially the same thickness as the combined thickness of said first ceramic layer and second ceramic !ayers.

4. The panel of claim 3 wherein said high tenacity fibers are selected from the group consisting of high molecular weight polyethylene, high molecular weight poly propylene, aramid, polyvinyl alcohol, polyacry lonitri le, polybenzazole, polyester and rigid rod fibers, and said second type of high tenacity fibers are selected from the group consisting of high molecular weight polyethylene, high molecular weight poly propylene, aramid. polyvinyl alcohol, polyacrylonitrile. polyben/azole. polyester and rigid rod fibers, and blends of two or more thereof.

5. The panel of claim 4 wherein said high tenacity fibers have tenacities of at least about 22 g/d.

6. The panel of claim 4 wherein said high tenacity fibers have tenacities of at least about 28 g/d.

7. The panel of claim 4 wherein said first fibrous layer is in the form of a non-woven unidirectionally oriented network of fibers w ith a resin matrix.

8. The panel of claim 7 wherein said resin comprises from about 5 to about 40 percent by weight of said first fibrous layer.

9. The panel of claim 7 wherein said first fibrous layer comprises a plurality of individual plies that are oriented with respect to each other.

10. The panel of claim 9 wherein said plies are oriented at an angle ofW with respect to adjacent plies.

1 1. The panel of claim 10 wherein said first fibrous layer comprises a plurality of prepregs comprising a plurality of fiber plies that are oriented with respect to each other.

12. The panel of claim 4 wherein said first fibrous layer is in the form of a woven fabric with a resin matrix.

13. The panel of claim 4 wherein said first layer comprises a plurality of individual plies that are oriented with respect to each other, and the number of plies ranges from about 2 to about 200.

14, The panel of claim 4 wherein said first fibrous layer comprises fibers selected from the group consisting of high molecular weight polyethylene fibers, aramid fibers, polybenzoxazole fibers and blends thereof.

15. The panel of claim 14 wherein said first fibrous layer comprises high molecular weight polyethylene fibers.

161 The panel of claim 1 wherein said ceramic iayer comprises a ceramic material selected from the group consisting of metal and non-metal nitrides, borides. carbides and oxides, and mixtures thereof

17. The panel of claim I wherein said ceramic layer comprises a ceramic material selected from the group consisting of silicon carbide, silicon oxide, silicon nitride, boron carbide, boron nitride, titanium diboride. alumina and magnesium oxide, and mixtures thereof.

18. The panel of claim I wherein said ceramic layer comprises a ceramic material selected from the group consisting of alumina, silicon carbide, boron carbide, and mixtures thereof.

19. The pane! of claim 3 wherein said ceramic layer comprises alumina.

20. The panel of claim ! wherein the thickness of each of said first and said second ceramic layers is from about 0.05 to about 0.6 inch ( 1.3 to 15.2 mm).

21. The panel of claim I wherein the thickness of each of said first and second ceramic layers is from about 0.1 to about 0.5 inch (2.5 to 12.5 mm).

22. The panel of claim 2 wherein said first ceramic layer has the same composition as said second ceramic layer, and said the fiber in said first fibrous layer are the same as the fibers in said second fibrous layer.

23. The panel of claim 1 wherein said first ceramic layer and said second ceramic layer are bonded together.

24. The panel of claim 23 wherein said first ceramic layer and said first fibrous layer are bonded together.

25. The panel of claim I further comprising a third relatively lhin ceramic layer having an outer facing surface and an inner facing .surface: said inner facing surface of said third ceramic layer being adjacent to said outer facing surface of said second ceramic layer, said third ceramic layer facing outwardly of said panel.

26. A ballistic resistant panel, said panel comprising: a first relatively thin ceramic layer having an outer facing surface and an inner facing surface; a first fibrous layer comprising a network of high tenacity fibers and having an outer facing surface and an inner facing surface, said outer facing surface of said first fibrous layer being adjacent to said inner facing surface of said ceramic layer: a second relatively thin ceramic layer and hav ing an outer facing surface and an inner facing surface: said inner facing surface of said second ceramic layer being adjacent to said outer facing surface of said first ceramic layer, said second ceramic layer facing outwardly of said panel: and a second fibrous layer comprising a network of high tenacity fibers and having an outer facing surface and inner facing surface, said second fibrous layer being interposed between said first ceramic layer and said second ceramic layer, with said outer facing surface of said second fibrous layer being adjacent to said inner facing surface of said second ceramic layer.

21 The panel of claim 26 wherein each of said first ceramic layer and said second ceramic Iayer comprises alumina.

28. The panel of claim 26 wherein each of said first and second fibrous lasers comprises a plurality of prepregs comprising a plurality of fiber plies that are oriented w ith respect to each other.

29. The panel of claim 28 wherein each of said first and second fibrous iaycr comprises fibers selected from the group consisting of high molecular weight poly ethylene fibers, aramid fibers, polybenzoxazole fibers and blends thereof.

30. The panel of claim 29 wherein each of said first and second fibrous layers comprises a network of high tenacity fibers and a resin matrix, said resin matrix comprising a styrene-isoprene-styrene block copolymer

31. In a ceramic faced baliistic resistant panel designed to protect against a certain threat level of ballistic projectiles, the improvement comprising forming said panel from a structure which comprises: a first relatively thin ceramic layer having an outer facing surface and an inner facing surface: a first fibrous layer comprising a network of high tenacity fibers and having an outer facing surface and an inner facing surface, said outer facing surface of said first fibrous layer being adjacent to said inner facing surface of said first ceramic layer: and a second relatively thin ceramic layer and having an outer facing surface and an inner facing surface, said inner facing surface of said second ceramic layer being adjacent to said outer facing surface of said first ceramic layer.

32. The panel of claim 31 wherein said panel has a ballistic resistance which is substantially equivalent to or higher than the ballistic resistance of a comparable ceramic panel construction that has only a single ceramic layer backed with a fibrous layer, which single ceramic layer has an overall thickness of substantially the same thickness as the combined thickness of said first ceramic layer and second ceramic layers.

33. The panel of claim 32 wherein said first fibrous layer comprises a plurality of prepregs comprising a plurality of fiber plies that are oriented with respect to each other, each of said fiber plies comprising fibers selected the group consisting of high molecular weight polyethylene fibers, aramid fibers, polybenzoxazole fibers and blends thereof, and each of said ceramic layers comprising a ceramic selected from the group consisting of alumina, silicon carbide, boron carbide, and mixtures thereof

34. The panel of claim 33 wherein said first fibrous iayer comprises a network of high tenacity fibers and a resin matrix, each of said ceramic layers has a thickness of from about O. I to about 0.5 inch (2.5 to 12.5 mm), and wherein each of said layers is bonded to said adjacent layers.